i^^B 
 

 
Ji 
 
 
 Jff 
 
COMMERCIAL ORGANIC ANALYSIS 
 
 Allen's 
 Commercial Organic Analysis 
 
 A Treatise on the Properties, Proximate Analytical Examination and Modes of 
 Assaying the Various Organic Chemicals and Products Employed in the Arts, Manu- 
 factures, Medicine, etc. , with Concise Methods for the Detection and Determination 
 of their Impurities, Adulterations, and Products of Decomposition. By ALFRED 
 H. ALLEN, F.I.C., F.C.S., Public Analyst for the West Riding of Yorkshire and 
 the City of 'Sheffield; Past President of the Society of Public Analysts of Great 
 Britain, etc. 
 
 Vol. I. Preliminary Examination of Organic Bodies. Alcohols, Neutral Alcoholic 
 Derivatives, Ethers, Starch and its Isomers, Sugars, Acid Derivatives of Alcohols 
 and Vegetable Acids, etc. Third Edition, with numerous additions by the 
 author, and revisions and additions by DR. HENRY LEFFMANN, Professor of 
 Chemistry in the Woman's Medical College of Pennsylvania, and in the Wagner 
 Free Institute of Science, Philadelphia, etc. With many useful tables. 8vo, 
 illustrated, 557 pages. Cloth, net $4.50 
 
 Vol. II. PART I. Fixed Oils, Fats, Waxes, Glycerin, Soaps, Nitroglycerin, 
 Dynamite and Smokeless Powders, Wool-Fats, Degras, etc. Third Edition, with 
 many useful tables. Revised by DR. HENRY LEFFMANN, with numerous addi- 
 tions by the author: 8vo, illustrated, 387 pages. Cloth, ^$3.50 
 Vol. II. PART II. Hydrocarbons, Mineral Oils, Lubricants, Asphalt, Benzene 
 and Naphthalene, Phenols, Creosote, etc. Third Edition, Revised by DR. 
 HENRY LEFFMANN, with numerous additions by the author. 8vo, illustrated, 
 330 pages. Cloth, net $3. 50 
 Vol. II. PART III. Terpenes, Essential Oils, Resins, Camphors, Aromatic 
 Acids, etc. Third Edition, Cloth, net $5.00 
 Vol. III. PART I. Tannins, Dyes, Coloring Matters, and Writing Inks. Third 
 Edition, Revised, Rewritten, and Enlarged, by J. MERRITT MATTHEWS, Pro- 
 fessor of Chemistry and Dyeing at the Philadelphia Textile School. 8vo, illus- 
 trated, 589 pages. Cloth, net $4.50 
 Vol. III. PART II. The Amines and Ammonium Bases, Hydrazines and De- 
 rivatives. Bases from Tar. The Antipyretics, etc. Vegetable Alkaloids, Tea, 
 Coffee, Cocoa, Kola, Cocaine, Opium, etc. Second Edition. 8vo, illustrated, 
 593 P a ges. Cloth, ^$4.50 
 Vol. III. PART III. Vegetable Alkaloids concluded, Non-basic Vegetable Bitter 
 Principles. Animal Bases, Animal Acids, Cyanogen and Its Derivatives, etc. 
 Second Edition. 8vo, illustrated, 534 pages. Clothj net $4.50 
 Vol. IV. Proteids and Albuminous Principles. Milk and Milk Products, Meat 
 . and Meat Products, Haemoglobin and its Allies. Proteoids or Albuminoids. 
 Second Edition, with elaborate appendices and a large number of useful tables. 
 8vo, illustrated, 584 pages. Cloth, net $4.50 
 
 'The general excellence of the work is such as to make it almost indispensable to any 
 chemist working in this field. * * * It is particularly satisfactory tc find, along with care- 
 ful consideration given to the work of others, so much evidence of individual laboratory 
 experience on the part of the author himself. Mr. Allen's book deserves its well established 
 place as one of the standard classics of the working chemical library." American Chemical 
 Journal. 
 
CHEMISTRY 
 INORGANIC AND ORGANIC 
 
 WITH EXPERIMENTS 
 
 BY 
 
 CHAELES LOUDON BLOXAM 
 
 NINTH EDITION, REWRITTEN AND REVISED 
 BY 
 
 JOHN MILLAR THOMSON, LL.D., F.K.S, 
 
 PROFESSOR OF CHEMISTRY, KING'S COLLEGE, LONDON 
 AND 
 
 ARTHUR G. BLOXAM, F.I.C. 
 
 CONSULTING CHEMIST AND CHARTEEED PATENT AGENT 
 
 OF THE 
 
 UNIVERSITY 
 
 PHILADELPHIA 
 P. BLAKISTON'S SON & CO 
 
 1012 WALNUT STREET 
 1907 
 
P E E F A C E. 
 
 NOTWITHSTANDING the many competitors for public favour that 
 have appeared during the past few years, the continued popularity 
 of Bloxam's " Chemistry " indicates that its particular qualities are 
 not to be met with in other works. Under the conviction that one 
 of the chief claims of the book for attention is the constant 
 reference to experiment, more especially in the earlier part, the 
 Editors have retained this feature in the Ninth Edition. 
 
 The treatment of the Inorganic and Organic portions of the 
 work in the one volume becomes increasingly more difficult, but 
 this arrangement is undoubtedly convenient to those who use the 
 book for the purpose of reference, and the temptation to divide 
 the volume into two to admit of the fuller treatment of the 
 Organic portion has been resisted. In the Editors' opinion the 
 main objection to the condensed character of this part of the book 
 is the necessary omission of many structural formulae which are 
 useful aids to students. It is believed, however, that sufficient 
 explanation is given to enable the reader to construct the formulas 
 for himself ; and the attempt to do so will prove far more instruc- 
 tive than the mere inspection of a printed formula. 
 
 A change has been made in the present edition in the order 
 of treatment of the non-metallic elements, the place of Carbon 
 having been changed so that its consideration occurs after that 
 of the three other typical elements, Hydrogen, Oxygen, and 
 Nitrogen. 
 
 Many of the old illustrations which had become obsolete have 
 
Ti PKEFACE. 
 
 been removed from the work and several new illustrations, some 
 in the division devoted to Organic Chemistry, have been intro- 
 duced. 
 
 The plan adopted throughout several editions of making no 
 division in the Organic portion between the treatment of the Fatty 
 and Aromatic Compounds, being advantageous, has been again 
 followed. 
 
 Due allowance being made for the time occupied in printing a 
 book of this size, the Editors trust that their revision has brought 
 the work up to date and that the present edition will be as 
 favourably received as the two which have previously left their 
 hands. 
 
 KING'S COLLEGE, LONDON. 
 August 1903. 
 
TABLE OF CONTENTS. 
 
 INORGANIC CHEMISTRY. 
 
 INTRODUCTION. NON-METALS. PARAGRAPHS 
 
 Water ............. i- 10 
 
 HYDROGEN n- 16 
 
 OXYGEN 17-^30 
 
 Water 31- 48 
 
 Hydrogen peroxide 49 
 
 Ozone ............. 50 
 
 Ai r 5 1 - 5 2 
 
 NITROGEN, Argon, Helium 53 
 
 Ammonia ............ 54- 57 
 
 Nitric acid . 58- 60 
 
 Oxides of nitrogen. Hydrazine. Hydrogen nitride . . . 61- 66 
 
 CARBON ............. 67- 70 
 
 Carbon dioxide .......... 71- 77 
 
 Carbon monoxide .......... 78- 85 
 
 Acetylene 86- 87 
 
 Ethylene 88 
 
 Marsh-gas. Flame 89- 92 
 
 Fuel 93-94 
 
 Types of Chemical Compounds ....... 95 
 
 CHLORINE ..,.-. 96-100 
 
 Hydrochloric acid loi-io^ 
 
 Hypochlorous acid ....... ., . . 105-106 
 
 Chloride of lime t , 107 
 
 Chloric a"cid ,...,,... 108-109 
 Perchloric acid . . . . . . . . . .no 
 
 Chlorine dioxide ..... .... ni-H2 
 
 Chlorides of carbon .......... 113-114 
 
 Chloride of nitrogen . . H5 
 
 Aqua regia. Nitrosyl chloride . 116 
 
 BROMINE. Hydrobromic acid ........ 117-118 
 
 ODINE. Hydriodic acid ......... 119-123 
 
 FLUORINE. Hydrofluoric acid 124-126 
 
Tiii TABLE OF CONTENTS. 
 
 PARAGRAPHS 
 
 Beriew of the halogens 127 
 
 SULPHUR 128-129 
 
 Hydrogen sulphides I3- I 3 I 
 
 Oxides of sulphur 132-133 
 
 Sulphuric acid I34- T 35 
 
 Thiosulphuric acid I3 6 
 
 Thionic acids . 137-140 
 
 Carbon disulphide . . . . . . . . .141 
 
 Chlorides and iodides of sulphur 142 
 
 SELENIUM AND TELLURIUM 143-144 
 
 KEVIEW OF THE SULPHUR GROUP 145 
 
 BORON 146-147 
 
 PHOSPHORUS 148-151 
 
 Phosphoric acids 152 
 
 Phosphorous and hypophosphorous acids 1 53-154 
 
 Structure of acids 155 
 
 Phosphides of hydrogen . . . . . . . . .156 
 
 Chlorides and sulphides of phosphorous ...... 157-158 
 
 Amides 159 
 
 ARSENIC 160 
 
 Arsenious and arsenic acids 161-162 
 
 Hydrides and sulphides of arsenic 163-166 
 
 KEVIEW OF NITROGEN GROUP . . . . . . .167 
 
 SILICON 168-175 
 
 Eeview of the carbon group . . . . . . . .176 
 
 GENERAL PRINCIPLES. Atoms and Molecules. Chemical Affinity 
 
 Molecular Structure. Spectrum Analysis . . . -177 
 METALS. 
 
 Potassium ........... 178-181 
 
 Sodium 182-185 
 
 Ammonium 186-190 
 
 Lithium. Kubidiurn. Csesium 191-192 
 
 Keview of alkali-metals 193 
 
 Barium 194 3 S" 
 
 Strontium 195 
 
 Calcium 196-198 
 
 Glass ............. 199 
 
 Review of alkaline earth metals ....... 200 
 
 Magnesium 201 
 
 Zinc . 202 
 
 Cadmium ... 203 
 
 Beryllium 204 
 
 Aluminium 205-207 
 
 Pottery, Porcelain and Bricks 208 
 
 Gallium 209 
 
TABLE OF CONTENTS. ix 
 
 METALS (continued.) PARAGRAPHS 
 
 Indium 210 
 
 Ee view of the aluminium metals . . . . . . .211 
 
 Scandium . . . .212 
 
 Yttrium 213 
 
 Lanthanum . . . .214 
 
 Ytterbium 215 
 
 Bare earths 216-217 
 
 Iron 218-229 
 
 Cobalt 230 
 
 Nickel 231 
 
 Manganese 232-234 
 
 Chromium ........... 235 
 
 Keview of iron metals ......... 236 
 
 Molybdenum 237 
 
 Tungsten 238 
 
 Uranium 239 
 
 Bismuth ............ 240-242 
 
 Antimony ; Vanadium ; Tantalum ....... 243-247 
 
 Tin 248-253 
 
 Titanium 254 
 
 Zirconium ; Thorium 255 
 
 Germanium ; Cerium ......... 256-257 
 
 Lead 258-268 
 
 Thallium 269 
 
 Copper ... 270-283 
 
 Silver 284-287 
 
 Mercury 288-295 
 
 Platinum 296-298 
 
 Palladium 299 
 
 Khodium 300 
 
 Osmium ............ 301 
 
 Euthenium ........... 302 
 
 Iridium ' 303 
 
 Eeview of platinoid metals ........ 304 
 
 Gold 305-307 
 
 OEGANIC CHEMISTEY. 
 
 Ultimate organic analysis ........ 308 
 
 Calculation of formulae ......... 309-312 
 
 Classification of organic compounds 313 
 
 HYDROCARBONS. 
 
 Paraffin hydrocarbons ......... 314-316 
 
 Olefine hydrocarbons . . . . . . . . 3 J 7 
 
 Acetylene hydrocarbons . . . . . . . .318 
 
 Benzene hydrocarbons and their constitution. Position isomerism . 319-328 
 
x TABLE OF CONTENTS. 
 
 OKGANIC CHEMISTKY (continued.) PARAGRAPHS 
 
 Terpene hydrocarbons ; Camphors ; Kesins ..... 3 2 9~333 
 ALCOHOLS. 
 
 Monohydric alcohols ; Isomeric alcohols 334-34^ 
 
 Dihydric alcohols or Glycols -347 
 
 Polyhydric alcohols ; Glycerols, &c 34^-349 
 
 ALDEHYDES 35~356 
 
 ACIDS. 
 
 Monobasic ; Acetic, Acrylic, Benzoic series ; Stereo-isomerism . 357~3 8 3 
 
 Dibasic 3^4-396 
 
 Polybasic : 397-398 
 
 KETONES 399-4! 
 
 ETHERS 402-409 
 
 HALOGEN DERIVATIVES. Hydrocarbons ; Alcohols ; Aldehydes ; Acids 410-417 
 
 ETHEREAL SALTS 418-433 
 
 Sulphonic acids . 434 
 
 Nitre-compounds .......... 435 
 
 ORGANO-MINERAL COMPOUNDS . . .- . . . 436-445 
 AMMONIA DERIVATIVES. 
 
 Amines ; Amides ; Amido-acids ....... 446-479 
 
 Diazo- and Azo-compounds ; Hydrazines ; Azo-imides . . . 480-485 
 
 CYANOGEN COMPOUNDS . 486-505 
 
 PHENOLS 506-518 
 
 QUINONES. Triphenylmethane dyestuffs . . . . . 519-522 
 
 CARBOHYDRATES 523-546 
 
 GTLUCOSIDES. Vegetable colouring-matters 547-553 
 
 ALBUMINOID COMPOUNDS. Animal colouring-matters .... 554-561 
 HETERONUCLEAL COMPOUNDS. 
 
 Pyrrol ; Pyridine ; Quinoline 562-577 
 
 Uric acid and the Alkaloids 578-591 
 
 PHYSICAL PROPERTIES OP ORGANIC COMPOUNDS. 
 
 Fusing- and Boiling-Points ....... . 592-594 
 
 Specific Volumes 595 
 
 Optical Properties .......... 596 
 
 Absorption Spectra 597 
 
 APPLIED OKGANIC CHEMISTKY. 
 
 DISTILLATION OP COAL 598 
 
 DYEING AND CALICO-PRINTING 599 
 
 TANNING 600 
 
 OILS AND FATS 601 
 
 SOAP ; CANDLES 602- 603 
 
 STARCH ; MALTING 604-605 
 
 BREWING ; WINE AND SPIRITS 606-607 
 
 BREAD 608 
 
 TEA, COFFEE, COCOA 609 
 
TABLE OF CONTENTS. xi 
 
 APPLIED OKGANIC CHEMISTKY (continued.) PARAGRAPHS 
 
 ANIMAL CHEMISTRY^ 
 
 Milk, blood, flesh, urine ......... 610-614 
 
 CHEMISTKY OF VEGETATION. 
 
 Soils, manures . . . . . . . . . . .615 
 
 Kotation of crops 616 
 
 Chemical changes in plants 617-619 
 
 NUTKITION OF ANIMALS 620-621 
 
 CHANGES AFTER DEATH . 622 
 
 INDEX .827 
 
ATOMIC WEIGHTS.* 
 
 Aluminium . 
 
 Al'" 
 
 26.9 
 
 Neon . 
 
 . 
 
 19.9 
 
 Antimony . 
 
 . Sb'"orSb v 
 
 II9-3 
 
 Nickel . 
 
 . Ni"orNi'" 
 
 58.3 
 
 Argon . 
 
 . 
 
 39-6 
 
 Niobium 
 
 . Nb v 
 
 93-3 
 
 Arsenic 
 
 . As"'orAs v 
 
 744 
 
 Nitrogen 
 
 . N"' or NV 
 
 13-9 
 
 Barium 
 
 . Ba" 
 
 136.4 
 
 Osmium 
 
 . Osviii 
 
 189.6 
 
 Beryllium .. 
 
 . Be" 
 
 9 
 
 Oxygen 
 
 . 0" 
 
 15-9 
 
 Bismuth 
 
 . Bi'" or Bi v 
 
 206.9 
 
 Palladium . 
 
 . Pd"orPd iv 
 
 105.7 
 
 Boron . 
 
 . B'" 
 
 10.9 
 
 Phosphorus . 
 
 . P'"orPv 
 
 30.8 
 
 Bromine 
 
 . Br' 
 
 794 
 
 Platinum 
 
 . Pt' or Pt iv 
 
 J93-3 
 
 Cadmium 
 
 . Cd" 
 
 iii.6 
 
 Potassium 
 
 . K' 
 
 3^-9 
 
 Caesium 
 
 . Cs' 
 
 132 
 
 Praseodymium 
 
 . 
 
 1394 
 
 Calcium 
 
 . Ca" 
 
 39-8 
 
 Kadium 
 
 . 
 
 223.3 
 
 Carbon . 
 
 . C iv 
 
 11.9 
 
 Khodiurn 
 
 . Ro'" 
 
 102.2 
 
 Cerium . 
 
 . Ce" 
 
 139 
 
 Kubidium 
 
 . Kb' 
 
 84.8 
 
 Chlorine 
 
 Cl' 
 
 35-2 
 
 Kuthenium . 
 
 . Ruiv 
 
 IOO.9 
 
 Chromium . 
 
 . Cr'" or Cr vi 
 
 5i-7 
 
 Samarium . 
 
 . Sm 
 
 148.9 
 
 Cobalt . 
 
 . Go" or Co'" 
 
 58.5 
 
 Scandium 
 
 . Sc 
 
 43-8 
 
 Copper . 
 
 . Cu' or Cu" 
 
 63-1 
 
 Selenium 
 
 . Se" 
 
 78.6 
 
 Erbium 
 
 . E" 
 
 164.8 
 
 Silicon 
 
 . Siiv 
 
 28.2 
 
 Fluorine 
 
 . F' 
 
 18.9 
 
 Silver . 
 
 . . Ag' 
 
 107.1 
 
 Gadolinium . 
 
 . 
 
 155 
 
 Sodium 
 
 . Na' 
 
 22.9 
 
 Gallium 
 
 . Ga'" 
 
 69.5 
 
 Strontium 
 
 . Sr" 
 
 87 
 
 Germanium . 
 
 . Ge"orGe iv 
 
 71.9 
 
 Sulphur 
 
 . S" or S* 
 
 31-8 
 
 Gold . 
 
 . Au'" 
 
 195-7 
 
 Tantalum 
 
 . Taiv 
 
 181.6 
 
 Helium 
 
 . 
 
 4 
 
 Tellurium 
 
 . Te" 
 
 126.6 
 
 Hydrogen 
 
 . H' 
 
 i 
 
 Terium 
 
 . 
 
 158-8 
 
 Indium 
 
 . In'" 
 
 113.1 
 
 Thallium 
 
 . Tl' 
 
 202.6 
 
 Iodine . 
 
 . I' 
 
 125.9 
 
 Thorium 
 
 . Th" 
 
 230.8 
 
 Iridium 
 
 . Iriv 
 
 I9I-5 
 
 Thulium 
 
 . 
 
 169.7 
 
 Iron 
 
 . Fe" or Fe'" 
 
 55-5 
 
 Tin . 
 
 . Sn" or Sn iv 
 
 II8.I 
 
 Krypton 
 
 
 81.2 
 
 Titanium 
 
 . Ti*v 
 
 47-7 
 
 Lanthanum . 
 
 . La" 
 
 137-9 
 
 Tungsten 
 
 . W vi 
 
 182.6 
 
 Lead . 
 
 . Pb" 
 
 205.4 
 
 Uranium 
 
 . U" or U'" 
 
 236.7 
 
 Lithium 
 
 . Li' 
 
 7 
 
 Vanadium . 
 
 . V'orVv 
 
 50.8 
 
 Magnesium . 
 
 . Mg" 
 
 24.2 
 
 Xenon . 
 
 . 
 
 127 
 
 Manganese . 
 
 . Mn" or Mn iv 
 
 54-6 
 
 Ytterbium . 
 
 . 
 
 I7I.7 
 
 Mercury 
 
 . Hg' or Hg" 
 
 198.5 
 
 Yttrium 
 
 . Y" 
 
 88.3 
 
 Molybdenum 
 
 . Mo* 
 
 95-3 
 
 Zinc . 
 
 . Zn" 
 
 64.9 
 
 Neodymiuui 
 
 . 
 
 142.5 
 
 Zirconium . 
 
 . Zr^ 
 
 89.9 
 
 * The accent or index affixed to each symbol expresses the number of atoms of hydrogen 
 for which the atomic weight of the element is usually exchangeable in chemical combinations. 
 Tne numbers given are referred to the standard H = 1. 
 
INTRODUCTION. 
 
 THE special province of Chemistry is the study of such changes in the 
 properties of matter as are typified by the rusting of iron. 
 
 When the rust is examined it is found to be essentially different 
 from the iron, which may be said to have changed its nature in 
 becoming rust. 
 
 The melting of iron when it is very strongly heated is also a change 
 in the nature of the metal, for the properties of a liquid are palpably 
 different from those of a solid. 
 
 The two changes are, however, dissimilar in character ; for the rust 
 does not again become iron when left to itself, whereas the liquid iron 
 again becomes solid when allowed to cool, and the cold mass in no way 
 differs from the original iron. 
 
 Both phenomena are accompanied by an alteration of the iron from 
 the grey, solid form in which it generally exists, but the phenomenon 
 of rusting produces a change which is permanent, whilst that of lique- 
 faction produces a change which is only temporary. 
 
 A. distinction is generally drawn between these two kinds of change 
 by calling the permanent kind a chemical change, and the temporary 
 kind a physical change. 
 
 An instrument indispensable for the study of chemistry is the 
 
 Fig. i. 
 
 balance (Fig. i) a pair of scales sufficiently sensitive to show small 
 differences of weight. 
 
2 INTRODUCTION. 
 
 If a portion of iron be weighed before and after it has rusted, the 
 iron, together with its coat of rust, will be found to be heavier than the 
 original iron. 
 
 Since matte); in a chemical sense, is anything which possesses weight, 
 the quantity of matter in the rust is greater than that in the iron. It 
 must not be supposed that any matter has been created during the rust- 
 ing. The matter which has now become attached to the iron has been 
 acquired from the atmosphere, where it previously existed in the in- 
 visible, but none the less weighable, form of matter, the gaseous state. 
 
 Another common example of a chemical change is furnished by heat- 
 ing a lump of marble at a red heat. There is here no very conspicuous 
 alteration in the appearance of the marble, although the structure of 
 the piece ia seen to have been somewhat modified. It can easily be 
 shown, however, that there has been a permanent; change wrought in 
 the marble, for when the lump has cooled it is found to become hot 
 again, and to crumble to powder when water is poured upon it ; neither 
 of these manifestations occurs when the original marble is wetted with 
 water. 
 
 By weighing the marble before and after it has been heated, a loss of 
 weight may be proved to have occurred during this chemical change 
 a quantity of matter has left the marble. 
 
 Here, however, there has been no destruction of matter ; that which 
 has left the marble has disappeared because it has been converted into 
 the invisible or gaseous form, and has spread itself through the sur- 
 rounding atmosphere. 
 
 By allowing iron to rust in a tightly corked bottle (containing air), 
 and by heating marble in an apparatus designed to prevent the gas 
 which is evolved from passing into the surrounding atmosphere, it can 
 easily be demonstrated that neither the bottle nor the apparatus alters 
 in weight during the rusting or heating. 
 
 A little reflection will show the reason for this. When an " empty " 
 bottle is tightly corked there is enclosed in it a portion of the atmos- 
 phere, which is weighed with the bottle and remains unchanged until 
 the cork is removed. If iron is also in the bottle, it rusts by attaching 
 to itself a portion of the atmosphere present, and the atmosphere loses 
 just as much matter as the iron gains during the process, so that the 
 total amount of matter, and therefore of weight, in the bottle remains 
 unaltered. 
 
 So, also, when the apparatus containing the marble is heated, the gas 
 which leaves the marble is restrained from disseminating itself through 
 the surrounding atmosphere and from no longer affecting the balance. 
 When kept, as it were, on the balance-pan by being suitably caught, it 
 is weighed with the rest of the marble, so that there is the same quan- 
 tity of matter on the pan as there was before, and the total weight 
 remains unaltered. 
 
 The above observations are concisely expressed in the definition of 
 the principle of the conservation of matter : In any space the total 
 quantity of matter remains the same, although the matter may move 
 from one part of the space to another or be transformed from one kind of 
 matter into another. The special enclosure of the iron and the marble 
 vyould be unnecessary for the above proof of the principle, were it pos- 
 sible to weigh the whole room in which the experiments are performed. 
 
INTRODUCTION. 
 
 The two chemical changes which have been so far discussed are essen- 
 tially different, in that the iron has had another kind of matter (the 
 oxygen gas of the atmosphere) added to it, whilst the marble has had 
 another kind of matter (the gas carbon dioxide) separated from it. 
 
 The first kind of change, the addition of two or more kinds of matter 
 to each other, producing a third kind, is known as chemical combination. 
 The latter, the separation of one kind of matter into two or more 
 different kinds, is known as chemical decomposition. 
 
 It has been found that iron can undergo only the first kind of 
 chemical change it can only be converted into another kind of matter 
 by chemical combination ; iron cannot be decomposed. Much investi- 
 gation has shown that this peculiarity of iron is shared by 76 other 
 kinds of matter, so that all substances fall into two classes, namely : 
 
 Elements, or those substances which cannot be decomposed. 
 
 Compounds, or those substances which can be decomposed. 
 
 The .substances in the latter class are, of course, much more numerous 
 than the elements. They may be decomposed into other, simpler 
 compounds, or into the elements of which they consist. 
 
 Thus, the first products of the decomposition of marble are lime (the 
 solid referred to above as becoming hot when water is poured upon it), 
 and carbon dioxide gas. Each of these, however, is itself a compound, 
 and can be further decomposed (not easily by heat), the first into 
 calcium and oxygen, the second into carbon and oxygen. These three 
 substances calcium, carbon, and oxygen are not capable of decom- 
 position, so far as we know. 
 
 The following list includes the various kinds of matter at present 
 believed to be elements. It will be understood that the category. is 
 liable to both extension and contraction; for the discovery of new 
 elements, the existence of which has been unsuspected, or the demon- 
 stration that what has heretofore been called an element is in reality a 
 compound, may at any time necessitate an alteration of the list. The 
 reason for the division of the elements into non-metals and metals will 
 be given hereafter. 
 
 The Non-Metallic Elements are (20). 
 
 *0xygen. 
 *Hydrogen. 
 *Nitrogen. 
 
 Sulphur. 
 Selenium. 
 Telluriura.f 
 
 *Fluorine. 
 Chlorine. 
 
 Bromine. 
 
 *Argon. 
 "Helium. 
 *Krypton. 
 
 Carbon. 
 
 
 Iodine. 
 
 *Neon. 
 
 
 Phosphorus. 
 
 
 *Xenon. 
 
 Boron. 
 
 Arsenic.f 
 
 
 
 Silicon. 
 
 
 
 
 * Gases at the ordinary temperature. 
 
 + Arsenic and tellurium are frequently classed among the metals, which they resemble in 
 some of their properties. 
 
INTRODUCTION. 
 The Metals are (56). 
 
 Caesium. 
 
 Aluminium. 
 
 Zinc. 
 
 Copper. 
 
 Mercury. 
 
 Rubidium. 
 
 Gallium. 
 
 Nickel. 
 
 Bismuth. 
 
 Silver. 
 
 Potassium. 
 
 Germanium, f 
 
 Cobalt. 
 
 Lead. 
 
 Gold. 
 
 Sodium. 
 
 Zirconium. 
 
 Iron. 
 
 Thallium. 
 
 Platinum. 
 
 Lithium. 
 
 Thorium. 
 
 Manganese. 
 
 Tin 
 
 Palladium. 
 
 Barium. 
 Strontium. 
 Calcium. 
 Magnesium. 
 Beryllium. 
 
 *Yttrium. 
 *Erbium. 
 *Samarium. 
 Scandium. 
 Cerium. 
 Lanthanum. 
 Neodymium. 
 
 Chromium. 
 Cadmium. 
 Uranium. 
 Indium. 
 
 -i in. 
 Titanium. 
 Tantalum. 
 Molybdenum. 
 Tungsten. 
 Vanadium. 
 Antimony, f 
 
 Rhodium. 
 Ruthenium. 
 Osmium. 
 Iridium. 
 
 
 Praseodymium. 
 
 
 
 
 
 Niobium. 
 
 
 
 
 
 * Terbium. 
 
 
 
 
 
 * Ytterbium. 
 
 
 
 
 
 Thulium. 
 
 
 
 
 Many of these elements are so rarely met with, that they have not 
 received any useful application, and are interesting only to the pro- 
 fessional chemist. This is the case with the elements in the last 
 column of the Table, p. 3, among the non-metallic elements, and with 
 a large number of the metals. 
 
 The following list includes those elements with which it is important 
 that the general student should become familiar, together with the 
 symbolic letters by which it is customary to represent them, for the 
 sake of brevity, in chemical writings : 
 
 Non-Metallic, Elements of practical importance (13). 
 
 Oxygen, 
 
 
 
 Sulphur, 
 
 S 
 
 Fluorine, 
 
 F 
 
 Hydrogen, 
 
 H 
 
 
 
 Chlorine, 
 
 Cl 
 
 Nitrogen, 
 
 N 
 
 Phosphorus, 
 
 P 
 
 Bromine, 
 
 Br 
 
 Carbon, 
 
 C 
 
 Arsenic, 
 
 As 
 
 Iodine, 
 
 I 
 
 Boron, 
 
 B 
 
 
 
 
 
 Silicon, 
 
 Si 
 
 
 
 
 
 Metallic Elements of pi'actical importance (28). 
 
 Potassium, K (JKaliwn) 
 
 Cadmium. 
 
 Cd 
 
 Sodium, Na (Natrium) 
 
 Uranium, 
 
 U 
 
 Barium, Ba 
 Strontium, Sr 
 
 Copper, 
 Bismuth, 
 
 Cu (Cuprum) 
 Bi 
 
 Calcium, Ca 
 Magnesium, Mg 
 
 Lead, 
 
 Pb (Plumbum) 
 
 Aluminium, Al 
 
 Tin, 
 Titanium, 
 
 Sn (Stannum) 
 Ti 
 
 Zinc, Zn 
 
 Tungsten, 
 Thorium, 
 
 W ( Wolframium) 
 Th 
 
 Nickel, Ni 
 
 Cerium, 
 
 Ce 
 
 Cobalt, Co 
 Iron, Fe (Ferrum) 
 
 Antimony, 
 
 Sb (Stibium) 
 
 Manganese, Mn 
 Chromium, Cr 
 
 Mercury, 
 Silver, 
 
 Hg (Hydrargyrum) 
 Ag (Argentum) 
 
 
 Gold, 
 
 Au (Aurum) 
 
 
 Platinum, 
 
 Pt 
 
 * -mere is some doubt as to the elementary nature of these substances 
 f Sometimes classed among the non-metals. 
 
INTRODUCTION. 5 
 
 Although the 41 elements here enumerated are of practical import- 
 ance, many of them derive their importance solely from their having 
 met with useful applications in the arts. The number of elements 
 known to play an important part in the chemical changes concerned in 
 the maintenance of animal and vegetable life is very limited. 
 
 Elements concerned in the Chemical Changes occurring in Life. 
 
 Non-Metallic. 
 
 Metallic. 
 
 Oxygen. 
 
 Sulphur 
 
 Potassium. 
 
 Aluminium. 
 
 Hydrogen. 
 
 
 Sodium. 
 
 
 Nitrogen. 
 Carbon. 
 
 Silicon. 
 
 Chlorine. 
 Iodine. 
 
 Calcium. 
 Magnesium. 
 
 Manganese. 
 
 These elements will, of course, possess the greatest importance for 
 those who study Chemistry as a branch of general education, since a 
 knowledge of their properties is essential for the explanation of the 
 simple chemical changes which are daily witnessed. 
 
 The student who takes an interest in the useful arts will also 
 acquaint himself with the remainder of the 41 elements of practical 
 importance, whilst the mineralogist and professional chemist must 
 extend his studies to every known element. 
 
 By far the greater proportion of the various materials supplied to us 
 by animals and vegetables consists of the four elements oxygen, 
 hydrogen, nitrogen, and carbon ; and if we add to these the two most 
 abundant elements in the mineral world, silicon and aluminium, we 
 have the six elements composing the bulk of all matter. 
 
 It is computed that of the mineral matter of the earth's crust oxygen 
 constitutes 50 per cent., silicon 2 5. 3, aluminium 7. 3, iron 5, calcium 3.5, 
 magnesium 2.5, sodium 2.3, potassium 2.2, and hydrogen i. No other 
 element is present to a greater extent than 0.3 per cent. 
 
 The formation of a chemical compound consists in the combination 
 of two or more elements, brought about by the inherent attraction of 
 the elements for each other. This attraction varies between different 
 elements. Whilst some combine with each other immediately they are 
 brought in contact, others show no such tendency. In the sequel, the 
 nature of chemical attraction will receive attention. It must here be 
 stated that the phenomenon of combination has long been attributed 
 to a force termed chemical affinity : thus the rusting of iron is said to 
 consist in the formation of a compound of iron with oxygen, determined 
 by the chemical affinity of these elements for each other.* 
 
 A characteristic of a chemical compound is homogeneity of struc- 
 ture. Pure compounds seldom exist in nature. The rock called granite, 
 for example, is not a single chemical compound, but a mixture of 
 chemical compounds, as, indeed, is rendered apparent by a merely 
 superficial examination, when it is seen that there are three distinctly 
 different substances in the granite. This at once stigmatises the rock 
 
 * For the sake of simplicity, no reference has been made to the necessity for the presence 
 of other substances besides oxygen and iron for the formation of rust. It will be familiar to 
 most readers that water is one of these essentials. 
 
6 INTRODUCTION. 
 
 as a mixture, for it is never possible to see the elements in a compound. 
 When the granite is powdered, a microscope is requisite to make its 
 heterogeneous character visible, but by taking advantage of some essen- 
 tial difference between the properties of the three constituent sub- 
 stances as, for instance, the different rates at which they sink in water 
 a separation, more or less perfect, may be effected. 
 
 No such differentiation of the parts of a lump of sugar can be detected. 
 This is a pure compound, and is homogeneous, so that when it is 
 powdered, every granule of it possesses the same properties as those 
 of the whole mass each will dissolve in water, will taste sweet, &c. 
 
 Thus, a mixture of elements or compounds is readily distinguished 
 from a pure compound by the fact that each constituent of the mixture 
 retains its individual properties, whereas in a pure compound the 
 properties of its constituents (elements) are entirely obliterated. 
 
 Most natural substances consist of mixtures of compounds. . The 
 classification of the science of chemistry into organic chemistry, dealing 
 with animal and vegetable substances, and inorganic chemistry, dealing 
 with mineral substances, is based on the supposition, formerly held, 
 that compounds produced through the operation of animal and vegetable 
 life (such as sugar, starch, &c.) are essentially different from those 
 which are, or have been, formed without the intervention of life. 
 This classification is still adopted as convenient for the purposes of study. 
 
 It is the object of the chemist both to determine the constituents of 
 every substance a process termed analysis and to build up every 
 substance from its constituents a process termed synthesis. 
 
 When these processes are directed merely to the determination of 
 the nature or quality of the constituents, they are said to be qualitative, 
 while when they take cognisance of the proportion which the con- 
 stituents bear to each other, they are quantitative gravimetric if the 
 proportion by weight is considered, volumetric if the proportion is by 
 volume. 
 
 In the early history of Chemistry, investigations were purely quali- 
 tative, and had they remained so the whole of chemical knowledge 
 might be told in a dozen pages of this book. It was the use of the 
 balance that revealed the very essence of the science the fact that 
 every compound is of constant quantitative composition. 
 
 Marble, chalk, and coral were early recognised by qualitative analysis 
 to consist of the same compound mixed with small amounts of other 
 substances. Afterwards, quantitative analysis showed that in each 
 case the compound in question contains, by weight, 56 per cent, of lime 
 and 44 per cent, of carbon dioxide. 
 
 Moreover, the same compound, now called calcium carbonate, was 
 soon synthesised by bringing together lime and carbon dioxide made 
 from other sources than any of the three minerals named ; it was found 
 that, whatever proportions of lime and carbon dioxide were used, the 
 compound produced always contained no more and no less than 56 per 
 cent, of the one and 44 per cent, of the other. 
 
 Thus, if 28 parts of lime were brought into contact with 72 parts of 
 carbon dioxide, not 100 but 50 parts of calcium carbonate were formed ; 
 the 28 parts of lime combined with only 22 parts of carbon dioxide 
 (the same ratio as 56 : 44) and 50 of carbon dioxide were left over 
 uncombined. 
 
INTRODUCTION. 7 
 
 It is sufficiently remarkable that calcium carbonate from marble 
 formed ages ago by solidification of a fused mass under great pressure, 
 from chalk deposited during ages as mud from suspension in water, 
 from coral built up by marine animals in our own day, and from 
 material made in a few minutes in a laboratory, should have the same 
 quantitative composition. 
 
 When a number of facts of this kind had been accumulated it became 
 possible to assert that constancy of quantitative composition is the 
 criterion by which a compound may be known. Any form of matter 
 showing variation of composition cannot be a single compound. 
 
 For instance, a mass of chalk which has been wetted with water 
 contains a considerable proportion of the latter, but one which varies 
 with the source of the chalk ; hence there is here no compound of chalk 
 with water. On the other hand, lime from any source absorbs always 
 32 per cent, of its weight of water the product is a compound. 
 
 Lime and carbon dioxide which have been spoken of as the con- 
 stituents of calcium carbonate are only the proximate, not the ultimate 
 constituents thereof. For each is capable of decomposition, though not 
 easily by heat, into elements, the lime into calcium and oxygen and 
 the carbon dioxide into carbon and oxygen. What is true of the 
 combination of lime with carbon dioxide is true of that of calcium or 
 carbon with oxygen; wherever or however these compounds are ob- 
 tained, they contain their constituent elements always in the same 
 proportion. 
 
 A collection of observed facts in agreement with each other enables 
 the investigator to formulate a law of Nature which remains valid so 
 long as newly discovered facts do not contradict it. In this case the 
 law, which may be regarded as the sheet-anchor of Chemical science, is 
 known as 
 
 The Law of Constant Proportions. Every compound contains its 
 constituent elements always in the same proportion, from whatever 
 source the compound may be obtained. 
 
 An attempt to explain this and other similar laws which the student 
 will learn presently, led Dalton, a century ago, to the hypothesis as to 
 the structure of matter, called the atomic theory. The facts and argu- 
 ments which justify this hypothesis will be referred to hereafter. It is, 
 however, essential that the student should attempt to grasp the funda- 
 mental conception on which the theory is based before embarking on a 
 study of the relationships between the elements. 
 
 The fundamental conception is this : When matter is submitted to 
 a process of subdivision, a certain fineness will ultimately be attained 
 beyond which disintegration will be impossible ; in other words, any 
 given mass of matter consists of a number of particles, each of which cannot 
 'be divided. Thus, when a piece of marble has been ground to powder, 
 the single particle has become a large number of particles. Now, by 
 the hypothesis stated above, could the process of grinding be perfected, 
 a stage would be reached when it would be impossible to further in- 
 crease the number of these particles, for each would be indivisible. 
 The ultimate particle of marble would then have been attained. These 
 ultimate particles of matter are called molecules. 
 
 But it has been already stated that when marble is heated, it is 
 decomposed into lime and carbon dioxide, so that it is possible to sub- 
 
INTRODUCTION. 
 
 divide marble by a process other than mechanical grinding; but the 
 product is no longer marble. What is true of the lump of marble 
 should be true also of its mechanically indivisible particle, or molecule. 
 The molecules of marble can still be divided by decomposing them. 
 
 It is highly probable that the molecules of marble, were they 
 separated, would be found to be invisible. The smallest visible particle 
 of marble is probably an aggregate of many molecules. It is not 
 possible to render marble invisible, because we have no means for 
 moving the molecules which make up these aggregates appreciably 
 further from each other. This is because the method usually adopted 
 for the purpose of separating molecules from each other namely, the 
 application of heat decomposes the molecules of marble. 
 
 There are many substances, however, the molecules of which are not 
 decomposed by a moderately intense heat, and are moved so far apart 
 from each other by the application of this agency, that the whole mass 
 becomes invisible. Water is a familiar example, steam being invisible 
 until it is so far chilled that the separated molecules have come 
 together again to form visible particles. Gases which remain such at 
 the ordinary temperature require to be very much chilled in order to 
 bring their molecules sufficiently close to each other to form visible 
 particles in other words, to convert the gas into a liquid. 
 
 There are several methods for subdividing a substance without 
 decomposing it, of which two (mechanical grinding and the application 
 of a moderate heat) have been quoted. Such methods may be called 
 physical methods of subdivision, inasmuch as they do not produce a 
 chemical change. 
 
 A MOLECULE may now be denned as the ultimate particle of a com- 
 pound or element, divisible only by chemical change. 
 
 Inasmuch as an element cannot be decomposed, its molecules must 
 be incapable of any further division such as that possible for the 
 molecule of a compound like marble. This is true when the molecules 
 of the element exist by themselves ; there is no evidence to show that 
 the molecules of oxygen, for instance, can be divided so long as the 
 oxygen exists by itself in an uncombined condition. 
 
 There is excellent evidence, however, that the molecules of many 
 compounds contain half the quantity of oxygen that the molecule of 
 this element contains. It must be admitted, therefore, that the oxygen 
 molecule consists of two parts, which can only be separated from each 
 other when the molecule enters into combination. The same argument 
 applies to other elements, the molecules of the majority of which 
 consist of parts, although several have no parts. 
 
 These parts of elementary molecules are indivisible either by physical 
 or chemical methods ; they are therefore the true indivisibles or atoms. 
 
 An ATOM may be denned as the smallest particle of an element 
 existing in a molecule, indivisible by any means. 
 
 A consideration of the above definition, together with that given for 
 a compound, will show that to speak of the atom of a compound would 
 be a contradiction of terms. 
 
 What has been said above as to the fundamental conception of the 
 atomic theory may be thus summarised. Matter is not capable of in- 
 finite subdivision, but consists of particles which are indivisible and are 
 called atoms ; these have no separate existence, but occur in combination 
 
INTRODUCTION 9 
 
 with each other to form molecules, which are the smallest particles 
 capable of separate existence. When the atoms thus united are of the 
 same kind, the molecule is that of an element ; when they are of dif- 
 ferent kinds the molecule is that of a compound. When compound 
 molecules are decomposed the atoms of the constituent elements are 
 momentarily liberated, but immediately recombine to form new mole- 
 cules. Each atom of the same element has the same weight ; but the 
 atoms of different elements have different weights. 
 
 How Dalton applied this conception to explain the laws of chemical 
 combination is fully set forth in the chapter on General Principles. 
 
 It is agreed among chemists that the symbol for an element shall 
 represent one atom, and a certain number of parts by weight, of the 
 element. This figure is termed the atomic weight of the element, and 
 is believed to be the number of times that an atom of the element is 
 heavier than an atom of the gaseous element hydrogen, which is said to 
 weigh i. It is an abstract number, and may represent any units of 
 weight. Thus, the symbol O means one atom of oxygen and 16 unit 
 weights of oxygen it may be 16 grains, 16 Ibs., 16 grams, &c. 
 
 Since the atomic theory does not admit the existence of the atom of 
 a compound, a compound cannot have an atomic weight. 
 
 The molecular weight of either an element or a compound is the 
 number of times that the molecule is heavier than that of hydrogen, 
 the molecule of which is said to weigh 2. 
 
 The molecular weight of a substance is ascertained by doubling the 
 number of times that a volume of the substance in the form of vapour 
 or gas is heavier than an equal volume of hydrogen, weighed at the 
 same temperature arid pressure.* This value is known as the vapour 
 density^ of the gas, and is determined by weighing a stoppered globe 
 (such as that shown in fig. 50) of known weight, first when it is full 
 of hydrogen, and then when it is full of the vapour or gas whose vapour 
 density is to be determined ; obviously, the vapour density will be the 
 quotient, 
 
 weight of (globe + gas) - weight of globe 
 weight of (globe + hydrogen) weight of globe. 
 
 Hence the MOLECULAR WEIGHT of an element or compound is twice 
 the number of times that a volume of it in the state of gas is heavier 
 than an equal volume of hydrogen weighed at the same temperature 
 and pressure. 
 
 As the molecule of an element contains only atoms of the same kind, 
 each having the same atomic weight, the molecular weight of the 
 element must be a multiple of the atomic weight by i, 2, 3, &c., accord- 
 ingly as the molecule contains i, 2, 3, &c., atoms. 
 
 Now the molecule of a compound can never contain less than one 
 atom of any of its constituent elements because an atom cannot be 
 divided. Hence the molecular weight of a compound can never contain 
 
 * It will be remembered that gases expand in volume when heated or when submitted to a 
 reduced pressure ; hence a given volume of gas never has the same weight unless its tem- 
 perature and pressure are the same each time it is weighed (except in the rare event of a 
 diminished temperature compensating for a diminished pressure). 
 
 f This term is used because the majority of substances must, like water, be vaporised by 
 heat before they are in the gaseous state. 
 
10 INTRODUCTION. 
 
 less than one atomic weight of each of the constituent elements, though 
 it may contain more, 
 
 It is possible, therefore, to define the ATOMIC WEIGHT of an element 
 as the smallest weight of it found in one molecular weight of any of its 
 compounds. 
 
 For example, by the method described above carbon dioxide is found 
 to have the vapour density 22, consequently its molecular weight is 44. 
 Now analysis shows that 44 parts by weight of carbon dioxide contain 
 1 2 parts by weight of carbon, and as this is the smallest weight of this 
 element that occurs in one molecular weight of any of its compounds, 
 it is the atomic weight. 
 
 When the molecule of an element contains only one atom the symbol 
 for the element represents both the atom and the molecule ; thus Hg 
 means both a molecule and an atom of mercury because the molecules 
 of this element are monatomic. On the other hand, the molecules of 
 hydrogen and oxygen are H 2 and 2 respectively, these elements having 
 diatomic molecules. Phosphorus is an element having tetratomic mole- 
 cules, expressed by the symbol P 4 . Such molecular symbols represent 
 twice or four times the atomic weight ; thus 2 =i6x2 = 32 parts by 
 weight. P 4 = 3i X4=i24 parts by weight. 
 
 It follows from what was said above as to the method of ascertaining 
 the molecular weight, that if the volume of one unit weight of hydrogen 
 be called unit volume, the molecular weight of any gas, expressed in the 
 same units, must be called two volumes. For example, if the volume 
 occupied by one gram of hydrogen be called one volume, 32 grams of 
 oxygen will occupy two volumes. The symbol for any molecule, there- 
 fore, represents two volumes of the substance in the state of gas. 
 
 The symbol for a compound is called a formula, and represents the 
 molecule of the compound, which consists of atoms of its constituent 
 elements united together, so that the formula is the symbols for these 
 atoms written side by side ; thus, HC1 represents a molecule of a com- 
 pound of hydrogen with chlorine ; HCN, the molecule of a compound 
 of hydrogen, carbon, and nitrogen ; and each represents two volumes of 
 the compound in the state of gas. When analysis shows that there are 
 2, 3. or 4 atomic weights, and therefore atoms, of the same element 
 present in one molecule of the compound, this is expressed by writing 
 2, 3, or 4 after the symbol for the element. Thus, H 2 S0 4 represents a 
 compound whose molecule contains two atomic weights or atoms of 
 hydrogen, one atomic weight or atom of sulphur, and four atomic 
 weights or atoms of oxygen. 
 
 Thus the number of parts by weight expressed by the formula for a 
 compound is the sum of the atomic weights of the elements present ; 
 HC1 means 1 + 35.5 = 36.5 parts by weight of hydrogen chloride; 
 HCN means 1 + 12 + 14 = 27 parts by weight of hydrogen cyanide; 
 H 2 S0 4 means (i x 2)4-32 f (16x4) = 98 parts by weight of sulphuric 
 acid. 
 
 The mere contact or mixture of substances is expressed by the sign 
 + ; thus H, + C1 2 implies that a molecule of hydrogen has been brought 
 into contact with a molecule of chlorine. 
 
 From the point of view of the atomic theory, chemical combination is 
 regarded as consisting in the exchange of atoms in one molecule for 
 those in another, when the molecules are brought in contact. 
 
INTRODUCTION. 1 1 
 
 For example, chemical combination occurs between hydrogen and 
 chlorine, to form hydrochloric acid, the change being represented by 
 the chemical equation H 2 + C1 2 = 2HC1, which implies that the molecules 
 of hydrogen and chlorine exchange atoms. 
 
 It will be seen from the statements made above, that this equation 
 also implies that 2 parts by weight or 2 vols. of hydrogen and 35.5 x 2 
 parts by weight or 2 vols. of chlorine, yield 36.5 x 2 parts by weight 
 or 4 vols. of hydrochloric acid. 
 
 It must be remembered that a chemical equation is only a short 
 mode of expressing the result of an experiment, and cannot be used, like 
 a mathematical equation, to effect the solution of a problem. 
 
 A chemical equation may be written to express what is likely to be 
 the result of the action of different molecules upon each other, but it 
 has no value until verified by experiment. 
 
 Chemical decomposition is the separation of the atoms composing a 
 molecule, which must precede the formation of a new molecule. Thus, 
 the decomposition of steam by a very high temperature is expressed by 
 the equation 2H 2 = 2H 2 + 2 , which conveys the information that two 
 molecules or 36 parts by weight or 4 vols. of steam have suffered 
 chemical decomposition, and have formed two molecules or 4 vols., or 
 4 parts by weight of hydrogen, and one molecule or 2 vols., or 32 parts 
 by weight of oxygen. 
 
 Chemical changes are always attended by evolution or absorption of 
 heat. As a general rule, the formation of compound molecules from 
 elementary molecules evolves heat, whilst the formation of elementary 
 molecules from compound molecules absorbs heat. Hence it will be 
 found that the application of heat is generally required for the com- 
 mencement of chemical change, in order to effect that separation of 
 atoms from their molecules which must precede every chemical trans- 
 formation of matter. When any chemical change appears to occur 
 without any change of temperature being observed, it is because the 
 total heat absorbed in the destruction of the original molecules is equal 
 to the total heat evolved in the construction of the new molecules. 
 
 The formation of water by the chemical combination of hydrogen 
 and oxygen consists in the separation of the atoms which compose the 
 oxygen molecule, and of those composing two hydrogen molecules, an 
 atom of hydrogen from each hydrogen molecule uniting with an atom 
 of oxygen from the oxygen molecule, as expressed in the equation, 
 00 + HH+TLH=IttIO + IfHO. Here, it is evident that the conver- 
 sion of a molecule of oxygen into water is effected by the exchange of 
 each of its oxygen atoms for two hydrogen atoms. 
 
 Since hydrogen is taken as the chemical standard or unit, and one 
 atom of oxygen is exchangeable for, or combines with, two atoms of 
 hydrogen, oxygen is said to be divalent or diad, often expressed by 
 writing it thus, 0". The atoms of some elements are exchangeable for, 
 or combine with, three atoms of hydrogen, and are said to be trivalent 
 or triad"' ; others for four, quadrivalent or tetrad, or for five, quinqui- 
 valent or pentad* , and so on. 
 
 A convenient classification, according to valency, is thus arrived at, 
 which is liable, however, to a great number of exceptions. 
 
12 INTRODUCTION. 
 
 Monads Br, 01, F, I, K, Ag, Na. 
 
 Diads Ba, Cd, Ca, Co, Cu, Fe, Pb, Mg, Mn, Hg, Ni, 0, Sr, S, Zn. 
 
 Triads Al, Sb, As, Bi, B, Or, Au, N, P. 
 
 Tetrads C, Pt, Si, Sn. 
 
 In studying the properties of bodies, a distinction must be drawn 
 between physical and chemical properties. The physical properties are 
 those in which either the mass or the molecules are alone concerned, 
 whilst the chemical properties concern the atoms. Thus, the condition 
 whether solid, liquid, or gas, the colour, odour, taste, hardness, relative 
 weight (or specific gravity), would come under the head of physical pro- 
 perties. For a solid, the geometrical form of its crystal and the tem- 
 perature at which it melts are important for identification ; and for a 
 liquid, the temperature at which it boils. 
 
 Chemists use the metric system of weights and measures. It will be 
 remembered that the unit of weight in this system is one gram, and 
 that the unit of capacity is that volume which one gram of water occu- 
 pies at 4 C. (at which temperature a given weight of water has a 
 smaller volume than at any other temperature) ; this unit of volume is 
 called a cubic centimetre. One thousand cubic centimetres make i litre. 
 One gram is equivalent to 15.43 grains, and one litre is equivalent to 
 1.76 pint. One metre or 100 centimetres or 1000 millimetres = 39. 37 
 inches. 
 
INORGANIC CHEMISTRY. 
 
 CHEMISTRY OF THE NON-METALLIC ELEMENTS 
 AND THEIR COMPOUNDS. 
 
 THE ELEMENTS OF WATER. 
 
 i. Until the latter half of the eighteenth century, water was regarded 
 as an elementary form of matter. It was first resolved into its con- 
 stituent elements, hydrogen and oxygen, by subjecting it to the in- 
 fluence of the voltaic current, which decomposes or analyses the water 
 by overcoming the chemical attraction by which its elements are held 
 together. 
 
 An arrangement for this purpose is represented in Fig. 2. 
 
 Fig-. 2. Electrolysis of water. 
 
 The glass vessel A contains water, to which a little sulphuric acid has been added 
 to increase its power of conducting electricity, for pure water conducts so imper- 
 fectly that it is decomposed with great difficulty. B and C are platinum plates 
 bent into a cylindrical form, and attached to the stout platinum wires, which are 
 passed through corks in the lateral necks of the vessel A, and are connected by 
 binding screws with the copper wires D and E, which proceed from the galvanic 
 battery G. H and are glass tubes with brass (or glass) caps and stop-cocks, and 
 are enlarged into a bell-shape at their lower ends for the collection of a consider- 
 able volume of gas. These tubes are filled with the acidified water by sucking out 
 
14 ELECTROLYSIS OF WATER. 
 
 the air through the opened stop-cocks; on closing these, the pressure of the 
 atmosphere will, of course, sustain the column of water in the tubes i. (* is a 
 Grove f s battery, consisting of five cells or earthenware vessels (A, Fig. 3) filled witi 
 
 Fig- 3- 
 
 Fig. 4. 
 
 diluted sulphuric acid (one measure of oil of vitriol to four of water). In each of 
 these cells is placed a bent plate of zinc (B), which has been amalgamated or 
 rubbed with mercury (and diluted sulphuric acid) to protect it from corrosion by 
 the acid when the battery is not in use. Within the curved portion of this plate 
 rests a small flat vessel of unglazed earthenware (C), filled with strong nitric acid, 
 in which is immersed a sheet of platinum-foil (D). The platinum (D) of each cell 
 is clamped, at its upper edge, to the zinc (B) in the adjoining cell (Fig. 4), so that 
 
 at one end (P, Fig. 2) of the battery there is a free 
 platinum plate, and at the other (Z) a free zinc 
 plate. These plates are connected with wires D 
 and E by means of the copper plates L and K, 
 attached to the ends of the wooden trough in 
 which the cells are arranged. The wire D (Fig. 2), 
 which is connected with the last zinc plate of the 
 battery, is often called the " negative pole," whilst 
 E, in connection with the last platinum plate, is 
 called the " positive pole." 
 
 When the connection is established by means of 
 the wires D and E with the " electrolytic cell " (A), 
 the " galvanic current " is commonly said to pass 
 along the \vire E to the platinum plate C, through 
 the acidified water in the electrolytic cell, to the 
 platinum plate B, and thence along the wire D 
 back to the battery. 
 
 Since the electricity travels into and out of the 
 electrolytic cell by the plates B and C, these are 
 called the electrodes (r]\eKTpov, amber root of elec- 
 tricity ; 66os, a way). The plate C, or way into the 
 cell, is called the anode (cwa, towards : 65os) ; the 
 plate B, or way out of the cell, is the cathode (/cara, 
 away from : 65os). 
 
 Another form of apparatus for this experiment 
 is shown in fig. 5. The water displaced by the 
 gases accumulating in the tubes A, o, collects in 
 the bulb 1) upon the longer branch, and exerts the 
 pressure necessary to force the gases out when the 
 stop-cocks are opened. The stop-cocks, being 
 made of glass, are not corroded by the acid. 
 
 2. During this "passage of the current" (which is only a figurative 
 mode of expressing the transfer of the electric influence), the water 
 intervening between the plates B and C is decomposed, its hydrogen 
 being attracted to the plate B (negative pole or cathode), and the 
 oxygen to the plate C (positive pole or anode). The gases can be seen 
 adhering in minute bubbles to the surface of each plate, and as they 
 
 Fig. 5. Electrolysis of water. 
 
ELECTROLYSIS OF WATER. 15 
 
 increase in size they detach themselves, rising through the acidified 
 water in the tubes H and O, in which the two gases are collected. 
 
 Since no transmission of gas is observed between the two plates, it 
 is evident that the H and O separated at any given moment from each 
 plate do not result from the decomposition of one particle of water, but 
 'from two particles, as represented in Fig. 5, where A represents the 
 particles of water lying between the plates P and Z before the 
 " current" is passed, and B the state of the particles when the current 
 has been established. P is (the anode) in connection with the last 
 platinum plate of the battery, and Z is (the cathode) in connection 
 with the last zinc plate. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 O 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 oooooooo 
 
 HHHt/Ht/HH 
 
 1- + -f 
 
 Fig. 6. 
 
 The signs + and - made use of in B refer to a common mode of 
 accounting for the decomposition of water by the battery, on the sup- 
 position that the oxygen is in a negatively electric condition, and 
 therefore attracted by the positive pole P ; whilst the hydrogen is in a 
 positively electric condition, and is attracted by the negative pole Z. 
 
 In the foregoing explanation, the part played by the sulphuric acid has been 
 omitted for the sake of simplicity. Pure water could not be decomposed unless by 
 a very much stronger battery. For a discussion of the part played by the sulphuric 
 acid the reader must refer to the chapter 011 General Principles. 
 
 The decomposition of compounds by galvanic electricity is termed 
 electrolysis.* When a compound of a metal with a non-metal is decom- 
 posed in this manner, the metal is usually attracted to the (negative) 
 pole in connection with the zinc plate of the battery, whilst the non- 
 metal is attracted to the (positive) pole connected with the platinum 
 plate of the battery. 
 
 Hence the metals are frequently spoken of as electro-positive elements, 
 and the non-metals as electro-negative. 
 
 3. If the passage of the "current" be interrupted when the tube H 
 has become full of gas, the tube will be only half full, since water is 
 a compound of hydrogen and oxygen in the proportion of two volumes of 
 hydrogen to one volume of oxygen." 1 ? When the wider portions of the 
 tubes (fig. 2) are also filled, the two gases may be distinguished by 
 opening the stop-cocks in succession and presenting a burning match. 
 The hydrogen will be known by its kindling with a slight detonation 
 and burning with a very pale flame at the jet ; whilst the oxygen will 
 very much increase the brilliancy of the burning match, and if a spark 
 
 * "HXerpov, amber root of electricity ; Avw, to loosen. 
 
 t The volume of the oxygen is always found to be slightly less than one-half the volume 
 of the hydrogen in this experiment, both because the solubility of oxygen in water is rather 
 greater than that of hydrogen, and because a small proportion of the oxygen is evolved in 
 the condition of ozone, which occupies only two-thirds of the volume occupied by an equal 
 weight of oxygen (see Ozone). 
 
!6 ELECTKOLYSIS OF HYDROCHLORIC ACID. 
 
 left at the extremity of the match be presented to the oxygen, the 
 spark will be kindled into a flame. 
 
 A volume of oxygen weighs 16 times as much as an equal volume 
 of hydrogen, so that if one volume of hydrogen be said to weigh one 
 part by weight, one volume of oxygen will weigh 16 parts by weight. 
 But in water the proportion of hydrogen to oxygen is 2 volumes : i 
 volume. Therefore the proportion by weight of these two element* 
 in the water must be 2 : 16, or water is a compound of hydrogen and 
 oxygen in the proportion of 2 parts by weight of hydrogen to 16 parts by 
 weight of oxygen. Since the atom of oxygen is believed to weigh 16 
 times as much as the atom of hydrogen, the simplest view of the com- 
 position of the molecule of water is that it contains 2 atoms of hydrogen 
 and i atom of oxygen; its formula may therefore be represented 
 
 asH 2 0. 
 
 4. The decomposition of water by electrolysis must be compared 
 with a like experiment in which the compound 
 decomposed is one of hydrogen with the ele- 
 ment chlorine, a gas called hydrogen chloride. 
 A solution of this gas in water, commonly 
 known as hydrochloric acid, yields equal 
 volumes of hydrogen and chlorine when elec- 
 trolysed. 
 
 The apparatus represented in Fig. 5 requires a little 
 alteration when it is to be used for the electrolysis of 
 hydrochloric acid, and generally takes the form shown 
 in Fig. 7. As chlorine attacks platinum, the electrodes 
 are of carbon, which cannot be sealed in glass but 
 must pass through corks. Strong hydrochloric acid is 
 poured into the bulb until both limbs are filled with 
 the acid : the stop-cocks are left open and the wires 
 from the electrodes are connected with the poles of a 
 battery of five or six Grove's cells. The gases are 
 allowed to escape until the liquid is saturated with 
 chlorine and cannot dissolve any more, this gas being 
 sufficiently soluble in water to vitiate the experiment, 
 ^o- 7- The stop-cocks are then closed and the gases allowed 
 
 to collect. The proportion of chlorine is always too 
 
 small, owing to the difficulty of saturating the liquid with it. By dissolving as 
 much common salt in the hydrochloric acid as it will take up, a better result is 
 obtained. 
 
 The chlorine is evolved at the electrode connected with the platinum 
 of the battery (the anode). It will be recognised by its greenish-yellow 
 colour and pungent odour. 
 
 A volume of chlorine weighs 35.5 times as much as an equal volume 
 of hydrogen, so that hydrogen chloride is a compound of hydrogen and 
 chlorine in the proportion of i part by weight of hydrogen to 35.5 parts 
 by weight of chlorine. The atom of chlorine is believed to weigh 35.5 
 times as much as that of hydrogen, hence a molecule of hydrogen 
 chloride may be regarded as a compound of i atom of hydrogen with 
 i atom of chlorine, represented by the formula HC1. 
 
 It will be noticed that 
 
 i vol. chlorine unites with i vol. hydrogen, 
 i vol. oxygen 2 vols. 
 Later it will be seen that i vol. of the element nitrogen unites with 
 
DECOMPOSITION OF STEAM. I/ 
 
 3 vols. of hydrogen, and there is excellent evidence that if carbon, 
 which is a solid very difficult to vaporise, could be obtained as a gas r 
 i vol. of it would combine with 4 vols. of hydrogen. No element is 
 known, i vol. of which combines with more than 4 vols. of hydrogen. 
 
 Here is an important basis for classification of the elements, for all those 
 that combine with hydrogen belong to one of the above four classes, 
 while the rest may be referred to the same classes as will be explained 
 presently and as has been indicated at p. n. 
 
 5. Another method of effecting the decomposition of water by electri- 
 city consists in passing a succession of electric sparks through steam. 
 It is probable that in this case the decomposition is produced rather 
 by the intense heat of the spark than by its electric influence. 
 
 For this purpose, however, the galvanic battery does not suffice, 
 since no spark can be passed through any appreciable interval between 
 the wires of the battery a fact which electricians refer to in the 
 statement that, although the quantity of electricity developed by the 
 galvanic battery is large, its tension or pressure is too low to allow it to 
 
 Fig. 8. Decomposition of steam by electric sparks. 
 
 discharge itself in sparks like the electricity from the machine or from 
 the induction coil, which possesses a very high tension, though its 
 quantity is small. 
 
 The most convenient instrument for producing a succession of 
 electric sparks is the induction-coil, in which a current of low tension, 
 sent from a weak battery through a coil of stout wire and back to the 
 battery, induces or excites a current of high tension in a coil of thin 
 wire of great length, wound outside the thick coil. This current is 
 capable of discharging itself in sparks, such as are obtained from the 
 electrical machine. 
 
 Fig. 8 represents the arrangements for exhibiting this experiment. 
 
 A is a half-pint flask furnished with a cork in which three holes are bored ; in 
 one of these is inserted the bent glass tube B, which dips beneath the surface of 
 the water in the trough C. 
 
 D and E are glass tubes, in each of which a platinum wire has been sealed so as 
 to project about an inch at both ends of the tube. These tubes are thrust through 
 the holes in the cork, and the wires projecting inside the flask are made to 
 approach to within about ^ of an inch, so that the spark may easily pass between 
 them. 
 
 The flask is somewhat more than half filled with water, the cork inserted, and 
 the tube B allowed to dip beneath the water in the trough, the wires in D and E 
 being connected with the thin copper wires passing from the induction-coil F, 
 which is connected by stout copper wires with the small battery G. 
 
 B 
 
1 8 DECOMPOSITION OF STEAM. 
 
 The water in the flask is boiled for about fifteen minutes, until all the air con- 
 tained in the flask has been displaced by steam. When this is the case it will be 
 found that if a glass test-tube (H) filled with water be inverted* over the oiifu 
 of the tube B, the bubbles of steam will entirely condense, with the usual shaip 
 rattling sound, and only insignificant bubbles of air will rise to the top ot the s test 
 tube. If now. whilst the boiling is still continued, the handle of the coil (F) be 
 turned so as to cause a succession of sparks to pass through the steam in the flask, 
 large bubbles of incondensable gas will accumulate in the tube H. This gas con- 
 sists of the hydrogen and oxygen gases in a mixed state, having been released from 
 their combined condition in water by the action of the electric sparks. I he gas 
 may be tested by closing the mouth of the tube H with the thumb, raising it to an 
 upright position, and applying a lighted match, when a sharp detonation will 
 indicate the re-combination of the gases.f 
 
 It has long been known that a very intense heat is capable of decomposing water. 
 The temperature required for the purpose is below the melting-point of platinum, 
 .as may be shown by the apparatus represented in fig. 9. 
 
 Fig. 9. Decomposition of steam by heat. 
 
 A platinum tube (t) is heated by the burner &, the construction of which is 
 shown at the bottom of the cut. It consists of a wide brass tube, from which the 
 coal-gas issues through two rows of holes, between which oxygen is supplied 
 through the holes in the narrow tube, brazed into a longitudinal slit between the 
 two rows of holes in the gas tube. The oxygen is supplied from a gas bag or gas- 
 holder, with which the pipe (V) is connected. 
 
 The flask (/) containing boiling water is furnished with a perforated cork, 
 Carrying a brass tube (a), which slips into one end of the platinum tube, into the 
 other end of which another brass tube (0) is slipped ; this is prolonged by a glass 
 tube attached by india-rubber so as to deliver the gas under a small jar standing 
 upon a bee-hive shelf in a trough. 
 
 The platinum tube is not heated until the whole apparatus is full of steam , and 
 no more bubbles of air are seen to rise through the water in the trough ; the gas 
 burner is then lighted, and the oxygen turned on until the platinum tube is 
 heated to a very bright red heat ; bubbles of the mixture of hydrogen and oxygen 
 produced by the decomposition of the water may then be collected in the small jar, 
 and afterwards exploded by applying a flame. 
 
 In these experiments, the high temperature to which the seam is exposed causes 
 its molecules to vibrate with such high velocities that the equilibrium of chemical 
 attraction between their component atoms is disturbed, and new molecules of 
 hydrogen and oxygen are produced. These are immediately carried out of the 
 heated region by the current of steam. 
 
 * The end of the tube B should be bent upwards and thrust into a perforated cork with 
 notches cut down the sides. By slipping this cork into the neck of the test-tube, the latter 
 will be held firmly. 
 
 t With a powerful coil, a cubic inch of explosive gas may be collected in about fifteen 
 minutes. 
 
ACTION OF METALS ON WATER. 19 
 
 6. In this case, the force of chemical attraction holding the atoms 
 of oxygen and hydrogen together in the form of water, has been over- 
 come by the physical force of heat. But water may be more easily 
 decomposed by acting upon it with some element which has sufficient 
 chemical energy to enable it to displace the hydrogen. 
 
 No non-metallic element is capable of effecting this at the ordinary 
 temperature. Among the practically important metals, there are five 
 which have so powerful an attraction for oxygen that it is necessary to 
 preserve them in bottles filled with some liquid free from that element, 
 such as petroleum (composed of carbon and hydrogen), to prevent them 
 from combining with the oxygen of the atmosphere. These metals are 
 capable of decomposing water with great facility. 
 
 Metals which decompose water at the ordinary temperature. Potas- 
 sium, Sodium, Barium, Strontium, Calcium. 
 
 7 . When a piece of potassium is thrown upon water, it takes fire and 
 burns with a fine violet flame, floating about as a melted globule upon 
 the surface of the water, and producing in the act of combination 
 enough heat to kindle the hydrogen as it escapes. The violet colour of 
 the flame is due to the presence of a little potassium in the form of 
 vapour. The same results ensue if the potassium be placed on ice. The 
 water in which the potassium has been dissolved is soapy to the touch 
 and taste, and has a remarkable action upon certain colouring matters. 
 Paper coloured with the yellow dye turmeric becomes brown when 
 dipped in it, and paper coloured with red litmus becomes blue. Sub- 
 stances possessing these properties have been known from a very remote 
 period as alkaline substances, apparently because they were first 
 observed by the alchemists in the ashes of plants called kali. The 
 alkalies are amongst the most useful of chemical agents. 
 
 8. Definition of an alkali. A compound substance, very soluble in 
 water, turning red litmus blue and turmeric brown. 
 
 These alkaline properties are directly opposed to the characters of 
 sour or acid* substances, such as vinegar or vitriol, which change the 
 blue litmus to red. When an acid liquid, such as vinegar (acetic acid) 
 or vitriol (sulphuric acid) is added to an alkaline liquid, the charac- 
 teristic properties of the latter are destroyed, the alkali being neu- 
 tralised. 
 
 An acid substance may be known by its property of neutralising an 
 alkali (either entirely or partly). 
 
 The minute investigation into the action of potassium upon the 
 water would require considerable manipulative skill. It would be 
 necessary to weigh accurately the potassium employed, to evaporate the 
 resulting solution in a silver basin (most other materials being corroded 
 by the alkali), and after all the water had been expelled by heat, to 
 ascertain the composition of the residue by a chemical analysis. 
 
 It would be found to contain by weight i part of hydrogen, 16 parts 
 of oxygen, and 39 parts of potassium. 
 
 Since water contains 2 parts by weight of hydrogen, combined with 
 1 6 parts by weight of oxygen, it is evident that the product of the 
 a,ction of potassium on water is formed by the substitution of 39 parts 
 of potassium for i part of hydrogen. 
 
 It is found that whenever potassium takes the place of hydrogen in a 
 
 * From a**?, a point, referring to the pungency or sharpness of the acid taste. 
 
20 
 
 ALKALIES AND ACIDS. 
 
 compound, 39 parts of the former are exchanged for one of the latter, 
 and this is generally expressed by stating that 39 is the chemical equi- 
 valent of potassium. 
 
 The chemical equivalent of a metal expresses the weight of it which 
 is required to be substituted for one part by weight of hydrogen in 
 compounds of hydrogen. 
 
 9. The action of potassium upon water is an example of the produc- 
 tion of compounds by substitution of one element for another, a mode 
 of formation which is far more common than the production of com- 
 pounds by direct combination of their elements. 
 
 If the symbol K represent 39 parts by weight of potassium, its action 
 upon water would be represented by the chemical equation. 
 
 H 2 + K = KOH + H. 
 Water. Caustic potash.* 
 
 But since the atoms cannot exist, except in combination as mole- 
 cules, it would be strictly correct to write the equation thus : 
 
 2H 2 + K 2 = 2KOH + H 2 . 
 
 Since the molecular equation can always be obtained by doubling the 
 atomic equation, the latter will be most commonly given in this work, 
 as involving fewer numbers. 
 
 Sodium has a less powerful attraction, or affinity, for oxygen than 
 potassium has ; it does not, therefore, evolve so much heat when it 
 combines with oxygen, for it is generally noticed that the greater the 
 
 affinity between two elements the 
 greater is the quantity of heat 
 evolved when they combine. Thus 
 sodium does not usually take fire 
 when thrown upon cold water, 
 although sufficient heat is evolved 
 to fuse at once the metal. By 
 holding a lighted match over the 
 globule as it swims upon the 
 water, the hydrogen may be 
 kindled, when its flame is bright 
 yellow, from the presence of the 
 
 Fio . I0 sodium. The solution is strongly 
 
 alkaline from the soda produced. 
 
 By placing the sodium on a piece of blotting-paper laid on the water, it 
 may be made to ignite the hydrogen spontaneously, because the paper 
 keeps the sodium stationary, and prevents it from being so rapidly 
 cooled by the water. Several cubic inches of hydrogen may easily be 
 collected by placing a piece of sodium as large as a pea in a small wire- 
 gauze box (A, Fig. 10), and holding it under an inverted cylinder (B) 
 failed with water and standing on a bee-hive shelf.f 
 
 The product of the action of sodium upon water contains i part by 
 weight of hydrogen, 16 of oxygen, and 23 of sodium, so that the 2* 
 parts of sodium have been exchanged for, or been found chemically 
 equivalent to, i part of hydrogen. 
 
 i, in allusion to its corrosive properties ; and potash, from its 
 cl from the washings of wood ashes * M - J J 
 
 t This experiment sometimes ends in an explosion. 
 
ACTION OF METALS ON WATER. 21 
 
 Taking the symbol Na to represent 23 parts by weight of sodium, its 
 action would be expressed thus : H 2 4- Na = NaOH + H. 
 
 Barium, strontium, and calcium decompose water less rapidly than 
 potassium and sodium do. 
 
 10. The increase in molecular motion caused by heat disturbs the 
 equilibrium of chemical attraction, so that metals which refuse to de- 
 compose water at the ordinary temperature will do so if the tempera- 
 ture be raised, and accordingly magnesium and manganese, which are 
 without action upon cold water, decompose it at the boiling-point, disen- 
 gaging hydrogen, and producing magnesia (MgO, a feebly alkaline 
 earth) and oxide of manganese (MnO). 
 
 But the greater number of the common metals must be raised to a 
 much higher temperature than this before they will decompose water. 
 The following metals abstract the oxygen from water at high tempera- 
 tures, those at the commencement of the list requiring to be heated to 
 redness (about 600 C.), and the temperature required progressively 
 increasing until it attains whiteness for those at the end of the list. 
 
 Metals which decompose water at a temperature above a red heat. 
 Zinc, Iron, Chromium, Cobalt, Nickel, Tin, Antimony, Aluminium, 
 Lead, Bismuth, Copper. 
 
 The noble metals, as they are called, which exhibit no tendency to 
 oxidise in air, are incapable of removing the oxygen from water, even 
 at high temperatures. 
 
 Metals which are incapable of decomposing water. Mercury, Silver, 
 Gold, Platinum. 
 
 Metals decompose water more readily when in a very fine state of division or 
 placed in a state of electrical polarisation by contact with other metals more 
 electro-negative than themselves. Thus zinc, in contact with precipitated copper, 
 decomposes water slowly at the ordinary temperature, hydrogen being evolved, 
 and zinc hydrate separated in white flakes. 
 
 The copper-zinc couple made by precipitating copper sulphate with zinc-foil in 
 excess, and washing, is very useful in many operations where a slow production of 
 hydrogen is required. 
 
 HYDROGEN. 
 
 H = i part by weight = I volume. 
 
 1 1 . Preparation of hydrogen. The simplest process, chemically speak- 
 ing, for preparing hydrogen in quantity, consists in passing steam over 
 red-hot iron. An iron tube (A, Fig. 1 1 ) is filled with iron nails and 
 
 B 
 
 Fig. it. Preparation of hydrogen from steam. 
 
22 PREPARATION OF HYDROGEN. 
 
 placed in a furnace (B), where it is heated to redness by gas burners. 
 A current of steam is then passed through it by boiling the water m 
 the flask (C), which is connected with the iron tube by a glass tube (D) 
 and perforated corks. The hydrogen is collected from the glass tube 
 (G) in cylinders (E) filled with water, and inverted in the trough ( ) 
 upon the bee-hive shelf (H), the first portions being allowed to escape, 
 as containing the air in the apparatus. 
 
 The iron combines with the oxygen of the water to form the black 
 oxide of iron (Fe 3 O 4 ) which will be found in a crystalline state upon the 
 surface of the metal. The decomposition is represented by the equa- 
 tion 4 H 9 + Fe 3 = Fe 3 O 4 + H 8 . 
 
 The atomic weight of iron being 56, the Fe 3 in the above equation 
 represent 56 x 3, or 168 parts by weight of iron. 
 
 Other methods for depriving steam of its oxygen, and therefore tor 
 preparing hydrogen, will be noticed in the sequel. 
 
 The process by which hydrogen is most commonly prepared con- 
 sists in dissolving iron or zinc in a mixture of sulphuric acid and 
 water. 
 
 Zinc is the most convenient metal for this purpose. It is used either 
 in small fragments or cuttings, or as granulated zinc, prepared by 
 
 melting it in a ladle and 
 pouring it from a height of 
 three or four feet into a 
 pailful of water ; when 
 thus granulated it exposes 
 a larger surface to tho 
 action of the acid. The 
 zinc is placed in the bottle 
 (A, Fig. 12), covered with 
 water to the depth of two 
 or three inches, and diluted 
 sulphuric acid slowly 
 poured in through the 
 funnel tube (B) until a 
 pretty brisk effervescence 
 Fig. 12. Preparation of hydrogen. j s observed. The hydrogen 
 
 is unable to escape through 
 
 the funnel tube, since the end of this is beneath the surface of 
 the water, but it passes off through the bent tube (C), and is col- 
 lected over water as usual, the first portion being rejected as con- 
 taining air. 
 
 By allowing the solution left in the bottle to cool in another vessel, 
 crystals of zinc sulphate (white vitriol) may be obtained. 
 
 It will be noticed that the liquid becomes very hot during the action 
 of the acid upon the zinc, the heat being produced by the chemical com- 
 bination. The black flakes which separate during the dissolution of the 
 zinc are metallic lead, which is always present in the zinc of commerce, 
 and much accelerates the evolution of hydrogen by causing galvanic 
 action. Pure zinc placed in contact with diluted sulphuric acid evolves 
 hydrogen very slowly. By attaching a piece of platinum to the pure 
 zinc, so as to form a galvanic couple, the reaction may be considerably 
 hastened. 
 
PROPEKTIES OF HYDROGEN. 23 
 
 The preparation of hydrogen by dissolving zinc in diluted sulphuric 
 acid may be represented by the equation* 
 
 H 2 S0 4 + Zn = ZnS0 4 + H 2 . 
 Sulphuric acid. Zinc sulphate. 
 
 The symbol Zn here represents an atom of zinc, which is 65 times as 
 heavy as the atom of hydrogen. An atom of zinc has here displaced 
 2 atoms of hydrogen, whereas it was found that an atom of potassium 
 displaced only i atom of hydrogen ; this is often expressed by saying 
 that potassium is a monovalent element i.e. is exchangeable for i atom 
 of hydrogen. But since 65 parts of zinc displace 2 parts of hydrogen, 
 zinc is a divalent element i.e. is exchangeable for 2 atoms of hydrogen. 
 This is commonly expressed by writing the symbol of zinc Zn". 
 
 It may be supposed that the atom of a monovalent element, such as 
 hydrogen or potassium, exerts its chemical attraction in one direction 
 only, as represented by a single line or bond attached to the symbol, 
 thus H-, K- ; whilst a divalent element, such as zinc, exerts chemical 
 attraction in two directions, represented by attaching two lines to the 
 symbol, thus -Zn-, or Zn<. Since an atom of oxygen combines with 
 two atoms of hydrogen, it must also exert chemical attraction in two 
 directions, so that a molecule of water may be represented as H H. 
 The displacement of half the hydrogen by potassium (p. 17) then pro- 
 duces K O H, caustic potash, and the displacement of both atoms 
 of hydrogen by zinc produces Zn< >O, or zinc and oxygen united by 
 both their bonds of chemical attraction, forming zinc oxide. . 
 
 Iron might be used instead of zinc, and the solution, when evaporated, 
 would then deposit crystals of green vitriol or copperas (sulphate of iron, 
 or ferrous sulphate, FeS0 4 ), the action of iron upon the sulphuric acid 
 being represented by the equation H 2 S0 4 + Fe = FeS0 4 + H 2 , which 
 shows that i atom (56) of iron has taken the place of 2 atoms of 
 hydrogen, and that the iron is divalent, like zinc. 
 
 12. Physical properties of hydrogen. This gas is invisible, and in- 
 odorous when pure. The hydrogen obtained by the ordinary methods 
 has a very disagreeable smell, caused by the presence of minute quan- 
 tities of compounds of hydrogen with sulphur, arsenic, and carbon ; but 
 the gas prepared with pure zinc and sulphuric acid is quite free from 
 smell. The most remarkable physical property of hydrogen is its 
 lightness. It is the lightest of all kinds of matter, being about T V as 
 heavy as air, and -^^-^Q as heavy as water. 
 
 The lightness of hydrogen may be demonstrated by many interesting experi- 
 ments. Soap bubbles or small balloons (of collodion, for example) will ascend very 
 rapidly if inflated with hydrogen. A light beaker glass maybe accurately weighed 
 in a pair of scales ; it may then be held with its mouth downwards, and the 
 hydrogen poured up into it from another vessel. If it be then replaced upon the 
 scale-pan with its mouth downwards, it will be found very much lighter than before. 
 Another form of the experiment is represented in Fig. 13, where a light glass shade 
 has been suspended from the balance and counterpoised, the equilibrium being, of 
 course, at once disturbed when hydrogen is poured up into the shade. If a 
 stoppered gas jar full of hydrogen be held with its mouth downwards, and a piece 
 of smouldering brown paper held under it, the smoke, which would rise freely in 
 the air, is quite unable to rise through the hydrogen, and remains at the mouth of 
 the jar until the stopper is removed, when the hydrogen quickly rises and the 
 smoke follows it. 
 
 * Iu this equation the excess of water which must be added to dissolve the zinc sulphate 
 is not set down. Hydrogen could not be prepared according to the equation as it stands, 
 because the zinc sulphate would collect round the metal and prevent further action. 
 
2 4 PROPERTIES OF HYDROGEN. 
 
 ii The employment of hydrogen for filling balloons renders a know- 
 ledge of the relation between the weights of equal volumes of hydrogen 
 and atmospheric air of great importance. The number expressing this 
 relation is termed the Specific Gravity of hydrogen. 
 
 (DEFINITION. The specific gravity of a gas or vapour is the weight 
 of a volume of it compared with that of an equal volume of some other 
 gas, selected as a standard, at the same temperature and pressure.) 
 ' If the weight of a given volume of purified and dried air be repre- 
 sented as unitv, an equal volume of hydrogen, at the same temperature 
 and pressure, "would weigh 0.0695, which is expressed by saying that 
 the specific gravity of hydrogen (air = i) is 0.0695. 
 
 Fig. 13- 
 
 In ascertaining the weights of different volumes of gases, it is of the 
 greatest importance that they should have some definite temperature 
 and pressure, since the volume of a given weight of gas is augmented 
 by increase of temperature and by decrease in pressure. It is usual 
 to state the weights of gases, either at 60 Fahrenheit and 30 inches 
 barometer, or at o Centigrade and 760 millimetres barometer. 
 
 One litre of hydrogen at o C. and 760 mm. Bar. weighs 0.09 gram, 
 so that one gram (15.43 grains) of hydrogen, at o 0. and 760 mm. Bar., 
 measures n.ii litres (one litre = 61.024 cubic inches = 1.76 pint). 
 
 One grain of hydrogen, at 60 F. and 30 inches Bar., measures 46.45 
 cubic inches. 
 
 It is now easy to calculate how much zinc it would be necessary to dissolve in 
 sulphuric acid in order to obtain any desired volume, say 100 litres, of hydrogen. 
 Referring to the equation for the preparation of hydrogen, Zn + H 2 S0 4 = H 2 + ZnS0 4 , 
 and remembering that Zn represents 65 parts by weight of zinc, and H 2 represent 
 2 parts by weight of hydrogen, such a problem can be solved by ordinary propor- 
 tion ; thus 
 
 (2 grams H) 22.22 litres : 100 litres : 165 grams zinc : x. 
 
 37 = 292 grams zinc give 100 litres of hydrogen at o C. and 760 mm. Bar, 
 
DIFFUSION. 25 
 
 14. It will be observed, in the experiment with the balance (Fig. 13), 
 that the gas gradually falls out of the jar, notwithstanding its lightness, 
 and is displaced by air ; so that, after a time, the equilibrium is restored, 
 proving that the molecules of hydrogen possess motion which is inde- 
 pendent of gravitation. This motion of the molecule gives rise to the 
 phenomenon known as diffusion. 
 
 Diffusion is the intermixture of molecules brought about by their 
 power of moving amongst each other. This power is possessed in the 
 highest degree by gaseous molecules, all gases being capable of perfect 
 and comparatively rapid intermixture. Some liquids, such as alcohol 
 and water, also intermix perfectly, although comparatively slowty, 
 whilst other liquids, such as oil and water, diffuse into each other only 
 to a very limited extent. "When alcohol is poured on to water, it 
 forms a separate layer on the surface of the water, because it is the 
 specifically lighter of the two ; after a time, however, the two layers 
 .are no longer discernible, and the liquid is a homogeneous mixture of 
 alcohol and water. In the same way hydrogen will float on air, but 
 only for a very short time, since the rate of diffusion of this gas is very 
 rapid. A homogeneous mixture of hydrogen and air is speedily 
 formed. 
 
 Even among solids the phenomenon of diffusion is not unknown ; 
 thus a piece of gold lying on a piece of lead will gradually diffuse 
 through the lead, but the process occupies years. 
 
 The molecules of all gases do not move with the same velocity, so 
 that some gases diffuse more rapidly than others. This has been 
 discovered by confining a gas in a vessel closed by some material having 
 very minute pores, and immersing the vessel in an atmosphere of some 
 other gas. The passage of the molecules through the pores of the 
 material closing the vessel is sufficiently slow to allow of a comparison 
 between the velocities of passage or rates of diffusion of the two gases. 
 
 The diffusion tube (Fig. 14) employed for this purpose is a glass tube 
 (A) closed at one end by a plate of plaster of Paris (B). If this tube 
 be filled with hydrogen,* and its open end immersed in coloured 
 water, the water will be observed to rise rapidly in the tube, on 
 account of the rapid escape of the hydrogen through the pores of the 
 plaster. The external air, of course, passes into the tube through 
 the pores at the same time, but much less rapidly than the hydrogen 
 passes out, so that the ascent of the column of water (C) marks the 
 difference between the volume of hydrogen which passes out, and that 
 of air which passes into the tube in a given time, and allows a measure- 
 ment to be made of the rate of diffusion ; that is, of the velocity with 
 which the gas issues as compared with the velocity with which the air 
 enters, this velocity being always taken as unity, t To determine the 
 rate of diffusion, it is of course necessary to maintain the water at the 
 same level within and without the diffusion tube, so as to exclude the 
 influence of pressure. 
 
 This method has disclosed the law of diffusion of gases, namely, that 
 
 * This tube must be filled by displacement (see Fig. 20), in order not to wet the plaster. A 
 piece of sheet caoutchouc may be tied over the plaster of Paris, so that diffusion may not 
 commence until the sheet is removed. 
 
 f Air being a mixture of nitrogen and oxygen, its rate of diffusion is intermediate 
 between the rates of those gases ; however, since the proportions of the gases are very 
 nearly constant, no error of any magnitude arises. 
 
26 DIFFUSION OF GASES. 
 
 the rates of diffusion of gases vary inversely as the square roots of their 
 relative weights. Thus, oxygen is 16 times as heavy as hydrogen, so 
 that the rate of diffusion of hydrogen : the rate of diffusion of oxygen 
 : : J\6 : ,Ji ; in other words, hydrogen will mix with another gas four 
 times as fast as oxygen will mix with that gas. 
 
 To prove that the ascent of the hydrogen due to its lightness is not instrumental 
 in drawing up the water in the diffusion tube, the experiment may be made as in 
 
 Fig. 14. Diffusion tube. Fig. 15. 
 
 Fig. 15, where the plate of plaster (o) is turned downwards, so that the diffusion is 
 made to take place in opposition to the action of gravity. This tube is filled by 
 passing hydrogen in through the tube (s), and allowing the air to escape through (t), 
 which is afterwards closed by a cork. The plaster of Paris (o) is tied over with 
 caoutchouc whilst the tube is filled. 
 
 Since the relation between the weights of equal volumes of hydrogen and air is 
 that of 0.069 : i, the rates of diffusion are as I : \/o 069 that is, hydrogen 
 diffuses about 3.8 times as rapidly as atmospheric air, or 3.8 measures of hydrogen 
 will pass out of the diffusion tube whilst one measure of air is passing in. In a 
 similar manner hydrogen would escape through minute openings with four times 
 the velocity of oxygen ; and laboratory experience shows that a cracked jar, or a 
 bottle with a badly fitting stopper, may often be used to retain oxygen but not 
 hydrogen. 
 
 A very striking illustration of the high rate of diffusion of hydrogen is arranged 
 as represented in Fig. 16. A is a cylinder of porous earthenware (such as are 
 employed in galvanic batteries) closed at one end, and furnished at the other with 
 a perforated caoutchouc stopper or a cork bung, through which passes a glass tube 
 B, about six feet long and half an inch in diameter. The bung is made air-tight 
 by coating it with sealing-wax dissolved in spirit of wine. This tube being sup- 
 ported so that its lower end dips about an inch below the surface of water, a jar of 
 coal-gas is held over the porous cylinder, when the velocity of the particles of the 
 gas is manifested by their being forced (not only out of the mouth of the jar C, 
 which is open at the bottom, but also) through the pores of the earthenware jar, 
 the air from which is violently driven out, as if by blowing, through the tube, and 
 is seen bubbling up rapidly through the water. When the air has ceased to bubble 
 out, and a large volume of gas has entered the porous jar, the bell- jar C is removed, 
 when the gas escapes so rapidly through the pores, that a column of twenty to 
 thirty inches of water is drawn rapidly up the tube B. If the greatest height to 
 which the water ascends be marked, and when it has returned to its former level, a 
 jar of hydrogen be held over the porous cylinder, it will be found that the above 
 phenomena are manifested in a much higher degree, showing that coal-gas, being 
 heavier than hydrogen, does not pass nearly so rapidly through the pores of the 
 earthenware as hydrogen does. 
 
 By connecting the porous cylinder A, by means of a short piece of tube, with a 
 two-necked bottle, like that represented in Fig. 20, and passing through a cork in 
 the other neck, a piece of tube extending to the bottom of the bottle and drawn out 
 
CONSTITUTION OF GASES. 
 
 to an open point at its upper extremity, water may be forced out in a stream 
 of two or three feet in height by holding the jar of hydrogen over the porous 
 cylinder. 
 
 The great difference in the rates of diffusion of hydrogen and oxygen may be 
 easily shown by the arrangement represented in Fig. 17. A is a jar filled with a 
 mixture of two volumes of oxygen with one volume of hydrogen, communicating 
 through the stop-cock and flexible tube with the 
 glass tube j5, which is fitted through a perforated 
 cork in the bowl of the common tobacco-pipe 6", 
 the sealing-waxed end of which dips under water 
 in the trough D. By opening the stop-cock and 
 pressing the jar down in the water, the mixed 
 gases may be forced rapidly through the pipe, 
 and if a small cylinder (.Z?) be filled with them, 
 the mixture will be found to detonate violently 
 on the approach of a flame. But if the gas be 
 made to pass very slowly through the pipe (at the 
 rate of about a cubic inch per minute), the hydro- 
 gen will diffuse through the pores of the pipe so 
 much faster than the oxygen, that the gas col- 
 lected in the cylinder will contain so little hydro- 
 gen as to be no longer explosive, and to exhibit 
 the property of oxygen to rekindle a partly ex- 
 tinguished match. 
 
 The fact that the phenomenon of diffu- 
 sion is shown by solids and liquids as well 
 as by gases has led to the conclusion that 
 in all three states of matter the molecules 
 are in constant motion. In a solid the 
 distance through which each molecule 
 moves is very small because the molecules 
 are so close together that they attract and 
 hinder each other. It is supposed that 
 heat increases the motion until presently 
 the molecules are moving rapidly enough 
 partly to counteract their attraction for 
 each other, whereupon the solid melts to 
 a liquid. In the liquid the molecules are 
 still under the influence of each other so 
 that they cannot move freely through 
 space, which is the characteristic of gaseous 
 molecules. By heating the liquid it 
 eventually boils and becomes a vapour, 
 which, when its temperature is consider- 
 ably above that at which the liquid boils, 
 has the properties of a gas. 
 
 In a true gas the molecules would move without influencing each 
 other in any regard, except in so far as they might collide and rebound 
 like billiard-balls. They would never stick together, so to speak. 
 
 Now it has been shown by experiment that the volume of a gas varies 
 inversely as the pressure to which it is subjected (Boyle's Law). Thus, 
 if 1000 c.c. of hydrogen be measured when the barometer stands at 
 760 min., this volume will become 500 c.c. when the pressure is in- 
 creased to 760x2 = 1520 mui., or 2000 c.c. when the pressure is 
 diminished to 380 mm. 
 
 It has further been shown that the volume of a gas is directly 
 
28 
 
 CONSTITUTION OF GASES. 
 
 proportional to its absolute temperature, that is, the temperature shown 
 by the Centigrade thermometer + 273 (Charles' Law). For example, 
 1000 c.c. of hydrogen at 273 abs. become 2000 c.c. at 546 abs. or 
 coo c.c. at 136.5 abs. . 
 
 But although these laws have been experimentally discovered, it 
 acknowledged that no known gas conforms with them absolutely, and 
 particularly do gases deviate from them when under high pressure or 
 at low temperature. This is because under these conditions the gases 
 are nearer the liquid condition than they are under low pressure or 
 at high temperature ; the molecules are nearer together and more under 
 the influence of each other. 
 
 It has been proved by mathematics that the ideal gas would obey the 
 
 Fig. 17. Separation of hydrogen and oxygen by atmolysis.* 
 
 laws of Boyle and Charles accurately, and different gases certainly differ 
 in the degree to which they deviate from the laws, so that degrees of 
 gaseous state, or good and bad gases, may be recognised. Those gases 
 deviate least which are the most difficult to liquefy, for they are farthest 
 removed from the liquid state. Hydrogen is the best gas, in this 
 sense, that is known, hence on this account, as well as on account of its 
 lightness, it is the best standard for comparison of weights and volumes 
 of gases. Carbon dioxide, on the other hand, is a poor gas at the 
 ordinary temperature and pressure, for it is then not far above its 
 liquefying point ; but it improves if its temperature is raised or its 
 pressure reduced. 
 
 The diminution which occurs in the volume of a gas when the 
 pressure upon it is increased, or when the temperature of it is de- 
 creased, can only be ascribed to the approachment of the molecules 
 nearer to each other. When the distance between the molecules is 
 
 * This term has been applied to the separation of gases by diffusion; dr/nos, vapour; A.VW, 
 to loosen. 
 
PROPERTIES OF HYDROGEN. 
 
 sufficiently diminished the gas becomes a liquid. Thus it is that all 
 gases can be liquefied by great pressure or extreme cold, or a com- 
 bination of the two. Hydrogen has been proved to be the most 
 difficult of common gases to liquefy, but this object has at length been 
 achieved, and liquid hydrogen is found to be transparent, colourless, 
 and mobile; it boils at - 252 C. and freezes to colourless crystals at 
 
 - 257 o. 
 
 There is a temperature for every gas above which no amount of 
 pressure can liquefy the gas ; this is called the critical temperature of 
 that gas, or the absolute boiling-point of the corresponding liquid. 
 
 This value for hydrogen appears to be 242 C., but for some gases, 
 such as carbon dioxide, it is above the ordinary temperature, so that 
 they can be liquefied by pressure alone. The pressure required to 
 liquefy a gas at its critical temperature is called the critical pressure of 
 the gas, that of hydrogen being 15 atmospheres. The liquefaction of 
 gases is further treated of under Air. 
 
 Fig. 18. 
 
 Fig. 19. 
 
 Fig. 20. 
 
 Hydrogen is one of the least soluble of gases ; 100 volumes of water 
 dissolve only 1.83 vols. of the gas at 15 C. This is only to be ex- 
 pected from the difficulty with which it is liquefied, it being generally 
 the case that the more easily liquefied gases are the more soluble. 
 
 15. Chemical properties of hydrogen. The most conspicuous chemical 
 property of hydrogen is its disposition to burn in air when raised to a 
 moderately high temperature, entering into combination with the 
 oxygen of the air to form water. The formation of water during the 
 combustion of hydrogen gave rise to its name (vSwp, water). 
 
 Since an atom of oxygen combines with two atoms of hydrogen to form water, 
 the gases will not combine unless under the influence of some force, such as heat or 
 electricity, to assist in resolving their molecules into the constituent atoms. 
 
 On introducing a taper into an inverted jar of hydrogen (Fig. 18), the flame of 
 the taper is extinguished, but the hydrogen burns with a pale flame at the 
 mouth of the jar, and the taper may be rekindled at this flame by slowly with- 
 drawing it. 
 
 The lightness and combustibility of hydrogen may be illustrated simultaneously 
 by some interesting experiments. If two equal gas cylinders be filled with 
 hydrogen, and held with their mouths respectively upwards and downwards, it 
 will be found on testing each with a taper after the same interval, that the 
 
3 o COMBUSTION OF HYDROGEN. 
 
 hydrogen has entirely escaped from the cylinder held with its mouth upwards, 
 whilst the other still remains nearly filled with the gas. 
 
 The hydrogen maybe scooped out of the jar A (Fig. 19) with the small cylinder 
 B attached to a handle. On removing B, and applying a taper to it, the gas will 
 
 V cylinder may be filled with hydrogen by displacement of air (Fig. 20), if the 
 tube from the hydrogen bottle be passed up into it. 
 
 If such a dry cylinder of hydrogen be kindled whilst held with its mouth down- 
 wards, the formation of water during the combustion of the hydrogen will be 
 indicated by the deposition of dew upon the sides of the cylinder. 
 
 Bv softening a piece of glass tube in the flame of a spirit-lamp, drawing it out 
 and filing it across in the narrowest part (Fig. 21), a jet can be made from which 
 the hydrogen may be burnt. This jet may be fitted 
 by a perforated cork to any common bottle for con- 
 taining the zinc and sulphuric acid (Fig. 22). 
 
 The hydrogen must be allowed to escape for some 
 minutes before applying a light, because it forms an 
 explosive mixture with the air contained in the bottle. 
 
 Fig. 21. 
 
 Fig-. 22. 
 
 This may be proved, without risk, by placing a little granulated zinc in a soda- 
 water bottle (old form), pouring upon it some diluted sulphuric acid, and quickly 
 inserting a perforated cork, carrying a piece of glass tube about three inches long, 
 and one-eighth of an inch wide. If this tube be immediately applied to a flame, 
 the mixture of air and hydrogen will explode, and the cork and tube will be pro- 
 jected to a considerable distance. 
 
 By inverting a small test-tube over the jet in Fig. 22, a specimen of the hydrogen 
 may be collected, and may be kindled, to see if it burns quietly, before lighting the 
 jet. 
 
 A dry glass, held over the flame, will collect a considerable quantity of water, 
 formed by the combustion of the hydrogen. 
 
 The combustion of hydrogen produces a greater heating effect than 
 that of an equal weight of any other combustible body. It has been 
 determined that i gram of hydrogen, in the act of combining with 
 8 grams of oxygen, produces enough heat to raise 34,462 grams of water 
 from o C. to i 0. The temperature of the hydrogen name is pro- 
 bably about 2000 C. Notwithstanding its high temperature, the flame 
 of hydrogen is almost devoid of illuminating power, on account of the 
 absence of solid particles. 
 
 1 6. If a taper be held several inches above a cylinder of hydrogen, 
 standing with its mouth upwards, the gas will be kindled with a loud 
 explosion, because an explosive mixture of hydrogen and air is formed 
 in and around the mouth of the cylinder. 
 
 A stoppered glass jar (Fig. 23) is filled with hydrogen and supported upon three 
 blocks ; if the hydrogen be kindled at the neck of the jar, it will burn quietly until 
 air has entered from below in sufficient proportion to form an explosive mixture, 
 which will then explode with a loud report. 
 
 The same experiment may be tried on a smaller scale, with the two-necked 
 copper vessel (Fig. 24), the lower aperture being opened some few seconds after the 
 hydrogen has been kindled at the upper one. 
 
 The explosion of the mixture of hydrogen and air is due to the sudden 
 expansion caused by the heat generated in the combination of the 
 
OXYGEN. 3 1 
 
 hydrogen with the oxygen throughout the mixture. After the explo- 
 sion of the mixture of hydrogen and air (oxygen and nitrogen), the 
 substances present are steam (from the combination of the hydrogen 
 and oxygen) and nitrogen, which are expanded by the heat developed 
 in the combination, to a volume far greater than the vessel can contain, 
 
 Fig. 24. 
 
 so that a portion of the gas and vapour issues very suddenly into the 
 surrounding air, the collision with which produces the report. 
 
 If pure oxygen be substituted for air, the explosion will be more 
 violent, because the mixture is not diluted with the inactive nitrogen. 
 The further study of this subject must be preceded by that of oxygen. 
 
 OXYGEN. 
 
 = 1 6 parts by weight = I volume. 
 
 17. Oxygen is the most abundant of the elementary substances. It 
 constitutes about one-fifth (by volume) of atmospheric air, where it is 
 merely mixed, not combined, with the nitrogen, which composes the 
 bulk of the remainder. Water contains eight-ninths (by weight) of 
 oxygen ; whilst silica and alumina, which compose the greater part of 
 the solid earth (as far as we know it), contain about half their weight 
 of oxygen. 
 
 Before inquiring which of these sources will most conveniently furnish 
 pure oxygen, it will be desirable for the student to acquire some know- 
 ledge of the properties of this element, and of the chemical relations 
 which it bears to other elementary bodies, for without such knowledge 
 it will be found very difficult to understand the processes by w T hich 
 oxygen is procured. 
 
 1 8. Physical properties of oxygen. From the fact that it occurs in 
 an uncombined state in the atmosphere, it will be inferred that oxygen 
 is perfectly invisible, and without odour. It is a little more than one- 
 tenth heavier than air, which is expressed in the statement that its 
 specific gravity is 1.105. 
 
 In the study of theoretical chemistry, it is expedient to select hydro- 
 gen instead of air as the standard with which the specific gravities of 
 
32 PROPERTIES OF OXYGEN. 
 
 gases are compared ; for the atomic weights are also referred to hydrogen 
 as the unit, and in the case of the common elementary gases the atomic 
 weights are identical with their specific gravities (H=i). Thus the 
 specific gravity of oxygen (H=i) is 16, or, more exactly, 15.88. It 
 will be found convenient to remember that the specific gravity of a gas 
 or vapour is the weight in grams of ii.n litres of it. 
 
 Oxygen boils at - 182 C. under atmospheric pressure, so that it is 
 liquid at temperatures below this. 
 
 The liquid has a steel-blue colour ; its sp. gr. at - 182 C. is 1.135 (water=i) ; 
 its critical temperature (p. 25) is -119 C., and its critical pressure is 51 atmo- 
 spheres. The liquid is attracted by a magnet. Owing to its low temperature 
 liquid oxygen is chemically very inactive, and has no action on such readily 
 oxidisable substances as phosphorus, sodium or potassium. A mixture of powdered 
 charcoal and liquid oxygen can, however, be detonated by exploding a small charge 
 of mercuric fulminate in it. 
 
 Oxygen is slightly soluble in water; 100 volumes of water absorb 
 4 volumes of oxygen at o C. and 3 volumes at 15 C. 
 
 19. Chemical properties of oxygen. This element is remarkable for 
 the wide range of its chemical attraction for other elementary bodies, 
 with all of which, except two, it is capable of entering into combination. 
 Fluorine and bromine are the only elements which are not known to unite 
 with oxygen* 
 
 With nearly all the elements oxygen combines in a direct manner ; 
 that is, without the apparent intervention of any third substance, 
 although, since it has been proved that perfectly dry oxygen will not 
 combine with other elements, it must be admitted that moisture (or 
 some other third substance) is essential to the chemical combination. t 
 
 There are only seven elements (among those of practical importance) 
 which do not unite in a direct manner with oxygen viz. chlorine, bromine, 
 iodine, fluorine, gold, silver, platinum. 
 
 (DEFINITION. The compounds of oxygen with other elements are 
 called Oxides.) 
 
 The act of combination with oxygen, or oxidation, is generally a slow 
 process, and its effects are not immediately perceived. Some familiar 
 examples of oxidation are the tarnishing or rusting of metals by air, 
 the gradual decay of wood, the drying of oils in paint, the formation of 
 vinegar from alcoholic liquids, the respiration of animals and com- 
 bustion. 
 
 In all these processes heat is generated ; but it is not usually noticed 
 unless it is sufficient to render the particles of matter luminous, which 
 is the case only with combustion. 
 
 (DEFINITION. Combustion is chemical combination attended with 
 heat and light.) 
 
 20. Phosphorus, the only non-metal which combines with oxygen at the. 
 ordinary temperature, affords a good illustration of oxidation. This 
 element, a solid at the ordinary temperature, is preserved in bottles 
 filled with water, on account of the readiness with which the oxygen of 
 the air combines with it. If a small piece of phosphorus be dried bv 
 
 * The newly discovered elements argon, helium, krypton, neon and xenon, do not combine 
 with oxygen. 
 
 f Charcoal may be heated to redness in dry oxygen without visible combustion. Sulphur 
 and phosphorus, which inflame in moist oxygen at 260 C. and 60 C. respectively, may be 
 distilled in the dry gas at 440 C. and 290 C. respectively. 
 
COMBUSTION IN OXYGEN. 
 
 33 
 
 Fig. 25. 
 
 gentle pressure between blotting-paper, and exposed to the air, its 
 particles begin to combine at once with oxygen, and the heat thus 
 developed slightly raises the temperature of the mass. 
 
 Now, heat generally encourages chemical union, so that the effect of 
 this rise of temperature is to induce a more extensive combination of 
 the phosphorus with the oxygen, causing a greater development of heat 
 in a given time, until the temperature is sufficient to render the particles 
 brilliantly luminous, and a true case of combustion results the com- 
 bination of the phosphorus with oxygen, attended with production of 
 heat and light. In cold weather, the phosphorus seldom takes fire until 
 rubbed, or touched with a hot wire. 
 
 (DEFINITION. Combustion in air is the chemical combination of the 
 elements of the combustible with the oxygen of the air, attended with 
 development of heat and light.) 
 
 If a dry glass (Fig. 25) be placed over the burning phosphorus, the 
 thick white smoke which proceeds 
 from it may be collected in the form 
 of snowy flakes. These flakes are 
 commonly termed phosphoric oxide or 
 phosphoric anhydride,* and are com- 
 posed of 80 parts by weight of oxygen, 
 and 62 parts of phosphorus (P 2 5 ). 
 
 If the white flakes are exposed to 
 the air for a short time, they attract 
 moisture and become little drops, 
 which have a very sour or acid taste. 
 It was mentioned at page 19 that all 
 substances which have such a taste have been found also to be capable 
 of changing the blue colour of litmus t to red ; whence the chemist is 
 in the habit of employing paper dyed with blue litmus for the recogni- 
 tion of an acid. 
 
 (DEFINITION. Anhydride, a compound which produces an acid when 
 brought into contact with water.) 
 
 For the exact definition of an acid, see page 35. 
 
 During the slow combination of phosphorus with the oxygen of the 
 air, before actual combustion commences, only 48 parts of oxygen unite 
 with 62 parts of phosphorus, forming the substance called phosphorous 
 oxide or phosphorous anhydride (P 2 3 ). 
 
 (DEFINITION. The endings -ous and -ic distinguish between two com- 
 pounds formed by oxygen with the same element ; -ous implying the 
 smaller proportion of oxygen.) 
 
 Unless the temperature of the air be rather high, the fragment of 
 phosphorus will not take fire spontaneously, but its combustion may 
 always be ensured by exposing a larger surface to the action of the 
 air. As a general rule, a fine state of division favours chemical combi- 
 nation, because the attractive force-inducing combination operates only 
 between substances in actual contact ; and the smaller the size of the 
 particles, the more completely will this condition be fulfilled. 
 
 Thus if a small fragment of dry phosphorus be placed in a test-tube, and 
 
 * Anhydride, or without water, from av, negative, and vSoup, water. 
 
 f A colouring- matter prepared from a lichen, Rocella tinctoria ; the cause of the change 
 of colour will be more easily understood hereafter. 
 
 C 
 
34 
 
 COMBUSTION IN OXYGEN. 
 
 dissolved in a little car bon bisulphide, the solution when poured upon blotting-paper 
 (Fig. 26), will part with the solvent by evaporation, leaving the phosphorus ma 
 very finely divided state upon the surface of the paper, where it is so rapidly 
 attacked by the oxygen of the air that it bursts spontaneously into a blaze. 
 
 Though the light emitted by phosphorus burning in air is very 
 TDrilliant, it is greatly increased when pure oxygen is employed ; for 
 since the nitrogen with which the oxygen in air is mixed takes no part 
 in the act of combustion, it impedes and moderates the action of the 
 
 Fig. 26. 
 
 Fig. 27. Phosphorus burning- in oxygen. 
 
 oxygen. Each volume of the latter gas is mixed, in air, with four 
 volumes of nitrogen, so that we may suppose five times as many 
 particles of oxygen to come into contact, in a given time, with the 
 particles of the phosphorus immersed in the pure gas, which will 
 account for the great augmentation of the temperature and light of the 
 burning mass. 
 
 To demonstrate the brilliant combustion of phosphorus in oxygen, a piece not 
 larger than a good-sized pea is placed in a little copper or iron cup upon an iron 
 stand (Fig. 27), and kindled by being touched with a hot wire. The globe (of thin 
 well-annealed glass), having been previously filled with oxygen, and kept in a plate 
 containing a little water, is placed over the burning phosphorus. 
 
 It will be observed that the same white clouds of phosphoric an- 
 hydride are formed, whether phosphorus is burnt in oxygen or in air, 
 exemplifying the fact that a substance will combine with the same pro- 
 portion of oxygen whether its combustion be effected in pure oxygen or in 
 
 atmospheric air. The apparent increase 
 of heat is due to the combustion of a 
 greater weight of phosphorus in a given 
 time and space. The total heating effect 
 produced by the combustion of a given 
 weight of phosphorus is the same whether 
 air or pure oxygen be employed. 
 
 21. Sulphur (brimstone) affords an 
 example of a non-metallic element which 
 will not enter into combination with 
 oxygen until its temperature has been 
 raised very considerably. When sulphur 
 is heated in air, it soon melts ; and when 
 its temperature reaches 500 F. (260 0.), 
 it takes fire, burning with a pale blue 
 flame. If the burning sulphur be plunged into a jar of oxygen, the blue 
 light will bocome very brilliant, but the same act of combination occurs 
 32 parts by weight of oxygen uniting with 32 parts of sulphur to form 
 
 Fig. 2i 
 
 Sulphur burning in 
 oxygen. 
 
NATUKE OF ACIDS. 35 
 
 sulphurous acid gas or sulphurous anhydride (S0 2 ), which may be recog- 
 nised in the jar by the well-known suffocating smell of brimstone matches. 
 The experiment is most conveniently performed by heating the sulphur 
 in a deflagrating spoon (A, Fig. 28), which is then plunged into the jar 
 of oxygen, its collar (B) resting upon the neck of the jar, which stands 
 in a plate containing a little water. The water absorbs a part of the 
 sulphurous acid gas, and will be found capable of strongly reddening 
 litmus-paper. It is possible to produce, though not by simple combus- 
 tion, a compound of sulphur with half as much more oxygen (S0 3 , 
 sulphuric anhydride), showing that a substance does not always take up 
 its fidl share of oxygen when burnt. 
 
 The luminosity of the flame of sulphur is far inferior to that of 
 phosphorus, because, in the former case, there are no extremely dense 
 particles in the flame corresponding with those of the phosphoric oxide 
 produced in the combustion of phosphorus. 
 
 22. Carbon, also a non-metallic element, requires the application of a 
 higher temperature than sulphur does to induce it to enter into direct 
 uni6n with oxygen ; indeed, perfectly pure carbon appears to require 
 a heat approaching whiteness to produce this effect. But charcoal 
 (the carbon in which is associated with not inconsiderable proportions 
 of hydrogen and oxygen) begins to burn in air at a much lower tempera- 
 ture; and if a piece of wood charcoal, with a single spot heated to 
 redness, be lowered into a jar of oxygen, the adjacent particles will 
 soon be raised to the combining temperature, and the whole mass will 
 glow intensely, 32 parts by weight of oxygen uniting with 12 parts 
 of carbon to form carbonic acid gas (C0 2 ) or carbonic anhydride, which 
 will redden a piece of moistened blue litmus-paper suspended in the 
 jar. It should be remembered that carbon is an essential constituent 
 of all ordinary fuel, and carbonic acid gas is always produced by its 
 combustion. 
 
 It will be noticed that the combustion of the charcoal is scarcely 
 attended with flame ; and when pure carbon (diamond, for example) is 
 employed, no flame whatever is produced in its combustion, because 
 carbon is not convertible into vapour, and all flame is vapour or gas in 
 the act of combustion ; hence, only those substances burn with flame which 
 are capable of yielding combustible gases or vapours. 
 
 23. The three examples of sulphur, phosphorus and carbon suffi- 
 ciently illustrate the tendency of non-metals to form acids by union with 
 oxygen and water, which originally led to the adoption of its name, 
 derived from 6vs, acid, and yewda), I produce. All the common non- 
 metallic elements, except hydrogen, bromine and fluorine, are capable of 
 forming anhydrides, by their union with oxygen. 
 
 Definition of an acid. A compound containing hydrogen, which, 
 
 when in contact with alkali (p. 19) exchanges its hydrogen, or a 
 portion of it, for the alkali metal. 
 For example 
 
 HC1 + NaOH = NaCl -f H 2 
 
 Hydrochloric acid. Soda. Sodium chloride. Water. 
 
 H 2 S0 4 + 2KOH = K 2 S0 4 + 2H 2 
 
 Sulphuric acid. Potash. Potassium sulphate. Water. 
 
 H 3 P0 4 + 2NaOH = Na<jHP0 4 + 2H 2 
 
 Phosphoric acid. Soda. Sodium phosphate. Water. 
 
 24. The metals, as a class, exhibit a greater disposition to unite 
 
36 NATURE OF BASES. 
 
 directly with oxygen, though few of them will do so in their ordinary 
 condition, and at the ordinary temperature. Several metals, such as 
 iron and lead, are superficially oxidised when exposed to air under 
 ordinary conditions, but this would not be the case unless the air con- 
 tained water and carbonic acid gas, which favour the oxidation in a 
 very decided manner. Among the metals which are of importance in 
 practice, five only are oxidised by exposure to dry air at the ordinary 
 temperature, viz., potassium, sodium, barium, strontium, and calcium, 
 the attraction of these metals for oxygen being so powerful that they 
 must be kept under petroleum, or some similar liquid free from oxygen. 
 On the other hand, three of the common metals, silver, gold, and 
 platinum, have so little attraction for oxygen that they cannot be 
 induced to unite with it directly, even at high temperatures. 
 
 If a lump of sodium be cut across with a knife, the fresh surfaces 
 will exhibit a splendid lustre, but will very speedily tarnish by combin- 
 ing with oxygen from the air, which gives rise to a coating of sodium 
 oxide, and this to some extent protects the metal beneath from oxidation. 
 The freshly cut sodium shines in the dark like phosphorus. Even when 
 the attraction of the sodium for oxygen is increased by the application 
 of heat, it is long before the mass of sodium is oxidised throughout, 
 unless the temperature be sufficiently high to convert a portion of the 
 sodium into vapour, which bursts through the crust of oxide, and burns 
 with a yellow flame ; if, when this has occurred, the spoon in which the 
 sodium is heated (see Fig. 28) be plunged into a jar of oxygen, the 
 yellow flame will be more brilliant. 
 
 Sixteen parts by weight of oxygen (i atom) here combine with 46 
 parts of sodium (2 atoms) to form sodium oxide (Na 2 O), which remains 
 in the spoon in a fused state. When the spoon is cool, it may be placed 
 in water, which will dissolve the oxide, converting it into the alkali soda, 
 
 Na^O + H 2 = 2NaHO 
 Water. Soda, 
 
 25. Zinc serves as an example of a metal which has no disposition 
 to enter into combination with oxygen at the ordinary temperature,* 
 but is induced to unite with it by a very moderate heat. If a little 
 zinc (spelter) be melted in a ladle or crucible, and stirred about with 
 an iron rod, it burns with a beautiful greenish flame, produced by the 
 union of the vapour of zinc with the oxygen of the air. But the 
 combustion is far more brilliant if a piece of zinc foil be made into a 
 tassel, gently warmed at the end, dipped into a little flowers of sulphur, 
 kindled, and let down into a jar of oxygen, when the flame of the 
 burning sulphur will ignite the zinc, which burns with great brilliancy. 
 On withdrawing what remains of the tassel after the combustion is 
 over, it will be found to consist of a brittle mass, which has a fine 
 yellow colour while hot, and becomes white as it cools. This is the 
 zinc oxide (ZnO), formed by the union of 16 parts by weight of oxygen 
 with 65 parts of zinc. 
 
 The zinc oxide does not possess the properties of an acid or an alkali 
 and belongs to another class of compounds termed bases, which are not 
 soluble in water as the alkalies are, but, like them, are capable of 
 neutralising the acids either partly or entirely. Thus, if the zinc oxide 
 were added to diluted sulphuric acid as long as the acid would dissolve 
 * Unless water and carbonic acid gas be present, as in common air. 
 
METALS AND OXYGEN. 37 
 
 it, the well-known corrosive properties of the acid would be destroyed, 
 although it would still retain the power of reddening blue litmus, and 
 the solution would now contain a new substance, or salt, called zinc 
 sulphate (ZnS0 4 ). 
 
 (DEFINITION. A base is a compound body which is capable of neu- 
 tralising an acid, either partly or entirely.) t 
 
 It will be observed that an alkali is only a particular species of base, 
 and might be defined as a base which is very soluble in water. 
 
 (DEFINITION. A salt is a compound formed when the hydrogen in 
 an acid is exchanged, either entirely or partly, for a metal ; thus sodium 
 chloride, NaCl, is formed by the exchange of the H in HC1, hydro- 
 chloric acid, for sodium ; sodium phosphate, Na 2 HP0 4 , is formed from 
 phosphoric acid, H 3 P0 4 , by the substitution of sodium for two-thirds of 
 the hydrogen.) 
 
 26. Iron, in its ordinary form, like zinc, is not oxidised by dry air or 
 oxygen at the ordinary temperature ; but if it be heated even to only 
 500 F. a film of oxide of iron forms upon its surface, and as the 
 temperature is raised, the thickness of the film increases, until eventually 
 it becomes so thick that it can be detached by hammering the surface, 
 as may be seen in a smith's forge. If an iron rod as thick as the little 
 finger be heated to whiteness at the extremity, and held before the 
 nozzle of a powerful bellows, it will burn 
 brilliantly throwing off sparks and drop- 
 ping melted oxide of iron. If a stream 
 of oxygen be substituted for air, the com- 
 bustion is of the most brilliant descrip- 
 tion A watch-spring (iron combined with 
 about i per cent, of carbon) may be easily 
 made to burn in oxygen by heating it in 
 a flame till its elasticity is destroyed, and 
 coiling it into a spiral (A, Fig. 29), one end 
 of which is fixed, by means of a cork, in 
 the deflagrating collar B ; if the other Fi S'- ^Watch-spring burning 
 end be filed thin and clean, clipped into a 
 
 little sulphur, kindled and immersed in a jar of oxygen (C) standing 
 in a plate of water, the burning sulphur will raise the temperature of 
 the iron to the point of combustion, and the spring will be converted 
 into molten drops of oxide. 
 
 The black oxide of iron formed in all these cases is really a combina- 
 tion of two distinct oxides of iron, one of which contains 16 parts by 
 weight of oxygen and 56 parts of iron, and would be written FeO, 
 whilst the other contains 48 parts of oxygen and 112 parts of iron, 
 expressed by the formula Fe 3 . To distinguish them, the former is 
 usually called ferrous oxide, and the latter ferric oxide, which, combined 
 with water, constitutes ordinary rust. 
 
 The black oxide usually contains one molecule of each oxide, so that 
 it would be written FeO.Fe 2 3 , or Fe 3 4 . It is powerfully attracted 
 by the magnet, and is often called magnetic oxide of iron. The 
 abundant magnetic ore of iron, of which the loadstone is a variety, has 
 a similar composition. 
 
 Iron in a very fine state of division takes fire spontaneously in air 
 as certainly as phosphorus does. Pyrophoric iron can be obtained (by 
 
38 PKEPARATION OF OXYGEN. 
 
 a process to be described hereafter) as a black powder, which must be 
 preserved in sealed tubes. When the tube is opened, and its contents 
 thrown into the air, oxidation occurs, and is attended with a vivid 
 glow. In this case the red oxide of iron is produced instead ot the 
 black oxide. . 
 
 Both these oxides of iron are capable of neutralising, or partly net 
 tralising, acids, and are therefore basic oxides or bases, like the oxides 
 of zinc and sodium obtained in previous experiments. So general is 
 the disposition of metals to form oxides of this class, that it may be 
 regarded as one of the distinguishing features of a metal, for no non- 
 metal ever forms a base with oxygen. 
 
 (DEFINITION. A metal is an element capable of forming a base by 
 combining with oxygen.) 
 
 Many metals are capable also of forming anhydrides with oxygen ; 
 thus, tin forms stannic anhydride (Sn0 2 ), antimony forms antimonic 
 anhydride (Sb 2 5 ), and it is always found that a metallic anhydride 
 contains a larger proportion of oxygen than any of the other oxides 
 which the metal may happen to form. 
 
 27. There is a third class of oxides, termed the indifferent oxides, 
 because they are neither anhydrides nor bases ; such oxides may be formed 
 either by non-metals or metals ; thus water (H 2 0), the oxide of hydrogen, 
 is an indifferent oxide, and the black oxide of manganese (Mn0 2 ) is an 
 example of an indifferent metallic oxide. 
 
 As the most stable compound of oxygen with hydrogen, namely, water, 
 has the formula OH 2 , oxygen is the type of the divalent elements (p. 23). 
 
 28. Preparation of oxygen. For almost all the useful arts in which 
 uncombined oxygen is required, the diluted gas contained in atmospheric 
 air is sufficient, since the nitrogen mixed with it does not interfere with 
 its action. 
 
 From atmospheric air pure oxygen was first obtained by Lavoisier 
 towards the end of the last century. His process is far too tedious to 
 be employed as a general method of preparing oxygen, but it affords a 
 very good example of the relation of heat to chemical action. Some 
 mercury was poured into a glass flask with a long narrow neck, which 
 was placed on a furnace, so that its temperature might be constantly 
 maintained at about 349 C. (660 F.) for twelve days. The mercury 
 boiled, and a portion of it was converted into vapour, which condensed 
 in the neck of the flask and ran back again. Eventually part of the 
 mercury was converted into a dark powder, which became red on 
 cooling, having combined with the oxygen of the air (or undergone 
 oxidation) to form the red oxide of mercury. 
 
 By heating this oxide of mercury to a temperature approaching, a red 
 heat (about 500 C. or 1000 F.) it is decomposed into mercury and 
 oxygen gas (HgO = Hg + O). 
 
 It is very generally found, as in this instance, that heat of moderate 
 intensity favours the operation of chemical attraction, whilst a more 
 intense heat annuls it. 
 
 For the purpose of experimental demonstration, the decomposition of the oxide 
 of mercury may be conveniently effected in the apparatus represented by Fig. 30, 
 where the oxide is placed in the hard glass tube A, and heated by the gas-burner 
 B, the metallic mercury being condensed in the bend C and the oxygen collected 
 in the gas cylinder D, filled with water, and standing upon the bee-hive shelf of 
 
PEEPAEATION OF OXYGEN. 39 
 
 the pneumatic trough E. It may be identified by its property of kindling into 
 flame the spark left at the end of a wooden match. If the heat be continued for a 
 sufficient length of time, the whole of the oxide of mercury will disappear, being 
 resolved into its elements. In technical language, the mercury is said to be reduced. 
 Upon the first application of heat the red oxide suffers a physical change, in conse- 
 quence of which it becomes black ; but its red colour returns again if it be allowed 
 to cool. 
 
 Fig. 30. Preparation of oxygen from oxide of mercury. 
 
 This method of obtaining unmixed oxygen from the air is much too costly to 
 be employed on a large scale. 
 
 Brings process for preparing oxygen from the air depends upon the facts that 
 when barium oxide (BaO) is heated in air it combines with oxygen, forming 
 barium dioxide (Ba0 2 ), and that when this latter is heated more strongly, or 
 under diminished pressure, it gives up oxygen, again becoming BaO, thus : 
 (i) BaO + = Ba0 2 ; (2) Ba0 2 = BaO + 0. The original barium oxide is used 
 again. 
 
 Air (purified from carbon dioxide) is pumped under pressure (10 Ibs. per square 
 inch) through retorts containing the barium oxide, heated at 700 C. ; when the 
 issuing gas is no longer approximately pure nitrogen, the air current is stopped 
 and the residual nitrogen in the retorts is pumped out until the pressure has 
 fallen to about 2 Ibs. per square inch. The barium dioxide then gives off much 
 of its oxygen, which is collected in a gasholder. The cycle of operations is 
 repeated. 
 
 Another process which has been used depends upon the principle that the oxides 
 of manganese, when heated in contact with alkalies and air, are capable of absorb- 
 ing the oxygen from the air, and of subsequently giving it up again if heated in a 
 current of steam. 
 
 To illustrate this process, about four ounces of dry sodium manganate (which 
 may be purchased cheaply in a crude state) are introduced into a porcelain tube * 
 (, Fig. 31) fixed in a furnace. One end of the tube is connected with a two-branched 
 glass tube, so that either a current of air may be passed through it by the tube #, 
 or a current of steam from the flask w. On heating the manganate in the tube to 
 dull redness, and passing the steam over it, oxygen is evolved, and may be collected 
 in the jar o. 2Na 2 Mn0 4 + 2H 2 = 4NaHO + Mn 2 3 + 3 . 
 
 Sodium Manganese 
 
 mauganate. CaustlC soda ' sesquioxide. 
 
 If the current of steam be discontinued and the air be slowly passed through 
 the tube , the oxygen of the air will be absorbed, and its nitrogen may be 
 collected in the jar n. 4NaHO + Mn 2 3 + 3(0 + N 4 ) = 2Na 2 Mn0 4 + 2H 2 + N 12 . 
 
 Air. 
 
 If the proper temperature be employed, the stream of gas issuing from the tube 
 may be constantly kept up, and may be made to consist of oxygen or nitrogen 
 accordingly as steam or air is passed through the tube. The current of air is 
 regulated by the nipper-tap <?. 
 
 The gas-furnace represented in Fig. 31 consists of a row of twelve Bunsen burners 
 each having a stop-cock by which the flame is regulated. The horizontal pipe &, 
 
 * A copper tube with screw-caps, into which narrow brass or copper tubes are brazed may 
 be advantageously substituted for the porcelain tube. The process is much facilitated by 
 mixing the manganate of soda with an equal weight of oxide of copper. 
 
40 PREPARATION OF OXYGEN. 
 
 from which they spring, is capable of being raised or lowered at pleasure The 
 porcelain tube t is laid in a semi-cylindrical trough made of stout iron rods, and 
 filled with pieces of pumice-stone or fire-brick. Above this is placed a correspond- 
 ing trough, so that the tube is entirely surrounded by glowing material. The heat 
 must be applied gradually to avoid splitting the tube. 
 
 Fig. 31. Extraction of oxygen from air. 
 
 Oxygen is now obtained approximately free from nitrogen by a 
 physical method which takes advantage of the fact that nitrogen has a 
 lower boiling-point than oxygen, so that when the temperature of liquid 
 air (p. 74) is slowly raised the nitrogen boils away before the oxygen. 
 
 29. The only other natural source from which it has been found con- 
 venient to prepare pure oxygen, is a black mineral composed of manga- 
 nese and oxygen. It is found in some parts of England, but much 
 more abundantly in Germany and Spain, whence it is imported for the 
 use of the bleacher and glassmaker. Its commercial name is manga- 
 nese, but it is known to chemists as binoxide of manganese or manganese 
 dioxide (Mn0 2 ), and to mineralogists by several names designating 
 different varieties. The most significant of these names is pyrolusite, 
 referring to the facility with which it may be decomposed by heat 
 (TTUJO, fire, and Xvw, to loosen). 
 
 One of the cheapest methods of preparing oxygen consists in heating 
 small fragments of this black oxide of manganese in an iron retort, 
 placed in a good fire, the gas being collected in jars filled with water, 
 and standing upon the shelf of the pneumatic trough, or in a gas- 
 holder *r gas-bag, if large quantities are required. 
 
 The attraction existing between manganese and oxygen is too power- 
 ful to allow the metal to part with the whole of its oxygen when heated, 
 so that only one-third of the oxygen is given off in the form of gas, a 
 brown oxide of manganese being left in the retort : tMnO 9 = 
 Mn 3 4 + 2 . 
 
 30. By far the most convenient source of oxygen, for general use in 
 the laboratory, is the artificial salt called chlorate of potash, or potassium 
 chlorate, which is largely manufactured for fireworks, percussion-cap 
 composition, &c. If a few crystals of this salt be heated in a test- 
 tube over a spirit lamp (Fig. 32) they soon melt (360 C.) to a clear liquid, 
 
PREPARATION OF OXYGEN. 41 
 
 which presently begins (400 C.) to boil from the disengagement of 
 
 bubbles of oxygen, easily recognised by introducing a match with a 
 
 spark at the end into the upper part 
 
 of the tube. If the action of heat 
 
 is continued until no more oxygen 
 
 is given off, the residue in the tube 
 
 is the salt termed potassium chloride ; 
 
 KCKX 
 
 KC1 
 
 Potassium Potassium 
 chlorate. chloride. 
 
 o r 
 
 To ascertain what quantity of oxygen would 
 be furnished by a given weight of the chlorate, 
 the atomic weights must be brought into use. 
 Referring to the table of atomic weights, it is 
 found that K = 39, = 16 and Cl = 35.5 ; hence 
 the molecular weight of potassium chlorate is 
 easily calculated. 
 
 One atomic weight of potassium 
 
 chlorine 
 
 Three atomic weights of oxygen 
 
 Fig'. 32. 
 
 39 
 
 35-5 
 48 
 
 KC10 3 = 122.5 
 So that 122.5 grams of chlorate would yield 48 grams of oxygen. 
 
 Since 16 grams of oxygen (more accurately 15.88) measure ii.n litre? (p. 32), 
 the 48 grams will measure 33.33 litres. 
 
 Hence it is found that 122.5 grams of potassium chlorate would give 33.33 
 litres of oxygen measured at o C. and 760 mm. Bar. 
 
 Since the complete decomposition of the potassium chlorate requires 
 a more intense heat than a glass vessel will usually endure, it is cus- 
 tomary to mix the chlorate with about one-fifth of its weight of 
 powdered black oxide of manganese, when the whole of the oxygen is 
 given off at a comparatively low temperature (about 360 C.), though 
 the oxide of manganese itself suffers no change, and its action has not 
 yet received any explanation which is quite satisfactory. 
 
 Fig. 33 shows a very convenient arrangement for preparing and collecting 
 oxygen for the purpose of demonstrating its relations to combustion. A is a 
 
 Fig. 33. Preparation of oxygen, 
 
 Florence flask in which the glass tube B is fixed by a perforated cork. C is a 
 tube of vulcanised india-rubber. The gas-jar is filled with water, and supported 
 upon a bee-hive shelf. If pint gas-jars be employed, 20 grams of potassium 
 
42 SYNTHESIS OF WATER. 
 
 chlorate, mixed with 4 grams of binoxide of manganese, will furnish a sufficient 
 supply of gas for the ordinary experiments. The binoxide of manganese should be 
 thoroughly dried by moderately heating it in a crucible before being mixed with 
 the chlorate. It is also advisable to test it by heating a little of it with the 
 chlorate, since charcoal and sulphuret of antimony, which form very explosive 
 mixtures with chlorate of potash, have sometimes been sold by mistake for bin- 
 oxide of manganese. The heat must be moderated according to the rate at which 
 the gas is evolved, and the tube C must be taken out of the water before the lamp 
 is removed, or the contraction of the gas in cooling will suck the water back into 
 the flask. The first jar of gas will contain the air with which the flask was filled 
 at the commencement of the experiment. The oxygen obtained will have a slight 
 smell of chlorine. 
 
 WATER. 
 
 H 2 18 grams z volumes (vapour). 
 
 31. Synthesis of water from its elements. It has been seen already 
 (p. 30) that the combination of hydrogen with oxygen to form water 
 is attended with great evolution of heat and consequent expansion, and 
 hence the mixture of these gases is found to explode violently on con- 
 tact with flame. 
 
 The experiment may be made safely in a soda-water bottle (old form). The 
 bottle is filled with water, and inverted with its mouth beneath the surface of the 
 water ; enough oxygen is then passed up into it to one-third of its volume ; if the 
 remainder of the water is then displaced by hydrogen, and the mouth of the bottle 
 presented to the flame of a spirit-lamp, a very violent explosion occurs, attended 
 with a vivid blue flash in the bottle. If the mouth of the bottle be presented 
 towards a screen of paper, at a distance of 20 or 30 inches, the paper will be 
 violently torn to pieces, bearing witness to the concussion between the expanded 
 steam issuing from the bottle and the external air. 
 
 If some of the mixture of oxygen with twice its volume of hydrogen be intro- 
 duced into a jar provided with a stop-cock to which is attached a piece of 
 caoutchouc tubing and a small glass tube, and if the jar be pressed down in a 
 
 34- 
 
 35- 
 
 trough of water, soap-bubbles may be inflated with the gas, and these will ascend 
 rapidly in the air, and explode violently when touched with a flame, which must 
 not, of course, be applied to the bubble until it is at some distance away, from the 
 tube, for fear of exploding the mixture in the jar. 
 
 The mixture of 2 volumes H and I volume explodes when heated to 600 C 
 but it may be exposed to a temperature of over 1000 C. without the occurrence of 
 
CAVENDISH EUDIOMETER. 
 
 43 
 
 any combination if it be carefully dried, by freshly distilled phosphoric anhy- 
 dride, in the dark. The precaution to exclude light is essential because the moist 
 gases combine even at the ordinary temperature when exposed to light, and 
 although the combination is extremely slow, the amount of water produced thereby 
 is sufficient to ensure explosion at 600 C.* 
 
 Contact with finely divided platinum starts the combination of H and at the 
 ordinary temperature, and a red hot platinum wire causes even the dried gases to 
 explode. Electric sparks also explode the dried gases. 
 
 32. In order to demonstrate the production of water in the explosion, the 
 Cavendish eudiometer -\ (Fig. 34) is employed. This is a strong glass vessel, with a 
 stopper firmly secured by a clamp (A), and provided with two platinum wires (P), 
 which pass through the stopper, and approach very near to each other within the 
 eudiometer, so that the electric spark may easily be passed between them. By 
 screwing the stop-cock B into the plate of an air-pump, the eudiometer may be 
 exhausted. It is then screwed on to the jar represented in Fig. 35, which contains 
 a mixture of two measures of hydrogen with one measure of oxygen, standing over 
 water. On opening the stop-cocks between the two vessels, the eudiometer 
 becomes filled with the mixture, and the quantity which has entered is indicated 
 by the rise of water in the jar. The glass stop-cock C having been closed to 
 prevent the brass cap from being forced off by the explosion, the eudiometer is 
 again screwed on to its foot, and an electric spark passed between the platinum 
 wires, either from a Ley den jar or an induction coil, when the two gases will 
 combine with a vivid flash of light,* attended with a very slight concussion, but 
 no noise, since there is no collision with the external air. For an instant a mist 
 is perceived within the eudiometer, which condenses into fine drops of dew, con- 
 sisting of the water formed by the combination of the gases, which was here 
 induced by the high temperature of the electric spark, as it was in the former 
 experiment by the high temperature of the flame. If the gases have been mixed 
 in the exact proportion of 
 two measures of hydrogen 
 to one measure of oxygen, 
 the eudiometer will now be 
 again vacuous, and if it be 
 screwed on to the capped 
 jar, may be filled a second 
 time with the mixture, 
 which may be exploded in 
 the same manner. 
 
 The entire disappearance 
 of the gases may be rendered 
 obvious to the eye by ex- 
 ploding the mixture over 
 mercury. For this purpose 
 the mixed gases should be 
 
 -. 36. Detonating gas collected from voltameter. 
 
 collected from water itself, which is strongly acidified with sulphuric acid, and 
 decomposed in the voltameter (A, Fig. 36) by the aid of five or six cells of Grove s 
 battery. The voltameter contains two platinum plates (B), attached to the 
 platinum wires C and D. which are connected with the opposite poles of the 
 battery. The first few bubbles of the mixture of hydrogen and oxygen evolved 
 having been allowed to escape, in order to displace the air, the gas may be collected 
 in the small eudiometer (E), which has been previously filled with water. This 
 eudiometer is a cylinder of very thick glass, closed at one end, and having two 
 stout platinum wires cemented into holes drilled near the closed end, the wires 
 approaching sufficiently near to each other to allow the passage of the electric 
 spark. Having been filled with the mixture of hydrogen and oxygen from tl 
 
 * In these experiments very pure electrolytic gas made by electrolysing a solution of 
 purified barium hydroxide was used. 
 
 f So named from evSios, fine or clear, and ^rpov, a measure, because an instrument upon 
 the same principle has been used to determine the degree of purity of the atmosphere. . 
 eudiometer was employed by Cavendish about the year 1770, for the synthesis of water. 
 
 t Since the steam produced at the moment of combination is here prevented from expana- 
 ing, the heat which would have expanded it is saved, so that the temperature is higher and 
 the flash of light brighter than when the combination is effected in an open vessel. 
 
 The bore of the eudiometer should be about half an inch in diameter, and the thicknes 
 of its sides about gths of an inch ; its length is 7 inches. 
 
44 
 
 EUDIOMETRIC ANALYSIS OF AIE, 
 
 voltameter, the eudiometer is closed with the finger, and transferred to a basin 
 containing mercury, where it is pressed firmly down upon a stout cushion of india- 
 rubber, and the spark passed through the mixed gases, either from the coil or the 
 Leyden jar. The combustion occurs with violent concussion, but without 
 noise ; and since the eudiometer is vacuous after the gases have combined, the 
 cushion will be found to be very firmly pressed against its open end. On loosening 
 the cushion, the mercury will be violently forced up into the eudiometer, which 
 will be completely filled with it, proving that when an electric spark is passed 
 through the mixture of 2 volumes of hydrogen and I volume of oxygen, no residue 
 of gas remains. 
 
 This may also be demonstrated with the siphon eudiometer, shown in Fig. 37, by 
 confining about a cubic inch of the explosive mixture in the closed limb, over 
 water, and stopping the open limb securely with a cork, so as to leave a space filled 
 with air between the cork and the water. The eudiometer must be very firmly 
 fixed on a stand, or it will be broken by the concussion. After it has been proved, 
 it may be held in the hand, as in the figure. By firing mixtures of hydrogen and 
 oxygen, in different proportions, in the same manner, it may be shown that any 
 excess of either gas above the ratio of 2H : will remain uncombined after 
 the explosion. Care is required in these experiments, since eudiometers are often 
 burst by the explosion of the mixture of 2 volumes of hydrogen with i volume of 
 oxygen. 
 
 The explosion and the flash of light in the foregoing experiments are both the 
 results of the heat generated in the act of combination ; so that the water produced 
 represents so much less energy as corresponds with the heat given off in the com- 
 bination. This heat has been measured by means of a calorimeter, and it has been 
 found that 2 grams of H and 16 grams of 0, in combining to form liquid water, 
 generate enough heat to raise 68,924 grams of water from o C. to i C. Of this 
 quantity, 9666 represent the heat generated by the change of state from the gas to 
 the liquid, so that the difference, 59.258, represents the heat generated by the 
 chemical action occurring between 2 grains of hydrogen and 16 grains of oxygen 
 in forming 18 grams of water in the state of gas. This may be expressed by 
 H 2 + = H 2 + 59,258 heat-units, the heat-unit being the quantity of heat required 
 to raise the temperature of I gram, of water from o C. to i C. 
 
 The quantity of heat produced in any chemical action is a measure of the amount 
 of chemical energy which is exerted. To decompose 18 grams of steam we must 
 employ an amount of energy, in the form, for example, of electricity, corresponding 
 with 59,258 heat-units. (See chapter on General Principles.) 
 
 33. The knowledge of the volumes in which hydrogen and oxygen 
 combine, is turned to account in the analysis of gases, to ascertain the 
 proportion of hydrogen or oxygen contained in them. Suppose, for 
 example, it be required to determine the amount of oxygen in a 
 sample of atmospheric air ; the latter is mixed with hydrogen, in 
 more than sufficient quantity to combine with the largest proportion 
 of oxygen which could be present, and when the 
 combination has been induced by the electric spark, 
 the volume of gas which has disappeared (2 
 volumes H + 1 volume 0) has only to be divided 
 by three to give the volume of the oxygen. 
 
 A bent eudiometer (Fig. 37) may be used. Having been 
 completely filled with water (previously boiled to expel 
 dissolved air), it is inverted in the trough, and the specimen 
 of air is introduced (say 10 c.c.). The open limb is then 
 closed by the thumb, and the eudiometer turned so as to 
 transfer the air to the closed limb. A stout glass rod is 
 thrust down the open limb, so as to displace enough water 
 to equalise the level in both limbs, in order that the 
 volume of the air may not be diminished by the pressure 
 in * +1, i A A - f ? ^ igher column of water in the open limb. The 
 volume of the included air having been accurately noted, the open limb of the tube 
 again filled up with water, inverted in the trough, and a quantity of hydrogen 
 introduced, equal to about half the volume of the air. This having been trans- 
 
 Fi g- 37- Siphon 
 eudiometer. 
 
SYNTHESIS OF STEAM. 
 
 45 
 
 ferred, as before, to the closed limb, the columns of water are again equalised, and 
 the volume of the mixture of air and hydrogen ascertained. The open limb is now 
 firmly closed with the thumb, and the electric spark passed through the mixture, 
 either from the Leyden jar or the induction-coil. On removing the thumb, after 
 the explosion, the volume of gas in the closed limb will be found to have diminished 
 very considerably. Enough water is poured into the open limb to equalise the 
 level, and the volume of gas is observed. If this volume be subtracted from the 
 volume before explosion, the volume of gas which has disappeared will be ascer- 
 tained, and one-third of this will represent the oxygen, which has condensed with 
 twice its volume of hydrogen into the form of water. Thus the numbers recorded 
 will be 
 
 Volume of air analysed 10 c.c. 
 
 Volume of air mixed with hydrogen 
 After explosion 
 
 Difference 
 
 \ 
 
 / ... 6.0,, 
 
 6 divided by 3 = 2 c.c. of oxygen. 
 
 In exact experiments, a correction would be required for any variation of the 
 temperature or barometric pressure during the progress of the analysis. 
 
 34. It will have been observed, in the experiment upon the synthesis 
 of water in the Cavendish eudiometer, that the volume of water obtained 
 is very small in comparison with that of the gases before combination, 
 about 1870 volumes of the mixed gases being required to form one 
 volume of liquid water, because after the chemical attraction has caused 
 the molecules of H and O to form steam, the cohesive attraction has 
 caused the molecules of steam to unite and form liquid water. In order 
 to watch the effect of the chemical attraction only, we must prevent the 
 steam from changing its state after it is produced. 
 
 If the mixture of hydrogen and oxygen be measured and exploded at 
 or above the boiling-point of water, it is 
 found that the steam produced occupies 
 two-thirds of the volume of the mixed 
 gases, measured at the same temperature 
 and atmospheric pressure. Hence, two 
 volumes of hydrogen combine with one 
 volume of oxygen to form two volumes of 
 aqueous vapour, at the same temperature and 
 pressure* 
 
 The combination of hydrogen and oxygen in 
 a vessel heated to the boiling-point of water is 
 effected in the apparatus shown in Fig. 38, where 
 the closed limb of the eudiometer is surrounded 
 by a tube into which steam is passed from a flask 
 connected with the wide tube by a cork and a 
 short wide piece of bent glass tubing, jacketed 
 with caoutchouc to prevent loss of heat. The 
 steam escapes through the tube () which enters 
 the cork at the bottom. The closed limb of the 
 eudiometer having been filled with mercury, a 
 small quantity of the mixture of hydrogen and 
 oxygen obtained from the voltameter (Fig. 36) is introduced into it through a tube 
 passed down the open limb, the displaced mercury being run out through the tube <?, 
 which is closed by a nipper-tap. The closed limb is then heated by the steam, and 
 the mercury in the two limbs levelled from time to time by running a little out 
 through c, until the gas in the closed limb no longer expands. Its volume is then 
 * The latest researches show that the exact volume ratio is 2.0024 H : i 0. 
 
 Fig-. 38. Synthesis of water 
 at 100 C. 
 
4 6 
 
 SYNTHESIS OF WATER BY WEIGHT. 
 
 observed, an inch more mercury poured into the open limb, which is then tightly 
 closed by a cork, and the spark from the induction-coil (Fig. 8) is passed by the 
 wires - and +. After the explosion, the cork is removed, and the mercury 
 levelled in the two limbs, when the volume of the steam will be found to be 
 just two-thirds of the volume of the gas before the explosion. On cooling down, 
 the steam condenses, and the mercury entirely fills the closed limb of the 
 eudiometer. 
 
 That 2 volumes of steam should contain 2 volumes of hydrogen and 
 i volume of oxygen would appear, on physical grounds, impossible, since 
 two bodies cannot occupy the same space at the same time ; but it must 
 be remembered that the two bodies in question have lost their individu- 
 ality in consequence of their chemical combination by which they have 
 become one body water. 
 
 35. The synthesis of water by weight is difficultly effected with 
 accuracy by weighing the gases themselves, on account of their large 
 volume. It is therefore accomplished by passing an indefinite quantity 
 of hydrogen over a known weight of pure hot oxide of copper, when 
 the hydrogen combines with the oxygen of the oxide to form water. 
 The loss of weight suffered by the oxide of copper gives the amount of 
 oxygen ; and if this be deducted from the weight of the water, that of 
 the hydrogen will be ascertained. In this way it is shown that water 
 contains 8 parts of oxygen to every i part of hydrogen.* 
 
 The apparatus employed for this purpose is represented in Fig. 39. li is the 
 bottle in which hydrogen is generated from diluted sulphuric acid and zinc ; the 
 gas passes, in p, through solution of potash, which absorbs any sulphuretted 
 hydrogen ; then through s, containing pumice-stone (used on account of its porous 
 character), saturated with a strong solution of silver nitrate, which 1 removes 
 
 Fig. 39. Synthesis of water by weight. 
 
 arsenic and antimony from the hydrogen ; the gas then passes through vv, contain- 
 ing pumice saturated with oil of vitriol to absorb moisture. The bulb c, with the 
 oxide of copper, is weighed before and after the experiment, as are the globe a, for 
 condensing the water, and the tube t, containing pumice and oil of vitriol, to 
 absorb the aqueous vapour. Of course the bulb o must not be heated until the 
 hydrogen has displaced all the air from the apparatus. 
 
 As an example, 10 grams of CuO were employed, and 7.98 grams Cu were 
 left, 2.2725 grams water being collected. 10-7.98 = 2.02 grams 0- 2272;- 
 2.02 = 0.2525 grams H ; 2.2725 : 2.02 : : 100 : 88.88 ; 2.2725 : 0.2525 : : 100 : ii.ii. 
 100 parts by weight of water, therefore, contain 88.88 and ii.n H. This is 
 the usual method of stating the composition of a substance. To deduce the 
 chemical formula, we must divide each constituent by its atomic weight 
 88.88 -r 16 = 5.5 atomic weights of 0; II.II-M = II.II atomic weights of H. Then 
 5.55 : 1 1. ii : : i atom : 2 atoms H. 
 
 I The above experiment would also serve for fixing the atomic weight of copper 
 
 for it shows that 100 parts by weight of cupric oxide contains 79.8 parts of copper 
 
 and 20.2 parts of oxygen. Then 20.2 : 79.8 : : 16 : 63.2 ; so that if cupric oxide 
 
 * The latest value for this ratio is 7.94 O : i H. 
 
FORMULA FOE WATER. 47 
 
 contains one atom of copper to one atom of oxygen, the atomic weight of copper 
 would be 63.2. 
 
 35. A volume of steam is found to weigh 9 times as much as an 
 equal volume of hydrogen weighs at the same temperature and pres- 
 sure. Now, evidence (the value of which will be better appreciated 
 after more experimental facts have been described) has been gathered, 
 from both the chemical and physical study of gases, that equal volumes 
 of gases measured at the same temperature and pressure contain the same 
 number of molecules (Avogadro's Law). It follows that the number of 
 times that a volume of one gas, A, is heavier than a volume of another 
 gas, B, is also the number of times that each molecule in A is heavier 
 than each molecule in B.* Consequently the molecule of steam weighs 
 9 times as much as the molecule of hydrogen ; but the molecule of 
 hydrogen contains 2 atoms, and therefore weighs two units, so the 
 molecule of steam must weigh 1 8 units. It is by similar reasoning that 
 that the molecular weights of all gases are decided. (See Introduction.) 
 
 It will now be understood that the formula for a compound is deter- 
 mined both by a quantitative analysis or quantitative synthesis of the 
 compound, and by ascertaining its specific gravity when H = i (its 
 vapour density). 
 
 A quantitative synthesis of water shows that it contains H and in 
 the proportion of i : 8 ; a determination of its vapour density shows 
 that its molecular weight is 18 ; hence its formula must be H 2 0, which 
 is in agreement with the proportion i : 8 (2 : 16), and with the molecular 
 weight 1 8 (2 -r 1 6). 
 
 It has been seen (p. 24) that one gram of hydrogen occupies (at 
 standard temperature and pressure) 1 1 . 1 1 litres, so that 2 grams occupy 
 22.22 litres. As the molecular weight of a gas is the number of 
 times that it is heavier than 2 unit weights of hydrogen, it follows that the 
 molecular weight of any gas expressed in grams occupies 22.22 litres at 
 standard temperature and pressure. 
 
 36. It is evident that, although hydrogen is generally designated the 
 combustible gas, and oxygen the supporter of combustion, the applica- 
 tion of these terms depends entirely upon circumstances, since the 
 phenomenon of combustion is a reciprocal operation in which both ele- 
 ments have an equal share. 
 
 This may be illustrated by a simple experiment. The hydrogen and oxygen 
 reservoirs, H and O, Fig. 40, are connected with two bent glass tubes passing 
 through a cork into an ordinary lamp glass <?, upon the upper opening of which a 
 plate of talc is laid. In order to prevent the ends of the glass tubes from being 
 fused by the burning gases, little platinum tubes, made by rolling up pieces of 
 platinum foil, are placed in the orifices, and the glass is melted round them 
 by the blowpipe flame. The hydrogen being lighted, and the oxygen turned on to 
 about the same extent, the lamp-glass is placed over the cork, when the hydrogen 
 burns steadily. If the oxygen be slowly turned off, the flame will gradually leave 
 the hydrogen tube and come over to the oxygen, which will continue burning in the 
 atmosphere of hydrogen. By again turning on the oxygen, the flame may be sent 
 over to the hydrogen tube. With a little care the flame may be made to occupy 
 an intermediate position between the two burners, and to leap from one to the other 
 at pleasure. The experiment may also be performed with coal gas and oxygen. 
 
 * This is, of course, only true if all the molecules in a gas have each the same weight. 
 There is no reason to suppose that the molecules of any one gas differ appreciably from each 
 other in weight, but even if they did the ai-gument would be true of the mean weight of each 
 molecule, i.e., the weight of the gas divided by the number of molecules in it. 
 
48 THE OXYHYDROGEN BLOWPIPE. 
 
 37 The great energy with which hydrogen combines with oxygen is 
 turned to account for the purpose of producing very high temperatures 
 (about 2500 C.) 
 
 The ox'uJiydrogen blowpipe (Fig. 41) is an apparatus for burning a jet of hydro- 
 gen mixed with half its volume of oxygen. The gases are supplied from separate 
 gas-holders (or bags with pressure-boards and weights) through the tubes Hand 
 0, which conduct them into the brass sphere B. Each of these tubes is provided 
 with a valve of oiled silk opening outwards, so as to prevent the passage of either 
 gas into the receptacle containing the other. The tube A is stuffed with thin 
 copper wires, which would rapidly conduct away the heat and extinguish the 
 
 Fig. 41. Oxyhydrog-en blowpipe. 
 
 Fig. 40. Reciprocal combustion. 
 
 flame of the mixed gases burning at the jet, should it tend to pass back and 
 ignite the mixture in B. The stop-cocks D and E allow the flow of the gases to 
 be regulated so that they may mix in the right proportions. If the hydrogen be 
 kindled first, it will be found that, as soon as the oxygen is turned on, the flame is 
 reduced to a very much smaller volume, because the undiluted oxygen required to 
 maintain it occupies only one-fifth of the volume of the atmospheric air, from 
 which the hydrogen was at first supplied with oxygen. The heat developed by 
 the combustion being therefore distributed over a much smaller area, the tem- 
 perature at any given point of the flame must be much higher, and very few sub- 
 stances are capable of enduring it without fusion.* Lime is one of these ; and if a 
 cylinder of lime be supported, as at L (Fig. 41), in the focus of the flame, its particles 
 become heated to incandescence, and a light is obtained which is visible at night 
 from very great distances, so as to be well adapted for signalling and lighthouses. 
 For such purposes coal-gas is often used instead of hydrogen (oxycalcium or 
 Dritmmond light). 
 
 If a shallow cavity be scooped in a lump of quicklime, a few scraps of platinum 
 placed in it, and exposed to the oxyhydrogen flame (Fig. 42), a fused globule of 
 platinum of very considerable size may be obtained in a few seconds. By em- 
 ploying a furnace made of lime, platinum is fused in quantities sufficient to, cast 
 large ingots, a result unattainable by any other furnace heated by combustion. 
 Pipeclay, which resists the action of all ordinary furnace-heats, may be fused into 
 a glass in this flame, whilst gold and silver are instantaneously melted, and vaporised 
 into a dense smoke. 
 
 * The temperature of the hydrogen flame in air is about 2000 C., while in oxygen it is 
 over 2500. The last temperature could not be surpassed, because it is that at which steam 
 is dissociated or resolved into its elements, which re-combine as soon as the temperature falls 
 below that point. 
 
OCCLUSION OF HYDROGEN. 49 
 
 38. In its chemical relations to other elements, hydrogen is diametri- 
 cally opposed to oxygen. Whereas the latter combines directly with the 
 greater number of the elements, hydrogen will enter into direct com- 
 bination with very few ; all the metals form compounds with oxygen,, 
 but very few combinations of metals with hydrogen have been obtained.. 
 Indeed, in its relations to other elements, hydrogen closely resembles 
 the metals, though it does not fall within the definition of a metal given 
 above, since it does not form a base with oxygen, and its combinations, 
 with the salt radicles (chlorine, &c.) are acids, and not salts, as is the 
 case with metals. 
 
 Hydrogen is absorbed, or occluded, by many metals to a greater extent than are 
 most other gases, and by palladium more than by any other metal. This pheno- 
 menon of occlusion, which may be compared with that of solution, generally occurs 
 more readily when the metal is heated, and allowed to cool, in the gas ; when 
 treated in this way hammered palladium absorbs some 600 times its volume of 
 hydrogen, though fused palladium does not absorb so much. When a metal 
 containing occluded gas is strongly heated (particularly in a vacuum or in an 
 atmosphere of another gas), the occluded gas is given off, just as a gas dissolved in 
 water is expelled when the solution is heated. Palladium absorbs most hydrogen 
 when it is used as the cathode in an electrolytic cell containing dilute acid (p. 14). 
 In this case the metal may take up about 900 times its volume, and in doing so it 
 increases about 1.5 per cent, in length. This expansion forms the basis of experi- 
 mental methods for demonstrating the occlusion. A palladium wire (24 inches) is 
 passed through the bottom cork of a vertical glass tube, containing dilute sulphuric 
 acid, and is there made fast ; the other end of the wire is attached to a long rod, 
 pivoted horizontally to serve as an index. The wire is attached to the zinc of a 
 Grove's battery, the platinum of the battery being attached to a platinum wire 
 which also passes through the glass tube. During the electrolysis of the dilute 
 sulphuric acid, the index descends, showing that the wire is increasing in length ; 
 the non-recovery of the index when the electrolysis is stopped shows that the 
 expansion was not a mere thermal effect. 
 
 It has been supposed that the palladium saturated with hydrogen is a compound 
 of the formula Pd 3 H 2 .* The hydrogenised palladium is a far more active reducing 
 agent than is free hydrogen, for it reduces chlorates to chlorides and nitrates to 
 nitrites. If the whole of the hydrogen be regarded as being occluded, its specific 
 gravity in this condition would be 0.62, and its atomic heat 5.88. The absorption 
 of i gram of hydrogen by palladium black evolves 4370 gram units of heat. At 
 atmospheric pressure no absorption of hydrogen by palladium occurs above 145 C., 
 but at higher pressures the absorption occurs at much higher temperatures. 
 
 39. Chemical relations of water to other substances. In its chemical 
 relations water presents this very remarkable feature, that, although it 
 is an indifferent oxide, its combining tendencies extend over a wider 
 range than those of any other compound. Its combinations with other 
 substances are generally called hydrates. Water combines with two of 
 the elementary substances, viz., chlorine and bromine, but no other 
 element is even dissolved by water in any considerable quantity. Oxygen, 
 hydrogen, and nitrogen are dissolved by water, in very small quantity, 
 but become only mechanically diffused through it, and do not enter 
 into chemical combination. 
 
 When water attacks a compound body, it may do so in one of two 
 ways : (i) A simple solution may be effected. In this case any chemi- 
 cal combination which may occur between the compound and the water 
 is of so loose a nature that it is possible to recover the compound un- 
 changed by merely evaporating the water. (2) The water may combine 
 
 * The term hydrogenium, applied by Graham to the hydrogen occluded by palladium, on 
 the supposition that it existed merely in a state of condensation in the metal, must be aban- 
 doned if the existence of this compotind be admitted. 
 
 D 
 
50 DISSOLUTION IN WATER. 
 
 with the compound to produce a new compound of such stability that 
 the original substance cannot be recovered by mere evaporation. The 
 new compound may then pass into simple solution. 
 
 It might at first be thought that simple solution was only a physical 
 phenomenon, since there is no permanent alteration in the properties of 
 the dissolved substance. This view would be supported by the obser- 
 vation that when a solid is dissolved, there is a reduction of tempera- 
 ture, such as is always noticed in the merely physical change from the 
 solid to the liquid form ; and that when a gas is dissolved there is a rise 
 of temperature such as is noticed when a gas passes to the liquid form. 
 When careful measurements are made, however, it is found that the 
 thermal change involved in the dissolution cannot be entirely accounted 
 for by the physical change of state. Consequently it must be allowed 
 that chemical combination is concerned in the process of dissolution 
 although the most obvious relations produced are of a physical nature. 
 At this juncture attention will be called to the principal facts concern- 
 ing solution, a discussion of the deductions to be drawn from them 
 being for the present postponed. 
 
 When common saltpetre (nitre or nitrate of potash) is shaken with 
 water, it is rapidly dissolved, the water becoming sensibly colder. If 
 fresh portions of saltpetre are added till the water is unable to dissolve 
 any more, it is found that 100 grams of water (at 60 F.) have dissolved 
 about 30 grams of saltpetre. Such a solution is a cold saturated solution 
 of saltpetre. If the solution be set aside in an open vessel, the water 
 will slowly pass off in vapour, and the saltpetre will be gradually 
 deposited, its particles arranging themselves in the regular geometrical 
 shape of the six-sided prism, which is its common crystalline form. 
 The crystals of saltpetre do not contain any water ; they are anhydrous. 
 
 If saltpetre is added to boiling water, and stirred (with a glass rod) 
 until the water refuses to dissolve any more, 100 grams of water is found 
 to have dissolved about 200 grams ; this is a hot saturated solution. 
 
 As a general rule, solids are dissolved more quickly and in larger 
 quantity by hot water than cold. 
 
 One of the commonest methods of crystallising a solid substance 
 consists in dissolving it in hot water and allowing the solution to 
 cool slowly. The more slowly it cools, the larger and more symmetrical 
 are the crystals. 
 
 A hot saturated solution is not generally the best for crystallising, 
 because it deposits the dissolved body too rapidly. Thus the hot 
 solution of saltpetre prepared as above would solidify to a mass of 
 minute crystals on cooling; but if 100 grams of saltpetre be dissolved 
 in 120 c.c. of boiling water, it will form crystals of 2 or 3 inches long 
 when slowly cooled (in a covered vessel). If the solution be stirred 
 while cooling, the crystals will be very minute, having the appearance 
 of a white powder. 
 
 Some solids, however, refuse to crystallise, even from a hot saturated 
 solution, if it be kept absolutely undisturbed. 
 
 Sodium sulphate affords a good example of this. If the crystallised sulphate be 
 added to boiling water in a flask, as long as it is dissolved, the water will take into 
 solution more than twice its weight of the salt, yielding a solution which boils at 
 220 F. (104. 5 C.). If this solution be allowed to cool in the open flask, an abundant 
 crystallisation will occur, for cold water dissolves only about one-third of its weight 
 of crystallised sulphate. But if the -flask (which should be globular) be tightly 
 
SUPERS ATUEATED SOLUTIONS. 51 
 
 corked whilst the solution is boiling, it may be kept for several days without 
 crystallising, although moved about from one place to another. In this condition 
 the solution is said to be super-saturated. On withdrawing the cork, the air enter- 
 ing the partly vacuous space above the liquid will be seen to disturb the surface 
 slightly, and from that point beautiful prismatic crystals will shoot through the 
 liquid until the whole has become a nearly solid mass. A considerable elevation 
 of temperature is observed, consequent upon the passage from the liquid to the 
 solid form. If the solution of sodium sulphate be somewhat weaker, containing 
 exactly two-thirds of its weight of the crystals, it may be cooled without crystallis- 
 ing, even in vessels covered with glass plates, but a touch with a glass rod will start 
 the crystallisation immediately. 
 
 The crystallisation of a supersaturated solution is provoked by contact with a 
 crystal of the salt itself. Minute crystals of sodium sulphate are present in th e 
 floating dust of the air, and cause the crystallisation when they fall into the 
 supersaturated solution. A perfectly clean glass rod may be dipped into the 
 liquid without causing crystallisation, but a rod which has been exposed to air 
 will have some particles of sodium sulphate on it, and will start crystallisation ; if 
 the rod be heated so as to render the sodium sulphate from the dust anhydrous, it 
 will no longer cause crystallisation unless it be drawn through the hand. Air 
 filtered through cotton-wool does not cause supersaturated solutions to crystallise. 
 If the solution of sodium sulphate containing two-thirds of its weight of the crystals 
 be allowed to cool in a flask closed by a cork furnished with two tubes plugged with 
 cotton-wool, it will be found that, on withdrawing the plugs and blowing through 
 one of the tubes dipping into the solution, no crystallisation occurs ; but if air be 
 blown by a pair of bellows into the same solution, it will crystallise at once. 
 
 Sodium hyposulphite (thiosulphate) and sodium acetate yield supersaturated 
 solutions which are less likely to be crystallised by dust than the sodium sul- 
 phate. If a warm supersaturated solution of sodium acetate be very carefully 
 poured upon a cold supersaturated solution of sodium hyposulphite, in a narrow 
 cylinder, which is then covered and allowed to cool, a crystal of the hyposulphite 
 may be dropped in without causing crystallisation till it reaches the lower layer 
 of hyposulphite solution ; a crystal of sodium acetate may then be dropped in to 
 start the crystallisation of the upper layer. 
 
 Supersaturated solution of sodium acetate is used in railway foot-warmers, 
 where the heat evolved in the crystallisation renders it four times as efficacious 
 as the same volume of hot water. 
 
 A most beautiful illustration of the power of unfiltered air to start crystallisation 
 is afforded by a solution of alum which has been dissolved in half its weight of 
 water at 194 F. (90 C.) and allowed to cool in a flask, the mouth of which is closed 
 by a plug of cotton-wool. In this state it may be kept for weeks without crystal- 
 lising, but. on withdrawing the plug, crystallisation will be seen to start at a few 
 points on the surface immediately under the opening of the neck, and will spread 
 slowly from these, octahedral crystals of alum of half an inch or more in diameter 
 being built up in a few seconds, the temperature, at the same time, rising very 
 considerably. 
 
 In the laboratory, stirring is always resorted to in order to induce crystallisa- 
 tion, if it does not occur spontaneously. Thus it is usual to test for potassium in 
 a solution by adding tartaric acid, which should cause the formation of minute 
 crystals of hydro-potassium tartrate (cream of tartar), but the test seldom succeeds 
 unless the solutions are briskly stirred together with a glass rod. An amusing 
 illustration of this is afforded by pouring a solution of tartaric acid into a solution 
 of saltpetre, and allowing the clear mixture to run over a large plate of glass. 
 Letters traced on the glass with the finger will now be rendered visible by the 
 deposition of the crystals of the tartrate upon the glass. 
 
 39A. Every crystal may be referred to one of comparatively few types, although 
 the identification of the parent form of a crystal is not always easy, and is an art 
 in itself, known as crystallography. 
 
 The classification of crystals is based on the symmetry of their faces around a 
 plane or an axis drawn through the crystal. A plane of symmetry in a geometrical 
 form is a plane dividing the form in such a manner that the two parts have the 
 relationship of object and image to each other. When a crystal is turned round on 
 a certain axis, it must be rotated through a certain angle before it appears again 
 of the same form to the observer ; accordingly as the rotation is through , , or 
 of 360, the crystal is said to have a 2-, 3-, 4-, or 6-fold axis of symmetry. 
 
cj 2 CRYSTALS. 
 
 The following are the principal fundamental forms, and 
 figures are indicated in Fig. 43 by corresponding numbers : 
 from an acute-angled parallelopipedon and devoid of symmetry. 
 having one plane of symmetry and derived from a parallelopipedon witl 
 singular and two acute-angled faces. (3) Rkomtic, derived from 
 parallelopipedon. and having two planes of symmetry at right angles to et 
 (4) Quadratic, having a four-fold axis of symmetry, and derived from a lect 
 angular parallelopipedon with a square base. (5) Trigonal, having a 1 three-fo Id 
 axis of symmetry, and derived from a right triangular prism, (b) Mexa V"^ 
 having a six-fold axis of symmetry, and derived from a right hexagonal pi ism 
 (7) Regular, derived from the cube, and having three two-fold axes of symmetry 
 at right angles to each other. 
 
 Fig'. 43. Forms of crystals. 
 
 40. Crystals of sodium sulphate contain, in a state of combination 
 with the salt, more than half their weight of water. Their composi- 
 tion is 
 
 Anhydrous sodium sulphate (Na 2 S0 4 ) 142 parts, or one molecule ; 
 Water 180 or ten molecules, 
 
 as expressed by the formula Na 2 S0 4 . ioH 2 0. If the crystals are left 
 exposed to the air, they gradually effloresce, or become covered with a 
 white opaque powder. This powder is the anhydrous sodium sulphate 
 into which the entire crystals would ultimately become converted by 
 exposure to air. Since most crystals containing water have their 
 crystalline form destroyed or modified by the loss of the water, it is 
 commonly spoken of as water of crystallisation. 
 
 Coloured salts, containing water of crystallisation, generally change 
 colour when the water is removed. The sulphate of copper (blue stone] 
 affords an excellent example of this. The beautiful blue prismatic 
 crystals of this salt contain 
 
 Anhydrous sulphate of copper (CuS0 4 ) 159.5 parts, or one molecule : 
 Water 90 or five molecules, 
 
 as expressed by the formula CuS0 4 -5H 2 0. 
 
WATER OF CRYSTALLISATION AND CONSTITUTION. 53 
 
 When these are exposed to the air at the ordinary temperature they 
 remain unchanged but if heated to the boiling-point of water they 
 become opaque, a^ may be easily crumbled down to a nearly white 
 powder. This powder contains 
 
 Anhydrous sulphate of copper (CuS0 4 ) 159.5 parts, or one molecule ; 
 Water . % 18 ., or one molecule, 
 
 and would therefore be represented by CuS0 4 .H.,O. The four molecules 
 of water, which have been expelled, constituted the water of crystallisa- 
 tion, upon which the form and colour of the sulphate of copper depend. 
 When the white powder is moistened with water, combination occurs 
 with great evolution of heat, 'and the blue colour is reproduced. The 
 one molecule of water which still remains is not expelled until the salt 
 is heated to 390 F. (199 0.), proving that it is held to the sulphato 
 of copper by a more powerful chemical attraction. On this account it 
 is spoken of as water of constitution, and, in order that the formula of 
 the salt may exhibit the difference between the water of constitution 
 and of crystallisation, it is usually written CuS0 4 .H,0.4Aq. (Aqua, 
 water.) 
 
 (DEFINITION. Water of crystallisation of salts is that which is gene- 
 rally expelled at 212 F. (100 C.), and is connected with the form and 
 colour of the crystals. Water of constitution is not generally expelled at 
 212 F., and is in more intimate connection with the chemical properties 
 of the salt.) 
 
 Several of the so-called sympathetic inks employed for writings which are 
 invisible until heated, depend upon the change of colour produced by loss of 
 water of crystallisation. Characters written with a weak solution of cobalt 
 chloride and allowed to dry, are very nearly invisible, since the pink colour of so 
 small a quantity of the salt is scarcely noticed : but on warming the paper, the 
 pink hydrated chloride of cobalt (CoCl 2 .6Aq) loses water of crystallisation, and the 
 blue chloride with one molecule of water is produced. On exposure to air this 
 again absorbs water, and the writing fades away. 
 
 Some salts have so great a tendency to combine with water that they 
 become moist or deliquesce when exposed to air. This deliquescence is 
 exhibited in a marked degree by calcium chloride and its great attrac- 
 tion for water is turned to advantage in drying air and other gases by 
 passing them through tubes filled with the salt. 
 
 Nearly all salts appear to combine with water at very low temperatures : such 
 compounds, which are decomposed at temperatures above o C., have been termed 
 cryo-liydrates (/c/>yos, frost). Common salt combines with ice to form the cryo- 
 hydrate NaCl.ioAq, which remains liquid down to - 20 C. Hence arises the use 
 of crushed ice and salt as a freezing mixture, for just as ice alone, in melting, 
 lowers the temperature to o C., the melting-point of ice, so the compound of ice 
 and NaCl, in melting lowers the temperature to about - 20 C., the melting-point 
 of the cryo-hydrate. 
 
 41. Most bases are capable of combining with water to form hydrates, 
 as exemplified in the slaking of lime. Anhydrous lime or quick-lime 
 (CaO), when w r etted with water, combines with it, evolving much heat, 
 and crumbling to a loose bulky powder, which is hydrate of lime or slake " 
 lime (CaO.H 2 0). This affords an example of the second mode of att 
 referred to above ; for some of the lime passes into solution when muc 
 water is used, but the original quick-lime cannot be recovered by me: 
 evaporating the water. At a red heat, however, the water is expell 
 and anhydrous lime remains. 
 
54 
 
 WELL, SPRING AND RIVER WATERS. 
 
 CO 
 
 I- 
 
 du 
 th 
 
 42. Since several hydrates do not yield water when heated, the 
 hydrate of a metal is defined as a compound formed^by the exchange of 
 a part of the hydrogen in water for a metal : thut^gpota^sium hydrate 
 KOH is formed from water HOH by the exchange of H for K : calcium 
 hydrate Ca(OH), is formed from two molecules of water (HOH) 2 by 
 the exchange of H 2 for (^iad) calcium. The imaginary group OH, 
 hydroxyl, would then be the radicle of ike hydrate^, which are often 
 termed hydroxides. 
 
 43. Water from natural sources. Pure water is not found in nature. 
 Rain is the purest form of natural water, but contains certain gases which 
 it collects from the atmosphere during $s fall. As soon as it reaches 
 the earth it begins to dissolve small portions of the various solid 
 materials with which it comes in contact, and thus becomes charged 
 with salts and other substances to an extent varying, of course, with 
 the nature of the soils and rocks which it has touched, and attaining 
 its highest point in sea water, which contains a larger proportion of 
 saline matters than water from any other natural source. 
 
 If a quantity of rain, spring, river, or sea water be boiled in a flask 
 furnished with a tube also filled with the water, and passing under a 
 gas cylinder standing in a trough of the same water (Fig. 44), it will be 
 found to give off a quantity of gas which was previously held in solution 
 by the water, and is now set free because gases are less soluble in hot 
 
 than in cold water. Tne 
 quantity of this gas varies 
 according to the source of the 
 water, but always contains 
 the gases existing in atmo- 
 spheric air, viz., nitrogen, 
 oxygen, and carbonic acid 
 gas. One gallon of rain 
 water will generally furnish 
 about 4 cubic inches of nitro- 
 gen, 2 cubic inches of oxygen, 
 and i cubic inch of carbonic 
 acid gas. It is worthy of 
 remark, that the nitrogen 
 and oxygen have been dis- 
 solved by the water, not in 
 the proportions in which they exist in the atmosphere, but in the pro- 
 portions in which they ought to be dissolved, if it be true that they 
 exist in the air in the condition of mere mechanical admixture. The 
 oxygen thus carried down from the air by rain appears to be service- 
 able in maintaining the respiration of aquatic animals, and in confer- 
 ring upon river waters a self-purifying power, by acting upon certain 
 organic matters which would probably prove hurtful to animals, and 
 converting them into harmless products of oxidation. In the cases 
 t rivers contaminated with the sewage of towns, this action of the 
 laso ved oxygen is probably of great importance. The carbonic acid 
 issolved in ram water also probably serves some useful purposes in 
 he chemical economy of nature. (See Carbonic Acid.) 
 
 Fig. 44- 
 
 Tk! a gaS ex P resses the volume of gas absorbed by one 
 
 I water. The numbers 0.02989 and 0.01478 respectively represent the 
 
HARD AND SOFT WATERS. 55 
 
 volumes of oxygen and nitrogen absorbed by one volume of water, when exposed 
 to the action of either gas, in a pure state, at 59 F. (15 C.). When a mixture of 
 gases is brought into contact with water, the proportions in which the gases are 
 absorbed can be ascertained by multiplying the co-efficient of solubility of each 
 gas by its proportion by volume in the mixture. Thus, when water is exposed to 
 air, containing i volume of oxygen and -f volume of nitrogen, the quantities dis- 
 solved by one volume of water are 
 
 Oxygen i x 0.02989 0.00597, 
 
 Nitrogen . i x 0.01478 =- 0.01182; 
 
 or almost exactly two volumes of N to one volume of 0. 
 
 44. The waters of wells, springs, and rivers, and especially those of 
 the two first-named sources, differ very much from each other, according 
 to the nature of the layers of rock or earth over or through which they 
 have passed, and from which they dissolve a great variety of substances, 
 some familiar to us in daily life, others only met with in chemical 
 collections. Under the former head may be enumerated Glauber's salt 
 (sodium sulphate), common salt (sodium chloride), Epsom salt (mag- 
 nesium sulphate), gypsum (calcium sulphate), chalk (calcium carbonate), 
 common magnesia (magnesium carbonate), carbonic acid, and silica. 
 
 Among the substances known only to the chemist may be mentioned 
 sulphuretted hydrogen, potassium sulphate, potassium chloride, calcium 
 chloride, magnesium chloride, phosphates, bromides and iodides of 
 calcium and magnesium (rarely), aluminium sulphate, carbonate of iron 
 (ferrous carbonate), and certain vegetable substances.* 
 
 The well waters of certain localities (as, for example, those of large 
 towns) also frequently contain salts of nitric and nitrous acids, and of 
 ammonia. 
 
 The waters of springs and rivers do not differ very materially from 
 well waters as to the nature of the substances which they contain, 
 though, in the case of river waters more particularly, the quantity of 
 these substances is materially influenced by the conditions of rapid 
 motion and exposure to air under which such waters are placed. 
 
 The palatable quality of a water is largely dependent upon the 
 quantity of dissolved gas which it contains. Thus, a water which is 
 agreeable for drinking will become insipid after it has been boiled and 
 the dissolved air in this way expelled. The presence of dissolved solid 
 matter in the water also influences its taste, preference being generally 
 expressed for those waters which are not exceedingly poor in such 
 solids; it is undesirable, however, that the quantity should exceed 35 
 grains per gallon (Thames water, as supplied to the metropolis, contains 
 about 22 grains per gallon). A decision as to the wholesomeness of a 
 water, or as to its fitness for feeding boilers, &c., can be given by the 
 analyst alone ; the considerations which influence his dictum are indi- 
 cated in the following statements. 
 
 Household experience has established a classification of the waters 
 from natural sources into soft and hard waters a division which depends 
 chiefly upon the manner in which they act upon soap. If a piece of 
 soap be gently rubbed in soft water (rain water, for example) it speedily 
 furnishes a froth or lather, and its cleansing powers can be readily 
 brought into action ; but if a hard water (spring water) be substituted 
 for rain water, the soap must be rubbed for a much longer time before 
 
 * Although it is certainly known that the acids and bases capable of forming- the salts 
 here enumerated may be detected in spring- and river waters, their exact distribution amongst 
 each other is still It matter of uncertainty. 
 
56 CAUSE OF HARDNESS. 
 
 a lather can be produced, or its effect in cleansing rendered evident ; a 
 number of white curdy flakes also make their appearance in the hard 
 water, which were not seen when soft water was used. The explanation 
 of this difference is a purely chemical one. 
 
 Soap is formed by the combination of a fatty acid with an alkali ; it is 
 manufactured by boiling oil or fat with potash or soda, the former for 
 soft, the latter for hard soaps. In the preparation of ordinary hard 
 soap, the soda takes from the oil or fat two acids stearic and oleic 
 ac id which exist in abundance in most varieties of fat, and unites 
 with them to form soap, which in chemical language would be spoken 
 of as a mixture of stearate and oleate of sodium. 
 
 If soap be rubbed in soft water until a little of it has dissolved, and 
 some Epsom salts (magnesium sulphate) be dissolved in water, and 
 poured into the soap water, curdy flakes will be produced, as when soap 
 is rubbed in hard water, and the soap water will lose its property of 
 frothing when stirred ; the magnesium sulphate has decomposed the 
 soap, forming sodium sulphate, which remains dissolved in the water, 
 and insoluble curdy flakes, which consist of stearate and oleate of 
 magnesium. 
 
 Similar to the effect of the magnesium sulphate is that of hard waters ; 
 their hardness is attributable to the presence of the different salts of 
 calcium and magnesium, all of which decompose the soap in the manner 
 exemplified above ; the peculiar properties of the soap in forming a 
 lather and dissolving grease can therefore be manifested only when a 
 sufficient quantity has been employed to decompose the whole of the 
 salts of calcium and magnesium contained in the quantity of water 
 operated on, and thus a considerable amount of soap must be rendered 
 useless when hard water is employed. 
 
 On examining the interior of a kettle in which spring, well, or river 
 water has been boiled, it will be found to be coated more or less thickly 
 with -a, fur or incrustation, generally of a brown colour, and the harder 
 the water the more speedily will this incrustation be deposited. A 
 chemical examination shows this deposit to consist chiefly of calcium car- 
 bonate (chalk) in the form of minute crystals, which may be discovered 
 by the microscope ; it usually contains, in addition, some magnesium car- 
 bonate, calcium sulphate, and small quantities of oxide of iron (rust) 
 and vegetable matter, the last two substances imparting its brown 
 colour. In order to explain the formation of this deposit, it is neces- 
 sary to become acquainted with the particular condition in which the 
 calcium carbonate exists in natural waters ; it is hardly dissolved to any 
 perceptible extent by pure water, though it may be dissolved in con- 
 siderable quantity by water containing carbonic acid. This statement, 
 which is of great importance in connection with natural waters, may 
 be verified in the following manner : A little slaked lime is well shaken 
 up in a bottle of distilled or rain water, which is afterwards set aside 
 for an hour or two ; as soon as that portion of the lime which has not 
 been dissolved has subsided, the clear portion is carefully poured into a 
 glass, and a little soda water (a solution of carbonic acid in water) is 
 added to it ; the first addition of the carbonic acid to the lime water 
 causes a milkiness, due to the formation of minute particles of calcium 
 carbonate; this being insoluble in the water, separates from it, or 
 precipitates, and impairs the transparency of the liquid ; a further 
 
BOILER INCRUSTATIONS. 57 
 
 addition of carbonic acid water renders the liquid again transparent, 
 for the carbonic acid dissolves the calcium carbonate which has 
 separated. 
 
 If this clear solution be introduced into a flask, and boiled over the 
 .spirit-lamp or gas-flame, it will again become turbid, for the free car- 
 bonic acid will be expelled by the heat, and the calcium carbonate will 
 be deposited, not now, however, in so fine a powder as befere, but in 
 small, hard grains, which have a tendency to fix themselves firmly upon 
 the sides of the flask, and, when examined by the microscope, are seen 
 to consist of small crystals. 
 
 In a similar manner, when natural waters are boiled, the carbonic 
 .acid gas which they contain is expelled, and the carbonates of calcium, 
 magnesium, and iron are precipitated, since they are insoluble in water 
 which does not contain carbonic acid. But, by the ebullition of the 
 water, a portion of it has been dissipated in vapour, and if there be 
 much calcium sulphate present, the quantity of water left may not be 
 sufficient to retain the whole of the salt in solution ; calcium sulphate 
 requires about 500 parts of cold water to dissolve it, and is nearly 
 insoluble in water having a higher temperature than 212 F., as would 
 be the case in boilers worked under pressure, so that it would readily 
 be deposited. It contributes much to the formation of compact incrus- 
 tations. Should the water contain much vegetable matter, this is often 
 deposited in an insoluble condition, the whole eventually forming to- 
 gether a hard compact mass, composed of successive thin layers, on the 
 bottom and sides of the vessel in which the water has been boiled. The 
 ^'furring" of a kettle is objectionable, chiefly in consequence of its 
 retarding the ebullition of the water, since the deposit is a very bad 
 conductor of heat, and therefore impedes the transmission of heat from 
 the fire to the water ; hence the common practice of introducing a 
 round stone or marble into the kettle, in order, by its perpetual rolling, 
 to prevent the particles of calcium carbonate from forming a compact 
 layer. In steam boilers, however, even more serious inconvenience 
 than loss of time sometimes arises if this deposit be allowed to accumu- 
 late, and to form a thick layer of badly conducting material on the 
 bottom of the boiler, since the latter is then liable to become red hot, 
 and to collapse. But even though this calamity be escaped, the wear 
 and tear of the boiler is very much increased in consequence of the for- 
 mation of this deposit, since its hardness often renders it necessary to 
 detach it with the hammer, much to the injury of the iron boiler-plates, 
 which are also subject to increased oxidation and corrosion in con- 
 sequence of the high temperature which the incrustation permits them 
 to attain by preventing their contact with the water. Moreover, it is 
 obvious that a greater expenditure of fuel is requisite in order to heat 
 the water through such a non-conducting " boiler scale." Many pro- 
 positions have been brought forward for the prevention of these in- 
 crustations ; some substances have been used, of which the action 
 appears to be purely mechanical, in preventing the aggregation of the 
 deposited particles. Clay, sawdust, and other matters have been 
 employed with this view ; but the action of sal ammoniac (ammonium 
 chloride), which has also been found efficacious, must be explained upon 
 purely chemical principles. When this salt is boiled with calcium car- 
 bonate, mutual decomposition ensues, producing calcium chloride and 
 
58 TEMPORARY AND PERMANENT HARDNESS. 
 
 ammonium carbonate, of which salts the former is very soluble in water, 
 while the latter passes off in vapour with the steam. The ammonium 
 chloride, however, corrodes the metal of the boiler. Solutions of the 
 caustic alkalies, of alkaline carbonates, arsenites, tannates, &c., are also 
 occasionally employed to prevent the formation of incrustations in 
 boilers, and probably act by precipitating calcium carbonate and other 
 calcium compounds which act as nuclei, around which the/wr collects 
 as a loose deposit or mud. 
 
 The deposit formed in boilers fed with sea water consists chiefly of calcium 
 sulphate and magnesium hydrate, the latter produced by the decomposition of the 
 magnesium chloride present in sea water. As hydrochloric acid is another product 
 of the decomposition of magnesium chloride solution, water containing any con- 
 siderable quantity of this salt is liable to corrode the plates of a boiler. 
 
 The incrustations formed in cisterns and pipes by hard water are also produced 
 by the carbonates of calcium and magnesium deposited in consequence of the 
 escape of the free carbonic acid which held them in solution. Many interesting 
 natural phenomena may be explained upon the same principle. The so-called 
 petrify ing springs, in many cases, owe their remarkable properties to the consider- 
 able quantity of calcium carbonate dissolved in carbonic acid which they contain ; 
 when any object, a basket, for example, is repeatedly exposed to the action of these 
 waters, it becomes coated with a compact layer of the carbonate, and thus appears 
 to have suffered conversion into limestone. The celebrated waters of the Sprudel 
 at Carlsbad, of San-Filippo in Tuscany, and of Saint Allyre in Auvergne are the 
 best instances of this kind. 
 
 The stalactites and stalagmites.* which are formed in many caverns or natural 
 grottoes, afford beautiful examples of the gradual separation of calcium carbonate 
 from water charged with carbonic acid. Each drop of water, as it trickles through 
 the roof of the cavern, becomes surrounded with a shell of calcium carbonate, the 
 length of which is prolonged by each drop, as it falls, till a stalactite is formed, 
 varying in colour according to the nature of the substances which are separated 
 from the water together with the carbonate (such as the oxides of iron and vege- 
 table matter) ; and as each drop falls from the point of the stalactite upon the 
 floor of the cavern, it deposits there another shell, which grows, like the upper one, 
 but in the opposite direction, and forms a stalagmite, thus adorning the grotto 
 with conical pillars of calcium carbonate, sometimes, as in the case of the oriental 
 alabaster, variegated with red and yellow, and applicable to ornamental purposes. 
 
 When water which has been boiled for some time is compared with 
 unboiled water from the same source, it is found to have become much 
 softer, and this can now be easily explained, for, a considerable portion 
 of the salts of calcium and magnesium having separated from the water, 
 the latter is not capable of decomposing so large a quantity of soap. 
 The amount of hardness which is thus destroyed by boiling is generally 
 spoken of as temporary hardness, to distinguish it from the permanent 
 hardness due to the soluble salts of calcium and magnesium which still, 
 remain in the boiled water. It is customary with analytical chemists, 
 in reporting upon the quality of natural waters, to express the hardness 
 by a certain number of degrees which indicate the number of grains of 
 chalk or calcium carbonate which would be dissolved in a gallon of 
 water containing carbonic acid, in order to render its hardness equal 
 to that of the water examined ; that is, to render it capable of decom- 
 posing an equal quantity of soap. Thus, when a water is spoken of as 
 having 16 degrees of hardness, it is implied that 16 grains of calcium 
 carbonate dissolved in a gallon of water containing carbonic acid, would 
 render that gallon of water capable of decomposing as much soap as a 
 gallon of the water under consideration. 
 
 , I drop ; trTaAa-yjua, a drop. 
 
CLAEK'S PROCESS. 59 
 
 The utility of a water for household purposes must be estimated 
 therefore, not merely according to the total number of degrees of 
 hardness which it exhibits, but also by the proportion of that hardness 
 which may be regarded as temporary ; that is, which disappears when 
 the water is boiled. Thus, the total hardness of the New River water 
 amounts to nearly 1 5 degrees, that of the Grand Junction Company to 
 14 degrees, and yet these waters are quite applicable to household uses, 
 since their hardness is reduced by boiling to about 5 degrees. It has 
 been ascertained that every degree of hardness in water gives rise to a 
 waste of about 10 grains of soap for every gallon of water employed, and 
 hence the use of 100 gallons of Thames or New River water in washing 
 will be attended with the loss of about 2 Ibs. of soap; this loss is 
 reduced, however, to about one-third when the temporary hardness has 
 been destroyed by boiling. The addition of washing soda (sodium 
 carbonate) removes the permanent hardness due to the presence of the 
 sulphates of calcium and magnesium in the water, for both these salts 
 are decomposed by the sodium carbonate which separates the calcium 
 and magnesium as insoluble carbonates, whilst sodium sulphate remains 
 dissolved in the water.* The household practice of boiling the water, 
 and adding a little washing soda, is therefore very efficacious in re- 
 moving the hardness. Clark's process for softening waters depends 
 upon the neutralisation of the free carbonic acid contained in the water 
 by the addition of a certain quantity of lime ; the calcium carbonate 
 so produced separates together with the carbonates of calcium and 
 magnesium, which were previously retained in solution by the free 
 carbonic acid ; this process, therefore, affects chiefly the temporary 
 hardness ; moreover, the earthy carbonates which are separated appear 
 to remove from the water a portion of the organic matter which it 
 contains, and thus effect a very important purification. The water 
 under treatment is mixed, in large tanks, with a due proportion of 
 lime or lime-water (the quantity necessary having been determined by 
 preliminary experiment), and the mixture allowed to settle until per- 
 fectly clear, when it is drawn off into reservoirs.t A modern improve- 
 ment in the process (Porter-Clark process) consists in separating the 
 deposit by a remarkably expeditious filtration, which dispenses with 
 much of the tank-space required by the original process. 
 
 Waters which are turbid from the presence of clay in a state of 
 suspension, are sometimes purified by the addition of a small quantity 
 of alum or of aluminium sulphate, when the alumina is precipitated by 
 the calcium carbonate present in the water, and carries down with it 
 mechanically the suspended clay, leaving the water clear. 
 
 The organic matter contained in water may be vegetable matter dis- 
 solved from the earth with which it has come in contact, or resulting 
 from the decomposition of plants, or it may be animal matter derived 
 either from the animalcules and fish naturally existing in it, or from 
 the sewage of towns, and, in the case of well waters, from surface 
 drainage. 
 
 It is believed upon good medical authority, that cholera, diarrhoea, 
 and typhoid fever are propagated by certain micro-organisms called 
 
 * CaSO 4 + Na 2 CO 3 = Na 2 SO 4 + CaCO 3 
 
 Calcium sulphate Sodium carbonate. Sodium sulphate. Calcium carbonate. 
 f Thames and New River water are softened, in this way, to 3.5, or to a lower point than 
 by an hour's boiling". 
 
60 ACTION OF WATER ON LEAD. 
 
 bacilli, which are present in the evacuations of persons suffering from 
 those maladios, and are conveyed into water which is allowed to become 
 contaminated by sewage. 
 
 On this account, much attention is paid, in the analysis of water 
 intended for drinking, to the detection of organic matters containing 
 nitrogen (so-called albuminoid matters) which would be conveyed into 
 the water in sewage. The analytical operations necessary for this pur- 
 pose require great care and skill, and the conclusions to be drawn from 
 their results are by no means finally agreed upon among scientific 
 chemists. Attempts are also made to determine the number of bacteria 
 (including bacilli) present in the water, which is rejected if these are 
 very numerous. 
 
 There are, however, certain simple tests, which may often determine whether it 
 is worth while to undertake a more elaborate examination of the water. 
 
 1. Pour half a pint of the water into a wide-mouthed bottle or decanter, close it 
 with the stopper or with the palm of the hand, and shake it violently up and down. 
 If an offensive odour is then perceived, the water is probably contaminated by 
 sewage gas, and possibly with other constituents from the same source. 
 
 2. Add to a little of the water a drop or two of dilute sulphuric acid, and 
 enough potassium permanganate (^Condy's red fluid or ozonised water} to tinge it 
 of a faint rose colour ; cover the vessel with a glass plate or a saucer. If the pink 
 tinge be still visible after the lapse of a quarter of an hour, the water is probably 
 wholesome. 
 
 3. Pour a little solution of silver nitrate (lunar caustic) into a carefully cleaned 
 glass, and see that it remains transparent ; then pour in some of the water ; should 
 a strong milkiness appear, which is not cleared up on adding a little diluted nitric 
 acid, the water probably contains much sodium chloride, which is always found in 
 sewage-water, but seldom in wholesome waters in any large quantity, unless near 
 the sea coast. 
 
 To render an impure water fit to drink, a chemist would naturally recommend 
 distillation, but in many cases this is impracticable, and the consumer may protect 
 himself to a great extent by boiling the water (a high temperature being inimical 
 to micro-organisms), or by filtering it through charcoal or spongy iron, or by 
 applying Clark's process, or treating it with alum (p. 59). 
 
 45. One of the most important points to be taken into account in 
 estimating the qualities of a water is its action upon lead, since this 
 metal is unfortunately so generally employed for the storage and trans- 
 mission of water, and cases frequently occur in which the health has 
 been seriously injured by repeated small doses of compounds of lead 
 taken in water which has been kept in a leaden cistern. If a piece of 
 bright, freshly-scraped lead be exposed to the air, it speedily becomes 
 tarnished from the formation of a thin film of the oxide of lead, pro- 
 duced by the action of the atmospheric oxygen ; this oxide of lead is 
 soluble in water to some extent, and hence, when lead is kept in 
 contact with water, the oxygen which is dissolved in the latter acts upon 
 the metal, and the oxide so produced is dissolved by the water ; but 
 fortunately, different waters act with very different degrees of rapidity 
 upon the metal, according to the nature of the substances which they 
 contain. 
 
 The film of oxide which forms upon the surface of the lead is in- 
 soluble, or nearly so, in water containing much sulphate or carbonate 
 pt calcium, so that hard waters may generally be kept without danger 
 in leaden cisterns, but soft waters, and those which contain nitrites or 
 nitrates, should not be drunk after contact with lead. 
 
 Nearly all waters which have been stored in leaden cisterns contain a trace of 
 the metal, and since the action of this poison, in minute doses, upon the system I 
 
SEA WATER. 6 1 
 
 so gradual that the mischief is often referred to other causes, it is much to be 
 desired that lead should be discarded altogether for the construction of cisterns 
 (See Lead.} 
 
 To detect lead in a water, fill a glass tumbler with it, place this on white paper, 
 add a drop or two of diluted nitric acid, and some hydrosulphuric acid ; a dark 
 brown tinge will be seen on looking through the water from above. 
 
 Mineral waters, as they are popularly called, are simply spring waters 
 containing so large a quantity of some ingredient as to have a decided 
 medicinal action. They are differently named according to the nature 
 of their predominating constituent. Thus, a chalybeate water contains 
 a considerable quantity of a salt of iron (usually ferrous carbonate dis- 
 solved by free carbonic acid) ; an acidulous water is distinguished by a 
 large proportion of carbonic acid, and is well exemplified in the cele- 
 brated Seltzer water ; a sulphureous or hepatic water has the nauseous 
 odour due to the presence of sulphuretted hydrogen. The Harrogate 
 water is eminently sulphureous. Saline waters are such as contain a 
 large quantity of some salt ; thus the saline springs of Cheltenham are 
 rich in common salt and sodium sulphate. 
 
 The chalybeate waters, which are by no means uncommon, become 
 brown when exposed to the air, and deposit a rusty sediment which 
 consists of the ferric hydrate, formed by the action of the oxygen of the 
 air on the carbonate. (See Iron.) 
 
 46. Sea water contains the same salts as are found in waters from 
 other natural sources, but is distinguished by the very large proportion 
 of sodium chloride (common salt). A gallon of sea water contains 
 usually about 2 500 grains of saline matter, of which 1890 grains consist 
 of common salt. The circumstance that clothes wetted with sea water 
 never become perfectly dry is to be ascribed chiefly to the magnesium 
 chloride present in the water, which is distinguished by its tendency to 
 deliquesce or become damp in moist air. There are two elements, 
 bromine and iodine, which are found combined with metals in appreciable 
 quantity in sea water, though they are of somewhat rare occurrence in 
 other waters derived from natural sources. 
 
 47. By distillation pure water may be obtained from most spring and 
 river waters. 
 
 (DEFINITION. -Distillation is the conversion of a liquid into a vapour 
 and its re-condensation into the liquid form in another vessel.) 
 
 Fig. 45 represents the ordinary form of still in common use, in which A is a 
 copper boiler containing the water to be distilled ; B the head of the still, which 
 lifts out at b, and is connected by the neck C with the worm D, a tin pipe coiled 
 round in the tub E and issuing at F. The steam from the boiler, passing into the 
 worm, is condensed to the liquid state, being cooled by the water in contact with 
 the worm ; this water, becoming heated, passes off through the pipe G, being 
 displaced by cold water, which is allowed to enter through H. If 10 gallons of 
 river water be taken, 8 may be distilled over, but the first half-gallon should be 
 collected separately, as it contains ammonia and carbonic acid. 
 
 A form of apparatus for distillation of water and other liquids is shown in 
 Fig. 46. A is a stoppered retort, the neck of which fits into the tube of a Liebig's 
 condenser (B), which consists of a glass tube (C) fitted by means of corks into a 
 glass, copper, or tinned iron tube D, into which a stream of cold water is passed 
 by the funnel E, the heated water running out through the upper tube F. The 
 water furnished by the condensation of the steam passes through the quilled 
 receiver Gr, into the flask H. Heat is gradually applied to the retort by a ring gas- 
 burner. 
 
 Many special precautions are requisite in order to obtain absolutely 
 
62 
 
 DISTILLATION. 
 
 pure distilled water for refined experiments, but for ordinary purposes 
 the common methods of distillation yield it in a sufficient pure con- 
 dition. 
 
 The saline matters present in the water are of course left behind in 
 the still or retort. Sea water is now frequently distilled on board ship 
 
 45- 
 
 when fresh water is scarce. The vapid and disagreeable taste of distilled 
 water, which is due to its having been deprived of the dissolved air 
 during the distillation, is remedied by the use of Normandy's still, which 
 provides for the restoration of the expelled air. 
 
 Fig. 46. Distillation : Liebig-'s condenser. 
 
 48 The physical properties of water are too well known to r 
 any detailed description. Its specific gravity in the liquid state 
 
PEROXIDE OF HYDROGEN. 63 
 
 being taken as the standard to which the specific gravities of liquid and 
 solid bodies are referred. 
 
 (DEFINITION. The specific gravity of a liquid or solid body is its 
 weight as compared with that of an equal volume of pure water at 
 60 F. 15.5 C.) 
 
 Water assumes the solid form, under ordinary circumstances, at 32 F. 
 (o C.), and may be obtained in six-sided prismatic crystals. Snow con- 
 sists of beautiful stellate groupings of these crystals. Ice has the 
 specific gravity 0.9184. In the act of freezing, water expands very 
 considerably, so that 174 volumes of water at 60 F. become 184 volumes 
 of ice. The breakage of vessels, splitting of rocks, &c., by the con- 
 gelation of water are due to this expansion. Water passes off in vapour 
 at all temperatures, the amount of water evolved in a given time of 
 course increasing with the temperature. The boiling-point of water is 
 212 F. (100 C.). Its absolute boiling-point (p. 29) is 365 C. 
 
 (DEFINITION. The boiling-point of a liquid is the constant tempera- 
 ture indicated by a thermometer, immersed in the vapour of the boiling 
 liquid, in the presence of a coil of platinum wire, to facilitate disengage- 
 ment of vapour, and at a pressure of 760 mm. Bar.) 
 
 At and above 212 F. at the ordinary atmospheric pressure (30 in. 
 Bar.), water is an invisible vapour of specific gravity 0.625 (air=i). 
 One cubic inch of water at 60 F. becomes 1696 cubic inches of vapour 
 at 212 F. 
 
 From the definition of molecular weight given on p. 47 it will be seen 
 that if the specific gravity of a gas in relation to air be required, it 
 may be obtained by multiplying half the molecular weight by 0.0695, 
 which represents the specific gravity of hydrogen referred to air as the 
 unit. Thus the specific gravity of steam (air=i) is 9x0.0695 = 
 0.625. 
 
 49. Peroxide of Hydrogen or Hydrogen Dioxide, H 2 O 2 (oxygenated 
 water). Minute quantities of this compound are found in snow and rain, but 
 no other natural occurrence of it has been proved with certainty.* 
 
 To prepare hydrogen dioxide the barium dioxide referred to on p. 39 is powdered, 
 suspended in water, and added gradually to water through which carbon dioxide is 
 passing ; the water is thus charged with hydrogen dioxide : 
 
 Ba0 2 + H ? + C0 2 = BaC0 3 f H 2 2 . 
 
 The barium carbonate (BaC0 3 ) is allowed to settle, and the clear solution of H 2 2 
 poured off. 
 
 Pure hydrogen dioxide is made by first dissolving Ba0 2 in the least possible 
 quantity of dilute nitric acid and adding to the solution one of barium hydroxide 
 (baryta water). The precipitate is Ba0 2 .8H 2 ; it is washed by decantation and 
 gradually added to dilute H 2 S0 4 , care being taken to leave the liquid very slightly 
 acid f : Ba0 2 + H 2 S0 4 = H 2 2 +BaS0 4 . The precipitate is allowed to settle, and 
 the clear liquid is evaporated either in a vacuum over oil of vitriol, or on the 
 water-bath at a temperature below 75 C., until it contains about 50 per cent, of 
 H 2 2 , when it is finally distilled under a pressure of 10-70 mm. ; the water passes 
 over first and then the pure dioxide. The operations of concentration and distil- 
 lation require great care, and the solution first made should be free from salts of 
 the heavy metals ; for incautious heating of, the access of dust to, or the presence 
 of such salts in, the concentrated dioxide renders it liable to explode by sudden 
 decomposition into water and oxygen: H 2 2 = H 2 + 0. Even when preserved 
 
 * H 2 O 2 is frequently produced when substances are oxidised by free oxygen in presence 
 of water ; thus it is invariably to be detected in water in which lead has been exposed to the 
 air. 
 
 t If the H 2 SO 4 were added to the BaO 2 .8H 2 O, instead of as recommended, the H 2 O 2 would 
 be decomposed by the remaining BaO 2 as fast as it was formed. 
 
64 TESTS FOR HYDROGEN DIOXIDE. 
 
 from adventitious matter the pure dioxide slowly decomposes, so that dangerous. 
 pressure due to accumulated oxygen may arise in any closed vessel containing it. 
 
 Pure hydrogen dioxide is a syrupy, colourless liquid of sp. gr. 1.5 and boiling at 
 69 C. under 26 mm. pressure. ' It is more soluble in ether than in water, so that 
 the former extracts it from its solution in the latter. It oxidises many organic 
 matters so rapidly that it sometimes ignites them. Its tendency to explode has- 
 been already mentioned. 
 
 When diluted with water, hydrogen dioxide is in no sense dangerous, although 
 far from a stable substance. The commercial " 10 volume " hydrogen peroxide 
 contains about 3 per cent, of H 2 2 , and yields, from I volume of the solution, 
 10 volumes of oxygen when decomposed. It may be preserved for a considerable 
 time if it contain a small proportion of acid ; alkali has the opposite effect, and 
 if the solution is neutral, it takes up alkali from the glass bottle and is decomposed 
 thereby. 
 
 A remarkable feature of hydrogen dioxide is the ease with which it decomposes 
 into water and oxygen, with evolution of heat, by mere contact with many sub- 
 stances which are themselves unchanged by the dioxide.* Thus, finely divided 
 gold, platinum, and silver, which have no direct attraction for oxygen, cause this 
 evolution of oxygen, Manganese dioxide also decomposes the H 2 2 in a solution 
 without undergoing any apparent change ; but if an acid be present the MnO a will 
 be reduced to MnO and will dissolve as a manganous salt, a fact which is some- 
 what surprising, seeing that the H 2 2 is so ready to part with its oxygen. There 
 are, however, a number of reactions in which hydrogen dioxide acts as a reducing 
 agent. If some of the 3 per cent, solution be added to some silver oxide suspended 
 in water, the brown colour of the oxide will pass into the black of finely divided 
 silver and minute bubbles of oxygen will escape : Ag 2 + H 2 2 - Ag 2 + H 2 + O. By 
 adding ammonia very carefully to silver nitrate solution until the precipitate formed 
 at first is only just re-dissolved, and then adding some H 2 2 and heating, the silver 
 will be deposited in its lustrous form, convincing the experimenter that it is indeed 
 in the metallic state. 
 
 Another reducing action of H 2 2 is its effect on an acid solution of potassium 
 permanganate (K 9 Mn 2 8 ), the pink colour of which it rapidly discharges, with 
 evolution of oxygen : K 2 Mn 2 8 + 3H 2 S0 4 + 5H 2 2 = K 2 S0 4 + 2MnS0 4 + 8H 2 + 50 2 . 
 Here 5 from the dioxide have united with 5 from the permanganate. 
 
 Notwithstanding its behaviour in the foregoing changes as a reducing agent, a 
 compound so ready to part with its oxygen, as is hydrogen dioxide, will, of course, 
 act as an oxidising agent. If some black lead sulphide is treated with hydrogen 
 dioxide it is rapidly oxidised to the white lead sulphate, PbS + 4.H 2 2 = PbS0 4 =;4H 2 0. 
 It is to be noted that in many cases the oxidising effect of the dioxide is much 
 accelerated by the presence of a small quantity of a reducing agent ; thus a mixture 
 of indigo solution and the dioxide is at once decolourised (by oxidation of the 
 indigo) on addition of a drop of ferrous sulphate solution. 
 
 A very striking reaction of hydrogen dioxide is that with chromic acid. If a 
 solution of H 2 2 be added to a weak solution of potatsium dichromate acidified 
 with sulphuric acid, the beautiful blue colour of perchromic acid appears ; 
 K 2 Cr. 2 7 + H 2 S0 4 + H 2 2 = K 2 S0 4 + H 2 + H 2 Cr 2 8 .t Af ter a few minutes, the blue 
 colour changes to a very pale green, the perchromic acid being decomposed by the 
 sulphuric acid, yielding the green chromium sulphate, and free oxygen, which 
 adheres in bubbles to the side of the vessel, H 2 Cr a 8 + 3H 2 S0 4 = Cr 2 (S0 4 ) 3 + 4H 2 O + 4 . 
 If the blue solution be shaken with a little ether, which dissolves the perchromic 
 acid and rises with it to the surface where it forms a blue layer, the colour is much 
 more lasting, and very minute quantities of hydrogen dioxide may thus be detected. 
 Still more delicate tests for hydrogen dioxide are the production of a yellow colour 
 with titam'c acid, and a yellowish precipitate with uranium salts. 
 
 The decomposition of H 2 2 into H 2 and is attended by evolution of heat, 
 amounting to 23,000 gram-units of heat for each gram-molecule of H 2 2 . When 
 H 2 and combine to form H 2 0, 69,000 units of heat are evolved ; hence, when 
 H 2 is decomposed, 69,000 units must be absorbed, so that we have, in the forma- 
 tion of water. H 2 +0 = H 2 + 69,000 heat-units. But since the decomposition of 
 H. 2 2 into H 2 and evolves 23,000 units, its formation from H 2 and would 
 
 * Such inexplicable changes as this are sometimes included under the general denomina- 
 tion of catalysis, or decomposition by contact or by catalytic action. 
 
 f It is by no means certain that this formula represents the composition of the blue com - 
 pound. 
 
OZONE. 
 
 absorb the same quantity, and we should have H 2 + = H 2 2 - 23,000 units. 
 From the two equations we get H 2 + 2 H 2 2 + 69,000 - 23,000 or H 2 -f0 2 = 
 H 2 2 + 46,000 heat-units. Now, by the laws of thermo-cheinistry, every chemical 
 change tends to produce that body in the formation of which most heat is liberated ; 
 hence water, and not hydrogen dioxide, is the general result of chemical changes 
 in which H and are concerned. 
 
 The uses of hydrogen peroxide are chiefly as an oxidising agent. 
 Thus it is applied for bleaching materials which are too tender to be 
 subjected to the drastic action of bleaching powder. A like effect is 
 produced on dark hair, which becomes yellow on treatment with hair- 
 wash containing this reagent. Photography, ivory-bleaching, and clean- 
 ing old pictures afford other outlets for hydrogen peroxide. 
 
 50. Ozone. This is the name given to a 
 modified form of oxygen, of the true nature of 
 which there is still some doubt, as it has never 
 been obtained unmixed with ordinary oxygen, 
 but it appears to be formed by the union of 3 
 atoms of oxygen (occupying 3 volumes), to pro- 
 duce a molecule of ozone (occupying 2 volumes). 
 Just as hydrogen dioxide (H 2 2 ) may be regarded 
 as formed by the combination of a molecule of 
 water (H 2 0) with an atom of oxygen, so ozone 
 may be viewed as a combination of a molecule of 
 oxygen (0 2 ) with an atom of oxygen. It would 
 then be half as heavy again as ordinary oxygen, 
 and experiment has shown that its rate of diffu- 
 sion is in accordance with this view. 
 
 It derives its name from its peculiar odour 
 (6fcii', to smell), which is often perceived in the 
 air of the sea or of the open country, and in 
 linen which has been dried in country air. 
 According to Hartley, I volume of ozone in 2\ 
 million volumes of air may be perceived by the 
 smell. Oxygen appears to be capable of assum- 
 ing this ozonised condition under various circum- 
 stances, the principal of which are, the passage 
 of silent electric discharges,* and the contact 
 with substances (such as phosphorus) undergoing 
 slow oxidation in the presence of water. A 
 portion f of the oxygen obtained in the decom- 
 position of water by the galvanic current also 
 exists in the ozonised condition, as may be per- 
 ceived by its odour. 
 
 The use of an induction-tube (Fig. 47) affords 
 the readiest method of demonstrating the cha- 
 racteristic properties of ozone. 
 
 Fig. 47. Ozonising apparatus. 
 
 The construction of the apparatus will be readily understood from the figure. 
 The outside cylinder and the innermost tube are filled with dilute sulphuric acid, 
 which serves the double purpose of conducting the electricity and keeping down 
 the temperature of the oxygen or air. When the wires are connected with the 
 poles of an induction-coil the two portions of dilute sulphuric acid are oppositely 
 electrified, so that the space between the two liquids is submitted to the high 
 pressure electrical discharge necessary for the resolution of the oxygen molecules 
 into their atoms, and the recombination of these to form molecules of ozone. 
 Through this space the air or oxygen (dried by passing through oil of vitriol) is 
 passed in the direction of the arrows. The induction-tube must be made of thin 
 glass, and the space between the inner and the outer tube must be as narrow as 
 possible. 
 
 The ordinary chemical test for ozone is a damp mixture of starch paste with 
 potassium iodide. If this mixture be brushed over strips of white cartridge paper 
 
 * It is the odour of ozone which is perceived in working an ordinary electrical machine. 
 } Varying from a trace to 17 per cent., according to the electrical conditions. 
 
 E 
 
66 OZONE. 
 
 these will remain unchanged in ordinary air ; but when they are exposed to 
 ozonised air (such as that which has passed through the induction-tube), they wjll 
 immediately assume a blue colour. The ozone sets free the iodine from the KI, 
 which has the specific property of imparting a blue colour to starch. Papers 
 impregnated with manganese sulphate, lead acetate, or thallous oxide, become 
 brown, in the first two cases from the formation of the peroxide of. the metal 
 and in the last case from the formation of thallic oxide, under the influence of 
 ozone. 
 
 . If the ozonised air be passed into a solution of indigo (sulphlndigotic acid largely 
 diluted) the blue colour will soon disappear, since the ozone oxidises the indigo, 
 and gives rise to products which, in a diluted state, are nearly colourless. Ordinary 
 oxygen is incapable of bleaching indigo in this manner. If the ozone is passed 
 through a tube of vulcanised caoutchouc, this will soon be perforated by the 
 corrosive effect of the ozone, whilst ordinary oxygen would be without effect upon 
 it. If ozonised air be passed into a flask with a little mercury at the bottom, the 
 surface of the mercury will soon become tarnished by the formation of oxide, 
 and when the mercury is shaken round the flask it will adhere to the sides, which 
 is not the case with pure mercury. It is stated that if both the mercury and the 
 ozone be dry, the gas will be converted into oxygen, but the mercury will not be 
 oxidised. 
 
 When ozone is passed slowly through a glass tube heated in the centre by a 
 spirit-lamp, it loses its power of affecting the iodised starch-paper, the ozone 
 having been re-converted into ordinary oxygen under the influence of heat ; 
 2(OO 2 ) = 3(0 2 ). A temperature of 250 C. is sufficient to effect this change. A 
 given volume of oxygen diminishes when a portion of it is converted into ozone 
 by the silent electric discharge, and it regains its original volume when the ozone 
 is re-converted by heat. The conversion of oxygen into ozone is attended by 
 absorption of heat ; 30 2 =203 59,200 units. 
 
 When a given quantity of oxygen is electrised, or subjected to the action of 
 surfaces charged with opposite electricities, as in the induction tube, only one-fifth, 
 at most, is converted into ozone ; but if the ozone be now removed by some sub- 
 stance which absorbs it, a fresh quantity of the oxygen may be ozonised.* 
 
 The facts that ozone can be produced in pure oxygen and that its formation is 
 accompanied by a contraction in volume, lead to the conclusion that ozone is a 
 condensed form of oxygen. When the ozonised oxygen has been heated it is 
 found to have expanded to exactly the same volume which the pure oxygen 
 occupied, and to no longer contain any ozone. By introducing turpentine into the 
 ozonised gas all the ozone is absorbed, and a measurement of the contraction 
 caused by this absorption reveals the fact that the volume which has disappeared 
 is twice the volume of the contraction effected by ozonising the oxygen. Thus, 
 if n c.c. of gas disappeared when the oxygen was ozonised, 2n c.c. will be absorbed 
 by the turpentine. Therefore 3 vols. of the original oxygen must have become 
 2 vols. of ozone, and if the gas had been heated, instead of having been treated 
 with turpentine, these 2 vols. of ozone would have expanded again to 3 vols. of 
 oxygen. If one atom of oxygen be regarded as occupying one volume, then one 
 molecule (2 atoms) must occupy 2 vols. ; so that in producing ozone one molecule 
 of oxygen has been combined with one atom of oxygen, forming a molecule of 
 ozone, 2 0. 
 
 When a neutral solution of potassium iodide is introduced into ozonised oxygen 
 there is no contraction in volume, and yet all the ozone is destroyed ; at the same 
 time iodine is liberated from the potassium iodide. If the quantity of this iodine 
 be determined, it is found to be as much as would (under other circumstances) be 
 liberated by a volume of oxygen identical with the volume which disappeared 
 when the oxygen was ozonised. The explanation of these observations is easy if 
 the above view of the constitution of ozone be adopted; for the facts maybe 
 expressed by the equation y 
 
 00 2 ( 2 vols.) + 2KI + HOH = 2 KOH + 1 2 + 2 (2 vols.), 
 showing that it is the third atom of oxygen in the molecule of ozone which has 
 
 electric e diSr? i0 ?h f Z ne f rmed dependS Up n the intensit y a d frequency of the 
 
 ratert ArcoS? t ^T^S "^ the tem P erature - Th last-named influence is the 
 
 Seat 2 ?C T! n?r % ? re S arches < l88o > 2O P er ce "t. of the oxygen becomes 
 
 -25 C, 12 per cent, at 20 C., and 2 per cent, at 100 C. ; more lately (i8oO it 
 
 SUEZ. 5 ' 2 Per Cent< at 2 C " and nly I0 '4 P er cent " ^en at -?c. cSbe 
 
ATMOSPHERIC OZONE. 67 
 
 liberated the iodine. If the solution of potassium iodide be acidified (and thus- 
 converted virtually into a solution of hydriodic acid), twice as much iodine will be< 
 liberated and the volume of the ozone will be reduced to one-half 
 OO 2 (2 vols.) + 4 HI = 2H 2 + I 4 + (i vol.). 
 
 By placing a freshly scraped stick of phosphorus (scraped under water to avoid 
 inflammation) at the bottom of a quart bottle, with enough water to cover half 
 of it, and loosely covering the bottle with a glass plate, enough ozone may be 
 accumulated in a few minutes to be readily recognised by the odour and the 
 iodised starch. The water at the bottom of the bottle is found to contain, besides 
 the phosphorus and phosphoric acids, formed by the slow oxidation of the phos- 
 phorus, some hydrogen dioxide, whence it has been supposed that the formation 
 of ozone is due to the decomposition of a molecule of oxygen into electro -negative 
 oxygen, which combines with another molecule of oxygen to form ozone, and 
 electro-positive oxygen, which combines with a molecule of water to form hydrogen 
 dioxide. Thus. 
 
 + + - 
 
 2 + 00 + H 2 = H 2 00 + 2 0. 
 
 This view is supported by the circumstance that hydrogen dioxide appears to be 
 produced in every case where ozone is formed in the presence of water. 
 
 When ozonised oxygen is shaken with hydrogen dioxide, the above equation is 
 reversed, water and ordinary oxygen being formed.* 
 
 Impure ether and essential oils, such as turpentine, slowly absorb oxygen (and 
 perhaps ozone) from the air. There are thus produced organic peroxides which 
 yield hydrogen dioxide in contact with water, so that old samples of these com- 
 pounds exhibit the reactions of hydrogen dioxide. A solution of hydrogen dioxide 
 in ether (ozonic ether) has been used as a test for blood stains. 
 
 Contact with blood decomposes hydrogen dioxide, and the oxygen which is 
 liberated is capable of blueing guaiacum resin. Accordingly, if a blood-stain be 
 moistened with tincture of guaiacum (a solution of the resin in spirit of wine), and 
 afterwards with the ozonic ether, it acquires an intense blue colour, which may 
 be detected, even on a coloured fabric, by pressing a piece of white blotting-paper 
 upon it. 
 
 Ozone has attracted much notice, because a minute proportion of the oxygen 
 in the atmosphere appears sometimes to be present in this form, and its active 
 properties have naturally led to the belief that it must exercise some influence 
 upon the sanitary condition of the air. This idea is encouraged by the circum- 
 stance that no indications of ozone can be perceived in crowded cities, where there 
 are so many oxidisable substances to consume the active oxygen, whilst the air in 
 the open country and at the seaside does give evidence of its presence. Some 
 chemists assert that their experiments have demonstrated the very important fact 
 that a portion of the oxygen developed by growing plants is in the ozonised form, 
 but the evidence on the subject is conflicting. Houzean fixes the maximum pro- 
 portion of ozone at T^fHJTRrth of the volume of air. The proportion is highest in 
 May and June, lowest in December and January. 
 
 Ozonised oxygen exhibits a sky-blue colour when viewed along a column of one 
 metre in length. The blue colour becomes very deep under a pressure of several 
 atmospheres. It has been suggested that the blue colour of the sky is due to our 
 regarding it through the ozonised atmosphere. By passing ozonised oxygen 
 through a tube immersed in liquid oxygen which is evaporating, the ozone is con- 
 densed to a blue liquid boiling at- 106 C. and yielding a violently explosive blue 
 gas. Ozone is slightly soluble in water ; 100 vols. water dissolve 0.83 vols. ozone 
 (at i C.). 
 
 In want of stability ozone resembles hydrogen dioxide ; contact with manga- 
 nese dioxide converts it into ordinary oxygen. Even shaking with powdered glass 
 will de-ozonise the ozonised oxygen. When kept for some days, all the ozone is 
 gradually re-converted into oxygen. 
 
 ATMOSPHERIC AIR 
 
 51. Atmospheric air consists chiefly of a mixture of nitrogen and 
 oxygen, roughly in the proportion of 4 vols. N : i vol. 0. There are 
 
 * The oxygen obtained by the action of warm sulphuric acid on barium dioxide, or on 
 crystallised potassium permanganate, resembles ozone in its odour and action on the iodised 
 starch paper. 
 
68 
 
 COMPOSITION OF AIE. 
 
 also present a small proportion of argon, and very small proportions 
 of carbonic acid gas (carbon dioxide) and ammonia. Vapour of water 
 is, of course, always present in the atmosphere in varying proportions. 
 Since the atmosphere is the receptacle for all gaseous emanations, other 
 substances may be discovered in it by very minute analysis, but in pro- 
 portions too small to have any perceptible influence upon its properties. 
 Thus marsh-gas or light carburetted hydrogen, sulphuretted hydrogen, 
 and sulphurous acid gas, can often be traced in it, the last especially in 
 or near towns. 
 
 Although the proportion of oxygen in the air at a given spot may be 
 much diminished, and that of carbonic acid gas increased, by processes 
 of oxidation (such as respiration and combustion) at that place, the 
 operation of wind and of diffusion so rapidly mixes the altered air with 
 the immensely greater general mass of the atmosphere, that the varia- 
 tions in the composition of air in different places are very slight. 
 Thus it has been found that the proportion of oxygen in the air in 
 the centre of Manchester was, at most, only 0.2 per cent, below the 
 average. 
 
 Composition of dry air by volume and by weight. 
 
 Volume. 
 Nitrogen 
 Oxygen . 
 Argon 
 Carbon dioxide 
 
 Weight. 
 
 . 78.40 per cent, 75.95 per cent. 
 
 20.94 . 23.10 
 
 0.63 . 0.90 
 
 0.03 . 0.05 
 
 The proportion of aqueous vapour may be stated, on the average, as 
 1.4 per cent, by volume, or 0.87 per cent, by weight of the air. The 
 total weight of atmospheric air surrounding the globe exceedes 300,000 
 million tons. A litre of dry air at o C. and 760 mm. weighs 1.293 
 grams. 
 
 The exact volumetric analysis of air has been already given (p. 44). 
 
 The proportion of oxygen to nitrogen in air may be exhibited by suspending 
 a stick of phosphorus upon a wire stand (A, Fig. 48) in a measured volume of 
 air confined over water. The cylinder (B) should have been previously divided 
 into five equal spaces, by measuring water into it, and marking each space by a 
 
 Fig. 49- 
 
 - a few hours, the phosphorus will have corn- 
 oxygen to form phosphorous and phosphoric acids. 
 by the water, leaving four of the spaces occupied by 
 
ANALYSIS OF AIR. 69 
 
 The same result may be arrived at in a much shorter time by burning the 
 phosphorus in the confined portion of air. 
 
 A fragment of phosphorus dried by careful pressure between blotting-paper, is 
 placed upon a convenient stand (A, Fig. 49) and covered with a tall jar, having an 
 opening at the top for the insertion of a well-fitting stopper (which should be 
 greased with a little lard), and divided into seven parts of equal capacity. The 
 jar should be placed over the stand in such a manner that the water may occupy 
 the two lowest spaces into which the jar is divided. The stopper of the jar is 
 furnished with a hook, to which a piece of brass chain (B) is attached, long enough 
 to touch the phosphorus when the stopper is inserted. The end of this chain is 
 heated, and the stopper tightly fixed in its place. On allowing the hot chain to 
 touch the phosphorus, the latter bursts into vivid combustion, filling the jar with 
 thick white fumes, and covering its sides for a few moments with white flakes of 
 phosphoric anhydride. At the commencement of the experiment, the water in the 
 jar will be depressed, in consequence of the expansion of the air due to the heat 
 produced in the burning of phosphorus, but presently, when the combustion begins 
 to decline, the water rises, and continues to do so until it has ascended to the line 
 (C), so as to occupy the place of one-fifth of the air employed in the experiment. 
 The phosphorus will then have ceased to burn, the white flakes upon the sides of 
 the jar will have acquired the appearance of drops of moisture, and the fumes will 
 have gradually disappeared, until, in the course of half an hour, the air remaining 
 in the jar will be as clear and transparent as before, the whole of the phosphoric 
 anhydride having been absorbed by the water. The jar should now be sunk in 
 water, so that the latter may attain to the same level without as within the jar. 
 On removing the stopper, it will be found that the nitrogen in the jar will no 
 longer support the combustion of a taper. 
 
 In the rigidly accurate determination of the proportion of oxygen to nitrogen 
 and argon in the air, it is of course necessary to guard against any error arising 
 from the presence of the water, carbonic acid gas, and ammonia. * With this view, 
 
 Fig. 50. Exact analysis of air. 
 
 Dumas and Boussingault, to whom we are originally indebted for our exact know- 
 ledge of the composition of the air, caused it to pass through a series of tubes 
 (A, Fig. 50) containing potash, in order to remove the carbonic acid gas, then 
 through a second series (B) containing sulphuric acid, to absorb the ammonia and 
 water ; the purified air then passed through a glass tube (C) filled with bright 
 copper heated to redness in a charcoal furnace, which removed the whole of the 
 oxygen, whilst the nitrogen passed into the large globe (N). 
 
 Both the tube (containing the copper) and the globe were carefully exhausted 
 of air and accurately weighed before the experiment ; on connecting the globe and 
 the tube with the purifying apparatus, and slowly opening the stop-cocks, the 
 pressure of the external air caused it to flow through the series of tubes into Hie 
 globe destined to receive the nitrogen. When a considerable quantity of air had 
 passed in, the stop-cocks were again closed, and after cooling, the weight of the 
 globe was accurately determined. The difference between this weight and that 
 of the empty globe, before the experiment, gave the weight of the nitrogen which 
 had entered" the globe ; but this did not represent the whole of the nitrogen con- 
 tained in the analysed air, for the tube containing the copper had, of course, 
 remained full of nitrogen at the close of the experiment. This tube, having been 
 weighed, was attached to the air-pump, the nitrogen exhausted from it, and the 
 tube again weighed ; the difference between the two weighings furnished the 
 
 * It would be satisfactory, of course, to deprive the air of its argon also, in making- this 
 experiment, and thus arrive at the true proportion of nitrogen to oxygen ; no method is 
 known, however, for removing argon from a gas. It muht be remembered that this gas has 
 only recently been discovered, and Dumas and Boussingault estimated it with the nitrogen, 
 thus making the proportion of this constituent too high. 
 
70 SPRENGEL'S AIR-PUMP. 
 
 weight of the nitrogen remaining in the tube, and was added to the weight of that 
 received in the globe. The oxygen was represented by the increase of the weight 
 of the exhausted tube containing the copper, which was partially converted into 
 CuO by combining with the oxygen of the air passed through it. 
 
 52. The nitrogen remaining (together with the argon) after the re- 
 moval of the oxygen from air in the above experiments was so called on 
 account of its presence in nitre (saltpetre, KN0 3 ). In physical pro- 
 perties it resembles oxygen, but is somewhat lighter than that gas, its 
 specific gravity being 0.967. 
 
 This difference in the specific gravities of the two gases is well exhibited by the 
 arrangement shown in Fig. 51. A jar of oxygen (0) is closed with a glass plate, 
 and placed upon the table. A jar of nitrogen 
 (TV'), also closed with a glass plate, is placed 
 over it, so that the two gases may come in con- 
 tact when the glass plates are removed. The 
 nitrogen floats for some seconds above the oxy- 
 gen, and if a lighted taper be quickly intro- 
 duced through the neck of the upper jar, it 
 will be extinguished in passing through the 
 nitrogen, and will be rekindled brilliantly when 
 it reaches the oxygen in the lower jar. 
 
 Fig. 51. 
 
 Fig. 52. Sprengel's pump. Dialysis of air. 
 
 It might at first sight appear surprising that oxygen and nitrogen, 
 though of different specific gravities, should exist in uniform proportions 
 in all parts of the atmosphere, unless in a state of chemical combina- 
 tion ; but an acquaintance with the property of diffusion (p. 25) 
 possessed by gases, teaches us that gases mix with each other in opposition 
 to gravitation, and when mixed always remain so. 
 
 It was shown by Graham that a partial separation of the nitrogen and oxygen 
 in air may be effected, on the same principle as that of hydrogen and oxygen at 
 page 28, by taking advantage of the difference in their rates of diffusion. He 
 devised, however, a more convenient process, founded upon the dialytlc (osmotic) 
 passage of the gases through caoutchouc, which he ascribed to the absorption of 
 the gas by the solid material upon one side, and its escape on the other. 
 
 A bag (, Fig. 52) is made of a fabric composed of a layer of caoutchouc between 
 two layers of silk, such as that employed for waterproof garments ; a piece of 
 carpet is placed inside the bag to keep the sides apart, and the edges of the bag 
 
DUST IN THE AIR. 71 
 
 are made perfectly air-tight with solution of caoutchouc. To maintain a vacuum 
 within the bag, it is supported by a rod v, and attached to SprengeVs air-pump, in 
 which a stream of mercury, allowed to flow from a funnel (/) down a tube (<?) six 
 feet long, draws the air out of the bag, through a lateral tube (A), until all the air 
 is exhausted, which is indicated by the barometer tube &, the lower end of which 
 dips into a cistern of mercury. When the mercury in this tube stands at almost 
 exactly the same height as the standard barometer, the exhaustion is complete. 
 If a test-tube (cT) filled with mercury be now inverted over the end of the long 
 tube c, which is bent upwards for that purpose, the bubbles of air which are drawn 
 through the sides of the vacuous bag, and carried down the long tube by the little 
 pistons of liquid mercury as they fall, will pass up into the test-tube ; when the 
 latter is filled with the gas, its mouth is closed with the thumb, withdrawn from 
 the mercury, and a match with a spark at the end inserted, when the spark will 
 burst out into flame, showing that the specimen of air collected is much richer in 
 oxygen than ordinary atmospheric air. The overflow tube g delivers the mercury 
 which is to be returned to the funnel/. 
 
 The dialytic passage of oxygen through caoutchouc into a vacuum is twice as 
 rapid as that of nitrogen, so that the air collected in the tube contains twice as 
 much oxygen as the external air. 
 
 This osmotic passage of gases through solids is quite unconnected with diffusibility 
 of the gases, and appears to depend rather upon the chemical nature of the gas 
 and of the solid. It is thus connected with the occlusion of gases by solids. In 
 consequence of this osmotic passage, tubes of iron or platinum, which are quite 
 impermeable by hydrogen at the ordinary temperature, allow it to pass rapidly 
 through their walls at high temperatures. 
 
 That air is simply a mechanical mixture of its component gases is 
 amply proved by the circumstance that it possesses all the properties 
 which would be predicted for a mixture of these gases in such propor- 
 tions ; whilst the essential feature of a chemical compound is, that its 
 properties cannot be foreseen from those of its constituents. (See p. 6.) 
 
 The absence of active chemical properties is a very striking feature 
 of nitrogen, and admirably adapts it for its function of diluting the 
 oxygen in the atmosphere. This is even more true of the small pro- 
 portion of argon in the air, for this gas appears to be devoid of all 
 chemical properties. 
 
 The chemical relations of air to animals and plants will be more 
 appropriately discussed hereafter. (See Carbonic Acid, Ammonia.) 
 
 In considering the composition of air, much attention has been 
 directed of late years to the dust or minute particles of solid matter 
 which, although much heavier than air, are suspended in it by the action 
 of currents, and may always be detected by a beam from the sun or the 
 electric lamp or the lime -light, which would be invisible along its track 
 through optically pure air. Such dust has been found to contain iron, 
 lime, silica, and other inorganic substances, besides organic matter. 
 
 The fine particles of mineral substances present in the dust are the 
 probable cause of the crystallisation of supersaturated solutions of salts 
 (p. 51) when exposed to air. The vegetable particles appear to contain 
 minute seeds which germinate when deposited in certain liquid or moist 
 solid substances, and give rise to mould, mildew, and fermentation. The 
 animal particles are believed to contain the germs by the agency of 
 which certain forms of disease are spread. 
 
 The dust of the air has also a considerable influence on the produc- 
 tion of fogs. Air at the ordinary temperature (16 0.) is said to be 
 " dry" when it contains less than 5 grams of water vapour per cubic 
 metre (35.37 cubic feet), and "damp " when it contains more than 10 
 grams of water vapour in this volume, the sensation of dryness or 
 
72 LIQUEFACTION OF GASES. 
 
 dampness having relation to the degree of rapidity with which the 
 water excreted by the skin is able to evaporate. When damp air is 
 chilled the water vapour is deposited from it in the form of fog, 
 unless the air be optically pure, when no condensation of the water 
 occurs. It would appear from this that the dust particles in the air 
 form nuclei around which the aqueous vapour can precipitate, much as 
 the crystals form around a particle in a super-saturated solution. The 
 aggravation of a fog by smoke may perhaps be partly due to such a cause. 
 
 It has been shown that dust particles are not alone in causing precipitation of 
 aqueous vapour, many gases which are free from suspended particles having a 
 similar effect. Sulphur dioxide is an example ; this gas is always present in 
 London air, being a product of the combustion of coal containing iron pyrites ; it 
 is more abundant in foggy weather, but whether it is a cause of the fog or is 
 merely retained thereby remains uncertain. 
 
 Liquid Air. The simplest method of liquefying a gas is to cool it 
 at atmospheric pressure to a temperature below that at which the 
 liquid to be formed boils. Liquefaction then ensues just as steam 
 condenses to water when cooled below 100 C. By increasing the 
 pressure on a liquid, its boiling-point is raised, hence if a gas be com- 
 pressed it requires less cooling to liquefy it, for the boiling-point of the 
 liquid to be formed is higher. Thus it is generally economical to 
 compress the gas, as well as cool it, and this was the method by which 
 the majority of the gases were originally liquefied ; it is illustrated in 
 the chapter on Ammonia. 
 
 Oxygen, having a low critical temperature (p. 29), was not liquefied 
 until a suitable means for obtaining such low temperature had been 
 found. Advantage was taken of the latent heat of evaporation, that 
 is, the heat absorbed when a liquid becomes a gas. An easily liquefied 
 gas was evaporated around a vessel containing one more difficulty 
 liquefied, which in its turn was evaporated around a still more difficulty 
 liquefied gas, and so on. The liquids had successively lower boiling- 
 points, so that the temperature descended by steps until at last the 
 critical temperature of oxygen was attained, whereupon this gas could 
 be liquefied by pressure. 
 
 The modern method of making liquid air depends on a disappearance 
 of heat quite analogous to the latent heat of evaporation. If the ideal 
 gas (p. 28) were allowed to expand without doing any work,* its 
 temperature would remain unchanged. But when an imperfect gas 
 expands it becomes a better gas, and in so doing absorbs heat for 
 precisely the same reason that a liquid absorbs heat when it becomes 
 a gas, but in much smaller degree. Now the higher the pressure or 
 
 B lower the temperature of a gas. the higher is its degree of imperfec- 
 tion (p. 28), so that expansion from a higher pressure or at a low 
 temperature absorbs more heat than when it occurs at a low pressure 
 or at a high temperature. 
 
 The actual quantity of heat absorbed by expansion is much too small 
 
 to lower the temperature of air to the liquefying-point, were it not for 
 
 an ingenious method of storing up the cold produced by the expansion. 
 
 In the Linde machine, for liquefying air, for example, the air which has 
 
 een slightly cooled by expansion is used to cool that about to be 
 
 of the U a C tmosp^ere d ** ^ Me * " expanded into a vacuum > instead of against the pressure 
 
LIQUEFACTION OF AIR. 
 
 73 
 
 expanded, and when this second quantity has expanded it cools a third 
 quantity, and so on. The cumulative eft'ect of this regenerative cooling 
 is to lower the temperature of the air until it liquefies. Of course, to 
 economise the cold, the same air is expanded and compressed alternately. 
 From what was said above it will be seen that as the temperature of 
 the air gets lower, each expansion entails a larger absorption of heat. 
 
 Fig. 53 represents an apparatus for applying the foregoing principles. Air com- 
 pressed at some 200 atmospheres is admitted at A into a lengthy coil B of metal 
 pipe, passing concentrically through a similarly coiled pipe C. The other end of 
 the inner coil opens into a box D and is provided with a valve E. One end of the 
 outer coil also opens into the box D, whilst the other end is connected with a com- 
 pressing pump T. The coils and box are embedded in a packing of wool, not 
 shown in the figure, contained in the casing H. To operate the apparatus the 
 valve E is opened until the air issues into the box D at a reduced pressure of some 
 20 atmospheres. The expanded and consequently cooled air passes up the outer 
 coil to pump 2, which compresses it again to 200 atmospheres and forces it through 
 
 Fig. 53. Liquefaction of air. 
 
 a coil of pipe round which water circulates in the cooler /. Here it is deprived of 
 the heat imparted to it by the work of the pump, and is passed back to the inner 
 coil to undergo the same cycle once more. It will be seen that as the air cooled 
 by expansion passes around the inner coil, it cools the air about to be expanded, 
 and that each portion of air issuing from the inner coil must be colder than that 
 which preceded it. After a time this accumulated cold becomes sufficient to lower 
 the temperature to - 193 C., whereupon liquid air collects in box D and may be 
 drawn off through tap K. It is found more economical not to let the gas expand 
 to atmospheric pressure, as the smaller amount of work necessary to pump air at 
 20 atmospheres pressure, and the increased cooling due to the work which the 
 expanding gas has to do in moving the expanded gas at this pressure, more than 
 balance the extra cooling which might be obtained by expansion to a lower 
 pressure. 
 
 To preserve liquid air for more than a few moments it must be 
 drawn off into a vacuum vessel, that is, a vessel surrounded by a shell 
 enclosing a vacuous space around the walls of the vessel. The vacuum 
 prevents passage of heat, and the effect is enhanced by silvering the 
 surface of the shell so as to reflect heat rays falling upon it. 
 
 Since oxygen boils at a temperature some io c higher than that 
 at which nitrogen boils, freshly made liquid air contains nearly 50 per 
 
74 SEPAKATION OF OXYGEN AND NITKOGEN. 
 
 cent, by volume of oxygen. It is turbid from the presence of crystals 
 
 JUKI Ul U. 411. VC1 V ilociiiT A. j. . n , 
 
 of oxygen which is obtained by fractionally distilling the liquid, so that 
 
 the nitrogen boils away first. 
 
 Fractional distillation is the operation of separating mixed liquids by 
 
 carefully raising their temperature so as to distil first that which has 
 
 the lowest boiling-point. 
 
 The apparatus employed for separating oxygen and nitrogen in this manner is of 
 
 the type shown in Fig. 54. Here the compressed air admitted at A passes through 
 the inner pipes of two concentric coils B and <7, the 
 two currents uniting again at D to pass through a coil 
 E situated in the receiver F. The valve G being 
 opened, the air expands into the receiver and passes 
 away through the outer pipe of the coil C. Presently, 
 liquid air begins to collect in F, as in the apparatus 
 already described, but its temperature is somewhat 
 higher than in that case because of the air passing 
 through the coil E. As a result nitrogen boils away 
 from the liquid, and passing up the outer pipe of coil 
 B, issues at H. By opening valve I the liquid oxygen 
 in the receiver may be allowed to evaporate through 
 the outer pipe of coil B, so as to be collected for use 
 at the extremity K. The valves L are adjusted so 
 that the proportion of hot gas passing through each 
 coil may be in relation to the larger proportion of 
 nitrogen than of oxygen passing away. 
 
 Attempts to liquefy hydrogen on the prin- 
 ciple employed in liquefying air fail unless the 
 hydrogen is first cooled to - 205 C. by passing 
 through a coil of metal pipe surrounded by 
 liquid air boiling at reduced pressure. This 
 may be ascribed to the fact that hydrogen is 
 a much better gas than air, so that it is less 
 cooled by expansion.* 
 
 One of the most remarkable of the many 
 interesting experiments that can be performed 
 with liquid air consists in absorbing it by a 
 wad of cotton wool which has been mixed with 
 finely divided charcoal and igniting the cotton ; it burns like gun- 
 cotton, and if fired by a small primer of mercuric fulminate it detonates 
 with violence. It is said that this form of explosive has been used in 
 blasting operations in excavating the Simplon tunnel. 
 
 Fig. 54. Separation of O 
 and N by liquefaction. 
 
 NITROGEN. 
 
 N = 14 parts by weight = i vol. 
 
 53. Besides its presence in air, nitrogen is elsewhere found in nature 
 as a constituent of saltpetre or potassium nitrate (KNO 3 ), and Chili 
 saltpetre or sodium nitrate (NaN0 3 ). It also occurs as ammonia (NH 3 ) 
 in the atmosphere and in the gaseous emanations from volcanoes. It 
 is contained in the greater number of animal, and in many vegetable, 
 
 * Indeed, it appears that the cooling of the hydrogen by expansion is negligible until the 
 temperature has fallen considerably, probably to about - 80 C. 
 
PROPERTIES OF NITROGEN. 
 
 75 
 
 substances, and therefore has a most important share in the chemical 
 phenomena of life. 
 
 Nitrogen is generally obtained by burning phosphorus in a portion 
 of air confined over water (Fig. 55). The phosphorus is floated on the 
 water in a small porcelain dish, kindled, and covered with a bell-jar. 
 The nitrogen remains mixed with clouds of phosphoric anhydride 
 (P 2 5 ), which may be removed by allowing the gas to stand over water, 
 100 vols. of which dissolve only 1.4 vols. of 
 nitrogen at the ordinary temperature. 
 
 When nitrogen is required in larger 
 quantity, it is more conveniently prepared 
 by passing air from a gas-holder, over 
 metallic copper heated to redness in a tube. 
 If the air be passed through solution 
 of ammonia before passing over the 
 heated copper, a short length of copper 
 will suffice, since the oxide formed 
 will be reduced by the ammonia ; 
 3 CuO + 2 NH 3 = Cu 3 + 3 H 2 O + N 2 . 
 
 The nitrogen separated from air, 
 however, always contains nearly i per 
 cent, by volume of argon. To prepare pure nitrogen some com- 
 pound of the element must be decomposed ; thus an oxide of nitrogen 
 may be passed over red hot copper. Or a solution of ammonium nitrite 
 (or mixed solutions of potassium nitrite and ammonium chloride) 
 may be boiled in a flask provided with a delivery tube; NH 4 N0 2 = 
 
 Fig. 55. Preparation of nitrogeu. 
 
 The remarkable chemical inactivity of free nitrogen has already been 
 alluded to (p. 71). It has been seen, however, to be capable of com- 
 bining directly with boron and silicon, and magnesium and titanium 
 unite with it even more readily at a high temperature. Although it is 
 so indifferent to oxygen at ordinary temperatures it unites with that 
 element when a mixture of the two is subjected to the high tem- 
 perature of electric sparks, forming oxides of nitrogen. Nitrogen 
 is conspicuous among the elements for forming, with hydrogen, a 
 powerful alkali (ammonia, NH 3 ), whilst the feeble chemical ties 
 which hold it in combination with other elements, joined to its 
 character of a permanent gas, render many of its compounds very 
 unstable and explosive, as is the case with the so-called chloride and 
 iodide of nitrogen, gun-cotton, the fulminates of silver and mercury, 
 nitro-glycerine, &c. 
 
 The discovery of nitrogen was made in 1772 by Rutherford (Pro- 
 fessor of Botany in the University of Edinburgh), who was led to it by 
 the observation that respired air was still unfit to support life when all 
 the carbonic acid had been absorbed from it by a caustic alkali. Hence 
 the name azote (a, priv., and faij, life), formally bestowed upon this 
 gas. 
 
 Nitrogen becomes a colourless liquid at - 194 C., the temperature at 
 which it boils under atmospheric pressure. Its critical temperature is 
 146 C., and its critical pressure is 35 atmospheres. When rapidly 
 evaporated a portion of the liquid nitrogen freezes to a colourless solid, 
 melting at - 214 C. 
 
76 ARGON. 
 
 Nitrogen is the type of the trivalent elements (p. u), its most 
 stable compound with hydrogen being NH 3 , ammonia. 
 
 ARGON. 
 A = 39.6 parts by weight = 2 vols. 
 
 Rayleigh (1894) found that whereas i litre of nitrogen prepared 
 from compounds of the element, such as from an oxide of nitrogen by 
 passing it over red-hot copper, weighs 1.2505 gram, i litre of nitrogen 
 prepared by depriving purified air of its oxygen weighs 1.2572 gram. 
 Cavendish had long before recorded that when oxygen is added in small 
 doses to atmospheric nitrogen through which electric sparks are passed 
 and which is contained in a vessel also containing alkali to absorb the 
 oxides of nitrogen produced, a small residue of gas is left which cannot 
 be caused to combine with oxygen under the influence of the sparks. 
 It has now been proved that Cavendish's residue is not obtainable when 
 nitrogen other than that from the atmosphere is used, and that it is 
 this residue which makes atmospheric nitrogen about \ per cent. 
 heavier than other nitrogen, as observed by Rayleigh. The latter, in 
 conjunction with Ramsay, examined the gas and concluded that it was 
 an element so devoid of any tendency to combine with other elements, 
 and therefore of chemical energy, that it might aptly be termed argon 
 (a, without, epyov, work). 
 
 Argon is prepared by passing air first over caustic potash to absorb 
 carbon dioxide, then through strong sulphuric acid to absorb aqueous 
 vapour, and finally over red-hot magnesium or lithium which combines 
 with the oxygen of the air to form magnesium or lithium oxide and 
 with the nitrogen to form magnesium or lithium nitride. 
 
 As the combination of nitrogen with either metal does not occur rapidly, the 
 passage of the gas through the red-hot tube containing the metal must be repeated 
 several times before the argon is pure. 
 
 A modification of Cavendish's experiment also serves for obtaining argon. A 
 large inverted flask (50 litres) is closed with a rubber cork through which pass five 
 glass tubes. Through two of these are passed conducting wires terminating within 
 the flask in platinum electrodes, and connected at their other ends with the poles 
 of an apparatus (an electrical transformer supplied with 40 amperes at 30 volts), 
 yielding electric current at very high pressure (6000 volts). A third tube serves 
 for the introduction of a jet of caustic soda solution which plays against the side 
 of the flask ; a fourth tube serves to remove this solution as it runs down into the 
 neck. Through the fifth tube, a mixture of 1 1 vols. oxygen and 9 vols. air is 
 introduced continuously into the flask. When the transformer is set to work, an 
 "electric flame " plays between the electrodes, and is probably an actual flame of 
 burning nitrogen, for the latter rapidly disappears, being dissolved as oxides of 
 nitrogen in the alkali.* About 20 litres of the gases maybe combined per hour, 
 and finally a mixture of argon and oxygen is obtained from which the latter may 
 be absorbed by admitting pyrogallic acid. 
 
 The argon thus obtained amounts to 0.6 per cent, of the air. It is a 
 colourless gas, without odour ; it is 19.8 times as heavy as hydrogen so 
 that its molecular weight is 39.6. It boils at - 186 C. and melts at 
 - 189.5 *> its critical temperature is - 117.4 and its critical pressure 
 53 atmospheres ; hence, at the ordinary temperature, it is far removed 
 from the liquid state and obeys the gas laws well. 100 vols. of water 
 dissolve 4.1 vols. of argon at 15 C., and the gas is found in the water 
 from several mineral springs. 
 
 Crookes has suggested the manufacture of nitrates in this manner from the atmosphere. 
 
EARE GASES. 77 
 
 The most remarkable feature of argon is the fact that it has resisted 
 all attempts to combine it with other elements ; no compound of it is 
 known. Hence its atomic weight has not been ascertained by the 
 method outlined at p. 10; but it behaves physically as though its 
 molecules were monatomic in which case its atomic weight is identical 
 with its molecular weight. 
 
 Helium. He = 4 parts by weight = 2 vols. When argon was discovered, 
 search was made for it in other places than the atmosphere, and while 
 submitting to spectrum analysis 0?.i\) some gas obtained by heating the 
 rare mineral clecelte, Eamsay (1895) detected a bright yellow line coin- 
 ciding with that first detected (1868) in the spectrum of the luminous atmo- 
 sphere which'is seen surrounding the sun when he is eclipsed. The line had been 
 ascribed to an element, provisionally named helium, but as no terrestrial matter 
 had shown the same spectrum, it was concluded that the element was non-existent 
 on the earth. 
 
 Ramsay's gas is no doubt the same matter as had been termed helium. It is 
 obtainable from several other minerals, besides cleveite, by heating them, particu- 
 larly such as contain uranium ; the mineral is placed in a glass tube, which is then 
 exhausted by a mercury pump (Fig. 70) and heated, the gas being collected by 
 pumping it out of the tube. The helium is generally only a fraction of the total 
 gas evolved, and must be separated from the other gases as argon is. 
 
 Helium is colourless, odourless, and exceedingly light, being only twice as 
 heavy as hydrogen; its sp. gr. (air = i) is 0.14. It is very slightly soluble in 
 water, 100 vols. of water dissolving about 1.4 vols. at 15 c!, and has resisted all 
 attempts to liquefy it. It has been identified as accompanying argon in the water 
 from the King's Well at Bath. 
 
 It is supposed that helium exists in minerals in a state of combination, but the 
 gas not yet been caused to combine with any other element ; hence its atomic 
 weight is not chemically known. It behaves physically, however, like a mona- 
 tomic gas, so that its atomic weight should be identical with its molecular weight, 
 namely 4. 
 
 Krypton, Xenon, and Neon. When a vessel containing argon, as it is 
 prepared from the atmosphere, is cooled by immersion in liquid air, the gas liquefies, 
 and on allowing the temperature to rise the first portion which boils off is a mixture 
 of helium and another gas, neon, the vapour density of which is 20.3. The next gas 
 to distil is argon, and the residue is a mixture of yet two other gases, krypton, of 
 vapour density 40.5, and xenon, of vapour density 63.5. By several such fractional 
 distillations the argon, krypton, and xenon are completely separated, and are 
 recognised by their characteristic spectra. Helium and neon are separated by 
 cooling them by liquid hydrogen, when the neon freezes. All these gases are 
 supposed to have monatomic molecules. The amount of helium, krypton, neon, 
 and xenon in the air is exceedingly small, about 0.0025 per cent, of the argon 
 present. 
 
 AMMONIA. 
 
 NH 3 =17 parts by weight = 2 volumes. 
 
 54. Ammonia belongs to organic rather than to inorganic nature. 
 It is generally a product of the decomposition of nitrogenous matter. 
 Dead animal and vegetable matters yield it in putrefaction. Bones 
 furnish it by destructive distillation ; so does coal, the fossilised plant. 
 Its compounds are found in beds of guano (the excrement of sea-fowl), 
 and the most important of them, sal ammoniac, was first made in Egypt 
 from the dung of camels. Its mineral sources are chiefly volcanic ; 
 ammonium sulphate is found in Tuscan boric acid, and occurs as 
 mascagnine in the form of an efflorescence on recent lavas. It may 
 be produced by the combination of nitrogen and hydrogen, induced by 
 electric discharge, but its formation soon stops unless it is absorbed 
 by an acid as fast as it is produced, because when 6 per cent, of the 
 
78 AMMONIA. 
 
 mixed gases has become converted into ammonia the compound begins 
 to be decomposed by the electric sparks.* 
 
 The proportion of ammonia existing in atmospheric air is so small 
 that it is difficult to determine it with precision ; it appears, however, 
 not to exceed 5 milligrams in a cubic metre, for although ammonia is. 
 constantly sent forth into the air by the putrefaction of animal and 
 vegetable substances containing nitrogen, it is soon absorbed by water, 
 and even by earth and other porous solids. Rain water contains from 
 i to 2 parts per million of ammonia. With the aid of certain micro- 
 organisms in the soil, certain families of plants can utilise the uncom- 
 bined nitrogen of the atmosphere as food for their growth, but for a, 
 large number of plants the chief supply of nitrogen is that contained 
 in the ammonia, nitrates and nitrites contained in the air, the soil, and 
 the water. During the life of an animal, it restores to the air the 
 nitrogen which formed part of its wasted organs, mainly as urea and 
 uric acid in the urine, the nitrogen of these being eventually converted 
 into ammonia when the excretion undergoes putrefaction. Dead 
 animal and vegetable matter, when putrefying, restores its nitrogen to 
 the air, chiefly in the forms of ammonia and substances closely allied to 
 it, but partly also, it is said, in the free state ; when such matter is 
 burnt all the nitrogen is liberated in an uncombined condition. Am- 
 monia appears to be formed from atmospheric nitrogen by the growth 
 of fungi (which evolve hydrogen) and by the decay of wood. Nitrogen 
 is also slowly absorbed from air by sawdust mixed with lime and by 
 glucose mixed with soda ; the nitrogen being evolved as ammonia when 
 these materials are afterwards heated with soda-lime. 
 
 The liquor ammonice, or solution of ammonia in water, which is so 
 largely used in medicine and the arts, is obtained chiefly from the 
 ammoniacal liquor resulting from the destructive distillation of coal for 
 the manufacture of gas.t The ammoniacal liquor of the gasworks con- 
 tains ammonia in combination with carbonic and hydrosulphuric acids. 
 To recover the ammonia the liquor is heated with lime in a still ; the 
 ammonia and hydrosulphuric acid are thus expelled and are conducted 
 into a covered tank containing sulphuric acid or hydrochloric acid, 
 which absorbs the ammonia and allows the hydrosulphuric acid to 
 escape through a pipe in the cover of the tank, to be burnt, or other- 
 wise disposed of, in order that it may not cause a nuisance by its evil 
 odour and poisonous properties. Ammonium sulphate or chloride 
 (according to which acid has been used) crystallises from the acid in 
 the tank. The former is sold as a manure ; the latter is generally used 
 for making pure ammonia. The crystals of ammonium chloride are 
 moderately heated in an iron pan to deprive them of tar, and are finally 
 purified by sublimation, that is, by converting them into vapour and 
 allowing this vapour to condense again into the solid form. For this 
 purpose the crystals are heated in a cylindrical iron vessel covered with 
 an iron dome lined with fireclay. The ammonium chloride rises in 
 vapour below a red heat, and condenses upon the dome in the form of 
 the fibrous cake known in commerce as sal ammoniac. 
 
 * The heat evolved in the combination N + H 3 =NH 3 is only 1195 gram units ; hence it is 
 not surprising 1 that the reaction is difficult to realise. 
 
 f Considerable quantities of ammonia are now being- recovered from the products of com- 
 bustion obtained from blastfurnaces (q.v.), in which, of course, it originates from the distilla- 
 tion of coal. The ovens in which coke is manufactured are also furnishing ammonia. 
 
PEEPAEATION OF AMMONIA. 
 
 79 
 
 To obtain ammonia from this salt, an ounce of it is reduced to coarse 
 powder, and rapidly mixed with 2 ounces of powdered quicklime. The 
 mixture is gently heated in a dry Florence flask (Fig. 56), and the gas 
 being little more than half as heavy as air (sp. gr. 0.59) may be collected 
 in dry bottles by displacement of air, the bottles being allowed to rest 
 upon a piece of tin plate which is perforated for the passage of the 
 tube. To ascertain when the bottles are filled, a piece of red litmus- 
 paper may be held at some little distance above the mouth, when it 
 will at once acquire a blue colour if the ammonia escapes. The bottles 
 should be closed with greased stoppers. 
 
 The action is explained by the following equation : 
 
 2NH 4 C1 
 
 Ammonium 
 
 chloride. 
 
 CaO = CaCl 2 
 Lime. Calcium 
 
 chloride. 
 
 H 9 
 
 2NH 3 . 
 Ammonia. 
 
 The readiest method of obtaining gaseous ammonia for the study of its pro- 
 perties consists in gently heating the strongest liquor ammonice in a retort or flask 
 
 0** 
 
 Fig. 56. Preparation 
 of ammonia. 
 
 Fig. 57- 
 
 provided with a bent tube for collecting the gas by displacement (Fig. 57). The 
 gas is evolved from the solution at a very low temperature, and may be collected 
 unaccompanied by steam. 
 
 Ammonia is readily distinguished by its very characteristic smell, 
 and its powerful alkaline action upon red litmus and turmeric papers. 
 It is absorbed by water in greater proportion by volume than any other 
 common gas, one volume of water absorbing more than 700 volumes of 
 ammonia at the ordinary temperature, and becoming ij volume of 
 solution of ammonia. During the dissolution of the gas much more heat 
 is evolved than corresponds with the heat of liquefaction of the gas ; * 
 this excess of heat can only be attributed to chemical combination ; but 
 no definite compound of ammonia with water has been obtained, and 
 the gas gradually escapes on exposing the solution to the air. As is 
 the case with all solutions of gases, the quantity of ammonia retained 
 by the water is dependent upon the temperature and pressure ; the 
 escape of the gas from the solution is attended with great production of 
 cold, much heat becoming latent in the conversion of the ammonia from 
 the liquid to the gaseous state. 
 
 * Seventeen grams of ammonia evolve 20,300 gram-units of heat when dissolved in excess 
 of water. 
 
So 
 
 SOLUTION OF AMMONIA. 
 
 The rapid absorption of ammonia by water is well shown by filling a globular 
 flask (Fig. 58) with the gas, keeping it with its mouth downwards in a small 
 capsule of mercury which is placed in a large basin. If this basin be filled with 
 water, it cannot come into contact with the ammonia until the mouth of the flask 
 is raised out of the mercury, when the water will quickly enter and fill the flask. 
 The water should be coloured with reddened litmus to exhibit the alkaline reaction 
 of the ammonia. 
 
 That the amount of ammonia in solution varies with the pressure may be proved 
 by filling a barometer tube, over 30 inches long, with mercury to within an inch 
 of the top, filling it up with strong ammonia, closing the mouth of the tube, and 
 inverting it with its mouth under mercury ; on removing the finger the diminished 
 pressure caused by the gravitation of the column of mercury in the tube will cause 
 
 Fig. 59- 
 
 Fig-. 60. 
 
 the solution of ammonia to boil, from the escape of a large quantity of the gas, 
 which will rapidly depress the mercury. If the pressure be now increased by 
 gradually depressing the tube in a tall cylinder of mercury (Fig. 59). the water will 
 again absorb the ammoniacal gas. 
 
 To exhibit the easy expulsion of the ammoniacal gas from water by heat, a 
 moderately thick glass tube, about 12 inches long and inch in diameter, may be 
 nearly filled with mercury, and then filled up with strong solution of ammonia ; on 
 closing it with the thumb, and inverting it into a vessel of mercury (Fig. 60), the 
 solution will, of course, rise above the mercury to the closed end of the tube. By 
 grasping this end of the tube in the hand, a considerable quantity of gas maybe 
 expelled, and the mercury will be depressed. If a little hot water be poured over 
 the top of the tube, the latter will become filled with ammoniacal gas, which will 
 be absorbed again by the water when the tube is allowed to cool, the mercury 
 returning to fill the tube. 
 
AMMONIA FREEZING-MACHINES. 8 1 
 
 The solution of ammonia, which is an article of commerce, may be 
 prepared by conducting the gas into water contained in a two-necked 
 bottle, the second neck being connected with a tube passing into another 
 bottle containing water, in which any escaping ammonia may be con- 
 densed. The strength of the solution is inferred from its specific 
 gravity, which is lower in proportion as the quantity of ammonia in the 
 solution is greater. 
 
 Thus, at 57 F. (14 C.), a solution of sp. gr. 0.8844 contains 36 parts by weight 
 of ammonia in 100 parts of solution (liquor ammonice fortissimus) ; 0.9251, 20 per 
 cent. ; 0.9593, 10 per cent. (British Pharmacopoeia). The specific gravity is ascer- 
 tained by comparing the weights of equal volumes of water and of the solution at 
 the same temperature. For this purpose a light stoppered bottle, or picnometer, is 
 provided, capable of containing about two fluid ounces. This is thoroughly dried, 
 and counterpoised in a balance by placing in the opposite pan a piece of lead, which 
 may be cut down to the proper weight. The bottle is then filled with solution of 
 ammonia, the temperature observed with a thermometer and recorded, the stopper 
 inserted, and the bottle weighed. It is then well rinsed out, filled with distilled 
 water, the temperature equalised with that of the ammonia by placing the bottle 
 either in warm or cold water, and the weight ascertained as before. The specific 
 gravity is obtained by dividing the weight of the solution of ammonia by that of 
 the water. The ammonia meter, a form of hydrometer (Fig. 61), is a convenient 
 instrument for rapidly ascertaining the specific gravity of liquids lighter than 
 water. It consists of a hollow glass float with a long stem, weighted with a bulb 
 containing shot or mercury, so that when placed in distilled water it may sink to 
 1000 of the scale marked on the stem, this number representing the specific 
 gravity of water. When placed in a liquid lighter than water, it must, of course, 
 sink lower in order to displace more liquid (since solids sink until they have dis- 
 placed their own weight of liquid). By trying it in liquids of known specific 
 gravities, the mark upon the scale to which it sinks may be made to indicate the 
 specific gravity of the liquid. The ammonia meter generally has a scale so divided 
 that it indicates at once the precentage weight of ammonia. In this country the 
 specific gravity of a liquid is always supposed to be taken at 62 F. (16 C.). 
 
 The common name for solution of ammonia, spirit of hart's horn, is 
 derived from the circumstance that it was originally obtained for 
 medicinal purposes by distilling shavings of that material. 
 
 Ammonia is far removed from the ideal gas (p. 27); its critical 
 temperature is about 130 C., so that it can be liquefied at the ordinary 
 temperature, 6J atmospheres sufficing 
 at 10 C. The liquid is colourless, has 
 sp. gr. at o C. = 0.63 and boils at 
 - 33.5 C., so that the gas liquefies at 
 this temperature under atmospheric 
 pressure. It freezes to a white crystal- 
 line mass which melts at 78 C. 
 The comparative ease with which the 
 gas may be liquefied has led to its 
 application in Carre's freezing ap- 
 paratus (Fig. 61), in which the gas 
 generated by heating a concentrated 
 solution of ammonia in a strong 
 iron boiler (A) is liquefied by its ^_^^_^^^^^^^ 
 own pressure in an iron receiver (B) ^ 
 
 placed in cold water. When the Fig .. 62. Carry's freezing apparatus. 
 
 boiler is taken off the fire and 
 
 cooled in water, the liquefied ammonia evaporates very rapidly 
 from the receiver back into the boiler, thereby producing so much 
 
 F 
 
82 
 
 LIQUEFACTION OF AMMONIA. 
 
 AID! 
 
 cold * that a vessel of water (C) placed in spirit of wine contained in 
 a cavity in the receiver, is at once congealed into ice. 
 
 To refrigerate large spaces by means of liquid NH 3 , the gas is compressed by a 
 pump into a coil immersed in a tank, and the liquid formed is allowed to evaporate 
 through another coil also immersed in a tank, the gas returning to the suction 
 side of the compression pump. Brine (which can be cooled considerably below 
 
 o C. without freezing) is passed 
 through the second tank where it is 
 cooled by the evaporating NH 3 , and 
 then through pipes in the space to be 
 cooled, then through the first tank, 
 where it cools the compressed NH 3 , 
 
 tank. 
 
 The liquefaction of ammonia is very 
 easily effected by heating the ammo- 
 niated silver chloride (AgC1.3NH 3 ) in 
 one limb of a sealed tube, the other 
 limb of which is cooled in a freezing- 
 mixture. A piece of stout glass tube 
 (A, Fig. 137), about 12 inches long and 
 | inch in diameter, is drawn out, at 
 about an inch from one end, to a 
 narrow neck. About 20 grams of silver 
 chloride (dried at 400 F.) are intro- 
 duced into the tube, so as to lie loosely in it. For this purpose a gutter of stiff 
 uaper (B) should be cut so as to slide loosely in the tube, the silver chloride 
 placed upon it, and when it has been thrust into the tube (held horizontally) the 
 latter should be turned upon its axis, so that the silver chloride may fall out of 
 the paper, which may be then withdrawn. The tube is now drawn out to a narrow 
 neck at about an inch from the other end, as in C, and afterwards carefully bent, 
 as in D, care being taken that none of the chloride falls into the short limb of the 
 tube, which should be about 4 inches long. The tube is then supported by 
 a holder, so that the long limb may be horizontal, and is connected by a tube and 
 
 Fig. 64. 
 
 cork with an apparatus delivering dry NH 3 , prepared by heating 80 grams of N"H 4 C1 
 with an equal weight of CaO in a flask, and passing the gas, first into an empty 
 bottle (A, Fig. 64) standing in cold water, and afterwards through a bottle (B) 
 filled with lumps of quicklime, to absorb all aqueous vapour. The long limb of the 
 tube must be surrounded with filtering paper, which is kept wet with cold water. 
 The current of ammonia should be continued at a moderate rate, until the tube and 
 its contents no longer increase in weight, which will occupy about three hours 
 
 * Seventeen grams of ammonia absorb 5661 gram units of heat in vaporising- at -40 C. 
 The specific heat of liquid ammonia between o and 20 C. is 1.02, being higher than that of 
 water, a rare occurrence. 
 
COMBUSTION OF AMMONIA. 
 
 about 2.2 grams of NH 3 being absorbed. The longer limb is sealed by the blow- 
 pipe flame whilst the gas is still passing, and then, as quickly as possible, the 
 shorter limb, keeping that part of the tube which is occupied by the arnmoniated 
 silver chloride still surrounded by wet paper. 
 
 When the shorter limb of this tube is cooled (Fig. 65), in a mixture of ice and 
 salt (or of 8 ounces of sodium sulphate and 4 measured ounces of common hydro- 
 chloric acid), whilst the longer limb is gently heated from end to end by waving a 
 spirit-lamp beneath it, the NH 3 evolved by the heat from the ammoniated silver 
 chloride, which partly fuses, condenses to a beautifully clear liquid in the cold 
 limb. When this is withdrawn from the freezing- 
 mixture, and the tube allowed to cool, the liquid 
 ammonia boils and gradually disappears entirely, 
 the gas being again absorbed by the silver chloride, 
 so that the tube is ready to be used again. 
 
 A small quantity of liquefied ammonia may be 
 more conveniently obtained by means of a tube 
 prepared as above, but containing about twelve 
 inches of fragments of well-dried wood charcoal 
 saturated with dry NH 3 . The shorter limb of the 
 tube should be drawn out to a long narrow point Fig . 65. Liquefaction of ammonia, 
 before sealing. This limb being immersed in the 
 
 freezing-mixture, the other is placed in a long test-tube containing water, which is 
 heated to boiling. The ammonia soon returns to the charcoal when the tube cools. 
 
 Liquefied ammonia dissolves potassium and sodium to a blue solution containing 
 the compounds KH 3 N - NH 3 K and NaH 3 N'NH 3 Na ; iodine, sulphur, and phosphorus 
 are also dissolved by it. 
 
 Ammonia is feebly combustible in atmospheric air, as may be seen by 
 holding a taper just within the mouth of an inverted bottle of the gas, 
 which burns with a peculiar livid flickering light around the flame, but 
 will not continue to burn when the flame is removed, because the tem- 
 perature produced by such a feeble combustion of the hydrogen in air 
 is not high enough to continue the decomposition of the ammonia. 
 During its combustion the hydrogen is converted into water, and the 
 nitrogen set free. In oxygen, however, ammonia burns with a con- 
 tinuous flame. 
 
 This is very well shown by surrounding a tube delivering a stream of ammonia 
 (obtained by heating strong solution of ammonia in a retort) with a much wider 
 tube open at both ends (Fig. 66) through which oxygen is passed by holding a 
 flexible tube from a gas-bag or gas- 
 holder underneath it. On kindling 
 the stream of ammonia it will give a 
 steady flame of 10 to 12 inches long. 
 
 The elements of ammonia are 
 easily separated from each other 
 by passing the gas through a red- 
 hot tube, or still more readily 
 by exposing it to the action of 
 the high temperature of the elec- 
 tric spark, when the volume of 
 the gas rapidly increases until 
 it is doubled, 2 volumes of 
 ammonia being decomposed into 
 i volume of nitrogen and 3 
 volumes of hydrogen, showing 
 
 Fig. 66. 
 
 that the molecule of ammonia probably contains atoms of N and H in 
 the proportion of i : 3. 
 
 For this experiment a measured volume of NH 3 is confined over mercury 
 
84 COMPOSITION OF AMMONIA. 
 
 (Fig. 67), in a tube through which platinum wires are sealed for the passage of 
 the spark from an induction-coil. The volume of the gas is doubled in a few 
 minutes, and if the tube be furnished with a stop-cock (A), the presence of free 
 hydrogen may be shown by filling the open limb with mercury and kindling the 
 gas as it issues from the jet. The decomposition ceases when only 3 per cent, of 
 ammonia remains (p. 77). 
 
 Another method of demonstrating that ammonia is formed from I volume N and 
 3 volumes H takes advantage of the fact that when chlorine reacts with ammonia, the 
 hydrogen of the latter combines with the former 
 to make hydrogen chloride, HC1, which may 
 readily be absorbed by water, leaving the nitro- , 
 
 gen. The tube A (Fig. 68), graduated into three 
 equal parts, is filled with chlorine. A strong solu- 
 
 Fig. 67. 
 
 Fig. 68. Decomposition of ammonia by chlorine. 
 
 tion of ammonia having been poured into the funnel B, the stop-cock is opened so 
 that some of the NH 3 may enter the tube. A violent reaction ensues, and white 
 fumes of ammonium chloride, NH 4 C1, are formed, due to the combination of the 
 HC1 produced with excess of NH 3 . More ammonia is now admitted, and the tube 
 is shaken. Owing to the fact that the NH 4 C1 produced is a solid and dissolves 
 in the water, the pressure in the tube is now below that of the atmosphere, so 
 that when the bent tube C, dipping into water, is attached to the funnel and the 
 stop-cock is opened, water rushes in to fill two-thirds of the 
 tube. The remaining gas is found to be nitrogen. 
 
 As might be expected from its powerfully alkaline 
 character, ammonia exhibits a strong attraction for 
 acids, which it neutralises perfectly. If a bottle of 
 ammonia gas, closed with a glass plate, be inverted 
 over a similar bottle of hydrochloric acid gas, and 
 the glass plates withdrawn (Fig. 69), the gases will 
 combine, unless they be perfectly dry, (cf. p. 32), 
 with disengagement of much heat, forming a white 
 solid, ammonium chloride (NH 4 C1), in which the 
 acid and alkali have neutralised each other. Again, 
 if ammonia be added to diluted sulphuric acid, the latter will be 
 entirely neutralised, and by evaporating the solution, crystals of 
 ammonium sulphate, (NH 4 ) 2 S0 4 , may be obtained. 
 
 Fig. 69. 
 
AMMONIUM AMALGAM. 85 
 
 The substances thus produced by neutralising the acids with solution 
 of ammonia bear a strong resemblance to the salts formed by neutralis- 
 ing the same acids with solutions of potash and soda, a circumstance 
 which would encourage the idea that the solution of ammonia must 
 contain an alkaline hydroxide (NH 4 OH), similar to KOH or NaOH. 
 
 Berzelius was the first to make an experiment which appeared strongly to favour 
 this view. The negative pole of a galvanic battery was placed in contact with 
 mercury at the bottom of a vessel containing a strong solution of ammonia, in 
 which the positive pole of the battery was immersed. Oxygen was disengaged at 
 this pole, whilst the mercury in contact with the negative pole swelled to four or 
 five times its original bulk, and became a soft solid mass, still preserving, however, 
 its metallic appearance. * At a very low temperature the mass becomes dark grey 
 and crystalline. So far, the result of the experiment resembles that obtained when 
 potassium hydroxide is decomposed under similar circumstances, the oxygen sepa- 
 rating at the positive pole, and the potassium at the negative, where it combines 
 with the mercury. Beyond this, however, the analogy does not hold ; for in the 
 latter case the metallic potassium can be readily separated from the mercury, whilst 
 in the former, all attempts to isolate the ammonium have failed, for the soft solid 
 mass resolves itself, almost immediately after its preparation, into mercury, am- 
 monia (NH 3 ), and hydrogen, one volume of the latter being separated for two 
 volumes of ammonia. This would also tend to support the conclusion that a sub- 
 stance having the composition NH 3 + H or NH 4 had united with the mercury ; and 
 since the latter is not known to unite with any non-metallic substance without 
 losing its metallic appearance, it would be fair to conclude that the soft solid was 
 really an amalgam of ammonium. However, the increase in the weight of the 
 mercury is so slight, and the " amalgam," whether obtained by this or by other 
 methods, is so unstable, that it would appear safer to attribute the swelling of the 
 mercury to a physical change caused by the presence of the ammonia and hydrogen 
 gases. This view is supported by the observation that when the amalgam is sub- 
 jected to pressure its volume varies nearly in the inverse ratio of the pressure. It 
 is difficult to believe that the solution of ammonia does really contain ammonium 
 hydroxide (NH 3 + H 2 = NH 4 OH), when we find it evolving ammonia so easily, 
 although at o C. the amount of ammonia dissolved approaches that required for 
 this formula ; but it is equally difficult, upon any other hypothesis, to explain the 
 close resemblance between the salts obtained by neutralising acids with this solu- 
 tion and those furnished by potash and soda. 
 
 The ordinary mode of exhibiting the production of the so-called amalgam of 
 ammonium consists in acting upon the ammonium chloride (NH 4 C1) with sodium 
 amalgam. A little pure mercury is heated in a test-tube, and a pellet of sodium 
 thrown into it, when combination occurs with great energy. When the amalgam 
 is nearly cool it may be poured into a larger tube containing a moderately strong 
 solution of ammonium chloride ; the amalgam at once swells to many times 
 its bulk, forming a soft solid lighter than the water, which may be shaken out of 
 the tube as a cylindrical mass, rapidly effervescing with evolution of NH 3 + H, 
 and soon recovering its original volume and liquid condition. 
 
 55. Ammonia is easily expelled from its salts by an alkali, so that 
 an ammonium salt is easily detected by boiling the suspected substance 
 with caustic soda, when the odour of ammonia will be perceived : 
 NH 4 C1 + NaOH = NaCl + NH 3 + H 2 0. 
 
 When an ammonium salt is heated it is split up into ammonia and 
 the acid from which it is formed, ammonium chloride, for example, 
 becoming ammonia and hydrogen chloride, NH 4 01 = NH 3 + HC1 1 ; but 
 if these products be allowed to cool together, they combine again to 
 produce the original salts. This behaviour furnishes an example of the 
 
 * This experiment is more conveniently made with a strong solution of ammonium sul- 
 phate in a common plate. A sheet of platinum connected with the positive pole of the 
 battery (five or six Grove's cells) is immersed in the solution, and a piece of filter-paper is 
 laid upon it, on which is a globule of mercury ; the negative pole is plunged into the latter. 
 
 f Ammonium chloride does not dissociate if perfectly dry. 
 
86 DISSOCIATION. 
 
 phenomenon called dissociation, which differs from decomposition in 
 that the constituents into which a compound is dissociated by heat re- 
 combine if they are allowed to cool together ; the products of the 
 decomposition of a compound, on the other hand, do not so recombine. 
 
 The dissociation of ammonium chloride may be demonstrated by taking ad- 
 vantage of the low specific gravity of NH 3 as compared with that of HC1 (NH 3 is 
 17 2 = 8.5, and HC1 36.5/2=18.25 times heavier than H). On this account NH 3 
 diffuses more rapidly than HC1. A fragment of ammonium chloride is placed in a 
 narrow test-tube with a plug of asbestos at a little distance above it, a piece of red 
 litmus-paper is placed in the tube, and the ammonium chloride and the asbestos 
 are heated ; the NH 3 , being lighter, diffuses through the asbestos before the HC1 
 does, and blues the red litmus-paper, but soon after the HC1 diffuses through, and 
 the litmus is again reddened. 
 
 The volatility of ammonia and of the ammonium salts renders a 
 solution of the gas useful as an alkali in cases, such as in analysis, 
 where the fixed alkalies, potash, and soda, would be objectionable on 
 account of their fixity. Ammonia finds application in making sodium 
 carbonate (q.v.) and, as already explained, in freezing-machines. 
 
 Ammonia has a tendency to combine as a whole with many metallic 
 salts, much as water does ; a typical compound of this sort is 
 CuS0 4 .5NH 3 . It readily loses ammonia when heated. 
 
 Although free nitrogen and hydrogen can only with difficulty be made to form 
 ammonia by direct combination, this compound is produced when the nitrogen 
 meets with hydrogen in the nascent state ; that is, at the instant of its liberation 
 from a combined form. Thus, if a few iron-filings be shaken with a little water 
 in a bottle of air, so that they may cling round the sides of the bottle, and a piece 
 of red litmus-paper be suspended between the stopper and the neck, it will be found 
 to have assumed a blue colour in the course of a few hours, and ammonia may be 
 distinctly detected in the rust which is produced. It appears that the water is 
 decomposed by the iron in the presence of the carbonic acid of the air and water, 
 and that the hydrogen liberated enters at once into combination with the nitrogen, 
 held in solution by the water, to form ammonia. 
 
 56. For many years ammonia was the only compound of nitrogen 
 with hydrogen which was known. Lately, two others have been dis- 
 covered namely, hydrazine, N 2 H 4 , a colourless gas, and hydrogen nitride 
 (hydrazoic acid), N 3 H, a volatile liquid, possessed, as its alternative name 
 implies, of the properties proper to an acid. The importance of these 
 compounds resides in the light which they throw upon the theory of 
 organic nitrogen compounds, and can only be appreciated when these 
 are being discussed. They have as yet received no practical application, 
 and since they are prepared by the action of reducing agents on nitric 
 acid or its derivatives, a further consideration of them will be found 
 after the treatment of this subject. 
 
 57. Production of nitrous and nitric acids from ammonia. If a few 
 drops of a strong solution of ammonia are poured into a pint bottle, and 
 ozonised air (from the tube for ozonising by induction, Fig. 47) is 
 passed into the bottle, thick white clouds speedily form, consisting of 
 ammonium nitrite (NH 4 N0 2 ), the nitrous acid having been produced by 
 the oxidation of the ammonia at the expense of the ozonised oxygen 
 
 2NH 3 + 3 = H 2 + NH 4 N0 2 . 
 
 If copper filings be shaken with solution of ammonia in a bottle of 
 air, white fumes will also be produced, together with a deep blue solu- 
 tion containing copper oxide and ammonium nitrite ; the act of oxida- 
 
OXIDATION OF AMMONIA. 87 
 
 tion of the copper appearing to have induced a simultaneous oxidation 
 of the ammonia. 
 
 A coil of thin platinum wire made round a pencil, if heated to redness 
 at the lower end and suspended in a flask (Fig. 70) with a little 
 strong ammonia at the bottom, will continue to glow 
 for a great length of time, in consequence of the 
 combination of the ammonia with the oxygen of the 
 air at its surface, attended with great evolution of 
 heat. Thick white clouds of NH 4 N0 2 are formed, 
 and frequently red vapour of nitrous anhydride 
 (N 2 3 ) itself. A coil of thin copper wire acts in a 
 similar manner. 
 
 When a tube delivering oxygen is passed down to the 
 bottom of the flask, the action is far more energetic, the heat 
 of the platinum rising to whiteness, whereupon an explosion 
 of the mixture of ammonia and oxygen ensues. After the 
 explosion the action recommences, so that the explosion repeats itself as often 
 as may be wished. It is unattended with danger if the mouth of the flask be 
 pretty large, but it is advisable to surround the flask with a cylinder of coarse 
 wire gauze. By regulating the stream of oxygen, the bubbles of that gas may be 
 made to burn as they pass through the ammonia at the bottom of the flask. 
 
 The oxidation of ammonia may also be shown by the arrangement represented 
 in Fig. 71. Air is slowly passed from the glass gas-holder B, through very weak 
 ammonia in the bottle , into a hard glass tube 
 having a piece of red litmus-paper at b and a 
 plug of platinised asbestos in the centre, heated 
 by a gas-burner ; a piece of blue litmus-paper is 
 placed at ^ , and the tube is connected with a 
 large globe (d~). The red litmus at b is changed 
 to blue by the ammonia, whilst the blue litmus 
 at c is reddened by the nitrous acid produced 
 
 Fig-. 71. Oxidation of ammouia. 
 
 in its oxidation, and clouds of ammonium nitrite, accompanied by red nitrous 
 fume*, appear in d. To obtain all the results in perfection, small quantities of 
 ammonia must be successively introduced into a. 
 
 When hydrogen or coal gas burns in air, small quantities of nitrous and nitric 
 acids are produced, apparently by the oxidation of atmospheric nitrogen. 
 
 58. In the presence of strong bases, and of porous materials to favour 
 the change, ammonia may suffer further oxidation to nitric acid, which 
 acts on the base to form a nitrate; thus, 2NH 3 + CaO + O 8 = Ca(N0 3 )., 
 (calcium nitrate) + 3H q O. 
 
 It has already been seen that the rapid oxidation (combustion) of 
 ammonia produces nitrogen and water. 
 
 This formation of nitrates from ammonia is commonly referred to as 
 nitrification, and appears to be concerned in the formation of the 
 
88 
 
 COMBINATION OF NITROGEN WITH OXYGEN. 
 
 natural supplies of saltpetre which are of so great importance to the 
 arts,* 
 
 It is brought about by a micro-organism (the nitrifying organism) 
 which accelerates the oxidation of the ammonia produced by the decay 
 of nitrogenous organic matter in the soil. 
 
 It would appear that at least two micro-organisms are concerned in the produc- 
 tion of nitrates. The one induces the formation of nitrites from the ammonia, 
 whilst the other induces oxididation of these to nitrates. Nitrification can only 
 occur when some basic substance, like calcium carbonate, is present to neutralise 
 the acids produced ; being dependent on a micro-organism, it can only proceed at 
 temperatures which are not inhibitory to the life of the organism (between o and 
 55 C.). Darkness favours the process. 
 
 COMPOUNDS OF NITROGEN AND OXYGEN. 
 
 59. Though these elements under ordinary conditions exhibit no 
 attraction for each other, six compounds, which contain them in 
 different proportions, have been obtained by different processes, viz. 
 N 2 0, NO, N 2 3 , N0 2 , N 2 5 . 
 
 When a succession of strong electric sparks from the induction-coil 
 is passed through atmospheric air in a dry flask (especially if the air be 
 mixed with oxygen), a red gas, nitric peroxide (N0 ? ), is formed ; if 
 water be present this is absorbed and converted into nitrous and nitric 
 acids; 2 N0 2 + H 2 = HN0 2 + HN0 3 . 
 
 If the experiment be made in a U-tube having one limb surmounted by a 
 stoppered globe into which platinum wires are sealed (fig. 72) filled Math water 
 coloured with blue litmus, the latter will very soon be reddened by the acid 
 formed, and the air will be found to diminish very 
 considerably in volume, eventually losing its power of 
 supporting combustion, in consequence of the removal 
 of oxygen. 
 
 When a few inches of magnesium tape are burnt in a 
 gas-jar of air, red fumes may be perceived on looking 
 down the jar at the close of the combustion, and the 
 presence of N 2 3 or N0 2 may be shown by drawing the 
 residual air through a mixture of potassium iodide with 
 a little starch and acetic acid, when the iodine is set free 
 and blues the starch. This renders it probable that the 
 electric spark causes the combination of nitrogen and 
 oxygen on account of its high temperature. 
 
 When ozonised air (p. 65) is passed into water, nitric 
 acid is found in solution. Kain water contains about 
 one part per million of nitric acid, in the form of 
 nitrates. 
 
 When hydrogen gas, mixed with a small 
 quantity of nitrogen, is burnt, the water collected 
 from it is found to have an acid taste and re- 
 action, due to the presence of a little nitric acid, 
 resulting from the combination of the nitrogen 
 with the oxygen of the air under the influence of 
 the intense heat of the hydrogen flame. 
 Since all the compounds of nitrogen and oxygen are obtained, in 
 
 practice, from nitric acid, the chemical history of that substance may 
 
 conveniently that of the oxides of nitrogen. 
 
 * The charcoal which has been used in the sewer ventilators has been found to contain 
 abundance of nitrates. 
 
 Fig. 72. 
 
PREPARATION OF NITRIC ACID. 89 
 
 NITRIC ACID, OR HYDROGEN NITRATE. 
 HNO 3 = 63 parts by weight = 2 volumes. 
 
 60. This most important acid is obtained from saltpetre, which is 
 found as an incrustation upon the surface of the soil in hot and dry 
 climates, as in some parts of India and Peru. The salt imported into 
 this country from Bengal and Oude consists of potassium nitrate 
 (KN0 3 ), whilst t/he Peruvian or Chilian saltpetre is sodium nitrate, or 
 " nitrate " (NaN0 3 ). Either of these will serve for the preparation of 
 nitric acid. 
 
 On the small scale, in the laboratory, nitric acid is prepared by dis- 
 tilling potassium nitrate with an equal weight of concentrated sulphuric 
 acid. 
 
 As an experiment, 4 ounces of powdered nitre, thoroughly dried, are introduced 
 into a stoppered retort (Fig. 73) and 2 J measured ounces of concentrated sulphuric 
 acid poured upon it. As soon as the 
 acid has soaked into the nitre, a 
 gradually increasing heat is applied 
 by an Argand burner, when the acid 
 distils. It must be preserved in a 
 stoppered bottle. 
 
 When the acid has ceased distil- 
 ling, the retort should be allowed 
 to cool, and filled with water. On 
 heating for some time the saline 
 residue will dissolve. The solution 
 may then be poured into an evapora- 
 ting dish, and evaporated to a 
 small bulk. On allowing the con- Fig. 73. Preparation of nitric acid, 
 
 centrated solution to cool, crystals 
 
 of bisulphate of potash or potassium hydrogen sulphate (KHS0 4 ) are deposited, a 
 salt which is very useful in many metallurgical and analytical operations. 
 
 The decomposition of potassium nitrate by an equal weight of sul- 
 phuric acid is explained by the equation 
 
 KN0 3 + H 2 S0 4 = HN0 3 + KHS0 4 . 
 
 It would appear at first sight that one-half of the sulphuric acid 
 might be dispensed with, inasmuch as one molecule could be made to 
 decompose two molecules of potassium nitrate, 2KN0 3 H-H 2 S0 4 = 
 2HNO 3 + K 2 SO 4 , but it is found that when a smaller quantity of 
 sulphuric acid is used, so high a temperature is required to effect the 
 complete decomposition of the saltpetre (the above equation then repre- 
 senting only the first stage of the action), that much of the nitric acid 
 is decomposed ; and the normal potassium sulphate (K 2 S0 4 ), which 
 would be the final result, is not nearly so easily dissolved out of the 
 retort by water as is the bisulphate. 
 
 For the preparation of large quantities of nitric acid, sodium nitrate 
 is substituted for potassium nitrate, being much cheaper, and furnish- 
 ing a larger proportion of nitric acid. 
 
 For the decomposition of the sodium nitrate can be represented by the above 
 equation, if Na be substituted for K, and on comparing the equations it will be 
 seen that 85 parts by weight of NaN0 3 yield the same quantity of HN0 3 as that 
 yielded by 101 parts by weight of KN0 3 . 
 
 The sodium nitrate is introduced into an iron cylinder (A, Fig. 74) and about 
 five-sixths of its weight of sulphuric acid is poured upon it through a stoppered 
 
9 o 
 
 PEOPEETIES OF NITRIC ACID. 
 
 opening at the back.* Heat is then applied by a furnace, into which the cylinders 
 are built in pairs, when the nitric acid passes off in vapour, and is condensed in a 
 series of stoneware bottles (B), surrounded with cold water. The commercial acid 
 is liable to contain chlorine, hydrochloric acid, and iodic acid (from sodium 
 chloride and iodate in the nitrate), sulphuric acid, sodium sulphate, nitrogen 
 
 oxides, and iron. It is purified 
 by redistillation, the middle 
 portion of the distillate being 
 pure. 
 
 In the preparation of 
 nitric acid, it will be ob- 
 served at the beginning 
 and towards the end of the 
 operation that the retort 
 becomes filled with a red 
 vapour. This is due to the 
 decomposition by heat of a 
 portion of the colourless 
 vapour of nitric acid, into 
 water, oxygen, and nitric 
 peroxide, 2HNO, = H 9 + 
 
 Fig. 74 Preparation of nitric acid. X , XT/-\ AT. 8 A * 
 
 O + 2N0 2 , this last form- 
 ing the red vapour, a portion of which is absorbed by the nitric acid, 
 and gives it a yellow colour (red fuming nitric acid). The pure nitric 
 acid is colourless, but if exposed to sunlight it becomes yellow, a 
 portion suffering this decomposition. In consequence of the accumula- 
 tion of the oxygen in the upper part of the bottle, the stopper is often 
 forced out suddenly when the bottle is opened, and care must be taken 
 that drops of this very corrosive acid be not spirted into the face. 
 
 The strongest nitric acid (obtained by distilling perfectly dry nitre 
 with an equal weight of pure oil of vitriol, and collecting the middle 
 portion of the acid separately from the first and last portions, which 
 are somewhat weaker) emits very thick grey fumes when exposed to 
 damp air, because its vapour, though itself transparent, absorbs water 
 very readily from the air, and condenses into very minute drops of 
 dilute nitric acid which compose the fumes. The weaker acids com- 
 monly sold in the shops do not fume so strongly. A criterion of the 
 strength of any sample of the acid is afforded by the specific gravity, 
 which may be ascertained by the methods described for ammonia, 
 using a hydrometer adapted for liquids heavier than water. Thus 
 the strongest acid (HN0 3 ) has the specific gravity 1.52 ;t whilst the 
 ordinary aquafortis or dilute nitric acid has the sp. gr. 1.29, and 
 contains only 46 per cent, of HN0 3 . The concentrated nitric acid 
 usually sold by the operative chemist (double aquafortis) has the sp. gr. 
 1.41, arid contains 67.5 per cent, of HN0 3 . 
 
 A very characteristic property of nitric acid is that of staining the 
 skin yellow. It produces the same effect upon most animal and vege- 
 table matters, especially if they contain nitrogen. The application of 
 
 * To avoid difficiilties due to frothing when strong H 2 SO 4 is used, it is now customary to 
 use a somewhat weaker acid (chamber acid, q.v.) and to redistil the Itss concentrated nitric 
 acid obtained, with strong stilphuric acid. 
 
 f It is extremely difficult to obtain the HNO 3 free iroin any extraneous wafer, as it under- 
 goes decomposition not only when vaporised at the boiling-point, but even at ordinary tem- 
 peratures. Distillation in a vacuum is more successful. 
 
OXIDATION BY NITRIC ACID. 91 
 
 this in dyeing silk a fast yellow colour may be seen by dipping a skein 
 of white silk in warm dilute nitric acid, and afterwards immersing it in 
 dilute ammonia, which converts the yellow colour into brilliant orange. 
 When sulphuric or hydrochloric acid is spilt upon the clothes, a red 
 stain is produced, and a little ammonia restores the original colour ; 
 but nitric acid stains are yellow, and ammonia intensifies instead of 
 removing them, though it prevents the cloth from being eaten into 
 holes. 
 
 Nitric acid changes most organic colouring matters to yellow, but, 
 unless very concentrated, it merely reddens litmus. If solutions of 
 indigo and litmus are warmed in separate flasks, and a little nitric acid 
 added to each, the indigo will become yellow and the litmus red. Here 
 the indigo (C 8 H 5 NO) acquires oxygen from the nitric acid, and is con- 
 verted into isatine (C 8 H 5 N0 2 ). 
 
 When nitric acid is heated, it begins to boil at 86 C., but it cannot 
 be distilled unchanged, for a considerable quantity is decomposed into 
 nitric peroxide, oxygen, and water, the two first passing off in the 
 gaseous form, whilst the water remains in the retort with the nitric 
 acid, which thus becomes gradually more and more dilute, until it con- 
 tains 68 per cent, of HN0 3 , when it passes over unchanged, at the 
 temperature of 248 F. (120 C.). The specific gravity of this acid is 
 1.42 ; its composition corresponds approximately with the hydrate 
 2HN0 3 .3H,0. If an acid weaker than this be submitted to distillation, 
 water will pass off until acid of this strength is obtained, when it distils 
 unchanged. A similar result is obtained when dry air is passed 
 through strong or weak nitric acid at 15 C. ; an acid of 64 per cent, 
 strength (corresponding with HN0 3 .2H 2 0) is produced in either 
 case. 
 
 The specific gravity of the vapour of nitric acid, at 86 C., has been 
 determined as 29.6 (H= i), which is sufficiently near to half of 63 to 
 warrant the formula HN0 3 , for the molecule of nitric acid (p. 47). 
 
 The facility with which nitric acid parts with a portion of its oxygen 
 renders it very valuable as an oxidising agent. Comparatively few 
 substances which are capable of forming compounds with oxygen can 
 escape oxidation when treated with nitric acid. 
 
 A small piece of phosphorus dropped into a porcelain dish containing 
 the strongest nitric acid (and placed at some distance to avoid danger), 
 is soon attacked by the acid, generally with such violence as to burst 
 into flame, and sometimes to shatter the dish ; the product is phosphoric 
 acid, the highest state of oxidation of phosphorus. 
 
 When sulphur is heated with nitric acid, it is actually oxidised to a 
 greater extent than when burnt in pure oxygen, for in this case it is- 
 converted into sulphurous anhydride (S0 2 ), whilst nitric acid converts 
 it into sulphuric acid, H,SO 4 . 
 
 Charcoal, which is so unalterable by most chemical agents at the 
 ordinary temperature, is oxidised by nitric acid. If the strongest nitric 
 acid be poured upon finely powdered charcoal, the latter takes fire at 
 once. Even iodine, which is not oxidised by free oxygen, is converted! 
 into iodic acid (HIO 3 ) by nitric acid. 
 
 But it is especially in the case of metals that the oxidising powers of 
 nitric acid are called into useful application. 
 
 If a little black oxide of copper be heated in a test-tube with nitric 
 
92 ACTION OF NITRIC ACID ON METALS. 
 
 acid, it dissolves, without evolution of gas, yielding a blue solution, 
 which contains copper nitrate, 2HNO 3 + CuO = H 2 + Cu(NO 3 ),. 
 
 But when nitric acid is poured upon metallic copper (copper turn- 
 ings), very violent action ensues, red fumes are abundantly evolved, 
 and the metal dissolves in the form of copper nitrate, nitric oxide being 
 formed, 8HNO 3 + Cu 3 = 3 Cu(NO 3 ) 2 + 4H 2 + 2 NO. The nitric oxide 
 itself is colourless, but as soon as it comes into contact with the oxygen 
 of the air, it is converted into the red nitric peroxide, NO + O = NO 2 . 
 
 A certain amount of nitric peroxide is always produced directly by the action 
 of copper on nitric acid, the proportion depending upon the concentration of the 
 acid and the ratio of acid to copper. When excess of concentrated nitric acid is 
 used the gas consists of N0 2 (with about 10 per cent, of N 2 3 ) and contains no 
 NO ; on the other hand, when the acid is diluted with twice its volume of water 
 nearly pure NO is evolved. The following view, although it may not represent 
 the actual course of the chemical change, is useful in expounding the nature of 
 the action. Since nitric acid tends to decompose into H 2 0,2N0 2 and 0, two 
 molecules of the acid might be expected to oxidise one atom of copper, 
 Cu + 2HN0 3 = CuO + H 2 + 2NO 2 ; the copper oxide would immediately react with 
 another portion of the nitric acid to give copper nitrate, CuO + 2HN0 3 = Cu(N0 3 ) 2 + 
 H 2 0. When more copper is present the N0 2 might be expected to be reduced to 
 NO, Cu + N0 2 = CuO + NO, the copper oxide dissolving as before. Since NO 2 re- 
 acts with water to form nitrous (and nitric) acid, little would be expected in the 
 gas from a dilute nitric acid, but the proportion of NO would be expected to be 
 increased because the reduction of the N0 2 would be more possible when it could 
 not escape from the solution as gas. 
 
 It has been shown that nitric acid which is free from nitrous acid (always 
 present in commercial samples) has a very tardy, if any, action on many metals, 
 so that it would seem as if the oxidation were really effected by the nitrous acid. 
 A very small quantity of this suffices to start the action, because the nitric oxide 
 produced reduces another portion of the nitric acid to nitrous acid, thus serving as 
 a carrier of oxygen from the nitric acid to the metal. 
 
 By the action of metals on nitric acid of various strengths all the reduction 
 products of nitric acid namely, the oxides of nitrogen, nitrogen, hydroxylamine, 
 hyponitious acid, and ammonia can be obtained. Those metals whose attraction 
 for oxygen is feeble (those which do not decompose water, or only do so at a very 
 high temperature, p. 21) do not reduce HN0 3 to a lower state of oxidation than 
 NO ; those metals which decompose water at a red heat yield all the reduction 
 products ; whilst those which decompose water either at the ordinary temperature 
 or below a red heat yield even hydrogen. The nature of the products varies with 
 the state of dilution, and with the temperature. Silver behaves like copper with 
 nitric acid. Iron evolves nearly pure NO when dissolved in nitric acid diluted 
 with either one part or 12 parts of water. Zinc, with i : 2 strength of acid (hot or 
 cold) evolves nearly equal volumes of NO and N 2 0, but with the strong acid it 
 evolves scarcely any NO, but a mixture of about 2 volumes N 2 and I volume N ; 
 with dilute nitric acid zinc yields ammonia (which of course remains combined with 
 the nitric acid in the form of ammonium nitrate), possibly produced by the 
 action of hydrogen, liberated by the dissolution of the metal in the acid 
 (just as when zinc is dissolved in dilute sulphuric acid), on the nitric acid, 
 
 Though all the metals in common use, except gold and platinum, are oxidised 
 by nitric acid, they are not all dissolved ; aluminium is superficially oxidised but 
 not further attacked ; tin and antimony are left by the acid in the state of insoluble 
 oxides, which possess acid properties and do not unite with nitric acid. When 
 concentrated nitric acid is poured upon tin, no action is observed ; * but on adding 
 a little water, N0 2 is evolved in abundance, and the tin is converted into a white 
 powder, metastannic acid. On stirring this white mixture with slaked lime the 
 smell of ammonia is perceived, this gas having been liberated from ammonium 
 
 * This is often noticed in the case of strong nitric acid, and is possibly to be explained by 
 supposing that the nitrous acid present is rapidly used up and cannot be re-formed in such a 
 concentrated acid (see above). The strongest nitric acid which has been obtained is without 
 action on chalk, even when boiled therewith. 
 
THE ANALYSIS OF NITRATES. 
 
 93 
 
 nitrate by the lime. Thus tin reduces even moderately strong nitric acid to 
 ammonia. 
 
 "When a solution of potassium nitrate is mixed with a strong solution of caustic 
 potash, and heated with granulated zinc, ammonia is abundantly disengaged, being 
 produced by the nascent hydrogen from the action of the zinc upon the caustic 
 potash. Aluminium acts thus even in dilute solutions. 
 
 Nitric acid is completely reduced, yielding only nitric oxide, when shaken with 
 strong sulphuric acid and mercury. On this fact is based the application of the 
 nitrometer (Fig. 75) for estimating the quantity of a nitrate present in a substance. 
 The apparatus is filled with mercury by opening the stop-cock and pouring the 
 metal into the open limb. The stop-cock having been closed, the right-hand limb 
 is lowered so that the mercury in it may be at a lower level than that in the other 
 limb. The solution to be tested is poured into the cup and sucked into the 
 graduated limb by opening the stop-cock until all liquid has passed through, care 
 being taken not to admit air. Oil of vitriol is next sucked in, in a similar manner, 
 and the closed limb is thoroughly shaken 
 to mix the mercury with the solution and 
 acid. Nitric oxide is rapidly evolved, 
 and when no more is seen to collect in 
 the graduated tube, the mercury is 
 brought to the same level in each limb, 
 as shown in the cut, and the volume of 
 nitric oxide is read by means of the 
 graduations on the tube. The stop-cock 
 has two holes bored in it, so that the 
 apparatus may be washed out through 
 the small tube beside the cup. The 
 weight of nitric acid present may be 
 calculated from the volume of nitric 
 oxide measured, for 63 grams of nitric 
 acid (HN0 3 ) yield 22.22 litres of nitric 
 oxide (NO) at 760 mm. pressure and o C. 
 
 All the metals in common use 
 are attacked by nitric acid, except 
 gold, platinum, and, in less degree, 
 aluminium, so that this acid is used 
 to distinguish and separate these 
 metals from others of less value. 
 The ordinary ready method of as- 
 certaining whether a trinket is 
 made of gold consists in touching 
 it with a glass stopper wetted with 
 nitric acid, which leaves gold un- 
 touched, but colours base alloys 
 blue, from the formation of copper 
 nitrate. The touch-stone allows this 
 mode of testing to be applied with great accuracy. It consists of a 
 species of black basalt, obtained chiefly from Silesia. If a piece of gold 
 be drawn across its surface, a golden streak is left, which is not 
 affected by moistening with nitric acid ; whilst the streak left by brass, 
 or any similar base alloy is rapidly dissolved by the acid. Experience 
 enables an operator to determine, by means of the touch-stone, pretty 
 nearly the amount of gold present in the alloy, comparison being made 
 with the streaks left by alloys of known composition. 
 
 Action of nitric acid on organic substances. The oxidising action of 
 nitric acid on some organic substances is so powerful as to be attended 
 with inflammation ; if a little of the strongest acid be placed in a 
 porcelain capsule, and a few drops of oil of turpentine be poured into it 
 
 1. 75. Nitrometer. 
 
94 RADICLES AND SUBSTITUTION. 
 
 from a test-tube fixed to the end of a long stick, the turpentine takes 
 fire with a sort of explosion. By boiling some of the strongest acid in 
 a test-tube (Fig. 76), the mouth of which is loosely stopped with a 
 plug of raw silk or of horse-hair, the latter may be made to take fire 
 and burn brilliantly in the vapour of nitric acid. 
 
 In many cases the products of the action of nitric acid exhibit a most 
 interesting relation to the substances from which they have been pro- 
 duced, one or more atoms of the hydrogen of 
 the original compound having been removed in 
 the form of water by the oxygen of the nitric 
 acid, whilst the spaces thus left vacant have 
 been filled up by the nitric peroxide resulting 
 from the de-oxidation of the nitric acid, pro- 
 ducing what is termed a nitro-substitution com- 
 pound. A very simple example of this displace- 
 ment of H by NO 2 , is afforded by the action of 
 _ nitric acid upon benzene. A little concentrated 
 
 Fio . 6 nitric acid is placed in a flask, and benzene 
 
 cautiously dropped into it ; a violent action 
 ensues, and the acid becomes of a deep red colour ; if the contents of 
 the flask be now poured into a large vessel of water, a heavy yellow oily 
 liquid is separated, having a powerful odour, like that of bitter almond 
 oil. This substance, which is used to a considerable extent in perfumery 
 under the name of essence of Mirbane, is called nitro-benzene, and its 
 formula, C 6 H 3 (N0 2 ), at once exhibits its relation to benzene, C 6 H 6 . 
 
 To understand the nature of this reaction the theory of radicles and 
 of substitution must be realised. Just as the molecules of most elements 
 may be regarded as consisting of two parts, neither of which is capable 
 of a separate existence, so the molecules of most compounds may be 
 looked upon as composed of two or more parts or radicles, none of 
 which can exist alone. Water, for example, consists of the radicles 
 H- and -OH, united by one " bond " from each, which bond causes 
 the radicle to enter into a new combination immediately it is liberated. 
 The acids which contain oxygen, or oxy -acids, consist of one or more 
 hydroxyl (- OH) radicles and an acid radicle. Thus nitric acid is 
 N0 2 *OH, containing the acid-radicle nitroxyl (N0 2 ) and one hydroxyl 
 radicle. 
 
 Such radicles take part in chemical reactions, and may be substituted 
 for elements, as though they were themselves elements. Thus when 
 the hydroxyl radicle exists in one of the reacting substances it may be 
 expected to occur in one of the products, unless the reaction be of so 
 drastic a character as to break up the radicles of the reacting sub- 
 stances. It follows that a large number of chemical changes (par- 
 ticularly in organic chemistry) are to be explained as exchanges between 
 the radicles of compounds, in the same way that many are to be 
 explained as exchanges between the elementary atoms constituting the 
 reacting compounds e.g., KI + HC1 = KOI + HI. 
 
 Benzene contains the radicle C 6 H 5 , so that the reaction between 
 benzene and nitric acid may be represented as an exchange of the 
 O^Hg radicle of the benzene for the OH radicle of the nitric acid, the 
 nitroxyl radicle having been substituted for hydrogen in the benzene, 
 H-C 6 H 5 + N0 2 OH = N0 2 -C 6 H 5 + H-OH. 
 
COMPOSITION OF NITRIC ACID. 95 
 
 It is by an action of this description that nitric acid gives rise to 
 gun-cotton, and other explosive substances of the same class, when 
 acting upon the different varieties of woody fibre, as cotton, paper, saw- 
 dust, tfcc. For making these, nitric acid finds extended application.* 
 
 61. Nitrates. Its powerful action on bases places nitric acid among 
 the strongest of the acids, though the disposition of its elements to 
 assume the gaseous state at high temperatures, conjoined with the 
 feeble attraction existing between nitrogen and oxygen, causes its salts 
 to be decomposed, without exception, by heat. 
 
 The nature of the decomposition varies with the metal contained in the nitrate. 
 The nitrates of alkali metals are first converted into nitrites by the action of heat ; 
 thus KN0 3 gives KN0 2 and O ; the nitrites themselves being eventually decom- 
 posed, evolving nitrogen and oxygen, and leaving the oxide of the metal. The 
 nitrates of copper and lead evolve nitric peroxide (N0 2 ) and oxygen, the oxides 
 being left. The nitrate of mercury leaves red oxide of mercury, which is decom- 
 posed at a higher temperature into mercury and oxygen. 
 
 Nitric acid is a monobasic acid, because it contains only one atom oi 
 hydrogen which can be exchanged for a metal. It will be found that 
 it is only the H of the OH radicles in an oxy-acid which can be exchanged 
 for metals ; the OH groups may thus be said to impart an acid character 
 to a compound. Comparatively few of the nitrates are in common use ; 
 they will be mentioned under the metals of which they are the salts. 
 
 The oxidising effects of nitric acid are shared to some extent by the 
 nitrates. A mixture of nitrate of lead with charcoal explodes when 
 sharply struck, from the sudden evolution of carbonic acid gas, produced 
 by the oxidation of the carbon. If a few crystals of copper nitrate be 
 sprinkled with water and quickly wrapped up in tinfoil, the latter will, 
 after a time, be so violently oxidised as to emit brilliant sparks. 
 
 But in the case of the nitrates of alkali metals, the oxidation takes place only at 
 a high temperature. If a little nitre be fused in an earthen crucible or an iron 
 ladle, and, when it is at a red heat, some powdered charcoal, and afterwards some 
 flowers of sulphur, be thrown into it, the energy of the combustion will testify to 
 the violence of the oxidation. In this manner the carbon is converted into potas- 
 sium carbonate (K 2 C0 3 ), and the sulphur into potassium sulphate (K 2 S0 4 ). (See 
 Ounpoicder.) 
 
 Determination of the composition of nitric acid. A definite weight, say 10 grams, 
 of pure lead oxide is mixed with 5 grams of nitric acid, and the mixture is gently 
 heated as long as vapour of water escapes ; PbO + 2HN0 3 = H 2 + Pb(N0 3 ) 2 . Say 
 that the residue weighs 14.27 grams ; then 
 
 From the weight of lead oxide and nitric acid . . 15.00 grams 
 Deduct weight of lead oxide and lead nitrate . . 14.27 
 
 Water which has been expelled . . . 0.73 
 
 corresponding with .3 or o<o g g r am H. 
 
 The mixture of lead nitrate and excess of lead oxide is then strongly heated in 
 a tube containing copper, when Pb(N0 3 ) 2 +Cu 5 PbO +5CuO-fN 2 ; the nitrogen 
 is collected and measured. Say that 884.7 c - c - of N are obtaine"d ; these weigh 
 884.7 x Trnr gram= 1. 19 gram, since I II 10 c.c. of N weigh 14 grams. 
 
 Hence we find, in 5 grams of nitric acid, i.n gram N, 0.08 gram H, and, by 
 difference, 3,73 grams 0. Dividing these numbers by the atomic weights, 14, I, 
 and 1 6, we obtain 0.08 atom of N, 0.08 atom of H, and 0.24 atom of 0, or i atom 
 of H to i atom of N and 3 atoms of O. This would give, for the molecule of 
 nitric acid, HN0 3 , 1 + 14 + 48= =63, a result agreeing from that obtained from 
 the sp. gr. of its vapour (see page 91). 
 
 * It is stated that nitrous acid in the nitric acid exerts the same kind of influence in sub- 
 stitution reactions of nitric acid as it exerts in the action of the acid on metals (p. 92). 
 
96 NITEOUS OXIDE. 
 
 62. Anhydrous nitric acid or nitric anhydride (N 2 5 ) is obtained by 
 gently heating silver nitrate in a slow current of chlorine, great care being taken 
 to exclude every trace of water ; 2AgN0 3 + Cl 2 = 2AgCl + 6 + N 2 5 . 
 
 It may also be obtained by adding anhydrous phosphoric acid to the strongest 
 nitric acid cooled in snow and salt, and carefully distilling at as low a temperature 
 as possible. The distillate separates into two layers, the lower of which is a 
 compound 2N 2 5 .H 2 O, called dinitric acid; the upper layer is separated and 
 cooled. 
 
 The anhydride is condensed as a crystalline solid. It forms transparent 
 colourless prisms which melt at 30 C., and boil at 47 C. By a slightly higher 
 temperature it is readily decomposed ; and it has been said to decompose even 
 at the ordinary temperature, in sealed tubes which were shattered by the evolved 
 gas. It is more stable in the dark. When the anhydride is brought in contact 
 with water, much heat is evolved, and nitric acid. H 2 O.N 2 05, is produced. 
 
 The specific gravity of the vapour of nitric anhydride being unknown, it is only 
 a surmise that its molecule is represented by N 2 O 5 . 
 
 63. Nitrous oxide or laughing gas (N 2 = 44 parts by weight = 2 
 volumes) is prepared by heating ammonium nitrate, when it is resolved 
 with evolution of heat, into water and nitrous oxide ; NH 4 N0 3 = 
 2 H 2 + N 2 0. 
 
 To obtain nitrous oxide, an ounce of ammonium nitrate may be gently heated 
 in a small retort, when it melts, boils, and gradually disappears entirely in the 
 forms of steam and nitrous oxide. The latter may be collected with slight loss 
 over water. 
 
 In the preparation of nitrous oxide, if the temperature be too high, the gas may 
 contain nitric oxide and nitrogen; NH 4 N0 3 = NO + N + 2H 2 0. Moreover, since 
 80 grams (i gram-molecule) of NH 4 N0 3 evolve some 31,000 gram-units of heat when 
 decomposed into H 2 and N 2 0, explosion is liable to occur. To purify the gas, it 
 should be passed through a strong solution of ferrous sulphate, to absorb the nitric 
 oxide, and afterwards through potash to absorb acid vapours. 
 
 Nitrous oxide is colourless, but has a slight odour and a sweetish 
 taste. Its characteristic anaesthetic property is well known. It accele- 
 rates the combustion of a taper like oxygen itself, and will even kindle 
 into flame a spark at the end of a match, for it is readily decomposed 
 into N 2 and by the temperature of burning wood. When C is burnt 
 into C0 2 by 2N 2 0, it evolves 36,000 more units of heat than when 
 burnt in O 2 , showing that, contrary to the usual law, heat is evolved in 
 the decomposition of the N 2 0, amounting to 18,000 units per molecule. 
 Such a compound is said to be endothermic, whilst a compound like 
 water, which is formed with evolution of heat is called exothermic. 
 Nitrous oxide can readily be distinguished from oxygen by shaking it 
 with water, which absorbs, at the ordinary temperature, about three- 
 fourths of its volume of the nitrous oxide. It is absorbed in larger 
 quantity by alcohol. It is also much heavier than oxygen, its specific 
 gravity being 1.53, and is liquefied by a pressure of 40 atmospheres at 
 7 C, and solidified at - 115 C. The liquid is now sold in wrought- 
 iron vessels for use as an anaesthetic in dental surgery. In small doses 
 it has an intoxicating effect, whence its title of " laughing gas." 
 
 The liquid nitrous oxide has a very low refractive index ; its sp. gr. is o. 94 at 
 O C., and it boils at - 90 C. A lighted match thrown into the liquid burns with 
 great brilliancy. When it is mixed with carbon bisulphide and evaporated in 
 vacuo, the temperature falls to 140 C. The critical temperature of N 2 is 39 C., 
 and the critical pressure is 73 atmos. 
 
 64. Nitric oxide (NO = 30 parts by weight = 2 volumes) is usually 
 obtained by the action of copper upon diluted nitric acid (see page 146). 
 
 Twenty grams of copper turnings or clippings are introduced into a retort, 
 
NITRIC OXIDE. 
 
 97 
 
 and 85 c.c. of a mixture of concentrated nitric acid with an equal volume 
 of water are poured upon them. A very gentle heat may be applied to assist 
 the action, and the gas may be collected over water (see Fig. 109), which absorbs 
 the red fumes (N0 2 ) formed by the union of the NO with the oxygen of the air 
 contained in the retort. 
 
 The nitric oxide prepared by the action of copper on nitric acid generally con- 
 tains nitrous oxide. Pure nitric oxide may be obtained by heating in a retort 
 6.5 grams potassium nitrate, 65 grams of ferrous sulphate, and 85 c.c. of dilute 
 sulphuric acid (containing one measure of acid to three measures of water), which 
 will yield about 1133 c.c. of gas; 2KN0 3 + 6FeS0 4 + 4ELSO, = KSO,+ 
 
 Nitric oxide is distinguished from all other gases by the production 
 of a red gas, when the colourless nitric oxide is allowed to come in 
 contact with uncombined oxygen, the presence of which, in mixtures of 
 gases, may be readily detected by adding a little nitric oxide. The red 
 gas consists chiefly of nitric peroxide (N0 2 ) when the oxygen is in 
 excess, otherwise it contains also some nitrous anhydride (N 9 O ). 
 
 The combination of nitric oxide with oxygen may be exhibited by decanting a 
 pint bottle of oxygen, under water, into a tall jar filled with water coloured with 
 blue litmus, and adding to it a pint 
 bottle of nitric oxide (Fig. 77). Strong 
 red fumes are immediately produced, 
 and on gently agitating the cylinder, 
 the fumes are absorbed by the water, 
 reddening the litmus. The oxygen 
 will now have been reduced to half its 
 volume, and if another pint of nitric 
 oxide be added, the remainder of the 
 oxygen will be absorbed, showing that 
 two volumes of nitric oxide combine 
 with one volume of oxygen, forming 
 nitric peroxide which is absorbed by 
 the water. In presence of water and 
 excess of oxygen, NO is entirely con- 
 verted into nitric acid ; 2NO + H 2 + 3 
 = 2HN0 3 . 
 
 The addition of nitric oxide to 
 atmospheric air was one of the 
 earliest methods employed for removing the oxygen in order to deter- 
 mine the composition of air ; but important variations were observed 
 in the results, in consequence of the occasional formation of N 2 3 in 
 addition to the N0 2 . 
 
 In all its properties nitric oxide is very different from nitrous oxide. 
 It is much lighter, having almost exactly the same specific gravity as 
 air, viz., 1.04, and is not dissolved to an important extent by water. It 
 is more difficult to liquefy, for its critical temperature is - 93 C. ; its 
 boiling point is - 153 0. When a lighted taper is immersed in nitric 
 oxide it is extinguished, although this gas contains twice as much oxy- 
 gen as nitrous oxide, which so much accelerates the combustion of a 
 taper, for the elements are held together by a stronger attraction in 
 the nitric oxide, so that its oxygen is not so readily available for the 
 support of combustion. (The nitric oxide prepared from copper and 
 nitric acid sometimes contains so much nitrous oxide that a taper 
 burns in it brilliantly.) Even phosphorus, when just kindled, is ex- 
 tinguished in nitric oxide, but when allowed to attain to full combus- 
 tion in air, and, therefore, to a temperature high enough to decompose 
 the nitric oxide into N and 0, it burns with extreme brilliancy in the 
 
9 8 
 
 REDUCTION OF NITRIC OXIDE. 
 
 gas. Indeed, nitric oxide appears to be the least easy of decomposition 
 of the whole series of oxides of nitrogen, which accounts for its being 
 the most common result of the decomposition of the other oxides. 
 Nitrous oxide itself, when passed through a red-hot tube, is partly con- 
 verted into nitric oxide ; and when a taper burns in a bottle of nitrous 
 oxide, the upper part of the bottle is often filled with a red gas, indica- 
 ting the formation of nitric oxide, and its oxidation by the air entering 
 the bottle. 
 
 The difference in the stability of the two gases is also shown by their 
 behaviour with hydrogen. A mixture of nitrous oxide with an equal 
 volume of hydrogen explodes when in contact with flame, yielding steam 
 and nitrogen, but a mixture of equal volumes of nitric oxide and hydra- 
 gen burns quietly in air, the hydrogen not decomposing the nitric 
 oxide except at the temperature of a strong electric spark. An excess 
 of hydrogen, however, is capable of decomposing nitric oxide, ammonia 
 and water being formed. 
 
 If two volumes of nitric oxide are mixed with five volumes of hydrogen and the 
 gas passed through a tube having a bulb filled with platinised asbestos (Fig. 78).* 
 the mixture issuing from the orifice of the tube produces the red gas by contact 
 
 with the air, which will strongly redden 
 blue litmus ; but if the platinised 
 asbestos is heated with a spirit-lamp, 
 the hydrogen, encouraged by the action 
 of the platinum (p. 87). decomposes 
 the nitric oxide, and strongly alkaline 
 vapours of ammonia are produced, re- 
 storing the blue colour to the reddened 
 litmus; NO + H 5 = NH 3 + H 2 0. It will 
 be remembered that when oxygen is in 
 excess, ammonia is converted, under 
 the influence of platinum, into water 
 and nitrous acid (p. 87). 
 
 Nitric oxide is readily absorbed 
 by ferrous salts, with which it 
 
 Fjg 78 forms dark brown solutions. If 
 
 a little solution of ferrous sulphate 
 
 (FeS0 4 ) be shaken in a cylinder of nitric oxide closed with a glass 
 plate, the gas will be immediately absorbed and the solution will 
 become dark brown. On applying heat, the brown compound is 
 decomposed. 
 
 When shaken with moist ferrous hydroxide, NO is reduced to N 2 O 
 and N. In the presence of caustic soda, sodium hyponitrite (Na 2 N 2 O 2 ) 
 and ammonia are also produced. By employing a large excess of soda, 
 one-fifth of the nitric oxide may be converted into the hyponitrite. 
 
 65. Nitrous anhydride (N 2 3 or NO.N0 2 = 76 parts by weight). 
 Ammonium nitrite is said to exist in minute quantity in rain water, 
 and nitrites are occasionally found in well-waters, where they have 
 probably been formed by the oxidation of ammonia (p. 87). Small 
 quantities of ammonium nitrite appear to be formed by the combustion 
 in air of gases containing hydrogen, this element uniting with the 
 atmospheric oxygen and nitrogen. 
 
 Nitrous anhydride may be obtained by heating starch with nitric 
 
 * Asbestos which has been wetted with solution of platinic chloride, dried, and heated to 
 redness, to reduce the platinum to the metallic state. 
 
NITROUS ANHYDRIDE. 
 
 99 
 
 acid, but the most convenient process consists in gently heating nitric 
 acid (sp. gr. 1.35) with an equal weight of white arsenic, and passing 
 the gas, first through a U-tube (Fig. 79) surrounded with cold water, 
 to condense undecomposed nitric acid, then through a similar tube 
 containing calcium chloride to absorb aqueous vapour, and afterwards 
 into a U-tube surrounded with ice. Through a small tube opening 
 into the bend of this 
 U-tube, the condensed 
 nitrous anhydride drops 
 into a tube drawn out to 
 a narrow neck, so that 
 it may be drawn off and 
 seale I by the blow- 
 pipe 
 
 White arsenic. 
 
 Fig\ 79. Preparation of nitrous anhydride. 
 
 Arsenic acid. 
 
 The white arsenic is here 
 used merely as a reducing 
 agent to remove oxygen from 
 the nitric acid. N 2 3 is the 
 anhydride of nitrous acid, 
 HN0 2 (H 2 O.N 2 3 ) ; this acid 
 
 is so unstable that it immediately breaks up into H 2 and N 2 3 ; 2HN0 2 = 
 H 2 + N 2 3 . The object of the above reaction, therefore, is to remove two atoms 
 of oxygen from two molecules of nitric acid 2HN0 3 = H 2 + N 2 3 + 2 . \ White 
 arsenic, As 4 6 , is arseniow* anhydride and readily oxidises to arsem'c anhydride, 
 As 4 10 , which then combines with water to form arsenic acid6H 2 O.As 4 10 ( = 4H 3 As0 4 ). 
 Hence one molecule of white arsenic combines with four atoms of oxygen and will 
 therefore reduce four molecules of nitric acid. The student should endeavour to 
 sift in this manner all chemical equations which appear to him complex. 
 
 Nitrous anhydride is also prepared by decomposing the acid nitrosyl 
 sulphate (see Aqua regia) with a small quantity of water 
 2NOHS0 4 + H 2 = 2H 2 S0 4 + N 2 3 . 
 
 If the gas liberated in these reactions be cooled to - 20 C., a pure 
 indigo-blue liquid, supposed to be N 2 3 , is formed ; but if the tempera- 
 ture be allowed to rise the colour becomes dirty and the liquid is a 
 mixture of nitrogen tetroxide (nitric peroxide), N 2 O 4 , and nitrous 
 anhydride. It boils below the ordinary temperature giving a red gas 
 which consists of equal volumes of nitric oxide and nitric peroxide, 
 the proportion of the latter gradually increasing until the remaining 
 liquid has the green colour and the composition of N 2 4 . It thus seems 
 that N 2 3 can only exist at low temperatures and in the liquid condi- 
 tion. The liquid is readily obtained, although not quite pure, by 
 passing nitric oxide into cooled liquid nitrogen tetroxide. But when 
 equal volumes of NO and N0 2 gases are mixed, no contraction occurs, 
 as would be the case if they combined to N 2 3 ; NO (2 volumes) + N0 2 
 (2 volumes) = N 2 3 (2 volumes). 
 
 Water at about o C. dissolves nitrous anhydride, yielding a blue 
 solution, which, as the temperature rises, becomes a solution of nitric 
 acid, nitric oxide escaping with effervescence ; 
 
 3N 2 3 + H 2 = 2HN0 3 + 4 NO. 
 
 The blue solution is believed to contain nitrous acid, HN0 2 or 
 
100 NITRIC PEROXIDE. 
 
 NO.OH; N 2 3 + H 2 = 2HNO 2 ; but this compound has not been ob- 
 tained in a pure state. A very dilute solution of the acid may be 
 preserved for some time, and even distilled, without decomposition. 
 
 The salts of nitrous acid, or nitrites, are interesting on account of 
 their production from the nitrates by the action of heat (p. 95). 
 
 When potassium nitrate is fused in a fire-clay crucible and heated to redness, it 
 evolves bubbles of oxygen, and slowly becomes potassium nitrite (KNOg). The 
 heat may be continued until a portion removed on the end of an iron rod, and dis- 
 solved in water, gives a strongly alkaline solution. The fused mass may then be 
 poured upon a dry stone, and, when cool, broken into fragments and preserved in 
 a stoppered bottle. On heating a fragment of the nitrite with dilute H 2 S0 4 , red 
 vapours are disengaged, but these contain little nitrous acid, the greater part of 
 this being decomposed by the water into HNO 3 and NO. When nitrous acid acts 
 on ammonia, both compounds are decomposed, water and nitrogen being produced ; 
 NH 3 + HN0 2 = N 2 + 2H 2 0. 
 
 When solutions of nitrites are heated in contact with air, they gradually absorb 
 oxygen, becoming converted into solutions of nitrates. 
 
 Nitrous acid may be regarded as a solution of NO and N0 2 in water 
 (H 2 O.N 2 3 or H 2 O.NO.N0 2 ). The former tends to combine with 
 oxygen to form N0 3 , and the latter tends to part with oxygen to form 
 NO, so that nitrous acid can behave, according to circumstances, either 
 as a reducing agent or an oxidising agent. Obviously any compound 
 capable of parting with oxygen to NO cannot obtain oxygen under the 
 same circumstances from N0 2 . 
 
 Nitrous acid reduces potassium permanganate, but oxidises ferrous sulphate. It 
 will also oxidise the hydrogen of hydriodic acid (HI), thereby liberating the iodine ; 
 since a very small quantity of the latter can be detected by taking advantage of its 
 property of bluing starch, the addition of hydriodic acid (KI and H 2 S0 4 ) to nitrous 
 acid (KN0 2 + H 2 S04) forms a very delicate test for the latter: - HI + NO-OH = 
 H-OH + I + NO. 
 
 66. Nitric peroxide (N0 2 = 46 parts by weight, or N 2 4 = 92 parts = 
 2 volumes). By passing a mixture of nitric oxide with half its volume 
 of oxygen, free from every trace of moisture, into a perfectly dry tube 
 cooled in a mixture of ice and salt, the dark red 
 gas is condensed into colourless prismatic crystals 
 which melt at - 12 C. into a nearly colourless 
 liquid. This gradually becomes yellow as the tem- 
 perature rises, and at 15 C. has a deep orange 
 colour. It is very volatile, boiling at 71 F. 
 (22 C.), to a red-brown vapour, which was long 
 mistaken for a permanent gas, on account of the 
 great difficulty of condensing it when once mixed 
 
 with air OT ox yg en - Nitric Peroxide is also ob- 
 tained, mixed with one-fourth of its volume of 
 oxygen, by heating lead nitrate (Fig. 80) ; Pb(N0 3 ) 2 = PbO + 2NO 2 + O. 
 The vapour of nitric peroxide is much heavier than atmospheric air. 
 
 Its vapour density diminishes as the temperature rises. At 140 C. the gas is 
 23 times as heavy as hydrogen, showing its molecular weight to be 46. This 
 variation in density, in conjunction with the other changes with increase of tem- 
 perature, leads to the belief that the molecule of nitric peroxide at low temperatures 
 (in its liquid state) is N 2 4 , and becomes dissociated into 2N0 2 at high tempera- 
 tures. At 500 C. the gas becomes nearly colourless, being almost entirely dis- 
 sociated into NO and O. 
 
 N0 2 is absorbed by many finely divided metals, forming compounds called 
 nitro -metals. These are very unstable, and yield most of the reactions of NO 2 . 
 
STRUCTURAL FORMULAE. IOI 
 
 Nitro-copper, Cu 2 N0 2 , is obtained when N0 2 is passed over freshly reduced Cu at 
 30 C. 
 
 By mixing N 2 5 with the green liquid obtained by condensing the vapours from 
 the action of HN0 3 on As 4 6 the N 2 3 contained in the liquid is converted into 
 N 2 4 ; N 2 5 + N 2 3 = 2N 2 4 . 
 
 Its colour varies with the temperature, becoming very dark at 100 F. 
 (30 C.). The smell of the vapour is very characteristic. The vapour 
 supports the combustion of strongly burning charcoal or phosphorus, and 
 oxidises most of the metals, potassium taking fire in it spontaneously. 
 Nitric peroxide must, therefore, rank as a powerful oxidising agent, 
 and it is the presence of this substance in considerable proportion in 
 the red fuming nitric acid that imparts to it higher oxidising powers 
 than those of the colourless nitric acid. This red acid, the so-called 
 nitrous acid of commerce, is prepared by introducing sulphur into the 
 retorts containing the mixture of sodium nitrate and sulphuric acid 
 employed in the preparation of the nitric acid, a portion of which is 
 de-oxidised by the sulphur and converted into nitric peroxide. 
 
 Water in excess immediately decomposes nitric peroxide into nitrous 
 acid and nitric acid, 2NO 2 + H 2 = HN0 3 + HNO 2 , so that the peroxide 
 is not an independent anhydride. 
 
 When water is gradually added to liquid nitric peroxide, the liquid effervesces 
 from escape of nitric oxide, and becomes green, blue, and ultimately colourless ; 
 3NO 2 + H 2 = NO + 2HN0 3 . If the red nitric acid of commerce be gradually diluted 
 with water, it will be found to undergo similar changes, always becoming colourless- 
 at last. The nitric acid which has been used in a Grove's battery has a green- 
 colour, from the large amount of nitric peroxide which has accumulated in it, in- 
 consequence of the decomposition of the acid by the hydrogen disengaged during 
 the action of the battery; H + HN0 3 = H 2 + N0 2 . If this green acid be diluted 
 with a little water it becomes blue, and a larger quantity of water renders it colour- 
 less, causing the evolution of nitric oxide. Similar colours are obtained by passing 
 nitric oxide into nitric acid of different degrees of concentration, apparently because 
 nitric peroxide is formed and dissolved by the acid. 
 
 When silver, mercury, and some other metals are dissolved in cold nitric acid, a 
 green or blue colour is often produced, leading a novice to suspect the presence of 
 copper, the colour being really caused by the dissolution, in the unaltered nitric 
 acid, of the nitric peroxide, produced by the de-oxidation of another portion. 
 
 The facility with which nitrous anhydride and nitric peroxide can 
 be decomposed with formation of nitric oxide renders it probable that 
 they really contain this group of elements as a radicle nitroxyl, NO. 
 To express this they may plausibly be represented as formed on the 
 same plan as that on which a molecule of water is formed. Just as 
 in H - - H, the two atoms of hydrogen are linked together by the 
 diatomic oxygen, so in nitrous anhydride, = N-0-N = 0, two mole- 
 cules of nitric oxide are linked together by the atom of oxygen, whilst 
 in nitric peroxide (N 2 4 ) a molecule of NO is bound up with a molecule 
 
 of N0 2 , thus, = N - O - N^f . If nitric anhydride be represented by 
 
 \N-O- N^f , it is easy to understand the behaviour of these 
 O^ ^0 
 
 three oxides with the alkalies. Thus, by the action of nitrous anhy- 
 dride on caustic potash, potassium nitrite K - - N = 0, in which K 
 is substituted f or : N - , is formed, whilst nitric anhydride gives 
 potassium nitrate K - O - NO 2 , and nitric peroxide gives a mixture of 
 
102 ANALYSIS OF OXIDES OF NITROGEN. 
 
 both salts. The remaining oxide of nitrogen N 2 O may be represented 
 as N.O.N 
 
 Such formulae as the above are termed structural formula, since they 
 essay to represent the way in which the molecule is built up, so far 
 as it is possible to represent a three-dimensional structure on one 
 plane. They must be written with due regard to the valency of the 
 elements ; thus nitrogen should always appear either as trivalent or 
 pentavalent, for its atom-linking power has always one or other of these 
 values. They must also be written with regard to the constitution of 
 the compound, that is, the relationships which the various atoms show 
 towards each other ; thus, since there is evidence that the nitrogen 
 atom and two of the oxygen atoms in nitric acid behave as the radicle 
 N0 2 , no structural formula failing to represent the N as directly 
 attached to two oxygen atoms could be accepted. 
 
 All the oxides of nitrogen are endothermic compounds (p. 96), which 
 accounts for the indisposition of N and to combine directly. The 
 following equations represent the number of calories or gram-units of 
 heat (p. 44) evolved by the decomposition of one gram-molecule (the 
 molecular weight expressed in grams) of N 2 0, NO and N0 2 : 
 
 N 2 = N 2 + + 18,000 cal. 
 ISO = N + O + 21,500 
 N0 2 = N + 2 + 7650 
 
 The general principle upon which the determination of the composi- 
 tion of these oxides has been determined is the decomposition of a 
 measured volume of the gaseous oxide either by heat alone, or by 
 burning some oxidisable substance in it, and measuring and analysing 
 the volume of the gases or gas obtained. 
 
 Thus, when nitrous oxide is passed through a red-hot tube, its volume is increased 
 by one-half, the gas becoming a mixture of I volume of oxygen and 2 volumes of 
 nitrogen. This shows that the ratio of atoms of nitrogen to oxygen in the gas is 
 2:1. That the formula is N 2 0. not N 4 2 , is decided by the specific gravity of 
 the gas. 
 
 When a known volume of nitric oxide is passed over a weighed quantity of red- 
 hot copper and the nitrogen which passes on is collected and measured, it is found 
 that for every 16 parts by weight of oxygen absorbed by the copper (judged from 
 its gain of weight) I i.i I litres of nitrogen are collected ; but this volume of nitrogen 
 weighs 14 grams (p. 47), so that the nitric oxide must contain : N = 16 : 14, or 
 one atom of oxygen to one atom of nitrogen. That the formula is NO, not N 2 O 2 , 
 follows from the specific gravity of the gas. 
 
 The other oxides of nitrogen are similarly analysed. 
 
 67. Reduction products of citric acid. By the action of nascent 
 hydrogen, that is, hydrogen at the moment of its liberation,* nitric 
 acid, the most highly oxidised nitrogen compound, may be made to 
 yield successive reduction products until the most highly hydrogenised 
 nitrogen compound, ammonia, is formed. The reduction may be re- 
 garded as occurring in the following stages, although to realise such 
 progressive steps is difficult, if not impossible, in practice. The first 
 stage of the reduction will be nitrous acid, N0 2 -OH-f-H 2 = NO'OH + 
 H 2 0. In the second stage, N'OH would be expected to be produced, 
 but in a compound of this formula only one of the atom-linking powers 
 
 * When it might be supposed to be still in the condition of free atoms, and therefore 
 more active. The usual method of applying nascent hydrogen is to liberate it in the liquid 
 on which it i-s to act by placing zinc and sulphuric acid, or merely sodium amalgam, therein. 
 
HYPONITEOUS ACID. 103 
 
 of the nitrogen would be satisfied ; hence this group of atoms is in- 
 capable of a separate existence, but, if produced, immediately combines 
 with a like group, forming hyponitrous acid, HON : N'OH. The third 
 stage of the reduction consists in the introduction of hydrogen into the 
 hyponitrous acid, whereby the molecule is made to yield either two 
 molecules of a compound called hydroxylamine, HON : N'OH + H 4 = 
 
 H H\ 
 
 + \N"-OH, or one molecule of a compound called hydra- 
 
 H W 
 
 zine, HON : N-OH + H 6 = H 2 N : NH 2 + 2 HOH. The final stage of the 
 reduction transforms the hydroxylamine into ammonia. 
 
 Hyponitrous acid, H 2 N. 2 0. 2 . Nitrous oxide might be expected to be the anhy- 
 dride of this acid, N 2 + H 2 = H 2 N 2 2 , but an aqueous solution of this gas does 
 not contain hyponitrous acid. The hyponitrites are obtained by reducing solutions 
 of the nitrates or nitrites by the nascent hydrogen generated when sodium amalgam 
 is introduced into the solution. Thus, a solution of sodium hyponitrite is obtained 
 when sodium amalgam is added, little by little, to a strong solution of sodium 
 nitrate, or nitrite, kept cool. The hyponitrite most easily obtained in a pure 
 condition is the silver salt, Ag 2 N 2 2 , which is thrown down as a yellow precipitate 
 when silver nitrate is added to the solution of sodium hyponitrite. The yellow 
 precipitate dissolves in ammonia and in dilute nitric acid, but is precipitated 
 unchanged by neutralising the solvent ; it is insoluble in acetic acid. By adding 
 hydrochloric acid to the silver salt, hyponitrous acid passes into the solution and 
 silver chloride remains undissolved ; the solution is colourless and acid to litmus, 
 but it will not liberate carbon dioxide from the alkali carbonates ; when kept it 
 decomposes with formation of N 2 and H 2 0. By adding the silver salt to a 
 solution of HC1 in ether, filtering and evaporating the ethereal solution, crystals 
 of H 2 N 2 2 are obtained ; they are very explosive, like other compounds containing 
 the group 'N ; N\ In acid solution potassium permanganate oxidises hyponitrous 
 acid to nitric acid, but in alkaline solution a nitrite is formed. The formation of 
 hyponitrous acid by the reduction of nitric oxide in presence of water has been 
 mentioned at p. 98 ; another reaction by which it is produced will be mentioned 
 below. 
 
 Hydroxylamine, NH./OH, may be obtained by the reduction of nitric acid, but is 
 better prepared by passing nitric oxide through a series of flasks containing tin and 
 strong hydrochloric acid. The hydrogen evolved from the metal and acid (the 
 evolution is generally hastened by the addition of a few drops of platinic chloride, 
 the platinum of which deposits on the tin and forms a galvanic couple) may be 
 regarded as converting the NO into NH 2 OH. The hydroxylamine, being possessed 
 of basic properties, combines with the hydrochloric acid and remains in the solution 
 as hydroxylamine hydrochloride, NH 2 OH.HC1, together with stannous chloride. 
 The tin is precipitated by the addition of H 2 S ; the SnS is filtered off and the filtrate 
 evaporated, when the hydroxylamine hydrochloride crystallises. 
 
 To obtain free hydroxylamine, the hydrochloride is dissolved in methyl alcohol 
 and a solution of sodium in the same solvent is added ; sodium chloride is precipi- 
 tated and is filtered off ; the filtrate is then distilled under reduced pressure, Avhen 
 methyl alcohol passes over, followed by hydroxylamine. In this process the sodium 
 methoxide, CH 3 ONa, contained in the solution of sodium in methyl alcohol, reacts 
 with the hydroxylamine hydrochloride, forming sodium chloride, hydroxylamine 
 and methyl alcohol : NH 2 .OH.HCl + CH 3 ONa = NH 2 OH + CH 3 OH + NaCl. Sodium 
 hydroxide cannot be substituted for the methoxide because water would be one of 
 the products, and this decomposes the hydroxylamine. 
 
 Hydroxylamine crystallises in white needles, jnelts at 33 C., and boils at 58 C. 
 under 22 mm. pressure, but explodes when heated to 90 C. under ordinary pres- 
 sure. It is odourless and has an alkaline reaction ; when exposed to air it 
 deliquesces and ultimately evaporates ; even in sealed tubes it slowly undergoes 
 decomposition. 
 
 Hydroxylamine and its salts are very easily oxidised to nitrous oxide and water 
 so that they reduce cupric oxide in alkaline solutions to cuprous oxide, 4CuO + 
 2NH 2 .OH = 2Cu 2 + N 2 + 3H 2 O. Ferrous hydroxide, however, is oxidised by hy- 
 droxylamine, which is thereby reduced to ammonia ; on the other hand, an acid 
 
104 CLASSIFICATION OF ACIDS. 
 
 ferric solution is reduced by hydroxylamine. An aqueous solution of the hydro- 
 chloride is used as a photographic developer. 
 
 The f rue base combines with many metallic salts in the same way that water and 
 ammonia do. 
 
 If hydroxylamine be regarded as formed on the type of water, it will 
 be seen to contain the radicle NH 2 in place of H in H.OH. Equally 
 well it may be said to be ammonia in which one hydrogen atom has 
 been exchanged for OH. Before hydroxylamine was known, it could be 
 prophesied that such a compound would be more basic than is water, 
 and less basic than is ammonia. For it is found that the presence of 
 an NH 2 group in a compound tends to make that compound basic, 
 whilst the presence of an OH group tends to make it acid. Thus the 
 basic properties of NH 2 H are enfeebled by the substitution of an OH 
 group for H. 
 
 The acid properties of N0 2 .OH are stronger than those of NO.OH, 
 which in their turn are stronger than those of HO.N : N.OH. It 
 would thus seem that N0 2 is a stronger acid radicle than NO, and 
 that the two hydroxyl groups in hyponitrous acid do not compensate in 
 acid-producing power for the absence of an oxy -nitrogen group. 
 
 Since there are two OH groups in hyponitrous acid, this is a dibasic 
 acid, that is to say, it contains two hydrogen atoms which can be dis- 
 placed by metals. 
 
 Classification of acids. Acids are classified into monobasic, dibasic, tribasic, 
 and tetrabasic according as they have one, two, three, or four hydroxyl groups. 
 Nitric acid is monobasic ; N0 2 .OH. Sulphuric acid is dibasic ; S0 2 (OH) 9 . Phos- 
 phoric acid is tribasic ; PO(OH) 3 . Silicic acid is tetrabasic ; Si(OH) 4 . 
 
 On considering these formulas it will be apparent that since - OH is a monovalent 
 radicle (NOg) 1 is a monovalent radicle, for it combines with only one OH. 
 Similarly, (SOg) 11 is a divalent radicle, (PO)" 1 a trivalent, and (Si) iv a tretravalent 
 radicle. 
 
 Normal salts are those in which all the H of the hydroxyl groups is exchanged for 
 metal, as, for instance, in normal potassium sulphate S0 2 (OK) 2 , normal sodium 
 phosphate P(ONa) 3 . Acid salts are those in which only part of the hydrogen has 
 been exchanged for the metal, as, for instance, acid potassium sulphate, S0 2 OH.OK, 
 diacid sodium phosphate, PO(OH) 2 (ONa). 
 
 In forming a normal salt from a divalent metal, like calcium, and a monobasic 
 acid, like nitric acid, it is necessary to have two molecules of the acid in order to 
 obtain sufficient hydrogen for the metal to displace ; thus Ca will displace the H 
 
 from 2(N0 2 OH) forming -$Q 2 .fy> Ca - Tne trivalent aluminium would require 
 
 2 N0 2 .0x 
 three molecules of nitric acid : N0 2 .0-^A1. A similar process of counterbalanc- 
 
 N0 2 .0/ 
 
 ing occurs when a dibasic acid forms a normal salt with a trivalent element ; thus, 
 aluminium sulphate can only be formed from 2 atoms of Al 1 " and three molecules 
 of H 2 S0 4 : 
 
 s a< ^Al or Al 2 i"(S0 4 ) 3 . 
 
 Basic salts are generally composed of a normal salt and a hydroxide of the 
 metal, as in basic bismuth nitrate Bi (N0 3 ) 3 .2Bi(OH) 3 . 
 
 Double salts are those in which the hydrogen of the hydroxyl has been 
 
 exchanged for different metals, as in potassium-sodium carbonate CO 
 potassium-aluminium sulphate 
 
AMIDES. 105 
 
 Equivalents Of acids and bases. When a metal is substituted for half 
 the hydrogen in water the compound is a hydroxide, e.g., sodium hydroxide Na J OH ; 
 
 OH /OH 
 
 calcium hydroxide Ca" < nTT aluminium hydroxide Al m <r OH. When both 
 
 \OH 
 atoms of hydrogen in water are exchanged for metal an oxide of the metal is pro- 
 
 o /\ 
 
 duced NaONa, or Na 2 0, Ca <Q>Ca, or CaO, A1^-0~)A1, or A1 2 3 . 
 
 When a base neutralises an acid, a salt is formed, a base being either the oxide 
 or the hydroxide of a metal. Thus the three bases, potash (KOH), soda (NaOH), 
 and lime (CaO), neutralise nitric acid in accordance with the equations : 
 
 KOH + HN0 3 = KN0 3 + H 2 ; NaOH + HN0 3 = NaN0 3 + H 2 : 
 56 63 40 63 
 
 CaO + 2HN0 3 = Ca(N0 3 ) 2 + H 2 0. 
 56 126 
 
 From these equations it is seen that 56 parts of KOH, 40 parts of NaOH, and 
 28 parts of CaO are required, respectively, to neutralise 63 parts of nitric acid. 
 Consequently these proportions of these bases are equivalent to each other in 
 neutralising power, and this will hold good towards other acids than nitric acid, 
 thus it will be found that 112 parts of KOH are required to neutralise 98 parts of 
 H 2 S0 4 , and that 80 parts of NaOH and 56 parts of CaO will suffice for the same 
 purpose, the ratio being 56 : 40 : 28, as before. 
 
 ^ The equivalent of a base is the number of grams of it which will neutralise one 
 /gram-molecule of a monobasic acid. 
 
 Again, if the quantity of different acids required to neutralise a given weight of 
 a base be compared, the ratio between the quantities will be found to be constant 
 for every base. Thus 63 parts of nitric acid, 49 parts of sulphuric acid, and 32 
 parts of phosphoric acid are required respectively to neutralise 56 parts by weight 
 of potash. These quantities of these acids are therefore equivalent to each other 
 in neutralising power ; and moreover the same ratio will be found to hold when 
 the acids are used to neutralise 40 parts of NaOH or 56 parts of CaO. 
 
 The equivalent of an acid is the number of grams of it which will neutralise one 
 gram-molecule of potash or soda. 
 
 It will be obvious that when a table of equivalents is constructed the quantity 
 of any acid which must be added to any base to form a neutral salt can be seen 
 at a glance, for this quantity is the equivalent of the acid and of the base 
 respectively. 
 
 For the hydrogen of ammonia there may be substituted potassium, 
 sodium, and a few other metals having a high affinity for oxygen. 
 Thus by passing dry ammonia over gently heated sodium, sodamide, 
 NaNH 2 , is formed ; potassamide, KN"H 2 , is similarly prepared. These 
 are white waxy substances which melt (at 155 and 270 C. respectively) 
 to greenish liquids and partly sublime ; at a red heat they are converted 
 into their elements. Water immediately decomposes them, yielding 
 NaOH, or KOH and NH 3 . 
 
 Compounds containing the amidogen group (NH 2 ) are called amides. 
 When nitrous acid is brought in contact with an amide at the ordinary 
 temperature (in aqueous solution), the amidogen group is exchanged 
 for the hydroxyl of the nitrous acid, and the NH 2 thus removed reacts 
 with the NO of the acid to form N 2 and H 2 O. Thus the simplest 
 amide, hydrogen amide or ammonia NH 2 'H, reacts with nitrous acid to 
 form hydrogen hydroxyl or water: NH 2 'H + NO'OH = HO'H + N 2 + 
 H'OH. This reaction is typical of one which is very commonly 
 employed in organic chemistry for substituting OH for NH 2 . When 
 
' 106 DIAZO-COMPOUNDS. 
 
 it is applied to hydroxylamine, or hydroxyl-amide, NH 2 'OH, it does not 
 occur on exactly the same lines, possibly because hydroxyl-hydroxyl, or 
 hydrogen dioxide, HOOH, which would be the product, is too unstable 
 to be formed under the circumstances. The actual reaction between 
 nitrous acid and hydroxylamine at ordinary temperatures may be 
 represented by the equation NH 2 OH + NOOH = HOH + N 2 + HOH. 
 Since nitrous acid cannot be preserved in aqueous solution its applica- 
 tion for such reactions is effected by generating it at the moment when 
 it is required by dissolving sodium nitrite in the solution to be treated, 
 and adding an acid to liberate nitrous acid from the nitrite. 
 
 In the case of a large number of amides, particularly those derived 
 from organic compounds, when the aqueous solution of the amide is 
 kept cool by ice, no nitrogen is evolved on the addition of nitrous acid. 
 This is because the nitrogen of the amidogen and of the nitrous acid 
 remain combined together to form a group, -N : N*. in which each 
 nitrogen atom is able to attach to itself a monovalent element or 
 radicle. Such a nitrogen group is called a diazo-group, and compounds 
 containing it are called diazo-compouuds. To exemplify the diazo- 
 reaction the following hypothetical equation for the reaction of ammonia 
 on nitrous acid at a low temperature may be written : HvNH 2 + NOOH 
 = HN : N'OH + HOH. The diazo compound represented by the for- 
 mula HN : N'OH has not been obtained, but it will be seen that hypo- 
 nitrous acid may be regarded as formed on this type, HO being exchanged 
 for the left-hand hydrogen atom. A comparison of the formula for 
 hydroxylamine with that for ammonia will at once lead to the con- 
 clusion that the reaction between nitrous acid and hydroxylamine at a 
 low temperature should produce hyponitrous acid ; this is the case, for by 
 mixing cold dilute solutions of hydroxylamine hydrochloride and sodium 
 nitrite, sodium chloride and hydroxylamine nitrite are formed, the 
 latter immediately passing into hyponitrous acid ; by adding acetic 
 acid and silver nitrate the yellow silver hyponitrite is precipitated : 
 (i) HO-NH 9 ,HCl + NaO-NO = NaCl + HO-NH 2 ,HO-NO; ( 2 )HONH 9 + 
 HONO = HO-N : N'OH + HOH. The diazo-compounds which contain 
 hydroxyl readily decompose when the temperature is raised, the products 
 of the decomposition being the same as those which result from the 
 interaction of the original amide with nitrous acid at a high tempera- 
 ture. Thus, if the above experiment be conducted at a high tempera- 
 ture (above 50 C.) nitrous oxide is rapidly evolved, and no hypo- 
 nitrous acid can be detected in the solution. 
 
 Hydrazine, N 2 H 4 . It has already been pointed out that radicles are 
 incapable of a separate existence ; they can, however, unite with them- 
 selves to form compounds. From this point of view hydrogen dioxide 
 is dihydroxyl HO'OH. Diamidogen or hydrazine, H 2 N'NH 2 is another 
 case of this kind ; as noticed at p. 103, it is produced by the reduction 
 of hyponitrous acid (sulphurous acid being the reducing agent), but this 
 is not a convenient method for preparing it. 
 
 To prepare hydrazine, 30 grams of potassium diazomethanedisulphonate (<?. r.) is 
 added in fine powder to a solution made by first saturating a 20 per cent, solution of 
 KOH with S0 2 and then adding 10 grams of KOH. The mixture is warmed until 
 colourless, healed to boiling with 150 c.c. of dil. H 2 S0 4 (i 15), filtered and cooled, 
 whereupon hydrazine sulphate, N 2 H 4 ,H 2 S0 4 crystallises. The sulphate is dissolved 
 in a very little water and mixed with the exact quantity of KOH to convert the 
 H 2 S0 4 into K 2 S0 4 , and with sufficient absolute alcohol to precipitate all the K 2 S0 4 . 
 
HYDKOGEN NITRIDE. 1 07 
 
 After filtration the alcohol is distilled and the temperature is raised to 115 C., 
 whereupon hydrazine hydrate, jS T 2 H 4 ,H 2 0, distils. This is added to a retort con- 
 taining BaO, heated for some hours at 1 10 C., and finally distilled under diminished 
 pressure in a current of hydrogen. A large quantity of hydrazine sulphate must 
 be used for a successful result. 
 
 Hydrazine is a colourless liquid of sp. gr. 1.013 '> ^ boils at 113.5 @. 
 and melts at 1.4 C. It dis^lves in water evolving much heat 
 (37,800 cals. per gram-molecule), forming a hydrate N 2 H 4 ,2H 2 O which 
 passes into N 2 H 4 ,H 2 O if the water is evaporated. The latter hydrate is 
 remarkably stable, resembling the caustic alkalies in many respects 
 but of even more caustic properties ; it is a colourless fuming liquid of 
 sp. gr. ro3, melts at -40 C. and boils at 120 C. It is powerfully 
 alkaline and corrodes cork, rubber, and even glass when heated, so that 
 these materials must be avoided in its manufacture ; hydrazine itself, 
 however, does not attack glass. With acids hydrazine hydrate yields 
 two classes of salts, e.g., N 2 H 4 , HCland N 2 H 4 ,2HC1 ; those with one mole- 
 cular proportion of acid are the more stable. 
 
 Hydrazine and its compounds are powerful reducing agents. 
 
 Hydrogen nitride, azoimlde, hydra-zoic acid, or hydronitrous acid. When hydra- 
 zine hydrate is treated with nitrous acid in a cooled dilute solution it is converted 
 
 into hydrogen nitride, ?> NFL ; H 2 N'NH 2 + NO'OH = ?>NH-i 2HOH. 
 
 This compound is a colourless liquid (b.p. 37 C.), characterised by its explosive- 
 ness and its foul odour. It is distinguished from the other compounds of nitrogen 
 with hydrogen by its acid properties. It dissolves many metals with evolution of 
 hydrogen and production of metallic nitrides, such as Zn 11 (N 3 ) 2 . It has been 
 sought to explain these acid properties by regarding hydrogen nitride as a nitric 
 acid derivative, the nitrogen of which might be supposed to retain an acid bias. 
 It is noticeable that most nitrogen compounds in which the nitrogen is not present 
 as NH 2 , or an equivalent group, have an acid character. 
 
 Hydrogen nitride is only obtained in small quantity by the above reaction. It 
 is most conveniently prepared by the interaction between sodamide and nitrous 
 oxide, sodium nitride, from which the free acid can be obtained, being produced ; 
 NH 2 Na + N 2 0=:N 3 Na + H 2 0. Sodium is gently heated in a porcelain boat con- 
 tained in a combustion tube through which dry ammonia is passed ; when the 
 metal has been completely converted into sodamide. a current of dry N 2 is sub- 
 stituted for the NH 3 , the temperature being raised to about 200 C. The sodium 
 nitride is transferred to a flask and distilled with dilute sulphuric acid. To the 
 dilute solution of N 3 H which distils over silver nitrate is added, whereby silver 
 nitride N 3 Ag is precipitated in a white crystalline form. This is washed and dis- 
 tilled with dilute H 2 S0 4 . A solution containing 27 per cent, of N 3 H is thus 
 obtained ; it is fractionally distilled, and the first fraction is dried over calcium 
 chloride and redistilled. The 27 per cent, solution is a slightly viscid liquid, 
 specifically heavier than water ; it evolves N 3 H at the ordinary temperature, and 
 the vapour gives thick clouds when in contact with ammonia. The acid corrodes 
 the skin and produces giddiness and headache when inhaled. Most of the salts 
 crystallise well, those of silver and mercurous mercury being insoluble ; they are 
 all explosive, except those of the alkali metals. 
 
 There is a remarkable similarity between hydrazoic acid and hydrochloric acid, 
 extending even to their salts which resemble each other in solubility and crystal- 
 line form ; indeed, in the case of sodium nitride the resemblance extends to the 
 salt taste. 
 
 Silver nitride may conveniently be obtained by cautiously warming 1.5 gram of 
 hydrazine sulphate with 4 c.c. of nitric acid of sp. gr. I 3 and passing the N 2 H 
 which is evolved into a solution of AgN0 3 . 
 
IO8 FORMS OF CARBON. 
 
 CARBON. 
 
 C= 12 parts by weight.* 
 
 68. This element is especially remarkable for its uniform presence in 
 organic substances. The ordinary laboratory test by which the chemist 
 decides whether a substance under examination is of organic origin, 
 consists in heating it with limited access of air, and observing whether 
 any blackening from separation of carbon (carbonisation) ensues. 
 
 Few elements are capable of assuming so many different aspects as 
 is carbon. It is met with transparent and colourless in the diamond, 
 opaque, black, and quasi-metallic in graphite or black lead, dull and 
 porous in wood charcoal, and under new conditions in anthracite, coke, 
 and gas-carbon. 
 
 In nature, free carbon may be said to occur in the forms of diamond, 
 graphite, and anthracite (the other varieties of coal containing con- 
 siderable proportions of other elements). 
 
 Apart from its great beauty and rarity, the diamond possesses a 
 special interest in chemical eyes, from its having perplexed philosophers 
 up to the middle of the last century, notwithstanding the simplicity of 
 the experiments required to demonstrate its true nature. The first idea 
 of it appears to have been obtained by Newton, when he perceived its 
 great power of refracting light, and thence inferred that, like other 
 bodies possessing that property in a high degree, it would prove to be 
 combustible (" an unctuous substance coagulated"). When the pre- 
 diction was verified, the burning of diamonds was exhibited as a 
 marvellous experiment, but no accurate observations appear to have 
 been made till 1772, when Lavoisier ascertained, by burning diamonds 
 suspended in the focus of a burning-glass in a confined portion of 
 oxygen, that they were entirely converted into carbonic acid gas. In 
 more recent times this experiment has been repeated with the utmost 
 precaution, and the diamond has been clearly demonstrated to consist 
 of carbon in a crystallised state. 
 
 A still more important result of this experiment was the exact determination of 
 the composition of carbon dioxide, without which it would not be possible to 
 ascertain exactly the proportion of carbon in any of its numerous compounds, since 
 it is always weighed in that form. 
 
 The classical experiments upon the synthesis of carbon dioxide were conducted 
 with the arrangement represented in Fig. 81. 
 
 Within a porcelain tube A, which is heated to redness in a charcoal fire, was 
 placed a little platinum tray, accurately weighed, and containing a weighed quantity 
 of fragments of diamond. One end of the tube was connected with a gas-holder B, 
 containing oxygen, which was thoroughly purified by passing through the tube C, 
 containing potash (to absorb any carbonic acid gas and chlorine which it might 
 contain), and dried by passing over pumice soaked with concentrated sulphuric 
 acid in I) and E. To the other end of the porcelain tube A, there was attached a 
 glass tube F, also heated in a furnace, and containing oxide of copper to convert 
 into carbon dioxide (CO^ gas any carbon monoxide (CO) which might have been 
 formed in the combustion of the diamond. The C0 2 was then passed over pumice 
 soaked with sulphuric acid in G, to remove any traces of moisture, and afterwards 
 into a weighed bulb-apparatus H, containing solution of potash, and two weighed 
 tubes I, K, containing, respectively, solid potash and sulphuric acid on pumice, to 
 guard against the escape of aqueous vapour taken up by the excess of oxygen in its 
 passage through the bulbs H. The increase of weight in H, I, K, represented the 
 
 * Inasmuch as carbon is non-volatile, the volume occupied by one atomic weight of it is 
 not known. 
 
COMBUSTION OF DIAMOND. 
 
 109 
 
 C0. 2 formed in the combustion of an amount of diamond indicated by the loss of 
 weight suffered by the platinum tray, and the difference between the diamond con- 
 sumed and the C0 2 formed would express the amount of oxygen which had com- 
 bined with the carbon. A large number of experiments conducted in this manner, 
 
 Fig-. 81. Exact synthesis of carbonic acid gas. 
 
 both with diamond and graphite, showed that 12 parts of carbon furnished 44 parts 
 of C0 2 , and consumed, therefore, 32 parts of oxygen. 
 
 A convenient arrangement for burning a diamond in oxygen is shown in Fig. 82. 
 The diamond is supported in a short helix of platinum wire A, which is attached to 
 the copper wires B B, passing through the cork C, and connected with the terminal 
 wires of a Grove's battery of five or six cells. The globe having been filled with 
 oxygen by passing the gas down into it till a match indicates that the excess of 
 oxygen is streaming out of the globe, the cork is inserted, and the wires connected 
 with the battery. When the heat developed in the platinum coil 
 by the passage of the current, has raised the diamond to a full ~~i<i 
 
 red heat, the connection with the battery may be interrupted, and **' 
 
 the diamond will continue to burn with steady and intense 
 brilliancy. 
 
 To an observer unacquainted with the satisfactory- 
 nature of this demonstration, it would appear incredible 
 that the transparent diamond, so resplendent as to 
 have been reputed to emit light, should be identical 
 in its chemical composition with graphite (plumbago or black lead), from 
 which, in external appearance, it differs so widely. For this difference 
 is not confined to their colour ; in crystalline form they are not in the 
 least alike, the diamond occurring generally in octahedral crystals, 
 whilst graphite is found either in amorphous masses (that is, having no 
 definite crystalline form), or in six-sided plates which are not geo- 
 metrically allied with the form assumed by the diamond. Carbon, 
 therefore, is dimorphous, or occurs in two distinct crystalline forms. 
 Even in weight, diamond and graphite are very dissimilar, the former 
 having an average specific gravity of 3.5 and the latter of 2.3. Again, 
 
110 DIAMOND AND GRAPHITE. 
 
 a crystal of diamond is the hardest of all substances, whence it is used 
 for cutting and for writing upon glass, but a mass of graphite is soft 
 and easily cut with a knife. The diamond is a non-conductor of elec- 
 tricity, but the conducting power of graphite renders it useful in the 
 electrotype process. 
 
 Diamonds are chiefly obtained from Golconda, Borneo, Kimberley in 
 South Africa, and the Brazils. They usually occur in sandstone rock 
 or in mica slate. The hardness of the diamond renders it necessary 
 to employ diamond-dust for the purpose of cutting and polishing it, 
 which is effected with the aid of a revolving disc of steel, to the surface 
 of which the diamond-dust is applied in the form of a paste made with 
 oil. The crystal in its natural state is best fitted for the purpose of 
 the glazier, for its edges are usually somewhat curved, and the angle 
 formed by these cuts the glass deeply, while the angle formed by 
 straight edges, like those of an ordinary jeweller's diamond, is only 
 adapted for scratching or writing upon glass. Drills with diamond 
 points have been employed in tunnelling through hard rocks. The 
 diamond-dust used for polishing, &c., is obtained from a dark amorphous 
 diamond (Carbonado) found at Bahia in the Brazils; 1000 ounces 
 annually are said to have been occasionally obtained from this source. 
 When burnt, the diamond always leaves a minute proportion of ash of 
 a yellowish colour in which silica and oxide of iron have been detected. 
 A genuine diamond may be known by its combining the three qualities 
 of extreme hardness, enabling it to scratch hardened steel, high specific 
 gravity (3.52), and insolubility in hydrofluoric acid.* Sapphire (A1 2 3 ) 
 is nearly as hard as diamond, but its specific gravity is about 4. 
 
 Although the diamond, when preserved from contact with the air, 
 may be heated very strongly in a furnace, without suffering any change, 
 it is not proof against the intense heat of the discharge taking place 
 between two carbon points attached to the terminal wires of a powerful 
 galvanic battery. If the experiment be performed in a vessel exhausted 
 of air, the diamond becomes converted into a black coke-like mass which 
 closely resembles graphite in its properties. 
 
 Graphite always leaves more ash than the diamond, consisting chiefly 
 of the oxides of iron and manganese, with particles of quartz, and some- 
 times titanic oxide. The purest specimens are those of compact amor- 
 phous graphite from Borrowdale in Cumberland ; an inferior variety, 
 imported from Ceylon, is crystalline, being composed of hexagonal 
 plates. Graphite is obtained artificially in the manufacture of cast 
 iron : in some cases, a portion of the carbon of the cast iron separates 
 in cooling, in the form of crystalline scales of graphite, technically 
 called kish. In the grey variety of cast iron these scales of graphite 
 are diffused through the mass of the metal, and are left undissolved 
 when the iron is dissolved by an acid. 
 
 Graphite is far more useful than the diamond, for, in addition to its 
 application in black-lead pencils, and for covering the surface of iron in 
 order to protect it from rust, it is largely employed, in admixture with 
 
 * Artificial diamonds have been made by dissolving amorphous carbon in molten iron 
 heated to nearly 3000 C. in the electric furnace, and suddenly cooling the metal by pouring- 
 it into molten lead. In this way only the surface of the globules of iron is immediately 
 solidified. The interior expands as it cools and creates that pressure on the carbon it contains, 
 which appears to be essential to the formation of diamond. By dissolving the iron in. adds 
 the diamonds are left. They are never comparable with the natural product. 
 
CHARCOAL. Ill 
 
 clay, for the fabrication of the plumbago crucibles (blue pots), which are 
 so valuable to the metallurgist for their power of resisting high tem- 
 peratures and sudden change of temperature. Graphite is also some- 
 times employed for lubricating, to diminish friction in machinery, and 
 hr facing or imparting a glazed surface to gunpowder. 
 
 Inferior kinds of graphite are treated by Profile's process. The graphite is 
 heated with 2 parts of sulphuric acid and iV^h or -jVtii o f potassium chlorate. A 
 part of the graphite is thus oxidised and converted into graphitic acid, C 11 H 4 5 . 
 When the graphite so treated is washed, dried, and heated to redness, the graphitic 
 acid is decomposed, evolving steam and carbonic oxide gas, which swells up the 
 graphite to a light voluminous powder which can be separated from the heavy 
 earthy impurities by floating it in water. When much silica is present in the 
 graphite, a little sodium fluoride is added after the potassium chlorate has been 
 decomposed. 
 
 (Anthracite and the other varieties of coal will be described in a 
 separate section.) 
 
 69. Several varieties of carbon (" pseudo-carbons "), obtained by 
 artificial processes, are employed in the arts. The most important of 
 these are lamp black, wood charcoal, and animal charcoal. 
 
 Lamp black approaches more nearly in composition to pure carbon 
 than either of the others, and is the soot obtained from the imperfect 
 combustion of resinous and tarry matters (or of highly bituminous 
 coal), from which source it derives the small quantities of resin, nitro- 
 gen, and sulphur which it contains. The uses of this substance, as an 
 ingredient of pigments, of printing-ink, and of blacking, depend evi- 
 dently more upon its black colour than upon its chemical properties. 
 Diamond black is a very pure variety of lamp black obtained by the 
 imperfect combustion of the natural hydrocarbon gas of the Ohio- 
 petroleum region. Spanish black is charcoal made from waste cork. 
 
 Wood charcoal presents more features which arrest the attention of 
 the chemist, as well on account of its specific properties as of the 
 influence exercised by the method adopted for obtaining it, upon 
 its fitness for the particular purpose which it may be destined to 
 serve. 
 
 If a piece of wood be heated in an ordinary fire, it is speedily con- 
 sumed, with the exception of a grey ash consisting of the incombustible 
 mineral substances which it contained ; if the experiment were per- 
 formed in such a manner that the products of combustion of the wood 
 could be collected, these would be found to consist of carbonic acid gas- 
 and water ; woody fibre is composed of carbon, hydrogen, and oxygen 
 in the proportion represented by the formula C 6 H 10 5 , and when it is 
 burnt, the oxygen, in conjunction with more oxygen derived from the 
 air, converts the carbon and hydrogen into carbon dioxide and water. 
 But if the wood be heated in a glass tube, closed at one end, it will be 
 found impossible to reduce it, as before, to an ash, for a mass of char- 
 coal will remain, having the same form as that of the piece of wood ; in 
 this case, the oxygen of the air not having been allowed free access to> 
 the wood, no true combustion has occurred, but the wood has under- 
 gone destructive distillation, that is, its elements have arranged them- 
 selves, under the influence of the high temperature, into different forms 
 of combination, for the most part simpler in their chemical composition 
 than the wood itself, and capable, unlike the wood, of enduring that 
 temperature without decomposition ; thus, it is merely an exchange of 
 
112 
 
 DESTRUCTIVE DISTILLATION OF WOOD. 
 
 an unstable for a stable equilibrium of the particles of matter com- 
 posing the wood. 
 
 (DEFINITION. Destructive distillation is the resolution of a complex 
 substance into simpler vapours and gases under the influence of heat, 
 out of contact with air.) 
 
 The vapours issuing from the mouth of the tube will be found acid 
 to blue litmus-paper ; they have a peculiar odour, and readily take fire 
 on contact with flame. These will be more particularly noticed here-- 
 after, as they contain some very useful substances. The charcoal which 
 is left is not pure carbon, but contains considerable quantities of oxygen 
 and hydrogen with a little nitrogen, and the mineral matter or ash of 
 the wood. 
 
 When the charcoal is to be used for fuel, it is generally prepared by 
 a process in which the heat developed by the combustion of a portion 
 
 of the wood is made to effect 
 the charring of the rest. With 
 this view the billets of wood 
 are built up into a heap 
 (Fig. 83) around stakes driven 
 into the ground, a passage 
 being left so that the heap 
 may be kindled in the centre. 
 This mound of wood, which 
 is generally from ^o to qo 
 
 Fig. 83-Charcoal heap. feet & in di a me ter, closely 
 
 covered with turf and sand, except for a few inches around the base, 
 where it is left uncovered to give vent to the vapour of water expelled 
 from the wood in the first stage of the process. When the heap has 
 been kindled in the centre, the passage left for this purpose is carefully 
 closed up. After the combustion has proceeded for some time, and it 
 is judged that the wood is perfectly dried, the open space at the base 
 
 is also closed, and the heap 
 left to smoulder for three or 
 four weeks, when the wood is 
 perfectly carbonised. 
 
 Upon an average, 2 2 parts 
 of charcoal are obtained by 
 this process from 100 of 
 wood. 
 
 On the small scale, the 
 operation may be conducted 
 
 Fig. ^-Distillation of wood. in a S laSS retort > as shown in 
 
 Fig. 84, where the water, tar, 
 
 and naphtha are deposited in the globular receiver, and the inflammable 
 gases are collected over water. 
 
 During the destructive distillation the hydrogen and oxygen of the 
 wood are for the most part expelled in the forms of wood naphtha 
 (CH 4 0), pyroligneous acid (C 2 H 4 2 ), carbon dioxide, carbon monoxide, 
 water, &c., leaving a residue containing a much larger proportion of 
 carbon than that contained by the original wood. 
 
 Much attention has been paid to the manufacture of charcoal for gunpowder (a 
 mixture of charcoal, sulphur, and saltpetre), and it has been found that the higher 
 
CHARCOAL FOR GUNPOWDER. 113 
 
 the temperature to which the charcoal is exposed in its preparation, the larger the 
 proportion of hydrogen and oxygen expelled, and the more nearly does the charcoal 
 approach in composition to pure carbon ; but it is not found advantageous in 
 practice to employ so high a temperature, since it yields a dense charcoal of difficult 
 combustibility, and therefore less fitted for the manufacture of powder. The 
 average composition of wood, exclusive of ash, is, in 100 parts 50 parts carbon, 
 6 parts hydrogen, and 44 parts oxygen. 
 
 The composition of the charcoal prepared at different temperatures is given in 
 the following table : 
 
 Temperature 
 of Cli irring. 
 
 C.irbou. 
 
 Hydrogen. 
 
 Oxygen. 
 
 Ash. 
 
 270 C. 
 
 71.0 
 
 4.60 
 
 23.00 
 
 1.40 
 
 363 
 
 80. 1 
 
 3-71 
 
 14-55 
 
 1.64 
 
 476 
 
 85.8 
 
 3-13 
 
 9-47 
 
 i. 60 
 
 519 
 
 86.2 
 
 3-" 
 
 9.11 
 
 i..<8 
 
 The charcoal employed for black gunpowder in this country is prepared at tem- 
 peratures between 360 C. and 520 C. It will be seen that the proportion of 
 carbon, upon which the heating value of the charcoal depends, increases with the 
 final temperature of carbonisation ; but it has been found that the rapidity with 
 which the temperature is raised has also a great effect in increasing the proportion 
 of carbon, as shown in the following table : 
 
 Final 
 Temperature. 
 
 Time of 
 Heating-. 
 
 Percentage 
 of Carliou. 
 
 Final 
 Temperature. 
 
 Time of 
 Heating. 
 
 Percentage 
 of Carbon. 
 
 410 C. 
 414 
 490 
 
 5 hours 
 
 2f 
 
 3i .. 
 
 81.65 
 
 83.14 
 84.19 
 
 490 C. 
 
 Sf 
 
 2f hours 
 
 3f 
 3 
 
 86.34 
 83-32 
 86.52 
 
 The charcoal prepared between 260 and 320 C. has a brown colour (char'bon 
 roux), and since it is more easily inflamed than the black charcoal obtained at 
 higher temperatures, it is used in powders where the proportion of sulphur is 
 reduced. It is prepared by exposing the wood, in an iron cylinder, to the action of 
 high pressure steam heated to about 280 C. Charcoal prepared at low tempera- 
 tures gives somewhat higher velocities to gunpowder in which it is used, but 
 absorbs much more moisture than that prepared at high temperatures. 
 
 Light woods, such as alder, willow, and dogwood,* are selected for the preparation 
 of charcoal for gunpowder, because they yield a lighter and more easily combus- 
 tible charcoal, dogwood being employed for the best quality of powder for small 
 arms. This wood is chiefly imported, since it has not been successfully grown in 
 this country. It is stripped of its bark, and either exposed for a length of time to 
 the air or dried in a hot chamber. Considerable loss of charcoal occurs if damp 
 wood be charred, a portion of the carbon being oxidised by the steam at a high 
 temperature. 
 
 In order to convert the wood into charcoal, i^ cwt. of wood is packed into a 
 sheet-iron cylinder or sl'q) (Fig. 85), one end of which is closed by a tightly-fitting 
 cover, and the other by a perforated plate, to allow of the escape of the gases and 
 vapours expelled during the carbonisation. This cylinder is then introduced into a 
 cylindrical cast-iron retort, built into a brick furnace, and provided with a pipe (L) 
 for the escape of the products, which are usually carried back into the furnace (B) 
 to be consumed. The process of charring occupies from 2\ to 3^ hours, and as soon 
 as it is completed, which is known by the violet tint of the (carbonic oxide) flame 
 
 * Dogwood charcoal is not made from the true dogwood (cornus), but from the alder 
 buckthorn (Ithamnus frangula), commonly called black dogwood. 
 
DEODORISING BY CHARCOAL. 
 
 from the pipe leading into the fire, the slip is transferred to an iron box or ex- 
 tinguisher, where the charcoal is allowed to cool. About 40 Ibs. of charcoal 
 are obtained from the above quantity of wood. Charcoal prepared by this process 
 is spoken of as cylinder charcoal, to distinguish it from pit charcoal, prepared by 
 
 the ordinary process of charcoal burning 
 (Fig. 83), and used for fuse composi- 
 tions, &c., but not for the best gun- 
 powder. The fitness of the charcoal 
 for the manufacture of powder is gener- 
 ally judged of by its physical characters. 
 It is of course desirable that the charcoal 
 should be as free from incombustible 
 matter as possible. The proportion of 
 the ash left by different charcoals varies 
 considerably, but it seldom exceeds 2 
 per cent. This ash consists chiefty of 
 the carbonates of potassium and cal- 
 cium ; it also contains calcium phos- 
 phate, magnesium carbonate, silicate 
 and sulphate of potassium, chloride of 
 sodium, and the oxides of iron and 
 manganese. 
 
 The charcoal is kept for about a, fort- 
 night before being ground for making 
 
 Fig. 85. Charcoal retort. 
 
 gunpowder, for if ground when fresh, before it has absorbed moisture and oxygen 
 from the air, it is liable to spontaneous combustion. 
 
 The infusibility of the charcoal left by wood accounts for its very 
 great porosity, upon which some of its most remarkable and useful 
 properties depend. The application of charcoal for the purpose of 
 " sweetening " fish and other food in a state of incipient putrefaction 
 has long been practised, and more recently charcoal has been employed 
 for deodorising all kinds of putrefying and offensive animal or vegetable 
 matter. This property of charcoal depends upon its power of absorbing 
 into its pores very considerable quantities of the gases, especially of 
 those which are easily absorbed by water. Thus, i cubic inch of 
 charcoal is capable of absorbing about 100 cubic inches of ammonia gas 
 and 50 cubic inches of sulphuretted hydrogen, both which are con- 
 spicuous among the offensive results of putrefaction. This condensation 
 of gases by charcoal is a mechanical effect, and does not involve a 
 chemical combination of the charcoal with the gas ; it is exhibited most 
 powerfully by charcoal which has been recently heated to redness in a 
 closed vessel, and cooled out of contact with air by plunging it under 
 mercury. Eventually, the offensive gases absorbed by the charcoal are 
 chemically acted on by the oxygen of the air in its pores. A cubic inch 
 of wood charcoal absorbs nearly 10 cubic inches of oxygen, and when 
 the charcoal containing the gas thus condensed is presented to another 
 gas which is capable of undergoing oxidation, this latter gas is oxidised 
 and converted into inodorous products. Thus, if charcoal be exposed 
 to the action of air containing sulphuretted hydrogen gas (H 2 S), it 
 condenses within its pores both this gas and the atmospheric oxygen, 
 which slowly converts the H 2 S into sulphuric acid (HjSOJ. The pre- 
 sence of so much air in charcoal renders it, like wood, apparently lighter 
 than water ; when powdered it sinks in water, its true specific gravity 
 varying from 1.4 to 1.9. 
 
 The great porosity of wood charcoal is strikingly exhibited by attaching a piece 
 of lead to a stick of charcoal (Fig. 86), so as to sink it in a cylinder of water, which 
 is then placed under the receiver of the air. pump. On exhausting the air, innumer- 
 
ABSOEPTION OF GASES BY CHARCOAL. 115 
 
 able bubbles will start from the pores of the charcoal, causing brisk effervescence. 
 If a glass tube 16 or 18 inches long be thoroughly tilled with ammonia gas (Fig. 87), 
 supported in a trough containing mercury, and 'a small stick of recently calcined 
 charcoal introduced through the mercury into the tube, the charcoal will absorb the 
 ammonia so rapidly that the mercury will soon be forced up and fill the tube, 
 carrying the charcoal up with it, On removing the charcoal and placing it upon 
 the hand, a sensation of cold will be perceived from the rapid escape of ammonia 
 perceptible by its odour. 
 
 By exposing a fragment of recently calcined wood charcoal under a jar filled with 
 hydrosulphuric acid gas for a few minutes, so that it may become saturated with 
 the gas, and then covering it with a jar of oxygen, the latter gas will act upon 
 the former with such energy that the charcoal will burst into vivid combustion. 
 The jar must not be closed air-tight at the bottom, or the sudden expansion 
 may burst it. Charcoal in powder exposed in a porcelain crucible mav also be 
 
 86. 
 
 Fig. 87. 
 
 employed in the same way. It should be pretty strongly heated in the covered 
 crucible, and allowed to become nearly cool before being exposed to the hydro- 
 sulphuric acid. 
 
 Charcoal prepared from hard woods absorbs the largest volume of gas. Thus 
 charcoal made from the shell of the cocoa-nut will absorb 170 times its volume of 
 ammonia gas and 18 times its volume of oxygen, although its pores are quite 
 invisible, and its fracture exhibits a semi-metallic lustre. 
 
 As the gases which are evolved in putrefaction are of a poisonous 
 character, the power of wood charcoal to remove them acquires great 
 practical importance, and is applied in very many cases ; the charcoal in 
 coarse powder is thickly strewn over matters from which the effluvium 
 proceeds, or is exposed in shallow trays to the air to be sweetened, as in 
 the wards of hospitals, &c. It has even been placed in a flat box of 
 wire gauze to be fixed as a ventilator before a window through which 
 the contaminated air might have access, and respirators constructed on 
 the same principle have been found to afford protection against 
 poisonous gases and vapours. The ventilating openings of sewers in 
 the streets may also be fitted with cases containing charcoal for the 
 same purpose. Water is often filtered through charcoal in order to 
 free it from the noxious and putrescent organic matters which it some- 
 times contains. For all such uses the charcoal should have been re- 
 cently heated to redness in a covered vessel, in order to expel the 
 moisture which it attracts when exposed to the air ; and the charcoal 
 which has lost its power of absorption will be found to regain it in 
 great measure when heated to redness. 
 
 This power of absorption which charcoal possesses is not confined to 
 
Il6 ANIMAL CHAKCOAL. 
 
 gases, for many liquid and solid substances are capable of being removed 
 by that agent from their solution in water. This is most readily traced 
 in the case of substances which impart a colour to the solution, such 
 colour being often removed by the charcoal ; if port wine or infusion of 
 logwood be shaken with powdered charcoal (especially if the latter has 
 been recently heated to redness in a closed crucible), the liquid, when 
 filtered through blotting-paper, will be found to have lost its colour ; 
 the colouring-matter, however, seems merely to have adhered to the 
 charcoal, for it may be extracted from the latter by treatment with a 
 weak alkaline liquid. 
 
 The decolorising power of wood charcoal is very feeble in comparison 
 with that possessed by bone-black or animal charcoal, which is obtained 
 by heating bones in vessels from which the air is excluded. Bones are 
 composed of about one-third of animal and two-thirds of mineral sub- 
 stances, the latter including calcium phosphate, which amounts to 
 more than half the weight of the bone, and a little calcium carbonate. 
 When bone is heated, as in a retort, so that air is not allowed to have 
 free access to it, the animal matter undergoes destructive distillation, 
 its elements carbon, hydrogen, nitrogen, and oxygen assuming other 
 forms, the greater part of the last three elements, together with a 
 portion of the carbon, escaping in different gaseous and vaporous 
 products, while a considerable proportion of the carbon remains behind, 
 intimately mixed with the earthly ingredients of the bone, and con- 
 stituting the substance known as animal charcoal. The great differ- 
 ence between the products of the destructive distillation of bone and 
 of wood deserves a passing notice. If a fragment of bone or a shaving 
 of horn be heated in a glass tube closed at one end, the vapours which 
 are evolved will be found strongly alkaline to test-papers, while those 
 furnished by the wood were acid ; this difference is to be ascribed 
 mainly to the presence of nitrogen in the bone, wood beirg nearly free 
 from that element; it will be found to hold good, as a general rule, 
 that the results of the destructive distillation of animal and vegetable 
 matters containing much nitrogen are alkaline, frcm the presence of 
 ammonia (NH 3 ) and similar compounds, while those furnished by non- 
 nitrogenised substances possess acid characters; the peculiar odour 
 which is emitted by the heated bone is characteristic, and affords us a 
 test by which to distinguish roughly between nitrogenised and non- 
 nitrogenised bodies. 
 
 An examination of the charred mass remaining as the ultimate result 
 of the action of heat upon bone, shows it to contain much less carbon 
 than that furnished by wood, for the bone charcoal contains nearly 
 nine- tenths of its weight of phosphate (with a little carbonate) of 
 calcium ; the consequence of the presence of so large an amount of 
 earthy matter must be to extend the particles of carbon over a larger 
 area, and thus to expose a greater surface for the adhesion of colouring- 
 matters, &c. This may partly help to explain the very great superiority 
 of bone-black to wood charcoal as a decolorising agent, and the explana- 
 tion derives support from the circumstance, that when animal charcoal 
 is deprived of its earthy matter, for chemical uses, by washing with 
 hydrochloric acid, its decolorising power is very considerably reduced. 
 The application of this variety of charcoal is not confined to the chemical 
 laboratory, but extends to manufacturing processes. The sugar refiner 
 
STABILITY OF CHARCOAL. Ii; 
 
 decolorises his syrup by filtering it through a layer of animal charcoal, 
 and the distiller employs charcoal to remove the fusel oil with which 
 distilled spirits are frequently contaminated. 
 
 Carbon is remarkable, among elementary bodies, for its indisposition 
 to enter directly into combination with the other elements, whence it 
 follows that most of the compounds of carbon have to be obtained by 
 indirect processes. This element appears, indeed, to be incapable of 
 uniting with any other at the ordinary temperature, and this circum- 
 stance is occasionally turned to useful account, as when the ends of 
 wooden stakes are charred before being plunged into the earth, when 
 the action of the atmospheric oxygen, which, in the presence of moisture, 
 would be very active in effecting the decay of the wood, is resisted by 
 the charcoal into which the external layer has been converted. Tlie 
 employment of black-lead to protect metallic surfaces from rust i* 
 another application of the same principle. At a high temperature, 
 however, carbon combines readily with oxygen, sulphur, and with some 
 of the metals, and, at a very high temperature, even with hydrogen and 
 nitrogen. The tendency of carbon to combine with oxygen under the 
 influence of heat, is shown when a piece of charcoal is strongly heated 
 at one point, when the carbon at this point at once combines with the 
 oxygen of the surrounding air (forming carbonic acid gas), and the heat 
 developed by this combustion raises the neighbouring particles of carbon 
 to the temperature at which the element unites with oxygen, and thus 
 the combustion is gradually propagated throughout the mass, which is 
 ultimately converted entirely into carbonic acid gas, nothing remaining 
 but the white ash, composed of the mineral substances derived from the 
 wood employed for preparing the charcoal. It is worthy of remark, that 
 if charcoal had been a better conductor of heat, it would not have been 
 so easily kindled, since the heat applied to any point of the mass would 
 have been rapidly diffused over its whole bulk, and this point could 
 not have attained the high temperature requisite for its ignition, until 
 the whole mass had been heated nearly to the same degree ; this is 
 actually found to be the case in charcoal which has been very strongly 
 heated (out of contact with air), when its conducting power is greatly 
 improved and it kindles with very great difficulty. The ignition 
 temperature of carbon (charcoal or coke) appears to be about 400 C. 
 The calorific value of carbon in the form of wood charcoal is represented 
 by the number 8080 that is, i gram of carbon, when burnt so as to 
 form carbonic acid gas, is capable of raising 8080 grams of water from 
 o C. to i 0. 
 
 A given weight of charcoal will produce twice as much available heat 
 as an equal weight of wood, since the former contains more actual fuel 
 and less oxygen, and much of the heat evolved by the wood is absorbed 
 or rendered latent in the steam and other vapours which are produced 
 by the action of heat upon it. The attraction possessed by carbon for 
 oxygen at a high temperature is turned to account in metallurgic 
 operations, when coal and charcoal are employed for extracting the 
 metals from their compounds with oxygen.* 
 
 The unchangeable solidity of carbon is another remarkable feature. 
 
 * Easily reducible oxides, such as oxide of lead, give carbon dioxide when heated with 
 charcoal : 2PbO + C = Pb 2 + CO 2 , but oxides which are not easily reducible, such as oxide 
 of zinc, give carbonic oxide : ZnO + C CO + Zn. 
 
Il8 ALLOTROPIC MODIFICATIONS. 
 
 Only at the temperature (3000 0.) attainable in the electric furnace 
 can carbon be vaporised ; even then it does not appear to pass through 
 the liquid condition. Melted iron and some other fused metals dissolve 
 carbon, but beyond these there is no solvent by the aid of which 
 carbon may be brought into the liquid form by the process of solution ; 
 for although charcoal gradually disappears when boiled with sulphuric 
 and nitric acids, it does not enter into simple solution, but is converted, 
 as will be seen hereafter, into carbon dioxide. 
 
 The very striking difference in properties exhibited by diamond, 
 graphite, and charcoal, lead to the belief that they consist of dissimilar 
 carbon molecules. The investigation of the specific heats and other 
 physical constants of these three varieties indicates that the diamond 
 molecule contains more atoms than the graphite molecule contains, and 
 that the charcoal molecule is still less complex. 
 
 When an element is capable of appearing in two or more forms, having 
 different physical properties, these forms are said to be allotropic. 
 
 (DEFINITION. Allotropy is the assumption of different properties 
 without loss of chemical identity.) 
 
 Such cases, like those of isomerism among the compounds of carbon 
 (see Organic Chemistry), will probably be explained by differences in 
 the position and arrangement of the atoms in the molecule. 
 
 The specific heat of diamond increases with rise of temperature more rapidly than 
 that of any other substance, ranging from 0.113 at ll c - to 0.459 at 985 C. The 
 specific heat of graphite at ordinary temperature is about 0.2. It is worthy of note 
 that graphite is the final form of any kind of carbon which is submitted to a high 
 temperature. Thus it is common to heat carbon rods or plates which are to be 
 used as electrodes and must therefore have the best possible electrical conductivity 
 and power of resisting chemical attack, to the highest attainable temperatures in 
 order to " graphitise " them. 
 
 Pure carbon is prepared with some difficulty ; the charcoal obtained by heating 
 some pure organic substance containing C, H. and O, such as white sugar-candy, 
 in a closed crucible, is heated in a porcelain tube, as strongly as possible, in a 
 current of dry chlorine gas until no more HC1 is produced. The residue in the 
 tube is nearly pure carbon. The carbon deposited when acetylene is passed through 
 a red hot tube is a very pure form. 
 
 70. Carbon is capable of combining with oxygen in two proportioijs, 
 forming the compounds known as carbonic oxide or carbon monoxide 
 (CO) and carbon dioxide (C0 2 ). 
 
 CARBON DIOXIDE OR CARBONIC ACID GAS. 
 C0 2 = 44 parts by weight 2 volumes. 
 
 71. It has been already mentioned that carbonic acid gas is a com- 
 ponent of the atmosphere, which usually contains about 3 volumes of 
 carbonic acid gas in 10,000 volumes of air. The proportion is smaller 
 at high altitudes. It is greater during the night than in the day, since 
 plants only decompose carbon dioxide in daylight. The oleander leaf 
 was found to decompose, on an average, in sunlight, 1108 cubic centi- 
 metres (67.6 cubic inches) of C0 2 per square metre (about n square 
 feet) of leaf -surface, per hour. 
 
 The proportion of CO 2 does not vary materially in the neighbourhood 
 of a town. 
 
 Carbonic acid gas is chiefly formed by the operation of the atmo- 
 spheric oxygen in supporting combustion and respiration. All sub- 
 
SOURCES OF CARBON DIOXIDE. 119 
 
 stances used as fuel contain a large proportion of carbon, which, in the 
 act of combustion, combines with the oxygen, and escapes into the 
 atmosphere in the form of carbonic acid gas. In the process of respira- 
 tion, the carbonic acid gas is formed from the carbon contained in the 
 blood and in the different portion> of the animal frame to which oxygen 
 is conveyed by the blood ; the latter, in passing through the lungs, 
 gives out, in exchange for the oxygen, a quantity of carbonic acid gas 
 produced by the union of a former supply of oxygen with the carbon of 
 the digested food, which has passed into the blood and has not been 
 required for the repair of wasted tissue. This conversion of the carbon 
 of the food into carbonic acid gas will be again referred to ; it will be 
 at once evident that it must be concerned in the maintenance of the 
 animal heat. 
 
 The leaves of plants, under the influence of light, have the power 
 of decomposing the carbon dioxide of the atmosphere, the carbon of 
 which is applied to the production of vegetable compounds forming 
 portions of the organism of the plant, and when this dies, the carbon 
 is restored, after a lapse of time more or less considerable, to the 
 atmosphere, in the same form, namely, that of carbon dioxide, in which 
 it originally existed there. If a plant should have been consumed as 
 food by animals, its carbon will have been eventually converted into 
 carbonic acid gas by respiration ; the use of the plant as fuel, either 
 soon after its death (wood), or after the lapse of time has converted 
 it into coal, will also consign its carbon to the air in the form of 
 carbon dioxide. Even if the plant be left to decay, this process in- 
 volves a slow conversion of its carbon into carbon dioxide by the 
 oxygen of the air. 
 
 Putrefaction and fermentation are also very important processes 
 concerned in restoring to the air, in the form of carbonic acid gas, the 
 carbon contained in dead vegetable and animal matter. Although, in 
 a popular sense, these two processes are distinct, yet their chemical 
 operation is of the same kind, consisting in the resolution of a complex 
 substance into simpler forms, produced by contact with some minute 
 living plant or animal. The discussion of the true nature of the pro- 
 cess (which is even now somewhat obscure) would 
 be premature at this stage, and it will suffice for the 
 present to state that carbonic acid gas is one of the 
 simpler forms into which the carbon is converted 
 by the metamorphosis which ensues so quickly 
 upon the death of animals and vegetables. 
 
 The production of carbon dioxide in combustion, respira- 
 tion, and fermentation, may be very easily proved by 
 experiment. If a dry bottle be placed over a burning wax 
 taper standing on the table, the sides of the bottle will be 
 covered with dew from the combustion of the hydrogen in 
 the wax ; and if a little clear lime-water be shaken in the 
 bottle, the milky deposit of calcium carbonate will in- 
 dicate the formation of carbon dioxide. 
 
 By arranging two bottles, as represented in Fig. 88, and 
 inspiring through the tube A, air will bubble through the 
 lime-water in B, before entering the lungs, and will then 
 be found to contain too little carbon dioxide to produce a 
 milkiness, but on expiring the air, it will bubble through C, and will render the 
 lime-water in this bottle very distinctly turbid. 
 
120 PREPARATION OF CAEBON DIOXIDE. 
 
 If a little sugar be dissolved in eight or ten times its weight of warm (not hot) 
 water, in a flask provided with a cork and delivery tube and a little dried yeast, 
 previously rubbed down with water, added, fermentation will begin in the course of 
 an hour or less, and carbonic acid gas may be collected in a jar standing in a 
 pneumatic trough. 
 
 72. In the mineral kingdom, carbon dioxide is pretty abundant. 
 The gas issues from the earth in some places in considerable quantity, 
 as at Nauheim, where there is said to be a spring exhaling about 
 1,000,000 Ibs. of the gas annually. Many spring waters, those of 
 Seltzer and Pyrmont, for example, are very highly charged with the 
 gas. 
 
 Carbon dioxide is found in the air of soils in larger proportion than 
 in the atmosphere, amounting to 20 or 30, and occasionally even to 
 600, vols. in 10,000. It increases with the temperature, and originates 
 from the decay of vegetable matter. 
 
 But it occurs in far larger quantity in the immense deposits of lime- 
 stone, marble, and chalk, which compose so large a portion of the crust 
 of the globe. Calcium carbonate is also met with in the animal king- 
 dom. Oyster-shells contain 98 per cent, and egg-shells 97 per cent, of 
 it, and pearls contain about two- thirds of their weight. 
 
 The expulsion of the carbonic acid gas from limestone (CaC0 3 ) forms 
 the object of the process of lime burning, by which the large supply of 
 lime (CaO) is obtained for building and other purposes. But if it be 
 required to obtain the carbonic acid gas without regard to the lime, it 
 is better to decompose the carbonate with an acid. 
 
 Preparation of carbonic acid gas. The form of the calcium car- 
 bonate, and the nature of the acid employed, are by no means matters 
 of indifference. If dilute sulphuric acid be poured upon fragments 
 of marble, the effervescence which occurs at first soon ceases, for the 
 surface of the marble becomes coated with the nearly insoluble calcium 
 sulphate, by which it is protected from the further action of the acid 
 
 CaC0 3 + H. 2 S0 4 = CaS0 4 + H 2 + C0 2 ; 
 Marble. Sulphuric Calcium 
 acid. sulphate. 
 
 if the marble be finely powdered, or if powdered chalk be employed, 
 each particle of the carbonate will be attacked. When lumps of 
 calcium carbonate are acted upon by hydrochloric acid, there is no 
 danger that any will escape the action of the acid, for the calcium 
 chloride produced is one of the most soluble salts 
 
 CaC0 3 + 2HC1 = CaCl 2 + H 2 + C0 2 . 
 Marble. Hydrochloric Calcium 
 acid. chloride. 
 
 For the ordinary purposes of experiment, carbonic acid gas is most 
 easily obtained by the action of hydrochloric acid upon small fragments 
 of marble contained either in a two-necked bottle (Fig. n) or in the 
 centre bulb of a Kipp's apparatus (Fig. 89). The gas should be washed 
 by passing it through a little water in a wash-bottle and may be collected 
 by downward displacement. 
 
 When carbon dioxide is required on a large scale it is used in the 
 form of furnace gases, which contain nitrogen from the air and C0 2 
 from the combustion of the fuel ; or of lime-kiln gases, the C0 2 in 
 which is derived from the limestone ; or of fermenting tun gases, con- 
 sisting of nearly pure C0 2 due to the fermentation of sugar. 
 
EXPERIMENTS WITH CARBON DIOXIDE. 
 
 121 
 
 73. Properties of carbon dioxide. Carbonic acid gas is invisible, like 
 the gases already examined, but is distinguished by a peculiar pungent 
 odour, as is perceived in soda-water. It is more than half as heavy 
 
 Fi 8c. Preparation of carbonic acid gas. 
 
 again as atmospheric air, its specific gjavity being 1.529, which causes 
 its accumulation near the floor of such confined spaces as the Grotto del 
 Cane, where it issues, from fissures in the rock. 
 
 The high specific gravity of C0 2 may be shown by pouring it into a light jar 
 attached to a balance, and counterpoised by a weight in the opposite scale (Fig. 90). 
 
 Fig-. 90. 
 
 Another favourite illustration consists in floating a soap-bubble on the surface of 
 a layer of the gas generated in the large jar (Fig. 91), by pouring diluted sulphuric 
 acid upon a few ounces of chalk made into a thin cream. with water. 
 
 If a small balloon, made of collodion, be placed in the jar A (Fig. 92) it will 
 ascend on the admission of carbonic acid gas through the tube B. 
 
122 
 
 EXPERIMENTS WITH CARBON DIOXIDE. 
 
 If smouldering brown paper be held at the mouth of a jar, like that in Fig. 93. 
 the smoke will float upon the surface of the carbonic acid gas, and will sink with it 
 on removing the stopper. 
 
 The power which carbonic acid gas possesses of extinguishing flame 
 is very important, and has received practical application in the case of 
 
 Fig. 92. 
 
 - 93- 
 
 Fig. 94. 
 
 burning mines which must otherwise have been flooded with water.* 
 Many attempts have also been made from time to time to employ this 
 gas for subduing ordinary conflagrations, but their success has hitherto 
 been very partial. It will be remembered that pure nitrogen is also 
 capable of extinguishing the flame of a taper, but a large proportion of 
 this gas may be present in air without affecting the flame, whereas a 
 
 * All gases which take no pirt in combustion may extinguish flame, even in the presence 
 of air, by absorbing heat and reducing the temperature below the burning -point. 
 
EFFECTS OF CARBON DIOXIDE ON COMBUSTION. , 123 
 
 taper is extinguished in air containing one-eighth of its volume of car- 
 bonic acid gas, and is sensibly diminished in brilliancy by a much 
 smaller proportion of the gas. 
 
 A candle is extinguished in air to which 14 per cent, of its volume of CO., has 
 been added ; 22 per cent, of nitrogen must be added to produce the same effect. 
 The corresponding figures for a coal-gas flame are 33 % and 46 % ; and for a 
 hydrogen flame 58 % and 70 %. 
 
 The power of extinguishing flame, conjoined with the high density of carbonic 
 acid gas, admits of some very interesting illustrations. 
 
 Carbon dioxide may be poured from some distance upon a candle, and will 
 extinguish it at once.' By using a gutter, made of thin wood or stiff paper, to 
 conduct the gas to the flame, it may be extinguished from a distance of several 
 feet. 
 
 A large torch of blazing tow may be plunged beneath the surface of the carbonic 
 acid gas in the jar (Fig. 91). 
 
 Carbon dioxide may be raised in a glass bucket (Fig. 93) from a large jar, 
 and poured into another jar, the air in which has been previously tested with a 
 taper. 
 
 A wire stand with several tapers fixed at different levels may be placed in the 
 jar A (Fig. 94), and carbon dioxide gradually admitted through a flexible tube con- 
 nected with the neck of the jar, from the cistern B, a hole in the cover of which 
 allows air to enter it as the gas flows out ; the flame of each taper will gradually 
 expire as the surface of the gas rises in the jar. 
 
 A jar of oxygen may be placed over a jar of C0 2 , as shown in Fig. 51, and a 
 taper let down through the oxygen, in which it will burn brilliantly, into the C0 2 , 
 which extinguishes it, and if it be quickly raised again into the oxygen, it will 
 rekindle with a slight detonation. This alternate extinction and rekindling may 
 be repeated several times. 
 
 On account of this extinguishing power of carbonic acid gas, a taper 
 cannot continue to burn in a confined portion of air until it has 
 exhausted the oxygen, but only until its combustion has produced a 
 sufficient quantity of carbon dioxide to extinguish the flame.* 
 
 To demonstrate this, advantage may be taken of the circumstance that phos- 
 phorus will continue to burn in spite of the presence of carbonic acid gas. Upon 
 the stand A (Fig. 95) a small piece of phosphorus is placed, and a taper attached to 
 the stand by a wire. The cork B fits air-tight into the jar, and carries a piece of 
 copper wire bent so that it may be heated by the flame of 
 the taper. A little water is poured into the plate to pre- 
 vent the entrance of any fresh air. If the taper be kindled, 
 and the jar placed over it, the flame will soon die out ; 
 and on moving the jar so that the hot wire may touch the 
 phosphorus, its combustion will show that a considerable 
 amount of oxygen still remains. 
 
 In the same manner, an animal can breathe a 
 confined portion of air only until he has charged 
 it with so much carbonic acid gas that the hurtful 
 effect of this gas begins to be felt, a considerable quantity of oxygen 
 still remaining. 
 
 If the air contained in the jar A (Fig. 96), standing over water, be breathed two 
 or three times through the tube B, a painful sense of oppression will soon be felt 
 in consequence of the accumulation of carbonic acid gas. The air may thus be 
 charged with 10 volumes of carbonic acid gas in 100 volumes, the oxygen becom- 
 ing reduced to about one-half its original quantity. By immersing a deflagrating 
 spoon C, containing a piece of burning phosphorus, and having a lighted taper 
 attached, it may be shown that, although there is enough carbonic acid gas to 
 
 * When the taper is extinguished, the air contains in 100 volumes 18^ volumes of oxygen 
 And 2 volumes of carbonic acid ya. 
 
124 
 
 RESPIRATION. 
 
 Fig. 96. 
 
 extinguish the taper, the oxygen is not exhausted, for the phosphorus continues to 
 burn rapidly. 
 
 Carbonic acid gas is not poisonous when taken into the stomach, but 
 acts most injuriously when breathed, by offering an obstacle to the 
 
 escape of carbonic acid gas, by diffu- 
 sion^ from the blood of the venous 
 circulation in the lungs, and its con- 
 sequent exchange for the oxygen 
 necessary to arterial blood. Any 
 hindrance to this interchange must 
 impede respiration, and such hind- 
 rance would of course be afforded by 
 carbonic acid gas present in the air 
 inhaled, in proportion to its quantity. 
 There is evidently a distinction be- 
 tween air which has had carbon 
 dioxide added to it and air in which 
 there is a like amount of carbon 
 dioxide produced by respiration. Thus 
 air which has had its content of carbon 
 dioxide raised to i per cent, by addi- 
 tion of the gas may be breathed with 
 impunity, but if there be this propor- 
 tion present as a result of respiration the effect on most persons would 
 be very deleterious. 
 
 Notwithstanding the many attempts which have been made to trace some other 
 product of respiration which might account for the harmful character of expired 
 air, there is still no satisfactory explanation of the observation that the air of a 
 room becomes progressively more unwholesome as the carbon dioxide in it is 
 increased by respiration. It has often been stated, and the statement has as often 
 been controverted, that a specific poison accompanies the products of respiration. It 
 is more probable that the oppressive character of a close room is due to other exhala- 
 tions from the body, and is not really an effect of the carbon dioxide of the breath. 
 
 It is agreed amongst those who concern themselves with ventilation 
 that the percentage of carbon dioxide in the air of a room or building 
 is an index of the wholesomeness of the air. Thus it is considered 
 inadvisable to breathe for any length of time in air containing more 
 than TO volumes of CO 2 in 10,000 volumes (o.i per cent.). The air of 
 a room contains too much C0 2 if half a measured ounce of lime-water 
 becomes turbid when shaken in a half -pint bottle of the air. 
 
 When the carbon dioxide amounts to 50 volumes per 10,000 volumes 
 of air (0.5 per cent.) most persons are attacked by the languor and 
 headache attending bad ventilation. A large proportion of carbonic 
 acid gas produces insensibility, and air containing 20 per cent, of its 
 volume causes suffocation. The danger in entering old wells, cellars, 
 and other confined places, is due to the accumulation of this gas, either 
 exhaled from the earth or produced by decay of organic matter. The 
 ordinary test applied to such confined air by introducing a candle is 
 only to be depended upon if the candle burns as brightly in the con- 
 fined space as in the external air ; should the flame become at all dim, 
 it would be unsafe to enter, for experience has shown that combustion 
 may continue for some time in an atmosphere dangerously charged 
 with carbonic acid gas. 
 
VENTILATION. 
 
 125 
 
 The accidents from choke damp and after damp in coal mines, and 
 from the accumulation, in brewers' and distillers' vats, of the carbonic 
 acid gas resulting from fermentation, are also examples of its fatal effect. 
 
 The air issuing from the lungs of a man at each expiration contains 
 from 4 to 4.5 volumes of carbonic acid gas in 100 volumes of air, and 
 could not, therefore, be breathed again without danger. The total 
 amount of carbonic acid gas evolved by the lungs and skin amounts to 
 about 0.7 cubic foot per hour. Adding this to the carbonic acid gas 
 already present in the air (say 0.04 per cent.), the total should be dis- 
 tributed through at least 3500 cubic feet, in order that it may be 
 breathed again with perfect safety, that is, in order that the CO.,, 
 which is regarded as the indicator, should not exceed 0.06 per cent, 
 by volume. Hence the necessity for a constant supply of fresh 
 air by ventilation, to dilute the expired air to such an extent that 
 it may cease to impede respiration. This becomes the more neces- 
 sary where a demand is made on the atmospheric oxygen by candles 
 or gas-lights. An ordinary gas-burner consumes at least 3 cubic 
 feet of gas per hour, which requires rather more than its own 
 
 Fig. 97. 
 
 Fig. 
 
 Fig. 99. 
 
 volume of oxygen for combustion, and produces about 1.7 cubic foot of 
 carbonic acid gas. Fortunately, a natural provision for ventilation 
 exists in the circumstance that the processes of respiration and com- 
 bustion, which contaminate the air, also raise its temperature, thus 
 diminishing its specific gravity by expansion, and causing it to ascend 
 and give place to fresh air. Hence the vitiated air always accumulates 
 near the ceiling of an apartment, and it becomes necessary to afford it 
 an outlet by opening the upper sash of the window, since the chimney 
 ventilates immediately only the lower part of the room. 
 
 These principles may be illustrated by some very simple experiments. 
 
 Two quart jars (Fig. 97) are rilled with carbonic acid gas, and after being tested 
 with a taper, a 4-02. flask is lowered into each, one flask containing cold and the 
 other hot water. After a few minutes the jar with the cold flask will still contain 
 enough carbonic acid gas to extinguish the taper, whilst the air in the other jar will 
 support combustion brilliantly. 
 
 A tall stoppered glass jar (Fig. 98) is placed over a stand, upon which three 
 lighted tapers are fixed at different heights. The vitiated air, rising to the top of 
 the jar, will extinguish the uppermost taper first, and the others in succession. By 
 quickly removing the stopper and raising the jar a little before the lowest taper has 
 expired, the jar will be ventilated and the taper revived. 
 
 A similar jar (Fig. 99), with a glass chimney fixed into the neck through a cork 
 
126 
 
 VENTILATION OF MINES. 
 
 or piece of vulcanised tubing, is placed over a stand with two tapers, one of which 
 is near the top of the jar, and the other beneath the aperture of the chimney ; if a 
 crevice for the entrance of air be left between the jar and the table, the lower taper 
 will continue to burn indefinitely, whilst the upper one will soon be extinguished 
 by the carbonic acid gas accumulating around it. 
 
 In ordinary apartments, the incidental crevices of the doors arid 
 windows are depended upon for the entrance of fresh air, whilst the 
 contaminated air passes out by the chimney; but in large buildings 
 special provision must be made for the two air currents. In mines 
 this becomes the more necessary, since the air receives much additional 
 contamination by the gases (marsh-g^s and carbon dioxide) evolved 
 from the workings, and by the smoke occasioned in blasting with 
 gunpowder. Mines are generally provided with two shafts for venti- 
 lation, under one of which (the upcast shaft) a fire is maintained to 
 produce the upward current, which carries off the foul air, whilst the 
 fresh air descends by the other (downcast shaft). The current of fresh 
 
 Fig. 100. 
 
 air is forced by wooden partitions to divide itself, and to pass through 
 every portion of the workings. 
 
 The operation of such provisions for ventilation is easily exhibited. 
 
 A tall jar (Fig. 100) is fitted with a ring of cork, carrying a wide glass chimney 
 (A). If this be placed over a taper standing in a plate of water, the accumulation 
 of vitiated air will soon extinguish the taper ; but if a second chimney (B), sup- 
 ported in a wire ring, be placed within the wide chimney, fresh air will enter 
 through the interval between the two, and the smoke from a piece of brown 
 paper will demonstrate the existence of the two currents, as shown by the 
 arrows. 
 
 A small box (Fig. 101) is provided with a glass chimney at each end. In one of 
 these (B) representing the upcast shaft, a lighted taper is suspended. A piece of 
 smoking brown paper may be held in each chimney to show the direction of the 
 current. On closing A with a glass plate, the taper in B will be extinguished, the 
 entrance of fresh air being prevented. By breathing gently into A the taper will 
 also be extinguished. The experiment may be varied by pouring carbon dioxide 
 and oxygen alternately into A, when the taper will be extinguished and rekindled 
 by turns. 
 
 A pint bell- jar (Fig. 102) is placed over a taper standing in a tray of water. If a 
 chimney (a common lamp-glass) be placed on the top of the jar, the flame of the 
 taper will gradually die out, because no provision exists for the establishment of the 
 two currents, but on dropping a piece of tinplate or cardboard into the chimney so 
 
SODA WATER. 
 
 127 
 
 as to divide it, the taper will be revived, and the smoke from the brown paper will 
 distinguish the upcast from the downcast shaft. 
 
 If a little water be poured into a wide-mouthed bottle of carbon 
 dioxide, and the bottle be then firmly closed by the palm of the hand, 
 it will be found, on shaking the bottle violently, that the gas is 
 absorbed, and the palm of the hand is sucked into the bottle. The 
 presence of carbonic acid in the solution may be proved by pouring it 
 into lime-water, in which it will produce a precipitate of calcium car- 
 bonate, redissolved by a further addition of the solution of carbonic 
 acid. 
 
 One pint of water shaken in a vessel containing carbonic acid gas, at 
 the ordinary pressure of the atmosphere, and at the ordinary tempera- 
 ture, will dissolve about one pint of the gas, equal in weight to nearly 
 1 6 grains. If the gas be confined in the vessel under a pressure equal 
 to twice or thrice that of the atmosphere that is, if twice or thrice 
 the quantity of gas be compressed into the same space the water will 
 still dissolve one pint of the gas, but the weight of this pint will now 
 be twice or thrice that of the pint of uncompressed gas, so that the 
 water will have dissolved 32 or 48 grains of the gas, accordingly as the 
 pressure had been doubled or trebled. As soon, however, as the pres- 
 sure is removed, the compressed carbonic acid gas will resume its 
 former state, with the exception of that portion which the water is- 
 capable of retaining in solution under the ordinary pressure of the- 
 atmosphere. Thus, if the water had been charged with carbonic acid 
 gas under a pressure equal to thrice that of the atmosphere, and had 
 therefore absorbed 48 grains of the gas, it would only retain 16 grains 
 when the pressure was taken off, allowing 32 grains to escape in 
 minute bubbles, producing the appearance known as effervescence. This 
 affords an explanation of the properties of soda-water, which is prepared 
 by charging water with carbonic acid gas under considerable pressure,, 
 and rapidly confining it in strong bottles. As soon as the resistance 
 offered by the cork to the expansion of the gas is removed, the excess 
 above that which the water can hold in solution at the ordinary pressure 
 of the air, escapes with effervescence. In. a similar manner the waters- 
 of certain springs become charged with carbonic acid gas, under high 
 pressure, beneath the surface of the earth, and when, upon their rising 
 to the surface, this pressure is removed, the excess escapes with 
 effervescence, giving rise to the sparkling appearance and sharp flavour 
 which render spring water so agreeable. On the other hand, the 
 waters of lakes and rivers are usually flat and insipid, because they hold 
 in solution so small a quantity of carbonic acid gas. 
 
 The solution of CO., in water is believed to contain the true carbonic 
 acid or hydrogen carbonate, H 2 C0 3 , or CO(OH) 2 , for C0 2 + H 2 = H 2 C0 3 , 
 but there is no direct evidence in support of this view. 
 
 The sparkling character of champagne, bottled beer, <fec., is due to the 
 presence in these liquids of a quantity of carbonic acid gas which has 
 been generated by fermentation subsequent to bottling, and has there- 
 fore been retained in the liquid under pressure. In the case of Seidlitz 
 powders and soda-water powders, the effervescence caused by dissolving 
 them in water is due to the disengagement of carbonic acid gas, by the 
 action of the tartaric acid, which composes one of the powders, upon 
 the bicarbonate of soda composing the other powder, producing tartrate- 
 
128 
 
 LIQUEFACTION OF CAEBON DIOXIDE. 
 
 of soda and carbonic acid gas. In the dry state these powders may be 
 mixed without any chemical change, but the addition of water imme- 
 diately causes the effervescence. Many baking powders are mixtures 
 of this kind, being used for imparting lightness and porosity to bread 
 and cakes, by distending the dough with bubbles of carbonic acid gas. 
 
 The solubility of carbonic acid in water is of great importance in the 
 chemistry of nature ; for this acid, brought down from the atmosphere 
 dissolved in rain, is able to act chemically upon rocks, such as granite, 
 which contain alkalies the carbonic acid attacking these, and thus 
 slowly disintegrating or crumbling down the rock, an effect much 
 assisted by the mechanical action of the expansion of freezing water in 
 the interstices of the rock. It appears that soils are thus formed by 
 the slow degradation of rocks, and when these soils are capable of 
 supporting plants, the solution of carbonic acid is again of service, not 
 only as possibly providing the plant with carbon through its roots, but 
 as a solvent for certain portions of the mineral food of the plant (such 
 as calcium phosphate), which pure water could not dissolve, and which 
 the plant cannot take up except in the dissolved state. 
 
 74. Liquefaction of carbon dioxide. It is generally found that the 
 greater the solubility of a gas in water the more easily the gas can be 
 liquefied ; thus C0 2 is much more easily liquefied than is either hydrogen 
 or oxygen. At about the ordinary temperature (63 F., 17 0.), a 
 pressure of 54 atmospheres (800 Ibs. per square inch) condenses the 
 gas to a colourless liquid of sp. gr. 0.83 (water = i), and boiling-point 
 80 C. If the temperature of the gas is reduced to o C., a pressure 
 of 35 atmospheres suffices to liquefy it. 
 
 Liquid carbon dioxide dissolves in alcohol and in ether, but not in 
 water. When allowed to evaporate rapidly so much heat is absorbed 
 by its passage into the gaseous state that a part of the liquid becomes 
 
 solid carbon dioxide, a 
 
 ( L ... snow-like substance, of 
 
 specific gravity 1.4. 
 
 Q^^><^; =3 The critical tempera- 
 
 ture (p. 29) of carbon 
 
 dioxide is 31 C. It is 
 
 c C~ ' ilJ worthy of note that 
 
 nitrous oxide, which 
 has the same molecular 
 weight as carbon dioxide, 
 has nearly the same 
 critical temperature and 
 boiling-point. 
 
 A small specimen of liquid 
 carbon dioxide is easily pre- 
 pared. A strong glass tube 
 (A, Fig. 103) is selected, 
 about 12 inches long, T \ inch 
 diameter in the bore, and 
 rV inch thick in the walls. 
 Fi - T 3- With the aid of the blow- 
 
 pipe flame this tube is 
 
 softened and drawn off at about an inch from one end. as at B, which is thus closed 
 (C). This operation should be performed slowly, in order that the closed end may 
 not be much thinner than the walls of the tube. When the tube has cooled, 
 
EXPERIMENTS WITH SOLID CARBON DIOXIDE. 
 
 129 
 
 between 30 and 40 grs. of powdered bicarbonate of ammonia (ordinary sesqui- 
 carbonate which lias crumbled down) are tightly rammed into it with a glass rod. 
 This part of the tube is then surrounded with a few folds of wet blotting-paper to 
 keep it cool, and the tube is bent, just beyond the carbonate of ammonia to a some- 
 what obtuse angle (D). The tube is then softened at about an inch from the open 
 end, and drawn out to a narrow neck (E), through which a measured drachm of oil 
 of vitriol is poured down a funnel-tube, so as not to soil the neck, which is then 
 carefully drawn out and sealed by the blowpipe flame, as at F. The empty space in 
 the tube should not exceed cubic inch. 
 
 When the tube is thoroughly cold, it is suspended by strings in such a position 
 that the operator, having retired behind a screen at some distance, may reverse the 
 tube, allowing the acid to flow into the limb containing the carbonate of ammonia ; 
 or the tube may be fixed in a box which is shut up, and reversed so as to bring the 
 tube into the required position. 
 
 If the tube be strong enough to resist the pressure, it will be found, after a few 
 hours, that a layer of liquid C0 2 has been formed upon the surface of the solution 
 of ammonium sulphate. By cooling the empty limb in a mixture of pounded ice 
 and salt, or of hydrochloric acid and sodium sulphate, the liquid can be made to 
 distil itself over into this limb, leaving the ammonium sulphate in the other. 
 
 Liquid C0 2 is now sold in steel cylinders provided with screw valves, like those 
 containing compressed oxygen (Fig. 40). When the cylinder is turned on its head 
 and the valve is opened, the liquid is ejected, and at once solidifies to carbonic 
 acid "snow," which may be collected by surrounding the nozzle with sacking. 
 The solid should be quickly shaken on to a sheet of paper, and emptied into a 
 beaker placed within a larger beaker, the interval being filled up by flannel. By 
 covering the beaker with a dial glass, the solid may be kept for some time. 
 
 The solid carbon dioxide evaporates without melting, for its own evaporation 
 keeps it at a temperature below its melting-point. It produces a sharp sensation of 
 cold when placed upon the hand, and if pressed into actual 
 contact with the skin causes a painful frost-bite. Its rapid 
 evaporation may be shown by placing a few fragments on the 
 surface of water in the globe (Fig. 104), which has a tube pass- 
 ing down to the bottom, through which the pressure of the 
 carbonic acid gas forces the water to a considerable height. 
 
 The solid carbon dioxide is soluble in ether, and it evapo- 
 rates from this solution far more rapidly, because the liquid is 
 a better conductor of heat than the highly porous solid, and 
 abstracts heat more rapidly from surrounding objects. 
 
 It thus lowers the temperature to the boiling-point of C0 2 . 
 
 If a layer of ether be poured upon water, and some solid 
 carbon dioxide be thrown into it, the water is covered with a 
 layer of ice. 
 
 'On immersing the bulb of a thermometer into the solution 
 of solid carbon dioxide in ether, the mercury becomes solid, and 
 the bulb may be hammered out into a disk. 
 
 By placing a piece of filter-paper in an evaporating dish, 
 pouring a pound or so of mercury into it, immersing a wire 
 turned into a flat spiral at the end, covering the mercury with 
 ether, and throwing in some solid carbon dioxide, the mercury, 
 may soon be frozen into a cake. If this be suspended by the 
 wire in a vessel of water, the mercury melts, descending in 
 silvery streams to the bottom of the vessel, leaving a cake of 
 ice on the wire, with icicles formed during the descent of the 
 mercury. This experiment is rendered more effective by using an inverted 
 gas-jar,' to the neck of which is attached, by a perforated cork, a test-tube to 
 catch the mercury. The round lid of a cardboard box gives a nice disk of frozen 
 mercury. 
 
 Even in a red-hot vessel, with prompt manipulation, the mercury may be solidi- 
 fied by the solution of solid carbon dioxide in ether. For this purpose a platinum 
 dish is heated to redness over a large Bunsen burner, a few lumps of carbon dioxide 
 are thrown into it, upon these is held a copper or platinum dish containing the 
 mercury, in which is also held a wire to serve as a handle for withdrawing the 
 mercury. Some more carbon dioxide is thrown upon the mercury, and ether is 
 spirted on to it from a small washing-bottle. One or two additions of the carbon 
 
 Fig-. 104. 
 
130 CARBONATES. 
 
 dioxide and ether alternately will freeze the mercury, which may be withdrawn 
 from the flames by the wire handle. 
 
 Carbon dioxide is advantageously used in freezing-machines on the principle 
 described for ammonia (p. 82) ; for although it absorbs much less heat in passing 
 from the liquid to the gaseous state (about 60 cals. per gram, at 10 C.' as against 
 320 cals. for ammonia), the volume to be pumped per unit weight is much less. 
 
 75. Carbonic acid gas maybe separated from most other gases by the 
 action of potash, which absorbs it, forming potassium carbonate. The 
 proportion of carbonic acid gas is inferred, either from the diminution 
 in volume suffered by the gas when treated with potash, or from the 
 increase of weight of the latter. 
 
 In the former case the gas is carefully measured over mercury (Fig- 105), with 
 due attention to temperature and barometric pressure, and a little concentrated 
 
 solution of potash is thrown up through 
 a curved pipette or syringe, introduced 
 into the orifice of the tube beneath the 
 surface of the mercury. The tube is 
 gently shaken for a few seconds to pro- 
 mote the absorption of the gas, and, 
 after a few minutes' rest, the diminu- 
 tion of volume is read off. Instead of 
 solution of potash, damp potassium 
 hydroxide in the solid state is some- 
 times introduced, in the form of small 
 sticks or balls attached to a wire. To 
 determine the weight of carbonic acid 
 gas in a gaseous mixture, the latter is 
 passed through a bulb-apparatus (H, Fig. 
 81), containing a strong solution of 
 potash, and weighed before and after 
 the passage of the gas. A little tube, 
 containing solid potash, or calcium 
 chloride, or pumice-stone moistened 
 Fip. 105. with sulphuric acid, must be attached 
 
 to the bulb-apparatus, for the purpose 
 
 of retaining any vapour of water which the large volume of unabsorbed gas might 
 carry away in passing through the solution of potash. 
 
 The method for proving the composition of carbon dioxide by weight 
 has been given at p. 109. Its composition by volume is dealt with 
 on p. 136. 
 
 76. Salts formed by carbonic acid. Although so ready to combine 
 with the alkalies and alkaline eirths (as shown in its absorption by 
 solution of potash and by lime-water), carbonic acid must be classed 
 among the weaker acids. It does not neutralise the alkalies completely, 
 and it may be displaced from its salts by most other acids. Its action 
 upon the colouring matter of litmus is feeble and transient. Tf a 
 solution of carbonic acid be added to blue infusion of litmus, a wine-red 
 liquid is produced, which becomes blue again when boiled, losing its 
 carbonic acid; whilst litmus reddened by sulphuric, hydrochloric, or 
 nitric acid, acquires a brighter red colour, which is permanent on 
 boiling. On forcing CO., into solution of litmus at several atmospheres 
 pressure a bright red colour is produced ; but this is not permanent. 
 
 With each of the alkalies carbonic acid forms two well-defined salts, 
 the carbonate and bicarbonate. Thus, the carbonates of potassium and 
 sodium are represented by the formulae, K 3 CO 3 and Na 2 CO 3 , whilst the 
 bicarbonates are KHC0 3 and NaHC0 3 . The existence of the latter 
 
COMPOSITION OF CARBON DIOXIDE. 131 
 
 salts would favour the belief in the existence of the compound H 3 CO 3 , 
 although this has not yet been obtained in the separate state. 
 
 The formula H 2 C0 3 represents carbonic acid as a dibasic acid, that is, 
 an acid containing two atoms of H for which metals may be substituted. 
 
 Carbonates may be normal, acid, or basic. A normal carbonate is 
 one in which all the hydrogen in H 2 C0 3 is exchanged for a metal or 
 metals, as in sodium carbonate, Na 2 CO 3 , and calcium carbonate, CaC0 3 . 
 
 An acid carbonate is one in which only half of the hydrog:n is 
 exchanged for a metal, as in hydrosodium carbonate, JSTaHCO r A 
 basic carbonate is a norm-al carbonate in combination with a hydrate of 
 the metal, as in white lead, basic lead carbonate, 2PbC0 3 .Pb(OH) 2 . 
 
 Perfectly dry carbonic acid gas is not absorbed by pure quicklime (CaO), until it 
 is heated to 35o-4OO C. 
 
 Two hard glass tubes closed at one end, and bent as in Fig. 106, are perfectly 
 dried, and filled, over mercury, with well-dried carbonic acid gas. Fragments of 
 lime are taken, whilst red hut, out of a crucible, cooled under the mercury, inserted 
 
 Fig. 106. 
 
 Fig-. 107. 
 
 into the tubes, and transferred to the upper end. No absorption of the gas occurs, 
 though the tubes be left for some days ; but if one of them be heated by a Bunsen 
 burner, the CO., is rapidly absorbed, and the mercury is forced up into the tube. 
 
 77. To demonstrate the presence of carbon in carbon dioxide, a pellet of 
 potassium is introduced into a bull) tube, through which a current of the gas 
 (dried by passing through oil of vitriol, or over chloride of calcium) is flowing, and 
 the heat of a spirit-lamp is applied to the bulb. The metal soon burns in the gas, 
 which it robs of its oxygen, leaving the carbon as a black mass in the bulb 
 (Fig. 107). The potassium remains in the form of potassium carbonate, 3C0 2 + K 4 = 
 2K CO 3 + C. If slices of sodium be arranged in a test-tube in alternate layers 
 with dried chalk (calcium carbonate), and strongly heated with a spirit-lamp, 
 vivid combustion will ensue, and much carbon will be separated (CaCO 3 + Na 4 = 
 aO + 2Na, 2 + C). 
 
 When C0. 2 is submitted to the action of electric sparks in an apparatus such as 
 that shown in Fig. 72, it expands slightly, having been partially converted into 
 CO + 0, but if the sparking is continued, the mixture explodes to form LO 2 , 
 restoring the original volume of the gas. In a partial vacuum in which the pressure 
 ihe CO 2 is only 5 millimetres nearly 70 per cent, of the C0 2 may be decomposed 
 this way. 
 
 CARBON MONOXIDE OR CARBONIC OXIDE. 
 
 CO = 28 parts by weight = 2 volumes. 
 
 78. The combustion of potassium or sodium in carbon dioxide 
 deprives the gas of all its oxygen, but other metals, which are not 
 
132 
 
 CARBON MONOXIDE. 
 
 endowed with so powerful an attraction for oxygen, do not carry the 
 decomposition of carbon dioxide to its final limit ; thus, iron, zinc and 
 magnesium at a high temperature only deprive the gas of one-half of 
 its oxygen, a result which may also be brought about at a red heat by 
 carbon itself. If an iron tube filled with fragments of charcoal be 
 heated to redness in a furnace (Fig. n), and carbon dioxide be trans- 
 mitted through it, it will be found, on collecting the gas which issues 
 from the other extremity of the tube, that on the approach of a taper 
 the gas takes fire, and burns with a beautiful blue lambent flame, similar 
 to that which is often observed to play over the surface of a clear fire. 
 Both flames, in fact, are due to the same gas, and in both cases this 
 gas is produced by the same chemical change, for, in the tube, the 
 carbon dioxide yields half of its oxygen to the charcoal, both becoming 
 converted into carbonic oxide ; CO 2 + C= aCO. In the fire, the carbon 
 dioxide is formed by the combustion of the carbon of the fuel in the 
 oxygen of the air entering at the bottom of the grate ; and this CO 2 , in 
 passing over the layer of heated carbon in the upper part of the fire, is 
 partly converted into carbonic oxide, which inflames when it meets 
 
 Fig. 108. Reverberatory furnace for copper-smelting-. 
 
 with the oxygen in the air above the surface of the fuel, and burns 
 with its characteristic blue flame, reproducing carbon dioxide.* The 
 carbon monoxide occupies twice the volume of the carbon dioxide from 
 which it was produced. 
 
 This conversion of carbon dioxide into carbon monoxide is of great 
 importance, on account of its extensive application hi metallurgic 
 operations. It is often desirable, for instance, that a flame should be 
 made to play over the surface of an ore placed on the bed or hearth of a 
 reverberatory furnace (Fig. 108). This object is easily attained when the 
 coal affords a large quantity of inflammable gas : but with anthracite 
 coal, which burns with very little flame, and is frequently employed in 
 such furnaces, it is necessary to pile a high column of coal upon the 
 grate, so that the carbon dioxide formed beneath may be convert? d into 
 carbonic oxide in passing over the heated coal above, and when this gas 
 reaches the hearth of the furnace, into which air is admitted, it burns 
 
 * It is stated that when the temperature of a fuel in a furnace has attained 1000 C., the 
 carbon burns directly to carbon monoxide. When cai'bon is heated in partially dried oxygen, 
 carbon monoxide alone is produced, showing that this is the first product of the combustion ; 
 it remains carbon monoxide because the oxygen is too dry to burn it to the dioxide (p. 133). 
 The carbon of gaseous carbon compounds burns tirst to carbon monoxide, which is further 
 oxidi-cd to the dioxide. 
 
PROPERTIES OF CARBONIC OXIDE. 133 
 
 with a flume which spreads over the surface of the ore. It is frequently 
 advantageous to make carbon monoxide in this way in a grate (producer) 
 at some distance from the furnace and to conduct it thither through 
 pipes. (See Chemistry of Fuel.} The temperature of the flame of 
 carbonic oxide burning in air is estimated at about 1400 C. 
 
 The attraction of carbonic oxide for oxygen is turned to account in 
 removing that element from combination with iron in its ores, as will 
 be seen hereafter. 
 
 Dry carbon monoxide will not combine with dry oxygen unless the 
 mixture of gases be very strongly heated. This fact is an instance of 
 the influence which water vapour exercises in chemical combination 
 (compare p. 32). 
 
 It follows that dry carbon monoxide will not burn in dry air or dry oxygen. To 
 demonstrate this fact, carbon monoxide is passed through strong sulphuric acid and 
 kindled at a jet ; the flame is introduced into an inverted gas jar containing 
 ordinary air to show that the combustion will continue in such a vessel ; the air in 
 a similar jar is now dried by shaking strong sulphuric acid in it, the acid is quickly 
 poured out, and the flame introduced into the inverted jar, whereupon combustion 
 immediately ceases. 
 
 Judging by analogy with other elements, whose combination with two atoms of 
 oxygen produces twice as much heat as their combination with one atom, the 
 conversion of C into C0. 2 should produce twice as much heat as its conversion into 
 CO. When C, in the form of charcoal, burns to form G0 2 , each gram of C produces 
 8080 gram units of heat; or C, 12 grams, + 2 , 32 grams, = C0. 2 + 96,960 units 
 of heat. Now carbon cannot be burned directly to form CO, but when CO burns 
 to form CO.,, I gram of CO produces 2403 units of heat ; or CO, 28 grams, + 0, 
 1 6 grams. = C0. 2 + 67.284 units of heat. In the first equation, 16 grams of 
 produce 48,480 units, and in the second 67,284 units of heat. But in the first case, 
 solid carbon is converted into gas, a change of state which must absorb much of 
 the heat produced. If the C were in the state of gas to begin with, in both cases, 
 it is probable that we should have O, 16 grams, + C, 12 grams. = CO + 67,284 
 units of heat, and 2 , 32 grams, + C, 12 grams, = C0 2 + 134,568 units of heat, so 
 that i gram of C would give 11,2 14 units of heat when burned to C0 2 . But when 
 i gram of solid C burns to C0 2 it gives only 8080 units of heat : hence 11,214- 
 8080, or 3134 units, represent the heat required to convert i gram of solid carbon 
 into gas. 
 
 79. Carbonic oxide is very poisonous ; and it appears that the acci- 
 dents which too frequently occur from burning charcoal or coke in 
 braziers and chafing-dishes in close rooms, result from the poisonous 
 effects of the small quantity of carbonic oxide which is produced and 
 escapes combustion, since the amount of carbonic acid gas thus diffused 
 through the air is not sufficient, in mo.vt cases, to account for the fatal 
 result. The carbonic oxide formed in cast-iron stoves diffuses through 
 the hot metal into the air of a room. It is certainly fatal to breathe 
 air | con taming i per cent, of CO, and it is said that so little as 0.05 per 
 cent, may prove fatal. 
 
 80. The poisonous character of carbon monoxide is raised as an 
 objection to the proposed use of this gas for purposes of illumination. 
 The character of the flame of carbonic oxide would appear to afford 
 little promise of its utility as an illuminating agent ; but that it is 
 possible so to employ it is easily demonstrated by kindling a jet of the 
 gas which has been passed through a wide tube containing a little 
 cotton moistened with rectified coal naphtha (benzene), when the 
 carbon monoxide will be found to burn with a very luminous flame. 
 The carbonic oxide destined to be employed for illuminating purposes is 
 prepared by passing steam over white hot coke, a mixture of carbon 
 
134 
 
 PREPARATION OF CARBONIC OXIDE. 
 
 monoxide and hydrogen being thus produced ; C + H 2 = CO + H 2 . 
 The water-gas always contains some carbon dioxide, the quantity being 
 greater the lower the temperature of the coke. This is because at 
 lower temperatures the coke burns in steam to carbon dioxide, not to 
 carbon monoxide; C+ 2H 2 O = CO 2 -f 2H 2 . Water-gas usually consists 
 of about 50 per cent, of H, 40 per cent, of CO, 5 per cent, of CO 2 , and 
 5 per cent, of N (from air and the coke). Since neither hydrogen nor 
 carbon monoxide is possessed of any odour, this mixture would not be 
 detected in the atmosphere of a room where there was a leaky gas- 
 pipe, and the presence of the poisonous carbon monoxide would remain 
 unsuspected. Thus, it becomes incumbent upon those supplying such 
 gas to dwelling-houses to render it, by mixing some gas or vapour with 
 it, at least. as odorous as is ordinary coal-gas, an escape of which is so 
 easily detected. 
 
 The application of water-gas in this country, for illuminating purposes, is at 
 present limited to its admixture with coal-gasj for which purpose it is rendered 
 luminous by hydrocarbons obtained from the destructive distillation of petroleum. 
 
 The decomposition of steam by red-hot carbon "is also taken advantage of in 
 order to procure a flame from anthracite coal when employed for heating boilers. 
 The coal being burnt on fish-bellied bars, beneath which a quantity of water is 
 placed, the radiated heat converts the water into steam, which is carried by the 
 draught into the fire, where it furnishes carbonic oxide and hydrogen, both capable 
 of burning with flame under the bottom of the boiler. The temperature of the 
 bars is also thus reduced, so that they are not so much injured by the intense heat 
 of the glowing fuel. 
 
 81. Carbonic oxide, unlike carbon dioxide, is nearly insoluble in 
 water. It is even lighter than air, its specific gravity being 0.967. 
 In its chemical relations it is an indifferent oxide, that is, it has neither 
 acid nor basic properties. It is liquid below - 190 C. (its boiling- 
 point), and solid at - 211 C. (its melting-point). Its critical tempera- 
 ture is 140 C. These con- 
 stants approximate to tile 
 corresponding constants for 
 nitrogen. 
 
 82. A very instructive process 
 for obtaining carbonic oxide, con- 
 sists in heating crystallised oxalic 
 acid with three times its weight of 
 oil of vitriol. If the gas be col- 
 lected over water (Fig. 109), and 
 one of the jars be shaken with a 
 little lime-water, the milkiness 
 imparted to the latter will indicate 
 abundance oi carbon dioxide ; 
 whilst, on removing the glass plate, 
 and applying a light, the carbonic 
 oxide will burn with its character- 
 istic blue flame. The gas thus obtained is a mixture of equal volumes of carbonic 
 oxide and carbonic acid gases. Crystallised oxalic acid is represented by the formula 
 C 2 H 2 4 .2Aq, and if the water of crystallisation be left out of consideration, its 
 decomposition maybe represented by the equation C 2 H 2 4 =H 2 O + CO + C0 2 , the 
 change being determined by the attraction of the oil of vitriol for water. To obtain 
 pure CO, the mixture of gases must be passed through a bottle containg solution 
 of potash, to absorb the CO 2 (Fig. no). 
 
 But pure CO is much more easily obtained by the action of sulphuric acid upon 
 crystallised potassium ferrocyanide (yellow prussiate of potash) at a moderate heat. 
 Since the gas contains small quantities of sulphurous and carbonic ucid gases, it 
 
 109. 
 
DECOMPOSITION OF CARBON MONOXIDE. 
 
 135 
 
 must be passed through solution of potash if it be required perfectly pure. The 
 chemical change which occurs in this process is expressed thus : 
 
 K 4 C 6 N 6 Fe + 6H. 2 + 6H. 2 S0 4 = 6CO + 2K. 2 S0 4 + 3 <NH 4 ) 2 SO 4 + FeS0 4 
 Pota.-sium Potassium Ammonium Ferrous 
 
 ferrocyanide. sulphate. sulphate. sulphate. 
 
 Ten grams of crystallised ferrocyanide, Avith 135 grams (73 c.c.) of sulphuric acid 
 (sp. gr. 1.84) and 13 grams of water, give about 3^ litres of CO. 
 
 If the boiling is continued after the evolution of CO has ceased', much sulphurous 
 acid gas is disengaged (2FeS0 4 + 2H. 2 S0 4 =:Fe. 2 (SO 4 ) 
 
 Fig-, no. Preparation of carbonic oxide. 
 
 83. To demonstrate the production of C0. 2 during the combustion of CO, a jar of 
 the gas is closed with a glass plate, and after placing it upon the table, the plate is 
 slipped aside and a little lime-water quickly poured into the jar. On shaking, no 
 milkiness indicative of carbonic acid gas should be perceived. The plate is then 
 removed and the gas kindled. On replacing the plate and shaking the jar, an 
 abundant precipitation of calcium carbonate will occur. 
 
 Carbonic oxide forms an explosive mixture with half its volume of oxygen ; if 
 the mixture be absolutely free from vapour of water, it does not explode on passing 
 an electric spark through it. 
 
 When carbonic oxide is passed through a red-hot porcelain tube, a portion of it is 
 decomposed into carbonic acid gas and carbon ; and when the experiment is con- 
 ducted without special arrangements, the carbonic oxide is reproduced as the 
 temperature of the gas falls.* But by passing through the centre of the porcelain 
 tube a brass tube, through which cold water is kept running, the decomposition 
 has been demonstrated by the deposition of carbon upon the cooled tube, and by 
 collecting the carbonic acid gas formed. Carbonic acid gas is also decomposed by 
 intense heat into carbonic oxide and oxygen ; but if these gases be allowed to cool 
 down slowly in contact, they recombine. The gas drawn from the hottest region 
 of a blast-furnace (see Iron), and rapidly cooled, so as to prevent rcombination, was 
 found to contain both carbonic oxide and oxygen. 
 
 When electric sparks are passed through carbon dioxide, about one-third of it 
 becomes CO + 0, but this reaction does not go any further because the CO + begin 
 to recombine. By passing a pellet of phosphorus into the gas and continuing the 
 sparks, all the C0, 2 may be decomposed into CO + 0, for the phosphorus will com- 
 bine with the oxygen, and C0. 2 cannot be reformed. 
 
 The reducing action of carbonic oxide upon metallic oxides, at high temperatures, 
 may be illustrated by passing the pure gas from a bag or gas-holder, first through a 
 bottle of lime-water (B, Fig. ill), to prove the absence of carbonic acid gas, then 
 
 * It is stated that CO heated at 500 C. alwa>s contains a little CO 2 , but no carbon is 
 deposited. If tins be true a lower oxi.te of carbon must be supposed to be fonne-i. 
 
136 COMPOSITION OF THE OXIDES OF CARBON. 
 
 over oxide of copper, contained in the tube C, arid afterwards again through liine- 
 water in D. When enough gas has been passed to expel the air, heat may be applied 
 to the tube by the gauze-burner E. when the formation of carbonic acid gas will be 
 immediately shown by the second portion of lime-water, and the black oxide of 
 copper will be reduced to red metallic copper. 
 
 Fig. in. Reduction of oxide of copper by carbonic oxide. 
 
 If precipitated peroxide of iron be substituted for oxide of copper, iron in the 
 state of black powder will be left, and if allowed to cool in the stream of gas, will 
 take tire when it is shaken out into the air. becoming reconverted into the peroxide 
 (Iron pyroplioi'iis). 
 
 Carbonic oxide is absorbed by potassium hydrate at 100 C., potassium formate 
 being produced: CO + KOH = HCOOK. If carbonic oxide be passed over soda- 
 lime in a glass tube heated by a gas furnace, sodium carbonate is formed, and 
 hydrogen liberated ; CO + 2XaOH = Xa. 2 CO 3 + H 2 . 
 
 84. Composition by volume of carbon monoxide and carbon dioxide. 
 When carbon burns in oxygen, the volume of the carbon dioxide pro- 
 duced is exactly equal to that of the oxygen, so that one volume of 
 oxygen furnishes one volume of carbon dioxide, or, since equal volumes 
 of gases contain the same number of molecules (p. 47), a molecule of 
 carbon dioxide contains a molecule of oxygen. 
 
 When one volume of carbon dioxide (containing one volume of oxygen) 
 is passed over heated carbon, it yields two volumes of carbonic oxide ; 
 hence two volumes, or one molecule, of this gas contain one volume, or 
 half a molecule, of oxygen. 
 
 85. It will be seen in the next few pages that carbon can combine 
 with hydrogen and with chlorine in the sense that one atom of carbon 
 can fix four atoms of hydrogen or of chlorine, but no more. Carbon is 
 therefore the type of the tetravalent elements (p. 1 1 ), and may be con- 
 sidered as exerting its affinity in four directions, >C<. When all of 
 these affinities are satisfied by the affinities of other elements, the carbon 
 will be unable to combine with any other element. Thus, the carbon 
 
 H \ ,/ H 
 
 in the compound y\ will be unable to combine with any more 
 
 ^ X H 
 
 hydrogen or with any chlorine ; this compound, CH 4 , is therefore said 
 to be a saturated compound. It has already been seen that oxygen 
 exerts affinity in two directions, -0 ; consequently one atom of oxygen 
 is equivalent to two atoms of hydrogen in saturating power, and carbon 
 dioxide is a saturated compound, O< >0< >O. On the other hand, 
 carbon monoxide should be an unsaturated compound, >C< >0, and 
 should be capable of combining with other elements in a manner not 
 possible for carbon dioxide. Thus it will be found in the sequel 
 that carbon monoxide is much more chemically active than the 
 
ACETYLENE. 137 
 
 dioxide ; it will combine directly with chlorine to form the compound 
 
 C1 \ 
 
 ^>C < > O, and with many of the metals. The fact that carbon 
 
 CK 
 
 monoxide combines with oxygen with liberation of heat is in itself an 
 
 indication of the residual affinity of the carbon in carbon monoxide. 
 
 COMPOUNDS OF CARBON WITH HYDROGEN. 
 
 86. No two other elements are capable of occurring in so many 
 different forms of combination as are carbon and hydrogen. The hydro- 
 carbons, as these compounds are generally designated, include most of 
 the inflammable gases which are commonly met with, and a great 
 number of the essential oils, naphthas, and other useful substances. 
 There is reason to believe that all these bodies, even such as are found 
 in the mineral kingdom, have been originally derived from vegetable 
 sources, and their history belongs, therefore, to the department of 
 organic chemistry. The three simplest examples of such compounds 
 will, however, be brought forward in this place to afford a general 
 insight into the mutual relations of these two important elements. 
 
 87. Acetylene (C 2 H 2 =26 parts by weight). When very intensely 
 heated, carbon can combine with hydrogen to form acetylene. The 
 necessary temperature is produced by the electric arc, that is, the 
 electrical discharge between two pieces of dense carbon (electrodes) 
 connected with the opposite terminals of a source of electric current, 
 such as a dynamo or a powerful galvanic battery. When this arc is 
 surrounded by an atmosphere of hydrogen some acetylene is formed. 
 The experiment has no practical importance, because but little 
 acetylene is obtained in proportion to the energy employed, but its 
 theoretical interest is very great, since it is the first step in the pro- 
 duction of organic substances by the direct synthesis of mineral 
 elements ; acetylene (C.,H 9 ) being convertible into olefiant gas (C 2 H 4 ), 
 this last into alcohol (C 2 H 6 O) and alcohol into a very large number of 
 organic products. 
 
 The electric arc is, however, used indirectly for the production of 
 acetylene. For this purpose a mixture of lime and carbon, in the form 
 of coke or charcoal, is heated by the arc in order to make calcium car- 
 bide, CaC 2 , an evil smelling, grey, crystalline substance which yields 
 acetylene and slaked lirne when treated with water, CaC., + 2H.,0 = 
 
 In places remote from gas-works, acetylene, made from calcium car- 
 bide and water, is burnt as an illummant instead of coal gas, which it 
 exceeds in illuminating value nearly 1 5-fold. Thus the manufacture of 
 calcium carbide has become an industry and will receive attention in 
 the section devoted to calcium compounds, but a word may be said here 
 about the electric furnace to the development of which in recent years 
 we owe several useful substances beside calcium carbide. 
 
 This furnace is varied in form to suit the particular requirement, 
 but consists in principle of an electric arc, radiation from which is pre- 
 vented by a fire-brick casing. The material to be heated is introduced, 
 .as far as possible, between the electrodes where the temperature may 
 rise as high as 3500 C. This is a much higher temperature than 
 
138 
 
 THE ELECTRIC FURNACE. 
 
 that attainable (about 1500 C.) in any furnace heated with ordinary 
 fuel, and chemical changes occur in the electric furnace which cannot 
 ba otherwise produced. Such a furnace is shown in perspective in 
 Fig. 112. The shell of the furnace A is here cut away to show the 
 position of the carbon electrodes B, which are mounted in metal clamp 
 
 Fi.4 1 . 112. Electric Fnruace. 
 
 carried on slides and connected by leads with the current supply terminals. 
 In series with the electrodes is an electromagmnt E, by means of which 
 the arc may be deflected in any required direction, for example, down 
 into the crucible C containing the body to be heated. The crucible is 
 
 carried on a suitable platform 
 which is raised or lowered by a 
 lever, the handle D of the lever 
 being held by a catch F, when the 
 platform which also forms the 
 bottom of the furnace, is in position. 
 When lowered, platform and cruci- 
 ble can be withdrawn from below 
 the furnace by means of the slide 
 shown in the figure. Fig. 113 
 shows another form of mounting 
 for the carbon electrode, adapted 
 for inserting the carbon through 
 a hole in the lid of the furnace 
 and turning, raising, or lowering it, so as to make any required angle 
 with the other carbon or the crucible. 
 
 Unless calcium carbide is preserved in hermetically sealed vessels it 
 is speedily decomposed by the moisture of the air, and it is to the impure 
 acetylene evolved by this action that the carbide owes its evil odour. 
 
 Fig. 113. 
 
PREPARATION OF ACETYLENE. 139 
 
 This chemical change evolves a considerable amount of heat (28, 500 gram- 
 units of heat per 64 grams of CaC 2 ), a fact which must not be neglected 
 in making acetylene from the carbide ; for the gas is not only explosive 
 when mixed with air or oxygen, as is hydrogen, but explodes by itself 
 when suddenly heated under a pressure of two atmospheres, a pressure 
 which may easily obtain in a carelessly constructed generator. This 
 explosion of the unmixed gas is due to the separation of its elements, 
 C.H 9 = C 2 + H 2 . 
 
 To prepare acetylene in the laboratory 10 grams of calcium carbide 
 are introduced into a flask which is then fitted with a dropping funnel 
 and a delivery tube (Fig. 114). Water* is allowed to drop slowly from 
 the funnel on to the carbide and the gas is collected over water, care 
 being taken that all air is first expelled from the flask by the issuing 
 gas (see above). It will bs noted that the carbide becomes hot and 
 swells, behaving like quicklime when it is slaked to calcium hydroxide, 
 which indeed is the residue left in the flask when all the gas has been 
 evolved. 
 
 On a large scale it is not considered safe to drop water on to the carbide, because 
 the temperature is liable to rise unduly. Instead, the carbide is dropped into water 
 so that there may always he an excess of the latter to absorb the heat and keep the 
 generator cool. Moreover, the excess of water dissolves some of the impurities, 
 ammonia and sulphuretted hydrogen, from the gas. 
 
 The amount of acetylene obtainable from a given weight of pure calcium carbide 
 lias been ascertained by careful analysis, and the result is expressed by the equation 
 CaC 2 +2H 2 = C 2 H 2 + Ca(OH) 2 , that is to say, 40+12x2 = 64 parts 'by weight of 
 CaC 2 yield 12x2+1x2 = 26 parts by weight of C. 2 H 2 . If the parts by weight be 
 grams the acetylene will measure 22.22 litres at 6 C. and 760 mm. (see p. 47). 
 Thus the 10 grains of the carbide used above would yield about 3.5 litres of acetylene. 
 But the commercial carbide is far from pure, and seldom yields more than 80 per 
 cent, of the theoretical volume of acetylene. The impurities in the carbide also 
 evolve gases, the chief of which are the evil smelling phosphoretted hydrogen and 
 sulphuretted hydrogen. To rid the acetylene of the latter it must be passed 
 through a wash-bottle containing caustic soda, and the former is then removed by 
 a second bottle containing nitric acid and cupric nitrate. 
 
 Acetylene is constantly found among the products of the incomplete 
 combustion and destructive distillation of sub.-tances rich in carbon; 
 hence it is always present in small quantity in coal gas. anel may be 
 produced in abundance by passing the vapour of ether through a red- 
 hot tube. Ths character by which acetylene is most easily recognised 
 is that of producing a fine led precipitate (cuprous acetylide) in an 
 ammoniacal solution of cuprous chloride. 
 
 The original process for preparing this precipitate, is that in which the acetylene 
 is produced by the imperfect combustion occurring when a jet of atmospheric air i& 
 allowed to burn in coal gas. 
 
 An adapter (A, Fig. 114) is connected at its narrow end with a pipe supplying: 
 coal gas. The wider opening is closed by a bung with two holes, one of which 
 receives a piece of brass tube (B) about three-quarters of an inch wide and 7 inches 
 long, Avhile in the other is inserted a glass tube (C) which conducts the gas to the 
 bottom of a separating funnel (D). The lower opening of the brass tube B is 
 closed with a cork, through which passes the glass tube E connected with a gas- 
 holder or bag containing atmospheric air. To commence the operation, the gas 
 is turned on through the tube F, and when all air is supposed to be expelled, the 
 tube E is withdrawn, together with its cork, and a light is applied to the lower 
 opening of the brass tube, the supply of coal gas being so regulated that it shall 
 burn with a small flame at the end" of the tube. A feeble current of air is then 
 
 * A saturated solution of salt has been recommended as preferable to pure water ; it has 
 a less euerg-etic action on the carbide, ?o that the temperature does not rise so high. 
 
140 
 
 ACETYLENE FROM IMPERFECT COMBUSTION. 
 
 allowed to issue from the tube E. which is passed up through the flame into the 
 adapter, where the jet of air continues to burn in the coal gas.* and may be kept 
 burning for hours with a little attention to the proportions in which the gas and 
 air are supplied. A solution of cuprous chloride in ammonia is poured into the 
 
 separating funnel through the lateral open- 
 ing G, so that the imperfectly burnt gas may 
 pass through it, when the cuprous acetylide 
 is precipitated in abundance. When a 
 sufficient quantity of precipitate has been 
 formed, or the copper solution is exhausted, 
 the liquid is run out through the stopcock 
 (H) on to a filter, and a fresh portion in- 
 troduced. By heating the precipitate with 
 HC1 acetylene is evolved. 
 
 A solution of cuprous chloride suitable 
 for this experiment is conveniently prepared 
 in the following manner : 500 grains of 
 black oxide of copper are dissolved in 7 
 measured ounces of common hydrochloric 
 acid, in a flask, and boiled for about twenty 
 minutes with 400 grains of copper in filings 
 or fine turnings. The brown solution of 
 cuprous chloride in hydrochloric acid, thus 
 obtained, is poured into about 3 pints of 
 water contained in a bottle ; the white 
 precipitate (cuprous chloride) is allowed to 
 subside, the water drawn off with a siphon, 
 and the precipitate rinsed into a 2O-ounce 
 bottle, which is then quite filled with water 
 and closed with a stopper. When the pre- 
 cipitate has again subsided, the water is 
 drawn off, and 4 ounces of powdered chloride 
 of ammonium are introduced, the bottle 
 being again filled up with water, closed and 
 shaken. The cuprous chloride is entirely 
 dissolved by the chloride of ammonium, 
 but would be precipitated if more water were added. When required for the pre- 
 cipitation of acetylene, the solution may be mixed with about one-tenth of its bulk 
 of strong ammonia (0.880), which may be poured into the separating funnel (D) 
 before the copper solution is introduced. Four measured ounces of the solution 
 are sufficient for one charge, and yield, in three hours, about 3 measured ounces of 
 the moist precipitate. The blue solution of ammoniacal cupric chloride, filtered 
 from the red precipitate, may be rendered serviceable again by being shaken, in a 
 stoppered bottle, with precipitated copper, prepared by reducing a solution of sul- 
 phate of copper, acidified Avith hydrochloric acid, with a plate of zinc. 
 
 If the acetylene copper precipitate be collected on a filter, washed, and 
 dried, either by mere exposure to the air, or over oil of vitriol, it will be 
 found to explode with some violence when gently heated, and it is said 
 that the accidental formation of this compound in copper or bra:?s pipes, 
 through which coal gas passes, has occasionally given rise to explosions. 
 
 When acetylene purified from phosphoretted and sulphuretted hydrogen is passed 
 through solution of nitrate of silver, a white curdy precipitate is formed, resembling 
 chloride of silver in appearance, but insoluble in ammonia (which turns it yellow) 
 as well as in nitric acid. 
 
 It may be more easily prepared by suspending a funnel over a Bunsen burner 
 which has caught fire inside the tube, and drawing the products of imperfect 
 combustion, by means of an aspirator, through a solution of silver nitrate. This 
 precipitate may also be used for the preparation of acetylene, by heating it with 
 hvdrochloric acid. 
 
 Fig. 1 14. 
 Preparation of cuprous acetylide. 
 
 * It is advisable to attach a piece of thin platinum wire to the mouth of the glass tube to 
 reiider the flame of the air more visible. 
 
PROPERTIES OF ACETYLENE. 141 
 
 When this precipitate is washed and allowed to dry, it is violently explosive if 
 heated or struck, particularly when it has been prepared from a slightly ammoniacal 
 solution of nitrate of silver. A minute fragment of it placed on a glass plate, 
 and touched with a red-hot wire, detonates loudly and shatters the glass like ful- 
 minate of silver. In a solution of hyposulphite of gold and sodium, acetylene gives 
 a yellowish, very explosive precipitate. 
 
 The copious formation of acetylene during the imperfect combustion of ether, is 
 very readily shown by introducing a few drops of ether into a test-tube, adding a 
 little ammoniacal solution of cuprous chloride, kindling the ether vapour at the 
 mouth of the tube, and inclining the latter so as to expose a large surface of the 
 copper solution, when a large quantity of the red cuprous acetylide is pi-oduced. If 
 nitrate of silver be substituted for the copper solution, the white precipitate of 
 silver acetylide is formed abundantly. 
 
 Acetylene is a colourless gas having a peculiar odour, which is always 
 perceived where co >1 gas is undergoing imperfect combustion. It burns 
 with an extraordinarily bright smoky flame, best seen by dropping a 
 piece of calcium carbide into a test-tube containing some water and 
 inserting a cork carrying a jet at which the gas may be ignited when 
 all the air has been expelled. Its most remarkable property is that of 
 inflaming spontaneously when brought in contact with chlorine. If a 
 jet of the gas be allowed to pass into a bottle of chlorine, it will take 
 fire and burn with a red flame, depositing much carbon. When 
 chlorine is decanted up into a cylinder containing acetylene standing 
 over water, a violent explosion immediately takes place, attended 
 with a vivid flash, and separation of a large amount of carbon ; 
 
 > 
 
 Water absorbs about its own volume of the gas. The solution smells 
 strongly of the gas, and yields a decided precipitate with ammoniacal 
 cuprous chloride and with silver nitrate. Alcohol is a better solvent 
 for acetylene, while acetone dissolves about 25 times its volume at 
 15 C. Acetylene is liquid at o C. under 38 atmospheres pressure 
 and at 85 C., at 760 mm. ; hence the latter temperature is its boiling- 
 point. The critical temperature is 37 C., and the critical pressure 67 
 atmospheres. Liquid acetylene is colourless and its sp. gr. is 0.45 at o C. 
 
 If the acetylene copper precipitate be suspended in solution of 
 ammonia, and heated with a little granulated zinc, the acetylene com- 
 bines with the (nascent) hydrogen to form olefiant gas (C 2 H 4 ). Further 
 particulars respecting acetylene are given under Organic Chemistry. 
 
 The heat evolved by the combustion of a given weight of acetylene is 
 more than that produced when the same weight of a mixture containing 
 the same proportion of carbon and hydrogen, such as would be obtained 
 by suspending carbon dust in hydrogen, is burnt. This shows that 
 acetylene is an endothermic compound (p. 96). 
 
 When 2.6 grams of CgHg, containing 24 grains of C and 2 grams of H, are burnt, 
 315,000 gram units of heat are evolved ; but when these weights of C and H are 
 burnt separately, or merely mixed together, only 257,000 units are evolved. The 
 difference, + 58,000 units, must be due to the disruption of the combination 
 between the C and H in the acetylene ; that is, the heat of formation of acetylene 
 must be - 58,000. 
 
 When 16 grams of methane, CH 4 . containing 12 grams of C and 4 grams of H, 
 are burnt, 213,000 gram units of heat are evolved. The same weights of C and H, 
 burnt in mixture give 231,000 units. In this case, therefore, 18,000 units of heat 
 must have been absorbed in disuniting the C and H in the methane, so that this 
 compound is exothermic, its heat of formation being + 18,000. 
 
 * It is sav.l that a trace of air is essential for the explosion. 
 
142 OLEFIANT GAS. 
 
 Endothermic compounds are liable to decompose suddenly, or detonate, when 
 subjected to a shock. Thus when a small quantity (o. i gram) of the explosive 
 compound mercuric fulminate is fired in acetylene, the gas explodes, although no 
 oxygen is present other than the small quantity in the fulminate. A similar 
 result follows if a wire heated to about 750 C. is introduced into the gas. These 
 effects are much more marked when the gas is under pressure and extend even to 
 liquid acetylene. 
 
 The explosion of a mixture of acetylene and air or oxygen is all the more violent 
 owing to the endothermic character of acetylene. As the equation for the com- 
 bustion is C 2 H 2 + 5 = 2C0 2 -*-H 2 0, the most explosive mixture is one of 2. volumes 
 of acetylene and 5 volumes of oxygen, or 25 volumes of air. 
 
 88. defiant gas or ethylene (C 2 H 4 = 28 parts by weight). This gas 
 is found in larger quantity than is acetylene, among the products of the 
 action of heat upon coal and other substances rich in carbon, and it is 
 
 an important constituent of the 
 illuminating gases obtained from 
 such materials. 
 
 Olefiant gas may readily be 
 prepared by the action of strong 
 sulphuric acid (oil of vitriol, 
 H.,SO 4 ) upon alcohol (spirit of 
 wine, C 2 H 6 0). 
 
 Two measures of oil of vitriol are 
 introduced into a flask (Fig. 115), and 
 one measure of alcohol is gradually 
 poured in, the flask being agitated 
 after each addition ; much heat is 
 evolved, and there would be danger 
 in mixing large volumes suddenly.* 
 Fig-. 115. Preparation of olefiant gas. On applying a moderate heat, the 
 
 liquid darkens and effervesces and 
 
 the gas may be collected in jars filled with water. When the mixture has become 
 thick, and the evolution of the gas is slow, the end of the tube must be removed 
 from the water and the lamp extinguished. Eighty-five c.c. of spirit of wine 
 generally give about 8 litres of olefiant gas. 
 
 The gas will be found to have a very peculiar odour, in which that of ether and 
 of sulphurous acid gas are perceptible. One of the jars may be closed with a glass 
 plate, and placed upon the table with its mouth upwards : on the approach of a 
 flame, the gas will take fire, burning with a bright white flame characteristic of 
 olefiant gas, and seen to best advantage when, after kindling the gas, a stream of 
 water is poured down into the jar in order to displace the gas. 
 
 Another jar of the gas may be well washed by transferring it repeatedly from one 
 jar to another under water, a little solution of potash may then be poured into it, 
 and the jar violently shaken, its mouth being covered 'with a glass plate ; the 
 potash will remove all the sulphurous acid gas, and the gas will now exhibit 
 the peculiar faint odour which belongs to olefiant gas. 
 
 The purified gas may be transferred, under water, to another jar, kindled, and 
 allowed to burn out ; if a little lime-water be then shaken in the jar, its turbidity 
 will indicate the presence of carbonic acid gas, which is produced together with 
 water, when olefiant gas burns in air, C 2 H 4 + 4 = 2C0 2 + 2H 2 O. 
 
 A somewhat better yield of gas is obtained by boiling syrupy phosphoric acid 
 (sp. gr. 1.75) in a flask and dropping in alcohol slowly, the temperature of the 
 mixture being kept at about 200 C. 
 
 On comparing the composition of olefiant gas (C.,H 4 ) with that of 
 alcohol (C 2 H 6 O), it is evident that the former may be supposed to be 
 produced from the latter by the abstraction of a molecule of water 
 (H 2 0) which is removed by the sulphuric acid, though other secondary 
 changes occur, resulting in the separation of carbonaceous matter and 
 
 * If methylated spirit be employed, the mixture will have a dark, red-brown colour. 
 
EXPERIMENTS WITH ETHYLENE. 
 
 143 
 
 the production of sulphurous acid gas. A more complete explanation 
 of the action of sulphuric acid upon alcohol must be reserved for the 
 chemical history of this compound. 
 
 Olefiant gas derives its name from its property of uniting with 
 chlorine and bromine to form oily liquids, a circumstance which is 
 applied for the determination of the proportion of this gas present in 
 coal gas, upon which part of the illuminating value of coal gas depends. 
 The compound with chlorine (C 3 H 4 C1 3 ) is known as Dutch liquid, having 
 been discovered by Dutch chemists, and is remarkable for its resem- 
 blance to chloroform in odour. 
 
 To exhibit the formation of Dutch liquid, a quart cylinder (Fig. 116) is half filled 
 with olefiant gas, and half with chlorine, which is rapidly passed up into it, from a 
 bottle of the gas, under water. The 
 cylinder is then closed with a glass 
 plate, and supported with its mouth 
 downwards under water in a xepa- 
 nitlng funnel, furnished with a 
 glass stop-cock. The volume of 
 the mixed gases begins to diminish 
 immediately, drop-; of oil being 
 formed upon the side of the cylin- 
 der and the surface of the water. 
 As the drops increase, they fall to 
 the bottom of the funnel. Water 
 must be poured into the funnel to 
 make good that which rises into 
 the cylinder, and when the whole 
 of the gas has disappeared, the oil 
 may be drawn out of the funnel 
 through the stop-cock into a test- 
 tube, in which it is shaken with a 
 little potash to absorb any excess of 
 chlorine. The fragrant odour of 
 the Dutch liquid will then be per- 
 ceived, especially on pouring it out 
 into a shallow dish. 
 
 In applying this principle to the 
 measurement of the illuminating 
 hydrocarbons in coal gas, daylight 
 must be excluded, or an error would 
 be caused by the union of the free 
 hydrogen with the chlorine or bro- 
 mine. The bromine test may be 
 applied in the tube represented in Fig. 117. The gas to be examined is measured 
 over water in the divided limb , with due attention to temperature and pressure ; 
 the tube being held perpendicularly, the limb b will remain filled with water, so 
 that gas cannot escape nor air enter. A drop or two of bromine is poured into 
 this limb, which is then depressed beneath the water in the pneumatic trough, and 
 closed by the stopper c. On shaking the gas with the water and bromine, the 
 latter will absorb the illuminating hydrocarbons ; and if the tube be again opened 
 under water, the volume of the gas in a will be found to have diminished, and the 
 diminution gives an approximate estimate of the olefiant gas and other illuminating 
 hydrocarbons. 
 
 A very instructive experiment consists in filling a three-pint cylinder one-third 
 full of olefiant gas, then rapidly filling it up, under water, with two pints of 
 chlorine, closing its mouth with a glass plate, shaking it to mix the gases, slipping 
 the plate aside and applying a light, when the mixture burns with a red flame 
 which passes gradually down the cylinder, and is due to the combination of the 
 hydrogen with the chlorine, the whole of the carbon being separated in the solid 
 state C 2 H 4 + C1 4 = 4HC1 + C. 2 . 
 
 When olefiant gas is subjected to the action of high temperatures, as 
 
 Fig. 116. 
 
 Fig. n 7 . 
 
I 4 4 
 
 MARSH GAS. 
 
 by passing through heated tubes, one portion is decomposed into marsh 
 gas (CH 4 ) with separation of carbon, acetylene (C 2 H 9 ) and hydrogen 
 being also produced ; this decomposition will be found" to be of great 
 importance in the manufacture of coal gas. 
 
 The action of heat upon olefiant gas is most conveniently shown by exposing it 
 to the spark from an induction-coil in the apparatus shown in Fig. 67. 
 
 The carbon separated during the sparking sometimes forms a conducting com- 
 munication, and allows the current to pass without a spark. This may be obviated 
 by reversing the current, or by gently shaking the tube. 
 
 The olefiant gas w T ill expand to nearly twice its former volume. 
 To show the production of acetylene, another arrangement may be found con- 
 venient (Fig. 118). A globe with four necks is employed; through two of these 
 necks are passed, airtight with perforated corks, the copper wires connected with 
 the induction-coil. A third neck receives a tube, conveying olefiant gas from a 
 gas-holder, whilst from the fourth proceeds a tube dipping 
 to the bottom of a small cylinder. When the whole of the 
 air has been displaced by olefiant gas, a solution of cuprous 
 chloride in ammonia is poured into the cylinder, and the 
 gas allowed to bubble through it, when the absence of 
 acetylene will be shown by there being no red compound 
 formed. As soon, however, as the spark is passed, the red 
 precipitate will appear, and in a very few minutes a large 
 quantity will be deposited. Coal 'gas may be employed 
 instead of olefiant gas, but of course a smaller quantity of 
 the copper compound will be obtained. 
 
 89. Marsh, gas, methane, or light carburetted 
 hydrogen (CH 4 =i6 parts by weight). Thi-< hy- 
 drocarbon is found in nature, being produced 
 wherever vegetable matter is undergoing decom- 
 position in the presence of moisture. The 
 bubbles rising from stagnant pools, when col- 
 lected and examined, are found to contain marsh 
 gas mixed with carbonic acid gas, and there is 
 reason to believe that these two gll ses represent 
 
 olefl:int gas. the principal forms in which the hydrogen and 
 
 oxygen respectively were separated from wood 
 
 during the process of irs conversion into coal. This would account for 
 the constant presence of marsh gas in the coal formations, where it is 
 usually termed fire-damp. It is occasionally found pent up under- 
 pressure between the layers of coal, and the pores of the latter are 
 sometimes so full of it that it may be seen rising in bubbles when the 
 freshly hewn coal is thrown into water. Perhaps a similar origin is to 
 be ascribed to the liquid hydrocarbons chemically similar to marsh gas, 
 which are found so abundantly in Pennsylvania and Canada, and are 
 known by the general name of petroleum. From certain gas-springs 
 in Pennsylvania, marsh gas. olefiant gas, and ethane, C 2 H 6 , are dis- 
 charged at very high pressure, and are employed for heating and lighting. 
 
 Marsh gas is obtained artificially by the folloAring process : 
 
 35 grams of dried sodium acetate are finely powdered and mixed, in a mortar, 
 with 35 grams of the mixture of calcium hydroxide and sodium hydroxide, which 
 is sold as soda-lime. The mixture is heated in a Florence flask (or better a copper 
 tube, for the alkali corrodes the glass) and the gas collected over water. 
 The decomposition will be evident from the following equation : 
 
 NaC 2 H 3 2 + NaOH = Na. 2 C0 3 + CH 4 . 
 Sodium acetate. Caustic sodi. Sodium carbonate. 
 
 The marsh gas will be easily recognised by its burning with a pale illuminating 
 
EXPLOSIONS OF FIRE-DAMP. 145; 
 
 flame, far inferior in brilliancy to those of olefiant gas and acetylene, but unattended 
 with smoke.* 
 
 By heating a mixture of alumina and carbon in the electric furnace, aluminium 
 carbide, A1 4 C 3 , is obtained. This is decomposed by water yielding methane just as 
 calcium carbide yields acetylene-- -A1 4 C 3 + I2H 2 = 3CH 4 + 4A1(OH) 3 (aluminium 
 hydroxide). 
 
 The properties of this gas deserve a careful study, on account of the 
 frequent fatal explosions to which it gives rise in coal-mines, where it is 
 often found accumulated under pressure, and discharging itself with 
 considerable force from the fissures or blowers made in hewing the coal. 
 March gas has no characteristic smell like that of coal gas, and the miner 
 thence receives no timely warning of its presence ; it is much lighter 
 than air (sp. gr. 0.5596), and therefore very readily diffuses itself 
 (page 25) through the air of the mine, with which it forms an explosive 
 mixture as soon as it amounts to one-fourteenth of the volume of the 
 air. The gas issuing from the blower would burn quietly on the 
 application of a light, since the marsh gas is not explosive unless mixed 
 with the air, when a large volume ot the gas is burnt in an instant, 
 causing a sudden evolution of a great deal of heat, and a consequent 
 sudden expansion or explosion exerting great mechanical force. The 
 most violent explosion occurs when i volume of marsh gas is mixed 
 with 2 volumes of oxygen, since this quantity is exactly sufficient to 
 effect the complete combustion of the carbon and hydrogen of the 
 gas, and therefore to evolve the greatest amount of heat : CH 4 + 4 = 
 CO 2 + 2H 2 0. The calculated pressure exerted by the exploding mixture 
 of marsh gas and oxygen amounts to 37 atmospheres, or 555 Ibs. upon 
 the square inch. Since air contains one-fifth of its volume of oxygen f 
 it would be necessary to employ 10 volumes of air to i volume of marsh 
 gas in order to obtain perfect combustion, but the explosion will be 
 much less violent on account of the presence of the 8 volumes of inert 
 nitrogen, the calculated pressure exerted by the explosion being only 
 14 atmospheres, or 210 Ibs. on the square inch. Of course, if more air 
 be employed, the explosion will be proportionally weaker, until, when 
 there are more than 14 volumes of air to each volume of marsh gas, the 
 mixture will be no longer explosive, but will burn with a pale flame 
 around a taper immersed in it. The severity of the explosion of a 
 gaseous mixture depends on the rate at which the chemical combination 
 proceeds throughout the mixture. If, on a certain number of particles- 
 combining, the heat evolved has to be shared between the neighbouring 
 combustible particles and a number of inert particles the temperature 
 of the former may not rise to the ignition point, whereupon propagation 
 of the combination ceases. It must be remembered that an excess of 
 either of the reacting gases also serves as an inert gas. Hence in every 
 explosive mixture there is an upper limit and a lower limit to the propor- 
 tion of the constituents, and it is only between these limits that explosion 
 occurs. In the case of methane and air the explosion only occurs if 
 the methane is mixed with between 6 and 14 times its volume of air. 
 The carbonic acid gas resulting from the explosion is called by miners 
 the after-damp, and its effects are generally fatal to those who may have 
 escaped death from the explosion itself. 
 
 Coal gas, which contains much hydrogen, requires a smaller volume 
 
 * The gas prepared by the above process contains acetone, which increases its luminosity. 
 For the preparation of pure marsh gas, see Organic Chemistry. 
 
 K 
 
146 
 
 DAVY'S SAFETY LAMP. 
 
 of air than does marsh gas to render it explosive. With i6-candle gas, 
 such as is used in London, 6 volumes of air to i volume of gas would 
 give the most powerful explosion, and the limits are about 3.5 and 
 14 volumes of air. 
 
 Fortunately, marsh gas requires a much higher temperature to in- 
 flame it than most other inflammable gases ; a solid body at an ordinary 
 red heat does not kindle the gas unless kept in contact with it for a 
 considerable period ; contact with flame, or with a body heated to white- 
 ness, being required to ignite it instantaneously. 
 
 If two strong gas cylinders be filled, respectively, with mixtures of 2 volumes 
 hydrogen and I volume oxygen, and of I volume marsh gas and 2 volumes oxygen, 
 it will be found, on holding them with their mouths downwards, and inserting a 
 red-hot iron bar that the marsh gas mixture will not explode, but if the bar be 
 transferred at once to the hydrogen mixture there will be an explosion. A lighted 
 taper may then be used to explode the marsh gas and oxygen. 
 
 In consequence of the high temperature required to inflame the mixture of marsh 
 gas and air, it is necessary that the mixture be allowed to remain for an appreciable 
 time in contact with the flame before its particles are raised to the igniting-point. 
 It was on this principle that Stephenson's original safety-lamp was constructed, the 
 flame being surrounded with a tall glass chimney, the rapid draught through which 
 caused the explosive mixture to be hurried past the flame without igniting. 
 
 To illustrate this, a copper funnel holding about two quarts is employed, the 
 neck of which has an opening of about ^ inch in diameter. The funnel being 
 
 placed mouth downwards 
 
 \ in the pneumatic trough, 
 
 the orifice is closed with the 
 finger, and a half-pint of 
 coal gas passed up into the 
 funnel. The latter is now 
 raised from the water, so 
 that it may become entirely 
 filled with air. By depress- 
 ing the funnel to a consider- 
 able depth in the water, the 
 aperture being still closed 
 by the finger, the mixture 
 will be confined under con- 
 siderable pressure, and if a 
 lighted taper be held to the 
 aperture, and the finger 
 Fig. 119. removed, it will be found 
 
 that the mixture sweeps 
 
 past the flame without exploding, until the water has reached the same level in 
 the funnel as in the trough, when the gas comes to rest and explodes with great 
 violence. 
 
 Davy's safety lamp (Fig. 120) is an application of the principle that 
 ignited gas (flame) is extinguished by contact with a large surface of 
 a good conductor of heat, such as copper or iron. 
 
 If a thin copper wire be coiled round into a helix, and carefully placed over the 
 wick of a burning taper (Fig. 121), the flame will be at once extinguished, its heat 
 being so rapidly transmitted along the wire that the temperature falls below the 
 point at which the combustible gases enter into combination with oxygen, and 
 therefore the combustion ceases. If the coil be heated to redness in a spirit-lamp 
 flame before being placed over the wick, it will not abstract the heat so readily, 
 and will not extinguish the flame. If a copper tube were substituted for the coiled 
 wire, the same result would be obtained, and by employing a number of tubes of 
 very small diameter, so that the metallic surface may be very large in proportion to 
 the volume of ignited gas, the most energetic combustion may be arrested, a fact of 
 which advantage is taken in the oxy-hydrogen blow-pipe (p. 48). It is evident that 
 the exposure of a large extent of cooling surface to the action of the flame may be 
 
DAVY'S SAFETY LAMP. 
 
 effected either by increasing the length or by diminishing the width of the metallic 
 tubes, so that wire gauze, which may be regarded as a collection of very short tubes, 
 will form an effectual barrier to flame, provided that it has a sufficient number of 
 meshes to the inch. 
 
 If a piece of iron wire gauze, containing about 400 meshes to the square inch, 
 be depressed upon a flame, it will extinguish that portion with which it is in 
 contact, and the combustible gas which escapes through the gauze may be kindled 
 by a lighted match held on the upper side. By holding the gauze 2 or 3 inches 
 
 Fig. 120. 
 
 Fig. 121. 
 
 Fig. 122. 
 
 above a gas jet, the gas may be lighted above it without communicating the flame 
 to the burner itself. 
 
 When blazing spirit is poured upon a piece of wire gauze (Fig. 122), the flame 
 will remain upon the gauze, and the extinguished spirit will pass through. A little 
 benzene or turpentine may be added to the spirit, so that its flame may be more 
 visible at a distance. 
 
 The safety lamp (Fig. 120) is an oil lamp, the flame of which is sur- 
 rounded by a cage of iron wire gauze, having 700 or 800 meshes in the 
 square inch, and made double at the top, where the heat of the flame 
 chiefly plays. This cage is protected by stout iron wires attached to a 
 ring for suspending the lamp. A brass tube passes up through the oil 
 reservoir, and in this there slides, with con- 
 siderable friction, a wire bent at the top, so that 
 the wick may be trimmed without taking off the 
 cage. The lower part of the cage is now made 
 of glass, to afford more light. 
 
 If this lamp be suspended in a large jar, closed at the 
 top with a perforated wooden cover A (Fig. 123), and 
 having an aperture (B) below, through which coal gas is 
 allowed to pass slowly into the jar, the flame will be seen 
 to waver, to elongate very considerably, and to be ulti- 
 mately extinguished, when the wire cage will be filled 
 with a mixture of coal gas and air burning tranquilly 
 within the gauze, which prevents the flame from passing 
 to ignite the explosive atmosphere surrounding the 
 lamp ; that an explosive mixture really fills the jar may 
 be readily ascertained by introducing through an aper- 
 ture (C) in the cover, the unprotected flame of a taper, when an explosion will 
 occur. 
 
 This experiment illustrates the action of the Davy lamp in a mine which contains 
 fire-damp. It would obviously be unsafe to allow the lamp to remain in the 
 explosive mixture when the cage is filled with flame, for the gauze would either 
 become sufficiently heated to kindle the surrounding gas, or would be oxidised and 
 eaten into holes, which would allow the passage of the flame. Nor should the 
 lamp be exposed to a very strong draught, which might possibly be able to carry 
 the flame through the meshes. 
 
 When the Davy lamp is brought into an atmosphere containing fire-damp, a 
 " cap " of blue flame is observed to play above the tip of the illuminating flame. 
 
148 COAL-MINE EXPLOSIONS. 
 
 This incipient combustion is more marked when a hydrogen flame is substituted 
 for an oil flame, and the height of the cap furnishes an indication of the quantity 
 of fire-damp present. Such a modified Davy lamp becomes a fire-damp indicator, 
 showing as little as 0.25 per cent. 
 
 All coal contains a considerable quantity of gas occluded or condensed in its 
 pores, part of which issues when the surface of the coal is exposed, and part 
 is retained, and can be extracted by exposure in vacuo and moderately heating. 
 Bituminous coals evolve more C0 2 and N, and less CH 4 , than anthracite does, 
 hence these coals may often be worked with naked lights, while seams of steam 
 coal and anthracite are dangerous. Cannel coal has occluded, beside the above 
 gases, some ethane, C 2 H 6 , and Whitby jet has been found to contain butane, C 4 H 10 . 
 The gas from blowers sometimes contains 97 per cent, by volume of marsh gas, with 
 a little C0 2 and N. 
 
 "Whenever naked flames are used in the mine, there must always be 
 great risk ; in most seams of coal there are considerable accumulations 
 of fire-damp ; when a fissure is made, the gas escapes very rapidly from 
 the llower, and the air in its vicinity may soon become converted into 
 an explosive mixture. In mines where small quantities of fire-damp 
 are known to be continually escaping from the coal, ventilation is 
 depended upon in order to dilute the gas with so large a volume of air 
 that it is no longer explosive, and finally to sweep it out of the mine ; 
 but it has occasionally happened that the ventilation has been interfered 
 with by a door having been left open in one of the galleries, or by a 
 passage having been obstructed through the accidental falling in of a 
 portion of the coal, and an explosive mixture has then been formed. 
 
 The presence of fine dust of coal in the air of the mine greatly 
 increases the liability to explosion ; indeed, there is no doubt that in 
 some cases the dust has been the sole cause of the explosion. Most 
 combustible substances mixed in a finely divided state with air, burn 
 so rapidly as to produce effects of explosion. Flour mills have been 
 destroyed from this cause in very dry weather. 
 
 If some lycopodlum, the seed of the club-moss, sometimes called vegetable brimstone, 
 be placed in a glass funnel, the stem of which has been lightly stopped with wool, 
 and has two or three feet of wide vulcanised tubing attached to it, the lycopodium 
 may be blown out in a cloud by a sudden puff of air, and if a lighted taper be held 
 in the cloud, an immense volume of flame may be formed. 
 
 Explosions in dusty mines are more common when gunpowder is used for blasting 
 than when the modern nitro-powders are used. This has been attributed to the 
 considerable quantity of CO which occurs among the products of explosion of 
 blasting gunpowder. This, or any other inflammable gas, serves to start the 
 explosion of the dusty air. 
 
 An ingenious fire-damp indicator has been constructed of two platinum wires, 
 which are heated by a magneto-electric current. One wire! is sheltered from the 
 fire-damp, and the other, being exposed to it, glows more strongly on account of 
 the slow combustion of the fire-damp at the surface of the platinum (see Platinum*). 
 By a careful comparison of the two wires, it is said that 0.25 per cent, of marsh 
 gas in air may be detected, whilst the Davy lamp will not indicate less than 
 2 per cent. 
 
 STRUCTURE OF FLAME. 
 
 90. The consideration of the structure and properties of ordinary 
 flames is necessarily connected with the history of olefiant gas and 
 marsh gas. Flame may be defined as gaseous matter heated to the 
 temperature at which it becomes visible, or emits light. Solid particles 
 begin, for the most part, to emit light when heated to about 500 C. ; 
 but gases, on account of their lower radiating power, must be raised to 
 a far higher temperature, and hence the point of visibility is seldom 
 
NATURE OF FLAME. 149 
 
 attained, except by gases which are themselves combustible, and there- 
 fore capable of producing, by their own combination with atmospheric 
 oxygen, the requisite degree of heat. The presence of a combustible gas 
 (or vapour), therefore, is one of the conditions of the existence of flame ; 
 a diamond, or a piece of thoroughly carbonised charcoal, will burn in 
 oxygen with a steady glow, but without flame, since the carbon is not 
 capable of conversion into vapour, while sulphur burns with a voluminous 
 flame, in consequence of the facility with which it assumes the vaporous 
 condition. It will be observed, moreover, that in the case of a non- 
 volatile combustible, the combination with oxygen is confined to the 
 surface of contact, whilst in the flame of a gas or vapour the combustion 
 extends to a considerable depth, the oxygen intermingling with the 
 gaseous fuel. 
 
 Flames ma}'' be conveniently spoken of as simple or compound, accord- 
 ingly as they involve one or more phenomena of combustion ; thus, for 
 example, the flames of hydrogen and carbonic oxide are simple, whilst 
 those of marsh gas, olefiant gas, and hydrocarbons generally, are com- 
 pound, since they involve both the conversion of hydrogen into water 
 and of carbon into carbon dioxide. 
 
 It is obvious that simple flames must be hollow in ordinary cases, 
 such as that of a gas issuing from a tube into the air, the hollow being 
 occupied by the combustible gas to which the oxygen does not pene- 
 trate. 
 
 All the flames which are ordinarily turned to useful account are com- 
 pound flames, and involve several distinct phenomena. Before examin- 
 ing these more particularly, it will be advantageous to point out the 
 conditions which regulate the luminosity of flames. 
 
 In order that a flame may emit a brilliant light, it is essential that it 
 should containi particles which, either from their own nature or from 
 the conditions Wilder which they are placed, do not admit of very much 
 expansion by the heat of the flame, but are capable of being heated to 
 incandescence. Thus the flame of the oxyhydrogen blowpipe (p. 48) 
 emits a very pale light, but if the mixture of oxygen and hydrogen be 
 restrained from expanding when fired, as in the Cavendish eudiometer, 
 it gives a bright flash ; or if the flame be directed upon some solid body 
 little affected by the heat, such as lime, the light is very intense. 
 
 Phosphorus and arsenic burn with very luminous flames, in con- 
 sequence of the formation of very dense vapours of phosphoric and 
 arsenious oxides during the combustion ; the density of the vapours 
 being here attended with the same result as that produced by the 
 restrained expansion of the steam formed in the Cavendish eudiometer. 
 
 It is not necessary that the incandescent matter should be a product 
 of the combustion ; any extraneous solid in a finely divided state will 
 confer illuminating power upon a flame. Thus, the flame of hydrogen 
 may be rendered highly luminous by blowing a little very fine charcoal 
 powder into it. 
 
 The luminosity of all ordinary flames is due to the presence of highly 
 heated carbon in a state of very minute division, and it remains to con- 
 sider the changes by which this finely divided carbon is separated in the 
 flame. 
 
 A candle, a lamp, and a gas-burner exhibit contrivances for procuring 
 light artificially in different degrees of complexity, the candle being the 
 
150 ILLUMINATING FLAMES. 
 
 most complex of the three. When a new candle is lighted, the first 
 portion of the wick is burnt away until the heat reaches that part 
 which is saturated with the wax or tallow of which the candle is com- 
 posed ; this wax or tallow then undergoes destructive distillation, yield- 
 ing a variety of products, among which olefiant gas is found in abund- 
 ance. The flame furnished by the combustion of these products melts 
 the fuel around the base of the wick, through which it then mounts by 
 capillary attraction, to be decomposed in its turn, and to furnish fresh 
 gases for the maintenance of the flame. In a lamp, the fuel being 
 liquid at the commencement, the process of fusion is dispensed with ; 
 and in a gas-burner, where the fuel is supplied in a gaseous form, the 
 process of destructive distillation has been already effected at a distance. 
 It will be seen, however, that the final result is similar in all three 
 cases, the flame being maintained by such gases as hydrogen, acetylene, 
 marsh gas, and olefiant gas arising from the destructive distillation of 
 wax, tallow, oil, coal, &c. 
 
 The shape of the candle flame is common to all flames which consist 
 of gas issuing from a small circular jet, like the wick of the candle. 
 The gas issues from the jet in the form of a cylinder, which, however, 
 immediately becomes a diverging cone by diffusing into the surrounding 
 air. When this cone is kindled, the margin of it, where intermixture 
 with the surrounding air is most complete, will be perfectly burnt, but 
 the gases in the interior of the diverging cone cannot burn until they 
 have ascended sufficiently to meet with fresh air ; since these unburnt 
 gases are continually diminishing in quantity, the successive circles of 
 
 combustion must diminish in diameter 
 and the conical shape is the only possible 
 form. 
 
 On examining an ordinary flame 
 that of a candle, for instance it is 
 seen to consist of three concentric 
 
 Fig. 124. Fig. 125. 
 
 cones (Fig. 124), the innermost, around the wick, appearing almost black, 
 the next emitting a bright white light, and the outermost being so pale 
 as to be scarcely visible in broad daylight. There is also apparent a 
 bright blue cup surrounding the base of the flame. 
 
 The dark innermost cone consists merely of the gaseous combustible 
 to which the air does not penetrate, and which therefore is not in a 
 state of combustion. 
 
STRUCTURE OF A CANDLE FLAME. 151 
 
 The nature of this cone is easily shown .by experiment : a strip of cardboard held 
 across the flame near its base will not burn in the centre where it traverses the 
 innermost cone ; a piece of wire gauze depressed upon the flame near the wick 
 (Fig. 125) will allow the passage of the combustible gas, which may be kindled 
 above it. The gas may be conveyed out of the flame by means of a glass tube, 
 inserted into the innermost cone, and may be kindled at the other extremity of the 
 tube, which should be inclined downwards (Fig. 126). 
 
 A piece of phosphorus in a small spoon held in the interior of the flame of a 
 spirit-lamp will melt and boil, but will not burn unless it be removed from the 
 flame, and may then be extinguished by replacing it in the flame. 
 
 Fig. 126. 
 
 Fig. 127. 
 
 The combustible gas from the interior of a flame may be collected in a flask 
 (Fig. 1 27) furnished with two tubes, one of which (A) is drawn out to a point for 
 insertion into the flame, whilst the other (B), which passes to the bottom of the 
 flask, is bent over and prolonged by a piece of vulcanised tubing so that it may 
 act as a siphon. The flask is filled up with water, the jet inserted into the interior 
 of a flame, and the siphon set running by exhausting it with the mouth. As the 
 water flows out through the siphon, the gas is drawn into the flask, and after 
 removing the tube from the flame, the gas may be expelled by blowing down the 
 siphon tube, and may be burnt at the jet. When a candle is used for this experi- 
 ment, some solid products of destructive distillation will be found condensed in 
 the flask. 
 
 In the second or luminous cone, combustion is proceeding, but it 
 is by no means perfect, being attended by the separation of a quantity 
 of carbon, which confers luminosity upon this part of the flame. The 
 presence of free carbon is shown by depressing a piece of porcelain 
 upon this cone, when a black film of soot is deposited. The liberation 
 of the carbon is due to the decomposition of the hydrocarbons by the 
 heat, which separates the carbon from the hydrogen,* and this latter 
 undergoing combustion evolves sufficient heat to raise the separated 
 carbon to a white heat, the supply of air which penetrates into this 
 portion of the flame being insufficient to effect the combustion of the 
 whole of the carbon. 
 
 According to Lewes the temperature of the innermost cone of a hydrocarbon 
 flame rises to about 1000 C. near the apex of the cone. This temperature is 
 sufficiently high to decompose the heavier hydrocarbons into acetylene. This 
 acetylene is decomposed, with liberation of carbon, in the luminous cone where 
 the temperature rises to 1300 C., owing to the combustion of the carbon monoxide 
 and hydrogen, the former produced by the imperfect oxidation, and the latter by 
 the decomposition, of the hydrocarbons in the innermost cone. 
 
 Some very simple experiments will illustrate the nature of the luminous portion 
 of flame. 
 
 * The action of heat 011 hydrocarbons is to break them down, or "crack" them, into such 
 as contain a higher percentage of carbon; these, in their turn, are decomposed with liberation 
 of carbon at very high temperatures. 
 
EXPERIMENTS ON FLAME. 
 
 Over an ordinary candle flame (Fig. 128) a tube may be adjusted so as to convey 
 the finely divided carbon from the luminous part of the flame into the flame of 
 hydrogen, which will thus be rendered as luminous as the candle flame, the dark 
 colour of the carbon being apparent in its passage through the tube. 
 
 One of the limbs of the U tube (Fig. 129) contains a tuft of cotton wool b. On 
 kindling the hydrogen supplied through c at the orifice of each tube, no difference 
 will be seen in the flames until a drop of benzene (C 6 H 6 ) is placed upon the 
 cotton, when its vapour, mingling with the hydrogen, will furnish enough carbon 
 to render the flame brilliantly luminous. 
 
 The pale outermost cone, or mantle, of the flame, in which the 
 separated carbon is finally consumed, may be termed the cone of perfect 
 combustion, and is much thinner than the luminous cone, the supply of 
 air to this external shell of flame being unlimited, and the combustion 
 therefore speedily effected. 
 
 The bright blue cup surrounding the base of the flame is formed by 
 the perfect combustion (without any separation of carbon) of a small 
 
 128. 
 
 Fig. 129. 
 
 Fig, 130. Air burning in 
 coal gas. 
 
 portion of the hydrocarbons owing to the complete admixture of air at 
 this point. 
 
 The mantle of the flame may be rendered more visible by burning a little sodium 
 near the flame, when the mantle is tinged strongly yellow. 
 
 According to another view, based on the observation that acetylene a constant 
 product of checked combustion can be discovered in the products of the combus- 
 tion of a hydrocarbon flame burning under ordinary conditions, the mantle is a thin 
 layer of the flame rendered non-luminous by admixture with the surrounding air, 
 the cooling effect of which gradually quenches the combustion. 
 
 By means of a siphon about one-third of an inch in diameter, the nature of the 
 different portions of an ordinary candle flame may be very elegantly shown. If the 
 orifice of the siphon be brought just over the extremity of the wick, the combus- 
 tible gases and vapours will pass through it, and may be collected in a small flask, 
 where they can be kindled by a taper. On raising the orifice into the luminous 
 portion of the flame, voluminous clouds of black smoke will pour over into the 
 flask, and if the siphon be now raised a little above the point of the flame, carbonic 
 acid gas can be collected in the flask, and may be recognised by shaking with lime- 
 water. 
 
 The reciprocal nature of the relation between the combustible gas and the air 
 
GAS BUENEES. 153 
 
 which supports its combustion may be illustrated in a striking manner by burning a 
 jet of air in an atmosphere of coal gas. 
 
 A quart glass globe with three necks is connected at A (Fig. 130) with thegaspipe 
 by a vulcanised tube. The second neck (B), at the upper part of the globe, is con- 
 nected by a short piece of vulcanised tube with a piece of glass tube about \ inch 
 wide, from which the gas may be burnt. Into the third and lowermost neck is 
 inserted, by means of a cork, a thin brass tube C (an old cork-borer), about \ inch 
 in diameter. When the gas is turned on, it may be lighted at the upper neck ; and 
 if a lighted match be then quickly thrust up the tube C, the air which enters it will 
 take tire, and burn inside the globe. 
 
 A simple experiment to show the burning of gas in air may be made with an 
 Argand burner (Fig. 131). The flame having been turned low, a dish (or dial-glass 
 containing water to prevent cracking) is placed so as to close the top of the chimney, 
 when the gas flame will be extinguished, and the air which enters the inner circle 
 will burn with a pale flame, which may be made more visible by thrusting up a 
 copper wire dipped in hydrochloric acid. A bottomless beaker makes a good 
 chimney for this purpose. 
 
 An interesting confirmation of the above views as to the structure of an illumi- 
 nating flame is furnished by observing what occurs when the rate at which the 
 gaseous combustible is supplied to the flame is very gradually increased, either by 
 kindling a candle the wick of which has been cut short, or by slowly increasing the 
 gas supply to an ordinary burner. When the flame is very small it is seen to consist 
 of a bright blue inner cone surrounded by a pale lilac mantle. The bright blue 
 cone is an area of combustion where there is sufficient air to burn the hydrocarbons 
 to gaseous products, without separation of carbon, but not sufficient to burn them 
 completely to C0 2 and H 2 0. It has been shown that under these conditions much 
 of the carbon in the hydrocarbons burns to carbon monoxide, and only a part of the 
 hydrogen is burnt. The CO and H escape from the inner cone and burn when they 
 come in contact with more air, forming the mantle. As the supply of gas is in- 
 creased a luminous spot becomes visible, and gradually increases in area until it 
 becomes the luminous cone, at the same time the core of unburnt gas makes its 
 appearance. What was at first the inner blue cone now becomes the bright blue 
 cup at the base of the flame, and the mantle remains. The advent of the luminous 
 spot indicates that the quantity of gas has so far increased that there is now 
 insufficient air to burn the carbon separated from the hydrocarbons by the heat of 
 the flame. 
 
 The luminosity of a flame is materially affected by the pressure of the atmosphere 
 in which it burns, a diminution of pressure causing a loss of illuminating power. If 
 the light of a given flame burning in the air when the barometer stands at 30 inches 
 be represented by 100, each diminution of i inch in the height of the barometer 
 will reduce the luminosity by 5 ; and, conversely, when the barometer rises I inch, 
 the luminosity will be increased by 5. This is not due to any difference in the rate 
 of burning, which remains prettj*- constant, but to the 
 more complete impenetration of the rarefied air and the 
 gases composing the flame ; this gives rise to the sepa- 
 ration of a smaller quantity of incandescent carbon. In 
 air at a pressure of 120 inches of mercury, the flame of 
 alcohol is highly luminous. 
 
 From this review of the structure of flame, 
 it is evident that, in order to secure a flame 
 which shall be useful for illumination, atten- 
 tion must be paid to the supply of oxygen (or 
 air), and to the composition of the fuel em- 
 ployed. Much attention has been paid to the 
 construction of burners which, by causing the 
 illuminant to issue into the air at a rate and 
 in a shape best suited to the production of Fig-. i 3 i._Argand Burner, 
 lighting effect, shall give the most economical 
 
 result, that is, the highest illuminating value (candle power) per unit of 
 combustible. The use of the chimney of an Argand burner (Fig. 132) 
 affords an instance of the necessity for attention to the proper supply 
 
154 SMOKELESS GAS BURNER. 
 
 of air. Without the chimney, the flame is red at the edges and smoky, 
 for the supply of air is not sufficient to consume the whole of the car- 
 bon which is separated, and the temperature is not competent to raise 
 it to a bright white heat, defects which are remedied as soon as the 
 chimney is placed over it and the rapidly ascending heated column of 
 air draws in a liberal supply beneath the burner, as indicated by the 
 arrows. 
 
 By using two chimneys, and causing the air to pass down between 
 them, so as to be heated before reaching the flame, and to be less 
 capable of chilling the flame, an equal amount of light may be obtained 
 from a much smaller supply of gas ; this is the principle underlying the 
 regenerative burner. 
 
 The importance of the chemistry of illuminating flames has, however, 
 much diminished during the past few years owing to the perfection to 
 which the system of illumination first put -on a practical basis by 
 Welsbach, has been brought. Whereas in an illuminating flame the 
 combustible supplies, not only the heat required to raise a dense sub- 
 stance to the temperature at which it can emit light, but also the 
 dense substance (carbon) itself, under the Welsbach or Auer system 
 the sole function of the combustible is to supply heat, the dense sub- 
 stance being an incombustible material suspended in the flame. Hence 
 the principle of the system is the same as that of the Drummond light 
 (p. 48) known many years before Welsbach. 
 
 Since a luminous flame contains carbon in a condition in which it is 
 very readily deposited on any surface held in the flame, it is desirable 
 that a gas burner which is to be used for heating, whether for pro- 
 ducing light or for any other purpose, should supply a non-luminous 
 flame. A deposit of soot forms a non-conducting layer through which 
 the heat travels slowly; moreover, every particle of soot which escapes 
 combustion signifies a loss in the calorific power of the gas. The 
 smokeless gas burners employed in laboratories and kitchens exhibit 
 the result of mixing the gas with a considerable proportion of air 
 before burning it, the luminous part of the flame then entirely dis- 
 appearing, because there is sufficient oxygen in the flame to burn the 
 hydrocarbons before they can be decomposed with separation of carbon. 
 By careful adjustment of the supply of air the combustion can be made 
 to take place in a smaller space than when the gas has to seek its air 
 supply from the surrounding atmosphere. For the same amount of gas 
 consumed, that flame which is the smaller will have the higher tempera- 
 ture, although it must be understood that the 
 same amount of heat is produced from a given 
 volume of gas, however it is burnt, provided 
 that the combustion is complete, i.e., that 
 the products are only C0 2 and H 2 0. 
 
 The principle upon which all air-gas 
 burners are constructed is illustrated by 
 Bunseris burner (Fig. 132), in which the 
 Fig. i 32 .-Bunsen's burner. g as is conveyed through a narrow jet into a 
 wide tube, at the base of which are two 
 
 large holes for the admission of air. When a good supply of gas is 
 turned on, a quantity of air, about 2^ times the volume of the gas, is 
 drawn in through the lower apertures, and the mixture of air and gas 
 
THE WELSBACH BURNER. 
 
 I 55 
 
 may be kindled at the orifice of the wide tube, its rapid motion pre- 
 venting the flame from passing down the tube. By closing the air-holes 
 with the fingers, a luminous flame is at once produced. 
 
 The luminosity of the flame may also be destroyed by supplying nitrogen instead 
 of air to the Bunsen burner, when the diminution of the light is partly due to the 
 increased area of the flame and partly to the cooling effect of the nitrogen, by which 
 the temperature is lowered below that at which the hydrocarbons are decomposed 
 with separation of carbon. This cooling effect occurs to some extent when air is 
 supplied to the burner ; the nitrogen in this air lowers the temperature of the flame 
 just at that point where, in a luminous flame, the hydrocarbons are decomposed, 
 although the more perfect combustion makes the temperature in other portions of 
 the non-luminous flame higher than at corresponding points of the luminous flame. 
 When the air and coal gas are heated before being supplied to the burner the cooling 
 effect of the nitrogen is counteracted, and the flame becomes luminous. The 
 ordinary Bunsen flame consists of only two cones ; the inner one is a core of 
 mixture of air and gas which cannot be kindled because its rate of passage is more 
 rapid than the rate at which a flame can travel in it ; the combustion occurs in the 
 outer cone, where the speed has diminished. 
 
 When the gas supply to a Bunsen burner is checked, the velocity of issue of the 
 mixture of air and gas becomes so far diminished that it i? no longer greater than 
 the rate at which the flame can travel in the mixture, consequently the flame passes 
 down the tube of the burner and burns at the jet from which the coal-gas issues ; here 
 the checked combustion will give rise to much acetylene, detected by its odour. 
 By slipping a glass tube, some three or four feet long, over the tube of the burner, 
 taking care not to cover the air inlet, and kindling the 
 gas at the orifice of this tube, the flashing back of the 
 flame may be observed. If the glass tube be constricted 
 at a point some foot or so away from the orifice, the 
 descending flame will be stopped at this constriction, 
 for here the velocity of issue will be again sufficiently 
 great to prevent further flashing back. Inasmuch as the 
 flame at the constriction is burning out of contact with 
 surrounding air, only such products are formed by its 
 combustion as can be produced by the action of the 
 oxygen supplied in the air from the burner ; these in- 
 clude much CO and H, so that a second flame composed 
 of these gases burning in the air will generally be seen 
 at the orifice of the tube. A more elaborate apparatus 
 for showing this experiment is seen in Fig. 133 ; in 
 this the height of the constriction can be varied by 
 sliding the outer tube on the rubber rings A A. Air 
 and gas are supplied through the T-piece. Fis?< I33 
 
 The Welsbach mantle is a skeleton of the 
 
 highly infusible oxide of thorium containing about i per cent, of oxide 
 of cerium. This mixture has a remarkable power of converting the heat 
 energy of the burning gas into light energy,* and when the mantle is 
 suspended in a suitable air-gas flame it produces light at about one- 
 fifth the cost for gas that is involved if the same gas is burnt as a 
 luminous flame. 
 
 The Welsbach mantle is made by soaking in a solution containing the nitrates of 
 thorium and cerium, and generally ammonium nitrate, a knitted cylinder of cotton 
 thread, drawn together by an asbestos thread at one end. After drying, the cotton 
 is ignited and allowed to burn away, leaving the mineral matter in the exact form 01 
 the original cotton thread. The mantle lis then heated very strongly to "harden 
 it, and dipped in a solution of collodion to stiffen it for the market ; when it 
 placed on the burner and the gas is kindled the film of collodion rapidly b 
 
 The air-gas burner for the Welsbach light is constructed in such a manner that 
 the mixture of air and gas issuing from the burner is nearly in the proper propor 
 * It is claimed that as much as 25 percent, is converted. 
 
156 THE BLOWPIPE FLAME. 
 
 tion for complete combustion ; that is to say, the mixture should be " self -burning," 
 requiring little or none of the surrounding air. In this manner the hottest attain- 
 able flame is produced. The burner generally has the form of the frusta of two 
 cones, the upper inverted on the lower ; the gas issues as a jet into the lower cone 
 and draws in some four or five times its volume of air. The orifice of the burner 
 tube must be covered with wire gauze to prevent the flame from flashing back. The 
 flame of a burner of this kind is characterised by the inner cone having a much 
 greener appearance than has that of the ordinary Bunsen flame. The temperature 
 of the hottest portion of the ordinary Bunsen flame, the centre of the outer cone, is 
 stated to be about 1500 C., whilst at the same point in this "solid " flame the tem- 
 perature is said to be about 1600 C. Fig. 134 shows an Argand burner converted 
 into such a gauze burtier by a covering of wire gauze. When this is placed over the gas 
 burner, a supply of air is drawn in at the bottom by the ascending stream of gas, 
 and the mixture burns above the gauze with a very hot smokeless flame, the metallic 
 meshes preventing the flame from passing down to the gas below. 
 
 The candle power of the Welsbach light is about 18 per cubic foot of gas per hour, 
 whilst that of a flat flame is between 2 and 3 on the same basis. 
 
 Fig 1 . 134. Gauze burner. Fig. 135. Blowpipe flame. 
 
 91. The blowpipe flame. The principles already laid down will render 
 the structure of the blowpipe flame easily intelligible. It must be 
 remembered that in using the blowpipe, the stream of air is not pro- 
 pelled from the lungs of the operator (where a great part of its oxygen 
 would have been consumed), but simply from the mouth, by the action 
 of the muscles of the cheeks. The first apparent effect upon the flame 
 is entirely to destroy its luminosity, the free supply of air effecting the 
 immediate combustion of the carbon. The size of the flame, moreover, 
 is much diminished, and the combustion being concentrated into a 
 smaller space, the temperature must be much higher at any given point 
 of the flame. In structure, the blowpipe flame is similar to the ordinary 
 flame, consisting of three distinct cones, the innermost of which (A, 
 Fig. 135) is filled with the cool mixture of air and combustible gas. 
 The second cone, especially at its point (R), is termed the reducing 
 flame, for the supply of oxygen at that part is not sufficient to convert 
 the carbon into carbon dioxide, but leaves it as carbonic oxide, which 
 speedily reduces almost all metallic oxides placed in that part of the 
 flame to the metallic state. The outermost cone (0) is called the 
 oxidising flame, for there the supply of oxygen from the surrounding 
 air is unlimited, and any substance prone to combine with oxygen at a 
 high temperature is oxidised when exposed to the action of that portion 
 of the flame : the hottest point of the blowpipe flame, where neither 
 fuel nor oxygen is in excess, appears to be a very little in advance of 
 the extremity of the second (reducing) cone. The difference in the 
 operation of the two flames is readily shown by placing a little red lead 
 (oxide of lead) in a shallow cavity scooped upon the surface of a piece 
 of charcoal (Fig. 136), and directing the flames upon it in succession) ; 
 
ANALYSIS OF HYDROCARBONS. 
 
 the inner flame will reduce a globule of metallic lead, which may be 
 reconverted into oxide by exposing it to the outer flame.* 
 
 Fig. 137. Hot-blast blowpipe. 
 
 Fig. 136. Keduction of metals on charcoal. 
 
 The immense service rendered by this instrument to the chemist and 
 mineralogist is well known. 
 
 By forcing a stream of oxygen through a flame, from a gas-holder or 
 bag, an intensely hot blowpipe flame is obtained, in which pipeclay and 
 platinum may be melted, and iron burns with great brilliancy. 
 
 Fletcher's hot-blast blowpipe (Fig. 137) produces a much higher temperature than 
 the ordinary blowpipe. Coal gas is supplied through the tube g, and is kindled 
 at the Bunsen burners b b and at the orifice/, the 
 supply to the former being regulated by the stop- 
 cock , and to the latter by the stop-cock d. The 
 flames of the Bunsen burners heat the spiral copper 
 tube e to redness, so that the air blown in through 
 the flexible tube a is strongly heated before being 
 projected into the flame through a blowpipe jet 
 at /. Thin platinum wires melt easily in this flame, 
 and thin iron wires burn away rapidly. 
 
 92. Determination of the composition of 
 gases containing carbon and hydrogen. In 
 order to ascertain the proportions of carbon 
 and hydrogen present in a gas, a measured 
 volume of the gas is mixed with an excess 
 of oxygen, the volume of the mixture carefully noted, and explosion 
 determined by passing the electric spark ; the gas remaining after the 
 explosion is measured and shaken with potash, which absorbs the 
 carbonic acid gas, from the volume of which the proportion of carbon 
 may be calculated. For example, 
 
 4 c.c. of marsh gas, mixed with 
 10 oxygen, and exploded, left 
 6 gas ; shaken with potash, it left 
 2 oxygen, 
 
 showing that 4 c.c. of carbonic acid gas had been produced. This 
 quantity would contain 4 c.c. of oxygen. Deducting this last from the 
 total amount of oxygen consumed (8 c.c.), we have 4 c.c. for the volume 
 of oxygen consumed by the hydrogen. Now, 4 c.c. of oxygen would 
 combine with 8 c.c. of hydrogen, which represents therefore the amount 
 of hydrogen in the marsh gas employed. It has thus been ascertained 
 that the marsh gas contains twice its volume of hydrogen. 
 
 The method by which the composition by weight of a gas containing 
 
 * By directing the reducing flame upon the metallic oxide in the cavity, and allowing the 
 oxidising flame to sweep over the surface of the charcoal, as shown in the figure, a yellow 
 incrustation of oxide of lead is formed upon the surface of the charcoal, which affords 
 additional evidence of the nature of the metal. 
 
158 COAL. 
 
 carbon and hydrogen can be ascertained will be appreciated when the 
 section on ultimate organic analysis has been studied. In the case of 
 marsh gas such an analysis shows that the carbon and hydrogen are 
 present in the gas in the proportion of 3 parts by weight of carbon 
 to one part by weight of hydrogen. If the atomic weight of carbon be 
 12, the simplest formula for marsh gas, expressing this ratio of C to H, 
 will be CH 4 . But the formula 2 H 8 would equally express the ratio 
 3 : i (12 x 2 : 1x8); this cannot be the formula for marsh gas, how- 
 ever, because the specific gravity (H= i) of the gas is 8, therefore its 
 molecular weight must be 16 (p. 9), and as the formula is to represent 
 one molecular weight (p. 9), the formula for marsh gas must be CH 4 
 (12 + 4=16), not C 2 H 8 (24 + 8 = 32). 
 
 For the purpose of illustration, the analysis of marsh gas may be effected in a 
 lire's eudiometer (Fig. 37), but a considerable excess of oxygen should be added to 
 moderate the explosion. The eudiometer having been filled with water, i c. c. of 
 marsh gas is introduced into it, as described at p. 44, and having been transferred to 
 the closed limb and accurately measured after equalising the level of the water, the 
 open limb is again filled up with water, the eudiometer inverted in the trough, and 
 12 c. c. of oxygen added ; this is also transferred to the closed limb and carefully 
 measured. The electric spark is passed through the mixture (see p. 44), the open 
 limb being closed by the thumb. The level of the water in both limbs is then 
 equalised, and the volume of gas measured. The open limb is filled up with a strong 
 solution of potash, and closed by the thumb, so that the gas may be transferred 
 from the closed to the open limb and back, until its volume is no longer diminished 
 by the absorption of carbon dioxide. The volume of residual oxygen having been 
 measured, the calculation is effected as described above. 
 
 The results are more exact when the eudiometer is filled with mercury instead of 
 water, and corrections for temperature and pressure are made. 
 
 FUEL. 
 
 93. Whilst any combustible substance is applicable for the purpose 
 of producing heat, the forms of fuel actually in use are dependent for 
 their calorific value on the combustion of carbon and hydrogen.* A table 
 showing the composition of the principal fuels will be found on p. 168. 
 
 Coal. The various substances which are classed together under the 
 name of coal are characterised by the presence of carbon as a largely 
 predominant constituent, associated with smaller quantities of hydrogen, 
 oxygen, nitrogen, sulphur, and certain mineral matters which compose 
 the ash. Coal appears to have been formed by a peculiar decomposition 
 or fermentation of buried vegetable matter, resulting in the separation 
 of a large proportion of its hydrogen in the form of marsh-gas (CH 4 ), 
 and similar compounds, and of its oxygen in the form of carbonic acid 
 gas (C0 2 ), the carbon accumulating in the residue. Thus, cellulose 
 (C 6 H 10 O 5 ), which constitutes the bulk of woody fibre, might be imagined 
 to decompose according to the equation 2C 6 H 10 () 5 = 5CH 4 + 5C0 2 + C 9 , 
 and the occurrence of marsh gas, and of the paraffin hydrocarbons of 
 similar compositions, as well as of carbonic acid gas, in connexion with 
 deposits of coal, supports this account of its formation. Marsh gas 
 and carbonic acid gas are the ordinary products of the fermentation of 
 vegetable matter, and a spontaneous carbonisation is often witnessed in 
 the " heating " of damp hay. But just as the action of heat upon wood 
 
 * The student will meet with a few cases in which the combustion of other elements affords 
 heat for useful purposes, so that such elements are fuels under the particular conditions. 
 For example, the sulphur in pyrites or the aluminium in the mixture known as thermite 
 may be regarded as fuels. 
 
COMBUSTION OF COAL. 159 
 
 produces a charcoal containing small quantities of the other organic 
 elements, so the carbonising process by which the plants have been 
 transformed into coal has left behind some of the hydrogen, oxygen, 
 and nitrogen ; the last, as well probably as a little of the sulphur, 
 having been derived from the vegetable albumin and similar substances 
 which are always present in plants. The chief part of the sulphur is 
 generally present in the form of iron pyrites (FeS 2 ), derived from some 
 extraneous source. The examination of a peat-bog is very instructive 
 with reference to the formation of coal, as affording examples of 
 vegetable matter in every stage of decomposition, from that in which 
 the organised structure is still clearly visible, to the black carbonaceous 
 mass which only requires consolidation by pressure in order to resemble 
 a true coal. In some cases an important part in the formation of coal 
 may have been played by slow oxidation or decay of the vegetable 
 matter at the expense of atmospheric oxygen held in solution by water ; 
 since the hydrogen of the compound would be removed by oxidation 
 taking place at a low temperature, giving rise to a gradual increase in 
 the percentage of carbon. 
 
 The three principal varieties of coal lignite, bituminous coal, and 
 anthracite present us with the material in different stages of carboni- 
 sation ; the lignite, or broivn coal, presenting indications of organised 
 structure, and containing considerable proportions of hydrogen and 
 oxygen, while anthracite often contains little else than carbon and the 
 mineral matter or ash. The following table shows the progressive 
 diminution in the proportions of hydrogen and oxygen in the passage 
 from wood to anthracite. 
 
 Carbon. Hydrogen. Oxygen. 
 
 Wood . . . loo ... 12. 18 ... 83.07 
 
 Peat ... . 100 ... 9.85 ... 55.67 
 
 Lignite . . . 100 ... 8.37 ... 42.42 
 
 Bituminous coal . 100 ... 6.12 ... 21.23 
 
 Anthracite . . 100 ... 2.84 ... 1.74 
 
 The combustion of coal is a somewhat complex process, in con- 
 sequence of the re-arrangement which its elements undergo when the 
 coal is subjected to the action of heat. 
 
 As soon as a flame is applied to kindle the coal, the heated portion 
 undergoes destructive distillation, evolving various combustible gases 
 and vapours, which take fire and convey the heat to remoter portions of 
 the coal. Whilst the elements of the exterior portion of coal are under- 
 going combustion, the heat thus evolved is submitting the interior of 
 the mass to destructive distillation, resulting in the production of 
 various compounds of carbon and hydrogen. Some of these products, 
 such as marsh gas (CH 4 ) and olefiant gas (C 2 H 4 ), burn without smoke ; 
 while others, like benzene (C 6 H 6 ) and naphthalene (C 10 H 8 ), which con- 
 tain a very large proportion of carbon, undergo partial combustion, and 
 a considerable quantity of carbon, not meeting with enough heated oxy- 
 gen in the vicinity to burn it entirely, escapes in a very finely divided 
 state as smoke or soot, which is deposited in the chimney, mixed with 
 a little ammonium carbonate and small quantities of other products of 
 the distillation of coal. "When the gas has been expelled from the coal, 
 there remains a mass of coke or cinder, which burns with a steady glow 
 until the whole of its carbon is consumed, and leaves an ash, consisting 
 
160 COKE. 
 
 of the mineral substances present in the coal.* The final results of the 
 perfect combustion of coal would be carbonic acid gas (CO.,), water 
 (H 2 0), nitrogen, a little sulphurous acid gas (S0 2 ), and ash. The pro- 
 duction of smoke in a furnace supplied with coal may be prevented by 
 charging the coal in small quantities at a time in front of the fire, so 
 that the highly carbonaceous vapours must come in contact with a 
 large volume of heated air before reaching the chimney. In arrange- 
 ments for consuming the smoke, hot air is judiciously admitted at the 
 back of the fire, in order to meet and consume the heated carbonaceous 
 particles before they pass into the chimney. 
 
 The difference in the composition of the several varieties of coal gives 
 rise to a great difference in their mode of burning. 
 
 The table on p. 168 exhibits the composition of representative speci- 
 mens of the four principal varieties, namely, lignite, bituminous coal, 
 cannel, and anthracite. 
 
 The lignites furnish a much larger quantity of gas under the action 
 of heat (and therefore burn with more flame than the other varieties), 
 leaving a coke which retains the form of the original coal ; while bitu- 
 minous coal softens and cakes together a useful property, since it 
 allows even the dust of such coal to be burnt, if the fire be judiciously 
 managed. Anthracite (stone coal or Welsh coal) is much less easily com- 
 bustible than either of the others, and, since it yields but little gas 
 when heated, it usually burns with little flame or smoke. This variety 
 of coal is so compact that it will not usually burn in ordinary grates, 
 but it is much employed for boiler furnaces. 
 
 Jet resembles cannel coal in composition. 
 
 Accidents occasionally arise from the spontaneous combustion of coal. 
 This appears to be due, in most cases, to the development of heat by 
 the slow combination of some constituents of the coal with atmospheric 
 oxygen, and unless due provision be made for the escape of the heat, its 
 accumulation may raise the temperature to a dangerous degree. The 
 oxidation is more likely to occur if, by careless loading of the coal 
 in the ship, much pulverisation of the fuel has occurred (compare 
 
 P- 34)> 
 
 Coke is the residue left by destructively distilling coal, an operation 
 which is conducted in coke-ovens when the object is to produce coke 
 for metallurgical use and in retorts when the object is to produce coal 
 gas, the coke being then a by-product. There is no essential difference 
 between the coke-oven and the retort save that the former is con- 
 siderably the larger of the two, thus distilling a greater weight of coal 
 and producing a denser coke. As all the volatile portions of the coal 
 have been expelled by the distillation, coke burns without flame or 
 smoke, but is correspondingly difficult to ignite. 
 
 Wood and Charcoal have already received attention. In this 
 country the use of the former as fuel is limited to its application for 
 kindling less inflammable fuel, like coal. Charcoal is useful in cases 
 where a fuel devoid of sulphur is desirable ; it stands in the same 
 relation to wood that coke does to coal as has already been explained 
 (p. in). 
 
 * This ash consists chiefly of silica, alumina and peroxide of iron. When lime is present 
 in the ash, it is liable to fuse into a rough glass or clinker, which adheres to the grate bars 
 and causes much inconvenience. 
 
COAL GAS. l6l 
 
 Petroleum finds an increasing application as fuel, particularly the- 
 residues from the fractional distillation of the oil (see Organic Chemistry)' 
 for obtaining illuminating oils. Such residues are known as astatki r 
 and when sprayed into a furnace burn with a high heating effect. An 
 advantage of this form of fuel is its freedom from ash. 
 
 Gaseous fuel. The fact that combustible gases can be burnt without 
 the production of smoke and ash renders them a formidable competitor 
 of coal notwithstanding that for an equal heating effect they are more 1 
 costly. But the more important function of gaseous fuel is as a source* 
 of power by its combustion in the cylinder of a gas engine. So far as 
 domestic heating is concerned coal gas is still the sole gaseous fuel 
 used ; an air-gas flame (p. 154) is caused to play upon some incombustible 
 and infusible substance like asbestos or fireclay, so that the heat of the 
 flame, which is a feeble radiator, may be converted into the radiant 
 heat of a red-hot solid. The cooling of the flame by contact with the 
 solid necessarily checks the combustion, giving rise to such gases as 
 carbon monoxide and acetylene which are unwholesome to breathe. A 
 flue for carrying away the products of the combustion is therefore 
 essential, but this is less necessary where the gas is allowed to burn 
 with a luminous flame, the radiation from which is considerable while 
 the combustion is practically complete. 
 
 94. Coal gas. The manufacture of coal gas is one of the most im- 
 portant applications of the principle of destructive distillation, and 
 affords an excellent example of the tendency of this process to develop 
 new arrangements of the elements of a compound body. The action of 
 heat upon coal, in a vessel from which air is excluded, gives rise to the 
 production of a very large number of compounds containing some two* 
 or more of the five elements of the coal, in different proportions, or in 
 different forms of arrangement. Although no clue has yet been obtained 
 to indicate the true arrangement of these elements in the original 
 coal (or, as it is termed, the constitution of the coal), it is certain that 
 these various compounds do not exist in it before the application of 
 heat, but are really the results of this application ; they are products, 
 not educts. 
 
 The illuminating gas obtained from coal consists essentially of free 
 hydrogen, marsh gas, olefiant gas, and carbonic oxide, with small! 
 quantities of acetylene, benzene vapour, and some other substances. 
 Its specific gravity is about 0.4, and is higher the higher the illuminating 
 value of the gas. 
 
 A fair general idea of the composition of coal gas is given in the 
 table on p. 168. 
 
 The constituents which contribute most largely to the illuminating 
 value of the gas are the vapour of benzene, acetylene, olefiant gas and 
 similar hydrocarbons, represented by C 2 H 4 in the table. 
 
 The most objectionable constituent is the sulphur present in very 
 small proportion as sulphuretted hydrogen and bisulphide of carbon, 
 for this is converted by combustion into sulphurous and sulphuric acids, 
 which seriously injure pictures, furniture, &c. The object of the 
 manufacturer of coal gas is to remove, as far as possible, everything 
 from it, except the constituents mentioned as essential, and at the same 
 time to obtain as large a volume of gas from a given weight of coal as 
 is consistent with good illuminating value. 
 
 L 
 
l62 
 
 ACETYLENE IN COAL GAS. 
 
 The other products of the destructive distillation of coal, the mode of 
 purifying the gas, and the general arrangements for its manufacture, 
 will be described in a later part of the book. 
 
 The destructive distillation of coal may be exhibited with the arrangement repre- 
 sented in Fig. 138. The solid and liquid products (tar, ammoniacal liquor, &c.) are 
 condensed in a globular receiver (A). The first bent tube contains, in one limb (B) 
 a piece of red litmus-paper to detect ammonia ; and in the other (C) a piece of paper 
 impregnated with lead acetate, which will be blackened by the sulphuretted 
 
 Fig. 138. Destructive distillation of coal. 
 
 hydrogen. The second bent tube (D) contains enough lime-water to fill the bend, 
 which will be rendered milky by the carbonic acid gas. The gas is collected over 
 water in the jar E, which is furnished with a jet from which the gas may be burnt 
 when forced out by depressing the jar in water. 
 
 The presence of acetylene in coal gas may be shown by passing the gas from the 
 supply-pipe (A, Fig. 139), first through a bottle (B) 
 containing a little ammonia, then through a bent 
 tube (C) with enough water to fill the bend, and a 
 piece of bright sheet copper immersed in the water in 
 each limb. After a short time the bright red flakes 
 of the copper acetylide will be seen in the water. 
 
 So long as coal gas is burnt for producing 
 an illuminating flame and is sold at so much 
 per cubic foot, it is essential that the maker 
 should be compelled to supply it of a standard 
 Fio . illuminating value.* This requirement, which 
 
 entails considerable expense in the manufac- 
 ture owing to the necessity for " enriching " the gas by adding to it petro- 
 leum vapour or some other hydrocarbon that increases the illuminating 
 value, should be changed into a standard heating value now that so 
 much of the gas is used for heating and power purposes, and that the 
 Welsbach system of lighting (which depends solely on the heating value 
 of the gas) is displacing illuminating flames. 
 
 Producer gas. In the manufacture of coal gas some 70 per cent, of 
 the carbon of the coal is left in the retort as coke. It is possible to 
 convert nearly the whole of the carbon of the coal into combustible gas 
 by taking advantage of the fact that C0 2 is reduced to CO by red -hot 
 carbon, C0, + = 2CO. The producer in which this change is effected, 
 consists of a deep grate into which the fuel is fed from above, the air 
 entering below the charge. The bottom portion of the fuel burns to 
 C0 2 , which is reduced to CO t by the hot fuel in the top of the pro- 
 
 * In London, i6-candle gas must be supplied; that is, when the g-as is burnt from a 
 standard burner at the rate of 5 cubic feet per hour the flame must have an illuminating- 
 value equal to that of 16 standard caudles. 
 
 t See foot-note, p. 132. 
 
CALORIFIC VALUE OF FUEL. 163 
 
 ducer ; this escapes through a flue to the furnace in which it is to be 
 burnt. Of course, producer gas is far from pure CO ; it must neces- 
 sarily contain the nitrogen of the air which supplied the oxygen, and, 
 in addition to this, some C0 2 and the products of the destructive 
 distillation of the coal used, are present. 
 
 Water gas. A gas of more than double the heating effect of producer 
 gas can be obtained from the original fuel by converting it into water 
 gas. This process depends on the fact that when steam is passed over 
 heated carbon, a mixture of hydrogen and carbon monoxide is obtained, 
 C + H 2 = CO + H 2 . Since this reaction is endothermic, the tempera- 
 ture of the carbon must be maintained if the production of the gas is 
 to continue. In practice water gas is made by passing steam into 
 a producer which is already at work, until the temperature has so far 
 fallen that the steam is no longer decomposed. The fuel is then again 
 brought up to the required temperature by a draught of air (producer 
 gas being formed during this stage of the process), and steam is again 
 turned in. 
 
 It will be obvious that by blowing an appropriate mixture of steam 
 and air into a producer, a mixture of water gas and producer gas (semi- 
 water gas, Dowson gas, and Mond gas] can be continuously produced. 
 
 Calorific value of fuel. For all practical purposes it may be 
 stated that the amount of heat generated by the combustion of a given 
 weight of fuel depends upon the weights of carbon and hydrogen, re- 
 spectively, which enter into combination with the oxygen of the air 
 when the fuel burns. 
 
 It has been ascertained by experiment that i gram of carbon (in the. 
 form in which it exists in wood-charcoal), when combining with oxygen 
 to form C0 2 , produces a quantity of heat which is capable of raising 
 8080 grams of water from o to i C. This is usually expressed by 
 saying that the calorific value of carbon is 8080, or that carbon produces 
 8080 units of heat during its combustion to C0 2 . If the fuel, therefore, 
 consisted of pure carbon, it would merely be necessary to multiply its 
 weight by 8080 to ascertain its calorific value. 
 
 One gram of hydrogen, during its conversion into water by combus- 
 tion evolves enough heat to raise 34,400 Ibs. of water from o C. to 
 i C., so that the calorific value of hydrogen is 34,400. 
 
 If the fuel consisted of carbon and hydrogen only, its calorific value 
 would be calculated by multiplying the weight of the carbon in i Ib. 
 of the fuel by 8080, and that of the hydrogen by 34,400, when the sum 
 of the products would represent the theoretical calorific value. But if 
 the fuel contains oxygen already combined with it, the calorific value 
 will be diminished, since less oxygen will be required from the air. 
 For example, i gram of wood contains 0.5 gram of carbon, 0.06 of 
 hydrogen, and 0.44 of oxygen. Now, oxygen combines with one-eighth 
 of its weight of hydrogen to form water, so that the 0.44 gram of 
 oxygen will convert 0.44 -r 8 = 0.055 of the hydrogen into water, without 
 evolution of available heat, leaving only 0.005 available for the produc- 
 tion of heat. The calorific value of the wood, therefore, would be 
 represented by the sum of 0.005x34400 (=172) and 0.5x8080 
 ( = 4040) which would amount to 4212 ; or i gram of wood should 
 raise 4212 grams of water from o C. to i C. 
 
 These considerations lead to the following general formula for caku- 
 
164 
 
 CALORIMETER. 
 
 lating the calorific value of a fuel containing carbon, hydrogen, and 
 oxygen, where c, h, and o, respectively represent the carbon, hydrogen, 
 and oxygen in i gram of fuel. 
 
 The calorific value (or number of grams of water which might be 
 
 heated by the fuel from o C. to i C) = 8080 c + 34400 
 
 * - 
 
 The calorific value of a coal, as determined by experiment in a calorimeter is 
 generally higher than that calculated by the above formula.* This arises from lack 
 of knowledge as to how the elements of the coal are combined together. 
 
 A convenient form of calorimeter, known as Mahler's bomb, is shown in Fig. 140, 
 and to a smaller scale in position for use in Fig. 141. The weighed substance to be 
 burnt (or the mixture the reaction between the constituents of which is to be started 
 by heat) is placed in a platinum boat C (Fig. 141), attached by metal rods to the 
 cover of the steel bottle B. The cover is screwed on to the bottle, the joint being 
 made tight by means of a lead washer P. The bomb is now connected at N with 
 
 JV 
 
 R 
 
 Fig. 140. Calorimetric bomb. 
 
 Fig. 141. Calorimetric bomb. 
 
 a tube leading from a bottle of compressed oxygen, and having a pressure gauge 
 inserted in it, and is filled with oxygen under pressure by slowly turning the screw 
 valve R and closing it againiwhen the pressure gauge marks 5-10 atmospheres. The 
 bomb is now placed in the calorimeter chamber Z>, containing a known weight of 
 water, and surrounded by an air jacket H, itself surrounded by a water jacket A. 
 One of the rods that supports the tray C passes through an insulating plug Ein the 
 cover of the bottle J5, while the other is in electrical contact with the bottle. Thus,, 
 by connecting the end of the insulated wire with one pole of a battery, and the 
 bottle with the other pole, an electric current may be passed through the tray C (or 
 through a platinum spiral embedded in the substance as shown in Fig. 141), so as to 
 heat it to ignite the substance to be burnt. (The quantity of electric current used 
 for this purpose may be measured, and the heat thus introduced into the calori- 
 meter may be calculated from the known equivalency of electric energy and heat 
 energy.) The battery is cut off as soon as ignition has occurred, and the stirrer S' 
 having been set in motion the thermometer T is read at intervals, note being taken of 
 the highest point attained and the time occupied in attaining it. 
 
 * Results more in accord with the practical value are claimed to be obtained from the 
 following formula, where Q = quantity of heat, C' = carbon left as coke on distilling the 
 coal, and C"=carbon contained in the volatile products : Q = 8080 C' +11214 " + 34462 H.. 
 If much O be present, one-eighth of its weight must be deducted from the H. 
 
CALORIFIC INTENSITY OF FUELS. 165 
 
 If .all the heat of the combustion (or reaction) passed into the water of the calori- 
 meter the calculation of the result would be easy ; for the weight of the water 
 multiplied by the rise of temperature would represent the heat of combustion. As, 
 however, the whole apparatus shares the heat with the water in the calorimeter 
 chamber, the capacity of the apparatus for heat must be ascertained. This is best 
 effected by burning a known weight of a substance of known calorific value 
 (naphthalene,* for example) in the bomb, and observing how much of the total heat 
 passes into the water in the calorimeter ; the difference between this quantity and 
 the known total heat is the amount of heat absorbed by the apparatus, and when 
 divided by the rise of temperature shows the heat capacity of the apparatus. 
 
 Suppose that I gram of coal has been burnt in the manner described, that the 
 weight of water in the calorimeter is w grams, that the rise of temperature observed 
 is t C, and that the heat capacity of the apparatus is k gram-units ; then the heat 
 of combustion of I gram of coal is wt + lit. In accurate work a correction must 
 be made for the heat lost by radiation and convection from the calorimeter during 
 the time occupied by the experiment ; for the methods of making this correction a 
 text-book on Physics must be consulted. 
 
 In the case of compounds of carbon and hydrogen, it has been ob- 
 served, that even when they have the same composition in 100 parts, 
 they have not of necessity the same calorific value, the latter being 
 affected by the difference in the arrangement of the component atoms 
 of the compound, which causes a difference in the quantity of heat 
 absorbed during its decomposition. Thus, olefiant gas (C 2 H 4 ) and 
 cetylene (C. 6 H 32 ) have the same percentage composition, and their 
 calculated calorific values would be identical, but the former is found 
 to produce 11,858 units of heats, and the latter only 11,055. 
 
 It must be remembered that the calorific value of a fuel represents 
 the actual amount of heat which a given weight of it is capable of 
 producing, and is quite independent of the manner in which the fuel 
 is burnt. Thus, a hundredweight of coal will produce precisely the 
 same amount of heat in an ordinary grate as in a wind-furnace, 
 though in the former case the fire will scarcely be capable of melt- 
 ing copper, and in the latter it will melt steel. The difference resides 
 in the temperature or calorific intensity of the two fires : in the wind- 
 furnace, through which a rapid draught of air is maintained by a 
 chimney, a much greater weight of atmospheric oxygen is brought into 
 contact with the fuel in a given time, so that, in that time, a greater 
 weight of fuel will be consumed and more heat will be produced : hence 
 the fire will have a higher temperature, for the temperature represents, 
 not the quantity of heat present in a given mass of matter, but the in- 
 tensity or extent to which that heat is accumulated at any particular 
 point. In the case of the wind-furnace here cited, a further advantage 
 is gained from the circumstance that the rapid draught of air allows a J 
 given weight of fuel to be -consumed in a smaller space, and, of course, y 
 the smaller the area over which a given quantity of heat is distributed, 
 the higher is the temperature within that area (as exemplified in the 
 use of the common burning-glass). In some of the practical applications 
 of fuel, such as heating steam boilers and warming buildings, it is the 
 calorific value of the fuel which chiefly concerns us ; but the case is 
 different where metals are to be melted, or chemical changes to be 
 brought about by the application of a very high temperature, for it is 
 then the calorific intensity, or actual temperature of the burning mass, 
 which has to be considered. No accurate method has yet been devised 
 
 * One gram evolves 96,920 gram-units of heat. 
 
1 66 CALCULATING CALORIFIC INTENSITY. 
 
 for determining by direct experiment the calorific intensity of fuel, nor 
 can this value be ascertained properly by calculation owing to lack of 
 complete data. 
 
 It will be instructive, however, to consider how some idea of calorific intensity 
 may be obtained from the calorific value. 
 
 Let it be required to calculate the calorific intensity, or actual temperature, of 
 carbon burning in pure oxygen gas. 
 
 Twelve grams of carbon combine with 32 grams of oxygen, producing 44 grams of 
 C0 2 ; hence I gram of carbon combines with 2.67 grams of oxygen, producing 3.67 
 grams of CO 2 . It has been seen above that, supposing that the water would bear 
 such an elevation of temperature, and that its specific heat would remain constant, 
 the i gram of carbon would raise i gram of water from o to 8080 C. If the 
 specAjic heat (or heat required to raise i gram through i) of C0. 2 were the same as 
 that of water, 8080 divided by 3.67 would represent the temperature to which the 
 3.67 grams of C0 2 would be raised, and therefore the temperature to which the 
 solid carbon producing it would be raised in the act of combustion. But the 
 specific heat of carbonic acid gas is only 0.2163, so that a given amount of heat 
 would raise i gram of C0 2 to nearly five times as high a temperature as that to 
 which it would raise i gram of water. * 
 
 Dividing 8080 units of heat (available for raising the temperature of the C0 2 ) by 
 0.2163 (the quantity of heat required to raise i gram of C0 2 through i), we obtain 
 37355 f r the number of degrees through which i gram of CO 2 might be raised by 
 the combustion of i gram of carbon. But there are 3.67 grams of CO 2 formed in 
 the combustion, so that the above number of degrees must be divided by 3.67 in 
 order to obtain the actual temperature of the C0 2 at the instant of its production, 
 that is, the temperature of the burning mass. The calorific intensity of carbon 
 burning in pure oxygen is therefore (37355 0.^3.67 = ) 10178 C. (or 18352 F.). 
 But if the carbon be burnt in air, the temperature will be far lower, because the 
 nitrogen of the air will absorb a part of the heat, to which it contributes nothing. 
 The 2.67 grams of oxygen required to burn i gram of carbon would be mixed, in air, 
 with 8.93 grams of nitrogen, so that the 8080 units of heat would be distributed over 
 3.67 grams of C0 2 and 8.93 grams of nitrogen. Since the specific heat of COois 
 0.2163, the product of 3.67 x 0.2163 ( or -794) represents the quantity of heat required 
 to raise the 3.67 grams of C0 2 from o to i C. 
 
 The specific heat of nitrogen is 0.2438 ; hence 8.93 x 0.2438 (or 2.177) represents 
 the quantity of heat required to raise the 8.93 grams of atmospheric nitrogen from 
 otoiC. 
 
 Adding together these products, we find that 0.794 + 2.177 = 2.971 represents the 
 quantity of heat required to raise both the nitrogen and carbonic acid gas from 
 o to i C. 
 
 Dividing the 8080 by 2.971, we obtain 2720 C. (4928 F.) for the number of 
 degrees through which these gases would be raised in the combustion, i.e., for the 
 calorific intensity of carbon burning in air. By heating the air before it enters the 
 furnace (as in the hot-blast iron furnace), of course the calorific intensity would be 
 increased ; thus, if the air be introduced into the furnace at a temperature of 600 F., 
 it might be stated, without serious error, that the temperature producible in the 
 furnace would be 5528 F. (4928 + 600). The temperature might be further in- 
 creased by diminishing the area of combustion, as by employing very compact fuel 
 and increasing the pressure of the blast. 
 
 In calculating the calorific intensity of hydrogen burning in air, from its calorific 
 value, it must be remembered that, in the experimental determination of the latter 
 number, the steam produced in the combustion was condensed to the liquid form, 
 so that its latent heat was added to the number representing the calorific value of 
 the hydrogen ; but the latent heat of the steam must be deducted in calculating the 
 calorific intensity, because the steam goes off from the burning mass and carries its 
 latent heat with it. 
 
 One gram of hydrogen, burning in air, combines with 8 grams of oxygen, pro- 
 ducing 9 grams of steam, leaving 26.77 grams of atmospheric nitrogen, and 
 evolving 34400 units of heat. 
 
 It has been experimentally determined that the latent heat of steam is 537, that is, 
 
 * It is here assumed that the specific heat of gases is constant as the temperature rises ; as 
 a fact it increases. The specific heat of steam is calculated to be doubled, and that of CO 2 to 
 be more than doubled, at 1200 C. 
 
THE REGENERATIVE FURNACE. 167 
 
 i gram of water, in becoming steam, absorbs 537 units of heat (or as much heat as 
 would raise 537 grams of water from o to i 0.) without rising in temperature as 
 indicated by the thermometer. The 9 grams of water produced by the combustion 
 of I gram of hydrogen will absorb, or render latent, 537x9 = 4833 units of heat. 
 Deducting this quantity from the 34400 units evolved in the combustion of i gram 
 of hydrogen, there remain 29567 units of heat available for raising the temperature 
 of the 9 grams of steam and 26. 77 grams of atmospheric nitrogen. The specific heat 
 of steam being 0.480 the number (o. 480 x 9^)4.32 represents the quantity of heat 
 required to raise the 9 grains of steam through i C. ; and the specific heat of nitro- 
 gen (0.2438) multiplied by its weight (26.77 grams) gives 6.53 units of heat required 
 to raise the 26.77 grams of nitrogen through i C. By dividing the available heat 
 (29567 units) by the joint quantities required to raise the steam and nitrogen through 
 iC. (4.32 + 6.53=10.85), we obtain the number 2725 C. U937 F.) for the calorific 
 intensity of hydrogen burning in air. 
 
 The actual calorific intensity of the fuel is not so high as it should be 
 according to theory, because a part of the carbon and hydrogen is con- 
 verted into gas by destructive distillation of the fuel, and this gas is not 
 actually burnt in the fire, so that its calorific intensity is not added to 
 that of the burning solid mass. Again, a portion of the carbon is con- 
 verted into carbonic oxide (CO), especially if the supply of air be im- 
 perfect, and much less heat is produced than if the carbon were converted 
 into carbon dioxide ; although it is true that this carbonic oxide may be 
 consumed above the fire by supplying air to it, the heat thus produced 
 does not increase the calorific intensity or temperature of the fire itself. 
 
 One gram of carbon furnishes 2.33 grams of carbonic oxide. These 2.33 grams of 
 carbonic oxide evolve, in their combustion, 5599 units of heat. But if the I gram 
 of carbon had been converted at once into carbon dioxide, it would have evolved 
 8080 units of heat, so that 8080- 5599, or 2481, represents the heat evolved during 
 the conversion of i gram of carbon into carbonic oxide, showing that a considerable 
 loss of heat in the fire is caused by ani imperfect supply of air. It has been 
 already pointed out that the formation of carbonic oxide is sometimes encouraged 
 with a view to the production of a flame from non-flaming coal, such as 
 anthracite. 
 
 The actual calorific intensity of fuel is diminished by the heat con- 
 sumed in bringing the portion of fuel yet unconsumed, as well as the 
 surrounding parts of the grate, up to the temperature of the fire. 
 
 In all ordinary fires and furnaces, a large amount of heat is wasted in 
 the current of heated products of combustion escaping from the chimney. 
 Of course, a portion of this heat is necessary in order to produce the 
 draught of the chimney. In boiler furnaces it is found that, for this 
 purpose, the temperature of the air escaping from the chimney must 
 not be lower than from 500 to 600 F. If the fuel could be consumed 
 by supplying only so much air as contains the requisite quantity of 
 oxygen, a great saving might be effected, but in practice about twice 
 the calculated quantity of air must be supplied in order to effect the 
 removal of the products of combustion with sufficient rapidity. 
 
 Much economy of fuel results from the use of furnaces constructed 
 on the principle of Siemens' regenerative furnace, in which the waste 
 heat of the products of combustion is absorbed by a quantity of fire- 
 bricks, and employed to heat the air before it enters the furnace, two 
 chambers of firebricks doing duty alternately, for absorbing the heat 
 from the issuing gas, and for imparting heat to the entering air, the 
 current being reversed by a valve as soon as the firebricks are strongly 
 heated. This system is best adapted for the use of gaseous fuel which 
 
i68 
 
 CHEMICAL TYPES. 
 
 can also be heated by the hot fire bricks before its combustion, a very 
 high temperature being thus attainable. 
 
 The following table shows the percentage composition of samples of 
 the principal varieties of fuel together with their calorific values : 
 
 
 C. 
 
 H. 
 
 0. 
 
 N. 
 
 S. 
 
 Ash. 
 
 Calorific 
 Value. 
 
 Wood (oak) . 
 
 50.18 
 
 6.08 
 
 42.64 
 
 O.IO 
 
 
 
 I.OO 
 
 3,OOO 
 
 Peat . 
 
 54.38 
 
 5.08 
 
 29-54 
 
 1.31 
 
 
 
 8.69 
 
 4,000 
 
 Lignite . 
 
 66.32 
 
 5.63 
 
 22.86 
 
 0.56 
 
 2.36 
 
 2.27 
 
 5,000 
 
 Bituminous coal 
 
 78.57 
 
 5- 2 9 
 
 12.88 
 
 1.84 
 
 0-39 
 
 1.03 
 
 8,250 
 
 Wigan cannel . 
 
 80.06 
 
 5-53 
 
 8.09 
 
 2.12 
 
 1.50 
 
 2.70 
 
 8,750 
 
 Charcoal . 
 
 81.97 
 
 2.30 
 
 14- i 5 
 
 
 
 
 1. 60 
 
 8,000 
 
 Anthracite 
 
 90-39 
 
 3-28 
 
 2.98 
 
 0.83 
 
 0.91 
 
 1.61 
 
 9,000 
 
 Coke . 
 
 92.48 
 
 0.47 
 
 0-93 
 
 0-73 
 
 I.I4 
 
 4-27 
 
 8,000 
 
 Petroleum . 
 
 85.00 
 
 13.00 
 
 2.OO 
 
 
 
 
 11,000 
 
 
 H. 
 
 CH 4 
 
 CO 
 
 C 2 H 4 * 
 
 C0 2 
 
 F. 
 
 0. 
 
 Calorific 
 Value.! 
 
 c M e } 
 
 43-99 
 
 39.36 
 
 6.42 
 
 4.12 
 
 
 
 5.40 
 
 0.40 
 
 170,000 
 
 cannel 
 
 41.72 
 
 41.88 
 
 4.98 
 
 8.72 
 
 
 
 2.71 
 
 ) 
 
 Producer gas . 
 
 2.20 
 
 7.40 
 
 22.80 
 
 
 3.60 
 
 63.50 0.50 
 
 28,000 
 
 Water gas 
 
 48.00 
 
 
 41.00 
 
 
 
 6.00 
 
 5.00 | 
 
 74,000 
 
 Mond gas 
 
 29.00 
 
 2.OO 
 
 I I.OO 
 
 
 
 16.00 
 
 42.00 
 
 
 40,000 
 
 TYPES OF CHEMICAL COMPOUNDS. 
 
 95. It has been seen in the preceding pages that 
 
 One vol. chlorine combines with one vol. hydrogen. 
 One oxygen ,, two vols. 
 
 One nitrogen three 
 
 One carbon four ,, 
 
 and that although other compounds of these elements with hydrogen 
 may exist they are less stable than the compounds in question and 
 contain, moreover, a smaller proportion of hydrogen. 
 
 The composition of the four compounds in question may be repre- 
 sented by the formulae C1H,OH 2 ,NH 3 and CH 4 respectively, and if the 
 valency of an element be defined as the maximum number of atoms of 
 hydrogen with which one atom of the element can combine, chlorine, 
 oxygen, nitrogen, and carbon are respectively mono- di- tri- and tetra- 
 valent elements. It will be found that no atom can combine with more 
 than four atoms of hydrogen. This being the case, the hydrogen com- 
 pounds of all elements must fall in one or other of the four classes of 
 which hydrochloric acid, water, ammonia, and marsh gas are the types. 
 
 One of the atoms of H in each of these typical molecules may be exchanged for 
 another atom, usually a metal ; thus C1H gives CINa. OH 2 gives OHNa, NH 3 gives 
 NH 2 Na, CH 4 gives CH 3 Na, It is evident that the groups OH, NH 2 , and CH 3 are 
 on the same footing as the elementary atom Cl in C1H ; as already explained, each 
 is a radicle that is. a group capable of being exchanged for an element. Since 
 
 * Including' benzene vapour, acetylene, etc. 
 f Gram units per cubic foot (28.315 litres). 
 
CHLORINE. 169 
 
 each of these radicles is equivalent to Cl, which unites with one atom of H, and is 
 therefore monovalent, each is a rnonovalent radicle. 
 
 The elements may be roughly divided into those which form stable compounds 
 with hydrogen and those which are substituted for hydrogen ; the latter class is 
 approximately coincident with that which includes the elements forming basic 
 oxides (i.e., the metals), whilst the former class contains those elements which form 
 acid oxides or anhydrides (i.0., the non-metals). The valency of a non-metal is 
 thus fixed by the number of atoms of hydrogen in a molecule of its maximum 
 hydrogen compound, whilst that of a metal is determined by the formula for its 
 compound with Cl or with 0. 
 
 Thus, sulphur, whose maximum hydrogen compound is SH 2 , falls under the oxygen 
 type, and is divalent towards hydrogen ; phosphorus, of which PH 3 is the hydrogen 
 compound containing the largest proportion of hydrogen, falls under the nitrogen 
 type, and is trivalent. 
 
 Again, the analysis of zinc oxide shows that the proportion of zinc to oxygen in 
 this compound is represented by the formula OZn ; zinc oxide, therefore, is of the 
 type OH 2 , one atom of the metal having been substituted for H 2 . Thus, Zn falls under 
 the oxygen type, and is divalent, from which fact it would be possible to foretell the 
 composition of its chloride ; for, since this can only be formed by the substitution 
 of two atoms of H, the type C1H must be doubled, C1 2 H 2 , before the zinc chloride 
 can be formed ; the formula in question would then be Cl 2 Zn. 
 
 The analysis of the higher chloride of iron (two are known) shows that the formula 
 for this chloride is FeCl 3 , showing that the iron has displaced the H in the type 
 C1H trebled, or C1 3 H 3 . From this fact the formula for the higher oxide of iron would 
 be prophesied to be 3 Fe 2 ; for, since Fe displaces H 3 , the type OH 2 must be 
 trebled, OgHg, in order that the H may be totally displaced by the'h-on, two atoms of 
 which will displace six of H. 
 
 It has been already noted that the valency of nitrogen towards H is not the limit 
 of the atom-fixing power of this element. It will be noted in the sequel that the 
 atom-fixing power which an element exhibits towards oxygen is generally greater 
 than that exhibited towards hydrogen. 
 
 CHLORINE. 
 
 Cl = 35.5 parts by weight = I volume. 
 
 96. This element is never found in the uncombined state, but is very 
 abundant in the mineral world in the forms of sodium chloride (common 
 salt) and potassium chloride. In these forms also it is an important con- 
 stituent of the fluids of the animal body, but as it is not found in sufficient 
 proportion in vegetable food, or in the solid parts of animal food, a 
 quantity of salt must be added to these in order to form a wholesome 
 diet. Sodium chloride is indispensable as a raw material for several of 
 the most useful arts, such as the manufacture of soaps and glass, bleach- 
 ing, &c. ; in fact, it is the source of three of the most generally useful 
 chemical products viz., chlorine, hydrochloric acid, and soda. 
 
 About the middle of the seventeenth century, a German chemist 
 named Glauber distilled some common salt with sulphuric acid, and 
 obtained a strongly acid liquid to which he gave the name muriatic acid 
 (from muria, brine) ; this was proved to be identical with the acid 
 long known to the alchemist as spirit of salt (obtained by distilling salt 
 with clay). The saline mass which was left after the experiment was 
 then termed Glauber's salt, but afterwards received its present name of 
 sodium sulphate. 
 
 It was undoubtedly a natural inference from this experiment that 
 common salt was composed of muriatic acid and soda, and that the 
 sulphuric acid had a greater attraction for the soda than the muriatic 
 acid had, which was therefore displaced by it. In accordance with this 
 
1 70 PEEPAEATION OF CHLORINE. 
 
 view, common salt was called muriate of soda, without further question, 
 until the year 1810, when the experiments of Davy proved that it was 
 really composed of the two elementary substances, chlorine and sodium, 
 and must therefore be styled, as it now is, sodium chloride, and repre- 
 sented by the formula Nad. It was further shown by Davy that the 
 muriatic acid was really composed of chlorine and hydrogen, and that 
 it was, in fact, HC1, or chloride of sodium (NaCl), in which the sodium 
 had been displaced by hydrogen. 
 
 Preparation of chlorine. In order to extract chlorine from common 
 salt, the salt is heated with black oxide of manganese and diluted 
 sulphuric acid, when the sulphates of sodium and manganese are left in 
 solution, and chlorine escapes in the form of gas 
 
 2NaCl + Mn0 2 + 2H 2 S0 4 = Na 2 S0 4 + MnS0 4 + 2H 2 + C1 2 . 
 
 40 grins, of common salt may be mixed with 30 grms. of binoxide of man- 
 ganese, introduced into a retort (Fig. 142) and a cold mixture of 44 c.c. of 
 
 Fi - . 142. Preparation of chlorine. 
 
 strong sulphuric acid with no c.c. of water poured upon it. The retort having been 
 well shaken, to wet the powder thoroughly with the acid, a very gentle heat is 
 applied, and the gas collected in bottles filled with water and inverted in the pneu- 
 matic trough ; the stoppers, previously greased, are then inserted under water into 
 the bottles. The first bottle or two contains the air from the retort, and therefore 
 has a paler colour than the pure chlorine afterwards collected. It is advisable to 
 keep a jar filled with water standing ready on the shelf of the trough, so that any 
 excess of chlorine may be passed into it instead of being allowed to escape into the 
 air and cause serious inconvenience. The bottles of moist chlorine must always be 
 preserved in the dark. Chlorine may also conveniently be prepared by gently heat- 
 ing 30 grms. of binoxide of manganese with no c.c. of common hydrochloric acid ; 
 Mn0 2 + 4HC1 = MnClg + 2H 2 + C1 2 . Either of the above methods will furnish about 
 2800 c.c. of chlorine. If chlorine be required free from HC1, it may be passed 
 through a strong solution of copper sulphate 
 
 CuS0 4 + 2HC1 = CuCl a + H 2 S0 4 . 
 
 On a large scale chlorine is made by heating manganese dioxide with hydrochloric 
 acid in stills built up of sandstone slabs. 
 
 In Weldorfs manganese recovery process for the manufacture of chlorine, the man- 
 ganese is made to act as a carrier of oxygen from the atmosphere to the hydrogen 
 of the HC1, setting the Cl free. For this purpose the chloride of manganese 
 obtained in the above process is decomposed by lime ; MnCl 2 +CaO=:CaCl 2 +MnO. 
 By mixing the MnO with more lime, and blowing air through the mixture MnO 2 
 is reproduced, and may be employed for decomposing a fresh quantity of HC1. In 
 Deacon's process, a mixture of air and hydrochloric acid gas is passed over hot fire- 
 
PEOPERTIES OF CHLOEINE. 171 
 
 brick which has been soaked in solution of copper sulphate and sodium sulphate, and 
 dried. The final result is expressed by the equation 2HC1 + (N 4 + O) = H 2 + C1 2 + N 4 , 
 so that the chlorine obtained is mixed with tw r ice its volume of nitrogen, which 
 does not interfere seriously with its useful application. The action of the copper- 
 salt has not been clearly explained, but it appears to depend upon the instability of 
 the chlorides of copper under the influence of heat and oxygen. 
 
 Chlorine is now made by electrolysing NaCl, a process which, among others, 
 will receive notice under Alkali. 
 
 Properties of chlorine. The physical and chemical properties of 
 chlorine are more striking than those of any element hitherto con- 
 sidered. Its colour, whence it derives its name (^Xwpo'c, pale green), is 
 bright greenish-yellow, its odour insupportable. It is twice and a half 
 as heavy as air (sp. gr. 2.47), and may be reduced to the liquid state by 
 cooling it to - 34 C. (its boiling-point), or by a pressure of 8.5 
 atmospheres at 12.5 C. If a bottle of chlorine be held mouth down- 
 wards in water, its stopper removed, one-third of the chlorine decanted 
 into a jar, and the rest of the gas shaken with the water in the bottle, 
 the mouth of which is closed by the palm of the hand, the water will 
 absorb about twice its volume of chlorine, producing a partial vacuum 
 in the bottle, which will be held firmly against the hand by atmospheric 
 pressure. If air be then allowed to enter, and the bottle again shaken 
 so long as there is any absorption, a saturated solution of chlorine 
 (liquor chlori, chlorine water) will be obtained. By exposing this yellow 
 solution to a temperature approaching o C., yellow crystals of chlorine 
 hydrate (C1.4H 2 0) are obtained, the liquid becoming colourless ; under 
 atmospheric pressure the crystals decompose into water and chlorine at 
 9.6 C. 
 
 When the water in the pneumatic trough, over which chlorine is being collected, 
 happens to be very cold, the gas is often so foggy as to be quite opaque, in conse- 
 quence of the deposition of minute crystals of the hydrate. On standing, the gas 
 becomes clear, crystals of the hydrate being deposited like hoar-frost upon the 
 sides of the bottle ; the gas also becomes clear when the bottles are slightly 
 warmed. 
 
 Chlorine hydrate affords a convenient source of liquid chlorine. The crystals are 
 rammed into a pretty strong tube closed at one end, about 12 inches long, and ^ an 
 inch in diameter, previously cooled in ice. The tube, having been nearly filled with 
 the crystals, is kept surrounded with ice, whilst its upper end is gradually softened 
 in the blowpipe flame and drawn off so as to be strongly sealed. When this tube is 
 immersed in water at 38 C., the chlorine separates from the water, and two layers 
 of liquid are formed, the lower one consisting of amber yellow liquid chlorine (sp. 
 gr. 1.33), and the upper of a pale yellow aqueous solution of chlorine. On allowing 
 the tube to cool again, the crystalline hydrate is reproduced, even at common 
 temperatures, being more permanent under pressure. It may even be sublimed in a 
 sealed tube. 
 
 Liquid chlorine is now an article of commerce, being transported in steel 
 bottles. 
 
 The critical temperature of chlorine is 146 C., and its critical pressure 93.5 atm. 
 
 The most characteristic chemical feature of chlorine is its powerful 
 attraction for many other elements at the ordinary temperature. 
 Among the non-metals, hydrogen, bromine, iodine, sulphur, selenium, 
 phosphorus, and arsenic combine spontaneously with chlorine, and 
 nearly all the metals behave in the same way.* 
 
 * The presence of moisture appears to be as essential for the combination of chlorine with 
 other elements as it is for the combination of oxygen with other elements. Thus sodium 
 may be fused in absolutely dry chlorine gas without alteration, while in ordinary chlorine 
 violent combustion occurs. When the sodium is heated to redness in the dry gas it burns 
 explosively. 
 
172 
 
 CHLORINE AND HYDROGEN. 
 
 A piece of dry phosphorus in a deflagrating spoon, immersed in a bottle of 
 chlorine (Fig. 143), takes fire spontaneously, combining with the chlorine to form 
 phosphorous chloride (PC1 3 ). A tall glass shade may be placed over the bottle, 
 which should stand in a plate containing water, so that the fumes may not escape 
 into the air. If phosphorus be placed in a bottle of oxygen, to which a small quan- 
 tity of chlorine has been added, it will burst out after a minute or two into most 
 brilliant combustion. 
 
 Powdered antimony (the metal, not the sulphide), sprinkled into a bottle of 
 chlorine (Fig. 144), descends in a brilliant shower of white sparks, the antimony 
 burning in the chlorine to form antimonious chloride (SbCl 3 ). A little water 
 .should be placed at the bottom of the bottle to prevent it from being cracked. 
 
 If a flask, provided with a stop-cock (Fig. 145), be filled with leaves of Dutch 
 metal (an alloy of copper and zinc resembling gold-leaf), exhausted of air, and 
 screwed on to a capped jar of chlorine standing over water, on opening the stop- 
 
 Fig-. 143. 
 
 Fig-. 144. 
 
 oocks so that the chlorine may enter the flask, the metal burns with a red light, 
 forming thick yellow fumes containing cupric chloride (CuCl 2 ), and zinc chloride 
 <ZnCl 2 ). A gold leaf suspended in chlorine is not immediately attacked, but gra- 
 dually becomes auric chloride (AuCl 3 ). 
 
 97. The most important useful applications of chlorine depend upon 
 its powerful chemical attraction for hydrogen. The two gases may be 
 mixed without combining, if kept in the dark ; but when the mixture 
 is exposed to light, they combine to form hydrogen chloride (HOI) 
 with a rapidity proportionate to the intensity of the actinic rays (or 
 rays capable of inducing chemical change) in the light employed. Ex- 
 posed to gas-light or ordinary diffused daylight, the H and Cl combine 
 slowly ; but direct sunlight causes sudden combination, attended with 
 explosion, resulting from the expansion which the hydrogen chloride 
 formed suffers by the heat evolved in the act of combination (22,000 
 gram units per 36.5 grams of HC1 formed). The light of magnesium 
 burning in air, and some other artificial lights, also cause sudden com- 
 bination. The gases also combine at about 300 C., and explode on 
 application of a lighted taper. 
 
 Two pint gas-bottles should be ground so that their mouths may be fitted accu- 
 rately to each other, and filled respectively with dry hydrogen and dry chlorine, 
 both gases having been dried by passing through oil of vitriol, and collected, the 
 hydrogen by upward, and the chlorine by downward, displacement of air. The 
 mouths should be slightly greased before the bottles are filled with gas, and after- 
 
CHLORINE AND HYDROGEN. 
 
 '73 
 
 wards closed with glass plates. On placing the bottles together, and removing the- 
 plates so that the gases may come in contact (see Fig. 69), the yellow colour of the 
 chlorine will be permanent so long as the mixture is kept in the dark, but on 
 exposure to daylight the colour will gradually disappear, the hydrochloric acid gas 
 being colourless. If the bottles be now closed with glass plates, the small quantity 
 of gas which escapes during the operation will be seen to fume strongly in air, a 
 property not possessed either by hydrogen or chlorine ; and when the necks of the 
 bottles are immersed in water, and the glass plates withdrawn, the water will gradu- 
 ally absorb the gas, and be forced into the bottles so as to fill them, with the excep- 
 tion of a small space occupied by the air accidentally admitted, showing that the- 
 hydrochloric acid gas possesses the 
 joint volumes of the hydrogen and 
 chlorine. If the water be tinged 
 with blue litmus, it will be strongly 
 reddened as it enters the bottles. 
 
 The sudden union of the gases with 
 explosion may be safely exhibited in 
 a Florence flask. The flask is filled 
 with water, which is then poured out 
 into a measure. Exactly half the 
 water is returned to the flask, and 
 its level in the latter carefully marked 
 with a diamond or file. The flask, 
 having been again filled with water, 
 is closed with the thumb and inverted 
 in the pneumatic trough, so that Fig. 146. 
 
 hydrogen may be passed up into it to 
 
 displace one-half of the water. A short-necked funnel is then inserted, under the 
 water, into the neck of the flask, and chlorine rapidly decanted up from a gas-bottle 
 (Fig. 146) until the rest of the water has been displaced. The flask is now raised 
 from the water and quickly closed with a cork (Fig. 147), through which pass two* 
 gutta-percha-covered copper wires, the ends of which have been stripped and brought 
 sufficiently near to each other to allow of the passage of the electric spark within 
 the flask. The ends external to 
 the flask are also stripped and 
 bent into hooks, for convenient 
 connection with the conducting 
 wires. The flask is placed upon 
 the ground, and covered with a 
 wooden box to prevent the pieces 
 from flying about. On connecting 
 the copper wires with the conduct- 
 ing wires from an induction coil 
 or an electrical machine, it will be 
 heard, on passing the spark, that 
 the mixture has violently ex- 
 ploded ; on raising the box, it will 
 be found filled with strong fumes Fig. 147. 
 
 of hydrochloric acid, and a heap 
 of small fragments of glass will represent the flask. 
 
 A flask filled in the same way with the mixture of hydrogen and chlorine may be 
 attached to the end of a long stick, and thrust out into the sunlight, when it explodes 
 with great violence. To illustrate the direct combination of H and Cl under the 
 influence of artificial light, a strong half -pint gas cylinder is half filled with H, over 
 water, then filled up quickly with Cl, also over water, closed with a thin plate of mica, 
 placed mouth upwards on the table, and a piece of burning magnesium tape held 
 close to the side of the cylinder ; the lightness of the mica plate obviates any danger. 
 
 A mixture of H and Cl which is to be exploded by light must consist of exactly 
 equal volumes, for a slight excess of either gas greatly diminishes the sensitiveness 
 of the mixture to light ; thus a mixture of 100 vols. of Cl. with 100.6 vols. H is 
 38 per cent, less sensitive than a mixture of equal volumes. 
 
 The attraction of chlorine for hydrogen enables it to decompose 
 water. Chlorine-water may be preserved in the dark without change ; 
 
CHLOEINE AND HYDROGEN. 
 
 but when exposed to light, it loses the smell of chlorine and becomes 
 converted into weak hydrochloric acid, the oxygen being liberated ; 
 H 2 + C1 2 = 2HC1 + 0.* The decomposition is much more rapid at a 
 red heat, so that oxygen is obtained in abundance by passing a mixture 
 of chlorine and steam through a red-hot tube. 
 
 For this experiment a porcelain tube is used, loosely filled with fragments of broken 
 porcelain, to expose a large heated surface. This tube is gradually heated to red- 
 ness in a gas furnace (Fig. 148). One end of it receives the mixture of chlorine with 
 steam, obtained by passing the chlorine evolved from hydrochloric acid and 
 
 Fig. 148. Steam decomposed by chlorine. 
 
 manganese dioxide in A, through a flask (B) of boiling water. The other end of 
 the tube is connected with a bottle (C) containing solution of potash, to absorb any 
 excess of chlorine and the hydrochloric acid formed ; from this bottle the oxygen 
 is collected over the pneumatic trough. 
 
 The combination of hydrogen with chlorine may obviously be 
 regarded as the substitution of an atom of chlorine for an atom of 
 hydrogen in a molecule of hydrogen, HH + C1C1 = HC1 + HC1, the 
 atom of hydrogen substituted having been removed as HC1. Thus 
 viewed it becomes typical of a large number of cases in which two 
 atoms of chlorine react with a hydrogen compound, one of them bear- 
 ing away a hydrogen atom in the form of HC1 whilst the other takes 
 the place of the hydrogen thus removed. Such a substitution of chlorine 
 for hydrogen is known as metalepsis, and is a very common reaction of 
 chlorine with hydrocarbons ; since the formation of hydrogen chloride 
 is initiated by light it is not surprising that metalepsis is aided by this 
 agency. 
 
 When equal volumes of marsh gas (CH 4 ) and chlorine are mixed and exposed to 
 sunlight the volume of the mixture remains unaltered, but after a time the yellow 
 colour of the chlorine is no longer observed, and the gas is found to consist of equal 
 volumes of methyl chloride and hydrogen chloride, CH 4 + C1 2 =CH 3 C1 + HC1. The 
 metalepsis may be carried further by mixing methyl chloride with more chlorine, 
 CH 3 C1 + C1 2 = CH 2 C1 2 + HC1. Again CH 2 C1 2 with Cl a will yield chloroform CHC1 3 , 
 and this with C1 2 will yield carbon tetrachlorlde CC1 4 . By mixing one volume of 
 marsh gas with its own volume of C0 2 , to prevent violent action, and adding four 
 volumes of chlorine, an oily mixture, containing chiefly CHC1 3 and CC1 4 is formed 
 under the influence of daylight. 
 
 Since water is decomposed by chlorine, it is not surprising that most 
 
 * A portion of this oxygen beeomes hypochlorous acid (HC1O), chloric acid (HC1O 3 ) and 
 perchloric acid (HC1O 4 ), particularly if the light be not very intense. 
 
OXIDISING ACTION OF CHLORINE. 175 
 
 other hydrogen compounds are attacked by it. Ammonia (NH 3 ) is 
 acted on with great violence. If a stream of ammonia gas issuing from 
 a tube connected with a flask in which solution of ammonia is heated 
 be passed into a bottle of chlorine, it takes fire immediately, buring 
 with a peculiar flame, and yielding thick white clouds of ammonium 
 chloride; 4NH 3 + C1 3 = 3NH 4 C1 + N. A piece of folded filter-paper 
 dipped in strong ammonia, and immersed in a bottle of chlorine, will 
 exhibit the same effect. When the chlorine is allowed to act upon 
 ammonium chloride, its operation is less violent, and one of the most 
 explosive substances, nitrogen chloride, NC1 3 , is produced. 
 
 Many of the compounds of hydrogen with carbon are also decomposed 
 with violence by chlorine. When a piece of folded filter-paper is dipped 
 into oil of turpentine (0 10 H 16 ), and afterwards into a bottle of chlorine, 
 it bursts into a red flame, liberating voluminous clouds of carbon and 
 hydrochloric acid. Acetylene (C 2 H 2 ) was found to explode spontaneously 
 with chlorine when exposed to light (page 141). The striking decom- 
 position of olefiant gas (C 2 H 4 ) by chlorine on the approach of a flame 
 has already been noticed (page 143). When a lighted taper is immersed 
 in pure chlorine, it is extinguished ; but if a little air be present, it 
 continues to burn with a small red flame, the hydrogen only of the wax 
 combining with the chlorine, whilst the carbon separates in black 
 smoke, mixed with the hydrochloric fumes. A mixture of chlorine 
 with an equal volume of oxygen burns up much of the carbon, with a 
 very pretty effect. When chlorine is brought in contact with the flame 
 of a spirit-lamp, it renders the flame luminous by causing the separation 
 of solid particles of carbon (page 149). It has been seen, in the case of 
 olefiant gas, that chlorine sometimes combines directly with the hydro- 
 carbons. 
 
 The attraction of chlorine for hydrogen enables the moist gas to act 
 as an oxidising agent. Thus, if marsh gas and chlorine be mixed in the 
 presence of water, and exposed to daylight, the water is decomposed, its 
 hydrogen combining with the chlorine, and its oxygen with the carbon 
 of the marsh gas ; CH 4 + 2 H 2 + C1 8 = C0 2 + 8HC1. 
 
 98. The powerful bleaching effect of chlorine upon organic colour- 
 ing matters is now easily understood. If a solution of chlorine in 
 water be poured into solution of indigo (sulphindigotic acid), the blue 
 colour of the indigo is discharged, and gives place to a comparatively 
 light yellow colour. The presence of water is essential to the bleaching 
 of indigo by chlorine, the dry gas not affecting the colour of dry indigo. 
 The indigo is first oxidised at the expense of the water and converted 
 into isatin, which is then acted upon by the chlorine and converted 
 by metalepsis into chlorisatin, having a brownish-yellow colour 
 
 C 16 H 10 N 2 2 (Indigo') + 2H,,0 + C1 4 = 2C 8 H 5 N0 2 (Isatin) + 4HC1 
 
 CgHgNOo (Isatin) + Cf 2 = C 8 H 4 C1N0 2 (C/ilor isatin) + HC1. 
 
 Nearly all vegetable and animal colouring matters contain carbon, 
 hydrogen, nitrogen, and oxygen, and are converted by moist chlorine 
 into products of oxidation or chlorination which happen to be colour- 
 less, or nearly so. 
 
 It might be thought that, since water is decomposed by chlorine only 
 in light, chlorine would not behave as an oxidising agent in the dark. 
 Bleaching by chlorine can, however, proceed in the absence of light 
 because the colouring matter, being ready to combine with oxygen, exerts 
 
I 7 6 
 
 CHLORINE AS A DISINFECTANT. 
 
 Tig. 149, 
 
 attraction on the oxygen of the water, sufficiently powerful to weaken 
 the union between the H and so that the chlorine can effect the 
 decomposition. 
 
 That dry chlorine will not bleach may be shown by shaking some oil of vitriol in 
 a bottle of the gas and allowing it to stand for an hour or two, so that the acid 
 may remove the whole of the moisture. A piece of crimson paper dried at a 
 moderate heat and suspended in the bottle while warm, remains unbleached for 
 hours ; but a similar piece suspended in a bottle of moist chlorine is bleached 
 almost immediately. If characters be written on crimson paper with a wet brush, 
 and the paper placed in a jar beside a bottle of chlorine 
 (Fig. 149), it will be found on removing the stopper 
 that white characters soon make their appearance on the 
 red ground. 
 
 When a collection of coloured linen or cotton fabrics, 
 or of artificial flowers, is exposed to the action of moist 
 chlorine or of chlorine-water, those which are dyed with 
 organic colouring matters are bleached at once, whilst 
 the mineral colours for the most part remain unaltered. 
 Green leaves immersed in chlorine acquire a rich autum- 
 nal brown tint, and are eventually bleached. All flowers 
 are very readily bleached by the gas. 
 
 Chlorine is very extensively employed for 
 bleaching linen and cotton, the gas acting upon 
 the colouring matter without affecting the fibre ; 
 but silk and wool present much less resistance 
 to chemical action, and would be much injured 
 by chlorine so that they are always bleached by sulphurous acid gas. 
 
 Neither chlorine itself nor its solution in water can be very con- 
 veniently used for bleaching on the large scale, on account of the 
 irritating effect of the gas, so that it is usual to employ it in the form 
 of chloride of lime, from which it can be easily liberated as it is wanted. 
 
 99. The explanation above given of the bleaching effect of chlorine 
 may probably be applied also to its so-called disinfecting properties. 
 The atmosphere, in particular localities, is occasionally contaminated 
 with micro-organisms, some of which are known only by their injurious 
 effects upon the health, their quantity being so small that they do not 
 appear in the results of the analysis of such air. Since, however, these 
 minute forms of life appear to be killed by the same agents which are 
 usually found to decompose organic compounds, chlorine has been very 
 commonly employed to combat these insidious enemies to health. 
 
 Among the offensive and unhealthy products of putrefaction of 
 animal and vegetable matter, sulphuretted hydrogen, ammonia, and 
 like bodies are found. That chlorine breaks up these hydrogen com- 
 pounds is well known ; hence its great value for removing the un- 
 wholesome properties of the air in badly drained houses, &c. 
 
 100. The discovery of chlorine, and the discussions which ensued with 
 respect to its real nature, contributed very largely to the advancement 
 of chemical science. About the year 1770, the Swedish chemist Scheele 
 (who afterwards discovered oxygen) first obtained chlorine by heating 
 manganese ore with muriatic acid. 
 
 The construction which Scheele put upon the result of this experiment 
 was one which was consistent with the chemistry of that date. He sup- 
 posed the muriatic acid to have been deprived of phlogiston, and hence 
 chlorine was termed by him dephlogisticated muriatic acid. This phlo- 
 giston had long been a subject of contention among philosophers, having 
 
HYDROGEN CHLORIDE. 
 
 177 
 
 been originally assumed to exist in combination with all combus- 
 tible bodies, and to be separated from them during their combustion. 
 Towards the decline of the phlogistic theory, attempts were made to prove 
 the identity of this imaginary substance with hydrogen, which shows 
 how very nearly Scheele's reasoning approached to the truth, even with 
 the very imperfect light which he then possessed. Berthollet's move- 
 ment was retrograde, when, ten years afterwards, he styled chlorine oxy- 
 genised muriatic or oxymuriatic acid ; but the experiments of Gay-Lussae 
 and Thenard, and more particularly those of Davy in 1811, proved de- 
 cisively that hydrochloric acid was composed of chlorine and hydrogen, 
 and that the effect of the black oxide of manganese in Scheele's experi- 
 ment was to remove the hydrogen in the form of water, thus setting the 
 chlorine at liberty. 
 
 HYDROCHLORIC ACID, OR HYDROGEN CHLORIDE. 
 HCl = 36-5 parts by weight = 2 vols. 
 
 101. This acid is found in nature among the gases emanating from 
 active volcanoes, and occasionally in the spring and river waters of 
 volcanic districts. For use it is always prepared artificially by the 
 action of sulphuric acid upon common salt 
 
 NaCl + H 2 S0 4 = HC1 + NaHS0 4 
 Common salt. Hydrogen-sodium sulphate. 
 
 the sodium of the common salt changing places with the hydrogen of 
 the sulphuric acid. 
 
 20 grams of common salt (previously dried in an oven) are introduced into a dry 
 flask (Fig. 150), to which has been fitted, by means of a perforated cork, a tube bent 
 twice at right angles, to allow the gas to be collected by downward displacement. 
 30 c.c. of strong H 2 S0 4 are poured 
 upon the salt, and, the cork having 
 been inserted, the flask is very gently 
 heated, in order to promote the dis- 
 engagement of the hydrochloric acid 
 gas, which is collected in a perfectly 
 dry bottle, the mouth whereof when 
 full, may be covered with a glass 
 plate smeared with a little grease. 
 While being filled, the bottle may be 
 closed with a perforated card. 
 
 At a red heat the whole of the 
 hydrogen in the H 2 S0 4 can be con- 
 verted into HC1. 2NaCl + H 2 S0 4 = 
 Na. 2 S0 4 + 2HCl ; but this is never 
 effected in practice. 
 
 Common salt in powder sometimes 
 froths to a very inconvenient extent 
 with sulphuric acid ; it is therefore 
 often preferable to employ fragments 
 of rock salt or of fused salt, prepared 
 by fusing the common salt in a clay crucible, and pouring it on to a clean dry stone. 
 
 Hydrogen chloride is also conveniently prepared by dropping strong H 2 S0 4 from a 
 funnel provided with a stopcock into commercial strong hydrochloric acid. The 
 apparatus may take the form shown in Fig. 156, the U-tube being omitted. 
 
 The bottle will be known to be filled with gas by the abundant escape 
 of the dense fumes which hydrogen chloride, itself transparent, pro- 
 duces by condensing the moisture of the air ; for since the gas is heavier 
 than air (sp. gr. 1.278), it will not escape in any quantity from the 
 
 Fig. 150. Preparation of hydrochloric acid gas. 
 
HYDROCHLORIC ACID. 
 
 bottle until the latter is full. The odour of the gas is very suffocating, 
 but not nearly so irritating as that of chlorine. The powerful attraction 
 for water is one of the most important properties of this gas. 
 
 If a jar of hydrogen chloride be closed with a glass plate and inverted underwater, 
 it will be found on removing the plate that the gas is absorbed with great rapidity, 
 the water being forced up into the bottle by the pressure of the external air, in pro- 
 portion as the gas is absorbed. The experiment may also be made as in the case of 
 ammonia (Fig. 69, see page 84). 
 
 The dissolution of 36.5 grams HC1 in excess of water evolves 17,200 
 calories. 
 
 The liquid hydrochloric, or muriatic acid of commerce, is a solution 
 of the gas in water, and may be recognised by the grey fumes, with the 
 peculiar odour of the acid, which it evolves when exposed to the air. 
 One pint of water at a temperature of 5 C. is capable of absorbing 
 480 pints of hydrochloric acid gas, forming ij pints of the solution, 
 having the specific gravity 1.21. The strength of the acid purchased 
 in commerce is usually inferred from the specific gravity, by reference 
 to tables indicating the weight of HOI contained in solutions of 
 different specific gravities. The strongest hydrochloric acid (sp.gr. 1.21) 
 contains 43 per cent., by weight of the gas. At - 18 C. it deposits 
 crystals of HC1.2Aq. The common acid has usually a bright yellow 
 colour, due to the accidental presence of a little ferric chloride 
 (Fe,01 6 ). 
 
 This acid is produced in enormous quantities in the alkali works, 
 where common salt is decomposed by sulphuric acid in order to convert 
 it into sodium sulphate, as a preliminary step to the production of 
 
 sodium carbonate. The alkali 
 manufacturer is compelled to 
 condense the gas, for it is found 
 to wither up the vegetation in the 
 neighbourhood. For this purpose 
 the hydrochloric acid gas is drawn 
 up from the furnace through 
 vertical cylinders filled with coke, 
 over which streams of water are 
 made to trickle. The water 
 absorbs the acid, and is drawn 
 off from below (see Alkali). 
 
 In preparing a pure solution of the 
 acid for chemical use on a small scale, 
 the gas prepared as above may be passed 
 into a small bottle containing a very 
 little water, to wash the gas, or remove 
 
 any sodium sulphate which may splash over, and then into a bottle about two-thirds 
 filled with distilled waier, the tube delivering the gas passing only about T V inch 
 below the surface, so that the heavy solution of hydrochloric acid may fall to the 
 bottom, and fresh water may be presented to the gas (Fig. 151). 
 
 Pure solution of hydrochloric acid is sometimes prepared on a large scale by 
 allowing concentrated sulphuric acid to run into the common hydrochloric acid, 
 when the gas is evolved, and is washed and passed into water. 
 
 When the concentrated solution of hydrochloric acid is heated in a 
 retort it evolves abundance of hydrochloric acid gas, rendering it pro- 
 bable that it is not a true chemical compound of water with the acid. 
 The evolution of gas ceases when the remaining liquid contains 20 per 
 
 Fig. 151. Preparation of solution of 
 hydrochloric acid. 
 
HYDROCHLORIC ACID AND METALS. 
 
 179 
 
 cent, of acid (and has a sp. gr. of i.io). If a weaker acid than this 
 be heated, it loses water until it has attained this strength, when it 
 distils unchanged at no j C.* 
 
 The concentrated solution forms a very convenient source from which to procure 
 the gas. It may be heated in a flask, and the gas dried by passing through a bottle 
 filled with fragments of pumice-stone wetted with concentrated sulphuric acid, 
 being collected over the mercurial trough (Fig. 152). 
 
 Fig. 152. 
 
 The avidity with which water absorbs hydrogen chloride is the 
 more remarkable, because this gas can be liquefied only under a very 
 high pressure, amounting at the ordinary temperature to about 40 
 atmospheres. The liquid boils at - 80 C. and solidifies at a lower 
 temperature, melting at - 112 C. The sp. gr. of the liquid is 0.91 
 at o C. The critical temperature of the gas is 52 C. and the critical 
 pressure is 86 atmospheres. 
 
 The liquefied hydrogen chloride has comparatively little action even 
 upon those metals which decompose its aqueous solution with great 
 violence ; quicklime is unaffected by it, and solid litmus dissolves in it 
 with a faint purple colour, instead of the bright red imparted by the 
 aqueous hydrochloric acid. Dry hydrochloric acid gas is not absorbed 
 by calcium carbonate.t 
 
 The injurious action of hydrochloric acid gas upon growing plants is 
 probably connected with its attraction for water. If a spray of fresh 
 leaves is placed in a bottle of hydrochloric acid, it becomes at oncfe 
 brown and shrivelled. One part of HC1 in 25,000 of air is fatal to plants. 
 
 1 02. Action of hydrochloric acid upon metals. Those metals which 
 have the strongest attraction for oxygen will also generally have the 
 strongest attraction for chlorine, so that in respect to their capability of 
 decomposing hydrochloric acid, they may be ranked in pretty nearly the 
 same order as in their action upon water (p. 19). Since, however, the 
 attraction of chlorine for the metals is generally superior to that of 
 oxygen, the metals are more easily attacked by hydrochloric acid than 
 
 * The proportion of acid thus retained by the water varies- directly with the atmospheric 
 pressure to which it is exposed during' the distillation. A hydrate HC1.8H 2 O would contain 
 20.2 per cent. HC1. 
 
 f The realisation of the fact that hydrochloric acid solution behaves similarly to the oxy- 
 acids, led to the ab mdonment of the view that oxygen is the acid former, and that all acids 
 must cont'in this element. The facts quoted with regard to the inactivity of anhydrous 
 HC1 seem to inilicite that oxygen (as water) is, after all, essential to an acid. 
 
180 HYDROCHLORIC ACID AND METALLIC OXIDES. 
 
 by water, the metal taking the place of the hydrogen, and a chloride of 
 the metal being formed. 
 
 Even silver, which does not decompose water at any temperature, is 
 dissolved, though very slowly, by boiling concentrated hydrochloric acid, 
 the chloride of silver formed being soluble in the strong acid, though it 
 may be precipitated by adding water. 
 
 Gold and platinum, however, are not attacked by hydrochloric acid ; 
 but if a little free chlorine be present, it converts them into chlorides. 
 
 Iron and zinc decompose the acid very rapidly in the cold, forming 
 ferrous chloride and zinc chloride respectively, and liberating hydrogen ; 
 
 When potassium or sodium is exposed to hydrochloric acid gas, it 
 immediately becomes coated with a white crust of chloride, which partly 
 protects the metal from the action of the gas ; but when these metals 
 are heated to fusion in hydrochloric acid gas, they burn vividly ; 
 
 The composition of hydrogen chloride may be exhibited by confining a 
 measured volume of the gas over mercury (see Fig. 106, p. 130), and 
 passing up a freshly cut pellet of sodium. On gently agitating the 
 tube, the gas diminishes in volume, and after a time will have contracted 
 to one-half, and will be found to have all the properties of hydrogen. 
 This result confirms that obtained by synthesis, as described above, 
 that 2 volumes of hydrogen chloride contain i volume of hydrogen 
 and i volume of chlorine. 
 
 The electrolysis of hydrochloric acid, which leads to the same con- 
 clusion, has been described at p. 16. 
 
 103. Action of hydrochloric acid upon metallic oxides. As a general 
 rule, it may be stated that, when hydrochloric acid acts upon the oxide 
 of a metal, the results are water and a chloride of the metal, in which 
 each atom of oxygen in the oxide has been displaced by 2 atoms of 
 chlorine. 
 
 Thus, silver oxide acted on by hydrochloric acid gas gives water and 
 silver chloride ; Ag 2 + 2HC1 = H 2 + 2 AgCl. 
 
 Suboxide of copper (cuprous oxide) yields water and subchloride of 
 copper (cuprous chloride) ; Cu 3 + 2HC1 = H 2 O + Cu,Cl 2 . 
 
 Ferric oxide gives water and ferric chloride; Fe 2 3 + 6HCl = 
 3 H 2 + Fe 2 01 6 . 
 
 With stannic oxide, water and stannic chloride are obtained ; 
 Sn0 2 + 4 HC1 = 3H 2 O + SnCl 4 . 
 
 Antimonious oxide is converted into water and antimonious chloride ; 
 Sb 2 O 3 + 6 HOI = 3H 2 + 2 Sb01 3 . 
 
 104. In cases where the corresponding chloride does not exist, or is 
 not stable under the conditions of the experiment, a chloride is formed 
 containing less chlorine than is equivalent to the oxygen in the oxide, 
 and the balance is evolved in the free state. Thus, when manganese 
 sesquioxide and dioxide are heated with hydrochloric acid 
 
 Mn 2 3 + 6HC1 = 3H 2 + 2MnCl 2 + C1 ; 
 Mn0 2 + 4HC1 = 2H 2 O + MnCl 2 + C1 2 . 
 
 It would seem that Mn 2 Cl 6 and MnCl 4 , corresponding with Mn 2 O $ 
 and Mn0 2 respectively, are first formed and that these decompose into 
 the stable chloride, Mn01 2 , and chlorine. 
 
 Chromic anhydride, a chloride corresponding with which is not known 
 
CHLOEINE OXIDES. l8l 
 
 to exist, when heated with hydrochloric acid, yields chromic chloride 
 and chlorine ; 2 Cr0 3 + 1 2HC1 = 6H 2 + Cr 2 Cl 6 + C1 6 . 
 
 Most metallic oxides containing i atom of oxygen have a correspond- 
 ing chloride of a stable character, but the higher oxides less frequently 
 form corresponding chlorides endowed with any stability. Basic oxides 
 rarely evolve chlorine from hydrochloric acid. When an oxide gives off 
 chlorine on boiling with hydrochloric acid it is probably a peroxide or 
 an add oxide, that is, an oxide containing more oxygen than suffices to 
 form a base with the metal. Thus, the basic oxide of manganese is MnO, 
 which dissolves in HC1 with evolution of chlorine ; but the dioxide 
 Mn0 2 , or MnO.O, contains an extra atom of oxygen which is able to 
 oxidise HOI; 2HC1 + = H 2 + C1 2 . 
 
 COMPOUNDS OF CHLORINE WITH OXYGEN. 
 
 105. It is worthy of notice, that whilst chlorine and hydrogen so 
 readily unite, there is 110 method by which chlorine can be made to 
 combine in a direct manner with oxygen, the compounds of these 
 elements having been hitherto obtained only by indirect processes. An 
 excellent illustration is thus afforded of the fact, that the more closely 
 substances resemble each other in their chemical relations, the less will 
 be their tendency to combine ; for chlorine and oxygen are both highly 
 electro-negative bodies, and therefore, having both a powerful attrac- 
 tion for the electro-positive hydrogen, their attraction for each other is 
 of a very low order. 
 
 Three oxides of chlorine, C1 8 0, C10 2 and C1 2 7 , and four oxyacids of 
 chlorine, HC10, HC10 2 , HC10 3 , and HC10 4 , are known. 
 
 1 06. Hypochlorous anhydride or chlorine monoxide (01,0), is 
 of some practical interest in connection with chloride of lime, chloride of 
 soda, and other bleaching compounds. It is prepared by passing dry 
 chlorine gas over dry precipitated mercuric oxide, and condensing the 
 product in a tube surrounded with a mixture of ice and salt ; 
 
 The hypochlorous anhydride is thus obtained as a dark brown liquid, 
 which boils at 6 0., evolving a yellow gas thrice as heavy as air, and 
 having a very powerful and peculiar odour. This gas is remarkably 
 explosive, the heat of the hand having been known to cause its separa- 
 tion into its constituents, when 2 volumes of the vapour yield 2 volumes 
 of chlorine and i volume of oxygen. As might be expected, most 
 substances which have any attraction for oxygen or chlorine, and 
 therefore raise the temperature of the gas by combining with a portion 
 of its oxygen or chlorine, will decompose the gas, sometimes with 
 explosive violence. This instability of chlorine monoxide is only to be 
 expected from the fact that it evolves heat (17,800 gram units for 87 
 grams) in its decomposition, and is therefore an endothermic compound, 
 i.e., one which could only be formed from its elements by the absorp- 
 tion of heat. It is generally true that endothermic compounds can be 
 exploded by a shock, such as that caused by a sudden rise of temperature. 
 Even hydrochloric acid decomposes C1 2 : i volume of chlorine mon- 
 oxide is entirely decomposed by 2 volumes of hydrochloric acid, yield- 
 ing water and chlorine ; C1 2 O + 2 HC1 = H 2 + C1 4 . Chlorine monoxide 
 is a powerful bleaching agent, both its chlorine and oxygen acting upon 
 the colouring matter in the manner explained at page 175. 
 
1 82 HYPOCHLOROUS ACID. 
 
 Hypochlorous anhydride is absorbed in large quantity by water 
 (200 vols. in i vol.) ; the solution is supposed to contain hypochlorous 
 acid, HC10 or Cl.OH, for H 2 + C1 2 = 2 HC1O ; but HC10 has not been 
 obtained in the separate state. The solution may be very readily pre- 
 pared by shaking mercuric oxide with water in a bottle of chlorine as 
 long as the gas is absorbed. The greater part of the mercuric chloride 
 which is produced combines with the excess of oxide to form a brown 
 insoluble oxychloride, HgO.HgCl 2 , whilst the hypochlorous acid and 
 a little mercuric chloride remain in solution. A solution of the acid, 
 containing calcium chloride, may also be obtained by passing Cl into 
 CaC0 3 suspended in water; CaC0 3 + H 2 + C1 4 = CaCl 2 + 2 HC10 + C0 2 . 
 This solution is a most powerful oxidising and bleaching agent, since it 
 readily decomposes into HC1 and ; it erases writing ink immediately, 
 and does not corrode the paper if it be carefully washed. Printing ink, 
 which contains lamp black and grease, is not bleached by hypochlorous 
 acid, so that this solution is very useful for removing ink stains from 
 books, engravings, &c. For the same weight of 01 it is twice as effective 
 as chlorine water ; 2 HC1O = HC1 + O 2 ; H 2 + 01, = 2 HC1 + 0. 
 
 The action of some metals and their oxides upon solution of hypochlorous acid is 
 instructive. Iron seizes upon the oxygen, whilst the chlorine is liberated ; copper 
 takes both the oxygen and chlorine ; whilst silver combines with the chlorine, and 
 liberates oxygen. Mercury yields, on shaking, the brown mercuric oxychloride. 
 This distinguishes solution of HC1O from chlorine water. Oxide of lead (PbO) 
 removes the oxygen, becoming peroxide of lead (Pb0. 2 ), and liberating chlorine, but 
 oxide of silver converts the chlorine into chloride of silver, and liberates the oxygen ; 
 Ag. 2 + C1 2 = 2 AgCl + 2 . 
 
 Hypochlorous acid is formed when a weak solution of hydrogen peroxide is added 
 to a large excess of chlorine water ; C1 2 + H 2 2 = 2HC10. With an excess of the 
 peroxide, HC10 + H 2 2 = HC1 + H 2 + 2 . 
 
 The salts of hypochlorous acid, or hypochlorites, are obtained in solu- 
 tion by neutralising hypochlorous acid with bases, only a few of them 
 are known in a pure state. They are decomposed even by carbonic 
 acid, with liberation of hypochlorous acid. 
 
 "When chlorine is passed into a solution of a metallic hydroxide the 
 hypochlorite and chloride of the metal are obtained, 2 NaOH + Cl 2 = 
 NaOCl + NaCl + HOH ; the hypochlorite may be supposed to be formed 
 by metalepsis (p. 174) with the hydroxide NaOH + C1 2 = NaOCl + HC1, 
 the hydrochloric acid thus formed being neutralised by another portion 
 of NaOH. 
 
 By the addition of any acid which can liberate hydrochloric acid, and 
 therefore also the much feebler hypochlorous acid, to the solution con- 
 taining the chloride and hypochlorite, chlorine will be evolved since 
 hydrochloric and hypochlorous acids react, the hydrogen being oxidised 
 and the chlorine set free, HC1 + HC10 = H 2 + C1 2 . If only a small 
 proportion of acid is added to the solution of hypochlorite and chloride, 
 the hypochlorous acid will alone be liberated, and may be distilled 
 together with the water. 
 
 When the solution of a hypochlorite is boiled, it undergoes self- 
 oxidation, that is, one part of the hypochlorite loses oxygen, becoming 
 chloride, whilst the remainder is oxidised by this oxygen to chlorate ; 
 3KC1O = KC10 3 + 2 KC1. This change is turned to practical account in 
 the manufacture of potassium chlorate. It is much hindered by the 
 presence of an excess of alkali. The solution of hypochlorous acid itself, 
 
CHLORIDE OF LIME. 183 
 
 when exposed to light, is decomposed into chloric acid and free chlorine 
 5 HC10 = HC10, + 2H 2 O + C1 4 . 
 
 A solution of hypochlorous acid may be obtained by adding boric acid 
 in excess to a solution of chloride of lime. 
 
 107. Chloride of lime or bleaching powder, or calx chlorata, is prepared 
 by passing chlorine gas into boxes of lead or stone in which a quantity 
 of moist slaked lime is spread out. The temperature is not allowed to 
 rise above 25 0. (77 F.), which is ensured by acting upon the fresh 
 lime with chlorine diluted by air. The lime absorbs nearly half its 
 weight of chlorine, and forms a white powder, which has a very peculiar 
 smell, somewhat different from that of chlorine. 
 
 The formula of chloride of lime is generally written CaCl.001. 
 
 The constitution of chloride of lime is not known with certainty. When the 
 calcium hydroxide, Ca(OH) 2 , is acted on by chlorine, the simplest reaction would be 
 Ca(OH) 2 + Cl 2 = CaCl(OCl) + H 2 0, according to which the chloride of lime would 
 result from the substitution of Cl for one of the OH groups, and the removal of the 
 H of the other as H 2 0, this atom of H being then exchanged for Cl ; but this would 
 require the calcium hydroxide to absorb nearly an equal weight of chlorine, whereas 
 the amount is not much more than half this quantity. This deficiency is partly 
 explained by the fact that a small portion of the lime is not attacked by the 
 chlorine. 
 
 Practically, the constitution of chloride of lime itself is of less importance than 
 that of the solution obtained by treating it with water, which is generally admitted 
 to contain calcium hypochlorite, Ca(OCl) 2 , and calcium chloride, CaCl 2 , with some 
 calcium hydroxide, Ca(OH) 2 , of which a quantity is left in the undissolved residue. 
 The decomposition of chloride of lime by water should be represented by the follow- 
 ing equation : 2CaCl(OCl) = CaCl 2 +Ca(OCl) 2 . 
 
 If the solution of chloride of lime is added to blue litmus, it exerts 
 little bleaching action ; but on adding a little acid (sulphuric, for 
 example), the blue colour is discharged, the acid setting free the 
 chlorine, which acts upon the colouring matter 
 
 Ca(OCl) 2 +CaCl 2 + 2H 2 S0 4 = 2CaS0 4 + 2H 2 + C1 4 . 
 Solution of chloride of lime. 
 
 Even carbonic acid will develop the bleaching property of chloride of 
 lime (by liberating hypochlorous acid), so that the above mixture may 
 be decolorised by breathing into it through a glass tube. 
 
 When chloride of lime is used for bleaching on the large tcale, the 
 stuff to be bleached is first thoroughly cleansed from any grease or 
 weaver s dressing, by boiling it in lime-water and in a weak solution of 
 soda, and is then immersed in a weak solution of the chloride of lime. 
 This, by itself, however, exerts very little action upon the natural 
 colouring matter of the fibre, and the stuff is therefore next immersed 
 in very dilute sulphuric acid, when the colouring matter is so far altered 
 as to become soluble in the alkaline solution in which the fabric is next 
 immersed, and a repetition of these processes, followed by a thorough 
 rinsing, generally perfects the bleaching. 
 
 The property possessed by acids of liberating chlorine from the chloride 
 of lime is applied, in calico-printing, to the production of white patterns 
 upon a red ground. The stuff having been dyed with Turkey-red, the 
 pattern is imprinted upon it with a discharge consisting of an acid 
 (tartaric, phosphoric, or arsenic) thickened with gum. On passing the 
 fabric through a bath of weak chloride of lime, the colour is discharged 
 only at those parts to which the acid has been applied, and where, con- 
 sequently, chlorine is liberated. 
 
184 BLEACHING POWDEE. 
 
 Chloride of lime is one of the most convenient forms in which to 
 apply chlorine for the purposes of fumigating and disinfecting. If a 
 cloth saturated with the solution be suspended in the air, the carbonic 
 acid gas in the latter causes a slow evolution of hypochlorous acid, which 
 is even a more powerful disinfectant than chlorine itself. In extreme 
 cases, where a rapid evolution of chlorine is required, the bleaching 
 powder is placed in a plate, and diluted sulphuric acid is poured over 
 it, or the powder may be mixed with half its weight of powdered 
 alum in a plate, when a pretty rapid and regular escape of chlorine will 
 ensue. 
 
 The best bleaching powder contains about 37 per cent, of chlorine 
 which can be liberated (" available chlorine ") in the above processes. 
 It is liable to decomposition when kept, evolving oxygen, and becoming 
 converted into calcium chloride, which attracts moisture greedily, and 
 renders the bleaching powder deliquescent. It has been known to 
 shatter the glass bottle in which it was preserved, in consequence of the 
 accumulation of oxygen ; * CaOCl 2 = CaCJ 2 + 0. 
 
 When a solution of a salt of manganese or cobalt is added to solution 
 of chloride of lime, a black precipitate of Mn0 2 or Co 2 3 is obtained. If 
 this precipitate be boiled with an excess of solution of chloride of lime, 
 ib causes a rapid disengagement of oxygen, in some manner that has 
 not yet been clearly explained. Large quantities of oxygen are easily 
 obtained by adding a few drops of solution of cobalt nitrate to solution 
 of chloride of lime, and applying a gentle heat. 
 
 Old chloride of lime always contains calcium chlorate ; 6Ca001 2 = 
 
 a01 3 + Ca(C10 3 ) 2 . 
 
 Sodium hypochlorite^ which is very useful for removing ink, is pre- 
 pared in solution by decomposing solution of chloride of lime with 
 solution of sodium carbonate, and separating the calcium carbonate by 
 filtration. The solution is generally called "chloride of soda" (liquor 
 sodce chloralce. Eau de Javelle). 
 
 1 08. Chloric acid (HC10 3 or C10 2 (OH)). This acid is appropriately 
 studied here, since its salts are usually obtained by the decomposition of 
 the hypochlorites. The only chlorate which possesses any great practical 
 importance is potassium chlorate (KC10 3 ), which is largely employed as 
 a source of oxygen, as an ingredient of several explosive compositions, 
 and in the manufacture of lucifer matches. 
 
 Potassium chlorate, or chlorate of potash. The simplest method of 
 obtaining this salt consists in passing an excess of chlorine rapidly into 
 a strong solution of potash when the liquid becomes hot enough to 
 decompose the hypochlorite first formed into potassium chloride, which 
 remains in solution, arid potassium chlorate, which is deposited in 
 tabular crystals, the ultimate result being expressed by the equation 
 
 6KOH + C1 6 = KC10 3 + 5KC1 + 3H 2 0. 
 
 If potassium carbonate or a weak solution of potash be employed, the 
 liquid will require boiling after saturation with chlorine, in order to 
 convert the hypochlorite into chlorate. 
 
 The following proportions will be found convenient for the preparation of potas- 
 sium chlorate on the small scale as a laboratory experiment. 20 grins, of potassium 
 
 * When rapidly made and hastily packed, it has been known to become so hot as to set fire 
 to the casks. 
 
POTASSIUM CHLORATE. 185 
 
 carbonate are dissolved, in a beaker, with 60 c.c. of water. 40 grins, of NaCl are 
 mixed with 30 grins, of Mn0 2 , and very gently heated in a flask with a mixture of 
 40 c.c. of strong H 2 S0 4 and 1 10 c.c. of water, the evolved chlorine being passed 
 through a rather wide bent tube into the solution of potassium carbonate. 
 
 At first no action appears to occur, although the solution absorbs the chlorine ; 
 because the first portion of that gas converts the potassium carbonate into a mixture 
 of potassium hypochlorite, potassium chloride, and hydropotassium carbonate, SDme 
 crystals of which will probably be deposited; 2K. 2 C0 3 + C1 ? + H 2 = KC1 + KOC1 + 
 2KHC0 3 . On continuing to pass chlorine, these crystals will redissolve, and brisk 
 effervescence will be caused by the expulsion of the carbonic acid gas ; 2KHC0 3 + 
 C1 2 = KC1 + KOC1 + H. 2 + 2CO 2 . When this effervescence has ceased, and the 
 chlorine is no longer absorbed by the liquid, the change is complete, the ultimate 
 result being represented by the' equation K 2 C0 3 +C1 2 :=KC1 + KOC1 + C02. The 
 solution (which often has a pink colour, due to a little potassium ferrate) is now 
 poured into a dish, boiled for two or three minutes, filtered, if necessary, from any 
 impurities (silica, &c.) derived from the potassium carbonate, and set aside to crys- 
 tallise. The ebullition has converted the potassium hypochlorite into chlorate and 
 chloride of potassium ; 3KOC1=KC10 3 + 2KC1. The latter, being soluble in about 
 three times its weight of cold water, is retained in the solution, whilst the chlorate, 
 which would require about sixteen times its weight of cold water to hold it dis- 
 solved, is deposited in brilliant rhomboidal tables. These crystals may be collected 
 on a filter, and purified from the adhering solution of potassium chloride by pres- 
 sure between successive portions of filter-paper. If they be free from chloride, 
 their solution in water will not be changed by silver nitrate, which would yield a 
 milky precipitate of silver chloride if potassium chloride were present. Should this 
 be the case, the crystals must be redissolved in a small quantity of boiling water, 
 and recrystallised. 
 
 The above processes for preparing potassium chlorate are far from 
 economical, since five-sixths of the potash are converted into chloride, 
 being employed merely to furnish oxygen to convert the chlorine into 
 chloric acid. In manufacturing the chlorate upon the large scale, a 
 much cheaper material, lime, is used to furnish the oxygen. The 
 lime is mixed with water, and saturated with chlorine gas in closed 
 leaden tanks ; 2 Ca(OH) 2 + C1 4 = Ca(OCl) 2 + CaCl 2 + 2 H 2 O. The liquid is 
 boiled down, when the calcium hypochlorite is decomposed into calcium 
 chlorate and chloride; 3Ca(OCl) 2 = Ca(C10 3 ) 2 + 2 CaCl 2 . The calcium 
 chlorate is now decomposed by boiling with potassium chloride, when it 
 yields calcium chloride which remains in solution, and potassium chlorate 
 which crystallises as the solution cools 
 
 Ca(C10 3 ) 2 + 2KC1 = CaCl 2 + 2KC10 3 . 
 
 Chlorate of potash is also made electrolytically as mentioned in the 
 section on potassium. 
 
 Chloric acid (HC10 3 ) may be procured by decomposing a solution of 
 potassium chlorate with hydrofluosilicic acid, when the potassium is 
 deposited as an insoluble silico-nuoride, and chloric acid is found in the 
 solution ; 2 KC10 3 + H 2 SiF 6 = 2 HC1O 3 + K 2 SiF 6 . 
 
 On evaporating the solution below 38 C., the chloric acid is obtained 
 as a yellow liquid, HC10 3 .yAq, with a peculiar pungent smell. 
 
 In its chemical characters, chloric acid bears a very strong resemblance 
 to nitric acid, but is far more easily decomposed. It cannot even be 
 kept unchanged for any length of time, and at temperatures above 
 40 C. it is decomposed into perchloric acid, chlorine, and oxygen ; 
 4 HC10 3 = 2 HC10 4 + H 2 + 01, + 3 . 
 
 Chloric acid is one of the most powerful oxidising agents : a drop of 
 it will set fire to paper, and it oxidises phosphorus (even the amorphous 
 variety) with explosive violence. Like hypochlorous acid it will oxidise 
 
1 86 COLOURED FIEES. 
 
 hydrochloric acid ; HC10 3 + 5 HC1 = 3H 2 + C1 6 .* Yet it dissolves Zn 
 with evolution of H. 
 
 109. Chlorates. Chloric acid, like nitric, is monobasic, containing 
 only one atom of hydrogen which can be exchanged for a metal. The 
 chlorates resemble the nitrates in their oxidising powder, but generally 
 act at lower temperatures, in consequence of the greater facility with 
 which the chlorates part with their oxygen. 
 
 A grain or two of potassium chlorate, rubbed in a mortar with a little sulphur, 
 for example, detonates violently, evolving a powerful odour of chloride of sulphur. 
 Potassium chlorate and sulphur were used in some of the first percussion caps, but 
 being found to corrode the nipple of the gun, they gave place to the anti-corrosive 
 caps containing mercuric fulminate. 
 
 If a little powdered chlorate be mixed on a card with some black antimony sul- 
 phide, and wrapped up in paper, the mixture will detonate when struck with a 
 hammer. The earliest lucifer matches were tipped with a mixture of potassium 
 chlorate, antimony sulphide, and starch, and were kindled by drawing them briskly 
 through a doubled piece of sand-paper. 
 
 A mixture of potassium chlorate and lead ferrocyanide is used in toy detonating 
 crackers. 
 
 At high temperatures the chlorates act violently upon combustible 
 bodies. A little potassium chlorate sprinkled upon red-hot coal causes 
 a very violent deflagration. If a little of the chlorate be melted in a 
 deflagrating spoon, and plunged into a bottle or flask containing coal 
 gas, the salt burns with great brilliancy, its oxygen combining with the 
 carbon and hydrogen in the gas, which becomes in this case the supporter 
 of combustion. 
 
 Potassium chlorate is much used in the manufacture of fireworks, 
 especially as an ingredient of coloured fire compositions, which generally 
 consist of potassium chlorate mixed with sulphur, and with some 
 metallic compound, to produce the desired colour in the flame. 
 
 They are not generally made of the best quality on the small scale, from want of 
 attention to the very finely powdered state of the ingredients, the absence of all 
 moisture, and the most intimate mixture, but if these precautions are attended to, 
 the following prescriptions will give very good coloured fires : 
 
 Red fire. 40 grains of strontium nitrate, thoroughly dried over a lamp, are 
 mixed with 10 grains of potassium chlorate, and reduced to the finest possible 
 powder. In another mortar 13 grains of sulphur are mixed with 4 grains of black 
 sulphide of antimony (crude antimony). The two powders are then placed upon 
 a sheet of paper, and very intimately mixed with a bone knife, avoiding any great 
 pressure. A little heap of the mixture touched with a red-hot iron ought to burn 
 with a uniform red flame, the colour being due to the strontium.f 
 
 Blue fire. 15 grains of potassium chlorate are mixed with 10 grains of potassium 
 nitrate and 30 grains of oxide of copper, in a mortar. The finely powdered mixture 
 is transferred to a sheet of paper, and mixed, by a bone knife, with 15 grains of 
 sulphur. The colour of the fire is given chiefly by the copper. 
 
 Green fire. 10 grains of barium chlorate are mixed with 10 grains of barium 
 nitrate in a mortar, and afterwards on paper with 12 grains of sulphur. The barium 
 is the cause of the bright green colour of the flame. 
 
 These compositions are rather dangerous to keep, since they are liable to sponta- 
 neous combustion. 
 
 White gunpowder is a mixture of two parts of potassium chlorate with one part 
 of dried yellow prussiate of potash, and one part of sugar, which explodes very 
 easily under friction or percussion. 
 
 The decomposition KC1O 3 = KC1 + O 3 is exothermic, 9700 calories being 
 evolved per gram molecule of potassium chlorate. If the chlorate be 
 
 * Perchloric acid and chlorine peroxide are also produced. 
 
 f The red fire made by pyrotechnists commonly contains charcoal i part, shellac 4 parts, 
 sulphur 8 parts, potassium chlorate 12 parts, strontium nitrate 40 parts. 
 
PERCHLORIC ACID. I 8/ 
 
 heated to the point at which it begins to decompose, and a little ferric 
 oxide be thrown into it, enough heat will be evolved to bring the mass 
 to a red heat, although the ferric oxide is not oxidised. This evolution 
 of heat must of course contribute to increase the energy of explosive 
 mixtures containing the chlorate, and may be accounted for on the 
 supposition that the heat evolved by the combination of the Kwith the 
 01 to form KC1 exceeds that which is absorbed in effecting the chemical 
 decomposition of the chlorate. 
 
 no. Perchloric acid (HC1O 4 or C10 3 (OH)), is obtained by evapo- 
 rating, at a boiling heat, the solution of chloric acid obtained by de- 
 composing potassium chlorate with hydrofluosilicic acid (see page 185), 
 when the chloric acid is decomposed into perchloric acid, chlorine, and 
 oxygen; 4 HC1O 3 = 2HC1O 4 + H 2 O + C1 2 + 3 . The pure acid is best 
 obtained by distilling potassium perchlorate (see below) with four times 
 its weight of strong H 2 S0 4 in a vacuum. At 56 mm. pressure it boils 
 at 39 C. 
 
 The pure perchloric acid is a colourless, very heavy liquid (sp. gr. 
 i. 764 at 22 C.), which soon becomes yellow from decomposition. It 
 cannot be kept for any length of time, but it is more stable than any 
 of the other oxyacids of chlorine. When heated, it decomposes, often 
 with explosion. In its oxidising properties it is more powerful than 
 chloric acid. It burns the skin in a very serious manner, and sets fire 
 to paper, charcoal, &c., with explosive violence. This want of stability, 
 however, belongs only to the pure acid. If water be added to it, heat 
 is evolved, and a crystalline acid, HC10 4 .H 2 0, melting at 50 C., may 
 be obtained. Diluted perchloric acid is much more stable than the 
 pure acid ; il does not even bleach, but reddens litmus in the ordinary 
 way. It dissolves Zn with evolution of H. 
 
 Perchloric acid is monobasic. The perchlorates are decomposed by 
 heat, evolving oxygen, and leaving chlorides ; thus -KC10 4 = KC1 + 4 . 
 
 The potassium perchlorate is one of the least soluble of the potassium 
 salts, requiring 150 times its weight of cold water to dissolve it. It is 
 always formed in the first stage of the decomposition of potassium 
 chlorate by heat ; 2 KC1O 3 = KC10 4 + KC1 + O 2 . 
 
 If a few crystals of potassium chlorate be heated in a test-tube, they first melt to 
 a perfectly clear liquid, which soon evolves bubbles of oxygen. After a time the 
 liquid becomes pasty, and if the contents of the tube, after cooling, be dissolved by 
 boiling with water, the latter will deposit, as it cools, crystals of potassium perchlo- 
 rate. These are readily distinguished from the chlorate by their not yielding a 
 yellow gas (C10 2 ) when "treated with strong sulphuric acid. Neither perchloric acid 
 nor any of its salts is applied to any useful purpose. 
 
 in. Chlorine dioxide or chlorine peroxide (C10 2 ) is dangerous to 
 prepare and examine on account of its great instability and violently 
 explosive character. It is obtained by the action of strong sulphuric 
 acid upon potassium chlorate 
 
 3KC10 3 + 2H 2 S0 4 = KC10 4 + 2KHS0 4 + 2C10 2 + H 2 0. 
 
 It is a bright yellow gas, with a chlorous and somewhat aromatic smell, 
 and sp. gr. 2.32 ; condensable to a red, very explosive liquid (b.p. 9 C.). 
 The gas is gradually decomposed into its elements by exposure to light, 
 and a temperature of 60 C. causes it to decompose with violent ex- 
 plosion into a mixture of chlorine and oxygen, the volume of which is 
 one and a half times that of the compound. 
 
1 88 CHLORINE PEROXIDE. 
 
 On a small scale, chlorine peroxide may be prepared with safety by pouring a 
 little strong sulphuric acid upon one or two crystals of potassium chlorate, in a 
 test-tube supported in a holder. The crystals at once acquire a red colour, which 
 gradually diffuses itself through the liquid, and the bright yellow gas collects in the 
 tube. If heat be applied, the gas will explode, and the colour and odour of chlorine 
 peroxide will be exchanged for those of chlorine. If the chlorate employed in this 
 experiment contains potassium chloride, explosion often happens in the cold, 
 since the hydrochloric acid evolved by the action of the acid upon that salt decom- 
 poses a part of the chlorine peroxide, and thus provokes the decomposition, of the 
 remainder. 
 
 C10 2 is easily absorbed by water, f ormiDg chlorous and chloric acids ; 
 the solution has powerful bleaching properties. Combustible bodies, 
 such as sulphur and phosphorus, decompose the gas, as might be expected, 
 with great violence. This powerful oxidising action of chlorine peroxide 
 upon combustible substances appears to be the cause of the property 
 possessed by mixtures of such substances with potassium chlorate, to 
 inflame when touched with strong sulphuric acid. 
 
 If a few crystals of potassium chlorate be thrown into a glass of water (Fig. 153), 
 one or two small fragments of phosphorus dropped upon them, and some strong 
 sulphuric acid poured down a funnel tube to the bottom of 
 the glass, the chlorine peroxide will inflame the phosphorus 
 with bright flashes of light and slight detonations. 
 
 Powdered sugar mixed with potassium chlorate on paper, 
 will burn brilliantly when touched with a glass rod dipped in 
 strong sulphuric acid. Matches may be prepared, which 
 inflame when moistened with sulphuric acid, by dipping the 
 end of splinters of wood in melted sulphur, and, when cool, 
 tipping them with a mixture of 5 grains of sugar and 15 grains 
 of potassium chlorate made into a paste with 4 drops of 
 water. When dry, they may be fired by dipping them into a 
 bottle containing asbestos moistened with strong sulphuric 
 acid. These matches, under the names of Eupyrion and Vesta 
 matches, were used before the introduction of phosphorus into 
 general use. The Promethean light was an ornamental scented 
 paper spill, one end of which contained a small glass bulb of 
 sulphuric acid surrounded with a mixture of chlorate and 
 sugar, which inflamed when the end of the spill was struck or 
 squeezed, so as to break the bulb containing the sulphuric acid. 
 The paper was waxed in order to make it inflame more easily. Percussion fuses, 
 &c., have been often constructed upon a similar principle. 
 
 Chlorous acid, HC10 2 or CIO(OH), is contained, together with 
 chloric acid, in the aqueous solution of chlorine peroxide (2C10 2 + H 2 = 
 HC1O, + HC10 3 ) which thus resembles nitric peroxide in not being a 
 separate anhydride. 
 
 The chlorous acid may be separated by neutralising the solution with potash and 
 evaporating until the potassium chlorate crystallises, leaving the chlorite (KC10 2 ) 
 in solution. Little is known about the acid or its salts ; they readily undergo 
 self-oxidation, like hypochlorous acid and its salts, yielding chloric acid and 
 chlorates. 
 
 112. Euchlorine, the deep yellow, dangerously explosive gas evolved by the 
 action of strong HC1 upon KC10 3 , appears to be a mixture of chlorine peroxide with 
 chlorine. It is resolved by explosion into 2 vols. Cl and i vol. 0. Mercurous 
 chloride absorbs Cl from it, leaving C10 2 . Hence its production may be explained 
 by the equation, 4KC1O ? + I2HC1 = 4KC1 + 6H 2 + 3C10 2 + C1 9 . 
 
 Cillorine heptoxide, presumably C1 2 7 , is obtained by dropping perchloric 
 acid on to phosphoric anhydride cooled below 10 C. and after a day or two warm- 
 ing the retort until the heptoxide distils. It is a colourless volatile oil, boiling at 
 82 C., and easily exploded. It is probably perchloric anhydride. 
 
CARBON TETEACHLORIDE. 
 
 CHLORIDES OF CARBON. 
 
 189 
 
 113. It has already been seen that chlorine has no direct attraction 
 for carbon, the two elements not being known to enter into direct com- 
 bination ; but several chlorides of carbon may be obtained by the 
 action of chlorine upon other compounds of carbon, particularly by 
 metalepsis with hydrocarbons. 
 
 Carbon tetrachloride, CC1 4 , has been mentioned (p. 174) as the final 
 result of the action of chlorine upon marsh gas (CH 4 ) and upon chloro- 
 form (CHC1 3 ). It is easily obtained in large quantity, by passing 
 chlorine (dried by passage through a tube containing pumice wetted 
 with strong H 2 S0 4 ) (Fig. 154), through a bottle containing carbon bisul- 
 phide, and afterwards through a porcelain tube, filled with fragments 
 of broken porcelain and maintained at a red heat by a gas furnace ; 
 the products are condensed in a bottle surrounded by ice. A mixture 
 
 Fig. 154. Preparation of carbon tetrachloride. 
 
 of carbon tetrachloride and sulphur dichloride is thus obtained ; 
 CS 2 + C1 6 = CC1 4 + S 2 C1 2 . This is shaken with potash, whereupon the 
 sulphur dichloride is decomposed and dissolved, whilst the carbon 
 tetrachloride separates and falls to the bottom. The two layers having 
 been separated by a separating funnel (p. 139), the tetrachloride maybe 
 purified by distillation. 
 
 Another method of preparing CC1 4 consists in distilling carbon bisul- 
 phide with antimonic chloride in a stream of chlorine. 
 
 Carbon tetrachloride is a colourless liquid, much heavier than water 
 (sp. gr. 1.6), having a peculiar odour, and boiling at 77 C. It may be 
 solidified at -23 C. The tetrachloride is insoluble in water, but 
 dissolves in alcohol and in ether. It is a very useful solvent for fats, 
 and also finds application in making dyestufls. 
 
 It will be obvious that since the number of hydrocarbons is very 
 large there must be a considerable number of chlorides of carbon 
 obtained by the complete substitution of chlorine for hydrogen, gener- 
 ally by metalepsis. Some of these are of very high molecular weight, 
 such as octachloronaphthalene C 10 C1 8 , obtained from naphthalene C 10 H 8 . 
 
 Carbon trichloride, perchlorethane or hexachlor ethane, C 2 C1 6 , is pro- 
 duced by treating Dutch liquid (p. 143) with excess of chlorine in sunlight. 
 
190 NITROGEN CHLORIDE. 
 
 It is a white crystalline solid, melting at 187 C. By treatment with 
 nascent hydrogen (zinc and sulphuric acid) it yields carbon dichloride, 
 or tetrachlorethylene, C 2 C1 4 , a colourless liquid which boils at 121 C. 
 
 114. Carbonyl chloride, carbon oxychloride, or phosgene gas, COC1 2 , 
 is produced by the direct combination of equal volumes of carbonic oxide 
 and chlorine gases under the influence of sunlight (whence its last name), 
 when the mixture condenses to half its volume of a colourless gas, con- 
 densable by cold (b.p. 8.4 C.), having a very peculiar pungent smell, and 
 fuming strongly when exposed to moist air by decomposing the moisture 
 and producing hydrochloric acid; COC1 2 + H 2 = C0 2 + 2HC1. It is 
 decomposed by alkalies, producing chlorides and carbonates. It is used 
 in the manufacture of some artificial dyestuffs. 
 
 COC1 2 may also be prepared by passing a mixture of equal volumes of CO and Cl 
 through a long tube filled with granulated animal charcoal, which favours the com- 
 bination of the gases ; or by passing dried carbonic oxide through antimony penta- 
 chloride ; SbCl 5 + CO = COC1 2 + SbCl 3 . 
 
 Phosgene gas has also been obtained by heating carbon tetrachloride with phos- 
 phoric anhydride, in a sealed tube ; 3CC1 4 + P 2 5 = 2?OC1 3 + 3COC1 2 ; and by heating 
 chloroform with sulphuric acid and potassium dichromate. 
 
 A convenient method for preparing phosgene gas consists in dropping fuming sul- 
 phuric acid (containing 80 per cent. S0 3 ) down an inverted condenser into a flask 
 in which carbon tetrachloride is boiling. The gas escapes through a side tube at 
 the top of the condenser and is washed by passage through strong H 2 S0 4 ; 
 CC1 4 + 2S0 3 = COC1 2 + S 2 5 C1 2 (jpyrosulphuryl chloride). 
 
 115. Nitrogen chloride is the name usually given to the very explo- 
 sive compound before referred to as being produced by the action of 
 chlorine on ammonium chloride. The oily liquid thus produced is a 
 mixture of several compounds which have been formed from the NH 4 C1 
 by the substitution of chlorine for hydrogen. Nitrogen chloride, NC1 3 , 
 is the most explosive constituent of the mixture, and can be isolated by 
 a process attended with considerable danger. 
 
 It is a yellow, heavy, oily liquid (sp. gr. 1.7), which volatilises easily, 
 yielding a vapour of very characteristic odour, which affects the eyes. 
 When heated to about 93 C. it explodes with great violence, emitting 
 a loud report and a flash of light.* Its instability is, of course, 
 attributable to the feeble attraction which holds its elements together ; 
 and the violence of the explosion, to the sudden expansion of a small 
 volume of the liquid into a large volume of nitrogen and chlorine. 
 
 As might be expected, its explosion is at once brought about by contact with 
 substances which have an attraction for chlorine, such as phosphorus and arsenic ; 
 the oils and fats cause its explosion, probably by virtue of their hydrogen ; oil of 
 turpentine explodes it with greater certainty than the fixed oils. Alkalies also 
 decompose it violently ; whilst acids, having no action upon the chlorine, are not 
 so liable to explode it. At 71 C. this substance has actually been distilled with- 
 out explosion. 
 
 Although practically unimportant, the violently explosive properties of this sub- 
 stance render it so interesting that it may be well to give some directions for its 
 safe preparation, which may be effected by the action of solution of hypochlorous 
 acid upon ammonium chloride. 
 
 Fifty grains of red oxide of mercury are very finely powdered and thrown into 
 a pint bottle of chlorine together with ^ oz. of water. The stopper is replaced, 
 and the bottle well shaken, loosening the stopper occasionally, as long as the 
 chlorine is absorbed. The solution of hypochlorous acid thus produced is filtered 
 from the residual mercuric oxychloride, and poured into a clean thumb-glass 
 
 * It is said to absorb 38,478 gram units of heat per equivalent, in the process of forma- 
 tion, and would therefore disengage that amount of heat in the act of decomposition. 
 
ACID CHLORIDES. 19! 
 
 (Fig. 155). A lump of ammonium chloride weighing 20 grains is then dropped 
 into the solution, and the glass is placed under a stout wooden box. After the 
 lapse of twenty minutes, the chloride of nitrogen may be exploded 
 by inserting, through a hole in the box, a stick dipped'in turpentine, 
 fixed at right angles to a longer stick. The glass will be shattered 
 into very small fragments. 
 
 1 1 6. Aqua regia. This name has been bestowed upon 
 the mixture of i measure of nitric, and 3 measures of 
 hydrochloric acid (nitromuriatic acid), which is employed Fig. 155. 
 for dissolving gold, platinum, and other metals which are 
 not soluble in the separate acids. A little gold leaf placed in hydro- 
 chloric and nitric acids contained in separate glasses remains unaffected 
 even on warming the acids; but if the contents of the glasses be 
 mixed, the gold will be immediately dissolved by the chlorine, which 
 is liberated in the action of the acids upon each other ; HN0 3 + 3HC1 = 
 
 The nitrosyl chloride (NOC1) is a red gas, condensable in a freezing mixture 
 to a dark red liquid, which boils at - 8 C. and dissociates above 700 C. It has 
 a very peculiar odour, and is decomposed by contact with water, nitrous acid and 
 hydrochloric acid being produced. Nitrosyl chloride is also produced by mixing 
 2 volumes of nitric oxide with I volume of chlorine ; it condenses to a red liquid 
 when cooled. When nitrosyl chloride is passed into oil of vitriol cooled to o C., 
 crystals of the acid nitrosyl sulphate (NOHS0 4 ) are deposited; NO*C1 + 
 S0 2 (OH)(OH) = HC1 + S0 2 (OH)(ONO)*. 
 
 Nitrosyl sulphate is also obtained by passing S0 2 into nitric acid, or N 2 3 into 
 sulphuric acid, or by burning a mixture of I part of sulphur and 3 parts of nitre 
 in moist air. 
 
 Nitrosyl chloride is best prepared by heating nitrosyl sulphate with sodium 
 chloride; NO'HS0 4 + NaCl = NO'Cl + NaHS0 4 . It is a useful reagent in organic 
 chemistry. 
 
 It has been proposed to manufacture chlorine by oxidising hydrochloric acid with 
 nitric acid as shown by the above equation for the decomposition of aqua regia. 
 The mixture of NOC1 and C1 2 is passed through strong sulphuric acid whereby 
 the NOC1 is absorbed and HC1 evolved in its stead ; this is removed from the Cl 
 by passage through water. By diluting the sulphuric acid containing the nitrosyl 
 sulphate and passing air through the liquid, N0 2 is evolved, which may be passed 
 (together with air) into water to form HN0 3 . In this way the nitric acid would 
 serve as a carrier of oxygen from the air to the hydrogen of the hydrochloric acid. 
 
 Nitrosyl chloride, NOC1, is an example of a large class of compounds 
 known as acid chlorides or chlor anhydrides. An acid chloride is formed 
 by the substitution of 01 for OH in an acid ; thus nitrosyl chloride is 
 formed from nitrous acid, NO 'OH. The reaction which most generally 
 produces an acid chloride is that between an oxy-acid and phosphoric 
 chloride, PC1 5 (see Phosphorus) ; if R represent the group of atoms com- 
 bined with OH in an acid, this reaction may be expressed by the equa- 
 tion, R-OH-f PC1 5 = R/C1 + POC1 3 + HC1, or, since the acid residue 
 may be combined with several OH groups, R(OH) w + ?iPCl 5 = 
 RCl n + nPOC] 3 + ?iHCl. It is from this fact, namely, that for every 
 atom of chlorine introduced into an acid by the action of phosphoric 
 chloride, one atom of oxygen and one atom of hydrogen are removed 
 (as POC1 3 and HCl respectively), that the inference is drawn that the 
 hydrogen in an oxyacid exists in the form of hydroxyl groups. For it 
 
 * In this formula for nitrosyl sulphate the nitrosyl group is exchanged for hydrogen in 
 one of the hydroxyl groups of sulphuric acid. Some chemists regard the compound as 
 nitrosulphuric or nitrosulphonic acid, that is, sulphuric acid in which NO 2 has been substi- 
 tuted for H : SO 2 (OH)(NO 2 ). 
 
1 92 BROMINE. 
 
 is obvious that a moriovalent atom like Cl can only be substituted for 
 another monovalent atom or a monovalent radicle, so that if and H 
 are together exchanged for Cl they must be present as - OH ; were they 
 present independently of each other they would represent three atom- 
 fixing powers (-O-and H-), and could not be exchanged for the 
 monovalent atom Cl. It will be found, particularly in organic 
 chemistry, that acids frequently contain and H, for which Cl cannot 
 be substituted, and therefore exist in some other relationship to the- 
 molecule than that represented by - OH. 
 
 The characteristic behaviour of acid chlorides is, that when brought- 
 into contact with water they exchange their chlorine for hydroxyl, and 
 are converted into the acids from which they were derived ;. 
 RCl M + wHOH = R(OH) M + wHCl. It is because these chlorides form 
 acids, in this way, when brought in contact with water, that they are- 
 also termed chloranhydrides. 
 
 It is noteworthy that whilst the acid chlorides yield acid hydroxides- 
 and hydrochloric acid by treatment with water, the basic hydroxides,, 
 such as NaOH, Ca(OH) 2 , yield basic chlorides and water by treatment 
 with hydrochloric acid ; thus it is instructive to compare the reactions i 
 
 NO-C1 + HOH = NO-OH + HC1, 
 and NaOH + HC1 = NaCl + HOH. 
 
 Nitroxyl chloride or nitryl chloride, N0 2 C1, is the acid chloride from, 
 nitric acid, N0 2 .OH. It is produced by heating N0 2 with Cl, NO, + CL 
 = NO 2 C1, and is a yellowish red liquid boiling at 5 C. 
 
 Carbonyl chloride, COC1 2 , is the acid chloride of carbonic acid,, 
 CO(OH) 2 . 
 
 BROMINE. 
 
 Br = 79.5 P af ts by weight. 
 
 117. It generally happens that elements between which any strong 
 family likeness exists are found associated in nature. This remark par- 
 ticularly applies to the three elements chlorine, bromine, and iodine 
 all of which are found in sea water, though the first predominates to- 
 such an extent that the others for a long time escaped notice. Bromine 
 was brought to light in the year 1826 by Balard in the examination of 
 bittem,which is the liquid remaining after the sodium chloride and some 
 other salts have been made to crystallise by evaporating sea water, which 
 contains bromine in the forms of bromide of magnesium and bromide of 
 sodium.* It has also been extracted from the waters of certain mineral 
 springs, as those of Kreuznach and Kissingen, which contain much 
 larger quantities of bromine, combined with potassium, sodium, or mag- 
 nesium. Now, almost the sole sources of bromine are the mother-liquors of 
 the salt-works at Stassfurt, and from certain saline springs in the United 
 States. 
 
 In extracting the bromine from these waters, advantage is taken of 
 the circumstance that chlorine displaces bromine from its combinations 
 with the metals. Aftermost of the other salts, such as sodium chloride,, 
 sodium sulphate, and magnesium sulphate, which are less soluble than 
 the bromides, have been separated from the water by evaporation and 
 
 * 4.9 grams of magnesium bromide per gallon have been found in the water of the Irish. 
 
PROPERTIES OF BROMINE, 195. 
 
 crystallisation, the remaining liquid, containing about 0.3 per cent, of 
 bromine, is run down a tower packed with earthenware balls, where it 
 meets a current of steam conveying chlorine which has been passed into- 
 it from a chlorine still. The bromine is liberated from the bromides,. 
 the chief of which is magnesium bromide (MgBr 2 + Cl, = Mg01 2 + Br 2 ), 
 and passes as vapour from the top of the tower through a condenser in 
 which it is condensed to the liquid state. 
 
 The chief impurity in the crude bromine thus obtained is bromine chloride, BrCl, 
 formed by the combination of excess of chlorine with the bromine. This is decom- 
 posed by shaking the crude product with potassium bromide, KBr + BrCl = KCl + 
 Br 2 ; and the bromine is distilled away from the KC1. 
 
 To illustrate on a small scale the manufacture of bromine, chlorine water may be 
 added to a solution of potassium bromide, which will at once become orange from 
 the liberation of the bromine, KBr + Cl = KC1 + Br. The bromine thus set free exists 
 now diffused through a large volume of water, which cannot be separated from it in 
 the usual way, by evaporation, because bromine is itself very volatile. An ingenious 
 expedient is therefore resorted to, of shaking the orange liquid briskly with ether, 
 which has a greater solvent power for bromine than is possessed by water, and there- 
 fore abstracts it from the aqueous solution : since ether does not mix to any great 
 extent with water, it now rises to the surface of the liquid, forming a layer of a 
 beautiful orange colour, due to the bromine which it holds in solution. This orange 
 layer is carefully separated and shaken with solution of potash, which immediately 
 destroys the colour by removing the bromine, leaving the ether to rise to the 
 surface in a pure state, and fit to be employed for abstracting the bromine from a 
 fresh portion of the water. The action of the bromine upon potash is precisely 
 similar to that of chlorine ; 6KOH + Br 6 = 5KBr + KBr0 3 + 3H 2 O. 
 
 After the solution of potash has been several times shaken with the ethereal solu- 
 tion of bromine, and has become highly charged with this element, it is evaporated 
 so as to expel the water, leaving a solid residue containing the potassium bromide 
 and bromate. This saline mass is strongly heated to decompose the bromate, and 
 convert it into bromide; KBr0 3 = KBr + 3 . From this salt the bromine is ex- 
 tracted by distilling it with manganese dioxide and sulphuric acid, when the bro- 
 mine is liberated and condensed in a receiver kept cold by iced water; 2KBr + 
 
 The aspect of bromine is totally different from that of any othei 
 element, for it distils over in the liquid condition, and preserves that 
 form at ordinary temperatures, being the only liquid non-metallic ele- 
 ment. Its dark red-brown colour, and the peculiar orange colour of the 
 vapour which it exhales continually, are also characteristic ; but, above 
 all, its extraordinary and disagreeable odour, from which it derives its 
 name (/Spw/zor, a stench), leaves no doubt of its identity. The odour 
 has some slight resemblance to that of chlorine, but is far more intoler- 
 able, often giving rise to great pain, and sometimes even to bleeding at 
 the nose. 
 
 Liquid bromine is thrice as heavy as water (sp. gr. 3.18 at o C.), and 
 boils at 63 C., yielding a vapour 5^ times as heavy as air (sp.gr. 5.54).* 
 It may be frozen at - 7 C. to a brown crystalline solid. It requires 
 33 times its weight of cold water to dissolve it, and forms a crystalline 
 hydrate (Br.5H 2 0) corresponding with chlorine hydrate. 
 
 In its bleaching power, its aptitude for direct combination, and its 
 other chemical characters, it very closely resembles chlorine, so closely, 
 indeed, that it is difficult to distinguish, in many cases, between the 
 compounds of chlorine and bromine with other substances, unless the 
 elements themselves be isolated. A necessary consequence of so great a 
 similarity is, that very little use has been made of bromine, since the far 
 
 * At high temperatures the vapour density (sp. gr.) of bromine decreases considerably. 
 
 N 
 
194 HYDRO BKOMIC ACID. 
 
 more abundant chlorine fulfils nearly all the purposes to which bromine 
 might otherwise be applied. In the daguerreotype and photographic 
 arts, however, some special applications of bromine have been discovered, 
 and for some chemical operations, such as the determination of the illu- 
 minating hydrocarbons in coal gas, bromine is sometimes preferred to 
 chlorine. It is applied in the manufacture of artificial dyestuffs and has 
 also been used in America as a disinfectant. The bromides of potassium 
 and ammonium are frequently employed in medicine. Bromide of cad- 
 mium is used in photography. Commercial bromine sometimes contains 
 bromoform and cyanogen bromide. In the composition of their com- 
 pounds chlorine and bromine exhibit great analogy, but no compound 
 of bromine with oxygen has been obtained. 
 
 Hypobromous acid (HOBr) has been obtained in solution by shaking 
 mercuric oxide with water and bromine. The solution is very unstable, 
 decomposing, especially when heated, with liberation of bromine and 
 formation of bromic acid. The action of bromine upon diluted solutions 
 of the alkalies, and upon the alkaline earths, produces bleaching liquids 
 similar to those formed by chlorine, and apparently containing the 
 hypobromites of the metals. 
 
 Bromic acid (HBr0 3 ) can be prepared in a similar manner to that 
 described for the preparation of chloric acid, to which it has a great 
 general resemblance, the bromates being also similar to the chlorates. 
 
 1 1 8. Hydrogen bromide or hydrobromic acid (HBr = 8i parts by 
 weight = 2 vols.) The inferiority of bromine to chlorine in chemical 
 energy is well exemplified in its relations to hydrogen ; for the vapour 
 of bromine mixed with hydrogen will not explode under the action of 
 flame or of the electric spark, like the mixture of chlorine and hydrogen. 
 Direct combination may be induced by contact with heated platinum. 
 
 When it is attempted to prepare this acid by distilling bromide of 
 sodium or potassium with sulphuric acid (as in the preparation of hydro- 
 chloric acid) the inferior stability of hydrobromic acid is shown by the 
 decomposition of a part of it, the hydrogen being oxidised by the 
 sulphuric acid, and the bromine set free; 2HBr + H 9 S0 4 = 2H 2 + S0 2 
 + Br 2 . 
 
 If a strong solution of phosphoric acid be employed instead of the 
 sulphuric, pure hydrobromic acid may be obtained. 
 
 But the most instructive method of obtaining hydrobromic acid con- 
 sists in attacking water with bromine and phosphorus simultaneously, 
 when the phosphorus takes the oxygen of the water, forming phosphoric 
 acid, and the bromine combines with the hydrogen to form hydrobromic 
 acid; 3 H 2 O + Br 5 + P = HPO 3 + 5HBr. 
 
 Phosphoric acid. 
 
 The experiment may be made in the apparatus shown in Fig. 156. 20 grams of 
 red phosphorus are introduced into the flask and are covered with 40 c.c. of water. 
 1 20 grams (40 c.c.) of bromine are allowed to fall, drop by drop, from the stop- 
 cock funnel into the flask. The hydrogen bromide is passed through a U-tube con- 
 taining fragments of glass mixed with moist red phosphorus, to absorb bromine, 
 and is collected by downward displacement. After a time the flask may be gently 
 heated. 
 
 Hydrogen bromide is very similar to hydrogen chloride ; it boils at 
 - 73 C. Like that gas, it is very soluble in water, and the solution 
 acts upon metals and their oxides in the same manner as does hydro- 
 chloric acid. Chlorine removes the hydrogen from hydrobromic acid, 
 
IODINE. 
 
 195 
 
 liberating bromine, which it converts into bromine chloride if employed 
 in excess. 
 
 Fig. 156. Preparation of hydrobromic acid. 
 
 Nitrogen bromide has been obtained by the action of bromide of potassium upon 
 chloride of nitrogen, which it resembles in general character and explosive pro- 
 perties. 
 
 Carbon tetrabromlde, CBr 4 , is obtained by heating CS 2 with Br at 160 C. It 
 crystallises in white tables, melts at 91 C. and boils at 189.5 @. 
 
 Bromine chloride, BrCl, is a very volatile red-brown liquid of pungent odour. 
 It is dissociated above 10 C. That chlorine should unite directly with bromine, 
 which it so much resembles in chemical character, illustrates its great tendency to 
 direct chemical combination. 
 
 IODINE. 
 
 1 = 126 parts by weight. 
 
 119. Iodine is contained in sea water in even smaller quantity than 
 bromine is, and appears to be present as calcium iodate, Ca (IO 3 ) 2 ,of which 
 4 parts are contained in a million of sea water,* but the iodine appears 
 to constitute a portion of the necessary food of certain varieties of sea- 
 weed, which extract it from the sea water, and concentrate it in their 
 tissues. The ash remaining after sea-weed has been burnt was long 
 used, under the name of kelp, in soap-making, because it contains a 
 considerable quantity of sodium carbonate; and in the year 1811, 
 Courtois, a soap-boiler of Paris, being engaged in the manufacture of 
 soda from kelp, obtained from the waste liquors a substance which 
 possessed properties different from those of any form of matter with 
 which he was acquainted. He transferred it to a French chemist, 
 Clement, who satisfied himself that it was really a new substance ; and 
 Oay-Lussac and Davy having examined it still more closely, it took its 
 rank among the non-metallic elementary substances, under the name of 
 
 * The iodate may be detected in sea water by shaking- with carbon disulphide and a little 
 of the water in which phosphorus has been kept ; the phosphorous acid reduces the iodate, 
 liberating iodine, which dissolves in the CS 2 with a rose colour. It has been shown that the 
 amount of iodine (2.3 milligrams per litre) in sea water is constant at all depths, but while it 
 is in inorganic combination at great depths it is organically combined near the surface. 
 
196 EXTEACTION OF IODINE. 
 
 iodine (toeiS?)?, violet-coloured), conferred upon it in allusion to the 
 magnificent violet colour of its vapour. 
 
 The history of the discovery of iodine affords a very instructive 
 example of the advantage of training persons engaged in manufactures 
 to habits of accurate observation, and, if possible, of accurate chemical 
 observation ; for had Courtois passed over this new substance as acci- 
 dental, or of no consequence, the community would have lost, at least 
 for some time, the benefits derived from the discovery of iodine. 
 
 For some years the new element was only known as a chemical 
 curiosity, but an unexpected demand for it at length arose on the part 
 of the physician, for it had been found that the efficacy of the ashes of 
 sponge, which had long been used in some particular maladies, was due 
 to the small quantity of iodine which they contained, and it was of 
 course thought desirable to place this remedy in the hands of the medical 
 profession in a purer form than the ash of sponge, where it is associated 
 with very large quantities of various saline substances. Much more 
 recently, the demand for this element has greatly increased on account 
 of its employment in photography, and in the manufacture of artificial 
 dyes, and large quantities of it were at one time produced from kelp. 
 
 Although the production of iodine from kelp is a dead industry, a brief de- 
 scription of it may be given as an excellent example of how an element may be 
 
 extracted from an enormously pre- 
 ponderating mass of other matter. 
 The sea- weed* is spread out to dry, 
 and burnt in shallow pits at as low 
 a temperature as possible ; for the 
 sodium iodide is converted into- 
 vapour and lost if the temperature 
 is very high. The ash, which is in 
 a half-fused state, is broken up and 
 treated with hot water, which dis- 
 solves about half, leaving a residue 
 consisting of calcium carbonate and 
 sulphate, sand, &c. The whole of 
 the sodium iodide is contained in 
 the portion dissolved by the water, 
 but is mixed with much larger 
 quantities of sulphate, carbonate f 
 Fig. 157. Extraction of iodine. hyposulphite, sulphide and bro- 
 
 mide of sodium, together with sul- 
 phate and chloride of potassium. A portion of the water is expelled by evaporation, 
 when the sulphate and carbonate of sodium and chloride of potassium, being far less 
 soluble than the iodide of sodium, crystallise. In order to decompose the hyposul- 
 phite and sulphide of sodium, the liquid is mixed with an eighth of its bulk of oil 
 of vitriol, which decomposes these salts, evolving sulphurous and hydrosulphuric acid 
 gases, with deposition of sulphur, and forming sodium sulphate, which is deposited 
 in crystals. The liquor thus prepared is next mixed with manganese dioxide, and 
 heated in an iron still lined with lead (Fig. 157), when the iodine is evolved as a 
 magnificent purple vapour, which condenses in the bottle-shaped glass or stoneware 
 receivers (aludels) in the form of dark grey scales with metallic lustre, and having 
 considerable resemblance to black lead. The liberation of the iodine is explained 
 by the following equation 2NaI + Mn0 2 + 2H 2 S0 4 = Na-jSO^ + MnS0 4 + 2H 2 + 1 2 . 
 
 When no more iodine passes over, some manganese dioxide is added, and "the 
 bromine then distils. The quantity of bromine obtained is about one-tenth that of 
 the iodine. A ton of kelp yields about 10 Ibs. of iodine. The crude iodine is re- 
 sublimed to purify it. 
 
 A far more economical process for the treatment of sea-weed consists in distilling 
 
 * The Laminaria digitata, or deep sea tangle, contains most iodine, amounting to 0.45 per 
 cent, of the dried weed. 
 
PEOPEETIES OF IODINE. 197 
 
 it, when ammonia, acetic acid, naphtha, tar, and illuminating gas are obtained, 
 whilst a porous charcoal remains in the retort, which is treated with water in order 
 to extract the iodides and other soluble salts. This charcoal somewhat resembles 
 animal charcoal in character, containing much phosphate and carbonate of calcium 
 and magnesium ; it is useful as a decolorising and deodorising agent. In France 
 the iodine is generally precipitated from the concentrated solution of kelp by 
 passing chlorine into the solution. The precipitate is washed and resublimed. 
 
 Iodine is now imported from Chili and Peru, where it is obtained 
 from caliche, the crude nitrate of soda found in certain districts 
 of those countries. In this mineral the iodine (about o.i per cent.) 
 occurs as sodium iodate (IS"aI0 3 ) which remains dissolved in the water 
 from which the sodium nitrate has been recrystallised for the market. 
 These mother liquors, containing about 22 per cent, of NaIO 3 , are 
 mixed with a solution containing sodium sulphite (Na 2 S0 3 ) and sodium 
 hydrogen sulphite (NaHSO 3 ), when the iodine is precipitated according 
 to the equation 
 
 2NaI0 3 + 3Na 2 S0 3 + 2NaHS0 3 = 5X8.5804 + L 2 + H 2 0. 
 
 The precipitate is drained, pressed, and resublimed. 
 
 Besides non- volatile matter (sand and calcium sulphate), which may be 
 eliminated by resublimation, commercial iodine is liable to contain chlorine, 
 bromine, and cyanogen iodide. It may be freed from these volatile impurities 
 by dissolving it in a strong solution of potassium iodide, precipitating it by 
 the addition of water and resubliming the dried precipitate after it has been 
 mixed with barium oxide to complete its desiccation. 
 
 The features of this element are extremely well marked : its metallic 
 lustre and peculiar odour sufficiently distinguish it from all others, and 
 the effect of heat upon it is very striking, in first easily fusing it (at 
 116 C.), and afterwards converting it (boiling-point, 183) into the 
 most exquisitely purple vapour, which is nearly nine times as heavy as 
 air (sp. gr. 8.72),* and condenses upon a cool surface in shining scales. 
 Iodine stains the skin intensely brown. The specific gravity of solid 
 iodine is 4.95. 
 
 When iodine is shaken with cold water, a very small quantity is dis- 
 solved (about 0.05 per cent.), forming a light-brown solution. Hot 
 water dissolves a larger quantity, but alcohol is one of the best solvents 
 for iodine, producing a dark red-brown solution from which part of the 
 iodine may be precipitated by adding water. A solution of potassium 
 iodide also dissolves iodine freely (Lugol's solution ; liquor iodi). Tincture 
 of iodine contains iodine with half its weight of potassium iodide 
 dissolved in alcohol. Benzene and carbon bisulphide dissolve it abun- 
 dantly, producing fine violet-red solutions, which deposit the iodine, if 
 allowed to evaporate spontaneously, in minute rhombic octahedral 
 crystals aggregated into very beautiful fern- like forms. If an extremely 
 weak aqueous solution of iodine be shaken with a little carbon bi- 
 sulphide, the latter will remove the iodine from the solution, and, on 
 standing, will fall to the bottom of the liquid, having a beautiful rose 
 colour. By dissolving a large quantity of iodine in carbon bisulphide, a 
 solution is obtained which is perfectly opaque to rays of light, though it 
 allows heat rays to pass freely, and is therefore of great value in physical 
 experiments. A solution of iodine in carbon teti achloride is also used 
 for the same purpose. 
 
 * The vapour density of iodine vapour falls with rise of temperature. 
 
198 IODINE AND STARCH. 
 
 Existing, as iodine does, in very minute quantity in the water from 
 various natural sources, it would often be overlooked if the chemical 
 analyst did not happen to possess a test of the most delicate description 
 for it. Iodine, in the uncombined state, dyes starch of a beautiful 
 blue colour, as may be proved by heating a grain or two of the element 
 with water, and adding to the cold solution a little thin starch, or by 
 placing a minute fragment of iodine in a stoppered bottle, and sus- 
 pending in it a piece of paper clipped in thin starch. This test, however, 
 though sensitive to the smallest quantity of free iodine, gives no indica- 
 tion whatever with iodine in combination, as it always exists in nature ; 
 in order, therefore, to test for iodine, a little starch-paste is added to the 
 suspected liquid, and then a drop of a weak solution of chlorine, which 
 will set free the iodine, and cause the production of the blue colour. It 
 is necessary, however, carefully to avoid adding too much chlorine, since 
 it would immediately destroy the colour of the iodised starch : if this 
 has been done, a very little sulphurous acid will bring back the blue tint, 
 which will be again bleached by more sulphurous acid.* Alkalies also 
 bleach it, and the colour of a mixture of the iodised starch with water is 
 removed by heating, but returns in great measure when the solution 
 cools. The starch appears to be only dyed by the iodine, and not 
 combined with it ; on shaking the blue iodised starch for some time with 
 CS 2 , the blue colour is removed, and the red solution of iodine in CS 2 is 
 obtained. 
 
 This delicate test for iodine has enabled the chemist to show that the 
 element is widely distributed in very small quantities. It has been 
 found in the floating matter of the air, in various fungi, in forest trees, 
 and in the animal body, particularly the thyroid gland. 
 
 Though very closely connected with chlorine and bromine in its general 
 chemical relations, there are several points in the history of iodine which 
 cause it to stand out in marked contrast by the side of these elements. 
 The attraction which binds it to hydrogen and the metals is certainly 
 weaker than that exerted by chlorine and bromine, so that either of 
 these is capable of displacing it from its compounds, and its bleaching 
 properties are very feeble. 01, uniting with H, produces 22,000 heat- 
 units; gaseous Br produces 12,100, but gaseous I produces practically no 
 thermal effect.t Hence HI is much less stable than HBr or HC1. On the 
 other hand, iodine exhibits a more powerful tendency to unite with 
 oxygen ; for boiling nitric acid converts it into iodic acid (HI0 3 ), though 
 this oxidising agent would not affect chlorine or bromine. Iodine is 
 also capable of direct oxidation by ozone. 
 
 Iodine pentoxide, I 2 5 , is the only oxide of iodine which is known with 
 certainty; it is the anhydride of iodic acid (H 2 O.I 2 O 5 =:2HI0 3 ), and is a white 
 crystalline substance obtained by heating the acid. The product of the oxidation 
 of iodine by ozone is a yellow deliquescent powder (formerly supposed to be 
 I 2 3 ), the exact composition of which has not been elucidated, 
 
 Evidence has been obtained, from the existence of certain organic compounds, 
 that iodine is able to form a base on the type of ammonia. When this base is 
 isolated it will probably have the formula IH 2 (OH), being the analogue of hydroxyl- 
 amine NH 2 (OH). 
 
 Some of the compounds of iodine with the metals are remarkable for their 
 
 * The following equations explain these changes : 
 
 (i) KI + Cl = KC1 + I ; (2) I + 3H 2 O + C1 5 = HIO 3 + 5HC1 ; 
 
 (3) 2HIO 3 + H 2 S0 3 =5H 2 SO 4 + I 2 + H 2 O; (4) I 2 + H 2 CH-H 2 SO 3 = 2HI + H 2 SO 4 . 
 t The formation of HI from H and solid I absorbs 6000 heat-units. 
 
IODIC ACID. 
 
 I 99 
 
 beautiful colours. The mercuric iodide, produced by mixing solutions of potassium 
 iodide and mercuric chloride, forms a tine scarlet precipitate, which dissolves in 
 an excess of potassium iodide to a colourless solution. 
 
 Lead iodide has a bright yellow colour, as may be seen by precipitating potas- 
 sium iodide with a solution of lead acetate. The precipitate is dissolved by 
 boiling with water (especially on adding a little hydrochloric acid), forming a 
 colourless solution, from which the lead iodide crystallises in very brilliant golden 
 scales on cooling. Silver iodide is produced as a yellow precipitate when silver 
 nitrate is added to potassium iodide. The bromide and chloride of silver would 
 form white precipitates. Silver iodide is more stable than the chloride or 
 bromide ; when exposed to light it appears to be unchanged, but if a reducing 
 agent, such as ferrous sulphate or pyrogallin, be afterwards poured over it, that 
 portion of the iodide which has been exposed to light is immediately blackened, 
 from the separation of silver in the metallic state. This is the principle of the 
 process for developing the negative photograph taken on a collodion film rendered 
 sensitive by silver iodide. The iodides of potassium, ammonium, and cadmium 
 are also used in photography. 
 
 120. lodic acid, HI0 3 or I0 2 (OH), is most easily prepared by boiling 
 iodine with the strongest nitric acid in a long-necked flask, when it is 
 dissolved in the form of iodic acid, which is left, on evaporating the 
 nitric acid, as a white mass. This may be purified by dissolving in water 
 and crystallising, when the iodic acid forms white hexagonal tables. 
 Heated to 180 C. the iodic acid is decomposed into water and iodic 
 anhydride, 2HI0 3 = H 9 + 1 9 5 . This last is decomposed at about 
 370 C. into iodine and oxygen. The iodic anhydride oxidises combus- 
 tible bodies, but not with any great violence. The acid is far more 
 stable than chloric or bromic acid. Its solution first reddens litmus- 
 paper, and afterwards bleaches it by oxidation. Its salts, the iodates, 
 are less easy soluble in water than are the chlorates and bromates, which 
 they resemble in their oxidising action upon combustible bodies. They 
 are all decomposed by heat, evolving oxygen, and sometimes even 
 iodine, showing how much inferior this element is to chlorine and bromine 
 in its attraction for metals. 
 
 Potassium iodide may be oxidised directly to potassium iodate, KI0 3 , by potas- 
 sium permanganate. Iodic acid forms acid potassium salts of the formula? KHI 2 6 
 and KH 2 I 3 9 , the existence of which, together with the fact that the acid readily 
 yields an anhydride and water when heated (an uncommon reaction for a mono- 
 basic acid), and with other evidence, indicates that the acid is di- or even tri-basic. 
 
 Periodates. The periodates (such as AgI0 4 ), analogous to the perchlorates, are 
 known, but the simple acid HI0 4 has not been isolated. The periodic acid, H 5 I0 6 or 
 IO(OH) 5 . is prepared as follows : Chlorine is passed through a solution of sodium 
 iodate containing NaOH, whereupon the salt IO(OH) 3 (ONa) 2 crystallises from the 
 solution ; NaI0 3 + 3NaOH + C1 2 == aNaCl + IO(OH) 3 (ONa) 2 . This sodium salt is dis- 
 solved in HN0 3 and AgNO 3 is added ; a brown precipitate of Ag 2 HI0 5 is obtained. 
 When this is dissolved in HN0 3 and the solution is evaporated red crystals of 
 AgI0 4 .H 2 separate, and by treating these with water HglOg passes into solution, 
 whilst Ag 4 I 2 9 .3H 2 remains undissolved. Periodic acid crystallises from this 
 solution in colourless prisms ; it decomposes when heated, yielding H 2 0, O and 
 Io0 5 . A solution of the acid is a powerful oxidant. 
 
 " The periodates are referable to four types, termed respectively, the meta-salts, 
 from the acid HI0 4 or I0 3 (OH) ; the meso-salts, from the acid H 3 I0 5 or I0 2 (OH) 3 ; 
 the para-salts, from the acid H 5 I0 6 or IO(OH) 5 ; and the dimeso-salts, from the 
 acid H 4 I 2 9 or 2l0 2 (OH) 3 -H 2 0. It thus happens that a large number of these 
 salts are known ; they are sparingly soluble. 
 
 When iodine is dissolved in an alkali an iodide and an iodate are 
 formed ; 6NaOH + I 6 = sNal + NaIO 3 + 3 HOH. In the case of chlorine 
 and bromine the analogous reaction yields a hypochlorite and a hypo- 
 bromite respectively ; but the evidence for the existence of a hypoiodite 
 
200 HYDRIODIC ACID. 
 
 in the alkaline solution of iodine is very feeble. When such an alkaline 
 solution of iodine is acidified, all the iodine is liberated, for the 
 hydriodic acid and the iodic acid set free immediately react, the iodic 
 acid oxidising the hydriodic acid ; HI0 3 + 5 HI = 3HOH + 1 6 . 
 
 121. Hydrogen iodide or hydriodic acid (111 = 128 parts by 
 weight =2 vols.). Iodine vapour combines with hydrogen at 450 C. 
 to form hydrogen iodide. The gas is best prepared by decomposing 
 water with iodine in the presence of phosphorus ; P + 1 5 + 4.HOH = 
 PO(OH) 3 + 5HI or, if a smaller proportion of iodine be used 
 P(OH) 3 
 
 6.5 grams of potassium iodide are dissolved in 3 c.c. of water in a retort (Fig. 158), 
 and 13 grams of iodine are added ; when this has dissolved, 0.65 gram of red 
 
 phosphorus are introduced, and the mixture 
 heated very gradually, the gas being collected 
 by downward displacement in stoppered 
 bottles, which must be placed in readiness, as 
 the gas comes off very rapidly. These quan- 
 tities will fill four pint bottles with the gas. 
 
 Hydrogen iodide is very similar in its 
 properties to hydrogen chloride and 
 bromide, fuming strongly in moist air, 
 very readily absorbed by water, lique- 
 fied only under strong pressure, and 
 solidified by extreme cold. It is much 
 heavier, its specific gravity being 4.44. 
 If a bottle of hydriodic acid gas be placed in contact with a bottle con- 
 taining chlorine or bromine vapour diluted with air (Fig. 69) the HI 
 will be instantly decomposed, with separation of the beautiful violet 
 vapour of iodine. The gas is decomposed by light at the ordinary 
 temperature and is dissociated when heated.* 
 
 The aqueous solution of hydriodic acid is most conveniently prepared 
 by passing hydrosulphuric acid gas through water in which iodine is 
 suspended, H 2 S + I ? = 2 HI + S, the separated sulphur being filtered off, 
 and the solution boiled to expel the excess of hydrosulphuric acid. By 
 this method it is not possible to obtain a solution of HI of greater 
 sp. gr. than 1.56 (50 per cent. HI ; the strongest solution has asp. gr. 
 of 1.99), for a strong solution of hydriodic acid converts sulphur into 
 H 2 S. 
 
 The iodine is only able to decompose the H 2 S by virtue of the fact that the 
 HI produced has an affinity for the water ; since this affinity diminishes as the 
 liquid grows stronger, a period is soon reached when the dissolution of the HI 
 in the water can no longer supply enough energy to enable the iodine to 
 decompose the H 2 S. In other words, the reaction only occurs so long as it is 
 exothermic, which will be the case until the heat produced by the dissolution 
 of the HI in water is equal to that absorbed in the decomposition of the H 2 S by 
 the iodine. 
 
 Solution of hydriodic acid differs greatly from hydrochloric and 
 hydrobromic acids, in being decomposed by exposure to air, particularly 
 in light, its hydrogen being oxidised and iodine separated, which dis- 
 solves in the liquid, and renders it brown. 
 
 This tendency of the hydrogen of hydriodic acid to combine with 
 
 * At 350 C. 17.3 per cent., at 394 C. 19.5 per cent., and at 448 C. 21.5 per cent, of the 
 gas is dissociated. 
 
I UNIVERSE 
 
 NITROGEN IODIDE. 2OI 
 
 oxygen renders that acid a powerful reducing agent. It is even capable 
 of reducing sulphuric acid to hydrosulphuric acid 
 H 2 S0 4 + SHI = H 2 S +4H 2 + I 8 
 
 so that when potassium iodide is heated with concentrated sulphuric 
 acid, hydrosulphuric acid is evolved in considerable quantity. It will be 
 remembered that HC1 does not reduce H 2 S0 4 , whilst HBr only reduces 
 it to H 2 S0 3 . 
 
 The action of hydriodic acid upon the metals and their oxides is gene- 
 rally similar to that of the other hydrogen acids. In organic chemistry, 
 hydriodic acid is often employed for introducing hydrogen into a coin- 
 pound ; thus, by heating benzene with hydriodic acid it may be made 
 to take up 6 atoms of hydrogen ; C 6 H 6 + 6HI = C 6 H 12 + 1 6 . Since the 
 attraction of iodine for hydrogen is so feeble, metalepsis does not occur 
 between this halogen and hydrocarbons. 
 
 The circumstance that the organic compounds containing iodine are 
 generally much less volatile, and therefore more manageable, than those 
 of chlorine and bromine, leads to the extensive employment of this 
 element in researches upon organic substances. 
 
 When potassium is heated in a measured volume of gaseous hydriodic 
 acid, the iodine is removed, and the hydrogen occupies half the original 
 volume. Hence i volume of hydrogen is combined with i volume of 
 iodine vapour in 2 volumes of hydriodic acid. 
 
 122. Compounds of carbon with iodine, analogous in composition to 
 the chlorine compounds of this element, are known. They are solids, it 
 being generally the case that iodine compounds are less volatile than the 
 corresponding chlorine compounds. 
 
 Nitrogen iodide. The action of chlorine, bromine, and iodine upon 
 ammonia exemplifies the difference in their attraction for hydrogen ; for 
 whilst chlorine and bromine, acting upon ammonia, cause the liberation 
 of a certain amount of nitrogen, iodine simply removes part of the 
 hydrogen, and itself fills up the vacancies thus occasioned, no nitrogen 
 being liberated, the hydriodic acid thus formed combining with more 
 ammonia to form ammonium iodide. Nitrogen iodide, NI 3 , is formed 
 at the same time. 
 
 It appears that when iodine is dissolved in dilute ammonia NH 4 1 and hypo- 
 iodous acid are formed ; NH 3 + I 2 + H 2 = NH 4 I + HOI. The hypoiodous acid then 
 reacts with more ammonia to form nitrogen iodide ; NH 3 + 3HOI = NI 3 + 3H 2 0. 
 
 By another theory the nitrogen iodide, alleged to have the formula N 2 H 3 I 3 , is 
 formed as a decomposition product of ammonium hypoiodite ; 3NH 4 OI = 
 N 2 H 3 I 3 + NH 3 + 2H 2 0. The hypoiodite would be formed when the iodine dis- 
 solved in excess of ammonia ; I 2 + 2NH 3 + H 2 = NH 4 I + ]SrH 4 OL 
 
 To prepare the iodide of nitrogen 1.3 gram of iodine is rubbed to powder 
 in a mortar and mixed with 14 c.c. of strong ammonia : the mortar is covered 
 with a glass plate, and after about half an hour the iodide of nitrogen is collected 
 in separate portions upon four niters, which are allowed to drain and spread 
 out to dry. The brown solution contains iodine dissolved in ammonium iodide. 
 
 Another method consists in dissolving iodine in a mixture of hydrochloric with 
 a little nitric acid, with the aid of heat, and adding ammonia, which decomposes 
 the IC1 in solution, and gives a black precipitate of the iodide of nitrogen. 
 
 When dry NH 3 gas is passed over iodine the two combine, several compounds, 
 such as (NH 3 ) 2 I, being formed. 
 
 The iodide is a black powder, which explodes with a loud report even 
 when touched with a feather, the violence of the explosion being 
 accounted for by the sudden evolution of a large volume of gas and 
 
202 HYDROFLUORIC ACID. 
 
 vapour from a small volume of solid. Even when allowed to fall from 
 the height of a few feet upon the surface of water, it explodes if perfectly- 
 dry. In the moist state it slowly undergoes decomposition. 
 
 123. Iodine forms two compounds with chlorine, mono chloride (IC1) and tri- 
 chloride (IC1 3 ). The former is obtained by passing dry chlorine over dry iodine 
 until it becomes a red-brown liquid. This solidifies when cooled and then melts 
 at 14 C., but is unstable, readily passing to another form which melts at 27 C. 
 
 The trichloride forms fine red needle-like crystals, and is produced when iodine 
 or hydriodic acid gas is acted upon with an excess of chlorine. It is useful as a 
 germicide. The chlorides of iodine are decomposed by water, yielding HI0 3 , 
 HC1, and iodine. From the aqueous solution of IC1, ether extracts a yellow 
 volatile compound having the composition IC1.HC1. 
 
 Iodine bromide, IBr, is a crystalline solid resembling iodine, fusing at 36 C. 
 and subliming with partial decomposition. Water decomposes it, iodine being 
 separated. 
 
 FLUORINE. 
 
 F = 19 parts by weight. 
 
 124. The most ornamental mineral substance occurring in any abun- 
 dance in this country is known as fluor spar, Derbyshire spar, or blue 
 John (fluoride of calcium), and is found with several beautiful shades of 
 colour blue, purple, violet, or green, and sometimes perfectly colour- 
 less, either in large masses or in crystals, which have the form of a 
 cube or of some solid derived from it. The use of this mineral as a flux 
 in smelting ores dates from a very remote period, and from this use the 
 name fluor appears to have been originally derived ; but we have no 
 record of its chemical examination until 1764, when Margraf found his 
 glass retort powerfully corroded in distilling this mineral with sul- 
 phuric acid, and Scheele soon after announced that it contained lime 
 and fluoric acid. But though this chemist had fallen into the error to 
 which analysts are continually liable, of mistaking products for educts, 
 his experiments, as they were afterwards perfected by Gay-Lussac and 
 Thenard, deserve particular consideration. 
 
 125. Hydrogen fluoride (HF = 20 parts by weight = 2 volumes).* 
 If powdered fluor spar be mixed with twice its weight of oil of vitriol, 
 
 and heated in a leaden retort (Fig. 159)7 
 the neck of which fits tightly into a leaden 
 condensing-tube, cooled in a mixture of 
 ice and salt, a colourless liquid distils 
 over, arid the residue in the retort is 
 found to consist of calcium sulphate ; "t* 
 CaF 2 + H 2 S0 4 = CaS0 4 + 2 HF. The 
 colourless liquid (hydrofluoric acid) pos- 
 
 sesses most remarkable properties ; it is 
 
 Fio . powerfully acid, fumes strongly in the air, 
 
 and has a most pungent irritating odour. 
 If the air is at all warm, the liquid begins to boil when taken out of the 
 freezing-mixture. Should the operator have the misfortune to allow a 
 
 * The vapour density of hydrogen fluoride is 25.6 at 26.4 C., and gradually diminishes 
 until the temperature reaches 89 C., when it remains constant at 10 ; this shows that at 
 temperatures below 89 C. the molecule of this gas is more complex than is represented by 
 the formula HF, but becomes HF at 89 C. 
 
 f The mineral kryolite (fluoride of aluminium and sodium) may be advantageously substi- 
 tuted for fluor spar, being more easily obtained in a pure state. 
 
THE ETCHING OF GLASS. 203 
 
 drop to fall upon his hand, it will produce a very painful sore, even its 
 vapour producing pain under the finger nails. Its attraction for water 
 is so great, that the acid hisses like red-hot iron when brought in contact 
 with water. But its most surprising property is that of rapidly corro- 
 ding glass, which has already been alluded to as noticed by Margraf . 
 Experiment soon proved that great analogy existed between the pro- 
 perties of this new acid and those of hydrochloric acid : and Ampere 
 was led to believe that the acid was a hydrogen acid, containing a new 
 salt radicle, which he named fluorine ; the name of the acid was then 
 changed from fluoric to hydrofluoric acid. 
 
 This liquid has since been proved to be a solution of hydrofluoric 
 acid in water; for if it be distilled with phosphoric anhydride,, 
 which retains the water, it evolves hydrofluoric acid gas, which re- 
 sembles hydrochloric acid gas in fuming strongly on contact with moist 
 air and being eagerly absorbed by water, but has a far more pungent 
 odour. 
 
 Pure hydrogen fluoride is prepared by heating dry potassium hydrogen 
 fluoride (KHF 2 ) to redness in a platinum still. It is then obtained as a 
 colourless liquid, which boils at 19 C., and has the specific gravity 
 0.985 at 12 C. It solidifies at -102 C. and melts again at -92. 
 The pure acid scarcely affects metals, excepting potassium and sodium. 
 It corrodes glass, however, rapidly, though its vapour has little action 
 on glass unless moisture be present. It combines eagerly with sul- 
 phuric and phosphoric anhydrides, with great evolution of heat, a 
 circumstance in which it resembles water, and differs altogether from 
 its more obvious analogue, hydrochloric acid. It is also found that it 
 combines energetically with the fluorides of potassium and sodium, 
 precisely as water combines with the oxides of those metals. 
 
 It is remarkable that the solution of hydrofluoric acid, in its concen- 
 trated form, is not so heavy as a somewhat weaker acid. Thus the acid 
 of sp r gr. i .06 acquires the sp. gr. 1.15 on addition of a little water ; but 
 on adding more water, its sp. gr. is again reduced. It would hence 
 appear that the acid of 1.15 is a definite hydrate of hydrofluoric acid ; 
 its composition corresponds with HF.2H 2 0. It distils unchanged at 
 248 F. (120 C.). 
 
 The solution of hydrofluoric acid is generally kept in bottles made of 
 gutta-percha. Its action on metals and their oxides resembles that of 
 hydrochloric acid. It dissolves all ordinary metals except gold, 
 platinum, silver, mercury, and lead. Strange to say, it has but little 
 action on magnesium. 
 
 The property which renders this acid so useful to the chemist is its 
 power of dissolving silica even in its most refractory form. When sand 
 or flint reduced to powder is digested in a leaden or platinum vessel 
 with hydrofluoric acid, it is gradually dissolved ; and if the solution 
 be evaporated, the whole of the silica will be found to have disappeared 
 in the form of gaseous silicon tetrafluoride ; SiO, + 4-HF = SiF 4 + 2lI 2 O. 
 If the silica be combined with a base, the metal will be left as a fluoride 
 decomposable by sulphuric or hydrochloric acid. This renders hydro- 
 fluoric acid a most valuable agent in the analysis of the numerous 
 mineral silicates which resist the action of other acids. 
 
 The corrosion of glass by hydrofluoric acid is now easily explained. 
 Ordinary glass consists of silicate of sodium or potassium combined with 
 
204 
 
 ISOLATION OF FLUORINE. 
 
 silicate of calcium or lead. The hydrofluoric acid attacks and removes 
 the silica, and thus eats its way into the glass. 
 
 In order to demonstrate the action of this acid upon glass, a glass plate is 
 warmed sufficiently to melt wax, a piece of which is then rubbed over it, until the 
 glass is covered with a thin and pretty uniform coating. Upon this a word or 
 drawing may be engraved with a sharp point so that the lines shall expose the 
 glass. The glass plate is then placed, wax downwards, over a leaden or platinum 
 dish containing a mixture of fluor spar and strong sulphuric acid, exposed to a 
 very gentle heat, and allowed to remain for a quarter of an hour ; the plate is 
 then gently warmed to melt the wax, which may be wiped off with a little tow, 
 when it will be found that the hydrofluoric acid evolved from the mixture has 
 corroded those portions of the glass from which the graver had removed the 
 wax. This process is applied to the marking of glass instruments. 
 
 The solution of hydrofluoric acid etches glass without deadening the surface, as 
 is the case with the vapour ; but a solution of fluoride of potassium or ammonium 
 mixed with sulphuric acid does produce a dead surface, and is much used for 
 engraving on glass. An ink sold for writing on glass with a steel pen is composed 
 of barium and ammonium fluorides and sulphuric acid. 
 
 126. When hydrofluoric acid was tirst obtained it was soon evident 
 that it was not an element, because it yielded hydrogen when treated 
 with metals, and its analogy to hydrochloric acid led naturally to the 
 assumption that it was a compound of hydrogen with only one other 
 element, which was called fluorine. All attempts to isolate this element, 
 however, failed, owing to the great attraction which it possesses for 
 other elements. It was not until Moissan, in 1886, prepared very pure 
 hydrogen fluoride, and discovered that an alloy of platinum with 10 per 
 
 cent, of iridium would 
 withstand the attack of 
 fluorine,, that he suc- 
 ceeded in electrolysing 
 HF with liberation of 
 fluorine at the anode in 
 quantity sufficient for 
 the properties of the 
 element to be examined. 
 
 Fig. 1 60 illustrates the 
 electrolytic cell used by 
 Moissan. The U-tube A is 
 made of the aforesaid alloy, 
 as also are the electrodes iB 
 passing through stoppers C 
 made of fluor spar, which 
 insulates them from the 
 metal of the U-tube. The 
 cell contains pure liquid 
 hydrogen fluoride, having 
 about 20 per cent, of potas- 
 sium fluoride dissolved in it, 
 and is immersed in a bath of 
 methyl chloride whereby it 
 is cooled to - 23 C. ; a cur- 
 rent from 25 Bunsen's cells 
 is passed through the liquid. 
 The liberated gases escape by the side tube D, the hydrogen being set free at the 
 negative electrode and the fluorine at the positive electrode. To free the fluorine 
 from the HF it is passed over dry KF. 
 
 Fluorine is a greenish-yellow gas, which becomes liquid at - 185 C. 
 
 Fig. 1 60. Isolation of fluorine. 
 
THE HALOGENS. 205 
 
 and has the properties of chlorine, but much more strongly marked. 
 It decomposes water immediately, seizing upon its hydrogen ^and 
 liberating oxygen in the ozonised condition ; it explodes with hydrogen 
 even in the dark,* and nearly all non-metals and many metals take fire 
 in it at ordinary temperatures. 
 
 Some metal?, however, become coated with fluoride and need to be heated before 
 they burn in the gas. Gold and platinum resist attack at temperatures below 
 300 C., and carbon is fairly resistant unless finely divided. Oxygen, nitrogen r 
 chlorine, and argon appear to be unattacked by fluorine ; hydrogen chloride 
 explodes with it, yielding HF and Cl. 
 
 Fluorine can also be obtained by heating the tetrafluorides of certain 
 metals (just as chlorine is evolved from their tetrachlorides). By this 
 method the element has been prepared from the tetrafluorides of lead 
 and of cerium. The great activity of the gas has rendered a detailed 
 study of its properties difficult ; it appears, however, that its vapour 
 density is slightly lower than 19, indicating that the gas contains free 
 atoms, as well as molecules of F 2 , at the ordinary temperature. This 
 may account for its activity. 
 
 Fluorides. Solutions of the fluorides of potassium and the other 
 alkali metals corrode glass slowly, like hydrofluoric acid. The fluorides 
 are capable of combining with the acid ; thus potassium fluoride forms 
 KF.HF, which, when dry, is a convenient source of HF gas when 
 moderately heated. The only fluoride possessed of much practical 
 interest, beside the fluoride of calcium, is the mineral kryolite (xpvos, 
 frost), which is a double fluoride of aluminium and sodium (Na 3 AlF 6 ), 
 found abundantly in Greenland, and valuable as a source of aluminium. 
 
 The topaz contains fluorine, but in what form of combination is not certain ; its 
 other constituents are alumina and silica. Tourmaline also contains fluorine, 
 together with alumina, silica, and FeO. In such minerals it is probable that the 
 F is substituted for part of the 0. 
 
 Magnesium fluoride (MgF 2 ) forms the mineral Sellaite which is found, crystal- 
 lised, in Savoy. Fluorides are also found, though in very small quantity, in sea 
 water, and they have been discovered in plants and animals. Human bone con- 
 tains about 2 per cent, of calcium fluoride. 
 
 No compound of fluorine with oxygen is known. 
 
 Carbon tetrafluoride, CF 4 , is a colourless gas made by burning lamp black in 
 fluorine ; it boils at 15 C. and is said to be produced in quantity, when kryolite is 
 electrolysed for winning aluminium 
 
 127. General review of chlorine, bromine, iodine, and fluorine. 
 
 These four elements compose a natural group, the members of which 
 are connected by the similarity of their chemical properties far more 
 closely than those of any other group of elements. They are usually 
 styled the halogens, from their tendency to produce salts resembling sea 
 salt in their composition (a\s, the sea), and such salts are called haloid 
 salts. These elements are also called salt-radicles, from their property of 
 forming salts by direct union with the metals. Each is monatomic, 
 and combines with an equal volume of hydrogen to form an acid which 
 occupies the joint volumes of its constituents. 
 
 The halogens also supply the most prominent example of the grada- 
 tion in properties observed among the members of the same natural 
 group of elements. 
 
 In the order of their chemical energy, that is, of the force with which 
 
 * Evolving 39,000 calories per 20 grams of HF formed. 
 
206 SULPHUR ORES. 
 
 they hold other elements in chemical combination with them, fluorine 
 should stand first, its combining energy being so great as to cause a 
 serious difficulty in isolating it ; chlorine would rank next, then bromine, 
 and iodine last. 
 
 The atomic weights follow the inverse order of their chemical energies : 
 fluorine, 19; chlorine, 35.5 ; bromine, 80 ; iodine, 127 numbers which, 
 of course, also represent their relative specific gravities in the state of 
 vapour. 
 
 A similar gradation is observed in their physical state and colour, 
 fluorine being a yellow gas, chlorine a yellow gas, bromine a red liquid 
 boiling at 63 C., and iodine a black solid boiling at 183 C. 
 
 Even in the exceptions which occur to the order of chemical energy 
 above alluded to, the same progression is noticed : thus fluorine has so 
 little attraction for oxygen that no oxide is known ; chlorine has less 
 attraction for oxygen than bromine (chloric acid being less stable than 
 bromic) ; whilst bromine has less than iodine, which is capable even of 
 uniting directly with ozonised oxygen. 
 
 The compounds of these elements with hydrogen are all gases distin- 
 guished by a powerful attraction for moisture and great similarity of 
 odour. Their potassium salts all crystallise in the same (cubical) form. 
 
 The silver fluoride is deliquescent and soluble in water ; the chloride 
 is insoluble in water, but dissolves very easily in ammonia; the bromide 
 dissolves with some difficulty in ammonia ; and the iodide is insoluble, 
 In some other particulars, fluorine stands apart from the other halogens ; 
 thus, the fluoride of calcium is a very insoluble substance, whilst the 
 chloride, bromide, and iodide are very soluble. Hydrofluoric acid forms 
 KHF 2 , which corresponds in composition with KHO. 
 
 It is noteworthy that these halogen elements are par excellence acid 
 elements ; that is to say, not only their oxygen compounds but their 
 hydrogen compounds exhibit acid properties. The carbon family gives 
 neutral hydrogen compounds ; the nitrogen family gives basic hydrogen 
 compounds, whilst the sulphur family gives feebly acid hydrogen 
 compounds. 
 
 SULPHUR. 
 
 8 = 32 parts by weight = I volume (at 1000 C.). 
 
 128. Sulphur is remarkable for its abundant occurrence in nature 
 in the uncombined state in many volcanic districts. It is also found, 
 as sulphuretted hydrogen, in many mineral waters, and very 
 abundantly in combination with metals, forming the numerous ores 
 known as sulphurets or sulphides, of which the following are the most 
 abundant : 
 
 Iron pyrites, Iron disulphide, FeS 2 
 
 Copper pyrites, Sulphide of iron and copper, Cu. 2 S.Fe 2 S 3 
 
 Galena, Sulphide of lead, PbS 
 
 Blende, Sulphide of zinc, ZnS 
 
 Crude antimony, Sulphide of antimony, Sb 2 S 3 
 
 Cinnabar, Sulphide of mercury, HgS. 
 
 Sulphur is plentifully distributed also, in combination with oxygen 
 and a metal, in the form of sulphates, of which the most conspicuous 
 are 
 
EXTRACTION OF SULPHUR. 2O/ 
 
 Gypsum, Sulphate of calcium, CaS0 4 .2H 2 
 
 Heavy spar, Sulphate of barium, BaS0 4 
 
 Celestine, Sulphate of strontium, SrS0 4 
 
 Epsom salts, Sulphate of magnesium, MgSO 4 .7H 2 
 
 Glauber's salt, Sulphate of sodium, Na,S0 4 .ioH 2 0. 
 
 In plants, sulphur is also found in the form of sulphates, and as a 
 constituent of the vegetable albumin (of which it forms about 1.5 per 
 cent.) present in the sap. It is also contained in certain of the essential 
 oils remarkable for their peculiar pungent odour, such as those of garlic 
 and mustard. 
 
 In animals, sulphur occurs as sulphates, as a constituent of albumin, 
 fibrin, and casein (in none of which does it exceed 2 per cent.), and 
 in bile, one of the products from which, taurine, contains 25 per cent, 
 of sulphur. 
 
 For our supplies of sulphur we are chiefly indebted to Sicily, where 
 large quantities of it are found in an uncombined state in beds of blue 
 clay. Magnificent crystalline masses of strontium sulphate are often 
 found associated with it ; the sulphur itself sometimes occurs in the 
 form of transparent yellow octahedra, but more frequently in opaque, 
 
 Fig-. 161. Distillation of sulplmr. 
 
 amorphous masses. The districts in which sulphur is found are usually 
 volcanic, and those which border the Mediterranean are particularly rich 
 in it. Sulphur has also been found in Iceland and New Zealand. 
 
 The native sulphur, being commonly distributed in veins through 
 masses of gypsum and celestine, has to be separated from these by the 
 action of heat. When the ores contain more than 12 per cent, of 
 sulphur, the bulk of it is melted out, the ore being thrown into rough 
 furnaces or cauldrons with a little fuel, and smothered up with earth, 
 so as to prevent the combustion of the sulphur, which runs down in the 
 liquid state to the bottom of the cauldron, and is drawn out into wooden 
 moulds.* But when the proportion of sulphur is small, the ore is 
 heated so as to convert the sulphur into vapour, which is condensed in 
 another vessel. The operation is conducted in rows of earthen jars 
 (A, Fig. 161) heated in a long furnace, and provided with short lateral 
 
 * High pressure steam has been applied with advantage for melting the sulphur out of 
 the ores, which are enclosed in an iron vessel ; or the ores are heated in a boiler with a 
 66 per cent, solution of calcium chloride at 120 C. The sulphur is sometimes extracted by 
 dissolving it with carbon bisulphide. When sulphur ores containing calcium sulphate are 
 distilled, part of the sulphur is lost as sulphur dioxide, which goes off as gas 
 CaSO 4 + S 2 = CaS + 2SO 2 . 
 
208 
 
 DISTILLATION OF SULPHITE. 
 
 pipes, which convey the sulphur into similar jars (B) standing outside* 
 the furnace, in which the vapour of sulphur condenses in the liquid 
 state, and flows out into pails of water. The sulphur obtained by this 
 process is imported as rough sulphur, and contains 3 or 4 per cent, of 
 earthy impurities. In order to separate these, it is redistilled, in this 
 country, in an iron retort (A, Fig. 162), from which the vapour is con- 
 ducted into a large brick chamber (B), upon the sides of which it is- 
 
 Fig. 162. Sulphur refinery. 
 
 deposited in the form of a pale yellow powder (flowers of sulphur, or 
 sublimed sulphur). When the operation has been continued for some 
 time, the walls of the chamber become sufficiently hot to melt the 
 sulphur, which is allowed to collect, and afterwards cast in wooden 
 moulds, forming roll sulphur or brimstone. Distilled sulphur is obtained 
 by allowing the vapour to pass from the retort into a small receiving 
 vessel (C) cooled by water, where it condenses in the liquid state ; this 
 variety of sulphur is preferred for the manufacture of gunpowder, for 
 reasons which will be stated hereafter. 
 
 Sulphur is readily distilled on a small scale in a Florence flask (Fig. 163),. 
 another flask cut off at the neck being employed as a receiver. The flask con- 
 taining the sulphur should be supported upon a thin 
 iron wire triangle, and heated by a gauze burner, at 
 first gently, and afterwards to the full heat. Flowers 
 of sulphur will at first condense in the receiver, and 
 will be followed by distilled sulphur when the tem- 
 perature increases. A slight explosion of the mix- 
 ture of sulphur vapour and air may occur at the 
 commencement of the distillation. An ounce of 
 sulphur may be distilled in a few minutes. 
 
 We are by no means entirely dependent 
 
 Fig. ^.-Distillation of sulphur, upon Sicily for sulphur, for this element 
 
 can be easily extracted from iron and copper 
 pyrites, both of which are found abundantly in this country. 
 
 Iron pyrites forms the yellow metallic-looking substance which is 
 often met with in masses of coal, sometimes in distinct cubical crystals, 
 and is to be picked up in large quantities on some sea-beaches, where 
 it occurs in rounded nodules, rusty outside, but having a fine radiated 
 metallic fracture. When this mineral is strongly heated, it gives up 
 part of its sulphur ; at a very high temperature one-half of the sulphur 
 
PROPERTIES OF SULPHUR. 209 
 
 may be separated, FeS 2 = FeS + S, but by an ordinary furnace heat only 
 about one-fourth can be obtained. The distillation of iron pyrites is 
 sometimes effected in conical fireclay retorts, but it is riot now much 
 practised. The sulphur obtained in this way has a green colour, due to 
 the presence of a little sulphide of iron carried over mechanically during 
 the distillation : in order to purify it, it is melted and allowed to cool 
 slowly, when the sulphide of iron subsides ; the upper portion of the 
 mass is then further purified by distillation. 
 
 Sulphur may also be obtained from copper pyrites (Cu 2 S.Fe 2 S 3 ) in the process of 
 roasting the ore, previously to the extraction of the copper. The ore is heaped up 
 into a pyramid, the base of which is about 30 feet square : a layer of powdered ore 
 is placed at the bottom, to prevent too rapid access of air : above this there is a 
 layer of brushwood : a wooden chimney is placed in the centre, and is lhade to 
 communicate with air-passages left between the faggots : around this chimney the 
 large fragments of the ore are piled to a height of about 8 feet, and a layer of 
 powdered ore, about 12 inches deep, is strewn over the whole. The heap contains 
 about 2000 tons of pyrites, and will yield 20 tons of sulphur. The fire, being 
 kindled by dropping lighted faggots down the chimney, burns very slowly, because 
 of the limited access of air, and after a few days sulphur is seen to exude from the 
 surface, and is received in cavities made for the purpose in different parts of the 
 heap. The roasting requires five or six months for its completion. In this 
 operation a part of the sulphur has been separated by the mere action of heat, and 
 another part has been displaced by the oxygen of the air, which has converted a 
 portion of the iron into an oxide. A part of the separated sulphur has been burnt, 
 the rest having escaped combustion on account of the limited access of air. The 
 sulphur extracted from pyrites is generally found to contain a little arsenic, which 
 is frequently associated with minerals. 
 
 Much sulphur is now prepared from the sulphuretted hydrogen from 
 the tank-waste of the alkali works, and from the aminoniacal liquor of 
 gas works, by a process which will be described under the manufacture 
 of carbonate of soda. 
 
 Immense quantities of sulphur are consumed in this country for the 
 manufacture of sulphuric acid, gunpowder, lucifer matches, vulcanised 
 caoutchouc, and for making the sulphurous acid gas employed in bleach- 
 ing processes. 
 
 129. Properties of sulphur. In its ordinary forms sulphur has a 
 characteristic yellow colour, though milk of sulphur, or precipitated 
 sulphur (obtained by adding an acid to the solution of sulphur in an 
 alkali), is white. It suffers electrical disturbance with remarkable faci- 
 lity, so that when powdered in a dry mortar it clings to the mortar 
 with great pertinacity. 
 
 Finely divided sulphur, especially sublimed sulphur, is gradually 
 oxidised and converted into sulphuric acid when exposed to moist air. 
 
 One of the most remarkable features of sulphur is its inflammability, 
 due to its tendency to combine with oxygen at a moderately elevated 
 temperature. It melts at 115 C. (239 F.), and inflames at about 
 260 C. (500 F.), burning with a pale blue flame and emitting the well- 
 known suffocating odour of sulphurous acid gas (S0 2 ). The changes in 
 the physical condition of this element under the influence of heat are 
 very extraordinary. If a quantity of sulphur be introduced into a 
 Florence flask and subjected to a gradually increasing heat (Fig. 164), 
 it is soon converted into a pale yellow limpid liquid (120 0.), the colour 
 of which becomes gradually brown as the temperature rises, until, at 
 about 200 C., it is nearly black and opaque, and is so viscid that the 
 
 o 
 
210 ALLOTBOPIC STATES OF SULPHUR. 
 
 flask may be inverted without spilling it : at this point the temperature 
 of the sulphur remains stationary for a time, notwithstanding that it is 
 still over the flame, showing that heat is becoming latent in converting 
 the sulphur into the new modification. On continuing the heat the 
 sulphur once more becomes liquid, though not so mobile as at first, and 
 at a much higher temperature, 440 C. (836 F.), 
 it boils, and is converted into a brownish red, 
 very heavy vapour : at this point of the experi- 
 ment an explosion of the mixture of sulphur 
 vapour with air often occurs. The flask may now 
 be removed from the flame, and a little of the 
 sulphur poured into a vessel of water, through 
 which it will descend in a continuous stream, 
 forming a soft elastic string like india-rubber : 
 the portion remaining in the flask will be observed, 
 as it cools, to pass again through the same states, 
 becoming viscid at 200 C., and very liquid at 
 - 164 I20 ^' > another portion may now be poured 
 
 into water, through which it will fall in isolated 
 drops, solidifying into yellow brittle crystalline buttons of ordinary 
 sulphur. As the portion of sulphur left in the flask cools, it will be 
 found to deposit small tufts of crystals, and ultimately to solidify alto- 
 gether to a yellow crystalline mass. 
 
 The brown ductile sulphur, when kept for a few hours, will become 
 yellow and brittle, passing, in great measure, spontaneously into the 
 crystalline sulphur. The change is accelerated by a gentle heat, and is 
 attended with evolution of the heat which the sulphur was found to 
 absorb at 200 C. Both these varieties of sulphur are, of course, inso- 
 luble in water, and they are not dissolved to any great extent by 
 alcohol and ether ; but these, when heated, will dissolve enough to be 
 deposited in white silvery needles on cooling. Glacial acetic acid also 
 dissolves sulphur, and deposits it in needles. If the crystalline variety 
 be shaken with a little carbon bisulphide, it rapidly dissolves, and on 
 allowing the solution to evaporate spontaneously, it deposits beautiful 
 octahedral crystals, resembling those of native sulphur (Fig. 165). 
 Ductile sulphur, however, is practically insoluble in carbon bisul- 
 phide. 
 
 "When flowers of sulphur are shaken with carbon bisulphide, a con- 
 siderable quantity passes into solution, the remainder consisting of the 
 amorphous, or insoluble sulphur. Roll sulphur dissolves to a greater- 
 extent, and sometimes entirely, in the bisulphide, and distilled sulphur 
 is always easily soluble. 
 
 According to the older investigations of Berthelot and others, when a solution of 
 sulphuretted hydrogen (H 2 S) is electrolysed the sulphur is separated at the anode r 
 and is therefore the electro-negative element of the compound. This sulphur was 
 found to be soluble in carbon bisulphide. So, also, the sulphur precipitated by an 
 acid from a solution of sulphur in an alkali sulphide is soluble in carbon bisulphide, 
 the assumed reason being that it is electro-negative to the metal with which it was 
 combined. 
 
 When, however, a solution of sulphurous acid is electrolysed the sulphur is 
 separated at the cathode showing that in this combination it is electro-positive ; 
 this sulphur is insoluble in carbon bisulphide. These observations do not appear 
 to have been satisfactorily confirmed. 
 
 It is well known that when a solution of sulphur in carbon bisulphide is exposed 
 
OCTAHEDRAL AND PEISMATIC SULPHITE. 211 
 
 to light sulphur is separated from it, showing that under this influence the soluble- 
 variety is converted into the insoluble. 
 
 Crystalline or soluble sulphur exists in several forms, of which two are> 
 well known. The natural form of crystallised sulphur is derived from 
 the octahedron with a rhombic base (Fig. 165), and it is a modification of 
 this form which sulphur assumes when crystallised from its solutions. 
 But if sulphur be melted in a covered cruci- 
 ble, allowed to cool until the surface has 
 congealed, and the remaining liquid portion 
 poured out after piercing the crust (with 
 two holes, one for admission of air), the 
 crucible will be lined with beautiful needles, 
 which are derived from an oblique prism 
 (Fig. 1 66). These crystals are brownish- 
 yellow and transparent, when freshly made, 
 but they soon become opaque yellow ; and Fig-. 165. Fig. 166. 
 ulthough they retain their prismatic appear- 
 ance, they have now changed into minute rhombic octahedra, the change 
 being attended with evolution of heat.* On the other hand, if a crystal 
 of octahedral sulphur be exposed for a short time to a temperature of 
 about 230 F. (no C.), in a boiling saturated solution of common salt, 
 for example, it becomes opaque, in consequence of the formation of a 
 number of minute prismatic crystals in the mass."}" 
 
 Both crystalline forms of sulphur may be obtained at the same tem- 
 perature from super/used sulphur, or from a supersaturated solution of 
 sulphur in benzene, by dropping in a crystal of the form required. 
 
 The difference between these two forms of crystalline sulphur 
 extends to their fusing-points and specific gravities, the prismatic 
 sulphur fusing at 248 F. (120 C.)., and the octahedral sulphur at. 
 239 F. (115 C.), the specific gravity of the prisms being 1.98, and that 
 of the octahedra 2.05. 
 
 Boll sulphur, when freshly made, consists of a mass of oblique pris- 
 matic crystals, but after being kept for some time, it consists of octa- 
 hedra, although the mass generally retains the specific gravity proper to- 
 the prismatic form. This change in the structure of the mass, taking 
 place when its solid condition prevented the free movement of the- 
 particles, gives rise to a state of tension which may account for the 
 extreme brittleness of roll sulphur. If a stick of sulphur be held in 
 the warm hand, it often splits, from unequal expansion. These pecu- 
 liarities of sulphur deserve careful study, as helping to elucidate the 
 spontaneous alterations in the structure of glass, iron, &c., under certain 
 conditions. 
 
 Flowers of sulphur do not present a crystalline structure, but consist 
 of spherical globules composed of insoluble sulphur enclosing soluble 
 sulphur. Hot oil of turpentine dissolves sulphur freely, and when the 
 solution is allowed to stand, the crystals which are deposited whilst the 
 solution is hot have the prismatic form, but as it cools, octahedra are 
 separated. 
 
 * Spring- has shown that a pressure of 6000 atmospheres converts prismatic sulphur and 
 plastic sulphur into the octahedral variety. 
 
 f The change from octahedral to prismatic sulphur is accompanied by the absorption of 
 650 cals. per gram molecule. 
 
212 COMBINATION OF SULPHUR WITH OTHER ELEMENTS. 
 The following table exhibits the chief allotropic forms of sulphur : 
 
 Sp. gr. Fusing-point. In Carbon Bisulphide. 
 
 Octahedral . . 2.05 115 C. Soluble. 
 
 Prismatic . . 1.98 120 Soluble. 
 
 Amorphous: I} '-95 Becomes octahedral. Insoluble. 
 
 The octahedral is by far the most stable of the three, and is the ulti- 
 mate condition which the others assume. Melted with a little iodine, 
 sulphur remains amorphous when it solidifies, and retains this form for 
 some time. 
 
 As has been seen the two forms of sulphur are easily converted the one into the 
 other by changing the conditions under which they exist. This is not an uncommon 
 phenomenon and is quite analogous to the relationship between a solid and the 
 liquid which it becomes when melted. Ice and water, for example, are convertible 
 into each other by varying the temperature, and there is a definite temperature, 
 o C., at which they are in equilibrium, that is, neither the ice nor the water in- 
 creases in quantity. So with the two forms of sulphur : at 96.5 C. both octahedra 
 and prisms may exist in equilibrium, but a slight rise of temperature will increase 
 the mass of the prisms while a slight fall will increase that of the octahedra. The 
 temperature is therefore known as the transition-point, and theitwo forms are said 
 to be enantiotropes. 
 
 Other varieties of sulphur, such as a black and a red modification, 
 have been described, but it is doubtful if they are pure sulphur.- A 
 colloidal variety, soluble in water, has been found in the solution formed 
 by passing hydrogen sulphide through an aqueous solution of sulphur 
 dioxide. 
 
 Sulphur enters into direct combination with several other elements. 
 It unites with chlorine and with some of the metals, if finely divided, 
 even at the ordinary temperature, and at a high temperature with all 
 the non-metals except nitrogen, and with most metals. 
 
 A mixture of 5 parts of iron-powder (ferruin redactum) and 3 parts of flowers 
 of sulphur will burn when kindled by a match, leaving a black mass of ferrous 
 sulphide. Zinc-dust mixed with half its weight of sulphur also burns freely, 
 leaving white zinc sulphide. 
 
 The so-called I/emery's volcano was made by mixing 
 iron filings with two-thirds of their weight of powdered 
 sulphur, and burying several pounds of the moist mixture 
 in the earth, when the heat evolved by the rusting of part 
 of the iron provoked the energetic combination of the 
 remainder with the sulphur, and the consequent develop- 
 ment of much steam.* Firework compositions contain- 
 ing iron filings and sulphur may cause ignition if damp. 
 
 Several metals may be made to burn in sulphur vapour, 
 as in oxygen, by heating the sulphur in a Florence flask, 
 with a gauze burner, so as to keep the flask constantly 
 filled with the brown vapour. Potassium and sodium, 
 introduced in deflagrating spoons, take fire spontaneously 
 in the vapour (Fig. 167). A coil of copper wire glows 
 vividly in sulphur vapour, and becomes converted into a 
 Fig-. 167. brittle mass of sulphide of copper. When sulphur is ex- 
 
 posed to sunshine in an atmosphere of hydride of anti- 
 mony or arsenic, it becomes converted into hydrosulphuric acid gas and sulphide of 
 antimony or arsenic. 
 
 Sulphur dissolves, though slowly, in boiling concentrated nitric and 
 
 * Rust-joint cement is a mixture of 80 p vrts iron filings, i of sal ammoniac, and 2 of sul- 
 phur, made into a paste with water ; it is very useful for making the joints of iron tubes 
 air-tight, for it sets into a hard cement, the iron combining with the sulphur. 
 
HYDROGEN SULPHIDE. 
 
 2I 3 
 
 sulphuric acids, being oxidised by the former into sulphuric acid, and by 
 the latter into sulphur dioxide. It is far more readily converted into 
 sulphuric acid by a mixture of nitric acid and potassium chlorate. The 
 alkalies dissolve sulphur when heated, yielding yellow or red solutions 
 which contain hyposulphites and sulphides of the alkali metals. 
 
 There is a very general resemblance in composition between the com- 
 pounds of sulphur and those of oxygen with the same elements. 
 
 Sulphur forms a good example of the diminution which may occur in 
 the vapour-density of an element as the temperature rises, a full dis- 
 cussion of which must be postponed to the chapter on General Principles. 
 Sulphur boils at 444 C., and if its vapour be weighed at a temperature 
 of 480 C., it is found to weigh 6.617 times as much as an equal volume 
 of air at 480 C., so that it is 96 times as heavy as hydrogen, or i atom 
 of sulphur would occupy J volume. But if the vapour of sulphur be 
 weighed at 1000 C., it is found to weigh only 2.23 times as much as an 
 equal volume of air at the same temperature and pressure, so that it is 
 only 32 times as heavy as hydrogen, and i atom of sulphur occupies i 
 volume. 
 
 HYDROGEN SULPHIDE, OR HYDROSULPHURIC ACID. 
 H 2 S = 34 parts by weight = 2 vols. 
 
 130. Sulphuretted hydrogen, or hydrogen sulphide, or hydrosulphuric 
 acid, has been already mentioned as occurring in some mineral waters, as 
 at Harrogate. It is also found in the gases emanating from volcanoes, 
 sometimes amounting to one-fourth of their volume. It is a product of 
 the putrefaction of organic substances containing sulphur, and is one of 
 the causes of the sickening smell of drains, &c. Eggs, which contain a 
 considerable portion of sulphur, evolve sulphuretted hydrogen as soon 
 as they begin to change, and hence the association between this gas and 
 the " smell of rotten eggs." The same smell is observed when a kettle 
 boils over upon a coke or coal fire, the hydrogen liberated from the 
 water combining with the sulphur present in the fuel. 
 
 Hydrosulphuric acid is also found among the products of destructive 
 distillation of organic substances containing sulphur ; it was mentioned 
 among the products from coal, in which it is for the most part combined 
 with the ammonia formed at the same time, producing ammonium 
 sulphide. 
 
 It may be produced, though not in large quantity, by the direct 
 union of hydrogen with sulphur vapour at a temperature about the 
 boiling-point of the sulphur, or by passing a mixture of sulphur vapour 
 and steam through a tube filled with red-hot pumice stone (the latter 
 encouraging the action by its porosity). Hydrosulphuric acid is more 
 readily formed by heating a damp mixture of sulphur and wood 
 charcoal, and may be obtained in large quantity by heating a mixture 
 of equal weights of sulphur and tallow or paraffin wax, the latter 
 furnishing the hydrogen. 
 
 Preparation of hydrosulphuric acid. For use in the laboratory, where 
 it is very largely employed in testing for and separating metals, hydro- 
 sulphuric acid is generally prepared by decomposing ferrous sulphide 
 with diluted sulphuric acid ; FeS + H 2 S0 4 = H 2 S + FeS0 4 
 
 To obtain ferrous sulphide, a mixture of 3 parts of iron filings with 2 parts of 
 
2I 4 
 
 HYDROSULPHUEIC ACID. 
 
 flowers of sulphur is thrown, by small portions at a time, into an earthen crucible 
 (A, Fig. 1 68) heated to redness in a charcoal fire, the crucible being covered after 
 each portion has been added. The iron and sulphur combine, with combustion, 
 
 and when the whole of the mix- 
 ture has been introduced, the 
 crucible is allowed to cool, the 
 mass of ferrous sulphide broken 
 out, and a few fragments of it 
 are introduced into a bottle (Fig. 
 169) provided with a funnel tube 
 for the addition of the acid, and 
 a bent tube for conducting the 
 gas through a small quantity of 
 water, to remove any splashes 
 of ferrous sulphate. From the 
 second bottle the gas is con- 
 ducted by a glass tube with a 
 caoutchouc joint, either down 
 into a gas-bottle, or into water, 
 or any liquid upon which the gas 
 is intended to act. The frag- 
 ments of ferrous sulphide should 
 
 Fig. 168. 
 
 Fig. 169. Preparation of 
 hydrosulphuric acid. 
 
 be covered with enough water to 
 fill the gas-bottle to about one- 
 third, and strong sulphuric acid 
 poured by degrees through the funnel, the bottle being shaken until effervescence 
 is observed. An excess of strong sulphuric acid stops the evolution of gas by 
 precipitating a quantity of white anhydrous ferrous sulphate, which coats the 
 sulphide and defends it from the action of the acid. 
 When no more gas is required, the acid liquid should 
 be at once poured away, leaving the fragments of 
 ferrous sulphide at the bottom of the bottle for a 
 fresh operation. The liquid, if set aside, will deposit 
 beautiful green crystals of copperas or ferrous sul- 
 phate (FeS0 4 .7H 2 0). 
 
 Since the ferrous sulphide prepared as above gene- 
 rally contains a little metallic iron, the sulphuretted 
 hydrogen is mixed with free hydrogen, which does 
 not generally interfere with its uses. The pure gas 
 may be prepared by heating antimony sulphide (crude 
 antimony) in a flask with hydrochloric acid 
 
 Sb 2 S 3 + 6HC1 = 3H 2 S + 2SbCl 3 . 
 If hydrochloric acid be diluted with more than 6 molecular proportions of water, 
 it cannot decompose the antimony sulphide ; hence, when the sulphide is heated 
 with an acid somewhat stronger than this, the subsequent addition of water repre- 
 cipitates the antimony sulphide with the orange colour which it always presents 
 when precipitated. 
 
 Generally speaking, it is only the sulphides of those metals which evolve 
 hydrogen from dilute acids that yield H 2 S when treated with acids ; thus copper 
 and mercury which do not dissolve in HC1 with evolution of H, yield sulphides 
 which are not attacked by HC1. Antimony, however, is an exception to this 
 statement. 
 
 Properties of hydrosulphuric acid. This gas is at once distinguished 
 from all others by its disgusting odour. It is one-fifth heavier than 
 air (sp. gr. 1.1912). The gaseous state is not permanent, but a pressure of 
 17 atmospheres is required to reduce it to a liquid (sp. gr. 0.9), which is 
 colourless, boils at 62 0., and congeals to a transparent solid at 85 C. 
 Water absorbs about three times its volume of sulphuretted hydrogen 
 at the ordinary temperature; both the gas and its solution are feebly 
 acid to blue litmus-paper. The gas is very combustible, burning with 
 a blue flame like that of sulphur, and yielding, as the chief products, 
 
OXIDATION OF SULPHURETTED HYDROGEN. 215 
 
 water and sulphurous acid gas, H 2 S + O 3 = H 2 + S0 2 ; a little sulphuric 
 acid (H 2 S0 4 ) is also formed, and unless the supply of air be very good, 
 some of the sulphur will be separated ; thus, if a taper be applied to a 
 bottle filled with sulphuretted hydrogen, a good deal of sulphur will be 
 deposited upon the sides. This combustibility of sulphuretted hydrogen 
 is of the greatest importance in those processes of chemical manufacture 
 in which this gas is evolved (as in the preparation of ammoniacal salts 
 from gas liquor), enabling it to be disposed of in the furnace instead of 
 becoming a nuisance to the neighbourhood. The gas causes fainting 
 when inhaled in large quantity, and appears much to depress the vital 
 energy when breathed for any length of time even in a diluted state. 
 
 When dissolved in water, hydrosulphuric acid is slowly acted upon by 
 the oxygen of the air (particularly in light), which converts its hydrogen 
 into water, and causes a white deposit of sulphur. 
 
 This is a great drawback to the use of this indispensable chemical in the 
 laboratory, since the solution of H 2 S is soon rendered useless. To obviate it as far 
 as possible, the solution should be made either with boiled water (free from dissolved 
 air), or with water which has already been once charged with the gas and spoilt by 
 keeping, for all the oxygen dissolved in this water will have been consumed by the 
 former portion of gas. The gas should be passed through the water until, on 
 closing the bottle with the hand and shaking violently, the pressure is found to 
 act outwards, showing the water to be saturated with the gas. In an inverted 
 bottle with a greased stopper, the solution may be preserved for some weeks, even 
 though occasionally opened for use. The solution in glycerine keeps better, and is 
 sold as a reagent. 
 
 In preparing the solution of hydrosulphuric acid, a certain quantity of the gas 
 always escapes absorption. To prevent this from becoming a nuisance, the bottle 
 containing the water to be charged with gas may be covered with an air-tight 
 caoutchouc cap having two tubes, through one of which passes the glass tube 
 conve3 r ing the gas down into the water, and through the other, a tube con- 
 ducting the excess of gas either into a gas burner, where it may be consumed, or 
 into a solution of ammonia which will absorb it, forming the very useful 
 ammonium sulphide. 
 
 Hydrogen sulphide is dissociated by a high temperature, just as water 
 is. Concentrated nitric acid acts upon hydrogen sulphide, oxidising the 
 hydrogen and a part of the sulphur, ammonium sulphate being found 
 in the solution, and a pasty mass of sulphur separated. Chlorine, 
 bromine, and iodine at once appropriate its hydrogen and separate the 
 sulphur. Nitrous acid acts very readilv upon hydrogen sulphide, yielding 
 much ammonia ; HONO + 3H 2 S = KH 3 + 2H 2 + S 3 . 
 
 In its action upon the metals and their oxides, hydrosulphuric acid 
 resembles hydrochloric and the other hydrogen acids. Many of the 
 metals displace the hydrogen and form metallic sulphides. This usually 
 requires the assistance of heat, but mercury and silver act upon the gas 
 at the ordinary temperature. Thus, if hydrogen sulphide be collected 
 over mercury, the surface of the latter becomes coated with a black 
 film of mercurous sulphide ; H 2 S + Hg 2 = H 2 + Hg 2 S. In a similar way 
 the surface of silver is slowly tarnished when exposed to air containing 
 sulphuretted hydrogen, its surface being covered with a black film of 
 silver sulphide. It is on this account that silver plate is so easily 
 blackened by the air of towns. An egg-spoon is always blackened by 
 the sulphur from the egg. Silver coins kept in the pocket with lucifer 
 matches are blackened, from the formation of a little silver sulphide. 
 The original brightness of the coin may be restored by rubbing it with 
 a solution of potassium cyanide, which dissolves the silver sulphide. 
 
2l6 SULPHIDES. 
 
 Friction with strong ammonia will also remove the tarnish, and its 
 application is safer than that of the poisonous cyanide. 
 
 When heated in the gas, several metals displace the hydrogen from 
 it. Thus, potassium acts upon it in a similar manner to that in which 
 it acts upon water, forming potassium hydrosulphide (KHS). 
 
 Tin removes the whole of the sulphur from hydrosulphuric acid at a 
 moderate heat ; Sn + H 2 S = H 2 + SnS. The hydrogen which is left may 
 be measured, and thus the fact that two volumes of H 2 S contain two 
 volumes of hydrogen may be demonstrated. 
 
 When hydrosulphuric acid acts upon a metallic oxide, it generally 
 converts it into a sulphide corresponding with the oxide, whilst the 
 hydrogen and oxygen unite to form water. Lead oxide in contact 
 with the gas yields black lead sulphide and water ; PbO + H S = 
 PbS -j- H 2 0. Paper impregnated with a salt of lead is used as a test 
 for the presence of this gas. Thus, if paper be spotted with a solution 
 of lead nitrate (or acetate) it will indicate the presence of even minute 
 quantities of hydrogen sulphide (in impure coal gas, for example) by 
 the brown colour imparted to the spots; Pb(NO 3 ) 2 + H 2 S - 2 HNO 3 + PbS. 
 
 It is in this manner that paints containing white lead (lead carbonate) 
 are darkened by exposure to the air of towns. Cards glazed with white 
 lead, and engravings on paper whitened with that substance, suffer a 
 similar change. Paintings, whether in oil or water-colours, in which 
 lead is an ingredient, are also injured by air containing sulphuretted 
 hydrogen. It has been found that such colours, damaged by the forma- 
 tion of lead sulphide, are restored by the continued action of light and 
 air, the black sulphide becoming oxidised and converted into the white 
 sulphate, PbS + 4 = PbS0 4 . In the dark this restoration does not occur, 
 so that it is often a mistake to screen pictures from the light by a 
 curtain. 
 
 The action of hydrosulphuric acid upon the chlorides and other 
 haloid salts of the metals generally resembles its action upon the oxides 
 of the same metals. 
 
 Most of the sulphides of the metals, like the corresponding oxides, 
 are insoluble in water, but many of the sulphides are also insoluble in 
 diluted acids and in alkalies, so that when hydrosulphuric acid is 
 brought into contact with the solutions of metals, it will in many cases 
 precipitate the metal in the form of a sulphide having some charac- 
 teristic colour or other property by which the metal may be identified. 
 
 Any solution of lead will give a black precipitate with solution of H 2 S, the lead 
 sulphide being insoluble in dilute acids and in alkalies. 
 
 A solution of antimony (tartar-emetic, the tartrate of antimony and potassium, 
 for example), mixed with an excess of hydrochloric acid, gives an orange- 
 coloured precipitate (Sb 2 S 3 ) on adding H 2 S ; but if another portion be mixed with 
 an excess of potash before adding the H 2 S, there will be no precipitate, for the 
 antimony sulphide is soluble in alkalies. 
 
 Cadmium chloride gives a brilliant yellow precipitate of cadmium sulphide. 
 
 Zinc sulphate yields a white precipitate of zinc sulphide (ZnS), but if a little 
 hydrochloric acid be previously added, no precipitate is formed, the zinc sulphide 
 being soluble in acids. On neutralising the hydrochloric acid with ammonia, 
 the zinc sulphide is at once precipitated. 
 
 It is evident that, in a solution containing cadmium and zinc, the metals may 
 be separated by acidifying the liquid with hydrochloric acid and adding excess 
 of hydrosulphuric acid, which precipitates the cadmium sulphide only. On 
 filtering the solution, and adding ammonia, the zinc sulphide is precipitated. 
 
OXIDATION OF SULPHIDES. 217 
 
 Those sulphides which are soluble in the alkalies are often designated 
 sulphur-acids, whilst the sulphides of the alkalies are sulphur-bases. 
 These two classes of sulphides combine to form sulphur-salts analogous 
 in composition to the oxygen-salts of the same metals. Thus, there 
 have been crystallised, the salts 
 
 Sodium sulphostannate Na 4 SnS 4 
 
 suiphantimonate .... Na SbS 3 
 sulpharsenate Na 3 AsS 4 
 
 Speaking generally, those metals which give feebly acid oxides also 
 give feebly acid sulphides, whilst the sulphides, which correspond with 
 powerful bases are themselves basic, for H 2 S is not capable of completely 
 neutralising the alkalies. 
 
 The action of air upon the sulphide.s of the metals is often turned to 
 account in chemical manufactures. At the ordinary temperature, the 
 sulphides of those metals which form alkaline oxides (such as sodium 
 and calcium), when exposed to the air in the presence of water, yield 
 sulphite and thiosulphate (hyposulphite). This change is sometimes 
 turned to account for the manufacture of sodium hyposulphite. 
 
 When the metal forms a less powerful base with oxygen, the sul- 
 phide is often converted into sulphate by exposure to moist air ; thus, 
 CuS + O 4 = CuS0 4 , which is taken advantage of for the separation of 
 copper from its ores. 
 
 The black ferrous sulphide (FeS), when exposed to moist air, becomes 
 converted into red ferric oxide, with separation of sulphur, 2FeS + 3 = 
 Fe 2 3 + S 2 , a change which enables the gas manufacturer to revive, by 
 the action of air, the ferric oxide employed for removing the sulphuretted 
 hydrogen from coal gas. 
 
 When roasted in air at a high temperature, the sulphides correspond- 
 ing with the more powerful bases are converted into sulphates ; thus, 
 ZnS + 4 = ZnSO 4 , which explains the production of zinc sulphate by 
 roasting blende. But in most cases part of the sulphur is converted into 
 sulphurous acid gas at the same time. Cuprous sulphide, for instance, is 
 partly converted into cupric oxide by roasting, Cu 2 S + 4 = 2CuO + S0 2 , 
 a change of great importance in the extraction of copper from its ores. 
 
 131. Hydrogen per sulphide. The composition of this substance is not yet satis- 
 factorily ascertained. The similarity of its chemical properties to those of 
 hydrogen peroxide prompts the wish that its formula may be H 2 S 2 . Some 
 analyses, however, seem to lead to the formula H 2 S 5 , but since the persulphide 
 is a liquid capable of dissolving free sulphur, which is not easily separated from 
 it, there is much difficulty in determining the exact proportion of this element 
 with which the hydrogen is combined. 
 
 When equal weights of slaked lime and sulphur are boiled with water, an 
 orange-coloured liquid is formed, which contains calcium hyposulphite, calcium 
 disulphide, and calcium pentasulphide (CaS 5 ) ; 3CaO + S 6 =CaS 2 3 + 2CaS 2 . 
 
 When HC1 is added to the filtered solution an abundant precipitation of sulphur 
 occurs, and much H 2 S is evolved; CaS 2 + 2HCl = CaCl 2 + H 2 S + S. But if the 
 solution be poured by degrees into a slightly warm mixture of HC1 with twice its 
 bulk of water, and constantly stirred, a yellow heavy oily liquid collects at the 
 bottom, which is the hydrogen persulphide; CaS 2 + 2HCl = H 2 S 2 (?)-r CaCl 2 . The 
 acid having been kept in excess, the persulphide has been preserved from the 
 decomposition which it suffered in the presence of the alkaline solution in the 
 former experiment. For the hydrogen persulphide very closely resembles the per- 
 oxide in the facility with which it may be decomposed into hydrosulphuric acid 
 and sulphur ; it undergoes spontaneous decomposition even in sealed tubes, and 
 the hydrosulphuric acid then becomes liquefied by its own pressure. Most of 
 
2lS SULPHUEOUS ACID GAS. 
 
 the substances, the contact of which promotes the decomposition of H 2 2 , have 
 the same effect upon the persulphide. This compound has a peculiar odour, which 
 affects the eyes ; of course, its vapour is mixed with H 2 S resulting from its decom- 
 position. Its specific gravity is 1.73. 
 
 OXIDES OF SULPHUR. 
 
 132. Only two important compounds of sulphur with oxygen have 
 been obtained in the separate state viz., sulphurous anhydride (SO.,) 
 and sulphuric anhydride (S0 3 ). fiulphur sesquioxide (S 2 3 ) and per- 
 sulphuric oxide (S 2 7 ) also exist. 
 
 SULPHUR DIOXIDE OR SULPHUROUS ANHYDRIDE. 
 S0 2 = 64 parts by weight = 2 vols. 
 
 133. In nature, sulphur dioxide (sulphurous acid gas) is but rarely 
 met with ; it exists in the gases issuing from volcanoes. Although con- 
 stantly discharged into the air of towns by the combustion of coal (con- 
 taining sulphur), it is so easily oxidised and converted into sulphuric 
 acid that no considerable quantity is ever found in the atmosphere. 
 Sulphurous acid gas has been already mentioned as the sole product of 
 the combustion of sulphur in dry air or oxygen,* but it is generally 
 prepared in the laboratory from sulphuric acid, by heating it with 
 metallic copper, 2 H 2 S0 4 + Cu = CuS0 4 + 2H 2 + S0 2 . 
 
 20 grams of copper clippings are heated in a flask with no c.c. of strong H 2 S0 4 , 
 the gas being conducted by a bent tube down to the bottom of a dry bottle closed with 
 a perforated card (see Fig. 150, p. 177). Some time elapses before the gas is evolved ; 
 for sulphuric acid attacks copper only at a high temperature ; but when the evolution 
 of gas fairly begins it proceeds very rapidly, so that it is necessary to remove the 
 flame from under the flask. The gas will contain a little suspended vapour of 
 sulphuric acid, which renders it turbid. 
 
 When the operation is finished, and the flask has been allowed to cool, it will be 
 found to contain a grey crystalline powder at the bottom of a brown liquid. The 
 latter is the excess of H 2 S0 4 used, and retains very little copper, since cupric 
 sulphate is insoluble in the strong acid. If the liquid be poured off', and the flask 
 filled up with water, and set aside for some time, the crystalline powder will dis- 
 solve, forming a blue solution of sulphate of copper, yielding that salt in fine 
 prismatic crystals by evaporation and cooling. The dark powder remaining un- 
 dissolved after extracting the whole of the sulphate, consists chiefly of cuprous 
 sulphide (Cu 2 S), the production of which is interesting, as showing how far the 
 de-oxidising effect of the copper may be carried in this experiment. 
 
 Sulphur dioxide is a very heavy (sp. gr. 2.25) colourless gas, charac- 
 terised by its odour of burning brimstone. It condenses to a clear liquid 
 at o F. (the temperature of a mixture of ice and salt, - 18 C.) even at 
 the ordinary pressure of the air, and has been frozen to a colourless 
 crystalline solid at - 76 C. The liquid has the sp. gr. 1.4 at 15 C., 
 and boils at -8 C. As would be anticipated from its comparatively 
 high boiling-point S0 2 is a very imperfect gas (p. 28). The cold pro- 
 duced by the evaporation of the liquefied gas is about 6500 cals. per 
 gram mol., and the liquid finds application in some forms of freezing- 
 machines. The critical temperature is 157 C., and the pressure 
 79 atmospheres. 
 
 The liquefaction of the gas is easily exhibited by passing it down to the bottom 
 of a tube (A, Fig. 170) closed at one end, and surrounded with a mixture of 
 
 * According to Berthclot, a notable quantity of SO 3 is produced at the same time. 
 
SULPHUR DIOXIDE. 219 
 
 pounded ice with half its weight of salt. The tube should have been previously 
 drawn out to a narrow neck at B, which may afterwards be sealed by the blow- 
 pipe, the lower part of the tube being still surrounded by the freezing-mixture. 
 The tube need not be very strong, for at the ordinary 
 temperature the vapour exerts a pressure of only 2.5 
 atmospheres. Liquid sulphur dioxide is a convenient 
 agent for producing (by its rapid evaporation) the low 
 temperature ( - 39 F.) required to effect the solidifi- 
 cation of mercury. A small globule of this metal may 
 readily be frozen by dropping some liquid sulphur 
 dioxide upon it in a watch-glass placed in a strong 
 draught of air. The tube containing the sulphur 
 dioxide should be held in a woollen cloth or glove. 
 The attractive experiment of freezing water in a red- 
 hot crucible may also be made with the liquid. A 
 platinum crucible being heated to redness, and some 
 liquid sulphur dioxide poured into it, from a tube 
 which has been cooled for half an hour in ice and 
 salt, the liquid becomes surrounded with an atmo- 
 sphere of sulphurous acid gas, which prevents its Fig. 170. 
 contact with the metal (assumes the spheroidal state), 
 
 and its temperature is reduced by its own evaporation to so low a degree that a 
 little water allowed to flow into it will at once become converted into opaque ice. 
 Liquid S0 2 is now sold in glass " siphons " similar to those in which soda-water is 
 supplied, and these form a convenient store of the gas. 
 
 Sulphurous acid gas is very easily absorbed by water, as may be shown 
 by pouring a little water into a bottle of the gas, closing the bottle with 
 the palm of the hand, and shaking it violently, when the diminished 
 pressure due to the absorption of the gas will cause the bottle to be 
 sustained against the hand by the pressure of the atmosphere. Water 
 absorbs 43.5 times its bulk of the gas at the ordinary temperature. The 
 solution is believed to contain sulphurous acid, H 2 S0 3 , formed by the 
 reaction H 2 + S0 2 = H 2 SO 3 , but this body has not been obtained in the 
 separate state. If the solution be exposed to a low temperature, a 
 crystallised hydrate, H 2 S0 3 .i4H 2 0, is obtained; this melts at 2 C. 
 When the solution of sulphurous acid is kept for some time in a bottle 
 containing air, its smell gradually disappears, the acid absorbing oxygen 
 and becoming converted into sulphuric acid. 
 
 Sulphur dioxide, like carbon dioxide, possesses in a high degree the 
 power of extinguishing flame. A taper is at once extinguished in a 
 bottle of the gas, even when containing a considerable proportion of air. 
 One of the best methods of extinguishing burning soot in a chimney 
 consists in passing up sulphurous acid gas by burning a few ounces of 
 sulphur in a pan placed over the fire. 
 
 The principal uses of sulphur dioxide depend upon its property of 
 bleaching many animal and vegetable colouring-matters. Although a 
 far less powerful bleaching agent than chlorine, it is preferred for 
 bleaching silks, straw, wool, sponge, isinglass, baskets, &c., which would 
 be injured by the great chemical energy of chlorine. The articles to be 
 bleached are moistened with water and suspended in a chamber in which 
 sulphurous acid gas is produced by combustion of sulphur. The 
 colouring-matters do not appear in general to be decomposed by the 
 acid, but rather to form colourless combinations with it, for in course of 
 time the original colour often reappears, as is seen in straw, flannel, &c., 
 which becomes yellow from age, the sulphurous acid probably being 
 oxidised into sulphuric acid. Stains of fruit and port wine on linen are 
 
220 
 
 SULPHUROUS ACID. 
 
 conveniently removed by solution of sulphurous acid. Hops are sulphured 
 by exposure to fumes of burning sulphur with the object of improving 
 their appearance. 
 
 The red solution obtained by boiling a few chips of logwood with river water 
 (distilled water does not give so fine a colour) serves to illustrate the bleaching 
 properties of sulphurous acid. A few drops of the solution of the acid will at 
 once change the red colour of the solution to a light 
 yellow ; but that the colouring power is suspended, and 
 not destroyed, may be shown by dividing the yellow liquid 
 into two parts, and adding to them, respectively, potash 
 and diluted sulphuric acid, which will restore the colour 
 in a modified form. To contrast this with the complete 
 decomposition of the colouring-matter, a little sulphurous 
 acid may be added to a weak solution of the potassium 
 permanganate, when the splendid red solution at once 
 becomes perfectly colourless, and neither acid nor alkali 
 can effect its restoration. 
 
 If a bunch of damp coloured flowers be suspended in a 
 bell-jar over a crucible containing a little burning sulphur 
 (Fig. 171), many of the flowers will be completely bleached 
 Fig. 171. by the sulphurous acid ; and by plunging them afterwards 
 
 into diluted sulphuric acid and ammonia, their colours 
 may be partly restored with some very curious modifications. 
 
 Another very useful property of sulphurous acid is that of arresting 
 fermentation (or putrefaction), apparently by killing the vegetable or 
 animal growth which is the cause of the fermentation. This is commonly 
 designated the antiseptic or antizymotic property of sulphurous acid, and 
 
 is turned to account when casks for wine 
 and beer are sulphured in order to prevent 
 the action of any substance contained in 
 the pores of the wood, and capable of 
 exciting fermentation, upon the fresh 
 liquor to be introduced. If a little solu- 
 tion of sugar be fermented with yeast in a 
 flask provided with a funnel tube (Fig. 
 172), a solution of sulphurous acid poured 
 in through the latter will at once arrest 
 the fermentation. The salts of sulphurous 
 acid (sulphites) are also occasionally used to 
 arrest fermentation, in the manufacture of sugar, for instance. Clothes 
 are sometimes fumigated with sulphurous acid gas to destroy vermin, 
 and the air of rooms is disinfected by burning sulphur in it, 4 Ibs. of 
 sulphur being recommended for every 1000 cubic feet of space. 
 
 The disposition of sulphurous acid to absorb oxygen and pass into 
 sulphuric acid, renders it a powerful de-oxidising or reducing agent. 
 Solutions of silver and gold are reduced to the metallic state by sul- 
 phurous acid and sulphites. As usual, however, the reducing power of 
 sulphur dioxide is only a comparative phenomenon. Towards several 
 substances the acid behaves as an oxidising agent, a noteworthy case 
 being its reaction with hydrogen sulphide, which (in presence of water) 
 occurs in the sense of the equation, 2H 2 S + S0 2 = 2H O + S 3 . 
 
 An aqueous solution of stannous chloride gives a precipitate of stannic sulphide 
 with sulphurous acid. 
 
 If a solution of sulphurous acid be heated for some time in a sealed tube at 
 150 C.. one portion of the acid de-oxidises another, sulphur is separated, and 
 sulphuric acid formed ; 3H 2 S0 3 = 2H 2 S0 4 + 
 
 Fig. 172. 
 
SULPHITES. 
 
 221 
 
 S0 2 and NH 3 combine to form two solid compounds (NH 3 ) 2 S0 2 and NH 3 .S0 2 . 
 
 The unsaturated character of S0 2 finds illustration in the fact that chlorine 
 combines with an equal volume of the gas, under the influence of bright sunshine, 
 or in presence of charcoal, to produce a colourless liquid, the vapour of which is 
 very acrid and irritating to the eyes. This is the chloranhydride (p. 191) of 
 sulphuric acid, sulphuryl chloride, SO 2 C1 2 . Its decomposition by water occurs 
 in two stages: (i) S0 2 C1 2 + H 2 = S0 2 .C1.0H + HC1 ; (2) S0 2 .C1.0H + H 2 = 
 S0 2 .OH.OH -t-HCl ; the final products being sulphuric and hydrochloric acids, so 
 thalt the formula S0 2 .OH.OH for sulphuric acid is justified. The chloride of 
 thionyl* or sulphurosyl chloride, SOC1 2 , is a colourless volatile liquid obtained by 
 the action of sulphurous acid gas on phosphorus pentachloride. It is decomposed by 
 water, yielding! hydrochloric and sulphurous acids, being the chloranhydride of 
 the latter. 
 
 Potassium and sodium, when heated in sulphur dioxide, burn vividly, producing 
 the oxides and sulphides of the metals. Iron, lead, tin, and zinc are also con- 
 verted into oxides and sulphides when heated in the gas ; S0 2 + Zn 3 = ZnS + 2ZnO. 
 
 Lead peroxide, Pb0 2 , is the best absorbent for S0 2 with which it combines (with 
 incandescence in the pure gas) to form lead sulphate : Pb0 2 + S0 2 = PbS0 4 . 
 
 That sulphur dioxide contains its own volume 
 of oxygen is best shown by burning sulphur 
 in a given volume of oxygen in the apparatus 
 represented in Fig. 173. 
 
 The stopper A having been removed, mercury is poured 
 into the open limb of the U-tube until it stands at a 
 point just below the bulb B, the air in which is then 
 displaced by oxygen. A pellet of sulphur is placed in 
 the metal spoon attached to the stopper and the latter 
 is inserted directly the tube delivering the oxygen has 
 been removed. A platinum helix rests upon the sulphur 
 and is now heated to redness by a current of electricity 
 passed through the wires attached to the spoon and the 
 helix. When the sulphur has burnt itself out and the 
 apparatus has cooled, it will be found that the volume of 
 gas has not varied, showing that the S0 2 produced con- 
 tains its own volume of oxygen. To relieve the pressure 
 produced by the heat of the combustion, it is well to 
 diminish the initial pressure, after the gas has been 
 measured, by drawing off some of the mercury through 
 the stop-cock C. 
 
 Sulphites. The acid character of sulphurous 
 acid is rather feeble, although stronger than 
 that of carbonic acid. There is much general 
 resemblance between the sulphites and carbonates in point of solubility, 
 the sulphites of the alkali metals being the only salts of sulphurous acid 
 which are freely soluble in water. Sulphurous acid, SO(OH) 2 , being 
 dibasic like carbonic acid, forms two classes of salts, the normal sulphites 
 (for example, sodium sulphite, Na 2 S0 3 ) and acid sulphites (as hydrogen 
 potassium sulphite, KHS0 3 ). 
 
 Sodium sulphite is extensively manufactured for the use of the paper- 
 maker, who employs it as an antichlore for killing the bleach, that is, 
 neutralising the excess of chlorine after bleaching the rags with chloride 
 of lime (see p. 183); Na 2 SO 3 + H 2 + 01 2 = Na 2 S0 4 + 2HC1. It is pre- 
 pared by passing sulphurous acid gas over damp crystals of sodium 
 carbonate, when CO., is expelled, and sodium sulphite formed, which is 
 dissolved in water and crystallised. It forms oblique prisms, having 
 the composition Na 2 S0 3 .yAq, which effloresce in the air, becoming 
 
 * Oetof, sulphur. 
 
 Fig'. 173- 
 Composition of SO 2 gas. 
 
222 
 
 SULPHUR TRIOXIDE. 
 
 opaque, and slowly absorbing oxygen, passing into sodium sulphate 
 (Na 2 S0 4 ). Its solution is slightly alkaline to test-papers. 
 
 For the manufacture of sodium sulphite the SO., is obtained either by 
 the combustion of sulphur or by heating sulphuric acid with charcoal ; 
 2H 2 S0 4 + C = 2H 2 + C0 2 + 2SO,. The carbon dioxide of course will 
 not interfere with this application of the sulphur dioxide. 
 
 The existence of sulphurosyl chloride, SO.CI 2 , and its behaviour with water 
 justify the formula SO(OH) 2 for sulphurous acid. There is some evidence, derived 
 from organic chemistry (see Sulplionic Acids), that the i metallic sulphites are not 
 
 S 
 
 which 
 
 derived from SO(OH) 2 , but from an acid of the form Q> H , wc may 
 
 be regarded as the parent substance of the sulphonic acids, and may therefore be 
 termed sulplionic acid. The potassium sulphite is supposed to be 2 S.OK.K. and 
 not SO.OK.OK. Two potassium-sodium sulphites have been prepared which 
 differ in properties and appear to be 2 S.OK.Na and 2 S.ONa.K respectively. 
 
 Solutions of the sulphites absorb nitric oxide in the cold, yielding nitro sulphites^ 
 such as the potassium salt K 2 S0 3 .2NO. At higher temperatures the sulphites 
 reduce NO to N 2 0. 
 
 Pyrosulpliites, derived from hypothetical pyrosulplmrous acid, H 2 S 2 5 , crystal- 
 lise from hot strong solutions of bisulphites, 2KHS0 3 = K 2 S 2 5 + H 2 0. Possibly 
 they are compounds of normal sulphites with S0 2 -K 2 S0 3 .S0 2 . 
 
 SULPHUR TRIOXIDE OR SULPHURIC ANHYDRIDE. 
 S0 3 = 8o parts by weight. 
 
 Sulphur dioxide and oxygen combine to form sulphur trioxide when 
 passed through a tube containing heated platinum or certain metallic 
 oxides, such as those of iron and chromium, the action of which in 
 
 promoting the combination is not 
 thoroughly understood. The reaction 
 is exothermic, evolving some 103,000 
 cals. per 80 grams of S0 3 formed. 
 
 The combination may be shown by pass- 
 ing oxygen from the tube A (Fig. 174), 
 connected with a gas-holder, through a 
 strong solution of sulphurous acid (B), so 
 that it may take up a quantity of S0 2 ; 
 afterwards through a tube (C) containing 
 pumice-stone soaked with oil of vitriol to 
 remove the water ; and then through a 
 bulb (D) containing platinised asbestos 
 (see p. 98). The mixture of the gases issuing into the air is quite invisible, but 
 when the bulb is gently heated combination occurs, and dense white clouds are 
 formed in the air, from the combination of the sulphuric anhydride (S0 3 ) produced, 
 with the atmospheric moisture. The clouds are best shown by conducting them T 
 through a bent tube attached to D, into a large flask. 
 
 Pure sulphur trioxide, prepared by repeated distillation out of con- 
 tact with moisture, is a mobile liquid which crystallises when cooled, 
 in long transparent prisms like nitre, which fuse at 14. 8 C. and boil 
 at 46 C. At temperatures below 25 C. these crystals easily change, 
 especially if they have absorbed a little water, into an opaque, fibrous, 
 crystalline mass which does not fuse, but vaporises at about 50 C., the 
 vapour condensing again to the prismatic variety which melts at 14.8. 
 The formula of the fibrous form appears to be S 2 O 6 , and it is much less 
 active than the prismatic form (SO 3 ). When sulphuric acid in small 
 quantity is added to S0 3 it dissolves it, and on cooling to 8 C. crystals 
 
 Fig-. 174. 
 
PROPERTIES OF SULPHURIC ANHYDRIDE. 223 
 
 of H 2 S0 4 .3SO 3 are deposited. "When more H 2 SO 4 is added, it forms- 
 pyrosulphuric acid, H,S0 4 .S0 3 or H 2 S 2 7 (m.p. 35 C.). S0 3 can dis- 
 solve much SO 2 . 
 
 When exposed to air, sulphur trioxide emits strong white fuines, its 
 vapour combining with the moisture of the air. It soon deliquesces- 
 and becomes sulphuric acid S0 3 + H 2 = H 2 S0 4 . 
 
 When thrown into water it hisses like red-hot iron, from the sudden 
 formation of steam. The vapour is decomposed into SO 2 and 0, when, 
 passed through a red-hot tube ; but if the tube contain platinum, or 
 another " contact substance," the vapour is only in a dissociated state, 
 for the SO, and recombine on cooling in contact with the platinum. 
 Phosphorus burns in its vapour, combining with the oxygen and 
 liberating sulphur. Baryta glows when heated in the vapour, com- 
 bining with it to form barium sulphate, unless both be quite dry. 
 
 Sulphuric anhydride mixes in all proportions with sulphuric acid, the 
 mixture being known as fuming sulphuric acid. The melting-point of 
 the mixture varies with the percentage of S0 3 in it ; that containing 
 80 per cent, is the most convenient for use, as it remains liquid at 
 ordinary temperature. Fuming sulphuric acid finds extended applica- 
 tion in Organic Chemistry for making sulphonic acids (q.v.). By gently 
 warming it, much S0 3 can be distilled from it for small experiments. 
 
 The pyrosulphuric acid, or anhydrosulpJiuric acid, H 2 S 2 7 , referred to above,. 
 contains 45 per cent, of S0 3 and is solid at ordinary temperature ; it may be 
 regarded as S0 3 which has insufficient water to form H 2 S0 4 (H 4 S 2 8 ), and since the- 
 acid chloride S 2 5 C1 2 (formed by the action of excess of PC1 5 on H 2 S0 4 ) exists, its 
 
 2 S/ OH 2 S/ C1 
 
 constitution may be represented as /O , the chloride being /O . An 
 
 acid containing a larger proportion of S0 3 remains liquid at low temperatures. 
 
 Sulphuric anhydride is capable of combining with olefiant gas (C 2 H 4 ) 
 and similar hydrocarbons, and absorbs these from mixtures of gases. 
 In the analysis of coal gas, a fragment of coke wetted with fuming 
 sulphuric acid is passed up into a measured volume of the gas standing 
 over mercury to absorb these illuminating hydrocarbons. S0 3 also- 
 combines with HC1, forming S0 2 .C1.0H, which may also be obtained by 
 distilling sulphuric acid with phosphoric chloride 
 
 3S0 2 (OH) 2 + PC1 5 = 3(S0 2 .C1.0H) + P0 2 .OH + 2HC1. 
 
 An interesting method of obtaining the sulphuric anhydride consists. 
 in pouring 2 parts by weight of oil of vitriol over 3 parts of phosphoric 
 anhydride, contained in a retort cooled in ice and salt, and afterwards 
 distilling at a gentle heat, when the phosphoric anhydride retains water,. 
 and the S0 3 may be condensed in a cooled receiver. 
 
 SULPHURIC ACID, OR HYDROGEN SULPHATE. 
 H 2 S0 4 or S0 2 (OH) 2 = 98 parts by weight. 
 
 134. More than four centuries ago the alchemist Basil Valentine 
 subjected green vitriol, as it was then called (sulphate of iron), to dis- 
 tillation, and obtained an acid liquid which he named oil of vitriol. 
 The process discovered by this laborious monk is even now in use at 
 Nordhausen in Saxony, and the Nordhausen oil of vitriol was at one 
 
224 HISTORY OF SULPHURIC ACID. 
 
 time an important article of commerce. The crystals of ferrous sulphate 
 (FeS0 4 .yH 2 0) exposed to the air absorb oxygen, and become basic ferric 
 sulphate ; 6FeS0 4 + 3 = 2Fe 2 (S0 4 ) 3 .Fe 2 3 . 
 
 When this salt is partially dried, and distilled in earthenware retorts, 
 a mixture of sulphuric acid and sulphuric anhydride distils over, and 
 constitutes Nordhausen or fuming sulphuric acid ; Fe.,(S0 4 ) 3 + 2H 2 O = 
 Fe 2 O 3 +2H 2 SO 4 + S0 3 . The ferric oxide (Fe 2 O 3 ) which is left in the 
 retorts, is the red powder known as colcothar, which is used for polishing 
 plate glass and metals. 
 
 The green vitriol employed for preparing the Nordhausen acid was obtained 
 from iron pyrites (FeS 2 ). A particular variety of this mineral, white pyrites (or 
 efflorescent pyrites), when exposed to moist air, undergoes oxidation, yielding 
 ferrous sulphate and sulphuric acid ; FeS 2 + H 2 + O l7 = FeS0 4 + H 2 S0 4 . 
 
 Large masses of this variety of pyrites in mineralogical cabinets may often be 
 seen broken up into small fragments, and covered with an acid efflorescence of 
 ferrous sulphate from this cause. Ordinary iron pyrites is not oxidised by 
 exposure to the air unless it be first subjected to distillation in order to separate 
 a portion of the sulphur which it contains. 
 
 The first step towards the discovery of the process which, until 
 within the last few years, has been the only profitable one by which 
 this acid could be manufactured on a large scale was also made by 
 Valentine, when he prepared his oleum sulphuris per campanum, by 
 burning sulphur under a bell-glass over water, and evaporating the 
 acid liquid thus obtained. The same experimenter also made a very 
 important advance when he burnt a mixture of sulphur, antimony 
 sulphide and nitre under a bell-glass placed over water ; but it was not 
 until the middle of the eighteenth century that it was suggested by 
 some French chemists to burn the sulphur and nitre alone over water ; 
 a process by which the acid appears actually to have been manufactured 
 upon a pretty large scale. The substitution of large chambers of lead 
 for glass vessels by Dr. Roebuck was a great improvement on the pro- 
 cess, and about the year 1770 the preparation of the acid formed an 
 important branch of manufacture ; since then the process has been 
 steadily improving until, at the present time, a very large quantity is 
 manufactured by this method. The diminution in the price of oil of 
 vitriol well exhibits the progress of improvement in its production, for 
 the original oil of sulphur appears to have been sold for about half a 
 crown an ounce, and that prepared by burning sulphur with nitre in 
 glass vessels at the same price per pound ; but when leaden chambers 
 were introduced, the price fell to a shilling per pound, and at present 
 oil of vitriol can be purchased at the rate of five farthings per pound. 
 
 The description of the present " chamber process " of manufacture 
 will be best understood after a consideration of the principles of the 
 chemical changes upon which it depends. 
 
 It has been seen that when sulphur is burnt in air sulphur dioxide is 
 produced. When this acts on nitric acid, in the presence of water, 
 sulphuric acid and nitric oxide are produced, 3S0 2 + 2HNO 3 + 2H 2 = 
 3H 2 SO 4 + 2NO.* The nitric oxide, in contact with air becomes nitric 
 peroxide, NO + O = N0 2 , which, in the presence of H 2 0. serves to 
 convert a further quantity of S0 2 into H 2 S0 4 , S0 2 + N0 2 + H 2 = 
 
 * According to some authorities, N 2 O 3 is the oxide of nitrogen produced ; since, however, 
 it has been shown that this compound can only exist at low temperatures, the view that 
 nitric oxide is the oxide formed in the chambers is here adopted. 
 
OIL OF VITRIOL. 225 
 
 H 2 S0 4 + NO; nitric oxide is thus regenerated and serves to convert 
 more SO 2 into sulphuric acid if the requisite quantities of air and steam 
 be supplied, the two last equations being repeated. 
 
 When the supply of steam is deficient, nitrosyl sulphate is found deposited in 
 crystals (chamber crystals) in the sulphuric acid chambers. This has been formed 
 according to the equation 2S0 2 + 2N0 2 + + H 2 = 2S0 2 .OH.ONO. In the presence 
 
 of a further quantity of S0 2 and H 2 the nitrosyl sulphate is decomposed thus 
 
 2S0 2 .OH.ONO + SO 2 + 2H 2 O = 3H 2 S0 4 + 2NO. 
 
 It is generally believed that these two equations represent the reactions in the 
 chamber rather than those quoted above. 
 
 It appears, therefore, that NO may be employed to absorb oxygen 
 from the air and to convey it to the S0 2 , so that, theoretically, an 
 unlimited quantity of sulphur might be converted into sulphuric acid 
 by a given quantity of NO, with a sufficient supply of air and steam. 
 
 The actual reactions involved in this process have received much 
 attention, and a full dis- 
 cussion of the probabilities 
 will be found in works on 
 sulphuric acid manufacture. 
 
 To illustrate the chemical 
 principles of the manufacture of 
 sulphuric acid, a large glass 
 flask or globe (A, Fig. 175) is 
 fitted with a cork through which 
 are passed () a tube connected 
 with a flask (D) containing 
 copper and strong sulphuric acid 
 for evolving S0 2 ; (i) a tube 
 connected with a flask (B) con- 
 taining copper and dilute nitric 
 acid (sp. gr. 1.2) for supplying 
 nitric oxide ; (c) a tube pro- 
 ceeding from a small flask (E) Fig. 175. Preparation of sulphuric acid, 
 containing water. 
 
 On heating the flask containing nitric acid and copper, the NO passes into the 
 globe and combines with the oxygen of the air,* filling the globe with a red 
 mixture of nitric peroxide and nitrous anhydride. The nitric oxide flask may then 
 be removed. Sulphur dioxide is now generated by heating the flask containing 
 sulphuric acid and copper ; the S0 2 soon decolourises the red gas, the contents of 
 the globe becoming colourless, and the crystalline compound forming abundantly 
 on the sides ; the sulphur dioxide flask may then be removed. Steam is sent into 
 the globe from the flask containing water, when the crystalline compound dissolves, 
 and sulphuric acid collects at the bottom of the globe. 
 
 If the experiment be repeated, the steam being introduced simultaneously with 
 the sulphur dioxide, no crystalline compound will be formed, the sulphur dioxide 
 being at once converted into sulphuric acid. 
 
 Since the cork is somewhat corroded in this experiment, it is preferable to have 
 the mouth of the flask ground and closed by a ground glass plate, perforated with 
 holes for the passage of the tubes. The perforations are easily made by placing 
 the glass plate flat against the wall and piercing it with the point of a revolving 
 rat's-tail file dipped in turpentine ; the file is then gradually worked through the 
 hole until the latter is of the required size. 
 
 The process employed for the manufacture of English oil of vitriol 
 will now be easily understood. 
 
 A series of chambers (about 100 ft. x 20 ft. x 20 ft., shown in trans- 
 verse section at F, Fig. 176), is constructed of leaden plates, the edges 
 
 * The operation is, of course, more striking if oxygen is employed instead of air, the globe 
 in Fig. 175 being filled with oxygen by displacement at the commencement. 
 
 P 
 
226 
 
 MANUFACTURE OF SULPHURIC ACID. 
 
 of which are united by autogenous soldering (that is, by fusing together 
 their edges without solder, which would be rapidly corroded by the acid 
 vapours.) The bottom or saucer (G) of the chamber is not attached to 
 
 the upper portion or curtain (F), the" sulphuric acid which collects in 
 the saucer serving to seal the communication between the interior of 
 the chamber and the outer air. A framework of timber supports the 
 curtain. 
 
 The sulphurous acid gas is generated by burning iron pyrites* or 
 * 2FeS 2 + O n = Fe 2 O 3 + 4SO 2 . 
 
REACTIONS IN THE VITRIOL CHAMBERS. 227 
 
 sulphur in suitable furnaces (A) adjoining the chambers, and so arranged 
 that the gas produced may be mixed with about the proper quantity of 
 air to furnish the oxygen required for its conversion into sulphuric acid.. 
 
 Nitric acid vapour is evolved from a mixture of sodium nitrate and 
 oil of vitriol (see page 89) contained in iron nitre pots (C) which are 
 heated by being placed in the flue (B), leading from the pyrites burners, 
 to the chamber, so that the nitric acid is carried into the chambers with 
 the current of sulphurous acid gas and air (through D). 
 
 Jets of steam are introduced at different parts of the chambers from 
 an adjacent boiler. 
 
 The sulphurous acid gas acts upon the nitric acid vapour, in the 
 presence of the water, forming nitric oxide and sulphuric acid which 
 rains down into the water on the floor of the chambers. If the NO 
 were permitted to escape from the chambers, and a fresh quantity of 
 nitric acid vapour introduced to oxidise another portion of sulphur 
 dioxide, 2 molecules (170 parts by weight) of sodium nitrate would be 
 required to furnish the nitric acid for the conversion of 2 atoms (64 
 parts by weight) of sulphur, whereas, in practice, only 4 parts by weight 
 of nitrate are employed for 96 parts of sulphur. 
 
 The nitrogen of the air takes no part in the change ; and since the 
 oxygen consumed in converting the sulphur into sulphuric acid is accom- 
 panied by four times its volume of nitrogen, there is a very large accu- 
 mulation of this gas in the chambers, and provision must be made for 
 its removal in order to allow space for those gases which take part in 
 the change. The obvious plan would appear to be the erection of a 
 simple chimney for the escape of the nitrogen at the opposite end of 
 the chamber to that at which the sulphurous acid gas and air enter it, 
 and this plan was formerly adopted ; but the nitrogen carries off with 
 it a portion of the oxides of nitrogen which are so valuable in the 
 chamber, and to save this the escaping nitrogen is now generally passed 
 through a lead-lined tower (Gay-Lussac's tower) (H) filled with per- 
 forated stoneware plates, through which oil of vitriol (sp. gr. 1.72) is 
 allowed to trickle : the oil of vitriol absorbs the nitrogen oxides, and flows 
 into a cistern (acid egg), wherefrom it is forced up, by air pressure, to 
 a cistern (K) at the top of another tower (Glover's tower) (E) packed 
 with acid-proof bricks, through which the hot SO, and air are made to 
 pass as they enter, when they take up the nitrogen oxides from the 
 " nitrous vitriol," and carry them into the chamber. 
 
 A. saving of over 50 per cent, of the weight of sodium nitrate used is 
 thus effected. 
 
 The sulphuric acid is allowed to collect on the floor of the chamber 
 until it has a specific gravity of about 1.6, and contains 70 per cent, 
 of oil of vitriol (H 2 S0 4 ). If it were allowed to become more concen- 
 trated than this, it would both attack the lead and absorb some of the 
 oxides of nitrogen in the chamber, so that it is now drawn off. 
 
 This acid (chamber acid) is quite strong enough for some of the appli- 
 cations of sulphuric acid, particularly for that which consumes the 
 largest quantity in this country, viz., the conversion of common salt into 
 sodium sulphate as a preliminary step in the manufacture of carbonate 
 of soda. To save the expense of transporting the acid for this purpose, 
 the vitriol chambers form part of the plant of the alkali works. 
 
 To convert this weak acid into the ordinary oil of vitriol of commerce, 
 
228 CONCENTRATION OF SULPHURIC ACID. 
 
 it is run off into shallow leaden pans set in brickwork and supported on 
 iron bars over the flue of a furnace, where it is heated until so much 
 ^water has evaporated that the specific gravity of the acid has increased 
 to 1.72. The concentration cannot be carried further in leaden pans, 
 because the strong acid acts upon the lead, and converts it into sulphate 
 2 H 2 S0 4 + Pb = PbS0 4 + 2 H 2 + S0 2 . 
 
 When a Glover's Tower is used the whole of the chamber acid is 
 passed down the tower together with the nitrous vitriol. The chamber 
 acid is thus concentrated by the heat of the furnace gases to sp. gr. 1.72 
 and the gases are at the same time cooled. 
 
 The acid of 1.72 sp. gr. contains about 80 per cent, of true oil of 
 vitriol, and is largely employed for making superphosphate of lime, and 
 in other rough chemical manufactures. It is technically called brown 
 acid (brown oil of vitriol, B.O.V.), having acquired a brown colour from 
 organic matter accidentally present in it. 
 
 To convert this brown acid into commercial oil of vitriol, it is boiled 
 down, either in glass retorts or platinum stills, when water distils over, 
 accompanied by a little sulphuric acid, and the acid in the retort becomes 
 colourless, the brown carbonaceous matter being oxidised by the strong 
 sulphuric acid, with formation of carbonic and sulphurous acid gases. 
 When dense white fumes of oil of vitriol begin to pass over, showing 
 that all the superfluous water has been expelled, the acid is drawn off 
 by a siphon. The strongest acid obtainable by this process still contains 
 about 2 per cent, of water, formed by the decomposition of some of the 
 H 3 S0 4 into H 2 and S0 3 , which escapes as vapour. 
 
 The cost of the acid is very much increased by this concentration. It cannot 
 be conducted in open vessels, partly on account of the loss of sulphuric acid, 
 partly because concentrated sulphuric acid absorbs moisture from the open air 
 even at the boiling-point. The loss by breakage of the glass retorts is very con- 
 siderable. although it is reduced as far as possible by heating them in sand, and 
 keeping them always at about the same temperature by supplying them with hot 
 acid. But the boiling-point of the concentrated acid is very high (640 F., 338 C.), 
 and the retorts consequently become so hot that a current of cold air or an 
 accidental splash of acid will frequently crack them at once. Moreover, the acid 
 boils with succussion or violent bumping, caused by sudden bursts of vapour, which 
 endanger the safety of the retort. 
 
 With platinum stills the risk of fracture is avoided, and the concentration may 
 be conducted more rapidly, the brown acid (sp. gr. 1.72) being admitted at the top, 
 and the oil of vitriol (sp. gr. 1.84) drawn off by a platinum siphon from the 
 bottom of the still, which is protected from the open fire by an iron jacket. But 
 since a platinum still costs ^2000 or ^3000, the interest upon its value increases 
 the cost of production of the acid. It is stated to be economical to protect the 
 platinum from the slight action of the vitriol on it by a lining of gold, which is 
 less attacked. 
 
 When the perfectly pure acid is required, it is actually distilled so as to leave 
 the solid impurities (sulphate of lead, &c.) in the retort. Some fragments of rock 
 crystal should be introduced into the retort to moderate the bursts of vapour, and 
 heat applied by a ring gas-burner with somewhat divergent jets. 
 
 Commercial sulphuric acid is liable to contain nitrogen oxides, lead sulphate, 
 arsenic (from the iron pyrites burnt in the kilns), and iron. Arsenic-free acid 
 may be made by passing H 2 S through the diluted acid, filtering off the precipitate 
 of As 2 S 3 , and concentrating. It is generally made, however, by using sulphur in 
 the kilns in place of pyrites. Nitrogen oxides are eliminated by adding a little 
 
 ammonium sulphate during concentration ; NO + N0 2 + (NH 4 ) 2 S0 4 = N 4 + 
 3H 2 0. To eliminate iron and lead sulphate the acid must be distilled. 
 
 For many years it has been the dream of the sulphuric acid maker to 
 
CONTACT-PROCESS FOR MAKING SULPHURIC ACID. 2 2Q 
 
 combine sulphur dioxide and atmospheric oxygen, by the method 
 described at p. 222 for making sulphuric anhydride, and to absorb the 
 product in water to obtain sulphuric acid. In such a process the " con- 
 tact substance " has the same function as that of the nitric oxide in the 
 chamber-process, that is to say, it acts as a carrier of oxygen from the 
 air to the sulphur dioxide, although in what manner is unknown. The 
 contact-substance has the great advantage over nitric oxide that, being 
 a solid, it requires less room in which to do its work, and is not liable to 
 loss by leakage. Thus the unit of plant might be expected to be con- 
 siderably smaller in a " contact-process " for making sulphuric acid 
 than in the chamber-process. An economy of greater importance than 
 the saving of interest on plant, however, consists in the possibility of 
 making by the contact-process strong sulphuric acid, or even a fuming 
 acid, at once, thus eliminating the cost of concentration ; for it is obvious 
 that by abjusting the proportion of water by which the sulphuric anhy- 
 dride is absorbed, an acid of any degree of concentration may be 
 obtained. 
 
 Unfortunately, there are several conditions which affect unfavourably 
 the combination of SO 2 and in the contact-process. The only contact- 
 substance which has proved so far sufficiently active in inducing the 
 combination is platinum, most economically used by spreading it over a 
 large surface as in the form known as platinised asbestos (p. 98). The 
 activity of this material, however, rapidly diminishes if the gases contain 
 impurities, because these are either deposited on the platinum or they 
 combine with it and render it ineffective. Such impurities are said to 
 *' poison " the metal, and the worst of them in this respect are com- 
 pounds of arsenic, phosphorus, and mercury. The first of these is 
 nearly always present in the pyrites burnt lor the production of S0 2 , 
 and, passing into the gases, is sufficient, together with the dust arising 
 from the pyrites burners, to render the platinum useless in a very short 
 time. It was the necessity for constantly renewing the platinum by 
 dissolving it from the asbestos by aqua-regia, and again precipitating it 
 thereon, that prevented the success of the contact- process in the past. 
 
 Another difficulty to be met in the contact-process (or catalytic pro- 
 cess) arises from the fact that the heat evolved when S0 2 and O combine 
 (p. 222) is apt to accumulate until the temperature of the contact-sub- 
 stance is so high that much of the S0 3 produced is decomposed again 
 into S0 2 and 0, or these gases never combine. 
 
 The demand for strong and fuming sulphuric acid by the manu- 
 facturers of artificial dyestuffs and other organic preparations, having 
 increased rapidly during the last few years, strenuous efforts have again 
 been made to produce the acid by the contact-process, and by rigorous 
 care in purifying the sulphur dioxide and air before they enter the 
 chamber containing the contact-substance, and by careful regulation of 
 the temperature of the latter great success has been attained. Indeed, 
 it is claimed that so much as 96 per cent, of the S0 2 may be converted 
 into S0 3 , and there is little reason to doubt that the process will ulti- 
 mately displace the chamber-process. 
 
 Sulphur dioxide is produced in a pyrites burner as in the chamber- 
 process, sufficient air for its conversion into S0 3 being drawn in through 
 the burner. This mixture of gases is then thoroughly washed, dried, 
 and passed into a chamber containing platinised asbestos spread on 
 
230 
 
 CONTACT-PEOCESS FOE MAKING SULPHURIC ACID. 
 
 shelves. At first the 
 chamber must be 
 artificially heated to a 
 temperature of about 
 250 to 300 C. in 
 order to induce the 
 combination, but after 
 this has once set in, it 
 becomes necessary to 
 withdraw the arti- 
 ficial heat and to cir- 
 culate the gases which 
 are to be combined, 
 around the contact- 
 chamber in order that 
 they may equalise the 
 temperature therein, 
 and prevent it from 
 rising at any one 
 point to that at which 
 decomposition of the 
 S0 3 occurs. The 
 sulphuric anhydride 
 is finally absorbed in 
 water to produce sul- 
 phuric acid. 
 
 Fig. 177 illustrates the 
 kind of plant used in the 
 contact-process for the 
 manufacture of sulphuric 
 acid. The gases from 
 the pyrites kiln A pass 
 through a dust chamber 
 B, where they are sub- 
 mitted to the action of 
 steam jets in order to 
 mix them, and at the 
 same time to dilute the 
 sulphuric acid, which is 
 always produced during 
 the combustion in the 
 pyrites burner, so that 
 afterwards it may not 
 attack the metal of the 
 apparatus. The gases 
 next pass through lead 
 pipes 6', exposed to the 
 atmosphere, in order to 
 cool them below 100 C., 
 and then up through 
 washing towers D sup- 
 plied with water. As 
 the presence of moisture 
 in the gases leads to 
 formation of H 2 S0 4 in 
 the contact - chamber, 
 which damages the plati- 
 num, the gases are next 
 
PROPERTIES OF SULPHURIC ACID. 23 1 
 
 dried in a tower E supplied with strong sulphuric acid. To ensure continued 
 activity of the platinum, it is desirable to watch carefully over the purity of the 
 gases entering the contact-chamber ; for this purpose they are passed through a 
 long box F, having glass ends so that the operative can observe from one end a light 
 burning at the other, and thus determine whether the gases are free from suspended 
 matter. A periodical chemical testing of the gases is also made by passing some 
 of them through water, which is afterwards analysed for arsenic and other 
 impurities. 
 
 The contact-chamber G (which is drawn to an exaggerated scale for the sake 
 of clearness) contains columns of perforated shelves on which platinised asbestos 
 is spread. At first the chamber is heated by the gas jets g, the products of com- 
 bustion of which pass up the flue Ji. The cold gases being admitted at i, and 
 passing around the columns of shelves, become heated by transmission through the 
 walls of the flue and enter the columns, as indicated by the arrows, at a tempera- 
 ture high enough to combine under the influence of the platinum. The gas jets 
 may now be turned off, for the heat of combination is communicated to the gases 
 as they pass around the columns, and the whole apparatus may be maintained at 
 the most favourable temperature for combination, about 350 C. 
 
 The S0 3 produced is absorbed by water in a series of vessel like H. 
 
 No means of circulating the gases is shown in the figure, but this is best effected 
 by pumps. 
 
 Properties of oil of vitriol. The properties of concentrated sulphuric 
 acid are very characteristic. Its great weight (sp. gr. 1.84),* freedom 
 from odour, and oily appearance, distinguish it from any other liquid 
 commonly met with, which is fortunate, because it is difficult to preserve 
 a label upon the bottles of this powerfully corrosive acid. Although, if 
 absolutely pure, it is perfectly colourless, the ordinary acid used in the 
 laboratory has a peculiar grey colour, due to traces of organic matter. 
 Its high boiling-point, 338 C. (640 F.) has been already noticed ; it 
 mast be added that vapour of H 2 S0 4 is not evolved by the ebullition 
 but the products of its dissociation, H 2 + S0 3 . When acid of 100 per 
 cent, strength is heated it begins to (apparently) boil at 290 C. and 
 loses SO 3 until its strength has fallen to 98 per cent., when both water 
 and S0 3 distil over and condense together in the receiver. The vapour 
 is perfectly transparent in the vessel in which the acid is boiled ; as soon 
 as it issues into the air it condenses into voluminous, dense clouds of a 
 most irritating description. Even a drop of the acid evaporated in an 
 open dish will fill a large space with these clouds. Oil of vitriol solidifies 
 when cooled to about - 34 C. ( - 30 F.), though pure H 2 S0 4 melts at 
 10. 5 C. (51 F.). Oil of vitriol rapidly corrodes the skin and other 
 organic textures upon which it falls, usually charring or blackening 
 them at the same time. Poured upon a piece of wood the latter speedily 
 assumes a dark brown colour ; and if a few lumps of sugar be dissolved 
 in a very little water, and stirred with oil of vitriol, there is a violent 
 action, and a semi-solid black mass is produced. This property of sul- 
 phuric acid is turned to account in the manufacture of blacking, in which 
 treacle and oil of vitriol are employed. These effects are to be ascribed 
 to the powerful attraction of oil of vitriol for water. Woody fibre 
 (C 6 H 10 5 ) (which composes the bulk of wood, paper, and linen) and 
 sugar (d 19 H 92 O n ), may be regarded, for the purpose of this explanation, 
 as composed of carbon associated with 5 and 1 1 molecules of water, 
 respectively, and any cause tending to remove the water would tend to 
 eliminate the carbon. 
 
 * The acid containing 97.7 per cent, has the highest sp. gr. 1.8413 ; that of 98 per cent., 
 1.8412 ; 99 per cent., 1.8403 ; 99.47 per cent., 1.8395 ; 100 per cent., 1.8384. 
 
232 SULPHUEIC ACID AND WATEK. 
 
 The great attraction of this acid for water is shown by the high tem- 
 perature (often exceeding the boiling-point of water) produced on mixing 
 oil of vitriol with water, which renders it necessary to be careful in 
 diluting the acid. 
 
 The water should be placed in a jug, and the oil of vitriol poured into it in a 
 thin stream, a glass rod being used to mix the acid with the water as it flows in. 
 Ordinary oil of vitriol becomes turbid when mixed with water, from the separation 
 of lead sulphate (formed from the evaporating pans), which is soluble in the 
 concentrated, but not in the diluted acid, so that if the latter be allowed to stand 
 for a few hours, the lead sulphate settles to the bottom, and the clear acid may 
 be poured off free from lead. Diluted sulphuric acid has a smaller bulk than is 
 occupied by the acid and water before mixing. 
 
 The heat evolved on combining one gram-molecule of H 2 S0 4 with one gram- 
 molecule of water amounts to 69.7 gram-units. Decreasing quantities of heat are 
 evolved for successive additions of water, until 200 gram-molecules of water have 
 been added. 
 
 The heat thus evolved must be regarded as equivalent to a chemical affinity 
 exerted between the acid and water ; several compounds of sulphuric acid with 
 water have been crystallised. The most notable of these is H 2 S0 4 .H 2 0, corre- 
 sponding with an acid of sp. gr. 1.78 ; it is called dihydrated sulphuric acid 
 (S0 3 .2H 2 0). in contradistinction to oil of vitriol, which is monohydrated sulphuric 
 acid (S0 3 .H 2 0) ; it solidifies to a mass of ice-like crystals at 8 0., and on this 
 account is called glacial sulphuric acid. When sold instead of oil of vitriol it may 
 be recognised by its freezing in winter. The hydrate H 2 S0 4 .2H 2 corresponds with 
 the maximum contraction which occurs when H 2 S0 4 and water are mixed, and with 
 an acid of sp. gr. 1.63 ; it is called trihydrated sulphuric acid or orthosulphuric 
 acid. 
 
 The so-called "solidified sulphuric acid " is sodium hydrogen sulphate saturated 
 with sulphuric acid. 
 
 Even when largely diluted, sulphuric acid corrodes textile fabrics 
 very rapidly, and though the acid be too dilute to appear to injure them 
 at first, it will be found that the water evaporates by degrees, leaving 
 the acid in a more concentrated state, and the fibre is then perfectly 
 rotten. The same result ensues at once on the application of heat; thus, 
 if characters be written on paper with the diluted acid, they will remain 
 invisible until the paper is held to the fire, when the acid will char the 
 
 paper, and the writing will appear 
 intensely black. 
 
 If oil of vitriol be left exposed to 
 the air in an open vessel, it very soon 
 increases largely in bulk from the 
 absorption of water, and a flat dish 
 of oil of vitriol under a glass shade 
 (Fig. 178) is frequently employed in 
 the laboratory for drying substances 
 without the assistance of heat. The 
 Fig. 178,-Desiccator for drying drying is of course much accelerated 
 
 over oil of vitriol. by placing the dish on the plate of 
 
 an air-pump, and exhausting the air 
 
 from the shade, so as to effect the drying in vacuo. It will be remem- 
 bered also that oil of vitriol is in constant use for drying gases. 
 
 At a red heat, the vapour of oil of vitriol is decomposed into water, 
 sulphur dioxide, and oxygen ; H 2 S0 4 = H 2 + S0 2 + O. 
 
 When sulphur is boiled with oil of vitriol, the latter gradually dis- 
 solves the melted sulphur, converting it into sulphur dioxide 
 
 S + 2 H 2 S0 4 - 3 S0 2 + 2H 2 0. 
 
COMPOSITION OF SULPHURIC ACID. 233 
 
 All ordinary metals are acted upon by concentrated sulphuric acid 
 when heated, except gold and platinum (the latter does not quite 
 escape when long boiled with the acid), the metal being oxidised by one 
 portion of the acid, which is thus converted into sulphur dioxide, the 
 oxide reacting with another part of the sulphuric acid to form a sul- 
 phate. Thus, when silver is boiled with strong sulphuric acid, it is 
 converted into silver sulphate, which is soluble in hot water 
 Ag 2 + 2H 2 S0 4 = Ag 2 S0 4 + 2H 2 + S0 2 . 
 
 Should the silver contain any gold, this is left behind in the form of a 
 dark powder. Sulphuric acid is extensively employed for the separation 
 or parting of silver and gold. This acid is also employed for extract- 
 ing gold from copper, and when sulphate of copper is manufactured 
 by dissolving that metal in sulphuric acid (see p. 218), large quan- 
 tities of gold are sometimes extracted from the accumulated residue 
 left undissolved by the acid. If the sulphuric acid contains nitric acid, 
 it dissolves a considerable quantity of gold, which separates again in 
 the form of a purple powder when the acid is diluted with water, the 
 sulphate of gold formed being reduced by the nitrous acid when the 
 solution is diluted. 
 
 Some of the uses of sulphuric acid depend upon its specific action on 
 certain organic substances, the nature of which has hot yet been clearly 
 explained. Of this kind is the conversion of paper into vegetable parch- 
 ment by immersion in a cool mixture of two measures of oil of vitriol 
 and one measure of water, and subsequent washing. The conversion is 
 not attended by any change in the weight of the paper. 
 
 Proof of the composition of sulphuric acid. 10 grams of sulphuric acid are 
 neutralised by 22.7 grams of PbO, when heated, giving off 1.82 grams of H 2 and 
 leaving 30.9 grams of lead sulphate. Hence sulphuric acid contains 2.02 per cent, 
 of H. 10 grams galena (PbS), containing 8.66 Pb and 1.34 S, when converted into 
 lead sulphate (PbS0 4 ) by nitric acid, yield 12.68 grams. Hence 12.68 grams lead 
 sulphate contain 1.34 S and 2.68 0, being the difference between the lead sulphate 
 and the lead sulphide. The 30.9 grams of lead sulphate furnished by 10 grams of 
 sulphuric acid would therefore contain 3.26 S and 65.2 0, so that 100 parts of 
 sulphuric acid contain 2.02 H, 32.6 S, and 65.2 0, which numbers, divided by the 
 atomic weights, give 2 atoms of H. I atom of S, and 4 atoms of 0. The molecular 
 weight of sulphuric acid cannot be deduced from the sp. gr. of its vapour because it 
 is dissociated into H 2 and S0 3 . But it yields with KOH two salts, one containing 
 an atom of K and an atom of H, and the other containing two atoms of K. 
 Hence these salts must be KHS0 4 and K 2 S0 4 , and the molecule of the acid must be 
 H 2 S0 4 . 
 
 135. /Sulphates. At common temperatures sulphuric acid displaces 
 all other acids from their salts ; many cases will be remembered in 
 which this power of sulphuric acid is turned to account. 
 
 So great is the acid energy of sulphuric acid, that when it is allowed 
 to act 011 an indifferent or acid metallic oxide, it causes the separation 
 of a part of the oxygen, and reacts with the basic oxide so produced. 
 Advantage is sometimes taken of this circumstance for the preparation 
 of oxygen ; for instance, when manganese dioxide is heated with 
 sulphuric acid, sulphate of manganese is produced, and oxygen dis- 
 engaged ; MnO >2 + H 2 S0 4 = MnS0 4 + O + H 2 0. 
 
 Again, if chromic "anhydride be treated in the same way, chromic 
 sulphate will be produced, with liberation of oxygen 
 2 Cr0 3 + 3H 2 S0 4 = Cr. 2 . 3 S0 4 + 3 + 3 H 2 0. 
 
234 
 
 SULPHATES. 
 
 A mixture of potassium bichromate (K 2 0.2Cr0 3 ) and sulphuric acid is 
 sometimes used as a source of oxygen. 
 
 Sulphuric acid is a dibasic acid, that is, it contains two atoms of 
 hydrogen which may be exchanged for a metal. In normal sulphates, 
 both atoms of H are so exchanged, as in K 2 SO 4 , the normal potassium 
 sulphate. When only a part of the H is exchanged, acid sulphates are 
 produced \ thus KHS0 4 is acid potassium sulphate, which is very use- 
 ful in blcwpipe and metallurgic chemistry, because, when heated, it 
 yields normal potassium sulphate and sulphuric acid; 2KHS0 4 = 
 K 2 SO 4 + H 2 S0 4 . When the two atoms of H in H 2 S0 4 are exchanged 
 for different metals, double sulphates are formed ; potassium alum, 
 KA1(SO 4 ) 2 , is an example of this class, in which one-fourth of the H in 
 2H 2 S0 4 is exchanged for potassium, and the other three atoms by tri- 
 atomic aluminium. 
 
 The following table exhibits the composition of the sulphates most 
 frequently met with : 
 
 Chemical Xame. 
 
 Common Name. 
 
 Formula. 
 
 Potassium sulphate 
 
 Sal polychrest . 
 
 K 2 S0 4 
 
 Sodium sulphate .... 
 
 Glauber's salt . 
 
 Na 2 S0 4 . ioH 2 
 
 Hydropotassium sulphate 
 
 Bisulphate of potash 
 
 KHSO* 
 
 Ammonium sulphate 
 Barium sulphate .... 
 
 Heavy spar 
 
 (NH 4 ) 2 S0 4 
 BaS0 4 
 
 Calcium sulphate .... 
 
 Gypsum . 
 
 CaS0 4 .2H 2 
 
 Magnesium sulphate 
 
 Epsom salts 
 
 MgS0 4 .7H 2 O 
 
 Potassium-aluminium sulphate 
 
 Potash-alum . 
 
 KAl(S0 4 ) 2 .i2H 2 
 
 Ammonium-aluminium sulphate . 
 
 Ammonia-alum 
 
 NH 4 Al(S0 4 ) 2 .i2H 2 
 
 Potassium-chromium sulphate 
 
 Chrome-alum . 
 
 KCr(S0 4 ) 2 .i2H 2 
 
 Ferrous sulphate . 
 
 Green vitriol . ) 
 Copperas . . / 
 
 FeS0 4 .7H 2 
 
 Manganese sulphate 
 
 
 MnS0 4 .5H 2 
 
 Zinc sulphate 
 
 White vitriol . 
 
 ZnS0 4 .7H 2 O 
 
 Lead sulphate .... 
 
 
 PbS0 4 
 
 Cupric sulphate 
 
 Blue vitriol . ^ 
 Blue stone . J 
 
 CuS0 4 ,5H 2 
 
 In consequence of the tendency of sulphuric acid to break up into sulphur dioxide 
 and oxygen at a high temperature, most of the sulphates are decomposed by heat ; 
 cupric sulphate, for example, when very strongly heated, leaves cupric oxide, whilst 
 sulphur dioxide and oxygen escape; CuS0 4 =CuO + S0. 2 + 0. Ferrous sulphate is 
 more easily decomposed, some of the S0 3 escaping decomposition, whilst the 
 remainder breaks up into S0 2 and 0, the latter oxidising the ferrous oxide which 
 would otherwise be left ; 2FeS0 4 = Fe 2 3 + S0 2 +S0 3 . 
 
 The normal sulphates of potassium, sodium, barium, strontium, calcium, and 
 lead are not decomposed by heat, and sulphate of magnesium is only partly decom- 
 posed at a very high temperature. 
 
 When a sulphate of an alkali or alkaline earth metal is heated with charcoal, the 
 carbon removes the whole of the oxygen, and a sulphide of the metal remains, thus : 
 K 2 S0 4 (Potassium sulphate) + C 4 = K 2 S (Potassium sulphide) + 4.CO . Hydrogen, at 
 a high temperature, effects a similar decomposition. 
 
 Even at the ordinary temperature, calcium sulphate in solution is sometimes de- 
 oxidised by organic matter ; this may occasionally be noticed in well and river 
 waters when kept in closed vessels ; they acquire a strong smell of hydrogen sul- 
 phide, in consequence of the conversion of a part of the calcium sulphate into 
 sulphide by the organic constituents of the water, and the subsequent decomposi- 
 tion of the calcium sulphide by the carbonic acid present in the water. 
 
THIOSULPKATES. 235 
 
 Sulphur sesquioxide, S 2 3 , is an unstable, blue, crystalline solid, obtained by 
 the gradual addition of sulphur to sulphuric anhydride in the cold. It dissolves 
 in fuming sulphuric acid to a blue liquid, but is decomposed by water, alcohol, or 
 ether, sulphur being liberated. 
 
 Persulphuric anhydride, S 2 7 , is a crystalline compound formed by electrising 
 <j). 65) a mixture of S0 2 and O. It is also produced by the interaction of hydro- 
 gen dioxide andH 2 SO 4 . It is very volatile and unstable, but its solution in fairly 
 concentrated sulphuric acid possesses oxidising properties and probably con- 
 tains per sulphuric acid HS0 4 (?H 2 S 2 8 ). Such a solution is formed at the anode 
 during the electrolysis of sulphuric acid of medium strength, and its presence is to be 
 detected in the ordinary lead electric accumulator. The persulphate* are easily pre- 
 pared by the electrolysis of solutions of the sulphates in dilute sulphuric acid. To 
 prepare potassium persulphate, KS0 4 (?K 2 S 2 8 ), a saturated solution of KHS0 4 is con- 
 tainedin a platinum dish, kept cool; a porous pot containing dilute H 2 S0 4 is immersed 
 in the solution, and in this a platinum wire is introduced to serve as a cathode ; the 
 platinum dish is made the anode. By continuing the electrolysis (current = 2- 3 
 amperes) for some time, crystals of KS0 4 are deposited in the dish. When dried 
 and heated they evolve S0 3 and 0, K 2 S0 4 being left. Barium chloride gives no 
 precipitate with a solution of a persulphate until heated, when the Ba(S0 4 ) 2 
 decomposes, BaSO 4 being precipitated. The persulphates behave as oxidising 
 agents in solution, and find application as bleaching agents, although the use of the 
 ammonium salt as a "reducer" in photography can hardly be explained by refer- 
 ence to its oxidising power. 
 
 It has been found that when a persulphate is treated with strong H 2 S0 4 the solu- 
 tion rapidly liberates iodine from an iodide, whereas persulphuric acid does so only 
 slowly. Hence such a solution (Cards acid} is supposed to contain another per- 
 sulphuric acid, to which the formula H 2 S0 5 has been given. 
 
 Besides the oxyacids of sulphur already described the following are 
 known : 
 
 Sulphurous H 2 S0 3 
 
 Sulphuric H 2 S0 4 
 
 Thiosulphuric (formerly hyposulphurous) H 2 S 2 3 
 
 Hydrosulphurous H 2 S 2 4 
 
 Dithionic H 2 S 2 6 
 
 Trithionic H 2 S 3 6 
 
 Tetrathionic H 2 S 4 6 
 
 Pentathionic , H 2 S 5 6 
 
 136. Thiosulphuric acid (H 2 S 2 3 or S0 2 .OH.SH). This acid has not 
 been obtained in the separate state ; but many salts are known which 
 are evidently derived from it, and such salts are called hyposulphites or 
 thiosulphates. 
 
 The sodium thiosulphate is by far the most important of these salts, 
 being very largely employed in photography, under the name of hypo- 
 sulphite, and as a substitute for sodium sulphite as an antichlore. The 
 simplest method of preparing it consists in digesting powdered roll 
 sulphur with solution of sodium sulphite (Na 2 S0 3 ), when the latter dis- 
 solves an atom of sulphur and becomes thiosulphate (Na 2 S 2 3 ), which 
 crystallises from the solution, when sufficiently evaporated, in fine 
 prismatic crystals, having the formula Na 2 S 2 O 3 .5H 2 O. 
 
 On a large scale, sodium thiosulphate is more economically prepared from the 
 calcium thiosulphate obtained by exposing the refuse (tank-waste or soda-ioaste) 
 of the alkali works to the air for some days. This refuse contains a large propor- 
 tion of calcium sulphide, which becomes converted into thiosulphate by oxidation ; 
 2CaS + 4 + H 2 = CaS 2 3 + Ca(OH) 2 . 
 
 The thiosulphate is dissolved out by water, and solution mixed with sodium 
 carbonate, when calcium carbonate is precipitated and sodium thiosulphate remains 
 in solution ; CaS 2 3 + Na 2 CO 3 = CaC0 3 + Na^S 2 3 . 
 
 The most remarkable and useful property of the sodium thiosulphate 
 
236 FIXING PHOTOGRAPHIC PRINTS. 
 
 is that of dissolving the chloride and iodide of silver, which are insoluble 
 in water and most other liquids ; hence its use in photography. 
 
 On mixing a solution of silver nitrate with one of sodium chloride, a white pre- 
 cipitate of silver chloride is obtained, the separation of which is promoted by stir- 
 ring the liquid ; AgN0 3 + NaCl = AgCl + NaNO 3 . The precipitate may be allowed to- 
 settle and washed twice or thrice by decantation. One portion of the silver 
 chloride is transferred to another glass, mixed with water, and solution of sodium 
 thiosulphate added by degrees. The silver chloride is very easily dissolved, yield- 
 ing an intensely sweet solution, which contains the thiosulphate of sodium and 
 silver, produced by double decomposition between the silver chloride and sodium 
 thiosulphate ; 2AgCl + sNa^Og = Ag 2 Na 4 (S 2 3 ) 3 + 2NaCl. The sodium silver thio- 
 sulphate may be obtained in crystals from the solution. 
 
 When the silver chloride is acted on by a weaker solution of the thiosulphate,. 
 another thiosulphate of sodium and silver is formed, which is very insoluble in 
 water ; AgCl + Na. 2 S 2 3 = NaCl + NaAgS 2 3 . Hence the necessity for using a strong 
 solution of the hyposulphite in fixing photographic prints. 
 
 If the other portion of the silver chloride be exposed to the action of light, and 
 especially of direct sunlight, it assumes by degrees a dark slate colour, possibly 
 from the formation of silver subchloride : 4AgCl + H 2 = 2Ag. 2 Cl + HCl + HOCl. By 
 treating this darkened silver chloride with the hyposulphite, as before, the un- 
 altered silver chloride will be entirely dissolved, but the subchloride will be decom- 
 posed into monochloride, which dissolves in the hyposulphite, and metallic silver, 
 which is left in a very finely divided state as a black powder. The application of 
 these facts in photography is well illustrated by the following experiments : A 
 sheet of paper is soaked for a minute or two in a solution of 10 grains of common 
 salt in an ounce of water contained in a flat dish. It is then dried, and soaked for 
 three minutes in a solution of 50 grains of silver nitrate in an ounce of water. The 
 paper thus becomes impregnated with silver chloride formed by the decomposition 
 between the sodium chloride and the silver nitrate. It is now hung up in a dark 
 place to dry. If a piece of lace, or a fern leaf, or an engraving on thin paper, with 
 well-marked contrast of light and shade, be laid upon a sheet of the prepared 
 paper, pressed down upon it by a plate of glass and exposed for a short time to sun- 
 light, a perfect representation of the object will be obtained, those parts of the 
 sensitive paper to which the light had access having been darkened by the forma- 
 tion of silver subchloride, whilst those parts which were protected from the light 
 remain unchanged. 
 
 But if this photographic print were again exposed to the action of light, it would 
 soon be obliterated, the unaltered silver chloride in the white parts being acted on 
 by light in its turn. The print is therefore J&gfti by soaking it for a short time in a 
 saturated solution of sodium thiosulphate, which dissolves the white unaltered silver 
 chloride entirely, and decomposes the subchloride formed by the action of light, 
 leaving the black, finely divided metallic silver in the paper. The print should now 
 be washed for two or three hours in a gentle stream of water, to remove all the 
 silver thiosulphate, when it will be quite permanent. 
 
 The power of sodium thiosulphate to dissolve silver chloride has also 
 been turned to account for extracting silver from its ores, in which it is 
 occasionally present in the form of chloride. 
 
 The behaviour of solution of sodium thiosulphate with powerful acids 
 explains the circumstance that the thiosulphuric acid has not been 
 isolated, for if the solution be mixed with a little dilute sulphuric or 
 hydrochloric acid, it remains clear for a few seconds, and then becomes 
 suddenly turbid from the separation of sulphur, at the same time evolv- 
 ing a powerful odour of sulphur dioxide ; H 2 S 2 3 = H 2 O + S + S0 3 . This 
 disposition of the thiosulphuric acid to break up into sulphur dioxide 
 and sulphur also explains the precipitation of metallic sulphides, which 
 often occurs when sodium thiosulphate is added to the acid solu- 
 tions of the metals. Thus, if an acid solution of antimonious chloride 
 (obtained by boiling crude antimony ore (Sb 2 S 3 ) with hydrochloric acid) 
 be added to a boiling solution of sodium "thiosulphate, the sulphur, 
 
THIONIC ACIDS. 237 
 
 separated from the thiosulphuric acid, combines with the antimony to 
 form a fine orange-red precipitate of antimonious sulphide (Sb 2 S 3 ), 
 which is used in painting under the name of antimony vermilion. On 
 the large scale, the solution of calcium thiosulphate obtained from the 
 alkali waste is employed in the preparation of antimony vermilion, as 
 being less expensive than the sodium-salt. Lead thiosulphate dissolved 
 in sodium thiosulphate is used as a hair-dye, depositing the black lead 
 sulphide. 
 
 A solution of sodium thiosulphate bleaches iodine solution, becoming 
 changed into a solution of sodium tetrathionate ; 2Na,S,O, + I 9 = 
 
 When crystals of sodium thiosulphate are heated in the air, they first fuse in 
 their water of crystallisation, then dry up to a white mass, which burns with a 
 blue flame, leaving a residue of sodium sulphate. If heated out of contact with 
 air, sodium pentasulphide will be left with the sodium sulphate ; 4/Na 9 S Oo. 
 
 H0 Na.S0 Na.S. 
 
 Some of the reactions of sodium thiosulphate become more intelligible when the 
 salt is represented as sodium sulphate, S0 2 (OJSTa) 2 , in which an atom of sulphur has 
 displaced an atom of oxygen, S0 2 .ONa.SNa. 
 
 Hydrosulphurous acid (H 2 S 2 4 ). In an aqueous solution of sulphurous acid 
 zinc dissolves, forming a yellow solution, without the usual evolution of hydrogen ; 
 the solution contains zinc hydrosulphite ; 2H 2 S0 3 + Zn = ZnS 2 4 + 2H 2 0. 
 
 The solution bleaches organic colours, even Prussian blue,"and reduces the salts 
 of silver, mercury, and copper to the metallic state ; it is used in the indigo vat for 
 reducing the indigo. It is very unstable, soon becoming colourless zinc sulphite ; 
 ZnS 2 4 + + H 2 = ZnS0 3 + H 2 S0 3 . 
 
 The sodium salt, Na^S^, is obtained by digesting zinc in solution of NaHS0 3 ; 
 2NaHS0 3 + Zn = Na 2 S 2 O 4 + Zn(OH) 2 . It forms needle-like crystals very soluble in 
 water, insoluble in strong alcohol, and becoming NaHS0 3 , by absorption of oxygen 
 from the air. By decomposing the sodium hydrosulphite with oxalic acid. H 2 S 2 4 
 is obtained as an orange-yellow unstable liquid. 
 
 137. Dithionic acid, or hyposulphuric acid (H 2 S 2 6 ), has not at present acquired 
 any practical importance. To prepare a solution of the acid, manganese dioxide 
 in a state of fine division is suspended in water and exposed to a current of sulphur 
 dioxide, the water being kept very cold whilst the gas is passing. A solution of 
 manganese dithionate is thus obtained ; 2S0 2 + Mn0 2 = MnS 2 6 . Some manganese 
 sulphate is always formed at the same time ; S0 2 +MnO 2 = MnS0 4 , and if the tem- 
 perature be allowed to rise, this will be produced in large quantity. 
 
 The solution containing the sulphate and dithionate is decomposed by solution 
 of baryta (baryta-water), when manganous oxide is precipitated, together with 
 barium sulphate, and barium dithionate is left in solution. To the filtered solution 
 dilute sulphuric acid is carefully added until all the barium is precipitated as 
 BaS0 4 , when the solution of dithionic acid is filtered and evaporated in vacua over 
 oil of vitriol. It is a colourless, inodorous liquid, which is decomposed, when 
 heated, into sulphuric acid and sulphur dioxide ; H 2 S 2 6 = H 2 S0 4 + S0 2 . Oxidising 
 agents (HNO 3 ,C1, &c.) convert it into H 2 S0 4 . 
 
 The dithionates are not of any practical importance ; they are all soluble, and are 
 decomposed by heat, leaving sulphates, and evolving sulphur dioxide. They are 
 distinguished from the thiosulphates in that they evolve S0 2 when heated with 
 HC1, without depositing sulphur. 
 
 138. Trithionic acid (H 2 S 3 6 ) is also a practically unimportant acid. It is pre- 
 pared from the potassium trithionate which is formed by boiling a strong solution 
 of potassium bisulphite with sulphur until the solution becomes colourless, 
 and filtering the hot solution from any undissolved sulphur; 6KHS0 3 + S = 
 2K 2 S 3 6 + K 2 S0 3 + 3H 2 0. The solution deposits potassium trithionate in prismatic 
 crystals. By dissolving these in water, and decomposing the solution with per- 
 chloric acid, the potassium is precipitated as perchlorate, and a solution of trithi- 
 onic acid is produced, from which the acid has been obtained in crystals. It is, 
 however, very unstable, being; easily resolved into sulphur dioxide, sulphuric acid, 
 and free sulphur ; H 2 S 3 6 = H 2 S0 4 + S0 2 + S. 
 
 139. Tetrathionic acid (H 2 S 4 6 ) is rather more stable than the preceding acid, 
 
238 CARBON BISULPHIDE. 
 
 though equally devoid of practical importance. It is formed when barium thio- 
 sulphate, suspended in a little water, is treated with iodine, when the tetrathionate 
 is obtained in crystals; 2(BaS. 2 3 ) + I 2 = BaI 2 + BaS 4 6 . (Compare the action of 
 iodine on sodium thiosulphate, p. 237.) By exactly precipitating the barium from 
 a solution of BaS 4 6 by dilute H 2 S0 4 , a solution of tetrathionic acid may be 
 obtained. When boiled, it is decomposed into sulphuric acid, sulphur dioxide, and 
 free sulphur ; H a S 4 O 6 =H 8 SO 4 +SO a -tS^. 
 
 When solution of ferric chloride is added to sodium thiosulphate, a fine purple 
 colour is at first produced, which speedily vanishes, leaving a colourless solution. 
 The purple colour appears to be due to the formation of the ferric thiosulphate- 
 which speedily decomposes, the ultimate result being expressed by the equation 
 F& 2 C1 6 + 2(Na 2 S 2 3 ) = Na.jS 4 6 + 2FeCl 2 + 2NaCl. 
 
 140. Pentathionic acid (H 2 S 5 6 ) possesses some interest as resulting from the 
 action of hydrogen sulphide upon sulphurous acid, when much sulphur is deposited, 
 and pentathionic acid remains in solution; 5H 2 S + 5H 2 S0 3 = H 2 S 5 6 + 9H 2 + S 5 . 
 Besides pentathionic acid, a colliodal form of sulphur, sulphuric acid, tetrathionic 
 acid and hexathionic acid (?) are found in the solution. To obtain a concentrated 
 solution of the acid, H 2 S and S0 2 are passed alternately through the same portion,, 
 of water until a large deposition of sulphur has occurred. This is allowed some 
 hours to settle ; the clear liquid poured off and the solution concentrated by 
 evaporation, first over a water-bath, and finally, in vacua, over oil of vitriol ; for a 
 concentrated solution of pentathionic acid is decomposed by heat into H 2 S0 4 and 
 S0 2 . with separation of sulphur ; H 2 S 5 6 -H 2 S0 4 -t-S0 2 +S 3 . 
 
 BISULPHIDE OF CARBON, OR CARBON BISULPHIDE. 
 
 CS 2 = 76 parts by weight. 
 
 141. This very important compound (also called bisulphuret of carbon) 
 is found in small quantity among the products of destructive distilla- 
 tion of coal, and is very largely manufactured for use as a solvent for 
 sulphur, phosphorus, caoutchouc, fatty matters, &c. It is one of the 
 few compounds of carbon which can be obtained by the direct union of 
 
 their elements, and is 
 ^^^ 1 1 ' . i "i prepared by passing 
 vapour of sulphur 
 over charcoal heated 
 to redness. The com- 
 bination is probably 
 endothermic. 
 
 In small quantity car- 
 bon disulphide is easily 
 
 Fig. 179. prepared in a tube of 
 
 German glass (combus- 
 tion-tube) about two feet long and half an inch in diameter (Fig. 179). 
 
 This tube is closed at one end, and a few fragments of sulphur dropped into it 
 so as to occupy two or three inches. The rest of the tube is filled up with small 
 fragments of recently calcined wood charcoal. The tube is placed in a combustion- 
 furnace, and its open end connected by a perforated cork with a glass tube, which 
 dips just below the surface of water contained in a bottle placed in a vessel, of very 
 cold water. The part of the tube which contains the charcoal is heated first, and 
 when it is red-hot the end containing the sulphur is heated, so that the vapour of 
 sulphur maybe slowly passed over the red-hot charcoal. The disulphide being- 
 insoluble in water, and much heavier (sp. gr. 1.2 at o C.), is deposited beneath the 
 water in the receiver. To purify it from the water and the excess of sulphur which 
 is deposited with it, the water is carefully drawn off with a small siphon, the CS 2 
 transferred to a flask, and a few fragments of calcium chloride dropped into it to 
 absorb the water. A condenser is attached to the flask (Fig. 180) by a perforated 
 cork, and the flask is gently heated in a water-bath, when the CS 2 is distilled over 
 as a perfectly colourless liquid. The inflammability of the disulphide renders 
 great care necessary. 
 
CARBON BISULPHIDE. 239 
 
 On a large scale, a fire-clay or cast-iron retort is filled with fragments 
 of charcoal and heated to redness, pieces of sulphur being occasionally 
 dropped in through an earthenware tube passing to the bottom of the 
 retort. When very large quantities are made, coke is employed, and 
 the vapour of sulphur is obtained from 
 iron pyrites. The carbon disulphide is 
 possessed of some very remarkable pro- 
 perties : it is a very brilliant liquid, the 
 light passing through which at certain 
 angles is partly decomposed into its com- 
 ponent coloured rays before it reaches 
 the eye. These properties are dependent 
 upon its high refractive and dispersive 
 powers, which are turned to great ad- 
 vantage in optical experiments, especially 
 in spectrum analysis, where the rays 
 emanating from a coloured flame are 
 analysed by passing them through a Fig-. 180. 
 
 prismatic bottle filled with carbon disul- 
 phide. It is also highly diathermic, that is, it allows rays of heat to 
 pass through it with comparatively little loss, so that if it be rendered 
 opaque to light by dissolving iodine in it, the rays of light emanating 
 from a luminous object may be arrested, whilst the calorific rays are 
 allowed to pass. Carbon disulphide is a very volatile liquid, readily 
 assuming the form of vapour at the ordinary temperature, and boiling 
 at 46 C. Its vapour, when diluted with air, has a very disgusting and 
 exaggerated odour of sulphuretted hydrogen, but the smell at the mouth 
 of the bottle is ethereal and not unpleasant if the disulphide has been 
 carefully purified. 
 
 The rapid evaporation of carbon disulphide is, of course, productive of great 
 cold. If a few drops be placed in a watch-glass and blown upon, they soon pass off 
 in vapour, and the temperature of the glass is so reduced that some of the disul- 
 phide is frozen ; * this melts when the glass is placed in the palm of the hand. If 
 a glass plate be covered with water, a watch-glass containing carbon disulphide 
 placed on it, and evaporation promoted by blowing through a tube, the watch- 
 glass will be frozen on to the plate, so that the latter may be lifted up by it. 
 
 The carbon disulphide is exceedingly inflammable ; it takes fire at a 
 temperature far below that required to inflame ordinary combustible 
 bodies, and burns with a bright blue flame, producing carbon dioxide 
 and sulphur dioxide (CS 2 + O 6 = CO, + 2S0 2 ), and having a great tendency 
 to deposit sulphur unless the supply of air be very good. 
 
 If a little carbon disulphide be dropped into a small beaker, it may be inflamed 
 by holding in its vapour a test-tube containing oil heated to about 300 F. (149 C.), 
 which will.be found incapable of firing gunpowder or of inflaming any ordinary 
 combustible substance. 
 
 The abundance of sulphur separated in the flame of carbon disulphide enables 
 it to burn iron by converting it into sulphide. If some carbon disulphide be 
 boiled in a test-tube provided with a piece of glass tube from which the vapour 
 may be burnt, and a piece of thin iron wire be held in the flame (Fig. 181), it will 
 burn with vivid scintillation, the fusible ferrous sulphide dropping off. 
 
 Carbon disulphide is endothermic (p. 96), 76 grams of the liquid absorbing 
 19,610 gram units in its formation ; like most other endothermic gases (C 2 H 2 , C 2 N 2 , 
 N 2 0, &c.), it may be suddenly decomposed into its elements by a violent shock. This 
 
 * This solid matter is probably a cryohydrate of CS 2 . Dry CS 2 melts at - 113 C. 
 
240 THIOCARBONATES. 
 
 experiment is performed by detonating 0.05 gram of mercuric fulminate, by means 
 of an electric spark, in an inclined tube open at one end, in which a paper satu- 
 rated with carbon disulphide has been suspended. After the explosion the carbon 
 
 and sulphur are seen deposited on the walls of 
 
 the tube. 
 
 The vapour of carbon disulphide acts 
 very injuriously if breathed for any 
 length of time, producing symptoms 
 somewhat resembling those caused by 
 sulphuretted hydrogen. Its poisonous 
 properties have been turned to account 
 for killing insects in grain without 
 injuring the grain. 
 
 The chief application of carbon disul- 
 phide depends upon its power of dissolv- 
 ing the oils and fats. After as much 
 oil as possible has been extracted from 
 seeds and fruits by pressure, a fresh 
 quantity is obtained by treating the 
 rig. 181. pressed cake with carbon disulphide, 
 
 which is afterwards recovered by dis- 
 tillation from the oil. In Algiers it is employed for extracting the 
 essential oils in which reside the perfumes of roses, jasmine, lavender, &c. 
 Carbon disulphide has often been made a starting-point in the 
 attempts to produce organic compounds by synthesis. It may be 
 employed in the formation of the hydrocarbons which are usually derived 
 from organic sources ; for if it be mixed with hydrogen sulphide (by 
 passing that gas through a bottle containing the disulphide gently 
 warmed), and passed over copper-turnings heated to redness in a porcelain 
 tube, olefiant gas will be produced; 2CS 2 + 2H 2 S + Cu 6 = 6CuS + C 2 H 4 . 
 Marsh gas may be obtained in the same way. When passed through a 
 red hot tube the vapour of CS 2 is decomposed into C and S. 
 
 The action of carbon disulphide upon ammonia is practically impor- 
 tant for the easy production of ammonium sulphocyanide, which is 
 formed when the disulphide is dissolved in alcohol, and acted on by 
 ammonia with the aid of heat ; CS 2 + 2NH 3 = H 2 S + NH 4 CNS. 
 
 Carbon disulphide is often called sulphocarbonic or thiocarbonic 
 anhydride to emphasise its analogy to carbonic anhydride ; it combines 
 with some of the sulphur-bases to form sulphocarbonates or thiocarbonates, 
 which correspond with the carbonates, containing sulphur in place of 
 oxygen. Thus, when a solution of potassium sulphide is mixed with an 
 excess of carbon disulphide, potassium thiocarbonate is obtained in 
 orange-yellow crystals. Even the hydrogen compound corresponding in 
 composition with the unknown H 2 C0 3 may be obtained as a yellow oily 
 liquid by decomposing potassium thiocarbonate with hydrochloric acid ; 
 K 9 CS 3 + 2HC1 = H 2 CS 3 + 2KC1. Potassium thiocarbonate is applied for 
 the destruction of the phylloxera insect which infests vines. As would 
 be expected, the thiocarbonates, when boiled with water, exchange their 
 sulphur for oxygen, becoming carbonates; K 2 CS 3 + 3H 2 = K 2 C0 3 + 3H 2 S. 
 
 Small quantities of CS 2 may be identified by dissolving in alcoholic potash and 
 adding cupric sulphate, which gives a yellow precipitate of cuprous xantliate, 
 Cu 2 S.CS.OC 2 H 5 . 
 
SULPHUR CHLORIDE. 241 
 
 The carbon disulphide vapour in coal gas is one of the most injurious of the 
 impurities, and one of the most difficult to remove with economy. 
 
 It is especially injurious, because, when burning in the presence of aqueous 
 vapour, a part of its sulphur is converted into sulphuric acid, the corrosive effects 
 of which are so damaging. Several processes have been devised for its removal, 
 but that which is now almost universally adopted consists in absorbing it in lime 
 which has already become saturated with H 2 S in the course of the purification of 
 the gas, and thus contains calcium hydrosulphide, Ca(SH) 2 . This compound com- 
 bines with the CS 2 to form calcium thiocarbonate, Ca(SH) 2 +CS 2 =:CaCS 3 + H2S. 
 
 Carbon monoswlphide, CS, is deposited when CS 2 is exposed to sunlight, or left 
 for some weeks in contact with iron wire ; 2CS 2 + Fe = FeS 2 + 2CS. The FeS 2 is 
 dissolved out by HC1, leaving the CS as a red-brown powder, of sp. gr. 1.66, 
 insoluble in alcohol and benzene, slightly soluble in hot ether and CS 2 . It is 
 soluble in boiling nitric acid and in boiling strong potash. At about 200 C. it 
 is decomposed into carbon, sulphur, and a little disulphide. It is converted into 
 the latter by heating with excess of sulphur. 
 
 Tricarbon disulphide, C 3 S 2 , has been obtained by boiling CS 2 in a flask, the upper 
 portion of which contains an electric arc, and condensing the vapour, after it has 
 been thus heated, so that it may fall back into the flask. It is a deep red liquid 
 (sp. gr. 1.27) which has a very irritating odour. When heated it is changed to a 
 black mass of the same percentage composition. 
 
 Cartoon Oxysulphide (COS = 60 parts by weight = 2 volumes). This com- 
 pound, which may be regarded as C0 2 in which S has been substituted for 0, is 
 formed when a mixture of carbonic oxide with sulphur vapour is acted on by 
 electric sparks, or passed through a red-hot porcelain tube ; also when carbon 
 disulphide vapour is passed over white-hot clay, and when CdS is heated in 
 COC1 2 . 
 
 It is easily prepared by gently heating potassium sulphocyanide, KCNS, with 
 oil of vitriol diluted with four-fifths of its volume of water, and collecting the gas 
 over mercury. The action of the sulphuric acid upon the sulphocyanide produces 
 hydrosulphocyanic acid ; KCNS + H 2 S0 4 = HCNS + KHS0 4 ; which is then decom- 
 posed by the water in the presence of the excess of sulphuric acid, into COS and 
 NH 3 , the latter combining with the sulphuric acid ; HCNS + H 2 = NH 3 + COS. The 
 gas has a peculiar, disagreeable odour, recalling that of carbon disulphide ; it is more 
 than twice as heavy as air (sp. gr. 2. n), and is very inflammable, burning with a 
 blue flame, and yielding C0 2 and S0 2 . Potash absorbs and decomposes it, yielding 
 carbonate and sulphide of potassium; COS + 4KOH = K 2 S + K2C0 3 + 2H 2 0. Am- 
 monia absorbs it freely, and, on evaporation, evolves H 2 S and deposits crystals of 
 urea ; COS + 2NH 3 = H 2 S + CO^H^. 
 
 141. Nitrogen tetrasulphide (N 4 S 4 ) is produced when chloride of sulphur, dissolved 
 in benzene, is acted on by gaseous ammonia, i6NH 3 + 6S 2 Cl 2 = I2NH 4 C1 + N 4 S 4 +S 8 . 
 The precipitate obtained is washed with water to remove NH 4 C1 and is then 
 fractionally crystallised from CS 2 to separate the N 4 S 4 and S, the latter being the 
 more soluble. This substance melts at 178 C. and is remarkable for its sparing 
 solubility, its irritating odour, and its explosibility when struck or sharply heated, 
 its elements being held together by a very feeble attraction. 
 
 Nitrogen pentasulphide, N 2 S 5 , is a red oil obtained by heating the tetrasulphide, 
 dissolved in CS 2 , in a sealed tube at 100 C., distilling the CS 2 , and extracting 
 the residue with ether which leaves the N 2 S 5 on evaporation. Its sp. gr. is 1.9 and 
 it melts at 10 C. It resembles iodine in odour and burns the skin. 
 
 142. Chlorides of Sulphur. The subchloride, or sulphur mono- 
 chloride (S 2 C1 2 = 135 parts by weight), is the most important of these, 
 since it is employed in the process of vulcanising caoutchouc. It is very 
 easily prepared by passing dry chlorine over sulphur very gently heated 
 in a retort (Fig. 182); the sulphur quickly melts, and the sulphur mono- 
 chloride distils over into the receiver as a yellow volatile liquid, boiling 
 at 280 F. (138 0.), which has a most peculiar odour. It fumes strongly 
 in air, the moisture decomposing it, forming hydrochloric and sulphurous 
 acids and causing a deposit of sulphur upon the neck of the bottle ; 
 
 9 C1 2 + 3 HOH = 4 H01 + SO(OH) 2 + S 3 . 
 When poured into water it sinks (sp.gr. 1.68) and slowly decomposes ; 
 
 Q 
 
242 SELENIUM. 
 
 the solution contains, beside hydrochloric arid sulphurous acids, some of 
 the acids containing a larger proportion of sulphur. If phosphorus dis- 
 solved in carbon disulphide be mixed with sulphur monochloride, the 
 liquid will take fire on addition of ammonia. The specific gravity of 
 the vapour of S 2 C1 2 is 4.7, showing that it is 68 times as heavy as- 
 hydrogen and therefore cannot have the formula SCI. 
 
 Fig. 182. Preparation of sulphur monochloride. 
 
 'iur dlchloride (SC1 2 ) is a far less stable compound than the preceding 
 chloride, from which it is obtained by the action of an excess of chlorine. It is a 
 dark-red fuming liquid, easily resolved, even by sunlight, into free chlorine and 
 sulphur monochloride. Sulphur tetrachlorlde (SC1 4 ) has also been obtained. 
 
 Corresponding bromides and iodides of sulphur are known. Of these the 
 di-iodide (SI 2 ) is a crystalline unstable substance, produced by the direct union of 
 its elements, and occasionally employed in veterinary medicine under the name 
 of black sulphur. 
 
 SELENIUM. 
 80 = 78.5 parts by weight. 
 
 143. Selenium (SeX^?;, the moon) is a rare element, very closely allied to sulphur 
 in its natural history, physical characters, and chemical relations to other bodies. 
 It is found sparingly in the free state associated with some varieties of native 
 sulphur, but more commonly in combination with metals, forming selenides, which 
 are found together with the sulphides. The iron pyrites of Fahlun, in Sweden, 
 is especially remarkable for the presence of selenium, and was the source whence 
 this element was first obtained. The Fahlun pyrites is employed for the manu- 
 facture of oil of vitriol, and in the leaden chambers a reddish-brown deposit is 
 found, which was analysed by Berzelius in 1817, and found to contain the new 
 element. 
 
 In order to extract selenium from the seleniferous deposit of the vitriol works 
 this may be boiled with sulphuric acid diluted with an equal volume of water, and 
 nitric acid added in small portions until the oxidation is completed, when no 
 more red fumes will escape. The solution, containing selenious and selenic acids, 
 is largely diluted with water, filtered from the undissolved matters, mixed with 
 about one-fourth of its bulk of hydrochloric acid, and somewhat concentrated by 
 evaporation, when the hydrochloric acid reduces the selenic to selenious acid 
 H 2 Se0 4 + 2HC1 = H 2 Se0 3 + H 2 O + C1 2 . 
 
 A current of sulphurous acid gas is now passed through the solution, when the 
 selenium is precipitated in fine red flakes, which collect into a dense black mass 
 when the liquid is gently heated ; H 2 Se0 3 + H 2 + 2S0 2 =:2H 2 S0 4 + Se. 
 
 The proportion of selenium in the deposit from the leaden chambers is variable. 
 The author has obtained 3 per cent, by this process. 
 
SELENIUM. 
 
 243- 
 
 Like sulphur, selenium exists in an amorphous and a crystalline form, and more 
 than one of the latter appear to exist. Amorphous selenium is the red precipitate 
 formed by precipitating the element, either as described above or by adding an 
 acid to a solution of it in potassium cyanide. When kept at 100 C. for some time 
 this form of selenium suddenly changes into the grey crystalline variety with 
 much evolution of heat. Amorphous selenium has sp. gr. 4.26 and is soluble 
 in CS 2 ; it becomes plastic a little above 100 C. and if melted and cooled quickly 
 it forms a vitreous mass (sp. gr. 4.28), still amorphous, but if carefully cooled so 
 that it may superfuse it solidifies to the grey crystalline form (sp. gr. 4.8) ; but 
 when less carefully cooled it solidifies to a mass of red monoclinic prisms 
 isomorphous with monoclinic sulphur and of sp. gr. 4.47. These crystalline forms 
 are insoluble in CS, 2 . 
 
 Amorphous and monoclinic selenium are very poor conductors of electricity, but 
 the grey crystalline form is a fair conductor and a better one in light than in 
 darkness, a property which is applied in apparatus for seeing at a distance. 
 
 Selenium boils at 680 C. and its vapour shows much the same variation in 
 density as that exhibited by sulphur. 
 
 Selenium is less combustible than sulphur ; when heated in air it burns with a 
 blue flame, and emits a peculiar odour like that of putrid horse-radish, which 
 appears to be due to the formation of a little selenietted hydrogen from the 
 moisture of the air. The odour serves for the detection of selenium compounds 
 when they are heated on charcoal. When heated with oil of vitriol, selenium 
 forms a green solution which deposits the selenium again when poured into water. 
 
 Selenium dioxide (Se0 2 ), corresponding with sulphur dioxide, is the product of 
 combustion of selenium in oxygen. It is best obtained by dissolving selenium in 
 boiling nitric acid (which would convert sulphur into sulphuric acid), and evapo- 
 rating to dryness, when the selenium dioxide remains as a white solid which 
 sublimes in needle-like crystals when heated. When dissolved in boiling water 
 it yields crystalline selenious acid, SeO(OH) 2 . 
 
 Selenle acid (H 2 Se0 4 or SeO 2 (OH) 2 ). Potassium selenate is formed when selenium 
 is oxidised by fused nitre ; 2KN0 3 +Se = K 2 Se0 4 + 2NO. By dissolving the potas- 
 sium selenate in water, and adding lead nitrate, a precipitate of lead selenate 
 (PbSe0 4 ) is obtained, and if this be suspended in water and decomposed by passing 
 hydrosulphuric acid gas, lead will be removed as insoluble sulphide, and a solution 
 of selenic acid will be obtained : PbSe0 4 + H 2 S = H 2 Se0 4 + PbS. This solution may 
 be evaporated till it has a sp. gr. of 2.6 (when it very closely resembles oil of 
 vitriol) and heated in a vacuum at 180 C. so long as any distils over ; the residue 
 will crystallise on cooling. The crystals (sp. gr. 2.95) melt at 58 C. and are 
 deliquescent ;-the hydrate, H 2 Se0 4 .H 2 0, melts at 25 C. It is decomposed at 260 C. 
 into H 2 5 Se0 2 , and 0. It oxidises the metals as oil of vitriol does, and even dis- 
 solves gold. The selenates closely resemble the sulphates, but they are decomposed 
 when heated with hydrochloric acid, chlorine being evolved and selenious acid 
 produced. 
 
 Hydroselenicacid, or selenietted hydrogen (H 2 Se), is the analogue of sulphuretted 
 hydrogen, and is produced by a similar process. It is even more offensive and 
 poisonous than that gas, and acts in a similar way upon metallic solutions, precipi- 
 tating the selenides. 
 
 There are two chlorides of selenium : the monochloride, Se 2 Cl 2 , a brown volatile 
 liquid corresponding with sulphur monochloride ; and the tetrachloride, SeCl 4 , a 
 white crystalline solid. SeOCl 2 is also known. 
 
 Notwithstanding the resemblance between the two elements, sulphides oj 
 selenium are known, probably SeS 2 and SeS 3 . The former is obtained as a yellow 
 precipitate when hydrogen sulphide is passed into solution of selenious acid. 
 
 TELLURIUM. 
 
 Te= 126 parts by weight. 
 
 144. Tellurium (from tellus, the earth) is connected with selenium by analogies 
 stronger than those which connect that element with sulphur. It is even less 
 frequently met with than selenium, being found chiefly in certain Transylvanian 
 gold ores. It occasionally occurs in an uncombined form, but more frequently in 
 combination with metals. It has recently been found in Colorado, masses of 
 native tellurium up to 12 kilos, in weight having been met with ; also coloradoite, 
 
244 TELLURIUM. 
 
 or murcuric telluride, HgTe. Bismuth telluride, or tetradymite, Bi 2 Te 3 , has been 
 found in California, and lead telluride, or altaite, in North Carolina. Foliated or 
 .graphic tellurium, or sylvanite, is a black material containing the tellurides of 
 silver and gold. Arsenical pyrites sometimes contains tellurium, apparently as 
 TeS 2 . 
 
 Tellurium is extracted from the foliated ore by a process similar to that for 
 'obtaining selenium. From bismuth telluride it is procured by strongly heating the 
 ore with a mixture of potassium carbonate and charcoal, when potassium telluride 
 is formed, which dissolves in water to a purple-red solution, wherefrom tellurium 
 is deposited on exposure to air ; K 2 Te -\- + H 2 = 2KOH + Te. It is purified by 
 sublimation in hydrogen when it is deposited as white lustrous hexagonal rhornbo- 
 liedra, isomorphous with S and Se. 
 
 Considerable quantities of tellurium are now obtainable from the sludge 
 deposited in the electrolytic cells in which copper is refined, the crude metal 
 having collected the tellurium contained in the original ore. 
 
 Tellurium much more nearly resembles the metals than the non-metals in its 
 physical properties (sp. gr. 6.2), and is on that account often classed among the 
 former, but it is not capable of forming a true basic oxide. In appearance it is 
 very similar to bismuth (with which it is so frequently found), having a pinkish 
 metallic lustre, and being, like that metal, crystalline and brittle. When precipi- 
 tated it is a black amorphous powder, which becomes crystalline, with evolution of 
 much heat, when warmed. It fuses at 455 C. and boils, yielding a yellow vapour, 
 of normal vapour density, at 1390 C. When heated in air it burns with a blue 
 flame edged with green, and emits fumes of tellurium dioxide (Te0 2 ) and a peculiar 
 odour. 
 
 Like selenium, tellurium is dissolved by strong sulphuric acid, yielding a purple- 
 red solution, from which water precipitates it unchanged. 
 
 The oxides of tellurium correspond in composition with those of sulphur. Tellu- 
 rous acid (H 2 Te0 3 ) is precipitated when a solution of tellurium in dilute nitric acid 
 is poured into water. If the nitric solution is boiled, a crystalline precipitate of 
 tellurous anhydride, Te0 2 , is obtained, but when the solution is evaporated a well 
 crystallised basic nitrate, Te 2 O 3 (OH)N0 3 , separates. Unlike selenious acid tellurous 
 acid is sparingly soluble in water. The anhydride is easily fusible, forming a 
 yellow glass, which becomes white on cooling, and may be sublimed unchanged. 
 Tellurous acid is rather a feeble acid, and with some of the stronger acids the 
 anhydride forms soluble compounds in which it takes the part of a very feeble base. 
 
 Telluric acid (H 2 Te0 4 ) is also a feeble acid obtained by oxidising tellurium with 
 nitre, precipitating the potassium tellurate with barium chloride, and decomposing 
 the barium tellurate with sulphuric acid. On evaporating the solution, crystals of 
 telluric acid (H 2 Te0 4 .2H 2 0) are obtained, which become H 2 Te0 4 at a moderate heat, 
 and when heated nearly to redness are converted into an orange-yellow powder, 
 which is the anhydride, Te0 3 . In this state it is insoluble in acids and alkalies. 
 When strongly heated it evolves oxygen, and becomes tellurous anhydride. The 
 tellurates are unstable salts which are converted into tellurites when heated. Solu- 
 tions of alkali tellurates yield a precipitate of tellurium when boiled with alkali 
 carbonates and glucose. 
 
 Telluretted hydrogen or hydrotelluric acid (H 2 Te) exhibits in the strongest 
 manner the chemical analogy of tellurium with selenium and sulphur. It is a gas 
 of dreadful odour and similar to H 2 S in most of its properties. When its aqueous 
 solution is exposed to the air, it yields a brown deposit of tellurium. When passed 
 into metallic solutions it precipitates the tellurides. The gas is prepared by decom- 
 posing telluride of zinc with hydrochloric acid. 
 
 The most characteristic property of tellurium compounds is that of furnishing 
 the purple solution of potassium telluride when fused with potassium carbonate 
 and charcoal, and treated with water ; in the total absence of oxygen, however, 
 the solution is colourless. Two solid chlorides of tellurium have been obtained ; 
 TeCl 2 is a black solid with a violet-coloured vapour, and is decomposed by water 
 into tellurium and TeCl 4 . The latter may be obtained as a white crystalline volatile 
 solid, decomposed, by much water, into hydrochloric and tellurous acids. 
 
 145. Review of the sulphur group of elements. The three 
 divalent elements sulphur, selenium, and tellurium exhibit a relation 
 of a similar character to that observed between the members of the 
 chlorine group, both in their physical and chemical properties. 
 
BORIC ACID. 
 
 2 45 
 
 Sulphur is a pale yellow solid, easily fusible and volatile, without any 
 trace of metallic lustre, and of sp. gr. 2.05, melting at 118 and boiling 
 at 444 C. Selenium is either a red powder or a lustrous mass appearing 
 black, but transmitting red light through thin layers, of specific gravity 
 4.8, melting-point 217 C., and boiling-point 680 C. Tellurium has a 
 brilliant metallic lustre, sp. gr. 6.2, melting-point 455 C., and boiling- 
 point 1390 C. 
 
 Sulphur (atomic weight 32) has the most powerful attraction for 
 oxygen, hydrogen, and the metals. Selenium (atomic weight 79) ranks 
 next in the order of chemical energy. Tellurium (atomic weight 126.5) 
 has a less powerful attraction for oxygen, hydrogen, and the metals, 
 than either sulphur or selenium has. This element appears to stand on 
 neutral ground between the non-metallic bodies and the less electro- 
 positive metals. 
 
 BORON. 
 
 B'"= II parts by weight. 
 
 This element resembles carbon in several respects, but is not properly 
 classed therewith because it is of the trivalent type, while carbon is 
 tetravalent. The element itself does not possess much importance ; it 
 is found only in combination with oxygen in the mineral world, whence 
 very small quantities find their way into some plants such as the grape- 
 vine and into sea-water. The oxide will be considered first. 
 
 Boric anhydride, or Anhydrous Boric Acid (B 2 O 3 = 69.8 parts by 
 weight). A saline substance called borax (Na 2 B 4 O 7 .ioAq) has long 
 been used in medicine, in working metals, and in making imitations of 
 precious stones ; this substance was originally imported from India and 
 Thibet, where it was obtained in crystals from the waters of certain 
 lakes, and came into this country under the native name of tincal, 
 consisting of impure borax, surrounded with a peculiar soapy substance. 
 Borax has recently been found in abundance in the bed of a dried-up 
 lake in the Sierra Nevada. 
 
 In 1702, in the course ot one of those experiments to which, though 
 empirical in their nature, scientific chemistry is now so deeply indebted, 
 Homberg happened to distil a mixture of borax and green vitriol (ferrous 
 sulphate), when he obtained a new substance in pearly plates, which was 
 found useful in medicine, and received the name of sedative salt. A 
 quarter of a century later Lemery found that this substance might be 
 separated from borax by employing sulphuric acid instead of ferrous 
 sulphate, and that it possessed acid properties, whence it was called 
 boracic acid, now abbreviated to boric acid. 
 
 Much more recently this acid has been obtained in a free state from 
 natural sources, and is now largely imported into this country from the 
 volcanic districts in the north of Italy, where it issues from the earth 
 in the form of vapour, accompanied by violent jets of steam, which are 
 known in the neighbourhood as soffioni. It would appear easy enough, 
 by adopting arrangements for the condensation of this steam, to obtain 
 the boric acid which accompanies it, but it is found necessary to cause 
 the steam to deposit its boric acid by passing it through water, for 
 which purpose basins of brickwork (lagunes, Fig. 183) are built up 
 around the soffioni, and are kept filled with water from the neighbouring 
 
246 
 
 BOEIC ACID. 
 
 springs or brooks ; this water is allowed to flow successively into the 
 different lagunes, which are built upon a declivity for that purpose, and 
 it thus becomes impregnated with about i per cent, of boric acid. The 
 necessity for expelling a large proportion of this water, in order to 
 obtain the boric acid in crystals, formed for a long time a great obstacle 
 to the success of this branch of industry in a country where fuel is very 
 expensive. In 1817, however, Larderello conceived the project of 
 evaporating this water by the steam-heat afforded by the soffioni them- 
 selves, and several hundred tons of boric acid are now annually produced 
 in this manner. The evaporation is conducted in shallow leaden evapo- 
 rating pans (A, Fig. 183), under which the steam from the soinoni is 
 conducted through the flues (F) constructed for that purpose. As the 
 demand for boric acid increased on account of the immense consumption 
 of borax in the porcelain manufacture, the experiment was made, with 
 success, of boring into the volcanic strata, and thus producing artificial 
 sofiiom, yielding boric acid. 
 
 Fig. 183. Boracic lagune and evaporating pans. 
 
 The crystals of boric acid, as imported from these sources, contain 
 salts of ammonia and other impurities. They dissolve in about three 
 times their weight of boiling water, and crystallise on cooling, since 
 they require 26 parts of cold water to dissolve them. These crystals 
 have the sp. gr. 1*435 an( ^ are represented by the formula 3H 2 O.B 2 O 3 
 (or H 3 B0 3 , or B(OH) 3 ). If they are sharply heated in a retort they 
 partly distil unchanged, together with the water derived from the 
 decomposition of another part ; but if they be not heated above 212 F., 
 they effloresce and become H 2 O.B 2 O 3 .* When heated for a long time to 
 140 C. this becomes H 2 0. 2 B 2 3 ," sometimes written H 2 B 4 O 7 , and called 
 pyroboric acid, whilst H 2 O.B 2 3 is HB0 2 , metaboric acid, and the crystals, 
 H 3 B0 3 , are orthoboric acid. When pyroboric acid is heated further 
 the whole of the water passes off, carrying with it a little boric acid, 
 and the B 2 3 fuses to a glass, which remains perfectly transparent on 
 cooling (vitreous boric acid}. This is slowly volatilised by the continued 
 action of a very high temperature. It dissolves very slowly in water. 
 Boric acid is an antiseptic, i.e., it hinders putrefaction, and is applied, 
 either alone or in combination with glycerine, for the preservation of 
 milk, meat, and other foods. It is also said to kill grass. 
 
 * According to Hehner, boric acid can be completely volatilised at 100 C. without at 
 any stage having the composition H 2 O.B 2 O S . 
 
BORATES. 
 
 2 47 
 
 A characteristic property of boric acid is that of imparting a green 
 colour to flames. Its presence may thus be detected in the steam 
 issuing from a boiling solution of boric acid in water ; for if a spirit- 
 flame or a piece of burning paper is held in the steam, the flame acquires 
 a green tint, especially at the edges. 
 
 The colour is more distinctly seen when the crystallised boric acid is heated on 
 platinum foil in a spirit-flame or an air-gas flame ; and still better when the 
 crystals are dissolved in boiling alcohol, and the solution burnt on a plate. The 
 presence oi ! boric acid in borax may be ascertained by mixing the solution of borax 
 with strong sulphuric acid to liberate the boric acid, and adding enough alcohol to 
 make the mixture burn ; or by moistening the borax with glycerine, when it gives 
 a green flame in the Bunsen burner. Another peculiar property of boric acid is its 
 action upon turmeric. If a piece of turmeric paper be dipped in solution of boric 
 acid and dried at a gentle heat, it assumes a fine brown-red colour, which is 
 changed to green or blue by potash or its carbonate. In applying this test to borax, 
 the solution is slightly acidified with hydrochloric acid, to set free the boric acidj 
 before dipping the paper. In the presence of oxalic acid the test is more delicate. 
 
 Bwates. Boric acid, like carbonic, must be classed among the feeble 
 acids. It colours litmus violet only, like carbonic acid, and does not 
 neutralise the action of the alkalies upon test-papers. At high tem- 
 peratures, fused boric anhydride combines with the alkalies and 
 metallic oxides to form transparent glassy borates, which have, in many 
 cases, very brilliant colours, and upon this property depend the chief 
 uses of boric acid in the arts. 
 
 Unlike the silicates, the borates are comparatively rare in the 
 mineral world. No very familiar mineral substance, except borax, 
 contains boric acid. A double borate of sodium and calcium, called 
 boro-natrocalcite, Na 2 B 4 O 7 .(CaB 4 O 7 ) 2 .i8H 2 0, is imported from Peru for 
 the manufacture of borax, and the mineral known as boracite is a 
 magnesium borate. The mineral tourmaline, an aluminium-ferrous 
 silicate, contains a considerable proportion of B 2 3 , apparently sub- 
 stituted for part of the A1 2 O 3 . 
 
 In determining the proportion of base which boric acid requires to form a chemi- 
 cally neutral salt, the same difficulties are met with as in the case of silicic acid 
 (p. 280) ; but since it is found that 69.8 parts of boric anhydride (the weight repre- 
 sented by B 2 3 ) displace 54 parts of water (three molecules) from sodium hydroxide 
 and from barium hydroxide, each employed in excess, it would appear that the 
 boric acid requires three molecules of an alkali fully to satisfy its acid character, 
 6NaOH + B 2 O 3 =2Na 3 B0 3 + 3H.,O. Hence, boric acid is a tribasic acid represented 
 by the formula H 3 BO 3 , which is the composition of the crystallised acid, but the 
 formula? of the common borates cannot be made to accord with this view. The 
 only orthoborate yet obtained is Mg 3 (BO 3 ) 2 . 
 
 The acid character of boron oxide (B 2 3 ) is so feeble as compared with that of 
 such anhydrides as S0 3 and P 2 5 , that boron oxide can even behave as a feeble 
 base towards these powerful acid oxides, forming salts such as B 2 3 . P 2 5 . 
 
 By treating borates with H 2 O 2 , or by electrolysing them as for the production of 
 persulphates (p. 235), perborates such as Na 3 B0 4 are obtained. They are unstable 
 and rapidly lose oxygen. 
 
 146. Boron. It was in the year 1808 that Gay-Lussac and Thenard 
 succeeded, by fusing boric anhydride with potassium, in isolating boron. 
 The element is more easily prepared by fusing magnesium with an 
 excess of boric acid and treating the product successively with alkalies 
 and acids. The amorphous boron thus obtained is a maroon-coloured 
 powder of sp. gr. 2.45. It is infusible, burns with a green flamo at 
 700 C., and is a very poor conductor of electricity. This form of 
 
248 BOEON CHLORIDE. 
 
 boron is attacked by hot concentrated mineral acids ; it behaves like 
 charcoal in its tendency to absorb gases. 
 
 The so-called diamond of boron is obtained by very strongly heating 
 amorphous boron with aluminium, extracting the aluminium from the 
 mass with hydrochloric acid, and afterwards separating the crystals of 
 mixed boron and aluminium from those of boron by boiling with nitric 
 acid. These crystals are brilliant transparent octahedra (sp. gr. 2.68), 
 which are sometimes nearly colourless, and resemble the diamond in 
 their power of refracting light, and in their hardness, which is so great 
 that they will scratch rubies, and will even wear away the surface of 
 the diamond.* This form of boron cannot be attacked by any acid, 
 but is dissolved by fused alkalies. It only undergoes superficial con- 
 version into boric anhydride when heated to whiteness in oxygen. 
 
 Boron forms a compound with hydrogen which has never been 
 obtained free from admixed hydrogen, but probably has the formula 
 BH 3 ; it is an inflammable gas, burning with a green flame, and is 
 obtained by heating fused boric anhydride with magnesium and treating 
 the mass with hydrochloric acid. Boron shows greater disposition to 
 combine with nitrogen than is manifested by most other elements. It 
 absorbs nitrogen readily when heated to redness, forming a white in- 
 fusible insoluble powder, the boron nitride (BN). 
 
 Boron nitride is also obtained by heating to redness anhydrous borax 
 with twice its weight of ammonium chloride and extracting with dilute 
 HC1 which leaves the nitride undissolved. When heated in steam it 
 yields boric acid and ammonia; BN + 3H 2 O = H 3 B0 3 + NH 3 . When 
 heated in air it phosphoresces greenish. 
 
 Boron carbide, CB 6 , is produced when boron and carbon are heated together in 
 the electric furnace, best in the presence of silver which dissolves both elements 
 and enables the carbide to crystallise. It is black and remarkably hard, ranking 
 next to diamond in this respect. It burns in oxygen at a high temperature, and is 
 attacked by fused alkalies but not by acids. 
 
 Boron trichloride, BC1 3 . Boron burns'^when heated at 410 C. in 
 chlorine forming the trichloride, which is more conveniently prepared 
 by heating a mixture of boric acid and charcoal in chlorine; 
 B 2 3 + C 3 + C1 6 =2BC1 3 + 3CO. It is a liquid of sp.gr. 1.35 and boils 
 at 17 C. It is the chloranhydride (p. 191) of metaboric acid, being 
 decomposed by water thus: BC1 3 + 3 H 2 = B(OH) 3 + 3HC1. It has a 
 remarkable tendency to combine with other chlorides. 
 
 147. Boron trifluoride (BF 3 ), may be prepared by strongly heating a mixture 
 of powdered boric anhydride with twice its weight of fluor spar in an iron tube ; 
 3CaF 2 + B 2 3 = 3CaO + 2BF 3 . 
 
 The boron fluoride is a gas which fumes strongly in moist air, like the silicon 
 fluoride. It is absorbed eagerly by water, with evolution of heat. One volume of 
 water at o C. is capable of dissolving 1057 volumes of boron fluoride, producing a 
 corrosive heavy liquid (sp. gr. 1.77), which fumes in air, and chars organic sub- 
 stances on account of its attraction for water. This solution is known as fluo ~boriv 
 or boro fluoric acid, and its formation is explained by the equation 2BF 3 + 3H 2 O = 
 B 2 3 .6HF (Fluoloric acid). 
 
 When the solution is heated, it evolves boron fluoride, until its specific gravity is 
 reduced to 1.58, when it distils unchanged. 
 
 Hydrofluoboric acid is obtained in solution by adding a large quantity of water 
 to fluoboric acid ; 2(B 2 3 .6HF) = H 3 B0 3 + 3H 2 + 3HBF 4 (hydrofuoboric acid). 
 
 * The author has known them to cut through the bottom of the beaker used in separa- 
 ting them from the aluminium. 
 
SOURCES OF PHOSPHORUS. 249 
 
 The hydrogen of this acid may be exchanged for metals to form borqfliwrides,. 
 which have been applied as antiseptics. Ammonium borofluoride NH 4 BF 4 is pro- 
 duced when boron nitride is heated with hydrofluoric acid. 
 
 Boron trimlpltide, B 2 S 3 , is made by strongly heating boron in H 2 S ; it forms 
 white needles, melts at 310 C., and yields B(OH) 3 and H 2 S when in contact with 
 water. Bo ron pentasulphide, B 2 S 5 , is a white crystalline powder (m.p. 390 C.)made 
 by heating BI 3 with S in CS 2 at 60. It is decomposed by water into B(OH) 3 , H 2 S 
 and S. 
 
 PHOSPHORUS. 
 
 P = 3i parts by weight.* 
 
 148. This element is never known to occur uncombined in nature,, 
 but is found abundantly in the form of phosphate of lime or tricalcic 
 diphosphate, 3CaO.P 2 5 or Ca 3 (P0 4 ) 2 , which is contained in the minerals 
 coprohte, phosphorite, and apatite, and occurs diffused, though generally 
 in small proportion, through all soils upon which plants will grow ; for 
 phosphorus, probably in this form, is an essential constituent of the 
 food of plants, and especially of the cereal plants, which form so large a 
 proportion of the food of animals. The seeds of such plants are espe- 
 cially rich in the phosphates of calcium and magnesium. 
 
 Animals feeding upon these plants still further accumulate the phos- 
 phorus, for it enters, chiefly in the form of calcium phosphate, into the 
 composition of almost every solid and liquid in the animal body, and is 
 especially abundant in the bones, which contain about three-fifths of 
 their weight of calcium phosphate. 
 
 Composition of the Bones of Oxen. 
 
 Fat 5.4 
 
 Nitrogenous matter 28.6 
 
 Calcium phosphate 56.5 
 
 fluoride 1.2 
 
 carbonate 7.3 
 
 Magnesium phosphate i.o 
 
 100.00 
 
 What is here termed nitrogenous matter is a cartilaginous substance, converted 
 into gelatine when the bones are heated with water under pressure, and containing^ 
 C, H, N and 0. It was formerly the custom to get rid of this by burning the bones 
 in an open lire, but the increased demand for chemical products, and the diminished 
 supply of bones, have taught economy, so that the cartilaginous matter is now 
 dissolved out by heating the bones with water at a high pressure for the manufac- 
 ture of glue ; or the bones are subjected to destructive distillation, so as to save 
 the ammonia which they evolve, and the bone charcoal thus produced is used by 
 the sugar-refiner until its decolorising powers are exhausted, when it is heated in 
 contact with air to burn away the charcoal, and leave the bone-asli, consisting 
 chiefly of calcium phosphate, Ca 3 (P0 4 ) 2 , and valuable as a manure, 
 
 Originally, phosphorus was made from bone-ash, but now the cheaper 
 calcium phosphate of mineral origin is employed as the raw material. 
 The coprolites, or other phosphates, are ground to powder and mixed 
 with enough chamber acid (H 2 S0 4 ) to convert the calcium into sulphate 
 and to liberate the phosphoric acid ; Ca 3 (P0 4 ) 2 + 3H 2 S0 4 = 3CaS0 4 + 
 2H 3 P0 4 . The liquor is evaporated and the solution of phosphoric acid 
 
 * The vapour of phosphorus is 62 times as heavy as hydrogen, so that its atom only 
 occupies half a volume, if the atom of hydrogen be taken to occupy one volume ; and the 
 molecule of phosphorus (P 4 ) occupying two volumes, would consist of four atoms instead of 
 two. At very high temperatvu-es the specific gi'avity of phosphorus vapour diminishes, 
 showing a tendency to conform with the ordinary law of volumes. 
 
250 PROPERTIES OF PHOSPHORUS. 
 
 separated from the calcium sulphate by filtration. This solution is 
 further evaporated to a syrup, absorbed by charcoal and dried, during 
 which the phosphoric acid loses water, becoming inetaphosphoric acid, 
 H 3 P0 4 = HPO 3 -f 2H 2 0. It is now only necessary to distil the mixture 
 of charcoal and metaphosphoric acid in bottle-shaped fireclay retorts 
 set in a furnace. The phosphorus distils, hydrogen and carbon mon- 
 oxide being evolved at the same time (4HP0 3 + C 12 = i2CO + P 4 + H 4 ), 
 and is condensed under warm water in which it melts. It is far from 
 pure, having a mahogany colour ; to eliminate this it is remelted with 
 a mixture of sulphuric acid and potassium bichromate ; the impuri- 
 ties are thus oxidised and the phosphorus becomes yellow. It is 
 cast into sticks or wedges which are packed in tins, containing water, 
 for the market. The yield is only 70 per cent, of the theoretical 
 yield. 
 
 Instead of liberating the phosphoric acid from the calcium phosphate 
 by sulphuric acid as described above, advantage may be taken of the 
 fact that at very high temperatures silicic anhydride (SiO 2 ), being less 
 volatile than phosphoric anhydride (P 2 O 5 ), can expel the latter from 
 its combination with lime, although a less powerfully acid oxide ; 
 Ca 3 (P0 4 ) 2 + 3SiO 2 = 30aSiO 3 + P 2 O 5 . The temperature of the electric 
 furnace (p. 138), however, is essential for this reaction; accordingly, 
 on a commercial scale a mixture of calcium phosphate, sand (Si0 2 ) and 
 coke (C) is heated in such a furnace provided with an arrangement for 
 collecting the phosphorus which distils from the mixture. The carbon 
 of the coke reduces the P 2 O 5 liberated according to the above equation ; 
 P.O. + O.-P. + sCO. 
 
 On a small scale, for the sake of illustration, phosphorus may be prepared by a 
 process which has also been successfully employed for its manufacture in quantity, 
 and consists in heating a mixture of bone-ash and charcoal in a stream of hydro- 
 chloric acid gas ; Ca 3 (P0 4 ) 2 + 6HC1 + C 8 = 3CaCl 2 + SCO + H 6 + P 2 . 
 
 A mixture of equal weights of well-dried charcoal and bone-ash, both in fine 
 powder, is introduced into a porcelain tube, and placed in a gas furnace. One end 
 of the tube is connected with a flask evolving HC1 (p. 177), and the other is 
 cemented with putty into a bent tube for conveying the phosphorus into a vessel 
 of water. On heating the porcelain tube to bright redness, phosphorus distils in 
 abundance. The hydrogen and carbonic oxide inflame as they escape into the air, 
 from their containing phosphorus vapour. 
 
 Pure ordinary, or vitreous, phosphorus is almost colourless and trans- 
 parent, but when exposed to light, and especially to direct sunlight, it 
 gradually acquires an opaque red colour, from its conversion into the 
 allotropic variety known as red phosphorus. By tying bands of black 
 cloth round a stick of phosphorus and exposing it, under water, to the 
 action of sunlight, alternate zones of red may be produced. 
 
 Even though the phosphorus be screened from light, it will not re- 
 main unchanged unless the water be kept quite free from air, which 
 irregularly corrodes the surface of the phosphorus, rendering it white 
 and opaque. This action is accelerated by exposure to light. 
 
 The most remarkable character of ordinary phosphorus is its easy 
 inflammability. It inevitably takes fire in air when heated a little 
 above its melting-point, 44 C. (m.5 F.), burning with a brilliant 
 white flame, which becomes insupportable when the combustion is in 
 oxygen (p. 34), and evolving dense white clouds of phosphoric anhydride. 
 When a piece of dry phosphorus is exposed to the air, it combines 
 
PHOSPHORESCENCE. 251 
 
 slowly with oxygen,* and its temperature often becomes so much 
 elevated during this slow combustion, that it melts and takes fire, 
 especially if the combustion be encouraged by the warmth of the hand 
 or by friction. Hence, ordinary phosphorus must never be handled or 
 cut in the dry state, but always under water, for it causes most painful 
 burns. 
 
 The slow oxidation of phosphorus is attended with that peculiar 
 luminous appearance which is termed phosphorescence (0ws, light, 0f'(ow, 
 to bear), but this glow is not seen in pure oxygen, except under 
 diminished pressure, or in air containing a minute proportion of olefiant 
 gas or oil of turpentine ; nor will phosphorus glow in compressed air at 
 the ordinary temperature. It will be remembered that the slow 
 oxidation of phosphorus in moist air is attended with the formation 
 of ozone. 
 
 The glow of phosphorus, which maybe regarded as an incipient flame, 
 is in some way connected with this ozone (possibly produced during the 
 oxidation of the phosphorus to P 2 O 5 ; P 2 + 363 = P 2 O 5 + O and 2 + = 3 ). 
 When phosphorus is exposed to pure oxygen at the ordinary pressure, 
 oxidation seems to proceed very slowly at the ordinary temperature ; 
 tout at an elevated temperature (25 C), or in oxygen at diminished 
 pressure,t the phosphorus is oxidised with formation of P 2 5 (and 
 ozone) and P 4 6 . This latter oxide is readily oxidised to P 2 O 5 and 
 phosphoresces during the change, particularly in the presence of ozone. 
 Moisture is essential to the oxidation (and the glow) of phosphorus at 
 any pressure. . 
 
 Ordinary phosphorus is slowly vapourised at common temperatures, 
 and emits in the air white fumes with a peculiar alliaceous odour, 
 which appear phosphorescent in the dark. It boils at 278 C., yielding 
 a colourless vapour. 
 
 The characteristic behaviour of phosphorus in air is best observed when the 
 phosphorus is in a finely divided state. The experiment described on p. 34 (Fig. 26) 
 will serve as an illustration. 
 
 If phosphorus be dissolved in olive oil, at a gently heat, the solution is strongly 
 phosphorescent when shaken in a bottle containing air, or rubbed upon the hand. 
 
 Characters may be written on paper with a stick of phosphorus held in a 
 thickly folded piece of damp paper (having a vessel of water at hand into which 
 to plunge the phosphorus if it should take fire). When the paper is held with its 
 back to the fire, or to a hot iron, in a darkened room, a twinkling combustion of 
 the finely divided phosphorus ensues and the letters are burnt into the paper. 
 Phosphorus which has been partly oxidised is even more easily inflamed than pure 
 phosphorus. If a few small pieces of phosphorus be placed in a dry stoppered 
 bottle, gently warmed till they melt, and then shaken round the sides of the bottle 
 so as to become partly converted into red oxide of phosphorus, it will be found, 
 long after the bottle is cold, to be spontaneously inflammable, so that if a wooden 
 match tipped with sulphur be rubbed against it, the phosphorus which it takes up 
 will ignite when the match is brought into the air. kindling the sulphur, which will 
 inflame the wood. This was one of the earliest forms in which phosphorus was 
 employed for the purpose of procuring an instantaneous light. If the stopper be 
 greased, the phosphorus may be preserved unchanged for a long time. 
 
 In the last experiment, if the wood had not been tipped with sulphur, the 
 
 * The white fumes evolved by phosphorus in moist air are said to consist partly of 
 ammonium nitrate, formed by the action of the ozonised oxygen (p. 65) upon the air and 
 aqueous vapour. 
 
 f It will be remembered that the pressure of the oxygen in the air is only about one-fifth 
 of the total pressure, BO that air contains oxygen at diminished pressure. The extent to 
 which the pressure must be diminished for the production of the glow depends on the tem- 
 perature. 
 
252 EED PHOSPHORUS. 
 
 phosphorus would not have kindled it, the flame of phosphorus generally being" 
 unable to ignite solid combustibles, because it deposits upon them a coating of 
 P 2 5 , which protects them from the action of air. Hence, in the manufacture of 
 lucifer matches, the wood is first tipped with sulphur, or wax, or paraffin, which 
 easily give off combustible vapours to be kindled by the flame of the phosphorus 
 composition, and thus to inflame the wood. 
 
 If a small stick of phosphorus be carefully dried with filtering paper, and dropped 
 into a cylinder of oxygen, which is afterwards covered with a glass plate, no- 
 luminosity will be observed in a darkened room until the cylinder is placed under 
 the air-pump receiver, and the air slowly exhausted. When the oxygen has thus 
 been rarefied to about one-fifth of its former density, the phosphorescence will be 
 seen. A similar effect may be produced by covering the cylinder of oxygen con- 
 taining the phosphorus (having removed the glass 
 plate) with another cylinder, about four times its 
 size (Fig. 184), filled with carbonic acid gas, which 
 will gradually dilute the oxygen and produce the 
 phosphorescence. By suspending in a bottle of 
 air containing a strongly luminous piece of phos- 
 phorus a piece of paper with a drop of oil of turpen- 
 tine upon it, the glow may be almost instantane- 
 ously destroyed. A small tube of olefiant gas or 
 coal gas dropped into the bottle will also extinguish 
 the luminosity.* 
 
 The luminosity of phosphorus vapour is seen to 
 advantage when a piece of phosphorus is boiled with 
 water in a narrow-necked flask or retort, or a test- 
 Fig-. 184. tube with a cork and narrow tube. The steam 
 charged with vapour of phosphorus has all the 
 
 appearance of a blue flame, in a darkened room, but of course combustibles are 
 not inflamed by it, since its temperature is not higher than 100 C. Phos- 
 phorus may be distilled, with perfect safety, in an atmosphere of carbonic acid 
 gas, the neck of the retort being allowed to dip under water in the receiver. 
 
 Advantage is taken of the fact that phosphorus distils in steam and renders it 
 luminous in testing for this poison in organic liquids. Very small quantities may 
 thus be detected. Conversely, the glow of phosphorus vapour may serve as a delicate 
 test for oxygen, as it can be detected until the last trace of this gas has dis- 
 appeared. 
 
 Although ordinary phosphorus is of a decidedly glassy or vitreous 
 structure, it may be obtained in dodecahedral crystals, by allowing its 
 solution in carbon disulphide to evaporate in an atmosphere of carbonic 
 acid gas, or by fusing it in a tube exhausted by a Sprengel pump, and 
 letting it cool in the dark. 
 
 The conversion of ordinary phosphorus into the red phosphorus is one 
 of the most striking instances of allotropic modification. When phos- 
 phorus is heated for a considerable length of time to about 450 F. 
 (232 C.) in vacuo, or in an atmosphere in which it cannot burn, it 
 becomes converted into an infusible mass of red phosphorus, 27,000 
 gram units of heat being evolved for every 31 grams converted. This 
 form of phosphorus differs as widely from, the vitreous form as graphite 
 differs from diamond. It is only slowly oxidised in warm moist air, 
 evolves no vapour, is not luminous, cannot be inflamed by friction, or 
 even by any heat short of 500 F. (260 C.) When it is heated above 
 350 C. it slowly sublimes as yellow phosphorus. By heating vitreous 
 phosphorus in an exhausted and sealed tube to about 500 C., it is con- 
 verted into a violet-black fused mass with cavities containing crystals. 
 Red phosphorus is insoluble in the solvents for ordinary phosphorus. 
 The two varieties also differ greatly in specific gravity, that of the 
 
 * Chappuis finds that when phosphorus is suspended in oxygen, the space glows for a 
 short time on adding a little ozone. 
 
PROPERTIES OF RED PHOSPHORUS. 
 
 253 
 
 Fig-. 185. 
 
 ordinary phosphorus being 1.83, and of the red variety 2.14. Of the 
 two, the red variety is the better conductor of electricity. 
 
 The conversion of vitreous into red phosphorus, or amorphous phosphorus as it was 
 called before it was proved to be microscopically crystalline, may be effected by 
 heating it in a flask (A, Fig. 185) placed in an oil-bath (B), maintained at a tempera- 
 ture ranging from 450 to 460 F. (232 to 238 C.), the flask being furnished with 
 ;abent tube (C) dipping into mercury, and with another tube (D) for supplying car- 
 bonic acid gas, dried by passing over calcium chloride. The flask should be 
 thoroughly filled with carbonic acid gas before applying heat, and the tube delivering 
 it may then be closed with a small clamp (E). After exposure to heat for about 
 forty hours, but little ordinary phosphorus will remain, and this may be removed 
 by allowing the mass to remain in 
 -contact with carbon disulphide for 
 some hours, and subsequently washing 
 it with fresh disulphide till the latter 
 leaves no phosphorus when evaporated. 
 
 On the large scale, the red phos- 
 phorus is prepared by heating about 
 200 Ibs of vitreous phosphorus to 450 
 F. (232 C.) in an iron boiler. After 
 three or four weeks the phosphorus is 
 found to be converted into a hard red 
 brittle mass, which is ground by mill- 
 stones under water, and separated 
 from the ordinary phosphorus either 
 by carbon disulphide or caustic soda, 
 in which the latter is soluble. The 
 temperature requires careful regula- 
 tion, for if it be allowed to rise to 
 350 C., the red phosphorus resumes 
 the vitreous condition. This reconversion may be shown by heating a little red 
 phosphorus in a narrow test-tube, when drops of vitreous phosphorus condense on 
 the cool part of the tube. The colour of different specimens of red phosphorus 
 varies considerably, depending upon the temperature at which the conversion has 
 been effected ; that prepared on the large scale is usually of a dark purplish colour, 
 but it may be obtained of a bright scarlet colour. Rhombohedral crystals of the 
 red phosphorus, resembling crystals of arsenic in form and metallic appearance, have 
 been obtained by fusing phosphorus with lead, and dissolving out the latter with 
 diluted nitric acid (sp. gr. i.i). Similar crystals have been obtained by heating 
 red phosphorus to 530 C. hi a vacuous tube. 
 
 Ordinary phosphorus is very poisonous (o. i gram being fatal), whilst 
 red phosphorus appears to be harmless. The former is employed, 
 mixed with fat by substances, for poisoning rats and beetles. Cases are, 
 unhappily, not very rare, of children being poisoned by sucking the 
 phosphorus composition on lucif er matches. The vapour of phosphorus 
 also produces a very injurious effect upon the persons engaged in the 
 manufacture of lucifer matches, resulting in the decay of the lower 
 jaw-bone. The evil is much mitigated by good ventilation, or by diffus- 
 ing turpentine vapour through the air of the workroom, and attempts 
 have been made to obviate it entirely by substituting red phosphorus 
 for the ordinary variety, but, as might be expected, the matches thus 
 made are not so sensitive to friction as those in which the vitreous 
 phosphorus is used. 
 
 The difference between the two varieties of phosphorus, in respect to 
 chemical energy, is seen when they are placed in contact with a little 
 iodine on a plate, when the ordinary phosphorus undergoes combustion 
 and the red phosphorus remains unaltered. 
 
 Ordinary phosphorus, when moist, is capable of direct union with 
 
254 LUCIFEE MATCHES. 
 
 oxygen, chlorine, bromine, iodine, sulphur, and most of the metals r 
 with which it forms phosphides or phosphurets. Even gold and plati- 
 num unite with this element when heated, so that crucibles of these 
 metals are liable to corrosion when heated in contact with a phosphate 
 in the presence of a reducing agent, such as carbon. Thus the inside 
 of a platinum dish or crucible is roughened when vegetable or animal 
 substances containing phosphates are incinerated in it. The presence 
 of small quantities of phosphorus in iron or copper produces consider- 
 able effect upon the physical qualities of these metals. 
 
 Phosphorus has the property, a very remarkable one in a non-metal,, 
 of precipitating some metals from their solutions in the metallic state. 
 If a stick of phosphorus be placed in a solution of sulphate of copper, it 
 becomes coated with metallic copper, the phosphorus appropriating the 
 oxygen. This has been turned to advantage in copying very delicate 
 objects by the electrotype process, for by exposing them to the action of 
 a solution of phosphorus in ether or carbon disulphide, and afterwards 
 to that of a solution of copper, they acquire the requisite conducting 
 metallic film, even on their finest filaments. Solutions of silver and gold 
 are reduced in a similar manner by phosphorus. 
 
 By floating very minute scales of ordinary phosphorus upon a dilute solution of 
 chloride of gold, the metal will be reduced in the form of an extremely thin film, 
 which may be raised upon a glass plate, and will be found to have various shades 
 of green and violet by transmitted light, dependent upon its thickness, whilst ita 
 thickest part exhibits the ordinary colour of the metal to reflected light. By 
 heating the films on the plate, various shades of amethyst and ruby are developed. 
 If a very dilute solution of chloride of gold in distilled water be placed in a 
 perfectly clean bottle, and a few drops of ether, in which phosphorus has been 
 dissolved, poured into it, a beautiful ruby-coloured liquid is obtained, the colour 
 of which is due to metallic gold in an extremely finely divided state, and on 
 allowing it to stand for some months, the metal subsides as a purple powder, 
 leaving the liquid colourless. If any saline impurity be present in the gold 
 solution, the colour of the reduced gold will be amethyst or blue. These ex- 
 periments illustrate very strikingly the use of gold for imparting ruby and purple 
 tints to glass and the glaze of porcelain. 
 
 149. Lucifer matches are made by tipping the wood with sulphur, or 
 wax, or paraffin, to convey the flame, and afterwards with the match com- 
 position, which is generally composed of saltpetre or potassium chlorate, 
 phosphorus, red lead, and glue, and depends for its action on the easy 
 inflammation, by friction, of phosphorus when mixed with oxidising 
 agents like saltpetre (KNO 3 ), potassium chlorate (KC1O 3 ), or red lead 
 (Pb 3 O 4 ), the glue only serving to bind the composition together and 
 attach it to the wood. The composition used by different makers varies 
 much in the nature and proportions of the ingredients. In this 
 country, potassium chlorate is most commonly employed as the oxi- 
 dising agent, such matches usually kindling with a slight detonation ; 
 but the German manufacturers prefer either potassium nitrate or lead 
 nitrate, together with lead dioxide or red lead, which produce silent 
 matches. 
 
 Sulphide of antimony (which is inflamed by friction with potassium 
 chlorate, see p. 186) is also used in those compositions in which a part 
 of the phosphorus is employed in the red form, and fine sand or 
 powdered glass is very commonly added to increase the susceptibility of 
 the mixture to inflammation by friction. 
 
 The match composition is coloured either with ultramarine blue, Prus- 
 
LUCIFER MATCHES. 255 
 
 sian blue, or vermilion. In preparing the composition, the glue and the 
 nitre or chlorate are dissolved in hot water, the phosphorus then added 
 and carefully stirred in until intimately mixed, the whole being kept at 
 a temperature of about 100 F. (38 C.). The fine sand and colouring 
 matter are then added, and when the mixture is complete, it is spread 
 out upon a stone slab heated by steam, and the sulphured ends of the 
 matches are dipped into it. 
 
 The safety matches, which refuse to ignite unless rubbed upon the 
 sides of the box, are tipped with a mixture of antimony sulphide, potas- 
 sium chlorate and powdered glass, which is not sufficiently sensitive to 
 be ignited by any ordinary friction, but inflames at once when rubbed 
 upon the red phosphorus mixed with glass, which coats the rubber on 
 the sides of the box. 
 
 It would be very desirable to dispense entirely with the use of phos- 
 phorus in lucifer matches, not only because of the danger from accident 
 and disease in the manufacture, but because a certain quantity of phos- 
 phate of lime is diverted from agricultural purposes to the preparation 
 of phosphorus, of which many tons are consumed annually for the 
 manufacture of matches. The most successful attempt in this direc- 
 tion appears to be the employment of a mixture of potassium chlorate 
 and lead hyposulphite, in place of the ordinary phosphorus com- 
 position. 
 
 For illustration, very excellent matches may be made upon the small scale in 
 the following manner. The slips of wood are dippped in melted sulphur so as to 
 acquire a slight coating. Thirty grains of gelatine or isinglass are dissolved in 
 2 drachms of water in a porcelain dish placed upon a steam-bath ; 20 grains of 
 ordinary phosphorus are then added, and well mixed in with a piece of wood ; to 
 this mixture are added, in succession, 15 grains of red lead and 50 grains of 
 powdered potassium chlorate. The sulphured matches are dipped into this paste, 
 and left to dry in the air. 
 
 To make the safety matches : 10 grains of powdered potassium chlorate and 
 10 grains of antimony sulphide are made into a paste with a few drops of a warm 
 solution of 20 grains of gelatin in 2 drachms of water, the sulphured matches 
 being tipped with this composition. The rubber is prepared with 20 grains of 
 red phosphorus, and 10 grains of finely-powdered glass, mixed with the solution 
 of gelatine, and painted on paper or cardboard with a brush. 
 
 150. A very sensitive detonating composition formerly used for igniting per- 
 cussion shells, may be prepared with care in the following manner : Four grains 
 of powdered potassium chlorate are moistened on a plate with 6 drops of spirit of 
 wine, 4 grains of powdered red phosphorus are added, and the whole mixed, at 
 arm's length, with a bone-knife, avoiding great pressure. The mixture, which 
 should be quite moist, is spread in small portions upon ten or twelve pieces of 
 filtering paper, and left in a safe place to dry. If one of these be gently pressed 
 with a stick, it explodes with great violence. ' It is dangerous to press it with the 
 blade of a knife, as the latter is commonly broken, and the pieces projected with 
 considerable force. A stick dipped in oil of vitriol of course explodes it imme- 
 diately. If a bullet be placed very lightly upon one of the pellets, and the paper 
 tenderly wrapped round it, a percussion shell may be extemporised, which explodes 
 with a loud report when dropped upon the floor. 
 
 The detonating toys known as amorces fulminantes are made by enclosing this 
 composition between two pieces of thin paper. 1000 of them contain 70 grains of 
 the composition. 
 
 151. Oxides of Phosphorus. Four compounds of phosphorus and 
 oxygen are known, their formulae being P 4 O, P 4 O 6 , P 2 O 4 , and P 2 5 . Of 
 these P 4 O 6 and P 2 O 5 are anhydrides, the others are neutral oxides. 
 
256 PHOSPHORIC ACID. 
 
 PHOSPHORIC ACIDS AND PHOSPHATES. 
 
 152. The phosphates are by far the most important of the compounds 
 of phosphorus. They have been already noticed as almost the only 
 forms of combination in which that element is met with in nature, and 
 as indispensable ingredients in the food of plants and animals. No 
 other mineral substance can bear comparison with calcium phosphate as 
 a measure of the capability of a country to support animal life. Phos- 
 phoric acid itself is very useful in calico-printing and in some other 
 arts. 
 
 The mineral sources of this acid appear to be phosphorite, coprolite, 
 and apatite, all consisting essentially of calcium phosphate, Ca 3 (PO 4 ) 2 , 
 but associated in each case with calcium fluoride, which is also contained, 
 with calcium phosphate, in bones, and would appear to indicate an 
 organic origin for these minerals. Phosphorite is any earthy-looking 
 substance, forming large deposits in Estremadura. Apatite (from 
 anarda), to cheat, in allusion to mistakes in its early analysis) occurs in 
 prismatic crystals, and is met with in the Cornish tin-veins. Both 
 these minerals are largely imported from Spain, Norway, and Florida, 
 for use in this country as a manure. Coprolites (KOKPOS, dung, \i6os, a 
 stone, from the idea that they were petrified dung) are rounded nodules 
 of calcium phosphate, which are found abundantly in this country. 
 
 Large quantities of phosphates of calcium and magnesium are 
 imported in the form of guano, the partially decomposed excrement of 
 sea-fowl. 
 
 Phosphoric acid is obtained from bone-ash, or mineral phosphate, by 
 decomposing it with sulphuric acid, so as to remove as much of the lime 
 as possible in the form of sulphate, which is strained off, and the acid 
 liquid neutralised with ammonium carbonate, which precipitates any 
 unchanged calcium phosphate, and converts the phosphoric acid into 
 ammonium phosphate. On evaporating the solution, and heating the 
 ammonium phosphate, ammonia and water are expelled, and meta- 
 phosphoric acid (HP0 3 ) is left in a fused state, solidifying to a glass on 
 cooling. Thus prepared, however, it always retains some ammonia. 
 
 This method of preparing phosphoric acid is illustrative of one very 
 generally employed in the preparation of those acids which cannot be 
 distilled. In the case of most of the acids heretofore considered, advan- 
 tage is taken of their great volatility, compared with that of sulphuric 
 acid, to obtain them from their sodium salts. It is possible to liberate 
 phosphoric acid from its sodium salt by the action of sulphuric acid ; 
 but since phosphoric acid is not more volatile than sulphuric acid, it is 
 difficult to separate the sodium sulphate produced by the combination 
 of the sulphuric acid with the sodium of the sodium phosphate, from 
 the phosphoric acid, both of them remaining in solution. In such cases 
 advantage is taken of the insolubility of calcium sulphate or of barium 
 sulphate ; when a calcium or barium salt of the required acid is treated 
 with sulphuric acid, calcium sulphate or barium sulphate is precipitated, 
 and may be separated from the solution containing the desired acid by 
 nitration. The treatment of a lead salt of the acid with hydrosulphuric 
 acid, whereby lead sulphide is precipitated, is another method for pre- 
 paring acids, based on the same principle. 
 
 Pure phosphoric acid is prepared by oxidising phosphorus with dilute 
 
PHOSPHORIC ANHYDRIDE. 
 
 257 
 
 nitric acid (sp. gr. 1.197) and evaporating the solution until the phos- 
 phoric acid begins to volatilise in white fumes; 5HNO 3 + P 3 = 3HP0 3 -t- 
 H 2 O + 5NO.* Some phosphorous acid is formed at an intermediate 
 stage. A transparent glass (glacial phosphoric acid) is thus obtained, 
 which eagerly absorbs moisture from the air, and becomes liquid. That 
 which is sold in sticks contains much sodium metaphosphate. 
 
 The addition of a little bromine greatly facilitates the action of nitric acid upon 
 phosphorus, apparently by forming the phosphorus pentabromide, which is then 
 decomposed by water ; PBr 5 + 4H 2 = H 3 P0 4 + sHBr. The hydrobromic acid being 
 then acted on by nitric acid, bromine is set free to act upon a fresh quantity of 
 phosphorus; 3HBr + HN0 3 = Br 3 + 2H 2 O + NO. When iodine is also added, the 
 action is still better. 28 grams of phosphorus are placed in 170 c.c. of water and 
 0.32 gram of iodine are added ; then, drop by drop, 1.94 grams of bromine. When 
 the action is over, 1700.0. of HNO 3 (sp. gr. 1.42) are added, and the vessel is placed 
 in cold water. When the phosphorus has dissolved, the solution is evaporated till 
 its temperature rises to about 204 C. in order to expel the excess of nitric acid, 
 the bromine, and the iodine. 
 
 Phosphoric anhydride, or phosphorus pentoxide (P,O 5 ), is pre- 
 pared by burning phosphorus in dry air. 
 
 When required in considerable quantity, the anhydride is prepared by burning 
 the phosphorus in a small porcelain dish (A, Fig. 186) placed under a bell-jar 
 which fits in a groove containing mercury and surrounding a glass funnel. Air 
 
 
 Fig. 186. 
 
 is drawn through the apparatus by an aspirator attached to the tube C, the empty 
 bottle serving to catch the P 2 5 carried over by the current. A drying- tube, con- 
 taining pumice moistened with oil of vitriol, is attached to the lateral neck of the 
 bell-jar in order to dry the entering air. When all the phosphorus has been burnt 
 the bell may be removed, and the P 2 5 swept down the stem of the funnel into a 
 dry bottle. A small quantity of phosphoric anhydride is more conveniently 
 prepared by burning phosphorus under a large bell-jar, as shown in Fig. 25. 
 
 Phosphoric anhydride as thus prepared is amorphous ; it may be fused 
 at a very high temperature, and even sublimed, when it condenses as 
 microscopic crystals. Its great feature is its attraction for water; left 
 exposed to the air for a very short time it deliquesces entirely, becoming 
 converted into phosphoric acid. It is often used by chemists as a 
 
 * Orthophosphoric acid is first formed, 5NO 2 .OH + P 3 + 2HOH = 3PO(OH) 3 + sNO ; but 
 this loses water during the evaporation, PO(OH) 3 -H 2 O = PO 2 (OH). 
 
 B 
 
258 PHOSPHOKIC ACIDS. 
 
 de-hydrating agent, and will even remove water from oil of vitriol. 
 When thrown into water it hisses like a red-hot iron, but does not 
 entirely dissolve at once, a few flakes of metaphosphoric acid (?) remain- 
 ing suspended in the liquid for some time. The commercial anhydride 
 is apt to contain lower oxides of phosphorus, and even red phosphorus. 
 
 The solution obtained by dissolving phosphoric anhydride in water 
 contains monohydrated phosphoric acid or metaphosphoric acid (H 2 O.P 2 O 5 
 or HP0 3 ) the analogue of nitric acid. If a little silver nitrate be added 
 to a portion of it, a transparent gelatinous precipitate is formed, which 
 is the silver metaphosphate ( AgN0 8 + HP0 3 = HNO 3 + AgP0 3 ). 
 
 If the solution of metaphosphoric acid is heated in a flask for a short 
 time, it loses the property of yielding a precipitate with silver nitrate, 
 unless one or two drops of ammonia be added to neutralise it, when an 
 opaque white precipitate of silver pyrophosphate (2 Ag 2 O.P 2 5 or Ag 4 P 2 O 7 ) 
 is obtained, for the phosphoric acid has now been converted into the 
 dihydrated or pyrophosphoric acid (2H 2 O.P 2 O 5 or H 4 P 2 O 7 ). The forma- 
 tion of the precipitate is thus expressed 
 
 H 4 P 2 7 + 4AgN0 3 + 4NH 3 = Ag 4 P 2 7 + 4NH 4 N0 3 . 
 
 When the solution of pyrophosphoric acid is mixed with more water 
 and boiled for a long time, it gives, when tested with silver nitrate and 
 a little ammonia, a yellow precipitate of silver orthophosphate r 
 (3Ag 2 O.P,0 5 or Ag 3 PO 4 ) ; the phosphoric acid having become converted 
 into trihydrated phosphoric acid or orthophosphoric acid (3H 2 O.P 2 O 5 or 
 H 3 P0 4 ), and acting upon the silver nitrate in the presence of ammonia r 
 thus H 3 P0 4 + 3AgN0 3 + 3 NH 3 = Ag 3 P0 4 + 3 NH 4 N0 3 . 
 
 The reverse changes occur when orthophosphoric acid is heated, this- 
 becoming pyrophosphoric acid at 300 C., and metaphosphoric acid at a 
 red heat. 
 
 The pyrophosphoric acid (H 4 P 2 7 ) cannot be obtained by the above 
 process without an admixture of one of the other acids, but it has been 
 obtained in crystals by decomposing the lead pyrophosphate (Pb 2 P 2 7 ) 
 with hydrosulphuric acid, and evaporating the filtered solution in vacuo 
 over oil of vitriol. 
 
 Trihydrated phosphoric acid may also be obtained in prismatic crystals,, 
 by evaporating its solution in a similar way. This acid is also called 
 orthophosphoric acid (opQdg, true), and common phosphoric acid, in allu- 
 sion to the circumstance that the phosphates found in nature and 
 commonly met with and employed in the arts are the salts of this acid. 
 
 Metaphosphoric acid is distinguished from the other two acids by the 
 fact that it coagulates white of egg (albumin). 
 
 It will be perceived, from their formulae, that metaphosphoric. HP0 3 , ortho- 
 phosphoric, H 3 P0 4 , and pyrophosphoric acid, H 4 P 2 7 , are respectively monobasic,, 
 tribasic, and tetrabasic acids. The normal sodium salts of these acids are, re- 
 spectively, metaphosphate, NaP0 3 , orthophosphate, Na 3 P0 4 , and pyrophosphate, 
 Na 4 P 2 7 . The hydrogen in orthophosphoric and pyrophosphoric acids may be 
 only partly exchanged for a metal ; thus there are two other orthophosphates of 
 sodium, viz., hydrogen-disodium phosphate, HNa^PO^ and dihydrogen-sodium phos- 
 phate, H 2 NaP0 4 . 
 
 The phosphates commonly met with are all derived from orthophosphoric acid : 
 for example, bone-ash, or tricalcium orthophosphate, Ca 3 (P0 4 ) 2 ; superphosphate, 
 or monocalcium orthophosphate, CaH 4 (PO 4 ) 2 ; common phosphate of soda, or 
 hydrogen-disodium orthophosphate, HNa. 2 P0 4 ; microcosmic salt, or hydrogen- 
 ammonium sodium orthophosphate, HNH 4 Na(P0 4 ). 
 
 Pyrophosphates and metaphosphates may be obtained by the action of heat on. 
 
PHOSPHOROUS ACID. 259 
 
 the orthohydrogen phosphates. Thus, if a crystal of the common rhombic sodium 
 phosphate (HNa. 2 PO 4 .i2Aq) be heated gently in a crucible, it melts in its water of 
 crystallisation, and gradually dries up to a white mass, the composition of which, 
 if not heated beyond 149 C., will be Na. 2 HPO 4 . A little of this white mass dis- 
 solved in water gives a solution alkaline to red litmus-paper ; and if silver nitrate 
 (itself neutral to test-papers) is added to it, a yellow precipitate of silver ortho- 
 phosphate is obtained, and the solution becomes strongly acid 
 
 Na 2 HP0 4 + 3AgX0 3 = Ag 3 P0 4 + 2NaNO 3 + HNO . 
 
 If the dried sodium phosphate be now strongly heated over a lamp, it will lose 
 water, and become pyrophosphate (jrvp, fi re) ; 2Na, 2 H P0 4 = H. 2 O + Na 4 P 2 O 7 . On dis- 
 solving this in water, the solution will be alkaline, and will give with silver nitrate 
 a white precipitate and a neutral solution ; Na 4 P 2 O 7 -H 4AgNO 3 = Ag 4 P. 2 7 + 4NaN0 3 . 
 
 Microcosmic salt (NaNH 4 HP0 4 .4Aq), when dissolved in water, yields an allta- 
 line solution which gives a yellow precipitate with silver nitate, the liquid becom- 
 ing acid; NaNH 4 HPO 4 + 3AgN0 3 = Ag 3 P0 4 + NaNO 3 + NH 4 N0 3 + HN0 3 . 
 
 But if the salt be heated in a crucible, it fuses, evolving water and ammonia, 
 and leaving a transparent glass of sodium metaphosphate ; NaNH 4 HPO 4 = 
 H 2 O + NH 3 + NaPO 3 , which may be dissolved by soaking in water, yielding a 
 slightly acid solution, which gives a white gelatinous precipitate with silver nitrate, 
 the liquid being neutral; NaP0 3 + AgN0 3 = AgP0 3 + NaNO 3 . 
 
 All the phosphates may be converted into orthophosphates, by fusing them with 
 an alkali, or by boiling them for some time with a dilute acid.* 
 
 153. Phosphorus anhydride (P 4 6 ) is a product of tl^e slow combustion of 
 phosphorus, and, by carefully regulating the combustion, may be made to consti- 
 tute 50 per cent, of the oxides produced, the remainder being P 2 5 . It is prepared 
 by drawing a slow current of air over ignited phosphorus and causing the product 
 to pass, first through a tube maintained at about 60 C.. a temperature at which 
 P. 2 5 condenses, and then through a U-tube surrounded by a freezing-mixture 
 wherein the P 4 O 6 solidifies. It forms feathery crystals which melt at 22.5 C. ; it 
 boils at 173 C., and is decomposed at higher temperatures (in a sealed tube) 
 according to the equation 2P 4 6 = 3P. 2 4 + P. 2 . It dissolves slowly in cold water, 
 forming phosphorous acid, P 4 6 + 6HOH = 4P(OH) 3 ; hot water decomposes it with 
 great violence. It burns in oxygen, forming P. 2 5 , and in chlorine, forming 
 POC1 3 and POr>Cl (?). Its combustion in oxygen is attended by all the phenomena 
 of phosphorescence shown by phosphorus, but no ozone is produced. 
 
 Phosphorus tetroxide, P 2 4 , corresponding with N 2 4 , is obtained as a very 
 deliquescent crystalline sublimate by heating P 4 6 to about 440 C. in a sealed 
 tube filled with C0 2 ; the white P 4 O 6 becomes orange, from the production of red 
 phosphorus, and P 2 4 sublimes in deliquescent colourless crystals. When dissolved 
 in water it is converted into a mixture of phosphorous and orthophosphoric acids, 
 just as nitric peroxide, N 2 O 4 , is converted into nitrous and nitric acids ; 
 P 4 + 3H 2 = H 3 P0 4 + H 3 P0 3 . 
 
 "Phosphorous acid, H 3 P0 3 or P(OH) 3 , or PHO(OH) 2 , is obtained in solution, 
 mixed with phosphoric acid, when sticks of phosphorus arranged in separate tubes 
 open at both ends and placed in a funnel over a bottle, are exposed under a bell- 
 jar, open at the top, to air saturated with aqueous vapour. To obtain the pure 
 acid, chlorine is very slowly passed through phosphorus fused under water, when 
 the phosphorous chloride first formed is decomposed by the water into phosphorous 
 and hydrochloric acids ; PC1 3 + 3H 2 = P(OH) 3 + 3HC1. The hydrochloric acid is 
 expelled by a moderate heat, when the phosphorous acid is deposited in prismatic 
 crystals. When heated, it is decomposed into phosphoric acid and gaseous phos- 
 
 phoretted hydrogen ; 33 = 34 3 . 
 
 Solution of phosphorous acid gradually absorbs oxygen from the air, becoming 
 phosphoric acid. This tendency to absorb oxygen causes it to act as a reducing- 
 agent upon many solutions ; thus it precipitates finely divided metallic silver 
 from a solution of the nitrate, by which its presence may be recognised in the 
 water in which ordinary phosphorus has been kept. The solution of phosphorous 
 acid even reduces sulphurous acid, producing sulphuretted hydrogen and sulphur, 
 the latter being formed by the action of the sulphuretted hydrogen upon the sul- 
 phurous acid; H 2 SO 3 + 3*H 3 P0 3 = 3H 3 P0 4 + H 2 S. Some metals dissolve in it, 
 evolving PH 3 . 
 
 * It has been remarked that the pliancy of the acid character of phosphoric acid particu- 
 larly fits it to take part in the vital phenomena. It may be regarded as three acids in one. 
 
260 STRUCTURE OF ACIDS. 
 
 If solution of phosphorous acid be poured into a hydrogen apparatus, some PH 3 
 is formed which imparts a fine green tint to the hydrogen flame. 
 
 ' It is doubtful whether phosphorous acid is dibasic or tribasic, that is, whether it 
 contains 2 or 3 hydroxyl groups. In the former case its formula should be 
 PHO(OH) 2 in the latter, P(OH) 3 . 
 
 As the salt Na 3 P0 3 has been prepared, the formula P(OH) 3 is indicated ; it is sup- 
 ported by the reaction between PC1 3 and HOH. 
 
 154. Hypophosphorous acid, H 3 P0 2 or PH 2 0(OH). When phosphorus is boiled 
 with barium hydroxide and water, the latter is decomposed, its hydrogen com- 
 bining with part of the phosphorus to form hydrogen phosphide (spontaneously in- 
 flammable), which escapes, whilst the oxygen of the water unites with another 
 part of the phosphorus, forming hypophosphorous acid, which acts on the baryta 
 to form barium hypophosphite ; this may be obtained, by evaporating the solution 
 in crystals having the composition (PH 2 0.0) 2 Ba. The action of phosphorus upon 
 barium hydroxide may be represented by the equation 
 
 3Ba(OH) 2 + 6H 2 + P 8 = 3(PH 2 0.0) 2 Ba + 2PH 3 . 
 Barium hydroxide. Barium hypophosphite. 
 
 Some barium orthophosphate is also formed at the same time, as the result of a 
 secondary action. 
 
 By dissolving the barium hypophosphite in water, and decomposing it with the 
 requisite quantity of sulphuric acid, so as to precipitate the barium as sulphate, a 
 solution is obtained which may be concentrated by careful evaporation. If this 
 hypophosphorous acid be heated, it evolves hydrogen phosphide, and becomes con- 
 verted into phosphoric acid ; 2H 3 P0 2 = H 3 P0 4 + PH 3 . When exposed to the air it 
 absorbs oxygen, and becomes converted into phosphorous and phosphoric acids. 
 It is a more powerful reducing-agent than phosphorous acid. The latter acid does 
 not reduce a solution of cupric sulphate, but hypophosphorous acid, when gently 
 warmed with it, gives a brown precipitate of cuprous hydride (CuH), which is 
 decomposed by boiling, evolving H and leaving Cu. 
 
 When heated, the hypophosphites evolve hydrogen phosphide, and are converted 
 into phosphates. The sodium hypophosphite, PH 2 O.ONa, is sometimes used in 
 medicine ; its solution has been known to explode with great violence during 
 evaporation, probably from a sudden disengagement of hydrogen phosphide. Hy- 
 pophosphites, when boiled with caustic alkalies, are converted into phosphates, 
 hydrogen being evolved ; phosphites are unchanged. 
 
 Hypophoxphorio acid, H 4 P 2 6 or PO(OH) 2 .PO(OH) 2 , exists in the water in which 
 phosphorus has been kept. 
 
 The following is a summary of the acids formed ~by phosphorus with oxygen and 
 hydrogen: 
 
 Hypophosphorous acid . . . . . . PH 2 0(OH) 
 
 Hypophosphoric acid ...... P 2 2 (OH) 4 & fi 
 
 Phosphorous ...... P(OH) 3 
 
 Metaphosphoric , ....... PO 2 .(OH) 
 
 Orthophosphoric . ..... /PO(OH) 3 Hvttjl 
 
 Pyrophosphoric , ....... P 2 3 (OH) 4 ^ - 
 
 155. Su'boxide of phosphorus, P 4 0, is supposed to constitute the yellow or red 
 residue which is left in the dish when phosphorus burns in air, but it is always 
 mixed with much phosphoric anhydride. It is also said to be obtained by allowing 
 phosphorus to dissolve slowly in an alcoholic solution of NaOH, and then adding 
 an acid, whereupon an orange red powder is precipitated. 
 
 Structure of acids. Attention has already been called to the theory 
 that oxy-acids contain hydroxyl groups and that they owe their basicity 
 to the number of these groups (pp. 104, 191). Since the group OH is 
 monovalent it is reasonable to suppose that the atom of an element 
 would be capable of combining with one of these groups for each atom 
 fixing-power which the element possesses. Thus, the maximum valency of 
 phosphorus being five (as seen from the chloride PC1 5 ) the acid P(OH) 5 
 might be expected to exist, although it is not known. It is customary to 
 term such hydroxyl compounds of the elements ortho-acids, and to regard 
 
ANHYDRO-ACIDS. 261 
 
 other oxy-acids as being derived from the ortho-acids by loss of water ; 
 these other oxy-acids are called auhydro- acids to express this view. 
 
 According to this conception, the name orthophosphoric acid, which 
 has been given to H 3 P0 4 , is a misnomer, for this acid is really the first 
 anhydro-acid of true orthophosphoric, P(OH) 5 , which is unknown. 
 Pyro-phosphoric acid is the second and metaphosphoric acid the third 
 anhydro-acid from true orthophosphoric acid, as will be apparent from 
 the following : 
 
 P(OH) 5 - H 2 = PO(OH) 3 , " orthophosphoric acid " ; 
 /0(OH) 2 
 
 ~~ 
 
 f ~~ / 
 
 \0(OH) 2 
 PO(OH) 3 - H 2 = P0 2 (OH), metaphosphoric acid. 
 
 Only a few ortho-acids are known, although the existence of several others is 
 indicated by the fact that some of their salts (chiefly organic salts) have been 
 isolated. The ortho-acids are generally very unstable, tending to lose water and 
 to become anhydro-acids. Thus, orthocarbonic acid, C(OH) 4 , has never been 
 prepared, although several organic ortho-carbonates of the type C(OM) 4 , in which 
 M is an organic basic radicle, are known. It will be remembered that the 
 anhydro-acid, CO(OH) 2 (=:C(OH) 4 - H 2 0), carbonic acid, is supposed to exist in 
 the aqueous solution of C0 2 ; but this also readily loses water, yielding the true 
 anhydride, C0 2 ( = CO(OH) 2 -H 2 0). Ortlionulphuric acid, S(OHJ 6 , probably exists 
 in an aqueous solution of sulphuric acid, for the maximum contraction which 
 occurs when H 2 S0 4 and H 2 are mixed takes place when the proportion of acid to 
 water is expressed by the formula H 2 S0 4 .2H 2 or H 6 S0 6 . It very readily loses 
 water, however, when heated, and if the evaporated solution be cooled to 8 C. the 
 anhydro-acid, SO(OH) 4 or H 2 S0 4 .H 2 0, crystallises, which in its turn loses water 
 when heated, becoming the most stable anhydro-acid of sulphur, H 2 S0 4 or 
 S0 2 (OH) 2 . The solution of S0 3 in H 2 S0 4 (H 2 S 2 7 ), which melts at 35 C. and is 
 called anhydrosulphuric acid, must be regarded as a further anhydride of sulphuric 
 acid 
 
 2 (OH) 
 
 _ 
 S0 2 (OH) 2 / ' 2 ~ 
 
 b \0 2 (OH) 
 
 Orthoxilicic acid, Si(OH) 4 , is believed to exist in solution (p. 278), but it very 
 easily loses water, becoming the anhydro-acid, SiO(Ofl) 2 , metasilicic acid. By 
 the loss of water from several molecules of orthosilicic acid, anhydro-acids of com- 
 plex type would be produced ; thus 
 
 Si /(OH) 3 
 
 Si(OH) 4 ] )o 
 
 Si(OH) 4 I - 2H 2 = Sif (OH) 2 
 Si(OH)J )0 
 
 S <(OH) 3 
 
 The mineral silicates are undoubtedly derived from such complex silicic acids, the 
 existence of which is, in many cases, also indicated by the isolation of acid 
 chlorides (p. 191) corresponding with them. 
 
 Orthoboric acid, B(OH) 3 , is well known. OrtJwnitric acid, N(OH) 5 , is not known : 
 ordinary nitric acid is the anhydro-acid N0 2 (OH). 
 
 The ortho-acid of chlorine should be C1(OH) 7 , for this element is probably, 
 heptavalent to elements other than hydrogen ; but no anhydro-acid intermediate 
 between this and C10 3 (OH), perchloric acid, is known. Ortlwwdic add, I(OH) 7 , 
 is unknown ; periodic acid, IO(OH) 5 , is the first anhydro-acid from orthoiodio ; 
 acid. 
 
 On reviewing the highest oxy-acids of the non-metallic elements, it will be found. 
 to be generally true that those acids are the most stable which contain the same, 
 
262 
 
 PHOSPHINE. 
 
 number of hydroxyl groups in the molecule as there are hydrogen atoms in the 
 highest hydrogen compound of the element. 
 
 PHOSPHIDES OF HYDROGEN. 
 
 156. Although phosphorus and hydrogen do not combine directly, 
 there are three compounds of these elements producible by processes of 
 substitution, viz., PH 3 , gas ; P 2 H 4 , liquid 5 P 4 H 2 , solid. 
 
 Gaseous hydrogen phosphide, or phosphoretted hydrogen, or 
 phosphine (PH 3 = 34 parts by weight), is by far the most important of 
 these. It has been mentioned above as produced by the action of heat upon 
 phosphorous acid, and when prepared by this process, it is a colourless 
 gas, with a most powerful odour of putrid fish, inflaming on the approach 
 of a light, and burning with a brilliant white flame, producing thick 
 clouds of phosphorus pentoxide. It is slightly heavier than air (sp. gr. 
 1.18), and has been liquefied at -90 0. and solidified at - 133 C. ; 
 it boils at -85. 
 
 The ordinary method of preparing this gas for experimental purposes consists in 
 "boiling phosphorus with a strong solution of potash, when water is decomposed, its 
 hydrogen combining with one part of the phosphorus, and its oxygen with another 
 part forming hypophosphorous acid, which unites with the potash 
 
 P 4 + sKOH + 3H 2 O = PH 3 + 3PH 2 0(OK). 
 
 A few fragments of phosphorus are introduced into a small retort (Fig. 187). 
 which is then nearly filled with a strong solution of potash (45 grams of stick 
 
 potash in 100 c.c. of water), and heated. 
 The extremity of the neck of the retort 
 should not be plunged under water until 
 the spontaneously inflammable gas is seen 
 burning at the orifice, and the retort must 
 not be placed close to the face of the 
 operator, since explosions sometimes 
 happen in preparing the gas, and the boil- 
 ing potash produces dangerous effects. 
 The gas may be collected in small jars 
 filled with water, taking care that no 
 bubble of air is left in them. It contains 
 hydrogen phosphide mixed with free 
 hydrogen, the latter being formed from 
 the de-oxidation of water by the potas- 
 sium hypophosphite. As each bubble of 
 this gas escapes into the air through the 
 water of the pneumatic trough, it burns 
 with a vivid white flame, producing 
 beautiful wreaths of smoke (phosphoric 
 anhydride), resembling the gunner's ring* 
 sometimes seen in firing cannon. Small 
 bubbles sometimes escape without spon- 
 taneously inflaming. If a bubble be sent up into a jar of oxygen, the flash of light 
 is extremely vivid, and the jar must be a strong one to resist the concussion. It is 
 advisable to add a trace of chlorine to the oxygen, to ensure the inflammation of 
 each bubble, for an accumulation of the gas would shatter the jar. 
 
 It is stated that phosphoretted hydrogen may be added to pure oxygen without 
 ignition until the pressure is reduced, when explosion suddenly occurs (compare 
 the phenomenon of phosphorescence, p. 251). 
 
 If the phosphoretted hydrogen be passed through a tube cooled in a freezing- 
 mixture of ice and salt, the gas escaping from the tube is found to have lost its 
 spontaneous inflammability, although it takes fire on contact with flame. The 
 cold tube contains the liquid hydrogen phosphide (P 2 H 4 ), which was present in the 
 gas in the state of vapour, and caused its spontaneous inflammability, for as soon as 
 the liquid comes in contact with air it takes fire. When exposed to light, the 
 
 Fig. 187. 
 Preparation of phosphoretted hydrogen. 
 
CHLORIDES OF PHOSPHORUS. 263 
 
 liquid phosphide is decomposed into the gaseous phosphide, and a yellow solid 
 phosphide (P 4 H 2 ), which is not spontaneously inflammable ; 5P 2 H 4 = P 4 H 2 + 6PH 3 . 
 It is for this reason that the spontaneously inflammable gas loses that property 
 when kept (unless in the dark), depositing the solid phosphide upon the sides of 
 the jar. 
 
 By passing a few drops of oil of turpentine up through the water into a jar of the 
 spontaneously inflammable gas, this property will be entirely destroyed. 
 
 Hydrogen phosphide, when passed through solutions of some of the metals, pre- 
 cipitates their phosphides. For example, with cupric sulphate it gives a black 
 precipitate of cupric phosphide ; 
 
 When this black precipitate is heated with solution of potassium cyanide, it 
 evolves self-lighting hydrogen phosphide. * In fact, this is one of the easiest and 
 safest methods of preparing this gas ; for the cupric phosphide is readily obtained 
 by simply boiling phosphorus in a solution of cupric sulphate. 
 
 Phosphine is absorbed by strong sulphuric acid, and, after a time, acts upon it 
 with great evolution of heat, S0 2 being formed and sulphur deposited. Sulphur 
 decomposes it in sunshine ; 2PH 3 +S 6 = P 2 S 3 + 3H 2 S. 
 
 The spontaneously inflammable hydrogen phosphide may also be obtained by 
 throwing fragments of calcium phosphide into water ; this substance is prepared by 
 passing vapour of phosphorus over red-hot quicklime, or simply by heating small 
 lumps of quicklime to bright redness in a crucible and throwing in fragments of 
 phosphorus, closing the crucible immediately. The dark brown mass thus obtained 
 is a mixture of pyrophosphate and phosphide of calcium, of somewhat variable 
 composition. The calcium phosphide has been used in life-buoys for indicating by 
 the flare their position on the water. 
 
 Phosphine has great pretensions to rank as the chemical analogue ot 
 ammonia, for although it has no alkaline properties, it is capable of 
 combining with hydrobromic and hydriodic acids to form crystalline 
 compounds such as phosphonium iodide, PH 4 I, analogous to ammonium 
 bromide and iodide ; these compounds, however, are decomposed by 
 water. It will be seen hereafter, that when the hydrogen in phosphine 
 is displaced by certain compound radicles, such as ethyl, powerful 
 organic bases are produced. 
 
 When phosphine is decomposed by a succession of electric sparks, 2 volumes of 
 the gas yield 3 volumes of hydrogen, the phosphorus being deposited in the red 
 form. 
 
 157. Two chlorides of phosphorus are known. The trichloride or phosphorous 
 chloride (PC1 3 ), the acid chloride of phosphorous acid, is prepared by acting 
 upon phosphorus with perfectly dry chlorine in the apparatus employed (p. 242) for 
 preparing the chloride of sulphur. Red phosphorus may be used, and the product 
 redistilled with a little vitreous phosphorus to decompose any PC1 5 . Phosphorous 
 chloride distils over very easily (boiling-point, 76 C.), as a colourless, pungent 
 liquid (sp. gr. 1.61), which fumes strongly in air, its vapour decomposing the 
 moisture of the air and producing hydrochloric acid fumes. In contact with water 
 the liquid is immediately decomposed, yielding hydrochloric and phosphorous 
 acids, as described for the preparation of the latter acid (p. 251). Its analogy to 
 phosphorous anhydride is shown by its absorbing oxygen when boiled in the pre- 
 sence of that gas, and forming the phosphorus oxy chloride or phosphoryl chloride 
 POC1 3 . the acid chloride of phosphoric acid. It also absorbs chlorine with avidity, 
 becoming converted into pentachlorlde of phosphorus ex phosphoric chloride (PC1 5 ). 
 This compound, however, is more conveniently prepared by passing chlorine 
 through a solution of phosphorus in carbon disulphide, carefully cooled. On 
 evaporation, the pentachloride of phosphorus is deposited in white prismatic 
 crystals, which volatilise below 100 C., and fume when exposed to air, from the 
 production of hydrochloric acid. When PC1 5 is heated above 148 C. it is disso- 
 ciated into PC1 3 and C1 2 , but this may be prevented by volatilising it in an 
 atmosphere of PC1 3 , and thus its vapour density has been determined. When 
 thrown into w r ater, it is decomposed into phosphoric and hydrochloric acids ; 
 PC1 5 + 4H 2 = H 3 PO 4 +5HC1. But if it be allowed to deliquesce in air, only a 
 
 * Cupric cyanide and potassium phosphide being formed, and the latter decomposed by 
 water, giving hydrogen phosphide and potassium hypophosphite. 
 
264 
 
 PHOSPHORUS SULPHIDES. 
 
 partial decomposition occurs, and the phosphorus oxychloride is formed ; 
 PC1 5 + H 2 = POC1 3 + 2HC1. The same compound is obtained by distilling P 2 5 
 with NaCl ; 2P 2 5 + sNaCl = POC1 3 + 3NaP0 3 . 
 
 This oxychloride may also be produced by heating phosphoric chloride with 
 phosphoric anhydride ; P 2 5 + 3PC1 5 = 5POC1 3 . A more instructive method of pre- 
 paring it consists in distilling the phosphoric chloride with crystallised boric acid ; 
 3PC1 5 + 2B(OH) 3 = 3POC1 3 + 6HC1 + B 2 3 . 
 
 Some of the organic acids (succinic, for example) may be converted into anhy- 
 drides, as the boric acid is in this case, by distilling with phosphoric chloride. 
 The phosphorus oxychloride distils over (boiling-point, 107 C.) as a heavy (sp. gr. 
 1.7) colourless fuming liquid of pungent odour. Of course, it is decomposed by 
 water, yielding hydrochloric and phosphoric acids. It will be found of the greatest 
 use in effecting certain transformations in organic substances. 
 
 Pyropkogphoryl chloride, P 2 3 C1 4 , the acid chloride of pyrophosphoric acid, is a 
 product of the action of N0 2 on PC1 3 . It is a fuming liquid. 
 
 The analogy between water and hydrosulphuric acid would lead to the expecta- 
 tion that a snip ko chloride of phosphorus or thiopJiosphoryl chloride (PSC1 3 ), corre- 
 sponding with the oxychloride, would be formed by the action of hydrosulphuric 
 acid upon phosphoric chloride ; PC1 5 + H 2 S = PSC1 3 + 2HC1. It is a colourless 
 fuming liquid (boiling-point 125 C., sp. gr. 1.68), which is slowly decomposed by 
 water, giving phosphoric, hydrochloric, and hydrosulphuric acids ; PSC1 3 + 4H 2 = 
 H 3 P0 4 + 3HC1 + H 2 S. When attacked by solution of soda, it loses its chlorine to 
 the sodium, and acquires the equivalent of oxygen, a sodium thiophosphate 
 (Na 3 POpS.i2H 2 0) being deposited in crystals. This salt evidently corresponds in 
 composition with sodium orthophosphate (Na 3 P0 4 .i2H 2 0), and its production is 
 expressed by the equation PS01 3 + 6NaOH = 3NaCl-f Na 3 P0 3 S + 3H 2 0. Salts of 
 similar composition may be obtained with other metallic oxides. 
 
 The bromides and oxybromide of phosphorus correspond with the chlorine 
 compounds ; as also do the fluorides. The latter are gaseous under ordinary 
 conditions. 
 
 Iodine in the solid state combines very energetically with phosphorus, but if 
 the two elements be brought together in a state of solution in carbon disulphide, 
 a more moderate action ensues, and two iodides of phosphorus may be obtained in 
 crystals ; a tri-iodide. (P1 3 ) corresponding with the trichloride, and phosphorus 
 di-iodide (P 2 I 4 ), which has no analogue either among the oxygen, chlorine, or 
 bromine compounds of phosphorus. P 2 I 4 forms orange-red crystals, which are 
 decomposed by water, with separation of red phosphorus; 3P 2 I 4 + I2H 2 = 
 
 The addition of a very small quantity of iodine to ordinary phosphorus, fused 
 in a flask filled with carbonic acid gas, materially accelerates its conversion into 
 the red modification, and allows the change to be effected at a much lower tem- 
 perature than that required when the phosphorus is heated alone, probably because 
 successive portions of vitreous phosphorus combine with the iodine to form an 
 unstable iodide, which is in turn decomposed by the heat into red phosphorus 
 and iodine. 
 
 158. The sulphides of phosphorus may be formed by the direct combination 
 of their elements. Yellow phosphorus liquefies when mixed with sulphur (an opera- 
 tion not unattended by danger), and the liquid dissolves as much as 25 per cent, of 
 sulphur. It fumes in air and readily ignites, but it appears to be only a solution 
 of sulphur in phosphorus, which, like most other solutions, has a lower melting- 
 point than that of the solvent (phosphorus). When a mixture of red phosphorus 
 and sulphur is heated, combination occurs, and either P 2 S 3 or P 2 S 5 is formed 
 according to the proportions used. A clay crucible is heated by a bunsen burner 
 and a mixture of red phosphorus (31 parts) and sulphur (48 parts) is added by 
 degrees, the crucible being covered after each addition until the reaction is over. 
 The crucible is allowed to cool until the mass is about to solidify, and the phos- 
 phorus trisulphide is then poured on to an iron plate. It is a dirty yellow crystal- 
 line mass of sp. gr. 2.0 and melting-point 167 C. 
 
 Phosphorus pentasulphide, P 2 S 5 , is similarly prepared and melts at 275 C. and 
 boils at 530 C. ; from CS 2 it separates in nearly colourless crystals. Both sul- 
 phides deliquesce in air, being decomposed into oxyacids of phosphorus with 
 evolution of H 2 S, and both are used in organic chemistry for substituting S for 0. 
 
 P 2 S 5 combines with alkali sulphides, forming thlophosp hates 
 2K 3 PS 4 . 
 
ARSENIC. 265 
 
 159. Amides. A general reaction between ammonia and an acid 
 chloride is the production of the amide corresponding with the acid 
 whose chloride is being treated. The amide of an acid contains NH 2 
 (amidogen) in place of the hydroxyl of the acid ; the reaction may be 
 regarded as consisting of an exchange of 01 for ]SH 2 ; thus, the action 
 of ammonia on phosphoryl chloride produces the amide of " ortho- 
 phosphoric acid," PO(NH 2 ) 3 , called phospho-triamide. The change may 
 be written POC1 3 + 3 NH" 2 'H = PO(NH a ) 3 + 3HC1, but it will not occur 
 unless excess of ammonia be present to combine with the liberated HC1, 
 o that the actual reaction is POC1 3 + 6NH 3 = 3NH 4 C1 + PO(NH 2 ) 3 . 
 
 When an amide is boiled with an acid or an alkali it reacts with the 
 water, producing the acid from which it is derived, and ammonia. Such 
 a decomposition by water is termed hydrolysis; PO(NH,) 3 + 3HOH = 
 PO(OH) 3 + 3 NH 3 . 
 
 If an acid be present the N H 3 will immediately become an ammonium 
 salt. If an alkali be present the ammonia will be evolved and the 
 alkali will combine with the phosphoric acid. If neither acid nor 
 alkali be present the change will not proceed far. 
 
 If the sulphochloride, PSCl 3 ,be substituted for the oxychloride and treated with 
 ammonia, the corresponding sulphosphotriamide, PS(KH 2 ) 3 , is obtained. 
 
 The action of ammonia on phosphoric chloride yields chlorophosphamide^ 
 PC1 3 (NH 2 ) 2 ; PC1 5 + 2NH 3 = 2HC1 + PC1 ? (NH 2 ) 3 , and phospham, PN 2 H, a white solid 
 which is the analogue of hydrogen nitride, N 3 H. 
 
 When chlorophosphamide is boiled with water, a very stable insoluble substance 
 is obtained, which is phosphodiamide ; N 2 H 4 PC1 3 + H 2 = 3HC1 + N 2 H 3 PO (phospho- 
 diamide). 
 
 When heated, it evolves ammonia and becomes phosphonitrile. the analogue of 
 nitrous oxide ; N 2 H 3 PO = NH 3 + NPO. 
 
 The phosphamides may be regarded as being derived from the ammonium ortho- 
 phosphates by the abstraction of 3H 2 ; thus 
 
 (NH 4 ) 3 P0 4 minus jH,/) = N 3 H 6 PO or PO(NH 2 ) 3 , Phosphotriamide. 
 (NH 4 ) 2 HP0 4 = N 2 H 3 PO or PO(NH 2 )NH, Phosphamide-imide. 
 NH 4 H 2 P0 4 = NPO, Phosphonitrile. 
 
 Nitrogen chlurophosphi'de, N V 3 P'" 3 C1 6 , is obtained by distilling phosphoric chloride 
 with ammonium chloride ; 3PC1 5 + 3NH 4 C1 = N 3 P 3 C1 6 + I2HC1. It forms colourless 
 rhombic prisms, melting at 114 C. and insoluble in water, but slowly decomposed 
 by it; 2P 3 N 3 C1 6 + I5H 2 = I2HC1 + 3P 2 3 (NH 2 ) 2 (OH) 2 , pyrophosphodiamic acid, 
 or pyrophosphoric acid, P 2 3 (OH) 4 , in which two NH 2 groups have been substi- 
 tuted for two OH groups. 
 
 ARSENIC. 
 As = 74.5 parts by weight.* 
 
 1 60. This element is often classed among the metals, because it has a 
 metallic lustre and conducts electricity, but it is not capable of forming 
 a base with oxygen, and the chemical character and composition of its 
 compounds connect it in the closest manner with phosphorus. 
 
 In its mode of occurrence in nature it more nearly resembles the 
 sulphur group of elements, for it is occasionally found in the uncombined 
 state (native arsenic), but far more abundantly in combination with 
 various metals, forming arsenides, which frequently accompany the sul- 
 phides of the same metals. The following are some of the chief arsenides 
 and arsenio-sulphides found in the mineral kingdom : 
 
 * The specific gravity of the vapour of arsenic, like that of phosphorus, indicates that 
 74.5 parts by weight only occupy half a volume. Hence the molecule of arsenic must be 
 represented as As 4 = 2 volumes ; but at very high temperatures a disposition to conform with 
 the law is shown by a diminution in the vapour density. 
 
266 EXTRACTION OF ARSENIC. 
 
 Kupfernickel NiAs 
 
 Arsenical nickel NiAs 2 
 
 Tin- white cobalt CoAs 2 
 
 Arsenical iron Fe 2 As 3 
 
 Mispickelor \ 
 
 Arsenical pyrites J 
 
 Cobalt-glance CoS 2 . CoAs 2 
 
 Nickel-glance NiS 2 .NiAs 2 
 
 But arsenic also occurs, like the metals, in combination with sulphur ; 
 thus we have red orpiment or realgar, As 2 S 2 , and yellow orpiment, 
 As 2 S 3 . It is from these minerals that arsenic derives its name 
 (apcrfviK&v, orpiment). 
 
 The sulphides of arsenic are also found in combination with other sulphides ; 
 thus Proustite is a compound of the sulphides of silver and arsenic (3Ag 2 S.As 2 S 3 ) ; 
 Tennantite contains sulphide of arsenic combined with the sulphides of iron and 
 copper ; and grey copper ore is composed of sulphide of arsenic with sulphides of 
 copper, silver, zinc, iron, and antimony. In an oxidised form arsenic is found in 
 condurrite, which contains arsenious anhydride (As 4 6 ) and cuprous oxide. 
 Cobalt-bloom consists of cobalt arsenate, Co 3 (As0 4 ) 2 . 
 
 Arsenical pyrites is one of the principal sources of arsenic and its 
 compounds, though a considerable quantity is also obtained in the form 
 of arsenious oxide as a secondary product in the working of certain ores, 
 especially those of copper, tin, cobalt, and nickel. 
 
 The substance used in the arts under the name of arsenic is really 
 the arsenious oxide (As 4 6 ) ; pure arsenic itself has very few useful 
 applications, so that it is not the subject of an extensive manufacture. 
 Arsenic can be extracted from mispickel (Fe 2 S 2 As 2 ) by heating it in 
 earthern cylinders fitted with iron receivers in which the arsenic 
 condenses as a metallic-looking crust, the heat expelling it from the 
 mineral in the form of vapour. 
 
 On a small scale it may be obtained by heating a mixture of white arsenic 
 with half its weight of recently calcined charcoal in a crucible (Fig. 188), the 
 
 mixture being covered with two or three inches 
 of charcoal in very small fragments, and the 
 crucible so placed that this charcoal may be 
 heated to redness first, in order to ensure the 
 reduction of any oxide which might escape from 
 below. In order to collect the arsenic, another 
 crucible, having a small hole drilled through the 
 bottom for the escape of gas, is cemented on 
 to the first, in an inverted position, with fire- 
 clay, and protected from the fire by an iron plate 
 with a hole in it for the crucible. The reduc- 
 tion of arsenious anhydride by charcoal is thus 
 represented As 4 6 + C 6 = As 4 + 6CO. 
 
 For the sake of illustration, a small quantity 
 of arsenic may be prepared from white arsenic 
 by a method commonly employed in testing for 
 that substance. A small tube of German glass 
 Fig. 188. Extraction of arsenic. is drawn out to a narrow point (A, Fig. 189), 
 
 and sealed with the aid of the blow-pipe. A 
 
 very minute quantity of white arsenic is introduced into the point of the tube, and 
 a few fragments of charcoal are placed in the tube itself at B. The charcoal is 
 heated to redness with a blow-pipe flame, and the point is then heated so as to 
 drive the white arsenic in vapour over the red-hot charcoal, when a shining black 
 ring of arsenic (C) will be deposited upon the cooler portion of the tube. 
 
 The arsenic thus obtained is a brittle mass of a dark steel-grey colour 
 and brilliant metallic lustre (sp. gr. 5.7). It vaporises at 180 C. 
 without melting unless it is heated in a sealed tube under the pressure 
 of its own vapour, when it melts at 480 C. It is not changed by 
 exposure to air, unless powdered and moistened, when it is slowly 
 
OXIDES OF ARSENIC. 267 
 
 Converted into As 4 O 6 . When heated in air it oxidises rapidly at about 
 71 C., giving off white fumes of arsenious oxide and a characteristic 
 garlic odour (recalling that of phosphorus), which is also produced when 
 arsenical pyrites is struck with a hammer or pick. At a red heat it 
 burns in air with a bluish-white flame, and in oxygen with great 
 brilliancy. 1 1 is not dis- 
 solved by water or any 
 simple solvent, but is 
 oxidised and dissolved by 
 nitric acid, 
 
 In its chemical relations 
 to other elements, arsenic 
 much resembles phos- 
 phorus, undergoing spon- 
 taneous combustion in 
 chlorine, and easily com- 
 bining with sulphur. Fig . l85 ._ Reduction of arsenious oxide . 
 Like phosphorus also, it 
 
 combines with many metals, even with platinum, to form arsenides, and 
 its presence often affects materially the properties of the useful metals. 
 
 Pure arsenic does not produce symptoms of poisoning till a consider- 
 able period after its administration, being probably first oxidised in the 
 stomach and intestines, and converted into arsenious acid. 
 
 Arsenic vapour is colourless, but when rapidly cooled it appears 
 yellow owing to the condensation of a cloud of minute yellow crystals 
 which are an allotropic modification of arsenic, soluble in CS 2 and re- 
 markably sensitive to light, which converts it into the black variety. 
 
 When arsenic is sublimed in a tube filled with hydrogen, ordinary 
 or crystalline arsenic condenses on the warmer part of the tube, but 
 on the cooler part, amorphous arsenic is deposited, of sp. gr. only 4.7. 
 This is not so easily oxidised in moist air as the crystalline variety. 
 At 360 C. it evolves heat and becomes converted into crystalline 
 arsenic.* 
 
 161. Oxides of Arsenic. Arsenic forms two oxides, corresponding 
 with phosphorous and phosphoric anhydrides, viz., As 4 6 and As 2 5 . 
 
 Arsenious oxide (As 4 6 = 396 parts by weight) Unlike phosphorus, 
 arsenic, when burning in air, only combines with oxygen to form its 
 lower oxide. Arsenious oxide, or white arsenic, is a very useful sub- 
 stance in many branches of industry. It is employed in the manufac- 
 ture of glass, and of several colouring-matters. A large quantity is 
 also consumed for the preparation of arsenic acid and arsenate of soda ; 
 it is, indeed, the source from which nearly all the compounds of arsenic 
 are procured. Small quantities of crystalline arsenious oxide are occa- 
 sionally found associated with the ores of nickel and cobalt. 
 
 White arsenic is manufactured by roasting the arsenical pyrites, 
 chiefly obtained from the mines of Silesia, in muffles or ovens, through 
 which air is allowed to pass, when the arsenic is converted into As 4 O 6 , 
 and the sulphur into SO 2 , which are conducted into large chambers 
 wherein the As 4 6 is deposited as a very fine powder. The iron of the 
 
 * Another amorphous variety of arsenic has been described as a brownish-black powder 
 of sp. gr. 3.7. Doubt has been expressed concerning the amorphous character of this allo- 
 trope of arsenic. 
 
268 WHITE AESENIC. 
 
 pyrites is left partly as oxide, and partly as sulphate of iron. The 
 removal of the As 4 O 6 from the condensing- chambers is a very unwhole- 
 some operation, owing to its dusty and very poisonous character. The 
 workmen are cased in leather, and protect their mouths and noses with 
 damp cloths, so as to avoid inhaling the fine powder. 
 
 This rough white arsenic is subjected to a second sublimation on a 
 smaller scale in iron vessels, when it is obtained in the form of a semi- 
 transparent glassy mass known as vitreous arsenious acid, which gradually 
 becomes opaque from crystallisation when kept, and ultimately resembles 
 porcelain. The white arsenic sold in the shops is a fine powder, 
 dangerously resembling flour in appearance, but so much heavier (sp. 
 gr. 3.7) that it ought not to be mistaken for it. When examined under 
 the microscope it appears in the form of irregular glassy fragments, 
 mixed with octahedral crystals. White arsenic softens when gently 
 heated, but does not fuse (unless in a sealed tube), being converted into 
 vapour at 193 C., and depositing in brilliant octahedral crystals upon 
 a cool surface. The experiment may be made in a small tube sealed at 
 one end, the upper part of which should be slightly warmed before 
 heating the arsenious oxide, so as to prevent too rapid condensation, 
 which is unfavourable to the formation of distinct crystals. The 
 octahedra are best examined with a binocular microscope. By satura- 
 ting a boiling solution of KOH with As 4 6 , and allowing the liquid 
 to cool, prismatic crystals (sp. gr. 4) separate. Thus As 4 6 is both 
 amorphous and dimorphous, the amorphous form (sp. gr. 3.7) being 
 condensed from the vapour on a hot surface, the octahedral (sp. gr. 3.7) 
 condensing on a cool surface, and the prismatic crystallising as described 
 above. When crystallised from water both the other forms become 
 octahedral. The change from amorphous to crystalline arsenious oxide 
 is attended by evolution of heat. 
 
 The amorphous and octahedral forms differ in solubility, one part 
 of the former dissolving in 108 parts of water at 15 C., and one part 
 of the crystalline in 355 parts. At the boiling-point these numbers 
 become 30 and 46 respectively. 
 
 This common poison may fortunately be easily recognised by sprink- 
 ling it upon a red-hot coal, when a strong odour of garlic is percep- 
 tible, due to the reduction of the As 4 O 6 by the heated carbon ; the 
 vapour of white arsenic, or that of arsenic, is itself inodorous. The 
 sparing solubility of white arsenic in water is very unfavourable to its 
 action as a poison, for, when thrown into ordinary liquids, it is dissolved 
 in very small quantity, the greater part of it collecting at the bottom. 
 Even when taken into the stomach in a solid state, its want of solubility 
 delays its operation sufficiently to give a better chance of antidotal 
 treatment than in the case of most other common poisons. Its com- 
 parative insolubility is shown by its being almost tasteless. Although 
 so little as 2.5 grains of white arsenic have been known to prove fatal, 
 the exhibition of gradually increasing doses will so inure the system to 
 the poison that comparatively large quantities can be administered at 
 frequent intervals. When exhibited in this manner, white arsenic 
 appears to have a remarkable effect on the animal body. Grooms 
 occasionally employ it to improve the appearance of horses, and in Styria, 
 it seems, it is taken by men and women for the same purpose, apparently 
 favouring the secretion of fat. It is said that a continuance of the 
 
SOLUBILITY OF WHITE AESENIC. 269 
 
 custom develops a craving for this drug, and enables it to be taken 
 without immediate danger, though the ultimate consequences are very 
 serious. The antidote to the poison is ferric hydroxide, made by mixing 
 magnesia with ferric chloride solution ; this acts by rendering the 
 arsenic insoluble. 
 
 The very general distribution of arsenic through the mineral kingdom 
 makes it necessary that the analyst should ever be on the watch for 
 this insidious poison. As has been already seen the arsenic in ordinary 
 pyrites finds its way into the sulphuric acid made therefrom, and then 
 into the commercial hydrochloric acid distilled with aid of this sulphuric 
 acid. The use of sulphuric acid containing arsenic for converting starch 
 into glucose subsequently used in making beer has been the cause of 
 many deaths in the district consuming the beer. This beverage appears 
 to be liable also to contain arsenic derived, it is alleged, from pyrites in 
 the fuel used to dry the malt, from which the beer is brewed. 
 
 When thrown into water, white arsenic exhibits great repulsion for the particles 
 of that liquid, and collects in a characteristic manner round little bubbles of air 
 forming small white globes which are not wetted by the water. Even if stirred, 
 with the water, and allowed to remain in contact with it for some hours, a pint of 
 water (20 oz.) would not take up more than 20 grains. If boiling water be poured 
 upon powdered white arsenic, and allowed to remain in contact with it till cold, 
 it will dissolve about ^^th of its weight (22 grains in a pint). 
 
 When powdered white arsenic is boiled with water for two or three hours, ico 
 parts by weight of \\ater may be made dissolve 11.5 parts, and when the solution 
 is allowed to cool, about 9 parts will be deposited in octahedral crystals, leaving 
 2.5 parts dissolved in 100 of water (219 grains in a pint). 
 
 This great increase in the solubility of the arsenious oxide by long boiling with 
 water is usually attributed to the conversion of the opaque or crystalline variety, 
 which always composes the powder, into the vitreous modification, which is the 
 more soluble in water (4 parts in 100 of water). Water, heated with white arsenic 
 in a sealed tube, may be made to dissolve its own weight of it ; as the solution 
 cools, it first deposits prismatic crystals, and afterwards the ordinary octahedral 
 form. The solution is very feebly acid to blue litmus-paper. Glycerine dissolves 
 As 4 6 easily when heated. 
 
 White arsenic dissolves abundantly in hot hydrochloric acid (a part of 
 it being converted into arsenious chloride), and as the solution cools, 
 part of the oxide is deposited in large octahedral crystals. The forma- 
 tion of these crystals is attended by flashes of light, visible in a 
 darkened room. 
 
 This experiment, which is exceedingly beautiful, is best performed by boiling 
 60 grams of arsenious oxide in 500 c.c, of a mixture of equal volumes of strong 
 hydrochloric acid and water in a flask, and allowing the solution to cool slowly ; 
 after a time the crystals begin to form, a flash of light accompanying the formation 
 of each, and the effect may be enhanced by carefully shaking the flask. It is said 
 that it is only the vitreous form which exhibits this phenomenon ; but the same 
 solution will generally serve for the above experiment any number of times if it 
 be reheated, although the arsenious oxide has, of course, been deposited in 
 the crystalline form ; it is, however, remarkable that the experiment sometimes 
 unaccountably fails. 
 
 Solutions of the alkalies readily dissolve arsenious oxide, forming 
 alkali arsenites, the solutions of which are capable of dissolving arsenious 
 oxide more easily than water can, and deposit it in crystals on cooling 
 (see above). On adding a small quantity of hydrochloric acid to the 
 solution of the alkali arsenite, a white precipitate of arsenious oxide 
 is formed. 
 
 White arsenic has the property of preventing the putrefaction of skin 
 
270 ARSENITES. 
 
 and similar substances, and is occasionally employed for the preservation 
 of objects of natural history, &c. 
 
 Arsenites. Arsenious acid, properly so called. has not yet been obtained 
 in the separate state. The aqueous solution of white arsenic, when 
 neutralised exactly with ammonia, yields, with silver nitrate, a yellow 
 precipitate having the composition Ag' 3 AsO 3 ; with cupric sulphate, a 
 green precipitate having the composition Cu"HAsO 3 ; with zinc sulphate, 
 a white precipitate containing Zn" 3 (AsO 3 ) 2 ; and with magnesium 
 sulphate, a white precipitate of Mg"HAsO 3 . It would appear, therefore, 
 that the arsenious acid from which these salts are derived is a tribasic 
 acid having the formula H 3 AsO 3 , or As(OH) 3 , corresponding with boric 
 acid, H 3 BO 3 . Arsenious acid does not destroy the alkaline reaction of 
 the alkalies, and it does not decompose the alkaline carbonates unless 
 heat is applied, proving it to be a feeble acid. The ammonium arsenite 
 is very unstable, evolving ammonia freely when exposed to the air. 
 When arsenious oxide is dissolved in a hot solution of ammonia, 
 octahedral crystals of it are deposited on cooling, notwithstanding the 
 presence of ammonia in large excess. The alkali arsenites are more 
 correctly metarsenites, for they are derived from HAs0 2 , or AsO(OH), 
 metarsenious acid ; the potassium arsenite is KAsO 2 . 
 
 When the carbonates of potassium and sodium are fused with an excess of 
 arsenious oxide, brilliant transparent glasses are obtained which are similar in 
 composition to glass of borax (K 2 As 4 7 and Na,2As 4 7 ). 
 
 If an alkali arsenite be fused in contact with platinum, the latter is easily melted,, 
 combining with a small proportion of arsenic to form a fusible platinum arsenide, 
 a portion of the arsenite being converted into arsenate. The alkali arsenates 
 (from arsenic acid, H 3 As0 4 ) are so much more stable than the arsenites that the 
 latter exhibit a great tendency to pass into the former, with separation of arsenic. 
 
 The arsenites of potassium and sodium in solution are sometimes employed as 
 sheep-dipping compositions ; and an arsenical soap, composed of potassium arsenite,. 
 soap, and camphor, is used by naturalists to preserve the skins of animals. Sodium 
 arsenite is also occasionally employed for preventing incrustations in steam boilers, 
 being prepared for that purpose by dissolving 2 molecules of white arsenic and 
 I molecule of sodium carbonate. 
 
 Scheele's green is an arsenite of copper (CuHAsO 3 ) prepared by dissolv- 
 ing white arsenic in a solution of potassium carbonate, and decomposing 
 the arsenite of potassium thus produced by adding sulphate of copper, 
 when the arsenite of copper is precipitated. This poisonous colour i& 
 used to impart a bright green tint to paper hangings, and is sometimes 
 injurious to the health of the occupants of rooms thus decorated, since 
 the arsenite of copper is often easily rubbed off the paper, and diffused 
 through the air in the form of a fine dust, a small portion of which is 
 inhaled with every breath. 
 
 The presence of the arsenite of copper in a sample of such paper is readily proved 
 by soaking it in a little ammonia, which will dissolve the arsenite of copper to a 
 blue liquid, the presence of arsenic in which may be shown by acidifying it with a 
 little pure hydrochloric acid, and boiling with one or two strips of pure copper, 
 which will become covered with a steel-grey coating of arsenide of copper. On 
 washing the copper, drying it on filter-paper, and heating it in a small tube 
 (Fig. 190), the arsenic will be converted into arsenious oxide, which will deposit in 
 brilliant octahedral crystals on the cool part of the tube. It is obvious that, to 
 avoid mistakes, the ammonia, hydrochloric acid, and copper should be examined 
 in precisely the same way, without the suspected paper, so as to render it certain 
 that the arsenic is not derived from them. 
 
 The effective green colour of the arsenite of copper also leads to its 
 
AESENIC ACID. 271 
 
 employment as a colour for feathers, muslin, &c., where it is very in- 
 jurious to the health of the workpeople. It has even been ignorantly 
 or recklessly used for colouring 
 twelfth-cake ornaments, &c. 
 
 Emerald-green (Paris green) is 
 a combination of arsenite and 
 acetate of copper obtained by 
 mixing hot solutions of equal 
 weights of white arsenic and 
 acetate of copper. Solution of 
 potassium arsenite (Fowler's solu- 
 tion) has long been used in medi- 
 cine. 
 
 Both Scheele's green and Paris 
 green are used as insecticides on 
 growing crops. 
 
 162. Arsenic acid (H 3 AsO 4 or AsO(OH) 3 ). Arsenic acid is prepared 
 by oxidising white arsenic with three-fourths of its weight of nitric acid 
 of sp. gr. 1.35, when it dissolves with evolution of much heat and 
 abundant red fumes of nitrous anhydride 
 
 As 4 6 + 4 HN0 3 + 4 H. 2 = 2N 2 3 + 4H 3 As0 4 . 
 
 After cooling, the solution deposits very deliquescent prismatic 
 crystals containing 2H 3 AsO 4 .H.,O. When heated to 100 C., these 
 melt, and the liquid deposits needle-like crystals of ortho-arsenic acid f 
 H 3 AsO 4 , corresponding with orthophosphoric ; at 180 C., 2H 3 As0 4 = 
 H 2 -f H 4 As 2 7 , pyro-arsenic acid, corresponding with pyrophosphoric ; 
 at 206 C., H 4 As 2 7 = H 2 O + 2HAs0 3 , metarsenic acid, corresponding 
 with metaphosphoric ; but here the resemblance ceases, for at 260 C. r 
 2HAsO 3 = H 2 O + As,O 5 , whereas HPO 3 may be vaporised without decom- 
 position. When metarsenic and pyro-arsenic acids are dissolved in 
 water, they at once become ortho-arsenic acid. The meta- and pyro- 
 arsenates are known only in the solid state. As 2 (X is decomposed at a 
 red heat into As 4 O 6 and oxygen. 
 
 Arsenic anhydride, As 2 O 5 , has very much less attraction for water than 
 has the phosphoric anhydride with which it corresponds ; it deliquesces 
 slowly in air, and dissolves rather reluctantly in water. Neither does it 
 appear that its combinations with water differ from each other, like the 
 phosphoric acids, in the salts to which they give rise, arsenic acid form- 
 ing tribasic salts only, like common phosphoric acid. The arsenates 
 correspond very closely with the orthophosphates, with which they are 
 isomorphous (i.e., identical in crystalline form). Thus the three 
 arsenates of sodium are similar in composition to the three ortho- 
 phosphates, the formulae being Na 3 AsO 4 .i2Aq ; Na 2 HAsO 4 .i2Aq ; and 
 2 (NaH 2 AsO 4 ).Aq. 
 
 The common arsenate of soda (Na 2 HAsO 4> 7Aq) is largely used by 
 calico-printers as a substitute for the dung-baths formerly employed, 
 since, like the common phosphate of soda, it possesses the feebly alkaline 
 properties required in that particular part of the process. It is manu- 
 factured by combining arsenious oxide with soda, and heating the 
 resulting arsenite with sodium nitrate, from which it acquires oxygen, 
 becoming converted into sodium arsenate. 
 
272 
 
 MARSH'S TEST FOR ARSENIC. 
 
 Calcium arsenate, 2CaHAs0 4 .7H 2 O, has been found in crystalline 
 crusts at Joachimsthal. Arsenio-siderite and xantho-siderite are calcium 
 ferric arsenates. 
 
 Arsenic acid is used by the calico-printer as an acid and by the dye- 
 stuff maker as an oxidant. It is a much more powerful acid than arsenious 
 acid, being comparable, in this respect, with phosphoric acid. It is less 
 stable than phosphoric acid, and acts as an oxidising agent. Sulphurous 
 acid, which is without action on phosphoric, reduces arsenic acid to 
 arsenious acid ; H 3 AsO 4 + H 2 S0 3 = H 3 AsO 3 + H 2 S0 4 . 
 
 1 63. Arsenetted hydrogen, hydrogen arsenide, or arsine ( AsH 3 = 
 78 parts by weight). The only compound of arsenic and hydrogen the 
 existence of which has been satisfactorily established is that which 
 corresponds with ammonia and phosphine. It is prepared by the action 
 of sulphuric acid diluted with three parts of water upon the zinc 
 arsenide, obtained by heating equal weights of zinc and arsenic in an 
 earthern retort; Zn 3 As 2 + 3H 2 S0 4 = 2AsH 3 + 3ZnS0 4 . The gas is so 
 poisonous in its character that its preparation in the pure state is 
 attended with danger. It has a sickly alliaceous odour, and may be 
 liquefied at -55 C. and solidified at -113 0. It is inflammable, 
 burning with a peculiar, livid flame, producing water and fumes of 
 arsenious oxide; 4AsH 3 + 12 = As 4 O 6 + 6H 2 0. The chief interest at- 
 taching to this gas depends upon the circumstance that its production 
 allows of the detection of very minute quantities of arsenic in cases of 
 poisoning. 
 
 The application of this test, known as Marsh's test, is the safest method of 
 preparing arsenetted hydrogen in order to study its properties, for it is obtained 
 so largely diluted with free hydrogen that it ceases to be so very dangerous. 
 Some fragments of granulated zinc are introduced into a half-pint bottle (Fig. 191), 
 
 provided with a funnel 
 tube (A), and a narrow 
 tube (B) bent at right 
 angles and drawn out to 
 a jet at the extremity ; 
 this tube should be made 
 of German glass, so that 
 it may not fuse easily. 
 The bottle having been 
 about one-third filled 
 with water, a little diluted 
 sulphuric acid is poured 
 down the funnel-tube so 
 as to cause a moderate 
 evolution of hydrogen, 
 and after about five 
 minutes (to allow the 
 escape of the air) the 
 hydrogen is kindled at 
 
 the jet. If a few drops of a solution obtained by boiling white arsenic with water 
 be now poured down the funnel, arsenetted hydrogen will be evolved together with 
 the hydrogen ; As 4 6 + Zn 12 + i2H 2 S0 4 = 4AsH 3 + i2ZnS0 4 + 6H 2 0. 
 
 The hydrogen flame will now acquire the livid hue above referred to, and a 
 white smoke of As 4 6 will rise from it. If a piece of glass or porcelain be depressed 
 upon the flame (Fig. 192), it will acquire a brown coating of arsenic, just as carbon 
 would be deposited from an ordinary gas-flame. Arsenetted hydrogen is easily 
 decomposed by heat (230 C.), so that if the glass tube through which it passes be 
 heated with a spirit-lamp (Fig. 193) a dark mirror of arsenic will be deposited a 
 little in front of the heated part, and the flame of the gas will lose its livid hue. 
 These deposits of arsenic are extremely thin, so that a very minute quantity of 
 
 Fig-. 192. 
 
 Fig. 193. 
 
ARSENIOUS CHLORIDE. 2/3 
 
 arsenic is required to form them, thus rendering the test one of extraordinary 
 delicacy. It must be remembered, however, that both sulphuric acid and zinc are 
 liable to contain arsenic, so that erroneous results may be very easily arrived at by 
 this test. 
 
 An electrolytic test for arsenic may also be employed which depends upon the 
 circumstance that when a fairly powerful galvanic current is passed through an 
 acid liquid containing arsenic, arsenetted hydrogen is evolved at the negative ter- 
 minal along with the hydrogen of the decomposed water. 
 
 Arsenetted hydrogen, like sulphuretted hydrogen, causes dark precipitates in 
 many metallic solutions. 
 
 Silver nitrate is reduced to the metallic state by AsH 3 ; AsH 3 + 6AgN0 3 + 3H 2 = 
 H 3 As0 3 + 6HN0 3 + 3Ag 2 . A piece of filter-paper, spotted with silver nitrate 
 solution, will have the spots blackened if held before the tube from which the 
 gas issues. The simplest test for arsenic in wall-paper, &c., is to drop a piece 
 of the paper into a glass containing some zinc and sulphuric acid, and to cover 
 the mouth of the glass with a piece of paper wetted with silver nitrate, which 
 will be blackened if arsenic be present. The purity of the materials should be 
 tested first in the same way, and the absence of sulphur, which also blackens 
 silver nitrate, should be proved by lead acetate, which is not blackened by arsenic. 
 
 Hydrogen phosphide, hydrogen arsenide, and ammonia constitute a 
 group of hydrogen compounds having certain properties in common, 
 which distinguish them from the compounds of hydrogen with other 
 elements. 
 
 Two volumes of each of these gases contain three volumes of hydrogen. 
 
 They are all possessed of peculiar odours, that of ammonia being the 
 most powerful and that of hydrogen arsenide the least. Ammonia is 
 powerfully alkaline, phosphine exhibits some tendency to play an alka- 
 line part, whilst arsine seems devoid of alkaline disposition. They are 
 all inflammable, ammonia being the least so of the group, and are 
 decomposed by heat, ammonia least easily, and hydrogen arsenide most 
 easily. They are all producible from their corresponding oxygen com- 
 pounds, viz., N 2 3 ,P 4 6 , and As 4 O 6 , by the action of nascent hydrogen 
 (e.g., by contact with zinc and diluted sulphuric acid). 
 
 All three are the prototypes of various organic bases which contain 
 some compound radicle in place of the hydrogen, thus 
 
 NH 3 is the prototype of triethylamine N(C 2 H 5 ) 3 
 
 PH 3 triethylphosphine P(C 2 H 5 ) 3 
 
 AsH 3 triethylarsine As(C 2 H 5 ) 3 
 
 164. Arsenic trichloride, or arsenious chloride. Only one compound of chlorine 
 with arsenic (AsCl 3 ) is well known.* The trichloride may be formed by the direct 
 union of its elements, but the simplest laboratory process for procuring it consists 
 in heating white arsenic in dry chlorine, in a tubulated retort (A, Fig. 194). The 
 arsenious anhydride soon melts, and the trichloride distils, leaving a melted 
 mass in the flask, which is a brilliantly transparent glass when cool ; its composition 
 varies somewhat with the temperature used, but appears to be essentially As 4 6 .As 2 5 . 
 The same vitreous compound may be obtained by fusing arsenious and arsenic 
 oxides together. The reaction may be represented by the equation 
 
 1 1 As 4 6 + C124 = 8AsCl 3 + 6(As 4 6 .As a 5 ). 
 
 Arsenic trichloride bears a great general resemblance to phosphorus trichloride ; 
 it is a heavy (sp. gr. 2.2, b.p. 134 C.), pungent, fuming liquid, decomposed by the 
 moisture of the air, its vapours depositing a white coating upon the objects in 
 its immediate neighbourhood. When poured into water it deposits arsenious 
 oxide ; 4AsCl 3 + 6H 2 O = As 4 O 6 + I2HC1 ; but when dissolved in the smallest possible 
 
 quantity of water it deposits crystals of the formula AsOCl. H 2 or AsCl(OH) 2 . 
 
 When white arsenic is dissolved in hydrochloric acid, arsenious chloride is 
 formed, As 4 6 + i2HCl = 4As01 3 + 6H 2 0, and remains undecomposed by the water 
 
 * It is said that the pentachloride can be formed by the action of hydrochloric acid gas 
 on As2O 5 in presence of ether. 
 
 S 
 
2 74 
 
 ORPIMENT. 
 
 in the presence of strong hydrochloric acid, but if water be added, arsenious oxide 
 is precipitated. When the solution in hydrochloric acid is distilled, the arsenious 
 chloride distils over, and this is sometimes a convenient method of separating 
 arsenic from articles of food, &c., in testing for that poison. When heated in 
 
 dry hydrochloric acid gas, white arsenic 
 yields a glassy compound, which con- 
 tains As 4 O 6 .2AsOCl ; 3As 4 O 6 + 4HCl = 
 2(As 4 6 .2AsOCl) + 2H 2 0. 
 
 AsCl 3 and AsH 3 decompose each 
 other, yielding 3HC1 and As 2 . 
 
 Arsenious bromide much resembles 
 the chloride in its chemical characters, 
 but is a solid crystalline substance, 
 fusing at 25 C. and boiling at 220 C. 
 165. Arsenic tri-iodide, or arsenious 
 iodide (AsI 3 ), is remarkable for not 
 being decomposed by water, like the 
 corresponding phosphorus compound. 
 When obtained by heating together 
 arsenic and iodine, it sublimes in brick- 
 Fig-. 194. red flakes, which, if prepared on a 
 large scale, hang in long laminae, like 
 
 sea-weed. It may be dissolved in boiling water, and crystallises unchanged. It 
 may even be prepared by heating 3 parts of arsenic with 10 of iodine and 100 of 
 water, when the solution deposits red crystals of the hydrated tri-iodide, from which 
 the water may be expelled by a gentle heat. 
 
 AsI 3 is precipitated as a golden crystalline powder on mixing a hot solution of 
 As 4 6 in HC1 with a strong solution of KI. 
 
 Arsenic di-iodide, AsI 2 , is obtained by heating i part of arsenic and 2 parts of 
 iodine in a sealed tube to 230 C., and crystallising from CS 2 in an atmosphere of 
 C0 2 . It forms red prismatic crystals which become black when treated with 
 water, according to the equation 3 AsI 2 = 2AsI 3 + As. 
 
 When iodine is dissolved in a solution of arsenious acid, this is oxidised to 
 arsenic acid ; H 2 As0 3 + H 2 + I 2 = H 3 As0 4 + 2HI. When the solution is concentrated 
 by evaporation, the change is reversed, and iodine liberated. 
 
 The arsenic tri-fluoride (AsF 3 ) resembles the trichloride, but is much more 
 volatile (b.p. 63 C.) It may be obtained by distilling 4 parts of arsenious oxide 
 with 5 of fluor spar and 10 of strong sulphuric acid, in a leaden retort (see 
 p. 202). It does not attack glass unless water be present, which decomposes it into, 
 arsenious and hydrofluoric acids. PC1 5 converts it into FP 5 and AsCl 3 . 
 
 1 66. Sulphides of Arsenic. There are three well-known sulphides 
 of arsenic, having the composition As 2 S 2 , As 2 S 3 , and As 2 S 3 , the two- 
 former being found in nature. 
 
 Realgar (As 2 S 2 ) is a beautiful mineral, crystallised in orange-red 
 prisms ; but the red orpiment used in the arts is generally prepared by 
 heating a mixture of white arsenic and sulphur, when sulphurous acid 
 gas escapes, and an orange-coloured mass of realgar is left. Another 
 process for preparing it consists in distilling arsenical pyrites with, 
 sulphur or with iron pyrites ; FeS 2 .FeAs 2 + 2FeS 2 = 4FeS + As 2 S 9 . The 
 realgar distils, and condenses to a red transparent solid. Realgar burns 
 in air with a blue flame, yielding arsenious and sulphurous oxides. If 
 it be thrown into melted saltpetre, it burns with a brilliant white flame, 
 being converted into arsenate and sulphate of potassium. This brilliant 
 flame renders realgar an important ingredient in Indian fire and similar 
 compositions for fireworks and signal lights. A mixture of one part of 
 red orpiment with 3.5 parts of sublimed sulphur and 14 parts of nitre 
 is used for signal light composition. 
 
 Eealgar is not easily attacked by acids ; nitric acid, however, dissolves it, with 
 the aid of heat, forming arsenic acid and sulphuric acid, with separation of part 
 
SULPHIDES OF ARSENIC. 2/5; 
 
 of the sulphur in the free state. Alkalies (KOH for example) partly dissolve^ 
 it, leaving a dark brown substance, which appears to contain free arsenic ; 
 3As 2 S 2 = 2As 2 S 3 + As 2 . When exposed to air realgar is partly oxidised and con- 
 verted into a mixture of As. 2 S. 2 and As 4 6 . 
 
 Yellow orpiment, or arsenious sulphide (As 2 S 3 ), is found native in 
 yellow prismatic crystals. The pigment known as Kings yellow is a 
 mixture of arsenious sulphide and arsenious anhydride, prepared by sub- 
 liming excess of sulphur with white arsenic; S 9 + As 4 6 = 2As 2 S 3 + 3S0 2 . 
 It is, of course, very poisonous. 
 
 This substance, like realgar, is not much affected by acids, excepting nitric acid ; 
 but it dissolves entirely in potash, forming potassium arsenite and thwarsenite ; 
 6KOH + As 2 S 3 := K 3 AsS 3 + K 3 AsO 3 + 3H 2 O.* Ammonia also dissolves it easily, form- 
 ing a colourless solution which is employed for dyeing yellow, since, if a piece of 
 stuff be dipped into it and exposed to air, the ammonia will volatilise, leaving the 
 yellow orpiment behind. When As 2 S 3 is boiled with a strong solution of sodium 
 carbonate, H 2 S is evolved and As 2 S 2 is deposited as a crystalline powder. 
 
 The formation of the characteristic yellow sulphide is turned to account in 
 testing for arsenic ; if a solution prepared by boiling white arsenic with distilled 
 water be mixed with a solution of hydrosulphuric acid, a bright yellow liquid is 
 produced, which looks opaque by reflected, but transparent by transmitted, light, 
 and may be passed through a filter without leaving any solid matter behind. 
 This solution probably contains a soluble colloidal form of arsenious sulphide ; this 
 is, however, rendered insoluble by evaporation. The addition of a little hydro- 
 chloric acid, or of sal-ammoniac, and many other neutral salts, will also cause a 
 separation of the sulphide from this solution; even the addition of hard water 
 will have that effect. If the solution of arsenious acid be acidified with hydro- 
 chloric acid before adding the hydrosulphuric acid, the bright yellow sulphide is 
 precipitated at once, and may be distinguished from any other similar precipitate 
 by its ready solubility in solution of ammonium carbonate. 
 
 Arsenic sulphide (As 2 S 5 ) possesses far less practical importance than the preced- 
 ing sulphides ; it may be obtained by fusing As 2 S 3 with sulphur, when it forms 
 an orange-coloured glass, easily fusible, and capable of being sublimed without 
 change. When hydrosulphuric acid gas is passed slowly through solution of 
 arsenic acid, very little, if any, arsenic sulphide is formed, a white precipitate of 
 sulphur being first obtained, the hydrogen reducing the arsenic acid to arsenious 
 acidf; H 3 As0 4 + H 2 S H 3 As0 3 + H 2 + S ; and if the passage of the gas be con- 
 tinued, the arsenious acid is decomposed, and arsenious sulphide is precipitated ; 
 these changes are much accelerated by heat. But a rapid current of H 2 S passed 
 through a solution of arsenic acid in presence of much free hydrochloric acid 
 throws down pure arsenic sulphide. If a solution of sodium arsenate be saturated 
 with H 2 S, it is converted into sodium tJiioarsenate, NagAsS 4 . On adding hydro- 
 chloric acid to this solution, a bright yellow precipitate of arsenic sulphide 
 is obtained. Cuprous sulphar senate, or Clarite (Cu 3 AsS 4 ), is found in the Black 
 Forest. 
 
 167. Review of Nitrogen, Phosphorus, and Arsenic. These 
 elements are connected together by the general analogy of their hydrogen 
 and oxygen compounds, the two last members of the group being far 
 more closely connected with each other than with nitrogen. With the 
 metals they are connected through arsenic, the hydrogen-compound of 
 which is very similar in properties, and probably in composition, to 
 antimonetted hydrogen ; arsenious oxide (As 4 6 ) is also capable of 
 occupying the place of antimonious oxide (Sb 4 6 ) in certain salts of 
 that oxide ; and the sulphides of antimony correspond in composition, 
 and in some of their properties, with those of arsenic. One form of 
 
 * Since the metarsenite, KAsO 2 , is the only potassium arsenite which has been prepared, 
 and the metathioarsenite, KAsS 2 , appears to exist in the solution, the reaction is better ex- 
 pressed by the equation, 2As 2 S 3 + 4KOH=:KA8O 2 + 3KAsS 2 + 2H 2 O. 
 
 t Under some conditions the solution remains clear at first, sulphoxyarsenic acid being- 
 formed which is decomposed by more H 2 S with precipitation of As 2 S 5 . (i) H 3 AsO 4 + H 2 S = 
 H 3 AsO 3 S + H 2 O; (2) 2 
 
276 FORMS OF SILICA. 
 
 .arsenious oxide (the prismatic) is isomorphous with native oxide of 
 -antimony, and this oxide may be obtained in octahedra, the ordinary 
 form of arsenious oxide, so that these oxides are isodimorphous. 
 
 These elements are also connected with the oxygen group through 
 'Sulphur, selenium, and tellurium, the relations of which to hydrogen and 
 the metals are somewhat similar to those of phosphorus and arsenic. 
 
 SILICON. 
 
 Si iv = 28.2 parts by weight. 
 
 168. In many of its chemical relations to other bodies this element 
 will be found to bear a great resemblance to carbon ; but whilst carbon 
 is the characteristic element of organic substances, silicon is the most 
 abundant in the mineral world, where it is chiefly found in combination 
 with oxygen, as silica (Si0 2 ), either alone or as silicates. 
 
 Silica (SiO 2 = 60 parts by weight). The purest natural form of 
 silica is the transparent and colourless variety of quartz known as rock 
 crystal, the most widely diffused ornament of the mineral world, often 
 seen crystallised in beautiful six-sided prisms, terminated by six-sided 
 pyramids (Fig. 195), which are always easily distinguished by their 
 
 great hardness, scratch- 
 ing glass almost as readily 
 as the diamond. Coloured 
 of a delicate purple, pro- 
 bably by a little organic 
 matter, these crystals are 
 known as amethysts ; and 
 Fig. 195. Crystal of quartz. when of a brown colour, 
 
 as Cairngorm stones or 
 
 Scotch pebbles. Losing its transparency and crystalline structure, we 
 meet with silica in the form of chalcedony and of carnelian, usually 
 coloured, in the latter, with oxide of iron. 
 
 Hardly any substance has so great a share in the lapidary's art as 
 silica, for in addition to the above instances of its value for ornamental 
 purposes, we find it constituting jasper, agate, cat's eye, onyx, so much 
 prized for cameos, opal, and some other precious stones. In opal the 
 silica is combined with water. 
 
 /Sand, of which the whiter varieties are nearly pure silica, appears to 
 have been formed by the disintegration of siliceous rocks, and has 
 generally a yellow or brown colour, due to the presence of oxide of 
 iron. 
 
 The resistance offered by silica to all impressions has become pro- 
 verbial in the case oi flint, which consists essentially of that substance 
 coloured with some impurity. Flints are generally found in compact 
 masses, distributed in regular beds throughout the chalk formation ; 
 their hardness, which even exceeds that of quartz, rendered them useful, 
 before the days of matches, for striking sparks with steel ; small 
 particles of metal are thus detached, and are so heated by the percussion 
 as to continue to burn (see p. 37) in the air, and to inflame tinder or 
 gunpowder upon which they are allowed to fall. 
 
 The part taken by silica in natural operations appears to be chiefly 
 a mechanical one, for which its stability under ordinary influences 
 

 
 DISSOLVING SILICA. 277 
 
 peculiarly fits -it, for it is found to constitute the great bulk of the soil 
 which serves as a support and food-reservoir for land plants, and enters 
 largely into the composition of the greater number of rocks. 
 
 But that this substance is not altogether excluded from any share in 
 life, is shown by its presence in the shining outer sheath of the stems 
 of the grasses and cereals, particularly in the hard external coating of 
 the Dutch rush used for polishing, and in the joints of the bamboo, 
 where it forms the greater part of the matter known as tabasheer. 
 This alone would lead to the inference that silica could not be 
 absolutely insoluble, since the capillary vessels of plants are known to 
 be capable of absorbing only such substances as are in a state of solu- 
 tion. Many natural waters also present us with silica in a dissolved 
 state, and often in considerable quantity, as, for example, in the 
 geysers of Iceland, which deposit a coating of silica upon the earth 
 around their borders. 
 
 Pure water, however, has no solvent action upon the natural varieties 
 of silica. The action of an alkali is required to bring it into a soluble 
 form. 
 
 To effect this upon the small scale, some white sand is very finely 
 powdered (in an agate mortar), mixed with about four times its weight 
 of dried sodium car- 
 bonate, placed upon a 
 piece of platinum foil 
 slightly bent up (Fig. 
 196), and fused by 
 directing the flame of 
 a blowpipe upon the 
 under side of the foil. 
 Effervescence will be 
 observed, due to the 
 escape of carbonic acid 
 gas. The piece of 
 
 platinum foil, when Fig". 196. Fusion on platinum foil. 
 
 cool, may be placed in 
 
 a little warm water, and allowed to soak for some time, when the melted 
 mass will gradually dissolve, forming a solution of sodium silicate. This 
 solution will be found decidedly alkaline to test-papers. 
 
 If a portion of the solution of sodium silicate in water be poured into 
 a test-tube, and two or three drops of hydrochloric acid added to it, with 
 occasional agitation, effervescence will be produced by the expulsion of 
 any carbonic acid gas still remaining, and the solution will be converted 
 into a gelatinous mass by the separation of silicic acid. But if another 
 portion of the solution be poured into an excess of dilute hydrochloric 
 acid (i.e., into enough to render the solution distinctly acid), the silicic 
 acid will remain dissolved in the water, together with the sodium 
 chloride formed. 
 
 In order to separate the sodium chloride from the silicic acid, the 
 process of dialysis * must be adopted. 
 
 Dialysis is the separation of dissolved substances from each other by 
 taking advantage of the different rates at which they pass through moist 
 diaphragms or septa. It is found that those substances which crystallise 
 
 * From SiaAv'w, to part asunder. 
 
2/8 SILICIC ACID. 
 
 (crystalloids) and the mineral acids pass through such septa in a solution 
 faster than do amorphous substances (colloids). 
 
 If the mixed solution of sodium chloride and silicic acid were poured upon an 
 ordinary paper filter, it would pass through without alteration ; but if parchment 
 paper be employed, which is not pervious to water, although readily moistened by 
 it, none of the liquid will pass through. If the cone of parchment paper be sup- 
 ported upon a vessel filled with distilled water (Fig. 197), so that the water maybe 
 in contact with the outer surface of the cone, the hydrochloric acid and the sodium 
 chloride will pass through the substance of the parchment paper, and the water 
 
 Fig-. 197. Fig. 198. Dialyser. 
 
 charged with them may be seen descending in dense streams from the outside of 
 the cone. After a few hours, especially if the water be changed occasionally, the 
 whole of the hydrochloric acid and sodium chloride will have passed through, and 
 a pure solution of silicic acid in water will remain in the cone. 
 
 A convenient form of dialyser is represented in Fig. 198 ; it consists of parchment 
 paper stretched over a gutta-percha ring and held in this position by a concentric 
 ring. It is suspended on a surface of water and the solution to be dialysed is poured 
 upon it. 
 
 This solution is believed to contain the orthosilicic acid, H 2 0.2Si0 2 , or 
 H 4 Si0 4 , or Si(OH) 4 . It is very feebly acid to blue litmus-paper, and 
 not perceptibly sour to the taste. It has a great tendency to set into a 
 jelly in consequence of the sudden separation of silicic acid. If it be 
 slowly evaporated in a dish, it soon solidifi.es; but, by conducting the 
 evaporation in a flask, so as to prevent any drying of the silicic acid at 
 the edges of the liquid, it may be concentrated until it contains 14 per 
 cent, of silicic acid. When this solution is kept, even in a stoppered 
 or corked bottle, it sets into a transparent gelatinous mass, which 
 gradually shrinks and separates from the water. When evaporated, in 
 vacuo, over sulphuric acid, it gives a transparent lustrous glass which is 
 composed of 22 per cent, of water and 78 percent, of silica (H 2 O.Si0 2 ). 
 This is also the composition of the gelatinous precipitate produced by 
 acids in the solution of sodium silicate. It is sometimes written H 2 Si0 3 
 or SiO(OH) 2 , and called metasilicic acid. 
 
 This behaviour of silicic acid is typical of colloids ; they can generally 
 exist in solution (the hydrosol form), but are apt to separate as a jelly 
 (the hydrogel form) from such solutions. Gelatine is a familiar example. 
 
 The hydrated silica cannot be redissolved in water, and is only soluble 
 to a slight extent in hydrochloric acid. If it be heated to expel the 
 water, the silica which remains is insoluble both in water and in hydro- 
 chloric acid, but is dissolved when boiled with solution of potash or soda, 
 or their carbonates. 
 
 Silica in the naturally crystallised form, as rock crystal and quartz, 
 
MODIFICATIONS OF SILICA. 
 
 279 
 
 is insoluble in boiling solutions of the alkalies, and in all acids except 
 hydrofluoric ; but amorphous silica (such as opal and tripoli) is readily 
 dissolved by boiling alkalies. These represent, in fact, two distinct 
 modifications of silica, which may be said to be dimorphous* A trans- 
 parent piece of rock crystal may be heated to bright redness without 
 change, but if it be powdered previously to being heated, its specific 
 gravity is diminished from 2.6 to 2.4, and it becomes soluble in boiling 
 alkalies, having been converted into the amorphous modification. The 
 natural forms of amorphous silica of sp. gr. 2.2 are always hydrated, and 
 even some of the varieties of sp. gr. 2.6, such as flint, agate, and chalce- 
 dony, contain a little water, pointing to the aqueous origin of all silica. 
 Crystals of quartz have been obtained artificially by the prolonged 
 action of water upon glass at a high temperature under pressure. When 
 fused with the oxyhydrogen blowpipe, silica does not crystallise, being 
 thus converted into the amorphous variety of sp. gr. 2.2, which may be 
 worked while soft into threads and even tubes, much as glass is. The 
 threads are useful in electrical apparatus on account of their excellent 
 insulating property, far surpassing that of glass in a moist atmosphere. 
 The tubes are useful on account of the high temperature and rapid 
 changes of temperature they can withstand without fusion or fracture. 
 
 To prepare the amorphous modification of silica artificially, white sand in very 
 fine powder may be fused, in a platinum crucible, with six times its weight of a 
 mixture of equal weights of the potassium and sodium carbonates, the mixture 
 being more easily fusible than either of the carbonates separately. The crucible 
 may be heated over a gas burner supplied with a mixture of gas and air, or may 
 be placed in a little calcined magnesia contained in a fire-clay crucible, which may 
 be covered up and introduced into a good fire. The platinum crucible is never 
 heated in direct contact with fuel, since the metal would become brittle by com- 
 bining with carbon, silicon, and sulphur derived from the fuel. The magnesia is 
 used to protect the platinum from contact with the clay crucible. When the 
 action of the silica upon the alkali car- 
 bonates is completed, which will be 
 indicated by the cessation of the efferves- 
 cence, the platinum crucible is allowed 
 to cool, placed in an evaporating dish, 
 and soaked for a night in water, when 
 the mass should be almost entirely dis- 
 solved. Hydrochloric acid is then added 
 to the solution, with occasional stirring, 
 until it is distinctly acid to litmus-paper. 
 On evaporating the solution, it will, at a 
 certain point, solidify to a gelatinous 
 mass of hydrated silica, which would be 
 ejected from the dish if evaporation over 
 the flame were continued. To prevent 
 this, the dish is placed over an empty 
 iron saucepan so that the heat from the 
 flame may be equally distributed over 
 the bottom of the dish. When the mass 
 is quite dry the dish is allowed to cool, 
 and some water is poured into it, which 
 dissolves the chlorides of potassium and 
 sodium (formed by the action of the 
 hydrochloric acid upon the silicates), and leaves the silica in white flakes. These 
 may be collected upon a filter, and washed several times with distilled water. The 
 
 * If tridymitea, mineral which occurs in anhydrous hexagonal crystals, has a sp. gr. of 
 2.3, and is not attacked by alkalies be regarded as the type of another crystalline variety of 
 silica, this must be said to be trimorphous. 
 
 I99> _Air-gas blowpipe. 
 
280 SILICATES. 
 
 filter is then carefully spread out upon a hot iron plate, or upon a hot brick, and 
 allowed to dry, when the silica is left as a dazzling white powder, which must be 
 strongly heated in a porcelain or platinum crucible to expel the last traces of water. 
 It is remarkable for its extreme lightness, especially when heated, the slightest 
 current of air easily blowing it away. 
 
 169. For effecting such fusions as that just described, an air-gas blowpipe (Fig. 
 199) supplied with air from a double-action bellows, worked by a treadle, will be 
 found most convenient. 
 
 170. Silicates. The acid properties of silicic acid are so feeble that it 
 is a matter of great difficulty to determine the proportion of any base 
 which is required to react with it in order to form a chemically neutral 
 salt. Like carbonic acid, it does not destroy the action of the alkalies 
 upon test-papers, and we are therefore deprived of this method of 
 ascertaining the proportion of alkali which neutralises it in a chemical 
 sense. In attempting to ascertain the quantity of alkali with which 
 silica combines, from that of the carbon dioxide which it expels when 
 heated with an alkaline carbonate, it is found that the proportion of 
 carbon dioxide expelled varies considerably, according to the temperature 
 and the proportion of alkaline carbonate employed. The limits of the 
 reaction however appear to be the formation of the alkali metasilicate 
 on the one hand and the alkali orthosilicate on the other : 
 SiO 2 + Na 2 C0 3 = CO, + Na.,Si0 3 (metasilicate) 
 Si0 2 + 2Na 2 C0 3 = C0 2 + Na 4 SiO 4 (orthosilicate). 
 
 By heating silica with sodium hydroxide (NaOH), it is found that 60 
 parts of silica expel 36 parts of water, however much NaOH is employed, 
 and the same proportion of water is expelled from barium hydroxide, 
 Ba(OH) 2 , when heated with silica. 
 
 The formula Si0 2 represents 60 parts by weight of silica, and 36 parts 
 represent two molecules of water. Hence it would appear that the 
 action of silica upon sodium hydroxide is represented by the equation 
 4NaOH + Si0 2 = Na 4 Si0 4 + 2H 2 O ; and that upon barium hydroxide by 
 2Ba(OH) 2 + Si0 2 = Ba 2 Si0 4 + 2H 2 : and since it is found that several 
 of the crystallised mineral silicates contain a quantity of metal equiva- 
 lent to H 4 , it is usual to represent silicic acid as a tetrabasic acid, H 4 Si0 4 , 
 containing 4 atoms of hydrogen exchangeable for metals. 
 
 The circumstance that silica is not capable of being converted into 
 vapour at a high temperature, enables it to decompose the salts of many 
 acids which, at ordinary temperatures, are able to displace silicic acid. 
 The feebly acid character of Si0 2 will recall that of C0 2 . Other com- 
 parison between these analogues is hardly possible on account of their 
 different physical condition. 
 
 The silicates form by far the greatest number of minerals. The 
 different varieties of clay consist of aluminium silicate ; felspar is 
 a silicate of aluminium and potassium ; meerschaum is a silicate of 
 magnesium. 
 
 The different kinds of glass are composed of silicates of potassium, 
 sodium, calcium, lead, &c. None but the silicates of the alkali metals 
 are appreciably soluble in water. 
 
 Scarcely any of the silicates are represented by formulae which express 
 their derivation from the acid H 4 Si0 4 ; they are generally represented 
 as derivatives of metasilicic acid and of polysilicic acids, i.e., compounds 
 of 7iH 2 with Si0 2 (compare p. 261). 
 
 This tendency of silicon to form complex mineral compounds is 
 
SILICON. 281 
 
 comparable with that of its analogue, carbon, to form complex organic 
 compounds, but whereas oxygen is the other element mostly concerned 
 in the formation of mineral silicates, hydrogen is the predominant 
 companion of carbon in organic derivatives. 
 
 171. Silicon or silicium. From the remarkably unchangeable 
 character of silica, it is not surprising that it was long regarded, 
 as an elementary substance. In 1813, however, Davy succeeded 
 in decomposing it by the action of potassium, and in obtaining an 
 impure specimen of silicon. It has since been produced, far more 
 easily, by converting the silica into potassium silico-fluoride (K 2 SiF 6 ), 
 and decomposing this at a high temperature with potassium or sodium, 
 which combines with the fluorine to form a salt capable of being dis- 
 solved out by water, leaving the silicon in the form of a brown powder 
 (amorphous silicon), which resists the action of all acids, except hydro- 
 fluoric, which it decomposes, forming silicon fluoride, and evolving 
 hydrogen (Si + 4HF = SiF 4 + H 4 ). It is also dissolved by solution of 
 potash, with evolution of hydrogen, and formation of potassium silicate. 
 It burns brilliantly when heated in oxygen, but not completely, for it 
 becomes coated with silica which is fused by the intense heat of the 
 combustion. When heated with the blowpipe on platinum foil, it eats 
 a hole through the metal, with which it forms the fusible platinum 
 silicide. 
 
 If potassium silico-fluoride be fused with aluminium, a portion of the 
 latter combines with the fluorine, and the remainder combines with the 
 silicon, forming aluminium silicide. By boiling this with hydrochloric 
 and hydrofluoric acids in succession, the aluminium is extracted, and 
 crystalline scales of silicon, with a metallic lustre resembling black lead, 
 are left (graphitoid silicon). In this form the silicon has a specific 
 gravity of about 2.5, and refuses to burn in oxygen, or to dissolve in 
 hydrofluoric acid. A mixture of nitric and hydrofluoric acids, however, 
 dissolves it. It burns spontaneously in fluorine, and when heated in 
 chlorine. Like graphite, this variety of silicon conducts electricity, 
 though amorphous silicon is a non-conductor. The amorphous silicon 
 becomes converted into this incombustible and insoluble form under the 
 action of intense heat. It is worthy of remark that the combustibility 
 of amorphous carbon (charcoal) is also very much diminished by exposure 
 to a high temperature. 
 
 Unlike carbon, however, silicon is fusible at a temperature somewhat 
 above the melting-point of cast-iron ; on cooling, it forms a brilliant 
 metallic-looking mass, which may be obtained, by certain processes, 
 crystallised in octahedra so hard as to scratch glass like a diamond. 
 
 In their chemical relations to other substances there is much resem- 
 blance between silicon and carbon. Silicon, however, is capable of dis- 
 placing carbon, for if potassium carbonate be fused with silicon, the 
 latter is dissolved, forming potassium silicate, and carbon is separated. 
 Silicon also resembles carbon in its disposition to unite with certain 
 metals to form compounds which still retain their metallic appearance. 
 Thus silicon is found together with carbon in cast-iron, and it unites 
 directly with aluminium, zinc, and platinum, to form compounds resem- 
 bling metallic alloys. Nitrogen enters into direct union with silicon at 
 a high temperature, though it refuses to unite with carbon except in 
 the presence of alkalies. 
 
282 CARBORUNDUM. 
 
 The most important analogy between carbon and silicon from a 
 theoretical point of view, resides in the fact that each of them combines 
 with hydrogen in the proportion of one atom of the element to four 
 atoms of hydrogen, showing that each is a tetravalent element. 
 
 Silicon carbide, SiC. As might be expected from their similarity, 
 carbon and silicon do not combine easily. At the temperature of the 
 electric furnace (3500 C.), however, the compound SiC is produced in 
 the form of colourless, transparent hexagonal plates of sp. gr. 3.12. It 
 is hard enough to scratch the ruby, and on this account is made on a 
 considerable scale for use as an abrasive material under the name car- 
 borundum which is generally dark coloured from impurities. It resists 
 the attack of all acids, but succumbs to fused alkali ; it does not oxidise 
 even at a white heat. 
 
 In the manufacture of carborundum the electric furnace consists of a brick box, 
 having a carbon electrode projecting into each end. The bottom of the box having 
 been covered up to the level of the electrodes with a mixture of sand, coke, and a 
 little salt, a layer of crushed coke of the same cross-section as the electrodes is built 
 up between the electrodes. The furnace is then filled with the aforesaid mixture. 
 When the electric current is supplied to the electrodes the layer of coke between 
 them attains a very high temperature owing to the resistance it offers to the passage 
 of the current, and the radiation from .this hot core causes the carbon in the charge 
 to reduce the silica and to combine with the silicon for a certain distance around 
 the core ; SiO 2 + C 3 = SiC + 2CO. 
 
 Silicon nitride, SiN (?), has been obtained by heating silica with carbon in a 
 blast furnace and treating the product successively with hydrofluoric acid and 
 potash, when the nitride is left as a green infusible powder which is attacked by 
 potash at a red heat, yielding potassium silicate, hydrogen, and ammonia. Si 2 N 3 is 
 formed by heating silicon in nitrogen. 
 
 Silicon hydride, SiH 4 , is the analogue of marsh gas, CH 4 , but is much less stable. 
 It is prepared by decomposing magnesium silicide Mg 2 Si (made by heating mag- 
 nesium with ;silica) with dilute HC1. It is a colourless gas which, unlike CH 4 , 
 ignites spontaneously in air, burning with a brilliant white flame which emits 
 clouds of silica and deposits a brown film of silicon upon a cold surface. Pure 
 SiH 4 does not appear to be spontaneously inflammable, resembling pure PH 3 in this 
 respect, and also in the influence which pressure has upon its spontaneous explosion 
 when mixed with oxygen. 
 
 Silico-acetylene, Si 2 H 2 , is produced when calcium silicide, CaSi 2 , the analogue of 
 calcium carbide (p. 137), is treated with dilute acid ; CaSi 2 + 2HCl = CaCl 2 +Si 2 H 2 . 
 The silicide is made by heating a mixture of lime, silica, and carbon in the electric 
 furnace, and the silico-acetylene is a yellow crystalline substance. 
 
 When cast-iron containing silicon is boiled with hydrochloric acid until the 
 whole of the iron is dissolved, a grey frothy residue is left. If this be collected on 
 a filter, well washed and dried, it is found to consist of black scales of graphite, 
 mixed with a very light white powder. On boiling it with potash, hydrogen is 
 evolved and the white powder dissolves, forming a solution containing potassium 
 silicate. This white powder appears to be identical with a substance obtained by 
 other processes, and called leucone,* which is believed to have the composition 
 Si 2 H 2 3 or 0(8iOH) 2 . Its action upon solution of potash would be explained by 
 the equation 
 
 Si 2 H 2 3 + 4KOH = 2K 2 Si0 3 + H 2 + H 4 
 
 Leucone is slowly converted into silicic acid, even by the action of water, hydrogen 
 being disengaged. It burns when heated in air. 
 
 Other compounds of this character have been prepared. 
 
 172. Silicon tetrachloride, SiCl 4 , unlike the chlorides of carbon, may 
 be formed by the direct union of silicon with chlorine at a high tempera- 
 ture ; but it is best prepared by passing dry chlorine over a mixture of 
 silica and charcoal, heated to redness in a porcelain tube connected with 
 
 * Aev/ebs, white. 
 
SILICON FLUORIDE. 283 
 
 a receiver kept cool by a freezing-mixture. Neither C nor 01 separately 
 attacks the silica, but when they are employed together, the combined 
 attractions of the carbon for the oxygen and the chlorine for the silicon 
 decomposes the silica ; Si0 2 + C 2 + C1 4 = SiCl 4 + 200. 
 
 The tetrachloride is a colourless heavy liquid (sp. gr. 1.52), which is 
 volatile (boiling-point, 59 C.), and fumes when exposed to air, the 
 moisture of which decomposes it yielding hydrochloric acid and silicic 
 acid ; Si01 4 + 4 HOH - Si(OH) 4 + 4 HC1. 
 
 When silicon is heated in hydrogen chloride a compound, which, 
 from its analogy with chloroform, CHC1 3 , is termed silico-chloroform, 
 SiHCl s , is obtained; Si + 3HC1 = SiH01 3 + H 2 . This is a colourless 
 liquid which boils at 36 C., and, unlike most chlorine compounds 
 (including chloroform), is inflammable, burning with a greenish flame, 
 and producing Si0 2 and HOI. 
 
 The chlorides of silicon have not received any practical application 
 on a large scale, but they are of theoretical importance as forming the 
 starting-point of a number of silicon compounds which are the analogues 
 of organic carbon compounds, C being exchanged for Si. 
 
 Silicon hexachloride, Cl 3 Si - SiCl 3 , is produced when SiCl 4 is passed over fused 
 silicon at a very high temperature. It forms colourless crystals melting at- i C. 
 and boiling at 147 C. Cold water decomposes it with formation of silico-oxalic 
 acid, Cl 3 Si Si01 3 + 4HOH = HOOSi-SiOOH + 6HCl. 
 
 Silicon tetrabromide. SiBr 4 , is a colourless liquid of sp. gr. 2.82, b.p. 150 C. and 
 m.p. - 12 C. Silicon tetraiodide, SiI 4 , crystallises in colourless octahedra, melts at 
 120 C., and boils at 290 C. 
 
 173. Silicon tetrafluoride (SiF 4 = 104 parts by weight). If a mix- 
 ture of powdered fluor spar and glass be heated, in a test-tube or small 
 flask, with concentrated sulphuric acid, a gas is evolved which has a 
 very pungent odour, and produces thick white fumes in contact with 
 the air : * it might at first be mistaken for hydrofluoric acid, but a glass 
 rod or tube moistened with water and exposed to the gas, becomes 
 coated with a white film, which proves, on examination, to be silica. 
 This result originated the belief that the gas consisted of fluoric (now 
 hydrofluoric) acid and silica ; but Davy corrected this view by showing 
 that it really contained no oxygen, and consisted solely of silicon and 
 fluorine. The gas is now called silicon tetrafluoride, and represents 
 silica in which the oxygen has been displaced by fluorine : the change 
 of places between these two elements in the above experiment is repre- 
 sented by the equation 
 
 2CaF 2 + Si0 2 + 2H 2 S0 4 = 2CaS0 4 + SiF 4 + 2H 2 0. 
 
 The formation of the crust of silica upon the wetted surface of the 
 glass is due to a reaction between the tetrafluoride and the water, in 
 which the oxygen and fluorine again change places; SiF 4 + 2H 2 = 
 Si0 2 + 4HF.f Since this latter equation shows that hydrofluoric acid 
 is again formed, it would be expected that the glass beneath the deposit 
 
 * SiF 4 becomes solid at - 102 C., and, at a higher temperature, evaporates without 
 fusing 1 . 
 
 f It will be noticed that the proportion of SiF 4 to H 2 O in this equation, representing the 
 decomposition of the gas by water, is the same as that in the preceding equation, represent- 
 ing the evolution of the gas together with water, so that the equations seem to contradict 
 each other. In reality it depends on the actual masses of water and other substances pre- 
 sent, and also on the temperature, whether SiF 4 and H 2 O can exist together or will at once 
 decompose each other. The excess of sulphuric acid used in the manufacture of SiF 4 will 
 combine with the water, and will prevent it from decomposing the SiF 4 . 
 
284 
 
 HYDROFLUOSILICIC ACID. 
 
 of silica would be found corroded by the acid ; this, however, is not the 
 case, and when the experiment is repeated upon a somewhat larger 
 scale, so that the water which has attacked the gas may be examined, 
 it is found to hold in solution, not hydrofluoric acid, but an acid which 
 has little action upon glass, and is composed of hydrofluoric acid and 
 silicon fluoride, the hydrofluoric acid produced when water acts on the 
 fluoride having combined with a portion of the latter to produce the 
 new acid, 2HF.SiF 4 , or H 2 SiF 6 , hydrofluosilicic acid. 
 
 For the preparation of silicon tetrafluoride, 30 grams of fluor spar and an equal 
 weight of powdered glass are mixed together, and heated in a Florence flask, with 
 200 c.c. of oil of vitriol, the gas being collected in dry bottles by downward dis- 
 placement (see Fig. 150, p. 177). If a little of the gas be poured from one of the 
 bottles into a flask filled up to the neck with water, the surface of the latter will 
 become covered with a layer of silica, so that if the flask be quickly inverted, the 
 water will not pour from it, and will seem to have been frozen. In a similar 
 manner, a small tube filled with water and lowered into a bottle of the gas, will 
 appear to have been frozen when withdrawn. A stalactite of silica some inches in 
 length may be obtained by allowing water to drip gently from a pointed tube into 
 a bottle of the gas. Characters written on glass with a wet brush are rendered 
 opaque by pouring some of the gas upon them. 
 
 The fact that silica is so easily volatilised in the form of SiF 4 is of 
 immense service in analytical chemistry for " opening up " mineral 
 silicates. By heating the silicate with H 2 SO t and HF in a platinum 
 vessel all the silica may be expelled, leaving the bases in the form of 
 sulphates. 
 
 174. Hydrofluosilicic acid (H 2 SiF 6 = 144 parts by weight). This 
 acid is obtained in solution by passing silicon tetrafluoride into water ; 
 3$iF 4 + 2 H 2 = 2H 2 SiF 6 + SiO 2 . 
 
 The gas must not be passed directly into the water, lest the separated 
 silica should stop the orifice of the tube, to prevent which the latter 
 
 should dip into a little mercury 
 at the bottom of the water, 
 when each bubble, as it rises 
 through the mercury into the 
 water, will become surrounded 
 with an envelope of gelatinous 
 silica, and if the bubbles be very 
 regular, they may even form 
 tubes of silica extending through 
 the whole height of the water. 
 
 Crystals of H 2 SiF 6 . 2 Aq have 
 been obtained by passing SiF 4 
 into solution of HF. 
 
 For preparing hydrofluosilicic acid, 
 it will be found convenient to employ 
 a gallon stoneware bottle (Fig. 200), 
 furnished with a wide tube dipping 
 into a cup of mercury placed at the 
 bottom of the water. 500 grams of 
 finely powdered fluor spar, an equal 
 
 weight of fine sand, and 2 litres of oil of vitriol are introduced into the bottle, which 
 is gently heated upon a sand-bath, the gas being passed into about 3 litres of water. 
 After six or seven hours the water will have become pasty, from the separation of 
 gelatinous silica. It is poured upon a filter, and when the liquid has drained through 
 as far as' possible, the filter is wrung in a cloth, to extract the remainder of the acid 
 solution, which will have a sp. gr. of about 1.078. 
 
 Fig. 200. Preparation of hydrofluosilicic acid. 
 
CAEBON GKOUP OF ELEMENTS. 285 
 
 A dilute solution of hydrofluosilicic acid may be concentrated by 
 evaporation up to a certain point, when it begins to decompose, evolving 
 fumes of SiF 4 , HF remaining in solution and volatilising in its turn if 
 the heat be continued. Of course, the solution corrodes glass and porce- 
 lain when evaporated in them. If the solution of hydofluosilicic 
 acid be neutralised with potash, and stirred, a very characteristic 
 crystalline precipitate of potassium silica -fluoride (potassium fluosilicate), 
 K 2 SiF 6 , is formed ; H 2 SiF 6 + 2 KHO = K 2 SiF 6 + 2 H ? O. 
 
 But if an excess of potash be employed, a precipitate of gelatinous 
 silica will be separated, potassium fluoride remaining in the solution 
 H 2 SiF 6 + 6KHO = 6KF + 4H 2 + SiO a . 
 
 One of the chief uses of hydrofluosilicic acid is to separate the potas- 
 sium from its combination with certain acids, in order to obtain these 
 in the separate state. 
 
 Tin and lead, which belong to the same group of elements as silicon 
 (see " Periodic Law "), form fluostannates and jluoplumbates, such as 
 Na 2 SnF 6 or 2NaF.SnF 4 , and K 2 PbF 6 or 2KF.PbF 4 , analogous to the 
 fluosilicates. 
 
 175. Silicon disulpliide (SiS 2 ), corresponding with carbon disulphide, is obtained 
 by burning silicon in sulphur vapour, or by passing vapour of carbon disulphide 
 over a mixture of silica and charcoal, in the form of volatile needles. Unlike the 
 carbon compound, it is a white amorphous solid, absorbing moisture when 
 exposed to air, and soluble in water, which gradually decomposes it into silica 
 and hydrogen sulphide. When heated in air it burns slowly, yielding silica and 
 sulphur dioxide. 
 
 176. The elements carbon, boron, and silicon possess many properties 
 in common. They all exist in the amorphous and the crystalline forms ; 
 all are incapable of being converted into vapour ; all exhibit a want of 
 disposition to dissolve ; all form feeble acid oxides by direct union with 
 oxygen, for which the order of their aflinity is boron, silicon, carbon ; 
 and all unite with several of the metals to form compounds which 
 resemble each other. Boron and silicon are capable of direct union 
 with nitrogen, and so is carbon if an alkali be present. Recent re- 
 searches attribute to silicon the power of occupying the place of carbon 
 in some organic compounds, and the formula of leucone, Si 2 H 2 3 strongly 
 reminds us of the organic compounds of carbon with hydrogen and 
 oxygen. In many of its physical and chemical characters silicon is 
 closely allied with the metals, and it will be found that tin and titanium 
 bear a particular resemblance to it in their chemical relations. 
 
 Notwithstanding these points of similarity between boron, carbon, 
 and silicon, boron is not regarded as belonging to the family of elements 
 which includes carbon and silicon, because whilst C and Si are tetra- 
 valent elements, boron is trivalent, and must, therefore, be classed with 
 nitrogen and phosphorus. 
 
CERTAIN GENERAL PRINCIPLES 
 
 ATOMS AND MOLECULES. 
 
 177. It is only after numerous facts have been observed, and accu- 
 rately described, that it is possible to deduce such general principles as 
 may enable future workers to conduct their experiments in such a 
 manner that they may discover and arrange fresh facts with the smallest 
 possible expenditure of energy and time. Thus, the generalisation 
 which receives the name of the Atomic Theory, and upon which the 
 science of Chemistry is now constructed, was enunciated at the begin- 
 ning of the last century only after the gravimetric and volumetric 
 composition of a large number of compounds had been determined by 
 both synthetical and analytical methods. 
 
 The theory arose from the contemplation of the quantitative com- 
 position of various compounds, when it was seen that chemical combina- 
 tion does not occur between masses of matter in indefinite quantities, 
 but is controlled by the following three laws : 
 
 (1) Law of Constant Proportions. In every compound the masses of 
 the constituent elements bear the same ratio to each other, from what- 
 ever source the compound may be obtained. 
 
 It is this law which determines how much of an element in a mixture 
 will enter into combination. For example, when a mixture of zinc and 
 sulphur is heated, complete combination will only occur when the ratio 
 of the mass of zinc to that of sulphur is 65*5 : 32 ; if the mixture 
 contain the elements in any other ratio, either zinc or sulphur will 
 remain uncombined after the heating. 
 
 (2) Law of Multiple Proportions. When two elements combine to 
 form more than one compound, the masses of the one element com- 
 bining with a constant mass of the other, must be simple multiples of 
 the smallest mass among them. 
 
 The hydrocarbons yield abundant examples of this law ; thus, 
 quantitative analysis of marsh gas, defiant gas, and acetylene shows 
 that they have the following gravimetric compositions per cent. : 
 
 Carbon. Hydrogen. Ratio of C : H. 
 
 Marsh gas 75 25 3:1 
 
 Olefiant gas 85.7 14.3 6:1 
 
 Acetylene 92.3 7.7 12 : i 
 
 It is apparent from the ratios that the proportion of carbon that 
 combines with one part by weight of hydrogen in the second and third 
 compounds, is a multiple of that in the first compound by a simple 
 whole number. 
 
= 
 
 18.7 
 
 6.2 
 
 or 
 
 3 
 
 : i 
 
 = 
 
 18.7 
 
 100 
 
 or 
 
 3 
 
 : 16 
 
 = 
 
 6.2 
 
 100 
 
 or 
 
 i 
 
 : 16 
 
 LAWS OF COMBINATION. 287 
 
 Another striking example is afforded by the oxides of nitrogen ; in 
 these there are, for 100 parts of nitrogen, 57.1, 114.2, 171.3, 228.4 a ^d 
 285.5 P ar t s of oxygen respectively, figures in the ratio 1:2:3:4:5. 
 
 (3) Law of Reciprocal Proportions. When an element forms a com- 
 pound with each of several other elements, the masses of the several 
 other elements which combine with a constant mass of the first element, 
 are also the masses of these elements which combine with each other, 
 or they bear some simple ratio to these masses. 
 
 Thus, sulphuretted hydrogen, sulphur dioxide, and carbon bisulphide 
 have the following gravimetric compositions : 
 
 Per cent. Per cent. 
 
 Sulphuretted hydrogen . Sulphur 94.1 . . Hydrogen 5.9 
 
 Sulphur dioxide . . Sulphur 50.0 . . . Oxygen 50.0 
 
 Carbon bisulphide . . Sulphur 84.2 . . Carbon 15.8 
 
 When these figures are calculated for 100 parts of sulphur in each 
 case, they become 
 
 Sulphuretted hydrogen . Sulphur 100 . . Hydrogen 6.2 
 Sulphur dioxide . . Sulphur 100 . . Oxygen 100 
 Carbon bisulphide . . . Sulphur 100 . . Carbon 18.7 
 
 The ratios of the proportions of C, H and which combine with 100 
 parts of sulphur in the above table are : 
 
 C :H 
 C :0 
 H: 
 
 Now 3 compounds of carbon with hydrogen, 2 of carbon with oxygen, 
 and 2 of hydrogen with oxygen are known, and the ratios of the ele- 
 ments in these compounds are : 
 
 C:H = 3:1 6 : i 12 : i 
 C : O = 3:8 3 : 16 
 H : = i : 8 I : 16 
 
 Thus the ratio in which any pair of these elements combine with each 
 other is either the same as that in which they combine with a constant 
 mass of sulphur or is some multiple or submultiple thereof by a simple 
 whole number. 
 
 In order to account for the existence of these laws, Dalton revived 
 the atomic theory. The fundamental conception on which this theory 
 is based has been stated in the Introduction; the new significance with 
 which Dalton invested it was, that each of the indivisible particles 
 (atoms) of which a kind of matter is composed has an invariable weight, 
 and that this weight is the same for each atom of the same kind of 
 matter. Furthermore, when combination of one kind of matter with 
 another occurs, the union takes place between the atoms of these kinds 
 of matter, and consists in the addition of one or more atoms of the first 
 kind to one or more atoms of the second kind. If these postulates 
 be granted, it at once becomes apparent why a compound always con- 
 tains its elements in the same gravimetric ratio ; water, for instance, is 
 always composed of oxygen and hydrogen in the ratio of 8 : i by weight ; 
 and this, according to Dalton, is clue to the fact that water is a compound 
 of one atom of oxygen with one atom of hydrogen, the atom of oxygen 
 weighing 8 times as much as the atom of hydrogen. The " atom " of 
 
288 DALTON'S ATOMIC WEIGHTS. 
 
 water, as Dalton called it, should therefore be represented as HO. The 
 considerations which led to the adoption of H,0 for the formula of 
 water will be dealt with presently. 
 
 Again, the law of multiple proportions follows of necessity from Dalton's hypo- 
 thesis. For if a compound of x atoms of one element with y atoms of another 
 element exist, a new compound can only be formed by adding another atom or by 
 taking one away ; and since each atom of the same element weighs the same, the 
 addition or subtraction of each atom must cause the same variation in the propor- 
 tional composition. Thus, if there be a compound of one atom of nitrogen with one 
 atom of oxygen, and the ratio between the weights of these atoms be 7 : 8 (or 
 loo : 114.2), it is only possible to produce another compound of these two elements 
 by adding one or more atoms of nitrogen, each weighing. 7, or one or more 
 atoms of oxygen, each weighing 8 ; so that any other oxide of nitrogen 
 must contain the elements in the ratio 7 x n : 8 x m by weight, n and m being 
 integers. 
 
 The third law of chemical combination is equally explicable, for the ratio by 
 weight in which two elements combine is either the ratio between the weights of 
 their atoms, or that between some multiples of these. Hence the ratio between 
 the weights of two elements in a compound must be represented by the same 
 numbers as those representing the weights of these elements in their compounds 
 with any other elements, or by some simple multiple or submultiple of these 
 weights. If the compound of carbon with sulphur which contains these elements 
 in the proportion of 18.7 : 100 or 3 : 16 parts by weight, contain only one atom of 
 sulphur and one atom of carbon, then any compound of sulphur with another 
 element, itself capable of combining with carbon in the proportion of x : 3, must 
 contain the sulphur and the other element in the proportion of 16 : x or 16 x n : a?, 
 where n is an integer ; if, on the other hand, the compound of carbon with sulphur 
 contain 2 or 4 atoms of sulphur, other compounds of this element may contain it 
 in the proportion of 8 or 4 parts by weight. 
 
 Dalton endeavoured to construct a table of atomic weights that is, a 
 table of the relative weights of the atoms by determining how many 
 parts by weight of each element combine with one part by weight of 
 hydrogen, the atomic weight of which he took as unity, hydrogen being 
 the lightest kind of matter. His numbers, however, agree only in a 
 few cases with the modern atomic weights, for two reasons. In the 
 first place, except in those cases in which two elements form more than 
 one compound the difference between which compounds he attributed 
 to their containing different numbers of atoms except in these cases, 
 he concluded that combination occurs between one atom and one atom, 
 whereas now the hypothesis is that in many cases the combination is 
 between 2 or 3 atoms and i atom, or, generally, between n and m atoms. 
 For instance, if the compound of carbon and hydrogen in which the 
 ratio by weight of C : H is 3 : i be a compound of i atom of C with 
 i atom of H the atomic weight of carbon will be 3 ; if, as now believed, 
 it is a compound of i atom of C with 4 atoms of H, the atomic weight 
 of carbon is 1 2 . 
 
 In the second place, Dalton had not conceived the existence of a 
 second kind of ultimate particle, now called a molecule. Thus, he spoke 
 of an " atom " of water and other compounds, notwithstanding that by 
 his hypothesis an atom is indivisible, while by definition a compound is 
 divisible. His studies of gases were limited to their combination by 
 weight. Gay-Lussac (1809) studied their combination by volume, and 
 experienced a difficulty in applying Dalton's hypothesis, which led to 
 the conception of molecules. 
 
 The difficulty is easily appreciated from the contemplation of the 
 combination of hydrogen with chlorine. Equal volumes of these gases 
 
DALTON'S ATOMIC WEIGHTS. 28^ 
 
 combine, and the product occupies twice the volume of either of its 
 constituents : one volume of H combines with one volume of 01 to form 
 two volumes of HC1. According to Dalton's theory, one atom of 
 hydrogen combines with one atom of chlorine to form one " atom " of 
 hydrogen chloride. If this be the case, equal volumes of hydrogen and 
 chlorine must contain the same number of atoms, for it is found that 
 equal volumes of these gases combine exactly that is, no residue of 
 either gas is left. This reasoning applies to the combination of several 
 other gases, whence Gay-Lussac attempted to deduce the generalisation 
 that equal volumes of all gases contain the same number of atoms. 
 But if this be the case, the two volumes of HC1, produced by the 
 combination of one volume of H with one volume of 01, must contain 
 twice as many atoms as the one volume of chlorine or of hydrogen 
 contains ; therefore one atom of 01 combines with one atom of H to 
 form two atoms of HC1, and consequently one atom of HC1 must contain 
 half an atom of 01, which is impossible, an atom being indivisible. 
 Gay-Lussac's generalisation, however, corrected some of Dalton's atomic 
 weights to the present values ; that of oxygen will serve as an example. 
 Two volumes of H combine with one volume of O to form water ; but 
 equal volumes of gases contain the same number of atoms, therefore 
 2 atoms of H combine with one atom of ; the ratio by weight of H to 
 O in water is, however, i : 8, so that 2 atoms of H weighing i combine 
 with i atom of weighing 8 ; but, as already denned, i atom of 
 hydrogen is to weigh i, therefore water contains 2 atoms of hydrogen 
 weighing 2, combined with one atom of oxygen weighing 16, and its 
 formula is H 2 O. 
 
 Avogadro (1811) conceived the existence of two kinds of ultimate 
 particle. Starting with the conception that gases are composed of 
 ultimate particles, which he preferred to call molecules, he attempted to 
 explain the combination of gases by volume, but encountered the diffi- 
 culty experienced by Gay-Lussac. To overcome this difficulty he had 
 recourse to the supposition that the molecules of the gases are shattered 
 before combination occurs, and that the parts of the molecules then re- 
 combine to form the molecules of the new gas. The particles produced 
 by the scission of the molecules were the true indivisibles, or Dalton's 
 atoms. Thus, Avogadro was able to support the generalisation now 
 known as Avogadro' s Law. namely, that equal volumes of gases at the 
 same temperature and pressure contain the same number of molecules. 
 The combination of hydrogen with chlorine is now easily explained ; 
 one volume of hydrogen contains the same number of molecules as is 
 contained in one volume of chlorine ; when these volumes combine, the 
 molecules are shattered and their component atoms recombine to form 
 molecules of hydrogen chloride ; one molecule of chlorine thus reacts 
 with one molecule of hydrogen to form two molecules of hydrogen 
 chloride, which (according to Avogadro's law) must therefore occupy 
 twice the volume occupied by either the chlorine or the hydrogen. 
 
 The definitions of an atom and of a molecule have been given on 
 p. 8. The hypothesis that the hydrogen molecule consists of two atoms 
 may be supported as follows : Hydrogen chloride contains half its volume 
 of hydrogen, and therefore half as much hydrogen as is contained in an 
 equal volume of hydrogen ; but equal volumes of hydrogen chloride and 
 hydrogen contain the same number of molecules (Avogadro's law), 
 
290 MOLECULAR MOTION. 
 
 therefore one molecule of hydrogen chloride contains half as much 
 hydrogen as one molecule of hydrogen contains. Now one molecule of 
 hydrogen chloride is supposed to consist of one atom of hydrogen com- 
 bined with one atom of chlorine, therefore one molecule of hydrogen 
 must be supposed to consist of one atom of hydrogen combined with one 
 atom of hydrogen. The same reasoning will apply to the molecule of 
 chlorine. 
 
 It is difficult to account for the spontaneous intermixture or diffusion 
 of gases (p. 25) unless it be granted that their molecules are always in 
 motion, and if this be postulated an explanation of the pressure of a gas 
 is at once found. For if the molecules are in constant motion they 
 must continually strike the sides of the containing vessel and the 
 numerous impacts must exert a pressure on those sides. 
 
 Liquids also have the property of diffusion, but the property is not 
 universal between all liquids; thus, oil and water do not intermix. 
 Moreover, the diffusion occupies a much longer time than that of gases. 
 It seems therefore that molecular motion must also exist in liquids, 
 but at a slower rate or more limited than that in gases. Diffusion 
 among solids is rare though not unknown (p. 25), but the process is so 
 exceedingly slow that molecular motion of solids must be more limited 
 than that of liquids. 
 
 Now by heating a gas its pressure is increased, and if the pressure is 
 due to the motion of the molecules, it follows that increase of the tem- 
 perature of the gas means increase of molecular motion. Conversely, 
 cooling a gas decreases its pressure, and therefore also its molecular 
 motion. All gases save hydrogen (which requires pressure) can be 
 liquefied by merely cooling them, that is, by depriving their molecules 
 of motion to a sufficient extent. 
 
 The movement of the molecules of a solid may be regarded as 
 limited to a species of oscillation, that is to say, the molecules cannot 
 move far from their original positions. As this movement is increased 
 by rise of temperature there is a tendency for the molecules to move so 
 fast that they break away from the influence of each other, and are 
 imbued with much more freedom of motion. The temperature at which 
 this happens is the melting-point of the solid, and is constant until the 
 whole mass is liquid, since heat is absorbed in order to effect the work 
 of separating the molecules. 
 
 The molecules of a liquid are still considerably under the influence of 
 each other, although those at the surface escape and move about in the 
 space above the liquid without influencing each other to any but a very 
 limited extent ; this is the evaporation of the liquid. When the space 
 is confined, it soon becomes saturated with these vapour molecules, and 
 evaporation apparently ceases. This happens when as many molecules 
 of vapour attach themselves to the surface of the liquid as escape from 
 it, in unit time. 
 
 As the temperature of the vapour is raised, the motion of the mole- 
 cules becomes more rapid, and the latter are less and less influenced by 
 each other. The vapour is then a gas, and conforms with the laws 
 which connect the volume of a gas with its pressure and temperature 
 (see p. 27). 
 
 If an ideal gas (see p. 28) consists of a number of elastic solid particles 
 in motion, its properties can be investigated by mathematics ; this 
 
KINETIC THEORY OF GASES. 291 
 
 has been done, and the results are generally spoken of as the kinetic 
 theory* of gases, which may be succinctly stated thus : The molecules 
 of a gas are in constant and rapid motion in straight lines, and continue 
 moving in the same direction until they are reflected by striking each 
 other or the walls of the containing vessel. The impacts against the 
 sides of the vessel give rise to the pressure of the gas. whilst the tem- 
 perature of the gas is a measure of the velocity of motion of the 
 molecules. 
 
 The theory is not strictly within the province of the chemist, but in 
 that of the physicist ; the former, however, finds in it an explanation 
 of many chemical changes, and, above all, a confirmation of Avogadro's 
 hypothesis, originally deduced from purely chemical considerations, that 
 equal volumes of gases at the same temperature and pressure contain 
 the same number of molecules. Moreover, the theory teaches him that 
 the hypothesis is absolutely true only of perfect gases. 
 
 A mathematical expression for the pressure of a gas may be deduced from con- 
 sideration of molecules moving in a hollow cube. Let a molecule of mass m in 
 such a vessel be moving in any direction with velocity w ; this can be resolved 
 into three components (a 1 , y. z) in directions parallel to the sides of the cube and 
 according to the principle of the resolution of velocities, w 2 = a? + y 2 + z 2 . When the 
 molecule moving towards the side of the cube with velocity x strikes the side, it 
 exerts a force equivalent to its momentum, which is mas, not only at the impact 
 but when it rebounds, making a total of 2m A: If I is the distance that the molecule 
 has to move from one side of the cube to the other, that is, the length of the side 
 of the cube, this force is repeated &/1 times every unit of time. Thus the force 
 exerted in unit time becomes 2m&x&'/l = 2mas 2 /l. What is true of components- 
 applies to the other components, so the expression becomes 2 w (* 2 + y^ + z 2 )/l = 2mw z /l, 
 and for the whole number n of the molecules, 2nmw 2 /l. The pressure p of a gas is 
 expressed per unit area, so the foregoing expression must be divided by 6Z 2 , the 
 
 number of units of surface in a cube ; hence the final formula is p = n . I s is the 
 volume (r) of the cube, so the expression may be written pv= , or for unit 
 
 volume p = 
 
 It is more instruct! veto write this formula ^=-1.%-^-, for is the kinetic 
 
 32 2 
 
 energy of the moving molecule and nmw' 2 /2 that of all the molecules. Now if p is 
 varied by altering the temperature of the gas, this variation can be due only to the 
 variation of the kinetic energy of the molecules for n is constant. Hence the tem- 
 perature of a gas must be a measure of its kinetic energy, and if unit volumes of 
 two gases have the same temperature they must also have the same kinetic energy, 
 or mw z /2 = m l w-^/2. Let the unit volumes be also at the same pressure, then 
 
 _ n mw , ^-n 1 m ' lWl - or mnw 2 =m l n l ii< l 2 , or since niio 2 = m l w-f by the previous 
 
 equation, n = %, that is to say, when gases are at the same temperature and pressure 
 the number of molecules in unit volume is the same (Avogadro's hypothesis). 
 
 The mass of a volume of gas must be the product of the mass of each molecule 
 and the number of molecules ; hence mn in the foregoing equations is the mass of 
 the gas. Taking I gram of hydrogen which measures 11,110 C.G. at 760 mm. 
 pressure and o C., mn will be i, and we have pv = w 2 /$ or w= V^pv. The pres- 
 sure of 760 mm. of mercury in absolute units of mass is 76 x 13.5 xff = ioi3i3Q. 
 Hence the rate w at which the hydrogen molecules move is ^3 x 1013130 x uiio 
 cm. per second, or 1838 metres per second. 
 
 The mass of unit volume is identical -with density, hence for mn in the foregoing 
 equations might be written d, and it will be obvious that if p and v are constants 
 must vary inversely as VdT That is to say, the velocity of the molecules of a gas 
 
 * KIITJ<TIS= motion. 
 
2Q2 DETERMINATION OF MOLECULAR WEIGHT. 
 
 varies inversely as the square root of the density of the gas. Since in equal 
 volumes of two gases at the same temperature and pressure mnuP = m l <n l w-f it 
 follows that dw 2 = d l w 1 2 ; that is to say, the rates of movement of the molecules 
 of different gases vary inversely as the square roots of their specific gravities. 
 
 Molecular Weights. The weight of a single molecule has never 
 been determined, and it is assumed that all the molecules of any single 
 substance have the same weight. To compare the weights of the mole- 
 cules of different substances is possible if Avogadro's hypothesis be true. 
 For if equal volumes of gases at the same temperature and pressure con- 
 tain the same number of molecules, the relative weights of these volumes 
 must also be the relative weights of the molecules of the gases. The 
 molecule of hydrogen being selected as the standard of comparison, the 
 unit of molecular weights is 2, since it is accepted that there are two 
 parts or atoms in each molecule of hydrogen, and the molecular weight 
 of any other gas, be it element or compound, is twice the number of times 
 that a volume of it in the state of gas is heavier than an equal volume oj 
 hydrogen at the same temperature and pressure. This is expressed 
 by the equation M = 2D, where M is the molecular weight, and D the 
 vapour density * of the gas, for the latter is the number of times that 
 the gas is heavier than hydrogen. 
 
 Hence, in order to ascertain the molecular weight of a substance it is- 
 necessary to determine the vapour density and to double this value. 
 When the substance is a gas at the ordinary temperature, the operation 
 consists in weighing a volume of the gas ; this weight is then divided 
 by that of the same volume of hydrogen at the same temperature and 
 pressure, calculated on the basis of the ascertained weight of one litre 
 of hydrogen at oC. and 760 mm. pressure, namely 0.09 gram. 
 
 In the actual process, the capacity (about 500 c.c.) of a globe (closed 
 by a stop-cock such as that shown in Fig. 50) is determined by weighing 
 it, first empty, and then full of water ; the weight of the water which 
 it can contain, and, therefore, its volume (i c.c. of water weighs i gram 
 at 4C.) is thus ascertained. The dried globe may then be filled with 
 the purified gas, the temperature and pressure being noted at the 
 moment when the stop-cock is closed, and again weighed. 
 
 Let the weight of the empty globe be w grams, and that of the globe full 
 of water at 4 C. be W grams ; then the capacity (V) of the globe is 
 W-w c.c. Let Wj be the weight of the globe filled with carbon dioxide. 
 (C0 2 ) at 15 C. and 770 mm. bar. Then Wj ifl grams is the weight of 
 V c.c. of G0. 2 at 15 and 770 mm. bar. Since the volume of a gas varies in- 
 versely as its pressure, and directly with its absolute temperature (degrees 
 
 c + 273), V c.c. of hydrogen at 15 C. and 770 mm. bar. will be V x ^|? x ?I3 c.c. 
 
 at o C. and 760 mm., and will weigh Y x ZZSL x -Zi x 0.0009 = A grams. 
 
 760 285 
 
 Thus * vapour density of C0 2 , and J~ is the molecular weight of 
 C0 2 . 
 
 When the substance has to be heated to convert it into a gas, the 
 same method may be adopted, the solid or liquid substance being intro- 
 duced into the globe, which is then heated in a bath of liquid at a suffi- 
 ciently high temperature to volatilise the substance entirely; the vapour,, 
 
 * The term vapour density is used here because so few substances being gaseous at the 
 ordinary temperature, it is nearly always necessary to vaporise the substance before it can 
 be regarded as a gas. 
 
VICTOR MEYER'S METHOD. 
 
 293 
 
 in escaping from the globe, expels the air, and when no more vapour 
 issues from the narrow orifice of the neck (which is substituted for the 
 stop-cock), a blowpipe flame is applied to seal this orifice, the tempera- 
 ture of the bath and the pressure of the atmosphere being noted at the 
 moment of sealing. The calculations involved are the same as those 
 stated above. For substances which volatilise at temperatures above 
 that at which glass becomes soft, globes made of porcelain must be 
 employed ; these are sealed by the oxyhydrogen blowpipe. When 
 modified in this way for solids and liquids, the method is known as 
 Dumas' method. 
 
 The foregoing method for deter- 
 mining vapour densities consists in 
 weighing a known volume of vapour. 
 The value can be equally well, and 
 somewhat more easily, ascertained by 
 measuring the volume occupied by a 
 known weight of vapour, an operation 
 which is most easily effected by the 
 Victor Meyer method. In this, a 
 weighed quantity of the substance is 
 converted into vapour in a vessel con- 
 taining air (or some other gas), and the 
 volume of air displaced by the vapour 
 is collected and measured. 
 
 Take, for example, the determination of the 
 vapour density of alcohol, which boils at 
 78.3 C. The vapourising tube (&, Fig. 201), 
 well closed by a cork, is heated in the cylinder 
 of boiling water a so long as any bubbles 
 of air pass from the opening of the delivery- 
 tube d through the water in the trough. 
 The end of the delivery-tube is then inserted 
 into the graduated tube /, which is full of 
 water. About o.i gram of alcohol is weighed 
 out into a small tube, which is dropped into 
 the opening of the vapourising-tube, this being 
 then quickly corked. A little asbestos is 
 placed at the bottom of the vapourising-tube 
 c to prevent breakage. 
 
 The alcohol vapour expels a volume of air 
 equal to its own, and this is collected in the 
 tube /, and accurately measured, with the 
 usual corrections for temperature and pres- 
 sure. The volume of a known weight of 
 alcohol in the form of vapour having been 
 thus ascertained, the vapour density may be calculated. 
 
 For example, o.i gram of alcohol expelled a volume of air which measured 
 48.5 c.c. when corrected to o C. and 760 mm. bar. Hence, supposing that alcohol 
 could retain the state of vapour at that temperature and pressure, 48.5 c.c. of 
 alcohol vapour would weigh o. i gram. 
 
 Now, 48.5 c.c. of hydrogen at o C. and 760 mm. weighs 0.00434 gram, so that 
 
 the vapour density of alcohol is : = 23, and its molecular weight is 
 
 0.00434 
 23x2 = 46. 
 
 For substances which can only be volatilised at very high temperatures porcelain 
 must be substituted for glass, and a liquid of high boiling-point must be used in the 
 bath surrounding the vapourising tube. 
 
 Fig. 201. Victor Meyer's apparatus. 
 
294 ABNORMAL VAPOUR DENSITY. 
 
 It will be obvious that the molecular weight of a compound which is 
 not capable of being vapourised without decomposition cannot be ascer- 
 tained from the vapour density. There are, however, other criteria, by 
 means of which the molecular weight of a compound may be ascertained ; 
 these will receive notice presently. 
 
 Inasmuch as Avogadro's law is true only of the ideal gas, the 
 foregoing method of determining molecular weights can give accurate 
 results only with gases which are far removed in temperature from the 
 boiling-point of the corresponding liquids, and thus approach perfection. 
 A criterion for the degree of gaseous character is the amount by which 
 a gas deviates from Boyle's law ; if, for instance, on doubling the 
 pressure on 1000 c.c. the volumes becomes} 400 c.c. instead of 500 c.c., 
 the gas is far removed from perfection. 
 
 Another criterion is the behaviour of the gas when heated ; if 
 1000 c.c. at o C. (273 absolute) expand to 2100 c.c. instead of 2000 
 c.c. when heated to 273 0. (546 absolute), the molecules of the gas 
 must have been considerably under the influence of each other at the 
 lower temperature, for the volume of a true gas must vary proportionally 
 to the absolute temperature. If on heating the gas in question beyond 
 273 C. its volume increases in direct proportion to the absolute 
 temperature, it may be concluded that at these higher temperatures 
 the gas is nearly a true gas. 
 
 Now hydrogen, the standard for vapour densities, expands like a 
 true gas, so that if the vapour density * of a gas which expands more 
 rapidly than a true gas (hydrogen) is determined at different tempera- 
 tures it is found not to be constant, but to grow less as the temperature 
 rises. For example, at 273 C., 1000 c.c. of hydrogen contain 1/2 the 
 matter contained in 1000 c.c. at o C., whereas in 1000 c.c. of the gas 
 cited above (as expanding to 2100 c.c. at 273 C.) there is at 273 (X 
 only 1/2. i the matter that is contained in 1000 c.c. at o C. Hence if 
 the vapour density were x at o C. it would be only x-x/2i at 
 273 C. 
 
 It follows that in order to apply Avogadro's law to determine the 
 vapour density of a substance the observations should be made at 
 successively higher temperatures until the value remains constant. 
 In most cases the fall in vapour density with rise of temperature is 
 very slight, bnt in some it is very considerable ; compare sulphur 
 (p. 213). 
 
 It is supposed that in the case of sulphur and certain other sub- 
 stances, there is more in this decrease of vapour density than a mere 
 improvement of gaseous character, as will be explained a little later. 
 
 It will presently be made clear that by the chemist the determina- 
 tion of vapour density for ascertaining molecular weights is used solely 
 as an indication as to which of two values is correct ; for this method 
 lacks the accuracy attainable by that which is particularly the chemist's 
 own gravimetric analysis. The whole system of molecular and atomic 
 weights has been built up by use of the balance to determine chemical 
 equivalents. 
 
 * Vapour density is distinct from specific gravity. Of course the latter decreases with 
 rise of temperature because it is the ratio between the Weight of a volume of the gas at the 
 particular temperature and that of an equal volume of the standard gas at standard tempe- 
 rature and pressure. The vapour density is determined by weighing both gases at the same 
 temperature, whatever that may be, and should be a constant. 
 
ATOMIC WEIGHTS. 
 
 2 95 
 
 Chemical Equivalents. It was seen above that Dalton constructed 
 a table of atomic weights, the figures in which represented the number 
 of parts by weight of the respective elements which combine with one 
 part by weight of hydrogen. These figures are what are now called 
 chemical equivalents and are determined by analysing the compounds 
 of the elements with hydrogen ; thus, it having been found that 100 parts 
 of the compound of sulphur with hydrogen contain 94.1 of sulphur and 
 5.9 of hydrogen, the chemical equivalent of sulphur is 94.1 ^5.9 = 16. 
 But the majority of elements do not combine with hydrogen, or do not 
 combine with it to form compounds which may easily be analysed with 
 accuracy. However, nearly all combine with oxygen, and as the 
 chemical equivalent of the latter is well established as 8, the chemical 
 equivalent of other elements may be ascertained by analysing their 
 oxygen compounds to find what weight of the element combines with 
 8 parts by weight of oxygen. 
 
 In cases where the element forms more than one compound with 
 hydrogen or oxygen, as for instance carbon (p. 137), there may be said 
 to be more than one equivalent. The lowest number, however, is 
 selected ; thus 3 is the equivalent of carbon, although 6 and 12 parts 
 of it also combine with i part of hydrogen. 
 
 Had the chemist to concern himself with weights alone, a list of 
 chemical equivalents would suffice ; indeed, until recently no account 
 was taken of any other numbers by the purely analytical chemist ; for 
 him the symbol of an element represented its chemical equivalent. 
 The progress of chemical investigation, however, would have been far 
 less rapid had not the chemist sought an insight into the actual 
 mechanism of chemical change by aid of an atomic hypothesis, which, 
 as explained for oxygen on p. 289, necessitates the abandonment of the 
 chemical equivalent as the unit weight of an element that enters into 
 chemical change, that is, the atomic weight. 
 
 Atomic Weights. Except in certain cases which have been satis- 
 factorily explained (as will be shown later in this work), there has 
 never been evidence that in any compound of hydrogen the ratio 
 between the number of atoms of H and the other element. X, is less 
 than 1:1. That is to say, compounds of the formula HX 2 , HX 3 , &c., 
 are not known, except as aforesaid ; they are limited to the form HX. 
 On the other hand, compounds of the types H 2 X, H 3 X, H 4 X are 
 quite common. 
 
 From this it is evident that (i) the atomic weight cannot be less than 
 the equivalent; (2) the atomic weight of an element forming the com- 
 pound HX must be identical with the equivalent ; and (3) the atomic 
 weights of elements forming H 2 X, H 3 X, and H 4 X respectively, must 
 be twice, thrice, and four times the equivalents respectively. 
 
 There are three methods for determining whether i, 2, 3, or 4 is the 
 factor for ascertaining the atomic weight from the equivalent. 
 
 (i) This method is best explained by an example. The vapour 
 density of a compound of nitrogen is ascertained, as described at p. 292, 
 to be 15, so that the molecular weight of the compound is 30. Gravi- 
 metric analysis shows that the compound contains 45.16 per cent, of 
 nitrogen. Hence 30 parts by weight of it contain 13.55 parts of this 
 element, that is to say, one molecule of the compound contains 
 n atoms of nitrogen weighing 13.55. If n is one, then 13.55 * s 
 
296 ATOMIC HEATS. 
 
 approximately the atomic weight of nitrogen ; if n is 2 the atomic 
 weight is 6.77, and so on. It is impossible to decide the value of n 
 from this experiment ; all that can be said is that by hypothesis it 
 cannot be less than i, so that the atomic weight of nitrogen, according 
 to this experiment, is not greater than 13.55 or a number very near 
 this. Supposing, however, that many other compounds of nitrogen 
 have been submitted to similar experiments, and it has been found that 
 in none of them does the molecular weight contain less than 13.55 
 parts of nitrogen, the presumption is large that this is indeed the 
 approximate atomic weight. 
 
 By analysing ammonia, the compound of nitrogen with hydrogen, it 
 is found to contain for every part of hydrogen 4.66 parts of nitrogen ; 
 4.66 is therefore the chemical equivalent of this element. Now 13.55 
 is nearly 3 times 4.66, so 3 is the factor required and 4.66 x 3 = 14 is 
 the atomic weight of nitrogen. 
 
 This method consists, then, in determining the molecular weights of 
 compounds of the element, and ascertaining how many parts by weight 
 of the element the molecular weight contains in each case. The lowest 
 value obtained is the maximum possible value for the atomic weight 
 and comparison with the chemical equivalent gives the required factor. 
 
 (2) It was observed by Dulong and Petit (1819), from the study of 
 elements of known atomic weight that the quantity of heat necessary to 
 raise the temperature of one atomic weight of any solid element is approxi- 
 mately the same, or, more generally, " the atoms of all the simple bodies 
 have exactly the same capacity for heat." 
 
 It will be remembered that the specific heat of a substance is the 
 quantity of heat required to raise its temperature through i as com- 
 pared with the quantity of heat required to raise the temperature of an 
 equal weight of water through i ; or, more concisely, the quantity of 
 heat required to raise one part by weight of the substance i (referred 
 to water as the unit). Thus, the specific heats of potassium, sodium, 
 and lithium are, respectively, 0.1696, 0.2934, and 0.9408, these numbers 
 representing the relative quantities of heat required to raise one part 
 by weight of each of these elements through i in temperature, suppos- 
 ing that an equal weight of water would be raised through i by a 
 quantity of heat expressed by one. No simple relation can be traced 
 between these numbers, but if the quantities of heat be calculated which 
 are required to raise atomic weights of these elements through i , the 
 case will be different. 
 
 If 0.1696 be the quantity of heat required to raise the temperature 
 of onepartby weight of potassium through i c , 0.1696 x 39, or 6.61, will 
 represent the quantity of heat required to raise the temperature of 39 
 parts b}' weight (one atomic weight) of potassium through i. In the 
 same way 0.2934 x 23, or 6.75, is the quantity of heat required to raise 
 the temperature of one atomic weight of sodium through i ; and 
 0.9408 x 7, or 6.59, is the quantity required to raise one atomic weight 
 of lithium through i . Allowing for experimental error in the deter- 
 mination of the specific heats, these numbers, 6.61, 6.75, and 6.59, may 
 be regarded as representing the same quantity of heat, and they are the 
 atomic heats of these metals. 
 
 The atomic heat of an element is the quantity of heat required 
 to raise the temperature of the number of unit weights of the solid 
 
VALENCY. 297 
 
 element expressed by the atomic weight through i ; it is ascertained 
 by multiplying the specific heat by the atomic weight and is approxi- 
 mately a constant, 6.4. 
 
 It is obvious that since specific heat x atomic weight = 6.4, the atomic 
 
 weight = . ' , - , and that from the equation an approximate value 
 
 for the atomic weight of an element can be ascertained if the specific 
 heat of the solid element is known. 
 
 When efforts to determine the specific heat of an element have failed, it is 
 sometimes possible to arrive at a value for the atomic heat by a consideration of 
 the molecular^ heat of compounds containing the element. The molecular heat of 
 k compound* is the quantity of heat required to raise the temperature of the 
 number of unit weights of the compound expressed by the molecular weight, 
 through i. It is supposed that the molecular heat of a compound is the sum of 
 the atomic heats of each of the atoms which the molecule contains a generali- 
 sation which is not fully substantiated. 
 
 Thus, the specific heat of solid chlorine is not known, but if the specific heats 
 of the chlorides of potassium, sodium, and rubidium are multiplied by the mole- 
 cular weights of these chlorides, the product in each case approaches very nearly 
 to the number 12.69. Supposing these chlorides to contain one atom of each of 
 their constituents, then, by subtracting the mean atomic heat (6.65) of the three 
 metals from the mean molecular heat (12.69) f the three chlorides, a value (6.04) 
 for the atomic heat of solid chlorine will, according to the above generalisation, be 
 obtained. 
 
 The specific heat of barium has not been determined so that its atomic weight 
 has not been ascertained directly by this method ; but the specific heat of barium 
 chloride is 0.09. Barium chloride contains 68.5 parts of barium for every 35.5 
 parts of chlorine ; if 68.5 be the atomic weight of barium, the formula for the 
 chloride will be BaCl, and its molecular heat 0.09x104 = 9.36; this only allows 
 an atomic heat of 3.36 for barium, because that of chlorine is 6.0. If the atomic 
 weight of barium be 137 the formula for the chloride will be BaCl 2 , and the mole- 
 cular heat will be 208x0.09=18.72 ; this will allow an atomic heat of 6.72 for 
 barium, for two atomic heats of chlorine must be subtracted from 18.72. As 6.72 
 is more nearly normal for the atomic heat than is 3.16, the atomic weight of 
 barium may be taken as 137. 
 
 The specific heat of all substances varies with the temperature ; this is parti- 
 cularly noticeable in the case of carbon, boron, silicon, and a few other elements. 
 At low temperatures the specific heats, and therefore the atomic heats, of C, B, 
 and Si are very low, but at higher temperatures they increase until the atomic 
 heats are about 5.5. Thus, the specific heat of diamond at 10 C. is 0.112, corre- 
 sponding with the atomic heat 1.34, whilst at 985 C. the specific heat is 0.458, 
 corresponding with atomic heat 5.5. 
 
 All elements whose atomic weight is above 30, obey Dulong and Petit's law. 
 
 (3) On page 1 1 the term valency was used to express the number of 
 atoms of hydrogen one atom of an element can combine with. It is 
 evident that the number expressing this valency is none other than the 
 factor now under discussion. The third method consists in studying 
 the general chemical analogies of the element with some other element 
 of known valency for the purpose of deciding the unknown valency. 
 
 In this respect the isomorphism of the compounds of the element with 
 those of other elements of known atomic weight, and therefore of 
 known valency, is most important. The principle of isomorphism, 
 originally stated by Mitscherlich (1821), is that certain elements may be 
 substituted for each other in their crystalline compounds ivithout alteration 
 of the form of the crystals. Such elements are said to be isomorphous 
 with each other, and the crystalline compounds, in which the substitution 
 occurs, are said to be isomorphous compounds. Thus, aluminium, 
 chromium, and iron are isomorphous elements because they all form 
 
298 EXAMPLE OF ATOMIC WEIGHT DETERMINATION. 
 
 alums of the type KR'"(SO 4 ) 2 .i2H 2 (where R'" is Fe, Al, or Or), which 
 crystallise in octahedra, and are capable of forming mixed crystals, the 
 most important criterion of isomorphism. For example, when a 
 mixture of solutions of aluminium alum and chromium alum is allowed 
 to crystallise, the crystals contain both aluminium and chromium in 
 proportion varying with the conditions of crystallisation. Supposing 
 that the valency of chromium were unknown it could be deduced from 
 this isomorphism with aluminium. For the valency of aluminium is 
 three, hence it is probable that the valency of chromium is also three, 
 in which case the atomic weight of the metal is thrice its equivalent. 
 
 As an example of the application of these three methods, the following experi- 
 ments may be supposed to have been performed with a view of ascertaining the 
 atomic weight of cadmium : 
 
 (1) 0.7232 gram of cadmium bromide * was dissolved in water, and the bromine 
 was exactly precipitated by adding a solution of silver nitrate (with the precautions 
 necessary to an accurate result). This solution was made by dissolving 10 grams 
 of pure silver in I litre of dilute nitric acid, and 57.43 c.c. were required for the pre- 
 cipitation. Hence 0.5743 gram of silver will combine with the bromine in 0.7232 
 gram of cadmium bromide ; but from the careful synthesis of silver bromide, it i& 
 known that this weight of silver will combine with 0.4254 gram of Br ; therefore 
 the 0.7232 gram of cadmium bromide contains 0.2978 gram of Cd combined with 
 
 0.4254 gram of Br. Since the equivalent of bromine is 80. =56 will 
 
 be the equivalent of cadmium that is, the number of parts by weight of 
 Cd which will combine with one equivalent of Br. The atomic weight of cadmium 
 must, therefore, be 56 x %, where n is a small integer. 
 
 (2) The vapour density of cadmium bromide was found to be 136, therefore its 
 molecular weight is 272 ; but, according to the above analysis, this number of 
 grams will contain 112 grams of Cd and 160 grams of Br, for these elements are 
 present in the ratio 56 : 80. It follows that the atomic weight of cadmium cannot 
 be greater than 112, or n cannot be greater than 2. 
 
 (3) A piece of cadmium weighing 100 grams was heated in boiling water until 
 it had attained the temperature of the water (100 C.) ; it was then transferred to 
 a calorimeter containing ] oo grams of water at o C. The temperature of this 
 water (allowing for the heat left in the calorimeter) rose to 5.3 C. Therefore the 
 loo grams of cadmium, in cooling from 100 to 5.3, have lost 100x5.3 = 530 
 gram-units of heat,f so that in cooling through i C. the 100 grams would lose 
 
 53 
 
 Q - - =5.6 units, or i gram would lose 0.056 unit that is, the specific heat of 
 
 cadmium is 0.056. But the specific heat x atomic weight will probably 6.4, 
 so that the atomic weight of cadmium should be ^ii^ (nearly). This is 
 
 approximately 56 x 2, therefore n is probably 2. 
 
 (4) Many cadmium salts are found to crystallise together with zinc salts, being 
 isomorphous with them ; but zinc is divalent, therefore cadmium is probably also 
 divalent, in which case its atomic weight must be twice its equivalent, or 112. 
 
 With regard to the standard for' the atomic weights, it may be said that many 
 chemists prefer to fix arbitrarily 16 as the atomic weight of oxygen, rather than 
 to adhere to Dalton s standard viz., H=i. The reason for this is that the 
 equivalents of the elements are far more frequently determined from oxygen- 
 compounds than from hydrogen-compounds, because the former are both more 
 numerous and better capable of exact analysis. 
 
 Atomicity of Molecules. The following paragraphs deal with 
 methods of ascertaining the number of atoms in a molecule, that is, the 
 atomicity of the molecule. 
 
 * It will be evident that the analysis of any compound of the element with another 
 element of well-established equivalent will serve to fix the equivalent of the first element. 
 
 f No allowance is here made for the slight alteration in the specific heat of water with 
 rise of temperature. 
 
ATOMICITY OF MOLECULES. 299 
 
 Considering first the atomicity of elementary molecules, the molecular 
 weight having been determined from the vapour density and the atomic 
 weight from the chemical equivalent, the atomicity is ascertained by 
 simply dividing the atomic weight into the molecular weight. For 
 instance, the vapour density of nitrogen being 14, and its atomic 
 weight also 14, its atomicity is two there are two atoms in the mole- 
 cule ; it is diatomic ; its molecular symbol is ~N 2 . 
 
 In the case of certain elements, the type of which is the newly discovered argon, 
 there is difficulty in ascertaining the atomic weight because the element shows so 
 little tendency to combine that the equivalent cannot be determined. A method 
 exists whereby it is possible to decide whether an element of this kind is mon- 
 atomic, diatomic, or polyatomic ; it depends on the following considerations : The 
 amount of heat required to raise the temperature of an ideal gas through i C. 
 should be that expended in increasing the kinetic energy of its molecules, provided 
 the gas is not allowed to expand, that is, if its volume is kept constant. If the gas 
 is allowed to expand the molecules do work in overcoming the external pressure, and 
 the heat required to raise the temperature i C. will be more than that necessary to 
 increase the kinetic energy by an amount equivalent to the work done. In the 
 former case the pressure of the gas increases when it is heated, while in the latter 
 case it remains constant. It follows that the specific heat of a gas at constant 
 pressure, Cp, is greater than that of the gas at constant volume, Cr. While Cp is 
 easily determined, Cv is very difficult to determine ; but the ratio Cp : Cv may be 
 calculated, from the kinetic theory of gases, to be 1.66. A discussion of the 
 calculations cannot be entered upon here, but it will be obvious from what was 
 said at p. 291 that if the molecular weight of the gas be considered, the increase in 
 kinetic energy will be proportional to mw 2 /2, while the work done in overcoming 
 the external pressure is proportional to mw 2 /3. Hence, while C'i< is measured by 
 the former value, Cp is measured by (mw 2 /2 + w* iv 2 /3) and the ratio of the latter 
 to the former 5/6 : 1/2 or 1.66 : I. 
 
 Now experimental methods have been devised for determining the ratio Cp : Cv, 
 chief of which is that depending on the velocity (u) of sound in the gas for which 
 the ratio is to be ascertained. The velocity is given by the equation u = */kpjd, where 
 p is the pressure, d the density, and k the ratio Cp : Cv. The velocity of sound in 
 air is a well-known experimental constant, and therefrom k is found to be 1.4 for 
 air. By filling a glass tube, clamped at one end, with a gas and rubbing the tube 
 so as to produce a musical note, the wave length of the note can be ascertained if 
 the tube contain a dust capable of marking the nodes by the disturbance it suffers. 
 By comparison of this wave length with that known for the note in air, the value 
 of u, and therefore of &, for the gas may be calculated. 
 
 In gases that are known to have diatomic molecules, =1.4 that is, the specific 
 heat at constant volume is more than it would be in the ideal gas. The assumption 
 is that in a diatomic gas, the atoms in the molecule have a movement relative to 
 each other, an intra-niolecular motion, which is increased by heat. Thus heat would 
 be absorbed which would not increase the kinetic energy of the moving molecules. 
 
 The method in question, therefore, consists in ascertaining the value Cp : Cv for 
 the gas the atomicity of whose molecules is to be ascertained. If this ratio is 1.66 
 the molecules are monatomic ; if it is 1.4 the molecules are diatomic. For poly- 
 atomic gases the ratio is still lower. Mercury vapour and the gases of the argon 
 group are found by this method to be monatomic. 
 
 As already indicated (p. 294), the vapour density of some elements 
 decreases as the temperature rises. It follows that the atomicity of 
 the molecules decreases ; thus, sulphur vapour at 480 0. ha,s a density of 
 95.1, which, divided by 32, the atomic weight 'of sulphur, gives S 6 as the 
 molecular symbol ; but at 1000 C. the density falls to 32.1, giving S 2 
 for the molecular symbol. It is supposed that in such cases the mole- 
 cule suffers a dissociation as the temperature rises quite analogous to 
 that which undoubtedly occurs in the case of many compound molecules, 
 and noticed at page 86. 
 
 The elements may be classified in this respect as follows : (i) Those whose 
 
300 DETERMINATION OF FORMULAE. 
 
 vapour densities are identical with their atomic weights at all temperatures ; * 
 H, O and N are the chief of these. Since M = 2D, the molecular weights of these 
 atoms must be twice their atomic weights, and the molecule must therefore 
 contain two atoms, it is diatomic at all temperatures. (2) Those whose vapour 
 densities are identical with their atomic weights at low temperatures but become 
 one-half at high temperatures. These are Cl, Br, I ; their molecules are diatomic 
 at low temperatures but monatomic at high temperatures. (3) Those whose vapour 
 densities are one-half of their atomic weights at all temperatures, so that their 
 molecular weights are identical with their atomic weights at all temperatures. 
 These are Na, K, Zn, Cd, Hg, A, He. Their molecules are monatomic at all tem- 
 peratures. (4) Those whose A'apour densities are twice their atomic weights at 
 low temperatures but identical with them at high temperatures. Such are P. 
 As, Sb. Since M = 2D, the molecular weights of each of these gaseous elements must 
 be four times their atomic weight at low temperatures, but only twice at high tem- 
 peratures. They are tetratomic at low, but diatomic at high, temperatures. 
 (5) Those whoseVapour densities are a greater multiple than twice their atomic 
 weights at low temperatures, becoming equal to their atomic weights at high 
 temperatures. Sulphur is the only example. 
 
 Turning now to the determination of the atomicity of a compound 
 molecule, that is, the selection of the formula for the compound, this 
 resolves itself into three steps : 
 
 (1) Quantitative analysis of the compound to determine the per- 
 centage composition of it. Here a distinction must be drawn between 
 a proximate analysis and an ultimate analysis. For instance, a sample 
 of beer may be analysed to determine the percentage of alcohol, water, 
 hop-extract, <fcc., in it ; this is a proximate analysis. If the operations 
 were directed to the determination of the carbon, hydrogen, oxygen, 
 <fcc., in the beer that is to say, its ultimate constituents an ultimate 
 analysis would have been performed. Taking alcohol as an example, 
 the result of an ultimate analysis would be, carbon 52.16 per cent., 
 hydrogen 13.04 per cent., oxygen 34.80 per cent. As these numbers 
 add up to 100 no other element can be present. 
 
 (2) Division of the percentage of each element by the atomic weight 
 of the element to ascertain the relative number of atoms of each in the 
 compound. 
 
 In the case of alcohol the following figures would be obtained : 
 
 52.16 divided by 12 gives 4.34 atomic weights of carbon. 
 13.04 .. i .. 13.04 hydrogen. 
 
 34.80 ,. 16 ,. 2.17 ,, oxygen. 
 
 In its lowest terms the ratio 4.34 : 13.04 : 2.17 is 2:6:1; that is, the 
 atoms of C, H and O are present in the molecule of alcohol in this 
 ratio. An experimental or empirical formula for alcohol is thus ob- 
 tained, and it is evidently C,H 6 O. This, however, may not be the 
 formula for the molecule or the molecular formula. It is certainly the 
 minimum formula, for by hypothesis it is impossible for the molecule to 
 contain half an atom, as would be the case if the formula be written 
 CH 3 Oj. But the true formula may be a multiple of C 2 H 6 0, such as 
 C 4 H 12 2 or C 6 H 18 3 all that is known so far is that the ratio of C:H:O 
 must be 2:6:1. 
 
 (3) The vapour density of the compound is determined. It will be 
 obvious that this settles the molecular formula, or the atomicity of the 
 molecule. For M = 2D, so that if the molecule is C 2 H 6 the vapour 
 
 density must be I2 x 2 + * x 6 + l6 x I = 23 ; if it is C 4 H 12 2 the vapour 
 
 * The temperatures referred to in this classification range from 100 C. to 1700 C. 
 
DISSOCIATION. 301 
 
 density must be 2 = 46. Now the determination 
 
 2 
 
 of the vapour density of alcohol, as described at p. 293, gives a number 
 near 23 ; therefore the molecular weight is 46 and the molecular 
 formula is C 2 H 6 O, 9 atoms in the molecule. 
 
 Dissociation. The only difficulty in following the foregoing steps 
 for determining the molecular formula for a compound, provided that 
 this is volatile, is in the doubt which sometimes exists whether the 
 vapour or gas into which the compound is converted by heat is indeed 
 the same compound. The gas produced by the vaporisation may con- 
 sist of products of decomposition or of dissociation of the compound. 
 The difference between these two phenonena has already been explained 
 (p. 86). An example will make clear how dissociation affects the 
 determination of molecular formulae. The ultimate analysis of am- 
 monium chloride shows that its empirical formula is NH 4 C1, and this 
 must be the minimum molecular formula, because the molecule cannot 
 contain less than one atom of N or one atom of Cl. A determination 
 of the vapour density of ammonium chloride, however, gives the number 
 13.35, corresponding with molecular weight 26.7. Now, the formula 
 NH 4 C1 corresponds with molecular weight 14+1x4 + 35.5 = 53.5 or 
 double that found from the vapour density, which indeed corresponds 
 with the impossible formula NjHgClj. 
 
 The experiment cited at p. 86 shows that the vapour of ammonium 
 chloride consists not of this compound but of a mixture of ammonia, 
 NH 3 , and hydrogen chloride, HC1. That is, instead of being composed 
 of NH 4 C1 molecules, the vapour consists of a mixture of NH 3 + HC1 
 molecules. Unless the vapour itself had been tested this change would 
 not have been detected, for it is a dissociation, not a decomposition, so 
 that when the vapour is cooled the ammonium chloride is re-formed, 
 just as water is obtained again when the steam from it is condensed. 
 
 To make clear how this dissociation affects the vapour density, it 
 must be explained that ammonium chloride is found to be produced 
 when equal volumes of NH 3 and HC1 are mixed. Hence the dissociated 
 vapour of ammonium chloride must consist of equal volumes of these 
 gases. Now a mixture of gases in equal volumes always has a vapour 
 density which is the mean of the vapour densities of the constituent 
 gases. In this case the vapour density of NH 3 being 8.5, and that of 
 HC1 1 8. 2, that of the mixture would be half the sum of these values, 
 or 13.35. 
 
 Classification of the Elements The Periodic Law. It has 
 been already shown that the elements may be classified into groups which 
 contain individuals possessed of similar chemical properties. Newlands, 
 in 1864, pointed out that when the elements are arranged in the order 
 of their atomic weights, this similarity is seen to exist between every 
 eighth element, the first being similar to the eighth, the second to the 
 ninth, and so on (law of octaves). In 1869 Mendeleeff and Lothar 
 Meyer made a similar discovery. 
 
 In seeking for a basis for a classification of the elements, it is 
 natural that the chemist should turn to the most strictly chemical 
 property of the elements, namely, their tendency to combine with 
 each other. Mendeleeff has pointed out that the limit to this tendency 
 is expressed by saying that one equivalent of an element never com- 
 
302 
 
 THE PERIODIC LAW. 
 
 bines with more than eight equivalents of another element. If oxygen 
 and hydrogen betaken as typical elements, it will be noticed that there 
 are never more than four atoms of oxygen or four atoms of hydrogen 
 united to one atom of an element. Furthermore, the sum of the 
 equivalents of O and H, which can combine with one atom of an 
 element is eight. Thus, if an element R forms as its highest salt- 
 forming oxide* a compound of the type RO 2 , it will form a hydride 
 RH 4 ; if an oxide, R0 3 , a hydride, RH 2 , and so on. For example, N 
 forms N 2 5 as its maximum oxide that is, a compound of five equiva- 
 lents of oxygen with one atom of nitrogen and its maximum hydride 
 is NH 3 ; S forms S0 3 (6 equivalents of oxygen), and SH 2 . 01 forms 
 C1H, so that its highest salt-forming oxide should be C1 2 O 7 (7 equivalents 
 of O to i atom of 01), which, however, is only known in such com- 
 pounds as K 2 O.C1 2 7 = 2KC10 4 . 
 
 It follows that there are eight types of higher salt-forming oxides, 
 viz. : R 2 O, R 2 O 2 , R 2 3 , R 2 O 4 , R 2 5 , R 2 6 , R 2 O 7 , and R 3 8 . 
 
 Those elements which form higher salt-forming oxides of the same 
 type are alone analogous. If this proposition be admitted, the ele- 
 ments must be classified in eight groups. Such a classification reveals 
 the fact that when the elements are arranged in the order of their 
 atomic weights, they follow the same order as that of their higher 
 oxides, so that the valency of the elements towards oxygen returns to 
 the same value at every eighth element, that is, periodically. This 
 return is noticeable in the case of all other properties of the elements 
 which have been accurately examined, that is to say, the properties of the 
 elements are periodic functions of their atomic weights. In general terms, 
 if the elements be arranged in the order of their atomic weights, the proper- 
 ties of consecutive elements will be found to differ, but the properties 
 will return to approximately the same value at definite periods. 
 
 Such an arrangement of the elements is shown in the appended table : 
 
 Group . 
 
 i. 
 
 ii. 
 
 iii. 
 
 iv. 
 
 v. 
 
 vi. 
 
 vii. 
 
 viii. 
 
 Series i 
 
 H 
 
 
 
 
 
 
 
 He 
 
 2 
 
 Li 
 
 Be 
 
 B 
 
 c 
 
 N 
 
 o 
 
 F 
 
 Ne 
 
 3 
 
 Na 
 
 Mg 
 
 Al 
 
 Si 
 
 P 
 
 S 
 
 ci 
 
 Ar 
 
 4 
 
 K 
 
 Ca 
 
 Sc 
 
 Ti ' 
 
 v 
 
 Or ' 
 
 Mn 
 
 Fe : Co.Ni.Cu 
 
 5 
 
 (Cu) 
 
 Zn 
 
 Ga 
 
 Ge 
 
 As 
 
 Se 
 
 Br 
 
 Kr 
 
 6 
 
 Rb 
 
 Sr 
 
 Y 
 
 Zr 
 
 Nb 
 
 Mo 
 
 
 
 Ru : Rh.Pd.Ag 
 
 7 
 
 '(Ag) 
 
 Cd 
 
 In 
 
 Sn 
 
 Sb 
 
 Te 
 
 I 
 
 Xe 
 
 8 
 
 Cs 
 
 Ba 
 
 La 
 
 Ce 
 
 Pr 
 
 Nd 
 
 Sa 
 
 
 
 9 
 
 Gd 
 
 
 
 Tb 
 
 
 
 Er 
 
 
 
 Tu 
 
 
 10 
 
 . 
 
 
 
 Yb 
 
 . 
 
 Ta 
 
 w 
 
 
 
 Os : lr.Pt.Au 
 
 ii 
 
 (Au) 
 
 ' Hg 
 
 Tl 
 
 Pb 
 
 Bi 
 
 . 
 
 . 
 
 
 , 12 
 
 
 
 
 Th 
 
 
 
 u 
 
 
 
 
 Higher oxide 
 type . 
 
 R 2 
 
 R 2 2 
 (BO) 
 
 R 2 3 
 
 R 2 4 
 
 BA 
 
 R 2 6 
 (R0 3 ) 
 
 BA 
 
 R 2 O 8 
 (R0 4 ) 
 
 Hydrides 
 
 
 
 
 RH 4 
 
 RH 3 
 
 RH 2 
 
 RH 
 
 
 Capable of behaving- as an anhydride or as a base. 
 
FAMILIES OF ELEMENTS. 303 
 
 In drawing up this table two main difficulties occurred. In the first 
 place, Co, being next to Fe in atomic weight, should have been written 
 in group i. ; but neither this metal nor Ni shows any analogy with the 
 elements in group i. Cu, on the other hand, shows some analogy 
 with the elements of both group viii. and group i., consequently its true 
 position is somewhat doubtful. Thus Co and Ni have to remain in 
 group viii., an arrangement also necessary in the case of Rh, Pd, Ir, 
 and Pt. 
 
 Within the last few years much difficulty has arisen owing to the 
 discovery of the helium and argon group of elements, as these do not 
 appear to form any chemical compounds and therefore have no valency. 
 In the foregoing table they are placed in group viii. pending a more 
 satisfactory elucidation of their probable position. 
 
 In the second place, the element Ru, which is next in atomic weight 
 to Mo, should come in group vii., but its position there is untenable, 
 because its higher oxide is of the type RO 4 and not R 2 7 . Consequently, 
 Ru must be placed in group viii., whilst the position in group vii. re- 
 mains vacant. Thus it is not always possible to locate each element in 
 the table immediately succeeding the next lower in atomic weight, so 
 that a certain number of blanks must be left. Where such blanks 
 occur elements are believed to exist, but to be as yet unknown. 
 Credence is afforded to this view by the fact that the number of such 
 blanks was larger when the table was first drawn up, some of these 
 spaces having been since filled by the discovery of elements (such as 
 Oa, Ge, and Sc), the atomic weights of which showed that they were 
 the missing elements. 
 
 It will be found that elements in the same group, and in even series, 
 are completely similar to each other, as, for example, Ca, Sr, and Ba ; 
 this is also the case with the elements in the same group and in odd 
 series, such as P, As, and Sb. The members of the odd series, however, 
 do not so closely resemble those of the even series, though in the same 
 group. Thus, Ca and Zn have far fewer properties in common than 
 have Ca and Sr. It seems, then, that the periodic return of properties 
 to the same value only occurs after two series have been traversed, so 
 that each period of the table is constituted by two series ; thus, K, Rb, 
 and Cs resemble each other very closely. It will be seen that since 
 this is the case, each group must consist of two sub-groups, indicated in 
 the table by the setting of the symbols in two vertical lines in each 
 group. 
 
 The members of these sub-groups or families resemble each other 
 more closely than do the members of a group taken as a whole. Whilst 
 this is true of the elements which follow Na, it is not true up to this 
 point ; thus, Be is more nearly allied to Mg than to Ca ; B to Al than 
 to Sc ; and C to Si than to Ti. These elements, therefore, do not appear 
 to be in their right places, a difficulty which is met by supposing that 
 they, and those from Na to Cl (inclusive) constitute two short periods ; 
 these elements have been termed the typical elements of the table. 
 
 It is only possible here to call attention to a very few of the properties of the 
 elements which return periodically to about the same value. The elements of the 
 same family form oxides which, when bases, are of the same order of basicity and, 
 when acid oxides, of the same order of acidity ; this is well illustrated by K, Rb, 
 Cs ; Ca, Sr, Ba ; P, As, Sb. 
 
 The specific gravities (mass of unit volume) of the elements exhibit a periodicity. 
 
304 APPLICATION OF THE PERIODIC LAW. 
 
 Instead of comparing specific gravities it is better to compare atomic volumes (or 
 number of unit volumes in the atomic weight). The atomic volume of an element 
 is the quotient of its atomic weight divided by its specific gravity at the melting- 
 point, A/d (at melting-point). Those elements which are most chemically active 
 have the lowest specific gravities and therefore the highest atomic volumes ; thus it 
 is found that the atomic volume falls from the beginning to the middle of a period, 
 but rises again from the middle to the end ; for instance, the atomic volume of K is- 
 45, of Ni 6.8, and of Br 26. In the same family the atomic volume rises with the 
 atomic weight ; e.g., Li=i2, K = 45, Eb = 57, Cs = 7i. Similar relations are main- 
 tained between the molecular volumes (molecular weight divided by specific gravity) 
 of the oxides and of some other compounds of the elements. 
 
 The same periodic fluctuation is to be noted in the melting-points, the electro- 
 positiveness, the brittleness and the ductility of the elements, and extends to the 
 colour of their salts. If, therefore, the atomic volumes be plotted on a curve, the 
 same curve will apply to many other of the properties. 
 
 The Periodic Table has found a twofold application : (i) It has served to enable 
 chemists to foretell the existence and properties of elements which have subsequently 
 been discovered ; (2) it has afforded a means for deciding the atomic weights of 
 some elements. 
 
 An example of the first of these is the prophecy by Mendeleeff of the existence 
 and properties of germanium ; the principle upon w r hich such predictions are made, 
 is that the properties of an element are approximately the mean of those of the four 
 elements which immediately surround it. There was a vacancy in the table between Si 
 and Sn ; Mendeleeff termed the element which had to be discovered to fill the gap,, 
 ekasilicon (eka is " one " in Sanscrit). According to the above principle, ekasilicon 
 when discovered should have properties identical with the mean of those of Si, As, 
 Sn, and Ga ; but Ga was itself unknown at the time, so Mendeleeff had to use Zn as 
 a member of the quorum. The mean of the atomic weights of these four elements 
 is 71.5, so that this would be the atomic weight of ekasilicon ; that found for ger- 
 manium is 72. Ekasilicon (Es) would probably form two oxides, EsO and Es0 2 , 
 an acid oxide ; for although SiO is not known, SnO is known, and both Si0 2 and 
 Sn0 2 are stable, acid oxides ; Ge0 2 , an acid oxide, is well known, and GeO probably 
 exists. EsCl 4 and EsCl 2 should exist, because SnCl 4 and SnCl 2 exist, but GeCl 2 
 should be less stable than SnCl 2 , for SiCl 2 is not known. As a fact, both GeCl 4 and 
 GeCl 2 exist, the latter being less stable than SnCl 2 . Further, the boiling-point of 
 EsCl 4 should be the mean of those of SnCl 4 and SiCl 4 namely, 88.5 ; it is found 
 to be 86. 
 
 The second application of the table is illustrated by the fixation of the atomic 
 weight of beryllium. The equivalent of beryllium is 4.5, and its atomic weight was 
 at first said to be 13.5, because its oxide was supposed to be Be 2 3 on account of its- 
 similarity to A1 2 3 . With this atomic weight, however, this element would have to 
 follow carbon in the periodic table, a position certainly at variance with its proper- 
 ties. It was therefore suggested that its atomic weight is really 9, in which case its- 
 oxide would be BeO and the element would fall into the then vacant place in 
 group ii., a position which has since been confirmed by the determination of the 
 vapour density of BeCl 2 , from which the maximum atomic weight of 9 is 
 obtained. 
 
 THE MEASUREMENT OF CHEMICAL AFFINITY. 
 
 Chemical affinity is a name conveniently employed to designate the 
 unknown force by which chemical change is effected. 
 
 Energy is that fundamental property which, in addition to mass, is possessed 
 by every kind of matter, and for the present purpose it may be defined as ability 
 to effect a change in the relative position of masses of matter, be they molar, 
 molecular, or atomic. It is of several kinds, of which chemical energy is one. 
 Heat energy, electrical energy, kinetic energy (or that resident in moving matter), 
 and potential energy (or that resident in matter by virtue of its position), are other 
 kinds of energy. 
 
 The nature of chemical energy is unknown ; but it rnaj- be compared with 
 potential energy, for it appears to depend upon the position of the matter in 
 which it resides. Thus a mixture of hydrogen and oxygen may be said to possess 
 a potential energy due to the position of close proximity of the molecules ; for, 
 just as the potential energy of a stone on the edge of a cliff requires an impulse 
 
PRINCIPLES OF THERMOCHEMISTRY. 305 
 
 in order to convert it into another form of energy the kinetic energy of its fall 
 to the foot of the cliff so the potential energy of a mixture of hydrogen and 
 oxygen requires an impulse, such as the heat of an electric spark, in order to 
 convert it into another form of energy heat energy. 
 
 The potential energy of a stone on a cliff is measured by multiplying the force 
 which impels the stone to fall to the foot of the cliff by the space through which 
 it has to fall, so that potential energy = force x space. Chemical energy may 
 also be regarded as composed of two factors ; one of these is, perhaps, chemical 
 affinity, the other is unknown. 
 
 It is not necessary to know the force impelling the stone to fall, or the space 
 through which it falls, in order to ascertain the potential energy of a stone on a 
 cliff. If the stone be allowed to fall, and steps be taken to receive it in such a 
 manner that all the heat generated by its impact with the earth is measured, then, 
 by the principle of the Conservation of Energy,* the potential energy can be cal- 
 culated from this heat, which is exactly equivalent to it. (The mechanical equiva- 
 lent of heat is : one gram-unit of heat = the energy represented by one gram 
 falling through 42.350 centimetres.) 
 
 It should be equally possible to measure the chemical energy of a mixture of 
 hydrogen with oxygen by ascertaining the quantity of heat evolved during the 
 combination of the gases, and although this method would not necessarily measure 
 the chemical affinity of the hydrogen for the oxygen, yet the value obtained would 
 probably be proportional to this affinity. 
 
 There are two methods by which a force may be directly measured : (i) A 
 force of known magnitude may be brought to bear upon the force to be measured 
 in such a manner that the two are in equilibrium. The two forces will then be 
 equal. Such a method may be called a static, wet/tod, and would be employed if a 
 force of known value were brought to bear upon a falling stone so as to bring it 
 to rest ; the force of the stone would then be equal to the opposing force ; (2) by 
 measuring the velocity of a moving mass in successive seconds, the force impelling 
 the motion is measured by the change which occurs in this velocity. This may be 
 called a kinetic method. 
 
 The attempts which have been made to measure chemical affinity involve 
 methods analogous to these two methods of measuring dynamical force. But the 
 attempt to measure the chemical energy of chemical reactions by ascertaining 
 their heat changes, and thus to obtain measurements which may be regarded as 
 proportional to chemical affinity, has been made to a much greater extent than 
 have attempts to apply the static or the kinetic method ; the measurement of 
 chemical energy by measuring thermal changes will therefore be considered first. 
 
 Thermochemistry is that branch of the science of chemistry which 
 deals with the study of the thermal changes accompanying chemical re- 
 actions. The prime object of the study is to obtain relative measure- 
 ments of the chemical affinities inducing the reactions. 
 
 Attention has been called in the preceding pages to some of the 
 principles of thermochemistry, but they may aptly be summarised here, 
 (i) Every chemical change is accompanied by a thermal change, which 
 is a constant quantity. (2) The thermal change occurring during the 
 combination of elements to form a compound is called the heat of 
 formation of the compound. It is generally a positive quantity, that 
 is, heat is evolved the compound is exothermic ; sometimes, however, 
 it is a negative quantity, that is, heat is absorbed the compound is 
 endothermic. (3) The thermal change occurring during the decomposi- 
 tion of a compound is called the heat of decomposition of the compound. 
 (4) The heat of decomposition of a compound is identical with, but of 
 opposite sign to, the heat of formation of that compound. 
 
 * This principle may be expressed thus : In any space the total quantity of energy remains 
 the same, although the energy may be transferred from one part of the space to another, or 
 transformed from one kind of energy into another. An example of the principle is furnished 
 by the firing of a mixture of H 2 -f-O in a vessel from which loss of heat is impossible. There 
 is the same quantity of energy in the vessel before the explosion und after it, bnt after the 
 explosion the energy is in the form of heat energy instead of chemical energy. 
 
 U 
 
306 DETERMINATION OF THERMOCHEMICAL DATA. 
 
 The last proposition follows from the principle of the conservation of 
 energy (see foot-note, p. 305). The potential energy of a mixture of 
 elements is lost to the system in the form of heat energy when the 
 elements combine ; and in order that the elements may be again 
 imbued with the same potential energy, heat energy, or some other 
 form of energy, must be restored to the system. 
 
 The measurement of the thermal changes of chemical reactions is 
 effected by causing the reaction to occur in a closed chamber which is 
 immersed in a calorimeter, such as that described at p. 164. 
 
 The heat of formation of a compound is expressed thus : H,OJ = 
 22,000, meaning that the combination of i gram of hydrogen with 
 35-5 grams of chlorine evolves 22,000 gram-units of heat. Again, 
 N,0 2 = 7700, means that when 14 grams of nitrogen combine with 
 32 grams of oxygen, 7700 gram-units of heat are absorbed. Again, 
 H 2 0,S0 3 = 21,320 means that when 18 grams of water combine with 
 80 grams of SO 3 , 21,320 gram-units of heat are evolved. The heat of 
 decomposition is expressed similarly, but with reversed signs, thus ; 
 -H,C1= - 22,000 ; -N,0 2 = +7700. 
 
 The value obtained in a calorimeter for the thermal change of a 
 reaction is not necessarily the thermal change due to that chemical 
 reaction whose heat is to be measured. Allowance must frequently be 
 made for secondary chemical reactions and for changes of physical state. 
 
 Two examples may be quoted in order to make this clear : 
 
 (1) 80 grams of S0 3 were mixed with a large excess of water (the quantity 
 being known) with the view of ascertaining the thermal change S0 3 , H. 2 O. The 
 value obtained was 39,177 ; but this obviously includes two thermal changes : 
 
 (a) that due to the combination of 80 grams of S0 3 with 18 grams of H 2 0, and 
 
 (b) that due to the combination of the H 2 S0 4 produced with an excess of water. 
 When sulphuric acid is diluted with water in a calorimeter, it is found that heat 
 continues to be evolved until the weight of water amounts to about thirty-six 
 times that of the sulphuric acid (corresponding with the formula H 2 S0 4 .2ooH 2 0) ; 
 this thermal change amounts to 17,857 gram-units per 98 grains of H 2 SO 4 , and 
 must be subtracted from that observed on mixing 80 grams of S0 3 with a large 
 excess of water in order to arrive at the value S0 3 ,H 2 0. This now becomes 21,320. 
 A similar action of excess of water has to be taken into account in many cases, and 
 it is customary to use the symbol Aq for such an excess. Thus, S0 3 ,Aq:=39,i77 
 means that when S0 3 is dissolved in so much water that the addition of a further 
 quantity will produce no further thermal change, 39,177 gram-units of heat 
 are evolved. 
 
 (2) O'l gram of hydrogen and o - 8 gram of oxygen were mixed and fired in a 
 calorimeter, the final temperature of which was 20 C. The gram-units of heat 
 evolved by the reaction (calculated from the rise of temperature) amounted to 3418. 
 This corresponds with H 2 ,0 = 68.360. But since we know of at least three sources 
 from which this thermal change is derived, this value cannot be regarded as ex- 
 pressing the amount of heat energy equivalent to the chemical energy of the com- 
 bination. The first source is the chemical energy of the combination. The second 
 and third sources are due to the change of aggregation which occurs after the gases 
 have combined. 
 
 The steain produced by the combination of H 2 +0 occupies two- thirds of the 
 volume previously occupied by the mixed gases ; now the contraction of the 
 volume of a gas always involves a transformation of some of the kinetic energy 
 of the gas into heat energy ;in other words, heat is evolved by the contraction. It 
 is unreasonable to suppose that the condensation of H 2 + into steam is an 
 exception to this rule, so that the heat evolved by this condensation must be 
 allowed for in the present case ; a value for it, however, can only be calculated 
 when the kinetic energy of the molecules of hydrogen and oxygen, and that of 
 the molecules of steam are known. The method by which these kinetic energies 
 are calculated cannot be given here ; suffice it to say that the difference between. 
 
HEATS OF FORMATION CALCULATED. 307 
 
 the kinetic energy of 18 grams of H 2 + and that of 18 grams of steam has been 
 calculated to be equivalent to 193 gram-units of heat. 
 
 Of much greater importance than the above item, is the difference between the 
 kinetic energies of steam molecules at iooC. and water molecules at the same- 
 temperature. This difference is well known, and is expressed by the heat of con- 
 densation of steam. One gram of steam at 100 C. evolves 536*5 gram-units of 
 heat in becoming water at 100 C. Therefore 18 grams will evolve 9666-,gram- 
 units. In the calorimeter the water formed by the reaction does not remain at 
 100 C., but cools to 20 C. before the temperature of the outside water in the 
 calorimeter is measured. In cooling from 100 to 20, i gram of water loses 
 80 gram-units of heat (supposing that the specific heat of water is constant over 
 this range of temperature) ; therefore 18 grams of water lose 1440 gram-units. 
 
 From these remarks it will be seen that of the total 68,360 gram-units evolved by 
 the reaction in the calorimeter, 11,299 are due to the changes of aggregation, 
 namely, 193 to the contraction of H 2 + O to steam, 9666 to the condensation of the 
 steam to water at 100 C., and 1440 to the cooling of water from 100 C. to 20 C. 
 By deducting these 11,299 units from the total, 57,061 gram-units are obtained as 
 the thermal equivalent of the potential chemical energy of a mixture of hydrogen 
 and oxygen, rendered kinetic by the combination. 
 
 It must be remembered that even when every allowance has been 
 made for such secondary reactions and such changes of aggregation, it 
 is by no means certain that the thermal value obtained represents the 
 energy of combination of the atoms concerned in the chemical change. 
 If the hypothesis be adopted that the molecules of hydrogen and 
 oxygen, for example, must be separated into their constituent atoms 
 before combination can occur, it must be admitted that some energy 
 is absorbed in this preliminary process. This energy will become 
 potential in the atoms, and may or may not be completely rendered 
 kinetic, and therefore evolved as heat, when the atoms combine to form 
 molecules of water. Thus it may happen that the heat evolved in the- 
 combination of hydrogen and oxygen, is only the excess of that due to 
 the combination of the atoms of H and over that absorbed by the- 
 decomposition of the molecules of H and into atoms. It will be 
 obvious, however, that for all practical purposes, such as for the calcu- 
 lation of the calorific value of a gaseous fuel (see Fuel), the calorimetrical 
 value for the combination of hydrogen and oxygen is a perfectly correct 
 one, inasmuch as the gases employed in the experiment are in the same 
 condition as those used in practice. 
 
 The heat of formation of many compounds cannot be directly deter- 
 mined because the compounds are not formed by the direct combination 
 of their elements. In such cases the value is calculated by methods 
 which can receive but short notice here. 
 
 The principle underlying one of these methods is that the thermal 
 change of any reaction in which a compound AB is concerned, must be 
 smaller or greater* than the thermal change of a reaction having the 
 same products in which the constituents A and Bare concerned, by the 
 heat of formation of AB. For example, the combustion of CH 4 is ther- 
 mally expressed thus : CH 4 ,O 4 = 2 1 1,930 gram-units ; but it is supposed 
 that the mechanism of this combustion consists in the decomposition of 
 CH 4 into its elements which are then burnt, and it will be at once evident 
 that in the two reactions, CH 4 + O 4 = C0 2 + 2H ? O and C + H 4 + O 4 = 
 C0 2 + 2H 2 0, the heat evolved in the latter will differ from that evolved 
 in the former by an amount representing the heat of decomposition of 
 CH 4 . Now C,O 2 = 96,96o gram-units when solid carbon is burnt, 
 
 * Accordingly as AB is exothermic or endothermic. 
 
3O8 APPLICATION OF THERMOCHEMICAL DATA. 
 
 and H 4 ,0 2 = 136,720 gram-units for gaseous hydrogen; therefore 
 (C + H 4 ),0 4 = 96, 960+ 136,720 = 233,680 gram-units. But CH 4 ,O 4 = 
 2 1 1,930, that is, the heat of combustion of the constituents of CH 4 exceeds 
 that of CH 4 itself by 21,750 ; consequently, CH 4 must have absorbed this 
 amount of heat in being decomposed into its elements before these were 
 burnt. Thus it is concluded that marsh gas is an exothermic com- 
 pound, and that C,H 4 =2i,75o gram-units, supposing that the gas 
 were produced from solid carbon and gaseous hydrogen. 
 
 Another instance : N 2 O cannot be formed directly from its elements, 
 but the heat of combustion of carbon in the gas is easily determined, 
 and it is found that the reaction C 4- 2lN" 2 O = C0 2 + N 4 evolves 133,900 
 gram-units. Now this reaction involves the decomposition of 2N 2 O and 
 the formation of C0 2 , so that the heat evolved should be smaller or 
 greater than that evolved in the reaction of C + 2 = C0 2 by the heat of 
 decomposition of 2N 2 0. Since 0,03 = 96,960, the heat of decomposition 
 of 2N 2 O must be 133,900 - 96,960 = 36.940 gram-units, and that of N 2 O 
 must be 18,470 gram-units; in other words, nitrous oxide evolves heat 
 in its decomposition, and is therefore an endothermic compound, or 
 N 2 ,0= -18,470. 
 
 Another method for indirectly determining the heat of formation of 
 a compound depends upon the fact that the total energy change in a 
 reaction is the same whether the reaction occurs in one stage or in 
 several. This is only an application of the principle of the conservation 
 of energy ; the total energy of a stone falling to the earth is the same 
 whether the fall occur in one stage or in several. An example of the 
 method is furnished by the determination of the heat of formation of 
 H 2 S0 4 . This compound cannot be made from its elements directly, 
 but the heat of the reaction H 2 + SO 2 + = H 2 S0 4 is determinate, 
 and that of H 2 + = H 2 0, and of S + 2 = S0 2 , are well known. The 
 total heat evolved in the formation of H 2 S0 4 will be the same whether 
 the change is in one stage, H 2 + S + 4 = H 2 S0 4 , or in three, viz., 
 ) H 2 + 0-H 2 + 68,360; (2) S + 2 = S0 2 + 71,080; (3) H 2 + SO 2 + 
 = H 2 S0 4 + 53,480; consequently, H 2 ,S,O 4 = 68, 360+ 71,080 + 53,480 = 
 192,920. 
 
 From what has been said, it will be apparent that the thermal changes 
 of chemical reactions, as they are at present determined, cannot be 
 regarded with certainty as equivalent to the total chemical energy con- 
 cerned in the reaction. They cannot, therefore, be said to be an abso- 
 lute measure of the chemical affinity of elements for each other. 
 
 Nevertheless, the thermochemical data which have been accumulated, and are 
 to be found in most books of chemical constants, are useful aids to the chemist 
 when it is remembered (i) that endothermic reactions rarely occur save by the 
 application of external energy (generally applied in the form of heat energy) ; 
 (2) that of two exothermic reactions, that is more likely to occur, under ordinary 
 conditions, which is the more exothermic ; and (3) that of two exothermic com- 
 pounds that which is the more exothermic is the more stable. 
 
 For example, it is seen from the thermal values Ca,O= 132,000 and 0,02 = 96,960 
 that it is not probable that carbon will reduce CaO at any but a very high 
 temperature ; for the reaction 2CaO + C = CO 2 + Ca2 is highly endothermic, since it 
 involves the heat of decomposition of 2CaO ( - 264,000), and the heat of formation 
 of C0 2 , leaving a balance of 167,040 gram-units. As a fact the reaction does 
 not occur at any temperature hitherto attained, for although in the manufacture of 
 calcium carbide reduction of CaO may be said to occur, it must be aided by the 
 affinity of Ca for C at the high temperature used. 
 
REVERSIBLE REACTIONS. 
 
 39 
 
 Again, in any competition between chlorine and bromine for hydrogen, chlorine 
 may be expected to prevail, for H,C1 = 22,000 and H,Br = 13,500. HC1 is the more 
 stable of these two because it is the more exothermic. 
 
 In attempting to use thermal data as a guide for prophesying what will occur in 
 a chemical reaction, it must not be forgotten that they have nearly all been 
 determined at an initial and final temperature of about 20 C., and are only true 
 for the elements in their usual condition at this temperature. There is no reason 
 to suppose that the thermal change at a high temperature is the same as it is at 
 20 C. Thus it has been shown that the heat of formation of hydrogen iodide is 
 negative at low temperatures, but positive at 400 C. 
 
 Static method of measuring chemical energy. For practical 
 purposes chemical reactions may be classified into complete and reversible 
 reactions. The former class includes those changes in which the whole of 
 the reacting substances is converted into the products of the reaction ; 
 for example, when a mixture of equal volumes of H and 01 is fired, the 
 two gases combine completely and are entirely converted into HC1. A 
 reversible reaction is of such a nature that the products of the reaction 
 will, under a slight alteration of conditions, react with each other to 
 re-form the original substances. Thus, when steam and iron are heated 
 together, a reaction expressed by the equation Fe 3 + 4H 2 O = Fe 3 O 4 + H 8 
 occurs ; but it is equally true that when hydrogen and Fe 3 4 are heated 
 together the reaction Fe 3 O 4 + H 8 = 4H 2 + Fe 3 occurs. N ow either of 
 these reactions may be carried to approximate completion under certain 
 conditions ; thus, by passing steam over red-hot iron the whole of the 
 iron can be converted into Fe 3 O 4 ; so also by passing hydrogen over Fe 3 4 
 at the same temperature the whole of this can be reduced to metallic 
 iron. But if iron and steam be heated together in a closed vessel, the 
 iron will never be completely oxidised. This is because the reaction is 
 reversible, that is to sa,y, as soon as any Fe 3 O 4 and Hare produced these 
 tend to react with each other to form H 2 O and Fe ; in other words, the 
 reaction Fe 3 + 4H 2 O^Fe 3 O 4 + H 8 , can take place in either direction at 
 the same time, a fact expressed by the substitution of ^ for = in the 
 equation. 
 
 It has been seen, however, that by passing steam over red-hot iron 
 the latter can be completely oxidised that is to say, the equation 
 Fe 3 + 4H 2 = Fe 3 4 + H 8 can be realised. This is only possible because 
 one of the products of the reaction (the hydrogen) is in such a physical 
 condition that it can be removed from the sphere of action (the tube in 
 which the reaction is performed) ; indeed, for the complete oxidation of 
 the iron a large excess of steam over that indicated as necessary by the 
 equation (72 parts of steam for 168 parts of iron) must be passed 
 through the apparatus containing the iron in order to sweep away the 
 hydrogen. If the hydrogen could not be removed in this manner, the 
 completion of the reaction would be impossible. The same remarks, 
 mutatis mutandis, apply to the complete reduction of Fe 3 O 4 by hydrogen. 
 
 A reversible reaction can only become complete when one of the 
 products of the reaction is removed from the sphere of action. Under 
 any other conditions the vessel in which the reaction is proceeding will 
 contain some of each of the reacting substances, and some of each of 
 the products of the reaction. 
 
 The question naturally arises, When iron and steam are heated in a 
 closed vessel, so that nothing can escape from the sphere of action, how 
 far will the reaction proceed ? How much iron oxide and hydrogen will 
 
310 THE ACTION OF MASS. 
 
 be produced ? How much steam and iron will be left ? To fully appre- 
 ciate the state of the case it must be realised that both the reactions ex- 
 pressed by the equation Fe 3 + 4H 2 O^Fe 3 O 4 + H 8 are proceeding at the 
 same time, and during the whole time, and that if the temperature be 
 kept constant a period will soon be reached, when the amount of iron 
 oxidised per unit time will be exactly equivalent to the amount of iron 
 oxide reduced per unit time. 
 
 When this state of affairs prevails the equation in the direction repre- 
 sented by the arrow->, which may conveniently be termed the equation 
 representing the positive change, will be realised to exactly the same 
 extent as the equation represented by the arrow<-(the negative change) 
 is realised, per second. This is called the equilibrium stag erf the rever- 
 sible reaction, and when it is attained an analysis of the contents of 
 the vessel will show the same proportion of iron, steam, iron oxide and 
 hydrogen to be present, however long the vessel is maintained at the 
 same temperature. An alteration in the temperature will cause an 
 alteration in the extent to which either the positive or negative change 
 will occur per second ; so that with every such change of temperature 
 a new equilibrium stage will be established, and an analysis will show a 
 new proportion between the quantities of the four substances present. 
 
 There is another factor besides temperature which influences the 
 quantity of each of the substances present at the equilibrium stage of 
 a reversible reaction. This is the mass of any one of the substances. 
 Thus, if iron and steam be heated in the proportion represented by 
 the equation (168 parts of iron: 72 parts of steam) at any given tem- 
 perature, exactly the same quantity of iron oxide and hydrogen will be 
 produced as would remain undecomposed if iron oxide and hydrogen 
 were heated in the proportion represented by the equation (232 parts 
 of Fe 3 O 4 : 8 parts of hydrogen), at the same temperature. But if the 
 mass of either the steam or the hydrogen be increased, then the quan- 
 tities of steam or hydrogen present at the equilibrium stage will be 
 altered. If the proportion of either of the constituents on the left hand 
 of the equation be increased, the positive change will have occurred to 
 a greater extent that is, more Fe 3 4 and H will have been produced 
 when the equilibrium stage is reached, than was the case with the 
 former proportion. If the proportion of either of the substances on 
 the right hand of the equation be increased, the negative change 
 will occur to a greater extent than before. Since Fe and Fe 3 O 4 are 
 solids while hydrogen and steam are gases, the system is in this case 
 heterogeneous, and of the four substances only the H 2 O and H can 
 intermix. Hence, here, an alteration of the proportion of Fe or Fe 3 4 
 has but little effect upon the change. 
 
 This mass action is of great importance in chemical change, and may 
 be generally expressed by stating that in a homogeneous system chemical 
 change is pi'oportional to the active mass of each of the substances taking 
 part in the reaction. By active mass is meant the number of molecules 
 of the substance in unit volume, such as gram -molecules per litre. 
 
 From a practical point of view mass action frequently influences chemical 
 change, a large mass compensating a feeble affinity, it being possible for reactions 
 to proceed which, considering the relative affinities, could not occur unless one of 
 the products were sufficiently insoluble to be removed from the homogeneous 
 system. Such a case w r ill be met in the description of the manufacture of caustic 
 soda, where the comparatively feeble affinity of lime for C0. 2 is nevertheless suffi - 
 
COEFFICIENTS OF AFFINITY. 311 
 
 cient to allow the reaction Na 2 C0 3 + Ca(OH) 2 = 2NaOH + CaC0 3 to occur in solution, 
 because the CaCO. { immediately separates from the liquid and the reaction in the 
 left hand direction cannot, in consequence, occur so rapidly as that in the right 
 hand direction. Nevertheless care must be taken that the active mass of the NaOH 
 does not increase too much, for then even the precipitated CaC0 3 will be attacked to 
 reproduce Na 2 C0 3 and Ca(OH) 2 . In other words, the solution must not be too 
 concentrated. 
 
 It is not difficult to imagine the mechanism of this mass action ; the greater 
 the number of molecules in a given space the more frequently will they come 
 into contact with each other, and since chemical change appears to occur only 
 between molecules in contact, the greater will be the amount of chemical change 
 produced. In the case of steam and red-hot iron, it is obvious that the greater 
 the number of steam molecules present, the more frequently these will come in 
 contact with the iron, and the more oxide of iron, and consequently hydrogen, 
 will be produced. 
 
 The subject of dissociation furnishes numerous examples of mass action. 
 
 The chemical equilibrium between two opposing reactions, such as 
 those concerned in the action of steam on red-hot iron, should serve as 
 a static method for determining chemical energy. For the equilibrium 
 is between two chemical affinities, the one tending to produce the 
 positive change, the other tending to produce the negative change ; and 
 the amount of each change must be proportional to the affinity which 
 produces it ; so that by analytically determining the quantities of sub- 
 stances present, and, therefore, the extent of the reaction, at the 
 equilibrium stage, it should be possible to form a comparison between 
 these affinities. 
 
 The action of steam on red-hot iron does not lend itself to the application of 
 this method as the system is heterogeneous. But a number of double decomposi- 
 tions has been studied from this point of view ; they are reversible reactions and 
 are mostly between organic compounds, so that in this place it will be useful to 
 express them by the general form AB + CD^AC + BD. The opposing forces which 
 bring about the equilibrium of such a change are the sum of the affinities of A for 
 C and B for D (say /<) against the sum of the affinities of A for B and C for D 
 (say It 1 ). The amount of chemical change which has occurred at the equilibrium 
 stage is proportional to the active masses of the reacting substances, and, pre- 
 sumably, also to these coefficients of affinity, It and k l . The amount of chemical 
 change can be measured by chemical analysis. Suppose AB and CD be mixed in 
 the proportion of one gram-molecule of each ; then, when equilibrium has been 
 attained, there will be present a fraction of a gram-molecule of AC, BD, AB, and 
 CD respectively : and the fraction will be the same for AC and for BD, and also 
 the same for AB and CD. Let this fraction of AC and BD be a; then that of AB 
 and CD must be i -x, for one gram-molecule was originally taken. 
 
 The active masses of AC and BD, tending to produce the negative change, are x 
 and x, and their total effect maybe represented as xx or a? 2 . The affinity tending to 
 produce the negative change is' & 1 , so that the total force producing the negative 
 change is ft 1 /-. 
 
 The active masses of AB and CD are i-x and i-a j , and the affinity is k; 
 therefore the total force tending to produce the positive change is h(i -a?)' 2 . 
 
 When the equilibrium stage is reached these two forces are equal to each other, 
 whence A-(i - ./)- = k l ,r 2 or It/It 1 = # 2 /( I - a?) 2 . Thus the ratio It jit 1 can be determined, 
 for x is determinable by analysis. For example, when acetic acid and ethyl 
 alcohol are heated together, ethyl acetate and water are produced, the reaction 
 being reversible. When x is determined (after no more change appears to occur), 
 it is found to be , whence, by the above formula, k/k l = 4. 
 
 By this static method the relative affinity, or avidity, of acids for bases has been 
 determined. The principle of the method is to mix equivalent quantities of two 
 acids with a quantity of base insufficient to saturate both, and to determine what 
 proportion of the base each acid will acquire. Thus, when NaOH is mixed with 
 HNO 3 and H 2 S0 4 (equal equivalents) two-thirds of the soda combines with the 
 nitric acid and one-third with the sulphuric acid, showing that the avidity of the 
 
312 DISSOCIATION. 
 
 nitric acid is twice as great as that of the sulphuric acid. If the avidity of nitric 
 acid be taken as I. that of sulphuric acid is 0.5. 
 
 The avidity of an acid may be denned as the proportion of base which 
 that acid will appropriate when equivalent quantities of the acid, a base and 
 HN0 3 are mixed in aqueous solution. It is independent of the nature of the 
 base. The following order of avidities is probably correct : HN0 3 =i ; HCl = i; 
 
 Thus, in solutions of equivalent concentration, HN0 3 and HC1 must be 
 accounted stronger acids than H 2 S0 4 ; but the greater volatility of the two 
 first will enable H 2 S0 4 to expel them when heated with their salts. 
 
 Kinetic method of measuring chemical affinity. This method of measuring 
 chemical affinity consists in determining the amount of chemical change which 
 occurs in unit time, not waiting for equilibrium to occur. This value is termed the 
 coefficient of velocity of the change, and the greater this coefficient of velocity the 
 greater the force inducing the change. 
 
 Most changes are too rapid for any determination of the coefficient of velocity, 
 but in the class of changes known as hydrolysis (p. 265), such a measure- 
 ment is possible because the change only occurs with moderate rapidity in the 
 presence of an acid. Thus, when cane sugar is boiled with water it is very slowly 
 converted into invert sugar ; C^H^Ojj + HOH^aCgH^Oe ; but in the presence of a 
 dilute acid the change is much more rapid, and can be measured by determining 
 the amount of invert sugar produced. The action of the acid is not understood, 
 but is generally ascribed to a predisposing affinity of the acid for the invert sugar ; 
 this means that the invert sugar is the more readily produced because of the 
 tendency which the acid has to form an unstable compound with it ; such a com- 
 pound must be soon decomposed again, because to all appearances the same amount 
 of free acid remains in the solution after the hydrolysis as was there before. 
 
 Different acids have a different influence on the rate of the hydrolysis of cane- 
 sugar, &c., and it is reasonable to suppose that this rapidity of action is in some 
 way proportional to the affinity, or avidity, of the acid. By determining the 
 velocity of hydrolysis that is, the amount of cane-sugar which has been hydro- 
 lysed per minute when different acids are present, the avidities of the acids may 
 be compared. The mathematical calculations involved are somewhat complex, 
 and cannot be discuseed here. The method yields values for the avidities of 
 acids which are in the same order of magnitude as those determined by the static 
 method. 
 
 A little consideration of the definition of dissociation (p. 86) will 
 show that the phenomenon belongs to the same class as the reversible 
 reactions, such as the action of steam on red-hot iron discussed above.* 
 The contemplation of the case of phosphorus pentachloride will render 
 this more evident. When this compound is heated above 300 C. it 
 dissociates to a very large extent into PC1 3 + C1 2 , a fact discovered by 
 attempting to determine the vapour density of PC1 5 . The amount of 
 dissociation depends on the temperature and on the active masses of 
 the substances present. The equilibrium between the positive and 
 negative changes of the reversible reaction PC1 5 ^PC1 3 + C1 2 , occurs 
 when the same quantity of PCJ 3 is dissociated and associated in unit 
 time, and this will vary for every temperature. 
 
 Since PC1 3 , PC1 3 , C1 2 each represents 2 vols., the total active mass 
 tending to produce the negative change is twice as greafc as the active 
 mass tending to produce the positive change. If the vessel containing 
 the three substances at the equilibrium stage be diminished in size, that 
 is, if the pressure be increased, the active masses of all three will be 
 increased ; for there will now be more of each in unit volume. Suppose 
 the pressure to have been trebled, the active mass of each will have 
 
 * Recently, certain phenomena have been noted, which seem to indicate that dissociation 
 of a compound can occur in the reverse sense to that usually observed, namely, as the com- 
 pound cools. The behaviour of ruthenium tetroxide (q.v.) may be cited as an example. 
 Further search for phenomena of this kind is needed. 
 
INFLUENCE OF PRESSURE ON EVAPORATION. 313. 
 
 been trebled ; but the negative change is proportional to the active 
 masses of PCI 3 and CI 2 so that it will have become nine-fold, whilst the 
 positive change is only dependent on the active mass of the PC1 5 and 
 will therefore have only been trebled. Consequently the negative 
 change will predominate over the positive change, and a new equili- 
 brium will be established in other words, the dissociation will be 
 diminished. Similar reasoning may be applied to all cases of the dis- 
 sociation of gases, when it will be found that if the products of dis- 
 sociation have a larger total volume than the volume of the substance 
 undergoing dissociation, an increase of pressure will diminish the dis- 
 sociation, whilst a diminution of pressure icill increase it. 
 
 The effect of introducing one of the products of the dissociation into 
 the vessel at the equilibrium stage would be to increase the active mass 
 of that product and to increase the negative change, that is, to cause 
 association. Thus, if PC1 3 were introduced there would immediately be 
 a reproduction of PCL. Advantage may be taken of this to prevent 
 dissociation from occurring at all ; for instance, if PC1 5 be heated in a 
 vessel containing PC1 3 , it will not undergo dissociation until a much 
 higher temperature than that at which it dissociates when heated alone. 
 
 The extent to which PC1 5 has undergone dissociation is calculated from the 
 observed vapour density. Let x be the percentage of molecules which have under- 
 gone dissociation ; then 100- tr is the percentage still associated. But the ,r mole- 
 cules have become 2-1- molecules when dissociated. Therefore 100 molecules have 
 become ioo-x + 2.z'= 100 + 2- molecules after partial dissociation, so that the 
 volume is increased in the ratio 100 : ioo + ./-. The vapour density, however, has 
 decreased inversely to the volume. If d be the vapour density before, and D that 
 
 after, partial dissociation, then 100 : 100 + x : : D : d or je= ^=r -. 
 
 The similarity between changes which are generally distinguished 
 as physical and chemical is well seen by a comparison of certain cases of 
 dissociation with the phenomenon of evaporation. It has been already 
 stated that when evaporation occurs in a confined space, it apparently 
 ceases when as many particles leave the space and attach themselves to 
 the surface of the liquid, as leave the surface and move about in the 
 space, in unit time. Thus, evaporation is a reversible change capable 
 of attaining an equilibrium stage. The number of particles of vapour 
 which attach themselves to the surface of the liquid in unit time 
 depends on the number which strikes the surface; according to the 
 kinetic theory of gases, this number is measured by the pressure of the 
 vapour, so that the evaporation ceases when the pressure of the vapour 
 has reached a certain value. The number of particles of liquid which 
 enter the space in unit time depends on the temperature of the liquid; 
 the higher this is, the greater the number of particles which leave the 
 liquid in unit time, and, therefore, the greater will have to be the 
 number of vapour particles striking the surface of the liquid, per unit 
 time, in order to bring about equilibrium. In other words, the higher 
 the temperature of the liquid, the greater will be its vapour pressure 
 when evaporation has apparently ceased. 
 
 It will be obvious from these remarks that the evaporation of a 
 liquid is increased by raising its temperature, and is decreased by 
 raising the pressure of its vapour above it. Thus, if the evaporation 
 be considered as a reversible change, it is analogous to the dissociation 
 of PC1 5 in that temperature and pressure are at war with each other in 
 
314 THE LAW OF PAKTIAL PRESSURES. 
 
 their effect on the extent of the change. It is interesting to note that 
 temperature eventually prevails, and that for every liquid there is a 
 temperature above which no amount of pressure will prevent it from 
 becoming vaporised; this is its absolute boiling-point (p. 29). 
 
 For a right understanding of the influence of pressure on evaporation 
 (and dissociation) it is necessary to realise the principle of partial pres- 
 sure. When two gases are mixed the resulting pressure on the sides of 
 the containing vessel is the sum of the pressure which each gas exerted 
 before the two were mixed ; so that a law of partial pressures may be 
 stated in this way : In a mixture of gases the pressure exerted by 
 each gas is exactly the same as the pressure which that gas would exert 
 did it alone occupy the volume filled by (he mixture. Thus, in air, 
 where the proportion of N : O is approximately 4:1, ith of the pres- 
 sure is exerted by the O and ith by the N. 
 
 From this it follows that in a mixture of vapour and air the vapour 
 exerts the same pressure as it would exert did it alone occupy the space 
 filled by the mixture, and that, since the extent to which a liquid will 
 evaporate depends, when the temperature is constant, solely on the 
 pressure of its vapour, evaporation must proceed to the same extent in 
 a vacuum and in air. Thus, at 15.3 0. water and its vapour are in 
 equilibrium when the pressure of the latter is equal to 12.9 mm. of 
 mercury, so that water will continue to evaporate until it has parted 
 with sufficient vapour to create this pressure in the space above it. If 
 that space originally contained a vacuum, a pressure-gauge will show a 
 pressure of 12.9 mm. when the evaporation has apparently ceased ; if 
 the space originally contained air at 760 mm. pressure, the gauge will 
 show a pressure of 760+ 12.9 mm. 
 
 The hastening of evaporation by a draught of air is simply due to 
 the prevention of the accumulation of vapour over the surface of the 
 liquid ; in this way the vapour pressure may be hindered from rising to 
 that which causes equilibrium. 
 
 From the foregoing it will be seen that the temperature and pressure of a vapour 
 in presence of its liquid are interdependent ; a given pressure of the vapour can 
 only be attained at a certain temperature, and for a given temperature the pressure 
 must have a certain value. In the case of unsaturated vapour and gases, pressure 
 and temperature can be varied independently, and by an alteration of volume 
 either temperature or pressure is varied. The sole effect of varying the volume of 
 a vapour in presence of its liquid is to cause more liquid to become vapour, or vice 
 versa, and the temperature and pressure remain constant. 
 
 Water is one individual, capable of existing in three 2 } l lase ** i ce water, and 
 vapour. A system comprising water and its vapour alone, is a two-phase system 
 and the phases can be in equilibrium at many different temperatures, a definite 
 pressure corresponding with each temperature. When the pressure of the water 
 vapour is reduced to 4.6 mm., the water passes into ice owing to the heat lost by its 
 own evaporation, and the temperature is then 0.007 C. ; any further reduction of 
 temperature or pressure will convert all the water into ice and the system again 
 becomes two-phase, consisting of ice and its vapour. But so long as the tempera- 
 ture and pressure are those named, the three-phase system ice, water, vapour 
 is in equilibrium. Thus, while a two-phase system is in equilibrium under different 
 conditions, there is only one condition of equilibrium for a three-phase system. 
 
 Water is one individual ; where there are two individuals in a system, three 
 phases may be in equilibrium at different temperatures, but when the two indi- 
 viduals are in four phases, only one condition of equilibrium is possible. Such a 
 case is presented by the two individuals chlorine and water. Chlorine hydrate 
 
 * The word " phase " is applied to any constituent of a system which is capable of differ- 
 entiation from the other constituents. 
 
INFLUENCE OF PRESSURE ON THE SOLUBILITY OF GASES. 315 
 
 separates at 9.6 C. if the pressure of the chlorine is that of the atmosphere ; by 
 raising the pressure, the temperature at which the hydrate separates is raised, and a 
 new temperature is established at each pressure ; this is an interdependence similar 
 to that in the case of evaporation, that is to say, the three-phase system 
 Cl, C1.4H. 2 0,H 2 is in equilibrium at different temperatures. As soon, however, as 
 ice begins to separate (at 0.24 C.) a fourth phase is introduced, and equilibrium 
 between the four is only possible at this temperature, the pressure being 244 mm. 
 
 When there is only one condition of equilibrium, this is called the transition- 
 point^ for if the pressure or temperature be varied, one of the phases must pass into 
 one of the others and disappear from the system. 
 
 The phase rule, which is believed to govern the equilibrium of heterogeneous 
 systems, states that a transition-point for a system of n individuals is only possible 
 when the number of phases is n + I . 
 
 Allotropic changes may also be brought under the phase rule. When the allo- 
 tropes are enantiotropes (that is, when the change from one to the other is rever- 
 sible, as in the case of octahedral and prismatic sulphur and red and yellow 
 phosphorus), there is a transition-point for the phases consisting of the two forms 
 the liquid element and the vapour. 
 
 The case of the dissociation of calcium carbonate by heat is closely 
 analogous to that of evaporation. The reversible change, CaC0 3 ^CaQ 
 + C0 2 , reaches equilibrium when the pressure of the C0 2 has attained a 
 certain value depending on the temperature. Since the pressure of the 
 C0 2 is a measure of the weight of it in unit volume, the equilibrium is 
 reached when the product, CO 2 , has a certain active mass dependent on 
 the temperature. Thus, at 740 C. the equilibrium pressure is 255 mm., 
 and when this has been attained no further dissociation can occur ; if 
 the calcium carbonate be heated in a vessel exposed to the open air, the 
 C0 2 will gradually diffuse away and its partial pressure will be reduced 
 below 255 mm., so that the change will continue. By exposing the 
 heated mass to a draught of air, the admixture of the C0 2 with the 
 surrounding atmosphere, and therefore the completion of the dissocia- 
 tion, will be more rapid. If the pressure of the C0 2 be not allowed to 
 rise to 255 mm., the complete conversion of CaC0 3 to OaO can be effected 
 at a correspondingly lower temperature. 
 
 A precisely similar influence is exerted by temperature and pressure 
 on the solubility of a gas in water. The solubility decreases with rise 
 of temperature and increases with rise of pressure. For perfect gases 
 the following generalisation is true : The solubility of a gas in a liquid 
 is directly proportional to the pressure exerted by the gas. Since the 
 volume of the gas varies inversely with the pressure, this statement may 
 be varied thus : a given volume of liquid will always dissolve the same 
 volume of a given gas, whatever the pressure. Thus, if a litre of water 
 dissolve 100 c.c. of a gas at 760 mm., it will dissolve twice this quantity 
 at 1520 mm.; but 200 c.c. measured at 760 mm. will be 100 c.c. at 
 1520 mm., so that the litre of water will still dissolve only 100 c.c. at 
 the higher pressure. 
 
 Since the coefficient of solubility of a gas (p. 54) is the volume of the gas 
 which unit volume of water will dissolve at 760 mm., it follows that the quantity 
 of gas soluble in the same volume of water, at the same temperature, and at any 
 other pressure, is found by multiplying the coefficient of solubility by the pressure 
 divided by 760. In a mixture of gases the pressure of each gas is only a part of 
 the whole, being the same fraction of the total pressure as the volume of the gas 
 is of the total volume. The method of calculating the solubility of the N and O 
 when air is shaken with water (p. 54) will now be easily understood, and, as a 
 further example, the volume of C0 2 which 100 c.c. of water will dissolve from 
 the air at o C. and 720 mm. may be calculated. Taking the percentage of C0 2 
 in the air at 0.035, its partial pressure, when the total pressure is 720 mm., will 
 
3l6 OSMOTIC PRESSURE. 
 
 be 35 x 720 = 0.25 mm. The coefficient of solubility of CO., at oC. and 760 
 100 
 
 mm. is 1.8 ; therefore at 0.25 mm. and o C. it will be 1.8 x ^>. This, therefore, 
 
 will be the volume of C0 2 dissolved by i vol. of water under the conditions named ; 
 when multiplied by 100, the value will express the number of c.c. dissolved by 
 100 c.c of water. 
 
 It must be remarked that gases which are easily liquefied, and thus deviate 
 from true gases, fail to obey with accuracy the law of solubility stated above. 
 
 When the space above the solution of a gas contains the same gas as that which 
 is dissolved, equilibrium is established when the same quantity of gas passes from 
 the space into the liquid, and from the liquid into the space, in unit time. If for 
 the gas in this space there be substituted another, the dissolved gas will go on 
 escaping from solution until its partial pressure in the space is the same as its pres- 
 sure was iwhen it alone filled the space. It will be obvious, therefore, that a few 
 such displacements of the gas in the space should cause the liquid to part with 
 practically all its dissolved gas. 
 
 Solution. In the case of most gases it is impossible to regard their 
 solutions in water as mere physical mixtures. Reference has been already 
 made to this difficulty and to the companion one concerning the solu- 
 bility of solids (p. 50). Besides the thermal changes there mentioned, 
 there are such facts as the constant boiling-point of solutions containing 
 gas and water in definite proportions e.g., HC1.8H 2 O (p. 179), and the 
 separation of salts containing water of crystallisation to compel the 
 conclusion that in many cases the dissolved substance enters into 
 combination with the solvent. 
 
 It is a fact, however, that many dilute solutions behave as would be 
 anticipated if the dissolved substance were present in a condition 
 independent of the solvent. Thus, it has been discovered that the mole- 
 cules of a dissolved substance exert a pressure on the solvent identical 
 with the pressure which they would exert on the sides of a vessel, of the 
 same volume as that of the solution, if they were in the gaseous state. 
 
 This discovery has given rise to a "physical theory" of dilute solutions, 
 which may be stated thus : The molecules of the dissolved substance 
 pervade the solvent without being influenced thereby, and possess the 
 same properties as they would possess did they alone, in the state of 
 gas, occupy the volume filled by the solution. 
 
 The pressure which a substance in solution exerts on the solvent is 
 called the osmotic pressure of the solution, because it is only by taking 
 advantage of the phenomenon of osmosis that it can be rendered 
 apparent and directly measured. It has been already shown (pp. 70, 
 277) that certain structureless substances (india-rubber, parchment 
 paper, &c.) will allow of a much more rapid passage through them 
 of some kinds of molecules than of other kinds. Several such substances 
 exist which allow water molecules to pass through them almost infinitely 
 faster than they allow many other kinds of molecules to pass. When 
 a membrane made of one of these substances is immersed in an aqueous 
 solution, it will generally happen that the water molecules will pass 
 through the membrane very much faster than the molecules of the 
 dissolved substance. This transition of molecules differs from that 
 called diffusion, in that it appears to depend rather upon the specific 
 nature of the membrane than upon its porosity (compare p. 22). The 
 term osmosis is introduced to indicate this difference. 
 
 The method employed for studying the pressure exerted by a dissolved 
 substance on the solvent, can now be easily understood. A vessel is 
 
OSMOTIC PRESSURE AND GASEOUS PRESSURE. 317 
 
 constructed of a material which allows of the osmosis of the solvent 
 molecules, but not of the dissolved molecules. The solution whose 
 osmotic pressure is to be studied, is introduced into this vessel, which is 
 then immersed in a bath of the pure solvent. The solvent molecules 
 will pass into the vessel and out of the vessel ; but since there are more 
 of these molecules in unit volume outside the vessel than there are 
 inside (on account of the presence of the dissolved molecules), more of 
 the solvent will pass into the vessel in unit time than will pass out, 
 and equilibrium will only be established when a certain pressure, com- 
 pensating for this difference between the number of solvent molecules 
 in unit volume, has been established inside the vessel. This pressure is 
 termed the osmotic pressure of the solution, and is attributed to the 
 dissolved molecules ; it can be measured by closing the vessel by an 
 ordinary pressure-gauge. 
 
 In practice it is found necessary to support the " osmotic membrane " which is 
 to form the walls of the vessel, by depositing it on the surface of a porous pot. 
 The most successful method consists in depositing copper ferrocyanide (a material 
 which behaves as an osmotic membrane to aqueous solutions) within the pores of 
 a biscuit- porcelain battery cell (3" x i") ; for this purpose the cell is filled with a 
 solution of copper sulphate (3 per cent.) and immersed in a solution of potassium 
 ferrocyanide (3 per cent.). The two solutions meet in the wall of the cell, and a 
 continuous sheet of copper ferrocyanide is deposited therein. An inverted funnel 
 is cemented in the mouth of the cell, and a U-shaped mercury gauge is sealed to 
 the stem of the funnel. The cell is nearly filled with the aqueous solution whose 
 osmotic pressure is to be measured, and is immersed in a bath of distilled water. 
 The pressure of the air trapped between the gauge and the solution is measured 
 by the variation in the height of the mercury in the gauge.* 
 
 It is found that the same relationship exists between the osmotic 
 pressure and the concentration of a solution as exists between the 
 pressure and the concentration of a gas. That is to say, the osmotic 
 pressure is directly proportional to the weight of dissolved substance 
 in unit volume of the solution, just as the pressure of a gas is directly 
 proportional to the weight of the gas in unit volume (Boyle's law). 
 Thus, a one per cent, sugar solution exerts an osmotic pressure equal to 
 535 mm. of mercury, whilst the osmotic pressure of a two per cent, 
 solution is equal to 1070 mm., provided the temperature is the same in 
 each case. 
 
 Again, the osmotic pressure of a solution varies directly as the 
 absolute temperature (thermometric temperature + 273) of the solution, 
 just as the pressure of a gas varies directly with its absolute tempera- 
 ture (Charles' law). Thus the one per cent, solution of sugar shows an 
 osmotic pressure of 544 mm. of mercury at 32 C., and of 512 mm. at 
 14.15 (305 : 287.15 = 544 : 512). 
 
 It seems, then, that the variations which occur in the osmotic pressure 
 of a dilute solution when the concentration of the solution is varied, 
 are controlled by the same laws as those which govern the variations in 
 the pressure of a gas when the concentration of the gas is varied. But 
 the analogy between the osmotic pressure and the gaseous pressure is 
 still closer than this ; for it is found that the osmotic pressure is identical 
 with the gaseous pressure which the weight of dissolved substance would 
 
 * A description and drawing of the apparatus will be found in Jour. Chem. Soc. Trans. 
 1891, p. 344, and directions for preparing the membrane by electrolysis are given in the 
 Amer. Chem. Jour., 1901, vol. 26, p. 80. 
 
3l8 ISOTONIC SOLUTIONS. 
 
 exert at the same temperature, if it were in the state of gas and occupied 
 the volume filled by the solution. 
 
 It is considered reasonable to deduce from this that the number of 
 molecules of dissolved substance in a volume v of a solution, having an 
 osmotic pressure p and a temperature t, is the same as the number of 
 molecules in a volume v of a gas at the pressure p and the temperature t. 
 
 Thus, a I per cent, solution of cane sugar (C^H^On) at o C. exerts an osmotic 
 pressure of 493 mm. Now the molecular weight corresponding with the formula 
 C^H^Oj! is 342. and, could the sugar be gasified, 342 grams of it would occupy 
 22.22 litres |at o C. and 760 mm. (p. 47) ; that is to say, 342 grams of gaseous 
 sugar in a volume of 22.22 litres at o C. would exert a pressure of 760 mm. The 
 concentration of 342 grams in 22.22 litres is the same as a concentration of 15.4 
 grams in one litre ; therefore 15.4 grams of gaseous sugar in I litre at o C. should 
 exert a pressure of 760 mm. It follows that 10 grams in i litre at o C. should 
 exert a pressure of 493 mm. This is practically identical with the osmotic pres- 
 sure of a (i per cent.) sugar solution containing 10 grams per litre. 
 
 Gases at high concentration that is, at high pressure cease to obey 
 the laws of Boyle and Charles. The same is true for solutions at high 
 concentration. 
 
 Since Avogadro's law is deducible mathematically from those of Boyle 
 and Charles, and since dilute solutions appear to be controlled by the 
 last-named laws, it seemed probable that an Avogadro's law should 
 exist for dilute solutions. This was first pointed out by Van't Hoff, 
 whose law of osmotic pressure is thus stated : Equal volumes of different 
 solutions, at the same temperature and osmotic pressure, contain equal 
 numbers of molecules of dissolved substance. 
 
 The similarity between this statement and that expressing Avogadro's 
 law (p. 289) will be at once evident. 
 
 Solutions which exert equal osmotic pressure are said to be isotonic. 
 
 Just as the relation between the weights of the molecules of two gases 
 can be deduced from Avogadro's law (p. 289), so can the relation between 
 the weights of the molecules of two dissolved solids be deduced from 
 Yan't Hoff's law. For it follows from this law, that when equal volumes 
 of two solutions are isotonic, and at the same temperature, the weight 
 of dissolved solid in the one is as much heavier than the weight of the 
 dissolved solid in the other, as the molecular weight of the first solid is 
 heavier than the molecular weight of the second (cf. footnote, p. 47). 
 
 Determination of molecular weights of non- volatile sub- 
 stances. The applicability of the measurement of osmotic pressure to 
 the determination of molecular weights will now be easily understood. 
 A solution of the solid whose molecular weight is unknown may be diluted, 
 or strengthened, until its osmotic pressure is identical with that of a solu- 
 tion containing a known weight of a solid whose molecular weight is 
 known. The ratio between the weights of the solids in one litre of each 
 solution is then the ratio between the molecular weights of the solids. 
 
 Example. A solution of a substance of unknown molecular weight was diluted 
 until its osmotic pressure was found to be identical with that of a solution of 
 sugar in water (at the same temperature). The weight of solid in i litre of each 
 solution was then determined ; that in the sugar solution was i gram ; that in 
 the other solution was 1.5 gram. By Van't Hoff's law these weights must have 
 the same ratio to each other as have the molecular weights of the substances. 
 Let x be the unknown mol. wt. ; the mol. wt. of sugar is 342, therefore : 
 342 : x : : i : 1.5 or x = 342 x 1.5. 
 
 The measurement of osmotic pressure is neither easy nor capable of 
 
METHODS FOE DETERMINING MOLECULAR WEIGHT. 319 
 
 very great accuracy ; it is not, therefore, well adapted for the determina- 
 tion of molecular weights. 
 
 There are, however, other methods of determining whether solutions 
 contain the same number of dissolved molecules in equal volumes, which, 
 owing to the ease and accuracy of making the required measurements, 
 are much adopted for checking, and even determining, the molecular 
 weights of substances which cannot be volatilised, and are therefore 
 excluded from the method depending on the determination of the vapour 
 density of the substance (p. 292). 
 
 The methods in question depend upon the influence which the mole- 
 cules of the dissolved substance have on many of the physical properties 
 of the solvent. Thus, the more numerous the dissolved molecules in a 
 solution the lower will be its freezing- point and its vapour pressure, so 
 that a measurement of the temperature at which the solution freezes, 
 or of the pressure exerted by its vapour, will serve as a measurement of 
 the molecular concentration of the substance in solution. 
 
 The method of determining molecular weights which depends upon 
 the measurement of the freezing-point of a solution is known as the 
 cryoscopic method, or the method of depression of the freezing-point, as 
 Kaoulfs method. 
 
 Raoult discovered, empirically, that the freezing-point of a solution is 
 always lower than that of the solvent, and that the depression is directly 
 proportional to the weight of substance in solution. Thus, if one gram 
 of a solid in a litre of water lowers the freezing-point by 0.1, two grams 
 will lower it 0.2. Collation of his results showed that when molecular 
 quantities of different substances are dissolved in the same amount of a 
 solvent, they lower the freezing-point of the solvent to the same extent. This 
 may now be expressed by saying that isotonic solutions in the same 
 solvent have the same freezing-point. 
 
 If Raoult's generalisation (italicised above) be true, there will be a 
 certain constant (T) for every solvent, representing the amount of 
 depression in the freezing-point of that solvent caused by the presence 
 of one gram-molecule of any substance in 100 grams of the solvent. 
 Thus, it is found that in the case of many salts, a solution of one gram- 
 molecule of the salt in 1000 grams of water freezes at - 1.9 C. ; con- 
 sequently a solution of one gram-molecule in 100 grams of water should 
 freeze at - 19 C., and the constant, T, for water is 19. This value does 
 not hold good for all classes of salts for a reason to be explained later. 
 
 A little consideration will show that when T is known for a solvent, 
 it should be possible to determine the molecular weight of a substance 
 by ascertaining the depression of the freezing point of a solution of the 
 substance in that solvent. 
 
 Suppose the constant T to have been ascertained for a solvent. This would be 
 effected by determining what depression is caused in the freezing-point of the sol- 
 vent by dissolving I gram-molecule of any substance of well-known molecular 
 weight in 100 grains of it. Let it be desired to determine the molecular weight (M) 
 of some other substance. One gram of the substance is dissolved in 100 grams 
 of the solvent, and the freezing-point of the solution is determined ; suppose this to 
 be k degrees lower than the freezing-point of the pure solvent. Then, if one gram 
 cause depression A, M grams (one gram-molecule) will cause depression M.k; but 
 this depression is the value T, whence, Wt = T or M = T/k. Since T and k are known, 
 M is thus determined. 
 
 The depression caused by one gram in 100 grams of solvent is generally too small 
 to measure, so a stronger solution, say P grams in 100 grams of solvent, is used. 
 
3 20 
 
 VAPOUR PPvESSUKE OF SOLUTIONS. 
 
 If P grams cause depression It, one gram will cause depression Jf/P. and M grams 
 
 will cause depression M&/P, Therefore M#/P = T or M = TP/k. 
 
 The value of T for water is 19 for several classes of salts ; for benzene it is 49 ; 
 
 for glacial acetic acid it is 39. 
 
 The method is conducted as follows : A known weight of the solvent is intro- 
 
 duced into a long test- tube (Fig. 202) which has a side neck closed by a cork ; a. 
 
 cork in the mouth of the test-tube carries a ther- 
 mometer, graduated to 0.01, and a stirrer. The 
 test-tube is passed through the cork of a -wider 
 test-tube (to serve as an air jacket, which shall 
 prevent too rapid a change of temperature), which is 
 immersed in a bath also provided with a stirrer and 
 at a temperature several degrees 'below the freezing- 
 point of the solvent. The bulb of the thermometer 
 being immersed in the solvent, the stirrer is con- 
 tinually agitated until the solvent begins to freeze, 
 whereupon the temperature is noted. The tube is 
 then withdrawn from the bath, the solvent allowed 
 to melt, and the weighed quantity of substance 
 added through the side neck. When this has dis- 
 solved, the freezing-point of the solutio'n is deter- 
 mined as before. Since superf usion of the solution 
 is liable to occur it is sometimes necessary to add 
 a crystal of a previously frozen solution (of the 
 same strength) in order to induce solidification. 
 
 Example. The freezing-point of 120 grams of 
 benzene was found to be 6 C. ; 6 grams of sulphur 
 were dissolved in the benzene and the freezing- 
 point was again determined ; it was found to be 
 4.68 C. In this case 120 grams of benzene con- 
 tained 6 grams of sulphur, so that P, the quantity 
 
 present in 100 grams, is 
 
 6-4.68 = 1.32. 
 
 M = 
 
 .32 
 
 = 5 grams. It = 
 T for benzene = 49. Therefore 
 Thus the molecular weight 
 
 of solid sulphur is 185.6, a number sufficiently close 
 Fig. 202. Beckmann's apparatus, to 192 to warrant the conclusion that the molecule 
 
 of solid sulphur is S 6 .* 
 
 The lowering of the vapour pressure of a solvent by the presence of a 
 substance in solution, is controlled by laws which are wholly similar to 
 those which apply to the lowering of the freezing-point of a solvent by 
 the presence of a dissolved substance. Since the vapour pressure varies 
 with the temperature, it is necessary to add that the lowering is always 
 the same fraction of the vapour pressure of the pure solvent, whatever 
 the temperature. 
 
 Inasmuch as the boiling-point of a liquid is that temperature at 
 which the pressure of its vapour is equal to the pressure of the atmo- 
 sphere, the presence of a dissolved substance must raise the boiling-point 
 of a solution pari passu with lowering its vapour pressure. 
 
 The apparatus shown in Fig. 203 is used for determining the rise of the boiling- 
 point of a solvent by the presence of a dissolved substance. To avoid heating 
 the solvent to a temperature above its boiling-point, which would vitiate the result, 
 the tube containing the solvent is surrounded by a jacket filled with an atmosphere 
 of the vapour of the solvent at its boiling-point. This vapour is generated in the 
 flask A and is passed through the tube B, provided with distributing holes at its lower 
 end, into the inner tube N which contains another portion of the solvent. When 
 
 * Determinations of the vapour pressure of CS 2 when sulphur is dissolved in it, show a 
 value of S 3 for the molecule of solid sulphur. 
 
SALINE SOLUTIONS. 
 
 321 
 
 the latter has been heated by the vapour to its boiling-point, the vapour passes un~ 
 condensed through the solvent and through the hole H, thus surrounding the tube 
 N and passing into the condenser C. The temperature is now noted by the ther- 
 mometer T, the tube N is emptied and the operation repeated with the addition to 
 the solvent (about 5 to 7 c.c.) of a weighed quantity of the substance (about 4 per 
 cent, of the weight of the solvent), the molecular weight of which is to be deter- 
 mined. The tube N, whose weight when empty is known, is now weighed to- 
 ascertain the weight of solvent used. The molecular elevation of the solvent having 
 been determined by the use of a substance of known molecular weight, the molecular 
 weight of the substance is calculated as in the freezing-point method described above. 
 
 Fig. 203. Landsberger's apparatus. 
 
 It must here be noted that there are many cases in which the mole- 
 cular weight of a compound, determined by the osmotic pressure of a 
 solution of it, or by the cryoscopic method, is only a fraction of the 
 molecular weight which must be assigned to the substance on account 
 of the other considerations which serve to settle molecular weights. A 
 flagrant case is that of potassium chloride. The osmotic pressure of a 
 dilute aqueous solution of this salt is nearly twice as great as it should 
 be if the molecular weight of the salt be 74.5 ; again, the depression of 
 the freezing-point of a dilute solution is nearly twice as great as it 
 should be if the molecular weight of the salt were 74.5. Both these 
 facts indicate that potassium chloride, in solution, has a molecular weight 
 
322 ELECTEOLYSIS. 
 
 about one half of 74.5, and yet a quantitative analysis of KC1 shows 
 that 74.5 parts by weight of it contain 35.5 parts by weight of chlorine, 
 so that the salt cannot well have a smaller molecular weight than 74.5. 
 This anomalous behaviour of KC1 is shared by a large number of salts, 
 acids and bases, all of which show a lower molecular weight when in 
 solution than that which is generally attributed to them. 
 
 This phenomenon is so analogous to that of the dissociation of a com- 
 pound (e.<7.,NH 4 Cl, PC1 5 ) by heat, which causes the molecular weight 
 determined by the vapour density to be lower than that inferred from 
 other considerations, that these salts, acids and bases are supposed to 
 have been more or less dissociated by the water which has dissolved 
 them. Thus, potassium chloride which gives an osmotic pressure nearly 
 twice that which it should give if its molecule, in dilute solution, were 
 represented by KC1 is supposed to be nearly completely dissociated 
 into K and 01 ; so that there are twice as many ultimate particles in the 
 solution as there would be if the dissociation did not occur just as 
 there are twice as many molecules, causing twice as great a pressure, 
 in the vapour of PC1 5 above 300 C. as there would be if no dissociation 
 occurred. 
 
 The realisation of the existence of osmotic pressure renders it possible 
 to regard the process of dissolution of a solid as belonging to the same 
 type of changes as that to which dissociation and evaporation have been 
 assigned. When a salt is immersed in water particles of salt leave the 
 mass and pervade the water, this process continuing until as many 
 particles leave the mass of salt as attach themselves to it. in unit time. 
 This equilibrium stage is the saturation of the water with the salt, and 
 for every temperature there is an appropriate pressure the osmotic 
 pressure at which equilibrium will occur, just as there is an appro- 
 priate vapour pressure for every temperature at which evaporation will 
 cease. 
 
 Electrolysis. The theory that many molecules are dissociated by 
 being dissolved, finds its chief support in a study of the phenomena 
 which accompany the conversion of chemical energy into electrical 
 energy and vice versd. 
 
 The chemical action which is most frequently employed to develop 
 chemical energy for conversion into electrical energy, is that involved in 
 the dissolution of zinc in an acid, generally dilute sulphuric acid. If 
 a piece of commercial zinc be immersed in dilute sulphuric acid, it dis- 
 solves, and a quantity of heat is developed equivalent to the chemical 
 energy of the dissolution of the zinc. If the zinc and acid be perfectly 
 pure no action will occur ; but if a piece of platinum be immersed in the 
 acid and be made to touch the zinc, whether beneath or above the 
 surface of the acid, action will begin and heat will be developed ; the 
 hydrogen will no longer appear to be evolved from the zinc, but will 
 rise from the surface of the platinum. In the case of both the impure 
 zinc and the zinc + platinum, the chemical energy has to a great extent 
 passed through the stage of electrical energy before it has become heat 
 energy.* 
 
 If the platinum and zinc be connected with a wire outside the acid, 
 
 * The impure zinc contains foreign metals which, by contact with the zinc, enable the 
 latter to dissolve, with generation of electrical energy, just as the platinum enables the pure 
 zinc to dissolve. 
 
THE GALVANIC CELL. 323 
 
 the electrical energy will " flow " through the wire and may be utilised 
 before it becomes converted into heat energy. 
 
 When such a "galvanic cell" is left to itself, the rapidity of the dissolution of 
 the zinc soon diminishes (and with it the intensity of the electrical energy) be- 
 cause the cell becomes polarised. ; this is chiefly due to the coating of the platinum 
 plate with hydrogen so that it virtually becomes a plate of hydrogen, which is much 
 less effective than is platinum in aiding the dissolution of zinc by contact. It 
 is for this reason that all cells which have any practical value contain an oxidising 
 agent or depolarizer (e.g.. nitric acid in a Grove cell) around the platinum plate ; 
 such an agent, by oxidising the hydrogen, diminishes the polarisation, and at the 
 same time develops a greater amount of chemical energy, and therefore of 
 electrical energy, in the cell. 
 
 The total amount of electrical energy developed by a galvanic cell in unit time, 
 depends on the amount of chemical energy occurring in the cell in that time, and 
 upon the nature of the plates which are used in the cell. The first of these con- 
 ditions is measured (in the zinc cell) by the amount of zinc which dissolves, and is 
 therefore related to the size of the zinc plate.* The influence of the nature of the 
 plates may be summed up by saying that the greater the antithesis between the 
 plates, in respect of the ease with which they are attacked by the exciting medium 
 of the cell, the greater will be the total amount of electrical energy obtained from 
 the cell. Thus, when dilute sulphuric acid is the exciting medium, the plates 
 should consist of a metal which is, in a high degree, attackable by this acid, and 
 one which is highly resistant ; zinc and platinum are the metals, among those 
 which are sufficiently cheap for use, which best fulfil these conditions ; zinc and 
 copper are frequently used, but since copper has a greater tendency to dissolve in 
 sulphuric acid than platinum has, this " couple " is not capable of giving so great a 
 total of electrical energy as that yielded by a zinc-platinum couple. It will be 
 obvious, however, that in the event of an exciting medium which has more action 
 on platinum than on copper being used, the zinc-copper couple may transcend the 
 zinc-platinum couple. 
 
 Since it is a sine qua mm that the plates used in a battery should be conductors 
 of electricity, the non-metals with a few exceptions (the most notable of which is 
 arbon) are put out of court for this purpose. 
 
 It is necessary to add that the total amount of electrical energy is made up of 
 two factors ; one of these is analogous to the factor expressed by the specific heat 
 of the hot body, in heat energy, and is generally called intensity of current; 
 whilst the other is analogous to the temperature of heat energy, and is generally 
 called electromotive force or pressure. It is the second factor, the pressure, 
 which varies with the nature of the plates. The first factor is dependent upon 
 the amount of chemical action, just as the number of units of heat evolved in a 
 chemical reaction is dependent upon the amount of chemical action. 
 
 , The word electrolysis is used to signify the decomposition of a com- 
 pound by the passage through it, or its solution, of the electric current. 
 Any compound which can be thus decomposed is termed an electrolyte, 
 and the portions into which it is decomposed are termed ions. An 
 -electrolyte must be a compound, but all compounds are not electrolytes. 
 Compounds may be classified with regard to their relation to the 
 electric current into (i) conductors which are not electrolytes, (2) con- 
 ductors which are electrolytes, and (3) non-conductors. 
 
 Electrolysis is effected by passing the current through the electrolyte, 
 most conveniently from two plates, made of some conductors and called 
 electrodes. The plate connected with the less attacked metal of the 
 battery (e.g., Pt.) is regarded as the one by which the electric current 
 enters the electrolyte, and is called the anode or the positive electrode. 
 The other plate, attached to the more attacked plate of the battery, is 
 
 * If the zinc plate be badly amalgamated (p. 14) the impurities in it will develop minor 
 electric currents, causing evolution of hydrogen " from the zinc," and the amount of electri- 
 cal energy thus developed will be unavailable for external use, and will be directly converted 
 auto heat. 
 
324 IONS. 
 
 supposed to afford an exit for the current, and is called the cathode or 
 the negative electrode. 
 
 The electrolyte is always split up into two chemically equivalent ions ; 
 these are either liberated at the electrodes, or there enter into reaction 
 with the electrolytic medium, as will be explained below. Ions which 
 are liberated at the anode are anions, whilst those liberated at the 
 cathode are cations. Since unlike electricities attract each other, and 
 the anode is supposed to contain positive electricity, the anions are 
 electro-negative elements or radicles ; the cations are the electro-positive 
 elements or radicles (p. 15). Attempts are made to catalogue the 
 elements in the order of their decreasing electro-positiveness ; that is, in 
 such an order, that if a compound of any two elements be submitted to 
 electrolysis, the one which comes first in the list will behave as the 
 cation. It is obvious that such an electro-chemical list must differ 
 according to the conditions of the electrolysis (such as whether the 
 compound be present in an acid or an alkaline electrolytic medium, &c.). 
 
 In nearly all cases, however, the metals precede the non-metals in these lists,. 
 and when the list is drawn up with reference to electrolysis in neutral or acid 
 solution, the metals follow each other in the order of their affinity for oxygen. 
 From what was stated with regard to the use of metals as battery plates, it 
 will be obvious that that metal which has least affinity for oxygen, and is, 
 therefore, least readily attacked by acids, will generally be best suited for the- 
 resistant plate in a cell. 
 
 The ions of an electrolyte are either atoms or radicles ; thus, when an 
 aqueous solution of HC1 is electrolysed, the ions are H and 01, these 
 being chemically equivalent ; the H atoms move towards the cathode, 
 each carrying its charge of positive electricity, the Cl atoms move 
 towards the anode, each carrying its negative charge. In the case of 
 an aqueous solution of K 2 SO 4 , the ions are K 2 and SO 4 , these being 
 chemically equivalent ; each K atom carries one positive charge, whilst 
 the SO 4 radical carries two negative charges. When the ions reach 
 the electrodes the charges (electrons) are neutralised, and the ions either 
 appear in the free state (when the atoms immediately combine to- 
 form molecules), or they react with the water or with the electrode ; in 
 the latter case the final products of the electrolysis will be the products- 
 of these reactions. In the case of hydrochloric acid electrolysed by 
 carbon electrodes, molecules of hydrogen and chlorine are evolved. In 
 the case of potassium sulphate electrolysed with carbon or platinum 
 electrodes, the final products are hydrogen at the cathode and oxygen 
 at the anode ; for the potassium atoms, so soon as they are discharged 
 at the cathode, react with the water in the well-known manner pro- 
 ducing 2KOH and H 2 , whilst the S0 4 , when it is discharged, reacts 
 with the water, producing H 2 SO 4 and O. The 2 KOH and H 2 S0 4 left 
 in solution speedily neutralise each other, re-forming potassium sul- 
 phate, the total quantity of which thus suffers no diminution during 
 the electrolysis. 
 
 It will now be realised that the electrolysis of water described on 
 p. 13 is the electrolysis of dilute sulphuric acid. Water, so far as' i& 
 known, is not an electrolyte ; when dilute sulphuric acid is electrolysed, 
 hydrogen is liberated at the cathode and SO 4 at the anode, where it at 
 once reacts with the water to form H 2 S0 4 and 0. 
 
 When copper sulphate solution is electrolysed with platinum elec- 
 
FARADAY'S LAW. 325 
 
 trodes, the ions are Cu" and SO 4 . The copper is deposited on the 
 cathode and oxygen is evolved at the anode, owing to the reaction 
 between discharged SO 4 and water. If the anode be made of some 
 material which is more easily attacked by S0 4 than is water, this will 
 react with S0 4 , Thus, a copper anode will be dissolved by com- 
 bining with the SO 4 , and the quantity of copper which will pass into 
 solution will be exactly equal to that deposited on the cathode ; this 
 fact is applied in the process of electro-plating (see Silver). 
 
 Faraday's law of electrolysis states that the same intensity of electric 
 current will liberate all ions in the proportion of their chemical equiva- 
 lents. For example, if the same current of electricity be passed 
 through electrolytic cells containing sulphuric acid and silver nitrate 
 respectively, there will be 108 grams of silver deposited on the cathode 
 of the one cell for every i gram of hydrogen liberated at the cathode 
 of the other cell, these quantities of silver and hydrogen being chemi- 
 cally equivalent. So also there will be 48 grams of S0 4 discharged at the 
 anode of the one cell, and 62 grams of N0 3 at the anode of the other 
 cell. 
 
 Since some elements have two chemical equivalents, ions composed 
 of them will have two electro-chemical equivalents. Thus, copper in 
 cupric chloride has an electro-chemical equivalent of 31.5, this propor- 
 tion being deposited for every i part of hydrogen evolved in a sulphuric 
 acid cell ; but copper in cuprous chloride has an electro-chemical equiva*- 
 lent of 63. 
 
 The converse of Faraday's law is equally true ; that is to say, the 
 chemical change of chemically equivalent quantities of ions gives rise to 
 the same intensity of electric current. Thus, in a galvanic cell the 
 same intensity of current will be generated, whether 32.5 parts of zinc 
 or 28 parts of iron be dissolved in acid. 
 
 The intensity of electric current necessary to decompose i grain -equivalent of 
 any electrolyte is 96,540 units (coitloinb*'). But this is only one factor of the 
 electrical energy required, for the latter is the product of the intensity of current 
 x the pressure at which it is delivered. The pressure necessary for electrolysing 
 any particular electrolyte depends on the chemical affinity of the ions for each 
 other. If now the heat equivalent to this chemical affinity be known, the electrical 
 energy can be calculated, because i unit of electrical energy (Joule) is equal to 0.24 
 gram-unit of heat. The joule = i coulomb x i volt (the unit of pressure). Let a 
 be the heat equivalent to the affinity between i gram equivalent of each of the 
 ions ; this will be equal to a/o.24 joules. But the intensity of current necessary to 
 effect the electrolysis is 96,540 coulombs, so that the electrical energy must be made 
 up of 96,540 coulombs x x volts ; thus the equation a jo. 24 = 96540 x a? is obtained, 
 from which the value of a 1 , the voltage necessary for the electrolysis, may be calcu- 
 lated. The value ascertained in this manner is, of course, open to the same 
 uncertainty as that which surrounds the value for the heat equivalent to the 
 affinity (p.' 308). 
 
 The best electrolytes are aqueous solutions of powerful acids and 
 bases, and of salts. Feeble acids are poor electrolytes. Fused salts are 
 generally electrolytes. It is necessary to refer to the question as to 
 what constitutes an electrolyte. 
 
 It is generally stated that the transmission of the electrical energy, 
 commonly called the electric current, can occur in two ways, either along 
 matter or with matter. The first method of transference happens when 
 electricity is conducted by a metal ; substances which are able to effect 
 such a transference are called conductors of the first class. The second 
 
326 DEGREE OF IONISATION. 
 
 method is that which obtains in electrolytes, which are called con- 
 ductors of the second class. 
 
 These facts were early recognised, but it was at first thought that 
 the electricity obtained the matter with which it was to move in the 
 electrolyte by tearing asunder the molecules. This, however, would be 
 inconsistent with the fact that even the smallest electrical pressure will 
 exert some electrolysis. It has only recently been realised that the 
 molecules in an electrolyte must be regarded as being already ionised, 
 nearly completely in dilute solutions, and to a certain extent in all 
 electrolytes. The free ions exist in the electrolytic medium, each bear- 
 ing its charge of electricity. It is this charge that prevents the ion 
 from behaving chemically like the free element or radicle, and it is only 
 when the ion has been conducted to the electrode by the electric current, 
 and is discharged, that it exhibits the chemical properties expected of the 
 free element or radicle. 
 
 That this view of the constitution of an electrolyte is correct is 
 evidenced by the facts concerning the conductivity of saline solutions. 
 If the passage of an electric current through an electrolyte depends 
 upon the presence of ions, a saline solution should offer a lower resist- 
 ance to this passage the more perfect the ionisation of the dissolved 
 salt. Hence the conductivity of a dilute solution, in which ionisation 
 is more perfect, should be proportionally better than that of one which 
 is stronger, and therefore less ionised. This is found to be the case ; as 
 the dilution of a saline solution is increased the conductivity tends to 
 become constant, the more perfect ionisation compensating for the 
 smaller number of ultimate particles in unit volume. 
 
 Judging by conductivity, ionisation appears to be practically complete when 
 one gram-equivalent of a salt is dissolved in 1000 litres of water ; the degree 
 of ionisation at any other dilution is equal to the ratio of the molecular conduc- 
 tivity (the conductivity calculated, from the observed value, for a solution con- 
 taining i gram-molecule per litre) at this dilution to the molecular conductivity 
 at a dilution of 1000 litres. This statement only applies to good electrolytes ; 
 poor electrolytes do not reach a constant conductivity at any dilution at which 
 it is practicable to make the necessary measurements. 
 
 The degree of ionisation may also be calculated from measurements of osmotic 
 pressure, for this is proportional to the ionisation. If N be the number of ulti- 
 mate particles present when the osmotic pressure is P, and N 1 the number when 
 it is P 1 , then P:P 1 = N:N 1 . The number of ultimate particles present at any 
 degree of ionisation depends on the nature of the dissolved substance : for this 
 may split up into n ions ; in the case of H 2 S0 4 ,% = 3 ; in the case of K 4 FeCy 6 ,fl = 5. 
 If ionisation were complete, the original number of molecules, N, would become 
 riN. Let a? be the fraction of the total number of molecules ionised, then i - x will 
 be the fraction left unionised. The total number of unionised molecules will be 
 N(i - a?), and Na? will be ionised. But N x molecules become riSsc ions, so that the 
 total number of ultimate particles in the ionised solution will be N(i a?) + wNa?, 
 and this is the value of N 1 in the above equation. Therefore P : P 1 = N:N(i - x) + 
 
 Whence x = 
 
 It is found in many cases that during electrolysis the concentration of the electro- 
 lyte at the anode (or cathode) becomes greater than that at the cathode (or anode). 
 This can only be explained by assuming that the anions (or cations) move faster 
 through the liquid than the cations (or anions) do. This difference in the rate of 
 migration of the ions is also indicated by the fact that the conductivity of solutions 
 containing equivalent quantities of various salts which are ionised in the same 
 degree, is different. When a solution of KC1 is electrolysed, the concentration at 
 the electrodes remains practically the same, so that the ions of K and Cl move at 
 nearly the same rate ; but the equivalent conductivity of NaCl solution of equiva- 
 
ELECTROLYTIC DISSOCIATION. 327 
 
 lent strength is only about 65 per cent, of that of KC1 solution ; hence the sodium 
 ion must migrate at only 65 per cent, of the speed of the potassium ion. 
 
 It is supposed that those solutions which are not electrolytes contain 
 no ionised molecules ; thus, sugar, a solution of which is not an 
 electrolyte, does not suffer ionisation when dissolved. 
 
 The solutions of all substances which are electrolytes show abnormal 
 osmotic pressures, abnormal depressions of the freezing-point, &c. ; this 
 supports the theory that many salts, acids and bases are dissociated 
 when they are dissolved. It must be remembered, however, that the 
 dissociation is always into ions, and not necessarily of the same character 
 as the dissociation effected by heat. 
 
 At the present day the theory of ionisation is being extensively 
 adopted as affording the best explanation of chemical reactions in 
 solution. The analytical tests for metals and acid radicles are the 
 reactions of the ions ; if a reaction occurs in a dilute solution which will 
 not occur in a strong one it is because there are no ions in the strong 
 solution, the salt not having been ionised therein. 
 
 From what has been said above on the physical theory of solution and the 
 evidence in support of it, it will be seen that a solvent has an effect upon a 
 soluble substance which may be well compared with the effect of heat on a 
 volatile substance. Just as there are many substances which resist in a high 
 degree the disgregating action of heat, so there are many which resist that of 
 solvents. Equally noteworthy is the similarity which exists between the influence 
 of solvents and of heat on chemical change : reactions occur between substances 
 in solution which have no tendency to happen between the solid substances, how- 
 ever finely these may be divided, and however intimately they may be mixed ; 
 so also, reactions occur at an elevated temperature which are impossible at low 
 temperatures. It is also worth while to call attention to the fact that the presence 
 of the best solvent, water, will enable a smaller stress to convert the potential 
 energy of a mixture into the kinetic energy represented by the combination of its 
 constituents than would otherwise be the case ; thus, as has been already stated, 
 a mixture of carbon monoxide and oxygen requires a far greater stress in the 
 form of high-pressure heat (high temperature) to start combination, when it is 
 perfectly dry than when moisture is present. Many cases have been cited in which 
 the presence of water enables a chemical change to be brought about by heat of 
 moderate temperature e.g., the combustion of carbon (p. 32) ; there is not sufficient 
 evidence to show whether or not the stress of a much higher temperature will 
 render these changes, also, independent of moisture. 
 
 There are, however, many changes, which are capable of occurring at the 
 ordinary temperature, that are dependent on the presence of water. It is also a 
 fact that many substances which are excellent electrolytes when dissolved in 
 water, have an almost infinite electrical resistance when anhydrous ; in other 
 words, these substances require the presence of water in order that they may 
 become partially ionised. On the basis of this latter observation it has been 
 suggested that an electrolytic medium, that is, one which will enable ionisation 
 to occur, is essential for chemical change ; on this hypothesis the fact that an- 
 hydrous HC1 will not attack calcium oxide, would be explained by stating that it 
 is only the ions of HC1 which can enter into reaction with CaO. A very little 
 water should suffice for the reaction, since when the first formed ions have been 
 removed by reaction with the CaO, further ionisation could occur. The dis- 
 covery of some other third substance which shall have a similar influence to that 
 of water is the present business of the chemist.* 
 
 As a final word on this subject, attention must be called to the fact that high 
 heat pressure and high electrical pressure are not alone in inducing chemical 
 
 * A tendency to return to the old view that chemical energy is to be regarded as due to a 
 difference of electrical potential between elements, seems at present prevalent, and it must 
 be admitted that support for such a view is derived from the recent observations of Baker, 
 who shows that when electrodes, carrying high pressure electricity, are introduced into a 
 mixture of hydrogen and oxygen, sufficiently dry to hinder combination, the gas around the 
 " positive " electrode is richer in oxygen than that around the opposite electrode. 
 
328 
 
 THE SPECTROSCOPE. 
 
 change ; it has been shown that high mechanical pressure is in many cases effec- 
 tive (such as in decomposing moist silver chloride), and the influence of another 
 form of energy, the shorter wave lengths of light, in inducing the numerous 
 changes on which the art of photography depends, is well known. 
 
 Spectroscopy. Heated solids have their molecules vibrating in so 
 many phases that they give rise to waves in the luminiferous ether 
 which are of every possible wave length ; consequently a heated solid 
 gives a continuous spectrum in which the red is more prominent at 
 lower temperatures. Heated gases, on the other hand, have their 
 molecules vibrating in such a way that they give out waves of com- 
 paratively few wave lengths. 
 
 By passing the light emitted from a hot gas through a prism the 
 wave lengths are separated and take up their proper positions in the 
 spectrum i.e., somewhere in the violet, indigo, blue, green, yellow, 
 
 Fig'. 204. Spectroscope. 
 
 orange, red in accordance with the length of the wave between the 
 limits 766 millionths of a millimetre for red, and 396 millionths of a 
 millimetre for violet. Of all the wave lengths from a given gas a few 
 will be more visible than the rest ; so that there are characteristic lines 
 in the spectrum for the gas of each element. Thus, heated sodium 
 vapour gives rise to two very prominent wave lengths (589.5 and 588.9 
 millionths of a millimetre) which give the sensation of yellow light. 
 
 When the white light emanating from an ordinary flame is allowed 
 to pass through the narrow slit, or collimator, of a spectroscope (Fig. 204),* 
 
 * This form of instrument has been found to be well suited to the general work required 
 of a spectroscope in a chemical laboratory. Either one or two prisms can be used, and the 
 central table is arranged so as to take the levelling 1 screws of a reflection grating. The 
 instrument is well adapted for determination of refractive indices and dispersive powers. 
 
SPECTEUM ANALYSIS. 
 
 329 
 
 .and is transmitted through a prism of flint glass, a continuous spectrum 
 composed of overlapping images of the slit in all the colours which make 
 up white light will be perceived through the telescope ; but if a Bunsen 
 flame be employed, a single image will be seen, forming a bright yellow 
 line in the place where the brightest yellow was seen in the continuous 
 spectrum ; this line is due to the presence of a little sodium in the 
 flame, from the dust in the air, and it becomes very intense if a little 
 sodium chloride be held in the flame on a loop of platinum wire. By 
 comparing the spectra of the flames containing vapours of the metals 
 with a map of the wave lengths in the solar spectrum (Fig. 205), the 
 exact position of the various colours may be noted, and thus, if several 
 metals are present in the same flame, they may still be distinguished by 
 the colours and positions of their bright lines. Thus, if a mixture of 
 the chlorides of potassium, sodium, and lithium be taken upon a loop of 
 
 Violet. Indigo. .Blue 
 
 Green. Yellnw. Oranae. Recb. 
 
 Spectrum furnished by a solar light decomposed by a prism. 
 
 K . g S 
 
 g S A - ,- .R 1 1 
 
 
 S B * 
 
 s f 'ji \S c (5! 
 
 g e B ^ ^ 
 
 Slran/li 
 
 s 
 
 li 
 
 
 
 K> 
 
 s 
 
 i 
 t 
 
 Pot as si 
 Jluttdi 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Xct 
 
 Coloured bands in the spectrum. 
 Fig'. 205. 
 
 platinum wire and held in the flame, the dull red line of potassium (K, 
 Fig. 205) is seen close to one end of the spectrum ; at some distance 
 from it the bright red band (L) of lithium ; at about the same distance 
 from this, the pale yellow lithium line ; and close to this the bright 
 yellow sodium lines (Na) ; whilst near the other end of the spectrum is 
 the feeble violet line of potassium (k). The chlorides of the metals are 
 most suitable for this experiment on account of their volatility. Since 
 a very little vapour (for instance, T owo~o m g m -) can be detected by its 
 characteristic wave lengths, the use of the spectroscope furnishes an 
 extremely delicate test for many elements. 
 
 The character of the spectrum of a gas differs with the temperature 
 and pressure. Increased temperature increases its complexity, the 
 bright lines becoming more numerous and broader. The same effect 
 is produced by increased pressure, which probably increases the 
 collisions between the molecules, and thus gives rise to a larger number 
 
330 
 
 SPECTRA OF GASES. 
 
 of phases of vibration, 
 continuous spectrum. 
 
 Thus, H 2 + O fired in a closed space gives a 
 
 Hence arises the custom of examining the spectrum of a gas at 
 much diminished pressure in a Geissler tube (Fig. 206). This consists 
 of a tube very much constricted at the middle part of its length and 
 having electrodes of aluminium sealed through the glass. The tube 
 is first exhausted by the air-pump, and then a small quantity of the 
 gas to be examined, sufficient to create a pressure of a few milli- 
 metres, is admitted. The electrodes are connected with the 
 terminals of a powerful induction coil, and the spectroscope is 
 directed to the constricted part of the tube for examination of the 
 spectrum of the gas. 
 
 When the vapour whose spectrum is to be examined is 
 heated by contact with a flame (as in the method for 
 obtaining the spectra of metallic vapours described above), 
 chemical reactions will frequently render the spectrum 
 
 Fig. 206. 
 Geissler tube. 
 
 Fig. 207. Radiant matter bulb. 
 
 different from that observed by volatilising the substance and heating 
 the vapour by electric sparks (spark spectrum). Thus, when cupric 
 chloride is introduced into the Bunsen flame, the reducing action of 
 
 Fig. 208. Air-pump. 
 
 the gases causes the spectrum to contain a blue line due to cuprous 
 chloride, a green line due to cuprous oxide, and a red line due to 
 copper, together with the other, fainter lines characteristic of these 
 vapours. 
 
ABSOKPTION SPECTEA. 331 
 
 A gas will absorb those wave lengths from the spectrum which it will 
 itself emit when heated. Thus, if white light be passed through sodium 
 vapour and then through a prism, black lines in the position of wave 
 lengths 589.5 and 588.9 millionths of a millimetre will appear in the 
 spectrum. 
 
 The black lines in the solar spectrum are presumed to be due to the 
 light passing through gaseous elements surrounding the sun.t Such 
 absorption spectra are also exhibited by some solutions, such as solutions 
 of didymium salts, of blood and of many dyes. Analytical use may be 
 made of these for identifying the substance in solution. 
 
 Another method for obtaining a characteristic spectrum is to expose 
 the substance in a vacuous glass bulb (Fig. 207) to a high pressure 
 electrical discharge (from an induction coil) delivered from two platinum 
 electrodes, attached to wires of the same metal sealed through the glass. 
 Many substances phosphoresce under this treatment, and when the 
 light thus emitted is viewed through a spectroscope it exhibits bright 
 bands which serve to identify the substance. A pump capable of cre- 
 ating, in a very short time, a sufficiently high vacuum for the observa- 
 tion of such phosphorescence is shown in Fig. 208. 
 
CHEMISTRY OF THE METALS. 
 
 178. The definition of a metal has already been given at p, 38, as an 
 element capable of forming a base by union with oxygen. It will also be 
 noticed that the metals are but little disposed to form combinations with 
 hydrogen ; but that they evince very powerful attraction for the chlorine 
 group of elements, with which they form, as a rule, compounds soluble, 
 without apparent decomposition, in water. 
 
 With a few exceptions the metals will be considered in the same 
 order as they occur in the families of the periodic grouping of the 
 elements, to the table of which the reader must refer for a true classifi- 
 cation of the metals. 
 
 POTASSIUM. 
 
 K' = 39.i parts by weight. 
 
 179. Potassium is found in abundance, as potassium chloride and 
 sulphate, in certain salt-mines (see below), and is contained in granite, 
 of which it forms about 5 or 6 per cent. The indispensable alkali, 
 potash, appears to have been originally derived from the granite rocks, 
 where it exists, in combination with silica and alumina, in the well- 
 known minerals felspar and mica. These rocks having, in course of 
 time, disintegrated to form soils for the support of plants, the potash 
 has been converted into a soluble state, and has passed into the plants 
 as a necessary portion of their food. 
 
 In the plant, the potash is found to have entered into various forms 
 of combination ; thus, most plants contain sulphate and chloride of 
 potassium ; but the greater portion of the potassium exists in the form 
 of salts of certain vegetable acids formed in the plant, and when the 
 latter is burnt, these salts are decomposed by the heat, leaving the 
 potassium in the form of carbonate. 
 
 Potassium carbonate, or carbonate of potash, K.,C0 3 . When the 
 ashes of plants are treated with water, the salts of potassium are dissolved, 
 those of calcium and magnesium being left. On separating the aqueous 
 solution and evaporating it to a certain point, a great deal of the 
 potassium sulphate, being much less soluble, is deposited, and the 
 carbonate remains in the solution ; this is evaporated to. dryness, when 
 the carbonate is left, mixed with much potassium chloride, and some 
 sulphate ; this mixture constitutes the substances imported from America 
 and other countries where wood (containing about 0.5 per cent, of 
 K 2 0) is abundant, under the name of potashes, which are much in 
 demand for the manufacture of soap and glass. When further purified, 
 

 
 pOTAgIL 
 OF 
 
 3 are sold;utUra*^e name of pearlash, but this is still far from being 
 potassium carbonate. 
 
 these ; 
 pure 
 
 During the fermentation of the grape-juice, in the preparation of wine, a hard 
 crystalline substance is deposited, which is known in commerce by the name of 
 argol, or, when purified, as cream of tartar. The chemical name of this salt is 
 bitartrate of potash or hydropotassium tartrate, for it is derived from potash and 
 tartaric acid, a vegetable acid having the composition H 2 C 4 H 4 6 . When this salt 
 (KHC 4 H 4 6 ) is heated, it leaves potassium carbonate mixed with carbon ; but if 
 the heat be continued, and free access of air permitted, the carbon will be entirely 
 burnt away, and potassium carbonate will be left (salt of tartar). 
 
 The residue left after the sugar has been extracted from the sugar beet is worked 
 up for the potassium carbonate it contains by first charring it, extracting it with 
 water, and fractionally crystallising the solution obtained ; the sulphate and 
 chloride of potassium crystallise first, leaving the K 2 C0 3 in the mother liquor. 
 
 The fleeces of sheep contain about 50 per cent, of fatty matter (suint or yolJt), rich 
 in potassium combined with an organic acid ; when the fleece is washed with water r 
 this salt is dissolved out, and on evaporating the liquid and burning the residue 
 this is converted into potassium carbonate. 
 
 Potassium carbonate is also made from potassium sulphate by a process similar 
 to that by which sodium sulphate is converted into carbonate (see Alkali Manu- 
 facture). Potassium chloride is converted into potassium carbonate by heating 
 it under pressure with magnesium carbonate and CO 2 , whereby "the salt 
 KHMg(C0 3 ) 2 4H 2 O is obtained ; when this is heated with water at 120 C. it yields 
 insoluble MgC0 3 and a solution of K 2 C0 3 which is evaporated. 
 
 Potassium carbonate is deliquescent and soluble in its own weight of 
 cold water, yielding a strongly alkaline solution. It may be crystallised 
 in prisms of the formula 2K 2 C0 3 .3H 2 0, which become K 2 C0 3 .H 2 at 
 1 00 C. It is insoluble in alcohol. It melts at 830 C. 
 
 Bicarbonate of potash, or hydropotassium carbonate, KHC0 3 , often 
 sold as the carbonate and used in medicine, is made by saturating moist 
 K 2 C0 3 with C0 2 , or by passing C0 2 through a strong solution of K 2 C0 3 
 (in three parts of water). It forms prismatic crystals which are much 
 less alkaline and less soluble in water (30.4 per cent, at 15 C.) than is 
 the normal carbonate, into which they are converted by heat ; 2KHC0 3 = 
 K 2 C0 3 + H 2 + C0 2 . The aqueous solution of KHCO 3 gradually loses 
 CO 2 when boiled. 
 
 Caustic potash, or potassium hydroxide, KOH. Potassium car- 
 bonate was formerly called potash, and was supposed to be an elementary 
 substance. It was known that its alkaline qualities were rendered far 
 more powerful by treating it with lime, which caused it to be termed mild 
 alkali, in order to distinguish it from the caustic alkali obtained by means 
 of lime, and possessed of very powerful corrosive properties. 
 
 The caustic potash, so largely employed by the soap-maker, is obtained 
 by adding slaked lime (Ca(OH) 2 ) to a boiling solution of the potassium 
 carbonate, in not less than 12 parts of water, when calcium carbonate is 
 deposited at the bottom of the vessel, whilst potassium hydrate remains 
 in the clear solution ; K 2 C0 3 + Ca(OH) 2 = CaC0 3 + 2KOH. 
 
 If the solution be too strong, the lime will not decompose the carbon- 
 ate, for the reaction is reversible (p. 309). 
 
 When the solution is evaporated, the potassium hydroxide remains as 
 a clear oily liquid, which solidifies to a white mass as it cools, and forms 
 the fused potash of commerce, which is often cast into cylindrical sticks 
 for more convenient use.* Potassium hydroxide is vapourised at high 
 
 * These have sometimes a greenish colour, due to the presence of some potassium 
 manganate. 
 
334 POTASSIUM. 
 
 temperatures without decomposition. It readily absorbs water and C0 2 
 from the air. Half its weight of water suffices to dissolve it, with great 
 evolution of heat. A strong solution deposits crystals of KOH.2Aq. 
 Alcohol dissolves it easily. The potassium hydroxide is the most 
 powerful alkaline substance in ordinary use, and is much used by the 
 chemist, generally in the state of solution, the strength of which is 
 inferred from its specific gravity, which increases with the amount of 
 potash contained in the solution. 
 
 Potassium. Of the composition of potassium hydroxide nothing 
 was known till the year 1807, when Davy succeeded in decomposing it by 
 the galvanic battery ; this experiment, which deserves particular notice 
 as being the first of a series resulting in the discovery of so many 
 important metals, was made in the following manner : A fragment of 
 potassium hydroxide, which, in its dry state, does not conduct elec- 
 tricity, was allowed to become slightly moist by exposure to the air, and 
 placed upon a plate of platinum attached to the copper end of a very 
 powerful galvanic battery ; when the wire connected with the zinc end 
 was made to touch the surface of the hydrate, some small metallic 
 globules resembling mercury made their appearance at the extremity of 
 this (negative) wire, at which the hydrogen contained in the hydroxide 
 was also eliminated, whilst bubbles of oxygen were separated on the 
 surface of the platinum plate connected with the positive wire (see 
 p. 324). By allowing the negative wire to dip into a little mercury 
 contained in a cavity at the surface of the potash, a combination of 
 potassium with mercury was obtained, and the mercury was afterwards 
 separated by distillation. This process, however, furnished the metal in 
 very small quantities, and, though it was obtained with greater facility 
 a year or two afterwards by decomposing potassium hydroxide with 
 white-hot iron, some years elapsed before any considerable quantity of 
 potassium was prepared by the present method of distilling in an iron 
 retort an intimate mixture of potassium carbonate and carbon, obtained 
 by calcining cream of tartar ; in this process the oxygen of the carbonate 
 is removed by the carbon in the form of carbonic oxide (K 2 C0 3 + C 2 = 
 
 The metal thus prepared requires re-distillation in order to decompose 
 the explosive compound of potassium with carbon monoxide, K 6 (CO) 6 , 
 which it always contains. 
 
 Some of the most striking properties of this metal have already been 
 referred to (p. 16); its softness, causing it to be easily cut like wax, the 
 rapidity with which its silvery surface tarnishes when exposed to the 
 air, its great lightness (sp. gr. 0.865), causing it to float upon water, 
 and its taking fire when in contact with that liquid, sufficiently distin- 
 guish it from other metals. It fuses at 62. 5 C. and boils at a low red 
 heat (667 C.), yielding a green vapour; if air be present, it burns with 
 a violet-coloured flame, the oxide K 2 4 being the chief product. In 
 dry air or oxygen the metal may be distilled unchanged. 
 
 The property of burning with this peculiar violet-coloured flame is 
 characteristic of potassium, and allows it to be recognised in its com- 
 pounds. 
 
 If a solution of potassium nitrate (saltpetre) in water be mixed with enough 
 spirit of wine to allow of its being inflamed, the flame will have a peculiar lilac 
 colour. This colour may also be developed by exposing a very minute particle of 
 
POTASSIUM SALTS. 335 
 
 saltpetre, taken on the end of a heated platinum wire, to the reducing (inner) 
 blowpipe flame (Fig. 209), when the potassium, being reduced to the metallic 
 state and passing into the oxidising (outer) flame in the state of vapour, imparts 
 to that flame a lilac tinge. 
 
 The difficulty and expense attending the preparation of potassium 
 have prevented its receiving any application except in purely chemical 
 
 Fig. 209. Coloured flame test. 
 
 operations, where its attraction for oxygen, chlorine, and other electro- 
 negative elements is often turned to account. 
 
 Potassium hydride, K 2 H, is formed when potassium is heated in hydrogen to 
 about 350 C. It forms a silvery brittle mass, which takes fire in air and is 
 dissociated in a vacuum at 200 C. 
 
 Oxides of Potassium. K 2 0, is alleged to be formed when K is heated with KOH, 
 H being expelled, but the evidence as to the existence of this oxide is very poor. 
 Potassium tetroxide, K 2 4 , is the yellow powder obtained when the metal is heated 
 in air or oxygen. It is decomposed by water yielding the dioxide, K 2 2 , and 
 evolving 0. By heating potassium in a limited supply of nitrous oxide, the 
 trioxide, K 2 3 , is formed as a buff powder. 
 
 Potassium chloride (KC1) is an important natural source of this 
 metal, occurring in combination with magnesium chloride as the mineral 
 carnallite (KCl.MgCl 2 .6H 2 O), an immense saline deposit overlying the 
 rock-salt in the salt-mines of Stassfurt, in Saxony. Carnallite re- 
 sembles rock-salt in appearance, but is very deliquescent. It yields a 
 magma of KC1 crystals when treated with water ; this is re-crystallised. 
 Potassium chloride crystallises in anhydrous cubes ; it is very soluble in 
 water and insoluble in alcohol ; it melts at 734 C. By melting KC1 
 with potassium a blue subchloride K,C1 is alleged to be obtained ; it 
 decomposes water evolving H. 
 
 Potassium chlorate, KC10 3 , is prepared as described at page 185. 
 It is also made by electrolysing a solution of KC1, but the methods are 
 kept secret ; the principle underlying them is noticed in the section on 
 soda. It crystallises in four-sided tables, soluble in 16 parts of cold and 
 2 parts of boiling water. It fuses at 360 C., and is decomposed at 400, 
 when it gives off oxygen, and leaves, at first, a mixture of chloride and 
 perchlorate, and lastly chloride only ; 2KC10 3 = KC10 4 + KC1 + O 2 . Its 
 action on combustible bodies and consequent useful applications have 
 been described at p. 186. 
 
 Potassium perchlorate, KC10 4 , is remarkable for its sparing solubility, for it 
 requires 70 parts of cold water to dissolve it. It is prepared by heating KC1O 3 
 until 1 2 grams have evolved a litre of oxygen, as shown in the above equation ; the 
 mass is boiled with just enough water to dissolve it, and the solution, on cooling, 
 
POTASSIUM SALTS. 
 
 deposits crystals of KC10 4 , leaving the KC1 in solution. The perchlorate is decom- 
 posed above 400 C. into KC1 and 4 . 
 
 Potassium bromide, KBr (in. p. 699 C.), forms cubical crystals very soluble in 
 water. 
 
 Potassium iodide, KI, is prepared by adding iodine in small quanti- 
 ties to solution of potash till it is coloured slightly brown, when a 
 mixture of potassium iodide and iodate is obtained ; 6KOH + 1 6 = 
 KIO 3 + 5KI + 3H 2 0. The solution is evaporated to dryness, the residue 
 mixed with one-tenth of its weight of powdered charcoal, thrown in 
 small quantities into a red-hot iron crucible and fused ; KIO 3 + C 3 = 
 KI + 3CO. The fused mass is dissolved in hot water, filtered, evapor- 
 ated till a film appears upon the surface, and set aside to crystallise. 
 It is also made by digesting iron filings with iodine and water, and 
 decomposing the solution of ferrous iodide, which is formed, with potas- 
 sium ca,rbonate. 
 
 Potassium iodide forms cubical crystals very soluble in water, but 
 sparingly soluble in alcohol. It is of the greatest importance in 
 medicine, in chemical analysis, and in photography. It melts at 
 634 C. 
 
 Potassium tri-iodide, KI 3 , obtained by saturating potassium iodide with iodine 
 and evaporating over sulphuric acid, forms dark brown needles with a metallic 
 lustre, very deliquescent, and easily decomposed into KI and I 2 . 
 
 Potassium iodate, KIO 8 , is useful in testing for S0 2 , and may be prepared for 
 that purpose by mixing 50 grains of iodine with an equal weight of potassium 
 chlorate in fine powder, adding, in a flask, about half a measured ounce of nitric 
 acid, and digesting till the colour disappears. The liquid is then boiled for a 
 minute, poured into a dish, evaporated to dryness, and moderately heated, when 
 it leaves a mixture of potassium iodate and a little potassium chloride which 
 may be dissolved in water. S0 2 at once liberates iodine from it, which gives a 
 blue colour to starch. 
 
 Potassium fluoride, KF (m. p. 789 C.), is prepared by neutralising HF with 
 K 2 C0 3 . Crystallised by slow evaporation of a cold solution, it gives KF.2H 2 O r 
 but above 35 C. it yields cubes of KF. It is deliquescent and easily soluble ; the 
 solution corrodes glass. It combines with HF, forming KF.FH, which is employed 
 for the preparation of pure HF. 
 
 Potassium sulphide, K 2 S, is obtained as a red crystalline mass by heating K 2 S0 4 
 in hydrogen. Solution of K 2 S is prepared by saturating solution of KOH with 
 H 2 S, and adding an equal quantity of KOH. From the solution, colourless 
 crystals of K 2 S.5H 2 may be obtained ; they deliquesce in air and are decomposed 
 by the C0 2 therein with evolution of H 2 S. 
 
 Potassium hydrogen sulphide, KSH, maybe formed by saturating a strong solution 
 of KOH with H 2 S and evaporating in vacuo, when colourless deliquescent crystals, 
 2KSH.H 2 0, separate. On exposure to air the solution of KHS evolves H 2 S owing 
 to the action of C0 2 ; if the air be free from C0 2 the solution is oxidised to potas- 
 sium thiosulphate, K 2 S 2 3 . 
 
 Potassium sulphate, K 2 S0 4 , is found in certain salt-mines, in the 
 mineral kainit, K 2 S0 4 .MgSO 4 .MgCl 2 .6Aq. This is decomposed by adding 
 KC1, whereupon all the MgS0 4 becomes Mg01 2 , and crystallising from 
 water when the K 2 S0 4 crystallises, on cooling, in rhombic prisms which 
 are rather sparingly soluble in cold water (10 parts), but easily in 
 boiling water (4 parts). It is also obtained as a by-product in some 
 chemical manufactures, and is used in making alum. It melts at 1066 C. 
 Kainit is largely used as an artificial manure. 
 
 Bisulphate of potash, or hydrogen-potassium sulphate, KHSO 4 , is 
 obtained as the residue in the preparation of nitric acid from saltpetre. 
 It is more fusible and more soluble in water than the normal sulphate 
 
SALTPETRE. 
 
 337 
 
 is. Its solution is strongly acid. Much water decomposes it into sul- 
 phuric acid and K 2 S0 4 . When heated, it undergoes decomposition in 
 two stages: (i) 2KHS0 4 --H 2 + K 2 S 2 7 (pyrosulphate or anhydro- 
 sulphate); (2) K 2 S 2 O 7 = K 2 SO 4 + S0 3 . This evolution of SO 3 makes the 
 bisulphate very useful in chemical operations for decomposing minerals 
 at high temperatures. 
 
 Potassium nitrate (KN0 3 ), or saltpetre, is found in India, especially 
 in Bengal and Oude, and other hot climates, where it sometimes appears 
 in the dry season as a white incrustation on the surface of the soil, and 
 is sometimes mixed with the soil to some depth. The nitre is extracted 
 from the earth by treating it with water, and the solution is evaporated, 
 at first by the heat of the sun, and afterwards by artificial heat, when 
 the impure crystals are obtained, which are packed in bags and sent to 
 this country as grough (or impure) saltpetre. It contains a quantity of 
 extraneous matter varying from i to 10 per cent., and consisting of the 
 chlorides of potassium and sodium, sulphates of potassium, sodium, and 
 calcium, vegetable matter from the soil, sand, and moisture. The 
 number representing the percentage of impurity present is usually 
 termed the refraction of the nitre, in allusion to the old method of 
 estimating it by casting the melted nitre into a cake and examining its 
 fracture, the appearance of which varies according to the amount of 
 foreign matter present. 
 
 Potassium nitrate is also made by decomposing sodium nitrate with 
 potassium chloride. 
 
 In order to understand this decomposition, it is necessary to be acquainted with 
 the solubility of these salts and of those produced by exchange of their elements. 
 
 TOO parts of boiling water dissolve 
 
 1 80 parts of sodium nitrate 
 57 potassium chloride 
 
 240 potassium nitrate 
 37 sodium chloride 
 
 100 parts of cold water dissolve 
 
 80 parts of sodium nitrate 
 28 ,, potassium chloride 
 30 potassium nitrate 
 36 ,, sodium chloride 
 
 It is a general rule that when two salts in solution are mixed, which are capable 
 of forming, by exchange of their metals, a salt which is less soluble in the liquid, 
 that salt will be produced and separated. 
 
 Thus, when sodium nitrate and potassium chloride are mixed, and the solution 
 boiled down, sodium chloride is deposited, and potassium nitrate remains in the 
 boiling liquid ; NaN0 3 + KCl = KNO 3 + NaCl. When this is allowed to cool, the 
 greater part of the potassium nitrate crystallises, leaving the remainder of the 
 sodium chloride in solution. 
 
 The method usually adopted is to add the potassium chloride by degrees to the 
 boiling solution of sodium nitrate, to remove the sodium chloride with a perforated 
 ladle in proportion as it is deposited, and after allowing the liquid to rest for some 
 time to deposit suspended impurities, to run it out into the crystallising pans. 
 
 Potassium nitrate was at one time prepared from the nitrates obtained in nitre- 
 heaps, which consist of accumulations of vegetable and animal refuse, with 
 limestone, old mortar, ashes, &c. These heaps are constructed upon an imper- 
 meable clay floor under a shed to protect them from rain. One side of the heap 
 is usually vertical and exposed to the prevailing wind, the other side being cut 
 into steps or terraces. They are occasionally moistened with stable drainings, 
 which are allowed to run into grooves cut in the steps at the back of the heap. 
 In such a mass, at an atmospheric temperature between 60 and 70 F., nitrates 
 of the various metals present in the heap are slowly formed, and, being dissolved 
 by the moisture, are left by it, as it evaporates on the vertical side, in the form of 
 an efflorescence. When this has accumulated in sufficient quantity, it is scraped 
 off, together with a few inches of the nitrified earth, and extracted with water, 
 which dissolves the nitrates, whilst the undissolved earth is built up again on 
 
338 
 
 PUEIFICATION OF NITRE. 
 
 the terraced back of the heap. After two or three years the heap is entirely 
 broken up and reconstructed. The principal nitrates which are found dissolved 
 in the water are those of potassium, calcium, magnesium and ammonium, the- 
 three last of which may be converted into potassium nitrate by decomposing them 
 with potassium carbonate. 
 
 The formation of nitrates in these heaps is probably the result of chemical 
 changes similar to those which occur in the soils in which nitre is naturally formed, 
 the nitrates being produced by the oxidation, under the influence of the nitrifying 
 organism (p. 88), of ammonia (page 88) evolved by the putrefaction of the nitro- 
 genised matters which the heaps contain. The oxidation is much promoted by 
 the presence of the strongly alkaline lime and of the porous materials capable of 
 absorbing ammonia and presenting it under circumstances favourable to oxidation. 
 
 In refining saltpetre for the manufacture of gunpowder, the impure 
 (grough) salt is dissolved in about an equal weight of boiling water in a 
 copper boiler, the solution run through cloth niters 
 to remove insoluble matter, and allowed to crystal- 
 lise in a shallow wooden trough lined with copper,, 
 the bottom of which is formed of two inclined planes- 
 (Fig. 210). Whilst cooling, the solution is kept in 
 continual agitation with wooden stirrers, in order 
 that the saltpetre may be deposited in the minute 
 crystals known as saltpetre flour, and not in the 
 large prisms which are formed when the solution is 
 allowed to crystallise tranquilly, and which contain 
 within them cavities enclosing some of the impure 
 liquor from which the saltpetre has been crystallised. 
 
 The saltpetre, being so much less soluble in cold than in. 
 hot water, is, in great part, deposited as the liquid cools,, 
 whilst the chlorides and other impurities, being present in 
 
 Fig-. 210. 
 
 small proportion, and not presenting the same disparity in their solubility at 
 different temperatures, are retained in the liquid. The saltpetre flour is drained 
 and washed with two or three successive small quantities of water ; it is then 
 allowed to drain thoroughly, and in that state, containing from 3 to 6 per cent, of 
 water, according to the season, is ready to be transferred to the incorporating mill 
 or to a hot-air oven, w r here it is dried if not required for immediate use. 
 
 The impurities most objectionable in saltpetre for gunpowder are 
 KC1 and NaCl, which absorb moisture from the air. Potassium per- 
 chlorate, KC10 4 , is also liable to be present in the saltpetre, and is said 
 to have led to spontaneous explosion of powder made with such salt- 
 petre. 
 
 Potassium nitrate is usually distinguishable by the long striated or 
 grooved six-sided prismatic form in which it crystallises (though it may 
 also be obtained in rhoinbohedral crystals like those of sodium nitrate), 
 and by the deflagration which it produces when thrown on red-hot 
 coals. Its solubility in water has been given at p. 337. It is insoluble 
 in alcohol. It fuses at 339 C. to a colourless liquid, which solidifies on 
 cooling to a translucent brittle crystalline mass. The sal prunelle of 
 the shops consists of nitre which has been fused and cast into balls. 
 At a red heat it effervesces from the escape of bubbles of oxygen, and 
 is converted into potassium nitrite (KN0 2 ), which is itself decomposed 
 by a higher temperature, evolving nitrogen and oxygen, and leaving a 
 mixture of potassium oxides. The fused salt attacks all oxidisable 
 bodies and the potassium oxide attacks siliceous bodies, so that it is 
 difficult to find a vessel capable of resisting it at a high temperature. 
 Platinum gives way, but gold is less corroded. In contact with any 
 
COMPOSITION OF GUNPOWDER. 339 
 
 combustible body, it undergoes decomposition with great rapidity, five- 
 sixths of its oxygen being available for the oxidation of the combustible 
 substance, and the nitrogen being evolved in a free state ; thus, in con- 
 tact with carbon, the complete decomposition of the nitre may be repre- 
 sented by the equation 2 KNO 3 + 3 = K 2 C0 3 + C0 2 + CO + N 2 . Since 
 the combustion of a large quantity of material may be thus effected in 
 a very small space and in a short time, the temperature produced is 
 much higher than that obtained by burning the combustible in the 
 ordinary way. 
 
 The specific gravity of saltpetre is 2.07, so that i c.c. weighs 2.07 grams. Since 
 202 grams (2 molecules) of nitre contain 80 grams (5 atoms) of oxygen available 
 for the oxidation of combustible bodies, 2.07 grams'(or I c.c. of nitre) would contain 
 0.8 gram (or 555 c.c.) of available oxygen, a volume which would be contained in 
 about 2700 c.c. of air ; hence, i volume of saltpetre represents, in its power of 
 supporting combustion, 2700 volumes of atmospheric air. It also enables some 
 combustible substances to burn without actual flame, as is exemplified by its use in 
 touchpaper or slow portfire, which consists of paper soaked in a weak solution of 
 saltpetre and dried, the combustion taking place between the solid combustible 
 and the solid oxygen in the nitre instead of between gases as in the case of 
 flame. 
 
 If a continuous design be traced on foolscap paper with a brush dipped in a 
 solution of 30 grams of saltpetre in 100 grams of water, and allowed to dry, it 
 will be found that when one part of the pattern is touched with a red-hot iron it 
 will gradually burn its way out, the other portion of the paper remaining 
 unaffected. A mixture of 6 grams of KN0 3 , 2 of sulphur, and 2 of moderately 
 fine dried sawdust (Baum&sflua;) will deflagrate with sufficient intensity to fuse a 
 small silver coin into a globule ; the mixture may be pressed down in a walnut- 
 shell or a small porcelain crucible, and the coin buried in it, the flame of a lamp 
 being applied outside until deflagration commences. 
 
 Pulvis fulminam (white gunpowder) is a mixture of 3 parts of KN0 3 , i part of 
 sulphur, and 2 of K 2 C0 3 , all carefully dried ; when it is heated on an iron plate 
 no action occurs till it melts, when it explodes very violently.* 
 
 Gunpowder is a very intimate mixture of saltpetre, sulphur, and 
 charcoal, which do not act upon each other at the ordinary temperature, 
 but, when heated together, arrange themselves into new forms, evolving 
 a very large amount of gas. 
 
 The great attention that has been paid to the manufacture of gun- 
 powder is due to the fact that until recently it was the sole explosive 
 available for warfare. Now, however, it may be said to be displaced 
 by the various forms of "smokeless powders" which are all products of 
 nitration (p. 94) of organic substances. Gunpowder is now made almost 
 solely for use as a blasting explosive for mining. 
 
 The proportions of the ingredients of gunpowder have been varied 
 somewhat in different countries, the saltpetre ranging from 74 to 77 
 per cent., the charcoal from 12 to 16 per cent., and the sulphur from 
 9 to 12.5 per cent. English military powder contains 75 per cent, of 
 nitre, 15 per cent, of charcoal, and 10 per cent, of sulphur. Mining 
 powder contains about 67 per cent, of nitre, 19 per cent, of charcoal, 
 and 14 per cent, of sulphur. 
 
 The powdered ingredients f are first roughly mixed in a revolving gun-metal 
 drum, with mixing arms turning in an opposite direction, and the mixture is 
 subjected, in quantities of about 50 Ibs at a time, to the action of the incorporating mill 
 
 * Probably 2KNO 3 + K 2 CO 3 + S 2 =K 2 SO 4 + K 2 S + CO 2 + NO + NO 2 . The XO and NO 2 
 would probably be decomposed into their elements by the high temperature attained. 
 
 t The amount of water in the moist saltpetre (p. 338) is ascertained by drying and melt- 
 ing a weighed sample before the proportions are weighed out. 
 
340 MANUFACTURE OF GUNPOWDER. 
 
 (Fig. 21 1), where it is sprinkled with water, poured through the funnel (F), or from 
 a can with a fine rose, and exposed to trituration and pressure under two cast-iron 
 edge-runners (B), rolling in different circular paths upon a cast-iron bed, a very 
 intimate mixture being thus effected by the same kind of movement as in a 
 -Common pestle and mortar, the distribution of the nitre through the mass being 
 "also assisted by its solubility in water. A wooden scraper (C) tipped with copper- 
 prevents the roller from getting clogged, and a plough (D) keeps the mixture in 
 the path. Of course, the water employed to moisten the powder must be as free 
 from deliquescent salts (especially chlorides, see page 338) as possible ; at Waltham, 
 condensed steam is employed : the quantity required varies with the state of the 
 
 atmosphere. The duration of the incor- 
 porating process is varied according to the 
 kind of powder required, the slow-burning 
 powder employed for cannon being suffi- 
 ciently incorporated in about three hours, 
 whilst rifle-powder requires five hours. 
 
 The dark grey mass of mill-cake which 
 is thus produced contains 2 or 3 per cent, 
 of water. It is broken up by passing 
 between grooved 1'ollers of gun-metal, and 
 is then placed, in layers of about half an 
 inch thick, between copper plates packed 
 in a stout gun-metal box lined inside and 
 outside with wood, in which it is subjected 
 for a quarter of an hour to a pressure of 
 about 70 tons on the square foot, in a 
 hydraulic press, which has the effect of 
 condensing a larger quantity of explosive 
 Fig. 2ii. Incorporating mill. material into a given volume, and of di- 
 
 minishing the tendency of the powder to 
 
 absorb moisture from the air, and to disintegrate or dust after granulation. The 
 press-cake thus obtained is very hard -and compact, resembling slate in appearance. 
 As far as its chemical nature is concerned it is finished gunpowder, but if it be 
 reduced to powder and a gun loaded with it, the combustion of the charge is found 
 to occur too slowly to produce its full effect, since the pulverulent form offers 
 so great an obstacle to the passage of the flame by which the combustion is com- 
 municated from one end of the charge to the other. The press-cake must, there- 
 fore, be granulated (corned) or broken up into grains of sufficient size to allow the 
 rapid passage of the flame between them, and the consequent rapid firing of the 
 whole charge. The granulation is effected by crushing the press-cake between 
 successive pairs of toothed gun-metal rollers, from which it falls on to sieves, 
 which separate it 'into grains of different sizes, the dust, or meal powder, passing 
 through the last sieve. The granulated powders are freed from dust by passing 
 them through revolving cylinders of wooden framework covered with canvas or 
 wire cloth, and the fine-grain powder is glazed by the friction of its own grains 
 against each other in revolving barrels. The large-grain powders are sometimes 
 glazed or faced with graphite, by introducing a little of that substance into the 
 glazing-barrels with the powder. The powder is dried in a chamber heated by 
 steam, very gradually, so as not to injure the grain, and is once more dusted in 
 canvas cylinders before being packed. 
 
 When it is required that the powder shall burn rapidly the grains are made 
 small, but where a slower combustion is required, as was the case with heavy 
 ordnance which were too much strained by the rapid combustion of fine grain 
 powder, the size of grain is much increased, being from f to i^ inch or more in 
 diameter. To the same end the percentage of sulphur, on which the inflammability 
 of the powder depends, is reduced, and a charcoal carbonised at a low temperature, 
 and therefore comparatively inflammable, is used. Thus cocoa-poioder, or 'brown- 
 powder, is made with 79 per cent, nitre, 2 per cent, sulphur, and 18 per cent, of 
 lightly burnt charcoal. In mining powders, rapidity of combustion is desirable, 
 so that the proportion of sulphur and charcoal is increased, as shown in the com- 
 position given above. 
 
 1 80. Good gunpowder is composed of hard angular grains, which do 
 not soil the fingers, and have a perfectly uniform dark grey colour. 
 
EXPLOSION OF GUNPOWDER. 341 
 
 Its specific gravity (absolute density), as determined by the densimeter* 
 varies between 1.67 and 1.84, and its apparent density (obtained by 
 weighing a given measure of the grain against an equal measure of 
 water) varies from 0.89 to 0.94, so that a cubic foot will weigh from 55 
 to 58 Ibs. When exposed to air of average dry ness, gunpowder absorbs 
 from 0.5 to i per cent, of water. In damp air it absorbs a much larger 
 proportion, and becomes deteriorated in consequence of the saltpetre 
 being dissolved, and crystallising upon the surface of the grains. 
 Actual contact with water dissolves the saltpetre and disintegrates the 
 grains. When very gradually heated in air, gunpowder begins to lose 
 sulphur, even at 100 C., this ingredient passing off rapidly as the tem- 
 perature rises, so that the greater part of it may be expelled without 
 inflaming the powder, especially if the powder be heated in carbonic 
 acid gas or hydrogen, to prevent contact with air. If gunpowder be 
 suddenly heated to 600 F. (315 C.) in air, it explodes, the sulphur 
 probably inflaming first; but out of contact with air a higher tempera- 
 ture is required to inflame it. The ignition of gunpowder by flame is 
 not ensured unless the flame be flashed among the grains of powder ; it 
 often takes some time to ignite powder with the flame of a piece of 
 burning paper or stick, but contact with a red-hot solid body inflames 
 it at once. A heap of good powder, when fired on a sheet of white 
 paper, burns without sparks and without scorching or kindling the 
 paper, which should exhibit only scanty black marks of charcoal after 
 the explosion. If the powder has not been thoroughly incorporated, it 
 will leave minute globules of fused nitre upon the paper. Two ounces 
 of the powder should be capable of throwing a 68-lb. shot to a distance 
 of 260 to 300 feet from an 8o-inch mortar at 45 elevation. 
 
 Very fortunately, it is difficult to explode gunpowder by concussion, though it 
 has been found possible to do so, especially on iron, and accidents appear to have 
 been caused in this way by the iron edge-runners in the incorporating mill, when 
 the workmen have neglected the special precautions which are laid down for them. 
 The use of stone upon iron in the incorporation is avoided, because of the great 
 risk of producing sparks, and copper is employed in the various fittings of a 
 powder-mill wherever it is possible. 
 
 The electric spark is, of course, capable of firing gunpowder, though it is not 
 easy to ensure the inflammation of a charge by a spark unless its conducting power 
 is slightly improved by mixing it with a little graphite, or by keeping it a little 
 moist, which may be effected by introducing a minute quantity of calcium chloride. 
 
 181. PRODUCTS OP EXPLOSION OF GUNPOWDER. In the explosion of gun- 
 powder, the oxygen of the nitre converts the carbon of the charcoal chiefly into 
 carbon dioxide (C0 2 ), part of which assumes the gaseous state, whilst the 
 remainder is converted into potassium carbonate (K 2 C0 3 ). The greater part of the 
 sulphur is converted into potassium sulphate (K 2 S0 4 ). The chief part of the 
 nitrogen contained in the nitre is evolved in the uncombined state. The rough 
 chemical account of the explosion of gunpowder, therefore, is that the mixture of 
 nitre, sulphur, and charcoal is resolved into a mixture of potassium carbonate, 
 potassium sulphate, carbon dioxide, and nitrogen, the two last being gases, the 
 elastic force of which, when expanded by the heat of the combustion, accounts for 
 the mechanical effect of the explosion. 
 
 But in addition to these, several other substances are found among the products 
 of the explosion. Thus, the presence of potassium sulphide (K 2 S) may be recog- 
 nised by the smell of hydrogen sulphide produced on moistening the solid residue 
 in the barrel of a gun, and hydrogen sulphide (H 2 S) itself may often be perceived 
 in the gases produced by the explosion, the hydrogen being derived from the 
 charcoal. A little marsh gas (CH 4 ) is also found among the gases, being produced 
 
 * This is a simple apparatus for determining- the weight of mercury displaced by a given 
 weight of gunpowder, from which all the air has been exhausted. 
 
342 EXPLOSION OF GUNPOWDER. 
 
 by the decomposition of the charcoal, a portion of the hydrogen of which is also 
 disengaged in the free state. Carbonic oxide (CO) is always detected among the 
 products. It is evident that the collection for analysis of the products of explo- 
 sion must be attended with some trouble, and that considerable differences are to 
 be expected between the results obtained by different operators, from the variation 
 of the circumstances under which the powder is fired and the products collected. 
 When the powder is slowly fired, a considerable proportion of the nitrogen in the 
 saltpetre is evolved in the form of nitric oxide gas .(NO), which is not found 
 among the products of the rapid explosion of powder. 
 
 The period over which the combustion of a given weight of powder extends will, 
 of course, depend upon the area of surface over which it can be kindled ; thus a 
 single fragment of powder weighing 10 grains, even if it were instantaneously 
 kindled over its entire surface, could not evolve so much gas in a given time 
 as if it had been broken into 10 separate grains, each of which was kindled at 
 the same instant, since the inside of the large fragment can only be kindled from 
 the outside. Upon this principle a given weight of powder in large grains will 
 occupy a longer period in its explosion than the same weight in small grains, so 
 that the large grain powder is best fitted for ordnance, where the ball is very heavy, 
 and the time occupied in moving it will permit the whole of the charge to be fired 
 before the ball has left the muzzle, whilst in small arms with light projectiles, a 
 finer-grained and more quickly burning charge is required. If the fine-grain 
 powder were used in cannon, the whole of the gas might be evolved before the 
 containing space had been sensibly enlarged by the movement of the heavy pro- 
 jectile, and the gun would be subjected to an unnecessary strain ; on the other 
 hand, a large grain powder in a musket would evolve its gas so slowly that the 
 ball might be expelled with little velocity by the first half of it, and the remainder 
 would be wasted. There is good reason to believe that even under the most 
 favourable circumstances a large proportion of every charge of powder is discharged 
 unexploded from the muzzle of the gun and is therefore wasted. In blasting 
 rocks and other mining operations, the space within which the powder is confined 
 is absolutely incapable of enlargement until the gas evolved by the combustion has 
 attained sufficient pressure to do the whole work, that is, to rend the rock, for 
 example, asunder. Accordingly, a slowly burning charge will produce the effect, 
 since the rock must give way when the gas attains a certain pressure, whether that 
 happen in one second or in ten. Indeed, a slowly burning charge is advantageous, 
 as being less liable to shatter the rock or coal, and bringing it away in larger masses 
 with less danger. Barium nitrate and sodium nitrate are sometimes substituted for 
 a part of the potassium nitrate in mining powder, its combustion being thus 
 retarded. 
 
 The same charge of the same powder produces very different results when 
 heated in different ways. If 5 grains of gunpowder be placed in a wide test-tube 
 and fired by passing a heated wire into the tube, a slight puff only is perceived ; 
 but if the same amount of powder be heated in the tube by a spirit lamp, it will 
 explode with a loud report, and perhaps shatter the tube (a copper or brass tube 
 is safer). In the first place, the combustion is propagated slowly from the par- 
 ticle first touched by the wire ; in the second, all the particles are raised at once 
 to pretty nearly the same temperature, and as soon as one explodes, all the rest 
 follow instantaneously. 
 
 When gunpowder is slowly fired, the products of its decomposition are different 
 from those mentioned above ; thus, nitric oxide (NO), arising from incomplete de- 
 composition of the nitre, is perceived in considerable quantity, and may be recog- 
 nised by the red colour produced when it is brought in contact with air. 
 
 The white smoke arising from the explosion of gunpowder consists chiefly of 
 the sulphate and carbonate of potassium in a very finely divided state : it seems 
 probable that at the instant of explosion they are converted into vapour, and are 
 afterwards deposited in a state of minute division as the temperatute falls. From 
 this it will be obvious that a powder that is required to be smokeless must be free 
 from such saline products of explosion (see Nitro-glycerine). The fouling or actual 
 solid residue in the gun is very trifling when the powder is dry and has been well 
 incorporated ; a damp or slowly burning powder leaves, as might be expected, a 
 large residue. The residue always becomes wet on exposure to air, from the great 
 attraction for moisture possessed by the carbonate and sulphide of potassium. 
 
 From the circumstance that the combustion of gunpowder is independent of 
 any supply of oxygen from the air, it might be supposed that it would be as easily 
 
COMMON SALT. 343 
 
 inflamed in vacuo as under ordinary atmospheric pressure. This is not found to be 
 the case, however, for a mechanical reason, viz., that the flame from the particles 
 which are first ignited escapes so rapidly into the vacuous space that it does not 
 inflame the more remote particles. For a similar reason, charges of powder in 
 fuses are found to burn more slowly under diminished atmospheric pressure, the 
 flame (or heating gas) escaping more rapidly and igniting less of the remaining 
 charge in a given time. It has been determined that if a fuse be charged so as to 
 burn for thirty seconds under ordinary atmospheric pressure (30 inches barometer), 
 each diminution of I inch in barometric pressure will cause a delay of I second in 
 the combustion of the charge, so that the fuze will burn for thirty-one seconds 
 when the barometer stands at 29 inches. 
 
 SODIUM. 
 
 Na' = 23 parts by weight. 
 
 182. Sodium is often found, in place of potassium, in the felspars and 
 other minerals, but we are far more abundantly supplied with it in the 
 form of common salt (sodium chloride, NaCl), occurring not only in the 
 solid state, but dissolved in sea water, and in smaller quantity in the 
 waters derived from most lakes, rivers, and springs. 
 
 Rock-salt forms very considerable deposits in many regions ; in this 
 country the most important is situated at Northwich, in Cheshire, where 
 very large quantities are extracted by mining. Wielitzka, in Poland, is 
 celebrated for an extensive salt-mine, in which there are a chapel and 
 dwelling-rooms, with furniture made of this rock. Extensive beds of 
 rock-salt also occur in France, Germany, Hungary, Spain, Abyssinia, 
 and Mexico. Perfectly pure specimens form beautiful colourless cubes, 
 and are styled sal gemme ; but ordinary rock-salt is only parcially trans- 
 parent, and exhibits a rusty colour, due to the presence of iron. In 
 some places the salt is extracted by boring a hole into the rock and 
 filling it with water, which is pumped up when saturated with salt, and 
 evaporated in boilers, the minute crystals of salt being removed as they 
 are deposited. 
 
 At Droitwich, in Worcestershire, the salt is obtained by evaporation 
 from the waters of certain salt springs. In some parts of France and 
 Germany the water from the salt springs contains so little salt that it 
 would not pay for the fuel necessary to evaporate the water, and a very 
 ingenious plan is adopted by which the proportion of water is greatly 
 reduced without the application of artificial heat. For this purpose a 
 lofty scaffolding is erected and filled with bundles of brushwood, over 
 which the salt water is allowed to flow, having been raised to the top 
 of the scaffolding by pumps. In trickling over the brushwood this 
 water exposes a large surface to the action of the wind, and a consider- 
 able evaporation occurs, so that a much stronger brine is collected in 
 the reservoir beneath the scaffolding ; by several repetitions of the 
 operation, the proportion of water is so far diminished that the rest may 
 be economically evaporated by artificial heat. In England the brine 
 (containing about 22 per cent, of salt) is run into large pans and 
 rapidly boiled for about thirty hours, fresh brine being allowed to flow 
 in continually, so as to maintain the liquid at the same level in the 
 boiler. During this ebullition a considerable deposit, composed of the 
 sulphates of calcium and sodium, is formed, and raked out by the work- 
 men. When a film of crystals of salt begins to form upon the surface 
 the fire is lowered, and the temperature of the brine allowed to fall to 
 
344 SALT FKOM SEA WATER. 
 
 about 82 C., at which temperature it is maintained for several days 
 whilst the salt is crystallising. The crystals are afterwards drained, 
 and dried by exposure to air. The grain of the salt is regulated by the 
 temperature at which it crystallises, the size of the crystals increasing 
 as the temperature falls. The coarsest crystals thus obtained are known 
 in commerce as bay-salt. It is not possible to extract the whole of the 
 salt in this way, since the last portions which crystallise will always be 
 contaminated with other salts present in the brine ; but the mother-liquor 
 is not wasted, for after as much salt as possible has been obtained, it is 
 made to yield sodium sulphate (Glauber's salt), magnesium sulphate 
 (Epsom salts), bromine, and iodine. 
 
 The process adopted for extracting the salt from sea water depends upon the 
 climate. In Kussia, shallow pits are dug upon the shore, in which the sea water is 
 allowed to freeze, when a great portion of the water separates in the form of pure 
 ice, leaving a solution of salt sufficiently strong to pay for evaporation. 
 
 Where the climate is sufficiently warm, the sea water is allowed to run very 
 slowly through a series of shallow pits upon the shore, where it becomes concentrated 
 by spontaneous evaporation, and is afterwards allowed to remain for some time in 
 reservoirs in which the salt is deposited. Before being sent into the market, it is 
 allowed to drain for a long time, in a sheltered situation, when the magnesium chlo- 
 ride with which it is contaminated deliquesces in the moisture of the air and drains 
 away. The bittern, or liquor remaining after the salt has been extracted, is employed 
 to furnish magnesia and bromine. 
 
 1000 parts of sea water contain about 29 parts of NaCl, 0.5 of KC1, 2 of MgCl 2 , 
 2.5 of MgS0 4 , 1.5 of CaS0 4 , &c. 
 
 In a warm climate, that of Marseilles, for example, the water is allowed to evapo- 
 rate spontaneously until it has a specific gravity of 1.24. During this operation it 
 deposits about four-fifths of its sodium chloride. It is then mixed with one-tenth 
 of its volume of water, and artificially cooled to O F. (see p. 82), when it deposits 
 a quantity of sodium sulphate, resulting from the decomposition of part of the 
 remaining sodium chloride by the magnesium sulphate. The mother-liquor is 
 evaporated till its specific gravity is 1.33, a fresh quantity of sodium chloride being 
 deposited during the evaporation. When the liquid cools, it deposits a double salt 
 composed of chlorides of potassium and magnesium, from which the latter chloride 
 may be extracted by washing with a very little water, leaving the potassium chlo- 
 ride fit for the market. 
 
 This process is instructive as illustrating the influence exerted upon the nature of 
 the salts which will be deposited from a solution by the temperature to which this 
 is exposed, the general rule being that that salt separates which is least soluble in 
 the liquid at the particular temperature. 
 
 The great tendency observed in ordinary table salt to become damp 
 when exposed to the air is due chiefly to the presence of small quan- 
 tities of chlorides of magnesium and calcium, for pure sodium chloride 
 has a very much smaller disposition to attract atmospheric moisture, 
 although it is very easily dissolved by water, 2^ parts being able to dis- 
 solve i part (by weight) of salt. The saturated solution boils at 107.5 V. 
 
 In the history of the useful applications of common salt is to be found 
 one of the best illustrations of the influence of chemical research upon 
 the development of the resources of a country, and a capital example of 
 a manufacturing process not based, as such processes usually are, upon 
 mere experience, independent of any knowledge of chemical principles, 
 but upon a direct and intentional application of these to the attainment 
 of a particular object. 
 
 Until the last quarter of the eighteenth century, the uses of common 
 salt were limited to culinary and agricultural purposes, and to the 
 glazing of the coarser kinds of earthenware, whilst a substance far more 
 useful in the arts, carbonate of soda, was imported chiefly from Spain 
 
LEBLANC ALKALI PROCESS. 
 
 345 
 
 under the name of barilla, which was the ash obtained by burning a 
 marine plant known as the salsola soda. But this ash only contained 
 about one-fourth of its weight of carbonate of soda, so that this latter 
 substance was thus imported at a great expense, and the manufacturer 
 of soap and glass, to which it is indispensable, were proportionately 
 fettered. 
 
 During the wars of the French Revolution the price of barilla had 
 risen so considerably that it was deemed advisable by Napoleon to offer 
 a premium for the discovery of a process by which the carbonate of 
 soda could be manufactured at home, and to this circumstance we are 
 indebted for the discovery, by Leblanc, of the process, which is only 
 now being superseded, for the manui'acture of carbonate of soda from 
 common salt, a discovery which placed this substance at once among 
 the most important raw materials with which a country could be 
 furnished. 
 
 183. Manufacture of sodium carbonate from common salt by the Leblanc 
 jjrocess. This process consists in heating salt with sulphuric acid, 
 
 Fig'. 212. Furnace for converting common salt into sulphate of soda. 
 
 whereby sodium sulphate and hydrogen chloride are produced (seep. 177). 
 Tho sodium sulphate, technically called salt cake, is then mixed with 
 small coal and limestone, and again heated in order to convert it into 
 sodium carbonate, a change which may be represented by the two 
 equations : 
 
 (i) Na. 2 S0 4 + C. 2 = Na 2 S + 2C0 2 
 Sodium sulphate. Sodium sulphide. 
 
 (2) Na 2 S 
 
 CaC0 = Na.C0 
 
 CaS 
 
 Calcium sulphide. 
 
 The resulting mixture of sodium carbonate and calcium sulphide, technically 
 called Mack ash being black from the presence of coal is leached with water to 
 dissolve the sodium carbonate and leave the calcium sulphide (tank-watte).* The 
 liquor is evaporated to crystallise the sodium carbonate (soda crystals). 
 
 In the first part of the process {salt cake process} the salt is introduced into the 
 iron pan, A, of a salt cake furnace (Fig. 212), where it is mixed with an equal weight 
 of H 2 S0 4 (sp. gr. 1.72) and heated by the fire in the grate, C. Much HC1 is expelled 
 and escapes through the flue B, whence it passes to the bottom of a brick tower 
 
 * The CaS in the waste is insoluble because combined with lime. 
 
34^ AMMONIA-SODA ALKALI PROCESS. 
 
 packed with coke down which water is trickled ; the water absorbs the HC1 from 
 the gases as they ascend the tower, forming the muriatic acid of commerce (p. 178). 
 The door F is then raised, and the partly decomposed salt raked from the pan into 
 the brick roaster D : this is virtually a muffle heated by the flames from a furnace, 
 which circulate in the flues surrounding it. The conversion of the salt into sodium 
 sulphate is here completed, the remaining HC1 escaping through the flue E to con- 
 densing towers similar to that described above. 
 
 In the second part of the process the mixture of ground salt cake (10 parts), lime- 
 stone (10 parts), and small coal (4-6 parts) is heated in a black ash furnace, which 
 is essentially a reverberator}" furnace, such as is shown in Fig. 109. 
 
 When the black ash is treated with water, the sodium carbonate is dissolved, 
 leaving the calcium sulphide,* and by evaporating the solution, and calcining the 
 residue, ordinary soda ash is obtained, f But this is by no means pure sodium car- 
 bonate, for it contains, in addition to a considerable quantity of common salt and 
 sodium sulphate, a certain amount of caustic soda, formed by the action of lime 
 (formed from the heating of the excess of limestone used) upon the carbonate. In 
 order to purify it, the crude soda ash is mixed with small coal or sawdust and again 
 heated, when the carbonic acid gas formed from the carbonaceous matter converts 
 the caustic soda into carbonate, and on dissolving the mass in water and evaporating 
 the solution, it deposits oblique rhombic prisms of common washing soda, having 
 the composition Na-jCOg. I oAq (soda crystals). 
 
 Hargreare's process dispenses with the use of sulphuric acid, and converts the 
 sodium chloride into sulphate by the action of sulphurous acid gas (obtained by 
 burning pyrites), steam, and air, at a dull red heat; 2NaCl + H 2 + S0 2 + = 
 Na2S0 4 + 2HCl. The hydrochloric acid is absorbed by water, as usual, and the 
 sodium sulphate converted into carbonate as described above. 
 
 A little reflection will show the important influence which this pro- 
 cess has exerted upon the progress of the useful arts in this country. 
 The three raw materials, salt, coal, and limestone, we possess in 
 abundance. The sulphuric acid, when the process was first introduced, 
 bore a high price, but the resulting demand for this acid gave rise to 
 so many improvements in its manufacture that its price has been very 
 greatly diminished a circumstance which has of course produced a 
 most beneficial effect upon all branches of manufacture in which the 
 acid is employed. 
 
 The large quantity of hydrochloric acid obtained as a secondary pro- 
 duct has been employed for the preparation of bleaching-powder, and 
 the important arts of bleaching and calico-printing have thence received 
 a considerable impulse. These arts have also derived a more direct 
 benefit from the increased supply of sodium carbonate, which is so 
 largely used for cleansing all kinds of textile fabrics. The manufactures 
 of soap and glass, which probably create the greatest demand for sodium 
 carbonate, have been increased and improved beyond all precedent by 
 the production of this salt from native sources. 
 
 Ammonia -soda process, or ftolvays process. This process for convert- 
 ting NaCl into Na,,C0 3 , which has almost completely superseded the 
 Leblanc process, depends upon the reaction between sodium chloride, 
 carbon dioxide, ammonia and water, NaCl + NH 3 + C0 2 + H 2 O = 
 NaHC0 3 + NH 4 C1. A solution of salt is saturated, first with ammonia 
 and then with carbon dioxide, whereupon sodium hydrogen carbonate 
 is precipitated. This is collected and calcined in order to convert it into 
 soda, ash; 2NaHC0 3 = Na 2 CO 3 + H 2 + C0 2 . The solution containing 
 NH 4 C1 is heated with lime to recover the ammonia 
 2NH 4 C1 + CaO = 2NH 3 + H 2 + CaCl 2 . 
 
 * The CaS in the waste is insoluble because combined with lime. 
 
 f Before evaporation, air is generally blown through the liquor to oxidise the sodium 
 sulphide which may remain unaltered (see p. 348, Sodium hydroxide). 
 
CHANCE'S SULPHUR RECOVERY PROCESS. 347 
 
 The brine pumped from the wells contains magnesium salts and other salts ; lime 
 is added to remove these, and the excess of lime is precipitated by ammonium car- 
 bonate. The liquor is then saturated with salt by addition of pure salt, and with 
 NH 3 by passing in this gas from the ammonia stills ; it is then made to flow down a 
 vertical iron cylinder containing perforated shelves and kept cool by water. C0. 2 is 
 pumped up this cylinder and meets the descending liquor, from which NaHC0 3 is 
 deposited and collected on the shelves, whence it falls as a sludge to the bottom of the 
 cylinder. The liquor from which the NaHC0 3 has separated is run into the ammonia 
 stills where it is heated with lime in order to recover the NH 3 . The CO 2 used in the 
 process is derived partly from the limekilns in which the lime for the ammonia stills 
 is burnt, and partly from the calcining of the NaHC0 3 to get 
 
 Recovery of waste in alkali manufacture. It is obvious that it should 
 be the object of every chemical manufacturer to utilise his raw materials 
 in such a manner that none of the elements in them shall ultimately 
 remain in an unmarketable form. A little reflection will show that in an 
 ideal process for making alkali, the only component of the raw materials 
 which should be finally rejected is the atmospheric nitrogen. In 
 practice, however, there has been, until lately, a large source of waste 
 in both the above processes. It will have been seen that in the Leblanc 
 process the whole of the sulphur of the H 2 SO 4 which is used makes its 
 appearance as CaS in the tank waste ; whilst in the ammonia-soda 
 process all. the chlorine in the salt makes its appearance as CaCl 2 in the 
 ammonia-still liquor. The tank waste and still liquor were originally 
 rejected, so that whilst the ammonia-soda process had the advantage 
 over the Leblanc process that it did not pay for sulphur which was 
 finally wasted, it had the accompanying disadvantage that it did not 
 recover the chlorine of the salt, which is a source of profit to the Leblanc 
 process. Whilst, therefore, CaS is the alkali ivaste of the older process, 
 CaCl., is that of the newer process, although since the sulphur is now 
 recovered from the CaS, and the Cl from the still liquor,* this term has 
 become a misnomer. It must be added that much of the soda in black 
 ash being in the form of caustic soda (see above), this product is more 
 easily made by the Leblanc process than by the ammonia-soda process ; 
 so that in many cases the Leblanc makers have ceased to produce 
 sodium carbonate, and are now manufacturers of caustic alkali, bleach- 
 ing-powder, and pure sulphur. The manufacture of chlorine and bleach 
 have been sketched on pp. 170 and 183, and the recovery of manganese 
 from the chlorine-still liquor on p. 170. 
 
 Recovery of sulphur from tank ivaste. This is now effected by Chance's 
 Access, which depends upon the fact that when carbon dioxide (lime-kiln 
 gases) is passed into alkali waste (CaS), made into a cream with water, 
 H 2 Sis evolved and CaC0 3 remains ; CaS + H 2 O + C0 2 = CaC0 3 + H 2 S.t 
 The sulphuretted hydrogen is mixed with a carefully regulated supply 
 of air and passed through a kiln (Claus kiln) containing some porous 
 material, when the hydrogen alone is burnt, the sulphur being subse- 
 quently deposited in condensing-chambers ; H 2 S + = H,O + S. The 
 CaC0 3 from this process is used again in making black ash. 
 
 Recovery of chlorine from ammonia-still liquor. When lime is used 
 in the ammonia stills calcium chloride remains in the liquor; it is 
 difficult to recover chlorine from this compound. If magnesia be 
 
 * Exact information as to the recovery of chlorine is not divulged, by the ammonia-soda 
 makers, but it is believed to have been successfully effected. 
 
 f An elaborate, systematically worked plant is essential in order that the evolved gas ir,ay 
 be as rich as possible in H 2 S. 
 
CAEBONATE OF SODA. 
 
 substituted for lime, magnesium chloride is left (2NH 4 Cl + MgO = 
 2NH 3 + H 2 + MgCl 2 ), from which chlorine may be recovered by the 
 Weldon-Pechiney process. This consists in mixing MgQ with the 
 concentrated MgCl 2 solution, whereby magnesium oxy chloride 
 (5MgO.4MgCl 2 ) is produced. This can be dried without . losing HC1, 
 which is not possible with MgCl., itself ; and when the dried mass is 
 heated in air at 1000 C., it gives up its chlorine in exchange for oxygen. 
 The MgO thus left is used again. 
 
 Mond seeks to prepare the MgCl 2 in a nearly anhydrous state by volatilising the 
 NH 4 C1 and passing the vapour over heated MgO, whereby NH 3 , H. 2 0, and MgCl 2 are 
 produced ; the first is used in the ammonia-soda plant, whilst the MgCl 2 may be 
 heated in air to yield MgO and Cl, as described above. The NH 4 C1 is obtained in 
 crystals by cooling the mother-liquor from the towers in which the NaHC0 3 is pre- 
 cipitated (see above). 
 
 Sodium carbonate, washing soda, Na 2 C0 3 .ioAq. The crystals of 
 sodium carbonate are easily distinguished by their property of efflor- 
 escing in dry air (p. 52), and by their alkaline taste, which is much 
 milder than that of potassium carbonate, this being, moreover, a 
 deliquescent salt. The crystals are very soluble in water, requiring 
 only 2 parts of cold, and less than their own weight of boiling water ; 
 the solution is strongly alkaline to test-papers. The crystals fuse at 
 50 C., evolve steam, and deposit a granular powder of the composition 
 Na 2 C0 3 .Aq (crystal carbonate). At a higher temperature it becomes 
 Na 2 CO 3 , and fuses at 850 C. If a solution of sodium carbonate be 
 crystallised between 30 and 50 C., the crystals are Na 2 C0 3 .7Aq. The 
 mineral natron found at the soda lakes of Egypt is Na 2 CO 3 .io Aq. The 
 chief impurities in soda crystals are NaCl and Na 2 S0 4 ; soda ash may 
 contain in addition NaOH and lsTa 2 S. 
 
 Bicarbonate of soda, or hydrogen sodium carbonate, NaHC0 3 , is 
 the substance commonly used in medicine as carbonate of soda. It is 
 prepared either by saturating the crystallised carbonate with CO 2 , or 
 by passing C0 2 through a strong solution of common salt mixed 
 with ammonia (see p. 346).* It forms small prismatic crystals much 
 less easily dissolved by water (8.85 per cent, at 15 C.) than the 
 carbonate. The solution is much less alkaline. When the solution 
 is heated it evolves CO 2 , and crystals of the sesquicarbonate 
 Na 2 C0 3 .NaHCO 3 .2Aq, may be obtained from it. A similar salt is the 
 mineral Trona. It has been seen that, when strongly heated, 2NaHC0 3 = 
 
 23 2 2 . 
 
 Potassium sodium carbonate, KNaC0 3 .6Aq, may be crystallised from 
 a mixture of solutions of the carbonates. 
 
 Soda lye, employed in the manufacture of hard soap, is a solution of 
 sodium hydroxide (NaOH), obtained by decomposing the carbonate 
 with calcium hydroxide (slaked lime); Na 2 C0 3 + Ca(OH) 2 = 2NaOH + 
 CaCO 3 . The solid NaOH of commerce, caustic soda, is prepared in the 
 Leblanc alkali process ; the solution obtained by treating the black ash 
 with water is causticised with lime, as represented in the above equation, 
 and concentrated by evaporation until it solidifies on cooling, at which 
 stage it is poured out into iron moulds. In properties it closely 
 
 * A saturated solution of NaCl mixed with one-third of its volume of NH 3 (sp. yr. 0.88) 
 and saturated with CO 2 >ives a copious precipitate of NaHCO 3 . 
 
ELECTEOLYSIS OF SALT. 
 
 349 
 
 resembles KOH ; its common impurities are carbonate, chloride, sul- 
 phate, and nitrite of sodium, sometimes accompanied by zinc oxide. 
 
 In practice, the tank liquor (from the black ash) is purified from sulphides before 
 it is causticised, partly by blowing air through it which oxidises the sulphides, 
 and partly by addition of zinc oxide which precipitates the sulphur as zinc 
 sulphide. The removal of the other salts (sulphate and chloride) occurs when the 
 caustic liquor is concentrated, for they then crystallise and may be fished out ; the 
 last traces of sulphide are oxidised by the addition of a little NaN0 3 to the melted 
 NaOH before it is cast. 
 
 Electrolytic production of alkali and chlorine. Since these main 
 products of the alkali industry contain much more chemical energy 
 than that of the salt from which they are derived, it is obvious that 
 they can only be obtained by transferring the chemical energy of other 
 substances, or by transforming some other kind of energy into chemical 
 energy. In the foregoing processes both these methods of procuring 
 the necessary energy are applied. There is an increasing tendency, 
 however, to apply electrical energy directly to the salt and thus to 
 convert it into the chemical energy of alkali and chlorine. There are 
 certain conveniences in converting heat energy first into electrical 
 energy, by means of a steam-engine and dynamo, and then applying 
 this electrical energy directly instead of the heat energy. But the use 
 of electrical energy has most to recommend it in places where dynamos 
 can be driven by the energy of running water. 
 
 Two methods of using the electrical energy present themselves : 
 (i) The current may be passed through fused salt, in which case the 
 sodium chloride will be electrolysed with separation of the sodium at 
 the cathode and chlorine at the anode. Since the heat of formation of 
 salt is Na,Cl = 97,7oo (p. 306), the electrical energy supplied must be 
 the equivalent of this heat energy. (2) The current may be used to 
 electrolyse a solution of salt, in which case hydrogen will appear at the 
 cathode instead of sodium (p. 324) while chlorine will be evolved at the 
 anode, as before. The reason why hydrogen is evolved from the cathode 
 may be said to be that the sodium at first liberated by the electrolysis 
 attacks the water forming NaOH and liberating hydrogen. As this 
 reaction is exothermic, viz., Na+ HOH = NaOH + 11 + 43,500, the 
 amount of electrical energy necessary to electrolyse the aqueous solution 
 is less than that required for the fused salt by the equivalent of this 
 amount of heat. Caustic soda being the product required, not sodium, 
 which when obtained must be treated with water to make the caustic, 
 it would seem preferable to electrolyse a solution of salt rather than 
 the fused material. 
 
 When fused salt is electrolysed the sodium must be collected in some solvent for 
 it, such as metallic lead, which is heavier than the liquid salt ; otherwise the 
 sodium would float to the surface and burn in the air or chlorine there present. 
 The cathode, therefore, consists of melted lead at the bottom of the crucible (of 
 iron lined with magnesia) containing the melted salt, and the anode is a carbon 
 rod immersed in the molten mass. Sodium is liberated at the cathode and dis- 
 solves in the melted lead, whilst chlorine is evolved at the anode and is led away 
 from the top of the crucible to a bleaching-powder chamber (p. 183). The alloy of 
 sodium and lead is treated with water to convert the Na into NaOH. 
 
 Instead of using a lead cathode the fused salt may contain lead chloride, so that 
 the alloy of lead and sodium is separated electrolytically at the carbon cathode and 
 sinks in the liquid salt. 
 
 When a solution of salt is electrolysed, the caustic soda collecting in solution 
 around the cathode is liable to mix with the saturated solution of chlorine collect- 
 
350 SODIUM. 
 
 ing around the anode, forming a solution of sodium of hypochlorite and chloride- 
 (p. 182), which has powerful bleaching properties (electrolytic bleacli). When the 
 anode and cathode are separated by a porous diaphragm the caustic soda liquor 
 may be drawn off and evaporated, whilst the chlorine may be conducted into lime 
 chambers. The diaphragm constitutes a serious difficulty in the process, as a 
 material which will satisfactorily resist the disintegrating effect of the electrolysis 
 does not exist. In the Castner-Kellner process the anode and cathode are separated 
 by a non-porous (and therefore less easily attacked) partition, which dips into a 
 layer of mercury ; in the anode compartment the mercury dissolves sodium, and 
 by rocking the vessel is made to flow to the cathode compartment where its sodium 
 is dissolved as caustic soda. Thus the vessel being continually rocked, the mercury 
 serves to convey the sodium from anode to cathode without allowing the liquids in 
 the compartments to mix. 
 
 184. Sodium. Potash and soda exhibit so much similarity in their 
 properties that we cannot be surprised at their having been confounded 
 together by the earlier chemists, and it was not till 17 36 that Du Hamel 
 pointed out the difference between them. The discovery of potassium 
 naturally led Davy to that of sodium, which can be obtained by processes- 
 exactly similar to those adopted for procuring potassium, to which it 
 will be remembered sodium presents very great similarity in properties 
 (p. 20). Sodium, however, is readily distinguished from potassium by 
 its burning with a yellow flame, which serves even to characterise it 
 when in combination. 
 
 This yellow flame is well seen by dissolving salt in water in a plate, and adding 
 enough alcohol to render it inflammable, the mixture being well stirred while 
 burning. A little piece of sodium burnt in an iron spoon held in a flame tinges- 
 yellow all the flames in the room, even at a remote distance. The blowpipe flame 
 may also be employed to detect sodium by this colour, as in the case of potassium 
 (p. 335). In fireworks, sodium nitrate is used for producing yellow flames. A 
 very good yellow fire may be made by carefully and intimately mixing, in a mortar, 
 74 grains of nitrate of soda, 20 grains of sulphur, 6 grains of sulphide of antimony,, 
 and 2 grains of charcoal, all carefully dried, and very finely powdered. 
 
 Sodium is manufactured by electrolysing fused caustic soda in an 
 iron vessel kept hot by a suitable furnace. Sodium and hydrogen are 
 separated at the cathode and oxygen at the anode. 
 
 The iron cathode is surrounded by iron wire gauze terminating at the surface of 
 the liquid in an inverted pot in which the sodium and hydrogen collect as they rise 
 through the liquid. The anode is an iron cylinder surrounding the gauze. The 
 object of the latter is really that of a porous diaphragm to keep the cathode and 
 anode products apart ; the reason why a material with such large pores can be used 
 is because the fused sodium has a high surface tension and will not pass through 
 the gauze. When sufficient sodium has collected in the inverted pot, the bottom 
 of this is removed and the metal ladled out. 
 
 Sodium is a whiter metal than potassium ; its sp. gr. is 0.973 '> & 
 melte at 95. 6 0., and boils at 742 C. When heated in air, it gives 
 a mixture of Na 2 O and Na 2 2 , which is converted into NaOH by 
 water, being evolved from the Na 2 2 . If water be gradually added 
 to Na 2 O 2 , it dissolves, and the solution yields crystals of Na 2 2 .8H 2 O. 
 
 Sodium is not attacked by perfectly dry chlorine, dry bromine, or dry 
 oxygen, but if a trace of aqueous vapour be present, combination occurs 
 with violence. When mixed with 10 to 30 per cent, of its weight of 
 potassium, sodium yields an alloy which is liquid at temperatures above 
 o 0. and is used for filling thermometers. 
 
 Sodium is far less costly than potassium, and is used on the large 
 scale for making sodium peroxide. An amalgam of sodium (p. 85) is 
 
GLAUBER'S SALT. 351 
 
 also employed with advantage in extracting gold and silver from their 
 ores. 
 
 Sodium hydride is similar to the potassium compound (p. 335). 
 
 Sodium peroxide, Na 2 2 , is manufactured by causing slices of sodium, disposed 
 on trays of aluminium (which is not attacked), to pass through a hot (400 C.) 
 tunnel which is traversed in the contrary direction by a current of dry air, freed 
 from C0. 2 . It is a yellowish- white powder much used as an oxidising and bleaching 
 agent. 
 
 Sodium chloride, NaCl, forms rock salt and table salt, the latter 
 consisting of minute crystals formed by boiling down the water of brine 
 springs (see p. 343). It forms cubical, anhydrous crystals of sp. gr, 
 2.15, and is almost equally soluble in hot and cold water ; 100 parts of 
 water at 15 C. dissolve 36 parts of salt, at 100 39 parts. It is in- 
 soluble in alcohol. It melts at 772 C., and is afterwards vaporised. 
 It forms two cryohydrates, NaC1.2Aq, deposited from a saturated solu- 
 tion cooled to - 10 C., and NaCl.ioAq, deposited at - 22 C. They 
 are decomposed at higher temperatures. Needles of Na01.2Aq are 
 obtained from a solution of salt in hot HC1. 
 
 Sodium fluoride, NaF, made by fusing fluor spar (CaF 2 ) with Na.,00^ 
 is used for softening boiler feed waters. 
 
 The sulphides of sodium are similar to those of potassium. 
 
 Sodium sulphate is found anhydrous as Thenardite. Glauber's salt, 
 Na 2 S0 4 .ioAq, is made by crystallising salt cake. It forms prismatic 
 crystals which effloresce in air, fuse at 33 C., and becomes anhydrous at 
 100. It is more soluble in water at 33 C. than at any other tempera- 
 ture, 100 parts of water dissolving 115 parts of the crystals. When 
 this solution is heated, it deposits anhydrous, Na 2 S0 4 , the temperature, 
 33 C., being the transition-point (p. 315) between the hydrate and the 
 anhydrous salt. When cooled quietly in a covered vessel, the solution 
 exhibits, in a high degree, the phenomenon of super saturation (p. 50), 
 and when the supersaturated solution is cooled to 5 C. crystals of 
 Na 2 S0 4 .7Aq may be obtained. The crystals of Na 2 S0 4 .ioAq, with half 
 their weight of strong HC1, form an excellent freezing-mixture, giving 
 the same temperature as ice and salt (18 C., o F.) 
 Na 2 S0 4 .ioAq + HC1 = NaHS0 4 + NaCl + loAq. 
 
 Anhydrous Na 2 S0 4 melts at 865 C. ; the double salt Na 2 S0 4 K 2 S0 4 
 crystallises in plates (plate sulphate) from hot water, a flash of light 
 accompanying the separation of each crystal. 
 
 Glauberite is Na 2 Ca(S0 4 ) 2 , and is nearly insoluble in water. 
 
 Hydrogen sodium sulphate, NaHS0 4 , or bisulphate of soda, crystallises 
 in prisms with lAq. It is more fusible and more easily decomposed by 
 heat than is KHS0 4 . It is decomposed by alcohol into H 2 S0 4 , and 
 Na 2 S0 4 , which remains undissolved. When moderately heated, 
 2NaHSO 4 = H 2 O + Na 2 S 2 7 (pyrosulphate}, decomposed by a red heat 
 into Na.,S0 4 and S0 3 . Sodium pyrosulphate is also formed when NaCl 
 is heated with S0 3 ; 2 NaCl + 380, = Na 2 S 2 O 7 + S0 2 C1 2 . 
 
 Sodium sulphite crystallises in prisms, Na 2 S0 3< 7Aq, which are very 
 soluble in water, yielding an alkaline solution. It is prepared by satu- 
 rating one-half of a solution of Na 2 C0 3 with SO 2 gas, and adding the 
 other half 
 
 (1) Na^COg + 2S0 2 + H 2 = 2NaHS0 3 + C0 ; 
 
 (2) 2NaHS0 3 + Na^CO-j = 2Na,jS0 3 + H 2 + C0 2 . 
 
352 BOEAX. 
 
 The sodium sulphite is useful in the laboratory as a reducing-agent 
 (p. 221), and the hydrogen sodium sulphite (bisulphite), NaHS0 3 , is used in 
 organic chemistry and by the brewer. 
 
 Sodium, thiosulphate, Na 2 S 2 O 3 , or hyposulphite of soda, crystallises 
 in glassy prisms, Na 2 S 2 3 .5Aq, the preparation and properties of which 
 have been described at p. 235. 
 
 Sodium thiosulphate is much used in photography for fixing prints 
 by dissolving the unaltered portion of the sensitive film of silver chloride, 
 bromide, or iodide. It is also used by bleachers as an antichlore. 
 
 Phosphate of soda, or hydrogen disodium phosphate, HNa 2 P0 4 , 
 crystallises in prisms, Na 2 HP0 4 . 12 Aq, which effloresce in air and dis- 
 solve easily in water, giving an alkaline solution. When heated, they 
 fuse easily, and lose the i2Aq at 45 C. ; at a red heat, 2Na 2 HP0 4 = 
 H 2 + Na 4 P 2 O 7 (pyrophosphate). 
 
 Na.,HPO 4 occurs in the blood and in urine. It is prepared by de- 
 composing a mineral phosphate, which contains Ca 3 (P0 4 ) 2 , with H 2 S0 4 , 
 so as to obtain the insoluble CaS0 4 and a solution of impure H 3 PO 4 . 
 This is decomposed by Na 2 C0 3 , the solution filtered from the small 
 quantity of CaC0 3 , evaporated and crystallised 
 
 H 3 P0 4 + NaaCOg = Na^HP0 4 + H 2 + C0 2 . 
 
 Arsenate of soda, or hydrogen disodium arsenate, HNa 2 As0 4 , forms 
 crystals with i2Aq, resembling those of the phosphate, but the salt as 
 commonly sold contains yAq. There exists also the salt Na 2 HP0 4> 7Aq, 
 but this is not that commonly sold. 
 
 Sodium arsenate is made by dissolving white arsenic in caustic soda, 
 adding sodium nitrate, evaporating to dryness, heating the residue to 
 iredness and dissolving in water 
 
 (1) As 4 6 + !2NaOH = 4Na 3 As0 3 + 6H 2 ; 
 
 (2) Na 3 As0 3 + NaN0 3 = Na 3 As0 4 + NaNOo 
 
 (3) Na 3 As0 4 + H 2 = Na^HAsC^ + NaOH. 
 
 185. Borax, biborate of soda (Na 2 0.2B 2 3 ), or sodium pyroborate 
 ; (Na 2 B 4 7 ). It has already been stated that borax is deposited during 
 the evaporation of the waters of certain lakes in Thibet, whence it is 
 imported into this country in impure crystals (tincal), which are covered 
 with a peculiar greasy coating. Borax has also been found abundantly 
 in Southern California. 
 
 The refiner of tincal powders the crystals and washes them, upon a strainer, 
 with a weak solution of soda, which converts the greasy matter into a soap and 
 dissolves it. The borax is then dissolved in water, a quantity of sodium carbonate 
 is added to separate some lime which the borax usually contains, and, after 
 filtering off the carbonate of lime, the solution is evaporated to the crystallising 
 point and allowed to cool, in order that it may deposit the pure crystals of borax. 
 Boracite, 2Ca0.3B 2 3 , from Asia Minor, is frequently used as a raw material for 
 making borax ; the mineral is boiled with Na^COg, the CaC0 3 filtered, and the 
 solution crystallised. 
 
 Borax is manufactured in this country by heating sodium carbonate with boric 
 acid, when the latter expels the carbonic acid.* The mass is then dissolved in 
 water, and the borax crystallised, an operation upon which much care is bestowed, 
 since the product does not meet with a ready sale unless in large crystals. The 
 solution of borax, having been evaporated to the requisite degree of concentration, 
 is allowed to crystallise in covered wooden boxes, which are lined with lead and 
 
 * The ammonia which is evolved from the Tuscan boracic acid employed in this process 
 is known in commerce as Volcanic ammonia, and is free from the empyreumatic odour which 
 generally accompanies that from coal and bones. 
 
CHILI SALTPETEE. 353 
 
 enclosed in an outer case of wood, the space between the sides of the case and 
 the box being stuffed with some bad conductor of heat, so that the solution of 
 borax may cool very slowly, and large crystals may be deposited. In about thirty 
 hours the crystallisation is completed, when the liquid is drawn off as rapidly as 
 possible, the last portion being carefully soaked up with sponges, so that no small 
 crystals may be afterwards formed upon the surface of the large ones ; the case is 
 then again covered up, so that the crystals may cool slowly without cracking. 
 When a solution of borax is crystallised above 56 C., it yields octahedral borax, 
 Na 2 B 4 7 .5Aq. which is also deposited when solution of prismatic borax is evaporated 
 in vacua. 
 
 The ordinary prismatic crystals of borax are represented by the 
 formula Na 2 B 4 O r .ioAq. They soon effloresce and become opaque when 
 exposed to air, and may readily be distinguished by their alkaline taste 
 and action upon test-papers, and especially by their behaviour when 
 heated, for they fuse easily and intumesce most violently, swelling up to 
 a white spongy mass of many times their original bulk ; this mass 
 afterwards fuses down to a clear liquid which forms a transparent 
 glassy mass on cooling (vitrejied borax), and since this glass is capable of 
 dissolving many metallic oxides with great readiness (borax being, by 
 constitution, an acid salt, and therefore ready to combine with more 
 base), it is much used in the metallurgic arts. Large quantities of borax 
 are also employed in glazing stoneware. 
 
 A dilute solution of borax dissolves iodine to a colourless solution, but on con- 
 centration the iodine is precipitated ; probably the borax is decomposed in the 
 dilute solution into boric acid and soda, which converts the iodine into iodide and 
 iodate ; on concentrating, the boric acid liberates hydriodic and iodic acids, which 
 react with each other, separating iodine (p. 200). 
 
 Sodium nitrate or nitrate of soda, NaN0 3 , also known as Peruvian 
 Chili saltpetre, is found in Peru and Chili in beds beneath the surface 
 soil, where it is dug out and crystallised from water. It is often spoken 
 of as cubical saltpetre, since it crystallises in rhombohedra, easily mis- 
 taken for cubes, whilst prismatic saltpetre, nitrate of potassium, crystal- 
 lises in six-sided prisms. Sodium nitrate cannot be substituted for 
 potassium nitrate as an ingredient of gunpowder, since it attracts 
 moisture from the air, becoming damp, and is less powerful in its 
 oxidising action upon combustible bodies at a high temperature. It is, 
 however, used for making potassium nitrate for gunpowder (p. 337), 
 A much more extended application is its use as a manure, for supplying 
 nitrogen ; large quantities are also used for making nitric acid. It 
 melts at 320 C. and dissolves in water to the extent of 87 per cent, at 
 20 C. and 180 per cent, at 100 C. 
 
 Sodium nitrite, NaN0 2 , is much used for diazotising organic amides (p. 106). It 
 is made by heating NaN0 3 to 420 C. in an iron vessel and stirring the molten 
 mass with metallic lead ; NaN0 3 + Pb = NaN0 2 + PbO. It crystallises in 
 colourless deliquescent prisms very soluble in water ; the solution of the commercial 
 salt is generally alkaline owing to the presence of a small quantity of caustic soda, 
 but the pure salt is neutral. 
 
 Sodium silicate. A combination of soda with silica has long been 
 used, under the name of soluble glass, for imparting a fire-proof character 
 to wood and other materials, and, more recently, for producing artificial 
 stone for building purposes, and for a peculiar kind of permanent fresco- 
 painting (stereochromy), the results of which are intended to withstand 
 exposure to the weather. 
 
 Sodium metasllicate has been obtained in prismatic crystals, Na^SiOg-SAq, by 
 
 z 
 
354 AMMONIUM SALTS. 
 
 dissolving amorphous silica in NaOH. It is soluble in water, and the solution is 
 decomposed by C0 2 . A solution of amorphous Si0 2 in hot aqueous Na 2 C0 3 
 gelatinises, on cooling. 
 
 Soluble glass is usually prepared by fusing 15 parts of sand with 8 parts of 
 carbonate of soda and I part of charcoal. The silicic acid, combining with the 
 oda, disengages the carbonic acid gas, the expulsion of which is facilitated by the 
 presence of charcoal, which converts it into carbonic oxide. The mass thus formed 
 is scarcely affected by cold water, but dissolves when boiled with water, yielding a 
 strongly alkaline liquid. 
 
 In using this substance for rendering wood fire-proof, a rather weak solution is 
 first applied to the wood, and over this a coating of lime-wash is laid ; a second 
 coating of soluble glass (in a more concentrated solution) is then applied. The 
 wood so prepared is, of course, charred, as usual, by the application of heat, but 
 its inflammability is remarkably diminished. 
 
 For the manufacture of Ransome's artificial stone, the soluble glass is prepared by 
 heating flints, under pressure, with a strong solution of caustic soda, to a tempera- 
 ture between 300 and 400 F. (149 and 204 C.), when the silica constituting the 
 flint enters into combination with the soda. Finely divided sand is moistened 
 with this solution, pressed into moulds, dried, and exposed to a high temperature, 
 when the silicate of soda fuses and cements the grains of sand together into a mass 
 of artificial sandstone, to which any required colour may be imparted by mixing 
 metallic oxides with the sand before it is moulded. 
 
 Silicate of soda is also sometimes used as a dung substitute in calico-printing (q.v.). 
 
 Sodium chlorate, NaC10 3 , resembles the potassium salt, but is very soluble, and is 
 on this account preferred for some purposes. It is made by substituting Na 2 S0 4 for 
 KC1 in the method described on p. 184 for making KC10 3 . 
 
 SALTS OF AMMONIUM. 
 
 1 86. The great chemical resemblance between some of the salts formed 
 by neutralising acids with ammonia, and the salts of potassium and 
 sodium, has been already pointed out as affording a reason for the 
 hypothesis of the existence of a compound metal, ammonium (NH 4 ), 
 equivalent in its functions to potassium and sodium (p. 85). 
 
 The compounds which are formed when ammonia (NH 3 ) combines 
 with the anhydrides, such as carbonic (CO,) and sulphuric (SO 3 ), do not 
 exhibit the resemblance to the salts of potassium and sodium until water 
 is added. Thus, by the action of dry ammonia gas upon sulphuric 
 anhydride, a compound called sulphuric ammonide is formed, having the 
 composition (NH 3 ) 2 S0 3 . This substance dissolves in water and crystal- 
 lises in octahedra, but its solution is not precipitated by barium chloride, 
 which always precipitates the true sulphates, nor by platinic chloride, 
 which precipitates the true ammonium salts. By long boiling with 
 water, however, it becomes ammonium sulphate, (NH 4 ) 2 S0 4 , which 
 yields precipitates with both the above tests.* The phosphoric, carbonic, 
 and sulphurous anhydrides also combine with nearly dry ammonia to 
 form ammonides, which do not respond to the ordinary tests for the 
 corresponding salts of ammonium until after water has been assimilated. 
 The true salts of ammonium are produced either by the combination of 
 an acid with ammonia, or by double decomposition. 
 
 Ammonium nitrate, NH 4 N0 3 , is prepared by neutralising ordinary 
 nitric acid with lumps of ammonium carbonate, when the nitrate 
 crystallises on cooling in six-sided prisms like those of KN0 3 , but they 
 are deliquescent and very soluble in water ; it absorbs one-third of its 
 
 1 * Representing sulphuric acid as sulphuryl hydroxide, SO 2 .OH.OH, ammonium sulphate is 
 SO 2 .ONH 4 .ONH 4 , and sulphuric ammonide is SO 2 .XB 2 .ONH 4 , the amidogen group, NH 2 , 
 being substituted for the ammon-oxyl group, O(NH 4 ). 
 
AMMONIUM CARBONATE. 
 
 355 
 
 weight of ammonia and becomes liquid, the ammonia being expelled 
 again at 25 C. When gently heated, it melts at 150 C., and is de- 
 composed at 210 0., when it boils and passes off entirely as water and 
 nitrous oxide ; N H 4 NO ? = 2 H 2 + N 2 0. If sharply heated, as by throw- 
 ing it on a red-hot surface, it deflagrates. If very carefully heated, it 
 may be sublimed. It is largely used for making nitrous oxide, and is 
 a constituent of some explosives.* 
 
 Ammonium nitrite, NH 4 N0 2 , is interesting on account of its easy decomposition 
 by heat ; NH 4 N0 2 = N 2 + 2H 2 0. This occurs even on boiling the solution, so that 
 a mixture of solutions of potassium nitrite and ammonium chloride is used for 
 preparing nitrogen, Ammonium nitrite is found, in very small quantity, in rain 
 water ; it can also be detected in the water condensed from hydrogen burning in 
 air. Ammonia is partly converted into this salt when oxidised by ozone or even 
 by air in presence of heated platinum ; 2NH 3 + 3 = NH 4 N0 2 + H 2 0. 
 
 187. Ammonium sulphate, (NH 4 ) 2 S0 4 , is largely employed in the 
 preparation of ammonia alum, and as an artificial manure, for which 
 purposes it is generally obtained from the ammoniacal liquor of the 
 gas-works by distillation with lime and absorption of the liberated 
 ammonia in H 2 SO 4 . The rough crystals are gently heated to expel 
 tarry substances, and purified by recrystallisation. The crystals have 
 the same shape as those of potassium sulphate, and are easily soluble in 
 water, but not in alcohol. When heated to about 260 C., the 
 (NH 4 ) 2 S0 4 is decomposed, yielding vapour of ammonium sulphite, water, 
 ammonia, nitrogen, and sulphur dioxide. If muslin be dipped into a 
 solution of ammonium sulphate in ten parts of water and dried, it will 
 no longer burn with flame when ignited. The mineral mascagnine 
 consists of ammonium sulphate. This salt is occasionally found in 
 needle-like crystals upon the windows of rooms in which coal gas is 
 burnt, 
 
 1 88. Ammonium carbonate, also called smelling salts, or Preston 
 salts, is largely used in medicine, and by bakers and confectioners, for im- 
 parting lightness or porosity to cakes, &c. It is commonly prepared by 
 mixing ammonium sulphate with twice its weight of chalk, and distilling 
 the mixture in an earthern or iron retort, communicating, through an 
 iron pipe, with a leaden chamber or receiver, in which the ammonium 
 carbonate collects as a transparent fibrous mass, which is extracted by 
 taking the receiver to pieces, and purified by resubliming it in iron 
 vessels surmounted by leaden domes. The action of calcium carbonate 
 upon ammonium sulphate would be expected to furnish the normal 
 carbonate, (NH 4 ) 2 C0 3 , but this salt (even if produced) is decomposed by 
 the heat employed in the process into hydrogen ammonium carbonate, 
 OO(ONH 4 )(ONH 4 ) = CO(ONH 4 )(OH) + NH 3 , and ammonium car- 
 bamate, CO(ONH 4 )(ONH 4 ) = CO(ONH 4 )(NH S ) + H 2 0. 
 
 The commercial carbonate is usually a mixture of 2 mols. of the 
 former to one of the latter. By treating it with strong alcohol, the 
 carbamate is dissolved and the hydrogen ammonium carbonate left. 
 
 When exposed to the air it smells of ammonia, and gradually be- 
 comes NH 4 HC0 3 or CO(ONH 4 )(OH), the carbamate being decomposed 
 and volatilised; CO(ONH 4 )(NH 2 ) = C0 3 + 2NH 3 . On treating the 
 commercial carbonate with a little water, the NH 4 HC0 3 is left un- 
 
 * The explosive Bellite consists of 5 parts of ammonium nitrate and i part of di-uitro- 
 bcnzene (q.v.) ; it is said to be 30 per cent, stronger than dynamite, and to explode only by 
 detonation. 
 
SAL AMMONIAC, 
 
 dissolved, whilst the car bam ate is converted into normal carbonate and 
 dissolved ; CO(ONH 4 )(NH 2 ) + H 2 O = (NH 4 ) 2 C0 3/ 
 
 Sal volatile is an alcoholic solution of ammonium carbonate and car- 
 bamate. 
 
 By saturating ammonia solution with C0 2 , crystals of ammonium 
 sesquicarbonate, (NH 4 ) 2 CO 3 .2NH 4 HC0 3 are obtained. 
 
 Ammonium carbonate, (NH 4 ) 2 C0 3 , is obtained in crystals by treating the com- 
 mercial carbonate with strong ammonia. The crystals contain lAq. They are 
 deliquescent in air, and evolve NH 3 , becoming converted into the bicarbonate ; 
 (NH 4 ) 2 C0 3 = NH 3 + NH 4 HC0 3 . 
 
 Ammonium bicarbonate, NH 4 HC0 3 or hydrogen ammonium carbonate, is the most 
 stable, and is obtained by dissolving the commercial carbonate in a little boiling 
 water, when it crystallises on cooling. 
 
 The ammonium carbamate is deposited as a white solid when ammonia gas is. 
 mixed with carbonic acid gas, unless both be quite dry. It may be obtained in 
 crystals by passing C0 2 and NH 3 into the strongest solution of ammonia. 
 
 Ammonium carbamate is easily soluble in water, which soon converts it into 
 ammonium carbonate. The aqueous solution, when freshly prepared, is not pre- 
 cipitated by calcium chloride, but the calcium carbonate is deposited on standing 
 or heating. When ammonium carbamate is heated in a sealed tube at 130 C. it 
 is decomposed into ammonium carbonate and urea; 2NH 4 C0 2 NH 2 =(JSTH 4 ) 2 C0 3 + 
 CON 2 H 4 . Carbamic acid, HC0 2 NH 2 , has not been isolated ; its relation to carbonic 
 acid is seen by a comparison of their formulae ; carbonic acid, CO. OH. OH ; 
 carbamic acid, CO.OH.NH 2 . Other carbamates have been obtained by passing 
 C0 2 through strongly ammoniacal solutions of different bases, and precipitating 
 the carbamates by alcohol. When potassium carbamate is heated, it yields water 
 and potassium cyanate ; KC0 2 NH 2 = KCNO + H 2 0. 
 
 Carbamates are remarkable for evolving nitrogen when treated with a mixture of 
 soda and sodium hypobromite, but not with the hypochlorite ; thus 
 
 2(CO.NH 2 .ONa) + sNaOBr + 2NaOH = 2CO(ONa) 2 + sNaBr + sH 2 +N 2 . 
 If solution of sodium carbamate be mixed with sodium hypochlorite and" soda, no 
 nitrogen is evolved until a soluble bromide is added, a reaction which will indicate 
 bromides even in dilute solutions. The solution of sodium carbamate may be pre- 
 pared by dissolving ammonium carbamate in a strong solution of soda, and 
 evaporating over strong sulphuric acid. 
 
 189. Ammonium chloride (NH 4 C1), also called muriate of ammonia 
 and sal ammoniac. When ordinarily dry NH 3 is brought in contact 
 with an equal volume of dry HC1, it has been seen (p. 84) that they 
 combine directly to produce this salt, the preparation of which on the 
 large scale has been noticed at p. 78. Its commercial form is that of 
 a very tough translucent fibrous mass, generally of the dome -like 
 shape of the receivers in which it has been condensed, and often 
 striped with brown, from the presence of a little iron. It has not the 
 least smell of ammonia, and is very soluble in water, requiring about 
 three parts of cold water, and little more than its own weight of boiling 
 water. As the hot solution cools, it deposits beautiful fern-like 
 crystallisations composed of minute cubes and octahedra. The dis- 
 solution of sal ammoniac in water lowers the temperature very con- 
 siderably, which renders the salt very useful in freezing-mixtures. A 
 mixture of equal weights of sal ammoniac and nitre, dissolved in its 
 own weight of water, lowers the temperature of the latter from 10 
 to - 12 C. In this case partial decomposition occurs, resulting in the 
 production of potassium chloride and ammonium nitrite, both of which 
 absorb much heat whilst being dissolved by water. The solution of 
 ammonium chloride in water is slightly acid to blue litmus-paper. 
 When sal ammoniac is heated, it vaporises, at a temperature below 
 redness, without fusing ; the vapour forms thick white clouds in the 
 
SULPHIDES OF AMMONIUM. 357 
 
 air, and may be condensed as a white crust upon a cold surface ; but it 
 is said that it cannot be sublimed without some loss, a portion being 
 decomposed into HC1, H and N. 
 
 As already stated (p. 85), ammonium chloride dissociates when 
 heated, so that the heat which becomes latent or is absorbed in vapor- 
 ising the NH 4 C1, is almost exactly that which is produced by the com- 
 bination of the hydrochloric acid and ammonia, viz., NH 3 , HC1 = 42,000. 
 
 When ammonium chloride is heated with metallic oxides, the hydro- 
 chloric acid often converts the oxide into a chloride which is either 
 fusible or volatile, so that sal ammoniac is often employed for cleansing 
 the surfaces of metals previously to soldering them. Even those metallic 
 oxides which are destitute of basic properties, such as antimonic and 
 stannic oxides, are convertible into chlorides by the action of sal am- 
 moniac at a high temperature. 
 
 Ammonium chloride is found in volcanic districts, and is present in 
 very small quantity in sea water. 
 
 190. Hydrosulphate of ammonia, 2NH 3 .H 2 S, or ammonium sul- 
 phide, (NH 4 ) 2 S, has been obtained in colourless crystals by mixing 
 hydrosulphuric acid gas with twice its volume of ammonia gas in a 
 vessel cooled by a mixture of ice and salt.* It is a very unstable com- 
 pound, decomposing in solution into free ammonia and ammonium 
 hydrosulphide, NH 4 HS, which may also be obtained in solution by 
 saturating with H 2 S at o C. strong ammonia diluted with four times 
 its volume of water. 
 
 Solution of ammonium sulphide, prepared by mixing the " hydrosulphide " 
 (made by saturating ammonia solution with H 2 S) with an equal volume of 
 ammonia, is much used in analytical chemistry, and is supposed to contain 
 (NH 4 ) 2 S. The solution has a very disagreeable odour. 
 
 When a strong solution of ammonia is saturated with hydrogen sulphide at o C., 
 a colourless solution is formed, from which colourless crystals separate, the com- 
 position of which varies with the strength of the ammonia, but may be expressed by 
 the general formula, (NH 4 ) 2 S.a;-NH 4 HS. The solution soon becomes yellow in con- 
 tact with the air, from the formation of ammonium poly sulphides of the form 
 (NH^Stf ; eventually the solution deposits sulphur and becomes colourless, thio- 
 sulphate, sulphite, and sulphate of ammonium being formed. When the freshly 
 prepared colourless solution is mixed with an acid, the solution remains clear, H 2 S 
 being evolved with effervescence ; NH 4 HS + HC1 = NH 4 C1 + H 2 S and (NH 4 ) 2 S + 
 2HC1 = 2NH 4 C1 + H 2 S ; but if the solution be yellow, a milky precipitate of sulphur 
 is produced, from the decomposition of the polysulphides ; (NH 4 ) 2 S a! 
 
 The fresh solution gives a black precipitate of lead sulphide when solution of 
 lead acetate is added to it, but after it has been kept till it is of a dark yellow or 
 red colour, it gives a red precipitate of the persulphide of lead. 
 
 Ammonium polysulphides are the chief constituents of Boyle's fuming liquor, a 
 fetid yellow liquid obtained by distilling sal ammoniac with sulphur and lime. 
 They are sometimes deposited in yellow crystals from this liquid. By dissolving 
 sulphur in ammonium disulphide, orange-yellow prismatic crystals of ammonium 
 pentasulphlde, (NH 4 ) 2 S 5 , maybe obtained. 
 
 Ammonium bromide (NH 4 Br) and ammonium iodide (NH 4 I) are useful in pho- 
 tography. They are both colourless crystalline salts, but the iodide is very liable 
 to become yellow or brown, from the separation of iodine, unless kept dry and in 
 the dark. Both salts are extremely soluble in water. 
 
 Microcosmic salt, phosphorus salt, or hydrogen sodium ammonium phosphate, 
 HNaNH 4 P0 4 .4Aq, is found in putrid urine and in guano. It is prepared by mixing 
 hot strong solutions of ammonium chloride and sodium phosphate 
 
 NH 4 C1 = HNaNH 4 P0 4 + NaCl. 
 
 * When the NH 3 is in large excess a volatile liquid, (NH 4 ) 2 S.2NH 3 , is formed, the vapour 
 of which is very poisonous. 
 
RUBIDIUM AND CAESIUM. 
 
 It forms prismatic crystals which are very soluble and fusible, boiling violently 
 when further heated, and finally leaving a transparent glass of sodium meta- 
 phosphate, which is valuable in blowpipe work for dissolving metallic oxides ; 
 NaNH 4 HP0 4 = NH 3 + H 2 + NaP0 3 . 
 
 LITHIUM. 
 
 Li = 7 parts by weight. 
 
 191. This comparatively rare metal is obtained chiefly from the minerals lepido- 
 lite (\eirls, a scale) or lithia-mica, containing silicate of alumina with fluorides of 
 potassium and lithium ; petallte (-rr6Ta\ov, a leaf), silicate of soda, lithia, and 
 alumina ; and triphane or spodumene (crTroSds, aslies), which has a similar composi- 
 tion. Its name (from \ldos, a stone] was bestowed in the belief that it existed 
 only in the mineral kingdom, but recent investigation has detected it in minute 
 proportion in the ashes of tobacco and other plants. The water of a hot spring in 
 Clifford United Mines, in Cornwall, contains 26 grains of lithium chloride per 
 gallon. 
 
 Metallic lithium is obtained by decomposing fused lithium chloride by a gal- 
 vanic current. It is remarkable as the lightest solid known (sp. gr. 0.59). It 
 bears a general resemblance to potassium and sodium, but it is harder and less 
 easily oxidised than those metals. It decomposes water rapidly at the ordinary 
 temperature, but does not inflame upon it. It melts at 186 C., but cannot be 
 distilled. 
 
 Lithium bears some resemblance to calcium as well as to potassium and sodium. 
 Thus it forms an oxide, L1 2 0, when it burns, which is earthy, and dissolves only 
 gradually in water, unlike oxides of K and Na. The hydroxide LiOH, obtained 
 by causticising the carbonate with lime, is less soluble than KOH and NaOH and 
 a less powerful alkali. Another leaning towards the calcium group of metals is 
 seen in the sparing solubility of lithium phosphate, Li 3 P0 4 (i in 2500), and car- 
 bonate, Li 2 C0 3 (i in 100). The latter, however, is not decomposed by heat as 
 calcium carbonate is ; it is made from lepidolite by fusing the mineral, powdering 
 it, boiling with HC1 and HN0 3 and precipitating the iron lime, &c., by Na^COg ; 
 the filtrate contains NaCl, KC1, and LiCl ; it is concentrated and mixed with 
 Na 2 C0 3 to precipitate the Li 2 C0 3 . 
 
 The "lithia" used as a remedy for gout is a mixture of lithium carbonate and 
 citric acid, the latter dissolving the former as lithium citrate with effervescence 
 when the mixture is put in water. 
 
 The compounds of lithium impart a red colour to a flame. 
 
 RUBIDIUM AND CAESIUM. 
 Rb' = 84.8 parts by weight, Cs' = i32 parts by weight. 
 
 192. These elements were discovered in 1860, by Bunsen and Kirchhoff, during the 
 analysis of a certain spring water which contained these metals in so minute quantity 
 (2 or 3 grains in a ton) that they would certainly have escaped observation if the 
 analysis had been conducted in the ordinary way. The discovery of these metals, 
 as well as of three others (thallium, indium, gallium), to be mentioned hereafter, 
 was the result of the application of the method of spectrum analysis (see p. 329). 
 
 When examining, with the spectroscope, the alkali chlorides extracted from the 
 spring water, Bunsen and Kirchhoff observed two red and two blue bands in the 
 spectrum, which they could not ascribe to any known substance, and which they 
 ultimately traced to the two new metals, rubidium (rubidus, I dark-red) and CEesium 
 (ccesius, sky-blue), which may be isolated by the electrolysis of their fused salts, or 
 by distilling them from a mixture of their hydroxides with magnesium. 
 
 Rubidium (m. p. 38 ; sp. gr. 1.52) has since been found in small quantity in 
 carnallite, in lepidolite, and in the ashes of many plants. This metal is closely 
 related in properties to potassium, but is more easily fusible and convertible into 
 vapour, and actually surpasses that metal in its attraction for oxygen, rubidium 
 taking fire spontaneously in air, forming Rb0 2 . It burns on water with exactly 
 the same flame as potassium. Its hydroxide is a powerful alkali, like potash, and 
 its salts are isomorphous with, and more soluble than, those of potassium. The 
 double chloride of platinum and potassium is eight times as soluble in boiling water 
 as the corresponding salt of rubidium, which is taken advantage of in separating 
 these two 'allied metals. Rubidium forms stable and sparingly soluble double salts 
 
REVIEW OF THE ALKALI METALS. 359 
 
 with many halides ; thus the borofluoride, RbBF 4 , requires 100 parts of boiling 
 water to dissolve it. 
 
 Caesium (m. p. 27 ; sp. gr. 1.88) appears to be even more highly electro-positive 
 than rubidium, forming a strong alkali, caesium hydroxide, and salts which are 
 isomorphous with those of potassium. Caesium carbonate, however, is soluble in 
 alcohol, which does not dissolve the carbonates of potassium and rubidium. 
 Moreover, the caesium bitartrate is nine times as soluble in water as the rubidium 
 bitartrate is. 
 
 Caesium has been found in lepidolite ; and the rare mineral pollux, found in 
 Elba, and resembling felspar in composition, is said to contain a very large quantity 
 of this metal. The alum of the island of Vulcano is mentioned as a rich source of 
 caesium and rubidium. 
 
 Metallic caesium cannot be obtained by reduction with carbon, but it has 
 been extracted by decomposing its cyanide by the galvanic current. 
 
 Both rubidium and caesium show a remarkable tendency to combine with halo- 
 gens as though they were trivalent or pentavalent, forming such compounds as 
 EbICl 4 , CsI 5 , and KbIBr 3 . 
 
 193. General review of the group of alkali metals. Caesium, 
 rubidium, potassium, sodium, and lithium constitute a group of elements 
 conspicuous for their highly electro-positive character, the powerfully 
 alkaline nature of their hydroxides, and the general solubility of their 
 salts. Their chemical characters and functions are directly opposite to 
 those of the electro-negative group containing fluorine, chlorine, bromine, 
 and iodine, and, like those elements, they exhibit a gradation of pro- 
 perties. Thus, caesium appears to be the most highly electro-positive 
 member, rubidium the next, then potassium and sodium, whilst lithium 
 is the least electro-positive ; and just as iodine, the least electro-negative 
 of the halogens, possesses the highest atomic number, so caesium, the least 
 electro-negative (or most electro-positive) of the alkali-metals, has a 
 higher atomic weight than any other member of this group, their 
 atomic weights being represented by the numbers, caesium, 132 ; rubi- 
 dium, 85 ; potassium, 39 ; sodium, 23 ; lithium, 7. As in the case of 
 the halogens, also, these are all monovalent elements. Just as chlorine 
 is accepted as the representative of chlorous radicles, so potassium is com- 
 monly regarded as the type of basylous radicles, the term radicle being 
 applied to all substances, whether elementary or compound, which are 
 capable of being transferred, like chlorine or potassium, from one com- 
 pound to another without suffering decomposition. 
 
 Attention has been called (p. 304) to the gradation exhibited in some 
 of the physical properties of these elements. 
 
 In some of their salts a similar gradational relation is observed ; the 
 carbonates, for example, of caesium, rubidium, and potassium are highly 
 deliquescent, absorbing water greedily from the air, while carbonate of 
 sodium is not deliquescent, and carbonate of lithium is sparingly soluble 
 in water. The difficult solubility of the carbonate and phosphate of 
 lithium constitutes the connecting link between this and the succeeding 
 group of metals, the carbonates and phosphates of which are insoluble 
 in water. 
 
 BARIUM. 
 
 Ba"= 136.4 parts by weight. 
 
 194. Barium, so named from the great weight of its compounds 
 (ftapvs, heavy), is found in considerable abundance in the north of 
 England, in two minerals known as Witherite (barium carbonate, BaC0 3 ) 
 
360 BARIUM SULPHATE. 
 
 and heavy spar or barytes (barium sulphate, BaS0 4 ). Witherite is 
 found in large masses in the lead mines at Alston Moor, and at Angle- 
 sark in Lancashire. It is said to be used for poisoning rats, and was 
 originally mistaken, on account of its great weight (sp. gr. 4.5), for an 
 ore of lead. All salts of barium are poisonous. 
 
 The metal itself is obtained by electrolysing fused barium chloride or 
 heating it with sodium. It is a pale yellow malleable metal of sp. gr. 
 3.6 ; it is easily oxidised by air, and rapidly decomposes water at common 
 temperatures. It requires a high temperature to fuse it. Barium and 
 its salts impart a green colour to a flame. 
 
 Such compounds of barium as are used in the arts are chiefly prepared 
 from heavy spar or barium sulphate, which is remarkable for its in- 
 solubility in water and acids. In order to prepare other compounds of 
 barium from this refractory mineral, it is ground to powder and strongly 
 heated in contact with charcoal or some other carbonaceous substance, 
 which removes the oxygen from the mineral in the form of carbonic 
 oxide, thus converting the barium sulphate into barium sulphide; 
 BaS0 4 + C 4 = 400 + BaS. This latter compound, being soluble in water, 
 can be readily converted into other barium compounds. 
 
 The artificial barium sulphate, which is used by painters, instead of 
 white lead, under the name of permanent white (blanc fixe), and is 
 employed for glazing cards, is prepared by mixing the solution of barium 
 sulphide with dilute sulphuric acid, when the barium sulphate separates 
 as a white precipitate, which is collected, washed, and dried 
 BaS + H 2 S0 4 = H 2 S + BaS0 4 . 
 
 The artificial barium carbonate, which is used in the manufacture of 
 some kinds of glass, is prepared by passing carbonic acid gas through a 
 solution of barium sulphide, when the carbonate is precipitated ; BaS + 
 H 2 + C0 2 = H 2 S + BaC0 3 . 
 
 In preparing compounds of barium from heavy spar on the small scale it is 
 better to convert the sulphate into barium carbonate. 50 parts of the finely 
 powdered sulphate are mixed with 100 of dried sodium carbonate, 600 of pow- 
 dered nitre, and 100 of very finely powdered charcoal. The mixture is placed in a 
 heap upon a brick or iron plate, and kindled with a match, when the heat evolved 
 by the combustion of the charcoal in the oxygen of the nitre fuses the barium 
 sulphate with the sodium carbonate, whereupon they react to form barium carbonate 
 and sodium sulphate; BaS0 4 + Na 2 C0 3 = Na 2 S0 4 + BaC0 3 . The mass is thrown 
 into boiling water, which dissolves the sodium sulphate and leaves the barium 
 carbonate. The latter may be allowed to settle, and washed several times, by 
 decantation, with distilled water, until the washings no longer yield a precipitate 
 with barium chloride, showing that the whole of the sodium sulphate has been 
 washed away and pure barium carbonate remains. 
 
 Barium oxide or baryta, BaO, may be obtained by strongly heating a 
 mixture of barium carbonate and charcoal, BaC0 3 + C = BaO + 2 CO, but 
 is now generally prepared by heating the nitrate, Ba(N0 3 ) 2 = 
 BaO + 2N0 2 + O. It is a heavy grey solid which combines with water 
 with great evolution of heat to form barium hydroxide. 
 
 Barium dioxide or peroxide, Ba0 2 , has been noticed under hydrogen 
 dioxide (p. 63) and under Erin's oxygen process (p. 39). 
 
 Barium hydroxide, Ba(OH) 2 , may be prepared by passing C0 2 and 
 steam over barium sulphide at a red heat, and decomposing the 
 carbonate thus produced by a current of superheated steam : (i) 
 BaS + CO, + H 2 = BaC0 3 + H 2 S ; (2) BaC0 3 + H 2 Ba(OH) 2 + C0 2 . It 
 dissolves in boiling water, and crystallises in prisms, Ba(OH) 2 .8Aq. 
 
BAEIUM NITRATE, 361 
 
 Crystallised barium hydroxide may be produced by adding 113 grams of powdered 
 barium nitrate to 340 c.c. of a boiling solution of NaOH, containing 85 grams of 
 commercial caustic soda in 567 c.c. of water ; the solution becomes turbid from the 
 separation of barium carbonate produced from the sodium carbonate in the 
 hydroxide ; it is boiled for some minutes and then filtered ; on partial cooling, 
 some crystals of undecomposed barium nitrate are deposited, and if the clear liquid 
 be poured off into another vessel and stirred, it deposits abundant crystals of 
 barium hydroxide having the composition Ba(OH) 2 .8Aq ; these effloresce and 
 become opaque when exposed to air, becoming Ba(OH) 2 .Aq ; when heated to red- 
 ness they become pure, Ba(OH) 2 , which fuses, but is not decomposed when further 
 heated. The hydroxide is moderately soluble in water (baryta water), 100 parts 
 of water dissolving 3 parts at the ordinary temperature ; the solution is strongly 
 alkaline and absorbs carbonic acid gas from the air, depositing barium carbonate. 
 
 Barium carbonate, BaC0 3 , or Witherite, has the sp. gr. 4.3. It may 
 be prepared by precipitating barium chloride with sodium carbonate. 
 It is very insoluble in water, and is not decomposed by a red heat. 
 
 Barium chloride, which is the barium compound most commonly 
 employed in the laboratory, may be obtained by dissolving the carbonate 
 in diluted hydrochloric acid, and evaporating the solution ; on cooling, 
 the chloride is deposited in tabular crystals, BaCl 2 .2Aq. 
 
 On the large scale, it is generally manufactured by fusing heavy spar with 
 calcium chloride (the residue from the preparation of ammonia, see p. 79) in a 
 reverberatory furnace, BaS0 4 + CaCL 2 = CaS0 4 + BaCl 2 . The mass is rapidly 
 extracted with hot water, which leaves the calcium sulphate undissolved, and the 
 clear solution of barium chloride is decanted and evaporated. If the calcium 
 sulphate and barium chloride were allowed to remain long together in contact 
 with the water, barium sulphate and calcium chloride would be reproduced. 
 This process has been improved by adding chalk and coal-dust to the mixture, 
 when (i) BaS0 4 +C 4 = BaS + 4CO ; (2) BaS + CaCl 2 = BaCl 2 + CaS. The calcium 
 sulphide forms an insoluble compound with the lime from the chalk. 
 
 Barium chloride is easily soluble in water, but insoluble in alcohol 
 and in strong acids. Barium bromide is soluble in alcohol. 
 
 Barium nitrate, Ba(N0 3 ) 2 , is obtained by dissolving the carbonate in 
 dilute nitric acid, and evaporating the solution, when octahedral crystals 
 of the nitrate are deposited. It is an ingredient in some kinds of 
 blasting powder used by miners. When heated, it fuses and is decom- 
 posed, leaving a grey porous mass of baryta. 
 
 Barium chlorate, Ba(C10 3 ) 2 , is employed in the manufacture of fireworks, being 
 prepared for that purpose by dissolving the artificial barium carbonate in solution 
 of chloric acid ; it forms beautiful shining tabular crystals. When mixed with 
 combustible substances, such as charcoal and sulphur, it imparts a brilliant green 
 colour to the flame of the burning mixture (see p. 186). 
 
 Barium sulphate, BaS0 4 , found as heavy spar or eawlt,, has the sp. gr. 4.5. It is 
 precipitated whenever sulphates and barium salts meet in solution. It is remark- 
 able for its insolubility in water and acids, and is the form in which either barium 
 or sulphur is determined in quantitative analysis. It dissolves in hot strong H 2 S0 4 , 
 and the solution, on cooling, deposits crystals of acid barium sulphate, BaH 2 (S0 4 ) 2 . 
 
 Barium sulphide, BaS, prepared as described above, dissolves in water with 
 decomposition, yielding barium hydroxide and sulphydrate ; 2BaS + 2H 2 = 
 Ba(OH) 2 + Ba(SH) 2 . It has the property of shining in the dark after it has been 
 exposed to the action of light. 
 
 Barium carbide, BaC 2 , is a grey amorphous substance made by heating BaC0 3 
 (26 parts) with magnesium powder (10.5 parts) and powdered coke (4 parts) in an 
 
 iron flask; BaC0 3 + Mg., + C = BaC 2 + 3MgO. It evolves acetylene when treated 
 with water, BaC 2 + 2H 2 O = C 2 H 2 + Ba(OH) 2 . 
 
362 STRONTIUM MINERALS. 
 
 STKONTIUM. 
 
 Sr" = 87 parts by weight. 
 
 195. Strontium is less abundant than barium, and occurs in nature 
 in similar forms of combination. /Strontianite, the strontium carbonate 
 (SrC0 3 ), was first discovered in the lead-mines of Strontian in Argyle- 
 shire, and has since been found in small quantity in some mineral 
 waters. Sr00 3 is more easily dissociated by heat than is BaC0 3 , but 
 less easily than is CaC0 3 . 
 
 Celestine (so called from the blue tint of many specimens*) is the 
 strontium sulphate (SrS0 4 ), and is found in beautiful crystals associated 
 with the native sulphur in Sicily. It is also met with in this country,, 
 and is the source from which the strontium nitrate employed in firework 
 compositions is derived. The strontium sulphate resembles barium 
 sulphate with respect to its insolubility, and is converted into the 
 soluble strontium sulphide (SrS) by calcination with carbonaceous 
 matter. The solution of strontium sulphide so obtained is decomposed 
 by nitric acid, and the strontium nitrate crystallised from the solution. 
 It has the property of imparting a magnificent crimson colour to flames, 
 and is hence largely used for the preparation of red theatrical fire (see 
 p. 186). 
 
 The metal itself is prepared in a similar manner to metallic barium. t 
 which it much resembles, but is lighter (sp. gr. 2.54) and more fusible. 
 It burns, when heated in air, with a crimson flame. 
 
 Strontia, SrO, resembles BaO, but does not absorb when heated. 
 
 /Strontium dioxide, SrO 2 , is precipitated, in combination with 8H 2 ? 
 when a solution of strontia in water is mixed with hydrogen peroxide. 
 
 /Strontium hydroxide, Sr(OH) 2 , is made on the large scale by heating 
 the native strontium sulphate with brown iron ore (hydrated ferric 
 oxide) and coal-dust. On treating the product with water, ferrous 
 sulphide remains undissolved, and Sr(HO) 2 passes into solution. It is- 
 used in sugar refining. It is less soluble than barium hydroxide, and 
 is converted into SrO by heat. 
 
 Strontium nitrate, Sr(N0 3 ) 2 , may be prepared by dissolving stron- 
 tianite in nitric acid. It crystallises from hot strong solutions in 
 anhydrous octahedra. Cold solutions deposit prisms of Sr(NO 3 ) 2 .4Aq. 
 (Barium nitrate is always anhydrous.) Strontium nitrate is easily 
 soluble in water, but insoluble in alcohol. 
 
 /Strontium chloride, SrCl 2 , differs from BaCl 2 in being deliquescent and 
 soluble in alcohol. It crystallises in prisms, SrCl 9 .6Aq. 
 
 Strontium sulphate, SrSO 4 , is not so heavy as BaS0 4 ; sp. gr. 3. It 
 is slightly soluble in water, and is easily converted into SrC0 3 by alka- 
 line carbonates, in the cold, which is not the case with BaS0 4 . 
 
 * Said to be due to the presence of ferroso-ferric phosphate. 
 
 f Strontium has been made in quantity by distilling strontium amalgam in hydrogen. 
 The amalgam was prepared by the action of sodium-amalgam on a saturated solution of 
 strontium chloride. 
 
VAEIETIES OF CALCIUM CARBONATE. 363 
 
 CALCIUM. 
 
 Ca" = 40 parts by weight. 
 
 196. No other metal is so largely employed in a state of combination 
 as is calcium, for its oxide, lime (CaO), occupies among bases much the 
 same position as that which sulphuric acid holds among the acids, and 
 is used, directly or indirectly, in most of the arts and manufactures. 
 
 Like barium and strontium, calcium is found, though far more abun- 
 dantly than these, in the mineral kingdom, in the forms of carbonate 
 and sulphate, but it also occurs in large quantity as calcium fluoride 
 (p. 202), and less frequently in the form of phosphate (p. 256). Calcium, 
 moreover, is found in all animals and vegetables, and its presence in 
 their food, in one form or other, is an essential condition of their 
 existence. 
 
 Metallic calcium may be obtained by decomposing fused calcium iodide 
 with metallic sodium. It crystallises from the excess of sodium as the 
 mass cools and may be isolated by dissolving the sodium in alcohol. It 
 has a silvery appearance and is as hard as Iceland spar, very ductile 
 and malleable. It melts at 760 C. and is lighter than barium and 
 strontium, its sp. gr. being 1.56. It oxidises slowly in air at the 
 ordinary temperature, but, when heated to redness, it fuses and burns 
 with a very brilliant white light, being converted into lime (calx). It 
 decomposes water at the ordinary temperature. Its salts impart a red 
 colour to a colourless flame. 
 
 Carbonate of lime, or Calcium carbonate (CaO.C0 2 or CaC0 3 ), 
 from which all the manufactured compounds of lime are derived, con- 
 stitutes the different varieties of limestone which are met with in such 
 abundance. 
 
 Chalk is simply calcium carbonate in an amorphous or uncrystallised 
 state ; it is known to the agriculturist as mild lime. Limestone consists 
 of minute crystals of calc spar (see below). The oolite limestone, of 
 which the Bath and Portland building-stones are composed, is so-called 
 from its resemblance to the roe of fish (o>oi>, an egg). Marble, in its 
 different varieties, is also an assemblage of minute crystals of calc spar, 
 sometimes variegated by the presence of oxides of iron and manganese, 
 or of bituminous matter. This last constituent gives the colour to black 
 niurble. Calcium carbonate is also found in large transparent rhombo- 
 hedral crystals, which are known to mineralogists as calcareous spar, 
 calc spar, or Iceland spar, and calcite (sp. gr. 2.7). When the crystals 
 have the form of a six-sided prism, the mineral is termed aragonite 
 (sp. gr. 2.94). 
 
 The attention of the crystallographer has long been directed to these two 
 crystalline forms of calcium carbonate, on account of the circumstance that if a 
 prism of aragonite be heated, it breaks .up into a number of minute rhombohedra 
 of calc spar. Satin spar is a variety of calcium carbonate. When slowly deposited 
 from its solution in carbonic acid, calcium carbonate gives six-sided prisms of 
 CaC0 3 .5Aq. Precipitated calcium carbonate is amorphous, and is the least stable 
 of the three forms and hence the most soluble (20 mgrns. per litre). When heated 
 to a high temperature it becomes aragonite, but when kept at moderate tempera- 
 tures, in contact with the liquid from which it was precipitated, it becomes calcite. 
 
 Calcium carbonate is a chief constituent of the shells of fishes and of egg-shells, 
 so that, except calcium phosphate, no mineral compound has so large a share in 
 the composition of animal frames. Corals also consist chiefly of calcium carbonate 
 
LIME-BURNING. 
 
 derived from the skeletons of innumerable minute insects. The mineral gaylussite 
 is a double carbonate of calcium and sodium (CaCO 3 .Na 2 C0 3 .5Aq), and is scarcely 
 affected by water unless previously heated, when water dissolves out the sodium 
 carbonate. Baryta-calcite is a double carbonate of barium and calcium 
 (BaC0 3 .CaC0 3 ). 
 
 The presence of calcium carbonate in spring waters and the solubility 
 of this compound in a solution of carbon dioxide have already been 
 considered (p. 56). 
 
 Lime (CaO). The process by which lime is obtained from the car- 
 bonate has been already alluded to under the name of lime-burning. 
 At a red heat calcium carbonate begins to decompose into CaO and C0 2 ; 
 but unless the C0 2 be removed, it prevents further decomposition, so 
 that marble or chalk cannot be completely decomposed in a covered 
 crucible, and a lime-kiln must have a good draught to carry off the C0 2 . 
 At 812 C. the dissociation-pressure (p. 315) of CaC0 3 is 753 mm., and 
 this is the best temperature for lime-burning.* 
 
 Accordingly, a kiln is commonly employed of the form of an inverted 
 cone of brickwork (Fig. 213), and into this limestone and fuel are thrown 
 in alternate layers. The former, losing its C0 2 before it reaches the 
 
 Fig. 213. Limekiln. 
 
 Fig. 214. Limekiln. 
 
 bottom of the furnace, is raked out in the form of burnt or quick lime 
 (CaO), whilst its place is supplied by a fresh layer of limestone thrown 
 in at the top of the kiln. Fig. 214 represents another form of kiln, in 
 which the limestone is supported upon an arch built with large lumps 
 of the stone above the fire, which is kept burning for about three days 
 and nights, until the whole of the limestone is decomposed. 
 
 The usual test of the quality of the lime thus obtained consists in 
 sprinkling it with water, with which it should eagerly combine, evolving 
 much heat,t swelling to about z\ times its bulk, and crumbling to a light 
 white powder of calcium hydrate (slaked lime), Ca(OH) 2 . Lime which 
 behaves in this manner is termed fat lime ; whereas, if it be found to 
 
 * When precipitated CaC0 3 is heated to about 1000 C. under such conditions that none 
 of its CO 2 can escape, it is converted into marble. 
 
 | The sudden slaking of a large quantity of lime may be a cause of fire. A rise of tem- 
 perature to 150 C. frequently occurs. 56 grams of CaO evolve 15,540 gram units of heat 
 when slaked. 
 
BUILDING MATERIALS, 365 
 
 slake feebly, it is pronounced a poor lime, and is known to contain a 
 considerable proportion of foreign substances, such as silica, aluminia, 
 magnesia, &c. Lime is said to be overburnt when it contains hard 
 cinder-like masses of silicate of lime, formed by the combination of the 
 silica, which is generally found in limestone, with a portion of the lime, 
 under the influence of excessive heat in the kiln. Air-slaked lime has 
 slaked by simple exposure to air ; it has absorbed C0 2 as well as H 2 0, 
 and contains 5 7 per cent. CaC0 3 and 43 per cent. Ca(OH) 2 . 
 
 Calcium hydroxide, Ca(OH) 2 , is much less soluble in water than is 
 barium or strontium hydroxide. It requires 700 parts of cold water to 
 dissolve it, and twice as much hot water, so that lime-water always gives 
 a precipitate when boiled. The solution is strongly alkaline, and 
 readily absorbs C0 2 from the air, which precipitates CaCO 3 . When 
 lime water is evaporated in vacua over H 2 S0 4 , it deposits small crystals 
 of Ca(OH) 2 . 
 
 Ca(OH) 2 is easily converted into CaO by heat. It is used in manu- 
 facturing chemistry as the cheapest alkaline substance. 
 
 197. Closely connected with limestone and lime is the chemistry of 
 building materials. 
 
 Chemical principles would lead to the selection of pure silica (quartz, 
 rock-crystal) as the most durable of building materials, since it is not 
 attacked by any of the substances likely to be present in the atmosphere; 
 but even if it could be obtained in sufficiently large masses for the 
 purpose, its great hardness presents an obstacle to its being hewn into 
 the required forms. Of the building stones actually employed, granite, 
 basalt, and porphyry are the most lasting, on account of their capability 
 of resisting for a great length of time the action of water and of atmo- 
 spheric carbonic acid ; but their hardness makes them so difficult to 
 work, as to prevent their employment except for the construction of 
 pavements, bridges, &c., where the work is massive and straightforward, 
 and much resistance to wear and tear is required. The millstone grit 
 is also a very durable stone, consisting chiefly of silica, and employed 
 for the foundations of houses. Freestone is a term applied to any stone 
 which is soft enough to be wrought with hammer and chisel, or cut 
 with a saw ; it includes the different varieties of sandstone and lime- 
 stone. The Yorkshire flags employed for paving are siliceous stones of 
 this description. The Craigleith sandstone, which is one of the free- 
 stones used in London, contains about 98 per cent, of silica, together 
 with some calcium carbonate. 
 
 The building stones in most general use are the different varieties of 
 calcium carbonate. The durability of these is in proportion to their 
 compact structure ; thus marble, being the most compact, has been found 
 to resist for many centuries the action of the atmosphere, whilst the 
 more porous limestones are corroded at the surface in a very short time. 
 Portland stone, of which St. Paul's and Somerset House are built, and 
 Bath stone, are among the most durable of these ; but they are all slowly 
 corroded by exposure to the atmosphere. The chief cause of this 
 corrosion appears to be the mechanical disintegration caused by the 
 expansion in freezing, of the water absorbed in the pores of the stone. 
 In order to determine the relative extent to which different stones are 
 liable to be disintegrated by frost, a piece of the stone may be saturated 
 with water and alternately frozen and thawed. Magnesian limestones 
 
366 MOETAR AND CEMENT. 
 
 (carbonate of calcium with carbonate of magnesium) are much valued 
 for ornamental architecture, on account of the ease with which they 
 may be carved, and are said to be more durable in proportion as they 
 approach the composition expressed by the formula CaC0 3 .MgCO 3 .* 
 The magnesian limestone from Bolsover Moor, of which the Houses of 
 Parliament are built, contains 50 per cent, of calcium carbonate, 40 of 
 magnesium carbonate, with some silica and alumina. 
 
 It is probable that a slow corrosion of the surface of limestone is 
 effected by the carbonic acid continually deposited in aqueous solution 
 from the air ; and it is certain that in the atmosphere of towns the 
 limestone is attacked by the sulphuric acid which results from the com- 
 bustion of coal and the operations of chemical works. The Houses of 
 Parliament have suffered severely, probably from this cause. Many 
 processes have been recommended for the preservation of building 
 stones, such as waterproofing them by the application of oily and 
 resinous substances, and coating or impregnating them with solution of 
 soluble glass and similar matters; but none seems yet to have been 
 thoroughly tested by practical experience. 
 
 Purbeck, Ancaster, and Caen stones are well-known limestones employed 
 for building. 
 
 The mortar employed for building is composed of i part of freshly 
 slaked lime and 2 or 3 parts of sand intimately mixed with enough 
 water to form a uniform paste. The hardening of such a composition 
 appears to be due, in the first instance, to the absorption of carbon 
 dioxide from the air, by which a portion of the lime is converted into 
 calcium carbonate, and this, uniting with the unaltered calcium hydrate, 
 forms a solid layer, adhering closely to the two surfaces of brick or 
 stone, which it cements together. In the course of time the lime would 
 act upon the silica, producing calcium silicate, and this chemical action 
 would render the adhesion more perfect. The chief use of the sand 
 here, as in the manufacture of pottery (q.v.) is to prevent excessive 
 shrinking during the drying of the mortar. 
 
 In constructions which are exposed to the action of water, mortars of 
 peculiar composition are employed. These hydraulic mortars, or cements, 
 as they are termed, are prepared by calcining mixtures of calcium car- 
 bonate with from 10 to 30 per cent, of clay, when carbonic acid gas is 
 expelled, and the lime combines with a portion of the silica and alumina 
 from the clay, producing tricalcium silicate, 3CaO.Si0 2 , and tricalcium 
 aluminate, 30aO.Al 2 3 . When the calcined mass is ground to powder 
 and mixed with water these silicates combine with water to form 
 hydrated silicates (with liberation of free lime), which dissolve in the 
 water and immediately crystallise again (in the manner described for 
 the setting of plaster of Paris), thus causing the cement to set. Roman 
 cement is prepared by calcining a limestone containing about 25 per 
 cent, of clay, and hardens in a very short time after mixing with water. 
 For Portland cement (so-called from its resembling Portland stone) a 
 mixture of river-mud (chiefly clay) and limestone is calcined at a very 
 high temperature. 
 
 Hydraulic cements are mixed for use with sand before they are 
 wetted with water. Concrete is a mixture of hydraulic cement (i vol.) 
 
 * Any excess of calcium carbonate above that required by this formula may be dissolved 
 out by treating- the powdered magnesium limestone with weak acetic acid. 
 
PLASTEE OF PAEIS. 367 
 
 with sand (2 vols.) and small gravel (4 vols.), the last being known as 
 the " aggregate." 
 
 Scott's cement is a mixture of quick-lime with a small proportion of 
 calcium sulphate. 
 
 Calcium dioxide, Ca0 2 , is precipitated in combination with 8H 2 0, 
 when solution of sodium peroxide is added to one of a calcium salt. 
 
 Calcium nitrate, Ca(IS"0 3 ) 2 .4Aq, differs from those of Ba and Sr by 
 being deliquescent, much more soluble in water, and soluble in alcohol. 
 It occurs in well-waters and in soils, the NO 3 having been formed by 
 oxidation of NH 3 . 
 
 198. Sulphate of lime, or Calcium sulphate, in combination with 
 water (CaS0 4 .2H 2 0), is met with in nature, both in the form of trans- 
 parent prisms of selenite, and in opaque and semi-opaque masses known 
 as alabaster and gypsum. It is this latter form which yields plaster of 
 Paris, for when heated to between 150 and 2ooC. it loses j- of 
 its water, becoming 2CaS0 4 .H 2 0, and if the mass be then powdered, 
 and mixed with water, the powder recombines with the water to 
 form a mass, the hardness of which nearly equals that of the original 
 gypsum. 
 
 In the preparation of plaster of Paris, a number of large lumps of 
 gypsum are built up into a series of arches, upon which the rest of the 
 
 fypsum is supported; under these arches the fuel is burnt, and its 
 ame is allowed to traverse the gypsum, care being taken that the tem- 
 perature does not rise too high, lest the gypsum be overburnt and set 
 very slowly with water. When the operation is supposed to be com- 
 pleted, the lumps are carefully sorted, and those which appear to have 
 been properly calcined are ground to a very fine powder. When this 
 powder is mixed with water to a cream, and poured into a mould, the 
 minute particles of calcium sulphate combine with water to reproduce 
 the original gypsum (CaSO 4 .2H 2 0), and this act of combination is 
 attended with a slight expansion which forces the plaster into the finest 
 lines of the mould. 
 
 The setting is due to the fact that a small portion of the plaster (2CaS0 4 .H 2 0) 
 dissolves in the water, crystallising again immediately as CaSO 4 .2H 2 0, thus leaving 
 the water free to dissolve another portion of 2CaS0 4 .H 2 0, which crystallises in its 
 turn as CaS0 4 .2H 2 0. Thus the mass soon becomes one of interlaced crystals of 
 CaS0 4 .2H 2 0. An addition of one-tenth of lime to the plaster hardens it and accele- 
 rates the setting. 
 
 It is not known why overburnt gypsum does not set, or sets only very slowly, but 
 it is supposed to be due to the fact that there is no nucleus of undecomposed gypsum 
 in it. This view is supported by the behaviour of anhydrous Na 2 S0 4 , which remains 
 as a powder underwater until a crystal of the hydrated salt is added, when the whole 
 mass solidifies. 
 
 The transition -point from CaS0 4 .2H 2 O to 2CaS0 4 .H 2 O is 107 C., at which tem- 
 perature the pressure of the water vapour from the gypsum is higher than that of 
 the vapour from water itself at this temperature. It follows that when gypsum is 
 heated in a sealed tube the water vapour condenses, and the gypsum becomes a 
 magma of plaster of Paris in water. The change at 107 C. is exceedingly slow, so 
 that the gypsum-burner is obliged to use a considerably higher temperature than 
 this. 
 
 Stucco consists of plaster of Paris (occasionally coloured) mixed with a solution 
 of size ; certain cements used for building purposes are prepared from burnt gypsum, 
 which has been soaked in a solution of alum and again burnt ; and although the 
 plaster thus obtained takes much longer to set than the ordinary kind, it is much 
 harder, and therefore takes a good polish. A similar hardening of objects cast from 
 plaster of Paris is effected by soaking them in solution of KHS0 3 , probably owing 
 
368 CALCIUM CHLORIDE. 
 
 to the slow formation of a double salt of CaS0 4 and K S0 4 ; this is applied in the 
 making of artificial marble. Plaster of Paris is much damaged by long exposure to 
 moist air, from which it regains a portion of its water, and its property of setting 
 is so far diminished. Precipitated calcium sulphate is used by paper-makers under 
 the name of pearl hardener. Calcium sulphate is useful in the farmyard and stables 
 for absorbing the ammonia of the decomposing excrements, which would otherwise 
 be lost to the manure. 
 
 CaS0 4 forms the mineral anhydrite, a bed of which, when exposed to 
 the air in a railway cutting, has been known to increase in bulk by 
 absorbing water to such an extent as to disturb the stability of the 
 sides of the cutting. Calcium sulphate is contained in most natural 
 waters, and is one of the chief causes of the permanent hardness which 
 is not removed by boiling. It is much more soluble in water than is 
 strontium sulphate, so that sulphates will precipitate calcium only from 
 strong solutions. The aqueous solution of CaS0 4 precipitates barium 
 salts immediately, but strontium salts only after an interval, on account 
 of the greater solubility of SrS0 4 . The calcium sulphate is more 
 soluble in water at 35 C. than at any other temperature, i part of 
 CaSO 4 then dissolving in about 400 parts of water. It is insoluble in 
 alcohol. Boiling HC1 dissolves it, and deposits it in needles on cooling. 
 
 Calcium chloride (CaCl 2 ) has been mentioned as the residue left in 
 the preparation of ammonia. The pure salt may be obtained by dis- 
 solving pure calcium carbonate (Iceland spar) in hydrochloric acid, and 
 evaporating the solution, when prismatic crystals of the composition 
 CaCl 2 .6Aq are obtained, which dissolve in one-fourth of their weight of 
 cold water. When these are heated they melt at 29 0., and at about 
 200 C. are converted into a white porous mass of CaCl 2 .2Aq, which is 
 much used for drying gases. At a higher temperature, fused calcium 
 chloride, free from water, is left; this is very useful for removing 
 water from some liquids. When heated in air, it evolves chlorine and 
 becomes alkaline. A saturated (325 per cent.) solution of calcium 
 chloride boils at 355 F. (180 C.), and is sometimes used as a con- 
 venient bath for obtaining a temperature above the boiling-point of 
 water. When mixed with snow the crystals CaCl 2 .6H 2 form a cryo- 
 hydrate, reducing the temperature to -48 C. In consequence of the 
 attraction of calcium chloride for water, surfaces wetted with a solution 
 of the salt never get dry. Rope mantlets, for the protection of gunners^ 
 are saturated with it to prevent their taking fire. Calcium chloride is 
 easily soluble in alcohol. 
 
 When Ca(OH) 2 is boiled with a strong solution of calcium chloride, 
 it is dissolved, and the filtered solution deposits prismatic crystals of 
 calcium oxychloride, CaCl 2 .3CaO.i5Aq, which are decomposed by water. 
 
 Chloride of lime ; seep. 183. 
 
 Calcium fluoride, CaF 2 , already described asfluor spar (p. 202), occurs 
 in the bones and teeth. Many specimens of it decrepitate and emit a 
 phosphorescent light when heated. It fuses at a red heat, and is used 
 in metallurgy as a flux, since it attacks silicates at a high temperature. 
 Calcium fluoride is slightly soluble in hot HC1, and is reprecipitated by 
 NH 3 . It is obtained as a gelatinous precipitate insoluble in acetic acid 
 when CaCl 2 is added to an alkali fluoride. Artificial teeth are made of 
 calcium fluoride. 
 
 Calcium sulphide (CaS) is present in Balmairis luminous paint. Its property of 
 shining in the dark after exposure to a bright light was observed by Canton in 1761 ; 
 
PHOSPHATE OF LIME, 369 
 
 his so-called phosphorus was obtained by strongly heating oyster-shells with sulphur. 
 The phosphorescence is not due to slow oxidation, since a specimen which has been 
 kept for more than a century in a sealed tube still exhibits it ; it does not appear to 
 be a property of the pure sulphide. 
 
 When Cab is acted on by H 2 S it yields a crystalline calcium hydrosulphide f 
 Ca(SH) 2 . When this is heated in H 2 S it is decomposed ; Ca(SH) 2 = CaS + H 2 S. 
 The CaS is a white solid, soluble in water. When Ca(SH) 2 is exposed to air it 
 deliquesces, evolves H 2 S, and becomes Ca(SH)(OH) ; Ca(SH) 2 + H 2 = H 2 S + Ca 
 (SH)(OH). Calcium sulphide occurs, combined with CaO, in the tank-waste of the 
 alkali works. A solution of Ca(SH) 2 is used as a depilatory. 
 
 Calcium phosphate, Ca 3 (PO 4 ) 2 , occurs in the minerals apatite, phos- 
 phorite, sombrerite, and coprolite ; in the two first it is combined with 
 calcium fluoride, forming 3Ca 3 (P0 4 ) 2 ,CaF 2 , and this is also contained in 
 bone ash, of which Ca 3 (P0 4 ) 2 forms the larger proportion (80 per cent.). 
 This is sold as a non-mercurial plate powder, under the name of white 
 rouge. Calcium phosphate is nearly insoluble in water, but it is dis- 
 solved by HC1 or HNO 3 , and is precipitated again by ammonia. When 
 CaCl 2 is added to Na 2 HP0 4 , a gelatinous precipitate is obtained, which 
 becomes crystalline after a short time. The gelatinous precipitate dis- 
 solves easily in acetic acid, but the crystalline precipitate does not, and 
 if the solution of the gelatinous precipitate in very little acetic acid be 
 allowed to stand, or briskly stirred, it deposits crystals of CaHP0 4 .2Aq. 
 This salt is found in calculi in the sturgeon. 
 
 Tetra-hydrogen calcium phosphate, CaH 4 (PO 4 ) 2 , commonly called super- 
 phosphate of lime, is made by decomposing Ca 3 (P0 4 ) 2 with sulphuric 
 acid; Ca 3 (P0 4 ) 2 + 2 H 2 S0 4 = CaH 4 (P0 4 ) 2 + 2 CaSO 4 ; the calcium sulphate 
 is filtered off, and the superphosphate is left in solution. The pure super- 
 phosphate may be prepared by dissolving bone-ash in HC1, precipitating 
 with ammonia, and digesting the washed precipitate of Ca 3 (P0 4 ) 2 with 
 H 3 PO 4 ; Ca 3 (P0 4 ) 2 + 4H 3 P0 4 = 3CaH 4 (P0 4 ) 2 . On allowing the solution 
 to evaporate spontaneously, the salt crystallises in rhomboidal plates 
 containing a molecule of water. It is dissolved by a small quantity of 
 water, but it is decomposed and precipitated by much water, or by 
 boiling ; CaH 4 (P0 4 ) 2 = H 3 P0 4 + CaHPO 4 . 
 
 The commercial superphosphate manure is a damp mixture of CaH 4 (P0 4 ) 2 , and 
 CaS0 4 , prepared by mixing ground mineral phosphates with sulphuric acid. It is 
 valued by the agriculturist for the large amount of soluble phosphate which it 
 contains ; in course of time, the proportion of this decreases, and the phosphate is 
 said to have reverted to the insoluble form, owing to the action of the superphos- 
 phate upon some undecomposed Ca 3 (P0 4 ) 2 remaining in the compound, resulting in 
 the formation of the insoluble hydrocalcium phosphate CaH 4 (P0 4 ) 2 + Ca 3 (PO 4 ) 2 = 
 4CaHP0 4 . Another cause for this retrogression of the superphosphate which has 
 been prepared from mineral phosphates, is the presence of the sulphates of alu- 
 minium, magnesium, and iron, which gradually convert the phosphoric acid into 
 insoluble forms. 
 
 Calcium jiyrapliasithate, Ca 2 P 2 7 , when exposed for several hours to a dull red 
 heat, forms a perfectly transparent glass of sp. gr. 2.6, which may be worked into 
 prisms and lenses like ordinary glass, its refractive power being equal to that of 
 crown glass. It is not acted on by acids in the cold, and even resists HF. 
 
 Calcium aniniii/i/iiiii arse-note, CaNH 4 As0 4 -7Aq, is obtained as a white precipitate 
 by mixing CaCl 2 with excess of NH 3 , and adding arsenic acid. The precipitate is 
 gelatinous at first, but changes rapidly into fine needles, especially if stirred. It is 
 slightly soluble in water, but almost insoluble in ammonia. Dried in vacua, over 
 sulphuric acid, it becomes Ca 3 NH 4 H 2 (As0 4 ) 3 .3Aq. Dried at ico C., it has the formula 
 Ca 6 NH 4 H 5 (As0 4 ) 6 .3Aq. Heated to redness, it becomes calcium pyro-arscnate,Ca<zA.& 2 7 . 
 Calcium urtho-arxenate, Ca 3 (As0 4 ) 2 , and metar senate, Ca(As0 3 ) 2 , have also been 
 obtained, 
 
 2 A 
 
37 WINDOW GLASS. 
 
 Calcium carbide, CaC 2 . Some of the properties of this substance have been 
 described at p. 137. Its manufacture is conducted by feeding a mixture of 100 parts 
 of powdered quicklime with 80 parts of powdered coke between the poles of 
 an electric arc, when the materials fuse, having reacted to form calcium carbide ; 
 CaO + C 3 = CaC 2 + CO. Several forms of electric furnace have been devised for this 
 manufacture ; one of them consists of an iron truck contained in a brickwork 
 chamber, and having suspended in it a bundle of carbon rods. The latter are con- 
 nected with one pole of the dynamo, the truck being connected with the other pole, 
 and thus conducting the current to the charge it contains, which forms the actual 
 electrode and protects the truck from the heat. The truck is run out of the furnace 
 and another substituted for it as soon as it is full of the carbide. 
 
 Pure calcium carbide forms colourless transparent crystals, but the commercial 
 product is a grey opaque crystalline substance of sp. gr. 2.2, which is decomposed by 
 aqueous vapour so that it smells of impure acetylene when exposed to the atmo- 
 sphere (p. 137). 
 
 Calcium silicates are found associated with other silicates in many materials. They 
 are also constituents of most forms of glass, which will therefore receive attention 
 here. 
 
 199. Grlass is defined chemically to be an amorphous mixture of two 
 or more silicates, one of which is a silicate of an alkali-metal, the other 
 being a silicate of calcium, barium, iron, lead, or zinc. Typical glass 
 may be said to correspond with the formula M 2 CaSi 6 14 , where M is an 
 alkali metal. The different kinds of glass may, however, vary consider- 
 ably from this formula. 
 
 If silica be fused with an equal weight of carbonate of potassium or 
 sodium, a transparent glassy mass is obtained, but this is slowly dissolved 
 by water, and would therefore be incapable of resisting the action of the 
 weather ; if a small proportion of lime or baryta, or of the oxides of iron, 
 lead, or zinc, be added, the glass becomes far less easily affected by atmo- 
 spheric influences. 
 
 The most valuable property of glass, after its transparency and per- 
 manence, is that of assuming a viscid or plastic consistence when fused, 
 which allows it to be so easily fashioned into the various shapes required 
 for use or ornament. 
 
 The composition of glass is varied according to the particular purpose 
 for which it is intended, the materials selected being fused in large clay 
 crucibles placed in reverberatory furnaces, and heated by a coal fire or 
 in a gas-furnace. 
 
 Ordinary window glass is a soda glass, essentially composed of sodium 
 silicate and calcium silicate, containing one molecule (13.3 %) of soda, 
 one molecule (12.9 %) of lime, and five molecules (69.1 %) of silica; it 
 also usually contains a little alumina. This variety of glass is manu- 
 factured by fusing sand (100 parts) with chalk (35) and soda-ash (35) : 
 a considerable quantity of broken window glass is always fused up at 
 the same time. Of course, C0 2 is expelled from the chalk and the 
 Na,C0 3 in the gaseous state ; and in order that this may not cause the 
 contents of the crucible to froth over during the fusion, the materials 
 are fast, fritted together, as it is termed, at a temperature insufficient to 
 liquefy them, when the C0 2 is evolved gradually, and the fusion after- 
 wards occurs without effervescence. 
 
 Occasionally, sodium sulphate is employed instead of the carbonate, when it is usual 
 to add a small proportion of charcoal in order to facilitate the decomposition of the 
 sulphate by removing part of its oxygen (Na 2 S0 4 + SiO 2 + C = ]Sra 2 Si03 + S0 2 + CO). 
 Before the glass is worked into sheets, it is allowed to remain at rest for some time 
 in the fused state, so that the air-bubbles may escape, and the glass-gall or scum 
 
FLINT GLASS. 371 
 
 (consisting chiefly of sodium sulphate and sodium chloride), which rises to the 
 surface, is removed. 
 
 Plate glass is also chiefly a silicate of sodium and calcium, but it con- 
 tains, in addition, a considerable quantity of silicate of potassium (74 
 per cent, of Si0 2 , 12 of Na 2 0, 5.5 of K 2 0, and 5.5 of CaO). The purest 
 white sand is selected, and great care is taken to exclude impurities. 
 
 Crown glass, used for optical purposes, contains no sodium, since that 
 metal has the property of imparting a greenish tint to glass, which is 
 nofc the case with potassium. This variety of glass, therefore, is pre- 
 pared by fusing sand with potassium carbonate and chalk in such pro- 
 portions that the glass may contain i mol. (22 %) of K 2 0, i mol. (12.5 %) 
 of CaO, and 4 mols. (62 %) of SiO 2 . 
 
 Bohemian glass, also a potash glass (silicate of K 2 and CaO), is less 
 fusible than soda glass, and less easily attacked by acids ; hence its use 
 for chemical vessels ; it appears to owe its infusibility to its high con- 
 tent of silica. 
 
 The alkali silicate in glass being the more soluble in water the richer 
 it is in alkali, a glass containing a high percentage of silica is the more 
 generally useful for chemical vessels, particularly as it is less fusible 
 than that poorer in this constituent. It is only comparatively recently, 
 however, that furnaces attaining the high temperatures necessary for 
 working glass rich in silica have been used. As stated at p. 279 the 
 introduction of the electric furnace may enable pure silica to be sub- 
 stituted for glass. 
 
 Acid solutions attack glass less than water does, while alkali pro- 
 duces the most effect. By steaming the glass for some time its surface 
 becomes more resistant. Glass containing both alkalies is more easily 
 attacked than that containing only one. 
 
 The glass of which wine bottles are made is of much cheaper and 
 commoner description, consisting chiefly of calcium silicate, but contain- 
 ing, in addition, small quantities of the silicates of sodium, of aluminium, 
 and of iron, to the last of which it owes its dark colour. 
 
 Flint glass, which is used for table glass and for ornamental purposes, 
 is a double silicate of potassium and lead, containing one mol. (13.67 %) 
 of K 2 0, one mol. (33.28 %) of PbO, and six mols. (51.93 %) of Si0 2 . 
 It is prepared by fusing 300 parts of the purest white sand with 200 
 parts of minium (red oxide of lead), 100 parts of refined pearl-ash, and 
 30 parts of nitre. The fusion is effected in crucibles covered in at the 
 top to prevent the access of the flame, which would reduce a portion of 
 the lead to the metallic state. The nitre is added in order to oxidise 
 any accidental impurities which might reduce the lead. 
 
 The presence of the lead in glass very much increases its fusibility, 
 and renders it much softer, so that it may be more easily cut into orna- 
 mental forms ; it also greatly increases its lustre and beauty. 
 
 Barium has also the effect of increasing the fusibility of glass, and 
 zinc, like lead, increases its brilliancy and refracting power, on which 
 account it is employed in some kinds of glass for optical purposes. Glass 
 of this description is also made by substituting boric oxide for a portion 
 of the silica. 
 
 All glass articles must be annealed by being slowly cooled, otherwise 
 they are liable to spontaneous fracture, due to the excessive strains pro- 
 duced in the structure of the glass. 
 
372 COLOURED GLASS. 
 
 Some varieties of glass, if heated nearly to their melting-point, and 
 allowed to cool slowly, become converted into an opaque very hard mass 
 resembling porcelain (Reaumur's porcelain). This change; which is known 
 as devitrification, is due to the crystallisation of the silicates contained in 
 the mass, and, by again fusing it, the glass may be restored to its original 
 transparent condition. 
 
 Toughened glass is made by heating the glass vessel to its softening 
 point, immersing it in a bath of oil or steam at 200 0., and cooling it 
 quickly. This treatment hardens it, increases its specific gravity, and 
 renders it less brittle externally, but puts the inner portion in a state of 
 tension, so that it sometimes breaks up spontaneously. 
 
 In producing coloured glass, advantage is taken of its property of dis- 
 solving many metallic oxides with production of peculiar colours. It has 
 been mentioned above that bottle glass owes its green colour to the 
 presence of iron; and since this metal is generally found in small 
 quantity in sand, and even in chalk, it occasionally happens that a glass 
 which is required to be perfectly colourless turns out to have a slight 
 green tinge. 
 
 In order to remove this, a small quantity of some oxidising agent is usually 
 added, in order to convert the ferrous oxide into ferric oxide, which does not 
 impart any colour when present in minute proportion. A little nitre is sometimes 
 added for this purpose, or some white arsenic, which yields its oxygen to the ferrous 
 oxide, and escapes in the form of vapour of arsenic ; red oxide of lead (Pb.}0 4 ) may 
 also be employed, and is reduced to oxide of lead (PbO), which remains in the 
 glass. Manganese dioxide (ylassm alters soap) is often added as an oxidising agent, 
 being reduced to the state of manganous oxide (MnO), which does not colour the 
 glass ; but care is then taken not to add too much of the dioxide, for a very minute 
 quantity of this substance imparts a beautiful amethyst-purple colour to glass. 
 
 Suboxide of copper is used to produce a red glass, and the finest ruby glass is 
 obtained by the addition of a little gold. The oxides of antimony impart a yellow 
 colour to glass ; a peculiar brown-yellow shade is given by charcoal in a fine state 
 of division, and sesquioxide of uranium produces a fine greenish-yellow glass. 
 Green glass is coloured either by oxide of copper or sesquioxide of chromium, 
 whilst oxide of cobalt gives a magnificent blue colour. For black glass a mixture 
 of the oxides of cobalt and manganese is employed. The white enamel glass is 
 a flint glass, containing about 10 per cent, of binoxide of tin. Bone-ash is also 
 used to impart this appearance to glass. The irisatlon of glass, giving it the tints 
 of mother-of-pearl, is effected by corroding its surface with hydrochloric acid of 
 15 per cent, strength, under heat and pressure. 
 
 Kryolite is employed in making opal-glass containing 64 per cent, of silica, 17 of 
 alumina, 16 of lead oxide, and 3 of potash. 
 
 200. General review of the metals of the alkaline earths. 
 Barium, strontium, and calcium form a highly interesting natural group 
 of metals related to each other in a most remarkable manner. They 
 exhibit a marked gradation in their attraction for oxygen : barium is 
 more readily tarnished or oxidised, even in dry air, than strontium, and 
 strontium more readily than calcium. The hydroxides of the metals 
 exhibit a similar gradation in properties; barium hydroxide does not lose 
 water, however strongly it may be heated, whereas the hydroxides of 
 strontium and calcium are decomposed at a red heat. Then barium 
 hydroxide and strontium hydroxide are far more soluble in water than 
 is calcium hydroxide, and all these three exhibit a very decided alkaline 
 reaction which entitles them to the name of alkaline earths. 
 
 Among the other compounds of these metals, the sulphates may be 
 named as presenting a gradation of a similar description ; for barium 
 sulphate may be said to be insoluble in water, strontium sulphate 
 
SOUECES OF MAGNESIUM. 373 
 
 dissolves to a very slight extent, and calcium sulphate is much more 
 soluble. 
 
 The manner in which these metals are associated in nature is also not 
 without its significance : for if two of them are found in the same 
 mineral they will usually be those which stand next to each other in 
 the group ; thus strontium carbonate is found together with barium 
 carbonate in witherite, whilst calcium carbonate is associated with 
 strontium sulphate in celestine. Again, strontium carbonate is often 
 found with calcium carbonate in aragonite. Such facts lend support to 
 the hypotheses of Crookes and others as to the possible evolution of the 
 elements. 
 
 MAGNESIUM. 
 
 Mg" = 24.2 parts by weight. 
 
 201. Magnesium is found, like calcium, though less abundantly, in 
 each of the three natural kingdoms. Among minerals containing this 
 metal, those with which we are most familiar are certain combinations 
 of silica and magnesia (silicates of magnesium) known by the names of 
 talc, steatite or French chalk, asbestos, and meerschaum, which always 
 contains water. Magnesite is a carbonate of magnesium. Most of the 
 minerals containing magnesium have a remarkably soapy feel. The 
 compounds of magnesium, which are employed in medicine, are derived 
 either from the mineral dolomite, or magnesian limestone, which contains 
 the carbonates of magnesium and calcium, or from the magnesium 
 sulphate which is obtained from sea water and from the waters of many 
 mineral springs. 
 
 Metallic magnesium is important as a source of light. When the 
 extremity of a wire of this metal is heated in a flame, it takes fire, and 
 burns with a dazzling white light,* becoming magnesia (MgO). If the 
 burning wire be plunged into a bottle of oxygen, the combustion is still 
 more brilliant. The light emitted by burning magnesium induces 
 chemical changes similar to those caused by sunlight, a circumstance 
 turned to advantage for the production of photographic pictures, for 
 which purpose the powdered metal is blown through a flame producing 
 a flash of very short duration but intense luminosity. Attempts have 
 been made to introduce magnesium as an illuminating agent for general 
 purposes, but the large quantity of solid magnesia produced in its com- 
 bustion forms a very serious obstacle to its use. The metal is obtained 
 by electrolysing fused carnallite (p. 335), which, when melted, loses its 
 water and becomes KCl.MgCl 2 . The liquid is contained in an iron 
 vessel externally heated and serving as the cathode. The anode is a 
 carbon rod surrounded by a porous cylinder and partly immersed in the 
 fused mass. The metal separates at the cathode and floats on the top 
 of the liquid, while the chlorine escapes at the anode and is kept from 
 the metal by the porous cylinder. To prevent the Mg from burning 
 the atmosphere in the vessel must be nitrogen. This electrolysis has 
 displaced the older method of reducing MgCl 2 by fusing it with 
 sodium. 
 
 * A wire of 0.33 millimetre diameter gives a light of 74 candle-power. Although the 
 illuminatiu" power of the sun's rays is 524 times that of burning Mg, their chemical activity 
 is only 5 times as great. The heat of combustion is Mg,O = 143,400 calories. 
 
374 MAGNESIA. 
 
 In most of its physical and chemical characters, magnesium resembles 
 zinc, though its colour more nearly approaches that of silver ; in ductility 
 and malleability, it also surpasses zinc. It is nearly as light, however, 
 as calcium, its specific gravity being 1.74. It fuses about 750 C., and 
 may be distilled like zinc. Cold water has scarcely any action upon 
 magnesium; even when boiled, it oxidises the metal very slowly. 
 In the presence of acids, however, it is rapidly oxidised by water. 
 Solution of ammonium chloride also dissolves it, owing to the tendency 
 of the magnesium salts to form double salts with those of ammonium ; 
 4NH 4 C1 + Mg = (NH 4 ) 2 MgCl 4 + H 2 + 2NH 3 . Magnesium is one of the 
 few elements which unite directly with nitrogen at a high temperature. 
 The magnesium nitride, Mg 3 N 2 , has been obtained in transparent 
 crystals, and is evidently composed after the type 2NH 3 , so that it is 
 not surprising that the action of water upon it gives rise to magnesia 
 and ammonia ; Mg 3 N 2 + 3H 2 O = 2NH 3 + 3MgO. If a foot of Mg tape 
 be burnt in air, the residue evolves much NH 3 when boiled with water. 
 
 Magnesia, MgO, occurs, crystallised in octahedra, as the mineral 
 periclase. It is prepared by decomposing magnesium carbonate by heat, 
 and is a light white powder, very infusible (so that it is used for making 
 basic fire-bricks) and scarcely affected by water. It dissolves easily in 
 acids. Magnesium hydroxide, Mg(OH) 2 , also occurs crystallised as 
 brucite. When MgO is mixed with water, combination occurs, but not 
 with much evolution of heat, as with BaO, SrO, and CaO. If excess 
 of water be avoided, the mass sets like plaster of Paris. Mg(OH) 2 is 
 precipitated when an alkali is added to a magnesium salt. The 
 hydroxide slowly absorbs CO 2 from the air, and is easily decomposed by 
 heat into MgO and H 2 O. It is used in extracting sugar from the beet. 
 
 Magnesium carbonate, MgC0 3 , is found as magnesite, which is 
 imported from Greece. It is unaffected by water, and does not effervesce 
 so briskly with acids as do the other carbonates. It is easily decomposed 
 by heat into MgO and C0 2 . When a salt of magnesium is precipitated 
 by an alkali carbonate, the precipitate is not the normal carbonate, as 
 in the cases of Ba, Sr, and Ca, but a basic carbonate, or a compound of 
 the carbonate and hydroxide. Ordinary magnesia alba, or light carbo- 
 nate of magnesia, is prepared by precipitating magnesium sulphate with 
 sodium carbonate, and boiling ; it generally has the composition 
 5MgC0 3 .2Mg(OH) 2 .7Aq. In preparing the heavy carbonate, the mixed 
 solutions are evaporated to dryness, and the sodium sulphate washed 
 out of the residue by water. These light and heavy carbonates, when 
 calcined, yield light and heavy magnesia, the former having 3^ times 
 the bulk of the latter. 
 
 Magnesium carbonate, like CaC0 3 , is soluble in carbonic acid, and is 
 present in most natural waters, causing temporary hardness, the MgCO 3 
 being precipitated by boiling. When magnesia alba is dissolved in 
 carbonic acid water, and the solution exposed to air, needles of 
 MgC0 3 -3Aq are deposited. If this be boiled with water, it loses C0 2 
 and becomes a basic carbonate. 
 
 Dolomite or magnesium limestone, is a mixture of magnesium carbonate 
 and calcium carbonate in variable proportions. Magnesium carbonate 
 is prepared from it by heating it sufficiently to decompose the MgCO 3 , 
 and exposing it, under pressure, to the action of water and C0 2 , when 
 the MgO is dissolved and the CaC0 3 is left. By passing steam through 
 
EPSOM SALTS. 375 
 
 the solution, the basic magnesium carbonate is precipitated. Pearl spar 
 is a crystalline form of the double carbonate, MgCa(CO 3 ) 2 . 
 
 The sulphate of magnesia or magnesium sulphate, so well 
 known as Epsom salts, is sometimes prepared by calcining dolomite to 
 expel the CO,, washing the residual mixture of lime and magnesia with 
 water to remove part of the lime, and treating it with sulphuric acid, 
 which converts the calcium and magnesium into sulphates ; and since 
 calcium sulphate is almost insoluble in water, it is readily separated from 
 the magnesium sulphate which passes into the solution, and is obtained by 
 evaporation in prismatic crystals, having the composition MgSO 4 .H 2 0.6Aq, 
 Epsom salts are now made from Kieserite, MgS0 4 .H 2 0, found in the 
 Stassfurt salt beds. This is almost insoluble in water, but, when kept 
 in contact with it, is slowly converted into MgS0 4 .7H 2 0. The prepara- 
 tion of Epsom salts from sea water has already been alluded to (p. 344). 
 
 In some parts of Spain, magnesium sulphate is found in large quantities (like 
 nitre in hot climates) as an efflorescence upon the surface of the soil. This sulphate, 
 as well as that contained in well-waters, appears to have been produced by the 
 action of the calcium sulphate, originally present in the water, upon magnesian 
 limestone rocks ; MgC0 3 + CaS0 4 = MgS0 4 + CaC0 3 . 
 
 The crystals MgS0 4 .7H 2 fuse easily, and become MgS0 4 .H 2 Oat 150 C. The 
 last H 2 0, can only be expelled at above 200, and is termed the water of constitu- 
 tion. 
 
 The water of constitution in the magnesium sulphate may be displaced by the 
 sulphate of an alkali-metal without alteration in its crystalline form ; a double 
 sulphate of magnesium and potassium (MgS0 4 .K 2 SO 4 .6Aq), and a similar salt of 
 ammonium may be thus obtained. The mineral polyhaUte (TTO\I/S, many, #Xs, salt) 
 is a remarkable salt, containing MgS0 4 .K 2 S0 4 .2CaS6 4 .2H 2 0.* Water decomposes 
 it into its constituent salts. 
 
 Epsom salts dissolve very easily in water, but not in alcohol. If the aqueous 
 solution be mixed with enough alcohol to render it turbid, small oily drops 
 separate, from which small crystals presently shoot out, and the liquid becomes, 
 by degrees, a pasty mass of very light needles closely interlaced. These contain 
 7H 2 0. An aqueous solution crystallised at above 70 C. deposits MgS0 4 .H 2 0.5Aq ; 
 at 6, crystals of MgS0 4 .H 2 0. iiAq are formed. 
 
 Phosphates of magnesium. Mg 3 (PO 4 ) 2 is contained in bones and in some seeds. 
 MgHP0 4 .7Aq is the precipitate produced by Na 2 HP0 4 in magnesium salts ; it is de- 
 composed by boiling with water ; 3MgHP0 4 = H 3 P0 4 + MggCPO^o. MgNH 4 P0 4 . 6Aq 
 is deposited in crystals from alkaline urine, and forms triple phosphate calculi. 
 It is precipitated by Na 2 HP0 4 from a magnesium salt to which NH 3 has been 
 added; MgS0 4 + NH 3 + Na 2 HP0 4 = Na 2 S0 4 + MgNH 4 P0 4 . Ammonium chloride 
 should be added first to prevent the separation of Mg(OH) 2 . The precipitation 
 is much promoted by stirring ; the MgNH 4 P0 4 is sparingly soluble in water, 
 and almost insoluble in ammonia ; when it is heated to redness, 2MgNH 4 P0 4 = 
 Mg 2 P 2 7 + NH 3 + H 2 0. In quantitative analysis, Mg and P are generally deter- 
 mined in this form. 
 
 Magnesium-ammonium arsenate, MgNH 4 As0 4 .6H 2 0, is very similar, and is used 
 in determining arsenic. 
 
 Magnesium .bo-rate and chloride compose the mineral stassfurtite ; hydroboracite 
 is a hydrated borate of calcium and magnesium. 
 
 Serpentine, 2SiO 2> 3(Mg,Fe)0, and olivine, Si0 2 .3(Mg,Fe)0, are silicates 
 of magnesia and ferrous oxide. Some of the varieties of serpentine are 
 used for preparing the compounds of magnesium, being easily decom- 
 posed by acids with separation of silica. The minerals, asbestos, meer- 
 schaum, steatite, and talc consist chiefly of magnesium silicates. 
 
 Magnesium chloride occurs in sea-water, in brine-springs, in many 
 natural waters and in the minerals carnallite (p. 335) and bischqfite, 
 
 * Polyhalite is found in the salt-beds of Stassfurt. Kainite, from the same locality, is 
 K 2 S0 4 .MgS0 4 .MgCl 2 .6Aq. 
 
376 USES OF ZINC. 
 
 MgCl 2 .6Aq. It is easily obtained in solution by neutralising hydro- 
 chloric acid with magnesia or its carbonate ; but if this solution be 
 evaporated in order to obtain the dry chloride, a considerable quantity 
 of the salt is decomposed by the water at the close of the evaporation, 
 leaving much magnesia mixed with the chloride (MgCl 2 + H 2 O = 
 2HCl + MgO). This decomposition may be prevented by mixing the 
 solution with three parts of chloride of ammonium for every part of 
 magnesia, when a double salt, MgCl 2 .2NH 4 Cl, is formed, which may be 
 evaporated to dry ness without decomposition, and leaves fused magne- 
 sium chloride when further heated, the ammonium chloride being 
 volatilised. The magnesium chloride absorbs moisture very rapidly 
 from the air, and is very soluble in water. Like all the soluble salts of 
 magnesium, it has a decidedly bitter taste. When magnesia is moist- 
 ened with a strong solution of magnesium chloride, it sets into a hard 
 mass like plaster of Paris, apparently from the formation of an oxy- 
 chloride. It may be mixed with several times its weight of sand, and 
 will bind the sand firmly together. 
 
 The ammonium magnesium chloride, NH 4 Cl.MgCl2.Aq, is not decom- 
 posed by ammonia, which therefore gives no precipitate in solutions of 
 magnesium to which NH 4 C1 has been added in sufficient quantity. 
 
 Magnesium stands apart from other metals, on the one hand, by the 
 non-precipitation of its sulphide, and, on the other, by the tendency of 
 all its salts, except the phosphate and arsenate, to form soluble com- 
 pounds with the salts of ammonium. 
 
 ZINC. 
 
 Zn" = 65 parts by weight = 2 vols. 
 
 2 02. Zinc occupies a high position among useful metals, being pecu- 
 liarly fitted, on account of its lightness, for the construction of gutters, 
 water-pipes, and roofs of buildings, and possessing for these purposes a 
 great advantage over lead, since the specific gravity of the latter metal 
 is about 11.5, whilst that of zinc is only 7. For such applications as 
 these, where great strength is not required, zinc is preferable to iron, on 
 account of its superior malleability; for although a bar of zinc breaks 
 under the hammer at the ordinary temperature, it becomes so malleable 
 at 250 F. (121 C.) as to admit of being rolled into thin sheets. This 
 malleability of zinc when heated was discovered only in the commence- 
 ment of the last century, until which time the sole use of the metal was 
 in the manufacture of brass. When zinc is heated to 400 F. (204 C.), 
 it again becomes brittle, and may be powdered in a mortar. The easy 
 fusibility of zinc also gives it a great advantage over iron, as rendering 
 it easy to be cast into any desired form ; indeed, zinc is surpassed in 
 fusibility (among the metals in ordinary use) only by tin and lead, its 
 melting-point being below a red heat, and usually estimated at 786 F. 
 (410 C.). Zinc is also less liable than iron to corrosion under the in- 
 fluence of moist air, for although a bright surface of zinc soon tarnishes 
 when exposed to the air, it merely becomes covered with a thin film of 
 zinc oxide (passing gradually into basic carbonate, by absorption of CO 2 
 from the air) which protects the metal from further action. 
 
 The great strength of iron has been ingeniously combined with the 
 durability of zinc, in the so-called galvanised iron, which is made by 
 
EXTRACTION OF ZINC. 377 
 
 coating clean iron with melted zinc, thus affording a protection much 
 needed in and around large towns, where the sulphurous and sulphuric 
 acids arising from the combustion of coal, and the acid emanations from 
 various factories, greatly accelerate the corrosion of unprotected iron. 
 The iron plates to be coated are first thoroughly cleansed by a process 
 which will be more particularly noticed in the manufacture of tin-plate, 
 and are then dipped into a vessel of melted zinc, the surface of which is 
 coated with sal ammoniac (ammonium chloride) in order to dissolve the 
 zinc oxide which forms upon the surface of the metal, and might 
 adhere to the iron plate so as to prevent its becoming uniformly coated 
 with the zinc.* A more firmly adherent coating of zinc is obtained by 
 first depositing a thin film of tin upon the surface of the iron plate by 
 galvanic action, and hence the name galvanised iron. 
 
 The ores of zinc are found pretty abundantly in England, chiefly in 
 the Mendip Hills in Somersetshire, at Alston Moor in Cumberland, in 
 Cornwall and Derbyshire, but the greater part of the zinc used in this 
 country is imported from Belgium and Germany, being derived from 
 the ores of Transylvania, Hungary, and Silesia. 
 
 Metallic zinc is never met with in nature. Its chief ores are cola- 
 mine or zinc carbonate (ZnC0 3 ), blende or zinc sulphide (ZnS), and red 
 zinc ore, in which zinc oxide (ZnO) is associated with the oxides of iron 
 and manganese. 
 
 Calamine is so called from its tendency to form masses resembling a bundle of 
 reeds (calamus, a reed). It is found in considerable quantities in Somersetshire, 
 Cumberland, and Derbyshire. A compound of zinc carbonate with zinc hydroxide 
 ZnC0 3 .2Zn(OH) 2 , is found abundantly in Spain. The mineral known as electric 
 calamine (hemimorphite) is a silicate of zinc (2ZnO.Si0 2 .H 2 0), which becomes 
 electrified when heated. Blende derives its name from the German blenden, to 
 dazzle, in allusion to the brilliancy of its crystals, which are generally almost black 
 from the presence of iron sulphide, the true colour of pure zinc sulphide being 
 white. Blende is found in Cornwall, Cumberland, Derbyshire, Wales, and the Isle 
 of Man, and is generally associated with galena or lead sulphide, which is always 
 carefully picked out of the ore before smelting it, since it would become converted 
 into lead oxide, which corrodes the earthern retorts employed in the process. 
 
 Before extracting the metal from these ores, they are subjected to a 
 preliminary treatment which brings them both to the condition of zinc 
 oxide. For this purpose the calamine is simply calcined in a reverbera- 
 tory furnace, in order to expel carbonic acid gas; but the blende is 
 roasted for ten or twelve hours, with constant stirring, so as to expose 
 fresh surfaces to the air, when the sulphur passes off in the form of 
 S0 2 , and its place is taken by the oxygen, the ZnS becoming ZnO. The 
 extraction of the metal from this zinc oxide depends upon the circum- 
 stance that zinc is capable of being distilled at a bright red heat, its 
 boiling-point being about 930 C. 
 
 The facility with which this metal passes oft' in the form of vapour is 
 seen w T hen it is melted in a ladle over a brisk fire, for at a bright red 
 heat abundance of vapour rises from it, which, taking fire in the air, 
 burns with a brilliant greenish-white light, throwing off into the air, 
 numerous white flakes of light zinc oxide (the philosophers wool, or nil 
 album of the old chemists). 
 
 * The sal ammoniac acts upon the heated zinc according to the equation, Zn + 2XH 4 Cl=: 
 ZnCl2 + 2XH 3 + H 2 , and the zinc chloride which is formed dissolves the oxide from the 
 surface of the metal, producing' zinc oxychloride. 
 
378 
 
 EXTRACTION OF ZINC. 
 
 The distillation of zinc may be effected on the small scale in a black-lead crucible 
 (A, Fig. 215) about 5 inches'high and 3 in diameter. A hole is drilled through the 
 bottom with a round file, and into this is fitted a piece of wrought-iron gas-pipe 
 (B) about nine inches long and I inch wide, so as to reach nearly to the top of the 
 inside of the crucible. Any crevices between the pipe and the sides of the hole 
 are carefully stopped up with fireclay moistened with solution of borax. A few 
 ounces of zinc are introduced into the crucible, the cover of which is then carefully 
 cemented on with fireclay (a little borax being added to bind it together at a high 
 temperature), and the hole in the cover is stopped up with fireclay. The crucible 
 having been kept for several hours in a warm place, so that the clay may dry, it is 
 placed in a cylindrical furnace with a hole at the bottom, through which the iron 
 pipe may pass, and a lateral opening, into which is inserted an iron tube (C) con- 
 nected with a forge bellows. Some lighted charcoal is thrown into the furnace, 
 and when this has been blown into a blaze, the furnace is filled up with coke 
 broken into small pieces. The fire is then blown till the zinc distils freely into a 
 vessel of water placed for its reception. Four ounces of zinc may be easily distilled 
 in half an hour. 
 
 The original English method for extracting zinc from the roasted ore& 
 consisted in mixing the ground ore with about half its weight of coke r 
 
 and strongly heating the 
 mixture in crucibles pro- 
 vided with tubes, like 
 that shown in Fig. 215; 
 the zinc was thus distilled 
 per descensum in the 
 manner described in the 
 preceding paragraph. 
 The reduction of zinc 
 oxide by carbon is repre- 
 sented by the equation 
 
 Fig. 215. 
 Distillation of zinc. 
 
 Fig. 216. 
 Belgian zinc furnace. 
 
 This reaction is found to be 
 endothermic when its thermal 
 value is calculated from 
 ordinary data (see p. 307),. 
 which will account for the 
 very high temperature (1300 
 C.) required to effect the 
 
 reduction ; this is probably aided by the volatility of zinc, which escapes from the 
 sphere of action as soon as it is liberated, and allows a mass action of the carbon to 
 come into play (see p. 310). 
 
 At the present day the reduction and distillation of zinc is effected 
 in retorts, which are either of the Belgian or the Silesian type ; the 
 construction of each will be understood from the accompanying figures. 
 
 At Liege, in Belgium, calamine is exposed to the rain for several months in 
 order -to wash out the clay ; it is then calcined and mixed with half its weight of 
 coal-dust, and distilled in cylindrical fireclay retorts (C, Fig. 216), holding about 
 40 Ibs. each, and set in seven tiers of six each in the same furnace, the vapour of 
 zinc being conveyed by a; short conical iron pipe (B) into a conical iron receiver 
 (D), which is emptied every two hours into a large ladle, from which the zinc is 
 poured into ingot moulds. Each distillation occupies about twelve hours. The 
 advantage of this particular mode of arranging the cylinders is, that it economises 
 fuel by allowing the poorer ores, which require less heat to distil all the zinc from 
 them, to be introduced into the upper rows of cylinders farthest from the fire (A). 
 There are two varieties of Belgian ore, one containing 33 and the other 46 per 
 cent, of zinc, but a large proportion of this is in the form of silicate, which is not 
 extracted by the distillation. 
 
 In Silesia the zinc oxide is mixed with fine cinders, and distilled in arched 
 
EXTRACTION OF ZINC. 
 
 379 
 
 earthen retorts (A, Fig. 217), into which the charge is introduced through a small 
 door (B), which is then cemented up. The retorts are arranged in a double row 
 in the same furnace (Fig. 218), and the vapour of zinc is condensed in a bent 
 earthenware pipe attached to each retort, and having an opening (C) near the 
 bend, which is kept closed, unless it is necessary to clear out the pipe. 
 
 The Silesian zinc is remelted, before casting into ingots, in clay in- 
 stead of iron pots, since melted zinc always dissolves iron, and a very 
 small quantity of that 
 metal is found to injure 
 zinc when required for 
 rolling into sheets. 
 
 A small quantity of 
 lead always distils over 
 together with the zinc, 
 and since this metal also 
 interferes with the roll- 
 ing of zinc into sheets, 
 a portion of it is sepa- 
 rated from zinc intended 
 for this purpose, by 
 melting the spelter, in 
 large quantity, upon the 
 hearth of a reverberatory 
 furnace, the bed of which 
 is inclined so as to form 
 a deep cavity at the end 
 nearest the chimney. 
 The specific gravity of 
 lead being 11.4, whilst that of zinc is 7, the former accumulates chiefly 
 at the bottom of the cavity, and the ingots cast from the upper part of 
 the melted zinc will contain but little lead, since zinc is not able to 
 dissolve more than 1.5 per cent, of that metal at 400 C. 
 
 The electrolytic extraction of zinc is said to be practised at some places. By one 
 process the roasted ore is leached with dilute sulphuric acid which dissolves the 
 zinc oxide as sulphate ; the solution is passed over metallic zinc to deposit other 
 metals electro- negative to zinc, and electrolysed with zinc cathodes and carbon 
 anodes. The zinc is deposited on the former, and oxygen evolved at the latter, 
 dilute H 2 S0 4 being left in the liquid to be used to leach more ore. 
 
 Ingots of zinc, when broken across, exhibit a beautiful crystalline 
 fracture, which, taken in conjunction with 'the bluish colour of the 
 metal, enables it to be easily identified. The spelter of commerce is 
 liable to contain lead, iron, tin, antimony, arsenic, copper, cadmium, 
 magnesium, and aluminium. Belgian zinc is usually purer than the 
 English metal. 
 
 Zinc being easily dissolved by diluted acids, it is necessary to be 
 careful in employing this metal for culinary purposes, since its soluble 
 salts are poisonous. 
 
 It will be remembered that the action of diluted sulphuric acid upon zinc is 
 employed for the preparation of hydrogen. Pure zinc, however, evolves hydrogen 
 very slowly, since it becomes covered with a number of hydrogen bubbles which 
 protect it from further action ; but if a piece of copper or platinum be made to 
 touch the zinc beneath the acid, these metals, being electro-negative towards the 
 zinc, will attract the electro-positive hydrogen, leaving the zinc free from bubbles, 
 and exposed on all points to the action of the acid, so that a continuous dis- 
 
 Fig. 218. Silesian zinc furnace. 
 
380 ZINC WHITE. 
 
 engagement of hydrogen is maintained. As a curious illustration of this, a thin 
 sheet of platinum or silver foil may be shown to sink in diluted sulphuric acid, 
 until it comes in contact with a piece of zinc, when the bubbles of hydrogen bring 
 it up to the surface. The lead, iron, &c.. met with in commercial zinc, are electro- 
 negative to the zinc, and thus serve to maintain a constant evolution of hydrogen. 
 
 Zinc also dissolves in boiling solutions of potash arid soda, evolving 
 hydrogen; 2KOH + Zn = Zn(OK) 2 + H 2 . Even solution of ammonia 
 dissolves it slowly. When heated with Ca(OH) 2 it evolves hydrogen. 
 
 A coating of metallic zinc may be deposited upon copper by slow 
 galvanic action, if the copper be immersed in a concentrated solution of 
 potash, at the boiling-point of water, in contact with metallic zinc, 
 when a portion of the latter is dissolved in the form of oxide, with 
 evolution of hydrogen, and is afterwards precipitated, on the surface of 
 the copper. 
 
 Zinc-dust is metallic zinc which has condensed in a fine powder in 
 smelting the ores. It is very useful in the laboratory as a reducing-agent. 
 
 Zinc oxide (ZnO). Zinc forms but one oxide, which is known in 
 commerce as zinc-white or Chinese white, and is prepared by allowing 
 the vapour of the metal to burn in earthen chambers through which a 
 current of air is maintained. It is practically insoluble in water, and 
 is sometimes used for painting in place of white lead (basic lead car- 
 bonate), over which it has the advantages of not injuring the health of 
 the persons using it, and of being unaffected by sulphuretted hydrogen, 
 an important consideration in manufacturing towns where tnat sub- 
 stance is so abundantly supplied to the atmosphere. Unfortunately, 
 however, the zinc oxide paint has less covering power and is more liable 
 to peel off than white lead paint. The zinc oxide has the character- 
 istic property of becoming yellow when heated, and white again as it 
 cools. Its sp. gr. is 5.6. It is sometimes used in the manufacture of 
 glass for optical purposes. At the temperature of the electric arc it is 
 volatile. 
 
 Zinc hydroxide, Zn(OH) 2 , is precipitated in a gelatinous state when caustic 
 alkalies are added to solutions containing zinc ; the precipitate dissolves in the 
 excess of alkali, and, if this be not too great, is reprecipitated by boiling. The 
 alkaline solution is said to contain an alkali zincate, e.g., K 2 Zn0 2 . Ammonia does 
 not precipitate zinc hydroxide from solutions containing ammonium salts, since 
 zinc resembles magnesium in forming double salts containing ammonium. Zinc 
 hydroxide is easily decomposed by heat ; Zn(OH) 2 = ZnO + H 2 0. 
 
 Zinc nitride, Zn 3 N 2 . When zinc ethide (see Org a no-mineral Compounds) is acted 
 on by ammonia, it is converted into zinc-diamine ; Zn(C 2 H g ) 2 + 2NH 3 = Zn(NH 2 ) + 
 2C 2 H 6 (ethyl hydride). When zinc-diamine is heated, out of contact with air, it 
 gives zinc nitride; 3Zn(NH 2 ) 2 = Zn 3 N 2 + 4NH 3 . The nitride decomposes with 
 water, evolving much heat ; Zn 3 N 2 + 3H 2 = 2NH 3 + 3ZnO. 
 
 Zinc carbonate, ZnCO 3 , as found in nature (calamine, timithsonite) 
 forms rhombohedral crystals. The place of part of the zinc in the 
 mineral is often taken by isomorphous metals, such as cadmium, 
 magnesium, and ferrous iron. ZnC0 3 is precipitated when ZnS0 4 is 
 boiled with KHC0 3 ; ZnS0 4 + 2 KHC0 3 = Zn00 3 + K 2 SO 4 + H 2 O + C0 2 . 
 The normal alkali carbonates precipitate basic carbonates of variable 
 composition (as is the case with magnesium). The precipitate produced 
 by ammonium carbonate is soluble in excess. 
 
 Zinc chloride, ZnCl 2 ( = 136.5 = 2 volumes), is prepared by dissolving 
 Zn or ZnO in HOI, and evaporating*. If the solution contains a little 
 
 * If iron be present, it may be separated by adding- a little chlorine water to peroxidise 
 it, and precipitating it aa hydrated Fe 2 O 3 by adding- zinc carbonate. 
 
ZINC SULPHATE. 381 
 
 HC1 in excess, it deposits octahedral crystals of ZnCl 2 .H 2 O. The solu- 
 tion, like that of MgCl,, undergoes partial decomposition when evapor- 
 ated leaving an oxychloride ; when this residue is distilled, ZnCl 2 passes 
 over. It may also be obtained by distilling a mixture of zinc sulphate 
 and sodium chloride. Zinc chloride is a deliquescent solid, very soluble 
 in water, alcohol, and ether; it melts at 250 C. and boils at 730 C. 
 Its attraction for water renders it a powerful caustic, and it is used as 
 such in surgery. A strong solution of ZnCl 2 dissolves much ZnO, and 
 if the solution of oxychloride thus formed be mixed with water, precipi- 
 tates are obtained which contain Zn(OH)Cl and Zn(OH) 2 . Solution of 
 ZnCl 2 dissolves paper and cotton, and the oxychloride dissolves wool and 
 silk. This is sometimes useful in examining textile fabrics. 
 
 When zinc oxide is moistened with a strong solution of zinc chloride, 
 an oxychloride is formed, which soon sets into a hard mass, forming a 
 very useful stopping for teeth. 
 
 Burnett's disinfecting fluid is a solution of zinc chloride, and is capable of 
 absorbing H 2 S, NH 3 , and other offensive products of putrefaction, as well as of 
 arresting the decomposition of wood and animal substances. Zinc chloride is also 
 used in soldering, to cleanse the metallic surface, and the careless use of this 
 poisonous salt in soldering tins of preserved food has frequently caused accidents. 
 
 Zinc chloride is sometimes made from pyrites containing blende. This is burnt 
 as usual to furnish S0 2 for the manufacture of sulphuric acid, when the ZnS is con- 
 verted into ZnS0 4 which is extracted from the spent pyrites by water, and decom- 
 posed with sodium chloride, when Na 2 SO 4 is deposited in crystals, leaving ZnCl 2 in 
 solution. 
 
 Zinc sulphate, or white vitriol, ZnS0 4 .H 2 O.6Aq, bears a dangerous 
 resemblance to Epsom salts, but it loses its water of crystallisation at 
 100 C., and is decomposed at a very high temperature into ZnO, 
 sulphur dioxide, and oxygen, whereas MgS0 4 bears fusion without 
 being decomposed. Hence ZnSO 4 , when heated to redness, leaves a 
 residue which is yellow when hot and white w T hen cold. 
 
 At temperatures above 40 C. zinc sulphate crystallises as ZnS0 4 
 H 2 0.5Aq. which is isomorphous with the corresponding salt of mag- 
 nesium. Like the magnesium sulphate, it forms double sulphates, in 
 which the H 2 O is exchanged for alkali sulphates. ZnSO 4 .K 2 S0 4 .6Aq 
 and ZnS0 4 .(NH 4 ) 2 S0 4 .6Aq are isomorphous with the Mg double salts. 
 Like all other truly isomorphous salts, the sulphates of magnesium and 
 zinc crystallise together from their mixed solutions. 
 
 It is made on the large scale by roasting blende (zinc sulphide, ZnS) 
 at a low red heat, when it combines with O from the air to form 
 ZnS0 4 , which is dissolved out by water and crystallised. It has a 
 metallic, nauseous taste, and is used medicinally and in dyeing. 
 
 Zinc sulphide, ZnS, as found native, is usually crystallised in octa- 
 hedra or dodecahedra, coloured black by ferrous sulphide (black Jack"). 
 Pale yellow specimens are sometimes found. When precipitated by a 
 soluble sulphide from a solution of a zinc salt it is perfectly white, but 
 it darkens somewhat when exposed to air and light. 
 
 An intimate mixture of zinc-dust with half its weight of flowers 
 of sulphur burns like gunpowder when kindled with a match, 
 leaving a bulky mass of ZnS, which is primrose-yellow while hot, and 
 white on cooling. Zinc sulphide is insoluble in water, in alkalies, 
 and in acetic acid, but dissolves in HC1 and in HN0 3 . It may be 
 sublimed in colourless crystals by strongly heating in a current of H 2 S. 
 
382 PROPERTIES OF CADMIUM. 
 
 Zinc silicate is found as electric calamine, Zn 2 Si0 4 .Aq, in rhombic 
 crystals. Zinc phosphate forms the mineral hopeite, Zn 3 (P0 4 ) 2 .4Aq. 
 
 Zinc differs from all the other common metals in being precipitated 
 as a white sulphide. 
 
 CADMIUM. 
 
 Cd"=m.6 parts by weight = 2 vols. 
 
 203. This metal is found in small quantities in the ores of zinc, its 
 presence being indicated during the extraction of that metal (p. 378) by 
 the appearance of a brown flame (brown blaze) at the commencement of 
 the distillation, before the characteristic zinc flame is seen at the orifice 
 of the receiver. Cadmium is more easily vaporised than zinc, boiling 
 at 778 C., so that the bulk of it is found in the first portions of the 
 distilled metal, If the mixture of cadmium and zinc be dissolved in 
 diluted sulphuric acid, and the solution treated with hydrosulphuric 
 acid gas, a bright yellow precipitate of cadmium sulphide (CdS) is 
 obtained, which is employed in painting under the name of cadmia or 
 cadmium yellow* By dissolving this in strong hydrochloric acid and 
 adding ammonium carbonate, cadmium carbonate (CdC0 3 ) is precipi- 
 tated from which metallic cadmium may be extracted by distillation 
 with charcoal. 
 
 Although resembling zinc in its volatility and its chemical relations, 
 in appearance it is much more similar to tin, and emits a crackling 
 sound like that metal when bent. Like tin, also, it is malleable and 
 ductile at the ordinary temperature, and becomes brittle at about 
 82 C. Cadmium is slightly heavier than zinc, sp. gr. 8.6, and has a 
 lower melting-point, 320 C., so that it is useful for making fusible 
 alloys. An alloy of 3 parts of cadmium with 16 of bismuth, 8 of lead, 
 and 4 of tin, fuses at 60 C. In its behaviour with acids and alkalies 
 cadmium is similar to zinc, but the metal is easily distinguished from 
 all others by its yielding a characteristic chestnut-brown oxide when 
 heated in air. This oxide (CdO) is the only oxide of cadmium. 
 
 An amalgam of cadmium and mercury is used by dentists for stopping 
 teeth, for while it is plastic when freshly made it rapidly hardens. It 
 is also electro-deposited as an alloy with silver instead of ordinary 
 electro-plating. 
 
 Cadmium chloride, CdCl 2 .2Aq, effloresces in air, whilst zinc chloride deliquesces. 
 Moreover, it may be dried without undergoing partial decomposition. It is fusible 
 and volatile like zinc chloride. Cadmium bromide, CdBr 2 .4Aq, and the iodide, CdI 2 , 
 are used in photography. Cadmium sulphate, 3CdS0 4 .8Aq is much less soluble 
 than zinc sulphate. 
 
 Cadmium differs from all the other metals in forming a yellow sulphide 
 insoluble in alkalies, so that its salts, mixed with excess of ammonia, 
 and treated with H 2 S, give a yellow precipitate. 
 
 BERYLLIUM, OR GLUCINUM. 
 Be" or Gr = 9 parts by weight. 
 
 204. This comparatively rare metal (which derives its name from the sweet 
 taste of its salts, yXvicts, sweet) is found associated with silica and alumina in 
 the emerald, which is a double silicate of A1 2 3 and BeO (Al 2 3 .3Be0.6Si0 2 ), and 
 
 * The darker varieties of this pigment contain thallium. 
 
OCCURRENCE OF ALUMINIUM. 383 
 
 appears to owe its colour to the presence of a minute quantity of chromium oxide. 
 The more common mineral beryl or aquamarine, has a similar composition, but is 
 of a paler green colour, apparently caused by iron. Chrysoben/l consists of 
 Al 2 3 .BeO, also coloured by iron. The earlier analysts of these minerals mistook 
 the beryllium oxide for alumina, which it resembles in forming a gelatinous pre- 
 cipitate on adding ammonia to its solutions, but it is a stronger base than alumina, 
 and is therefore capable of displacing ammonia from its salts, and of being dissolved 
 by them. Ammonium carbonate is employed to separate the beryllium oxide from 
 alumina, since it dissolves the former in the cold, forming a double carbonate of 
 beryllium and ammonium, from which the beryllium carbonate is precipitated on 
 boiling. Beryllium oxide, BeO, is intermediate in properties between alumina and 
 magnesia, resembling the latter in its tendency to absorb carbonic acid from the air, 
 and to form soluble double salts with the salts of ammonium, and so much re- 
 sembling alumina in the gelatinous form of its hydrate, its solubility in alkalies, and 
 the sweet astringent taste of its salts, that it was formerly regarded as a sesquioxide 
 like alumina. By the radiant matter test (p. 330), beryllium oxide phosphoresces of 
 a bright blue colour. 
 
 The metal itself is very similar to aluminium ; it is prepared by passing the 
 vapour of its chloride, BeCl 2 , over melted sodium. Its sp. gr. is 1.6. and it melts at 
 about 1000 C. It is not seriously oxidised by air and decomposes hot water very 
 slowly. 
 
 General review of the magnesium group of metals. This group 
 includes Be, Mg, Zn, Cd and Hg. As in the case of the preceding groups 
 of metals, the melting-point falls with the rise of atomic weight (Hg = 200 
 melts at -36 C.), whilst the specific gravity and atomic volume 
 (p. 304) rise with the atomic weight (sp. gr. Hg= 13.5).* Their order 
 of chemical energy, on the other hand, is the reverse of that of the 
 metals of the preceding groups, falling with rise of atomic weight. 
 Their oxides are practically insoluble in water, and are less basic as the 
 molecular weight increases. The carbonates are easily decomposed by 
 heat ; the sulphates are more easily decomposed than those of the 
 metals of the preceding groups and appear to decrease in stability with 
 rise of molecular weight. The vapours of these metals contain mon- 
 atomic molecules (p. 300). 
 
 Mercury will be considered later. 
 
 ALUMINIUM. 
 
 Al'" = 27 parts by weight. 
 
 205. Aluminium is distinguished among metals, as silicon is among 
 non-metallic bodies, for its immense abundance in the solid mineral 
 portion of the earth, to which, indeed, it is almost entirely confined, for 
 it is present in vegetables and animals in so small a quantity that it can 
 scarcely be regarded as forming one of their necessary components. 
 Church has, however, found it in certain cryptogamous plants, especially 
 in the Lycopodiums ; the ash of Lycopodium alpinum yielding one-third 
 of its weight of alumina. 
 
 One of the oldest rocks, which appears to have originally formed the 
 basis of the solid structure of the globe, is that known as granite. This 
 mineral, which derives its name from its conspicuous granular structure, 
 is a mixture, in variable proportions, of quartz, felspar, and mica, tinged 
 of various colours by the presence of small quantities of the oxides of 
 iron and manganese. 
 
 Quartz, which forms the translucent or transparent grains in the 
 
 * The atomic volume of Mg is greater than that of Zn. 
 
384 CLAY. 
 
 granite, consists simply of silica; felspar, the dull, cream-coloured,, 
 opaque part, is a combination of silica with oxides of aluminium and 
 potassium, of the composition K 2 O.3SiO 2 .Al 2 3 .Si0 2 . 
 
 Mica, so named from the glittering scales which it forms in the 
 
 franite, is also a double silicate of alumina and potash, K 9 0.3Al 2 3< 4Si0 2 , 
 ut the A1 2 3 is very frequently displaced by Fe 2 3 and the K by 
 MgO. 
 
 By the long-continued action of air and water, the granite is gradually 
 crumbled down or disintegrated, an effect which must be ascribed to a 
 concurrence of mechanical and chemical causes. Mechanically, the rock 
 is continually worn down by variations of temperature, and by the 
 congelation of water within its minute pores, the rock being gradually 
 split by the expansion attendant upon such congelation. Chemically, 
 the action of water containing carbonic acid would tend to remove 
 the potash from the felspar and mica in the form of carbonate of 
 potash, whilst the silicate of alumina and the quartz would subsequently 
 be separated by the action of water ; the former being so much lighter, 
 would be soon washed away from the heavy quartz, and, when again 
 deposited, would constitute clay, the purest form of which is kaolin 
 (Al 2 3 .2Si0 2 .2H 2 0). 
 
 Although clay, therefore, always consists mainly of silicate of alumina, 
 it generally contains some uncombined silicic acid, together with 
 variable proportions of lime, of oxide of iron, &c., which give rise to the 
 numerous varieties of clay. Thus a pure Chinese kaolin will contain, 
 per cent. 
 
 Si0 2 A1 2 3 H 2 Fe 2 3 MgO Alkalies 
 5-5 33-7 * i "2 1.8 0.8 1.9 
 
 whilst Stourbridge fireclay will contain about 85 per cent, of this clay- 
 substance and some 15 per cent, of silica as quartz. 
 
 The silicate of alumina also constitutes the chief portion of several 
 other very important mineral substances, among which may be mentioned 
 slate, fuller s earth, and pumice-stone. Marl is clay containing a con- 
 siderable quantity of carbonate of lime. Loam is also an impure variety 
 of clay. The different varieties of ochre, as well as umber and sienna, 
 are simply clays coloured by the oxides of iron and manganese. 
 
 Notwithstanding the abundance of aluminium in the form of clay, it 
 is only comparatively recently that the metal has been extracted in 
 quantity sufficient to make it of practical importance. Originally the 
 metal was prepared by fusing the chloride, preferably in the form of 
 the double chloride, Al 2 Cl 6 .2NaCl, with sodium, which abstracted the 
 chlorine. Now, however, aluminium is prepared by the electrolysis of 
 a bath of fused cryolite (the double fluoride of aluminium and sodium, 
 Na 3 AlF 6 ), containing aluminium oxide (alumina, A1 8 O 3 ), dissolved in it ; 
 the metal is deposited around the cathode, oxygen, and probably also 
 fluorine, being evolved at the anode. 
 
 An iron box with double walls between which water is circulated has a steel plug 
 protruding through its bottom ; this plug serves as the cathode, the anode being a 
 bundle of carbon rods suspended a short distance above the plug. At first an arc is 
 struck between these electrodes and cryolite is fed into the vessel. As the cryolite 
 melts the anode is drawn up and electrolysis begins, the bath being kept melted, by 
 the heat generated by its electrical resistance, except the layer next the cooled walls 
 of the vessel which are thus protected from the heat. Alumina is now fed into the 
 
PROPERTIES OF ALUMINIUM. 385. 
 
 vessel in proportion as the aluminium separates around the cathode and is 
 tapped off. 
 
 The alumina for this process is obtained from bauxite, a mineral found at Baux, 
 near Aries in the South of France, and in Antrim, Ireland. It contains alumina 
 56 per cent, ferric oxide 3, silica 12, titanic acid 3, and water 26. To obtain alumina, 
 from it, it is roasted to oxidise any organic matter and ferrous oxide, and heated 
 under pressure with caustic soda solution whereby the alumina is dissolved a 
 sodium aluminate, 3Na20.Al 2 O 3 . After nitration a small proportion of alumina is 
 added to the liquid and the whole is agitated. In the course of some hours the 
 greater part of the alumina is deposited from the solution, recalling the separation 
 of a salt from a supersaturated solution by addition of a nucleus. The liquor from 
 which the alumina has been separated is used for extracting another portion of the 
 ignited bauxite. The deposited alumina is filtered, washed, and heated to expel 
 water. 
 
 Aluminium is less fusible than tin and zinc, but more so than silver,, 
 its fusing-point being 655 0.* It requires a very high temperature to- 
 vaporise it. Like zinc, it is most easily rolled and bent between 100 
 and 150 C. It is much more sonorous than most other metals. A bar 
 of it suspended from a string, and struck with a hammer, emits a clear 
 musical sound. It is remarkable as being the lightest metal (sp. gr. 2.7) 
 capable of resisting the action of air even in the presence of moisture. 
 This lightness renders it valuable for the manufacture of small weights, 
 such as the grain and its fractions, since these, when made of aluminium, 
 are more than three times as large as when made of brass, and nearly 
 nine times as large as platinum weights of the same denomination ; and 
 for canteen vessels, for which purpose it is applicable since it is suffi- 
 ciently resistant to the attack of vegetable and animal juices. t It is 
 also employed for ornamental purposes, for, though not so brilliant as 
 silver, it is not blackened by sulphuretted hydrogen, which so easily 
 affects that metal (see p. 215). Aluminium leaf has largely displaced 
 silver leaf as a decorative material, and is capable of being printed on 
 fabrics. Iron and silicon are the chief impurities in commercial 
 aluminium. 
 
 Another characteristic feature of aluminium is its comparative resist- 
 ance to the action of nitric acid even at a boiling heat. No other metal 
 commonly met with, except platinum and gold, is capable of resisting 
 the action of nitric acid to the same extent. Hydrochloric acid, how- 
 ever, which will not attack gold and platinum, dissolves aluminium 
 with facility, converting it into aluminium chloride, with disengage- 
 ment of hydrogen ; A1 2 + 6HC1 = A1 2 C1 6 + H 6 . Solutions of potash and 
 soda also easily dissolve it, forming the so-called aluminates of 
 those alkalies ; thus, 6NaOH + AJ 3 = Al 2 (ONa) 6 + H 6 . Even when very 
 strongly heated in air, aluminium is oxidised to a very slight extent, 
 probably because the coating of alumina which is formed remains 
 infusible and protects the metal beneath it. For a similar reason, 
 apparently, aluminium decomposes steam but slowly, even at a high 
 temperature. 
 
 When aluminium is rubbed with a solution of mercuric chloride it 
 becomes amalgamated with mercury on the surface and is then remark- 
 ably active, decomposing water at the ordinary temperature with 
 violence, and serving as a useful neutral reducing-agent. 
 
 It is not easily fused before the blowpipe, as its surface becomes covered with infusible- 
 oxide. 
 
 f The metal is not easily soldered and many alloys have been suggested for the purpose;, 
 of late one containing i of Al, o.i of P, 8 of Zn and 30 of Sn has been used. 
 
 2 B 
 
386 ALLOYS OF ALUMINIUM. 
 
 Although massive aluminium does not oxidise more than superficially 
 when heated, the powdered metal burns with ease like powdered 
 magnesium. The heat of combustion is A1 2 ,O 3 = 360,000 cals., and the 
 temperature produced is very high. Indeed, it' the oxygen be supplied 
 by an admixture of a metallic oxide the temperature becomes compar- 
 able with that of the electric arc, and even highly refractory metals are 
 both reduced and melted when their oxides are mixed with powdered 
 aluminium and the mixture is ignited.* 
 
 Metallic chromium has been produced in this manner. A mixture of ferric oxide 
 and aluminium powder has been used under the name " thermite," for the produc- 
 tion of local high temperatures ; the mixture is ignited in a crucible by a fuse com- 
 posed of a mixture of barium peroxide and aluminium powder and when the 
 combustion is over the white hot molten iron with its superincumbent layer of 
 molten aluminium is poured on-to the surface to be heated, such as two rails which 
 are to be butt- jointed by fusing the ends together. When the mixture is ignited 
 on an iron plate it fuses its way through the metal. 
 
 When aluminium is fused with nine times its weight of copper, it 
 forms an alloy [aluminium bronze) very similar to gold in appearance, 
 but almost as strong as iron. This alloy was strongly recommended as 
 a substitute for gold for ornamental purposes, but it does not retain its 
 brilliancy so completely as that metal. Aluminium does not dissolve 
 in cold mercury nor in melted lead, both of which are capable of dis- 
 solving nearly all other metals. 
 
 An alloy of aluminium with from TO to 25 per cent, of magnesium is 
 sold as " magnalium " ; it is of lower specific gravity than aluminium and 
 is more easily worked. 
 
 Aluminium is also used for reducing any oxide which may be present 
 in molten steel when it is being cast, a small amount being added to the 
 steel just before it is poured. 
 
 206. Alum, which is the chief compound of aluminium employed in 
 the arts, is always obtained either from clay or slate, but there are 
 several processes by which it may be manufactured. 
 
 The simplest process is that in which pipe-clay, or some other clay 
 containing very little iron, is calcined, ground to powder, and heated on 
 the hearth of a reverberatory furnace with half its weight of sulphuric 
 acid, until it becomes a stiff paste, which is then exposed to air for 
 several weeks. During this time the alumina of the clay is attacked by 
 the sulphuric acid to form aluminium sulphate, which may be obtained 
 by washing the mass with water, when the sulphate dissolves, and the 
 undissolved silica (still retaining a portion of the alumina) is left. 
 When the solution containing the aluminium sulphate is evaporated 
 to a syrupy consistence and allowed to cool, it solidifies into a white 
 crystalline mass, which is used by dyers under the erroneous name of 
 concentrated alum or cake-alum, and contains about 47.5 per cent, of 
 the dry salt. The aluminium sulphate can be obtained in crystals 
 containing Al 2 (S0 4 ) 3 .i8Aq,f but there is considerable difficulty in 
 obtaining these crystals on account of the extreme solubility of the salt. 
 It is on account of this circumstance that the aluminium sulphate is 
 usually converted into alum, which admits of very easy crystallisation 
 
 * A mixture of aluminium powder and sodium peroxide ignites spontaneously when 
 moistened. 
 
 t The mineral alunogen found in New South Wales has this composition (Liversidge). It 
 forms fibrous masses like satin-spar, and occurs in sandstone rocks. 
 
MANUFACTUKE OF ALUM. 387 
 
 and purification. In order to transfer the sulphate into alum, its 
 solution is mixed with potassium sulphate, when, by suitable evapora- 
 tion, beautiful octahedral crystals are obtained, having the composition 
 AlK(S0 4 ),.i2Aq. 
 
 Alum is more commonly prepared from the mineral termed alum shale, which 
 contains silicate of alumina, together with a considerable quantity of finely divided 
 iron pyrites and some bituminous matter. This shale is coarsely broken up, and 
 built into long pyramidal heaps, together with alternate layers of coal, unless the 
 shale should happen to contain a sufficient amount of bitumen. These heaps are 
 kindled in several places, and are partly smothered with spent ore in order to prevent 
 too great a rise of temperature. During this slow roasting of the heap, the iron pyrites 
 (FeS 2 ) loses half its sulphur, which is converted by burning into sulphurous acid gas 
 (S0 2 ), and this, in contact with the porous shale and the atmospheric oxygen, be- 
 comes converted into S0 3 (p. 222). This latter combines with the alumina to 
 produce sulphate of alumina. The roasted heap is then allowed to remain for some 
 months exposed to the air, and moistened from time to time, in order to promote 
 the absorption of oxygen by the sulphide of iron (FeS), and its conversion into sul- 
 phate of iron (FeSO 4 ). This heap is afterwards lixiviated with water, which 
 dissolves out the sulphates of aluminium and iron, together with some magnesium 
 sulphate, which has also been formed in the process. When this crude alum liquor 
 is evaporated to a certain extent, a large quantity of ferrous sulphate (green vitriol) 
 crystallises out, and the liquid from which these crystals have separated is then 
 mixed with so much solution of potassium chloride as a preliminary experiment 
 has show T n to be necessary to yield the largest amount of alum. The potassium 
 chloride is obtained either from Stassfurt, or as soap-boiler's waste, or as the refuse 
 from saltpetre refineries and glass-houses. The ferrous sulphate still left in the 
 solution is decomposed by the potassium chloride, yielding ferrous chloride, and 
 potassium sulphate, which combines with the aluminium sulphate to form alum ; 
 (T) FeS0 4 + 2KCl = K 2 S0 4 + FeCl 2 ; (2) K 2 S0 4 + A] 2 (S0 4 )3 = 2KA1(S0 4 ) 2 . The hot 
 liquor is stirred while cooling, when alum meal is deposited in small crystals, and 
 the FeCl 2 remains in solution. The alum is redissolved in boiling water, and 
 crystallised in barrels, which are taken to pieces to get out the large crystals. If 
 there be much magnesium sulphate in the liquor, it is subsequently obtained in 
 crystals and sent into the market. 
 
 Where ammonium sulphate can be obtained at a cheap rate (as in the 
 neighbourhood of gasworks), it is very commonly substituted for the 
 potassium sulphate, when ammonia-alum is obtained instead of potash- 
 alum. The former is similar in all respects to the latter salt, except 
 that it contains the hypothetical metal ammonium (NH 4 ) in place of 
 potassium, and its formula is therefore AlNH 4 (S0 4 ) 2 .i2 Aq. 
 
 For all the uses of alum, in dyeing and calico-printing, in paper- 
 making, and in the manufacture of colours, ammonia-alum answers 
 quite as well as potash-alum, and hence both these salts are sold under 
 the common name of alum. 
 
 These alums are the representatives of an important class of double 
 sulphates, containing a monatomic and a triatoinic metal. They all con- 
 tain 1 2 molecules of water of crystallisation, and their crystalline form 
 is that of the cube or octahedron. Alum dissolves in one-third of its 
 weight of boiling water, and in seven parts of cold water ; it is insoluble 
 in alcohol. When heated, it fuses and swells up to a light porous mass 
 of burnt alum, having lost its water. 
 
 The solution of alum is acid to test-papers. When solution of 
 
 * When a supersaturated solution (p. 51) of these crystals is concentrated in a flask, stop- 
 pered with cotton-wool, until a film of solid appears on the surface of the liquor, the solution 
 sets, on cooling, to a mass of prismatic crystals. By carefully removing- the cotton-wool and 
 introducing- a crystal of the ordinary, octahedral alum, the whole of the already solidified 
 substance may be made to break up, the prismatic crystals being- transformed into the octa- 
 hedral variety, with much evolution of heat. 
 
388 ALUMINA. 
 
 sodium carbonate is added to it by degrees, a precipitate of aluminium 
 hydroxide is formed, which, at first, is redissolved on stirring. The 
 solution, to which sodium carbonate has been added as long as the 
 precipitate redissolves, is used under the name of basic alum in dyeing, 
 because stuffs immersed in it become impregnated with alumina, which 
 serves as a mordant to attract and fix the colouring-matter when the 
 stuff is transferred to a dye-bath. 
 
 Aluminium sulphate is superseding alum in many applications ; being 
 prepared by treating clay or bauxite (see p. 385) with sulphuric acid, 
 and precipitating the iron either as ferric arsenate or as Prussian blue. 
 
 Alumina. When ammonia-alum is strongly heated it leaves a white 
 insoluble earthy substance which is alumina itself (A1 2 O 3 ), and differs- 
 widely from the metallic oxides which have been hitherto considered, 
 by the feebly basic character which it exhibits.* Not only is alumina 
 destitute of alkaline properties, but it is not even capable of entirely 
 neutralising the acids, and hence both aluminium sulphate and alum 
 are exceedingly acid salts. Indeed, alumina has feebly acid properties 
 towards the powerful bases, forming aluminates such as sodium alu- 
 minate, 3Na 2 O.Al 2 O 3 . 
 
 Pure crystallised alumina is found in nature as the mineral corundum, 
 distinguished by its extreme hardness, in which it ranks next to the 
 diamond. An opaque and impure variety of corundum constitutes the 
 very useful substance emery. The ruby, oriental amethyst, and sapphire^ 
 consist of nearly pure alumina ; spinelle is a compound of magnesia 
 with alumina, MgO.Al 2 3 ; whilst in the topaz the alumina is associated 
 with silica and aluminium fluoride. In these forms the alumina is in- 
 soluble in acids, but it may be rendered soluble by fusion with acid 
 potassium sulphate, or with alkali hydroxides. The sp. gr. of alumina 
 varies from 3.7 to 4.2. 
 
 The mineral diaspore is a hydrate of alumina (A1 2 3 .2H 2 O), so named from its 
 falling to powder when heated (5ta<r7ro/?d, dispersion). 
 
 Artificial corundum has been made by fusing alumina either in the electric 
 furnace or by the combustion of aluminium (p. 386) and allowing the fused mass to- 
 cool. 
 
 Aluminium hydroxide, A1 2 (OH) 6 , is found crystallised as kydrargillite, or Gibbsite. 
 Artificially prepared aluminium hydroxide is characterised by its gelatinous appear- 
 ance. If a little alum be dissolved in warm water, and some ammonia added to the 
 solution, the alumina will precipitate as a semi-transparent gelatinous mass of the 
 hydrate A1 2 (OH) 6 .2H 2 0. It is nearly insoluble in ammonia, but dissolves in potash 
 and soda. Aluminium hydroxide may be obtained in solution in water by dis- 
 solving it in solution of A1 2 C1 6 , and dialysing (see p. 278). It resembles solution of 
 silicic acid in being very easily gelatinised. When washed and dried, the gelatinous 
 hydroxide shrinks very much, and forms a mass resembling gum. The hydroxide 
 has a great attraction for most colouring-matters, with which it forms insoluble 
 compounds called lakes. Thus, if a solution of alum be mixed with infusion of 
 logwood, and a little ammonia added, the aluminium hydroxide will form, with the 
 colouring-matter, a purplish-red lake, which may be filtered off, leaving the solution 
 colourless. This property is turned to advantage in calico-printing, where the 
 compounds of alumina are largely used as mordants. 
 
 By the radiant matter test (p. 330) alumina phosphoresces crimson. 
 
 * The great absorption and disappearance of heat during the evaporation of the water and 
 ammonia from this alum, has led to its employment for filling- the space between the double 
 walls of fire-proof safes, which may become red-hot outside^ whilst the inside is kept below 
 the scorching- point of paper. 
 
 f Small crystals of alumina resembling natural sapphire have been obtained by the action 
 of vapour of aluminium fluoride upon boric anhydride at a high temperature. By adding- a 
 little chromium fluoride, crystals similar to rubies and emeralds have been produced. 
 
SILICATES OF ALUMINA. 389 
 
 Aluminium chloride, A1C1 3 . If the alumina obtained by calcining 
 ammonia-alum be intimately mixed with charcoal, and strongly heated 
 in an earthen tube or retort through which a stream of well-dried 
 chlorine is passed, the oxygen of the alumina is abstracted by the 
 charcoal, to form carbonic oxide, whilst the chlorine combines with the 
 aluminium, yielding aluminium chloride, which passes off in vapour, 
 and may be condensed, in an appropriate receiver, as a white crystalline 
 solid; A1 2 3 + C 3 + C1 6 = 2 A1C1 3 + 3 CO. 
 
 A1C1 3 absorbs moisture from the air, and becomes partly decomposed 
 into Al,0 3 and HC1. By dissolving alumina in HC1 and evaporating, 
 needles of A1C1 3 .6H 2 are obtained, but they are decomposed, when 
 heated, into A1 2 3 , 6HC1, and 9H 2 0. An impure solution of aluminium 
 chloride is sold as a disinfectant under the name of chloralum. 
 
 Aluminium fluoride, A1F 3 , occurs in kryolite, 3NaF.AlF 3 . 
 
 207. Mineral silicates of alumina. Many of the chemical formulae 
 of minerals which contain silicates of alumina associated with the silicates 
 of other metallic oxides, are complicated, from the circumstance that 
 iron often takes the place of a part of the aluminium, which is possible 
 because Fe 2 O s is isomorphous with A1 2 3 , and therefore capable of taking 
 its place without altering the crystalline form and general character 
 of the mineral. In a similar manner, the other metals present in the 
 mineral may be exchanged for isomorphous representatives ; thus, there 
 are two well-known felspars, potash-felspar (orthoclase) and soda-felspar 
 (albite), having the formula? K 2 O.Al 2 3 .6Si0 2 and Na 2 O.Al 2 O 3 .6SiO 2 . 
 These minerals are sometimes mingled in one and the same crystal 
 (potash-albite or pericline) without bearing any definite equivalent pro- 
 portion to each other ; the formula of such a mineral would be written 
 (KNa) 2 O.Al 2 O 3 .6Si0 9 . Porphyry has the same chemical composition as 
 felspar. 
 
 Mica includes the two minerals muscorite, K 2 0.3A] 2 3 .4Si0 2 , and biotite, 
 3MgO.Al 2 3 . 3 Si0 2 . 
 
 Garnet is essentially a double silicate of alumina and lime, but often contains 
 magnesium, iron, or manganese, in place of part of the calcium, and iron in place of 
 part of the aluminium, being written 3[CaMgFeMn]0.[AlFe] 2 3 .3Si0 2 . This 
 mineral is sometimes formed artificially in the slag of the iron blast-furnaces. 
 Chlorite has the composition ; [6MgFe]0.[AlFe] 2 3 .3Si0 2 .4H 2 0. 
 
 Basalt is a felspathic rock containing crystals of augite ([Fe,Mg]O.Si0 2 ) and 
 magnetic oxide of iron. Cyanite, Jtyanite, or disthene is Al 2 3 .Si0 2 ; a crystal of 
 this is said to point north and south when freely suspended. 
 
 Gneiss is chemically composed like granite, but the mica is arranged in regular 
 layers. Trap rock contains felspar together with hornblende, (Fe0.fMgO)Si0 2 . 
 Hornblende is sometimes found in the place of mica in syenitic granite. Lava, 
 from volcanoes, consists essentially of ferrous, calcium, and aluminium silicates ; 
 the presence of a considerable proportion of potassium and of phosphoric acid 
 renders the soil formed by the weathering of lava very fertile. 
 
 Lapis lazuli, the valuable mineral which furnishes the natural ultra- 
 marine used in painting, consists chiefly of silica and alumina, which con- 
 stitute respectively 45 and 25 per cent, of it, but there are also present 
 10 per cent, of soda, 6 per cent, of sulphuric acid, about 3 per cent, of sul- 
 phur, and a somewhat smaller quantity of iron, together with a variable 
 proportion of lime. The cause of its blue colour is not understood, since 
 neither of its predominant constituents is concerned in the production of 
 such a colour in other cases. In consequence of the rarity of the mineral, 
 the natural ultramarine has a very high price, but the artificial ultra- 
 
39 ULTRAMARINE. 
 
 marine is manufactured in very large quantities at a low cost, and forms 
 a very good imitation. 
 
 One of the processes for preparing it consists in heating to bright redness in a 
 covered crucible, for three or four hours, an intimate mixture of 100 parts of pure 
 white clay (kaolin), 100 of dried carbonate of soda, 60 of sulphur, and 12 of charcoal. 
 This would be expected to yield a mixture of silicate of soda, aluminate of soda, and 
 sulphide of sodium, the two first being white, and the last yellow or brown, but the 
 mass is found to have a green colour (green ultramarine). It is finely powdered, 
 washed with water, dried, mixed with a fifth of its weight of sulphur, and gently 
 roasted in a thin layer till the sulphur has burnt off, this operation being repeated, 
 with fresh additions of sulphur, until the residue has a fine blue colour. In the 
 opinion of some chemists, the presence of a small proportion of iron is essential to 
 the blue colour, whilst others believe the colour to be due to sodium sulphide or 
 thio-sulphate, or both. * 
 
 Ultramarine is a very permanent colour under ordinary conditions 
 of exposure to the air and light, but acids bleach it at once, with 
 separation of gelatinous silica and evolution of sulphuretted hydrogen. 
 Blue writing paper is often coloured with ultramarine, so that its 
 colour is discharged by acids falling upon it in the laboratory. Chlorine 
 also bleaches ultramarine. Starch is often coloured blue with this 
 substance. 
 
 Phosphate of alumina, or aluminium, phosphate, AlPOj, is found naturally in 
 several forms. It occurs in large quantities in the West India Islands. Turquoise 
 is a hydrated aluminium phosphate, owing its colour to the presence of oxide of 
 copper.f Wavellite has the composition 3A1 2 3 .2P 2 5 .I2H 2 0. None of the earlier 
 analysts detected the phosphoric acid in this mineral, on account of the difficulty in 
 separating it from the alumina, so that even in comparatively modern chemical 
 works it is described as a hydrate of alumina. 
 
 A gelatinous precipitate of A1P0 4 is formed when Na 2 HP0 4 is added to solution 
 of alum. It is soluble in HC1 and in potash, but insoluble in acetic acid, which 
 distinguishes it from aluminium hydroxide. 
 
 208. Pottery, Porcelain and Bricks. The manufacture of these 
 articles is frequently termed the clay industries, since clay of one kind 
 or another is the basis of the industry in each case ; the subject is 
 therefore conveniently considered as an appendix to the chemistry of 
 aluminium compounds. 
 
 The manufacture of pottery obviously belongs to an earlier period of 
 civilisation than that of glass, since the raw material, clay, would at 
 once suggest, by its plastic properties, the possibility of working it into 
 useful vessels, and the application of heat would naturally be had re- 
 course to in order to dry and harden it. Indeed, at the first glance, it 
 would appear that this manufacture, unlike that of glass, did not involve 
 the application of chemical principles, but consisted simply in fashioning 
 the clay by mere mechanical dexterity into the required form. It is 
 found, however, at the outset that the name of clay is applied to a large 
 class of minerals, differing very considerably in composition, and pos- 
 sessing in common the two characteristic features of plasticity and a 
 predominance of aluminium silicate. 
 
 It has already been stated (page 384) that kaolin is a hydrated alu- 
 minium silicate, and it is from this material that the best variety of 
 
 * Heumann assigns to ultramarine the formula 2Na2AJ 2 Si 2 O 8 .Na 2 S 2 . Knapp attributes 
 the blue colour to the presence of a modification of sulphur which is only blue when spread 
 over a large surface ; in this case acids would bleach the colour by destroying- the surface. 
 Potassium ultramarine, in which K takes the place of Na, is also blue, whilst silver ultra- 
 marine, in which Ag is substituted for the Na, is yellow. 
 
 f False or bone turquoise is fossil ivory, owing its colour to the presence of the natural 
 blue phosphate of iron. Redonda phosphate consists chiefly of A1PO 4 . 
 
PORCELAIN. 391 
 
 porcelain is made. This clay is eminently plastic, and can therefore be 
 readily moulded, but when baked it shrinks very much, so that the 
 vessels made from it lose their shape and often crack in the kiln. In 
 order to prevent this, the clay is mixed with a certain proportion of 
 sand, chalk, bone-ash, or heavy-spar; but another difficulty is thus 
 introduced, for these substances diminish the tenacity of the clay, and 
 would thus render the vessels brittle. A further addition must there- 
 fore be made of some substance which fuses at the temperature employed 
 in baking the ware, and thus serves as a cement to bind the unfused 
 particles of clay, &c., into a compact mass. Felspar (silicate of alumi- 
 nium and potassium) answers this purpose ; or carbonate of potassium 
 or of sodium is sometimes added, to convert a portion of the silica into 
 a fusible alkaline silicate. With a mixture of clay with sand and fel- 
 spar (or some substitutes), a vessel may be moulded which will preserve 
 its shape and tenacity when baked, and will be impervious to water if it 
 have been " fired " at a temperature sufficiently high to fuse the felspar 
 and clinker the ware throughout. This is the case with porcelain and 
 stoneware ; earthenware, on the other hand, is not clinkered throughout 
 and must be waterproofed by the application of some easily-fusible 
 material which shall form a glaze over the surface of the ware. Porce- 
 lain is generally glazed in order to present a perfectly smooth surface, 
 unless biscuit ware is to be manufactured. A distinction is drawn 
 between hard porcelain, the constituents of which are such that the 
 ware is exceedingly infusible, and soft porcelain, which is far more easily 
 fused. Berlin hard porcelain is made from a mixture of some 55 parts 
 of kaolin, 22.5 of quartz, and 22.5 of felspar. 
 
 These materials are ground up with water before being mixed, and 
 the coarser particles are allowed to subside ; the creamy fluids containing 
 the finer particles in suspension are then mixed in the proper proportions 
 and allowed to settle ; the paste deposited at the bottom is drained, 
 thoroughly kneaded, and stored away for some months in a damp place, 
 by which its texture is considerably improved, and any organic matter 
 which it contains becomes oxidised and removed, the oxidation being 
 effected partly by the sulphates present, which become reduced to 
 sulphides. It is then moulded into the required forms, and dried by 
 simple exposure to the air. The vessels are packed in cylindrical cases 
 (saggers) of very refractory clay, which are arranged in a furnace or kiln 
 of peculiar construction, and very gradually heated at about 800 0. 
 When sufficiently baked, the biscuit porcelain has to be glazed, and great 
 care is taken that the glaze may possess the same expansibility by heat as 
 the ware itself, for otherwise it would crack in all directions as the 
 glaze ware cooled. The glaze employed is a mixture of felspar, quartz, 
 kaolin, marble, and broken porcelain very finely ground, and suspended 
 in water. When the porous ware is dipped into this mixture, it absorbs 
 the water, and retains a thin coating of the mixture of quartz and felspar 
 upon its surface. It is now again fired, this time at 1700 C., when 
 the glaze fuses, partly penetrating the ware, partly remaining as a varnish 
 upon the surface. 
 
 When the ware is required to have some uniform colour, a mineral pigment 
 capable of resisting very high temperatures is mixed with the glaze ; but coloured 
 designs are painted upon the ware after glazing, the ware being then baked a third 
 time, in order to fix the colours. These colours are glasses coloured with metallic 
 
392 BEICKS. 
 
 oxides, and ground up with oil of turpentine, so that they may be painted in the 
 ordinary way upon the surface of the ware ; when the latter is again heated in the 
 kiln the coloured glass fuses, and thus contracts firm adhesion with the ware. 
 
 Gold is applied either in the form of precipitated metallic gold, or of f ulminating 
 gold, being ground up in either case with oil of turpentine burnt in, and burnished. 
 
 English soft porcelain is made from Cornish clay mixed with ground 
 flints, burnt bones, and sometimes a little sodium carbonate, borax, and 
 binoxide of tin, the last improving the colour of the ware. It is glazed 
 with a mixture of Cornish stone (consisting of quartz and felspar), flint, 
 chalk, borax, and sometimes white lead to increase its fusibility. 
 
 Stone-ware is made from less pure materials, and is covered with a glaze 
 of sodium silicate, in a very simple manner, by a process known as salt- 
 glazing. The ware is coated with a thin iilm of sand by dipping it in a 
 mixture of fine sand and water, and is then intensely heated in a kiln 
 into which a quantity of damp salt is presently thrown. The water is 
 decomposed, its hydrogen taking the chlorine of the salt to form hydro- 
 chloric acid, and its oxygen converting the sodium into soda, which com- 
 bines with the sand to form sodium silicate ; this fuses into a glass upon 
 the surface of the ware. 
 
 Pipkins, and similar earthenware vessels, are made of common clay 
 mixed with a certain proportion of marl and of sand. They are glazed 
 with a mixture of 4 or 5 parts of clay with 6 or 7 parts of litharge. 
 The colour of this ware is due to the presence of ferric oxide. 
 
 Bricks and tiles are also made from common clay mixed, if necessary, 
 with sand ; such common clay contains sufficient fusible material to sinter 
 the bricks. These are very often grey, or blue, or yellow, before 
 baking, and become red under the action of heat, since the iron, which 
 is originally present as carbonate (FeC0 3 ), becomes converted into the 
 red peroxide (Fe 2 3 ) by the atmospheric oxygen.* 
 
 For the manufacture of the refractory bricks for lining furnaces, of 
 glass-pots, crucibles for making cast-steel, &c., a pure, and therefore 
 infusible, clay is employed, to which a certain quantity of broken pots of 
 the same material is added, to prevent the articles from shrinking whilst 
 being dried. 
 
 Dinas firebricks are made from a peculiar siliceous material found in the Vale 
 of Neath, and containing alumina with about 98 per cent, of silica. The ground 
 rock is mixed with i per cent, of lime and a little water before moulding. These 
 bricks are expanded by heat, whilst ordinary firebricks, contract. 
 
 Blue bricks are glazed by sprinkling with iron scurf, a mixture of particles of 
 stone and iron produced by the wear of the siliceous grindstones employed in 
 grinding gun-barrels, &c. When the bricks are fired, a glaze of silicate of iron is 
 formed upon them. 
 
 GALLIUM. 
 Ga'" = 69.5. 
 
 209. This metal is found in very small quantities in certain ores of zinc, particu- 
 larly in the blende from Bensberg, in the Pyrenees. 
 
 The powdered ore is treated with aqua regia, care being taken that the blende is 
 in excess, so that the nitric acid may be destroyed as far as possible. Lumps of 
 zinc are immersed in the cooled filtrate from the undissolved ore, whereupon all 
 metals appreciably electro-negative to zinc are precipitated ; the filtrate from these 
 is mixed with more zinc and boiled for some hours so that the acid may be com- 
 pletely neutralised by the zinc and basic salts of Al, Zn and Ga precipitated. They 
 
 * The efflorescence frequently noticed on bricks consists mainly of sulphate and chloride 
 of sodium, which existed in the original clay ; the former salt is frequently formed when 
 iron pyrites is a constituent of the clay. 
 
INDIUM. 393 
 
 are dissolved in HC1, ammonium acetate is added and the Ga and Zn are pre- 
 cipitated by H 2 S. The sulphides are dissolved in HC1, H 2 S is boiled off and a 
 deficiency of Na 2 C0 3 added to precipitate Ga (which is less basic than Zn) as 
 carbonate. The carbonate is dissolved in H 2 S0 4 and excess of NH 3 is added ; Ga^Og 
 is precipitated, any ZnO present being soluble in NH 3 . The precipitate is dissolved 
 in KHO and the solution electrolysed to deposit Ga on the cathode. 
 
 Gallium is a hard white metal of sp. gr. 6 remarkable for its low fusing-point 
 (30 C.), so that it melts with the heat of the hand. It will remain liquid when 
 cooled far below this temperature, but solidifies when touched with a piece of the 
 solid metal. It is not oxidised by dry air until heated nearly to redness, and the 
 oxidation is then only superficial. Nitric acid scarcely attacks it in the cold, but 
 dissolves it on heating. Hydrochloric acid dissolves it, with evolution of hydrogen. 
 Potash has a similar action. 
 
 Gallium xcxyulojeide, Ga 2 3 , left on igniting the nitrate, is white. When heated 
 in hydrogen, a part sublimes, and the rest is converted into a bluish grey 
 substance, which appears to be gallium, oj-lde, GaO. Two chlorides, GaCl 2 and 
 GaCl 3 , exist ; they are very fusible, and deliquescent ; they boil at 535 C. and 
 :2200. respectively. GaCl 2 is oxidised to GaCl 3 by potassium permanganate 
 solution. 
 
 Gallium sulphate, Ga 2 (S0 4 ) 3 , is very soluble in water ; the solution deposits a 
 basic salt when boiled. It combines with ammonium sulphate to form an alum, 
 the solution of which is also precipitated by boiling. 
 
 Ammonia precipitates solutions of gallium, but the precipitate is more easily 
 soluble in excess than in the case of aluminium. Ammonium sulphide precipi- 
 tates Ga^Sg only if zinc be present, when ZnS is precipitated at the same time. 
 Potash gives a precipitate which dissolves easily in excess. Potassium f errocyanide 
 produces a white precipitate, similar to that yielded by zinc. 
 
 The most delicate test for gallium (which led to its discovery in 1875) is the 
 production of two violet bands in the spectrum, when an induction spark 
 passes from the positive terminal of a secondary coil to the surface of the 
 solution under examination, into which the negative terminal of the coil is 
 made to dip. 
 
 From the description of its properties, it will be seen that gallium bears 
 considerable resemblance to aluminium. 
 
 INDIUM. 
 IN'" = 113. i. 
 
 210. Indium was discovered (1863) with the help of the spectroscope, in a 
 specimen of blende from Freiberg, and in some calamines. Its name refers to an 
 indigo-blue line in the spectrum. It is a white malleable metal, and dissolves in 
 hydrochloric acid. Its specific gravity is 7.42. Fusing-point, 176 C. Less easily 
 vaporised than zinc or cadmium. Indium dissolves in HC1, forming InCl 3 ; in 
 HN0 3 , forming In(NO 3 ) 3 ; and in H 2 S0 4 , forming In 2 (S0 4 ) 3 , which crystallises with 
 9H 2 0, and forms an alum. 
 
 Ammonia produces, in solutions of indium, a white precipitate, In(OH) 3 ; 
 insoluble in excess. Ammonium carbonate gives a precipitate soluble in excess 
 and reprecipitated by boiling. When ignited, In(OH) 3 yields the sesquioxide, 
 In. 2 0o, which is brown when hot but yellow when cold. When this is heated in 
 hydrogen, InO is produced. The chlorides, InCl, InCl 2 , and InCl 3 have been 
 prepared ; they have all been volatilised. In 2 S 3 is a yellowish precipitate thrown 
 down by H 2 S from feebly acid solutions of indium. 
 
 To extract indium from the Freiberg zinc, the metal is boiled with dilute 
 sulphuric acid, employed in such quantity as to leave part of the zinc undissolved, 
 together with indium and lead. The residue is dissolved in nitric acid, the lead 
 and cadmium precipitated by hydrosulphuric acid, the latter expelled by boiling, 
 and the oxide of indium precipitated from the solution by barium carbonate. 
 When this precipitate is dissolved in hydrochloric acid, and excess of ammonia 
 added, the white indium hydroxide is precipitated, and may be reduced by heating 
 in hydrogen. At a bright red heat it burns with a violet blue flame, yielding 
 In 2 3 . 
 
 211. Review of the aluminium group of metals. This group comprises Al, Ga, 
 In, and Tl (thallium = 204). The last-named bears the same relation to the other 
 metals of the group as mercury bears to the other metals of the magnesium 
 
394 RAKE EAETHS. 
 
 group (p. 381). The melting-points of the metals of the Al group do not descend 
 with the rise of atomic weight ; it is true that Al, which has the lowest atomic 
 weight, has the highest melting-point, but the remaining metals show a rise of 
 melting-point for increase of atomic weight (Tl melts at 290 C.). The sp. gr. 
 rises with the atomic weight (Tl has sp. gr. 11.9). As the atomic weight increases 
 there is a tendency for the formation of stable oxides lower than that typical of 
 the group (E 2 3 ), and this typical oxide becomes less stable ; this will be evident 
 when the properties of thallium have been considered, a matter best postponed 
 until lead has been treated of. 
 
 The metals in the odd series of this group (see table, p. 302) are the rare 
 elements scandium, yttrium lanthanum, and ytterbium. 
 
 212. Scandium (80 = 43.8) is the metal existing in the basic oxide scandia, Sc 2 3? 
 found in the mineral gadolinite, a mixture of silicates occurring at Ytterby, in 
 Sweden. The oxide is infusible and insoluble in alkalies. The metal has not 
 been isolated, but the atomic weight is deduced from the equivalent of the oxide. 
 Mendeleeff prophesied the existence of a metal (ekaboron) whose oxide would 
 have the properties since discovered for scandia (see p. 304). 
 
 213. Yttrium (Yt = 88.3) is the metal ofi the oxide yttria, Yt 2 3 , which is extracted 
 from gadolinite and a similar mineral, samarsMte. Its properties are not yet 
 known. Yttria is a white oxide insoluble in alkalies and soluble in alkali 
 carbonates. It has been recently shown to contain five or six oxides of basicity 
 differing very slightly from its own, and separable by fractional precipitation ; 
 these may be identified by the difference between their radiant spectra (p. 330), 
 though their spark-spectra are identical with that formerly ascribed to yttrium. 
 
 214. Lanthanum (La =137) also occurs in gadolinite, but is more abundant in 
 cerite, a mineral of the same type, also containing the metal cerium. The mixture 
 of lanthana, La 2 3 , and ceria obtained from this mineral is converted into nitrates 
 which are fractionally crystallised, when the lanthanum nitrate separates first. 
 When this is ignited it is converted into oxide which may be dissolved in HC1, 
 and the chloride thus prepared maj r be fused with potassium to yield the metal 
 lanthanum. It is a white malleable metal (sp. gr. 6.16), decomposes hot water, 
 and oxidises rapidly in air. 
 
 215. Ytterbium (Yb = i72). This metal is only known as its oxide, Yb. 2 3 , at 
 present ; this is extracted from gadolinite. 
 
 216. Besides the above oxides, several others have been described as obtainable 
 from the gadolinite minerals e.g., terbia, erbia, holmia, thulia, samaria, and 
 didymia. These rare earths have received much attention from the spectro- 
 scopist, to whom the evidence of their existence is due, and who is gradually 
 arriving at the conclusion that they are of more complex composition than was 
 at first supposed. They have also received much attention from those interested in 
 incandescence gas lighting (p. 155). 
 
 For example, the metal didymium, which was originally regarded as a chemical 
 unit yielding the oxides DiO, Di 2 3 , and Di 2 5 , has been shown to contain two 
 constituents, praseodymium and neodymium. When the red-coloured didymium 
 nitrate is fractionally crystallised, it yields two salts, one of which, the praseo- 
 salt, is green, whilst the other, the neo-salt, is red. Solutions of these give different 
 absorption spectra (p. 331), but when they are mixed the absorption spectrum 
 characteristic of didymium nitrate is obtained. 
 
 217. For a detailed account of the rare earths the reader must consult a more 
 exhaustive treatise than the present one. It is possible that when the elements 
 contained in them have been isolated, these will be found to occupy the ninth 
 series of the periodic table (p. 302). 
 
 IRON. 
 
 Fe" = 56 parts by weight. (Fe^ 1 =112. 
 
 2 1 8. This most useful of all metals is one of those most widely and 
 abundantly diffused in nature. It is to be found in nearly all forms of 
 rock, clay, sand and earth, its presence in these being commonly indi- 
 cated by their colours, for iron is the commonest of natural mineral 
 colouring ingredients. It is also found, though in small proportion, in 
 plants, and in larger quantity in the bodies of animals, especially in the 
 
IRON ORES. 
 
 395 
 
 blood, which contains about 0*5 per cent, of iron in very intimate asso- 
 ciation with its colouring-matter. 
 
 But iron is very rarely found in the metallic state in nature, being 
 almost invariably combined either with oxygen or sulphur. 
 
 Metallic iron is met with, however, in the meteorites or metallic 
 masses, sometimes of enormous size, and of unknown origin, which 
 occasionally fall upon the earth. Of these, iron is the chief component, 
 but there are also generally present cobalt, nickel, chromium, man- 
 ganese, copper, tin, magnesium, carbon, phosphorus, and sulphur. 
 
 The chief forms of combination in which iron is found in sufficient 
 abundance to render them available as sources of the metal, are shown 
 in the following table : 
 
 Ores of Iron. 
 
 Common Name. 
 
 Chemical Name. 
 
 Composition. 
 
 Magnetic iron ore . 
 
 Ferroso-ferric oxide . 
 
 FeA 
 
 Red haematite ) 
 Specular iron } 
 
 Ferric oxide .... 
 
 Fe 2 3 
 
 Brown hsematite . 
 
 Ferric hydrate .... 
 
 2Fe 2 3 .3H 2 
 
 Spathic iron ore 
 
 Ferrous carbonate 
 
 FeC0 3 
 
 Clay ironstone 
 
 Ferrous carbonate with clay 
 
 
 Blackband 
 
 Ferrous carbonate with clay and 
 
 
 
 bituminous matter 
 
 
 Iron pyrites . 
 
 Bisulphide of iron 
 
 FeS 2 
 
 These ores are frequently associated with extraneous minerals, some 
 of the constituents of which are productive of injury to the quality of 
 the iron. It is worthy of notice that scarcely one of the ores of iron is 
 entirely free from sulphur and phosphorus, substances which will be 
 seen to have a very serious influence on the quality of the iron extracted 
 from the ores, and the presence of which increases the difficulty of 
 obtaining the metal in a marketable condition. 
 
 The following table illustrates the general composition of the most 
 important English ores of iron, with reference to the proportions of iron, 
 and of those substances which materially influence the character of the 
 iron extracted from the ore viz., manganese (present as oxide or car- 
 bonate), phosphorus (present as phosphates), and sulphur (present as 
 bisulphide of iron). The maximum and minimum quantities found in 
 each ore are specified. 
 
 British Iron Ores. 
 
 In ioo Parts. 
 
 Iron. 
 
 Oxide of 
 Manganese, 
 MnO. 
 
 Phosphoric 
 Anhydride, 
 P 2 5 . 
 
 Bisulphide 
 of Iron 
 (Pyrites). 
 
 No. of 
 Samples 
 Analysed. 
 
 Clay ironstone from coal-measures 
 Clay ironstone from the lias . 
 Brown haematite .... 
 Red haematite .... 
 Spathic ore 
 Magnetic ore . 
 
 Max. 
 
 43-30 
 49.17 
 63.04 
 69.10 
 49.78 
 57 
 
 Min. 
 
 20.95 
 J7-34 
 11.98 
 47-47 
 13.98 
 
 OI 
 
 Max. 
 
 3-3 
 1.30 
 i. 60 
 
 "3 
 
 12.64 
 
 o 
 
 Min. 
 
 0.46 
 
 trace 
 trace 
 i-93 
 J 4 
 
 Max. 
 
 1.42 
 5-05 
 3-i7 
 trace 
 
 O.22 
 O 
 
 Min. 
 
 0.07 
 
 trace 
 
 IO 
 
 Max. 
 
 I. 21 
 
 1. 60 
 0.30 
 0.06 
 O. II 
 O 
 
 Min. 
 
 07 
 
 77 
 
 12 
 2 3 
 
 I 
 
 I 
 
 
 From this table it will be gathered that, among the most abundant of 
 the iron ores of this country, red haematite is the richest and purest, 
 
IRON OEES. 
 
 whilst the brown haematite often contains considerable proportions of 
 sulphur and phosphorus, and the spathic ore, though containing little 
 sulphur and phosphorus, often contains much manganese. 
 
 The argillaceous ores, or clay iron-stones found in the lias, contain 
 more phosphorus than those from the coal-measures ; and these latter, 
 a,s a general rule, contain more sulphur (pyrites) than the former, 
 although the maximum in the table does not show this. 
 
 Clay iron-stone is the ore from which the largest quantity of iron is extracted 
 in England, since it is found abundantly in the coal-measures of Staffordshire, 
 Shropshire and South Wales ; and it is a circumstance of great importance in the 
 economy of English iron-smelting that the coal and limestone required in the 
 smelting process, and even the fireclay employed in the construction of the 
 furnace, are found in the immediate vicinity of the ore. 
 
 Blacltband is the clay -iron-stone found in the coalfields of Scotland, and often 
 contains between 20 and 30 per cent, of bituminous matter, which contributes to 
 the economy of fuel in smelting it. 
 
 Red haematite (Fe 2 3 ) is the most characteristic of the ores of iron, occurring in 
 hard, shining, rounded masses, with a peculiar fibrous structure and a dark red- 
 brown colour, whence the ore derives its name (afyca, blood). It is found in con- 
 siderable quantities in Lancashire, Cornwall, the Spanish Peninsula, Algiers, and 
 North America. 
 
 Red ochre is a soft variety of this ore, containing a little clay. 
 
 Brown hcematite (2Fe 2 3 .3H 2 0) is found at Alston Moor (Cumberland) and in 
 Durham, but it is more abundant on the Continent, and is the source of most of 
 the Belgian and French irons. Pea iron ore and yellow ochre are varieties of brown 
 haematite. The Scotch ore, called kidney-form clay iron-stone, is really an ore of 
 this class. 
 
 The red and brown haematites of Lancashire, Cumberland, and Spain are the 
 chief ores used in the manufacture of the variety of pig-iron known as " Bessemer 
 or haematite pig." 
 
 Specular iron ore (Fe 2 3 ) (oligist ore or iron-glance), although of the same 
 composition as red haematite, is very different from it in appearance, having a 
 steel-grey colour and a brilliant metallic lustre. The island of Elba is the chief 
 locality where this ore is found, but it also occurs in Germany, France, and 
 Russia. The excellent quality of the iron smelted from this ore is due partly to 
 the purity of the ore, and partly to the circumstance that charcoal, and not coal, 
 is employed in smelting it. 
 
 Magnetic iron ore (Fe 3 4 ),of which the loadstone is a variety, has a more granular 
 structure and a dark iron-grey colour. It forms mountainous masses in Sweden, 
 and is also found in Russia and North America. It is generally smelted with 
 charcoal and yields Jin excellent iron. Iron sand, a peculiar heavy black sand 
 of metallic lustre, consists in great measure of the magnetic ore, but contains a 
 very large proportion of titanium. It is found abundantly in India, Nova Scotia, 
 and New Zealand ; but its fine state of division prevents it from being largely 
 available as a source of iron. 
 
 Spathic iron ore (FeC0 3 ) is found in abundance in Saxony, and often contains 
 a considerable quantity of manganese carbonate, which influences the character 
 of the metal extracted from it. 
 
 The oolitic iron ore, occurring in the Northampton oolite, contains both hydrated 
 sesquioxide and carbonate of iron, together with clay. 
 
 Iron pyrites (FeS 2 ) is remarkable for its yellow colour, its brilliant metallic 
 lustre and crystalline structure, being generally found either in distinct cubical 
 or dodecahedral crystals, or in rounded nodules of radiated structure. It was 
 formerly disregarded as a source of iron, on account of the difficulty of separating 
 the sulphur ; but an inferior quality of the metal has been extracted from the 
 residue left after burning the pyrites in the manufacture of oil of vitriol (p. 226). 
 the residue being first well roasted in a lime-kiln to remove as much as possible 
 of the remaining sulphur. 
 
 219. Metallurgy of iron. Iron owes the high position which it occupies 
 among useful metals to a combination of valuable qualities not met with 
 in any other metal. Although possessing nearly twice as great tenacity 
 
THE BLAST-FURNACE. 397 
 
 or strength as the strongest of the other metals commonly used in the 
 metallic state, it is yet one of the lightest, its specific gravity being only 
 7-7, and is therefore particularly well adapted for the construction of 
 bridges and large edifices, as well as for ships and carriages. It is the 
 least yielding or malleable of the metals in common use, and can there- 
 fore be relied upon for affording a rigid support ; and yet its ductility is 
 such that it admits of being rolled into the thinnest sheets and drawn 
 into the finest wire, the strength of which is so great that a wire of y^th 
 inch in diameter is able to sustain 705 pounds, while a similar wire of 
 copper will not support more than 385 pounds. 
 
 Being, with the exception of platinum, the least fusible of useful metals, 
 iron is applicable to the construction of fire-grates and furnaces. Nor 
 are its qualifications all dependent upon its physical properties, for it not 
 only enters into a great number of compounds which are of the utmost 
 use in the arts, but its chemical relations to one of the non-metallic 
 elements, carbon, are such, that the addition of a small quantity of this 
 element converts it into steel, far surpassing iron in the valuable proper- 
 ties of hardness and elasticity ; whilst a larger quantity of carbon gives 
 rise to cast-iron, the greater fusibility of which permits it to be moulded 
 into vessels and 'shapes which could not be produced by forging. 
 
 220. English process of smelting clay iron-stone. -The first step towards 
 the extraction of the metal consists in calcining (or roasting) the ore, in 
 order to expel water and carbonic acid gas. To effect this the ore is 
 sometimes built up, together with a certain amount of small coal, into 
 long pyramidal heaps, resting upon a foundation of large lumps of coal ; 
 blackband often contains so much bituminous matter that any other fuel 
 is unnecessary. These heaps are kindled in several places, and allowed 
 to burn slowly until all the fuel is consumed. This calcination has the 
 effect of rendering the ore more porous, and better fitted for the smelting 
 process. If the ore contained much sulphur, a part of it would be ex- 
 pelled by the roasting in the form of sulphurous acid gas. The FeCO 3 is 
 converted into Fe 2 O 3 , which, being a feebler base than FeO, is less likely 
 to combine with silica and form a fusible slag. 
 
 More commonly the calcination is effected in kilns resembling lime- 
 kilns, and it is often altogether omitted as a separate process, the expul- 
 sion of the water and carbonic acid gas being then effected in the 
 smelting-furnace itself as the ore descends. 
 
 The calcined ore is smelted in a huge blast-furnace A (Fig. 219) from 
 fifty to eighty feet high, built of massive masonry, and lined internally 
 with firebrick. Since it would be impossible to obtain a sufficiently high 
 temperature with the natural draught of this furnace, air is forced into it 
 at the bottom, under a pressure of three to seven pounds upon the square 
 inch, through tuyere or twyer pipes H, the nozzles G of which pass through 
 apertures in three sides of the furnace. As the nitrogen of the air thus 
 forced through the furnace carries away much heat with it, a hot-blast 
 is found to economise fuel. To heat the blast the air is passed over 
 firebricks which have been raised to a high temperature by the com- 
 bustion of the gases which escape from the furnace (see over). In 
 this way the temperature of the blast is frequently raised to 800 C. and 
 that of the furnace when the combustion is most vigorous to 1930 C. 
 
 It would be very easy to reduce to the metallic state the oxide of iron 
 contained in the calcined ore, by simply throwing it into this furnace, 
 
398 
 
 SMELTING IRON ORES. 
 
 together with a proper quantity of coal, coke, or charcoal; but the 
 metallic iron fuses with so great difficulty, that it is impossible to sepa- 
 rate it from the clay or gangue, as it is called, unless this latter is 
 brought into a liquid state ; and even then the fusion of the iron, which 
 is necessary for complete separation, is only effected after it has formed 
 a more easily fusible compound with a small proportion of carbon 
 derived from the fuel. 
 
 Fig. 219. Blast-furnace for smelting iron ores. 
 
 Now, clay is even more difficult to fuse than iron, so that it is neces- 
 sary to add, in the smelting of the ore, some substance capable of form- 
 ing with the clay a combination which is fusible at the temperature of 
 the furnace. If clay (aluminium silicate) be mixed with limestone 
 (CaC0 3 ), and exposed to a high temperature, C0 2 is expelled from the 
 limestone, and the lime unites with the clay, forming a double silicate 
 of alumina and lime, which melts completely, and, when cool, solidifies 
 to a glass or slag. The limestone acts as a flux, inducing the clay to 
 flow in the liquid state. In order, therefore, that the clay may be 
 readily separated from the metallic iron, the calcined ore is mixed with 
 a certain proportion of limestone before being introduced into the 
 furnace. 
 
KEACTrONS IN THE BLAST-FUKNACE, 399 
 
 Great care is necessary in first lighting the blast-furnace lest the new 
 masonry should be cracked by too sudden a rise of temperature, and, 
 when once lighted, the furnace is kept in constant work for years until 
 in want of repair. When the fire has been lighted, the furnace is 
 filled up with coke, and as soon as this has burnt down to some distance 
 below the top opening or throat, a layer of the mixture of calcined ore 
 with the requisite proportion of limestone is thrown upon it ; over this 
 there is placed another layer of coke, then a second layer of the mixture 
 of ore and flux, and so on, in alternate layers, until the furnace has 
 been filled up; when the layers sink down, fresh quantities of fuel, ore, 
 and flux are added, so that the furnace is kept constantly full. As the 
 air passes from the tuyere pipes into the bottom of the furnace it parts 
 with its oxygen to the carbon of the fuel which it converts into C0 2 ; 
 the latter, passing over the red-hot fuel in the widest part or boshes B of 
 the furnace, becomes CO (see p. 132). It is this carbonic oxide, amount- 
 ing to some 33 per cent, of the gases, which reduces the calcined ore to 
 the metallic state when it comes in contact with it at that part of the 
 throat of the furnace where the ore has already attained a red-heat. In 
 effecting this reduction, the CO is of course oxidised to C0 2 . The 
 metallic iron being infusible at the temperatures at which it is reduced, 
 remains disseminated through the gangue of the ore and as it descends 
 into a hotter region of the furnace some of it reduces CO liberating carbon 
 with which the rest of the iron combines to form cast-iron. At this 
 stage, the clay or gangue of the ore is attacked by the lime which has 
 been produced from the calcination of the limestone flux at a somewhat 
 higher point in the furnace and a fusible slag of silicate of lime and 
 alumina is formed. This melts and liberates the disseminated cast-iron 
 at the hottest portion C of the furnace, just above the tuyeres. The cast- 
 iron now melts and runs together, collecting in the crucible or cavity D for 
 its reception at the bottom of the furnace. The slag, which has five or 
 six times the bulk of the iron, is allowed to accumulate in the crucible, 
 and to run over its edge down the incline upon which the blast-furnace 
 is built ; but when a sufficient quantity of cast-iron has collected at the 
 bottom of the crucible, it is run out through a hole provided for the 
 purpose, either into .channels made in a bed of sand, or into iron 
 moulds, where it is cast into rough semi-cylindrical masses called pigs, 
 whence cast-iron is also spoken of as pig-iron. 
 
 A furnace consumes, in the course of twenty-four hours, about 50 tons of coal, 
 30 tons of ore, 6 tons of limestone, and 100 tons of air. The cast-iron is run off 
 from the crucible once or twice in twelve hours, in quantities of five or six tons 
 at a time. The average yield of calcined clay ironstone is 35 per cent, of iron. 
 
 The gases escaping from the blast-furnace are highly inflammable, 
 for they contain as much as 25 per cent, of carbon monoxide ; * in 
 modern furnaces the throat is closed when the furnace has been charged, 
 by a bell E, and the gases are made to pass through a flue into the 
 stoves L, where they are burnt in flues M in order to heat the brickwork 
 N which is subsequently to raise the temperature of the blast. When 
 one stove has been heated the combustible gases are turned into another 
 stove and an air blast is passed through the first one from pipe R 
 in a direction contrary to that of the combustible gases. The pipe P 
 
 * If coal be used as fuel hydrogen and hydrocarbons will also be present. The gases from 
 a coke-fed furnace contain in 100 vols. : N, 55 ; CO 2 , 18.5 ; CO, 26.4 ; H, o.i vols. 
 
400 BLAST-FUENACE SLAG. 
 
 conducts the blast to the tuyeres, and the products of combustion leave 
 the stove by flue 0. As there is generally more than sufficient com- 
 bustible gas for this purpose, in some works a portion is burnt in gas- 
 engines to supply power for the blowing engines, &c. 
 
 When coal is used as fuel it is sometimes profitable to pass the gases through 
 cooling apparatus before they are burnt, in order to condense the tar and 
 ammonia which they contain. 
 
 Although the bulk of the nitrogen present in the air escapes unchanged from 
 the furnace, it is not improbable that a portion of it contributes to the formation 
 of the cyanide of potassium (KCN), which is produced in the lower part of the 
 furnace, the potassium being furnished by the ashes of the fuel. Cyanogen is 
 generally found in the escaping gases. 
 
 The slag from the blast-furnace is essentially a glass composed of a 
 double silicate of aluminium and calcium, the composition of which varies 
 much according to the nature of the earthy matters in the ore and the 
 composition of the flux. Its colour is generally grey, streaked with 
 blue, green, or brown. 
 
 The nature of the flux employed must, of course, be modified according 
 to the composition of the gangue present in the ore. Where this con- 
 sists of clay (silicate of alumina), that is, is acid in character, the 
 addition of lime (which is sometimes added in the form of limestone 
 and sometimes as quicklime) will provide for the formation of the 
 double silicate of alumina and lime. But if the iron-ore happened 
 already to contain limestone, a basic gangue, an addition of clay would 
 be necessary, or if quartz were present, consisting of silica only, both 
 lime and alumina (in the form of clay) will be necessary as a flux. It 
 is sometimes found economical to employ a mixture of ores containing 
 different kinds of gangue, so that one may serve as a flux to the other. 
 If a proper proportion of lime were not added, a portion of the oxide of 
 iron would serve as the base to combine with the silica and be carried 
 off in the slag ; but if too large a quantity of lime be employed, it will 
 diminish the fusibility of the slag, and prevent the complete separation 
 of the iron from the earthy matter. 
 
 The most easily fusible slag which can be formed by the action of lime upon 
 clay has the composition 6CaO.Al 2 3 .9Si0 2 ; but in English furnaces, where coal 
 and coke are employed, it is found necessary to use a larger proportion of lime to 
 convert the sulphur of the fuel into calcium sulphide, so that the slag commonly 
 has a composition more nearly represented by the formula i2Ca0.2Al 2 3 .9Si0 2r 
 which would express a compound of 6 molecules of normal calcium silicate with 
 I molecule of normal aluminium silicate ; 6Ca, 2 Si0 4 .Al 4 (Si0 4 ) 3 . 
 
 Since iron, manganese, and magnesium are commonly found occupying the place 
 of a portion of the calcium, a more general formula for the slag from English 
 blast-furnaces would be 6(CaFeMnMg) 2 Si0 4 .Al 4 (Si0 4 ) 3 . 
 
 A fair impression of the ordinary composition of the slag from blast-furnaces is 
 conveyed by the following table : 
 
 Slag from Blast- Furnace ; in 100 parts. 
 
 Silica 43-07 
 
 Alumina . . -14-85 
 
 Lime 28.92 
 
 Magnesia 
 
 Oxide of manganese (MnO) . 1.37 
 
 Potash (K 2 0) . . .1.84 
 
 Sulphide of calcium . . 1.90 
 
 Phosphoric oxide (P 2 5 ) . trace 
 
 Oxide of iron (FeO) . . 2.35 
 
 From i o to 30 cwt. of slag are produced per ton of cast-iron smelted. 
 
 These slags are sometimes run from the blast-furnace into iron moulds, 
 in which they are cast into blocks for rough building purposes. The 
 
CAST IRON. 401 
 
 presence of a considerable proportion of potash has led to experiments- 
 upon their employment as a manure, for which purpose they have been 
 blown out, when liquid, into a finely divided frothy condition fit for 
 grinding and applying to the soil. They are also used for making 
 cement. By blowing air through the slag, it is converted into a sub- 
 stance resembling spun glass, and used, under the name of slag wool or 
 mineral cotton, for packing round steam-pipes, &c. 
 
 220. CAST IRON is, essentially, composed of iron with from 2 to 5 per 
 cent, of carbon, but always contains other substances derived either from 
 the ore or from the fuel employed in smelting it. On taking into con- 
 sideration the energetic deoxidising action in the blast-furnace, it is not 
 surprising that portions of the various oxygen compounds exposed to it 
 should part with their oxygen, and that the elements thus liberated should 
 find their way into the cast iron. In this way the silica is reduced, and 
 its silicon is found in cast iron in quantity sometimes amounting to 3 or 
 4 per cent. Haematite pig is usually rich in silicon, from the presence 
 of silica in an easily reducible condition in the ore. Sulphur and phos- 
 phorus are also generally present in cast iron, but in very much smaller 
 proportion; their presence diminishes its tenacity, and the smelter 
 endeavours to exclude them as far as possible, though a small quantity 
 of phosphorus appears to be rather advantageous for some castings, 
 since it augments the fusibility and fluidity of the cast-iron. The 
 sulphur is chiefly derived from the coal or coke employed in smelting, 
 and for this reason charcoal would be preferable to any other fuel if it 
 could be obtained at a sufficiently cheap rate. The ironworks of some 
 parts of Europe enjoy a great advantage in this respect over those of 
 England. The phosphorus is derived chiefly from the phosphates 
 existing in the ore or in the flux.* The proportion of phosphorus taken 
 up by the cast iron increases with the temperature of the blast-furnace. 
 Manganese, amounting to i or 2 per cent., is often met with in cast 
 iron, having been reduced from the oxide of manganese, which is 
 usually found in iron ores ; its presence generally enables the iron to 
 hold more carbon and less sulphur. Other metals, such as chromium, 
 cobalt, &c., are also occasionally present, though in such small quantities 
 as to be of no importance in practice. 
 
 The following table exhibits the largest and smallest proportion of the 
 various elements determined in the analysis of upwards of a hundred 
 specimens of cast iron : 
 
 Composition of Cast Iron. 
 
 Maximum. Minimum. 
 
 Carbon 
 
 Silicon 
 
 Sulphur 
 
 Phosphorus 
 
 Manganese 
 
 Iron 
 
 4.81 
 
 4-77 
 i. 06 
 1.87 
 6.08 
 
 1.04 per cent. 
 0.08 
 
 trace 
 trace 
 
 In order to understand the difference observed in the several varieties 
 of cast iron, it is necessary to consider the peculiar relations between 
 iron and carbon. Iron fused in contact with carbon is capable of com- 
 bining with nearly 6 per cent, of that element, to form a white, brilliant, 
 
 * It appears to exist in the iron, at least in some cases, as Fe 4 P. 
 
 2 C 
 
402 
 
 VARIETIES OF CAST IEON, 
 
 and brittle compound, which may be represented pretty nearly as com- 
 posed of Fe 4 G. Under certain circumstances, as this compound of iron 
 and carbon cools, a portion of the carbon separates from the iron, and 
 remains disseminated throughout the mass in the form of minute 
 crystalline particles very much resembling natural graphite. If a broken 
 piece of iron containing these scales be examined, the fracture will be 
 found to exhibit a more or less dark grey colour, due to the presence of 
 the uncombined carbon, and for this reason a cast iron in which a por- 
 tion of the carbon has thus separated is commonly spoken of as grey 
 iron, whilst that in which the whole of the carbon has remained in com- 
 bination with the metal exhibits a white fracture, and is termed white 
 iron or bright iron. Intermediate between these is the variety known 
 as mottled iron, which has the appearance of a mixture of the grey and 
 white varieties. 
 
 The different condition of the carbon in the two varieties of cast iron 
 is rendered apparent when the metal is dissolved in diluted sulphuric or 
 hydrochloric acid, for any carbon which exists in the uncombined state 
 will then be left, whilst that which had been in combination with the 
 iron passes off in the form of peculiar compounds of carbon and hydro- 
 gen, which impart the disagreeable odour perceived in the gas evolved 
 when the metal is dissolved in an acid. 
 
 The properties of these two varieties of cast iron are widely different, 
 grey iron being so soft that it may be turned in a lathe, whilst the 
 white iron is extremely hard, and of higher specific gravity, 7.5, that of 
 grey iron being 7.1. Again, although white iron fuses at a lower tem- 
 perature (1100 C.) than grey iron (1200 C.), the latter is far more 
 liquid when fused, and is therefore much better fitted for casting. 
 
 Although the presence of uncombined carbon is the chief point which 
 distinguishes grey from white iron, other differences are commonly 
 observed in the composition of the two varieties. The white iron 
 usually contains less silicon than grey iron, but a larger proportion of 
 sulphur. 
 
 The difference in the composition of these three varieties of cast iron 
 is shown in the following table : 
 
 
 Grey. 
 
 Mottled. 
 
 White. 
 
 Iron 
 
 92.00 
 
 92-75 
 
 94.04 
 
 Combined carbon . 
 
 0.30 
 
 0-75 
 
 3.20 
 
 Graphitic carbon . 
 
 3-70 
 
 2.90 
 
 
 Silicon . 
 
 2.50 
 
 I.OO 
 
 0.64 
 
 Sulphur . 
 
 0.04 
 
 0.15 
 
 0.20 
 
 Phosphorus 
 
 1.50 
 
 i. 60 
 
 1.32 
 
 Manganese 
 
 0.72 
 
 0.47 
 
 O.6O 
 
 As might be expected, it is not easy to tell where a cast iron ceases to be grey and 
 begins to be mottled, or where the mottled iron ends and white iron begins. There 
 are, in fact, eight varieties or grades of cast iron in commerce, distinguished by the 
 numbers one to eight, of which No. I is dark grey and contains the largest propor- 
 tion of graphite, which diminishes in the succeeding numbers up to No. 8, which is 
 the whitest iron, the intermediate numbers being more or less mottled. 
 
 The particular variety of cast iron produced is to some extent under the control of 
 the smelter. A furnace working with siliceous ores and a high percentage of fuel, 
 at a high temperature, yields an iron containing much silicon, and therefore a grey 
 pig, for the presence of silicon determines the separation of carbon as graphite. 
 
PIG-IRON, 403 
 
 When the furnace is working with a minimum of fuel the iron will contain but little 
 silicon, and will consequently retain all its carbon in combination, giving a white 
 pig. But the metal sometimes varies considerably at different levels in the crucible 
 of the furnace, so that pigs of different degrees of greyness are obtained at 
 the same tapping. Mottled cast iron surpasses both the other varieties in 
 tenacity, and is therefore preferred where this quality is particularly desirable. 
 
 The extra consumption of fuel, of course, renders the grey iron more expen- 
 sive. When a furnace is worked with a low charge of fuel to produce a white 
 iron, a larger quantity of iron is lost in the slag, sometimes amounting to 5 per 
 cent, of the metal, whilst the average loss in producing grey iron does not ex- 
 ceed 2 per cent. Ores containing a large proportion of manganese are generally 
 found to yield a white iron. 
 
 White iron is usually used as forge-iron (that is for conversion into 
 malleable iron), whilst grey iron is used as foundry-iron (for making 
 castings) and for conversion into steel. 
 
 When grey iron is melted, the particles of graphite to which its grey 
 colour is due are dissolved by the liquid iron, and if it be poured into a 
 cold iron mould so as to solidify it as rapidly as possible, the external 
 portion of the casting will present much of the hardness and appearance 
 of white iron, the sudden cooling having prevented the separation of 
 the graphite. This affords the explanation of the process of chill-casting 
 by which shot, &c., made of the soft fusible grey iron, are made to 
 acquire, externally, a hardness approaching that of steel. It is a com- 
 mon practice to produce compound castings, that portion of the mould 
 where chilling and consequent hardness is required being made of thick 
 cast iron, and the other part, which is to give a tougher and a softer 
 casting, of sand. When white pig-iron is melted at an extremely high 
 temperature (in a Siemens furnace) and slowly cooled, it becomes grey. 
 
 When grey iron is re-melted in the foundry for casting it becomes harder, both 
 because some of the silicon is eliminated by oxidation, causing a corresponding 
 amount of the graphite to pass into combination, and because sulphur is absorbed 
 from the fuel with which the iron is melted. 
 
 By the use of ores containing an unusually large proportion of any of the 
 foreign constituents which enter into the reduced iron, the blast-furnace may be 
 made to produce special irons, which have particular applications. Thus, ferro- 
 silicon (iron rich in silicon) used for converting white iron into grey iron, ferro- 
 manganese (iron containing 68-80 per cent, of Mn ; spiegel-eisen contains about 
 10 per cent of Mn), and ferro-chromiutn (containing 60-70 per cent, of Cr) are 
 made ; the last two are used in steel-making. 
 
 Pig-iron has a very limited application as a building material on 
 account of its low tensile strength (8 tons per sq. in.) and its lack of 
 malleability. For constructional use it must be converted into malleable 
 iron which possesses a high tensile strength and is capable of being 
 forged. In order to effect this conversion the silicon, phosphorus and 
 .sulphur of the pig-iron must be removed, and the content of carbon 
 must be reduced to below 2 per cent. The attainment of these ends is 
 rendered possible by the fact that the impurities are more readily 
 oxidised than is the iron, and this oxidation may be effected either by 
 mixing the hot iron with iron oxide, or by blowing air through the 
 molten metal. The carbon is thus evolved in the form of CO, whilst 
 the silicon and phosphorus are oxidised to Si0. 2 and P 2 O 5 , both of which 
 oxides are capable of uniting with a base (FeO or CaO) and of being 
 removed as slag. 
 
 Before the production and maintenance of very high temperatures 
 was understood, it was customary to heat the iron until it became pasty 
 
404 
 
 KEFINING CAST IKON. 
 
 and to mix it with iron oxide whilst in this condition (a process known 
 as puddling) ; the impurities, oxidised at the expense of the ferric oxide, 
 were then squeezed out of the iron by working the pasty mass under 
 the hammer. The product was known as wrought iron, and, since it 
 was not necessary to fuse the iron at any stage of the process, it was 
 possible to reduce the carbon to a very low percentage, for it will be 
 remembered that it is the presence of this element which lowers the 
 fusing-point of iron. At the present day it is possible to keep iron con- 
 taining very little carbon in a state of fusion, so that the iron oxide can 
 be mixed with it in this condition and the decarburised iron can be cast 
 into ingots prior to being rolled into plates or bars (Siemens- Martin pro- 
 cess). Instead of iron oxide, air is frequently used as the oxidant, in 
 which case it is blown through the molten iron, the heat generated by 
 the oxidation of the impurities serving to keep the metal in fusion 
 (Bessemer process). By this method also the metal is obtained in the 
 form of cast ingots. 
 
 The original distinction between cast iron, wrought iron and steel lay 
 in their content of carbon. Cast iron contains 3-5 per cent, of C ; 
 wrought iron under o.i per cent., and steel 0.5-2.0 per cent. The 
 term ingot iron is now employed to signify all iron made by methods 
 involving fusion, and includes all grades of refined iron except the very 
 softest and the very hardest (hard steel) ; the expression mild steel is 
 nearly synonymous with ingot iron. 
 
 Conversion of cast iron into bar or wrought iron. Puddling. With 
 pig-iron containing much graphite and silicon, namely grey iron, the 
 puddling process is preceded by the process of refining, which will there- 
 fore be first described. 
 
 Refining cast iron. This process consists essentially in exposing the 
 
 metal, in the fused 
 state, to the action of a 
 blast of air in which 
 part of the oxygen has 
 been converted into 
 carbonic oxide by pass- 
 ing over red-hot coke 
 or charcoal. 
 
 The refinery (Fig. 220) is 
 a rectangular trough with 
 double walls of cast iron, 
 between which cold water 
 is kept circulating to pre- 
 vent their fusion. This 
 trough is about 3^ feet 
 long by 2\ feet wide, and 
 usually lined with fireclay ; 
 on each side of it are ar- 
 ranged three tuyere pipes 
 for the supply of air, in- 
 clined at an angle of 25 to- 
 
 30 to the bottom of the furnace, which is fed with coke, unless the very best iron 
 is required, as for the manufacture of tin-plate, when charcoal is generally used in 
 the refinery. 
 
 This furnace having been filled to a certain height with fuel, five or six pigs of 
 iron (from 20 to 30 cwt.) are arranged symmetrically upon it, and covered with 
 coke, a blast of air being forced in through the tuyeres, under a pressure of about 
 
 Fig. 220. Hearth for refining pig-iron. 
 
PUDDLING, 405 
 
 3 Ibs. upon the square inch. In about a quarter of an hour the metal begins to fuse 
 gradually, and to trickle down through the fuel to the bottom of the refinery, a 
 portion of the iron being converted into oxide in its descent, by the air issuing from 
 the tuyere pipes. When the whole of the metal has been fused, the air is still 
 allowed to play for some time upon its surface, when the fused metal appears to 
 boil in consequence of the escape of bubbles of carbonic oxide. 
 
 After about two hours the tap-hole is opened, and the molten metal run out into 
 a flat cast-iron mould kept cold by water, in order to chill the metal and render it 
 brittle. The plate of refined iron thus obtained is usually about 2 inches thick. 
 The slag (or finery chide;-) is generally received in a separate mould ; its compo- 
 sition may be generally expressed by the formula 2FeO.Si0 2 , the silica having been 
 derived from the silicon contained in the cast iron. 
 
 The change effected in the composition of the iron by the process of 
 refining will be apparent from the following percentage composition of 
 refined iron : Fe, 95.14 ; C, 3.07 ; Si, 0.63; S, 0.16; P, 0.73 ; Mn, trace ; 
 slag, 0.44. The carbon, therefore, is not nearly so much diminished as 
 the silicon, which is in some cases reduced to T \j- of its former propor- 
 tion by the refining process. The main effect of the refining is to con- 
 vert the graphite into combined carbon, that is, to make the grey iron 
 white iron ; no doubt this conversion is connected with the removal of 
 the silicon ; its practical advantage resides in the fact that the white 
 iron passes through a pasty stage before it melts, so that it is better 
 fitted than grey iron for puddling. Half of the sulphur is also some- 
 times removed by the refining, being found in the slag as sulphide of 
 iron. The phosphorus is not removed to the same extent, though some 
 of it is converted into ferrous phosphate, which may be found in the 
 finery cinder. 
 
 It will be seen that the term " refining " is somewhat misapplied to 
 the process of the refinery hearth, as but iittle of the carbon which 
 must be removed in order to obtain a malleable iron is separated by the 
 operation. The purification proper could not be effected in the refinery, 
 since the fusibility of the iron is so greatly diminished, as it approaches 
 to a pure state, that it could not be kept fluid at the temperature attain- 
 able in this furnace, and a more spacious hearth is required upon which 
 the pasty metal may be kneaded into close contact with the oxide of 
 iron which is to complete the oxidation and separation of the carbon. 
 For this reason the metal is transferred to the puddling furnace. 
 
 The puddling process is carried out in a reverberatory furnace 
 (Figs. 221, 222) connected with a tall chimney provided with a damper, 
 so as to admit of a very perfect regulation oi the draught. A bridge of 
 firebrick between the grate and the hearth prevents the contact of the 
 coal with the iron to be puddled. The hearth is composed either of 
 fire-brick or of cast-iron plates, covered with a layer of very infusible 
 slag, and cooled by a free circulation of air between them. This hearth 
 is about 6 feet in length by 4 feet in the widest part near the grate, 
 and 2 feet at the opposite end ; it is slightly inclined towards the end 
 farthest from the grate, and finishes in a very considerable slope, at the 
 lowest point of which is the floss-hole for the removal of the slag. 
 Since the metal is to attain a very high temperature in this furnace 
 (estimated at i3ooC.), the latter is usually covered with an iron casing, 
 so as to prevent any entrance of cold air through chinks in the brick- 
 work. 
 
 About 5 cwt. of the fine metal is broken up and heaped upon the 
 hearth of this furnace, together with about i cwt. of iron scales (black 
 
406 
 
 PUDDLING. 
 
 oxide of iron, Fe 3 4 ), and of hammer-slag (basic silicate of iron, obtained 
 in subsequent operations), which are added in order to assist in oxidising 
 the impurities. When the metal has fused, the mass is well stirred or 
 puddled, so that the oxide of iron may be brought into contact with 
 every part of the metal, to effect the oxidation of the impurities. The 
 metal now appears to boil, in consequence of the escape of carbonic 
 oxide, and in about an hour from the commencement of the puddling, 
 
 Fig-. 221. Puddliug-furuace (elevation). 
 
 Fig. 222. Puddling-furnace (section). 
 
 so much of the carbon has been removed that the fusibility of the metal 
 is considerably diminished, and instead of retaining a fused condition 
 at the temperature prevailing in the furnace, it assumes a granular 
 sandy or dry state, spongy masses of pure iron separating or coming to 
 nature in the fused mass. The puddling of the iron is continued until 
 the whole has assumed this granular appearance, when the evolution of 
 carbonic oxide ceases almost entirely, showing that the removal of the 
 carbon is nearly completed. The damper is now gradually raised so as 
 to increase the temperature and soften the particles of iron, in order 
 that they may be collected into a mass ; and, the more easily to effect 
 this, a part of the slag is run off through the floss-hole. The workman 
 then collects some of the iron upon the end of the paddle, and rolls it 
 
BAR-IRON. 
 
 407 
 
 about on the hearth until he has collected a sort of rough ball of iron, 
 weighing about half a hundredweight. When all the iron has been 
 collected into balls in this way, they are placed in the hottest part of 
 the furnace, and pressed occasionally with the paddle, so as to squeeze 
 out a portion of the slag with which their interstices are filled. The 
 doors are then closed to raise the interior of the furnace to a very high 
 temperature, and after a short time, when the balls are sufficiently 
 heated, they are removed from the furnace, and placed under a steam 
 hammer, which squeezes out the liquid slag, and forces the softened 
 particles of iron to cohere into a continuous oblong mass or bloom, which 
 is then passed between rollers, by which it is extended into bars. These 
 bars, however (Rough or Puddled, or No. i Bar), are always hard and 
 brittle, and are not fit for use. In order to improve the tenacity of the 
 iron, the rough bars are cut up into short lengths, which are made into 
 bundles, and, after being raised to a high temperature in the mill- furnace, 
 are passed through rollers, which weld the several bars into one com- 
 pound bar, to be subsequently passed through other rollers until it has 
 acquired the desired dimensions. By thus fagoting or piling the bars, 
 their texture is rendered far more unifurm, and they are made to 
 assume a fibrous structure, which greatly increases their strength 
 (Merchant Bar, or No. 2 Bar). To obtain the best, or No. 3 Bar, or wire- 
 iron, these bars are doubled upon themselves, raised to a welding-heat, 
 and again passed between rollers. These repeated rollings have the 
 effect of thoroughly squeezing out the slag which is mechanically 
 entangled among the particles of iron in the rough bar, and would 
 produce flaws if allowed to remain in the metal. A slight improvement 
 appears also to be effected in the chemical composition of the iron 
 during the rolling, some of the carbon, silicon, phosphorus, and sulphur, 
 still retained by the puddled iron, becoming oxidised, and passing away 
 as gas and slag. 
 
 The following table exhibits the change in chemical composition 
 which occurs in pig-iron when puddled (without previous refining) and 
 rolled into wire-iron : 
 
 Effect of Puddling and Forging on Cast Iron. 
 
 In 100 parts. 
 
 Carbon. 
 
 Silicon. 
 
 Sulphur. 
 
 Phosphorus. 
 
 0.645 
 0.139 
 0.117 
 
 Grey pig-iron 
 Puddled bar . 
 Wire-iron 
 
 2.275 
 0.296 
 
 O.I 1 1 
 
 2.720 
 
 0.120 
 
 0.088 
 
 0.301 
 0.134 
 0.094 
 
 About 90 parts of bar-iron are obtained from 100 of refined iron by the puddling 
 process, the difference representing the carbon which has passed off as carbonic 
 oxide, and the silicon, sulphur, phosphorus, and iron which have been removed in 
 the slag or tap-cinder, this being essentially a mixture of ferrous and ferric sili- 
 cates, varying much in composition according to the character of the iron employed 
 for puddling, and the proportions of iron-scale and hammer-slag introduced into 
 the furnace. Of course, also, the material of which the hearth is composed (the 
 fettling} will influence the composition of the slag. The following table affords an 
 illustration of its percentage composition : 
 
 Tap-cinder from Puddling -Furnace. 
 
 Ferrous oxide (FeO) . . 57.67 
 
 Ferric oxide (Fe 2 O 3 ) . . 13.53 
 
 Silica 8.32 
 
 Phosphoric oxide (P 2 5 ) . 7.29 
 
 Ferrous Sulphide . 
 
 Lime 
 
 Oxide of manganese 
 
 Magnesia 
 
 7.07 
 4.70 
 0.78 
 0.26 
 
408 BAR-IRON. 
 
 The lime in the above cinder was probably derived from the hearth of the furnace, 
 which is sometimes lined with that material to assist in removing the sulphur. 
 
 When grey pig-iron is puddled without undergoing the refining process, it becomes 
 much more liquid than white pig or refined iron, and the process is sometimes 
 described as the pig-boiling process, whilst refined iron undergoes dry puddling. In 
 the latter, the oxygen of the air has more share in the de-carburising of the iron 
 than it has in the former. 
 
 Formerly it was sometimes the custom to make a puddled-steel, by arresting the 
 puddling process at an earlier stage than usual, so as to leave a proportion of carbon 
 varying from 0.3 to I per cent. 
 
 It will be observed that this process of puddling is attended with some 
 important disadvantages ; it involves a great expenditure of manual 
 labour, and of a most exhausting kind ; the wear and tear of the pudd- 
 ling furnace is very considerable, and since it receives only ten or eleven 
 charges of about 5 cwts. each in the course of twenty-four hours, it is 
 necessary to work five or six puddling- furnaces at once, in order to 
 convert into bar-iron the whole of the cast iron turned out from a 
 single blast-furnace. These considerations have led to several attempts 
 to improve the puddling process by employing revolving furnaces and 
 other mechanical arrangements to supersede the heavy manual labour. 
 In Dankes' rotating puddling -furnace the pig-iron is run into a cylindrical 
 chamber lined with a mixture of haematite and lime. Air is supplied 
 by a fan, and the cylinder is revolved so as to bring the metal thoroughly 
 into contact with the oxides of iron, which form part of the charge, as 
 in the ordinary puddling process. The charge of about 600 Ibs. is 
 turned out in a single ball, which is further treated as usual. 
 
 Properties of bar -iron. Even the best bar-iron contains from o.i to 
 0.2 per cent, of carbon, together with minute proportions of silicon, 
 sulphur, and phosphorus. Perfectly pure iron is inferior in hardness 
 and tenacity to that which contains a small proportion of carbon. 
 
 Bar-iron is liable to two important defects, which are technically 
 known as cold- shortness and red- shortness. Cold-short iron is brittle at 
 ordinary temperatures, and appears to owe this to the presence of 
 phosphorus, of which element 0.5 per cent, is sufficient materially to 
 dimmish the tenacity of the iron. When the iron is liable to brittleness 
 at a red heat, it is termed red-short iron, and a very little sulphur is 
 sufficient to affect the quality of the iron in this respect. 
 
 Not only may the proportions of carbon, silicon, sulphur, phosphorus, 
 and manganese be supposed to affect the quality of the iron, but the 
 state of combination in which these elements exist in the mass is not 
 unlikely to cause a difference. It also appears certain that the mechani- 
 cal structure, dependent upon the arrangement of the particles compos- 
 ing the mass of metal, has at least as much influence upon the tenacity 
 of the iron as has its chemical composition. 
 
 The best bar-iron, if broken slowly, always exhibits a fibrous structure, 
 the particles of iron being arranged in parallel lines. This appears to 
 contribute greatty to the strength of the iron, for when it- is wanting, 
 and the bar is composed of a fused mass of crystals, it is weaker in 
 proportion to the size of the crystals. The presence of phosphorus is 
 said to favour the formation of large crystals, and hence to produce 
 cold-shortness. There is some reason to believe that the fibrous is some- 
 times exchanged for the crystalline texture under the influence of 
 frequent vibrations, as in the case of railway axles, girders of suspension- 
 bridges, &c. 
 
THE SIEMENS-MARTIN PROCESS. 409 
 
 Considering the difficult fusibility of bar-iron, it is fortunate that it 
 possesses the property of being welded ; that is, of being united by 
 hammering when softened by heat. It is customary first to sprinkle the 
 heated bars with sand or clay in order to convert the superficial oxide 
 of iron into a liquid silicate, which will be forced out from between them 
 by hammering or rolling, leaving the clean metallic surfaces to adhere. 
 
 221. Production of ingot-iron (mild steel). In the Siemens- Martin or 
 open-hearth process the pig-iron is melted in a saucer-shaped depression 
 made of iron plates lined with ganister, a fairly pure sand ; this hearth 
 is built in a furnace which is so constructed that a flame of carbon 
 monoxide (producer gas), raised to a very high temperature by the sys- 
 tem of regenerative firing (see Chemistry of Fuel), plays across the 
 hearth. When the pigs have been thoroughly melted, scraps of iron 
 plate, which, since they are of no other value, may be used to dilute the 
 impure iron, are stirred in, and these are followed by an appropriate 
 quantity of iron oxide, generally haematite. The oxidation of the im- 
 purities in the iron is effected in part by the oxygen of the haematite 
 and in part by the excess of oxygen in the flame used to heat the hearth, 
 the temperature of which is about 1500 C. When the aspect of a test 
 piece withdrawn and hammered by the furnace-man indicates that the 
 process is complete (in 8-10 hours), the tamping-hole of the hearth is 
 unstopped, the metal run into a ladle, and thence into ingot-moulds. 
 
 In this process the silicon and phosphorus are removed, chiefly in the 
 form of iron silicate and phosphate, as slag, which floats on the surface 
 of the metal, and in order that the complete removal of the phos- 
 phorus may be effected the oxidation must be carried sufficiently far 
 to oxidise nearly the whole of the carbon in the iron, producing a 
 very soft metal. Since for most purposes this product would be 
 too soft, it is customary to bring up the carbon content of the metal 
 in the ladle by the addition of a small quantity of ferro-manganese, 
 which immediately melts and mixes with the charge. Eerro-manganese 
 is an alloy of iron and manganese (74 per cent.), the presence of which 
 enables the alloy to hold much carbon (5 per cent.). The yield by this 
 process is about 95 per cent, of the iron charged into the furnace. 
 
 In the Bessemer process the molten 
 pig-iron is run into a converter, which 
 is a large vessel of the shape shown 
 in Fig. 223. It is made of iron plates 
 and is lined with ganister. At the 
 bottom of the vessel there is a number 
 of openings of about ^-inch in diameter 
 '(A) through which air is blown at a 
 pressure of 15 or 20 Ibs. to the 
 square inch. The charge (about 10 
 tons) having been melted in a separate F1 22 
 
 furnace is run into the converter which Bessemer's converting- vessel, 
 
 is suspended on trunnions so that it 
 
 may be turned into a horizontal position for this purpose, and then erected 
 again into the vertical position. The converter is previously heated by 
 a little burning coke, and the blast is turned on before the iron is 
 charged in so that the liquid iron may not run into the air tubes. The 
 silicon and manganese burn first in the stream of air, producing a very 
 
410 THE BESSEMER PEOCESS. 
 
 high temperature, then the carbon is converted into carbon monoxide,, 
 which burns with a long name at the mouth of the converter, and a 
 little of the iron is burnt to oxide, which forms a slag with the silica, 
 and is carried up as a froth to the surface of the liquid iron. The blast 
 of air, or blow, is continued for about twenty minutes, when the dis- 
 appearance of the flame of CO indicates the completion of the process ;. 
 but the remaining purified iron is not pasty as in the puddling-furnace, 
 being retained in a perfectly liquid condition by the high temperature 
 (1580 C.) resulting from the combustion of the silicon and manganese, 
 so that the metal may be run out into ingot-moulds by tilting the con- 
 verter. As in the case of the Siemens- Martin process, the desired 
 hardness is imparted to the metal by the addition of ferro-manganese 
 to the converter just before the iron is poured. The yield is about 85 
 per cent. 
 
 In the original Bessemer process the converter was lined, as described 
 above, with ganister (sand) ; this rendered the method applicable only 
 to such grades of pig-iron as were fairly free from phosphorus, because 
 the most efficient means of removing this element, namely, the admix- 
 ture of the strong base lime with the charge, was impossible, on account 
 of the ease with which lime combines with silica, destroying the lining 
 of the furnace. It is now customary to line converters which are to be 
 used for phosphoric pig with a basic material, namely, a mixture of 
 magnesia and lime, made by calcining dolomite. This basic Bessemer- 
 process is conducted as described above, save that lime to the extent of 
 15-20 per cent, of the charge of iron is thrown into the converter 
 before the iron is run in. This lime combines with the P 2 O 5 produced 
 by the oxidation of the phosphorus, as well as with the silica produced 
 by the oxidation of the silicon^ The basic slag formed in this way is 
 useful as a manure, for the sake of its phosphorus (see Chemistry of 
 Vegetation). The following percentage compositions illustrate the effect 
 of the two processes : 
 
 C. Si. Mn. S. P. 
 
 
 Acid Bessemer pig 
 
 After blow . 
 
 After ferro-manganese 
 
 Basic Bessemer pig . 
 
 After blow . 
 
 After ferro-manganese 
 
 3.57 2.26 0.04 o.io 0.07 
 
 0.19 trace trace o.io 0.07 
 
 0.37 trace 0.54 0.09 0.05 
 
 3.57 1.70 0.71 0.06 1.57 
 
 trace trace 0.05 0.08 
 
 o.i 2 0.03 0.27 0.04 0.02 
 
 Properties of ingot iron (mild steel). Owing to the fact that bar-iron 
 is not fused whilst ingot iron is completely fused in the process of its 
 manufacture, the main difference between these two forms of iron is that 
 ingot iron does not show the fibrous structure of bar-iron, and is, more- 
 over, free from particles of intermixed slag. Ingot iron is liable to the 
 same defects as bar-iron, and these are due to the same causes. 
 
 222. Manufacture of tool-steel (hard steel). Steel differs from bar- 
 iron in possessing the property of becoming much harder when heated 
 to redness, and then suddenly cooled by being plunged into water. 
 Perfectly pure iron obtained by the electrotype process is not hardened 
 by sudden cooling ; but all bar-iron which contains carbon exhibits 
 this property in a greater or smaller degree according to the proportion 
 of carbon present. It does not become decidedly steely, however, until the 
 
CEMENTATION. 411 
 
 carbon amounts to 0.25 per cent. The term steel was formerly applied 
 only to iron containing enough carbon (not less than 0.75 per cent.) to 
 harden it sufficiently for cutting implements, but all iron containing 
 more than 0.2 per cent, of carbon is now referred to as (mild) steel. The 
 hardest steel contains about 1.2 per cent, of carbon, and when the pro- 
 portion reaches 1.5 per cent, the metal begins to assume the properties 
 of white cast iron. Bar-iron may, therefore, be converted into hard steel 
 by the addition of about i per cent, of carbon, and, conversely, cast 
 iron is converted into mild steel when the quantity of carbon contained 
 in it is reduced to from 0.2 to 0.5 per cent.* 
 
 Since the presence of even the small quantities of impurities, other 
 than carbon, which cannot be eliminated by the above processes for 
 making ingot iron are fatal to the best hard steel, this material must 
 be made from the best bar-iron. 
 
 The process is known as cementation, the bars of iron being imbedded 
 in charcoal and exposed for several days to a high temperature. 
 
 The operation is effected in large chests of firebrick or stone, about 
 10 or 12 feet long by 3 feet wide and 3 feet deep. 
 
 Fig. 224. Furnace for converting bar-iron into steel. 
 
 Two of these chests are built into a dome-shaped furnace (converting - 
 furnace, Fig. 224), so that the flame may circulate round them, and the 
 furnace is surrounded with a conical jacket of brickwork in order to 
 allow a steady temperature to be maintained in it for some days. The 
 charcoal is ground so as to pass through a sieve of J-inch mesh, and 
 spread in an even layer upon the bottom of the chests. Upon this the 
 bars of iron, which must be of the best quality, are laid in regular 
 order, a small interval being left between them, which is afterwards 
 filled in with the charcoal powder, with a layer of which the bars are 
 now covered ; over this more bars are laid, then another layer of char- 
 coal, and so on until the chest is filled. Each chest holds 5 or 6 tons 
 of bars. One of the bars is allowed to project through an opening in 
 the end of the chest, so that the workmen may withdraw it from time 
 to time and judge of the progress of the operation. The whole is 
 covered in with a layer of about 6 inches of damp clay or sand, or 
 grinders waste (silica and oxide of iron). 
 
 * Many metallurgists are of opinion that manganese has an influence similar to that of 
 carbon in converting iron into steel. 
 
412 CEMENTATION, 
 
 The fire is carefully and gradually lighted, lest the chests should be 
 split by too sudden application of heat, and the temperature is eventually 
 raised to about the fusing-point of copper (2000 F., 1090 C.), at 
 which it is maintained for a period varying with the quality of steel 
 which it is desired to obtain. Six or eight days suffice to produce 
 steel of moderate hardness ; but the process is continued for three 
 or four days longer if very hard steel be required. The fire is 
 gradually extinguished, so that the chests are about ten days in cooling 
 down. 
 
 On opening the chests the bars are found to have suffered a remark- 
 able change both in their external appearance and internal structure. 
 They are covered with large blisters, obviously produced by some gaseous 
 substance raising the softened surface of the metal in its attempt to 
 escape. It is conjectured that the blisters are caused by carbonic oxide 
 produced by the action of the carbon upon particles of slag accidentally 
 present in the bar. On breaking the bars across, the fracture is found 
 to have a finely granular structure, instead of the fibrous appearance 
 exhibited by bar-iron. Chemical analysis shows that the iron has com- 
 bined with about j per cent, of carbon, and the most remarkable part 
 of the result is that this carbon is not only found in the external layer 
 of iron, which has been in direct contact with the heated charcoal, but 
 is also present in the very centre of the bar. It is this transmission of 
 the solid carbon through the solid mass of iron which is implied by the 
 term cementation. The chemistry of the process probably consists in the 
 formation of carbonic oxide from the small quantity of atmospheric oxy- 
 gen in the chest, and the removal of one-half of the carbon from this 
 carbonic oxide, by the iron, which it converts into steel, leaving carbonic 
 acid gas (200 C = C0 2 ) to be re-converted into carbonic oxide by taking 
 up more carbon from the charcoal (C0 2 + C = 200), which it transfers 
 again to the iron. Experiment has shown that soft iron is capable of 
 absorbing mechanically 4.15 volumes of carbonic oxide at a low red 
 heat, so that the action of the gas upon the metal may occur through- 
 out the substance of the bar. The carbonic oxide is retained unaltered 
 by the iron after cooling, unless the bar is raised to the temperature 
 required for the production of steel. 
 
 The blistered steel obtained by this process is, as would be expected, 
 far from uniform either in composition or in texture ; some portions of 
 the bar contain more carbon than others, and the interior contains 
 numerous cavities. In order to improve its quality it is subjected to a 
 process of fagoting similar to that mentioned in the case of bar-iron ; 
 the bars of blistered steel, being cut into short lengths, are made up 
 into bundles, which are raised to a welding heat, and placed under a 
 tilt-hammer weighing about 2 cwt., which strikes two or three hundred 
 blows in a minute ; in this way the several bars are consolidated into 
 one compound bar, which is then extended under the hammer till of the 
 required dimensions. The bars, before being hammered, are sprinkled 
 with sand, which combines with the oxide of iron upon the surface, and 
 forms a vitreous layer which protects the bar from further oxidation. 
 The steel which has been thus hammered is much denser and more 
 uniform in composition ; its tenacity, malleability, and ductility are 
 greatly increased, and it is fitted for the manufacture of shears, files, 
 and other tools. It is commonlv known as shear steel. Double shear 
 
PROPERTIES OF STEEL, 
 
 413 
 
 steel is obtained by breaking the tilted bars in two, and welding these 
 into a compound bar. 
 
 The best variety of steel, however, which is perfectly homogeneous in 
 composition, is that known as cast steel or crucible steel, to obtain which 
 about 50 Ibs. of blistered steel are broken into fragments, and fused in 
 a fireclay or plumbago crucible, heated in a wind-furnace, the surface of 
 the metal being protected from oxidation by a little glass melted upon 
 it. The fused steel is cast into ingots, several crucibles being emptied 
 simultaneously into the same mould. 
 
 Cast steel is far superior in density and hardness to shear steel, but since it is 
 exceedingly brittle at a red heat, great care is necessary in forging it. It has been 
 found that the addition, to 100 parts of the cast steel, of I part of a mixture of 
 charcoal and oxide of manganese, produces a fine-grained steel which admits of 
 being cast on to a bar of wrought iron in the ingot-mould, so that the tenacity of 
 the latter may compensate for the brittleness of the steel when the compound bar 
 is forged, the wrought iron forming the back of the implement, and the steel its 
 cutting edge. Manganese has a stronger attraction than iron has for oxygen and 
 sulphur ; hence it would decompose any sulphide or oxide of iron present in the 
 metal, and carry those elements into the slag. The soundness of steel ingots is often 
 impaired by minute bubbles or blow-holes, formed by CO or H, the former produced 
 by the action of the carburised iron on a portion of oxidised iron, the latter by the 
 decomposition of moisture in the air. To obviate this, the steel is sometimes sub- 
 jected to a pressure of several tons on the square inch, while it is solidifyin^ 
 (WhitwortVs steel). 
 
 Some small instruments, such as keys, gun-locks, &c., which are exposed to con- 
 siderable wear and tear by friction, and require the external hardness of steel without 
 its brittleness, are forged from bar-iron, and converted externally into steel by the 
 process of case-hardening, which consists in heating them in contact with some 
 substance containing carbon (such as bone-dust, yellow prussiate of potash, &c. ), and 
 afterwards chilling in water. A process which is the reverse of this is adopted in 
 order to increase the tenacity of stirrups, bits, and similar articles made of cast iron ; 
 by heating them for some hours in contact with oxide of iron or manganese, their 
 carbon and silicon are removed in the forms of carbonic oxide and silica, and they 
 become converted into malleable cast iron. A similar effect is produced by heating 
 in sand, the air between its grains affording the required oxygen. 
 
 Properties of steel. After the steel has been forged into the shape of 
 any implement, it is hardened by being heated to redness, and suddenly 
 chilled in cold water, or oil,* or mercury. It can thus be rendered 
 nearly as hard as diamond, at the same time increasing slightly in 
 volume (sp. gr. of cast-steel 7.93 ; after hardening, 7.66), and consider- 
 ably in tensile strength, but diminishing in ductility. If the hardened 
 steel be heated to redness and allowed to cool slowly, it is again con- 
 verted into soft steel, but by heating it to a temperature short of a red 
 heat, its hardness may be proportionally reduced. This is taken advan- 
 tage of in annealing the steel or " letting it down " to the proper 
 temper. The very hardest steel is almost as brittle as glass, and totally 
 unfit for any ordinary use ; but by heating it to a given temperature 
 and allowing it to cool, its elasticity may be increased to the desired 
 extent, without reducing its hardness below that required for the im- 
 plement in hand. On heating a steel blade gradually over a flame, it 
 will acquire a light yellow colour when its temperature reaches 430 F., 
 from the formation of a thin film of oxide ; as the temperature rises, 
 the thickness of the film increases, and at 470 a decided yellow colour 
 is seen, which assumes a brown shade at 490, becomes purple at 520, 
 
 * Chilling in oil cools the steel less suddenly, on account of the lower specific heat of oil, 
 and therefore does not render it so hard and brittle. It is often spoken of as toughening. 
 
414 
 
 THE TEMPEE OF STEEL, 
 
 and blue at 550. At a still higher temperature the film of oxide 
 becomes so thick as to be black and opaque. Steel which has been 
 heated to 430, and allowed to cool slowly, is said to be tempered to the 
 yellow, and is hard enough to take a very fine cutting edge ; whilst, if 
 tempered to the blue, at 550, it is too soft to take a very keen edge, but 
 has a very high degree of elasticity. The following table indicates the 
 tempering heats for various implements : 
 
 Tempering of Steel. 
 
 Temperature, F. 
 
 Colour. 
 
 Implements thus Tempered. 
 
 430 to 450 
 470 . 
 490 . 
 510 . . 
 520 . 
 530 to 570 
 
 Straw-yellow 
 Yellow. 
 Brown-yellow ' 
 Brown-purple 
 Purple . 
 Blue . 
 
 Kazors, lancets. 
 Penknives. 
 Large shears for cutting metal. 
 Clasp-knives. 
 Table-knives. 
 Watch-springs, sword-blades. 
 
 If a knife-blade be heated to redness its temper is spoilt, for it is con- 
 verted into soft steel. In general the steel implements are ground 
 after being tempered, so that they are not seen of the colours mentioned 
 above, except in the case of watch-springs. A steel blade may be easily 
 distinguished from iron by placing a drop of diluted nitric acid upon it, 
 when a dark stain is produced upon the steel, from the separation of 
 the carbon. 
 
 According to modern views the change which occurs in the character 
 of steel during the process of hardening, is primarily due to the exist- 
 ence of two allotropic forms of iron, which are distinguished as a-iron 
 and /3-iron, the former being present in soft iron, the latter in hard 
 iron. 
 
 When pure iron is allowed to cool slowly from a temperature near its melting- 
 point, it is noticed that at 864 C. the rate at which the iron cools undergoes a 
 change, and that the temperature is four-fold as long a time in falling from 
 864 C. to 852 C., as it is in falling through an equal number of degrees during the 
 whole of the rest of its cooling. The mean of these temperatures, 858 C., is called 
 the critical temperature or transition-point of iron. It will be obvious that this 
 delay in cooling can only be due to an evolution of heat by the iron, which must 
 indicate some profound change in the nature of the metal at this temperature. 
 Thus, iron below 858 C. must be different in nature from the metal above this 
 temperature. Iron below 852 C. is said to be in the ft-condition (a-ferrite), whilst 
 above 864 C. it is in the /3-condition (j3-ferrite). 
 
 When the polished surface of a sample of iron or steel is etched with a solution of 
 iodine in potassium iodide or of hydrochloric acid in alcohol and viewed by reflected 
 light through the microscope, it is possible to obtain some idea of the structure of 
 the metal. Examination in this manner of many specimens of different grades has 
 led to the conclusion that there are three distinct forms in which the carbon in iron 
 exists, namely, the compound Fe 3 C, called cementite, the solid solution of carbon in 
 iron, called martensite, and pet-lite, a mixture of cementite and iron in constant 
 proportion. Of these forms martensite is that characteristic of steel which has been 
 hardened by quenching from a temperature of about 1000 C. ; the structure of such 
 metal is homogeneous and crystalline, and as the same appearance is to be noted in 
 hardened steels of different carbon content no compound of carbon and iron can well 
 be supposed to exist in this case. 
 
 When a steel containing 0.8 per cent, of carbon is slowly cooled, there is an arrest 
 in the temperature at 670 C. similar to that occurring at 858 C. in pure iron. 
 
DIRECT EXTRACTION OF IRON. 415 
 
 This arrest corresponds with the transformation of the mass into perlite, showing 
 under the microscope an etched surface different from that of hardened steel, con- 
 stituting, in fact, unhardened steel. Thus the hardening of steel may be supposed 
 to consist in cooling /3-iron, which has carbon dissolved in it, so quickly that the 
 mass remains in this form (martensite) and is not transformed into perlite. 
 
 When iron containing more than 0.8 per cent, of carbon is cooled there are two 
 arrests noticed, the one above 670 C. and varying with the percentage of carbon, 
 and the other at 670 C. The first corresponds with the separation of cementite, 
 Fe 3 C, from the solution of carbon in iron, until the solution contains 0.8 per cent, 
 of carbon, whereupon perlite separates at 670 C. The etched surface appears as a 
 mass of perlite with flakes of cementite embedded therein. 
 
 When less than 0.8 per cent, of carbon is present there are also two arrests in the 
 cooling, the first corresponding with the separation of ct-iron while the second is at 
 670 C., as before, and is due to the separation of perlite. The a-iron is malleable 
 iron. 
 
 The following chemical observations, which are much older than the foregoing 
 physical demonstration, fully conform with the theory at present held. If hardened 
 steel be dissolved in dilute HC1 or H 2 S0 4 , nearly the whole of the carbon is evolved 
 as hydrocarbons, but when the temper has been let down, so that the steel is com- 
 pletely softened, the carbon is left, on dissolution of the metal in acid, as a dark 
 powder consisting of a carbide of iron, Fe 3 C. Steel which has been partially tempered 
 in the manner described above, is found to contain the carbon both in the invisible 
 form, which yields hydrocarbons when the metal is dissolved in acids, and in the 
 form of carbide disseminated as grey scales throughout the mass. 
 
 Manganese, nickel, chromium, and tungsten, respectively, in steel appear to make 
 it hard however it is cooled, and are used for making specially hard steel. Man- 
 ganese steel containing 12 per cent, of that metal is non-magnetic, until it has been 
 heated for some hours at 500-600 C., when it becomes magnetic ; if it then be 
 heated above 800 C. and quickly cooled it again becomes non-magnetic. Steel 
 containing 25 per cent, of nickel is magnetic when heated above 500 C. and cooled 
 slowly. 
 
 223. Direct extraction of wrought iron from the ore. Where very rich 
 and pure ores of iron, such as haematite and magnetic iron ore, are 
 obtainable, and fuel is abundant, the metal is sometimes extracted with- 
 out being converted into cast iron. It is probable that the iron of anti- 
 quity was extracted in this way, for it is doubtful whether cast iron was 
 known to the ancients, and the slag left from old ironworks does not 
 indicate the use of any flux. For such direct extraction the ore is 
 heated in a crucible with charcoal, the combustion being urged by a 
 blast of air from a tuyere pipe. The spongy mass of bar iron thus 
 obtained is hammered as in the puddling process. 
 
 The wrought iron produced 
 by this process always contains 
 a larger proportion of carbon 
 than puddled iron, and is there- 
 fore somewhat steely in charac- 
 ter. In India the native 
 smelters produce iron or steel 
 at will by this process. 
 
 224. Extraction of iron on the 
 small scale. In the laboratory, iron Fi 8"- 22 5- Fletcher's injector furnace, 
 
 may be extracted from hcematite in 
 
 the following manner : A fireclay crucible, about 3 inches high, is filled with char- 
 coal powder, rammed down in successive layers ; a smooth conical cavity is scooped 
 in the charcoal, and a mixture of 8 grams red haematite, 2 grams chalk, and 2 grams 
 pipeclay, is introduced into it ; the mixture is covered with a layer of charcoal, and 
 a lid placed on the crucible, which is heated in a Fletcher's furnace (Fig. 225) for 
 about half an hour. On breaking the cold crucible a button of cast iron will be 
 obtained. 
 
41 6 CEfEMICAL PROPERTIES OF IRON, 
 
 Nearly pure iron may be prepared by fusing the best wire-iron with about one- 
 fifth of its weight of pure ferric oxide, to oxidise the carbon > and silicon which it 
 contains. Some powdered green glass, perfectly free from lead, must be employed 
 as a flux, and the crucible (with its cover well cemented on with fireclay) exposed 
 for an hour to a very high temperature. A silvery button of iron will then be 
 obtained. 
 
 225. Chemical properties of iron. Pure iron is prepared by electro- 
 lysis. Its sp. gr. is 7.9 and it melts at 1600 C. In its ordinary con- 
 dition iron is unaffected by perfectly dry air, but in the presence of 
 moisture and carbonic acid gas it is gradually converted into hydrated 
 ferric oxide (2Fe 2 O 3 .3H 2 0) or rust* The water is decomposed, and 
 ferrous carbonate formed (Fe + H 2 + 00 2 = FeC0 3 + H 2 ) ; this is dis- 
 solved by the carbonic acid present, and the solution rapidly absorbs 
 oxygen from the air, depositing the ferric oxide in a hydrated state ; 
 2FeCO 3 + = Fe 2 3 + 2CO 2 . When iron nails are driven into a new 
 oaken fence, a black streak will soon be observed descending from each 
 nail, caused by the formation of tannate of iron (ink) by the action of 
 the tannic acid in the wood upon the solution of carbonate of iron 
 formed from the nails. The diffusion of iron-mould stains through the 
 fibre of wet linen by contact with a nail, is also caused by the formation 
 of solution of carbonate of iron. The iron in chalybeate waters is also 
 generally present in the form of carbonate dissolved in carbonic acid,, 
 and hence the rusty deposit which is formed when they are exposed to 
 the air. Iron does not rust in water containing a free alkali, or alkaline 
 earth, or an alkaline carbonate. 
 
 Concentrated H 2 S0 4 and HN0 3 do not act upon iron at the ordinary 
 temperature, though they dissolve it rapidly when diluted. Even when 
 boiling, strong sulphuric acid acts upon it but slowly. When iron has- 
 been immersed in strong nitric acid (sp. gr. 1.45), it is found to be 
 unattackedf when subsequently placed in HN0 3 of sp. gr. 1.35, unless- 
 previously wiped ; it is then said to have assumed the passive state. If 
 iron wire be placed in HNO 3 of sp. gr. 1.35, it is attacked immediately ; 
 but if a piece of gold or platinum be made to touch it beneath the acid, 
 the iron assumes the passive state, and the action ceases at once. A 
 state similar to this, the cause of which has not yet been satisfactorily 
 explained, is sometimes assumed by the other metals, though in a less 
 marked degree. In the case of iron it has been attributed to the forma- 
 tion of a coating of the magnetic oxide, which is sparingly soluble in 
 strong HN0 3 . 
 
 Ferrum redactum is iron in powder obtained by reducing Fe 2 3 with 
 hydrogen at a red heat in an iron tube. It always contains some 
 Fe 3 4 . 
 
 226. Oxides of iron.. Three compounds of iron with oxygen are 
 known in the separate state ; FeO, Fe 3 O 4 , Fe 2 O 3 . 
 
 Ferrous oxide, or protoxide of iron, FeO, is obtained by heating ferric oxide to 
 500 C. in dry hydrogen; Fe 2 3 + H2 = H 2 + 2FeO. It is obtained as a grey 
 powder, which readily absorbs O from the air, taking fire and becoming Fe 3 4 . It 
 is a basic oxide, yielding ferrous salts. In the finely divided state it decomposes 
 water. 
 
 Ferrous hydroxide, Fe(OH) 2 , is precipitated by alkalies from the ferrous salts. 
 When pure it forms a white precipitate, but if air be present it becomes green from 
 
 * Most samples of rust are magnetic, indicating the presence of the magnetic oxide, 
 f It is doubtful whether the iron ever remains quite unattacked, although no gas is 
 evolved. 
 
OXIDES OF IRON. 
 
 417 
 
 the production of ferroso-ferric oxide, and ultimately brown ferric hydroxide. 
 These changes are best seen when potash or ammonia is added to the ferrous 
 salt obtained by shaking iron turnings or filings with a strong solution of 
 sulphurous acid. This disposition of the ferrous hydroxide to absorb oxygen is 
 turned to advantage when a mixture of ferrous sulphate with lime or potash 
 is employed for converting blue into white indigo. 
 
 Ferric oxide, or peroxide of iron, Fe 2 3 , occurs as specular iron ore in 
 six-sided crystals, and in haematite, as already noticed among the ores of 
 iron, and has also been referred to as occurring in commerce under the 
 names of colcothar, jewellers rouge, and Venetian red, which are ob- 
 tained by the calcination of the green sulphate of iron; 2Fe!30 4 
 Fe 2 3 + SO., + S0 3 . The ferric hydroxide obtained by decomposing a 
 solution of ferric chloride with an alkali, forms a brown gelatinous pre- 
 cipitate, which is easily dissolved by acids. When freshly precipitated 
 and well washed it dissolves in a solution of ferric chloride, forming a 
 basic chloride which by dialysis is slowly decomposed, HC1 passing 
 through the dialyser and a blood-red colloidal solution of Fe(OH) 3 being 
 left in the dialyser. When dried at 100 C., the hydroxide becomes 
 2Fe 2 3 .H 2 O. If a hot solution of a ferric salt be precipitated by an alkali, 
 and the precipitate dried over sulphuric acid, it becomes Fe 2 (OH) 6 .Fe 2 3 , 
 which is the composition of iron-rust and of some brown haematites. 
 When either of the hydroxides is heated to dull redness, it exhibits a 
 sudden glow, and is converted into a modification of Fe 2 O 3 , which is 
 dissolved with great difficulty by acids, although it has the same com- 
 position as the soluble form which has not been strongly heated. 
 When the ferric oxide is heated to whiteness, it loses oxygen, and is 
 converted into magnetic oxide of iron; 3Fe 2 3 = 2Fe 3 O 4 + O. Existing 
 as it does in all soils, ferric oxide is believed to fulfil the purpose of 
 oxidising the organic matter in the soil, and converting its carbon into 
 carbon dioxide, to be absorbed by the plant : the ferric oxide being thus 
 reduced to ferrous oxide, which is oxidised by the air, and fitted to 
 perform again the same office. Ferric oxide, like alumina, is a weak 
 base, and even exhibits some tendency to play the part of an acid 
 towards strong bases, though not in so marked a degree as alumina. 
 When heated in a stream of H or CO, it yields Fe 3 4 at 350 C., pyro- 
 phoric FeO at 500 C., and metallic iron at from 700 to 800 C. 
 
 Magnetic or black oxide of iron, or magnetite, Fe 3 O 4 , is generally 
 regarded as a compound of ferrous oxide with ferric oxide (FeO.Fe 8 3 ), 
 a view which is confirmed by the occurrence of a number of minerals 
 having the same crystalline form as the native magnetic oxide of iron, in 
 which the iron, or part of it, is displaced by other metals. Thus, 
 spinelle is MgO.Al 2 3 ; FranJdinite, ZnO,Fe 2 3 ; chrome-iron ore, 
 FeO.Cr,0 3 ; pleonaste, MgO.Fe 2 3 ; Gahnite, ZnO.Al 2 3 . The natural 
 magnetic oxide was mentioned among the ores of iron, and this oxide 
 has been seen to be the result of the action of air or steam upon iron at 
 a high temperature. The hydrated magnetic oxide of iron (F 3 e0 4 .H 2 0) 
 is obtained as a black crystalline powder by mixing i molecule of ferrous 
 sulphate with i molecule of ferric sulphate, and pouring the mixture 
 into a slight excess of solution of ammonia, which is afterwards boiled 
 with it. Magnetic oxide of iron, when acted upon by acids, yields 
 mixtures of ferrous and ferric salts, so that it is not an independent 
 basic oxide. 
 
 The very stable character of Fe 3 4 has led to its application for 
 
 2 D 
 
4 l8 GEEEN VITEIOL. 
 
 protecting iron from rust. When superheated steam is passed over the 
 red-hot metal, a very dense strongly adherent film of Fe 3 O 4 is produced, 
 which effectually protects the metal (Barff's process). A similar coat- 
 ing is produced by the action of a mixture of air and carbonic acid gas 
 (Bower's process}. 
 
 Ferric acid, H 2 Fe0 4 , has not been obtained in the free state, but some 
 of its salts are known.* 
 
 When iron filings are strongly heated with nitre, and the mass treated with a 
 little water, a fine purple solution of potassium ferrate is obtained. A better 
 method of preparing this salt consists in suspending I part of freshly precipitated 
 ferric hydrate in 50 parts of water, adding 30 parts of solid potassium hydrate 
 and passing chlorine till a slight effervescence commences ; Fe 2 3 + C] 6 + ioKOH = 
 6KCl + 2(K 2 Fe0 4 )-t-5H 2 ; the ferrate forms a black precipitate, being insoluble 
 in the strongly alkaline solution, though it dissolves in pure water to form a 
 purple solution, which is decomposed even by dilution, oxygen escaping, and 
 hydrated ferric oxide being precipitated. A similar decomposition happens 
 on boiling a strong solution, or on adding an acid with a view to liberate the 
 ferric acid. The ferrates of barium, strontium, and calcium are obtained as fine 
 red precipitates when solutions of their salts are mixed with potassium ferrate. 
 
 As a lecture experiment, the ferrate is readily prepared by dissolving a frag- 
 ment of KOH in a little solution of Fe 2 Cl 6 , adding a few drops of bromine, and 
 gently heating. On dissolving the cold mass in water, a fine red solution is 
 obtained, which gives a red granular precipitate with Ba01 2 . 
 
 The pink solution obtained by boiling some samples of chloride of lime with 
 water contains calcium ferrate, and gives a pink precipitate with BaCl 2 . By 
 boiling Fe 2 Cl 6 with excess of chloride of lime, a fine pink solution of calcium 
 ferrate is obtained. 
 
 Ferrous carbonate, FeC0 3 , or spat/tic iron ore, or siderite, is found in rhombo- 
 hedral crystals associated with the carbonates of Ca, Mg, and Mn, which are 
 isomorphous with it. It occurs in chalybeate waters, dissolved in carbonic acid, 
 and deposits as ferric hydrate when the water is exposed to air. If powdered 
 iron which has been reduced from the oxide by hydrogen (ferrum redactuni) be 
 suspended in water, and a stream of C0 2 be passed for some time, a solution of 
 FeC0 3 in carbonic acid is obtained, which, when filtered, is colourless, becomes 
 rusty when exposed to air, and gives, when boiled, an abundant precipitate of 
 FeC0 3 , which is nearly white, and becomes green when exposed to air. Sodium 
 carbonate added to a ferrous salt gives a white precipitate if all air be excluded ; 
 otherwise oxygen is absorbed, and a dingy green precipitate containing Fe 3 4 is 
 formed. 
 
 The substance sold as ferric carbonate, obtained by precipitating a ferric salt 
 with sodium carbonate, is mainly ferric hydrate, since weak bases like Fe 2 3 do not 
 form carbonates. 
 
 227. Ferrous sulphate, copperas, green vitriol, or sulphate of iron, 
 is easily obtained by heating i part of iron wire with i J part of strong 
 sulphuric acid, mixed with 4 times its weight of water, until the whole 
 of the metal is dissolved, when the solution is allowed to crystallise. 
 Its manufacture on the large scale by the oxidation of iron pyrites has 
 been already referred to. It forms fine green monoclinic crystals, having 
 the composition FeS0 4 .H 2 O.6Aq. Rhombic crystals, isomorphous with 
 the sulphates Zn and Mg, can also be obtained. 
 
 The colour of the crystals varies somewhat, from the occasional pre- 
 sence of small quantities of ferric sulphate, Fe 2 (S0 4 ) 3 . It dissolves very 
 easily in twice its weight of cold water, yielding a pale green solution. 
 One part of boiling water dissolves about 3 parts of the crystals. When 
 the commercial sulphate of iron is boiled with water it yields a brown 
 
 * The common ferrates correspond with an anhydride, FeO 3 . Lately a barium perferrate 
 corresponding- with FeO 4 has been prepared, a fact important from the point of view of the 
 periodic law (p. 302). 
 

 SALTS OF IEON. 419 
 
 muddy solution, in consequence of the decomposition of the ferric sul- 
 phate contained in it, with precipitation of a basic sulphate. Ferrous 
 sulphate has a great tendency to absorb oxygen, and to become con- 
 verted into ferric sulphate, and is thus useful as a reducing-agent. For 
 example, it is employed for precipitating gold in the metallic state from 
 its solutions. But its chief use is for the manufacture of ink and black 
 dyes by its action upon vegetable infusions containing tannic acid, such 
 as that of nut-galls. 
 
 Crystals of FeS0 4 .H 2 0.4Aq, isomorphous with CuS0 4 .H 2 0.4Aq, may be obtained 
 by dropping a crystal of cupric sulphate into a supersaturated solution of ferrous 
 sulphate. As in the case of MgS0 4 .7H 2 (p. 375) one molecule of the H 2 in 
 FeS0 4 .7H may be exchanged for other sulphates ; thus, ammonium ferrous sul- 
 phate, FeS"0 4 .(NH 4 ) 2 S0 4 .6H 2 0, is well known. 
 
 The salt FeS0 4 .S0 3 is obtained in minute prismatic crystals when a saturated 
 solution of ferrous sulphate is added to an excess of strong sulphuric acid. 
 
 Ferric sulphate, Fe 2 (S0 4 ) 3 , is found in Chili as a white silky crystalline mineral, 
 coquimbite, having the composition Feo(S0 4 ) 3 .9Aq. Iron alums, constructed on the 
 type of the common alums (p. 387), with Fe'" in place of Al"' (e.g., NH 4 .Fe'" 
 (S0 4 ) 2 . 12H 2 0), are commercial salts. 
 
 Ferrous phosphate, Fe 3 (P0 4 ) 2 , and arsenate, Fe 3 (As0 4 ) 2 , are used in medicine, 
 being prepared by precipitating ferrous sulphate with a mixture of sodium 
 acetate and sodium phosphate or arsenate. The acetate is used so that the resulting 
 liquid may contain free acetic acid instead of the free sulphuric formed by the H in 
 the sodium salt; 3FeSO 4 +2Na a HP0 4 =Fei(P0 4 ) ft +2Na a S04+H a SO 4 . Both the 
 phosphate and arsenate are white when perfectly pure, but they become blue when 
 exposed to air, from the production of a little ferroso-ferric salt. The precipitated 
 ferric phosphate is 2FeP0 4 -5A.q. Ferrous phosphate is found in the mineral 
 Virianite or native Prussian blue, Fe 3 (P0 4 ) 2 .8Aq. 
 
 Ferrous silicate, Fe 2 Si0 4 , is found crystallised in finer y cinder of the ironworks. 
 
 Ferrous chloride, FeCl 2 , sublimes in colourless six-sided scales when iron is heated 
 in HC1 gas. It is deliquescent, and crystallises from water in pale green crystals, 
 FeCl 2 4Aq, which are oxidised by air. 
 
 Ferrous iodide, FeI 2 , is prepared by digesting fine iron wire with twice its weight 
 of iodine and about eight parts of water for some time, afterwards boiling till the 
 red colour has disappeared, filtering, and evaporating in contact with clean iron. 
 It forms green crystals, FeI 2 .5Aq, which are deliquescent and very soluble in water. 
 The solution absorbs oxygen from the air, and deposits a brown precipitate unless 
 kept in contact with clean iron or mixed with strong syrup. 
 
 228. Ferric chloride, or perchloride of iron (FeCl 3 ), is obtained in 
 beautiful dark green crystalline scales when iron wire is heated in a 
 glass tube through which a current of dry chlorine is passed, the ferric 
 chloride passing off in vapour, and condensing in the cool part of the 
 tube. The crystals almost instantly become wet when exposed to air 
 on account of their great attraction for water. Ferric chloride may be 
 obtained in solution by dissolving iron in hydrochloric acid, and con- 
 verting the ferrous chloride (FeCl 2 ) thus formed into ferric chloride by 
 the action of nitric and hydrochloric acids (p. 191). A strong solution 
 yields crystals of FeCl 3 .6Aq. The aqueous solution reddens litmus. 
 The crystals are decomposed by heat, leaving an oxychloride. The 
 solution of ferric chloride has been recommended in some cases as a 
 disinfectant, being easily reduced to ferrous chloride, and thus affording 
 chlorine to oxidise unstable organic matters (p. 175). In contact with 
 paper, FeCl 3 becomes reduced to Fe01 2 when exposed to light. A 
 solution of perchloride of iron in alcohol is used in medicine under the 
 name of tincture of iron. It is also soluble in ether and benzene. 
 
 Solution of ferric chloride dissolves a very large quantity of pure freshly precipi- 
 tated ferric oxide (p. 417), nine molecules of Fe 2 3 being dissolved by one molecule 
 
420 SULPHIDES OF IRON. 
 
 of ferric chloride. The solution of ferric oxy chloride thus obtained has a very dark- 
 red colour, and yields a very copious brown precipitate with common water, or any 
 solution containing even a trace of a sulphate. When the aqueous solution of FeCl 3 
 is heated, it dissociates into a similar soluble hydroxide and HC1. 
 
 Ferrous sulphide, FeS, is formed when a red-hot bar of iron is rubbed with a 
 stick of sulphur, the fused FeS running off in globules, and is prepared as described 
 at p. 214. It is obtained as a black precipitate when an alkaline sulphide is added 
 to a ferrous salt. It is easily oxidised iwhen exposed to air in a moist state, and 
 dissolves readily in HC1, being indeed the only black sulphide which dissolves easily 
 in dilute HC1. It is used in the laboratory for making H 2 S. 
 
 Magnetic pyrites, Fe 7 S 8 , is found in yellow six-sided crystals. 
 
 Iron pyrites, or mundic, FeS 2 , forms yellow cubes or octahedra of sp. gr. 5.2. It 
 is formed by the slow reduction of ferrous sulphate by organic matter, and its 
 presence in coal appears to be accounted for in this way. Minute crystals of iron 
 pyrites are sometimes found as rough casts of organic substances. It burns 
 when heated, yielding Fe 2 3 and S0 2 , and is largely used as a source of the 
 latter by the vitriol manufacturer. Sulphur itself may be obtained from it by 
 distillation at a high temperature, Fe 3 S 4 being left. FeS 2 is insoluble in HC1, 
 which distinguishes it from FeS. It may be dissolved by nitric acid. Radiated 
 pyrites, or white pyrites, or marcasite, has the same composition, but its sp. gr. is 
 only 4. 8. 
 
 Some kinds of pyrites explode with considerable violence when heated, and 
 create much alarm when they occur in household coal ; these have been found 
 to contain small cavities filled with highly compressed (probably liquid) COg, 
 which expands suddenly when heated. 
 
 Compact yellow iron pyrites is not oxidised by exposure to air, but white 
 pyrites is easily converted into ferrous sulphate and sulphuric acid. Even yellow, 
 pyrites in minute crystals diffused through clay will behave in the same way. 
 
 The FeS 2 may be obtained artificially by heating iron with excess of sulphur to 
 a temperature below redness, or by heating ferric oxide or hydrate moderately in 
 a stream of H 2 S as long as it increases in weight. 
 
 Iron nitride, a compound of iron with about 9 per cent, of nitrogen, has been 
 found as a silvery deposit on the lavas of Etna. It yields ammonia when heated 
 in hydrogen. 
 
 Iron carbonyls. When finely divided iron, prepared by igniting ferrous oxalate 
 and reducing the resulting oxide in a current of hydrogen, is allowed to remain 
 in the cold in contact with CO, a compound Fe(CO) 5 , iron pentacarbonyl, is formed 
 and can be distilled from the unaltered iron at 120 C. and condensed in a receiver 
 surrounded by ice and salt. It is an amber-coloured liquid of sp. gr. 1.46 ; it 
 boils at 103 C. and crystallises below - 21 C. ; at 180 C. it is decomposed into 
 Fe and CO. It dissolves in many organic solvents, and is slowly decomposed 
 with precipitation of Fe 2 (OH) 6 on exposure to air. When exposed to sunlight it 
 deposits golden scales which appear to have the composition Fe(CO) 7 , iron hepta- 
 car'bonyl. The properties of these compounds should be compared with those of 
 nickel carbonyl (p. 425). Iron carbonyl has been detected in coal gas which has 
 been compressed in iron cylinders. 
 
 229. Atomic weight of iron. When iron is dissolved in hydrochloric 
 acid, 28 parts by weight of iron combine with 35.5 parts of chlorine, 
 displacing i part of hydrogen. The specific heat of iron, and its iso- 
 morphism with magnesium, zinc, and cadmium, show that its atomic 
 weight must be represented by 56, so that iron is a diad or divalent 
 element, one atom of iron being exchangeable for two atoms of 
 hydrogen. 
 
 The molecular formula of ferric chloride has been confirmed by the 
 determination of the vapour density at 400 C., which has been found 
 to be 165, corresponding with the formula Fe 2 01 6 . But at higher tem- 
 peratures the vapour density approaches 81.25, corresponding with the 
 formula FeCl 3 , although it does not quite reach this value, since a 
 certain amount of dissociation into FeCl 2 and C1 2 occurs. 
 
 It will be remarked that iron possesses a different valency accordingly 
 
OXIDES OF COBALT. 421 
 
 as it exists in ferrous or ferric compounds. Thus, in ferrous oxide (FeO) 
 and ferrous chloride (FeCl 2 ) it occupies the place of two atoms of hydro- 
 gen, and is divalent ; but in ferric oxide (Fe,0 3 ) and ferric chloride 
 (Fed 3 ) each atom of iron occupies the place of three atoms of hydrogen, 
 and is trivalent. 
 
 Iron is remarkable for its two series of fairly stable salts, the ferrous 
 and ferric, the former acting as reducing-agents, and the latter as 
 oxidising agents. Ferrous iron resembles magnesium and zinc in its 
 disposition to form double salts with salts of ammonium, hence its 
 solutions are imperfectly precipitated by ammonia ; but ferric iron 
 resembles aluminium, and is completely precipitated. Nitric acid, 
 chloric acid, and chlorine will always convert ferrous into ferric salts, 
 and ensure complete precipitation by ammonia. 
 
 Some chemists designate the divalent iron existing in ferrous compounds by 
 the name ferrosum (Fe"), and the trivalent iron of the ferric compounds by 
 ferricum (Fe'"). Others regard iron as a tetravalent metal Fe iv , existing in the 
 ferrous salts as a group of two atoms united by two bonds, and in the ferric salts 
 as a group of two atoms united by one bond. On this view, ferrous chloride 
 would be Fe. 2 Cl 4 , or Cl2=Fe=Fe=Cl 2 , and ferric chloride would be Fe 2 Cl 6 , or 
 Cl 3 =Fe Fe=Cl 3 . 
 
 COBALT. 
 
 Co'' = 58. 5 parts by weight. 
 
 230. Some of the compounds of cobalt are of considerable importance 
 in the arts, on account of their brilliant and permanent colours. It is 
 generally found in combination with arsenic and sulphur, forming tin- 
 white cobalt, CoAs 2 , and cobalt glance, CoAs 2 .CoS 2 , but its ores also 
 generally contain nickel, copper, iron, manganese, and bismuth. 
 
 The metal itself is obtained by strongly heating cobalt oxide with 
 charcoal, in the manner to be described for preparing nickel from its 
 oxide, or by heating the oxide with aluminium powder (p. 386). In its 
 properties it closely resembles iron, but it is said to surpass iron in 
 tenacity. It is magnetic. It is heavier than iron, sp. gr. 8.5, and rather 
 more easily fusible (1500 C.). It has been substituted for nickel in 
 plating goods which are usually nickel-plated. 
 
 Three oxides of cobalt, corresponding with those of iron, are known : 
 cobaltous oxide, CoO ; cobaltic oxide, Co 2 3 ; and cobalto-cobaltic oxide, 
 Co 3 4 or CoO.Co 2 3 . The first of these, CoO, is a brown powder left 
 when Co(OH) 2 is ignited in absence of air ; it is a basic oxide, dissolv- 
 ing in acids to form cobaltous salts. When heated in air, it oxidises to 
 CoO.Co 2 3 . When heated in the electric furnace, it melts and forms 
 rose-coloured crystals. 
 
 Cobaltic oxide is left as a black powder when cobaltous nitrate is 
 gently heated. It is a feeble base, and the cobaltic salts are very un- 
 stable ; thus the oxide dissolves in cold HC1, yielding a brown solution 
 of cobaltic chloride, Co 2 Cl 6 , which is easily decomposed when heated, 
 evolving C1 2 and leaving 2CoCl.,. When Co 2 3 is heated it becomes 
 CoO.Co 2 3 . It is doubtful whether a cobalt dioxide, Co0 2 , exists, but 
 when Co 2 3 is fused with MgO in the electric furnace, red crystals of 
 MgCoO 3 are obtained. 
 
 Cobalto-cobaltic oxide is the commercial oxide of cobalt employed 
 for painting on porcelain, and for preparing other commercial cobalt 
 
422 COBALT SALTS. 
 
 products. It is a black powder, which evolves chlorine when boiled with 
 HC1, yielding a solution of CoCl 2 . It is generally prepared as a by- 
 product in the manufacture of nickel from its arsenical ores (see Nickel). 
 Co 3 4 is not an independent base, but gives cobaltous and cobaltic 
 salts when dissolved in acids. 
 
 Cobaltous hydroxide, Co(OH) 2 , is obtained by adding potash in excess 
 to a solution of a cobaltous salt, and boiling. The blue precipitate pro- 
 duced at first is a basic salt which becomes converted into the red 
 hydroxide on boiling with excess of potash. If air be allowed access it 
 oxidises the red precipitate, converting it into brown cobaltic hydroxide. 
 Co(OH) 9 dissolves in ammonia, giving a fine red solution, which absorbs 
 oxygen from the air and becomes brown. Cobaltic hydroxide, Co 2 (OH) 6 , 
 forms the black precipitate when the solution of a hypochlorite or hypo- 
 bromite is added to one of a cobaltous salt. 
 
 Cobaltous nitrate, Co(N0 3 ) 2 .6Aq, obtained by dissolving cobalt oxide 
 in HN0 3 and crystallising, forms red prisms, which become blue when 
 their water is expelled, and black Co 2 O 3 on further heating. 
 
 Cobalt-yellow or potassium- cobaltic nitrite, K 6 CO /// 2 (NO 2 ) 12 , is obtained 
 as a yellow precipitate when cobaltous nitrate is acidified with acetic 
 acid, and potassium nitrite added ; the acetic acid liberates nitrous acid, 
 which oxidises the cobaltous salt; 2Co"(N0 3 ) 2 + ioKNO 2 + 4HN0 2 = 
 K 6 Co' // 2 (N0 2 ) 1? + 4KN0 3 + 2NO+ 2H 2 0. It forms a yellow crystalline 
 precipitate, slighly soluble in water, and not decomposed by cold HC1 
 or HN0 3 . Caustic alkalies decompose it, separating C0 2 (OH) 6 . 
 
 Cobaltous chloride (CoCl 2 ), obtained by dissolving any of the oxides 
 in hydrochloric acid, forms red prisms, CoCl 9 .6Aq, which become blue 
 CoCl 2 .2Aq at 120 C., and at 140 C., CoCl 2 , which may be sublimed 
 in dark blue scales in a current of chlorine. If strong hydrochloric 
 acid be added to a red solution of this salt, it becomes blue ; if enough 
 water be now added to render it pink, the blue colour may be produced 
 at pleasure by boiling, the solution first passing through a neutral tint.* 
 Chloride (muriate) of cobalt is employed as a sympathetic ink, for charac- 
 ters written with its pink solution are nearly invisible until they are 
 held before the fire, when they become blue and resume their original 
 pink colour if exposed to the air ; a little chloride of iron causes a green 
 colour. 
 
 The cobaltous sulphide (CoS) is obtained as a black precipitate when an alkaline 
 sulphide is added to a solution of a salt of cobalt. It differs from FeS by being 
 insoluble in HC1. A cobaltic sulphide (Co 2 S 3 ) is found in grey octahedra, forming 
 cobalt pyrites. The disulphide (CoS 2 ) has been obtained artificially. 
 
 Cobaltous sulphate, CoSO 4 .7H 2 0, is found as cobalt 'vitriol. It forms red prisms 
 isomorphous with ferrous sulphate. It does not become blue when dried, and 
 bears a high temperature without decomposing. Cobaltic sulphate and cobaltic 
 alums have been prepared. 
 
 Cobaltous arsenate, or cobalt bloom, Co 3 (As0 4 ) 2 .8Aq, is found in pink needles. 
 
 Cobalt di-arsenide, CoAs 2 is found crystallised as tin-wliite cobalt and speiss 
 cobalt, in which it is associated with the isomorphous arsenides of nickel and 
 iron, so that it is written [CoNiFe]As 2 . CoAs 3 is also found in nature. 
 
 The cobaltous silicate associated with potassium silicate forms the 
 blue colour known as smalt, which is prepared by roasting the cobalt ore, 
 so as to convert the bulk of the cobalt into oxide, leaving, however, a 
 
 * A solution containing- so small a quantity as 0.015 per cent, of cobalt will give a distinct 
 blue colour when boiled with an equal bulk of strong hydrochloric acid. 
 
COBALT AMMONIA COMPOUNDS. 423 
 
 considerable quantity of arsenic and sulphur still in the ore, The residue 
 is then fused in a crucible with ground quartz and carbonate of potash, 
 when a blue glass is formed, containing cobalt silicate and potassium 
 silicate ; whilst the iron, nickel, and copper, combined with arsenic and 
 sulphur, collect at the bottom of the crucible and form a fused mass of 
 metallic appearance known as speiss, which is employed as a source of 
 nickel. The blue glass is poured into cold water, so that it may be 
 more easily reduced to the fine powder in which the smalt is sold. If 
 the cobalt ore destined for smalt be over- roasted, so as to convert the 
 iron into oxide, this will pass into the smalt as a silicate, injuring its 
 colour. Smalt much resembles ultramarine, but is not bleached by 
 acids. Zaffre is prepared by roasting a mixture of cobalt ore with two 
 or three parts of sand. 
 
 Thenard's blue, or cobalt ultramarine, consists of cobalt phosphate and 
 aluminium phosphate, and is prepared by mixing precipitated alumina 
 with cobalt phosphate and calcining in a covered crucible. The phos- 
 phate is obtained by precipitating a solution of cobalt nitrate with 
 phosphate of potassium or sodium. 
 
 Rinmanris green is prepared by calcining the precipitate produced by 
 sodium carbonate in a mixture of cobalt sulphate with zinc sulphate. 
 It is a compound of the oxides of cobalt and zinc. 
 
 The relations of ammonia to the cobalt salts are very remarkable and 
 characteristic, the NH 3 combining both with cobaltous and cobaltic salts 
 to form compounds which behave like salts of new bases containing 
 cobalt, nitrogen, and hydrogen, known as cobaltosamines and cobalta- 
 mines. 
 
 When NH 3 is added to the solution of a cobaltous salt, air being excluded, a 
 cdboltosamine salt of the general type CoX 2 .6NH 3 , where X is an acid radicle, is 
 formed. When these are exposed to the air they undergo oxidation, yielding 
 oxy cobaltamine salts of the type CoOX 2 . 5NH 3 , in which the cobalt may be regarded 
 as tetrad, corresponding with the oxide Co0 2 ; these salts lose oxygen, becoming 
 cobaltamine salts, when their solutions are heated. If the cobaltosainine solution 
 be fairly dilute when it is exposed to the air, the oxy-salt will not be formed, and 
 on addition of an acid a cobaltamine salt will be separated. These are of six 
 types, represented by CoX 3 .wNH 3 , where n= I, 2, 3, 4, 5 or 6 ; they are all coloured 
 salts and distinguished by prefixes signifying the colour characteristic of the series 
 for example, xantko- (yellow), luteo- (yellow), roseo-, purpureo-, croceo- (saffron), 
 and.fu.sco- (brown). 
 
 Cobalt is seen to resemble iron in many respects, but the cobaltic 
 compounds are much less stable than the ferric compounds. Cobaltous 
 compounds become oxidised to cobaltic compounds only in solutions 
 which are neutral or alkaline, while ferrous compounds are easily 
 oxidised in acid solutions. Both iron and cobalt form remarkable 
 compounds with potassium and cyanogen, iron forming the ferro- 
 cyanide, K 4 Fe"Cy 6 , and ferricyanide, K 3 F'"Cy 6 , while cobalt forms the 
 cobalticyanide, K 3 Co"'Cy 6 (see Cyanides). No carbonyl of cobalt has 
 yet been obtained. 
 
 NICKEL. 
 
 Ni" = 58-3 parts by weight. 
 
 231. Nickel owes its value in the useful arts chiefly to its property of 
 imparting a white colour to the alloys of copper and zinc, with which it 
 forms the alloy known as German silver, and to the ease with which it 
 
424 METALLURGY OF NICKEL. 
 
 can be deposited by electrolysis on other metals (electro-plating), as a 
 lustrous and coherent film, which is only slowly tarnished by the atmo- 
 sphere. Dishes and crucibles of this metal .are used in the laboratory 
 in many cases as substitutes for those of platinum and silver, though 
 they are, of course, more ea.sily oxidised. It has been found possible 
 to weld sheet nickel upon iron and steel plates, and culinary vessels, &c., 
 have been made of such plates, which are not liable to rust. Steel con- 
 taining nickel is exceptionally hard. Alloys of copper and nickel are 
 used in coinage. Nickel is very nearly allied to cobalt, and generally 
 occurs associated with that metal in its ores. 
 
 Recently a nickel ore has been discovered in Canada, which consists 
 of magnetic iron pyrites (Fe.^) in which nickel takes the place of some 
 3-8 per cent, of the iron. This promises to become the most important 
 ore of nickel, though at present the mineral garnierile, a silicate of 
 nickel and magnesium found in New Caledonia, furnishes the largest 
 supply of the metal. The first of these ores contains a little cobalt, but 
 the second is free from that metal. The Saxon and Bohemian ores of 
 nickel contain cobalt, arsenic, sulphur, and iron ; the chief are kupfer- 
 nickel, NiAs, nickel glance, NiAs 2 .NiS 2 , and nickel blende, NiS. 
 
 In the extraction of metals from ores which contain much iron sul- 
 phide, as is always the case with sulphureous nickel ores, advantage is 
 taken of the ease with which iron sulphide can be roasted to oxide,* 
 and the oxide fluxed as ferrous silicate by fusion with silica. This 
 method of removing iron may be extended to those nickel ores which 
 contain no sulphur, by heating them with gypsum and coke, when the 
 iron becomes converted into sulphide. When the iron has been removed, 
 a mixture (matte} of the sulphides of nickel and copper (when this is 
 present in the ores) remains. This is completely oxidised by roasting 
 in air,t and the mixture of oxides of nickel and copper is treated with 
 dilute sulphuric acid, which dissolves the copper oxide; the nickel oxide 
 is made into a paste with charcoal, the paste is cut into cubes and 
 heated to reduce the nickel, which retains the shape of the cubes. The 
 commercial metal contains carbon, iron, silicon, and sulphur. The 
 furnace operations necessary for the above process will be understood by 
 reference to the metallurgy of copper. 
 
 The arsenical nickel ores are treated as described above for the removal of iron, 
 and the speiss thus obtained, consisting essentially of nickel and arsenic, but con- 
 taining a little cobalt and copper, is treated by a wet method for the separation of 
 the cobalt. This is effected by roasting the speiss to expel most of the arsenic, 
 dissolving in HC1, peroxidising the solution by bleaching-powder, and neutralising 
 with chalk ; in this way the iron is precipitated as basic ferric carbonate, and the 
 remaining arsenic as ferric arsenate. H 2 S is passed through the solution to 
 precipitate bismuth and copper as sulphides, leaving cobalt and nickel in solution. 
 The latter, having been boiled to expel the excess of H 2 S, is neutralised with lime 
 and mixed with bleaching-powder, which precipitates the cobalt as Co 2 3 , leaving 
 NiO in solution, from which it may be precipitated by adding lime ; it is reduced 
 as described above. The Co 2 3 becomes Co 3 O 4 when ignited. 
 
 Mond's process for extracting nickel depends on the fact that when 
 the finely divided metal is heated in a current of CO at 50 100 C. it is 
 volatilised in the form of nickel carbonyl (see below), and thus separated 
 from any other metals, &c., which may accompany it. The nickel 
 
- OXIDES OF NICKEL. 425 
 
 carbonyl vapour is then heated in another vessel, whereby it is decom- 
 posed and deposits its nickel. 
 
 In practice the finely divided roasted matte or speiss is caused to descend a tower 
 containing hollow shelves heated internally by hot gas to 250 C., where it meets 
 .an ascending stream of water-gas. The oxides are thus reduced to metal, and the 
 material is next conveyed to the top of a second tower, not heated, in descending 
 which it meets a current of gas rich in CO and at a temperature of 50 C. Nickel 
 -carbonyl is produced and carried forward as vapour by the gas into an apparatus 
 in which a mass of granules of nickel is kept in motion so that the granules 
 perpetually roll over each other and are prevented from cohering. The tempera- 
 ture of this apparatus being about 200 C., the carbonyl deposits its nickel on the 
 granules while its CO passes on to be used again in the second tower for volatilising 
 more 'nickel. By keeping the temperature of the volatilising tower as low as 
 possible, the production of iron carbonyl (p. 420) is avoided. 
 
 Nickel closely resembles iron, but is less attacked by air and water ; 
 its sp. gr. is 8.8, and it melts at 1600 C. At ordinary temperatures it 
 is magnetic, but it loses this property at 250 C. 
 
 The oxides of nickel correspond in composition with those of cobalt. 
 The salts formed by nickelous oxide (NiO) are usually green, and give 
 bright green solutions. The hydroxide has a characteristic apple-green 
 colour, and does not absorb oxygen from the air like the cobaltous 
 hydroxide. It dissolves in ammonia with a blue colour unchanged by 
 air. The greater facility with which the cobalt is converted into 
 sesquioxide has been applied (as above described) to effect the separation 
 of the two metals. NiO has been found native in octahedral crystals, 
 which have also been obtained accidentally in a copper-smelting furnace ; 
 it melts and crystallises in the electric arc. 
 
 Ni 3 O 4 is obtained by passing moist oxygen over NiCl 2 at about 400 C. 
 It has a metallic appearance, and is seen in octahedral crystals under 
 the microscope. It is converted into NiO when heated, and dissolves 
 in hydrochloric acid with evolution of chlorine. 
 
 Nickel sulphate (NiS0 4 .H 2 0.6Aq) forms fine green prismatic 
 crystals, the water of constitution in which may be displaced by K 2 S0 4 
 or (NH 4 ) 9 S0 4 . Nickel ammonium sulphate, NiS0 4 .(NH 4 ) 2 S0 4 .6H 2 0, is 
 used in electro-plating with nickel. It is almost insoluble in ammonium 
 sulphate solution. 
 
 Nickel sulphate maybe obtained by dissolving nickel in dilute sul- 
 phuric acid. It is isoinorphous with the sulphates of Mg, Zn, Fe, and 
 Co. When ammonia is added to its solution, it produces a green pre- 
 cipitate of a basic salt, which dissolves in excess of ammonia to a violet 
 solution, depositing violet crystals of NiS0 4 .4NH 3 .2H 2 0. 
 
 Four sulphides of nickel are known Ni 2 S, FiS, Ni 3 S 4 and NiS 2 . NiS 
 is found native as capillary pyrites, and is obtained as a black precipitate 
 by the action of an alkaline sulphide on a salt of nickel ; like cobalt 
 sulphide, it is insoluble in HC1 ; but ammonium disulphide dissolves it 
 to a dark brown liquid. 
 
 Nickel carbonyl, Ni(CO) 4 , is a colourless liquid (sp. gr. 1.3) which 
 boils at 43 C. and crystallises at- 25 C. It is prepared by passing 
 dry CO through a tube containing finely divided nickel which has been 
 reduced from NiO by heating it in hydrogen at 400 C. The Ni(CO) 4 
 is condensed from the excess of CO used by passing the gas through a 
 tube surrounded by ice and salt. It is insoluble in water, but dissolves 
 in alcohol, benzene, and chloroform. Its vapour is decomposed at 
 
426 OXIDES OF MANGANESE. 
 
 150 C. into CO and Ni, which is deposited in the form of a mirror on 
 the sides of the vessel ; it is a powerful reducing-agent. Theoretically,, 
 it is of great importance as furnishing a volatile compound, by means 
 of which the atomic weight of nickel can be determined. 
 
 Nickel is farther removed from iron than cobalt is ; its peroxide, 
 Ni 2 3 , shows no disposition to form salts, and it does not form any com- 
 pound corresponding with ferro- or cobalti-cyanides. It has far less 
 colouring power than cobalt, and its salts are commonly green. In 
 many respects nickel more nearly resembles copper than iron. 
 
 Nickel salts are poisonous. 
 
 MANGANESE. 
 
 Mn" = 54.6 parts by weight. 
 
 232. Manganese much resembles iron in several particulars relating 
 both to its physical and chemical characters, and is often found asso- 
 ciated, in small quantities, with the compounds of that metal. It is 
 found chiefly as pyrolusite, Mn0 2 , braunite, Mn 2 3 , and manganese spar, 
 MnC0 3 . The metal itself has not been applied to any useful purpose. 
 It is obtained either by reducing one of the oxides with charcoal at a 
 very high temperature when a fused mass, composed of manganese 
 combined with a little carbon (corresponding with cast iron), is obtained, 
 and may be freed from carbon by a second fusion in contact with man- 
 ganous oxide by reducing Mn01 2 with magnesium, or by igniting a 
 mixture of aluminium powder and manganese oxide (p. 386). 
 
 Manganese is grey with a red tinge, hard and brittle, sp. gr. 8, very 
 difficult to fuse (1900 C.), and more easily oxidised than iron, so that 
 it decomposes water when slightly warmed. It is not magnetic unless 
 cooled to - 20 C. It appears to be more volatile than iron. 
 
 Manganese dissolves easily in diluted hydrochloric or sulphuric acid, 
 Mn displacing H 2 , like Fe and Or. It resembles iron in its tendency 
 to combine with carbon at a high temperature to form a compound 
 corresponding with cast iron, and in this form the manganese is not 
 oxidised by air. It decomposes water gradually at ordinary tempera- 
 tures, and boiling water more quickly. 
 
 Spiegel-eisen and ferro-manganese are alloys containing iron, manga- 
 nese, and carbon, which are largely used in the production of steel. 
 
 233. Oxides of manganese, MnO, Mn 2 3 , Mn 3 4 , Mn0 2 , Mn0 3 , 
 Mn 2 O 7 ; the first two are bases, the last two anhydrides. 
 
 Manganese dioxide or peroxide, Mn0 2 , is the chief form in which 
 this metal is found in nature, and is the source from which all other 
 compounds of manganese are obtained. Its chief mineral form is 
 pyrolusite, which forms steel-grey prismatic crystals of sp. gr. 4.9 ; but 
 it is also found amorphous, as psilomelane, and in the hydra ted state as 
 wad. In commerce, pyrolusite is known as black manganese, or simply 
 manganese, and is largely imported from Germany, Spain, &c., for the 
 use of the manufacturer of bleaching-powder and the glass-maker. It 
 is also used as a cheap source of oxygen, which it evolves when heated 
 to redness, without fusing, leaving the red oxide of manganese, Mn 3 O 4 . 
 The manganese dioxide is an indifferent oxide, and does not combine 
 with acids. Strong HC1, however, dissolves it, giving a brown solution 
 from which water precipitates a brown oxychloride. If the brown 
 
OXIDES OF MANGANESE. 427 
 
 solution, which probably contains Mn 2 01 6 and MnCl 4 , be heated, it evolves 
 C1 2 and becomes colourless MnCl 2 . Nitric acid is almost without action 
 on'Mn0 2 . Strong sulphuric acid evolves oxygen from it ; MnO 2 + H 2 S0 4 = 
 MnS0 4 + H 2 + 0. Even dilute sulphuric acid effects the same change 
 if some substance ready to combine with oxygen is added, such as 
 ferrous sulphate or oxalic acid. Hence a mixture of Mn0 2 and H 2 S0 4 
 is much used as an oxidising agent, and it will be seen from the above 
 equation that only half the oxygen in the Mn0 2 is available for purposes 
 of oxidation. It becomes necessary, therefore, to value the commercial 
 black oxide by ascertaining how much FeS0 4 a given weight of it will 
 oxidise in the presence of dilute acid, H 2 S0 4 . 
 
 2(FeO.S0 3 ) + Mn0 2 + 2(H 2 O.S0 3 ) = Fe 2 3 .(S0 3 ) 3 + MnO.S0 3 + 2H 2 0. 
 
 When heated in hydrogen, the oxides of manganese are not reduced 
 to the motal, like those of iron, but are converted into MnO. 
 
 Manganous oxide, MnO, obtained in this way, is a greenish powder. It has been 
 obtained in transparent emerald-green crystals. It easily absorbs oxygen from 
 the air. It is a basic oxide, dissolving in acids to form the manganous salts. It 
 has been found native in a manganiferous dolomite. 
 
 Manganic oxide, or manganese sesquioxide, Mn 2 3 , is found in the mineral 
 braunite in octahedral crystals. By its general appearance it might be mistaken 
 for Mn0 2 , but it dissolves in moderately strong sulphuric acid, forming a red 
 solution of manganic sulphate, Mn 2 (S0 4 ) 3 . 
 
 Mn 2 3 is a feebly basic oxide." It may be obtained by heating any of the 
 oxides of manganese to redness in a current of oxygen, while Mn 3 4 is formed 
 when any one of the oxides is heated in air. When Mn0 2 in very small quantity 
 is added to melted glass, it imparts a purple colour, which is probably due to the 
 formation of a manganic silicate. The amethyst is believed by some to owe its 
 colour to the same cause. 
 
 Red oxide of manganese (Mn 3 4 ) is the most stable of the oxides of this metal, 
 and is formed when any of the others is heated in air. Thus obtained, it has a 
 brown or reddish colour ; but it is found in nature as the black mineral hausmannite. 
 In composition it resembles the magnetic oxide of iron, but it seems probable that 
 the true formula is 2MnO.Mn0 2 , for when treated with diluted nitric acid it leaves 
 the black hydrated dioxide. Strong sulphuric acid dissolves it to a red liquid 
 containing manganous and manganic sulphates. Dilute sulphuric acid leaves 
 Mn0 2 undissolved. HC1 dissolves it when heated, evolving Cl and leaving MnClg. 
 
 Mn0 3 or manganic anhydride, is formed in small quantity by dropping a solution 
 of potassium permanganate in concentrated H 2 S0 4 upon dry Na 2 C0 3 , and con- 
 densing the pink cloud which arises, in a tube cooled by ice and salt. It is a red 
 amorphous mass, yielding manganic acid in contact with water. 
 
 Permanganic anhydride, Mi^O^, is a red oily liquid formed when potassium 
 permanganate is decomposed by strong sulphuric acid; K 2 Mn 2 8 + 2H 2 S0 4 = 
 2KHS0 4 + Mn 2 7 + H 2 0. It decomposes slowly, even at common temperatures, 
 evolving oxygen, together with violet vapour of Mn 2 7 . When heated, it decom- 
 poses with explosion. It is a most powerful oxidising agent, setting fire to most 
 combustible bodies. In contact with water, it yields permanganic acid, H 2 Mn 2 8 . 
 
 Manganous hydroxide, Mn(OH) 2 , is obtained as a white precipitate when an 
 alkali is added to a manganous salt, out of contact with air. When exposed to 
 air it rapidly becomes brown, forming manganic hydroxide. 
 
 Manganic hydroxide, Mn 2 2 (OH) 2 , may be regarded, as Mn 2 3 , in which has 
 been exchanged for (OH) 2 , or as Mn 2 3 .H 2 0, hydrated manganese sesquioxide. It 
 is found in dark grey prismatic crystals, as manganite, associated with Mn0 2 , from 
 which it differs by giving a brown instead of a black streak on unglazed earthen- 
 ware. Moreover, on boiling it with dilute nitric acid, part of it is dissolved as 
 manganous nitrate, leaving a hydrated manganese dioxide, which dissolves to a 
 brown solution when thoroughly washed. A hydrated manganese dioxide is also 
 precipitated when chloride of lime is added to a manganese salt. 
 
 Manganic acid, H 2 MnO 4 , has not been isolated, but several man- 
 
428 PERMANGANATES. 
 
 ganates are known, which are isomorphous with the chromates and 
 sulphates. 
 
 Potassium manganate, K 2 MnO 4 , is formed when MnO 2 is fused with 
 potash; 3 Mn0 2 + 2KOH = K 2 Mn0 4 + Mn 2 3 + H 2 O. If an oxidising 
 agent, such as air or nitre, be present, the Mn 2 O 3 is also converted into 
 K 2 MnO 4 ; Mn 2 O 3 + 4 KOH + O 3 = 2 K 2 Mn0 4 + 2 H 2 O. The extraction of 
 oxygen from air upon this principle has been described at p. 39. 
 
 Sodium manganate (Na 2 MnO 4 ), obtained by heating manganese 
 dioxide with sodium hydroxide under free exposure to air, is employed 
 in a state of solution in water, as Condy's green disinfecting fluid. It is 
 also used as a bleaching-agent, and in the preparation of oxygen at a 
 cheap rate. The manganates of potassium and sodium dissolve in water 
 containing potash or soda, forming green liquids, but when dissolved in 
 pure water they are decomposed, yielding the red permanganates 
 
 3Na 2 Mn0 4 + 2H 2 = Na 2 Mn 2 8 + Mn0 2 + 4NaOH. 
 Barium manganate forms the pigment known as Cassel green. 
 
 Manganous acid, of which Mn0 2 would be the anhydride, might be expected to 
 exist, but is not known. When Mn(OH) 2 is oxidised in presence of an alkali, the 
 resulting brown substance contains more or less of the alkali combined with 
 Mn0 2 . These compounds are known as manganites e.g., CaO.Mn0 2 . 
 
 Permanganic acid, H 2 Mn 2 8 , has been obtained in a hydrated crystalline state 
 by decomposing the barium permanganate with sulphuric acid, and evaporating 
 the solution in vacua. It is a brown substance, easily dissolving in water to a red 
 liquid, which is decomposed at about 90 F. (32 C.), evolving oxygen, and 
 depositing manganese dioxide. 
 
 Potassium permanganate, K 2 Mn 2 8 , forms rhombic prisms isomor- 
 phous with the perchlorate, KC10 4 , on which account it is sometimes 
 written KMnO 4 . It dissolves in 20 parts of cold water, forming a 
 purple solution, which becomes green K 2 MnO 4 by contact with many 
 substances capable of taking up oxygen. When crystallised perman- 
 ganate is heated to 240 C. it gives manganate 
 
 K 2 Mn 2 8 K 2 Mn0 4 + Mn0 2 + 2 . 
 
 It is largely used in many chemical operations. In order to prepare it, 4 parts of 
 finely powdered manganese dioxide are intimately mixed with 3^ parts of KC10 3 , 
 and 5 parts of KOH dissolved in a very little water. The pasty mass is dried, and 
 heated to dull redness for some time in an iron tray or earthen crucible. The 
 potassium chlorate imparts the required oxygen. On treating the cool mass with 
 water, potassium manganate is dissolved, forming a dark green solution. This is 
 diluted with water, and a stream of C0 2 passed through it so long as any change of 
 colour is observed; 3K 2 Mn0 4 + 2C0 2 = K 2 Mn 2 8 + Mn0 2 + 2K 2 C0 3 . The precipi- 
 tated Mn0 2 is allowed to settle, and the clear red solution poured off and evapo- 
 rated to a small bulk. On cooling, it deposits prismatic crystals of the per- 
 manganate (K 2 Mn 2 8 ), which are red by transmitted light, but reflect a dark green 
 colour. The K 2 C0 3 , being much more soluble in water, is left in the solution. 
 
 Potassium permanganate is remarkable for its great colouring power, 
 a very small quantity of the salt producing an intense purplish-red 
 colour in a large quantity of water. Its solution in water is very easily 
 decomposed and bleached by substances having an attraction for oxygen, 
 such as sulphurous acid or a ferrous salt. If a very small piece of iron 
 wire be dissolved in diluted sulphuric acid, the solution of ferrous sul- 
 phate so produced will decolorise a large volume of weak solution of the 
 permanganate, being converted into ferric sulphate 
 
 K 2 Mn 2 8 + ioFeS0 4 + 8H 2 S0 4 = K 2 S0 4 + 2MnS0 4 + 5Fe 2 (S0 4 ) 3 + 8H 2 0. 
 
CHLORIDES OF MANGANESE. 429 
 
 or K 2 O.Mn 2 7 + io(FeO.S0 3 ) + 8(H O.S0 3 ) = 
 
 K 2 O.S0 3 + 2(MnO.S0 3 ) + 5(Fe 2 O 3 .3S0 3 ) = 8H 2 0, 
 
 which shows that the molecule of K,Mu 2 8 has 5 atoms of oxygen avail- 
 able for purposes of oxidation. 
 
 This decomposition forms the basis of a valuable method for deter- 
 mining the proportion of iron in its ores. 
 
 Many organic substances are easily oxidised by potassium perman- 
 ganate, and this is the case especially with the offensive emanations 
 from putrescent organic matter. Hence it is extensively used, under 
 the name of Condys red disinfecting Jluicl, in cases where a solid or 
 liquid substance is to be deodorised. 
 
 The oxidising power of potassium permanganate is effectively illus- 
 trated by pouring a little glycerine into a cavity made in a small heap of 
 the powdered crystals on a porcelain crucible lid ; the glycerine slowly 
 sinks into the permanganate, and after a minute or two bursts into 
 vivid combustion. 
 
 An alkaline solution of the permanganate is sometimes used as an 
 oxidising agent, since it parts with oxygen when boiled with oxidisable 
 substances, becoming green from the production of manganate 
 
 K 2 Mn 2 8 + 2KOH = 2K 2 Mn0 4 + H 2 + 0. 
 
 /Sodium permanganate, Na 2 Mn 2 8 , is often used as a disinfectant, being 
 cheaper than the potassium salt. It is made by heating Mn0 2 with 
 NaOH, in a flat vessel, exposed to air, for 48 hours, to dull redness ; the 
 mass is boiled with water to convert the manganate into permanganate ; 
 3 Na 2 MnO 4 + 2 H 2 = Na 2 Mn 2 O 8 + Mn0 2 f 4 NaOH. 
 
 234. There appear to be three chlorides of manganese corresponding 
 with three of the oxides, viz., MnCl 2 , Mn 2 Cl 6 , and MnCl 4 ; but only the 
 first is obtainable in the pure state, the others forming solutions which 
 are easily decomposed with evolution of chlorine. There is also some 
 evidence of the existence of a chloride MnCl r 
 
 By dissolving potassium permanganate in oil of vitriol, and adding fragments 
 of fused sodium chloride, a remarkable greenish-yellow gas is obtained, which 
 gives purple fumes with moist air. and is decomposed by water, yielding a red 
 solution which contains hydrochloric and permanganic acids. It, therefore, 
 must contain manganese and chlorine, and is sometimes regarded as the per- 
 chloride (MnCl 7 ) ; but it is more probably an oxychloride of manganese (see 
 Chlorochromic acid). Care is required in its preparation, which is sometimes 
 attended with explosion. 
 
 The manga nous chloride (MnCl 2 ) is obtained in large quantity as a waste pro- 
 duct in the preparation of chlorine for the manufacture of bleaching-powder. 
 Since there is no useful application for it, the manufacturer sometimes reconverts 
 it into the black oxide by Weldon's process (see p. 170). As the native binoxide 
 always contains iron, the liquor obtained by treating it with HC1 contains ferric 
 chloride (Fe 2 Cl 6 ) mixed with MnCl 2 . In order to separate the iron, advantage is 
 taken of the circumstance that sesquioxides are weaker bases than the protoxides, 
 so that if a small proportion of lime or chalk be added to the solution, the iron 
 may be precipitated as ferric oxide, without decomposing the chloride of man- 
 ganese ; Fe 2 Cl 6 + 3CaO = Fe 2 3 + 3CaCl 2 . 
 
 After separating the Fe 2 O 3 , an excess of lime is added and air blown through 
 the mixture at about 150 F., when the white precipitate of MnO, formed at first, 
 absorbs the oxygen, and becomes a black compound of Mn0 2 with lime, which is 
 used over again for the preparation of chlorine. Unless the lime is added in 
 excess, only MnO.Mn0 2 is formed, so that the excess of lime displaces the MnO 
 and allows it to be converted into Mn0 2 . In another process Weldon employs 
 magnesia instead of lime, with the view of afterwards recovering the chlorine 
 
430 POTASSIUM BICHROMATE. 
 
 from the chloride of magnesium, in the form of hydrochloric acid (see p. 348), and 
 using the magnesia over again. 
 
 Manganous sulphate, MnS0 4 .H 2 0.6Aq. isomorphous with green vitriol, forms 
 faintly pink crystals easily soluble in water. It is prepared by adding strong H 2 SO 4 
 to Mn0 2 , heating the paste to redness to decompose any ferric sulphate, extracting 
 with water, precipitating the last traces of iron by adding manganous carbonate, 
 filtering, and crystallising. Manganous sulphate is employed by the dyer and 
 calico-printer in the production of black and brown colours. Crystals have been 
 obtained of MnS0 4 .H 2 0.4Aq., isomorphous with copper sulphate. 
 
 Manganous sulphide, MnS, occurs as manganese blende in steel-grey masses. It 
 may be obtained as a greenish powder by heating any of the oxides of manganese 
 in a current of H 2 S. When precipitated by alkaline sulphides from manganese 
 salts, it has a pink colour and contains water. When the pink precipitate is 
 boiled with an excess of alkali sulphide, it becomes a green crystalline powder, 
 3MnS.H 2 0. The manganous sulphide has a tendency to form soluble compounds 
 with the alkali sulphides, so that a solution of manganese often requires boiling 
 with ammonium sulphide before a precipitate is formed. It dissolves easily in 
 HC1. Manganese disulpTiide, MnS 2 , is found, in crystals belonging to the regular 
 system, as Hauerite, in Hungary. 
 
 Manganese, though more nearly allied to iron than to any other 
 metal, is parted from it by the greater stability of the manganous salts, 
 which are less easily oxidised than the ferrous 'salts, as well as by the 
 far greater stability of the manganates than of the ferrates, and by the 
 existence of permanganates, which have no parallel in the iron series. 
 
 The chlorides of manganese give a green colour to a colourless flame. 
 
 CHROMIUM. 
 
 = 51.7 parts by weight. 
 
 235. This metal derives its name from xpw/*a, colour, in allusion to 
 the varied colours of its compounds, upon which their uses in the arts 
 chiefly depend. It is comparatively seldom met with, its principal ore 
 being the chrome-iron ore ( FeO.Cr 2 3 ), which is remarkable for its re- 
 sistance to the action of acids and other chemical agents.* It is chiefly 
 found in the Shetland Islands, Sweden, Russia, Hungary, and the 
 United States, and is imported for the manufacture of bichromate of 
 potash (K 2 0.2Cr0 3 ), which is one of the chief commercial compounds of 
 chromium. The ore is first heated to redness and thrown into water, 
 in order that it may be easily ground to a fine powder, which is mixed 
 with carbonate of potash, chalk being added to prevent the fusion of 
 the mass, and strongly heated in a current of air on the hearth of a 
 reverberatory furnace, the mass being occasionally stirred to expose 
 a fresh surface to the air. The ferrous oxide is thus converted into 
 ferric oxide, and the oxide of chromium (O 2 3 ) into potassium chromate 
 (K 2 Cr0 4 ) ; 2(FeO.O 2 O 3 ) + 4K 2 C0 3 + O 7 = Fe 2 O 3 + 4K,Cr0 4 + 4 C0 2 . Nitre 
 is sometimes added to hasten the oxidation. On treating the mass with 
 water, a yellow solution of potassium chromate is obtained, which is 
 drawn off from the insoluble residue of ferric oxide and lime, and mixed 
 with a slight excess of acid, e.g., nitric acid 
 
 2(K 2 Cr0 4 ) + 2HN0 3 = K 2 Cr 2 7 + 2KN0 3 + H 2 0. 
 
 The solution, when evaporated, deposits anhydrous, red, tabular crystals 
 of bichromate of potash (potassium dichromate), which dissolve in 
 
 * There appear to be four types of chrome-iron ore, viz., FeO.Cr 2 O 3 , 2FeO.Cr 2 O, 
 3FeO.2Cr 2 O 3 , and 2FeO.3Cr 2 O 3 . 
 
CHROMIC ANHYDRIDE. 431 
 
 10 parts of cold water, forming an acid solution. It is from this salt 
 that the other compounds of chromium are immediately derived. 
 
 Metallic chromium has received no useful application. It is obtained 
 by reducing chromic chloride with zinc (or magnesium) at a high tem- 
 perature, and removing the excess of zinc with dilute nitric acid. Or 
 Cr,0 3 may be reduced by aluminium at a high temperature (p. 386). It 
 has a grey colour, is about as heavy as iron (sp. gr. 6.8), is extremely 
 hard, and less fusible (about 3000 C.) than platinum. It resembles 
 aluminium in not being attacked by nitric acid, very readily becoming 
 passive (p. 416) therein, but HOI dissolves it, yielding chromous chloride, 
 CrCl 2 , a property which connects chromium with iron. Chromium, like 
 aluminium, is attacked by the alkali hydroxides at high temperatures, 
 evolving hydrogen and producing chromates. By the action of sodium 
 on chromic chloride the metal has been obtained in octahedral crystals, 
 which are not dissolved even by nitro-hydrochloric acid. 
 
 236. Oxides of chromium. Three oxides of chromium are known 
 in the separate state chromic oxide, Cr 2 3 , chromium dioxide, Cr0 2 , and 
 chromic anhydride, Cr0 3 . Monoxide of chromium or chromous oxide (CrO) 
 is known in the hydrated state, and perchromic acid (H 2 Cr 2 8 ) is believed 
 to exist in solution. The chromous salts correspond with the ferrous 
 salts, but are much more susceptible of oxidation. 
 
 Chromic anhydride (often called chromic acid), the most important of 
 these, is obtained by adding to one measure of a solution of potassium 
 dichromate, saturated at 54 C., one measure and a half of concentrated 
 sulphuric acid, by small portions at a time, and allowing the solution 
 to cool, when chromic anhydride crystallises out in fine crimson needles, 
 which are deliquescent, very soluble in water, fusing easily, and decom- 
 posed at 250 C. into oxygen and chromic oxide. Chromic anhydride 
 is a powerful oxidising agent ; most organic substances, even paper, will 
 reduce it to the green chromic oxide. A mixture of potassium dichro- 
 mate and sulphuric acid is employed for bleaching some oils, the 
 colouring-matter being oxidised at the expense of the chromic acid, and 
 chromic sulphate being produced 
 
 K 2 Cr 2 7 + 4H 2 S0 4 = K 2 S0 4 + Cr 2 (S0 4 ) 3 + 3 
 
 The dichromate itself evolves oxygen when heated to bright red- 
 ness, being first fused (about 400 C.), and afterwards decomposed; 
 2 K 2 Cr 2 7 = 2K,CrO 4 + Cr 2 O 3 + O s . Heated with strong HC1, it evolves 
 01; K,Cr,O 7 +i4HCl = 2KCl + Cr g Cl 6 + 7H 8 q + 01 6 . The oxidising effect 
 of the potassium dichromate, under the action of light, upon gelatine 
 and albumin, receives very important applications in photography. 
 
 Sodium dichromate, Na, 2 Cr 2 O 7 .2H 3 O, is much more soluble than the 
 potassium salt, requiring only an equal weight of water ; it is now often 
 substituted for K 2 Cr 2 7 , being similarly prepared, and containing, of 
 course, a higher percentage of available oxygen owing to the lower 
 atomic weight of sodium. 
 
 Chromic acid, H 2 Cr0 4 , is not known in the pure form. Its salts, 
 the chromates, are isomorphous with the sulphates. 
 
 Chromate of potash, or normal potassium chr ornate (K 2 O.Cr0 3 or 
 K 2 Cr0 4 ), is formed by adding potassium carbonate to the red solution 
 of potassium dichromate until its red colour is changed to a fine yellow, 
 when it is evaporated and allowed to crystallise. It forms yellow 
 
432 CHROMIC OXIDE. 
 
 prismatic crystals, having the same form as those of potassium sul- 
 phate, and is five times as soluble in water as the dichromate is, yielding 
 an alkaline solution, which is partly decomposed by evaporation, with 
 formation of the dichromate. Acids, even carbonic, change its solution 
 from yellow to red, from production of dichromate. It becomes red 
 when heated, and yellow again on cooling, and fuses without decompo- 
 sition. Potassium chromate has been found in some yellow samples 
 of saltpetre from Chili. No compound corresponding with KHSO 4 is 
 known. 
 
 Trichromate of potash (K 2 0.3Cr0 3 ) has been obtained in red crystals by adding 
 nitric acid to the dichromate. 
 
 It will be observed that the chromates of potassium are rather exceptional salts. 
 The yellow or normal chromate, K 2 CrO 4 , is formed upon the model of imaginary 
 chromic acid, H 2 Cr0 4 . The red chromate, or potassium dichromate, is not a true 
 acid salt, for it contains no hydrogen ; it is sometimes called anhydro-chromate t 
 and written K 2 Cr0 4 .Cr0 3 . The trichromate would be K 2 Cr0 4 .2Cr0 3 . 
 
 Barium chromate, BaCr0 4 . is used in painting, as yellow ultra-marine,, being pre- 
 cipitated by potassium chromate from barium chloride ; it is insoluble in acetic 
 acid ; i million parts of H 2 dissolve 15 parts of BaCr0 4 at 18 C. 
 
 Chrome yellow is the chromate of lead (PbCr0 4 ), prepared by mixing dilute solu- 
 tions of lead acetate and potassium chromate. The precipitate is insoluble in acetic 
 acid. It is largely used in painting and calico-printing, and by the chemist as a 
 source of oxygen for the analysis of organic substances, since, when heated, it fuses 
 to a brown mass, which evolves oxygen at a red heat. Chrome yellow being a 
 poisonous salt, its occasional use for colouring confectionery is very objectionable. 
 Chromate of lead in prismatic crystals forms the rather rare red lead ore of Siberia, 
 in which chromium was first discovered. 
 
 Orange chrome is a basic chromate of lead (PbCr0 4 .PbO), and maybe obtained by 
 boiling the yellow chromate with lime ; 2(PbCr0 4 ) + CaO = PbCr0 4 .PbO + CaCr0 4 . 
 The calico-printer dyes the stuff with yellow chromate of lead, and converts it into 
 orange chromate by a bath of lime-water. Chrome-orange is also made by precipi- 
 tating a lead salt with a weak alkaline solution of potassium chromate, which gives- 
 a mixture of the two chromates of lead. 
 
 Silver chromate, Ag 2 Cr0 4 , is obtained as a red crystalline precipitate when silver 
 nitrate is added to potassium chromate. When K 2 Cro0 7 is added gradually to 
 AgN0 3 , a scarlet precipitate of silver dichromate, Ag 2 Cr 2 6 7 , is obtained ; and if this- 
 be boiled with water, it leaves Ag 2 Cr0 4 in dark green crystals, which become red 
 when powdered. 
 
 The colour of the ruby (crystallised alumina) appears to be due to the presence 
 of a small proportion of chromic anhydride. 
 
 Sesquioxide of chromium, or chromic oxide (Cr 2 3 ), is valuable as a 
 green colour, especially for glass and porcelain, since it is not decomposed 
 by heat. Being extremely hard, it is used in making razor-strops. It is 
 prepared by heating potassium dichromate with one-fourth of its weight 
 of starch, the carbon of which removes oxygen, leaving a mixture of 
 chromic oxide with potassium carbonate, which may be removed by 
 washing with water. If sulphur be substituted for the starch, potas- 
 sium sulphate will be formed, which may also be removed by water. 
 "When hydrated chromic oxide is strongly heated, it loses its water and 
 exhibits a sudden glow, becoming 'darker in colour, and insoluble in 
 acids which previously dissolved it easily ; in this respect it resembles 
 aluminia and ferric oxide. Like these oxides, the chromic oxide is a 
 feeble base ; it is remarkable for forming two classes of salts, having the 
 same composition, but differing in the colour of their solutions, and in 
 some other properties. Thus, there are two modifications of the chromic 
 sulphate the green sulphate, O 2 (S0 4 ) 3 .6Aq, and the violet sulphate, 
 Cr 2 (S0 4 ) 3 .9Aq. The solution of the latter conducts electricity well and 
 
CHROMIUM CHLORIDES. 
 
 433 
 
 gives the reactions of a sulphate, but when boiled ifc becomes green y 
 conducts badly, and gives no precipitate with BaCl 2 . Chrome alum 
 forms dark purple octahedra (KCr"'(S0 4 ) 2 .i2Aq) which contain the 
 violet modification of the sulphate ; and if its solution in water be 
 boiled, its purple colour changes to green, and the solution refuses to 
 crystallise.* It is obtained as a secondary product in certain chemical 
 manufactures, and may be prepared by the action of sulphurous acid 
 gas on a mixture of potassium dichromate and sulphuric acid ; K 2 O 3 7 
 + H 2 S0 4 + 3S0 2 = 2KCr(S0 4 ) 2 + H 3 O. The anhydrous chromic sul- 
 phate forms red crystals, which are insoluble in water and acids. 
 Guignet's green, used in painting and calico-printing, is hydrated Cr 2 O 3 
 prepared by heating K 2 Cr 2 O 7 with 3 parts of boric acid (when oxygen 
 is evolved) and washing the product until it is free from potassium 
 borate ; it generally retains a little boric acid, perhaps as chromic 
 borate. Cr 2 O 3 combines with the oxides of the magnesium group of 
 metals to form very insoluble and infusible compounds, crystallising in 
 octahedra, e.g., ZnO.Cr,O 3 , MnO.Cr 2 3 , FeO.O 2 O 3 , which have been 
 termed chromites, and are isomorphous with the spinelles (p. 388). 
 
 Crystallised Cr 2 O 3 , prepared by passing chromyl chloride (p. 434) 
 through a red-hot tube, is isomorphous with A1 2 3 and Fe 2 3 . 
 
 Chromic hydroxide. Cr. 2 (OH) 6 , is thrown down by alkalies from solutions of 
 chromic salts, such as chrome alum, as a greenish-blue precipitate. It dissolves 
 sparingly in ammonia to a pink solution, from which chromic oxide is precipitated 
 by boiling. Potash dissolves it to a fine green solution, which becomes gelatinous 
 when boiled, from precipitation of chromic oxide. It yields a hydrosol by the 
 dialysis of its solution in CrCl 3 . 
 
 Chromium dioxide, Cr0 2 . When potassium dichromate is reduced by nitric 
 oxide or sodium thiosulphate, a brown precipitate is obtained ; this is a compound 
 of water with Cr0 2 , which is left, on heating to 250 C. , as a black powder, which 
 evolves oxygen at 300 C., becoming Cr 2 3 . It may be regarded as chromic 
 cht'omate, Cr 2 3 .Cr0 3 . 
 
 Chro mous oxide (CrO) is not known in the pure state, but is precipitated as a brown 
 hydrate when chromous chloride is decomposed by potash. It absorbs oxygen 
 even more readily than ferrous oxide does, becoming converted into CrO.Cr 2 3 , 
 corresponding in composition with the magnetic oxide of iron. Chromous oxide 
 is a feeble base ; a double sulphate, K 2 Cr"(S0 4 ) 2 .6Aq, is known, isomorphous 
 with the corresponding iron salt, K 2 Fe"(S0 4 ) 2 .6Aq ; it has a blue colour, and gives 
 a blue solution, which becomes green when exposed to air. 
 
 Perchromlc acid. (H 2 Cr 2 8 ) is believed to exist as the blue solution obtained by 
 the action of H 2 2 upon solution of chromic acid, but neither the acid nor its 
 salts have been obtained in a separate state (p. 64). A sodium perchramnte, 
 Na 6 Cr 2 15 .28H 2 0, crystallises from a solution made by adding Na/) 2 to a thin 
 paste of Cr 2 (OH) 6 in water. Acids decompose it, the blue colour of perchromic 
 acid being first produced. 
 
 237. Chlorides of chromium. The chromic chloride (CrCl 3 ) obtained by passing 
 dry chlorine over a mixture of chromic oxide with charcoal, heated to redness 
 in a glass tube, is converted into vapour, and condenses upon the cooler part 
 of the tube in shining leaflets, having a fine violet colour. When heated in air, 
 it is decomposed, evolving 01, and leaving Cr 2 O 3 . Very soluble green crystals 
 of CrCl 3 .6Aq may be obtained, but the water cannot be expelled without decom- 
 posing the chloride. Cold water does not affect CrCl 3 , but boiling water slowly 
 dissolves it to a green solution resembling that obtained by dissolving Cr 2 3 in 
 HC1. If a little chromous chloride be added to water in which CrCl 3 is suspended, 
 the latter dissolves quickly and with evolution of heat, yielding the green solution, 
 which becomes violet after some time. Only two-thirds of the Cl is precipitated 
 from the green solution by AgN0 3 when this is first added. 
 
 Chromous chloride (CrCl 2 ) is obtained by heating CrCl 3 in hydrogen. It is white, 
 
 * Exposure to cold, it is said, again converts it into the crystallisable violet form. 
 
 2 E 
 
434 REVIEW OF THE IRON GROUP. 
 
 and dissolves in water to form a blue solution, which absorbs oxygen from the air, 
 becoming green. CrCl 2 is also formed when chromium is dissolved in HC1. A 
 solution of chromic chloride or sulphate, mixed with HC1, is reduced to chromous 
 chloride by metallic zinc, the liquid becoming greenish blue and giving a pink 
 precipitate of chromous acetate on addition of ammonium acetate, becoming 
 blue when shaken with air. Chromous chloride resembles ferrous chloride in 
 absorbing NO to form a brown compound. 
 
 Chromyl chloride, Cr0 2 Cl 2 ( = 2 vols.), or chromic oxychloride. formerly called 
 vhlorochromic acid, bears the same relation to Cr0 3 that sulphuryl chloride, S0 2 C1 2 , 
 bears to S0 3 . It is a brown-red liquid, obtained by distilling 10 parts of NaCl and 
 17 of K 2 Cr 2 0. 7 , previously fused together and broken into fragments, with 40 parts 
 of oil of vitriol 
 
 K 2 Cr 2 7 + 4NaCl + 3H 2 S0 4 = K 2 S0 4 + 2Na 2 S0 4 + 3H 2 + 2Cr0 2 Cl 2 . 
 It much resembles bromine in appearance, and fumes very strongly in air, the 
 moisture of which decomposes its red vapour, forming chromic and hydrochloric 
 acids ; Cr0 2 Cl 2 + 2H 2 = H 2 CrO 4 + 2HCl. Its sp. gr. is 1.92, and it boils at 118 C. 
 It is a very powerful oxidising and chlorinating agent, and inflames ammonia and 
 alcohol when brought in contact with them. 
 
 It is occasionally used to illustrate the nature of illuminating flames ; for if 
 hydrogen be passed through a bottle containing a few drops of it, the gas becomes 
 charged with its vapour, and, if kindled, burns with a brilliant white flame, which 
 deposits a beautiful green film of chromic oxide upon a cold surface. When heated, 
 in a sealed tube, to 190 C., it is converted into a black solid body, according to 
 the equation 3Cr0 2 Cl 2 = Cl 4 +CrCl 2 .2Cr0 3 . When K 2 Cr 2 7 is gently warmed with 
 HC1, the solution deposits red prisms of KClCr0 3 , formerly known as potassium 
 chlorochromate, which may be regarded as Cr0 2 Cl(OK), being derived from the at 
 present unknown Cr0 2 Cl(OH), corresponding with S0 2 C1(OH). 
 
 Cliromyl fluoride, Cr0 2 F 2 , is another volatile compound of chromium obtained 
 by distilling lead chromate with fluor spar and sulphuric acid ; it is a red gas, 
 condensible to a red liquid at a low temperature. Water decomposes it, yielding 
 chromic and hydrofluoric acids. Chromic fluoride, CrF 3 4H 2 0, is a green crystalline 
 powder used as a mordant. 
 
 Chromic sulphide (Cr 2 S 3 ) is formed when H 2 S is passed over chromic oxide heated 
 to redness. It forms black lustrous scales resembling graphite. 
 
 By fusing chromic hydroxide with sodium carbonate and sulphur, sodium thio- 
 chromite, Na 2 Cr 2 S 4 , is obtained as a dark red body insoluble in water, and not 
 easily attacked "by hydrochloric or sulphuric acid. Thiochromites of other 
 metals have also been obtained. 
 
 Chromium nitride, ON, has been obtained by heating chromium to redness in 
 nitrogen. 
 
 Chromium salts form a series of amines analogous to the cobalt- 
 amines (p. 423). 
 
 Chromium is nearly allied to iron by its property of forming 
 chromous and chromic salts, and to manganese through the chromates 
 which correspond and are isomorphous with the manganates, and rival 
 them in colour. Soluble chromium compounds are very poisonous. 
 
 238. Review of iron, cobalt, nickel, manganese, and chromium. 
 Many points of resemblance will have been noticed in the chemical 
 history of these metals. They are all capable of decomposing water at 
 a red heat, and easily displace hydrogen from hydrochloric acid. Each 
 of them forms a base by combining with one atom of oxygen, and these 
 oxides produce salts which have the same crystalline form. All these 
 oxides, except that of nickel, easily absorb oxygen from the air, and 
 are converted into sesquioxides. The sesquioxide of nickel is very 
 feebly basic, whilst that of cobalt is slightly more basic ; the sesquioxide 
 of manganese is a stronger base, and the basic properties of the sesqui- 
 oxides of chromium and iron are very decided. Nickel does not exhibit 
 any tendency to form a well-marked acid oxide, but the existence of an 
 acid oxide of cobalt is suspected ; and iron, manganese, and chromium 
 
MOLYBDENUM. 
 
 435 
 
 form undoubted acid oxides with three atoms of oxygen. Nickel is only 
 known to form one compound with chlorine ; cobalt and manganese 
 form, in addition to their protochlorides, very unstable perchlorides 
 known only in solution, but iron and chromium form very stable 
 volatile perchlorides. The metals composing this group are all divalent 
 in their protoxides and the corresponding salts, and are found associated 
 in natural minerals ; this is especially the case with iron, manganese, 
 cobalt, and nickel. They all require a very high temperature for their 
 fusion. Iron and chromium connect this group with aluminium, their 
 sesquioxides being isomorphous with alumina, and their perchlorides 
 volatile like aluminium chloride. In the periodic table (p. 302) Cr falls 
 in group vi., since its highest salt-forming oxide is Cr0 3 ; Mn forms salts 
 corresponding with Mn 2 7 (permanganates), and is therefore in group vii. 
 Fe, Co, and Ni are placed in group viii., although oxides of the type R0 4 
 have yet to be discovered. 
 
 MOLYBDENUM, Mo = 95. 3. 
 
 239. This metal derives its name from //,oAt}/35cuj>a, lead, on account of the 
 resemblance of its chief ore, molybdenite, to black lead. Molybdenite, or molyb- 
 denum glance, is the disulphide (MoS 2 ), and is found chiefly in Bohemia and 
 Sweden ; it may be recognised by its remarkable similarity to plumbago, and by 
 its giving a blue solution when boiled with strong sulphuric acid. It is chiefly 
 employed for the preparation of ammonium molybdate, which is used in testing for 
 phosphoric acid. For this purpose the disulphide is roasted in air at a dull red- 
 heat, when S0 2 is evolved, and molybdic anhydride (Mo0 3 ) mixed with oxide of 
 iron is left. The residue is digested with strong ammonia, which dissolves the 
 former as ammonium molybdate, obtainable in prismatic crystals (NH 4 HMo0 4 ) on 
 evaporation. When a solution of ammonium molybdate is added to a phosphate 
 dissolved in dilute nitric acid, a yellow precipitate of ammonium phosplio-molyb- 
 date * is produced, containing molybdic and phosphoric acids combined with 
 ammonia, by the formation of which very minute quantities of phosphoric acid can 
 be detected. If hydrochloric acid be added in small quantity to a strong solution 
 of molybdate of ammonium, the molybdic acid is precipitated, but it is dissolved by 
 an excess of hydrochloric acid, and if the solution be dialysed, the molybdic acid, 
 H 2 Mo0 4 , is obtained in the form of an aqueous solution which reddens blue litmus, 
 has an astringent taste, and leaves a soluble gum-like residue when evaporated. Be- 
 sides this simple acid, salts of many complex acids are known, recalling the poly- 
 silicates. Molybdic anhydride fuses at a red heat to a yellow glass, and may be 
 sublimed in a current of air in shining needles. In contact with dilute hydro- 
 chloric acid and metallic zinc, it is converted into a blue compound of the com- 
 position Mo0 2 .2Mo0 3 (molybdenum molybdate') which is soluble in water, but is 
 precipitated on adding a saline solution. Molybdate of lead (PbMo0 4 ) is found as a 
 yellow crystalline mineral ( Wulfenite). When Mo0 3 is heated in hydrogen it is 
 successively reduced to Mo0 2 arid Mo 2 O 3 and finally to metal. The molybdic oxide 
 (Mo0 2 ) is basic, and forms dark red-brown salts. Molybdous oxide (MoO) is ob- 
 tained by adding an alkali to the solution resulting from the prolonged action of 
 zinc upon a hydrochloric solution of molybdic acid. It is a black, basic oxide which 
 absorbs oxygen from the air. 
 
 Metallic molybdenum is obtained by heating a mixture of an excess of Mo0 3 with 
 charcoal in the electric furnace. The pure metal is like the best wrought iron. It 
 is of about the same colour and malleability, easily polished and capable of being 
 forged. Its sp. gr. is 9.01 and its melting-point very high. At 600 C. it oxidises 
 slowly in air and volatilises as Mo0 3 ; it is also attacked by halogens at this 
 temperature but not violently. It decomposes steam when hot and is oxidised by 
 hot strong H 2 S0 4 , by nitric acid and by fused alkalies from which it evolves H, 
 but it is not attacked by HC1. The resemblance to iron extends to its relation to 
 carbon, with which it maybe combined by cementation (p. 411) to form a metal of 
 .steely properties, hard enough to scratch glass, and capable of being tempered by 
 
 * Its composition varies with the conditions ; it is commonly 6NH 4 .P 2 O 8 .24MoO3. 
 
436 TUNGSTEN. 
 
 quenching from 300 C. With a larger proportion of carbon it forms a metal 
 capable of being cast and containing the carbide Mo 2 C ; the sp. gr. of such metal 
 is about 8.7. 
 
 When heated in chlorine Mo yields molybdenum pentachloride (MoCl 5 ), which 
 forms a red vapour, and condenses in crystals resembling iodine, soluble in water. 
 A subchloride (Mo 3 Cl 6 ), trichloride (MoCl 3 ), tetrachloride (MoCl 4 ), and several oxy- 
 chlorides are also known. The trisulphide (MoS 3 ) and tetrasulpMde (MoS 4 ) of 
 molybdenum are soluble in alkali sulphides. 
 
 In addition to the natural sources of molybdenum above mentioned, there may 
 be noticed molybdic ochre (an impure rnolybdic anhydride), and the difficultly 
 fusible masses called bear, from the copper works in Saxony, which contain a 
 large amount of molybdenum combined with iron, copper, cobalt, and nickel. 
 Molybdenum has been detected in the mud deposited by the Buxton thermal 
 water. 
 
 TUNGSTEN, W = 182.6. 
 
 240. Tungsten is chiefly found in the mineral wolfram, which occurs, often 
 associated with tin-stone, in large brown shining prismatic crystals, which are 
 even heavier than tin-stone (sp. gr. 7.3), from which circumstance the metal 
 derives its name, tungsten, in Swedish, meaning heavy stone. The symbol (W) 
 used for tungsten is derived from the Latin name wolfratiiium. Wolfram contains 
 the tungstates of iron and manganese in variable proportions, and may be regarded 
 as an isomorphous mixture of tungstates of iron and manganese (MnFe)W0 4r 
 Scheelite, tungstate of calcium (CaW0 4 ), and a tungstate of copper are also found. 
 
 Tungstate of sodium, Na 2 W0 4 .2H 2 O, is employed by calico-printers as a mordant, 
 and is sometimes applied to muslin, in order to render it uninflammable. It is ob- 
 tained by fusing wolfram with Na 2 C0 3 , an operation to which tin ores containing 
 this mineral in large quantity are sometimes submitted previously to smelting 
 them. Water extracts the sodium tungstate, which may be crystallised in 
 rhomboidal plates. When a solution of this salt is mixed with an excess of hydro- 
 chloric acid, white hydrated tungstic acid (H 2 W0 4 .Aq) is precipitated, while hot 
 solutions give a yellow precipitate of H 2 W0 4 ; but if dilute HC1 be carefully added 
 to a 5 per cent, solution of sodium tungstate in sufficient proportion to neutralise 
 the alkali, and the solution be then dialysed (p. 278), the sodium chloride passes 
 through, and a pure aqueous solution of tungstic acid is left in the dialyser. This 
 solution is unchanged by boiling, and when evaporated to dryness, vitreous scales,, 
 like gelatine, are left, which adhere very strongly to the dish, and redissolve in one- 
 fourth of their weight of water, forming a solution of the very high specific gravity 
 3.2, which is, therefore, able to float glass. The solution has a bitter and astringent- 
 taste, and decomposes Na^COg with effervescence. It becomes green when exposed 
 to air, from the de-oxidising action of organic dust. When tungstic acid is heated,. 
 it loses water, and becomes of a straw-yellow colour, and insoluble in acids. There 
 are at least two modifications of tungstic acid, which bear to each other a relation 
 similar to that between stannic and metastannic acids (q.v.). 
 
 Barium tungstate has been employed as a substitute for white lead in painting. 
 
 The most characteristic property of tungstic acid is that of yielding a blue oxide 
 (W0 2 .2W0 3 ), when placed in contact with HC1 and metallic zinc. 
 
 A very remarkable compound containing tungstic acid and soda is obtained when 
 sodium ditung state (Na2W 2 7 .4H 2 0) is fused with tin. If the fused mass be treated 
 with strong KOH, to remove free tungstic acid, washed with water, and treated 
 with HC1, yellow, lustrous, cubical crystals, probably iNa 2 O.W0 2 . 2 W0 3 , are obtained, 
 which are remarkable, among sodium compounds, for their resistance to the action 
 of water, of alkalies, and of all acids except HF. This salt is called gold- or saffron- 
 bronze. The corresponding potassium salt is violet- or magenta-bronze. 
 
 The tungstob orates are remarkable salts, containing W0 3 and B 2 3 , combined 
 with metallic oxides. Their solutions have a very high specific gravity ; that of 
 cadmium tungstoborate has the sp. gr. 3.6, and is used to effect the mechanical 
 separation of minerals of different specific gravities. Thus, a diamond (sp. gr. 3.5) 
 would float ; whilst a white sapphire (sp. gr. 4.0) would sink in the solution. 
 Tungstosilicates also exist. 
 
 Tungsten trioxide, W0 3 , is obtained by decomposing metallic tungstates with 
 nitric acid, and heating the tungstic acid thus precipitated. It is a canary yellow 
 powder, becoming orange when heated and yellow again on cooling. 
 
 The tungsten dioxide (W0 2 ) appears to be an indifferent oxide, and is obtained 
 
URANIUM. 437 
 
 by reducing tungstic anhydride with hydrogen at a low red heat, when it forms 
 a brown powder, which is dissolved by boiling in solution of potash, hydrogen 
 being evolved, and potassium tungstate formed. 
 
 Metallic tungsten is obtained by reducing tungstic anhydride with charcoal (or 
 hydrogen) at a white heat. It may also be obtained by igniting a mixture of 
 W0 3 and aluminium powder, but in order to obtain the necessarily high tempera- 
 ture the mixture must be moistened with about of its volume of liquid air. It 
 is an iron-grey infusible metal of sp. gr. 18.7, very hard, very infusible, not affected 
 by hydrochloric or diluted sulphuric acid, but converted into tungstic acid by the 
 action of nitric acid. Tungsten dissolved in about 20 times its weight of fused 
 steel increases the hardness of the steel without diminishing its tenacity. 
 
 When tungsten is heated in chlorine, the tungstic chloride (WC1 2 ) sublimes in 
 bronze-coloured needles. When gently heated in hydrogen, it is converted into 
 the tetrachloride (WC1 4 ), but if its vapour be mixed with hydrogen and passed 
 through a glass tube heated to redness, metallic tungsten is obtained in a form 
 in which it is not dissolved even by aqua regia, though it may be converted into 
 potassium tungstate by potassium hypochlorite mixed with potash in excess. 
 WC1 6 is also obtained in steel-blue needles, together with WOC1 4 and W0 2 C1 2 by 
 the action of PC1 5 on W0 3 . 
 
 Tungsten disulphide (WS 2 ) is a black crystalline substance resembling plum- 
 bago, obtained by heating a mixture of potassium ditungstate with sulphur, and 
 washing with hot water. Tungsten tri sulphide (WS 3 ) is a sulphur-acid, obtainable 
 as a brown precipitate by dissolving tungstic acid in an alkaline sulphide, and 
 precipitating by an acid. 
 
 Both Mo0 3 and W0 3 form a number of complex salts with the alkali oxides and 
 the pentoxides of As, P, and V. These are the tungsto- and molybdo- arsenates, 
 phosphates, and vanadates. 
 
 URANIUM, U = 237.y. 
 
 241. This metal occurs in the pitchblende (U0. 2 .2U0 3 ) of Cornwall, It is not 
 used in the metallic state, but in the form of the black oxide, U0 2 .U0 3 , and of 
 will nin uranate, Na2U 2 7 .6H 2 (uranium yellow), for imparting black and yellow 
 colours respectively to glass" and porcelain.* The latter compound is prepared 
 from pitchblende by roasting the mineral with lime, decomposing the calcium 
 uranate thus formed with sulphuric acid, and treating the solution of uranyl 
 sulphate with sodium carbonate. This precipitates the foreign metals and the 
 Na. 2 U 2 7 , which redissolves in the excess of sodium carbonate, and is precipitated 
 by neutralisation with sulphuric acid and boiling. 
 
 Uranium forms two oxides, U0 2 , a basic oxide known as uranyl, and U0 3 , an acid 
 oxide. Pitchblende (the green oxide) and the black oxide may be regarded as 
 uranyl diuranate and uranyl uranate respectively. Of the uranyl (also called 
 uranic) salts, the nitrate, UO 2 (N0 3 ) 2 .6H 2 0, and acetate, U0 2 Ac 2 .2H 2 0, are used as 
 laboratory reagents, and in photographic printing, for which they are fitted by 
 the fact that they are reduced by light in contact with organic matter to uranous 
 salts, corresponding with the base, UO. These latter salts have been but little 
 studied, but they give a brown precipitate with potassium ferricyanide, by which 
 means the photographic print may be developed. Some organic salts of uranyl 
 are decomposed by light without reduction ; thus the oxalate in water evolves 
 CO and C0 2 , leaving a precipitate of uranylhydroxide, U0 2 (OH) 2 . 
 
 Sodium perura-nate, Na 4 U0 8 .ioH 2 0, is obtained by the addition of sodium per- 
 oxide to a solution of a uranyl salt. Uranium tetrachloride, UC1 4 (which is volatile, 
 so that its vapour density is known), and uranyl chloride, U0 2 C1 2 , have been pre- 
 pared. UC1 3 and UC1 5 are also known. 
 
 Metallic iirn /iium is prepared by reducing UC1 4 with sodium. It is white and 
 malleable ; sp. gr. 18.7 ; dissolves in acids evolving hydrogen. When reduced 
 from the oxide by carbon it contains 5-13 per cent, of C, is very hard, melts at a 
 temperature higher than the melting-point of platinum, and decomposes water at 
 the ordinary temperature. 
 
 There must here be noticed a curious phenomenon first observed in uranium 
 salts, namely, the power possessed by certain substances of emitting radiations 
 which produce the same effect as that of light on a photographic plate and also so 
 influence the air that its conductivity for electricity is increased. Thus if a crystal 
 
 * " Urauiuui glass " exhibits a strong- greenish-yellow fluorescence. 
 
43$ REVIEW OF THE CHROMIUM GROUP. 
 
 of an ordinary uranium salt be placed on a material opaque to light, such as black 
 paper, or to electricity such as glass or aluminium, and the material be laid upon 
 a photographic plate, the position and shape of the crystal will be faithfully 
 recorded as an invisible image capable of development, in the course of a short 
 time varying with the degree of activity. Again, if the crystal be held at a short 
 distance from a charged electroscope this will lose its charge more quickly than it 
 would normally. 
 
 It has been shown that uranium nitrate recrystallised from ether is free from 
 this property, indicating that the activity is due to some other substance. 
 
 Certain specimens of pitchblende containing bismuth are particularly active, and 
 when the bismuth is extracted the activity is found to have accompanied it, but 
 the radiations differ from those of uranium salts in that they are not deviated by 
 an electro-magnet. It has been supposed that such bismuth contains an element, 
 polonium, which is the source of the activity. A second supposed element, radium, 
 having great " radio-activity " and closely resembling barium in character, has 
 been detected in pitchblende. The rays from the compounds of this substance 
 colour glass, ozonise oxygen and convert yellow phosphorus into red. besides 
 having the properties already cited for such radiations. The effect of radium 
 radiation on the skin is remarkable, creating painful sores which are slow to heal. 
 This effect has been shown to occur even through the clothing and when the absolute 
 quantity of radium is very small. 
 
 Thorium compounds also possess radio-activity, and it has been shown that both 
 in this case and that of radium part of the radiation is an emanation of material 
 particles which may be deposited on other substances, especially if they be 
 negatively electrified, rendering them also radio-active temporarily. ' A negatively 
 electrified platinum wire becomes radio-active when it has been exposed to the air 
 for some time. At present these phenomena must be regarded as inexplicable, and 
 the existence of new elements cannot be safely deduced from the observation of 
 such properties. 
 
 Review of the chromium family of metals. The members of this 
 family, chromium, molybdenum, tungsten, and uranium, exhibit great 
 similarity in their tendency to form acid oxides of the type R0 3 , and 
 oxychlorides of the type R0 2 CJ 2 . They also enter into the composition 
 of many complex salts analogous to the phospho-molybdates and the 
 boro-tungstates. Sulphur, selenium, and tellurium belong to the same 
 group, and form oxyacids of the same type. 
 
 BISMUTH. 
 
 Bi'" = 206.9 parts by weight. 
 
 242. Bismuth, though useful in various forms of combination, is too 
 brittle to be employed in the pure metallic state. It is readily distin- 
 guished from other metals by its peculiar reddish lustre and its highly 
 crystalline structure, which is very perceptible upon a freshly broken 
 surface ; large crystals (apparently cubes) of bismuth are easily obtained 
 by melting a few ounces in a crucible, allowing it to cool till a crust 
 has formed upon the surface, and pouring out the portion which has 
 not yet solidified, when the crystals are found lining the interior of the 
 crucible. It is isomorphous with antimony. It is somewhat lighter 
 than lead (sp. gr. 9.8), and volatilises more readily at high tempera- 
 tures. It is less volatile than antimony, and burns like it in air. 
 
 Unlike most other metals, bismuth is found chiefly in the metallic 
 state, disseminated in veins, through gneiss and clay-slate. The chief 
 supply is derived from the mines of Schneeberg, in Saxony, where it is 
 associated with the ores of cobalt. Native bismuth, together with the 
 oxides and sulphides, is found abundantly in Bolivia and Australia, 
 accompanied by tin-stone and sometimes by silver and gold. 
 
EXTRACTION OF BISMUTH. 439 
 
 In order to extract the metal from the masses of earthy matter 
 through which it is distributed, advantage is taken of its very low 
 fusing-point (268 C.). The ore is broken into small pieces, and in- 
 troduced into iron cylinders which are fixed in an inclined position over 
 a furnace (Fig. 226). The upper opening of the cylinders, through which 
 the ore is introduced, is 
 provided with an iron door, 
 and the lower opening is 
 closed with a plate of fire- 
 brick perforated for the 
 escape of the metal, which 
 flows out, when the cylin- 
 ders are heated, into iron 
 receiving pots, which are 
 kept hot by a charcoal fire. 
 
 Commercial bismuth 
 generally contains arsenic, 
 
 copper, Sulphur, and Sll- Fig. 226. Extraction of bismuth. 
 
 ver ; it is sometimes 
 
 cupelled in the same manner as lead, in order to extract the silver, the 
 oxide of bismuth being afterwards again reduced to the metallic state 
 by heating it with charcoal. Pure bismuth dissolves entirely and 
 easily in diluted nitric acid (sp. gr. 1.2); but if it contains arsenic, a 
 white deposit of bismuth arsenate is obtained. Hydrochloric and 
 diluted sulphuric acids will not attack bismuth. 
 
 The chief use of bismuth is in the preparation of certain alloys with 
 other metals. Some kinds of type metal and stereotype metal contain 
 bismuth, which confers upon them the property of expanding in the 
 mould during solidification, so that they are forced into the finest lines 
 of the impression. 
 
 This metal is also remarkable for its tendency to lower the fusing- 
 point of alloys, which cannot be accounted for merely by referring to 
 the low fusing-point of the metal itself. Thus, an alloy of 2 parts bis- 
 muth, i part lead, and i part tin, fuses below the temperature of boiling 
 water, although the most fusible of the three metals, tin, requires a 
 temperature of 227 C. An alloy of this kind is used for soldering 
 pewter. Wood's fusible alloy consists of 4 of Bi, 2 of Pb, i of Sn, and 
 i of Cd ; it melts at 60.5 C. Bismuth is also employed, together with 
 antimony, in the construction of thermo-electric piles. 
 
 243. Oxides of bismuth. There are four oxides, BiO, Bi 2 3 , Bi 2 O 4 , 
 and Bi 2 5 . 
 
 Bismuth mboxlde, BiO, is a black powder obtained by heating bismuth oxalate 
 in C0 2 . When bismuthic chloride mixed with stannous chloride is added to an 
 excess of potash, a black precipitate is obtained, alleged by some to be the suboxide, 
 by others metallic bismuth. 
 
 Bismuthous oxide, Bi 2 3 , is the basic and most important oxide. It 
 is formed when bismuth is heated in air, or when bismuth nitrate is 
 decomposed by heat, and is a yellow powder becoming brown when 
 heated, and fuses easily. Bismuthous oxide forms the rare mineral 
 bismuth-ochre. This oxide of bismuth is obtained in tine needles by 
 precipitating a boiling solution of a bismuth salt with potash. 
 
440 SALTS OF BISMUTH. 
 
 Bismuthic anhydride, Bi 2 5 , is formed when Bi 2 3 is suspended in a strong 
 solution of potash through which chlorine is passed, when a brown substance is 
 formed which, when treated with warm strong HN0 3 , yields bismuthic acid 
 (HBi0 3 ) as a red powder, which becomes brown at 120 C.. losing H 2 and 
 becoming Bi 2 5 . When further heated, it loses and becomes Bi 2 4 or 
 Bi 2 O 3 .Bi 5 . When heated with acids it also evolves O, and forms salts of 
 Bi 2 3 . 
 
 Bismuth hydroxide, Bi(OH) 3 , is obtained as a white precipitate when a caustic 
 alkali is added to a bismuth salt ; it does not dissolve in excess of alkali. Acted 
 on by chlorine in the alkaline liquid, it becomes dark brown HBi0 3 . 
 
 Bismuthic acid, HBi0 3 , the analogue of HN0 3 , is formed when basic bismuth 
 nitrate is fused with potash, in contact with air, until it has become dark brown. 
 On dissolving in dilute nitric acid, HBi0 3 is left as a red powder. The bismuthates 
 of the alkali metals are very unstable, being decomposed by water. Pyrolismuthic 
 acid, H 4 Bi 2 7 , is said to have been obtained. 
 
 244. The only two salts of bismuth which are known in the arts are 
 the basic nitrate (trisnitrate of bismuth, or flake-white) and the oxy- 
 chloride of bismuth (pearl-white). The preparation of these com- 
 pounds illustrates one of the characteristic properties of the salts of 
 bismuth, viz., the facility with which they are decomposed by water 
 with the production of insoluble basic salts. 
 
 If bismuth be dissolved in nitric acid, it becomes bismuth nitrate, 
 Bi(NO 3 ) 3 , and this may be obtained in prismatic crystals containing 
 5Aq. If the solution be mixed with a large quantity of water, it de- 
 posits a precipitate of flake-white, Bi(NO 3 ) 3 . 2 Bi(OH) 3 , or Bi(OH) 2 N0 3 , 
 the remainder of the nitric acid being left in the solution 
 
 Bi(N0 3 ) 3 + 2H 2 = Bi(OH) 2 N0 3 + 2 HN0 3 . 
 
 The basic nitrate, when long washed, becomes Bi(OH) 3 . It is a crystal- 
 line powder, which is acid to moist test-paper. It is used as a paint 
 and cosmetic, and in enamelling porcelain. 
 
 Pearl-white has the composition 6BiOCl.Aq, and is obtained by dis- 
 solving bismuth in nitric acid, and pouring the solution into water in 
 which common salt has been dissolved. 
 
 Bismuthite, which is, next to native bismuth, the most important of the bismuth 
 ores, is composed of 3Bi 2 3 .C0 2 .H 2 0. 
 
 Bismuthic chloride, BiCl 3 ( = 2 vols.), may be distilled over when bismuth is 
 heated in a current of dry chlorine ; it is a deliquescent, fusible, volatile, crystalline 
 solid, easily dissolved by a small quantity of water, but decomposed by much water, 
 with formation of the above-mentioned o,rychloride of bismuth; BiCl 3 + H 2 0=: 
 BiOCl + 2HCl. This compound is so insoluble in water that nearly every trace of 
 bismuth may be precipitated from a moderately acid solution of the trichloride by 
 adding much water. 
 
 Bismuth tri-iodide, BiI 3 . is obtained as a dark brown precipitate when potassium 
 iodide is added to a solution of a bismuthic salt. If the solution be dilute or very 
 acid, a red or yellow colour is produced, without precipitation, and if a solution of 
 a lead salt be added to this, a brown or red precipitate of a double iodide of bismuth 
 and lead is produced, which dissolves in hot dilute HC1, and separates in minute 
 crystals, like bronze powder, on cooling. 
 
 Sismuthous sulphide (Bi 2 S 2 ) is sometimes found in nature, but more frequently 
 bi-smuthic sulphide (Bi 2 S 3 ) or bismuth glance, which occurs in dark grey lustrous 
 prisms isomorphous with native sulphide of antimony. Bi 2 S 3 is also obtained as a 
 brown precipitate by the action of hydrosulphuric acid upon bismuthic salts. Bis- 
 muthic sulphide is not soluble in diluted sulphuric or hydrochloric acid, but dis- 
 solves easily in nitric acid. Bolirite is an oxysulphide, Bi 2 S 3 .Bi 2 3 . 
 
METALLURGY OF ANTIMONY. 441 
 
 ANTIMONY. 
 
 Sb"' = 119 parts by weight. 
 
 245. Antimony is nearly allied to bismuth in its physical and 
 chemical characters. It is even harder and more brittle than that 
 metal, being easily reduced to powder. Its highly crystalline structure 
 is another very well-marked feature, and is at once perceived upon the 
 surface of an ingot of antimony, where it is exhibited in beautiful fern- 
 like markings (star antimony). Its crystals belong to the same system 
 (the rhombohedral) as those of bismuth and arsenic. It is much lighter 
 than bismuth (sp. gr. 6.715), and requires a higher temperature (630 C.) 
 to fuse it, though it is more easily converted into vapour, so that, when 
 strongly heated in air, it emits a thick white smoke, the vapour being 
 oxidised. Like bismuth, it is but little affected by hydrochloric or 
 dilute sulphuric acid, but nitric acid oxidises it, though it dissolves very 
 little of the metal, the greater part being left in the form of antimonic 
 acid. The best method of dissolving antimony is to boil it with hydro- 
 chloric acid and to add nitric acid, or some other oxidising agent, by 
 degrees. The metal decomposes steam at a red heat. 
 
 Antimony is chiefly found in nature as grey antimony ore, stibnite, 
 which is a sulphide of antimony (Sb 2 S 3 ), occurring in Cornwall, but 
 much more abundantly in Hungary, in veins associated with galena, 
 iron pyrites, quartz, and heavy spar. To purify it from these, advan- 
 tage is taken of its fusibility, the ore being heated upon the hearth of 
 a reverberatory furnace, with some charcoal to prevent oxidation, when 
 the sulphide of antimony melts and collects below the impurities, whence 
 it is run off and cast into moulds. The product is known in commerce 
 as crude antimony, and contains sulphides of arsenic, iron, and lead. 
 
 To obtain regulus of antimony, or metallic antimony, the sulphide is 
 fused in contact with refuse iron (such as tin-plate clippings), when 
 sulphide of iron is formed, and collects as a fused slag upon the surface 
 of the melted antimony ; Sb 2 S 3 + Fe 3 = 3FeS + Sb 2 . The antimony always 
 contains a considerable proportion of iron. 
 
 To refine it the metal is melted again with sufficient Sb 2 S 3 to convert the iron 
 into sulphide. To eliminate sulphur and obtain star antimony, the product must 
 be fused with an alkali sulphide which dissolves the Sb 2 S 3 , producing a slag con- 
 sisting mainly of 3Na 2 S.Sb 2 S 3 , and called crocus vf antimony. 
 
 In some places the antimony ore is roasted to convert the bulk of it into oxide, 
 which is then heated with fresh ore, in order that the mixture may undergo " self- 
 reduction" ; 2Sb 2 S 3 + 3Sb 2 4 = Sb 10 + 6S0 2 . 
 
 Antimony is now obtained by leaching the ore with a solution of sodium sul- 
 phide, whereby the Sb 2 S 3 is dissolved. The solution is then electrolysed, Sb being 
 deposited on the cathode, leaving a solution of sodium sulphide to be used for 
 leaching more ore. 
 
 On the small scale, antimony may be extracted from the sulphide by fusing it in 
 an earthen crucible with 4 parts of commercial potassium cyanide, at a moderate 
 heat ; or by mixing 4 parts of the sulphide with 3 of bitartrate of potash and i^ of 
 nitre, and throwing the mixture, by small portions, into a red-hot crucible, when 
 the sulphur is oxidised, and converted into potassium sulphate, by the nitre, which 
 is not present in sufficient quantity to oxidise the antimony, so that the metal 
 collects at the bottom of the crucible. 
 
 When tartar-emetic is strongly heated in a closed crucible, an alloy of antimony 
 and potassium is obtained which decomposes water rapidly, and becomes hot when 
 exposed to air. 
 
 The brittleness of antimony renders it useless in the metallic state, 
 
44 2 ANTIMONY OXIDES. 
 
 except for the construction of thermo-electric piles, where it is in con- 
 junction with bismuth. Antimony is employed, however, to harden 
 several useful alloys, such as type-metal, shrapnel-shell bullets, Britannia 
 metal, and pewter. 
 
 Amorphous antimony. The ordinary crystalline form of antimony may be ob- 
 tained, like copper and other metals, by electrolysing a solution containing about 7 
 per cent, of antimonious chloride ; but in some cases the antimony is deposited from 
 very strong solutions in an amorphous condition, having properties very different from 
 those of ordinary antimony. One part of tartar-emetic is dissolved in 4 parts of a 
 strong solution of antimony trichloride and the solution is slowly electrolysed. The 
 deposit of antimony which forms upon the cathode has a brilliant metallic appear- 
 ance, but is amorphous, and not crystalline, like the ordinary metal. Its specific 
 gravity is 5.78. If it be gently heated, scratched or sharply struck, its temperature 
 rises suddenly to about 200 C., and it becomes converted into a form more nearly 
 resembling crystalline antimony. At the same time, however, thick fumes of 
 antimony trichloride are evolved, for this substance is always present in the amor- 
 phous antimony to the amount of 5 or 6 per cent. ; * so that, as yet, there is not 
 sufficient evidence to establish beyond a doubt the existence of a pure amorphous 
 form of antimony corresponding with amorphous phosphorus, however probable 
 this may appear from the chemical resemblance between these elements. 
 
 246. Oxides of antimony, Sb 4 O 6 ,t Sb 2 O 4 , Sb 2 5 . Antimonious oxide, 
 Sb 4 6 , is formed when antimony burns in air (flowers of antimony), and 
 is prepared on a large scale by roasting either the metal or the sulphide 
 in air, for use in painting as a substitute for white lead. It is also 
 found in nature as white antimony ore, or valentinite. Antimonious 
 oxide forms a crystalline powder (sp. gr. 5.56), usually composed of 
 minute prisms having the shape of the rarer form of arsenious oxide 
 (page 268), whilst occasionally it is obtained in crystals similar to those 
 of the common octahedral arsenious oxide, with which, therefore, anti- 
 monious oxide is isodimorphous. The octahedral form appears to be 
 produced only when the prismatic form is slowly sublimed in a non- 
 oxidising atmosphere. The mineral exitele is prismatic oxide of anti- 
 mony, and senarmontite is the octahedral form of that oxide. When 
 heated in air the oxide assumes a yellow colour, afterwards takes fire, 
 smoulders, and becomes converted into the antimonious antimonate 
 (Sb 2 O 3 .Sb 2 5 = 2Sb 2 4 ), which was formerly regarded as an independent 
 oxide. Sb 4 6 may be obtained by oxidising antimony with very weak 
 nitric acid, or better, by dissolving antimony sulphide in strong HC1, 
 boiling off all H 2 S, diluting largely with water, washing the precipitated 
 oxy chloride by decantation till it is no longer acid, and boiling it; with a 
 strong solution of sodium carbonate; 4SbOCl + 2Na 2 C0 3 = Sb 4 O 6 -f 
 4NaCl + 2C0 2 . The oxide is insoluble in water, but acids dissolve it, 
 forming salts, though its basic properties are feeble, and its salts rather 
 ill-defined. A hot solution of hydropotassium tartrate, HKC 4 H 4 6 , 
 dissolves it, forming tartar-emetic, SbO.KC 4 H 4 6 . Potash and soda are 
 also capable of dissolving it, whence it is sometimes called antimonious 
 anhydride, corresponding with nitrous anhydride. Two crystallised 
 antimonites of sodium have been obtained, the neutral antimonite 
 NaSb0 2 .6Aq, and the triantimonite NaSbO 2 .Sb 2 3 .Aq ; the former is 
 sparingly soluble, the latter almost insoluble in water. 
 
 * It has been plausibly suggested that the sudden rise of temperature may be due to the 
 presence of an endothermic antimony compound analogous to the so-called chloride of nitro- 
 gen, the latter element being connected with antimony by several chemical analogies. 
 
 f The vapour density of this oxide shows that its formula cannot be .Sb 2 O 3 , as formerly 
 supposed. 
 
ANTIMONATES. 443 
 
 Antimony tetroxide, Sb 2 4 , is important because it is the product of 
 the action of heat upon either of the other oxides in contact with air, 
 so that antimony is often weighed in this form in quantitative analysis. 
 It is readily obtained by boiling antimony with nitric acid, evaporating 
 to dryness, and heating the residue to redness. It is yellow while hot, 
 and becomes white on cooling. 
 
 Antimony ash, obtained by roasting the grey sulphide in air, consists 
 chiefly of Sb 2 4 , and is used for preparing other antimony compounds. 
 
 Thus, tartar-emetic may be obtained by boiling Bb.,0 4 with hydro- 
 potassium tartrate; Sb 2 O 4 + HKC 4 H 4 6 = SbO.KC 4 H 4 6 (tartar-emetic) 
 + HSb0 3 (antimonic acid). This leads to the belief that Sb 2 4 is really 
 antimonyl antimonate, SbO.SbO 3 , in which case this formation of tartar- 
 emetic would merely consist in the exchange of SbO for H. 
 
 The presence of Sb 2 4 in Sb 4 O 6 can be detected by dissolving in HC1 
 and adding KI, when iodine will be liberated 
 Sb 2 4 + 2KI + 8HC1 = 2SbCl 3 
 
 Antimonic oxide, Sb 2 O 5 , is formed when antimony is oxidised by nitric 
 acid, and the product well washed and dried at 280 C. It is a yellow 
 powder (sp. gr. 6.5). It will be remembered that As 2 O 5 may be obtained 
 in a similar way, but not P 2 3 . Sb 2 5 is a pale yellow amorphous 
 powder, insoluble in water, and decomposed at 300 C., leaving Sb 2 O 4 . 
 It is dissolved by potash, forming the antimonate, KSbO 3 . 
 
 Antimoniwts acid* HSb0 2 , corresponding with nitrous acid, is said to have been 
 obtained as 2HSb0 2 .3Aq, in the form of a white precipitate, by decomposing 
 sodium antinionite with nitric acid. 
 
 Antimonic acid, HSb0 3 , corresponding with nitric acid, is precipitated as 
 HSb0 3 .2Aq by adding nitric acid to solution of potassium antimonate. It is a 
 white powder, slightly soluble in water, and easily so in potash. 
 
 Potassium antimonate, KSb0 3 , is made by gradually adding I part of powdered 
 antimony to 4 parts of nitre fused in a clay crucible. The mass is powdered and 
 washed with warm water to remove the excess of nitre and the potassium nitrite, 
 when the anhydrous potassium antimonate is left ; and on boiling this for an 
 hour or two with water, it becomes hydrated, and dissolves. The solution, when 
 evaporated, leaves a gummy mass of potassium antimonate, having the composition 
 2KSb0 3 -5Aq. This dissolves in warm water, and is decomposed by boiling for 
 some time, yielding an acid antimonate, K 4 H 2 (Sb0 3 ) 6 .9Aq. 
 
 Sodium antimonate, 2NaSb0 3 .yAq, is prepared like the potassium salt. 
 
 Ammonium antimonate, NH 4 SbO 3 , is obtained as a crystalline powder, insoluble 
 in water, by dissolving HSb0 3 in warm ammonia. 
 
 A basic lead antimonate is used in oil-painting as Naples yellow. 
 
 Metantimonic acid, H 4 Sb 2 O 7 , should really be called pyro-antimonic acid, since 
 it corresponds with pyrophosphoric acid, H 4 P 2 7 . It is obtained as a white precipi- 
 tate by decomposing antimonic chloride with water ; 2SbCl 5 + 7H 2 = H 4 Sb 2 7 + 
 loHCl. It is rather more soluble in water than is antimonic acid, and dissolves in 
 cold ammonia. When heated to 200 C., it is converted into antimonic acid ; 
 H 4 Sb 2 O 7 = 2HSb0 3 + H 2 0. This resembles the conversion of pyrophosphoric into 
 metaphosphoric acid by the action of the heat. It is said that orthantimonic acid, 
 H 3 Sb0 4 , has been isolated. 
 
 Potassium, met ant intonate. K 4 Sb 2 7 , is made by fusing the antimonate with 
 potash, in a silver crucible ; 2KSb0 3 + 2KOH = K 4 Sb 2 O 7 + H 2 0. On dissolving in 
 water and evaporating, crystals of the metantimonate are obtained, but water 
 decomposes these into potash and potassium dimetantimonate, K 2 H 2 Sb 2 7 , which 
 forms a crystalline powder containing 6Aq. It is sparingly soluble in cold water, 
 but dissolves in warm water. The solution forms a valuable test for sodium, 
 which it precipitates in the form of Na2H 2 Sb 2 7 .6Aq. When long kept, the solu- 
 tion of potassium dimetantimonate becomes converted into antimonate, which 
 
 * Strictly metantimonious acid ; orthantimonfous acid, Sb(OH) 3 , lias not been prepared. 
 
444 TESTING FOR ANTIMONY. 
 
 does not precipitate sodium ; K 2 Sb 2 O l7 + H 2 = 2KSbO 3 + 2KOH. Acids precipitate 
 metantiinonic acid, which dissolves in HC1. Nearly all metallic solutions yield 
 precipitates with the potassium dimetantimonate, so that all other metals must 
 be removed from the solution before testing for sodium. 
 
 247. Antimonetted hydrogen, or hydrogen antimonide, SbH 3 , is not 
 known in the pure state, but is obtained, mixed with H, when an alloy 
 of antimony with zinc is attacked by dilute sulphuric acid, or when a 
 solution of an antimony salt (tartar-emetic, for example) is poured into 
 a hydrogen apparatus containing zinc and dilute sulphuric acid (see 
 page 272). Its production forms the most delicate test for antimony, 
 as in the parallel case of arsenic, but the one cannot be mistaken for 
 the other, if the following differences be observed. The SbH 3 burns to 
 Sb 4 6 and H 2 O with a greenish flame, which deposits a soot-black spot 
 upon a porcelain crucible lid (Fig. 192). This spot dissolves when a 
 drop of yellow ammonium sulphide is placed on it with a glass rod, and 
 on evaporation gives an orange film of Sb 2 S 3 . When the tube through 
 which the gas passes is heated to 150 C. (Fig. 193), metallic antimony 
 is deposited at the heated part, and not beyond it, like arsenic. When 
 the gas is passed into silver nitrate, the antimony is precipitated as 
 black silver antimonide; SbH 3 + 3AgN0 3 = SbAg 3 + 3HN0 3 (whereas 
 arsenic passes into solution as arsenious acid, and gives a black precipi- 
 tate of metallic silver). 
 
 Sulphur decomposes SbH 3 in sunlight or at 100 C., but not in the dark ; 
 2SbH 3 + 3S 2 = Sb. 2 S 3 + 3H 2 S. The reactions with silver nitrate and with sulphur 
 prove the composition of the gas to be SbH 3 , so that it is analogous to AsH 3 , PH 3 , 
 and NH 3 . 
 
 If the hydrogen antimonide be prepared by the action of dilute sulphuric acid 
 upon an alloy of 2 parts of antimony with 3 parts of zinc, and the first portions 
 collected separately and cooled to 91 C., it solidifies, but on raising the tem- 
 perature to about 60 it is decomposed, antimony being deposited. This 
 explains why so little of the compound is obtained in the gas made under ordinary 
 conditions. 
 
 248. Chlorides of antimony. Chlorine and antimony combine 
 readily with evolution of heat and light ; the chlorides are among the 
 most important compounds of this metal. 
 
 Trichloride of antimony, or antimonious chloride, SbCl 3 , may be pre- 
 pared by dissolving powdered antimony sulphide (100 grams) in com- 
 mercial hydrochloric acid (500 c.c.), adding gradually potassium chlorate 
 (4 grams), filtering from sulphur and distilling. HC1 distils first, then 
 a solution of SbCl 3 and finally SbCl 3 itself, which forms white crystals in 
 the receiver. The trichloride is a soft crystalline solid, whence its old 
 name of butter of antimony. It fuses at 73 C. and boils at 223 C. It 
 may be dissolved in a small quantity of water, but a large quantity 
 decomposes it, forming a bulky white precipitate, which is an oxy chloride 
 of antimony; SbCl 3 + H 2 = 2HC1 + SbOCl ; this is a decomposition 
 similar to that which occurs with PC1 3 , AsCl 3 , and BiCl 3 . By long 
 washing, 4SbOCl + 2H 2 = 4HC1 + Sb 4 O 6 . When hot water is added to 
 a hot solution of trichloride of antimony in hydrochloric acid, minute 
 prismatic needles are deposited, containing Sb 4 Cl 2 O 5 , and formerly called 
 powder of Algaroth. The same body is formed when SbOCl is heated; 
 5SbOCl = SbCl 3 + Sb 4 Cl 2 5 . Trichloride of antimony is occasionally used 
 in surgery as a caustic ; it also serves as a bronze for gun-barrels, upon 
 which it deposits a film of antimony. 
 
ANTIMONY SULPHIDES, 445 
 
 Pentachloride of antimony, or antimonic chloride (SbCl 5 ), is prepared 
 by heating coarsely powdered antimony in a retort, through which a 
 stream of dry chlorine is passed (Fig. 182), the neck of the retort being 
 fitted into an adapter, which serves to condense the pentachloride. One 
 ounce of antimony will require the chlorine from about 6 oz. of common 
 manganese and 18 oz. (measured) of hydrochloric acid. The pure 
 pentachloride is a colourless fuming liquid of a very suffocating odour ; 
 it combines energetically with a small quantity of water, forming a 
 crystalline hydrate, SbCl 5 .4Aq, but an excess of water decomposes it 
 into hydrochloric and metantimonic acids, the latter forming a white 
 precipitate ; 2 SbCl 5 + 7H 2 O = loHCl + H 4 Sb 2 7 . 
 
 If it be dropped into water kept cool by ice, it yields antimony oxytrichloride as a 
 deliquescent crystalline body; SbCl 5 + H 2 = SbOCl 3 + 2HCl. Pentachloride of 
 antimony is employed by the chemist as a chlorinating agent ; thus, olefiant gas 
 (C 2 H 4 ), when passed through it, is converted into Dutch liquid (C 2 H 4 C1 2 ), and 
 carbonic oxide into phosgene gas, the pentachloride of antimony being converted 
 into trichloride. ^SbClg is partially dissociated into SbCl 3 and C1 2 at 140 C. and 
 completely at 200 C., and can only be distilled in chlorine. 
 
 The pentachloride of antimony is the analogue of pentachloride of phosphorus, 
 and a chlorosulpliide of antimony (SbCl 3 S), corresponding with chlorosulphide of 
 phosphorus, is obtained as a white crystalline solid by the action of hydrosulphuric 
 acid upon pentachloride of antimony. 
 
 249. Sulphides of antimony. Antimonious sulphide, or sesquisul- 
 of antimony (Sb 2 S 3 ), has been noticed as the chief ore of antimony. 
 It is abundant in Borneo. It is a heavy mineral (sp. gr. 4.63), of a dark 
 grey colour and metallic lustre, occurring in masses which are made up 
 of long prismatic needles. It fuses easily, and may be sublimed un- 
 changed out of contact with air. When melted and suddenly cooled 
 it forms a dark brown amorphous mass of sp. gr. 4.15, which is not a 
 conductor of electricity, whereas the grey form conducts. It is easily 
 recognised by heating it, in powder, with hydrochloric acid, when it 
 evolves the odour of hydrosulphuric acid, and if the solution be poured 
 into water, it deposits an orange precipitate (page 214). This orange 
 sulphide, which is a compound of Sb 2 S 3 with water, is also obtained by 
 adding hydrosulphuric acid to a solution of a salt of antimony (for 
 example, tartar-emetic) acidified with HC1. It may be converted into 
 the grey sulphide at 210 C., and becomes black when boiled with HC1 
 in a current of C0 2 . The orange variety constitutes the antimony ver- 
 milion, the preparation of which has been described at p. 232. Native 
 sulphide of antimony is employed, in conjunction with potassium 
 chlorate, in the friction-tube for firing cannon ; it is also used in per- 
 cussion caps, together with potassium chlorate and mercuric fulminate. 
 Its property of deflagrating with a bluish-white flame, when heated with 
 nitre, renders it useful in compositions for coloured fires. 
 
 Glass of antimony is a transparent red mass obtained by roasting 
 antimonious sulphide in air, and fusing the product; it contains about 
 8 parts of oxide and i part of sulphide of antimony. It is used for 
 colouring glass yellow. 
 
 Red antimony ore is an oxysulphide of antimony, Sb.,0 3 .2Sb 2 S 3 . 
 
 Antimonic sulphide (Sb 2 S 5 ) is obtained as a bright orange-red precipi- 
 tate by the rapid action of H 2 S upon a solution of pentachloride of 
 antimony in HC1 ; it is decomposed by heat into Sb 2 S 3 and S,. When 
 boiled with hydrochloric acid, Sb 2 S. + 6HC1 = 2SbCl 3 + 3H 2 S + S 8 , show- 
 
446 VANADIUM. 
 
 ing the trivalence of antimony to be stronger than the pentavalence. 
 It is prepared on a large scale under the name of golden sulphuret of 
 antimony by boiling Sb a S 3 with KOH and S, and adding acid to the 
 solution of potassium thioantimonate (liver of antimony) thus obtained. 
 It is used for vulcanising india-rubber. 
 
 When H 2 S acts slowly on SbCl 5 a mixture of Sb. 2 S 5 , Sb. 2 S 3 and S is obtained. In 
 presence of Cr 2 Cl 6 more Sb 2 S 3 is formed. When exposed to light under water or 
 boiled with water, Sb 2 S 5 yields black crystalline Sb 2 S 3 and S. 
 
 Both Sb 2 S 3 and Sb 2 S 5 are dissolved by the alkali sulphides, forming tliio- 
 metantimonites (from HSbS 2 ) and thwantimonates (from H 3 SbS 4 ) respectively. 
 Thus, like the sulphide of arsenic, they dissolve in alkalies yielding the appropriate 
 oxy-salts and thio-salts ; for example, 2Sb 2 S 3 + 4KOH = 3KSbS 2 + KSb0 2 + 2H 2 O, 
 and 4Sb 2 S 5 + 24KOH = 5K 3 SbS 4 + 3K 3 Sb0 4 + i2H 2 0. When the solutions are acidi- 
 fied, all the Sb is precipitated again as sulphide. Even metallic antimony, in 
 powder, is dissolved when gently heated with solution of potassium sulphide 
 in which sulphur has been dissolved, any lead or iron which may be present 
 being left in the residue, so that the antimony may be tested by this process as 
 to its freedom from those metals. 
 
 Mineral Itermes is a variable mixture of oxide and sulphide of antimony, which 
 is deposited as a reddish-brown powder from the solution obtained by boiling 
 sulphide of antimony with potash or soda. It was formerly much valued for 
 medicinal purposes. Kermes was the Arabic name of an insect used in dyeing 
 scarlet. 
 
 Schlippe's salt is the sodium thioantimonate (Na 3 SbS 4 .9H 2 0), and may be 
 obtained in fine transparent tetrahedral crystals by dissolving Sb 2 S 3 in NaOH and 
 adding sulphur. This salt is sometimes used in photography. 
 
 Antimonious sulphate, Sb 2 (S0 4 ) 3 , is formed when antimony is boiled with strong 
 H 2 S0 4 . It crystallises in needles, which are decomposed by water into a soluble 
 sulphate, and an insoluble basic sulphate. 
 
 VANADIUM.* 
 
 This metal was originally discovered in certain Swedish iron ores, but its 
 chief ore is the vanadate of lead, which is found in Scotland, Mexico, and Chili. 
 Vanadic acid has also been found in some clays, in the cupriferous sandstone at 
 Perm in Kussia, and Alderley Edge in Cheshire ; it is contained in some specimens 
 of coal. By treating the vanadate of lead with HN0 3 , expelling the excess of acid 
 by evaporation, and washing out the lead nitrate with water, impure vanadic 
 anhydride (V 2 5 ) is obtained, which may be purified by dissolving in ammonia, 
 crystallising the ammonium metavanadate NH 4 V0 3 , and decomposing it by heat, when 
 vanadic anhydride is left as a reddish-yellow fusible solid, which crystallises on 
 cooling, and dissolves sparingly in water to a yellow solution. It dissolves in HC1, 
 and if the solution be treated with a reducing-agent (such as H 2 S) it assumes a 
 fine blue colour. If a solution of ammonium vanadate be mixed with tincture of 
 galls, it gives an intensely black fluid, which forms an excellent ink, for it is not 
 bleached by acids (which turn it blue), alkalies, or chlorine. 
 
 Vanadium has been obtained by heating its chloride in hydrogen, or by electro- 
 lysing a solution of an alkali vanadate in HC1, as a silver white metal (sp. gr. 5.5). 
 It is not oxidised by air, and does not decompose water, but burns when strongly 
 heated in air. Its melting-point is not known. It is insoluble in HC1, but soluble 
 in HN0 3 . Fused NaOH converts it into sodium vanadate. 
 
 The oxides of vanadium correspond in composition with those of nitrogen. 
 VO is a basic oxide forming salts which give lavender- coloured solutions ; these 
 absorb oxygen rapidly from the air, and act as powerful reducing agents. V 2 3 
 is a black crystalline body resembling plumbago, and capable of conducting 
 electricity, obtained by heating vanadic anhydride in a current of hydrogen ; it 
 is insoluble in acids, and combines with bases to form ranadites (KV0 2 ). V 2 4 is 
 produced when V 2 3 is heated in air ; it dissolves in acids forming salts of vanadyl 
 (VO), and in alkalies forming hypovanadates (K 2 V 4 9 ). Vanadic anhydride, V 2 5 , 
 forms purple and green compounds with the above oxides. Metavanadic acid, 
 
 * Vanadis, a Scandinavian deity. 
 
THE BISMUTH GKOUP. 
 
 447 
 
 crystallises in beautiful golden scales. The yellow fuming liquid, formerly 
 called chloride of vanadium, is really an oxychloride, vanadyl trichloride, VOC1 3 . 
 The oxychlorides, V 2 2 C1, VOC1, and VOC1 2 , have also been obtained. There are 
 two compounds of vanadium with nitrogen, VN and VN 2 . Ammonium meta- 
 vanadate is now used as an oxygen-carrier for blacks in calico-printing, in con- 
 junction with chlorates and aniline hydrochloride. The slag of the Creusot steel 
 works is now the chief source of vanadic acid, of which it contains 2 per cent. 
 
 NIOBIUM,* Nb = 93.3, and TANTALUM, Ta = i8i.6. 
 
 249^. These metals occur as niobates and tantalates respectively in several rare 
 minerals, of which columbite from Massachusetts is most important. By fusing the 
 mineral with KHS0 4 , treating with water, digesting the insoluble residue with 
 (NH 4 ). 2 S (to remove Sn and W), and with HC1 to remove FeS, a mixture of Nb 2 5 
 and Ta. 2 5 is obtained. This is dissolved in HF, and KHF 2 is added ; on concen- 
 trating K 2 TaF 7 crystallises first and is followed by NbOF 3 .2KF ; each yields the 
 corresponding pentoxide when boiled with much water. 
 
 To extract Nb from Nb 2 5 this is first converted into NbCl 5 (by ignition with 
 charcoal and chlorine), the vapour of which is mixed with H and passed through 
 a red-hot tube. The deposited metal is steel-grey (sp. gr. 7), burns to Nb 2 5 , and 
 is insoluble in all acids except in a mixture of HF and HN0 3 and in H 2 S0 4 cone. 
 
 By heating a mixture of Nb 2 5 and C in the electric furnace a button of the 
 metal is obtained, hard enough to scratch quartz. It melts above 1800 C. 
 
 NioMc anhydride, Nb 2 5 , is a white powder soluble in alkalies to form meta- 
 niobates, KNb0 3 . NbO and Nb0 2 are also known. NbCl 3 and NbCl 5 have been 
 prepared as well as oxychlorides analogous to those of vanadium. 
 
 A fused button of tantalum (containing 0.5 per cent. C.) may be obtained by 
 heating a mixture of Ta 2 5 and C in the electric furnace ; it scratches quartz and 
 has sp. gr. 12.79. 
 
 When heated at 600 C. in oxygen both niobium and tantalum burn to the 
 pentoxide. They are both active reducing-agents at moderately high temperatures, 
 niobium being the more active in this regard. Fused alkalies or nitre oxidise 
 them to the corresponding metaniobate or metatantalate. 
 
 lu its compounds tantalum resembles niobium. 
 
 The bismuth group of metals. The metals JBi, Sb, Ta, Nb, and 
 V belong to the same group of elements, which also includes N, P, and 
 As. All these are characterised by their acid pentoxides. Ta, Nb, and 
 Y do not form hydrides analogous to PH 3 , nor is BiH 3 known. Many 
 points of resemblance may be noted between vanadium and chromium, 
 whilst niobium and tantalum recall tungsten. 
 
 TIN. 
 
 Sn = 1 1 7. 6 parts by weight. 
 
 250. Tin is by no means so widely diffused as most of the other metals 
 which are largely used, and is scarcely ever found in the metallic state 
 in nature. Its only important ore is that known as tin-stone, which is 
 a binoxide of tin, Sn0 2 , and is generally found in veins traversing 
 quartz, granite, or slate. It is generally associated with arsenical iron 
 pyrites, and with a mineral called wolfram, which is a tungstate of iron 
 and manganese. 
 
 Tin-stone is sometimes found in alluvial soils in the form of detached 
 rounded masses ; it is then called stream tin ore, and is much purer than 
 that found in veins, for it has undergone a natural process of oxidation 
 and levigation exactly similar to the artificial treatment of the impure 
 ore. These detached masses of stream tin ore are not unfrequently 
 rectangular prisms with pyramidal terminations. 
 
 * Niobe, daughter of Tantalus. 
 
448 SMELTING TIN-STONE. 
 
 The Cornish mines, and those of Malacca and Banca, furnish the 
 largest supplies of tin. Tin-stone is also found in Bohemia, Saxony, 
 California, and Australia. At the Cornish tin-works the purer portions 
 of the ore are picked out by hand, and the residue, which contains 
 quartz and other earthy impurities, together with copper pyrites and 
 arsenical iron pyrites, is reduced to a coaroe powder in the stamping- 
 mills, and washed in a stream of water. The tin-stone, being extremely 
 hard, is not reduced to so fine a powder as the pyritic minerals associated 
 with it, and these latter are therefore more readily carried away by the 
 stream of water than is the tin-slone. The removal of the foreign 
 matters from the ore is also much favoured by the high specific gravity 
 of the binoxide of tin, which is 6.5, whilst that of sand or quartz is only 
 2.7, so that the latter would be carried off by a stream which would not 
 disturb the former. So easily and completely can this separation be 
 effected, that a sand containing less than i per cent, of tin-stone is found 
 capable of being economically treated. 
 
 In order to expel any arsenic and sulphur which may still remain in 
 the washed ore, it is roasted in quantities of 8 or 10 cvvts. in a rever- 
 beratory furnace, when the sulphur is disengaged in the form of sul- 
 phurous acid gas, and the arsenic in that of arsenious oxide, the iron 
 being left in the state of ferric oxide, and the copper partly as sulphate 
 of copper, partly as unaltered sulphide. To complete the oxidation of 
 the insoluble sulphide of copper, and its conversion into the soluble sul- 
 phate, the roasted ore is moistened with water and exposed to the air for 
 some days, after which the whole of the copper may be removed by again 
 washing with water. 
 
 A second washing in a stream of water also removes the ferric oxide 
 in a state of suspension, and this is much more easily effected than when 
 the iron was in the form of pyrites, since the difference between the 
 specific gravity of this mineral (5.0) and that of the tin-stone (6.5) is 
 far less than that between the sp. gr. of ferric oxide and tin-stone. 
 
 The ore thus purified contains between 60 and 70 per cent, of tin ; it 
 is mixed very intimately with about Jth of powdered coal, and a little 
 lime or fluor spar, to form a fusible slag with the siliceous impurities, 
 and reduced in a reverberatory furnace, a comparatively easy task since 
 binoxide of tin readily parts with its oxygen to carbon at a red heat. 
 
 The tin-smelting furnace is shown in Fig. 227. The mixture of ore and coal is 
 moistened to prevent its dispersion by the draught of air, and spread on the 
 hearth (A) in charges of between 20 and 25 cwts. 
 
 The temperature is not permitted to rise too high at first, lest a portion of the 
 oxide of tin should combine with the silica to form a silicate, from which the metal 
 would be reduced with difficulty. During the first six or eight hours the doors of 
 the furnace are kept shut, so as to exclude the air and favour the reducing action of 
 the carbon upon the binoxide of tin, the oxygen of which it converts into carbonic 
 oxide, leaving the tin in the metallic state to accumulate upon the hearth beneath 
 the layer of slag. When the reduction is deemed complete, the mass is well stirred 
 with an iron paddle to separate the metal from the slag ; the latter is run out 
 first, and the tin is then drawn off into an iron pan (B), where it is allowed 
 to remain at rest for the dross to rise to the surface, and is ladled out into ingot 
 moulds. 
 
 The slags drawn out of the smelting-furnace are carefully sorted, those which 
 contain much oxide of tin being worked up with the next charge of ore, whilst 
 those in which globules of tin are disseminated are crushed, so that the metal may 
 be separated by washing in a stream of water. 
 
 The tin, when first extracted from the ore, is far from pure, being contaminated 
 
PURIFICATION OF TIN. 
 
 449 
 
 with small quantities of iron, arsenic, copper, and tungsten. In order to purify it 
 from these, the metal is submitted to a process of liquation, in which the easy 
 fusibility of tin is taken advantage of ; the ingots are piled into a hollow heap near 
 the fire-bridge of a reverberatory furnace, and gradually heated to the fusing- 
 point, when the greater portion of the tin flows into an outer basin, whilst the 
 remainder is converted into the binoxide, which remains as dross upon the hearth, 
 together with the oxides of iron, copper, and tungsten, the arsenic having passed 
 off in the form of arsenious oxide. Fresh ingots of tin are introduced at intervals, 
 until about 5 tons of the metal have collected in the basin, which is commonly 
 the case in about an hour after the com- 
 mencement of the operation. 
 
 The specific gravity of tin being very 
 low (7.285), any dross which may still 
 remain mingled with it does not separate 
 very readily ; to obviate this, the molten 
 metal is well agitated by stirring with 
 wet wooden poles, or by lowering billets 
 of wet wood into it,?when the evolved 
 bubbles of steam carry the impurities up 
 to the surface in a kind of froth ; the 
 stirring is continued for about three 
 hours, and the metal is allowed to re- 
 main at rest for two hours, when it is 
 skimmed and ladled into ingot moulds 
 (block tifi). It is found that, in conse- 
 quence of the lightness of the metal, and 
 its tendency to separate from the other 
 metals with which it is contaminated, 
 the ingots which are cast from the metal 
 first ladled out of the pot are purer than 
 those from the bottom ; this is shown by 
 striking the hot ingots with a hammer, 
 when they break up into the irregular 
 prismatic fragments known as dropped 
 or grain tin, the impure metal not 
 exhibiting this extreme brittleness at 
 a high temperature. The tin imported from Banca is celebrated for its purity 
 (Straits tin). 
 
 When the tin ore contains wolfram, [FeMn]W0 4 , which has sp. gr. 7.3, this 
 remains behind with the prepared tin ore, and must be removed before smelting by 
 fusion with sodium carbonate in a reverberatory furnace, when the tungstic acid is 
 converted into sodium tungstate, which is dissolved out by water, and crystallised. 
 This salt finds an application in calico-printing. 
 
 On the small scale, tin maybe extracted from tin-stone by fusing 100 grains with 
 20 grains of dried sodium carbonate, and 20 of dried borax, in a crucible lined with 
 charcoal, exactly as in the extraction of iron (see p. 415). 
 
 The extraction is more easily effected by fusing 100 grains of tin-stone with 500 
 grains of potassium cyanide for fifteen minutes at a red heat. 
 
 251. Properties of Tin. Tin is remarkable for its lustre and white- 
 ness, in which it rivals silver, but is at once distinguished from the latter 
 by its greater fusibility, and by its oxidising when heated in air. It is the 
 most fusible of the metals in common use (233 C.), much lighter than 
 silver, sp. gr. 7.28, and emits a curious grating sound when bent; it is 
 harder than lead, but softer than zinc ; very malleable at ordinary tem- 
 peratures (tin-foil), brittle at 200 C. (dropped or grain tin), not vapor- 
 ised except at very high temperatures. It has the lowest tenacity of all 
 the metals in common use, and therefore its ductility is very low, only 
 one other common metal, lead, being more difficult to draw into wire at 
 the common temperature. Tin may, however, be drawn at 100 C. 
 Only gold, silver, and copper surpass it in malleability. 
 
 Tin decomposes steam at a red heat. It is scarcely affected by air or 
 
 2 P 
 
45 MANUFACTURE OF TIN-PLATE. 
 
 water at common temperatures,* and is therefore used for tinning other 
 metals. Tin is easily soluble in strong hydrochloric acid, which distin- 
 guishes it from silver, and it is converted into a white nearly insoluble 
 powder by nitric acid, which distinguishes it from all other metals except 
 .antimony. 
 
 Exposure to extreme cold converts tin into a modification which has 
 lost its reflecting surface, and has thus acquired a grey appearance (grey 
 tin). A spontaneous disintegration of the tin may even occur from this 
 cause.f The sp. gr. of grey tin is 5.73. 
 
 The transition temperature of these enantiotropic forms of tin is 20 C., so that 
 the grey form must become white when heated above this temperature ; but the 
 change from white to grey below 20 C. is very slow until the temperature has 
 fallen considerably lower. The conversion is most rapid at - 48 C., and is acceler- 
 ated by contact with grey tin already formed, and with stannic chloride. 
 
 Tin-foil is made from bars of the best tin, which are hammered down 
 to a certain thinness, then cut up, laid upon each other, and again beaten 
 till extended to the required degree. 
 
 Tin-plate is made by coating sheets of iron with a layer of tin ; to 
 effect this, the sheets, cleansed from oxide, are dipped into melted tin, a 
 coating of which adheres to the iron when the sheet is withdrawn. Tin 
 being unaltered by exposure to air at the ordinary temperature, will 
 effectually protect the iron from rust as long as the coating of tin is 
 perfect, but as soon as a portion of the tin is removed so as to leave the 
 iron exposed, corrosion occurs very rapidly, because the two metals form, 
 a galvanic couple, which decomposes the water (charged with carbonic 
 acid) deposited upon them from the air, and the iron, having the greater 
 attraction for oxygen, is the metal attacked. In the case of galvanised 
 iron (coated with zinc), on the contrary, the zinc would be the metal 
 attacked, and hence the greater durability of this material under certain 
 conditions. 
 
 For the manufacture of tin-plate, the best mild steel is employed, and the most 
 important part of the process consists in cleansing the iron plates from every trace 
 of oxide which would prevent the adhesion of the tin. To effect this, and to anneal 
 the iron, they are made to undergo several processes, of which the most important 
 are (i) immersion in diluted sulphuric acid ; (2) heating to redness to anneal the 
 plate ; (3) rolling to improve the surface ; (4) a second annealing ; (5) immersion 
 in diluted sulphuric acid ; (6) scouring with sand ; (7) washing with water ; they 
 are then dried for an hour in a vessel of melted tallow, which prevents contact of 
 air, and immersed for an hour and a half in melted tin, the surface of which is 
 protected from oxidation by tallow ; after draining, they are dipped a second time 
 into the tin to thicken the layer ; then transferred to a bath of hot tallow to allow 
 the superfluous tin to run down to the lower edge, whence it is afterwards removed 
 by passing the plate through rollers. About 8 Ibs. of tin are required to cover 225 
 plates, weighing 112 Ibs. 
 
 To recover the tin from tin-plate cuttings they are boiled with caustic soda 
 and litharge; Sn + 2NaOH + 2PbO = Na 2 Sn0 3 + Pb 2 4-H 2 0. The sodium stannate, 
 Na 2 SnO 3 , is used in dye-works, and the precipitated lead is again converted into 
 litharge by heating in air. 
 
 Term-plate is iron coated with an alloy of tin and lead. 
 
 In tinning the interior of copper vessels, in order to prevent the contamination 
 
 * Crystalline tin (sp. gr. 7.18), deposited upon zinc from neutral stannous chloride, and 
 powdered tin, made by shaking molten tin in a wooden box, oxidise to a considerable extent 
 at the ordinary temperature ; when heated, the superficial oxide prevents the tin from 
 fusing, and it burns like tinder. 
 
 f The disintegration of the tin pipes of church organs, observed in cold climates, has been 
 attributed to the conversion of the tin into the grey modification by the cold, perhaps aided 
 by the vibrations to which the pipes are subjected. 
 
ALLOYS. 451 
 
 of food with the copper, the surface is first thoroughly cleaned from oxide by heat- 
 ing it and rubbing over it a little sal-ammoniac, which decomposes any oxide of 
 copper, converting it into the volatile chloride of copper (CuO + 2NH 4 C1 = 
 CuCl 2 + H 2 + 2NH 3 ). A little resin is then sprinkled upon the metallic surface, to 
 protect it from oxidation, and the melted tin is spread over it with tow. 
 
 Pins (made of brass wire) are coated with tin by boiling them with cream of 
 tartar (bitartrate of potash), common salt, alum, granulated tin, and water ; the tin 
 is dissolved by the acid liquid, from which solution it is reduced by electrolytic 
 action, for the tin is more highly electro-positive than the brass, and the latter acts 
 as the negative plate. 
 
 252. Alloys. The term alloy is applied to any homogeneous mass 
 consisting of two or more metals. In the majority of cases, it is not 
 possible to detect the properties of the individual metals in such a mass, 
 so that the alloy cannot be regarded as a mere mixture. In many cases, 
 on the other hand, the alteration of properties induced in one metal by 
 the addition of another does not show any definite relationship with the 
 mass of the added metal, as would be the case if such alteration were 
 wholly due to chemical combination. A little consideration will show 
 that the difficulty thus experienced in assigning the phenomenon of 
 alloy-formation to its proper position in the classes of change, usually 
 distinguished as physical and chemical, is parallel to that experienced in 
 assigning the phenomenon of solution to one of these two classes (p. 50). 
 It has thus become customary to regard alloys as solidified solutions, 
 which in some cases are analogous to what has been already termed a 
 simple solution that is, the alloy shows no evidence of containing a 
 chemical compound and in other cases are analogous to those solutions 
 which undoubtedly contain a compound of the solvent with the dissolved 
 substance in a state of simple solution. The majority of alloys belong 
 to the second class, and consist of solutions of compounds of the con- 
 stituent metals in an excess of one of the metals. 
 
 Two important pieces of evidence in favour of these views must be quoted, 
 (i) In many instances, when one metal is alloyed, in small proportion, with 
 another, the freezing-point of the preponderating metal is lowered to an extent 
 which is in accord with the laws controlling the lowering of the freezing-point of 
 a solvent by a dissolved solid (p. 319).* This indicates that the alloy is but a 
 solidified solution. (2) When a compound plate (of copper and zinc, for instance), 
 consisting of one metal closely attached to another, is used as the attackable 
 plate of a galvanic cell, the electro-motive force of the cell is that which would be 
 produced were the more attackable of these metals (zinc, for instance) alone used 
 as the attackable plate. When an alloy is thus treated, the E.M.F. is in some 
 cases that which would be produced by the more attackable constituent, and is 
 in some cases different from this. Identity of the E.M.F. with that of the more 
 attackable metal indicates that the alloy is a solidified simple solution, whereas 
 a difference from this value can only be due to the existence of a compound in the 
 alloy. 
 
 Alloys are industrially made by mixing the constituent metals in a 
 melted condition, although they have been also prepared both by strongly 
 compressing a mixture of the powdered metals at the ordinary tempera- 
 ture, and by electrolysing a solution containing salts of the constituent 
 metals ; the metallic deposit obtained by the latter method consists, in 
 some cases, of an alloy. 
 
 2$2a. Alloys of Tin. Tin is the chief metal used for making white 
 alloys, some of which resemble silver in appearance. Britannia metal 
 consists chiefly of tin (about 80 per cent.) hardened by antimony (about 
 
 * It may be remarked that evidence as to the molecular weight of metals has been ob- 
 tained from alloys by a method analogous to that of Kaoult (p. 319). 
 
452 ALLOYS OF TIN. 
 
 10 per cent.) and a little copper. Base silver coin consists chiefly of tin. 
 Pewter consists of 4 parts of tin and i part of lead. Much inferior tin- 
 foil is made of pewter. The fusibility of tin recommends it for solder. 
 The solder employed for tin-wares is an alloy of tin and lead in various 
 proportions, sometimes containing 2 parts of tin to i of lead (fine solder), 
 sometimes equal weights of the two metals (common solder), and some- 
 times 2 parts of lead and i of tin (coarse solder). All these alloys melt 
 at a lower temperature than tin, and, therefore, than lead. In applying 
 solder, it is essential that the surfaces to be united be quite free from 
 oxide, which would prevent adhesion of the solder ; this is insured by 
 the application of sal ammoniac, or of hydrochloric acid,* or sometimes 
 of powdered borax, remarkable for its ready fusibility and its solvent 
 power for the metallic oxides. 
 
 Gun metal is an alloy of 90.5 parts of copper with 9.5 of tin, especially 
 valuable for its tenacity, hardness, and fusibility. 
 
 In preparing this alloy, it is usual to melt the tin in the first place with twice its- 
 weight of copper, when a white, hard, and extremely brittle alloy (Jiard metaT) is 
 obtained. The remainder of the copper is fused in a de-oxidising flame on the 
 hearth of a reverberatory furnace, and the hard metal thoroughly mixed with it, 
 long wooden stirrers being employed. A quantity of old gun metal is usually 
 melted with the copper, and facilitates the mixing of the metals. When the 
 metals are thoroughly mixed, the oxide is removed from the surface and the gun- 
 metal is run into moulds made of loam, the stirring being continued during the 
 running, in order to prevent the separation, to which this alloy is very liable, of a 
 white alloy containing a larger proportion of tin, which has a lower specific gravity, 
 and would chiefly collect in the upper part of the casting (forming tin-spots). The 
 purest commercial qualities of copper and tin are always employed in gun-metal. 
 
 The brittle white alloy alluded to above as hard metal appears to be a chemical 
 compound having the formula SnCu 4 (which requires 31.8 per cent, of tin and 68.2 
 per cent, of copper), though the alloy which has the highest density, and bears 
 repeated fusion without alteration in its composition, corresponds with the 
 formula SnCu 3 (38.2 per cent, of tin). It is probably one of these alloys which 
 forms the tin-spots or flaws in gun-metal castings. 
 
 Bronze is essentially an alloy of copper and tin, containing more tin 
 than gun-metal contains ; its composition is varied according to its 
 application, small quantities of zinc and lead being often added to it. 
 Bronze is affected by changes of temperature, in a manner precisely the 
 reverse of that in which steel is influenced, for it becomes hard and 
 brittle when allowed to cool slowly, but soft and malleable when quickly 
 cooled, a property which the ancients applied in the manufacture of 
 weapons. Bronze coin (substituted for the copper coinage) is composed 
 of 95 copper, 4 tin, and i zinc. Manganese-bronze, an alloy of ordinary 
 bronze containing Mn, is said to rival bar-iron in tenacity and extensi- 
 bility ; it is used for ships' propellers. Phosphor-bronze contains about 
 J per cent, of phosphorus added as tin phosphide. 
 
 Bell-metal is an alloy of about 4 parts of copper and i of tin, to which 
 lead and zinc are sometimes added. The metal of which musical instru- 
 ments are made generally contains the same proportions of copper and 
 tin as bell-metal. At a little below a dark red heat, this alloy may be 
 hammered into thin plates, imitating the celebrated Chinese gongs. 
 
 Speculum metal, employed for reflectors in optical instruments, con- 
 sists of 2 parts of copper and i of tin, to which a little Zn, As, and 
 Ag are sometimes added to harden it and render it susceptible to a high 
 
 * It is customary to kill the hydrochloric acid by dissolving some zinc in it. The chloride 
 of zinc is probably useful in protecting the work from oxidation. 
 
OXIDES OF TIN. 453 
 
 polish. A superior kind of type-metal is composed of i part of Sn, i 
 of Sb, and 2 of Pb. 
 
 Tin is not dissolved by nitric acid, but is converted into a white 
 powder, metastannic acid ; hydrochloric acid dissolves it with the aid of 
 heat, evolving hydrogen ; but the best solvent for tin is a mixture of 
 hydrochloric with a little nitric acid. When the metal is acted upon by 
 hydrochloric acid, it assumes a crystalline appearance, which has been 
 turned to account for ornamenting tin-plate. If a piece of common 
 tin-plate be rubbed over with tow dipped in a warm mixture of hydro- 
 chloric and nitric acids, its surface is very prettily diversified (moire 
 metallique) ; it is usual to cover the surface with a coloured transparent 
 varnish. 
 
 A mixture of i vol. H 2 SO 4 , 2 vols. HN0 3 , and 3 vols. water dissolves 
 tin in the cold, evolving nearly pure nitrous oxide. The solution is pre- 
 cipitated when heated. Poured into boiling water, all the tin is thrown 
 down as metastannic acid. 
 
 Commercial tin is liable to contain minute quantities of lead, iron, 
 copper, arsenic, antimony, bismuth, gold, molybdenum, and tungsten. 
 Pure tin may be precipitated in crystals by the feeble galvanic current 
 excited by immersing a plate of tin in a strong solution of stannous 
 chloride, covered with a layer of water, so that the metal may be in 
 contact with both layers of liquid. 
 
 253. Oxides of tin. Two oxides of this metal are known stannous 
 oxide, SnO, and stannic oxide, SnO 2 . 
 
 Protoxide of tin (SnO), or stannous oxide, is a substance of little practical 
 importance, obtained by heating stannous oxalate out of contact with air ; 
 SnC 2 4 =:SnO + C0 2 +CO. It is a black powder which burns when heated in air, 
 becoming Sn0 2 . It is a feebly basic oxide, and therefore dissolves in the acids ; 
 it may also be dissolved by a strong solution of potash, but is then easily 
 decomposed into metallic tin and stannic oxide, which combines with the potash. 
 By heating tin with caustic soda a " stannite " of soda is obtained ; this is 
 substituted for stannate of soda, into which it is converted, with precipitation of 
 tin. by boiling. 
 
 Binoxide of tin (Sn0 2 ) or stannic oxide, has been mentioned as the 
 chief ore of tin, and is formed when tin is heated in air. Tin-stone, or 
 cassiterite, as the natural form of this oxide is called, occurs in very hard 
 square prisms, usually coloured brown by ferric oxide. In its insolu- 
 bility in acids it resembles crystallised silica, and, like that substance, 
 it forms, when fused with alkalies or their carbonates, compounds which 
 are soluble in water ; these are termed stannates, the binoxide of tin 
 being known as stannic anhydride. The artificial Sn0 2 dissolves in hot 
 strong H 2 S0 4 , and is precipitated on adding water. It is easily reduced 
 when heated in hydrogen, and is converted into SnCL when heated in 
 HC1 gas. 
 
 Sodium stannate, Na 2 O.Sn0 2 , is prepared, on the large scale, for 
 use as a mordant by calico-printers. The prepared tin ore (p. 448) is 
 heated with solution of caustic soda, and boiled down till the tem- 
 perature rises to 600 F. (315 0.) ; or the tin ore is fused with sodium 
 nitrate, when the nitric acid is expelled. It crystallises easily in hex- 
 agonal tables having the composition Na 2 Sn0 3 .3Aq, which dissolve 
 easily in cold water, and are partly deposited again when the solution 
 is heated. Prismatic crystals have been obtained of Na 2 Sn0 3 .ioAq, 
 like Na 2 C0 3 .ioAq. Most normal salts of the alkalies also cause a 
 
454 STANNOUS CHLOKIDE. 
 
 separation of sodium stannate from its aqueous solution. The solution 
 of sodium stannate has, like the silicate, a strong alkaline reaction, and 
 when neutralised by an acid yields a precipitate of stannic acid, H 2 SnO 3 , 
 or SnO(OH) 2 , which may be obtained as a hydrosol and a hydrogel 
 exactly as described for silicic acid (p. 278). The great similarity 
 between stannic and silicic acids is here very remarkable. When 
 heated, stannic acid is converted into Sn0 2 . 
 
 Stannic or metastannic acid, H 2 Sn0 3 (dried at 100 C.), is obtained as a white 
 crystalline hydrate when tin is oxidised by nitric acid. When heated, it assumes a 
 yellowish colour, and a hardness resembling that of powdered tin-stone. Putty 
 2)owder, used for polishing, consists of metastannic anhydride ; as found in 
 commerce, it generally contains much oxide of lead. Metastannic acid is insoluble 
 in water and diluted acids, but when boiled with dilute HC1 it combines with 
 some of the acid, and when the excess of HC1 has been removed by washing, the 
 compound passes into solution, from which it is reprecipitated by HC1, or by 
 boiling. When fused with hydrated alkalies it is converted into a soluble 
 stannate, but if boiled with solution of potash it is dissolved in the form of 
 potassium metastannate, which will not crystallise, like the stannate, but is 
 obtained as a granular precipitate by dissolving potassium hydrate in its solu- 
 tion. This precipitate has the composition K 2 Sn 5 O i;i .4Aq ; it is very soluble in 
 water, and is strongly alkaline. When it is heated to expel the water, it is 
 decomposed, and the potash may be washed out with water, leaving metastannic 
 anhydride. The sodium metastannate, Na 2 Sn 5 11 4Aq, has also been obtained as a 
 sparingly soluble crystalline powder, by the action of cold sodium hydroxide on 
 metastannic acid. It is claimed that the precipitate formed by alkalies in stannic 
 chloride is orthostannic acid, Sn(OH) 4 . 
 
 Stannate of tin is obtained as a yellowish hydrate by boiling stannous chloride 
 with ferric hydroxide ; Fe 2 3 + 2SnCl 2 = SnSn0 3 + 2FeCl 2 . It is sometimes written 
 Sn 2 3 , and called sesquioxide of tin. 
 
 Stannous nitrate, Sn(N0 3 ) 2 . is formed when tin is dissolved in cold very dilute 
 nitric acid ; Sn 4 + ioHN0 3 = 4Sn(N0 3 ) 2 + NH 4 N0 3 + 3H 2 0. It forms a yellow solu- 
 tion, which absorbs oxygen and deposits Sn0 2 . Stannic nitrate, Sn(N0 3 ) 4 , has 
 been crystallised from a solution of stannic acid in nitric acid. 
 
 254. Chlorides of tin. The two chlorides of tin correspond in 
 composition with the oxides. 
 
 Stannous chloride, or protochloride of tin (SnCl 2 ), is much used by dyers 
 and calico-printers,* and is prepared by dissolving tin in hydrochloric 
 acid, when it is deposited, on cooling, in lustrous prismatic needles 
 (Sn01 2 .2Aq) known as tin crystals or salts of tin. In vamio, over H 2 S0 4 , 
 they become SnCl 2 (m. p. 249 C.). The dissolution of the tin is 
 generally effected in a copper vessel, in order to accelerate the action by 
 forming a voltaic couple, of which the tin is the attacked metal. When 
 gently heated, the crystals lose their water, and are partly decomposed, 
 some hydrochloric acid being evolved (SnCl, -f H 2 O = SnO + 2HC1) ; at a 
 higher temperature (610 0.) the anhydrous chloride may be distilled. 
 The crystallised stannous chloride dissolves in about one-third of its 
 weight of water, but if much water be added, a precipitate of stannous 
 hydroxy chloride, 2Sn(OH)Cl.Aq, is formed, which dissolves on adding 
 HC1. A moderately dilute solution of stannous chloride absorbs oxygen 
 from the air, and deposits the hydroxychloride, leaving stannic chloride 
 in solution ; 3SnCl 2 + H 2 O + = SnCl 4 + 2Sn(OH)Cl. If the solution 
 contains much free hydrochloric acid, it remains clear, being entirely 
 converted into stannic chloride. A strong solution of the chloride is 
 not oxidised by the air, and the weak solution may be longer preserved 
 in contact with metallic tin. Stannous chloride has a great attraction 
 
 * It is sometimes used for imparting a fine golden colour to sugar. 
 
STANNIC CHLORIDE. 455 
 
 for chlorine as well as for oxygen, and is frequently employed as a 
 de-oxidising or de-chlorinating agent. Tin may be precipitated from 
 stannous chloride by the action of zinc, in the form of minute crystals. 
 A very beautiful tin tree is obtained by dissolving granulated tin in 
 strong hydrochloric acid, with the aid of heat, in the proportion of 8 
 measured oz. of acid to 1000 grs. of tin, diluting the solution with four 
 times its bulk of water, and introducing a piece of zinc. 
 
 Stannous chloride is also obtained by heating tin in HC1 gas, or by 
 distilling tin with mercuric chloride; Sn + HgCl 2 = SnCl 2 + Hg. The 
 mercury distils over, leaving the stannous chloride as a transparent 
 vitreous mass. Above 880 C. the density of its vapour is 94.5 (H= i), 
 agreeing with the formula SnCl 2 , but below 700 C. it is 189, corre- 
 sponding with Sn 2 Cl 4 . 
 
 Stannic chloride or tetrachloride of tin (SnCl 4 ), is obtained in solution 
 when tin is heated with hydrochloric and nitric acids ; for the use of 
 the dyer, the solution (nitromuriate of tin) is generally made with 
 chloride of ammonium (sal-ammoniac) and nitric acid. The anhydrous 
 tetrachloride is obtained by heating tin in a current of dry chlorine, 
 when combination occurs with combustion, and the tetrachloride distils 
 over as a heavy (sp. gr. 2.28) colourless volatile liquid (boiling-point, 
 114 C.), giving suffocating white fumes in the air. When it is mixed 
 with a little water, there is energetic combination, and three crystalline 
 compounds may be produced, containing 3, 5, and 8 molecules of water. 
 A large quantity of water causes precipitation of stannic acid. The 
 commercial crystals are SnCl^Aq. The anhydrous chloride is also 
 obtained by distilling tin with an excess of mercuric chloride ; 
 Sn-i- 2Hg01 2 = SnCl 4 -l-Hg 2 ; but here, the result is opposite to that in 
 the case of stannous chloride, as the stannic chloride distils over before 
 the mercury. Stannic chloride forms crystallisable double salts with 
 the alkali chlorides. Pink salt, used by dyers, is a compound of stannic 
 chloride with ammonium chloride, 2NH 4 Cl.SnCl 4 ; it is colourless, but 
 is used in dying red with madder. The compound 2H01.SnCl 4 .6Aq 
 has been obtained in crystals. 
 
 Stannic bromide, SnBr 4 , is crystalline, fuses at 30 C., and boils at 
 201 C. It dissolves in water without immediate decomposition. 
 
 255. Sulphides of tin. The p)*otosulphide, or stannous sulphide 
 (SnS), may be easily prepared by heating tin with sulphur, when it 
 forms a grey crystalline mass. It is also obtained as a dark brown 
 precipitate by the action of H 2 S upon a solution of SnCl 2 . Stannous 
 sulphide is not dissolved by alkalies unless some sulphur be added, 
 which converts it into stannic sulphide. It dissolves in hot strong 
 HC1. 
 
 Bisulphide of tin, or stannic sulphide (SnS 2 ), is commonly known as 
 mosaic gold or bronze powder,* and is used for decorative purposes. It 
 cannot be made by heating tin with sulphur, because it is decomposed 
 by heat into SnS and S. It is prepared by a curious process, which 
 was devised in 1771, and must have been the result of a number of 
 trials. 1 2 parts by weight of tin are dissolved in 6 parts of mercury ; 
 the brittle amalgam thus obtained is powdered and mixed with 7 parts 
 of sulphur and 6 of sal-ammoniac. The mixture is introduced into a 
 
 * A bronze powder is also made by powdering finely laminated alloys of copper and zinc 
 a little oil being- used to prevent oxidation. 
 
456 TITANIUM. 
 
 Florence flask, which is gently heated in a sand-bath as long as any 
 smell of H 2 S is evolved ; the temperature is then raised to dull redness 
 until no more fumes are disengaged. The mosaic gold is found in 
 beautiful yellow scales at the bottom of the flask, and sulphide of 
 mercury and calomel are deposited in the neck. The mercury appears 
 to be used for effecting the fine division of the tin, and the sal-ammoniac 
 to keep down the temperature (by its volatilisation) below the point at 
 which the SnS 2 is converted into SnS. 
 
 Mosaic gold, like gold itself, is not dissolved by hydrochloric or nitric acid, but 
 easily by aqua regia. Alkalies also dissolve it when heated. On adding H 2 S to a 
 solution of stannic chloride, the stannic sulphide is obtained as a yellow precipitate, 
 which is sometimes formed only on boiling. It dissolves easily in alkalies and 
 alkali sulphides, forming thiostannates. The sodium salt, Na 2 SnS 3 .2H 2 0, has 
 been crystallised in yellow octahedra. When fused with iodine, SnS 2 forms 
 SnS 2 I 4 , a fusible yellow body which does not lose iodine when heated, and dis- 
 solves in carbon disulphide, forming a brown solution which deposits red crystals 
 like potassium dichromate ; these are decomposed by boiling with water, yielding 
 Sn0 2 , sulphur, iodine, and HI, 
 
 Tin pyrites contains either SnS or SnS 2 , or both, accompanied by sulphides of 
 copper and iron. 
 
 Stannic sulphate, Sn(S0 4 ) 2 , is left as a white mass when tin is boiled to dryness 
 with sulphuric acid. 
 
 Stannic phosphate, Sn 3 (P0 4 ) 4 , is insoluble in nitric acid, and is sometimes used 
 in separating phosphoric acid in quantitative analysis. 
 
 Stannic arsenate is left in the residue obtained by oxidising alloys containing 
 tin and arsenic with nitric acid. 
 
 Tin is very closely connected with silicon by the composition, hard- 
 ness, and insolubility of Sn0 2 , and by the characters of SnCl 4 . Among 
 metals it is conspicuous by the feebly basic character of its oxides and 
 by the powerful reducing properties of SnCl 2 . 
 
 TITANIUM, Ti= 47.7. 
 
 256. This metal stands in close chemical relationship to tin ; it is found in con- 
 siderable quantity in iron ores and clays, although no very important practical 
 application has hitherto been found for it. The form in which it is generally found 
 is titanic oxide (or anhydride), Ti0 2 , which occurs uncombined in the minerals 
 rutile, anatase, and brookite, the first of which is isomorphous with tin-stone, and 
 is extremely hard, like that mineral, while the second crystallises in the quadratic 
 system and the third in the rhombic. The mineral perowsltite is (CaFe)Ti0 3 . In 
 combination with oxide of iron, titanic oxide is found in iron-sand, iserine, or 
 menaccanite (found originally in Menaccan, in Cornwall), which resembles gun- 
 powder in appearance, and is now imported in abundance from Nova Scotia and 
 New Zealand. Some specimens of this mineral contain 40 per cent, of titanic 
 oxide as ferrous titanate. To extract titanic oxide from it, the finely ground 
 mineral is fused with three parts of K 2 C0 3 , when CO 2 is expelled and potassium 
 titanate (K 2 Ti0 3 ) formed ; on washing the mass with hot water, this salt is decom- 
 posed, a part of its alkali being removed by the water, and an acid titanate left, 
 mixed with the oxide of iron. This is dissolved in HC1, and the solution evapo- 
 rated to dryness, when the titanic oxide, and any silica which may be present, are 
 converted into the insoluble modifications, and are left on digesting the residue 
 again with dilute hydrochloric acid ; the residue is washed with water (by 
 decantation, for titanic oxide easily passes through the filter), dried, and fused at 
 a gentle heat with KHS0 4 . This forms a soluble compound with the titanic 
 oxide, which may be extracted by cold water, leaving the silica undissolved. The 
 solution containing the titanic oxide is mixed with about twenty times its volume 
 of water, and boiled for some time, when the Ti0 2 is separated as a white pre- 
 cipitate, exhibiting a great disposition to cling as a film to the surface of the flask 
 in which the solution is boiled, and giving it the appearance of being corroded. 
 The titanic oxide becomes yellow when strongly heated, and white again on 
 cooling ; it does not dissolve in solution of potash, like silica, but when fused with 
 
COMPOUNDS OF TITANIUM. 457 
 
 potash it forms a titanate, which is decomposed by water ; the acid titanate of 
 potassium which is left may be dissolved in HC1, and if the solution be neutralised 
 with ammonium carbonate, hydrated titanic acid, Ti(OH) 4 , is precipitated, very 
 much resembling alumina in appearance. By dissolving the gelatinous hydrate in 
 cold HC1, and dialysing, a solution of titanic acid in water is obtained, which is 
 liable to gelatinise spontaneously if it contains more than i per cent, of the acid. 
 Titanic acid is employed in the manufacture of artificial teeth, and for imparting 
 & straw-yellow tint to the glaze of porcelain. 
 
 If a mixture of titanic acid and charcoal be heated to redness in a porcelain 
 tube through which dry chlorine is passed, titanium tetrachloride (TiCl 4 ) is obtained 
 as a colourless volatile liquid (Jb. p. 136 C.), very similar to tetrachloride of tin. 
 By passing the vapour of the tetrachloride over heated sodium, the metallic titanium 
 is obtained in prismatic crystals (sp. gr. 3.6) resembling specular iron ore in 
 appearance ; it fuses at a very high temperature, but can be prepared massive by 
 heating a mixture of TiO 2 and C in the electric furnace, when it contains about 
 2 per cent, of carbon, is hard enough to scratch rock crystal and has sp. gr. 4.87. 
 Like tin, it is said to dissolve in , hydrochloric acid with liberation of hydrogen. 
 The most remarkable chemical feature of titanium is its direct attraction for 
 nitrogen, with which it combines when strongly heated in air. By passing 
 ammonia gas over titanic oxide heated to redness, a yellow powder is formed, 
 which is nitride of titanium (Ti. 2 N 2 ). When suspended in water, it is blue by 
 transmitted and yellow by reflected light. Ti 3 N 4 , corresponding with TiCl 4 , is also 
 known. Beautiful cubes of a copper colour and great hardness, formerly believed 
 to be metallic titanium, are found adhering to the slags of blast furnaces in which 
 titaniferous iron ores are smelted ; these are believed to consist of a compound of 
 cyanide with nitride of titanium, TiCy 2 .3Ti 3 N 2 . A similar compound is obtained 
 by passing nitrogen over a mixture of titanic oxide and charcoal heated to 
 whiteness. 
 
 Violet-coloured crystals of titanium trichloride (Ti 2 Cl 6 ) are obtained by passing 
 hydrogen charged with vapour of the tetrachloride through a red-hot porcelain 
 tube ; it forms a violet solution in water, which resembles stannous chloride in 
 its reducing properties. 
 
 Titanium dichloride. TiCl 2 , is obtained by heating the trichloride to dull redness 
 in hydrogen. It is a black solid which quickly absorbs moisture, and takes fire 
 if water be dropped upon it. When dissolved in water or alcohol, it evolves 
 hydrogen from them. Bromine combines with it, causing much heat, and form- 
 ing TiCl 2 Br. 2 . The dichloride volatilises in hydrogen without fusing, and if cooled 
 in hydrogen it occludes the gas, and takes fire on exposure to air. It glows when 
 heated on platinum, evolving TiCl 4 , and leaving a residue of Ti0 2 . 
 
 Titanium tetrafluoride, TiF 4 is prepared like SiF 4 , and is a fuming colourless 
 liquid. TheJIuotitanates, e.g., K 2 TiF 6 , are prepared by dissolving Ti0 2 in HF and 
 neutralising with alkali. 
 
 When a solution of titanic oxide (or acid titanate of potassium) in hydrochloric 
 acid is acted on by zinc, a violet solution is formed, which deposits, after a time, 
 a blue (or green) precipitate ; this appears to be a sesquioxlde of titanium (Ti 2 3 ), 
 and rapidly absorbs oxygen from the air, being converted into titanic oxide. 
 This oxide is also obtained in the preparation of TiCl 2 unless air be very carefully 
 excluded. It then forms small shining copper-coloured crystals with a violet 
 reflection, which have the same crystalline form as specular iron ore (Fe 2 3 ). 
 Ti. 2 Q3 is a basic oxide. The sulphate Ti 2 (S0 4 ) 3 .8Aq crystallises from the violet 
 solution obtained by dissolving titanium in sulphuric acid. Nitric acid oxidises 
 it to titanic sulphate, Ti(S0 4 ) 2 .3Aq, which forms a yellowish, transparent, deliques- 
 cent mass. Thus. Ti0 2 appears to possess feebly basic as well as feebly acid 
 properties. The patagrio-tttanic sulphate, K 2 Ti ( s C) 4 ) 3 .3Aq. is formed when TiO 2 is 
 fused with KHS0 4 . A titanoug oxide (TiO) is said to be obtained as a black powder 
 when titanic oxide is strongly heated in a crucible lined with charcoal. 
 
 Titanium tno.nde Ti0 3 , is obtained as a yellow precipitate, Ti(OH) 6 , when TiCl 4 
 is mixed with a dilute solution of H 2 2 in alcohol. It is probably a peroxide, and 
 is the cause of the yellow colour developed by H 2 2 in solution of titanic acid 
 forming a test for H 2 2 (p. 64). 
 
 Titanium digulpkide is not precipitated, like tin disulphide when H 2 S acts upon 
 the tetrachloride ; but if a mixture of the vapour of titanium tetrachloride with 
 hydrosulphuric acid is passed through a red-hot tube, greenish-yellow scales of the 
 disulphide, resembling mosaic gold, are deposited. 
 
45* 
 
 THORIUM. 
 
 ZIRCONIUM, Zr = go. 
 
 257. This metal occurs in the rare minerals zircon (sp. gr. 4.5) and hyacinth, in 
 which the oxide zirconia (Zr0 2 ) is combined with silica (Zr0 2 .Si0 2 ). The Zr0 2 is 
 obtained from these minerals by heating with KHF 2 , and boiling with water 
 when K 2 SiF 6 is left and K 2 ZrF 6 dissolved ; this is heated with H 2 S0 4 to expel HF, 
 and ZrO(OH) 2 is precipitated by ammonia ; when this is ignited, it incandesces, 
 loses water, and becomes Zr0 2 , which is a feebly acid oxide, liberating C0 2 from 
 fused Na^COg, and forming sodium zirconate. Na 4 Zr0 4 . 
 
 Zr closely resembles Si, and is obtained like that element ; it exists in an 
 amorphous and a crystalline (sp. gr. 4.25) form. It dissolves in HF and in aqua 
 regia and decomposes water slowly at 100 C. Its melting-point is very high. 
 Zinconia is more basic than silica, and the metal displaces silicon when heated 
 with silica. The sulphate, Zr(S0 4 ) 2 .4Aq, is decomposed by boiling with K 2 S0 4 , 
 recalling the behaviour of titanium. ZrCl 4 is known ; it is more stable than SiCl 4 . 
 Evidence of the existence of higher oxides than Zr0 2 has been obtained. 
 
 THORIUM, Th iv = 23o.8. 
 
 Although a rare element, thorium in the form of thoria, Th0 2 (sp. gr. 10.2), is 
 used in considerable quantity for the manufacture of Welsbach mantles (p. 155). 
 The mineral thorite, Th0 2 .Si0 2 , is the most fruitful source of thoria but it is rare, 
 and the oxide is commonly produced from monazite sand, which is comparatively 
 poor in thorium, by fusion with caustic alkali, extraction with sulphurous acid and 
 evaporation of the residue with strong H 2 S0 4 ; the dry mass is added in small doses 
 to water at o C. in which anhydrous thorium sulphate is readily soluble. Sodium 
 sulphate is next added to precipitate cerium and thorium hydroxide, Th(OH) 4 , is 
 then thrown down by some substance acting as a feeble base, like sodium nitrite. 
 Thoria is more basic than Zr0 2 but less acid, as it does not expel C0 2 from fused 
 NagCOg. Its anhydrous sulphate, Th(S0 4 ) 2 , is soluble in ice-cold water, but when 
 the solution is heated crystals of Th(S0 4 ) 2 .4H 2 O separate. Thoria does not dissolve 
 in HC1 or HN0 3 , but when the acid is expelled on the steam bath, the residue 
 dissolves in the water to an emulsion in which acids cause a curdy precipitate 
 soluble in pure water (compare metastannic acid). NH 3 produces a bulky pre- 
 cipitate of hydroxide which dissolves in cold nitric acid yielding the nitrate 
 Th(N0 3 ) 4 .6H 2 0. Thorium fluoride is a precipitate insoluble in HF ; the double 
 fluoride K 2 ThF 6 .4H 2 is a sparingly soluble crystalline powder. 
 
 Thorium prepared by dissolving the hydroxide in HC1, evaporating with KC1, 
 and fusing the double chloride with sodium, is a grey crystalline metal isomorphous 
 with silicon, of sp. gr. u.i. It is very infusible, burns in air below a red heat, 
 dissolves in dilute acids, and does not decompose water. 
 
 The radio-activity of thorium compounds has already been noticed (p. 438). 
 
 GERMANIUM, 66=71.5. 
 
 258. This occurs in argyrodite, a silver ore. It is extracted by fusing the powdered 
 mineral with Na 2 C0 3 and S, extracting with water, neutralising the solution with 
 H 2 S0 4 , filtering from the precipitated S, As 2 S 3 , and Sb 2 S 3 , and saturating with H 2 S, 
 which precipitates white germanic sulphide, GeS 2 . This is roasted to oxide, from 
 which the metal is reduced by heating with H or C. It is a white brittle metal 
 (sp. gr. 5.47), melts about 900 C., and volatilises at higher temperatures ; the 
 fused metal crystallises in octahedra. It is dissolved by H 2 S0 4 , but not by HC1 ; 
 HN0 3 oxidises it to Ge0 2 . 
 
 Germanium stands between silicon and tin in the periodic table (p. 302), but 
 it is more nearly related to tin than to silicon ; its existence was prophesied 
 (ekasilicon) by Mendeleeff previously to its discovery (1885). It is believed to 
 form two classes of salts, corresponding with oxides GeO and Ge0 2 , respectively. 
 The only germanous salt, which is authentically known, however, is the sulphide 
 GeS. Germanic chloride, GeCl 4 , is obtained like stannic chloride and boils at 
 86 C. When Ge is heated in HC1 it yields germanium chloroform, GeHCl 3 , which 
 boils at 72 C. It is doubtful whether GeCl 2 exists. Ge0 2 dissolves in HF and 
 the solution yields double fluorides like K 2 GeF 6 , similar to the silico-fluorides. 
 
 Germanic oxide, Ge0 2 , is white, and sparingly soluble in water, from which it 
 may be crystallised ; it functions as an acid oxide. 
 
 GeS 2 is a white precipitate obtained by adding H 2 S to a solution of Ge0 2 in 
 
LEAD ORES. 
 
 HC1 or H 2 S0 4 . In the absence of acid it is somewhat soluble in water. It is 
 dissolved by alkali sulphides. When reduced by hot H it yields GeS in dark grey 
 lustrous crystals, decomposed by potash into GeSo, which dissolves, and Ge which 
 separates. 
 
 CERIUM, 6 = 139. 
 
 259. This element is now classed with those related to tin, but in many respects 
 it resembles those of the aluminium group. It occurs chiefly in cerite, which is 
 essentially a silicate of the metal containing about 60 per cent, of Ce 2 3 . This 
 oxide, ceria, is obtained for the manufacture of Welsbach mantles (p. 155) from 
 monazite sand, as has been described under thorium. 
 
 The metal is prepared by electrolysing fused cerous chloride Ce 2 Cl 6 , itself obtained 
 by evaporating Ce 2 3 with HC1 and NH 4 C1 and igniting. Cerium is a grey, 
 lustrous, malleable, ductile metal, unchanged by dry air, but becoming iridescent 
 in moist air ; its sp. gr. is 6.7 and it melts about 700 C. It burns in air more 
 easily than magnesium does, and with a brighter light ; it is soluble in dilute acid, 
 and decomposes water slowly. 
 
 Three oxides, cerous oxide. Ce 2 3 , eerie oxide, Ce0 2 , and a peroxide, Ce0 3 , are 
 known. The first is obtained by igniting the oxalate"in hydrogen. It is grey, and 
 rapidly oxidises to the pale yellow Ce0 2 , which is easily reduced again to Ce 2 3 ; 
 thus when it is boiled with HC1 it liberates Cl and dissolves as Ce 2 Cl 6 . The per- 
 oxide is a reddish yellow precipitate formed on adding NH 3 and H 2 2 to a solution 
 of a cerous salt. 
 
 Ce 2 3 is a stronger base than Ce0 2 which, however, has no acid properties. The 
 cerous salts (corresponding with Ce 2 O 3 ) are colourless and more stable than the eerie 
 salts (corresponding with Ce0 2 ), which are yellow or red, and are easily reduced to 
 cerous salts. No eerie chloride is known, but the fluoride, CeF 4 .H 2 0, yielding the 
 double fluoride 2CeF 4 .3KF.2H 2 0, has been obtained. 
 
 LEAD. 
 
 Pb" = 2O5.4 parts by weight. 
 
 260. Lead owes its usefulness in the metallic state chiefly to its softness 
 and fusibility. The former quality allows it to be easily rolled into thin 
 sheets and to be drawn into the form of tubes or pipes ; it is indeed the 
 softest of the metals in common use, and at the same time the least 
 tenacious, so that it can only be drawn with difficulty into thin wire, and 
 is then very easily broken. The ease with which it makes a dark streak 
 upon paper shows how readily minute particles of the metal may be 
 abraded. Its want of elasticity also recommends it for some special 
 uses, as for deadening a shock or preventing a rebound. 
 
 In fusibility it surpasses all the other metals commonly employed in 
 the metallic state, except tin, for it melts at 617 F. (325 C.), and this 
 circumstance, taken in conjunction with its high specific gravity (11.4), 
 particularly adapts it for the manufacture of shot and bullets. For one 
 of its extensive uses, however, as a covering for roofs, it would be better 
 suited if it were lighter and less fusible, for in case of fire in houses so 
 roofed, the fall of the molten lead frequently aggravates the calamity. 
 Its resistance to strong acids is turned to account in manufacturing 
 chemistry. 
 
 With the exception, perhaps, of the ores of iron, none is more abun- 
 dant in this country than the chief ore of lead, galena, a sulphide of 
 lead (PbS). This ore might at the first glance be mistaken for the metal 
 itself, from its high specific gravity (7.5) and metallic lustre. It is found 
 forming extensive veins in Cumberland, Derbyshire, and Cornwall, tra- 
 versing a limestone rock in the first two counties, and a clay slate in the 
 last. Spain also furnishes large supplies of this important ore. Galena 
 
4^0 EXTRACTION OF LEAD. 
 
 presents a beautiful crystalline appearance, being often found in large 
 isolated cubes, which readily cleave or split up in directions parallel to 
 their faces. Blende (sulphide of zinc) and copper pyrites (sulphide of 
 copper and iron) are frequently found in the same vein with galena, and 
 it is usually associated with quartz (silica), heavy spar (barium sulphate), 
 or fluor spar (calcium fluoride). Considerable quantities of sulphide of 
 silver are often present in galena, and in many specimens the sulphides 
 of bismuth and antimony are found. 
 
 Though the sulphide is the most abundant natural combination of lead, 
 it is by no means the only form in which this metal is found. The metal 
 itself is occasionally met with, though in very small quantity, and the 
 carbonate of lead (PbC0 3 ), white lead ore or cerussite, forms an important 
 ore in the United States and in Spain. The sulphate of lead, anglesite 
 (PbS0 4 ), is also found in Australia, and is largely imported into this 
 country to be smelted. 
 
 261. The extraction of lead from galena is effected by one of three 
 methods, the first of which is the oldest, and is still employed in the 
 Flintshire works. 
 
 (i) Advantage is taken of the circumstance that, in the case of many 
 metals, when a combination of the metal with oxygen is raised to a high 
 temperature in contact with a sulphide of the same metal, the oxygen 
 and sulphur unite, and the metal is liberated (self -reduction), thus, 
 PbS + 2 PbO = Pb 3 + SO 2 . Since galena, when heated with free access of 
 air, becomes to a great extent oxidised to PbO, it will be apparent that 
 the necessary mixture of oxide and sulphide can be obtained by roasting 
 the galena for a certain time, namely, until two-thirds of the lead has 
 become oxide. This change cannot be brought about, however, without 
 the simultaneous oxidation of some of the PbS into lead sulphate 
 (PbS0 4 ) ; fortunately, this is of no consequence, since PbS and PbS0 4 
 react with each other at a high temperature, in accordance with the 
 equation, PbS0 4 + PbS = Pb 2 + 2SO 2 . 
 
 It will now be understood that the essential operations in this metal- 
 lurgical process consist in roasting the ore (PbS) in presence of air until 
 a sufficient proportion of it has been oxidised, and in then raising the 
 temperature in order that the mixture of PbS, PbO, and PbS0 4 , pro- 
 duced by the roasting, may react in the sense of the above equations. 
 
 The ore, having been separated by mechanical treatment, as far as possible, from 
 the foreign matters associated with it, is mixed with a small proportion of lime to 
 flux the siliceous matter of the ore, and spread over the hearth of a reverberatory 
 furnace (Fig. 228), the sides of which are considerably inclined towards the centre, 
 so as to form a hollow for the reception of the molten lead. 
 
 During the first or roasting stage of the smelting process the temperature is kept 
 below that at which galena fuses. The ore is stirred from time to time, to expose 
 fresh surfaces to the action of the atmospheric oxygen. When the roasting is 
 sufficiently advanced, some fuel is thrown into the grate, the damper is slightly 
 raised, and the doors of the furnace are closed, so that the charge may be heated to 
 the temperature at which the oxide and sulphate of lead act upon the unaltered 
 sulphide, furnishing metallic lead. 
 
 During this part of the operation the contents of the hearth are constantly raked 
 up towards the fire-bridge, so as to facilitate the separation of the lead, and to 
 cause it to run down into the hollow provided for its reception. It is also found 
 that the separation of the lead from the slags is much assisted by occasionally 
 throwing open the doors to chill the furnace. After about four hours the charge 
 is reduced to a pretty fluid condition, the lead having accumulated at the bottom of 
 the depressed portion of the hearth with the slag above it ; this slag consists chiefly 
 
SMELTING LEAD ORES. 
 
 461 
 
 of the silicates of lime and of oxide of lead, and would have contained a larger nrn 
 portion of the latter if the lime had not been added as a flux at the commencement 
 of the operation. In order still further to reduce the quantity of lead in the SM 
 a few more shovelfuls of lime are now thrown into the hearth, together with 
 little small coal, the latter serving to reduce to the metallic state the oxide of lead 
 displaced by the lime from its combination with the silica. But since silicate of 
 lime is far less fusible than silicate of lead, the effect of this addition of lime is to 
 dry up the slags to a semi-solid mass, and it will now be seen that if the whole of 
 the lime had been added at the commencement of the smelting, the diminished 
 fusibility of the slag would have opposed an obstacle to the separation of the 
 metallic lead. 
 
 During the last hour or so the temperature is very considerably raised, and at the 
 expiration of about six hours, when the greater portion of the lead is thought to 
 have separated, the slag is raked out through one of the doors of the furnace 
 and the melted metal allowed to run out through a tap-hole in front of the 
 lowest portion of the hearth into an iron basin, from which it is ladled into pig- 
 moulds. The rich slags are worked up again with a fresh charge of ore. 
 
 Fig-. 228. Furnace for smelting- lead ores. 
 
 In the smelting of galena a very considerable quantity of lead is! carried off in 
 the form of vapour (lead-fume) ; and in order to condense this, the gases from the 
 furnace are made to pass through flues, the aggregate length of which is sometimes 
 three or four miles, before being allowed to escape up the chimney. When these 
 flues are swept, many tons of lead are recovered in the forms of oxide and 
 sulphide. 
 
 It has lately been asserted that the reactions stated above as being representa- 
 tive of the changes which occur in the Flintshire lead-smelting process, have no 
 real existence. Instead, it is maintained, the greater part of the S is removed 
 directly as S0 2 , leaving a product containing about 3-5 per cent, of S, which is 
 then liquated, when the greater part of the lead separates, much oxygen being at 
 the same time absorbed, and a slag, having the composition PbS.PbO, formed. This 
 must be thickened with lime and removed from the lead to prevent its sulphur from 
 passing into the metal. It is also stated that a volatile compound, PbS.S0 2 , is 
 formed in the furnace, and is the cause of lead fume. 
 
 The treatment of galena in Bessemer converters, whereby the same reactions that 
 occur in the Flintshire furnace could easily be effected, has been suggested. 
 
 (2) Poor lead ores, rich in silica, are roasted until nearly free from 
 sulphur, mixed with coke and flux (iron ore and lime), and smelted in 
 small blast-furnaces ; the lead is thus reduced from its oxide by the 
 coke, and the gangue is fluxed as ferrous and calcium silicates. 
 
 A small blast-furnace for this process is shown in Fig. 229. Air is supplied to the 
 furnace through three blast-pipes (A), and the ore and fuel being charged in at B, 
 the lead runs into a cavity (C) at the bottom of the furnace, whilst the slag flows 
 
462 
 
 THE IMPROVING PROCESS. 
 
 over into a reservoir (D) outside the furnace. The charge is sprinkled with water 
 through the rose (E) fixed just above the opening into the chimney (F), to prevent 
 it from being blown away by the current of air. 
 
 (3) In the third process for smelting lead ores, mostly adopted on 
 the Continent, advantage is taken of the fact that iron will desulphurise 
 galena at a high temperature ; PbS + Fe = Pb + FeS. The galena is 
 mixed with scrap iron (or, what comes to the same thing, iron ore and 
 coke), and charged into a small blast-furnace. 
 
 262. Some varieties of lead, particularly those smelted from Spanish 
 ores, are known as hard lead, their hardness being chiefly due to the 
 presence of antimony ; and since this hardness interferes materially 
 with some of the uses of the metal, such lead is generally subjected to 
 an improving or calcining process, in which the impurities are oxidised 
 and removed, together with a portion of the lead, in the dross.* 
 
 Fig-. 230. 
 
 Fig. 229. 
 
 To effect this, 6 or 8 tons of the hard lead are fused in an iron pot (P, Fig. 230). 
 and transferred to a shallow cast-iron pan (C) measuring about 10 feet by 5. In 
 this pan, which is set in the hearth of a reverberatory furnace, and is about 8 inches 
 deep nearest the grate, and 9 inches at the other end, the lead is kept in fusion by 
 the flame which traverses it from the grate G to the flue F, for a period varying 
 with the degree of impurity, some specimens being found sufficiently soft after a 
 single day's calcination, whilst others must be kept in a state effusion for three or 
 four weeks. The workman judges of the progress of the operation by a peculiar 
 flaky crystalline appearance assumed by a small sample on cooling. When suffi- 
 ciently purified, the metal is run off and cast into pigs. 
 
 At first sight it is not intelligible how antimony should be removed 
 from lead by calcination, since lead is the more easily oxidised metal. 
 
 * The following analyses illustrate the percentage composition of hard lead : 
 
 Pb. Sb. Cu. Fe. 
 
 English 
 Spanish 
 
 99.27 
 95.81 
 
 o-57 
 3-66 
 
 O.I2 
 0.32 
 
 O.O4 
 O.2I 
 
PATTINSON'S DESILVERISING PROCESS. 
 
 4 6 3 
 
 The result must be ascribed to the tendency of antimony to form an 
 acid oxide, Sb 2 O 5 , which combines with the base oxide of lead. The 
 dross (antimonate of lead) formed in this process, when reduced to the 
 metallic state, yields an alloy of lead with 30 or 40 per cent, of antimony, 
 which is much used for casting type furniture for printers. 
 
 263. Extraction of silver from lead. The lead extracted from galena 
 often contains a sufficient quantity of silver to allow of its being pro- 
 fitably extracted. Previously to the year 1829 this was practicable 
 only when the lead contained more than n ounces of silver per ton, for 
 the only process then known for effecting the separation of the two 
 metals was that of cupellation, which necessitates the conversion of the 
 whole of the lead into oxide, which has then to be separated from the 
 
 
 Fig-. 231. Pattinson's desilverisiiig; process. 
 
 silver, and again reduced to the metallic state, thus consuming so large 
 an amount of labour that a considerable yield of silver must be obtained 
 to pay for it. By the simple and ingenious operation known as Pattin- 
 son's desilvering process, a very large amount of the lead can be at once 
 separated in the metallic state with little expenditure of labour, thus 
 leaving the remainder sufficiently rich in the more precious metal to 
 defray the cost of the far more expensive process of cupellation, so that 
 2 or 3 ounces of silver per ton can be extracted with profit. Pattmson 
 founded his process upon the observation that when lead containing a 
 small proportion of silver is melted and allowed to cool, being constantly 
 stirred, a considerable quantity of the lead separates in the form of 
 crystals containing a very minute proportion of silver, almost the whole 
 of this metal being left behind in the portion still remaining liquid. 
 
464 CUPELLATION. 
 
 Eight or ten cast-iron pots, set in brick -work, each capable of holding about 
 6 tons of lead, are placed in a row, with a fire-place underneath each of them 
 (Fig. 231). Suppose that there are ten pots numbered consecutively, that on the 
 extreme left of the workman being No. I, and that on his extreme right No. icx 
 About 6 tons of the lead containing silver are melted in pot No. 5, the metal 
 skimmed, and the fire raked out from beneath so that the pot may gradually cool,, 
 its liquid contents being constantly agitated with a long iron stirrer. As the 
 crystals of lead form, they are well drained in a perforated ladle (about 10 inches 
 wide and 5 inches deep) and transferred to pot No. 4. When about iths of the 
 metals have thus been removed in the crystals, the portion still remaining liquid, 
 which retains the silver, is ladled into pot No. 6, and the pot No. 5, which is now 
 empty, is charged with fresh argentiferous lead to be treated in the same manner. 
 
 When pots Nos. 4 and 6 have received, respectively, a sufficient quantity of the 
 crystals of lead and of the liquid part rich in silver, their contents are subjected to 
 a perfectly similar process, the crystals of lead being always passed to the left, and 
 the rich argentiferous alloy to the right. As the final result of these operations, 
 the pot No. 10, to the extreme right, becomes filled with a rich alloy of lead and 
 silver, sometimes containing 300 ounces of silver to the ton, whilst pot No. I, to 
 the extreme left, contains lead in which there is not more than half an ounce of 
 silver to the ton. This lead is cast into pigs for the market. The ladle used in 
 the above operation is kept hot by a small temper pot containing melted lead. A 
 fulcrum is provided at the edge of each pot, for resting the ladle during the 
 shaking of the crystals to drain off the liquid metal. Any copper present in the 
 lead is also left with the silver in the liquid portion.* 
 
 In Parkes' process for desilvering lead, advantage is taken of the 
 fact that fused lead only dissolves a small proportion of zinc, and that 
 zinc alloys more readily with silver than does lead, so that when zinc 
 (about 2 per cent.) is stirred into molten argentiferous lead, the bulk 
 of it speedily rises to the surface again, bringing with it the silver and 
 some lead. Thus, a dross consisting of these three metals and the 
 oxides of zinc and lead t is obtained. This is distilled with carbon to 
 recover the zinc, and the alloy of lead and silver left in the retort is 
 cupelled. The desilverised lead is freed from zinc by the improving 
 process (p. 462). 
 
 264. In order to extract the silver from the rich alloy, it is subjected 
 to a process of refining, or cupellation, which is founded upon the 
 oxidation suffered by lead when heated in air, and upon the absence of 
 any tendency on the part of silver to combine directly with oxygen, so 
 that by melting the lead and exposing it to a blast of air it may be 
 oxidised, and the oxide carried away by the blast, leaving, eventually, 
 pure silver on the cupel. 
 
 The refinery or cupelling furnace (Fig. 232) in which this operation is performed 
 is a reverberatory furnace, the hearth of which consists of a cupel (C), made by 
 ramming moist powdered bone-ash mixed with a little wood-ash into an oval iron 
 frame about 4 inches deep, and provided with four cross-bars at the bottom, each 
 about 4 inches wide. When this frame has been well filled with bone-ash, part of 
 the latter is scooped out, so as to leave the sides about 2 inches thick at the top 
 and 3 inches at the bottom, the bone-ash being left about i inch thick above the 
 iron cross-bars. 
 
 The cupel, which is about 4 feet long by z\ feet wide, is fixed so that the flame 
 from the grate (Gr) passes across it into the chimney (B), and at one end, the 
 nozzle (N) of a blowing apparatus directs a blast of air over the surface of the 
 contents of the cupel. The latter is carefully dried by a gradually increasing 
 heat, and is then heated to redness ; the alloy of lead and silver, having been pre- 
 viously melted in an iron pot (P) fixed by the side of the furnace, is ladled in 
 
 * The employment of a jet of steam for stirring the bath of lead has much reduced the 
 time and labour required in the above process. This also removes the copper as oxide, and 
 the antimony is carried off in the steam. 
 
 f The addition of a little Al diminishes the amount of oxide in the dross. 
 
CUPELLATION. 
 
 through a gutter until the cupel is nearly filled with it ; a film of oxide soon 
 makes its appearance upon the surface of the lead, and is fused by the high tem- 
 perature. When the blast is directed upon the surface, it blows off this film of 
 oxide, and supplies the oxygen for the formation of another film upon the clean 
 metallic surface thus exposed. A part of the oxide of lead or litharge thus 
 formed is at first absorbed by the porous material of the cupel, but the chief part 
 of it is forced by the blast through a channel cut for the purpose in the opposite 
 end to that at which the blast enters, and is received, as it issues from A, in an 
 iron vessel placed beneath the surface. In proportion as the lead is in this 
 manner removed from the cupel, fresh portions are supplied from the adjoining 
 melting-pot, and the process is continued until about 5 tons of the alloy have 
 been added. 
 
 The cupellation is not continued until the whole of the lead has been removed, 
 but until only 2 or 3 cwts. of that metal are left in combination with the whole of 
 the silver (say 1000 ounces) contained 
 in the 5 tons of alloy. The metal 
 is run through a hole made in the 
 bottom of the cupel, which is then 
 again stopped up, so that a fresh 
 charge may be introduced. The 
 fumes of oxide of lead which are 
 freely evolved during this process are 
 carried off by a hood and chimney 
 (H) situated opposite to the blast of 
 air. 
 
 When three or four charges have 
 been cupelled, so as to yield from 
 3000 to 5000 ounces of silver alloyed 
 with 6 or 8 cwts. of lead, the removal 
 of the latter metal is completed in 
 another cupel, since some of the 
 silver is carried off with the last 
 portions of litharge. The appear- 
 ances indicating the removal of the 
 last portion of lead are very striking ; 
 the surface of the molten metal, 
 which has been hitherto tarnished, 
 becomes iridescent as the film of 
 oxide of lead thins off, and after- 
 wards resplendently bright, and when 
 the cake of refined silver is allowed 
 to cool, it throws up from its surface 
 a variety of fantastic arborescent 
 excrescences, caused by the escape of 
 oxygen which has been mechanically 
 absorbed by the fused silver, and is given off during solidification. 
 
 The litharge obtained from the cupelling furnaces is reduced to the metallic 
 state by mixing it with small coal, and heating it in a furnace similar to that em- 
 ployed in smelting galena. 
 
 265. On the small scale, lead may easily be extracted from galena by mixing 300 
 grains with 450 grains of dried sodium carbonate and 20 grains of charcoal, intro- 
 ducing the mixture into a crucible, and placing in it two tenpenny nails, heads 
 downwards. The crucible is covered and heated in a moderate fire for about 
 half an hour. The remainder of the nails is carefully removed from the liquid 
 mass, which is then allowed to cool, the crucible broken, and the lead extracted 
 and weighed. In this process the sulphur of the galena is removed, partly by the 
 sodium of the carbonate and partly by the iron of the nails, the excess of sodium 
 carbonate serving to flux any silica with which the galena may be mixed. 
 
 Or 300 grains of galena may be mixed with 600 grains of sodium carbonate and 
 200 grains of nitre (which oxidises the sulphur), and fused for half an hour. 
 
 To ascertain if it contains silver, the button of lead is placed on a small bone 
 ash cupel (Fig. 233), and heated in a muffle (Fig. 235), until the whole of the lea 
 is oxidised and absorbed into the bone-ash of the cupel, leaving the minute glo 
 of silver. 
 
 2 G 
 
 Fig-. 232. Cupellation furnace. 
 
4 66 
 
 APPLICATIONS OF LEAD. 
 
 A gas muffle furnace, also capable of being used as a crucible furnace, is 
 .shown in Fig. 234. 
 
 Small globules of lead may be conveniently cupelled on charcoal before the 
 blowpipe, by pressing some bone-ash into a cavity scooped in the charcoal, 
 placing the lead upon its surface, and exposing it to a good oxidising flame 
 (p. 156) as long as it decreases in size. If any copper be present, the bone-ash 
 will show a green stain after cooling. Pure lead gives a yellow stain. 
 
 Fig. 234. Muffle and crucible furnace. 
 
 Fig. 235. Muffle furnace. 
 
 266. Uses of lead. The employment of this metal for roofing, &c., 
 has been already noticed. Its fusibility adapts it for casting type for 
 printing, but it would be far too soft for this purpose ; accordingly, 
 type-metal consists of an alloy of 4 parts of lead with i of antimony. A 
 similar alloy is used for the bullets contained in shrapnel shells, since 
 bullets of soft lead would be liable to be jambed together, and would not 
 scatter so well on the explosion of the shell. On the other hand, rifle 
 bullets are made of very pure soft lead, in order that they may more 
 easily take the grooves of the rifle. 
 
 Small shot are made of lead to which about 40 Ibs. of arsenic per ton 
 has been added. The arsenic dissolves in the lead, hardening it and 
 causing it to form spherical drops when chilled. The fluid metal is 
 poured through a sort of colander fixed at the top of a lofty tower (or 
 at the mouth of a deserted coal shaft), and the minute drops into which 
 the lead is thus divided are allowed to fall into a vessel of water, after 
 having been chilled by the air in their descent. They are afterwards 
 sorted, and polished in revolving barrels containing plumbago. If too 
 little arsenic is employed, the shot are elongated or pyriform ; and if 
 the due proportion has been exceeded, their form is flattened or 
 lenticular. 
 
 Composition tube (" compo-pipe ") used by plumbers is made of lead 
 hardened by a little antimony. /Solder has been already noticed (p. 452). 
 
 Leaden vessels are much used in manufacturing chemistry, on account 
 
CORROSION OF LEAD. 467 
 
 of the resistance of this metal to the action of acids. Neither concen- 
 trated sulphuric,* hydrochloric, nitric, or hydrofluoric acid will attack 
 lead at the ordinary temperature. The best solvent for the metal is 
 nitric acid of sp. gr. 1.2, since the nitrate of lead, being insoluble in an 
 acid of greater strength, would be deposited upon the metal, which it 
 would protect from further action. 
 
 Lead is easily corroded in situations where it is brought in contact 
 with air highly charged with carbonic acid gas, when it absorbs oxygen, 
 forming oxide of lead, which combines with C0 2 and water to produce 
 the basic carbonate of lead, PbC0 3 .Pb(OH) 2 . The lead of old coffins is 
 often found converted into a white earthy-looking brittle mass of basic 
 carbonate, with a very thin film of metallic lead inside it. The basic 
 carbonate is formed as a crystalline silky-looking precipitate when a 
 piece of clean lead is left in distilled water for a few minutes. 
 
 When lead is exposed to the joint action of air and of the acetic acid 
 contained in beer, wine, cider, &c., it becomes converted into acetate of 
 lead or sugar of lead, which is very poisonous. Hence the accidents 
 arising from the reprehensible practice of sweetening cider by keeping 
 it in contact with lead, and from the accidental presence, in beer and 
 wine bottles, of shot which have been employed in cleansing them. The 
 action of water upon leaden cisterns has been already noticed. Contact 
 with air and sea- water soon converts lead into oxide and chloride. 
 
 267. Oxides of lead. Five compounds of lead with oxygen are 
 known Pb 2 0, PbO, Pb 2 O 3 , Pb 3 4 , Pb0 2 . 
 
 Lead suboxide, or plumbous oxide, Pb 2 0, is obtained by heating lead 
 oxalate; 2PbC 2 4 = Pb 2 O + CO + 3C0 2 . "it is a black powder which is 
 decomposed by acids, yielding plumbic salts and metallic lead. 
 
 The bright surface of lead soon tarnishes when exposed to the air, 
 becoming coated with a dark film, which is believed to consist of sub- 
 oxide of lead. In a very finely divided state, lead takes fire when thrown 
 into the air, and is converted into oxide of lead. 
 
 The lead pyrophorus, for exhibiting the spontaneous combustion of lead, is pre- 
 pared by placing some lead tartrate in a glass tube 
 closed at one end (Fig. 236), drawing the tube out to a 
 narrow neck near the open end, and holding it nearly 
 horizontally, whilst the lead tartrate is heated with a gas 
 or spirit flame as long as any fumes are evolved ; the 
 neck is then fused with a blowpipe flame and drawn off. 
 Lead tartrate (PbC 4 H 4 6 ), when heated, leaves a mix- 
 ture of metallic lead with charcoal, which prevents the 
 lead from fusing into a compact mass. This mixture 
 may be preserved unchanged in the tube for any length 
 of time ; but when the neck is broken off and the con- 
 tents scattered into the air, they inflame at once, pro- 
 ducing thick fumes of oxide of lead. Lead tartrate is Fig. 236. 
 prepared by adding solution of lead acetate to a solution 
 
 of tartaric acid constantly stirred, as long as a precipitate is formed. The precipi- 
 tated lead tartrate is collected upon a filter, washed several times, and dnec 
 gentle heat. 
 
 Lead monoxide, or protoxide of lead, PbO, is sometimes found in 
 nature, crystallised in rhombic octahedra, and is prepared on a large 
 scale by heating lead in air. When the metal is only moderately heated, 
 the oxide forms a yellow powder (sp. gr. 9.2), which is known in 
 
 * It has been found that pure lead is slowly acted on by sulphuric acid, hydrogen being: 
 -evolved. The presence of a little antimony almost entirely prevents the action. 
 
468 RED LEAD. 
 
 commerce as massicot, but at a higher temperature the oxide melts, and 
 on cooling forms a brownish scaly mass, which is called litharge (\i6os, 
 stone ; apyvpos, silver). The litharge of commerce often has a red 
 colour, caused by the presence of some red oxide of lead ; from i to 3, 
 per cent, of finely divided metallic lead may also sometimes be found 
 in it. When heated to dull redness, litharge assumes a dark brown 
 colour, and becomes yellow on cooling. At a bright red heat it fuses,. 
 and readily attacks clay crucibles, forming a fusible silicate of lead, and 
 soon perforating the sides. When boiled with distilled water, PbO is 
 dissolved in small quantity, yielding a solution which is decidedly 
 alkaline, and becomes turbid when exposed to the air, absorbing 
 carbonic acid gas, and depositing lead carbonate. The presence of a small 
 quantity of saline matter in the water hinders the dissolution of the 
 oxide ; but organic matter, and especially sugar, favours it. Oxide of 
 lead is a powerful base, and has a strong tendency to form basic salts. 
 Hot solutions of potash and soda dissolve it readily, and deposit it in 
 pink crystals on cooling; according to some, such solutions contain 
 sodium or potassium plumbite, K 2 Pb0 2 . 
 
 Litharge, from its easy combination with silica at a high temperature, 
 is much used in the manufacture of glass, and in glazing earthenware. 
 The assayer also employs it as a flux. A mixture of litharge with lime 
 is sometimes applied to the hair,- which it dyes of a purplish-black 
 colour, due to the formation of lead sulphide from the sulphur existing 
 in hair. Dhil mastic, used by builders in repairing stone, is a mixture 
 of i part of massicot with 10 parts of brick-dust, and enough linseed oil 
 to form a paste ; it sets into a very hard mass, which is probably due 
 partly to the formation of lead silicate, and partly to the drying of the 
 linseed oil by oxidation favoured by the oxide of lead. 
 
 Lead sesquioxide, Pb 2 3 , is obtained as a yellow precipitate by dis- 
 solving PbO in caustic soda and adding sodium hypochlorite. Cold 
 HC1 dissolves it to a yellow liquid, which slowly evolves chlorine. 
 Nitric acid partly dissolves it, leaving a brown residue of Pb0 2 . Heat 
 converts it into PbO. 
 
 Eed lead, or minium, Pb 3 4 , is prepared by heating massicot in air to 
 about 300 0, when it absorbs oxygen, and becomes converted into red 
 lead. The massicot for this purpose is prepared by heating lead in a 
 reverberatory furnace to a temperature insufficient to fuse the oxide 
 which is formed, and rejecting the first portions which contain iron,, 
 cobalt and other metals more easily oxidisable than lead, as well as the 
 last, which contain copper and silver, less easily oxidised than lead. 
 The intermediate product is ground to a fine powder and suspended in 
 water ; the coarser particles are thus separated from the finer, which 
 are dried, and heated on iron trays placed in a reverberatory furnace, 
 till the requisite colour has been obtained. Minium is largely used in 
 the manufacture of glass, whence it is necessary that it should be free 
 from the oxides of iron, copper, cobalt, &c., which would colour the 
 glass. It is also employed as a common red mineral colour, and in the 
 manufacture of lucifer matches. Red lead becomes dark brown when 
 heated, and regains its original colour when cooled. 
 
 When minium is treated with dilute nitric acid, lead nitrate, Pb(N0 3 ) 2 , 
 is obtained in solution, and peroxide of lead (Pb0 2 ) is left as a brown 
 powder, showing that minium is probably a compound of the oxide and 
 
LEAD PEROXIDE. 469 
 
 peroxide of lead. The minium obtained by heating massicot in air till no 
 further increase of weight is obtained, has the composition 2PbO.PbCX 
 or Pb 3 4 , which would appear to represent pure minium ; commercial 
 minium, however, has more frequently a composition corresponding with 
 3PbO.Pb0 2 , but when this is treated with potash, PbO is dissolved out, 
 and 2PbO.Pb0 2 remains. Minium evolves oxygen at a red heat, 
 becoming PbO; hence the necessity for keeping the temperature 
 about 300 C. during its preparation. Hydrochloric acid, heated with 
 minium, evolves chlorine by reaction with the Pb0 2 contained in it, and 
 leaves the white sparingly soluble PbCl 2 formed from the PbO contained 
 in the Pb 3 4 . A mixture of dilute nitric acid and sugar, or some other 
 oxidisable body, will dissolve minium entirely as Pb(N0 3 ) 2 . Glacial 
 acetic acid dissolves minium, without evolution of gas, to a colourless 
 liquid, which deposits Pb0 2 when exposed to air, or evaporated, or 
 diluted ; a hot saturated solution deposits colourless crystals of lead 
 tetr acetate Pb(C 2 H 3 2 ) 4 on cooling. 
 
 Peroxide, or dioxide, or puce oxide of lead, Pb0 2 , is found in the mineral 
 kingdom as heavy lead ore, forming black, lustrous, six-sided prisms. It 
 may be prepared from red lead by boiling it, in fine powder, with nitric 
 acid, diluted with five measures of water, washing and drying. The 
 dioxide of lead easily imparts oxygen to other substances ; sulphur, 
 mixed with six times its weight of Pb0 2 , may be ignited by friction ; 
 hence this oxide is a common ingredient in lucifer-match compositions. 
 Its oxidising property is frequently turned to account in the laboratory ; 
 for example, in absor bing sulphur dioxide from gaseous mixtures by con- 
 verting it into sulphate of lead ; PbO 2 + S0 2 = PbS0 4 . Dioxide of lead 
 is not dissolved by dilute acids, and has no basic properties, although 
 certain salts of the type PbX 4 are known ; it is even sometimes called 
 plumbic anhydride, for it acts upon potassium hydroxide, yielding 
 potassium plumbate (K 2 Pb0 3 .3H 2 0.), which has been crystallised from 
 an alkaline solution, but is decomposed by pure water.* Lead dioxide 
 evolves 01 from HC1 when heated, and gives, at first, a brown solution 
 (containing Pb01 4 ) which yields a brown precipitate with ammonia, but 
 if the solution be boiled till all the 01 is expelled, it becomes colourless 
 Pb01 2 , and gives a white precipitate with ammonia. PbO is converted 
 into Pb0 2 by ozone and by hydrogen peroxide. 
 
 Lead peroxide is almost the only available material for making the " active 
 mass" for electric accumulators or storage or secondary cells. When two lead 
 plates, one coated with Pb0 2 , are immersed in dilute H 2 S0 4 an electrical pressure 
 of about 2 volts is created, and if the current be used, both plates become coated 
 with PbS0 4 before the energy ceases to flow. The ultimate change may be ex- 
 pressed thus : Pb + Pb0. 2 + 2H 2 S0 4 = 2PbS0 4 + 2H 2 0. If, when this stage has been 
 reached, current be passed into the cell in the direction opposite to that of the 
 current which has been used, the PbS0 4 on the one plate will be oxidised to H 2 S0 4 
 and Pb0 2 , while that on the other will be reduced to Pb and H 2 S0 4 . Hence the 
 cell will again be ready to deliver current, which, however, will be smaller m 
 amount than that used to charge the cell by the inevitable loss due to resistance, etc. 
 It will be seen that during discharge the free H 2 S0 4 disappears from the cell, 
 while during charging it is liberated again ; thus by watching the indications of a 
 
 * Advantage is taken of the tendency for PbO to absorb O when heated with an alkali in 
 Kassner's oxygen process. A mixture of CaO and FbO is heated in air, CaPbO 3 being pro- 
 duced. This is heated (below 100 C.) in CO 2 , when it becomes CaCO 3 and PbO 2 ; th 
 is then made to part with half its oxygen by a red heat, after which the CaCO 3 is canst 
 by being heated in a current of steam. The mixture of CaO and PbO thus regenerated 
 put through the same cycle of operations. 
 
470 WHITE LEAD. 
 
 hydrometer immersed in the liquid, the progress of either operation may be 
 judged. 
 
 Lead hydroxide, Pb(OH) 2 , has not been obtained, but Pb(OH) 2 .PbO is formed as 
 a white precipitate when air and water, free from C0 2 , attack lead, hydrogen 
 peroxide being formed at the same time nearly in the proportion represented by the 
 equation Pb + 2H 2 + 2 = Pb(OH) 2 + H 2 2 (of. footnote, p. 63). The same 
 hydroxide is precipitated by alkalies from solutions of lead salts. It becomes PbO 
 when heated to 145 C. The compound Pb(OH) 2 .2PbO crystallises in octahedra 
 from a solution of basic lead acetate mixed with ammonia. 
 
 Lead nitrate, Pb(ISr0 3 )2, crystallises in white octahedra from a solu- 
 tion of lead or its oxide in dilute nitric acid. It dissolves easily in water, 
 but not in nitric acid or in alcohol. It is employed in dyeing and 
 calico-printing. Several sparingly soluble basic lead nitrates are known. 
 When digested with water and metallic lead, the nitrate gives a 
 yellow solution, which deposits vellow scaly crystals of the compound 
 Pb.OH.N0 3 .Pb.OH.N0 2 . 
 
 268. Lead carbonate, PbC0 3 , is found in nature, as cerussite, in 
 transparent rhombic crystals isomorphous with aragonite. It may be 
 precipitated by mixing solutions of ammonium carbonate and lead 
 acetate, or by passing C0 2 , into a weak solution of lead acetate. Potas- 
 sium and sodium carbonates precipitate basic lead carbonates. 
 
 White lead, or ceruse, is a basic carbonate, or combination of lead car- 
 bonate, PbC0 3 , with variable proportions of lead hydroxide, Pb(OH) 2 . 
 This substance is a constant product of the corrosive action of air and 
 water upon the metal. Its formation is, of course, very much encouraged 
 by the presence of organic matters in a state of decay, which evolve OO 2 . 
 
 White lead is manufactured on the large scale by several processes, 
 which depend, however, upon the same principle, namely, the formation 
 of a basic lead salt, which is subsequently decomposed by C0 2 . The 
 chemistry of the commonest process may be stated as follows ; lead 
 oxide, PbO, with acetic acid, HC 2 H 3 2 , yields lead acetate Pb(0 2 H 3 O 2 ) 2 , 
 conveniently written PbA 2 . This combines with lead hydroxide, form- 
 ing basic lead acetate, PbA 2 .2Pb(OH) 2 . This is decomposed by carbonic 
 acid gas, yielding basic lead carbonate and normal lead acetate ; 
 3 [PbA 2 .2Pb(OH) 2 ] + C0 2 = 2 [2Pb00 3 .Pb(OH) 2 ] + sPbA 2 + 4 H 2 0. The 
 normal acetate, in contact with lead, atmospheric oxygen, and water 
 is converted into the basic acetate; PbA 2 + Pb 2 + O 2 + 2H 2 = 
 PbA 2 .2Pb(OH) 2 ; this is again acted on by C0 2 , and the process is con- 
 tinuous. To effect these changes, lead is exposed to the simultaneous 
 action of air, water vapour, carbon dioxide, and acetic acid vapour. 
 
 In the oldest process (still used to make the best pigment), commonly known as 
 the Dutch process, metallic lead, in the form of square gratings cast from the 
 purest lead, is placed over earthen pots containing a small quantity of common 
 vinegar ; a number of these pots being built up into heaps, together with alternate 
 layers of dung or spent tan, the heaps are entirely covered up with the same 
 material. The metal is thus exposed to conditions most favourable to its oxida- 
 tion, viz., a very warm and moist atmosphere produced by the fermentation of the 
 organic matters composing the heap, and the presence of a large quantity of acid 
 vapour generated from the acetic acid of the vinegar. The lead is therefore soon 
 converted into oxide, a portion of which unites with the acetic acid to form the 
 tribasic acetate of lead, which is then decomposed by the carbonic acid gas, 
 evolved from the fermenting dung or tan, yielding carbonate of lead, which 
 combines with another portion of the oxide of lead and water to form the white 
 lead. The neutral acetate of lead left after the removal of the oxide of lead from 
 the tribasic acetate, is now ready to take up an additional quantity of the oxide, 
 
LEAD POISONING. 
 
 and the process is thus continued until, in the course of a few weeks, the lead 
 has become coated with a very thick crust of white lead ; the heaps are then 
 destroyed, the crust detached, washed to remove adhering acetate of lead, ground 
 to a paste with water, and dried. Eolled lead is not so easily converted as cast 
 lead. 
 
 Other processes for making white lead exist, but for a description of them larger 
 works on technical Chemistry must be consulted. 
 
 The usual composition of white lead is expressed by the formula 
 Pb(OH) 2 .2PbC0 3 , though other basic carbonates of lead are often mixed 
 with it. 
 
 White lead being very poisonous, its use by painters and others is 
 generally attended with symptoms of lead poisoning, arising in many 
 cases, probably, from neglecting to wash the hands before eating, the 
 effect of lead being cumulative, so that minute doses may show their 
 combined action after many days. Diluted sulphuric acid and solutions 
 of the sulphates of magnesia and the alkalies are sometimes taken 
 internally to counteract its effect ; they are of doubtful efficacy. 
 
 All paints containing lead, and cards glazed with white lead, are 
 blackened even by minute quantities of sulphuretted hydrogen, from 
 the production of black sulphide of lead. If the blackened surface 
 remain exposed to the light and air. it is bleached again, the sulphide 
 of lead (PbS) being oxidised and converted into white sulphate of 
 lead (PbSO 4 ), but this does not happen in the dark. A little sulphide 
 of lead or powdered charcoal is sometimes mixed with commercial white 
 lead to give it a bluish tint. It is probable that white lead owes a 
 part of its value in oil-painting to the formation of a lead-salt with the 
 fatty acid. Its "covering" power is due to its amorphous character, 
 which renders it completely opaque. Pure white lead is easily soluble 
 in acetic and dilute nitric acids. 
 
 Lead sulphate, PbSO 4 , is found naturally as anglesite or lead vitriol, 
 in transparent rhombic prisms (sp. gr. 6.3) isomorphous with celestine 
 and heavy spar, and is obtained as a heavy granular precipitate when 
 sulphuric acid is added to a salt of lead. Stirring much promotes the 
 precipitation. Lead sulphate is very slightly soluble in water, and even 
 less so in dilute sulphuric acid and in alcohol. It is soluble in strong 
 sulphuric and hydrochloric acids, in sodium chloride and thiosulphate, 
 and in ammonium acetate and tartrate. At a red heat it fuses without 
 decomposition. 
 
 An acid lead sulphate, PbH 2 (S0 4 ) 2 .Aq, has been crystallised. The minerals 
 lanarkite "and leadhillite are compounds of sulphate and carbonate of lead, 
 PbS0 4 (PbC0 3 ) 2 .H 2 0. The chromates of lead have been already noticed. 
 
 Lead phosphate, Pb 3 (P0 4 ) 2 , and arsenate, associated with lead chloride and ( 
 bonate, are found in certain minerals. . 
 
 269. Lead chloride (PbCl 2 = 2 vols.) forms the mineral termed horn lead. It 
 one of the few chlorides which are not readily soluble in water, and is Pfecip 
 when hydrochloric acid or a soluble chloride is added to a solution of lead. tio\\\vg 
 water dissolves about -^thof its weight of lead chloride, and deposits it in beau 
 shining white needles on cooling. Cold water dissolves abont rfoth of its weigni 
 It fuses easily (510 C.) and solidifies again to a horny mass, like fusee 
 chloride. It is converted into vapour at a high temperature. Lead chloride ais- 
 solves easily in strong HC1, and is precipitated by water. The solution oi leaa 
 chloride in water is precipitated by adding strong HC1 ; hence, a di 
 solution, when cold, retains very little lead chloride. Like silver c 
 chloride is soluble in sodium thiosulphate. . , . . 
 
 The lead oxychloride (PbCl 2 .PbO) is formed when lead chloride is he i ti-d m air, 
 and occurs in nature as matlocldte. Pattimon's oseychlonde, PbCl.OH, is 
 
47 2 LEAD SULPHIDES. 
 
 employed as a substitute for white lead in painting, being prepared for this purpose 
 by decomposing finely powdered galena with concentrated hydrochloric acid 
 (PbS + 2HCl:=PbCl 2 + H 2 S), washing the resulting lead chloride with cold water, 
 dissolving it in hot water, and adding lime-water, which precipitates the oxy- 
 chloride ; 2PbCl 2 + Ca(OH) 2 = 2PbCl(OH) + CaCl 2 . 
 
 Cassel yellow ( Paris yellow, patent yellow, mineral yellow) is another oxychloride 
 of lead (PbCl 2 .7PbO), prepared by heating a mixture of litharge and sal-ammoniac. 
 It has a fine golden-yellow colour, is easily fused, and crystallises in octahedra on 
 cooling. Turner's yellow, PbCl 2 .3PbO. is made by allowing a strong solution of 
 NaCl to react with PbO. The mineral mendipite is an oxychloride of lead 
 (PbCl 2 .2PbO) which occurs in colourless prismatic crystals. 
 
 Lead tetracliloride, PbCl 4 , probably exists in the brown solution of Pb0 2 in cold 
 HC1, which gives a brown precipitate of Pb0 2 when diluted. A solution made by 
 suspending PbCl 2 in water and passing chlorine maybe supposed to contain chloro- 
 plumbic acid, H 2 PbCl 6 , for with salts of rubidium and ammonium it yields yellow 
 crystalline precipitates of Rb 2 PbCl 6 and (NH 4 ) 2 PbCl 6 respectively. When the 
 latter is added to strong H 2 S0 4 a heavy oil (sp. gr. 3. 18) separates ; this is PbCl 4 . 
 
 Lead chlorobromide (PbBrCl) has been found in crystals resembling lead 
 chloride among the furnace-products in smelting lead carbonate ore. 
 
 Lead iodide (PbI 2 ) is obtained as a bright yellow precipitate on mixing solutions 
 of nitrate or acetate of lead and potassium iodide. If it be allowed to settle, the 
 liquid poured off, and the precipitate dissolved in boiling water (with one or two 
 drops of hydrochloric acid), it forms a colourless solution, depositing golden 
 scales as it cools. Hydriodic acid converts metallic lead into PbI 2 . Like mercuric 
 iodide, PbI 2 dissolves in the alkali iodides. When heated, it becomes red, then 
 black, fuses, und becomes a yellow crystalline mass on cooling. It is decomposed 
 by light with liberation of iodine. 
 
 270. Sulphides of lead. Lead sulphide, PbS, is found as galena 
 (p. 459). It fuses when strongly heated, and vaporises in a current of 
 gas, condensing in small crystals. When heated in air, it is converted 
 into a mixture of PbO and PbS0 4 . Strong HC1 dissolves it when 
 heated, evolving H 2 S. Nitric acid dissolves it partly as lead nitrate, 
 leaving some undissolved lead sulphate mixed with sulphur. Lead 
 sulphide is obtained as a black precipitate when hydrosulphuric acid or 
 a soluble sulphide acts upon a solution containing lead, even in minute 
 proportion. 
 
 A persulpldde of lead, the composition of which has not been ascertained, is 
 formed as a red precipitate when a solution of lead is mixed with a solution of an 
 alkaline sulphide saturated with sulphur (or with solution of ammonium sulphide 
 which has been kept till it has acquired a red colour). It is probably PbS 5 . 
 
 Lead chlorosulphide (PbS.PbCl 2 ) is obtained as a bright red precipitate when 
 hydrosulphuric acid is added in small quantity to a solution of lead chloride in 
 hydrochloric acid, or when freshly precipitated PbS is heated with solution of 
 PbCl 2 . It is decomposed by hot water, 
 
 Lead selenide (PbSe) occurs associated with the sulphide in some lead ores ; it 
 much resembles galena, and has the same crystalline form. 
 
 Tin group of metals. This group comprises Ti, Zr,Co,Th,Ge, Sn and 
 Pb. These metals belong to the group of elements which includes C and 
 Si, the higher salt-forming oxide being R0 2 , which in most cases behaves 
 as a feeble acid oxide, resembling C0 2 and Si0 2 . Their tetrafluorides 
 have a tendency to combine with the alkali fluorides to form compounds 
 which recall the salts of hydrofluosilicic acid, and their tetrachlorides form 
 similar double salts with alkali chlorides (e.#.,2NH 4 Cl.Pb01 4 ,2KCl.SnCl 4 ), 
 which resemble the double chlorides formed by metals of the platinum 
 group. 
 
 THALLIUM, Tl = 202.6. 
 
 271. The discovery of this metal in 1861 was one of the first results of the 
 application of the new method of testing by observation of coloured lines in the 
 
THALLIUM. 473 
 
 spectrum of a flame, described at p. 328. Crookes was examining the spectrum 
 obtained by holding in the flame of a Bunsen burner the deposit formed in the 
 flues of a sulphuric acid chamber, in which pyrites was employed as the source of 
 sulphur. A green line appeared in the spectrum, which a less acute and practised 
 observer might have mistaken for one of the lines due to barium (see Fig. 213), 
 with which it nearly coincides in position ; but the line was much brighter than 
 that of barium, and on instituting a searching analysis of the deposit, a metal was 
 obtained which did not agree in properties with any hitherto described, and was 
 named thallium from 8a\\6s, a young shoot, in allusion to the vernal green colour 
 of its spectrum line. It has since been detected in several mineral waters ; but 
 the pyrites obtained from Spain and Belgium appears to be its best source. From 
 the flue-dust of the sulphuric acid chambers the metal is extracted by a simple 
 process, but large quantities must be operated on to obtain any considerable 
 amount. The deposit is treated with boiling water, and the solution mixed with 
 much strong hydrochloric acid, which precipitates the thallium as thallous 
 -chloride (T1C1) ; this is converted into acid thallous sulphate (T1HS0 4 ) by treat- 
 ment with sulphuric acid, and this salt having been purified by recrystallisation, 
 is decomposed by zinc, which precipitates metallic thallium in a spongy form, 
 fusible into a compact mass in an atmosphere of coal gas. 
 
 Thallium is now classed with the metals of the aluminium group (p. 393), 
 although it differs considerably from these in the stability of its lower oxide T1 2 0. 
 
 In external characters thallium is very similar to lead; (sp. gr. n.8.; m. p. 
 590 C.; volatile below 800 C.) ; but it tarnishes much more rapidly when ex- 
 posed to air, and the streak which it makes on paper soon becomes yellowish, 
 being converted into thallous oxide, T1 2 0. If a tarnished piece of the metal be 
 allowed to touch the tongue, a strongly alkaline taste is perceived, for the thallous 
 oxide (T1 2 0) is very soluble in water, so that the tarnished metal becomes bright 
 when immersed in water. If granulated thallium be exposed to moist air in a 
 warm place, it absorbs oxygen and C0 2 . On boiling with water and filtering, the 
 alkaline solution deposits white needles of thallous carbonate (T1 2 C0 3 ), and afterwards 
 yellow needles of thallous hydroxide (T10H). The ready solubility of the oxide 
 seemed to require thallium to be classed among the alkali-metals, a view which 
 was encouraged by the circumstance that its specific heat proved it to be mona- 
 tonric, like potassium and sodium. But thallium appears to be more nearly related 
 to another monatomic metal, silver, by the sparing solubility of its chloride and 
 the insolubility of its sulphide. The circumstance that it may be kept unaltered 
 in water, and may be precipitated from its salts by zinc, at once removes it from 
 the group of alkali-metals. The ready solubility of its oxide in water is only an 
 exaggeration of the behaviour of the oxides of lead and silver, both of which 
 dissolve slightly in water, yielding alkaline solutions. Moreover, its hydroxide is 
 far less stable than those of potassium and sodium, for it becomes T1 2 when dried 
 in vacuo over oil of vitriol. Dilute H 9 S0 4 acts on thallium as on zinc, evolving 
 hydrogen. It is not much affected by "dilute HN0 3 in the cold ; even on heating, 
 the action is slow unless the acid is very weak. On cooling, the solution becomes 
 filled with needles of thallous nitrate. Thallium burns in oxygen with a beautiful 
 green flame, and the thallous chlorate has been recommended for the manufacture 
 of green fires in place of barium chlorate (page 186). 
 
 Thallous sulphate, T1.,S0 4 , is obtained by dissolving thallium in sulphuric acid 
 and evaporating; the" acid sulphate, T1HS0 4 , first produced, being decomposed 
 by further heating. T1 2 S0 4 is isomorphous with K 2 S0 4 , and it foTmsthallout <ilnni. 
 TlAl(S0 4 ) 2 .i2Aq, crystallising like potash-alum,. Thallous chloride, T1C1, resernbh 
 lead chloride, being precipitated by adding HC1 to a solution of a thallous salt, 
 and being dissolved by boiling water, from which it crystallises on cooling. 
 Thallous iodide, Til, is obtained as a yellow precipitate on adding potassi 
 iodide to a thallous salt ; when dried and heated, it fuses to a red liquid, wnicf 
 remains red after solidifying, and changes, after a time, to yellow. When spre 
 on paper, the yellow iodide becomes red when heated, and remains red on cooling, 
 but becomes yellow when rubbed with a hard body. Thallous sulpindc Il 2 fc, 
 is deposited as a brownish-black precipitate oh adding ammonium sulphide to 
 thallous salt. Thallic oxide, T1 2 3 , is obtained by adding sodium hypocnloi 
 thallous chloride mixed with excess of sodium carbonate. It is a dark r< 
 stance, which evolves oxygen and leaves thallous oxide when heated. It is also 
 a basic oxide, its sulphate having the composition Tl 2 (S0 4 ) 3 .H 2 O.6Aq. ^J*r*~ 
 chloride, T1C1 3 , is formed by heating thallium in excess of chlorine ; it i 
 
474 COPPEK ORES. 
 
 and crystallisable. By passing Cl through a solution of KOH in which T1 2 3 is 
 suspended, a liquid is obtained which gives a violet precipitate with barium 
 salts ; this precipitate is alleged to contain T10 2 . 
 
 Thallous silicate can take the place of alkali silicate in glass, and thallium glass,. 
 made from thallous carbonate, red lead and sand is similar to flint-glass, but has a 
 higher sp. gr. (5.6) and refractive index. It is also more fusible and harder than 
 ordinary flint-glass. 
 
 Salts of thallium, like those of lead, are poisonus. 
 
 COPPER. 
 
 Cu" = 63.i parts by weight. 
 
 272. Metallic copper is met with in nature more abundantly than 
 metallic iron, though the compounds of the latter metal are of more 
 frequent occurrence than those of the former.* A very important vein, 
 of metallic copper, of excellent quality, occurs near Lake Superior, in 
 North America, from which 6000 tons were extracted in 1858. Metallic 
 copper is also sometimes found in Cornwall, and copper sand, containing 
 metallic copper and quartz, is imported from Chili. 
 
 The most important English ore of copper is copper pyrites, which is 
 a double sulphide, containing copper, iron, and sulphur in the propor- 
 tions indicated by the formula Cu 2 S.Fe 2 S 3 . It may be known by its 
 beautiful brass-yellow colour and metallic lustre. Copper pyrites is 
 found in Cornwall and Devonshire, and is generally associated with 
 arsenical pyrites (FeS 2 .FeAs 2 ), tin-stone (Sn0 2 ), quartz, fluor spar, and 
 clay. A very attractive variety of copper pyrites is called variegated 
 copper ore, or peacock copper, in allusion to its rainbow colours ; its 
 simplest formula is Cu 3 FeS 3 . This variety is found in Cornwall and 
 Killarney. 
 
 Copper glance (Cu 2 S) is another Cornish ore of copper, of a dark grey 
 colour and feeble metallic lustre. 
 
 Grey copper ore, also abundant in Cornwall, is essentially a compound 
 of the sulphides of copper and iron with those of antimony and arsenic, 
 but it often contains silver, lead, zinc, and sometimes mercury. 
 
 Malachite, a basic carbonate of copper, is imported from Australia 
 (Burra-Burra), and is also found abundantly in Siberia. Green mala- 
 chite, the most beautifully veined ornamental variety, has the composi- 
 tion CuCO 3 .Cu(OH) 2 , and blue malachite is 2 CuC0 3 .Cu(OH) 2 . 
 
 Red copper ore (Cu 2 0) is found in West Cornwall, and the black oxide 
 (CuO) is abundant in the north of Chili. 
 
 273. The seat of English copper smelting is at Swansea, which is 
 situated in convenient proximity to the bituminous coal employed in the 
 furnaces. The chemical process by which copper is extracted from the 
 ore includes three distinct operations (i) the roasting, to expel the 
 arsenic and part of the sulphur, and to convert the sulphide of iron into 
 oxide of iron, the copper remaining as sulphide ; (2) the fusing with 
 silica, to remove the oxide of iron as silicate, and to obtain the copper in 
 combination with sulphur only ; and (3) the roasting of this combination 
 
 * Copper is not at all frequently found in animals or vegetables ; but Church has made 
 the remarkable observation that the red colouring-matter (turacine) of the feathers of the 
 plantain-eater (touraco) contains as much as 7 per cent, of copper. It has also been found 
 in the blood of the cuttle-fish, as luemocyanin, which is blue in its oxidised condition in the 
 arterial blood, and colourless in the venous blood. 
 
COPPER SMELT 
 
 475 
 
 of copper with sulphur, in order to expel the latter and obtain metallic 
 copper by the process of self -reduction, Cu 2 S + 2CuO = Cu 4 + S0 2 . 
 
 The details of the smelting process appear somewhat complicated, 
 because it is divided into several stages to allow of the introduction of 
 the different varieties of ore to be treated. Thus, the first roasting 
 process is unnecessary for the oxides and carbonates of copper, and 
 the fusion with silica is not needed for those ores which are free from 
 iron, so that they may be introduced at a later stage in the operations. 
 Owing to the fact that rich ores of copper and copper precipitates are 
 now much worked, the omission of the earlier processes is frequently 
 practised, the ore being directly smelted to white metal (fine metal) as 
 described below. 
 
 The processes of the older practice could be reduced in number if the original ore 
 were a pure copper pyrites, but since the ores as worked always contain a larger 
 proportion of iron and sulphur than copper pyrites does, the first two operations 
 are designed to produce a material (coarse metal) which shall be, in effect, a pure 
 copper pyrites. 
 
 (i) Calcining or roasting the ore to expel arsenic and part of the sulphur. The 
 ores having been sorted, and broken into small pieces, are mixed so as to contain 
 from 8 to 10 per cent, of copper, 
 and roasted, in quantities of about 
 three tons, for at least twelve hours, 
 on the spacious hearth (H, Fig. 
 237) of a reverberatory furnace 
 
 (Fig. 109, p. 132) at a temperature 
 insufficient for fusion, being occa- 
 sionally stirred to expose them 
 freely to the action of the air, 
 which is admitted into the furnace 
 
 through an opening (0) in the *' 2 3' 
 
 side of the hearth upon which 
 
 the ore is spread. The oxygen of the air converts a part of the sulphur into 
 and the bulk of the As into As 4 6 , which passes off in the form of vapour. A part 
 of the sulphide of iron is converted into ferrous sulphate (FeS0 4 ) by absorb] 
 oxygen at an early stage of the process, and this sulphate is afterwards decompose 
 at a higher temperature, evolving SO and S0 3 , and leaving oxide of iron. A por 
 tion of the sulphide of copper is also" con verted into oxide of copper during tne 
 roasting, so that the roasted ore consists essentially of a mixture of oxide 
 phide of copper with oxide and sulphide of iron. Since the sulphide of iron is 
 easily oxidised than sulphide of copper, the greater part of the J 
 unaltered in the roasted ore. , , 
 
 During the roasting of copper ore dense white fumes escape from the ' i rna 
 This copper smoke, as it is termed, contains As 4 6 , S0 2 , S0 3 , and I 
 being derived from the fluor spar associated with the ore ; if allowed 
 these fumes seriously contaminate the air in the neighbourhood, so 
 usually condensed in flues and rain-chambers by showers of water. 
 
476 COPPER SMELTING. 
 
 (2) Fusion for coarse metal to remove the oxide of iron by dissolving it with silica, 
 at a high temperature. The roasted ore is now mixed with metal slag from 
 process 4, and with ores containing silica and oxides of copper, but no sulphur ; the 
 mixture is introduced into the orejurnace (Fig. 238) (the hearth of which is made 
 narrower than that of the roasting furnace, since a higher temperature is required) 
 and fused for five hours at a higher temperature than that employed in the previous 
 operation. In this process fluor spar is sometimes added in order to increase 
 the fluidity of the slag. 
 
 The oxide of copper attacks the sulphide of iron still contained in the roasted 
 ore, with formation of sulphide of copper and oxide of iron, but since there is more 
 sulphide of iron present than the oxide of copper can decompose, the excess of sul- 
 phide of iron combines with the sulphide of copper to form a fusible compound, 
 which separates from the slag, and collects in the form of a matte or regulus of 
 coarse metal, in a cavity (C) on the hearth of the furnace : it is run out into a tank 
 of water (T) in order to granulate it, so that it may be better fitted to undergo the 
 next operation. 
 
 The oxide of iron combines with the silica contained in the charge, to form a 
 fusible ferrous silicate (ore-furnace slag), which is raked out into moulds of sand, 
 and cast into blocks used for rough building purposes in the neighbourhood. 
 
 The composition of the coarse metal corresponds pretty closely with the 
 formula CuFeS 2 . It contains from 33 to 35 per cent, of copper ; whilst the 
 original ore, before roasting, is usually sorted so that it may contain about 8.5 per 
 cent. 
 
 The ore-furnace slag is approximately represented by the formula FeO.Si0 2 ; 
 but it contains a minute proportion of copper, as is shown by the green efflores- 
 cence on the walls in which it is used around Swansea. Fragments of quartz are 
 seen disseminated through this slag. 
 
 (3) Calcination of the coarse metal to convert the greater part of the sulphide, of iron 
 into oxide. The granulated coarse metal is roasted at a moderate temperature 
 for twenty-four hours, as in the first operation, so that the oxygen of the air may 
 decompose the sulphide of iron, removing the sulphur as sulphuric acid, and 
 leaving the iron in the form of oxide. 
 
 (4) Fusion J "or white metal to remove the whole of the iron as silicate. The roasted 
 coarse metal is mixed with roaster and refinery slags from processes 5 and 6, and 
 with ores containing carbonates and oxides of copper, and fused for six hours, as 
 in the second operation. Any sulphide of iron which was left unchanged in the 
 roasting is now converted into oxide of iron by the oxide of copper, the latter 
 metal taking the sulphur. The whole of the oxide of iron combines with the 
 silica to form a fusible slag, the composition of which is approximately represented 
 by the formula 3Fe0.2Si0 2 . 
 
 The matte QIC regulus of white metal, which collects beneath the slag, is nearly 
 pure cuprous sulphide (Cu 2 S). The white metal is run into sand-moulds 
 and cast into ingots. The tin and other foreign metals usually collect in 
 the lower part of the ingot, so that, for making best selected copper, the 
 upper part is broken off and worked separately, the inferior copper obtained 
 from the lower part of the ingot being termed tile-copper. The ingots of 
 white metal often contain beautiful tufts of metallic copper in the form of 
 copper moss. 
 
 The slag separated from the white metal (jnetal slag) is much more fluid than 
 the ore-furnace slag, and contains so much silicate of copper that it is preserved 
 for use in the melting for coarse metal. 
 
 (5) Roasting the ivhite metal to remove the sulphur and obtain blister copper. The 
 ingots of white metal (to the amount of about 3 tons) are placed upon the hearth 
 of a reverberatory furnace, and heated for four hours to a temperature just below 
 fusion, so that they may be oxidised at the surface, the sulphur passing off as 
 sulphurous acid gas, and the copper being converted into oxide. During this 
 roasting the greater part of the arsenic, generally present in the fine metal, is 
 expelled as As 4 6 . The temperature is then raised, so that the charge may be 
 completely fused, after which it is lowered again till the twelfth hour. The 
 oxide of copper now acts upon the sulphide of copper to form metallic copper and 
 sulphurous acid gas, which escapes, with violent ebullition, from the melted mass ; 
 Cu 2 S + 2CuO = S0 2 + Cu 4 . When this ebullition ceases, the temperature is again 
 raised so as to cause the complete separation of the copper from the slag, and the 
 metal is run out into moulds of sand. Its name of blister copper is derived from 
 
REFINING COPPEE. 
 
 477 
 
 the appearance caused by the escape of the last portions of S0 2 from the metal 
 when solidifying in the mould. 
 
 The slag (roaster slag) is formed in this operation by the combination of a 
 part of the oxide of copper with silica derived from the sand adhering to 
 the ingots and from the hearth of the furnace. The slag also contains the 
 silicates of iron and of other metals, such as tin and lead, which might have 
 been contained in the white metal. This slag is used again in the melting for 
 white metal. 
 
 (6) Refining to remove foreign metals. This process consists in slowly fusing 
 7 or 8 tons of the blister copper in a reverberatory furnace, so that the air 
 passing through the furnace may remove any remaining sulphur as sulphurous 
 acid gas, and may oxidise the small quantities of iron, tin, lead, &c., present 
 in the metal. Of course, a large proportion of the copper is oxidised at the 
 same time, and the cuprous oxide, together with the oxides of the foreign 
 metals, combine with the silica (from the hearth or from adhering sand), to 
 form a slag which collects upon the surface of the melted copper.* A portion of 
 the cuprous oxide is dissolved by the metallic copper, rendering it brittle or dry 
 copper. 
 
 (7) Toughening or poling to remove a part of the oxygen and bring the copper to 
 tough-pitch. After about twenty hours the slag is skimmed from the metal, a 
 quantity of anthracite is thrown over the surface to prevent further oxidation, and 
 the metal is poled i.e.. stirred with a pole of young wood until a small sample, 
 removed for examination, presents a peculiar silky fracture, indicating it to be at 
 tough-pitch, when it is cast into ingots. 
 
 Products obtained in smelting Ores of Copper. 
 
 In 100 parts. 
 
 Ore. 
 
 Roasted 
 Ore. 
 
 Coarse 
 Metal. 
 
 Roasted 
 Coarse 
 Metal. 
 
 White 
 Metal. 
 
 Blister 
 Copper. 
 
 Refined 
 Copper. 
 
 Tough- 
 pitch 
 Copper. 
 
 
 
 CO 
 
 (2) 
 
 (3) 
 
 (4) 
 
 ft)' 
 
 (6) 
 
 (7) 
 
 Copper 
 
 8.2 
 
 8.6 
 
 33-7 
 
 33-7 
 
 77-4 
 
 98.0 
 
 99-4 
 
 99.6 
 
 Iron . 
 
 17.9 
 
 17.6 
 
 33-6 
 
 33-6 
 
 0.7 
 
 -5 
 
 trace 
 
 trace 
 
 Sulphur 
 
 19.9 
 
 12.5 
 
 29.2 
 
 13.0 
 
 21.0 
 
 0.2 
 
 trace 
 
 trace 
 
 Oxygen 
 
 I.O 
 
 4-5 
 
 
 II.O 
 
 
 
 0.4 
 
 0.03 
 
 Silica . 
 
 34-3 
 
 34-3 
 
 
 
 
 
 
 
 Slags. 
 
 Ore 
 Furnace. 
 
 
 Metal. 
 
 Roaster. 
 
 Refinery. 
 
 
 
 (2) 
 
 
 (4) 
 
 fc) 
 
 (6) 
 
 
 Oxide of iron (FeO) . 
 
 54-o 
 
 
 50.0 
 
 28.0 
 
 3- 1 
 
 
 Suboxide of copper (Cu 2 0) . 
 
 0-5 
 
 
 0.9 
 
 16.9 
 
 39-2 
 
 
 Silica 
 
 45- 
 
 
 33-8 
 
 47-5 
 
 47-4 
 
 
 The chemical change during the poling appears to consist in the removal of the 
 oxygen contained in the cuprous oxide present in the metal, by the reducing 
 action of the combustible gases disengaged from the wood. The presence of a 
 small proportion of cuprous oxide is said to confer greater toughness upon the 
 metal, so that if the poling be continued until the whole of the oxygen i, 
 removed, over-poled copper of lower tenacity is obtained. On the other hand, 
 the brittleness of under-poled copper is due to the presence of cuprous oxide 
 in too large proportion. Tough-cahe copper is that which has been poled to the 
 proper extent. 
 
 The addition of about 0.07 per cent, of phosphorus, as copper phosphide, be 
 
 * When the removal of arsenic, which forms an acid oxide, is specially desired, it is 
 advantageous to line the hearth with a basic material, such as that used in tl 
 processes. 
 
478 WET EXTRACTION OF COPPER. 
 
 the final poling, shortens the process and increases the density of the metal. The 
 copper phosphide is made by dissolving about 7 per cent of phosphorus in melted 
 copper. 
 
 When the copper is intended for rolling, a small quantity (not exceeding ^ per 
 cent.) of lead is generally added to it before it is ladled into the ingot moulds. 
 Apparently the oxide of lead formed by the action of the air assists in removing 
 some of the impurities in the form of slag (scorijication) . 
 
 The chemical changes which take place during the above processes will be more 
 clearly understood after inspecting the table on page 477, which exhibits the 
 composition of the products obtained at different stages of the process, these being 
 distinguished by the same numerals as were employed in the above description. 
 
 Blue metal is the term applied to the regulus of white metal (from process 4) 
 when it still contains a considerable proportion of sulphide of iron, in con- 
 sequence of a deficient supply of oxide of copper in the furnace. Pimple metal is 
 obtained in the same operation when the oxide of copper is in excess, so that a 
 portion of the copper is reduced, as in process 5, with evolution of sulphurous 
 acid gas, which produces the pimply appearance in escaping. The reduced copper 
 gives a reddish colour to the pimple copper. Coarse, or Uacli copper, is a similar 
 intermediate stage between white metal and blistered copper. Tile copper is 
 that extracted from the bottoms of the ingots of white metal, when the tops 
 have been detached for making best selected copper. Rosette or rose copper is 
 obtained by running water upon the toughened metal, so as to enable the metal 
 to be removed in films. Anglesea or Mona copper is a very tough copper, reduced 
 by metallic iron from the Hue water of the copper mines, which contains sulphate 
 of copper. 
 
 The application of the Bessemer converter to the refining of blister copper has 
 been attempted, but the impurities to be oxidised are incapable of giving, by their 
 combustion, a temperature sufficiently high to keep the copper in fusion. The 
 converter is, however, employed on the Continent for the conversion of fused 
 white metal into blister copper, there being sufficient sulphur in the white metal 
 to yield a temperature high enough to maintain the fusion of the copper. 
 
 For the extraction of copper from poor ores (3 per cent. Cu) a wet 
 method is generally adopted. This is rendered economically possible by 
 the fact that when moist copper sulphide is exposed to the air* it 
 becomes oxidised to copper sulphate, which may be dissolved in water. 
 The recovery of the copper from the solution is effected by the intro- 
 duction of pig-iron, when this metal takes the place of the copper 
 which is precipitated, CuS0 4 + Fe = FeS0 4 + Cu. The copper precipitate 
 thus obtained is melted and refined. Electrolytic deposition of the 
 copper from the solution is also practised. 
 
 Two other methods of dissolving the copper sulphide from the ore are employed. 
 In the one. the ore is treated with a solution of a ferric salt containing common 
 salt. The former converts the Cu 2 S of the ore into Cu 2 Cl 2 , which is dissolved by 
 the solution of salt; Cu 2 S + Fe 2 Cl6 = 2FeCl 2 +Cu 2 Cl. 2 +S. The dissolved copper is 
 then precipitated by iron. In the second method (applied to the spent pyrites of 
 the vitriol works, p. 226) the ore is submitted to a chlorinating roasting that is to 
 say, it is ground, mixed with NaCl and roasted ; the copper sulphide is thus 
 converted, first into sulphate by roasting, and then into chloride by double 
 decomposition with the salt. The copper chloride is leached out and the copper 
 is precipitated by iron. 
 
 The crude blister copper or precipitate copper obtained by the above 
 processes is now largely refined by electrolysis. For this purpose the 
 metal is cast into plates which are suspended in a bath of copper sul- 
 phate solution, acid with H 2 SO 4 , and are made the anodes, the cathodes 
 being thin sheets of pure copper. When a current (0.2 volt pressure) 
 is passed through the solution from a dynamo, the anodes dissolve and 
 the copper is deposited on the cathodes. 
 
 * The ore is exposed in heaps, kept constantly moist. 
 
IMPURITIES IN COPPER. 
 
 The copper refined in this manner is almost chemically pure, but 
 requires remelting before being hammered or rolled, on account of the 
 crystalline condition in which it is deposited. In this process the gold, 
 silver, and other metals (except iron, which passes into solution), which 
 may be present in the blister copper, remain in the tanks in the form 
 of a fine mud. 
 
 274. For the purpose of illustration, copper may be extracted from copper 
 pyrites on the small scale in the following manner : 
 
 200 grains of the powdered ore are mixed with an equal weight of dried borax, 
 and fused in a covered earthen crucible (of about 8 oz. capacity), at a full red 
 heat for about half an hour. The earthy matters associated with the ore are 
 dissolved by the borax, and the pure copper pyrites collects at the bottom of the 
 crucible. The contents of the latter are poured into an iron mould (scorifying 
 mould, Fig. 239), and when the mass has set, it is dipped into water. The semi- 
 mettalic button is then easily detached from the slag by a gentle blow ; it is 
 weighed, finely powdered in an iron mortar, and introduced into an earthen 
 crucible, which is placed obliquely 
 over a dull fire, so that it may not 
 become hot enough to fuse the ore, 
 which should be stirred occasionally 
 with an iron rod to promote the 
 oxidation of the sulphur by the air. 
 When the odour of S0 2 is no longer 
 perceptible, the crucible is placed in a 
 Fletcher's injector furnace (Fig. 225), 
 and exposed for a few minutes to a Fig. 239. 
 
 bright red heat, in order to decompose 
 
 the sulphates of iron and copper. When no more white fumes of S0 3 are perceived, 
 the crucible is lifted from the furnace, held over the iron mortar, and the roasted 
 ore quickly scraped out of it with a steel spatula. This mixture of the oxides of 
 copper and iron is reduced to a fine powder, mixed with 600 grains of dried 
 carbonate of soda and 60 grains of powdered charcoal, returned to the same 
 crucible, covered with 200 grains of dried borax, and again heated in the furnace 
 for twenty minutes. The crucible is then allowed to cool, and carefully broken 
 to extract the button of metallic copper, which is weighed to ascertain the 
 amount contained in the original ore. 
 
 275. Effect of impurities upon the quality of copper. The information 
 possessed by chemists upon this subject is still very limited. It has been 
 already mentioned that the presence of a small proportion of cuprous 
 oxide in commercial copper is found to increase its toughness. It is 
 believed that copper, perfectly free from metallic impurities, is not im- 
 proved in quality by the presence of the oxide, but that this substance 
 has the effect of counteracting the red-shortness (see p. 408) of com- 
 mercial copper, caused by the presence of foreign metals. 
 
 Sulphur, even in minute proportion, appears seriously to injure the 
 malleability of copper. Arsenic is almost invariably present in copper, 
 very frequently amounting to o.i per cent., and does not appear to 
 exercise any injurious influence in this proportion; indeed, its presence 
 is stated to increase the malleability and tenacity of the metal. Phos- 
 phorus is not usually found in commercial copper. When purposely added 
 in quantity varying from 0.12 to 0.5 per cent., it increases the hardness 
 and tenacity of the copper, though rendering it somewhat red-short. 
 
 Tin, in minute proportion, is also said to increase the toughness of 
 copper, though any considerable proportion renders it brittle. Anti- 
 mony is a very objectionable impurity, and is by no means uncommon 
 in samples of copper. Nickel is believed to harden copper in which it 
 occurs. Bismuth and silver are very generally found in marketable 
 
480 PROPERTIES OF COPPER. 
 
 copper, but their effect upon its quality has not been clearly deter- 
 mined. All impurities appear to affect the malleability and tenacity 
 of copper more perceptibly at high than at low temperatures. 
 
 The conducting power of copper for electricity is affected in an extra- 
 ordinary degree by the presence of impurities. Thus, if the conducting 
 power of chemically pure copper be represented by 100, that of the very 
 pure native copper from Lake Superior has been found to be 93, that of 
 the copper extracted from the malachite of the Burra Burra mines in 
 South Australia was 89, whilst that of Spanish copper, remarkable for 
 containing much arsenic, was only 14. 
 
 Copper can be obtained in octahedral crystals. When copper sul- 
 phate is heated with a very strong solution of sugar, crystalline copper 
 is deposited. 
 
 276. PROPERTIES OF COPPER. The most prominent character which 
 confers upon copper so high a rank among the useful metals is its malle- 
 ability, which allows it to be readily fashioned under the hammer, and 
 to be beaten or rolled into thin sheets ; among the metals in ordinary 
 use, only gold and silver exceed copper in malleability, and the com- 
 parative scarcity of those metals leads to the application of copper for 
 most purposes where great malleability is requisite. 
 
 Although, in tenacity or strength, copper ranks high among metals y 
 it is still very far inferior to iron, for a copper wire of Yfrth inch in 
 diameter will support only 468 Ibs., while a similar iron wire will carry 
 705 Ibs. without breaking ; and, in consequence of its inferior tenacity, 
 copper is less ductile than iron, and does not admit of being so readily 
 drawn into exceedingly thin wires. 
 
 The comparative ease with which copper may be fused allows it to 
 be cast much more readily than iron ; for it will be remembered that the 
 latter metal can be liquefied only by the highest attainable furnace heat, 
 whereas copper melts at 1057 C.,a temperature generally spoken of as- 
 a bright red heat. 
 
 As one of the most sonorous of metals, copper has been, from time 
 immemorial, employed in the construction of bells and musical instru- 
 ments. Its high conductivity for electricity is turned to account in 
 telegraphic communication, its conducting power being almost equal 
 to that of silver, which is the best of electric conductors. In conduc- 
 tivity for heat, copper is surpassed only by silver and gold. 
 
 Copper is not so hard as iron, and is somewhat heavier, the specific 
 gravity of cast copper being 8.92, and that of hammered or drawn 
 copper 8.95. 
 
 The resistance of copper to the chemical action of moist air gives it a> 
 great advantage over iron for many uses, and the circumstance that it 
 does not decompose water in presence of dilute sulphuric acid enables it 
 to be employed as the negative plate in galvanic couples. 
 
 Nitric acid is the best solvent for copper, but the presence of nitrous 
 acid seems to be necessary for the attack of the metal (see p. 146). 
 Hydrochloric acid attacks it in presence of oxidising agents. 
 
 277. When copper is placed in a solution of salt in water, no percep- 
 tible action occurs ; but in the course of time, if the air be allowed 
 access, it becomes covered with a green coating of oxychloride of copper 
 (CuCl 2 .3Cu0.4H 2 O), the action probably consisting, first, in the conver- 
 sion of the copper into oxide by the air, and afterwards in the decom- 
 
NEED FOR CLEANLINESS IN COOKING UTENSILS. 481 
 
 position of the oxide by the sodium chloride ; 4CuO + 2NaCl -f H,0 = 
 CuCL,.3CuO + 2NaOH. The surface of the copper is thus corroded, 
 and in the case of a copper-bottomed ship, the action of sea-water not 
 only occasions a great waste of copper, but roughens the surface of the 
 sheathing, and affords points of attachment to barnacles, &c., which 
 injure the speed of the vessel. Many attempts have been made to 
 obviate this inconvenience. Zinc has been fastened here and there to 
 the outside of the copper, placing the latter in an electro-negative 
 condition ; the copper has been coated with various compositions, but 
 with very indifferent success. Muntz metal, or yellow sheathing, or 
 malleable brass, an alloy of 3 parts of copper and 2 parts of zinc, has 
 been employed with some advantage in place of copper, for it is very 
 much cheaper and somewhat less easily corroded ; but the difficulty is by 
 no means overcome. Copper containing about o. 5 per cent, of phosphorus 
 is said to be corroded by sea- water much less easily than is pure copper. 
 
 278. The use of copper for culinary vessels has occasionally led to 
 serious consequences, from the poisonous nature of its compounds, and 
 from ignorance of the conditions under which these compounds are 
 formed. A perfectly clean surface of metallic copper is not affected by 
 any of the substances employed in the preparation of food, but if the 
 metal has been allowed to remain exposed to the action of the air, it 
 becomes covered with a film of oxide of copper, and this subsequently 
 combines with water and carbonic acid gas derived from the air to 
 produce a basic carbonate of copper,* which, becoming dissolved or 
 mixed with the food prepared in these vessels, confers upon it a 
 poisonous character. This danger may be avoided by the use of vessels 
 which are perfectly clean and bright, but even from these certain 
 articles of food may become contaminated with copper, for this metal 
 is more likely to be oxidised by the air when in contact with acids 
 (vinegar, juices of fruits, &c.), or with fatty matters, or even with 
 common salt; and if oxide of copper be once formed, it will be readily 
 dissolved by such substances. Hence it is usual to coat the interior of 
 copper vessels with tin, which is able to resist the action of the air, 
 even in the presence of acids and saline matters. 
 
 279. Alloys of copper. Copper forms a greater number of useful 
 alloys than any other metal. Those of copper with tin (gun-metal 
 and bronze) have been already noticed (p. 452). With from one- 
 third to one-half its weight of zinc, copper forms brass, much harder 
 than copper, and capable of being hammered into thin leaves as a sub- 
 stitute for gold. The most important alloys of which copper is a 
 predominant constituent are the following : 
 
 Brass 64 copper, 36 zinc (sp. gr. 8.3). 
 
 Muntz metal 60 to 64 copper, 40 to 36 zinc (sp. gr. 8.2). 
 
 German silver 61 copper, 19.5 zinc, 19.5 nickel. 
 
 Aich or Gedge's metal 60 copper, 38.2 zinc, 1.8 iron. 
 
 Sterro-metal 55 copper, 42.4 zinc, 2.6 iron. 
 
 Bell metal 78 copper, 22 tin. 
 
 Speculum metal 66.6 copper, 33.4 tin. 
 
 Bronze 85 copper, 10 tin, 5 zinc. 
 
 Gun-metal 90.5 copper, 9.5 tin (sp. gr. 8.5). 
 
 Bronze coinage 95 copper, I zinc, 4 tin. 
 
 Aluminium bronze 90 copper, 10 aluminium. 
 
 * Often erroneously called verdigris, which is really a basic acetate of copper. 
 
 2 H 
 
482 ALLOYS OF COPPEK. 
 
 Brass is made by melting copper in a crucible, and adding rather more 
 than half its weight of zinc. An alloy containing 3 2 per cent, of copper 
 and 68 per cent, of zinc would correspond with the formula Zn 2 Cu ; thus 
 ordinary brass may be regarded as a solidified solution of this compound 
 in copper. A small quantity of tin is added to brass intended for 
 door-plates, which renders the engraving much easier. When it has to 
 be turned or filed, about 2 per cent, of lead is usually added to it, in 
 order to prevent it from adhering to the tools employed. Brass cannot 
 be melted without losing a portion of its zinc in the form of vapour. 
 When exposed to frequent vibration (as in the suspending chains of 
 chandeliers), it suffers an alteration in structure and becomes extremely 
 brittle. The solder used by braziers consists of equal weights of copper 
 and zinc. In order to prevent ornamental brass-work from being tar- 
 nished by the action of air, it is either lacquered or bronzed. Lacquering 
 consists simply in varnishing the brass with a solution of shellac in spirit, 
 coloured with dragon's blood. Bronzing is effected by applying a solution 
 of arsenic or mercury, or platinum, to the surface of the brass. By the 
 action of arsenious oxide dissolved in hydrochloric acid, upon brass, the 
 latter acquires a coating composed of arsenic and copper, which imparts 
 a bronzed appearance, the zinc being dissolved in place of the arsenic, 
 which combines with the copper at the surface. A mixture of corrosive 
 sublimate (mercuric chloride HgCl 2 ) and acetic acid is also sometimes 
 employed, when the mercury is displaced by the zinc, and precipitated 
 upon the surface of the brass, with which it forms a bronze-like amalgam. 
 For bronzing brass instruments, such as theodolites, levels, &c., a solution 
 of chloride of platinum is employed, the zinc of the brass precipitating 
 a very durable film of metallic platinum upon its surface (PtCl 4 + Zn 2 = 
 Pt + 2ZnCl 2 ). 
 
 Aicli metal is a kind of brass containing iron, and has been employed for cannon, 
 on account of its great strength. At a red heat it is very malleable. 
 
 Sterro-ntetal (crre/3p6s, strong) is another variety of brass containing iron and 
 tin, said to have been discovered accidentally in making brass with the alloy of 
 zinc and iron obtained during the process of making galvanised iron (page 377) . 
 It possesses great strength and elasticity, and is used by engineers for the pumps 
 of hydraulic presses. 
 
 Aluminium bronze has been already noticed. 
 
 A very hard white alloy of 77 parts of Zn, 17 of Sn, and 6 of Cu, has been 
 employed for the bearings of the driving-wheels of locomotives. 
 
 Other bearing alloys consist of copper, tin, lead alloys (e.g., Cu 76.8, Sn 8.0, Pb 
 15.0, P 0.2), and of lead, tin antimony, zinc and copper alloys (e.g., white metals, 
 such as Pb 40, Sn 45.5, Sb 13, Cu 1.5). 
 
 Iron and steel are coated with a closely adherent film of copper, by placing 
 them in contact with metallic zinc in an alkaline solution of oxide of copper, 
 prepared by mixing sulphate of copper with tartrate of potash and soda, and 
 caustic soda. The copper is thus precipitated upon the iron by slow voltaic 
 action, the zinc being the attacked metal. By adding a solution of stannate of 
 soda to the alkaline copper solution, a deposit of bronze may be obtained. 
 
 280. Oxides of copper. Two oxides of copper are well known in 
 the separate state, viz., the suboxide, Cu 2 O, and the oxide, CuO. 
 Another oxide, Cu 4 0, has been obtained in a hydrated state, and there 
 is some evidence of the existence of an acid oxide, Cu0 2 . 
 
 The black oxide of copper (cupric oxide), CuO, is employed by the 
 chemist in the ultimate analysis of organic substances by combustion, 
 being prepared for this purpose by acting upon copper with nitric 
 acid to convert it into cupric nitrate (p. 92), and heating this to 
 
CUPROUS OXIDE. 483 
 
 dull redness in a rough vessel made of sheet copper, when it leaves 
 the black oxide (sp. gr. 6.3) ; Cu(N0 3 ) 2 = 2 N0 2 + + CuO. At a higher 
 temperature the oxide fuses into a very hard mass ; it evolves very little 
 oxygen when strongly heated. Oxide of copper absorbs water easily 
 from the air, but it is not dissolved by water ; acids, however, dissolve it, 
 forming the salts of copper, whence the use of oil of vitriol and nitric 
 acid for cleansing the tarnished surface of copper ; a blackened coin, 
 for example, immersed in strong nitric acid, and thoroughly washed \ 
 becomes as bright as when freshly coined. Silica dissolves oxide of 
 copper at a high temperature, forming cupric silicate, which is taken 
 advantage of in producing a fine green colour in glass. 
 
 Red oxide or suboxide of copper (cuprous oxide), Cu 9 0, is found crys- 
 tallised in regular octahedra, and is formed when copper is heated in 
 air, that portion of the copper-scale which is in contact with the air 
 becoming CuO, while that in contact with the metal is Cu 2 0. It is 
 made by heating a mixture of 5 parts of the black oxide with 4 parts 
 of copper filings in a closed crucible. It may also be prepared by boil- 
 ing a solution of cupric sulphate with a solution containing sodium 
 sulphite and sodium carbonate in equal quantities, when the cuprous 
 oxide is precipitated as a reddish-yellow powder, which should be 
 washed, by decantation, with boiled water 
 
 2CuS0 4 + 2Na 2 C0 3 + Na 2 S0 3 = Cu 2 + S^a^ + 2C0 2 . 
 Cu 2 is precipitated in minute octahedral' crystals when solution of 
 CuS0 4 mixed with glucose is boiled with excess of potash. 
 
 Cuprous oxide is a feeble base, but its salts are not easily obtained 
 by direct action of acids, for these generally decompose it into metallic 
 copper and cupric oxide, yielding cupric salts. In the moist state it is 
 slowly oxidised by the air. Ammonia dissolves cuprous oxide, forming 
 a solution which is perfectly colourless until it is allowed to come into 
 contact with air, when it assumes a fine blue colour, becoming converted 
 into an ammoniacal solution of cupric oxide. If the blue solution be 
 placed in a stoppered bottle (quite filled with it) with a strip of clean 
 copper, it will gradually become colourless, the cupric oxide being again 
 reduced to cuprous oxide, a portion of the copper being dissolved. 
 When copper filings are shaken with ammonia in a bottle of air, the 
 same blue solution is obtained (compare p. 86). If the blue solution be 
 poured into a large quantity of water, a light blue precipitate of cupric 
 hydroxide is obtained. The ammoniacal solution of cupric oxide has the 
 unusual property of dissolving paper, cotton, tow, and other varieties of 
 cellulose, this substance being reprecipitated from the solution on adding 
 an acid. 
 
 Cuprous oxide, added to glass, imparts to it a fine red colour, which 
 is turned to account by the glass-maker. 
 
 Quadrant o.ride of copper, Cu 4 0, has been obtained in combination with water, 
 by the action of stannous chloride and potash upon a cupric salt. 
 
 " Cuprom hydride, Cu 2 H 2 , is precipitated when cupric sulphate is heated with 
 hypophosphorous acid ; or a strong solution of cupric sulphate may be strongly 
 acidified with dilute sulphuric acid, solution of sodium hypophosphite added, and 
 heated till a brown precipitate forms ; this is the hydride, which must not be 
 further heated, as it is decomposed into its elements at 60 C. HC1 dissolves it 
 easily, with brisk effervescence from escape of H, and formation of a colourless 
 solution of cuprous chloride, Cu 2 H 2 +2HCl:=Cu2Cl2 + 2H 2 . 
 
 Cuprous hydrate, 4di 2 O.H 2 0, is obtained as a yellow precipitate when a solution 
 
484 COPPER SULPHATE. 
 
 of a cuprous salt is added to excess of KOH. If air be excluded, it may be dried 
 at 100 C. without decomposition. Air oxidises it to cupric hydrate. With NH 3 
 it behaves like cuprous oxide. 
 
 Cupric hydroxide, Cu(OH) 2 , is obtained as a blue precipitate when potash or 
 soda is added to a cupric salt. When boiled in the liquid, it becomes black CuO, 
 but if it be allowed to dry over sulphuric acid, it may be heated to 100 C. with- 
 out decomposition. Its solubility in ammonia and the properties of the solution 
 have been noticed above. In the presence of tartaric acid, sugar, and many other 
 organic substances, cupric hydroxide dissolves in caustic potash and soda, form- 
 ing dark blue solutions. The paint known as blue rerditer is cupric hydroxide 
 obtained by decomposing cupric nitrate with calcium hydroxide. 
 
 Cupric acid is believed to be formed when metallic copper is fused with nitre 
 and caustic potash, and when Cu(OH) a is digested with H 2 2 . The mass from 
 the former reaction yields a blue solution containing K 2 CuO 4 in water, which 
 is very easily decomposed with evolution of oxygen and precipitation of cupric 
 oxide. By adding KOH and Br to a solution containing copper a black precipitate, 
 believed to be Cu0 2 , is formed even in very dilute solutions. The existence of an 
 unstable oxide of copper, containing more than one atom of oxygen, is also rendered 
 probable by the circumstance that oxide of copper acts like manganese dioxide 
 in facilitating the disengagement of oxygen from potassium chlorate by heat 
 (page 41). 
 
 Cuprous nitride, Cu 6 N 2 . is formed by passing ammonia over precipitated CuO at 
 250 C. It is a dark green powder which decomposes at a high temperature, 
 evolving heat. 
 
 Cupric nit rate, Cu(N0 3 ) 2 .3Aq, crystallises in blue prisms from a solution of copper 
 in nitric acid. It is deliquescent and soluble in water and alcohol. When heated 
 to 65 C., it becomes a green baalc nitrate, Cu(N0 3 ) 2 .3Cu(OH) 2 . Cupric nitrate is 
 used as an oxidising-agent in dyeing and calico-printing. Cupric ammonio-nitrate, 
 Cu(N0 3 ) 2 .4NH 3 , is deposited in dark blue crystals from a mixture of cupric nitrate 
 with excess of ammonia. 
 
 281. Cupric sulphate. The beautiful prismatic crystals known as 
 blue vitriol, blue stone, blue copperas, or sulphate of copper, have been 
 already mentioned as formed from the residue in the preparation of 
 S0 2 (p. 218), by dissolving copper in oil of vitriol, a process occasionally 
 used for the manufacture of this salt. 
 
 The sulphate of copper is also manufactured by roasting copper 
 pyrites (Cu 2 Fe 2 S 4 ) with free access of air, when it becomes partly 
 converted into a mixture of cupric sulphate with ferrous sulphate ; 
 Cu 2 Fe 2 S 4 + 16 =2FeS0 4 + 2CuS0 4 . The ferrous sulphate, however, is 
 decomposed by the heat, leaving ferric oxide (see p. 234). When 
 the roasted mass is treated with water, the ferric oxide is left undis- 
 solved, but the cupric sulphate, which withstands a higher temperature 
 than ferrous sulphate does, enters into solution, and may be obtained in 
 crystals by evaporation. 
 
 Since ferrous sulphate and cupric sulphate are isomorphous, they 
 crystallise together (v.i.), and can be separated only by converting the 
 ferrous into ferric sulphate by an oxidising-agent such as nitric acid. 
 
 The crystals, as they are found in commerce, are usually opaque, but 
 if they are dissolved in hot water and allowed to crystallise slowly, they 
 become perfectly transparent, and have then the composition expressed 
 by the formula CuS0 4 .5H 2 (sp. gr. 2.28). If the crystals be heated to 
 the temperature of boiling water, they lose four-fifths of their water, and 
 crumble down to a greyish-white powder, which has the composition 
 CuS0 4 .H.,0, and if this be moistened with water, it becomes very hot, 
 and resumes its original blue colour. The whitish opacity of the 
 ordinary crystals of blue stone is due to the absence of a portion of the 
 water of crystallisation. The fifth molecule of water can be expelled 
 
CUPPJC CHLORIDE. 485 
 
 only at a temperature of nearly 200 0., and is therefore generally 
 called water of constitution (see p. 53), the formula of the crystals 
 being then written CuS0 4 .H 2 0.4Aq. The crystals dissolve in 2.5 parts 
 of cold and 0.5 part of boiling water. The solution reddens litmus. 
 
 The sulphate of copper is largely employed by the dyer and calico- 
 printer, and in the manufacture of pigments. It is also occasionally 
 used in medicine, in the electrotype process, and in galvanic batteries. 
 In agriculture it is found useful as a preservative, wheat which is to be 
 sown being steeped in a solution of it to protect the grain from the 
 attack of smut. 
 
 When ammonia is added to solution of cupric sulphate, a basic sulphate is first 
 precipitated, which is dissolved by an excess of ammonia to a dark blue liquid. On 
 allowing this to evaporate, dark blue crystals of aniinonio-cupric sulphate, 
 CuS0 4 .4NH 3 .H 2 0, are deposited. They lose their ammonia when exposed to the 
 air. 
 
 A tattle cupric sulphate, CuS0 4 .3Cu(OH). 2 .Aq, is found as brocliantite. 
 Sulphate of copper cannot easily be separated by crystallisation from the 
 sulphates of iron, zinc, and magnesium, because it forms double salts with them, 
 which contain, like those sulphates, seven molecules of water, and are isomorphous 
 with magnesium sulphate (unless the CuS0 4 is the predominant constituent, when 
 the salts contain five molecules of water and are isomorphous with cupric sulphate). 
 An instance of this is seen in the Mack vitriol obtained from the mother-liquor of 
 the sulphate of copper at Mansfield, and forming bluish-black crystals isomorphous 
 with green vitriol, FeS0 4 ,7H 2 0. The formula of black vitriol may be written 
 [CuMgFeMnCoNi]S0 4 .7H 2 0, the six isomorphous metals being interchangeable 
 without altering the general character of the salt. 
 
 Cupric arsenlte (Sclieelds greeti), CuHAs0 3 , has been noticed at p. 270. It is 
 a yellowish-green powder, insoluble in water, but easily soluble in acids and alkalies. 
 Its solution in potash has a dark blue colour, and deposits cuprous oxide when 
 boiled, potassium arsenate being produced. Emerald green has also been noticed 
 (p. 271). 
 
 The basic enpric phosphates compose the minerals tagllite and libethenite. 
 The basic cirpric carbonate* have been noticed as forming the very beautiful 
 mineral blue malacJiite, a~urite, or cliewylite, and green malachite. 
 
 Mineral green, CuC0 3 .Cu(OH). 2 , has the same composition as green malachite, 
 and is prepared by mixing hot solutions of sodium carbonate and cupric sulphate. 
 When boiled in the liquid, it is gradually converted into black oxide of copper. 
 The green deposit formed on old copper by exposure to air has the same compo- 
 sition. 
 
 The blue precipitate produced in cupric solutions by alkaline carbonates in the 
 cold is CuC0 3 .Cu(OH). 2 .Aq. 
 
 Cupric silicates are found in the minerals dioptase, or emerald copper, and chry- 
 socolla, CuH 2 Si0 4 .H a O. 
 
 282. Chlorides of copper. The chloride of copper (cupric chloride), 
 CuCl,, is produced by the direct union of its elements, when it forms a 
 brown mass, which fuses easily, and is decomposed into chlorine and 
 cuprous chloride, the latter being afterwards converted into vapour. 
 When dissolved in water, it gives a solution which is green when con- 
 centrated, and becomes blue on dilution. The hydrated cupric chloride 
 is readily prepared by dissolving the black oxide in hot hydrochloric 
 acid, and allowing the solution to crystallise ; it forms green needle-like 
 crystals (CuCl,.2H,0) which become blue when dried in vacua. A 
 solution of chloride of copper in alcohol burns with a splendid green 
 flame, and the chloride imparts a similar colour to a gas flame. 
 
 Oxychloride of copper (Cud 2 .3CuO.4H,O) is found at Atacama in 
 prismatic crystals, and is called atacamite. The paint Brunswick green 
 has the same composition, and is made by moistening copper wit] 
 solution of hydrochloric acid or sal-ammoniac, and exposing it to the 
 
486 CUPROUS CHLORIDE. 
 
 air in order that it may absorb oxygen; Cu 4 -j- 2HC1 + 3H.,0 + O 4 = 
 CuCl 2 .3Cu0.4H 2 0. It is also made by boiling cupric sulphate with 
 chloride of lime. The Brunswick green of the shops frequently consists 
 of a mixture of Prussian blue, chromate of lead, and barium sulphate. 
 
 Subchloride of copper (cuprous chloride), Cu,Cl v , is formed as a 
 sublimate when copper is heated in HC1 gas. It is also produced when 
 fine copper turnings are shaken with strong hydrochloric acid in a 
 bottle of air; Cu 2 + 2HCl + = Cu 2 Cl 2 + H 2 0. The cuprous chloride 
 dissolves in the excess of hydrochloric acid, forming a brown solution, 
 from which water precipitates it white, for this is one of the few chlorides 
 insoluble in water. When exposed to light, it assumes a purplish -grey 
 tint. A copper plate dipped into a strong neutral solution of cupric 
 chloride acquires a thin coating of cuprous chloride upon which photo- 
 graphs may be taken. Cuprous chloride may be prepared as described 
 on p. 140. 
 
 If the solution in HC1 be moderately diluted and set aside, it deposits 
 tetrahedral crystals of cuprous chloride. Ammonia (free from air) dissolves 
 cuprous chloride to a colourless liquid which becomes dark blue by contact with air, 
 absorbing oxygen ; it is used as a test for acetylene (p. 140). The solution may be 
 preserved in a colourless state by keeping it in a well- stoppered bottle, quite full, 
 with strips of clean copper. When copper, in a finely divided state, is boiled with 
 solution of ammonium chloride, the solution deposits colourless crystals of the salt, 
 Cu 2 Cl 2 (NH 3 ) 2 . If the solution of this salt be exposed to the air, blue crystals are 
 deposited, having the formula Cu 2 Cl. 2 .CuCl 2 .4NH 3 .H 2 0, and on further exposure, a 
 compound of this last salt with ammonium chloride ia deposited. The solution of 
 cuprous chloride in hydrochloric acid is employed for absorbing carbonic oxide in 
 the analysis of gaseous mixtures. When this solution is exposed to air it absorbs 
 oxygen, and deposits cupric oxychloride. A strong solution of ammonium or 
 sodium or potassium chloride readily dissolves the cuprous chloride, even in the 
 cold, forming soluble double chlorides, such as Cu 2 Cl 2 4KCl. The solution in 
 potassium chloride does not absorb oxygen quite so easily as that in ammonium 
 chloride. 
 
 (htprvtu iodide, Cu 2 I 2 , is a very insoluble white precipitate formed when a 
 mixture of cupric and ferrous sulphates is added to the solution of an iodide ; 
 2CuS0 4 + 2FeS0 4 + 2KI = Cu 2 I 2 + Fe 2 (S0 4 ) 3 + K 2 S0 4 . It is also precipitated, 
 together with iodine, when cupric sulphate is added to an iodide ; 2CuS0 4 + 4KI = 
 Cu 2 I 2 + I 2 + 2K 2 S0 4 . 
 
 283. Sulphides of copper. Copper has a very marked attraction for 
 sulphur, even at the ordinary temperature. A bright surface of copper 
 soon becomes tarnished by contact with sulphur, and hydrosulphuric acid 
 blackens the metal. Finely divided copper and sulphur combine slowly 
 at the ordinary temperature, and, when heated together, they combine 
 with combustion. A thick copper wire burns easily in vapour of sulphur 
 (p. 212). Copper is even partly converted into sulphides when boiled 
 with sulphuric acid, as in the preparation of sulphurous acid gas. This 
 great attraction of copper for sulphur is taken advantage of in the pro- 
 cess of kernel roasting for extracting the copper from pyrites containing 
 as little as i per cent, of the metal. The pyrites is roasted in large 
 heaps (p. 209) for several weeks, when a great part of the iron is con- 
 verted into peroxide, and the copper remains combined with sulphur, 
 forming a hard kernel in the centre of the lumps of ore. This kernel 
 contains about 5 per cent, of copper, and can be smelted with economy. 
 Children are employed to detach the kernel from the shell, which con- 
 sists of ferric oxide mixed with a little cupric sulphate, which is washed 
 out with water. 
 
CUPRIC SULPHIDE. 487 
 
 The subsulphide of copper, or cuprous sulphide (Cu 2 S), has been men- 
 tioned among the ores of copper and among the furnace products in 
 smelting, when it is sometimes obtained in octahedral crystals. It is 
 formed when H 2 S is passed over red-hot CuO, and when coal-gas is 
 passed over red-hot CuS. It is not attacked by hydrochloric acid, but 
 nitric acid dissolves it readily. Copper pyrites is believed to contain 
 the copper in the form of cuprous sulphide, its true formula being 
 Cu 2 S.Fe 2 S 3 ;* for if the copper be present as cupric sulphide, CuS, the 
 iron must be present as ferrous sulphide, and the mineral would have 
 the formula CuS.FeS. Now, FeS is easily attacked by dilute sulphuric 
 or hydrochloric acid, which is not the case with copper pyrites. Nitric 
 acid, however, attacks it violently. 
 
 Sulphide of copper, or cupric sulphide (CuS), occurs in nature as indigo 
 copper or blue copper, and may be obtained as a black precipitate by the 
 action of hydrosulphuric acid upon solution of cupric sulphate. When 
 this precipitate is boiled with sulphur and ammonium sulphide, it is 
 dissolved in small quantity, and the solution on cooling deposits fine 
 scarlet needles containing a higher sulphide of copper combined with 
 sulphide of ammonium. When copper and sulphur are heated together 
 in atomic proportions to a temperature below the boiling-point of sulphur 
 (448 C.), CuS is produced; but at a higher temperature this is con- 
 verted into Cu S. Pentasulphide of copper (CuS 5 ) is obtained by decom- 
 posing cupric sulphate with potassium pentasulphide ; it forms a black 
 precipitate distinguished from the other sulphides of copper by its solu- 
 bility in potassium carbonate. The sulphides of copper, when exposed 
 to air in the presence of water, are slowly oxidised and converted into 
 cupric sulphate, which is dissolved by the water. It appears to be in 
 this way that the blue ivater of the copper mines is formed. By 
 thoroughly washing CuS with dil. H 2 S0 4 and then with water, it can be 
 made to pass into solution, but it is immediately precipitated by saline 
 matter. 
 
 Phosphide of copper, cupric phosphide (Cu 3 P 2 ), obtained as a black powder by 
 boiling solution of cupric sulphate with phosphorus, or by passing PH 3 into a 
 solution of CuS0 4 , has been already mentioned as a convenient source of phosphine. 
 Another phosphide, obtained by passing vapour of phosphorus over finely divided 
 copper at a high temperature, is employed in Abel's composition for magneto- 
 electric fuses, in conjunction with Cu 2 S and KC10 3 . Phosphide of copper em- 
 ployed for toughening commercial copper is made by running melted copper into 
 a conical iron crucible lined with loam, at the bottom of which are placed sticks 
 of phosphorus which have been coated with copper by soaking them in cold solu- 
 tion of CuS0 4 . 
 
 Silicon may be made to unite with copper by strongly heating finely divided 
 copper with silica and charcoal. A bronze-like mass is thus obtained containing 
 about 5 per cent. Si. It is said to rival iron in ductility and tenacity, and fuses 
 at about the same temperature as bronze. 
 
 SILVER. 
 
 Ag' = 107.1 parts by weight. 
 
 284. In silver we meet with the first metal hitherto considered which 
 is not capable of undergoing oxidation in the air, and this, in conjunc- 
 tion with its beautiful appearance, occasions its manifold ornamental 
 
 * Crystals of Cu 2 S.Fe 2 S s are obtained by shaking faintly aininoniacal Cu 2 Cl 2 solution with 
 
488 EXTRACTION OF SILVEE. 
 
 uses, which are much favoured also by the great malleability and 
 ductility of this metal (in which it ranks only second to gold), for 
 the former property enables it to be rolled out into thin plates or 
 leaves, so that a small quantity of silver suffices to cover a large 
 surface, whilst its ductility permits the wire-drawer to produce that 
 extremely thin silver wire which is employed in the manufacture of 
 silver lace. 
 
 Silver, although pretty widely diffused, is found in comparatively 
 small quantity, and hence it bears a high value, which adapts it for a 
 medium of currency. 
 
 As might be expected from its want of direct attraction for oxygen, 
 silver is found frequently in the metallic or native state, crystallised in 
 cubes or octahedra, which are sometimes aggregated together, as in the 
 silver-mines of Potosi, into arborescent or dendritic forms ; it generally 
 contains copper and gold, and sometimes mercury. Silver is more 
 frequently met with, however, in combination with sulphur, forming 
 the sulphide of silver (Ag,S), which is generally associated with large 
 quantities of the sulphides of lead, antimony, and iron. The largest 
 supplies of silver are obtained from the United States, Mexican, Peruvian, 
 and Australian (Broken Hill) mines, but the quantity furnished by 
 Saxony and Hungary is by no means insignificant. Silver chloride 
 is found in considerable quantity in the spongy deposits of silica round 
 the Great Salt Lake in Utah. 
 
 The process by which silver is extracted from galena has been already 
 described under the history of lead. Silver may be separated from 
 copper, in the ores of which (particularly grey copper ore) it frequently 
 exists to a considerable extent, by taking advantage of the facility with 
 which the former metal is dissolved by melted lead. The process of 
 liquation, as it is termed, consists in fusing the argentiferous copper 
 with about thrice its weight of lead, arid casting the alloy thus obtained 
 into cakes or discs, which are afterwards gradually heated upon a 
 hearth, so contrived that the lead, which melts much more easily than 
 the copper, may flow off in the liquid state, carrying with it. in the 
 form of an alloy, the silver which was associated with the copper, 
 leaving this last metal in porous masses, having the form of the original 
 discs, upon the hearth. The lead and silver are separated by the pro- 
 cess of cupellation (p. 464). 
 
 In the extraction of silver from its ores the method adopted depends 
 upon the conditions at the locality where the ore is mined. Thus, 
 where fuel is available it is customary to smelt the ore either with lead 
 ores or copper ores, the noble metal being eventually obtained either 
 in solution in lead or in a copper matte. In the latter case the silver 
 may be extracted by taking advantage of the fact that by carefully 
 roasting a mixture of the sulphides of copper and silver the copper may 
 be completely oxidised to oxide and the silver to sulphate, so that when 
 the roasted mass is leached with water, silver sulphate passes into solu- 
 tion ; the metal is precipitated from this by introducing metallic 
 copper, and the precipitate is refined by roasting it to oxidise the 
 impurities, and fusing it. Dissolution in lead followed by cupellation 
 frequently forms a convenient method for refining silver, but electro- 
 lytic refining of the metal on the same lines as those adopted for copper 
 (p. 478) is becoming general ; the electrolyte is a dilute solution of silver 
 
THE AMALGAMATION PROCESS. 
 
 489 
 
 nitrate, the crude silver cast into plates forms the anode, while sheets 
 of pure silver constitute the cathodes. 
 
 Where fuel is scarce an amalgamation process is adopted. That in 
 vogue in Mexico is complicated in its chemical details, but primarily 
 depends upon the reduction of the silver from the form of chloride by 
 means of mercury (iron being sometimes substituted as a reducing- 
 agent), AgCl + Hg = HgCl + Ag, and the dissolution of the reduced 
 silver in mercury, which is subsequently distilled, leaving the silver 
 to be refined as described above. 
 
 The crushed ore is made into a mud with water, and mixed with common salt, 
 mercury, and roasted copper pyrites (magistral?), the mixing being generally per- 
 formed by the feet of mules. A hot solution of CuS0 4 and more mercury are then 
 added, and after these have been well mixed with the charge the whole is stirred 
 up with water, when the heavy silver amalgam sinks to the bottom. It is drawn 
 off and filtered through canvas, in order to separate the semi-solid amalgam from 
 the excess of mercury. The amalgam is then distilled, the arrangement shown in 
 Fig. 240 being often employed ; in this the amalgam is spread on iron trays 
 .arranged on an upright beneath an iron bell, the lower part of which stands in 
 water, whilst the upper portion is surrounded by burning fuel, the heat of which 
 distils the mercury into the water. 
 
 It would appear that in this process the CuS0 4 
 (which is added both as such and in the form of 
 magistral) reacts with the common salt, yielding 
 cupric chloride. The CuCl 2 then reacts with the 
 silver sulphide of the ore. yielding silver chloride, 
 which is dissolved by the solution of salt and reduced 
 by the mercury. The excess of mercury then 
 .amalgamates with the silver. 
 
 In another class of processes for extracting 
 silver from its ores, these are roasted with 
 common salt, whereby the silver sulphide is 
 first converted into sulphate by oxidation, 
 and then into chloride by double decomposi- 
 tion with the NaCJ. The silver chloride is 
 dissolved out of the mass by means of a strong 
 solution of common salt, from which the silver 
 is afterwards precipitated in the metallic state 
 
 by copper, or as silver iodide, the silver iodide being reduced by zinc, 
 and the zinc iodide used to precipitate a fresh portion of silver. 
 Sodium thiosulphate is also employed to dissolve out the silver chloride, 
 and the solution precipitated by sodium sulphide, the silver sulphide 
 thus obtained being roasted to remove the sulphur and leave metallic 
 silver. 
 
 Although silver is capable of resisting the oxidising action of the 
 atmosphere, it is liable to considerable loss by wear and tear, in con- 
 sequence of its softness, and is therefore always hardened, for useful 
 purposes, by the addition of a small proportion of copper. The standard 
 silver employed for coinage and for most articles of silver plate in this 
 country, contains, in 1000 parts, 925 of silver and 75 of copper, whilst 
 that used in France contains 900 of silver and 100 of copper. English 
 standard silver is said to have a fineness of 925, and French, of 900. 
 
 Standard silver, for coining and other purposes, is whitened by being 
 heated in air and immersed in diluted sulphuric acid, which dissolves 
 out the oxide of copper, leaving a superficial film of nearly pure silver. 
 Dead or frosted silver is produced in this manner. Oxidised silver is 
 
 Fig. 240. 
 
49 ELECTRO-PLATING. 
 
 covered with a thin film of sulphide by immersion in a solution obtained 
 by boiling sulphur with potash. 
 
 The solder employed in working silver consists of 5 parts of silver, 
 2 of zinc, and 6 of brass. 
 
 Plated articles are manufactured from copper or one of its alloys, 
 which has been united, by rolling, with a thin plate of silver, the 
 adhesion of the latter being promoted by first washing the surface of 
 the copper with a solution of silver nitrate, when a film of this metal is 
 deposited upon its surface, the copper taking the place of the silver in 
 the solution. 
 
 Electro-plating consists in covering the surface of baser metals with a 
 coating of silver, by connecting them with the negative (or zinc) pole of 
 the galvanic battery, and immersing them in a solution made by dis- 
 solving silver cyanide in potassium cyanide,* the positive (copper or 
 platinum) pole being connected with a silver plate, also immersed in the 
 solution ; the current gradually decomposes the silver cyanide, and 
 this metal is of course (see p. 324) deposited upon the object connected 
 with the negative electrode, whilst the cyanogen liberated at the silver 
 plate attacks the silver, so that the solution is always maintained at the 
 same strength, the quantity of silver dissolved at this electrode being 
 precisely equal to that deposited at the opposite one. 
 
 Brass and copper are sometimes silvered by rubbing them with a 
 mixture of 10 parts of silver chloride with i of corrosive sublimate 
 (mercuric chloride) and 100 of bitartrate of potash. The silver and 
 mercury are both reduced to the metallic state by the baser metal, and 
 an amalgam of silver is formed, which readily coats the surface. The 
 acidity of the bitartrate of potash promotes the reduction. The surface 
 to be silvered should always be cleansed from oxide by momentary 
 immersion in nitric acid, and washed with water. For dry silvering, an 
 amalgam of silver and mercury is applied to the clean surface, and the 
 mercury is afterwards expelled by heat. 
 
 Silvering upon glass is effected by means of certain organic substances 
 which are capable of precipitating metallic silver from its solutions. 
 Looking-glasses have been made by pouring upon the surface of plates 
 of glass a solution containing silver tartrate and ammonium tartrate. 
 On heating the glass plates to a certain temperature the tartrate is 
 reduced, and the metallic silver is deposited in a closely adhering film. 
 Glass globes and vases are silvered internally by a process which is 
 exactly similar in principle. The coating is rendered more adherent by 
 sprinkling it with a weak solution of potassio-mercuric cyanide, which 
 amalgamates the silver. 
 
 Small surfaces of glass for optical purposes may be silvered in the following 
 manner : Dissolve one gram of AgN0 3 in 20 c.c. of distilled water, and add weak 
 NH 3 carefully until the precipitate is almost entirely dissolved. Filter the solution 
 and make it up to 100 c.c. with distilled water. Then dissolve 2 grains of AgN0 3 . 
 in a little distflled water, and add it to a litre of boiling distilled water. Add 1.66 
 gram of Rochelle salt (tartrate of potassium and sodium), and boil till the pre- 
 cipitated silver tartrate becomes grey ; filter while hot. Clean the glass to be 
 silvered very thoroughly with HNO 3r distilled water, KOH, distilled water, alcohol, 
 distilled water ; place it in a clean glass or porcelain vessel, with the side to be 
 silvered uppermost. Mix equal measures of the two silver solutions (cold), and 
 
 * A solution of potassium cyanide in 10 parts of water, with 50 grains of silver chloride 
 dissolved in each pint of the liquid, will answer the pujrpose. 
 
PROPEETIES OF SILVER. 
 
 49 1 
 
 pour the mixture in so as to cover the glass, which will be silvered in about an 
 hour. After washing, it may be allowed to dry, and varnished. 
 
 Very good mirrors may be made by adding ammonia to weak silver nitrate till 
 the precipitate just redissolves, then a little potash, then ammonia till the liquid 
 is clear, and then a very little glycerine. If a watch-glass be floated on this liquid, 
 and a gentle heat applied, a good mirror will be formed in a few minutes. 
 
 Pure silver is easily obtained from standard silver by dissolving it in 
 nitric acid, with the aid of heat, diluting the solution with water, adding 
 solution of common salt as long as it produces any fresh precipitate of 
 silver chloride, washing the precipitate by decantation as long as the 
 washings give a blue tinge with ammonia, and fusing the dried precipi- 
 tate with half its weight of dried sodium carbonate in a brisk fire, when 
 a button of silver will be found on breaking the crucible 
 ' 2AgCl + Xa 2 C0 3 = Ag 2 + 2NaCl + + C0 2 . 
 
 The pure silver employed by Stas in his researches on atomic weights 
 was prepared by distilling the metal. 
 
 When fused in air, silver occludes oxygen, a portion of which it 
 evolves during solidification, causing sprouting on the surface of the 
 partly solidified metal, and sometimes projection of portions of the 
 mass. After cooling, it still retains oxygen, which can only be ex- 
 pelled by heating to about 600 C. in a vacuum. This may amount to 
 0.025 per cent, by weight, and has to be taken into consideration in 
 determining atomic weights in terms of silver.* 
 
 285. Properties of silver. The brilliant whiteness of silver distin- 
 guishes it from all other metals. It is lighter than lead, its specific 
 gravity being 10.53 ; harder than gold, but not so hard as copper; more 
 malleable and ductile than any other metal except gold, which it sur- 
 passes in tenacity. It fuses at a somewhat lower temperature than 
 gold or copper (960 C.), and is the best conductor of heat and elec- 
 tricity. It is comparatively easily distilled. It is not oxidised by dry 
 or moist air, either at the ordinary or at high temperatures, but is oxi- 
 dised by ozone, and tarnished by air containing sulphuretted hydrogen, 
 from the production of silver sulphide, which is easily removed by solu- 
 tion of potassium cyanide. Pure H 2 S does not attack silver. It is 
 unaffected by dilute acids, with the exception of nitric, and in this case 
 the presence of nitrous acid is essential ; but hot concentrated sulphuric 
 acid converts it into silver sulphate, and when boiled with strong hydro- 
 chloric acid it dissolves to a slight extent in the form of silver chloride, 
 which is precipitated on adding water. Strong hydriodic acid dissolves 
 silver, evolving hydrogen ; silver iodide is precipitated on addition of 
 water. The alkali hydroxides do not act on silver to the same extent 
 as on platinum when fused with it ; hence silver basins and crucibles 
 are much used in the laboratory. 
 
 Colloidal silver appears to be formed by the action of certain reducing-agents 
 on a solution of silver nitrate, and has lately been applied in medicine. When a 
 solution of ferrous citrate is added to one of silver nitrate, a red solution which 
 deposits a lilac precipitate is obtained ; this precipitate is washed with ammonium 
 nitrate solution, and is then found to contain over 97 per cent, of silver, and to be 
 soluble in water to a red solution. By similar methods an insoluble ll<>trn/nr 
 xilw and an insoluble goM-lllte allotroph' *ilrer have been obtained. The physic 
 properties of silver deposited as a mirror seem to show that it is colloidal silver. 
 
 * At 300 C. and 15 atmospheres pressure Ag absorbs as much oxygen as corresponds 
 with the formula Ag 4 O. 
 
49 2 LUNAR CAUSTIC. 
 
 286. Oxides of silver. There are three compounds of silver with 
 oxygen the suboxide, Ag 4 ; the oxide Ag 2 ; and the peroxide, pro- 
 bably Ag 2 0.,, which is not known in the pure state. The oxide alone 
 has any practical interest, as being the base of the salts of silver. 
 
 Silver oxide (Ag 2 0) is obtained as a brown precipitate when solution 
 of silver nitrate is decomposed by potash, or, better, poured into an 
 excess of lime-water. "When alcoholic solutions of KOH and AgN0 3 
 are mixed at - 40 C. a white precipitate of silver hydroxide, AgOH, is 
 produced ; as the temperature rises, however, it becomes dark from loss 
 of water and formation of Ag 2 0. The oxide is a powerful base, slightly 
 soluble in water, to which it imparts a weak alkaline reaction. A tem- 
 perature of 270 C. decomposes it into its elements. It acts as a 
 powerful oxidising-agent. When moist freshly precipitated silver oxide 
 is covered with a strong solution of ammonia, and allowed to stand for 
 some hours, it becomes black, crystalline, and acquires dangerously ex- 
 plosive properties. The composition of this fulminating silver is not 
 accurately known, but it is supposed to be a silver nitride, NAg 3 , cor 
 responding in composition with ammonia. 
 
 Silrer peroxide is a black precipitate obtained by mixing solutions of potassium 
 persulphate and AgN0 3 . With ammonium persulphate there is less precipitate, and 
 if NH 3 be present there is a violent evolution of nitrogen, the silver salt acting 
 catalytically to decompose the mixture in the sense of the equation 3(NH 4 ). 2 S 2 8 + 
 8NH 3 = 6(NH 4 ) 2 S0 4 + N2. The peroxide is also deposited on the anode during the 
 electrolysis of silver salts as black octahedra which dissolve in HN0 3 to a deep 
 brown solution of strongly oxidising properties. 
 
 Silver nitrate (AgN0 3 ), or lunar caustic (silver being distinguished as 
 luna by the alchemists), is procured by dissolving silver in nitric acid,* 
 with the aid of a gentle heat, evaporating the solution to dryness, and 
 heating the residue till it fuses, in order to expel the excess of acid. It 
 fuses at 218 C. For use in surgery, the fused nitrate is poured into 
 cylindrical moulds, so as to cast it into thin sticks ; but for chemical 
 purposes it is dissolved in water and crystallised, when it forms colour- 
 less square tables (sp. gr. 4.3), easily soluble in water and alcohol. The 
 action of nitrate of silver as a caustic depends upon the facility with 
 which it parts with oxygen, the silver being reduced to the metallic 
 state, and the oxygen combining with the elements of the organic 
 matter. This effect is very much promoted by exposure to sunlight or 
 diffused daylight. Pure silver nitrate is not changed by exposure to 
 light, but if organic matter be present, a black deposit, containing 
 finely divided silver, is produced. Thus, the solution of silver nitrate 
 stains the fingers black when exposed to light, but the stain may be 
 removed by potassium cyanide or, more safely, by tincture of iodine. 
 If solution of silver nitrate be dropped upon paper and exposed to 
 light, black stains will be produced, and the paper corroded. Silver 
 nitrate is a frequent constituent of marking-inks, since the deposit of 
 metallic silver formed on exposure to light is not removable by washing. 
 The linen is sometimes mordanted by applying a solution of sodium car- 
 bonate before the marking-ink, when the insoluble silver carbonate is 
 precipitated in the fibre, and is more easily blackened than the nitrate, 
 especially if a hot iron is applied. Marking-inks without preparation, 
 are made with silver nitrate containing an excess of ammonia, which 
 
 * For 3 ounces of silver, take if fluid ounce of strong nitric acid, and 5 fluid ounces of 
 water. 
 
SILVER CHLORIDE. 493 
 
 appropriates the nitric acid, and hastens the blackening on exposure to 
 light or heat. Hair-dyes often contain AgN0 3 . The important use of 
 this salt in photography has been noticed already (p. 236). 
 
 In order to prepare silver nitrate from standard silver (containing copper), the 
 metal is dissolved in moderately strong nitric acid, and the solution evaporated to 
 dryness in a porcelain dish, when a blue residue containing the nitrates of silver 
 and copper is obtained. The dish is now moderately heated until the residue has 
 fused, and become uniformly black, the blue copper nitrate being decomposed 
 and leaving black copper oxide, at a temperature which is insufficient to decom- 
 pose the silver nitrate. To ascertain when all the copper nitrate is decomposed, 
 a small sample is removed on the end of a glass rod, dissolved in water, filtered, 
 and tested with ammonia, which will produce a blue colour if any copper nitrate 
 be left. The residue is treated with hot water, the solution filtered from the 
 copper oxide and evaporated to crystallisation. 
 
 Silver nitrate forms crystalline double salts with one molecule of potassium or 
 ammonium nitrate. It absorbs ammonia with evolution of heat, and silrei- 
 ammonio-nltrate, AgN0 3 .2NH 3 , may be crystallised from a strong solution of silver 
 nitrate saturated with ammonia. 
 
 Silrer nitrite, AgN0. 2 , is obtained as a white precipitate from KN0 2 and AgNO. 
 It is soluble in hot water and crystallises in prisms. By long boiling with water 
 it is decomposed, 2AgN0 2 = AgN0 3 + Ag + NO. Silrer Itijponitrlte, Ag 2 N 2 0., (see 
 p. 103). 
 
 Silrer carbonate, Ag 2 C0 3 , is obtained in transparent yellow crystals when moist 
 silver oxide is acted on by C0 2 . It dissolves in solution of CO^ like CaC0 3 . and 
 is deposited in crystals when the solution is exposed to the air. It is feebly 
 alkaline to moist test-paper. It bears heating to nearly the boiling-point of oil, 
 and fuses just before decomposition. Silver carbonate forms a yellowish white 
 precipitate when silver nitrate is decomposed by an alkaline carbonate. 
 
 287. Silver chloride, AgCl, is an important compound, as being the 
 form into which silver is commonly converted in extracting it from its 
 ores, and in separating it from other metals. It separates, as a white 
 curdy precipitate, when solution of hydrochloric acid or a chloride is 
 mixed with a solution containing silver. The precipitate is brilliantly 
 white at first, but soon becomes violet, and eventually black, if exposed 
 to daylight, or more rapidly in sunlight, the chloride of silver being 
 reduced to subchloride (Ag 2 Cl), with separation of chlorine (see p. 236). 
 The blackening is more rapid in the presence of an excess of silver 
 nitrate or of organic matter, upon which the liberated chlorine can act. 
 In the presence of chlorine the blackening does not occur ; nor will per- 
 fectly dry AgCl darken. If the white silver chloride be dried in the 
 dark and heated in a crucible, it fuses at 457 C. to a brownish liquid, 
 which solidifies, on cooling, to a transparent, nearly colourless mass 
 (sp. gr. 5.59), much resembling horn in external characters (horn silver) ; 
 a strong heat converts it into vapour, but does not decompose it. If 
 fused silver chloride be covered with hydrochloric acid, and a piece of 
 zinc placed upon it, it will be found entirely reduced, after a few hours, 
 to a cake of metallic silver; the first portion of silver having been 
 reduced in contact with the zinc, and the remainder by the galvanic 
 action set up by the contact of the two metals beneath the liquid. Fusion 
 with Na.,C0 3 reduces AgCl, first converting it into Ag 2 C0 3 which breaks 
 up into ~Ag,, O, and CO.. Silver chloride is slightly soluble in strong 
 HCJ, and in strong solutions of alkali chlorides. Potassium cyanide 
 dissolves it readily, and the solution is used in electro-plating. Ammonia 
 readily dissolves silver chloride, and the solution deposits colourless 
 crystals of the chloride when evaporated. If the ammonia be very 
 strong the solution deposits a crystalline compound of silver chloride 
 
494 SILVEE HALIDES. 
 
 with ammonia, 2AgC1.3NH 3 . The absorption of ammoniacal gas by 
 silver chloride has been noticed at p. 82, and the photographic appli- 
 cation of the chloride at p. 236. 
 
 From photographic fixing solutions containing sodium hyposulphite the silver 
 cannot be precipitated by salt, because the silver chloride is soluble in the hyposul- 
 phite. A piece of sheet copper left in this for a day or two will precipitate the 
 silver at once in the metallic state. 
 
 Several chemists have claimed to have isolated a dark silver sub-chloride, to 
 w r hich the formulae Ag 2 Cl and Ag 4 Cl 3 have been ascribed. The interest in this 
 supposed sub-chloride arises from the fact that metallic silver cannot be found in 
 the silver chloride which has been darkened by light, although chlorine has 
 undoubtedly been removed. By adding a reducing-agent (such as SnCl 2 ) to an 
 ammoniacal solution of AgCl, a black precipitate is obtained, which becomes 
 coloured pink or brown (according to the nature of the reducing-agent) when it is 
 washed with nitric acid. A number of such coloured salts has been obtained 
 by Carey Lea from the halides of silver ; these are termed photo-salts of silver and 
 are supposed to be identical with the products of the action of light on the silver 
 halides ; they appear to consist of the normal silver halides with small admixtures 
 of sub-halides. They are dissolved by ammonia with the exception of a slight 
 residue of silver. 
 
 Silver bromide (AgBr) is a rare Chilian mineral, bromargyrite. Asso- 
 ciated with AgCl it forms the mineral embolite. It much resembles the 
 chloride, but is somewhat less easily dissolved by ammonia. Dry silver 
 bromide does not absorb NH 3 . It melts at 427 C. ; sp. gr. 6.35. When 
 heated to 700 C. in HC1, silver bromide is converted into the chloride, 
 but, at the ordinary temperature, HBr converts silver chloride into 
 bromide. Modern photographic plates are made with silver bromide. 
 
 Ammonium bromide is dissolved in a warm aqueous solution of gelatine and 
 a solution of silver nitrate, less than equivalent to the bromide, is poured in, the 
 room being lighted by red light. The mixture, with the finely divided silver 
 bromide suspended in it, is warmed for some time in order to "ripen" the 
 emulsion. By this expression it is implied that the silver bromide becomes more 
 sensitive to light, a fact which has not been explained ; the sole effect of the 
 ripening on the silver bromide, so far as has been observed, is the aggregation of the 
 particles, so that they become somewhat coarser. The emulsion is now allowed to 
 set, and washed in water to remove the ammonium nitrate produced by the inter- 
 action of the NH 4 Br and AgNO 3 , and the excess of NH 4 Br ; if the latter be 
 not present during the manufacture of the emulsion a less sensitive plate is produced. 
 The gelatine emulsion is again melted and poured on to the plates. 
 
 What has been said (p. 493) with reference to the action of light on AgCl maybe 
 applied to AgBr. The chemistry of the action and of the development of the 
 invisible image is even yet shrouded in mystery. 
 
 Silver iodide (Agl) is also found in the mineral kingdom. It is worthy 
 of remark that silver decomposes hydriodic acid much more easily than 
 hydrochloric acid, forming silver iodide, and evolving hydrogen. The 
 silver iodide dissolves in hot hydriodic acid, and the solution deposits 
 crystals of Agl, HI, which are decomposed in the air. If the hot solu- 
 tion be left in contract with silver, prisms of Agl are deposited. By 
 adding silver nitrate to potassium iodide, the silver iodide is obtained as 
 a yellow precipitate, which, unlike the chloride, does not dissolve in 
 ammonia, but is bleached, forming 2AgLNH 3 , which is also produced 
 when dry silver iodide absorbs ammonia. 
 
 Silver iodide is remarkable for its behaviour when heated. It becomes more 
 yellow as the temperature rises and melts to an orange liquid at 527 C. The 
 melted mass contracts considerably on solidifying and on cooling, until the tem- 
 perature is 116 C., whereupon a sudden expansion occurs, concomitant with the 
 passage of the red amorphous to the yellow crystalline modification. When the 
 
SALTS OF SILVEE. 
 
 molten iodide is poured into cold water it becomes yellow, but remains amorphous. 
 The sp. gr. of the fused iodide is 5.6. 
 
 Silver iodide is the most stable of the silver halides ; when exposed to light it 
 requires a more vigorous sensitislng-agent (I.e.. halogen-absorbent) than do the 
 other halides in order that it may undergo photo-reduction. It dissolves in a 
 boiling saturated solution of silver nitrate, and the solution, on cooling, deposits 
 crystals having the composition AgI.AgN0 3 ; these are sensitive to light since 
 the halogen-absorbent (AgN0 3 ) is ready to hand. The crystals are decomposed 
 by water with separation of silver iodide. 
 
 Silver fluoride, AgF, is deliquescent and very soluble in water, forming crystals 
 which may contain one or two molecules of water. It fuses to a horny mass, like 
 AgCl, but is reduced to the metallic state when heated in moist air. Ammonia 
 also reduces it to the metallic state when heated. Fused AgF conducts the electric 
 current without undergoing decomposition. 
 
 Silrer sulphide (Ag 2 S) is found as silrer glance, which may be regarded as the 
 chief ore of silver ; it has a metallic lustre, and is sometimes found in cubical or 
 octahedral crystals. The minerals known as roslclers or red silrer ores contain 
 sulphide of silver combined with the sulphides of arsenic and antimony. The black 
 precipitate obtained by the action of hydrosulphuric acid upon a solution of silver 
 is silver sulphide. It may also be formed by heating silver with sulphur in a 
 covered crucible. Silver sulphide is remarkable for being soft and malleable, so 
 that medals may even be struck from it. It is not dissolved by diluted sulphuric 
 or hydrochloric acid, but nitric acid readily dissolves it. Metallic silver dissolves 
 silver sulphide when fused with it, and becomes brittle even when containing only 
 i per cent, of the sulphide. Ag 2 S fuses unchanged, but when roasted in air it 
 becomes Ag 2 S0 4 . 
 
 Silrer sulphate, Ag 2 S0 4 , forms a crystalline precipitate when a strong solution of 
 silver nitrate is stirred with dilute sulphuric acid. It requires 200 parts of cold 
 water to dissolve it. It fuses at 654 C. AgHS0 4 has been crystallised. 
 
 Silrer sulphite, Ag 2 S0 3 , forms a white precipitate when sulphurous acid is added 
 to silver nitrate. Boiling with water reduces it to metallic silver ; 
 Ag 2 S0 3 + H 2 = Ag 2 + H 2 S0 4 . 
 
 Silrer orthophoxphate, Ag 3 P0 4 , forms a yellow precipitate when sodium phosphate 
 is added to silver nitrate (p. 259). It is soluble in nitric acid and in ammonia, and 
 is thus distinguished from silver iodide. 
 
 Silrer arsenite, Ag 3 As0 3 , is obtained as a yellow precipitate when ammonia is 
 cautiously added to a mixture of silver nitrate and arsenious acid ; it is soluble in 
 nitric acid and in ammonia. Silrer ar senate, Ag 3 As0 4 , is a red precipitate, soluble 
 in nitric acid and in ammonia, formed when silver nitrate is added to arsenic acid. 
 
 Silrer sulpharsenlte, Ag 3 AsS 3 , is found as light red silrer ore. 
 
 Silrer mlphantimonate, Ag 3 SbS 3 , is dark red silrer ore. 
 
 MERCURY. 
 
 Hg" = 199 parts by weight = 2 vols. 
 
 288. Mercury (quicksilver) is conspicuous among metals by its fluidity, 
 and among liquids by its not wetting or adhering to most solids, such 
 as glass, a property of great value in making philosophical instruments. 
 It is the only metal which is liquid at the ordinary temperature, and 
 since it does not freeze until -39 F. (-39. 5 0.), this metal is particularly 
 adapted for the construction of thermometers and barometers. Its high 
 boiling-point (662 F., 357 C.) and low specific heat (0.033) also recom- 
 mend it for the former purpose, as its high specific gravity (13.54) does 
 for the latter, a column of about 30 inches in height being able to 
 counterpoise a column of the atmosphere having the same sectional area. 
 The symbol for mercury (Hg) is derived from the Latin name for this 
 element, hydrargyrum (vSwp, water, referring to its fluidity, apyvpos, 
 silver). 
 
 Mercury is not met with in this country, but is obtained from Idna 
 
496 
 
 EXTRACTION OF MERCURY. 
 
 (Austria), Almaden (Spain), China, and New Almaden (California). It 
 occurs in these mines partly in the metallic state, diffused in minute 
 globules or collected in cavities, but chiefly in the state of cinnabar, 
 which is mercuric sulphide, HgS (sp. gr. 8.2). 
 
 The metal is extracted from the sulphide at Idria by roasting the ore 
 in a kiln (Fig. 241), which is connected with an extensive series of con- 
 
 Fig'. 241. Extraction of mercury at Idria. 
 
 densing-chambers built of brickwork. The sulphur is converted, by the 
 air in the kiln, into sulphurous acid gas, whilst the .mercury passes off 
 in vapour and condenses in the chambers. 
 
 At Almaden, the extraction is conducted upon the same principle, 
 but the condensation of the mercury is effected in earthen receivers 
 (called aludels) opening into each other, and delivering the mercury into 
 a gutter which conveys it to the receptacles. 
 
 The cinnabar is placed upon the arch (A, Fig. 242) of brickwork, in which there 
 are several openings for the passage of the flame of the wood fire kindled at B ; 
 
 this flame ignites the sulphide of 
 mercury, which burns in the air 
 passing up from below, forming sul- 
 phurous acid gas and vapour of 
 mercury (HgS + 2 = Hg + S0 2 ), 
 which escape through the flue (F) 
 into the aludels (C), where the chief 
 part of the mercury condenses and 
 runs down into the gutter (G). The 
 sulphurous acid gas escapes through 
 the flue (H), and any mercury which 
 may have escaped condensation is 
 Fig-. 242. collected in the trough (D), the gas 
 
 finally passing out through the 
 chimney (E), which provides for the requisite draught. 
 
 In the Palatinate the cinnabar is distilled in cast-iron retorts with 
 lime, when the sulphur is left in the residue as calcium sulphide and 
 sulphate, whilst the mercury distils over 
 
 4 HgS + 4 CaO = sCaS + CaS0 4 + Hg 4 . 
 
 The mercury found in commerce is never perfectly pure, as may be shown by 
 scattering a little upon a clean glass plate, when it tails or leaves a track upon the 
 glass, which is not the case with pure mercury. Its chief impurity is lead, which 
 may be removed by exposing it in a thin layer to the action of nitric acid diluted 
 with two measures of water, which should cover its surface, and be allowed to 
 remain in contact with it for a day or two with occasional stirring. The lead is 
 far more easily oxidised and dissolved than the mercury, though a little of this 
 also passes into solution. The mercury is afterwards well washed with water and 
 
LOOKING-GLASSES. 497 
 
 dried, first with blotting-paper, and then by a gentle heat. Mercury is easily 
 freed from mechanical impurities by squeezing it through a duster. Zinc, tin and 
 bismuth are sometimes present in the mercury of commerce, and may be partly 
 removed, as oxides, by shaking the mercury in a large bottle with a little powdered 
 loaf-sugar for a few minutes, and straining through cloth. The sugar appears to 
 act mechanically by dividing the mercury. 
 
 289. In its chemical properties mercury much resembles silver, being 
 unaffected by ordinary air and tarnished by air containing H 2 S. In 
 course of time, however, it becomes oxidised, as may be seen 2 in old 
 instruments containing mercury and air ; and it is slowly oxidised when 
 heated in air, which is not the case with silver. It also appears to 
 undergo a partial oxidation when reduced to a fine state of division, as 
 in those medicinal preparations of the metal which are made by tritu- 
 rating it with various substances which have no chemical action upon it, 
 until globules of the metal are no longer visible. Blue pill and grey 
 powder, or hydrargyrum cum cretd, afford examples of this, and probably 
 owe much of their medicinal activity to the presence of one of the 
 oxides of mercury. 
 
 Nitric acid (containing nitrous acid) dissolves mercury, and converts 
 it into two nitrates mercurous, HgN0 3 , corresponding with AgN0 3 , 
 and mercuric, Hg(NO 3 ) 2 . Hot concentrated sulphuric acid also con verts 
 it into mercurous (Hg 2 S0 4 ) and mercuric (HgSO 4 ) sulphates. Mercury 
 is precipitated from solutions of its salts by reducing-a gents, stannous 
 chloride, for example, in what looks like a dark grey powder ; but if 
 this be boiled in the liquid, the minute globules of which it is composed 
 gradually unite into fluid mercury. Conversely, if mercury be dili- 
 gently triturated with chalk or grease, it may be divided into extremely 
 minute globules which behave like a powder. 
 
 290. Uses of Mercury. One of the chief uses to which mercury is 
 devoted is the silvering of looking-glasses, which is effected by means of 
 an amalgam of tin in the following manner : A sheet of tinfoil of the 
 same size as the glass to be silvered is laid perfectly level upon a table, 
 and rubbed over with metallic mercury, a thin layer of which is after- 
 wards poured upon it. The glass is then carefully slid on to the table, 
 so that its edge may carry before it part of the superfluous mercury 
 with the impurities upon its surface ; heavy weights are laid upon the 
 glass, so as to squeeze out the excess of mercury, and in a few days the 
 combination of tin and mercury is found to have adhered firmly to the 
 glass ; this coating usually contains about i part of mercury and 4 parts 
 of tin. In this and all other arts in which mercury is used (such as 
 barometer-making) much suffering is experienced by the operatives, 
 from the poisonous action of the mercury. 
 
 The readiness with which mercury unites with most other metals to 
 form amalgams is one of its most striking properties, and is turned to 
 account for the extraction of silver and gold from their ores. The attrac- 
 tion of the latter metal for mercury is seen in the readiness with which 
 it becomes coated with a silvery layer of mercury, whenever it is brought 
 in contact with that metal, and if a piece of gold leaf be suspended at a 
 little distance above the surface of mercury, it will be found, after a 
 time, silvered by the vapour of the metal, which rises slowly even at 
 the ordinary temperature. From the surface of rings which have been 
 accidentally whitened by mercury it may be removed by a moderate 
 
49^ RED OXIDE OF MERCURY. 
 
 heat, or by warm dilute nitric acid, but the gold will afterwards require 
 burnishing. 
 
 Zinc plates are amalgamated, as already explained (p. 14), for use in 
 the galvanic battery. An amalgam of 6 parts of mercury with i part 
 of zinc and i of tin is used to promote the action of frictional electrical 
 machines. 
 
 The addition of a little amalgam of sodium to metallic mercury gives 
 it the power of adhering much more readily to other metals, even to 
 iron. Such an addition has been recommended in all cases where 
 metallic surfaces have to be amalgamated, and especially in the extrac- 
 tion of silver and gold from their ores by means of mercury. Gold 
 amalgam and cadmium amalgam are used by dentists. Sodium amalgam, 
 in contact with water, forms a convenient source of nascent /'atomic) 
 hydrogen. 
 
 Iron and platinum are the only metals in ordinary use which can be 
 employed in contact with mercury without being corroded by it. Mer- 
 cury, however, adheres to platinum. 
 
 The following definite compounds of mercury with other metals have been 
 obtained by combining them with excess of mercury, and squeezing out the fluid 
 metal by hydraulic pressure, amounting to 60 tons upon the inch ; Pb Hg, AgHg, 
 FeHg,* Zn 2 Hg, CuHg, PtHg 2 . AgHg has been found in nature, in dodecahedral 
 crystals. 
 
 A very beautiful crystallisation of the amalgam of silver (Arbor Dianee) may be 
 obtained in long prisms having the composition Ag 2 Hg 3 , by dissolving 400 grains 
 of silver nitrate in 40 measured ounces of water, adding 160 minims of concen- 
 trated nitric acid, and 1840 grains of mercury ; in the course of a day or two 
 crystals of 2 or 3 inches in length will be deposited. 
 
 291. Oxides of Mercury. Two oxides of mercury are known the 
 suboxide, Hg 2 0, and the oxide, HgO ; both combine with acids to form 
 salts. Suboxide of mercury, black oxide, or mercurous oxide, Hg 2 0, is 
 obtained by decomposing calomel with solution of potash, and washing 
 with water; Hg 2 Cl 2 + 2KOH = Hg 2 O + 2KC1 + H 2 0. It is very easily 
 decomposed, by exposure to light or to a gentle heat, into mercuric 
 oxide and metallic mercury. 
 
 Red oxide of mercury, or mercuric oxide (HgO), is formed upon the 
 surface of mercury, when heated (237 C) for some time to its boiling- 
 point in contact with air. The oxide is black while hot, but becomes 
 red on cooling. It is used, under the name of red precipitate, in oint- 
 ments, and is prepared for this purpose by dissolving mercury in nitric 
 acid, evaporating the solution to dryness, triturating the mercuric nitrate 
 with an equal weight of mercury, and heating as long as acid fumes are 
 evolved; Hg(N0 3 ) 2 + Hg 2 = 3HgO + N 2 3 . The name nitric oxide of 
 mercury refers to this process. It is thus obtained, after cooling, as a 
 brilliant red crystalline powder (sp. gr. i i.o), which becomes nearly black 
 when heated, and is resolved into its elements at a red heat. It dissolves 
 slightly in water, and the solution has a very feeble alkaline reaction. 
 A bright yellow modification of the oxide is precipitated when a solution 
 of corrosive sublimate is decomposed by potash (HgCl 2 + 2KOH = 
 HgO + 2KC1 + H 2 0) ; the yellow variety is chemically more active than 
 the red. 
 
 * Hg 3 Fe 2 has been obtained by the action of finely divided iron on sodium amalgam in 
 presence of water. 
 
SALTS OF MERCURY. 499 
 
 When mercuric oxide is attacked by strong ammonia it becomes converted into 
 a yellowish -white powder which possesses the properties of a strong base, absorb- 
 ing carbonic acid eagerly from the air, and combining readily with other acids 
 It is easily decomposed by exposure to light, and if rubbed in a mortar when 
 dry, is decomposed with slight detonations, a property in which it feebly resembles 
 fulminating silver (p. 492). The composition of this substance is represented by 
 the formula NHg" 2 .OH.Aq. When exposed in racuo over oil of vitriol, it loses 
 Aq, becoming NHg" 2 .OH, or diinercuramnioniutn hydroxide, which is a brown 
 explosive base.* When treated with aqueous ammonia it yields Millon's luxe, 
 3(2HgO.NH 3 ).2H 2 0, which is not decomposed by boiling potash, but explodes if 
 evaporated to dryness with the potash. This base will deprive all soluble and 
 most insoluble salts of their acids ; thus it will remove sulphates and chlorides 
 from impure soda solution. 
 
 By passing ammonia gas over the yellow oxide of mercury as long as it is 
 absorbed, and heating the compound to about 127 C. in a current of ammonia as 
 long as any water is evolved, a brown explosive powder is obtained which is 
 believed to be a nitride of mercury, N 2 Hg" 3 , representing a double molecule of 
 ammonia in which the hydrogen has been displaced by mercury. It yields salts of 
 ammonium when decomposed by acids. 
 
 292. The salts formed by the oxides of mercury with the oxygen-acids are not 
 of great practical importance. Protonitrate of mercury, or mercurous nitrate, 
 Hg(N0 3 )Aq, is obtained when mercury is dissolved in cold HN0 3 diluted with five 
 volumes of water. The prismatic crystals which are sometimes sold as proto- 
 nitrate of mercury consist of a basic nitrate, Hg 4 (N0 3 ) 3 OH, prepared by acting with 
 dilute nitric acid upon mercury in excess. When this salt is powdered in a mortar 
 with a little common salt, it becomes black from the separation of mercurous 
 oxide 2Hg 4 (N0 3 ) 3 OH + 6NaCl = 6NaN0 3 + 6HgCl + Hg a O + H 2 0; but the normal 
 nitrate is not blackened (Hg(N0 3 ) + NaCl = HgCl + NaN0 3 ). Mercurous nitrate is 
 soluble in a little hot water, but much water decomposes it into nitric acid and a 
 basic nitrate ; 2Hg(N0 3 ) + H 2 = Hg 2 N0 3 .OH + HN0 3 . 
 
 y it-rate of mercury or mercuric nitrate, 2Hg(N0 3 ) 2 .Aq, is formed when mercury 
 is dissolved in an excess of strong nitric acid, and" the solution boiled until it is 
 no longer precipitated by NaCl. Water decomposes it, precipitating a yellow basic 
 nitrate, which leaves mercuric oxide when long washed with water. Mercuric 
 nitrate stains the skin red. When nitric acid is heated with an excess of mercuric 
 oxide, the solution, on cooling, deposits crystals of a basic mercuric nitrate; 
 Hg. 2 (N0 3 ) 3 .OH.Aq. 
 
 Mercurous sulphate (Hg. 2 S0 4 ) is precipitated as a white crystalline powder when 
 dilute sulphuric acid is added to a solution of mercurous nitrate. 
 
 Mercuric sulphate (HgS0 4 ) is obtained by heating 2 parts by weight of mercury 
 with 3 parts of oil of vitriol, and evaporating to dryness. Mercurous sulphate is 
 first produced, and is oxidised by the excess of sulphuric acid. It forms a white 
 crystalline powder, which becomes brown-yellow when heated, and white again 
 on cooling. It is decomposed by water into a soluble acid sulphate, and an 
 insoluble yellow basic sulphate of mercury, HgS0 4 .2HgO, known as turbith or 
 turpetJi mineral, said to have been so named from its resembling in its medicinal 
 effects the root of the Convolculua turpetkum. 
 
 293. Chlorides of Mercury. The chlorides are the most important 
 of the compounds of mercury, one chloride being calomel (HgCl) and the 
 other corrosive sublimate (HgCL,). Vapour of mercury burns in chlorine 
 gas, corrosive sublimate being produced. 
 
 Corrosive sublimate, chloride of mercury, bichloride or perchloride of 
 mercury, or mercuric chloride, is manufactured by heating 2 parts by 
 weight of mercury with 3 parts of strong sulphuric acid, and evapo- 
 rating to dryness, to obtain mercuric sulphate 
 
 Hg + 2H,S0 4 = HgS0 4 + 2H 2 + S0 2 , 
 
 * It has been stated that by heating it for some time in a current of dry ammonia, it 
 undergoes further change, becoming- the oxide of mercurammonium, (XHg". 2 ). 2 O, winch 
 is very explosive, and combines with water to form a hydrate which produces salts with 
 the acids. 
 
500 CORROSIVE SUBLIMATE. 
 
 which is mixed with i J part of common salt and heated in glass vessels 
 (HgS0 4 + 2NaCl = Na 2 SO 4 + HgCl 2 ), when sodium sulphate is left, and 
 the corrosive sublimate is converted into vapour, condensing on the 
 cooler part of the vessel in lustrous colourless masses, which are very 
 heavy (sp. gr. 5.4), and have a crystalline fracture. It fuses very 
 easily (288 C.) to a perfectly colourless liquid, which boils at 303 C., 
 emitting an extremely acrid vapour, which destroys the sense of smell 
 for some time. This vapour condenses in fine needles, or sometimes in 
 octahedra. Corrosive sublimate dissolves in twice its weight of boiling 
 water, but requires 16 parts of cold water, so that the hot solution 
 readily deposits long four-sided prismatic crystals of the salt. It is 
 remarkable that alcohol and ether dissolve corrosive sublimate much 
 more easily than water does, boiling alcohol dissolving about an equal 
 weight of the chloride, and cold ether taking up one-third of its weight. 
 By shaking the aqueous solution with ether, the greater part of the 
 corrosive sublimate is removed, and remains dissolved in the ether which 
 rises to the surface. An aqueous solution of ammonium chloride will 
 take up corrosive sublimate more easily than pure water will, a soluble 
 double chloride (sal alembroth) being formed, which may be obtained in 
 tabular crystals, HgCl 2 .2NH 4 Cl.H 2 0. A solution of corrosive sublimate 
 in water containing sal-ammoniac is a very efficacious bug-poison. 
 
 Sulphuric acid does not decompose mercuric chloride, though it attacks 
 mercurous chloride. Hydrochloric acid combines with it, forming crys- 
 talline compounds HCl.HgOl, and HC1.2HgCl 2 , which lose HC1 when 
 exposed to air. A crystalline compound, HgCl 2 .H 2 S0 4 , is formed by 
 the action of hydrochloric acid on mercuric sulphate. 
 
 The poisonous properties of corrosive sublimate make it the most 
 powerful antiseptic, and are very marked, so little as three grains having 
 been known to cause death in the case of a child. The white of egg is 
 commonly administered as an antidote, because it is known to form an 
 insoluble compound with corrosive sublimate, so as to render the poison 
 inert in the stomach. The compound of albumin with corrosive 
 sublimate is also much less liable to putrefaction than albumin itself, 
 and hence corrosive sublimate is sometimes employed for preserving 
 anatomical preparations and for preventing the decay of wood (by com- 
 bining with the vegetable albumin of the sap). Mercuric chloride 
 unites with many other chlorides to form soluble double salts, and with 
 mercuric oxide, forming several oxychlorides, which have no useful 
 applications. 
 
 Mercuric chloride has been found native in one of the Molucca Islands. 
 
 White precipitate, employed for destroying vermin, is deposited when 
 a solution of corrosive sublimate is poured into an excess of solution of 
 ammonia ; HgC] 2 + 2NH 3 = NH 4 C1 + NH 2 Hg"Cl (white precipitate). 
 
 The true constitution of white precipitate has been the subject of much discus- 
 sion, but the changes which it undergoes, under various circumstances, appear to 
 lead to the conclusion that it represents ammonium chloride, NH 4 C1, in which half 
 of the hydrogen has been displaced by mercury. When boiled with potash it yields 
 ammonia and mercuric oxide; NH 2 Hg"Cl + KOH = NH 3 + HgO + KCl. If it be 
 boiled with water, it is only partly decomposed in a similar manner, leaving a yellow 
 powder having the composition (NH 2 HgCl).HgO, produced according to the 
 equation 2(NH 2 HgCl) + H 2 = NH 4 Cl + (NH 2 HgCl).HgO. A compound correspond- 
 ing with this yellow powder, but containing mercuric chloride in place of oxide, is 
 precipitated when ammonia is gradually added to solution of corrosive sublimate 
 
CALOMEL. CQI 
 
 in large excess, the result being a compound of white precipitate with a molecule of 
 undecomposed mercuric chloride (NH 2 HgCl).HgCl 2 . A compound having the same 
 formula as the yellow powder, and probably identical with it, is obtained by the 
 action of dilute hydrochloric acid on Millon's base (p. 499) ; it loses water at 
 200 C. and is mercuranunonlum, chloride hydrate, NHg 2 Cl.H 2 0. 
 
 If white precipitate be heated to about 315 C., it evolves ammonia, and yields 
 a sublimate of ammoniated mercuric chloride, HgCl 2 .NH 3 , leaving a red crystalline 
 powder which is insoluble in water and in diluted acids, and is unchanged by boil- 
 ing with potash ; it may be represented as a compound of mercuric chloride with 
 ammonia in which the whole of the hydrogen has been displaced by mercury, 
 JS 2 Hg 3 .2HgCl 2 . When strongly heated, white precipitate yields a sublimate of 
 calomel ; 3NH 2 Hg"Cl = 3 HgCl + N + 2 NH 3 . White precipitate inflames in contact 
 with chlorine or bromine. If it be mixed with about twice its weight of iodine and 
 moistened with alcohol, an explosion occurs in about half an hour, from production 
 of nitrogen iodide. 
 
 When solution of corrosive sublimate is added to a hot solution of sal-ammoniac, 
 mixed with ammonia, a crystalline deposit is obtained on cooling the liquid ; this 
 is also obtained when ammoniacal mercuric chloride is precipitated by an alkaline 
 carbonate ; it is known as fusible white precipitate, and represents two molecules of 
 ammonium chloride, in which one-fourth of the hydrogen has been displaced by 
 mercury, its composition being N 2 H 6 Hg"Cl 2 . The same compound is formed when 
 white precipitate is boiled with solution of sal-ammoniac 
 NH 2 Hg"Cl + NH 4 C1 = N 2 H 6 Hg"Cl 2 . 
 
 The above compounds possess a special interest for the chemist, as they were 
 among the first to attract attention to the mobility of the hydrogen in ammonia, 
 which has since been so well exemplified in the artificial production of organic 
 bases by the action of ammonia upon the iodides of the alcohol-radicles. The 
 relation of these compounds to each other is here exhibited : 
 
 White precipitate NH 2 Hg"Cl 
 
 Produced with corrosive sublimate in excess . (NH 2 HgCl).HgCl 2 
 by boiling with water .... (NH 2 HgCl).HgO 
 
 11 sal-ammoniac . . N H 6 Hg"Cl 2 
 
 by heating to 315 C N 2 ~Hg" 3 .2HgCl 2 
 
 According to Kammelsberg the infusible or true white precipitate loses half of 
 its N as NH 3 when it is boiled with an alkali, while the fusible white precipitate 
 loses three-quarters of its N as NH 3 under the same treatment ; he concludes that 
 they are both double compounds of ammonium chloride and mercurammoniuin 
 chloride, the infusible being NHg 2 Cl.NH 4 Cl, and the fusible NHg 2 C1.3NH 4 Cl. 
 
 294. Calomel, subchloride or protochloride of mercury, or mercuroiw 
 chloride (HgCl), unlike corrosive sublimate, is insoluble in water, so 
 that it is precipitated when hydrochloric acid or a soluble chloride is 
 added to mercurous nitrate. The simplest mode of manufacturing it 
 consists in intimately mixing a molecular weight of corrosive sublimate 
 with an atomic weight of metallic mercury, a little water being added 
 to prevent dust, drying the mixture thoroughly, and subliming it; 
 HgCl 2 + Hg=2HgCl. But it is more commonly made by adding 
 another atomic weight of mercury to the materials employed in the pre- 
 paration of corrosive sublimate ; HgS0 4 + Hg + 2NaCl = 2HgCl + Na 2 S0 4 . 
 The calomel condenses as a translucent, fibrous cake on the cool part of 
 the subliming vessel. For medicinal purposes, the calomel is obtained 
 in a very fine state of division by conducting the vapour into a large 
 chamber so as to precipitate it in a fine powder by contact with a large 
 volume of cold air. Steam is sometimes introduced to promote its fine 
 division. Sublimed calomel always contains some corrosive sublimate, 
 so that it must be thoroughly washed with water before being employed 
 in medicine. When perfectly pure calomel is sublimed, a little is always 
 decomposed during the process into metallic mercury and corrosive 
 sublimate. 
 
 Calomel is met with either as a semi-transparent fibrous mass, or an 
 
5O2 IODIDES OF MEECUEY. 
 
 amorphous powder, with a slightly yellow tinge. Light slowly decom- 
 poses it, turning it grey from separation of mercury. It is heavier than 
 corrosive sublimate (sp. gr. 7.18), and does not fuse before subliming; 
 it may be obtained in four-sided prisms by slow sublimation. Dilute 
 acids will not dissolve it, but boiling nitric acid gradually converts it 
 into mercuric chloride and nitrate, which pass into solution. Boiling 
 hydrochloric acid turns it grey, some mercury being separated, and 
 mercuric chloride dissolved. Mercuric nitrate dissolves it, forming 
 mercuric chloride and mercurous nitrate. Alkaline solutions convert 
 it into black mercurous oxide, as is seen in black-wash, made by treating 
 calomel with lime water ; Hg ? Cl 2 + Ca(OH) 2 = Hg 2 + CaCl 2 + H 2 0. Solu- 
 tion of ammonia converts it into a grey compound (NH 2 Hg.,Cl), which is 
 the analogue of white precipitate (NH 2 Hg"Cl), containing Hg' 2 in place 
 of Hg". Calomel is found as horn quicksilver at Idria and Almaden, 
 crystallised in rhombic prisms. 
 
 It is asserted that calomel is dissociated by heat into Hg and HgCl 2 so that its 
 vapour density does not decide its molecular weight. When, however, the 
 vaporisation is performed in presence of HgCl 2 , so that the dissociation is hindered 
 (p. 313), the vapour density is found to be about 117.5, showing that HgCl is most 
 probably the molecular formula for calomel. The presence of metallic mercury in 
 calomel vapour is shown by the deposition of minute globules of mercury on a cold 
 tube coated with gold immersed in the vapour at 440 C. 
 
 Mercurom Iodide, Hgl, is a green unstable substance, formed when iodine is 
 triturated with an excess of mercury and a little alcohol, or by precipitating 
 mercurous nitrate with potassium iodide. It owes its green colour to the presence 
 of excess of mercun r ; when precipitated in a solution containing HN0 3 it is yellow. 
 With care, it may be sublimed in yellow crystals, isomorphous with mercurous 
 chloride, but if sharply heated it is decomposed into Hg and Hgl. 2 . Potassium 
 iodide decomposes it in a similar way, dissolving the mercuric iodide. When 
 mercuric chloride is boiled with HC1 and copper the solution gives with KI a dark 
 red precipitate of mercui'oso-mer curie iodide, insoluble in excess of the KI. 
 
 Mercuric iodide, or iodine scarlet, HgI 2 , is the bright red precipitate produced by 
 potassium iodide in mercuric chloride. At the moment of precipitation it is yellow, 
 rapidly becoming fawn coloured and red. When the dry mercuric iodide is heated, 
 it becomes bright yellow at temperatures above 126 C., and remains so on cooling 
 until touched with a hard body, when it becomes red again, the colour spreading 
 from the point touched. Under the microscope, the red iodide is seen to be 
 octahedral and the yellow to consist of rhombic tables. When the yellow iodide is 
 heated, it fuses easily (238 C.), becomes brown, and is converted into a colourless 
 vapour which condenses in yellow crystals on a cold surface. 
 
 A very beautiful experiment is made by gently heating mercuric iodide in a large 
 porcelain crucible covered with a dial-glass ; the yellow iodide is deposited in 
 crystals projecting from the under surface of the glass, and if this be placed o-n the 
 table with the crystals upwards, and some of these be touched with a needle, the 
 red spots appear like poppies among corn, and the blush gradually spreads over the 
 entire field, attended by a rustling movement caused by the change in crystalline 
 form.* 
 
 The transformation of the yellow HgI 2 into the red HgI 2 evolves 3000 gram-units 
 of heat. Mercuric iodide dissolves in hot alcohol, and crystallises in red octahedra, 
 Ether also dissolves it. It is freely soluble in solutions of mercuric chloride and 
 potassium iodide. The latter yields yellow prisms of 2(HgI 2 .KI).3Aq. The solution 
 of this salt mixed with potash forms Nettfer'if solution, which gives a brown 
 precipitate with very minute quantities of ammonia 
 
 2HgI 2 + 3KOH + NH 3 = NHg 2 I.H 2 + 3KI + 2H 2 0. 
 
 The vapour density of mercuric iodide is of course very high, being 15.68 times 
 that of air, showing that the formula HgI 2 represents two volumes. 
 
 295. Sulphides of Mercury. When mercury is triturated with sul- 
 phur, the black subsulphide of mercury, or mercurous sulphide (Hg 2 S), is 
 
 * The author is indebted for this experiment to Mr. Herbert Jackson, of King's College. 
 
VERMILION. 503 
 
 formed ; it was termed by old writers Ethiopia mineral, and is an 
 unstable compound easily resolved into metallic mercury and mercuric 
 sulphide (HgS). The latter has been mentioned as the principal ore of 
 mercury, and is important as composing vermilion. The native mer- 
 curic sulphide, or cinnabar, is found sometimes in amorphous masses, 
 sometimes crystallised in six-sided prisms varying in colour from dark 
 brown to bright red. It may be distinguished from most other 
 minerals by its great weight (sp. gr. 8.2), and by its red colour when 
 scraped with a knife. Neither hydrochloric nor nitric acid, separately, 
 will dissolve it, but a mixture of the two dissolves it as mercuric 
 chloride, with separation of sulphur. Some specimens of cinnabar have 
 a bright red colour, so that they only require grinding and levigating to 
 be used as vermilion ; and if the brown cinnabar in powder be heated 
 for some time at 120 F. (49 C.) with a solution of sulphur in potash, 
 it is converted into vermilion. 
 
 Of the artificial mercuric sulphide there are two varieties the black, 
 which is precipitated when corrosive sublimate is added to hydrosulpburic 
 acid or a soluble sulphide, and the red (vermilion), into which the black 
 variety is converted by sublimation, or by prolonged contact with 
 solutions of alkali sulphides containing excess of sulphur, though, so 
 far as is known, the conversion is effected without chemical change, the 
 red sulphide having the same composition as the black. 
 
 In Idria and Holland, 6 parts of mercury and I of sulphur are well agitated 
 together in revolving casks for several hours, and the black sulphide thus obtained 
 is sublimed in tall earthen pots closed with iron plates, when the vermilion 
 is deposited in the upper part of the pots, and is afterwards ground and levigated. 
 One of the wet processes for making vermilion consists in triturating 300 parts of 
 mercury with 114 parts of sulphur for two or three hours and digesting the black 
 product, at about 120 F. (49 C.), with 75 parts of caustic potash and 400 of water 
 until it has acquired a fine red colour. The vermilion made by the dry process 
 is the more highly prized. The permanence of vermilion paint, is, of course, 
 attributable to the circumstance that it resists the action of light, of oxygen, 
 carbonic acid, aqueous vapour, and even of the sulphuretted hydrogen, and 
 sulphurous or sulphuric acid which contaminate the air of towns, whereas the red 
 paints containing lead are blackened by sulphuretted hydrogen, and all vegetable 
 and animal reds are liable to be bleached by atmospheric oxygen and by sulphurous 
 acid. 
 
 The conversion of the black mercuric sulphide into the red form is quickly 
 effected by boiling it with freshly prepared ammonium poly sulphide (made by 
 saturating ammonia with H 2 S and dissolving sulphur in the liquid, gently warmed, 
 until it has a dark sherry colour). If this solution be poured upon the freshly 
 precipitated black sulphide, and boiled for a minute, the sulphide assumes a 
 crystalline appearance, and a bright vermilion colour (Herbert Jackson). - 
 appears that the black form is more soluble than the red, so that when the pplysu 
 phide solution becomes saturated with the black form it is supersaturated with tm 
 red, which therefore separates ; another portion of the black then dissolves, ar 
 on, until the conversion is complete. , , 
 
 If the black sulphide be boiled with potassium sulphide and potash, it is 
 and the solution deposits white needles of HgS.K 2 S.5H 2 0, which are decompos 
 "wi it- Gi* 
 
 When the black precipitated mercuric sulphide is boiled with solution of corro- 
 sive sublimate, it is converted into a white chloromlphide of mercury, t\\ 
 which is also formed when a small quantity of hydroRulphuric acic is aoo 
 corrosive sublimate, becoming yellow, brown, and black on adding mor 
 
 Vermilion may be prepared bv adding HgCl 2 to a slight excess of dilute aim 
 nearly dissolving the precipitate in sodium thiosulphate (hyposulphite) and h 
 when a bright yellow precipitate is obtained, which becomes 
 boiling. 
 
504 EXTE ACTION OF PLATINUM. 
 
 By suspending HgS in air-free water and passing H 2 S, a dark-coloured solution 
 of colloidal mercuric sulphide can be obtained. 
 
 At 1560 C. the vapour density of mercuric sulphide is 78, indicating 
 that the molecule has dissociated into Hg + Hg -f S 2 . 
 
 Mercury belongs to the Magnesium family of metals (p. 383). 
 
 PLATINUM. 
 
 Pt= 193.3 P ai 'ts by weight. 
 
 296. Platinum (platina, Spanish diminutive of silver) is remarkable 
 for (i) its high specific gravity of 21.5 ; (2) its very high fusing-point, 
 1775 G- (3) its slight expansion when heated, which allows it to be 
 sealed into glass without cracking by unequal contraction on cooling ; 
 (4) its being unchanged by air at all temperatures ; (5) its resistance 
 to the action of strong acids ; (6) its power of inducing the combination 
 of oxygen with other bodies ; (7) its being found in nature only in the 
 metallic state. It is found distributed in flattened grains through alluvial 
 deposits similar to those in which gold is found ; indeed, these grains are 
 generally accompanied by grains of gold, and of a group of very rare 
 metals only found in platinum ores, viz., palladium, iridium, osmium, 
 rhodium, and ruthenium. Russia furnishes the largest supply of 
 platinum from the Ural Mountains, but smaller quantities are obtained 
 from Brazil, Peru, Borneo, Australia, and California. 
 
 The process for obtaining the platinum in a marketable form is rather 
 a chemical than a metallurgical operation. The ore containing the grains 
 of platinum and the associated metals, is heated with hydrochloric acid 
 to dissolve base metals, and then, in retorts, under slightly increased 
 pressure to hasten the dissolution, with aqua regia, which dissolves 
 palladium, rhodium, platinum, and a little iridium as chlorides. The 
 osmium in the ore partly distils as osmic acid and partly remains 
 undissolved as an alloy with the iridium (osmiridiuni), together with 
 ruthenium, chrome iron ore, and titanic iron. The solution containing 
 the platinum as PtCl 4 is neutralised with Na,C0 3 and the palladium is 
 precipitated as cyanide, Pd(CN) 2 , by the addition of mercuric cyanide. 
 The platinum is now precipitated by the addition of ammonium chloride, 
 with which platinic chloride combines to form a yellow, sparingly soluble 
 salt (ammonium platinochloride (NH 4 ) 2 PtCJ 6 or 2NH 4 Cl.PtCl 4 ).* This 
 precipitate is collected, washed, and heated to redness, when all its 
 constituents, except the platinum, are expelled in the form of gas, that 
 metal being left in the peculiar porous condition in which it is known 
 as spongy platinum. To convert this into compact platinum it is melted 
 in a lime furnace by means of the oxyhydrogen blow r -pipe (Fig. 243), 
 whence it is poured into an ingot mould made of gas-carbon. The 
 melted platinum absorbs oxygen, as melted silver does, and evolves it 
 again on cooling. 
 
 This method is now modified by fusing the ore with 6 parts of lead, and treating 
 the alloy with dilute nitric acid (i : 8), which dissolves most of the lead, together 
 
 * When rhodium is present, the liquid from which this precipitate has been deposited will 
 have a rose colour. The precipitate is then mixed with bisulphate of potassium and a little 
 bisulphate of ammonium, and heated to redness in a platinum dish. The rhodium is then 
 converted into a double sulphate of rhodium and potassium, which may he removed from the 
 spongy platinum by boiling with water. 
 
PKOPERTIES OF PLATINUM. 505 
 
 with copper, iron, palladium, and rhodium. The residue, containing platinum lead 
 and indium, is treated with dilute aqua regia, which leaves the indium undfoeolved' 
 The lead is precipitated by sulphuric acid, and the solution of platinic chloride 
 
 tT6iltCCi RS clDOVG. 
 
 Another process based upon the use of lead consists in fusing the platinum ore 
 m a small reverberatory furnace, with an equal weight of lead sulphide and the same 
 quantity of lead oxide when the sulphur and oxygen 
 escape as S0 2 , and the reduced lead dissolves the 
 platinum, leaving undissolved a very heavy alloy 
 of osmium and iridium, which sinks to the bottom. 
 The upper part of the alloy of lead and platinum is 
 then ladled out and cupelled (p. 465), when the 
 latter metal is left in a spongy condition, the lead 
 being removed in the form of oxide. 
 
 Its resistance to the action of high tem- 
 peratures and of most chemical agents 
 renders platinum of the greatest service in 
 chemical operations. It will be remem- 
 bered that platinum stills are employed, 
 even on the large scale, for the concen- 
 tration of sulphuric acid. In the form of 
 
 basins, small crucibles, foil, and wire, this metal is indispensable to the 
 analytical chemist. Unfortunately, it is softer than silver, and there- 
 fore ill-adapted for wear, and is so heavy that even small vessels must 
 be made very thin in order not to be too heavy for a delicate balance. 
 Commercial platinum generally contains a little iridium, which hardens 
 it and increases its elasticity. Its malleability and ductility are very 
 considerable, so that it is easily rolled into thin foil and drawn into fine 
 wires ; in ductility it is surpassed only by gold and silver, and it has 
 been drawn, by an ingenious contrivance of Wollaston's, into wire of 
 only 3-^.i.^th of an inch in diameter, a mile of which (notwithstanding 
 the high specific gravity of the metal) would only weigh a single grain. 
 
 This remarkable extension of the metal was effected by casting a cylinder of silver 
 around a very thin platinum wire obtained by the ordinary process of wire-drawing ; 
 when the cylinder of silver, with the platinum wire in its centre, was itself drawn 
 out into an extremely thin wire, of course, the platinum core would have become 
 inconceivably thin, and when the silver casing was dissolved off by nitric acid, 
 this minute filament of platinum was left. Platinum is sometimes employed for 
 the touch-holes of fowling-pieces on account of its resistance to corrosion. An 
 alloy of 4 parts platinum, 3 parts silver, and I part copper is used for pens. 
 
 The widest application of platinum, however, is in the form of wire 
 for conveying the electric current to the filament in an electric 
 incandescence lamp. As such lamps must be vacuous the leading-in 
 wires must be hermetically sealed in the glass, which is possible only 
 with platinum, its coefficient of expansion being nearer to that of glass 
 than is the coefficient of any other metal. 
 
 The remarkable power possessed by platinum, of inducing chemical 
 combination between oxygen and other gases, has already been noticed. 
 Even the compact metal possesses this property, as may be seen by 
 heating a piece of platinum foil to redness in the flame of a gas-burner, 
 rapidly extinguishing the gas, and turning it on again, when the 
 cold stream of gas will still maintain the metal at a red heat, in con- 
 sequence of the combination with atmospheric oxygen at the surface of 
 the platinum. 
 A similar experiment may be made by suspending a coil of platinum wire in the 
 
506 PLATINUM BLACK. 
 
 flame of a spirit lamp (Fig. 244), and suddenly extinguishing the flame, when the 
 metal is intensely heated, by placing the mouth of a test-tube over it ; the wire 
 will continue to glow by inducing the combination of the spirit vapour with oxygen 
 on its surface. By substituting a little ball of spongy platinum for the coil of 
 platinum wire, and mixing some fragrant essential oil with the spirit, an elegant 
 perfuming lamp has been contrived. Upon the same principle an instantaneous 
 light apparatus has been made, in which a jet of hydrogen gas 
 is kindled by impinging upon a fragment of cold spongy platinum, 
 Y/hich at once ignites it by inducing its combination with the 
 oxygen condensed within the pores of the metal (Dobfireiner'x 
 lattt/j'). Spongy platinum is obtained in a very active form by 
 heating the ammonio-chloride of platinum very gently in a stream 
 of coal gas or hydrogen as long as any fumes of HC1 are evolved. 
 If platinum be precipitated in the metallic state from a solution, 
 it is obtained in the form of a powder, called platinum black, 
 which possesses this power of promoting combination with oxygen 
 in the highest perfection. This form of platinum may be obtained 
 Fig. 244. by boiling solution of platinic chloride with Rochelle salt (potas- 
 
 sium sodium tartrate), or by dropping it into a boiling mixture of 
 3 vols. glycerine and 2 vols. KOH of sp. gr. 1.08, when the platinum black is pre- 
 cipitated, and must be filtered off, washed, and dried at a gentle heat. 
 
 Platinum in this form is capable of absorbing 800 times its volume of oxygen, 
 which does not enter into combination with it, but is simply condensed into its 
 pores, and is available for combination with other bodies. A jet of hydrogen 
 allowed to pass on to a grain or two of this powder is kindled at once, and if a 
 few particles of it be thrown into a mixture of hydrogen and oxygen, explosion 
 immediately follows. A drop of alcohol is also inflamed when allowed to fall 
 upon a little of the powder. Platinum black loses its activity after having been 
 heated to redness. It has been stated that platinum black is really an oxide, and 
 that the combustion of hydrogen and oxygen in presence of platinum is to be 
 explained by the formation, at first, of an unstable hydride of platinum, with de- 
 velopment of heat, which is oxidised with a still further development of heat. 
 By a continued repetition of these changes, the platinum is raised to the tempera- 
 ture necessary for ignition. 
 
 Although platinum resists the action of hydrochloric and nitric acids, 
 unless they are mixed, and is unaffected at the ordinary temperature by 
 other chemical agents, it is easily attacked at high temperatures by 
 phosphorus, arsenic, carbon, boron, silicon, and by a large number of 
 the metals ; the caustic alkalies and alkaline earths also corrode it whei 
 heated, so that some discretion is necessary in the use of vessels mad( 
 of this costly metal.* When platinum is alloyed with 10 parts of silver, 
 both metals may be dissolved by nitric acid. 
 
 If platinum be dissolved in 4 or 5 parts of melted tin, and the alloy boil* 
 with hydrochloric acid mixed with an equal bulk of water, glistening scales ai 
 left, resembling graphite, and soiling the fingers. This contains platinum, tin, 
 chlorine, hydrogen, and oxygen. By treatment with warm dilute ammonia, it 
 becomes brownish, and when dried in a vacuum over sulphuric acid, has the 
 composition Ptv,Sn 3 4 H 2 . When this is heated in dry oxygen, it becomes Pt 2 Sn 3 4 . 
 Heated in hydrogen it leaves a greyish almost infusible powder containing Pt 2 Sn 3 . 
 
 297. OXIDES OF PLATINUM. Only one compound of platinum with oxygen is 
 known in the separate state, the other having been obtained in combination with 
 water. Platinou* oxide, PtO, is precipitated as a black hydrate by decomposing- 
 platinous chloride with potash, and neutralising the solution with dilute sulphuric 
 acid. It is a feeble base, and decomposes when heated, leaving metallic platinum. 
 Platinic oxide, Pt0 2 , is also a weak base, but is characteristically an acid oxide. 
 
 Platinic lt,ydroj'ide, Pt(OH) 4 , is obtained by boiling platinic chloride \vith potash, 
 and treating the precipitate with acetic acid ; this leaves a nearly white powder, 
 Pt(OH) 4 .2H 2 0. At 100 C. this becomes brown Pt(OH) 4 . Acids dissolve it, forming- 
 
 * When platinum leaf is heated with HC1 at 150 in a sealed tube it dissolves, but the 
 chloride is subsequently reduced by the hydrogen evolved, and the metal reappears as 
 crystals on the sides ol the tube. The same lias been observed of yold and silver leaf. 
 
PLATINIC CHLORIDE. 
 
 507 
 
 platinic salts. Alkalies dissolve it, forming platinates. Heat reduces the oxides 
 and hydroxides to metallic platinum. 
 
 Sodium platinate, Na 2 0.3Pt0 2 .6Aq, may be crystallised from a solution of the 
 hydroxide in soda. Calcium platinate is convenient for the separation of platinum 
 from iridium, which is generally contained in the commercial metal ; for this 
 purpose, the platinum is dissolved in nitre-hydrochloric acid, the solution 
 evaporated till it solidifies on cooling, the mixed chlorides of iridium and platinum 
 dissolved in water, and decomposed with an excess of lime without exposure to light ; 
 the platinum then passes into solution as calcium platinate. and the platinic acid 
 may be separated as a calcium salt from the filtered solution, by exposure to light. 
 If platinic hydroxide be dissolved in diluted sulphuric acid and the solution mixed 
 with excess of ammonia, a black precipitate of fulminating platinum is obtained, 
 which detonates violently at about 400 F. (204 C.). This compound is said to 
 have a composition corresponding with the formula N 2 H 2 Pt iv .4H 2 0, or a com- 
 bination of water with a double molecule of ammonia (N 2 H 6 ), in which 4 atoms of 
 hydrogen are exchanged for i atom of tetravalent platinum. 
 
 298. Chlorides of Platinum. The per chloride or platinic chloride, 
 (PtCl 4 ), is the most useful salt of the metal, and may be prepared by 
 dissolving scraps of platinum-foil in a mixture of four measures of 
 hydrochloric acid with one of nitric acid (6.5 grams of platinum require 
 56 c.c. of hydrochloric acid), evaporating the liquid at a gentle heat to 
 the consistence of a syrup, redissolving in hydrochloric acid, and again 
 evaporating to expel excess of nitric acid. The syrupy liquid solidifies, 
 on cooling, to a red-brown mass, which is very deliquescent, and dis- 
 solves easily in water or alcohol to a red-brown solution. If the con- 
 centrated solution be allowed to cool before all the free hydrochloric 
 acid has been expelled, long brown prismatic crystals of a combination 
 of platinic chloride with hydrochloric acid are obtained (PtCl 4 .2HC1.6Aq). 
 If these are heated in dry HC1, the anhydrous PtCl 4 is obtainecF in a 
 non-deliquescent condition ; it decomposes Na 2 C0 3 , evolving C0 2 . 
 Platinic chloride is remarkable for its disposition to form sparingly 
 soluble double chlorides with the chlorides of the alkali metals and the 
 hydrochlorides of organic bases, a property of great value to the chemist 
 in effecting the detection and separation of these bodies. These double 
 chlorides are generally regarded as platinochlorides or chloroplatinates, 
 derived from hydrogen platinochloride, or chloroplatinic acid, H 2 PtCl 6 . 
 
 A good example of this has lately been afforded in the separation of potassium, 
 rubidium, and caesium. The chlorides of these three metals having been 
 separated from the various other salts contained in the mineral water in which 
 they occur, are precipitated with platinic chloride, which forms combinations 
 with all the three chlorides. The platino-chloride of potassium is more easily 
 dissolved by boiling water than are those of rubidium and cesium, and is removed 
 by boiling the mixed precipitate with small portions of water as long as the latter 
 acquires a yellow colour. The remaining platino-chlorides of rubidium and 
 caesium are then heated in a current of hydrogen, which reduces the platinum to 
 the metallic state, and the chlorides may then be extracted by water, in which they 
 are very soluble. 
 
 Potassium platinochloride ( 2 KCl.PtCl 4 ) forms minute yellow octa- 
 hedral crystals ; those of rubidium and caesium have a similar r.omposi- 
 tion and crystalline form. Sodium platinochloride differs from these 
 in being very soluble in water and alcohol ; it may be crystallised in 
 long red prisms, having the composition 2NaCl.PtCl 4 .6Aq. Ammonium 
 platinochloride ( 2 NH 4 Cl.Pt01 4 ) has been already noticed as the form m 
 which platinum is precipitated in order to separate it from other metals. 
 It crystallises, like the potassium-salt, in yellow octahedra, which are 
 very sparingly soluble in water and insoluble in alcohol. It is the torm 
 
5O8 PLATINOUS CHLORIDE. 
 
 into which nitrogen is finally converted in analysis in order to determine 
 its weight. When heated to- redness, this salt leaves a residue of spongy 
 platinum. Silver nitrate, added in excess to platinic chloride containing 
 HC1, precipitates all the platinum as 2AgCl.Pt01 4 , a yellow precipitate 
 decomposed by water. 
 
 Platinic chloride is sometimes used for browning gun-barrels, &c., 
 under the name of muriate ofplatina. 
 
 Protocldorlde, or plat i turns chloride (PtCl 2 ). Platinic chloride may be heated to 
 450 F. (232 C.) without decomposition, but above that temperature it evolves 
 chlorine, and is slowly converted into the platinous chloride, which is reduced, at 
 a much higher temperature, to the metallic state. Platinous chloride forms a dingy 
 green powder, which is insoluble in water and in HN0 3 and H 2 S0 4 , but dissolves 
 in hot HC1, and in solution of platinic chloride, yielding in the former a bright red, 
 in the latter a very dark brown-red solution. Platinous chloride is capable of 
 absorbing ethylene, C 2 H 4 . At 250 C. it absorbs CO and forms the crystalline com- 
 pounds PtCl 2 .CO, PtCl 2 (CO) 2 , and (PtCl 2 ) 2 (CO) 3 , and the non-volatile compound 
 PtCl 2 .2COCl 2 ; the first of these volatilises unchanged. The solution of PtCl 2 in 
 HC1 is not precipitated by KC1, but a soluble double chloride (2KCl.PtCl 2 ) may be 
 crystallised |from the liquid. If NH 4 C1 be added to the hydrochloric solution, a 
 double salt, 2NH 4 Cl.PtCl 2 . ammonium- cldoroplatimte, may be obtained in yellow 
 crystals by evaporation. If, instead of NH 4 C1, free NH 3 be added in excess to the 
 boiling solution of platinous chloride in HC1. brilliant green needles (f/reen suit of 
 Maynus) are deposited on cooling, which contain the elements of platinous chloride 
 and ammonia, PtCl 2 (NH 3 ) 2 ; but from the behaviour of this compound with 
 chemical agents, its true formula would appear to be N 2 H 6 Pt"Cl 2 , in which the 
 place of two atoms of hydrogen in 2 molecules of NH 4 C1 is occupied by platinum. 
 By heating this salt with an excess of ammonia, the solution, on cooling, 
 deposits yellowish- white prismatic crystals of diplatosamine hydrochlorlde, 
 N 4 H ]0 Pt".2HCl.Aq, the production of which may be represented by the equation 
 N 2 H 6 Pt"Clo + 2NH 3 = N 4 H 10 Pt".2HCl. By decomposing a solution of this salt with 
 silver sulphate, the dl platosamine mlpltate is obtained. 
 
 N 4 H 10 Pt".2HCl + Ag 2 S0 4 = N 4 H 10 Pt".H 2 S0 4 + 2AgCl. 
 
 When the solution of diplatosamine sulphate is treated with barium hydroxide, 
 barium sulphate is precipitated, and a powerfully alkaline solution is obtained, 
 which yields crystals of diplatosamine liydrate, N 4 H 10 Pt".2H 2 0, a strong alkali 
 which may be iregarded as a compound of water with 4 molecules of ammonia 
 (N 4 H 12 ), in which two atoms of hydrogen are exchanged for platinum. The dipla- 
 tosamine hydrate has a strong resemblance to the alkalies, eagerly absorbing C0 2 
 from the air, and expelling NH 3 from its salts. When the hydrate of diplatosamine 
 is heated to 1 10 C. it gives off water and ammonia, and becomes converted into a 
 grey insoluble substance, which is platoxamine hydrate, N. 2 H 4 Pt".H 2 0, and may be 
 regarded as a compound of water with a double molecule of ammonia (N 2 H 6 ), in 
 which one-third of the hydrogen is exchanged for platinum. This substance is also 
 a base, and forms salts, most of which are insoluble ; the hydrochloride (N 2 H 4 Pt,2HCl) 
 is isomeric with the green salt of Magnus, and may be obtained from that com- 
 pound by dissolving in a hot solution of (NH 4 ) 2 S0 4 *from which it crystallises on 
 cooling.* 
 
 If the platosamine liydrochloride, suspended in boiling water, be treated with 
 chlorine, it is converted into platinamine h-ydrochlorid-e, N 2 H 2 Pt iv .4HCl. The con- 
 version of the platosamine hydrochloride into platinamine hydrochloride may 
 be represented by the equation N 2 H 4 Pt.2HCl + Cl 2 = N 2 H 2 Pt.4HCl. By boiling 
 the platinamine hydrochloride with silver nitrate, it is converted into platinamine 
 nitrate, N 2 H 2 Pt(HN0 3 ) 4 ; and when this is dissolved in boiling water and decom- 
 posed by ammonia, the platinam ine hydrate (N 2 H Pt.4H 2 0) is obtained in yellow 
 prismatic crystals, having the same composition as that assigned to fulminating 
 platinum. 
 
 * The salts of diplatosamine are distinguished from those of platosamine by the action of 
 nitrous acid, which gives a tine blue or green precipitate or coloration with the former. For 
 the cause of this change, and for many other interesting points in the history of these 
 platinum compounds, the reader is referred to the elaboi-ate and accurate memoir by Hado\v, 
 Journal of the Chemical Society, August 1866. 
 
PROPERTIES OF PALLADIUM. 509 
 
 Some of the salts of diplatinamim (N 4 H 8 Pt iv ) have been obtained, this base being 
 derived from 4 molecules of ammonia in which H 4 have been exchanged for Pt iv 
 
 Potassium platinonitrite, K 2 Pt(N0 2 ) 4 , crystallises when a hot mixture of potassium 
 nitrite and potassium platinous chloride solution is allowed to cool ; it readily 
 combines with 2 atomic proportions of a halogen. The acid H Pt(N0 9 ), has been 
 prepared. 
 
 Platinw iodide, PtI 4 , is a dark brown amorphous substance which is soluble 
 in HI, yielding a purple-red solution containing 2HI.PtI 4 .9Aq, which may be 
 crystallised. Hence the dark red colour when an acid solution of PtCl 4 is added 
 to potassium iodide. 
 
 The sulphides of platinum correspond in composition with the oxides and 
 chlorides, and may be obtained by the action of hydrosulphuric acid upon the 
 respective chlorides, as black precipitates. PtS 2 combines with alkaline sulphides 
 to form soluble compounds. K 2 S.3PtS.PtS is obtained by fusing spongy platinum 
 with KOH and sulphur. 
 
 Platinum phosphide, PtP 2 , and arsenide, PtAs^ are lustrous metallic bodies formed 
 by direct combination at a high temperature. 
 
 PALLADIUM, Pd=io5.2. 
 
 299. This metal is found in small quantity associated with native gold and 
 platinum. It presents a great general resemblance to platinum, but is distinguished 
 therefrom by being far more easily oxidised, and by forming an insoluble cyanide. 
 This circumstance is taken advantage of in separating palladium from the platinum 
 ores (p. 504). The cyanide yields spongy palladium when heated, which may be 
 fused in the same manner as platinum. When alloyed with native gold, palladium 
 is separated by fusing the alloy with silver, and boiling it with ni+- ic acid, which 
 leaves the gold undissolved. The silver is precipitated from the solution as chloride, 
 by adding NaCl, and metallic zinc is placed in the liquid, which precipitates the 
 palladium, lead, and copper as a black powder. This is dissolved in HN0 3 , and the 
 solution mixed with an excess of NH 3 , which precipitates the lead oxide, leaving the 
 copper and palladium in solution. On adding HC1 in slight excess, a yellow 
 precipitate of palladamlne liydrochloride (N 2 H 4 Pd.2HCl) is obtained, which 'leaves 
 metallic palladium when heated. 
 
 Palladium is much lighter (sp. gr. n.8) than platinum; it is malleable and 
 ductile like that metal from which it is distinguished by being stained black by 
 an alcoholic solution of iodine. It is capable of being highly polished and is 
 useful for mirrors. It melts at 1500 C. It is unchangeable in air unless heated, 
 when it becomes blue from superficial oxidation, but regains its whiteness when 
 further heated, the oxide being decomposed. Unlike platinum, it may be dissolved 
 by nitric acid, forming palladium nitrate, Pd(N0 3 ) 2 , which is sometimes employed 
 in analysis for precipitating iodine from the iodides, in the form of black palladium 
 iodide (PdI 2 ). Palladium is useful, on account of its hardness, lightness, and 
 resistance to tarnish, in the construction of philosophical instruments ; alloyed with 
 twice its weights of silver, it is used for small weights. Its capacity for absorbing 
 hydrogen has been already noticed (p. 49). 
 
 Palladium forms three oxides ; Pd.,0 is formed when the metal is heated in air : 
 PdO is left when Pd(N0 3 ) 2 is gently heated ; Pd0 is precipitated by boiling 
 PdCl 4 with Na, 2 CO 3 . Palladia chloride (PdCl 4 ) is "very unstable, being easily 
 decomposed, eve~n in solution, into palladom chloride (PdCl 2 ) and free chlorine. 
 The latter chloride is reduced by hydrogen in the cold, and may be applied as 
 a test for this gas. Both the chlorides form double salts with the alkali chlorides ; 
 ammonium chloropalladite, PdCl 2 .2NH 4 Cl, has a dark green colour. PdCl is said to 
 be formed when PdCl 2 is gently heated. Pulverulent palladium cat-hide is formed 
 when the metal is heated in the flame of a spirit-lamp, or in gaseous hydrocarbons. 
 
 RHODIUM, Rh=io2.2. 
 
 300. Rhodium, another of the metals associated with the ores of platinum, hot* 
 acquired its name from the red colour of many of its salts (p68oi>, a rose). 
 
 is obtained from the solution of the ore in aqua regla by precipitating the platin 
 with ammonium chloride, neutralising with sodium carbonate, adding mercuric 
 cyanide to separate the palladium, and evaporating the filtered solution to dry- 
 ness with excess of hydrochloric acid. On treating the residue with alcohol, tl 
 double chloride of rhodium and sodium is left undissolved as a red powder, i5y 
 
510 OSMIUM. 
 
 heating this in a tube through which hydrogen is passed, the rhodium is reduced 
 to the metallic state, and the sodium chloride may be washed out with water, 
 leaving a grey powder of metallic rhodium. Avhich is fused by the oxyhydrogen 
 blow-pipe at 200 C., and forms a very hard malleable metal (sp. gr. 12.1) not 
 dissolved even by aqua regla, although this acid dissolves it in ores of platinum, 
 because it is alloyed with other metals. If platinum be alloyed with 30 per cent, of 
 rhodium, however, it is not affected by aqua regia, which will probably render the 
 alloy useful for chemical vessels. Rhodium may be brought into solution by 
 fusing it with bisulphate of potash, when S0 2 escapes, and a double sulphate of 
 rhodium and potassium is formed, which gives a pink solution in water. When 
 rhodium is melted with zinc and the alloy is boiled with an acid, the rhodium 
 is left as a black powder which is apparently an allotropic form of the metal, 
 for when it is heated it explodes, but remains metallic rhodium. Finely divided 
 rhodium is oxidised, when heated in air, to KhO. There appear to be three other 
 oxides, namely, Rh 2 3 , which is left when the nitrate is gently heated ; Rh0 2 , 
 formed when the metal is fused with KOH and KN0 3 ; Rh6 3 , formed by heating 
 the hydrated dioxide (which is a green precipitate obtained when chlorine is 
 passed into potash containing Kh 2 3 ) with nitric acid. The sesquioxide (Rh 2 3 ) is 
 the most stable of these ; it is not easily decomposed by heat, and is insoluble in 
 acids, though it is a basic oxide, and its salts, which have a red colour, are obtained 
 by indirect methods. 
 
 The salts of rhodium are only of one type RX 3 . Rhodium, trichloride, RhCl 3 , 
 obtained by heating the metal in chlorine, has a brownish-red colour and is 
 insoluble ; it may, however, be obtained in a red solution by dissolving the 
 hydrated Rh 2 3 in HC1. Rhodium recalls chromium in that its salts are 
 capable of existing in two forms ; thus, when the red solution of rhodium chloride 
 is boiled with a strong solution of alkali, black Rh(OH) 3 is thrown down, but when 
 the alkali is added by degrees, yellow Rh(OH) 3 is precipitated ; this dissolves to a 
 yellow solution in acids, which becomes red only on boiling. Like chromium, too, 
 rhodium salts form a series of amines (p. 434). RhCl 3 forms two classes of double 
 salts with the alkali chlorides for instance, K 3 Rh01 6 .3H 2 and K 2 RhCl 5 .H 2 0. 
 The double chloride of rhodium and sodium (3NaCl.RhCl 3 ) is prepared by heating 
 a mixture of pulverulent rhodium and NaCl in a current of chlorine. It crystallises 
 in red octahedra with QAq. On boiling a solution of RhCl 3 with NH 3 in excess, 
 a yellow ammoniated salt (RhCl 3 .5NH 3 ) may be crystallised, from which the 
 metallic rhodium may be obtained by ignition. 
 
 With sulphur, rhodium combines energetically at a high temperature ; a mono- 
 sulphide and a sesquisulphide have been obtained. 
 
 An alloy of gold with between 30 and 40 per cent, of rhodium has been found in 
 Mexico. 
 
 An alloy of platinum with 10 per cent, of rhodium is used as one of the metals, 
 platinum being the other, of the thermo-electric couple used as a pyrometer. 
 
 OSMIUM, 08=189.6. 
 
 301. This metal is characterised by its yielding a very volatile acid oxide (jwosm'u; 
 anhydride, Os0 4 ), the vapours of which have a very irritating odour ((5<r/u^, odour'). 
 It occurs in the ores of platinum in flat scales, consisting of an alloy of osmium, 
 iridium, ruthenium, and rhodium. This alloy is also found associated with native 
 gold, and, being very heavy, it accumulates at the bottom of the crucible in 
 which the gold is melted. The osmium alloy is extremely hard, and has been 
 used to tip the points of gold pens. When a grain of it happens to be present 
 in the gold which is being coined, it often seriously injures the die. When tl 
 platinum ore is treated with aqua rer/ia, this alloy is left undissolved, together wit 
 grains of chrome-iron ore and titanic iron. To extract osmium from this residiw 
 it is heated in a porcelain tube through which a current of dry air is passed, when 
 the osmium is converted into perosmic anhydride, the vapour of which is carried 
 forward by the current of air and condensed in bottles provided to receive it. 
 The perosmic anhydride forms colourless prismatic c^stals which fuse and 
 volatilise below the boiling-point of water, yielding a most irritating vapour, 
 resembling chlorine. It is very soluble in water, giving a solution which exhales 
 the same odour and stains the skin black ; tincture of galls gives a blue precipitate 
 with the solution. Its acid properties are feeble, for it neither reddens litmus 
 nor decomposes the carbonates, and its salts are decomposed by boiling their 
 solutions. Its solution in HC1 gives a black precipitate of OsS 4 , with H 2 S. By 
 
RUTHENIUM. 5 1 1 
 
 passing a mixture of CO and vapour of Os0 4 through a red-hot porcelain tube 
 amorphous osmium is obtained, and may be converted into the crystalline form by 
 fusing it with tin and dissolving in HC1, when blue lustrous cubical crystals of 
 osmium are obtained, which scratch glass, and are heavier than any other body 
 having the specific gravity 22.48. It can be fused in the electric arc. 
 
 By dissolving perosmic anhydride in potash, potassium, pet-ornate, KOsO,, is 
 supposed to be formed, but this has not been isolated. When alcohol is added 
 to this solution the Os0 4 , is presumably reduced to OsO.,, for rose-coloured 
 crystals of pofasrivm osmate, K 2 O.Os0 3 .2H 2 0, are deposited ; by treating this salt 
 with nitric acid, osmlc acid, H 2 0s0 4 , is obtained as a sooty-black powder, which 
 tends to oxidise in air, yielding an odour of perosmic anhydride. 
 
 "When Os0 4 is dissolved in solution of S0 2 , osmium sulphite, OsS0 3 , is obtained ; 
 this is almost the only osmium oxy-salt which is known. By adding an alkali to 
 the solution, hydrated osmium monoxide, OsO.H 2 0, is obtained as a blue-back 
 powder soluble in HC1 to a blue solution and easily oxidised. Os 3 and Os0 2 are 
 obtained by heating potassium osmochlorlde, 3KC1.0sC] 3 , and osnrichlorlde, 
 2KC1.0sCl 4 , respectively with an alkali carbonate in absence of air. 
 
 Osmium, dlchlorlde, OsCl 2 , and tetrachloride, OsCl 4 , are obtained as two distinct 
 sublimates when the metal is heated in chlorine ; OsCl 2 is less votatile, and forms 
 green needles, whilst OsCl 4 is a dark-red powder. By mixing Os with KC1, heating 
 the mixture in chlorine, treating the mass with water, and evaporating, red 
 octahedra of 2KC1.0sCl 4 separate, whilst from the mother liquor 3KC1.0sCl 3 .3H 2 
 is crystallised. When osmic acid is heated with HC1 and alcohol and the solution 
 is evaporated, crystals having the formula Os. 2 Cl 7 .7H 2 are formed ; these are red 
 when dry, but dissolve in water and in alcohol to a green solution ; by adding KC1 
 to the alcoholic solution, K 2 OsCl 6 is precipitated, and when the filtrate is evaporated, 
 OsCl 3 .3H 2 crystallises. 
 
 Several compounds of osmium salts with ammonia (psmamines) are known, and 
 a "potassium osmiamate" KNOs0 3 , is obtained by the action of NIL on a solution 
 of Os0 4 in KOH. 
 
 RUTHENIUM, Ru = 
 
 302. In the process of extracting osmium from the residue left on treating the 
 platinum ore with aqua, ref/ia, by heating in a current of air, square prismatic 
 crystals of rutJtenium dioxide (Ru0 2 ) are deposited nearer to the heated portion of 
 the tube than the perosmic anhydride, for the dioxide is not itself volatile, being 
 only carried forward mechanically ; or it may be that the volatile Eu0 4 is formed 
 in the hot part of the tube, and dissociated into Ru0 2 and 2 in a cooler part. 
 When Ku0 2 is heated in H the metal is obtained ; it can be melted (1800 C.) in 
 the electric arc, and is then a grey metal, very hard, brittle when cold but malle- 
 able when hot ; its sp. gr. is 12.26. It is insoluble in acids. When fused with 
 zinc it yields an allotropic form similar to that described above for rhodium. 
 
 When ruthenium is heated at 1000 C. in oxygen the volatile oxide Ru0 4 is 
 formed, and may be isolated if rapidly cooled, but when allowed to cool slowly 
 it decomposes. The same oxide may be obtained by heating ruthenium with 
 KN0 3 and KOH, and saturating the solution of the fused mass with chlorine, 
 when Ru0 4 sublimes. It is soluble in water, melts at 25.5, and sublimes easily ; 
 at 107 it decomposes explosively. It is decomposed by light, yielding, apparently, 
 RuO 3 . 
 
 The oxides RuO and Ru 2 3 are probably also known. Ruthenates analogous to 
 the osmates have been prepared. RuCl 2 and RuCl 3 are formed when the metal is 
 heated in chlorine. The latter is insoluble in cold water, but dissolves in absolute 
 alcohol to a purple-violet solution which becomes indigo-blue from absorption of 
 water and formation of RuCl 2 .OH ; the solution gradually deposits Ru(OH) 3 . 
 Double chlorides analogous to those of osmium exist. 
 
 Sulphates corresponding with RuO and Ru 2 3 have been obtained. 
 
 IRIDIUM, Ir= 191.5. 
 
 303. Named from Iris, the rainbow, in allusion to the varied colours of its com- 
 pounds, this metal occurs in the insoluble alloy from the platinum ores. It is also 
 sometimes found separately, and occasionally alloyed with platinum, the alloy 
 
 * A mineral found in Borneo, and named laurfte, contains sulphides of ruthenium and 
 osmium. It forms small lustrous granules. 
 
512 
 
 THE PLATINUM GROUP OF METALS. 
 
 crystallising in octahedra, which are even heavier than platinum (sp. gr. 22.3). If 
 the insoluble osmiridium alloy left by aqua regla be mixed with common salt and 
 heated in a current of chlorine a mixture of the sodio-chlorides of the metals is 
 obtained and may be extracted by boiling water. If the solution be evaporated 
 and distilled with nitric acid, the osmium is distilled off as perosmic anhydride, 
 and by adding ammonium chloride to the residual solution, the iridium is pre- 
 cipitated as a dark red-brown ammonio-chloride, 2NH 4 Cl.IrCl 4 , which leaves 
 metallic iridium when heated. Like platinum, it then forms a grey spongy mass, 
 but is oxidised when heated in air, and may be fused (2200 C.) with the oxy- 
 hydrogen blowpipe to a hard brittle mass (sp. gr. 22.4), which doe- not oxidise in 
 air. Like rhodium, it is not attacked by aqua regla, unless alloyed with platinum. 
 By fusion with zinc it yields an allotropic form similar to that described for 
 rhodium. The product of the oxidation of finely divided iridium in air is the 
 sesquloxide (Ir 2 3 ), which is a black powder used for imparting an intense black to 
 porcelain ; it is insoluble in acids. The monoxide (IrO) is also more easily acted 
 upon by alkalies than by acids ; its solution in potash becomes blue when exposed 
 to air, from the formation of the dioxide (Ir0 2 ). The trioxlde (Ir0 3 ) is green. The 
 dichloride (IrCI 2 ) and tetrachloride (IrCl 4 ) of iridium resemble the corresponding 
 chlorides of platinum in forming double salts with the alkali chlorides. There 
 is also a trichloride (IrCl 3 ), the solution of which has a green colour, and gives a 
 yellow precipitate with mercurous nitrate, and a blue precipitate, soon becoming 
 white, with silver nitrate. Double compounds of the chloride with ammonia 
 (irldamlnes) are known. Iridium resembles palladium in its disposition to combine 
 with carbon when heated in the flame of a spirit-lamp. 
 
 Salts of iridium correspond with the oxides IrO and Ir 2 3 . 
 
 An iridio- platinum allot/ containing from 15 to 20 per cent, of iridium has been 
 found very useful for making standard rules and weights, on account of its inde- 
 structibility, extreme rigidity, hardness, and high density. 
 
 The following table exhibits a general view of the analytical process by which 
 the remarkable metals associated in the ores of platinum may be separated from 
 each other, omitting the minor details which are requisite to ensure the purity of 
 each metal : 
 
 Analysis of the Ore of Platinum. 
 Boil with aqua regla. 
 
 Dissolved ; 
 PLATINUM, PALLADIUM, RHODIUM. 
 
 Add ammonium chloride. 
 
 Undissolved ; 
 IRIDIUM, OSMIUM, RUTHENIUM. 
 Chrome iron, Titanic iron, &c. 
 
 Heat in a current of dry air. 
 
 Precipitated ; 
 PLATINUM 
 
 2 NH 4 Cl!ptCl 4 . 
 
 Solution ; 
 Neutralise with sodium carbonate; 
 add mercuric cyanide. 
 
 Volatilised ; 
 OSMIUM 
 as Os0 4 . 
 
 Carried 
 forward by 
 the current ; 
 RUTHENIUM 
 as Ru0 2 . 
 
 Residue ; 
 Mix with sodium 
 chloride, and heat in a 
 current of chlorine. 
 Treat with boiling ivater. 
 
 Precipitated ; 
 PALLADIUM 
 as PdCy 2 . 
 
 Solution ; 
 Evaporate with 
 hydrochloric acid. 
 Treat with alcohol. 
 Insoluble ; 
 RHODIUM 
 as 3 NaCl.RhCl 3 . 
 
 Dissolved ; 
 IRIDIUM 
 as 
 2 NaCl.IrCl 4 . 
 
 Residue ; 
 Titanic iron, 
 Chrome iron, 
 &c. 
 
 304. The platinoid metals fall into two classes according to the proximity which 
 exists between their specific gravities and between their atomic weights viz., 
 Os, Ir, Pt, and Ru, Rh and Pd. Gold is associated with the former class by its 
 sp. gr., atomic weight, and insolubility, whilst silver is related to the latter class 
 also by its atomic weight and sp. gr., and by its solubility in nitric acid, resembling 
 that of Pd. The first member of each class (Os and Ru) gives a volatile tetroxide, 
 whilst the highest state of oxidation of the remaining metals is R0 3 . In the 
 periodic classification (p. 302), they fall in the same group as Fe, Co andiKi, with 
 which they have several features in common, such as the marked colour of their 
 salts, their infusibility and their tendency to form salts in two stages of oxidation. 
 
EXTRACTION OF GOLD. 513 
 
 GOLD. 
 Au=: 195.7 parts by weight. 
 
 305. The individuality of gold among metals is strongly marked, on 
 account of its colour, its high specific gravity. 19.3, its extreme malle- 
 ability and ductility, its perfect resistance to air, its high conducting 
 power for heat and electricity, its high fusirig-point, 1064 C., its 
 resistance to acids, and its rarity and consequent intrinsic value. 
 Gold is one of those few metals which are always found in the metallic 
 state, and is remarkable for the extent to which it is distributed, though 
 in small quantities, over the surface of the earth. The principal sup- 
 plies of this metal are derived from Australia, the Transvaal Colony,. 
 California, Mexico, Brazil, Peru, and the Ural Mountains. Small 
 quantities have been occasionally met with in our own islands,, 
 particularly at Wicklow, at Cader Idris in Wales, Leadhills in Scot- 
 land, and in Cornwall. 
 
 The mode of the occurrence of gold in the mineral kingdom resembles 
 that of the ore of tin, for it is either found disseminated in the primi- 
 tive rocks, or in alluvial deposits of sand, which appear to have been 
 formed by the disintegration of those rocks under the continued action 
 of torrents. In the former case, the gold is often found crystallised in 
 cubes and octahedra, or in forms derived from these, and sometimes 
 aggregated together in dendritic or branch-like forms. In the alluvial 
 deposits, the gold is usually found in small scales (gold dust), but some- 
 times in masses of considerable size (nuggets), the rounded appearance of 
 which indicates that they have been subjected to attrition. Australian 
 gold is the purest, especially that from Victoria. 
 
 The extraction of the particles of gold from the alluvial sands is 
 effected by taking advantage of the high specific gravity of the metal 
 (19.3), which causes it to remain behind, whilst the sand, which is very 
 much lighter (sp. gr. 2.6), is carried away by water. The washing is 
 commonly performed by hand, in wooden or metal bowls, in which the 
 sand is shaken up with water, and the lighter portions dexterously 
 poured off, so as to leave the grains of gold at the bottom of the vessel. 
 On a somewhat larger scale, the auriferous sand is washed in a cradle 
 or inclined wooden trough, furnished with rockers, and with an opening 
 at the lower end for the escape of the water. The sand is thrown 011 to 
 a grating at the head of the cradle, which retains the large pebbles, 
 whilst the sand and gold pass through, the former being washed away 
 by a stream of water which is kept flowing through the trough. 
 
 When the gold is disseminated through masses of quartz or other 
 rock, much labour is expended in crushing the latter before the gol 
 can be separated. This is effected either by passing the coarse fragments 
 between heavy rollers of hard cast-iron, or by stamping them, with 
 _wooden beams shod with iron, in troughs through which water is con- 
 tinually flowing. . 
 
 In some cases it is found advantageous to smelt the ore by fusing r 
 with some substance capable of uniting with the gold, and ot 
 afterwards readily separated from it. Lead is peculiarly adapted ioi 
 this purpose ; the crushed ore is mixed with a suitable proportion, ei 
 of metallic lead, or of litharge (oxide of lead) and charcoal, o 
 
5 14 REFINING GOLD. 
 
 of galena (sulphide of lead), together with some lime and oxide of iron 
 or clay, to flux the silica, and is fused on the hearth of a reverberatory 
 furnace, when the fused lead dissolves the particles of gold, and collects 
 'beneath the lighter slag. The lead is afterwards separated from the 
 .gold by cupellation (see p. 464). 
 
 In smelting the ores of gold in Hungary, the metal is concentrated by means 
 ^of sulphide of iron. The ore consists of quartz and iron pyrites (FeS 2 ), containing 
 =a little gold. On fusing the crushed ore with lime, to flux the quartz, the pyrites 
 ioses half its sulphur, and becomes ferrous sulphide (FeS), which fuses and sinks 
 <!>elow the slag, carrying with it the whole of the gold. If this product be roasted 
 so as to convert the iron into oxide, and be then again fused with a fresh portion 
 of the ore, the oxide of iron will flux the quartz, whilst the fresh portion of FeS 
 will carry down the whole of the gold contained in both quantities of ore. This 
 operation having been repeated until the FeS is rich in gold, it is fused with a 
 certain quantity of lead, which extracts the gold and falls to the bottom. The 
 lead is then cupelled in order to obtain the gold. 
 
 When the ores of lead, silver, or copper contain gold, it is always found to have 
 accompanied the silver extracted from them, and is separated from it by a process 
 to be presently noticed. 
 
 Gold is sometimes separated from the impurities remaining with it 
 after extraction by washing, by the process of amalgamation, which con- 
 sists in shaking the mixture with mercury in order to dissolve the gold- 
 dust, and straining the liquid amalgam through chamois leather, which 
 allows the excess of mercury to pass through, but retains the solid 
 portion containing the gold, from which the mercury is then separated 
 by distillation.* 
 
 Chlorine (or bromine) water is sometimes employed to extract the gold 
 by converting it into AuCl 3 , the gold being afterwards precipitated from 
 the solution by adding ferrous sulphate, or by nitration through charcoal 
 which retains the gold, which is subsequently separated by burning the 
 charcoal. 
 
 The cyanide process, particularly applicable to the extraction of 
 gold from the tailings or material which contains the metal so finely 
 divided that it> has escaped separation by the washing process, depends 
 on the solubility of gold in a i per cent, solution of potassium cyanide 
 in presence of air ; Au 2 + 4 KCN + H. 2 O + = 2 (AuCN.KCN) + 2 KOH.t 
 The soluble double cyanide of Au and K is decomposed either by running 
 the solution through boxes containing zinc which precipitates the gold, 
 or by electrolysing the solution when the gold is deposited on the 
 oathode. 
 
 Gold, as found in nature, is generally alloyed with variable propor- 
 tions of silver and copper, the separation of which is the object of the 
 gold refiner. It may be effected by means of nitric acid, which will 
 dissolve the silver and copper, provided that they do not bear too small 
 a proportion to the gold. Sulphuric acid, however, being very much 
 cheaper, is generally employed. The alloy is fused and poured into 
 water, so as to granulate it and expose a larger surface to the action of 
 the acid ; it is then boiled with concentrated sulphuric acid (oil of 
 vitriol), which converts the silver and the copper into sulphates, with 
 
 * A small quantity of sodium dissolved in the mercury has been found very materially to 
 facilitate the amalgamation of gold and silver ores, apparently because the amalgam of 
 .sodium is more highly electro-positive than mercury, in relation to the gold. 
 
 f It is said that H 2 O 2 is produced, the equation being 
 
 Au 2 + 8KCX + O 4 + 4H 2 O = aKAu(CN) 4 + 6KOH + H 2 O . 
 
STANDAED GOLD. - r - 
 
 evolution of sulphurous acid gas, whilst the gold is left untouched. In 
 order to recover the silver from the solution of the sulphates in water, 
 scraps of copper are introduced into it, when that metal decomposes the 
 sulphate of silver, producing sulphate of copper, and causing the deposi- 
 tion of the silver in the metallic state. Finally, the sulphate of copper 
 may be obtained from the solution by evaporation and crystallisation. 
 This process is so effectual when the proportion of gold in an alloy is 
 very small, that even -^ part of this metal may be profitably extracted 
 from 100 parts of an alloy, and much gold has been obtained in this 
 way from old silver plate, coins, &c., which were manufactured before 
 so perfect a process for the separation of these metals was known. On 
 boiling old silver coins or ornaments with nitric acid, they are generally 
 found to yield a minute proportion of gold in the form of a purple 
 powder. But this plan of separation is not so successful when the alloy 
 contains a very large quantity of gold, for the latter metal protects the 
 copper and silver from the solvent action of the acid. Thus, if the alloy 
 contains more than ith of its weight of gold, it is customary to fuse it 
 with a quatity of silver, so as to reduce the proportion of gold below 
 that point before boiling it with the acid. Again, if the alloy contains 
 a large quantity of copper, it is found expedient to remove a great deal 
 of this metal in the form of oxide by heating the alloy in a current of 
 air. 
 
 Gold which is brittle and unfit for coining, in consequence of the pre- 
 sence of small quantities of foreign metals, is sometimes refined by 
 melting it with oxide of copper or with a mixture of nitre and borax, 
 when the foreign metals, with the exception of silver, are oxidised and 
 dissolved in the slag. Another process consists in throwing some cor- 
 rosive sublimate (mercuric chloride) into the melting-pot, and stirring 
 it up with the metal, when its vapour converts the metallic impurities 
 into chlorides, which are volatilised. An excellent method consists in 
 fusing the gold with a little borax, and passing chlorine gas into it 
 through a clay tube. Antimony, arsenic, &c., are carried off as chlorides, 
 whilst the silver, also converted into chloride, rises to the surface of the 
 gold in a fused state, afterwards solidifying into a cake, which is reduced 
 to the metallic state by placing it between plates of wrought-iron and 
 immersing it in diluted sulphuric acid. 
 
 When the crude gold is made the anode in an electrolytic cell con- 
 taining nitric acid, the foreign metals dissolve in the acid while the gold 
 is deposited as a sludge, conveniently caught by surrounding the anode 
 with a bag of cloth. This forms another method of refining gold. _ 
 
 Pure gold, like pure silver, is too soft to resist the wear to which it is 
 subjected in its ordinary uses, and it is therefore alloyed for coinage in 
 this country with ^th of its weight of copper, so that gold coin con- 
 tains i part of copper and n parts of gold. The gold used for articles 
 of jewellery is alloyed with variable proportions of copper and silver. 
 The alloy of copper and gold is much redder than pure gold. 
 
 The English sovereign contains 91.67 per cent, of gold and 8.33 per 
 cent, of copper. Its sp. gr. is 17.157, and its weight is 123.274 grains. 
 
 The Australian sovereign contains silver in place of copper, and i 
 lighter in colour than pure gold. 
 
 The degree of purity of gold is generally expressed by quoting it 
 of so many carats fine. Thus, pure gold is said to be 24 carats fine : 
 
516 ASSAYING GOLD. 
 
 English standard gold 22 carats fine, that is, contains 22 carats of gold 
 out of the 24. Gold of 18 carats fine would contain 18 parts of gold 
 out of the 24, or |thsof its weight of gold. The other legal standards 
 are 15, 12, and 9 carat gold. The fineness sometimes refers to the 
 quantity of gold in 1000 parts of the alloy ; thus, English coin has a 
 fineness of 916.7, German and American coin, of 900. 
 
 In order to impart to gold ornaments the appearance of pure gold, 
 they are heated till the copper in the outer layer is oxidised, and then 
 dipped into nitric or sulphuric acid, which dissolves the copper oxide and 
 leaves a film of pure gold. 
 
 Pure gold is easily prepared from standard or jeweller's gold by dissolving it 
 in hydrochloric acid mixed with one-fourth of its volume of nitric acid, evaporating 
 the solution to a small bulk to expel excess of acid, diluting with a considerable 
 quantity of water, filtering from the separated silver chloride, and adding a solution 
 of green sulphate of iron, when the gold is precipitated as a dark-purple powder, 
 which may be collected on a filter, well washed, dried, and fused in a small clay 
 crucible with a little borax, the crucible having been previously dipped in a hot 
 saturated solution of borax, and dried, to prevent adhesion of the globules of gold. 
 The action of ferrous sulphate upon the trichloride of gold is explained by the 
 equation 2AuCl 3 + 6FeS0 4 = Au 2 + F 2 Cl 6 + 2Fe2(S0 4 )3. The gold precipitated by 
 ferrous sulphate appears, under the microscope, in cubical crystals. 
 
 By employing oxalic acid instead of ferrous sulphate, and heating the solution, 
 the gold is precipitated in a spongy state, and becomes a coherent lustrous mass 
 under pressure. The rnetal is employed in this form by dentists. 
 
 When standard gold is being dissolved in aqua regla, it sometimes becomes 
 coated with a film of silver chloride which stops the action of the acid ; the 
 liquid must then be poured off, the metal washed, and treated with ammonia, 
 which dissolves the silver chloride ; the ammonia must then be washed away 
 before the metal is replaced in the acid. In the case of jeweller's gold, it is advisable 
 to extract as much silver and copper as possible by boiling it with nitric acid, 
 before attempting to dissolve the gold. Gold lace should be incinerated to get rid 
 of the cotton before being treated with acid. 
 
 The genuineness of gold trinkets. <fcc., is generally tested by touching them with 
 nitric acid, which attacks them if they contain a very considerable proportion of 
 copper, producing a green stain, but this test is evidently useless if the surface be 
 gilt. The weight is, of course, a good criterion in practised hands, but even these 
 have been deceived by bars of platinum covered with gold. The specific gravity 
 maybe taken in doubtful cases ; that of sovereign gold is 17.157. 
 
 In assaying gold, the metal is wrapped in a thin piece of paper together with 
 about three times its weight of pure silver, and added to twelve times its weight of 
 pure lead fused in a bone-ash cupel (see p. 465) placed in a muffle (or exposed to 
 a strong oxidising blow-pipe flame), when the lead and copper are oxidised, and the 
 fused oxide of lead dissolves that of copper, both being absorbed by the cupel. 
 When the metallic button no longer diminishes in size, it is allowed to cool, 
 hammered into a flat disc which is annealed by being heated to redness, and rolled 
 out to a thin plate, so that it may be rolled up by the thumb and finger into 
 a cornette, which is boiled with nitric acid (sp. gr. 1.18) to extract the silver ; the 
 remaining gold is washed with distilled water, and boiled with nitric acid of 
 sp. gr. 1.28, to extract the last traces of silver, after which it is again washed. 
 heated to redness in a small crucible, and weighed. 
 
 The stronger nitric acid could not be used at first, since it would be likely to break 
 the cornette into fragments which could not be so readily washed without loss. 
 The addition of the three parts of silver (quartatioii) is made in order to divide the 
 alloy, and permit the easy extraction of the silver by nitric acid, which cannot be 
 effected when the gold predominates. 
 
 306. The physical characters of gold render it very conspicuous 
 among the metals ; it is the heaviest of the metals in common use, with 
 the exception of platinum, its specific gravity being 19.3. In malleability 
 and ductility it surpasses all other metals ; the former property is turned 
 to advantage for the manufacture of gold leaf, for which purpose a bar 
 
PEOPERTIES OF GOLD. 
 
 of gold, containing 96.25 per cent, of gold, 2.5 per cent, of silver, and 
 1.25 per cent, of copper, is passed between rollers which extend it' into 
 the form of a riband ; this is cut up into squares, which are packed 
 between layers of fine vellum, and beaten with a heavy hammer ; these 
 thinner squares are then again cut up and beaten between layers of gold- 
 beater's skin until they are sufficiently thin. An ounce of gold may 
 thus be spread over 100 square feet ; 282,000 of such leaves placed upon 
 each other form a pile of only i inch high. These leaves will allow 
 light to pass through them, and always appear green or blue when held 
 up to the light, though they exhibit the ordinary colour of gold bv 
 reflected light. 
 
 If a gold leaf adhering to a glass plate be heated to nearly the boiling-point of 
 oil for some time, it becomes nearly transparent and invisible by transmitted light, 
 though still showing the colour of gold by reflected light ; if it be pressed with a 
 moderately hard body, it again transmits a green light. When gold wire or leaf is 
 deflagrated by electricity on a glass plate, the finely divided metal transmits ruby, 
 - violet, or green light, according to its thickness, though it has the golden colour 
 by reflected light. On heating these deposits to dull redness on the glass, they all 
 change to the ruby colour while still golden by reflection. Pressure with a hard 
 body changes the colour of the transmitted light from red to green. A solution of 
 gold trichloride, containing 0.6 grain of gold in a quart, if shaken with a little 
 solution of phosphorus in ether, in a chemically clean bottle, gives a ruby-red 
 liquid in which the reflected colour of gold may be seen by bringing the solar rays 
 to a focus in the liquid by a convex lens. This liquid will continue to deposit fine 
 particles of gold for many months. The first deposits are blue by transmitted light, 
 and the last are ruby. The supernatant liquid is eventually colourless. If a little 
 sodium chloride be added to the ruby liquid, it transmits a blue light, and the gold 
 which has remained suspended for six months may be deposited in a few hours. 
 By using a filter arranged so that the liquid is passed through the paper in a radial 
 instead of an a.nal direction as is usual, the particles of gold, which pass through 
 in ordinary axial filtration, may be collected on the paper, having the various 
 colours, and leaving the liquid colourless. These colours of finely divided gold are 
 taken advantage of in painting upon porcelain, and the well-known magnificent 
 ruby-red glass owes its colour to the same cause. T^-h of a grain of gold is capable 
 of imparting a deep rose colour to a cubic inch of fluid. 
 
 The extreme ductility of gold is exemplified in the manufacture of 
 gold thread for embroidery, in which a cylinder of silver having been 
 covered with gold leaf it is drawn through a wire-drawing plate and 
 reduced to the thinness of a hair ; in this way 6 ounces of gold are 
 drawn into a cylinder two hundred miles in length. Although fusing 
 at about the melting-point of copper, gold is seldom cast, on account of 
 its great contraction during solidification. 
 
 Gold is not even affected to the same extent as silver by exposure to 
 the atmosphere, for sulphuretted hydrogen has no action upon it, arid 
 hence no metal is so well adapted for coating surfaces which are required 
 to preserve their lustre. 
 
 The gold is sometimes applied to the surfaces of metals in the form 
 of an amalgam, the mercury being afterwards driven off by heat. 
 Metals may also be gilt by means of a boiling solution prepared by 
 dissolving gold in aqua regia, and adding an excess of bicarbonate 
 of potash or of soda. But the most elegant process of gilding is that of 
 electro-gilding, in which the object to be gilt is connected by a wire 
 with the zinc end of the galvanic battery, and immersed in a solution 
 of cyanide of gold in cyanide of potassium, in which is also placed a 
 gold plate connected with the copper end of the battery, and intended, 
 
518 SALTS OF GOLD. 
 
 by gradually dissolving, to take the place of the gold abstracted from 
 the solution at the negative pole. 
 
 A gold crucible is very useful in the laboratory for effecting the fusion 
 of substances with caustic alkalies, which would corrode a platinum 
 crucible. The only single acid which attacks gold is selenic, H 2 SeO 4 , 
 which the gold reduces to selenious acid, H Se0 3 . A mixture of hydro- 
 chloric with one-third of its volume of nitric acid is usually employed 
 for dissolving gold. It is also dissolved by a mixture of sulphuric acid 
 with a little nitric, the latter becoming reduced to nitrous acid, which 
 precipitates the gold again in the metallic state on pouring the solution 
 into a large volume of water. On account of its high resistance to 
 sulphuric acid, platinum vitriol retorts are now frequently lined with 
 gold. Fused caustic alkalies are not without action on gold, but they 
 attack platinum more strongly. 
 
 307. OXIDES OP GOLD. Three compounds of gold with oxygen have been 
 obtained, Au 2 0, AuO, and Au. 2 3 , but none of them is of any great practical im- 
 portance. 
 
 Aurous oxide, Au. 2 0, obtained by decomposing aurous chloride with potash, is a 
 violet-coloured powder which is decomposed by hydrochloric acid 
 3Au 2 + 6HCI = 2AuCl 3 + 3H 2 + Au 4 . 
 
 Auric oxide, Au 2 3 , is obtained by gently heating auric hydroxide, Au(OH).,. 
 This is prepared by heating a weak solution of auric chloride with excess of potash, 
 and adding sodium sulphate, when auric hydroxide is precipitated, of a brown 
 colour like ferric hydroxide. It is very unstable, evolving oxygen when exposed to 
 light. Nitric acid dissolves it, and it is reprecipitated by water. It dissolves in 
 potash, and the solution yields crystals of potassium aurate, KAu0 2 .3Aq. By heat- 
 ing Au(OH) 3 at 1 60 C. AuO is formed. 
 
 When precipitated gold is attacked by chlorine gas, it yields auroxoauric chloride, 
 AuCl.AuCI 3 , a dark red hard substance decomposed by water into AuCl and AuCl 3 , 
 or auric chloride, which may also be obtained by dissolving gold in hydrochloric 
 acid with one-fourth of its volume of nitric acid, and evaporating on a water bath 
 to a small bulk ; on cooling, yellow prismatic crystals of a compound of the tri- 
 chloride with hydrochloric acid (AuCl 3 .HC1.4Aq) are deposited, from which the 
 hydrochloric acid may be expelled by a gentle heat (not exceeding 120 C.), when 
 the trichloride forms red-brown deliquescent crystals of AuCl 3 .2Aq, dissolving very 
 readily in water, giving a bright yellow (solution which stains the skin and other 
 organic matter purple when exposed to light, depositing finely divided gold ; the 
 solution appears to contain an acid, ELjAuClgO, of which the silver salt is known. 
 Almost every substance capable of combining with oxygen reduces the gold to the 
 metallic state. The inside of a perfectly clean flask or tube may be covered with a 
 film of metallic gold by a dilute solution of the trichloride mixed with citric acid 
 and NH 3 , and gently heated. The facility with which it deposits metallic gold, 
 and the resistance of the deposited metal to atmospheric action, has rendered 
 AuCl 3 very useful in photography. Alcohol and ether readily dissolve the trichlo- 
 ride, the latter being able to extract it from its aqueous solution. Ked crystals of 
 AuCl 3 are sublimed when thin gold foil is gently heated in a current of chlorine. 
 Trichloride of gold (like platinic chloride) forms crystallisable compounds with 
 the alkali chlorides and with the hydrochlorides of organic bases, and affords great 
 help to the chemist in defining these last. Aurochloride of sodium forms reddish- 
 yellow prismatic crystals (NaCl.AuCl 3 .2Aq), which are sold for photographic pur- 
 poses. 
 
 Protochloride of gold, or aurous chloride (AuCl), is obtained by gently heating 
 the trichloride, when it fuses and is decomposed at 177 C., leaving the protochlo- 
 ride, which is reduced to metallic gold at about 205 C. Aurous chloride is 
 sparingly soluble in water, and of a pale yellow colour. Boiling water decomposes 
 it into metallic gold and the trichloride. 
 
 Fulminating gold is obtained as a buff precipitate when ammonia is added to 
 solution of auric chloride ; its composition is not well established, but appears to 
 be Au 2 3 4NH 3 or 2(NH 3 .NAu'").3H 2 0. It explodes violently when gently heated. 
 
 The Sel d'or of the photographer is a hyposulphite (thiosulphate) of gold and 
 
PUEPLE OF CASSIUS. 
 
 519 
 
 sodium, Au 2 S 2 O 3 .3Na 2 SoO 3 .4Aq, which is obtained in fine white needles by pourin" 
 a solution of I part of auric chloride into a solution of 3 parts of sodium hypo*- 
 sulphite, and adding alcohol, in which the double salt is insoluble. Its formation 
 may be explained by the equation 
 
 8Xa. 2 S 2 3 + 2AuCl 3 = Au. 2 S 2 ;? .3Xa. 2 S 2 3 + 6XaCl + 2Xa. 2 S 4 6 . 
 It is doubtful whether the above formula represents the true constitution of this 
 salt, for it is not decomposed by adds in the same manner as ordinary thiosulphates 
 are.* HX0 3 separates all the gold in the metallic state. 
 
 Purple of Caszhis, which is employed for imparting a rich red colour to glass and 
 porcelain, is a compound of gold, tin, and oxygen, which are believed to be grouped 
 according to the formula Au. 2 Sn0 3 .Sn.Sn0 3 4Aq.f It maybe prepared by adding 
 stannous chloride to a mixture of stannic chloride and auric chloride ; 7 parts of 
 gold are dissolved in aqua reyia and mixed with 2 parts of tin also dissolved in 
 aqua rctjla ; this solution is largely diluted with water, and a weak solution of 
 i part of tin in hydrochloric acid is added, drop by drop, till a fine purple colour is 
 produced. The purple of Cassius remains suspended in water in a very fine state 
 of division, but subsides gradually, especially if some saline solution be added, as a 
 purple powder. The fresh precipitate dissolves in ammonia, but the purple solu- 
 tion is decomposed by exposure to light, becoming blue, and finally colourless, 
 metallic gold being precipitated, and stannic oxide left in solution. 
 
 The snljthldex of y old are not thoroughly known. Gold does not combine directly 
 with sulphur, but if it be heated with sulphur and alkali sulphides, it forms soluble 
 compounds. In this way, sodium awrowlphide, XaAuS.4Aq, may be obtained in 
 colourless prisms soluble in alcohol. When H. 2 S is passed into solution of AuCl 3 , a 
 black precipitate of Au. 2 S.Au 2 S 3 or Au. 2 S. 2 is obtained 
 
 2AuCl 3 " + 3H 2 S^= Au. 2 S 2 + S + 6HC1. 
 
 The precipitate is soluble in alkali sulphides. The precipitated sulphide of gold is 
 not dissolved by the acids, with the exception of aqua reyla. Nitric acid oxidises 
 the sulphur, leaving metallic gold. When hydrosulphuric acid is added to a boil- 
 ing solution of auric chloride, the metal itself is precipitated 
 
 8AuCl 3 + 3H 2 S + i2H. 2 = Au 8 + 24HC1 + 3H 2 S0 4 . 
 
 A yellowish-grey brittle arsenide of (/old (AuAs.,) has been found in quartz in 
 Australia. 
 
 * It appears to be sodium, (inrothiosulphate, Na 3 AuS 4 O 6 .2Aq, which is supported by the 
 preparation of a corresponding barium salt and by decomposing this with sulphuric acid 
 when aurothiomlphuric acid, H : jA.uS 4 O 6 , is obtained. 
 
 f Debray asserts that it is merely a mixture of precipitated gold and stannic hydrate. 
 
ORGANIC CHEMISTRY. 
 
 308. The division of chemistry into inorganic and organic was ori- 
 ginally intended to distinguish mineral substances from those derived 
 from animal and vegetable life ; but since many of the latter may now 
 be produced in the laboratory from the elements obtainable from mineral 
 sources, it has become usual to define organic chemistry as the chemistry 
 of the compounds of carbon, since this element is always present in the 
 substances formerly spoken of as organic. 
 
 Organic chemistry differs from inorganic in being chiefly concerned 
 with the compounds produced by the arrangement, in different pro- 
 portions or in different positions, of the elements carbon, hydrogen, 
 oxygen, and nitrogen, though the other elements occasionally enter into 
 the composition of organic compounds. 
 
 Perhaps the most striking difference between compounds of carbon 
 and those of other elements is the large number of atoms contained in 
 one molecule of the majority of carbon compounds. So far as evidence 
 is available it is rare in inorganic chemistry to find a compound whose 
 molecule contains so many as six atoms of any one element ; yet the 
 majority of carbon compounds contain more than six atoms of carbon 
 in the molecule, so that it would appear to be a characteristic property 
 of carbon to combine with itself. 
 
 A useful practical distinction between organic and inorganic substances 
 is afforded by their behaviour when heated. An organic substance is 
 either converted into vapour when moderately heated, or decomposed 
 into volatile products, generally leaving a residue of charcoal, which 
 burns away when heated in air. 
 
 Upon this is based the ultimate analysis of organic compounds for the 
 purpose of ascertaining the relative proportions of their elements.* 
 
 The nuiltinf/ a cotnbvxtion, as it is technically called, consists in burning the 
 organic compound so as to convert its carbon into C0 2 and its hydrogen into 
 H 2 0, from the weight of which the proportions of those elements are obtained 
 by calculation. The substance to be analysed, having been carefully dried and 
 weighed (about 0.5 gram), is placed in a small boat-shaped tray of porcelain or 
 platinum, which is introduced into one end of a glass tube about 30 inches long, 
 of which about 24. inches are filled with small fragments of carefully dried cupric 
 oxide. The end of the tube where the boat is placed is connected with an appa- 
 ratus for transmitting air or oxygen, which has been purified from C0. 2 by passing 
 through potash, and from H. 2 O by calcium chloride. To the other end of the tube 
 is attached, by a perforated cork, a weighed tube (B) filled with small fragments 
 of calcium chloride to absorb H 2 0, and to this is joined, by a caoutchouc tube, a 
 Inilb-apparatus (C) containing strong potash to absorb C0 2 , and a small guard-tufa 
 
 * For exact details of the methods of organic analysis the reader must consult works on 
 analytical chemistry. 
 
ULTIMATE ORGANIC ANALYSIS. 
 
 521 
 
 with calcium chloride to prevent loss of water from the potash. The 
 ;md guard tube are accurately weighed. The cotnbmt ion-tube is supported in ;i 
 gas-furnace, and that portion which contains the CuO is heated to redness. Tin- 
 end containing the boat is then gradually heated, so that the organic substance is 
 slowly vaporised or decomposed. The vapour or the products of decomposition, 
 an passing over the red-hot cupric oxide, will acquire the oxygen necessary to 
 
 Fig - . 245. Apparatus for organic analysis. 
 
 convert the C into CO 2 and the H into H. 2 O, which are absorbed in the potash 
 bulbs and calcium-chloride tube. At the end of the process, which commonly 
 occupies about an hour, a slow stream of pure air or oxygen is passed through. 
 Avhilst the entire tube is red-hot, in order to burn any charcoal which may remain 
 in the boat, and to carry forward all the CO. 2 and H. 2 O into the absorption 
 apparatus. The weight of the C0. 2 is given by the increase in weight of the calcium 
 chloride. 
 
 When nitrogen is present in the substance, it may be partly converted into X0. 2 . 
 which would increase the weight of the absorption-apparatus. To avoid this, 
 three or four inches of the front end of the combustion-tube are filled with metallic 
 copper, which, being heated to redness, absorbs the from the N0. 2 . leaving X. 
 which passes through the absorption-apparatus and escapes. When it is desired to 
 make a determination of the nitrogen, 
 the combustion-tube is arranged in the 
 same way. but the absorption-apparatus 
 is exchanged for a bent tube to permit 
 the collection of the gas in a measured 
 tube tilled with strong potash. Before 
 commencing the combustion, the air is 
 swept out of the tube by a stream of 
 pure CO.,. which is continued during the 
 combustion, and is absorbed by the 
 potash, the nitrogen being collected and 
 measured. 
 
 Another method of estimating nitro- 
 gen in organic substances consists in 
 heating them with xoda-Hme. when the 
 X is evolved as XH,. which is absorbed 
 by hydrochloric acid in the absorption 
 bulb shown in Fig. 246. and precipi- 
 tated by platinic chloride, the weight 
 of X being calculated from that of the 
 
 Pt< '1 4 .2XH 4 C1 obtained : or the NH S is absorbed in a known quantity of acid w hi. 
 is afterwards titrated with a standard solution of alkali, and the quantity \\ 
 has been neutralised by the evolved ammonia thus determined. 
 
 Kirtfldlir* method of estimating nitrogen consists in oxidising the substance DA 
 heating it with H.,S0 4 and acid potassium sulphate (KHS0 4 ). whereby the . 
 converted into XH,. which forms ammonium sulphate. The XH, is sn >se M nentlv 
 liberated by boiling with alkali, absorbed by hydrochloric acid and dete 
 either with platinic chloride or standard alkali, as described above. 
 
 ' \ur and phoxphoru* are estimated in organic compounds by coi 
 
 246. Estimation of nitrogen. 
 
522 DETERMINATION OF MOLECULAR FORMULAE. 
 
 them into sulphuric and phosphoric acids, respectively, by the action of powerful 
 oxidising-agents (nitric acid, chloric acid, bromine, &c.), and determining these- 
 acids by the usual methods. The halogen* are determined by oxidising the 
 substance by heating it with strong HNO 3 under pressure, whereby the halogen 
 is converted into its hydrogen compound and may be precipitated by AgNO ;; and 
 weighed as silver halide. 
 
 The proportion of oxygen in an organic substance is generally ascertained In- 
 difference, that is, by deducting the sum of the weights of all the other elements 
 from the total weight of the substance. 
 
 As an example of the ultimate analysis of an organic compound, that of alcohol 
 may be given (volatile liquids are weighed in a small glass bulb with a thin stem r 
 the end of which is sealed for weighing, and broken off when the bulb is intro- 
 duced into the combustion-tube) : 
 
 .5 gram alcohol, burnt with ctipric oxide, as above, gave .9565 gram C0 and 
 .5869 gram H 2 0. 
 
 Since 44 grams C0 2 contain 12 grams C., \\ of .9565, or .2608, is the weight of 
 C found. 
 
 Since 18 grams H 2 contain 2 grams H, T % of .5869, or .0652, is the weight of 
 H found. 
 
 The sum of C and H is .2608 + .0652, or .3260. Deducting this from .5 gram 
 alcohol, we have .174 gram for the weight of O contained in it. 
 
 So that .5 gram alcohol contains 
 
 .2608 gram carbon or 52. 16 per cent. 
 .0652 hydrogen,, 13.04 
 .1740 ,, oxygen ,, 34.80 ,, 
 
 It is usual to express the results of such an analysis in an empirical formula, which 
 gives, in the simplest form, the relative number of atoms of the elements present. 
 
 309. To deduce the empirical formula from the percentage composition, the per- 
 centage of each element is divided by its atomic weight, and the ratio of the 
 resulting quotients expressed in its lowest terms ; thus 
 
 52.16 divided by 12 gives 4.34 atomic weights of carbon 
 13.04 i 13.04 ., hydrogen 
 
 34.80 1 6 ., 2.17 oxygen 
 
 If the ratio 4.34 : 13.04 : 2.17 be expressed in its lowest terms, it becomes 
 2 : 6 : i, giving for the empirical formula of alcohol, C.>H 6 0. 
 
 The question now arises whether this formula is a true representation of the 
 molecule or indivisible particle of alcohol, or whether the molecule should be 
 written C 4 H 12 2 , or C 6 H 18 3 , or in any other form which would preserve the ratio 
 established beyond dispute by the above analysis. 
 
 310. To deduce the molecular formula of a compound from vY-s- enipirical formula 
 the molecular weight of the compound must be determined, for it is evident that 
 the formula C 2 H 6 represents 2 atoms of C, weighing 12x2, 6 atoms of H, Aveigh- 
 ing 1x6, and i atom of 0, weighing 16 ; the sum of these numbers, or 46, would 
 be the weight of alcohol represented by C 2 H 6 0, whereas the formula C 4 H 12 O 2 
 would express 46 x 2 parts by weight, and C 6 H 18 :5 would express 46 x 3 parts by 
 weight of alcohol. 
 
 The methods for determining the molecular weight of a volatile compound have 
 been described at p. 292. 
 
 In the case of a substance which cannot be converted into vapour without 
 decomposition, the molecular weight is determined by the cryoscopic method 
 (p. 319), or is inferred from a consideration of the chemical relations of the sub- 
 stance, and its determination is sometimes a difficult matter. The general 
 character of the latter method will be seen from the following examples : 
 
 Determination of the molecular formula of anacid. The substance yielded, on 
 combustion with cupric oxide, in 100 parts carbon, 40. hydrogen, 6.66, oxygen 
 53-33 5 which lead to CH 2 as the simplest or empirical formula of the acid. 
 
 The acid was found to give only one class of salts with K and Na, showing that 
 it only contains one atom of H exchangeable for a metal, or is monobasic (p. 104). 
 
 By neutralising the acid with ammonia, and stirring with solution of silver 
 nitrate, a crystalline silver salt was obtained, which was purified by recrystal- 
 lisation from hot water, dried, weighed in a porcelain crucible of known weight, 
 and gradually heated to redness. On again weighing the crucible, after cooling, 
 it was found to contain a quantity of metallic silver amounting to 64.66 per cent, 
 of the weight of the salt. Now, as a general rule, a silver salt is formed from an 
 
DETERMINATION OF MOLECULAR FORMULAE. 52$ 
 
 acid by the displacement of an atom of hydrogen by an atom of silver so that 
 what remains of a silver salt, after deducting the silver, represents the acid 
 itself minn* a quantity of hydrogen equivalent to the silver. 
 
 From the silver salt .... 100.00 
 Deduct the silver . . . 64.66 
 
 Acid residue . . . -35-34 
 
 Then 64 66 4- 108 -' Aff ln om '" wlf "} - . , c -, . en f ftcifj ''''*'<?* in 
 1611 b4 ' 66 Ag ' I08 lffe of the salt j ' ^-M - 59{ ime >>>t> i ec(d ^ 
 To the acid residue ...... 50 
 
 Add the hydrogen equivalent to an atom of Ag i 
 
 Molecular weight of the acid . . 60 
 
 The formula CH. 2 represents 12 + 2+16 = 30. Hence the molecular formula is 
 C.Jf 4 Oo = 6o ; and the silver salt is C 2 H 3 Ag0 2 . 
 
 Determination of the molecular formula of an organic base. The substance yielded 
 on combustion with cupric oxide, in 100 parts, carbon 77.42, hydrogen 7.53. A 
 determination of nitrogen gave 15.05 per cent,, so that there was no oxygen. 
 These numbers lead to C 6 H 7 N as the simplest or empirical formula of the base. 
 By dissolving the base in hydrochloric acid and adding platinic chloride, a yellow 
 crystalline precipitate was obtained, resembling the ammonio-platinic chloride 
 formed when ammonia is treated in the same way. This precipitate was washed 
 with alcohol, dried, weighed in a porcelain crucible, and heated to redness, when 
 t left a residue of metallic platinum, which amounted to 32.72 per cent, of the 
 weight of the salt. As a general rule, a platinum-chloride salt is formed by the 
 combination of PtCl 4 with two molecules of the hydrochloride of the base ; in the 
 case of the ammonio-platinic chloride, the formula is Pt01 4 .2(NH 3 .HCl) ; so that 
 what remains of a platinum salt after deducting the platinum represents two 
 molecules of the base + two molecules of HC1 + 4 atoms of chlorine. 
 
 From the platinum salt . . . 100.00 
 Deduct the platinum . . 32.72 
 
 Remainder .... 67.28 
 
 Then 3 3. 7 a Pt : ^SftfcSjT) : : **' * 
 
 Hence two inols. base + 2 mols. HC1 + 4 atoms 01 = 400.9 
 Deduct 2HC1 + C1 4 =215.0 
 
 Weight of two molecules of the base . 185.9 
 
 The molecular weight of the base, therefore, is 92.9. The formula C 6 H 7 N repre- 
 sents 72 + 7 + 14-93. This is therefore the molecular formula. 
 
 The law of ere n numbers is sometimes a useful guide in fixing molecular formula. 
 It may be thus expressed : The total number of atoms of monad or triad clement* 
 united witlt carbon in an organic compound must be an even number. The law is a 
 result of the tetrad nature of carbon, as will be seen in the next few pages. 
 
 For example, the empirical formula for glycol, deduced from ultimate analysis, i^ 
 CH 3 ; but this is an impossible formula, by the law of even numbers, and the 
 molecular formula for glycol must be at least double this, C.,H 6 2 . 
 
 311. The ultimate analysis of an organic compound serves to decide its 
 empirical formula i.e., the formula expressing the ratio between the 
 number of atoms of each element in the compound ; a determination of 
 the molecular weight decides whether the molecular formula (i.e., the 
 formula expressing the actual number of atoms of each element in one 
 molecule of the compound) is identical with, or a multiple of, the em- 
 pirical formula. Thus, the empirical formula for benzene is CH, but 
 its molecular formula is undoubtedly six times this viz., C 6 H 6 . 
 
 From what was said in the chapter on nitrogen, and again on p. 191, 
 it will be apparent that much light may be thrown upon the behaviour 
 of compounds by a study of the way in which the component atoms are 
 
.524 STRUCTURAL FORMULAE. 
 
 combined together. In this manner the existence of radicles in com- 
 pounds can be traced, and it becomes possible to assign a constitutional 
 or rational formula i.e., a formula which indicates the radicles that 
 compose it to a compound. Furthermore, it becomes necessary, in the 
 case of carbon compounds, to provide some working hypothesis which 
 shall account for the fact that many substances exist which have 
 different properties, but nevertheless have the same ultimate composition 
 and the same molecular formula : such cases are included under the 
 term isomerism, which will shortly receive closer attention. The 
 necessary hypothesis is supplied by supposing the atoms in the compound 
 to be linked together by bonds in such a way that this linkage can be 
 represented by a graphic or structural formula on one plane, as explained 
 on p. 101. 
 
 It is only by such a study of the structure of carbon compounds that any 
 success has been achieved in the main object of chemistry, namely, the 
 synthesis of compounds. The study involves a careful consideration of 
 the reactions of the compound, and many examples will be met with 
 hereafter; the following may, however, be now quoted as a typical 
 simple case. 
 
 312. Example. Determination of the rational or structural formula of alcohol. 
 When sodium is placed in alcohol, it is dissolved with the evolution of much 
 hydrogen, and the alcohol is converted into a crystalline substance called sodium 
 ethoxide, which has the composition C 2 H 5 ONa. Comparing this with the formula 
 of alcohol, it is seen that Na has been substituted for one atom of H. Since the 
 -compound still contains H 5 , it might be supposed that by the use of an excess 
 of Na more might be substituted for H, producing ultimately a compound C 2 Na 6 0. 
 But this is not the case ; Na can be substituted in this way for only one of the 6 
 atoms of H in alcohol ; hence it is seen that one atom of the six is on a different 
 footing from the other five. This would be expressed by writing the formula 
 C 2 H 5 OH. 
 
 Again, when alcohol is acted on by hydrogen chloride, and distilled at a low 
 temperature, it yields water and a very volatile liquid known as ethyl chloride, 
 having the composition C 9 H 5 C1. This decomposition would be expressed by the 
 equation, C. 2 H 5 OH + HC1 = C 2 H 5 C1 + HOH, from which it is evident that the Cl of 
 the HC1 has been exchanged for OH in the alcohol, leading to the conclusion that 
 alcohol is made up of at least two separate groups, and that one way of writing 
 its rational formula is C 2 H 5 'OH. 
 
 313. By investigating the nature of the radicles contained in an 
 organic substance, this may generally be assigned to one of the following- 
 divisions : 
 
 (1) HYDROCARBONS, composed of carbon and hydrogen only, in various 
 modes of grouping ; as ethyl hydride or ethane, C,H.'H. 
 
 Hydrocarbons from which hydrogen has been removed give rise to 
 hydrocarbon radicles, thus, C 2 H 5 is the hydrocarbon radicle, ethyl, from 
 ethane ; like all other radicles they are incapable of a separate existence 
 (p. 94). Since in chemical reactions the hydrocarbon radicles behave 
 towards other radicles analogously to the manner in which the metals 
 behave towards the non-metals, they are frequently termed positive 
 radicles, other radicles such as (OH),(COOH), etc., being termed negative. 
 
 (2) ALCOHOLS, composed of carbon, hydrogen, and oxygen, and con- 
 taining one or more hydroxyl (OH) radicles ; as ethyl- alcohol, C 2 H 5 'OH. 
 
 (3) ALDEHYDES, or dehydrogenated alcohols ; products of the partial 
 oxidation of the alcohols, containing the group (COH) ; as ethyl-aldehyde, 
 CH 3 -COH. 
 
 (4) ACIDS, the products of the further oxidation of the alcohols, 
 
CLASSIFICATION OF CARBON COMPOUNDS. 525 
 
 containing one or more carboxyl radicles, C0 2 H; as acetic acid, CH -COOH 
 ' 
 
 (5) KETONES, formed from the acids by the substitution of a hydro- 
 carbon radicle for the OH in the carboxyl ; so that the ketones contain 
 the group CO ; as acetic ketone or acetone, CH 3 'CO'CH 3 . 
 
 (6) ETHERS, formed from the alcohols by the substitution of a hydro- 
 carbon radicle for the H in the hydroxyl, as ethyl-ether, C.,H 5 '0'C,H.. 
 
 (7) HALOID COMPOUNDS, formed from the foregoing groups by the 
 substitution of a halogen radicle for hydrogen or hydroxyl ; as chloro- 
 form, CHC1 3 ; ethyl chloride, C 2 H 5 C1 ; acetyl chloride, CH 3 'CO'C1. 
 
 (8) ETHEREAL SALTS (or esters), formed from the acids by the sub- 
 stitution of a hydrocarbon radicle for the hydrogen in the carboxyl radicle 
 as ethyl acetate, CH 3 -CO'OC 2 H 5 . 
 
 (9) ORGAXO-MIXERAL COMPOUNDS, formed upon the type of the- 
 chlorides of metals or non-metals by the substitution of hydrocarbon 
 radicles for the chlorine ; as zinc ethide, Zn(C 2 H 5 ) 2 . 
 
 (10) AMMONIA-DERIVATIVES, formed upon the model of ammonia, NH.,,. 
 by the substitution of a radicle for hydrogen ; as ethylamine NH -C H 
 acetamide, NH 2 'C 2 H 3 O. 
 
 (n) CYANOGEN COMPOUNDS, containing the group CIS"; as hydro- 
 cyanic acid, H'C]S\ 
 
 (12) PHENOLS, resembling the alcohols in composition, by containing 
 the hydroxyl group, but resembling the acids in some of their pro- 
 perties, and not yielding aldehydes when partially oxidised ; as phenok 
 C G H 5 -OH. 
 
 (13) QUINONES, formed from hydrocarbons by the substitution of a 
 group of two oxygen atoms for two hydrogen atoms ; as quinane, 
 C 6 H 4 (0 2 ), from benzene, C 6 H G . 
 
 Compounds for which sufficient evidence of a rational formula bas- 
 net been obtained are classified according to similarity in properties,. 
 ultimate composition, or products of decomposition. The following are 
 the most important of such classes : 
 
 (14) CARBOHYDRATES, or compounds containing six, or some multiple 
 of six, atoms of carbon, together with some multiple of the group H 2 ; 
 as starch, C 6 H 10 0,, glucose, C 6 H ]2 6 , sugar, C 12 H 22 O n . 
 
 (15) GLUCOSIDES, or compounds which yield glucose as one of their 
 products of decomposition ; as salicin, C ]3 H 18 7 . 
 
 (16) ALBUMINOIDS and GELATINOIDS, or compounds containing C, H, 
 N, and O, often with small quantities of S, and sometimes of P, 
 distinguished by their tendency to putrefy when moist ; albumin, fibrin. 
 and casein are examples of such compounds, but they cannot at present 
 be represented by satisfactory formulae. 
 
 (17) HKTEROCYCLIC COMPOUNDS. The nature of these will be explained 
 later. 
 
 With few exceptions, one or other of the typical formulae cited in the 
 foregoing classification contains a hydrocarbon radicle ; it is, indeed, 
 possible to build up the members of each group by starting with one or 
 other of the hydrocarbons. Hence, nearly all organic compounds are 
 either hydrocarbons or hydocarbon derivatives. 
 
 In 1813 Chevreul showed that a fat is composed of glycerine and a fulfil </<!</. 
 and in 1848 Kolbe obtained hydrocarbons by electrolysing salts of fatty acids. 
 Later the aromatic substances, like the essential oils and balsams, were studied and 
 
526 PARAFFIN HYDROCARBONS. 
 
 found to yield hydrocarbons richer in carbon than those obtainable from the fatty 
 compounds. A classification of hydrocarbons into a fatty* and an aromatic series 
 was a natural consequence. But in the advance of a science definitions become 
 blurred by more accurate knowledge, and, for a reason which will be apparent 
 later, the terms open-chain and closed-chain (or acyclic and cyclic) have been 
 adopted as more accurately expressing the differences implied by the words fatty 
 and aromatic respectively. Even this division is losing its aptness, for bodies of 
 fatty nature have been detected among closed-chain compounds. For this reason 
 no actual division is made in the following pages. 
 
 HYDROCARBONS. 
 
 314. As will be explained, these are either saturated or unsaturated, 
 accordingly as they behave towards chemical agents. 
 
 SATURATED HYDROCARBONS. 
 
 Paraffin Series of Hydrocarbons. The only hydrocarbon which 
 contains one atom of carbon is methane or marsh gas, CH 4 , the more 
 important properties of which have been already considered. 
 
 It has been seen that when CH 4 undergoes metalepsis with chlorine, one of its 
 H atoms is exchanged for Cl, the compound CH 3 C1 being produced (p. 174). Now 
 there are several other methods of producing a compound of this formula, and, 
 whichever be adopted, the product always has the same properties, showing that 
 only one compound of the formula CH 3 C1 exists. It is contrary to experience, 
 acquired in other cases, to suppose that all the methods of producing CH 3 C1 
 would result in the substitution of Cl for the same H atom, and it may be fairly 
 inferred that whilst one method would produce CHHHC1, another would produce 
 CHHC1H, a third CHC1HH, and a fourth CC1HHH. In each case the substance 
 produced is the same. It is therefore supposed that all the four H atoms in 
 methane have an equal position with regard to the carbon atom, so that which- 
 ever is substituted the centre of gravity of the molecule will remain the same. 
 
 It is in order to express, or to attempt to explain, this equality of position of 
 
 the hydrogen atoms in relation to the carbon, that they are often represented on 
 
 paper as symmetrically arranged round the centre carbon 
 
 H atom (Fig. 247), so that whichever H is exchanged for Cl, 
 
 I the figure has only to be turned round in order to appear the 
 
 H C H same. On paper the atoms are, of necessity, written on the 
 
 same plane, but it is not to be supposed that this represents 
 
 H their arrangement in the molecule. At present we have no 
 
 satisfactory knowledge of the shapes of molecules, but we 
 
 Fi - 2 47- Methane. are obliged to think of them as having three dimensions. 
 
 The most fruitful hypothesis as to the structure of the 
 
 methane molecule is that the carbon atom occupies the centre of a regular tetra- 
 hedron, the hydrogen atoms being attached to the four angles thereof. 
 
 Inasmuch as methane has the formula CH 4 , generally written as in 
 Fig. 247, it must be regarded as a saturated compound devoid of any 
 residual affinity such as that possessed by CO (p. 136). 
 
 In the case of all other hydrocarbons it is assumed that the carbon 
 atoms are directly united together, since it does not appear to be possible 
 for H to behave other than as a monovalent element, so that it cannot 
 be supposed to act as an intermediary, that is, in a manner represented 
 by the expression 0-H-C. Of those hydrocarbons which have two carbon 
 atoms, or a two-carbon nucleus, there are at least three, of which two, 
 ethylene, C 2 H 4 , and acetylene, C 2 H 2 , have received notice (pp. 142 and 
 137) and will be referred to again. The third is called ethane, and has 
 
 * Attempts have been made to substitute aliphatic for fatty. 
 
HOMOLOGOUS SERIES. 527 
 
 the formula C.H 6 , which is generally represented as shown in Fig 248 
 but is equally well written H 3 C CH 3 . 
 
 The evidence for this formula is of a similar character to that for the methane 
 formula, only one compound C 2 H 5 C1 being obtainable. If two regular tetrahedra 
 be placed with one solid angle of each in contact, a two- 
 carbon nucleus will be represented in which each carbon is H H 
 at the centre of a tetrahedron, the six H atoms being at the | | 
 remaining three angles of each tetrahedron (see Fig. 257). H C C H 
 
 Ethane is also a saturated hydrocarbon, for all the 
 bonds of the two carbon atoms are satisfied. Pass- 
 ing to those hydrocarbons which contain three car- Fi - 248. Ethane. 
 bon atoms, or a three-carbon nucleus, that which is 
 saturated, and therefore contains the highest number of hydrogen atoms, 
 is C 3 H 8 , called propane, and is represented as in Fig. 240, or more simply 
 as CH 3 -OH 2 -CH 3 . 
 
 The evidence for this formula is derived from the methods H H H 
 
 by which propane is prepared, and will be appreciated when 
 
 these are described. The reasoning applied to methane will H C C C H 
 
 not serve in this case, for two compounds of the formula | | | 
 
 C 3 H 7 C1 are known, as will be explained later. H H H 
 
 A comparison of these three hydrocarbons will Yig. 249. Propane, 
 show that ethane may be regarded as derived from 
 methane, and propane from ethane, by substituting CH 3 for H. By 
 continuing this process a whole series of hydrocarbons is obtained, each 
 of which is saturated and differs from the one preceding it by CH 2 . 
 Thus butane, the next member of the series, is CH^CH^CH^CHg, 
 pentane is CH 3 -CH 2 -CH 2 -CH 2 'CH 3 , and so on. Any series 'of carbon 
 compounds, each member of which differs from the one preceding it by 
 OH 2 , is called an homologous series, and the compounds are homologues 
 of each other. 
 
 It will be seen that in the homologous series under consideration, the 
 number of hydrogen atoms must always exceed twice the number of 
 carbon atoms by 2, and that a general formula for the series may there- 
 fore be written C w H 2n+2 . Since each terminal carbon atom has three 
 hydrogen atoms attached to it, the general formula may be extended to 
 H 3 C-C H H 2K -OHo. As already stated, hydrocarbons which conform with 
 this general formula are termed saturated because they cannot have any 
 free affinities by which other elements can attach themselves to the 
 molecule. It must be understood that this title does not represent a 
 mere theoretical speculation, but is the expression of actual experience, 
 since it is found to be impossible to produce a new compound from any 
 of these hydrocarbons save by substitution ; for example, no compound 
 containing chlorine can be obtained from methane except by exchanging 
 one or more atoms of 01 for one or more atoms of H. On account of this 
 inactivity the series has been called the paraffin series of hydrocarbons, 
 the name paraffin (parum, little, affinis, affinity) having been originally 
 bestowed upon the wax-like substance obtained in the distillation of coal 
 and peat, because of its resistance to chemical agents ; this solid was 
 subsequently shown to consist mainly of saturated hydrocarbons. 
 
 The paraffin hydrocarbons may be regarded as the hydrides of posi- 
 tive radicles of the general formula M H 2jl+1 , the formula for the 
 hydrocarbons being C, Z H. 7H+1 H. These radicles have been termed alkyl 
 
528 PETROLEUM OIL. 
 
 radicles ; they are obviously monovalent. They are designated similarly 
 to the hydrocarbons which constitute their hydrides, the suffix ~yl being 
 substituted for -ane. 
 
 The natural source of the paraffin hydrocarbons is the oil known as 
 petroleum, mineral naphtha, or rock-oil. This is found in nearly all 
 countries, but especially at Baku, on the Caspian Sea, and in Canada 
 and Pennsylvania, and occurs in almost all geological formations. It is 
 to be noted, however, that the Russian petroleum consists largely of 
 hydrocarbons (naphthenes) allied to the aromatic series (q.v.), whilst 
 that of Pennsylvania consists almost entirely of a mixture of paraffin 
 hydrocarbons. 
 
 The Pennsylvanian oil-wells discharge large volumes of gas containing 
 H, CH 4 , and C 2 H 6 , which are used for heating and lighting in the 
 neighbouring district. The liquid pumped out of the wells still retains- 
 a quantity of ethane in solution. It consists chiefly of members of the 
 paraffin series, of which a list is here given 
 
 Methane CH 4 Gas 
 
 Ethane C 2 H 6 
 
 Propane C 3 H 8 
 
 Butane C 4 H 10 
 
 Boils at 
 
 Pentane C 5 H 12 36 C. 
 
 Hexane C 6 H 14 69 
 
 Boils at 
 
 Heptane ( V^io 9^ ^- 
 
 Octane (V^is 125 
 
 Nonane ^'<)H 20 149 
 
 Decane ( ' 10 H 2 ., 173 
 
 Dodecane ^12^26 214 
 
 Hexadecane C^H^ 287 
 
 The liquid constituents of the petroleum are separated by the process 
 of fractional distillation, which depends upon the difference in their 
 boilin g-poin ts. 
 
 When the petroleum is heated, the hydrocarbons, ethane, propane, and butane, 
 are evolved in the gaseous state ; these are collected and subjected to the action 
 of a condensing pump, which liquefies a portion of them, yielding the liquid sold 
 as cymogene. (sp. gr. 0.59), which is used in freezing-machines, on account of the 
 cold produced by its rapid evaporation. It consists chiefly of butane, C 4 H 10 . 
 
 The portion which first distils over requires special condensation, for it boils at 
 18 C. ; it contains a considerable proportion of pentane, and is sold as rli'xjnhnc 
 (sp. gr. 0.62), being used as an anaesthetic, and for a standard of light. The 
 portion which distils over about 60 C. consists mainly of hexane, and is sold as 
 petroleum spirit, petroleum ether, or gasolene (sp. gr. 0.66) ; it is used for dissolving 
 india-rubber. The next fraction is chiefly heptane, and is collected until the 
 temperature rises to 110 C.; its sp. gr. is 0.7, and it is used, in some kinds of 
 lamps, as a burning oil, and as a solvent, under the names naphtha, ligroin, and 
 benzoline. The next fraction is collected below 150 C., and is known as ben-zinc 
 (sp. gr. 0.74), a solvent which must not be confounded with benzene, the coal-tar 
 product. A similar fraction is the petrol burnt in the engines of motor-cars. The 
 Iterosene oil, so much in use for paraffin lamps, is the portion which distils between 
 150 and 300 C., and is generally refined by agitation with about 2 per cent, of 
 sulphuric acid (which removes the olefines contained in the oil) before being sent 
 into the market. It is unsafe to use oils of low boiling-point as illuminants in 
 ordinary lamps, because they so easily evolve vapour, which forms an explosive 
 mixture with air, and bursts the lamp. 
 
 The temperature at which the hydrocarbon evolves enough vapour to form an 
 inflammable mixture with the air above it is termed its flashing-point. Xo paraffin 
 oil is considered safe for burning, in England, which kindles from a flame 
 brought near to its surface when it is heated to 38 C. (100 F.) in an open vessel ; a 
 teacup placed in a basin of hot w r ater in which a thermometer is plunged, 
 answers for a rough test. In a closed vessel, where the vapour more rapidly 
 accumulates in sufficient quantity, the flashing-point is much lower, and no oil is 
 considered safe which kindles at or below 23 C. (73 F.) in a covered vessel when 
 a flame is brought near its surface : a small beaker covered with a piece of tin 
 
FRACTIONAL DISTILLATION. 
 
 5 2 9 
 
 plate having a small hole for introducing a match, may be placed in warm water 
 for the close text. 
 
 The distillation of the petroleum is finally pushed until a tarry residue is left 
 in the retort. The distillate above 300 C. consists of heavy (sp. gr. 0.9) lulncut- 
 iiuj HI?* containing parqffin-ivax, which melts at about 55 C., and may, therefore, 
 be separated from the oils by freezing ; this wax contains the highest known homo- 
 logues of the paraffin series. The softer varieties of paraffin are known as vaseline. 
 
 Ozokerite, a crude form of which is known as ceresln, is imported from Galicia, 
 Hungary, and Kussia, for the manufacture of candles. It consists of solid hydro- 
 carbons which appear to contain a smaller proportion of hydrogen than do the 
 paraffin hydrocarbons ; its melting-point varies from 60 C. to 100 C. 
 
 Paraffin oils, both illuminating and lubricating, and paraffin-wax are also 
 obtained by distilling certain minerals allied to coal, such as the Torbane Hill 
 mineral, or Boghead cannel, found at Bathgate, in Scotland. Such shale oils con- 
 tain more olefines than do the American oils. 
 
 All the oils above mentioned are colourless when quite pure, although the com- 
 mercial products are frequently yellow or brown. 
 
 315. On the small scale, the process of fractional distillation for the separation of 
 liquids of different boiling-points is conducted in a flask (A, Fig. 250) provided 
 
 Fig. 250. Fractional distillation. 
 
 with a long neck through which a thermometer (T) passes to indicate the tempera- 
 ture at which the liquid boils. The first portion which distils over will, of course, 
 consist chiefly of that liquid which has the lowest boiling-point, particularly if the 
 neck of the flask consist of a series of bulbs and thus expose a large surface to be 
 cooled by the air ; if the receiver (R) be changed at stated intervals corresponding 
 with a certain rise in the temperature, a series of liquids will be obtained, con- 
 taining substances the boiling-point of which lie within the limits of temperature 
 between which the liquids were collected. 
 
 When these liquids are again distilled separately in the same way, a great part 
 of each is generally found to distil over within a few degrees on either side of 
 some particular temperature, which is the boiling-point of the substance of which 
 that liquid chiefly consists ; and if the receivers be again changed at stated 
 intervals, a second series of distillates will be obtained, the boiling-points o 
 which are comprised within a narrower range of temperature. It will be evider 
 that, by repeated distillations, the original mixture will eventually be resolved 
 
 2 L 
 
530 
 
 METHANE. 
 
 into a number of liquids, each distilling over entirely at about one particular 
 temperature, which is the boiling-point of its chief constituent. 
 
 316. Methane, or methyl hydride, CH 4 . The following must be added 
 to the description of methane which has already been given (p. 144). 
 
 To prepare the pure gas, methyl iodide is dropped slowly into a flask 
 A (Fig. 251) containing a copper-zinc couple (p. 21) covered with dilute 
 
 alcohol ; the flask is very gently 
 heated, whereupon methane is 
 evolved in accordance with the 
 equation CH 3 I + C 2 H 5 OH + 
 Zn= CH 3 H + Zni.OC 2 H 5 , and 
 passes up the tube B contain- 
 ing granulated zinc which 
 decomposes any unchanged 
 CH 3 T, allowing the methane 
 to be collected in the usual 
 manner from the delivery 
 tube. Methane is also formed 
 when zinc methide is decom- 
 posed by water, Zn(CH 3 ) 2 + 
 2 HOH = Zn(OH) 2 + 2 CH 4 , and 
 by the action of sodium amal- 
 gam and water (to supply H) 
 on carbon tetrachloride, CC1 4 + 
 H 8 = CH 4 + 4HC1, and bypass- 
 ing a mixture of CS 2 vapour 
 and H 3 S (or steam) over red-hot 
 copper, CS 2 + 2H 2 S + Cu 8 = 
 4Cu 2 S + CH 4 . The last two methods are of great importance, since 
 they, amount to the preparation of the gas from its elements, and, 
 therefore, to the synthesis of the paraffin hydrocarbons generally, for 
 the majority of these can be built up from marsh-gas by the aid of a 
 few elements which act as intermediaries. 
 
 Methane is nearly inodorous ; its sp. gr. is 0.56 (air=i); it burns 
 with a feebly luminous flame ; water dissolves about 5 per cent., and 
 alcohol 50 per cent, of the gas. It boils at - 160 C., but is liquid at 
 - 11 0., under 180 atmospheres pressure ; the sp. gr. of the liquid is 
 0.415 at 164 C. 
 
 When methane is mixed with chlorine and exposed to sunlight, a 
 violent reaction occurs, and often an explosion, HC1 being formed, and 
 C separated ; but when the Cl is diluted with C0 2 and allowed to act 
 gradually, chlorine substitution-products are obtained. 
 
 CH 4 + C1 2 = HC1 + CH 3 C1 monochloromethane. 
 CH 4 + 2C1 2 = 2HC1 + CH 2 C1 2 dichloromethane. 
 CH 4 + 3C1 = 3HC1 + OH01 8 chloroform. 
 CH 4 + 4013 = 4HC1 + CC1 4 tetrachloromethane. 
 
 The chlorine in these compounds is not precipitated by silver nitrate, 
 like the Cl in HC1 and the chlorides of the raetals. 
 
 Ethane, or ethyl hydride, C 2 H 6 , is prepared from ethyl iodide, C 2 H 6 I, 
 just as methane is prepared from methyl iodide. It is also formed 
 when methyl iodide is heated with zinc in a sealed tube, 2CH 3 
 
 Fig-. 251. Preparation of methane. 
 
 ZnI 
 
 ; hence, ethane has been termed dimethyl. 
 
NUCLEAL SYNTHESIS. 
 
 531 
 
 Ethane is evolved from the anode when a solution of potassium acetate, 
 CH 3 COOK, is electrolysed ; this salt dissociates into the ions CH 3 COO and K,' 
 the former of which breaks up into C 2 H 6 and C0 2 , whilst the latter reacts with 
 the water to form KOH and H, which is evolved at the cathode ; the KOH 
 absorbs the C0 2 , so that the ultimate result may be approximately represented 
 by the equation 2CH 3 COOK + 2H 2 = C 2 H 6 + 2KHC0 3 + H 2 . 
 
 Ethane resembles methane in properties, but is more easily liquefied 
 (46 atm.) ; it is about twice as soluble in alcohol as methane is. 
 
 Propane, or pi'opyl hydride, C 3 H 8 , is prepared by the action of nascent 
 hydrogen on propyl iodide, C 3 H 7 I + H 2 = C 3 H 8 + HI. It is also formed 
 when a mixture of ethyl iodide and methyl iodide is heated with zinc, 
 CH 3 -CH 2 -I + CH 3 I + Zn = CH 3 -CH 2 -CH 3 + ZnI 2 , the reaction being of 
 importance as confirming the constitution of propane (Fig. 249), for it 
 shows that the hydrocarbon is formed by the combination of methyl 
 with ethyl. Propane is a colourless gas which boils at - 45 C. 
 
 It will have been noticed that precisely similar methods serve for 
 the preparation of methane, ethane, and propane. This is illustrative 
 of the fact that the members of an homologous series of carbon com- 
 pounds can generally be prepared from the members of another homo- 
 logous series by the same reaction ; thus the series of alkyl iodides 
 (CH 3 I, C 2 HJ, C 8 H 7 I, <fec.) yield the corresponding series of alkyl 
 hydrides (hydrocarbons) by metalepsis with (nascent) hydrogen. For 
 each series of carbon compounds, therefore, there is a number of general 
 methods of formation. 
 
 It will be noted that the hydrocarbons which are of industrial im- 
 portance are either natural products, like the parafiins, or are obtained, 
 like benzene, as products of destructive distillation, a process the 
 mechanism of which has not yet been explained. Acetylene alone is 
 manufactured by a process which may be said to be well understood. 
 For the purposes of chemical investigation, however, several methods 
 are available for preparing hydrocarbons, and are more or less generally 
 applicable, whatever the family to which the desired hydrocarbon may 
 belong. 
 
 Nucleal synthesis or nucleal condensation is the most general of these 
 methods. The term implies the creation of a new carbon nucleus, 
 either by adding another carbon atom to an existing nucleus or by 
 converting a single bond between two carbon atoms in the molecule 
 into a double or treble bond (intra-molecular condensation). In the 
 case of the paraflftns, in which the carbon atoms are always singly linked, 
 the process must consist in adding new carbon atoms to the nucleus, 
 and for this purpose two substituted hydrocarbons are treated with an - 
 agent capable of removing the substituent from each, leaving the carbon . 
 atoms of the two nuclei to combine at the points thus exposed. The 
 equation given above for the formation of propane from ethyl or methyl 
 iodides illustrates the process; in general terms RI + IR' + Na 2 = 
 2NaI + R-R', in which R and R' may be the same or different alkyl 
 nuclei. The halogen substitution-products and sodium or zinc as the 
 halogen remover are best suited for the method (Wurtz's reaction). 
 
 A less general method is the removal of carbon as C0 ? from an 
 organic acid by heating it with alkali, as in the preparation of methane 
 by heating sodium acetate with caustic soda (p. 144)- This method is 
 of much importance in the paraflin series, and is expressed by the 
 general equation R'COONa + NaOH = RH + NaOCOONa. In a sense 
 
532 ISOMEEIC BUTANES. 
 
 it is the converse of the first method, since it forms a new carbon 
 nucleus by removing carbon from an existing one. 
 
 A similar removal of carbon dioxide from salts of organic acids may 
 be effected by electrolysis (see ethane, p. 531), and this method is 
 applicable to several classes of hydrocarbons. It generally involves a 
 nucleal condensation. 
 
 Other methods for preparing paraffins are (i) treatment of alkyl 
 halides with nascent hydrogen, RCl + H 2 = RH + HC1 (see methane), and 
 (2) interaction of alkyl iodides with zinc alkyl compounds, 2R1 + ZnR, = 
 2(R.R) + ZnI 2 (see ethane). 
 
 Butane, 4 H 10 , is made by treating ethyl iodide with zinc (not in 
 excess) in a sealed tube at 150 C. ; 2C 2 H 5 I + Zn == ZnI 2 + C 4 H 10 . It is 
 much more easily condensed to a liquid than is either of the preceding 
 hydrocarbons, and is much more soluble in alcohol. Liquid butane 
 (sp. gr. 0.6) boils at i C. Since butane is prepared from ethyl iodide, 
 it may be regarded as diethyl in the same sense that ethane is dimethyl, 
 and it is justifiable to write its formula, CH 3 'CH 2 'CH 2 'CH 3 , or as in 
 Fig. 252. 
 
 H H H 
 
 H H H H H-C-C-C-H 
 
 I I I I III 
 
 H-C-C-C-C-H H C H 
 
 H H H H 
 
 Fig. 252. Normal butane. 
 
 1 1' 
 
 S H 
 
 Fig-. 253. Secondary 
 butane. 
 
 For ethyl iodide is the iodine substitution product of ethane, 
 CH 3 'CH 3 , and its formula is CH 3 'CH 2 L "When the diad zinc acts 
 upon this, it must take the I 2 , which it requires to form zinc iodide,, 
 from two molecules of ethyl iodide, leaving the residues to combine 
 and produce butane, thus : 
 
 CH 3 -CH 2 I + Zn + ICH 2 -CH 3 = ZnI 2 + CH 3 -CH 2 -CH 2 -CH 3 . 
 
 There is a second hydrocarbon of the formula C 4 H ]0 ; it is prepared 
 by the action of nascent hydrogen on a compound called tertiary butyl 
 iodide (q.v.), C 4 H 9 I. It might be mistaken for butane but for the fact 
 that it will not liquefy until cooled to - 17 C. This second butane 
 has been called secondary butane or isobutane ('ia-os, equal), the first 
 butane being termed normal butane, from norma, a rule, because it is 
 the product of the usual general methods of formation ot the paraffins, 
 and possesses the physical properties which the hydrocarbon, C 4 H 10 ,. 
 should possess from its position in the homologous series of paraffins 
 (e.g., a boiling-point about 30 lower than the next higher member in 
 the series). In order to explain the existence of this secondary butane 
 it is supposed that the four carbon atoms are arranged in space differ- 
 ently from the manner in which they are arranged in the case of normal 
 butane. A little consideration will show that the only possible second 
 method of arrangement of the carbon atoms on one plane is that shown 
 in Fig. 253, in which the fourth C atom is attached to the central C atom 
 of the propane formula. The same arrangement may be expressed by 
 the formula CH 3 -C(CH 3 )H'CH 3 or (OH 8 ) f : OH ; CH 3 , and may be cle- 
 
ISOMEPJDES. 533 
 
 scribed as consisting of methane in which three atoms of H have been 
 exchanged for methyl, that is as trimethylmethane. Tertiary butyl iodide 
 has the formula CH 3 -C(CH 3 )I-CH 3 , and the action of nascent hydro- 
 gen in converting it into trimethylmethane, or secondary butane, is 
 apparent. 
 
 Pentane, C 5 H 12 . Three hydrocarbons of this formula exist ; that which 
 is made by the general methods, and, therefore, has a right to the title 
 normal pentane, is a colourless liquid, boiling at 36 C. Secondary pen- 
 tane, or isopentane, boils at 28 C., and tertiary pentane or tetramethyl- 
 methane, at 9 C. To account for the existence of these three hydro- 
 carbons, it is necessary to suppose that the five carbon atoms are 
 arranged in three different ways; this will be found to be pos- 
 sible, the results being indicated in Figs. 254-256, or by the formulae 
 CH 3 -CH 2 -CH 2 -CH 2 -CH 3 , CH 3 -CH 2 -C(CH 3 )H-CH 3 , andC(CH 3 ) 4 . 
 
 H 2 H 
 Ho H 2 H 2 H 3 C C C CH 3 H 3 C\ /CH 3 
 
 H 3 c-c-c-c-CH 3 I ir/ c V H 
 
 CH 3 H 3 C " H 3 
 
 Fig. 254. Normal Fig. 256. Tertiary 
 
 pentane. Fig. 255. Iso-pentaue. pentane.* 
 
 If it were possible to arrange the 5 carbon atoms in a way essentially 
 different from any of these three, a fourth pentane might be expected to 
 exist. It will be evident that the greater the number of carbon atoms 
 in the hydrocarbon, the greater the variety of arrangement and therefore 
 the greater the number of possible isomerides. Thus, there may be dis- 
 covered 802 compounds of the formula C 13 H 28 . 
 
 Isomerides are those compounds which have the same percentage 
 composition and the same molecular weight, but different properties. 
 Cases of isomerism are very numerous among the carbon compounds ; 
 attempts have been made to explain them by reference to the arrange- 
 ment of the atoms of the compounds in space, although in some cases 
 special difficulty is experienced ; these will be referred to in due course. 
 
 Polymerides have the same percentage composition, but different 
 molecular weights ; e.g., C 2 H 2 and C 6 H 6 ; CH 2 O and C 6 H 12 6 . 
 
 Since the valency of carbon is always four, there can only be three 
 modes in which the carbon atoms can be linked to each other, giving 
 rise to three main classes of isomerides, which are illustrated by the 
 three classes of paraffin hydrocarbons. Normal paraffins are those in 
 which all the carbon atoms are united in a single chain without branches. 
 so that the formula begins and ends with CH 3 , every other link being 
 CH 2 (Fig. 254). Secondary paraffins or iso-paraffins, have at least one 
 branch, that is, at least one carbon atom is united with three other 
 carbon atoms, as in Fig. 255. Tertiary paraffins or neo-paraffins, have at 
 least one carbon atom united to four others, as in Fig. 256. 
 
 The remaining hydrocarbons of the paraffin series do not need 
 detailed consideration here. Those from hexane to pentadecane (C 15 H 32 ) 
 are colourless liquids the boiling-points of which increase, in the normal 
 series, by about 30 C. for each increment of CH,. Those in the normal 
 series, from hexadecane (C 16 H 34 ) to pentatriacontane (C 33 H 72 ), the highest 
 
 * That this is really the constitution of neo-pentane is shown by the steps for obtain inn 
 it synthetically ; acetone, H 3 C(CO)CH 3 , treated with FC1 5 , yields H 3 C(CCI 2 )CH3, ai 
 acted on by zinc methyl, gives H 3 C[C(CH 3 )2]CH 3 , or neo-pentam-. 
 
534 CONSTITUTION OF UNSATURATED HYDROCARBONS. 
 
 known member, are colourless solids of which the melting-point increases 
 by 3-4 C. for each increment of CH 2 , that of hexadecane being 19 C. 
 
 UNSATURATED HYDROCARBONS. 
 
 317. All hydrocarbons which do not correspond with the general 
 formula C H H 2)Z+2 are found to be capable of combining directly with the 
 halogens without exchanging hydrogen for them. Such are, there- 
 fore, termed unsaturated hydrocarbons. No hydrocarbon has yet been 
 discovered which contains an uneven number of hydrogen atoms, nor 
 has any unsaturated hydrocarbon containing only one atom of carbon 
 ever been isolated. To account for these facts it is supposed that 
 all unsaturated hydrocarbons contain two or more carbon atoms 
 which are united to each other by two or three atom-fixing powers, 
 
 thus : H >C = C/ H , and H - C= C - H. 
 
 It may be said that, in a hydrocarbon, an unsaturated carbon atom cannot exist ; 
 if there be not a sufficiency of other elements to saturate the carbon atom, it will 
 combine by all its available atom-fixing powers with another carbon atom. The 
 fact that no such hydrocarbon as H 3 C - CH 2 is known, is in support of this 
 
 statement. Of these two carbon atoms the unsaturated one will take up an atom- 
 fixing power of the saturated carbon atom, at the expense of one of the hydrogen 
 atoms united to this latter, forming H 2 C = CH 2 , in which neither carbon atom can be 
 said to be unsaturated, although the compound as a whole is unsaturated. Treatment 
 of this compound with chlorine will open up the double linking, yielding H 2 C - CH 2 . 
 
 Cl Cl 
 If the compound were represented by the formula H 2 C - CH 2 , there would be no 
 
 apparent reason w r hy, when the compound is mixed with the proper proportion 
 of chlorine, one carbon atom alone should not combine with Cl yielding H 2 C - CH 2 , 
 
 ' Cl 
 a result which, however, has never been obtained. The same objection applies to 
 
 a third possible method of representing this hydrocarbon, viz. : H 3 C - CH ; more- 
 
 over, if this formula were correct the addition of chlorine to the hydrocarbon 
 
 Cl 
 might be expected to produce H.,C - CH, whereas there is evidence that the two 
 
 Cl 
 
 chlorine atoms in the compound formed by addition of chlorine to C 2 H 4 are 
 attached to different carbon atoms. 
 
 A similar line of reasoning serves for supporting the formula HC CH for the 
 hydrocarbon C 2 H 2 . 
 
 If two regular tetrahedra be placed with one edge of each coincident, there will 
 be two solid angles of each tetrahedron left unattached. Such an arrangement 
 may be supposed to represent the structure of the hydrocarbon C 2 H 4 in space ; 
 each carbon atom would occupy the centre of a tetrahedron, and each hydrogen 
 atom would be attached to a free solid angle. By placing the two tetrahedra 
 with one face of each coincident, the structure of the hydrocarbon C 2 H 2 may be 
 represented. 
 
 The following figures (Fig. 257) may represent hydrocarbons containing singly- 
 linked, doubly-linked, and trebly-linked carbon atoms respectively. 
 
 Olefine Series of Hydrocarbons. The Olefine hydrocarbons are 
 unsaturated hydrocarbons containing a pair of doubly-linked carbon 
 atoms ; they correspond in composition with the general formula C M H 2W . 
 The first three members of the homologous series are ethylene, H 2 C : CH 2 ; 
 propylene, H 2 C : CH'CH 3 ; and butylene, H 2 C : CH-CH 2 'CH 3 . It will be 
 seen that the nomenclature adopted differs from that for the paraffins by 
 the substitution of the suffix -ylene for -ane, an alternative name for the 
 olefines being alkylenes. 
 
ETHYLENE. 535 
 
 The defines are found in petroleum -oil and in the products of the 
 destructive distillation of coal, wood, &c. The first three members of 
 the series are gaseous under ordinary conditions ; the majority of the 
 remainder are colourless liquids, but the highest members are solid. A 
 gradation of boiling-points and melting-points is observed, similar to' that 
 existing in the paraffin series. The properties of ethylene may be con- 
 sidered as typical of those of the other members of this group of hydro- 
 carbons. 
 
 Fig. 257. 
 
 Oleflant gas, ethylene, or ethene, C 2 H 4 , is obtained by the action of 
 powerful dehydrating agents on alcohol ; C 2 H 5 'OH = C 2 H 4 + HOH. It 
 may be prepared, as described at p. 142, by heating alcohol with twice 
 its volume of strong sulphuric acid ; secondary changes cause a carboni- 
 sation of the mixture, and the ethene is accompanied by some ether 
 vapour, and by CO 2 and SO 2 ; the ether may be removed by passing 
 the gas through strong sulphuric acid, and the dioxides by potash or 
 soda. 
 
 It is also obtained by heating an ethyl halide with a caustic alkali in 
 alcohol, e.g., C 2 H 5 Br + KOH = C a H 4 + KBr + HOH. 
 
 Properties of ethylene. It has a faint ethereal odour, sp. gr. 0.97, and 
 boils at - 103 C. Slightly soluble in water; more soluble in alcohol. 
 Burns with a bright luminous flame, which renders it very useful as an 
 illuminating constituent of coal-gas. When mixed with chlorine, ethy- 
 lene combines with it to form a fragrant liquid known as ethylene chloride 
 or Dutch liquid, C1H,OCH 2 C1. Bromine forms a similar compound 
 with it. Sulphuric acid slowly absorbs ethylene, forming C 2 H 5 HS0 4 , 
 sulphethylic or sulphovinic acid or ethyl hydrogen sulphate, from which 
 alcohol may be obtained by distillation with much water, and ethene 
 by heating it alone, 0,H,HSO 4 + HOH = C 2 H 5 OH + H 2 S0 4 , C,H 5 HS0 4 = 
 C 2 H 4 + H 2 S0 4 . Sulphuric anhydride absorbs ethene much more 
 easily, and a strong solution 'of S0 3 in H,SO 4 (fuming sulphuric 
 acid) is employed for absorbing it in the analysis of coal-gas. The 
 compound formed by SO 3 with ethylene is crystalline, and is termed 
 carbyl sulphate or ethionic anhydride, C 2 H 4 (S0 3 ),. In contact with 
 water, this forms ethionic acid, CH 2 (OS0 3 H)-CH S (S0 3 H), and when 
 this is boiled with water it yields isethionic acid, H 2 C 2 H 4 S 2 7 + H S = 
 H,S0 4 + CH 2 (OH)-CH 2 (SO 3 H). It will be noticed that isethionic acid 
 has the same composition as ethyl hydrogen sulphate, but it is a more 
 stable compound. 
 
 In presence of platinum-black, ethylene combines v ith hydrogen to 
 
536 PREPARATION OF OLEFINES. 
 
 i 
 
 form* ethane, C 2 H 6 . With HBr and HI it combines to form ethy- 
 bromide, C 3 ILBr, and iodide, C.,H 5 I, respectively. 
 
 Oxidising-agents, such as nitric and chromic acids, convert ethene 
 into oxidised bodies containing two carbon atoms, such as oxalic acid, 
 C 2 H 2 O 4 , aldehyde, C 2 H 4 O, and acetic acid, C 9 H 4 2 . 
 
 From the above description of the properties of ethene, it will be seen 
 that it differs greatly from methane and the other paraffins, in the readi- 
 ness with which it combines with other bodies, especially with chlorine, 
 bromine, and sulphuric anhydride, forming addition-products instead of 
 substitution-prod u cts. 
 
 Experiments which may be performed with the gas will be found at 
 
 P- 143- 
 
 Propylene, C 3 H 6 or CH 3 - CH:CH 2 , occurs in small quantity in coal-gas. It may 
 be obtained by heating glycerine with zinc-dust ; 
 
 C 3 H 5 (OH) 3 + Zn, = C 3 H 6 + H + 3 ZnO. 
 
 In properties it resembles ethylene, but it is, of course, half as heavy again. It is 
 more easily absorbed by strong sulphuric acid. Only one propylene is known, but 
 another hydrocarbon, trimethylene, has the same formula (p. 539). 
 
 Bytylene, C 4 H 8 or CH 3 'CH 2 *CH:CH 2 , occurs largely in the illuminating gas made 
 by distilling the vegetable and animal oils. It is also found in the odorous hydro- 
 carbons which are evolved when cast iron is dissolved in hydrochloric or dilute 
 sulphuric acid. It boils at - 5 C. 
 
 Consideration of the formula for butylene will show that three isomerides of this 
 hydrocarbon can exist, viz., a- or normal butylene, CH S 'CH 'CH:CH ; /3- GV pseiido- 
 butylene, CH 3 'CH:CH-CH 3 ; and 7- or iso-'butylftne (CH 3 ) 2 C:CH 2 / The butylene 
 described above is the normal hydrocarbon. Pseudo-butylene exists in two modi- 
 fications called geometrical isomerides (see p. 542). 
 
 Amylene or pentylene, C g H 10 or CH./CH./CH 2 'CH:CH 2 , can exist in five isomeric 
 forms. They occur in petroleum and paraffin oil. The normal amylene, which 
 has the formula given above, boils at 40 C. 
 
 The moderate oxidation of the olefines, in presence of water, produces com- 
 pounds in which the opened up bonds are attached to hydroxyl groups ; thus, 
 CH 3 -CH:CH 2 yields CH 3 .CHOITCH. 2 OH. 
 
 General methods for preparing olefine hydrocarbons. (i) It is obvious 
 that if one of the single bonds in a paraffin be converted into a double 
 bond the corresponding olefine will be produced, e.g., propane, CH 3 *CH 2 ' 
 CH 3 , will become propylene, CH' 3 CH : CH 2 . Thh is a nucleal condensa- 
 tion, and may be effected similarly to that by which new paraffins may 
 be formed (p. 531). Thus, a dihalogen substituted paraffin may be 
 heated with zinc, CH 2 Br'CH 2 Br + Zn = CH, : CH 2 = ZnBr 2 . For this 
 kind of condensation, however, heating a monohalogen derivative with 
 an alcoholic solution of an alkali is generally best ; in this case the 
 halogen atom and a hydrogen atom are removed, presumably as hydrogen 
 halide, by the alkali ; CH 3 'CH 2 Br = CH 2 : CH 2 + HBr. 
 
 (2) By the dehydration of the alcohols of the paraffin series 
 (q.v.) by strong sulphuric acid, zinc chloride, or phosphoric acid, e.g., 
 CH 3 -CH 2 -CH 2 OH = CH 3 -CH : CH 2 + HOH. 
 
 The second method frequently produces a mixture of the olefine and its polymerides 
 (p. 533), for the olefines tend to polymerise under the influence of acids and 
 dehydrating agents ; thus, when amylene is prepared in this way, C 10 H 20 and 
 C 15 H 30 are also produced. 
 
 (3) The salts of some of the dicarboxylic acids (#.r.) yield olefines when 
 electrolysed (cf. p. 531) ; thus potassium succinate yields ethylene : 
 
 C0 2 K-CH 2 -CH 2 -C0 2 K + 2HOH = CH 2 :CH 2 + 2KHC0 3 + H 2 . 
 
 (4) The process of nucleal condensation may be reversed ; that is to say, a 
 treble or double linking may be converted into a single linking by treating the 
 
ACETYLENE. 
 
 537 
 
 compound with nascent hydrogen. Thus some of the acetylene compounds yield 
 the corresponding- olefine when so treated: CH CH + H 2 =CH 2 : CH 2 (similarly, 
 ethylene may be transformed into ethane see above). 
 
 (5) Wurtz's reaction (p. 531) may be applied to produce new olefines by treat ing 
 & mixture of a monohalogen-substituted olefine and an alkyl halide with sodium. 
 
 318. Acetylene Series of Hydrocarbons. The acetylene hydro- 
 carbons are unsaturated hydrocarbons containing a pair of trebly-linked 
 carbon atoms : they correspond in composition with the general formula 
 C H Ho,,_2. The first two members of the series, acetylene, HC : CH, and 
 allylene, H 3 C'C : CH, are gaseous under ordinary conditions, whilst 
 most of the others are colourless liquids. 
 
 It will be seen that the hydrocarbon, C 3 H 4 , is capable of being represented by 
 the two formula; CHyC : CH, and CH 2 : C : CH 2 , so that two modifications of 
 this compound may be expected ; these have been prepared, the former being 
 called <tUi/lcitc and the latter allene or propadiene.* For every true acetylene (a 
 hydrocarbon containing a pair of trebly-linked carbon atoms) there may also be a 
 hydrocarbon containing two pairs of doubly-linked carbon atoms. These d'wlejinex 
 differ considerably in properties from the acetylenes ; they are unimportant, and 
 cannot be further considered here. 
 
 Acetylene, or ethine, C 2 H 2 , is the only hydrocarbon which can be 
 formed in more than mere traces by the direct union of its elements. 
 Its preparation and most of its properties have been described at p. 137. 
 
 Pure acetylene may be prepared from ethylene by combining this 
 with bromine to form ethylene bromide which is then heated with 
 caustic potash in alcohol : 
 
 BrH 2 OCH 2 Br + 2KOH = HC : CH + 2KBr + 2HOH ; 
 
 .and from methane by converting this into chloroform which is then 
 heated with sodium : 
 
 HC = CL + C1 3 : CH + Xa (; = HC I CH + 6NaCl ; 
 
 These two reactions are typical of the general methods for preparing 
 acetylene. 
 
 In the presence of platinum-black acetylene combines with hydrogen 
 to form ethene, C S H 4 . Strong sulphuric acid absorbs acetylene slowly 
 as it does ethene ; but when the solution is mixed with water and 
 distilled, it yields, not alcohol as with ethene, but croton-aldeltyd. 
 C 3 H/CHO ; 2C,H + H,0 = C 4 H 6 0. Chromic acid oxidises acetylene to 
 acetic acid; C 2 H 2 + H 8 O + = C,H 4 0,. Alkaline potassium perman- 
 ganate converts it into oxalic acid, C. > H 2 + 4 = C 2 II 2 4 . 
 
 The most remarkable feature of acetylene is the facility with which 
 its hydrogen is displaced by metals. By heating sodium in acetylene, 
 CJEENa, mono-sodium acetylide and C 2 Na 2 , disodium acetylide may be 
 obtained. Cuprous acetylide, C.,Cu., has been noticed at p. 140. 
 
 Silver acetylide, C 2 Ag 2 , is produced as a white precipitate when 
 acetylene is passed into" ammoniacal silver nitrate ; in absence of 
 ammonia the precipitate is a compound of the acetylide with silver 
 nitrate. 
 
 When acetylene is passed into antimonic chloride, kept cool, crystals 
 
 * According to one system of nomenclature the terminations -dime, -triene, -Mn //< , AT.. 
 are used to indicate hydrocarbons containing: 2. 3, 4, &c., double linking^ respeci 
 position of the double bonds are indicated by the numbers of the C atoms inimedu 
 ceding- them in the chain. Thus i : 4 -hexadiene is CH 2 : CH CH 2 CH : CH 
 hydrocarbons containing- 2, 3, 4, &c., treble bonds terminate in -diinc, -trnne, -t< 
 respectively. 
 
538 OPEN- AND CLOSED-CHAIN HYDROCARBONS. 
 
 of C 2 H 2 01 2 *SbCl 3 are formed, which, on heating, yield the acetylene 
 dichloride, C 2 H 2 C1 2 , as a liquid smelling like chloroform, and boiling at 
 55 C. CJEE 2 C1 4 , acetylene tetrachloride and C 2 HC1, monochlor acetylene r 
 have also been obtained. 
 
 When heated in a sealed tube, acetylene is partially converted into a 
 mixture of two liquids, benzene, C 6 H 6 and styrolene, C 8 H 8 . By passing 
 electric sparks through a mixture of acetylene with nitrogen, hydro- 
 cyanic acid is produced; C 2 H 2 + N 2 = 2HCN. Hence this acid, from 
 which a large number of organic bodies may be derived, has been 
 synthetised from its elementary constituents. Cuprous acetylide, in con- 
 tact with zinc and solution of ammonia, yields ethylene, which is con- 
 vertible into alcohol, and from this a very large number of organic 
 compounds may be made. 
 
 Acetylene is regarded as one of the most important intermediate 
 bodies in the synthesis of organic compounds from their elements. 
 
 Allylene, or propim, CH 3 'C : CH, resembles acetylene, but its cuprous compound 
 is yellow instead of red. 
 
 The hydrocarbon C 4 H 6 (buti-ne) can exist in two forms, each of which will 
 have a pair of trebly-linked carbon atoms, namely, CH 3 'CH 2 'C : CH (ethylacetylene} 
 and CH 3 *C : C 'CH 3 (crotonylene or dimethylacetylene} ; besides these true acetylenes, 
 there is dtrinyl, CH 2 : CH'CH : CH 2 , a diolefine found in compressed illuminating 
 gas. 
 
 Crotonylene is a liquid (b.-p. 27 C.) ; its vapour is one of the illuminating- 
 hydrocarbons in coal-gas. It does not form any metallic derivatives, and it 
 appears that this is generally the case with those acetylenes which have not the 
 group *C : CH in their composition. 
 
 The other members of the series have no practical importance at present. 
 They are prepared by treating the bromo-substitution products of the paraffins- 
 and defines with alcoholic potash. 
 
 319. The paraffins, olefines, and acetylenes are supposed to have their 
 carbon atoms linked together in what may be termed an open chain, in 
 which there are terminal carbon atoms, each attached to only one other 
 carbon atom. The hydrocarbons next to be considered, notably benzene 
 and its homologues, exhibit properties which show that while they are 
 strictly unsaturated in the sense that they do not correspond with the 
 general formula C w H 2tt+2 (p. 527), they behave more like the paraffins 
 than the olefines towards chemical agents. The most fruitful hypothesis 
 in explanation of this difference is that in these hydrocarbons no carbon 
 atom is attached to only one other carbon atom. This can only be the 
 case if the terminal carbon atoms are attached to each other, thus :- 
 
 C - C - C - 0. Such hydrocarbons are termed closed-chain hydro- 
 carbons, or ring or cyclic hydrocarbons since the arrangement of the 
 carbon atoms in the form of a ring is somewhat more convenient, e.y., 
 : C - C : 
 
 I 
 : C - C : 
 
 The only other series of open-chain hydrocarbons which are known besides the 
 three already considered are those corresponding with the general formula? 
 C w H 2H _ 4 and C W H 2W _ 6 . The hydrocarbons of the former series must have either 
 one pair of trebly- and one pair of doubly-linked carbon atoms, as in the formula 
 CH 3 -CH : CH-C : CH (plefine-acetylenes}, or three pairs of doubly-linked carbon 
 atoms, as in CH 3 'CH : C : C : CH 2 (triolejineg). The C M H 2w - 6 open-chain hydro- 
 carbons must contain either two trebly-linked or four doubly-linked carbon atoms ; 
 
CYCLIC HYDROCAKBONS, 
 
 539 
 
 the treble linking is the more common, e.g., dl-acetylene, CH : C'C : CH, and 
 dlpropargyl (liexadiine), CH C'CH 2 'CH 2 'C : CH, which is isomeric with benzene. 
 Both these hydrocarbons form copper and silver compounds like those of acetylene. 
 
 Closed-chain Hydrocarbons. It is obvious that a closed-chain 
 hydrocarbon must contain at least three carbon atoms, and that such a 
 one would be obtained if a hydrogen atom could be removed from each 
 end of the propane chain, leaving the carbon bonds thus liberated 
 to unite : H 3 C CH 2 CH 3 - H 2 = H 2 C CH 2 CH 2 . This has not been 
 
 accomplished directly, but if a bromine atom is substituted for a 
 hydrogen atom in each CH 3 group, producing trimethylene bromide, 
 BrHjC CH 2 ' CH 2 Br, these bromine atoms can be removed by sodium, 
 whereupon the gas trimethylene * or cyclopropane is formed by nucleal 
 condensation (cf. p. 531). Several polymethylenes or cycloparaffins of this 
 type have been prepared in an analogous manner. Pentamethylene or 
 
 /CH 9 ' CH., 
 cyclopentane, CH 2 \ " J^TT"' * s important as a near relative of 
 
 X L/H 2 OH., 
 
 camphor, while hexamethylene or cyclchexane is transitional between the 
 paraffins and benzene. All these hydrocarbons are isomeric with the 
 olefines, from w r hich they differ in not being attacked by permanganate ; 
 this is presumed to be conclusive that they do not contain double linking, 
 and allies them to the saturated hydrocarbons. 
 
 Tetramethylene has not been prepared, but methyltet-ra methylene is known. 
 Penta- and hexamethylene (naphthene) are found in Caucasian petroleum ; the 
 former boils at 50 C. Ileptametlt ylene boils at 117 C. and is related to the acid 
 found in cork (suberic acid). 
 
 When the iodo-substitution products of these hydrocarbons are treated with 
 potash, the iodine is removed as HI, and a double linking is introduced; for 
 
 f" 1 TT T C* TT C* TT O TT 
 
 instance, CH 2 \ : 2 yields CH\ i 2 , cyclopentene, which may be 
 
 " CH, CH 9 CH 2 'CH 2 
 
 X CH:CH 
 termed a cydo-olejine. By repeating the operation, eyelopentadlene, CH<' i r 
 
 is obtained ; this is a cyclodiolejine found in crude benzene and boils at 41 C. It 
 is easily attacked and yields addition-products, indicative that it contains double 
 linking. If the closed chain contains three double bonds it is called a cyclo- 
 triolejine ; thus benzene is cycloliexatriene. 
 
 There are several methods of producing nucleal condensation, besides that here 
 given, for obtaining polymethylene derivatives ; some of these will receive notice 
 in the proper place. 
 
 Benzene Series of Hydrocarbons. The general formula for this 
 series is C W H 2M _ 6 where n is any whole number not smaller than 6. The 
 series was originally called the aromatic series because the first hydro- 
 carbons discovered were obtained from aromatic balsams and resins. 
 Benzene itself is C G H 6 , and its homologues are formed from it by ex- 
 changing hydrogen for CH 3 ; thus, toluene, C 6 H 5 CH 3 ; xylene C 6 H 4 (CH 3 ) 3 ; 
 &c. Before the structure of these hydrocarbons is considered some of 
 their properties must be described. 
 
 320. Benzene, C 6 H 6 , occurs abundantly in the light oil obtained 
 in the distillation of coal-tar. It is also found in petroleum. From 
 the light oil it is obtained by fractional distillation ; the portion which 
 distils between 79 and 82 C. consists chiefly of benzene, and is purified 
 by cooling it below o C. when the benzene crystallises, while the otl 
 
 * The group CH 2 is termed methylene. 
 
540 REACTIONS OF BENZENE. 
 
 hydrocarbons remain liquid and are removed by pressure. A charac- 
 teristic impurity of commercial benzene is thiophen, C 4 H 4 S (q.v.). 
 
 Benzene is an ethereal liquid, having the odour of coal-gas, of which its 
 vapour is one of the illuminating constituents. Sp. gr. 0.88 ; m.-p. 
 5.5 C. ; b.-p. 80 C. It is very inflammable, and burns with a red smoky 
 flame ; but its vapour, when mixed with air or hydrogen (as in coal-gas), 
 burns with a bright white flame. Benzene is nearly insoluble in water, 
 but dissolves in alcohol and ether. It is chiefly used for conversion 
 into aniline (q.v.), but also for dissolving fats, caoutchouc, &c. If 
 benzene be dropped into the strongest nitric acid, or into a mixture 
 of ordinary concentrated nitric acid with an equal volume of strong 
 sulphuric acid, a violent action occurs, red fumes are evolved, and the 
 liquid becomes red. On pouring it into several times its volume of 
 water, a heavy, oily liquid falls which is nitrobenzene, C 6 H r NO., ; 
 O 6 H 6 + N0 2 -OH = C 6 H 3 NO 2 + HOH. 
 
 The red fumes are the result of a secondary reaction not expressed in 
 the equation. The sulphuric acid is used to combine with the water, 
 since weak nitric acid does not act on benzene. Nitrobenzene has a 
 powerful odour of almonds, and is sold, dissolved in alcohol, as Mirbane 
 essence, for use in confectionery and perfumery. It is, however, a 
 poisonous substance in large doses. It is also largely employed for the 
 preparation of aniline. Nitrobenzene boils at 209 C. ; its sp. gr. at 
 o C. is 1.2 ; m.-p. 3 C. 
 
 If the mixture of nitric arid sulphuric acids be boiled with the ben- 
 zene, the liquid deposits on cooling, a yellowish crystalline solid which 
 is dinitrobenzene, C 6 H 4 (NO,).,, a compound used in some explosives ; 
 
 C 6 H 6 + 2(N0 2 'OH) = C 6 H 4 (N02) 2 + 2HOH 
 
 Strong sulphuric acid also oxidises part of the hydrogen in benzene, 
 when heated with it, leaving in its place the sulphonic group, or sulphonic 
 acid residue, SO./OH, which bears the same relation to sulphuric acid, 
 SO,(OH) 9 , as nitroxyl, NO 9 , bears to nitric acid, NO./OH ; thus, 
 C 6 H 6 + S6,(OH) 2 = HOH + C 6 H 5 -S0 2 -OH (benzene-sulphonic acid}. If 
 fuming sulphuric acid be used, a second atom of hydrogen may be 
 exchanged, forming benzene- disulphonic acid, C 6 H 4 (S0 2 'OH) r 
 
 When chlorine is passed into benzene (containing a little iodine, which 
 assists the reaction), monochlorobenzene, C 6 H 5 C1, is formed ; it is an 
 almond-smelling liquid, which boils at 132 C., is not decomposed by 
 caustic alkalies, and is reconverted into benzene by water and sodium- 
 amalgam (to yield nascent hydrogen). The further action of chlorine 
 on benzene yields 
 
 Dichlorobenzene, C 6 H 4 C1 
 Trichlorobenzene, C 6 H 3 C1 
 
 Tetrachlorobenzene, C 6 H 2 C1 4 
 Pentachlorobenzene, C 6 HC1 5 
 
 Hexachlorobenzene, C 6 C1 6 
 
 These are all crystalline solid bodies. 
 
 Besides these substitution-products, benzene is capable of forming addi- 
 tion-products with chlorine ; benzene dichloride, C 6 H 6 C1 2 ; tetrachloride, 
 C 6 H 6 C1 4 ; hexachloride, C 6 H 6 C1 6 . These are less stable than the substi- 
 tution-products ; thus, the hexachloride, when heated with potash dis- 
 solved in alcohol, yields trichlorobenzene ; 
 
 C 6 H 6 C1 6 + 3KOH = C 6 H 3 C1 3 -f 3 KC1 + 3H 2 0. 
 
CONSTITUTION OF BENZENE. 54 r 
 
 When benzene is treated with hydrogen dioxide, it is slowly converted 
 into hydroxybenzene or phenol ; C 6 H 6 + H 2 2 = C 6 H 5 'OH + H 2 0. 
 
 Benzene was so called because it was first prepared by distillino- 
 benzoic acid with slaked lime (3 parts); C 6 H 5 'CO 9 H + G'a(OH) = 
 C 6 H 6 + CaC0 3 + H 2 0. This method is still adopted" for preparing 
 perfectly pure benzene. 
 
 Benzene is detected by first converting it into nitro-benzene and 
 reducing this to aniline (q.v.), which is recognised by its reaction with 
 bleaching-powder. 
 
 321. Constitution of benzene. A saturated hydrocarbon is one which 
 corresponds with the general formula C M H 2H+2 , so that it is evident 
 that benzene is an unsaturated hydrocarbon. It has been seen that 
 the unsaturated hydrocarbons already considered (ethylene, acetylene, 
 &c.) are so termed because of their capability of uniting directly with 
 chlorine or bromine, and it has been noticed that the molecule of a 
 hydrocarbon will combine with 2, 4, &c., atoms of 01 or Br according to 
 its degree of unsaturation, so that the final product of such combination 
 is always a compound of the general type, C^H^^X^, where X is Cl 
 or Br. This compound is a stable one and does not combine with any 
 more halogen. Moreover, this reaction between the unsaturated 
 hydrocarbon and the halogen is the primary reaction between the two 
 substances. 
 
 The reaction between benzene and a halogen is of a different nature 
 from this. As has been stated above, it is more easy to obtain halogen- 
 substitution-products i.e., those in which halogen is substituted for 
 hydrogen from benzene, than it is to obtain mere addition-products, 
 containing halogen added to the hydrocarbon. This recalls the behaviour 
 of paraffin hydrocarbons. 
 
 It seems, then, that benzene resembles both the saturated and un- 
 saturated hydrocarbons in its behaviour towards halogens. It differs, 
 however, from the former class in that it can form addition-products 
 with the halogens, and from the latter (e.g., its isomeride dipropargyl) 
 in that the most saturated derivative obtainable from it corresponds 
 with the general formula C )t X.' 2n and not with C M X 2w+2 . When ben- 
 zene is heated with excess of hydriodic acid it is converted into the 
 hydrocarbon C 6 H 12 , thus : C 6 H 6 + 6HI = C 6 H 12 + I 6 . This benzene 
 hexahydride (cyclohexane) is isomeric with the olefine hexylene, which, 
 however, might be expected to become hexane, C 6 H 14 , when heated with 
 excess of hydriodic acid. 
 
 These facts with regard to benzene may easily be explained on the 
 hypothesis that the six carbon atoms form a closed chain (p. 538). 
 It will be seen at once that all closed-chain compounds must contain a 
 carbon nucleus which is possessed of two fewer atom-fixing powers than 
 the corresponding carbon nucleus in an open-chain compound has ; for 
 instance, the nucleus C'C'O'O'O'C' has 14 atom-fixing powers, whilst 
 the nucleus 'O'O'C'C'O'O' has only 12 atom-fixing powers. 
 
 The closed-chain formula for benzene must contain three pairs of 
 doubly-linked carbon atoms, if all the affinities of each atom are to be 
 represented as satisfied in the same way as they are represented in open- 
 chain compounds. Since, as will be shown, there is reason to believe 
 that the structure of the benzene molecule in space is symmetrical, it is 
 
542 POSIT10N-ISOMERISM. 
 
 customary to represent these three double bonds symmetrically in the 
 formula, which is therefore written in the form shown in Fig. 258, and 
 known as Kekules benzene ring. 
 
 Some support is lent to this formula by the fact that acetylene polymerises into 
 benzene when it is heated, HC CH + HC CH + HC : CH becoming 
 HC:CH-HC:CH-HC:CH ; and that allylene CH : OCH 3 is polymerised by strong 
 
 H 2 S0 4 to 1:3:5 -trimethylbenzene or mesitylene (^.f.). There are, however, 
 some grave objections to Kekule's formula which will be noticed 
 H in the sequel. 
 
 / ^ 322. Position-isomerism. Isomerides have already 
 
 HC CH been defined as compounds which have the same percent- 
 
 || I age composition and the same molecular weight, but 
 
 HC CH different properties. The isomerism may be due to one 
 
 \ c ^ of three causes, (i) The isoineric compounds may be 
 H composed of different radicles, thus, the compounds 
 
 Fig. 258. C 2 H 5 -(X)-C 2 H 5 and CH 3 'COC 3 H 7 are isomeric ; such 
 isomerides are sometimes termed metamerides. (2) The 
 isomeric compounds may consist of the same radicles, but these may be 
 attached to different carbon atoms ; an example was met with in the 
 case of pentane (p. 533) ; such isomerides may be termed position- 
 isomerides. (3) The isomeric compounds may have the same radicles, 
 attached to the same carbon atoms but differently situated in space 
 with regard to each other; such cases will be met with hereafter 
 (lactic acids) ; these isomerides are termed stereo-isomerides, and in 
 one class of this kind of isomerides the main difference between the 
 members is in their action on polarised light, each existing in two 
 optically active forms namely, one which rotates the plane of polari- 
 sation of light to the right (dextro-rotatory) and another which rotates 
 the plane equally to the left (laevo- rotatory) and in two optically 
 inactive forms. 
 
 An account of the polarisation of light must be sought in a work on Physics. 
 It may be said here that when a ray of light is passed through a certain kind of 
 crystal (a polariser) in a certain direction, it is broken into two rays pursuing 
 different paths. Each of these rays is of such a nature (polarised) that while it 
 will pass through a similar crystal (the analyser) placed with its axis parallel to 
 that of the first, it is extinguished if the second crystal be rotated through an 
 angle of 90. If, while the axes of the crystals are in this relative position, a 
 solution of a dextro-rotatory compound be placed between them, the ray will pass 
 again through the analyser (a result expressed by saying that the plane of polarisa- 
 tion has been rotated) and this must be turned to the right through a certain angle 
 before the light is again extinguished ; the measure of this angle is a measure of 
 the optical activity or rotatory power of the compound dissolved. A laevo-rotatory 
 compound produces the same effect, but in the opposite direction. 
 
 The instrument whereby the rotatory power is ascertained is called the polari- 
 meter, and is shown in Fig. 260. The essential parts of it are the prisms and 
 lenses, the arrangement of which is represented in Fig. 259. The light from the 
 lamp, shown in Fig. 260 (which burns with a non-luminous flame, made luminous 
 by the introduction of a sodium compound, so that it yields light of one colour 
 only), passes first through a plate G cut from a crystal of potassium bichromate to 
 ensure monochromatism, then successively through a lens F to make the beam 
 parallel, the Nicol polarising prism E, a quartz plate D covering one half of the 
 field of vision, the tube 6 7 , with glass ends and containing the solution to be 
 examined, the Nicol prism analyser B, and the opera-glass combination of lenses A 
 focusing on to the plate D. According to the relative angular positions of E and 
 J?, the field viewed through A will be either of uniform shade or will have one-half 
 darker than the other, this effect being due to the quartz plate D. In using the 
 
THE POLARIMETER. 
 
 543 
 
 instrument the tube C is inserted after the analyser has been rotated to produce 
 the uniform shade ; if the solution has rotatory power the field will no longer be of 
 uniform shade, the one half or the other being the darker accordingly as the 
 rotation is dextro- or laevo-. The analyser is then again rotated to produce the 
 uniform tint, and the angle of rotation is read off on the circular scale through one 
 of the eye pieces. 
 
 Fig-. 259. Parts of the polarimeter. 
 B a D 
 
 F G 
 
 Fig\ 260. Polarimeter. 
 
 Position-isomerides which are mono-substitution derivatives* of a 
 hydrocarbon have only been found to exist in those cases where the 
 carbon atoms in the nucleus are not all similarly united to each other. 
 Thus, two monobromethanes, C 2 H 5 Br, have never been prepared, and 
 it is concluded that more than one cannot exist because, since there 
 are only two carbon atoms in the nucleus, these must be similarly 
 united to each other. There can, however, be two monobromopropanes 
 C 3 H 7 Br, because the carbon nucleus contains three carbon atoms, one 
 of which is united with two other carbon atoms and two hydrogen 
 atoms, whilst the other two are, each of them, only united to one other 
 carbon atom and to three hydrogen atoms ; thus, the two compounds 
 H 3 OCH 9 -CH 2 Br (normal pi*opyl bromide) and H 3 OCHBrCH 3 (isopropyl 
 bromide) may be expected to be different from each other, probably 
 because the centre of gravity of the molecule of each is not the same, 
 owing to the difference in the point of attachment of the bromine 
 atom. That these two compounds exist there is no doubt, and that 
 they have the formula? above ascribed to them is rendered highly 
 probable from the methods of their formation, which will be discussed 
 anon. 
 
 * Substitution-derivatives are mono-, di-, tri-, &c., accordingly as the element or radicle is 
 substituted for one, two, three, &c., hydrogen atoms. 
 
544 POSITION-ISOMEEISM. 
 
 From what has been said, it will be understood that the fact that 
 only one mono-substitution product of benzene can be found to exist, no^ 
 matter what the substituting element or radicle be, is strong support in 
 favour of the similarity of linking between all the carbon atoms, and 
 of the symmetrical structure of the molecule. Thus monobromobenzene, 
 C 6 H 5 Br, can be produced in several ways, yet it always has precisely 
 the same properties. 
 
 It can, of course, be objected that it may happen that by the various methods of 
 preparing this compound the same H atom is always exchanged for Br, so that 
 this element is always attached to the same carbon atom, and could it be attached 
 to some other of the six atoms a different monobromobenzene would be produced. 
 The following line of argument, involving reactions which will be understood 
 later, refutes this objection. Monobromobenzene is prepared by the direct action 
 of bromine on benzene, and may have been formed by the substitution of Br for 
 any one of the six H atoms in the benzene ring (Fig. 258). Assume that H (i) has 
 
 been substitued, so that the product may be represented as C 6 BrHHHHH. By 
 treating this with HN0 3 , the compound C 6 H 4 Br(N0 2 ) is produced, and it is reason- 
 able to admit that the second H atom, which has been exchanged for JST0. 2 , is not 
 the same H atom as that previously exchanged for Br. Assume that H (2) has 
 
 been exchanged for N0 2 , then the nitro-compound will be C 6 Br(N0 2 )HHHH. En- 
 treating this with nascent hydrogen (neglecting another reaction) the Br may be 
 removed, and the H whose place it occupied reinstated, so that nitrobenzene of the 
 
 1 3456 
 
 formula C 6 H(N0. 2 )HHHH is produced. By treatment with reducing-agents this 
 
 is converted into an amido-substitution-derivative C 6 H(NH 2 )HHHH. When this 
 is treated, under certain conditions, with nitrous acids it yields the compound 
 
 called diazobenzene, C 6 H(N 2 )HHHH, and by decomposing this with hydrobromic 
 
 acid, monobromobenzene, C 6 HBrHHHH is obtained, and this is found to be 
 identical with the bromobenzene produced directly from bromine and benzene, 
 showing that whether H (i) or H (2) is exchanged for Br, the same substance is 
 produced. 
 
 The cases of position-isomerism among poly-substitution derivatives 
 of hydrocarbons are very numerous. Two dibromo-derivatives of 
 ethane are known to exist, viz. : CH 2 Br-CH,Br and CH 3 'CHBr 2 . It 
 has been found that there &re four dibromopropanes, C 3 H 6 Br 2 , and 
 from the methods of their formation there is reason to believe that 
 they are represented by the formulae, (i) CH 2 Br-CH -CH 9 Br, 
 (2) CH 3 CHBr-CH 2 Br, (3) CH 3 'CH 2 -CHBr,, and (4) CH 3 'CBiyCH 3 . 
 Only two other methods of writing this formula are possible, viz., 
 
 (5) CH 2 Br-CHBr-CH 3 and (6) CHBr 2 'CH 2 -CH 3 ; but in (5) the Br 
 atoms are attached to carbon atoms, which are the same, so far as their 
 linking to other atoms is concerned, as the carbon atoms to which the 
 Br atoms are attached in (2), and there is the same similarity between 
 
 (6) and (3). It is evident that if the number of carbon atoms in the 
 open-chain hydrocarbon-nucleus, or the number of substituting bro- 
 mine atoms, be increased, the number of forms in which the formula 
 can be written so that this is essentially different each time, will be 
 increased. It has been supposed that as many isomerides may exist as 
 there are essential differences in the formulae which can be written 
 for the compound ; whilst many isomerides, thus prophesied, have been 
 prepared, the number remaining to be discovered is so large that some 
 hesitancy may reasonably be shown in accepting the supposition. 
 
ORIENTATION OF BENZENE. 545 
 
 In the case of benzene the poly-substitution-products have been very 
 thoroughly examined. Most of the di-substitution-products are known 
 in three isomeric forms, but no di- substitution-product of 'benzene has been 
 'prepared in more than three isomeric forms. 
 
 Thus, although benzene yields only one mono-substitution-product, 
 it forms three di-substitution-products, in each of which two atoms of 
 hydrogen have been exchanged for radicles or for other elements. 
 
 There are, then, three di-bromobenzenes, all having the formula, 
 C 6 H 4 Br 2 , and therefore strictly isomeric, and yet having different- 
 properties ; so there are three di-nitro-benzenes, C 6 H 4 (NO,) 9 , and three 
 benzene di-sulphonic acids, C 6 H 4 (S0 3 H),, and such compounds form 
 perfectly distinct series, so that if they be distinguished as a, b, and c 
 compounds, a-di-bromobenzene will yield a-di-nitrobenzene, and 
 ct-bunzene-di-sulphonic acid, while b- and c-di-brornobenzenes will also- 
 yield their proper series of derivatives. 
 
 To explain the existence of these three isomeric di substitution- 
 products, it is necessary to assume that different pairs of hydrogen 
 atoms in benzene have different chemical values, and that the properties 
 of the di-substitution-products depend upon the particular pair of 
 hydrogen atoms exchanged. In order to investigate this it became 
 necessary to orient (as it is termed in surveying) the plan of the ben- 
 zene formula, that is, to mark the situation or bearing of its different 
 parts. 
 
 To effect this orientation of the benzene ring, it is neces- 
 
 sary to distinguish the carbon atoms, for which purpose / ^ 
 they are numbered consecutively as on a watch-face 6C c2 
 
 (Fig. 261). 
 
 The pairs of hydrogen atoms occupying places i and 2, 5C Ci5 
 
 2 and 3, 3 and 4, 4 and 5, 5 and 6, 6 and i, bear the same c 
 
 relation to the figure, and are therefore of equal value, * 
 
 so that whichever pair is exchanged for other radicles, Fig-. 261. 
 the same di-substitution-product will be obtained. 
 
 Again, i and 3, 2 and 4, 3 and 5, 4 and 6, 5 and i, 6 and 2, being 
 alternate atoms, bear the same relation to the figure, and their substitu- 
 tion would give rise to the same di-substitution-product. 
 
 But consecutive atoms, such as i and 2, or 2 and 3, have a different 
 relation to the figure from that belonging to alternate atoms, such as 
 i and 3, or 2 and 4, so that the substitution of two consecutive atoms 
 of hydrogen would give one kind of derivative (say the a-substitution- 
 product), and that of two alternate atoms would produce another kind 
 (say the 6-substitution-product). 
 
 Lastly, the pairs i and 4, 2 and 5, 3 and 6, have the t^ame relation 
 to the figure, and, when exchanged for other radicles, would give 
 identical products, but these would be different from the a and b pro- 
 ducts, and may be called the c-substitution-products. 
 
 As the above lists exhaust all the possible pairs of hydrogen atoms, 
 there can be only three di-substitution derivatives of benzene. Instead 
 of using a, 6, and c to distinguish the three isomerides, it is customary 
 to use the prefixes ortho-, meta-, and para-, respectively. When adjacent 
 ^hydrogen atoms in the benzene ring are exchanged for other radicles, 
 tie product is an or^o-compound ; when alternate hydrogen atoms are 
 substituted, the product is a meta-comvound ; when opposite hydrogen 
 
 2 M 
 
546 FORMULAE FOR BENZENE, 
 
 atoms are substituted, the product is a para-compound. This is some- 
 times denoted by figures prefixed to the formula : thus i : 2-dibromo- 
 benzene is ortho-dibromobenzene ; i : 3 is meta- dibromobenzene ; and i : 4 
 is para -dibromobenzene, all having the formula C 6 H 4 Br 2 . 
 
 This fact, that there are only three di-substitution-products of benzene, consti- 
 tutes the main objection to Kekule's formula. It is not in accord with experience 
 obtained from the open-chain compounds, that a substitution-derivative containing 
 the substituent groups attached to carbon atoms doubly linked together, should 
 be identical with one which contains the groups attached to singly-linked carbon 
 atoms : thus i : 2-dinitrobenzene should differ in properties from i : 6-dinitro- 
 benzene, though as a fact these two compounds are identical, and four di-substitution- 
 products are not known. Kekule gets over this objection by supposing that the 
 ring is in constant vibration, the double links and single links changing places 
 every swing. Several other formula? have been proposed, notably the so-called 
 " diagonal formula " of Glaus, the conception underlying which will 
 be appreciated from Fig. 262. 
 
 An argument in support of this formula is the high resistance 
 shown by benzene and some of its substitution-products to direct 
 oxidation (by alkaline permanganate, for example), thus indicating 
 * na * "ethylenic linking " i.e., carbon doubly linked, as in ethylene 
 does not occur. On the other hand many addition products of 
 benzene, in which all the carbon atom-fixing powers are not satisfied 
 Fig. 262. are so easily oxidised that ethylenic linking may be supposed to 
 exist in them. Baeyer believes in the existence of ethylenic linking 
 in some benzene compounds and of central or "para-" Uniting (much as in Fig. 
 262) in others. 
 
 Pending a better knowledge as to the disposition of the fourth atom-linking- 
 power of each carbon atom, the maiority of chemists prefer to represent benzene 
 compounds as derived from a plain hexagon. 
 
 Tri-substitution derivatives of benzene, in which the same radicle 
 is substituted for all three atoms of hydrogen, are found to exist in 
 three isomeric forms ; thus, there are three tribromobenzenes, C 6 H 3 Br 3 , 
 distinguished as adjacent (1:2:3), symmetrical (i 13:5), and asym- 
 metrical (1:2:4). If the substituted radicles are of two different 
 kinds, say chlorine and bromine, six isomerides may be formed, 
 and if three different radicles are introduced, say chlorine, bromine, 
 and NO 2 , ten isomerides are possible. 
 
 Tetra-substitution derivatives of benzene may also be adjacent (i : 2 : 3 : 4), 
 symmetrical (1:2:4:5), and asymmetrical (1:3:4:5). With a 
 single substituted radicle, only these three isomerides are possible, but 
 two radicles may give 20, three radicles may give 16, and four radicles 
 may give 30 tetra-substitution-products. Evidently only one penta- 
 substitution-product is possible with one radicle. 
 
 The experimental investigation of the orientation of a benzene derivative 
 consists in attempting to introduce fresh substituents into the nucleus, 
 or in exchanging some substituent for hydrogen ; how this settles the 
 orientation will be understood from the following : 
 
 By treating a dibromobenzene with bromine it is possible to convert 
 it into tribromobenzenes (though this means of converting a dibromo- 
 into a tribromo-benzene is not the most convenient). It is found that 
 the dibromobenzene which boils at 224 C. yields two tribromobenzenes, 
 whilst that which boils at 219.5 ^. yields three tribromobenzenes, and 
 that which boils at 219 C. and melts at 89 C. (the others melt at about 
 i C.) yields only one tribromobenzene. Now, an inspection of the 
 formulae for the three dibromobenzenes as written on the plane of the 
 paper, will show that the i : 2 -dibromobenzene can only yield two 
 
THE SETTLEMENT OF ORIENTATION. 
 
 547 
 
 tribromobenzenes, viz., 1:2:3 and 1:2:4, since 1:2:5 = 1:2-4 
 and i : 2 : 6 = i : 2 : 3. Again, it will be seen that the i : 3 -dibromo- 
 benzene can yield three tribromobenzenes, viz., i : 2 : 3, i : 3 : 4 and 
 J . : 3 : 5 (i : 3 : 6 = * : 3 : 4), whilst the i : 4-dibromobenzene can only 
 yield one tribromobenzene, viz., i : 2 : 4 (or i : 3 : 4, or i : 4 : 5, or 
 1:4:6, all these being identical with 1:2:4). The diagram will 
 make this more clear : 
 
 Br 
 
 Br 
 
 Br 
 
 yields 
 
 Br 
 
 Br 
 
 yields 
 
 Br 
 
 Br 
 
 Br 
 
 yields 
 
 Br 
 Br 
 
 Br 
 Br 
 
 Bl- 
 
 and 
 
 Br 
 
 /\ 
 
 Br 
 
 Br 
 
 Bi 
 
 Br 
 
 and 
 Br Br \ /' Br 
 
 Br 
 
 Br 
 
 Br 
 
 It is evident that, of the three known dibromobenzenes, that must be 
 the i : 2 -derivative which yields two tribromo-derivatives ; that the i : 3- 
 derivative which yields three tribromo-derivatives ; and that the i : 4- 
 derivative which yields only one tribromo- derivative. 
 
 The orientation of tri-substitution derivatives may be similarly 
 settled by exchanging one of the substituents for hydrogen, and thus 
 obtaining one or more di-derivatives. If the derivative be the 1:2:3- 
 derivative it will yield two di-derivatives, viz., i : 2 and i : 3 ; if it be 
 the 1:3: 5 -derivative it can only yield one di-derivative. 
 
 The orientation of certain derivatives, which may be called standard derivatives, 
 having been settled by investigations involving the principle stated above, the 
 -orientation of any new compound may be settled by converting it into one of 
 these. Chief among these standards are the bromo-derivatives and the carboxylic 
 acids (phthalic acid, &c.). Thus, the orientation of a newly discovered nitro- 
 derivative could be settled by submitting it to a treatment (such as that indi- 
 cated on p. 544) which would exchange the N0 2 groups for Br atoms ; a study of 
 the properties of the bromo-derivative thus produced would decide its orientation 
 and therefore that of the original nitro-derivative. 
 
 It is to be noticed that a polyvalent element can never be substituted for several 
 hydrogen atoms in the benzene-nucleus ; thus, C 6 H 4 is not known. 
 
 The desire to prophesy what compound will be produced when a benzene deri- 
 vative is treated with a substituting agent, has led to the formulation of several rules. 
 Thus, it has been laid down that, when in a compound C 6 H 5 X, X is N0 2 ,-S0 2 OI 
 or -COOH, any new radicle entering into C 6 H 5 X will take up the meta-posit 
 to X. If X be any other group, the newly entering substituent will generally 
 produce the para-derivative, but accompanied by a little of the ortho- and some- 
 times of the meta-derivative. 
 
 If X be an element or radicle which forms a compound HX, capable of c 
 oxidation to HOX, the newly entering substituent will take the meta-position ; 
 
ALKYL BENZENES. 
 
 if, on the other hand, it be not so capable of oxidation, the newly entering sub- 
 stituent will take up the ortho- and para-positions (Crum Brown and Gibson). Thus, 
 the introduction of a substituent into C 6 H 5 C1 will give ortho- and para-derivatives 
 because HC1 is incapable of direct oxidation to HOC1, whilst its introduction into 
 C 6 H 5 *COOH will give a meta-derivative because HCOOH is capable of direct 
 oxidation to HOCOOH. 
 
 323. Homologues of Benzene. These are derivatives of benzene 
 containing alkyl radicles in place of hydrogen, such substituting radicles 
 being termed side-chains. Methylbenzene (toluene), C 6 H 5 'CH 3 , dimethyl- 
 benzenes (xylenes), C 6 H 4 (CH 3 ) 2 , trimethylbenzenes, C 6 H 3 (CH 3 ) 3 (see Fig. 
 263), and tetramethylbenzenes, C 6 H 2 (CH 3 ) 4 , occur in coal-tar; numerous 
 others, such as ethylbenzene, C 6 H 5 'CH 2 'CH 3 , methylethylbenzene, 
 C 6 H 4 (CH 3 )(CH 2 -CH 3 ), &c., have been prepared synthetically. 
 
 CCH, 
 
 Methylbeazene i : 2-Dimethylbenzene i : 3 : 5-Triinethylben- 
 
 or toluene. or orthoxylene. zene or mesitylene. 
 
 Fig. 263. 
 
 The residues of the benzene hybrocarbons, or aromatic radicles, are 
 named similarly to the alkyl radicles; thus, corresponding with methyl,, 
 ethyl, and propyl, there are phenyl, G^^methylphenyl or to/?//,*C 6 H 4 'CH 3 , 
 dimethylphenyl or xylyl, C 6 H 3 (CH 3 ) 2 . 
 
 Isomerism among these alkylbenzenes is similar to that among other 
 substituted benzenes, except that there may be cases of isomerism in 
 the side-chains. Thus there is only one methylbenzene and one ethyl- 
 benzene, but there are two propylbenzenes, one containing the normal 
 propyl group, the other the iso-group (p. 567). These have the empirical 
 formula C 9 H 12 , which also belongs to trimethylbenzene, of which there 
 are three isomerides, as of other tri-substitution derivatives, and to 
 methylethylbenzene, a di-substitution-product also existing in three- 
 forms. 
 
 Toluene and the xylenes are alone of any great practical importance 
 among these homologues. They are extracted from the coal-tar obtained 
 by the distillation of coal for the manufacture of coal-gas. A large 
 quantity of the tar is distilled in an iron retort, when water passes over,, 
 holding salts of ammonia in solution, and accompanied by a brown, oily, 
 offensive liquid which collects upon the surface of the water. This is 
 the light oil containing the benzene hydrocarbons. To purify it, it is 
 shaken with sulphuric acid, which removes aniline and other basic 
 compounds, and afterwards with caustic soda, to dissolve carbolic acid 
 (phenols). It is then subjected to a process of fractional distillation, 
 similar in principle to the process described at p. 529. 
 
 * Much confusion is caused by modern nomenclature of hydrocarbon radicles. It was- 
 proposed to call radicles, such as tolyl and xylyl, alphyl radicles. Lately, however, this 
 term has been applied to alkyl and substituted alkyl (benzyl) radicles, while tolyl, &c., have 
 been termed arryl radicles, and benzyl, C 6 H 5 - CH 2 , xylylene, C 6 H 4 (CH 2 ) 2 , &c., have been, 
 called alpharryl or aralkyl radicles. 
 
AROMATIC HYDROCARBONS. 
 
 Toluene, C 6 H 5 'CH 3 , is always present in commercial benzene. It was 
 originally distilled from balsam of Tolu,and may be prepared by distilling 
 toluic acid, C 6 H 4 (CH 3 )CO 2 H, with lime. It resembles benzene in odour 
 but it does not solidify even at - 20 C. It boils at no C. and 
 its sp.gr. is 0.871. Benzene may be converted into toluene by nrst 
 obtaining bromobenzene, C 6 H 5 Br, and treating this with methyl iodide 
 and sodium, in the presence of ether, C 6 H.Br + CH 3 I + Na, = 
 C 6 H 5 -CH 3 + NaBr + Nal. Under the action of oxidising-agents, toluene 
 yields benzoic acid. 
 
 Toluene is used chiefly for making aniline dyes, and artificial oil of 
 bitter almonds ; it is also used as a solvent. 
 
 Xylene, C 6 H 4 (CH 3 ) 2 , being a di-substitution-product, exists in three 
 forms ; but besides these there is a fourth hydrocarbon of the formula 
 Qfto namely, ethylbenzene, which, however, is a metameride of xylene. 
 The portion of the light oil which distils at 136-141 contains about 
 70 per cent, of metaxylene (isoxylene), 20 per cent, of paraxylene, and 10 
 per cent, of orthoxylene. The mixture is used as a solvent. 
 
 By shaking the mixture with H 2 S0 4 of 80 per cent, strength, the metaxylene is dis- 
 solved ; by treating the residue with ordinary strong H 2 S0 4 , the orthoxylene is ex- 
 tracted leaving the paraxylene. The action of the H 2 S0 4 is to convert the xylene 
 into a sulphonic acid, C 6 H 3 (CH 3 ) 2 'S0 2 OH, from which the hydrocarbon can be 
 obtained by dilution with water and distillation. Orthoxylene boils at 142 C. ; 
 metaxylene at 139 C. ; &ndpara&ylene&t 138 C. (m. p. 15 C.). By oxidation the 
 methyl groups may be successively converted into COOH groups, yielding toluic acids, 
 C 6 H 4 (CH 3 ) (COOH), and phthalic acids, C 6 H 4 (COOH) 2 , of each of which there 
 are three, yielded respectively by ortho-, rneta-, and paraxylene. Oxidising-agents 
 do not act equally on the three isomerides, however. Chromic acid oxidises 
 orthoxylene completely to C0 2 and H 2 0, but converts para- and metaxalene into 
 para- and metaphthalic acid respectively. Dilute HN0 3 oxidises the ortho- and 
 paraxylene to ortho- and paratoluic acid respectively, while metaxylene is not 
 attacked. 
 
 Metltylene is i : 3 : 5-trimethylbenzene, C 6 H 3 (CH 3 ) 3 , obtained by the action of 
 sulphuric acid on acetone, 3(CH 3 -CO-CH 3 )r=C 6 H 3 (CH 3 ) 3 + 3H 2 0, and by heating 
 allylene with strong H 2 S0 4 , 3CH i C-CH 3 = C 6 H 3 (CH 3 ) 3 ; it boils at 165 C. and is 
 metameric with cumene, or isopropylbenzene, C 6 H 5 'CH(CH 3 ) 2 . Durene is i : 2 : 4 : 5- 
 tetramethylbenzene (in. p. 79 C.) and has an odour of camphor ; it is metameric 
 with cymene or i : ^-methyluopropylbenzene, C 6 H 4 (CH 3 )'CH(CH 3 ). 2 , which is found 
 in oil of cummin and is a product of the dehydration of camphor. 
 
 324. The chief distinction between benzene hydrocarbons and open-chain 
 hydrocarbons resides in the ease with which the former may be con- 
 verted into nitro-substitution-products by the action of strong nitric acid, 
 and into sulphonic acids by the action of strong sulphuric acid. Moreover, 
 the homologues of benzene easily undergo oxidation resulting in the 
 conversion of the side-chains into the group carboxyl, COOH, character- 
 istic of acids. 
 
 General methods for preparing benzene hydrocarbons are : (i) The distillation of 
 the corresponding carboxylic acid with lime, which removes C0 2 from the carboxyl 
 group : C 6 H 4 (CH 3 XCOOH) = C 6 H 5 -CH 3 + C0 2 . (2) The interaction of the bromo- 
 substitution derivative and an alkyl iodide with sodium in ether : C 6 H 5 'Br + C. 2 H 5 *I 
 + Nsuj = C 6 H 6 -C 2 H 5 + Nal + NaBr (Fittig's reaction, cf. the general methods for 
 preparing paraffins, p. 531). (3) The interaction of a benzene hydrocarbon with an 
 alkyl iodide in the presence of ALCL, the precise function of which is not under- 
 stood ; C 6 H 5 -CH 3 + 2 CH 3 C1 = C 6 H 3 (CH 3 ) 3 + 2HC1. (Jf-riedel and ( 'ruff* reaction.) 
 
 325. The above benzene hydrocarbons contain, as side-chains, the residues ot 
 saturated open-chain hydrocarbons. There also exist hydrocarbons containing 
 residues of define and acetylene hydrocarbons. The olejine-benzencs correspond 
 with the general formula C M H 2n _ 10 , and the acetylene-benzenes correspond witt 
 general formula CH 2>1 _ 12 . 
 
550 HYDKOAROMATIC HYDROCARBONS. 
 
 Cinnamene, styrolene, or styrene, C 6 H 5 'CH : CH 2 , is phenyl-ethylene. It is 
 obtained by distilling cinnarnic acid with lime ; CgHg-CH : CH'COOH + Ca(OH). 2 = 
 C 8 H 8 + CaC0 3 + H 2 0. It can also be prepared by distilling balsam of storax, or "by 
 distilling the resin known as dragon's blood with zinc dust. Cinnamene is a 
 fragrant liquid of sp. gr. 0.924, and boiling-point 145 C. It resembles the olefine 
 hydrocarbons in uniting directly with chlorine, bromine, and iodine. When heated 
 in a sealed tube to 200 C., it becomes a transparent solid known as metacinna- 
 mene, or metastyrolene, which is polymeric with cinnamene, into which it is recon- 
 verted by distillation. When heated with hydrochloric acid to 170 C., cinnamene 
 is converted into di-cinnamene, C 16 H 16 . 
 
 Phenylacetylene, C 6 H 5 'C : CH, a liquid boiling at 139 C., yields the explosive 
 silver and copper derivatives characteristic of the true acetylenes (p. 538]. 
 
 Hydroaromatic hydrocarbons. When heated with hydriodic acid the 
 aromatic hydrocarbons are converted into the corresponding hexamethylenes 
 (p. 539) ; thus benzene yields hexamethylene \(liexahijdrobenzene, benzenehexa- 
 
 hydride or naphthene], H 2 C/ CH2 ' CH 2)>CH 2 , while toluene yields methylhexa- 
 MDH 2 CHo 
 
 methylene (Jieaeahydrotoluene or heptanaphthene), H 2 C<^ 2 2 ^>CH'CH 3 . These 
 
 
 
 are colourless liquids, boiling at 81 C. and 103 C. respectively, and occur in 
 Caucasian petroleum. 
 When monobromohexahydrobenzene is heated with quinolene it undergoes nucleal 
 
 condensation, yielding tetrahydi-o'bemene (cylcohexene), H 2 C<^ 2 T /CH, and 
 
 MJJHjj'CH^f 
 
 when the dibromo-derivative of this is similarl)' treated, dihydrobenzene (cyclohexa- 
 
 / CTT'CTT \ 
 diene), HC^ 2 ^:CH, is obtained. The relation of these two compounds to 
 
 benzene (cycloJiexatriene) is apparent, and it will be seen that, if the formula? 
 are correct, cases of isomerism among the substitution derivatives should exceed 
 those found among the corresponding benzene derivatives. For in both cases 
 the character of the derivative may be expected to be influenced by the position 
 of the double bond or bonds relatively to the substituent or substituents. 
 
 Thus H 2 C<^ CH2 ' C [ V-Br should differ from H 2 C/ CH2 ' CH ' 2 ^CHBr, and 
 MJH 2 CHjj/ ^ CH : CH' 
 
 H C/CH-CH 2 \CBr from H C/ CH 2' CH V<Br. Many such isomerides are known, 
 M3H'CBr^ \CH : CBr/ 
 
 and. the nomenclature used to distinguish them consists in numbering the C atoms. 
 as in benzene (No. I being always one to which a substituent is attached), and insert- 
 ing the symbol A before the number of that C atom which is doubly linked to the one 
 following it ; thus the above bromo-derivatives are A i-bromocyclohexene, 
 A 5-bromocyclohexene, A 4, 6-orthodibromocyclohexene, and A i, 5-orthodibromo 
 cyclohexene, respectively. 
 
 326. Hydrocarbons containing more than one benzene- 
 nucleus. These hydrocarbons can be classified into several groups : (i) 
 Those which contain benzene-nuclei directly united, such as dipkenyl t 
 C 6 H 5 'C 6 H 5 . (2) Those in which two or three nuclei are united by one 
 carbon atom, as in diphenyl-methane, C 6 H 5 'CH 2 'C 6 H., and triphenyl- 
 methane, CH(C 6 H 5 ) 3 . (3) Those which contain two benzene-nuclei 
 united by two carbon atoms, like dibenzyl, C 6 H 5 -CH./CH/C 6 H 5 . 
 (4) Those which contain condensed nuclei, as explained under naphtha- 
 lene and anthracene. 
 
 Many of the derivatives of these hydrocarbons are of importance in 
 the arts, but, with the exception of those from naphthalene and an- 
 thracene, the hydrocarbons do not form the raw materials for making 
 them. 
 
 Diphenyl or plienyl-phenyl, C 6 H 5 *C 6 H 5 , is prepared by the action of sodium on 
 bromobenzene dissolved in ether; 2C 6 H 5 Br + 2Na 2 =:(C 6 Hg) 2 -i-2XaBr, a mode of 
 
DIPHENYL. 
 
 551 
 
 formation which settles its constitution. It may also he obtained by passing 
 benzene vapour over red-hot pumice-stone ; 2C 6 H 5 H = (C 6 H 5 ) 2 + H 2 ; or by distillin^ 
 potassium phenol with potassium benzoate, C 6 H 5 'OK + C 6 H 5 'CO.,K = (C 6 H,) 2 + K 2 CO, 
 potassium oxalate may be substituted for benzoate, 2C 6 H 5 OK + (COOK) 2 = 
 ( C 6 H 5)2 + 2CO(OK) 2 . It is also found among the last products of the distillation 
 of coal-tar (at about 260 C.) Diphenyl crystallises from alcohol or ether in 
 leafy crystals which have a pleasant odour and are insoluble in water. It fuses 
 at 71 C., and boils at 254 C. When it is dissolved in glacial acetic acid, and 
 treated with chromic acid, one of the C 6 H, groups is destroyed, while the other 
 forms benzoic acid, C 6 H 5 -C0 2 H. It forms numerous substitution derivatives, like 
 benzene ; since it may be regarded as already being a mono-substituted benzene, 
 containing phenyl in the place of H, its mono-substitution derivatives will be 
 di-substituted benzenes and occur in three isomeric modifications. Its di-deriva- 
 tives occur in many forms, for substitution may occur in each ring. The orienta- 
 
 3' 2' 2 3 
 
 tion is expressed as follows : 4'^ \4. Phenyl-tolyls, C 6 H 5 'C 6 H 4 -CH 3 , 
 
 5' 6' 65 
 
 and ditolyls, C t5 H 4 (CH 3 )-C 6 H 4 (CH 3 ), are examples of mono- and di-substituted 
 diphenyl ; the 4- and 4 : 4'-derivatives are the most common. By treating a mix- 
 ture of i : 4-C 6 H 4 Br 2 and C 6 H 5 Br with sodium, i : ^-diphenylbenzene. C 6 H 4 (C 6 H 5 ).,, 
 is obtained ; it melts at 205 C. 
 
 DipJienylmethane (benzylbenzene), C 6 H 5 'CH 2 'CgH 5 . It is obvious that toluene may 
 be regarded as phenylmethane, CH 3 (C 6 H 5 ), and just as toluene may be prepared by 
 the interaction of methyl chloride and benzene in presence of A1 2 C1 6 , so diphenyl- 
 methane, CH 2 (C 6 H 5 ) 2 , can be prepared from phenylmethyl chloride, commonly 
 called benzyl chloride (</.v.), C 6 H 5 'CH 2 C1, and benzene in presence of A1 2 C1 6 ; 
 C 6 H 5 H + C 6 H 5 -CH a Cl = C 6 H 5 -CH 2 -C ? H 5 + HCl. It crystallises in needles which 
 smell like the orange and dissolve in alcohol and ether ; it melts at 26 C. and boils 
 at 261 C. Chromic acid oxidises it to diphenyl-ketone (q.r.). When passed 
 through a red-hot tube it undergoes the same kind of condensation as benzene does 
 when it yields diphenyl (p. 550) under the same conditions ; the product, dipheny- 
 
 r* FT 
 
 lene-methane* QY Ji-uorene, ' 6 4 )>CH 2 , is found in the last runnings (300- 305 C.) 
 
 C 6 H 4 
 
 from coal-tar and crystallises from alcohol with a blue fluorescence. Oxidation 
 converts it into diphenylene ketone. It melts at 113 C. and boils at 295 C. 
 Triphenylmethane, CH(C 6 H 5 ) 3 , is obtained by the interaction of chloroform and 
 benzene in presence of A1 2 C1 6 ; 3C 6 H 5 H -H CHC1 3 = CH(C 6 H 5 ) 3 + 3HC1. It crystallises 
 in colourless prisms, which when formed from a benzene solution contain ^one 
 molecule of benzene of crystallisation. It dissolves in hot alcohol, melts at 93 C., 
 and boils at 359 C. The aniline dyes are derivatives of this hydrocarbon. 
 
 Dibenzyl, C 6 H~-CH 2 -CHvC 6 H 5 . Toluene can give rise to two hydrocarbon residues 
 or radicles, viz.,'tolyl, C 6 H 4 'CH 3 . and benzyl, C^-CH^ When the chloride of the 
 latter radicle is treated with sodium, dibenzyl is produced, 2(C 6 H 5 -CH 2 Cl) + Na2- 
 C 6 H 5 -CH 2 -CH 2 -C 6 H 5 + 2XaCl. It may also be regarded as dipkenylethaM ; it melts 
 at 52 C. and boils at 284 C. ; when oxidised it yields benzoic acid. Dip/ie/n/l- 
 'tltylene, or xtilbene, or toluylene, C 6 H 5 'CH : CH'C 6 H 5 , is formed by treating 
 benzal chloride (</.r.) with sodium; 2C 6 H 3 -CHCl 2 + Na, 2 = C 6 H 5 -C] [ ' L ^ + . 
 
 2NaCl. Also by partially oxidising toluene or dibenzyl, by passing it over hot 
 PbO. It crystallises in prisms, melts at 125 C., boils at 306 C. and dissolves 
 hot alcohol. It contains true ethylenic linking, for the first action of broi 
 it is the formation of the dibromide C 6 H 5 -C!TBrCHBrC 6 H ? . Vijtiw/lwtyleM or 
 tolane, C 6 H 5 'C : C'C 6 H 5 , is formed by boiling stilbene dibromide with alc< 
 potash. It melts at 60 C., and behaves as an acetylene, save that, not conta.n.n; 
 
 a -C i CH group it yields no metallic derivative. 
 
 which 
 
 C 6 H 5 'C C-C : C-C^isof importance as the hydrocarbon ^f 
 is descended ; it melts at 88 C. 
 
 327. Naphthalene, C 10 H 8 , is a crystalline hydrocarbon with an odoui 
 of coal-gas ? and is occasionally deposited in gas-pipes in cold weather, 
 causing an obstruction. It is a very common product oJ 
 
 * (C 6 H 4 )" is called phenylene, bj analogy with <C 2 H 4 )", ethylcne. 
 
552 NAPHTHALENE. 
 
 high temperature upon substances rich in carbon ; coal and wood yield 
 it on distillation ; marsh-gas, alcohol vapour, and ether vapour, when 
 passed through a red-hot tube, deposit crystals of naphthalene in the 
 cooler part. Burmese petroleum and Rangoon tar contain naphthalene. 
 
 When coal-tar is distilled, the benzene hydrocarbons which distil over 
 in the light-oil, are succeeded, as the temperature rises, by a yellow oil 
 which is heavier than water. This, known as dead-oil, is much more 
 abundant than the light-oil, amounting to about one-fourth of the 
 weight of the tar, and containing those constituents of the tar which 
 have a high specific gravity and boiling-point. When the temperature 
 has risen to about 200 C., the distilled liquid partly solidifies on cooling, 
 from the crystallisation of naphthalene. This portion is pressed to 
 expel the liquid part, washed successively with caustic soda and sulphuric 
 acid, and distilled ; or the washed naphthalene may be sublimed. 
 
 Properties. Transparent crystals, smelling of gas, melting at 80 C., 
 and inflammable, burning with a smoky flame. It sublimes much 
 below its boiling-point (218 C.). Insoluble in water, soluble in alcohol, 
 ether, and benzene. 
 
 In its chemical relations, naphthalene is closely connected with 
 benzene, but it shows a greater disposition to form addition-products 
 with chlorine and bromine, with which it also yields numerous substi- 
 tution-products. Naphthalene absorbs chlorine, forming a yellow liquid, 
 naphthalene dichloride, C 10 H 8 C1 2 , and a crystalline solid, naphthalene 
 tetrachloride, C 10 H 8 C1 4 . The non-existence of C 10 H 8 C1 3 is in accordance 
 with the law of even numbers (p, 523). 
 
 Naphthalene is used for making phthalic acid, into which it is con- 
 verted by oxidation ; for increasing the illuminating value of coal-gas 
 (albo-carbon light) ; and as an insecticide. Many of its derivatives are 
 used for making synthetic dyes. 
 
 Constitution of naphthalene. The similarity of the behaviour of naphthalene 
 with that of benzene indicates an analogous structure for these two compounds, 
 and since when it is oxidised naphthalene yields a benzene dicarboxylic acid, 
 C 6 H 4 (COOH) 2 , it must be assumed to contain a benzene ring. Thus, six of the 
 ten carbon atoms are accounted for ; two of the remaining four must be attached 
 directly to two of the carbon atoms of the benzene ring, otherwise a dicarboxylic 
 acid could not have been obtained by oxidation ; moreover, since the dicarboxylic 
 acid proves to be phthalic acid, which is believed to have the carboxyl groups 
 attached to adjacent carbon atoms of the ring, the two carbon atoms must be 
 attached to the benzene ring in the ortho-position to each other. The two 
 
 remaining carbon atoms are believed to form a 
 closed chain with the two just considered. Post- 
 Pining, for the moment, the evidence for this belief, 
 *^ e f rnm l a to which it gives rise may be regarded 
 as consisting of two benzene rings, so condensed 
 together that they have two carbon atoms in com- 
 mon. Fig. 264 furnishes a representation of the 
 C/3 2 structure of naphthalene (the H atoms, attached 
 one to each numbered C atom, having been omitted) 
 5^ and at the same time indicates the numbering of 
 
 the carbon atoms for purposes of orientation. To 
 Fig-. 264. avoid the representation of ethylenic linking ((/. 
 
 p. 546) many chemists omit the five double bonds 
 in the formula. The Greek letters are sometimes used instead of the numbers. 
 
 That naphthalene consists of two benzene-nuclei condensed as represented by the 
 formula is supported by the following facts : When nitronaphthalene is oxidised 
 nitrophthalic acid, C 6 H 3 (NOo)(COOH) 2 . is produced ; from this reaction it is 
 evident that the nitro-group in nitronaphthalene is in a benzene ring, whether 
 
 i 
 6 C. 
 
 ^^ *k/ ^\ 
 
ANTHRACENE. 
 
 553 
 
 there be a second benzene ring or not, and we may suppose that it occupies the 
 position 8 in the formula (Fig. 264). By reducing the nitronaphthalene it becomes 
 amidonaphthalene, that is, the nitre-group has become an amido-group, and it is 
 reasonable to suppose that the new group occupies the same position as the nitro- 
 grpup did. Now if this amidonaphthalene be oxidised it is not an amidophthalic 
 acid which is obtained, but simply phthalic acid itself ; since an oxidising action 
 cannot substitute H for NH 2 , it must be concluded that it is the ring in which the 
 NH 2 group was situated that has been removed by the oxidation, and yet a benzene 
 ring compound (phthalic acid) has been left, showing that the naphthalene must 
 contain two such rings. 
 
 It is found that two isomerides of every mono-substitution product of naphtha- 
 lene exist ; this is in accord with the formula, for it will be seen that whilst the 
 carbon atoms i, 8, 4 and 5, are similarly situated towards the whole molecule, 
 they are differently situated from 2, 3, 6 and 7, which, however, are similarly 
 .situated towards the molecule. When a substituent takes up any of the first-named 
 positions, it is termed an a-derivative, whilst the other positions yield /3-derivatives. 
 It will be found that 10 di- and 14 tri-derivatives are possible ; all the mono-, di-, 
 .and tri-chloronaphthalenes are known and orientated, so that the orientation of a 
 new derivative may be settled by its conversion into one of these. The I : 8-deriva- 
 tives are sometimes called peri-derivatives. 
 
 The general expression for the naphthalene hydrocarbons would be C M H 2 H- 12 . 
 Examples of members of the homologous series are methyl- naphthalenes, C 10 H 7 'CH3, 
 and ethyl-naphthalenex, C 10 H/C 2 H 5 . These are liquid even at low temperatures, and 
 are constituents of coal-tar. 
 
 OPT 
 
 Ethene-naphthalene, or acemphthene, C 10 H 6 <^- 2 , which is found in small 
 
 quantity in coal-tar is obtained by passing vapour of a -ethyl-naphthalene 
 through a red-hot tube, when hydrogen is separated. It forms colourless prisms 
 (m.-p. 95 C.;b.-p. 277). 
 
 /-ITT 
 
 Acetylene- naphthalene, C 10 H 6 /.. , is obtained as a fusible solid (92 C.) by 
 
 X CH 
 passing vapour of acenaphthene over red-hot lead oxide, which removes H 2 . 
 
 Dinaphthyl, C 10 H 7 'C 10 H 7 , is produced when vapour of naphthalene is passed 
 through a red-hot tube, by the oxidising action of Mn0 2 with H 2 S0 4 on naphtha- 
 lene, and by treating C 10 H 7 Br with Na. It forms scaly crystals, m.-p. 154 C. 
 
 The naphthalenes behave in a rather characteristic way with picric acid. If 
 they be dissolved in hot alcohol and mixed with a hot solution of picric acid in 
 alcohol, stellate tufts of yellow or red needles are deposited on cooling. These 
 consist of a compound of single molecules of the naphthalene and picric acid. 
 
 Hydronaphthalenes. Like the aromatic hydrocarbons, naphthalene readily 
 forms hydrogen addition-products when treated with nascent hydrogen or hydriodic 
 acid. These products range from dihydronaphthalene, C 10 H 10 to dodekahijdro- 
 naphthalene, C 10 H 18 , in which all the double bonds have been converted into single 
 bonds, leaving the molecule capable of attaching 10 atoms of H. When the hydro- 
 genisation is in one ring only which is the case with the di- and the tetra-hydro- 
 naphthalenes most easily obtained the hydrogenised ring has properties resembling 
 those of an open-chain hydrocarbon, so that the molecule is more like a phenyl 
 derivative, having an open side-chain, than a naphthalene. The substitution 
 derivatives of such hydronaphthalenes are therefore distinguished as tinnmitlc (ar-) 
 or alicydic (ac-) accordingly as the substituent is in the phenyl ring or the liy<ln>- 
 genised ring. Thus C 6 H 4 : C 4 H 7 (NH 2 ) is ac-amidotetrahydronaphtlmlrnr. 
 C 6 H 3 (NH 2 ) : C 4 H 8 is ar-amidotetrahydronaphthalene, whilelC 6 H 3 (NH 2 ) : C 4 H 7 (NH,) 
 is an ar-ac-derivative. 
 
 328. Anthracene, C 14 H 10 , is found among the last products of the 
 distillation of coal-tar (especially from Newcastle coal), and may be 
 distinguished from naphthalene by its being almost insoluble in alcohol 
 and fusing only at 213 C. It crystallises in colourless tables having 
 a blue fluorescence, and boils at 351 C. That fraction of the coal-tar 
 distillate which comes over at about 360 C. solidifies on cooling to a 
 mass of crude anthracene. It is freed from liquid hydrocarbons by 
 
554 PHENANTHEENE. 
 
 pressure, washed with light petroleum, and purified by crystallisation 
 from hot benzene, or by sublimation as for naphthalene. Commercial 
 anthracene is employed for the manufacture of alizarin. 
 
 Anthracene is formed when vapour of toluene is passed through a red-hot 
 tube containing pumice-stone to expose a large heated surface ; 2C 7 H 8 = 
 C 14 H 10 + 3H 2 . Lead oxide, by oxidising the H, effects the change at a lower 
 temperature. It absorbs chlorine, forming crystals of anthracene dlchloride, 
 C 14 H 10 C1 2 , and chloranthracene, C 14 H 9 C1. With nitric acid, anthracene behaves in a 
 different way from benzene and naphthalene, showing less disposition to the 
 formation of nitro-compounds. When heated with nitric acid it undergoes- 
 oxidation and is converted into a yellow crystalline body called antliraqu'mone, 
 C 14 H 8 2 or (C 6 H 4 ) 2 (CO) 2 . 
 
 Constitution of anthracene. From the fact that anthracene can be obtained 
 synthetically from benzene and tetrabromethane in the presence of A1 2 C1 6 , it is 
 concluded that this hydrocarbon has a constitution represented by the formula 
 
 C 6 H 4 <^>C 6 H 4 ; thus, C 6 H 6 
 
 CH 
 
 CH CH CH CH CO CH 
 
 Anthracene. Anthraquinone. 
 
 Fi<>. 265. 
 
 The C 6 H 4 groups constitute two benzene rings (Fig. 265). whilst the central carbon 
 atoms may be regarded as the residue of a third ring which has two carbon atoms 
 in common with each of the other rings. By treatment with hydrogenising agents 
 (hydriodic acid, for example) the para-union between the central carbon atoms may 
 
 be opened up and dihydroanthracene or anthracene dlhydrlde. C 6 H 4 <^ 2 Nc (3 H 4 . 
 
 CH 2 
 
 formed. Support is lent to this formula for anthracene by the synthesis of ant lira- 
 quinone (</.t\). 
 
 The orientation of anthracene-substitution-products is expressed similarly to 
 that of naphthalene derivatives. Three mono-substitution-produets are possible 
 viz., the a- and j8-, like the a- and /3-naphthalene derivatives, and the 7- or meso-deri- 
 vatives, containing a substituent in place of the H of one of the middle carbon 
 atoms, which may be numbered 9 and 10. 
 
 Paranthracene (C 14 H 10 ) 2 . crystallises in plates from a cold saturated solution of 
 anthracene in benzene exposed to sunshine. It does not fuse until heated to 
 244 C., when it is converted into anthracene. Bromine and nitric acid attack it 
 with difficulty. 
 
 Phenanthrene, C 14 H 10 , is isomeric with anthracene, which it accompanies in coal- 
 tar. It is more soluble in petroleum spirit and in alcohol than is anthracene ; 
 the former solvent serves to separate it from the bulk of the crude anthracene, 
 the separation being finished by fractional distillation. It is used for making 
 blacks. It melts at 99 C., and boils at 340 C. 
 
 Phenanthrene is formed when stilbene or orthoditolyl is passed through a red- 
 hot tube ; since stilbene is known to contain ethylenic linked carbon (p. 546), 
 and ditolyl to be a diphenyl derivative, it is concluded that phenanthrene has 
 
 C IT - CH 
 
 the constitution . 6 4 ", which is confirmed by the fact that its oxidation 
 C 6 H 4 'CH 
 
 C 6 H 4 -COOH 
 yields aiphenic acid, 
 
 Retene, C 18 H 18 , is a methylisopropytyhenanthrem found in wood-tar. 
 
 ie, y^ 4 ~9 H , and pleenc, 9 loH(5 ~9. H , which contain the naphthylene 
 CH - CH Ci^e - CH 
 
TURPENTINE. 
 
 555 
 
 group C 10 H 6 , are similar to anthracene in properties. The former melts at 250 C. 
 and boils at 448 C. ; it is a final product in coal-tar distillation, and owes its 
 name to its yelloAv colour in the crude state ; when purified it is white with a 
 violet fluorescence. Picene melts at 364 C., a higher melting-point than that of 
 any other hydrocarbon ; it is found in the tar from lignite, and is highly insoluble. 
 Fluomnthrene (idryl~), C 15 H 10 , andpyrene, C 16 H 10 , occur in -'stubb" or "tupp," the 
 unctuous matter Avhich distils during the Avinning of mercury from Idrian ores. 
 
 329. Terpene Hydrocarbons. Oil of turpentine, C, H 16 , is obtained 
 by distilling the viscous exudation procured by cutting into the bark 
 of various species of pine. Several varieties of turpentine are met 
 with in commerce, of which the two best known are the common 
 turpentine which is obtained from the Scotch fir, and Venice turpentine 
 from the larch. These are both solutions of colophony, or common 
 rosin, in oil of turpentine, and, when distilled, yield from 75 to 90 per 
 cent, of rosin, which remains in the still, and from 25 to 10 percent, of 
 the oil, commonly sold as spirits of turpentine. 
 
 The oil of turpentine boils at 158 160 C.,and hasthesp.gr. 0.864. 
 It is very sparingly soluble in water, but dissolves in alcohol and ether. 
 It burns with a smoky luminous flame. Its property of dissolving resins 
 and fats renders it useful in preparing paints and varnishes. It is also 
 a good solvent for caoutchouc. 
 
 Oil of turpentine is the representative of a large class of hydro- 
 carbons called the terpenes, derived like itself from the vegetable king- 
 dom. All the members of this group contain the same proportions of 
 carbon and hydrogen, and the greater number have the same molecular 
 formula as turpentine, C 10 H 16 . The terpenes resemble each other in 
 their liability to suffer conversion into isomerides, in their optical 
 activity (p. 542), in their solidification by absorption of oxygen when 
 exposed to air, in their combination with water to form crystalline 
 hydrates, and, above all, in their tendency to combine with hydrochloric 
 acid to form crystalline compounds. 
 
 The essential oils of bergamotte, birch, chamomile, caraway, hops, juniper, 
 lemons, myrtle, nutmeg, orange, parsley, pepper, savin, thyme, tolu, and 
 valerian are all terpenes (for the most part mixtures of terpenes) of the 
 formula C 10 H 16 , accompanied by its oxygenated derivatives (alcohols, 
 aldehydes, and ketones). 
 
 Essential oil of poplar is a di-terpene, C 20 H 32 . The oils of calamus, 
 cascarilla, cloves, cubebs, patchouli, cedar, and rosewood are sesrjui-terpenes, 
 (J 15 H 2J . 
 
 The essential oils are generally extracted from the flowers, fruit, 
 leaves, or seeds, by distillation with water, the portion of the plant 
 selected being suspended in the still by means of a bag or cage, to 
 prevent it from being scorched by contact with the hot sides of the 
 still, and so contaminating the distillate with empyreumatic matters. 
 The water which distils over always holds a little of the essential oil in 
 solution, and it is in this way that the fragrant distilled waters of the 
 druggist are obtained. When the essential oil is present in large pn 
 portion, it collects as a separate layer on the surface of the water, tror 
 which it is easily decanted. The oil which is dissolved in the water may 
 be separated from it by saturating the liquid with common salt, whe 
 the oil rises to the surface ; or by shaking it with ether, which dis 
 the oil and separates from the water, the ethereal solution floating o 
 the surface, and leaving the oil when the ether is distilled off. 
 
TEEPENES. 
 
 In cases like that of jasmine, where the delicate perfume of the flower 
 would be injured by a high temperature, the flowers are pressed between 
 woollen cloths saturated with oil of poppy-seeds, which thus acquires a 
 powerful odour of the flower. Carbon bisulphide is also sometimes 
 employed as a solvent for extracting the essential oils. 
 
 330. The terpenes are all polymerides of the formula C 5 H 8 . A hydrocarbon 
 having this molecular formula and belonging to the diolefines (p. 537) is called 
 isoprene (b.-p. 37 C.), and appears to have the constitution CH 2 : C(CH 3 )'CH : CH 2 
 (methyldirinyl') ; many terpenes yield isoprene (liemiterpene) Avhen heated, and 
 isoprene polymerises to dipentene. 
 
 A few terpenes of minor importance, except that they are the hydrocarbons 
 corresponding with some valuable essential oils, appear to be open-chain compounds 
 of the olefine, diolefine and triolefine series. Rhodinol, C 10 H 20 O, and geran'ml, 
 C 10 H 18 0, are alcohols belonging to these terpenes, and are constituents of the oils 
 of geranium, roses, and pelargonium ; Unalool, C 10 H ]8 0, is a similar alcohol from the 
 oils of lavender, bergamotte, limes, and marjoram. Citral, C^H^O, is an aldehyde 
 found in lemon oil, lemon-grass oil, and verbena oil. By snaking a mixture of 
 citral and acetone with baryta water and distilling, an oil, pseudo'wnone, C 13 H 20 0, 
 is obtained ; this open-chain ketone is converted by treatment with sulphuric acid 
 into a hydroaromatic ketone of the same molecular formula, iontme, the odour of 
 which resembles that of the oil from the root of the violet. lonone is made in the 
 above manner and sold as "artificial oil of violets." 
 
 The majority of the terpenes, however, appear to be cyclic compounds and fall 
 into two classes accordingly as they absorb two or four atoms of bromine, indicat- 
 ing one or two ethylenic linkings respectively in the molecule. Those which 
 absorb four atoms of bromine comprise limonene, dipentene, sylre^trine^nAtej^ino- 
 lene as chief members. They yield I : 4-benzenedicarboxy'lic acid (terephthalic 
 acid) when oxidised, thus indicating that they contain a benzene nucleus which 
 probably has two alkyl groups in the I : 4-positions. Moreover, when dehydro- 
 genised they yield cymene, which is I : 4-methylisopropylbenzene (p. 549), and 
 contains two H atoms fewer than the terpenes contain. These terpenes appear, 
 therefore, to be isomeric modifications of dihydrocymene, 
 
 The terpenes which absorb only two atoms of bromine, and have therefore only 
 one ethylenic linking, are closely related to camphor (</.r.), the constitution of 
 which has been much discussed ; the chief axe pinene, camphene, and fenc/iene. 
 
 Two terpenes terplnene and phellondrene, do not appear to contain ethylenic 
 linking, as they do not combine with bromine. They combine with N 2 3 . 
 
 The terpenes boil at about the same temperature (155 1 80 C.), so that their 
 separation by fractional distillation is not possible, and fractional crystallisation of 
 some of their compounds is the only available method of purifying them. Most of 
 them combine with NOC1 to form crystalline compounds, C 10 H 16 'NOC1, nitroso- 
 chlorides. 
 
 Limonene exists in two forms : Desctrolimonene (citrene, hesperidene, carvene) 
 occurs in oil of orange-peel and, with pinene, in oil of citron ; it boils at 175 C., 
 and has sp. gr. 0.846. Lcerolimonene has the same properties, except that, as its 
 name implies, it rotates the plane of polarised light in the opposite direction ; it 
 occurs with he vopinene in "oil of fir-wool." Each limonene yields two nitroso- 
 chlorides, which are isomerides, differing only in their physical properties. When 
 equal volumes of the two limonenes are mixed, dipentene (cinene) is produced ; 
 this has no action on polarised light ; it is found with sylvestrene in Kussian and 
 Swedish turpentine, and is a product of 'the destructive distillation of caoutchouc 
 and of the polymerisation of isoprene ; acids convert it into terpinene. 
 
 Sylvestrene (b.-p. 176 C.) is a very stable terpene, known only in a dextro-form ; 
 it is characterised by giving a blue colour with acetic anhydride and strong 
 H 2 S0 4 . 
 
 Terpinolene (b.-p. 183 C.), obtained by heating terpineol (</.''.) with oxalic or 
 formic acid, has not been found in nature. 
 
 Terpinene (b.-p. 180 C.), found in oil of cardamoms, is one of the most stable 
 compounds of this group, and, with phellandrene (b.-p. 170 C.), which occurs in 
 dextro- and Isevo-form, is characterised by its compound with N 2 3 (nitrosite). 
 
INDIA-RUBBER. 
 
 Plwne (terjtene) is the chief constituent of turpentine oil, the d^-tnnn /-/ 
 tewtralene) being characteristic of American and English turpentine and 
 fovopinene (tereberthew) of French turpentine ; an inactive pinene. has also been 
 obtained. All three forms boil at 155 C. When HC1 is passed into oil' of tur 
 pentine, well-cooled, demtrafinene hydrochloride, C 10 H 17 C1, is obtained. This is 
 called artificial camphor, since it resembles the natural product in its crystals and 
 its odour ; it melts at 125 C. and boils at 208 C., and is optically inactive, though 
 the hydrochloritle from Irevopinene is laevo-rotatory. 
 
 ('amphene is solid, melting at 48 C. and boiling at 160 C. It occurs in three 
 optical modifications, and is prepared by heating pinene hydrochloride with a 
 feeble alkali (aniline) ; it has been detected in oil of ginger and citronella oil 
 On oxidation it yields camphor. 
 
 Fenchem, from oil of fennel, exists in the usual three optical modifications which 
 boil at about 150 C. 
 
 Hydroterpenes are also known. Chief among them is menthene, C ]0 H 18 , obtained 
 from oil of peppermint. B.-p. 169 C. 
 
 331. Caoutchouc, or india-rubber, may be classed among the terpene 
 hydrocarbons, its chief constituent (a so-called polyprene) having the 
 empirical formula C 5 H S , but a molecular formula (C 5 H 8 ) B . It is 
 procured from a milky exudation furnished by several tropical plants, 
 particularly by the Hcevcea guianensis and Jatropha or Siphonia elastica. 
 Incisions are made in these trees, and the milky liquid thus obtained 
 is spread upon a clay bottle-shaped mould, which is then suspended 
 over a fire ; a layer of caoutchouc is thus deposited, and its thickness 
 is afterwards increased by repeated applications of the milky liquid, 
 the mould being eventually broken out of the caoutchouc bottle thus 
 formed. The dark colour of commercial india-rubber is believed to 
 be due to the smoke from the fire over which it is dried, for pure 
 caoutchouc is white, and may be obtained by dissolving india-rubber 
 in chloroform, and precipitating with alcohol ; the precipitate forms 
 a gummy mass when dried. Commercial india-rubber contains a small 
 quantity of albumin, derived from the original milky liquid, this 
 being really a solution of albumin holding in suspension about 30 per 
 cent, of caoutchouc, which rises to the surface like cream when the 
 juice is mixed with water and allowed to stand, becoming coherent and 
 elastic when exposed to air. It will be remembered that many of the 
 chief uses of caoutchouc depend upon its physical rather than upon its 
 chemical properties, its lightness (sp. gr. 0.93) and impermeability to 
 water adapting it for waterproof clothing, life-buoys, <fec., while its re- 
 markable elasticity gives rise to a still greater variety of applications. 
 
 For the manufacture of waterproof cloth caoutchouc is dissolved in rectified 
 turpentine, and the solution is spread, in a viscid state, over the surfaces of two 
 pieces of cloth of the same size, which are then laid face to face and passed 
 between rollers, the pressure of which causes perfect adhesion between the sur- 
 faces. Waterproof felt is made by matting together fibres of cotton impregnated 
 with a solution of caoutchouc in naphtha, and passing the felt between rollers. 
 When kept for a long time, its strength and waterproof qualities are deteriorated, 
 in consequence of the oxidation of the caoutchouc, which is thus converted into a 
 resinous substance resembling shell-lac and easily dissolved by alcohol. 
 
 Caoutchouc is slowly dissolved by carbon disulphide, benzene, chloroform, coal- 
 naphtha, petroleum, turpentine, and the fixed oils. 
 
 Marine glue is a solution of caoutchouc with a little shell-lac in coal-naphtha. 
 
 The alkalies and diluted acids are without action on caoutchouc. When gently 
 warmed, it becomes far more soft, pliable, and extensible; it fuses at about 
 250 F. (121 C.) to an oily liquid, which becomes viscid on cooling, but will not 
 solidify, and is useful for lubricating stop-cocks. When further heated m air, it 
 burns with a bright smoky flame. Heated in a retort, caoutchouc is decomposed 
 
GUTTA-PERCHA. 
 
 into several hydrocarbons, among which are isoprene, dipentene (caoutchene), and 
 heveene, a sesquiterpene, C 15 H 24 (b.-p. 260 C.). 
 
 Vulcanised rubber, the chemical constitution of which is not understood, is pro- 
 duced by incorporating india-rubber with 2 or 3 per cent, of sulphur, which not 
 only greatly increases its elasticity, but prevents it from cohering under pressure, 
 and from adhering to other surfaces unless strongly heated. It also becomes in- 
 soluble in turpentine and naphtha. Ordinary vulcanised rubber generally contains 
 more sulphur than is stated above, which causes it to become brittle after a time ; 
 for some purposes, such as the manufacture of overshoes, other substances are 
 added besides sulphur, such as lead carbonate and zinc oxide. 
 
 When a sheet of caoutchouc is allowed to remain for some time in fused sulphur 
 at 120 C., it absorbs 12 or 15 per cent, without any material alteration, but if it 
 be heated for a short time to 150 C. it becomes vulcanised ; and when still further 
 heated, is converted into the black horny substance called vulcanite or ebonite, and 
 used for the manufacture of combs, &c., and as an electrical insulator. 
 
 Vulcanised caoutchouc is sometimes made by mechanically incorporating the 
 sulphur with india-rubber softened by heat ; or by immersing the rubber in a 
 mixture of sulphur with chloride of lime, or in carbon disulphide mixed with 
 2.5 per cent, of S 2 C1 2 . It can also be made by dissolving the sulphur in turpen- 
 tine, which is afterwards used to dissolve the caoutchouc ; when the turpentine 
 has evaporated, a mixture of caoutchouc and sulphur is left, which may be easily 
 moulded into any required shape, and afterwards vulcanised by exposure to high r 
 pressure steam having a temperature of about 140 C. 
 
 By treating vulcanised caoutchouc with sodium sulphite, the excess of sulphur 
 above 2 or 3 per cent, may be dissolved out. The whole of the sulphur may be 
 removed, and the caoutchouc devulcanised, by boiling with a 10 per cent, solution 
 of caustic soda. 
 
 Caoutchouc is by no means rare in the vegetable world, being found in the 
 milky juices of the poppy (and thence in the opium), of the lettuce, and of the 
 eupJwrbium and asclepia families. 
 
 Gutta-percha (empirical formula C 5 H 8 ), like caoutchouc, is originally 
 a milky exudation from incisions made into the wood of the Isonandra 
 ptrcha, a native of the Eastern Archipelago. This juice soon solidifies, 
 when exposed to air, to a brown mass heavier than caoutchouc (sp. gr. 
 0.98) and differing widely from it by being tough and inelastic when 
 cold, and becoming quite soft and plastic when heated nearly to the 
 boiling-point of water. Being impervious to water, it is used as a 
 waterproof material and for water-pipes, and its want of conducting 
 power for electricity is turned to account for insulating telegraph 
 cables. 
 
 Gutta-percha is dissolved by those substances which dissolve caout- 
 chouc. It is not affected by diluted acids and alkalies, and is used for 
 keeping hydrofluoric acid. It melts easily, and is afterwards decom- 
 posed, yielding products similar to those from caoutchouc. 
 
 Commercial gutta-percha contains only about 80 per cent, of the hydrocarbon, 
 which may be dissolved out by boiling with ether ; the solution, when evaporated, 
 leaves the hydrocarbon as a white powder fusing at 100 C. The portion insoluble 
 in ether contains two resinous bodies soluble in boiling alcohol, which deposits, 
 on cooling, a white crystalline resin, of the empirical formula C 10 H 16 0, and retains 
 in solution an amorphous resin, C 20 H 32 O. The existence of these bodies renders 
 it probable that gutta-percha is C 20 H 32 , the crystalline resin being C 20 H >S o0 2 . Ex- 
 posure to air and light gradually converts pure gutta-percha into these resinous 
 bodies. 
 
 332. Camphors. Closely allied to the essential oils are the different 
 varieties of camphors, which are formed by oxidation of the hydrocarbons 
 contained in the essential oils. Recently they have been shown to be 
 alcohols or ketones, and in a strict classification should receive notice 
 
CAMPHOR. 
 
 under these headings. Their natural connection with the parent hydro 
 carbons, however, warrants their consideration here. 
 
 Menthol or mentkocamphor C 10 H 20 0, is a secondary alcohol, forming the chief 
 constituent of oil ot peppermint ; its relationship to cymene (p. 549), f s indicated 
 
 by the formula, CH 3'CH<^^^ H >CH-CH(CH 3 ) 2 . It melts at 42 C. and boils 
 
 at 212 C. ; it is used for external application as an anti-neuralgic. Heated with 
 dilute H 2 S0 4 it yields menthene, and by oxidation it becomes menthone a keton^ 
 differing from menthol in that CO is substituted for CHOH in the above formi 
 and also occurring in oil of peppermint. It boils at 206 C. and occurs in dextro' 
 and laevo-form. 
 
 Terpin, C 10 H 18 (OH). 2 , is a dihydric alcohol existing in a cis- and trans-form (see 
 fumarlc acid) : the former melts at 104 C., boils at 258 C., and combines readily with 
 one mol.H 2 to form terpin hydrate (m.-p. 117 C.), which is a product of the action 
 of dilute acids on turpentine, limonene, and dipentene. Trans-terpin melts at 157 C 
 boils at 264 C., and forms no hydrate. When terpin hydrate is heated with dilute 
 acid it yields, besides cineol, C 10 H 18 O (the chief constituent of eucalyptus oil) 
 dipentene, &c., terpineol, a monohydric alcohol melting at 35 C. and probably 
 
 PTT . pTT 
 
 An isomeric ter Pineol melts at 69 C. 
 
 Can-one or carvoL C 10 H 14 0, boils at 225 C., and occurs in dextro-. hevo-, and 
 inactive form, like limonene, to which it is closely related. It is probably a ketone 
 
 CH'CH PIT 
 
 of the form CH 3 C '^. 2 > CH ' C ^ 3 , differing from limonene by having 
 
 in place of H 2 . d-Carvone occurs in liunnnel oil and oil of dill, and when heated 
 with KOH, becomes 1:4: 2-inethylisopropylphenol, or carvacrol (q.i\). 
 
 Japan or common camphor (C 10 H 16 0) is found deposited in minute 
 crystals in the wood of the Laurus camphora, or camphor laurel, from 
 which it is obtained by chopping up the branches and distilling them 
 with water in a still, the head of which is filled with straw, whereon 
 the camphor condenses. It is purified by subliming it in large glass 
 vessels containing a little lime. 
 
 Camphor passes into vapour easily at the ordinary temperature of 
 the air, and is deposited in brilliant octahedral crystals upon the sides 
 of the bottles in which it is preserved. It fuses at 347 F. (175 C.), 
 and boils at 399 F. (204 C.), and is very inflammable, burning with a 
 bright smoky flame. It is sometimes dissolved in the oil used for the 
 lamps of magic-lanterns, to increase its illuminating power. Camphor 
 is lighter than water (sp. gr. 0.985), and whirls about upon its surface 
 in a remarkable way, dissolving meanwhile very sparingly (i part in 
 1000), alcohol and ether being its appropriate solvents. 
 
 An alcoholic solution of ordinary camphor is dextro-rotatory, but the camphor 
 from some species of Matrwaria is leevo-rotatory. When the two are mixed an 
 inactive camphor is produced. 
 
 When distilled with P 2 5 ordinary camphor yields cymene. C 10 H 14 , and when 
 heated with iodine it yields carvacrol, C 10 H 14 0. The former is I : 4-methyliso-pro- 
 pylbenzene of which carvacrol is the hydroxy-derivative, the OH group being in the 
 2-position. It would seem from this that camphor must be derived from a benzene 
 ring having a methyl, an isopropyl, and an oxygen atom in the 1:4: 2-positions 
 respectively. The oxygen does not appear to be present as an OH group, but rather 
 as a ketonic group (CO), and ethylenic linking seems to be absent in the molecule 
 as addition-products are not easily formed. These facts led to the formula 
 
 CH 'CO 
 
 (CH 3 ) 2 CH-C^~ -^C-CH 3 as the most probable representation of camphor. 
 
 ' 
 
560 RESIN. 
 
 The oxidation of camphor with nitric acid, however, produces successively cam- 
 phoric acid, C 10 H 16 4 , campJianic acid, C 10 H 16 5 , and camplim-onic acid, C 9 H 14 (i . 
 Xow the last of these is an open-chain compound trimethyltricarballylic acid,. 
 COOH-C(CH 3 ) 2 -C(CH 3 )(COOH)-CH 2 -COOH. There is no isopropyl group in this 
 compound, but, instead, two CH 3 groups attached to a C atom itself attached to- 
 two other C atoms. It is therefore probable that camphor is more correctly 
 
 CH 2 -CO 
 
 expressed by the formula CH^-C(CH 3 ) 9 ^C-CH 3 than by that given above. 
 X CH 2 -CH/ 
 
 As stated on p. 557 camphene, which contains an ethylenic linking, is readily 
 
 CH : CH 
 oxidised to camphor, indicating, the formula CH/ C(CHL) 2 >C'CHo for camphene. 
 
 \CHaCHa / 
 Pinene and fenchene have similar constitutions. 
 
 The reactions of camphor generally produce either benzene derivatives (e.t/. 
 cymene) or compounds which may be regarded as derivatives of the pentamethylene 
 ring (p. 539). Camphoric acid (v.s.) is of the latter type, being a dibasic acid. 
 COOH COOH 
 
 probably of the form CH C(CH 3 ) 2 -^ C'CHo, the lower part of which con- 
 
 x CH 2 -CH 2 / 
 
 stitutes the 5-carbon ring, there being no bond between the COOH groups. It 
 occurs in six isomeric forms, two dextro-rotatory, two laevo-rotatory, and two- 
 inactive ; the common dextro-form melts at 187 C. 
 
 Borneo camphor, C ]0 H 18 O, is obtained from the exudation of the Dryobalan-ops 
 cam-pit ora. It is neither so fusible nor so volatile as common camphor (m.-p. 203 C. ; 
 b. -p. 212 C.) and has a different odour ; it also crystallises in prisms instead of 
 octahedra. When camphor is reduced in alcoholic solution by sodium it yields 
 Borneo camphor, and, conversely, when this is oxidised with HX0 3 it yields 
 common camphor. Hence Borneo camphor is believed to be an alcohol, borneol. of 
 similar formula to that of camphor save that CH(OH) takes the place of CO. 
 Borneol occurs in dextro-form (borneo camphor), laevo-form, and inactive form, the- 
 two latter occurring in baldrian oil (baldrian camp/tor'). 
 
 Fenchone, C 10 H 16 (m.-p. 5 C. ; b.-p. I93C.) is a ketonic camphor, distinguished 
 from Japan camphor by the fact that it yields meta-cymene instead of para-cymene- 
 when dehydrated. By reduction it yields fenchyl alcohol. 
 
 333. Resins and Balsams. Resins are probably oxidation-products 
 of essential oils, and the natural products occur dissolved in the oils as 
 they exude from the tree, the mixture being known as an oleoresin. 
 The balsams are oleoresiris characterised by the presence of considerable 
 proportions of aromatic acids. 
 
 Colophony or common rosin is best known among the resins, which 
 are generally distinguished by their resinous appearance, fusibility, in- 
 flammability, burning with a smoky flame, insolubility in water, and 
 solubility in alcohol. They are all rich in carbon and hydrogen, and 
 contain a small proportion of oxygen ; they generally have an acid 
 character (resin acid), being soluble in alkalies. 
 
 Kosin melts between 100 C. and 135 C. and consists largely of aUetic ac'xl.. 
 C 19 H280 2 ; it is' used in making varnishes and soaps, and is destructively distilled 
 to procure rosin spirit and rosin oil. Other resins used for varnish-making are 
 copal, sandarach, shellac, animi, and elemi. To make a spirit varnish the resin 
 is dissolved in alcohol or wood spirit (acetone), but the commoner varnish is an 
 oil varnish made by dissolving the resin in a drying oil, like linseed oil and 
 turpentine. 
 
 Guaicum resin is distinguished by its tendency to become blue under the 
 influence of the more refrangible and chemically active (violet rays) of the 
 solar spectrum, as well as under that of certain oxidising-agents, like chlorine 
 and ozone. 
 
 Amber, a fossil resinous substance, more nearly resembles this class of bodies 
 than any other, and contains several resinous bodies. It is distinguished by its 
 insolubility, for alcohol dissolves only about one-eighth and ether about one-tenth, 
 
CLASSIFICATION OF ALCOHOLS. 561 
 
 of it. After fusion, however, it becomes soluble in alcohol, and may be used for 
 varnishes. 
 
 Balsam of Peru, balsam of Tolu, and Storax are characterised by the presence of 
 cinnamic acid, while gum benzoin is the parent substance of benzoic acid. 
 
 DERIVATIVES OF HYDROCARBONS. 
 
 334. As has been already indicated, all carbon compounds may be 
 considered as derivatives of the hydrocarbons, containing one or more 
 elementary atoms or compound radicles in place of hydrogen, and in 
 every compound there is a characteristic hydrocarbon radicle, which is 
 monovalent, divalent, or trivalent accordingly as one, two, or three 
 hydrogen atoms have been removed from a saturated hydrocarbon in 
 order to form it. Typical hydrocarbon radicles are (CH 3 )', (C S H 4 )", and 
 
 I. ALCOHOLS. 
 
 335. These compounds are comparable with the metallic hydroxides, 
 for they contain one or more (OH)' groups, and react with acids forming 
 water and salts containing hydroc-arbon radicles. Thus, the reaction 
 C,H 5 -OH + H 9 S0 4 = C 9 H 5 HSO 4 + HOH is comparable with the reaction 
 XaOH + H 2 SO 4 = NaH SO 4 + HOH. Just as a divalent or a trivalent 
 metal forms a hydroxide containing two or three hydroxyl groups, so a 
 divalent or trivalent radicle forms an alcohol containing two or three 
 such groups, e.g., C 2 H 4 (OH) 2 , C 3 Hs(OH) 3 . Hence alcohols are classified 
 into monohydric, dihydric, trihydric, &c., accordingly as they have one, 
 two, three, &c., OH groups. 
 
 Several general methods for preparing the alcohols exist. Thus they 
 may be formed from the halogen substitution derivatives of the corre- 
 sponding hydrocarbons by treating them with moist silver oxide 
 C.,HJ + AgOH = CJLOH + AgI; from the ethereal salts (q.v.) by 
 saponification CH 3 -COOC 2 H 5 (ethyl acetate) + HOH = CH 3 COOH + 
 C.,H 3 OH ; from hydrocarbon derivatives containing the NH 2 group by 
 treatment with nitrous acid C 2 H 5 -NH 2 (ethylamine) + NO'OH = 
 C,H,OH + N 2 + HOH. This last reaction is typical of a widely applic- 
 able method for introducing an OH group into a compound, and is 
 strictly comparable with the reaction between ammonia and nitrous 
 acid at ordinary temperature (p. 106). 
 
 Alcohols have a slightly basic tendency. They easily undergo oxida- 
 tion, whereby hydrogen is removed with or without the introduction of 
 an equivalent quantity of oxygen. The products are the aldehydes (or 
 ketones) and acids. 
 
 Monohydric alcohols of the paraffin series These contain OH 
 in place of one H atom in a paraffin hydrocarbon ; consequently there 
 is an homologous series of these alcohols corresponding with the homo- 
 logous series of hydrocarbons, CH 4 yielding CH 3 -OH, C 2 H 6 yielding 
 C,H 5 -OH, C 3 H 8 yielding C 3 H/OH, and so on. Thus, there is a general 
 formula, C H H 2w+1 OH, for this series of alcohols. The substance origin- 
 ally called alcohol will be considered first. 
 
 Alcohol, C 9 H 5 -OH, is systematically termed ethyl alcohol. It has 
 been already stated that it can be obtained synthetically by combining 
 C and H to form acetylene, C.,H 9 , which may be converted into ethene, 
 
562 FERMENTATION. 
 
 C 3 H 4 , by nascent hydrogen ; ethene can be combined with sulphuric 
 acid to form ethyl hydrogen sulphate, C 2 EL:HS0 4 , from which alcohol 
 may be made by distillation with water. Or C 2 H 4 may be combined 
 with HI to obtain ethyl iodide, C 2 H 5 I, which, when distilled with 
 caustic potash, yields alcohol, C 2 H 5 I -KKOH = C 2 H 5 'OH 4- KI. The fact 
 that ethyl iodide (moniodoethane), CH 8 *CH 9 I, will give alcohol in this 
 reaction justifies the formula CH 3 'CH 2 OH for this compound. 
 
 In nature, alcohol is found in some unripe fruits. It occurs in coal- 
 -tar, in bone-oil, and in the products of distillation of wood. 
 
 . Alcohol is usually made by the fermention of glucose or grape- 
 'sugar brought about by yeast. For a laboratory experiment, two ounces (or 
 60 grammes) of brown sugar may be dissolved in a pint (or 500 c.c.) of water in a 
 flask, and about a table-spoonful of brewers' yeast (or of German yeast rubbed up 
 with water) added ; in a warm room, fermentation soon begins, as indicated by the 
 froth on the surface caused, by bubbles of C0 2 . By closing the flask with a cork 
 furnished with a tube dipping under water, the rate of fermentation may be 
 inferred from the escaping gas. When very little more gas is disengaged (usually 
 after about 24 hours) the flask is fitted with a tube connected with a condenser, and 
 the liquid distilled as long as the distillate smells strongly of alcohol. The distillate 
 is then rectified, or submitted to a second distillation in a smaller flask or retort, 
 when the first portion which distils over will be much richer in alcohol. This is 
 placed in a narrow bottle, and dried potassium carbonate, in powder, is added by 
 degrees, with frequent shaking, as long as the liquid dissolves it. On standing, two 
 layers are formed, the lower containing the potassium carbonate dissolved in water, 
 and the upper containing the alcohol with about 10 per cent, of water. This upper 
 layer is transferred to a small flask or retort, and allowed to remain for some hours 
 in contact with powdered quick-lime to remove the water ; the alcohol is then 
 distilled off in a water-bath. 
 
 The mode of action of the yeast in causing the production of alcohol 
 from sugar is not yet known. Yeast is a vegetable substance (torula 
 or saccharomyces cerevisice) which develops from minute spores or germs 
 carried by the air ; when these come in contact with a liquid containing 
 the nutriment necessary for the yeast plant, 
 they multiply into a number of round or oval 
 cells arranged in branching chains, visible 
 under the microscope (Fig. 266). It is during 
 this growth of the yeast that the conversion 
 of the sugar into alcohol occurs. The pure 
 yeast spores will not produce alcohol from 
 pure sugar, because it does not contain the 
 substances required to nourish the yeast ; but 
 when the spores are introduced into grape- 
 juice, or infusion of malt (wort), which contain 
 the necessary albuminous matters and phos- 
 phates, &c., they grow and cause the forma- 
 Fig . 265, tion of alcohol. The crop of yeast thus raised 
 
 may be used to ferment fresh portions of 
 sugar, and is the more efficacious because, when it is removed from the 
 surface of the liquid in which it has grown, it is accompanied by some 
 of the nutrient materials. When yeast is added to a solution of cane- 
 sugar (C 12 H 22 H ) it causes it to become glucose, by combining with the 
 elements 6f a molecule of water ; C J2 H 22 O n + H 2 = 2C 6 H 12 6 . The bulk 
 of the glucose is then decomposed into alcohol and carbonic acid gas; 
 C 6 H 10 O 6 - 2C 2 H fi O + 2C0 2 . About 95 per cent, of the glucose undergoes 
 this change, and the remainder is converted into other substances, of 
 
PROPERTIES OF ALCOHOL. 563 
 
 which the most important are glycereiie, C 3 H 5 (OH) 3 , (about 3 per cent.), 
 succinic acid, C,H 4 (C0 2 H) 2 (about 0.5 per cent.), and some of the higher- 
 members of the paraffin alcohols (fusel oil), which are always present in 
 fermented alcoholic liquids. The liquid rises in temperature during fer- 
 mentation, on account of the development of heat in the formation of 
 carbon dioxide. The specific gravity of the solution decreases as the 
 fermentation proceeds, because solution of alcohol is lighter than 
 solution of sugar. A solution containing more than one-third of its 
 weight of sugar is not fermented by yeast, and when the alcohol 
 produced in the fermentation amounts to about one-sixth of the weight 
 of the liquid, the growth of the yeast, and therefore the fermentation, 
 is arrested. No fermented liquor, therefore, can contain so much as 
 20 per cent, of alcohol ; port wine, the strongest fermented drink, 
 contains at most 1 7 per cent. The yeast does not grow, and ferment- 
 ation does not occur, at temperatures below o C. (32 F.) or above 
 35 C. (95 F.), 25-30 C. being most favourable. The fermentation is 
 also arrested by strong acids, and by antiseptics such as common salt, 
 kreasote, corrosive sublimate, sulphurous acid, and turpentine. Air 
 is not essential to the fermentation, but favours it, In sweet wort 
 (infusion of malt) the yeast increases to six or eight times its original 
 weight. 
 
 Recently it has been shown that the liquid obtained by triturating yeast with 
 sand and filtering is capable of fermenting sugar. All traces of yeast cells having 
 been removed by the filtration it must be concluded that yeast contains an 
 unorganised alcoholic ferment. 
 
 On the large scale, alcohol is usually made from the starch contained in potatoes, 
 rice, and other grains. The starch, C 6 H 10 5 , is converted either into glucose, 
 by heating it with very diluted sulphuric acid (afterwards neutralised with chalk) 
 when it combines with a molecule of water and becomes glucose, C 6 H 12 6 or 
 into maltose, G 12 S 22 U , by mixing it with infusion of malt ; the glucose, or 
 maltose, is fermented by yeast. The wash, as it is termed, is then distilled, the 
 stills being constructed with much ingenuity, to effect the concentration of the 
 alcohol at the least expense. 
 
 Even woody fibre, paper, linen, &c., which have the same empirical 
 formula as starch, may be converted into glucose by the action of sul- 
 phuric acid, and may thus be made to yield alcohol. New bread, made 
 with yeast, contains about 0.3 per cent, of alcohol, and stale bread about 
 0.12. 
 
 336. Properties of alcohol. Characteristic odour and burn- 
 ing taste; sp. gr. of pure or absolute alcohol 0.794 at 15 C. 
 Freezes at - 112 C. ; boiling-point 78. 3 C. ; takes fire when 
 a flame is brought near its surface, and burns with a pale, 
 smokeless flame. Evaporates easily when exposed to the air, 
 without combining with oxygen. Kept in a badly stoppered 
 bottle, it absorbs water from the air. Alcohol may be mixed 
 with water in all proportions, evolving a little heat, and giving 
 a mixture rather smaller in bulk than the sum of its consti- 
 tuents. This may be shown by filling the vessel (Fig. 267) 
 with water up to the neck joining the two globes, carefully Fiy. 267. 
 filling the upper globe to the brim with (methylated) alcohol, 
 inserting the stopper, and inverting the vessel, when the contraction 
 of the mixture will leave a vacuum in the tube. The greatest contrac- 
 tion occurs when the volumes of alcohol and water are nearly equal 
 (at o C., 53.9 measures of alcohol to 49.8 of water). The attraction 
 
564 PEOOF SPIRIT. 
 
 of alcohol for water affords one reason for its power of preserving 
 animal and vegetable substances from putrefaction by removing the 
 water necessary for that change. 
 
 By oxidation alcohol is converted first into aldehyde, CH 3 'CHO, and 
 then into acetic acid, CH 3 'COOH. 
 
 Next to water, alcohol is the most valuable simple solvent. It is especially useful 
 for dissolving resins and alkaloids which are insoluble in water. Many salts are 
 capable of combining with alcohol, just as they do with water of crystallisation ; 
 examples of such alcoholates, as they are termed, are 
 
 LiC1.4C 2 H 6 ; CaCl 2 .4C 2 H 6 ; MgCl 2 .6C 2 H 6 ; Mg(N0 3 ) 2 .6C 2 H 6 0. 
 
 Ethoxides or ethylates are compounds formed by the exchange of hydrogen in 
 alcohol for metals ; they correspond with the hydroxides, having C 2 H 5 in place 
 of H ; e.g., sodium ethoxide, C 2 H 5 .ONa, aluminium ethoxide, (C 2 H 5 0) 6 A1 2 . Sodium 
 ethoxide is used in surgery as a caustic. Water decomposes the ethoxides, yielding 
 alcohol and hydroxides ; C 2 H 5 ONa + HOH =C 2 H 5 OH + NaOH. 
 
 Barium ethoxide. (C 2 H 5 0) 2 Ba, is obtained by the action of anhydrous baryta on 
 absolute alcohol. A trace of water precipitates barium hydroxide from the solution. 
 On heating the alcoholic solution, the barium ethoxide precipitates, being less 
 soluble in hot alcohol. 
 
 Aluminium, ethoxide, (C 2 H 5 0) 6 A1 2 , is produced by heating aluminium in alcohol 
 with a little iodine or stannic chloride. It melts at 135 C. and distils unchanged at 
 240 C. under 23mm. pressure. 
 
 Thallium ethoxide, C 2 H 5 OT1, is a liquid remarkable for its high specific gravity 
 (3.68) and great refractive and dispersive action upon light. 
 
 The simplest chemical test fur alcohol is to add to the suspected liquid hydro- 
 chloric acid and enough potassium dichromate to colour it orange-yellow, to 
 divide it between two test-tubes for comparison, and to heat one of them till the 
 liquid boils ; if alcohol be present, the liquid will become green, and evolve the 
 peculiar fragrant smell of aldehyde 
 
 2Cr0 3 + 6HC1 + 3C 2 H 6 = Cr 2 Cl 6 (green) + 6H 2 + 3C 2 H 4 0. 
 
 Alcohol may also be recognised by the production of acetic acid when its vapour 
 is mixed with air and exposed to the action of platinum-black, which acts by 
 favouring oxidation ; C 2 H 6 + 2 = C. 2 H 4 2 (acetic acid) + H 2 0. If a small beaker 
 be wetted with alcohol and inverted over a watch-glass containing a few grains 
 of platinum black, the liquid will soon become acid to litmus. 
 
 In contact with air and heated platinum alcohol yields much aldehyde, as well a& 
 ascetic acid (see Lamp without jiame, p. 506). 
 
 337. The usual method of determining the strength of alcohol is to 
 take its specific gravity by measuring a few cubic centimetres of it into 
 a light stoppered bottle, the weight of which has been ascertained. The 
 weight of i c.c. of the alcohol in grammes will be its specific gravity,, 
 very nearly. Rectified spirit has the sp. gr. 0.838, and contains 84 per 
 cent, by weight of alcohol ; proof spirit (spiritus tenuior) has sp. gr. 0.92, 
 and contains only 49 per cent, by weight of alcohol ; this is the weakest 
 spirit which will answer to the old rough proof of firing gunpowder which 
 has been moistened with it and kindled. Any spirit weaker than this 
 leaves the powder too wet to explode, and is said to be below proof, whilst 
 a stronger spirit is termed over proof. 
 
 A spirit of 30 per cent, (or degrees), for example, over proof, is one 
 which requires 100 measures of it to be diluted with water to 130- 
 measures, in order to reduce it to the strength of proof spirit. A spirit 
 of 30 per cent, below proof contains, in every 100 measures, 70 measures 
 of proof spirit. Some confusion occasionally arises, in commerce, from 
 the practice of calling the percentage of proof spirit, in a weak spirit, 
 the percentage of alcohol, which amounts to only about half the per- 
 centage of proof spirit. Ordinary alcoholic liquids must be distilled 
 
MONOHYDRIC ALCOHOLS. 565 
 
 before their alcoholic strength can be ascertained by specific gravity, on 
 account of the presence of sugar, colouring-matter, &c. 
 
 A measured quantity of the liquid is rendered slightly alkaline with sodium 
 carbonate, to retain volatile acids, and distilled in a flask or retort connected with 
 a good condenser, as long as the distillate contains alcohol ; usually one-third of 
 the bulk may be distilled over for wines, and more for spirits. The volume of the 
 distillate is then made equal to that of the liquid before distillation, by adding 
 water, and the specific gravity is determined and compared with a Table of 
 alcoholic strengths, which has been prepared by ascertaining the sp. gr. of alcohol 
 of various strengths. Since the volume of the weak spirit obtained is the same as 
 that of the original liquid, the percentage of alcohol indicated by the Table will be 
 that present in the liquid under examination. 
 
 The weakest fermented alcoholic liquor is porter, which contains about 4 per 
 cent, by weight of alcohol ; the strongest is port, which contains about 17 per cent. 
 Distilled spirits vary greatly in strength, 50 per cent, of alcohol being about the 
 average, though some samples contain 70 per cent. 
 
 Methylated spirit is a mixture of 90 parts by weight of rectified spirit with 
 10 parts of purified wood-spirit added to it by the Excise in order to prevent its use 
 for drinking. It may be distinguished by its odour, and by becoming red-brown 
 with strong sulphuric acid. Since wood spirit has proved an insufficient deterrent, 
 f per cent, by vol. of mineral naphtha (sp. gr. o'8) is now also added ; its presence 
 may be recognised by the spirit becoming turbid when mixed with water. 
 
 When vapour of alcohol is passed through a red-hot tube, it is decomposed into a 
 large number of products, among which are naphthalene, benzene, phenol, aldehyde, 
 acetic acid, acetylene, ethene, marsh gas, carbonic oxide, and hydrogen. A mixture 
 of one molecular weight of alcohol (46) and four molecular weights of water (72) 
 crystallises at -34 C. When a weak spirit is cooled, ice separates until the com- 
 pound C 2 H 6 0.4H 2 is left as the unfrozen liquid, and when the temperature 
 reaches -34 it remains constant till the whole has solidified. 
 
 338. The principal members of the class of monohydric alcohols derived 
 from the hydrocarbons of the paraffin series, at present known, are shown 
 in the following table : 
 
 Monohydric alcohols, C M H. 2rt+ j'OH. 
 
 Chemical Xame. 
 
 Source.* 
 
 Formula. 
 
 Boiling-point.t 
 
 I. Methyl alcohol 
 
 Distillation of wood . -v 
 
 CH 3 'OH 
 
 66 C. 
 
 2. Ethyl , 
 
 Fermentation of sugar 
 
 C 2 H 5 'OH 
 
 78 
 
 3- Propyl 
 
 grapes . 
 
 C 3 H/OH 
 
 97 
 
 4. Butyl , 
 
 beet . 
 
 C 4 H 9 -OH 
 
 117 
 
 5. Amyl , 
 
 potatoes . 
 
 C 5 H n -OH 
 
 137 
 
 6. Caproyl , 
 
 grapes . 
 
 C 6 H 13 -OH 
 
 157 
 
 7. (Enanthyl , 
 
 /Distillation of castor oil\ 
 ( with potash . . / 
 
 C 7 H 15 'OH 
 
 175 
 
 8. Capryl 
 
 Essential oil of hog-weed . 
 
 C 8 H 17 -OH 
 
 191 
 
 9. Nonvl , 
 
 Nonane from petroleum 
 
 C 9 H 19 'OH 
 
 213 
 
 10. Rutyl 
 
 Oil of rue .... 
 
 C 10 H 21 -OH 
 
 
 1 6. Cetyl 
 
 Spermaceti. 
 
 CjgHgg'OH 
 
 
 27. Ceryl , 
 
 Chinese wax 
 
 CasHo-OH 
 
 
 30. Melissyl , 
 
 Bees' -wax .... 
 
 CjoH^OH 
 
 
 The usual gradation in properties attending gradation in composition among the 
 members of homol no-mis srifis. is strikinerlv exemplified in the alcohols. Ine first 
 
 seven members of the series are liquid at the ordinary temperature, 
 peculiar and powerful odours, and may be easily distilled unchanged^ 
 and ethyl alcohols mix in all proportions with water, but the t 
 
 f Of the normal alcohol (p. 567). 
 
 Of the commonest isomeride. 
 
566 WOOD-SPIKIT. 
 
 propyl achohol, though feebly soluble in water, is not so to an unlimited extent, 
 while butyl alcohol is less soluble, and amyl alcohol is very sparingly soluble, in 
 water. Caproyl alcohol, the next member, is insoluble in water, while capryl 
 alcohol is not only insoluble, but possesses an oily character, leaving a greasy stain 
 upon paper. The three last members in the Table are solids of a wax-like character. 
 Those members of the series of alcohols which may be distilled without decom- 
 posing show a nearly regular increase in the boiling-point for each addition of 
 CH 2 in the formula ; it will be seen from the Table that, excluding the difference 
 between methyl and ethyl alcohols, the average difference in boiling-point is 
 19.5 C. for each CH 2 added. 
 
 339. Methyl alcohol, CH 3 'OH, is met with, in a very impure state, 
 as wood-spirit, or pyroxylic spirit, or pyroligneous ether, or wood-naphtha. 
 When wood is distilled, the condensed products separate into two layers, 
 the lower of which is wood-tar, and the upper is a mixture of water 
 with methyl alcohol, pyroligneous or acetic acid, CH 3 'CO 2 H, acetone, 
 CH 3 -COCH 3 , methyl acetate, CH 3 COOCH 3 , &c. On distilling this 
 upper layer, the portion collected below ioo c C. contains these bodies; 
 on adding chalk and re-distilling, the acetic acid is retained in the still 
 as calcium acetate, and the distillate is sold as wood-naphtha. Its yellow 
 colour is probably due to pyroxanthin, and the milkiness produced by 
 adding water is due to certain oily substances which cause its peculiar 
 odour. In order to obtain methyl alcohol, the wood-naphtha is distilled 
 with quick-lime to remove water, and heated with fragments of fused 
 calcium chloride, which dissolves in the methyl alcohol to form a 
 crystalline compound, CaCl 2 (CH 4 0) 4 . This mixture is then poured into 
 a retort placed in a water-bath, and heated to 100 C. as long as acetone 
 and methyl-acetate distil over. An equal weight of water is then added, 
 which decomposes the compound with Ca01 2 , and on continuing the 
 distillation, methyl alcohol passes over accompanied by some water, 
 which may be removed by contact with quick -lirne and distillation. 
 
 Methyl alcohol is more easily obtained pure by boiling the wood- 
 naphtha with anhydrous oxalic acid in a flask with a long condensing- 
 tube, or a reversed condenser, until the methyl alcohol is converted into 
 methyl oxalate, (CO 'OCH^, which separates in crystals on cooling. The 
 crystals are collected on a filter, washed with water, and distilled with 
 solution of potash ; (COOCH 3 ) 2 + 2 KOH = (COOK), + 2 (CH 3 'OH). The 
 methyl alcohol distils over with some water, which may be removed by 
 quicklime. 
 
 Much methyl alcohol is now obtained by distilling the refuse of the beet-root 
 sugar manufactory, and has become important as the source of many methyl- 
 compounds employed in making dyes. 
 
 Methyl alcohol in an impure state is used as a solvent for resins in making 
 varnishes. 
 
 Clean magnesium dissolves in absolute methyl alcohol even at ordinary tem- 
 perature, evolving hydrogen and forming crystals of magnesium rnethoxide com- 
 bined with methyl alcohol (CH 3 0) 2 Mg + 3CH 3 OH. 
 
 Properties of methyl alcohol. Much resembling ethyl alcohol, with a 
 somewhat different odour; sp. gr. 0*7997 at 16 C., b.-p. 66 C. ; 
 rn.-p. - 95 C., very inflammable, burning with a pale flame. In 
 presence of air and platinum-black, yields formic aldehyde (HCHO) and 
 formic acid (HC0 2 H) ; CH 3 OH + 2 = HC0 2 H + H 2 O. The formic acid 
 may be distinguished from acetic by its property of reducing silver 
 ammonio-nitrate to the metallic state when warmed with it. Hence, 
 methyl and ethyl alcohols may be distinguished by distilling them with 
 
ISOMERIC ALCOHOLS. 
 
 567 
 
 dilute sulphuric acid and potassium dichromate, when the former yields 
 formic and the latter acetic acid. 
 
 A suitable apparatus for distilling small quantities of liquids in making such 
 tests is shown in Fig 268. The condenser consists of a vessel containing cold 
 water and surrounded by a jacket, the 
 lower part of which terminates in a 
 tube. The vapour entering by the 
 side tube condenses within the jacket. 
 
 340. Isomerism among the 
 monohydric alcohols, Since 
 methyl and ethyl alcohols are 
 mono - substitution derivatives 
 from methane and ethane re- 
 spectively, it is riot surprising 
 that no position isomerides of 
 these compounds are known 
 (see p. 542). It has already 
 been noticed that two mono- 
 substitution derivatives of pro- 
 pane are possible, namely, those 
 which have the substituent 
 attached to the end of the three - 
 carbon-chain, and those in which 
 the substituent is attached to 
 the centre carbon atom ; the 
 former kind is known as the normal propyl derivative, the latter as the 
 isopropyl derivative. Thus, the general formula for a normal propyl 
 derivative is CH 3 'CH 2 -CH.,X', whilst that for an isopropyl derivative 
 is CH 3 -CHX'-CH 3 or X'CH:(CH 3 ) 2 . Hence there is a normal propyl 
 alcohol and an isopropyl alcohol, 
 
 Since butane may be regarded as methylpropane (a mono-substitution 
 product of propane) it may be expected to exist in two modifications 
 (P- 53 2 )- The first of these, normal butane, can yield two mono-substi- 
 tution derivatives, viz., CH 3 -CH 2 'CH 2 'CH 2 X' and CH 3 'CH 2 'CHX'-CH 3 ; 
 whilst the second, secondary butane, can also yield two mono-substitution 
 derivatives, viz., (CH 3 ) 2 : CHCH 2 X' and (CH 3 ) 2 : CX'-CH 3 . Hence 
 there should be four butyl alcohols. 
 
 Pentane is methylbutane, but it only exists in three instead of four 
 modifications (p. 519) because the methylbutanes corresponding with 
 the second and third formulas given above would have the same struc- 
 ture. By writing the formulas for a mono-substitution-product of pen- 
 tane, it will be found that eight different compounds are possible, and 
 in many cases eight are known ; eight pentyl (amyl) alcohols, for instance. 
 
 All these isomeric alcohols are divided into three classes as follows : 
 (i) Those in which the OH group is attached to a carbon atom, which is 
 itself attached to only one other carbon atom ; these are called primary 
 
 Fig. 268. 
 
 alcohols and contain the group - 
 
 OH 
 
 (2) Those in which the OH 
 
 group is attached to a carbon atom, which is itself attached to two other 
 carbon atoms ; these are called secondary alcohols, and contain the group 
 
 :C/ H . (3) Those in which the OH group is attached to a carbon 
 OH 
 
568 PRIMARY, SECONDARY, AND TERTIARY ALCOHOLS. 
 
 atom, itself attached to three other carbon atoms ; these are called 
 tertiary alcohols, and contain the group i OOH. 
 
 The following list of alcohols will furnish examples of the three 
 classes : 
 
 Methyl alcohol .... H'CH 2 OH Primary. 
 
 Ethyl alcohol .... CH 3 'CH 2 OH Primary. 
 
 Normal propyl alcohol . . CH 3 'CH 2 -CH 2 OH Primary. 
 
 Isopropyl alcohol . . . (CH 3 ) 2 : CHOH Secondary. 
 
 Normal butyl alcohol . . CH 3 -CH 2 'CH 2 -CH 2 OH Primary. 
 
 Primary isobutyl alcohol . . (CH 3 ) 2 : CH'CH 2 OH Primary. 
 
 P FT C 1 - FT 
 
 Secondary butyl alcohol ' 3 ^ TT 2 \CHOH Secondary. 
 
 Tertiary butyl alcohol . . (CH 3 ) 3 \ COH Tertiary. 
 
 Of the eight pentyl alcohols, 4 are primary, 3 secondary, and I tertiary. 
 
 Greater facility in naming these numerous compounds is attained by taking 
 methyl al'cohol or carbinol as the starting-point, and supposing the alcohols to 
 be derived from it by substitution of alcohol radicles for the hydrogen in the 
 methyl group. Then, the primary alcohols will be mono-substitution derivatives 
 o f carbinol, as shown in the following formula; : 
 
 Carbinol, CH 3 'OH. Primary propyl alcohol, or ethyl carbinol, CH 2 (C 2 H 5 )-OH. 
 Primary butyl alcohol, or propyl carbinol, CH 2 (C 3 H 7 )'OH. Primary iso-butyl alco- 
 hol, or iso-propyl carbinol, CH 2 (C 3 H T )'OH (the difference here consisting in propyl, 
 CH 2 (CH 2 CH 3 ), formed by the methylation of ethyl, CH 2 (CH 3 ), and iso-propyl, 
 CH(CH 3 ) 2 , formed by the di-methylatlon of methyl. 
 
 The secondary alcohols may be regarded as di-substitution-products of carbinol ; 
 secondary propyl alcohol or dimethyl carbinol, CH(CH 3 ) 2 'OH, is evidently iden- 
 tical with iso-propyl alcohol. Secondary butyl alcohol is ethyl methyl carbinol, 
 CH(C 2 H 5 )(CH) 3 'OH. Secondary amyl alcohol is methyl propyl carbinol 
 
 CH(CH 3 )(C 3 H 7 )-OH. 
 
 Another secondary amyl alcohol is di-ethyl carblnol, CH(C 2 H 5 ) 2 'OH. The tertiary 
 alcohols would be tri-substitution-products of carbinol. Tertiary butyl alcohol is 
 trimethyl carblnol, CfCHoVOH. Tertiary pentyl alcohol is ethyl dimeth ill carbinol. 
 C(C 2 H 5 )(CH 3 ) 2 -OH.* 
 
 The three classes of alcohols are distinguished by their behaviour 
 under the action of oxidising-agents, which also serves to settle 
 their constitution. When oxidised, a primary alcohol yields an 
 aldehyde, and ultimately an acid, containing the same number of 
 
 carbon atoms as the alcohol ; thus, ethyl alcohol, CH 3 'C^ 2 , yields 
 
 OH 
 
 ethyl aldehyde, CILO^ , and acetic acid OIL'Cx A secondary 
 
 X H X OH 
 
 alcohol ytelds a ketone containing the same number of carbon atoms ; 
 
 thus, secondary propyl alcohol, (CH 3 ) 2 : C/ , yields di-methyl ketone, 
 
 H 
 
 (CH 3 ) 2 : C : ; a tertiary alcohol is either broken up into two or more 
 acids containing less carbon, or it may yield a ketone containing one 
 atom less carbon than itself, the atom of carbon being oxidised to 
 carbonic or formic acid ; thus, tertiary butyl alcohol, C(CH 3 ) 3 'OH yields 
 acetone, (CH 8 ) 3 : CO, and formic acid, H'COOH. 
 
 Another method for distinguishing between a primary, secondary, and tertiary 
 alcohol is as follows : The alcohol is converted into the corresponding iodide by 
 
 * According- to another system, the alcohols are named by adding -ol to the name of the 
 parent hydrocarbon ; thus CH 3 'OH is methanol, C.HyOH is propanol. Tolyhydric alcohols 
 are distinguished as diols, tr/ol8,>&c. ; CH a OH'CH 8 OH is ethanedtol, CH 2 OH'CHOH-CH 2 OH 
 is propanetriol, CH 2 OH'CH 2 -CH 2 OH is n^ropanediol. 
 
GENERAL METHOD FOR PREPARING ALCOHOLS. 569 
 
 distilling with iodine and phosphorus (see ethyl iodide) ; the iodide is distilled with 
 .a mixture of silver nitrite with dry sand (to dilute it), when the corresponding 
 nitro-paraffin is obtained ; thus ethyl iodide yields nitro-ethane (C 2 H 5 N0 2 ) 
 
 CH 3 -CH 2 -I + AgN0 2 = CH 3 -CH 2 -N0 2 + Agl. 
 
 The distillate is mixed with potassium nitrite and weak potash, and dilute 
 sulphuric acid is gradually added ; if the alcohol be primary, a red solution of 
 the corresponding potassium nitrolate will be obtained, the nitro-paraffin having 
 been converted into the corresponding nitrolic acid by the nitrous acid ; thus, 
 nitro-ethane yields nitrolic acid 
 
 CH 3 -CH 2 -N0. 2 + HN0 2 = CH 3 -C(N0 2 ) : NOH + H 2 0. 
 
 Nitrolic acids are colourless, but their alkali salts have a dark red colour ; they 
 are very unstable, being decomposed into nitrous oxide and a fatty acid ; thus 
 nitrolic acid yields nitrous oxide and acetic acid. If the alcohol be secondary, a 
 blue solution of a pseudonitrol will be obtained ; thus secondary amyl alcohol, 
 CH(CH 3 )(C 3 H 7 )-OH, would yield the secondary nitro-paraffin, CH(CH 3 )(C 3 H 7 )-N0 2 . 
 which would be converted by HN0 2 into the pseudonitrol, C(NO)(CH 3 )(C 3 H 7 )'N0 2 , 
 .giving a blue solution. If the alcohol be tertiary, no colour is produced, the 
 tertiary nitre-paraffins being unattacked by nitrous acid. 
 
 The simplest general method for preparing tlie alcohols consists in 
 treating the corresponding halogen substitution derivatives of the 
 hydrocarbons with moist silver oxide, which behaves as if it were AgOH ; 
 thus, if normal butyl bromide be so treated, it yields normal butyl 
 alcohol, CH 3 -CH 2 -CHvCH a Br + AgOH = CH 3 -CH,-CH/CH,OH + AgBr. 
 The secondary bromide, "CH 3 -CH 8 -CH 2 BrCH 3 , yields the secondary 
 alcohol. The tertiary bromide yields the tertiary alcohol. 
 
 As the alcohols form the basis for the production of a large number 
 of compounds on the small scale, their general reactions will be best 
 understood when these other compounds are considered. Here it need 
 only be mentioned that they dissolve alkali metals with evolution of 
 hydrogen, forming the corresponding metallic alkyloxide or alcoholate, 
 like aE 
 
 341. JVorwal propyl alcohol, or ethyl carbinol, C 3 H 7 'OH, or C 2 H 5 - CH 2 'OH, is 
 'found in the latter portions of the distillate obtained in rectifying crude spirit of 
 wine. It smells like ialcohol, has the sp. gr. 0.804, and boils at 97 c - When 
 mixed with water it may be separated by saturating with calcium chloride, when 
 the propyl alcohol rises to the surface, which would not be the case with ethyl 
 alcohol. When oxidised, it yields propionic aldehyde, C 2 H g 'CHO, and propionic 
 acid, C 2 Hg-C0 2 H. Iso-propyl alcohol boils at 83 C., and is obtained by reducing 
 acetone with nascent hydrogen. 
 
 The butyl alcohol. C 4 H 9 'OH, originally so called, and mentioned in the table at 
 p. 565 as obtained by the' fermentation of beet-root, and also by the distillation of 
 crude spirits, is now called fermentation butyl alcohol, or primary isobutyl alcohol. 
 to distinguish it from the normal butt/I alcohol, which is the real member of this 
 homologous series of alcohols. Fermentation butyl alcohol boils at 108 C., and 
 smells of fusel oil, which often contains it. It has sp. gr. 0.802, and is much lett 
 soluble in water than propyl alcohol is, requiring ten times its weight to dissolve 
 Most salts soluble in water cause it to separate on the surface of the I"!" 1 .*}- 
 Normal butyl alcohol, or prop t/ 1 carbinol, C 3 H 7 'CH 2 -OH, has sp. gr. 0.810, and boih 
 at 117 C. It is obtained by acting upon butyl aldehyde with water and s 
 amalgam, to furnish nascent hydrogen, C 3 H/CHO + H 2 = C 3 H/CH 2 'OH. 
 
 342. The history of amyl alcohol resembles that of butyl alcohol, the i 
 having been originally given to the well-known offensive and poisonous Liqul< 
 called fusel oil, obtained in the distillation of spirits from fermented gram or 
 potatoes. This contains, however, at least two isomenc alcohols, vix., <*">' "//' 
 tarbinol, (CH 3 ) a : CH'CH 2 -CH 2 'OH (b.-p. 131 C), WOOL secondary butyl (o 
 
 carbinol, H3 )>CH-CH 2 OH (b.-p. 127 C.) ; this latter is optically art ire, for it 
 
 contains an asymmetric carbon atom (see xteren-i*onieri*m'). Fusel oil has the 
 sp. gr. 0.83, and is so sparingly, soluble in water that it separates from it 
 
570 OLEFINE AND ACETYLENE ALCOHOLS. 
 
 in distilled spirits on dilution with water, rendering the liquid turbid. Its odour 
 is very characteristic, and the vapour occasions coughing and a sensation of 
 swelling of the head. 
 
 On writing the formula; for the possible amyl alcohols, it will be found that 4 
 are primary, 3 secondary, and I tertiary, and that 3 of them have an asymmetric 
 carbon atom, so that each exists in a Ia3vo-. dextro, and inactive form making. 
 14 amyl alcohols in all. 
 
 Tertiary amyl alcohol, dimethylethyl carlinol, (CH 3 ) 2 C 2 H 5 COH, is a liquid 
 (b.-p. 102 C) smelling of camphor, and used as a substitute for chloral as a 
 narcotic ; it is prepared from the amyl alcohol of fusel oil. 
 
 343. Normal hexyl alcohol, CgH^CIL/OH, boiling at 157 C., is not that pro- 
 duced by fermentation, but is obtained from the essential oil of an umbelliferous 
 plant, Heracleumgiganteum, which contains hexyl butyrate, and yields the alcohol 
 when distilled with potash, C 3 H/COOC 6 H 13 +KOH = C 6 H 13 -OH + C 3 H 7 -COOK. 
 
 The fermentation hexyl alcohol, or caproyl alcohol (b.-p. 150 C.), is that obtained 
 by distilling fermented grape-husks ; it has a more unpleasant smell than the 
 normal alcohol. 
 
 Normal capryl or octyl alcohol, C 8 H 17 'OH, is obtained from the essential oil of 
 the cow-parsnip or hog-weed (Heracleum, spondyliuni), an umbelliferous plant, by 
 distilling it with potash, which decomposes the octyl acetate, of which the oil 
 chiefly consists, CH 3 -COOC 8 H 17 + KOH = C 8 H 17 'OH + CH 3 'COOK (potassium acetate). 
 It has the sp. gr. 0.83, and boils at 199 C. 
 
 Cetyl alcohol, C 16 H 33 'OH, or ethal, is obtained from spermaceti, found in the 
 brain of the sperm-whale. This substance is cetin or cetyl palmitate, and when 
 boiled for some time with potash dissolved in alcohol, it yields cetyl alcohol and 
 potassium palmitate; C 15 H 31 -COOC 16 H 33 + KOH = C 16 H 33 -OH + C 15 H 31 'COOK. On 
 mixing the alcoholic solution with water, the cetyl alcohol is precipitated in the 
 solid state, being insoluble in water. Cetyl alcohol is a crystalline body, fusing at 
 4O.5 C., and boiling at 344 C. 
 
 Ceryl alcohol, C 27 H 55 'OH, is prepared from Chinese ivax, the produce of an 
 insect of the cochineal tribe. It consists chiefly of cerotln or ceryl cerotate^ 
 CaeHgg'COOC^Hgg, and when fused with potash gives ceryl alcohol and potassium 
 cerotate. By treating the fused mass with water, the cerotate is dissolved, and the 
 ceryl alcohol is left, and may be obtained in crystals by dissolving it in ether. Its 
 f using-point is 79 C. It occurs in flax. Kecent analyses seem to show that ceryl 
 alcohol is C^H^OH. 
 
 Melissyl alcohol, or myricyl alcohol, C 30 H 61 'OH, is derived from bees' -wax . When 
 this is boiled with alcohol, about one-third of its weight is left undissolved ; this 
 is myricin or mellissyl palmitate, C 15 H 31 'COOC 30 H 61 . When fused with potash it 
 yields potassium palmitate and melissyl alcohol, which is a crystalline substance, 
 fusing at 85 C. 
 
 344. Monohydric Alcohols of the Oleflne and Acetylene 
 Series. These may be regarded as formed from the olefine and acetylene 
 hydrocarbons in the same manner that the ordinary alcohols are derived 
 from the paraffin hydrocarbons. They therefore correspond with the 
 general formulae C^Haj^OH and C n H 2B _ 3 OH. Those which are 
 known are primary alcohols ; thus, allyl alcohol is CH 2 : CH'CH,OH, 
 derived from propylene. The alcohol from ethylene, CH., : CH'OH, is a 
 secondary alcohol (vinyl alcohol) and probably exists in crude ether, 
 but it cannot be isolated because it is immediately transposed into 
 aldehyde, CH 3 'CHO ; this is in accord with other experience of the 
 grouping : : OHOH, which is always found to be unstable. 
 
 The alcohols of these two classes are, of course, unsaturated compounds, 
 and readily combine with H to form the alcohols of the preceding 
 class. 
 
 Allyl alcohol, C 3 H 5 'OH, or CH 2 : CH'CH 2 OH, is obtained by heating four parts of 
 glycerol with one part of crystallised oxalic acid in a retort at 195 C., so long 
 as water passes over, and afterwards raising the temperature, when the allyl alcohol 
 distils (addition of a little NH 4 C1 facilitates the change). The glycerol is first 
 converted into monoformin 
 
AROMATIC ALCOHOLS. 
 
 571 
 
 CH 2 OH-CHOH-CH,OH + (COOH) 2 - CH 2 OH'CHOH'CH 2 (OCHO) + C0 2 + H 2 0. 
 The monoformin is then decomposed into allyl alcohol, C0 9 and H 
 CH 2 OH-CHOH-CH 2 (OCHO) = CH 2 : CH-CH 2 OH + H 2 + c6 2 . 
 
 It has a pungent smell, sp. gr. 0*87, b.-p. 96. 6 C. By very careful oxidation it 
 yields glycerol, but when oxidised by Ag 2 it yields acrylic aldehyde or acrolein, 
 CH 2 : CH-CHO, and acrylic acid, CH 2 : CH'COOH. This shows it to be a primary 
 alcohol. Crude wood spirit contains a little allyl alcohol. 
 
 Propargyl ov propinyl alcohol, C 3 H 3 -OH, or CH C'CH 2 OH, is the alcohol corre- 
 sponding with allylene. It is obtained by boiling bromallyl alcohol (itself obtained 
 by a somewhat intricate process), CH 2 : CBrCH 2 OH, with KOH ; CH 2 : CBrCH 2 OH 
 + KOH = CH : C -CH 2 OH + KBr + HOH. It is a fragrant liquid of sp. gr. 0.97 and 
 b.-p. 115 C. ; it burns with a luminous flame. Since it contains the CH : C. 
 group, it is capable of yielding metallic derivatives ; cuproso-propargyl alcohol, 
 CCu : C :CH 2 OH is a green precipitate. 
 
 345. Monohydric Alcohols of the Benzene Hydrocarbons. 
 
 It would seem at first sight as though the hydroxyl compound produced 
 by introducing OH in the place of one of the H atoms of benzene should 
 be an alcohol. If the structure of benzene be correctly represented by 
 the benzene ring, however, this alcohol would partake of the nature of a 
 tertiary alcohol, since the OH would be combined to a carbon atom 
 itself attached by three atom-fixing powers to two other carbon atoms. 
 As a fact, however, the hydroxy-substitution-products of the benzene 
 hydrocarbons cannot be classed with the alcohols when the substitution 
 occurs in the benzene nucleus. Such compounds as C 6 H 5 (OH),C 6 H 4 (OH) 2 , 
 6 H 4 (OH)(CH 3 ), differ to such an extent from the alcohols that they are 
 classed apart as phenols. 
 
 Only such hydroxy-derivatives of benzene hydrocarbons are alcohols 
 (aromatic alcohols) as have OH substituted for H in the side-chain ; thus, 
 whilst C 6 H 4 (OH)CH 3 is a phenol, its isomeride, C 6 H,-CH 2 OH, is a 
 primary alcohol, and may be termed benzyl alcohol or phenyl carbinol 
 (p. 568). Secondary alcohols, e.g., C 6 H 5 'CHOH-CH 3 (from ethyl ben- 
 
 /CH 3 
 
 zene), and tertiary alcohols, e.g., C 6 H 5 'C(OH)^ ^ (from isopropyl 
 
 CH 3 
 
 benzene), also exist, as in the paraffin series. For every alcohol there is 
 an isomeric phenol, and it is possible to have a phenol-alcohol, e.g., 
 C 6 H 4 (OH)-CH 2 OH (from hydroxy toluene), or any other substituted 
 aromatic alcohol (Fig. 269). 
 
 a 
 
 OH 
 
 Ben/yl alcohol Orthohydroxytolueue Orthohydroxybenzyl 
 
 C 6 H 5 CH 2 OH. (a phenol). alcohol (a phenol-alcohol). 
 
 Fig. 269. 
 
 Like the paraffin alcohols, the aromatic alcohols may be prepared from 
 the halogen substituted hydrocarbons by the action of moist silver oxi 
 or an alkali, but the substituted halogen must, of course, be in the sid 
 chain, e.g., C 6 H 3 'CH 2 C1 (benzyl chloride). 
 
 Benzyl alcohol, or phenylcarbinol, C 6 H 5 'CH 2 OH, may be obtained from t^i:yl 
 aldehyde (bitter-almond oil) by the action of reducing-agents ; since Denz 
 aldehyde is itself capable of undergoing oxidation, it is possible to o 
 
57 2 MERC APT AN. 
 
 reduction product, benzyl alcohol, and its oxidation-product, benzoic acid, by heat- 
 ing it with alcoholic potash ; 2C,.H 5 -CHO + KOH = C 6 H 5 -CH 2 OH ^-C 6 H 5 'COOK. 
 
 It can also be made from benzoic acid by the action of nascent H, generated by 
 adding Na-amalgam to a boiling solution of the acid ; C 6 H 5 'COOH + H 4 = 
 C 6 H5'CH 2 OH + H 2 O. The balsams of Tolu and of Peru and storax yield benzyl 
 alcohol when distilled with alkalies which decompose the benzyl benzoate. 
 C 6 H 5 'COO(C 6 H 5 CH 2 ), and cinnamate contained in them. 
 
 Benzyl alcohol is an oily liquid heavier than water (sp. gr. 1.06), boiling at 
 206 C. Oxidising-agents convert it into benzaldehyde and benzoic acid, proving 
 it to be a primary alcohol. 
 
 Salicyl alcohol, or hydroxybenzyl alcohol, C 6 H 4 (Ofl)-CH 2 OH, shows the properties 
 of a phenol (#.r.) as well as those of a primary alcohol, and is a type of the phenol 
 alcohols. It is a di-substituted benzene, and therefore exists in three isomeric 
 forms. The i : 2-derivative was first called saligenin, made from salicin, a crystal- 
 line substance extracted from willow-bark. This substance is a glucoside, and 
 when hydrolysed (p. 265) yields glucose (C 6 H 10 6 ) and salicyl alcohol ; 
 
 C 6 H 4 (OC 6 H n 5 )-CH 2 OH + HOH - C^O^GH) + C 6 H 4 (OH)-CH 2 OH. 
 I : 2-salicyl alcohol forms tabular crystals, soluble in hot water, alcohol, and 
 ether, fusing at 82 C. and subliming at 100 C. When oxidised it yields salicyl 
 aldehyde, C 6 H 4 (OH) -CHO, and salicylic acid, C 6 H 4 (OH)'COOH. It gives an intense 
 blue colour with ferric chloride (cf. Phenol*). 
 
 Cinnatnyl alcohol is the primary alcohol corresponding with the unsaturated 
 hydrocarbon cinnamene (p. 550) ; its formula is C 6 H 5 'CH : CH'CH 2 OH, phenyl 
 ally I alcohol. It also is obtained from storax-, a fragrant balsam exuded by the 
 Styrax officinale, a tree found in Syria and Arabia, sometimes used as a pectoral 
 remedy. When this is digested for some hours with a weak solution of 
 soda, and the residue extracted with a mixture of ether and alcohol, needle- 
 like crystals of styracin are obtained. This substance is cinnamyl cinnamate, 
 C 6 H 5 'CH :CH-COO(C 6 H 5 -CH : CH'CH 2 ), and yields cinnamyl alcohol and potassium 
 cinnamate when distilled with KOH ; C 9 H 9 -C 9 H 7 2 + KOH = C 9 H 9 'OH + KC 9 H 7 0. 2 . 
 
 The alcohol smells of hyacinths, melts at 33 C. and boils at 250. It dissolves 
 sparingly in water, but easily in alcohol or ether. When oxidised it yields 
 cinnainic aldehyde and cinnamic acid. 
 
 Alcohols of the hydrocarbons containing more than one benzene nucleus are of 
 minor importance. Diplienylcarbinol (Jbenzhydrol), (C 6 H 5 ) 2 CH.OH, is a secondary 
 alcohol obtained by reducing benzophenone (</.'.) ; it melts at 68 C. 
 
 Triphewylearbvnol, (C 6 H 5 ) 3 C.OH, is a tertiary alcohol, important from its 
 relation to the " aniline dyes." It is formed by oxidising triphenylmethane 
 (P- ^550 with chromic acid in glacial acetic acid, melts at 159 and boils at 360 C. 
 
 Naphthalene and anthracene alcohols also exist. 
 
 346. Thio-alcohols or mercaptans are analogous to the alcohols, but contain S in 
 place of O, and as the latter are hydroxides of the alcohol radicles, so the 
 thio-alcohols (R'SH) are the hydrosulphides. The thw-etherx, R 2 S, or sulphides of 
 the alcohol radicles, may also be considered here ; they are the analogues of the 
 ethers, R 2 0. 
 
 Mercaptan, C 2 H 5 'SH, was named from its remarkable action on mercury com- 
 pounds (mercurio upturn). It is made (for making sulphonal) by distilling KSH 
 with C 2 H 5 C1 in alcoholic solution, or. on a smaller scale, with calcium sulphethy- 
 late (q.v.) : Ca(C 2 H 5 S0 4 ) 2 + 2KSH = CaS0 4 + K 2 S0 4 + 2(C 2 H 5 'SH). 
 
 A solution of KSH is made by saturating potash of sp. gr. 1.3 with H 2 S, and this is 
 distilled, in a salt-and-water bath, with an equal volume of solution of calcium 
 .sulphethylate of sp. gr. 1,3. The mercaptan forms the upper layer of the distillate, 
 and is characterised by its powerful smell of garlic. It is a volatile liquid, of 
 sp. gr. 0.835, an d boils at 36 C. A drop exposed to the air is frozen to a crystal- 
 line mass by its own evaporation. It burns with a blue flame. Mercaptan i.s 
 sparingly soluble in water, but dissolves in alcohol and ether. It is unaffected by 
 caustic alkalies, but alkali metals act on it as in the case of alcohol, displacing 
 hydrogen and forming mercaptides, e.g., C 2 H 5 'SK, which are crystalline bodies 
 soluble in water. 
 
 Mercuric oxide evolves much heat with mercaptan, forming a white crystalline 
 inodorous compound ; HgO + 2(C 2 H 5 -SH) = H 2 O + (C 2 H 5 S) 2 Hg (mercuric* mercap? 
 tide). This is insoluble in water, but may be crystallised from alcohol, or from 
 strong HC1. Potash doos not decompose it. H 2 S converts the mercury into 
 sulphide and reproduces mercaptan. Mercaptides (thio-etlwxides) of other 
 
GLYCOLS. 
 
 metals may be precipitated by metallic salts from an alcoholic solution of 
 mercaptan. 
 
 By distilling mercuric thio-ethylate, di-ethyl sulphide or thw-ether, C,H -S'C H 
 maybe obtained; (C 2 H 6 S) 2 Hg = (C 2 H 5 ) 2 S + HgS. This may also be prepared 2 by 
 distilling potassium sulphethy late with potassium sulphide; 2KC H 5 SO; + K.,S = 
 2K 2 S0 4 + (CoH 5 ) 2 S. It resembles mercaptan, but boils at 91 C." Its alcoholic 
 solution gives, with mercuric chloride, a white crystalline precipitate of 
 (C 2 H 5 ) 2 S-HgClo. 
 
 Allyl sulphide, (C 3 H 5 ) 2 S, is the main constituent of essential oil of garlic, and 
 occurs in several cruciferous plants. It boils at 140 C., dissolves sparingly in 
 water, and behaves like ethyl sulphide. 
 
 Ethyl duulphide, (C 2 H 5 ) 2 S 2 , is obtained when potassium disulphide and sul- 
 phethylate are distilled. It may also be formed by heating mercaptan to 150 C. 
 with sulphur; 2(C 2 H 5 SH) + S 2 =(C 2 H 5 ) 2 S 2 + H 2 S ; or by decomposing sodium mer- 
 captide with iodine ; 2(C 2 H 5 SNa) + 1 2 = 2NaI + (C 2 H 5 ) 2 S 2 . It is an alliaceous liquid, 
 boiling at 151 C. Ethyl sulphoxide, (C 2 H 5 ). 2 OS, is a syrupy liquid resulting from 
 the action of dilute nitric acid on ethyl sulphide. 
 
 Ethyl sulphone, (C 2 H 5 ) 2 SO 2 , is a very stable crystalline body formed when ethyl 
 sulphide is oxidised by strong nitric acid ; it fuses at 70 C. and boils at 248 C. r 
 but sublimes at 100 C. It is soluble in water and alcohol. 
 
 When ethyl sulphide and ethyl iodide are heated together with a little water 
 for some hours in a flask with an inverted condenser, the mixture, on cooling,, 
 deposits colourless prisms of tri-ethyl-sulphine iodide, (C 2 H 5 ) 3 S'I, which are soluble 
 in water and alcohol, but insoluble in ether. This compound is remarkable for 
 producing a series of compounds in which the iodine may be exchanged for other 
 chlorous radicles, giving rise to tri-etht/l-sulphine salts, in which the S is quad- 
 rivalent ; thus, in the iodide, it is attached to four monad radicles, viz., (C 2 H 5 )o 
 and I. By decomposing the iodide with silver hydroxide, the tri-ethyl-fidpkine 
 ]tydro,vide, (C 2 H 5 ) 3 S'OH, is obtained ; it is a deliquescent crystalline body pos- 
 sessing the properties of a powerful caustic alkali. 
 
 Compounds similar to the foregoing have been obtained from the alcohols formed 
 by the other radicles of this series. 
 
 347. Dihydric Alcohols, or Glycols. The dihydric alcohols may 
 be regarded as derived from the saturated hydrocarbons by the substitu- 
 tion of hydroxyl groups for two H atoms ; equally well, they may be 
 said to be olefine hydrocarbons which have combined with two hydroxyl 
 groups, and this is the view expressed by their nomenclature ; ethylene 
 glycol, C.,H 4 (OH).,, and propylene glycol, C 3 H 6 (OH) 2 , are examples. Like 
 the monohydric alcohols, a general method for their preparation consists 
 in the treatment of the corresponding bromo- derivatives with alkalies, 
 or, what is equivalent, an alkali carbonate, or lead hydroxide, and 
 water. 
 
 The simplest glycol would be CH 9 (OH) 2 from methane ; but this has 
 never been isolated, and it appears "to be a fact that no compound can 
 exist which has two hydroxyl groups attached to one carbon atom (cf. the 
 non-existence of carbonic acid, OC(OH) 2 ; p. 127). There is evidence to 
 show that in all the glycols the OH groups are attached to different 
 carbon atoms. For example, ethylene glycol is CH 2 OH*CH 2 OH, not 
 CH 3 -CH(OH) 2 , and cannot exist in isomeric forms ; propylene glycol may 
 be either CH 2 OH'CH 2 -CH 2 -OH, or CH 3 -CHOITCH 2 OH, the former 
 of which contains two primary alcohol groups, and may be termed a 
 diprimary glycol, whilst the latter is a secondary -primary glycol.* Since 
 disecondary, ditertiary, secondary-tertiary and j primary-tertiary glycols 
 
 * The glycols are either a-, -, or y-, &c., glycols accordingly as the^OH groups are 
 attached to the 1:2, 1:3, 1:4, &c., C atoms of the chain, respectively ; thus 
 
 CH 2 OH CH 2 CH 2 OH 
 is /3-propyleue glycol, the a.jsorneride being CH 3 - CHOH ' CH 2 OH. 
 
5/4 PEEPAKATION OF GLYCOL. 
 
 are also possible, the cases of isomerism among the glycols are very 
 numerous. 
 
 The OH groups in the glycols are capable of the same transformations 
 as is the OH in a monohydric alcohol ; the H in them can be exchanged for 
 alkali metals ; the hydroxyl groups can be exchanged for acid radicles, &c. 
 Two series of such substituted glycols exist, those in which both OH 
 groups have undergone the change, and those in which only one has been 
 altered; thus, CH 9 ONa'CH 9 OH and CH 2 ONa'CH,ONa ; CH 9 C1'CH 9 OH 
 and CH 2 C1-CH 2 C1/ 
 
 The oxidation of the glycols yields the same kind of products as 
 those from the oxidation of the alcohols ; but since there are two 
 alcoholic groups to be oxidised, a very large number of products is ob- 
 tainable; for example, the two primary alcohol groups in CH,OH'CH 2 OH 
 can both be oxidised to aldehyde groups, CHO'CHO, or to acid groups, 
 COOH'COOH; or only one of them may be so oxidised, yielding alcohol- 
 aldehydes, CHO'CH 2 OH, or alcohol acids, COOH'CH 2 OH ; aldehyde- 
 acids, CHO'COOH, will also be possible. If the glycol contain a 
 secondary alcohol group (: CHOH), ketone-alcohols, ketone-aldehydes, 
 ketone-acids, and diketones may also be prepared. Hence the glycols give 
 rise to a very large number of derivatives, many of which are very 
 important, although the same cannot be said of the glycols them- 
 selves. 
 
 The dialcohols, alcohol-aldehydes, alcohol-acids, and alcohol-ketones, 
 containing the group CH 2 OH, are frequently termed hydroxy- or oxy- 
 derivatives of the corresponding paraffin compounds. Thus CH 2 OIT 
 CH 2 OH may be regarded as hydroxyethyl alcohol (oxyethyl alcohol}, i.e., 
 ethyl alcohol, in which H has been exchanged for OH ; CH 2 OH'CHO as 
 hydroxyacetic aldehyde, and CH,OH'COOH as hydroxyacetic acid. 
 
 The glycols are somewhat viscid, neutral liquids. The increase in the 
 number of OH groups in an alcohol seems to tend to increase the boil- 
 ing point, the viscidity and the solubility in water ; solubility in alcohol 
 and ether decreases. The glycols have a sweetish taste, a property much 
 enhanced in glycerol and the sugars. 
 
 Glycol, CH 2 OH'CH 2 OH, or ethylene glycol, is a much more artificial product than 
 alcohol, having been discovered as lately as 1856. It is prepared by decomposing 
 ethylene bromide with potassium carbonate. Ethylene (p. 535) is first converted 
 into ethylene bromide by passing it slowly into 50 grams of bromine under 
 water, well cooled, until the bromine is bleached, or nearly so. The heavy layer 
 of ethylene bromide is shaken with a little weak potash, the upper watery layer 
 drawn off, and 50 grams of the bromide heated with 40 of potassium car- 
 bonate, and 100 of water, for eighteen hours, in a flask provided with a reversed 
 condenser (Fig. 270) ; when the bromide no longer condenses and runs back, 
 the condenser is placed in its proper position and the contents of the flask distilled. 
 After all the water has passed over, the flask is strongly heated by a large Bunsen 
 burner, when the glycol distils. The reaction is expressed by the equation 
 C 2 H 4 Br 2 + K 2 C0 3 + H 2 = C 2 H 4 (OH) 2 + 2KBr + C0 2 , which exemplifies the tendency 
 of alkaline reagents, in the presence of water, to effect the substitution of hydroxyl 
 for halogens. 
 
 Glycol is a colourless liquid, less mobile than alcohol, and almost inodorous. 
 It has a sweet taste, sp. gr. 1.125 at o, and the high boiling-point 197 C. Its 
 vapour is inflammable, but will not take fire at common temperatures like 
 alcohol. Glycol mixes with water and alcohol in all proportions, but ether does 
 not dissolve it. 
 
 Sodium dissolves in glycol, as in alcohol, evolving hydrogen, and yielding 
 monosodium glycol, CH 2 OH'CH 2 ONa, corresponding with sodium ethoxide, 
 C 2 H 5 'ONa. On heating this with more sodium, a second atom of H is displaced, 
 
OXIDATION OF GLYCOL. 
 
 yielding disodium glycol, C 2 H 4 (ONa) 2 . Water converts both compounds into 
 glycol and sodium hydroxide. 
 
 Glycol chlmhydrin is glycol in which Cl has been substituted for one hvdroxol 
 group ; CH 2 OH-CH 2 C1 ; and is prepared by saturating glycol with HC1, and heatmg 
 in a sealed tube to 100 C. ; C 2 H 4 (OH) 2 + HC1 = C 2 H 4 -OH-C1 + HOH. It has alsS 
 been obtained by the combination of ethylene, C 2 H 4 , with hypochlorous acid 
 C10H. It permits the conversion of a dihydric into a monohydric alcohol for it 
 yields ethyl alcohol when acted on by (the nascent hydrogen from) water and 
 sodium-amalgam; C 2 H 4 -OH-C1 + 2 H = C 2 H 5 -OH + HC1. When oxidised it yields 
 monochloracetic acid, CH 2 C1'COOH, in which it is obvious that the Cl cannot be 
 attached to the same carbon atom as that to which the and OH are attached 
 (or the substance would not be an acid) ; this proves that glycol chlorhydrin 
 must contain Cl and OH attached to different carbon atoms, and settles the 
 constitution of glycol. 
 
 Fig-. 270. Reversed condenser. 
 
 The first stage in the oxidation of glycol is the formation of glycol dialdehyde, 
 or glyoxal ; the relation of this body to glycol is shown thus : glycol, 
 CH 2 OH-CH 2 OH ; glyoxal, CHO'CHO. 
 
 The further oxidation of glycol yields two acids, glycollic acid, COOH'CH 2 OH, 
 and oxalic acid, COOH'COOH.' 
 
 The glycols from the hydrocarbons containing one or more benzene nuclei, 
 have the hydroxyl groups in the side-chains ; they have been little studied. 
 
 Hydrobenzoin, (C 6 H 5 )CHOH : CHOH(C 6 H 5 ), toluylene-glycol, is derived from 
 stilbene (p. 551); it crystallises in plates, and melts at 134 C. An isonieride, 
 isohydrohen-oin, melts at 119 C. and occurs in two optically active and one 
 inactive forms ; both isomerides are produced when benzaldehyde (<?.<.) is reduced 
 with nascent hydrogen. 
 
 The pinacones are di-tertiary glycols, obtained, together with secondary alcohols, 
 by the action of nascent hydrogen on the ketones. Thus, acetone undergoes a con- 
 densation according to the equation, 2(CH 3 ) 2 CO + H 2 = (CH 3 ) 2 (HO)C-C(OHXCH 3 ) 2 , 
 dimethyl p'macone, 
 
 348. Trihydric Alcohols, or Glycerols. These may be regarded 
 as derived from saturated hydrocarbons, by substituting three OH groups 
 for three H atoms. Since two OH groups cannot remain combined 
 with one carbon atom (p. 573), there can be no glycerol which contains 
 
576 PREPARATION OF GLYCERINE. 
 
 fewer than three carbon atoms; thus, C 3 H 5 (OH) 3 must be the first 
 member of the series. The radicles of the glycerols may obviously be 
 regarded as-trivalent radicles e.g. (C 3 H 5 )"', glyceryl or propenyl. Com- 
 paratively few of the glycerols are known ; what was said with regard 
 to isomerism, substitution derivatives, and oxidation products of the 
 glycols, applies with even more cogency to glycerols, where there are- 
 three hydroxyl groups to be substituted and three alcoholic groups to be 
 oxidised. It will be noted, however, that a glycerol formed from an open- 
 chain saturated normal hydrocarbon must always contain at least one 
 secondary alcoholic group. 
 
 Glycerine, or Glycerol, C 3 H,(OH) 3 , or CH 2 OH'CHOH-CH 2 OH, was 
 formerly termed the sweet principle of fats, on account of the facility with 
 which it may be prepared from most of the natural fats, which are 
 thence called glycerides. Glycerine is also formed during the alcoholic 
 fermentation of sugar, and is present in small quantity in beer and 
 wine. 
 
 Preparation of glycerine. Glycerine is contained in the refuse liquor 
 (spent lyes) of the soap-maker, being always produced when oils and fats 
 are saponified by alkalies, and remaining in solution when the soap is 
 separated by adding salt. The chemistry of the saponification of oils- 
 and fats will be considered under the head of ethereal salts, to which class 
 these bodies belong. The soap lyes are concentrated until most of the 
 salt has crystallised and most of the water evaporated. The crude 
 glycerine thus obtained is distilled under diminished pressure in a 
 current of superheated steam, when water passes over first and is fol- 
 lowed by glycerine, the temperature of the receiver being high enough 
 to prevent much of the superheated steam from condensing. The more 
 or less dilute glycerine thus obtained is concentrated in a vacuum pan. 
 
 Only within recent years have methods of evaporation been so far improved that 
 it has paid the soap-maker to recover glycerine from his lyes. The candle-maker 
 used to be the sole producer. In this industry palm-oil is decomposed by super- 
 heated steam to obtain palmitic acid for making candles. The operation is con- 
 ducted in a still, and the distillate consists of a layer of palmitic acid floating on 
 an aqueous solution of glycerine. The latter is drawn off and concentrated as 
 described above, the process being simplified by the absence of salt. The palmitic 
 acid solidifies to a white crystalline substance. 
 
 Previously to 1850, glycerine was made only on a laboratory scale by the process 
 discovered by Scheele in 1779, which consisted in boiling olive oil with lead 
 oxide (litharge, PbO) and water, when lead oleate, or lead plaster, remained, while 
 the glycerine dissolved in the water from which it was obtained by evaporation, 
 after precipitating the dissolved lead by H 2 S. 
 
 Glycerine has been made artificially from propylene by com- 
 bining it with chlorine to form propylene chloride, CH,C1'CHC1'CH 3 , 
 which is heated with iodine chloride to convert it into propenyl 
 tri-iodide, CH 2 I'CHI-OH 2 I ; by heating this in a sealed tube, with much 
 water, at 160 0., it is converted into glycerine; C 3 H 5 I 3 + 3HOH == 
 C 3 H 5 (OH) 3 + 3HI. This synthesis, together with the fact that glycerine 
 can be made by oxidising ally! alcohol, CH 2 : CITCH 2 OH, establishes 
 the constitution of glycerol, if it be admitted that one carbon atom 
 cannot hold two OH groups. 
 
 Properties of glycerine. Resembles syrup in taste and consistence ; 
 sp. gr. 1.269 at 12 C. ; boils at 290 C., but then undergoes partial 
 decomposition. At 12 mm. pressure it boils at 170 C. It is slightly 
 
PEOPEETIES OF GLYCERINE. 577 
 
 volatile at 100 C., but not at the ordinary temperature. If kept at 
 o C. for some time, a strong aqueous solution of glycerine deposits 
 crystals, especially if a ready-made crystal be introduced ; pure glycerine 
 solidifies at - 40 0. to a gummy mass, which melts at 17 C. It does 
 not inflame until heated to 150 C., when it burns with a flame resem- 
 bling that of alcohol. It absorbs water easily from the air, and dissolves 
 without limit in water and alcohol, but is insoluble in ether. 
 
 On account of its never drying, glycerine is useful in many cases when 
 it is desired to keep any substance moist and supple. Water mixed 
 with an equal weight of glycerine is sometimes used in gas-meters, being 
 much less easily frozen than water, and less liable to dry up. Glycerine 
 is used in pharmacy, but its chief application is in making nitro- 
 glycerine (q.v.). 
 
 Glycerine possesses extensive solvent powers, like alcohol, dissolving 
 most substances which are soluble in water, and some others, such as- 
 metallic oxides, which are insoluble in water. 
 
 A characteristic property of glycerine is that of yielding an exceedingly 
 pungent and irritating substance, known as acrolein, or acrylic aldehyde? 
 C.,H 3 'CHO, when sharply heated, or subjected to the action of dehy- 
 drating agents, 3 H 3 (OH) 3 = C 3 H 3 'CHO + 2H 2 O. The best test for 
 identifying glycerine is to mix it with powdered KHS0 4 and heat it 
 strongly, when the intolerable odour of acrolein is perceived. It is this 
 substance which causes the offensive smell of smouldering candles made 
 of tallow and other glycericles. 
 
 By treatment with a mixture of nitric and sulphuric acids glycerine 
 is converted into nitroglycerine or glyceryl trinitrate, C 3 H 5 (N0 3 ) 3 , a 
 powerfully explosive compound which will be described in the section 
 on ethereal salts. 
 
 As glycerol contains two primary alcohol groups, CH 2 OH, which are known to 
 be oxidisable first to aldehyde groups, CHO, and then to" acid groups, COOH, and 
 also a secondary alcohol group, which is oxidisable to a ketone group, CO, no fewer 
 than ii oxidation-products of glycerol are theoretically possible. Only six, how- 
 ever, are at present known, namely : glyceric aldehyde, CHO*CHOH'CH 2 OH : 
 dihydroxyacetene, CH 2 OH-CO'CH 2 OH ; glyceric acid, COOH-CHOH'CH 2 OH : 
 tartronic acid, COOH'CHOITCOOH ; mesoxalic acid, COOH'C(OH) 2 -COOH ; and 
 hydroxypyroracemic acid, CH OH'CO'COOH. Except the last named, all these 
 are obtainable by the direct oxidation of glycerol. When H 2 2 (in presence of a 
 small quantity of a ferrous salt) is the oxidant, a mixture of glyceric aldehyde and 
 dihydroxyacetone is formed which was originally supposed to be a single com- 
 pound and was called " glycerose." Dilute nitric acid produces glyceric and 
 tartronic acids, while oxidation with bismuth nitrate and nitre forms mesoxa 
 acid. More energetic oxidising-agents yield glycollic acid, CH 2 OH'COOH ; oxalic 
 acid, COOH-COOH ; and glyoxylic acid, CHO'COOH. 
 
 When reduced with hydriodic acid glycerol yields allyl iodide, CH 2 : CH -,H 2 1 ; 
 isopropyl iodide, CH 3 'CHrCH 3 ; and propylene, CH 3 'CH : CH 2 . 
 
 Two compounds corresponding with the ethoxides may be 5*~ n ~_!j^JP 
 action of sodium ethoxide on glycerol in alcohol, sodium propenoxide, C 3 H 6 (OH> 2 UiNa, 
 and disodium . propenoxlde, C.,H 5 OH(ONa) 2 . 7/7 
 
 By treating a-chlorhydrin (V/.r.), with BaO, HC1 is abstracted and glyctde 
 
 is obtained : ^' H * ,- HC1 = 0<?* 2 _ W ; this is a colourless liquid, boiling 
 
 HOC'OH 2 Orl N LI 2 U1 
 
 with decomposition at "162 C. It combines with water to form glycerol. 
 
 349. Tetrahydric and Higher Polyhydric Alcohols-.Alcohols 
 ntaining 4, 5, 6, 7, 8, and 9 hydroxyl groups are known. 
 
 eatin t 
 
 contanng 4, 5, , 7, , an 9 yroxy group . 
 
 of hydroxyl groups present in an alcohol is ascertained by heating t 
 
578 POLYHYDEIC ALCOHOLS. 
 
 ^alcohol with acetic anhydride, (CH 3 CO) 2 0, and sodium acetate, when as 
 many acetic acid radicles (acetyl, CH 3 CO) enter into the composition of 
 the alcohol, as there are hydroxyl groups in the alcohol ; for example, 
 the compound called erythrite is known to be a tetrahydric alcohol, 
 because it forms an acetate containing four acetyl groups ; 
 
 C 4 H 6 (OH) 4 + 4 (CH 3 CO) 2 = C 4 H 6 (OCH 3 CO) 4 + 4 CH 3 COOH. 
 The lowest member of each series of polyhydric alcohols must have at 
 least as many carbon atoms as it has OH groups, otherwise one carbon 
 atom would have to hold two hydroxyl groups, and the compound would 
 break up (p. 573). The derivatives and oxidation-products of these 
 alcohols are similar in constitution to those of glycol. 
 
 Most of the higher alcohols that are known are obtained from natural 
 sources ; they are many of them sweet, and some were for long classed 
 with the sugars, with which, indeed, they are closely connected. 
 
 Erythrite, erythritol, or phycite, C 4 H 6 (OH) 4 , or CH 2 OH-[CHOH]o-CH 2 OH, is 
 obtained from certain lichens, such as the Itoccella tinctoria, or Orchella weed, by 
 boiling with milk of lime, filtering, precipitating the excess of lime by C0 2 , 
 evaporating the filtrate to a small bulk, and treating with alcohol, when erythrite 
 crystallises in prisms, which fuse at 126 C. and sublime at 300, though not quite 
 undecornposed. It is easily soluble in water, and has a sweet taste ; sparingly 
 soluble in cold alcohol, and insoluble in ether. 
 
 In several of its reactions erythrite resembles glycerine. When it is dissolved 
 in nitric acid, and sulphuric acid added, it yields a crystalline precipitate of nitro- 
 erythrite, C 4 H 6 (N0 3 ) 4 , which is explosive like nitroglycerine. 
 
 If, in the treatment of the lichen, cold milk of lime be used, the filtrate, when 
 saturated with C0 2 , gives a mixed precipitate of calcium carbonate and erytlu-ni, 
 which may be extracted by alcohol, and crystallised. Erythrin is erythrite di- 
 orsellinate, C 4 H 6 (OH) 2 (OC 8 H 7 3 ) 2 , and belongs to the class of ethereal salts. It 
 appears to exist as such in the lichen, and is decomposed into erythrite and calcium 
 orsellinate when boiled with calcium hydroxide. Erythrite exists ready formed in 
 certain algcc, notably in Protococcus vulgaris. This natural erythrite is optically 
 inactive. Both it a,nd another inactive form (believed to be internally compensated 
 see p. 621) may be synthetised from divinyl CH 2 : CH'CH : CH 2 by adding Br 
 to form two dibromides, which are stereoisomerides and can be oxidised by per- 
 manganate to corresponding bromhydrins CHoBr[CHOH] 2 CH 2 Br ; these yield the 
 natural erythrite and its isomeride (m. p. 72 C.) when treated with KOH and 
 water. A dextro- and a lasvo-erythritol have also been obtained. 
 
 Arabite, or araUtol, CH 2 OH-|~CHOH] 3 -CH 2 OH, is obtained by reducing arabiwnt 
 (q.v.) with nascent hydrogen. It melts at 102 C. 
 
 Mannite,ormawm'^,CH 2 OH'[CHOH] 4 -CH 2 OH,ahexahydric alcohol, 
 is a sweet substance contained in manna, from which it may be ex- 
 tracted by boiling with alcohol, when it crystallises, on cooling, in fine 
 needles, fusing at 166 C. It is rather sparingly soluble in cold water 
 and alcohol, but easily on heating, and is insoluble in ether. When 
 oxidised in presence of platinum black, it yields the sugar mannose, 
 C 6 H 19 6 (q.v.), and when this is further oxidised it becomes mannonic 
 acid, CH 2 OH-[CHOH] 4 -C0 2 H. The natural mannite is dextro-rotatory ; 
 a IJEVO- and an inactive form are also known, as will be explained later, 
 
 By treatment with nitric acid, mannite is converted into an explosive crystalline 
 body, which is nitromannite, or mannyl hexanitrate, C 6 H 8 (N0 3 ) 6 , re-converted into 
 mannitol by (NH 4 ) 2 S. When treated with HI, mannite becomes secondary hexyl 
 iodide, 
 
 CH 2 OH-CHOH-CHOH-CHOH-OHOH-CH 2 OH + n HI = 
 
 CH 3 -CH 2 -CH 2 -CH 2 -CHrCH.5 + 6HOH + I 10 . 
 
 Mannite is found among the products of the viscous fermentation of saccharine 
 liquors, when they are said to become ropy ; beet-root juice is especially liable to 
 this change. 
 
CONSTITUTION OF ALDEHYDES. 
 
 Mamiite is an important substance in vegetable chemistry, since it occurs not 
 only in manna, the dried exudation of the Ornus, or manna ash, growing in the 
 South of Europe, but also in the sap of the common ash (Fraaeinu* excelsior*) of the 
 larch, apple, cherry, and lime ; in the leaves of the syringa and privet in the bulbs 
 of Cyclamen europawm (sow-bread), in the bark of the wild cinnamon in some 
 lichens, seaweeds, sugar-cane, mushrooms, celery, asparagus, olives, and onions 
 The seaweed Laminaria saccliarina, or sugar-wrack, contains 12 per cent of 
 mannite, which is sometimes found as an efflorescence on the surface of the weed. 
 It has also been found in the root of the monkshood (Aeonitum napellus). The 
 Agaricus Integer, a common fungus, contains when dry about 20 per cent, of 
 mannite. 
 
 Mannitane, C 6 H 8 (OH) 4 0, is prepared by heating mannite to 200 C. ; C ri H 8 (OH) 6 = 
 C 6 H 8 (OH) 4 + H 2 0. It is a viscous substance very similar to glycerol. and form- 
 ing compounds when heated with the fatty acids which closely resemble the 
 glycerides, and are saponified by alkalies in the same way. 
 
 Dulcite, or chdcitol, is isomeric with mannite, and much resembles it. It is 
 extracted from Madagascar manna by boiling water. It is nearly twice as soluble 
 in water as mannite is, but much less soluble in alcohol. It melts at 188 C. 
 
 Sorbitol, C 6 H 8 (OH) 6 , another isomeride of mannite, is found in the berries of the 
 mountain ash (tiorbus aucuparia). It is more fusible (110 C.) than the others. 
 
 II. ALDEHYDES. 
 
 350. These compounds are the first products of the oxidation of 
 
 ^H 2 
 
 all alcohols containing the primary alcoholic group -C\ , which 
 
 X OH 
 
 //VL 
 becomes 'C ? + HOH. They differ from the parent alcohols by two 
 
 atoms of hydrogen ; thus, ethyl alcohol, CH 3 'CH,OH, yields acetic 
 aldehyde, CH 3 'CHO, and so on, there being one or more aldehydes 
 corresponding with each of the alcohols already described. They 
 readily pass by oxidation into the corresponding acids, the group 
 
 ^ //> 
 
 C \ becoming 'C \ , and are named after the acids into which 
 
 H OH 
 
 they are converted. Since the oxidation of primary alcohols to 
 aldehydes consists merely in the removal of H 2 (whence the name 
 al[cohol] dehyd\rogenatum\), and since the aldehyde in all its reactions 
 appears still to contain the hydrocarbon radicle which was con- 
 tained in the alcohol, the above view of the constitution of these com- 
 pounds may be presumed to be correct. It is supported by the fact 
 that when an aldehyde reacts with PC1 5 the oxygen atom is exchanged 
 for two chlorine atoms, CH 3 'CHO + P01 5 = CH 3 'CHCl a + POC1 3 , showing 
 that the aldehyde cannot contain the in the form of OH. For when 
 a compound containing OH reacts with PCl b , the OH is exchanged for Cl 
 and II Cl is a product of the reaction, e.g., CH 3 'CH 2 OH + PC1 5 = 
 CH,'CH 2 C1 + POC1 3 + HC1. Position isomerism can only occur in the 
 radicle of the aldehyde ; thus, in the general formula, R'CHO, R may 
 occur in isomeric forms, but there are no secondary and tertiary 
 aldehydes in the sense that there are secondary and tertiary alcohols. 
 
 As already stated (p. 573), glycols of the type R'CH(OH) 2 do not 
 exist, although many compounds are known which might be expected 
 to yield them under appropriate treatment ; for instance, by analogy 
 with the reaction between ethyl chloride and moist silver oxide, that 
 
580 PARAFFIN ALDEHYDES. 
 
 between this oxide and ethylidene chloride, CH 3 'CHC1 2 , might be expected 
 to yield ethylidene glycol CH 3 'CH(OH) 2 , but as a fact yields aldehyde 
 and water, CH 3 'CH(OH) 2 , becoming CH 3 'CHO + HOH. Thus the 
 aldehydes may be regarded as the anhydrides of these unknown 
 glycols, and it may be supposed that the latter are the true products of 
 oxidation of the primary alcohols, being formed by the substitution of 
 OH for a second H atom in the parent hydrocarbon ; the glycol thus 
 formed, however, at once passes into its anhydride, the aldehyde. This 
 view of the process of oxidation is supported by the oxidation of the 
 aldehyde to the acid, consisting of the substitution of OH for H. The 
 following formulae make these remarks clear, but it must be remem- 
 bered that the alcohol is not formed by oxidation of the hydrocarbon : 
 
 /H /OH /OH; 
 
 R-C(-H R-C^-H R-CeOH R C \ 
 
 \H \H NH H X OH 
 
 Hydrocarbon. Primary Unknown Aldehyde. Acid. 
 
 alcohol. 
 
 R\ /H R v /OH 
 
 R><H K><H 
 
 Hydrocarbon. Secondary Unknown Ketone. 
 
 alcohol. glycol. 
 
 The aldehydes are unsaturated in the sense that the oxygen atom is 
 doubly linked to carbon, and they show a tendency to combine as a 
 whole with other compounds, the aldehyde group 'CH = becoming 
 
 *CH/ . This tendency leads to the formation of derivatives of 
 
 the aforesaid unknown glycols and to a number of nucleal condensa- 
 tions (p. 531), which render the aldehydes useful in building up new 
 carbon nuclei. The chief reactions of this kind will be noticed in the 
 description of acetic aldehyde, the behaviour of which is identical with 
 that of the majority of aldehydes. 
 
 The readiness with which the aldehydes undergo oxidation to the 
 corresponding acids makes them powerful reducing-agents. 
 
 351. Aldehydes from the Paraffin Alcohols. The oxidation of 
 the primary alcohols is not the only general reaction for preparing the 
 aldehydes of this series. They may be obtained by distilling a dry 
 mixture of calcium formate and the calcium salt of the acid corre- 
 sponding with the adlehyde required. 
 
 HCOO V C 2 H 5 COO V C 2 H 5 COH 
 
 >Ca + _)>Ca = + 2CaCO 3 
 
 HCOO C 2 H 5 COO C 2 H 5 COH 
 
 Calcium Calcium Propionic 
 
 formate. propionate. aldehyde. 
 
 Formic aldehyde, formaldehyde, or methyl aldehyde, H'CHO, is a gas 
 and boils at 2 1 C. It is formed when a mixture of methyl alcohol 
 vapour and air is passed over a red-hot platinum wire, CH 3 t OH + = 
 H'CHO + HOH. It is now made on a large scale by a secret process 
 and sold in aqueous solution containing 40 per cent, under the name of 
 formaline f or use as an antiseptic and in the manufacture of dye-stuffs ; 
 
ALDEHYDE. 581 
 
 the solution has a suffocating odour and reduces ammoniacal silver 
 
 nitrate. 
 
 Formaldehyde is formed when a mixture of CO and H 2 is treated in an ozoniser 
 (p. 65) and in small quantity when calcium formate is destructively distilled. By 
 cautiously oxidising methyl alcohol with Mn0 2 and H 2 S0 4 some of the CH 3 OH 
 is oxidised to H'CHO and combines with more CH 3 OH to form methylal or 
 formal (inethylene dimethyl ether"), CH 2 (OCH 3 ) 2 , a liquid (b.-p. 42 C.) used as a 
 soporific and as a solvent ; when this is distilled with a dilute acid it yields 
 formaldehyde and methyl alcohol. 
 
 Paraformaldehyde is a solid polymeride (CH 2 0) X formed when an aqueous 
 solution of formaldehyde is allowed to evaporate ; when heated it is converted into 
 another polymeride, tr'wxymethylene or meta formaldehyde (CH 2 0) 3 which melts at 
 171 C. and then becomes the gas CH 2 0. By prolonged contact with lime-water 
 formaldehyde is polymerised to a mixture of sugars (formose), a change which may 
 occur, through some agency, in the synthesis of sugar by plants, since formaldehyde 
 has been found in green plants. 
 
 Formaldehyde is used in synthetic chemistry for introducing the methylene 
 group (CH 2 ) into compounds, its oxygen atom readily combining with H 2 and 
 removing them as water, leaving the : CH,, group to take their place, thus : 
 K-NH 2 + : CH 2 = R'N : CH 2 + H 2 0. 
 
 Acetic aldehyde, CH 3 -CHO, is obtained by distilling alcohol with 
 potassium bichromate and sulphuric acid. This process requires much 
 care, on account of the violence of the action and the volatility of the 
 aldehyde. 
 
 Three parts of potassium bichromate, in crystals free from powder, are placed in 
 a flask or retort surrounded by ice (or by a mixture of sodium sulphate crystals 
 with half their weight of HC1), and a mixture of 2 parts of ordinary alcohol, 
 4 parts sulphuric acid, and 12 parts of water, also previously cooled in ice, is added. 
 The flask or retort is then connected with a condenser containing iced water, and 
 the refrigerating mixture removed, when the aldehyde will generally be distilled 
 over by the heat attending the reaction. The impure aldehyde thus obtained is 
 re-distilled on the water-bath in the apparatus shown in Fig. 271. The aldehyde, 
 
 Fig. 271. Preparation of aldehyde. 
 
 freed from alcohol and aqueous vapour which condense in 
 passes over and is dissolved in dry ether contained in the 
 The ethereal solution of aldehyde is saturated with dry ammonia, wheieupor 
 
582 PROPERTIES OF ALDEHYDE. 
 
 whole of the aldehyde is separated in the form of colourless crystals of aldeliy de- 
 ammonia, which is sparingly soluble in ether ; this is drained upon a filter, and 
 distilled with diluted sulphuric acid in- a flask or retort, heated by a water-bath, and 
 connected with a condenser filled with ice water. The aldehyde may be freed from 
 water by standing over fused calcium chloride, and distillation. 
 
 The preparation of aldehyde illustrates the use of K 2 Cr 2 O 7 and 
 H 3 S0 4 as an oxidising-agent upon organic bodies. Neglecting certain 
 secondary reactions, the production of aldehyde may be represented by 
 the equation 
 
 3(CH 3 -CH 2 OH) + K 2 0'2Cr0 3 + 4(H 2 0'S0 3 ) = 
 3 (CH 3 -CHO) + 7H 2 + K 2 OS0 3 + Cr 2 3 '3S0 3 . 
 
 On a large scale, aldehyde is obtained as a by-product in the manu- 
 facture of alcohol, when it comes over with the first portion of the 
 distillate. Commercial alcohol generally contains a little aldehyde. 
 
 Aldehyde may also be obtained by distilling a mixture of an acetate 
 and a formate (see above). 
 
 Properties of aldehyde. Sp. gr. 0.80 at o 0. ; boiling-point 20. 8 C. 
 Aldehyde has a peculiar acrid odour, which affects the eyes. It mixes 
 in all proportions with water, alcohol, and ether. It has a great dis- 
 position to combine with oxygen to form acetic acid : CH 3 -CHO + = 
 CH 3 -COOH. Hence aldehyde acts as a reducing-agent, and one of the 
 tests for it is the reduction of silver from its salts. If a few crystals of 
 aldehyde-ammonia be dissolved in water, a little silver nitrate added, 
 and a gentle heat applied, the silver will be deposited on the sides of 
 the vessel, giving them the reflecting power of a mirror. A general 
 test for aldehydes is their power of restoring the red colour to a 
 solution of a salt of rosaniline which has been bleached by sulphurous 
 acid. 
 
 Another characteristic property of aldehydes is that of forming 
 crystalline compounds with sodium bisulphite. If aldehyde be 
 mixed with a saturated solution of NaHS0 3 , it forms a crystalline 
 compound, which is the sodium salt of ethylidene glycol sulphonic acid, 
 CH 3 -CH(OH)(S0 2 ONa), combined with H 2 ; from this the aldehyde 
 may be obtained by distillation with either acid or alkali. 
 
 When mixed with potash, and gradually heated to boiling, most of 
 the paraffin aldehydes yield brown-yellow substances of peculiar odour, 
 known as aldehyde resins ; their chemical constitution is uncertain. 
 
 Nascent hydrogen (water and sodium amalgam) converts aldehyde 
 into alcohol ;" OH^CHO + H 2 = CH 3 -CH 2 OH (alcohol). 
 
 Aldehyde combines with ammonia forming a compound, aldehyde- 
 ammonia, which is probably an amine of the hypothetical ethylidene 
 glycol, CH 3 -CH(OH)(NH S ) ; with HCN" to form ethylidene cyanohydrin 
 or lactonitrile, CH 3 'CH(OH)(CN); with alcohol to iovrndiethyl ethylidene 
 ether or acetal, CH 3 'CH(OC 2 H 5 ) 2 , a liquid which boils at 104 C. and is 
 formed in old wine and in the last runnings of spirit stills. 
 
 When there is no other compound with which aldehyde can combine, 
 it tends to combine with itself or polymerise. 
 
 For example, perfectly pure acetic aldehyde can be kept unchanged, but in the 
 presence of a very little dilute acid or of zinc chloride it is converted into aldol, 
 which is a (secondary) alcohol-aldehyde, CH 3 -CHOH'CH 2 -CHO (hydroxy-fadyric 
 aldehyde) ; this resembles aldehyde in appearance and general reactions, but its 
 sp. gr. is 1. 1 20 and it does not distil unchanged ; it becomes viscous on standing. 
 
OLEFINE ALDEHYDES. 
 
 583 
 
 A condensation of two or more molecules in this way occurs in many other com- 
 pounds, and is always termed, by analogy, an aldol condensation. 
 
 By adding a drop of strong H 2 S0 4 to aldehyde, much heat is evolved and the 
 liquid becomes specifically heavier (sp. gr. o.99at 20 C.) : this liquid is paraldehude 
 <^H 12 3 , or /0-CH(CHA 
 
 CH 3 -CH< 3 
 
 N 
 
 It boils at 124 C. and melts at 10 C. ; it is less soluble in hot water than in cold, 
 and when distilled with dilute H 2 S0 4 it becomes aldehyde again. Metaldelujde is a 
 stereoisomeride of paraldehyde, produced in the same way, but at o C. It forms 
 white crystals, insoluble in water, but soluble in ether and in alcohol ; it sublimes 
 when heated to 112 C., without melting, and when heated in a sealed tube at 116 
 C., it becomes aldehyde again ; the crystals are said to become brittle and opaque 
 after a time, owing to a further polymerisation to C 8 H ]6 4 , tetraldehyde. 
 
 Other characteristic reactions of the aldehydes are the formation of 
 
 aldoximes by reaction with hydroxylamine (p. 103): CH 3 'CH|0 + H^:N-OH = 
 
 phenylhy 
 
 <!<>]( ide h 
 
 (acetaldoxime) ; and the formation of hydrazones with 
 ydrazine; CH 3 -CHO + H 2 :N-NHC 6 H 5 = HOH + CH 3 -CH:N-NHC 6 H 5 (acetal- 
 di'Jti/de ltydra:one. 
 
 Aldehyde, in the form of paraldehyde, and some of its derivatives, such as acetai 
 (>-?.), are used as soporifics (cf. chloral). Aldehyde also finds application in the 
 manufacture of dyes. 
 
 352. The chief known homologues of acetic aldehyde are shown in the following 
 table :* 
 
 Chemical Xame. Source. Formula. 
 
 Propionic aldehyde Oxidation of propyl alcohol . C 2 H 5 CHO (49) 
 
 Butyric . butyl . C 3 H 7 CHO (74) 
 
 Valeric . amyl . C 4 H 9 CHO (102) 
 
 Caproic . / Distillation of calcium formatej CH . C HO (128) 
 
 ^ with calcium caproate . J 
 
 (Enanthic ., . Distillation of castor oil . . C 6 H ]3 CHO (155) 
 
 Caprylic ., ., . . C 7 H 15 CHO (160) 
 
 Kutic . Oil of rue C 9 H 19 CHO - 
 
 Laurie . ..... C n H 23 CHO [44-5] 
 
 Myristic C^H^ ' CHO 52.5] 
 
 Palmitic . . C 15 H 31 CHO 58.5] 
 
 Stearic . . . . . -. . C^H^ CHO 63.5^ 
 
 Acetic, propionic, and butyric aldehydes occur among the products of the oxidis- 
 ing action of a mixture of manganese dioxide with sulphuric acid upon albumin, 
 fibrin, and casein. 
 
 Thioaldehydes, in which sulphur takes the place of oxygen, are known only in 
 polymeric form, corresponding with the polymerised aldehydes. TrtohioformM* 
 dehtjde (CH 2 S) 3 melts at 216 C., trithioacetadehyde (CH 3 CHS) 3 , occurs in an a and 
 |8 form melting at 101 and 125 C. respectively. Mercaptal is the thio-denvative, 
 corresponding with acetai (p. 582). By oxidation the thio-aldehydfs yirl 
 sulphones. 
 
 . . 
 
 353. Aldehydes from the Olefine Alcohols. Acrolein, or acrylic aMehya* 
 CH :CH-CHO, the aldehyde of allyl alcohol, is prepared by distilling glvcerftw ' 
 twice its weight of KHS0 4 , which abstracts the elements of two molecules on 
 C,H 5 (OH) 3 =C.-H 3 -CHO + 2H 2 O. The crude acrolein is shaken with I 
 remove S0 2 , and rectified over CaCL, to remove the water. 
 
 Acrolein is a liquid distinguished" by a very powerful irritating odour, 
 sp. gr. 0-84, and boils at 52 C. It dissolves sparingly in water, but easil 
 and ether. Unlike most aldehydes, it does not combine with NaHM>, . 
 forms a resinous body with alkali, and reduces ammoniacal AgJs0 3 , whi< 
 it into acrylic acid, C H.,-C0 2 H. Sodium amalgam and water (nascent li 
 convert it into allyl alcohol, C 2 H 3 'CH 2 OH. When kept, acrolein b 
 
 * The boiling-points are in round brackets (...), the melting-points in square b 
 Centigrade scale. According to the new system the aldehydes are named ] 
 the termination -at being substituted for -ol (see foot-note p. 568). 
 
584 AROMATIC ALDEHYDES. 
 
 solid, disacryl, probably a polymeride. HC1 gas passed into acrolein converts it 
 into a crystalline body, ft-chloropropylaldehyde, CH 2 01'CH 2 'CHO, which, when 
 distilled with potash, yields metacrolein, C 9 H 12 O 3 (m.-p. 45 C.), corresponding with 
 paraldehyde. 
 
 Crotonic aldehyde, CH 3 'CH:CITCHO, is prepared by heating acetic aldehyde to 
 100 C. for two days in contact with ZnCl 2 and a little water. The ZnCl 2 acts as 
 a dehydrating agent; 2(CH 3 -CHO) = H 2 + C 3 H 5 'CHO (aldehyde condensation'). 
 The unchanged aldehyde is distilled off, some water added, and the distillation 
 continued, when water and crotonic aldehyde distil over. It has an irritating- 
 odour like acrolein, boils at 104 C.. and is sparingly soluble in water. When 
 oxidised by air or silver oxide, it yields crotonic acid, C 3 H 5 'C0 2 H. It occurs in 
 some kinds of fusel oil. 
 
 353. Aldehydes from Dihydric and Polyhydric Alcohols. 
 
 These may be di- or poly-aldehydes and aldehyde-alcohols ; the latter are 
 of much importance, as they include several sugars, like glucose and 
 mannose. These compounds are not considered under this heading, 
 however, for their near relationship to compounds in other classes will 
 be best set forth by treating them in a separate section. The student 
 is therefore referred to the chapter on carbohydrates for a description 
 of the sugars. 
 
 Glyoxal, or oxalic aldehyde, CHO'CHO, is prepared by slowly oxidising acetic 
 aldehyde with dilute nitric acid. It occurs among the products of the regulated 
 action of nitric acid on alcohol and glycol. (See p. 575.) 
 
 It is a deliquescent solid, soluble, in water, alcohol, and ether, forming a crys- 
 talline compound with two mols. NaHS0 3 , and reducing silver nitrate, becoming 
 oxidised to oxalic acid, C0 2 H/C0 2 H, and glyoxylic acid, CHO'C0 2 H. Alkalies 
 oxidise one CHO group and reduce the other, forming glycollic acid, CH 2 OITCOOH. 
 With ammonia, it yields gly cosine ; 3C 2 H 2 2 + 4NH 3 :=6H 2 + N 4 (C 2 H 2 J 3 . Glyoxal 
 combines with 2HCN to form the nitrile of tartaric acid, CH(OH)(CN)'CH(OH)(CN). 
 
 Gly eerie aldehyde or glycerose, CH 2 OH'CHOH'CHO, is an aldehyde-alcohol 
 obtained by the careful oxidation of glycerol (p. 577). By condensation it is con- 
 verted into acrose, one of the sugars. 
 
 354. Aldehydes from the Aromatic Alcohols. Benzaldehyde, 
 
 benzole aldehyde, or bitter-almond oil, C 6 H 5 -CHO, was originally made by 
 distilling the moistened bitter-almond cake from which the fixed oil had 
 been extracted by pressure. The cake was placed in a perforated vessel 
 and subjected to the action of steam, which carried over the oil and 
 deposited it as a heavy layer on standing. 
 
 The bitter-almond oil does not exist ready formed in the almond, 
 but is a product of the decomposition of the bitter substance, amygdalin, 
 C 20 H 27 NO n , of which the bitter almond contains about 5 per cent. 
 This substance is a glucoside, and is decomposed, in the presence of 
 water and of a peculiar albuminoid ferment present in the almond 
 and known as emulsin* into glucose, bitter almond-oil, and hydrocyanic 
 acid, C 20 H ?7 N0 11 + 2H 2 O=2C 6 H 12 6 + C 7 H 6 O + HCN. The presence of 
 hydrocyanic acid renders the crude oil of bitter almonds poisonous. It 
 may be purified either by re-distilling with lime and ferrous chloride, 
 when the HCN is converted into a ferrocyanide ; or by shaking it with 
 an equal volume of a strong solution of NaHS0 3 , which combines with 
 the benzoic aldehyde to form a crystalline compound, from which the 
 pure oil may be obtained by distillation with sodium carbonate. 
 
 Benzaldehyde is now made artifically from toluene. When chlorine 
 is passed into boiling toluene, preferably in sunlight, benzol chloride, 
 
 * The terms zymase, enzyme, and liydrolyst have be?n applied to such unorganised 
 ferments. 
 
BENZALDEHYDE. 585 
 
 C 6 H.-CHC1 2 , is produced. By heating this with lime under pressure, it 
 is converted into bitter-almond oil 
 
 C 6 H 5 -CHCL> + Ca(OH) 2 = CaCl. 2 + H 2 + C 6 H 5 'CHO. 
 Or the chlori nation of the toluene is stopped when benzyl chloride, 
 CgH. 5 -CH 8 Cl, has been formed, and this is then heated with lead 
 nitrate 
 
 2C 6 H 5 -CH 2 C1 + Pb(N0 3 ) 3 - 2 C 6 H 5 -CHO + PbCl 2 + 2 HN0 2 . 
 
 Benzoic aldehyde is a colourless or pale yellow liquid, of characteristic 
 odour, boiling at 179 C., and of sp. gr. 1.05. It is very sparingly 
 soluble in water, but dissolves in alcohol, and is precipitated on addition 
 of water. It is often sold in alcoholic solution. The oxidising action 
 of air gradually converts benzoic aldehyde into crystals of benzoic acid ; 
 C 6 H 5 -CHO + = C 6 H,-C0 2 H. The presence of hydrocyanic acid retards 
 this conversion. 
 
 The aromatic aldehydes show reactions very similar to those of the 
 fatty aldehydes. They are, however, less powerful reducing-agents, 
 and instead of resinifying with alkalies, they are converted into the 
 corresponding alcohol and acid, one part being reduced and the other 
 oxidised : 2 C 6 H 5 -CHO + KOH = C 6 H 5 'CH 2 OH + C 6 H 5 'COOK. 
 
 Moreover, with NH 3 they do not combine directly, but are converted 
 into compounds like hydrobenzamide, a crystalline substance, m.-p. 
 no c C. ; 3 (C 6 H 5 -CHO) + 2NH 3 = (C 6 H 5 -CH) 3 -N 2 + 3H 2 0. 
 
 They show a remarkable tendency to condense with other compounds 
 under influence of dehydrating agents, the aldehydic oxygen combining 
 with two H atoms from the other compound. Thus by action of HC1 
 gas on a mixture of benzaldehyde and acetic aldehyde, cinnamic alde- 
 hyde is formed ; C 6 H 5 CHO + CH 3 'CHO = C 6 H 5 'CH : OH'CHO + H 2 0. 
 
 Beuzaldehyde dissolves in a strong solution of Na. 2 S0 3 , and if dilute H 2 S0 4 be 
 added, drop by drop, to the solution, voluminous crystals of C 6 H 5 'CHONaHS0 3 
 are deposited ; these dissolve on heating but are deposited again on cooling. By 
 reduction with Na-amalgam, benzaldehyde yields benzyl alcohol and hydro- 
 benzoin (p. 575). 
 
 Benzaldoxime, C 6 H 5 'CH : N'OH exists in an a-form (m.-p. 35 C.), and a 
 0-form (m.-p. 125 C.), which passes into the a-form when heated. These are 
 stereoisomerides (see acetoximes). 
 
 Cmii'tnic', or cumic aldehyde, or cuminol, is I : ^-itopropylfanz&ldekydt, C 6 H 4 'C 3 H/ 
 CHO, and occurs in the aromatic oils of cummin, caraway, and water-hemlock, all 
 umbelliferous plants ; it is extracted from the oil by shaking with solution of 
 NaHSOo, which forms a crystalline compound with it. It is liquid, fragrant, and 
 boils at 235 C. 
 
 Cinnamic aldehyde, C 6 H 5 'CH : CH'CHO, occurs in the essential oils of cinnamo 
 and cassia, and is very similar in its chemical properties to benzaldehyde. When 
 oxidised, it yields cinnamic acid, C 8 H/C0 2 H. It may be obtained from benzoic and 
 acetic aldehydes, as above mentioned. 
 
 355. The hydroxy-aromatic aldehydes, like salicylic aldehyde, 
 C 6 H 4 (OH)-CHO (hydroxybenzaldehyde), have an OH attached directly 
 to the benzene ring, and are therefore phenol aldehydes, corresponding 
 with the phenol alcohols (p. 5 7 1 ). Besides their formation by oxidation 
 of these alcohols, the hydroxy-aromatic aldehydes are produced by I 
 nucleal condensation between the phenols and chloroform, producec 
 heating the mixture with aqueous alkali (Reimer's reaction). 
 (\.H 5 -OH + CHC1 3 + 4 KOH = C 6 H 4 (OK)'CHO + 3KC1 
 Phenol. Chloroform. Potassium salicylaldeliyde. 
 
5"86 FUEFUEAL. 
 
 The potassium compound is distilled with dilute acid to obtain the 
 aldehyde. 
 
 In this reaction the alkali is required to absorb the HC1 which is formed when 
 water alone is used, and which must be removed to prevent back action, the 
 change being reversible. 
 
 Salieyl aldehyde is 0rMe-hydroxybenzaldehyde, there being, of course, three 
 isomerides of this disubstitution product. It exists in oil of spir&a (meadow- 
 sweet), and is made by oxidising saligenin (p. 572), or from phenol as described 
 above. Its sp. gr. is 1.17, and it boils at 196 C. It dissolves in alcohol, but 
 sparingly in water. It resembles benzaldehyde in most reactions but exhibits some 
 characteristic of its phenol character, such as the ferric chloride coloration 
 and the exchange of H for K by treatment with KOH forming C 6 H 4 (OK)'CHO. 
 Like other orthohydroxyaldehydes it stains the skin yellow. 
 
 Anisic aldehyde, C 6 H 4 (OCH 3 )-CHO, is paramethojnjlenzaUehtjde. the methyl 
 derivative of parasalicylic aldehyde ; it is prepared by heating the essential oils of 
 anise and fennel (both umbelliferous plants) with dilute HXO^, being forme d by 
 the oxidation of anethol (#.r.) which these oils contain. It is a fragrant li'iuid, 
 boiling at 248 C. 
 
 Dihydroxybenzaldehydes are also known. The I : 3 ^-derivative. 
 
 aldehyde, C 6 H S (OH;. 2 -CHO[CHO : (OH) 2 =i : 3 14] is obtained from pyroeatechol, 
 C 6 H 4 (OH>, and chloroform by Reimer's reaction (r.*.) ; it melts at 153 C. When 
 methylpyrocateehol, C 6 H 4 (OH)(OCH 3 ), is similarly treated it yields the methyl 
 derivative of protocatechuic aldehyde, CgHgCOHXOCH^-CHO ; this is m/< 
 an aromatic substance, much used for flavouring, extracted from the poi- 
 Vanilla planifolia, a Mexican orchidaceous plant, by boiling them with alcohol. 
 It forms needles, melts at 80 C., and sublimes. It is sparingly soluble in water, 
 Vanillin is now made artificially by oxidising eoniferine, C^H.^Og, by chromic acid. 
 Coniferine is a crystalline glucoside. extracted from pinewood ; when oxidised it 
 yields glycora nillin, the glucoside of vanillin, C^^CCH^O C 6 H U O5)-CHO. which 
 yields glucose and vanillin on hydrolysis. 
 
 Piperonal or heliatropine is m'ethyleneprotocatecJnite aldehyde C 6 H 3 (O. 2 CH 
 made by oxidising piperic acid (j.r.) It melts at 263 C. and is valued tV ka 
 odour of heliotrope. 
 
 356. Pyromucic aldehyde, furfural, or furfurol, C 4 H 3 OCHO. is the aldehy. 
 
 furfurane (#.*'.). O< " . It is prepared by distilling the bran of wheat. 
 
 ^CH =CH 
 
 freed from starch and gluten by steeping in a cold weak solution of potash, with 
 half its weight of sulphuric acid, previously diluted with an equal bulk of water, a 
 current of steam being forced through the mixture : the furfural distils over with 
 the water, from which it may be separated by adding common salt. A hundred 
 parts of bran yield about three of furfural. It is a product of the hydrolysis of 
 certain carbohydrates, particularly such as are pentiws. It is also present in 
 fusel oil from crude spirits. Furfural is a colourless liquid smelling of bitter 
 almonds, of sp. gr. 1.17 and boiling-point 162 C. It dissolves in twelve time- its 
 weight of water, and is freely soluble in alcohol. Strong sulphuric acid dis> 
 it to a purple liquid, from which water precipitates it unchanged. It becomes 
 brown when exposed to the air. Furfural combines with XaHSO 3 , reduce- silver, 
 and yields an intense red colour with aniline acetate. With ammonia it behaves 
 as an aromatic aldehyde, forming furfwraniide (C 4 H 3 OCH) 3 X.>. in which three 
 molecules of furfural have exchanged O" 3 for N'" . 
 
 By oxidation, furfural is converted into pyromucic acid, C 4 H 3 OCO. 2 H. Air. >ln -lie 
 solution of potash converts it into potassium pvromucate and furfur' 
 C 4 H 3 0-CH ? OH. 
 
 Funtsol is isomeric with furfural, and is prepared, in a similar way, from certain 
 varieties of furus (seaweed). 
 
 III. ACIDS. 
 
 357. The acids are the second oxidation-products of the primary alcohols. 
 
 The group -C\ ' in the alcohol is converted into (.' . carl 
 
 X OH X OH 
 
 in the acid, so that a general formula for an acid is R'COOH, where R is a 
 
FATTY ACIDS. 587 
 
 hydrocarbon residue or radicle. This view of the constitution of acids 
 is supported mainly by the three following facts : (j) Two acids can 
 be synthetised from sodium -substituted hydrocarbons and CO,, showing 
 that the acid produced (or its sodium salt) probably contains the hydro- 
 carbon radicle and both the oxygen atoms attached to the same carbon 
 atom; e.g., CH 3 Na + CO 2 = CH 3 COONa. (2) The monochlorohydro- 
 carbons, e.g., CH 3 *CH 2 C1, can be converted by double decomposition with 
 KCN into cyanides, e.g., CH 3 -CH 2 'C i N, and when these are boiled with 
 water the N is removed as NH 3 , and an acid remains ; CH ,-CHvC : N + 
 2HOH = CH 3 -CH 2 -COOH + NH 3 . (3) The acids contain a'hydroxyl 
 group, for, by interaction with PC1 5 , they exchange and H for Cl, 
 hydrogen chloride being evolved (p. 579) : 
 
 CH 3 -COOH + PC1 5 = CH 3 -COC1 + POC1 3 + HC1. 
 
 It will be found that the formula H'COOH is the only formula which 
 can be written for formic acid, which resembles all the other acids in its 
 behaviour. 
 
 Two methods generally applicable for producing the acids are (i) oxi- 
 dation of the corresponding alcohol, R'CH,OH + 2 = R-COOH + HOH, 
 and (2) hydrolysis (p. 265) of the cyanogen derivatives of the corre- 
 sponding hydrocarbons, R-CN + 2HOH = R'COOH + ]S[H 3 . 
 
 Isomerism among the acids is confined to the hydrocarbon radicles in 
 them ; thus there will be two acids of the formula C 3 H 7 'COOH, since 
 there are two propyl radicles. 
 
 The basicity of an acid (p. 104) is found to be limited by the number 
 of COOH groups which it contains, thus showing that it is the H in 
 this group which is exchanged for metals to form salts. When an acid 
 contains two CO.,H groups, it is a dibasic acid, or if there are three 
 C 4 O,H groups, it is a tribasic acid, and so on. 
 
 358. Acids from Monohydric Paraffin Alcohols (Acetic or Fatty 
 Series). The acids originally obtained by decomposing soap with a 
 mineral acid were termed fatty acids because the soap had been made 
 by saponifying fat. Later, the more important of them were shown to 
 belong to the same series of acids as acetic acid, hence the term fatty 
 acids was applied to the series. 
 
 The fatty acids correspond with the general formula C M H 2/<+1 'C001 
 and are produced, by two general methods given above, from the alcohols 
 and cyanides of the paraffin series. 
 
 An important method of obtaining fatty acids consists in treating alkyl 
 derivatives of ethyl acetoacetate (0.r.) with an alkali. This compon 
 CH. ; CO-CH.,-COOC.,H 5 , contains a CH 2 group, attached to two CO groups: wlw 
 tliis is the casr Na ran siibstitut.-d for the H in the CH 2 and by treating the sodi 
 derivative with an alkyl iodide, compounds of the type CH 3 CO'CHR-C H ,H, ai 
 ( ' 1 LCOCKo COOCoH/are obtained. By treatment with potash these yiel 
 shun 
 
 .jV/\_/ * 
 
 CH CO' ^* ____ 
 
 In the Iatter7ase~the add contains a secondary radicle. The reaction is soim-th 
 complicated bv the formation of a ketone. 
 
 The ethvl salt of the dibasic acid malonic acid, CH./COOH).,, also conta 
 CH., group attached to two CO groups, so that when it is appropr.aU-Iv 
 first Na or Xa, and then one or two alkyl groups may be substituted f;;'' 1 li- 
 the CH, group. In this way compounds of the type I 
 CR/COOC-HA, and from these the corresponding acids < 
 CiMCOOH), are obtained. When heated, these acids lose CO* yielding a 
 
588 ACETIC SERIES OF ACIDS. 
 
 the acetic series. The preparation of ethyl malonate, CH 2 (COOC 2 H 5 ) 2 , is described 
 later ; the reactions by which it may be converted into butyric acid, for ex- 
 ample, are as follows : 
 
 CH 2 (COOC 2 H 5 ) 2 + C 2 H 5 ONa = CHNa(COOC 2 H 5 ) 2 + C 2 H 5 OH 
 CHNa(COOC 2 H 5 ) 2 + C H 5 I = CHC 2 H 5 (COOC 2 H 5 ) 2 + Nal 
 CHC H 5 (COOC 2 H 5 ) 2 + 2KOH = CHC 2 H 5 (COOK) 2 + 2C 2 H 5 OH 
 CHC 2 H 5 (COOK) 2 + 2HC1 = CHC 2 H 5 (COOH 2 ) + ~2KC1 
 CHC 2 H 5 (COOH) 2 (heated) = CH 2 C 2 H 5 (COOH) + C0 2 
 
 As malonic acid can be made from acetic acid (p. 614) this series of reactions 
 serves for the preparation of the homologues of acetic acid from the acid itself. 
 
 The principal members of the series are : 
 
 Monobasic acids of the acetic series, C w H 2n+1 C0 8 H. 
 
 Acid. 
 
 Source. 
 
 Formula. 
 
 M.-P. 
 
 B.-P. 
 
 Formic . 
 
 Red ants, nettles 
 
 H 
 
 C0 2 H 
 
 9 
 
 C. 
 
 100.6 C. 
 
 Acetic . 
 Propionic 
 
 Vinegar .... 
 Oxidation of oils 
 
 CH 3 
 C 2 H 5 - 
 
 C0 2 H 
 CO 2 H 
 
 - 
 
 C. 
 
 c. 
 
 118 
 140 
 
 C. 
 
 c. 
 
 Butyric 
 
 Rancid butter 
 
 C 3 H 7 
 
 C0 2 H 
 
 - 8 
 
 c. 
 
 163 
 
 c. 
 
 Valeric . 
 
 Valerian root 
 
 C 4 H 9 
 
 C0 2 H 
 
 -59 
 
 c. 
 
 1 86 
 
 c. 
 
 Caproic 
 
 Rancid butter 
 
 C^HU 
 
 C0 2 H 
 
 8 
 
 c. 
 
 205 
 
 c. 
 
 (Enanthic 
 
 Oxidation of castor oil 
 
 CeH 13 ' 
 
 C0 2 H 
 
 -11 
 
 c. 
 
 223 
 
 c. 
 
 Caprylic 
 
 Rancid butter . . 
 
 ^1^15 ' 
 
 C0 2 H 
 
 t7 
 
 c. 
 
 237 
 
 c. 
 
 Pelargonic . 
 
 Geranium leaves 
 
 C 8 H 17 * 
 
 CO 2 H 
 
 13 
 
 c. 
 
 254 
 
 c. 
 
 Rutic or Capric 
 
 Rancid butter 
 
 C 9 H 19 
 
 C0 2 H 
 
 3i 
 
 c. 
 
 268 
 
 c. 
 
 Undecylic 
 
 Oil of rue .... 
 
 C 10 H 21 a 
 
 C0 H 
 
 29 
 
 c. 
 
 
 
 
 Laurie . 
 
 Bay berries .... 
 
 C n H ?3 - 
 
 C0 2 H 
 
 44 
 
 c. 
 
 
 
 
 Tridecylic 
 
 Cocoa-nut oil 
 
 
 C0 2 H 
 
 41 
 
 c. 
 
 
 
 
 Myristic 
 
 Nutmeg-butter . 
 
 CjgH^' 
 
 C0 2 H 
 
 54 
 
 c. 
 
 
 
 
 Pentadecylic 
 
 Agaricus integer (a fungus) 
 
 G U H W ' 
 
 C0 2 H 
 
 51 
 
 c. 
 
 
 
 
 Palmitic 
 
 Palm oil 
 
 QU^SL' 
 
 C0 2 H 
 
 62 
 
 c. 
 
 
 
 
 
 
 
 C0 2 H 
 
 60 
 
 c. 
 
 
 
 Stearic . 
 
 Tallow .... 
 
 P 16 33 . 
 ^iT-ttss 
 
 C0 2 H 
 
 69 
 
 c. 
 
 
 
 
 Arachidic or Butic 
 
 Butter ; earth-nut 
 
 
 COoH 
 
 77 
 
 c. 
 
 
 
 
 Behenic 
 
 Oil of ben . 
 
 CmH^* 
 
 C0 2 H 
 
 84 
 
 c. 
 
 
 
 
 Cerotic . 
 
 Bees'-wax .... 
 
 ^25^51* 
 
 C0 2 H 
 
 78 
 
 c. 
 
 
 
 
 Melissic 
 
 .... 
 
 P TT . 
 
 ^29^59 
 
 C0 2 H 
 
 9i 
 
 c. 
 
 
 
 
 As in other homologous series, the volatility of the acids decreases as 
 the number of carbon atoms increases, so that palmitic acid and those 
 richer in carbon can be distilled only under diminished pressure or in a 
 current of superheated steam. The solubility in water diminishes in 
 the same order ; acetic acid mixes with water in all proportions while 
 palmitic acid is quite insoluble. With the exception of formic and 
 acetic acids they are decidedly oily in character. 
 
 The acid strength also diminishes with the increase in the carbon atoms, and 
 this is turned to account in separating the volatile fatty acids from each other by 
 the method of partial saturation. Suppose it to be required to separate butyric and 
 valeric acids. The mixture is divided into equal parts, one of which is exactly 
 neutralised by soda, yielding butyrate and valerate of sodium. The other half of 
 the acid mixture is then added, and the whole distilled. Since butyric acid is the 
 stronger acid, it will expel the valeric acid from the sodium valerate. If the 
 mixture contained equal molecules of the two acids, the distillate would contain 
 valeric acid only, and the residue would contain the sodium butyrate. If the 
 valeric acid preponderated, the residue would contain both valerate and butyrate, 
 and, when distilled with sulphuric acid, would yield a fresh mixture of the acids, 
 which could be again treated in the same way. But if butyric acid preponderated, 
 the residue would be only sodium butyrate, while the distillate would contain both 
 butyric and valeric acids, to be again treated by partial saturation. 
 
 The non-volatile fatty acids may be separated from each other by fractional pre- 
 cipitation, which depends on the principle that the insolubility of their barium, 
 
FORMIC ACID. 589 
 
 magnesium, and lead salts increases with the number of carbon atoms. The 
 mixture of fatty acids is dissolved in alcohol, and is partially precipitated' by an 
 alcoholic solution of the acetate of Ba, Mg, or Pb. This precipitate will contain 
 the acid or acids richest in carbon. It is filtered off, and another precipitate is 
 obtained from the solution in the same way. This will contain acids poorer in 
 carbon, and so on. Each precipitate is decomposed by HC1, and the new mixture 
 of acids so obtained is subjected to the same treatment, until the separated acid is 
 found to have a constant melting-point. 
 
 The constitution of the fatty acids is disclosed when they are sub- 
 jected to electrolysis, for they then evolve one atom of carbon as CO., ; 
 thus, acetic acid yields dimethyl (ethane), C0 2 and H 
 
 2(CH 3 -C0 2 H) = (CH 3 ) 2 + 2 C0 2 + Ho. 
 Again, valeric acid yields dibutyl, C0 2 and H 
 
 2(C 4 H 9 -C0 2 H) = (C 4 H 9 ) 2 + 2 C0 2 + H 2 . 
 
 To prepare an acid higher in the series from one lower in the series, 
 advantage may be taken of such reactions as the following : 
 
 (1) CH 3 -CH 9 -COOH + H 4 = CH 3 -CH 2 -CH 9 OH. 
 
 (2) 3 CH 3 -CH 2 -CH 2 OH + PI, = 3 CH 3 -CH 2 -CHoI + P(OH) 3 . 
 
 (3) CH 3 -CH 9 -CH 9 I + KCN = CH 3 'CH 2 'CH 9 -CN + KI. 
 
 (4) CH 3 -CH 2 -CH 2 CN + 2HOH = CH 3 -CH 2 r CH 2 'COOH + NH 3 . 
 
 359. Formic acid, H'C0 2 H, was originally obtained from ants. It 
 occurs in nettles and other plants, in some animal fluids, and occasion- 
 ally in mineral waters. It is prepared by distilling oxalic acid with 
 glycerine. 30 grams of crystallised oxalic acid and 200 c.c. of glycerine 
 are heated, in a half-litre flask provided with a thermometer and 
 condenser, to about 80 C., when formic acid distils over together with 
 the water of crystallisation of the oxalic acid, and carbonic acid gas is 
 evolved; C0 2 H'C0 2 H = H'C0 2 H + C0 2 . When the evolution of CO, 
 ceases, a fresh quantity of oxalic acid may be introduced and the opera- 
 tion continued, the same glycerine serving for the conversion of a large 
 quantity of oxalic acid. The formic acid first produced converts the 
 glycerine into monoformin 
 
 C 3 H 5 (OH) 3 + H-C0 2 H = C 3 H 5 (OH) 2 (O.CHO) + HOH. 
 
 The monoformin is then decomposed by the water of crystallisation of 
 the oxalic acid, the equation being reversed, and glycerine being repro- 
 duced. By continuing the process, formic acid of 56 per cent, may be 
 obtained. To prepare the pure acid, this is neutralised with lead oxide, 
 the lead formate crystallised, dried, and heated to 100 C. in a current of 
 dry HjjS; (H'CO 2 ) 2 Pb + H 2 S = 2 H'C0 2 H + PbS. The formic acid is 
 carefully condensed and redistilled with a little lead formate to re- 
 move H 2 S. 
 
 Formic acid is obtained synthetically by heating caustic alkalies to 
 100 C. in carbonic oxide; CO + KOH = H'C0 2 K (potassium formate) ; 
 again, potassium, acting on carbon dioxide in presence of water, yield 
 acid potassium carbonate and potassium formate 
 
 2C0 2 + H 2 + K 2 = KHC0 3 + H'C0 2 K. 
 
 It is also produced in other reactions in which carbonic acid is acted 
 on by reducing-agents. Carbonic acid may be regarded as %*racy- 
 formic acid, HO'CO.H, that is, formic acid, H'C0 2 H, in which U 
 substituted for H. When starch and other organic bodies are violent y 
 oxidised, they yield carbonic acid, but if they are gradually and quietly 
 
590 ACETIC ACID. 
 
 oxidised, they yield formic acid. The quiet oxidation of organic bodies 
 is often effected by heating them with Mn0 2 and dilute H,S0 4 . 
 
 Formic acid is also formed by oxidising methyl alcohol, and when 
 hydrocyanic acid is hydrolysed by boiling it with dilute acids, H'CN + 
 2 HOH = H-C0 2 H + NH 3 . 
 
 Properties of formic acid. Colourless liquid, fuming slightly in air 
 and of pungent smell ; it blisters the skin. Formic acid boils at ioo.6 C. 
 and melts at 9. Its sp. gr. is 1.22 at 20. The diluted acid boils at 
 a higher temperature ; an acid of 77 per cent, boils at 107. 
 
 The formates are all soluble in water ; their solutions yield a red 
 colour with ferric chloride, and reduce silver from the nitrate, when 
 boiled with it, on account of the tendency of formic acid to become 
 carbonic (hydroxyformic) acid. Solid formates evolve carbonic oxide 
 (burning with a blue flame) when heated with strong H 2 S0 4 , which 
 removes the elements of water; H'C0 2 H = HOH + CO. A formate 
 heated with excess of baryta yields the oxalate; (HC0 2 ) 2 Ba== 
 
 > 
 Formic acid is used in making some of the coal-tar dyes. 
 
 Formic acid differs in some respects from the other members of the series. Thus 
 its powerful reducing action relates it to the aldehyde acids (p. 607) ; indeed, if 
 its formula be written HO'CHO it might be regarded as liydroxy formaldehyde. 
 No acid chloride or anhydride, such as are characteristic derivatives of the higher 
 acids of the series, can be obtained from formic acid. By loss of water it yields 
 CO not (H-CO) 2 0. which would be the true anhydride. When heated at 160 C. 
 it breaks up into H & CO^ the same change occurring at the ordinary temperature 
 in contact with platinum black. 
 
 360. Acetic acid, or methyl -formic acid, CH 3 'C0 2 H, is found either 
 free or combined in many plants and in some animal fluids. It is 
 obtained by the destructive distillation of wood or of sawdust, or spent 
 dye-woods. The aqueous layer in the condenser (p. 566) is neutralised 
 by sodium carbonate, and the methyl alcohol and acetone are distilled off. 
 The evaporated liquor deposits impure crystals of sodium acetate which 
 are heated to expel some tarry matters, and distilled with H 2 S0 4 , when 
 acetic acid passes over; CH 3 -C0 2 Na + H 2 S0 4 = CH 3 -C0 2 H + NaHS0 4 . 
 The crude acid from wood is termed pyroligneous acid. 
 
 Acetic acid is also made by the oxidation of alcohol for the produc- 
 tion of vinegar; CH 3 'CH 2 OH (ethyl alcohol) + 2 = OH 3 'C0 2 H + H 2 0. 
 But this equation cannot be realised unless some third substance be 
 present. It was seen at p. 564 that platinum black would answer the 
 purpose, and in some chemical works this process has been employed 
 for making acetic acid. Weak fermented liquors, such as beer and the 
 lighter wines, are very liable to become sour, which is never the case 
 with distilled spirits, however much diluted. This is due to the pre- 
 sence in the fermented liquid of albuminous (nitrogenised) matters and 
 salts, which afford nourishment to a microscopic organism, termed 
 Mycoderma aceti, which appears to convey the oxygen of the air to the 
 alcohol. 
 
 Quick vinegar process. A weak spirit mixed with a little yeast or beet-root 
 juice, heated to about 27 C., is caused to trickle slowly from pieces of cord fixed 
 in a perforated shelf over a quantity of wood shavings previously soaked in 
 vinegar to impregnate them with the acetic ferment or mother of vinegar. The 
 shavings are packed in a tall cask (Fig. 272) in which holes have been drilled in 
 order to allow the passage of air. The oxidation of the alcohol soon raises the 
 temperature to about 38 C., which occasions a free circulation of air among the 
 
VINEGAR. 59 ! 
 
 shavings. The mixture is passed three or four times through the cask, and in 
 about thirty-six hours the conversion into vinegar is completed. If the supply of 
 air be insufficient, alcohol is lost in the form of aldehyde vapour, the irritatinir 
 odour of which pervades the air of the factory. 
 
 White- wine vinegar is prepared from light wines by a similar process. Malt 
 vinegar is made from infusion of malt fermented by yeast with free contact of air . 
 Vinegar contains, on an average, about 5 per 
 cent, of acetic acid. Its aroma is due to 
 the presence of a little acetic ether. The 
 vinegar of commerce is allowed to be mixed 
 with TT ,Vtf of its weight of sulphuric acid in 
 order to prevent it from becoming mouldy. 
 By distilling vinegar a weak acetic acid is 
 obtained, which may be concentrated by re- 
 distilling and receiving separately the por- 
 tion distilling between 110 and 120 C. 
 
 Pure acetic acid is prepared by 
 distilling 5 parts by weight of fused 
 sodium acetate with 6 parts of con- 
 centrated sulphuric acid (see above). 
 The distillate may be redistilled with 
 a little Mn0 2 to remove S0 2 . 
 
 The acid is also produced when Fio- 272 
 
 CH 3 Na is treated with C0 2 (p. 587), 
 
 and when methyl cyanide is hydrolysed by boiling dilute acids ; 
 CH 3 -C1S T + 2 HOH = CH 3 -COOH + NH 3 . 
 
 Properties of acetic acid. Colourless, pleasant smell, blistering the 
 skin, boiling at 1 18 C., and giving a vapour which burns with a flame 
 like that of alcohol. Its true melting-point is 17 C., but it maybe 
 cooled far below this without solidifying, unless a crystal of the acid be 
 introduced, when the whole crystallises in beautiful plates ; hence the 
 term glacial acetic acid. The sp. gr. of the pure acid is 1.063 at 18, 
 but the strength of the acid cannot, as in other cases, be inferred from 
 the sp. gr., because the latter is increased by addition of water, till it 
 reaches 1.079 (7 P er cent, of acid), when it is diminished by more 
 water, so that a 43 per cent, acid has the same sp. gr. as the pure acid. 
 
 Acetic acid is one of the most stable of the organic acids. It is 
 unattacked by most oxidising-agents. When its vapour is passed 
 through a red-hot tube it yields several products, among which marsh 
 gas and acetone are conspicuous. Most of its salts are soluble in water, 
 so that it is not easily precipitated ; but if it be exactly neutralised by 
 ammonia, and stirred with silver nitrate, a crystalline precipitate of 
 silver acetate, CH 3 'CO 9 Ag, is obtained ; mercurous acetate, CH 3 'C0 2 Hg, 
 may be obtained in a similar way. Ferric chloride added to the neutral 
 solution gives a fine red colour. 
 
 361. Many of the acetates are employed in the arts. Those formed by the 
 weaker bases, such as Fe 2 0^ and A1 2 3 , are easily decomposed by boiling with 
 water, basic acetates being" precipitate*d ; hence the aluminium m-rtatr and femo 
 iicrttitc (red liquor) are much used by dyers and calico-printers as mordants, the 
 basic acetates being deposited in the fabric, and forming insoluble compounds 
 with colouring-matters. 
 
 Lead acetate, or avgar of lead, (CH 3 C0 2 ) 2 Pb.3Aq, is the commonest commerc 
 acetate, and is prepared by dissolving litharge (PbO) in an excess of acetic acid, 
 when the solution deposits prismatic crystals of the salt. On the large scale, 
 acetic acid vapour is passed through copper vessels with perforated shelves on 
 which litharge is placed. Lead acetate is intensely sweet and very soluble in 
 
592 ACETATES. 
 
 water (i^ part). Commonly, the solution is turbid from the precipitation of lead 
 carbonate by the carbonic acid in the water ; a drop of acetic acid clears it. 
 The acetate is soluble in alcohol. When heated, it fuses at 75 C. and becomes 
 anhydrous at 100. The anhydrous salt melts when further heated, evolves the 
 pleasant smell of acetone, and becomes again solid as a basic lead acetate, which 
 is decomposed at a higher temperature, evolving C0 2 and acetone, and leaving a 
 yellow residue of PbO mixed with globules of lead. 
 
 There are several basic lead acetates, but the only one of practical importance 
 is the tribasic lead acetate, Goulard's extract (CH 3 -C0 2 ) 2 Pb.2PbO.H 2 0, which is 
 prepared by boiling lead acetate with litharge. It forms needle-like crystals, 
 which are very soluble in water, but insoluble in alcohol. A strong solution of 
 the salt is not affected by the air, but a weak solution is rendered turbid by the 
 smallest quantity of C0 2 in air or water. Tribasic lead acetate is very useful in 
 the laboratory for precipitating tannin, gum, &c., from vegetable infusions in 
 order to extract the alkaloids. 
 
 Verdigris is a mixture of several basic cupric acetates prepared by acting on 
 sheet copper with the refuse grapes of the wine-press, which yield acetic acid by 
 oxidation of the alcohol ; the acid combines with the cupric oxide formed by the 
 action of air upon the copper. Commercial verdigris consists chiefly of the 
 compound (CH 3 'C0 2 ) 2 Cu.Cu0.6H 2 0. When this is treated with water it is only 
 partly dissolved, the residue having the composition (CH 3 'C0 2 ) 2 Cu.2Cu0.2H 2 0. 
 By dissolving verdigris in acetic acid, the normal cupric acetate may be obtained 
 in crystals of the formula (CH 3 'C0 2 ) 2 Cu.H 2 0. It forms blue prisms soluble in water. 
 Verdigris is used in the manufacture of colours, and in dyeing and calico-printing. 
 
 Emerald-green or cupric aceto-arsenite, (CH 3 'C0 2 ) 2 Cu.Cu 3 (As0 3 ) 2 .As 4 6 , is made 
 by boiling verdigris with w r hite arsenic and water. It is used for colouring wall- 
 paper and other fabrics, and is dangerous to the makers and purchasers. 
 
 Sodium acetate, CH 3 .C0 2 Na.3Aq, prepared by neutralising acetic acid with 
 sodium carbonate, crystallises in prisms which are very soluble in water, and yields 
 one of the best examples of a supersaturated solution (see p. 51), which is used in 
 foot- warmers for railway carriages, on account of the continuous evolution of heat 
 during its crystallisation. It is four times as effective as an equal volume of water. 
 
 The acetates of sodium and potassium are remarkable for their fusibility and 
 their stability at high temperatures ; they do not carbonise so readily as do most 
 salts of organic acids. Potassium, sodium, and ammonium acetates combine with 
 one and with two molecules of acetic acid to form crystalline compounds. 
 
 Calcium acetate, when dissolved in water together with CaCl 2 , yields the com- 
 pound (CH 3 -COO) 2 Ca.CaCl 2 .ioAq, which crystallises easily, and is sometimes 
 produced for effecting the purification of crude acetic acid (Condy's patent). 
 
 Zinc acetate, (CHg-CO^Zn^Aq, is remarkable for being capable of sublimation 
 at a moderate heat, when dried. 
 
 Acetic acid is very useful in organic chemistry as a simple solvent, 
 especially for resins and hydrocarbons, such as naphthalene and 
 anthracene. 
 
 362. Acetic acid may be produced by the reaction of zinc methyl, 
 Zn(CH 3 ) 2 , with COC1 2 (p. 190) which yields acetyl chloride (q.v.), a 
 compound which furnishes acetic acid when decomposed by water 
 Zn(CH 3 ) 2 + 2COC1 2 = 2CH 3 -COC1 + ZnCl 2 . CH 3 'COC1 + HOH = CH 3 -COOH + HC1. 
 The group CH 3 'CO, which remains unchanged during the latter 
 reaction is termed acetyl, 2 H 3 O, and may be regarded as ethyl, CH 3 'CH 2 , 
 in which 0" has been substituted for H 2 . 
 
 There is a similar acid radicle corresponding with each alcohol radicle ; 
 a few examples are here given 
 
 Alcohol radicles. 
 
 Methyl CH 3 
 
 Ethyl CH 3 -CH 
 
 Propyl C 2 H 5 'CH 
 
 Butyl C 3 H 7 -CH 
 
 Amyl C 4 H 9 'CH 
 
 Acid radicles* 
 
 Formyl CHO 
 
 Acetyl CH,-CO 
 
 Propionyl C 2 H 5 'CO 
 
 Butyryl C 3 H 7 'CO 
 
 Valeryl C 4 H 9 'CO 
 
 Termed acidyl or acyl radicles. 
 
ACIDS OF THE ACETIC SERIES. 
 
 It will be seen later that the alcohol radicles combine in pairs 
 
 with oxygen to produce ethers of the type \0, the two radicles being 
 
 the same or different. The acid radicles combine with oxygen in a 
 
 OH r*o 
 
 similar manner to produce acid anhydrides, such as \Q, acetic 
 
 CH,CO 
 
 CH 3 CO v 
 anhydride, ^ ;0, aceto-propionic anhydride. 
 
 C.,H 5 CO 
 
 Acetic anhydride, or di-acetyl oxide, or anhydrous acetic acid (CHo'CO) is 
 prepared by distilling acetyl chloride with an equal weight of perfectly anhydrous 
 sodium acetate ; CH 3 COCl + CH 3 -COONa = (CH 3 -CO) + NaCl. It distils over as 
 a colourless liquid, smelling of acetic acid, but irritating the eyes; its sp. gr. is 
 1.073, an d boiling-point, 137 C. It dissolves slowly in water, with evolution of 
 heat and formation of acetic acid (CH 3 'CO) 2 + H 2 = 2(CH 3 -COOH). 
 
 Acetic anhydride may also be formed by heating lead acetate with carbon 
 disulphide ; 2Pb(CH 3 'C0 2 ) 2 + CS 2 = 2(CH 3 'CO) 2 + 2PbS + CO^ Also by heating 
 acetyl chloride with anhydrous oxalic acid; C 2 H 3 OC1 + (COOH). 2 =:(C 2 H 3 0) 2 + 
 HC1 + CO + COg. 
 
 By carefully acting on acetic anhydride with sodium-amalgam and water (or 
 snow), it has been converted into aldehyde and alcohol 
 
 (CH 3 -CO) 2 + 2H 2 = 2(CH 3 -CHO) + H 2 0, and CH 3 'CHO + H 2 = CH 3 'CH 2 'OH. 
 With HC1 it yields acetyl chloride and acetic acid, (CH 3 CO) 2 + HC1 = CH,COC1 + 
 CH 3 COOH. 
 
 Acetyl dioxide, or acetic peroxide, (CH 3 'CO) 2 2 , is obtained by adding barium 
 dioxide to an ethereal solution of acetic anhydride 
 
 2(CH 3 -CO) 2 + Ba0 2 = (CH 3 'CO) 2 2 4- Ba(CH 3 'C0 2 ) 2 .. 
 
 It melts at 30 C. and is insoluble in water. It explodes violently when heated, 
 and has the powerful oxidising properties which would be expected from its 
 chemical resemblance to hydrogen peroxide. 
 
 363. Corresponding with the thioalcohols, the alkyl sulphides and disulphides 
 (p. 572)5 there are thioacids, thioanhydrides, and thioperoxides, the oxygen outside 
 the acid radicle, having been exchanged for sulphur in each case. 
 
 Thioacetic acid, CH 3 'COSH, is obtained by the action of P 2 S 5 on acetic acid : 
 
 5CH 3 -COOH + P 2 S 5 = 5C 2 H 3 0-SH + P 2 5 . 
 
 It is a colourless, evil-smelling liquid, boiling at 93 C., and sparingly soluble in 
 water. Acetyl sulphide (thioacetic anhydride), (CH 3 'CO) 2 8, is obtained by the 
 action of P 2 S 5 on acetic anhydride, and acetyl disulphide (thioacetic peroxide), 
 (CH 3 CO) 2 S 2 . by the action of K 2 S 2 on acetyl chloride. 
 
 364. Propionic acid, C 2 H 5 'C0 2 H, is not produced upon a large scale like acetic 
 acid. It is formed in the putrefaction of various organic bodies, and in the 
 destructive distillation of wood and of rosin. It may be separated from formic 
 and acetic acids by saturating the mixture with PbO, evaporating to dryness and 
 extracting with cold water. On boiling the solution, it deposits bane lead 
 propionate, leaving the basic lead formate and acetate in solution. From the lead- 
 salt the acid may be obtained by the action of H 2 S or H 2 S0 4 . 
 
 Sodium propionate is obtained by the action of CO upon sodium ethoxide, just 
 as sodium formate is obtained from sodium hydroxide (see p. 589) 
 CO + C 2 H 5 -ONa = C 2 H 5 -C0 2 Na. 
 
 Propionic acid, as would be expected, resembles acetic acid. Its sp. gr. is 0.99, 
 and it boils at 140 C. It has no practical importance. The propionates are 
 mostly soluble in water, but silver propionate is sparingly soluble. Lead propionate 
 is much more difficult to crystallise than lead acetate. 
 
 Butyric acid, C 3 H 7 'C0 2 H. The normal acid (ethylacetic acid) is made from 
 cane sugar by dissolving it in water (5 parts), adding a little tartaric acid ( 7 ^th 
 part), boiling to convert the sucrose into glucose, and adding to the cooled 
 liquid some putrid cheese (^th part) rubbed up in about thirty times its weight 
 of milk. Some chalk ( part) is stirred into the mixture, which is then allowed 
 to ferment for a week at a temperature of 3O-35 C. The glucose, C 6 H 12 6 , ui 
 goes the lactic fermentation, and is converted into lactic acid, C 3 H 6 3 , which is 
 
 2 P 
 
594 VALEEIC ACID. 
 
 converted, by the chalk, into calcium lactate, forming a pasty mass of crystals. 
 After a time the mass becomes liquid again, evolving bubbles of hydrogen and 
 carbon dioxide, and forming a strong solution of calcium butyrate, produced by the 
 butyric fermentation. When this is mixed with strong hydrochloric acid, the 
 butyric acid rises to the surface and forms an oily layer, which may be puritied by 
 distillation. The passage of lactic acid into butyric acid is expressed by the 
 equation 2C 3 H 6 3 = C 3 H 7 'C0. 2 H + 2C0 2 + 2H 2 . 
 
 Butyric acid is a strongly acid liquid, smelling of rancid butter, having the 
 sp. gr. 0.96, and boiling at 163 C. It mixes readily with water, but separates 
 again when the water is saturated with a salt. The butyrates are rather less 
 soluble than the acetates. Calcium butyrate is less soluble in hot water than in 
 cold. Silver butyrate is very sparingly soluble. 
 
 Butyric acid is found in the products of distillation of wood and of some other 
 organic bodies. It exists in the perspiration of the skin, and, as a glyceride, in 
 butter, in cod-liver oil, and in some vegetable oils. 
 
 Isobutyrlc acid (dimethylacetic acid) (CH 3 ) 2 CH'COOH boils at 155 C. and is 
 made from isopropyl chloride through the cyanide reaction (p. 587). 
 
 Valeric or valerianic acid. Four of these are possible ; that commonly called 
 valeric acid is isopropylacetic acid, (CH 3 ) 2 CH'CH 2 'COOH. It is prepared by 
 oxidising amyl alcohol (fusel oil) with potassium bichromate and sulphuric acid. 
 
 It is an oily liquid smelling like old cheese ; its sp. gr. is 0.95, and it boils at 
 174 C. It is much less soluble in water than are the preceding acids, requiring 
 thirty times its weight. The valerates are, as a rule, easily soluble in water, but 
 the silver salt is sparingly soluble. Zinc valerate is used medicinally. 
 
 Valeric acid occurs in valerian root, in the elder, in the berries of the guelder 
 rose, and in many other plants ; also in some fish oils and in the perspiration. 
 
 Normal caproic or hexylic acid, C 5 H n *C0 2 H (sp. gr. 0.94, b.-p. 205 C.), is found 
 in butter from cows and goats, and in Limburg cheese, being one cause of its 
 odour ; it is also found in some plants, and in the perspiration. Caproic acid is 
 formed, together with butyric and acetic acids, in the butyric fermentation 
 described above. It dissolves very sparingly in water, and has a repulsive 
 odour. The caproates of barium and calcium are rather sparingly soluble in water, 
 and silver caproate is nearly insoluble. 
 
 365. (Enanthic or normal heptylic acid, C 6 H 13 'C0 2 H, is obtained by oxidising 
 oenanthic aldehyde (oenanthol). It has a faint odour and sp. gr. 0.93 ; it boils at 
 223 C. Many of the cenanthates are nearly insoluble in water. The strong 
 solutions of the alkali oenanthates become gelatinous on cooling, like solution of 
 soap. 
 
 Normal caprylic or octylic acid, C 7 H 15 -C0 2 H, is found in the fusel oil from wines, 
 in old cheese, and, as a glyceride, in butter, human fat, and cocoa-nut oil. It is 
 the first acid of this series which is solid at common temperatures, forming needle- 
 like crystals or scales fusible at 16 C. and boiling at 237. It has an offensive 
 smell, and is very sparingly soluble in water. The caprylates, except those of the 
 alkalies, are sparingly soluble in water, but they dissolve in alcohol. 
 
 Pelargonic or normal nonylic acid, C 8 H 17 'C0 2 H, was originally obtained from 
 the essential oil of Pelargonium roseum, and is found among the products of 
 oxidation of oleic acid by nitric acid. It is also formed when essential oil of rue 
 (nonylmethylltetone) is oxidised by nitric acid. It is an oily liquid, of faint odour, 
 crystallising at 12 C. and boiling at 253. It has sp. gr. 0.91, and is insoluble in 
 water. The pelargonates are sparingly soluble in water, except those of the 
 alkalies. 
 
 Laurie or normal dodecylic acid, CjjH^'CC^H, is obtained from a fatty substance 
 found in the fruit of the sweet bay (Laurus nobilis) and in sassafras-nuts or 
 pichurim beans, which are used for flavouring chocolate, and are the seeds of 
 another of the Lauraceas (Nectandra Puchury). A similar substance is found in 
 the mango and in a variety of cochineal insect. The fat is saponified by boiling 
 with potash, the solution decomposed by hydrochloric acid, and the separated 
 fatty acid distilled, when lauric acid is found in the first fractions. 
 
 The crystals of lauric acid fuse at 44 C. It cannot be distilled at ordinary 
 pressures without decomposition. 
 
 366. Palmitic acid, C 15 H 31 -C0 2 H, crystallises in needles (m. -p. 62 C.), 
 and is the first of the fatty acids, properly so called, which occur as 
 glycerides in the vegetable and animal fats, and form true soaps with 
 
STEARIC ACID. 
 
 the alkalies, such soaps being the salts formed by the fatty acid with 
 the alkali-metal, characterised by easily lathering when dissolved in soft 
 water, by being precipitated from their aqueous solutions by common 
 salt, and by giving an oily layer of the melted fatty acid when boiled 
 with any of the common acids. 
 
 On the large scale, palmitic acid is made from palm-oil, as described 
 at p. 576. It is also manufactured by heating oleic acid with caustic 
 soda: 
 
 CwHjB-COOH + 2NaOH = C 15 H 31 'COONa + CH 3 -COONa + H 2 . 
 
 On the small scale, palm-oil is boiled with potash, which converts it into 
 potassium palmitate and oleate ; on adding dil. H 2 S0 4 to the solution, a mixture of 
 
 Fig. 273. Distillation under diminished pressure. 
 
 palmitic and oleic acids is precipitated ; this is washed, dried, and dissolved in hot 
 alcohol, from which the palmitic acid crystallises on cooling, leaving the oleic acid 
 in solution. It may be purified by distillation under diminished pressure. An 
 arrangement suitable for this operation is shown in Fig. 273. Palm-oil contains 
 the glycerides palmitin and olein, which are saponified by the potash, with liberation 
 of glycerine, as will be further explained under the head of Ethereal salts, to which 
 the glycerides belong. 
 
 The substance known as adipocere, a wax-like mass left when animal bodies 
 decompose in the earth, is a mixture of palmitates of calcium and potasium. 
 
 The formation of palmitic acid from spermaceti has been explained at p. 
 570. 
 
 Stearic acid, C 17 H 35 'CO 2 H, may be prepared from suet by boiling it 
 with potash, decomposing with hydrochloric acid the soap thus obtained, 
 drying the separated fatty acids, and dissolving in the least possible 
 quantity of hot alcohol. This retains the oleic acid in solution and 
 deposits a mixture of stearic and palmitic acids on cooling ; the mixture 
 is well pressed in blotting-paper, and repeatedly crystallised from 
 alcohol till it fuses at 69 C. The stearic acid exists in the suet and in 
 most other solid fats, in the form of the glyceride stearin, mixed with 
 palmitin and a little olein. When saponified by the potash, these yield 
 the stearate, palmitate, and oleate of potassium, respectively. 
 
 Stearic acid is a white crystalline solid, of the same sp. gr. as water, 
 fusing at 69 C., and not distilling without partial decomposition, except 
 at low pressures or in a current of superheated steam. It is insoluble in 
 
5Q6 ACIDS OF THE ACEYLIC SEKIES, 
 
 water, but dissolves in alcohol and in ether. It burns with a luminous 
 flame. The alkalies dissolve stearic acid on heating, forming stearates, 
 which are components of ordinary soaps. 
 
 White curd soap made from tallow and soda consists chiefly of sodium, stearate, 
 C ]7 H 35 'C0 2 Na, which may be crystallised from alcohol. It dissolves in a little water 
 to a clear solution, but when this is largely diluted it deposits scaly crystals of the 
 acid sodium stearate, (C 17 H 35 'C0 2 ) 2 HNa. Potassium stearate behaves in a similar 
 way. The other stearates are insoluble. Those of calcium and magnesium are 
 precipitated when hard water is brought in contact with soap. Magnesium stearate 
 may be crystallised from alcohol. 
 
 Stearic acid mixed with palmitic acid is the material of the so-called stearin 
 candles. 
 
 Margaric acid, C 16 H 33 'C0 2 H, is obtained by boiling cetyl cyanide with an alkali. 
 It crystallises like palmitic, and fuses at 60 C. 
 
 367. Acids from Monohydric Oleflne Alcohols (Acrylic or Oleic 
 Series). These correspond with the general formula C^EL^jCOOH 
 and contain the ethylenic linking characteristic of the defines, e.g., 
 CH 3 'CH : CH'COOH, crotonic acid. They may be prepared from the 
 corresponding alcohols and cyanogen derivatives by the general methods 
 (p. 587), and also by two methods which recall the preparation of the 
 olefines. These are (i) by nucleal condensation from the monohalogen 
 substituted fatty acids, thus : 
 
 CH 3 -CH 2 -CHC1'COOH + KOH = CH 3 'CH : CH'COOH + KC1 + HOH, 
 and (2) by dehydration of the alcohol acids (p. 574) by destructive 
 distillation ; CH 2 (OH)-CH 2 'CH 2 -COOH = CH 2 : OH-CH 2 'COOH + HOH. 
 Attention must here be called to the nomenclature of isomerides 
 among derivatives of open-chain hydrocarbons. The letters, a, /3, y, 
 <fec., are prefixed to the name of the derivative to indicate the carbon 
 atom to which the substituent is attached, a signifying the atom next 
 the end characteristic group, j3 the next but one, y the next but two, 
 and so on, thus : 
 
 a-Chlorobutyric acid = CH 3 -CH 2 'CHC1-COOH 
 /3-Chlorobutyric acid = CH 3 -CHC1-CH 2 'COOH 
 7-Chlorobutyric acid = CH 2 C1'CH 2 -CH 2 -COOH 
 It is by no means a matter of indifference whether an a, /3 ,or y derivative is us 
 
 in the two last named reactions ; in both cases the /3-derivative is most easily coi 
 
 verted into the acid of the olefine series. 
 
 Having an ethylenic linking, the acids of the acrylic series show th* 
 property, characteristic of the olefines, of combining directly with two 
 atoms of bromine and with two atoms of (nascent) hydrogen. In the 
 former case a dibro mo-derivative of the corresponding fatty acid, and in 
 the latter the fatty acid itself, is formed, the double linking being 
 opened up in each case. 
 
 A characteristic reaction of the acids of this series is that when fused 
 with an alkali they yield alkali salts of two acids of the acetic series, 
 the rupture of the molecule generally occurring at the double linking ; 
 thus acrylic acid, CH 2 : CH'COOH yields acetate and formate, and 
 crotonic acid yields two molecules of acetate. 
 
 This reaction is not a criterion of the position of the double linking in the chain 
 because of the influence which alkalies have in causing the double bond to shift, mere 
 heating with aqueous alkali sufficing in many cases to convert a J3y-acid (one in 
 which the double bond is between the /3 and y carbon atom) into an a/3-acid. 
 
 Isomerism among acids of the acrylic series may bedue to variation in position of the 
 doublebonds, as, for instance, CH 3 -CH : CH-CH 2 -COOHandCH 3 'CH 2 -CH: CH'COOH 
 
ACRYLIC ACID. -Q 
 
 *' CH *' Cfl : W-COOH, 
 f the Same ki ^ as that between 
 Since the polymethylenes (p. 539) are isomeric with the defines, the monocar- 
 
 waw4^2g are isomeric with the acryiic acids ' i 3n; 
 
 The following are the best-known acids of the aeries, but although 
 they form an homologous series, many of them differ in structure so 
 much from the type, acrylic acid, and from each other that their 
 physical properties cannot advantageously be compared. 
 
 Acid. Source. Formula. 
 
 Acrylic . . . Oxidation of acrolein . . C 9 H,-C0 H 
 
 Angelic . . Angelica root .... cS'Coi 
 
 ryroterebic . . Oxidation of turpentine . . C.H Q -C0 H 
 
 OlT^ 610 ' ' Earth-nut oil . . . . C X'CO. 
 
 / eic .- Most oils .... Ci-- 
 
 Erucic Rape oil ... . C 
 
 Acrylic acid, CH 2 : CH'C0 2 H, is obtained by heating acrolein, the corresponding 
 aldehyde, (p. 583) with water and silver oxide in the dark : C 2 H 3 'CHO + Ag 2 = 
 C 2 H 3 -C0 2 H + Ag 2 . It is also obtained, by the general methods given above, from 
 bromopropionic and hydroxypropionic acids. It is a pungent liquid, miscible with 
 n a i ei nd boilin at I ^ c - Nascent hydrogen converts it into propionic acid, 
 O 2 H 5 -CO 2 H. Fused with potassium hydroxide, it yields potassium acetate and 
 formate CH 2 : CH'C0 2 K + KOH + H 2 = CH 3 'C0 2 K + H-CO^ + H . -~* N 
 While it is possible to write the formula C 3 H 5 'COOH, the next homologue 
 to acrylic acid, in four isomeric forms, two alone are known with certainty 
 viz., crotonic add, CH 3 'CH : CH'COOH, which occurs in a solid and a liquid 
 modification, and methylacrylic acid, CH 2 :C(CH 3 )'COOH. Vinylacetic acid 
 CH 2 : CH-CH 2 -COOH, is also alleged to have been obtained. 
 
 Solid crotonic acid occurs in crude pyroligneous acid, and is obtained by 
 oxidation of croton adelhyde (p. 584) with Ag 2 0. Its formation by heating ap- 
 dibromobutyric acid with KI solution indicates the position of the double 
 linking : 
 
 CH 3 -CHBr-CHBr-COOH + 2 KI = CH 3 'CH : CH'COOH + 2KBr + I 2 . 
 It crystallises in needles, melts at 72 C., and boils at 180 C.,its vapour condensing 
 in plates. It is moderately soluble in water, and has an odour like that of butyric 
 acid, into which it is converted by nascent hydrogen. Fused, KOH converts it into 
 potassium acetate C 3 Hg-C0 2 H + 2KOH = 2(CH 3 C0 2 K) + H 2 . "Liquid" 
 crotonic or isocrotonic acid occurs in croton oil. When PC1 5 acts on ethylaceto- 
 acetate (#..) it produces -chloroisocrotonic acid, CH 3 'CC1 : CH'C0 2 H, which, by 
 treatment with nascent H, yields isocrotonic acid ; this crystallises in needles or 
 prisms, melts at 15 C., boils at 169 C., and is converted into the solid acid at 
 1 80 C. It appears to be a stereoisomeride of the solid acid, the relation between the 
 two being similar to that between fumaric and malaeic acids G/.f.). Methylacryl'u} 
 acid occurs in chamomile oil, and has an odour of mushrooms. It is prepared by 
 a complicated process. It melts at 16 C. and boils at 160 C. ; nascent H converts 
 it into isobutyric acid, whilst with fused KOH it yields propionate and formate. 
 
 Angelic acid, CH 3 'CH : C(CH 3 )'COOH, is obtained by boiling angelica root (an 
 umbelliferous plant) with lime and water, filtering, acidifying with sulphuric acid, 
 and distilling. The acid appears to be contained in the root as an ethereal salt, 
 which is decomposed by the lime. Chamomile flowers and some other aromatic 
 plants also yield this acid. It crystallises in prisms, fusing at 45 C., and boiling at 
 185. It has an aromatic odour, is soluble in hot water and in alcohol and 
 ether. When boiled for some time, it is converted into its stereoisomeride, tifU* 
 acid (m.-p. 64 C,, b.-p. 198 C.), which is also obtained from croton oil (CfrfltM 
 tigliwri), and, together with angelic acid, from cummin oil (Cuimnum cijmuiuni). 
 Fused with KOH, angelic acid yields acetate and propionate. There are several 
 isomerides. 
 
59 8 OLEIC ACID. 
 
 368. Oleic acid, C 17 H 33 -C0 2 H, or C 8 H 17 'CH : CH[CH 2 ] 7 -COOH, the 
 
 most important member of the acrylic series of acids, is prepared by 
 boiling olive-oil with potash, and decomposing the solution with hydro- 
 chloric acid, which separates the oleic acid as an oily layer, containing 
 some stearic and palmitic acids. To purify it, it is heated with litharge 
 at 1 00 C. for some hours, when a mixture of oleate, palmitate, and 
 stearate of lead is obtained. The oleate is extracted from this mixture 
 by ether, and the solution shaken with HC1, which precipitates the lead 
 as Pbd 2 , while the oleic acid remains dissolved in the ether, which rises 
 to the surface. The ether is distilled off and the oleic acid is purified 
 by fractional distillation under diminished pressure. 
 
 The olive-oil contains the glyceride olein, which is decomposed by 
 boiling with potash into glycerine and potassium oleate. Olein is ii 
 general constituent of the fixed oils ; the soft soap made by saponifying 
 whale and seal oils with potash consists chiefly of potassium oleate. 
 Oleic acid is a by-product in the manufacture of candles, in which its 
 presence would be injurious by lowering the fusing-point. It is used in 
 greasing wool for spinning, being much more easily removed by alkalies 
 than is olive-oil, which was formerly employed. Ammonium oleate is 
 sometimes employed as a mordant for the aniline dyes on cotton. 
 
 Oleic acid is an oily liquid which crystallises at o C. and melts at 14. When 
 distilled, it yields a number of products of decomposition, among which sebaclc ac'n 1 , 
 C'8H 1 6(C0 2 H) 2 , is conspicuous. In a current of superheated steam, at 250 C., it may 
 be distilled without decomposition. In its commonly impure state, it absorbs 
 oxygen readily when exposed to air. 
 
 Fusion with KOH converts oleic acid into acetate and palmitate (see p. 596). 
 
 The constitution of oleic acid follows from the fact that when treated with Br it 
 yields a dibromostearic acid, which is converted by alcoholic potash into stearolic 
 acid containing a treble linking. By oxidation stearolic acid yields two acids, each 
 containing C 9 ; as acids from acetylene alcohols break up on oxidation at the treble 
 linking, stearolic acid, must contain that linking between the ninth and tenth 
 C atoms, and this must also be the position of the double bond in oleic acid. 
 
 By the action of N 2 3 , oleic acid is converted into the isomeric elaidic acid, which 
 is crystalline, and fuses at 51 C. When oxidised by nitric acid, oleic acid yields 
 several acids of the acetic and oxalic series. When heated with amorphous 
 phosphorus and strong hydriodic acid at about 200 C., it yields stearic acid, 
 
 
 The alkali oleates are decomposed by much water into free alkalies and insoluble 
 acid oleates. Sodium oleate is present in ordinary soap, and may be crystallised 
 from absolute alcohol. 
 
 Barium oleate is a crystalline powder, insoluble in water, and sparingly soluble in 
 boiling alcohol. Lead oleate, which forms the chief part of lead plaster, fuses at 
 80 C., and solidifies on cooling to a translucent brittle mass, soluble in ether. 
 
 Erucic acid, C 8 H 17 ' CH :CH[CH 2 ] n ' COOH occurs as a glyceride in rape oil and in 
 the fatty oils of mustard and grape seed. It fuses at 34 C. When heated with 
 phosphorus and hydriodic acid, it gives behenic acid, C^H^'CO^H. Heating with 
 HN0 3 dil. converts it into the isomeride brassidic acid (m.-p. 66 C.). 
 
 369. Acids from Monohydric Acetylene Alcohols. Acids of the 
 general form, C M H 2w _ 3 COOH, may be acetylene derivatives, containing 
 trebly linked carbon atoms, or diolefine derivatives, containing two 
 doubly linked carbon atoms. 
 
 The acetylene acids are obtained from the acids of the oleic series by 
 combining them with two atoms of Br to form dibromacetic acids and 
 treating the products with alcoholic potash ; thus, a/3-dibromopropionic 
 acid yields propiolic acid 
 
 CH 2 BrCHBrCOOH + 2KOH = CH C'COOH + 2KBr + 2HOH. 
 
ACIDS OF THE AEOMATIC SEEIES. 599 
 
 They are also obtained by heating monohalogen substituted oleic acids 
 with alkali 
 
 CH 2 : CBrCOOH + KOH = CH OCOOH + KBr + HOH. 
 These methods should be compared with those for obtaining acetylenes. 
 Another method consists in heating the alkali acetylides with C0 2 
 
 CH 3 CNa + C0 2 = CH 3 C \ OCOONa. 
 
 Like the acetylenes, these acids combine with two or four atoms of 
 Br or other monovalent element, arid those which contain the group 
 * C : CH yield explosive metallic derivatives (p. 538). 
 
 370. Propiolic acid, CH : C'C0 2 H, corresponding with propargyl alcohol, is 
 prepared, as its potassium salt, by heating potassium hydrogen acetylene-dicar- 
 boxylate in aqueous solution ; 
 
 C0 2 H-C : C-C0 2 K = C0 2 + HC i C'C0 2 K. 
 
 It melts at 6 C., boils at 144 C., and yields explosive metallic derivatives. Just 
 as acetylene polymerises to benzene (p. 538), so propiolic acid polymerises (in 
 sunlight) to trimesic acid, C 6 H 3 (COOH) 3 
 
 Tetrollc acid, C 3 H 3 'C0 2 H, has no practical importance. It is produced when 
 /3-chlorocrotonic acid is heated at 100 C. with alcoholic potash. It is also formed 
 by heating sodium allylide in carbon dioxide ; m.-p. 76, b.-p. 203 C. 
 
 Sorbic acid, CH 3 'CH : CH'CH : CH'COOH, is a diolefinic acid, produced by 
 boiling with acid or alkali the yellow fragrant oil obtained by distilling the juice 
 of unripe mountain-ash berries (Sorbus). By oxidation with K 2 Mn 2 8 it yields 
 aldehyde and tartaric acid. 
 
 Sorbic acid fuses at i34-5 C., and is decomposed when distilled, unless in 
 presence of steam. It is sparingly soluble in water, but dissolves in alcohol. 
 
 Linoleic acid, C l7 H 31 'COOH, occurs as a glyceride in linseed oil and some other 
 drying oils. The oil is saponified with KOH, the aqueous solution is precipitated 
 by CaCl 2 and the calcium linoleate extracted by ether. It is a yellowish oil, not 
 altered by N 2 3 . Palmitollc acid is an isomeride. Homolinoleic acid and 
 ttearolic acid, C 8 H 17 'C i C[CH 2 ] 7 -COOH, are also isomerides. 
 
 Linolenic and isolinolenic acids are isomerides of the formula C-^^fiv belonging 
 to the C M H 2w _g-C0 2 H series of acids. They occur as glycerides in linseed oil and 
 other drying oils. 
 
 371. Acids from Monohydric Aromatic Alcohols (Aromatic or 
 Benzole Series). These may be of two kinds : 
 
 (1) Acids containing the COOH group attached to the benzene 
 nucleus, such as benzole acid, C 6 H 5 'COOH,~and toluic acid, C 6 H 4 (CH 3 )' 
 COOH. These are obtainable (a) by oxidising the hydrocarbons con- 
 taining side-chains (p. 548), (b) by oxidising the corresponding alcohols 
 or aldehydes, (c) by the action of sodium and carbon dioxide on 
 the monohalogen substituted hydrocarbons C 6 H 5 Br + CO, + Na, = 
 C 6 H 5 COONa + NaBr, (d) by fusing the alkali salts of the sulphonic 
 acids (p. 648) with alkali formate C 6 H 5 S0 3 Na + HCOONa = 
 C 6 H 5 COONa + NaHS0 3 , (e) by hydrolysis of the cyanogen substitution 
 products of the hydrocarbons C 6 H 5 CN + 2HOH = C 6 H 5 COOH + NH,. 
 
 (2) Acids containing the COOH group as part of the side-chain ; 
 these may be regarded as open-chain acids in which aromatic radicles 
 (CJL; C fi H 4 (CHA &c.) have been substituted for H, as in phenylacetic 
 acid, C 6 H 3 -OH 2 -COOH, and tolylacetic acid, C 6 H 4 (CH 3 )'CH,'COOH. 
 They may be prepared by hydrolysis of the corresponding cyanogen 
 derivatives C 6 H 5 -CH 2 -CN + 2 HOH = C 6 H 5 -CH 2 'COOH + NH 3 . 
 
 The aromatic acids are crystalline, volatile, sparingly soluble in 
 water, but soluble in alcohol and ether. They show most of the reactions 
 of the fatty acids, and like them are converted into hydrocarbons when 
 heated with lime, which abstracts CO 2 . 
 
600 BENZOIC ACID. 
 
 372. Benzole acid, C 6 H 5 'C0 2 H (phenyl formic acid). This acid was 
 originally extracted from gum benzoin, a resinous exudation from Styrax 
 benzoin, a tree of the Malay Islands. 
 
 When the gum is gently heated in an iron or earthen vessel, covered with 
 perforated paper and surmounted by a drum of paper, the benzoic acid, which 
 exists uncombined in the resin, rises as vapour and condenses in the drum. A 
 better yield is obtained by boiling the benzoin with lime and water, and decom- 
 posing the filtered solution of calcium benzoate with hydrochloric acid. 
 
 It is also made from the urine of cows- and horses, which contains 
 hippuric acid, easily convertible into benzoic acid (see Hippuric acid). 
 
 But the chief source of modern benzoic acid is toluene, C 6 H 5 'CH 3 . 
 This is directly convertible into benzoic acid by oxidation with nitric 
 acid, C 6 H 5 -CH 3 + 2 HNO 3 = C 6 H.-C0 2 H + 2 HOH + 2 NO. 
 
 It is cheaper, however, to convert the toluene into benzo-trichloride 
 by passing chlorine into it at 180 C., and to heat the product with 
 lime ; C 6 H 5 -CH 3 + C1 6 = C 6 H 5 'CC1 3 + 3 HC1 ; 2C 6 H 5 C1 3 + 4 Ca(OH) 2 = 
 3CaCl 2 + (C 6 H 5 -C0 2 ) 2 Ca + 4HOH. The calcium benzoate is decomposed 
 by hydrochloric acid, when benzoic acid separates. 
 
 Much benzoic acid is obtained as a by-product in making benzalde- 
 hyde from toluene (p. 584), for much of the benzaldehyde is converted 
 into benzyl alcohol and calcium benzoate by the excess of lime used 
 
 (P- 585). 
 
 Benzene, C 6 H 6 , may be partly converted into benzoic acid by oxidising 
 
 it with MnO 2 and H 2 S0 4 . Addition of formic acid increases the yield 
 of benzoic acid ; C 6 H 6 + H'C0 2 H + = C 6 H 5 'C0 2 H + H 2 0. 
 
 Properties of benzoic acid. It crystallises in shining needles or in 
 feathery scales, usually having a faint aromatic odour. It fuses at 
 120 C. and boils at 250 C., subliming without decomposition; it 
 volatilises when boiled with water. It is sparingly soluble in cold 
 water (200 parts), more easily in hot water (24 parts) ; alcohol and 
 ether dissolve it 'readily. Potash and ammonia also dissolve it imme- 
 diately, and it is precipitated on adding an acid, Most of the benzoates 
 are soluble, but ferric benzoate is obtained as a buff-coloured precipitate 
 when ferric chloride is added to a neutral benzoate. 
 
 By distillation with excess of lime, benzoic acid yields benzene 
 C 6 H 5 -C0 2 H + CaO = CaC0 3 + C 6 H 6 . 
 
 When vapour of benzoic acid is passed over heated zinc-dust, it is 
 converted into bitter-almond oil (benzoic aldehyde) 
 C 6 H 5 -C0 2 H + Zn = C 6 H 5 -CHO + ZnO. 
 
 By boiling with strong HNO 3 , benzoic acid is converted into nitro- 
 benzoic acids, C 6 H 4 (NOj)'CO 2 H, of which three exist. 
 
 By distilling benzoic acid with PC1 5 , benzoyl chloride is obtained; 
 C 6 H 5 -COOH + PC1 5 = C 6 H 5 -COC1 + POCI 3 + HC1. This chloride bears 
 the same relation to benzoic acid as acetyl chloride bears to acetic acid, 
 the radicles benzoyl and acetyl being related in a similar way to benzyl 
 and ethyl : 
 
 Ethyl, CH 3 -CH 2 ; Acetyl, CH 3 'CO Benzyl, C 6 H 5 'CH 2 ; Benzoyl, C 6 H 5 'CO 
 
 Ethyl hydride (ethane), GH.'CH 8 Benzyl hydride (toluene), C 6 H 5 'CH S 
 
 Ethyl hydroxide (alcohol), CH 3 -.CH./OH Benzyl hydroxide, C 6 H 5 'CH 2 OH 
 
 Acetyl hydride (aldehyde), CH 3 'COH Benzoyl hydride, C 6 H 5 'COH 
 
 Acetyl hydroxide (acetic acid), CH 3 'COOH Benzoyl hydroxide, C 6 H 5 'COOH 
 
CINNAMIC ACID. 6oi 
 
 ibenzoyl oxide, (C 6 H 5 'CO) 2 0, is produ 
 um benzoate 
 C 6 H 5 -COC1 + C 6 H 5 -COONa = (C 6 H 5 'CO) 2 + NaCl. 
 
 373. Benzole anhydride, or dibenzoyl oxide, (C 6 H 5 'CO) 2 0, is produced by heatinir 
 benzoyl chloride with dry sodium benzoate 
 
 mass is washed with water and the anhydride crystallised from alcohol. It 
 at 42 C. and boils at 360 C. Boiling with water converts it slowly into 
 
 The mass 
 fuses 
 benzoic acid. 
 
 By heating benzoyl chloride with dry sodium acetate, lenzoacetlc anhydride is 
 obtained ; C 6 H 5 -COCl + CH 3 -COONa = (C 6 H 5 -CO)(CH 3 -CO)0 + NaCl. 
 
 Benzoic peroxide (C 6 H 5 'CO) 2 2 , is obtained by acting on benzoyl chloride with 
 barium dioxide ; 2C 6 H 5 'COC1 + Ba0 2 = (CgHg-CO)^ + BaCl 2 . It may be crystallised 
 from ether. Like hydrogen peroxide, it is decomposed "explosively when mode- 
 rately heated. Alkalies resolve it into benzoic acid and oxygen. 
 
 374. Toluic acids, or methyl-lenzoic adds, C 6 H 4 (CH 3 )'C0 2 H, are obtained by oxidis- 
 ing the three xylenes, C 6 H 4 (CH 3 ) 2 , with dilute nitric acid. The i : 2-acid crystal- 
 lises in needles, fusing at 102 C., and is sparingly soluble in water. 
 
 Mesttylenic acid, 1:3: 5-C 6 H 3 (CH 3 ) 2 'C0 2 H, is prepared by oxidising mesitylene, 
 (P- 549) 5 with dilute nitric acid. It is a crystalline volatile acid, fusing at 166 C. 
 and soluble in boiling water and in alcohol. 
 
 Cuminic or isopropyl-benzoic acid, i : 4-C 6 H 4 (C 3 H 7 )'C0 2 H, is prepared from the 
 aldehyde existing in Roman cummin oil, by boiling it with alcoholic solution of 
 potash, which converts it into cuminic alcohol and potassium cuuiinate. On 
 adding an acid to the aqueous solution of potassium cuminate, the cuminic acid 
 is precipitated, and may be crystallised from alcohol ; it fuses at 116 C., and may 
 be sublimed. 
 
 375. Phenylolefinecarboxylic acids are those in which the COOH group occurs 
 in an un saturated side-chain (p. 549). 
 
 Cinnamic or B-phenyl-aorylic acid, C 6 H 5 'CH : CH'C0 2 H, is prepared by boiling 
 storax with soda, and decomposing the solution of sodium cinnamate with HC1, 
 which precipitates the cinnamic acid in feathery crystals like benzoic acid, fusing 
 at 133 C., boiling at 300, and subliming undecomposed. It is soluble in boiling 
 water and in alcohol. 
 
 Its connection with acrylic acid is shown by fusing it with potash, which yields 
 acetate and benzoate of potassium, whilst acrylic acid yields acetate and formate ; 
 
 Oxidising agents convert cinnamic acid into benzoic aldehyde (bitter-almond 
 oil); C 6 Hg-CH : CH-C0 2 H + 4 = C 6 H 5 'CHO + 2C0 2 + H 2 0. When distilled with 
 excess of lime, it yields cinnamene or phenyl-ethylene (p. 550). 
 
 Nascent hydrogen converts it into fi-phenyl-propionic acid or hydrocinnamic acid; 
 C 6 H 5 -CH : CH-C0 2 H + H 2 = C 6 H 5 'CH 2 -CH 2 C0 2 H. 
 
 Cinnamic acid may be obtained synthetically by the action of sodium acetate 
 on bitter-almond oil, in presence of acetic anhydride, which probably acts as a 
 dehydrating agent; CH 3 -C0 2 Na + C 6 H 5 'CHO = C 6 H 5 -CH : CH'C0 2 Na + H 2 ; and 
 by heating benzal chloride with sodium acetate 
 
 C 6 H 5 -CHC1 2 + CH 3 -COONa = C 6 H 5 'CH : CH'COONa + 2 HC1. 
 
 Atropic acid, a-phenyl-acrylic acid, C 6 H 5 'C^ , is produced when atropine, 
 
 CH 2 
 the Q alkaloid of deadly nightshade, is boiled with baryta or with HC1. It fuses at 
 
 The'napthoic acids (a and j8), C 10 H 7 'C0 2 H, are monocarboxylic naphthalenes, 
 obtained by the hydrolysis of the corresponding cyanogen derivatives. 
 
 376. Monobasic Acids from Polyhydric Alcohols. As already 
 noticed (p. 574), these acids may be alcohol- acids, or aldehyde-acn 
 if the polyatomic alcohol be a glycol, and keto-acids, or even toeft 
 alcohol- or keto-aldehyde-acids, if the alcohol be polyhydric, in v 
 case it must contain both primary and secondary alcohol groups. -J 
 
 Alcohol-acids are termed hydroxy-acids, a title which is warrants 
 the fact that they can be prepared from the chloro-substituted open- 
 chain acids of the foregoing series by treatment with silver oxicl. 
 water, showing that OH has been substituted for the 01, as, t 
 
602 GLYCOLLIC ACID. 
 
 instance, when monochloracetic acid is converted into glycollic acid ; 
 CH 2 C1-COOH + AgOH = CHOH-COOH + AgCl. 
 
 It will be found that the hydrogen of the hydroxyl group in a 
 hydroxy-acid can be exchanged for a metal, just as it is in the hydroxyl 
 group of an alcohol, so that the acid possesses the functions of both 
 an alcohol and an acid. Thus, the monobasic hydroxy-acids may con- 
 tain two or more H atoms, which can be exchanged for a metal, although 
 they are strictly monobasic, since they contain only one C0 2 H group ; 
 hence they are sometimes termed diatomic (triatomic, &c.) monobasic 
 -acids. 
 
 Besides the treatment of the monohalogen substituted fatty acids 
 with silver oxide or alkali, referred to above, there is a number of other 
 methods available for preparing hydroxy-acids. One of these is, of 
 course, the oxidation of the polyhydric alcohols ; another is the 
 oxidation of fatty acids containing the group R 2 CH, such as iso- 
 butyric acid, (CH 3 ) 2 CH COOH, which yields hydroxyisobutyric acid, 
 (CH 3 ) 2 C(OH)'COOH, when oxidised with alkaline permanganate. Or 
 the olefine acids may be converted by hydrolysis into hydroxy-acids, 
 CH : CH-COOH + H 2 = CH 2 'CH(OH) COOH. Again, the amido- 
 .acids may be treated with nitrous acid, CH 2 (NH 2 )'COOH (amido-acetic 
 acid) + NO'OH = CH 2 (OH)'COOH + N 2 + H 2 (cf. p. 105). The general 
 method of hydrolysing cyanogen derivatives is also available ; thus the 
 -aldehydes, when treated with HCN, yield cyanohydrins, such as 
 CH 3 -CH(OH)'CN, and these may be hydrolysed to acids (p. 587). 
 
 The simplest hydroxy-acid, hydroxy '-formic acid, HO'COOH, would 
 be the first anhydride of orthocarbonic acid (p. 261), carbon monoxide 
 Tjeing the second anhydride. It does not exist, probably for the reason 
 already given (p. 573), but if it did,it might be identical with carbonic 
 acid. 
 
 When copper sulphate solution is added to a strong solution of potassium car- 
 bonate, a deep blue solution is obtained which is similar to, although less stable than, 
 the solutions obtained by adding copper sulphate to other hydroxy-acids. This 
 .supports the supposition that carbonic acid is hydroxy-formic acid. 
 
 Glycollic or hydroxy acetic acid, CH^OH'COaH, is a product of 
 the oxidation of glycol, CH 2 OH'CH 2 OH, by dil. HN0 3 , but is best pre 
 pared by the careful oxidation of alcohol by nitric acid. 
 
 Into a narrow glass cylinder (2 inches in diameter) pour 118 cubic centimetres 
 of 80 per cent, alcohol ; insert a funnel tube drawn out to a fine opening, to the 
 bottom of the vessel, and pour in 50 c.c. of water, so as to form a layer below the 
 alcohol ; then pour in carefully through the funnel 126 c.c. of nitric acid of 
 sp. gr. 1.35, to form a layer below the water. Place the vessel aside, without 
 shaking, for about five days at about 20 C., when the three layers will have 
 mixed. Evaporate the liquid upon the water-bath, in separate portions of about 
 20 c.c. to a syrup, dilute it with 10 volumes of water, boil, and neutralise with 
 powdered chalk. To the crystalline paste which forms on cooling, add an equal 
 bulk of alcohol, and filter. The precipitate is boiled with water, and filtered, 
 while boiling, from undissolved calcium oxalate. On cooling, it deposits calcium 
 .glyoxylate, whilst calcium glycollate remains in solution ; this is boiled with a 
 little lime to decompose any glyoxylate, and the filtered solution evaporated and 
 treated with enough oxalic acid to precipitate the calcium as oxalate, leaving 
 glycollic acid in solution. 
 
 The action of nitric acid upon alcohol is of a representative character. 
 The groups OH 3 and CH 2 'OH, contained in ethyl alcohol, are converted 
 under the influence of oxidising-agents into CHO, characteristic of the 
 
LACTIC ACID. 
 
 aldehydes, and COOH, characteristic of the acids respectively Accord- 
 ingly, we find, among the products of the oxidation by nitric acid 
 acetic aldehyde, CH 3 'CHO ; acetic acid, CH 3 'COOH ; glyoxal, CHOCHO- 
 glyoxylic acid, CHOCOOH; glycollic acid, CHyOH'COOH; and oxalic 
 acid, COOH-COOH. 
 
 Glycollic acid has been obtained by allowing the vinegar ferment 
 bacterium aceti, to grow in a dilute solution of glycol (ethene-alcohol) 
 
 Properties of glycollic acid. Crystallises with some difficulty ; fuses 
 at 80 C., and volatilises slowly at 100. Very soluble in water, alcohol 
 and ether. 
 
 As might be expected, oxidising-agents convert it into oxalic acid, from which it 
 may be obtained by reduction. When heated with sulphuric acid it yields formic 
 aldehyde and formic acid ; CH 2 OH-C0 2 H = H-CHO + H'C0 2 H. The formic alde- 
 hyde is converted into formic paraldehyde, (HCOH) 3 , and most of the formic acid 
 is decomposed in H 2 and CO. 
 
 When glycollic acid is heated with HC1 it yields chloracetic acid- CH OH- 
 2 H+HClCH 2 Cl-C0 2 H + H 2 0. With PC1 5 it yields chloracetyl chloride, 
 
 Hydriodic acid reduces glycollic to acetic acid 
 
 CH 2 OH-C0 2 H + 2HI = CH 3 -C0 2 H + H 2 +I 2 . 
 
 The gly collates of calcium, copper, and silver are sparingly soluble in cold water 
 but dissolve in boiling water. 
 
 Glycollic acid occurs in unripe grapes, and in the leaves of the Virginia creeper. 
 It can be made from glucose by oxidising it with silver oxide, in the presence 
 of calcium carbonate to keep the solution neutral, or else the glycollic acid becomes 
 oxalic acid. 
 
 377. Lactic acids or hydroxypropionic acids, C 2 H 4 (OH)-C0 2 H. 
 Since propionic acid is CH 3 -CH 2 -COOH, there can be two hydroxy- 
 propionic acids, viz., the a-acid, CH 3 -CHOITCOOH, and the /3-acid, 
 GH 2 OH-CH 2 'COOH ; the former is called ethylidetie lactic acid, and the 
 latter ethylene lactic acid. 
 
 Ethylidene lactic acid, CH ? -CHOH'COOH, is also known as fermenta- 
 tion lactic acid, being the acid of sour milk produced by the fermenta- 
 tion of the milk sugar by the lactic bacillus. As pointed out at p. 593, 
 glucose also undergoes this fermentation, the source of the bacillus in 
 that case being putrid cheese ; the chemical change is expressed by the 
 equation C 6 H 12 6 =-- 2 C 3 H 6 3 . 
 
 On a large scale a mash of starchy material, such as maize, is treated with malt to 
 convert the starch into maltose, and is then mixed with a cultivation of the bacillus. 
 chalk being stirred in for the purpose of neutralising the lactic acid as it is formed, 
 lest it kill the bacillus. The most favourable temperature is about 50 C. When all 
 the maltose has been converted, the solution of calcium lactate is treated with 
 sulphuric acid, the precipitated CaS0 4 is filtered off, and the dilute lactic acid 
 is concentrated in a vacuum pan to a strength of about 50 per cent., in which form 
 it is sold for use as a mordant and as an addition to the tanning liquors in leather 
 factories. 
 
 Pure lactic acid, obtained by decomposing zinc lactate with H 2 S, is a 
 colourless, strongly acid liquid which crystallises when cooled and then 
 melts at 18 C. It can be distilled at 120 C. under 12 mm. pressure, 
 but at higher temperatures it loses water, yielding a much more stable 
 
 /CH(CH 3 )C(\ 
 compound, lactide, O< xr.Tr/ which melts at I2 5 - and 
 
 boils^at 255 C. 
 
604 STEREOISOMERISM. 
 
 It is characteristic of the a-alcohol acids that they yield anhydrides from two- 
 molecules by the loss of water derived from the alcoholic groups or from the 
 carboxylic groups, or from both. Thus from two molecules of glycollic acid may be 
 obtained, by loss of one molecule of water, COOH'CH 2 - - CH 2 COOH (diglycollic 
 acid), CH 2 OH-CO-0-CO-CH 2 OH (not known), or CH 2 OH'CO -0-CH 2 .COOH 
 (glycolglycolUc acid, an ethereal salt formed from the add glycollic acid and the 
 alcohol glycollic acid). If the first and second of these lose another mol. H 2 the same 
 
 compound will be formed, namely 0<^ No (diglycollic anhydride) ; from 
 
 CHo'CO 
 
 /-ITT .rir\ 
 
 the third, the subtraction of another mol. H 2 yields glycolide, 0<^ ^ ^>0, of 
 
 CO *CH 2 
 which lactide is a homologue. 
 
 Ethylidene lactic acid is found in the gastric juice, and in opium. 
 
 When lactic acid is heated at 130 C. with dilute sulphuric acid, in a sealed 
 tube, it yields aldehyde and formic acid; C 2 H 5 (>C0 2 H = CH 3 'CHO + H'C0 2 H. 
 Oxidation with K 2 Mn 2 8 converts this lactic acid into the ketonic acid, pyruvic 
 acid, CH 3 'CO'COOH. This is only to be expected, since ethylidene lactic acid 
 contains a secondary alcohol group CHOH (see p. 568). Nitric acid oxidises lactic 
 acid to oxalic acid. Chromic acid converts it into acetic acid, C0 2 and H 2 0. Since 
 lactic acid is hydroxypropionic, it may be reduced to propionic acid by strong 
 hydriodic acid ; C 2 H 4 (OH)-C0 2 H + 2HI = C 2 H g -C0 2 H + H 2 + I 2 . Conversely, 
 propionic acid may be converted into lactic by the following steps : 
 (i) CH 3 -CH 2 -C0 2 H + Br., = CH 3 CHBrC0 2 H + HBr. ; (2) CH 3 'CHBr-C0 2 H + 
 KOH = CH 3 -CHOH-C0 2 H + KBr. 
 
 Lactic acid is producible from aldehyde through its HCN derivative (see above). 
 
 The lactates are mostly soluble ; the most important of them is the zinc lactate 
 (C 2 H 5 0'C0 2 ) 2 Zn.3H 2 0, which is sparingly soluble in water, and is precipitated 
 in prismatic crystals when zinc sulphate is added to lactic acid neutralised by 
 ammonia. Salts of the type CH 3 'CHOM'C0 2 M are known : thus sodium sodio- 
 lactate, CHg'CHONa'COoNa, is prepared by the action of sodium on sodium 
 lactate. 
 
 378. Stereoisomerism as Illustrated by Ethylidene Lactic 
 Acid. Ethylidene lactic acid is also found in juice of flesh (Liebig's 
 extract of meat), in bile, and in the urine of persons poisoned by 
 phosphorus. This lactic acid has been termed sarcolactic acid or 
 paralactic acid, because it is not identical in all its properties with the 
 fermentation lactic acid described above. Chemically speaking, the 
 difference is exceedingly slight, amounting mainly to a greater solubility 
 of zinc sarcolactate (which crystallises with 2H 2 0) than of zinc ferment- 
 ation lactate, and a smaller solubility of the calcium salt (4H 2 0). The 
 physical difference between the two is considerable, for whilst the fer- 
 mentation acid is inactive towards polarised light, sarcolactic acid rotates 
 the plane of polarisation to the right. This property leads to the 
 distinctive titles, dextro-ethylidene lactic acid for sarcolactic acid, and 
 inactive ethylidene lactic acid for the fermentation acid. If kept in a 
 desiccator for some time, the dextro-acid becomes converted into an 
 anhydride the solution of which is Isevo-rotatory, but the lactide 
 obtained by heating the acid yields inactive lactic acid when dissolved. 
 The salts of the dextro-acid are Isevo-rotatory. 
 
 When cane sugar is fermented by means of a certain bacillus, a Icevo- 
 ethylidene lactic acid is produced, the salts of which are dextro-rotatory. 
 
 It seems that there are three ethylidene lactic acids, which may be 
 distinguished as i-, d-, and I- ethylidene lactic acid respectively. But 
 when equal weights of the d- and I- acids are mixed together the pro- 
 duct is found to be optically inactive ; hence it may be concluded that 
 the inactive acid is made up of an equal number of molecules of the 
 
STEREOISOMEEISM. 605 
 
 d- and I- acids, which neutralise each other, so that in considering a 
 theory to account for the existence of these three acids, it is only 
 necessary to attempt to explain the isomerism of the dextro- and Isevo- 
 modifications. The theory of position isomerism, already mentioned, 
 will not suffice to furnish an explanation, because the only possible 
 position isomeride of ethylidene lactic acid, according to the theory, 
 is ethylene lactic acid, from which both the d- and the I- acids differ 
 chemically. 
 
 The examination of a large number of compounds which are optically 
 active has shown that each contains one or more carbon atoms to which 
 are attached four different elements or radicles ; thus, in ethylidene lactic 
 acid, CH 3 'CHOH'COOH, the middle carbon atom has each of its atom- 
 fixing powers satisfied by a different radicle ; viz., CH 3 , H, OH, and 
 COOH. Such a carbon atom is said to be asymmetric, and it is believed 
 that an optically active compound is one which possesses one or more 
 asymmetric carbon atoms.* 
 
 Several cases of isomerides differing from each other in optical 
 activity have been noticed in the preceding pages ; in each case it will 
 be found that the accepted formula for the compound contains one or 
 more asymmetric carbon atoms. Thus three of the 14 isomeric amyl- 
 alcohols (p. 569) occur in the d-, 1-, and i-form ; and in each the 
 original methane carbon atom has four different radicles attached to 
 it, namely in one OH 3 , CH 3 'CH 2 , H and CH 2 OH ; in another 
 CH 3 , CH 3 -CH 2 -CH 9 , H and OH ; and in the third CH 3 , (CH 3 ) 2 CH, H 
 and OH. 
 
 Where a compound contains more than one asymmetric carbon atom 
 the cases of isomerism are more numerous and such will receive notice 
 under Tartaric Acid and the Sugars. 
 
 No hypothesis has been suggested upon which it is possible to 
 prophesy whether a given compound, containing an asymmetric carbon 
 atom will be dextro- or Isevo-rotatory. 
 
 The most fruitful hypothesis for explaining the existence of d- and l- 
 isomerides having an asymmetric carbon atom is that the four groups 
 attached to this carbon atom are differently arranged in space, in the 
 two isomerides, which are therefore called stereoisomerides (o-rfpeos, 
 solid). If the carbon atom be considered to occupy the centre of a 
 tetrahedron in space, as suggested at p. 534, it will be found that no 
 essentially different structures can be made, unless each corner of the 
 tetrahedron has a different radicle attached to it. 
 
 For if two tetrahedra be constructed, the corners of which are represented by 
 A, A, A, B, or A, A, B, B, or A. A, B, C, or any combination of four letters, two or 
 more of which are the same, it will be found to be always possible to put the one 
 tetrahedron inside the other in such a manner that the four letters on the corners 
 of the one shall coincide with the four letters on the corners of the other. If, how- 
 ever, the four corners of each be represented by the four different letters A, B, 0, D, 
 it will be found possible so to arrange these letters that the one tetrahedron cannot 
 be introduced into the other in such a manner that the four corners correspond. 
 The arrangement necessary will be understood from the statement that i 
 observer be opposite those faces of the tetrahedra which are similarly 1< 
 order of the letters on the one face,willibe the reverse of the order of the letters on th 
 other face ; if the letters A, B, C, for instance, be in the order of the motion of 
 hands of a clock on the face of one tetrahedron they will be in the reverse orae- 
 C, B, A, on the face of the other. Such an arrangement is depicted m Fig. 274, tr< 
 
 * Cf. Amyl alcohol (p. 569). 
 
6o6 STEREOISOMERISM. 
 
 which it will be seen that the two arrangements bear the same relationship to each 
 other as an object bears to its image. 
 
 It is in the above manner that Le Bel and Van't Hoff have sought to explain why 
 no isomerides of methane substitution-products, except of those of the type 
 CRjRaRgR^ exist. If the compound which is arranged in the clock-wise manner 
 in Fig. 274 be dextro-rotatory, then that which is anticlock-wise will be lasvo- 
 rotatory. 
 
 The theory has been tested by investigating compounds which, by the process of 
 their formation, ought to contain an asymmetric carbon atom, although they were 
 known only in an inactive form. By appropriate treatment many such compounds 
 have been resolved into a dextro- and lasvo-form ; the principal methods of treat- 
 ment are (i) Crystallisation from water, advantage being taken of the greater 
 solubility of one of the active forms ; in this manner the zinc-ammonium salt of 
 i-lactic acid has been resolved into the zinc-ammonium salts of the d- and Z-acids. 
 (2) Treatment of the inactive compound with another active compound, and 
 crystallising the product ; thus, if the inactive compound is acid it is crystallised 
 with an active base, such as strychnine ; if it is basic it is crystallised with an 
 active acid, such as tartaric acid. In either case, the salt formed is separated by 
 crystallisation into a d- and I- modification, the one or the other being the more 
 soluble. Fermentation lactic acid is split up by crystallising it with strychnine, 
 the Z-strychnine lactate separating first. (3) Fermentation of the inactive com- 
 pound with some bacillus which feeds on one of the active forms rather than upon 
 the other ; some fungi show a similar preference. 
 
 The second method has proved the most fruitful, and by its means optically 
 active sulphur, tin and nitrogen compounds, containing an asymmetric S, Sn, and 
 N atom respectively, have been prepared. 
 
 As Sn falls in the same periodic group as C (p. 302) and is a true tetravalent 
 element, the fact that it forms optically active compounds is of particular interest. 
 By a series of reactions, which will be understood better after the student has 
 perused the section on organo-mineral compounds, an inactive methylethylpropyl 
 
 CHg v xCgHf 
 
 tin iodide, >Sn< , has been obtained. This obviously contains an asym- 
 
 C 2 H/ X I 
 
 metric tin atom, and by treating it with the silver salt of an optically active 
 acid, d-camphorsulphonic acid, so as to exchange the iodine for the radicle of 
 the active acid, and then evaporating the solution, crystals are obtained which 
 are more dextro-rotatory than is the d-camphorsulphonic acid. From these 
 crystals a dextro-rotatory methylethylpropyl tin iodide is obtained by treatment 
 with KI. 
 
 Sulphur is in the sixth group of the periodic classification ; nevertheless, there 
 are some organic derivatives of this element in which it appears to be tetravalent, 
 e.g., the thetines. One of these is prepared by the action of bromacetic acid, 
 CH 2 BrCOOH, on methylethylsulphide, CH 3 -S'C 2 H 5 ; it is inactive, and is known as 
 
 Br .CH 3 
 
 methylethylthetine bromide, > S < .If this view of the structure of 
 
 C 2 H/ X CH 2 -COOH 
 
 the thetine is correct, the S atom is asymmetric and the inactive compound should 
 be capable of yielding optically active components. By applying ^-camphor- 
 sulphonic acid in the manner described above, the d-form has been isolated. 
 
 The discovery of optically active nitrogen compounds has extended the theory 
 of the connection between asymmetry and optical activity to pentavalent elements. 
 
ETHYLENE LACTIC ACID. 
 
 If in ammonium iodide, NHJ, there is substituted for each H atom a different 
 hydrocarbon radicle, an asymmetric nitrogen compound will be produced Snr h 
 quaternary ammonium compounds are well known, and lately one, ben-vlvhenvl 
 rilylmetkylammommi iodide, N(C 6 H 5 -CH. 2 )(C 6 H 5 )(C 3 H 5 )(CH 3 )I, has been ^ esoTved 
 into optically active components by the aid of d-camphorsulphonic acid. 
 
 Ethylene lactic acid, or fi-hydroxypropionic acid,CH (OHVCH 
 C0 2 H,is also found in juice of flesh, and is made by treating/3-ioflopro' 
 pionic acid, CH 2 I-CH 9 -C0 2 H, with moist silver oxide. Its formula is 
 confirmed by its formation from glycol chlorhydrin, CH Cl'CH OH 
 (and therefore from ethylene, p. 575), by conversion into "the cyano- 
 hydrin, CH 2 CN.CH 2 OH, and hydrolysis of the latter. It is a syrupy 
 mass, and is distinguished from ethylidene lactic acid by yielding no- 
 anhydrides, but acrylic acid, CH 2 : CH'C0 2 H, and water, when heated ; 
 hence it is sometimes called hydracrylic acid. This is characteristic of 
 /3-alcohol acids, which generally yield a/3-olefine acids when heated. 
 
 When oxidised it yields carbonic and oxalic acids instead of acetic. Its zinc 
 salt (4H 2 0) is very soluble in water. 
 
 379. Hydroxybutyricacidssirefourmnumber: thea-acid,CH 3 'CHo-CH(OHyCO H 
 the -acid, CH 3 -CH(OH)-CH 2 'C0 2 H, the 7 -acid, CH 2 OH'CH 2 -CH 2 -C0 2 H, and the V 
 iso-acid (CH 3 ) 2 : C(OH)'C0 2 H. A fifth, viz., the /3-iso-acid (CH 3 )(CH 2 OH): CH'C0 2 H 
 is obviously possible, but is not known. 
 
 The 7-hydroxy-acids are very unstable, and when an attempt is made to- 
 liberate them from their salts by addition of a more powerful acid they immediately 
 lose water, becoming " intramolecular anhydrides," or lactoms. These are interest- 
 ing compounds, for they may be regarded as internally formed ethereal salts 
 (cyclic esters), just as ethyl acetate is an externally formed ethereal salt (c/.glycol- 
 
 glycollic acid, p. 604). Thus, 7-hydroxybutyric acid, 2 2 , yields butyro- 
 
 CH 2 *COOH 
 
 r^TT OTT 
 
 lactone, 2 \0. The acids containing five carbon atoms can yield 5-hydroxy 
 
 CHo'CO 
 
 acids and these lose water forming 8-lactones. Both 7- and 5-lactones are fairly 
 stable, being only partially converted into the corresponding acids by boiling 
 water, but into salts of these acids by alkalies. 
 
 o.-Hydro.%'ycaproic acid, or leucic acid ; see Leucine. 
 
 RiciTioleic and iso-ricinoleic acids are hydroxyoleic acids, C 17 H32(OH)'C0 2 H, 
 which occur as glycerides in castor oil. 
 
 379. Polyhydroxy-monobasic acids. Gly eerie acid, CH 2 OH-CHOH-C0 2 H, is a 
 primary-secondary-alcohol-acid ; it has been already mentioned as an oxidation 
 product of glycerine. When produced in this way it is optically inactive, but both 
 an I- and a d- variety have been obtained. 
 
 A number of polyhydric monobasic acids is produced by the oxidation of the 
 sugars ; these are known as hexonic acids, CH 2 OH > [CHOH]4'C0 2 H. They are 
 stereoisomerides of each other, being either d- acids, I- acids, or i- acids. They 
 will receive further notice under the sugars. 
 
 379*. Aldehyde-acids. Glyoxylic, or glyoxalic acid, CHO'C0 2 H, is a product of 
 the oxidation of glycol and of alcohol. It crystallises in prisms and distils with 
 steam. Being aldehydic in nature, it forms a crystalline compound with NaHS0 8 . 
 and reduces silver salts, being thereby oxidised to oxalic acid. 
 
 Glycuronic acid, CHO-[CHOH] 4 'C0 2 H, is obtained by reducing saccharic acid 
 (q.r.) with sodium amalgam ; it is a syrup which is readily converted into a lactone 
 (see above), 
 
 380. Monobasic Acids from Hydroxy-Benzenes. The OH 
 groups in these acids may be attached either to the benzene nucleus, in 
 which case the acids are phenol acids, not alcohol-acids, or they may 
 occur in the side-chain, in which case the acid is an alcohol-acid ; thus, 
 salicylic acid is a phenol-acid, C 6 H 4 (OH)-COOH, whilst pJienyl-glycolhc 
 acid is an alcohol-acid, C 6 H 5 -CHOH'COOH. 
 
608 SALICYLIC ACID. 
 
 The most important general reactions for obtaining the phenolic acids 
 are as follows : (i) The sodium phenols are heated with CO 2 (see 
 salicylic acid). (2) The phenols are boiled with CC1 4 and KOH ; 
 C 6 H 6 OH + CC1 4 + 5KOH = C 6 H 4 (OH)-COOK + 4 KC1 + 3 HOH. (Cf. the 
 method for making hydroxy -aldehydes ; p. 585.) (3) The homologues 
 of phenol are oxidised by fusion with KOH; C fi H 4 (OHVCIL + 2KOH = 
 C 6 H 4 (OK)-COOK + 3 H 2 . 
 
 The alcohol-acids are made by reactions similar to those used in 
 making the paraffin alcohol-acids. 
 
 Like the alcohol-acids, the phenol-acids yield two classes of salts, e.g., 
 C 6 H 4 (OH)-OO 1 Na, and C 6 H 4 (ONa)'C0 2 Na, the former being produced 
 when the acid is dissolved in Na 2 C0 3 , the latter when NaOH is used. 
 
 Hydroxybenzoic acids, C~H 4 (OH)-CO 2 H. Being di-substituted 
 benzenes, these are three in number. The most important is the 1:2- 
 acid or salicylic acid. This is prepared artificially by combining phenol 
 with soda, and heating the product in carbonic acid gas. 
 
 The phenol, with half its weight of NaOH, is dissolved in a little water and 
 evaporated to dryness. This sodium-phenol is powdered, placed in a flask or retort, 
 and heated at 100 C. in a slow stream of dry C0 2 for some hours. The tem- 
 perature is then raised to 180 C., when phenol distils over, and continues to do so 
 till the temperature has risen to 250 C. The residue is dissolved in a small 
 quantity of water, and strong HC1 added to precipitate the salicylic acid, which 
 may be purified by crystallisation from water. 
 
 By dissolving phenol in soda, sodium-phenol is produced 
 
 C 6 H 5 -OH + NaOH = C 6 H 5 'ONa + HOH. 
 
 When this is heated in C0 2 , it yields phenol and sodio-salicylate of 
 sodium; 2 C 6 H 5 ONa + C0 2 = C 6 H 5 OH + C 6 H 4 (ONa)'C0 2 Na; this last, 
 decomposed by HC1, yields salicylic acid 
 
 C 6 H 4 (ONa)-C0 2 Na + 2HC1 = C 6 H 4 (OH)'C0 2 H + 2NaCl. 
 
 Salicylic acid was formerly made from oil of winter-green (Gaultheria, 
 a North American plant of the heath order), which is the methyl 
 salicylate, C 6 H 4 (OH)'C0 2 CH 3 . Its original source was salicin, a glu- 
 coside extracted from willow-bark, which yields the salicylate when 
 fused with potash. Salicylic acid has been found in the leaves, stems, 
 and rhizomes of some of the Violacece, and in the garden-pansy. 
 
 Properties of salicylic acid. It forms four-sided prisms which fuse at 
 155 C., and sublime, if carefully heated ; but a temperature of 220 
 decomposes it into phenol and CO 2 ; C 6 H 4 (OH)'C0 2 H = C0 2 + C 6 H 5 'OH. 
 This change occurs more readily in presence of an alkali, to absorb the 
 C0 2 . It dissolves sparingly in cold water, more easily on heating, and is 
 soluble in alcohol and ether. Its solution gives an intense violet colour 
 with ferric chloride, a reaction not exhibited by the p- and w-hydroxy- 
 benzoic acids. It possesses antiseptic properties, and is used for the 
 preservation of articles of food, being free from taste and smell. It is 
 also used in making dyes, and sodium salicylate is a well-known anti- 
 rheumatic. 
 
 The salicylates of K and Na are crystalline : barium salicylate (C 6 H 4 OH 
 C0 2 ) 2 Ba.Aq, also crystallises, and, when boiled with baryta- water, yields a sparingly 
 soluble salt, C 6 H 4 BaOC0 2 .2Aq, in which the diad Ba is exchanged for the H of the 
 hydroxyl as well as that of the carboxyl. 
 
 Anisic acid, or para-met hoxy benzole acid, C 6 H 4 (OCH 3 )'C0 2 H, is isomeric with oil 
 of winter-green, and is formed by the oxidation of its aldehyde, which occurs in oil 
 
GALLIC ACID. 609 
 
 of anise (p. 586). It may be formed artificially from salicylic acid by heating its 
 potassium salt to 220 C., when it yields di-potassium parahydroxy-benzoate, which 
 is converted into potassium anisate when treated successively with methyl iodide 
 and caustic potash 
 
 2 (C 6 H 4 (OH)-C0 2 K) = C 6 H 5 -OH + CO., -f C 6 H 4 (OK)'C0 2 K. 
 
 C 6 H 4 (OK>C0 2 K + 2 CH 3 [ = C 6 H 4 (OCH 3 )-C0 CH 3 (methyl aniwte) + 2KI ; 
 
 C 6 H 4 tOCH 3 )-C0. 2 CH 3 + KOH = C^ 4 (f)CR 3 )'C0 2 KQjo( a ^iumani.s fl t^ + CH 3 'OH. 
 
 Hydrochloric acid precipitates the anisic acid, which may be dissolved in alcohol 
 
 and crystallised. It forms prisms fusing at 185 C. and subliming undecomposed. 
 
 ffydroatytoluic acids or cresatinic acids C 6 H 3 (CH 3 )(OH)-COOH are ten in 
 number as they are trisubstitution products with 3 different radicles. All the 
 possible isomerides are known. 
 
 Protocatechuic or dihydroxybenzoic acid, C 6 H 3 (OH) 2 -C0 2 H [C0 2 H:(OH 2 ) = 
 i : 3 : 4], is prepared by the action of fused caustic soda on the large class of 
 bodies known as gum-resins, and acquired its name from its production in this 
 way from catechu (Cutch or Terra japonica), a substance much used in dyeing 
 black, extracted by boiling water from the inner bark wood of the Mimosa catechu 
 of the East Indies ; khw, a gum-resin exuding from certain Indian and African 
 leguminous plants, and employed in medicine as an astringent, also yields the 
 acid. It crystallises in plates or needles containing H 2 0, which fuse at 199 C., 
 and are soluble in water, alcohol, and ether. Ferric chloride gives a green colour 
 with the acid, which is changed to blue and red by alkalies. When heated, it is 
 decomposed, yielding pyrocatechol ; C 6 H 3 (OH). 2 - C0 2 H = C0 2 + C 6 H 4 (OH) 2 . 
 
 It will be found that the formation of this acid during the potash-fusion of an 
 organic substance often throws light upon its constitution. 
 
 Vanillic or ^-methyl-protocatech uic acid, C 6 H 3 (OH)(OCH 3 )'C0 2 H.is produced when 
 vanillic aldehyde (vanillin) is exposed to moist air. It may also be made by 
 oxidising the glucoside coniferin with potassium permanganate. It crystallises 
 in plates, fusing at 211 C. and subliming unchanged. When heated in a sealed 
 tube with dilute HC1 at 160 C., it yields protocatechuic acid and methyl chloride ; 
 C 6 H 3 <OH)(OCH 3 ) -C0 2 H + HC1 = C 6 H 3 (OH). 2 -C0 2 H + CH 3 C1. 
 
 381. Aromatic Paraffin Alcohol-acids. Mandelic acid or jj/ieni/lali/cottic add, 
 C 6 H 5 -CH(OH)'C0 2 H, is prepared from amygdaline (</.r.) or by the hydrolysis 
 of the hydrocyanic compound of benzaldehyde, C 6 H 5 CH(OH)CN. It melts at 
 133 C. and is soluble in water. It exists in stereoisomeric forms, which is to be 
 expected from the presence of an asymmetric carbon atom. 
 
 382. Trihydroxybenzoic acids. Of the six possible isomerides gallic 
 acid is the most important. 
 
 Gallic acid, 3:4:5- C 6 H 2 (OH) 3 -CO,H * is produced by the hydro- 
 lysis of the tannin in gall-nuts (gallotannic acid), C 13 H 9 7 'CO, + H,0 = 
 2C 6 H,(OH) 3 -CO,H. It is therefore prepared either by boiling the 
 tannin with dilute sulphuric acid, or by keeping the moistened powdered 
 nut-galls some weeks in a warm place, so that they may undergo 
 fermentation, and extracting the gallic acid with boiling water, from 
 which it crystallises in fine needles containing H 2 0. It dissolves in 
 3 parts of boiling water and 100 of cold water. It becomes anhydrous 
 at 100 C., and melts at about 220 C., yielding a crystalline sublimate 
 of pyrogallol; C 6 H 2 (OH) 3 -CO 2 H = C 6 H 3 (OH) 3 + C0 2 . 
 
 Solution of gallic acid is not precipitated by H 2 S0 4 or HC1, or by gelatine. 
 Lead acetate precipitates it, but the precipitate is soluble in acetic acid. A 
 and potash give a precipitate easily soluble in potash. Copper sulphate does not 
 precipitate it immediately. Ferric salts give a bluish-black precipitate, and the 
 alkalies give a brown-red colour, especially on exposure to air. Alcoholic alkali 
 converts gallic acid into a yellow dye-stuff, gaUoflarin. C 13 H 6 9 . Gallic a 
 found in several vegetable products, some of which are used in dyeing and t 
 as in diri-diri, the fruit of a leguminous plant (Ceegalj/i/iia roritina). in 
 
 In expressing orientation it is customary to assume that the characteristic <rroup of a 
 compound occupies position i, and to name the positions of the other groups n 
 this. Thus 3:4: 5-trihydroxy beuzoic acid means that if the CO 2 H group has posi 
 OH groups will be 3:4:5. 
 
6lO TANNIC ACID. 
 
 mangoes, and the leaves of the wild vine, a tropical plant of the Moon-seed order 
 (Clssampelos pare.ira), useful in medicine. 
 
 Gallic acid may be obtained artificially by heating di-iodosalicylic acid with 
 solution of potassium carbonate to 140 C. in a sealed tube 
 
 C 6 H 2 I 2 (OH)-C0 2 H + K 2 C0 3 + H 2 = C 6 H 2 (OH) 3 'C0 2 H + 2KI + C0 2 . 
 
 When gallic acid is heated with 4 parts of strong H 2 S0 4 to 75 C., it gives a 
 dark-red solution ; and if this be cooled and poured into water, a red precipitate 
 is obtained which has the composition C 14 H 8 8 .2Aq, or twice gallic acid, minus 
 '2H 2 0. This was formerly termed rujigallic acid, but is really hexa-hydroxy- 
 anthraqulnone, C 14 H 2 (OH) 6 2 , for zinc-dust reduces it to anthracene, C 14 H 10 . 
 
 Ellagic acid, C 13 H 5 6 'C0 2 H, is obtained by oxidising gallic acid with arsenic 
 anhydride ; it is a yellowish crystalline powder sparingly soluble in water and 
 alcohol. It is found in bezoar-stones, the calculi sometimes formed in the intes- 
 tines of wild goats in Persia. 
 
 Basic bismuth gallate, C 6 H 2 (OH) 3 -COOBi(OH) 2 is an antiseptic sold as dermatol. 
 
 383. Tannic acid or tannin. This name has been applied to a number 
 of plant-constituents, all of which are capable of precipitating gelatine, 
 and therefore of more or less completely tanning hide into leather. 
 They are also characterised by the dark blue or green colour which they 
 give with ferrous salts ; hence their use in the manufacture of inks. 
 The tannins apparently occur in the plants as unstable glucosides, and 
 when hydrolysed they are converted into glucoses and monobasic acids 
 which seem to be related to the polyhydroxybenzoic acids. The only 
 tannic acid which can be said to be thoroughly known is that obtained from 
 gall-nuts, and commonly called gallotannic acid, C 13 H 9 7 'CO,H + 2H 2 0. 
 
 240 grammes of powdered gall-nuts are digested for some hours, with frequent 
 shaking, with 1800 cubic centimetres of ether and 150 of water. The mixture is 
 poured into a funnel loosely plugged with cotton, and the filtered liquid allowed 
 to stand, when it separates into two layers, the upper one being the ethereal 
 solution of colouring-matter, &c., and the lower an aqueous solution of tannic 
 acid, which is evaporated to dryness at a low temperature. 
 
 Gallotannic acid does not crystallise, but is left, on evaporation, in 
 brownish-white shining scales, which are very easily soluble in water, 
 but sparingly in alcohol and in anhydrous ether. Its solution is 
 astringent, feebly acid, and gives a bluish-black precipitate with ferric 
 chloride. H 2 S0 4 and HOI combine with it to form white precipitates, 
 and a solution of gelatine precipitates a very insoluble compound with 
 tannic acid. By hydrolysis gallotannic acid yields gallic acid (p. 609). 
 
 The view that gallotannic acid is identical with di-gallic acid 
 
 C 6 H 2 (OHVCO'O-C 6 H 2 (OH) 2 -COOH, 
 
 which represents two molecules of gallic acid minus one molecule of water, and is 
 produced by action of dehydrating agents (e.g., POC1 3 at 130 C.) on gallic acid, has 
 been proved incorrect. 
 
 Albumin, starch, and most of the alkaloids are also precipitated by tannic acid. 
 Common salt causes the separation of tannic acid from its solution. Lead 
 acetate precipitates it as basic tannate, which is insoluble in acetic acid. Copper 
 sulphate also precipitates it immediately. Alum and potash added to tannic 
 acid give a precipitate insoluble in cold potash. Potash or ammonia added to a 
 solution of tannic acid renders it brown, especially if shaken with air, absorption 
 of oxygen occurring. Tannic acid acts as a reducing-agent upon alkaline cupric 
 solutions, producing cuprous oxide. It is decomposed by distillation, one of the 
 products being pyrogallol, C 6 H 3 (OH) 3 . 
 
 Alcoholic solutions of tannic acid and potash yield a precipitate of potassium 
 tannate, C 13 H 9 OyC0 2 K, and if this is dissolved in water, and BaCl 2 added, barium 
 tannate, (C 13 H 9 CyC0 2 ) 2 Ba, is precipitated. 
 
 The tannic acids or tannins used in commerce, in the form of extracts of 
 various parts of plants, are slightly different in properties, and pending exact 
 knowledge as to their constitution, they are distinguished by names implying the 
 

 TANNINS. 6ll 
 
 sources from which they are derived. Thus, qverci-tannic acid is from oak-bark, 
 quino-tannic acid from cinchona bark, caffeo-tannic acid from coffee, moritannic 
 acid from fustic (a yellow dyewood from a tree of the Mulberry order, Mont* 
 tinctoria). 
 
 Sumach, the leaves of the Rhm coriaria, a tropical plant of the Cashew order, 
 and Myrobalans, the fruit of several species of Termlnalia, Indian trees, contain 
 gallotannic acid. Myrobalans also contains ellagitannic acid, very similar to 
 gallotannic acid, and likewise contained in diri-diri. 
 
 The tannins may be classified into pyrogallol-tannin? and purocatechol tannin*, 
 accordingly as they yield pyrogallol or pyrocatechol when heated. Those belonging 
 to the first class yield gallic and ellagic acids when heated with alkalies, .vhilst - 
 those of the latter class yield protocatechuic acid, and either phlorogiucol or 
 acetic acid, by the same treatment. The deposit of ellagic acid which is formed 
 by the oxidation of pyrogallol tannins is probably the "bloom" noticed by 
 tanners on the surface of leather prepared by means of materials such as 
 myrobalans, sumach, and divi-divi. The pyrocatechol tannins are liable to deposit 
 complex anhydrides termed phlobaphenes,* which have a red colour ; such are the 
 tannins of oak bark, mimosa and ralonia. 
 
 Quinic or kinic acid, or h-en'ahydrotetrahydroxyben-zoie acid, C 6 Hi7(OH) 4 'C0 2 H, 
 is a hydroxy-acid from hexahydrobenzene (p. 550) found in cinchona bark, in coffee 
 and some other plants. It is crystalline, soluble, and melts at 162 C. It gives 
 pyrocatechol when distilled, and protocatechuic acid when fused with KOH. 
 When heated with Mn0 2 and H 2 S0 4 , it is oxidised to quinone, which sublimes in 
 yellow needles. 
 
 383(1. Hydroxyphenyl-Fatty and Olefine Acids. These may be regarded as 
 phenols in which a nucleal H atom has been exchanged for an open-chain acid 
 radicle. There are three position isomerides of each of the monohydroxyacids. 
 
 I : 2-Hyd)-o.i-yphenylacetic acid, C 6 H 4 (OH)'CH 2 -COOH, melts at 137 C. and is 
 important as a relative of indigo. 
 
 i : 2-Hyd)'o<vy-fi-2)henylacryUc acid or I : z-hydroxycinnanric acid 
 
 C 6 H 4 (OH)'CH : CH'COOH 
 commonly called coumaric acid is obtained from I : 2-amidocinnamic acid 
 
 C 6 H 4 (NH 2 )-CH : CH'COOH 
 
 through the diazo-reaction ; it melts at 208 C. Its salts are also obtained from 
 coumarin by heating it with alkalies. Coumarin is the lactone of coumaric acid, 
 
 C 6 H 4 / | , and is the substance which causes the smell of hay and of the 
 
 X CH : CH 
 
 Tonka bean (Coumaroma odorata') from which it may be extracted by boiling with 
 alcohol, when crystals of coumarin are deposited on cooling. It is made artificially 
 by heating salicyl aldehyde with sodium acetate and acetic anhydride (cf. cmnamic 
 acid, p. 601). The salts from coumarin are however isomeric with those prepare 
 from coumaric acid, the origin of the isornerism being still unknown. 
 
 Caffeic acid, or dihydi-oxy-cinnamic acid, [(OH) 2 : (CH : CH'G0 2 H) = 3 : 4 
 
 (m.-p. 213 C.) on cooling, ana is soiuoie in aicc KM. L jic > F 'vv""T|: 
 heated, and is converted into acetate and protocatechuate when fused with 
 Plperic Acid is derived from a 3 : 4 -dihydroxyphenyldiolefine acid, d- 
 'innamenylao-yUc acid, by substituting methylene, CH 2 , for the two 
 
 ctnnameni 
 
 the two OH groups ; hence its formula is 3 : 4 -CH 2 <>C 6 H 3 -CH : CH'CH : CH'COOH. 
 
 It melts at 217 C. and is found as a derivative of piperidine (V/.r.) in pepper. 
 
 384. Dibasic Acids from Paraffin Hydrocarbons (Oxalic or 
 Succinic Series), C M H 2tt (COOH) 2 . -These acids may be - 
 derived from the hydrocarbons by substitution ot two 
 for two H atoms. They are oxidation products of diprimary 
 might be expected (p. 574), and are also obtainable by nucleal coi 
 
 99, b:irk ; |3<M, colour. 
 
6l2 OXALIC ACID. 
 
 tion from the fatty acids, as for instance when bromacetic acid is 
 treated with metallic silver, producing succinic acid : 
 
 HOOC'CH 2 Br + BrCH 2 'COOH + Ag 2 = HOOC-CH 2 -CH 2 -COOH + 2AgBr. 
 
 These methods are not much used, however; more impoitant is the 
 introduction of the CN group into a fatty acid and hydrolysis of the 
 product. Thus, hydrolysis of cyanoacetic acid, obtained from chlor- 
 acetic acid by action of KCN, yields malonic acid : 
 
 CH 2 C1'COOH -> CH 2 CN-COOH -> CH 2 (COOH) 2 (</. p. 587). 
 
 An analogous method is the hydrolysis of the dicyanides of the olefine 
 radicles, CH 9 CN'CH 2 CN yielding succinic acid, for example. 
 
 Isomerism among these acids is like that among other disubstituted 
 paraffins (p. 567). 
 
 /COOH 
 
 The typical members of the series are malonic acid, CH./ 
 
 X COOH 
 CH COOH 
 
 and succinic acid, ' . Acids like the former, in which the two 
 
 CH 2 COOH 
 
 carboxyls are attached to the same carbon atom break up when heated 
 with formation of C0 2 and an acid of the acetic series. Acids of the 
 succinic type, in which the carboxyls are attached to different carbon 
 
 CH-CO\ 
 atoms, lose water and yield internal anhydrides, like ">0, when 
 
 CH 2 -CO X 
 
 heated ; this behaviour, however, is not shown by acids in which the 
 COOH groups are separated by more than three CH 2 groups. Both 
 types lose C0 2 when fused with KOH, yielding an acid of the acetic 
 series. 
 
 385. Oxalic acid, (C0 2 H) 2 , is the final product of the oxidation of 
 glycol, and one of the products of the hydrolysis of cyanogen, 
 CN-CN + 4 HOH - COOH-COOH + 2NH 3 . It is prepared on the small 
 scale by oxidising sugar with nitric acid, and on the large scale by 
 oxidising sawdust with potash. 
 
 Preparation of oxalic acid from sugar. 50 grins, of sugar are gently heated in a 
 flask with 250 c.c. of ordinary concentrated nitric acid, sp. gr. 1.4. After the 
 action commences, remove the heat, when the oxidation will continue violently. 
 On cooling, part of the oxalic acid crystallises, and more is obtained by concen- 
 trating the mother-liquor. Drain the crystals on a funnel, and dissolve them in as 
 little boiling water as possible, so as to purify the acid by re-crystallisation. It 
 may be allowed to dry by exposure to air. 
 
 Preparation of oxalic acid from sawdust. Common pine sawdust is made into a 
 thick paste with a solution containing KOH + 2NaOH of sp. gr. 1.35. This is 
 spread on iron plates, dried up, and heated just short of carbonisation. The 
 cellulose, C 6 H 10 5 , is thus oxidised, with evolution of hydrogen, and converted 
 into oxalic acid, which remains in the mass as oxalates of potassium and sodium. 
 These are dissolved in water, and boiled with lime, which produces the insoluble 
 calcium oxalate. together with solution of the caustic alkalies, which may be 
 used again. The calcium oxalate is decomposed by dilute sulphuric acid, the 
 solution of oxalic acid filtered from the calcium sulphate and crystallised. 
 
 Strictly speaking, in carrying out this process, the fused mass is treated with a 
 small quantity of hot water, which leaves the bulk of the sodium oxalate undis- 
 solved ; this is decomposed by lime, as stated above. The liquor, which contains 
 but little oxalate, is boiled to dryness, the residue heated, and the alkaline 
 carbonate causticised by lime. It is worth noting that caustic soda alone would 
 produce very little oxalate. When potash is cheap, it may be used alone. 
 
OXALATES. 613 
 
 Oxalic acid occurs in sorrel, rhubarb, and many other plants. Potas- 
 sium oxalate is formed when potassium formate is gently heated ; 
 2(H-CO'OK) = H 2 + (CO 2 K),. Sodium oxalate is produced when sodium,' 
 mixed with sand to moderate the action, is heated at 360 C in dry 
 C0 2 ; Na 2 + 2 CO 2 = (C0 2 Na) 2 . 
 
 Properties of oxalic acid. It forms monoclinic prisms containing 2Aq, 
 which are soluble in nine parts of cold water and in alcohol. It is a 
 very strong acid, able to decompose the nitrates and chlorides. In 
 large doses it is poisonous. "When gently heated, the crystals effloresce, 
 from loss of water, and begin to vaporise slowly at 100 C. When 
 sharply heated the crystallised acid melts at 101 C. and the anhydrous 
 at 189 C. At 165 it sublimes freely, part being decomposed into 
 formic acid and C0 3 ; (C0 2 H) 2 = ITC0 2 H + C0 2 . A weak solution of 
 oxalic acid is decomposed by boiling. When heated with strong 
 sulphuric acid, (00 2 H) 2 = C0 2 + CO + H 2 O, the CO burning on applying 
 a flame. From twelve parts of warm oil of vitriol the acid crystallises 
 in large rhombic octahedra, which are anhydrous. Oxalic acid is largely 
 used in dyeing, calico-printing, and bleaching, in cleaning brass, and in 
 removing iron-mould from linen. 
 
 Normal potassium oxalate, (C0 2 K) 2 .Aq, is moderately soluble in water. Hydro- 
 potassium oxalate, ov potassium binoxalate, or salt of sorrel, is (C0 2 ) 2 KH. It is also 
 Called essential salt of lemons, though lemons contain no oxalic acid. It dissolves 
 in 40 parts of cold water, and has occasionally caused accidents by being mistaken 
 for cream of tartar, potassium hydrogen tartrate, from which it is readily distin- 
 guished by the action of heat, which chars the tartrate, but not the oxalate. 
 
 Trikydropotassium oxalate, or potassium quadroxalate, (C0 2 ) 2 H 3 K.2Aq, is more 
 commonly sold as salt of sorrel, and sometimes as salt of lemon. It is even less 
 .soluble than the preceding. 
 
 Sodium oxalate, (C0 2 Na) 2 , is found in various plants which grow in salt marshes. 
 It is less soluble than potassium oxalate. The alkali oxalates, when heated, evolve 
 CO and leave carbonates, (C0 2 K) 2 =CO + CO(OK) 2 . 
 
 Ammonium oxalate, (CO 2 NH 4 ) 2 .Aq, occurs in Peruvian guano. It is used in 
 analysis for the precipitation of calcium, and crystallises, in needles, from solution 
 of oxalic acid neutralised with ammonia. 
 
 Calcium oxalate, (C0 2 ) 2 Ca.Aq, is often found crystallised in plant-cells. Some 
 lichens growing on limestones contain half their w'eight of calcium oxalate. It is 
 occasionally found in urine and in calculi. Calcium chloride is the best test for 
 oxalic acid, giving a white precipitate insoluble in acetic acid. When heated, 
 (C0 2 ) 2 Ca = CO + CaC0 3 . 
 
 Ferrous oxalate, (C0 2 ) 2 Fe, occurs as oxalite in brown coal. Ferric oxalate, 
 (CO 2 ) 6 Fe , when exposed to sunlight in presence of water, evolves COa, and deposits 
 a yellow "crystalline precipitate of (C0 2 ) 2 Fe.2Aq. Ferric oxalate is used in photo- 
 graphy. Potassium ferrous oxalate, (C0 2 ) 4 K 2 Fe, prepared by adding potassium 
 oxalate in excess to ferrous sulphate, is a very powerful reducing-agent, used as 
 a photographic developer. 
 
 Potassium chromic oxalate, (CO^KgCr.sAq, is obtained in crystals so intensely 
 blue as to look black, by dissolving in hot water I part of potassium dichromate, 
 2 parts of hydropotassium oxalate, and 2 parts of oxalic acid. Neither the oxalic- 
 acid nor the Cr 2 8 can be precipitated from this salt by the usual tests. 
 
 Potassium calcium chromic oxalate, (C0. 2 ) 6 KCaCr.3Aq, is soluble in water, and 
 gives a precipitate of calcium oxalate on adding calcium chloride. 
 
 Barium chromic oxalate, (CO 2 ) 1 ,,Ba 8 O a .8Aq, is also a soluble salt, and, when d< 
 composed by sulphuric acid, yields a red solution which probably contains the acic 
 (COjUELCra or H 3 (C02) 6 Cr-Cr(C0 2 ) 6 H 3 . . , 
 
 Potassium antimony 5S^, (Cot) 8 K 8 Sb.6Aq f obtained by dissolving precipitated 
 Sb 4 6 in hydropotassium oxalate, is used in fixing certain colours. 
 
 Silver oxalate, (C0 2 Ag) 2 , is obtained as a white precipitate when silver i 
 added to an oxalate. It explodes slightly when heated, leaving metallic silver. 
 
 Manganese oxalate, (C0 2 ). 2 Mn, is used lor mixing with drying-oils. 
 
614 SUCCINIC ACID. 
 
 Oxidising-agents easily convert oxalic acid into water and C0 2 ; if a 
 hot solution of the acid be poured on manganese dioxide, brisk effer- 
 vescence is caused by the C0 2 produced. A similar result ensues if 
 manganese dioxide be added to the mixture of an oxalate with dilute 
 sulphuric acid. Nascent hydrogen reduces oxalic acid to gly collie acid ; 
 (C0 2 H) 2 + H 4 = CH 2 (OH)-C0 2 H + H 2 O. 
 
 386. Malonic acid, CH 2 (C0 2 H) 2 , is prepared from chloracetic acid, CH 2 C1 - C0 2 H, 
 by converting it into the potassium salt, and boiling this with potassium cyanide, 
 when potassium cyanacetate, CH 2 (CN)'C0 2 K, is formed. This is boiled with pot- 
 ash, which converts it into potassium malonate ; CH 2 (CN)'C0 2 K + H 2 + KOH = 
 CH 2 (C0 2 K) 2 +NH 3 . The excess of potash is neutralised by HC1, and calcium 
 chloride added, which precipitates calcium malonate ; by boiling this with the 
 molecular proportion of oxalic acid, the calcium is left as oxalate, and the solution 
 deposits tabular crystals of malonic acid. It fuses at 132 C. and afterwards 
 decomposes into C0 2 and acetic acid ; CH 2 (C0 2 H) 2 = C0 2 + CH 3 -C0 2 H. It will be 
 remembered that oxalic acid is decomposed into"C0 2 , and formic acid, H'C0 2 H. 
 
 Calcium malonate, like the oxalate, is very slightly soluble in water, and is 
 found in the sugar beet ; the silver and lead salts are insoluble. Malonic acid is 
 found among the products of oxidation of allylene, amylene, and propylene with 
 potassium permanganate. 
 
 The other acids of the malonic acid type are alkyl substitution derivatives 
 of malonic acid, and may be built up therefrom by the treatment of its ethereal 
 salts first with a sodium alkyloxide and then with an alkjd iodide. The series of 
 reactions and their import has been given at p. 587. 
 
 Methylmalonic acid, CH 3 'CH(COOH) 2 , is ethylidene succinic acid, isomeric with 
 succinic acid, which is an ethylene derivative ; hence it is called isosuccinic acid. 
 It is prepared by hydrolysis of a-cyanopropionic acid, and from ethyl sodiomalonate 
 and methyl iodide (see above). It should also be obtainable by treating ethylidene 
 bromide, CHg-CHBr^ with KCN and hydrolysing the cyanide, but this leads to 
 ordinary succinic acid. It melts at 130 C., and decomposes into C0 2 and pro- 
 pionic acid. 
 
 387. Succinic acid, C 2 H 4 (C0 2 H) 2 , \&ethylene succinic acid, and occurs ready formed 
 in amber, from which it was originally obtained by distillation. It is prepared by 
 the fermentation of tartaric acid, which may be regarded as dihydroxysuccinic 
 acid, C 2 H 2 (OH) 2 (C0 2 H) 2 , and becomes reduced to succinic acid. 
 
 The tartaric acid is neutralised with ammonia, largely diluted, and mixed with 
 a little potassium phosphate, magnesium sulphate, and calcium chloride, to afford 
 mineral food for the bacteria, which soon grow if the liquid be kept warm (25- 
 30 C.). The flask should be loosely closed to exclude air. After about two months, 
 the ammonium tartrate has become ammonium succinate and carbonate ; it is 
 boiled to expel the latter, milk of lime added, and again boiled as. long as NH 3 
 is expelled ; the calcium succinate is decomposed by a slight deficiency of dilute 
 H 2 S0 4 , the liquid filtered from the CaS0 4 and evaporated. 
 
 Succinic acid crystallises in prisms, which require about 20 parts of cold and 
 3 parts of hot water to dissolve them. It dissolves in alcohol but sparingly in 
 ether. When heated, it emits vapour at 120 C., fuses at 185, and at 235 distils 
 as water and succinic anhydride, C 2 H 4 (CO) 2 ; the vapours provoke coughing in a 
 remarkable way, thus affording a test for the acid. It is very stable, and little 
 affected by oxidising-agents. Fusion with KOH converts it into carbonate and 
 propionate ; C 2 H 4 (C0 2 H) 2 + 3KOH = CO(OK) 2 + C 2 H 5 'C0 2 K + 2H 2 0. 
 
 Calcium succinate, C 2 H 4 (CO-2) 2 Ca.3Aq. is somewhat sparingly soluble in water ; it 
 occurs in the bark of the mulberry-tree. Basic ferric succinate, Fe'" 2 (C 4 H 4 4 )" 2 (OH)' 2 , 
 is precipitated when ferric chloride is added to a succinate ; it has a rich brown 
 colour, and its production forms a good test for succinic acid, and is useful in 
 quantitative analysis for separating Fe from Mn and some other metals. 
 
 Malic acid is hydroxysuccinic acid, and is also reduced by fermentation to succinic 
 acid. Both malic and tartaric acid are reduced to succinic acid by the action of 
 hydriodic acid. Succinic acid has been obtained synthetically by boiling ethene 
 dibromide with potassium cyanide dissolved in alcohol, and boiling the ethene 
 cyanide thus obtained with KOH dissolved in alcohol. 
 
 C 2 H 4 Br 2 + 2KCN = C 2 H 4 (CN) 2 + 2KBr ; and 
 C 2 H 4 (CN) 2 + 2KOH + 2H 2 = C 2 H 4 (C0 2 K) 2 + 2N 
 
FUMAEIC AND MALEIC ACIDS. 
 
 615 
 
 Succinic acid is always produced in small quantity in the fermentation of sugar 
 and is therefore always present in beer, wine and vinegar. It is also produced 
 when nitric acid oxidises fatty acids containing four or more carbon atoms. It 
 occurs in unripe grapes, whilst ripe grapes contain tartaric (dihydroxysuccinic) 
 acid. It is found in several plants, such as lettuce, poppies, and wormwood, and in 
 certain lignites. It has also been found in the urine of the horse, goat, and rabbit. 
 
 When electrolysed, succinic acid yields C 2 H 4 , C0 2 , and H, as might be expected' 
 from its formula, C 2 H 4 (C0 2 H) 2 . 
 
 Methylsvccinic acid, COOH-CHCCH^-CHa'COOH, is also called pyrotartaric acid 
 because it is formed by distilling tartaric acid (mixed with powdered pumice to 
 diffuse the heat). The distillate is mixed with water, filtered, evaporated on the 
 water bath and crystallised from alcohol. It is formed from propene as succinic 
 acid is from ethene, and crystallises in prisms which melt at 112 C. and decompose 
 into water and the anhydride. Having an asymmetric carbon atom it occurs in 
 stereoisomeric forms. 
 
 Glutaric acid, COOH-CH 2 -CH 2 -CH 2 'COOH, isomeric with pyrotartaric acid (and 
 with ethylmalonic acid and dimethylmalonic acid) melts at 97 C., and is obtained 
 from trimethylene bromide (p. 539) through the KCN reaction. It yields an anhy- 
 dride when heated. 
 
 The higher acids of this series do not yield anhydrides ; the chief are : 
 
 Adipic, C 4 H 8 (COOH) , from oxidation of oleic acid ; m.-p. 153 C. 
 Pimelic, C 5 H 10 (COOH) 2 , 105 C. 
 
 Suberic, C^B^COOH)^ cork 
 
 A.zelaic, C 7 H 14 (COOH) 2 castor oil 
 
 distillation of oleic acid 
 
 Sehwic, C 8 H 16 (COOH) 2 
 Brassi/Uc, C 11 H 22 (COOH) 2 f 
 
 Tom oxidation of erucic acid 
 Rocellic, C 15 H 30 (COOH) 2 , " Rocella tinctoria 
 
 140 C. 
 1 06 C. 
 
 133 t'. 
 n 4 C. 
 132 C. 
 
 388. Dibasic Acids from Oleflne Hydrocarbons, C M H 2H _ 4 4 . 
 
 The acids of this series are rnsaturated, like those of the acrylic series, 
 and can therefore combine with two atoms of bromine to become 
 dibromo-derivatives of the acids of the preceding class, or with two 
 atoms of hydrogen to become the acids of that cla^s. Conversely, acids 
 of this series are obtained by treating with KOH the dibromo-acids 
 of the succinic series. 
 
 The first member of the series has the formula C 2 H 2 (C0 2 H) 9 , and might 
 obviously exist in two forms, C0 2 H'CH : CH-C0 3 H and CH 2 ": C(C0 2 H) 2 . 
 There is insufficient evidence to show, however, that the two &cid$fumanc 
 and maleic, both of which have the molecular formula C 2 H 2 (C0 2 H) S , 
 are position isomerides ; they appear rather to be stereoisomeridt s. 
 
 The acid CH 2 : C(COOH) 2 , methylenemalonic acid, is known only in the form of 
 its ethereal salts. 
 
 Futnaric acid, C 2 H 2 (C0 2 H) 2 , is obtained by heating malic acid at 150 C. as 
 long as water distils over ; C 2 H 3 (OH)(C0 2 H) 2 =C 2 H 2 (C0 2 H) 2 + H 2 0. The residue is 
 treated with cold water to extract unaltered malic acid and the fumaric acid is 
 crystallised from hot water or alcohol. At 200 C. it partly sublimes undecomposed, 
 and the rest decomposes into water and maleic anhydride. Heated with much 
 water at 150 C., it is reconverted into malic acid. NaOH at 100 C. slowly converts 
 it into sodium malate. Nascent hydrogen, from water and sodium-amalgam, con- 
 verts it into succinic acid, C 2 H 4 (C0 2 H) 2 . Hydriodic acid effects the same change, 
 iodine being liberated. The fumarates of barium, calcium, and lend :uv sparingly 
 soluble. Silver fumarate is very insoluble, and explodes when heated. The alkali 
 fumarates, when electrolysed, yield C 2 H 2 , C0 2 , which forms a carbonate, and H, 
 thus justifying the formula given for the acid. Fumaric acid is found in several 
 plants, especially in fumitory, Iceland moss, truffles, and other fungi. * urns 
 acid is not oxidised by boiling with nitric acid. 
 
 Maleic acid, isomeric with fumaric acid, is produced when malic acid i> -im. 
 distilled. It is crystalline, melts at 130 C. and is easily decomposed by heat in 
 water and maleic anhydride. It differs from fumaric acid by its ready M 
 in cold water, by the solubility of its barium and calcium salts, and by i 
 
6l6 MALEINOID AND FUMAROID STRUCTURE. 
 
 unpleasant taste. It is converted into fumaric acid if heated in a sealed tube at 
 200 C., or if boiled with dilute acids. 
 
 In order to represent the isomerism between fumaric and maleic acid, 
 it is supposed that the C0 2 H groups are differently situated with regard 
 to a plane drawn through the two nucleal carbon atoms of the molecule. 
 On the plane of the paper, the supposed difference may be represented 
 
 H-C-C0 9 H H-OCO.H. 
 
 by the formula? and The first of these two 
 
 H-OC0 2 H C0 2 H-OH 
 
 formulae is called ihe plane-symmetrical, or cz's-c?'s-formula, whilst the second 
 is called the axial-symmetrical, centri- symmetrical ^ or c 
 
 H-OCOx. 
 Since maleic acid very easily foi ms an anhydride, \O it may 
 
 H-c-ccr 
 
 be supposed to have the first formula, because the formation of an 
 anhydride would occur the more easily the greater the proximity cf the 
 C0 2 H groups.* Many cises of stereoisomerism among eth)lenic eri- 
 vatives (cf. pseudo-but} lene and crotonic acid) are believed to be 
 explicable by formula? resembling those given above, so that the expres- 
 sions malewtoid andfumaroid structure are u*ed.t 
 
 The main argument in favour of this view of the structure of the fumaric and 
 maleic molecules is that the former yields racemic acid and the latter mesotartaric 
 acid, by oxidation with K 2 Mn 2 8 . Comparison of the above formula? with those 
 for racemic and mesotartaric acids on p. 622 shows that the acid having the cis-cis- 
 formula would be the more likely to yield mesotartaric acid than the other acid 
 would, because in mesotartaric acid both H atoms are on one side of the central 
 plane. 
 
 By grouping the H and COOH groups at the four solid angles of the two tetra- 
 hedra represented in the middle diagram of Fig. 257, so as to produce the plane and 
 axial symmetry of the above formula?, some idea of the possible stereo-formula^ of 
 maleic and fumaric acids may be obtained. Ingenious arguments have been 
 advanced to explain the conversion of the one acid into the other by supposing 
 that, by addition of elements, the double linking is opened up, so as to produce the 
 left hand diagram of Fig. 257, the tetrahedra of which then rotate on their common 
 axis, and, losing the added elements, again assume the form of the middle diagram ; 
 but this time the COOH and H groups would have assumed the opposite sym- 
 metrical relationship to that which they had before. Such arguments are open to 
 well-found contradiction and cannot be detailed here 
 
 Citraconic (m.-p. 91 C.) and mesaconic (m.-p. 202 C.) acids, C 3 H 4 (COOH) 2 . are 
 homologues of fumaric and maleic acid, the former being metliyltualeic acid, while 
 the latter is niethylfumaric acid. Thus they have the same relationship to each 
 other as fumaric and maleic have. Citraconic acid, being the m-form, yields an 
 anhydride which is found in the products of destructive distillation of citric acid 
 together with the anhydride of itaconic acid (m.-p. 161 C.), another isomeride which 
 is methylene succinic acid, COOH*CH 2 - C(: CH 2 )'COOH ; hence these acids were 
 formerly termed pyrocitric acids. If citraconic acid be heated for some time with 
 dilute HN0 3 or strong HC1, it is converted into mesaconic acid. Mesaconic dis- 
 solves in about 40 parts of cold water, itaconic in about 20 parts, and citraconic in 
 i part. All three are reduced by nascent H to pyrotartaric acid. They combine with 
 the haloid acids to form isomeric substitution-products of pyrotartaric acid. 
 
 389. Of the dibasic acids from the acetylene hydrocarbons, acetylene dicarbonyUc 
 acid, C0 2 H'C : C/C0 2 H, need alone be noticed. It is produced by heating 
 dibromosuccinic acid, C 2 H 2 Br 2 (C0 2 H) 2 , with alcoholic potash, whereby 2HBr are 
 removed. It crystallises with 2H 2 0, and decomposes when fused. 
 
 * Compare the ease with which 1:2- phthalic acid yields an anhydride (p. 617). 
 f The special term alloisomerism or geometrical isomerism has been applied to these cases ; 
 it is not necessary. 
 
PHTHALIC ACIDS. 6l/ 
 
 390. Dibasic Acids from Aromatic Hydrocarbons. These are 
 
 obtained by oxidising benzene hydrocarbons containing side-chains. 
 Thus, the most important of them, the three phthalic adds, C 6 H 4 (COOH) ,* 
 can be prepared by oxidising the three xylenes, C 6 H 4 (CH 3 ) 2 , and indeed 
 most other disubstituted benzenes in which carbon is attached directly 
 to the nucleus. 
 
 i : 2-phthalic acid is the most important isomeride and is charac- 
 terised by yielding an anhydride when heated, owing, no doubt, to the 
 fact that the COOH groups are in the adjacent position. It is made 
 in large quantity, for the manufacture of dye-stuffs, by oxidising 
 naphthalene with strong H 2 S0 4 in presence of mercury. 
 
 On a small scale naphthalene tetrachloride is oxidised with HN0 3 . i part of 
 C 10 H 8 is carefully mixed, on paper, with 2 parts, by weight, of KC10 3 , and added, 
 in small portions, to 10 parts of strong HC1. The naphthalene tetrachloride, C 10 H 8 C1 4 , 
 thus formed, is washed with water till free from acid, and allowed to dry. It is 
 introduced into a flask and treated with strong HN0 3 (sp. gr. 1.45), which must be 
 very gradually added, amounting to ten times the weight of naphthalene taken. 
 The mixture is heated till all is dissolved, the nitric acid boiled off, and the residue 
 distilled, when plithallc anhydride distils over and is converted into phthalic acid 
 
 co POOH 
 
 by dissolving in hot water and crystallising ; C 6 H 4 / \0 + H 2 = C 6 H 4 / 
 
 X CO X X COOH 
 
 Phthalic acid crystallises in rhombic prisms, which are easily fusible, and 
 readily decomposed into water and the anhydride. It is sparingly soluble in cold 
 water, but dissolves readily in hot water, in alcohol, and in ether ; with NH 3 and 
 BaCl 2 it yields a precipitate of barium phthalate. When heated with lime to 340 C., 
 it yields benzoate and carbonate of calcium. Chromic acid oxidises phthalic acid 
 completely into C0 2 and H 2 0. 
 
 i : $- Phthalic acid or uuphthalic acid crystallises in needles ; it is soluble in 
 hot water, is not precipitated by BaCl 2 in presence of NH 3 , and yields no anhy- 
 dride when heated, but sublimes unchanged. 
 
 i : ^-Phthalic acid, or terephtlialic acid, is difficult to crystallise, and is in- 
 soluble in water, so that it is precipitated from its solutions in alkali by adding 
 acid. The barium salt is sparingly soluble. The acid sublimes unchanged. 
 
 These differences in the properties of the three phthalic acids are of importance, 
 since the production of one or other of the acids frequently serves to decide the 
 constitution of a benzene derivative. 
 
 Phthalic anhydride crystallises in long prisms, in.-p. 128 C.; b.-p. 284 C. It is 
 used in making eosin dyes. 
 
 By treating the phthalic acids with nascent hydrogen a large number of hydro- 
 gen-addition products, hydrophthalic acids, e.g., C 6 H 4 -H 4 -(COOH)2, has been 
 obtained. These are remarkable for the numerous cases of isonierisin which 
 they exhibit ; the cause of this has been traced, first, to the existence of cix- 
 and f?'aft.s'-forms, as in the case of maleic and fumaric acids, and secondly, to 
 the different positions of the double linking between the carbon atoms of the 
 benzene nucleus, e.g., the two dihydroterephthalic acids (cf. p. 550), 
 
 C0.H CH2 ' CH C-C0H and 
 
 Naphtliallc acids are diabasic acids from naphthalene, C 10 H 6 (C0 2 H> 2 ; six out of 
 ten possible isomerides are known. 
 
 39 1 . Dibasic Hydroxy- acids. These may be regarded as oxidation 
 products of diprimary polyhydric alcohols, or, in the case of those 
 containing a benzene nucleus, as dicarboxylic acids from phenols. 
 
 Tartronic or hydroxymalonic acid, CH(OH)(C0 2 H) 2 , is formed by the action of 
 nascent hydrogen on mesoxalic acid (see below), which is a product of the oxidation 
 of uric acid. Its crystals melt at 158 C. and are then decomposed mtc .water, CO* 
 and an amorphous polymer of glycolide (p. 604). Tartronic acid was 
 
6l8 MALIC ACID. 
 
 obtained by heating solution of dinitrotartaricacid ; C 2 H 2 (ON0 ) 2 (CO,>H)o = 
 CH(OH)(C0 2 H) 2 + N 2 p 3 + C0 2 . It is also formed when glucose is oxidised by an 
 alkaline cupric solution, and when glycerine is oxidised by K 2 Mn 2 8 . Barium 
 tartronate, from which the acid is readily obtained, may be prepared by heating 
 glyoxalic acid with potassium cyanide and baryta- water 
 
 CHOC0 2 H + KCN + Ba(OH) 2 + HOH = CH(OH)(C0 2 ) 2 Ba + KOH + NH 3 
 Jfesoxalic acid is regarded by some as diliydroxymalomc acid, C(OH)o(C0 2 H) 2 , 
 but since this compound contains two OH groups attached to one carbon atom, 
 it is more probable that the acid is a ketonic acid of the form CO(CO 2 H) 2 + H 2 0, 
 a view supported by the fact that it forms a compound with NaHS0 3 , and com- 
 bines with hydroxylamine (see Ketones}. It is best obtained by boiling alloxan 
 (q.K.)with baryta water. It crystallises in deliquescent prisms with iH 2 0, and 
 melts without loss of water at 115 C. 
 
 Malic, or Hydroxysuccinic acid, COOH'CH 2 -CHOH'COOH, is one 
 of the chief natural vegetable acids, occurring in apples, gooseberries, 
 currants, &c. Tt will be noted that its alcoholic C atom is asymmetric, 
 hence it is known in the usual three optically isomeric forms. Strong 
 solutions of the natural acid are dextro-rotatory, though when diluted 
 they are Isevo-rotatory. It is extracted from the juice of the unripe 
 berries of the mountain ash. 
 
 The juice is boiled, filtered, nearly neutralised with milk of lime, and boiled, 
 when calcium malate. C 2 H 3 (OH)(C0 2 ) 2 Ca.Aq, is precipitated in minute crystals. This 
 is dissolved to saturation in hot nitric acid diluted with ten times its weight of water. 
 On cooling, crystals of hydrocalcium malate, [C 2 H 3 (OH)(C0 2 H)-C0 2 ] 2 Ca.8Aq, are 
 deposited. These are dissolved in hot water, and decomposed by lead acetate, when 
 lead malate is precipitated ; this is suspended in water, and H 2 S passed, when 
 PbS remains precipitated, and malic acid is found in solution, from which it 
 crystallises, though not very readily, in tufts of deliquescent needles. 
 
 The acid melts at 100 C. and at a higher temperature yields a feathery 
 sublimate of maleic and fumaric acids and of maleic anhydride. Oxida- 
 tion with chromic acid converts it into malonic acid, fusion with potash 
 into oxalate and acetate. Hydriodic acid reduces it to succinic acid : 
 C 2 H 3 (OH)(COOH) 2 + 2HI = C 2 H 4 (COOH) 2 + H 2 + I 2 . 
 
 By boiling bromosuccinic acid, C 2 H 3 Bi (COOH).,, with AgOH (silver 
 oxide and water) the Br is exchanged for OH and inactive malic acid is 
 produced. The d- and Z-acids are obtained by reducing the tartaric 
 acids (q.v.\ of corresponding activity, with HI. 
 
 The active forms are also separated by crystallising the cinchonine salt of the 
 inactive acid (ef. p. 606). 
 
 Some of the salts of malic acids also occur in nature. Cherries and rhubarb 
 contain acid potassium malate, C 2 H 3 (OH)(C0 2 H)(C0 2 K), while tobacco contains 
 acid calcium malate. Normal calcium malate is less soluble in hot water, and is 
 therefore precipitated on neutralising the acid with lime-water and boiling. Lead 
 malate forms a white precipitate containing 3Aq., distinguished by fusing under 
 water to a gummy mass, becoming crystalline on cooling. 
 
 392. Tartaric or dihydroxysuccinic acid, CO 2 H'CHOH CHOH 
 CO 2 H, is one of the most important vegetable acids, being often found 
 in fruits associated with malic acid. It is prepared from arc/ol or tartar, 
 a crude form of acid potassium tartrate, C 2 H 2 (OH) 2 (COOH)(COOK), 
 deposited in crystalline crusts during the fermentation of grape-juice. 
 
 This (45 ounces) is boiled with (2 gallons) water, and neutralised by adding 
 ( 1 2.\ ounces) powdered chalk, which converts the hydropotassium tartrate of the 
 argol into calcium tartrate and potassium tartrate 
 
 2C 4 H 4 6 KH + CaC0 3 = C 4 H 4 6 K 3 + C 4 H 4 6 Ca + H 2 
 
TARTARIC ACID. 
 
 The potassium tartrate dissolves and the calcium tartrate precipitates. Solution of 
 calcium chloride (13^ oz. dissolved in 2 pints of water) is then added, to precipitate 
 the potassium tartrate as calcium tartrate; C 4 H 4 6 K 2 + CaCl 2 =C 4 H 4 6 Ca + 2KCl. 
 The calcium tartrate is strained off, washed, and heated for half an hour with dilute 
 sulphuric acid (13 fluid ounces of acid in 3 pints of water), when calcium sulphate 
 remains undissolved, and tartaric acid may be crystallised by evaporating the 
 filtered solution; C 4 H 4 06Ca + H 2 S0 4 = C 4 H 4 6 H 2 +CaS0 4 . The crude acid is dis- 
 solved in water, decolorised by animal charcoal, and again crystallised. A little 
 sulphuric acid is generally added to promote the formation of large crystals. 
 These often contain lead derived from the evaporating pans. 
 
 Properties of tartaric acid. The crystals are monoclinic prisms, very 
 soluble in water, and fairly so in alcohol, but nearly insoluble in ether. 
 When heated rapidly to 170 C. it fuses, and becomes an amorphous 
 deliquescent mass of metatartaric acid, isomeric with it. At 145 C. it 
 becomes tartralic acid, C 8 H 10 O n , two molecules of the acid having lost a 
 molecule of water; at 180 C. it yields tartaric anhydride, C 8 H 8 10 . All 
 these may be re-converted into tartaric acid by digestion with water. On 
 further heating, it undergoes destructive distillation, yielding chiefly 
 pyruvic and pyrotartaric acids, together with dipyrotartracetone, C 8 H 12 8 , 
 which has a peculiar odour, like that of burnt sugar, by which tartaric 
 acid may be recognised. 
 
 Fused KOH converts tartaric acid into acetate and oxalate. Boiled 
 with nitric acid, much of it is oxidised to oxalic acid. Distilled with 
 sulphuric acid and MnO 2 , or K 2 Cr 2 7 , it yields formic acid and C0 2 . 
 
 Natural tartaric acid is dextro-rotatory and when heated with HI, in 
 strong aqueous solution, at 120 C., in a sealed tube, it is reduced to 
 dextro-malic acid, which is again reduced to succinic acid 
 
 C 2 H 2 (OH) 2 (C0 2 H) 2 + 2HI = C 2 H 3 (OH)(C0 2 H) 2 (malic acid) + H 2 + Lj. 
 
 And C 2 H 3 (OH)(C0 2 H) 2 + 2HI = C 2 H 4 (C0 2 H) 2 (succinic acid) + H 2 + I 2 . 
 Conversely, tartaric acid can be obtained by the treatment of dibromo- 
 succinic acid with moist silver oxide. 
 
 393. SALTS OF TARTARIC ACID. A distinguishing character of tartaric acid is 
 the sparing solubility of the acid potassium tartrate, HK 4 H 4 6 , which is precipi- 
 tated in minute crystals when almost any potassium salt is added to tartaric acid, 
 and the solution is stirred with a glass rod, when the precipitate attaches itself to 
 the lines of friction. Commercially this salt is known as cream of tartar, and is 
 prepared by re-crystallising argol from hot water, which dissolves ^th of i 
 weight, and only retains ^th on cooling. It is nearly insoluble in alcohol, whicl 
 precipitates it from the aqueous solution, and this explains its separation from Ul 
 grape-juice, as the proportion of alcohol increases during the fermentation. . 
 dissolves easily in acids and in alkalies, which convert it into normal tartrate, 
 K 2 C 4 H 4 6 . When heated, it evolves the burnt-sugar odour, and leaves a b 
 mass of charcoal and potassium carbonate (salt of tartar). ^ 
 
 Sodio-potassiuni, tartrate, NaKC 4 H 4 6 4Aq, Roclielle or Seigmttes xalt, : 
 prepared by neutralising a boiling solution of sodium carbonate with ci 
 tartar, when it crystallises on cooling, in fine rhombic prisms. 1 
 medicine. T , . 
 
 Calcium tartrate, CaC 4 H 4 6 . 4 Aq, occurs in grapes and in senna leaves. 
 sparingly soluble in water, and is precipitated when CaCl 2 is added to an a 
 niacal solution of a tartrate. It is soluble in potash and in ammonium chl 
 
 Cupric tartrate, CuC 4 H 4 C>3Aq, is sparingly soluble in water, but disi 
 alkalies to a deep blue solution, in which two atoms of the alkali metal h.iv 
 displaced H 2 . Such a solution is often used in analysis, as alkaline cupn 
 or Fehliwfs test. Tartaric acid behaves in a similar way with seven 
 metals, retaining them in alkaline solutions when they would otherwise 
 cipitated as hydroxides ; in the cases of Al and Fe, this is turned to a 
 analysis. 
 
620 STEEEOISOMERISM. 
 
 Silcer tartrate, Ag 2 C 4 H 4 6 , is precipitated by silver nitrate from a normal 
 tartrate ; it dissolves in ammonia, and the solution deposits metallic silver when 
 heated, the tartaric acid being oxidised to carbonic and oxalic acids. This is 
 taken advantage of in some processes for silvering mirrors. 
 
 Potassium-antimonyl-tartrate, K(SbO)C 4 H 4 6 , or tartar emetic, is prepared 
 by boiling cream of tartar (6 oz.) with water (2 pints) and (5 oz.) antimonious 
 oxide ; Sb 2 3 + 2KHC 4 H 4 6 = 2KSbOC 4 H 4 6 + H 2 O. From the filtered 
 solution, on cooling, the salt crystallises in rhombic prisms of the formula 
 2KSbOC 4 H 4 6 .Aq. It is soluble in three parts of hot water and in fifteen 
 parts of cold water. The crystals lose their water of crystallisation at 100 C., 
 and when heated over 200 the emetic loses the elements of another molecule 
 of water, and becomes KSbC 4 H 2 O 6 , which is reconverted into emetic by boiling 
 with water. 
 
 When barium chloride is added to tartar-emetic, a precipitate is formed, 
 according to the equation 2KSbOC 4 H 4 6 + BaCl 2 = Ba(SbOC 4 H 4 6 ) 2 + 2KC1. By 
 decomposing this barium salt with sulphuric acid, an acid solution is obtained, which 
 soon deposits antimonious hydroxide, but if it be neutralised with potash before 
 decomposition occurs, it yields tartar-emetic. Hence it would seem that the 
 emetic is the potassium salt of the acid H(SbOC 4 H 4 ? ) or C 2 H 2 (OH) 2 (C0 2 ) 2 SbOH, 
 which is derived from tartaric acid by exchanging one atom of H in the 
 (C0 2 H) 2 for the monad radicle antimomjl, Sb'"0". The emetic acid has been 
 named tartryl antimonious acid, so that tartar-emetic would be potassium tartryl 
 antimonite. Other tartryl-antinionites have been obtained. By dissolving Sb 2 O 3 
 in tartaric acid, and adding alcohol, a crystalline precipitate of antimonyl tartrate, 
 (SbO) 2 C 4 H 4 6 , is obtained, and this becomes tartar-emetic when boiled with 
 normal potassium tartrate (SbO). 2 C 4 H 4 6 +K 2 C 4 H 4 6 = 2KSbOC 4 H 4 6 . For the 
 antimony in tartar-emetic arsenic or boron may be substituted. 
 
 When excess of Sb 2 3 is boiled with solution of tartaric acid, and the liquid 
 evaporated to a syrup, it deposits crystals of H(SbO)C 4 H 4 6 , which is decomposed 
 by water, and appears to be identical with the tartryl-antimonious acid. 
 
 394. Stereoisomerism as illustrated by tartaric acid, When natural 
 (dextro) tartaric acid, is heated with about one-tenth of its weight of 
 water, in a sealed tube at 175 C. for some 30 hours, in the apparatus 
 
 shown in Fig. 275, it is 
 converted into an inactive 
 isomeride, racemic acid, 
 which crystallises with iH.,0 
 in triclinic prisms, meltss at 
 202 C. and is much less 
 soluble in water than dextro- 
 tartaric acid is. By pre- 
 cipitating as acid potassium 
 tartrate, the unaltered 
 tartaric acid remaining in 
 the mother-liquor obtained 
 Fig. 275. Heating in sealed tubes. in crystallising racemic acid, 
 
 there is left in solution the 
 
 acid potassium salt of another inactive acid, mesotartaric acid, which 
 crystallises in rectangular tables (with iH 2 0).* 
 
 The differences between racemic and mesotartaric acid are sufficiently marked. 
 The acid potassium racemate is more soluble than the tartrate, while the corre- 
 sponding mesotartrate has not been crystallised. Calcium racemate, CaC 4 H 4 6 '4Aq. 
 is less sparingly soluble than calcium tartrate and than calcium mesotartrate, 
 CaC 4 H 4 6 .3Aq. so that calcium sulphate precipitates free racemic acid but neither 
 of the other free acids. Calcium racemate is insoluble in ammonium chloride and 
 
 * For obtaining mesotartaric acid the sealed tube containing- the tartaric acid and water 
 should be healed at 165 C. for 2 hours. 
 
STEREOISOMERISM. 6 2 I 
 
 in dilute acetic acid, which also fails to dissolve the inesotartrate the tartrate 
 however, is soluble in both. 
 
 Racemic acid is found mixed with the tartaric acid from certain samples of argol 
 and its crystals may be distinguished from those of tartaric acid by the cloudy 
 appearance which they assume at 100 C. due to the loss of their water of crystal- 
 lisation. 
 
 It has been found that racemic acid, like the inactive forms of other 
 compounds containing an asymmetric carbon atom, can be split up by 
 the methods referred to on p. 606 into the dextro-tartaric acid and 
 kevo-tartaric acid, which is practically identical with the dextro-acid, 
 save that it rotates the plane of polarisation to an equal extent to the 
 left. 
 
 The classical researches of Pasteur on sodium-ammonium racemate are the 
 foundation of stereochemistry. 
 
 The sodium-ammonium racemate, NaNH 4 C 4 H 4 6 , has the same crystalline form 
 as the tartrate, but when formed at a temperature below 28 C. the crystals of the 
 racemate differ from each other in the position of a certain unsymmetrical (hemi- 
 hedral) face ; this is on the right hand in the one kind and on the left hand in the 
 other (enantiomorphous). When these are picked out, and the acid extracted from 
 them, the right-handed crystals yield ordinary dextro-rotatory tartaric acid, whilst 
 the left-handed crystals yield lasvo-tartaric acid. From a solution of cinchonine 
 racemate, cinchonine lasvo-tartrate separates first. The mould penicMlium glaucum 
 consumes dextro-tartaric acid in preference to the laevo-form when growing in 
 racemic acid. 
 
 By mixing equal weights of dextro- and laevo-tartaric acid, heat 
 i> evolved and racemic acid is formed. So also calcium racemate 
 is precipitated when solutions of the I- and d-calcium salts are 
 mixed. 
 
 Three of the isomeric tartaric acids are thus accounted for, but the 
 fourth,* mesotartaric acid, finds no analogue among the isomerides of 
 compounds containing an asymmetric carbon atom so far considered. 
 Ic is not capable of being split up into active components, nor is it 
 produced by mixing the active forms. It is obtained practically pure 
 by oxidising maleic acid with permanganate. 
 
 It is supposed that this fourth tartaric acid owes its existence to the 
 fact that the molecule contains two asymmetric carbon atoms, so that 
 it is possible for the one to have its groups arranged to give dextro- 
 rotation while the groups of the other are arranged to give laevo- 
 rotation. In this cass the molecule would be internally compensated 
 and would be optically inactive, just as the racemic acid molecule is 
 externally compensated, consisting of two oppositely active molecules. 
 
 Tartaric acid belongs to the type of two tetrahedra having one solid angle in 
 common (p. 535), and to the other solid angles of each tetrahedron there must be 
 three different radicles, H, OH, C0 2 H, attached. It is evident that these three 
 radicles may be similarly or differently arranged around each tetrahedron, 
 are similarly arranged, then it will be possible on severing the tetrahedra to place 
 one inside the other, so that each solid angle shall correspond : if they are 
 differently arranged, this will not be possible. It is supposed that when the 
 radicles are similarly arranged, the tartaric acid is either dextro- or heyo-rotatory, 
 according as the arrangement is clockwise or anti-clockwise ; but 
 differently arranged, the dextro-rotatory power of one tetrahedron wi II annul 
 laevo-rotatory power of the other, and an inactive compound will result, 
 lowing figures will illustrate what has been said : 
 
 * A fifth acid, CO 2 H-C(OH) 2 -CH 2 -CO 2 H, which contains two OH groups attached to the 
 same carbon atom, has not been obtained. 
 
622 MECONIC ACID. 
 
 C0 2 H C0 2 H C0 2 H C0 2 H C0 H 
 
 HO-C-H H-C-OH HO-C-H HO-C-H + H-C-OH 
 
 H-C-OH HO-C-H HO-C-H H-C-OH HO'C'H 
 
 C0 2 H C0 2 H C0 2 H C0 2 H C0 2 H 
 
 Laevo-tartaric Dextro-tartaric Internally compensated Externally compensated tar- 
 
 acid, acid. or meso-tirtaric taric acid. 
 
 acid. Racemic acid. 
 
 It is worthy of note that in whatever manner tartaric acid is synthesised the 
 inactive forms are produced, and it is generally the case that artificial compounds 
 are inactive whether they contain an asymmetric carbon atom or not. This is to 
 some extent confirmatory of the foregoing theory ; for it would seem to be an even 
 chance which way the groups arrange themselves round the asymmetric carbon 
 atom, so that both forms are produced in equal amounts. 
 
 It is customary to speak of externally compensated compounds as racemlsed coin- 
 pounds and the passage of the active form into the externally compensated inactive, 
 as race mi sat ion. In many cases such racemisation occurs spontaneously under 
 influences which are somewhat obscure, and the passage of an unstable active form 
 into the more stable active form is known to occur. 
 
 395. Saccharic acid, C0 2 H-[CHOH]- 4 C0 2 H, is obtained by oxidising sugar or 
 starch with nitric acid, stopping short of the formation of oxalic acid. Sugar is 
 heated with 3 parts of nitric acid of sp. gr. 1.3, till violent action begins. When 
 no more red fumes are evolved, it is kept at 50 C. for some hours, diluted with 
 two or three volumes of water, neutralised with K 2 C0 3 . and acidified strongly 
 with acetic acid. On standing, acid potassium saccharate, C 4 H 8 4 (C0 2 ) 2 HK, 
 crystallises. This is dissolved in a little potash, and precipitated by cadmium 
 chloride. The precipitate of cadmium saccharate is suspended in water and 
 decomposed by H 2 S, the CdS filtered off, and the solution of saccharic acid 
 evaporated. Saccharic acid forms a deliquescent amorphous mass, soluble in 
 alcohol and in water. Its salts are somewhat similar to those of tartaric acid, 
 the acid salts of potassium and ammonium being sparingly soluble. Calcium, 
 saccharate, C 4 H 8 4 (C0 2 ) 2 Ca.Aq, is crystalline, nearly insoluble in water, but soluble 
 in acetic acid. The stereochemistry of saccharic acid will be noticed later. 
 
 Mucic acid, C0 2 H-[CHOH] 4 - C0 2 H, stereoisomeric with saccharic, is prepared by 
 oxidising gum arabic or milk sugar with nitric acid. Milk sugar is heated with 
 3 parts of nitric acid of sp. gr. 1.3 until red fumes are abundant ; the heat is then 
 removed, when the acid separates as a granular powder sparingly soluble in water 
 and alcohol. The mucates differ greatly from the saccharates, most of them being 
 insoluble ; the acid potassium salt is more soluble than the normal salt. By 
 boiling mucic acid with water for some time, it is converted into paramuclc acid, 
 which is isomeric with it, but more soluble in alcohol. Hydriodic acid reduces 
 saccharic and mucic acids to adipic acid 
 
 C 4 H 8 4 (C0 2 H) 2 + SHI = C 4 H 8 (C0 2 H) 2 + 4H 2 + 4l. 2 . 
 
 Pyromucic acid, or furfurane (L-monocarboxylic acid, C 4 H 3 0'C0 2 H, is a pro- 
 duct of the distillation of mucic acid, and may also be obtained by boiling furfural 
 (pyromucic aldehyde, p. 586) with silver oxide and water. It forms prismatic 
 crystals sparingly soluble in cold water, soluble in hot water, alcohol, and ether. 
 It may be sublimed. The pyromucates are very soluble. 
 
 / CH = C(C0 2 H)v 
 Meconic acid, CO^ >0, hydroxypyrone dicarboxylic acid, is 
 
 x C(OH):C(CO 2 Hr 
 
 extracted from opium by digesting it with hot water, neutralising the solution 
 with calcium carbonate, and adding calcium chloride, which precipitates acid 
 calcium meconate, HCaC 7 H0 7 .Aq, from which meconic acid may be crystallised by 
 dissolving it in hot dilute HC1. It crystallises (with 3H 2 O) in plates, dissolving 
 rather sparingly in cold water and ether, easily in hot water and alcohol. When 
 heated, it loses C0 2 , and becomes comenic acid, C 6 H 4 O 5 , and when further heated, 
 hydroxypyrone (pyrocomenic acid) C 5 H 5 (OH)0 2 . Solution of meconic acid gives a 
 fine red colour with ferric chloride, not bleached by mercuric chloride With 
 silver nitrate, it gives a white precipitate of hydrodiargentic meconate, HAg 2 C 2 H07, 
 but if a drop of ammonia be added, and the liquid boiled, the precipitate becomes 
 bright yellow nwrmal silver meconate, Ag 3 C 2 H0 7 . Meconic acid is closely related, by 
 
CITRIC ACID. 623 
 
 its composition, to chelidonic acid, C 7 H 4 6 , an acid obtained from celandine 
 (CheUdonlum majns), which belongs to the same botanical order as the opium 
 poppy, which yields meconic acid. 
 
 396. Polybasic acids. Very few of these are of any importance Trlciii-- 
 ballylic acid, CH 2 (C0 2 H)'CH(C0 2 H)-CH 2 (C0 2 H), may be obtained by heating 
 citric acid with hydriodic acid. It may also be built up from glycerol, C,H,(OH ) 
 by first converting this into allyl tribromide, C 3 H 5 Br 8 (p. 636), and heating the tri- 
 bromide with alcohol and potassium cyanide to obtain tricyanhydrin, or allyl 
 tricyanide, C 8 H 5 (CN) 8 , which yields potassium tricarballylate and ammonia when 
 boiled with potash ; C 3 H ? (CN) 3 + 3 KOH + 3 H 2 = C 3 H 5 (C0 2 K) 3 + 3 NH 3 . 
 
 The calcium salts of tricarballylic, citric, and aconitic acids occur in the deposit 
 formed in the stills of beet-sugar manufactories. Tricarballylic acid melts at 
 165 C. and crystallises in rhombic prisms, which are easily soluble in water and 
 alcohol. 
 
 397. Citric acid, or hydroxytricarballylic acid, CH 2 (C0 2 H)'C(OH) 
 (C0 2 H)'CH 2 (C0 2 H), the most important polybasic acid, is found in 
 many fruits, associated with malic? and tartaric acid. The potassium 
 and calcium salts are present in many vegetables and in the indigo 
 and tobacco plants. The acid is prepared from lemon juice 
 
 The juice is heated and chalk is added as long as effervescence occurs ; this 
 precipitates part of the acid as calcium citrate, leaving the rest in solution as an 
 acid salt ; this is precipitated by adding milk of lime, and boiling. The calcium 
 citrate is washed with boiling water, decomposed by exactly the required quantity 
 of dilute sulphuric acid, the liquid filtered from the calcium sulphate, and 
 evaporated to crystallisation. It is sometimes recommended to ferment the lemon- 
 juice with yeast for two days, and to filter before adding the chalk. 
 
 It is said that the acid can also be obtained industrially by fermenting glucose 
 with a particular fungus. 
 
 The synthesis of citric acid from acetone is by the following steps : (i) Acetone 
 treated with chlorine yields dicfdoracetone, CH 2 C1'CO'CH 2 C1, which (2) heated with 
 strong HCX yields " dichloracetotie cyanhydrin, CH 2 C1'C(OH)(CN)-CH 2 C1 ; on 
 (3) hydrolysis this gives dichloracetonic acid, CH 2 C1-C(OH)(C0 2 H)-CH 2 C1. (4) The 
 two Cl atoms are now exchanged for CN by treatment with KCN, dicyanoacetonic 
 acid being produced, CH 2 CN-C(OH)(C0 2 H)-CH 2 CN, which (5) by hydrolysis yields 
 citric acid. 
 
 Citric acid crystallises in rhombic prisms (with iH 2 0) very soluble in 
 water and fairly so in alcohol, but little in ether ; they melt at 100 C., 
 become anhydrous at 130, and then melt at 153. Further heated to 
 175, the acid loses water and becomes aconitic add, C 3 H 3 (C0 2 H) 3 . 
 
 By further heating, the aconitic acid becomes aconitic anhydride which then 
 loses C0 2 and passes into the anhydride of itaconic acid (ntethylene suecinic acid) 
 (COOH)CH 2 -C( : CH 2 )(COOH), which crystallises in the neck of the retort. The 
 liquid portion of the distillate contains the anhydride of citraconic acid (methyl 
 maleic acid] isomeric with itaconic, into which it is converted by heating its con- 
 centrated solution to 120 C. Oxidising agents convert citric acid into acetone and 
 its derivatives. When dehydrated by phosphoric or sulphuric acid, it also yields 
 acetone, together with CO and C0 2 ; C 3 H 4 (OH)(C0 2 H) 3 =2C0 2 + CO + H 2 + 
 CH 3 -CO-CH 3 (acetone). Fusion with potash converts it into acetate and oxalate 
 C 3 H 4 (OH)(C0 2 H) 3 + 4KOH = 2(CH 3 'C0 2 K) + (C0 2 K) 2 + 3H 2 0. 
 
 Solution of citric acid, mixed with excess of lime-water, gives no precipitate 
 in the cold, distinguishing it from tartaric and oxalic acid : but when heated, it 
 deposits calcium citrate, Ca 3 (C 6 H 5 7 ) 2 4Aq, which is more soluble in cold than in 
 water, but it is insoluble in potash, which dissolves calcium tartrate ; ami 
 chloride and acetic acid dissolve it. . , . . 
 
 Magnesium citrate, Mg 3 (C 6 H 3 7 ) v .i4Aq, is easily soluble in water ; mixed 
 NaHC0 3 , citric acid, and sugar, and" rendered granular by moistening with alec 
 and drying, it forms effervescent citrate of magnesia. 
 
 Ferric citrate, Fe 2 (C 6 H 5 7 ) 2 .6Aq, used in medicine, forms transparent i 
 
624 KETONES. 
 
 prepared by dissolving ferric hydroxide in citric acid and evaporating. Ferric- 
 amtnonlo-cltrate, Fe 2 (NH 4 ) 3 (C 6 H50 7 ) 3 , is also used medicinally. 
 
 Aconitic acid, C0 2 H.CH : C(C0 2 H)-CH 2 -C0 2 H, a tribasic acid of the olefine series, 
 is obtained by heating citric acid in a retort till oily drops appear in the neck, and 
 extracting the mass with ether, which leaves the unaltered citric acid undissolved. 
 On evaporating the ether, aconitic acid is left in small crystals, easily soluble in 
 water and alcohol. It is distinguished from citric acid by not precipitating when 
 boiled with excess of lime water. Aconitic acid is found in monkshood {Aco-mtum 
 napellus], beet-root, and sugar-cane, and in some other plants. 
 
 398. Trlmesic acid, or i : 3 : $-be*senetriowboanflieaoia, C 6 H 3 (C0 2 H) 3 , results from 
 the oxidation of mesitylene ; it sublimes. 
 
 Mellitlc acid, C 6 (COOH) 6 , is a hexabasic acid of the aromatic series (for it yields 
 benzene when distilled with lime), which occurs as its aluminium salt in a mineral 
 melllte or honey-stone. It crystallises in fine silky needles. 
 
 ACIDS CONTAINING NiTKOGEN. See Ammonia Derivatives emdCyanogen 
 Derivatives. 
 
 IV. KETONES OR ACETONES. 
 
 399. The relationship between an aldehyde and a ketone has already 
 been noticed (p. 580) ; both contain a CO group, attached in the former 
 to a hydrocarbon radicle and a hydrogen atom, as CH 3 ' CO'H, and in 
 the latter to two hydrocarbon radicles, as CH 3 'CO'CH 3 , acetone. Both 
 may be regarded as formed from an acid, the aldehyde by substituting 
 an H atom, the ketone by substituting a hydrocarbon radicle, for the 
 OH of the COOH group. Thus both may be formed from the acid 
 chloride, e.g., CH 3 CO*C1 the aldehyde by action of nascent hydrogen, 
 the ketone by action of the sodium compound of a hydrocarbon 
 radicle : 
 
 CHg-CO-Cl + HH = CHg-CO'H + HC1 
 CH 3 -CO-C1 + CH 3 Na = CH 3 -COCH 3 + NaCl. 
 
 It has already been shown (p. 568) that the ketones are, so to speak, 
 the aldehydes of the secondary alcohols, into which they are converted 
 by nascent hydrogen. For the formation of ketones from esters of 
 ketonic acids see p. 644. 
 
 It was shown at p. 580 that the aldehyde of an acid can generally be 
 obtained by distilling a mixture of a calcium salt of that acid with 
 calcium formate. If calcium acetate is distilled with calcium formate, 
 acetic aldehyde is produced 
 
 (CH 3 -CO-0) 2 Ca 4- (H-COO) 2 Ca = 2(CH 3 'CO'H) + 2(CaOC0 2 ). 
 But if calcium acetate be distilled with calcium acetate that is, by 
 itself the products will be acetone and calcium carbonate 
 
 (CH 3 -COO) 2 Ca + (CH 3 -COO) 2 Ca = 2(CH 3 'COCH 3 ) + 2(CaOC0 2 ). 
 
 Ketones are simple or mixed accordingly as the hydrocarbon radicles 
 attached to the CO group are the same or different ; thus, by distilling 
 a mixture of calcium acetate arid propionate, the mixed ketone 
 acetone- propione is obtained 
 
 (CH 3 -COO) 2 Ca + (C 2 H 5 -COO) 2 Ca = 2 (CH 3 -COC 2 H 5 ) + 2(CaO-COJ. 
 
 The ketones are less easily oxidised than the aldehydes ; for instance, 
 they do not reduce alkaline silver solutions. By more powerful 
 oxidants they are generally converted into tw r o acids, the rupture of 
 the molecule occurring at the CO group. Thus, propione CjHg'CO'CjHj, 
 yields propionic acid, C 2 H 5 'C0 2 H, and acetic acid, CH 3 'C0 2 H. 
 
ACETONE. 625 
 
 As in the aldehydes, the CO group is unsaturated, so that the ketones 
 yield a number of combinations similar to those obtained with the 
 aldehydes. Ketoximes, R,C : NOH, like the aldoximes from aldehydes, 
 are formed by reaction of ketones with hydroxylamine. 
 
 The oximes show a number of cases of stereo-isomerism. most of them, both 
 aldoximes and ketoximes, existing in a stable and an unstable (labile) modifi- 
 cation. This has been explained by supposing that a difference exists in the 
 relative positions of the radicles attached to the carbon and nitrogen 
 respectively^/, maleic and funiaric acids). This difference maybe represented 
 
 thus : and (in the aldehydes R' is H). This theory is supported 
 
 N'OH HO'N 
 
 by the fact that one of the two aldoximes nearly always loses water more easily 
 than the other, showing that the H and OH are probably nearer to each other in 
 this aldoxime than in its isomeride. The syllables syn- and anti- are used to 
 distinguish the forms, the first being syn-RK'-oxime the second anti-RR'-oxime. 
 
 With phenylhydrazine the ketones yield hydrazones, R 2 C:N-NHC G H 5 . 
 Ketones containing a methyl group combine with NaHS0 3 to form 
 sodium hydroxysulphonates, e.g., (CH 3 ) 2 'C(OH)-S0 3 lS"a. By the action of 
 PCL, the of the CO group is exchanged for 01, forming chlorides of 
 the type R.,CC1 2 in which the CL> is easily exchanged for H 2 to form a 
 secondary paraffin hydrocarbon. 
 
 From their constitution, the ketones must afford many cases of isomerism 
 (metamerism) ; thus, propione and methyl-propyl ketone have the same ultimate 
 composition ; so have methyl-butyl and propyl-ethyl ketones ; methyl-amyl ketone 
 and butyrone form another pair. Moreover, each ketone of the acetic series is 
 isomeric with the aldehyde of the acid following next in the series ; thus, acetic 
 ketone, (CH 3 ). 2 CO, is isomeric with propionic aldehyde, C 2 H 5 - COH. 
 
 400. Acetone, or dinwthyl-ketone, CH 3 *CO t CH 3 , or pyro-acetic spirit, 
 is obtained among the products of distillation of wood (p. 566), and may 
 be prepared by distilling the acetate of lead, calcium, or barium, the 
 last yielding the purest product (see the above equation). The crude 
 distillate is shaken with a saturated solution of NaHS0 3 and the 
 crystalline compound thus formed (see above) is freed from the mother- 
 liquor and distilled with sodium carbonate, when acetone distils over, 
 mixed with water, which is removed by fused calcium chloride. 
 
 Acetone is a colourless fragrant liquid, of sp. gr. 0.80, and boiling at 
 56. 3 C. It is inflammable, burning with a luminous flame. It mixes 
 with water, alcohol, and ether. On adding solid KOH to its aqueous 
 solution, the acetone separates and rises to the surface. It is a good 
 solvent for certain resins and camphors, and is also used for making 
 chloroform, iodoform and sulphonal. It is not so powerful a reducing- 
 agent as aldehyde, and does not reduce silver nitrate. "When oxidised 
 by K Mn,O 8 or by K.,Cr.,0 7 and H.,S0 4 it yields acetic and carbonic 
 acids CH 3 -CO-CH 3 + 6 4 = CH 3 -CO'OH + CO(OH) 2 . 
 
 Acetone is formed when vapour of acetic acid ig passed through a red-hot tube, 
 and when starch, sugar, and many other organic bodies undergo destructive distil- 
 lation. It occurs in the urine of diabetic patients. 
 
 When acted on by dehydrating agents, such as sulphuric or hydrochloric acid 
 or quicklime, acetone loses the elements of water, and yields condensation-pro- 
 duct*, richer in carbon ; thus, two molecules of (CH 3 ). 2 CO, losing H 2 0, give 
 (CH 3 ) 2 C : CH-CO-CH 3 , wesltyl o.ride, a liquid smelling of peppermint, and boiling 
 at 130 C. Three molecules of (CH 3 ) 2 CO, losing 2H 2 0, yield [(CH 3 ) 2 :C : CH] 2 CO, 
 phot-one, a crystalline solid, smelling of geraniums, and boiling at 196 C., whilst the 
 loss of another H gives CH 10 , mesltylene (p. 549). 
 
 2 II 
 
626 PYRUYIC ACID. 
 
 Acetone peroxide, (C 3 H 6 O 2 ) 3 , is formed by mixing concentrated solutions of H. 2 0. 2 
 and acetone. It forms crystals, melting at 97 C., insoluble in water and explosive. 
 
 An important thio-derivative of acetone is obtained by heating a mixture of 
 acetone and mercaptan with HC1. 
 
 (CH S ) 2 CO + 2C 2 H 5 SH = (CH 3 ) 2 C(SC 2 H 5 ) 2 + H 2 O. 
 
 This is known as mercaptol and when oxidised by permanganate it yields svlpJtonal 
 (acetonedlethylsulphom), (CH 3 ) 2 C(S0 2 C 2 H 5 ) 2 , an important soporific which crystal- 
 lises well and melts at 126 C. 
 
 Met-hyl-ethyl "ketom may be obtained by the reaction between acetyl chloride and 
 zinc ethide ; 2(CH 8 'C6'C1) + Zn(C 2 H 5 ) 2 = 2(CH 3 -CO-C 2 H 5 ) + ZnCl 2 . It boils at 81 C., 
 and is present in small proportion in commercial acetone. When oxidised, it yields 
 only one acid, acetic ; CH S -CO-C 2 H 5 + 3 = 2(CH 8 -CO-OH). 
 
 Benzophenone or dlpKenyl Itetotie, (C 6 H 5 ) 2 CO, prepared by distilling calcium ben- 
 zoate, forms stable prisms which melt at 46 C., and labile rhombohedra which 
 melt at 26 C. ; the labile changes into the stable form on addition of a trace of the 
 latter. Benzophenone boils at 307 C. 
 
 Acetophenone, metliyl-plienyl Itetone, CH 3 *CO'C 6 H 3 , from calcium acetate and 
 benzoate, melts at 20 C.. boils at 202 and is used as an hypnotic Qiypnone). 
 
 Jlethyl-nonijl Itetone, CH 3 'COC 9 H 19 , is the chief constituent of oil of rue, from 
 which it may be precipitated by NaHSO 3 . It may be obtained artificially by dis- 
 tilling calcium acetate with calcium rutate (in.-p. 15 ; b.-p. 225 C.). 
 
 Naphthyl-plienyl Itetone, C 10 HyCOC 6 H 5 , forms a dibromide, which is useful in 
 optical experiments, on account of its high refractive power. 
 
 401. Ketone-alcohols, ketone-aldehydes, ketone-acids, di- 
 ketones. It was shown at p. 574 that these compounds may be 
 regarded as oxidation products of polyhydric alcohols containing a 
 secondary alcohol group, which might be expected to become a 
 ketonic group on oxidation (p. 568) while the primary alcohol group 
 would yield the aldehyde or acid group. Thus from a-propylene 
 glycol, CH 3 'CHOH-CH,OH, would be obtained the ketone-alcohol, 
 OH 8 -COCH,OH,the ketone-aldehyde,CH 3 -C(>CHO, and the ketone-acid, 
 OHgCOCOOH, and from /3-butylene glycol, CH 3 'CHOH-CHOH-CH 3 , 
 the diketone, CH 3 'CO'CO'CH 3 . All these compounds share with the 
 ketones and \ aldehydes a tendency to combine and to undergo nucleal 
 condensation ; hence many are of great value in synthetic chemistry 
 as steps to more complex compounds. 
 
 Isomerides are distinguished as a- and /3- &c., as indicated on page 596. 
 
 Ketone-alcohols or hetols are exemplified by acetylocarbinol or acetol, 
 CH 3 -COCH. 2 OH. which boils about 150 C. and is obtained by cautious oxidation 
 of d-propylene glycol with bromine water. Several of the sugars are ketols. 
 
 Pyroracenilc aldehyde, or methyl f/lyo.ral. CH.^COCHO. is the type of the ketone- 
 aldehydes ; it is a volatile yellow oil. 
 
 Pyromcem'H' a eld or pyrurlc acid, CH 3 COCOOH, is the typical a-ketonic-acid. 
 It is obtained by the destructive distillation of tartaric or racemic acid (p. 619), as 
 an oxidation product of ethylidene lactic acid. CH 3 'CHOITCOOH, and by hydro- 
 lysing acetyl cyanide, CH 3 COCN. This last method, the hydrolysis of an acidyl 
 cyanide, is a general one for preparing a-ketone-acids. It 'is a colourless liquid 
 smelling of acetic acid, boiling about 167 C.. and soluble in water. It shows most 
 of the reactions of a ketone and an acid : in addition, it is a strong reducing-agent, 
 reducing alkaline silver nitrate, probably because the CO group has COOH attached 
 to it instead of the second hydrocarbon radicle of a ketone. Baryta water converts 
 it into uritic acid, a dibasic aromatic acid. With nascent H it yields lactic 
 acid. 
 
 Aceto-acetlc acid, or acetonecarboarylic acid, CH.,-COCH 2 COOH, is the typical 
 j3-ketone-acid, all of which are very unstable, tending to break down into C0 2 , from 
 the carboxyl group, and the corresponding ketone. Its ethyl salt (xee Ethereal 
 Salts) is more stable than the acid and is an important compound for synthetical 
 work ; by saponifying this salt potassium aceto-acetetate, and from this the free 
 acid is obtained. It is a liquid soluble in water and decomposing into acetone and 
 COo when heated. 
 
ETHERS. 
 
 Lt-ruluuc acid, CH,-CO-CH g -CH a COOH, is the type of the 7 -ketone-acids. which 
 are also easily broken down by heat: but instead of losing CO, they lose HO 
 yielding y-lactones (p. 607) from unsaturated hydroxy-acids. Thus, levulinie -.rid 
 yields y-lactones from angelic acid ; 
 
 CH 3 C : CH-CH 2 COO and CH 2 : (>CH 2 -CH 2 Co6. 
 
 Levulinie acid is a product of the action of acids on various carbohydrate* 
 especially levulose. It melts at 32-5 C. and boils at 239 C., dissolves in water 
 and is used in calico-printing. 
 
 PJtenylglyojpyliG add or benzoyl formic add, C 6 H 6 -CO'COOH, is produced bv 
 oxidising mandehc acid and by hydrolysing benzoylcyanide. It melts at 65 C 
 
 Diacetyl, OH 3 CO-COCH S , is the simplest a-diketone.* It is made by hotting 
 Lwnitrosoniethylacetone, CH 3 -C(NOH)-CO-CH 3 with acid, and is a greenish-yellow 
 liquid, smelling of quinine and boiling at 87 C. The /3-diketones, like acetvlacetone 
 CH 3 -COCHoCOCH 3 , are remarkable for forming metallic salts (acetylwetonafe*) 
 the true constitution of which is in doubt. The 7-diketones, like avetonylacetone. 
 CH 3 -CO-CH. 2 'CH 2 -CO-CH 3 , do not share this property, but are important because of 
 the ease with which they pass into closed-chain compounds of the furfurane or 
 pyrrol type (</.f.) 
 
 V. ETHERS. 
 
 402. The ethers are derived from the alcohols by the substitution of a 
 hydrocarbon radicle for the hydrogen in the OH group ; thus, if methyl 
 alcohol, CH 3 'OH, be treated with Na, the hydroxl hydrogen is displaced 
 by sodium, and CH 3 'ONa, or sodium methoxide, is obtained. If this be 
 acted on by methyl iodide CH 3 -ONa + CH 3 I = CH 3 '0-CH 3 + NaI the 
 H in CH 3 OH is displaced by CH 3 , and methyl ether, CH 3 'OCH 3 , is 
 formed. It will be evident that a similar reaction between sodium 
 methoxide and ethyl iodide, C 2 H.I, would furnish the mixed ether, 
 methyl-ethyl ether, CH 3 'OC 2 H 5 , so that the number of ethers obtainable 
 would exceed that of the alcohols. 
 
 Just as the alcohols are comparable with the metallic hydroxides 
 (p. 561), albeit far less prone to chemical change, so the ethers may be 
 compared with the metallic oxides deprived of most of their chemical 
 energy. This view is supported by a second general method of pre- 
 paring them, namely, by heating the alkyl halides with metallic oxides, 
 2CH 3 I-i- Ag 3 O = (CH 3 ) 2 + 2AgI ; and by their reaction with hot hy- 
 driodic acid to yield an iodide and water, as the alkali oxides do 
 
 K 2 + 2 HI = H 2 + KI ; and (CH 3 ) 2 + 2 HI = H 2 + 2 CH 3 I. 
 
 The usual method for obtaining the ethers is by the action of sul- 
 phuric acids on alcohols, as will be explained below. 
 
 The ethers are generally insoluble in water, and lighter and more 
 volatile than the corresponding alcohols. They are almost as indifferent 
 to reagents as the hydrocarbons are, and probably for a like reason, 
 viz., that all the hydrogen is combined with carbon. The reaction of 
 the ethers will be gathered from those of ethyl ether. 
 
 It will be remarked that the ethers derived from the alcohols of the 
 series C W H 2W+2 form an homologous series isologous with the alcohols, 
 that each ether is metameric with the isologous alcohol, and that the 
 ethers containing an odd number of carbon atoms are mixed ethers. 
 
 * By the now system of nomenclature, ketones are named like the alcohols (see foot-note 
 p. 568), -on being substituted for -ol. Thus, CH 3 -CO'CH 2 -CH 2 -CH 3 is a-pentanon (tin- O beiiiu 
 attached to the second C atom). CH 3 -CO-CH 2 'CO-CH 3 is 
 
628 ETHEPJFICATION. 
 
 Ethers. Alcohols. 
 
 Methyl . . . CH 3 "O CH 3 
 
 Methyl-ethyl . . CH 3 '0-C 2 H 5 
 
 Ethyl . . . C 2 H 5 -OC 2 H 5 
 
 Ethyl-propyl . . C 2 H g -0'C 3 H 7 
 
 Propyl . . . C 3 H 7 -0'C 3 H 7 
 
 Ethyl . . . C H 5 -OH 
 
 Propyl . . . C 3 H 7 -OH 
 
 Butyl . . . C 4 H 9 'OH 
 
 Amyl . . . C 5 H n 'OH 
 
 Caproic . . . C 6 H 13 'OH 
 
 403. Methyl ether, or dimethyl oxide, CH 3 '0'CH 3 , is a fragrant inflammable (/as 
 prepared by adding methyl alcohol (2 parts by weight) to cooled strong H 2 S0 4 
 (3 parts) and heating to about 140 C., keeping up a supply of methyl alcohol, as 
 in the preparation of ether (q.r.), the reaction being the same as in the preparation 
 of ether, if methyl be written for ethyl. The gas may be stored for use by passing 
 it into cooled H 2 S0 4 , which dissolves 600 volumes of it and gives it up again when 
 mixed with water. It is condensed by cold or pressure to a liquid boiling at 
 -21 C., and used for producing cold. Water absorbs about 37 times its volume of 
 the gas. 
 
 404. Ether, or sulphuric ether, C 2 H 5 'OC 2 H 5 , is prepared by distilling 
 alcohol with sulphuric acid. If two measures of alcohol be carefully 
 added to one measure of strong sulphuric acid, and the mixture distilled, 
 ether passes over together with water, and if alcohol be added from 
 time to time, a small quantity of sulphuric acid suffices to etherify a 
 large quantity of alcohol. The alcohol is first converted into hydrogen 
 ethyl sulphate, sulphethylic acid or ethylsulphuric acid 
 
 S0 2 (OH 2 ) + C 2 H 5 -OH = S0 2 (OH)(OC 2 H 5 ) + HOH. 
 
 When this is heated to about 140 C. with more alcohol, it is decom- 
 posed into ether and sulphuric acid, which then acts in the same way 
 upon a fresh quantity of alcohol 
 
 S0 2 (OH)(OC 2 H 5 ) + C 2 H 5 -OH = C 2 H 6 -OC 2 H 5 + S0 2 (OH) 2 . 
 
 Hence the process has been termed the continuous etherification process 
 and is carried out in the following manner : 
 
 Alcohol of sp.gr. 0.83 is carefully added, with continued shaking, to an equal 
 volume of strong sulphuric acid, cooled in a vessel of water. When the mixture is 
 cold, it is poured into a retort or flask (Fig. 276), which is connected with a reser- 
 voir of alcohol and a well-cooled condenser. The mixture is quickly heated till it 
 boils, when its temperature will be about 140 C. (284 F.), and alcohol is then 
 allowed to pass in slowly from a siphon tube furnished with a stop-cock, and 
 dipping below the liquid in the flask ; the temperature should remain as nearly as 
 possible at 140 C., which will be the case if the rate of flow of the alcohol is so 
 regulated as to keep the mixture at the same level. A thermometer is fixed in the 
 cork with its bulb in the liquid. When the total quantity of alcohol used amounts 
 to six or seven times that originally taken, the process must be stopped, because 
 secondary reactions, attended by carbonisation, have used up much of the sulphuric 
 acid. The liquid collected in the receiver contains about two-thirds of its weight 
 of ether, with about one-sixth of water, an equal quantity of alcohol, and a little 
 sulphurous acid. It usually separates into two layers, of which the upper is ether. 
 The whole is introduced into a narrow stoppered bottle, and shaken with cold water, 
 added in small portions, as long as the layer of ether on the surface increases in 
 volume ; a little potash is then added to fix SO 2 , and, after shaking, the upper 
 layer of ether is drawn off, by a siphon or separator, into a flask containing lumps 
 of fused calcium chloride, to remove water and alcohol. After standing for some 
 hours, the ether is distilled off in a water-bath at as low a temperature as possible. 
 To free it entirely from water, it must be again rectified after digestion with 
 powdered quick-lime, and finally with bright sodium, till no more hydrogen bubbles 
 are visible. Methylated ether is prepared from methylated, spirit, and is much 
 cheaper than pure ether, for which it may often be substituted. 
 
 It has been found that benzene sulphonic acid (C 6 H 5 S0 3 H) may advantageously 
 be substituted for the sulphonic acid, as it will etherify about 100 times its'weight 
 
PROPERTIES OF ETHER. 
 
 629 
 
 The acid is melted in the flask and alcohol run in slowly, the tenner. 
 kept about 140 C. C 6 H 5 S0 3 C 2 H 5 is first formed and is decomposed by 
 10! into C 6 H 5 S0 3 H and (C 2 H 5 ) 2 0. 
 
 of alcohol, 
 ture being 
 more alcohol 
 
 Theonj of etherljicatwn. The processdescribed above for the preparation of ether 
 had long been practised before a satisfactory explanation of it was arrived at One 
 of the earliest views regarded the formation of ether as a simple removal of 'water 
 by the sulphuric acid from the alcohol, which was then believed to be a compound 
 of ether and water ; but against this it was urged that the water was not retained 
 by the acid, but distilled over with the ether, and that the same acid would etherify 
 
 Fig-. 276. Continuous ethcrincation. 
 
 successive additions of alcohol. Passing over the theory of catalytic action, or 
 decomposition by contact, which was a mere statement of the facts without any 
 real explanation, we come to the important observation that the first product of the 
 action of sulphuric acid on alcohol is sulphethylic acid, which is decomposed, when 
 distilled with more alcohol at 140, into ether, water, and sulphuric acid, as in the 
 equations given on p. 628. 
 
 Very strong evidence that the above equations represent the reactions 
 occurring in the etherification process is furnished by the following 
 experiment : Amyl aloohol,C 5 H u *OH, is converted by sulphuric acid 
 into sulphamylic acid, C 5 H n 'S0 4 H, which is heated in the flask 
 (Fig. 276), whilst ethyl alcohol, C a H 5 'OH, is allowed to flow in from the 
 reservoir ; this decomposes the sulphamylic acid, yielding sulphuric 
 acid, and amyl-ethyl ether 
 
 C 5 H n -S0 4 H + C 2 H 5 -OH = C 5 H n -0-C 2 H 5 + H 2 S0 4 . 
 
 If the process is continued after all the amyl-ethyl ether has passed 
 over, only ethyl ether is obtained. In this manner any mixed ether can 
 be prepared. 
 
 405. Properties of ether. A very mobile colourless liquid with a charac- 
 teristic odour ; sp. gr. at 15 C. 0.70. It boils at- 35 C., evaporates 
 very rapidly in air, producing intense cold, and yielding a very heavy 
 vapour, of sp. gr. 2.59, which is very inflammable, and renders ether 
 dangerous in unskilled hands. It melts at 113 C. It is sparingly 
 soluble in water, so that, when shaken with it, the ether generally rises 
 to the surface on standing, rendering it very useful for collecting certain 
 substances, such as bromine and alkaloids, from large bulks of aqueous 
 
630 EEACTIONS OF ETHER. 
 
 solutions into a small bulk of ether. Ten volumes of water dissolve one 
 volume of ether. Thirty-four volumes of ether are required to dissolve 
 one volume of water, so that ether, free from alcohol, could not contain 
 much water, but commercial ether contains alcohol, which enables it to 
 take up a larger quantity of water. Ether and alcohol may be mixed 
 in all proportions, but the addition of much water generally brings the 
 ether to the surface. Ether is much used in laboratories as a solvent, 
 especially for fatty substances and alkaloids, and by the photographer 
 in making collodion. 
 
 Ether containing water becomes turbid when shaken with OS, and 
 that containing alcohol dissolves sufficient aniline violet to become 
 coloured when shaken with this dye-stuff. 
 
 The properties of ether admit of some interesting experiments. 
 
 1. If a little ether be evaporated by blowing upon it in a watch-glass, with a drop 
 of water hanging from its convexity, the water will be speedily frozen. A thin 
 beaker containing ether may be frozen to a wet table by blowing into it with the 
 bellows. 
 
 2. A piece of tow, wool, or sponge, wetted with ether, is placed at the upper end 
 of a sloping trough or gutter of wood or metal, over six feet long ; a match applied 
 at the lower end fires the train of vapour. 
 
 3. A jug is warmed with a little hot water, emptied, and a little ether poured into 
 it ; the vapour may be poured into a row of small beaker-glasses, each of which is 
 afterwards tested with a taper. 
 
 4. A pneumatic trough is filled with warm water, and a small test-tube filled 
 with ether is inverted with its mouth under the water, and quickly decanted up 
 into a gas-jar filled with warm water, when it will be vaporised, and may be 
 decanted through the water into other vessels, and treated like a permanent gas. 
 Some cold water poured over the jar containing it at once proves its condensable 
 character. 
 
 406. Ether is also produced by the reactions given on p. 627, C 2 H 5 being substi- 
 tuted for CH 3 in the equations. Ethyl iodide, heated with a small quantity of 
 water, under pressure, yields, first alcohol, and afterwards ether 
 
 C 2 H 5 I + HOH = C 2 H 5 -OH + HI, and C 2 H 5 I + C 2 H 5 -OH = C 2 H 5 'OC 2 H 5 + HI. 
 
 Other acids besides sulphuric are able to produce ether from alcohol, especially 
 those which ave non-volatile and polybasic, such as phosphoric, arsenic, and 
 boric, which probably act in the same way as sulphuric. But certain salts, 
 such as zinc chloride and aluminium sulphate, also generate ether from alcohol, 
 and the explanation of this is less simple. It will be found that such salts are 
 capable of decomposition by water, with formation of basic salts and free acid ; 
 thus, ZnCl 2 + HOH = ZnCl-OH + HCl, or A1 2 (S0 4 ) 3 + 4HOH = A1 2 S0 4 (OH) 4 + 2H 2 S0 4 . 
 
 If these reactions occur with alcohol, C 2 H 5 -OH, instead of with HOH. the 
 products would be C 2 H 5 C1 instead of HC1, and C 2 H 5 'HS0 4 instead of H 2 80 4 , and 
 either of these would react with the excess of alcohol to produce ether. 
 
 Ether may be converted into alcohol by heating it with water and a very little 
 sulphuric acid, in a sealed tube, at 180 C. The ether is probably converted at 
 first into sulphethylic acid, and this into alcohol and sulphuric acid, the etherifica- 
 tion reaction (p. 628) being reversed. 
 
 When ether is acted on by hydriodic acid gas, in the cold, it yields alcohol and 
 ethyl iodide ; (C 2 H 5 ) 2 O + Hi = C 2 H 5 'OH + C 2 H 5 I. If a mi. red ether, such as ethyl- 
 amyl ether, be treated in this w r ay, the radicle containing more carbon is the one 
 converted into an alcohol ; C 2 H 5 -6-C 5 H n + HI = C 5 H n -OH + C 2 H 5 L 
 
 Ordinary oxidising-agents convert ether into aldehyde and acetic acid. Ozonised 
 oxygen converts it into formic, acetic, and oxalic acids and hydrogen peroxide. 
 
 When ether vapour is passed over heated potash, hydrogen, marsh gas, and 
 potassium carbonate are formed, potassium acetate being probably produced in 
 the first stage of its reaction ; (C 2 H 5 ) 2 + 2KOH + H 2 = 2KC 2 H 3 2 + 4H 2 . 
 
 Ether enters into combination with several metallic chlorides and bromides, 
 forming crystalline compounds ; stannic chloride combines with two molecules 
 of ether, forming SnCl 4 (C 4 H 10 0) 2 ; aluminium bromide forms Al 2 Br 6 (C 4 H 10 0) 2 . 
 
 Ether is inflamed by contact with chlorine ; but if it be very well cooled, and 
 
ZEISEL'S METHOD. 
 
 6 3 I 
 
 light be excluded, at yields a series of substitution-products. Monorhlorether 
 dtehloretker and tetracUor ether are known. Per chlorinated 'ether (' '1 re' 
 c'mhor ^ f rmati n ' is a cl> Y s talline body (m.-p. 68 C.) smelling like 
 
 Distilled with PC1 5 , ether yields C 2 H 5 C1 and POC1 3 but no HC1 (rf p < 7Q ) 
 
 CHrOHUOV^ ^T^ alc0hols '- B y treating monosodium^glycol 
 < 2H 4 (OH)(0^a) with C^H 5 I, as in the general reaction (p. 627), monoethul ff Lol 
 ether <\H 4 (OH)(OC 2 H 5 ) (b.-p. 127 C.) is obtained. If disodium glycol be similarly 
 treated, the d.ethyl ether C 2 H 4 (OC 2 H 5 ) 2 (b.-p. 123 C.) is obtained? 
 
 .Regarding the formation of an ether as the abstraction of HOH from the two 
 OH groups of two molecules of an alcohol, glycol might be expected to form an 
 
 CH.x 
 internal ether, ^0. This compound, ethylene oxide, is produced when glycol 
 
 \-Slf) 
 
 chlorhydrin (p. 575) is distilled with potash : 
 
 CH 2 OH CH. 
 
 CH 2 C1 + KOH = CH > + HOH. 
 It is isomeric with ethyl aldehyde, boils at 12-5 C. and easily passes back into glycol 
 
 / CH 2x 
 
 derivatives. Trim ethylene oxide, CH 2 ^- V), boils at 50 C. and is similarly 
 
 CH 2 
 
 5 (OH) 3 , in 
 
 - ~ -- - - v Jy is formed 
 
 when glycerine is distilled with CaCl 2 , and is a colourless, inodorous liquid, boiling 
 at about 170 C., and of sp. gr. 1.16 ; it mixes with water. Its behaviour with 
 hydriodic acid is analogous to that of ethyl ether, for it is converted into glycerine 
 and glyceryl tri-iodide, C 3 H 5 I 3 . 
 
 409. Aromatic Ethers. these may be either the true ethers corresponding 
 with the aromatic alcohols, or ethers derived from phenols, which, it will be re- 
 membered, differ from the alcohols in having the OH group attached directly to 
 the benzene nucleus. 
 
 Benzyl ether, (C 6 H 5 'CH 2 ) 0, is prepared by distilling benzyl alcohol with B 2 3 
 which removes the elements of water, 2C 6 H 5 ' CH 2 OH- HOH = (C 6 H g -CH ).,0. "it 
 is a colourless liquid not miscible with water, and boiling at 296 C. 
 
 Dlphemjl wide, or phenyl ether, C 6 H 5 -0'C 6 H 5 , obtained by distilling phenol with 
 aluminium chloride, forms prisms, fusing at 28 C. and boiling at 252 C. It smells 
 like the geranium leaf, and is remarkable for its stability under the influence of 
 oxidising- and reducing-agents. Water does not dissolve it, but alcohol and ether 
 do so. 
 
 Phenyl- in ethyl ether, C 6 H 5 '0-CH 3 , is prepared by passing methyl chloride through 
 .sodium phenol at 200 C. It is a fragrant liquid, of sp. gr. 0.991, boiling at 152. 
 This ether is identical with AniWil, obtained by distilling anisic acid (p. 608) 
 with baryta. Methyl salicylate, or winter green oil, C 6 H 4 (OH)'C0 2 -CH 3 , is nieta- 
 ineric with anisic acid, and also yields phenyl-methyl ether when distilled with 
 baryta. Hydriodic acid heated to 140 C. with aniso'il, in a sealed tube, converts 
 it into phenol and methyl iodide ; C 6 H 5 'OCH 3 + HI C 6 H 5 'OH + CH 3 1. 
 
 This reaction is typical of the method commonly employed in determining the 
 number of methoxy-groups (OCH 3 ) in the molecule of a compound. It is known 
 as ZelseVs method, and consists in boiling a known weight (0.3 gram) of the substance 
 with fuming hydriodic acid (10 c.c.) in a flask ^1 (Fig. 277) through which a gentle 
 -current of C0 2 is passed. This carries the CH 3 I water vapour and HI through the 
 condensing-tube B, containing a number of aludels shown drawn to an enlarged 
 scale at C. The temperature of the water-bath D is regulated to ensure that the 
 distillation shall not be too rapid, which is indicated by the thermometer J? marking 
 a temperature of 50 C. The methyl iodide does not condense at this temperature 
 and passes through the absorption flasks E, containing water and red phosphorus, 
 where it leaves the HI and a little free I that it contains, and then into a wash 
 bottle containing an alcoholic solution of silver nitrate. Here the methyl iodide 
 is decomposed yielding a precipitate of Agl, which is collected, washed, and 
 weighed. From its weight that of the CH 3 I and therefore of the OCH 3 in the 
 compound taken, is calculated. 
 
632 
 
 HALOGEN DERIVATIVES OF HYDROCARBONS. 
 
 The methyl ethers of the phenols are formed at the ordinary temperature when 
 diazomethane, CH 2 N 2 , and a phenol are brought in contact, e.;/.. C 6 H 5 OH + CH 2 N 2 =: 
 C 6 H 5 OCH 3 + N 2 . They are not changed when heated with alcoholic potash. 
 
 Fig-. 277. Apparatus for determining methoxyl roups. 
 
 Anetliol, the camphor-like substance in oil of anise is i : 4-propenyl-aniso'il r 
 CH 3 -CH : CH-C 6 H 4 -OCH 3 ; it melts at 22 C. and boils at 233 C. 
 
 Phenyl ethyl ether, C 6 H 5 '0'C 2 H 5 , or pUenetoil is obtained by distilling ethyl 
 salicylate with baryta ; it boils at 172 C. 
 
 VI. HALOGEN DERIVATIVES. 
 
 410. Halogen Compounds from Hydrocarbons. (A) Prom 
 open-chain hydrocarbons. It has been already noticed (p. 530) 
 that these products result in many cases from the direct action of the 
 halogens on the hydrocarbons, but whilst Cl and Br react thus by 
 metalepsis with hydrocarbons, iodine seldom does so unless an absorbent 
 for HI (e.g., HgO) be present ; this is because the metalepsis is a 
 reversible reaction (p. 309), e.g., CH 4 + I 2 ^:CH 3 I + HI. 
 
METHYL CHLORIDE. 633 
 
 Since the unsaturated hydrocarbons generally combine with the- 
 halogen to form addition products (p. 534), which are either identical 
 or isomeric with the halogen substituted saturated hydrocarbons,* some 
 other method must generally be resorted to in order to prepare halogen 
 substitution-products of unsaturated hydrocarbons. Thus, they are 
 obtained either by treating the halogen substituted saturated hydro- 
 carbons with reagents which will remove halogen hydride, or by only 
 partially saturating still more unsaturated hydrocarbons with halogen ; 
 e.g., C 2 H 4 C1 2 - HC1 = C 2 H 3 C1 ; C 2 H 2 + 01, = C 2 H 2 C1 2 . 
 
 The halogen substitution- products from all hydrocarbons are obtain- 
 able by the interaction of the alcohols with phosphorus halides, or, what 
 is equivalent, with phosphorus and a halogen. Examples will be met 
 with in the following pages. In a large number of cases the mere 
 treatment of an alcohol with halogen hydride, particularly in the 
 presence of a dehydrating agent, will produce the halogen substitution- 
 product, the reaction being of the type R'OH + HX = EX + HOH. 
 
 Methyl choride, or monochloro-methane CH 3 C1, is prepared by passing 
 HC1 gas into a boiling solution of zinc chloride in twice its weight of 
 methyl alcohol, contained in a flask connected with a reversed condenser. 
 The methyl chloride is evolved as a gas which may be washed with a 
 little water to remove HC1, dried by passing over calcium chloride, and 
 condensed in tubes cooled in a mixture of ice and calcium chloride 
 crystals. The final result is expressed by the equation CH 3 OH + HC1 = 
 CH 3 C1 + HOH. The action of the zinc chloride is little understood. 
 Methyl chloride is an inflammable gas of ethereal odour, liquefied by a 
 pressure of 2^ atm. at o C. Its boiling-point is - 24 C. Water dis- 
 solves 4 vols. of the gas and alcohol 35 vols. 
 
 Methyl chloride may also be prepared by distilling methyl alcohol with sodium 
 chloride and sulphuric acid. It is made on a large scale, for use in freezing- 
 machines, from the trimethylamine obtained by distilling the refuse of the beet- 
 sugar factories ; this is neutralised with hydrochloric acid, and heated to 260 C., 
 when it is decomposed into trimethylamine, ammonia and methyl chloride ; 
 3N(CH 3 ) 3 HC1 = 2N( CH s)3 + NH s + 3CH 3 C1. 
 
 Methyl chloride is very stable ; potash decomposes it with difficulty, yielding 
 methyl alcohol and potassium chloride. It is used in the preparation of some of 
 the aniline colours. 
 
 Ethyl chloride, or monochlor ethane, C 2 H 5 C1, is prepared by substi- 
 tuting ethyl for methyl alcohol in the foregoing prescription. The 
 purified vapour is passed into 95 per cent, alcohol kept cool by water. 
 The alcohol absorbs half its weight of ethyl chloride, which may be 
 evolved from it by gently heating, and purified by passing through a 
 little sulphuric acid. It is a fragrant liquid of sp. gr. 0.92 and boiling- 
 point 1 2. 5 C. It is sparingly soluble in water, and burns with a 
 bright flaire edged with green. Ethyl chloride is formed when olefiant 
 gas and HC1 are heated together for some time. 
 
 Methyl lironnde, CH 3 Br, is prepared by acting upon methyl alcohol with phos- 
 phorus and bromine ; 3CH 3 OH + Br s + P = 3CH 8 Br + P(OH) 3 . Four parts of methyl 
 alcohol are poured on i part of red phosphorus in a well-cooled retort witl 
 reversed condenser, and 6 parts of bromine are gradually added. After two or thret 
 
 * It will be remembered that the unsaturated hydrocarbon will also combine directly with 
 halogen-hydrides to form substituted saturated hydrocarbons. It is to be noted that whe 
 this is the case the halogen attaches itself to the carbon atom which has the smallest numl 
 of hydrogen atoms attached to it. Thus, from propylene, CH ; ,' CHiCIta and jiU, tu 
 results CH.j- CHC1- CH,, isopropyl chloride, not CH 3 ' CH 2 ' CH a CL 
 
634 ETHYL IODIDE. 
 
 hours, heat is applied by a water-bath, and the vapour condensed by a freezing- 
 mixture. Methyl bromide boils at .-j..5, burns feebly, and smells like chloroform. 
 
 Ethyl bromide, C 2 H 5 Br, may be prepared like methyl bromide, using 16 parts of 
 absolute alcohol, 4 parts of red phosphorus, and 10 parts of bromine. It is a 
 liquid boiling at 39 C. ; sp. gr. 1.419. 
 
 Methyl iodide, CH 3 I, is prepared on the same principle as the bromide, 10 parts 
 of iodine being dissolved in 4 parts of methyl alcohol, and I part of red phos- 
 phorus added in small portions. After heating in a water-bath for some time, 
 the mixture is distilled. The methyl iodide is the lower layer of the distillate. 
 It has a pleasant smell, sp. gr. 2.29, and boils at 44 C. It mixes with alcohol, 
 but not with water. When kept, it becomes brown from separation of iodine. 
 It is converted into CH 3 C1 gas when heated with HgCL, dissolved in ether. 
 Hydriodic acid, at 150 C., converts it into CH 4 . Methyl iodide is used in making 
 aniline dyes. 
 
 Jletliyl fluoride, CH 3 F, is a combustible gas obtained by heating KF with 
 potassium methyl sulphate, KCH 3 S0 4 . Ethyl fluoride boils at -48 C. 
 
 Ethyl iodide, C 2 H 5 I, is prepared by pouring 5 parts of absolute 
 alcohol on one part of red phosphorus in a retort, adding gradually 
 10 parts of iodine in powder, setting aside for twelve hours, and 
 distilling in a water-bath with a good condenser. Ethyl iodide mixed 
 with alcohol distils over, leaving phosphoric acid in the retort (together 
 with somo phosphethylic acid formed by its action on some of the 
 alcohol), 3C 2 H 5 OH + P + 1 3 = 3C 2 H 5 I + P(OH) 3 . The distillate is sha.ken, 
 in a stoppered bottle, with about an equal measure of water and enough 
 soda to render it alkaline. The ethyl iodide collects as an oily layer at 
 the bottom ; this is separated from the upper layer by a tap-funnel or 
 pipette or siphon, allowed to stand with a little fused calcium chloride 
 in coarse powder, to remove the water, and distilled. 
 
 Ethyl iodide has a pleasant smell, sp. gr. 1.93, and boiling-point 
 72 C. It becomes brown when kept, especially in the light, iodine 
 being liberated, and butane formed; 2C 2 H.I = C 4 H 10 + I 2 . Ethyl iodide 
 is sparingly dissolved by water, but readily by alcohol and ether. 
 
 Ethyl iodide is a very important reagent in organic researches for 
 introducing the group C,H 5 into the places of other radicles. 
 
 The monohalogen substitution-derivatives of the paraffins higher in 
 the series than ethane, exist in isomeric forms exactly analogous to the 
 isomeric alcohols (p. 567), a halogen being substituted for OH. 
 
 411. Dihalogen derivatives of ethane can obviously exist in two 
 modifications, CH 2 X'CH,X, or ethylene halides, and CH 3 'CHX 2 , 
 ethylidene halides/ The "former are obtained by the direct addition 
 of halogen to ethylene, and since by judicious treatment with moist 
 silver oxide they can be converted into glycol haiogen-hydrins (e.g., 
 glycol chlor-hydrin, q.v.} they most probably have the formula assigned 
 to them above ; moreover, they may be prepared from the glycols by 
 distillation with phosphorus halides. The ethylidene halides can be 
 obtained from aldehyde by treatment with phosphorus pentahalides 
 (P- 579)- 
 
 Ethylene chloride, etheiie di chloride, or Dutch liquid, C 2 H 4 C1 2 , may be obtained 
 from glycol by distilling it with PC1 5 
 
 C 2 H 4 (OH) 2 + 2PC1 5 = C 2 H 4 C1 2 + 2 POC1 3 + 2HC1 ; 
 
 but it is generally prepared by allowing equal volumes of dry ethene gas and dry 
 chlorine to pass into a large inverted globe or flask, the neck of which passes 
 through a cork into a receiver for the condensed liquid. Ethene dichloride 
 smells lather like chloroform ; its sp. gr. is 1.28, and it boils at 84 C. ; it is nearly 
 insoluble in water, but dissolves in alcohol. 
 
CHLOROFORM. 
 
 635 
 
 EtJujUdene chloride CH 3 CH 2 C1, is best prepared by the action of COCL, on 
 CHg'CHO, carbon dioxide being liberated. B-.p. 60 C 
 
 Ethylene bromide, or ethene dllromlde, C 2 H 4 Br,, is prepared a* described at 
 p. 574. It resembles the dichloride, but its sp. gr. is 2.16, and it boils at m 
 
 Ethylem iodide, C,H 4 I 2 , obtained by heating iodine in olefiant gas, forms silky 
 needles, which may be sublimed in the gas, but are easilv decomposed into 
 CoH 4 and I 2 . 
 
 The difference in the stability of ethene chloride, bromide, and iodide is shown 
 by the action of alcoholic solution of potash, which converts ethene dichloride 
 into monocJt lorethene, or nnyl clt lor'tde, C,H 4 C1. 2 + KOH = C 2 H 3 C1 + KC1 + H.,0 : whilst 
 the dibromide yields, in addition to the vinyl bromide," a /quantity of acetylene; 
 C 2 H 4 Br 2 + 2KOH = C 2 H 2 + 2KBr + H 2 ; and the di-iodide is much more easily de- 
 composed, giving very little vinyl iodide and much acetylene. 
 
 Metliylene iodide, CH 2 I 2 , may be obtained by heating iodoforin with strong HI 
 in a sealed tube, at about 130 C., for some hours ; CHI s -f HI = CH 2 I +I . It is 
 a liquid remarkable for its high specific gravity, 3.328, and is used for determin- 
 ing the specific gravities of precious stones. It boils at 181 C. 
 
 412. Chloroform, or tri-chloromethane, CHC1 3 , the anesthetic, is pre- 
 pared by distilling i part of alcohol (sp. gr. 0.834) with 10 parts of 
 chloride of lime and 40 parts of water, at 65 C., until about ij part 
 has passed over ; the distilled liquid, consisting chiefly of water and 
 chloroform, separates into two la)ers; the chloroform which is at the 
 bottom, is drawn off, shaken with strong sulphuric acid to remove 
 some impurities, and when it has risen to the surface it is separated 
 and puritied by distillation until it boils regularly at 61 C. (142 F.). 
 Chloroform is prepared from acetone in a similar manner. 
 
 The action of chloride of lime on alcohol has not been clearly explained ; it 
 might be expected that chloral would be formed at first by the" oxidising and 
 chlorinating actions, and that this would be converted into chloroform and 
 calcium formate by the strongly alkaline calcium hydroxide in the chloride of 
 lime (see Chloral), but much C0 2 is given oft', causing frothing during the distil- 
 lation. Probably the chloroform is produced by some such reaction as the 
 following : 3C,H 6 p + 8Ca(OCl) 2 = 2CHC1 3 + SH 2 + C0 2 + sCaCl a -f 3CaC0 3 . 
 Pure chloroform is more easily prepared by decomposing chloral hydrate with 
 potash or soda. 
 
 Chloroform is a very fragrant liquid of sp. gr. 1.50, and boiling-point 
 6i*5 C. It is very useful in the laboratory as a solvent, and is much 
 used for extracting strychnine and other alkaloids from aqueous solu- 
 tions. It is also one of the best solvents for caoutchouc. Chloroform 
 is very slightly soluble in water, and gives it a sweet* taste. Alcohol 
 dissolves it in all proportions, and it is nearly as soluble in ether. Strong 
 sulphuric acid does not affect it, and it is not coloured by pure chloroform. 
 Aqueous solution of potash does not decompose it, but the alcoholic 
 solution converts it into potassium chloride and potassium formate ; 
 CHC) 3 + 4 KOH = 3 KC1 + HCOOK + 2 HOH. If Dutch liquid (C,H 4 C1 2 ) 
 be present as an impurity in the chloroform, gaseous chlorethylene 
 (C,H 3 Ci) is evolved. When heated with alcoholic potash and aniline, it 
 yie'lds phenyl-carbamine (q.v.), the powerful odour of which renders 
 this a delicate test for chloroform. 
 
 Heated with alcoholic solution of ammonia in a sealed tube at 180 C.. chloroform 
 gives ammonium chloride and cyanide ; CHC1 3 + 5NH 3 = 3NH 4 C1 + NH 4 'CN. ^ When 
 potash is present a similar reaction occurs at the ordinary temperature, CHi.'l ; ,+ 
 NH 3 + 4 KOH = KCN + 3KC1 + 4H 2 0. Heated with potassium-amalgam, chloroform 
 evolves acetylene; 2CHC1 3 + 3K 2 =C 2 H 2 + 6KC1. That chloroform is really a 
 substitution-derivative from methane is shown by its conversion into that gas 
 when dissolved in alcohol and heated with zinc-dust ; by the formation of 
 tetrachloro-methane. CC1 4 , by the action of chlorine (in presence of iodine) upon 
 
636 IODOFOEM. 
 
 chloroform, and by that of dichloro-methane, CH 2 C1 2 , by the action of zinc and 
 sulphuric acid. 
 
 When chloroform is heated with sodium ethoxide, it is converted into ortho- 
 formic ether ; CHC1 3 + 3NaOC 2 H 5 = sNaCl + CH(OC 2 H 5 ) 3 . 
 
 lodoform, CHI 3 , or tri-iodo-m ethane, is a product of the action of 
 iodine upon alcohol in an alkaline solution, the immediate agent being 
 probably a hypo-iodite, whilst chloroform is produced by a hypo-chlorite. 
 To prepare it, dissolve 32 parts of potassium carbonate in 80 parts of 
 water, add 16 parts of alcohol of 95 per cent, and 32 parts of iodine ; 
 heat gently till the colour of the iodine has disappeared, when iodoform 
 will be deposited on cooling. 
 
 CH 3 -CH 2 OH + 6KOH + I 8 = CHI 3 + HCOOK + 5KI + H 2 0. 
 
 To recover the iodine left as KI, the nitrate from the iodoform is mixed 
 with 20 parts of HC1 and 2.5 parts of potassium dichromate, which 
 liberates the iodine. The liquid is neutralised with potassium carbonate, 
 and 32 parts more of that salt are added, together with 6 parts of 
 iodine and 16 of alcohol ; the operations of heating and cooling are 
 then repeated. 
 
 lodoform is deposited in yellow shining hexagonal plates, smelling of 
 saffron. It fuses at 120 0., and may be sublimed with slight decom- 
 position. It is insoluble in water, but dissolves in alcohol and ether. 
 When boiled with potash, it is partly volatilised with the steam, and 
 partly decomposed, yielding potassium iodide and formate. The pro- 
 duction of CHI 3 on adding iodine and dilute KOH and stirring, is a 
 very delicate test for alcohol, but many other substances also yield it. 
 lodoform is used in medicine and surgery. 
 
 &rotnaform, CHBr 3 , is produced when bromine is added to an alcoholic solution 
 of potash. It has a general resemblance to chloroform, but boils at 151 C. Crude 
 bromine sometimes contains bromoform. 
 
 ChJ/oriodoform, CHIC1 2 , is obtained by distilling iodoform with HgCL 2 . It is a 
 yellow liquid, b.-p. 131 C. The corresponding Br compound has been prepared. 
 
 Trichloi'opropane, exists in several forms. The commonest of these is glyceryl 
 trichloride or trichlorhydrin. CH 2 C1'CHC1'CH 2 C1 ; it is obtained by the action of 
 PC] 5 upon glycerine, C^H^OR^ + ^PC^C^G^ + ^Cl + ^POC^. It is a liquid 
 of pleasant smell, sp. gr. 1.42, and boiling at 158 C. It is sparingly soluble in 
 water. Tribromhydrin, C 3 H 5 Br 3 , is a crystalline solid ; m.-p. 17 C. ; b.-p. 220 C. 
 The iodine compound corresponding with this does not appear capable of existing. 
 
 413. All yl chloride, CH 2 : CH'CH 2 C1, is obtained by distilling allyl alcohol with 
 PC1 3 . It has a pungent smell, sp. gr. 0.95, and boiling-point 46 C. ; it is insoluble 
 in water. Allyl bromide may be prepared by distilling allyl alcohol with KBr and 
 H 2 S0 4 , mixed with an equal bulk of water. It is capable of combining with 
 bromine to form f/lycerijl or allyl tribromide, C 3 H 5 Br 3 , and with HBr to form 
 CH 2 BrCH 2 'CH 2 Br, trimetliylene bromide. Allyl iodide, C 3 H 5 I, is prepared from 
 glycerine (200 parts) by adding iodine (135), filling the retort with C0 2 and adding, 
 very gradually, vitreous phosphorus (40). The distilled liquid is washed with a 
 little NaOH, and dried with CaCl 2 . Probably, glyceryl tri-iodide is first produced ;. 
 C 3 H 5 (OH) 3 + P + I 3 = C 3 H 5 I 3 +P(OH) 3 ; the tri-iodide is then decomposed into 
 C 3 H 5 I and I 2 . Allyl iodide has a very pungent odour of leeks, sp. gr. 1.8, and 
 boiling-point 101 C. It is remarkable for combining with mercury, shaken with 
 its alcoholic solution, to form mercury allyl iodide, Hg"C 3 H 6 I, deposited in colour- 
 less crystals, which become yellow in light, and yield Hgi 2 and C ;5 H 5 I when treated 
 with iodine. Ag 2 0, in presence of H 2 0, substitutes OH for the I, producing. 
 HgC 3 H 5 - OH, mercury allyl hydroxide, an alkaline base. Bromine converts allyl 
 iodide into tribromhydrin. C 3 H g Br s . 
 
 The halogen propylenes e.g.. a-ckloropropylene, CH 3 *CH : CHC1, isomeric with 
 the allyl halides, exist in a maleinoid and a fumaroid modification (p. 616). 
 
CHLOEOBENZENE. 
 
 637 
 
 Propargyl chloride, CH i C-CH 2 C1, is obtained by acting on propargvl alcohol 
 with phosphorus chloride ; it boils at 65 C. 
 
 414. (B) Halogen derivatives of closed-chain hydrocarbons. 
 These may be halogen substitution or addition products. The substitu- 
 tion may be either in the benzene or other nucleus, or in side-chains, or 
 in both. Thus, while only i compound of the formula C 6 H 5 X exists, 
 there are 4 of the formula C 7 H 7 X, namely, C 6 H 4 X'CH 3 (3) andC 6 H.-CH x! 
 Again, 3 compounds of the form C 6 H 4 X 2 are known, and 10 of the form 
 C 7 H 6 X 2 , viz., C 6 H 3 X 2 -CH 3 (6), O fl H 4 X-OH f X( 3 ) and C 6 H 5 'CHX,. 
 
 The nucleal substitution-products are more stable than are the open- 
 chain hydrocarbon substitution-products. Thus, C 6 H 5 C1 will not yield 
 C G H.OH when treated with AgOH, whilst C 2 ELC1 yields C 2 H 5 OH by 
 this treatment. But the side-chain substitution-products "behave as 
 open-chain derivatives. 
 
 The direct action of halogens on benzene itself produces chiefly 
 substitution-products. In the case of its homologues, nucleal sub- 
 stitution occurs if the action be allowed to proceed in the cold, 
 especially in the dark and in presence of iodine ; whilst at higher 
 temperatures, and in sunlight, side-chain substitution occurs. Thus, 
 C 6 H 4 BrCH 3 is formed when Br attacks cold toluene, but Cg 
 if the temperature is higher. 
 
 The treatment of phenols (or alcohols) with phosphorus halides, and 
 a special reaction to be described under Diazo-compounds, also yield 
 these halogen derivatives. 
 
 C'Jdorolenzene or phenyl chloride, C 6 H 5 C1, may be prepared bypassing Cl into 
 C 6 H 6 , containing 3 per cent, of A1 2 C1 6 , until the calculated gain of weight is observed; 
 or by the action of PClg on phenol ; C 6 H 5 OH + PC1 5 = C 6 H 5 C1 + POC1 3 + HC1 ; it is 
 a colourless liquid, boiling at 132 C. Bromobenzene (b.-p. 155 C.) is similarly 
 prepared. lodohenzene (b.-p. 188 C.) may be obtained by heating benzene with 
 iodine and HI0 3 (to absorb HI ; p. 632) at 200 C. By dissolving it in CHC1 3 and 
 passing Cl through the solution the dichloride^ C 6 H 5 I : C1 2 is prepared ; this is of 
 theoretical importance, since the iodine in it is trivalent ; when it is treated with 
 XaOH it yields wdosobenzene, C 6 H 5 I : 0, which is a base forming salts such as 
 C 6 H 5 I : OCr0 3 ; when heated it becomes iodobenzene and iodo.fi/benzene, C 6 H 5 IO.,, 
 an explosive substance presumably containing pentavalent iodine. 
 
 o-smd-p-C/ilorotoluenes, C 6 H 4 C1'CH 3 , are obtained by passing Cl into cold toluene 
 containing iodine. 
 
 Ben; ijl chloride, C 6 H 5 -CH 2 C1 (b.-p. 176 C.), lenzal (ben;tjUdene) chloride, 
 C 6 H.5-CHC1 2 (b.-p. 213 C.), and benzotrichlorlde, C 6 H 5 'CC1 3 (b.-p. 213 C.), are 
 obtained by chlorinating boiling toluene, the Cl being passed into the liquid until 
 the increase of weight calculated for the particular compound required, has been 
 attained. They are colourless liquids * and can be prepared by the action of PC1 5 
 on the corresponding oxygen compounds viz., benzyl alcohol, benzoic aldehyde, 
 and benzoic acid into which they are converted by hydrolysis. They are inter- 
 mediate products in the manufacture of benzaldehyde from toluene (p. 584). 
 
 Two of each of the monohalogen tubstitwtion product* of naphthalene exist (p. 552). 
 0,-Chloro-naphthalene, C 10 H 7 C1, is a colourless liquid (b.-p. 263 C.) and is the product 
 of passing Cl into boiling naphthalene. fi-Cliloro-naphthaleue crystallises in lamina? 
 (m.-p. 61 C. ; b.-p. 257 C.), and is obtained by treating j8-naphthol. C 10 H 7 'OH, 
 with PC1 5 . Ten dichloro-naphthalenes are known. When naphthalene is chlori- 
 nated in the cold, the addition-product, naphthalene tetracJtloride, C 10 H 8 C1 4 , is 
 formed ; this crystallises in colourless rhombohedra, melts at 182 C., and becomes 
 C 10 H 6 C1 2 when boiled with KOH. Since it yields phthalic acid and not a chloro- 
 phthalic acid when oxidised, all the Cl atoms must be in the same benzene nucleus, 
 and the compound must have the orientation i : 2 : 3 : 4 (p. 55 2 )- 
 
 Anthracene dlchlorlde, C 6 H 4 : (CHC1) 2 : C 6 H 4 , is formed when chlorine is passed 
 
 * Benzyl chloride and benzyl bromide have a tear-exciting odour. 
 
638 CHLORAL. 
 
 over cold anthracene, whilst at a high temperature y-chloranthracenf (m.-p. 103 C.) 
 and y-dichlorantkracene (m.-p. 209 C.) are produced (p. 554) as yellow needles. 
 
 The halogen derivatives from other condensed benzene nuclei are of little 
 importance. 
 
 415. Halogen Compounds from Aldehydes and Acids. 
 Chloral or tri-chlor aldehyde, CC1 3 'CHO, prepared by passing thoroughly 
 dried chlorine into absolute alcohol, which must be placed in a vessel 
 surrounded by cold water at first, because the absorption of chlorine is 
 attended by great evolution of heat. The passage of chlorine is con- 
 tinued for many hours, and when the absorption is slow, the alcohol is 
 gradually heated to boiling, the chlorine being still passed in until the 
 liquid refuses to absorb it. The principal reaction is represented by the 
 equation, CH :{ -CH 2 'OH + 4 C1 2 = 5HC1 + CC1 3 'CHO ; but the HC1 attacks 
 part of the alcohol, forming ethyl chloride and water. On cooling, the 
 product solidifies to a crystalline mixture of the compounds of water 
 and alcohol with chloral, from which the latter may be obtained by 
 distillation with sulphuric acid. 
 
 On the large scale, chlorine is passed into alcohol of at least 96 per cent, for 12 
 or 14 days. The crude product is heated with an equal weight of strong H. 2 S0 4 , in 
 a copper vessel lined with lead. HC1 escapes at first, and the chloral distils over 
 at about 100 C. The distillate is rectified, and mixed with water in glass flasks, 
 when chloral hydrate, CC1 3 'CHO.H 2 0, is formed, which is poured into porcelain 
 basins, where it crystallises. 
 
 Chloral is a liquid of sp. gr. 1.5, and boiling-point 97 C. It has a 
 pungent, tear-exciting odour, and irritates the skin. Exposed to air, it 
 absorbs water and forms crystals of the hydrate, which is produced at 
 once when choral is stirred with a few drops of water, heat being 
 evolved. When quite pure it may be kept unchanged, but, in presence 
 of impurities, especially of sulphuric acid, it soon becomes an opaque 
 white mass of metachloral, which is insoluble in water, alcohol, and ether. 
 This is probably formed by the condensation of three molecules of 
 chloral, into which it is reconverted at 180 C. It will be remembered 
 that aldehyde is liable to a similar polymerisation. Chloral also re- 
 sembles aldehyde in forming crystalline compounds with NaHS0 3 , and in 
 giving a mirror of silver with silver ammonio-nitrate. With ammonia 
 it forms CC1 3 'CH(NH. ) )(OH), corresponding with aldehyde-ammonia. 
 Zinc and HC1 substitute H 3 for the C1 3 in chloral, converting it into 
 aldehyde. Nitric acid oxidises it to trichloracetic acid, CC1./ C0 2 H, which 
 forms deliquescent crystals and boils at 195 C. When heated with 
 KCN and H 2 it yields dichloracetic acid (b.-p. 191 C.), 
 
 CCL/CHO + KCN + H 2 = CHCL 2 'C0 2 H + KC1 + HCN. 
 Potash decomposes it easily; CC1 3 -CHO + KOH = CC1 3 H + H-CO-OK. 
 Chloral is formed when starch or sugar is distilled with HC1 and Mn0 2 . 
 
 Chloral hydrate, CC1 3 'CH(OH) 2 , trichlorethylideneglycol, forms pris- 
 matic crystals, which are very soluble in water and alcohol, and have 
 the odour of chloral. It fuses at 57 C., and boils at 97, but is 
 dissociated into chloral and steam, which recombine on cooling. It is 
 employed medicinally for procuring sleep. 
 
 Chloral alcoholate, CC1 3 -CH(OH)(OC 2 H 5 ), formed when choral is dissolved in 
 alcohol, crystallises like the hydrate, but is rather less soluble in water. 
 
 Brumal, obtained by action of Br on alcohol, is very similar to chloral. 
 
 Croton-chloral, or butyl chloral, CH 3 -CHC1-CC1 2 -CHO, is wp-trithl&robvtynt 
 aldehyde, and is prepared by substituting aldehyde for alcohol in the preparation 
 
ACETYL CHLORIDE. 
 
 of chloral, when croton-aldehyde is first produced, and is converted into butv! 
 chloral ; (i) 2CH,CHO = CH 8 -CH : CH'CHO + H 2 ; (2) CH 3 'CH : CH-CHO + 2CU 
 C S H 4 C1 3 'CHO + HC1. It is an oily liquid of pungent odour, sp. gr. 1.4, and boiliu"-- 
 point 164 C. It combines with water to form a hydrate which dissolves in hot 
 water, and crystallises, on cooling, in plates which have a very irritatino- odour 
 It has been used in medicine. 
 
 416. Halogen compounds from acids by substitution of 
 halogen for hydroxyl Acidyl halides. These bodies have th en- 
 counter-parts among inorganic compounds ; thus, nitrosyl chloride, NOC1, 
 is obtained by substituting 01 for OH in nitrous acid, NO'OH ; and,' 
 in acetic acid, CH 3 'CO'OH, a similar exchange gives acetyl chloride, 
 CK/CO'Cl. Thus they are haloidanhydrides (p. 191), or the halides of 
 negative radicles, just as the alkyl halides may be regarded as halides 
 of positive radicles and compared with KC1. 
 
 They are generally prepared by the action of phosphorus halides 
 on the acids. 
 
 No compound of this kind has been obtained from formic acid. 
 
 417. Acetyl chloride, CH 3 'CO'C1, or acetic chloride, is prepared by 
 distilling acetic acid with phosphorus trichloride ; 3CH 3 COOH + PC1 3 = 
 3CH 3 -COC1 + P 2 3 + 3HC1. To 5 parts by weight of glacial acetic 
 acid, kept cool, are gradually added 4 parts of phosphorus trichloride, 
 and the mixture distilled on a water -bath. The distillate may be 
 rectified over fused sodium acetate to remove any phosphorus tri- 
 chloride. The pentachloride may also be used, 
 
 CH 3 -COOH + PC1 5 = CH 3 -CO-C1 + POC1 3 + HC1. 
 
 Acetyl chloride is a colourless liquid, which fumes in air, and has 
 an irritating odour; its sp. gr. is i.n, and it boils at 55 C. Water 
 decomposes it with violence, yielding hydrochloric and acetic acids ; 
 CH 3 -CO-C1 + HOH = CH 3 -CO-OH + HC1. If alcohol be employed 
 instead of water, ethyl acetate is produced ; CH 3 ' CO 01 + C 2 H 5 - OH = 
 CH 3 - CO' OC 2 H 5 + HC1. This mode of reaction renders acetyl chloride 
 a most useful reagent for discovering the constitution of alcohols. 
 
 Some other instructive reactions produce acetyl chloride, such as that between 
 acetic anhydride (di-acetyl oxide) and phosphorus pentachloride (C 2 H 3 0). 2 + PC1 5 = 
 2C 2 HoOCl + POOL ; or between phosphorus oxychloride and sodium acetate 
 POCl 3 + 2CH 3 C06Na = 2CH 3 COCl + NaP0 3 + NaCl ; it was thus that acetyl chloride 
 was first made. By distilling sodium acetate with acetyl chloride, acetic anhy- 
 dride is obtained C. 2 H 3 0-ONa + C 2 H 3 0-Cl = (C 2 H 3 0) 2 + NaCl. By careful treat- 
 ment with sodium-amalgam and snow, ethyl alcohol has been prepared from 
 acetyl chloride ; aH 3 OCl + H 4 = C 2 H 5 OH + HCl. 
 
 Acetyl bromide, OHg-CO'Br, is prepared by distilling acetic acid with bromine 
 and phosphorus ; it resembles the chloride, but boils at 81 C., and becomes yellow 
 when kept. Acetyl iodide, CH S ! CO-I, is less stable, and is prepared by distilling 
 acetic anhydride with iodine ; it boils at 108 C. 
 
 Benzoyf chloride, or benzole chloride, C 6 H 5 -COC1, is prepared by distilling benzoie 
 acid with PCl g . It is a pungent smelling liquid, of sp. gr. i.ii, and boiling-point 
 199 C. It is decomposed by water, but more slowly than is acetyl chloride, 
 yielding benzoie, and hydrochloric acids. It may also be obtained by the action 
 of chlorine on bitter-almond oil (benzoie aldehyde); C 6 H 6 -CO-H + CI 2 
 C 5 H 5 -COC1 + HC1. 
 
 When hydroxy-acid* are distilled with PC1 5 , the alcoholic OH groups are also 
 exchanged for Cl. Thus lactic acid yields a-chhrujtropionic chlorxle (I art,// 
 chloride), CH,-CHC1-COC1. Salicylic acid yields I : 2-chloroben:oic chloride 
 (salicylic chloride). With water these chlorides yield HC1 and the corresponding 
 chloro-acid. 
 
 Sueelnyl dichloride, C 2 H 4 (COC1) 2 . is obtained by distilling succinic acid with 
 
'640 ESTEES. 
 
 PC1 5 ; C. 2 H 4 (CO'OH> 2 + 2PC1 5 = C. 2 H 4 (COC1). 2 + 2POC1,, + 2HC1. It is a fuming liquid, 
 of sp. gi\ i -39, boiling at 190 C. With water it yields HC1 and succinic acid, but 
 it is doubtful whether it is a true acid chloride, or resembles phthalyl chloride (r.v). 
 
 Fumaryl dichloride, C. 2 H 2 (CO'C1) 2 , is the product of the distillation of fumaric 
 acid, C 2 H 2 (COOH). 2 , and of its isomeride, maleic acid, with phosphoric chloride. 
 It boils at" 1 60 C. Malic acid also yields fumaryl dichloride when distilled with 
 PC1 5 ; C. 2 H S (OH)(CO-OH) 2 +3PC1 5 = C 2 H. 2 (CO-C1). 2 + 3POC1 3 + 4HC]. 
 
 Tartaric acid, C 2 H 2 (OH) 2 (COOH) 2 , heated with phosphoric chloride, is converted 
 into chloromaleic chloride. C 2 HC1(CO'C1) 2 , an oily liquid which yields crystals of 
 chloromaleic acid, C 2 HC1(CO'OH)2, when decomposed by water. 
 
 Phthalyl dichloride is obtained by distilling phthalic acid, C 6 H 4 (COOH) 2 , with 
 PC1 5 . It is a yellow, oily liquid, boiling at about 275 C. It is more stable than 
 most other compounds of this class, being slowly decomposed by water into HC1 
 ;and phthalic acid. Even solution of NaOH only slowly decomposes it. It appears 
 
 /CCU /COC1 
 
 to have the constitution C 6 H 4 <^ ^>0, not C 6 H 4 <^ ^ , since nascent H con- 
 
 verts it into pht/ialide, C 6 H 4 <^ 2 ^>0, a lactone from i : 2-hydroxymetliyllen:olc 
 
 CO 
 
 acid, CH. 2 OH-C 6 H 4 -COOH. 
 
 VII. ETHEREAL SALTS OR ESTERS. 
 
 418. These compounds, formed by the substitution of a hydrocarbon 
 radicle for the hydroxylic hydrogen in an acid, are numerous and 
 important. They correspond in composition with the salts formed from 
 .acids by substitution of metals for basic hydrogen. For example : 
 ,OK /OCH 3 
 
 Potassium sulphate, SOo^ ; methyl sulphate, S0 2 <^ 
 
 CH, 
 
 Potassium hydrogen sulphate, S0 ^ ; methyl hydrogen sulphate. SO.-/' 
 
 X OH "\)H 
 
 Potassium acetate, CH 3 'COOK ; methyl acetate, CH 3 'CqOCH 3 . 
 
 It will be seen that the ethereal salts of the organic acids consist of an acidyl 
 ;group and a hydrocarbon radicle united by an oxygen atom, thus resembling the 
 ethers ; hence the name esters, or compound ethers. 
 
 They may be formed (a) by heating an alcohol with an acid, 
 whereby water is eliminated : 
 
 (1) CH 3 -OH + N0 2 -OH ^ NO.vOCHg + HOH. 
 
 (2) CH 3 OH + S0 2 (OH), <_ S0 2 (OH)(OCH 3 
 
 (3) CH 3 OH + CH 3 COOH ^ CH 3 'COOCH 3 
 
 These reactions are reversible and consequently never complete. "With polybasic 
 acids the hydrogen salts are generally obtained. 
 
 (b) By heating a chloranhydride with an alcohol : 
 
 (4) CH 3 OH + CH 3 -COC1 = CH 3 -COOCH 3 + HC1 ; 
 
 (c) by heating a halogen derivative of a hydrocarbon with the silver 
 salt of an acid : 
 
 (5) 2CH 3 I + Ag 2 S0 4 = (CH 3 ) 2 S0 4 + 2AgI. 
 
 The ethereal salts exhibit a resemblance to the metallic salts in being 
 decomposed by the hydroxides of the alkali-metals, with formation of 
 the alcohol corresponding with the radicle of the ethereal salt, and of a 
 salt of the alkali-metal ; thus, ethyl acetate, heated with potash, 
 
ALKYL SULPHATES. 
 
 641 
 
 yields ethyl alcohol and potassium acetate; CH'COC.H +KOH = 
 C,H/OH + CH 3 -C0 2 K. A reaction of this kind is termed the sapvni- 
 fication of the ethereal salt, because the formation of soap is effected in 
 a similar way by the action of alkalies on the fats and oils, which are 
 ethereal salts formed by glycerine with the higher members of the acetic 
 series of acids. 
 
 Many of the ethereal salts are volatile liquids, having characteristic 
 fruity odours. 
 
 When treated with NH 3 they yield an alcohol and an acid amide 
 CH 3 -COOCH 3 + NH 3 = CH 3 CONH 2 + CH 3 OH. Heated with water or 
 dilute acids they are hydrolysed to the free acid and the alcohol- 
 CH 3 -COOCH 3 + HOH = CH 3 -COOH + CH 3 -OH. With strong halo-en 
 acids they yield the free acid and the halide of the hydrocarbon radicle 
 CH 3 -COOCH 3 + HC1 = CH 3 -COOH + CH 3 C1. 
 
 419. Sulphuric Esters. Methyl hydrogen sulphate or sulphom-ethylic acid, 
 CH 3 HS0 4 . Methyl alcohol (i weight) is slowly added to strong H 2 S0 4 (2 weights)' 
 and the mixture is heated to boiling, cooled, and neutralised with BaC0 3 , which 
 precipitates the excess of H 2 S0 4 as BaS0 4 , leaving barium mlphomethylate in solu- 
 tion ; this is evaporated on a steam-bath, and finally in vacua, when square tables 
 of Ba(CH 3 S0 4 ) 2 .2Aq. crystallise. By adding an, equivalent of H 2 S0 4 to a solution 
 of these, the barium is precipitated and the solution of sulphomethylic acid mav 
 be concentrated in vacua to a syrupy liquid. See equation 2 above. It is an 
 unstable compound, decomposed at 130 C. into H 2 S0 4 and methyl sulphate, 
 2CH 3 HS0 4 = (CH 3 ). 2 S0 4 + H 2 S0 4 , and by boiling with water, into CH,OH and H 2 S0 4 . 
 Heated with an alcohol, it gives the corresponding mixed ether, CH 3 HS0 4 + R'OH = 
 CH 3 -p-K + H 2 S0 4 . The basic hydrogen in CH 3 HS0 4 may be exchanged for a metal 
 forming sulphoHiethylates, which are all soluble in water. The acid is also formed 
 by gradually adding CH,OH to well-cooled chlorosulphonic acid (a chloranhydride, 
 cf. equation 4 above) : CH 3 OH + S0 2 (OH)C1 = HC1 + CH 3 HS0 4 . 
 
 Methyl sulphate, (CH 3 ) 2 S0 4 , is prepared by gradually adding CH 3 OH (i weight) 
 to strong H 2 S0 4 (8 weights) and distilling the mixture. The portion which distils 
 at 150 C. is shaken with water, and the lower layer rectified over CaCl 2 . Much of 
 the CH 3 group is, however, broken up in this process. A better result is obtained 
 by distilling sulphomethylic acid at 130 under diminished pressure. It is a liquid 
 of peculiar odour, sp. gr. 1.32, and boiling-point 188 C. It does not dissolve in 
 water, but is slowly decomposed, yielding methyl alcohol and sulphomethylic acid. 
 Many of its reactions resemble those of inorganic salts ; thus, if distilled with 
 NaCl, it yields methyl chloride, CH 3 C1, and Na^S0 4 . With sodium formate it 
 gives methyl formate and Na. 2 S0 4 . 
 
 Sulphethylic or ethyl-sulphuric or sulphovinic acid, HC 2 H 5 S0 4 , is prepared in the 
 same way as sulphomethylic acid, employing equal weights of alcohol and sulphuric 
 acid. It is a viscid liquid, very similar in its properties and reactions to sulpho- 
 methylic acid. The sidp/iet/iylates are soluble and easily crystallisable salts, 
 prepared by adding the metallic carbonate to a solution made by heating alcohol 
 with twice its weight of strong H 2 S0 4 , and, after cooling, diluting with water. 
 The solution is then crystallised. The calcium salt is Ca(C 2 H 5 S0 4 ) 2 .2Aq. 
 
 Sulphethylic acid is formed when ethylene is absorbed by H 2 S0 4 (p. 535). 
 
 Etliyl sulphate, (C 2 H 5 ) 2 S0 4 , is obtained by the reaction between ethyl iodide 
 and Ag 2 S0 4 in a sealed tube at 150 C. ; 2C 2 H 5 I + Ag 2 S0 4 = 2AgI + (C 2 H 5 ) 2 S0 4 . It 
 is a fragrant liquid, of sp. gr. 1.18, and boiling-point 208 C. It does not mix 
 with water, and is scarcely decomposed by it in the cold, but when heated with 
 it yields alcohol and Sulphethylic acid. Heated alone, it is decomposed into 
 ethene and sulphuric acid ; (C 2 H 5 ) 2 S0 4 = 2C 2 H 4 + H 2 S0 4 . 
 
 Ethyl sulphate may also be obtained by passing vapour of SO., into well-cooled 
 ether ; S0 3 + (C H 5 ) 2 = (C 2 H 5 ) 2 S0 4 . It is obtained as a secondary product in the 
 preparation of ether, forming the bulk of the liquid called heavy oil of //////. 
 
 Phenyl-mlphunc add is unknown ; patassium phenyhulphate, S0 2 'OC 6 H e 'OK, is 
 obtained by the prolonged action of KHS0 4 on phenol dissolved in potash ; 
 C 6 H 5 -OK + 2S0 2 OHOK^S0 2 -OC 6 H 5 'OK + S0 2 (OK) 2 + H 2 0. The product is ex- 
 tracted with hot alcohol, from which it crystallises in tables soluble in water. It 
 
 2 3 
 
642 SWEET SPIKIT OF NITRE. 
 
 is decomposed by exposure to moist air, or by boiling with water or dilute HC1, 
 yielding phenol and KHS0 4 ; S0 2 ;OC 6 H 5 'OK + HOH = HO-C 6 H 5 + S0. 2 -OH-OK. 
 
 420. Nitric Esters. The type is etJujl nitrate or nitric ether, prepared, on a 
 small scale only lest explosion occur, from C. 2 H 5 OH and HN0 3 , carefully purified 
 from HN0 2 . 80 grams of nitric acid of sp. gr. i'4 are heated on a steam-bath, 
 and about 2 grams of urea nitrate are added, the urea of which decomposes any 
 nitrous acid, 2HN0 2 + CO(NH 2 ) 2 = C0 2 + N 4 + 3H 2 0. After a time the mixture is 
 well cooled and 15 grams more urea nitrate are added, followed by 60 grams of 
 alcohol of sp. gr. 0.81. By fractional distillation dilute alcohol is first obtained, and 
 then a mixture of alcohol and nitric ether, from which the latter is separated by 
 adding water containing a very little KOH ; the lower layer is draAvn off, dried 
 with calcium chloride, and distilled, C ? H 5 OH + HN0 3 = C 2 H 5 -N0 3 + HOH. The 
 nitrous acid is destoyed because it rapidly oxidises the alcohol to aldehyde and 
 other products which react very violently with nitric acid. 
 
 Ethyl nitrate has a very pleasant smell, and sp. gr. i.i ; it boils at 86 C., and 
 its vapour explodes when heated, from the sudden disengagement of H 2 and 
 C0 2 . Water dissolves it very sparingly. Alcoholic solution of potash converts 
 it into KNOs and alcohol. 
 
 421. Nitrous Esters. Ethyl nitrite, C 2 H 5 N0. 2 , is the chief product of the 
 action of nitric acid upon alcohol, until it becomes very violent, the nitric radicle 
 N0 3 being reduced to the nitrous radicle N0 2 by the conversion of part of the 
 alcohol into aldehyde. To prepare pure ethyl nitrite, 100 c.c. of a solution con- 
 taining 46 grams of potassium nitrite are mixed with 50 c.c. of alcohol, and the 
 mixture allowed to run slowly into a cooled mixture of 50 c.c. of alcohol. 100 c.c. 
 of water, and 75 grams of sulphuric acid. The ethyl nitrite is distilled over by the 
 heat of reaction, and is condensed b} r ice. It is purified by shaking with a little 
 dry potassium carbonate. 
 
 Ethyl nitrite is much lighter and more volatile than the nitrate, its sp. gr. 
 being 0.95, and its boiling-point 16 C. It has a yellowish colour, and a pleasant 
 odour of apples. Like many other nitrous and nitric ethereal salts, it may be 
 preserved unchanged if perfectly pure, but if water or other impurities be present, 
 it decomposes, becoming acid, evolving red vapours, and bursting the bottle. 
 Alcoholic potash converts it into KN0 2 and alcohol. 
 
 The spiritus tct/teris nitrosi, or sweet spirit of nitre, used in medicine, is made by 
 carefully adding 2 measured ounces of sulphuric acid to a pint of rectified spirit, 
 slowly adding 2.\ measured ounces of nitric acid to the cooled mixture, pouring it 
 upon 2 ounces of fine copper wire in a retort with a good condenser, and distilling 
 between 77 C. and 80, until 12 measured ounces have distilled. Half an ounce 
 more nitric acid is then poured into the retort, and three more ounces distilled 
 over ; the distillate is then mixed with two pints of rectified spirit. Hence the 
 sweet spirit of nitre consists chiefly of spirit of wine, holding in solution ethyl 
 nitrite, aldehyde, and some other products of the reaction. The proportion of 
 ethyl nitrite present varies greatly, according to the efficiency of the condenser. 
 Less is found in old samples, in consequence of volatilisation and chemical 
 change. The presence of aldehyde is shown by the brown colour (aldehyde-resin) 
 which it gives when shaken with alcoholic potash. Neglecting secondary changes, 
 the formation of the ethyl nitrite in the above process may be represented by 
 C 2 H 5 -OH + HN0 3 + H 2 S0 4 + Cu = C 2 H 5 N0 2 + CuS0 4 + 2H 2 0. 
 
 It will be noticed that the alkyl nitrites are isomeric with the nitro-paraffins. 
 
 Amyl nitrite, C 5 H 11 N0 2 , may be prepared by distilling amyl alcohol with potas- 
 sium nitrite and sulphuric acid, or by passing N 2 3 into amyl alcohol ; it is a yellow 
 liquid of sp. gr. 0.9, and boiling-point 96 C. It has a remarkable smell, and the 
 peculiar effect of its vapour when inhaled has led to its employment in medicine. 
 The vapour of amyl nitrite explodes when heated. 
 
 422. Esters from polyfoasic acids are mainly of theoretical importance, 
 helping to settle the number of OH groups in the acid. They are generally 
 obtained by the action of organic acids on the chloranhydrides, such as POOL, 
 PC1 3 , AsCl 3 , BC1 3 , SiCl 4 , &c. Three ethyl phosphates, PO(C 2 H 5 ) 3 , PO(OH)(CoH 5 ). 2 
 and PO(OH). 2 (OC 2 H 5 ) and an ethyl metaphosj>/tate, P(OC. 2 H 5 ) 3 are known. So" also 
 ethyl arsenite As(OC. 2 H 5 ) 3 , b.-p. 166 C. ; ethyl borate or boric ether, B(OC. 2 H 5 ) 3 , 
 b.-p. 119 C., which burns with a green flame ; and several ethyl silicates or silicic 
 ethers, such as Si(OC 2 H 5 ) 4 , (b.-p. 165 C.), which burns with a bright flame emitting 
 clouds of Si0 2 , are known. Water decomposes them into alcohol and acid. 
 
 Particularly interesting is the formation of ethereal salts of acids which cannot 
 
ALKYL ACETATES. 643 
 
 exist in the free state. Thus ethyl carbonate, CO(OCoH 5 ) , b.-p. 126 C., is obtained 
 by heating silver carbonate with ethyl iodide in a sealed tube, although H.,CO., is 
 unknown. Potassium ethyl carbonate, potassium carbethylate or carbovi-nate 
 CO(OC. 2 H 5 )(OK), is precipitated in crystals when C0 2 is passed into a cooled solution 
 of KOH in absolute alcohol. 
 
 Again, ethyl orthocarbonate, C(OC. 2 H 5 ) 4 , b.-p. 159 C., formed on the type of 
 orthocarbonic acid C(OH) 4 (p. 261), is obtained when chloropicrin is treated with 
 sodium ethoxide in alcohol, CCl 3 N0. 2 + 4C 2 H g ONa = C(OC.,H 5 ) 4 + 3NaCl + NaN0. 2 . 
 
 Xanthic acid, CS(OC 2 H 5 )(SH), may be regarded as the acid ethyl salt of sulpho- 
 thiocarbonic acid, HO'CS'SH,* which is not known in the free state. Xanthic 
 acid is obtained as a potassium salt by saturating alcohol with KOH and stirrin- 
 with excess of CS. 2 ; C 2 H 5 -OH + CS. 2 + KOH = HOH + CS(OC 2 H 5 )(SK). This salt 
 forms colourless crystals with a faint odour, soluble in water "and alcohol, but not 
 in ether. When it is added to dilute HC1 cooled in ice, xanthic acid separates as a 
 heavy colourless oily liquid, which is decomposed at 24 C. into alcohol and CS. 2 . 
 The characteristic reaction of the xanthates is that with cupric sulphate, which 
 gives at first a dark -brown precipitate of cupric xanthate, rapidly decomposing into 
 a yellow oil xantliogen persulpkide, and bright yellow flakes of cuprous .ranthate, 
 the reaction being apparently 2(C 2 H 5 0'CS 2 ). 2 Cu = (C 2 H g O-CS 2 ) 2 Cu 2 + 2(C2H 5 0-CS2). 
 
 From this reaction the acid was named (%av6os, yellow). 
 
 423. Formic "Ester*. Methyl formate, HCOOCH. ? , is obtained by distilling 
 sodium formate with KCH 3 S0 4 ; HC0 2 Na + KCH 3 S0 4 = HC0 2 CH 3 + KNaS0 4 . It 
 is isomeric with acetic acid, CH 3 C0 2 H, but boils at 32 '5 C. The whole of its 
 hydrogen may be exchanged for chlorine, yielding C1C0 2 CC1 3 , chloromethyl formate, 
 which is decomposed by heat into 2COC1 2 , carbonyl chloride. 
 
 Ethyl formate, or formic ether, HC0 2 C 2 H 5 (b.-p. 55 C.) is prepared by distilling 
 sodium formate (7 weights) with H 2 S0 4 (10) and alcohol (6). The distillate is freed 
 from acid by shaking with a little lime, and redistilled. It is a fragrant liquid, 
 used for flavouring rum. It dissolves in nine times its weight of water. Formic 
 ether is also prepared by heating molecular proportions of alcohol and oxalic acid 
 with glycerine for some time in a flask with a reversed condenser, and distilling 
 (see p. 589). 
 
 424. Acetic Esters. Methyl acetate, CH 3 C0 2 CH 3 (b.-p. 57 C.), prepared by 
 distilling methyl alcohol with dried lead acetate and sulphuric acid, is a fragrant 
 liquid, lighter than water, with which it mixes freely. It is a constituent of crude 
 wood-spirit. 
 
 Ethyl acetate or acetic ether, CH 3 'COOC 2 H 5 . Mix 50 c.c. of absolute alcohol 
 with 50 c.c. of strong H 2 S0 4 and heat to 140 C. in a flask with a good condenser. 
 Kun in through a tap funnel a mixture of 400 c.c. of alcohol and 400 c.c. of glacial 
 acetic acid at the rate at which the ethyl acetate distils. Neutralise the distillate with 
 Na. 2 C0 3 , separate and shake the upper layer with equal weights of water and CaCl 2 to 
 extract alcohol. Separate, dry the upper layer with CaCl 2 , and distil. 
 
 Ethyl acetate boils at 77 C. and smells of cider ; its sp. gr. is 0.91 and it dis- 
 solves in ii times its weight of water, slowly decomposing into CH 3 COOH and 
 C 3 H 5 OH. It mixes readily with alcohol and ether, and is useful as a solvent and for 
 flavouring. Chlorine converts it into perchloracetic ether, CC1 3 -C0 2 'C 2 C1 5 , which 
 smells of chloral. 
 
 425. Ethyl aceto-acetate, CH 3 CO-CH 2 C0 2 C 2 H 5 (see aceto-acetic acid, p. 626), is 
 prepared by acting on ethyl acetate with sodium, treating the product with a dilute 
 acid, diluting with saturated brine and distilling the light oil which separates. It 
 boils at 181 C. The simplest equation is 
 
 2CH 3 -C0 2 C 2 H 5 + Na 2 = CH 3 COCHNaC0 2 C 2 H 5 + C 2 H 5 ONa + H 2 . 
 The sodium in the ethyl sodacetoacetate being then exchanged for H by the dilute 
 acid. But the change does not occur between pure ethyl acetate and Na ; some 
 alcohol must be present. It is supposed, therefore, that the first step is the direct 
 addition of sodium ethoxide, C. 2 H 5 ONa, to ethyl acetate producing the compound 
 CH 3 C(OC.,H 5 ) 2 (ONa). This is a derivative of the hypothetical ort/ioacetic acid, 
 CH'. S C(OH) ;! , and with another molecule of ethyl acetate yields the ethyl sodaceto- 
 acetate and alcohol which reacts with more sodium to repeat the cycle. 
 
 Ethyl acetoacetate is a colourless liquid, smelling of hay. It is sparingly sc le 
 
 * In two-acids, the S which is substituted for the carbonyl O is indicated by the prefix 
 mlpho-, or thion-, the prefix thio- being confined to the S that is substituted 
 hydroxyl O. 
 
6 4 4 
 
 ETHYL ACETO-ACETATE. 
 
 in water, but dissolves in alcohol, the solution giving a violet colour with Fe 2 Cl,;. 
 and a green crystalline precipitate, Cu(C 6 H 9 O 3 ). 2 , with a strong solution of copper- 
 acetate. It has an acid bias, for alkalies dissolve it and acids re-precipitate it from 
 the solutions ; but alkali carbonates will not dissolve it. 
 
 Ethyl acetoacetate is of great utility in synthetic chemistry, since through its- 
 means a variety of complex acids and ketones can be synthesised. This is rendered 
 possible by two facts : (i) When ethyl acetoacetate is heated with alkalies it 
 yields either a ketone (acetone) or an acid (acetic acid) according to the con- 
 centration of the alkaline solution. Thus, with dilute aqueous alcoholic potash the- 
 reaction is 
 
 C0 2 C 2 H 5 + 2KOH = CH 3 -CO'CH 3 + K 2 C0 3 + C 2 H 5 OH, 
 ited alcoholic potash the reaction is 
 
 CH 3 -CO'CH 2 
 whilst with concentrated 
 CH 3 -CO 
 
 The first type of decomposition is called hetonic decomposition, the second is acidic- 
 decomposition. (2) Only one of the two inethylene H atoms can be exchanged for 
 sodium, but when ethyl sodacetoacetate is treated with an alkyl iodide, the sodium 
 is exchanged for the alkyl group ; thus, ethyl ethylacetoacetate may be prepared,. 
 CH 3 -COCHNa-C0 2 C 2 H 5 + C 2 H 5 I = CH 3 -CO'CHC 2 H 5 -C0 2 C 2 H 5 + Nal. By treat- 
 ing' this with Na, ethyl xodethylacetoacetate, CH.5-CO-CNaC 2 H 5 -C0 2 C 2 H 5 , is formed,. 
 and with C 2 H 5 I this becomes ethyl diethylacetoacetate CH 3 -CO-C(C 2 H 5 ) 2 -C0 2 C 2 H g . 
 Other alkyl radicles may be substituted instead of ethyl. These substituted 
 acetoacetates may be represented by the general formula CH 3 'CO'CRR''C0 2 C 2 H 5r 
 and such a compound yields the substituted ketone CH./CO-CHRR' or the 
 substituted acid CHRR' - C0 2 H (together with acetic acid), accordingly as it is made 
 to undergo the ketonic or the acidic decomposition described above. 
 
 Ethyl acetoacetate combines with phenylhydrazine and hydroxylamine like a 
 ketone (p. 615), indicating a ketone group. By reduction it yields the secondary 
 alcoholic-acid, CH 3 'CHOH'CH 2 -C0 2 H (ft-hydro.fi/butt/ric acid). It is a fact, however r 
 that in many respects ethylacetoacetate behaves as though it were ethyl fi-hydroxy.- 
 isocrotonate, CH 3 'COH : CH'C0 2 C 2 H 5 . This is explained by supposing that it can 
 exist both in this form and in that given above, under the influence of different 
 reagents (Tautotnerism. See Cyanic Acid). 
 
 When ethyl acetoacetate is heated it yields dehydracetic acid, C 8 H 8 4 , (6-meth>jl 
 -^-acetopyronone). which forms sparingly soluble, fusible crystals, unchanged 
 by the strongest acids, but hydrolysed by alkalies, C 8 H 8 4 +3H = C0 2 + 
 CH 3 -CO'CH 3 (iicetone) + 2(CH 3 'C0 2 H). 
 
 Phenijl acetate, C 6 H 5 .C 2 H. } 2 maybe obtained by the reaction, C 6 H 5 -OH + C 2 H 3 0'C1 
 = C 6 H 5 'OC 2 H 3 + HCi, proving that phenol contains an OH group. It boils at 
 195 C. A piece of hard glass tube becomes invisible in phenyl acetate, its index 
 of refraction for light being the same as that of the liquid. 
 
 One of the amijl acetates, CH 3 'C0 2 C 5 H n , is sold as pear essence; and is prepared 
 by distilling fusel oil with acetic and sulphuric acids ; boils at 140 C. 
 
 426. Esters of Higher Fatty Acids. Ethyl, fyityrate, or butyric ether,. 
 C 3 H 7 -C0 2 C 2 H 5 , prepared by distilling butyric acid with C 2 H 5 OH and H 2 S0 4 is sold, 
 dissolved in alcohol, as ananas oil, or essence of pineapple, which it resembles in 
 odour. B.-p. 121 C. 
 
 Ethyl pelargonate, or pelaryonic ether, C 8 H ll7 'C0 2 C 2 H g , prepared from oil of rue,, 
 is used in flavouring as quince oil, and is present in the fruit. 
 
 Ethyl caprate, or capric ether, C 9 H 19 'C0 2 C 2 H 5 (b.-p. 187 C.), was formerly called 
 cenanthic ether, because it is found in old wine. It is made by distilling wine-lees,. 
 and, when pure, is a colourless, fragrant, oily liquid. It is sold for flavouring. 
 
 Amijl ralerate, C 4 H 9 'C0 2 C 5 H n , or apple oil, is obtained by distilling fusel oil 
 with sodium valerate and sulphuric acid ; its boiling-point is 188 C. 
 
 The ethyl salts of acids of the acetic series containing more than ten atoms of 
 carbon are generally prepared by dissolving the acids in alcohol and passing HC1 
 into the solution ; probably this converts the alcohol into C 2 H 5 C1. which acts upon 
 the acid to form the ethyl salt ; this is deposited in crystals from the alcoholic- 
 solution. Ethyl pa Imitate, and stearate are very fusible crystalline solids-, 
 
 427. Cetyl palmltate (m.-p. 49 C.) and ceri/l cerotate (m.-p. 81 C.) See p. 570.^ 
 Melissyl palmitate, or myricin, C l5 R sl 'C0 2 C. ]0 B. 6l . forms about one-third of been;- 
 
ETHEREAL SALTS. 645 
 
 was, the colour, odour, and tenacity of which appear to be due to the presence of 
 about 5 per cent, of a greasy substance called cerolein. 
 
 428. Aromatic Esters. Ethylbenzoate or ben:oicether, C 6 H 6 'C0 2 C 2 H B , is prepared 
 by dissolving benzoic acid in alcohol, saturating with HC1, distilling, and mixing 
 the distillate with water, when ethyl benzoate separates as a fragrant liquid of 
 sp. gr. 1.05, boiling at 213 C. Benzyl benzoate, C 6 H 5 'C0. 2 C 7 H 7 , is a crystalline 
 substance, contained in balsam of Peru ; m.-p. 20 C. ; b.-p. 323 C. Benzyl ci/um- 
 mate, C 8 H 7 -C0 2 C 7 H 7 , (evrm&m&iri), is present in the balsams of Peru and Tolu. 
 
 Methyl salicylate, C 6 H 4 OH'C0 2 CH 3 , occurs in oil of winter-green, extracted from 
 the flowers of Gaulthena procumbent, and was one of the first vegetable products 
 prepared artificially. It is obtained by distilling methyl alcohol with sulphuric 
 acid and salicylic acid. It is a fragrant liquid of sp. gr. 1.2, and boiling-point 
 224 C. Ferric chloride colours it violet. On treating it with strong solution of 
 soda, in the cold, it yields crystals of C 6 H 4 ONa-C0 2 CH 3 . When this is heated 
 with methyl iodide in a sealed tube, it gives C 6 H 4 OCH 3 -C0 2 CH 3 , or methyl methyl- 
 mallei/late, an oily liquid. If this be saponified by potash, it yields the 'potassium 
 salt of methyl salicylic acid, C 6 H 4 OCH 3 'C0 2 H, a crystalline acid isomeric with 
 methyl salicylate, but not giving the violet colour with ferric chloride. The 
 ethyl salicylate. resembles the methyl compound. 
 
 Phenyl salicylate, C 6 H 4 OH'C0 2 C 6 H g , is prepared by the action of POC1 3 on a 
 mixture of salicylic acid and phenol, 2C 6 H 4 OH'COOH + 2C 6 H 3 OH + POC1 3 = 
 2C 6 H 4 OH-C0 2 C 6 H 5 + HP0 3 + 3HC1 ; it crystallises in tables, melts at 43 C., and is 
 used as an anti-pyretic under the name of salol. 
 
 Cinnamijl cinnamate, or styracin, C 8 H 7 'C0 2 -C 9 H 9 , is a crystalline ethereal salt 
 obtained from storax by treatment with soda. 
 
 429. Esters from Dibasic Organic Acids. These may be acid or normal, 
 both being generally obtained by distilling the anhydrous acid with an alcohol and 
 fractionating the distillate. 
 
 Methyl otalate, (C0 2 ) 2 (CH 3 ) 2 , (b.-p. 163 C.), obtained by distilling CH 3 OH with 
 an equal weight of H 2 SO 4 and oxalic acid, solidifies in scales (m.-p. 51 C.) in the 
 receiver ; when distilled with water it is hydrolysed. 
 
 Ethyl oxalate, or o.ralic ether, (C0 2 'C 2 H 5 ) 2 , is prepared by boiling equal weights 
 of dried oxalic acid and absolute alcohol for six hours in a retort with a reversed 
 condenser, and then adding. water, which separates the oxalic ether as a fragrant 
 liquid of sp. gr. 1.09, boiling at 186 C. It is hydrolysed by boiling with water, 
 and saponified by potash. If mixed with one equivalent of potash, it yields pearly 
 scales of potassium oxalethylate ; (C0 2 -C 2 H 5 ) 2 + KOH = (C0 2 ) 2 KC 2 H 5 + C 2 H 5 'OH. 
 By decomposing this with hydrofluosilicic acid, oj-alethylic or twaloe'tnic acid, 
 (C0 2 ) 2 HC 2 H 5 , is obtained, but it is easily decomposed by water. 
 
 By the action of sodium on an ethereal solution of ethyl oxalate and acetate, 
 the sodium derivative of ethtjl o-i-alacetate is obtained ; this has the formula 
 C0 2 C 2 H 5 -CO-CH 2 -C0 2 C 2 H 5 , and', when heated with dilute H 2 S0 4 yields pyniric acid, 
 (p/62~6). 
 
 Ethyl malonate, or malonic ether, CH 2 (C0 2 -C 2 H 5 ) 2 , is prepared by passing HC1 gas 
 into absolute alcohol, containing calcium malonate in suspension 
 
 CH 2 (C0 2 ) 2 Ca + 2(C 2 H 5 OH) + 2HC1 = CH 2 (C0 2 'C 2 H 5 ) 2 + CaCl 2 + 2 HOH. 
 After some hours' standing, the liquid is boiled on a steam-bath, again saturated 
 with HC1 gas, the alcohol distilled off, the liquid neutralised with sodium carbonate, 
 and mixed with water, when the malonic ether separates as a bitter aromatic liquid 
 of sp. gr. 1. 068, and boiling-point 198 C. Its application for the preparation 
 of fatty acids has been already noted (p. 587). 
 
 The' ethereal salts of an alcohol radicle may be converted into those of another 
 alcohol radicle by mixing them with the alcohol in question, and adding a small 
 quantity of a metallic alkyl oxide, the action of which has not been fully explained. 
 Thus, methyl oxalate dissolved in ethyl alcohol, and mixed, in the cold, with a 
 small quantity of sodium ethoxide, C 2 H g 'ONa, becomes in great measure converted 
 into ethyl oxalate, and, conversely, ethyl oxalate is transformed into methyl 
 oxalate by dissolving it in methyl alcohol, and adding a minute quantity of 
 sodium in ethoxide. 
 
 430. Esters from Polyhydric Alcohols. Glijcol esters are very numerous, 
 because either one or both of the OH groups in aH 4 (OH). 2 may be exchanged, and 
 two different acid radicles may be introduced. None of them, however, as yet, 
 possesses any practical importance. 
 
 431. Glycerol Esters or Propenyl Salts. These compounds are even 
 
646 NITEOGLYCERINE. 
 
 numerous than those derived from glycol, since each of the three OH groups in 
 C 3 H g (OH) ;} may be exchanged for a different acid radicle. 
 
 The glyceryl chlorides are known as cMorhydrlns. a-Monochlorhydrin, 
 CH 2 C1-CHOH : CH 2 OH, and a.-dlchlorhydrin, CH 2 C1-CHOH-CH 2 C1, are prepared by 
 saturating glycerol with HC1, heating for several hours at 100 C., neutralising with 
 Na. 2 CO :3 , and extracting with ether. On fractionating the ethereal solution the 
 dichlorhydrin distils first (b.-p. 174 C.). They are liquids heavier than water, in 
 which the mono- is more soluble than the di-chlorhydrin. The /3-chlorhydrins, 
 CH 2 OH-CHC1-CH 2 OH and CH 2 OH-CHC1'CH 2 C1, are both obtained from allyl 
 alcohol, the former by action of"HC10, the latter by action of Cl. Tnchlorliydnn 
 is i : 2 : 3-trichloropropane (#./.). 
 
 EpiclilorJiydnn, CH 2 'CH-CH 2 C1 is obtained by treating a- or /3-dichlorhydrin 
 with alkali, which removes HC1. It is a mobile liquid smelling of chloroform and 
 insoluble in water ; sp. gr. 1.2, b.-p. H7C. It is sometimes used as a solvent. 
 
 Sulpliogly eerie acid, C 3 H 5 (OH) 2 S0 4 H. is formed with considerable evolution of 
 heat, when glycerol is dissolved in strong sulphuric acid. The acid may be 
 obtained as in the case of sulphethylic acid. It is only known in solution, being 
 easily decomposed even by evaporation in 'cacuo. 
 
 432. Nitroglycerine, or glyceryl trinitrate, C 3 H 5 (N0 3 ) 3 , is prepared 
 by the action of nitric acid on glycerine C 3 H 6 (OH) 3 + 3(HN0 3 ) = 
 C 3 H 5 (N0 3 ) 3 + 3H 2 0. It is a heavy oily liquid, of sp. gr. 1*6, without 
 smell, very explosive, and poisonous. It is insoluble in water, sparingly 
 soluble in alcohol, but soluble in ether and in methyl alcohol. When 
 saponified by potash, it yields glycerol and potassium nitrate. 
 
 On a large scale a mixture of concentrated HNOo with twice its volume of strong 
 H 2 S0 4 is placed in a tank lined with lead and cooled by water circulating in leaden 
 coils. Glycerine is sprayed into the acid, care being taken that the temperature 
 does not rise above 30 C. The mixture is allowed to settle, when much of the 
 nitroglycerine floats to the top and is run into water and washed. The lower layer 
 is then run into water to separate the dissolved nitroglycerine, which sinks to 
 the bottom. A little alkali is added to the last washing water to remove any trace 
 of free acid remaining. 
 
 This oil is very violent in its explosive effects. If a drop of nitroglycerine be 
 placed on an anvil and struck sharply, it explodes with a very loud report, even 
 though not free from water, and if a piece of paper moistened with a drop of it 
 be struck, it is blown into small fragments. On the application of a flame or of 
 a red-hot iron to nitroglycerine, it burns quietly ; and when heated over a lamp 
 in the open air it explodes but feebly. In a closed vessel, however, it explodes 
 at about 360 F. (182 C.) with great violence. For blasting rocks, the nitro- 
 glycerine is poured into a hole in the rock, tamped by filling the hole with water, 
 and exploded by the concussion caused by a detonating fuze (see below), the effect 
 in blasting being about five times that of an equal weight of gunpowder, and 
 much damage has occurred from the accidental explosion of nitroglycerine in 
 course of transport. When nitroglycerine is kept, especially if it be not 
 thoroughly washed, it decomposes, with evolution of nitrous fumes and forma- 
 tion of crystals of oxalic acid ; and it may be readily imagined that, should 
 the accumulation of gaseous products of decomposition burst one of the bottles in 
 a case of nitroglycerine, the concussion would explode the whole quantity. 
 
 Nitroglycerine, like gun-cotton, is particularly well fitted for blasting, because 
 it will explode with equal violence whether moisture be present or not, but it has 
 the advantage of containing enough oxygen to convert all its carbon into carbonic 
 acid gas. On the other hand, it is very poisonous, and is said to affect the system 
 seriously by absorption through the skin, and the gases resulting from its explosion 
 are exceedingly acrid. Again, its fluidity prevents its use in any but downward 
 bore-holes. To overcome these objections, and to diminish the danger of trans- 
 port. several blasting compounds have been proposed, of which nitroglycerine is 
 the basis. 
 
 Dynamite is composed of a particularly porous siliceous earth (Kieselguhr), 
 obtained from Oberlohe in Hanover, impregnated with about 70 or 75 per cent, of 
 nitroglycerine. Kieselguhr contains 63 per cent, of soluble silica, about 18 of 
 organic matter, 1 1 of sand and clay, and 8 of water. It is incinerated to expel the 
 
GLYCERYL SALTS. 647 
 
 organic matter, and mixed with the nitroglycerine in wooden troughs lined with lead 
 When used in solid rock, dynamite is six or seven times as strong as blaatin*- 
 powder. 
 
 JoM'x detonators for nitroglycerine contain 7 parts of mercuric fulminate and 
 3 parts of potassium chlorate, pressed into small copper tubes. 
 
 masting gelatine is made by dissolving collodion-cotton in about nine times its 
 weight of nitroglycerine ; its detonation is even more powerful than that of nitro- 
 glycerine itself. Gelatine-dynamite consists of 65 per cent, of thinly gelatinised 
 nitroglycerine, 8.4 per cent, of woodmeal, 26.25 potassium nitrate, and 0.35 per cent. 
 of soda. It is slow in detonation and is an excellent blasting-agent, 
 
 Cordite is made by Incorporating 58 parts of nitroglycerine with 37 parts of 
 gun-cotton , and 19.2 parts of acetone ; 5 parts of vaseline are added and after 
 this has been mixed the compound is forced through dies, so that it assumes the 
 form of cords, from which the acetone is allowed to evaporate. 
 
 Nitroglycerine is readily soluble in ether and in wood-naphtha, but somewhat 
 less so in alcohol ; it is re-precipitated by water from these last solutions. It 
 becomes solid at 40 F. (4.5 C.), a circumstance which is unfavourable to its use 
 in mining operations, partly because it is then less susceptible of explosion by 
 the detonating fuse, and partly because serious accidents have resulted from 
 attempts to thaw the frozen nitroglycerine by heat, or to break it up with tools. 
 It is remarkable that, when made on the small scale, the nitroglycerine may gene- 
 rally be cooled down to oF. (- 1 8 C.) without becoming hard. This and other 
 observations render it probable that some other substitution-product is occasionally 
 mixed with it. 
 
 Berthelot finds that, in the formation of nitric ether by the action of nitric acid 
 upon alcohol, 5800 heat units are disengaged for each molecule of nitric acid 
 entering into the reaction, whereas, in the formation of nitroglycerine, only 4300 
 heat units per molecule of nitric acid are disengaged. Less energy having been 
 converted into heat in the latter case, more is stored up in the nitroglycerine, 
 and hence its formidable effect as an explosive. In the formation of gun-cotton, 
 each molecule of nitric acid disengaged 11,000 heat units, to which Berthelot attri- 
 butes the stability and inferior explosive effect of gun-cotton in comparison with 
 nitroglycerine. 
 
 Nitroglycerine is reconverted into glycerine by alkali sulphides with rise of tem- 
 perature and separation of sulphur ; C 3 J^(N0 3 ) 3 + 3KHS = C 3 H 5 (OH) 3 + 3KN0 2 + S 3 . 
 Compare Gun-cotton. 
 
 Gl I) eeryl- phosphoric or pJutsplwytyeerie acid, C 3 H 5 (OH) 2 P0 2 (OH). 2 , is formed by 
 the action of metaphosphoric acid on glycerol, but has only been obtained in 
 solution. It is a product of decomposition of lecithin (/.*'.). 
 
 Glijcenjl arxenite, C 3 H 5 'As0 3 , is obtained by dissolving white arsenic in 
 glycerol, and evaporating; 4C 3 H 5 (OH) 3 + As 4 6 = 4C 3 H 5 As0 3 + 6HOH. It forms a 
 
 yellowish glass, fusing at 50 C. It is sometimes used for fixing aniline dyes. 
 
 Glycenjl lorate, or lorof/lyceride, C 3 H 5 B0 3 , is prepared from boric acid and 
 glycerol ; it is also a transparent glass, dissolving slowly in water, and has been 
 recommended for the preservation of food. 
 
 433- By- far the most important ethereal salts are the fats and oils 
 which are mixtures of glyceryl salts of the fatty acids, also called 
 glycerides. Like other esters the oils arid fats are easily hydrolysed 
 into the alcohol (glycerol) and the acid. When an alkali is the hydro- 
 lytic agent the alkali salt of the fatty ucid, a soap, is obtained. Thus 
 when tallow is saponified it yields a soap composed chiefly of alkali 
 stearate and oleate, from the stearin (glyceride of stearic acid) and olein 
 (glycericle of oleic acid) of which it is mainly composed : 
 
 (C 17 H, 5 COO) 3 C 3 H 5 + 3 NaOH = 3 C 17 H 35 COOXa + C 3 H.,(OH) 3 
 (C'X;COO) 3 aH - + S^aOH = sC^COONa + C 3 H 5 (OH) 3 
 Palmitin, the glyceride of palmitic acid, the chief constituent of palm- 
 oil, is the other principal glyceride. 
 
 Xonofonnin, C,H g (OH) 'C0 2 H, and difi>raun, C 3 H 5 (OH)(C0 2 H) 2 , are produced 
 when oxalic acid is heated with glycerol, in making formic acid- 
 
 C 3 H 5 (OH) 3 + (C0 2 H) 2 - C 3 H 6 (OH) 2 -C0. 2 H + C0 2 + H 2 0. 
 
648 SULPHONIC ACIDS. 
 
 Tri-acetin, C 3 H 5 (C 2 H 3 2 ) 3 , is present in cod-liver oil, and may be obtained by 
 acting on glycerol with acetic acid. Tributyrin, C 3 H 5 (C 4 H 7 2 ) 3 , occurs in butter. 
 
 Tripalmitin or palmitin, C 3 H 5 (C 16 H 31 2 ) 3 , is obtained from palm-oil or from 
 Chinese wax, by pressing and crystallising from alcohol. It fuses at 46 C. 
 
 Tristearin or stearin, C 3 H 5 (C 18 H 35 2 ) 3 , prepared by repeatedly recrystallising the 
 harder natural fats, such as tallow, from their solution in ether, fuses at 63 C. 
 
 Tri-olein or olein, C 3 H 5 (C 1 8H 33 0.2) 3 , is obtained by cooling olive-oil to o C.. press- 
 ing out the liquid part, dissolving this in a little alcohol, again freezing, to 
 separate the rest of the stearin, and distilling off' the alcohol. Olein is less easily 
 decomposed by alkalies than are palmitin and stearin, and is left unaltered when 
 olive-oil is treated with a cold concentrated solution of NaOH, which converts 
 the palmitin and stearin into soaps and glycerol. 
 
 The three glycerides, palmitin, stearin, and olein, are found in most animal 
 and vegetable fats. Olive-oil and Chinese wax consist almost entirely of palmitin 
 and olein. Palm-oil contains all three. Mutton suet is chiefly stearin, with a 
 little palmitin and olein. Beef suet contains more palmitin ; these constitute 
 tallow. Lard has a similar composition. Human fat contains more palmitin. 
 Goose fat and butter contain, besides the above glycerides, those of volatile acids, 
 such as butyric, capric, caprylic, and caproic. Coco-nut oil contains trilaui-in, 
 
 ,OC,H 5 
 
 Palmitin, stearin, and olein, may be made artificially by heating glycerol with 
 the corresponding acids ; for example 
 
 C 3 H 5 (OH) 3 + 3 HC 18 H 35 0. 2 = CaH^CjgHaBOak + 3HOH. 
 
 SULPHONIC ACIDS. 
 
 434. The ethereal salts of sulphurous acid are metameric with the 
 compounds known as the sulphonic acids ; thus, both ethyl hydrogen 
 sulphite and ethyl sulphonic acid, have the empirical formula 2 H 6 S0 3 . 
 The sulphonic acids, however, differ from the sulphites in that when 
 treated with reducing-agents they yield the corresponding thio-alcohols; 
 thus, ethyl sulphonic acid, C 2 H 5 S0 3 H, yields mercaptan (ethyl thio- 
 alcohol) C 2 H 5 SH. This reaction indicates that the sulphur in ethyl 
 sulphonic acid is combined directly with the carbon of the ethyl group, 
 for there can be no doubt that the S in mercaptan is so combined. 
 The constitution of ethyl sulphonic acid, is therefore probably 
 
 /C 2 H 5 A 
 
 OJSx , whilst that of ethyl hydrogen sulphite is OS< 
 
 X)H \OH 
 
 When a strong solution of sodium sulphite is heated with ethyl iodide at 140 C., 
 sodium ethyl sulphonate and sodium iodide are produced; Na2S0 3 + C 2 H 5 I = 
 C 2 H 5 -S0 2 ONa + NaI. If sodium sulphite were a salt of SO(OH) 2 , viz., SO(ONa) 2 , 
 this reaction would be expected to produce ethyl sodium sulphite SO(ONa)(OC 2 H 5 )f* 
 Since this is not the case, Na-jSOg must have the constitution S0 2 (ONa)Na ; this 
 constitutes the evidence referred to on p. 222. 
 
 The sulphonic acids bear the same relationship to sulphuric acid, as the 
 carboxylic acids bear to carbonic acid, that is, they contain an alcohol 
 radicle or a hydrocarbon radicle in place of one of the OH groups. They 
 are monobasic acids since they still retain one OH group. By partial 
 reduction they generally yield sulphinlc acids, which bear the same 
 relationship to the SO(OH) 2 form of sulphurous acid as the sulphonic 
 acids bear to sulphuric acid. 
 
 The sulphonic acids are also produced by oxidation of the mercaptans. 
 
 * Ethyl sulphite, SO(OC 2 H 5 ) 2 , is prepared by the action of SOC1 2 on alcohol. When heated 
 with one equivalent of NaOH it yields ethyl sodium sulphite; when this is treated with an 
 acid with a view to removing' the Na, it is decomposed, so that ethyl hydrogen sulphite has 
 not been prepared. 
 
NITRO-COMPOUNDS. ^49 
 
 Ethyl sidphinic acid C 2 H 5 ;SOOH, is obtained as a zinc salt bv the action of 
 b0 2 on a cooled ethereal solution of zinc ethide ; ZnfC H ^ + 2 SO -ir H -?n \ ?? 
 
 r h R self is s-r? py li( r d - li mi ht S^S^WftS^ 
 
 Srboxyl m tetrav alent sulphur is substituted for the carbon o f the 
 
 Ethyl-mlphonic acid C 2 H 5 'S0 2 -OH, is produced when ethyl-sulphinic acid mer- 
 captan, ethyl polysulphides, and ethyl sulphocyanate are oxidised by nitric add 
 also from C 2 H 5 I and Na 2 S0 3 , as stated above. Ethyl-sulphonic acid isan oily l^uTd 
 of sp gr. 1.3 and may be crystallised by cooling. It forms very soluble salts 
 which are not easily decomposed by heat. By oxidation with HNO, it vields 
 ethyl hydrogen sulphate. 
 
 Ethionic acid baa already been noticed (p. 535). It is a mixed ethereal salt and 
 sulphonic acid from glycol, CH 2 (OS0 3 H)'CH 2 (S0 3 H). By hydrolysis the ethereal 
 8 H2S ad i** 1 " * 1 * acid ^r^- 
 
 mm p m lphonic add, 
 
 2 (OH)-CH 2 (S0 3 H). being produced. 
 
 It is characteristic of closed-chain compounds (at all events such as 
 contain a benzene nucleus) that they readily yield sulphonic acids when 
 heated with strong sulphuric acid (p. 549). These are very useful for 
 preparing other compounds, e.g., phenols (q.v.), and, on account of their 
 solubility, for use as dye-stuffs. They yield chloranhydrides (p 101} 
 when treated with PC1 5 . 
 
 When benzene is warmed with H 2 S0 4 cone., benzene sulphonic acid, C 6 H 5 -S0 2 OH 
 is produced ; if fuming acid be employed the three (chiefly 1:3) benzene di- 
 sulphonic acids, C 6 H 4 (S0 2 OH) 2 , are produced. Naphthalene may be similarly 
 sulphonated to produce isorneric naphthalene mono- and di-mlphomc acids. 
 Sulphonic acids of most benzene hydrocarbon derivatives are easily obtainable ; 
 some of these will receive passing mention later. 
 
 NITRO-COMPOUNDS. 
 
 435. The ethereal salts of nitrous acid are metameric with the 
 nitre-substituted hydrocarbons ; thus, ethyl nitrite, C.,H 5 ON : 0, is 
 metameric with nitro-ethane, C 2 H 5 'NO,. The difference In constitution 
 represented by these two formula is "justified as follows: (i) When 
 an ethereal nitrite is treated with an alkali, it is readily converted 
 into an alcohol and an alkali nitrite : this shows that the compound 
 is a true ethereal salt of nitrous acid, the formula for which, as already 
 shown (p. 101), is probably HON : O. (2) When a nitro-hydrocarbon 
 is treated with a reducing-agent, it yields an amine (e.g., C 2 H.'NH,), a 
 compound which, since it contains only C, H, and N, must coutain the 
 N attached directly to carbon. On the other hand, when an ethereal 
 nitrite is treated with a reducing-agent it yields the corresponding 
 alcohol and ammonia ; since the alcohols contain O attached directly to 
 carbon, the ethereal nitrite probably also contains attached directly 
 to carbon, in which case the N is probably not attached directly to 
 carbon, a conclusion confirmed by the ease with which the C and N are 
 parted in these compounds by sapooification. The nitro-com pounds 
 may be regarded as derived from nitric acid in the same way that the 
 sulphonic acids are derived from sulphuric acid. 
 
 The nitre-paraffins are produced by the inter-action of silver nitrite 
 and alkyl iodides, e.g., C 2 HJ + AgNO 2 = C 2 H 3 'N0 2 + Agl.* The nilro- 
 
 * This reaction would seem to show that silver nitrite is derived from a form of nitrous 
 acid in which H was attached directly to X, thus, H NO 2 . It may be that nitrites txist in 
 two forms, as has been argued for sulphites (p. 648). It is necessary to add, however, that 
 in most cases much ethereal nitrite is produced, tog-ether with the nitro-paramn, by this 
 method. 
 
650 
 
 NITROBENZENE. 
 
 hydrocarbons of the benzene series, however, result from the direct 
 action of nitric acid on the hydrocarbons (p. 549). 
 
 When the hydrocarbon has a side-chain, strong nitric acid yields a nucleal nit.ro- 
 compound, but dilute acid introduces the nitro-group into the side-chain. While 
 it is easy to introduce one or two nitro-groups into an aromatic nucleus, the 
 direct introduction of the third is difficult, and more than three have not been 
 introduced. 
 
 The nitro-paraffins can be primary, secondary, or tertiary like all other open- 
 chain hydrocarbon substitution-products. The three forms have the same 
 structure as the three forms of alcohols, N0 2 being substituted for OH (p. 567). 
 The distinctive behaviour of the three kinds with nitrous acid has been given at 
 p. 569. The primary and secondary nitro-paraffins contain hydrogen attached to 
 the same carbon atom as that to which the N0 2 is attached ; the close proximity 
 of the N0 2 to the H imparts an acid character to the latter, so that this may 
 be exchanged for metals, such compounds as CHg'CHNa'NOo and (CH 3 ) 2 : CNa'N0 2 
 being produced by the action of alcoholic soda on the nitro-paramn ; compare the 
 influence of two COOH group on a CH 2 group (p. 587). The nitro-aromatic com- 
 pounds having the nitro-group or groups in the nucleus are of a tertiary character, 
 but when the group or groups are in the side-chain all three kinds may exist.* 
 
 Nitre-methane boils at 101 C. ; hydrolysis (by strong HC1 at 150 C.) converts 
 it into formic acid and hydroxylamine. Nitro-ethane boils at 113 C. ; it gives a 
 blood-red colour with ferric chloride, and burns with a luminous flame. Both are 
 heavier than water. 
 
 Trichloronitromethane or chloropicrin or n'dro-chloroform, CC1 3 N0 2 , is a pro- 
 duct of the joint action of nitric acid and chlorine on many hydrocarbon 
 derivatives. It is best obtained by heating picric acid (</.<'.) with chloride of 
 lime, when it distils over as a heavy liquid (sp. gr. 1.69), boiling at 112 C. and 
 possessed of a tear-exciting odour. Nascent H reduces it to -methylaniine, HC1 
 and H 2 0. 
 
 Nitrobenzene, C 6 H 5 'N0 2 , has already been noticed (p. 540). It is prepared on 
 the large scale by slowly running a mixture of 1280 Ibs. of strong HN0 3 and 
 1790 Ibs. of strong H 2 S0 4 into 1000 Ibs. of benzene contained in a cast-iron 
 cylinder well cooled by water, and provided with an agitator ; after some 8 or 
 10 hours the process is complete and the product is washed with water. If the 
 temperature be allowed to rise above 50 C. during the preparation of nitro- 
 benzene, the three dinitrobenzenes are produced. Since they may be regarded 
 as being formed from the further nitration of nitrobenzene, it is only in accord- 
 ance with the general rule (p. 547) that I : 3-dinitrobenzene is the chief product ; 
 this crystallises in pale yellow needles and melts at 90 C. The i : 2- and i ; 4- 
 dinitrobenzenes are colourless and melt at 116 and 172 C. respectively. The 
 three can be separated by fractional crystallisation from alcohol. They yield 
 the corresponding nitranitines, C 6 H 4 (NH 2 )(N0 2 ), and dianudobenze.net or yhemjl- 
 enediamlnes, C 6 H 4 (NH 2 ) 2 when reduced." The" i : 2-derivative differs from the 
 others in the comparative ease with which one nitro-group can be exchanged for 
 other radicles (<?.</., for OH, forming i : 2-nitrophenol, C 6 H 4 (OH)(N0 2 ), when heated 
 with hot alkalies). 
 
 By nitrating toluene, i : 2- and i : ^-mtrotoluene, C 6 H 4 (CH 3 )(N0 2 ), are mainly pro- 
 duced ; the former is a liquid boiling at 223 C., the latter a solid melting at 54 C. 
 and boiling at 237 C. i : $-Xitrotoluene has m.-p. 16 C., and b.-p. 230 C. 
 
 Trlnitrotertlarybutyltoluene, (N0 2 ) 3 C 6 H(CH 3 )C(CH 3 ) 3 [(N0 2 ) 3 : CH 3 : C(CH 3 ) 3 =: 
 2 : 4 : 6 : I : 3], is obtained by nitrating various butyltoluene derivatives, and is sold 
 as artificial -tnuslt,. 
 
 tk-Nitronaphthalene^ C 10 H 7 N0 2 , is produced by boiling naphthalene in glacial 
 acetic acid with strong nitric acid ; it crystallises in yellow prisms, melts at 61 C. 
 and boils at 304 C. It is used for making dyes and for destroying the fluorescence 
 of paraffin oils when these are used to adulterate vegetable oils. It is soluble in 
 alcohol but not in water. 
 
 * The salts of the primary and secondary nitre-compounds appear to be derived from a 
 tautomeric form, the isonitro-compound, e.g., CHyCHrNC^H ; for when treated with acids 
 they yield a free iiitro-compouiid which at first shows reactions differing from those of the 
 original nitre-compound, such as a colouration with Fe 2 Cl 6 ; afterwards it resumes the usual 
 properties. 
 
ZINC ETHYL. 651 
 
 Other nitre-derivatives will be considered under the classes of bodies from which 
 they are derived. 
 
 VIII. ORGANO-MINEKAL COMPOUNDS. 
 
 436. The importance of these compounds resides mainly in the light 
 they throw upon the theory of valency and in the fact that many of 
 them are volatile without decomposition, thus yielding evidence of the 
 atomic weight of their elements (p. 318). They maybe regarded as 
 formed on the type of the chlorides of the mineral elements by the sub- 
 stitution of hydrocarbon radicles for the chlorine. Those containing 
 alkyl groups (alkides) have been best studied, and it has been found 
 that in the case of the compounds from the more electro-negative ele- 
 ments the subtraction of one or more alkyl groups from the saturated 
 compound yield monovalent or polyvalent radicles. For example, tin 
 methide, Sn(CH 3 ) 4 , is a saturated alkyl derivative of Sn iv ; by treatment 
 with iodine, one CH 3 is removed and Sn(CH 3 ) 3 I is produced. This is 
 the iodide of a monovalent radicle, Sn(CH 3 ) 3 , which behaves like an 
 alkali metal, forming a powerful base, Sn(CH 3 ) 3 OH, obtained by treating 
 the iodide with NaOH. Like other monovalent radicles, such as CH 3 , 
 Sn(CH 3 ) 3 cannot exist alone, but is known in its double form, Sn 2 (CH 3 ) 6 , 
 like C 9 H 6 . When two alkyl groups are removed, the divalent radicle, 
 Sn(CH 3 ) 2 , is produced ; this resembles a divalent metal and forms a 
 base Sn^CEy.jO ; like CH 2 it exists alone only in the form Sn 2 (CH 3 ) 4 . 
 
 The most important method of producing these compounds is by 
 the action of metals on the monohalogen substituted hydrocarbons. 
 The typical case is that of zinc ethide, which will be considered first. 
 
 Zinc alkides. Zinc ethyl or zinc ethide, Zn(C 2 H 5 ) 2 , is prepared in 
 accordance with the equation Zn., + 2C 2 H.I = Zn(C 2 H 5 ) 2 + ZnI 2 . 
 
 
 Fig. 278. Preparation of zinc ethyl. 
 
 Fifty grams of bright, freshly granulated and well-dried zinc are placed in a 
 flask E (Fig. 278) connected with a C0 2 apparatus A, the gas from which is 
 by strong H S0 4 in bottles B and C. The flask is also connected th the tube , 
 of condenser F, the other end of which is sealed by mercury in D. The appai 
 having been filled with C0 2 , the cork of the flask is removed, and 25 gia 
 
652 PREPARATION OF ZINC ETHYL. 
 
 ethyl iodide (perfectly free from moisture) are introduced, the cork being then 
 replaced.* C0 2 is again passed for a short time, and then cut off by closing the 
 nipper-tap (T), when the gas escapes through the mercury seal (G-). A gentle heat 
 is then applied by a water-bath to the flask (E) till the ethyl iodide boils briskly, 
 the vapour being condensed in the tube (/), and running back into the flask. In 
 about five hours the conversion is complete, and the iodide ceases to distil. The 
 nipper-tap (T) is again opened, and a slow current of C0 2 is passed, the position of 
 the condenser (F) is reversed (Fig. 279), and the tube (/) is connected by the cork 
 (K) with the short test-tube (0) ; the longer limb of a very narrow siphon (I) of 
 stout tube passes through a second perforation in the cork (K), the shorter limb 
 
 Fig. 279. Collection of zinc ethyl. 
 
 passing into the very short test-tube (P), the cork of which is also furnished with 
 the short piece of moderately wide tube (L). For receiving and preserving the 
 zinc ethyl, a number of small tubes are prepared of the form shown in Fig. 280. 
 The long narrow neck (R) of one of these is passed down the short tube (L) to the 
 bottom of P, the other end (N) of the tube being connected with an apparatus for 
 passing dry C0 2 . The whole of the apparatus being filled with this gas, the nipper- 
 tap is closed, and the flask (E) heated on a sand-bath, so that the zinc ethyl may 
 
 distil over, a slow stream of car- 
 
 if bonic acid gas being constantly 
 
 ** passed into P, the excess escaping 
 
 through L. When enough zinc 
 ethyl has collected in the tube 
 (0), a blowpipe flame is applied 
 Fig. 280. to the narrow tube (N), which 
 
 is drawn off and sealed ; the 
 
 siphon tube (I) is then gradually pushed down, so that its longer limb may be 
 sufficiently immersed in the zinc ethyl, and the nipper-tap (T, Fig. 278) is opened, 
 when the pressure of the carbonic acid gas forces over a part of the zinc ethyl into 
 the tube (P). By heating the tube (M) with a spirit-lamp, so as to expel part of 
 the gas, allowing it to cool, it will become partly filled with zinc ethyl, and may be 
 withdrawn and quickly sealed by the blow-pipe. The spontaneous inflammability 
 of the zinc ethyl, and its easy decomposition by water, render great care necessary 
 in its preparation. If an alloy of zinc with one-fourth its weight of sodium be 
 employed, the conversion may be effected in an hour. 
 
 The reaction in the preparation of zinc ethide really occurs in two stages ; when 
 the ethyl iodide ceases to distil, the flask contains zinc- iodo-et/tide, ZnIC 2 H 5 , 
 as a crystalline solid, decomposed by a higher temperature into zinc ethide and 
 zinc iodide ; 2ZnIC 2 H 5 = Zn(C 2 H 5 ) 2 + ZnI. The action is more rapid if the zinc be 
 polarised by copper. To effect this, CuO is reduced by heating it in a tube in a 
 current of hydrogen or coal-gas, and 10 grams of it are mixed with 90 grams of 
 zinc-filings in a 300 c.c. flask, which is then .heated with continual shaking, until 
 the mixture forms grey granular masses. After cooling, 87 grams of ethyl iodide 
 are added, and the mixture heated to about 90 C. with the reversed condenser, 
 
 * The process is said to be much accelerated if about g^th of zinc ethyl is dissolved in the 
 ethyl iodide. 
 
BORON AND SILICON ALKIDES. 
 
 653 
 
 till no more liquid distils back, which requires about 15 minutes ; the rest of the 
 operation is conducted as described above, using a sand-bath or an oil-bath. 
 
 Zinc ethide is a colourless liquid of peculiar odour, sp. gr. 1.18, b.-p. 
 1 1 8 C. In contact with air, it inflames spontaneously, burning' with 
 a bright greenish-blue flame, emitting a white smoke of ZnO. If a piece 
 of porcelain be depressed upon the flame, a deposit of metallic zinc is 
 formed, surrounded by a ring of oxide, yellow while hot and white on 
 cooling. Dissolved in ether and treated with oxygen, it yields zinc 
 ethoxide, Zn(OC 2 H 5 ) 2 , a white powder. Water decomposes it readily, 
 ethane or ethyl hydride being evolved; Zn(C 2 H 5 ) 9 + H 2 = ZnO V 
 2(C 2 H 5 'H). When NH 3 is passed into the solution of zinc ethide in 
 ether, C 2 H 6 is evolved, and a white precipitate of zinc amide deposited 
 Zn(C 2 H 5 ) 2 + 2 NH 3 = 2(C 2 H 5 -H) + Zn(NH 2 ) 2 . 
 
 Zinc ethide and ethyl iodide, dissolved in ether and heated to 170 C., 
 yield butane, or di-ethyl ; Zn(C 2 H 5 ) 2 + 2C 2 ELI = ZnI 2 + 2(C 2 H 5 ) 2 . Heated 
 with sulphur, zinc ethide is converted into zinc mercaptide, Zn(SC 2 H 5 ) 9 , 
 the analogue of zinc ethoxide and zinc hydroxide. Zinc ethide is much 
 used in organic research, especially for effecting the substitution of C H 
 for Cl, Br, I, or OH. 
 
 Dissolved in ether and heated with Na in a sealed tube, zinc ethide exchanges 
 one-third of its Zn for Na, forming a crystalline compound of zinc ethide with 
 sodium ethide, 3Zn(C 2 H 3 ) 2 + Na, 2 = 2(Zn(C 2 H 5 ) 2 -NaC 2 H 5 ) + Zn. When this is treated 
 with dry C0 2 , zinc ethide distils, and sodium propionate remains ; NaC 2 H 5 + COo = 
 C 2 H 5 -C0 2 Na. 
 
 Zinc met/tide, or zinc methyl, Zn(CH 3 ) 2 , prepared from methyl iodide, like zinc 
 ethide, which it resembles, boils at 46 C., and has a more powerful odour, pro- 
 ducing irritation. It is more energetic in its reactions than zinc ethide, and is 
 decomposed, with inflammation and explosion, by water, yielding methane. 
 
 437. Boron Alkides. Boron methide, B(CH 3 ) 3 , formed by the action of a strong 
 ethereal solution of Zn(CH 3 ) 2 upon ethyl 'borate, 2(C 2 H 5 ) 3 B0 3 + 3Zn(CH 3 ) 2 = 
 2B(CH 3 ) 3 + 3Zn(0'C 2 H 5 ) 2 , is a gas with an intolerably pungent, tear-exciting odour, 
 liquefied by three atmospheres pressure. When issuing very slowly into the air, it 
 undergoes partial oxidation, with phosphorescence, but when it comes rapidly into 
 contact with air, it burns with a green flame, remarkable for the immense quantity 
 of large flakes of carbon which it emits. 
 
 Boron ethide, or triborethijl, B(C 2 H 5 ) 3 , is prepared bypassing vapour of boron 
 chloride into zinc ethide ; 2BCl 3 + 3Zn(C 2 H 5 ) 2 = 2B(C 2 H 5 ) 3 + 3ZnClg. It is a colour- 
 less liquid of irritating odour, and insoluble in water. Its sp. gr. is 0.69, and it 
 boils at 95 C. It inflames spontaneously in air, burning with a green flame, and 
 explodes in contact with pure oxygen. Water slowly converts it into B(C 2 H 5 ) 2 OH,. 
 another spontaneously inflammable liquid. By gradual oxidation in air it becomes 
 BC 2 H 5 (OC 2 H 5 ) 2 , decomposed by water, into alcohol and et/tyl-boricacid,BC 2 }i s (OH) 2 , 
 which is a volatile crystalline body, subliming in scales like boric acid, and having 
 a very sweet taste and a pleasant smell ; it is very soluble in water, alcohol, and 
 ether. 
 
 438. Silicon Alkides. Silicon methide, Si(CH 3 ) 4 , produced by the action of 
 SiCl 4 upon Zn(CH 3 ) 2 , is a liquid lighter than water, burning in^air, and producing; 
 a white smoke of silica. It is stable in water, and boils at 30 C. Silicon ethide, 
 or Si(C 2 H 5 ) 4 , obtained by a similar process, resembles the methide, but boils at 
 153 C. In its chemical relations it resembles the paraffin hydrocarbons, and is 
 sometimes called silico-nonane, the ninth member of the paraffin series, CflH^, in 
 which silicon is exchanged for an atom of carbon. When acted on by chlorine,, 
 it yields SiC 8 H iq Cl; when this is heated with potassium acetate, in alcoholic 
 solution, it yields the acetate SiC 8 H 19 'C2H 3 2 , and by heating this with alcoholic 
 solution of potash, it is converted into silico-nonyl alcohol, SiC 8 H 19 'OH, boiling at 
 
 I9 By acting on ethyl orthosilicate, Si(OC 2 H 5 ) 4 , with zinc ethide and sodium, siliron 
 triethyl ethoxide Si(C 2 H 5 )./OC 2 H 5 , silicon diethyl-diethoxide, Si(C 2 H 5 )fc(OC 2 H g ) 2 , and 
 
654 PHOSPHINES. 
 
 silicon et/iyl-triethoj'ide, SiC. 2 H 5 (OC. 2 H 5 ) 3 , may be produced. When the last named 
 is heated with acetyl chloride, it yields silicon ethyl trichloride, SiC 2 H 5 Cl 3 , which 
 is converted by water into silico-2)ropionic acid, C. 2 H 5 -SiOOH, a solid, feeble acid. 
 Silica-acetic acid, CH 3 'SiOOH, is also known. 
 
 439. Phosphines. These compounds being formed on the type of 
 PH 3 , the analogue of NH 3 , are primary, secondary, and tertiary, like 
 the alkylamines, as explained in the next section. 
 
 Tri-ethyl phosphine, P(C 2 H 5 ) 3 , a tertiary phosphine,fis prepared by 
 very gradually dropping PC1 3 into a solution of zinc ethide in ether, 
 in a retort connected with a receiver filled with C0 2 ; a very violent 
 action occurs 2PC1 3 + 3Zn(C 2 H 5 ) 2 = sZnCL, + 2P(C 2 H 5 ) 3 . The upper 
 layer of the distillate contains the excess of PC1 3 and ether, the lower 
 being a compound of ZnCl 2 with tri-ethyl phosphine, which may be 
 separated by careful distillation with KOH in a retort filled with H. 
 It is also obtained by heating phosphonium iodide with alcohol, in 
 a sealed tube, to 180 C. ; PH 4 I + 3 C 2 H 5 OH = P(C 2 H 5 ) 3 'HI + 3 HOH ; 
 the hydriodide is distilled with KOH. Tri-ethyl phosphine is a 
 liquid of strong odour, sp. gr. 0.81, and b.-p. 127 C. It behaves 
 like a divalent metal of the calcium group, absorbing "0 from the air, 
 becoming hot and exploding below 100 C. It forms salts with the 
 acids and its oxide, P(C 2 H 5 ) 3 0, is a very stable crystalline substance, 
 obtained, together with ethane, by distilling tetrethyl phosphonium. 
 iodide with potash ; P(0,H 5 ) 4 I + KOH = P(C 2 H 5 ) 3 + KI + C 2 H 5 'H. The 
 tetrethyl-phosphonium iodide is obtained by heating ethyl iodide with 
 P in a sealed tube; 4.C 2 H 5 I + P 2 = P(C 2 H 5 ) 4 I + PI 3 . By decomposing 
 its aqueous solution with Ag 2 0, tho tetrethyl phosphonium hydroxide, 
 P(C 2 H 5 ) 4 OH, is produced, a strongly alkaline substance, which may- 
 be crystallised and is comparable with the hydroxides of the alkali 
 metals. 
 
 The primary and secondary phosphines, ethyl phosphine P(C 2 H 5 )H 2 , 
 and di-ethyl phosphine, P(C 2 H 5 ) 2 H, are prepared by heating PH 4 I with 
 C 2 H 3 I and ZnO, in a sealed tube for some hours ; crystalline compounds 
 of zinc iodide with the hydriodides of ethyl phosphine and di-ethyl 
 phosphine are first formed ; 
 
 2PH 4 I + 2C.,H 5 I + ZnO = H + ZnI 2 + 2(P(C. 2 H 5 )H .HI), and 
 PH 4 I +"C. 2 H 5 I + ZnO = "H 2 + ZnI 2 + P(C 2 H 5 ) 2 H.HI. 
 
 These are decomposed by distillation with water out of contact with 
 air, when the phosphines distil over. 
 
 Ethyl phosphine is a feebly basic liquid, boiling at 25 C., having an intolerable 
 odour, insoluble in water. Di-ethyl phosphine is also liquid, but boils at 85 C., 
 and is more strongly basic. Both compounds, being composed upon the PC1 3 
 model, are disposed to unite with other bodies to form compounds upon the PCI, 
 model. When oxidised by nitric acid, they yield, respectively, ethyl phosphinic. 
 acid, PO(C 2 H 5 )(OH) 2 , and di-ethyl phosphinw acid, PO(C 2 H 5 ) 2 OH, composed upon 
 the 'model of orthophosphoric acid, PO(OH) 3 , by the substitution of eth} r l for 
 hydroxyl. 
 
 "Tri-ethyl phosphine combines violently with methyl iodide, forming 
 P(C. 2 H 5 ) 3 CH 3 -I, which yields an alkaline hydroxide when decomposed with water 
 and "silver oxide. 
 
 Tri-ethyl phosphine combines with sulphur, evolving heat, and forming 
 P(C. 2 H 5 ) 3 S, which crystallises in needles from solution in hot water. It also com- 
 bines energetically with CS 2 , forming a fine red crystalline compound soluble in 
 alcohol, and forming a test for CS 2 in coal gas. 
 
 The methyl phosphines are similar to the ethyl compounds and are similarly 
 prepared. 
 
KAKODYL. 
 
 Phe.nylphosphlne (phosphamlhw), PH 2 'C 6 H 5 , is prepared by the action of HI on 
 phosphenyl chloride, PC 6 H 5 C1 2 ; it is a liquid of intense and repellent odour, boils 
 at 1 60 C., and absorbs oxygen from the air to form the soluble crystalline p/iem/l- 
 phosphnie oxide, C 6 H 5 PH. 2 0. 
 
 Phospkenyl chloride, PC 6 H 5 CL 2 , obtained when mercury diphenyl (C 6 H 5 ) 2 Hg is 
 heated with PC1 3 , is a liquid which combines with Cl to form crystals of the 
 tetrach loride, PC 6 H 5 C1 4 . When treated with water it yields phenyl h yi>ophwphorou* 
 acid (phosphenylons add), C 6 H 5 'PHO(OH). From the tetrachlorid'e, phenyl p/iox- 
 phlnic acid (phosphenylic acid], C 6 H 5 'PO(OH) 2 , is similarly prepared. 
 
 Phosphenyl chloride arid phenylphosphine react to form ph-oxnhoben~ene 
 C 6 H 5 -P : P'C 6 H 5 , the analogue of azobenzene, C 6 H 5 'N : N'C 6 H 5 . 
 
 440. Arsines. While the alkyl derivatives of NH 3 and PH 3 are 
 strongly basic, those of AsH 3 are not. Moreover, only the tertiary and 
 secondary derivatives are known. The divalent radicles like As(CH 3 ).,, 
 however, give rise to salt-forming oxides, and the radicles themselves 
 exist in double form. 
 
 Trimethyl arsine, As(CH 3 ) 3 , or Kd., is obtained by the action of AsCl 3 
 on zinc methide. It is a strong-smelling liquid, boiling at about 70 C., 
 and resembling P(C 2 H 5 ) 3 , but not forming salts with the acids. 
 
 Ar sen- dimethyl, or kakodyl, As(CH 3 ) 2 , has a special interest as hav- 
 ing been one of the first bodies recognised as a compound radicle capable 
 of behaving like an elementary substance. The formula As(CH 3 ) 2 repre- 
 sents only one volume of vapour, so that it must be doubled to represent 
 a molecule, conveniently termed dikakodyl. The oldest compound of 
 kakodyl is the dikakodyl oxide, Kd 2 0, or alcarsin, or arsenical alcohol, 
 named, after its discoverer, Cadet's fuming liquid, and obtained by dis- 
 tilling a mixture of equal weights of white arsenic and potassium acetate 
 
 As 4 6 + 8CH 3 C0 2 K = 2[As(CH 3 ) 2 ] 2 + 4C0 2 + 4K 2 C0 8 . 
 
 The distillate has a strong odour of garlic, and takes fire spontaneously, 
 owing to the presence of dikakodyl. It is received in water, when it 
 sinks to the bottom; sp. gr. 1.46, b.-p. 120 C. It combines with 
 acids to form salts, and dissolves in alcohol, the solution giving, with 
 alcoholic mercuric chloride, a crystalline precipitate of Kd.,0.2HgCl.,. 
 By distilling this precipitate with strong HC1 in a retort filled with 
 C0 2 , kakodyl chloride, KdCl is obtained as a heavy spontaneously 
 inflammable liquid, of terrible odour. When this is heated to 100 C. 
 with zinc in an atmosphere of C0 2 , a compound of ZnCl 2 with kakodyl 
 is produced, and on treating this with water dikakodyl separates as a 
 heavy oily liquid which boils at 170 C. It inflames spontaneously in 
 air, and when its vapour is passed through a tube heated to 400 C., it 
 is decomposed As 2 (CH 3 ) 4 = 2CH 4 + C 2 H 4 + As 2 . When slowly oxidised 
 by air, it is converted into Kd 2 O, which is afterwards converted, in 
 presence of water, into kakodylic acid, KdO'OH, or dimethyl-arsenic acid, 
 AsO(CH 3 ) 2 -OH, i.e., arsenic acid, AsO(OH) s , in which two OH groups 
 are exchanged for (CH 3 ) 2 . This acid is best prepared by oxidising 
 Kcl.,0 with mercuric oxide in presence of water Kd 2 + 2HgO + H 2 = 
 2Kd0 2 H + Hg 9 . It crystallises from the aqueous solution, and is a 
 stable acid. 
 
 Sulphur dissolves in dikakodyl, forming Kd 2 S, a colourless liquid of unpleasant 
 smell, which behaves like an alkali sulphide/ Kd 2 S 2 is a solid which may. be 
 crystallised from alcohol. 
 
 Kakodyl cyanide, KdCN, prepared by distilling kakodyl chloride with mercuric 
 cyanide, forms lustrous prismatic crystals, m.-p. 37 C., b.-p. 140. It is nearly 
 insoluble in water, but dissolves in alcohol. Its vapour is very poisonous. 
 
656 HEAVY METAL ALKIDES. 
 
 Kaltodyl trichloride, As(CH :j ) 2 Cl 3 , is composed upon the model of AsCl 5 . whilst 
 the chloride, As(CH 3 ) a Cl, is formed after AsCl 3 . The chloride ignites in Cl, but, 
 if it be dissolved in CS 2 , the action of Cl converts it into crystals of the trichloride. 
 When this is heated, it evolves CH 3 C1, and a heavy irritating liquid distils, which 
 is arsenmethyldichloride. AsCH 3 C] 2 , boiling at 133 C., andsoluble in water without 
 decomposition. By evaporating the solution with Na^CO.,, and extracting the 
 residue with alcohol and crystallising, arsenmethyl oxide, AsCH 3 0, is obtained. The 
 crystals smell like assafcetida. Mercuric oxide in the presence of water, converts 
 the oxide into metJiyl-arsiiiic acid, AsCH 3 0(OH) 2 . 
 
 With methyl iodide, dikakodyl yields kakodyl iodide and tetrameth yl-ar$onium 
 iodide, As 2 (CH 3 ) 4 +2CH 3 I = As(CH 3 ) 2 I + As(CH 3 ) 4 I ; this last, when decomposed by 
 moist silver oxide, yields the corresponding hydroxide, As(CH 3 ) 4 OH, which is 
 strongly alkaline, and may be crystallised. 
 
 Dimethylarsine, (CH 3 ) 2 AsH, is a spontaneously inflammable liquid (b.-p. 36 C.), 
 obtained by the action of Zn and HC1 on an alcoholic solution of KdCl. 
 
 The ethyl compounds of arsenic are in every respect similar to the 
 methyl compounds. 
 
 441. Antimony Alkides. Antimony forms compounds with the hydrocarbon 
 radicles, composed upon the models SbCl 3 and SbCl 5 . 
 
 Stibio-trimethyl, or trimethyl stibi'iie, Sb(CH 3 ) 3 , is prepared by distilling in a 
 current of C0 2 methyl iodide with the potassium antimonide obtained by strongly 
 heating tartaVemetic ; 3CH 3 I + K 3 Sb = 3KI + (CH 3 ) 3 Sb. The powdered anti- 
 monide must be mixed with sand to moderate the action. The product is a 
 garlic-smelling liquid, of sp. gr. 1.52, and boiling at 80 C. It is insoluble in 
 water, but dissolves in ether. By the slow action of air it is converted into 
 Sb(CH 3 ) 3 0, but is liable to take fire. It combines with chlorine and iodine, forming 
 Sb(CH 3 ) 3 Cl 2 and Sb(CH 3 ) 3 I 2 , which may be crystallised, and are formed upon the 
 model of SbCl 5 . Stibio-trimethyl combines at once with methyl iodide, forming 
 Sb(CH 3 ) 4 I as a white solid, crystallising in six-sided plates from hot water. When 
 decomposed by Ag 2 in presence of water, it yields a strong alkali, tetrameth yl- 
 stibonium hydroxide, Sb(CH 3 ) 4 OH, which may be crystallised, and forms crystal- 
 Usable salts. 
 
 Stibio-pentamethyl, Sb(CH 3 ) 5 , composed on the model of SbCl 5 , is obtained by 
 distilling stibio-trimethyl iodide with zinc methide. 
 
 Stlbio-tri-etliyl, or tri-ethijl stibine, Sb(C 2 H 5 ), is obtained like stibio-trimethyl ; 
 or by acting on antimonious chloride with zinc ethide ; 2SbCl 3 + 3Zn(C 2 H 5 j 2 =: 
 2Sb(C 2 H 5 ) 3 +3ZnCl 2 . It resembles the methyl compound, but boils at 158 C. It 
 is remarkable for behaving like a metal ; even decomposing hydrochloric acid and 
 liberating hydrogen; Sb(C 2 H 5 ) 3 + 2HCl = Sb(C 2 H 5 ) 3 Cl 2 + H 2 . The chloride is an 
 oily liquid smelling like turpentine. Its salts behave like those of the alkalies. 
 
 Bismuth tri-ethyl, Bi(C 2 H 5 ) 3 , is prepared by acting on ethyl iodide with an alloy 
 of potassium and bismuth. It is a spontaneously inflammable liquid which is 
 very unstable, depositing bismuth even below 100 C., and exploding at 150. 
 As might be expected from the non-existence of BiCl 5 , bismuth tri-ethyl shows no 
 disposition to combine directly with the halogens, its derivatives being formed on 
 the model of BiCl 3 . 
 
 442. Lead Alkides. The compounds of lead with alcohol radicles are not 
 composed upon the model of the stable chloride, PbCl 2 , but upon that of PbCl 4 , 
 which is not known in the pure state. 
 
 Lead tetrameth yl, Pb(CH 3 ) 4 , is formed by the action of zinc-methyl upon lead 
 chloride; 2Zn(CH 3 ) 2 + 2PbCl 2 = 2ZnC] 2 + Pb(CH 3 ) 4 + Pb ; it distils at 110 C., and 
 has the sp. gr. 2.03. It has a faint odour, is unaffected by air, and is insoluble in 
 water. Heated with HC1 Pb(CH 3 ) 4 + HCl = Pb(CH 3 ) 3 Cl + CH 4 . The chloride is 
 crystalline, and may be sublimed ; by reaction with KI it gives colourless crystals 
 of Pb(CH 3 ) 3 I, and when this is distilled with potash, Pb(CH 3 ) 3 'OH is obtained as a 
 strongly alkaline body smelling like oil of mustard. 
 
 Lead tetrethyl, Pb(C 2 H 5 ) 4 , and its derivatives resemble the methyl compounds. 
 
 Lead tri-ethyl, Pb(C 2 H 5 ) 3 , is obtained by the action of ethyl iodide upon an alloy 
 of sodium and lead. This combines with iodine in alcoholic solution, forming 
 Pb(C 2 H 5 ) 3 I, which yields a hydroxide, like the corresponding methyl compound. 
 
 443. Mercury Alkides. Mercuric met/tide, Hg(CH 3 ) 2 , may be obtained by the 
 reaction between mercuric chloride and zinc methide, but better by dissolving 
 
TIN ALKIDES. 657 
 
 one part of sodium in one hundred parts of mercury, and adding the amalgam by 
 degrees, to methyl iodide mixed with one-tenth of its volume of ethyl acetate 
 the action of which has not yet been explained. On distillation, the mercuric 
 methide is obtained as a colourless liquid which is one of the heaviest known its 
 sp. gr. being 3.07, so that glass floats in it. It is unchanged by exposure to air, 
 but gives otf a faint odour which is very poisonous. It boils at 95 C and burns 
 with a bright flame. With strong HC1, Hg(CH 3 ) 2 + HC1 = HgCH.,Cl + CH 3 'H. 
 
 Mercuric ethide, Hg(C 2 H 5 ) 2 , is prepared like the methide. It has the sp. gr. 2.4, 
 and boils at 159 C. Its vapour is decomposed at 200 C. into Hg and butane, 
 but with strong H 2 S0 4 it gives ethane. 
 
 Mercury ethyl chloride, HgC 2 H 5 Cl, is obtained by acting on mercuric ethide with 
 mercuric chloride dissolved in alcohol ; Hg(C 2 H 5 ) 2 + HgCl 2 = 2HgC 2 H 5 Cl : this shows 
 it to be composed upon the mercuric type, HgCl 2 , and not derived from the mer- 
 curous compound Hg 2 (C 2 H 5 ) 2 , corresponding with Hg 2 Cl 2 . The chloride is insoluble 
 in water, but crystallises from alcohol, and is easily sublimed. Silver oxide con- 
 verts it into the mercury ethyl hydroxide, HgC 2 H 5 OH, a caustic alkaline liquid 
 which blisters the skin. The iodide, HgC 2 H 5 I, obtained by treating Hg(C 2 H 5 ) 2 
 with I 2 , is remarkably stable, crystallising from hot caustic soda, almost without 
 decomposition. It is hardly soluble in water or alcohol. 
 
 Mercury diphenyl, (C 6 H 5 ) 2 Hg, is formed when Na-amalgam acts on C 6 H 5 Br. 
 It is a crystalline solid (m.-p. 120 C.), subliming almost unchanged, insoluble in 
 water, and sparingly soluble in alcohol and ether, but soluble in benzene. When 
 heated, in a sealed tube, with HgCl 2 and alcohol, it yields mercury -phenyl chloride, 
 HgC 6 H 5 Cl, which, with silver hydroxide, yields mercury -phenyl hydroxide, 
 HgC 6 H 5 'OH, a crystalline strongly alkaline base. 
 
 444. Tin Alkides. Tin tetrametJiide, Sn(CH 3 ) 4 , composed upon the model of 
 stannic chloride, SnCl 4 , is obtained by the action of an alloy of Sn, Hg, and Na 
 upon CH 3 I. It boils at 78 C. By the action of iodine, one CH 3 group is removed, 
 and tin trimetltyl iodide, Sn(CH 8 ) 3 I, obtained ; this, acted on by NaOH, yields 
 Sn(CH 3 ) 3 OH, a sparingly soluble, crystalline, volatile, alkaline base. 
 
 When CH 3 I is heated to 160 C., in a sealed tube, with tin-foil, tin dimethyl 
 iodide, Sn(CH 3 ) 2 I 2 is formed. It crystallises in yellow prisms soluble in water ; 
 NH 3 gives a white precipitate of the base Sn(CH 3 ) 2 with the solution. 
 
 Tin tetrethide, or stannic ethide, Sn(C 2 H 5 ) 4 (b.-p. 181 C.), prepared by distilling 
 stannic chloride with zinc ethide, is remarkably stable, even when boiled with 
 sodium. It is not precipitated by H 2 S. 
 
 Like the tetramethide, it yields the iodides Sn(C 2 H 5 ) 2 I 2 and Sn(C 2 H5) 3 I. By 
 treatment with Na these undergo nucleal condensation yielding a mixture of 
 Sn 2 (C 2 H 5 ) 4 and Sn 2 (C 2 H 5 ) 6 , which may be separated by alcohol in which the former, 
 stannous ethide, or tin dietliide, is insoluble. It is a liquid of sp. gr. 1.56, decom- 
 posed when heated ; 8n 2 (C 2 H 5 ) 4 =Sn(C 2 H 5 ) 4 + Sn. It is an unsaturated compound, 
 absorbing oxygen from the air, and forming Sn(C 2 H 5 ) 2 0, which forms crystalline 
 salts, like Sn(C 2 H 6 ) 2 (N0 3 ) 2 . 
 
 Tin he,rethide, Sn 2 (C 2 H 5 ) 6 . boils at 270 C., decomposing into Sn(C 2 H 5 ) 4 and Sn. 
 
 445. Aluminium methide, A1(CH 3 ) 3 , and the corresponding ethide are obtained by 
 decomposing mercuric methide and ethide by Al. They are spontaneously inflam- 
 mable liquids, violently decomposed by water, yielding A1 2 (OH) 6 and methane or 
 ethane. Their vapour densities are known. 
 
 Maffoesiunt methide, Mg(CH 3 ) 2 , and ethide me prepared by decomposing CH 3 I or 
 CftHgl with Mg, when a solid iodide, MgCH,I, is first formed, which is decomposed 
 when distilled in C0 2 ; 2MgCH 3 I = Mg(CH 3 ) 2 + MgI 2 . They are spontaneously 
 inflammable liquids, yielding Mg(OH) 2 and CH 4 or C 2 H 6 , with water. 
 
 Organo-mineral compounds similar to those which have been described 
 are formed by other alcohol radicles and benzene hydrocarbon residues, 
 and mixed compounds are obtainable. 
 
 Thus, Sn(CH 3 ). > (C,H 5 ) 2 may be produced by the action of zinc methide 
 upon Sn(C 2 HA,Cl ; and Sn(CH 8 ) 3 C 9 H 5 is formed by zinc ethide with 
 Sn(OH 8 ) 8 01. 
 
 2 T 
 
658 
 
 AMINES. 
 
 IX. AMMONIA-DERIVATIVES. 
 
 446. The organic compounds classed under this head are derived from 
 NH 3 by substitution of radicles for H, and are in many cases very 
 nearly related to the organo -mineral compounds, since such compounds 
 as P(CH 3 ) 3 , As(CH 3 ) 3 , Sb(CH 3 ) 3 , B(CH 3 ) 3 , are formed upon the type of 
 PH 3 , AsH 3 , SbH 3 , and BH 3 , which are nearly allied to NH 3 ; but the 
 strongly alkaline character of ammonia impresses special characters upon 
 the bodies derived from it. These may be divided into 
 
 (1) Amines or ammonia-bases, formed by the substitution of alcohol 
 radicles for the hydrogen in ammonia, such as NH 2 'CH 3 , NH(CH 3 ) 2 , 
 N(CH 3 ) 3 . This class also includes the ammonium bases, formed by the 
 substitution of alcohol radicles for hydrogen in ammonium hydroxide, 
 NH 4 OH, such as N(CH 3 ) 4 OH. All these are basic, many of them 
 powerfully so. 
 
 (2) A mides, derived from ammonia by the substitution of acid radicles 
 for hydrogen, such as NH 2 (CH 3 CO), NH(CH 3 CO) 2 , N(CH S CO) 3 . These 
 may also be regarded as formed from acids by the exchange of i, 2, 
 or 3 OH groups from the COOH groups of the acid for (NH,)', (NH)", 
 and N'" respectively. They are only slightly basic compounds, since 
 the acid radicle has nearly neutralised the basic character of the parent 
 ammonia. 
 
 (3) Amido-acids, derived from acids by the substitution of (NH.,)' for H 
 in the hydrocarbon residue, such as CH 2 (NH 2 )-COOH from CH 3 : COOH. 
 These are both basic and acid in character. 
 
 A compound containing the group NH 2 is known as an amide, one 
 containing NH is an imide, whilst one containing N> attached to carbon 
 only, is a nitrile. 
 
 AMINES OR AMMONIA-BASES AND AMMONIUM-BASES. 
 
 447. These are called p>*imary, secondary, tertiary, or quaternary ', 
 accordingly as one, two, three, or four atoms of H in NH 3 have been 
 exchanged. The quaternary bases can only be derived from NH 4 OH. 
 
 Amines or ammonia bases. 
 
 Ammonium -bases. 
 
 Primary or 
 Amido-bases. 
 
 Secondary or 
 Imido-bases. 
 
 Tertiary or 
 Nitrile-bases. 
 
 Quaternary 
 bases. 
 
 NH 2 R' 
 
 NHB' a 
 
 NHR" 
 
 Nil', 
 
 NR"' 
 
 NR' 4 OH 
 
 Amines are also distinguished as monamines, diamines, and triamines, 
 accordingly as they are derived from one, two, or three molecules of 
 ammonia. The amines in the above table are examples of monamines, 
 and the following are examples of the other two classes : 
 
 Diamines. 
 
 Primary 
 
 Secondary 
 
 Tertiary 
 
 N 2 H 4 R" 
 
 N 2 H 2 R 2 " ; N 2 R 2 "R ' 
 
 N 3 R 3 " ; N 9 R"R 4 ' 
 
 Triamines. 
 
 N 3 H 6 B'" 
 
 N 3 H 3 R'"R 3 ' ; N-jH-j 
 N-R 3 '" ; N 3 R"'R 6 '. 
 
PREPARATION OF AMINES. 
 
 6 59 
 
 
 The secondary and tertiary amines may be either simple or mixed, 
 that is to say, the radicles H may be either the same or different 
 
 Generally speaking the amines share the properties of ammonia 
 forming crystalline salts with acids, which, however, differ from the 
 ammonium salts in being soluble in alcohol. The amines containing 
 open-chain radicles are somewhat more basic than NH 3 , and the basicity 
 increases with the number of radicles, NHR 2 being a stronger base than 
 NH 2 R, and NR 3 stronger than either. The" amines containing aromatic 
 radicles may have the NH,, NH, or N group attached either to the 
 closed-chain, like NH 2 'C 6 H 5 or NH : (C 6 H 5 ) 2 , or to the side-chain, like 
 NH/CH 2 -C 6 H. and NH : (CH 2 'C 6 H.) 2 ; those of the latter class behave 
 in every respect like the fatty amines, but those in which the nitrogen 
 is attached to the closed-chain show slight differences, due to the fact 
 that a closed-chain nucleus is always somewhat more acidic than an open- 
 chain nucleus ; thus, phenylamine (C 6 H 5 'NH 2 ) is less basic than ethyl- 
 amine (C 2 H.'NH 2 ), because the basic properties of ammonia have been 
 more neutralised by phenyl than by ethyl. For the same reason, the 
 nucleal aromatic amines show some relationship to the amides and 
 amido-acids (p. 658) ; for instance, they readily undergo the diazo- 
 reaction (p. 680) characteristic of amides and amido-acids. Hence some 
 chemists term the aromatic amines amido-compounds. The difference 
 here denned is precisely similar to that between the alcohols and phenols 
 (see Phenols). 
 
 The most generally applicable method for preparing the amines 
 consists in reducing the corresponding nitro-compounds with nascent 
 hydrogen. Since the nitro-compoimds are more easily obtained from 
 closed-chain than from open-chain hydrocarbons, this method is most 
 frequently used for preparing aromatic amines ; C 6 H 3 N0 2 + H 6 = 
 C 6 H 5 NH 2 + 2 H 2 0. 
 
 The cyanides of hydrocarbon radicles are convertible into amines by 
 treatment with nascent H; C 2 H 5 'CN + H 4 = C 2 H 5 -CH 2 'NH 2 . 
 
 The open-chain amines can be prepared by heating the hydrocarbon 
 halides with ammonia in alcohol, but the aromatic amines cannot 
 be similarly produced from the nucleal halogen-substituted benzene 
 hydrocarbons. For example, methylamine, NH 2 CH 3 , dimethylamine, 
 NH(CH 3 ) 2 , and trimethylamine, N(CH 3 ) 3 , in the form of their 
 hydriodides, and tetramethyl ammonium iodide, N(CH 3 ) 4 I, are all 
 obtained when a strong solution of ammonia in alcohol is heated with 
 methyl iodide for some hours, in a sealed tube at 100 C. The re- 
 actions which occur may be represented by the following equations 
 (Me = CH 3 ): 
 
 (1) NH, + Mel = NH 2 Me-HI ; 
 
 (2) 2NH 3 + 2MeI = NHMeaHI + NH 4 I ; 
 
 (3) 3^H 3 + 3MeI = NMe 3 'HI + 2NHJ ; 
 
 (4) 4 NH 3 + 4MeI = NMe 4 I + 3NH 4 I. 
 
 The NH 4 I being nearly insoluble in alcohol separates at once and the hydriodides 
 of the three amines crystallise on cooling, leaving the NMe 4 I in solution. They 
 are distilled with KOH into a receiver cooled in ice, when a mixture of NMe s , 
 NHMe.,, and a little NH 2 Me is condensed, much of the last escaping as gas with 
 the NH 3 from the NH 4 I. Any NMeJ not previously separated by crystallisation 
 remains in the retort, as it is not decomposed by KOH. The mixed amines are 
 then digested with ethyl oxalate, when the NMe 3 is not acted on, and may be dis- 
 tilled off. The methylamine is converted into methyloxamide, and the dimethyl- 
 amine into ethyl dimethyloxamate (E = C 2 H 3 ) 
 
660 DISTINCTION BETWEEN AMINES. 
 
 CODE CONHMe 
 
 2NH. 2 Me + = + 2EOH 
 COOE CONHMe 
 
 COOE CONMe., 
 600E - COOE 
 
 Water at o dissolves the last-named compound, and leaves the methyloxamide 
 undissolved. On distillation with potash, the methyloxamide yields potassium 
 oxalate and methylamine ; (CONHMe) 2 + 2KOH = (COOK 2 ) + 2NH 2 Me ; and the 
 ethyl dirnethyloxamate yields potassium oxalate, dimethylamine, and alcohol 
 C 2 2 (NMe 2 )(OE) + 2KOH = (COOK) 2 + NHMe 2 + EOH. 
 
 The primary and secondary amines in which there is still ammoniacal 
 H are capable of many of the reactions of NH 3 ; the tertiary amines, 
 having no ammoniacal H, are less reactive. 
 
 On this depend the reactions which distinguish between primary, 
 secondary, and tertiary amines. The amine is treated with nitrous acid 
 (or, what comes to the same thing, NaNO 2 is added to a strong solution 
 of the amine hydrochloride). A primary amine yields the corresponding 
 alcohol with evolution of nitrogen ; C 2 H 5 'NH 2 + HON : = C 9 H 5 'OH + 
 N 2 + HOH. (Of. the action of NH 3 on HNO r ) A secondary amine 
 yields a nitrosamine, which separates in oily drops 
 
 (C 2 H 5 ) 2 NH + HO'N : = (C 2 H 5 ) 2 N'NO + HOH. 
 A tertiary amine is unchanged. 
 
 A primary amine can also be distinguished by the carlylamine reaction. 
 The hydrochloride is warmed with chloroform and alcoholic KOH ; the 
 characteristically disagreeable odour of a carbylamine (q.v.) is Droduced ; 
 
 A nitrosamine can be further recognised by Liebermann's nitroso-reactlcni ; 
 the suspected compound is mixed with phenol and H 2 S0 4 cone. A nitroso- 
 compound gives a dark green solution, becoming red when diluted and blue 
 when made alkaline. 
 
 Another method of investigating the constitution of an amine, is to heat its 
 alcoholic solution with methyl iodide in a sealed tube ; a tertiary amine 
 yields a substituted ammonium iodide by direct union with methyl iodide ; 
 N(C H 5 ) 3 + CH 3 I = N(C 2 H 5 ) 3 *CH 3 I : a secondary amine yields an ammonium 
 iodide containing two methyl groups' ; NH(C 2 H 5 ) 2 + 2CH 3 I = HI + N(C 2 H 5 ) 2 (CH 3 ) 2 I ; 
 a primary amine yields an ammonium iodide containing three methyl groups. 
 NH 2 (C 2 Hg) + 3CH 3 I = N(C 2 H 5 )(CH 3 ) 3 I + 2HL See, also, Mustard-oil reaction. 
 
 With organic chloranhydrides the primary and secondary amines react to 
 form amides in which the H of the NH 2 group is exchanged for hydrocarbon- 
 radicles (cf, p. 667) ; thus, with acetyl chloride, methylamine, NH 2 CH 3 reacts 
 to form acetmethylamideCH 9 CO'Cl + NH CH 3 = CH,CO-NHCHo + HC1 ; 
 dimethylamine, NH(CH 3 ) 2 , yields acetdimefhylamide, CH 3 CO'N(CH 3 ) 2 . The 
 secondary amines also react with inorganic chloranhydrides to form similar 
 substituted amides (c.f. p. 265) ; thus, from POC1 3 and NH(CH 3 ) 2 is obtained 
 PO[N(CH 3 ) 2 J 3 . Primary amines are apt to give substituted imides. such as 
 CH 3 N : SO from NH 2 CH 3 and SOC1 2 . 
 
 448. Monamlnes. Simple alkylamines are prepared as described 
 above for methylamines. Mixed alkylamines are obtained by heating 
 the amine of one radicle with the iodide of another (see above). The 
 amines of methyl and ethyl are here described as typical. 
 
 Methylamine, NH 2 CH 3 , is a gas (b.-p. - 6 C.) resembling ammonia, 
 but more combustible and more soluble in water ; in this it surpasses 
 all gases, one volume of water dissolving 1150 volumes of methylamine. 
 The solution is strongly alkaline. In its reactions with metallic salts it 
 resembles ammonia, but it dissolves aluminium hydroxide and will not 
 
TRIMETH YLAMINE. 66 1 
 
 dissolve the hydroxides of Cd, Ni, and Co. Its behaviour with acids and 
 with PtCl 4 is similar to that of ammonia. 
 
 Heated to redness it yields hydrocyanic acid, HCN, and NH.CN. Potassium 
 converts it into potassium cyanide NH 2 CH 3 + K = KCN + H 5 . Conversely 
 methylamme is formed by the action of nascent hydrogen on hydrocyanic acid; 
 HCN + H 4 =: NH 2 CH 3 . It is also produced by distilling methvl isocyanate 
 with potash (see Cyanogen}. Methylamine occurs in the fruit of Mercurialiarix 
 (dog-mercury), a plant of the order EuphwUacece. Several of the alkaloids yield 
 it when distilled with potash. 
 
 Dimethi/lamine, NH(CH 3 ) 2 , is a gas boiling at 7 C., and resembling methv- 
 lamine. It has been found in wood-spirit and in guano. 
 
 Trimethylamine, N(CH 3 ) 3 , is obtained on a large scale by distilling 
 the vinasses obtained in refining beet-root sugar, which corresponds with 
 the molasses from cane-sugar, but is not tit for food. It contains 
 sugar, by fermentation of which alcohols are obtained, and substances 
 containing nitrogen,* which furnish ammonia and amines derived from 
 the alcohols when distilled. 
 
 By neutralising the distillate with HC1, the hydrochlorides of ammonia, trime- 
 thylamine, <fcc., are obtained. The NH 4 C1, being less soluble, is crystallised out 
 and the X(CH 3 ) 3 HC1 is distilled with lime, when trimethylamine comes off as a gas 
 which may be absorbed by water. The solution also contains dimethylamine, 
 ethylamine, propylamine, and butylamine. It has been used for converting KC1 
 into K 2 C0 3 , by a process resembling the ammonia-soda process (p. 315), which 
 depends on the fact that NaHC0 3 is less soluble in water than is NH 4 C1 ; but 
 KHC0 3 has about the same solubility as NH 4 C1, so that trimethylamine, whose 
 hydrochloride is much more soluble, is substited for ammonia. 
 
 Trimethylamine boils at 3.5 C. ; it has a fish-like smell, is inflam- 
 mable, and mixes easily with water. It forms salts by direct com- 
 bination with acids, like ammonia. It is not unfrequently found in 
 plants, as in the flowers of hawthorn, pear, and wild cherry, and in 
 arnica and ergot of rye. It also occurs in the roe of the herring, and 
 may be obtained by distilling herring-brine with lime. It is often 
 found in the products of distillation of animal substances, together with 
 amines containing other alcohol -radicles. Bones, when distilled, yield 
 trimethylamine, methylainine, ethylamine, propylamine, and buty- 
 lamine. The putrefaction of flour and other nitrogenous substances 
 furnishes these ammonia-derivatives. The hydrochloride of trimethyl- 
 amine is employed for making methyl chloride on the large scale, as 
 described on p. 633. 
 
 449. Tetramethylammonium hydroxide, N(CH 3 ) 4 OH, is pre- 
 pared by decomposing the iodide with AgOH ; NMe 4 I + AgOH = 
 NMe 4 OH + AgL The iodide (tetramethylium iodide), obtained as 
 already described, forms prismatic crystals, and may be purified by 
 crystallisation from water, in which it is rather sparingly soluble. 
 Evaporated in vacuo, the solution of the hydroxide yields a crystalline 
 deliquescent mass, which acts like a caustic alkali, and absorbs C0 2 from 
 the air. When heated, it yields methyl alcohol and trimethylamine ; 
 NMe 4 OH = NMe 3 + MeOH. The ammonium bases form salts with acids 
 in the same way as the alkali hydroxides ; thus, NMe 4 OH + HNO 3 = 
 NMe 4 N0 3 + H 9 ; 2 NMe 4 OH + H 2 S0 4 = (NMe 4 ) 2 S0 4 + 2 H ? 0. These 
 are not decomposed by potash, even on boiling a distinction between 
 the salts of amines and ammonium bases. 
 
 * Particiilarly bttaine (Beta vulgaris, beet), or trimethyl glijcocine, C(CH S V NH 2 CO 2 CH 3 . 
 
662 ETHYLAMINES. 
 
 450. The ethylamines may be prepared by the action of ammonia on 
 ethyl iodide and may be separated from each other in the same way as the 
 methylamines. 
 
 They are prepared on a large scale by the action of NH 3 upon the impure ethyl 
 chloride obtained as a secondary product in the manufacture of chloral. This is 
 heated for an hour in a closed vessel with a saturated alcoholic solution of NH 3 . 
 The volatile matters are then distilled off, and the hydrochlorides crystallised ; on 
 decomposing these with strong soda solution, the three ethylamines form an oily 
 layer on the surface. They are separated as described under the methylamines. 
 
 Ethylamine, NH 2 C 2 H 5 , is an ammoniacal inflammable liquid, of sp. 
 gr. 0.696, and boiling-point 18.7 0. It mixes with water in all pro- 
 portions. It is a stronger base than ammonia, and dissolves alumina, 
 though it does not easily dissolve cupric hydroxide. Its salts resemble 
 those of ammonia, e.g., NH,E.HC1, (NH 2 E) 2 H 2 S0 4 , (NH 2 E.HCl) 2 PtCl 4 . 
 
 Di-eth yla wine, NH(C 2 H 5 ) 2 , is also an auimoniacal liquid, boiling at 56 C., and 
 mixing easily with water. Unlike ethylamine, it does not dissolve Zn(OH) 2 . 
 When its hydrochloride is distilled with potassium nitrite and a little water, 
 ethylnitrpsamine is obtained ; this contains the group 'NO in place of the imido- 
 hydrogen atom, (C H 5 ) 2 N > NO. Di-ethylamme nitrite is probably first formed 
 and then decomposed (C 2 H 5 ) 2 NH.HONO = (C 2 H 5 ) 2 N'NO + HOH. Ethylnitro- 
 samine is a yellow aromatic liquid insoluble in water, of sp. gr. 0.95 and b.-p. 177 C. 
 Nascent H reconverts it into di-ethylamine 2NE 2 NO + H 4 = 2NE 2 H + H 2 + N 2 0. 
 When it is dissolved in hydrochloric acid, and HC1 gas passed into the solution, it 
 yields nitrosyl chloride and di-ethylamine hydrochloride 
 
 NE 2 NO + 2HC1 = NE 2 H.HC1 + NOC1. 
 
 Tri-ethylamine, N(C 2 H 5 ) 3 , differs from the other amines in having a pleasant 
 smell, and being sparingly soluble in water. It boils at 89 C. Its reaction is strongly 
 alkaline, and it resembles ammonia in its action upon metallic salts, except that it 
 dissolves alumina, and scarcely dissolves silver oxide, which is readily soluble in 
 ammonia. 
 
 451. Tetrethylammonium hydroxide, N(C 2 H 5 ) 4 'OH, is prepared like the methyl 
 compound, which it much resembles, but crystallises rather more easily. In its 
 chemical behaviour, it is very similar to potassium hydroxide, but it produces, in 
 chromic salts, a precipitate of chromic hydroxide, which does not dissolve in excess. 
 When heated to 100 C., it does not yield alcohol, but ethane, water, and tri- 
 ethylamine; N(C 2 H 5 ) 4 -OH = C 2 H 4 + H 2 + N(C 2 H 5 ) 3 . If it be heated with ethyl 
 iodide, alcohol and tetrethylummonium Iodide are formed ; KE 4 OH + EI = 
 EOH + NEJ. The iodide may be obtained by the combination of N(C 2 H 5 ) 3 with 
 C 2 H 5 I, just as NH 4 I is formed by NH 3 and HI, the combination producing heat. 
 It crystallises in cubes like the alkali iodides, and becomes brown, when exposed 
 to air, from the formation of the tr iodide, NE 4 I 3 . It is very soluble in alcohol and 
 in water, but is insoluble in solution of potash, which precipitates it from the 
 aqueous solution, but without decomposing it. When heated, tetrethylainmonium 
 iodide undergoes dissociation, like ammonium chloride, yielding ethyl iodide, 
 which distils over, and is followed by tri-ethylamine, these afterwards combining 
 to reproduce the iodide. 
 
 By heating a primary amine, NH 2 R', successively with R"I, KOH, B'"I, KOH 
 and E iv l, a mixed quaternary ammonium iodide, of the form NB'B"B'"B iv I, may 
 be obtained. The importance of such compounds to the theory of stereoisomerism 
 has been noted at p. 607. 
 
 452. CJdoramlnes are formed from primary and secondary amines by action of 
 Cl or HC10 on amines, just as NC1 3 is formed from NH 3 , only here there are only 
 one or two H atoms to be exchanged for Cl. lodaiulnes and broinainlnes are also 
 known.- 
 
 The nitramines, such as metliyUiitramine, CH 3 NH'N0 2 , were originally supposed 
 to be nitro-derivatives of the primary and secondary amines in which N0 2 was 
 substituted for the ammoniacal H. This view has been traversed, and certain 
 isomeric forms have been discovered. 
 
 453. Phenylamine, or aniline, or amidobenzene, C 6 H 5 'NH 2 , is 
 
PREPARATION OF ANILINE. 
 
 663 
 
 prepared from nitrobenzene, C 6 H 5 -X0 9 , by reducing it with metallic 
 iron 111 conjunction with acetic or hydrochloric acid 
 
 Pet.on The aniline is purified by distillation, and the iron !Staii?irtS 
 
 thereto* 
 
 4C 6 H N0 2 + 4 H 2 + Fe 9 = 4 C 6 H 5 NH a + 3 Fe- 5 4 . 
 
 The process requires care, because, if the action becomes too violent, benzene and 
 ammonia are produced ; C 6 H 8 -NO a + H 8 = C 6 H 5 'H + NH 3 + 2 H.,0. 
 
 On the small scale, tin is more convenient than iron. Granulated tin is placed 
 in a retort with inverted condenser, and covered with strong HC1 ; nitroben/ene 
 is added m small portions, and when the action has moderated, he mixture is 
 
 Fig-. 281. Distillation in a current of steam. 
 
 boiled till all the nitrobenzene has disappeared ; C 6 H B N0 2 + 3SnCI 2 
 C 6 H 5 NH. 2 + 3SnCl 4 + 2H. 2 ; the liquid is decanted from the excess of tin, when it 
 deposits, on cooling, a crystalline compound of aniline hydrochloride with stannic 
 chloride ; (C 6 H ? NH 2 HCl) 2 .SnCl 4 . By distilling this with excess of potash or soda 
 in a current of superheated steam the aniline is set free. The apparatus for this 
 purpose is shown in Fig. 281. The steam generated in the boiler passes through 
 the coil of copper tube, which is heated by the burner, into the distillation flask, 
 carrying the aniline with it through the ccmdenser. 
 
 Nitrobenzene may also be converted into aniline by dissolving it in alcohol, 
 saturating the solution with NH 3 , then with H<,S gas repeatedly, as long as the 
 latter is acted on; C 6 H 5 N0 2 + 3H 2 S = C 6 H 5 NH2-f-2H 2 + S 3 . The liquid is de- 
 canted from the S, and the alcohol and ammonium sulphide distilled off in a 
 water-bath ; the mixture of aniline and any unaltered nitrobenzene is treated 
 with HC1, which dissolves only the aniline ; this may be liberated by distillation 
 with potash. 
 
 Since commercial benzene contains toluene and other hydrocarbons, the aniline 
 prepared from it contains toluidine and other bases. To purify it, the crude aniline 
 is boiled with glacial acetic acid, in a flask with a reversed condenser, when it is 
 converted into acetan'didp., C 6 H ? -NH *C 2 H 3 O. This is distilled, washed with c"irl>on 
 bisulphide, and recrystallised from water till its melting-point is 115 C.. when 
 pure aniline may be obtained from it by boiling with NaOH 
 
 (1) NH.,-C 6 H 5 + CoH^O-OH = NH'C 6 H 5 -CoH.jO + HOH ; 
 
 (2) NH : C 6 H 5 -C. 2 H 3 6 + NaOH = NH 2 'C 6 H; + NaO'C,H,0. 
 
664 PROPERTIES OF ANILINE. 
 
 Aniline was originally obtained by distilling indigo, either alone or 
 with caustic alkalies, and was named from anil, the Portuguese name 
 of indigo. It is also found in coal tar, and in the products of distilla- 
 tion of bones and peat. 
 
 Properties of aniline. Colourless when pure, but generally of a 
 yellow or even brown colour, having a characteristic rather ammoniacal 
 smell; sp. gr. 1.03, and boiling-point 184 C. When shaken with 
 water, it appears almost insoluble, but the water dissolves about ^th 
 of its weight of aniline, and the latter about ^V^ n ^ ^ s weight of water. 
 It is easily soluble in alcohol and ether, which collects it from an 
 aqueous solution. It has no alkaline reaction, and is less strongly basic 
 than the alky lam ines, though it precipitates hydroxides of Zn, Al, and Fe. 
 Most of its salts crystallise easily. The hydrochloride, C 6 H 5 'NH 2 .HC1, 
 is commercially known as aniline-salt. The oxalate, (C 6 H 7 N) 2 .H 2 C 2 4 , 
 is rather sparingly soluble in water. Aniline has the rare property of 
 dissolving indigo. 
 
 Many oxidising-agents produce intensely coloured products with 
 aniline. The usual test for it is solution of chloride of lime (bleach ing- 
 powder), which gives a purple-violet colour, changing to brown. 
 Solutions of aniline give a bright green precipitate, (C 6 H.NH 2 ) 2 CuS0 4 , 
 with CuS0 4 . By Caro's reagent (a persulphate in strong H 2 S0 4 ) aniline 
 is oxidised to nitrosobenzene, C 6 H 5 'NO. 
 
 Substitution products of aniline are obtained by the reduction of the correspond- 
 ing nitro-compounds ; thus i : 2-chloronitro-benzene, C 6 H 4 C1'N0 2 , will yield 
 i : 2-chloramUne, C 6 H 4 C1'NH 2 . By the action of chlorine or bromine water on 
 aniline, the trichloranuine* and tribromaniline* are produced, the latter form the 
 white precipitate which bromine-water gives with aniline. 
 
 Nitranilines, or nitrophenylamines, C 6 H 4 N0 2 *NH 2 , are obtained by the partial 
 reduction of the dinitro-benzenes with NH 4 HS (p. 663). The presence of the acidic 
 N0 2 or Cl greatly reduces the basic character of aniline. Thus dinitraniline is 
 neutral, and trinitraniline, CfH^NOaVNHj, is acidic in properties. 
 
 Aniline-sulphonic acid, or I : ^amidobenzenesulphonic acid, or sulphanilie t-'xL 
 C 6 H 4 (S0 3 H)'NH 2 , is obtained by heating aniline with twice its weight of fuming 
 sulphuric acid at 180 C. until S0 2 is given off. When the liquid is diluted, the 
 acid is precipitated. Sulphanilic acid is the parent substance of several dyes. 
 
 454. Alkylanilines. Aniline, being a primary amine, may be converted into 
 secondary and tertiary amines by action of iodides of other radicles. Thus, metlnjl- 
 aniline, C 6 H 5 'NHCH 3 , and dimethylaniline, C 6 H 5 N(CH 3 ) 2 , are obtained by the 
 action of methyl iodide on aniline, or by heating methyl alcohol with aniline 
 hydrochloride, in a closed vessel, at 250 C.. when the hydrochlorides of the 
 methyl bases, and water, are produced. Dimethylaniline is also prepared on a 
 large scale by the action of methyl chloride on a heated mixture of aniline and 
 caustic soda 
 
 2CH 3 C1 + C 6 H 5 NH 2 + 2NaOH = C 6 H 5 N(CH 3 ) 2 + 2NaCl + 2H 2 0. 
 They are liquids boiling at about 190 C., and used in the manufacture of certain 
 aniline dyes. Such alltylanilmes are more basic than aniline, and behave generally 
 like phenyl-substituted open-chain amines. The dialkylanilines, however, react 
 with nitrous acid, notwithstanding that they are tertiary amines (p. 660). The 
 products are iso-nitroso-derivatifes i.e., the NO group is attached directly to C ; 
 thus, isoniti'oso-dimethylaniline is C 6 H 4 (NO)'N(CH 3 ) 2 . 
 
 455. Diphenylamine, GT phenylaniline, NH(C 6 H 5 ) 2 , is a secondary amine obtained 
 by heating aniline hydrochloride with aniline at 250 C., in a closed vessel from 
 which the NH 3 is allowed to escape from time to time 
 
 C 6 H 5 -NH 2 HC1 + C 6 H B -NH 2 = NH(C 6 H 5 ) 2 + NH 3 -HC1 ; 
 
 the excess of aniline employed decomposes the NH 4 C1, so that a mixture of aniline 
 hydrochloride and diphenylamine is left ; on adding water, the latter is left undis- 
 solved. It is a crystalline solid, soluble in alcohol and ether, and having feeble 
 basic properties. It melts at 54 C. and boils at 310 C. When acted on by HN0 3t 
 
ANILINE-OIL, 66=; 
 
 ^ 
 
 three atoms of the phenyl hydrogen are exchanged for NO* producing kerauifn,- 
 diphcnylamine,im(CjBL@K)&)v an acid which combines with ammonia form in cr 
 N(NH 4 )(C 6 H 2 (N0 2 ) 3 ) 2 , an orange dye, aurantia. 
 
 Diphenylamine is used as a delicate test for nitrous acid, with which it gives a 
 deep blue colour in strong sulphuric acid. 
 
 The ammonia-hydrogen in aniline may be evolved by dissolving potassium in 
 the base, when NHK>C 6 H 5 and NK 2 C 6 H 5 are produced. By acting on the latter 
 with phenyl bromide (bromobenzene) the tertiary amine, triphenylamine, N(C fi H.) 
 is produced ; NK 2 C 6 H 5 + 2C 6 H 5 Br = N(C 6 H 5 ) 3 + 2 KBr. This compound is not basic 
 it is insoluble in water, but may be crystallised from ether. 
 
 456. The three toluidines, or amido-toluenes, C 6 H 4 CH 3 -NH,,, are 
 metameric with methyl-aniline and benzylamine. They are prepared 
 by reducing the nitrotoluenes, just as aniline is prepared from nitro- 
 benzene. Orthotoluidine resembles aniline; sp.gr. 1.003, and boiling- 
 point 197 C. It becomes pink in air. Chloride of lime gives it a 
 brown colour, which is changed to red by acids. Metatoluidine is a 
 liquid of sp. gr. 0.998, and boiling at 199 C. Paratoluidine, which 
 forms about 35 per cent, of commercial toluidine, is crystalline, fusing 
 at 45 C. and boiling at 198 C. It is sparingly soluble in water, and 
 is feebly alkaline ; alcohol and ether dissolve it. It is not coloured by 
 chloride of lime. Its basic properties are weak. Its oxalate is insoluble 
 in ether, which dissolves orthotoluidine oxalate. When methylaniline, 
 hydrochloride is heated to 350 0., it is converted into the isomeric 
 paratoluidine hydrochloride ; C 6 H 5 -NHCH S ,H01 = C 6 H 4 (CH 3 )'NH 2 ,HC1. 
 This migration of a group from a side-chain into the nucleus is frequently 
 noticed. 
 
 Commercial aniline-oil is never free from toluidine, so that it gives a brown 
 colour with chloride of lime, as well as the violet due to aniline. Ether extracts 
 the toluidine brown, which becomes pink by shaking the ethereal layer with acetic- 
 acid. Aniline-oil for Hue is approximately pure aniline ; aniline-oil for red contains 
 equimolecular proportions of aniline and orthotoluidine ; aniline-oil fur safranine 
 is a mixture of aniline and orthotoluidine recovered during the manufacture of 
 magenta. 
 
 Commercial toluidine is obtained by reducing the product obtained by nitrating 
 toluene (p. 650). and consists of ortho- and para-toluidine. The latter is the 
 stronger base of the two, so that when the mixture is partially saturated with H 2 S0 4 
 and distilled, it remains in the retort as sulphate. 
 
 457. Xylidines, C 6 H 3 (CH 3 ) a -NH 2 . These are six in number, and are metameric 
 with dimethylaniline. Commercial xylidine is chiefly amidoparaxijlen^ and is 
 prepared by heating dimethylaniline hydrochloride, when a change occurs 
 analogous to that involved in the conversion of methylaniline hydrochloride into 
 paratoluidine hydrochloride (r..) ; C 6 H 5 'N(CH 3 )2, HC1 = C 6 H 3 (CH 3 ) 2 'NH 2 , HC1. It 
 is used for making dyes. 
 
 Ben: ilia mine, C 6 H 5 'CH 2 NH , is produced by the action of benzyl chloride on Mi 3 
 in alcoholic solution ; C 6 H 5 'CH 2 C1 + NH 3 = C 6 H 5 'CH 2 NH 2 , HC1. By distilling the 
 hydrochloride with KOH, it is obtained as a colourless liquid, boiling at 187 . 
 metameric with toluidine, but is easily soluble in water, and is a strongly alkaline 
 base. lytieHzylam'tRe, (C 6 H 6 'CH a ) 2 NH, and tril>en;ylamine, (C 6 H 5 'CH 2 ) 3 N, are 
 formed in the same reaction as benzylamine. 
 
 a-Naphthylamine, or naphtkalid'me, C 10 H 7 ;NH2, or amido-naphttwlrne, prepar 
 from a-nitro-naphthalene like aniline from nitro-benzene, forms colourless needles, 
 smelling of mice ; m.-p. 50 C., b.-p. 300 C. It dissolves sparingly in water, but 
 easily in alcohol, and forms well-crystallised salts, which give, with ferric chloride, 
 a blue precipitate, changing to purple o-vynaphthi/lamine, C 10 H 9 NO. It i 
 obtained by heating aniline with pyromucic acid, C0 2 + H 2 being eliminated. 
 fl-naphthylamine gives no colour with ferric chloride. 
 
 458. Diamines. The commonest open-chain diamines are those 
 which are derived from ethylene. If ethylene diamine, C 2 H 4 (NH 2 ) 2 , be 
 
666 PTOMAINES. 
 
 regarded as glycol in which NH 2 is substituted for OH, it will be seen 
 that alcohol-amines, such as C 2 H 4 (OH)(NH 2 ), can exist ; these are 
 monamines, and have been called hydramines, or hydroxy amines. 
 Thus, C 2 H 4 (OH)(NH 2 ) is hydroxy-ethylamine. The diamines are diacid 
 bases, i.e., they are equivalent to 2NH 3 in their relation to acids. 
 
 Etijlene diamine, CH 2 NH 2 CH 2 NH 2 (b.-p. ii6C.). Ethylene bromide is heated 
 with an alcoholic solution of NH 3 at iooC. ; 2NH 3 + C 2 H 4 Br 2 = C 2 H 4 (NH 2 )2.2HBr. 
 The hydrobromides of d't ethylene diamine, N 2 H 2 (C 2 H 4 ) 2 " (b.-p. 145 C.), and tri- 
 etliylene diamine, N 2 (C 2 H 4 ) 3 " (b.-p. 210 C.), are produced at the same time. The 
 three diamines are liberated by KOH and fractionally distilled. 
 
 Ethylene diamine smells feebly of ammonia, but dissolves in water and is 
 alkaline. It is also formed by reducing cyanogen with HC1 + Sn ; CN -CN + H 8 = 
 CH 2 NH 2 'CH 2 NH 2 . Citrous acid converts it into ethylene oxide, though glycol 
 is probably first formed. 
 
 xCH9'CH 2 \ 
 
 Diet-hylene diamine has the structure NH\ >NH and is identical with 
 
 \prqr .p IT / 
 O1 2 O1 2 
 
 piperasine (see Pyrazine) which is used as a remedy for gout, since it readily dis- 
 solves uric acid. It melts at 104 C., and boils at 145 C. 
 
 Hydroxy-ethylamine, CH 2 OH'CH.,NH 2 , is obtained by the action of ammonia on 
 ethylene chlorhydrin; C 2 H 4 (OH)C1 + 2NH 3 =C 2 H 4 (OH)NH 2 + NH 4 C1. The secon- 
 dary monamine, dihydroxy-et-kylamine, (C 2 H 4 OH) 2 NH, is produced at the same time, 
 
 PTT 'PIT 
 and when this is dehydrated it yields -morpholine, O/ /NH, a base 
 
 Cxi2CH.2 
 closely allied to morphine. 
 
 Two important animal products have been shown to be ammonium 
 bases connected with the hydramines ; these are choline, which occurs 
 in bile, egg-yolk, and the brain ; and neurine, which is also obtained 
 from the brain. The latter is typical of the class of poisonous substances 
 resulting from decomposing animal matter, and known as ptomaines 
 (Trrw/za, a corpse) or toxines. 
 
 Clioline is kydroxyfltJiyl-trimffJtyl amntO'niuin hydroxide, Js(C 2 H 4 OH)(CH 3 ) 3 'OH, 
 and can be artificially prepared by heating ethylene chlorhydrin with trimethyl- 
 amine in aqueous solution. It is strongly alkaline and crystallises with difficulty ; 
 it is not poisonous, but when oxidised by nitric acid it yields muse-urine or 
 hydroxycholine, N[C 2 H 3 (OH) 2 ](CH 3 ) 3 'OH, which is a poisonous base found in the 
 toad-stool, Agaric-ids muscarius. 
 
 When treated with hydriodic acid, choline yields the iodine derivative 
 N(C 2 H 4 I)(CH 3 ) 3 'I, which with AgOH yields neurine or trimetliyl-'rinyl ammonium 
 hydroxide, N(C 2 H 3 )(CH 3 ) 3 'OH. This is strongly alkaline and poisonous, but has 
 not been crystallised ; it is a product of the putrefaction of many kinds of 
 animal matter. 
 
 Other ptomaines, beside neurine (from flesh) and muscarine (from fish), are 
 neuridine, C 5 H 14 N 3 (from flesh), gadinine, C 6 H 17 N0 2 (from fish), cadarerine, or 
 pentametliylene diamine, C 5 H 16 N 2 , putrescine or tetra-methylene diamine C 4 H 12 N 2 , 
 'inydine, C 8 H n NO, and mydato&ine, C 6 H 13 N0 2 . 
 
 '459. Diamido-benzenes, C 6 H 4 (NH 2 ) 2 , or phenylene diamines, X 2 H 4 (C 6 H 4 )", being 
 disubstituted benzenes, exist in three forms, which are obtainable by the reduction 
 of the corresponding dinitro-benzenes, or by distilling the three diamido-benzoic 
 acids, C 6 H 3 (NH 2 ) 2 'C0 2 H, with baryta. They are diacid bases. Metaphenylene 
 diamine melts at 63 C. and boils at 287 C. ; it is very soluble in water and gives 
 a yellow colour with nitrous acid ; it is used for the estimation of small quantities 
 of nitrites. Tri-, tetra-, an dpenta-amido-benze ties are also known. 
 
 Dlamido-naphthalenes, C 10 H 6 (NH 2 ) 2 , or naphthijlene diamines, corresponding with 
 phenylene diamine, are obtained by the reduction of dinitronaphthalenes. 
 
 460. Diamidodiphenyl, or benzidine, XH 2 'C 6 H 4 'C 6 H 4 > NH 2 , is produced by reducing 
 the corresponding dinitro-derivative. obtained by direct nitration of diphenyl 
 (P- 550) 5 ^ is also formed by the intramolecular change of hydrazo -benzene (q. /.), 
 i\ product of the reduction of azo-benzene. and is generally prepared on a large 
 
AMIDES, 66? 
 
 scale from this source. It crystallises in colourless plates, melts at i22C dig 
 solves in hot water, and sublimes. Its sulphate, C 12 H 8 (NH 2 ) 2 .H 2 S0 4 , is" very 
 sparingly soluble. It is the parent substance of many important dyes The two 
 NH 2 groups occupy the para-positions with regard to the link between 'the ohenvl 
 groups. 
 
 (~1 TT 
 
 Carbazole is imldlphenijl, - 6 4 ^NH; lit is formed by passing vapour of 
 
 C 6 H 4 
 
 diphenylamine through a red-hot tube (C 6 H 5 ) 2 NH = (C 6 H 4 ) 2 NH + H 2 (rf. diphenyl) 
 It is also obtained at the end of the distillation of coal-tar, and as a secondary 
 product in the preparation of aniline. It crystallises in plates (in.-p. 238 C 
 b.-p. 351 C.), sublimes easily, and dissolves in alcohol and in ether. 
 
 AMIDES AND AMIO ACIDS. 
 461. Amides are derived from NH 3 , by the substitution of a negative 
 
 or acid radicle for hydrogen ; thus, in acetamide, CH 3 C^ 2 the 
 
 radicle acetyl, CH 3 CO, has been substituted for one-third of the H in 
 NH 3 . The amides, like the amines (p. 638), may be primary, secondary, 
 or tertiary, accordingly as one, two, or three atoms of H in the NH 3 
 group have been exchanged, and they may be monamides, diamides, or 
 triamides, accordingly as they are formed upon the model of one, two, 
 or three ammonia molecules. 
 
 Amides may be formed from ammonia in the same manner as amines, 
 by the action of the chloride of an acid radicle, when the chlorine removes 
 the ammonia-hydrogen, CH 3 COC1 + 2 NH 3 = CH 3 CONH 2 + NH 3 HC1 
 (cf. p. 660), or by the action of an ethereal salt, when the hydrogen is 
 exchanged for the acid radicle, CH 3 CO'OC 2 H 5 + NH 3 = CH 3 CONH 2 + 
 C 2 H 3 'OH. Amides may also be formed by dehydrating the ammonium 
 salts of the acids, by heat or otherwise, when the ammonia-hydrogen 
 and the OH group of the acid form water, leaving the NH 2 group in 
 combination with the acid radicle, CH 3 CQ'ONH 4 = CH 3 CO'NH 2 + H 2 0. 
 This mode of formation explains the characteristic property of the 
 amides to be converted by hydrolysis into ammonia-salts, CH 3 CO'NH 2 + 
 
 If primary or secondary amines be substituted for ammonia, or amine 
 salts for ammonium salts, in the foregoing reactions, substituted amines, 
 such as ethylacetamide, CH 3 CO'NHC 2 H, and acetanilide, CH 3 CO'NHC 6 H 5 , 
 are formed. 
 
 Nitrous acid converts the primary amides into the corresponding 
 acids, CH 3 CONH 2 + HON : = CH 3 COOH + N 2 + HOH. Dehydra- 
 ting agents convert them into nitriles (cyanides) of hydrocarbon radicles ; 
 CH 3 CO-NH 2 = CH 3 'C : N + H 2 0. 
 
 The amides are distinctly basic, forming salts with acids, but far less 
 so than the amines owing to the acid radicles. Indeed, the amidogen H 
 has even an acid character, for it may be exchanged for metals. 
 
 Monamides. Formamide, HCONH 2 , obtained by distilling ammonium formate, 
 or by saturating ethyl formate with NH 3 and heating to 100, for two days, in a 
 sealed tube, is a liquid, boiling at 193 (1, with decomposition 2(HCO'NH.,) = 
 HoO + CO + NH a + HCN . Strong KOH converts it at once into potassium formate 
 
 Acetamide, CH 3 CO 
 of ammonium acetate 
 
 NH 2 , is prepared by the methods mentioned above. Instead 
 i, a mixture of NH 4 C1 with dry sodium acetate may be us.-d in 
 
668 SACCHARINE. 
 
 the third method. It crystallises in needles smelling of mice, fusing at 82 C. and 
 boiling at 222 C., soluble in water and alcohol, but sparingly in ether. It is a 
 weak base, forming unstable crystalline salts. Solution of acetamide dissolves 
 silver oxide, and deposits silver acetamide, C 2 H 3 O -NHAg. With mercuric oxide, 
 crystals of mercuric acetamide, (C 2 H 3 ONH) 2 Hg, are obtained. Boiling with water, 
 especially in the presence of acids or alkalies, converts acetamide into acetic acid 
 and ammonia. When distilled with powerful dehydrating agents, such as P 2 5 or 
 ZnCl 2 , it yields acetonitrile, or methyl cyanide, CH 3 'CN. 
 
 The three chloracetic acids yield corresponding amides monochlor acetamide, 
 WSL&Q&T&l^Awhl&ra*^^ 
 all crystalline solids with high boiling-points. 
 
 Acetanilide, CH 3 CO'NH(C 6 H 5 ) is prepared by boiling aniline with glacial acetic 
 acid ; it forms white prisms, soluble in hot water, melts at 112 C. and boils at 
 304 C. It is used as a febrifuge under the name of amtifebrlne. The methyl- 
 acetanilide. CH 3 CO.NCH 3 (C 6 H 5 ),is a remedy for headaches ; it is called ejcalgin and 
 melts at 102 C. 
 
 Di-acetamide, (CH 3 CO) 2 NH, is obtained by heating acetamide in HC1 gas ; 
 2CH 3 CO-NH 2 + HC1 = (CH 3 CO) 2 NH + NH 4 C1; or by acting on acetamide with 
 acetyl chloride; CH 3 CO'NH. 2 +CH 3 CO-C1 = (CH 3 CO) 2 NH + HC1. It is a feeble 
 acid and forms crystals soluble in water, melting at 77 C. and boiling at 223 O 
 
 Tri-acetamide, ( > O 2 H 8 0) 8 N is obtained by heating acetonitrile with acetic anhy- 
 dride to 200 C. ; CH 3 CN + (C 2 H 3 0) 2 = (C 2 H 3 0) 3 N. It maybe crystallised from 
 ether, and is neither basic nor acid. 
 
 The amides of the higher fatty acids are formed when their glyceryl salts, such 
 as palmitine, stearine. and oleine, are treated with strong ammonia. 
 
 Benzamide, C 6 H 5 CONH 2 , is precipitated when benzoyl chloride is treated with 
 NH 3 . It may be crystallised from hot water in plates, fuses at 130 C., and boils 
 at 288 C. It is soluble in alcohol and ether, and resembles acetamide in its 
 reactions ; it forms a crystalline compound with HC1, and its aqueous solution dis- 
 solves mercuric oxide, benzomercuramide, C 6 H 5 CONHg, being produced. 
 
 Glycolamide, CH 2 (OH)CONH 2 , from ethyl glycolate and NH 3 , crystallises in 
 needles (m.-p. 120 C.), dissolves in water, and is easily converted by alkalies and 
 acids into ammonia and glycollic acid. Glycolamide is also formed by heating 
 glycolide in ammonia gas 2NH 3 + (CH 2 'CO) 2 2 = 2CH 2 (OH)CO-NH 2 . 
 
 Lactamide, C 2 H 4 (OH)CO'NH 2 , from NH 3 and ethyl lactate or lactide, forms 
 crystals which fuse at 74 C. and volatilise unchanged. 
 
 462. Sulphonamides are amides from sulphcnic acids, e.g., C 6 H 5 'S0 2 NH 2 , 
 benezene sulponamide, and are prepared like the foregoing amides from the 
 corresponding sulphonic acid derivatives. The compound C 6 H 4 (C0 2 H) - S0 2 NH 2 , 
 i : 2-benzoic sulphonamide, is of some importance as the parent substance of 
 saccharine, the sugar-substitute made from toluene. Saccharine is i : 2-benzoic 
 
 / C0 \ 
 sulpho-imide, C 6 H 4 <^ /NH, also called benzoic sulphinide and 2-anhydro sulph- 
 
 S0 2 
 
 amine benzoic acid. By treating toluene with sulphuric acid it yields o- and p- 
 toluenesulphonic acids, CgH 4 (CH 3 )'S0 2 OH ; these are oxidised to the correspond- 
 ing benzoic sulphonic acids, C 6 H 4 (C0 2 H)'S0 2 OH, which by treatment with PC1 5 
 become the dichlorides, C 6 H 4 (COC1)'S0 2 C1. Ammonia converts the i : 4-derivative 
 into C 6 H 4 (CONH 2 )'S0 2 NH 2 , which is insoluble in water, and the I : 2-derivative 
 into C 6 H 4 (C0 2 NH 4 )-SO 2 NH 2 , which is soluble; when an acid is added to the 
 solution of the latter, saccharine is precipitated. It is said to be 500 times 
 sweeter than cane 'sugar ; it melts at 224 C. It is sparingly soluble in water, but 
 readily in alkalies since the H of the NH group is exchanged for metals to form 
 soluble salts. The sodium salt is the commercial saccharine. 
 
 463. Amidines. It is possible to represent the primary amides by two formula?, 
 
 OH 
 
 K'Cf and E'C^ ; the two amides corresponding with these formulae do 
 NH 2 , NH 
 
 not, however, appear to exist, except in the case of glycolamide. Many derivatives 
 of the amides exist in both forms ; thus, the ethyl acetamide described above is 
 CH 3 C(>NHC 2 H 5 , but the compound CH 3 C(NH)-OC 2 H 5 is also known, and is called 
 acetimidoether. By acting on acetamide with PC1 5 , acetamldo-chloride, CH 3 CC1 2 'NH 2 , 
 is obtained ; but this readily loses HC1, and passes into acetimido-chloride, 
 
UREA. 
 CH 3 C(NH);, a derivative of the second general formula given above, Cl having 
 
 x,NH 
 Amidines, R'C< , may be regarded as derived from either formula, 
 
 -tlo 
 
 although the fact that they are obtained by treating the imido-chlorides with 
 ammonia (or primary amines) seems to indicate that they are from the second 
 
 formula : R-C(NH)-C1 + NH 2 R = R-C(NH)-NHR + HC1. The amldoximet 
 
 NH., 
 
 may be regarded as derived from the arnidines ; they are the products of the 
 action of hydroxylamines on the cyanides (nitrilea) ; thus, hydrogen cyanide and 
 hydroxylamine yield isuret (methenyl-amidoxiine), isomeric with urea _ 
 HCN + NH 2 OH = HC(N-OH)-NH 2 . 
 
 464. Diamides. Ox-amide, CONH 2 'CONH 2 is best prepared by shaking ethyl 
 oxalate with solution of ammonia, when the mixture becomes hot and a white 
 crystalline precipitate of oxamide separates; (COOC 2 H 5 ) 2 + 2NH 3 = (CONHo) 2 + 
 2(HOC 2 Hg). If an alcoholic solution of ammonia be employed, or if ammonia gas 
 be passed into ethyl oxalate, only half the ethoxyl (OC 2 H 5 ) is exchanged for NH 2 , 
 and ethyl oxamate (jwa methane), COOC 2 H 5 'CONH 2 , is obtained. Oxamide is 
 scarcely dissolved by water, alcohol, or ether, and is a perfectly neutral body. It 
 may be crystallised in needles from a hot saturated solution of calcium chloride. 
 When heated, a part sublimes unchanged. A red-hot tube decomposes the vapour, 
 forming hydrocyanic acid and urea, 2(CONH 2 ) 2 = HCN + CO(NH 2 ) 2 + CO + C0 2 + NH 3 . 
 By hydrolysis it yields oxalic acid and NH 3 . 
 
 Oxamide is obtained by the distillation of ammonium oxalate, showing that the 
 ammonium salt of a dibasic acid yields a di-amide. Since it contains the elements 
 of cyanogen, it is not surprising to meet with oxamide in many reactions of 
 cyanogen compounds ; it can be formed by mixing aqueous solutions of hydro- 
 cyanic acid and hydrogen di-oxide ; 2HCN + H 2 2 = 2(CONH 2 ) 2 . The reaction of 
 aldehyde with solution of cyanogen also produces oxamide ; and it is found among 
 the products of the action of nitric acid on potassium ferrocyanide. The oxida- 
 tion of potassium cyanide with manganese dioxide and dilute sulphuric acid also 
 forms oxamide. 
 
 Dimethyl o.ramtde (CONHCH 3 ) 2 , SLnddi-ethyl oxamide (CONHC 2 H 5 ) 2 , are formed 
 by the action of inethylamine and ethylamine on ethyl oxalate. They crystallise 
 from hot water. By acting on diethyl oxamide with PC1 5 , a remarkable tertiary 
 amine has been obtained, called chloroxaletliyUne, and having the formula C 6 H 9 C1N 2 ; 
 it is an alkaline liquid, which boils at 217 C., and when acted on by hydriodic 
 acid and red phosphorus, it yields, on distillation with soda, another liquid base, 
 OJcaletlujliiie, C 6 H 10 N 2 , which is poisonous, and produces the same symptoms as 
 atropine, notably the dilatation of the pupil of the eye. 
 
 465. Suceitiainide, C 2 H 4 (CONH 2 ) 2 , produced like oxamide, crystallises in sparingly 
 soluble needles. At 200 C. it yields ammonia and xuccinimide ; C 2 H 4 (CONH 2 ) 2 = 
 NH 3 +r. 2 H 4 (CO). 2 NH. This body is also formed when ammonium succinate is 
 distilled. It is crystalline, and soluble in water and alcohol. By mixing the 
 hot alcoholic solution with a little ammonia and silver nitrate, silver succinimitlr, 
 C. 2 H 4 (CO). 2 NAg, is obtained in crystals. 
 
 The unifies, which contain the group NH (imidogen), exhibit an acid character, 
 allowing the H of this group to be exchanged for a metal. 
 
 466. Carbamide, or urea, CO(NH 2 ) 2 , is the diamide of carbonic 
 acid, CO(OH),, and is produced by heating NH 3 with ethyl carbonate at 
 !8o C. CO(OC 9 H,)o + 2NH 3 = CO(NHJ 9 + 2 HOC 2 H 5 ; by treating 
 NH 3 with car bony 1 "chloride (phosgene) COC1 2 + 4NH 3 = CO(NH 2 ) 3 + 
 2NH 4 C1 ; by heating oxamide with mercuric oxide (CON H,) 2 + HgO = 
 CO(NH,), + Hg + CO 2 ; or by heating a solution of CO in ammoniacal 
 cuprous" chloride CO + 2NH 3 + Cu 2 Cl' 2 = CO(NH 2 ) 2 + 2 HC1 + Cu. But 
 the best process for preparing it is to heat a solution of ammonium 
 isocyanate, NH 4 'NCO, which is metameric with urea CO : N'NH, = 
 CO(NH 2 ) 2 . (See below.) 
 
670 AETIFICIAL UEEA. 
 
 Urea is the chief form in which the nitrogen of the effete tissues is 
 excreted from the human organism, and it is present in urine to the 
 amount of about 1.4 per cent, by weight. 
 
 To extract it, the urine is filtered to separate mucus, evaporated to about an 
 eighth of its bulk, cooled and mixed with about an equal volume of strong HN0 3 , 
 which must be quite colourless, showing it to be free from nitrous acid, which 
 would decompose the urea ; the latter is precipitated in pearly scales of urea 
 nitrate, which is nearly insoluble in the acid, and sparingly soluble in water. This 
 is collected on a filter, washed with ice-cold water till the washings are but slightly 
 coloured, dissolved in boiling water, and mixed with precipitated BaC0 3 , rubbed 
 to a cream with water, as long as a fresh addition of the carbonate causes effer- 
 vescence 
 
 2(NoH 4 COHN0 3 ) + BaC0 3 = C0 2 + 2N 2 H 4 CO + H 2 + Ba(N0 3 ) 2 . 
 After filtering from the excess of BaCO 3 , the liquid is evaporated on a steam-bath, 
 when a mixture of urea and barium nitrate is obtained, from which the urea may 
 be extracted by strong alcohol, and crystallised by evaporation. 
 
 Artificial urea. The preparation of urea without having resource to 
 urine attracted much attention as one of the earliest examples of the 
 artificial formation of an animal product from mineral sources. The 
 original process (Liebig and Wohler) was the following : 56 parts of 
 well-dried potassium ferrocyanide, are mixed with 28 parts of dried 
 manganese dioxide, the mixture heated to dull redness in an iron dish, 
 and stirred until it ceases to smoulder. The cool residue is treated 
 with cold water, filtered, and the solution (of potassium (iso)cyanate) 
 decomposed with 41 parts of crystallised ammonium sulphate. It is 
 then evaporated to dryness on a steam-bath, and treated with strong 
 alcohol to extract the urea. 
 
 As a class experiment, a strong solution of potassium isocyanate may be mixed 
 with an equal volume of a strong solution of ammonium sulphate, and divided into 
 two parts, one of which is boiled for a minute, and cooled. If both portions be 
 now stirred with strong (colourless) nitric acid, the first will simply effervesce 
 violently, but the second will deposit abundant crystals of urea nitrate. 
 
 Urea crystallises in long prisms resembling nitre, which dissolve in 
 an equal weight of cold water, and in five parts of cold alcohol ; it 
 is almost insoluble in ether. When heated, urea fuses at 132 C., and 
 evolves much ammonia and some ammonium cyanate. If kept for 
 some time at 150 C., the bulk of it is converted into biuret, produced 
 from two molecules of urea by the loss of one molecule of ammonia ; 
 2CO(NH 2 ) 2 = NH 3 + NH(CONH 2 ) 2 . When the temperature is raised 
 to 170 C., the biuret again evolves ammonia, and is converted into 
 cyanuric acid ; 3 NH(CONH 2 ) 2 = 3 NH 3 + 2 (CNOH) 3 . 
 
 Urea is not alkaline, but, like many amides, it is a weak base, and, 
 though a diamide, forms salts like a monacid base ; these are acid to 
 litmus. The nitrate and oxalate are best known because they are 
 sparingly soluble, and are obtained as crystalline precipitates when 
 nitric and oxalic acids are stirred with solution of urea. 
 
 The nitrate, Avhen heated, evolves a very pungent smell, and is decomposed with 
 almost explosive violence at 150 C. Urea o-ralate crystallises with 2Aq ; 
 (N 2 H 4 CO) 2 .H 2 C 2 4 .2Aq. Urea hydrochloride, N 2 H 4 CO.HC1, is formed, with 
 evolution of heat, when HC1 gas acts on dry urea ; it solidifies to a crystalline 
 deliquescent mass, which is decomposed by water. 
 
 Urea, like many other amides, forms compounds with the oxides of silver and 
 mercury. The compound N 2 H 4 C0.3Ag 2 is obtained as a grey crystalline powder 
 when silver oxide is digested in solution of urea. When mercuric oxide is treated 
 in the same way the compound N 2 H 4 CO.HgO is formed ; on adding mercuric 
 
DERIVATIVES OF UREA. 671 
 
 chloride to a solution of urea mixed with potash, a white precipitate of 
 2X 2 H 4 C0.3HgO is obtained, but if mercuric nitrate be employed, the precipitate 
 is X 2 H 4 C0.2HgO. The formation of the last compound is the basis of Liebio-'s 
 method for the determination of urea. 
 
 Urea also forms compounds with certain salts : the compound X 2 H 4 CO.XaCl An 
 is obtained in crystals when urine is evaporated to a small bulk. When strong 
 solutions of urea and AgX0 3 are mixed, -crystals of X 2 H 4 CO.AgXO 3 are deposited 
 Bv mixing dilute solutions of urea and mercuric nitrate, a m-ecioitate i* forma 
 having the formula X 2 H 4 CO(HgO) 2 HX0 3 . 
 
 By hydrolysis urea yields ammonia and carbonic acid, hence its transformation 
 into ammonium carbonate when urine is allowed to putrefy. 
 
 Xitrous acid acts on urea, as on amides generally, converting the XH 2 into OH, 
 and liberating^ N, but ^the (HO) 2 CO formed is at once decomposed into H 2 and' 
 C0 2 ; (XH 2 ) 2 CO + 2HX0 2 X 4 +C0 2 + 3H 2 0. Hypochlorites and hypobromites 
 
 (prepared by dissolving Br in alkalies) also expel all the nitrogen as gas 
 
 (XH 2 ) 2 CO + 3XaOBr + 2XaOH = X 2 + 3H 2 + Xa^COs + 3XaBr. This method is 
 sometimes adopted for determining urea by measuring the nitrogen. The nitrogen 
 is also liberated when urea is boiled with potash and a large excess of potassium 
 permanganate, whereas, in most other amides, the bulk of the nitrogen is oxidised 
 to nitric acid. When chlorine is passed into fused urea, hydrochloric acid and 
 nitrogen are evolved, and the residue is a mixture of cyanuric acid with ammonium 
 chloride 3X. 2 H 4 CO + C1 3 = HC1 + X + (CX) 3 (HO) 3 + 2XH 4 C1. 
 
 By boiling" solution of urea with AgX0 3 , a crystalline precipitate of silver 
 isocyanate is obtained ; X 2 H 4 CO + AgX0 3 = XH 4 X0 3 + AgXCO. 
 
 Urea has been formed by passing XH 3 and CO 2 together through a red-hot 
 tube ; and by passing a mixture of benzene- vapour, ammonia and air over red-hot 
 platinum wire. 
 
 Although most of the derivatives of urea behave as though they were derived 
 from the formula CO(XH 2 ) 2 , there are certain compounds which appear to be 
 derivatives of a pseudourea of the form XH:C(XH 2 )(OH). 
 
 Biuret or alloplianamide, XH(COXH 2 ) 2 , is obtained by heating urea to 150 C.as 
 long as it evolves XH 3 freely, extracting the residue with cold water, which leaves 
 most of the cyunuric acid undissolved, precipitating the rest by lead acetate, 
 removing the lead by H 2 S, and evaporating the filtered solution, when the biuret 
 crystallises with iH 2 0. It is soluble in alcohol. Its alkaline aqueous solution 
 gives a fine violet colour with CuS0 4 . When heated in HC1 gas, biuret is con- 
 verted into guanidine hydrochloride ; XH( COXH 2 ) 2 + HC1 = C0 2 + C(XH)(XH 2 ) 2 .HC1. 
 Biuret is also obtained by heating ethyl allophanate with XH 3 . 
 
 Allophanic acid has not been obtained ; when liberated from its salts, it decom- 
 poses into C0 2 and urea ; XH 2 CO'XH'COOH = CO(XH 2 ) 2 + C0 2 . Ethyl allophanate 
 is formed when urea is acted on by ethyl chlorocarbonate (prepared by saturating 
 alcohol with carbonyl chloride) ; CO(XH 2 ) 2 + COCl-OC 2 H 5 = NH 2 CO-NH'COOC a H B + 
 HC1. It crystallises in prisms soluble in water and alcohol. 
 
 The hydrogen in urea, like that in other primary amides, may be exchanged for 
 radicles, forming so-called compound ureas. Those containing positive radicles, 
 such as methyl carbamide, CO(XH 2 )(XHCH 3 ), and dimethyl carbamide, CO(XHCH 3 ) 2 , 
 are derived' from the isocyanates of the amines, just as urea is derived from 
 ammonium isocyanate. Those containing acid radicles, such as acetyl carbamide 
 or acetyl urea, CO(XH2)(XHC 2 H 3 0), obtained by the action of acetyl chloride upon 
 urea, are called ureides. Di-acetyl carbamide is formed when acetamide is heated 
 
 to 50 C. with COC1 2 ; 2XH 2 C 2 H 3 + COC1 2 = CO(XHC 2 H 3 0) 2 + 2HC1. 
 
 The action of XH. ? on bromacetylurea, NH 2 -CO'XHCH 2 BrCO, produces hydanto>n, 
 which is a reduction-product of'alloxan (//.r.). The Br may be supposed to be 
 exchanged for OH by the action of the ammonia solution, but hydantom appears 
 to be an internal anhydride of the glycolylurea which would thus be formed, 
 XH. 2 -CO-XH-CH 2 OHCO giving NHCO'NH-CH 2 CO + H 2 0. 
 
 Carbanilide, or diphenyl vrea, (NHC 6 H 5 ) 2 CO, is prepared by heating urea with 
 aniline ; (NH,),CO + 2XH 2 C 6 H 5 = (XHC 6 H 5 ) 2 CO + 2NH 3 . It is slightly soluble in 
 water, more soluble in alcohol, melts at 235 C. and boils at 260' C. Carbanilide 
 is also formed when aniline is acted on by carbonyl chloride. 
 
 467. Thiocarbumide or sulpho-urea, CS(NH 2 ) 2 , is the amide of thiocarbomc acid, 
 CS(OH) 2 . It is obtained from ammonium (iso)thiocyanate, OS : N'NH 4 , just as 
 urea is obtained from the isocyanate. It crystallises easily from hot water, and 
 
672 AMIC ACIDS. 
 
 resembles urea in its chemical reactions ; it melts at 169 C. PbO abstracts sulphur 
 from it, converting it into cyanamide (</.v.). Its salts appear to be derived from 
 the tautomeric form NH : C(NH 2 )(SH). 
 
 T1iiocar~banHide, or dipheni/l sulphurea, is formed when aniline is heated with 
 carbon disulphide ; 2NH 2 C 6 H 5 + CS 2 ^CS(NHC 6 H 5 ). 2 + H 2 S. It forms colourless 
 crystals, insoluble in water, soluble in alcohol and ether, and melts at 154 C. 
 
 468. Amic Acids. If only one of the acid hydroxyl groups of a 
 dibasic acid is exchanged for NH 2 an amic acid, like succinamic acid, 
 C 2 H 4 (CONH 2 )(COOH), is obtained. These acids are primary amides, 
 and are generally obtained by heating the acid ammonium salts of the 
 dibasic acids, just as the normal salts yield the diamides. Or the acid 
 ethereal salts, like ethyl hydrogen oxalate, COOH-COOC 2 H 5 , may be 
 treated with NH 3 . 
 
 Oxamic acid, CONH 2 'COOH, is prepared by heating ammonium hydrogen 
 oxalate till it begins to give off C0 2 (see above). A mixture of oxamide and 
 oxamic acid is left, from which water extracts the acid. Ammonium oxamate is 
 formed when oxamide is boiled with solution of ammonia; (CONH 2 ) 2 + H 2 = 
 CONH 2 'COONH 4 . On adding HC1, the oxamic acid is obtained as a crystalline 
 precipitate, sparingly soluble in water, alcohol, and ether, and converted into 
 hydrogen ammonium oxalate by boiling with water. It fuses at 210 C., and de- 
 composes, yielding oxamide, formic acid, and water. Treated with PC1 5 , it yields 
 oxlmide (C0 2 ) : NH, a soluble neutral substance. 
 
 469. Carbamic acid, CO(NH,)OH, has not been obtained in the free 
 state, but ammonium carbamate is formed when ammonia combines 
 with C0 2 ; 2NH 3 + C0 2 = CO(NH 2 )(ONH 4 ). The ammonium salt is 
 best prepared by saturating absolute alcohol with dry ammonia gas, 
 and passing dry C0 2 into the solution, when the ammonium carbamate 
 crystallises. It is soluble in water, and is converted into ammonium 
 carbonate by boiling the solution ; CO(NH 2 )'ONH 4 + H 2 = CO(ONH 4 ) 2 . 
 Ammonium carbamate sublimes and dissociates below 100 C., and 
 when heated, in a sealed tube, to 135 C., yields urea and ammonium 
 carbonate ; 2 CO(NH 2 )'ONH 4 = CO(NH 2 ) 2 + CO(ONH 4 ) 2 . 
 
 When ammonium carbonate is distilled, part of it is converted into the car- 
 bamate ; CO(ONH 4 ) 2 =CO-NH 2 (ONHi) + H 2 0. This accounts for the presence of 
 ammonium carbamate in the commercial carbonate (p. 355). 
 
 Ethyl carbamate, wurethane, CO(NH 2 )OC 2 H 5 , is formed by the action of solution 
 of ammonia upon ethyl carbonate at 100 C. 
 
 CO(OC 2 H 5 ) 2 + NH 3 = CO(NH 2 )OC 2 H 5 -f HO'C 2 H 5 . 
 
 It forms tabular crystal's, soluble in water, alcohol, and ether, melts at 50 C., and 
 boils at 184 C. Boiled with potash, it yields the carbonate, alcohol, and ammonia ; 
 CO(NH 2 )OC 2 H 5 + 2KOH^CO(OK) 2 + NH 3 + HO-C 2 H 5 . Heated with ammonia, it 
 gives alcohol and urea ; CO(NH 2 )OC 2 H 5 + NH 3 = CO(NH 2 ) 2 + HO-C 2 H 5 . 
 
 Thiocarbamic acid, CS(NH 2 )SH, is obtained as an ammonium salt 
 by acting on carbon bisulphide with ammonia in alcoholic solution ; 
 2NH 3 + CS 2 = CS(NH 2 )SNH 4 , the reaction corresponding with that 
 between NH 3 and CO 2 . The ammonium thiocarbamate crystallises in 
 yellow prisms. When decomposed by HC1, it yields thiocarbamic acid 
 as a yellow unstable crystalline body, which decomposes spontaneously ; 
 CS(NH 2 )SH = H 2 S + HSON (thiocyanic acid). 
 
 470. Gruanidines. These compounds, which are of much importance 
 on account of their physiological significance, are amidines (p. 668) of 
 carbonic acid. Guanidine itself, the parent substance, is also called 
 imido-urea, since it may be regarded as containing an imodo-group in 
 the place of the oxygen of urea; thus, CO(NH,) 2 , urea ; C(NH)(NH f ) f 
 guanidine. The guanidines can be prepared synthetically by heating 
 
GUANIDINE. 673 
 
 the hydrochloride of an amine with cyanamide dissolved in alcohol 
 e.g., CN-NH 2 + NH 3 ,HC1 = C(NH)(NH 2 ) 2 ,HC1. 
 
 Guanidine, or carbon-diamide-imide, C(NH)(NH 2 ) 8 , occurs in vetch 
 seeds and sugar beet. It was so called because originally obtained by 
 the oxidising action of KC10 3 and HC1 on guanine, a feeble base 
 extracted from guano. It is prepared by heating ammonium thio- 
 cyanate in a retort at 190 C. for several hours. A portion of the 
 thiocyanate becomes thiocarbamide, which then reacts with the re- 
 maining ammonium thiocyanate yielding guanidine thiocyanate 
 CS(NH 2 ) 2 + NH 3 ,CNSH = C(NH)(NH 2 ) 2 ,CNSH + H 2 S. This is dissolved 
 in a little water mixed with half its weight of potassium carbonate, and 
 evaporated to dry ness, when a mixture of guanidine carbonate and 
 potassium thiocyanate is obtained. This is boiled with alcohol, which 
 dissolves the thiocyanate, and leaves guanidine carbonate (N 3 H 5 C) 2 .H 2 C0 3 , 
 which may be recrystallised from water. This is converted into 
 guanidine sulphate, (N 3 H 5 C) 2 .H 2 S0 4 , and decomposed by baryta-water ; 
 the filtrate from the BaS0 4 is evaporated over sulphuric acid, when 
 guanidine is obtained as a deliquescent crystalline substance, which is 
 strongly alkaline, and absorbs C0 2 from the air. It is a strong monacid 
 base, and yields well-crystallised salts. 
 
 Guanidine nitrate, N 3 H 5 C.HN0 3 , like urea nitrate, is sparingly soluble in water, 
 and crystallises in plates. Guanidine is soluble in alcohol. Its platinum salt, 
 (N 3 H 5 C.HCl) 2 PtCl 4 , is sparingly dissolved by absolute alcohol. When hydrolysed 
 with baryta-water, guanidine yields urea and ammonia; C(NH 2 ) 2 NH + H 2 = 
 (NfL>) 2 CO + NH. V Heated with strong potash, it gives potassium carbonate and 
 ammonia ; C(NH 2 ) 2 (NH)" + 2KOH + H 2 = C(OK) 2 + sNH 3 . Hot dilute H 2 S0 4 
 converts it into NH 3 and urea, which combine with the acid. 
 
 Guanidine hydriodide is obtained when cyanogen iodide is heated with alcoholic 
 ammonia in a sealed tube at 100 C. ; 
 
 I-CN + 2NH 3 = C(NH)(NH2) 2 .HI. 
 
 Xitroguanidine, C(NH)(NH 2 )(NHN0 2 ), is obtained by nitrating guanidine, and 
 yields ainidoguanidine, C(NH)(NH 2 )(NHNH 2 ), when reduced. This compound is 
 of interest as yielding hydrazine, NH 3 and C0 2 , when hydrolysed, Hydrazoic 
 acid (p. 107) may also be obtained from it by first treating it with nitrous acid 
 to form diazo-ffuanidine, C(NH)(NH 2 )(NHN : N-OH), and hydrolysing this. 
 "^Dlphenyl guanidine, or melaniline, C(NH'C 6 H 5 ) 2 NH, is a crystalline base pro- 
 duced by the action of cyanogen chloride on aniline 
 
 Cl-CN + 2NH 2 C 6 H 5 = C(NH-C 6 H 5 ) 2 NH.HC1. 
 
 AMIDO-ACIDS. 
 
 471. These may be prepared from the chloro-substituted acids by treat- 
 ment with ammonia ; thus amido-acetic acid results from the action of am- 
 monia on monochloracetic acid, CH 2 C1'C0 2 H + 2 NH 3 = CH 2 (NH 2 )-C0 2 H 
 + NH 3 .HC1 ; also by the reduction of the nitro-acids or the cyano-acids 
 by nascent hydrogen 
 
 CH 2 (N0 2 )'C0 2 H + H 6 = CH 2 (NH 2 )'C0 2 H + 2 H 2 0. 
 CH 2 (CN)-COOH + H 4 = CH 2 -CH 2 (NH 2 )-COOH. ^ 
 
 In the aromatic group the nitro-acids are reduced to obtain the amido- 
 acids. They are metameric with the amides of hydroxy-acids, but are 
 distinguished by their greater stability towards hydrolysing agents, the 
 amido-group being more firmly held and less easily evolved as NH 3 . 
 Like other ammonia derivatives they may be primary, secondary, 
 or tertiary, as NH 2 (CH 2 COOH), NH(CH 2 COOH) 2 , N(CH 2 COOH) 3 , 
 obtained from the mono- di- and tri-chloracetic acids respectively. J he 
 
 2 u 
 
674 GLYCOCINE. 
 
 open-chain derivatives may be a-, /3-, or y-amido-acids, like other 
 open-chain substituted acids.* 
 
 By action of nitrous acid the NH 2 group is converted into an OH 
 group, as in the case of the amines and amides, a hydroxy-acid being pro- 
 duced CH 2 (NH 2 )-C0 2 H + NOOH = CH 2 (OH)'C0 2 H + 1ST 2 + HOH. 
 But there is a tendency for the amido-acids to undergo the diazo-reaction 
 (p. 106). 
 
 When heated with baryta the amido-acids lose C0 2 and give the corre- 
 sponding amines - CH 2 NH 2 'COOH = CH 3 NH 2 + C0 2 . 
 
 Just as the a-hydroxy-acids form lactides by loss of water from both the COOH 
 and the OH groups (p. 603), so the amido-acids are converted by dehydrating 
 agents into anhydrides by loss of water from the NH 2 and COOH groups ; thus 
 
 OO*O FT 
 
 two mols. glycocoll, CH 2 NH 2 -COOH, yield NH/ 2 \NH. Further, the 
 
 X CH 2 'CO / 
 
 y- and S-amido-acids yield internal anhydrides, lactams, corresponding with the 
 lactones (p. 607) ; y-amidcbwtyric acid, CH 2 NH 2 -CH 2 -CH 2 -COOH, yields y-lnttyro- 
 lactam, CH 2 NH-CH 2 'CH 2 CO. 
 
 472. Amidoformic acid, NH 2 'C0 2 H, is identical with carbamic acid. 
 
 Glycocoll, glycocine, or gli/cine, is amido-acetic acid, CH 2 (N"H 9 )C0 9 H, 
 and is prepared by heating hippuric acid (benzoyl amido-acetic) for half 
 an hour with 4 parts of strong HC1, which converts it into benzoic acid 
 and glycocine hydrochloride 
 
 CH 2 (NHC 6 H 5 CO)-C0 2 H + HC1 +H 2 = C 8 H 5 C0 2 H + CH 2 (NH 2 )C0 2 H.HCL 
 Hippuric acid. Benzoic acid. Glycocine hydrochloride. 
 
 The solution is mixed with water and cooled, when most of the benzoic acid 
 crystallises out ; the nitrate is evaporated to dryness on a steam-bath, the glycocine 
 hydrochloride extracted by water, boiled with lead hydroxide, filtered from the 
 lead oxychloride, the dissolved lead precipitated by H 2 S, and the filtrate evaporated. 
 when it deposits the glycocine in transparent rhombic prisms, easily soluble in 
 water, sparingly in alcohol, and insoluble in ether. 
 
 Glycocoll has a sweet taste, fuses at 232 0., evolving ammonia and 
 methylamine. Its solution gives a red colour with Fe 2 Cl 6 , and a blue 
 with CuS0 4 ; if this blue solution be mixed with potash and alcohol, it 
 deposits blue needles of the formula (NH 2 'CH 2 'C0 2 ) 2 Cu.Aq. A sparingly 
 soluble silver salt, NH 2 'CH 2 C0 2 Ag, may also be obtained, but these 
 compounds do not behave like ordinary salts of the metals (cf. synthesis 
 of hippuric acid). Like other amido-acids, glycocine plays the part of 
 a base and an acid. It forms hydrochlorides containing, respectively, 
 one and two molecules of glycocine, and the latter forms a crystalline 
 platinum salt. Crystalline compounds of glycocine with salts are also 
 known. 
 
 From the behaviour of the metallic and other derivatives of glycocoll, 
 it appears probable that the constitution of this (and of other) amido- 
 acids is not that represented, but partakes of the nature of an intra- 
 
 molecular ammonia salt CH 2 <^ 
 
 Glycocoll can also be prepared by heating bromacetic acid with ammonia, and 
 by passing cyanogen into a boiling saturated aqueous solution of hydriodic acid 
 C 2 N 2 + 2lI 2 + 5HI = CH 2 (NH 2 )-C0 2 H + NH 4 I + I 4 . 
 
 * The prefixes amino-, imhto-, anilino-, &c., are now often substituted for aniido-, imido-. 
 anilido-, &c. 
 
HIPPUKIC ACID. 
 
 Both methods afford a means of synthesising glycocol, which derives its name from 
 the fact that it may be obtained by boiling glue (or gelatine) with dilute sulphuric 
 acid (sugar of gelatine ; y\vKvs, sweet ; xoXXa, give.) 
 
 Sbrcosine, or methyl glycocoll, CH 2 (NHCH 3 )-C0 2 H, may be obtained by heating 
 bromacetic acid with methylamine (in place of ammonia, which yields glycocine) 
 .t is also formed when the creatine extracted from flesh is boiled with baryta 
 Caffeine yields it under similar treatment. Sarcosine forms prismatic crystals 
 very soluble in water and of sweet taste. It is sparingly soluble in alcohol' 
 insoluble in ether, and may be sublimed. Its reaction is neutral, but it combines 
 with acids and bases. 
 
 Betaine, or tri-methyl-glycocoll, CH 2 [N(CH 3 ) 2 ]-C0 2 CH 3 , or more probably 
 
 is found in the juice of beet-root (Beta vulgaris), and may be formed synthetically 
 by the action of trimethylamine on chloracetic acid 
 
 CH 2 C1-C0 2 H + N(CH 3 ) 3 = CH 2 [N(CH 3 ) 2 ]-C0 2 CH 3 + HC1. 
 
 Betaine hydrochloride is also obtained by the careful oxidation of choline 
 hydrochloride 
 
 N(C 2 H 4 OH) (CH 3 VC1 + 2 = CH 2 [N(CH 3 ) 2 ] -C0 2 CH 3 ,HC1. + H 2 0. 
 Betaine is soluble in water and alcohol, arid forms salts with the acids. 
 
 Anilido-acetic acid or phenylglycocine, CH 2 (NHC 6 H 5 )-COOH, prepared from 
 bromacetic acid and aniline, melts at 127 C. It is important as the parent sub- 
 stance of artificial indigo. 
 
 Acetylglycocine, or aceturlc acid, CH 2 (NHCH 3 CO)'COOH, from acetyl chloride 
 and silver glycocine, melts at 206 C. 
 
 473. Hippuric acid, or benzoylglycocoll, or benzamidoacetic acid, 
 CH 2 (NHC 6 H 5 CO)'CO.,H, is prepared from the urine of horses or cows 
 (preferably the latter) by evaporating it to about an eighth of its bulk 
 and adding an excess of HC1. On standing, long prisms of hippuric 
 acid are deposited, which may be decolorised by dissolving in boiling 
 water and adding a little chlorine- water, when the colourless acid will 
 crystallise out on cooling. If the animal has undergone much exercise, 
 or the urine has decomposed, benzoic acid is obtained instead of 
 hippuric, and if a dose of benzoic acid is taken, it is found as hippuric 
 acid in human urine, which contains naturally but a minute pro- 
 portion. 
 
 It may be synthesised by heating benzoyl chloride with silver 
 glycocoll (of. salts of glycocoll, p. 674). 
 
 CH 2 (NH 2 VC0 2 Ag + C 6 H 5 COC1 = CH 2 (NHC 6 H 5 CO)'C0 2 H + AgCl ; 
 or benzamide with chloracetic acid 
 
 CH 2 C1-C0 2 H + C 6 H 5 CONH 2 = CH 2 (NHC 6 H 5 CO)'C0 2 H + HC1. 
 
 Hippuric acid crystallises in rhombic prisms, sparingly soluble in cold 
 water, soluble in hot water and in alcohol, but insoluble in ether, which 
 distinguishes it from benzoic acid. Like benzoic, it dissolves easily^ in 
 ammonia, and is precipitated, in feathery crystals, by hydrochloric acid ; 
 but these are not dissolved on adding ether. 
 
 The more complex character of hippuric acid is shown by the action of heat ; 
 for, whereas benzoic acid sublimes without decomposition, hippuric assumes a red 
 colour, gives a small sublimate of benzoic acid and evolves hydrocyanic acid, 
 benzamide, C 6 H 5 CONH 2 , and benzonitrile, or pttenyl cyanide, C 6 H 5 'CN, whicl 
 smells of bitter almonds. 
 
 The hippurate* resemble the benzoates ; in solution, they give a butt precipiti 
 with ferric chloride. 
 
 474. Glycocoll may be regarded as the parent substance of two 
 physiologically important compounds, creatine and creatinine. 
 
676 CREATINE AND CREATININE. 
 
 When solutions of cyanamide and glycocoll are mixed, glycocyamine, or guanl- 
 doacetic acid, CH 2 [C(:NH)(NH 2 )(NH)] C0 2 H, is formed. If glycocoll be regarded 
 as an amine, NH 2 (CH 2 'C0. 2 H),then the formation of glycocyamine is only in accord 
 with the general method for producing guanidines (p. 672). When glycocyamine 
 hydrochloride is heated at 160 C. it becomes glycocyamidiiie hydrochloride by loss 
 of water 
 
 + H 2 0. 
 NHCH 2 
 
 Creatine and creatinine are methylglycocyamine and methylglycocyarnidine 
 respectively. 
 
 Creatine, or methylglycocyamine (/cpe'ay, flesh), C 4 H 9 N 3 2 , or 
 
 /NH, 
 
 NH : C\ , is obtained from chopped flesh by soaking 
 
 X N(CH 3 )-CH 2 -C0 2 H 
 
 it in cold water, squeezing it in a cloth, heating the liquid till the 
 albumin coagulates, straining, adding baryta to precipitate phosphoric 
 acid, and evaporating the filtrate to a syrup on the steam-bath ; on 
 standing for some hours the creatine crystallises out. 
 
 It may also be prepared from Liebig's extract of meat by dissolving it in 20 parts 
 of water, adding tribasic lead acetate, filtering, removing the excess of lead by 
 H 2 S, and evaporating to crystallisation. Granular crystals of creatine are some- 
 times met with in Liebig's extract. The flesh of fowls yields 0.32 per cent, of 
 creatine, that of cod-fish 0.17, beef 0.07 per cent. 
 
 Creatine forms prismatic crystals (with iH 2 0) easily soluble in hot 
 water, but very sparingly in alcohol and ether. It is neutral in reaction, 
 but behaves as a feeble monacid base. Creatine nitrate, C 4 H 9 N 3 2 .HNO 3 , 
 crystallises in prisms. When the solutions of its salts are heated above 
 30 C., they are converted into salts of creatinine, a stronger base con- 
 taining H, and O less than creatine. When boiled with baryta water, 
 creatine is hydrolysed to sarcosine and urea 
 
 CH 2 [C(:NH)(NH 2 )(NCH 3 )]-C0 2 H + H 2 = CO(NH 2 ) 2 + CH 2 NH(CH 3 )'C0 2 H. 
 
 Creatine has been prepared synthetically by heating cyanamide with an 
 alcoholic solution of sarcosine or methyl glycocoll, thus settling its constitution. 
 When it is warmed with solution of sodium hypobromite, two-thirds of its nitrogen 
 is liberated. By heating creatine in aqueous solution with mercuric oxide, it is 
 converted into oxalic acid and methyl-guanidine, C(NH)(NH 2 )(NHCH 3 ). 
 
 Creatinine, or methylglycocyamidine, 4 H 7 N 3 0, or 
 
 /NH - -CO 
 
 NH : C<f , is prepared by heating creatine in a water-bath 
 
 and passing a current of pure HC1 over it as long as any water is 
 formed. The hydrochloride thus obtained is dissolved in water, decom- 
 posed by lead hydroxide, the solution filtered and slowly evaporated, 
 when it deposits prismatic crystals of C 4 H 7 N 3 0.2Aq, which lose water 
 on exposure to air, becoming opaque. If it be dissolved in cold water, 
 and evaporated in vacua, the original hyclrated crystals are reproduced, 
 but if it be dissolved in boiling water and the solution evaporated, it 
 deposits tabular crystals which contain no water. The solution of these 
 crystals when kept for some time at 60 C. deposits the prismatic 
 hydrated creatinine. 
 
 Creatinine is much more soluble in water than creatine is, requiring 
 about 1 2 parts of cold water. It dissolves in about i oo parts of cold 
 alcohol. It has an alkaline reaction, and is a strong monacid base. It 
 
LEUCINE. 
 
 is characterised by forming a sparingly soluble crystalline compound 
 with zinc chloride, (C 4 H 7 N 3 0) 2 ZnCl 2 . In contact with water, especially 
 in presence of bases, creatmine is converted into creatine by hydration. 
 
 Creatinine does not appear to exist as such in flesh, though it is easily produced 
 from it by the dehydration of the creatine. A substance having the same composi- 
 tion as creatinine exists in considerable quantity <in urine (about two grams in 
 the urine of twenty-four hours), but its properties are not quite the same as those 
 of the creatinine prepared from the creatine of flesh. In order to prepare urinary 
 creatinine, the urine is mixed with one-twentieth of its volume of a cold saturated 
 solution of sodium acetate, and with one-fourth of its volume of a cold saturated 
 solution of mercuric chloride ; this produces an amorphous precipitate which is 
 quickly filtered off, and the filtrate is set aside for forty>eight hours, when it 
 deposits a granular precipitate, appearing in spheres under the microscope. This 
 precipitate is suspended in cold water, and decomposed by H 2 S, the mercuric sul- 
 phide is filtered off, and the acid filtrate evaporated over sulphuric acid, when it 
 leaves crystals of the hydrochloride, C 4 H 7 N 3 O.HC1. The concentrated aqueous 
 solution of this salt is decomposed, in the cold, with lead hydrate, when an alkaline 
 filtrate is obtained, which has a bitter taste, and, by spontaneous evaporation, 
 yields prismatic crystals of C 4 H 7 N 3 0.2H 2 0, which rapidly become opaque and 
 anhydrous when exposed to air. If heat be employed during the preparation of 
 the body, tabular crystals of C 4 H 7 N 3 are obtained, which are unchanged by 
 exposure to air. The urinary creatinine requires 362 parts of cold alcohol to dis- 
 solve it, while flesh-creatinine requires only 102 parts. It is a more powerful 
 reducing-agent than creatinine prepared from flesh-creatine. 
 
 475. Propionic acid can give rise to two substituted acids (cf, p. 580), conse- 
 quently there are two amido-prdpionic acids. The a-acid is called alanine, 
 
 CH 3 -CH(NH 2 )-C0 2 H, 
 
 prepared by the action of ammonia on a-chloropropionic acid. It dissolves in 
 water and becomes ethylidene lactic acid when treated with nitrous acid. 
 Hutalanine, which occurs in the pancreas of the ox is a-afnido-isovaleric acid, 
 (CH 8 ) 2 : CH'CH(NH 2 )-C0 2 H. 
 
 476. Leucine, or a-amido-caproic cwid, CH 3 -[CH 2 ] 3 > CH(NH 2 ) < C0 2 H, 
 is prepared by boiling horn shavings (one part) with sulphuric acid 
 (2^ parts) and water (6J parts) in a reflux apparatus, for twenty-four 
 hours. The hot liquid is neutralised by lime, filtered, and evaporated 
 to about one- third ; it is then carefully neutralised with H 2 S0 4 and 
 evaporated till crystals of leucine and tyrosine are deposited on cooling; 
 by recrystallisation from water the tyrosine crystallises first. 
 
 Several other animal substances yield leucine and tyrosine when boiled with 
 dilute sulphuric acid, or fused with potash. The elastlne composing the cervical 
 ligament of the ox yields more than horn. Leucine also occurs extensively in 
 animals and vegetables. It is found in the liver, spleen, lungs, and pancreas ; also 
 in caterpillars and spiders ; in the white sprouts of vetch, in yeast, and in putre- 
 fying cheese. 
 
 Leucine crystallises in pearly scales, moderately soluble in water, 
 slightly in alcohol, and insoluble in ether. It fuses at 170 C., and may 
 be partly sublimed, though much of it decomposes, yielding amylamine ; 
 C 5 H 10 (NH 9 )-C0 9 H = NH 9 -C 5 H U + C0 2 . Its reaction is neutral, but it 
 forms compounds both with acids and bases. Hydriodic acid converts 
 it into caproic acid and ammonia 
 
 C 5 H 10 (NH2)-C0 2 H + 2HI = C B H u -CO a H + NH 3 + I 2 . 
 With nitrous acid it yields leucic or hydroxy -caproic acid 
 
 C 5 H 10 (NH 2 )'C0 2 H + HN0 2 = C 5 H 10 (OH)'C0 2 H + N 2 + H 2 0. 
 
6/8 TYEOSINE. 
 
 Leucine is obtained synthetically from ammonia and bromocaproic 
 acid; NH 3 + C 5 H 10 BrC6 2 H = C 3 H 10 (NH 2 )-C0 2 H + HBr ; also by the 
 reaction between valeraldehyde-ammonia, HCN,HC1 and H 2 0. 
 
 C 5 H 10 0'NH 3 + HCN + HC1 + H 2 = C 3 H 10 (NH 2 )-CO a H + NH 3 HC1. 
 
 The leucine from plants appears to differ from that from animals, 
 being optically active and existing in the usual three modifications 
 (p. 604). 
 
 Tyrosine (rvpds, cheese) or ^-hydroxy-phenyl-amido-propionic acid 
 
 CH 2 (C 6 H 4 OH)-CH(NH 2 )-C0 2 H, 
 
 is obtained, together with leucine, when albuminoid or gelatinoid bodies 
 are boiled with dilute sulphuric acid or fused with potash. It crystal- 
 lises in needles, which are sparingly soluble, even in hot water, sparingly 
 soluble in alcohol, and insoluble in ether. It melts at 235 C., and is 
 laevo-rotatory. Like leucine, it behaves both as a feeble acid and a 
 feeble base. When its aqueous solution is boiled with mercuric nitrate 
 it gives a yellow precipitate, which becomes red when boiled with nitric 
 acid containing nitrous acid. With chlorine, it yields chloranil, 6 C1 4 2 , 
 and with fused potash, NH 3 , and potassium parahydroxy-benzoate and 
 acetate ; 
 C 6 H 4 OH-C 2 H 3 NH 2 -C0 2 H + 2KOH = NH 3 + C 6 H 4 OH'C0 2 K + CH 3 -C0 2 K + H 2 . 
 
 477. Amido-succinamic acid, CH 2 CONH 2 'CHNH 2 C0 2 H, or asparagine, is found 
 in the shoots of asparagus and of other plants grown in the dark. It is of very 
 frequent occurrence in plants, being found in marsh-mallow, vetches, peas, beans, 
 mangold-wurzel, lettuces, potatoes, chestnuts, and dahlia roots. It may be ex- 
 tracted from the expressed juices of the plants by boiling to coagulate the albumin, 
 filtering, and evaporating to a syrup, when the asparagine crystallises, on standing, 
 in rhombic prisms (with iH 2 0) which may be recrystallised from boiling water. 
 It is nearly insoluble in alcohol and ether. It behaves as a weak acid and a weak 
 base. By ferments, asparagine is converted into ammonium succinate ; by nitrous 
 acid into malic acid 
 
 . C 2 H 3 NH 2 (CO-NH 2 )(CO-OH) + 2HX0 2 = C 2 H 3 OH(CO'OH)(CO-OH) + N 4 + 2H 2 0. 
 From this reaction it was formally inferred that asparagine was the amide of 
 malic acid, with which, however, it is only isomeric. Ordinary asparagine is 
 laevo-rotatory ; the dextro-form has been found in the mother-liquor from crude 
 asparagine, and is much sweeter than ordinary asparagine. A solution of the two 
 in equal proportions is inactive, but the asparagines are deposited from it in 
 crystals, which are, respectively, right- and left-handed. The isomeric derivatives 
 from each kind retain the optical properties of their source. When asparagine is 
 boiled with acids or alkalies, it is converted into l-am'idosucclnlc or aspartie acid 
 
 C 2 H 3 NH 2 (CO-NH 2 )(CO-OH) + H 2 = C 2 H 3 NH 2 (CO'OH)(CO-OH) + NH 3 . 
 Aspartie acid is sparingly soluble in cold water and alcohol, but may be crystal- 
 lised from hot water. Nitrous acid substitutes OH for the NH 2 in aspartie acid, 
 converting.it into malic acid. Aspartie acid is found in the molasses from beet- 
 root juice, and occurs among the products of the action of sulphuric acid and of 
 zinc chloride upon albuminous substances. 
 
 478. Amidobenzoic acids, C 6 H 4 (NH 2 )-C0 2 H. Of these the I : 2-acid or anthranilic 
 acid is of importance, being an oxidation product of indigo. It is prepared by 
 reducing I : 2-nitrobenzoic acid ; it sublimes in needles, melts at 145 C. and dis- 
 solves in hot water ; the solution tastes sweet and fluoresces blue. 
 
 Methyl anthranilate (m.-p. 25'5 C.) in dilute solution smells of orange-blossom 
 oil (iieroli oil'), of which it is a constituent. 
 
 /COv 
 
 The internal anhydride or lactam, anthranil, C 6 H 4 <^ \ might be expected to 
 
 be formed by dehydration of anthranilic acid, this being a i : 2-derivative (cf. p. 674) ; 
 it cannot be so obtained, however, but is a product of the reduction of i : 2-nitro- 
 benzaldehyde. It dissolves in alkalies to form salts of anthranilic acid. By 
 
TAURINE. 679 
 
 treating it, or anthranilic acid, with COC1 2 , isatoic anhydride, C 6 H 4 / C '? 
 
 NH'CO' ' 
 
 oxidation-product of indigo, is obtained. 
 
 Amidophenylacetic acids, C 6 H 4 (NH. 2 )-CH.,COoH, are obtained by reducing the 
 corresponding nitre-acids, but only the -HI- and j>- acids are known in the free 
 
 pTT 
 
 .state ; attempts to prepare the I : 2-acid produce oxindol, C 6 H,/ ^CO, which 
 
 X NH X 
 
 is an internal anhydride or lactam of the acid (p. 674). The same .happens in the 
 case of i : 2-emidopkettylglyv&ylic acid or isatic acid, C 6 H 4 (NH2)-CO-C0 2 H, a 
 
 CO 
 
 ketonic acid ; in this case the anhydride is a lactim, isatin, C 6 H 4 / \OOH. 
 
 These compounds are closely related to indigo and will receive further attention in 
 connection with that substance. 
 
 479. Amidosulphonic Acids. Taurine, amido-ethyl-sulphonic acid, 
 or amido-isethionic acid, C 2 H 4 (NH 2 )S0 3 H, is a decomposition-product of 
 taurocholic acid (q.v.) and is prepared by boiling ox-gall with dilute 
 HC1, evaporating to dryness on the steam-bath, and treating the residue 
 with absolute alcohol, which leaves the taurine undissolved. This is 
 dissolved in water, from which it crystallises in large four-sided prisms 
 sparingly soluble in cold water, and insoluble in alcohol and ether. It 
 fuses at 240 C. and is decomposed. It has no acid reaction, but it 
 forms salts with bases. When fused with KOH, it yields the acetate 
 and sulphite of potassium 
 
 C 2 H 4 (NH 2 )-S0 3 H + sKOH = CH 3 'COOK + K 2 S0 3 + NH 3 + H 2 + H 2 . 
 Nitrous acid substitutes OH for the NH 2 , producing isethionic acid. 
 
 Synthesis of taurine : C 2 H 4 is absorbed by S0 3 , the product dissolved in water, 
 neutralised with NH 3 , and evaporated to crystallisation ; C 2 H 4 +S0 3 + H 2 + NH 3 = 
 CoH 4 OH-SO.}NH 4 (ammonium isethionate). When this is heated to 220 C., it yields 
 taurine C 2 H 4 OH -S0 3 NH 4 = C 2 H 4 NH 2 .S0 3 H + H 2 0. 
 
 Taurine may also be synthesised by converting ethene into glycol-chlorhydrin, 
 HO'CoH 4 -Cl, heating this with K 2 S0 3 to obtain potassi umisethionate 
 
 HO-C 2 H 4 -C1 + K 2 S0 3 = HO-C 2 H 4 -S0 3 K + KC1 ; 
 distilling the isethionate with phosphoric chloride 
 
 HO-C 2 H 4 'S0 3 K + PC1 5 = P0 2 C1 + HC1 + KC1 + Cl'C a H 4 -S0 2 Cl (isethionic chloride] ; 
 heating this with water 
 
 C1'C 2 H 4 -S0 2 C1 + HOH = HC1 + C1-C 2 H 4 -S0 2 'OH (chlor-etlbtjlsul^honic acid) ; 
 and heating this to 100 C. with ammonia in a sealed tube 
 
 C1'C 2 H 4 -S0 2 -OH + 2NH 3 = NH 3 HC1 + NH 2 -C 2 H 4 -S0 2 'OH (taurine}. 
 
 Some taurine exists as such in the bile ; it has been found in the kidneys, lungs, 
 and muscles. When solution of taurine is evaporated with potassium cyanate, it 
 yields potassium tauro-carbamate, NH 2 CONH-CH 2 'CH 2 S0 3 K ; tauro-carbamic a. 
 is found in the urine when taurine is taken internally ; it forms crystj 
 .soluble in water. 
 
 Amidobenzemsulphoriic acid (see p. 664). 
 
 DlAZO- AND AZO-COMPOUNDS. 
 
 480. Diazo- Compounds. It has been already noticed that the amines 
 of open-chain hydrocarbons show no tendency to undergo the diazo- 
 reaction described on p. 106, whereas the amines of closed-chain nydi 
 carbons" readily do so at low temperatures. It thus happens that 
 diazo-compounds of the type R'N : N'X, where R is a positive and X a 
 
680 DIAZO-COMPOUNDS. 
 
 negative radicle, are only known when R is a radicle containing a ben- 
 zene ring. 
 
 There is, however, a tendency for the amido-acids of the open-chain series to 
 undergo the diazo-reaction, although the diazo-acids produced appear to be 
 differently constructed from the true diazo-coinpounds, and have only been 
 isolated as ethereal salts or as amides. 
 
 Diazoacetic acid, \CH'C0 2 H, has not been isolated, but ethyl diazoacetate, 
 
 N 2 CH-C0 2 C 2 H 5 , is precipitated as a yellow oil when the hydrochloride of ethyl 
 amidoacetate (ethyl glycocoll) is dissolved in a little water and treated with 
 sodium nitrite ; it boils at 143 C. and is decomposed by acids with evolution of 
 nitrogen, which becomes explosively rapid if the acid be strong ; it reduces hot 
 Fehling's solution (p. 619). When it is slowly dissolved in strong ammonia it is 
 converted into diazoacetamide, N 2 CH - CONH 2 , which is soluble in water and forms 
 crystals : it detonates when suddenly heated. When attacked by halogens ethyl 
 diazoacetate exchanges its nitrogen for two atoms of halogen ; this indicates that 
 its constitution differs from that of diazobenzene, for instance. 
 
 By reduction, ethyl diazoacetate yields NH 3 and glycocoll, but an intermediate 
 product is a salt of hydraziacetic acid which yields a hydrazine salt and glyoxylic 
 acid when treated with an acid. 
 
 Strong NaOH saponifies and polymerises ethyl diazoacetate yielding the sodium 
 
 salt of lisdiazoacetic acid, COoH'CH/ \CH'COoH, formerly called triazoacetic 
 
 X N :W 
 
 acid. The acid crystallises in orange red tables (with 2H 2 0) and gives a charac- 
 teristic red colour with nitric acid. When heated with dilute acids it is hydrolysed 
 to oxalic acid and hydrazine ; 
 
 C0 2 H-CH[N 4 ]CH-C0 2 H + 2 H 2 S0 4 + 4 H 2 = 2(N 2 H 4 ,H 2 S0 4 ) + 2(COOH) 2 . 
 
 N x 
 
 Diazomethane^ ^>CH 2 , is obtained by treating various nitroso-derivatives of 
 
 methylamine such B& nitrosomethylurethane, with alkalies : CO(NCH 3 -NO)OC 2 H 5 4- 
 NaOH = CH 2 N 2 + H 2 + CO(ONa)(OC 2 H 5 ). When solutions of KCN and KHSO a 
 are mixed and allowed to remain for some days, potassium amidomethane-disul- 
 phonate, (S0 3 K) 2 : CHNH 2 , crystallises. If the mixture is warmed and then acidified 
 the corresponding hydrogen potassium salt, (S0 3 K)(S0 3 H) : CHNH 2 , is obtained ; 
 this yields, when treated with KN0 2 , potassium diazometh'ane disulphonate, 
 
 /N 
 (S0 3 K) 2 C^.., the best source of hydrazine (p. 106). Diazomethane is a yellow, 
 
 odourless, poisonous gas, yielding methylhydrazine when reduced. Diazoetbane 
 has also been prepared. 
 
 At moderately high temperatures the aromatic amines react with 
 nitrous acid just as the fatty amines do, the NH 3 being exchanged for 
 OH ; C 6 H 5 NH 2 + ON'OH = C 6 H 5 OH + N 2 + HOH. But at low temper- 
 atures, particularly when a salt of the aniine is employed, the diazo- 
 compound is formed as an intermediate product 
 
 C 6 H 5 -NH 2 ,HN0 3 + ON'OH = C 6 H 5 'N : N'N0 3 + 2HOH. 
 Aniline nitrate. Diazobenzene 
 
 nitrate. 
 
 The salts of diazo-compounds are usually prepared in aqueous solution, 
 since they are only used as transition-products in the preparation of 
 other compounds (v.i.), or for the production of azo-compounds. The 
 amido-compound (amine) is dissolved in a dilute acid, the solution cooled 
 in ice, and the calculated quantity of sodium nitrite added. 
 
 For preparing the crystalline salts, arnyl nitrite is the best nitrite and the 
 reaction should be effected in absolute alcohol ; the amine and the amyl nitrite 
 
 
REACTIONS OF DIAZO-COMPOUNDS, 68 1 
 
 are dissolved in the alcohol, and an acid is added to the cooled solution ; after a 
 few minutes the diazo-salt crystallises and may be washed with alcohol and ether 
 C 6 H 5 -NH 2 ,HC1 + C 5 H n N0 2 - C 6 H 5 'N :NC1 + C 5 H n 'OH + HOH. 
 
 Diazobenzene nitrate is best prepared by passing N 2 3 (p. 98) into a thin paste 
 of aniline nitrate and water, cooled by ice and salt, until KOH no longer precipi- 
 tates aniline. A brown product is filtered off, and alcohol added to the filtrate 
 when the nitrate separates in colourless needles. These are soluble in water' 
 but insoluble in ether and sparingly soluble in alcohol. At 90 C., or when struck 
 it detonates with extreme violence. 
 
 By decomposing diazobenzene nitrate with potash, the compound C 6 H 5 N 2 'OK, 
 diazobenzene pctassoxide, is obtained, in which the potassium may be exchanged for 
 other metals, producing unstable and sometimes explosive compounds. By acting 
 on the potassium compound with acetic acid, dlazobenzene hydroxide, C^jNyOH, 
 is obtained as a very unstable liquid. 
 
 Dlazobenzene butyrate is said to be identical in chemical behaviour and physio- 
 logical effect, with tyrotoxicon, a poison which has been isolated from decom- 
 posing milk. 
 
 The diazo-bases, e.g., C 6 H 5 'N : N'OH, have never been isolated owing 
 to their instability. 
 
 The value of the diazo-compounds in effecting chemical syntheses will 
 be appreciated from the following typical reactions when it is re- 
 membered that the conversion of an aromatic hydrocarbon into a 
 nitro-derivative, this into an amido-derivative, and the amido- into a 
 diazo-derivative (diazotising), is easily performed. 
 
 (1) For the diazo-group may be substituted a hydroxyl group by 
 warming the compound with water, a phenol being produced ; 
 
 C 6 H 5 -N : N-C1 + HOH = C 6 H 5 'OH + N 2 +HC1. 
 
 (2) The diazo-group may be exchanged for a halogen or cyanogen, 
 producing a halogen substituted hydrocarbon or a cyanide. This is best 
 effected by warming the diazo-compound with the corresponding cuprous 
 salt (Sandmeyer's reaction). The cuprous salt forms a double compound 
 with the diazo-salt which decomposes with the re-formation of the 
 cuprous salt ; C 6 H 5 'N : NCl,Cu 2 Cl 2 = C 6 H 5 'C1 + N 2 + Cu 2 Cl 2 . 
 
 The cuprous salt need not be pre-formed ; thus, to produce cyanobenzene 
 (phenyl cyanide, C 6 H 5 CN), diazobenzene chloride may be treated with a mixture of 
 copper sulphate and potassium cyanide (potential cuprous cyanide, p. 675). 
 Similarly, nitre-benzene may be formed when the diazobenzene chloride is treated 
 with KX0 2 and freshly precipitated Cu 2 (potential cuprous nitrite). Finely 
 divided metallic copper will frequently cause the separation of nitrogen and the 
 attachment of the acid radicle to the benzene nucleus in a diazo-salt. 
 
 The cyanides can be converted into acids by hydrolysis (p. 587), so 
 that acids may be synthesised through Sandmeyer's reaction. 
 
 (3) For the diazo-group hydrogen may be substituted, the hydro- 
 carbon being formed, by boiling the compound with alcohol 
 
 C 6 H 5 -N : XC1 + C 2 H 5 OH = C 6 H 5 'H + N 2 + HC1 + CH 3 'CHO. 
 
 The above reactions conclusively show that diazobenzene-compounds 
 must contain the C 6 H. group ; that the nitrogen atoms are linked in 
 the manner represented, is concluded from the fact that diazobenzene 
 salts yield phenylhydrazine salts (p. 684) when reduced. 
 
 C 6 H 5 'X : NCI + H 4 = C 6 H 5 'XH-NH 2 ,HC1. 
 
 On the other hand, the behaviour of solutions of the diazo-salts indicate that 
 they are ionised by solvents in the same sense as the ammonium salts. Hence it 
 is probable that they are really quaternary ammonium derivatives, or ******** 
 
682 AZO-COMPOUNDS. 
 
 P TT 
 
 mlts of the form /NssK, corresponding with tetramethylium chloride, 
 
 Cl x 
 
 3 \N==(CH 3 ) 3 , for example. 
 
 or 
 
 The salts like C 6 H 5 N 2 r OK are apt to pass, when heated, into an unstable form 
 which cannot be coupled readily to make an azo-compound when treated with an 
 aniine or phenol, as the normal salts can. These isodiazo-salts have been supposed 
 to be really salts of the nitrosamines, of the form C 6 H 5 NK*NO. 
 
 481. Diazo-amido-compounds. When it is attempted to prepare a diazo- 
 compound in the absence of an acid, a diazo-amido-compound is obtained ; 
 probably, one portion of the amine is diazotised and immediately combines with 
 another portion. Thus, diazoamidobenzene, C 6 H 5 'N : N'NH'C 6 H 5 , is prepared by 
 passing N 2 3 into a cooled solution of aniline in alcohol ; diazobenzene hydroxide 
 may be supposed to be first formed and then to combine with aniline ; 
 C 6 H 5 -N : N-OH + NH 2 -C 6 H 5 = C 6 H 5 -N : N'NHC 6 H 5 + HOH. It is also prepared by 
 the interaction of diazobenzene chloride and aniline, HC1 being liberated, 
 C 6 H 5 N : NC1 + C 6 H 6 NH 2 =C 6 H 5 N :N-NHC 6 H 8 + HC1 ; by substituting other primary 
 (or secondary) amines for aniline, other diazo-amido-compounds are formed, and 
 if two molecular proportions of diazobenzene chloride to one of the amine be used, a 
 disdiazo-amido-compouiid is produced: 2C 6 H 5 N : NCl + NH 2 C fi H g =[C 6 H 5 N : N] : 
 NC 6 H 6 + 2HC1. 
 
 Diazo-amidobenzene crystallises in yellow prisms (m.-p. 96 C.), and is not basic ; 
 like most other diazo-amido-compounds, it readily undergoes an intra-molecular 
 transformation when in solution, becoming the corresponding amido-a~o-compound, 
 C 6 H 5 'N : N'C 6 H 4 (NH 2 ) (v.i.). This is particularly liable to happen in the presence 
 of an amine, so that during the preparation of diazo-amido-benzene the excess of 
 aniline may cause the change. The diazo-amido-compounds are readily split up 
 into diazobenzene compounds and aniline, so that they show most of the reactions 
 of the former compounds. 
 
 482. Azo-Compounds. When a nitro -compound is reduced in acid 
 solution the corresponding amido-derivative is immediately produced, 
 but when the liquid is alkaline there are formed, in the case of the 
 aromatic nitro-compounds, three intermediate products, derived from two 
 molecules of the nitro-compound. Thus, nitro-benzene in alkaline 
 solution will yield azoxybenzene, azobenzene and hydrazobenzene, accord- 
 ing to the reducing capacity of the agent employed. 
 
 C 6 H 5 N0 2 C 6 H B Nv C 6 H 5 N C 6 H 5 NH 
 
 I >0 || | 
 
 C 6 H 5 N0 2 C 6 H B ir C 6 H 5 N C 6 H 5 NH 
 
 2 mols. Nitro-benzene. Azoxybenzene. Azobenzene. Hydrazobenzene. 
 
 formed when nitrobenzene is reduced by alcoholic potash, but 
 is best prepared by oxidising azobenzene by chromic acid in acetic acid. It 
 crystallises in yellow needles (m.-p. 36 C.), insoluble in water, but soluble in 
 alcohol. 
 
 Azo-compounds may be symmetrical, like azobenzene, or mixed, like 
 benzeneazometkane, C 6 H 5 ']Sr : N'CH 3 ; the latter kind are produced by 
 oxidation of the corresponding hydrazines. 
 
 Azobenzene, C 6 H 5 N : NC 6 H 5 , is produced when an alcoholic solution of 
 nitrobenzene is treated with sodium amalgam or with zinc-dust andNaOH. 
 It is readily obtained by dissolving nitrobenzene in alcohol, adding an 
 equal weight of KOH, and distilling, when the alcohol is oxidised to 
 acetic acid, and the nitrobenzene reduced to azobenzene. At the end 
 of the distillation it comes over as a dark red oil, which solidifies after 
 a time to a crystalline mass ; it is insoluble in water, but may be 
 
AZO-DYESTUFFS. 683 
 
 crystallised from alcohol or ether in beautiful red tables resembling 
 K Cr 2 O 7 ; it melts at 68 C. and boils at 293 C. 
 
 Azobenzene is also formed when aniline is oxidised with KMn0 4 . It forms 
 .substitution products like benzene does. Alkaline reducing-agents convert it into 
 hydrazobenzene, but acid reducing-agents convert it into aniline. 
 
 483. Azo-dyestuffs. Since the dyeing of a fabric involves the formation of an 
 insoluble coloured substance in the fibre, it is essential that a dyextuff shall be 
 capable of combining either with the fibre itself or with some substance (a mordant) 
 previously fixed in the fibre, to form an insoluble compound (the dye). Most dyestuffs 
 are capable of forming dyes with wool, and to a smaller extent with silk, without 
 the intervention of a mordant ; the dyes thus produced are termed substantive dyes. 
 With cotton, on the other hand, a mordant is nearly always requisite, the dye 
 obtained being called, in this case, an adject I ce dye. It will be seen that since a dye- 
 stuff must enter into some form of chemical combination before it can become a dye, 
 it must be a substance possessed of a certain amount of chemical activity. Thus it 
 happens that those substances which have been found to be successful dyestuffs are 
 generally either acid or basic in character ; this observation has proved of great 
 value, since it has shown that although a compound may be useless as a dyestuff 
 it may become useful if it be treated in such a manner that the necessary acidity 
 or basicity be imparted to it. It is possible to impart acidity to an organic com- 
 pound by the introduction of certain radicles, such as OH or S0 2 OH, and basicity 
 by introducing the NH 2 radicle. It is, of course, only certain organic compounds* 
 which can be converted into dyestutt's by the introduction of such groups ; these 
 compounds are called chromogem, whilst the groups that lend them their dyeing 
 capacity are called auxochromes. An acid auxochrome yields an acid dyestuff, 
 capable of being fixed by a basic mordant (alumina, &c.) ; whilst a basic auxo- 
 chrome yields a basic dyestuff, capable of being fixed by an acid mordant (tannin). 
 That a dyestuff must be soluble in water hardly needs stating ; it will be equally 
 obvious that a dyestuff need not be itself a coloured substance, although the in- 
 soluble compound which it forms in the fibre must be coloured. 
 
 Azobenzene is a highly coloured substance, but is at the same time both chemi- 
 cally indifferent and insoluble in water, so that it is not a dyestuff. It is, however, 
 a ctiromogen, for, by the introduction of the OH or NH 2 group, compounds are 
 produced which are either dyestuffs (when soluble in water) or become dyestuffs 
 when rendered soluble by conversion into sulphonic acids. 
 
 The dwzo-dyestuff* are compounds containing the *N : N group and are made 
 by diazotising an amido-compound and combining the product with an amido- or 
 hydroxy-compound (a "dyestuff component"). 
 
 Amido-azo-oomptntnd* are produced by the intramolecular change of diazo- 
 amido-compounds (p. 682), especially in presence of the salt of an ainine which, 
 hoAvever, is not consumed. The change generally produces an amido-azo- 
 compound in which the amido-group is in the para-position to the azo-group, hence 
 if an aromatic amine is used to prepare the diazo-amido-compound, the para- 
 position to the amido-group should be unoccupied. 
 
 p-Aniido-azobenzene is prepared by heating diazo-amidobenzene (10 grams) with 
 aniline hydrochloride (5 grams) and aniline (25 grams) at 45 C., dissolving 
 out the amiline with acetic acid and crystallising the residue from HC1. The 
 hydrochloride thus formed is in steel-blue needles and was formerly sold as 
 aniline yellow, a dyestuff. The base, liberated by NH :? from the hydrochloride, 
 forms yellow needles and melts at 127 C. By sulphonation it yields a mixture of 
 mono- and di-sulphonic acids, known as acid yellow or fast yellow. It is largely used 
 for making indulines (#.r.). By reduction, amido-azobenzene yields aniline and 
 paraphenylenediamine. 
 
 plniethylantidobetizenesidphoHlG acid is prepared from diazo-benzenesulpnc 
 acid chloride and dimethylaniline 
 
 C 6 H 4 (S0 3 H)-N: N-C1 + C 6 H 5 'N(CH 3 ) 2 = C 6 H 4 (S0 3 H)-N : N'C 6 H 4 N(CH 3 ) 2 4- I 
 The sodium salt is -methyl orange (tropaeulin O, helianthin or orange III.), ui 
 the laboratory as an indicator. 
 
 2 : 4-])iamidoa:oben.ene, C 6 H 5 'X : N'C 6 H 3 (NH 2 ) 2 , is made by the action o 
 diazobenzene chloride on metaphenylene-diamine C 6 H 5 N : JSU <-/ 6 tl 4 (iNJi 2 ). 2 
 O 6 H 5 -N : N-C 6 H 3 (NH 2 ) 2 + HC1. It melts at 117 C. and its hydrochloride is an or 
 
 * Almost always such as contain one or more benzene nuclei, and a special group, like the 
 <Jiazo-group, called a chroinophore. 
 
684 HYDEAZINES. 
 
 yellow dyestuff called chrysoldlne. The 4 : ^'-diamido-azobenzene, NH 2 'C 6 H 4 *N : N 
 C 6 H 4 'NH 2 gives rise to the red basic dyestuffs, the azylines, which are the tetra- 
 alkyl derivatives of the above compound and are obtained by diazotising a dialkyl-jw- 
 phenylenediainine and combining the product with a dialkylaniline 
 
 NE 2 -C 6 H 4 -N: N-C1 + C 6 H 5 NK 2 = NK 2 -C 6 H 4 'N : N'C 6 H 4 -NK 2 + HC1. 
 
 Bismarck 'brown (phenylene brown, Manchester brown) is the hydrochloride of a 
 mixture of bases prepared by the action of nitrous acid on metaphenylendiamine ; 
 it consists largely of the hydrochloride of triamido-azobenzene, C 6 H 4 (NH 2 )-N : N 
 C 6 H 3 (NH 2 )2, formed by diazotising one NH 2 in the metaphenylene-diamine and 
 combining the diazo-compound with another mol. of the diamine. 
 
 Hydroxyazo-compounds are prepared by the interaction of a diazo-chloride and a 
 phenol. Thus hydt'oxyazo-benzene is prepared from diazo-benzene chloride, and 
 phenol ; C 6 H 5 'N : N'Cl + C 6 H 5 OH = C 6 H 5 'N : N'C 6 H 4 (OH) + HC1. They are also 
 formed by an intra-molecular change of the azoxy-compounds, just as the amidoazo- 
 result from the diazoamido-compounds. 
 
 Dihydroxyazobenzenesulphonic acid, C 6 H 4 (S0 3 H)'N : N 'CgH^OH)^ is prepared 
 from the chloride of diazobenzenesulphonic acid and resorcinol (cf. methyl 
 orange). Its sodium salt is resorcin yellow. 
 
 Diazo-dyestuffs. These contain the 'N : N - group twice, and are of three kinds, 
 (i) The two N 2 groups may be attached to the same benzene nucleus which also 
 contains the auxouhrome (OH or NH 2 ). For instance, by the reaction of diazo- 
 benzene chloride on resorcinolazobenzene, resorcinoldisazobenzene is obtained 
 C 6 H 5 N 2 C1 + C 6 H 5 N 2 C 6 H 3 (OH) 2 = C 6 H 5 'N : N'C 6 H 2 (OH) 2 'N : N'C 6 H 5 + HC1. (2) The 
 two N 2 groups may be attached to the same benzene nucleus and the auxochrome 
 to another nucleus. Biebrich scarlet is a dyestuff of this type made by diazotising 
 amidoazobenzene disulphonic acid to produce 
 
 C 6 H 4 (S0 3 H)-N : N'C 6 H 3 (S0 3 H)-N : N'Cl, 
 which is then combined with /3-naphthol, producing 
 
 C 6 H 4 (S0 3 H)-N :N'C 6 H 3 (S0 3 H)-N :N'C 10 H 6 (OH). 
 (3) The two N 2 groups may be attached to different nuclei. To this class belong 
 the numerous benzidlne dyestuffs or tetrazo-dyest'itjfs, which are valuable as substan- 
 tive dyestuffs for cotton, most others requiring a mordant. Congo-red serves as a 
 type; benzidine, NH 2 *C 6 H 4 - C 6 H 4 'NH 2 (p. 666) is diazotised to tetrazodijpkenyl 
 chloride, C1N : N'C 6 H 4 -C 6 H 4 'N : NCI, which is then combined with a-naphth ij- 
 laminesulphonic acid, C 10 H 6 (SO 3 H)'NH 2 to form congo-red, the formula for which is 
 NH 2 -(S0 3 Na)C 10 H 5 -N : N'C 6 H 4 -C 6 H 4 -N : N'C 10 H 5 (S0 3 Na)-NH 2 . 
 
 DERIVATIVES OF HYDRAZINE AND HYDROGEN NITRIDE (DIAZOIMIDES). 
 
 484. Hydrazines. These bases are derived from hydrazine (p. 106), 
 H 2 N'NH 2 , by substituting a hydrocarbon radicle for H. They may be 
 primary, B/NH'NH 2 , or secondary, E, 2 :N'NH 2 , and symmetrical, 
 KHN'NHR (hydrazo-compounds), or asymmetrical, RHN'NH 2 (hydra- 
 zine compounds). When R is an alkyl radicle, the hydrazines are best 
 prepared by the action of reducing-agents on the nitrosoamines ; 
 R 2 : N-NO + H 4 = R 2 : N'NH 2 + H 2 0. But the alkyl hydrazines 
 are of very little importance at present. When R, is an aromatic 
 radicle, the hydrazines are best prepared by the reduction of the 
 diazo-compounds. The reaction of the hydrazines with compounds 
 containing ketonic or aldehydic oxygen has been already noticed 
 (PP- 5 8 3^25). 
 
 Phenylhydrazine, C 6 H 3 *NH'NH 2 , is prepared by dissolving aniline 
 (i part by weight) in strong HC1 (20 parts), cooling by adding ice, and 
 slowly adding an ice-cold solution of NaN0 2 (0.75 parts), in water 
 (4 parts). The aniline hydrochloride is thus converted into di-azoben- 
 zene chloride (p. 680). A solution of stannous chloride (4.5 parts) in 
 an equal weight of HC1 is now carefully added ; this converts the 
 
PHENYLHYDRAZINE. 685 
 
 diazobenzene chloride into phenylhydrazine hydrochloride, which is 
 precipitated 
 
 C 6 H 5 N : N-C1 + 4 HC1 + 2 SnCl 2 = C 6 H 5 -NH'NH 2 ,HC1 + 2 SnCl 4 . 
 
 The precipitate is washed with a mixture of alcohol and ether, 
 dissolved in a little water, and decomposed by strong NaOH, when the 
 hydrazine separates as an oily layer, which is freed from water by 
 distilling with potassium carbonate. 
 
 Phenylhydrazine is thus obtained as a colourless aromatic liquid of 
 sp. gr. 1.091, and boiling-point 241 C. It solidifies in a freezing 
 mixture to tabular crystals, fusing at 23 C. It is sparingly soluble 
 in cold water, but dissolves in alcohol and ether. Phenylhydrazine is 
 a strong reducing-agent and absorbs oxygen from air, becoming brown. 
 It reduces alkaline cupric solution, even in the cold, precipitating yellow 
 cuprous hydroxide, and evolving nitrogen, while aniline and benzene 
 are found in the solution. This is a general reaction for identifying 
 hydrazines, and may also be employed for diazo -compounds by boiling 
 their aqueous solutions with KHS0 3 , to reduce them to hydrazines, and 
 adding potash and alkaline cupric solution. It also reduces mercuric 
 oxide in the cold, forming nitrogen, aniline, benzene, and mercury- 
 diphenyl. It is a monacid base, and forms crystalline salts. Solution 
 of phenylhydrazine hydrochloride, mixed with sodium acetate, forms a 
 general test for aldehydes and ketones, with which it forms insoluble oily 
 or crystalline compounds (hydrazones, p. 625, see also osazones), thus 
 precipitating them from their aqueous solutions ; by warming these 
 compounds with HC1 they are reconverted into their parent substances. 
 When heated with nascent hydrogen phenylhydrazine yields C 6 H 5 NH 2 
 and NH 3 , a fact which settles its constitution, as well as that of the 
 other hydrazines. It is used technically for making antipyrine (q.v.) 
 
 Sodium dissolves in phenylhydrazine evolving H and forming C 6 H 5 NaN'NH 2 . 
 
 Hydrazine yields derivatives on the same lines as NH 3 does, but as it has four 
 H atoms and two N atoms, the latter allowing of dissymmetry, the number of such 
 derivatives is even greater than that obtainable from NH 3 . Moreover, the hydra- 
 zine derivatives have a remarkable tendency to undergo internal condensation, 
 yielding nitrogen ring compounds (cf. antipyrine). The following are the leading 
 types : 
 
 (i) Asymmetrical and secondary hydrazines ; hydra zonluni and azonlum com- 
 pounds, corresponding with the amines. Hydrazobenzene or sym-diplienyl-hydm- 
 zine, C 6 H 5 HN-NHC 6 H 5 (p. 684), is prepared by dissolving azobenzene in alcohol, 
 passing NH 3 , and afterwards H 2 S till the solution is colourless. 
 
 C 6 H 5 N : NC 6 H 5 + H 2 S = C 6 H 5 HN'NHC 6 H 5 + S. 
 
 On adding water, the hydrazobenzene is precipitated, and may be crystallised from 
 alcohol. It forms colourless tables (m.-p. 131 C.) becoming orange in air, from 
 production of azobenzene, and smelling of camphor. A convenient method of 
 converting azobenzene into hydrazobenzene is to boil its alcoholic solution with 
 zinc-dust until it is colourless. 
 
 When heated, hydrazobenzene is decomposed into azobenzene and aniline 
 
 2(C 6 H B HX-NHC 6 H 6 ) = C 6 H 5 N'NC 6 H 5 + 2(C 6 H 5 'H 2 N). 
 
 When dissolved in hydrochloric or sulphuric acid, it is converted into its meta- 
 meride benzidine, NH 2 C 6 H 4 'C 6 H 4 NH 2 (p. 666). This change recalls that of a diazo- 
 amido-compound into an amido-azo-compound (p. 682) and like the latter only 
 occurs when the 4-positions in the benzene rings are free. Thus o- or m-Ayaraxo- 
 toluene yields tolidine by this intramolecular change (lenzidim munition), 
 but in tf-hydrazotoluene only one of the NH groups shifts (semidme migration), 
 producing C 7 H 7 NHC 7 H 6 NHa, in which NH 2 is in the 2-position. These changes 
 may also be compared with that of methylaniline into paratoluidme (p. 665), and n 
 
686 CYANOGEN COMPOUNDS. 
 
 should be noted that all migrations of this type tend to produce a compound of 
 more basic properties. 
 
 Examples of other hydrazines of this class are a- and fi-ethylphenylhy&razine, 
 C 6 H 5 N(C 2 H 5 )-NH 2 and C 6 H 5 HN-NHC 2 H 5 . The former combines with' C 2 H 5 Br 
 forming diethylphenylhydrazonvum bromide, C 6 H 5 N(C 2 H 5 ) 2 BrNH 2 , while afi-dlethyl- 
 phmylhydrazine, C 6 H 5 iST(C 2 H 5 )-NHC 2 H 5 , combines with C 2 H 5 Br to form the 
 azonium compound, C 6 H 5 N(C 2 H 5 ) 2 BrNHC 2 H 5 . 
 
 (2} Plienylhydrazones. Already noticed (p. 685). 
 
 (3) Hydrazldes. These are acidyl derivatives corresponding with the amides and 
 prepared analogously. For example, a.-acetylphenylhydrazide, C 6 H 5 N(CH 3 CO)'XH.,. 
 from sodium phenylhydrazine and acetyl chloride (m.-p. 124 C.). 
 
 Semicarbazide, NH 2 CO'NH'NH 2 , may be regarded as the hydrazide of carbamic 
 acid, and is obtained by heating urea with hydrazine sulphate at 100 C. It gives 
 rise to many derivatives, combining with aldehydes and ketones as phenylhydrazine 
 does ; the products are called semlcarbazones. 
 
 (4) Hydrazido-acids are like amido-acids and are either symmetrical, e.y., 
 C 6 H 5 NH-NH-CH 2 COOH, or asymmetrical, e.g., C 6 H 5 N(NH 2 )'CH 2 COOH. 
 
 . (5) Hydrazidines (amidoazones) are analogues of the amidines (p. 668), the NH 
 group of the latter having been exchanged for the phenylhydrazone group, pro- 
 
 x,N-NHC 6 H 5 
 ducing compounds of the type, RC\ . When the NH 2 group is exchanged 
 
 for the diazobenzene group, formaziil-deriratives are obtained, RC\ 
 
 \\:NC 6 H 5 
 
 which are highly coloured and may be viewed as azo-dyestuffs, prepared from 
 diazobenzene and phenylhydrazones. 
 
 (6) Tetrazones are produced when two mols. of a secondary hydrazine are oxidised 
 with HgO 
 
 2C 6 H 5 N(CH 3 )'NH 2 + 2 = C 6 H 5 N(CH 3 )'N : N<CH,)KC^. 
 
 485. Diazoimides. The derivatives of hydrogen nitride, or azoimide, HN 3 
 (p. 107), are also called diazoimides, or tr'tazo-compounds. They are obtainable by the 
 action of NH 3 on the diazo-perbromides. Thus, when diazobenzene bromide is 
 brominated, C 6 H 5 'N : NBr + Br 2 = C 6 H 5 - NBrNBr 2 ; when the perbromide is 
 
 treated with ammonia, C 6 H 5 'NBrNBr 2 + NH 3 = 3HBr + C 6 H 3 'X<(^ (phenyl- 
 
 azoimide). When heated with alcoholic potash the dm\tro-pUenylazo\m\de yields 
 dinitrophenol and potassium nitride, KN 3 . 
 
 Benzoyl azoimide, C 6 H 5 CON 3 , formed when benzoyl-hydrazhle, C 6 H 5 CO'NH'NH 2 . 
 is diazotised, yields sodium benzoate and sodium nitride when boiled with 
 NaOH. 
 
 X. CYANOGEN AND ITS COMPOUNDS. 
 
 486. In the beginning of the eighteenth century, a manufacturer of 
 colours at Berlin accidentally obtained a blue powder when precipitating 
 sulphate of iron with potash. This substance was used as a colour 
 under the name of Prussian blue, for several years, before any explana- 
 tion of its production was attempted, or even before the conditions 
 under which it was formed were exactly determined. It 17 24 it was 
 shown that Prussian blue could be prepared by calcining dried animal 
 matters with potashes, and mixing the aqueous solution of the calcined 
 mass, first with sulphate of iron and afterwards with hydrochloric acid ; 
 but the most important step towards the determination of its composi- 
 tion was made by Maquer, who found that, by boiling it with an alkali, 
 Prussian blue was decomposed, yielding a residue of red oxide of iron, 
 and a solution which reproduced the blue when mixed with a salt of 
 iron ; hence he inferred that the colour was a compound of the oxide of 
 iron with an acid for which the alkali had a more powerful attraction 
 
CYANOGEN. 687 
 
 a belief, confirmed in 1782, by Scheele's observations, that when an 
 alkaline solution prepared for making the blue was exposed to the air, 
 or to the action of carbonic acid, it lost the power of furnishing the 
 colour, but the escaping vapour struck a blue on paper impregnated 
 with oxide of iron. Scheele also prepared this acid in a pure state, and 
 it soon after obtained the name of prussic acid. 
 
 In 1787, Berthollet found prussic acid to be composed of carbon, 
 hydrogen, and nitrogen, but he also showed that the power of the alka- 
 line liquor to produce Prussian blue depended upon the presence of a 
 yellow salt crystallising in octahedra, and containing prussic acid, 
 potash, and oxide of iron, though the latter was so intimately bound 
 up with the other constituents that it could not be separated by those 
 substances which are usually employed to precipitate iron. 
 
 Porrett, in 1814, applying the greatly increased resources of 
 chemistry to the investigation of this subject, decomposed Prussian 
 blue with baryta, and subsequently removed the baryta from the salt 
 thus obtained by means of sulphuric acid, when he obtained a solution 
 of the acid, which he named ferruretted chyazic acid. 
 
 In 1815, Gay-Lussac, having boiled Prussian blue (or prussiate of 
 iron, as it was then called) with red oxide of mercury and water, and 
 crystallised the so-called prussiate of mercury, exposed it, in the dry 
 state, to the action of heat, and obtained a gas having the composition 
 CN", which was called cyanogen* in allusion to its connection with 
 Prussian blue. It was then seen that the substance which had been 
 called ferruretted chyazic acid contained iron and the elements of 
 cyanogen, whence it was called ferrocyanic acid, and its salts were 
 spoken of as ferrocyanates. Robiquet first obtained this acid in the 
 crystallised state, having the composition C 6 H 4 N 6 Fe ; and since it was 
 found that, when brought in contact with metallic oxides, it exchanged 
 the H, for an equivalent quantity of the metal, according to the equa- 
 tion, H 4 -C 6 N 6 Fe + 2M // = M/'C 6 N 6 Fe + 2H 2 0, it was concluded that 
 the C 6 N 6 Fe composed a distinct group or radicle, which was named 
 ferrocyanogen (Fey), the acid being called hydro- 
 ferrocyanic acid, and the salts ferrocyanides. 
 
 487. Cyanogen and Cyanides. Cyanogen, 
 (CN) 9 or NC'CX, is obtained by heating mercuric 
 cyanide in a glass tube or retort (Fig. 282), and 
 collecting the gas over mercury ; Hg(ON) 2 = 
 Hg + (CN) 2 ; the metallic mercury collects in 
 globules on the cool glass. The whole of the 
 cyanogen is not obtained, part being converted 
 into a brown solid called paracyanogen, which is 
 left behind. This is polymeric with cyanogen, Fig- 282 . 
 
 into which it may be converted by a high tempe- 
 rature. By heating together solutions of potassium cyanide and CuS0 4) . 
 cyanogen is evolved ; 2 CuS0 4 + 4KCN = Cu 2 (CN) 2 + (ON), + 2K 2 S0 4 . 
 
 Cyanogen is identified by its remarkable odour, and by its burning 
 with a pink flame edged with green. Its sp. gr. is 1.806 (air = i), and 
 it may therefore be collected by displacement of air. It is easily 
 liquefied by a pressure of 4 atmospheres at 15 C. and ij atmosphere 
 
 * From Kvai'eos, blue. 
 
688 REACTIONS OF CYANOGEN. 
 
 at o C. Liquid cyanogen has sp. gr. 0.87, and solidifies to a crystal- 
 line mass at -34 C. and boils at -21 C. Water dissolves about 
 4 volumes of cyanogen, yielding a solution which soon deposits a brown 
 flocculent substance termed azulmic acid. C 4 N 5 H 5 0. The solution is 
 then found to contain ammonium salts, especially carbonate, formate, 
 and oxalate, together with urea. 
 
 The first reaction between cyanogen and water, on standing, probably resembles 
 that between chlorine and KOH in the cold. viz.. C1 2 + 2KOH = KC1 + KC10 + H 2 ; 
 the reaction in the case of cyanogen being (CN) 2 + H 2 = HCN + H(CN)0, producing 
 hydrocyanic, HCN, and cyanic, HCNO, acids. The cyanic acid yields NH 4 HC0 3 
 by reaction with water; HCNO + 2H 2 = NH 4 HC0 3 . Hydrocyanic acid, with 
 water, yields ammonium formate; HCN + 2H 2 = HCO 2 NH 4 . Cyanogen, with 
 water, yields ammonium oxalate; (CN) 2 + 4H 2 O=:C 2 4 (NH 4 )2. Cyanic acid, 
 with ammonia, yields urea; HCNO + NH 3 = (NH 2 ) 2 CO. The azulmic acid 
 appears to result from a reaction between cyanogen, ammonia, and water ; 
 2(CN) 2 + NH 3 + H 2 = C 4 HgN 5 ; it may be prepared by passing cyanogen into 
 dilute ammonia, and heating in a closed vessel. When dry ammonia gas acts 
 upon cyanogen gas, a black substance is produced, which is called hydrazulmin ; 
 2NH 3 + 2(CN) 2 = C 4 H 6 N 6 . This appears to be azulmanride, for, when acted on by 
 water, it yields azulmic acid and ammonia ; C 4 H 6 N 6 + H 2 = C 4 H 5 N 5 + NH 3 . 
 
 In most of its reactions, cyanogen exhibits the mutability which is 
 generally observed in organic groups, but in some cases it exhibits a 
 stability which allows it to be compared with the halogens. Thus, 
 alkali metals take fire in cyanogen when gently heated, producing their 
 respective cyanides ; K 2 + (CN) 2 = 2KCN ; cyanogen, acting on solution 
 of potash, yields potassium cyanide and cyanate ; (CN) 2 +2KOH = 
 KCN + KCNO + H 2 0, just as chlorine yields chloride and hypochlorite. 
 Cyanogen combines with H, under influence of the silent electric 
 discharge, to form hydrocyanic acid, H(CN), which forms cyanides by 
 exchanging its hydrogen for metals, just as hydrochloric acid forms 
 chlorides ; but the cyanides of potassium and sodium are much less 
 stable compounds than the corresponding chlorides. When boiled with 
 water, the alkali cyanides are converted into alkali formates, the 
 nitrogen being evolved as NH 3 , and the carbon converted into the 
 COOH group ; KCN'" + 2 H 2 = KCO"(OH)' + NH 3 . 
 
 The facility with which the ON group is transformed by hydrolysis into 
 the C0 2 H group, is of very great importance in organic research, since it 
 is often easy to introduce the ON group into an organic molecule, and, 
 by afterwards converting it into CO 2 H, to effect the synthetical forma- 
 tion of an organic acid, as has been already explained (p. 587). 
 
 Cyanogen is produced in small quantity by the direct union of 
 carbon and nitrogen at the extremely high temperature of the electric 
 spark, but to produce it in quantity, one, at least, of its elements must 
 be in the form of a compound ; thus, if ammonia be passed over red-hot 
 charcoal, hydrogen cyanide is produced ; NH 3 + C = HCN + H 2 ; again, 
 if acetylene is mixed with nitrogen and " sparked," hydrogen cyanide is 
 formed, C 2 H 2 + N 2 = 2 HCN. If one of the alkali metals be present, 
 nitrogen is much more easily converted into cyanogen ; potassium 
 cyanide may be obtained by passing nitrogen through an iron tube con- 
 taining a heated mixture of charcoal and potassium N 2 + C 2 + K 2 = 
 2 KCN. In place of the costly potassium, the materials for making it, 
 viz., potassium carbonate and charcoal, may be used (see below). A 
 better yield is obtained by employing a compound of nitrogen with 
 
YELLOW PRUSSIATE OF POTASH. 689 
 
 carbon, such as refuse horn or cuttings of hides and old leather, which 
 are rich in nitrogen. 
 
 On a large scale, potassium cyanide is made in this way, but as it 
 cannot be crystallised easily, it is converted into the ferrocyanide, 
 which is the source whence all cyanogen compounds are obtained. 
 
 488. Potassium ferrocyanide, K 4 FeC 6 N 6 . 3 Aq or 4 KCN.Fe" 
 (CN) 2 .3Aq, yellow prussiate of potash, is manufactured by meltino- 
 potashes (crude K 2 C0 3 ) mixed with iron filings in an iron vessel, and 
 adding any cheap material containing carbon and nitrogen, such as old 
 leather. Sometimes the animal matter is distilled for the sake of the 
 ammonia which it will yield, and the remaining charcoal, still rich in 
 nitrogen, is used for making ferrocyanide. The fused mass is heated with 
 water in open boilers, when a yellow solution is obtained, which, after 
 evaporation, deposits truncated pyramidal crystals of potassium ferro- 
 cyanide. 
 
 The chemistry of this process is somewhat abstruse, but is generally 
 explained as follows : ( i ) The carbon containing nitrogen decomposes 
 the potassium carbonate at a high temperature, producing potassium 
 cyanide and^CO; K 2 C0 3 + C 4 + N 2 = 2 KCN + 3 CO. (2) Sulphur, derived 
 from the animal matters, and partly from potassium sulphate present as 
 an impurity in the potashes, combines with iron to form ferrous sulphide. 
 (3) On treating the fused mass with water, the ferrous sulphide is 
 dissolved by the KCN, yielding potassium sulphide and ferrocyanide ; 
 FeS + 6KCN = K 4 Fe(CN) 6 + K 3 S. 
 
 It has been suggested to avoid the presence of K 2 S in the liquor (which hinders 
 crystallisation) by melting pure K 2 C0 3 with animal charcoal, extracting the 
 KCJST from the residue by treatment with water, and digesting with finely ground 
 spathic iron ore (FeC0 3 ) ; FeC0 3 + 6KCN = K 4 Fe(CN) 6 +K 2 C0 3 . 
 
 The ferrocyanide dissolves in twice its weight of boiling and in four 
 times its weight of cold water, but is insoluble in alcohol. The aqueous 
 solution assumes a darker yellow colour when exposed to air for some 
 time, oxygen being absorbed and potassium ferricyanide (see below) 
 produced in small quantity. The neutral solution then becomes slightly 
 alkaline from formation of potash. 
 
 Crystallised ferrocyanide does not lose water till 60 C., when it gradually be- 
 comes white and opaque. At 100 C. it may be dried completely, though with 
 difficulty, unless finely powdered and heated in, a current of dried air. When the 
 undried salt is moderately heated, it evolves ammonia and hydrocyanic acid, 
 and becomes brown. The thoroughly dried salt does not evolve ammonia, but 
 fuses at a high temperature, evolving nitrogen, and leaving a residue of 
 potassium cyanide andiron carbide ; K 4 C 6 N 6 Fe = 
 
 Nearly all acids decompose the ferrocyanide, evolving hydrocyanic 
 acid, and producing compounds containing cyanogen and iron, which 
 become blue when exposed to air, from the formation of Prussian blue 
 and similar compounds. It is for this reason that the yellow crystals 
 become blue and green when exposed to the air of a laboratory. 
 Oxidising-agents convert the ferrocyanide into ferricyanide, as will be 
 seen later. With a large number of metallic salts, the ferrocyann 
 gives precipitates, so that it is an indispensable test. It is also largely 
 employed in the manufacture of colours, and in dyeing and calico- 
 printing. The constitution and chemical relations of the ferrocyamd* 
 will be better understood later in the history of cyanogen compounds. 
 
 / v 
 
690 PRUSSIC ACID. 
 
 Hydrogen cyanide, hydrocyanic, or prussic acid, H.C : N (or 
 HCy), is prepared, in aqueous solution, by distilling potassium ferro- 
 cyanide (prussiate of potash) with dilute H 2 S0 4 . 50 grammes of the 
 crystallised ferrocyanide are dissolved in 200 cubic centimetres of warm 
 water in a flask or retort connected with a good condenser. 20 c.c. of 
 strong sulphuric acid are diluted with 60 c.c/of water, cooled, and added 
 to the solution of ferrocyanide ; heat is applied by a ring-burner to 
 avoid bumping, until about 140 c.c. of liquid has passed into the receiver. 
 
 The potassium ferrocyanide gives up half of the cyanogen, ON, as 
 hydrocyanic acid, leaving the remainder combined with the iron and 
 half of the potassium as potassio-ferrous ferrocyanide, K 2 Fe".Fe"(CN) 6 , 
 a yellow ealt which quickly becomes blue when exposed to air, oxygen 
 being absorbed, and Prussian blue, or ferric ferrocyanide, Fe"' 4 .3Fe"(CN) 6 , 
 produced. The following equation represents the preparation of hydro- 
 cyanic acid ; 2K 4 FeCy 6 + 6H 2 SO 4 = 6HCy + K 2 Fe" 2 Cy 6 + 6KHS0 4 . 
 
 Hydrocyanic acid is generally used diluted, but it may be obtained anhydrous 
 by gently heating the diluted acid in a retort connected with a condenser cooled 
 by iced water, and receiving the distillate in a bottle cooled in ice and con- 
 taining fused calcium chloride in coarse powder. This bottle is afterwards 
 placed in a water-bath connected with a receiver cooled in ice and salt, and 
 gently heated, when the pure hydrocyanic acid distils over. The anhydrous 
 HCy may also be obtained by passing dry H 2 S gas into a long tube filled with 
 mercuric cyanide and connected with a receiver cooled in ice and salt ; the 
 operation must be stopped when an inch or two of mercuric cyanide remains 
 undecornposed, to avoid contamination of the HCy with H 2 S ; HgCy 2 + H 2 S = 
 HgS + 2HCy. 
 
 Properties of hydrocyanic acid. A colourless liquid, sp. gr. 0.7, which 
 evaporates rapidly, so that a few drops in a watch-glass are solidified 
 by the cold of evaporation, the freezing-point being - 12 C. The acid 
 boils at 25 C., and its vapour burns with a purple flame. The smell 
 of the vapour is quite characteristic, and is compared by some to a faint 
 odour of almonds ; it generally produces a sensation of dryness at the 
 back of the throat. The inhalation of the vapour, unless largely 
 diluted with air, is very dangerous, and an extremely small quantity of 
 the acid taken internally generally kills immediately. When the pure acid 
 is mixed with an equal volume of water, a contraction ensues, amounting 
 to about one-twentieth of the total volume, and cold is produced. The 
 aqueous acid is decomposed when exposed to light, depositing a brown 
 substance, whilst ammonia formate and other products are found in 
 solution ; HCN + 2H 2 = H'C0 2 NH 4 . A trace of sulphuric acid, which 
 generally splashes over in preparing prussic acid, prevents this decom- 
 position. Acids and alkalis, when boiled with the acid, convert the 
 HCN into formic acid and ammonia. 
 
 The acid properties of HCy are very feeble ; it hardly reddens litmus, 
 and does not destroy the alkaline reaction of the alkalies or their 
 carbonates. The salts formed by displacing its hydrogen by alkali- 
 metals are easily decomposed by water and carbonic acid, and therefore 
 smell of HCy, but the cyanides formed by many of the metals are very 
 stable bodies. 
 
 Although HCy is so much more easily liquefied than HC1, its vapour 
 continually escapes even from a weak aqueous solution, so that the 
 strength is diminished every time the stopper is removed from the 
 bottle ; it thus happens that the weak prussic acid (2 per cent.) dis- 
 
POTASSIUM CYANIDE. 69! 
 
 pensed by the druggists, is sometimes found to have become nearly pure 
 water. 
 
 Hydrocyanic acid is found in laurel-water, and in water distilled 
 from the kernels of many stone-fruits, such as peach, apricot, and 
 plum. In these cases it appears to be produced from amygdalin (see 
 p. 584). 
 
 Hydrocyanic acid is produced synthetically by passing a succession of 
 electric sparks through a mixture of nitrogen with an equal volume of 
 acetylene, this being itself produced by carbon intensely heated in 
 hydrogen (p. 100). HCy is also found among the products of distilla- 
 tion of coal, and occurs in imperfectly-purified coal-gas. 
 N Tests for hydrocyanic acid. Silver nitrate produces a white precipitate of 
 silver cyanide, AgCN, which is dissolved by boiling with strong nitric acid, and 
 precipitated in microscopic needles, AgCN.2AgN0 3 , on cooling. Prussian-blue 
 test : Add potash in slight excess, to form KCy ; then add ferrous sulphate 
 solution (which always contains ferric sulphate).* to form potassium ferro- 
 cyanide : 6KCy + Fe"S0 4 =K 4 Fe"Cy 6 + KjSO^ ; this acts on the ferric sulphate, 
 and produces ferric ferrocyanide, or Prussian blue: 3K 4 Fe"Cy 6 + 2Fe"' 2 (S0 4 ) 3 
 = Fe'" 4 (Fe"Cy 6 ) 3 + 6K 2 S0 4 . But the excess of potash decomposes the blue; to 
 correct this, add excess of hydrochloric acid to neutralise the potash, the blue 
 will then be visible. SulpJwcya tilde test : Add yellow ammonium sulphide (which 
 contains some disulphide), to form ammonium sulphocyanide ; HCN + (NH 4 ) 2 S 2 = 
 NH 4 CNS + NH 4 HS ; evaporate till the smell of ammonium hydrosulphide has 
 disappeared, and add ferric chloride, which will produce the blood-red colour of 
 ferric sulphocyanide, bleached on adding mercuric chloride. A very fugitive 
 purple colour is due to ammonium thiosulphate produced by the action of air, 
 and does not indicate HCy. 
 
 Potassium cyanide, KCN, or KCy, is prepared by fusing, in an iron 
 crucible, a mixture of well-dried potassium ferrocyanide (8 parts) with 
 dried K 2 C0 3 (3 parts); K 4 Cy 6 Fe + K 2 00 3 = 5KCy + KCyO + Fe + C0 2 . 
 As soon as the escape of C0 2 has ceased, and the metallic iron has sub- 
 sided, the clear fused mixture of cyanide and cyanate of potassium is 
 poured into an iron mould. The presence of cyanate does not interfere 
 with most of the uses of the cyanide ; its quantity may be diminished 
 by adding some powdered charcoal to the mixture. 
 
 A purer product is obtained, though less economically, by fusing the dried ferro- 
 cyanide alone (see above), and crystallising the product by dissolving in hot alcohol. 
 The purest potassium cyanide is made by passing vapour of hydrocyanic acid 
 into solution of potash in absolute alcohol, when the cyanide is deposited in small 
 octahedral crystals. 
 
 Potassium cyanide, as met with in commerce, is in white opaque lumps, and con- 
 tains about 98 per cent, of cyanide, the rest being cyanate and carbonate. When 
 exposed to air, it deliquesces, and smells of hydrocyanic acid and ammonia, the 
 former being produced from the cyanide, and the latter from the cyanate, by tho 
 action of water 
 
 (i) KCN + H 2 = KOH + HCN. (2) KCNO + 2H 2 = NH 3 + KHCOa. 
 
 It dissolves very readily in water, yielding a strongly alkaline solution, 
 which evolves HCy and NH 3 when boiled, and becomes a solution 
 of potassium formate; KCN + 2 H 2 = NH 3 + HC0 2 K. When the 
 commercial cyanide is boiled with moderately strong alcohol, the 
 cyanide, together with a little cyanate, is dissolved, and may be 
 crystallised from the solution, while the carbonate is left undissolved. 
 Potassium cyanide fuses at a low red heat, becoming very fluid ; it then 
 
 * It is well either to shake with air or to add a drop of ferric chloride to ensure the 
 presence of ferric salt. 
 
692 CYANIDES. 
 
 absorbs oxygen from the air, forming cyanate. This disposition to 
 combine with oxygen causes it to act as a powerful reducing-agent 
 upon metallic oxides ; tin-stone is assayed by fusing it with potassium 
 cyanide, when a button of tin collects at the bottom of the fused mass ; 
 Sn0 2 + 2KCy = Sn + 2 KCyO. When heated with KN0 3 or KC10 3 , it 
 causes a violent explosion, from evolution of C0 2 and N. 
 
 Pure potassium cyanide is alkaline, but does not effervesce with acids, like the 
 commercial cyanide. Solution of potassium cyanide dissolves silver chloride and 
 iodide, which leads to its use in electro-plating and in photography, while its pro- 
 perty of dissolving silver sulphide is useful in cleaning gold and silver. It is one 
 of the most dangerous poisons. It is also used in gold-extraction (p. 514), for which 
 purpose it may be made by heating K 4 FeCy 6 with sodium ; K 4 FeCy 6 + Na 2 = 4KCy + 
 2NaCy + Fe. The product is a mixture of the two cyanides which is as effective as 
 pure KCN. 
 
 Potassium cyanide is sometimes obtained in considerable quantity from the blast- 
 furnaces of iron-works being formed from the potassium carbonate in the ash 
 of the fuel. 
 
 Ammonium cyanide, NH 4 CN, may be sublimed in cubes by heating a mixture 
 of mercuric cyanide and ammonium chloride. It dissociates, at 36 C., into 
 NH 3 and HON. It is very soluble in water and alcohol, and smells of hydro- 
 cyanic acid and ammonia. When kept it becomes brown, azulmin being produced 
 (p. 688). 
 
 The cyanides of barium, strontium, and calcium are less soluble than the alkali 
 cyanides, and are easily decomposed by carbonic acid. Zinc ci/anide, ZnCy 2 , is 
 precipitated by KCy from ZnS0 4 ; it dissolves in KCy, forming ZnCy 2 (KCy). 2 
 which crystallises in octahedra. Nlcltel cyanide, NiCy 2 , obtained in a similar way, 
 forms a pale green precipitate, readily soluble in excess, forming NiCy 2 (KCy) 2 , 
 from which hydrochloric acid re-precipitates the nickel cyanide 
 
 NiCy 2 (KCy) 2 + 2HC1 = NiCy 2 +2KC1 + 2HCy. 
 
 If the solution of nickel cyanide in potassium cyanide be heated with mercuric 
 oxide, nickel oxide is precipitated: NiCy 2 (KCy) 2 + HgO = HgCy. 2 (KCy) 2 + NiO. 
 This reaction is important in quantitative analysis. Nickel cyanide is remarkable 
 for its insolubility even in boiling hydrochloric acid. 
 
 489. Cobalt cyanide, CoCy 2 , is precipitated of a reddish-brown colour when 
 potassium cyanide is added to cobalt nitrate ; it dissolves easily in excess of 
 potassium cyanide, forming jtotaxshtm coba Itocyanide, K 4 (CoCy 6 ), which may be 
 obtained in red deliquescent crystals by adding alcohol. This compound corre- 
 sponds with potassium ferrocyanide, K 4 (FeCy 6 ), but is far less stable ; when 
 exposed to air, or boiled with water, it undergoes oxidation, the cobaltous com- 
 pound being converted into a cobaltic compound, the potassium cobalt icijunide 
 2K 4 (Co"Cy 6 ) + + H 2 = 2K 3 (Co'"Cy 6 ) + 2KOH. The potassium cobalti- 
 cyanide is a pale yellow salt, its solution being nearly colourless, so that the brown 
 solution formed at first when KCy in excess is added to a cobalt salt gradually 
 becomes pale yellow when boiled in contact with air. This solution, when mixed 
 with hydrochloric acid in excess, yields hydro-cobalticyanic acid, H 3 CoCy 6 . which 
 is soluble, forming a distinction between cobalt and nickel. When both metals 
 are present, the addition of HC1 to the solution in excess of KCy produces a 
 yellowish-green precipitate of nickel cobalt icij a nide, Ni 3 (CoCy 6 ) 2 , which is decom- 
 posed by boiling with potash, the nickel being precipitated as hydroxide, and the 
 cobalt passing into solution as potassium cobalticyanide; Ni 3 (CoCy 6 ) 2 + 6KOH = 
 3Ni(OH) 2 + 2K 3 CoCy 6 . The solution of potassium cobalticyanide is not decom- 
 posed by digestion with HgO (to precipitate the NiO), but a solution of mercurous 
 nitrate gives a white precipitate of mercurous cobalticyanide, Hg 3 Co 2 Cy 6 , which is 
 converted into oxide of cobalt when heated in air. 
 
 The potassium cobalticyanide may be obtained in crystals ; it is analogous to. 
 and isomorphous with, the potassium ferricyanide, to be presently described. 
 nydrocobaltici/anic add fa prepared by mixing a strong solution of the potassium- 
 salt with sulphuric acid and alcohol, when K 2 S0 4 is precipitated, and the solution 
 yields colourless crystals of H 6 (CoCy 6 ) 2 .H 2 0, which is a very stable and powerful 
 acid. Potassium cobalticyanide gives, with ferrous salts, a white precipitate of 
 ferrous cobalticyanide, Fe 2 (CoCy 6 ) 3 ; and with cobalt salts a red precipitate of 
 
PRUSSIAN BLUE. 693 
 
 ,anlde, Co" 3 (Co'"Cy 6 ). 2 .i 4 Aq, which loses its water at 200 C., and 
 
 490. Cyanogen and iron-Fe>>r<> i(S cyanide, Fe(CN) 2 , or FeCv* is obtained 
 (apparently m combination with some KCy) as a red-brown precipitate bv addin- 
 potassium cyanide to a ferrous salt ; it dissolves when boiled with an excess of the 
 cyanide, and the solution, when evaporated, deposits vellow crystals of potassium 
 ferrocyamde-FeCy 2 + 4KCy = K 4 FeCy 6 . This might be regarded as 4 KCv.FeCv,, 
 but the iron cannot be detected by any of the tests for that metal thui 
 ammonium sulphide, which produces a black precipitate in ferrous salts does not 
 change the ferrocyanide ; moreover, the K 4 may be exchanged for hvdrozen or 
 for other metals without affecting the iron and cyanogen, leading to the con- 
 clusion that the group FeCy 6 contains the iron in a state of intimate association 
 with the cyanogen, so that its ordinary properties are lost. Again, the 
 ferrocyanide is not poisonous, so that it cannot be believed to contain potassium 
 cyanide. 
 
 Hydrogen ferrocyanide, or hydroferrocyanic add, H 4 FeCy 6 , is prepared by 
 mixing a cold saturated solution of potassium ferrocyanide with an equal volume 
 of strong hydrochloric acid. It forms a white crystalline precipitate, soluble in 
 water, but not in HC1. If it be drained, dissolved in alcohol, and ether added, it 
 may be obtained in large crystals. It is a strong acid. When exposed to air, it 
 absorbs oxygen, and evolves hydrocyanic acid, leaving a residue of Prt/wiati Uue or 
 ferric ferrocyanide. Fe 4 (FeCy 6 ) 3 . The acid is decomposed by boiling its solution, 
 into hydrocyanic acid and ferrous ferrocyanide, Fe 2 (FeCy 6 ), which is white, but 
 becomes blue when exposed to air ; 3H 4 FeCy 6 = 1 2HCy + Fe.,(FeCy 6 ). These changes 
 are applied to produce blue patterns in calico-printing. 
 
 Hydroferrocyanic acid is tetrabasic, its four atoms of hydrogen admitting of 
 displacement by a metal to form a ferrocyanide. The group" FeCy 6 , ferrocyanogen, 
 Fey or Cfy, is a tetrad group, consisting of ferrous iron, which is diad, Fe",' and six 
 monad cyanogen groups, (CN)', leaving four vacant bonds. 
 
 Prussian blue or ferric ferrocyanide, Fe'" 4 Fcy iv 3 , (Fey = FeC 6 N 6 ), is 
 prepared by adding potassium ferrocyanide to a solution of ferric chloride, 
 or ferric sulphate ; 2Fe 2 Cl 6 + 3K 4 Fcy = Fe 4 Fcy 3 + 1 2KC1. When washed 
 and dried, it is a dark-blue amorphous body, which assumes a coppery 
 lustre when rubbed. It cannot be obtained perfectly free from water, 
 always retaining about 20 per cent. (Fe 4 Fcy + 12 Aq). On heating, the 
 water decomposes it, hydrocyanic acid and ammonia being evolved, and 
 ferric oxide left. The water appears essential to the blue colour, for 
 strong sulphuric acid converts it into a white powder, becoming blue 
 again on adding water. Strong hydrochloric acid dissolves Prussian 
 blue, forming a brown solution, which gives a blue precipitate with 
 water. Oxalic acid dissolves it to a blue solution, used as an ink. 
 Some ammonium salts, such as acetate and tartrate, also dissolve it. 
 Alkalies destroy the blue colour, leaving ferric hydroxide and a solution 
 of an alkali ferrocyanide ; Fe 4 Fcy 3 + I2KOH = 2Fe 2 (OH) 6 + 3K 4 Fcy. 
 This is turned to account, in calico-printing, for producing a buff or 
 white pattern upon a blue ground. The stuff having been dyed blue 
 by passing, first through solution of a ferric salt, and afterwards through 
 potassium ferrocyanide, the pattern is discharged by an alkali, which 
 leaves the brown ferric hydroxide capable of being removed by a dilute 
 acid, when the stuff has been rinsed, so as to leave the design white. 
 Prussian blue is present in large quantity in many black silks, and may 
 be extracted by heating with hydrochloric acid, and precipitating the 
 brown solution with water. 
 
 Soluble Prussian Uue, or potaxsio-ferric ferrocyanide, K 2 Fe'" 2 (Fcy) iv 2 , is formed 
 when solution of ferric chloride or sulphate is poured into potassium ferrocyanide, 
 so that the latter may be present in excess during the reaction ; FegCLj- al^Fcy * 
 K 2 Fe. 2 Fcy 2 + 6KCl. This blue is insoluble in the liquid containing saline matter 
 
694 RED PRUSSIATE OF POTASH. 
 
 but dissolves as soon as the latter has been removed by washing. The addition of 
 an acid or a salt re-precipitates it. By decomposing soluble Prussian blue with 
 ferrous sulphate, a blue precipitate of ferroso-ferric ferrocyanide, Fe"Fe'" 2 Fcy 2 . is 
 obtained, which is erroneously called Turnbull's blue (ferrous ferricyanide}. 
 
 Potassio-ferrous ferrocyanide, K 2 Fe"Fcy, is obtained as a white precipitate when 
 a solution of ferrous salt quite free from ferric salt, such as a solution of ferrous 
 hydrosulphite (p. 237) made by dissolving iron in H 2 S0 3 , is added to potassium 
 ferrocyanide quite free from ferricyanide; FeS0 4 + K 4 Fcy = K 2 S0 4 + K 2 FeFcy. 
 The precipitate is snow-white, and remains so for some time at the bottom of the 
 liquid, but if it be exposed to air, it eagerly absorbs oxygen and becomes blue ; 
 6K 2 FeFcy + 3 = 3K 4 Fcy + Fe 4 Fcy 3 + Fe 2 3 . Oxidising-agents, such as chlorine- 
 water and nitric acid, change it at once into Prussian blue. When potassium 
 ferrocyanide is added to ordinary ferrous sulphate, some Prussian blue is always 
 formed from the ferric sulphate present in the ordinary salt. In making the Prussian 
 blue of commerce, this precipitate is oxidised by solution of chloride of lime (p. 183), 
 and afterwards washed with dilute HC1, to remove Fe 2 3 . 
 
 Calcium chloride gives, with potassium ferrocyanide, a white crystalline 
 precipitate of potassio-calcium ferrocyanide, K 2 CaFcy, which is insoluble in acetic 
 acid, but dissolves in HC1, and is reprecipitated by ammonia. Potass w-barium 
 ferrocyanide, K 2 BaFcy.3Aq, is similar. Manganese ferrocyanide, Mn 2 Fcy, and :inc 
 ferrocyanide, Zn 2 Fcy, are white precipitates. When potassium ferrocyanide is 
 added to a zinc-salt mixed with excess of ammonia, a white crystalline precipitate 
 of ammonio-zinc ferrocyanide is obtained. Nickel ferrocyanide, Ni 2 Fcy, is a pale 
 green precipitate. Cobalt ferrocyanide, Co 2 Fcy, forms a pale blue-green precipitate. 
 Uranic ferroctjanide, U 4 Fcy 3 (?), is a rich brown-red precipitate. Cupric ferro- 
 cyanide, Cu 2 Fcy, is also obtained as a brown-red precipitate by adding potassium 
 ferrocyanide to cupric sulphate ; it forms the colour known as Hatchctfs brown. 
 Its formation is a delicate test for copper, a very dilute solution giving a pink 
 colour with the ferrocyanide. 
 
 Silver ferrocyanide, Ag 4 Fcy, is obtained as a white precipitate from silver 
 nitrate and potassium ferrocyanide ; it is insoluble in dilute nitric acid, like 
 silver chloride, but it is also insoluble in ammonia, which is the case with few 
 silver salts. When boiled with nitric acid it is converted into the red-brown 
 xilrer ferricyanide, which is soluble in ammonia. When silver ferrocyanide is 
 boiled with ammonia (or KOH), it deposits metallic silver and ferric oxide, leaving 
 silver cyanide and ammonium (or potassium) cyanide in solution 
 
 2Ag 4 FeCy 6 + 6NH 3 + 3H 2 = Ag 2 + Fe 2 3 + 6AgCy + 6NH 4 Cy. 
 
 Ferric cyanide, Fe 2 Cy 6 , is very unstable. When KCy is added to ferric chloride, 
 the solution soon becomes turbid, depositing ferric hydroxide and evolving HCy ; 
 Fe 2 Cy 6 + 6H 2 = Fe 2 (OH) 6 + 6HCy. 
 
 Potassium ferricyanide, or red prussiate of potash, K 3 Fe'"C 6 N 6 , or 
 3KCN.Fe"'(CN) 3 , is prepared by the action of chlorine upon potassium 
 ferrocyanide ; K 4 Fe"Cy 6 + Cl = K 3 Fe'"Cy 6 + KC1. Chlorine is passed 
 into the solution of ferrocyanide until a little of the solution tested 
 with ferric chloride no longer gives a blue precipitate. On the small 
 scale, chlorine-water may be added to the ferrocyanide. The yellow 
 colour is changed to greenish-yellow, and the solution, when evaporated 
 and cooled, deposits dark-red prisms of the ferricyanide. It is very 
 soluble in water, yielding a dark yellowish-green solution, but is nearly 
 insoluble in alcohol. The aqueous solution is slowly decomposed by 
 exposure to light, depositing a blue precipitate, and becoming partly 
 converted into ferrocyanide. If the solution be mixed with acetic acid, 
 and heated, it deposits a blue precipitate, a reaction which is turned to 
 account in dyeing. An alkaline solution of potassium ferricyanide acts 
 as a powerful oxidising-agent, becoming reduced to ferrocyanide ; 
 2K 3 Fe' "Cy 6 + 2 KOH = 2K 4 Fe"Cy 6 + H 2 + O. Such a solution converts 
 chromic oxide into potassium chromate, and bleaches indigo, whence it 
 is used as a discharge in calico-printing, for white patterns on an indigo 
 
FEERICYANIDES. 
 
 69- 
 
 ground. Potassium ferricyanide is also reduced to ferrocyanide when 
 boiled with potassium cyanide 
 
 2K 3 Fe'"Cy 6 + 2 KCN + 2 H 2 = 2 K 4 Fe"Cy 6 + HCN + NH 3 + CO,. 
 Hydrogen ferricyanide, or hydroferricyanic acid, H 3 Fe'"Cy 6 , is obtained by de- 
 composing lead ferricyanide with H 2 S0 4 , not in excess. It may be crystallised in 
 brown needles by evaporation in vacua. Its solution is decomposed by boiling, 
 with evolution of HCy and separation of a blue precipitate. Hydroferricyanic acid 
 is tribasic, the 3 atoms of hydrogen being displaced by metals to form ferri- 
 cyanides. 
 
 * Ferrous ferricyanide, or TurnbulVs blue, Fe" 3 Fe'" 2 Cy 12 . Whilst potassium ferro- 
 cyanide gives a light blue precipitate with common FeS0 4 , the ferricyanide gives a 
 dark blue precipitate, resembling Prussian blue. This contains the same proportions 
 of iron and cyanogen as the ferroso-ferric ferrocyanide, Fe"Fe'" 2 (Fe"Cy 6 )2, and it 
 is sometimes regarded as identical with it, on the supposition that the" ferrous 
 sulphate reduces the ferricyanide to ferrocyanide. Ferric salts give no precipitate 
 with the ferricyanide, but only a dark brown solution, probably containing ferric 
 ferricyanide, which yields a blue precipitate of ferrous ferricyanide with reducing- 
 agents such as H 2 SO 3 , and is used as a test. 
 
 Lead ferricyanide, Pb 3 Fe 2 Cy 12 .i6Aq, is deposited in red-brown crystals on mixing 
 strong solutions of lead nitrate and potassium ferricyanide. Silver ferricyanide, 
 Ag 6 Fe 2 Cy 12 , has been already mentioned as a red-brown precipitate formed by 
 boiling the ferrocyanide with dilute nitric acid. Cold potash converts it into 
 black Ag 2 and potassium ferricyanide ; on boiling, the black changes to pink ; 
 3Ag 2 + K 6 Fe 2 Cy 12 = 6AgCy + 6KCy + Fe 2 3 . The pink precipitate is a compound 
 of AgCy with silver ferricyanide, which may also be obtained by boiling silver 
 ferricyanide with silver oxide; Ag 6 Fe 2 Cy a2 -f 3Ag 2 = Fe 2 3 + i2AgCy, which com- 
 bines with undecomposed silver ferricyanide. On continuing to boil the silver 
 ferricyanide with potash, the pink precipitate again becomes black, for the potas- 
 sium cyanide reduces the silver ferricyanide to ferrocyanide, which is ultimately 
 decomposed by the silver oxide, with separation of metallic silver 
 
 (1) 2Ag 6 Fe 2 Cy 12 + 4KCN-f 4H 2 = 3Ag 4 FeCy 6 + K 4 FeCy 6 + 2HCN + 2C0 2 + 2NH 3 ; 
 
 (2) 4Ag 4 FeCy 6 + 2Ag 2 = Ag^e^y^ + i2AgCy + 2FeO + Ag 2 . 
 
 In the preparation of K 3 FeCy 6 , if an excess of chlorine be employed, the liquid 
 when evaporated deposits a precipitate of Prussian green, which appears to be a 
 compound of ferric ferrocyanide and ferricyanide, 2Fe 4 Fcy 3 .FeFcy, for, when 
 boiled with potash, it yields 5 molecules of ferric hydroxide, 3 molecules of 
 potassium ferrocyanide, and i molecule of potassium ferricyanide. 
 
 491. Nitroprussides. When potassium ferricyanide is acted on by a 
 mixture of NaN0 2 and acetic acid, it is converted into potassium nitro- 
 prusside, K 4 Fe 2 Cy ]0 (NO) 2 , probably according to the equation 
 
 K 6 Fe 2 Cy 12 + 4HN0 2 = K 4 Fe 2 Cy 10 (NO) 2 + 2HCy + H 2 + KN0 3 + KN0 2 . 
 If HgCl 2 be added to the solution, HgCy 2 crystallises, and, on further 
 evaporation, red prisms of sodium nitroprusside are deposited 
 
 K 6 Fe 2 Cy 12 + 4NaN0 2 +2HA + HgCl 2 = 
 Na 4 Fe 2 Cy 10 (NO) 2 + HgCy 2 + 2KC1 + 2KA + KN0 2 + KN0 3 + H 2 0. 
 
 Sodium nitroprusside, Na 4 Fe 2 Cy 10 (NO) r 4Aq, is prepared by a process 
 founded upon the above reactions (Hadow). 
 
 332 grains of potassium ferricyanide are dissolved in half a pint of boiling water 
 and 800 grains of acetic acid 'are added. Into this hot solution is poured a 
 cold solution containing 80 grains of sodium nitrite and 164 grams of mercuric 
 chloride in half a pint of water. The solution is kept at 60 C. for some hours, 
 until a little no longer gives a blue coloration with ferrous sulphate (a HI 
 
 )dium nitrite and acetic acid may be added if necessary). The mixture is then 
 .iled down till it solidifies to a thick paste on cooling ; this is squeezed in linen 
 to drain off the solution of potassium acetate ; the mass is dissolved m boili] 
 water, and allowed to cool, when most of the mercuric cyanide crystallises. < 
 concentrating the red filtrate, and cooling, crystals of sodium mtroprus 
 obtained, and may be purified by recrystallisation. 
 
696 CYANIDES. 
 
 Sodium nitroprusside was originally prepared by boiling ferrocyanide with nitric 
 acid (Playfair). Potassium ferrocyanide, in powder, is dissolved in twice its 
 weight of strong HN0 3 (1.42) mixed with an equal volume of water ; effervescence 
 occurs, from escape of C0 2 and N, and the odours of (CN) 2 , HCN and cyanic acid 
 may be distinguished. When the salt has dissolved, the solution is heated on a 
 steam bath till it no longer gives a blue with FeS0 4 . It is then allowed to cool, 
 when KN0 3 crystallises, and the solution is boiled with excess of Na^COg and 
 filtered ; the nitrate when evaporated deposits crystals of nitroprusside. 
 
 Sodium nitroprusside is very soluble in water ; the solution deposits 
 a blue precipitate when exposed to light. When its solution is rendered 
 alkaline by soda, and boiled, the NO group exerts a reducing action, 
 ferrous hydroxide being precipitated, and sodium ferrocyanide and nitrite 
 remaining in solution. Alkali sulphides have also a reducing effect 
 upon the solution, producing a fugitive violet-blue co)our, even in very 
 weak solutions, rendering sodium nitroprusside a most delicate test 
 for sulphur in organic compounds, which yield sodium sulphide when 
 fused with sodium carbonate. The sulphur in an inch of human 
 hair may be detected by this test. The higher (yellow) alkali sul- 
 phides should be reduced by warming with KCN" solution. Alcoholic 
 solutions of nitroprusside and sulphide of sodium yield a purple oily 
 compound soon decomposing into ammonia and several cyanogen com- 
 pounds. 
 
 With silver nitrate, sodium nitroprusside gives a buff precipitate of silrer 
 nitroprusside, Ag 4 Fe 2 Cy 10 (NO) 2 , and by decomposing this with HC1 the Injdro- 
 nitroprussic acid, H 4 Fe 2 Cy 10 (NO) 2 , may be obtained, by evaporation, in racuo, in 
 red deliquescent prisms (with iH 2 0). It is very unstable. 
 
 Potassium carbonyl ferrocyanide. K 3 FeCOCy 5 is obtained by heating a solution 
 of K 4 FeCy 6 with CO. 
 
 492. Chromic cyanide, Cr 2 Cy 6 , is a pale green precipitate produced by KCy with 
 chrome alum ; heated with excess of KCy, it yields 2)otassium chromicyanide, 
 K 6 Cr 2 Cy 12 , which may be obtained in yellow prisms. 
 
 Manganous cyanide, MnCy 2 , is probably contained in the greenish precipitate 
 by KCy in manganous acetate ; an excess of KCy dissolves it to a colourless 
 solution, from which alcohol separates blue crystals of potassium manganocyanide, 
 K 4 MnCy 6 .3Aq, isomorphous with the ferrocyanide. When exposed to air, the 
 solution of the manganocyanide absorbs oxygen, and deposits red prisms of 
 potassium mangani cyanide, KgMn 2 Cy 12 , isomorphous with the ferricyanide. 
 
 Cuprous cyanide, Cu 2 Cy 2 , is obtained as a white precipitate by boiling cupric 
 sulphate with KCy, when cupric cyanide, CuCy 2 , is first formed as a brown pre- 
 cipitate, which evolves cyanogen when boiled. Cuprous cyanide dissolves in 
 KCy. and the solution yields colourless crystals of potassium cupro-cyanide, 
 K 2 Cu' 2 Cy 4 , which gives a precipitate of plumbic cupro-cyanide, PbCu 2 Cy 4 , with lead 
 acetate. By decomposing the lead salt with H 2 S, a solution of the corresponding 
 acid, H 2 Cu 2 Cy 4 , is obtained, but this soon decomposes into 2HCy and Cu 2 Cy 2 . 
 
 493. Silver cyanide, AgCy, is obtained as a white precipitate when hydrocyanic 
 acid or a cyanide is added to silver nitrate. Its insolubility in water renders its 
 formation a very delicate test for HCy (in the absence of other acids forming 
 insoluble silver salts) and an accurate method of estimating its quantity. 
 
 Silver cyanide is not altered by sunlight like silver chloride, and is dissolved 
 when boiled with strong nitric acid, which does not dissolve the chloride. The 
 nitric solution, when cooled, deposits flocculent masses of minute needles of the 
 composition AgCy.2AgNO 3 , which detonate when heated. 
 
 Silver cyanide, when heated, fuses, evolves cyanogen, and leaves a residue of 
 silver mixed with silrer paracyamde, AgC 3 N 3 . Silver cyanide dissolves in ammonia 
 like the chloride, but the latter is deposited in microscopic octahedra, while the 
 cyanide forms distinct needles ; a mass of silver cyanide, moistened with ammonia 
 and warmed, becomes converted into needles. Potassium hydroxide does not 
 decompose silver cyanide. Potassium cyanide readily dissolves silver cyanide, 
 forming KAgCy 2 , which may be crystallised in six-sided tables. It is used in 
 electro-plating. 
 
PLATINOCYANIDES. 697 
 
 Mercuric cyanide, HgCy. 2 , is prepared by dissolving precipitated HgO in excess 
 of solution of HCN, and evaporating, when the cyanide is deposited in four-sided 
 prisms, which dissolve in eight parts of cold water, and are insoluble in alcohol For 
 its behaviour when heated see p. 687. It is one of the most stable of the cyanides, 
 scarcely allowing the cyanogen to be detected by the ordinary tests. Dilute 
 H. 2 y0 4 and HN0 3 do not decompose it, but HC1 liberates HCy. KOH and NH, do 
 not precipitate its solution. 
 
 Mercuric cyanide dissolves mercuric oxide when boiled, giving an alkaline 
 solution, which deposits needles of mercuric oacycyanide, JAg^OCy.^ When solutions 
 of mercuric cyanide and silver nitrate are mixed, the solution becomes acid, and, 
 on stirring, deposits fine needles containing Ag.Hg.N0 3 .Cy 2 .2Aq. The acid 
 reaction of the solution proves that some of the mercuric cyanide has become 
 converted into mercuric nitrate ; the same salt may be obtained by dissolving 
 silver cyanide in mercuric nitrate. Neither mercuric cyanide nor silver nitrate 
 is precipitated by excess of ammonia, but a mixture of the two salts gives an 
 abundant precipitate, containing HgCy. 2 7AgCy.2HgO, which explodes when 
 heated. The crystalline salt is probably AgCy.CyHgN0 3 .2Aq, containing HgCy.,, 
 in which N0 3 is substituted for Cy. Other crystalline compounds of the same kind 
 are formed by HgCy. 2 ; such as NaCy.CyHgCl and KCy.CyHgl. A potassio- 
 mercuric cyanide, KCy.CyHgCy.CyK, "may be obtained "in "fine crystals, which 
 may be decomposed by mercuric chloride, yielding HgCL 2 .HgCy 2 or Hg"Cy'Cr. 
 
 Mercuric cyanide was originally prepared by Scheele, when he discovered that 
 prussic acid could be prepared from Prussian blue. This was boiled with mercuric 
 oxide and water till the blue colour had disappeared; Fe 4 (Cy 6 Fe) 3 + 9HgO 
 9HgCy. 2 -r2Fe. 2 3 + 3FeO. The filtered solution was mixed with sulphuric acid, 
 shaken with iron filings, which precipitated the mercuiy, and distilled to obtain 
 hydrocyanic acid ; HgCy 2 + H 2 SO 4 + Fe = 2HCy + FeS0 4 + Hg. 
 
 Mercuric cyanide may be directly obtained from potassium ferrocyanide by 
 boiling it with mercuric sulphate (2 parts) and water (8 parts) 
 
 2K 4 FeCy 6 + ;HgS0 4 = 6HgCy 2 + 4K 2 S0 4 + Fe 2 (S0 4 ) 3 + Hg. 
 
 The mercurous cyanide is not known ; when mercurous nitrate is decomposed 
 by potassium cyanide, a solution of mercuric cyanide is formed, and metallic mer- 
 cury is precipitated ; Hg 2 (N0 3 ) 2 + 2KCy = HgCy 2 + Hg + 2KN0 3 . 
 
 Gold cyanides. Potassium aurocyanide, 2KAu'Cy 2 , is obtained by dissolving 
 gold in KCN solution (p. 514), or by dissolving fulminating gold (p. 518) in hot 
 water containing pure potassium cyanide. The filtered solution deposits colourless 
 crystals of the aurocyanide, which are very soluble in hot water. Aurmis cyanide, 
 AuCy, is obtained as a crystalline precipitate by adding HC1 to solution of the 
 aurocyanide of potassium. 
 
 Potassium aurlcyanlde, KAu'"Cy 4 , is prepared by mixing hot strong solutions 
 of gold trichloride and potassium cyanide. It forms colourless tables (with iH 2 0). 
 With AgN0 3 a precipitate of silver aurlcyanlde, AgAuCy 4 , is obtained, and if this 
 be treated with HC1, avoiding excess, the silver is precipitated as AgCl, and the 
 solution, evaporated in vacuo, yields crystals of auric cyanide, AuCy 3 .3Aq. 
 
 Both aurocyanide and auricyanide of potassium are used in electro-gilding. 
 
 494. Platinum cyanides. The cyanides of platinum have not been prepared in 
 a pure state, but the salts known as platinocyanides exceed the ferrocyanides in 
 the force with which they retain the platinum disguised to the ordinary tests. 
 When KCN is strongly heated on platinum foil, the metal is attacked, and an 
 orange-coloured mass is produced. Spongy platinum is slowly dissolved by a 
 boiling solution of KCN, and if mixed with the solid cyanide, and heated to 6 
 in steam, pota&xiuvi platlnocijan\de is formed 
 
 Pt + 4KCy + 2H 2 = K 2 Pt"Cy 4 + 2KOH + H 2 . 
 
 When solutions of potassium cyanide and platinic chloride are boiled together 
 till colourless, the platinocyanide is found in solution 
 
 PtCl 4 + 6KCN + 4 H 2 = K 2 Pt(CN) 4 + 4^C1 + 2NH 3 + H 2 C 2 4 . 
 Or the ammonio-platinic chloride may be boiled with pptash and a strong solution 
 of potassium cvanide until no more ammonia is evolved. hWiHo \ 
 
 Potassium platinocyanide is also prepared by dissolving platmous chloride m 
 solution of potassium cyanide; PtCl 2 + 4 KCy;=K 2 PtCy 4 + 2KU. it .allies 
 in prisms (with 3 HoO), which are yellow by transmitted, light, and reflect a blue 
 colour. They are very soluble in water. The solution is colourlebs, and gives a 
 
698 CHLOEIDE OF CYANOGEN. 
 
 characteristic blue precipitate with mercurous nitrate. CuSO 4 also gives a blue 
 precipitate, and if this be decomposed by aqueous H. 2 S, it yields a solution of 
 kydroplatinocyanic acid, H 2 PtCy 4 , which crystallises from ether in red prisms (with 
 5H 2 0) with a blue reflection. 
 
 Barium platinocyanide, BaPtCy 4 4Aq, is prepared by decomposing the cupric 
 salt with baryta. It is dichroic. being green when looked at along the primary 
 axis of the crystal, and yellow across it. It is remarkable for its property of 
 becoming luminous when exposed to the Rb'ntgen rays, in which respect it re- 
 sembles, but excels, many other platinocyanides. 
 
 Magnesium, platinocyanide, MgPtCy 4 .7Aq, obtained by decomposing the barium 
 salt with MgS0 4 , crystallises in large prisms, deep red by transmitted light, but 
 when viewed by reflected light, the sides of the prisms exhibit a brilliant beetle- 
 green, and the ends a deep blue or purple colour. When the red salt is gently 
 warmed, even under water, it becomes bright yellow, from production of 
 MgPtCy 4 .6Aq, which may be obtained in crystals from the solution at 71 C. 
 Heated at 100 C., the yellow salt becomes white MgPtCy 4 .2Aq, and at about i8oC. 
 it again becomes yellow, and is then anhydrous. If a little of the yellow anhydrous 
 salt be placed on the powdered red salt (with 7Aq), it abstracts water from it, and 
 converts it into the yellow salt with 6Aq, while it is itself changed to the white 
 salt with 2Aq, so that a white layer is formed between two yellow layers. The 
 yellow salt may also be obtained by crystallisation from alcohol. 
 
 When the platinocyanides are attacked, in solution, by oxidising-agents, such 
 as chlorine, bromine, or nitric acid, new salts are formed, which have a coppery 
 lustre, and act as oxidising-agents in alkaline solutions, like the ferricyanides. 
 These were formerly called platinicyanides, but were shown by Hadow to contain 
 chloro-, bromo-, &c., platinocyanides. When chlorine is passed into a hot solution 
 of potassium platinocyanide, it deposits, on evaporation, colourless crystals of 
 the chloroplatinocyanide, K. 2 PtCy 4 Cl 2 .2Aq. When these are treated with a strong 
 solution of the platinocyanide, they are converted into copper-red needles of 
 5K 2 PtCy 4 .K2PtCy 4 Cl 2 .3H 2 O.i8Aq. This compound, when boiled with potash, 
 yields the platinocyanide and potassium hypochlorite 
 
 5K 2 PtCy 4 .K 2 PtCy 4 Cl 2 + 2KOH = 6K 2 PtCy 4 + KOC1 + KC1 + H 2 0. 
 
 495. Cyanogen Halides. Cyanogen chloride, C ! N'Cl, is prepared 
 by the action of chlorine upon moist mercuric cyanide, in the dark ; 
 HgCy 2 + 2Cl 2 = HgCl 2 + 2CyCl. On gently heating, the cyanogen 
 chloride passes off in vapour, and may be condensed in a tube sur- 
 rounded with a freezing-mixture. It is a colourless liquid, boiling at 
 15 C., and yielding a vapour which irritates the eyes, causing tears. 
 When exposed to light, or treated with acids, it polymerises into 
 cyanuric chloride, Cy 3 01 3 , which fuses at 146 and boils at 190 C. 
 This has also an irritating effect on the eyes. It is sparingly soluble in 
 cold water, and is decomposed by boiling water, yielding cyanuric acid; 
 C y 3 cl 3 + 3 H 2 = Oy s (OH) 3 + 3HC1. Both these chlorides may be obtained 
 by the action of chlorine on hydrocyanic acid. 
 
 In practice cyanogen chloride is generally required in solution which is best 
 prepared by dissolving 260 grams of KCN and 90 grams of crystallised ZnS0 4 in 
 8 litres of water, and passing Cl until the ZnCy 2 at first thrown down is nearly 
 redissolved. 
 
 Cyanogen bromide, CyBr, is obtained in crystals, mixed with KBr, when bromine 
 is gradually added to a strong well-cooled solution of KCy. On gently heating, 
 it sublimes in crystals, which are very volatile and cause tears. When heated in 
 a sealed tube, it becomes Cy 3 Br 3 . It melts at 52 C. and boils at 61 C. 
 
 Cyanogen iodide. Cyl. is prepared by dissolving iodine in a warm strong solution 
 of KCy, when a crystalline mass of KI and Cyl is obtained on cooling, from which 
 the Cyl may be extracted by gently heating or by treatment with ether. It 
 crystallises easily in colourless needles or tables, which are sparingly soluble in 
 water, very volatile, and have a tear-exciting odour. It sometimes occurs in 
 commercial iodine, from which it may be sublimed in a tube or flask plunged in 
 boiling water. When heated to 100 C., in a sealed tube, with alcoholic ammonia, 
 it yields hydriodide of guanidine, CNI + 2NH 3 = CN 3 H 5 .HI. 
 
NITRILES. 
 
 496. Cyanides of Hydrocarbon Radicles, or Acid Nitriles. The 
 term nitrile was originally applied to the final product of the removal 
 of water from an ammonium salt (cf. p. 667), the amide being the 
 
 intermediate product. Thus, when the group C/ , characteristic 
 
 of the organic ammonium salts, loses i mol. H 2 0, it passes into the 
 C^ group of the amides, and when this loses i mol. H,0, it 
 
 becomes C=N, the nitrile group. It was later found that the nitriles 
 are identical with the cyanides of the hydrocarbon radicles. 
 
 Hence there are two general lines on which these compounds may be 
 prepared, viz., (i) by reactions which produce cyanides, such as (a) by 
 heating the iodide of a hydrocarbon radicle with KCN in alcoholic 
 solution, CH 3 I + KCN = KI + CH 3 -CN, or (b) by distilling an alkali 
 alkyl sulphate with KCN, KCH 3 S0 4 + KCN = CHyCN + K 2 S0 4 ; (2) by 
 dehydrating ammonium salts or amides by distillation" with P 8 0., 
 CH 3 -CONH 2 - H 2 = CH 3 -CN. 
 
 The ease with which the CIS" group reverts to the COOH group when 
 the cyanides or nitriles are hydrolysed and the importance thus attach- 
 ing to these compounds in synthetic chemistry have been dwelt upon 
 already (p. 688). When an acid is the hydrolytic agent the ammonium 
 salt is produced CH 3 -CN + 2 HOH = CH 3 -COONH 4 ; but when it is an 
 alkali the NH 3 is evolved, CH 3 'CN + HOH + KOH = NH 3 + CH 3 -COOK. 
 The reaction shows that of two possible formulae for the cyanide, 
 H 3 C'C N and H 3 C'N I C, the former must be correct, since the 
 hydrolysis does not part the C atoms, which must therefore be directly 
 united in the cyanide. The action of nascent hydrogen on the cyanide 
 
 <**j 
 . 
 
 JN -tlo 
 
 Cyanogen itself is oxalonitrile, and may be obtained by dehydrating 
 ammonium oxalate COONH 4 -COONH 4 = CN'CN + 4 H 2 0. Hydrocyanic 
 acid is formonitrile, obtained from ammonium formate; HCOONH 4 = 
 HCN + 2 H 2 0. 
 
 Methyl cyanide, or acetonitrile, CH 3 'CN, prepared as above, is a 
 volatile liquid of pleasant odour boiling at 8i.6 C. Its sp. gr. is 0.8, 
 and it is soluble in water and alcohol. 
 
 The tendency for the nitrogen in the C : N group to become pentavalent, leads 
 to the formation of crystalline compounds of CH 3 CN with Br 2 , HBr and HI, &c. 
 Certain chlorides also combine with methyl cyanide to form crystalline volatile 
 substances, decomposed by water ; such compounds are formed with PC1 3 , SbCl 5 , 
 and SnCl 4 . When methyl cyanide is acted on by sodium, part of it is decomposed 
 with violent evolution of methyl hydride, and the remainder is polymerised to 
 form cyanmethlne (CH 3 ) 3 (CN) 3 , an organic base, soluble in water, and having a 
 very bitter taste. It forms prismatic crystals, which may be sublimed. 
 
 An instructive reaction yielding methyl cyanide is that between diazomethane 
 and HCN ; CH : N 2 + HCN = CH 3 CN + N 2 . This illustrates the application of diazo- 
 methane in the" formation of a number of organic compounds. 
 
 Methyl cyanide is present, in small quantity, in coal-naphtha, and in the c 
 tillate from' beet-sugar refuse. 
 
 Ethyl cyanide, or pnyw-nitrlle, C 2 H 5 'CN, is similarly obtained. It resembles 
 methyl cyanide, except in being less soluble in water, and in boiling at 95 L/. 
 
700 CAEBAMINES. 
 
 combines with HC1 to form a sparingly soluble crystalline compound, which 
 absorbs water from the air, and yields propionic acid and ammonium chloride. 
 
 Sodium acts on ethyl cyanide in the same way as on CH 3 *CN : one part is decom- 
 posed, with evolution of butane (di-ethyl) 2C 2 H 5 CN + Na 2 = C 4 H 10 + 2NaCN. 
 The remainder is polymerised to cyanetldne (C 2 H 5 ) 3 (CN) 3 . 
 
 Phenyl cyanide, or benzonitrile, C 6 H 5 'CN, also called cyanohenzene, may be 
 prepared by dehydrating ammonium benzonate. also by distilling potassium 
 benzenesulphonate with KCN (or well-dried K 4 FeCy 6 ) ; C 6 H 5 'S0 3 K + KCN = 
 C fi H 5 'CN + K 2 S0 3 . It is a colourless liquid smelling of bitter almonds ; sp. gr. 
 1.023, Boiling at 191 C. By hydrolysis it becomes ammonium benzoate. Nascent 
 hydrogen converts it into benzylamine, C 6 H 5 CH 2 'NH 2 . Its formation from 
 diazobenzene has already been noticed (p. 681). 
 
 Benzyl cyanide, C 6 H 5 'CH 2 'CN, or phenyl-acetonitrile, is obtained by heating 
 benzyl chloride with potassium cyanide and alcohol. It occurs in the essentail oils 
 of nasturtium and cress. When boiled with alkalies, it yields ammonia and frfienyl 
 acetic (or a-toluic) acid, C 6 H 5 -CH 2 -C0 2 H. 
 
 497. Isocyanides, Isonitriles, or Carbylamines (Carbamines). 
 These compounds are isomeric with the cyanides of the hydrocarbon 
 radicles, but differ from them in being much less easily attacked by 
 alkalies and in yielding formic acid and an amine of the hydrocarbon 
 radicle when hydrolysed by acids, methyl isocyanide, for example, 
 yielding methylamine, H 3 C'NH 2 , and formic acid, HCOOH. This 
 reaction shows that the C atoms in the isocyanide are not united 
 directly, but through the N atom ; in other words, the second of the 
 two possible formulae given above for the cyanide, H 3 C'N I C, must be 
 ascribed to the isocyanide.* The formation of two carbon compounds 
 on hydrolysis is easily explained on this assumption ; CH 3 *NC + 2HOH = 
 CH 3 -NH 2 + HCOOH. 
 
 The isocyanides are obtained in small proportion together with the 
 cyanides when the iodides of the hydrocarbon radicles are heated with 
 KCN, but they are almost the sole products when AgCN is substituted 
 for the KCN. The iodide and AgCN are heated in a sealed tube with 
 ether at 140 C., when a crystalline compound of the isocyanide with 
 AgCN is formed ; this is distilled with water and KCN, whereupon the 
 isocyanide distils ; CH 3 I + 2 AgCN = CH 3 'NC, AgCN + Agl ; 
 
 CH 3 -NC,AgCN + KCN = CH 3 NC + KCN,AgCN. 
 
 The term carbamine refers to the idea formerly entertained that the 
 isocyanides were amines in which carbon is substituted for hydrogen ; 
 thus, methyl carbamine, NC'CH 3 , might be regarded as methylamine, 
 NH 2 CH 3 , in which C" is substituted for H 2 . Their connection with 
 the amines is illustrated by the fact that they can be prepared by 
 the action of chloroform and alcoholic potash on the amines ; e.g., 
 CH 3 -NH 2 + CHC1 3 + 3 KOH = CH 3 -NC + 3 KC1 + 3 HOH. 
 
 The isocyanides often accompany the cyanides of the alcohol-radicles, especially 
 when prepared by distilling the acid ethereal salts, such as potassium ethylsulphate, 
 with potassium cyanide. For this reason the cyanides of alcohol-radicles were 
 formerly described as having an offensive smell, which is really characteristic 
 of the isocyanides mixed with them. 
 
 Methyl isocyanide or methyl carbamine, H 3 ONC, is prepared as described above. 
 It is lighter than water (sp. gr. 0.76) and moderately soluble in it. It has an 
 extremely unwholesome smell, and boils at 59 C. Methyl carbamine is slightly 
 alkaline ; it combines with HC1 gas. forming a crystalline hydrochloride, which is 
 decomposed by water into formic acid and methylamine hydrochloride ; 
 H 3 C-NC.HC1 + 2H 2 = H 3 ONH 2 -HC1 + HC0 2 H. 
 
 * According- to Nef the isocyauides must be regarded as containing bivalent carbon, 
 H-.C-NiC. 
 
TAUTOMERISM. 
 
 Ethyl m-i/amde, or ethyl carbarn ine, H 5 C 2 'NC, prepared like the methyl 
 compound, boils at 79 C., and has a repulsive odour like that of hemlock 
 is lighter than water, and slightly alkaline. When heated with water at 180 C for 
 some hours it is converted into ethylatnine formate ; 
 
 H 5 C 2 -NC + 2 H 2 = H 5 C 2 -NH 2 .HC0 2 H. 
 
 Heated alone in a sealed tube at 230 C., it is metamerised into propionitrile ; 
 H s C 2 -:NC = HgC 2 -CN. Ethyl carbamine torms a crystalline salt with HC1 from 
 which very strong, well cooled potash separates an oily layer of eth.,1 for,,, amide ; 
 CN C 2 H 5 + H. 2 O = ICO NHC 2 H 5 . Glacial acetic acid also converts ethyl carbamine 
 into ethyl formamide, producing acetic anhydride and much heat _ 
 
 CN-C 2 H 5 + 2(C 2 H 3 OOH) = HCO-NHC 2 H 5 + (C 2 H 3 0) 2 0. 
 
 Phenyl isocyanide, or phenyl carbamine, H 5 C 6 'NC, is prepared by mixing aniline 
 with a saturated alcoholic solution of potash, and gradually adding chloroform ; 
 the distillate is treated with oxalic acid to remove aniline, with potash to remove 
 water, and re-distilled. Phenyl carbamine has a very terrible odour ; it is green 
 by transmitted light, and shows a blue reflection, "it begins to boil at 166 C., 
 but soon decomposes, being converted, at 230 C., into an odourless liquid which 
 crystallises on cooling. When heated, in a sealed tube, at 200 C., phenyl 
 carbamine slowly metamerises into phenyl cyanide, or benzonitrile, H 5 C 6 'CN. 
 Treated with acids, it yields formic acid and salts of phenylamine (aniline) " 
 H 5 C 6 'NC + 2H 2 = H 5 C 6 -NH 2 + HC0 2 H. 
 
 498. Tautomerism. It has been seen that the cyanides of alcohol- 
 radicles exist in two forms, as though they were derived, from two 
 hydrocyanic acids, H'C=N and H'N=C. It will be seen later that 
 derivatives of cyanamide also appear to be derived from two isomerides, 
 H 9 N'C : N and HN : C : NH. Two hydrocyanic acids or two 
 cyanamides, however, have never been prepared. It is the case with 
 a large number of substances that, although they do not exist in 
 isomeric forms, they behave in different reactions as if they had two 
 structural formulae, either of which could be assumed according to the 
 conditions. Such compounds are said to possess tautomeric structures. 
 The derivatives of one form (the stable form) are generally more stable 
 than those of the other (the labile form or pseudoform). 
 
 Tautomerism is generally connected with the migration of a H atom, as will be 
 seen from the above examples. It is very common among ketonic compounds, in 
 which the grouping -CH : COH' occurs, this tending to become 'CH./CO (ef. ethyl 
 acetoacetate, p. 643) ; the former is the hydroxtjl- or enol- form, while the latter 
 is the lieto- form. Cf. also lactanis and lactims (pp. 674, 679), and (iinidhtrx (p. 698). 
 
 From the fact that the chief product of the action of CH 3 I on KCN is methyl 
 cyanide, it may be supposed that potassium cyanide is a salt of H'C N. Silver 
 cyanide, on the other hand, must be a salt of H'N j C. for the chief product of 
 its reaction with methyl iodide is methyl isocyanide. 
 
 499. Hydroxy- and Thio-Cyanogen Compounds. Cyanuric 
 acid, Cy 3 (OH) 3 , is obtained by heating urea till the melted mass solidifies ; 
 
 (CN) 3 (OH) 3 . The residue is washed with water, 
 
 dissolved in KOH, and the cyanuric acid precipitated by adding HC1. 
 A better yield is obtained by passing dry chlorine over urea kept in 
 fusion by a gentle heat 3 CO(NH 2 ) 2 + C1 3 - 2NH 4 C1 + HC1 + N + 
 (CN) 3 (OH) 3 . The residue is washed with cold water, and crystallised 
 from hot water. Cyanuric acid crystallises in prisms containing 2Aq. 
 It is insoluble in alcohol. It is a tribasic acid. It is probable that 
 cyanuric acid is a closed-chain compound, and it may be represented by 
 
 - 
 
 either of the tautomeric formulae C(OH)< C /QO\/ ' or 
 
702 CYANIC ACID. 
 
 x 
 
 CCX' /NH, derivatives (the cyanuric esters, e.g., C 3 lSr 3 03(CH 3 ) 3 ) 
 
 NH'CO 
 of both forms being known. 
 
 Trisodium cyanurate, (CN) 3 (ONa) 3 , is insoluble in hot solution of soda and forms 
 a crystalline precipitate on heating solution of cyanuric acid mixed with excess of 
 soda. Barium cyanurate, Cy 3 3 HBa, is obtained as a crystalline precipitate by 
 dissolving cyanuric acid in NH 3 , and stirring with BaCl 2 . It has a great tendency 
 to deposit on the lines of friction by the stirring-rod. The most characteristic 
 test for cyanuric acid is ammoniacal CuS0 4 , which gives a violet crystalline 
 precipitate containing Cy 6 (OH) 4 '0 2 'Cu(NH 3 ) 2 . Stiver cyanurate, Cy 3 (OAg) 3 is 
 obtained as a crystalline precipitate by adding ammonium cyanurate to silver 
 nitrate. 
 
 500. Cyanic acid, CyOH, is prepared by distilling cyanuric acid 
 (dried at iooC.), and condensing in a receiver surrounded by a freezing- 
 mixture ; Cy 3 (OH) 3 = 3CyOH. The cyanic acid is a colourless liquid, of 
 sp. gr. 1.14 at o C., which smells rather like acetic acid. It cannot be 
 kept, for when the receiver is taken out of the freezing-mixture the 
 acid becomes turbid, and presently begins to boil explosively, being 
 entirely converted in a few minutes into a white hard solid, known as 
 cyamelide, which is a polymeride of cyanic acid, into which it is recon- 
 verted by distillation. When cyanic acid is mixed with water, heat is 
 evolved, and the liquid becomes alkaline ; CN'OH + 2H 2 O = NH 4 'HC0 3 . 
 A compound of HC1 and CNOH is obtained as a fuming liquid by 
 acting on a cyanate with dry HC1 gas. 
 
 It is doubtful whether cyanic acid is HOC : N (the nitrile of car- 
 bonic acid) or HIS" : C : (carbimide). The former would be cyanic 
 acid and the latter isocyanic acid. At one time it was supposed that 
 derivatives of both were known, but the compounds formerly called 
 esters of cyanic acid have been shown to have a different constitution. 
 
 Potassium cyanate. The compound formerly so called is probably the 
 isocyanate, K'N : C : 0, since it has been found to give rise to alkyl 
 isocyanates when heated with potassium alkyl sulphates. It is formed 
 when the cyanide is oxidised by fusion in contact with air or with 
 metallic oxides. 
 
 It may be prepared by oxidising potassium ferrocyanide with potassium di- 
 chrornate. Four parts of perfectly dried K 4 FeCy 6 are intimately mixed with 3 parts 
 of K 2 Cr 2 7 ; the mixture is thrown, in small portions, into a porcelain or iron dish, 
 heated sufficiently to kindle it. When the whole has smouldered and blackened, 
 it is allowed to cool, introduced into a flask, boiled with strong alcohol, and filtered 
 hot ; the isocyanate crystallises out on cooling, and the mother liquor may be 
 employed to extract a fresh portion. 
 
 Potassium isocyanate is also prepared by passing cyanogen chloride 
 into well-cooled potash; CN'C1 + 2KOH = KCNO + KC1 + H 2 0. It 
 crystallises in plates ; it is decomposed b}' moist air into KHC0 3 and 
 ammonia; K'NC : + 2H 2 = KHC0 3 + NH 3 . It is very soluble in 
 water, but the solution soon decomposes, especially if heated 
 sK-NC : + 4H 2 = CO(OK) 2 + CO(ONH 4 ) 2 . If the freshly pre- 
 pared solution be mixed with dilute acetic acid, a crystalline precipitate 
 of potassium dihydrogen cyanurate is obtained; 3 KNCO + 2HA = 
 KH C 3 N 3 3 + 2KA. Solution of potassium isocyanate effervesces with 
 acids evolving C0 2 , together with some pungent vapour of cyanic (or 
 isocyanic) acid, and leaving an ammonium salt in solution. 
 
 Ammonium cyanate, NH 4 -0'CN, or O : C : N(NH 4 ) is prepared by 
 
POTASSIUM SULPHOCYANIDE. 703 
 
 mixing vapour of cyanic acid with ammonia gas in excess, when it 
 is deposited in minute crystals, which effervesce with acids, evolving 
 C0 2 . The cyanate or isocyanate is also formed when potassium iso- 
 cyanate is decomposed by ammonium sulphate. By employing strong 
 solutions and cooling artificially, the bulk of the potassium sulphate 
 may be crystallised out. The isocyanate has not been crystallised, for, 
 when its solution is evaporated, it metamerises into urea NH *NC -0=' 
 (NH 2 ) 2 CO (p. 670). 
 
 501. Thiocyanic acid, HSCN (sulphocyanic), is obtained by decom- 
 posing mercuric thiocyanate with hydrogen sulphide. It is a colourless 
 pungent liquid, boiling below 100 C., being then decomposed into 
 hydrocyanic and persulphocydnic acids; sCySH = HCy + Cy 2 S 3 H 2 . It 
 mixes with water, but the solution soon decomposes 
 
 3 HSCN + 6H 2 = CS 2 + H 2 S + NH 4 HC0 3 + (NH 4 ) 2 C0 3 . 
 Thiocyanic acid and the thiocyanates give an intense blood-red colour 
 with ferric salts, producing ferric thiocyanate ; the red is bleached by 
 HgCl 2 , which distinguishes it from ferric acetate and meconate. 
 
 Potassium thiocyanate, or sulphocyanide, KCSN, may be obtained by 
 direct fusion of potassium cyanide with sulphur, or by boiling sulphur 
 with solution of the cyanide. 
 
 It is best prepared by fusing dried potassium ferrocyanide (3 parts), potassium 
 carbonate (i part), and sulphur (2 parts), at a low red heat, in a clay crucible. 
 The cooled mass is extracted by hot water, evaporated, and the residue boiled with 
 alcohol, which deposits the thiocyanate on cooling. KCy is formed by the reaction 
 between the ferrocyanide and the carbonate (p. 691), and combines with the sulphur. 
 
 Potassium thiocyanate forms prismatic crystals, which are deliquescent 
 and very soluble in water, producing great reduction of temperature. 
 It fuses easily, becoming a dark blue colour, which fades on cooling ; it 
 burns when heated in air, potassium sulphate being produced. When 
 hydrochloric acid is added to a strong solution of potassium thio- 
 cyanate, a yellow precipitate of persulphocyanic acid is obtained ; 
 this may be crystallised from hot water, and yields a yellow precipi- 
 tate of lead per sulphocyanate, PbCy 2 S 3 , with lead nitrate. When heated 
 with sulphuric acid mixed with an equal volume of water, potassium 
 thiocyanate yields carbon oxysulphide, an offensive gas which burns 
 with a blue flame ; KSCN + 2 H 2 S0 4 + H 2 = KHS0 4 + NH 4 HS0 4 + COS. 
 
 Potassium -isothhcyanate, K'NCS, is said to be obtained by heating persulpho- 
 cyanic acid with alcoholic solution of potash. The crystals are soluble in water ; 
 the solution does not give the red thiocyanate reaction with ferric salts. It is con- 
 verted into normal thiocyanate by boiling or fusing. Sodium thiocyanate occurs 
 in saliva. 
 
 Perthiocyanoyen, or ineiidosulphocyanogen, C 3 N 3 S 3 H, is obtained as a yellow pre- 
 cipitate when potassium thiocyanate is heated with potassium chlorate and hydro- 
 chloric acid. It is used in dyeing (canarln). 
 
 Ammonium t/tior//(jnate is prepared by acting on carbon bisulphide (7 parts by 
 weight) dissolved in alcohol (30 parts) with strong ammonia (30 parts). After 
 standing for a day or two, with occasional shaking, until all the CS 2 has dissolved, 
 the red solution is distilled down to one-third of its bulk, when it becomes colour- 
 less, filtered if necessary, and allowed to crystallise ; 
 
 CS 2 + 4 NH 3 = CNS-NH 4 + (NH 4 ) 2 S. 
 
 It is also made on a large scale by boiling sulphur with the solution of ammonium 
 cyanide from the gasworks. It crystallises like the potassium salt, and is very 
 soluble in water, producing great cold. When heated, it fuses easily, and at 
 170 C., is metamerised into tMooarbamide (p. 671). 
 
704 CYANOGEN DEEIVATIVES. 
 
 Leadth'toeyanate, Pb(CyS)2, forms a yellow crystalline precipitate. 
 
 Silver thioeyanate, AgCyS, is a white precipitate, very insoluble in water and in 
 nitric acid, and sparingly soluble in ammonia. 
 
 Mercuric thioeyanate, Hg(CyS) 2 , is a crystalline precipitate formed on stirring- 
 mercuric chloride with an alkali thioeyanate. It attracted much notice formerly 
 as the toy called Pharaoh's serpent, which was a small cylinder of the thioeyanate 
 mixed with gum, which burnt when kindled, evolving mercury and other vapours, 
 and swelling to a bulky vermiform mass of mellone. 
 
 Cuprous thioeyanate, Cu 2 (CyS) 2 , precipitated by potassium thioeyanate from a 
 cuprous salt, is very insoluble in water and in cold dilute acids, so that copper is 
 sometimes precipitated in this form in quantitative analysis. 
 
 502. Cyanogen sulphide. Cy 2 S, is obtained by decomposing cyanogen iodide, 
 dissolved in ether, with silver thioeyanate; CyI + AgCyS = Cy 2 S + AgI. It is a 
 crystalline, fusible, volatile solid, soluble in alcohol and ether, but decomposed by 
 water ; potash converts it into cyanate and thioeyanate. 
 
 Phosphorus tricyanide, Cy :5 P, is sublimed in tabular crystals from a mixture of 
 silver cyanide and phosphorus trichloride, heated in a sealed tube at 140 C. for 
 some hours, and distilled in a current of C0 2 . It inflames at a very low tempera- 
 ture, and is decomposed by water into hydrocyanic and phosphorous acids ; 
 Cy.,P + 3 HOH = 3 CyH + P(OH) 3 . 
 
 Cyanamide, H 2 N'CN, which also behaves as carbodiitwide, NH : C : NH, may be 
 obtained by fusing urea with sodium (NH 2 ) 2 CO + Na = H. 2 N -ON + NaOH + H. The 
 mass is dissolved in water, ammonia added in excess, and silver nitrate, which 
 gives a yellow precipitate of Ag 2 N'CN ; this is washed, dried, covered with ether, 
 and decomposed byH 2 S, when Ag 2 S and H 2 N'CN are produced, the latter dissolv- 
 ing in the ether, from which it may be crystallised. 
 
 Cyanamide may also be prepared, like other amides, by acting on NH.,, dissolved 
 in ether, with gaseous CNC1 ; NH 3 + CN;C1 = H 2 N'CN + NH 4 C1. 
 
 Another reaction which furnishes it is that between thiourea (p. 671) and mer- 
 curic oxide ; (NH 2 ) 2 CS + HgO = H 2 N'CN + HgS + H 2 0. It forms crystals soluble in 
 water, alcohol, and ether, and melting at 40 C. HC1 passed into its ethereal 
 solution gives crystals of H 2 N'CN,2HC1. Hydrolysis converts it into urea, and 
 H 2 S into thio-urea. With NH 3 it yields guanidine.. 
 
 Dicyanimlde, HN(CN) 2 , is produced by the action of potash on solution of 
 potassium cyanate ; 3KOCN + H 2 = (KO) 2 CO + KOH + HN(CN 2 .) On neutralising 
 the solution with HN0 3 and adding AgN0 3 , a precipitate of AgN(CN)2 is obtained. 
 Potassium isocyanate, K'NCO, does not yield dicyanimide. 
 
 The amides of cyanuric acid are (i) melamine or cyanuramide, C 3 N 3 (NH. 2 ) 3r 
 obtained by the action of NH 3 on cyanuric chloride, (2) ammeline, C 3 N 3 (NH 2 ).,OH, 
 produced \>\ boiling melamine with HC1, and (3) ammelide, C 3 N 3 NH 2 (OH)2, formed 
 by boiling melamine with KOH. Melamine crystallises from water, but the others, 
 are insoluble. 
 
 When NH 4 SCN is heated, it loses NH 3 and H 2 S, and is converted successively 
 into melam, C 6 H 9 N n , melem, C 6 H 6 N 10 , and mellone, C 6 H 3 N 9 , white amorphous com- 
 pounds. Potassium mellonide, C 9 K 3 N 13 , is formed when KSCN is heated out of 
 contact with air, CS 2 being evolved ; this crystallises with 3 Aq and yields a corre- 
 sponding silver salt and free acid. 
 
 Chrysean, [CN'CH(SH)] 2 NH, is obtained by covering potassium cyanide with 
 water, in a flask, and saturating with H 2 S gas ; 
 
 4KCN + 5H 2 S = C 4 H 5 S 2 N 3 + 2K 2 S + NH 4 HS. 
 
 It crystallises from boiling water in golden needles, soluble in alcohol, ether, acids, 
 and alkalies. Its alcoholic solution is red, and changes to a fugitive green on 
 adding a little alkali. 
 
 503. Alltyl cyanurates and isocyanates. The compounds recently described as 
 alkyl cyanates are proved to be esters of imido-carbonic acid. By the action of 
 CNC1 on sodium alkyloxides, products are obtained which rapidly polymerise to 
 alkyl cyanurates e.g., 3Cl'CN + 3CH 3 ONa = 3NaCl + (CH 3 ) 3 3 C 3 N 3 . 
 
 Methyl isocyanate, or methyl carbimlde, H 3 C'NC:0, was formerly regarded as the 
 normal cyanate, being obtained by distilling potassium methyl sulphate with 
 potassium cyanate ; KCH 3 S0 4 + K'O CN = H 3 ONC :0 + K 2 S0 4 . It is also obtained 
 by oxidising methyl isocyanide with mercuric oxide ; 
 
 H 3 C'NC + HgO = H 3 C-NC:0 + Hg. 
 It is a volatile liquid (b.-p. 44 C.) with a suffocating odour. When distilled 
 
OIL OF MUSTARD. 705 
 
 with potash it yields- methylamine, showing that the methyl is attached to the 
 S nxr e R /rn^\ A 6 com P. ound is the isocyanate: H 3 ON : CO + 2KOH = 
 ?Tt P T?P t<? ( VH ^R'TRrR ^converts methyl ^cyanate into ,%* 
 (H 3 L JNb . U + JSH 3 = NH 2 -NHCH 3 -CO) resembling urea itself 
 
 m ^W%^%'^W<>**a*d by the action of water on methyl iso- 
 
 cyanate ; - - 
 
 Ethyl isocyanate, or ethyl carUmide, H 5 C 2 'NC : 0, is prepared like the methyl 
 compound, which it resembles. Its sp. gr. is 0-9 and it boils at 60 C It yields 
 ethylamine when distilled with potash, and triethylamine with sodium ethoxide 
 H 5 C 2 -NC : + 2(C 2 H 5 -ONa) = (H 5 C 2 ) 3 N + CO(ONa) 2 . 
 
 Ai i?* yl Ur ' ( NHC 2 H 5 ) 2 CO, and Methyl urea 
 
 5 ) 2 -CO, have been obtained. 
 Methyl-ethyl urea, NHCH 3 'NHC 2 H 5 -CO, is formed by the action of methylamine 
 ethyl isocyanate ; H 5 C 2 'NC : + NH 2 CH 3 = (NHCH 3 )NHC 2 H 3 'CO. 
 
 on 23 323 
 
 504. The isothiocyanates of the hydrocarbon radicles are called 
 mustard oils or thiocarbimides. 
 
 Allyl isothiocyanate, H 5 C 3 'NCS, is the essential oil of mustard, 
 obtained by grinding black mustard seeds with water and distilling. It 
 does not exist in the seed, but is produced by the decomposition of 
 potassium myronate contained in the seed, induced by a peculiar ferment 
 called myrosin, which decomposes the myronate into the essence of 
 mustard, glucose, and KHSO 4 ; K0 10 H 18 NS,0 10 = H 5 C 3 'NCS + C 6 H 12 6 + 
 KHS0 4 . The seed yields about 0-5 per cent, of the oil. 
 
 The potassium myronate may be obtained from ground mustard by 
 rendering the myrosin inactive by boiling alcohol, and then extracting 
 the myronate with cold water. The solution is evaporated to a small 
 bulk and mixed with alcohol, which precipitates the potassium 
 myronate. The free acid is not known, being very unstable. 
 
 Myrosin is prepared by extracting ground white mustard with cold 
 water, evaporating the nitrate to a syrup below 40 C., and adding 
 alcohol in small quantity, when the myrosin is precipitated. It some- 
 what resembles albumin, being coagulated and rendered inactive by 
 heat. Its aqueous solution, when added to potassium myronate, 
 causes it in a few minutes to smell of mustard and become acid ; it 
 also becomes turbid from the separation of small globular cells like 
 those of yeast. Myrosin occurs in other plants than mustard, such 
 as the radish, rape, cabbage, and swede, all belonging to the same 
 natural order as mustard (Cruciferce). Mignonette root furnishes phenyl 
 ethyl mustard oil, or phenyl ethyl isothiocyanate. 
 
 % Essential oil of mustard has sp. gr. 1.017, and boils at 150 C. It is insoluble in 
 water, but dissolves in alcohol and ether. It is the cause of the pungent odour 
 of mustard paste and of its power to redden and irritate the skin. It is slowly 
 decomposed by light, depositing a yellow precipitate. When heated with water 
 at 100 C. for some time it loses sulphur and becomes crotono-mtrile, C 3 H 5 -CN, 
 which is present in considerable quantity in commercial mustard oil. When 
 mustard oil dissolved in alcohol is acted on by HC1 and Zn, it yields allylamine : 
 H 5 C 3 -NCS + H 4 = H 5 C 3 'NH 2 + HCHS (thhformaldehyde). By mixing mustard oil 
 with ammonia and passing ammonia gas, allijl-thw-urea, or MtMMMMMM, 
 NH 2 -NH(CoH B )-CS, is obtained, forming prismatic crystals soluble in water, 
 alcohol, and ether, and having a bitter taste. It is a weak base. Whenheated witj 
 lead hydroxide, it loses H 2 S, and becomes allyl-cyanamide, NHGA^i luch 
 afterwards polymerises into sinamine, or trl-allyl melamine, (1 iO 3 U 6 ) 3 CO. 
 This is a strongly alkaline base. 
 
 If allyl bromide be decomposed by ammonium thiocyanate, at a low tem- 
 perature, alliil thiocyanate, H,C S 'SCN, is formed, which has no smell of mustard. 
 When this is heated, it boils at i6iC., but the boiling-point soon falls, and < 
 strong smell of mustard is perceived. When the boiling-point has re 
 
706 MERCUEIC FULMINATE. 
 
 150 C., the whole distils over as allyl isothiocyanate, H 5 C 3 'NCS, or mustard oil. 
 Allyl thiocyanate, decomposed by potash, yields potassium thiocyanate and allyl 
 alcohol ; H 5 C S -SON + KOH = H 5 C 3 'OH + K-SCN ; allyl isothiocyanate gives allyl- 
 amine ; H 5 C 3 : NCS + 4 KOH = H 6 C 3 -NH 2 + K 2 S + CO(OK) 2 + H 2 0. 
 
 Mustard oil is also obtained artificially by distilling allyl iodide (p. 636) with 
 
 th 
 
 potassium thiocyanate; C 3 H 5 I + KSCN = C 3 H 8 -NCS + KI. When ethyl iodide is 
 treated in the same way, ethyl- thiocyanate, C 2 H 5 'SCN is obtained. To obtain 
 the ethyl isothiocyanate, or ethyl mustard oil, or ethyl tlitocarbimide, C 2 H 5 'NCS, 
 ethylamine dissolved in alcohol is digested with carbon bisulphide, "distilled 
 nearly to dryness. and the residue in the retort boiled with solution of HgCl 2 . All 
 primary amines yield the corresponding mustard oils when treated in this manner, 
 and, since the odour is quite characteristic, the treatment with CS 2 iand HgCl 2 is 
 known as the mustard-oil tent for primary lases. 
 
 The mustard-oil reaction is easily explained. When C0 2 is combined with dry 
 NH 3 , ammonium carlamate is formed; C0 2 + 2NH 3 = CO(ONH 4 )(NH 2 ). If CS 2 be 
 substituted for C0 (the CS 2 employed in alcoholic solution), ammonium tkioearba- 
 mate is produced CS 2 + 2NH 8 = CS(SNH 4 )(NH 2 ). 
 
 When ethylamine is used instead of ammonia, the product is etht/l ammonium, 
 ethyl-thiocarbamate ; CS 2 + 2NH 2 (C 2 H 5 ) = CS-SNH 3 (C 2 H 5 )NH(C 2 H 5 ). On decompos- 
 ing this with mercuric chloride, it yields the corresponding mercuric salt, which 
 is decomposed, by boiling with water, into ethyl isothiocyanate. mercuric sulphide 
 and hydrogen sulphide ; Hg(CS-S'NHC 2 H 6 ) 2 = HgS + H 2 S + 2C 2 H 5 NCS.. 
 
 Butyl isothiocyanate, C 4 H 9 'NCS, is the essential oil of scurvy-grass, another 
 cruciferous plant, and is sometimes sold as mustard oil. but it has a higher 
 boiling-point, 160 C. 
 
 505. Fulminates. The salts known as fulminates are prepared from 
 the fulminates of mercury and silver, obtained when those metals are 
 treated with nitric acid and alcohol. It is still doubtful what is their 
 constitution, but the latest researches seem to show that they are salts 
 of the acid C : N*OH, which may be regarded as the oxime (p. 625) of 
 C carbyloxim e . 
 
 Mercuric fulminate (C : N'0) 2 Hg, is prepared on a small scale, with 
 safety, by carefully observing the following directions : Dissolve 
 1.6 grm. of mercury in 14 c.c, of ordinary concentrated nitric acid 
 (sp. gr. 1.42) in a half-pint beaker, covered with a dial-glass ; the dis- 
 solution may occur in the cold, or may be accelerated by gently heating. 
 The solution contains Hg(NO 3 ) 2 , HN0 3 arid HN0 2 . When all the 
 mercury is dissolved, remove the beaker to a distance from any flame 
 and pour into it, at arm's length, 17.5 c.c. of alcohol (sp. gr. 0.87). 
 Very brisk action soon begins, and the fulminate separates as a crystal- 
 line precipitate ; dense white fumes pour over the sides of the beaker, 
 having the odours of nitrous ether and aldehyde; they also contain 
 mercury compounds and HCN, and are very poisonous. When red 
 fumes begin to appear abundantly, some water is poured in to stop 
 the action (which occupies only two or three minutes), and the ful- 
 minate is collected on a filter, washed with water as long as the washings 
 taste acid, and dried by exposure to air. 
 
 On a large scale the preparation is carried out under sheds. At Montreuil r 
 300 grams of mercury are dissolved in 3 kilos of colourless HN0 3 , of sp. gr. 1.4 in 
 the cold. The solution is transferred to a retort, and 2 litres of strong alcohol are 
 added. In summer no heat is required, and the vapours are condensed in a receiver 
 and added to a fresh charge. When the action has ceased, the contents of the retort 
 are poured into a shallow pan, and, when cold, the fulminate is collected in a conical 
 earthen vessel partially plugged at the narrow end. It is washed with rain-water, 
 and drained until it contains 20 per cent, of water, being stored in that state. 
 
 Mercuric fulminate, thus prepared, has a grey colour from the presence of 
 finely divided mercury, and sometimes contains mercuric oxalate. It may be 
 purified by dissolving it in 100 parts of boiling water, which leaves the metal 
 
CAP COMPOSITION. 
 
 70? 
 
 and the oxalate undissolved, and deposits the fulminate on cooling in lustrous 
 white prisms. It should not be kept in a Btofbered bottle, as it would easily 
 detonate by friction between the stopper and the neck of the bottle. The blow 
 of a hammer causes it to detonate sharply with a bright flash and grey fumes of 
 mercury ; HgC 2 N 2 2 = Hg + 2 CO + N 2 . It is also d&onated by being touched with 
 a wire heated to 195 C.. or by an electric spark, or by contact with strong sulphuric 
 or nitric acid. Its sp. gr. being 4.4, a small volume of it evolves a large volume of 
 gas ; according to the above equation, the gas and vapour would occupy more than 
 1340 times the volume of the solid, at the ordinary temperature, and the volume at 
 the moment of detonation would be much greater, because the fulminate evolve* 
 403 units of heat (per unit) in its decomposition, and this would expand the evolved 
 gases and greatly increase their mechanical effect. It is estimated that a pressure 
 of 48,0x30 atmospheres is thus produced. 
 
 Fulmlnlc add, C : N'OH, is isomeric with cyanic acid, and was long supposed to 
 contain the cyanogen group. It is doubtless obtained when fulminates are treated 
 with HC1, when a smell of HCN is perceived although none is to be detected ; 
 but the fulminic acid immediately combines with the HC1, forming chlorofttrmojrlme, 
 C1HC : N'OH, an indication that the carbon is unsaturated, as in CO. This oxiim- 
 rapidly breaks up into formic acid and hydroxylamine hydrochloride ; C1HC :N'OH 
 + 2H 2 = NH 2 OH.HC1 + HCOOH. Thus these two compounds and mercuric 
 chloride are the products of the action of strong HC1 on mercuric fulminate ; by 
 precipitating the mercury by H 2 S and evaporating~the solution, hydroxylamine hydro- 
 chloride may be crystallised, and this is one of the best methods for preparing this 
 salt. 
 
 Mercuric fulminate is formed when HgCl2 is added to sodium nitromethane, 
 CH 2 : NO'ONa, water being formed. This confirms the above constitution, but it 
 must be added that the behaviour of the fulminate with halogens indicates the 
 presence of a CN group. With Cl it yields HgCl. 2 . CNC1 and CC1 3 NO 2 (chlorpicrin), 
 and with Br the reaction is similar, but dibromonitro-aceto-nltrile, Br 2 (N0 2 )C'CN, is 
 an intermediate product. Again, NH 3 converts the fulminate into urea and 
 guanidine, as though it contained an isocyanic-group (see Isocyanates). 
 
 Cap composition. The explosion of mercuric fulminate is so violent and rapid 
 that it is necessary to moderate it for percussion-caps. For this purpose it is 
 mixed with potassium nitrate or chlorate, the oxidising property of these salts 
 possibly causing them to be preferred to any merely inactive substances, since they 
 would tend to increase the temperature of the flash by burning the carbonic oxide 
 into carbon dioxide, and would thus ensure the ignition of the cartridge. In the 
 military caps, in this country, potassium chlorate is always mixed with the 
 fulminate, and powdered glass is sometimes added to increase the sensibility of 
 the mixture to explosion by percussion. Antimony sulphide is sometimes substi- 
 tuted for powdered glass, apparently for the purpose of lengthening the flash by 
 taking advantage of the powerful oxidising action of potassium chlorate upon 
 that .compound (p. 186). Since the composition is very liable to explode under 
 friction, it is made in small quantities at a time, and without contact with any 
 hard substance. After a little of the composition has been introduced into the 
 cap, it is made to adhere and waterproofed by a drop of solution of shell-lac in 
 spirit of wine. 
 
 If a thin train of mercuric fulminate be laid upon a plate, and covered, except 
 a little at one end, with gunpowder, it will be found, on touching the fulminate 
 with a hot wire, that its explosion scatters the gunpowder, but does not inflame 
 it. On repeating the experiment with a mixture of 10 grains of the fulminate 
 and 15 grains of potassium chlorate, made upon paper with a card, the explosion 
 will be found to inflame the gunpowder. 
 
 By sprinkling a thin layer of the fulminate upon a glass plate, and firing it with 
 a hot wire, the separated mercury may be made to coat the glass, so as to give 
 all the appearance of a looking-glass. 
 
 Although the effect produced by the explosion of mercuric fulminate is very 
 violent in its immediate neighbourhood, it is very slightly felt at a distance, am 
 the sudden expansion of the gas will burst firearms, because it does not 
 time for overcoming the inertia of the ball, though, if the barrel escape desti 
 tion, the projectile effect of the fulminate is found inferior to that ot po^ 
 It has been proved by experiment that the mean pressure exerted by the explosi< 
 of mercuric fulminate is very much lower than that produced by gun-cotton, and 
 only three-fourths of that produced by nitroglycerine. Its great pressure 
 
708 
 
 FULMINATES. 
 
 to its instantaneous decomposition into CO, N, and Hg vapour within a space not 
 -sensibly greater than the volume of the fulminate itself, which volume being very 
 -small, on account of the high density of the fulminate, the escaping gases exert 
 an enormous pressure at the moment of explosion. This detonating property of 
 mercuric fulminate renders it exceedingly useful for effecting the detonation of 
 -gun-cotton and nitroglycerine. Berthelot finds that even such stable gases as 
 ^acetylene, cyanogen, and nitric oxide are decomposed into their elements by the 
 detonation of mercuric fulminate. CS 2 is similarly decomposed (p. 239). 
 
 Silver fulminate, (CN) 2 (OAg) 2 (?), is prepared 'in a similar way to the mercury 
 'salt. 0.65 gram of silver is dissolved, by gently heating, in 5 c.c. of ordinary 
 strong HN0 3 (sp. gr. 1.42) and 3.5 c.c. of water. As soon as the silver is dissolved, 
 the lamp is removed, and 14 c.c. of alcohol (sp. gr. 0.87) are added. If the action 
 does not start shortly, a very gentle heat may be applied until effervescence begins, 
 when the fulminate will be deposited in fine needles, and may be further treated 
 like the mercuric salt. In some cases a little red HN0 3 is necessary to start the 
 action. It may also be obtained as a crystalline precipitate by warming solution 
 of AgN0 3 with HN0 3 and alcohol until effervescence begins. 
 
 Silver fulminate is far more dangerous than mercuric fulminate, and, if stored 
 dry, should be wrapped up, in small portions, in paper. Even if wet, it is not safe, 
 in a glass bottle. When dry, it should be lifted with a slip of card. 
 
 Silver fulminate crystallises in shining prisms, and is mere soluble in boiling 
 water (36 parts) than is mercuric fulminate ; it detonates sharply when pressed with 
 a hard body, or when heated a little above 100 C. When 'touched with a hot 
 wire upon a piece of glass or thin metal, it gives a sharp report and shatters the 
 plate, whilst mercuric fulminate emits a dull sound, and does not shatter unless 
 closed in. Silver fulminate is used in toy crackers, such as the pull crackers, 
 where it is mixed with powdered glass to increase the friction, and the throw- 
 down crackers, where it is twisted up in thin paper with some fragments of quartz- 
 pebble. It is occasionally mixed with mercuric fulminate in detonating tubes, to 
 raise the note of the report. 
 
 Warm ammonia dissolves silver fulminate, and deposits, on cooling, crystals of 
 silver-ammonium fulminate, NH 4 0'CN'0'NCAg, which is even more violently 
 explosive, and is dangerous while still moist. A similar compound is formed with 
 mercuric fulminate. Potassium chloride, added to a hot solution of silver ful- 
 minate, removes only half the silver as precipitated chloride, and the solution 
 deposits shining plates of silver-potassium fulminate, KOCN'O'NCAg, which is 
 very explosive. By the careful addition of HN0 3 the K may be exchanged for H, 
 and the silver hydrogen fulminate, HO'CN'ONCAg, obtained, which dissolves 
 easily in boiling water and crystallises on cooling ; by boiling with silver oxide, 
 it is converted into silver fulminate, or, with mercuric oxide, into silver-mercury 
 fulminate. 
 
 Zinc and copper fulminates may be obtained by decomposing moist mercuric 
 fulminate with those metals ; they are soluble, crystalline, and explosive. 
 
 Sodium fulminate is obtained by the action of sodium amalgam on an aqueous 
 solution of mercuric fulminate. On evaporating over lime and sulphuric acid, the 
 sodium salt is deposited in prisms (with 2H 2 0), which explode when rubbed. A 
 crystalline compound of single molecules of sodium fulminate and mercuric 
 fulminate, and 4Aq, has been obtained. 
 
 Fulminuric or isocyanuric acid, HO'NC(OONH) 2 , is obtained as a potassium 
 salt by boiling mercuric fulminate with potassium chloride. On adding silver 
 nitrate, the sparingly soluble silver fulminurate crystallises out, and by decompos- 
 ing this with H 2 S, and evaporating the filtrate, a solution of the acid is obtained ; 
 it crystallises with difficulty, and is soluble in alcohol. 
 
 XI. PHENOLS. 
 
 506. The phenols are hydroxy-benzenes, naphthalenes, &c., derived from 
 aromatic hydrocarbons by substituting hydroxyl for the nucleal hydrogen 
 atoms, e.g., phenol, C 6 H 5 'OH ; orcinol, C 6 H 3 CH 3 < (OH). > ; pyrogallol, 
 C 6 H 3 (OH) 3 ; naphthol, C 10 H/OH. If the hydroxyl is introduced into the 
 methyl group instead of the phenyl group in the homologues of benzene 
 
CARBOLIC ACID. y O o 
 
 (p 548), an alcohol is produced; thus, C 6 H 5 'CH 2 (OH) is benzyl alcohol, 
 whereas C 6 H 4 (OH)-CH 3 is methyl phenol or cresol. 
 
 Phenols are distinguished from alcohols in combining more readily 
 with alkalies, which caused them originally to be mistaken for acids 
 The phenolic hydroxyl is more acidic in character than the alcoholic 
 hydroxyl, C 6 H 5 , c., being more negative (acidic) than alcohol radicles ; 
 it is less acid, however, than the carboxylic hydroxyl contained in the true 
 acids. Thus sodium phenoxide, C 6 H.'ONa, is formed when phenol is 
 dissolved in NaOH, but phenol does not dissolve in Na 2 C0 3 . Again, 
 they do not yield aldehydes (or ketones) and acids when oxidised, being 
 comparable in this respect with the tertiary alcohols ; and when attacked 
 by HN0 3 and H 2 S0 4 , they yield substitution-products, whereas the 
 alcohols yield ethereal salts; thus, phenol yields tri-nitrophenol orpicrio 
 acid, C 6 H 2 (NO,) 3 -OH, and phenol- sulphonic acid, C 6 H 4 (OH)-S0 2 'OH. 
 The phenols have a great tendency to produce coloured products of oxi- 
 dation, and ferric salts generally colour them intensely. 
 
 The phenols are frequently products of the dry distillation of com- 
 plex organic substances, e.g., coal. They are alsn obtained by fusing 
 the sulphonic acids with alkalies ; thus benzenesulphonic acid yields 
 phenol; C 6 H.-S0 2 OK + KOH = C 6 H.'OH + K 2 S0 3 . The formation of 
 phenols through the diazo-reaction has been already noticed (p. 68 1). 
 Another general method sometimes employed is the distillation of 
 aromatic hydroxy-acids either alone or with lime (see Pyrogallol). 
 
 The halogen-substituted benzenes are not attacked easily by alkalies, but when 
 they contain nitro-groups they more readily exchange Cl for OH, forming nitro- 
 phenols ; thus C 6 H 4 (N0. 2 )C1 yields C 6 H 4 (N0. 2 )OH. The greater the number of 
 nitro-groups the more readily this change occurs. The same remarks apply to the 
 amido- and nitramido- benzenes. 
 
 Monohydric Phenols, (i) Monohydroxybenzenes. Phenol, or 
 phenic acid, or carbolic acid or hydroxybenzene, C 6 H 5 'OH, is extracted 
 from that portion of the heavy oil of coal-tar which boils between 
 150 C. and 200 C. 
 
 This is allowed to cool, when it deposits crystals of naphthalene, and is then 
 well stirred with caustic soda of sp. gr. 1.34. On standing, two layers are formed, 
 the upper consisting of 'the higher homologues of benzene, and the lower of an 
 aqueous solution of sodium phenoxide. This is diluted with water, and exposed 
 to air, when tarry oxidation-products separate, and the liquid is neutralised by 
 successive additions of H. 2 S0 4 , which first precipitates more tarry matters, then 
 cresol and other homologues of phenol, and finally phenol itself as a light oil. It 
 is purified by fractional distillation, the portion distilling between 180 C. and 
 190 C. being" collected and artificially cooled, to crystallise the phenol. 
 
 Phenol is present in small quantity in urine, and in the trunk, leaves, and cones 
 of the Scotch fir. It may be produced by the action of hydrogen peroxide on 
 benzene; C 6 H 5 -H + HO-OH = C 6 H 5 -OH + HOH. Benzene may also be directly 
 oxidised to phenol by mixing it with aluminium chloride and passing oxygen gas. 
 Benzenesulphonic acid, when distilled with fused potash, yields phenol 
 C 6 H 5 -S0 2 -OH + KOH = C 6 H 5 'OH + KH80 3 . 
 
 Properties of phenol Phenol crystallises in needles, often several 
 inches long, which smell strongly of coal-tar. It fuses at 43 C. and 
 boils at 183 C. Fused phenol is slightly heavier than water 
 (sp. gr. 1.084 at o C.). It dissolves in 15 parts of water at 20 C., and 
 easily in alcohol and ether. It becomes pink or brown when kept, from 
 the presence of some impurity. When two molecules of phenol (198 
 parts) are heated with one molecule (18 parts) of water, and cooled to 
 
710 PROPERTIES OF PHENOL. 
 
 4 C., six-sided prisms of phenol aquate, (C 6 H 5 - OH) 2 Aq, are obtained, 
 which fuse at 16 C. (61 F.). The commercial carbolic acid crystals 
 generally consist of the aquate, and soon become liquid when the bottle 
 is placed in warm water. It has a great tendency to remain super- 
 fused after cooling, solidifying suddenly on opening the bottle. The 
 homologues of phenol, which accompany it in coal-tar, do not form 
 crystalline aquates. Carbolic acid blisters the skin immediately ; it 
 is very poisonous, and arrests fermentation and putrefaction, so that it 
 is largely used as an antiseptic. MacDougaUs disinfectant is a mixture 
 of phenol with calcium sulphite. Calvert's disinfecting powder consists 
 of clay, with 12 or 15 per cent, of phenol. 
 
 When phenol vapour is passed through a red-hot tube, it yields 
 benzene, toluene, xylene, naphthalene, anthracene, and phenanthrene. 
 The aqueous solution of phenol gives a purple-blue colour with ferric 
 chloride. With ammonia and chloride of lime, it gives a blue colour. 
 With the mixture of mercuric nitrate and nitrous acid obtained by 
 dissolving mercury in cold nitric acid, it gives a yellow precipitate, 
 which dissolves with a dark-red colour in nitric acid. 
 
 Sulphuric acid (concentrated^, to which 6 per cent, of potassium 
 nitrite has been added, gives a brown colour, changing to green and 
 blue, when gently heated with phenol. This is Liebermanris general 
 reaction for identifying phenols. 
 
 Bromine water added to an aqueous solution of phenol produces a 
 pale yellow precipitate of tribromophenol, C 6 H 2 Br 3 < OH, which redissolves 
 until the bromine is in excess. This a fiords an excellent qualitative and 
 quantitative test for phenol. If the precipitate be warmed with water 
 and sodium amalgam, sodium phenoxide is produced, which gives the 
 smell of phenol when heated with dilute sulphuric acid. 
 
 507. By passing phenol vapour over heated zinc-dust, it is converted into 
 benzene; C 6 H 5 'OH + Zn = C 6 H 6 +ZuO. This is a general method for the conversion 
 of phenol* into the corresponding hydrocarbons. 
 
 Phenol forms a crystalline compound with CO 2 , which is only stable under 
 pressure, and may be obtained by heating salicylic acid in a sealed tube at 
 260 C. ; C 6 H 4 (OH>C0 2 H = C 6 H 5 -OH,C0 2 . 
 
 Potassium- and sodium- phenol, or phenolates, C 6 H 5 'OK, C 6 H 5 'OXa, are soluble 
 crystalline bodies obtained by heating phenol with hydroxide or carbonate of the 
 alkali (see p. 709). 
 
 508. Phenol is not attacked by acids, as alcohol is, yielding ethereal salts, but 
 corresponding phenyl compounds are obtained by indirect processes. When 
 phenyl is heated with PC1 5 , it yields cJdorobenzene and phenyl ortliophosphate ; 
 the formation of chlorobenzene proves the existence of OH in phenol ; 
 C 6 H 5 'OH + PC1 5 = POC1 3 + C 6 H 5 -C1 + HC1. The phenyl orthophosphate results from 
 the action of more phenol on the POC1 3 ; POC1 S + 3C 6 H 5 OH + PO(C 6 H 5 0) 3 + 3HC1. 
 
 Phenyl hydrosulj)hide,or thiophenol, w phenyl mercaptan, C 6 H 5 'SH, is formed by 
 the action of phosphoric sulphide on phenol 
 
 8C 6 H 5 OH + P. 2 S 5 = 2C 6 H 3 SH + 2 (C 6 H 5 ) 3 P0 4 + 3 H 2 S. 
 
 It has an offensive odour, and boils at 169 C. Its extra-radicle hj'drogen may be 
 exchanged for metals, as usual with mercaptans. With mercuric oxide, it yields 
 mercuric t/tio-p/ienol. (C 6 H 5 S) 2 Hg. When mixed with ammonia and exposed to air, 
 phenyl hydrosulphide is converted into dlphenyl disulphide. a crystalline solid : 
 2C 6 H 5 SH + = (C 6 H 5 ) 2 S 2 + H 2 0. Dlphenyl sulphide, (C 6 H 5 ) 2 S, is obtained by distil- 
 ling sodium benzene sulphonate with P 2 S 5 . It is an offensive liquid, boiling at 
 about 292 C. Nitric acid converts it into dlphemjUulpJione or sulp/iobenzide, 
 (C 6 H 5 ) 2 S0 2 , which is also produced by the action of sulphuric anhydride on 
 benzene ; 2C 6 H 5 H + 2S0 3 = (C 6 H 5 ) 2 S0 2 + H 2 S0 4 . 
 
 509. Chloro phenols, C 6 H 4 C1'OH. and the corresponding bromine and iodine sub- 
 stitution-products, are obtained by the action of those elements on phenol. 
 
PICRIC ACID. 
 NitrophenoU , C 6 H 4 (N0 2 )OH, dinitrophenoU, 
 
 Nitropheno , C 6 H 4 (N0 2 )OH, dinitrophenoU, C^NO^/ OH, and tnnltronhenol 
 C 6 H 2 (N0 2 V OH, are produced when nitric acid acts on phenol. The last is known 
 as picric (ic id (v.i.). 
 
 By reducing nitrophenols with tin and HC1, the N0 2 group is converted into the 
 NH 2 group, and amido-phenols are produced. Dinitro- and trinitro-phenols admit 
 of a partial conversion of the N0 2 groups, so that anrido-nitrophenoh are formed 
 The antipyretic p/ienacetine is a derivative of i : 4-amido-phenol and has the 
 formula C 6 H 4 (OC 2 H 5 )(NHCH 3 CO), p-acetamidophenetml. 
 
 510. Picric or carbazotic acid, or trinitrophenol, C 6 H 2 (N0 3 ) 3 'OH, is 
 best prepared by dissolving phenol (i part) in strong sulphuric acid 
 (i part) and adding the solution of phenolsulphonic acids thus ob- 
 tained to strong nitric acid (3 parts) by degrees. When the violent 
 action is over the mixture is heated on the water-bath as long as much 
 red gas is disengaged. On cooling, a crystalline mass of picric acid is 
 obtained, which is purified by dissolving in boiling water, filtering, and 
 crystallising. It is deposited in yellow plates or prisms, which are 
 sparingly soluble in cold water, but more easily on heating, imparting a 
 bright yellow colour to a large volume of water; alcohol dissolves 
 it readily. Its solution has an intensely bitter taste (whence its 
 name), and stains the skin and other organic matters yellow, which is 
 turned to account in dyeing silk and wool. When heated, the crystals 
 fuse at 122 C., with partial sublimation, and explode slightly at a 
 higher temperature, in consequence of the sudden formation of gas and 
 evolution of heat by the action of the N0 2 upon the C and H. This 
 nitration of phenol into picric acid may be represented by the equation 
 C 6 H 5 - OH + 3 (HO'N0 2 ) . C 6 H,(NO f ) 8 OH + 3 HOH. 
 
 Picric acid is one of the very few acids which form sparingly soluble potassium 
 salts ; a cold saturated aqueous solution of picric acid is even a better test for 
 potassium than is tartaric acid, giving, especially on stirring, a yellow adherent 
 crystalline precipitate of potassium picrate, C 6 H 2 (N0 2 ) 3 OK. This salt explodes 
 violently when heated or struck, and has been used as an explosive. Ammonium 
 picrate is also a very explosive salt. Picric acid precipitates several of the alkaloids. 
 An alcoholic solution of picric acid forms crystalline compounds with several 
 hydrocarbons in alcoholic solution, particularly with benzene, naphthalene, and 
 anthracene. Keducing-agents, such as glucose, in alkaline solutions, convert 
 picric acid into picramic acid, C 6 H 2 (N0 2 ) 2 (NH 2 )OH, which forms red salts. 
 Gently heated with solution of chloride of lime, picric acid yields chloropicrin, or 
 kitrochloroform, C(N0 2 )C1 3 , recognised by its pungent tear-provoking odour. 
 
 Picric acid is a very common product of the action of nitric acid upon organic 
 substances ; indigo, silk, and many resins furnish it in considerable quantity, 
 especially the fragrant red resin known as Botany Bay gum, obtained from one of 
 the grass-trees of New South Wales, which is sometimes used for preparing picric 
 acid. It is said that picric acid is used as a hop-substitute in beer ; its presence 
 would be shown by the fast yellow colour imparted to a thread of white wool 
 soaked in the warm liquid. 
 
 The constitution of picric acid is expressed by the orientation [OH : (NO 2 ) 3 - 
 1:2:4:6]; this follows from the fact that it can be obtained by oxidising 
 symmetrical trinitrobenzene with potassium ferricyanide, a change which results 
 in the substitution of an OH for a hydrogen atom. A little consideration will 
 show that this hydroxyl group can only take up a position between two mtro-groups 
 if the trinitrobenzene is the symmetrical one (p. 547). 
 
 51 1. Picramlc acid, or 2-amido- w-dinitrop/ienol, C 6 H 2 (N0 2 ) 2 (NH 2 )OH, is prepared 
 by reducing ammonium picrate in alcoholic solution by passing hydrogen sulphide, 
 evaporating to drvness, and decomposing the ammonium picramate with acel 
 acid;C 6 H 2 (N0 2 ),-ONH 4 ;3H,S = C 6 H 2 (N0 2 ). 2 (NH 2 )ONH 4 + 2H 2 + S 3 . TheplcrAnic 
 acid crystallises in red needles, which fuse at 165 C. It is soluble in water and 
 alcohol, forming red solutions, which become blood-red on adding an alkali. 
 change of the yellow colour of potassium picrate to the dark red of potassi 
 picramate by the action of a reducing-agent in the presence of excess of potash, 
 
712 NAPHTHOLS. 
 
 is employed in the examination of urine for the detection and estimation of 
 glucose, which easily converts the picrate into picramate when heated. The 
 picramates of potassium and ammonium form dark-red crystals. 
 
 512. Phetwl-sulphonic, C 6 H 4 (OH)S0 2 OH, and dimlphonic, C 6 H 3 (OH)(S0 2 OH). 2 , 
 acids, are obtained by dissolving phenol in strong sulphuric acid, S0 2 OH'OH. 
 Orthophenolsulphonic acid rapidly changes by migration of the OH group, into 
 the para-acid when warmed. The antiseptic aseptol is a solution of phenol- 
 sulphonic acid. 
 
 The sodium salt of di-lodo-{parci)phenolsulplionic acid, C 6 H 2 I 2 OH'S0 2 OH, has 
 lately been introduced under the name of sozoldol as an antiseptic ; it is said to 
 be as effective as iodoform, and has no smell. 
 
 513. Cresols, or methyl-phenols, or hydroxy toluenes, C 6 H 4 (CH 3 )OH, 
 accompany phenol in coal-tar. The coal-tar kreasote is a mixture of 
 phenol and cresol. The cresols may be prepared by dissolving the cor- 
 responding toluidines in sulphuric acid, adding potassium nitrate, and dis- 
 tilling by steam ; C 6 H 4 (CH 3 )NH 2 + HN0 2 = C 6 H 4 (CH 3 )OH + 2 H 2 O + N 2 . 
 
 Orthocresol is solid, fuses at 31 C., and boils at 188 C. Metacresol 
 is liquid, and boils at 201 C. Paracresol is solid, fusing at 36 C., 
 and boiling at 198 C. ; they are metameric with benzyl alcohol, 
 C 6 H 5 * CH 2 - OH. Paracresol occurs in urine, and is a product of the 
 putrefaction of albumin ; its dinitro-derivative is a yellow dye, Victoria 
 orange. Meta- and para-cresol give a blue colour with ferric chloride. 
 
 The presence of the OH group in the cresols protects the methyl group from 
 the easy oxidation which characterises the methyl group of the toluenes. But 
 the substitution of a radicle for the H of the OH group destroys the protective 
 influence, and the methyl cresols C 6 H 4 (CH 3 ) - OCH 3 are easily oxidised to methoxy- 
 benzoic acids, C 6 H 4 (COOH)'OCH 3 . 
 
 Creoline and It/sol are sold as disinfectants ; they are solutions of crude cresol 
 in soap and water. 
 
 Methylisopropylphenols. Thymol [CH 3 : CH(CH 3 ) 2 : OH = i 14:3] occurs in oil 
 of thyme. Carracrol [CH 3 : CH(CH 3 ) 2 : OH I : 4 : 2] exists in the oil of Origanum 
 hlrtum, and is obtained by heating camphor with iodine. 
 
 514. (2) Monohydroxynaphthalenes. Naphthols, C ]0 H 7 'OH, are prepared from 
 naphthalenesulphonic acids or naphthylamines by the reactions described on 
 pp. 68 1, 709. a-^Yap/tthol melts at 94 C. and boils at 280 C. ; fi-Xaphtliol melts 
 at 122 C. and boils at 286 C. The latter is the more soluble in water, and is 
 used as an antiseptic.* The naphthols are true phenols, but they resemble the 
 alcohols more nearly than the benzene phenols do. They give rise to a number of 
 important dyestuffs, which are chiefly nitro-derivatives and diazo-derivatives. 
 Thus, dinitro-a-naphthol, C 10 H 5 (NO 2 ) 2 'OH, is Martins' yellow or na-phthalene yellow, 
 and the sodium yalt of its sulphonic acid is naphthol yellow, or fast yellow. The 
 photographic developer eilionogen is sodium amido-fi-naplithol sulphonate, 
 C 10 H 5 (OH)(NH 2 )(S0 3 Na). 
 
 NaphthoUulphonic acids are very numerous and a large number has been prepared 
 both for settling the constitution of naphthalenes and for use as dyestuffcomponents 
 (p. 683), for which purpose the most important are the I : 4-monosulphonic acid, 
 C 10 H 6 (OH)-SO 3 H, (Neville and Winther's acid) and the 2:3:6- and 2 : 6 : 8- 
 disulphonic acids, C IO H 5 (OH)(S0 3 H) 2 , (R. and G. acids). 
 
 515. Dihydric Phenols. Dihydroxybenzenes. Pyrocatechol, 
 i : 2-C 6 H 4 (OH) 2 , obtained by fusing potassium phenol-sulphonate with 
 potash, C 6 H 4 (OH)Sp 2 OK + KOH = C 6 H 4 (OH) 2 + K 2 SO 3 , is found among 
 the products of distillation of catechu, an astringent body extracted 
 by boiling water from the inner bark wood of Acacia catechu and used 
 in tanning. Kino, a similar extract from certain varieties of Ptero- 
 carpus, an Indian tree of the same botanical order, also furnishes it ; as 
 
 * Betol, or fi-naphthyl salicylatf, CeH 4 (OH) COOC 10 H 7 , is used iu medicine like phenyl 
 salicylate (salol). 
 
PYROCATECHOL. 
 
 do most vegetable extracts which contain tannin. The leaves of the 
 Virginia creeper, a plant of the vine order, contains pyrocatechol. It 
 is present in crude pyroligneous acid distilled from wood, and is said to 
 
 is very soluble in water, alcohol, and ether. It is a reducing-agent, 
 precipitating Cu,O from alkaline cupric solutions on warming, and 
 reducing silver nitrate in the cold. In presence of alkalies it absorbs 
 oxygen from the air, becoming brown. With ferric chloride, it gives a 
 green colour, changed to red by alkalies. Nitric acid oxidises it to 
 oxalic acid. It has weak acid properties, and was formerly called 
 oxyphenic acid. 
 
 Guaiacol, or methylpyrocatechol, C 6 H 4 (OH)OCH 3 , may be obtained by distilling 
 guaiacum, a resinous exudation from the West Indian tree called lignum ri*<9< 
 The distillate is dissolved in ether, and mixed with alcoholic potash, which pro- 
 duces a crystalline mass of potassium guaiacol, which is washed with ether and 
 decomposed by dilute sulphuric acid. It is also produced by heating to 180 C. a 
 mixture of pyrocatechol, potassium methyl sulphate, and potash 
 
 C 6 H 4 (OH) 2 + KCH 3 S0 4 + KOH = C 6 H 4 (OH)OCH 3 + K 2 S0 4 + HOH. 
 Beech-wood kreasote also contains it. Guaiacol forms colourless crystals, m.-p. 
 28 C. and b.-p. 203 C. It mixes sparingly with water, but easily with alcohol 
 It gives an emerald-green colour with ferric chloride, and acts as a reducing-agent 
 in alkaline solutions. When heated with hydriodic acid, it yields methyl iodide 
 and pyrocatechol ; C 6 H 4 (OH)OCH 3 + HI = C6H 4 (OH) 2 + CH 3 L It has the properties 
 of a weak acid. When potassium guaiacol is heated with methyl iodide, it yields 
 veratrol or methyl guaiacol ; C 6 H 4 'OK-OCH 3 + CH 3 I = C 6 H 4 (OCH 3 ) 2 + KL Veratrol 
 is an aromatic liquid, which may also be obtained by heating with baryta the 
 veratric (dlmethyl-protocatechuic) acid, extracted from sabadilla seeds ; 
 C 6 H 3 (OCH 3 ) 2 -C0 2 H + BaO = C 6 H 4 (OCH 3 ) 2 + BaC0 3 . 
 
 Wood-tar kreasote contains phenol, cresol, phlorol, C 6 H 3 (CH 3 ) 'OH, guaiacol, and 
 creosol, C 6 H 3 (OCH 3 )(CH 3 )OH. This last is obtained from that" portion of the tar 
 which distils at 221 C., by dissolving it in ether, and adding very strong KOH, 
 which precipitates potassium-creosol, from which creosol is separated by H 2 S0 4 . 
 It is an aromatic liquid, which yields acetyl-creosol, C 6 H 3 (OCH 3 )CH 3 (OC 2 H S 0), 
 when treated with acetyl chloride, and this, when oxidi&ed by permanganate, 
 becomes acetijl-ranillic acid, C 6 H 3 (OCH 3 )C0 2 H(OC 2 H 3 O), from which vanillic acid 
 may be obtained by treatment with XaOH. 
 
 516. Resorcinol, i : 3-C 6 H 4 (OH) 2 , was named from resin, being 
 obtained from several bodies of that class, and orcin, with which it is 
 homologous. It is now prepared on a large scale for the manufacture 
 of colours by the action of caustic alkalies on benzene-disulphonic acid. 
 
 This acid is prepared by gradually adding benzene (4 parts) to fuming 
 sulphuric acid, sp. gr. 2244 (is parts), gently heating for some hours, and 
 finally at 275 C. ; C 6 H fi + 2H 2 S0 4 = C 6 H 4 (S0 2 'OH) 2 + 2H 2 0. The I : 3-benze*+ 
 d'mdphanie acid forms a deliquescent crystalline mass on cooling. This is 
 dissolved in a large quantity of water, neutralised with lime, and strained from the 
 calcium sulphate formed by the excess of sulphuric acid. The solution of calcium 
 benzene-disulphonate is decomposed by Na 2 C0 3 , the precipitated CaC0 3 filtered 
 off, the solution evaporated to dryness, and the residue of sodium benzene- 
 disulphonate fused with 2^ times its weight of caustic soda, at 270 C., for eight or 
 nine hours; C 6 H 4 (S0 2 -ONa) 2 + 2NaOH = C 6 H 4 (OH) a + 2S0 3 Na* The fused mass u 
 dissolved in hot water, and boiled with HC1 till all the S0 2 is expelled. The 
 resorcinol is then extracted from the cooled aqueous solution by agitation with 
 ether, and is obtained in crystals when the ether is distilled off. 
 
 Resorcinol is obtained in considerable quantity by distilling extract of Jirazil- 
 wood, a dye made by boiling the wood of Ctesalplnht fcasiliensi* with water, and 
 evaporating the solution. It was originally prepared by fusing with potash the 
 
714 ORCIN. 
 
 gum-resin known as galbanum. obtained in Turkey and the East Indies as an 
 exudation from the Galbanum officinale, an umbelliferous plant. Other gum-resins 
 obtained from plants of the same order also yield resorcinol when fused with 
 potash ; such as ammoniacuni, assafcetida, sagapenum, all more or less foetid- 
 smelling medicinal bodies imported from the East. When these gum-resins are 
 distilled alone, they yield vmbelliferone, C 9 H 6 O 3 , or C 6 H 4 (CHO) 2 CO, which is con- 
 verted into resorcinol when fused with potash. 
 
 Resorcinol crystallises in prisms or tables which fuse at 118 C., and 
 boil at 276 C., but may be sublimed at a much lower temperature. 
 It has a sweet taste, and is easily soluble in water, alcohol, and ether. 
 Its solution gives a violet colour with ferric chloride. Exposed to air, 
 it absorbs oxygen and becomes brown. Ammoniacal copper and silver 
 solutions are reduced when heated with it. The most characteristic 
 test for resorcinol consists in heating it with phthalic anhydride, 
 (p. 617), dissolving in dilute sulphuric acid, and adding ammonia, when 
 a splendid green fluorescence is produced, due to the formation of 
 resorcin-phtkalein, or fluorescein (q-v.^). 
 
 The resorcinol of commerce sometimes contains thioresorclnol, C 6 H 4 (SH)2, which 
 may be obtained by reducing benzenedisulphonlc chloride, C 6 H 4 (S0 2 C1) 2 , with tin 
 and hydrochloric acid ; it melts at 179 C. 
 
 Styphnlc acid, or trinitroresorcin, C 6 H(N0 2 ) 3 (OH) 2 , so named from its astringent 
 taste (<TTi>(f>vos) is prepared from resorcinol just as picric acid is prepared from 
 phenol, and by the action of nitric acid on those gum resins which yield resorcinol 
 on fusion with potash. Styphnic acid forms yellow six-sided prisms or tables, 
 sparingly soluble in cold water, but dissolving in alcohol and ether. It fuses at 
 J 75 C., and explodes when strongly heated, though it sublimes when heated 
 gradually. It is a dibasic acid, and forms salts which are more explosive than the 
 picrates. Ferrous sulphate and lime-water give a green colour with styphnic 
 acid, and a blood-red with picric acid. 
 
 Dinitroso-resorcinol, C 6 H 2 (NO) 2 (OH) 2 . produced by the action of nitrous acid on 
 a solution of resorcinol, is a dyestuff known as fast green or solid green. 
 
 Hydroquinone, or quinol, is the third (1:4) dihydroxybenzeue ; it 
 will be considered under quinone. 
 
 517. Orcin, or orcinol, or 1:3: $-dihydroxiitoluene, C 6 H 3 CH 3 (OH) 2 , 
 is prepared from certain lichens, which are used by dyers for preparing 
 the colours known as litmus, cudbear, and archil ; such as Lecanora tar- 
 tarea, or rock-moss, Roccella tinctoria, or orchella weed, and others. The 
 lichens are boiled with lime and water for some time, the solution filtered, 
 evaporated to one-fourth, treated with C0 2 to precipitate the lime, and 
 shaken with ether to extract the orcin. Some orcin appears to exist 
 ready formed in the lichens, but the greater part of it is formed by the 
 action of the lime and water upon certain acids, which may be extracted 
 from the lichens by lime in the cold, and obtained as gelatinous preci- 
 pitates by adding HC1. Thus, orsellinic acid, C 6 H 2 CH 3 (OH) 2 00 2 H, 
 when boiled with lime, yields carbon dioxide and orcin, C 6 H 3 CH 3 (OH) 2 . 
 
 Erythric acid, C^H^O^, yields orcin and erythrite (p. 578) ; erernic acid, 
 C 17 H 16 7 , from the lichen Erernia prunastri, yields orcin and ererninic acid, 
 C 9 H 10 4 . 
 
 Lecanoric acid. C I6 H 14 CVH 2 0, when boiled with water, yields two molecules of 
 orsellinic acid, C 8 H 8 4 . 
 
 Orcin is also produced by the action of fused potash on aloes, the juice of a 
 plant of the Liliaceous order (dragon's blood, obtained from the same order, yields 
 phloroglucol). Orcin may be prepared from toluene, C 6 H 5 'CH 3 , by converting it 
 into (ortho)chlorotoluenesulphonic acid, and fusing this with excess of potash 
 C 6 H 3 C1(CH 3 )-S0 3 H + 2KOH = KC1 + KHS0 3 + C 6 H 3 CH 3 (OH) 2 . 
 
 Orcin crystallises in colourless six-sided prisms (with iH 2 0), melting 
 
PYROGALLOL. 7:5 
 
 at 58 C., or when anhydrous at 107, and boils at 289 C\ It tastes 
 sweet and dissolves in water, alcohol, and ether ; ferric chloride colours 
 it violet. 
 
 It forms a crystalline compound with a molecule of ammonia and when its 
 .solution in ammonia is exposed to air, it absorbs oxygen, becoming purple, and 
 yielding with acetic acid a red colouring-matter, orcein, C 7 H 8 2 t-NH 3 + 3 = 
 2H 2 + C 7 H 7 N0 3 . This substance is the chief colouring-matter of the dyes pre- 
 pared from lichens, by mixing them with lime and urine (to furnish ammonia), 
 and exposing them to the air for some weeks. The colour is pressed out and 
 made into cakes with chalk or plaster of Paris. 
 
 Orcein is sparingly soluble in water, but dissolves easily in alcohol and in 
 .alkaline liquids, yielding purple solutions which are reddened by acids, orcein 
 being precipitated. 
 
 518. Trihydric Phenols. Trihydroxybenzenes. Pyrogallin, 
 or pyrogallol, 1:2: 3-C 6 H 3 (OH) 3 , formerly called pyrogallic acid, is a 
 phenol obtained by heating gallic acid 
 
 C 6 H 2 (OH) 3 -C0 2 H = C 6 H 3 (OH) 3 + C0 2 . 
 
 To prepare it, gallic acid is heated with 2\ parts of water in a digester (autorlure) 
 at 2io-220 C. for half an hour. The solution thus obtained is decolorised by 
 animal charcoal and crystallised. 
 
 Pyrogallol maybe sublimed from nut-galls heated to about 215 C.. when the 
 tannin is decomposed into pyrogallol and carbon dioxide ; C 13 H 9 7 -C0 2 H + H 2 = 
 2C 6 H 3 (OH) 3 + 2COo. It may be obtained synthetically by fusing chloro2>henol- 
 -sulphonic add (i 12:3) with potash 
 
 C 6 H 3 C1(OH)S0 3 H + 2KOH = C 6 H 3 (OH) 3 + KC1 + KHS0 3 . 
 
 Pyrogallol crystallises in line needles, which are felted together in 
 light white tufts. It fuses at 132 C. and boils at 210 C. It is very 
 soluble in water (2^ parts), alcohol, and ether. When its solution is 
 mixed with an alkali, it at once absorbs oxygen from the air, becoming 
 brown, and forming a carbonate, acetate, and other products, a little 
 carbonic oxide being evolved. A mixture of potash and pyrogallin is 
 employed to absorb oxygen in gas analysis. Pyrogallin is a strong 
 reducing-agent, precipitating silver and mercury in the metallic state ; 
 its action on silver-salts renders it useful in photography and in hair- 
 dyeing. 
 
 A pure ferrous salt gives no colour with pyrogallin, but a trace of ferric salt 
 causes a blue coloration, while a pure ferric salt gives a red colour. When heated 
 with phthalic anhydride, it yields pyrogallol phthalein, or gallein, C^H^O-. which 
 is used as a red dye. When chlorine is passed through a cooled solution of i>yn>- 
 gallol in acetic acid, triehloro-pyrogalUl^ C 6 C1 3 (OH) 3 , is obtained, and may !> 
 crystallised in needles, melting at 177 C. 
 
 Phloroglucol. 1:3:5 -C 6 H 3 (OH) 3 , was first obtained from a glucoside called 
 phlorizin, existing in the bark of the apple-tree ; the glucol refers to its swtvt 
 taste. It is also made, like resorcinol, by fusing certain vegetable extracts and 
 gum-resins with caustic potash. It is thus obtained from gamboge, the irsiii..u> 
 juice of Ganilwf/ui t/ufta (Ceylon), from dragon's Mood, the resin of Drae&na 
 draco, from kino (p. 712), catec/w, and from the yellow dye-wood, futtie. The 
 residue of the preparation of extract of fustic is fused with potash and a lit 
 water, dissolved in water, acidified with sulphuric acid, and shaken with ether, 
 which extracts phloroglucol and protocatechuic acid : the ether is distilled ott, 
 and the aqueous solution of the residue mixed with lead acetate to precipitate 
 the protocatechuic acid. The lead is precipitated by H 2 S, and the phloroglin 
 again extracted by ether. It may also be prepared by fusing resorcinol (I par 
 with soda (6 parts) until the mass has a light chocolate colour, when it 
 as above, omitting the separation of protocatechuic acid. 
 
 Phloroglucol is formed by fusing i : 3 : $-benze>te-tn><ulp1ionir <-id, C 6 H 3 (MVUrt) 3 , 
 with soda, or better by hydrolysing 1:3: 5-triamido-benzene with HC1. 
 
716 INOSITE. 
 
 It crystallises in prisms with 2Aq, which it loses at 100 C. It fuses at 218, and 
 may be sublimed ; it dissolves easily in water, alcohol, and ether, and reduces 
 alkaline cupric solution. Ferric chloride gives a violet colour. Its solution in 
 hydrochloric acid stains wood violet-red, and is an excellent test for woody tissue. 
 Alkaline solutions of phloroglucol are oxidised by air, and become brown. 
 When dissolved in ammonia, it yields a crystalline base; C 6 H 3 (OH) 3 + NH 3 = 
 H 2 O + C 6 H 3 NH 2 (OH) 2 (phloramtne). Other phenols do not so readily exchange OH 
 for NH 2 . 
 
 When phloroglucol is dissolved in acetic acid and treated with potassium nitrite, 
 at a low temperature, it yields, on addition of excess of potash and alcohol, green 
 needles of a very explosive body, which is the potassium salt of tri-nitroso-pliloro- 
 glucol, C 6 3 (NOK) ? . When this is gradually added to a mixture of nitric and 
 sulphuric acids, it is converted into trinitro-phloroglucol, C 6 (N0 2 ) 3 (OH) 3 , which 
 crystallises in yellow explosive prisms, and dyes wool and silk yellow like picric 
 acid. It is a tribasic acid, and forms three series of coloured salts. 
 
 In most of its reactions, phloroglucol behaves as symmetrical tri-hydroxyben- 
 zene ; but in the remainder it behaves as a triketone, yielding, for instance, a 
 trioxime, C 6 H 6 (N'OH) 3 , with hydroxylamine (p. 625). From this it seems probable 
 that phloroglucol exists in tautomeric forms (p. 701), namely, 
 
 /X C(OH)-CH X /CO-CH- 
 
 CHf ^C(OH) and CH / ~>CO. 
 
 X C(OH):CH X " X CO-CH/ 
 
 The first of these would represent a trihydroxybenzene (the enol form) containing 
 a tertiary benzene ring, and the latter a triketone of hexamethylene, containing a 
 secondary benzene ring. 
 
 1:2:4 -Trihydroxybenzene is called hydroxyhydroquinone. 
 
 51 8ft. Inosite, C 6 Hi 2 6 + 2H 2 0. This compound was formerly included among 
 the sugars under the name ot~Jiesh-svgar, but inasmuch as (i) it does not behave 
 as a reducing agent (see Su-gars), (2) it yields a hexanitrate, C 6 H 6 (ON0 2 ) 6 , when 
 dissolved in strong HN0 3 , and (3) it is converted into benzene and tetriodophenol 
 when heated at 170 C. with HI, it is now known to be a cyclohexane derivative, 
 probably he&ahydroasy-cyclohexane) C 6 H 6 (OH) 6 . It is obtained from the juice of 
 beef ; the chopped heart or lung of the ox is exhausted with water, the liquid 
 pressed out, mixed with a little acetic acid, and heated to boiling. The liquid 
 filtered from the coagulated albumin is mixed with lead acetate, filtered, and basic 
 lead acetate added ; this precipitates a lead compound of inosite, 2C 6 H 12 6 .5PbO, 
 which is to be suspended in water and decomposed by H 2 S. when the inosite 
 passes into solution. The lead sulphide is filtered off, the solution evaporated 
 on the water-bath, to a syrup, and mixed with ten volumes of alcohol and one of 
 ether, when the inosite is precipitated. It forms prismatic crystals, which are 
 sweet and soluble in 6 parts of water. It is but slightly soluble in weak alcohol, 
 and insoluble in absolute alcohol and in ether. The crystals effloresce in air, and 
 become anhydrous at 100 C. Inosite is optically active, occurring in the usual 
 modifications. It undergoes lactic fermentation and is oxidised by nitric acid 
 to oxalic acid. Inosite may be identified by moistening it with dilute nitric 
 acid, evaporating almost to dryness, and adding ammoniacal calcium chloride, 
 which produces a rose colour. Inosite solution mixed with a drop of mercuric 
 nitrate gives a yellow precipitate, which becomes red when heated. 
 
 The proportion of inosite obtained from flesh is very small ; many vegetables 
 contain it more abundantly. The unripe French bean yields 0.75 per cent, of 
 inosite ; walnut-leaves in August, 0.3 per cent. It is also present in the leaves of 
 ash and vine ; grapes contain it, so that inosite is found in wine. Unripe peas, 
 asparagus, and dandelions contain inosite. From these vegetables it may be ex- 
 tracted as from flesh. It has been found in urine in cases of Bright's disease. 
 
 He.jcahydro,ry-benzene, C 6 (OH) 6 , has been obtained by a circuitous process. It is 
 crystalline, sparingly soluble in cold water, alcohol, and ether ; the solutions 
 absorb oxygen, becoming violet, and reduce silver nitrate. It is converted into 
 benzene by distillation with zinc-dust. 
 
 He.r,ahydro,i-ydlphenyl, C 6 H 2 (OH) 3 'C 6 Ho(OH) :? , is the parent of the quinone 
 fioei'ulignone, O : C 6 H 2 (OCH 3 ) 2 'C 6 H 2 (OCH 3 ) 2 : 0, which is obtained during the refining 
 of crude acetic acid from wood by K 2 Cr. 2 O 7 ; it is soluble in ordinary solvents, but 
 crystallises from phenol in blue needles. It was formerly called cedrlret in allusion 
 to its interlaced crystals, (cedria, pitch ; rate, a net). Tin and HC1 convert it into 
 
QUINONE. 
 
 kydrocoerulignone, HO.C 6 H 2 (OCH 3 ) 2 -C 6 H 2 (OCH 3 ) 2 -OH, which is colourless, and 
 yields hexahydroxydiphenyl when boiled with HC1. Hexahvdroxvdiphenvl 
 dissolves in potash with a blue colour. 
 
 XII. QUINONES. 
 
 519. QUINONES are formed from aromatic hydrocarbons by the 
 substitution of (O,)" for H 2 , and are therefore products of oxidation. 
 
 Quinone, C 6 H 4 (0 2 )", or benzoquinone, may be obtained by heatino- 
 benzene with chromyl chloride, when HC1 is evolved and a brown solid 
 compound produced ; this is decomposed by water with formation of 
 quinone, which remains dissolved in the excess of benzene 
 
 (1) C 6 H 6 + 2CrOoCl 2 = 2HC1 + C 6 H 4 (Cr0 2 Cl) ; 
 
 (2) C 6 H 4 (Cr0 2 Cl) 2 + H 2 = C 6 H 4 (O 2 )" + Cr 2 3 + 2 HC1. 
 
 Many benzene derivatives also yield quinone when oxidised. It is best 
 prepared by oxidising aniline with potassium dichromate and sulphuric 
 acid. 
 
 One part of aniline is dissolved in a mixture of 8 parts of sulphuric acid with 
 30 parts of water, and 3^ parts of powdered potassium dichromate are slowly 
 added to the cooled solution, which is then heated for some hours at about 35 0. 
 After cooling, the liquid is shaken with ether, which extracts the quinone, and 
 leaves it in golden yellow crystals when evaporated. 
 
 It is also obtained when quinic acid is oxidised with manganese dioxide and 
 sulphuric acid; C 6 H 7 (OH) 4 C0 2 H + 2 =C 6 H 4 (0) 2 " + C0 2 + 4H 2 0. Many plant- 
 extracts yield quinone when thus treated. 
 
 Quinone crystallises very easily in yellow prisms or plates, which sub- 
 lime even in the cold, and fuse at n6C., emitting a characteristic 
 odour, and subliming in long golden needles in the presence of steam. 
 It is sparingly soluble in cold water, but dissolves in hot water, and 
 crystallises on cooling ; alcohol and ether dissolve it. Its solution stains 
 the skin brown. Quinone acts as an oxidisiiig-agent, liberatiog iodine 
 from hydriodic acid, and becoming converted into hydroquinone, or 
 quinol, C 6 H 4 (OH) 2 , which is i : 4 - dihydroxybenzene. 
 
 In many reactions quinone behaves like a diketone ; for instance, 
 with hydroxylamine it yields both a monoxime, : C 6 H 4 : N*OH, and a 
 dioxime, HON : C 6 H 4 : N'OH (cf. p. 625). The formula 
 
 has therefore been proposed (by Fitlig) for quinone. 
 
 It has been pointed out, however, that if quinone contain true ketone 
 groups, it should yield a secondary alcohol HOHC<f ^>CH'OH when 
 
 reduced, instead of, as is actually the case, the quasi-tertiary alcohol, hydroquinone, 
 C-OH.* Moreover, when substituted quinones react with PC1 8 . 
 
 each of the atoms is exchanged for one Cl atom instead of two, as would 
 be expected if the were doubly linked to carbon. These considerations I 
 
 * Aainst this argument it may be urged that a ketone may give rise to a tertiary alcohol 
 by redaction, as, for example, in the formation of piuacoue from acetone (p. 575). 
 
7 i8 
 
 CHLOBANIL. 
 
 Graebe to the " peroxide " formula, C^- Q-0 -^C for quinone. Fittig's formula, 
 is, however, preferred. 
 
 That the oxygen atoms in quinone occupy the i : 4-position is shown 
 by its easy conversion into i : 4-dihydroxybenzene, and by the fact 
 that its dioxirne yields i : 4-diamidobenzene when reduced. 
 
 Qulnonemonoxlme appears to be identical with the compound obtained by the 
 action of nitrous acid on phenol, nitroso-phenol, C 6 H 4 (OH)NO, also obtained by 
 treating nitrosobenzene, C 6 H 5 NO, with NaOH. 
 
 Hydroquinone is a constant product of the action of reducing-agents on quinone, 
 and is best prepared by passing S0 2 through a warm saturated solution of quinone, 
 when it is deposited in six-sided prisms, which fuse at 169 C., and sublime in 
 monoclinic tables, so that hydroquinone is dimorphous. It is moderately soluble 
 in water, and easily in alcohol and ether. Hydroquinone is distinguished from 
 other dihydroxybenzenes (p. 712) by the action of oxidising-agents, such as Fe 2 Cl 6 , 
 which converts it into fine green metallic prisms of green liydroqulnone, or quin- 
 hydrone, C 6 H 4 2 'C 6 H 4 (OH) 2 , also obtained by mixing aqueous solutions of quinone 
 and hydroquinone. This is sparingly soluble in cold water, but dissolves in hot 
 water to a brownish-red solution, which deposits the splendid green crystals on 
 cooling. It dissolves in alcohol and ether with a yellow colour. It is readily 
 dissociated into quinone and hydroquinone. Hydroquinone occurs among the 
 products of distillation of the succinates, and has been produced from ethyl 
 succinate by the following steps : Ethyl succinate, C 2 H 4 (CO 2 C 2 H 5 ) 2 , acted on by 
 sodium, yields ethyl succinyl succinate, C 2 H 4 'C 2 H 2 (CO) 2 '(C0 2 'C 2 H 5 ) 2 ; when this is 
 treated with bromine, hydrogen is abstracted, leaving ethyl quinol-dicarbo.vylate t 
 C 6 H 4 2 (CO./C 2 H 5 ) 2 . The acid obtained from this ethereal salt, qulnol-dlcarbu.xylic 
 acid, C 6 H 4 O 2 (C0 2 H) 2 , crystallises in needles, and yields a blue colour with ferric 
 chloride. When distilled, it yields hydroquinone, C 6 H 4 (OH) 2 , and 2CO 2 . As ethyl 
 succinyl succinate may also be obtained by the action of sodium on ethyl bromaceto- 
 acetate, hydroquinone may be built up from acetic acid. It is used as a photo- 
 graphic developer. 
 
 Tetrachloroquinone, or chloran'd, C 6 C1 4 (0 2 )", is a frequent product of the action of 
 chlorine or of a mixture of KC10 3 and HC1 upon aromatic compounds, such a& 
 phenol, aniline, salicin, and isatin. It may be prepared from quinone by the action 
 of KC1O 3 and HC1. but more cheaply from phenol, by mixing it with potassium 
 chlorate (4 parts) and adding it gradually to hydrochloric acid diluted with an 
 equal volume of water. The mixture is gently heated, and more chlorate added, 
 when a yellow mixture of tricJiloroqulnone, C 6 HC1 3 (0 2 )", and tetrachloroquinone is 
 precipitated. This is treated with sulphurous acid, which reduces the quinones to 
 hydroquinones. The tetrachlorohydroquinone, C 6 C1 4 (OH) 2 , is insoluble in water, 
 whilst the trichlorohydroqulnone, C 6 HC1 3 (OH) 2 , dissolves. The former is then 
 oxidised by strong nitric acid, which converts it into chloranil. This body, which 
 is used in colour-making, is yellow, insoluble in water, and sparingly soluble in 
 alcohol ; ether and benzene dissolve it, and deposit it in yellow crystals which 
 may be sublimed. It is unattacked even by concentrated acids. Potash dissolves 
 it with a purple colour, and yields purple crystals of potassium chloranilate ; 
 C 6 C1 4 2 + 4KOH = 2KC1 + 2H 2 + C 6 C1 2 (OK) 2 2 . By dissolving the sparingly soluble 
 potassium salt in hot water, and adding HC1, a red crystalline body is precipi- 
 tated, which is chloranlllc acid, C 6 Cl 2 (OH] 2 O 2 .Aq. It is soluble in water, with a 
 violet colour, but sulphuric or hydrochloric acid precipitates it from the aqueous 
 solution. Bromanil, C 6 Br 4 (0 2 )", has also been obtained from phenol. 
 
 // // NGl 
 
 Quinone chlorimides, C 6 H 4 x^ and C 6 H 4 / , are obtained by the action of 
 
 ^NCl ^NCl 
 
 chloride of lime on i : 4-amidophenol and I : 4-diamidobenzene respectively. 
 
 By reaction of quinonechlorimide with phenols, indophenols are obtained ; these 
 are also formed by the oxidation of a mixture of phenol and a p-amidophenol. 
 The typical indophenol is : C 6 H 4 : N;C 6 H 4 -OH. 
 
 Quinonechlorimide and a dialkylaniline react to form an indoaniline. These 
 compounds are dyestuffs and are manufactured by oxidising a mixture of a 
 paraphenylenediamine and a phenol. Thus phenol blue, : C 6 H 4 : N'C H 4 'N(CH 3 ) 2 , 
 
ANTHRAQUINONE. 
 
 is made by oxidising a mixture of .s-dimethylparaphenylenediamine and phenol 
 By hydrolysis with H. 2 S0 4 it yields quinone and the original diamine. 
 
 By substituting an aniline for the phenol in the foregoing reaction, an \,nl /;///? 
 is produced. Phenylene blue, NH : C 6 H 4 : N'C 6 H 4 'NH 2 , is the compound obtained 
 when a mixture of paraphenylenediamine and aniline is oxidised 
 
 Naphthoquinones, C 10 H 6 (0 2 )". <L-Naphthoqulnone [0 :.0 = i : 4] is a truey^/v/- 
 quinom, possessing the characteristic yellow colour, volatility and pungent odour 
 of these quinones, and being reduced to naphthohydroquinone, C 10 H 6 (OH) 2 . It is 
 prepared by dissolving naphthalene (i part), C 10 H 8 , in glacial acetic acid (6 parts) 
 and oxidising with chromic anhydride (3 parts), dissolved in glacial acetic acid 
 (2 parts). The mixture is boiled, and distilled after adding more water, when the 
 naphthoquinone passes over with the steam. It is insoluble in water, sparingly 
 soluble in cold alcohol, but dissolves in hot alcohol and in ether, crystallising in 
 yellow tables, which fuse at 125 C., and sublime below 100. Alkalies dissolve 
 it, and it is oxidised by strong nitric acid into phthalic acid, CeH^CO.^H)^ 
 
 B-Napkthoqmnone, [0 : = i : 2], is an example of an oi-tlio-tiit'mone, possessing the 
 red colour, the non-volatility and the lack of odour characteristic of these. It is 
 obtained by oxidising i : 2-derivatives of naphthalene. 
 
 / C0 \ 
 520. Anthraquinone, C 6 H 4 /^ ^>C 6 H 4 , is prepared by dissolving 
 
 anthracene, C 14 H 10 , in glacial acetic acid, and adding chromic anhydride 
 to the hot solution ; on adding water, the anthraquinone is precipitated 
 and may be purified by sublimation ; it has no quinone odour. It sub- 
 limes in yellow needles, which are sparingly soluble in alcohol and ether, 
 but dissolve in hot benzene and in nitric acid. It fuses at 285 C. and 
 boils at 382 C. Potash does not dissolve it, but, when fused with 
 KOH, it yields potassium benzoate. Sulphurous acid does not con- 
 vert it into a hydroquinone, nor does hydriodic acid, but the latter 
 reduces it to anthracene ; as intermediate products of the reduc- 
 tion there are obtained the secondary alcohols, hydroxyanthranol, 
 
 CO -- v X CH(OH) X 
 
 D.H/ >CH 4 , and anthranol, C,H 4 < >C 6 H 4 . Hence 
 
 IX 
 
 anthraquinone is more nearly a true diketone (diphenylenediketone) than 
 is benzoquinone. 
 
 Anthraquinone may be synthetically prepared by heating phthalyl 
 dichloride with benzene and zinc-dust ; 
 
 orvf^i r^o 
 
 C 6 H 4 < + C 6 H 6 + Zn = C 6 H 4 / >C 6 H 4 + ZnCl, + H 2 . 
 
 CO'Cl CO 
 
 This synthesis shows that the CO groups must be attached to one of the benzene 
 rings in the ortho-position to each other. That this is the case also with the 
 other benzene ring is seen from the fact that when bromanthraquinone, C 8 H 3 Br 
 (CO) C 6 H 4 (synthesised, as above, from bromophthalyl chloride, C 6 H 3 Br(COCl)2), is 
 oxidised, the product is phthalic acid, not broniophthalic acid, showing that the 
 brominated-ring has been removed, and that the CO groups must have been 
 attached to the non-brominated-ring in the ortho-position. 
 
 Anthraquinone is chiefly important as the source of arti6cial alizarin. 
 521. Alizarin, or i : 2-dihydroxyanthraquinone* C 6 H 4 (CO) 3 
 C 6 H,(OH),, may be prepared from anthraquinone by treating it with 
 bromine, which converts it into dibromanthraquinone, C 6 H,(CO).,C 6 H 2 Br 2 , 
 and when this is heated to about 180 C. with potash, it yields potassium 
 alizarate, C 6 H 4 (CO) 2 C 6 H 2 (OK) 2 ; from the aqueous solution of this, 
 hydrochloric acid precipitates alizarin. 
 
 * Anthracene derivatives are orientated similarly to those of naphthalene (p. 554). 
 
720 ALIZARIN. 
 
 Alizarin, one of the chief vegetable dyes, was formerly obtained ex- 
 clusively from madder, the root of Rubia tinctorum, imported from the 
 South of France and the Levant. It does not occur ready formed in 
 the plant, but is produced by the decomposition of ruberythric acid, 
 C 26 H 28 O 14 , which may be extracted from madder root by cold water, and 
 crystallises in yellow prisms. When the root is allowed to ferment, or 
 is treated with H 2 S0 4 , the ruberythric acid is hydrolysed into alizarin 
 and glucose, C 26 H 28 O 14 + 2H <J O = C 14 H 8 4 + 2C 6 H J2 O 6 . Alizarin is pre- 
 pared on a large scale from anthraquinone by converting it into the 
 sulphonic acid and fusing this with caustic soda. 
 
 The anthraquinone is made by treating anthracene, in leaden tanks, with potas- 
 sium dichromate and diluted sulphuric acid, the reaction being completed by 
 boiling. The anthraquinone is dissolved in strong sulphuric acid and re-precipi- 
 tated by water, which retains the impurities in solution. After being washed and 
 dried, it is heated for eight or ten hours at 160 C. with fuming sulphuric acid in 
 an iron pot, being constantly stirred ; on diluting with water, any unaltered 
 anthraquinone is precipitated, and anthraquinone mono- and di-sulphonic acids, 
 C 6 H 4 (CO) 2 C 6 H 3 (S0 3 H), and C 6 H 3 (S0 3 H)(CO) 2 C 6 H 3 (SO 3 H), remain in solution. 
 
 The mixed sulphonic acids are neutralised with lime, and the calcium salts are 
 decomposed by sodium carbonate. The concentrated solution of the sodium salts 
 is heated with caustic soda and a little sodium chlorate, in a closed iron boiler, 
 at about i8oC. for twenty-four hours, when a purple solution is obtained, con- 
 taining the alizarate and anthrapurpurate of sodium. The sodium anthraquinone 
 monosulphonate is first decomposed by the NaOH yielding sodoxyanthraquinone 
 
 C 6 H 4 (CO) 2 C 6 H 3 -S0 3 Na + 2NaOH = C 6 H 4 (CO) 2 C 6 H 3 (ONa) + SOgNa^ + H 2 0. 
 The sodoxyanthraquinone is then oxidised, by the oxygen from the chlorate, in 
 presence of the excess of NaOH, into sodium alizarate 
 
 C 6 H 4 (CO) 2 C 6 H 3 (ONa) + O + NaOH = C 6 H 4 (CO) 2 C 6 H 2 (ONa) 2 + H 2 0. 
 The sodium anthraquinone disulphonate yields sodium dnthrapvrpurafa 
 
 C 6 H 3 (S0 3 Na)(CO) 2 C 6 H 3 (S0 3 Na) + ;NaOH = 
 C 6 H 3 (ONa)(CO) 2 C 6 H 2 (ONa) 2 + 2Na 2 S0 3 + 4 H,-0. 
 
 The solution is run into dilute sulphuric acid, when a mixture of alizarin and 
 anthrapurpurin is obtained as a yellow precipitate. 
 
 Alizarin forms orange prisms (with 3H 2 0) very sparingly soluble in 
 water, but easily soluble in alcohol and ether, and becomes red when 
 dried. It fuses at about 290 C., and may be sublimed. It dissolves 
 in strong H 2 S0 4 with a deep-red colour, and is precipitated by water. 
 It acts like a dibasic acid, dissolving in alkalies to purple solutions, 
 which give purple-blue precipitates with salts of alkaline earths. The 
 insolubility and the brilliant colours of the alizarates are of great value 
 in dyeing and calico-printing. Alizarin gives red precipitates (madder 
 lakes) with salts of Sn and AJ, and a dark violet with salts of iron. 
 
 That alizarin is an adjacent dihydroxyanthraquinone follows from the fact 
 that it can be synthesised from phthalic anhydride and i : 2-dihydroxybenzene 
 (pyrocatechol) in the presence of sulphuric acid at i5oC. That the OH groups 
 occupy the I : 2 (or 3 : 4 or i' -.2' or 3' : 4', all these being the same in value as 
 I : 2) position follows from the fact that alizarin yields two mono-substitution pro- 
 ducts in which the substituent is in the same ring as the OH groups ; if the hydroxyl 
 groups occupied the 2 : 3-positions this would not be possible, since the positions 
 i and 4, which would then be vacant, are of the same value. 
 
 Anthrapurpurin, C 6 H 3 -OH-(CO) 2 'C 6 H 2 (OH) 2 , is formed as above mentioned in 
 the preparation of alizarin, and may be obtained by oxidising alizarin with Mn0 2 
 and H 2 S0 4 . It resembles alizarin, but fuses at a higher temperature (330 C.), 
 and is more soluble in water. The colours of its metallic salts are more brilliant 
 than those given by alizarin, so that its presence in the artificial dye is ad- 
 vantageous. 
 
ANILINE DYES. y 2I 
 
 PurpurinoTi : 2 : 4-tri-hydroxy-anthraquinone, C 6 H 4 (CO) 2 C 6 H(OH) 3 , is isomeric 
 with the preceding, and is found accompanying alizarin in old madder root, and 
 may be separated from it by boiling with alum, which dissolves only the purpurin 
 It may also be obtained by oxidising natural alizarin with Mn<X and H SCh 
 
 Flavo-purpurin, C 6 H 3 OH(CO) 2 C 6 H 2 (OH) 2 , is sometimes formed in the manu- 
 facture of alizarin. It crystallises in golden needles soluble in alcohol. 
 
 Tetrahydroxy-anthraquinone, anthrachrysone, C 6 H 2 (OH) ? (CO) 2 C 6 H,(OH) 9 , or 
 alizarine-bordeaux, is obtained by heating I : 3 : 5-dihydroxybenzoic acid. 
 C 6 H 3 (OH) 2 -COOH, with H 2 S0 4 , which abstracts the elements 7 of ^"5 from two 
 molecules of the acid. 
 
 Hexa-hydroxy-anthraquinone, C 6 H(OH) 3 (CO) 2 C 6 H(OH) 3 , rufigallic acid, or 
 alizarine cyamne (seep. 610), is prepared by heating gallic acid with H 2 S0 4 , which 
 removes the elements of 2H 2 Ofrom two molecules of gallic acid, C 6 H 2 (OHVCOOH. 
 It is used as a red dye. 
 
 All these anthracene derivatives yield that hydrocarbon when heated with zinc- 
 dust. 
 
 C 6 H 4 -CO 
 522. Plienanthraquinone, , is prepared by oxidising phenanthrene 
 
 C 6 H 4 *CO 
 
 (P- 554) with chromic acid. It crystallises in orange-yellow needles, melts at 
 198 C., and dissolves in hot alcohol. It is an ortho-quinone giving most of the 
 reactions of a diketone. 
 Coerulignone (p. 716) is a derivative of the quinone of diphenyl. 
 
 TRIPHENYLMETHANE DYESTUFFS. 
 
 These compounds include the majority of the colouring-matters 
 commonly called the aniline dyes.* Although they are amido- or 
 hydroxyl derivatives, consideration of them has been postponed until 
 now because they contain a benzene nucleus to which other groups 
 are attached in a manner similar to that in which the oxygen 
 atoms of quinone are linked to the benzene ring (quinonoid 
 structure). 
 
 When three amido-groups or three hydroxyl-groups are introduced into triphenyl- 
 methane, CH(C 6 H 5 ) 3 (p. 551), compounds are produced which are colourless, but 
 readily become coloured when oxidised and treated with an acid. For example,. 
 triamido-triphenylmethane, CH(C 6 H 4 NH 2 ) 3 , is a colourless substance ; when 
 oxidised it becomes triamidotriphenyl carbinol, C(OH)(C 6 H 4 NH 2 ) 3 , which is also a. 
 colourless substance, and yields colourless salts (with one equivalent of acid) 
 when treated with cold acids, but coloured salts when treated with warm acids. 
 The latter salts are dyestuffs ; they are formed from the carbinol by loss of a 
 molecule of water, and since the only oxygen in the carbinol is that of the alcoholic 
 group, OH, it must be supposed that this group forms water with the hydrogen of 
 the acid. This loss of the OH group entails the conversion of the ordinary benzene 
 linking of one of the benzene rings into the quinonoid linking, the change being 
 accompanied by a development of colour, just as the conversion of the ordinary 
 linking of hydroquinone (colourless) into the quinonoid linking of quinone, develops 
 a colour. HO'C 6 H 4 -OH becoming : 6 H 4 : 0. The following equation will make 
 the change more clear : 
 
 HC1,NH 2 -C 6 H 4 -C(OH)(C 6 H 4 -NH 2 ) 2 = C1NH 2 : C 6 H 4 : C(C 6 H 4 'NH 2 ) 2 + H 2 0. 
 Triamidotriphenylcarbinol hydro- Coloured salt f 
 
 chloride (colourless). (Pararosaniline chloride). 
 
 The foregoing reactions are typical of the behaviour of every triphenylmethane 
 
 * It is here only possible to call attention to some typical " aniline dyes " ; for information 
 as to the chemical constitution of dyes of trivial names, the student must consult a work on 
 dyestuffs. 
 
 t A simpler view of the constitution of this salt is that it is that of an ethereal chloride, 
 derived from the carbinol by exchange of OH for Cl ; (C 6 H 4 - NH 2 ) 8 C Cl. This view is not 
 regarded as t- instantiated. 
 
 2 Z 
 
722 ROSANILINE SALTS. 
 
 dyestuff ; that is to say, each may be obtained by oxidising a derivative of 
 triphenylmethane and treating the product with a warm acid. The parent 
 triphenylmethane derivative is called the leuco-base of the dyestuff ; the carbinol 
 into which it is converted by oxidation is called the colour-base of the dyestuff ; 
 whilst the coloured salt is the dyestuff itself. Thus, triamidotriphenylmethane 
 is called leuco-pararosaniline ; triamidotriphenyl carbinol is pararosamline base, 
 whilst the coloured salt with the quinonoid linking is pararosanlline chloride. 
 The converse changes are possible ; that is to say, by treating the dyestuff with a 
 caustic alkali the colour-base is precipitated, and if this be treated by reducing- 
 agents (nascent hydrogen) it yields the leuco-base. 
 
 The triphenylmethane dyestuffs are classified into derivatives of : 
 (i) Diamido-tripheni/lmethane, 6 H 5 *CH(C 6 H 4 < NH 2 ) 2 ; the type of these 
 is malachite green. (2) Triamidotriphenylmethane, CH(C 6 H 4 'NH 2 ) 3 ; 
 the type of these is rosaniline (magenta). (3) Trihydroxytriphenyl- 
 methane, CH(C 6 H 4 -OH) 3 ; the type of these is aurin. (4) Triphenyl- 
 methane carboxylic acid, CH(C 6 H 5 ) 2 (C 6 H 4 *C0 2 H) ; the type of these is 
 eosin. 
 
 Malachite green or tetramethyl-i : ^-diamido-triphenylmethane chloride 
 
 C1N(CH 3 ) 2 : C 6 H 4 : C(C 6 H 5 )[C 6 H 4 -N(CH 3 ) 2 ]. 
 
 The leuco-base of this dyestuff is prepared by heating benzaldehyde with 
 dimethylaniline and zinc chloride (to act as a dehydrating agent) 
 
 C 6 H 5 -CHO + 2C 6 H 5 -N(CH 3 ) 2 - C 6 H 5 -CH[C 6 H 4 'N(CH 3 ) 2 ] 2 + H 2 0. 
 
 The leuco-base is oxidised by Pb0 2 (when it yields the corresponding carbinol or 
 colour-base, see above) in the presence of HC1 (to produce the colour-salt). The 
 dyestuff is then precipitated by zinc chloride and sold in the form of a double 
 zinc-salt. 
 
 Bosaniline salts constitute the bulk of the dyestuff known as 
 magenta (fuchsine). They are formed by the action of acids on 
 rosaniline-base, which is triamidotolyldiphenyl carbinol 
 
 NH 2 -C 6 H 3 (CH 3 )-C(OH)(C 6 H 4 -NH 2 ) 2 . 
 
 The chloride, C1NH 2 : C ? H 3 (CH 3 ) : C(C 6 H 4 -NH 2 ) 2 , nitrate and acetate are 
 the most common salts in the market. They are prepared by heating 
 aniline oil for red (p. 665), which should contain equi-molecular pro- 
 portions of aniline, orthotoluidine and paratoluidine, with an oxidising- 
 agent (arsenic acid or nitrobenzene * is generally used) ; 
 
 C 6 H 4 (CH 3 )-NH 2 /C 6 H 3 (CH 3 )-NH 2 
 
 NH 2 -C 6 H 4 -CH 3 + + 3 = NH 2 -C 6 H 4 -C(OH)< +2H 2 0. 
 
 C 6 H 5 -NH 2 X C 6 H 4 -NH 2 
 
 The rosaniline base made in this way is converted into the chloride 
 by adding hydrochloric acid, and this salt is precipitated by adding 
 common salt. When recrystallised, rosaniline salts form bronze-green 
 crystals which are sparingly soluble in cold water, but more readily ii 
 hot water, to a red solution. When the hot solution is mixed with 
 ammonia and filtered quickly the rosaniline base crystallises from th< 
 . filtrate in colourless plates which become red in air, from absorption of 
 C0 2 > Reducing-agents bleach the red solution with formation of 
 leucaniline, NH 2 -C 6 H 3 (CH 3 )-CH(C 6 H 4 'NH 2 ) 2 ,t the leuco-base of rosani- 
 line. 
 
 * This oxidising-ag'ent is now more common than any other. When it is employed, HC1 
 and iron filings form a part of the charge, so that the nitrobenzene is first reduced to aniline 
 (which enters into the reaction), and the ferric chloride formed by its reduction is the imi 
 diate oxidant. 
 
 f When diazotised (p. 681), and heated with alcohol, leucaniline yields metatolyldiphenyl- 
 methane, C 6 H 4 (CH 3 ) CH(C 6 H 5 ) 2 , (cf. p. 681), showing that leucauiline, and therefore rosani- 
 line must be a derivative of this hydrocarbon. 
 

 
 AURIN AND EOSIN. 723 
 
 Pararosaniline or triamidotriphenol carbinol, C(OH)(C H -NH ) , i 
 prepared by oxidising a mixture of paratoluidine* (i mol.) aid aniline 
 (2 mols.) in the same way as is described for rosaniline. The salts are 
 red dyestuffs, like the rosaniline salts. 
 
 In both oxidations it may be supposed that the paratoluidine is oxidised to - 
 amidobenzaldehyde, which then condenses with the orthotoluidine and aniline (in 
 the case of rosaniline) or with the aniline alone (in the case of pararosaniline). 
 
 Many derivatives of pararosaniline and rosaniline, containing methyl, ethyl and 
 phenyl groups in place of the amido-hydrogen atoms, are prepared by heating 
 pararosaniline or rosaniline chloride with alkyl or phenyl halides ; these are also 
 used as dyestuffs, the shade produced by them becoming more blue as successive 
 alkyl or phenyl groups are introduced, Thus pentamethyl-pararowniline is known 
 as methyl violet, and triphenyl-rosaniline chloride as aniline blue. The combination 
 of tetramethylrosaniline, which is saturated with methyl groups, with methyl 
 chloride or iodide, produces a green dyestuff known as iodine green. 
 
 Aurin. When pararosaniline base is diazotised (p. 68 1), the three 
 NH 2 groups are converted into diazo-groups, and when the resulting 
 compound is boiled with water it yields trihydroxytriphenyl carbinol, 
 (C 6 H 4 -OH) 3 C'OH, (cf. p. 681). This compound is very unstable and 
 loses a molecule of water, becoming aurin, : C 6 H 4 : C(C 6 H 4 OH) 2 , com- 
 parable in structure with pararosaniline chloride. It crystallises in 
 green needles which dissolve in alkalies to a red solution, but are 
 precipitated again by acids. Thus aurin behaves as an acid substance, 
 as, indeed, is to be anticipated from the presence of phenolic OH 
 groups. It will be noticed that, whilst pararosaniline is a type of basic 
 dyestuffs, tending to combine with acid mordants, aurin is a type of 
 acid dyestuffs tending to combine with basic mo7'dants. 
 
 Rosolic acid bears the same relation to rosaniline as aurin bears to 
 pararosaniline. 
 
 Eosin. Triphenylmethane-carboxylic acid (see above), or rather its 
 hydroxy-derivative triphenyl carbinol- 1: 2 -carboxylic acid 
 
 (C 6 H B ) a (C 6 H 4 -COOH)C-OH, 
 
 gives rise to the dyestuffs of this class. Diphenylphthalide is the lactam 
 (p. 674) of this alcohol acid ; it may also be regarded as derived from 
 phthalic anhydride by substituting (C 6 H 5 ) 2 " for 0", for it is prepared by 
 the interaction of phthalyl chloride and benzene in presence of A1 2 C1 6 
 
 Diphenylphthalide. 
 
 By substituting phthalic anhydride for the chloride, a phenol for the 
 benzene and a dehydrating agent for the A1 2 C1 6 in this reaction, the 
 eosin dyestuffs are obtained. 
 
 Thus, phenol-phthalein is obtained when phthalic anhydride is heated with two 
 molecular proportions of phenol and ZnCl 2 
 
 /C0\ C(C 6 H 4 'OHk 
 
 C 6 H 4 <( >0 + 2 6 H 5 OH - C 6 H 4 < CQ __>0 4- H 2 0. 
 
 CO 
 
 The mass is dissolved in an alkali and the phenophthalein precipitated by an acid. 
 Its alkali salts are pink in solution, and are decomposed by the feeblest acids 
 
 * Its prefix appears to have been given to pararosaniline on account of the fac^that para- 
 toluidine is used in its manufacture. Since it has been recognised. that paratoluidine n 
 necessary for rosaniline, the name has lost its significance. 
 
724 CARBOHYDRATES. 
 
 p. 709), so that phenolphthalein is useful as an indicator in acidimetry. It can 
 hardly be termed a dyestuff. 
 
 It has been supposed that phenolphthalein may behave as dikydroaryphthalein, 
 C 6 H 4 (COC 6 H 4 OH) 2 . As this does not import a quinonoid structure into its consti- 
 tution, it has also been suggested that the salts of phenolphthalein are from the 
 
 pseudoform COOH'C fi H 4 <^ 6 4 . The ease with which the salts are decomposed 
 
 \J 8 H 4 :0 
 
 by all acids seems to show, however, that they are derived from phenolic, not 
 carboxylic groups. 
 
 .C[(C 6 H 3 'OH) 2 0] X 
 Fluor 'esc&in, C 6 H 4 <^ ^0, is formed when phthalic anhydride is 
 
 OO 
 
 heated with resorcinol, 2 mols. H 2 being liberated. It forms red crystals and dis- 
 solves in dilute alkalies, giving a solution which is red with a green fluorescence ; 
 this is also noticeable on the dyed fabric, hence the dyestuff is frequently mixed 
 with others for producing a fluorescent green. 
 
 Eosin itself is a tetrabromo-derivative of fluorescein, and is made by brominating 
 the latter in acetic solution. It dissolves in alkalies, giving a deep red solution 
 which fluoresces green when diluted. 
 
 XIII. CARBOHYDRATES. 
 
 523. It has been already indicated (p. 584), that this group of organic 
 compounds is only a temporary one in chemical classification, and that 
 it will be broken up so soon as the true constitution of the compounds 
 which it now comprises is understood. Indeed, it is already on the 
 eve of extinction, since several of the sugars, formerly the typical 
 members of the group, have been shown to be either aldehyde-alcohols 
 or ketone-alcohols. 
 
 Originally, the compounds belonging to this class were such as contain 
 hydrogen and oxygen in the proportion to form water, combined with 
 six atoms, or some multiple of six atoms, of carbon. This is still true 
 for a majority of the compounds of the class, but it is necessary now to 
 describe several substances which do not fall in with the above defini- 
 tion, among the carbohydrates. 
 
 The carbohydrates may be divided into two groups : (i) the Sugars, 
 and (2) the Starches and Celluloses. 
 
 The group of sugars contains compounds which are comparable in taste and 
 other properties with the substance commonly called sugar. The molecular 
 formulae for the sugars may be said to be known in almost all cases, and it is 
 found that whilst a number of them, such as glucose, C 6 H 12 6 , correspond with 
 the general formula, C K (H 2 0) K , others, such as cane-sugar, C 12 H220 n , correspond 
 with the general formula. C w (H 2 0) w _i. The molecular formulae for the starches 
 and celluloses are not known ; but the percentage composition of these compounds 
 indicates that their molecular formula is (C 6 H 10 5 ) W . As may be expected, the 
 compounds C w (H 2 0) w _i yield the compounds C M (H 2 0) W when decomposed by 
 hydrolysis, and the compounds (C 6 H 10 5 ) M undergo a similar change. 
 
 The above considerations have given rise to a classification of the carbo- 
 hydrates into (i) saccharifies or monoses, C M (H 2 O) M ; (2) disaccharides or saccharo- 
 bioses, C^H^OH ; (3) trisaccharides or saccharotrioses, C 18 R^0 IQ ; (4) polyBaccharide$^ 
 (C 6 H 10 5 ) W . 
 
 THE SUGARS. 
 
 524. These may be subdivided into glucoses (aldoses and ketoses)j 
 having the general formula C W (H 2 0) M , disaccharides (formerly sucroses) 
 or saccharo-bioses, having the formula C 12 H 22 O n , and trisaccharides 
 
GLUCOSES. 
 
 725 
 
 or saccharo-trwses, having the formula C 18 H 32 16 .* The sugars of the 
 second and third classes are converted into sugars of the first class by 
 hydrolysis. The type of the sugars of the first class is grape-sugar 
 that of the second cane-sugar, whilst that of the third is rafftnose. " 
 
 Since the sugars contain asymmetric carbon atoms, they give rise 
 to a large number of optically active stereo-isornerides (p. 542). 
 
 525. The Glucoses. These are named according to the number 
 of carbon atoms which they contain e.g., triose, C 3 H 6 3 ; tetroses, C 4 H 8 4 ; 
 pentoses, C 5 H 10 5 ; hexoses, C 6 H 12 6 ; heptoses, C 7 H 14 O 7 , &c. In constitu- 
 tion they are either aldehyde-alcohols or aldoses (containing the group 
 CH(OH)-CHO), or ketone-alcohols or ketoses (containing the group 
 COCH 2 OH), and accordingly behave as reducing-agents and yield 
 hydrazones just as other compounds containing the aldehyde or the 
 ketone group do. 
 
 The glucoses must be regarded as the first oxidation-products of 
 polyhydric alcohols, the most important of which have been mentioned 
 (P- 577)- The aldoses would be formed by oxidation of the primary 
 alcohol group, and the ketoses by oxidation of the secondary group. 
 All the glucoses have asymmetric carbon atoms, and each exists in two 
 stereoisomeric forms, the d- and the I- form, and in a third, externally 
 compensated or racemic, inactive (d + 1) form t (p. 605). 
 
 526. Thus the simplest aldose would be gly collie aldehyde, CH 2 OH'CHO, from 
 glycol ; glycerol yields both an aldose, glycerose (aldotriose), CH 2 OH'CHOH'CHO 
 (p. 584) and a ketose, dihydroxyacetone (ketotriose), CH 2 OH*COCH 2 OH. 
 
 (1) Tetroses. Erythrose, obtained by the oxidation of erythritol (p. 578) by the 
 action of dilute nitric acid, is probably 'a mixture of the aldotetrose, 
 
 CH 2 OH-[CHOH] 2 -CHO, 
 and the ketotetrose, CH 2 OH-CHOH-CO'CH 2 OH. A d- and an I- form are known. 
 
 (2) Pentoses. The aldopentoses, CH 2 OH'[CHOH] 3 'CH 2 OH are alone known at 
 present. They are natural sugars, occurring in many plants. They resemble the 
 aldohexoses (v:i.) in their general behaviour except that they are not fermented by 
 yeast. Other characteristics are that they yield furfural (p. 586) or its homologues 
 when distilled with dilute acids, and that they give a red colour with phloro- 
 glucinol and HC1. 
 
 Eight optically active and four externally compensated aldopentoses are possible 
 (p. 621). I- Arabinose, the chief member of the class, is prepared by boiling with 
 dilute H 2 S0 4 gum arabic and other gums which yield little mucic acid when 
 oxidised by HN0 3 . It crystallises in sweet prisms, melts at 160 C. and is strongly 
 dextro-rotatory.f 
 
 By reduction it yields the pentatomic alcoholiarabitol, CH 2 OH-[CHOH] 3 -CH 2 OH. 
 Xylose (from wood-gum, straw, and jute), and ribose are isomerides of arabinose. 
 Rhamnose (from quercitrin) and fucose (from sea-weed) are methyl arabinose, 
 C 5 H 9 (CH 3 )0 5 . 
 
 (3) Hexoses, C 6 H 12 6 . These are the compounds which were origin- 
 ally called glucoses. They are widely distributed in nature, but are 
 mainly found in unripe fruit, the chief being dextrose, or grape-sugar, 
 and Isevulose, or fruit-sugar ; they are produced by the hydrolysis of 
 the disaccharides and poly sacchar ides, the change being effected both 
 by enzymes and by dilute acids or alkalies. d-Glucose, d-mannose, 
 
 * According to one system of nomenclature the termination -ose is employed to designate 
 sugars of the first class, and the termination -on to indicate sugars of the second class. T, 
 C fi H 12 O fi is hexose, whilst C 12 HoQO n is dihexon. 
 
 t Much confusion is engendered by Fischer's custom of naming the sugars d- and J- with- 
 out reference to their actual rotation, but according to the way in whjch they a 
 from each other. 
 
726 GBAPE-SUGAR. 
 
 d-galactose, and d-fructose are fermented by yeast, yielding alcohol. A 
 few have been synthesised, and the constitution of nearly all has been 
 settled (see below). 
 
 (a) -Aldohexoses, CH 2 OH-[CHOH] 4 'CHO. The substance commonly 
 called glucose, grape-sugar or dextrose is d-glucose, there being also 
 an ^-glucose and a (d + Q-glucose. It is the aldehyde of sorbitol (p. 5 79). 
 
 d-Glucose is the crystallised sugar found in honey, raisins, and many 
 other fruits ; it is almost always accompanied by Isevulose, a keto- 
 hexose, which is far more difficult to crystallise. Dextrose is also 
 found in small quantity in several animal fluids, and in the liver, and 
 it is abundant in urine in cases of diabetes. 
 
 Dextrose may be obtained from honey by mixing it with cold alcohol 
 to dissolve the Isevulose, which forms about one-third of its weight, and 
 leaves about an equal quantity of dextrose, which may be dissolved in 
 boiling alcohol and crystallised. To extract it from fruits, they are 
 crushed with water, strained, the liquid boiled to coagulate albumin, 
 filtered, evaporated to a syrup, and set aside for some days, when crystals 
 of dextrose are deposited. Fresh fruits contain chiefly Isevulose, which 
 is gradually converted into dextrose. 
 
 Dextrose is also a product of the hydrolysis of glucosides (q.v.), and 
 di- and poly-saccharides (cane-sugar, starch, &c.). 
 
 From cane-sugar it is best prepared by heating a mixture of 250 c.c. of alcohol 
 (sp. gr. 0.823) with 10 c.c. of strong HC1 to 45 C. and adding 80 grams of finely 
 powdered cane-sugar in small doses. When the sugar has entirely dissolved, the 
 whole is set aside for a week and stirred to induce crystallisation. The crystals of 
 dextrose are drained from the solution containing laevulose and washed with 
 alcohol. 
 
 Commercial glucose or starch-sugar is made by heating starch with diluted sul- 
 phuric acid,* which first converts it into dextrin and finally into ^-glucose, 
 (C 6 H 10 5 ) W + %H 2 = rcC 6 H 12 6 . 
 
 Water containing about 1.5 per cent, of H 2 S0 4 is heated to boiling and a hot 
 mixture of starch and water is allowed to flow gradually into it. The mixture is 
 boiled for half an hour, neutralised with chalk, and concentrated by evaporation, 
 when it deposits crystals of calcium sulphate. The clear syrup is drawn off and 
 evaporated in a vacuum-pan till it is strong enough to crystallise, some glucose 
 from a previous batch being added to promote crystallisation. The glucose thus 
 obtained contains about 70 per cent, of ^-glucose and also maltose, dextrin, and 
 some calcium salts of organic acids ; it may be purified by washing with strong 
 alcohol mixed with 3 per cent, of HC1, and afterwards with commercial absolute 
 alcohol. 
 
 When crystallised from an aqueous solution, dextrose forms six-sided 
 scales (with iH 2 0) ; these fuse at 86 C., and become anhydrous at 
 110 C. ; it crystallises from alcohol at 30 C. in small anhydrous 
 needles, which melt at 146 C. It is less sweet than cane-sugar, and 
 can be directly fermented by yeast (p. 561). Glucose dissolves in 1.2 
 parts of cold water, in 50 parts of cold, and in 5 parts of boiling, 
 alcohol (sp. gr. 0.837). When heated to 170 C., it is converted into 
 dextrosan (glucosan), C 6 H 10 5 , a nearly tasteless substance, convertible 
 into glucose by dilute acids. When boiled with caustic potash, glucose 
 gives a dark brown solution, being ultimately converted into humus- 
 like acids. In presence of alkalies, glucose acts as a strong reducing- 
 agent. If a solution of glucose be mixed with CuS0 4 , and KOH be 
 gradually added, the blue precipitate of cupric hydroxide produced at 
 
 * Care should be taken that the sulphuric acid is free from arsenic, lest the latter pass 
 into the glucose and thence into the beer brewed therefrom. 
 
FEUIT-SUGAE. 
 
 first dissolves in excess of potash to a fine blue solution ; if this be 
 gently heated, a yellow precipitate of cuprous hydroxide is produced 
 which becomes red cuprous oxide when boiled ; a little metallic copper 
 is precipitated at the same time, and the glucose is oxidised to a number 
 of organic acids. Glucose precipitates metallic silver when warmed 
 with ammonia-nitrate of silver, and metallic mercury from HefCN^ 
 mixed with KOH. 
 
 Solution of glucose mixed with NaCl deposits crystals of 2C 6 H 12 O fi NaCl H 
 which is sometimes deposited from diabetic urine. Glucose is not so easily 
 blackened by H 2 S0 4 as is sucrose, but forms an unstable compound with it. With 
 alkaline earths dextrose combines to form compounds like C 6 H 12 6 .CaO, which are 
 precipitated by alcohol. Other reactions will be discussed under Constitution of the 
 Sugars. 
 
 Dextrose rotates the plane of polarisation to the right hand, but a 
 solution which has been kept for some hours has only half the effect of 
 a freshly made solution, a phenomenon known as bi-rotation, and 
 probably due to the formation of hydrates. 
 
 Glucose is used by brewers and distillers for making alcohol, and by 
 confectioners ; dyers and calico-printers use it to reduce indigo. 
 
 d-Mannose is obtained, together with Isevulose, by the cautious oxidation of 
 mannitol (p. 578), with platinum black or nitric acid. It may be prepared by 
 boiling seminine, the reserve-cellulose of many seeds, with dilute H 2 S0 4 ; it is 
 sometimes called seminose. Mannose has not been crystallised ; it is very soluble 
 in water, and its solution is dextro-rotatory ; a I and a (d + I)- form are also 
 known. 
 
 d-Galactose is obtained, together with ^-glucose, when milk-sugar and some 
 varieties of gum arabic are boiled with dilute H 2 S0 4 . To prepare it, milk-sugar is 
 boiled for six hours with four parts of water containing 5 per cent, of H 2 S0 4 . 
 The solution is precipitated by baryta, filtered, evaporated to a syrup, and induced 
 to crystallise by adding a few crystals of dextrose. The crystals are washed with 
 alcohol of 80 per cent., and recrystallised from hot alcohol of 70 per cent. It 
 crystallises in rhombic prisms, which are less sweet than cane-sugar, and melts at 
 1 66 C. It is not very soluble in cold water, and is insoluble in absolute alcohol. 
 Galactose is also obtained by hydrolysing galactitol, C 9 H 18 7 , a crystalline substance 
 extracted by alcohol from yellow lupines. I- and (d + Z)-galactose are known. 
 
 The guloses and taloses are artificial aldohexoses. Methylhexose or rhamnohexose, 
 C 6 H 11 (CH 3 )0 6 , has also been prepared. 
 
 (b) Ketohexoses, CH 2 OH-[CHOH] 3 -CO'CH 2 OH. d-Fructose is the 
 most important of these. It is commonly known as fruit-sugar or 
 Isevulose, and is prepared by heating cane-sugar with water and a very 
 little sulphuric acid on a water-bath for half an hour, removing the 
 acid by barium carbonate, and evaporating to a syrup. This syrup 
 contains invert-sugar^ a mixture of equal weights of dextrose and 
 Isevulose, which mixture deposits crystals of dextrose when exposed to 
 light. To obtain pure Isevulose, it is mixed with water, cooled in ice, 
 and stirred with calcium hydroxide, which precipitates a sparingly 
 soluble lime compound of Isevulose. This is suspended in water and 
 decomposed by C0 2 ; the filtrate from the calcium carbonate is then 
 evaporated on a water-bath. The syrup is washed with cold alcohol 
 and set aside in a cold place, when the Isevulose crystallises. 
 
 Lasvulose is much sweeter than dextrose, rivalling cane-sugar in this 
 respect. It does not ferment so readily as dextrose, so that when invert- 
 sugar is mixed with yeast, the dextrose is the first to disappear. It also 
 reduces alkaline cupric solutions (p. 6 1 9) less readily. Lsevulose rotates 
 the plane of polarisation of light to the left, whence its name, but a 
 
728 SYNTHESIS OF SUGARS. 
 
 dextro- (I) and an inactive (d + I) laevulose also exist. It forms two 
 crpstalline compounds with lime, C 6 H 12 6 .Ca0.2Aq and C 6 H l2 6 .3CaO, 
 dissolving respectively in 137 and 333 parts of cold water. 
 
 When heated to 170 C., laevulose is converted into Icevulosan, C 6 H 10 5 , 
 which is dextro-rotatory. "When heated with alkalies it is partly con- 
 verted into d-glucose and cZ-mannose. 
 
 527. (4) Heptoses, C 7 H 14 7 , octoses, CgHigOg, and nonoses, C 9 H 18 9 . It has been 
 found possible to produce a glucose containing x carbon atoms from one containing 
 fc-i carbon atoms by treating the latter with hydrocyanic acid, whereby it is con- 
 verted into a cyanohydrin (p. 582) just as any other aldehyde or ketone would be. 
 This cyanohydrin is convertible into a carboxylic acid by hydrolysis ; this may 
 be reduced to a new sugar by sodium amalgam ; thus, dextrose yields the cyano- 
 hydrin CH 2 OH-[CHOH] 4 -CH(OH)-CN, which is converted into dextrose-carloxylic 
 acid (gluco-heptonic acid), CH 2 OH-[CHOH] 5 -C0 2 H, by hydrolysis, and when this 
 acid is reduced it yields glucoheptose, CH 2 OH-[CHOH] 5 -CHO. By these means 
 each glucose may be made to yield a heptose, which, in its turn, may be converted 
 into an octose and a nonose ; consequently the possible number of these sugars is 
 very large. They have not been found in nature. 
 
 528. Synthesis of the Glucoses. The key to the synthetical production of the 
 glucoses was phenylhydrazine. Like other aldehydes and ketones the glucoses 
 form hydrazones when heated with a solution of phenylhydrazine hydrochloride 
 and sodium acetate (p. 685). Thus the aldohexoses form the hydrazones 
 
 CH 2 OH-[CHOH] 3 -CHOH-CH : N'NC 6 H 5 , 
 while the hydrazones from the ketohexoses have the form 
 
 CH 2 OH-[CHOH] 3 -C( : N'NHC 6 H 5 )-CH 2 OH. 
 
 When an excess of phenylhydrazine is used, the hydrazones lose H 2 on account of 
 the tendency for C 6 H 5 NH'NH 2 to absorb H 2 and become C 6 H 5 NH 2 and NH 3 
 (p. 685). This converts the aldose hydrazone into a ketonic compound and the 
 ketose hydrazone into an aldehydic compound 
 
 CH 2 OH-[CHOH] 3 'CO-CH : N'NHC 6 H 5 
 CH 2 OH-[CHOHJ 3 -C( : N'NHC 6 H 5 )-CHO. 
 
 These immediately combine with a second molecule of phenylhydrazine to form 
 osazones, both of which have the formula, 
 
 CH 2 OH-[CHOH] 3 -C( : N'NHC 6 H 5 )-CH : N'NHC 6 H 5 . 
 
 Thus the aldoses and ketoses yield the same osazones except in so far as these may 
 differ stereochemically. 
 
 The hydrazones are generally soluble in water, but the osazones are bright 
 yellow, sparingly soluble, and easily crystallised. Thus their formation is often 
 the best method of identifying a known sugar or of isolating a new one. 
 
 For this latter purpose the osazone is dissolved in cold strong HC1 ; it is thus 
 converted into the corresponding osone, a ketone-aldehyde ; 
 CH 2 OH-[CHOHJ 3 'C( : N'NHC 6 H 5 )-CH : 
 = CHOH-CHO 
 
 The red liquid which is formed deposits phenylhydrazine hydrochloride ; it is 
 filtered and neutralised with PbC0 3 ; the lead compound of the osone remains in 
 solution ; it is precipitated by baryta and the precipitate decomposed by H. 2 S0 4 . 
 To convert the solution of the osone, thus obtained, into a sugar it is reduced by 
 means of zinc and acetic acid ; 
 
 CH 2 OH-[CHOH] 3 -CO'CHO + H 2 =CH 2 OH-[CHOHJ 3 -CO-CH 2 OH. 
 
 When dextrose is treated in this way it is converted into lasvulose. 
 
 529. Formaldehyde is the first step in synthesising glucoses from their elements. 
 Treated with lime-water, it is polymerised to a mixture of sugars, termed formose ; 
 a similar mixture (methylenitan) is obtained from trioxymethylene (p. 581) in like 
 manner. Two sugars, a- and (3-acrose, have been isolated from this mixture and 
 also from the mass obtained by treating glycerose (p. 584) with alkalies. They are 
 separated by taking advantage of the greater solubility of /3-acrosazone, than of 
 o-acrosazone, in ethyl acetate. 
 
 The glucose recovered from ct-acrosazone in the manner described above appears 
 to be identical with (d- + ^-fructose, which by fermentation with yeast is converted 
 
CONSTITUTION OF GLUCOSES. 729 
 
 into Z-fructose, the ^-constituent having been used by the yeast (see D 606) 
 This Z-fructose is dextro-rotatory (see foot-note, p. f*c\ * J^t X^:': 
 
 reduction yield first I- and <*-mannose anYthenT 
 
 nn Se Ugh the P hen y lh y d ^ine reactions they yield I- and I 
 
 fructose 
 
 When I- and d- mannonic acids are heated with quinoline they are converted 
 into I- and d- glucomc acids, which are stereo-isomeric with them. By reduction 
 nlaCleld *~ and ^ gluCOSe C dextrose ^ Thus a number of hexoses 
 
 has 
 
 It will be observed that the monocarboxylic acids derived from the polyhydric 
 alcohols are useful transition products in the syntheses, as they readily lend them- 
 selves to resolution by means of their salts with the alkaloids. 
 
 Through these acids also it is possible to pass from the pentoses to the hexoses 
 and vice versa. Thus Z-arabinose combines with HCN as any other aldehyde does 
 (p. 582), forming the cyanohydrin CH 2 OH-[CHOH] 3 -CH(OHYCN, which by 
 hydrolysis yields Z-mannonic acid, the CN becoming COOH as usual. Again by 
 oxidising d-gluconic acid with H 2 O 2 in presence of ferric acetate it yields 
 d-arabinose ; or by treating d-glucoseoxime, CH 2 OH[CHOH] 4 'CH : N(OH) with 
 acetic anhydride and sodium acetate, it yields a pentacetyl derivative which 
 becomes d-arabinose when treated with HC1. 
 
 530. Constitution of the Glucoses. The molecular weight of many of the sugars 
 has been settled by Raoult's method (p. 3 19). That the hexoses (the same arguments 
 apply to the pentoses) are alcoholic aldehydes or ketones is shown by the following 
 reactions : 
 
 When heated with acetic anhydride and sodium acetate the hexoses yield 
 pentacetyl-derivatives, C 6 H 7 0(OCH 3 CO) 5 , showing that they contain 5 alcoholic 
 hydroxyl groups (p. 578) and are pentahydric alcohols. Five out of the six 
 atoms of oxygen are thus disposed of : that the sixth must be present either as an 
 aldehyde or as a ketone group, is shown by the fact that these sugars give a number 
 of the reactions which characterise aldehydes and ketones. In the aldohexoses 
 this remaining oxygen atom must be present as an aldehyde group, for on oxida- 
 tion these sugars yield acids containing the same number of carbon atoms, which 
 would not be the case if the sugars were ketones (p. 624). Thus, the dextroses 
 yield first gluconic acids, CH 2 OH-[CHOH] 4 'CO 2 H, and then, by further oxidation, 
 saccharic acids, C0 2 H-[CHOH] 4 -C0 2 H ; the mannoses yield mannonic acids and 
 manno-saccharic acids, stereo-isomeric with the above acids ; whilst the galactoses 
 yield galactonic and mucic acids, also stereo-isomeric with the preceding acids. 
 Moreover, when reduced by sodium amalgam these sugars yield hexahydric 
 alcohols ; e.g., the mannoses yield mannitols, the dextroses sorbitol, and the 
 galactoses dulcitol. This behaviour on reduction shows that the sugars are certainly 
 open-chain compounds, for the above-named alcohols are all convertible into normal 
 hexane by hydriodic acid. The rule already referred to as guiding us in the 
 interpretation of chemical constitution, namely, that one carbon atom cannot hold 
 more than one hydroxyl group, may be applied to these sugars, when it becomes 
 evident that the five hydroxyl groups must be attached to five separate carbon 
 atoms, forming one primary and four secondary alcohol groups ; the sixth carbon 
 atom may constitute the aldehydic carbon. 
 
 The ketonic character of the ketohexoses follows from the fact that wtien oxidised 
 they yield two acids (p. 624). Thus, the lasvuloses yield trihydroxybutyric acids, 
 CH 2 OH-[CHOH] 2 -CO 2 H, and glycollic acid, CH 2 OH C0 2 H. By reduction, these 
 sugars yield mannitol. The position of the ketone group in the open-chain repre- 
 senting the Isevuloses may be said to be settled by the following facts. When 
 Isevulose is treated with HCN it yields a cyano-hydrin which is almost certain to 
 contain the group :C(OH)(CN) in place of the group :CO (p. 582) ; when this 
 cyano-hydrin is hydrolysed it yields a corresponding carboxylic acid which is 
 equally certain to contain the group :C(OH)(COOH) ; when this acid is reduced by 
 hydriodic acid, it yields methylbutylacetic acid, the structure of which shows that 
 the carbonyl carbon of the original laevulose must have had one carbon atom 
 attached to it on the one hand and four carbon atoms attached to it on the other 
 hand. The following equations will make this apparent : 
 
73 STEREOISOMERISM. 
 
 ( i ) CH 2 OH -[CHOH] 3 - ^O-CHgOH + HCN = CH 2 OH-[CHOH] 3 ' 6 r (OH)(CN) 'CH 2 OH 
 (2) CH 2 OH-[CHOH] 3 -6'(OH)(CN)-CH 2 OH + 2HOH = 
 
 CH 2 OH-[CHOH] 3 -6'(OH)(COOH)-CH 2 OH + NH 3 
 
 (3) CH 2 OH-[CHOH] 3 -6'(OH)(COOH)-CH 2 OH + i2HI = 
 
 CH 3 -[CH 2 ] 3 '6'H(COOH)-CH 3 + I 12 + 6H 2 0. 
 
 CH 3 -[CH 2 ] 3 -CH(COOH)'CH 3 or ' >CH'COOH is methylbutylacetic acid. 
 
 CUtf 
 
 When dextrose is submitted to a similar series of reactions it yields normal hep- 
 tylic acid, CH 3 -[CH 2 ] 4 -CH 2 -COOH, showing that the aldehyde group is at the end 
 of the open-chain, a position, indeed, which is the only possible one for the 
 
 
 C^ H group. 
 
 531. Keference must now be made to the stereoisomerism of compounds con- 
 taining a number of asymmetric carbon atoms, as do these polyhydroxy-alcohols, 
 aldehydes, ketones and acids. 
 
 It was shown at p. 621, that a compound containing two asymmetric carbon 
 atoms can exist in four stereo-chemical modifications, when, as in the case of 
 tartaric acid, each carbon atom is attached to the same groups, that is, when the 
 compound is of the type abcC Cabc. Two of these are optically active, one 
 inactive, by internal compensation and one inactive by external compensation. 
 
 In the case of a compound of the type abcC Ca'b'c' there can be no inactivity 
 by internal compensation. A little reflection will show that, instead, there will be 
 four optically active isomerides, one in which abc and a'Vc' are both arranged to 
 cause dextro-rotation, one in which they are both arranged to cause Isevo-rotation, 
 and two in which they are oppositely arranged. In addition there will be two 
 externally compensated, inactive forms. 
 
 Now the pentahydric alcohols, CH 2 OH-CHOH'CHOH-CHOH-CH 2 OH, and the 
 corresponding dicarboxylic acids, have two asymmetric carbon atoms (printed in 
 heavy type) and are of the form abcC Cabc. Hence, like tartaric acid, they occur 
 in a d-form, an Z-form, an externally compensated or d + Z-form, and an internally 
 compensated or i-form. There is, however, a fifth, viz., a second internally com- 
 pensated form ; for although the central carbon atom is not asymmetric, being 
 balanced on either side, it has an H and an OH attached to it, the positions of 
 which may be reversed. 
 
 The aldopentoses, CH 2 OH-CHOH-CHOH'CHOH-CHO, and the corresponding 
 monocarboxylic acids. CH 2 OH[CHOH] 3 COOH, have 3 asymmetric carbon atoms. 
 Each of these should give rise to a + and a - form, and since the nature of the 
 whole compound will depend on which carbon atoms have their attached groups 
 in the + form, and which have them in the - form, there should be as many aldo- 
 pentoses as there are ways of writing + or - three times, e.g., + + +, - -, 
 + +,- + -, and so on. This number is eight, so that there are 8 optically 
 active isomerides. As the aldopentoses are of the type abcG Ca'b'c', there are no 
 internally compensated forms, but by combining pairs of the optically active forms, 
 four racemic or externally compensated forms are possible. 
 
 The hexahydric alcohols, CH 2 OH-CHOH'CHOH-C HOH'CHOH'CH 2 OH, and 
 corresponding dicarboxylic acids, have four asymmetric carbon atoms, so that the 
 number of optically active isomerides, should be discoverable by finding the 
 number of ways of writing + and - four times. This will be found to be 16. 
 But these alcohols are of the type abcCCabc, wherefore those forms in which the 
 + and - are similarly arranged, but in opposite order, e.g., + - + -,- + -+, 
 are identical, reducing the essentially different ways of writing + and - to 10, 
 two of which represent internally compensated molecules, leaving 8 active 
 isomerides. In addition there should be four racemic forms. 
 
 Now the aldohexose formula, CH 2 OH'C HOH-CHOH'CHOH-CHOH'CHO, 
 also contains four asymmetric carbon atoms, and is of the type abcC Ca'b'c', so 
 that all 1 6 isomerides exist, none of which is internally compensated. Besides 
 these there should be 8 racemic forms. At present 1 1 of the optically active forms 
 are known, viz., d- and Z-mannose, d- and Z-glucose, d- and Z-gulose, d- and Z-galac- 
 tose, d- and Z-idose, and ^-talose. 
 
 The ketohexoses, CH 2 OH'C HOH'C HOH-CHOH-CO'CH 2 OH, contain 3 asym- 
 metric carbon atoms and are of the type abcC Ca'b'c' ; stereoisomerism among 
 them, therefore, is similar to that among the aldopentoses. 
 
CANE-SUGAR. 
 
 It has been found to be possible to orientate those carbon atoms which have a 
 + arrangement of groups and those which have a - arrangement in the glucosee 
 but for a description of the arguments employed, the student must be referred 
 the chemical dictionaries. 
 
 532. The Disaccharides. The members of this class of sugars are 
 characterised by being converted by hydrolysis into two molecules of 
 glucoses (hence the synonym, saccharo-bioses)* 
 
 Cane-sugar or sucrose, G l2 R 2 fl lv is not found only in the sugar- 
 cane, but in many other plants, such as beetroot, sorghum, maize, barley, 
 almonds, walnuts, hazel-nuts, coffee-beans, and madder root. It occurs 
 also in the sap of the maple, lime, birch, and sycamore, as well as in the 
 juices of many fruits ; in these, it is generally accompanied by invert- 
 sugar (v.i.). During the early period of vegetation, it appears that 
 grape-sugar and fruit-sugar are formed, and that these become cane- 
 sugar during the ripening. The green sugar-cane contains much dextrose 
 and laevulose, which are afterwards converted into sucrose. Honey con- 
 tains cane-sugar and invert-sugar, in varying proportions, depending 
 on the food of the bees. 
 
 To extract sugar from plants, they should be cut up, dried at a tem- 
 perature not exceeding 100 C., and boiled repeatedly with alcohol of 
 sp. gr. 0.87, which deposits the sugar in crystals, on cooling. 
 
 On the large scale, sugar is manufactured by crushing the cane between rollers, 
 when an acid juice is obtained, containing about 20 per cent, of sucrose ; this is 
 neutralised by lime, to prevent inversion of the sugar, and heated to coagulate 
 the albumin. This is skimmed off the surface, and the syrup is evaporated till 
 it is strong enough to crystallise. About half the sugar is thus obtained in brown 
 crystals (moist sugar'), the remainder being partly extracted as an inferior sugar 
 (foots sugar') by another evaporation, and partly left as uncrystallisable sugar in 
 the molasses or treacle. To refine the raw sugar, it is dissolved in water, decolor- 
 ised by filtering through a thick bed of animal charcoal, and evaporated at 60 C. 
 (140 F.) in a copper vacuum-pan connected with an air-pump, since a higher 
 temperature would invert the sugar. It may then be obtained in large crystals, 
 sugar-candy, or, by stirring, in minute crystals which are drained in conical 
 moulds, and washed with a saturated solution of sugar till they form white loaf- 
 sugar. 
 
 Sugar is extracted by a similar process from the juice of the white beetroot. 
 The juice contains about 10 per cent, of sugar, about half of which is obtained in 
 a crystallised state. 
 
 A larger yield of crystallisable sugar has been obtained from cane and beet 
 juice by the strontia process, which consists in precipitating the sugar from the 
 boiling solution by adding strontium hydroxide ; the precipitate, C l2 R^O u (SrO^ 
 is washed with hot water, and afterwards suspended in boiling water and allowed 
 to cool, when most of the strontia is deposited as hydroxide, and the remainder is 
 precipitated from the solution by C0 2 . 
 
 Sometimes the potassium salts which are present in the molasses, and hinder 
 crystallisation, are precipitated in the form of alum by adding aluminium sulphate. 
 
 533. Properties of Sucrose. It crystallises in monoclinic prisms, which 
 are insoluble in absolute alcohol, but dissolve to almost any extent in 
 boiling water. 100 parts of saturated syrup at 20 C. contain 67 of 
 sugar ; the solution of sugar is dextro-rotatory. When boiled with 
 dilute acids it is hydrolysed to a mixture of equal weights of dextrose 
 (d-glucose) and tevulose (d-f ructose), C I2 H 22 O n + H 2 = C 6 H 12 6 + C 6 H 12 6 . 
 
 * In one system of nomenclature, they are termed dipentons, dihexom, &c., according- as the 
 glucoses produced by the hydrolysis are pentoses or hexoses. Thus, arabinon, C 10 H 18 O ft 
 (from gum), is a dipenton, since it yields two molecules of arabinose by hydrolysis ; cane- 
 sugar is a dihexon, since it yields dextrose and lasvulose by hydrolysis. 
 
732 COMPOUNDS OF SUGAR. 
 
 This mixture is known as invert-sugar, since it is Isevo -rotatory (the 
 laevo-rotation of leevulose being greater than the dextro-rotation of 
 dextrose). It is prepared for the use of brewers (see foot-note, p. 726). 
 Sucrose fuses at 160 C. (320 F.), and does not crystallise on cooling. 
 If kept melted for some time, it is converted into a mixture of dextrose 
 and Icevulosan ; C 12 H 22 O H = C 6 H 12 6 + C 6 H 10 5 . If this be dissolved 
 in water, and yeast added, the dextrose ferments, but the Isevulosan is 
 unaltered. When further heated, but below 190 C. (374 F.), 
 sucrose loses 2H 2 O and becomes brown, yielding caramelan, C 12 H ]8 9 , 
 an amorphous, brittle, very deliquescent body, colourless when pure, and 
 not capable of reconversion into sugar. Commercial caramel, used for 
 colouring liquids, is a mixture of this with other bodies formed at 
 higher temperatures, and is usually made by heating starch-sugar. It 
 is bitter. Cane-sugar does not reduce Fehling's solution unless boiled 
 with it sufficiently long to effect the inversion of the sugar. 
 
 When sugar is melted in a little water (barley-water was formerly used), it 
 cools to a glassy mass (barley-sugar*) enclosing a little water ; this dissolves some 
 of the sugar and deposits it in crystals, until in course of time the whole mass is 
 opaque and crystalline. Heated with water at 160 C., sucrose yields formic 
 acid, carbon dioxide, and charcoal. At 280 C. some pyrocatechin is produced. 
 Dilute acids, even carbonic, convert sucrose into dextrose and Isevulose, slowly in 
 the cold, and quickly on heating. 
 
 Fused with potash, sucrose gives the potassium-salts of oxalic, formic, acetic, 
 and propionic acids, together with acetone. 
 
 Sucrose acts as a reducing-agent ; if ammonio-nitrate of silver is added to its 
 solution, followed by sodium hydroxide, a mirror of silver is deposited on heating. 
 The antiseptic properties of sucrose are well known : a strong syrup arrests fermenta- 
 tion. Weak solution of sucrose, in contact with yeast, is first converted into 
 dextrose and lasvulose, and then into alcohol aad carbon dioxide (see p. 562). 
 Sugar absorbs ammonia gas, forming C 12 H 21 (NH 4 )0 U , which decomposes again on 
 exposure to air. 
 
 Sucrose behaves like a weak acid to strong bases. Sodium sucrate, C 12 H 21 NaO n , 
 is precipitated when strong caustic soda is added to an alcoholic solution of 
 sugar. Slaked lime is easily dissolved by solution of sugar ; if equal molecules 
 of sugar and lime be dissolved in cold water, and alcohol added, a precipitate of 
 CaO.C^HsoOn, is obtained, but if an excess of lime be employed, the precipitate, 
 is 2CaO.C ]12 H 22 11 . When the solution of either of these is boiled, it deposits 
 3CaO. C 12 HijO u , which requires more than 100 parts of cold water and 200 parts 
 of boiling water to dissolve it, but dissolves readily in solution of sugar. All 
 these compounds are decomposed by C0 2 . 
 
 If strontium hydroxide be added to a boiling solution containing 15 per cent, 
 of sucrose, the compound 2SrO.Cj2H2.jOn, separates as a granular precipitate, 
 and when 2.5 molecular weights of the hydroxide have been added, the precipi- 
 tation of the sugar is nearly complete. If the precipitate be stirred with boiling 
 water, it decomposes, on cooling, forming sugar and strontium hydroxide. 
 
 Iron is much corroded by sugar, in the presence of air, the metal being dis- 
 solved as ferrous sucrate, C 12 H 20 Fe"0 11 (?), which, in contact with air and mois- 
 ture, deposits ferric hydroxide, and is reconverted into sugar, which attacks a 
 fresh portion of the iron. Lead is also attacked and dissolved by sugar solution, 
 especially when heated. On boiling lead hydroxide with solution of sugar, it is 
 dissolved, and, as the solution cools, it deposits diplumbic sucrate, C 12 H ]8 Pb 2 O u .Aq, 
 as a white powder, which loses its water at 100 C. The sugar may be completely 
 precipitated in this form. Triplumbic sucrate, C 12 H 16 Pb 3 O n , is precipitated when 
 soda is added to a mixture of solutions of lead acetate and sugar ; it may be 
 crystallised in needles from sugar solution. 
 
 Many metallic oxides form compounds with sugar which are readily soluble in 
 alkalies, so that the addition of sugar to solutions of copper and iron, for example, 
 prevents their precipitation by alkalies. If solution of sucrose be mixed with cupric 
 sulphate, and potash gradually added, a blue precipitate of Cu(OH) 2 is formed, 
 which dissolves, when more potash is added, to a deep-blue liquid, which may be 
 
MILK-SUGAR. 733 
 
 heated to boiling without change, but if long boiled or kept, deposits cuprous oxide 
 or hydroxide as a red or yellow precipitate. 
 
 When a solution containing sugar with one-fourth of its weight of common 
 sat is allowed to evaporate spontaneously, it deposits deliquescent rhombic 
 prisms of 
 
 ^^n... 
 
 Strong sulphuric acid converts dry sucrose into a brown mass, but if water be 
 present, or if heat be applied, the mixture froths up and blackens, evolving CO 
 C0 2 , and S0 2 gases. Dilute sulphuric and hydrochloric acids, when boiled with 
 sugar, convert it into a brown substance, partly soluble in alkalies, and containing 
 about 63 per cent, of carbon (sugar contains 42). Formic acid (containing only 
 26 per cent, of carbon) is found in the solution. Strong nitric acid dissolves 
 sucrose, and converts it, on heating, into oxalic and saccharic acids. When 
 heated with dilute nitric acid, it yields, besides these, acetic, tartaric, hydrocyanic, 
 and carbonic acids, with evolution of N, NO, and N 2 3 . A cold mixture of strong 
 nitric and sulphuric acids converts sugar into a resinous mass, which is insoluble 
 in water and soluble in alcohol. It explodes when heated or struck, and appears 
 to be sucro-tetra-nitrate, C 12 H 18 7 (N0 3 ) 4 . 
 
 534. Milk-sugar or lactose (lactobiose), C I2 H 22 O n + H 2 0, is prepared 
 by evaporating the whey of milk to a syrup, and setting it aside in a 
 cold place to crystallise. The commercial product is generally crystal- 
 lised round strings or slender wooden rods. It is purified by dissolving 
 it in water and precipitating by alcohol. The crystals lose their water 
 of crystallisation at 130 C. Lactose is much less sweet and less 
 soluble than sucrose, requiring 6 parts of cold and 2.5 parts of hot 
 water. It is insoluble in alcohol and ether. By rapidly boiling 
 the aqueous solution, lactose may be obtained in anhydrous crystals, 
 which dissolve in 3 parts of cold water, but quickly deposit in the 
 hydrated form. Cow's milk contains about 4.7 per cent, of milk- 
 sugar. 
 
 Lactose is a much stronger reducing-agent than sucrose, and precipi- 
 tates cuprous oxide when gently heated with alkaline cupric solution ; 
 a fine mirror of silver is deposited when silver nitrate is mixed with 
 ammonia, potash, and lactose, and gently warmed. Milk-sugar also 
 differs from cane-sugar in becoming brown when heated with potash. 
 It is dextro-rotatory and shows bi-rotation. When boiled with diluted 
 acids, it is hydrolysed to dextrose (^-glucose) and galactose. Yeast 
 causes a similar change, subsequently fermenting the dextrose to 
 alcohol (as in koumiss). Putrefaction -ferments, such as old cheese, 
 ferment milk-sugar to lactic acid (see p. 603). It is unchanged by 
 heating to 100 C, with solution of oxalic acid, which inverts sucrose. 
 When oxidised by nitric acid, it yields mucic and saccharic acids. By 
 reduction with sodium-amalgam, lactose yields mannite, dulcite, iso- 
 propyl alcohol, and secondary hexyl alcohol. In its behaviour with 
 bases milk-sugar resembles cane-sugar. 
 
 Maltose, C 12 H 22 O n + H 2 O, is formed by the action of malt upon starch, 
 and was formerly mistaken for dextrose, but it is less soluble in alcohol, 
 more dextro-rotatory, and does not reduce a weak acetic solution of 
 cupric acetate. To prepare maltose, starch (100 parts) is ground up 
 with water (450 parts) and gelatinised by heating on a water-bath ; after 
 cooling, crushed malt (7 parts) is added, and the mixture kept at about 
 65 C. (149 F.) for an hour. The malt (germinated barley) contains 
 an albuminoid substance termed diastase, which acts like a ferment upon 
 the starch, causing it to undergo hydrolysis into maltose and dextrin 
 
 3 C 6 H 10 5 (starch) + H 2 = C^H^On (mattose) + C 6 H 10 6 (dextrin). 
 
734 STARCH. 
 
 The mixture, which has now become much more liquid, is boiled, filtered, 
 evaporated to a syrup on a water- bath, and boiled with alcohol, which 
 leaves the dextrin undissolved, and, on standing for some days, deposits 
 the maltose in crusts of fine needles, which become anhydrous at 100 C. 
 Maltose is easily fermented by yeast, yielding alcohol and carbon dioxide; 
 C 12 H 22 U + H 2 = 4C 2 H 6 + 4CO 2 . Boiling with dilute acids converts 
 it into glucose; C 12 H 22 U + H 2 O = 20 6 H 12 6 . It reduces the alkaline 
 cupric solution when warmed, but not the acetic solution. 
 
 Trehalose, or my cose, C^H^O-u + 2H 2 0, is found in the trekala manna, or nest- 
 sugar, of Persia, an edible substance produced by an insect from the tree on which 
 it lives. It is also found in the ergot of rye and in certain edible fungi, whence its 
 name of mycose. Alcohol extracts it from the manna. It crystallises in prisms 
 which have a sweet taste, and fuses at 100 C., losing their water at 130 C. It is 
 soluble in water and in hot alcohol, but not in ether. It is more strongly dextro- 
 rotatory than cane-sugar. 
 
 535. The constitution of the disaccharides is not yet known ; all that can be 
 said is that they are probably anhydrides formed from two molecules of glucoses, 
 since they break up into these by absorption of water. The two molecules may be 
 of the same glucose (as in the case of maltose) or of different glucoses (as in the 
 case of cane-sugar). Cane-sugar and milk-sugar yield octacetyl-derivatives when 
 treated with acetic anhydride and sodium acetate, showing that they are octohydric 
 alcohols. It will be noticed that maltose is the only disaccharide which is directly 
 fermentable with yeast and directly reduces Fehling's solution. Maltose and 
 lactose yield osazones, showing that they are aldehydic. 
 
 536. Trisaccharides. These yield three molecules of hexoses when hydrolysed. 
 Rajfinose, or. melitose, C 18 H 32 16 + 5H 2 0, is the chief constituent of Australian 
 manna, an exudation from Eucalyptus mannifera, and occurs in cotton seeds and 
 sugar-beets. It crystallises in fine needles. It is but slightly sweet, and dissolves 
 in water and alcohol. Melitose does not reduce alkaline cupric solution, and is 
 dextro-rotatory. Diluted acids and yeast convert it into ^-fructose and melibiose, 
 C^H^O-u, which subsequently breaks up into dextrose and galactose. 
 
 Melezitose, CjgH^Ojg + 2H 2 0, is extracted by alcohol from the manna exuding 
 from the larch. Its crystals lose H 2 at 100 C. and are sweet enough to be used 
 as a substitute for sugar. It does not easily reduce alkaline cupric solution, and is 
 dextro-rotatory. It is converted, though not easily, into dextrose by boiling with 
 dilute acids. 
 
 THE STABCHES AND CELLULOSES (POLYSACCHARIDES). 
 
 537. Starch, or amylose, (C 6 H 10 O 5 ) K , differs from the sugars in being 
 insoluble in cold water, and therefore tasteless, and in not forming 
 crystals, but having an organised structure visible under the microscope, 
 which is not seen in any artificial product of the laboratory. It is an 
 indispensable constituent of all plants (except fungi), and is stored up 
 in their seeds and tubers, for the nourishment of the young shoots. 
 
 To obtain starch on the small scale, flour (which contains about 60 per 
 cent.) is mixed with cold water to a stiff dough, which is tied up in fine 
 muslin and well kneaded in a basin of distilled water, when the grains 
 of starch pass through, leaving the tenacious gluten in the muslin. The 
 milky fluid is left to settle for a few hours, the bulk of the water 
 poured off, the starch collected on a filter, and dried by exposure to 
 air. 
 
 On the large scale, in England, starch is commonly made from rice, which 
 contains about 80 per cent. The rice is soaked for 24 hours in water containing 
 about 0.3 per cent, of caustic soda ; it is then washed, ground into flour, and again 
 soaked for two or three days in a fresh alkaline solution ; the starch is allowed to 
 settle, and the alkaline liquid, holding the gluten in solution, is drawn off.* The 
 
 * The gluten is sometimes precipitated by sulphuric acid, and used as a feeding-stuff. 
 
KINDS OF STAECH. 
 
 starch is then stirred up with water, the heavier woody fibre allowed to subside 
 and the milky liquid run off into another vessel, where it deposits the starch 
 Ihis is transferred to drainers where it partly dries, and the drying is finished by 
 gradual application of heat ; this splits the starch into roughly prismatic fragments 
 which still retain about 18 per cent, of water. Commercial starch is glneralh' 
 coloured blue by a little ultramarine or smalt, in order to correct the yellow tint of 
 
 Being possessed of an organised structure, starch varies in external 
 aspect, according to the plant from which it is obtained. When 
 powdered starch is examined by the microscope, it appears in grains 
 resembling some of those in Fig. 283 : the largest are those of potato- 
 starch (P), about ^ inch in the longer diameter ; the smallest are 
 those of rice (B), about ^^ inch in diameter: wheat-starch (W) has 
 nearly spherical granules, T ^ w inch in diameter ; (A) is the starch of 
 arrowroot, from Maranta arundinacea, a tropical plant. When 
 
 Fig. 283. 
 
 moistened with water and viewed under a microscope, provided with a 
 polariser and analyser, starch granules behave like doubly refracting 
 crystals, exhibiting a black cross when the planes of polarisation of the 
 polariser and analyser are at right angles, which becomes white when 
 the analyser is turned through an angle of 90 ; this is best seen in the 
 starch of potato, Indian corn, and tons le mois (from Canna coccinea of 
 the Arrowroot order). The starch granules are composed externally of 
 starch cellulose, or farinose, and internally of granulose, and, perhaps, 
 other isomeric bodies. 
 
 Cold water does not attack starch, unless the cell-walls are broken by 
 trituration, when a part of the granulose dissolves, yielding a solution 
 strongly dextro-rotatory and coloured blue by iodine, which gives a 
 violet colour to farinose. When starch is heated with water to about 
 50 0., the granules begin to burst, which is completed at about 
 70 C. ; the granulose then dissolves to a viscous liquid, becoming a 
 jelly on cooling and a gummy mass when dried. The cell-wall may be 
 dissolved in the cold by strong alkalies, acids, and zinc chloride. 
 Heated with glycerine at 190 C., starch is dissolved, and if the solution 
 be mixed with alcohol, soluble starch is precipitated, and, while moist, 
 may be dissolved by water or weak alcohol. Its strong aqueous 
 solution becomes a jelly on standing. 
 
 The conversion of starch into maltose and dextrin by the action of 
 diastase has already been mentioned. Other enzymes, notably the 
 ptyalin of the saliva, effect a similar change. 
 
 The aqueous solution of starch is precipitated by alcohol, by baryta and lime, 
 and by ammoniacal lead acetate, which gives C 6 H 10 5 .PbO. For the behaviour 
 of starch with iodine, see p. 194. When boiled with diluted sulphuric or hydro- 
 chloric acid, starch is converted into d-glucose, maltose and dextrin (p. 726). 
 
 When starch is heated with acetic anhydride, it yields an insoluble compound, 
 
73^ BRITISH GUM. 
 
 which may be represented as C 12 H 14 O 4 (C 2 H 3 02) 6 . This yields starch and potassium 
 acetate when saponified by potash, showing that starch is a hexahydric alcohol,. 
 C 12 Hi 4 4 (OH) 6 . Strong sulphuric acid dissolves starch in the cold, apparently 
 forming a soluble sulpho-acid. When heated, carbonisation occurs. 
 
 Heated at about 205 C. for some hours, starch becomes brownish and soluble in 
 cold water, having been converted into the isomeric compound dextrin. This 
 conversion of starch into a soluble form is important in the preparation of food. 
 In toasting bread a portion of the starch becomes dextrin, which is dissolved in 
 toast and water. Further heated, starch is carbonised and yields products of 
 destructive distillation resembling those from sugar. 
 
 538. Dextrin, or British gum, C 6 H 10 O 5 , is prepared by moistening 
 starch with one-third of its weight of weak nitric acid (0.66 per cent.), 
 drying it in air, and heating to 115 C. There are several varieties, 
 e.g., erythro-dextrin, coloured red by iodine- water : and achro-dextrin,, 
 not coloured by iodine. The erythro-dextrin is formed at first when 
 starch is boiled with diluted sulphuric acid, so that the blue starch- 
 reaction with iodine gives place to a red, and finally ceases. Commercial 
 dextrin gives a violet colour with iodine, because it contains unaltered 
 starch ; and erythro-dextrin ; it is sweet from the presence of glucose. 
 It may be purified by dissolving in water and precipitating by alcohol. 
 
 Dextrin dissolves when soaked in water, and is left on evaporation as 
 a transparent mass. Its solution has twice the dextro-rotatory power of 
 dextrose. Pure dextrin does not reduce Fehling's solution ; commercial 
 dextrin does, though not so quickly as glucose. It shows aldehydic 
 properties, and when boiled with dilute H 2 S0 4 , or HC1, it is converted 
 into dextrose. Nitric acid oxidises it to oxalic acid, while ordinary guin 
 yields mucic acid. Heated with acetic anhydride, it yields an acetyl- 
 compound isomeric with that from starch (see above), which is converted 
 into the dextrin- derivative at 160 C. Dextrin is used by calico- 
 printers for thickening their colours ; it is used for adhesive stamps, for 
 confectionery, and for stiffening surgical bandages. 
 
 Inulin, (C 6 H 10 5 ) 6 'H 2 0, was first obtained from elecampane root (Inula helenium), 
 an aromatic medicinal plant. It is also found in the roots of the dahlia, and in the 
 Jerusalem artichoke, which belong to the same sub-order (Corymbiferce), and in 
 the roots of dandelion and chicory, belonging to the Cichoracetc ; all being plants 
 of the natural order Composites. It may be extracted from dahlia roots, which 
 contain 10 per cent., by boiling with water, which deposits the inulin in minute 
 spheres on cooling. It 'is not coloured blue by iodine, and does not reduce Fehling's 
 solution. It is insoluble in alcohol. Solution of inulin is laevo-rotatory. When 
 boiled with dilute sulphuric acid, it yields laevulose. It also differs from starch in 
 being unchanged by diastase. It melts at 160 C. 
 
 Glycogen, or animal starch, (C 6 H 10 5 ) W , occurs in the liver, blood, flesh, yolk of 
 egg, and oysters, where it is said to amount to 9.5 per cent, of the dried fish. It is 
 most abundant in the liver during active digestion, and disappears quickly after 
 death, being converted into dextrose by fermentation. To prepare glycogen, the 
 minced liver is extracted with water as long as it runs off milky ; the albumin is 
 coagulated by boiling, and the filtrate mixed with alcohol, which precipitates the 
 glycogen ; it is purified by boiling with weak acetic acid to remove albuminoids, 
 again precipitating with alcohol, and washing with ether to remove traces of fat. 
 When dried over CaCl 2 , glycogen has the formula (C 6 H 10 5 ) 2 .H 2 O ; it loses the H 2 
 at 100 C. It is an amorphous powder like starch, swelling in water, and yielding 
 a turbid solution on heating. The solution is strongly dextro-rotatory, and gives 
 a wine-red colour with iodine. Glycogen does not reduce Fehling's solution, and 
 is not fermented by yeast. Diastase converts it into maltose and dextrin, as it does 
 starch (p. 733). It is converted into dextrose when boiled with dilute H 2 S0 4 or 
 HC1, or when placed in contact with saliva or pancreatic juice. 
 
 539. Gums. The carbohydrates of this group resemble dextrin in 
 yielding viscous solutions in water, in being precipitated by alcohol, and 
 
GUMS. 737 
 
 in conversion into sugars by boiling with dilute acids : but the gums 
 have a marked acid tendency, though they do not form well-defined 
 salts. Moreover, the gums yield mucic acid when oxidised by nitric acid 
 
 Arabin, or arabic acid, 2C 6 H 10 5 + H 2 0, occurs in gum arable, an 
 exudation from various tropical acacias. It is extracted by dissolving 
 the gum m water, acidifying with HC1, and adding alcohol, which 
 precipitates it in white flakes ; or the acid solution may be dialysed 
 (p. 278), when the aqueous solution of arabin remains in the dialyser. 
 The pure aqueous solution is not precipitated by alcohol, but the 
 presence of a minute quantity of a base or a salt determines the preci- 
 pitation. The aqueous solution has an acid reaction, and, on evapora- 
 tion, leaves a vitreous mass, which loses water above 120 C., yielding 
 metarabin isomeric with dextrin. This does not dissolve in water, but 
 increases greatly in bulk. Arabic acid decomposes alkali carbonates, 
 and^ the composition of its salts indicates the formula C^H^O^ or 
 -^-2^36^-64^33- ^ appears to occur in gum arabic as arabates of calcium, 
 magnesium, and potassium, since, when incinerated, the gum leaves 
 about 3 per cent, of ash containing those metals. 
 
 Arabin gives a characteristic reaction with CuS0 4 , followed by KOH, which 
 produces a blue precipitate, insoluble in excess, and neither blackened nor reduced 
 
 by boiling, but collecting into a blue mass, leaving the liquid colourless. 
 arabin is boiled with dilute H 2 S0 4 it is converted into arabinose or gum- 
 
 ' 
 
 When 
 
 -sugar^ 
 
 (p. 725) ; substances which yield pentoses on hydrolysis are' known as 
 pentosans. 
 
 Gum Senegal, obtained from similar sources, is used by calico-printers to thicken 
 their colours. It is darker in colour than gum arabic, but also consists essentially 
 of arabin. 
 Metarabin, or cerasin, C^H^Ojo, is found in the gum of the cherry-tree and 
 
 , , ^ 
 
 beech-tree (wood-gum}, probably as calcium metarabate, which remains undissolved 
 after the calcium arabate which accompanies it has been extracted by water ; when 
 heated with lime-water, it is converted into calcium arabate, which dissolves. It 
 is also found in the residue of beet-root from which the juice has been expressed. 
 By hydrolysis it yields xylose (p. 725), and is therefore a pentosan. 
 
 Bassorin, very similar to cerasin, occurs in Bassora gum and in gum tragacanth^ 
 the exudation from Astragalus tragacantha, a Papilionaceous plant. These gums 
 do not dissolve in water like gum arabic, but swell up immensely by absorption 
 of water, and form a mucilage. When boiled with dilute acids it is converted 
 into dextrose. A substance very similar to bassorin is formed in the ropy or 
 viscous fermentation of saccharine liquids. The mucilaginous liquids obtained by 
 boiling linseed (linseed tea), quince-seed, and marshmallow root with water, contain 
 bassorin, or some allied body. 
 
 Gelose, orparabin, C^H^Ojj, forms the greater part of Ceylon moss (Gracilaria 
 lichenoides) and China moss (#. spinosa), sea- weeds which are used for making 
 soups and jellies. Carrots and beet also contain gelose. When dissolved in as 
 much as 500 parts of hot water, it sets to a jelly on cooling. It also differs from 
 the other bodies of this group by dissolving in dilute acids and being precipitated 
 by alkalies. When long heated with alkalies it is converted into arabin. It does 
 not appear to yield a sugar when boiled with dilute acids. 
 
 540. Cellulose, (C 6 H 10 O 5 ) 12 , is the substance which composes the walls 
 of plant-cells, and is left undissolved after the matters contained in 
 and encrusting the cells have been removed by various solvents. 
 Hence, white filter-paper, prepared cotton-wool, and well-washed linen 
 consist of nearly pure cellulose. To purify these they are digested 
 successively with dilute KOH, dilute HC1, water, alcohol, and ether ; 
 the encrusting substances of the cellulose are thus removed. 
 
 When pure, cellulose is white, opaque, exhibits an organised structure, 
 is infusible and insoluble in all ordinary solvents. It may be dissolved 
 
73$ CELLULOSE. 
 
 by Schweitzer's reagent, a solution of cupric hydroxide in ammonia. 
 The cellulose is precipitated in flakes on addition of an acid. When 
 contact with the Schweitzer's reagent is sufficiently brief to attack the 
 superficial fibres only, and the cellulose fabric is then pressed and dried, 
 it becomes impervious to water ; in this way the green waterproof 
 coverings known as Willesden paper are manufactured. Chlorine, in 
 presence of moisture, slowly attacks cellulose, so that paper becomes 
 brittle if the excess of bleach be not killed by an antichlore (p. 221). 
 Iodine does not give a blue colour with pure cellulose, but the cellular 
 tissue of plants is often blued by it, from the presence of a little 
 starch. Ferric oxide slowly oxidises cellulose, and, since the ferrous 
 oxide is repeatedly oxidised again, a continual oxidation and corrosion 
 of the cellulose is kept up, as may be seen from the effect of iron-mould 
 on linen and of rusty nails on wood. 
 
 Strong sulphuric acid converts dry cellulose into a gummy mass 
 which dissolves in the acid with very little colour in the cold. If this 
 solution be immediately poured into water, it yields a gelatinous 
 precipitate, but after digestion for some hours with the acid, a clear 
 solution is formed in water, and if this be largely diluted and boiled, 
 the cellulose is converted, first into dextrin, and then into dextrose, 
 which may be obtained as a syrup by neutralising the acid liquid with 
 chalk, filtering, and evaporating. By fermenting this dextrose, the 
 curious transformation of rags into alcohol may be accomplished. 
 Cotton-wool dissolves in a mixture of sulphuric acid with one-fourth 
 its weight of water, and, on dilution, a precipitate of amyloid is 
 obtained, which is isomeric with cellulose, but is coloured a fugitive 
 blue by iodine. 
 
 By immersing unsized paper in a cold mixture of strong sulphuric 
 acid with half its volume of water, it becomes converted externally 
 into amyloid. This is turned to account for making vegetable parch- 
 ment, which is five times as strong as paper, and is waterproof. 
 After immersion in the acid, the paper is thoroughly washed with 
 water and finally with weak ammonia. A strong solution of zinc 
 chloride affects the paper in the same way. The parchment paper is 
 translucent ; it may be boiled in water without disintegration ; it 
 receives many useful applications, as for luggage labels which are not 
 easily torn or destroyed by rain, as a substitute for bladder in tying 
 over preserves, &c., and for making dialysers. 
 
 "When cellulose is left for twelve hours in H 2 S0 4 of sp. gr. 1.453, or i n HC1 of sp. 
 gr. 1.16, it is converted into a brittle mass of hydro-cellulose, C 12 H 22 11 (?), which is 
 more easily oxidised than cellulose, and dissolves in hot potash. This is applied 
 for dissolving the cotton from old fabrics containing wool, the latter being left as 
 shoddy. Dry rot is ascribed to a similar change in the wood caused by acid 
 substances generated in its fermentation. 
 
 Cellulose swells up and becomes gummy when in contact with strong potash or 
 soda ; on heating to 160 C. with strong potash, it dissolves, and the solution, 
 when acidified, yields a precipitate isomeric with cellulose, but easily soluble in 
 alkalies. If calico be soaked for half an hour in very strong potash or soda, and 
 washed with alcohol, it is converted into C^B^K^O-u, or C^H^N^O^ (inercerisa- 
 tion). Both compounds are decomposed by CO 2 . When treated with CS 2 they 
 form thio-carbonates which are soluble in water ; the solution coagulates spon- 
 taneously, and immediately on the addition of salt solution, the coagulum being 
 regenerated cellulose. Viscose is the viscid solution of these thiocarbonates, and is 
 applied for producing a glaze of cellulose on fabrics. When cellulose is boiled with 
 
PYROXYLIN. 
 
 potash of ep. gr. 1.5 it dissolves to a brown solution which deposits brown flakes 
 (ulmicacid) when acidified ; but on prolonged heating, the colour disappears and 
 carbonate oxalate formate and acetate of potassium* are found in solution By 
 heating cellulose with fused potash, abundance of potassium oxalate is obtained 
 
 (S6G LstEal'lC CtClCLjm 
 
 Cellulose was the name originally given to the constituent of plants which 
 remains after treatment with reagents that may be supposed to remove all other 
 constituents. It is now realised that this residue when obtained from different 
 plants is not necessarily the same substance. Modern workers have distinguished 
 between cotton cellulose, jute cellulose, and straw cellulose. The first of these is 
 characterised by its resistance to chlorine, by the fact that it yields no furfurol 
 when distilled with acid, and by being precipitated unchanged from its solution in 
 a mixture of CS 2 and NaOH solution. Jute cellulose is somewhat attacked by 
 chlorine, yields some 3-5 per cent, of furfurol when distilled with acid, and is 
 decomposed by NaOH and CS 2 . Straw cellulose absorbs a considerable proportion 
 of chlorine, yields some 15 percent, of furfurol, and is coloured red by aniline salts : 
 it also is decomposed by NaOH and CS 2 . 
 
 For the detection of cellulose in the microscopic examination of tissues, advan- 
 tage is taken of its conversion into amyloid by zinc chloride, and of the bluing of 
 this by iodine. The reagent is prepared by dissolving 6 per cent, of KI in solu- 
 tion of ZnCl 2 of sp. gr. 1.8, and adding as much iodine as will dissolve. 
 
 By heating cellulose with 8 parts of acetic anhydride in a sealed tube at 180 C., 
 it may be converted into hexacetyl cellulose, or cellulose hexacetate 
 
 C 12 H 20 10 + 6(CH 3 CO) 2 = C 12 H 10 4 (OCH 3 CO) 6 + 6(CH 3 COOH). 
 
 Cellulosetetr acetate is made by heating cellulose at uoC. with zinc acetate solu- 
 tion and treating the cooled mass with acetyl chloride. It dissolves in chloroform, 
 from which it may be obtained in films by evaporation. 
 
 Oxy cellulose is the name given to the product of aldehydic nature obtained by 
 the action of various oxidising-agents on cellulose. 
 
 541. Action of nitric acid on cellulose. Cold dilute nitric acid (sp.gr. 
 1.2) does not act on cellulose in the form of filter-paper, and scarcely 
 when heated to 100 C. Acid of 1.42 corrodes it, producing amyloid and 
 malic acid, and, on boiling, suberic and oxalic acids. Cotton, linen, or 
 paper, soaked for two or three minutes in the strongest nitric acid and 
 washed, resembles parchment, and is waterproof and very combustible, 
 having become partly converted into cellulose hexanitrate, or pyroxylin 
 (gun-cotton) ; C 12 H 14 4 (OH) 6 + 6(HON0 2 ) = C 12 H 14 4 (ON0 2 ) 6 + 6HOH. 
 This change, which is analogous to the conversion of alcohol into the 
 ethereal salts, is, like that conversion, much facilitated by the presence 
 of strong sulphuric acid, which may either act simply as a dehydrating- 
 agent or may form an intermediate sul phonic acid. 
 
 If pure dry cellulose (prepared cotton- wool) be steeped for some time 
 in a cold mixture of equal molecular weights of the strongest nitric 
 and sulphuric acids, and afterwards thoroughly washed, and dried by 
 exposure to air, it has the composition of cellulose hexanitrate above 
 given, retaining the organised structure of the original cotton, but 
 being somewhat harsher to the touch, and becoming highly electrified 
 when drawn through the dry hand. 
 
 Pyroxylin is insoluble in water, alcohol, and ether, either separately 
 or mixed, but it dissolves in acetic ether and in ethereal solution of 
 ammonia. It is not oxidised by potassium permanganate, as cellulose 
 is, so that it may be used for filtering its solution. When moderately 
 heated, it burns more rapidly than gunpowder, and it is detonated by 
 the blow of a hammer or by the rapid vibration caused by a smart 
 detonation in its vicinity. Pyroxylin dissolves in strong sulphuric acid, 
 and the solution is not blackened by heat. Strong nitric acid also 
 
740 GUN-COTTON. 
 
 dissolves it when heated, but it is reprecipitated by strong sulphuric 
 acid or by water. Strong potash dissolves it with formation of potas- 
 sium nitrate, nitrite, and oxalate, together with glucose and some other 
 organic bodies. The formation of potassium nitrate would be expected 
 if pyroxylin be a nitrate of cellulose. 
 
 Potassium hydrosulphide, in alcoholic solution, reconverts pyroxylin into cellu- 
 lose, potassium nitrite being found in solution 
 
 C 12 H 14 4 (0'N0 2 ) 6 + 6KHS = C 12 H 14 4 (OH) 6 + 6KN0 2 + S 6 . 
 This shows that pyroxylin is not, as was formerly supposed, the trinitro-cellulose 
 C 6 H 7 (N0 2 ) 3 5 , since, in that case, the N0 2 group would be reduced to the NH 2 
 group, and an amido-compound would be formed (p. 659). 
 
 A strong aqueous solution of ferrous chloride containing HC1 also converts 
 pyroxylin into cellulose, with evolution of nitric oxide 
 
 C 12 H 14 4 (0-N0 2 ) 6 + i2FeC! 2 + I2HC1 = C 12 H 14 4 (OH) 6 + 6Fe 2 Cl 6 + 6NO + 6H 2 0. 
 This would be the result expected from cellulose hexanitrate. Iron filings and 
 acetic acid reduce pyroxylin to cellulose, the nascent hydrogen converting the 
 N0 3 group into NH 3 
 
 C 12 H 14 4 (N0 3 ) 6 + H 48 = C 12 H 14 4 (OH) 6 + 6NH 3 + I 2 H 2 0. 
 
 Pyroxylin behaves like a nitrate when shaken with mercury and strong sulphuric 
 acid, evolving the whole of its nitrogen as nitric oxide. 
 
 542. The following proportions may be recommended for preparation of gun- 
 cotton on a small scale : Dry 1000 grains of pure nitre (p. 338) at a very 
 moderate heat, place it in a dry retort (Fig. 73), pour upon it 10 drachms (by 
 measure) of strong sulphuric acid, and distil until 6 drachms of nitric acid have 
 passed over into the receiver. Dry some pure cotton-wool, and weigh out 30 
 grains of it. Mix 2.\ measured drachms of the nitric acid with an equal volume 
 of strong sulphuric acid in a small beaker. Allow the mixture to cool, immerse 
 the cotton-wool in separate tufts, pressing it down with a glass rod, cover the 
 beaker with a glass plate, and set it aside for fifteen minutes. Lift the cotton 
 out with a glass rod, throw it into at least a pint of water, and wash it thoroughly 
 in a stream of water till it no longer tastes acid or reddens blue litmus-paper. 
 Dry the cotton by exposure to air or to a very moderate heat. 
 
 Gun-cotton is manufactured from the waste cuttings from spinning-machines 
 (cotton-waste), which is first thoroughly cleansed. One part of nitric acid (sp. 
 gr. 1.52) and 3 parts by weight (or 2.45 by volume) of sulphuric acid (sp. gr. 1.84) 
 are placed in separate stoneware cisterns with taps, and allowed to run simul- 
 taneously, in slow streams, into another stoneware cistern furnished with a tap 
 and an iron lid, through a second opening in which an iron stirrer is moved 
 to mix the acids thoroughly. The mixture is set aside for several hours to become 
 perfectly cool. 
 
 A quantity of the mixed acids is drawn off into a deep stoneware pan standing 
 in cold water, and provided with a perforated iron shelf, upon which the cotton 
 may be drained. The well-dried cotton is immersed, a little at a time, in the 
 acid, and stirred about in it for two or three minutes with an iron stirrer. It is 
 then placed upon the perforated shelf, and the excess of acid squeezed out with 
 the stirrer. Enough acid is drawn from the cistern to make good that which has 
 been absorbed by the cotton, and more cotton is treated in the same way. Since 
 a considerable rise of temperature is produced by the action of the nitric acid 
 upon the cotton, it is necessary to keep the pan surrounded with cold water. A 
 large proportion of the cotton is doubtless converted into gun-cotton in this 
 preliminary immersion in the mixed acids ; but in order to convert the remainder, 
 it is necessary to allow the cotton to remain in contact with the acid for a much 
 longer period, so as to ensure its penetration into every part of the minute twisted 
 tubes of the fibre. 
 
 The skeins are next transferred to a jar with a well-fitting cover, in which they 
 are pressed down and completely covered with the mixed acids, of which from 
 10 to 15 times the weight of the cotton will be required, according to the close- 
 ness with which the skeins are packed in the jar. The jar is placed in cold water, 
 and the cotton allowed to remain in the acid for about twelve hours. 
 
 The skeins are then removed, with the aid of an iron hook, to a centrifugal 
 extractor, which is a cylinder made of iron gauze, through which the bulk of the 
 
EXPLOSION OF GUN-COTTON. 74! 
 
 acid is whirled out by the rapid rotation of the cylinder upon an axle. In order 
 to wash away the remainder of the acid, the cotton is plunged, suddenly, to avoid 
 rise of temperature, into a cascade of water, and is then drained in the centrifugal 
 extractor, and again rinsed in much water. It is next reduced to pulp in a rag 
 engine such as is employed in paper-mills. The pulp is thoroughly washed by being 
 well stirred by a poaching '-engine for about forty-eight hours in a stream of warm 
 water, so as to remove every trace of acid, which is assisted by rendering the water 
 alkaline with a little lime or carbonate of soda or with ammonia. The pulp is 
 then drained, moulded into discs or any other required form, condensed b v 
 hydraulic pressure until it has at least the same specific gravity as that of water 
 and dried upon heated plates. As it leaves the hydraulic press, the cotton contains 
 about one-fifth of its weight of water, so that it may, if required, be cut up or bored 
 without danger of explosion. 
 
 543. When a mass of the gun-cotton wool is exploded in an unconfined state, the 
 explosion is comparatively slow (though appearing to the eye almost instantaneous), 
 since each particle is fired by the flame of that immediately adjoining it, the heated 
 gas (or flame) escaping outwards, so that some time elapses before the interior of 
 the mass is ignited. But when the gun-cotton is enclosed in a strong case, so that 
 the flame from the portion first ignited is unable to escape outwards, and must 
 spread into the interior of the mass, this is ignited simultaneously at a great number 
 of points, and the decomposition occurs far more rapidly ; a given weight of cotton 
 being thus consumed in a much shorter time, a far higher temperature is produced, 
 and the ultimate results of the explosion are much less complex, as would be ex- 
 pected from the well-known simplifying effect of high temperatures upon chemical 
 compounds. 
 
 If a tuft of gun-cotton wool be placed at the bottom of a tall glass cylinder 
 and inflamed by a heated wire, it will be seen that, immediately after the explosion, 
 the gas within the cylinder is colourless, but soon becomes red, showing that NO 
 was present among the products, and became converted into N0 2 by the oxygen 
 of the air. The water formed by the combustion of the hydrogen converts the N0 2 
 into HJSI0 2 and HN0 3 (p. 101), and hence the acid character of the moisture deposited 
 in the barrel of a fowling-piece in which gun-cotton cartridges are employed. 
 A little HCN can be detected among the products of combustion of loose gun- 
 cotton. 
 
 Berthelot estimates the pressure produced by the detonation of gun-cotton, 
 compressed to a density of i.i, at 24,000 atmospheres, or about 160 tons per 
 square inch, being only half the pressure assigned by him to the detonation of 
 mercuric fulminate. 
 
 If a piece of compressed gun-cotton be kindled with a hot wire, it burns rapidly 
 away, producing a large volume of flame, but without any explosive effect.* In 
 order that gun-cotton fired in this manner might be used for destructive purposes, 
 it was found necessary to confine it in strong cases, so that the flame of the por- 
 tion first ignited should be employed in raising the temperature of the rest to the 
 exploding-point. 
 
 The unconfined gun-cotton, however, can be made to explode or detonate with 
 most destructive violence, by exploding in contact with it a detonating fuze, con- 
 sisting of a little tube of quill or thin metal charged with a few grains of mercuric 
 fulminate. Such detonation can be communicated along a row of pieces of com- 
 pressed cotton placed at short distances from each other. This sympathetic 
 explosion is by no means confined to gun-cotton, but exists in the case of nitro- 
 glycerine, and even gunpowder. The modus operandi of the detonating fuze 
 appears to consist in the influence of vibratory motion, and the nature of the 
 motion necessarily depends upon the nature of the explosive. That it is not a 
 result of the action of heat is proved by the circumstance that wet gun-cotton may 
 be exploded by a detonating fuze, so that torpedoes may be charged with a 
 mixture of gun-cotton pulp and water, containing 15 per cent, of the latter, if a 
 small charge of dry gun-cotton be placed in contact with the fuze. It has been 
 found that the wet gun-cotton is more easily detonated when in a frozen state. 
 
 * Too much stress, however, should not be laid upon this as rendering gun-cotton maga- 
 zines safer in case of fire than gunpowder magazines. The experiment with gunpowder 
 mentioned at p. 342 shows that if all the particles of an explosive be raised at once t< 
 nearly the inflamiug-point, the first particle which inflames will cause the detonation o 
 remainder. Since the inflaming-point of gun-cotton is low, the above conditi 
 easily fulfilled in a conflagration. 
 
742 COLLODION. 
 
 The very destructive effect of the gun-cotton exploded in this way is, of course, 
 due to the sudden manner in which the whole mass is resolved into gaseous pro- 
 ducts. When heat is the cause of the explosion, it must be comparatively slow, 
 for gun-cotton transmits heat slowly, but the vibration caused by detonation is 
 transmitted with the velocity of sound, and the explosion becomes rapid in pro- 
 portion. 
 
 544. Gun-cotton is more easily exploded than gunpowder ; the latter requires a 
 temperature of at least 600 F. (316 C.), whilst gun-cotton may explode at 277 F. 
 (136 C.), and must explode at 400 F. (204 C.). It is very difficult to explode 
 gunpowder by percussion, even between a steel hammer and anvil ; but gun-cotton 
 invariably detonates in this way, though the explosion is confined to the part 
 under the hammer. The explosion of gun-cotton is approximately represented by 
 the equation, C 12 H 14 4 (N0 3 ) 6 = 500 + 7C0 2 + H 8 + 3H 2 + N 6 , and is attended by the 
 evolution of 1071 heat-units per unit weight, but by no smoke, a most important 
 advantage in mines, the atmosphere of which is sometimes rendered almost 
 intolerable by the smoke of gunpowder used in blasting ; but death has been 
 caused by the carbonic oxide generated. The absence of residue from the gun- 
 cotton prevents the fouling of guns, and renders it unnecessary to sponge them 
 after each discharge, for the amount of incombustible mineral matter present in 
 the cotton is very small (from I to 2 per cent.), and is entirely scattered by the 
 explosion. 
 
 Nitrated cellulose is the main constituent of several modern sporting powders 
 such as E. C. sporting powder, E. C. rifle powder , and Schultze's powder. 
 
 545. Soluble pyroxylin, or collodion cotton, is a mixture of cellulose 
 nitrates lower than the hexanitrate e.g., the penta-, tetra-, tri-, and di- 
 nitrates. It is the product of the action upon cellulose of a mixture of 
 HNO 3 (i mol.) and H 2 S0 4 (i mol.) slightly diluted with water 
 (if mols.). It differs from pyroxylin in being soluble in a mixture of 
 ether with one-seventh of alcohol, yielding a viscous solution, which 
 leaves the transparent collodion film when evaporated. It is much less 
 rapidly combustible than pyroxylin. 
 
 In order to prepare the soluble cotton for collodion, 3 measured ounces of 
 ordinary HN0 3 (sp. gr. 1.429) are mixed with 2 ounces of water in a pint beaker. 
 Nine measured ounces of strong H 2 S0 4 (sp. gr. 1.839) are added to this mixture, 
 with continual stirring. A thermometer is placed in the mixture, which is 
 allowed to cool to 140 F. ; 100 grains of dry cotton-wool, in ten separate tufts, are 
 immersed in the mixture for five minutes, the beaker being covered with a glass 
 plate. The acid is then poured into another beaker, the cotton squeezed with a 
 glass rod, and thrown into a large volume of water ; it is finally washed in a stream 
 of water till it is no longer acid, and dried by exposure to air. 
 
 Collodion balloons. These balloons may be made in the following manner : ' 
 Six grains of collodion-cotton, prepared according to the above directions, are 
 dissolved in a mixture of i drachm of alcohol (sp. gr. 0.835) an d 2 drachms of 
 ether (sp. gr. 0.725) in a corked test-tube. The solution is poured into a dry 
 Florence flask, which is then turned about slowly, so that every part of its 
 surface may be covered with the collodion, the excess of which is then allowed to* 
 drain back into the tube. Air is then blown into the flask through a long glass 
 tube attached to the bellows as long as any smell of ether is perceptible. A pen- 
 knife blade is carefully inserted between the flask and the neck of the balloon, 
 which is thus detached from the glass all round ; a small piece of glass tubing is 
 introduced for an inch or two into the neck of the balloon, so that the latter may 
 cling round it. Through this tube air is drawn out by the mouth, until one-half 
 of the balloon has left the side of the flask and collapsed upon the other half ; by 
 carefully twisting the tube, the whole of the balloon may be detached and drawn 
 out through the neck of the flask, when it must be quickly untwisted, distended by 
 blowing through the tube, tied with a piece of silk, and suspended in the air to dry. 
 The average weight of such balloons is 2 grains. 
 
 Celluloid, or artificial ivory, or xylonite, used for combs, billiard-balls, &c., is 
 essentially compressed collodion-cotton mixed with camphor and zinc oxide. 
 
 When collodion-cotton is kept for some time, especially if at all damp, it 
 
SALICIN. 
 
 undergoes decomposition, filling the bottle with H f,, 
 verted into a gummy mass, whA contains oSte ac?d ' * 
 
 546. Tunicin, C^0 5 , or animal cellulose, is prepared from the outer covering or 
 ,nantle of the mollusks belonging to the class Tuntata. The manUe is LnTbofled 
 with hydrochloric acid and potash, in succession, and the residue wSdwHh 
 water, alcohol and ether. Tunicin is left as a translucent mas^s so^ 
 Ambling cellulose in properties that it is believed by some cheS to 
 
 XIV. GLUCOSIDES. 
 
 547- The compounds belonging to this class arecapable of conversion 
 into a sugar and some other compound by the action of acids, alkalies 
 and certain ferments, the change being generally the result of hydrolysis' 
 (p. 265). They are chiefly found in plants, and generally yield products 
 of decomposition belonging to the aromatic group. Some of them have 
 been already noticed.* 
 
 Salicin, C 6 H 11 5 ;0-C 6 H 4 CH 2 OH, is extracted from willow-bark 
 (&ahx) by boiling it in water, removing the colouring-matter and tannin 
 from the solution by boiling with lead hydroxide, precipitating the 
 excess of lead by H 2 S, and evaporating the filtered liquid, when the 
 salicin crystallises in needles which may be recrystallised from alcohol 
 It forms bitter colourless prisms (m.-p. 188 C.) soluble in about 30 parts 
 of cold water, in less alcohol, but not in ether. It is readily distin- 
 guished by the bright red colour which it gives with strong sulphuric 
 acid, which detects it when applied to the inner bark of the willow. 
 With emulsin (p. 566) or saliva, its aqueous solution yields glucose and 
 salicyl-alcohol or saligenin : 
 
 C 13 H 18 7 + H 2 = C 6 H 12 6 + C 6 H 4 (OH)-CH 2 -OH. 
 The saligenin gives a blue colour with ferric chloride. 
 
 Salicin is occasionally administered as a febrifuge, and is a common 
 adulteration of quinine. 
 
 When solution of salicin is boiled for some time with dilute sulphuric or hydro- 
 chloric acid, it yields an amorphous precipitate of saliretln, a product of the 
 decomposition of saligenin 
 
 2C 7 H 8 2 (saligenin) = H 2 + C 14 H 14 3 (saliretiri). 
 
 Sulphuric acid and potassium dichromate convert salicin into oil of spiraea 
 (p. 586). Fused with potash, it yields potassium salicylate. Dilute nitric acid 
 converts salicin into helicln: C 13 H 18 7 + = C 13 H 16 7 + H 2 0. This is also a gluco- 
 side, yielding glucose and oil of spiraea when hydrolysed by ferments or acids ; 
 C 13 H 16 7 + H 2 = C 6 H 12 6 + C 7 H 6 2 . Strong nitric acid converts salicin into nltro- 
 salicyUc acid, C 6 H 3 (OH)(N0 2 )C0 2 H. When acted on by chlorine, salicin yields 
 substitution-products containing one, two, and three atoms of chlorine, and these, 
 when boiled with dilute acids, yield the corresponding chlorosaligenins. 
 
 Populin, or benzoyl-salicin, C 13 H 17 (C 7 H 5 0)0 7 + 2H 2 0, is a sweet crystalline body 
 existing, together with salicin, in the bark and leaves of the aspen (Populus tremula), 
 a tree of the Willow order, and may be extracted in the same way as salicin. 
 When boiled with Ba(OH) 2 , it yields salicin and benzoic acid (which becomes 
 barium benzoate) ; C 13 H 17 (C 7 H50)0 7 + H 2 = C 13 H 18 7 + C 7 H 6 0'OH. Boiled with 
 dilute acids, it is converted into benzoic acid, saliretin, and glucose. It is 
 obtained artificially by fusing salicin with benzoic anhydride 
 
 C 13 H 18 7 + (C 7 H 5 0) 2 = C 13 H 17 (C 7 H 6 0)0 7 + C 7 H 6 OOH. 
 
 * They will probably be shown to be ethereal alcohol derivatives, for several compound*, 
 closely resembling glucosides in behaviour, have been synthesised by dissolving sugars in 
 alcohols and saturating with hydrogen chloride. In this way, methyl alcohol and glucose 
 have yielded methylglucoside, C 6 H n (OCH 3 )O 5 . 
 
744 AMYGDALIN. 
 
 Arbutin, C 12 H 16 7 , is found in the leaves of the bear-berry (Arbutus uva ursi), 
 an astringent plant of the Heath order, sometimes used medicinally, and in Pyrola 
 umbellata, also a medicinal plant of the closely allied Winter-green order. It may 
 be prepared like salicin, and crystallises in bitter needles from its aqueous solution. 
 Emulsin or dilute acids decompose it into glucose and hydroquinone 
 C 12 H 16 7 + H 2 = C 6 H 12 6 + C 6 H 4 (OH) 2 . 
 
 Phlorizin, C 21 H240 10 (<Xoi6y, bark, and pifa, roof), is extracted by hot alcohol 
 from the root-bark of the apple, pear, plum, and cherry tree. It crystallises from 
 hot water in bitter needles with 2Aq. When boiled with dilute acids, it yields 
 glucose and phloretin ; C Z1 H 24 W + H 2 = C 6 H 12 6 + C 15 H 14 5 . When exposed to air 
 in the presence of ammonia, it is converted into a fine purple colouring-matter, 
 phlorizein, 21 H 30 N 2 13 = ( CaH^O^ + 2NH 3 + 8 ) . It melts at 1 08 C . 
 
 Qlycyphyilin, C 21 IT 24 9 , is a crystalline substance allied to phlorizin, extracted 
 from the leaves of Sniilax glycyphylla, an Australian plant of the Sarsaparilla order. 
 It is sparingly soluble in cold water, but dissolves in hot water and in alcohol. 
 Its solution tastes like liquorice. It does not reduce alkaline copper solutions, 
 and is not precipitated by normal lead acetate, though it is by the basic acetate. 
 When boiled with dilute sulphuric acid, it yields phloretin and rhamnose (p. 725) 
 CjaHjaO. + H 2 = C 15 H 14 5 + C 5 H 9 (CH 3 )0 5 . 
 
 Hesperidin, C^H^O^, is contained in the fruit, leaves, and stalks of the orange- 
 tree and other members of the same family ; it is resolved by acids into glucose 
 and hesperitin, C 16 H 14 6 . 
 
 JBCUlin, C 15 H 16 9 , is extracted by boiling water from the bark of the horse- 
 chestnut (&sculus hippocastanum), sometimes used as a febrifuge. The infusion 
 of the bark is mixed with lead acetate, to precipitate the tannin and colouring- 
 matter, filtered, the excess of lead precipitated by H 2 S, and the filtered solution 
 evaporated, when aesculin crystallises in colourless needles containing ^Aq, 
 sparingly soluble in cold water, but readily in hot water and in alcohol. The 
 aqueous solution is slightly bitter, and has a strong blue fluorescence, destroyed 
 by acids and restored by alkalies. Emulsin and boiling dilute acids convert 
 assculin into glucose and cssculetin, a dihydroxycoumarin (p. 611) 
 
 Ci 5 Hi 6 9 + H 2 = C 6 H 12 6 + C 9 H 6 4 . 
 
 jEsculetin exists, in small quantity, in horse-chestnut bark. Paviin or fraxin, 
 C 16 H 18 10 , accompanies assculin in horse-chestnut bark. It is more soluble in ether 
 than is aesculin, and has a green fluorescence. Fraxin is obtained in larger quantity 
 from the bark of the ash (JFraxinus excelsior), which is also febrifugal. Trees of 
 the genus Pavia, belonging to the same order as horse-chestnut (soap-worts), yield 
 more paviin than aesculin. 
 
 548. Amygdalin, C 20 H 27 NO n , is extracted from bitter almonds, the 
 kernels of the fruit of Amygdalus communis, of which one variety 
 yields the sweeet almond, containing no amygdalin. The almonds are 
 pressed to extract the fixed oil (not the essential oil, but a glyceride), 
 and the bitter-almond cake is boiled with alcohol, from which the amyg- 
 dalin crystallises in pearly scales which dissolve in water, and crystallise 
 from it in prisms with 3Aq. Amygdalin may also be extracted from 
 the kernels of peaches and nectarines, both fruits of varieties of ainyg- 
 dalus. It is also present in the leaves and kernels of several species of 
 cherry, and the bitter-almond oil formed from it confers the flavour 
 upon cherry- brandy, noyau, ratafia, and maraschino. The production 
 of glucose, hydrocyanic acid, and benzoic aldehyde, by the action of 
 emulsin on solution of amygdalin, has been already noticed (p. 584). 
 When long boiled with baryta, it yields ammonia and the barium salt of 
 amygdalic acid, C 20 H 28 0, 3 . This acid is a glucoside, for when boiled 
 with dilute acids it is converted into glucose and mandelic acid (p. 609) 
 C 20 H 28 13 + 2 H 2 = 2C 6 H 12 6 + C 8 H 8 3 . 
 
 Daphnin, C 15 H 16 9 , isomeric with aesculin, is obtained from the bark of Daphne 
 mezereitm, used as a remedy for toothache. Dilute acids convert it into glucose 
 and daphnetin, a dihydroxy-coumarin (p. 591) ; C ig H 16 9 + H 2 = C 6 H 12 O 6 + C 9 H 6 4 . 
 
BITTER PRINCIPLES. 
 
 ,SftJ^^ 
 
 amorphous bodies, which yield glucose, and, respectively, convolrulinol C H O 
 Ktdjalapinol, C 16 H 30 O 3 , when hydrolysed by acids or emulsin. Turpethin Somerir 
 with jalapin, is extracted from the roots of Convolvulus turpethum also used as 
 purgative. 
 
 Helleborein C X H^O WJ is the narcotic poison from the root of black Mlebore a 
 plant of the Buttercup order. It crystallises in needles, which dissolve easily in 
 water, but sparingly m alcohol. 
 
 Digitalin is the poisonous glucoside extracted from the seeds of the foxelove 
 (Digitalis purpurea) It is crystalline, sparingly soluble in water and ether, but 
 dissolves in alcohol and chloroform. Strong sulphuric and hydrochloric acids 
 dissolve it with a green colour. Its formula is not known. 
 
 Saponin, C 32 H 54 18 , is found in the soap-wort, in the root of the clove-pink which 
 belongs to the same natural order (Ca,ryophyllacea\ in the pimpernel, and 'in the 
 fruit of the horse-chestnut. It may be extracted by boiling alcohol, which 
 deposits it as an amorphous powder on cooling. It is soluble in water, and its 
 solution lathers like soap. This leads to the use of decoctions containing it, such 
 as that of the soap-nut of India, for cleansing delicate fabrics. The dry powder 
 of saponin causes sneezing. 
 
 Coniferin, C l6 K^0 8 .2Aq, crystallises from the gummy liquid found, in the spring, 
 between the inner and outer barks of coniferous trees. In contact with water and 
 emulsin, it yields glucose and coniferyl alcohol 
 
 CieHsA + H 2 = C 6 H 12 6 + C 10 H 12 3 . 
 
 The latter is a crystalline body, soluble in ether, and smelling of vanilla. When 
 distilled with potassium dichromate and sulphuric acid, it yields acetic aldehyde 
 and vanillin ; C 10 H 12 3 + = C 2 H 4 + C 8 H 8 3 (p. 586). 
 
 Quercitrin, C^H.^O^, is the colouring-matter of quercitron bark, and is also found 
 in horse-chestnut flowers, and in grape-vine, sumach and catechu. It may be 
 extracted from quercitron bark by alcohol, the tannin precipitated by solution of 
 gelatine, and the filtrate evaporated. Quercitrin forms yellow crystals, sparingly 
 soluble in water. Dilute sulphuric acid converts it into rhamnose and quercetin; 
 CggHgaOao + H 2 = 2C S H 9 (CH 3 )0 5 + C 24 H 16 O n . This last, also called flavin, is found in 
 heather, in tea, and in the root bark of apple and other trees. It is a yellow 
 crystalline body, which is sparingly soluble in water and more soluble in alcohol. 
 It may be sublimed in yellow needles. Rutin, which occurs in rue and in capers, 
 much resembles quercitrin. 
 
 Antiarin, C^H^Og.aAq, is the principle of the Javanese arrow-poison, upas- 
 antiar, the juice of Antiaris toxicaria, a large tree of the Bread-fruit tribe. It may 
 be crystallised from the alcoholic extract of upas, and is soluble in water and 
 ether. With acids, it behaves like a glucoside. 
 
 549. Bitter Principles. Picrotoxin, C^H^O^, is a narcotic poison contained in 
 Cocculus indicus, the fruit of Anamirta paniculata, a tropical trailing shrub of the 
 order Menispermacece. The fruit has been sometimes used as a hop-substitute by 
 brewers. Picrotoxin may be extracted from the seeds by boiling with alcohol, 
 from which it crystallises in needles ; it is sparingly soluble in water, and soluble 
 in ether ; it is a mixture of picrotoxinin, C 15 H 16 6 + H 2 0, and picrotin, C 15 H 8 7 . 
 Quassiin, C^H^Ojo, is another crystalline bitter principle, extracted by alcohol from 
 quassia chips, the wood of Picrasma excelsa (bitterwood). This is also said to be 
 used as a hop-substitute, and is not poisonous, except to flies. It is administered 
 as a tonic. Water dissolves it sparingly, but acquires a bitter taste. Calumbin, 
 CaHaaO?, is a substance of the same kind, extracted from calumba root (Cocculux 
 palmatus). 
 
 Santonin, C 15 H 18 3 , is the bitter principle of the seeds of Artemisia santonica 
 (worm-seed) and of Artemisia absinthium (wormwood) ; it may be extracted from 
 absinthium by mixing it with lime and boiling with weak alcohol ; the solution is 
 evaporated and the residue boiled with acetic acid, which deposits colourless 
 prisms of santonin, which become yellow when exposed to light. It is insoluble 
 in water, but dissolves in alcohol and ether ; it is dissolved by alkalies, yielding 
 santonates, e.g., sodium santonate, NaC 15 H 19 4 , from which santonic acid, HC 15 H 19 4 , 
 may be obtained by shaking with HC1 and ether ; thus it appears to be a lactone. 
 It contains a ketonic group. Santonin is moderately poisonous, and affects the 
 perception of colours, rendering violet invisible ; it is contained in the liqueur 
 known as creme d 'absinthe, or Wermuth. Gentianin, C 14 H ]0 5 , is extracted by ether 
 
746 CHLOEOPHYLL. 
 
 from the roots of the yellow gentian, used as a bitter and tonic. It forms yellow 
 needles, sparingly soluble in water, but freely in alcohol and ether : also soluble 
 in alkalies, with a strong yellow colour. 
 
 Elaterin (efXarTj/nos, driving away, in allusion to its drastic quality), G^H^O^ is 
 the active principle of the drug elaterium, obtained from the juice of the squirting 
 cucumber (Momordica elateriurri). It is crystalline, insoluble in water, but soluble 
 in alcohol and ether. It admits of sublimation. Kosine, C^H^O^, is the active 
 principle of Kousso, an Abyssinian plant used as a vermifuge ; it crystallises in 
 yellow needles, which are insoluble in water, but soluble in ether and alcohol. 
 Aloin, C 17 H 18 7 , is a crystalline bitter-sweet substance extracted from aloes, the 
 dried juice of various species of aloe. 
 
 Glycyrrhizic acid (formerly called glycyrrhizin), C^H^NO^, is extracted from 
 dried liquorice root ( Glycyrrhiza glabra) by dilute acetic acid ; alcohol is added 
 and the nitrate evaporated to a syrup. It is amorphous and has a sweet taste. 
 
 Cantharidin, C 10 H 12 4 , is extracted from the Spanish fly and other insects. It 
 is a bitter substance, melting at 218 C. and subliming. It blisters the skin. 
 
 550. Vegetable Colouring-Matters. Notwithstanding the great 
 variety and beauty of the tints exhibited by plants, comparatively 
 few yield colouring-matters which are sufficiently permanent to be 
 employed in the arts, the greater number of them fading rapidly as 
 soon as the plant dies, since they are unable to resist the decomposing 
 action of light, oxygen, and moisture, unless supported by the vital 
 influence in the plant ; some of them even fade during the life of the 
 plant, as may be seen in some roses which are only fully coloured in 
 those parts which have been screened from the light. Diligent re- 
 search has disclosed the constitution of many of the vegetable colouring- 
 matters, such as those of the madder and indigo plants ; these are 
 considered under the classes of compounds to which they belong. 
 Those which are described here are still under investigation, and 
 little is yet known of their chemistry save that many are glucosides. 
 
 Chlorophyll (from ^Xwpdc, green; ^vXXoi/, a leaf), the abundant green 
 colour of plants, has not been obtained in a pure state, because it 
 neither crystallises nor volatilises. The want of exact knowledge of 
 the chemistry of this body is especially felt, because its physiological 
 importance to plants is of the highest order. It is evidently active 
 in constructing the tissues of the plant from carbonic acid, water, 
 ammonia, &c., derived from the air and soil. It may be extracted from 
 the leaves of plants by boiling with alcohol, ether, or benzene. 
 
 The alcoholic extract of the leaves is allowed to stand for some time, then 
 filtered and shaken with one volume of ether and two volumes of water. The 
 ethereal layer, which contains all the chlorophyll, is shaken with water as long 
 as the latter reduces Fehling's solution ; it is then allowed to evaporate, the 
 chlorophyll remaining as a bright green residue. When this is dissolved in alcohol, 
 and boiled with dilute H 2 S0 4 or HC1, the solution gives the glucose reaction with 
 Fehling's solution, rendering it probable that chlorophyll is a glucoside. Chloro- 
 phyll dissolves, in cold strong sulphuric acid, to a green solution which gives a 
 dark green precipitate on dilution, and the nitrate gives the glucose reaction. 
 
 An alcoholic solution of chlorophyll is very unstable in air, especially 
 when exposed to light, but gives rise to two stable colouring-matters, 
 phylloxanthin and phyllocyanin when treated with acids ; the precipitate 
 obtained is dissolved in ether and the solution is shaken with strong 
 HC1, which dissolves the phyllocyanin and settles as a bright blue layer 
 below the ethereal solution of the phylloxanthin, which is yellowish- 
 green. The phyllocyanin yields a remarkably stable bright green 
 colouring-matter with copper, the production of which is probably the 
 
VEGETABLE COLOURING-MATTERS. 747 
 
 cause of the improved colour of preserved vegetables which have been 
 treated with a small dose of a copper salt. 
 
 When distilled with zinc-dust chlorophyll yields pyrrol, and the same result has 
 been obtained with the colouring-matter of the blood ; thus these two substances 
 so mysteriously essential to life, appear to be offspring of the same chemical 
 parent, 
 
 Iron is said to be an essential constituent of chlorophyll ; if iron be 
 absent from the plant's food, chlorophyll is not developed. 
 
 The blue colouring-matter contained in many flowers, such as the violet, has 
 been named cyanin. Acids redden it, and hence only those flowers which have a 
 neutral juice are blue ; red flowers yielding an acid juice. The colouring-matter 
 of grapes and of red wine appears to be cyanin. 
 
 551. Saffron is a yellow colouring-matter, obtained from the flowers of Crocus 
 sativus, which are purple, with yellow anthers. When these are dried and pressed 
 into cakes they form the saffron of commerce, which has an agreeable odour. It 
 is chiefly imported from Spain, and is often adulterated. It gives up to water and 
 alcohol a yellow amorphous glucoside, termed polychroite. Annatto, or arnotto, 
 is another yellow colouring-matter, which forms the pulp round the seeds of 
 Biaca orellana, a West Indian shrub. It is used for colouring butter and cheese. 
 The colouring principle has been called Usein ; it is sparingly soluble in water, but 
 dissolves in alcohol and in alkalies ; acids reprecipitate it without much change 
 of colour. 
 
 Turmeric is the root of an East Indian plant, the Curcuma longa, and is used in 
 curry. It contains a crystalline yellow body, curcumin, C 21 H.^O & which may be 
 extracted by boiling benzene. It is insoluble in water, but dissolves in alcohol 
 with a green fluorescence. Alkalies dissolve it, forming red salts, from which acids 
 precipitate it of a yellow colour. Paper dyed with turmeric is used as a delicate 
 test for alkalies, which turn it brown. When acted on by boric acid and strong 
 sulphuric acid, it is converted into rosocyanin, which crystallises in green needles 
 dissolved by alcohol, with a red colour, which is changed to deep blue by alkalies. 
 Turmeric-paper is used in testing for boric acid (p. 274). 
 
 Weld is the Reseda luteola, a plant of the Mignonette order, the leaves of which 
 give a yellow solution when boiled with water. The hot decoction, mixed with 
 alum and chalk, gives a yellow precipitate, which is used in paper-staining. It 
 contains a crystalline yellow body, luteolin, C 15 H 10 6 , sparingly soluble in water, 
 but dissolved by alcohol and by alkalies. It sublimes in yellow needles. 
 
 Fustic is a yellow dyestuff, of which there are two kinds. Old fustic is the 
 wood of a tree of the Mulberry order (Mvru*, or Madura tinctorla), grown in the 
 West Indies. Young fustic is the wood of Rhus cotinus, or Venice sumach, from 
 Italy and the South of France. When old fustic is boiled with water, the solution 
 deposits yellow needles of morin, C 13 H 8 6 , soluble in alcohol. The mother-liquor 
 of morin, when evaporated, yields maclurin or moritannic acid (p. 61 1). 
 
 Gamboge is a yellow gum-resin, originally obtained from Camboja in Asia, and 
 is exuded by certain species of Guttiferge. It contains about 30 per cent, of a 
 yellow gum, soluble in water, and 70 per cent, of resin soluble in alcohol and 
 alkalies, called gambodic acid. 
 
 Purree (pwri), or Indian yellow, imported from India and China, and said to be 
 the dried excrement of buffaloes fed on mango leaves, is a compound of magnesia 
 with euxanthin (or euxanthic acid), C 19 H 16 10 . By extracting it with hydrochloric 
 acid and alcohol, the euxanthin is obtained in yellow prisms, sparingly solub e in 
 water, soluble in alcohol, ether, and alkalies. When heated, it yields a yellow 
 crystalline sublimate of euxanthone, C 13 H 8 4 . On fusion with potash, euxanthone 
 yields hydroquinone, and nitric acid converts it into trinitroresorcm, wni< 
 oppose the idea that purree is of animal origin. 
 
 552. Safflower, which yields rouge, consists of the dried flowers vttarthamus 
 tinctorius, cultivated in Egypt. It contains a yellow substance, which may De 
 extracted by water, and a red colour, carthamin, C 14 H 16 07, which may be dissolved 
 out by sodium carbonate, and precipitated by acetic acid. Alcohol dissolves i 
 
 a red solution. It is used in dyeing, but soon fades when exposed to light. 
 Carotin, C^O, is a red substance, found in small crystals m the cell 
 carrot. It crystallises from alcohol in cubes of agreeable odour. 
 
748 SHELLAC. 
 
 Santalin, C 15 H 4 5 , is the colouring-matter of red sanders wood (Pterocarpus santa- 
 linus), from which it may be extracted by alcohol, which deposits it in red crystals 
 insoluble in water, but giving violet solutions with alkalies. 
 
 Haematoxylin. C 16 H 14 6 .3H 2 0, is extracted from logivood (Hcematoxylon campe.chi- 
 anum), which grows at Cam peachy in the Bay of Honduras, by boiling the chips 
 with water. It is deposited from the solution in yellow needles, which are soluble 
 in water, alcohol and ether. It resembles the phenols by dissolving in alkalies to 
 a purple solution, which absorbs oxygen and forms a red colouring-matter, hcema- 
 tein, C 16 H 12 6 , sparingly soluble in cold water, which may also be obtained by 
 oxidising hasmatoxylin, in ethereal solution, with nitric acid. Reducing-agents, 
 such as sulphurous acid, convert it into haematoxylin. When fused with potash, 
 haematoxylin yields pyrogallol. It contains five OH groups. 
 
 Potassium chromate gives an intense black colour with infusion of logwood, 
 which has been used as an ink, but is fugitive. Logwood boiled with distilled 
 water gives a yellow solution, but with common water it gives a fine purple-red, 
 from the production of hasmatein by the oxidation of the htematoxylin in presence 
 of the calcium carbonate in the water. The solution of logwood is sometimes 
 used as an indicator in alkalimetry. 
 
 Brazilin, C 16 H 14 5 , is contained in Brazil wood ( Ccesalpiniea brasiliensis) ; peach- 
 wood (C. echinata), and Sappan wood (O. sappan) all dyewoods from the same 
 botanical sub-order as logwood. Brazilin, when quite pure, forms colourless 
 crystals, and yields colourless solutions in air-free water and alcohol ; but it soon 
 becomes yellow by oxidation, and dissolves in alkalies with a fine red colour, 
 which is bleached by reducing-agents. It contains four OH groups. 
 
 553. Lac is a red dye extracted from the resinous exudation of certain tropical 
 trees of the Fig tribe, punctured by an insect (Coccus). In its crude, natural 
 state, encrusting the small branches, it is known as stick-lac, and has a deep red 
 colour ; when broken oft' the branches and boiled with water containing sodium 
 carbonate, it gives a red solution, from which the colouring-matter is precipitated 
 as a lake by adding alum, and made into cubical cakes for the market. The 
 resinous matter (about 68 per cent.) left undissolved by sodium carbonate, is 
 termed seed-lac ; this is melted, strained through a cloth, and allowed to solidify 
 in thin layers, when it forms shell-lac, which is much used in the manufacture of 
 sealing-wax and varnishes. The lacquer applied to brass is named after this resin, 
 being an alcoholic solution of shell-lac, sandarach, and Venice turpentine. Indian 
 ink is made by mixing lamp-black with a solution of 100 grains of lac in 20 grains 
 of borax and 4 ounces of water. 
 
 Carmine owes its colour to carminic acid, C^H.^O^, a glucoside extracted by 
 boiling water from the cochineal insect, which is found upon a species of cactus in 
 Mexico and Peru. Carmine-lake is precipitated by alum and potassium carbonate 
 from the aqueous extract of the cochineal insect. The acid itself is an amorphous 
 purple solid, easily soluble in water and alcohol, and sparingly in ether. It dis- 
 solves unchanged in strong sulphuric acid. 
 
 XV. ALBUMINOID COMPOUNDS. 
 
 554. Under this head are classed several nitrogenous products of 
 animal and vegetable life, which are not crystalline or volatile. They 
 resemble each other very closely in composition, containing from 50 to 
 55 per cent, carbon, 21 to 25.5 oxygen, 15 to 18 nitrogen, 6.7 to 7.3 
 hydrogen, and 0.4 to i .7 sulphur. If the sulphur be regarded as essential 
 to the formula, the mean of these numbers would give, approximately, 
 the formula C, 3] H 210 N 35 44 S. Concerning the constitution of these com- 
 pounds very little is known. They are generally Isevo-rotatory. 
 
 It has become customary among physiologists to distinguish between proteids* 
 and albuminoids. The former term is applied to such compounds as resemble 
 albumin, or white of egg, in properties, whilst the albuminoids are typified by 
 gelatine. The two classes of compounds dift'er mainly in the fact that the 
 
 * A name originally given to compounds supposed to be derived from a primary source, 
 protein (Trpumiov, pre-eminence). 
 
ALBUMIN. 
 
 majority of the proteids are coagulated by heat. In what follows, only a few 
 of the more important proteids and albuminoids will be described, since it is i 
 possible in a general text-book to enter into details of the modern classification o 
 these compounds. 
 
 Albumin, or white of egg, C 72 H 1]3 N 18 22 S,* may be extracted from its 
 aqueous solution contained in the egg, by stirring it briskly to break up 
 the membrane, adding a little acetic acid to neutralise the soda present 
 in the white, filtering, placing for twelve hours on a dialyser (p. 278) to 
 separate the sodium chloride and acetate, evaporating the contents of 
 the dialyser below 50 0., powdering the residue, and treating with 
 ether to extract fatty matters. The albumin so prepared is an amorphous 
 solid, of sp. gr. i.3i.t When heated, it swells up, carbonises, and 
 evolves offensive alkaline vapours, usually leaving a slight alkaline ash, 
 containing a trace of calcium phosphate, which is very difficult to 
 separate completely from the albuminoids. 
 
 In cold water, albumin slowly softens and dissolves, like gum ; if this 
 solution be heated to about 70 0., the albumin is converted into an 
 insoluble form, becoming a white, soft solid, as in boiled eggs, if the 
 albumin amounts to 12 per cent., and a nocculent precipitate if the 
 solution be diluted. The coagulated albumin is not easily dissolved by 
 acids or alkalies, and is believed to be the anhydride of soluble albumin, 
 for if it be heated in water in a sealed tube to above 150 C., it is dis- 
 solved to a reddish liquid, which behaves like a solution of ordinary 
 albumin, but is not coagulated by heat. Raw white of egg is inodorous, 
 and does not blacken silver; but after boiling it smells of H 3 S, and 
 blackens silver, showing that it suffers some decomposition during 
 coagulation. When dried, coagulated albumin forms a translucent 
 brittle mass, which becomes white and opaque in water. Soluble 
 albumin, completely dried below 50 C., may afterwards be heated to- 
 100 C., without becoming insoluble. 
 
 Alcohol precipitates albumin from its solution, and the soluble is 
 converted into the insoluble form by digestion with strong alcohol. It 
 is also precipitated by shaking with ether or turpentine. 
 
 In many reactions albumin resembles the amido-compounds, as in playing the 
 part of a weak acid and a weak base. Strong potash added to a solution of albumin 
 precipitates a gelatinous compound of potash and albumin, which is soluble in 
 boiling water, and gives, with metallic salts, precipitates containing albumin and 
 metallic oxides. Acids coagulate the solution of potash-albumin. 
 
 The mineral acids, except ortho- and pyro-phosphoric acids, precipitate a solution 
 of albumin, the precipitate being a compound of the acid with albumin, but the 
 organic acids, except picric, do not. as a rule, precipitate it. Many of the compounds 
 of albumin and acid have been proved to have a definite composition. Nitric acid 
 has long been employed as a test for albumin (in urine, for example), since it forms 
 a precipitate even in a very weak solution, but if the liquid be mixed with a very 
 minute quantity of the acid, the flocculent precipitate formed at first disappears on 
 shaking, and the clear acid liquid is not precipitated by boiling. The same thing 
 is observed with sulphuric and hydrochloric acids. 
 
 To obtain definite compounds of albumin with the acids, beaten white of egg 
 is placed in a dialyser suspended upon the surface of the very diluted acid for 
 about 24 hours, when the acid passes through the dialyser and combines with the 
 albumin. The products are nearly colourless jellies soluble in hot water. 
 
 The reagents commonly employed for precipitating albumin are nitric 3id, 
 
 * The simplest formula for crystallised albumin is said to be C 720 H 11 34N 218 S B O 3 4 8 . 
 f It is stated that by adding a saturated solution of ammonium sulphate to egg albumin v 
 filtering and evaporating the filtrate, crystals of albumin may be obtained. 
 
750 SERUM ALBUMIN. 
 
 mercuric chloride, potassium ferrocyanide, and picric acid. Of these, nitric and 
 picric acids precipitate all the above compounds of albumin with the acids ; 
 potassium ferrocyanide precipitates all except the metaphosphate, citrate, and 
 oxalate ; mercuric chloride only precipitates the hydrochloride and the meta- 
 phosphate. 
 
 Strong hydrochloric acid gives with albumin a precipitate which dissolves in 
 excess, and gives a purplish solution when boiled in contact with air. Strong 
 nitric acid colours coagulated albumin yellow ; alkalies dissolve the yellow mass to 
 an orange liquid, from which acids precipitate yellow flakes (xantho-proteic acid). 
 Albumin also gives a fine red colour with mercuric nitrate containing nitrous 
 acid (Mi lion's test; prepared by dissolving mercury in twice its weight of nitric 
 acid, in the cold, and adding twice its bulk of water). When boiled with moder- 
 ately dilute sulphuric acid, albumin yields leucine and tyrosine (p. 678). With 
 solution of potash, on boiling, it also gives leucine and tyrosine, evolves one-third 
 of its nitrogen as ammonia, and its sulphur is converted into potassium sulphide, 
 which gives a black precipitate on adding a salt of lead. When heated with 
 baryta-water to 150 C., it evolves part of its nitrogen as ammonia, and barium 
 carbonate is formed in the same ratio to the ammonia as when urea is heated 
 with baryta ; this has led to the conclusion that albumin contains one-fifth of its 
 nitrogen in a form nearly allied to urea, and that it is probably a complex ureide 
 (p. 671). When oxidised by potassium permanganate, it yields benzoic acid. 
 Boiled with a mixture of potassium permanganate and potash, it evolves the whole 
 of its nitrogen as ammonia, whilst with potash alone it only gives off one-third of 
 its nitrogen. 
 
 The putrefaction of the albuminoids gives rise to the ptomaines or toxines ; 
 p. 666. Such poisonous products are also formed by the bacilli of diseases like 
 diphtheria, and it is upon the introduction into the system of antidotes (anti- 
 toxines), derived from animals that have been able to survive the poisons, that the 
 principle of inoculation depends. 
 
 555. The gastric juice dissolves coagulated albumin digested with it 
 at about 37 C., and the solution is not precipitated by potassium ferro- 
 .cyanide, nor coagulated by heating. In this condition it is said to have 
 been peptonised, or converted into peptone (neTr, to digest). The con- 
 stituent of the gastric juice which effects this change is termed pepsin, 
 and may be precipitated from the juice by alcohol. It resembles albu- 
 min in composition, but is much less putrescible. When dissolved in 
 dilute hydrochloric; acid, also present in the gastric juice, it yields a 
 mixture which peptonises most albuminoids if digested at about 40 C. 
 The pepsin prepared from the stomach of the pig and other animals is 
 sometimes administered medicinally to assist digestion. 
 
 The action of pepsin and HC1 on albuminoids is hydrolytic and occurs in several 
 etages, the successive products between the original compound and peptone being a 
 syntonin or acid-albumin and an albumose or propeptone. 
 
 Serum albumin forms nearly 8 per cent, of the serum of blood, and is found in 
 other liquid secretions. It may be prepared by precipitating the diluted serum 
 with lead acetate, suspending the washed precipitate in water, and decomposing 
 it with C0 2 ; the filtered liquid is then evaporated below 50 C. It appears to 
 contain less sulphur than ovalbumin (egg albumin) in the ratio of 1.2 : 1.6, but 
 rather more oxygen (23.1 : 22.4). In properties it very closely resembles oval- 
 bumin, but it is not coagulated by ether, and gives precipitates with nitric and 
 hydrochloric acids, which are more easily dissolved by excess than are those of egg 
 albumin. It is more powerfully leevo-rotatory than egg albumin. 
 
 Vegetable albumin is the substance which is precipitated by heat from the juices 
 of plants, and from their infusions in cold water. It has not been obtained pure in 
 the soluble condition. It appears to contain less sulphur even than serum albumin 
 contains. 
 
 Globulin, or serum globulin, is very like albumin, but is insoluble in pure water ; 
 it dissolves in a very weak solution of salt, and in very weak acids and alkalies. 
 It dissolves in water saturated with oxygen, and is precipitated by carbon dioxide. 
 This gas precipitates it in a granular form from the serum of blood ; saturation of 
 
FIBRIN. 75 ! 
 
 the serum with salt also precipitates it. Crystallin is found in the aqueous humour 
 and crystalline lens of the eye. 
 
 Myosin (/tus, a muscle) separates from muscle plasma (the liquid contained in 
 living muscle) after death, producing rigor mortis. Chopped flesh is triturated to 
 a pulp with common salt, 9 parts of water are added for i of salt, the whole 
 digested for some time at 24 C., pressed through linen and filtered ; the myosin is 
 precipitated on adding much water or salt. 
 
 556. Fibrin is the albuminoid which separates from the blood when 
 this has been shed from the animal, causing the coagulation or clotting 
 of the blood plasma. It appears to be formed from jibrinogen a soluble 
 albuminoid existing in the plasma by a ferment (thrombin) contained 
 in the white blood corpuscles. Human blood yields about 0.25 per cent, 
 of fibrin, which resembles myosin, but is not dissolved by solution of 
 salt. It may be obtained from freshly drawn blood by whipping it 
 with a bunch of twigs, when the fibrin adheres to them in threads which 
 become nearly white when washed, and may be freed from fat by 
 alcohol and ether. If the blood be not stirred when freshly drawn, it 
 forms a red clot, caused by the coagulation of the fibrin, and the en- 
 tanglement in it of the red blood corpuscles ; if the clot be cut up and 
 washed in a cloth, the corpuscles and blood serum may be washed away 
 and the fibrin left. If 7 measures of blood be drawn into a vessel 
 containing i measure of a cold saturated solution of Na 2 S0 4 , the fibrin 
 w r ill remain in solution, whilst the blood-globules will be deposited on 
 standing. The clear yellow solution containing albumin, globulin, and 
 fibrinogen is largely diluted with water, when fibrin is precipitated. 
 
 Fibrin forms elastic strings which dry into a yellow horny mass. When fresh, 
 it readily absorbs oxygen, and evolves C0 2 ; when moist it decomposes H 2 2 , 
 evolving 0. It is insoluble in water, alcohol, solution of salt, and in cold very 
 dilute HC1 (o.i per cent.), but this dissolves it at 60 C. Solution of nitre at 40 C. 
 also dissolves it. When heated for some time with water at 72 C., it becomes 
 insoluble in dilute acids and salts, but dissolves in alkalies. Boiled for many hours 
 with water, one-fifth of it may be dissolved, yielding a solution having some of the 
 properties of gelatine. Heated with water at 120 C. for some hours, it is almost 
 entirely dissolved. The solution of fibrin in weak HC1 is precipitated by neutralisa- 
 tion and by saline solutions. The precipitate always contains a little calcium 
 phosphate. Fibrin soaked in weak potash becomes gelatinous and, if heated to 
 60 C., dissolves to a solution resembling that of albumin. Fibrin is hardened and 
 rendered non-putrescible when soaked in solution of tannin. Moist fibrin soon 
 begins to putrefy when exposed to air, and becomes fluid in a week ; the products 
 of putrefaction resemble those from albumin. 
 
 Fibrinogen may be precipitated from blood plasma by a solution of salt which is 
 semi-saturated, and can in this way be separated from the serum globulin. 
 
 Fibrin from blood contains more nitrogen than the albumin of serum (17.4 : 15.6) 
 and a little less oxygen (21.8 : 23.1). It does not appear that blood-fibrin and flesh- 
 fibrin are identical. 
 
 557. Casein is the chief constituent of the curd of milk, and differs 
 from 'the other albuminoids in not coagulating spontaneously or on 
 heating. It exists in milk as a soluble compound with a little potash 
 or soda, and is separated as curd when the alkali is neutralised either 
 by adding an acid, or by the formation of acid (lactic) by the decom- 
 position of milk-sugar caused by spontaneous fermentation. 
 
 It is prepared by precipitating diluted milk with acetic acid and washing the 
 precipitate with water, alcohol, and ether in succession, to remove soluble matte 
 and fat ; it is further purified by dissolving in weak soda and precipitating : 
 acetic acid. Coagulated casein is characterised by the facility with which 
 dissolved by weak alkaline solutions, yielding a liquid upon the surface Of WW 
 when boiled, an insoluble pellicle forms, like that produced on the surface ot b 
 
752 CASEIN. 
 
 milk. Coagulated casein may also be dissolved by acetic or oxalic acid, but sul- 
 phuric or hydrochloric acid reprecipitates it, these acids forming compounds with 
 casein which are insoluble in the acids, but soluble in water. If skimmed milk be 
 carefully evaporated to dryness, and the fat extracted from the residue by ether, 
 the casein is left in the soluble form mixed with milk-sugar, and may be dissolved 
 in water or in dilute alcohol. 
 
 A distinctive property of casein is its coagulation by rennet, the 
 mucous membrane of the stomach of the calf, a small quantity of which 
 or of its solution in brine,* coagulates the casein in a large quantity of 
 milk ; the coagulation does not appear to depend upon the formation of 
 lactic acid, but upon a specific action of the rennet ; the curd thus 
 produced contains calcium and magnesium phosphates, and is not easily 
 soluble in sodium carbonate. The casein of milk is more readily 
 coagulated by acids and by rennet when the milk is warmed ; hence 
 milk which has undergone very slight fermentation is curdled when 
 heated, but if fresh milk be heated to boiling, the decomposition will be 
 prevented. The casein of milk is precipitated by some neutral salts, 
 such as sodium chloride or magnesium sulphate, and even by an excess 
 of sodium carbonate. 
 
 At the present time, the condition in which casein exists in milk and the cause 
 of its coagulation by rennet are subjects of much discussion. Some chemists claim 
 that the milk contains caseinogen, which is precipitated by acids, and differs from 
 casein into which it is converted by rennet. According to Hammarsten, caseinogen 
 is only coagulated by rennet when it contains earthy phosphates, which combine 
 with the casein produced and precipitate it. A solution of casein free from lime 
 salts is not precipitated by rennet, but the precipitation occurs on adding a lime 
 salt, even though the rennet has been made inactive by heating the casein solution 
 containing it. 
 
 The general chemical behaviour of casein resembles that of albumin. It contains 
 a little less sulphur than albumin and fibrin contain, and phosphorus appears to 
 be an essential constituent (0.85 per cent.). 
 
 Casein combines with slaked lime to form a hard insoluble mass, so that a mix- 
 ture of cheese with lime is sometimes used as a cement for earthenware. The curd 
 of milk, washed and dried, is used by calico-printers, under the name of lactarine, 
 for fixing colours. If it be dissolved in weak ammonia, mixed with one of the 
 aniline dyes, printed on calico, and steamed, the colour is left as an insoluble com- 
 pound with the casein. By treating coagulated casein with formaldehyde it 
 becomes similar to horn, for which it is substituted in making combs and the 
 like. 
 
 Legumin, or vegetable casein, is found in peas, beans, and most leguminous seeds. 
 If dried peas be crushed and digested for some time in warm water, a turbid 
 liquid is obtained, holding starch in suspension ; this is allowed to settle, the super- 
 natant liquid precipitated by acetic acid, and the legumin purified from fat by 
 washing with alcohol and ether. It closely resembles casein, its solution forming 
 a pellicle when heated, and being coagulated by rennet. In composition it differs 
 somewhat from casein, containing about I per cent, more nitrogen, and only about 
 half as much sulphur. When boiled with dilute sulphuric acid, legumin yields 
 much less leucine than albumin and fibrin furnish, and very little tyrosine ; but 
 it gives more aspartic acid and glutamic acid, C 3 H 5 (NH 2 )(C0 2 H)2, homologous 
 with aspartic acid. 
 
 Gluten is the tough, sticky substance which is left when flour is made into dough, 
 tied up in muslin, and kneaded in water as long as any starch passes through. It 
 speedily putrefies when exposed to the air, and dries up to a brittle, horny mass at 
 100 C. When fresh gluten is boiled with dilute alcohol, a portion is left undissolved, 
 and has been named vegetable fibrin, as it forms a tough elastic mass. It dissolves 
 in very dilute HC1 and in dilute alkalies, and is precipitated by acetic acid and by 
 salts. When the alcoholic solution cools, it deposits white flakes of mucedin, 
 
 * The active principle (lab or chymosin) of the rennet nauy be obtained from rennet 
 extract by saturating it with salt, when the lab will rise to the surface. 
 
GELATINE. 
 
 and on adding water to the nitrate, glladin is precipitated. These substances- 
 resemble legumm in composition, but contain twice as much sulphur 
 
 It has been asserted that gluten does not exist, as such in flour, but is produced 
 from the proteids in the flour by the action of water, which may enable a ferment 
 
 to effect the conversion. 
 
 558. Gelatine. This substance is so called from gelu, ice, because its- 
 solution in hot water becomes a transparent jelly on cooling. It con- 
 tains 50 per cent. C, 25.7 0, 17.7 N, and 6.6 H, numbers which 
 approximate to C 42 H 66 N 13 16 , but its molecular formula has not been 
 determined, because it cannot be converted into vapour, and does not 
 form well-defined compounds with other bodies. It may be obtained 
 by digesting bones in cold dilute hydrochloric acid, till the calcium 
 phosphate and other salts are dissolved, leaving a residue of the same 
 form as the bone, but of a soft, flexible character. This is termed ossein, 
 and has the same composition as gelatine, into which it is converted by 
 long boiling with water, especially under pressure, a solution being 
 obtained which becomes a jelly on cooling, and leaves a brittle, trans- 
 parent mass (glue) when dried. Gelatine does not fuse when heated, but 
 swells up and decomposes, yielding very offensive alkaline vapours, con- 
 taining ammonia and compound ammonias (methylamine, &c.), pyrrol, 
 and its derivatives, toluene, naphthalene, ammonium cyanide, water, &c. 
 DippeVs oil, obtained by distilling bones, contains these products, 
 together with others, in the formation of which the fat of the bones 
 takes part, such as the cyanides of the fatty acid series (propionitrile, 
 &c.), pyridine bases, phenol, and aniline. 
 
 Gelatine softens and swells in cold water, but does not dissolve ; hot 
 water dissolves it, and the solution gelatinises on cooling, even when it 
 contains only i per cent. Continued boiling of the solution destroys 
 the tendency to gelatinise. Gelatine is insoluble in alcohol, which pre- 
 cipitates it in white flakes from its aqueous solution. It is also precipi- 
 tated by tannin, which combines with it to form an insoluble non- 
 putrescible compound. Mercuric chloride also precipitates solution of 
 gelatine. If gelatine solution be mixed with potassium dichromate, the 
 jelly formed on cooling becomes insoluble on exposure to light, which 
 is turned to account in photography ; the action probably consists in an 
 oxidation of the gelatine. Acetic acid dissolves gelatine (liquid glm) ; 
 alkalies also dissolve it. When boiled with strong alkalies or with di- 
 luted sulphuric acid for a long time, it yields leucine and glycocine 
 (sugar of gelatine). Heated with sulphuric acid and potassium dichro- 
 mate or manganese di-oxide, gelatine yields numerous products of 
 oxidation, among which are found many of the fatty acids, with their 
 corresponding aldehydes and cyanides, with benzoic acid, bitter-almond 
 oil, &c. 
 
 Gelatine may also be obtained by the action of water at a high temperature on 
 skin, sinews, and connective tissue. Isinglass is very similar to gelatine and i 
 prepared from the air-bladder of fish, especially of the sturgeon. It differs from 
 gelatine in being liable to settle in flocks when stirred up with water ; hence _ 
 application as a " fining" for beer, for which purpose it is made into an emulsn 
 by treatment with sulphurous acid (cutting}. Glue is made from the refuse and 
 parings of hides, after being cleansed from hair and blood by steeping in lime- 
 water, and exposed to the air for some days to convert the lime into carbonate, and 
 prevent the injurious effect of its alkaline character -upon the gelatine, 
 then boiled with water till the solution gelatinises firmly on cooling, when il 
 run off into another vessel, kept warm to allow the impurities to settle down, af 
 
 3 B 
 
754 MUCIN. 
 
 which it is allowed to set in shallow wooden coolers. The jelly is cut up into slices 
 and dried upon nets hung up in a free current of air. Spring and autumn are 
 usually selected for drying glue, since the summer temperature would liquefy it, and 
 frost would, of course, split it and render it unfit for the market. Size is made in 
 a similar manner, but finer skins are employed, and the drying is omitted, the size 
 being used in the gelatinous state. The best size is made from parchment cuttings. 
 Moist gelatine easily putrefies, becoming very offensive : for this reason size is often 
 treated with sulphurous acid. 
 
 Clwndnn (x&vfyos, cartilage) is prepared by the action of water at a high 
 temperature on the cartilages of the ribs and joints, and resembles gelatine in 
 composition and properties, but contains less N and a small quantity of S. The 
 aqueous solution of chondrin is precipitated by acetic acid, by alum, and by lead 
 acetate, which do not precipitate gelatine. When boiled with dilute sulphuric acid, 
 it yields leucine, but no glycocine. Boiled with hydrochloric acid, it gives a 
 solution which reduces Fehling's solution like glucose. 
 
 Sericin, or silk-gelatine, C lg H ?5 N 5 8 , is the so-called gum extracted from silk by 
 boiling with water ; it resembles gelatine, but is precipitated by basic lead acetate, 
 and, when boiled with sulphuric acid, yields leucine, tyrosine, and amldogly eerie 
 acid (serin), C 2 H 3 (OH)(NH 2 )C0 2 H. (Cystine, C 3 H 7 N0 2 S,"found in some rare urinary 
 calculi, appears to be a sulphur derivative of serin.) 
 
 Keratin forms the chief part of horns, claws, nails, feathers, hair, and wool, 
 and remains when these have been treated with all ordinary solvents. It is 
 softened by long boiling with water, and is dissolved when heated with water 
 under pressure. It swells up and gradually becomes soluble in strong alkalies 
 and in acetic acid, especially on boiling. It contains more sulphur than do the 
 albuminoids. Fibroin from silk, and spongln from sponge, are similar bodies. 
 
 CJiitin, C 18 H 30 N 2 12 , is the chief constituent of the shells of lobsters, crabs and 
 beetles, and is left after exhausting them with water, alcohol, ether, acetic acid, and 
 alkali. It is a white translucent substance, soluble in cold strong H 2 S0 4 to a solu- 
 tion which yields glucose when diluted ; the change appears to be a hydrolysis, 4'H 2 
 being absorbed to produce ghieosamlne, C 6 H n (NH 2 )0 5 , (2 mols.) and acetic acid 
 (3 mols.). 
 
 Mucin is the substance which gives the viscous character to bile, saliva, and 
 some other animal secretions, and to the slime of the snail. To prepare it, snails 
 are cut up, triturated with sand to a pulp, boiled with water, filtered while hot, 
 and precipitated by excess of acetic acid ; the precipitated mucin is washed with 
 weak acetic acid as long as the washings are precipitated by tannic acid, indi- 
 cating peptone. Dry mucin is unaffected even by hot water. Moist mucin swells 
 up in a remarkable manner in water, but does not dissolve ; a little acid causes it 
 to separate in flocks which do not easily dissolve in an excess of acid. Alkalies 
 dissolve it and acids reprecipitate it. Mucin dissolves in a strong solution of 
 salt, and is precipitated again by water. Alcohol coagulates mucin into flocks. 
 Acid solutions of mucin are not precipitated by potassium ferrocyanide (unlike 
 albumin). Boiling dilute acids dissolve mucin, converting it into a substance 
 having the properties of glucose and another which resembles albumin. The 
 composition of mucin has not been well established ; it contains the same 
 elements as albumin, but much less nitrogen. 
 
 Nuclein is contained in the nuclei of pus-globules, in the blood globules of 
 birds and snakes, in yolk of egg, in brain, and in milk. It stands apart from 
 other proteids, by containing about 2 per cent, of phosphorus, in actual organic 
 combination (and not as calcium phosphate, which so constantly accompanies the 
 albuminoids). In extracting it, advantage is taken of its insolubility in the 
 digestive fluids. Pus-globules are treated with warm alcohol, which removes 
 lecithin, and afterwards with a pepsin solution made from extract of pig's stomach, 
 and containing I per cent, of strong HCL The insoluble residue consists of 
 nuclein. Pus-globules are obtained by treating the discharge, or the bandages to 
 which it adheres, with a mixture of i part of a saturated solution of sodium sul- 
 phate and 9 parts of water, when the serum remains in solution, and the pus- 
 globules sink and may be washed by decantation ; if these be digested with cold 
 dilute HC1 and afterwards shaken with a mixture of ether and water, the nuclei 
 remain as a fine powder at the bottom. Nuclein is remarkable for its insolubility 
 in all ordinary solvents, it appears to have an acid character, and dissolves in 
 sodium carbonate or acetate, the solution in the latter giving precipitates with 
 salts of zinc, copper and lead. It is of considerable importance in the chemistry 
 
HEMOGLOBIN. 
 
 the group C.,H 5 (glyceryl), and probably the mdSl^^Jm^T ^ 1 1 t . cont ^ 1 J 18 
 and a phosphorised group, N(CH,) 3 C 2 H 4 (PO V) wlv ? f ^ ? leiC a ' d8 ' 
 N(CH 3 ) -C H 3 -OH (p. 666). A variation ffai^ jftSUj^^ft 
 
 Lecithin may be prepared from the substance of the brain by exhausting it 
 with ether, treating the residue with alcohol, and cooling the alcohoHc *o ution 
 in ice, when a mixture of lecithin and cerebrin is deposited On trattai 
 with ether, the lecithin is dissolved, and may be purified^^po^^^ 
 redissolvmg m alcohol, adding an alcoholic solution of platinfc chforide and 
 decomposing the platinum salt (C 42 H 84 NP0 8 HCl) 2 .PtCl 4 , withH 2 S on e?a^atiSg 
 the nitrate, the lecithin is obtained as a fusible crystalline body, insofuWe if 
 water and sparing y soluble in cold alcohol and ether. It combines both wi h 
 bases and acids. When boiled with acids or with potash or baryta i vSds 
 neurme, phosphoglyceric acid, C 3 H 5 (OH) 2 .P0 2 (OH) 2 , palmitic and oleic acids 
 
 .Cerebrin obtained from brain as above described, is a white powder which 
 swells up like starch when boiled with water. It yields a substance resemblin- 
 glucose when boiled with dilute acids. The formula of cerebrin or metric 
 1 * ^ 8 metimeS Called ' a PP ears to be CwHgsNOs. It is also found in pus- 
 
 The so-called pratagon appears to be a mixture of lecithin and cerebrin. 
 
 560. Haemoglobin. The colouring-matter contained in the red 
 globules of arterial blood is called oxyhcemoglobin, and resembles albumin 
 in composition, except that it contains only 0.4 per cent, of sulphur 
 and 0.43 per cent, of iron. To extract it from blood, the fibrin is 
 separated by whipping (p. 751), and the defibrinated blood is mixed 
 with ten volumes of a solution containing 3 per cent, of NaCl. This 
 prevents the coagulation of the albuminoids, and the red globules sub- 
 side after a day or two ; the clear liquid is poured off, and the globules 
 shaken with water and an equal volume of ether, which dissolves the 
 envelopes of the globules, and allows the colouring-matter to pass into 
 the water. The aqueous layer is separated, cooled in ice, one-fourth of 
 its volume of alcohol added, and the cooling carried to - 5 C., when the 
 oxyhsemoglobin crystallises in forms which vary in different animals. 
 That obtained from the blood of men, oxen, sheep, pigs, and rabbits is 
 not easily crystallised, the best for this purpose being the blood of dogs, 
 guinea-pigs, hedgehogs, and rats. The crystals contain oxygen in a 
 loosely combined form, which they evolve when exposed in a vacuum, 
 especially if warmed, becoming thus converted into hcemoglobin, which 
 again absorbs oxygen on exposure to air ; this change is attended with 
 production of a much brighter red colour, and with a difference in the 
 action on transmitted light, for if white light be allowed to pass through 
 the solution of oxyhsemoglobin contained in a test-tube placed before 
 the slit of a spectroscope (p. 328), the green of the spectrum is seen to 
 be crossed by two broad black bands, which are also seen when arterial 
 blood is employed, whilst the solution of haemoglobin exhibits only one 
 band in the middle of the green, which is seen when venous blood is 
 employed. This difference in the absorption-spectrum is best shown by 
 reducing the solution of oxyhaemoglobin with a little ferrous sulphate, 
 mixed with tartaric acid and ammonia in excess. The oxygen of oxy- 
 
756 BILE. 
 
 haemoglobin is also displaced by passing hydrogen or C0 2 , haemoglobin 
 being left, and the colour changing from red to purple. 
 
 Oxyhsemogoblin, when shaken with CO, parts with its oxygen and 
 absorbs an equal volume of CO, its colour changing to purple ; the 
 absorption-spectrum exhibits two dark bands, which are situated further 
 from the sodium-line (D) and nearer to the blue of the spectrum than 
 is the case with haemoglobin. This is turned to account in cases of 
 poisoning by carbonic oxide. The compound of haemoglobin and CO 
 may be obtained in bluish-red four-sided prisms. When solution 
 of oxy haemoglobin is heated above 70 C., it is decomposed into 
 albumin, which coagulates, and another red colouring-matter, termed 
 haematin. 
 
 Hcematin, C 34 H 34 N 4 Fe0 5 , is formed when oxyhasmoglobin is decomposed by 
 acids. If a solution of that substance, mixed with a little NaCl, is evaporated 
 over sulphuric acid to a syrup, mixed with 15 times its volume of glacial acetic 
 acid, and heated on a steam-bath for several hours, it yields, on cooling, flat 
 rhombic prisms of hasmatin hydrochloride (formerly known as hcemin, or blood- 
 crystals) of a dark, violet-red colour, and metallic lustre, containing single mole- 
 cules of hasmatin and HC1. The formation of these crystals is employed for the 
 identification of blood-stains, the suspected matter being placed on a microscope 
 slide, a little sodium chloride added, and glacial acetic acid allowed to run under 
 the cover-glass ; on heating till bubbles appear, and cooling, the dark red hasmin 
 crystals become visible. Hasmatin is a magnetic substance, while oxyhasmoglobin 
 and carbonic oxide haemoglobin are diamagnetic. 
 
 561. Bile Constituents. The chief colouring-matter of the bile is bilirubin, 
 C 16 H 18 N 2 3 , which is accompanied by bilifuscin, C 16 H 20 N 2 4 , and biliprasin, 
 CjgH^NaOg. These may be extracted from gall-stones, in which they exist in com- 
 bination with calcium. The powdered calculi are boiled with alcohol and ether to 
 extract the cholesterin, and with dilute HC1 to remove the lime. After washing 
 and drying, the residue is boiled with chloroform, which extracts bilirubin and 
 bilifuscin ; the chloroform is distilled off and the residue boiled with alcohol, which 
 dissolves the latter. The original residue, un dissolved by chloroform, contains 
 biliprasin, which may be extracted by boiling with alcohol. 
 
 Bilirubin crystallises from chloroform in dark-red prisms, insoluble in water 
 and alcohol, but soluble in alkaline liquids, and imparting a yellow colour to a 
 very large volume of solution. It appears to have acid properties. Its alkaline 
 solutions absorb oxygen and become green, yielding a green precipitate of bili- 
 verdin, C ]6 H 18 N 2 4 , on addition of an acid. Bilifuscin and biliprasin are obtained 
 as very dark green amorphous bodies, insoluble in water. The alkaline solutions 
 of the biliary colouring-matters, when treated with nitric acid, yield successive 
 tints of green, blue, violet, red, and yellow, which serve to indicate the presence 
 of bile in other secretions. 
 
 Olyoooholic acid, C 24 H 39 4 < NH'CH 2 C0 2 H, exists in bile as a sodium salt, together 
 with the sodium salt of taurocholic acid, C 24 H 39 4 -NH'CH 2 CH 2 S0 3 H. To extract 
 them, ox-gall is mixed with bone-black to a paste, which is dried on the steam-bath 
 and digested with absolute alcohol, which dissolves the sodium salts together with 
 cholesterin and cholin. Ether is then added, to precipitate the sodium salts. 
 These are dissolved in water, and decomposed by dil. .H 2 S0 4 , which precipitates 
 the glycocholic acid, at first amorphous, but changing into colourless needles. It 
 is sparingly soluble in water, but dissolves in alcohol, though not in ether. The 
 alkali salts are very soluble and sweet. It is characterised by its behaviour with 
 solution of sugar and strong H 2 S0 4 , which give a purple-red colour (Pettenltofer 's 
 test for bile). It is an amido-acid, and yields ohologlycholic acid, C^H^NO^ when 
 treated with nitrous acid. When boiled with alkalies, glycocholic acid is hydro- 
 lysed into glycocine (amido-acetic acid) and cholic acid; C 26 H 43 N0 6 + H = 
 CH 2 (NH 2 ) -C0 2 H + C^opg. Boiling with dilute HC1 effects the same change" but 
 converts the cholic acid into dy sly sin, C 24 H 36 3 , an amorphous precipitate, which 
 becomes potassium cholate when boiled with alcoholic KOH. 
 
 Taurocholic acid is not precipitated by normal lead acetate, which precipitates 
 the glycocholic acid from ox-gall, and the filtrate gives a precipitate of lead 
 taurocholate on adding basic lead acetate. When this is suspended in water and 
 
CHOLESTERIN. 
 
 decomposed by H 2 S a solution of the acid is obtained, which may be concen- 
 trated and mixed with ether, when the acid separates as a syrup which deposits 
 needle- ike crystals. Dog's bile yields more taurocholic acid than that of the ox 
 Taurocholic acid dissolves readily in water and alcohol. It is decomposed, like 
 glycochohc acid by boiling with alkalies or acids, but it yields taurine, C Q H,NSO, 
 instead of glycocme ; C. 26 H 45 NS0 7 + H 2 = C 2 H 7 NS0 3 + C 24 H 40 5 . 
 
 Cholesterin, or cholesterol, C^H^OH, is a crystalline alcohol found in bile, and 
 composing the chief part of gall-stones or biliary calculi, from which it may be 
 extracted by boiling with alcohol, which deposits the cholesterin in transparent 
 lustrous plates on cooling. It is insoluble in water, but soluble in ether fuses at 
 145 C. and sublimes at 200 C. It is unchanged by boiling with potash, and 
 yields ethereal salts when heated with the fatty acids in sealed tubes. HC1 con- 
 ^ 61 S ^^iocholesteryl chloride, C^H^Cl, and ammonia into cholester ,;,>. 
 ^26 H 43' NH -2- When dissolved in petroleum and treated with sodium it evolves 
 hydrogen and forms crystalline C 26 H 43 'ONa. When moistened with strong HNO, 
 and dried, cholesterin gives a yellow residue which becomes red with NH 3 . Strong 
 HC1 and a little Fe 2 Cl 6 give a violet-blue colour with cholesterin on evaporation. 
 Cholesterin occurs in the blood, in brain, in yolk of egg, in cod-liver oil, and in 
 muslt, the dried secretion of the musk deer. It is also found in sheep's wool 
 together with isocholesterin, having the same composition, but crystallising in 
 needles which melt at 138 C. Cholesterin can absorb over 100 per cent, of water, 
 and in this condition is used as an emollient (lanolin). 
 
 Phytosterin, CggH^O, is a similar substance found in peas and other seeds, and 
 in olive oil. 
 
 XVI. HETEROCYCLIC COMPOUNDS. 
 
 562. Nearly all the compounds hitherto considered have been hydro- 
 carbons or derivatives thereof. There remains a class of substances 
 having closed-chain nuclei, composed not of carbon alone, as are the 
 benzene and naphthalene nuclei, for example, but containing one or 
 more atoms of N, O or S as member or members of the closed chain. 
 Thus they are not strictly derivatives of hydrocarbons. In other 
 respects they might have been considered under the preceding classes, 
 for they are hydrides, alcohols, acids, &c., derived from these heterocyclic 
 nuclei instead of from open-chain nuclei or from carbocydic nuclei (like 
 the benzene nucleus). 
 
 A few compounds which are strictly within this class have already 
 been described, such as succinic anhydride and the various lactones. 
 These are, however, more of the nature of open-chain derivatives than 
 are those that remain to be discussed. A number of the three and four 
 membered heterocyclic compounds have also received passing notice 
 e.g., ethylene oxide, trimethylene oxide, diazo-methane, &c. The five- 
 and six-membered* rings of this kind, together with the condensed 
 nuclei corresponding with naphthalene, c., will now receive attention. 
 
 563. Five-membered heterocyclic compounds. The prototypes 
 of these are furfurane, thiophen, and pyrrol, which are believed to 
 possess constitutions expressed by the following formulae : 
 
 CH : CH, CH : CH X CH : CH, 
 
 >0- / s - / NIL 
 CH : CH/ CH : CH/ CH : CH/ 
 
 Furfurane. Thiophen. Pyrrol. 
 
 They resemble benzene in that they yield derivatives similar to those 
 of that of hydrocarbon, and show little disposition to form addition- 
 
 As in the case of the carbocyclic compounds, 7, 8, &c., membered rings are little known. 
 
75$ THIOPHEN. 
 
 products with the halogens. In fact, the arguments which lead to the 
 closed-chain formula for benzene (p. 541) are equally applicable to these 
 compounds. 
 
 Eloquent of their constitution is their formation from y-diketones, 
 such as acetonylacetone (p. 647) ; by dehydration this compound yields 
 i : 4-dimethylf urfurane. 
 
 CH 2 - CO CH 3 CH : C(CH 3 \ 
 
 - H 2 = >0. 
 
 CH 2 - CO CH 3 CH : C(CH 3 )/ 
 
 With P 2 S 5 it yields i : 4-dimethylthiophen, and with NH 3 i : 4-di- 
 methyl pyrrol. 
 
 Two classes of mono-substitution products are known from these compounds 
 the a-derivatives, which contain the substituent attached to a carbon atom 
 adjacent to the 0, S or 1ST, and the /^-derivatives, in which a hydrogen atom of one 
 of the far carbon atoms has been displaced. A third class is possible in the case 
 of pyrrol, for the H of the NH group can be substituted. The possible di- 
 derivatives are more numerous than in the case of benzene ; their orientation is 
 expressed by numbering the near carbon atoms i and 4, and the far atoms 
 2 and 3 ; or by numbering the N, or S atom i and the C atoms 2, 3, 4, 5 suc- 
 cessively. A reaction common to all three compounds is the blue colour produced 
 by their reaction with isatin ($.f.) and strong H 2 S0 4 . 
 
 Furfurane, C 4 H 4 0, together with several of its derivatives, is found in the first 
 runnings of the distillation of wood-tar. It is made artificially by distilling 
 pyromucic acid with lime. Pyromucic acid is itself obtained by the destructive 
 distillation of mucic acid (p. 622), thus 
 
 CHOH-CHOH-COOH CH : C(C0 2 H\ 
 
 = >0 + 3HOH + C0 . 
 CHOH-CHOH-COOH CH : CH 
 
 This indicates the constitution of pyromucic acid, and since this acid yields 
 furfurane when distilled with lime it is probably furfurane-carboxylic acid (just 
 as benzoic acid, which yields benzene on distillation with lime, is benzene- 
 carboxylic acid). Thus the constitution of furfurane is settled. 
 
 Furfurane is a colourless liquid, smelling of chloroform, insoluble in water am 
 boiling at 32 C. Its aldehyde (furfural) and carboxylic acid (pyromucic acid) 
 have been already considered. 
 
 Uvinic acid or pyrotritartaric acid, C 4 H(CH 3 ) 2 0'C0 2 H, found among theproduci 
 of the destructive distillation of tartaric acid, is -a 1 -dimethylfurfurane-/3-carboxylic 
 acid ; it is also produced together with vritie acid (5:1: $-methylpkthalic acid) by 
 heating pyrotartaric acid with baryta water. It melts at I35C. and deconi] 
 into C0 2 and dimethylfurfurane. 
 
 TMophen, C 4 H 4 S, its homologues and substitution-derivatives, are remarkable for 
 their similarity to benzene, its homologues and derivatives respectively ; thus with 
 a large number of benzene derivatives there are corresponding thiophen derivativ 
 of approximately the same boiling-point. Thiophen and its homologues accompany 
 benzene and its homologues in coal-tar, commercial benzene containing about 0.6 
 percent, of thiophen. To separate it the benzene is shaken with about 10 per cent, 
 of strong H 2 S0 4 , which extracts the thiophen as a sulphonic acid. Or the benzene 
 may be heated with mercuric acetate, which forms a complex precipitate with the 
 thiophen, decomposable by HC1 into thiophen and HgCl 2 . 
 
 The thiophen passes over when the sulphonic acid is distilled with steam ; it is 
 colourless liquid (sp. gr. 1.06) which smells of benzene, boils at 84 C. and yields 
 blue colour when mixed with isatin and strong H 2 SO 4 ; this reaction due to the 
 formation of indophenin, C 12 H 7 NOS serves to detect thiophen or its homologues in 
 benzene. 
 
 Several fatty compounds yield thiophen when heated with P 2 S 3 ; sodium succinate, 
 for example 
 
 CH 2 -COONa CH : CH, 
 
 gives j>S. 
 
 CHyCOONa CH : CH/ 
 
 Derivatives of selenophen, C 4 H 4 Se, are also known. 
 
Pyrrol, 
 
 INDOL. 
 is a secondary amine and 
 
 '^,^'1 /"_ .X * 
 
 fatty acids and benzene hydrocarbons a ml 
 
 ' which 
 
 
 
 pyirol treated with 
 
 There are 3 mono-substitution products from rrol, because the H in the 
 
 lodopyrroli C 4 I 4 NH, is an odourless substitute for chloroform 
 Several hydrojtyrroU and their derivatives are known ; pyrrollne is 
 
 4 6 ; ' 
 
 29 
 
 564 Condensed Nuclei from the Five-membered heterocyclic Compounds These 
 are believed to consist of one or two benzene nuclei condensed with a furfurane 
 thiophen, or pyrrol nucleus, just as naphthalene consists of two, and anthracene of 
 three benzene nuclei condensed together. They are probably represented b y the 
 following formulae 
 
 CH 
 
 ^0 
 
 Benzofurfurane. 
 
 GE 
 
 CH, 
 
 -C 6 H 4 
 
 Dibenzofurfuraue. 
 
 >CH(a) 
 8 / 
 Beuzothiophen. 
 
 C 6 H 4 - C 6 H 4 
 
 Dibenzothiophen. 
 
 Beuzopyrrol. 
 
 CH 
 
 Those derived from one benzene nucleus are formed by treating the corre- 
 
 CH * CHC1 PH 
 
 spending chloro-styrolene with alkali, C 6 H 4 / ' gives C 6 H 4 (^ ^CH, 
 
 XH X 
 
 where X = 0, S or NH. 
 
 Benzofurfurane or coumarone is a product of the action of alcoholic KOH on 
 coumarin (p. 611) ; it is found in coal-tar and boils at 177 C. Countarilic acid is 
 its a-carboxylic acid. 
 
 Benzothlophen melts at 31 C. and boils at 221 C. 
 
 Benzopyrrol or indol is the most important member of the group, as it is constitu- 
 tionally the parent substance of indigo. It may be obtained by distilling reduced 
 indigo (<?.r.) with zinc dust, and by reducing o-nitro-cinnaniic aldehyde with Zn 
 and KOH 
 
 C 6 H 4 
 
 CH-CHO 
 
 / X 
 H 7 - C 6 H/ 3CH + 3 H 2 0. 
 
 It crystallises in colourless prisms (m.-p. 52 C.) of disagreeable odour, and may be 
 distilled in a vacuum or with steam. It is soluble in water and has weak basic 
 properties, forming a sparingly soluble hydrochloride. A shaving of deal moistened 
 with HC1 and exposed to its vapour gives the pyrrol red colour. The hydrochloric 
 solution is coloured red by potassium nitrite. Indol is produced by the action 
 of the peculiar ferment of the pancreatic juice upon the albumin of blood or eggs, 
 and the indican occasionally present in the urine appears to be formed from it. 
 
 Many derivatives of indol are known, but only the most important can receive 
 notice here. The orientation of the substitution derivatives is expressed by the 
 
760 
 
 INDOXYL. 
 
 letters a, /3, n in the pyrrol ring (cf. formula above) and by the numbers I, 2, 3, 4 
 in the benzene ring ; or by numbering the N atom i and the C atoms successively 
 2 and 3 in the pyrrol ring, and 4, 5, 6, 7 in the benzene ring. Py-i, 2, 3 and 
 Bz-i, 2, 3, 4 are obvious variations. 
 
 The alkylindols are obtained by heating phenylhydrazones of aldehydes or 
 ketones with HC1 or ZnCl 2 , uucleal condensation occurring with evolution of NH 3 . 
 Thus, p-methylindol or sltatol is formed when propionic aldehyde phenylhydrazone 
 is so treated 
 
 C 6 H 5 NH'N : CH'CH 2 -CH 3 = C 6 H 4 / ^CH + NH 3 . 
 
 Skatol is also a product of the pancreatic fermentation of albumin, and is the 
 chief constituent of the volatile portion of human excrement (cr/:ar6s, of dung). It 
 crystallises from hot water in colourless plates, melts at 95, boils at 263 C., and 
 has a faecal odour. Skatol is found among the products of the distillation of 
 strychnine with lime, and in the wood of Celtis reticulosa, a plant of the Nettle- 
 tree order. 
 
 Indoxylic acid is fi-hydroxymdol-ai-car'boxylic acid, and is obtained as its ethyl 
 salt by heating ethyl o-phenylglycocinecarboxylate with sodium ethoxide 
 
 /COOEt /C(OH) 
 
 C 6 H 4 / = C 6 H 4 / \0-COoEt + EtOH. 
 
 x NH-CH 2 C0 2 Et X NH / 
 
 The free acid is obtained by heating the ethyl salt with fused NaOH. dissolving 
 in water and precipitating by acid ; when heated with alkali and air it yields indigo. 
 It is sold as indopJwr for cotton printing, since it is readily converted into indigo 
 by oxidation on the fibre. 
 
 Indoxyl is fi-hydroxyindol and is produced by heating indoxylic acid, which 
 loses CO^ also by heating indigo with KOH in absence of air. It is an oily liquid, 
 soluble in water to a yellow fluorescent solution. In alkaline solution it is easily 
 oxidised to indigo, 2C 8 H 7 ON + 2 = (C 8 H 5 ON) 2 + 2H 2 p. 
 
 The indoxyl derivatives are either from /3-hydroxyindol or the pseudo-form viz., 
 
 /C(OH) 
 '\NH 
 
 or C 6 H 4 
 
 ,00 
 
 NCHg, respectively. The indogenides are deriva- 
 
 tives of the latter form in which the =CH 2 group has condensed with a =00 
 group of an aldehyde or ketone to form a =0 = 0= nucleus. 
 
 Indoxyl occurs in the form of potassium, indoxyl-sulplionate in the urine (urine- 
 indicari) of herbivora. 
 
 OTT 
 
 a.-MethyUndolin, C 6 H 4 / ^CH'CHo, is a liquid boiling at 227 C., obtained by 
 
 X NH X 
 
 reducing a-methylindol with Sn and HOI ; by carrying the reduction further, with 
 HI and P, 0-propylaniline is produced. It will be seen that this compound is a 
 methyl-derivative of dihydroindol, which does not exist ; the oxygenated dihydro- 
 indols, however, are known and are closely related to indigo. They are called 
 indolinones and are lactams of amidophenylacetic acid and its homologues (p. 679). 
 They are also obtained by heating the phenylhydrazides (p. 686) of the acids with 
 lime (see oxindol). 
 
 Oxindol, or a-indoUnone, has been already noticed (p. 679) ; it is produced when 
 acetylphenylhydrazide is heated with lime 
 
 ,CH^ 
 
 C 6 H 3 NH-NH-COCH 3 = C 6 H 4 / X CO + NH 3 . 
 
 X NH X 
 
 It melts at 120 C. and is easily oxidised to diox'mdol or fi-hydroxyoxyindol^ which 
 in its turn may be oxidised to isatin. 
 ret nn 
 
 , is prepared by oxidising indigo with 
 
 nitric or chromic acid. It crystallises in orange-coloured prisms (m.-p. 201 C.), 
 soluble in boiling water and alcohol. When heated, it sublimes with partial 
 decomposition. It dissolves in KOH to a violet solution, and is precipitated again 
 by acids. AgN0 3 added to the potash solution gives a carmine-red crystalline 
 
INDIGO. 76! 
 
 precipitate of silrer imtin C 8 H 4 AgN0 2 . Isatin forms crystalline compounds with 
 NaHb0 3 (like the aldehydes and ketones). It yields aniline when distilled with 
 strong KOH. With chlorine it yields chlorisatin and dichhrrimtin, also formed 
 when chlorine acts on indigo. When these are distilled with KOH, they yield 
 mono- and di-chloraniline. Keducing agents convert isatin into hydro-iaatin or 
 isatide, C 16 H 12 N 2 4 , and then into dioxindol and oxindol. 
 
 Isatin is also produced by treating Q-nitrophenylpropiolic acid with alkali 
 
 /C : C-COOH X CO K 
 
 c e H 4\ = C 6 H 4 / \CO + C0 2 . 
 
 Isatin condenses with indoxyl under action of alkalies to form the isogenide (r. *.) 
 indirubin, an isomeride of indigo ; 
 
 /CO /C 6 H 4 GO C 6 H 
 
 <NH> CH2 + C <CO> H = C6 <NH> : 
 Indoxyl. Isatin. Indirubin. 
 
 4v 
 : <CO> H 
 
 CO 
 
 Isatin reacts with PC1 5 in benzene, yielding isatin chloride, C 6 H 4 / )>CC1, the 
 
 formula for which supports the second formula given above for isatin. When this 
 chloride is reduced it yields indigo-blue. 
 
 565. Indigotin or indigo blue, C 16 H 10 N 2 2 , is prepared from Indigo- 
 fera tinctoria and ccerulea, plants of the same natural order (Leguminosse) 
 as those furnishing the dye-woods described on p. 747, and like the 
 colours obtained from those, it does not exist as such in the plant, but 
 is a product of alteration of a nearly colourless substance termed indican. 
 Woad (I satis tinctoria), a crucifer, also yields indigo. 
 
 Indican may be extracted from the leaves and twigs of the plant by 
 digestion with cold alcohol, which leaves it, when evaporated, as a 
 brown, bitter, syrupy liquid. It appears to be a glucoside of indoxyl 
 and is hydrolysed by fermentation or by boiling dilute acids into indoxyl 
 and a glucose called indiglucin. The indoxyl is rapidly oxidised by the 
 air into indigotin, which forms a blue precipitate 
 
 C 8 H 6 ON(C 6 H U 5 ) + H 2 = C 6 H 12 6 + C 8 H 7 ON 
 Indican. Indoxyl. 
 
 C 6 H 4 < >CH 2 + H 2 C< C >C 6 H 4 + 2 = C 6 H 4 < } >C : C< D >C 6 H 4 + 2 H 2 0. 
 X NIT X NET X NH X X NH X 
 
 Indoxyl. Indoxyl. Indigotin. 
 
 For the preparation of indigo on the large scale, the plants are cut just before 
 they blossom, chopped up, covered with cold water, and allowed to ferment for 
 twelve or fifteen hours, when the indican is hydrolysed as explained above. As 
 soon as a blue scum appears upon the surface, a little lime is added, and the yellow 
 liquid is run into shallow vats and well beaten with sticks to promote the action 
 of air, which oxidises the indoxyl. The indigo-blue is precipitated and collected, 
 on calico strainers, to be pressed and cut up into cakes. As purchased, indigo-blue 
 contains about half its weight of indigotin ; it may be purified by boiling, first, with 
 acetic acid, which extracts a substance termed indigo-yluten, then with weak 
 potash, to extract indigo-brown, and, lastly, for some time with alcohol, wni< 
 removes indigo-red. 
 
 Indigotin may be prepared from commercial indigo by boiling it with 
 aniline, or heating it with melted paraffin ; both solvents deposit the 
 indigotin in dichroic, rhombic crystals on cooling. From hot turpen- 
 tine it crystallises in blue tables and from fused phthahc anhydrid 
 needles 
 
762 ARTIFICIAL INDIGO. 
 
 When commercial indigo is carefully heated, it is converted into a 
 violet vapour, the sp. gr. of which settles the molecular formula for the 
 compound. The vapour condenses in dark blue needles, with a coppery 
 reflection. The best indigo-blue floats upon water. 
 
 Indigotin is insoluble in water, alcohol, ether, and diluted acids and 
 alkalies. Strong sulphuric acid and, more easily, fuming sulphuric acid, 
 dissolve it, forming indigotin-monosulphonic acid, C 16 H 9 (SO 2 'OH)N 2 2 , 
 and indigotin-disulphonic or sulphindylic acid, C^ 
 
 On adding water, a blue precipitate of the mono-acid is obtained, which is soluble 
 in pure water and in alcohol. It in mono-basic, audits concentrated solution gives 
 a purple precipitate of the potassium salt on addition of potassium acetate. The 
 precipitate produced by K 2 C0 3 in the solution of indigo in H 2 SO 4 is known as 
 indigo-carmine, and consists chiefly of potassium sulphlndylate ; it is soluble in 
 water. The sulphonic acids of indigo are bleached by zinc-dust, being converted 
 into the corresponding acids of indigo-white, which become blue again when shaken 
 with air. Sulphindylic or sidphindigotic acid is used in dyeing Saxony blue 
 cloth. 
 
 Indigo-white (leucindigo or hydrindigotin) is prepared by shaking 
 powdered indigo with 2 parts of ferrous sulphate, 3 parts of slaked lime, 
 and 200 parts of water, in a stoppered bottle placed in warm water, till 
 the indigo has dissolved to a yellow liquid, when the calcium sulphate and 
 ferroso-ferric hydroxide are allowed to subside, and the clear solution 
 drawn off into dilute hydrochloric acid in a vessel from which air has 
 been expelled by C0 2 . The hydrindigotin is precipitated in white flakes, 
 which quickly become blue indigo when exposed to air. Other reducing- 
 agents are sometimes substituted for ferrous sulphate in preparing the 
 dyer's indigo-vat. A mixture of indigo, madder, potassium carbonate, 
 and lime, left to ferment, gives an alkaline solution of reduced indigo. 
 Hydrosulphites (p. 237) and lime, or zinc-dust and alkali, are also 
 employed for this purpose, and it has been suggested to apply electro- 
 lysis for the reduction. When linen and cotton are immersed in the 
 indigo-vat and exposed to air, the indigo-white is oxidised to indigo- 
 blue, which is precipitated upon the fabric. Hydrindigotin precipi- 
 tated by acids from its alkaline solutions becomes crystalline after a 
 time ; it is soluble in alcohol and ether. It probably is of the same 
 form as indigotin, but containing OH groups in place of the O atoms. 
 
 When indigo is heated with dilute HN0 3 , it is oxidised into isatin, 
 which gives a yellow solution, and sulphindylic acid is sometimes em- 
 ployed as a test for HNO 3 . By fusion with KOH it is converted, 
 first into potassium anthranilate, and afterwards into aniline, which 
 distils. 
 
 566. Artificial indigo. The unremitting skill and labour which have 
 been concentrated during the last 20 years on the attempt to make 
 indigo from materials the cost of which would be comparable with that 
 of cultivating the indigo plant, have at length succeeded. It may now 
 be said that indigo is made from coal, wood and air, and that the 
 cultivation of the plant is a doomed industry. 
 
 Naphthalene and ammonia from coal, acetic acid from wood and 
 oxygen from air are the immediate raw materials for the manufacture ; 
 sulphuric acid, chlorine, mercury and alkali are used as agents, but 
 these may be recovered and returned to the process. 
 
 The naphthalene is oxidised to phthalic anhydride, which is con- 
 verted by NH 3 into phthalimide. When the latter compound is 
 
MANUFACTURE OF INDIGO. 
 
 acid. This acid is heated with 
 
 The operations are as follows 
 
 i^*^$3^f^SSSA ft** * 
 
 ot 100 Der r.fint. at. o-fh r~ ir mei tui\ with sulphuric acid 
 
 ulphateand aids the reaction ; the 
 
 ph^altofd thallC a " hydride !S treated With NH . d P" -hen it becomes 
 
 . 
 
 (4) The solution of alkali anthranilate thus obtained is boiled for 
 
 (5) This acid is heated with NaOH in a closed vessel at 200 C. until the orange 
 colour no longer increases in intensity. 
 
 Jli 6 ,p f H >h l mas } f' c , ontai . ni /?g indoxyl, is quickly cooled, dissolved in water and 
 ?JUh,S + T 1 : i th ?. solu ^ n to Precipitate indigo ; if the precipitate is too 
 crystalline it is dissolved in sulphuric acid and precipitated by adding water. 
 The following equations explain the chemistry of these processes : 
 CH : CH co 
 
 CH :CH CO 
 
 / CO N CO 
 
 (2) C 6H 4 < co ^O + NH 3 = C 6 H 4 / \NH + H 2 0. 
 
 (3) C 6 H 4 <^\NH + NaOCl + 3 NaOH = C 6 n 4 / C< Na + XaCl + Na. 2 C0 3 
 
 (4) C 6 H 4 / + CH.C1-COOH + Na.CO, = C 6 H C Na 
 
 NH-CH 2 -COONa 
 NaCl + C0 2 + H 2 0. 
 
 (6) The equation for the oxidation of indoxyl has been given above. 
 
 It is probable that the process will shortly be simplified, for it has been found 
 that the product obtained by heating anthranilic acid with a polyatomic alcohol or 
 a carbohydrate and KOH yields indigo when treated with water and oxidised. 
 
 Another promising method consists in heating phenylglycocine, made from ani- 
 line and mono-chloracetic acid, with sodamide. 
 
 567. It is proposed to synthesise indigo from aniline by first heating it with CS 2 
 to produce thiocarbanilide (p. 672) ; the aqueous solution of this is to be heated 
 with white lead and KCN, of which the former appropriates the S, while the latter 
 introduces a cyanogen group, the product being a hydrocyaMOOarbodi^henylvm&de^ 
 which becomes a thioamide by treatment with (NH 4 ) 2 S. The thioamide is to be 
 heated with strong H 2 S0 4 to produce the anilide of isatin. and this is to be reduced 
 with (NH 4 ) 2 S when it yields aniline and indigo : 
 C 6 H 5 NH\ C 6 H 5 NH\ C 6 H 6 NH\ /CO \ 
 
 >CS ; >C'CN ; >C'SNH 2 ; C 6 H 4 < >C:NC',1 1:,. 
 
 CeH^H/ C 6 H 5 N^ C 6 H 5 N ^ \\H X 
 
 Thiocarbanilide. Cyanogen derivative. Thioamide. Isatiu anilide. 
 
764 ANTIPYEINE. 
 
 568. Other methods of synthesising indigo are now only of academic interest* 
 either because the yield is too small or because the raw materials are too costly. 
 
 From aniline it has been synthesised by heating the base with chloracetic acid to 
 produce phenylglycocine, which yields indigo when heated with fused NaOH and 
 afterwards treated with air. The fusion converts the phenylglycocine into 
 indoxyl. 
 
 From benzaldehyde the synthesis is byway of dissolving I : 2-nitrobenzaldehyde 
 in acetone and adding NaOH, whereupon indigotin is precipitated. It is probable 
 that the first action of the acetone and soda is to convert the I : 2-nitrobenzalde- 
 hyde into I : 2-nitrophenyl-lactomethyl Itetone ; C Q H 4 (NO 2 )-CHO + CH 3 -CO'CH 3 = 
 C 6 H 4 (N0 2 )-CH(OH)-CH 2 -CO-CH 3 . This then breaks up into indigotin,' acetic acid 
 and water under further action of NaOH ; 2[C 6 H 4 (N0 2 )-CH(OH)-CH 2 -CO'CH 3 ] = 
 C 16 H 10 N 2 2 + 2CH 3 -C0 2 H + 2H 2 0. The ketone has been sold as its NaHS0 3 compound 
 (p. 625), under the name indigo salt for printing on the fabric, which is then im- 
 mersed in a bath of caustic soda. 
 
 When cinnamic acid is treated with nitric acid, it is converted into nitro- 
 cinnamic acid. This combines directly , with two atoms of bromine, to form 
 dibromo-nitro-pkenyl-propionic acid, C 6 H 4 (N0 2 )'CHBr-CHBrC0 2 H. When this 
 is treated with caustic soda, two molecules of HBr are removed, producing the 
 sodium salt of nitrophenylpropiolic acid, C 6 H 4 (N0 2 )'C : OC0 2 H. By heating this 
 with an alkali and a reducing-agent, it is converted into indigotin. 
 
 569. Dibenzofurfurane (p. 759) is identical with diplienylene oxide and is obtained 
 by distilling phenol with PbO. It melts at 81 and boils at 288 C. 
 
 Dibenzothiophen is diplienylene sulphide, obtained by heating phenyl sulphide ; 
 m.-p. 97, b. p. 333 C. 
 
 Dibenzopyrrol is identical with carbazole (p. 667). 
 
 570. Azoles. Within the last few years a large class of compounds has been dis- 
 covered the members of which are regarded as derived from furfurane, thiophen 
 and pyrrol by substitution of a trivalent N atom for a trivalent CH member of the 
 ring, and are known as mono-, di- or tri-azoles accordingly as i, 2, or 3 of the CH 
 members have been exchanged for N. 
 
 By one system, theazoles are distinguished by the prefixes/wro-, tkio-,&ad.pyrr6a 
 to indicate the parent ring, also by the numbers 2, 3, 4, or 5, or the letters , 1? b, 
 or Z>!, to show which of the four CH members has or have been exchanged. By 
 another system they are classified as oxazoles, thiazoles, and pyrazoles, accordingly 
 as they are allied to furfurane, thiophen, and pyrrol respectively. Condensed azole 
 nuclei, distinguished by the prefix beJizo, are also known (cf. furfurane, <kc., p. 757). 
 Generally speaking, the azoles are products of condensation of aldehydes or 
 ketones with substitution-derivatives of NH 3 or N 2 H 4 , or H 2 NOH. 
 
 CH:N 
 Pyrazole or pyrro-2-azole, ^X^H, is produced by combining acetylene 
 
 CH : GW 
 
 with diazomethane (p. 680), but better by distilling 3:4: ^jyrazole-tricarboxylic 
 acid, made by condensing ethyl diazoacetate with ethyl acetylenedicarboxylate and 
 saponifying. It is a feeble base, melts at 70 C. and boils at 187 C. 
 
 The substituted pyrazoles are nucleal condensation products from the hydrazones 
 of /3-diketones. Thus benzoylacetone-hydrazone yields 1:3: ^-dlphenylmethyl-2- 
 pyrazole : 
 
 C 6 H 5 -C-CH 2 -CO-CH 3 C 6 H 5 -C-CH : C-CH 3 
 
 + H 2 0. 
 
 N NHC 6 H 5 N N-C 6 H 5 
 
 By reduction with Na in alcohol the pyrazoles yield dihydropyrazoles derived 
 
 CH 2 -CH 2 , 
 from >NH, and called pyrazolines. 
 
 CH:N 7 
 Pyrazolones are lietodihydropyr azoles, and are important as including the febri- 
 
 CMe-NMe, 
 fuge antipyrine which is 1:2: '\-phenyldimethylpyrazolone, \NC 6 H 5 , 
 
 CH CO 7 
 
 prepared by first heating ethyl aceto-acetate with phenylhydrazine to produce 
 phenylmethylpyrazolone, which is then heated with CH 3 I in CH 3 OH to introduce 
 the second CH., group ; the alcohol is distilled and the antipyrine precipitated by 
 NaOH. Antipyrine crystallises in white plates, melts at 114 C., dissolves fairly 
 
AZOLES. 
 
 easily in cold water and is a strong base ; its salicylate is sold as taUovrine and 
 the homologue in which tolyl takes the place of phenyl, as tolypyrine ' 
 
 Another very complex pyrazolone derivative is the yellow dyestuff 'tartra-lne 
 The tetrahydropyrazoles are called pyrazolidines, and the corresponding keto- 
 denvatives are py>-azolido)tes. They are unimportant. 
 
 OFT 
 
 The indazoles are benzopyrazoles from the isomeric forms C 6 H 4 /. \NH and 
 
 ,CH, 
 C 6 H 4^ / N > and are so called by analogy with indol, the name given to benzo- 
 
 pyrrol. Indazole itself has the first form and is made by heating o-cinnamic- 
 hydrazide. 
 
 N : CH 
 The glyoxalims are pyrrol-azote, . ^>NH, obtained by condensing 
 
 OTT . OTT/ 
 vyJjL . V^XX 
 
 a-diketones with NH 3 . Several of them, particularly lophin (triphenylglyoxaline) 
 phosphoresce when decomposed by caustic alkali. Lyndine, used as a remedy for 
 gout because of the high solubility of its urate, is a methyldihydroglyoxaline. 
 
 Isoxazole or furo-2-azole, and thiazole or thio-^-azole, \0, and 
 
 /^ITT . OTJ/ 
 
 V^Jl . vyXl 
 
 N : CH, 
 
 >S respectively, yield a number of derivatives. The amidothiazoles, made 
 
 PTT PTT' 
 \ j n . \_ji 
 
 by condensing chloracetone with thiourea, behave like aniline and may be diazo- 
 tised to produce thiazole dyestuffs. 
 
 The true diazoles and triazoles of the pyrrol type have sometimes been mis- 
 called triazoles and tetrazoles respectively, the prefix referring to the total number 
 of N atoms. 
 
 CFT TsT 
 Thus, pyrro-2 : $-diazole, ' \N[H, has been called osotriazole. Its derivatives 
 
 CH:N X 
 are obtained by distilling the osazones of ortho-diketones. 
 
 CH : K N : CH. 
 
 Pyrro-2 : 5 : ^-triazole may be either %NH or . ^>NH, and is also 
 
 known as tetrazole. 
 
 The derivatives of these compounds as also those of the corresponding oxy- and 
 thio-compounds are at present of theoretical interest only 
 
 571. Six-membered heterocyciic compounds. The most impor- 
 tant members of this class are the substances pyridine, quinoline and 
 acridine. These may be regarded as analogous in constitution to ben- 
 zene, naphthalene and anthracene respectively, containing, in each case, 
 N in place of CH. This will be clear from the following formulae : 
 
 H c c c c 
 
 n/ \H K/ 9 \ H HC 9~~ N c CH 
 
 H 
 Pyridine. Quinoline. Acridine. 
 
 Their behaviour towards reagents indicates that they are closed-chain 
 compounds (c/. benzene, p. 527), and a study of their substitution- 
 products shows that the number of position-isomerides which has been 
 prepared is in accord with that prophesied from the above formulae. 
 
766 PYKIDINE. 
 
 An inspection of the formulas shows that there should be three isomeric mono- 
 substituted pyridines, seven isomeric mono-substituted quinolines and five mono- 
 substituted acridities. The orientation is expressed similarly to that of the 
 corresponding hydrocarbons, the N in pyridine and quinoline being i. 
 
 By another system of orientation for pyridine, position 2 = a, 6 = a', 3=/3, 5=/3', 
 and 4 = 7 ; for quinoline 2 = a, 3 = /3, 4 = 7. 
 
 572. Pyridine bases. The destructive distillation of bones yields 
 ammonia and other bases, produced by the decomposition of the bone- 
 gelatine, or ossein, which forms about 30 per cent, of the bones, and 
 contains about 18 per cent, of nitrogen. These bases form an homo- 
 logous series, of which pyridine is the first member ; many of them are 
 also found in coal-tar. They are liquids of disagreeable odour, and are 
 tertiary monamines (p. 658). They may be extracted from the offensive 
 oil known as DippeVs animal oil, obtained by distilling bones, by 
 shaking it with warm dilute H 2 S0 4 , which dissolves the bases as 
 sulphates, and yields them up on adding alkali. They are separated by 
 fractional distillation. Their solubility in water decreases with the 
 increase of C atoms and is generally greater in cold water than in hot. 
 
 Pyridine . . C 5 H 5 N ... 115 C. 
 
 Picoline . . C 6 H 7 N ... 130 
 
 Lutidine . . C 7 H 9 N ... 142 
 
 Collidine . . C 8 H n N... 179 
 
 Parvoline . . C 9 H 13 N ... 188 C. 
 
 Coridine . . C 10 H 15 N ... 211 
 
 Kubidine . . C n H 17 N ... 230 
 
 Viridine . . C 12 H ]9 N ... 251 
 
 Pyridine bases are often present in commercial ammonia, and cause 
 it to become pink when neutralised with hydrochloric acid. 
 
 Like other tertiary amines the pyridines combine with alkyl iodides to form 
 alkylpyridinium iodides, e.g., C 5 H 5 N'CH 3 I, and when these are heated they become 
 alkyl-substituted pyridines, e.g., C 5 H 4 (CH 3 )N'HI, a behaviour similar to that of 
 alkylanilines (p. 664). 
 
 Pyridine is a colourless liquid which is soluble in water ; it forms a deliquescent 
 hydrochloride, C 5 H 5 N'HC1, the solution of which is precipitated by HgCl 2 , K 4 FeCy 6 
 and PtCl 4 . By the action of sodium in alcohol, pyridine is hydrogenised to liexa- 
 hydro-pyridine, C 5 H n ]Sr, which is identical with piperidine (r.-/.) and may be 
 reconverted into pyridine by heating at 300 C. with H 2 S0 4 
 
 C 6 H n N + 3H 2 S0 4 = C 5 H 5 N + 3S0 2 + 6H 2 0. 
 
 This conversion of pyridine into piperidine establishes the constitution of the 
 former, that of the latter being known. Pyridine is obtained by heating amyl 
 nitrate with P 2 5 , which removes the elements of water ; C 5 H n N0 3 = 3H 2 + C 5 H 5 N. 
 It is also formed when a mixture of hydrocyanic acid and acetylene is passed 
 through a red-hot tube, HCN + 2C 2 H 2 = C 5 H 5 N. Like benzene, pyridine resists 
 oxidation in high degree. 
 
 Pyridine has been suggested as a remedy for asthma ; on the Continent it is used 
 for denaturing alcohol. 
 
 The alkylpyridines may be obtained by distilling the aldehyde-ammonias, either 
 by themselves or with aldehydes or ketones. Thus acrolein-ammonia yields 
 ^-methylpyridine {picoline), which is also obtained by heating glyceryl tribromide 
 in a sealed tube at 250 C. with alcoholic NH 3 ; 2C 3 H 5 Br 3 + NH 3 = 6HBr + C 6 H 7 N. 
 
 The alkylpyridines are readily oxidised to pyridinecarboxylic acids. 
 
 // ydroxy-py ridin 
 they are really phenolic or ketonic compounds (pyridones ; cf. phloroglucol, p. 716). 
 
 The hydroxy -pyridines behave in a manner which leaves it doubtful whether 
 
 Hexahydropyridine or piperidine, C 5 H n N, obtained by reducing pyridine with 
 Na and boiling alcohol, or electrolytically, maybe regarded as pentamethylencimlde, 
 for it is obtained by distilling the hydrochloride of pentamethylene diamine 
 CH.-OH.-NH, m CH /CH 2 -CH + 
 
 X CH 2 -CH 2 'NH 2 X CH 2 'CH/ 
 
 It is a secondary amine, boiling at 106 C., smelling of pepper and NH 3 , soluble in 
 water and forming crystalline salts (cf. piperine). It combines with alkyl iodides 
 to form alkylpiperidinium iodides. 
 
QUINOLINE. 
 
 573. Quinoline bases -These may be regarded as benzo-pyridrnes. 
 They occur in bone oil and in coal-tar, and are products of the distilla 
 tion of many alkaloids with KOH. They form an homologous series 
 qmnolme being the lowest member : Quinoline, CHN- levidin, 
 C 9 H 6 (CH 3 )N ; cryptidine, C 9 H 5 (CH 3 ) 9 N. 
 
 The qumolme bases are synthetically prepared (Skraup's method) 
 by heating aniline and its homologues with glycerine, a debydrating- 
 agent (cone. H 2 S0 4 ) and an oxidant (nitrobenzene/ ; 
 
 H CH H 
 
 C 6 H 4 + >CH(OH) + = C 6 H 4 / 
 
 X XH 2 CH 2 (OH/ x N : CH 
 
 This synthesis shows that the N atom in quinoline must be attached to a benzene 
 nucleus ; that it occurs in a pyridine ring is proved by the fact that when quino- 
 Hn ^/?^ i j? d . "7 th KMn0 ^' 5:6-pyridine dicarboxylic acid ( f/ uhw/i /t ir ami). 
 G 6 H 3 (CO 2 H) 2 N, is formed (cf. the deduction drawn concerning the constitution of 
 naphthalene from the oxidation of the hydrocarbon to phthalic acid). 
 
 Quinoline, or cliinoUne, is prepared by the action of H 2 S0 4 (50 parts) and nitro- 
 benzene (12 parts) upon aniline (19 parts) and glycerine (60 parts). The mixture 
 is cautiously heated at 130 C. in a flask with a reflux condenser, the lamp being 
 removed when the reaction begins ; it is then again heated for three hours, and 
 distilled with lime, when quinoline distils over together with aniline ; the latter is 
 converted into phenol by the diazo-reaction (p. 681) and the mixture again dis- 
 tilled with alkali when quinoline passes over. It is a colourless liquid of tarry 
 smell, of sp. gr. 1.09 and boiling-point 239 C. It is sparingly soluble in water, and 
 is a tertiary amine ; it forms a sparingly soluble chromate. It combines with alkyl 
 iodides to form alkylquinotinium iodides which, when heated with potash, yield 
 blue dyestuffs termed cyanines, used in orthochromatic photography. Quinolinic 
 derivatives are very numerous ; a few only can be considered. 
 
 2-HcthylquinoUne or quinaldine (b.-p. 247 C.) is synthesised by boiling paral- 
 dehyde and aniline with HC1. By substituting other aldehydes for paraldehyde, 
 the reaction becomes a general one for preparing alkylquinolines. ^-Methylquiiw- 
 line or lepidine boils at 257 C. Both occur in coal-tar and the CH 3 group in each 
 shows a remarkable tendency to react with aldehydic and ketonic compounds. 
 Quinaldine combines in this manner with phthalic anhydride, forming qu'uto1iiu> 
 yellow, a dyestuff, (C 9 H 6 N)CH : (C 2 2 )C 6 H 4 . 
 
 Carbostyril is 2-Jiydrojcy -quinoline and is prepared by dehydrating o-amido- 
 
 /CH : CH-C0 2 H CH : CH 
 
 cinnamic acid, C 6 H 4 < ' = C 8 H,< +H 2 0, and by tivatin- 
 
 X NH 2 x N : C(OH) 
 
 acetamidobenzaldehyde with NaOH. It melts at 199 C. 
 
 The tetrahydroquinolvnes, C 9 H n Isr, are produced by reducing the quinolines with 
 nascent H. They behave like fatty amines, readily forming nitroso- and di;i/.<>- 
 derivatives. That obtained by reducing carbostyril boils at 224 C. and yields with 
 methyl iodide the compound kairolin, C 9 H 10 N'CH 3 , the hydroxy-derivative of which 
 is Itairine, C 9 H 9 (OH)N-CH S ; these two substances and thaliine, C 9 H 9 (OCH 3 )NH 
 are used as substitutes for quinine. 
 
 574. Isoquinolines yield 4 : 5-pyridine-dicarboxylic acid when oxidised, showing 
 
 CH:CH 
 
 that the N atom is in the 2-position of the naphthalene ring, C 6 H 4 / . 
 
 X Cfl :N 
 
 Isoquinoline accompanies the quinoline from coal-tar and is separated therefrom 
 by fractionally crystallising the sulphates. It melts at 23 C. and boils at 24O'5 C. 
 When a mixture of it with quinaldine is treated with benzotrichloride, quinoline red, 
 a dyestuff used in making orthochromatic photographic films, is obtained (cf. method 
 of making malachite green, p. 722). 
 
 Napkthoquinoline, C 13 H 9 N, and anthraquinoline, C 17 H n N, are obtained by sub- 
 stituting naphthylamine and amidoanthracene, respectively, for aniline in 8knnp'l 
 reaction (see above). When m- or^-phenylenediamine is the amine used, a j>lientin- 
 throline, C 12 H 8 N 2J is the product. These compounds are bases similar to quino- 
 line and of complex constitution which cannot be discussed here. Alisorifie l>h>r 
 
768 
 
 LAUTH'S VIOLET. 
 
 is a dihydroxyanthraquinoline obtained by applying Skraup's reaction to 
 w-amidoalizarin. 
 
 C 6 H 4 -CH 
 Phenanthridine, , bears the same relationship to phenanthrene (p. 554), 
 
 C 6 H 4 -N 
 
 that quinoline bears to naphthalene, and is obtained by heating benzylideneaniline* 
 C 6 H 5 CH : NC 6 H 5 . It melts at 104 C. 
 
 575. Acridine bases. Acridine, C 13 H 9 lSr, occurs in crude anthracene, from which 
 it is extracted by dilute acids, yielding a fluorescent solution ; potassium bichro- 
 mate precipitates it. It forms colourless needles, readily sublimes and has a very 
 irritating vapour. It is a feebler base than pyridine and quinoline, but, like these, 
 combines with alkyl iodides to form acridlnium derivatives. The synthesis that 
 establishes the constitution of acridine is from diphenylamine and formic acid by 
 heating with ZnCl 2 ; formt/ldiphenylamine is first formed and then loses H 2 : 
 
 CHO CH 
 
 C 6 H 5X ^ ^H, = C 6 H 4 /^ \C 6 H 4 + H 2 0. 
 
 The dyestuff chrymniline or phosphine, obtained as a by-product in making aniline, 
 is meso-p-amidop/ienyl-2-amidoacridine. Acridine yellow and benzqflavine are also 
 dyestuffs of this series. 
 
 576. Azines. Just as the azoles (p. 764) may be regarded as derived from the 
 N-, 0-, and S- five-membered heterocyclic rings, by substituting an N atom for a 
 CH group, so the azines are derived by a similar substitution from the six-membered 
 heterocyclic rings. They are either oxazines. thiazines, or diazines (also triazines 
 and tetr azines) accordingly as they contain and N, S and N, or N alone. They 
 are further distinguished by the prefixes ortho-, meta-, and para- accordingly as the 
 and N, S and N, or N and N are in the I : 2, I : 3 or I : 4 positions to each other 
 respectively. Very few of these numerous compounds can be mentioned here. 
 
 
 Phenoxazine is a dibenzoparoxazine, C 6 H 4 / \C 6 H 4 , produced by heating o- 
 
 NH 
 
 amidophenol with pyrocatechol ; it melts at 148 C. and only deserves notice as the 
 progenitor of the dyestuffs resorujine,* : C 6 H 3 : [NO] : C 6 H 3 OH, obtained by 
 heating resorcinol with nitrosophenol and an oxidant to remove H 2 , and gallo- 
 cyanine, a more complex derivative made by heating gallic acid with nitrosodi- 
 methylaniline ; the former dyes red, the latter violet. 
 
 NH 
 To the dibenzoparathiazines belongs thio-diphenylamine, C 6 H 4 <^ \C 6 H 4 , the 
 
 product of heating diphenylamine with sulphur. It melts at 180 C. and is the 
 parent substance of the diphenylamine dyes ; thus, by oxidising paraphenylene- 
 diamine in presence of H 2 S is obtained LautWs violet or thionine, 
 
 NH 2 -C 6 H 3 / N ^C 6 H 3 : NH. 
 
 S 
 
 The tetramethyl derivative of this thionine is methylene blue, N(CH 3 ) 2 'C 6 H 3 : [NS] 
 : C 6 H 3 : N(CH 3 ) 2 C1, obtained by treating dimethylaniline hydrochloride with 
 sodium nitrite and reducing the isonitroso-dimethylaniline (p. 664) with H 2 S ; the 
 dlmethyl-para-plienylenedianiirie, C 6 H 4 (NH 2 )'N(CH 3 ) 2 , thus produced is then 
 oxidised by Fe 2 Cl 6 in presence of the excess of H 2 S ; the blue solution is next satu- 
 rated with NaCl, and ZnCl 2 is added to precipitate the ZnCl 2 compound of the dye- 
 stuff, which forms bronze-green crystals, soluble in cold water to a fine blue liquid, 
 from which the colour is fixed on cotton with a tannin mordant. The produc- 
 tion of methylene wliite, C 12 H 7 (CH 3 ) 4 N 3 S, by the action of reducing-agents has led to 
 the use of methylene blue for measuring the reducing power of different portions 
 of the body. The formation of the blue is one of the most delicate tests for H 2 S 
 in solution ; the liquid to be tested is mixed with excess of HC1, a little dimethyl- 
 para-phenylene diamine sulphate added, followed by a drop of Fe 2 CL. 
 
 CH:N-CH 
 The simplest metadlazine is pyrimidine, , a soluble base melting at 
 
 CH : CH-N 
 
 * It will be noticed that thes3 dyestuffs are represented as containing' quinonoid linking 
 (p. 721). 
 
INDULINES AND SAFRANINES. 769 
 
 21 C. and boiling at 124 C. The pyrimidines are obtained by heating fl-diketon 
 with amidmes ; they are also products of the polymerisation of alkyl cyanides bv 
 150 C., and were originally called cyanalkines. Thus ***** 
 
 (CH 3 CN) 3 , from methylcyamde is constitutionally dimetkylamidopyrim&iw \ it is 
 a crystalline base having a bitter taste and soluble in water. 
 
 CH N 
 The lenzonietadiazines are derivatives of quinazoline, C 6 H 4 / ' not it- 
 
 X N :CH 5 
 
 self known ; its a-methyl derivative is produced by treating o-amidobenzaldevhde 
 with NH 3 ; it melts at 35 C. and boils at 238 C. " 
 
 The paradlazines are derived from pyrazine, .. , obtained bv distilling 
 
 CH : N-CH 
 
 amidoacetaldehyde with HgCl 2 solution. It melts at 55 and boils at 115 C., but 
 sublimes at the ordinary temperature and smells of heliotrope. Hexahydropyra- 
 zine, C 4 H 10 N 2 , is called piperazlne from its analogy to piperidine; it is a remedy for 
 gout. 
 
 N C FT 
 Quinoxaline is a lenzoparadiazine, C 6 H 4 / J , obtained by heating glyoxal 
 
 N : CH 
 CHOCHO. with orthophenylenediamine ; m.-p. 27 ; b.-p. 229 C. 
 
 Phenazine is a dilenzoparadiazine, C 6 H 4 / . \C 6 H 4 , obtained by condensing 
 
 o-phenylenediamine with pyrocatechol, 2H 2 and H 2 being lost. It crystallises in 
 yellow needles, melting at 171 C. Several important dyestuffs belong to this class ; 
 thus the red fluorescent dyestuffs called eur /iodines are amido-derivatives of 
 naphthophenazine, C 6 H 4 [N 2 ]C 10 H 6 , while the eurhodoles are corresponding hydroxy- 
 derivatives. Toluylene red, is dimethyldiamidotoluphenazlne, 
 
 NH 2 C 6 H 2 (CH 3 )[N 2 ]C 6 H 3 N(CH 3 ) 2 . 
 
 The indulines and safranines are dyestuffs which may be regarded as derived 
 from azoniums, i.e., the ammonium bases corresponding with the tertiary amines, 
 the azines, such as C 6 H 4 : [N'NCH 3 C1] : C 6 H 4 . The indulines are mostly blue dye- 
 stuffs made by heating ^-amido-azo-compounds with monamines and an acid, 
 thus 
 
 NK,C 6 H 4 N : NC 6 H 5 + H 2 NC 6 H 5 = NH : C 6 H 3 ^ ~)C 6 H 4 + NH 3 + H 2 . 
 
 They are of three kinds ; the benzindulenes, having the above formula derived from 
 phenazine ; the rosindulenes, derived from naphthophenazine ; and the naphthin- 
 dulines, derived from naphthazine, C 10 H 6 [N 2 ]C 10 H 6 . 
 
 The safranines are diamido-derivatives of the azonium salts and maybe classified 
 like the indulines. Tolusafranine, NH 2 C 6 H 2 (CH 3 ) : [N'N(C 2 H 5 )C1] : C 6 H 3 NH 2 , 
 the commercial red dyestuff called safranine, is made by oxidising a mixture of 
 >-toluylenediamine, o-toluidine and aniline. 
 
 577. Pyrone, O/ No, is the only other six-membered ring to which 
 
 N/~1TT . /^TT/ 
 
 Uxl . Uil 
 
 attention can be called ; it is a neutral substance obtained by heating comanic 
 acid, C 5 H 3 2 'C0 2 H. See meconic acid (p. 622). 
 
 URIC ACID AND THE ALKALOIDS. 
 
 578. Uric acid and its derivatives. Although these are strictly 
 heteronucleal compounds, they are more nearly related to open-chain 
 compounds than are the substances just considered ; however, their 
 connection with the vegetable bases, originally all classed together as 
 alkaloids, warrants their discussion at this place. 
 
 Uric acid, or lithic acid, C 5 H 4 N 4 3 , or C 2 (CO) 3 (NH) 4 . Uric acid is 
 generally prepared from the excrement of the boa-constrictor (serpent's 
 
UKIC ACID. 
 
 urine from the Zoological Gardens), which consists chiefly of acid 
 ammonium urate, H(NH 4 )C 3 H 2 N 4 O 3 ; this is dissolved by boiling with 
 dilute potash, which expels NH 3 , and converts it into normal potassium 
 urate, K 2 C 5 H 2 N 4 3 ; by passing C0 2 through this, the sparingly soluble 
 add potassium urate, HKC 5 H 2 N 4 3 , is precipitated ; this is washed, 
 dissolved in hot water, and decomposed by HC1, which precipitates the 
 uric acid. Human urine also yields uric acid in small crystals when 
 concentrated by evaporation, mixed hot with a little HC1, and set aside ; 
 the crystals are much tinged with urinary colouring-matter, and may 
 be purified by dissolving in potash and treating as above ; healthy urine 
 yields, at most, one thousandth, by weight, of the acid. 
 
 Guano, the partly decomposed excrement of sea-birds, contains much 
 uric acid, which may be extracted from it by boiling it with a5-per-cent. 
 solution of borax, and adding HC1 to the filtered solution. 
 
 Uric acid is a white crystalline powder, appearing under the micro- 
 scope in peculiar modifications of the rhombic prism. It is very 
 sparingly soluble in water, requiring 1800 parts of boiling water and 
 14,000 parts of cold water; and it is insoluble in alcohol and ether, but 
 dissolves in glycerine and in alkaline liquids. 
 
 When heated, it is carbonised and decomposed, emitting odours of NH 3 and 
 HCN ; urea and cyanuric acid are also found among the products. Strong H 2 S0 4 , 
 heated with uric acid, dissolves it without blackening, and, on cooling, deposits 
 crystals containing 2H 2 S0 4 ; water separates uric acid from them. Nitric acid 
 dissolves uric acid easily when gently warmed, effervescing from escape of N, C0 2 , 
 and oxides of nitrogen. On evaporating the solution, the yellow residue becomes 
 red when further heated. This residue is a mixture of several oxidation-products 
 of uric acid, and assumes fine purple colours when treated with NH 3 or KOH 
 (murexide test). Uric acid is a reducing-agent ; it precipitates cuprous oxide from 
 alkaline cupric solutions, and reduces silver nitrate to the metallic state, if a little 
 Na 2 C0 3 is added. 
 
 When uric acid is heated with strong hydriodic acid in a sealed tube 
 to i6o-i7o C., it yields glycocine, CH 2 NH 2 'C0 2 H, and the products 
 of decomposition of urea, viz., NH 3 and C0 2 . Conversely, if glycocine 
 be heated with excess of urea to 230, uric acid is formed 
 
 CH 2 NH 2 'C0 2 H + 3 CO(NH 2 ) 2 = C 2 (CO) 3 (NH) 4 + 3 NH 8 + 2 H 2 0. 
 
 Urea is found among the products of distillation and oxidation of 
 uric acid. The acid character of uric acid is feeble, and its salts are, for 
 the most parb, sparingly soluble; it is dibasic. 
 
 Acid sodium urate, HNaC 5 H 2 N 4 3 , occurs in the gouty concretions termed chalk- 
 stones, and sometimes as a deposit from urine. 
 
 The acid ammonium urate is the buff or pink deposit so often formed in urine on 
 cooling ; it disappears on gently_ warming ; the colour does not belong to the salt 
 itself. Acid lithium urate, HLiU, is the most soluble urate, requiring 370 parts of 
 cold and 40 parts of boiling water, whilst the sodium salt requires uoo parts cold 
 and 124 parts boiling, and the ammonium salt requires 1600 parts of cold water. 
 
 Uric acid and urates are very common constituents of urinary calculi. They are 
 also found in minute quantity in blood and some other animal fluids, and in the 
 .solid parts of some animals. 
 
 There is no evidence that uric acid contains *COOH groups, or even 
 OH groups ; it probably owes its acid character to the presence of : NH 
 groups, which, as has been already explained (p. 669), impart acid 
 properties to compounds containing them. When lead urate is heated 
 with methyl iodide, dimethyl uric acid, containing two methyl groups 
 in place of two H atoms, is obtained. This is also a dibasic acid, 
 
PURINE. 
 
 showing that it must still contain two NH groups, and when its 
 lead salt is heated with methyl iodide, tetramethyluric acid is obtained. 
 When these methyl uric acids are decomposed, the N appears as 
 methylamme ; hence each of the methyl groups is directly united to 
 a nitrogen atom, in which case there must have been four NH 
 groups in the original uric acid. The various decompositions of uric 
 acid, described below, indicate that it contains three carbon atoms 
 directly united, and that at least two of its NH groups must be attached 
 directly to a CO group (for urea, 00(NH 2 ) 2 , is a product of its decom- 
 position). These considerations have led to the structural formula for 
 uric acid 
 
 /NH-COONEL 
 CO/ \CO. 
 
 X NH - C-NB/ 
 
 This formula represents uric acid as a diureide, a ureide being a com- 
 pound which may be supposed to be formed by condensation of urea 
 with a dibasic acid. Thus parabanic acid (v.i.) may be regarded as 
 formed from urea and oxalic acid : 
 
 NH 2 COOH NH-CO 
 
 C NH 2 + COOH NH-CO 
 
 It will be seen that uric acid contains two urea residues, but the acid of 
 which it is a diureide is not known. The view is supported, however, 
 by the fact that most of its derivatives are of the ureide form. 
 
 /N : CH-ONEL 
 
 579. Purine, CH/ .. ^ CH > is obtained from uric acid by treating it 
 
 with POC1 3 whereby it becomes trichloropurine, which yields successively diiodo- 
 2)ii fine and purine when treated with HI and Zn-dust. It melts at 216 C., is very 
 soluble in water and is both an acid and a base. The orientation of the nucleus 
 
 1657 
 common to uric acid and purine will be understood from the scheme 2 
 
 3 49 
 
 580. When uric acid is added by degrees to strong nitric acid, it dissolves with 
 effervescence, caused by liberation of C0 2 and N, and the liquid becomes hot. On 
 
 /NH-CO V 
 
 cooling, it deposits octahedral crystals of alloxan, C0< >CO, or mesoxalyl- 
 
 X - X 
 
 urea, which stains the skin pink, and gives an intense purple colour with ferrous 
 sulphate and a trace of potash. The octahedral crystals contain lAq, but it may 
 be crystallised in prisms with 4Aq. 
 
 When alloxan is boiled with baryta-water, it deposits the barium salt of 
 alloxanic acid ; C 3 3 (NH) 2 CO + H 2 = NHa'CO'NH'COOl-OOOH, If the boiling be 
 long continued, the products are urea and (the barium salt of) mesoxalic acid 
 
 NHa-CO-NHtCOVCOaH + 2HOH = CO(NH 2 ) 2 + C(OH) 2 (C0 2 H) 2 . 
 By hydrogenising alloxan by passing H 2 S through its boiling solution, it is converted 
 into dialuric acid, or tartromjl-urea, CO/ \CHOH. Dialuric acid crystal- 
 
 Uses in needles which absorb oxygen when exposed to air, and are converted into 
 alloxa-ntin, C 8 H 4 N 4 7 , with loss of 2H 2 0. This body is also precipitated together 
 with sulphur, when H 2 S is passed into a cold solution of alloxan, when the d 
 acid formed at first reacts with the excess of alloxan, and the alloxantm, being 
 nearly insoluble in cold water, is removed from the further action of t H 2 b. 
 
 Alloxantin is precipitated on mixing solutions of alloxan and dialuric acid 
 that it is a diureide formed from these two ureides by loss of one mol. H 2 O. When 
 
772 OXALUPJC ACID. 
 
 uric acid is dissolved in hot dilute nitric acid, alloxantin is the chief product, and 
 its preparation may be combined with that of alloxan by treating the cooled 
 mother-liquor from the alloxan with H 2 S, and boiling the precipitate with 
 water, which extracts the alloxantin and deposits it, on cooling, in prisms con- 
 taining 3Aq. It has an acid reaction, and produces a fine violet precipitate with 
 baryta-water, which is bleached by boiling, being converted into the alloxanate 
 and dialurate. Ferric chloride and a trace of ammonia give a blue colour with 
 alloxantin. It becomes red when exposed to air containing ammonia. On 
 adding ammonium chloride to a hot saturated solution of alloxantin, it becomes 
 first purple and then colourless, depositing a crystalline precipitate of uramil 
 
 /NH-CCK 
 (murexari) or dialuramide. C0< >CHNH 2 , and leaving alloxan in solution. 
 
 If an ammoniacal solution of uramil be mixed with an ammoniacal solution of 
 alloxan, a purple solution is formed which deposits crystals, with a green 
 metallic lustre, of murexide, or acid ammonium purpurate, NH 4 .C 8 H 4 N 5 6 .H 2 0, 
 the constitution of which is uncertain, but the formula is the sum of one mole- 
 cule of uramil, one of alloxan, and one of ammonia. Since alloxan and uramil 
 are both produced when uric acid is evaporated with nitric acid, it is easy to 
 account for the purple colour produced by treating the residue with ammonia. 
 
 Murexide is also formed by heating alloxantin to 100 C. in a current of 
 ammonia-gas, when water is eliminated, and by boiling uramil with water and 
 HgO, when an atom of oxygen from the latter acts on 2 mol. of uramil, yielding 
 murexide and water. Murexide is sparingly soluble in cold water, and insoluble 
 in alcohol and ether. Potash dissolves it with a rich purple colour. Acids bleach 
 it, apparently producing uramil. 
 
 When alloxantin is heated with strong H 2 S0 4 , at 100 C., as long as S0 2 is 
 evolved, it is converted into barbituric acid, or malonyl-urea, which is also obtained 
 synthetically by heating urea with nialonic acid and phosphorus oxy chloride 
 
 /CO-NIL 
 3CH 2 (CO-OH) 2 + 3CO(NH 2 ) 2 + 2POC1 3 = 3CH 2 / \CO + 2PO(OH) 3 + 6HCI. 
 
 L/L/-N xi 
 
 Barbituric acid is sparingly soluble in cold water. "When boiled with alkalies, it 
 yields malonic acid and urea. Amido-barbituric acid is identical with uramil. 
 
 /NH'CO 
 
 Parabanic acid, or oxalyl-urea, C0< , is the chief product of the more 
 
 X NH-CO 
 
 violent oxidation of uric acid, and is prepared by gradually adding uric acid to 
 6 parts of HN0 3 (sp. gr. 1.3) at 70 C., evaporating to dryness on the steam-bath, 
 and re-crystallising from water. It forms prisms which are strongly acid, .dissolve 
 in alcohol, but not in ether. It is a dibasic acid ; its solution gives, with silver 
 nitrate, a characteristic crystalline precipitate of CO:N 2 Ag 2 (C 2 2 ).H 2 O. When 
 boiled with dilute acids, parabanic acid yields urea and oxalic acid, and it may be 
 synthesized from these substances in the presence of phosphorus oxychloride. 
 Most oxidising-agents convert uric into parabanic acid. 
 
 Oxaluric acid, NH 2 'CONH'COC0 2 H, is formed when parabanic acid is boiled 
 with NH 3 , ammonium oxalurate crystallising in needles after cooling. If these be 
 dissolved in hot water, HC1 precipitates oxaluric acid as a crystalline powder. 
 This acid has the same relation to parabanic acid as alloxanic acid has to alloxan 
 
 Alloxan . . N 2 H 2 (CO) 4 I Parabanic acid . N 2 H 2 (CO) 3 
 
 Alloxanic acid . N 2 H 3 (CO) 3 'C0 2 H | Oxaluric acid . . N 2 H 3 (CO) 2 -C0 2 H 
 
 A small quantity of ammonium oxalurate may be extracted from urine by 
 animal charcoal ; after having served for the filtration of a large volume of urine, 
 the charcoal is well washed with water, and boiled with alcohol, which leaves the 
 oxalurate mixed with colouring-matter, when evaporated. 
 
 Oxaluramide, N 2 H 3 (CO) 2 'CO']SI"H 2 , is metameric with ammonium parabanate, 
 CO-N 2 H(NH 4 )-C 2 2 , and is obtained by heating that salt to 100 C. 
 
 Dimethyl-parabanle acid, CO-N 2 (CH 3 ) 2 'C 2 2 , or cholestrophane, is formed when 
 silver parabanate is heated with methyl iodide. It is interesting from having 
 been originally obtained by the oxidation of caffeine (see Caffeine). 
 
 The principal immediate products of the oxidation of uric acid in solution 
 have been seen to be alloxan, parabanic acid, and urea ; but, when an alkaline 
 
SYNTHESIS OF URIC ACID. 
 
 * ^^afstWA 
 
 be precipitated by HC1 ; C^^+zttM+T^C H$? ""' 
 
 ija^iK^^ 
 
 C^ACalZMNMtM) + 2(CN-NH 2 )(^m^) J?aSSSS ftowioooun 4- O 
 
 Some alloxan is formed at the same time by the J^^^IEU^ 
 antm, which thus serves as the necessary reducing-agent 
 
 Uric acid has been synthesised by the following reactions : 
 
 Action of urea on ethyl aceto-acetate yields methyl uracyl 
 
 NJTCO 
 
 Action of HN0 3 on this yields nitrouracylcarboxylic acid CO/ NH C(C 
 
 X NH-CO 
 
 By heating with lime this yields nitrouracyl . CO/ N H 
 
 X NH-CO X 
 
 NH' 
 
 By reduction this yields isobarbituric acid . . . CO/ 
 
 X NH-CO 
 
 NTT 'POTT 
 
 By oxidation this yields isodialuric acid . . . CO/ 
 
 X NH-CO- X 
 which yields uric acid when warmed with urea and H 2 S0 4 . 
 
 581. Theoretically, the parent of uric acid is purine (p. 771), from which are also 
 derived the bases 
 
 c HH.COC.NH HN :C 
 
 X NH - ON 4 NH _ C-N 
 
 Xanthine. Guaniue. 
 
 c NH-CO.C.NH 
 
 ^N -- C-N ^ ^N ____ C-N '' 
 
 Hypoxanthine. Adenine. 
 
 These, like uric acid, are products of degradation of the animal organism and are 
 also present in some vegetable products, such as the juice of the beet root. They 
 are all obtainable from uric acid through trichloropurine (r. purine, p. 771), which 
 yields these four bases by different reactions. Guanine is converted into xanthine 
 and adenine into hypoxanthine by HN0 2 . 
 
 Guanine, C 5 H 5 N 5 0, is extracted from guano (the excrement of sea-fowl) by 
 boiling it with lime and water, and boiling the undissolved residue with NaOH, 
 which dissolves the guanine and uric acid ; these are precipitated by acetic acid, 
 and the guanine dissolved out by hydrochloric acid, and precipitated by NH 3 . It 
 is amorphous, insoluble in water and alcohol, and is at once a feeble di-acid base 
 and dibasic acid. It gives the murexide reaction, and when oxidised by KC10 3 and 
 HC1, it yields C0 2 , parabanic acid, and guanidine 
 
 C 5 H 5 N 5 + 3 + H 2 = C0 2 + C 3 H 2 N 2 3 + C(NH)(NH 2 )2. 
 
 Guanine is found in the pancreas of the horse, in gouty deposits in pigs, in the 
 excrement of spiders and the scales of bleak. It is formed, together with xan- 
 thine and sarcine, when yeast is allowed to decompose in water at 35 C. 
 
774 ALKALOIDS. 
 
 Xanthine, C 5 H 4 N 4 2 , is prepared by the action of nitrous acid on guanine ; 
 C 5 H 5 N 5 + HN0 2 = C 5 H 4 N 4 2 + H 2 + N 2 . It forms minute white crystals sparingly 
 soluble in water, insoluble in alcohol, dissolved by alkalies, and reprecipitated by 
 acids. It gives the murexide reaction. Its crystalline salts with acids are decom- 
 posed by water. Its ammoniacal solution yields, with AgN0 3 , a gelatinous 
 precipitate containing C 5 H 2 Ag 2 N 4 2 .H 2 0, which, when treated with CH 3 I, yields 
 theobromine (q.r.). 
 
 Xanthine occurs in certain rare urinary calculi, and, in small quantity, in urine, 
 in the liver, pancreas, spleen, and brain ; also in guano and yeast. 
 
 Sarcine, or hypoxanthine, C 5 H 4 N 4 0, exists in extract of meat, amounting to about 
 0.6 per cent., and may be precipiated from the mother-liquor of the extraction 
 of creatine (p. ^676) by boiling with cupric acetate. The brown precipitate is 
 dissolved in HN0 3 and precipitated by AgN0 3 , which forms an insoluble compound 
 from which the sarcine may be extracted by decomposing with H 2 S and boiling 
 with much water. It crystallises in minute needles, and is more soluble than 
 xanthine, though it forms a less soluble hydrochloride. It is feebly basic arid 
 acid. Nitric acid oxidises it to xanthine. Sarcine is generally found together 
 with xanthine, and occurs in many parts of the animal body, especially in marrow. 
 
 Adenine, C 5 H 5 N 5 , found in the pancreas of the ox and in tea, crystallises in 
 lustrous laminae (with 3H 2 0) and is soluble in water. 
 
 Gamine, C 7 H 8 N 4 3 , is also found in extract of meat, and much resembles 
 xanthine and sarcine. Nitric acid or bromine-water oxidises it to sarcine. 
 
 582. The Alkaloids. These compounds possess particular interest 
 for the chemist, on account of their powerful action on the animal 
 economy, many of them being the active principles of the medicinal or 
 poisonous plants from which they are extracted. Hitherto few of them 
 have been prepared artificially, though the study of their properties in- 
 dicates that they are ammonia-derivatives. They all contain nitrogen, 
 but rarely more than two atoms in a molecule, though there may be 
 twenty or thirty carbon-atoms ; they all contain oxygen with the excep- 
 tion of coniine, nicotine, and sparteine, which are volatile liquids. 
 Most of them refuse to sublime without partial decomposition, which 
 unfits them for ranking as amines; they dissolve sparingly in water, 
 which renders it unlikely that they are ammonium bases, and brings 
 them nearer to the amides, which many of them also re.semble in their 
 feebly basic character. The alkaloids are soluble in alcohol, and their 
 solutions are generally alkaline and bitter. Their salts are formed, like 
 those of ammonia, by the direct union of the base and the acid, with- 
 out separation of water, and, as a rule, the salts are soluble in water. 
 The hydrochlorides of the alkaloids resemble those of all amines, as 
 well as the chlorides of the alkali-metals and the ammonium bases, in 
 forming crystalline double salts with platinic chloride, mercuric chloride. 
 and auric chloride. Most of the alkaloids may be precipitated from 
 their solutions by iodine dissolved in potassium iodide, by potassio-mer- 
 curic iodide, by potassio-bismuthic iodide, by picric acid, tannin, meta- 
 tungstic acid, and phosphomolybdic acid. 
 
 583. Xanthine -alkaloids. The alkaloids, theobromine and caffeine^ 
 are methyl derivatives of xanthine : 
 
 / NH-CO-ON(CH 3 \ /N(CH 3 )-CO-C-N(CH 3 X 
 C0< .. 3 \CH. CO/ .. 3y \CH. 
 
 X N(CH 3 )-C'N X N(CH 3 ) C-N 
 
 Theobromine, or 3 : y-dimethylxanthine. Caffeine, or i : 3 : y-trimethylxanthine. 
 
 Theobromine, C 7 H 8 N 4 2 , is extracted from the seeds of the cacao tree (Tlieolroma 
 cacao), which grows in Demerara. These are known as cocoa-nibs, and are the raw 
 material of cocoa and chocolate. The cocoa-beans contain 1-2 per cent, of theo- 
 bromine, which may be extracted from them in the same way as caffeine (which it 
 
CAFFEINE. 
 
 inuch resembles) from tea or coffee. When treated with KC10, and HC1 it yields 
 methy alloxan and methyl-urea. When theobromine is dissolved in ammo 
 and boiled with silver nitrate, a white precipitate of Mwth^}% i^ 
 is obtained, and when this is heated with methyl iodide, it yields S-2uS& 
 or cafteme. Theobromine is similarly obtained from silver xanthine (p. 774) 
 
 Caffeine or theine, C 8 H ]0 N 4 2 , is extracted from a plant of Gin- 
 chonaceous order, the coffee-tree (Caffea arabica), the seeds of which 
 contain about 1.5 per cent, of caffeine. It is also found in the leaves - 
 but those of the tea-plant (Thea) yield more of it, the proportion in the' 
 dried leaf varying from 2 to 4 per cent. To prepare caffeine, tea-dust is 
 boiled with water to extract all the soluble matter, which amounts to 
 about 30 per cent., and consists of tannin, cafteine, aromatic oil, and 
 other bodies. The decoction is filtered, mixed with excess of 'lead 
 acetate, which precipitates the tannin, again filtered, the lead precipitated 
 by H 2 S, and the filtrate from the lead sulphide evaporated to a small 
 bulk,^when the caffeine crystallises and maybe purified by recrystallij-a- 
 tion from alcohol. 
 
 The waste tea-leaves which have been exhausted in the tea-pot yield a consider- 
 able proportion of caffeine when treated in this way. Caffeine may be similarly 
 extracted from ground unroasted coffee-beans. It may be sublimed from tea-leaves 
 or coffee-beans by gently heating them in an evaporating-dish covered with a dial- 
 glass ; one of the best processes for obtaining it is to precipitate decoction of tea 
 with tribasic lead acetate, to evaporate the filtrate to dryness, on the steam-bath, 
 at last, and to cautiously heat the dry residue in an evaporating-dish, when the 
 caffeine sublimes on to the cover. 
 
 Caffeine is contained in several plants which are used in various places for 
 chewing or preparing drinks. Paraguay tea is made from the leaves of one of the 
 llicacece, or Holly order, the Ilex 'paraguayemis, and is drunk, under the names of 
 mate and congonka, in Paraguay, Brazil, Chili and Peru. The leaves contain caffeine. 
 Another beverage containing caffeine is used by the Indians of Brazil and called 
 Guarana, being prepared from the seeds of the Paullinia sorMlis, a tree of the Soap- 
 wort order, to which the horse-chestnut belongs. The kola-nut, or seeds of Cola 
 acuminata, used as food and medicine by the natives of West-Central Africa, 
 contains about 2 per cent, of caffeine. 
 
 Caffeine crystallises in fine silky needles (with iH 2 0). It becomes 
 anhydrous at 100 C. and then melts at 233 C., and sublimes unde- 
 composed. It dissolves in 90 parts of cold water, yielding a bitter 
 solution, which is not alkaline. It is soluble in alcohol and ether, and 
 more easily in benzene and chloroform. 
 
 Caffeine is a very feeble base, its salts being decomposed by water. 
 The hydrochloride, C 8 H 10 N 4 O 2 .HC1.2Aq, crystallises from strong hydro- 
 chloric acid in prisms, which leave pure caffeine at 100 C. The 
 sulphate, C 8 H 10 N 4 O 2 .H 2 SO 4 , is obtained in needles by adding dilute 
 sulphuric acid to a hot alcoholic solution of caffeine. The acetate is 
 C 8 H 10 N 4 8 (C 2 H 1 2 ) 2 . 
 
 Chlorine-water (or HC1 + KC10 3 ) converts caffeine into amalic acid, or tetra- 
 methyl alloxantin, C 8 (CH 3 ) 4 lsr 4 7 .Aq. In the presence of air, water, and ammonia, 
 this yields murexoln, or tetramethyl murexide, C 8 (CH 3 ) 4 N 5 6 (NH 4 ), which crystal- 
 lises from hot water in scarlet prisms with a golden lustre. The test for caffeine 
 is based on this : dissolve it in strong HC1, add a crystal of potassium chlorate, 
 and evaporate to dryness. A red residue is left, which becomes purple with 
 ammonia, and is bleached by potash. 
 
 The final product of the action of chlorine-water on caffeine is cholestrophane 
 (p. 772). When long boiled with baryta-water, caffeine is converted into cajfei 
 dine, C 7 H 12 N 4 0, which is a stronger base than caffeine 
 
 C 8 H 10 N 4 2 + Ba(OH) 2 = C 7 H 12 N 4 + BaC0 3 . 
 
776 NICOTINE. 
 
 Theophyllin or i : 3-dimethylxanthine accompanies caffeine in tea ; it 
 melts at 264 C. 
 
 584. Pyridine-alkaloids. The alkaloids piperine, coniine, and nico- 
 tine, are derivatives of pyridine. 
 
 Piperine, or piperidine piper ate, C n H 9 2 'CONC 5 H 10 , bears the same relationship 
 
 /0\ 
 
 to piperic acid, CH,/ >C 6 H 3 'CH : CH'CH : CH'C0 2 H, that acetamide bears to 
 XT 
 
 acetic acid, the piperidine (p. 766) residue, -NC 5 H 10 , behaving like the ammonia 
 residue, 'NH 2 . It is a feeble base extracted by alcohol from white pepper, the ripe 
 fruit of Piper nigrum (the unripe fruit is black pepper). It crystallises in prisms 
 (m.-p. 128 C.), which are insoluble in water, but soluble in ether. The alcoholic 
 solution tastes hot. When boiled with potash it yields piperidine, and potassium 
 piperate. It dissolves in H 2 SO 4 , cone, with a red colour. 
 
 Coniine. or 2-norntal-propyl piperidine, C 5 H 9 (C 3 H 7 )NH, is extracted from the 
 seeds of hemlock (Conium maculatuni) by crushing them and distilling with weak 
 KOH. The distillate, which contains NH 3 and coniine, is neutralised with H 2 S0 4 , 
 concentrated by evaporation, and mixed with alcohol to precipitate the (NH 4 ) 2 S0 4 . 
 On evaporating the filtrate and distilling with strong KOH, coniine distils with 
 water, upon the surface of which it floats. It is dehydrated with dried K 2 C0 3 , 
 and fractionated. 
 
 Coniine has a strong odour of mice ; its sp. gr. is 0.89, and it boils at 167 C. 
 It is sparingly soluble in cold water, giving an alkaline solution. It dissolves in 
 alcohol and ether. When exposed to air, it becomes brown, and evolves NH 3 . 
 Oxidising-agents, such as nitric and chromic acids, convert it into butyric acid. 
 When coniine is heated in a sealed tube with CH 3 I, it exchanges H for CH 3 , show- 
 ing it to be a secondary monamine, NH(C 8 H 16 )". The methylconiine, NCH 3 (C 8 H 16 )", 
 sometimes occurs in hemlock. It combines with CH 3 I to form a crystalline 
 coniine-methylium iodide, N(C 8 H 16 )"(CH 3 ) 2 I, which yields a caustic base when 
 decomposed by AgOH. Hemlock also contains another base, conhydrine, C 8 H 17 NO, 
 crystallising in plates. 
 
 Coniine has been obtained artificially by the action of sodium on an alcoholic 
 solution of ally l-pyri dine, C 5 H 4 (C 3 H 5 )N, a liquid product of the action of paraldehyde 
 upon picoline, C 5 H 4 (CH 3 )N. The base obtained in this way, however, is optically 
 inactive ; when its tartrate is fractionally crystallised, it is split up into a leevo- 
 base and a dextro-base (cf, p. 606) ; the latter is coniine. 
 
 Paraconiine, C 8 H 15 ,N, propyl tetrahydropyridine, is obtained by distilling the 
 product of the action of alcoholic ammonia on butyric aldehyde 
 
 2C 3 H 7 CHO + NH 3 = H 2 + C 8 H 17 NO 
 
 (dibutyraldine) ; C 8 H 17 NO = H 2 + C 8 H 15 N (paraconiine). This base is very similar 
 to coniine, and, like it, a powerful narcotic poison, but is optically inactive, and 
 appears to be a tertiary monamine. 
 
 Nicotine, C 10 H 14 K 2 , is found chiefly as malate, in the seeds and leaves 
 of tobacco, Nicotiana tabacum, a plant of the order of Atropacese, 
 many of which, especially deadly nightshade, thorn-apple, henbane, and 
 mandrake, yield narcotic poisons. Nicotine is extracted from tobacco 
 leaves by digesting them with very dilute H 2 S0 4 , evaporating to a small 
 bulk, and distilling with excess of KOH. The distillate is shaken with 
 ether, the ethereal layer is drawn off, the ether distilled, and the 
 nicotine placed in contact with quick-lime to remove the water, and 
 distilled in a current of hydrogen, since it is decomposed when distilled 
 in air at the ordinary pressure. 
 
 Nicotine is colourless when freshly prepared, but soon becomes brown 
 in air. It smells strongly of tobacco, has sp. gr. i.oi, and boils at 
 247 C. It is soluble in water, alcohol, and ether; its solution is alka- 
 line. It is a di-acid base, but its salts do not crystallise well. When 
 heated with ethyl iodide, it behaves as a tertiary amine, yielding 
 
TOBACCO. jjj 
 
 nicotine-ethyliumdi-iodide, N 2 (C 10 H 14 )"(C 2 H 5 ) 2 T 2 , which yields the cor- 
 responding caustic base when decomposed by AgOH. 
 
 By oxidation with chromic acid, nicotine yields nicotinic acid (wrltl'm,--- 
 carboxylic acid} C 5 H 4 (C0 2 H)N which yields pyridine, when distilled with lime ' 
 
 Nicotine is a-pyridyl-w-methyltetrahydropyrrol, being obtainable by a some- 
 what complex series of reactions from the amide of nicotinic 
 acid by introduction of a pyrrol group in place of the ru .PTT 
 
 CONH 2 group. CH 3 N/ CH2CH2 
 
 Virginia tobacco contains more nicotine than other CH 'CH 
 
 varieties, the alkaloid amounting to nearly 7 per cent, of 
 the weight of the leaf dried at 212 F., whilst the Maryland /C = CH 
 
 and Havana varieties contain only 2 or 3 per cent. HC<^ \N 
 
 Tobacco is remarkable for the very large amount of ash 
 which it leaves when burnt, amounting to about one- Nicotine, 
 
 fifth of the weight of the dried leaf, and containing about 
 
 one-third of K 2 C0 3 , resulting from the decomposition of the malate, citrate, and 
 nitrate of potassium during the combustion. The latter salt is frequently present 
 in larger quantity than is found in most other leaves and aids the combustion, for 
 which purpose it is sometimes added ; but it is often present only in very small 
 proportion and the burning quality of the tobacco is not impaired by its absence. 
 
 Cigars are made directly from the moistened tobacco leaves which may or may 
 not have undergone a fermentation ; but Snuff, after being moistened, is subjected, 
 in large heaps, to a fermentation extending over 18 or 20 months, when it becomes 
 alkaline from the development of (NH^COg (by the putrefaction of the vegetable 
 albumin in the leaf) and of a minute quantity of free nicotine, which imparts the 
 peculiar pungency to this form of tobacco. The aroma of the snuff appears to be 
 due to the production of a peculiar volatile oil during the fermentation. The 
 proportion of nicotine in snuff is only about 2 per cent., being one-third of that 
 found in the unfermented tobacco ; and a great part of this exists in the snuff in 
 combination with acetic acid, which is also a result of the fermentation. 
 
 585. iSparteine, C 15 H 26 N 2 , is a narcotic alkaloid extracted from the common broom 
 (Spartium scopariwni) by digestion with weak sulphuric acid and decomposing the 
 sulphate by distilling with potash. It is liquid, heavier than water, boiling at 
 311 C. It is sparingly soluble in water, giving an alkaline solution with a bitter 
 taste. It smells rather like aniline, and becomes brown when exposed to air. It 
 acts as a di-acid base, and appears to be a tertiary di-amine. 
 
 586. Tropine- alkaloids. Atropine, hyoscyamine and cocaine are derivatives of 
 a base tr opine which behaves as a i-methyl-4-hydroxypiperidine wherein the 
 2- and s-C atoms are linked by a -CHa'CHa group. Atropine and hyoscyamine are 
 isonieric forms of a salt of this base with tropic acid or a-phenylhydr acrylic acid. 
 
 CH 9 'CH- 
 
 NCHo CH(OH) 
 
 NCH, CH-OCO-CH(C 6 H 5 )-CH 2 OH. 
 
 CH 2 'CH CH 2 CH 2 -CH CH 2 
 
 Tropine. Atropiue. 
 
 Tropine, C 8 H 15 NO, is a crystalline base melting at 62 C. and boiling at 263 C., 
 obtained by hydrolysis of atropine. 
 
 Atropine and hyoscyamine, C^H^NOg, are physical isomerides associated in 
 several plants of the order Solanacea, the former particularly in deadly night- 
 shade (Atropa belladonna) and thorn-apple (Datura stramonium), the latter 
 especially in , hyoscyamus (henbane). Both alkaloids have the characterist 
 (mydnatic) effect of dilating the pupil of the eye. 
 
 Atropine is obtained by expressing the sap from the flowers of belli 
 heating it to 90 C. to coagulate albumin, filtering, adding KOH to liberate the 
 base, and shaking with chloroform, which collects it and sinks to the bottom T 
 chloroform is distilled, and the atropine recrystalhsed from alcohol I 
 prisms, fusing at 115 C., sparingly soluble in cold water, and having a bitter burn- 
 ing taste and a very poisonous action. Atropine is optically inactive and 
 hyoscyamine lajvo-rotatory, but the laevo-atropine obtained by resolving 1 
 inactive form is not identical with hyoscyamine. 
 
77 8 OPIUM MOKPHIA. 
 
 Solanine, C 42 H 87 N0 16 , is contained in plants of the same order, especially in 
 Solatium nigrum and in the shoots of potatoes (Solatium tuberosu-ni) which have been, 
 kept in a cellar during winter. To extract it, the plant is digested with weak 
 sulphuric acid, and the solution precipitated with ammonia. It crystallises from 
 alcohol in prisms, which are nearly insoluble in water. It gives a red solution 
 when heated with sulphuric acid and alcohol. 
 
 Cocaine, C 17 H 21 N0 4 , is extracted from the leaves of Erythroxylon coca, a 
 Peruvian stimulant. It crystallises in prisms, melts at 98 C. and dissolves in 
 alcohol. It is Isevo-rotatory and is a valuable local anaesthetic, for which purpose 
 the hydrochloride is sold. When hydrolysed cocaine yields tropine carboxylic 
 acid or ecgonine, benzoic acid and methyl alcohol. It "is, therefore, a benzoate 
 of methyl tropine carboxylate, and may be represented by substituting the benzoic 
 acid residue for that of tropic acid, and C0 2 CH 3 for H in the 3-position of the- 
 piperidine ring, in the formula for atropine (v.s.^). 
 
 587. Opium- alkaloids. Opium (OTTOS, juice) is obtained from the 
 Papaver somniferum, or opium-poppy, cultivated in Turkey, Egypt, 
 India, and other Oriental countries. A few days after the poppy-flower 
 has fallen, incisions are made in the poppy-head, when a milky juice 
 exudes. After twenty-four hours this becomes a soft solid mass of 
 brown colour, and is scraped off and wrapped in leaves for the market. 
 Opium contains about 25 per cent, of a gummy substance, 20 per cent, 
 of ill-defined organic matters, a little caoutchouc, resin, oil, and water, 
 and variable proportions of a large number of alkaloids, of which mor- 
 phine, narcotine, papaverine, and narceine are the most abundant. 
 Little is known of the constitution of morphine, but the investigation, 
 of narcotine, papaverine, and narceine has been more fruitful ; the 
 results, however, are too complex for discussion here. 
 
 Laudanum is supposed to contain about 7 parts by weight of opium 
 in 100 measures of proof spirit. 
 
 Morphine, or morphia, C 17 H. 9 !N0 3 , is extracted from opium (which 
 contains 6-15 per cent.) by steeping it in warm water, which dissolves 
 the meconate and sulphate of morphine, straining, and adding CaCl 2 , 
 which precipitates calcium meconate. The filtered solution is 
 evaporated to a small bulk and set aside, when the hydrochlorides of 
 morphine, codeine, and oxymorphine crystallise. These are dissolved 
 in water, and the morphine precipitated by adding ammonia. It is 
 recrystallised from alcohol in prisms (with iH 2 0), which become anhy- 
 drous and melt at 120 C. It is almost insoluble in water, requiring 
 T 0,000 parts of cold and 500 parts of boiling water, and nearly 
 insoluble in ether and chloroform, both of which dissolve most other 
 alkaloids. 
 
 Morphine is soluble in ethyl acetate (acetic ether) and in aniyl alcohol, either of 
 which may be employed to extract it from an aqueous solution. Even ether may 
 be employed to extract morphine from an alkaline solution, if shaken with it 
 immediately after adding the alkali, and before the morphine has precipitated. 
 Morphine differs from most other alkaloids by being very soluble in potash ; if 
 a drop of weak potash be stirred with solution of a salt of morphine, the alkaloid is. 
 precipitated, but it is redissolved by a very little more potash. Ammonia does not 
 easily redissolve it unless NH 4 C1 be present. 
 
 Morphine behaves like a tertiary monarnine ; it contains two OH groups and 
 resembles, in some reactions, a phenol-alcohol. Its solutions are alkaline, and it 
 combines with acids, like ammonia. 
 
 Morphine hydrochloride, C 17 H 19 N0 3 .HC1, or muriate of morphia, is the chief form 
 in which morphine is used in medicine. It crystallises in needles with 3Aq, and i& 
 easily soluble in water and alcohol. Morphine meconate, the most soluble of the 
 salts, is also used in medicine. 
 
NARCOTINE. 
 
 Morphine and its salts act as powerful narcotic poisons; they are easily 
 identified by giving a blue colour with ferric chloride (purple in the case of meconate^ 
 and a golden yellow with strong nitric acid. Morphine acts, in many cases as a 
 reducmg-agent ; it liberates iodine from iodic acid in solution ; it reduces potassium 
 ferricyanide to ferrocyanide, and precipitates silver when boiled with silver 
 nitrate. When distilled with potash, morphine yields methylamine. 
 
 Morphine perwdide, C 17 H 19 N0 3 I 4 , is obtained as a brown precipitate when solu- 
 tion of iodine in KI is added to morphine hydrochloride. 
 
 Apomorphine, C 17 H 17 N0 2 , is formed when morphine is heated with a large 
 excess of strong HC1 for some hours, at 150 C. ; C 17 H 19 N0 3 = C 17 H n NO + H O. 
 From the hydrochloride thus obtained, Na^CC^ precipitates apomorphine as "an 
 amorphous powder, rapidly turning green in air, and then dissolving in ether with 
 a pink colour. It is much more soluble in alcohol and ether than is morphine, 
 and is a powerful emetic, even when injected under the skin. 
 
 Codeine, codeia, or methyl morphine, C 17 H 18 (CH 3 )N0 3 , is obtained from opium 
 by adding potash or soda to the ammoniacal filtrate from the morphine. It 
 may be purified by crystallisation from ether. Codeine has been obtained from 
 morphine by heating it with methyl iodide in alcoholic solution. 
 
 Codeine melts at 150 C. and is easily soluble in hot water, alcohol, and ether. 
 It crystallises from ether in anhydrous octahedra, and from water in rhombic 
 prisms, which contain Aq. The crystals fuse under water. It is a narcotic poison, 
 though less powerful than morphine, and amounts in opium to only about 0.5 per 
 cent. It is strongly alkaline, gives no colour with ferric chloride, and does 
 not reduce iodic acid like morphine. It is a tertiary monamine. When heated with 
 caustic alkalies, it yields methylamine and trimethylamine. Heated with strong 
 HC1 at 150 C., it yields apomorphine and methyl chloride. 
 
 Narcotine, C^H^NOf, is extracted by digesting with acetic acid the residue 
 left after exhausting opium with water. The narcotine is dissolved and is 
 precipitated on adding NH 3 . It crystallises from alcohol in prisms, which contain 
 Aq., but like morphine, is almost insoluble in water ; it dissolves in ether, however, 
 which extracts it from powdered opium, leaving the morphine. Narcotine is 
 insoluble in potash, and melts at 176 C. It is a very feeble- base, not alkaline, 
 dissolving in acids, but not forming well-defined salts. It has a narcotic effect, but 
 is not nearly so poisonous as morphine. Opium contains usually about I per 
 cent, of narcotine, and the presence of this drug is more easily detected by testing 
 for narcotine than for morphine, on account of the solubility of the former 
 in ether. The material to be tested is extracted with ether, the latter evaporated, 
 the residue dissolved in dilute HC1, and a little euchlorine-water added (made by 
 adding strong HC1 to a weak solution of KC10 3 till it has a bright yellow colour, 
 and adding water till it is pale yellow) ; this produces, with narcotine, a yellow 
 colour in the cold, becoming pink on boiling and adding more of the euchlorine 
 water. 
 
 When narcotine is long boiled with water it yields a new base, cotarnine, 
 C 12 H 15 N0 4 (m.-p. 132 C. ) soluble in water, and meconine or 5 :6-dimethoxyph- 
 
 CO 
 
 thaUd^(CB. s O). 2 C Q E^ \0, (pM^/de being the lactone of I : 2-methylbenzoic 
 CH2 
 
 acid). Meconine is sparingly soluble in water and melts at 102 C. It occurs in 
 opium to the extent of i per cent. Cotarnine appears to be an oxy-derivative of 
 /<-methylisoquinoline, containing a methoxy-group. When reduced it yields hydro- 
 cotarnine, C 12 H 15 N0 3 , and when this is heated with opianic acid, an oxidation 
 product from nieconine, (CH 3 0) 2 C 6 H 4 (CHOH)(C0 2 H), and H 2 S0 4 , uowrcotiw is 
 formed. This melts at 194 C. and is coloured red by strong H 2 S0 4 . *rom thest 
 reactions it is concluded that narcotine is a meconinehi/drocotarniii<<. 
 
 Thebaine, C 17 H 15 (OCH 3 )*NO, is contained in opium in small proportion; 
 remains in the solution from which the hydrochlorides of morphine and codeine 
 have crystallised. This solution is mixed with ammonia, which precipitates 
 thebaine together with some narcotine ; the precipitate is dissolved in a h 
 acetic acid, and the narcotine precipitated by tribasic lead acetate. 
 is precipitated from the filtrate by dilute sulphuric acid, after which ammo 
 is added to precipitate the thebaine. This alkaloid, like morphine, is msolubh 
 water, but dissolves in alcohol and ether, and crystallises in plates ; m.-p. 193 ^ 
 It is insoluble in alkalies. Its alcoholic solution is alkaline. Thebaine gives 
 
7^0 QUININE. 
 
 a blood-red solution with strong sulphuric acid. When heated with hydrochloric 
 acid, it yields an isomeride, thebenine, which gives a blue colour with sulphuric 
 acid. Thebaine is very poisonous, producing tetanic convulsions. 
 
 Narceine, C^H^NOg, remains in the solution from which the thebaine and 
 narcotine have been precipitated by NH 3 . This is mixed with lead acetate, to 
 precipitate the rest of the narcotine, filtered, the lead removed by H 2 S0 4 , the 
 filtrate neutralised by NH 3 , and evaporated, when the narceine crystallises, 
 leaving meconine in solution, which may be extracted by shaking with ether. 
 Narceine crystallises from water in prisms with 3Aq ; it is soluble in alcohol, 
 but not in ether. It is a narcotic poison. Iodine colours its solution blue. It is 
 also formed by heating narcotine methoiodide with KOH solution. 
 
 Papaverine, or tetramethoxy~benzyluoqiiinoline, (CH 3 0)2C 9 H 4 N'CH 2 C 6 H 3 (OCH :3 )o, 
 is contained, in small proportion, in the precipitate produced by excess of KOH 
 in the aqueous solution of opium. The precipitate is dissolved in ether, and 
 shaken with dilute acetic acid ; the lower layer then contains the acetate of 
 narcotine, thebaine, and papaverine ; these are again precipitated by KOH and 
 treated with oxalic acid, which leaves the acid papaverine oxalate undissolved. 
 Papaverine is sparingly soluble in water, but dissolves in hot alcohol and ether. It 
 gives a violet-blue solution with strong H 2 S0 4 . Its poisonous properties appear to 
 be feeble. It melts at 148 C. 
 
 588. Cinchona-alkaloids. The plants of the natural order Cin- 
 chonacece are remarkable for their medicinal properties. Conspicuous 
 among them are cinchona, which furnishes quinine ; the coffee-tree, which 
 yields caffeine ; and the ipecacuanha, which produces emetine. 
 
 Cinchona, or Peruvian bark, is obtained chiefly from the districts 
 around the Andes, and owes its valuable febrifuge qualities to the 
 presence of certain alkaloids, of which the most important are 
 
 Quinine . 
 Conquinine 
 
 Cinchonine . . C 19 H 22 N 2 
 Cinchonidine . , C 1Q HooN 
 
 Quinamine 
 
 Of these, quinine and cinchonine are by far the most important. The different 
 species of cinchona yield a bark containing these alkaloids in different proportions. 
 The yellow bark yields from 2 to 3 per cent, of quinine, and only 0.2 or 0.3 
 of cinchonine ; the red bark, about 2 per cent, of quinine and i per cent, of 
 cinchonine ; and the pale or grey bark about 0.8 per cent, of quinine and 2 per 
 cent, of cinchonine. The alkaloids exist in combination with quinic acid and 
 with a variety of tannin known as quinotannic acid. 
 
 Quinine, C, H 24 N 2 O 2 , is prepared by boiling the bruised bark with 
 diluted hydrochloric acid, and mixing the filtered solution with lime 
 diffused through water, until it is alkaline. The precipitate, containing 
 quinine, cinchonine, and colouring-matter, is filtered oft' and boiled 
 with alcohol, which dissolves both the alkaloids, leaving the excess of 
 lime undissolved. A part of the alcohol is then recovered by distilla- 
 tion, and the solution neutralised with sulphuric acid, boiled with 
 animal charcoal till decolorised, and filtered. On standing, quinine 
 sulphate crystallises out, leaving the cinchonine sulphate in solution. 
 The quinine sulphate is dissolved in water, and decomposed by 
 ammonia, which precipitates the quinine. 
 
 Quinine crystallises in prisms containing 3Aq, which dissolve in 1900 
 parts of cold water and easily in alcohol, ether, and chloroform ; when 
 anhydrous it melts at 117 C. Its solutions are alkaline, and bitter. 
 It appears to be a tertiary di-amine, because, when heated with the 
 iodides of alcohol radicles, it yields iodides which furnish ammonium 
 bases when decomposed by AgOH ; thus, methyl iodide gives 
 C 20 H 24 N 2 2 *CH 3 I, which yields the alkaline hydroxide, 
 C 20 H 24 N 2 2 -CH 3 -OH. 
 
CINCHOXINE. 7 gj 
 
 Quinine is characterised by exhibiting a beautiful blue fluorescence 
 when dissolved m dilute sulphuric acid, and by producing a fine green 
 colour when its dilute acid solutions are mixed with a little chlorine or 
 bromine- or euchlorine-water (see p. 779), and afterwards with ammonia 
 The green colour is due to the thalleiochin, formed by the reaction 
 CaoH^NaOa + NH 3 + 4 = C^H^O,. 
 
 Quinine is a di-acid base, but it sometimes forms salts in which it is monacid 
 P w vn *Sni h y^ r ? chlo ^ d 5 C 20 H 24 N 2 2 . 2 HC1 is converted by water into 
 C2oH,yX 2 2 . HC1, which crystallises in needles of the formula 2(C 00 Ho l N 9 (X, HCH lAa 
 
 ^i-mal quinine sulphate, C2oH24N202.H2S04.7Aq, is soluble "in u parts of cold 
 water, but the basic sulphate, (C ao H a4 N 9 O a ) a .H a SO 4 .8Aq ) requires 780 parts of cold 
 water to dissolve it. This is the quinine salt generally used in medicine it forms 
 very light silky needles, which dissolve easily in dilute sulphuric acid, forming 
 the acid sulphate, Ca ft H04N a O 2 .(H a SO^ a .7Aq, which is very soluble. 
 
 Quinine is very slightly soluble in potash, and sparingly in ammonia, though it 
 is more soluble in NH 3 than is any other cinchona alkaloid. If normal quinine 
 sulphate be dissolved in strong acetic acid, warmed, and an alcoholic solution of 
 iodine added gradually, thin rectangular plates are deposited on cooling having 
 the formula (C 20 H 24 N 2 2 ) 4 .(H2S0 4 )3.(HI)2.l4.6H 2 0. These crystals (herapathite, or 
 artificial tourmaline) are bronze green by reflection, but transmit light of a pale 
 olive colour, which is perfectly polarised, like that transmitted by tourmaline, so 
 that, if another plate be laid upon the first, no light is transmitted when their 
 principal axes are at right angles. 
 
 Quinidine, or conquinine, C^H^N^, is isoineric with quinine, and is extracted 
 from a brown substance called quinoidine, or amorphous quinine, which is obtained 
 from the mother-liquors of quinine sulphate and is sold as a cheap substitute for 
 quinine. It is also obtained in quantity from some of the inferior varieties of 
 cinchona, such as Cinchona cordifolia, which yields the Carthagena bark. Quin- 
 idine forms larger prismatic crystals than quinine, and these contain only 2Aq. 
 Its salts are more soluble than those of quinine, and they are strongly dextro- 
 rotatory for polarised light, whilst those of quinine are la?vo-rotatory. 
 
 Quinicine, also isomeric with quinine, is formed by heating quinine or quinidine 
 with dilute sulphuric acid to 130 C. It is resinous, but its salts crystallise. It:v 
 solutions are feebly dextro-rotatory. 
 
 Cinchonine, CjgHgoNgO, remains as sulphate in the mother-liquor from quinine 
 sulphate (r.s.), and may be precipitated by ammonia. It is almost insoluble in 
 water, and sparingly soluble in alcohol. Ether scarcely dissolves it, and is used 
 to distinguish it from quinine. It crystallises from hot alcohol in anhydrous 
 prisms, which have an alkaline reaction. It melts at 225 C. and sublimes in 
 hydrogen. The salts of cinchonine are more soluble than those of quinine, and 
 give a much more voluminous precipitate with ammonia, which is insoluble in 
 a large excess, and is not cleared up by shaking with ether, as in the case of 
 quinine. 
 
 Cinchonine sulphate, (C 19 H22]Sr. 2 0)2.H 2 S04.2Aq, fuses when heated, evolving an 
 aromatic odour and becoming red. Solution of cinchonine sulphate is less 
 strongly fluorescent than one of quinine sulphate. Cinchonine also differs from 
 quinine in yielding solutions which are strongly dextro-rotatory. 
 
 Cinchonidine is isomeric with cinchonine, but is strongly lasvo-rotatory. 
 
 Cinchonicine, another isomeride, resembles quinicine in origin and properties. 
 
 When quinine, cinchonine, and their isomerides are fused with KOH, they yield 
 the quinoline bases, indicating that they are closely connected with quinoline. 
 The tarry odour on heating cinchonine is probably due to these. Thus both 
 cinchonine and quinine are supposed to contain the quinoline group, the former 
 being C 9 H 6 N-C 10 H 15 (OH)N, and the latter (CH 3 0)C 9 H 5 N'C 10 H 15 (OH)N. 
 
 Emetine, C 30 H 40 N 2 5 , is a little-known base extracted from the root of Cephaelis 
 ipecacuanha, a cinchonaceous plant much used in medicine. 
 
 589. Strychnos- alkaloids. Strychnine and brucine are obtained 
 from nux-vomica, the seeds of the tropical plant, Strychnos nux-vomica, 
 from false anyostura bark* which is the bark of the same tree, and from 
 
 * True angostura bark is obtained from Galipea officinalis and G. cusparia, belonging to. 
 the order Rutaceae. It is used as a febrifuge. 
 
782 STRYCHNINE. 
 
 Ignatia amara, or St. Ignatius' bean. Nux-vomica, or crow-Jig, contains 
 about i per cent, of strychnine and i per cent, of brucine. 
 
 Strychnine, C 21 H 22 N 2 0,, is extracted from the crushed seeds of nux- 
 vomica by boiling them with very dilute HCL The solution is mixed 
 -with milk of lime, and the precipitate filtered off and boiled with alcohol, 
 which dissolves the strychnine and brucine, and deposits the strychnine 
 first when evaporated. The mother-liquor is neutralised with HN0 3 , 
 when strychnine nitrate crystallises out, leaving brucine nitrate in 
 .solution. Both alkaloids are Isevo-rotatory. 
 
 Strychnine crystallises in rhombic prisms, soluble in 7000 parts of 
 water, and melting at 284 C. It is insoluble in ether and in absolute 
 alcohol, but dissolves in dilute alcohol. It is very soluble in chloroform, 
 which is the best agent for collecting it from aqueous solutions. Its 
 intensely bitter taste is very remarkable, and may be imparted to one 
 million parts of water (one grain in fourteen gallons). Its alcoholic 
 solution is alkaline, and it is a monacid tertiary base, combining with 
 methyl iodide to form strychnine-methylium iodide, N 2 C 21 H 22 9 .CH 3 I, 
 which yields the corresponding hydroxide base when decomposed by 
 AgOH. But this ammonium base is not bitter, nor poisonous unless 
 injected under the skin, when it induces paralysis. Strychnine is 
 extremely poisonous, giving rise to tetanic convulsions. Potash pre- 
 cipitates strychnine from its solution in acids, and an excess does not 
 dissolve it ; the precipitate by ammonia dissolves in excess, but the 
 strychnine crystallises out after a time. The smallest particle of strych- 
 nine may be identified by dissolving it in strong sulphuric acid and 
 adding a minute fragment of potassium bichromate, which produces a 
 fugitive blue-violet colour. 
 
 When strychnine is warmed with dilute HN0 3 , it gives a faint pink solution, 
 which becomes scarlet on adding a particle of powdered KC10 3 ; NH 3 changes this 
 to brown, and, on evaporating to dryness, the residue is green and dissolves in 
 water to a green solution, changed to orange by KOH, and becoming green again 
 with HN0 3 . Euchlorine- water (p. 779), or bromine-water, added to a solution of 
 strychnine in HC1, gives, on boiling, a fine red colour, bleached by excess, and 
 returning when boiled. 
 
 One of the N-atoms in strychnine is the tertiary ammonia nitrogen ; the other 
 
 /CO /COOH 
 
 appears to be in the form of a lactam group (p. 674) < which becomes < 
 
 ^N ^NH 
 
 yielding stry clinic acid, when strychnine is heated with sodium ethoxide. When 
 
 ,N(CH 3 )I 
 the methylium iodide (see above) is treated with AgOH, the grouping ^_CO 
 
 ^NH 
 K(CH) 3 
 
 becomes ^-CO 
 NH 
 
 Brucine, C 23 H 26 N 2 4 , is precipitated by KOH from the solution of brucine 
 nitrate obtained in the extraction of strychnine. It is more soluble in water and 
 alcohol than strychnine is, and crystallises in prisms with 4Aq, melting at 178 C. 
 when anhydrous. Like strychnine, it is nearly insoluble in ether. It is intensely 
 bitter and strongly basic. HN0 3 dissolves it with a fine red colour, which becomes 
 violet on adding stannous chloride. Both strychnine and brucine yield quinoline 
 bases when distilled with KOH ; indicating their relationship with quinoline. The 
 proportion of methyl alcohol obtainable from brucine by distilling it with Mn0 2 
 
VERATRINE. 783 
 
 and H 2 S0 4 shows that it contains 2(OCH 3 ) ; it may, therefore, be regarded ai 
 dimethoxy-strychnine. 
 
 590. Aconitine, C 33 H 43 N0 12 , is extracted from the root of Aconltinn nunellus a 
 plant of the Ranunculaceous or Buttercup order, known as monk's /umd. 1,1 HP rocket 
 -and wolfs bane. The root has often been scraped and eaten by mistake for ////- 
 radish (Cochlearia armoracia, a cruciferous plant), but the two roots are reallv 
 very unlike, and the scrapings of monk's hood become pink when exposed to air 
 while those of horse-radish remain white. To extract the aconitine, the scrapings 
 of the root are boiled with amyl alcohol ; the solution is shaken with dil. H 2 SO , 
 which extracts the aconitine, and the aqueous liquid is neutralised with Na^CO 
 The aconitine thus precipitated is crystallised from ether. It crystallises from 
 alcohol in anhydrous plates (rn.-p. 188 C.), and forms well-defined salts. Aconitine 
 is one of the most poisonous alkaloids, and, as yet, no trustworthy chemical test 
 for it is known, so that the toxicologist is obliged to place a little of the suspected 
 substance on the tongue, when aconotine produces a numbing, tingling feeling, 
 lasting for some time. When heated with potash, aconitine yields potassium 
 Tsenzoate and aconine, C 2 gH 41 NO n . The preparations sold as aconitine are often 
 impure bases of very variable quality. 
 
 Pseudaconitine, C 36 H 49 N0 12 + H 2 0, is a poisonous alkaloid obtained from Aconltinn 
 /erox, an Indian plant of the same natural order. Heated with potash, it yields 
 pseudaconine, C^H^NOg, and the potassium salt of dimethyl dihydroxybenzoic 
 (or dimethyl protocatechuic) acid. 
 
 Veratrine, C 37 H 53 NO n , is extracted from the root of white hellebore (Veratrum. 
 album*), and from the seeds of Veratrum sabadilla, plants of the natural order Col- 
 chicacefe. The alkaloid is present in very minute quantity. It is extracted by 
 digesting the root with alcohol containing a little tartaric acid, evaporating the 
 alcohol from the filtered solution, dissolving the residue in water, liberating the 
 alkaloid by caustic soda, and shaking with ether, which dissolves it. The ethereal 
 layer leaves the alkaloid when evaporated. Veratrine is characterised by its 
 power to cause violent sneezing when a particle of the powder is drawn into the 
 nose. It dissolves in HC1, and the solution becomes red when gently heated. 
 Strong H 2 S0 4 gives a yellow solution passing into carmine-red, and becoming 
 purple with bromine-water. Cevadine, C 32 H 49 N0 9 , is another alkaloid which 
 causes sneezing, and is extracted from Cevadilla seeds (Veratrum sabadl/la'). 
 Veratralbine, C^H^NOg ; jervine, C 26 H 37 N0 3 ; pseudojervine, C^H^NC^ ; and rubi- 
 j err hie, C 26 H 43 N0 2 , are also extracted from the Veratrums. These plants are 
 chiefly used for poisoning vermin. 
 
 JBebeerine, C ]9 H 21 N0 3 , is extracted from the bark of the bibiru-tree, a tree of the 
 Laurel order, which grows in British Guiana, and yields the green-heart wood 
 used in shipbuilding, because it resists the attacks of marine animals. It 
 is amorphous, insoluble in water, but soluble in alcohol. The sulphate, 
 
 MeKitpermwm fenestratuni), both belonging to the Menispermacea?. Berberine 
 crystallises in yellow needles with 5^Aq, and forms yellow salts. It is soluble in 
 water. 
 
 591. Hydrastin, C 21 H 21 ]Sr0 6 , (m.-p. 132 C.) is an alkaloid of constitution similar 
 to that of narcotine also obtained from barberry. 
 
 Physostigmine, or eserine, C 15 H 21 N 3 p 2 , is obtained from the Calabar bean, the seed 
 of a Papilionaceous plant. It is sparingly soluble in water, but dissolves in alcohol, 
 is strongly alkaline, and very poisonous. It has the property of contracting the 
 pupil of the eye. 
 
 Colchici-ne, C^H^NOg, occurs in meadow saffron, Colchicum autumnale (belonging 
 to the same order as the Veratrums) ; much used as a remedy in gout. It is a 
 very feeble base, soluble in water and alcohol, and does not crystallise. 
 
 Cytisine, C n Hi 4 N 2 0, is the poisonous alkaloid contained in the seeds of Gytimi 
 laburnum, a Papilionaceous plant. 
 
 Chelidonine, C^H^NOg, has been extracted from celandine (Chehdonnnn, M^M), 
 a plant of the Poppy order. 
 
 Delphinine, CooH, 5 N0 6 , is the poisonous alkaloid contained in larkspur or staves- 
 acre (Delphinium staphisagria), the seeds of which are used for destroying vermin 
 (aconite belongs to the same order). 
 
 Pilocarpine, C U H 16 N 2 2 , is extracted from the leaves of Pilocarpms pennatijolnt*. 
 
784 MELTING-POINTS. 
 
 a plant of the Eue order. The base itself is not crystalline, but the hydrochloride 
 and nitrate are crystalline salts, which are used in medicine. 
 
 Jaborandine, C 10 H 12 N 2 3 , is another alkaloid obtained from the same source. 
 
 PHYSICAL PROPERTIES OF ORGANIC COMPOUNDS. 
 
 592. In investigating the chemical structure of the molecules of 
 organic bodies, much assistance is derived from the observation of their 
 physical properties, among which the following are the most im- 
 portant : 
 
 (1) The fusing -point of a solid, the boiling-poinfoi a liquid, and the 
 specific gravity of a vapour. 
 
 (2) The specific volume of a liquid, obtained by dividing its molecular 
 weight by its specific gravity (calculated for the temperature at which 
 the liquid boils). 
 
 (3) The optical properties of a liquid, or of a solid body in solution ; 
 especially the action on polarised light, the refractive power, the absorp- 
 tion spectrum, and the magnetic rotatory power deduced from its action 
 on a ray of polarised light when under the influence of magnetism. 
 
 593. Fusing-points of organic compounds. In order that a solid may fuse, 
 it must first attain to a degree of temperature called the fitting-point of the solid, 
 and must then have a certain amount of motion imparted to its molecules by the 
 transformation (into motion) of an amount of heat which is termed latent heat or 
 heat of fusion. This motion enables the molecules to circulate more or less freely 
 among themselves, and to extend themselves in a horizontal plane. 
 
 The fusing-point, as indicated by the thermometer, therefore, is the temperature 
 at which the molecules become capable of converting the heat subsequently 
 acquired into the motion proper to the liquid condition. This temperature will 
 depend upon the constitution of the molecules, which regulates their relation to 
 adjacent molecules. 
 
 If the cohesion which limits the motion of molecules in a solid mass be similar 
 in character to the gravitation which limits the motion of masses of matter, it 
 will be greater among those molecules which have the larger mass, that is, the 
 highest molecular weight, and these should have the highest fusing-points, since 
 a larger amount of progressive motion (or temperature) must be imparted to them 
 to render them capable of acquiring the freedom of motion proper to the liquid 
 condition. But it is by no means true that the fusing-point is always higher 
 when the molecular weight is greater ; for palmitin, with a molecular weight of 
 806, fuses at 63 C., while urea, with a molecular weight of 60, fuses at 130 C. 
 It may be stated, however, that in the case of homologous series, the fusing- 
 point generally rises as the molecular weight increases ; thus the paraffin and olefine 
 hydrocarbons are liquids until they contain sixteen atoms of carbon. The sub- 
 stitution of HO for H tends to raise the fusing-point, so that the paraffin alcohols 
 containing more than seven carbon-atoms are solids, and this is also the case with 
 the aldehydes. 
 
 In the case of the metameric paraffin derivatives the fusing-point is generally 
 higher in those compounds which contain most carbon in the form of CH 3 ; thus, 
 pseudo-valeric or tertiary valeric acid, C(CH 3 ) 3 - C0 2 H, fuses at about 35 C., while 
 normal valeric acid, CH 3 [CH 2 ] 3 'C0 2 H, fuses at -59 C. Again, tertiary butyl- 
 alcohol, C(CH 3 ) 3 -OH, fuses at 25 C. ; and normal butyl-alcohol, CH 3 [CH 2 ] 3 'OH, is 
 liquid even below o C. 
 
 In the benzene-hydrocarbons, the substitution of CH 3 for H raises the fusing- 
 point ; thus, toluene, C 6 H 5 'CH 3 , and xylene, C 6 H 4 (CH 3 ) 2 , are liquids ; but durene, 
 C 6 H 2 (CH 3 ) 4 , fuses at 80 C. In these also, when they have the same molecular 
 weight, the fusing-point rises with the number of methyl groups directly united 
 to carbon ; for example, amyl-toluene, C^HyfCKy^CHg, is liquid, while hexamethyl- 
 benzene, C 6 (CH 3 ) 6 , is solid, fusing at 164 C. Even in compounds which are 
 strictly isomeric, the position of the component radicles will affect the fusing- 
 point, the para-compound having generally the highest fusing-point ; thus, ortho- 
 xylene and meta-xylene are liquids, but pa'ra-xylene is a solid fusing at 15 C. 
 
BOILING-POINTS. 785 
 
 594. Boiling-points of organic compounds. The boiling-point of a liquid U 
 that temperature at which its molecules are capable of converting heat into motion 
 sufficient to enable them to overcome entirely the attraction holding them to each 
 other, and to extend themselves in all directions through space. Under ordinary 
 conditions, their extension is impeded by the pressure of the atmosphere upon 
 the surface of the liquid, so that, for experimental work, the boiling-point is that 
 temperature at which the molecules are capable of acquiring sufficient motion to 
 overcome a pressure of 760 millimetres of mercury (at o C.). Since the boiling- 
 point refers to a certain standard of external work, it exhibits a more definite 
 relation to the constitution of the molecules than is the case with the fusing-point. 
 In homologous series, the boiling-point increases with the molecular weight, but 
 the increase due to each addition of CH 2 varies in different series. It is most 
 uniform in the normal primary alcohols of the paraffin series (p. 565), where each 
 addition of CH 2 increases the boiling-point, on the average, by 19.5 C. In the 
 series of aldehydes derived from these alcohols (p. 583), the increase in boiling- 
 point is also fairly regular, but it averages 26.2 for each addition of CH 2 . In the - 
 corresponding acids, the increase is much less uniform, but the average increase 
 is about 19. In the single ketones (p. 624), the mean increase in boiling-point for 
 each CH 2 added is 20.5. In the simple ethers, the increase is 26. 
 
 In the homologous series of hydrocarbons, the increase in boiling-point for each 
 addition of CH 2 is irregular, but generally diminishes as the number of carbon- 
 atoms increases. Those hydrocarbons of the paraffin and olefine series which contain 
 the same number of carbon-atoms exhibit a similarity in their boiling-points : 
 
 Paraffins C 5 H 12 37 C 6 H 14 69 C 7 H 16 98 C 8 H 18 125 C 16 H W 288 
 Olefines C 5 H 10 35 C 6 H 12 69 C 7 H 14 99 C 8 H 16 123 C w H a 275 
 
 The isologous hydrocarbons of the acetylene series have higher boiling-pointy 
 and those of the benzenes are higher still 
 
 Acetylenes C 5 H 8 45 C 6 H 10 80 C 7 H 12 106 C 8 H U 133 C 10 H 18 165 
 Benzenes ... C 6 H 6 8o'i C 7 H 8 111 C 8 H 10 142 C 10 H 14 196 
 
 The substitution of HO for H in the conversion of the paraffin hydrocarbons into 
 alcohols increases the boiling-point greatly, but in a ratio which decreases in nearly 
 the same proportion in which the molecular weight of the alcohol increases 
 
 Hydrocarbons C 5 H 12 37 C 6 H 14 69 C 7 H 16 98 C 8 H 18 125 
 Alcohols . . C 5 H 12 Oi37 C 6 H 14 157 C 7 H 16 170 C 8 H 18 191 
 
 A similar increase in boiling-point is produced by the substitution of HO for H 
 in the conversion of an aldehyde into an acid 
 
 Aldehydes C 2 H 4 20.8 C 3 H 6 48 C 4 H 8 74 C 5 H 10 103 
 Adds . C 2 H 4 2 118-3 C 3 H 6 2 140.7 C 4 H 8 2 162 C 5 H 10 2 186 
 
 Metameric bodies which belong to the same class often have nearly the same 
 boiling-points e.g., propione, C 2 H 5 -CO'C 2 H 5 101 ; methyl-propyl ketone, 
 CH 3 -CO-C 3 H 7 102. 
 
 But this is not the case when they belong to different classes e.g., methyl-ethyl 
 ketone, CH 3 -CO'C 2 H 5 81 ; methyl-allyl ether, CH 3 -0-C 3 H 5 46. 
 
 The ethereal salts have lower boiling-points than the acids which are metameric 
 with them e.g., methyl formate, CH 3 'CH0 2 36 ; acetic acid, H-C 2 H 3 2 118 . 
 
 In the isomeric hydrocarbons, the normal compound has the highest boiln 
 point, which falls as the number of methyl groups increases ; thus, normal butane, 
 H 3 C[CH. 2 ] 2 CH 3 , is liquefied at i C., while iso-butane, H 3 C'CH(CH 3 )-CH 3 , remain 
 
 ^Th" boiling-point is lowered, in these isomeric hydrocarbons, by the substitution 
 of ethyl and methyl for hydrogen, and is lowest in those compounds in which 
 carbon is united to the compound radicles only. The same tendency is observe 
 in the isomeric olefines ; thus amylene, H 3 C[CH 2 ] 2 CH : CH* boils at 73 , and wo- 
 amylene, (H 3 C) 2 C : CH(CH 3 ) at 35. 
 
 The normal primary alcohols have the highest boiling-points, then come the 
 iso-alcohols, while the secondary and tertiary alcohols have the lowest boiling- 
 points. The same may be said of the aldehydes and acids. 
 
 When any other element or group is substituted for hydrogen in an orgams 
 compound, the boiling-point is raised, and if more than one atom of hydrogen be 
 displaced, the boiling-point, in the isomerides thus produced will 
 
786 SPECIFIC VOLUMES. 
 
 be higher where the substituting radicles are at the greatest distance from 
 each other. Thus, ethylidene dichloride, H 3 C'CHC1 2 , boils at 58 ; whilst ethene 
 dichloride, C1H 2 C > CH.,C1, does not boil till 85. Again, dibromo propane, 
 H 3 C'CBr 2 -CH 3 . boils ftt 114; propene dibromide, H 3 C'CHBrCH 2 Br, at 142 ; and 
 trimethene dibromide, BrH 2 C'CH 2 'CH 2 Br, at above 160. Ortho-cresol, 
 6 H 4 CH 3 -OH (i : 2), boils at 190 ; meta-cresol (i : 3) at 195 ; and para- 
 cresol (1:4) at 198. Ortho-chloraniline, C 6 H 4 C1'NH 2 (i : 2), boils at 207 ; 
 meta-chloraniline (1:3) at 230; and para-chloraniline (i 14) at 231. Diamido- 
 toluene, C 6 H 3 (CH 3 )(NH 2 ) 2 (i : 2 : 3), boils at 270 ; and (i : 2 : 4) at 280. Further 
 investigation of the boiling-points of isomerides is necessary fully to establish this 
 law. 
 
 595. Specific volumes of organic liquids. It has been seen that the 
 specific volumes of the vapours of organic compounds, obtained by dividing the 
 molecular weight by the vapour-density, are in all cases alike ; but this is not the 
 case with the specific volumes of liquids, which depend upon the attraction exerted 
 between their molecules, which must of course vary with the nature of the mole- 
 cules themselves. Since, at their respective boiling-points, all liquids are in a 
 similar condition in regard to the further effect of heat upon them, it might be 
 expected that their molecular weights, divided by their specific gravities (at the 
 boiling-point), would yield quotients bearing some definite relation to each other, 
 since these quotients represent the molecular volumes of the compounds in the 
 liquid state (at the boiling-point) ; that is, the relative (or specific) volumes, 
 within which the motions of each molecule are restricted, or the space in which 
 each molecule keeps free from other molecules. 
 
 The molecular volume of water, calculated in this way, is 18*8 ; that of methyl 
 alcohol is 42. Then CH 4 - H. 2 = CH 2 ; and 42 - 18.8 = 23.2, which is the increase 
 in molecular volume, due to the addition of CH 2 to H 2 0. The molecular volume 
 of ethyl-alcohol is 62.5, or higher than that of methyl -alcohol by 20.5, which 
 represents the increase due to CH 2 . The molecular volume of acetic acid is 64, 
 and that of formic acid 42, giving 22 as the increase due to CH 2 . The mean 
 of the three values is 21.9, and this is almost exactly the difference in the molecular 
 volumes calculated for the homologous acids, from formic to valeric. 
 
 At one time it was stated with confidence that the molecular volume depends on 
 the number and nature of the atoms contained in the molecule rather than 
 on their grouping ; thus, ethyl acetate, CH 3 *COOC 2 H 5 , has the same molecular 
 volume as its metameride, butyric acid, C 3 H 7 'COOH. Recently, much doubt has 
 been cast on this statement ; and it has been asserted that, instead of the molecular v 
 volume being the sum of the atomic volumes, it depends on the manner in which 
 the atoms are united. The following is the evidence in favour of the older view. 
 
 Octane, C 8 H 18 , has a molecular volume=i87, and if we deduct from this 
 (CH 2 ) 8 =i76, the difference, u, represents the molecular volume of H 2 , giving 5.5 
 for the atomic volume of hydrogen. Cymene, C 10 H 14 , has the molecular volume 187, 
 which differs from (CH 2 ) 7 , or 22 x 7, by 33, which represents the increase in 
 molecular volume due to C 3 , and gives 1 1 for the atomic volume of carbon. 
 
 By deducting the volume of H 2 (n) from that of H 2 (18.8), 7.8 is obtained for 
 the atomic volume of oxygen. 
 
 From these values the specific volumes of many molecules may be calculated 
 and are found to agree very nearly ; with those obtained by dividing the molecular 
 weight by the specific gravity of the liquid at its boiling-point ; for example 
 Methyl alcohol, CH 4 0, gives 1 1 + (5.5 x 4) +7.8= 40.8 instead of 42 
 Ethyl C 2 H 6 (n x 2) + (5. 5x6) +7.8= 62.8 62.5 
 
 Ether C 4 H 10 (11 x 4) + (5.5. x 10)4-7.8=106.8, which is correct. 
 Phenol C 6 H 6 (11 x 6) + (5.5 x 6)4-7.8= 106.8 
 
 But formic acid, CH 2 2 , the specific volume of which is 41.5, gives only 37.6 as 
 the sum of n + (5.5 x 2) + (7.8 x 2). 
 
 Again, acetone, C 3 H 6 0, with a specific volume = 77.6, gives only 73.8 (which 
 agrees with that found for allyl-alcohoi, also C 3 H 6 0) by the addition of 
 (11x3) + (5.5x6) + 7.8 
 
 The structural formula of acetone is (CH 3 ) 2 'C: 0, the oxygen being doubly 
 linked to a carbon atom, whilst in the alcohols, ethers, and phenols it is only 
 singly linked to a carbon atom. 
 
 Deducting from the specific volume of acetone (77.6) that of C 3 H 6 (66), there re- 
 mains 1 1. 6 as the atomic volume of oxygen, when doubly linked to a carbon atom. 
 
OPTICAL PROPERTIES OF ORGANIC COMPOUNDS. 787 
 
 Formic acid contains a singly linked and a doubly linked oxygen atom her 
 its molecular volume should be the sum of u +(5.5 x 2) + 7.8+ 1^6 = 4 4 which is 
 very nearly correct. 
 of Acetic acid, H 3 C(C: 0)OH, gives (5.5 x 4 ) + (n x 2 ) + 7 .8+ 11.6 = 63.4, instead 
 
 The specific volume of an atom of nitrogen singly linked 'to carbon, as in methyl- 
 amme, H.C-NH, 1B 23; but when trebly linked to carbon, as in methyl cyanide, 
 
 r* ' , Wen rey ne to carbon ' as ^ methyl cyanide, 
 C=N, its specific volume is 17. 
 
 Sulphur, singly linked to carbon, has the specific volume 23 ; but when doubly 
 linked, it is 28.6. The specific volume of chlorine is 22.8, of bromine 27 8 and of 
 iodine 37.5 
 
 rn. There ^ r ? man ? 1 ex . c fPtions to the simple laws of specific volume here set forth. 
 Thus, ethylene chloride, C1H 2 C.CH 2 C1, and ethylidene chloride, H 3 OCHC1- which 
 have the calculated specific volume 89.5, give, by experiment, respectively 8^4 
 and 88.96, a difference too great to be ascribed to experimental errors. Benzene and 
 some other members of the aromatic group, also exhibit considerable deviation 
 the observed specific volumes being lower than those calculated. 
 
 596. Optical properties of organic compounds. Since the phenomena of 
 light depend upon the waves excited in the asther which fills the spaces between 
 the molecules of matter, the motions of these molecules must exert an influence 
 upon the optical properties of the substances which they compose. 
 
 The molecular conditions which regulate the colour of compounds, by enabling 
 them to absorb certain of the waves composing white light, and to reflect or trans- 
 mit others, are not as yet understood, but colour is most commonly associated 
 with high molecular weight. (See also Qu'monoid structure, p. 721.) 
 
 Much attention has been devoted to the comparison of the refractive powers of 
 liquid organic compounds, that is, to the amount of deviation from its original 
 path which a wave of light suffers in passing through the liquid in any direction 
 except that perpendicular to the surface. The full discussion of this subject 
 requires the study of optics, but it may be stated that from the amount of devia- 
 tion is calculated the specific refractive power of the liquid, which is closely con- 
 nected with the nature of its molecules. The molecular refractive energy, or 
 refraction-equivalent, is found by multiplying the molecular weight by the specific 
 refractive power. Compounds which have the same molecular weight and belong 
 to the same or to nearly related classes of organic compounds, generally have 
 nearly the same refraction-equivalent ; thus, the number for methyl acetate, 
 CH 3 -C 2 H 3 2 , is 28.78 and that for ethyl formate, C 2 H 5 'CH0 2 , is 28.61. Butyl- 
 alcohol, C 4 H 9 'OH, gives 36.11, and ether, C 2 H 5 '0 - C 2 H 5 , 36.26. Polymeric bodies 
 have refraction-equivalents nearly proportionate to their molecular weights ; thus, 
 aldehyde, C 2 H 4 0, has the refraction-equivalent 18.5, butyric acid, C 4 H 8 02, 36.6, 
 .and paraldehyde, C 6 H 12 3 , 52.5. In the homologous alcohols and acids derived 
 from the paraffin hydrocarbons, the refraction-equivalent increases by about 7.6 
 for each addition of CH 2 ; thus, acetic acid, C. 2 H 4 2 , having the refraction-equiva- 
 lent 21. i, oananthic acid should give 21.11 + (7.6 x 5) = 59-i, which nearly agrees 
 -with that observed, 59.4. 
 
 By a method similar to that explained in the case of specific volumes, the 
 refraction-equivalents to the elements may be calculated, and they are found to be, 
 for the wave-length corresponding with the yellow sodium line, for carbon 4-7 1 ? f r 
 hydrogen 1.47, for oxygen singly linked to carbon, 2.65, and for oxygen doubly 
 linked, 3.33. From these numbers the refraction-equivalent of a liquid may be 
 calculated from its formula, as in the case of its specific volume, and the result 
 agrees very nearly, in a great many cases, with that obtained by experiment. But 
 there is sufficient deviation to indicate that the grouping of the atoms, as well as 
 their nature and number, influences the refraction-equivalent. Thus, in the 
 terpenes, the observed equivalent exceeds that calculated by the constant number 3, 
 while in the benzenes the excess amounts to 6. It would appear that when a 
 carbon atom is doubly linked to another carbon atom, its refraction-equivalent 
 is 5.71 instead of 4.71, so that the six doubly-linked carbon atoms in the benzene 
 ring would explain the excess in the refraction-equivalent. 
 
 When liquids having different refraction-equivalents are mixed, the refraction- 
 equivalent of the mixture is the sum of those of its constituents, so that the 
 proportions in which these are present may be calculated. 
 
788 
 
 ABSORPTION SPECTRA. 
 
 The rotation of the plane of polarised light (p. 542) affords another optical 
 method of investigating the constitution of organic substances. 
 
 The angle of rotation, in the case of any given substance, varies directly as the 
 strength of the solution, its specific gravity, and the length of the column of liquid 
 through which the light passes. For different substances, the angle of rotation also 
 varies with the specific rotatory power, which is found by dividing the angle 
 of rotation by the product obtained by multiplying together the weight of 
 the substance in one gramme of the liquid, the specific gravity of the liquid, and the 
 length of the column in decimetres. For example, a beam of polarised light 
 was passed through a tube with glass ends, 0.50 decimetre long, filled with 
 turpentine, of specific gravity (at the temperature of the experiment) 0.8712, and it 
 was requisite to turn the analyser 16 in the opposite direction to the hand of 
 a watch in order to prevent light from reaching the eye of the observer. This 
 
 would give for the specific (laevo) rotatory power, = 36.7. It is 
 
 i x 0.8712x0.5 
 
 evident that if the specific rotatory power of a substance be known, a calculation 
 like this would give the weight contained in each gramme of the solution, and this 
 is turned to account in the saccharimeter for determining the proportion of sugar 
 in a solution. 
 
 This rotatory power is found most commonly in vegetable and animal products 
 and their immediate derivatives, as will have been seen in the description of 
 such bodies, and it has been pointed out that it depends upon some peculiarity 
 in the structure of the molecule. Recent observations render it probable that 
 much information will be derived from the study of circular polarisation with 
 respect to the true configuration of molecules, as has been indicated at p. 605. 
 
 All liquids exhibit some rotatory power for polarised light when they are under 
 the influence of a powerful (electro) magnet, and the amount of the rotation,, 
 compared with that produced by water under the same conditions, is called the 
 magnetic rotatory power. The molecular magnetic rotation obtained by multiplying 
 the rotatory power by the molecular weight, and dividing by the specific gravity of 
 the liquid, exhibits a definite relation to the composition of the molecule, and 
 increases by 1.023 f r each addition of CH 2 in homologous series. Proceeding on 
 the same principle as in the case of specific volumes (p. 786), the atomic mag- 
 netic rotatory power of carbon is found to be 0.515, that of hydrogen, 0.254, of 
 singly linked oxygen, 0.194, and of doubly linked oxygen, 0.263, and from these, 
 in many cases, the molecular magnetic rotatory power of compounds may be 
 calculated, or conversely, a knowledge of the rotatory power may be applied to 
 determine a molecular formula. 
 
 597. Absorption spectra of organic compounds for chemical rays. The light 
 emanating from the sun and from the electric spark is accompanied by many 
 other waves whose period of vibration is so short that they produce no impression 
 upon the eye, or upon the thermometer, and are only detected by their power of 
 chemically decomposing the salts of silver and other photographic materials. The 
 shortness of these waves causes them to suffer a greater amount of deviation 
 or refraction than the luminous waves when the light is passed through a prism,, 
 so that their effects are chiefly perceived in that part of the spectrum which lies 
 beyond the violet light, and is usually termed the ultra-violet. Many substances 
 which are perfectly transparent are able to intercept a large proportion of these 
 actinic waves, as they are termed, and are said to be adiactinic, whilst those which 
 transmit them freely are diactinic. 
 
 Rock crystal, or quartz, is much more diactinic than glass, and lenses and 
 prisms of this material are used in experiments upon this subject, the light of a 
 stream of electric sparks being allowed to pass through the slit of a spectroscope 
 (p. 328), through a cell with quartz sides containing the liquid under examina- 
 tion, then through a quartz lens and prisms and afterwards received upon a sensi- 
 tive photographic plate upon which that portion of the ultra-violet waves which 
 has passed through leaves its impression. 
 
 It has been shown, by such experiments, that the normal alcohols derived from 
 the paraffins are highly diactinic, and that the corresponding acids are somewhat 
 less so, absorbing more of the highly refrangible waves remote from the violet 
 end of the spectrum ; the diactinic character decreasing, in both acids and alcohols, 
 as the molecular weight increases. Benzene and its derivatives are highly adiactinic,. 
 
ABSORPTION SPECTRA. 789 
 
 and, when employed in strong solutions, are often capable of absorbing all the 
 ultra-violet waves ; but when diluted to a certain extent with water or alcohol, 
 they allow some of the waves to pass, and produce photographs of spectra exhibiting 
 absorption-bands due to this selective absorption. Since isomeric benzene derivatives 
 exhibit very different absorption-bands, the selective absorption must be due to 
 vibrations within the molecules, while the general absorption, which varies with 
 the molecular weight, is caused by the vibration of the molecules themselves. 
 There is very strong evidence that the absorption-bands in the ultra-violet spectrum 
 are exhibited only by those compounds in which the carbon atoms form closed 
 chains, as in benzene (p. 542), and naphthalene (p. 552), in which there are three 
 pairs of doubly linked carbon atoms. 
 
 Starch, glucose, saccharose, diastase, and gelatine are highly diactinic, and show 
 no absorption-bands, while albumin, casein, and serin exhibit absorption-bands in 
 dilute solution. 
 
 The photographic absorption-spectra afford a most accurate method of identi- 
 fying organic substances, and a most delicate test of their purity, since the 
 absorption-bands are visible in solutions of extreme dilution. 
 
ON SOME OF THE 
 
 USEFUL APPLICATIONS OF THE PRINCIPLES OF 
 ORGANIC CHEMISTRY. 
 
 DESTRUCTIVE DISTILLATION OF COAL. 
 
 598. An extraordinary progress has been made by chemistry since the intro- 
 duction of the manufacture of coal-gas. No other branch of manufacture has 
 brought into notice so many compounds not previously obtained from any other 
 source, and above all, offering, at first sight, so very little promise of utility, as 
 to press urgently upon the chemist the necessity for submitting them to investi- 
 gation. 
 
 Although many important additions to chemical knowledge have resulted from 
 the labours of those who have engaged in devising f,he best methods of obtaining 
 the coal-gas itself in the state best fitted for consumption, far more benefit has 
 accrued to the science from investigations into the nature of the secondary pro- 
 ducts of the manufacture, the removal of which was the object to be attained in 
 the purification of the gas. 
 
 Of the compounds of carbon and hydrogen, very little was known previously to 
 the introduction of coal-gas ; and although the liquid hydrocarbons composing 
 coal-naphtha were originally obtained from other sources, the investigation of 
 their chemical properties has been greatly promoted by the facility with which 
 they may be obtained in large quantities from that liquid. The most important 
 of these hydrocarbons, benzole or benzene, was originally procured from benzoic 
 acid ; but it would have been impossible for it to have fulfilled its present useful 
 purposes unless it had been obtained in abundance as a secondary product in the 
 manufacture of coal-gas ; for, leaving out of consideration the various uses to 
 which benzene itself is devoted, it yields the nitrobenzene so much used in per- 
 fumery, and from this we obtain aniline, from which many of the most beautiful 
 dyes have been prepared. 
 
 The naphthalene found so abundantly in coal-tar possesses a peculiar interest, as 
 having formed the subject of the classical researches by which Laurent was led to 
 propose the doctrine of substitution, which has since thrown so much light upon 
 the constitution of organic substances. 
 
 We are also especially indebted to coal-tar for our acquaintance with the very 
 interesting and rapidly extending class of volatile alkalies, of which the above- 
 mentioned aniline is the chief representative, and for phenic or carbolic acid, 
 from which are derived the large number of substances composing the phenyl 
 series. 
 
 The retorts in which the distillation of coal is effected are made of fire-clay, 
 generally having the form of a flattened cylinder, and arranged in sets of three or 
 five, heated by the same coal-fire or gas furnace (Fig. 284). The coal is thrown on 
 to the red-hot floor of the retort, as soon as the coke from the previous distillation 
 has been raked out ; the mouth of the retort is then closed with an iron plate 
 luted with clay. An iron pipe rises from the upper side of the front of the retort 
 projecting from the furnace, and is curved round at the upper extremity, which 
 passes into the side of a much wider tube, b, called the hydraulic main, running 
 above the furnaces, at right angles to the retorts, and receiving the tubes from all 
 of them. This tube is always kept half full of the tar and water condensed from 
 
GAS MANUFACTURE. 
 
 791 
 
 the gas, and below the surface of this liquid the delivery tubes from the retorts 
 are allowed to dip, so that, although the gas can bubble freely through the liquid, 
 as it issues from the retort, none can return through the tube whilst the retort is 
 open for the introduction of a fresh charge. 
 
 Exhausters are used in most gas-works, to prevent the pressure in the retort 
 from exceeding that of the atmosphere, thus diminishing loss by leakage, and 
 quickly removing the gas from the injurious effect of the hot retort. 
 
 The aqueous portion of the liquid deposited in the hydraulic main is known as 
 the ammoniacal liquor, from its consisting chiefly of a solution of various salts 
 of ammonium, the chief of which is the carbonate ; sulphide, cyanide and sulpho- 
 cyanide of ammonium are also found in it. 
 
 * From the hydraulic main the gas passes into the condenser, e, which is composed 
 of a series of bent iron tubes kept cool either by the large surface which they 
 expose to the air. or sometimes by a stream of cold water. In these are deposited, 
 in addition to water, any of the volatile hydrocarbons and ammonium salts whioh 
 may have escaped condensation in the hydraulic main. Even in the condenser 
 the removal of the ammoniacal salts is not complete, so that it is usually necessary 
 to pass the gas through a scrubber or case containing fragments of coke, over 
 which a stream of water is allowed to trickle, in order to absorb the remaining 
 ammoniacal vapours. 
 
 Fig. 284. Manufacture of coal-gas. 
 
 The tar which condenses in the hydraulic main is a very complex mixture, of 
 which the following are some of the leading components : 
 
 NEUTRAL HYDROCARBONS. 
 
 Liquid. 
 Benzene 
 Toluene. 
 Xylene. 
 Isocumene. 
 
 Solid. 
 
 Naphthalene. 
 Anthracene. 
 Chrysene. 
 Pyrene. 
 
 ALKALINE PRODUCTS. 
 
 Ammonia. 
 
 Aniline. 
 
 Picolire. 
 
 Quinoline. 
 
 Pyridine. 
 
 ACID PRODUCTS. 
 Carbolic acid. 
 Kresylic. 
 Rosolic. 
 Acetic. 
 
792 
 
 PURIFICATION OF COAL-GAS. 
 
 The gas is now passed through the lime-purifier, /, which is an iron bex with 
 shelves on which dry slaked lime is placed in order to absorb the carbonic acid 
 gas, sulphuretted hydrogen, and carbon bisulphide. 
 
 A great many other methods have been devised for the purification of the gas 
 from sulphuretted hydrogen, but none appears to be so efficacious and economical 
 as that which consists in passing the gas over hjdrated iron oxide* mixed with 
 sawdust (which is employed to prevent the material from caking). 
 
 The action oil the sulphuretted hydrogen on the ferric oxide is represented by 
 two equations (i) Fe 2 O 3 + H 2 S = 2FeO + H 2 + S; (2)Fe 2 3 + 3H 2 S = 2FeS + 3H 2 + S; 
 and the circumstance which especially conduces to the economy of the process 
 is the facility with which the ferrous sulphide and oxide may be reconverted into 
 the ferric oxide by mere exposure to the action of atmospheric oxygen ; for 
 2FeS + O 3 = Fe 2 3 + S 2 , thus reviving the power of the mixture to absorb sul- 
 phuretted hydrogen. Accordingly, the material is periodically exposed to the 
 action of air ; or, as is sometimes practised, a small quantity of air is admitted 
 into the purifier together with the gas ; this reconverts the ferrous sulphide and 
 oxide into ferric oxide, and the oxidation is attended with enough heat to convert 
 into vapour any benzene which may have condensed in the purifying mixture, and 
 of which the illuminating value would otherwise be lost. The same purifying 
 mixture may thus be employed to purify a very large quantity of gas, until the 
 separated sulphur (55 per cent.) has increased its bulk to an inconvenient extent, 
 when the spent oxide is burnt for making vitriol (p. 225). The process for 
 removing the carbon bisulphide vapour is mentioned at p. 241. 
 
 The purified gas is passed into the gasometers, g, from which it is supplied for 
 consumption. 
 
 In the manufacture of coal-gas, attention is requisite to the temperature (1800 
 to 2000 F.), at which the distillation is effected, for, if it be too low, the solid and 
 liquid hydrocarbons will be formed in too great abundance, not only diminishing 
 the volume of the gas, but causing much inconvenience by obstructing the pipes. 
 On the other hand, if the retort be too strongly heated, the vapours of volatile 
 hydrocarbons, as well as the olefiant gas and marsh gas, may undergo decompo- 
 sition, depositing their carbon upon the sides of the retort, in the form of gas- 
 carbon, and leaving their hydrogen to increase the volume and dilute the illu- 
 minating power of the gas. 
 
 These effects are well exemplified in the following table, which contains 
 analyses of the gas collected at different periods of the distillation : 
 
 In 100 volumes. 
 
 After 10 mins. 
 
 After i^ hours. 
 
 After 3^ hours. 
 
 After 5^ hours. 
 
 Sulphuretted hydro- 
 
 
 
 
 
 gen 
 
 1.30 
 
 1.42 
 
 0.49 
 
 0. II 
 
 Carbon dioxide 
 
 2.21 
 
 2.09 
 
 1.49 
 
 1.50 
 
 Hydrogen 
 
 20.10 
 
 38.33 
 
 52.68 
 
 67.12 
 
 Carbon monoxide . 
 
 6.19 
 
 5 .68 
 
 6.21 
 
 6.12 
 
 Marsh gas 
 
 57.38 
 
 44-03 
 
 33-54 
 
 22.58 
 
 Illuminants (see p. 
 
 
 
 
 
 161) . 
 
 10.62 
 
 5.98 
 
 3-04 
 
 1.79 
 
 Nitrogen . 
 
 2. 2O 
 
 2.47 
 
 2-55 
 
 0.78 
 
 Much advantage is said to be gained by mixing the coal with a certain propor- 
 tion of lime, which diminishes the sulphur in the gas and increases the yield of 
 ammonia. 
 
 One of the most useful of the secondary products of the coal-gas manufacture 
 is the ammonia, and this process has been already noticed as a principal source 
 of the ammoniacal salts found in commerce. 
 
 Next in the order of usefulness stands the coal-tar, which deserves attentive 
 consideration, not only on that account, but because the extraction of the various 
 useful substances from this complex mixture affords an excellent example of 
 
 * Browii haematite (bog- ore) is frequently employed. 
 
COAL-TAR DYES. 
 
 793 
 
 proximate organic analysis, that is, of the separation of an organic mixture into 
 its immediate components. 
 
 For the separation of the numerous volatile substances contained in coal-tar 
 advantage is taken of the difference in their boiling-points. 
 
 A large quantity of the tar is distilled in an iron retort, when water passes over, 
 holding salts of ammonia in solution, and accompanied by a brown oily offensive 
 liquid which collects upon the surface of the water. This is a mixture of the 
 hydrocarbons, which are lighter than water, viz., benzene, toluene, xylene, and 
 isocumene, all having a specific gravity of about 0.85. 100 parts of the tar yield, 
 at most, 10 parts of this light oil. 
 
 As the distillation proceeds and the temperature rises, a yellow oil distils over, 
 which is heavier than water, and sinks in the receiver. This oil, commonly called 
 dead oil, is much more abundant than the light oil, amounting to one-fourth 
 of the weight of the tar, and contains those constituents of the tar which have a 
 high specific gravity and boiling-point, particularly naphthalene, aniline, quino- 
 line, and carbolic acid. The proportion of naphthalene in this oil increases with 
 the progress of the distillation, as would be expected from its high boiling-point, 
 so that the last portions of the oil which distil over become nearly solid on cool- 
 ing. When this is the case, the distillation is generally stopped, and a black 
 viscous residue is found in the retort, which constitutes pitch, and is employed 
 for the preparation of Brunswick black and of asphalt for paving. 
 
 The light oil which first passed over is rectified by a second distillation, and is 
 then sent into commerce under the name of coal-naphtha, a quantity of the heavy 
 oil being left in the retort, the lighter oils having lower boiling-points. 
 
 This coal-naphtha may be further purified by shaking it with sulphuric acid, 
 which removes several of the impurities, whilst the pure naphtha collects on the 
 surface when the mixture is allowed to stand. When this is again distilled it 
 yields the rectified coal-naphtha. 
 
 The distillation of cannel coal, and of various minerals nearly allied to coal, at 
 low temperatures, is now extensively carried on for the manufacture of paraffin 
 and paraffin oil (see Paraffin). 
 
 Coal-tar dyes. The first dye ever manufactured from aniline on a large scale 
 was that known as mauve,* or aniline purple, which is obtained by dissolving ani- 
 line in diluted sulphuric acid, and adding solution of bichromate of potash, when 
 the liquid gradually becomes dark-coloured, and deposits a black precipitate which 
 is filtered off, washed, boiled with coal-naphtha to extract a brown substance, and 
 afterwards treated with hot alcohol, which dissolves the mauve. The chemical 
 change by which the aniline has been converted into this colouring-matter cannot 
 at present be clearly traced, but the basis of the colour has been found to be a 
 substance which has the composition C^H^^ and has been termed mauvdine. It 
 forms black shining crystals, resembling specular iron ore, which dissolve in 
 alcohol, forming a violet solution, and in acids, with production of the purple 
 colour. Mauveine combines with the acids to form salts ; its alcoholic solution 
 even absorbs carbonic acid gas. The hydrochloride of mauveine, C^R^N^Hd, 
 forms prismatic needles with a green metallic lustre. 
 
 Very brilliant red dyes are obtained from commercial aniline by the action of 
 carbon tetrachloride, stannic chloride, ferric chloride, cupric chloride, mercuric 
 nitrate, corrosive sublimate, and arsenic acid. It will be noticed that all these 
 agents are capable of undergoing reduction to a lower state of oxidation or chlori- 
 nation, indicating that the chemical change concerned in the transformation of 
 aniline into aniline-red is one in which the aniline is acted on by oxygen or 
 chlorine. The easiest method of illustrating the production of aniline red on the 
 small scale consists in heating a few drops of aniline in a test-tube with a frag- 
 ment of corrosive sublimate (mercuric chloride), which soon fuses and acts upon 
 the aniline to form an intensely red mass composed of aniline red, calomel, and 
 various secondary products. By heating this mixture with alcohol, the red dye is 
 dissolved, and a skein of silk or wool dipped into the liquid becomes dyed of a 
 fine red, which is not removed by washing. 
 
 On the large scale, magenta (as aniline red is commonly termed) is gene 
 prepared by heating aniline to about 320 F. (160 C.) with arsenic acid when a 
 dark semi-solid mass is obtained, which becomes hard and brittle on cooling, and 
 exhibits a green metallic reflection. This mass contains, in addit 
 
 * French for marshmallow, iii allusion to the colour of the flower. 
 
794 ANILINE DYES. 
 
 red, several secondary products of the action, and arsenious acid. On boiling it 
 with water, a splendid red solution is obtained, and a dark resinous or pitchy 
 mass is left. If common salt be added to the red solution as long as it is dis- 
 solved, the bulk of the colouring-matter is precipitated as a resinous mass, which 
 may be purified from certain adnering matters by drying and boiling with coal- 
 naphtha. The red colouring-matter is the arsenate of a colourless organic base, 
 which has been called rosaniline (p. 722). If the red solution of arsenate of 
 rosaniline be decomposed with calcium hydroxide suspended in water, a pinkish 
 precipitate is obtained, which consists of rosaniline mixed with calcium arsenate, 
 and the solution entirely loses its red colour (cf, p. 722). 
 
 By treating the precipitate with a small quantity of acetic acid, the rosaniline 
 is converted into rosaniline acetate (C 20 H 19 N3.C 2 H 4 O 2 ), forming a red solution, which 
 may be filtered off from the undissoived calcium arsenate. On evaporating the 
 solution to a small bulk, and allowing it to stand, the acetate is obtained in 
 crystals which exhibit the peculiar green metallic lustre of the wing of the rose- 
 beetle, characteristic of the salts of rosaniline. This salt is the commonest com- 
 mercial form of magenta ; its colouring power is extraordinary, a very minute 
 particle imparting a red tint to a large volume of water. Silk and wool easily 
 extract the whole of the colouring-matter from the aqueous solution, becoming 
 dyed a fast and brilliant crimson ; cotton and linen, however, have not so strong 
 an attraction for it, so that if a pattern be worked in silk upon a piece of cambric, 
 which is then immersed in a solution of magenta and afterwards washed in hot 
 water, the colour will be washed out of the cambric ; but the red silk pattern will 
 be left. 
 
 Water dissolves but little rosaniline ; alcohol dissolves it abundantly, forming a 
 deep red solution. Kosaniline forms two classes of salts with acids, those with 
 i molecule of acid (monacid salts) being crimson, and those with three molecules 
 (triacid salts) having a brown colour. Thus, if colourless rosaniline be dissolved 
 in a.little dilute hydrochloric acid, a red solution is obtained, which contains the 
 monacid rosaniline hydrochloride, C 20 H 19 N 3 .HC1 ; but if an excess of hydrochloric 
 acid be added, the red colour disappears, and a brown solution is obtained, from 
 which the triacid hydrochloride. C 20 H 19 N 3 .3HC1, may be crystallised in brown red 
 needles. 
 
 For experimental illustration of the properties of rosaniline, the liquid obtained 
 by boiling a solution of the acetate with a slight excess of lime diffused in water, 
 and filtering while hot, is very well adapted. The solution has a yellow colour, 
 and may be preserved in a stoppered bottle without alteration. If air be breathed 
 into it through a tube, the liquid becomes red from production of rosaniline car- 
 bonate. Characters painted on paper with a brush dipped in the solution are 
 iavisible at first, but gradually acquire a beautiful rose colour. 
 
 The other properties of rosaniline will be found described at p. 722. 
 
 Aniline-yelloiv, or cJirysanilinc (from %pi)creos, golden), is found among the secondary 
 products obtained in the preparation of aniline red. It forms a bright yellow 
 powder, resembling chrome-yellow, and having the composition C^H-^Ng. It 
 is nearly insoluble in water, but dissolves in alcohol. Chrysaniline has basic 
 properties, and dissolves in acids, forming salts. On dissolving it in diluted 
 hydrochloric acid, and mixing the solution with the concentrated acid, a scarlet 
 crystalline precipitate of chrysaniline hydrochloride (C 20 H 17 N 3 .2HC1) is obtained, 
 which is insoluble in strong hydrochloric acid, but very soluble in water. A 
 characteristic feature of chrys-aniline is the sparing solubility of its nitrate. 
 Even from a dilute solution of the hydrochloride, nitric acid precipitates chrys- 
 aniline nitrate (C2oH l7 N 3 .HN0 3 ) in ruby -red needles. 
 
 Aniline-blue is produced as described on p. 723. 
 
 The hydrochloride is an ordinary commercial form of aniline-blue ; it has a 
 brown colour, refuses to dissolve in water, but yields a fine blue solution in 
 alcohol. 
 
 DYEING AND CALICO-FEINTING. 
 
 599. The object of the dyer being to fix certain colouring-matters permanently 
 in the fabric, his processes would be expected to vary with the nature of the latter 
 and of the colour to be applied to it. In order that uniformity of colour and its 
 perfect penetration into the fibre may be obtained, it is evident that the colouring- 
 matter must always be employed in a state of solution ; and it must be rendered 
 
DYEING. 
 
 fast, or not removable by washing, by assuming an insoluble condition in the 
 fibre. 
 
 The simplest form of dyeing is that in which the fibre itself forms an insoluble 
 compound with the colouring-matter. Thus, if a skein of silk be immersed in a 
 solution of indigo in sulphuric acid, it removes the whole of the colouring-matter 
 from the liquid, and may then be washed with water without losing colour but 
 if the same experiment be tried with cotton, the indigo will not be withdrawn 
 from the solution, and when the cotton has been well squeezed and rinsed with 
 water, it will become white again. It may be stated generally, that the animal 
 fabrics (silk and wool) will absorb and retain colouring-matters with much 
 greater facility than vegetable fabrics (cotton and linen). In the absence of so 
 powerful an attraction between the fibre and the colouring-matter, it is usual to 
 impregnate the fabric with a mordant or substance having an attraction for the 
 colour, and capable of forming an insoluble combination with it, so as to retain it 
 permanently attached to the fabric. Thus, if a piece of cotton be boiled in a 
 solution of acetate of alumina, the alumina will be precipitated in the fibre ; and 
 if the cotton be then soaked in solution of cochineal or of logwood, the red 
 colouring-matter will form an insoluble compound (or lake) with the alumina, and 
 the cotton will be dyed of a fast red colour. 
 
 Another method of fixing the colour in the fabric consists in impregnating 
 the latter with two or more liquids in succession, by the admixture of which 
 the colour may be produced in an insoluble state. If a piece of any stuff be 
 soaked in solution of ferric chloride, and afterwards in potassium terro- 
 cyanide, the Prussian blue which is precipitated in the fibre will impart a fast 
 blue tint. 
 
 An indispensable preliminary step to the dyeing of any fabric is the removal of 
 all natural grease or colouring-matter, which is effected by processes varying with 
 the nature of the fibre, and is preceded, in the cases of cotton and woollen 
 materials which are to receive a pattern, by certain operations of shaving and 
 singeing for removing the short hairs from the surface. 
 
 From linen and cotton, the extraneous matters (such as grease and resin) are 
 generally removed by weak solutions of carbonate of potassium or of sodium, 
 and the fabrics are afterwards bleached by treatment with chloride of lime 
 (p. 183). 
 
 But since the fibres of silk and wool are much more easily injured by alkalies and 
 by chlorine, greater care is requisite in cleansing them. Silk is boiled with a 
 solution of white soap to remove the gum, as it is technically termed ; but the 
 natural grease, suint or yolk, is extracted from wool by soaking at a moderate tem- 
 perature in a weak bath either of soap or of ammoniacal (putrefied) urine. Both 
 silk and wool are bleached by sulphurous acid (p. 220). 
 
 Among the red dyes the most important are madder, alizarine, Brazil wood, 
 cochineal, lac, and the aniline reds. 
 
 In dyeing red with madder or Brazil wood, the linen, cotton, or wool is first 
 mordanted by boiling in a solution containing alum and bitartrate of potash, 
 when it combines with a part of the alumina, and on plunging the stuff into a hot 
 infusion of madder, the colouring-matter forms an insoluble combination with 
 that earth. 
 
 To dye Turkey-red, the stuff is also mordanted with alum, but has previously 
 to undergo several processes of treatment with oil and with galls, the necessity p 
 which is satisfactorily established in practice, though it is not easy to explain 
 their action. The colour is finally brightened by boiling the stuff with chloi 
 of tin. 
 
 Woollen cloth is dyed scarlet with lac or cochineal, having been fin-t mordant* 
 by boiling in a mixture of perchloride of tin and bitartrate of potash. 
 
 The aniline colours (see p. 794) are employed for dyeing silk and wool, ei 
 without any mordant or with the help of albumin. 
 
 Slues are generally dyed with indigo (p. 761), or with Prussian blue ; m tl 
 latter case the stuff is steeped successively in solutions of a salt of peroxide 01 
 iron and of potassium ferrocyanide. Aniline blue is also much employed 
 and woollen fabrics. ... , 
 
 The principal yellow dyes are weld, quercitron, fustic, annatto, chrysamline, ai 
 lead chromate. For the first four colouring-matters aluminous mordants are 
 generally applied. Lead chromate is produced in the fibre of the stuff, which 11 
 soaked for that purpose, first in a solution of acetate or nitrate of lead, and 1 
 
796 CALICO-FEINTING. 
 
 in potassium chromate. Carbazotic or picric acid (p. 711) is also sometimes 
 employed as a yellow dye. 
 
 In dyeing blacks and broivns, the stuffs are steeped first in a bath containing 
 some form of tannin (p. 610), such as infusion of galls, sumach, or catechu, and 
 afterwards in a solution of salt of iron, different shades being produced by the 
 addition of indigo, of copper sulphate, &c. 
 
 The art of calico printing differs from that of dyeing in that the colour is re- 
 quired to be applied only to certain parts of the fabric so as to produce a pattern 
 or design either of one or of several colours. 
 
 A common method of printing a coloured pattern on a white ground consists in 
 impressing the pattern by passing the stuff under a roller, to which an appropriate 
 mordant thickened with British gum (p. 736) is applied. The stuff is then 
 dunged i.e., drawn through a mixture of cow-dung and water, which appears to 
 act by removing the excess of the mordant, and afterwards immersed in the hot 
 dye-bath, when the colour becomes permanently fixed to the mordanted device, 
 but may be removed from the rest of the stuff by washing. 
 
 If the pattern be printed with a solution of acetate of iron, and the stuff im- 
 mersed in a madder-bath, a lilac or black pattern will be obtained according to 
 the strength of the mordant employed. By using acetate of alumina as a mordant, 
 the madder-bath would give a red pattern. 
 
 A process which is the reverse of this is sometimes employed, the pattern being 
 impressed with a resist, that is, a substance which will prevent the stuff from 
 taking the colour in those parts which have been impregnated with it. For 
 example, if a pattern be printed with thickened tartaric or citric acid, and the 
 stuff be then passed through an aluminous mordant, the pattern will refuse to 
 take up the alumina, and subsequently the colour from the dye-bath. Or a 
 pattern may be printed with nitrate of copper, and the stuff passed through 
 a bath of reduced indigo (p. 762), when the nitrate of copper will oxidise the 
 indigo, and, by converting it into the blue insoluble form, will prevent it from 
 sinking into the fibre of those parts to which the nitrate has been applied, whilst 
 elsewhere the fibre, having become impregnated with the white indigo, acquires a 
 fast blue tint when exposed to the air. 
 
 Sometimes the stuff is uniformly dyed, and the colour discharged in order 
 to form the pattern. A white pattern is produced upon a red (madder) or blue 
 (indigo) ground by printing with a thickened acid discharge, and passing the stuff 
 through a weak bath of chloride of lime, which removes the colour from those 
 parts only which were impregnated with the- acid (p. 183). By adding lead 
 nitrate to the acid discharge, and finally passing the stuff through a solution of 
 potassium chromate, a yellow pattern (lead chromate) may be obtained upon the 
 madder-red ground. By applying nitric acid as a discharge, a yellow pattern may 
 be obtained upon an indigo ground (p. 91). 
 
 Very brilliant designs are produced by mordanting the stuff in a solution of 
 stannate of potassium or sodium (p. 453), and immersing it in dilute sulphuric 
 acid, which precipitates the stannic acid in the fibre. 
 
 When the thickened colouring-matters are printed on in patterns and steamed 
 an insoluble compound is formed between the colour and the stannic acid. 
 
 It is evident that, by combining the principles of which an outline has just been 
 given, the most varied parti-coloured patterns may be printed. 
 
 TANNING. 
 
 600. When infusion of nut-galls is added to a solution of gelatine, the latter 
 combines with the tannic acid, and a bulky precipitate is obtained. If a piece of 
 skin, which has approximately the same ultimate composition as gelatine, be 
 placed in the infusion of nut-galls, it will absorb the whole of the tannic acid 
 and become converted into leather, which is much tougher than the raw skin, 
 less permeable by water, and not liable to putrefaction. 
 
 The first operation in the conversion of hides into leather, after they have been 
 cleansed, consists in soaking them for three or four weeks in pits containing lime 
 and water, which saponifies the fat and loosens the hair. The same object is 
 sometimes attained by allowing the hides to enter into putrefaction, when the 
 ammonia produced has the same effect as the lime. The loosened hair is then 
 scraped off, and the hides are soaked in water, which removes adhering lirne. A 
 further effect of the lime is to open the pores of the skin, so as to fit it to receive 
 
TANNING. 
 
 the tanning liquid ; if lime have not been used, a dilute acid should be employed 
 to effect the same purpose. 
 
 The tanning material generally employed for hides is the infusion of oak bark 
 which contains querci-tannic acid, very similar in properties to tannic acid The 
 hides are soaked in an infusion of oak bark for about six weeks being passed in 
 succession through several pits, in which the strength of the infusion is gradually 
 increased. They are then packed in another pit with alternate layers of coarsely 
 ground oak bark ; the pit is filled with water and left at rest for three months 
 when the hides are transferred to another pit and treated in the same way but 
 of course, the position of the hides will now be reversed that which was upper- 
 most, and in contact with the weakest part of the tanning liquor, will now be at 
 the bottom. After the lapse of another three months the hide is generally found 
 to be tanned throughout, a section appearing of a uniform brown colour. It has 
 now increased in weight from 30 to 40 percent. The chemical part of the process 
 being thus completed, the leather is subjected to certain mechanical operations 
 to give it the desired texture. For tanning the thinner kinds of leather, such as 
 morocco, a substance called sumach is used, which consists of the ground shoots 
 of the Rhus coriaria, and contains a large proportion of tannic acid. 
 
 Morocco leather is made from goat and sheep skins, which are denuded of hair 
 by liming in the usual way, but the adhering lime is afterwards removed by 
 means of a bath of sour bran or flour. In order to tan the skin so prepared, it is 
 sewn up in the form of a bag, which is filled with infusion of sumach, and allowed 
 to soak in a vat of the infusion for some hours. A repetition of the process, with 
 a stronger infusion, is necessary ; but the whole operation is completed in twenty- 
 four hours. The skins are now washed and dyed, except in the case of red 
 morocco, which is dyed before tanning, by steeping it first in alum or chloride of 
 tin, as a mordant, and afterwards in infusion of cochineal. Black morocco is 
 dyed with acetate of iron, which acts upon the tannic acid. The aniline dyes are 
 now much employed for dyeing morocco. 
 
 The kid of which gloves are made is not actually tanned, but submitted to an 
 elaborate operation called taiving, the chief chemical features of which are the 
 removal of the excess of lime,* and opening the pores of the skin by means of a 
 sour mixture of bran and water, in which lactic acid is the agent ; and the sub- 
 sequent impregnation of the porous skin with aluminium chloride, by steeping it 
 in a hot bath containing alum and common salt. The skins are afterwards 
 softened by kneading in a mixture containing alum, flour, and the yoke of eggs. 
 The putrefaction of the skin is as effectually prevented by the aluminium chloride 
 as by tanning. 
 
 Wash-leather and buckskin are not tanned, but s/tamoyed, which consist in 
 sprinkling the prepared skins with oil, folding them up, and stocking them under 
 heavy wooden hammers for two or three hours. When the grease has been well 
 forced in, they are exposed in a warm atmosphere, to promote the drying of the 
 oil by absorption of oxygen (p. 798). These processes having been repeated the 
 requisite number of times, the excess of oil is removed by a weak alkaline bath, 
 and the skins are dried and rolled. The buff colour of wash-leather is imparted 
 by a weak infusion of sumach. 
 
 Parchment is made by stretching lamb or goat skin upon a frame, removing the 
 hair by lime, and scraping, as usual, and afterwards rubbing with pumice-stone, 
 until the proper thickness is acquired. 
 
 OILS AND FATS. 
 
 601. A very remarkable feature in the history of the fats is the close resem- 
 blance in chemical composition and properties which exists between them, 
 whether derived from the vegetable or the animal kingdom. They all contain 
 two or more neutral substances which furnish glycerine when saponified, together 
 with some of the acids of the acetic series or of series closely allied to it. 
 
 One of the most useful vegetable fatty matters is palm, oil, which is extracts 
 by boiling water from the crushed fruit of the Elau t/nmsr/txix, an African palm. 
 It is a semi-solid fat, which becomes more solid when kept, since it then und 
 goes a species of fermentation, excited apparently by an albuminous substance 
 contained in it, in consequence of which the palmitin (C^H^O^is conver 
 
 * Tolysulphides of sodium or calcium are sometimes employed for removing the hair. 
 
OILS. 
 
 glycerine and palmitic acid. The bleaching of palm oil is effected by the action 
 of a mixture of sulphuric or hydrochloric acid and potassium dichromate, which 
 oxidises the yellow colouring-matter. 
 
 Cocoa-nut oil is also semi-solid, and is remarkable for the number of acids of the 
 acetic series which it yields when saponified viz., caproic, caprylic, rutic, lauric, 
 myristic, and palmitic. 
 
 These fats are chiefly used in the manufacture of soap and candles. 
 
 Salad oil, 0t sweet oil(olire oil), is obtained by crushing olives, and an inferior 
 kind which is used for soap is obtained by boiling the crushed fruit with water. 
 When exposed to a temperature of about 32 F. a considerable portion of the oil 
 solidifies ; this solid portion is generally called margarin (C 54 H 104 O 6 ) ; it is much 
 less soluble in alcohol than stearin is, though more so than palmitin. When saponi- 
 fied, margarin yields glycerine and margaric acid (C 17 H 34 2 ). This acid appears to 
 be really composed of stearic and palmitic acids, into which it may be separated 
 by repeated crystallisation from alcohol, when the palmitic acid is left in solution. 
 The fusing-point of margaric acid is 140 F., that of stearic being 159, and that 
 of palmitic, 144, but a mixture of 10 parts of palmitic with i part of stearic acid 
 fuses at 140. 
 
 That portion of the olive oil which remains liquid below 32 F. consists of olein 
 (C 57 H 104 O 6 ). 2 , and forms nearly three-fourths of its weight. 
 
 It is well known that salad* oil becomes rancid and exhales a disagreeable odour 
 after being kept for some time. This appears to be due to a fermentation similar 
 to that noticed in the case of palm oil, originally started by the action of atmo- 
 spheric oxygen upon albuminous matters present in the oil ; the neutral fatty 
 matters are thus partly decomposed, as in saponification ; their corresponding 
 acids being liberated, and giving rise (in the case of the higher members of the 
 acetic series, such as caproic and valerianic) to the disagreeable odour of rancid 
 oil. By boiling the altered oil with water, and afterwards washing it with a weak 
 solution of soda, it may be rendered sweet again. 
 
 Almond oil, extracted by a process similar to that employed for olive oil, is also 
 very similar in composition ; but colza oil (rape oil), obtained from the seeds of the 
 Srassicaoleifera, contains only half its weight of olein, and hence solidifies more 
 readily than the others. 
 
 Colza oil is largely used for burning in lamps, and undergoes a process of puri- 
 fication from the mucilaginous substances which are extracted with it from the 
 seed, and leave a bulky carbonaceous residue when subjected to destructive dis- 
 tillation in the wick of the lamp. To remove these, the oil is agitated with about 
 2, per cent, of oil of vitriol, which carbonises the mucilaginous substances, but 
 leaves the oil untouched. When the carbonaceous flocks have subsided, the oil is 
 drawn off, washed to remove the acid, and filtered through charcoal. 
 
 Linseed oil, obtained from the seeds of the flax plant, is much richer in olein 
 than any of the foregoing, exhibiting no solidification till cooled to 15 or 20 F. 
 below the freezing-point. It exhibits, however, in a far higher degree, a tendency 
 to become solid when exposed to the air, which has acquired for it the name of 
 a drying oil, and renders it of the greatest use to painters. This solidification is 
 attended with absorption of oxygen, which occurs so rapidly in the case of linseed 
 oil that spontaneous combustion has been known to take place in masses of rag 
 or tow which have been smeared with it.* 
 
 The tendency of linseed oil to solidify by exposure is much increased by heat- 
 ing it with about ^V-h of litharge, or T Vth of black oxide of manganese; these 
 oxides are technically known as dryers, and oil so treated is called boiled linseed 
 oil. The action of these metallic oxides is net well understood. 
 
 The strong drying tendency of linseed oil is supposed to be due to a peculiarity 
 in the olein, which is said not to be ordinary olein, but to furnish a different 
 acid, linoleic acid, when saponified. When linseed oil is exposed for some time to 
 a high temperature, it becomes viscous and treacly, and is used in this state for 
 the preparation of printing ink. If the viscous oil be boiled with dilute nitric 
 acid, it is converted into artificial caoutchouc, which is used in the manufacture of 
 surgical instruments. This property appears to be connected with the drying 
 qualities of the oil. 
 
 Castor oil, obtained from the seeds of Ricinus communis, also yields a peculiar 
 
 * During 1 the oxidation, a volatile compound is formed which resembles acrolein in smell, 
 and colours unsized paper brown. It has been suggested that the brown colour and musty 
 smell of old books may be due to the oxidation of the oil in the printing-ink. 
 
BUTTER. 
 
 acid when saponified, termed ricinoUie (H-C 18 H 33 O :j ), containing one more atom 
 of oxygen than o.eic acid, which it much resembles. The destructive distillation 
 of castor oil yields cenantliic add (iTC 7 H 13 2 ) and temnthol, or cenanthn- ,//,/,.// ,/fe 
 (C 7 H 14 0), and by distilling it with caustic potash, caprylic alcohol (C.H..O) is 
 obtained. As in the case of olive oil, the cold-drawn castor oil, which is expressed 
 from the seeds without the aid of heat, is much less liable to become rancid 
 Castor oil is much more soluble in alcohol than is any other of the fixed oils 
 
 The various fish oils, such as seal and whale oil, also consist chiefly of olein 
 and appear to owe their disagreeable odour to the presence of certain volatile 
 acids, such as valerianic. 
 
 Cod-liver oil appears to contain, in addition to olein and stearin, a small quan- 
 tity of acetin (C 9 H 14 O 6 ), which yields acetic acid and glycerine when saponified. 
 Some of the constituents of bile have also been traced in it, as well as minute 
 quantities of iodine and bromine. 
 
 Butter contains about half its weight of solid fat, which consists in great part 
 of palmitin and stearin, but contains also butin, which yields glycerine and bufir 
 acid (H-C 20 H 39 0. 2 ) when saponified. The liquid portion consists chiefly of olein. 
 Butter also contains small quantities of butyrin, caproin, and caprin, which 
 yield, when saponified, glycerine and butyric (H'C 4 H 7 2 ), caproic (H-C 6 H n O.,), 
 and capric (H'OpH^Oa) acids, distinguished for their disagreeable odour. Fresh 
 butter has very little odour, being free from these volatile acids, but if kept for 
 some time, especially if the casein of the milk has been imperfectly separated in 
 its preparation, spontaneous resolution of these fats into glycerine and the volatile 
 disagreeable acids occurs. By salting the butter this change is in great measure 
 prevented. Margarine, the butter substitute, is made from the less solid portion 
 of mutton suet. 
 
 The fat of the sheep and ox (suet, or, when melted, tallow) consists chiefly of 
 stearin, whilst in that of the pig (lard) olein predominates to about the same 
 extent as in butter. Palmitin is also present in these fats. Benzoated lard con- 
 tains some gum benzoin, which prevents it from becoming rancid. 
 
 Human fat contains chiefly olein and margarin (or, if we do not admit the 
 independent existence of the latter, palmitin and stearin). 
 
 Sperm oil, which is expressed from the spermaceti found in the brain of the 
 sperm whale, owes its peculiar odour to the presence of a fat which has been 
 called phocen'm, but which appears to be valerin, as it yields glycerine and 
 valerianic acid (H -0511902) when saponified. 
 
 The beautiful solid crystalline fat, known as spermaceti or cetin, differs widely 
 from the ordinary fatty matters, for when saponified (which is not easily effected), 
 it yields no glycerine, but in its stead cetyl alcohol (p. 570). 
 
 The soap prepared from spermaceti, when decomposed by an acid, yields palm- 
 itic acid (H-C 16 H 31 2 ). 
 
 Ambergris, used in perfumery, is a fatty substance found in the intestines of 
 the spermaceti whale. Boiling alcohol extracts from it about 80 per cent, of 
 ambrein. 
 
 Chinese wax, the produce of an insect of the Cochineal tribe, is analogous in its 
 chemical constitution to spermaceti. When saponified by fusion with caustic 
 potash, it yields cerotin, or ceryl alcohol (C^H^'OH), and ceroticacid(E.'Cy,E. m O.,). 
 Cerotic acid is also contained in ordinary bees'-wax, from which it may be 
 extracted by boiling alcohol, and crystallised as the solution cools. It forms 
 about two-thirds of the weight of the wax. Cerotic acid is found among the 
 products of oxidation of paraffin by chromic acid. 
 
 Sees' -wax also contains about one-third of its weight of myricin (C^H^O.,), a 
 substance analogous to spermaceti, which yields, when saponified, palmitic acid 
 and melissin, or myricyl alcohol (C 30 H 61 'OH). The colour, odour, and tenacity 
 of bees'-wax appear to be due to the presence of a greasy substance called Offvfei*, 
 which forms about -fa of the wax, and has not been fully examined. The tree wax 
 of Japan is said to be pure palmitin. 
 
 Wax is bleached for the manufacture of candles, by exposing it in thin strips or 
 ribands to the oxidising action of the atmosphere, or by boiling it with nitrate of 
 soda and sulphuric acid. Chlorine also bleaches it, but displaces a portion of the 
 hydrogen in the wax, taking its place and causing the evolution of hydroc 
 acid vapours when the wax is burnt. 
 
 The following table includes the principal fatty bodies and their c< 
 acids, with their f using-points : 
 
8oo 
 
 MANUFACTUEE OF SOAP. 
 
 Neutral 
 Fats. 
 
 Formula. 
 
 Chief 
 Source. 
 
 Fusing- 
 point, 
 Fahr. 
 
 Fatty 
 Acids. 
 
 Formula. 
 
 Fusing- 
 point, 
 Fahr. 
 
 Stearin 
 
 CWHuflOg 
 
 Tallow 
 
 125 to 157 
 
 Stearic 
 
 Qw^gs^a 
 
 !59 
 
 Palmitin 
 
 C^lHggOg 
 
 Palm oil 
 
 114 to 145 
 
 Palmitic 
 
 C 16 H 32 2 
 
 144 
 
 Margarin 
 
 ^54^104^6 
 
 Olive oil 
 
 116 
 
 Margaric 
 
 C ]7 H 34 2 
 
 140 
 
 Olein 
 
 ^57^104^6 
 
 n 
 
 Below 32 
 
 Oleic 
 
 C 18 H 34 
 
 40 
 
 Cetin 
 
 C 32 H 642 
 
 Spermaceti 
 
 120 
 
 Palmitic 
 
 Ci6H 32 2 
 
 144 
 
 Myriciu 
 
 C 46 H 922 
 
 Bees' -wax 
 
 162 
 
 ?5 
 
 
 
 CHEMISTRY OF SOAP. 
 
 602. The manufacture of soap affords an excellent instance of a process which 
 was in use for centuries before anything was known of the principles upon which 
 it is based, for it was not till the researches of Chevreul were published in 1813 
 that any definite ideas were entertained with respect to the composition of the 
 various fats and oils from which soaps are made. 
 
 The investigations of Chevreul are conspicuous among the labours which have 
 contributed in so striking a manner to the rapid advancement of chemistry during 
 the nineteenth century ; undertaken when the chemistry of organic substances had 
 scarcely advanced beyond the dignity of an art, when the principles of classifica- 
 tion were almost entirely empirical, and hardly any research had been published 
 which would serve as a model, these investigations reflect the remarkable sagacity 
 and accuracy of their author. 
 
 The sense of our obligation to this eminent chemist is further increased, when 
 we remember that the ultimate analysis of organic substances was then effected 
 by a very difficult and laborious process, whilst the doctrine of combining pro- 
 portions was so imperfectly understood, that it could afford but little assistance 
 in confirming or interpreting the result of analysis. 
 
 All soaps are formed by the action of the alkalies upon the oil and fats. 
 
 In the manufacture of soap, potash and soda are the only alkalies employed, the 
 former for soft, the latter for hard soaps. 
 
 The fatty matters used by the soap-maker are chiefly tallow, palm oil, coco- 
 nut oil, and kitchen stuff, for hard soaps, and seal oil and whale oil for soft 
 soaps. 
 
 In the manufacture of hard soap, the alkali is prepared by decomposing or 
 caustifying sodium carbonate (soda-ash) with slaked lime, Na 2 CO 3 + Ca(OH) 2 = 
 CaC0 3 + 2NaOH, the clear solution of sodium hydroxide, or soda-ley, being drawn 
 off from the insoluble calcium carbonate. 
 
 The tallow is at first boiled with a weak soda-ley,* because the soap which is 
 formed is insoluble in a strong alkaline solution, and would enclose and protect a 
 quantity of undecom posed tallow ; in proportion as the saponification proceeds, 
 stronger leys are added, until the whole of the grease has disappeared. In order 
 to separate the soap which is dissolved, advantage is taken of the insolubility of 
 soap in solution of salt ; a quantity of common salt being thrown into the boiler, 
 the soap rises to the surface, when the spent ley is drawn off from below, and the 
 soap transferred to iron moulds that it may harden sufficiently to be cut up into 
 bars. 
 
 In order to understand the chemistry of this process, it is necessary to know 
 that tallow contains two fatty substances, one of which, stearin^ (C 57 H 110 O 6 ), is 
 solid, and the other, ole'tn (C 57 H 104 6 ), liquid, the quantity of stearin being about 
 thrice that of olein. 
 
 When these fats are acted upon by soda, they undergo decomposition, furnish- 
 ing stearic and oleic acids, which combine with the soda to form soap, whilst a 
 peculiar sweet substance, termed glycerine, passes into solution ; the nature of the 
 decomposition in each case will be understood from the following equations 
 
 * Soap is now sometimes made by the action of the sodium carbonate upon the fat, thus 
 saving- the expense of caustifying (Morfit's process), 
 f Sre'ap, tallow. 
 
SOAP AND CANDLES. 8OI 
 
 C 3 H 5 -(C 18 H 35 0) 3 -0 3 + 3 NaOH = 3Na(C 18 H M 0)0 + C 3 H 8 3 
 .Stearin. Sodium stearate. Glyceriae. 
 
 C 3 H 5 -(C 18 H 33 0) 3 -0 3 + 3 NaOH = 3Na(C 18 H :a O)0 + C,H 8 0, 
 
 Olem - Sodium o'leate. Glycerine ; 
 
 so that the soap obtained by boiling tallow with soda is a mixture of the sodium- 
 stearate with about a third of its weight of sodium oleate and 20 to to per cent 
 of water. 
 
 Palm oil is composed chiefly of palmitin (C K H K 9 ) t a solid fat which is 
 resolved, by boiling with soda, into sodium palmitate (palm oil soap) and gly- 
 cerine ; C 3 H 5 -(C 16 H 31 0) 3 -0 3 + 3 NaOH = 3 Na(C 16 H 31 0)0 + C 3 H 8 3 
 Palmitin. Sodium palmitate. Glycerine. 
 
 In the fish oils the predominant constituent is olein, so that when boiled with 
 potassium hydroxide, they yield potassium oleate (KC 18 H 33 2 ), which composes the 
 chief part of soft soap. 
 
 Castile soap is made from olive oil, which contains olein and a solid fat known 
 as margarln. The latter appears to be really composed of palmitin and 
 stearin, so that the Castile soap is a mixture of oleate, palmitate, and stearate 
 of sodium. 
 
 The peculiar appearance of mottled soap is caused by the irregular distribution 
 of a compound of the fatty acid with oxide of iron, which arranges itself in veins 
 throughout the mass. If the soap contained too much water, so as to render it 
 very fluid when transferred to the moulds, this iron compound would settle down 
 to the bottom, leaving the soap clear, so that the mottled appearance is often 
 regarded as an indication that the soap does not contain an undue proportion of 
 water ; it is imitated, however, by stirring into the pasty soap some ferrous 
 sulphate and a little impure ley containing sodium sulphide, so as to produce the 
 dark sulphide of iron by double decomposition.* 
 
 In the manufacture of yellow soap, in addition to tallow and palm oil, a con- 
 siderable proportion of common rosin (see p. 560) is added to the soap shortly 
 before it is finished. Soft soap is not separated from the water by salt like hard 
 soap, but is evaporated to the required consistency. Transparent soaps are 
 obtained by drying hard soap, dissolving it in hot spirit of wine, and pouring the 
 strong solution into moulds after the greater part of the spirit has been distilled 
 off. Silicated soap is a mixture of soap with silicate of soda. Glycerine soap is 
 prepared by heating the fat with alkali and a little water at about 400 F. for two 
 or three hours, and running the mass at once into moulds. It is, of course, a 
 mixture of soap and glycerine. 
 
 The proportion of water in soap is very variable, some specimens containing 
 between 70 and 80 per cent. The smallest proportion is about 30 per cent. 
 
 The theory of saponification, stated above, has received the strongest confirma- 
 tion within the last few years, by the synthetic production of the fats from 
 glycerine and the fatty acids formed in their saponification. 
 
 CANDLES. 
 
 603. Since tallow fuses at about 100 F., and stearic acid not below 159, it is 
 evident that, independently of other considerations, the latter would be better 
 adapted for the manufacture of candles, for such candles would never soften at 
 the ordinary atmospheric temperature in any climate, and would have much less 
 tendency to gutter in consequence of the excessive fusion of the fuel around the 
 base of the wick. The gases furnished by the destructive distillation of stearic 
 acicl in the wick of the candle burn with a brighter flame than those produced 
 from tallow. Accordingly, the manufacture of stearin (or more correctly, stearic 
 acid) candles f has now become a very important and instructive bram 
 
 ln The r original method of separating the stearic acid from tallow on the large 
 scale consisted in mixing melted tallow with lime and water, and heating tl 
 mixture for some time at 212 F. by passing steam through it. nf ,: 
 
 The tallow was thus converted into the insoluble stearate and oleate of c 
 which was drained from the solution containing the glycerine, and c 
 
 A soap which contains more than 30 per cent, of water is said not to admit of mottling. 
 f Composite candles are made of a mixture of stearic and palm 
 
802 SAPONIFICATION BY ACIDS. 
 
 sulphuric acid. The mixture of stearic and oleic acids thus obtained was cast 
 into thin slabs, which were packed between pieces of coco-nut matting, and well 
 squeezed in a hydraulic press, which forced out the oleic acid, leaving the stearic 
 and palmitic acids in a fit state for the manufacture of candles. 
 
 The separation of the solid fatty acids from tallow and other fats may also be 
 effected by the action of sulphuric acid, a process extensively applied in this 
 country to palm and coco-nut oils. These fats are mixed in copper boilers with 
 about one-sixth of their weight of concentrated sulphuric acid, and heated by 
 steam at about 350 F. for some hours, when part of the glycerine is converted 
 into sulphoglyceric acid (C 3 H 8 O 3 'S0 3 ), and the remainder is decomposed by the 
 sulphuric acid, carbonic and sulphurous acid gases being disengaged, whilst a 
 dark-coloured mixture of palmitic, stearic and oleic acid is left. A part of the 
 oleic acid becomes converted in this process into elaidic acid, which has the same 
 composition, but differs from oleic acid in fusing at about 113 F., so that the 
 amount of solid acid obtained by this process is much increased. This mixture 
 is well washed from the adhering sulphuric and sulphoglyceric acids, and trans- 
 ferred to a copper still into which a current of steam is passed, which has been 
 raised to about 600 F. by passing through hot iron pipes. These fatty acids 
 co aid not be distilled alone without decomposition, but under the influence of a 
 current of steam they pass over readily enough, leaving a black pitchy residue 
 in the retort, which is employed in making black sealing-wax, and for other 
 useful purposes. 
 
 The distilled fatty acids are broken up and pressed between coco-nut matting 
 to remove the oleic acid. 
 
 One great advantage of this process, which is commonly, though incorrectly, 
 styled the saponification by sulphuric acid, is its allowing the conversion of the 
 worst kinds of refuse fat into a form fit for the manufacture of candles ; thus, the 
 fat extracted from bones in the manufacture of glue, and that removed from wool 
 in the scoring process, may be turned to profitable account. 
 
 It will be remarked that in this process the palmitic, stearic, and oleic acids 
 are formed from the palmitin, stearin, and olein existing in the fats, by the 
 assimilation of the elements of water and the subsequent separation of glycerine, 
 just as in the ordinary process of saponification by means of alkalies. 
 
 Strictly speaking, the action appears to consist of two stages ; for when con- 
 centrated sulphuric acid is allowed to act upon the natural fats in the cold, it 
 combines with each of their ingredients, forming the acids known as sulpho- 
 stearic, sulphopalmitic, sulpholeic, and sulphoglyceric, which are soluble in 
 water, though not (with the exception of the last) in water containing sulphuric 
 acid. 
 
 The second stage consists in the decomposition of the sulpho-fatty acids by the 
 high temperature in contact with steam, the sulphoglyceric acid having been in 
 great measure decomposed into secondary products before the distillation is com- 
 menced. 
 
 Within the last few years, the extraction of the solid acids from the natural 
 fats has been effected by a process known as saponification by steam, which allows 
 the glycerine also to be obtained in a pure state. It is only necessary to subject 
 the fat, in a distillatory apparatus, to the action of steam, at a temperature of 
 about 600 F., to cause both the fatty acids and the glycerine to distil over ; the 
 former may be separated as usual into solid and liquid portions by pressure, 
 whilst the glycerine, which is obtained in aqueous solution below the layer of 
 fatty acid?, is concentrated by evaporation, and sent into commerce as a very 
 sweet colourless viscid liquid. The saponificaticn of palmitin, for instance, by 
 steam, would be represented by the equation 
 
 C 3 H 5 -(C ]6 H 31 2 ) 3 + 3 H 2 = 3 (H-C 16 H 31 2 ) + C 3 H 5 (HO) 3 
 Falmitin. Palmitic acid. Glycerine. 
 

 Potatoes. 
 
 Wheat. 
 
 Starch 
 
 . 20.2 
 
 60.8 
 
 Water 
 
 . 75.9 
 
 12. 1 
 
 Gluten . . . 
 Albumin 
 
 2.3 
 
 10.5 ;; 
 
 2.O 
 
 Dextrin and sugar 
 Woody fibre 
 
 0.4 
 
 10.5 
 1.5 
 
 Oily matter 
 
 O.2 
 
 J 
 
 Mineral matter . 
 
 I.O 
 
 
 MANUFACTURE OF STARCH. 803 
 
 STARCH. 
 
 604. Starch is manufactured chiefly from potatoes, wheat, and rice, the solid 
 portion of which consists chiefly of starch, as appears in the following result of 
 analysis : 
 
 Rice. 
 83.0 
 
 6.0 
 
 1.0 
 
 4-8 
 
 O.I 
 O.I 
 
 IOO.O IOO.O IOO.O 
 
 In order to extract the starch, the potatoes are rasped to a pulp, which is 
 washed upon a sieve under a stream of water, as long as the latter is rendered 
 milky by the starch suspended in it, the woody fibre being left behind upon the 
 sieve. The milky liquid is allowed to settle, and the clear water drawn off ; the 
 deposited starch is then stirred up with fresh water, and again allowed to subside, 
 this process being repeated as long as the water is coloured, after which the starch 
 is mixed up with a small quantity of water, and passed through a fine sieve to 
 separate mechanically mixed impurities ; it is finally drained and dried, first in a 
 current of air, and afterwards by a gentle heat. 
 
 Starch cannot be extracted from wheat so easily as from potatoes, on account 
 of the much larger proportion of other solid matters from which it must be 
 separated. 
 
 To extract the starch, the coarsely ground wheat is moistened with water, and 
 allowed to putrefy, as it easily does, in consequence of the alterable character of 
 the gluten (which contains carbon, hydrogen, nitrogen, oxygen, and sulphur) ; 
 the putrefying gluten excites fermentation in the sugar and part of the starch, 
 producing acetic and lactic acids. These acids are capable of dissolving the 
 remainder of the gluten, which may then be washed away by water, the subse- 
 quent processes being similar to those employed in the extraction of potato 
 starch. 
 
 A far more economical and scientific method of extracting the starch consists 
 in dissolving the gluten by means of a weak alkaline solution, which leaves the 
 starch untouched, This process is especially applied in the manufacture of starch 
 from rice (p. 735). 
 
 Arrowroot is the starch extracted from the root of the Maranta arundinacea, 
 and of some other tropical plants. 
 
 In the preparation of tapioca and sago, the starch is dried at a temperature 
 above 140 F., so that it loses its ordinary farinaceous appearance and becomes 
 semi-transparent. 
 
 Sago is manufactured from the pith of certain species of palm, natives of the 
 East Indian islands. The tree is split so as to expose the pith, which is mixed 
 with water, and the starch, having been separated from the woody fibre in the 
 usual manner, is pressed through a perforated metallic plate, which moulds it 
 into small cylinders ; these are placed in a revolving vessel and broken into rough 
 spherical grains, which are steamed upon a sieve and dried. 
 
 Tapioca is obtained from the roots of the Jatropha manihot, a native of America. 
 The roots are peeled and subjected to pressure, which squeezes out a juice 
 employed by the Indians to poison their arrows, and containing a deleterious sub- 
 stance which has been named jatrophine. When the juice is allowed to stand n 
 deposits starch, which is well washed, pressed through a colander, and dned at 
 
 212 F. 
 
 Osw'ego, or corn-flour, is the flour of Indian corn deprived of gluten by treat- 
 ment with a weak solution of soda. 
 
 605. MALTING. The tendency of starch to combine with the elements of water 
 and pass into glucose (p. 733) is o f immense importance in the chemistry of veg 
 tation, as well as in that of food. It is, indeed, the chief chemical change con- 
 cerned in the development of living from inanimate matter, being one of the I 
 
804 GERMINATION OF SEEDS. 
 
 processes involved in the germination of seed the first step in the production of 
 vegetables, which must precede the animals whose food they compose. 
 
 The components of all seeds are similar to those of wheat, which have been 
 enumerated above ; if the seeds be perfectly dried immediately after the removal 
 from the parent plant, they may be preserved for a great length of time unchanged 
 and without losing the power of germinating under favourable circumstances. 
 The essential conditions of germination are the presence of air and moisture, and 
 a certain temperature, which varies with the nature of the seed. These conditions 
 being fulfilled, the seed absorbs oxygen from the air, and evolves carbonic acid 
 gas, produced by the combination of the oxygen with the carbon of one or more 
 of the most alterable constituents of the seed, such as the vegetable albumin or 
 the gluten. This process of oxidation is attended with evolution of heat, which 
 serves to maintain the seed at a degree of warmth most favourable to germina- 
 tion. The component particles of the albumin or gluten, having been set in 
 motion by the action of the atmospheric oxygen, induce a movement or chemical 
 change in the starch with which they are in contact, causing it to pass into 
 dextrin and glucose, which, unlike the starch, are perfectly soluble in water, 
 and capable of affording to the developing shoot the carbon, hydrogen, and oxygen 
 which it requires for the increase of its frame. The production of glucose and of 
 dextrin in germination is well illustrated by the sweet gummy character of the 
 bread made from sprouted wheat, and is turned to practical account in the process 
 of malting. 
 
 During the germination of all seeds there is formed, apparently by the oxidation 
 of one of the more alterable constituents, a peculiar substance containing carbon, 
 hydrogen, nitrogen, and oxygen, which has never yet been obtained from any 
 other source, and is characterised by its remarkable property of inducing the 
 conversion of starch into dextrin and grape-sugar. This substance has been 
 termed diastase (Stcia-racm, dissensions ; metaph. fermentation), but has never yet 
 been obtained in a state of sufficient purity to enable its formula to be satis- 
 factorily determined. It may be extracted, however, from malt, by grinding it 
 and mixing it with half its weight of warm water, which dissolves the diastase ; 
 the solution squeezed out of the malt is heated to about 179 F., filtered from any 
 coagulated albumin, and mixed with absolute alcohol, which precipitates the 
 diastase in white flakes. One part of diastase dissolved in water is capable of 
 inducing the conversion of 2000* parts of starch into dextrin and grape-sugar, the 
 diastase itself being exhausted in the process. A temperature of about 150 F. is 
 most favourable to the action of diastase, which may be arrested entirely by 
 raising the liquid to the boiling-point. 
 
 The great importance of diastase in the art of the brewer and distiller is at 
 once apparent. In the process of malting barley, the grain is soaked in water, 
 and afterwards spread out in thin layers upon the floor of a dark room (thus 
 imitating the natural condition under which the seed germinates), which is main- 
 tained as nearly as possible at a constant and moderate temperature (between 
 55 and 62 F.) ; spring and autumn are, therefore, more favourable to malting 
 than summer and winter. It soon evolves heat, and the grains begin to swell ; 
 in the course of twenty-four hours the germination commences, and the radicle 
 makes its first appearance as a whitish protuberance ; the grain is turned two or 
 three times a day, in order to equalise the temperature. In about a fortnight the 
 radicle has grown to about half an inch, by which time a sufficient quantity of 
 diastase has been formed. In order to prevent the germination from proceeding- 
 further, the grain is killed by drying it at a temperature of 90 F. on perforated 
 metallic plates, where it is afterwards heated to about 140 F., so as to render it 
 brittle, after which it is sifted in order to separate the radicle, which is now 
 easily broken off. This radicle is found to contain as much as of the total 
 quantity of the nitrogen present in the barley, so that the malt dust, as the siftings 
 are called, forms a valuable manure. 
 
 One hundred parts of barley generally yield about 80 parts of malt, but a part 
 of the loss is due to water present in the barley, so that 100 parts of dry barley 
 yield 90 parts of malt and 4 parts of malt dust, the difference, viz., 6 parts. 
 representing the weight of the carbon converted into carbonic acid gas, of the 
 hydrogen (if any) converted into water during the germination, and of soluble 
 matters removed from the barley in steeping. Malt contains about T of its. 
 
 * 100,000, according to more modern authorities. 
 
BREWING. 
 
 the 
 
 The following table illustrates the change in composition suffered br barley 
 during the process of malting, leaving the moisture out of consideration :- 
 
 
 
 Barley. 
 
 After 
 Steeping. 
 
 14^ Days 
 on Floor. 
 
 Malt after 
 Sifting. 
 
 Malt Dust. 
 
 Sugar 
 Starch ) 
 
 2.56 
 
 I. 5 6 
 
 12.14 
 
 II. OI 
 
 "35 
 
 Dextrin j ' 
 
 80.42 
 
 8l.I2 
 
 70.09 
 
 72.03 
 
 43-68 
 
 Woody fibre 
 Albuminous matter . 
 Mineral matter . 
 
 4-69 
 9-03 
 2.50 
 
 5,22 
 
 9.83 
 2.27 
 
 5-03 
 10.39 
 
 2-35 
 
 4.84 
 
 9-95 
 2.17 
 
 9.67 
 26.90 
 8.40 
 
 
 IOO.OO 
 
 IOO.OO 
 
 100.00 
 
 100.00 
 
 100.00 
 
 BREWING. 
 
 606. In order to prepare beer, the brewer washes the ground malt with water at 
 about 1 80 F., for some hours, when the diastase induces the conversion, into 
 dextrin and sugar, of the greater part of the starch which has not been so 
 changed during the germination, and the wort is ready to be drawn off for con- 
 version into beer. The undissolved portion of the malt, or brewers' grains, still 
 contains a considerable quantity of starch and nitrogenised matter, and is 
 employed for feeding pigs. 
 
 That malt contains far more diastase than is necessary to convert its starch 
 into sugar, is shown by adding a little infusion of malt to the viscid solution of 
 starch, and maintaining it at about 150 F. for a few hours, when the mixture 
 will have become far more fluid, and will no longer be coloured blue by solution 
 of iodine. In distilleries, advantage is taken of the excess of diastase in malt, 
 by adding three or four parts of unmalted grain to it, when the whole of the 
 starch in this latter is also converted into dextrin and sugar, and the labour and 
 expense of malting it are avoided. 
 
 The wort obtained by infusing malt in water contains not only glucose, dextrin, 
 and diastase, but a considerable quantity of nitrogenised matter formed from the 
 gluten (or albuminous matter) of the barley. Before subjecting it to fermenta- 
 tion it is boiled with a quantity of hops, usually amounting to about T V of the 
 weight of the malt employed, which is found to prevent, in great measure, the 
 tendency of the beer to become sour in consequence of the conversion of the 
 alcohol into acetic acid. 
 
 The hop contains about 10 per cent, of an aromatic yellow powder called lujwIiH, 
 which appears to be the active portion, and contains a volatile oil of peculiar 
 odour, together with a very bitter substance. 
 
 The hopped wort is run off into a vat, where it is allowed to deposit the undis- 
 solved portion of the hops, and the clear liquor is drawn off into shallow coolers, 
 where its temperature is lowered as rapidly as possible to about 60 F., the cooling 
 being usually hastened by cold water circulating through pipes which traverse 
 the coolers. * If the wort be cooled too slowly, the nitrogenised matter which it 
 contains undergoes an alteration by the action of the air, in consequence of which 
 the beer is very liable to become acid. 
 
 The wort is now transferred to the fermenting tun, where it is made to ferment 
 by the addition of yeast, usually in the proportion of T J T of its volume. 
 * Yeast has been depicted and described at p. 562. 
 
 The yeast cells contain a substance somewhat resembling albumin enclosed 
 a thin membrane, the composition of which is similar to that of cellulose. Ihey 
 also contain a peculiar nitrogenised body (iiwerUue) resembling diastase, and 
 capable of inducing the conversion of cane-sugar (C l2 H^O n ] into glucose (C 6 H,aO 6 ). 
 Accordingly, when yeast is added to a solution of cane-sugar the liquid 
 
8o6 
 
 COMPOSITION OF BEEES. 
 
 to increase in specific gravity (a solution of cane-sugar having a lower density 
 than one containing an equivalent quantity of glucose) previously to the com- 
 mencement of fermentation, and the application of tests readily proves the 
 presence of glucose in the solution. 
 
 The glucose then undergoes the decomposition known as alcoholic fermentation, 
 described at p. 562. 
 
 During the fermentation, the yeast cells are gradually broken up, so that a given 
 quantity of yeast is capable of fermenting only a limited quantity of sugar. On 
 an average a quantity of yeast containing between two and three parts of solid 
 matter is required to complete the fermentation of 100 parts of sugar. The solu- 
 tion remaining after the fermentation is found to contain salts of ammonium, 
 which have been formed at the expense of the nitrogen of the yeast. 
 
 If the liquid in which the yeast excites fermentation contains nitrogenised 
 matters and phosphates, the yeast-plant grows, and its quantity increases ; 
 thus in the sweet wort from malt, the yeast is nourished by the altered gluten 
 and by the phosphates, so that it increases to six or eight times its original 
 weight. 
 
 If yeast be heated to the boiling-point of water, the plant is killed, as might be 
 expected, and loses its power of inducing alcoholic fermentation ; but it may be 
 dried at a low temperature, or by pressure, without losing its fermenting power, 
 and dried yeast is an article of commerce. German dried yeast is produced in the 
 fermentation of rye for making Hollands. 
 
 In the fermentation of beer, the yeast is carried up to the surface by the effer- 
 vescence due to the escape of the carbonic acid gas, and is eventually removed, 
 in order to be employed for the fermentation of fresh quantities of wort. When 
 the fermentation has proceeded to the required extent, the beer is stored for 
 consumption. 
 
 It will be seen that the chief constituents of beer are the alcohol, the nitrogen- 
 ised substance derived from the albuminous matter of the barley and not con- 
 sumed in the growth of the yeast, the unaltered glucose and dextrin, the brown 
 or yellow colouring-matter formed during the fermentation, the essential oil and 
 bitter principle of the hop. 
 
 Beer also contains acetic acid (formed by the oxidation of the alcohol, 
 p. 590), free carbonic acid, which gives it its sparkling character, together with 
 the lactic and succinic acids and glycerine, formed as secondary products of the fer- 
 mentation, and ammoniacal salts derived from the yeast. The soluble mineral 
 substances from the barley are also present, minus the phosphates abstracted by 
 the yeast. 
 
 The proportions of the constituents of course vary greatly, as will be seen from 
 the following examples : 
 
 Percentage. 
 
 Allsopp's 
 Ale. 
 
 Bass's Ale. 
 
 Strong Ale. 
 
 WMtbread's 
 Porter. 
 
 Whitbread's 
 Stout. 
 
 Alcohol 
 
 6.00 
 
 7.00 
 
 8.65 
 
 4.20 
 
 6. CO 
 
 Acetic acid 
 
 O.2O 
 
 0.18 
 
 0. 12 
 
 0.19 
 
 0.18 
 
 Sugar and other \ 
 solid matters J 
 
 5.00 
 
 4.80 
 
 6.60 
 
 5-40 
 
 6.38 
 
 The dark colour of porter and stout is caused by the addition of a quantity of 
 high-dried malt which has been exposed to so high a temperature in the kiln as to 
 convert a portion of its sugar into a dark brown soluble substance called caramel. 
 The peculiar aroma of beer is probably due to the presence of acetic ether, pro- 
 duced during the fermentation. 
 
 In some cases, when the operation of brewing has been badly conducted, the 
 beer becomes ropy, or undergoes the viscous fermentation. In this case the glucose 
 suffers a peculiar transformation, resulting in the production of a mucilaginous 
 substance resembling gum in its composition. This change may be induced by 
 yeast which has been boiled, or by water in which flour or rice has been steeped. 
 During this viscous fermentation a part of the glucose is often converted into 
 mannite (C 6 H 14 6 ). 
 
WINES. 8o; 
 
 WINES AND SPIRITS. 
 
 607. Wine is essentially composed of 8 or 10 parts of alcohol v 
 water, together with minute quantities of certain fragrant ethcrT of colourfn 
 
 addition of ferment is necessary, the iti^^SF G 
 juice contains, in addition to grape-sugar, vegetable albumin, potassium tartnS 
 and the usual mineral salts found in vegetable juices. The husks 
 stalks of the grape contain a considerable quantity of tann n tVrther'wUh 
 certain blue, red, and yellow colouring-matters. 
 
 When the expressed juice remains for a short time in contact with th- air 
 the germs or spores of yeast (p. 562) which float in the air are deposited oi 
 surface of the juice, at the expense of which tbev begin to grow excit ne 
 the vinous fermentation in the sugar, and a scum of yeast if formed 2 
 the surface. If this fermentation takes place in contact with the husks Jf 
 the dark grapes, the alcohol dissolves the colouring-matter, and a red wine 
 results ; whilst for the production of white wines, the husks, &c., are separated 
 previously to the fermentation, and the juice is exposed as little as possible to 
 triG tiir. 
 
 White wines are rather liable to become ropy from viscous fermentation but 
 this is prevented by the addition of a small quantity of tannin, which precipitates 
 the peculiar ferment. The tannin for this purpose is extracted from the husks 
 and stalks of the grapes themselves, and already exists in red wine. 
 
 ^ Red wines, such as port and claret, are often very astringent from the tannin 
 dissolved out of the husks, &c., during the fermentation. Port wine, when freshly 
 bottled, still retains in solution a considerable quantity of acid potassium tartrate 
 or bitartrate of potash (KHC 4 H 4 O 6 ), but after it has been kept some time, and 
 become more strongly alcoholic, this salt is deposited, together with a quantity 
 of the colouring-matter, in the form of a crust upon the side of the bottle. Thus 
 a dark, fruity port becomes tawny and dry when kept for a sufficient length of 
 time, the sugar having been converted into alcohol. 
 
 When the wine contains an excess of tartaric acid, it is customary to add to it 
 some neutral potassium tartrate (K 2 C 4 H 4 6 ), which precipitates the acid in the 
 form of bitartrate. 
 
 The preparation of champagne is conducted with the greatest care. The juice 
 or must is carefully separated from the marc or husks, and is often mixed with 
 I per cent, of brandy before fermentation. After about two months the wine is 
 drawn off into another cask, and clarified with isinglass dissolved in white wine, 
 and added in the proportion of about half an ounce 1040 gallons. This combines 
 with the tannin to form an insoluble precipitate, which carries with it any im- 
 purities floating in the wine. After another interval of two months, the wine is 
 again drawn off, and a second clarification occurs ; and in two months more 
 the wine is drawn off into bottles containing a small quantity of pure sugar-candy 
 dissolved in white wine. The bottles, having been securely corked and wired, 
 are laid down upon their sides for eight or ten months, during which time the 
 fermentation of the newly added sugar happens, and the carbonic acid pro- 
 duced dissolves in the wine, whilst a quantity of yeast is separated. In order to 
 render the wine perfectly clear, the bottle is left for about three weeks in such a 
 position that the deposit may subside into the neck against the cork, which is 
 then unwired so that the pressure of the accumulated carbonic acid gas may force 
 it out together with the deposit ; the bottle, having been rapidly tilled up with 
 white wine, is again corked, wired, covered with tinfoil, and sent into the market. 
 Pink champagne is prepared from the must which is squeezed out of the marc 
 after it has cea&ed to run freely, and contains a little of the colouring-matter of 
 the husk. The colour is also sometimes imparted by adding a little tincture of 
 litmus. 
 
 The proportion of alcohol in wines varies greatly, as will be seen from the 
 following statement of the weight of alcohol in 100 parts of the wine : 
 
8o8 SPIEITS. 
 
 Port . . . . 15 to 17 
 Sherry . . . 14 to 16 
 Champagne . . 11.5 
 
 Claret . . . . 8 to 9 
 Eudesheimer . . 7 to 8.5 
 
 Sherry contains from I to 5 per cent, of sugar, port from 3 to 7 per cent., and 
 Tokay 17 per cent. ; in the last case the sugar is increased by adding some of the 
 must, concentrated by evaporation, to the wine, previously to bottling. 
 
 The bouquet or fragrance of wine is due to the presence of certain fragrant 
 ethers (ethereal salts), especially of oenanthic, pelargonic and acetic ether, formed 
 during the fermentation or during the subsequent storing of the wine. It is to 
 the increased quantity of such fragrant ether that the superior bouquet of many 
 old wines is due. 
 
 Distilled spirits. The varieties of ardent spirits are obtained from fermented 
 liquids by distillation, so that they consist essentially of alcohol more or less 
 diluted with water, and flavoured either with some of the volatile products of the 
 fermentation, or with some essential oil added for the purpose. 
 
 Brandy is distilled from wine, and coloured to the required extent with burnt 
 sugar (caramel). Its flavour is due chiefly to the presence of cenanthic ether de- 
 rived from the wine. The colour of genuine pale brandy is due to its having re- 
 mained so long in the cask as to have dissolved a portion of brown colouring- 
 matter from the wood, and is therefore an indication of its age. Hence arose the 
 custom of adding caramel, and sometimes infusion of tea, to impart the colour 
 and astringency due to the tannin dissolved from the wood by old brandy. 
 
 Whiskey is distilled from fermented malt which has been dried over a peat fire, 
 to which the characteristic smoky flavour is due. 
 
 Gin is also prepared from fermented malt or other grain, and is flavoured with 
 the essential oil of juniper, derived from juniper berries added during the distil- 
 lation. 
 
 Rum is distilled from fermented molasses, and a.ppears to owe its flavour to the 
 presence of butyric ether, or of some similar compound. 
 
 Arrack is the spirit obtained from fermented rice. 
 
 Kirschwasser and maraschino are distilled from cherries and their stones, which 
 have been crushed and fermented. 
 
 Some varieties of British brandy and whiskey are distilled from fermented 
 potatoes, or from a mixture of potatoes and grain, when there distils over, together 
 with ordinary alcohol, especially towards the end of the distillation, another spirit 
 belonging to the same class, but distinguished from alcohol by its nauseous and 
 irritating odour. This substance, which is known as potato-spirit, amylic alcohol, 
 or fusel oil (C 5 H 12 0), also occurs, though in very minute quantity, in genuine wine 
 brandy. The manufacturers of spirit from grain and potatoes remove a consider- 
 able part of this disagreeable and unwholesome substance by leaving the spirit 
 for some time in contact with wood-charcoal. 
 
 BREAD. 
 
 608. The chemistry of fermentation is intimately connected with the ordinary 
 process of bread-making. It will be remembered that wheaten flour (p. 803) 
 consists, essentially, of starch and gluten, with a little dextrin and sugar. On 
 mixing the flour with a little water, it yields a dough, the tenacity of which is 
 due to the gluten present in the flour. If this dough be tied up in a piece of 
 fine muslin, and kneaded under a stream of water, the starch will be suspended 
 in the water, and will pass through the muslin, whilst the gluten will remain 
 as a very tough elastic mass, which speedily putrefies if exposed to the air in 
 a moist state, and dries up to a brittle horny mass at the temperature of boiling 
 water. 
 
 On analysis, gluten is found to contain carbon, hydrogen, nitrogen, and oxygen, 
 in proportions which may be represented by the empirical formula Co 4 H 40 N 6 7 , 
 though it cannot be regarded as a single independent substance, but as a mixture 
 of three substances very closely allied in composition. 
 
 When gluten is boiled with alcohol, one portion refuses to dissolve, and has 
 been named vegetable fibrin, from its resemblance to the substance forming the 
 muscles of animals. When the solution in alcohol is allowed to cool, it deposits 
 a white flocculent matter, very similar to the casein which composes the curd of 
 milk. On adding water to the cold alcoholic solution, a third substance 
 
BREAD-MAKING. 809 
 
 (tjlutin) is separated, which much resembles the albumin found so abundantly in 
 the blood. 
 
 The presence in gluten of three substances, similar to the three principal 
 components of the animal body, leads us to form a high opinion of its value as a 
 nutritive compound. But gluten itself, separated from the flour by the process 
 above described, would be found very difficult of digestion, on account of its 
 resistance to the solvent action of the fluids in the stomach ; indeed, the dough 
 composed of flour and water is proverbially indigestible even when baked. In 
 order to make it fit for food, it must be rendered spongy or porous, so as to 
 expose a larger surface to the action of the digestive fluids of the body ; the most 
 direct method of effecting 'this is the one adopted in the manufacture of the 
 aerated bread, and consists in mixing the flour with water which has been highly 
 charged, under pressure, with carbonic acid gas; the mixing having been effected 
 in a strong closed iron vessel, an aperture in the lower part of this is opened, 
 when the pressure of the accumulated gas forces the dough out into the air, and 
 the gas which has been imprisoned in the dough expands, conferring great 
 porosity and sponginess upon the mass in its attempt to escape. In another 
 process for preparing unfermented bread, the flour is mixed with a little bicar- 
 bonate of soda, and is then made into a dough with water acidified with 
 hydrochloric acid ; the latter, decomposing the bicarbonate of soda, liberates 
 carbonic acid gas, which renders the bread porous. The sodium chloride formed 
 at the same time remains in the bread. In the preparation of cakes and pastry, 
 the same object is sometimes attained by adding carbonate of ammonia to the 
 dough ; when heat is applied in the baking, the salt is converted into vapour 
 which distends the dough. 
 
 In the common process of bread-making, however, the carbonic acid gas 
 destined to confer sponginess upon the dough is evolved by the fermentation of 
 the sugar contained in the flour ; the latter having been kneaded with the proper 
 proportion (usually about half its weight) of water, a little yeast and salt are 
 added, and the mixture is allowed to stand at a temperature of about 70 F. for 
 some hours. The dough swells or rises considerably in consequence of the escape 
 of carbonic acid gas, the sugar being decomposed into that gas and alcohol, as in 
 ordinary fermentation. The spongy dough is then baked in an oven, heated to 
 about 500 F., when a portion of the water and the whole of the alcohol are 
 expelled, the carbonic acid gas being also much expanded by the heat, and the 
 porosity of the bread increased. The granules of starch are much altered by the 
 heat, and become far more digestible. Although the temperature of the inside of 
 the loaf does not exceed 212 F., the outer portion becomes torrefied or scorched 
 into crust. 
 
 Occasionally, instead of yeast, leaven is employed, in order to ferment the 
 sugar, leaven being dough which has been left in a warm place until decomposi- 
 tion has commenced. 
 
 The passage of new into stale bread does not depend, as was formerly supposed, 
 upon the drying of the bread consequent upon its exposure to air, but it is a true 
 molecular transformation which occurs equally well in an air-tight vessel, and 
 without any loss of weight. It is well known that when a thick slice of stale 
 bread is toasted, which dries it still further, the crumb again becomes soft and 
 spongy as in new bread ; and if a stale loaf be again placed in the oven, it is 
 entirely reconverted into new bread. 
 
 Wheaten flour is particularly well fitted for the preparation of bread on accour 
 of the great tenacity of its gluten. Next to wheat in this respect stands rye, 
 whilst the other cereals contain a gluten so deficient in tenacity that it is impos 
 sible to convert them into good bread. 
 
 Barley bread is close and heavy, since its nitrogenised matter is chiefly pre 
 in the form of albumin, which does not vesiculate like gluten during the tern 
 tation. Even in wheaten flour the tenacity of the gluten is liable to variation, 
 and in order to obtain good bread from a flour the gluten of which is 
 in this respect, it is customary to employ a minute proportion oi alum, l 
 addition being considered unwholesome by some persons, it would 
 to substitute lime-water, which has been found by Liebig to have a si 
 effect. Sulphate of copper improves in a very striking manner the c 
 the bread prepared from inferior flour, but this salt is far more obj 
 than alum. 
 
8 10 COMPOSITION OF COFFEE. 
 
 TEA, COFFEE, ETC. 
 
 609. A very remarkable instance of the application of chemistry to explain the 
 use of widely different articles of diet by different nations, with a view to the 
 production of certain analogous effects upon the system, is seen in the case of 
 coffee, tea, Paraguay tea, and the kola nut (of Central Africa), which are very dis- 
 similar in their sensible properties, and afford little or no gratification to the 
 palate, owing what attractions they possess chiefly to the presence, in each, of 
 one and the same active principle or alkaloid, which has a special effect upon the 
 animal economy. This alkaloid is known as caffeine or theine, and is associated, 
 in the three articles of diet mentioned above, with various substances, which give 
 rise to their diversity in flavour. 
 
 The raw coffee-berry presents, on the average, the following composition : 
 
 100 parts of Raw Coffee contain 
 
 Woody fibre 34.0 
 
 Water .......... 12.0 
 
 Fat 12.0 
 
 Sugar and gum ......... 15.5 
 
 Legumin, or some allied substance 13.0 
 
 Caffeine 1.5 
 
 Caffeic acid ......... 4.0 
 
 Mineral substances ........ 7.0 
 
 When the raw berry is treated with hot water, the infusion, which contains the 
 sugar and gum, the legumin, caffeine, and caffeic acid (C 9 H 8 O 4 ), has none of the 
 peculiar fragrance which distinguishes the ordinary beverage, and is due to an 
 aromatic volatile oily substance termed caffeol (C 8 H 10 O 2 ) formed during the roast- 
 ing to which the berry is subjected before use. This volatile oil, which is present 
 in very minute quantify, is produced from one of the soluble constituents of the 
 berry (probably from the caffeic acid), for if the infusion of raw coffee be evapo- 
 rated to dryness, the residue, when heated, acquires the characteristic odour of 
 roasted coffee. 
 
 Acetic and palmitic acids are also found among the products of coffee-roasting. 
 
 The roasting is effected in ovens at a temperature rather below 400 F., when 
 the berry swells greatly, and loses about | of its weight, becoming brittle, and 
 easily ground to powder. It also becomes very much darker in colour, from the 
 conversion of the greater part of its sugar into caramel (p. 732), which imparts 
 the dark brown colour to the infusion of coffee. If the roasting be carried too 
 far, a very disagreeable flavour is imparted to the coffee, by the action of heat 
 upon the legumin and other nitrogenised substances contained in the berry. 
 
 From ico parts of the roasted coffee, boiling water extracts about 20 parts, 
 consisting ftf caffeine, caffeic acid, caramel, legumin, a little suspended fatty 
 matter, fragrant volatile oil (caffeone), and salts of potassium (especially the phos- 
 phate). The undissolved portion of the coffee contains, beside the woody fibre, a 
 considerable quantity of nitrogenised (and nutritious) matter, and hence the 
 custom, in some countries, of taking this residue together with the infusion. 
 
 The constituents of the leaves of the tea-plant (Thea sinensis) exhibit a general 
 similarity to those of the coffee-berry. In the fresh leaf we find, in addition to 
 the woody fibre, a large quantity of a substance containing nitrogen, similar to 
 legumin, an astringent acid similar to tannic acid, a small quantity of caffeine, and 
 some mineral constituents. 
 
 The aroma of tea does not belong to the fresh leaf, but is produced, like that of 
 coffee, during the process of drying by heat, which develops a small quantity of 
 a peculiar volatile oil, having powerful stimulating properties. The freshly dried 
 leaf is comparatively so rich in this oil that it is not deemed advisable to use it 
 until it has been kept for some time. 
 
 Green and black tea are the produce of the same plant, the difference being 
 caused by the mode of preparation. For green tea the leaves are dried over a 
 fire as soon as they are gathered, whilst those intended for black tea are allowed 
 to remain exposed to the air in heaps for several hours, and are then rolled with 
 the hands and partially dried over a fire, these processes being repeated three or 
 four times to develop the desired flavour. The black colour appears to be due to 
 the action of the air upon the tannin present in the leaf. 
 
ANIMAL SUBSTANCES. 8ll 
 
 black tea 
 
 varies from 
 
 leaves contain the greater part of the legumin and a considerable 
 quan ity of caffeine, which may be extracted by boiling them with water, and 
 treating the decoction as at p. 775. 
 
 Cocoa and chocolate are prepared from the cacao-nut, which is the seed of 
 fheolroma cacao and is i characterised by the presence of more than half of its 
 weight (minus the husk) of a fatty substance known as cacao-butter, and consist- 
 ing of olem and stearin, which does not become rancid like the natural fats 
 generally. The cacao-nut also contains a large quantity of starch, a nitrogenis-ed 
 substance resembling gluten, together with gum, sugar and t/teobroHiine, a feeble 
 base very similar to caffeine, but having the composition C 7 H 8 N,0,. 
 
 ihe seeds are allowed to ferment in heaps for a short time, Which improves 
 their flavour, dried in the sun and roasted like coffee, which develops the peculiar 
 aroma of cocoa. The roasted beans having been crushed and winnowed to sepa- 
 rate the husks, are ground in warm mills, in which the fatty matter melts and 
 unites with the ground beans to a paste, which is mixed with sugar and pressed 
 into moulds. In the preparation of chocolate, vanilla and spices are also added. 
 
 From the composition of cocoa and chocolate it is seen that, when consumed, 
 as is usual, in the form of a paste, they would prove far more nutritious than mere 
 infusions of tea and coffee. 
 
 ANIMAL CHEMISTKY. 
 
 610. Our acquaintance with the chemistry of the substances composing the 
 bodies of animals is still very limited, although the attention of many accom- 
 plished investigators has been directed to this branch of the science. The reasons 
 for this are to be found, first, in the susceptibility to change exhibited by 
 animal substances when removed from the influence of life ; and secondly, in the 
 absence, in such substances, of certain physical properties by which we might be 
 enabled to separate them from other bodies with which they are associated, and 
 to verify their purity when obtained in a separate state. Two of the most im- 
 portant of these properties are volatility and the tendency to crystallise. When a 
 substance can suffer distillation without change, it will be remembered that its 
 boiling-point affords a criterion of its purity ; or if it be capable of crystallising, 
 this may betaken advantage of in separating it from other substances which 
 crystallise more or less easily than itself, and its purity may be ascertained from 
 the absence of crystals of any other form than that belonging to the substance. 
 But the greater number of the components of animal frames can neither be crys- 
 tallised nor distilled, so that many of the analyses which have been made of such 
 substances differ widely from each other, because the analyst could never be sure 
 of the perfect purity of his material ; and even when concordant results have 
 been obtained as to the percentage composition of the substance, the formula 
 deduced from it has been of so singular and exceptional a character as to cast 
 very strong suspicion upon the purity of the substance. 
 
 Accordingly, the chemical formulae of a great many animal substances are per- 
 fectly unintelligible, conveying not the least information as to the position in 
 which the compound stands with respect to other substances, or the changes 
 which it might undergo under given circumstances. 
 
 Animal chemistry is, for the above reasons, in a very backward condition, as 
 compared with vegetable and mineral chemistry, though an observation of the 
 progress of research affords us the consolation, that a steady advance is being 
 made towards a generalisation of the facts which have been discovered, especially 
 by deductive reasoning from those two other departments of the science. 
 
 611. Milk. The chemistry of milk is well adapted to introduce the study o: 
 animal chemistry, because that liquid contains representatives of all the sub- 
 stances which make up the animal frame ; and it is on this account 
 occupies so high a position among articles of food. 
 
 Although, to the unaided eye, milk appears to be a perfectly homogeneo' 
 fluid, the microscope reveals the presence of innumerable globules floating in a 
 transparent liquid, which is thus rendered opaque. If milk be very viol 
 
8l2 MILK AND CHEESE. 
 
 agitated for several hours, masses of an oily fat (butter, p, 799) are separated 
 f i om it, and leave the liquid transparent. This tat was originally distributed 
 throughout the milk, in minute globules, which were made to coalesce by the 
 violent agitation. 
 
 For the preparation of butter, it is usual to allow the milk to stand for some 
 hours, when a layer of cream collects upon the surface, the proportion of which is 
 very variable, but is generally about ^ of the volume of the milk.* The 
 skimmed milk retains about half of the fatty matter. This cream contains about 
 35 per cent, (by weight) of fat, 3 per cent, of casein, and water. When the cream 
 is churned, the fat globules are broken, and the fat unites into a semi-solid mass of 
 butter, from which the butter-milk containing the casein may be separated. If this 
 be not done effectually, the casein which is left in the butter, being a nitrogenised 
 substance, will soon begin to decompose, and will induce a decomposition in the 
 butter (p. 799), resulting in the formation of certain volatile aoids, which impart 
 to ic a rancid and offensive taste and odour. To prevent this, salt is generally 
 added to butter which has been less carefully prepared in order to preserve the 
 casein from decomposition. Butter-milk contains about one-fourth of the fatty 
 matter of the milk. 
 
 Pure butter is essentially a mixture of stearin, palniitin and olein with smaller 
 quantities of other fats, such as butyrin, caprin, and caproin (p. 799). 
 
 Fresh milk is slightly alkaline to test-papers, but after a short time it acquires 
 an acid reaction ; and if it be then heated, it coagulates from the separation of 
 the casein. This spontaneous acidification of milk is caused by the fermentation 
 of the sugar of milk, which results in the production of lactic acid. 
 
 If milk be maintained at a temperature of about 90 F., the fermentation results 
 in the production of alcohol and carbonic acid, for although milk-sugar is not 
 fermented like ordinary sugar, by contact with yeast, it appears, under the 
 influence of the changing casein at a favourable temperature, to be converted 
 first into grape-sugar (p. 726), and afterwards into alcohol and carbonic acid. 
 The Tartars prepare an intoxicating liquid, which they call koumiss, by the fermen- 
 tation of milk. 
 
 When an acid is added to milk, the casein is separated in the form of curd, in 
 consequence of the neutralisation of the soda which retains it dissolved in fresh 
 milk, and this curd carries with it, mechanically, the fat globules of the milk, 
 leaving a clear yellow ivhey. 
 
 In the preparation of cheese, the milk is coagulated by means of rennet, which 
 is prepared from the lining membrane of a cali's stomach. This is left in contact 
 with the warm milk for some hours, until the coagulation is completed. The curd 
 is collected and pressed into cheeses, which are allowed to ripen in a cool place, 
 where they are occasionally sprinkled with salt. The peculiar flavour which the 
 cheese thus acquires is due to the decomposition of the casein, giving rise to the 
 production of certain volatile acids, such as butyric, valerianic, and caproic, 
 which have very powerful and characteristic odours. If this ripening be allowed 
 to proceed very far, ammonia is developed by the putrefaction of the casein, and 
 in some cases the ethers of the above-mentioned acids are produced, at the expense 
 probably of a little sugar of milk left in the cheese, conferring the peculiar aroma 
 perceptible in some varieties of it. 
 
 The different kinds of cheese are dependent upon the kind of milk used in their 
 preparation, the richer cheeses being, of course, obtained from milk containing a 
 large proportion of cream ; such cheese fuses at a moderate heat, and makes good 
 toasted cheese, whilst that which contains little butter never fuses completely, 
 but dries and shrivels like leather. Double Gloucester and Stilton are made from 
 a mixture of new milk and cream ; Cheddar cheese is made from new milk alone ; 
 Cheshire and American cheeses from milk robbed of about one-eighth of its 
 cream ; Dutch cheese and the Skim Dick of the midland counties, from skimmed 
 milk. 
 
 The characteristic constituents of milk are the casein and milk-sugar, but the 
 proportions in which these are present vary widely not only with the animal from 
 which the milk is obtained, but with the food and condition of the animal. A 
 general notion of their relative quantities, however, may be gathered from the 
 following table : 
 
 * The separation of cream is now effected, in large dairies, by means of a centrifugal 
 separator, making several thousand revolutions per minute. 
 
BLOOD. 
 
 813 
 
 
 Cow. 
 
 Ass. 
 
 Goat. 
 
 Woman. 
 
 Water . 
 Fat .... 
 Casein .... 
 Albumin 
 
 87.2 
 3-7 
 3-0 
 
 89.6 
 
 1-7 
 
 0.7 
 
 85-7 
 4-8 
 3-2 
 
 87.4 
 3-8 
 
 I.O 
 
 Milk-sugar 
 Mineral salts . 
 
 4-9 
 0.7 
 
 6.0 
 
 4-5 
 0.7 
 
 6.1 
 o-3 
 
 The soluble salts present in milk include the phosphates and chlorides of 
 potassium and sodium, whilst the insoluble salts are the phosphates of calcium 
 magnesium, and iron. All these salts are in great request for the nourishment of 
 the animal frame. 
 
 The milk supplied to consumers living in towns is subject to considerable 
 adulteration ; but in most cases this is effected by simply removing the cream and 
 diluting the skimmed milk with water, a fraud which is not easily detected as 
 might be supposed, by determining the specific gravity of the milk, for since 
 milk is heavier than water (1.032 sp. gr.), and the fatty matter composing cream 
 is lighter than water, a certain quantity of cream might be removed, and water 
 added, without altering the specific gravity of the milk. 
 
 The simplest method of ascertaining the quality of the milk consists in setting 
 it aside for twenty-four hours in a tall narrow tube (lactometer or crcumometer) 
 divided into 100 equal parts, and measuring the proportion of cream which 
 separates, this averaging, in pure milk, from eleven to thirteen divisions. The 
 measurement of the cream is effected in fifty minutes by using a centrifugal 
 separator, in which the tube containing the milk is placed in a case attached to a 
 centrifugal apparatus making 1200 revolutions per minute. By shaking milk 
 with a little potash and ether, the butter may be dissolved in the ether which 
 rises to the surface, and if this be poured off and allowed to evaporate, the weight 
 of the butter may be ascertained ; or the milk may be evaporated by a steam 
 heat, and the fat dissolved by treating the residue with ether. The amount of 
 fat is sometimes found by taking the specific gravity of the ethereal solution, 
 and referring to a table giving the corresponding quantity of fat. One thousand 
 grains of milk should give, at least, 27 or 28 grains of butter. Since, however, 
 the milk of the same cow gives very different quantities of cream at different 
 times, it is difficult to state confidently that adulteration has been practised. 
 The standard usually adopted by analysts is 25 grains of fat or butter and 90 
 grains of " solids not fat " in 1000 grains of milk. 
 
 612. Blood. The blood, from which the various organs of the body directly 
 receive their nourishment, is the most important, as well as the most complex, of 
 the animal fluids. Its chemical examination is attended with much difficulty, on 
 account of the rapidity with which it changes after removal from the body of the 
 animal. 
 
 On examining freshly drawn blood under the microscope, it is observed to pre- 
 sent some resemblance to milk in its physical constitution, consisting of opaque 
 flattened globules floating in a transparent liquid ; the globules, in the case of 
 blood, having a well-marked red colour. % 
 
 In a few minutes after the blood has been drawn, it begins to assume a gela- 
 tinous appearance, and the semi-solid mass thus formed separates into a red solid 
 portion or clot, which continues to shrink for ten or twelve hours, and a clear 
 yellow liquid or serum. It might be supposed that this coagulation is due to the 
 cooling of the blood, but it, is found by experiment to take place even more 
 rapidly when the temperature of the blood is raised one or two degrees after it 
 has been drawn ; and. on the other hand, if it be artificially cooled, its coagula- 
 tion is retarded. Indeed, the reason for this remarkable behaviour of the blood 
 is not yet understood. 
 
 If the coagulum or clot of blood be cut into slices, tied m a cloth, and well 
 washed in a stream of water, the latter runs off with a bright red colour, and a 
 tough yellow filamentous substance is left upon the cloth ; this substance is called 
 fibrin and its presence is the proximate cause of the coagulation of the blood, 
 for if the fresh blood be wel) whipped with a bundle of twigs or glass rods, the 
 
8 14 FLESH. 
 
 fibrin will adhere to them in yellow strings, and the defibrinated blood will no 
 longer coagulate on standing. If this blood, from which the fibrin has been ex- 
 tracted, be mixed with a large quantity of a saline solution (for example, 8 times 
 its bulk of a saturated solution of sodium sulphate), and allowed to stand, the 
 red globules subside to the bottom of the vessel. 
 
 These globules are minute bags of red fluid, enclosed in a very thin membrane 
 or cell-wall, and if water were mixed with the defibrinated blood, since its specific 
 gravity is lower than that of the fluid in the globules, it would pass through the 
 membrane (by osmosis}, and so swell the latter as to break it and disperse the 
 contents through the liquid. 
 
 The red fluid contained in these blood globules consists of an aqueous solution, 
 containing as its principal constituents a substance known as globulin, which 
 very nearly resembles albumin, and the peculiar colouring-matter of the blood, 
 which is called hee matin. 
 
 Beside these, the globules contain a little fatty matter and certain mineral con- 
 stituents, especially the iron (which is associated in some unknown form with the 
 colouring-matter), the chlorides of sodium and potassium, and the phosphates of 
 potassium, sodium, calcium, and magnesium. 
 
 Though the quantities of these constituents are not invariable, even in the 
 same individual, the following numbers may be taken as representing the average 
 composition of these globules : 
 
 1000 parts of Blood Globules contain 
 
 Water .... 688.00 
 Globulin . . 282.22 
 
 Hsematin . . . . 16.75 
 Fat 2.31 
 
 The Mineral Substances consist of 
 
 Organic substances of un-\ , 
 
 known nature . . / 
 Mineral substances * . 8. 12 
 
 Potassium . . . 3.328 
 Phosphoric oxide (P 2 O 5 ) . 1.134 
 
 Sodium .... 1.052 
 Chlorine . 1.686 
 
 Oxygen .... 0.667 
 Calcium phosphate . . 0.114 
 
 Magnesium phosphate . 0.073 
 Sulphuric oxide (S0 3 ) . 0.066 
 
 The liquid in which the blood globules float is an alkaline solution containing 
 albumin, fibrin and saline matters in about the proportions here indicated. 
 
 IOQQ parts of Liquor Sangulnis contain 
 
 Water .... 902.90 
 
 Albumin .... 78.84 
 
 Fibrin . . . . 4.05 
 
 Fat 1.72 
 
 Organic substances of un-\ 
 
 known nature . j 3-94 
 Mineral substances . -8.55 
 
 The Mineral Substances comist of 
 
 Phosphoric oxide (P 2 O 5 ) . 0.191 
 
 Sulphuric oxide (S0 3 ) . 0.115 
 
 Calcium phosphate . . 0.311 
 
 Magnesium phosphate . 0.222 
 
 Sodium . . . .3.341 
 Chlorine .... 3.644 
 Potassium . . . 0.323 
 Oxygen .... 0.403 
 
 The alkaline character of this liquid appears to be due to the presence of car- 
 bonate and phosphate of sodium. 
 
 613. Flesh. The fibrin composing muscular flesh contains about three-fourths 
 of its weight of water, a part of which is due to the blood contained in the vessels 
 traversing it, and another part to the juice of flesh, which may be squeezed out of 
 the chopped flesh. In this juice of flesh there are certain substances which 
 appear to play a very important part in nutrition. The liquid is distinctly acid, 
 which is remarkable when the alkaline character of the blood is considered, and 
 contains phosphoric, lactic, and butyric acid, together with creatine (p. 676), 
 inosite (p. 716), and saline matters. By soaking minced flesh in cold water and 
 well squeezing it in a cloth, a red fluid is obtained containing the juice of flesh 
 mixed with a little blood. 
 
 The saline constituents of the juice of flesh are chiefly phosphates of potassium 
 and magnesium, with a little chloride of sodium. It is worthy of notice that 
 potassium is the predominant alkali-metal in the juice of flesh, whilst sodium 
 predominates in the blood, especially in the serum. 
 
 * Exclusive of the iron wbicli is associated with the hasmatiii. 
 
URINE. 815 
 
 According to Liebig, the acidity of the juice of flesh is chiefly due to the acid 
 phosphate of potassium, KH 2 P0 4 , whilst the alkalinity of the blood is caused by 
 sodium phosphate, Na 2 HPO 4 ; and it has been suggested that the electric currents 
 which have been traced in the muscular fibres are due to the mutual action 
 between the acid juice of flesh and the alkaline blood, separated only by thin 
 membranes from each other, and from the substance of the muscles and nerves. 
 
 The average composition of flesh may be represented as follows : _ 
 
 Water ........ 78 
 
 Fibrin, vessels, nerves, cells, &c. . . .17 
 
 Albumin . . . . . . .2.5 
 
 Other constituents of the juice of flesh . 2.5 
 
 100.0 
 
 Lieblcfs extract of meat is prepared by exhausting all the soluble matters from 
 the flesh with cold water, separating the albumin by coagulation and evaporating 
 the liquid at a steam heat to a soft extract. It contains about half its weight of 
 water, 40 per cent, of the organic constituents of the juice of flesh (albumin 
 excepted), and 10 per cent, of saline matter. 
 
 Cooking of meat. A knowledge of the composition of the juice of flesh explains 
 the practice adopted, in boiling meat, of immersing it at once in boiling water, 
 instead of placing it in cold water, which is afterwards raised to the boiling- 
 point. In the latter case, the water would soak into the meat, and remove the 
 important nutritive matter contained in the juice ; whilst, in the former, the 
 albumin in the external layer of flesh is at once coagulated, and the water is 
 prevented from penetrating to the interior. In making soup, of course, the 
 opposite method should be followed, the meat being placed in cold water, the 
 temperature of which is gradually raised, so that all the juice of flesh may be 
 extracted and the muscular fibre and vessels alone left. 
 
 The object to be attained in the preparation of beef-tea is the extraction of the 
 whole of the soluble matters from the flesh, to effect which the meat should be 
 minced as finely as possible, soaked for a short time in an equal weight of cold 
 water, and slowly raised to the boiling-point, at which it is maintained for a few 
 minutes. The liquid strained from the residual fibrin contains all the constituents 
 of the juice except the albumin, which has been coagulated. 
 
 When meat is roasted, the internal portions do not generally attain a suffi- 
 ciently high temperature to coagulate the albumin of the juice, but the outside 
 is heated far above 212 F. ; so that the meat becomes impregnated to a greater 
 extent with the melted fat, and some of the constituents of the juice in this part 
 suffer a change, which gives rise to the peculiar flavour of roast meat. The brown 
 sapid substance thus produced has been called osmazomc, but nothing is really 
 known of its true nature. In salting meat, for the purpose of preserving it, a 
 great deal of the juice of flesh oozes out, and a proportionate loss of nutritive 
 matter is sustained. 
 
 614. Urine always contains a large proportion of alkaline and earthy salts, 
 especially of sodium chloride, phosphate and sulphate of potassium, and phos- 
 phates of calcium, magnesium, and ammonium. 
 
 The average composition of human urine may be thus stated : 
 
 Water , ....... 
 
 Urea .......... J 4- 2 3 
 
 Uric acid ......... -37 
 
 Mucus ....... . 
 
 Hippuric acid, creatinine, ammonia, colouring-matter. \ I$JQ$ 
 
 and unknown organic matters . . ) 
 Chloride of sodium ....... 
 
 Phosphoric oxide (P 2 5 ) ...... 
 
 Potash .......... 
 
 Sulphuric oxide (S0 3 ) ...... JJ 
 
 Lime .... 
 
 :.:.:; : : : 
 
 999-94 
 
8l6 NOURISHMENT OF PLANTS. 
 
 CHEMISTEY OF VEGETATION. 
 
 615. Comparatively few of the elements enter into the composition of plants^ 
 and of those that do so only ten are, according to our present knowledge, abso- 
 lutely essentialto the growth of the jplants ; these are carbon, hydr&gen, oxygen, 
 nitrogen, sulpftur. phospiiorus, potassium, calcrum, magnesium, and for plants 
 containing chlorophyll, iron. At the same time sodfum, silicon, and chlorine 
 are invariably present, while manganese, fluorine, and minute quantities of other 
 elements are generally to be found. 
 
 The carbon, hydrogen, and oxygen occur in all the organic constituents of the 
 plant. The nitrogen occurs in the albuminoids, together with a small quantity 
 of the sulphur ; also in the amides, alkaloids, and nitrates. The metals occur as 
 phosphates, nitrates, sulphates, and vegetable salts chiefly oxalates, malates, 
 tartrates, and citrates. 
 
 The carbon is derived by green plants from the carbon dioxide of the air, while 
 plants destitute of chlorophyll are capable of deriving carbon from organic matter 
 in the soil. The hydrogen and oxygen are derived from the water of the soil. 
 
 The source from which the plant derives its nitrogen has long been a subject of 
 discussion. This element, as it exists uncombined in the air, is not absorbed by 
 the plant to any appreciable extent, if at all ; and the' small quantities of ammonia 
 and nitric acid in the air are quite inadequate to furnish the necessary supply for 
 any extensive growth. The conclusion is that the nitrogen must be derived from 
 the soil, and the beneficial effect of manuring with nitrates and ammonium salts 
 supports this view. That nitrates are absorbed in solution by plant roots is 
 certain, and nitrates are always fairly abundant in a fertile soil during the growing 
 season, being produced by the nitrification (p. 87) of the ammonia derived from 
 decaying vegetable matter, and in smaller degree from the rainfall ; it appears 
 probable also that ammonia and amide-like substances in the soil can be absorbed 
 to some extent directly, without previous nitrification. The old observation that 
 the nitrates in the soil will not account for all the nitrogen in a leguminous crop, 
 and that such crops are not benefited by the application of nitrogenous manures 
 to the same extent as are other crops, points to the conclusion that legumes have 
 some exceptional source of nitrogen at their disposal. The discovery on the roots 
 of these plants of tubercules containing organisms which appear to be in symbiosis 
 (crtiv, together with ; /St'os, life) with the plant, and to transform nitrogen, either from 
 organic matter, or from the atmosphere, into nitrogenous compounds which can 
 be absorbed by the roots, and the discovery that inoculation with some soil which 
 is productive for legumes will render fertile one previously barren for such growth, 
 are recent results of this interesting and important inquiry. 
 
 The sulphur and phosphorus are derived by the plant from sulphates and 
 phosphates in the soil, while the other constituent elements are also derived from 
 the mineral matter of the soil. 
 
 It is thus seen that the plant takes up its elements in a highly oxidised con- 
 dition, and that the chemical tendency of vegetables is to reduce to a lower state 
 of oxidation the substances presented in their food, whilst animals exhibit a 
 reciprocal tendency to oxidise the materials on which they feed. 
 
 Soil is disintegrated rock, so that its composition will depend largely on the 
 nature of the rock. To be fertile it must contain all the elements essential for 
 plant growth (save carbon) in a condition available for absorption by the roots. 
 Rarely more than i per cent, of the soil is in such a condition, the rest serving 
 to support the plant mechanically, and becoming slowly available by the process 
 of weathering (p. 128), which is much aided by ploughing, draining, and the 
 various other operations of the farm. 
 
 The chief constituents of a soil are sand, clay, carbonate of lime, and humus. 
 The proportion which these bear to each other greatly influences the physical 
 properties of the soil, and consequently its fertility and cost of working. It is also 
 closely connected with the absorptive \)ower of the soil, or its capability of fixing 
 fertilising matter ; thus, humus retains the all-important ammonia, while the 
 hydrated silicates, including clay, fix potash and phosphoric acid, from any solu- 
 tion containing these which may filter through the soil. 
 
 The first three of the above constituents need no comment here. Humus is the 
 name applied to the organic matter in the soil ; it consists of the brown and black 
 substances resulting from the decay of previous vegetation. Sodium carbonate 
 dissolves this brown humus to a brown solution, from which an acid precipitates 
 
FARM- YARD MANURE. 817 
 
 a brown substance having a faintly acid reaction, and therefore termed w////,V 
 acid (tt&MM, an elm) ; according to some, the humus contains a portion insoluble 
 in sodium carbonate, to which the name ulmin has been given Black humus 
 yields by the same treatment humic acid and hnmln. Two other acids crenic and 
 apocrewf, the former convertible into the latter by oxidation, have also been 
 obtained from the humus, and these have been found in mineral waters All 
 these substances are of ill-ascertained composition. 
 
 The humus is the store of nitrogenous matter, which, by slow nitrification 
 becomes available for the plant. 
 
 When a soil comes under tillage, the crops raised upon it are consumed by 
 animals, and often removed to a distance, so that the mineral food and nitrogen 
 contained in the soil are by degrees exhausted, and unless these are restored the 
 soil becomes barren. To restore its fertility is the object of manuring, which con- 
 sists in adding to the soil substances which shall serve directly as plant-food, or 
 shall so modify by chemical action some material already present in the soil as 
 to convert it into an available form. These two objects are often attained by one 
 and the same manure. 
 
 Manures either supply all the necessary plant-foodswhen they are termed 
 general manures or they supply some food which is especially wanting to enable 
 the plant to nourish, and make use of food already existing in the soil, or perhaps 
 to excite rapid growth at a critical period of its existence, when it is most sensitive 
 to attacks of insects or vicissitudes of weather. Such are termed special manures. 
 
 Nitrogen, phosphorus, and potassium are the plant foods which are most rapidly 
 exhausted and most generally needed. A general manure is accordingly valued 
 by its content of these three elements, regard being had to the condition in 
 which they exist ; for, if they are soluble, they will be more rapidly and thoroughly 
 distributed through the soil, thus becoming immediately available as food ; if, on 
 the other hand, they are in a condition not so available, the immediate benefit of 
 the manure will be smaller, but it will last over a longer period, the constituents 
 becoming soluble in the course of time. 
 
 The various manures can receive but short notice here. Of general manures 
 the most valuable is farm-yard manure, consisting of the solid and liquid excre- 
 ment of the farm stock, together with the litter used to absorb the liquid. Its 
 value will be controlled by the quality and quantity of this litter ; by the nature 
 of the animals ; the richness of their food in N, P 2 5 , and K 2 ; whether they are in 
 active work, in which case as much N, P 2 O 5 and K 2 is voided as is consumed in 
 the food ; or being fattened, milked, or shorn, in which case some of the N, P 2 5 , 
 and K 2 O will be stored in the carcase or removed as milk or wool. But its value 
 is most affected by its after-treatment. If it be stacked, exposed to rain, and 
 the drainings not preserved, much soluble N, P 2 5 , and K 2 will be lost, which 
 is not the case if it be spread directly on the land. Fresh farmyard manure in a 
 heap rapidly becomes rotten, fermenting and losing much carbon as carbon dioxide 
 and marsh gas, but very little nitrogen. It thus becomes more valuable, as it is 
 less weighty when rotten and contains more of its N and P 2 5 in a soluble con- 
 dition. ^Rotten manure contains on an average 70 per cent. H 2 0, 2.7 per cent. 
 true ash, 0.6 per cent. N, 0.3 per cent. P 2 O 5 , and 0.5 per cent. KoO. 
 
 Seaweed is allowed to have a manurial value approaching that of farmyard 
 manure. 
 
 Guano (Peruvian), the dried excrement of sea-birds, contains, when it has been 
 deposited in sheltered places, ammonium urate and other ammonium salts and 
 nitrogenous matter (equivalent in all to 12 per cent. N) ; and the presence of 
 calcium phosphate (26 per cent.) and small quantities of potassium salts render 
 this variety a valuable general manure. If, however, the guano has been deposited 
 in exposed places (Mejillones), its nitrogen has been lost, and it becomes a special 
 phospJiMtio manure, containing about 70 per cent, of calcium phosphate. 
 
 Animal refuses of various kinds form general manures, valuable chiefly for their 
 N, and vegetable matters will of course restore to the soil those mineral consti- 
 tuents which they have previously removed. Rape cake, the compressed refuse of 
 the colza-oil factory, is a general manure of this kind, (,'reen iminitnn'j has a 
 special value, as it consists in keeping covered with vegetation soil which would 
 otherwise be left fallow (and lose by drainage), and then ploughing-in the crop ; 
 as this is generally a deep-rooted one, mineral constituents and nitrogen are 
 thus brought up from the subsoil and left in a quickly available form in the surface 
 soil for the use of shallower-rooted crops. 
 
 3 F 
 
8l8 CHEMICAL MANURES. 
 
 Special manures supply either nitrogen, phosphorus, potassium, or calcium, and 
 less frequently sulphur, chlorine, and magnesium. 
 
 The term nitrates as applied to manure usually implies sodium nitrate, the 
 potassium salt being too expensive for use. Sodium nitrate supplies nitrogen in a 
 very soluble, and therefore readily available, form, stimulating rapid growth. 
 Its solubility renders it less effective in wet weather, as it is then washed through 
 the soil; for the same reason, it is best applied as a top-dressing after growth has 
 begun. As the sodium is not taken up by the crop, it partly remains in the soil 
 as sodium carbonate and silicate, and tends to render it stiff . Ammojiium sulphate 
 also supplies nitrogen, but is less rapid in its action, and better fitted for wet 
 weather than is nitrate. The ammonia rapidly undergoes nitrification, and the 
 nitric acid formed combines with the lime in the soil. The sulphuric acid, not 
 being used by the plant, also combines with the lime. Both these lime salts tend 
 to get washed away, so that this manure is liable to remove lime from the soil. 
 Diluted gas liquor is sometimes used as a manure on account of its ammonia. 
 Soot owes its chief value to its i or 2 per cent, of ammonia. 
 
 Bones are of value for their phosphates (50 per cent.) and their nitrogen (3.5 
 percent.); they are slow in action, and last long. Bone ash and mineral phos- 
 phates (coprolites, &c.), all of which contain no nitrogen, are occasionally used 
 finely ground, but are generally employed for making superphosphate (p. 334). 
 This most important manure is valued by the amount of monocalcium phosphate 
 which it contains, though the manufacturer insists on this being calculated into 
 tricalcium phosphate and then called ' ' soluble phosphate " or " phosphate rendered 
 soluble." For this soluble constituent, which should average 18 to 20 per cent, in 
 a mineral superphosphate, is rapidly spread through the soil by the rain, and is 
 there reconverted into phosphates which are insoluble in pure water, but are very 
 finely divided, and thus easily soluble in carbonic acid, and available as food. 
 Dissolved hones have been partially converted into superphosphate by treatment 
 with sulphuric acid, and of course contain nitrogen. Basic slay, or Thomas or 
 Thomas- Gilchrist slag (p. 410), is now employed as a manure on account of its 
 phosphorus ; it must be used in a very fine state of division. It contains 14 to 
 19 per cent, of P 2 O 5 , chiefly as the compound 4CaO.P. 2 5 , which is more soluble in 
 saline solutions than is 3CaO.P 2 O 5 . 
 
 Potassium is supplied in kainit (p. 311), which contains 13 to 14 per cent. K 2 0. 
 Other sources of this element are carnallite, wood ashes, beet-sugar refuse, and the 
 suint or yolli of raw wool. 
 
 Lime as used by the agriculturist includes chalk, caustic lime, and slaked 
 lime. It is more often employed for attacking the constituents of the soil 
 than as a direct plant-food, there generally being enough in the soil for that 
 purpose. Lime neutralises organic acids in the soil, sweetening it, and hastens 
 the decay of organic matter, rendering the N available and furnishing CO., as a 
 solvent for minerals. Its action on minerals is specially serviceable for decom- 
 posing injurious iron compounds and the felspars, rendering the K 2 O of these 
 latter available. Some limestones, and all shells, contain small quantities of 
 P 2 O 5 , itself valuable. 
 
 Common salt is chiefly of value for its chemical action on the soil and for de- 
 stroying weeds and pests. Sodium chloride is always brought down in small 
 quantity from the air by the rain. 
 
 Gypsum and magnesium sulphate are. occasionally used for a supply of sulphur. 
 
 6 1 6. In some cases fertility is restored to an apparently exhausted soil, with- 
 out the addition of manure, by allowing it to lie fallow for a time, so that, under 
 the influence of air, moisture, and frost, such chemical changes may occur in it 
 as will again replenish it with food available for the crops. It is not even 
 necessary in all cases that the soil should be altogether released from cultivation ; 
 for, even though it may refuse to feed any longer one particular crop, it may 
 furnish an excellent crop of a different description, and, what is more remark- 
 able, it may, after growing two or three different crops, be found to have regained 
 its power of nourishing the very crop for which it was before exhausted. Experi- 
 ence of this has led to the adoption of a system of rotation of crops, by which a 
 soil is made to yield, for example, a crop of barley, and then successive crops of 
 clover, wheat, turnips, and barley again. 
 
 The possibility of this rotation is partly accounted for by the difference in the 
 mineral food removed by different crops ; thus, turnips and clover require much 
 potash and lime, while wheat and barley require much phosphoric acid, so that, 
 
GROWTH OF PLANTS'. 819 
 
 in alternating the turnips and clover with the wheat and barley there may be 
 sufficient time for some of the locked-up phosphoric acid of the soil to become 
 available as food. 
 
 Moreover, the farm crops appear to differ in their capacity for feeding on the 
 mineral substances present in the soil ; thus, there may be phosphoric acid in a 
 soil which would be available for wheat, but perfectly useless for turnips which 
 are for this reason always greatly benefited by manuring with superphosphate 
 Again, cereal crops are more benefited by application of nitrates than are most 
 other crops. 
 
 An explanation of this is afforded by our knowledge of the difference in the 
 depth to which the roots of various crops are capable of penetrating into the soil, 
 and consequently of drawing a supply of food from the subsoil. The benefit of 
 rotation is also partly to be accounted for in this way. For where the residue of 
 the preceding deep-rooted crop is allowed to remain on the land, the surface soil 
 will become enriched with food collected from the subsoil, and tLus rendered 
 available for the shorter-rooted crop when the residue is ploughed up. At the 
 same time the opening up of the soil to different depths, caused by the differently 
 penetrating roots, prevents the formation of the hard layer, or pan, which gene- 
 rally forms at the limit of the roots if the same crop be grown continually. 
 
 617. Our knowledge of the chemical operations occurring in the plant, and 
 resulting in the elaboration of the great variety of vegetable products, is very 
 slight indeed. We appear to have sufficient evidence that starch and sugar, for 
 example, are constructed in the plant from carbonic acid and water, and that 
 albuminoids result from the interaction of the same compounds, together with 
 nitric acid, or ammonia, and certain sulphates and phosphates ; but the inter- 
 mediate steps in these conversions are as yet unknown. 
 
 All seeds contain starch or fat (or both), albuminoids, and mineral matters, 
 these being provided for the nourishment of the young plant till its organs are 
 sufficiently developed to enable it to procure its own food from the air and soil. 
 The necessary conditions for germination are a suitable temperature (best at 28 
 to 34 C.), the presence of free oxygen, and moisture. It is to obtain this last 
 that the seed is buried, light or darkness having little or no effect. The seed 
 absorbs water and oxygen and evolves carbon dioxide ; since the albuminous 
 constituents are the most changeable substances present, it is probably these 
 which undergo oxidation, part forming diastase, which excites the conversion of 
 insoluble starch into soluble starch and sugar ; some of the albuminoids at the 
 same time become soluble amides. The water absorbed dissolves these altered 
 substances and the mineral matters, forming the sap to nourish the embryo. 
 The seed swells, and the integument bursts, the radicle growing first and then the 
 plumule; the former develops into the root, which absorbs the mineral constitu- 
 ents and nitrogen in aqueous solution from the soil, while the latter, as the sap 
 ascends, develops the leaves, the sugar of the sap becoming converted into cellu- 
 lose for the purpose. Chlorophyll is then developed, and the decomposition of 
 carbon dioxide and assimilation of carbon begins. As the roots act more quickly 
 than the leaves, the young plant is relatively richer in mineral constituents and 
 nitrogen than is the mature plant. The assimilation of carbon and decomposition 
 of carbon dioxide proceed only in light, the volume of oxygen evolved being 
 equal to that of the carbon dioxide absorbed,* so that the formation of cellulose 
 might be regarded as occurring directly by the action of the carbon dioxide on 
 the water of the sap, thus : 6C0 2 + 5H 2 = C 6 H 10 5 + 12 . The compounds what- 
 ever they may be, that are formed by the assimilating process are altered and 
 rendered soluble by a process of oxidation known as metobolu, accompanied by 
 evolution of carbon dioxide a veritable respiration, in fact, which goes on in li ; 
 or dark, though in the light the evolved carbon dioxide is masked by the larger 
 evolution of oxygen. Osmosis is concerned in the passage of the soluble matt 
 from cell to cell. 
 
 By growing plants in water in which one particular constituent element is cor 
 tained in very small proportion or is absent, it has been ascertained that potassium 
 is concerned in the formation of starch and other carbohydrates ; calcium in 
 the formation of cellulose ; iron in the formation of chlorophyll ; chloi 
 
 * It has been suggested that formic aldehyde is first produced, 
 and that this is subsequently polymerised to glucose, C 6 H 12 O 6 . The recent production of 
 acrose from formic aldehyde (p. 728) supports this view. 
 
820 EIPENING OF FRUIT. 
 
 translocation of starch ; phosphorus, sulphur, and nitrogen in the formation of 
 albuminoids. The mission of calcium is also shown by the fact that wheat has a 
 tendency to lay or lodge where the soil is poor in this element. 
 
 In annual plants the formation of seed is carried on at the expense of the rest 
 of the plant, which becomes exhausted, starch and albuminoids being transferred 
 to the seed. In-jjbiennial and perennial plants the advent of autumn is accompanied 
 by a transference of food from the stem and leaves to the roots, tubers, or pith, 
 to form a basis for growth next spring, exhaustion and death occurring in the 
 case of biennial plants at seed-time, and the rotation recurring in the case of 
 perennials. 
 
 618. With respect to the ripening of fruit, we know a little more concerning 
 the chemical changes which it involves. Most fruits, in their unripe condition, 
 contain cellulose, starch,* and some one or more vegetable acids, such as malic, 
 citric, tartaric, and tannic, the last being almost invariably present, and causing 
 the peculiar roughness and astringency of the unripe fruit. The characteristic 
 constituent of unripe fruits, however, is pectose, a compound of carbon, hydrogen, 
 and oxygen, the composition of which has not been exactly determined. Pectose 
 is quite insoluble in water, but during the ripening of the fruit it undergoes a 
 change induced by the vegetable acids, and is converted into pectin (C 32 H 40 0. 2 8), 
 which is capable of dissolving in water, and yields a viscous solution. " As the 
 maturation proceeds, the pectin itself is transformed into pectic acid (C^H^O^) 
 &ndpectosic acid (C 32 H46O 3 i), which are soluble in boiling water, yielding solutions 
 which gelatinise on cooling. It is from the presence of these acids, therefore, 
 that many ripe fruits are so easily convertible into jellies. 
 
 Whilst the fruit remains green, its relation to the atmosphere appears to be the 
 same as that of the leaves, for it absorbs carbon dioxide and evolves oxygen ; but 
 when it fairly begins to ripen, oxygen is absorbed from the air and carbon dioxide 
 evolved, whilst the starch and cellulose are converted into sugar under the 
 influence of the vegetable acids (p. 726), and the fruit becomes sweet. The con- 
 version of starch and cellulose (C6H 10 O 5 ) into sugar (CeH^Oe) would simply require 
 the assimilation of the elements of water, so that the absorption of oxygen and 
 evolution of carbon dioxide are probably necessary for the conversion of the 
 tannic and other acids into sugar. For example 
 
 C 14 H 10 9 + H 2 O + 12 = C 6 H 12 O 6 + 8C0 2 . 
 Tannic acid. Fruit-sugar. 
 
 3C 4 H 6 6 + 3 = C 6 H 12 6 + 3 H 2 + 6C0 2 . 
 Tartaric acid. 
 
 When the sugar has reached its maximum, the ripening is completed ; and if the 
 fruit be kept longer, the oxidation takes the form of ordinary decay. 
 
 A change in composition, similar to that caused by ripening, is effected by 
 cooking the unripe fruit. 
 
 619. The scheme of natural chemistry would not be complete unless provision 
 were made for the restoration of the constituents of plants, after death, to the 
 atmosphere and soil, where they might afford food to new generations of plants. 
 Accordingly, very shortly after the death of a plant, if sufficient moisture be 
 present, the spores of ferments acquired from the air begin to develop, the change- 
 able nitrogenised (albuminous) constituents begin to putrefy, and the change is 
 communicated to the other parts of the plant, under the form of decay, so that 
 the plant is slowly consumed by the atmospheric oxygen, its carbon being recon- 
 verted into carbonic acid, its hydrogen into water, and its nitrogen into ammonia, 
 these substances being then transported in the atmosphere to living plants which 
 need them, while the mineral constituents of the dead plants are washed into the 
 soil by rain. 
 
 Moist wood is slowly converted by decay into humus. When it is desired to 
 preserve wood from decay, it is impregnated with some substance which shall 
 form an unchangeable compound with the albuminous constituents of the sap. 
 Kreasote (p. 712) and corrosive sublimate (ky uniting) are occasionally used for 
 this purpose, the wood being made to imbibe a diluted solution of the preserva- 
 tive, either by being soaked in it or under pressure. 
 
 In Boucherie's process for preserving wood, the natural ascending force of the 
 sap is ingeniously turned to account in drawing up the preservative solution. A 
 
 * Some doubt exists as to the presence of starch in fruit. 
 
DIGESTION. 3 2I 
 
 large incision being made around the lower Dart of tbp fr.,nt n f *u 
 a trough of clay is built up around it, SSffiSft weak soludof oTsSfphS 
 of copper, peracetate of iron, or calcium. chloride. Even after the tree has bee 
 felled, it may be made to imbibe the preserving solution wmlst in a horTzont^ 
 position by enclosing the base of the trunk in an impermeable bag suppHed wfth 
 the liquid from a reservoir. The impregnation of the wood with such 
 
 NUTEITION OF ANIMALS. 
 
 620. Between the chemistry of vegetable and that of animal life there is this 
 fundamental distinction, that the former is eminently constructive and the latter 
 destructive. The plant, supplied with compounds of the simplest kind carbonic 
 acid, water, and ammonia constructs such complex substances as albumin and 
 sugar ; whilst the animal, incapable of deriving sustenance from the simpler 
 compounds, being fed with those of a more complex character, converts them 
 eventually, for the most part, into the very materials with which the construc- 
 tive work of the plant began. It is indeed true that some of the substances 
 deposited m the animal frame, such as fibrin, and gelatinous matter rival in com- 
 plexity many of the products of vegetable life ; but for the elaboration of these 
 substances, the animal must receive food somewhat approaching them in chemical 
 composition. It is to this nearer resemblance between the food of animals and 
 the proximate constituents of their frames, that we may partly ascribe the greater 
 extent of our knowledge on the subject of the nutrition of animals, which is, 
 however, far from being complete. 
 
 The -idtlm-ate elements contained in the animal body are the same as those of the 
 vegetable, but the proximate constituents are far more numerous and varied. 
 
 The bones containing the phosphates and carbonates of calcium and magnesium 
 together with gelatinous matter, require that the animal should be supplied with 
 food which, like bread, contains abundance of phosphates, as well as the nitro- 
 genised matter (gluten) from which the gelatinous substance may be formed. In 
 milk, the food of the young animal, we have also the necessary phosphates, whilst 
 the casein affords the supply of nitrogenous matters. 
 
 Muscular flesh finds, in the gluten of bread and the casein of milk, the nitro- 
 genised constituent from which its fibrin might be formed with even less trans- 
 formation than is required for the gelatinous matter of bone, since the com- 
 position of fibrin, gluten, and casein is very similar. The albumin and fibrin of 
 the blood have also their counterparts of the gluten and casein of bread and 
 milk, whilst all the salts of the blood may be found in either of these articles of 
 food. 
 
 Bread and milk, therefore, may be taken as excellent representatives of the food 
 necessary for animals, and the same constituents are received in their flesh diet by 
 animals which are purely carnivorous, but the flesh contains them in a more 
 advanced stage of preparation. 
 
 It is natural to suppose that the fat, which contains no nitrogen, should be 
 supplied by those constituents of the food which are free from that element, such 
 as the starch in bread, and the sugar and fat in milk. 
 
 Before the food can be turned to account for the sustenance of the body, it 
 must undergo digestion, that is, it must be either dissolved or otherwise reduced 
 to such a form that it can be absorbed by the blood, which it accompanies into 
 the lungs to undergo the process of respiration, and thus to become fitted to serve 
 for the nutrition of the various organs of the body, since these have to be con- 
 tinually repaired at the expense of the constituents of the blood. 
 
 The first step towards the digestion of the food is its disintegration effected by 
 the teeth with the aid of the saliva, by which it should be reduced to a pulpy mass. 
 The saliva is an alkaline fluid characterised by the presence of a peculiar albumin- 
 ous substance called ptyalin (irrtfw, to spit), which easily putrefies. The action of 
 saliva in mastication is doubtless in great part a mechanical one, biit it is possil 
 that its alkalinity assists the process chemically, by partly emulsifying the fatty 
 portions of the food. The ptyalin also acts as a ferment, converting starch into 
 sugar. This disintegration of the food is of course materially assisted by the 
 cooking to which it has been previously subjected, the hard and fibrous portions 
 having been thereby softened. 
 
822 PRODUCTION OF BLOOD. 
 
 The food now passes to the stomach, in which it remains for some time, at the 
 temperature of the body (98 F.), in contact with the yastrlc juice, the chief 
 chemical agent in the digestive process. The gastric juice which is secreted by 
 the lining membrane of the stomach is an acid liquid, containing hydrochloric 
 and lactic acids. It is characterised by the presence of a peculiar substance 
 belonging to the albuminous class of bodies which is called pepsin (TreVrw, to 
 digest), and possesses the remarkable power of enabling dilute acids, by its mere 
 presence, to dissolve such substances as fibrin and coagulated albumin, which 
 would resist the action of the acid alone for a great length of time. 
 
 An imitation of the gastric juice may be made by digesting the mucous mem- 
 brane of the stomach for some hours in warm very dilute hydrochloric acid. The 
 acid liquid thus obtained is capable of dissolving meat, curd, &c., if it be main- 
 tained at the temperature of the body. The pepsin prepared from the stomach 
 of the pig and other animals is sometimes administered medicinally in order to 
 assist digestion. 
 
 The principal change which the food suffers by the action of the gastric juice 
 is the conversion of the fibrinous and albuminous constituents into soluble forms 
 (peptones) ; the starch is also partly converted into dextrin and sugar, but the 
 fatty constituents are unchanged. 
 
 The food which has thus been partially digested in the stomach is called by 
 physiologists chyme, and passes thence into the commencement of the intestines 
 (the duodenum), where it is subjected to the action of two more chemical agents, 
 the bile and the pancreatic juice. 
 
 621. Bile consists essentially of a solution of two salts known as glycocholate 
 and taurocholate of sodium. Both glycocbolic and taurocholic acids are resinous, 
 and do not neutralise the alkali, so that the bile has a strong alkaline character. 
 Another characteristic feature of this secretion is the large proportion of carbon 
 which it contains. GlycucJiolic acid contains 67 per cent, of carbon, whilst taut-o- 
 c/tolic acid contains 61 per cent. 
 
 The special function of the bile in the digestion of the food has not been ex- 
 plained, but from its strongly alkaline reaction it does not appear improbable that 
 it assists in the digestion of fatty substances. 
 
 The pancreatic juice is another alkaline secretion which differs from the bile in 
 containing a considerable quantity of albumin, and is very putrescible. Its par- 
 ticular office in digestion appears to consist in promoting the conversion of the 
 starchy portions of the food into sugar, though it also has a powerful action 
 upon the fats, causing them to form an intimate mixture, or emulsion, with 
 water, and partly saponifying them. The digestion of the starch and sugar is 
 completed by the action of the intestinal fluid in the further passage of the food 
 through the intestines, so that when it arrives in the small intestines, all the 
 soluble matters have become converted into a thin milky liquid called chyle, which 
 has next to be separated mechanically from the insoluble portions, such as woody 
 fibre, &c., which are excreted from the body. 
 
 This separation is effected in the small intestines by means of two distinct sets 
 of vessels, one of which (the mescnteric reinfi) absorbs the dissolved starchy por- 
 tions of the food, and conveys them to the liver, whence they are afterwards 
 transferred to the right auricle of the heart. The other set of vessels (lacteals) 
 absorbs the digested fatty matters, and conveys them, through the thoracic duct, 
 into the subclavian vein, and thence at once into the right auricle of the heart. 
 
 From the right auricle this imperfect blood passes into the right ventricle of 
 the heart, and is there mixed with the blood returned from the body by the veins, 
 after having fulfilled its various functions in the system. The mixture, which has 
 the usual dark brown colour of venous blood, is next forced, by the contraction 
 of the heart, into the lungs, where it is distributed through an immense number 
 of extremely fine vessels traversing the lungs, in contact with the minute tubes 
 containing the inspired air, so that the venous blood is only separated from the 
 air by very thin and moist membranes. Through these membranes the dark 
 venous blood gives up the carbonic acid gas with which it had become charged 
 by the oxidation of the carbon of the organs in its passage through the body, and 
 acquires, in return, about an equal volume of oxygen, which converts it into the 
 bright crimson arterial blood. In this state it returns to the left side of the heart, 
 whence it is conveyed, by the arteries, to the different organs of the body. The 
 chemistry of the changes effected and suffered by the blood in its circulation 
 through the body is very imperfectly understood. One of its great offices is the 
 
RATIONAL FEEDING. 
 
 supply of the oxygen necessary to oxidise the components of the various organs 
 and thus to evolve the heat which maintains the body at its high temperature' 
 The results of the oxidation of these organs are undoubtedly very numerous ' 
 among them we may trace carbonic, sulphuric, phosphoric, lactic, butvric and 
 uric acids, as well as urea and some other substances. The destroyed tissues must 
 at the same time be renewed by the deposition., from the blood, of fresh particles 
 similar to those which have been oxidised. In the course of the blood through 
 the circulation, the above products of oxidation have to be removed from it the 
 carbonic acid by the lungs and skin- the sulphuric, phosphoric, and uric acids 
 and the urea, by the kidneys. 
 
 The various liquid secretions of the body, such as the bile, the saliva, the gastric 
 juice, &c., have also to be elaborated from the blood during its circulation through 
 the arteries, after which it returns, by the veins, to the heart, to have its com- 
 position restored by the matters derived from the food, and to be reconverted 
 into arterial blood in the lungs. 
 
 When it is remembered that the body is exposed to very considerable variations 
 of external heat and cold, a question occurs as to the provision made for main- 
 taining it at its uniform temperature. This is effected through the agency of the 
 fat which is deposited in all the organs of the body. Since fatty substances in 
 general are particularly rich in carbon and hydrogen, their oxidation within the 
 body would be attended with the production of more heat than that of those parts 
 of the organs which contain much nitrogen and oxygen. Accordingly, when the 
 body is exposed to a low temperature, a larger quantity of its fat is consumed by 
 the oxidising action of the blood, and a corresponding increase occurs in the 
 amount of heat evolved, thus compensating for the greater loss of heat suffered 
 by the body in the cooler atmosphere. Of course, in cold weather, when more 
 oxygen is required to maintain the heat of the frame, a larger quantity of that 
 gas is inhaled at each breath, on account of the higher specific gravity of the air, 
 in addition to which we have the quickened respiration which always attends ex- 
 posure to cold. To supply this extra demand for carbon and hydrogen in cold 
 weather, we instinctively have recourse to such substances as fat, starch, sugar, 
 &c., which contain them in large proportion, and these aliments, free from nitro- 
 gen, are often spoken of as the respiratory constituents of food ; whilst flesh, gluten, 
 albumin, &c., which contain nitrogen, are styled the plastic elements of nutrition 
 (7rXcur<ra>, to for HI). 
 
 Bearing in mind that the food has a two-fold office to nourish the frame and 
 to maintain the animal heat it will be evident that a judiciously regulated diet 
 will contain due proportions of these nitrogenous constituents, such as albumin, 
 fibrin, and casein, which serve to supply the waste of the organs, and of such 
 non-nitrogenised bodies as starch and sugar, from which fat may be elaborated 
 to sustain the bodily warmth. 
 
 Albuminoid ratio. The proportion which these two parts of the food should 
 bear to each other will, of course, depend upon the particular condition of exist- 
 ence of the animal. Thus, for a growing animal a larger proportion of the 
 nitrogenised or plastic portion of food would be required than for an animal 
 whose growth has ceased ; and animals exposed to a low temperature would 
 require more of the non-nitrogenised or heat-giving portion of the food. 
 
 Accordingly, we find that a man can live upon a diet which contains (as in the 
 case of wheaten bread) 5 parts of non-nitrogenised (starch and sugar) to i part 
 of nitrogenised food (gluten) ; whilst an infant, whose increasing organs require 
 more nitrogenised material, thrives upon milk, in which this amounts to i part 
 (casein) for every 4 parts of the non-nitrogenised portion (milk-sugar and fat). The 
 inhabitants of cold climates consume, as is well known, much more oil and 
 than do those of the temperate and hot regions. 
 
 An examination of the composition of different articles of food affp 
 explanation of the custom which experience has warranted, of associating par 
 ticular varieties of food. Thus, assuming as our standard of comparison tne 
 
 All muscular or mental exertion is attended with a corresponding oxidation > of 
 the tissues of the frame, just as each movement of a ^^J^^J^^J 
 to the combustion of a proportionate quantity of coal 
 
824 DECAY AFTEE DEATH. 
 
 such exertion both creates a demand for food, and quickens the respiration to 
 obtain an increased supply of oxygen. 
 
 CHANGES IN THE ANIMAL BODY AFTEE DEATH. 
 
 622. After the death of animals, just as after that of plants, a change occurs 
 in some of the nitrogenous constitutents, attended by the development of 
 living organisms of a very low order, and this change is soon communicated to all 
 parts of the body, which undergoes a putrefaction or metamorphosis, of which the 
 ultimate results are the conversion of the carbon into carbonic acid, the hydrogen 
 into water, the nitrogen into ammonia, nitrous and nitric acids, and the sulphur 
 into sulphuretted hydrogen and sulphuric acid. The mineral constituents of the 
 animal frame then mingle with the surrounding soil, and are ready to take part 
 in the nourishment of plants, which construct the organic components of their 
 frames from the carbonic acid and ammonia furnished by the putrefaction of the 
 animal, and then serve in their turn as sustenance for animals whose respiration 
 supplies the air with carbonic acid gas and takes in exchange the oxygen elimi- 
 nated by the plant. 
 
 The functions of the two divisions of animate nature are, therefore, perfectly 
 reciprocal, and this relationship must be regarded as the foundation of economical 
 agriculture. If it were possible to prevent the change of the atmosphere, it is 
 quite conceivable that a perpetual succession of plants and animals could be raised 
 upon a given farm, without any importation of food, provided that there was also 
 no exportation. Or even, permitting an exportation of food, the succession of 
 plants and animals raised upon the same land might be, at least, a very long one, 
 if the solid and liquid excrement of the animals, to feed whom was the object of 
 this exportation, were restored to the land upon which this food was raised. The 
 explanation of this is, that the solid and liquid excrements of the animal contain 
 a very large proportion of the mineral constituents of the soil, in the very state in 
 which they are best fitted for the assimilation by the crop, and as long as the soil 
 contains the requisite supply of mineral food, the plant can derive its organic 
 constituents from the atmosphere itself. 
 
 Forasmuch, however, as the vegetable and animal food produced upon a farm 
 is generally exported to feed the dwellers in towns, whose excrements cannot, 
 without excessive outlay, be returned to the soil whence the food was derived, it 
 becomes necessary for the agriculturist to purchase farm-yard manure, guano, 
 &c., in order to prevent the exhaustion of his soil. A great manufacturing 
 country, in which the majority of the inhabitants are congregated in very large 
 numbers around a few centres of industry, at a distance from the land under 
 tillage, is thus of necessity dependent for a considerable proportion of its food 
 upon more thinly populated countries where manufactures do not flourish, to 
 which it exports in return the produce of the labour which it feeds. 
 
 The parts of the frames of animals differ very considerably in their tendency 
 to putrefaction. The blood and muscular flesh undergo this change most readily, 
 as being the most complex parts of the body, whilst the fat remains unchanged 
 for a much longer period, and the bones and hair will also resist putre- 
 faction for a great length of time. The comparative stability of the fat is 
 observed in the bodies of animals which have been buried for some time in a 
 very wet situation, when they are often found converted almost entirely into a 
 mass of adijjocere, consisting of the palmitic and stearic acids derived from the 
 fat. 
 
 When an animal body is thoroughly dried, it may be preserved unchanged for 
 any length of time, and this is the simplest of the methods adopted for the pre- 
 servation of animal food, becoming far more efficacious when combined with the 
 use of some antiseptic substance, such as salt, sugar, spice, or kreasote. The 
 preservative effects of salt and sugar are sometimes ascribed to the attraction 
 exerted by them upon moisture, which they withdraw from the flesh, whilst spices 
 owe their antiseptic power to the essential oils, which appear to have a specific 
 action in arresting fermentative change, a character which also belongs to krea- 
 sote, carbolic acid, and probably to other substances which occur in the smoke of 
 wood, well known for its efficacy in curing animal matter. Such substances are 
 often called anti-zymotic bodies ; carbolic, salicylic, benzoic, and boric acids are 
 classed under this head. 
 
 A process commonly adopted for the preservation of animal and vegetable food 
 
ANTISEPTIC PRESERVATION. 825 
 
 -consists in heating them with a little water in tin canisters, which are sealed air- 
 tight as soon as the steam has expelled all the air, and if the organic matter be 
 perfectly fresh, this mode of preserving it is found very successful, though, if 
 putrefaction has once commenced, to ever so slight an extent, it will continue 
 even in the sealed canister quite independently of the air. 
 
 Modern experiments have disclosed a great imperfection in our acquaintance 
 with the conditious under which putrefaction occurs, and indicate the presence 
 in the atmosphere of some minute solid particles which appear to be minute ova 
 or germs, and have the power of inducing the commencement' of this change. 
 It has been found that milk, for example, may be kept for a very considerable 
 period without putrefying, if it be boiled in a flask, the neck of which is after- 
 wards loosely stopped with cotton wool, whilst, if the plug of cotton wool be 
 omitted, the other conditions being precisely the same, putrefaction will set in 
 very speedily. 
 
 Perfectly fresh animal matters have also been preserved for a length of time in 
 that state, in vessels containing air which has been passed through red-hot tubes 
 with the view of destroying any living germs which might be present, and such 
 substances have been found to putrefy as soon as the unpurified air was allowed 
 access to them. 
 
 The extremes of the scale of animated existence would appear to meet here. 
 The highest forms of organised matter, immediately after death, serve to nourish 
 some of the lowest orders of living germs, these helping to resolve the complex 
 matter into the simpler forms of carbonic acid, ammonia, &c., which are returned 
 to the atmosphere, the great receptacle for the four chief elements of living 
 matter carbon, hydrogen, nitrogen, and oxygen. 
 
INDEX. 
 
 The names of minerals are printed in italics. 
 
 ABSINTHE, 745 
 
 Absolute boiling-point, 27 
 
 Absorption bauds, 331, 789 
 
 spectra, 331, 789 
 Acacia catechu, 712 
 Acenapb.tb.ene, 553 
 Acetacetic acid, 627 
 ether, 643 
 Acetal, 582 
 
 Acetaldehyde hydrazone, 583 
 Acetamide, 667 
 Acetamido-chloride, 668 
 Acetanilide, 663, 667, 668 
 Acetates, 592 
 Acetic acid, 590 
 
 anhydrous, 593 
 glacial, 59 1 
 synthesis of, 592 
 aldehyde, 581 
 anhydride, 593 
 chloride, 639 
 esters, 643 
 ether, 643 
 peroxide, 593 
 series of acids, 588 
 Acetification, 590 
 Acetimido-ether, 668 
 Acetimethylarnide, 660 
 Aceto-acetic acid, 626 
 Acetol, 626 
 Acetone, 625 
 
 peroxide, 626 
 propione, 624 
 Acetones, 624 
 Aceto-nitrile, 667, 699 
 Acetophenoue, 626 
 Aceturic acid, 675 
 Acetyl, 592 
 
 bromide, 639 
 carbamides, 671 
 chloride, 639 
 creosol, 713 
 dioxide, 593 
 hydrate, 600 
 hydride, 581 
 iodide, 639 
 sulphide, 593 
 urea, 671 
 vanillic acid, 713 
 Acetylene, 137, 537 
 
 Acetylene detected in coal-gas, 162 
 dichloride, 538 
 formed from ethylene, 144 
 heat of formation, 141 
 preparation of, 139 
 prepared from ether, 139 
 properties of, 141 
 series, 537 
 synthesis of, 137 
 tetrachloride, 538 
 Acetylglycocine, 675 
 Acetylides, 537 
 Achro-dextriu, 736 
 Acid, 19, 35 
 
 albumin, 750 
 calcium meconate, 622 
 chlorides, 191 
 egg-, 227 
 potassium malate, 618 
 
 racemate, 620 
 saccharate, 622 
 radicles, 94, 592 
 salts, defined, 104 
 Acids, acetic series, 593 
 acrylic series, 596 
 anhydro, 261 
 aromatic series, 599 
 basicity of, 104 
 benzoic series, 585, 599 
 classification of, 104 
 dibasic, 104 
 lactic series, 603 
 monobasic, 104 
 
 diatomic, 602 
 organic, 586 
 oxalic series, 612 
 polybasic, 104, 623 
 sorbic series, 599 
 structure of, 260 
 tetrabasic, 104 
 tribasic, 104 
 
 volatile, separation of, 598 
 Acidic decomposition, 644 
 Acidulous waters, 61 
 Aconine, 783 
 Aconitic acid, 623 
 Aconitine, 783 
 Acridine, 768 
 
 yellow, 768 
 Acridinium derivatives, 768 
 
828 
 
 INDEX. 
 
 Acrolein, 577, 583 
 Acrose, 728 
 Acrylic acid, 597 
 
 aldehyde, 583 
 series of acids, 583 
 Actinic rays, 172 
 Acyclic compounds, 526 
 Adapter, 139 
 Adipic acid, 622 
 Adipocere, 595 
 
 Adjacent substitution-products, 546 
 Adjective dyes, 683 
 Aerated bread, 809 
 JEsculetin, 744 
 jEsculin, 744 
 Affinity, coefficients of, 311 
 
 measurement of, 304 
 predisposing-, 312 
 residual, 136 
 After-damp, 125, 145 
 Agate, 276 
 Aich-metal, 482 
 
 Air, analysis of, by eudiometer, 44 
 nitric oxide, 97 
 phosphorus, 68 
 aqueous vapour in, 68, 71 
 atmospheric, 67 
 burnt in coal-gas, 152 
 composition of, 68 
 effect of combustion on, 123 
 exact analysis of, 69 
 liquid, 71 
 optically pure, 71 
 pump, 330 
 
 tested for impurity, 124 
 Alabaster, 367 
 
 oriental, 58 
 Alanine, 677 
 Albite, 389 
 
 Albumin of blood, 750 
 eggs, 749 
 vegetables, 750 
 
 Albuminoid ammonia, 502, 750 
 compounds, 748 
 ratio, 823 
 Albuminoids, 748 
 Albuminose, 750 
 Alcarsin, 655 
 Alcohol, 561 
 
 absolute, 563 
 acids, 596 
 amines, 666 
 
 chemical constitution of, 561 
 methylated, 566 
 properties of, 563 
 radicles, 565, 592 
 synthesis of, 561 
 test for, 564 
 Alcoholates, 564 
 
 Alcoholic fermentation, 562, 806 
 Alcohols, 561 
 
 aromatic, 571 
 boiling-points of, 565 
 classification of, 561 
 dihydric, 573 
 distinguished, 568 
 general preparation of, 569 
 iso, 567 
 
 monohydric, 565 
 normal, 567 
 
 Alcohols, polyhydric, 578 
 primary, 568 
 secondary, 568 
 tertiary, 568 
 tetrahydric, 577 
 trihydric, 575 
 unsaturated, 570 
 Aldehyde, 581 
 
 acids, 579 
 ammonia, 582 
 
 chemical constitution of, 580 
 condensation, 584 
 resin, i;82 
 Aldehydes, 579 
 
 aromatic, 584 
 
 constitution of, 579 
 
 general reaction for obtaining, 
 
 580 
 
 test for, 582 
 Aldol, 582 
 
 condensation, 583 
 Aid oses, 724 
 Aldoximes, 583 
 Ale, composition of, 806 
 Algaroth, powder of, 444 
 Alizarates, 720 
 Alizarin, 719 
 
 artificial, 720 
 blue, 767 
 bordeaux, 721 
 cyauine, 721 
 Alkali defined, 19 
 
 manufacture, 345 
 metals, group of, 359 
 waste, 347 
 works, 171 
 Alkaline cupric solution, 619 
 
 earth metals, 372 
 Alkaloids, 774 
 Alkides, 651, 656, 657 
 Alkylanilines, 664 
 
 acetates, 643 
 benzenes, 548 
 Alkyl cyanurates, 704 
 cyanides, 699 
 radicles, 528 
 sulphates, 641 
 
 Alkylpiperidiuium iodides, 766 
 Alkylpyridines, 766 
 Alkylpyridinium iodides, 766 
 Alkylquiuolinium iodides, 767 
 Allantoin, 773 
 Allan turic acid, 773 
 Allophanamide, 671 
 Allophanic acid, 671 
 Allotropy, 118 
 Alloxan, 771 
 Alloxanic acid, 771 
 Alloxautin, 771 
 Alloys, 451 
 Allyl-alcohol, 570 
 bromide, 636 
 chloride, 636 
 cyanamide, 705 
 ether, 631 
 iodide, 636 
 isothiocyanate, 705 
 pyridine, 776 
 sulphide, 573 
 thiocyanate, 705 
 
INDEX. 
 
 829 
 
 Allyl-thio-urea, 705 
 
 tricyanide, 623 
 Allylene, 538 
 Almond cake, 584 
 
 oil, 798 
 Almonds, 584 
 Aloes, 746 
 Aloin, 746 
 Aludels, 196, 496 
 Alum, 386 
 
 basic, 388 
 burnt, 387 
 concentrated, 386 
 shale, 387 
 Alumina, 388 
 Aluminium, 383, 385 
 
 acetate, 591 
 bronze, 386, 481 
 carbide, 145 
 chloride, 389 
 ethide, 657 
 ethoxide, 564 
 extraction, 384 
 fluoride, 389 
 group, review of, 393 
 hydroxide, 388 
 methide, 657 
 phosphates, 390 
 properties, 385 
 silicates, 389 
 silicide, 281 
 sulphates, 386 
 Alums, 234, 387 
 Alunogen, 386 
 Amalgam, ammonium, 85 
 electrical, 498 
 sodium, 85 
 
 Amalgamating battery plates, 14, 497 
 Amalgamation of gold-ores, 514 
 
 silver-ores, 489 
 Amalgams, 498 
 Amalic acid, 775 
 Amber, 560 
 Ambergris, 799 
 Ambrein, 799 
 Amethyst, 276 
 Amic acids, 667, 672 
 Amides, 105, 265, 658, 667 
 Amidines, 668 
 Amido-acetic acid, 674 
 acids, 658 
 amid-acids, 673 
 azobenzenes, 683 
 barbituric acid, 772 
 benzene, 662 
 
 sul phonic acid, 664, 679 
 benzoic acids, 678 
 caproic acid, 677 
 chlorides, 668 
 cinnamic acid, 767 
 dinitrophenol, 711 
 ethyl-sulphonic acid, 679 
 glyceric acid, 754 
 isovaleric acid, 677 
 malonyl urea, 772 
 naphthalenes, 665 
 nitroplieuols, 711 
 paraxyliue, 665 
 phenols, 711 
 phenylacetic acid, 679 
 
 Amido-phenylamidoacridine, 768 
 propiouic acid, 677 
 succinamic acid, 678 
 succinic acid, 678 
 sulphonic acids, 679 
 thiazole, 765 
 toluene, 665 
 Amidoformic acid, 674 
 Amidogen, 105 
 Amidoximes, 669 
 Amines, 658 
 
 converted into guanidines, 672 
 distinction between, 660 
 mixed, 660 
 Ammelide, 704 
 Ammeline hydrochloride, 704 
 Ammonia, 77 
 
 absorbed by charcoal, 115 
 action of chlorine on, 175 
 
 iodine on, 201 
 albuminoid, 502 
 alum, 387 
 bicarbonate, 356 
 carbonate, 356 
 combustion of, 83 
 decomposed by spark, 83 
 
 chlorine, 84 
 derivatives, 658 
 dissolution of, in water, 79 
 formed from nitric acid, 93 
 gas, dried, 79 
 heat of dissolution, 79 
 formation, 78 
 vaporisation, 82 
 identified, 79 
 liquefied, 82 
 Nessler's test for, 502 
 nitrification of, 87 
 oxidation of, 87 
 preparation of, 79 
 salts, 354 
 soda process, 346 
 solution, 8 1 
 sources of, 77, 78 
 sulphate, 355 
 volcanic, 352 
 
 Ammoniacal liquor, 78, 791 
 Ammoniacum, 714 
 Ammonia-meter, 81 
 Ammonia compounds, 66r 
 Ammonide, sulphuric, 354 
 Ammonium, 354 
 
 alum, 387 
 amalgam, 85 
 arsenite, 270 
 bases, 658 
 bromide, 357 
 carbamate, 356, 672, 706 
 carbonates, 355, 356 
 chloride, 356 
 cyanate, 702 
 cyanide, 692 
 disulphide, 357 
 hydrate, 81 
 iodide, 357 
 isethiouate, 679 
 isocyanate, 703 
 molybdate, 435 
 nitrate, 354 
 nitrite, 355 
 
830 
 
 INDEX. 
 
 Ammonium oxalate, 613 
 
 parabanate, 772 
 picrate, 711 
 purpunte, 772 
 suits, 354 
 sulphate, 355 
 sulphides, 357 
 
 yellow, 357 
 theory, 85 
 thiocarbamate, 706 
 thiocyanate, 703 
 urate, 770 
 
 Amorces fulminantes, 255 
 Amorphous condition, 109, 268 
 
 phosphorus, 253 
 Amygdalic acid, 744 
 Amygdalin, 584, 744 
 Amyl, 592 
 
 acetate, 644 
 alcohol, 569 
 carbiuol, 569 
 nitrite, 642 
 valerate, 644 
 Amylene, 536 
 Amylethylic ether, 629 
 Amyloid, 738 
 Amylose, 734 
 Analysis, 6 
 
 gravimetric, 6 
 
 of gaseous hydrocarbons, 157 
 
 organic, 520, 521 
 
 calculation of, 522, 523 
 qualitative, 6 
 quantitative, 6 
 volumetric, 6 
 Ananas oil, 644 
 Anatase, 456 
 Ancaster stone, 366 
 Anethol, 632 
 Angelic acid, 597 
 Anglesite, 460, 471 
 Angostura bark, 781 
 Anhydride denned, 32 
 Anhydrides, ethereal, 669 
 Anhydrite, 368 
 Anhydrous, 50 
 Anilides, 663 
 Anilido-acetic acid, 675 
 Anilido-acids, 664 
 Aniline, 662 
 
 blue, 723, 794 
 colours, 721 
 dyes, 721, 794 
 oil, 665 
 
 for blue, 665 
 red, 665 
 safraniue, 665 
 salts, 664 
 
 sulphonic acid, 664 
 test for, 664 
 yellow, 683, 794 
 Animal charcoal, in, 116 
 chemistry, 811 
 substances, 811 
 
 Animals and plants, reciprocity of, 820 
 changes in, after death, 824 
 nutrition of, 821 
 Animi resin, 560 
 Anions, 324 
 Aniseed, essential oil of, 586 
 
 Anisic acid, 608 
 Anisic aldehyde, 586 
 Anisoil, 631 
 Annatto, 747 
 Anode, 14 
 Anthracene, 553 
 
 constitution of, 554 
 dichloride, 554, 637 
 dihydride, 554 
 Anthrachrysone, 721 
 Anthracite, 159, 168 
 Anthranil, 678 
 Anthranilic acid, 678 
 Anthranol, 719 
 Anthrapurpurin, 720 
 Anthraquinoline, 767 
 Anthraquiuone, 554, 719 
 
 disulphonic acid, 720 
 Antiarin, 745 
 Antichlore, 221, 235 
 Anti-corrosive caps, 186 
 Antifebrine, 668 
 Autimonates, 443 
 Antimonic acid, 443 
 
 oxide, 443 
 sulphide, 445 
 
 Antimonietted hydrogen, 444 
 Antimonious acid, 442 
 Antimony, 441 
 
 alkides, 656 
 
 amorphous, 442 
 
 ash, 443 
 
 butter of, 444 
 
 chlorides, 444 
 
 chlorosulphide, 445 
 
 crocus of, 441 
 
 crude, 441 
 
 detected, 441 
 
 flowers of, 442 
 
 glass of, 445 
 
 grey ore of, 441 
 
 liver of, 446 
 
 metallurgy of, 441 
 
 ores, 441 
 
 oxides, 442 
 
 oxychloride, 444 
 
 oxysulphide, 445 
 
 oxytrichloride, 445 
 
 pentachloride, 445 
 
 pentasulphide, 445 
 
 potassio-tartrate, 442 
 
 red ore, 445 
 
 regains of, 441 
 
 sulphate, 446 
 
 sulphides, 445 
 
 tested for impurity, 444 
 
 trichloride, 444 
 
 uses of, 442 
 
 vermilion, 237, 445 
 
 white ore, 442 
 Antimonyl, 620 
 Antipyrine, 764 
 Antiseptics, 220, 246 
 Antiseptic preservation, 825 
 Antitoxines, 750 
 Anti-zymotics, 220, 824 
 Ants, acid of, 589 
 Apatite, 249, 369 
 Apocrenic acid, 817 
 Apomorphine, 779 
 
INDEX. 
 
 831 
 
 Apple oil, 644 
 
 Aq., water of crystallisation, 53 
 
 Aqua fortis, 90 
 
 regia, 191, 456 
 Aquamarine, 383 
 Aquate, 171 
 Arabic acid, 737 
 Arabin, 737 
 Arabinose, 725, 731 
 Arabitol, 578 
 
 Arachidic (butic) acid, 588 
 Aragonite, 363 
 Arbor Dianae, 498 
 Arbutin, 744 
 Arc, electric, 137 
 Archil, 714 
 Argand lamp, 153 
 Argillaceous iron ores, 396 
 Argol, 333 
 Argon, 76 
 
 in air, 68 
 Argyrodite, 458 
 Aromatic acids, 599 
 
 alcohols, 599 
 aldehydes, 585 
 esters, 645 
 ethers, 631 
 hydrocarbons, 549 
 series, 549 
 Arrack, 808 
 Arrowroot, 735, 803 
 Arsenates, 271, 352 
 Arsendimethyl, 655 
 Arsenetted hydrogen, 272 
 Arsenic, 265 
 
 acid, 271 
 anhydride, 271 
 detected, 270, 272 
 di-iodide, 274 
 
 extracted from organic matters, 274 
 in copper, 479 
 native, 265 
 oxides, 267 
 pentasulphide, 275 
 sulphides, 274 
 tests for, 270, 272 
 tribromide, 274 
 trichloride, 273 
 trifluoride, 274 
 tri-iodide, 274 
 white, 267 
 Arsenical iron, 266 
 
 nickel, 424 
 Arsenical paper hangings, 270 
 
 soap, 270 
 Arsenides, 265 
 Arsenio di-ethyl, 655 
 Arsenic siderite, 272 
 Arsenio sulphides, 275 
 triethyl, 655 
 trimethyl, 655 
 Arsenious acid, 267 
 
 chloride, 273 
 iodide, 274 
 oxide, 267 
 
 crystalline, 268 
 opaque, 268 
 vitreous, 268 
 Arseuites, 270 
 Arsen-methyl dichloride, 656 
 
 Arsen-methyl oxide, 656 
 Arsiue, 272 
 Artificial indigo, 762 
 musk, 650 
 Asbestos, 373 
 
 platinised, 98 
 Ashes of coal, 113 
 Asparagine, 678 
 Asparagus, 678 
 Aspartic acid, 678 
 Assafoetida, 714 
 
 Assay of gold by cupellation, ci6 
 Astatki, 161 
 Asymmetric-carbon atoms, 605 
 
 substitution-products, 1:46 
 Atacamite, 485 
 Atmolysis, 23 
 
 Atmosphere, composition of, 68 
 Atmospheric air, 67 
 
 germs, 71 
 Atom defined, 8 
 
 -fixing power, 573 
 Atomic heat, 296 
 Atomicity, 299 
 Atomic theory, 287 
 
 volumes, 304, 786 
 weight, 10, 295 
 
 determined, 46, 296 
 Atoms, 286 
 Atropic acid, 601, 755 
 Atropine, 601, 777 
 Attraction, chemical, defined, 5 
 Augite, 389 
 Aurantia, 665 
 Auric-chloride, 518 
 
 cyanide, 697 
 
 oxide, 518 
 Auricyanides, 697 
 Aurin, 723 
 
 Aurothiosulphuric acid, 519 
 Aurous chloride, 518 
 cyanide, 697 
 oxide, 518 
 
 Autogenous soldering, 226 
 Auxochromes, 683 
 Available chlorine, 184 
 Avidity of acids, 311 
 Avogadro's la\v, 289 
 Azines, 768 
 Azobenzene, 682 
 Azo-compounds, 679-682 
 
 dye-stuffs, 683 
 Azoimide, 107 
 Azoimides, 683 
 Azoles, 764 
 Azote, 75 
 Azoniurns, 769 
 Azoxybenzene, 682 
 Azulmamide, 688 
 Azulmic acid, 688 
 Azurite, 485 
 Azyliues, 684 
 
 BAKING powders, 128 
 Balloons, 24 
 
 Balmain's luminous paint, 368 
 Balsam of Peru, 561, 645 
 
 Tolu, 561 
 Balsams, 560 
 Banca tin, 448 
 
INDEX. 
 
 Barbituric acid, 772 
 
 Barilla, 345 
 
 Bar-iron, best, 408 
 
 crystalline, 408 
 fibrous, 410 
 manufacture, 404 
 
 Barium, 359 
 
 bromide, 361 
 carbide, 361 
 carbonate, 361 
 chlorate, 361 
 chloride, 361 
 chromate, 432 
 chromic oxalate, 613 
 di-oxide, 360 
 ethoxides, 564 
 hydroxide, 360 
 hypophosphite, 260 
 manganate, 428 
 nitrate, 361 
 oleate, 598 
 oxide, 360 
 peroxide, 360 
 sulphate, 360, 361 
 sulphide, 361 
 sulpho-methylate, 641 
 tannate, 610 
 tungstate, 436 
 
 Barley sugar, 732 
 
 Baryta, 360 
 
 in glass, 371 
 sulphate, 361 
 water, 361 
 
 Baryto-calcite, 364 
 
 Basalt, 365 
 
 Base, defined, 37 
 
 Basic bricks, 411 
 
 Basicity of acids, 104 
 
 Basic oxides, 38 
 
 process (steel), 410 
 salts, 104 
 slag, 818 
 
 Bassorin, 737 
 
 Bathgate coal, 529 
 
 Bath stone, 365 
 
 Battery, galvanic, 14, 323 
 
 Baume's flux, 339 
 
 Bauxite, 385 
 
 Bay salt, 344 
 
 Beans, inosite in, 716 
 
 Bear, 436 
 
 Bebeeriue, 783 
 
 Beckmann's apparatus, 320 
 
 Beef-tea, 815 
 
 Beehive shelf, 20 
 
 Beer, composition, 806 
 ropy, 806 
 sparkling, 127 
 
 Bees' wax, 644, 799 
 
 Behenic acid, 588 
 
 Belladonna, 777 
 
 Bellite, 355 
 
 Bell -metal, 452 
 
 Bengal saltpetre, 337 
 
 Benzal chloride, 584, 637 
 
 Benzaldehyde, 584 
 
 Benzaldoxime, 585 
 
 Beuzamide, 668, 675 
 
 Benzamido-acetic acid, 675 
 
 Benzene, 539 
 
 Benzene chlorides, 540 
 
 constitution of, 541 
 dichloride, 540 
 disulphonic acid, 540, 713 
 hexachloride, 540 
 hexahydride, 541 
 homologues of, 548 
 hydrocarbons, general preparation 
 
 of > 549 
 nucleus, 542 
 orientation of, 545, 547 
 reactions of, 540 
 ring, 542 
 series, 539 
 
 substitution-products of, 546 
 sulphonic acid, 540, 649 
 tetrachloride, 540 
 trisulphonic acid, 540 
 Benzcneazomethane, 682 
 Benzidine, 666 
 
 dye-stuffs, 684 
 migration, 685 
 Benzine, 528 
 Benzindulenes, 769 
 Benzoacetic anhydride, 601 
 Benzoates, 599 
 Benzoated lard, 799 
 Benzoflavine, 768 
 Benzofurfurane, 7^9 
 Benzoic acid, 600" 
 alcohol, 599 
 aldehyde, 584 
 anhydride, 60 1 
 chloride, 639 
 ether, 645 
 peroxide, 601 
 series of acids, 599 
 Benzoine, 585 
 Benzoin gum, 600 
 Benzole, 539, 790 
 Benzoline, 528 
 Benzomercuramide, 668 
 Benzometudiazines, 769 
 Benzonitrile, 67;, 700 
 Benzoparadiazine, 769 
 Benzophenone, 626 
 Benzopyrazoles, 765 
 Benzopyrrol, 759 
 Benzothiophen, 759 
 Benzoquinone, 717 
 Benzotrichloride, 637 
 Benzoyl, 600 
 
 azoiinide, 686 
 chloride, 600, 639 
 compounds, 600 
 glycocine, 675 
 hydrate, 600 
 hydrazine, 686 
 hydride, 600 
 salicm, 743 
 Benzyl, 600 
 
 alcohol, 571, 709 
 amine, 665, 700 
 benzoate, 645 
 bromide, 637 
 chloride, 637 
 cinnamate, 645 
 cyanide, 700 
 ether, 631 
 hydrate, 600 
 
INDEX. 
 
 Benzyl hydride, 600 
 Benzylidene see Beiizal 
 Benzylideneaniliue, 768 
 Berberiue, 783 
 
 Bergamotte, essential oil of ccc 
 Beryl, 383 
 Beryllium, 382 
 Bessemer's process, 409 
 Betaine, 661 
 Betol, 712 
 Bezoar-stones, 610 
 Biborate of soda, 352 
 Bicarbonate of soda, 348 
 Bicarbonates, 130 
 Bichromate, 430 
 Biebrich scarlet, 684 
 Bile, 756, 822 
 
 colouring-matters of, 756 
 constituents of, 756 
 Bilifuscin, 756 
 Biliprasin, 756 
 Bilirubin, 756 
 Biliyerdin, 756 
 Bioses, 731 
 Biotite, 389 
 
 Birch, essential oil of, 551 
 Bischofite, 375 
 Biscuit porcelain, 391 
 Bismarck brown, 684 
 Bismuth, 438 
 
 extraction of, 439 
 Bismuth glance,. 440 
 Bismuth iodide, 440 
 nitrate, 440 
 Bismuth ochre, 439 
 Bismuth gal late, 610 
 oxides, 439 
 oxychloride, 440 
 sulphide, 440 
 telluride, 244 
 trichloride, 440 
 triethyl, 656 
 trisnitrate, 440 
 Bismuthic acid, 440 
 Bismuthite, 440 
 Bisulphate of potash, 336 
 Bisulphide of carbon, 238 
 Bisulphites, 221 
 Bisulphuret of carbon, 238 
 Bitter almond oil, 584 * 
 Bitter principles, 745 
 Bittern, 192, 344 
 Bituminous coal, 159, 168 
 Biuret, 670 
 Bixin, 747 
 Black ash, 345 
 Black band, 396, 397 
 Black dyes, 796 
 Black-jack, 381 
 lead, 109 
 
 crucibles, in 
 Black vitriol, 485 
 
 wash, 502 
 Blacking-, 231 
 Blast-furnace, 397 
 
 chemical changes in, 398 
 gases, 399 
 Blasting-gelatine, 647 
 
 with gunpowder, 341 
 Bleaching by chloride of lime, 184 
 
 833 
 
 Bleaching by chlorine, 184 
 ozone, 66 
 
 sulphurous acid, 210 
 powder, 184 
 Bleach electrolytic, icn 
 
 killed, 220 
 Blende, 377 
 Blistered steel, 412 
 Block tin, 449 
 Blood, 755, 813 
 
 absorption spectrum of, 756 
 action of oxygen on, 755 
 aeration of, 755, 813 s 
 coagulation of, 813 
 crystals, 756 
 deflbrinated, 814 
 formation of, 813 
 globules, 814 
 production of, 822 
 venous and arterial, 822 
 Bloom (iron), 407 
 Blowers in coal mines, 145 
 Blowpipe, cupellation with, 466 
 flame, 156 
 hot blast, 157 
 oxyhydrogen, 48 
 reduction of metals by, 1 57 
 table, 279 
 Blue, bricks, 392 
 copperas, 484 
 dyes, 723, 795 
 fire composition, 186 
 flowers, 747 
 John, 202 
 malachite, 485 
 metal (copper), 478 
 opal, 723 
 oxide of molybdenum, 435 
 
 tungsten, 436 
 pill, 497 
 pots, in 
 Prussian, 693 
 stone, 484 
 Thdnard's, 423 
 Turnbull's, 695 
 verditer, 484 
 vitriol, 484 
 
 water of copper-mines, 478 
 writing-paper, 390 
 Boghead cannel, 529 
 Boiler fluids, 57, 270 
 
 incrustations, 57 
 scale, 57 
 Boiling meat, 815 
 
 -point, absolute, 29] 
 
 denned, 63 
 -points, 785 
 
 of alcohols, 565 
 of solutions, 320 
 process (iron), 408 
 Bolivite, 440 
 Bolsover stone, 366 
 Bone-ash, 249 
 
 as manure, 818 
 black, 116 
 oil, 766 
 Bones as manure, 818 
 composition, 249 
 destructive distillation, 116, 753 
 dissolved, 818 
 
 3G 
 
834 
 
 INDEX. 
 
 Boracic (boric) acid, 246 
 
 vitreous, 246 
 ether, 642 
 lagunes, 246 
 Boracite, 352 
 Borates, 247 
 Borax, 245, 352 
 
 lake, 246 
 
 vitrefied, 353 
 Boric acids, 245, 246 
 anhydride, 245 
 ether, 642 
 
 Borneo camphor, 560 
 Borneol, 560 
 Borofluoric acid, 248 
 Borofluorides, 248 
 Boroglyceride, 647 
 Boron, 245, 247 
 
 alkides, 653 
 
 amorphous, 247 
 
 carbide, 248 
 
 crystallised, 248 
 
 diamond of, 248 
 
 ethide, 653 
 
 graphitoid, 248 
 
 methide, 653 
 
 nitride, 248 
 
 sulphide, 249 
 
 trichloride, 248 
 
 trifluoride, 248 
 Botany Bay gum, 711 
 Boucherie's process, 820 
 Bouquet of wines, 808 
 Boyle's fuming liquor, 57 
 
 law, 27 
 Brain, 755 
 Brandy, 808 
 Brass, 482 
 Brassidic acid, 598 
 Braunite, 426 
 Brazilin, 748 
 Brazil wood, 713 
 Bread, 808 
 
 aerated, 809 
 
 new and stale, 809 
 Brewing, 805 
 Bricks, 390 
 Bright-iron, 402 
 Brimstone, 208 
 Brin's oxygen process, 39 
 Britannia metai, 451 
 Brochantite, 485 
 Brodie's graphite, in 
 Bromacetylurea, 671 
 Bromal, 638 
 Bromamines, 662 
 Bromanil, 718 
 Bromanilines, 664 
 Bromargyrite, 494 
 Bromates, 194 
 Bromhydrins, 636 
 Bromic acid, 194 
 Bromine, 192 
 
 aquate, 193 
 chloride of, 195 
 Bromobenzene, 637 
 Bromoform, 636 
 Bromosuccinic acid, 618 
 Bronze, 441, 452, 481 
 
 annealing of, 452 
 
 Bronze coin, 441, 452, 481 
 
 powder, 455 
 Bronzing, 482 
 Brookite, 456 
 
 Brown acid (sulphuric), 228 
 blaze, 382 
 coal, 159 
 dyes, 796 
 hematite, 396 
 Brucine, 782 
 Brucite, 374 
 Brunswick green, 485 
 Bubbles, explosive, 42 
 Buckskin, 797 
 Bug-poison, 500 
 Building materials, 365 
 stones, 365 - ; 
 Bullets, rifle, 466 
 
 shrapnel, 466 
 Burner, air-gas, 54 
 Argand, 153 
 Bunsen's, 154 
 gauze, 156 
 regenerative, 154 
 ring, 6 1 
 smokeless, 154 
 
 Burnett's disinfecting fluid, 381 
 Butalanine, 677 
 Butane, 532 
 
 normal, 532 
 Butanes, isomeric, 532 
 Butene, 536 
 Butic acid, 799 
 Butiu, 799 
 Butine, 538 
 Butter, 648, 799 
 -milk, 812 
 preparation of, 812 
 Butyl, 565 
 
 alcohols, 568 
 aldehyde, 583 
 carbinol, 568 
 isothiocyanate, 706 
 Butylene, 536 
 Butylic alcohol, 569 
 
 fermentation, 569 
 normal, 569 
 secondary, 568 
 tertiary, 568 
 Butyric acid, 593 
 
 aldehyde, 583 
 ether, 644 
 Butyrone, 625 
 
 CACAO-BUTTER, 811 
 Cacodyl, 655 
 
 chloride, 655 
 
 Cadaveric alkaloids, 666, 750 
 Cadaverine, 666 
 Cadet's fuming liquor, 655 
 Cadmia, 382 
 Cadmium, 382 
 
 salts, 382 
 Caen-stone, 366 
 Caesium, 359 
 
 carbonate, 359 
 Caffeic acid, 611, 810 
 Caffeidine, 775 
 Cafleiue, 775, 810 
 Caffeone, 810 
 
INDEX. 
 
 835 
 
 Caffeo-tannic acid, 611 
 Cairngorm-stones, 276 
 Caking-coal, 117 
 Calamine, 377 
 
 electric, 377 
 Calamus, oil of, 555 
 Calcareous waters, 57 
 
 spar, 363 
 Calcite, 363 
 Calcium, 363 
 
 acetate, 592 
 
 action on water, 19 
 
 arsenates, 369 
 
 carbide, 370 
 
 carbonate, 363 
 
 chloride, 368^ 
 
 citrate, 623""^ 
 
 dioxide, 367 
 
 disulphide, 217 
 
 fluoride, 368 
 
 hydrosulphides, 369 
 
 hydroxide, 365 
 
 hypochlorite, 183 
 
 hyposulphite, 235 
 
 iodate, 195 
 
 malate, 618 
 
 meconate, 622 
 
 mesotartrate, 620 
 
 nitrate, 367 
 
 oxalate, 613 
 
 oxide, 364 
 
 oxychloride, 368 
 
 pentasulphide, 217 
 
 phosphates, 369 
 
 phosphide, 263 
 
 platinate, 507 
 
 pyrophosphate, 369 
 
 racemate, 620 
 
 saccharate, 622 
 
 silicates, 370 
 
 succinate, 614 
 
 sulphate, 367 
 
 sulphide, 368 
 
 superphosphate, 369 
 
 tartrate, 619 
 Calc-spar, 363 
 Calculation, chemical, 24 
 
 of formulae, 522 
 Caliche, 197 
 Calico-printing-, 796 
 Calomel, 501 
 Calorific intensity, 165 
 
 value, 163 
 Calorimeter, 164 
 Calorimetric bomb, 164 . 
 Calumba root, 745 
 Calumbin, 745 
 
 Calvert's disinfecting' powder, 710 
 Calx chlorata, 185 
 Cameoe, 276 
 Camphanic acid, 560 
 Camphene, 557 
 Camphor, 559 
 
 artificial, 557 
 
 oil of, 559 
 Camphoric acid, 560 
 
 peroxide, 557 
 Camphoronic acid, 560 
 Camphors, 558 
 Canarin, 703 
 
 Candle, chemistry of, 150 
 
 power, I53 , 162 
 Candles, 801 
 Cane-sugar, 731 
 Cannel, 168 
 Cannel-gas, 168 
 Cantharidiu, 746 
 Canton's phosphorus, 368 
 Caoutchene, 558 
 Caoutchouc, 557 
 
 artificial, 798 
 vulcanised, 558; 
 Cap composition, 707 
 Capric ether, 644 
 Caproic acid, 594 
 
 aldehyde, 583 
 Caproin, 812 
 Caprylic acid, 594 
 Capryl alcohol, 570 
 
 aldehyde, 583 
 Caramel, 732 
 Caramelan, 732 
 Caraway, essential oil of, 555 
 Carbamates, 355 
 Carbamic acid, 356, 672 
 Carbamide, 669 
 Carbamides, 672 
 Carbamines, 700 
 Carbanilide, 671 
 Carbazole, 667, 764 
 Carbazotic acid, 711 
 Carbinols, 568 
 Carbodiamine, 669 
 Carbohydrates, 724 
 Carbolic acid, 709 
 Carbon, 108 
 
 atomicity, 522 
 
 bisulphide, 238 
 
 calorific intensity, 166 
 value, 163 
 
 chlorides, 189 
 
 combustion of, 132 
 
 determination of, 521 
 
 diamide-imide, 673 
 
 dichloride, 190 
 
 dioxide, 1 18 (see also Carbonic acid 
 gas) 
 
 composition of, 136 
 liquid, 128 
 
 properties of, 121, 128 
 solid, 129 
 synthesis of, 109 
 
 disulphide, 238 
 
 electrodes, 118 
 
 heat of vaporisation of, 130 
 
 iodide, 201 
 
 monoxide, 131 (see also Carbonic 
 
 oxide) 
 
 combuBtion of, 133, 135 
 composition of, 136 
 
 oxides, 118 
 
 oxychloride, 190 
 
 oxysulphide, 241 
 
 pure, preparation of, 118 
 
 sulphides, 241 
 
 tetrabrouiide, 195 
 
 tetrachloride, 189 
 
 trichloride, 189 
 Carbonado, no 
 Carbonate of lime in waters, 57 
 
8 3 6 
 
 INDEX. 
 
 Carbonates, 130 
 
 alkaline, 360 
 -Carbonic acid, 127, 130 
 
 gas, 118 (see also Carbon 
 
 dioxide) 
 
 absorption by water, 127 
 decomposed by carbon, 132 
 electric 
 
 sparks,i3i 
 potassium, 
 131 
 
 determined, 130 
 evolved by plants, 119 
 experiments with, 122 
 in breathed air, 125 
 injurious effects of, 124 
 liquefaction, 128 
 sources, 119 
 synthesis of, 109 
 anhydride, 35 
 ether, 643 
 
 oxide, 131 (see also Carbon mon- 
 oxide) 
 
 absorbed, 486 
 calorific value, 166 
 formed in fires, 132 
 metallurgic uses, 132 
 poisonous properties, 133 
 preparation, 134 
 properties of, 134 
 reduction by, 135 
 Carbonisation, 108 
 Carbonising fermentation, 158 
 Car bony 1 chloride, 190 
 Carborundum, 282 
 Carbostyril, 767 
 Carbotriamine, 673 
 Carboxyl, 586 
 
 diamine, 669 
 
 Carburetted hydrogen, 144 
 Carbylamine reaction, 660 
 Carbylamines, 700 
 Carbyloxime, 706 
 Carbyl sulphate, 535 
 Carmine, 748 
 
 lake, 748 
 red, 748 
 
 Carminic acid, 748 
 Carnallite, 335, 373 
 Carnelian, 276 
 Carnine, 774 
 Carotin, 747 
 
 Carry's freezing apparatus, 81 
 Carthamin, 747 
 Cartilage, 754 
 Carvacrol, 712 
 Cascarilla. oil of, 555 
 Case-hardening, 413 
 Casein, 751 
 
 vegetable, 752 
 Cassel green, 428 
 yellow, 472 
 Cassia, oil of, 585 
 Cassiterite, 453 
 Cast-iron, 397, 401 
 grey, 402 
 malleable, 403 
 mottled, 402 
 varieties of, 402 
 white, 402 
 
 Castner's process, 350 
 Castor-oil, 798 
 Cast steel, 413 
 Catalysis, 64 
 Catechu, 609, 712, 715 
 Cathode, 14, 324 
 Cations, 324 
 Cat's eye, 276 
 Caustic alkali, 20 
 lunar, 492 
 potash, 333 
 soda, 348 
 
 Cavendish eudiometer, 43 
 Cedar-wood, essential oil of, 555 
 Cedriret, 716 
 Celestine, 362 
 Celluloid, 742 
 Cellulo-nitrins, 739 
 Cellulose, 734, 737, 738 
 
 action of nitric acid on, 739 
 
 animal, 743 
 
 converted into sugar, 738 
 
 cotton, 739 
 
 hexanitrate, 739 
 
 jute, 739 
 
 solvent for, 483, 738 
 
 straw, 739 
 
 Cement, Portland, 366 
 Roman, 366 
 rust- joint, 212 
 Scott's, 367 
 
 Cementation process, 411 
 Cerasin, 737 
 Cerebric acid, 755 
 Cerebrin, 755 
 Ceresin, 529 
 Cerite, 394, 459 
 Cerium, 459 
 Cerolein, 799 
 Cerotic acid, 799 
 Cerotin, 570, 799 
 Ceruse, 470 
 Cerussite, 460, 470 
 Ceryl alcohol, 570, 799 
 Ceryl cerotate, 570, 644 
 Cetin, 570, 799 
 Cetyl alcohol, 570 
 Cetyl palmitate, 570, 644 
 Cevadilla seeds, 783 
 Cevadine, 783 
 Ceylon moss, 737 
 Chalcedony, 276 
 Chalk, 363 
 
 in waters, 56 
 Chalkstones, 770 
 Chalybeate waters, 61, 416 
 Chamber acid, 227 
 Chamomile, essential oil of, 555 
 Champagne, 808 
 
 Chance's sulphur recovery process, 347 
 Charbon roux, 113 
 Charcoal, in 
 
 absorption of gases by, 114 
 
 action of steam on, 133 
 
 animal, in, 116 
 
 as fuel, 117, 160 
 
 ash, 114 
 
 burning, 112 
 
 decolorising by, 116 
 
 deodorising by, 115 
 
INDEX. 
 
 837 
 
 Charcoal for gunpowder, 113 
 
 oxidised by nitric acid, 91 
 
 prepared at diffei-ent tempera- 
 tures, 113 
 
 retort, 114 
 
 suffocation, 131 
 
 wood, in 
 Charles' law, 28 
 Charring- by steam, 113 
 Cheese, 812 
 Chelidouic acid, 623 
 Chelidouine, 783 
 Cheltenham water, 61 
 Chemical affinity, 304 
 
 measurement of, 304 
 
 calculations, 24 
 
 change, velocity of, 310 
 
 combination, laws of, 287 
 
 influence of moisture 
 on, 327 
 
 energy, static method of measur- 
 ing, 309 
 
 equivalent defined, 20, 289 
 
 manures, 818 
 
 properties defined, 12 
 Chessylite, 485 
 
 Chevreul's investigations, 800 
 Chill-casting, 403 
 Chimney, hot air, for lamps, 153 
 
 ventilation by, 126 
 China moss, 737 
 Chinese wax, 570, 648. 799 
 
 white, 380 
 Chinoline, 767 
 Chitin, 754 
 Chloracetamides, 668 
 Chloracetic acid, 638 
 Chloral, 638 
 
 alcoholate, 638 
 hydrate, 638 
 Chloralum, 389 
 Chloramines, 662 
 Chloranhydrides, 191 
 Chloranil, 718 
 Chlorauillic acid, 718 
 Chloranilines, 664 
 Chloranthraceues, 638 
 Chlorate of potash, 184 
 Chlorates, 186 
 Chlorhydrins, 646 
 
 of glycol, 646 
 Chloric acid, 184, 756 
 Chloride of calcium tube, 521 
 lime, 183 
 nitrogen, 190 
 soda, 184 
 Chlorine, 169 
 
 bleaching by, 175 
 
 dioxide, 187 
 
 disinfecting by, 176 
 
 experiments with, 172 
 
 group of elements, 205 
 
 heptoxidf, 188 
 
 hydrate or aquate, 171 
 
 monoxide, 181 
 
 he.it of formation, 181 
 
 oxides, 181 
 
 peroxide, 187 
 
 water, 171 
 Chloriodoform, 636 
 
 Chlorisatins, 760 
 Chlorite, 389 
 Chlorites, 188 
 Chlorobenzenes, 637 
 
 benzole chloride, 639 
 chromic acid, 434 
 malaeic acid, 640 
 
 chloride, 640 
 methylfonnate, 643 
 naphthalenes, 552, 637 
 phenols, 710 
 
 phenol sulphonic acid, 715 
 propionic chloride, 639 
 Chloroform, 530, 635 
 Chlorofoi-moxime, 707 
 Chlorophosphamide, 265 
 Chlorophyll, 746 
 Chloropicrin, 650, 711 
 Chlorosulphuric acid, 221 
 Chlorous acid, 188 
 Chloroxalethyline, 6(39 
 Chocolate, 8n 
 Choke-damp, 125 
 Cholesteramiue, 757 
 Cholesterin, 757 
 Cholesterol, 757 
 Cholesteryl chloride, 757 
 Cholestrophane, 772, 775 
 Cholic acid, 756 
 Choline, 666 
 Chologlycholic acid, 756 
 Chondrin, 754 
 Chromates, 432 
 
 of lead, 432 
 
 potash, 431 
 Chrome-alum, 433 
 
 iron-ore, 417, 430 
 yellow, 432 
 Chromic acid, 431 
 
 anhydride, 431 
 oxide, 431 
 Chromites, 433 
 Chromium, 430 
 
 clilorides, 433 
 dioxode, 433 
 hydroxide, 433 
 metallic, 431 
 nitride, 434 
 oxides, 431 
 oxychloride, 434 
 sulphate, 432 
 sulphide, 434 
 Chromogens, 683 
 Chromyl chloride, 434 
 fluoride, 434 
 Chrysaniline, 794 
 Chrysean, 704 
 Chrysene, 554 
 Chrysoberyl, 383 
 Chrysocolla, 485 
 Chrysoidine, 684 
 Chrystalliu, 751 
 Churning, 812 
 Chyme, 822 
 Cigars, 777 
 Cinchona bark, 780 
 Cinchonicine, 781 
 Cinchonidine, 781 
 Clnchouiue, 781 
 Cinder, 159 
 
8 3 8 
 
 INDEX. 
 
 Cinnabar, 503 
 Cinnamene, 550 
 Cinnamic acid, 60 1 
 
 aldehyde, 585 
 
 Cinnamon, essential oil of, 585 
 alcohol, 572 
 cinnamate, 645 
 Circulation of blood, 813 
 Cisterns, incrustations in, 60 
 Citraconic acid, 616, 623 
 Citrates, 623 
 Citrenes, 555 
 Citric acid, 623 
 Clarite, 275 
 Clark's process, 59 
 Classes of organic compounds, 525 
 Classification of the elements, 301 
 Claus kiln, 347 
 Clay, 384, 390 
 
 ironstones, 396, 397 
 Cleveite, 77 
 Clinker, 391 
 
 Closed-chain hydrocarbons, 538, 539 
 Cloves, essential oil of, 555 
 Coal, 158 
 
 ash of, 1 60 
 bituminous, 159 
 brown, 159 
 combustion of, 159 
 composition of, 168 
 distillation of, 161, 790 
 -dust explosions, 148 
 formation of, 158 
 -gas, 161 
 
 enriching, 16? 
 explosions of, 145 
 manufacture, 791 
 purification, 238, 792 
 sulphur in, 161 
 mines, explosions in, 148 
 
 firedamp of, 145 
 -naphtha, 793 
 stone, 1 60 
 
 spontaneous comoustion of, 160 
 -tars, 793 
 
 bases, 793 
 
 distillation of, 539, 792 
 dyes, 793 
 varieties of, 159 
 Welsh, 160 
 Coarse copper, 479 
 
 -metal (copper), 476 
 Cobalt, 421 
 
 amine compounds, 423 
 
 arsenate, 266, 422 
 
 arsenides, 422 
 
 bloom, 266, 422 
 
 chloride, 422 
 
 cyanide, 692 
 
 glance, 421 
 
 hydroxide, 422 
 
 nitrate, 422 
 
 nitrite, 422 
 
 chides, 421 
 
 phosphate, 423 
 
 py rites, 422 
 
 salts, 422 
 
 separated from nickel, 424 
 
 silicate, 422 
 
 sulphate, 422 
 
 Cobalt sulphides, 422 
 
 ultramarine, 423 
 vitriol, 422 
 yellow, 422 
 Cobalticyanides, 692 
 Cocaine, 777 
 Cocculus indicus, 745 
 Cochineal, 795 
 Cocoa, 8n 
 
 (gun) powder, 340 
 Cocoa-nut oil, 648, 798 
 Codeia, 779 
 Codeine, 779 
 Cod-liver oil, 799 
 Co-efficient of solubility, 54 
 affinity, 311 
 velocity, 312 
 Coerulignone, 716 
 Coffee, composition, 810 
 
 roasting, 810 
 Coin-bronze, 452, 481 
 Coke, 1 60 
 
 action of steam on, 133 
 composition of, 168 
 Colchicine, 783 
 Colcothar, 224, 417 
 Cold-shortness, 408 
 Collidine, 766 
 Collodion, 742 
 
 balloons, 742 
 cotton, 742 
 Colloids, 278 
 Colophony, 560 
 Colour- base, 722 
 Coloured fires, 186 
 Colouring-matters, animal, 756 
 
 vegetable, 746, 747 
 Columbite, 447 
 Colza oil, 798 
 Combination, chemical, 5 
 laws of, 287 
 
 Combined carbon in iron, 402 
 Combining proportions, 10 
 Combustion defined, 33 
 furnace, 521 
 in oxygen, 32 
 reciprocal, 48, 153 
 temperature of, 520 
 tube, 521 
 
 Comanic acid, 769 
 Comenic acid, 622 
 Common salt, 343, 818 
 Composition tube, 466 
 Compound and mixture, 6, 71 
 
 defined, 3 
 Concrete, 366 
 Condensation, 531 
 
 Condensation products of acetone, 625 
 Condenser, Liebig's, 62 
 Condurrite, 266 
 
 Condy's disinfecting fluid, 428 
 Congonha, 775 
 Congo red, 684 
 Conhydrine, 776 
 Coniferin, 745 
 Coniferyl alcohol, 745 
 Couiine, 776 
 
 -methylium hydroxide, 776 
 
 iodide, 776 
 Conquiniue, 781 
 
INDEX. 
 
 Conservation of energy, 305 
 
 matter, 2 
 Constitution of compounds, 102 
 
 salts, 104, 105 
 
 Contact process for sulphuric acid manufac- 
 ture, 230 
 Converting- furnace, 411 
 
 vessel, Bessemer's, 409 
 Convolvulin, 745 
 Convolrulinol, 745 
 Cooking- of meat, 815 
 Copal, 560 
 Copper, 474 
 
 acetate, 592 
 
 aceto-arsenite, 271, 592 
 
 acetylide, 139, 537 
 
 action of ammonia and air on, 483 
 nitric acid on, 92 
 
 alloys of, 481 
 
 amalgam, 498 
 
 ammonio-sulphate, 485 
 
 Ang-lesea, 478 
 
 arsenite, 261, 484 
 
 best selected, 476 
 
 blister, 476 
 
 carbonates, 434, 484 
 
 chlorides, 485 
 
 cleaned, 481 
 
 dry, 477 
 
 effect of sea-water on, 480 
 
 electric conductivity of, 480 
 
 emerald, 485 
 
 extracted in laboratory, 479 
 
 fusing- point, 480 
 
 glance, 474 
 
 hydrate, 483 
 
 hydride, 483 
 
 impurities in, 479 
 
 Lake Superior, 480 
 
 lead in, 477 
 
 metallurgy of, 474 
 
 moss, 476 
 
 natire, 474 
 
 nitride, 484 
 
 ores, 474 
 
 roasting, 474 
 
 treatment of, for silver, 489 
 
 overpoled, 477 
 
 oxides, 482 
 
 oxychloride, 480, 485 
 
 peacock, 474 
 
 phosphates, 485 
 
 phosphide, 487 
 
 poling-, 477 
 
 precipitate, 478 
 
 properties of, 480 
 
 pyrites, 474, 487 
 
 reduced by hydrogen, 46 
 
 refining-, 477 
 
 rose, 478 
 
 sand, 474 
 "silicates, 485 
 
 smeltiug, 475, 476 
 
 smoke, 475 
 
 Spanish, 480 
 
 subchloride, 486 
 
 suboxide, 482 
 
 sulphate, 484 
 
 in bread, 809 
 
 sulphides, 486 
 
 839 
 
 Copper, tinned, 453, 481 
 
 tough-cake, 477 
 
 uses of, 481 
 
 underpoled, 477 
 
 verdigris, 481 
 
 vessels for cooking, 481 
 
 wet extraction of, 478 
 Copperas, 418 
 
 blue, 484 
 
 Copper-zinc couple, 21 
 Coprolite, 369 
 Coquimbite, 419 
 Coral, 363 
 Cordite, 647 
 Coridine, 766 
 Corn-flour, 803 
 Corrosive sublimate, 499, coo 
 Corundum, 388 
 Cotarnine, 779 
 Cotton, 737 
 
 separated from wool, 738 
 solvent for, 483 
 Coulomb, 325 
 Coumarilic acid, 759 
 Coumarin, 759 
 Coumarone, 759 
 Crackers, detonating, 708 
 Cream, 812 
 
 of tartar, 333, 619 
 Creasote, 712, 713 
 Creatine, 676 
 Creatiniue, 676 
 Crenic acid, 817 
 Creoline, 712 
 Cresol, 709, 712 
 Critical temperature, 29 
 Croceo-cobalt salts, 423 
 Crocin, 747 
 
 Crocus of antimony, 441 
 Crookes' discovery of thallium .-73 
 Croton aldehyde, 537 
 Croton-chloral, 638 
 Crotonic acid, 584, 597 
 
 aldehyde, 584 
 Crotononitrile, 705 
 Crotonylene, 538 
 Crow-fig, 782 
 Crucibles, black lead, TTI 
 Cryohydrates, 53 
 Cryolite, 389 
 Cryoscopic metl od 310 
 Cryptidine, 767 
 Crystal carbonate, 348 
 Crystallisation, 50 
 Crystals, forms of, 51 
 Crystalloids, 278 
 
 Crystals from vitriol chambers, 225 
 Cubebs, essential oil of, 555 
 Cudbear, 714 
 Cumic aldehyde, 585 
 Cuminic acid, 601 
 
 aldehyde, 585 
 Cuminol, 585 
 
 Cummin, essential oil of, 585 
 Cupel-furnace, 465 
 Cupellation on the large scale, 464 
 small scale, 465 
 Cupric acetate, 592 
 
 aceto-arsenite, 592 
 acid, 484 
 
840 
 
 INDEX. 
 
 Cupric arsenite, 485 
 
 carbonates, 485 
 chloride, 485 
 hydroxide, 484 
 nitrate, 484 
 oxide, 482 
 phosphates, 485 
 phosphide, 487 
 silicates, 485 
 sulphate, 484 
 sulphide, 487 
 tartrate, 619 
 xanthate, 643 
 Cuprocyanides, 696 
 Cuprous acetylide, 140, 537 
 chloride, 140, 486 
 hydrate, 483 
 hydride, 483 
 iodide, 486 
 nitride, 484 
 oxide, 483 
 sulphide, 487 
 xanthate, 240, 643 
 Curcumin, 747 
 Curd of milk, 751 
 Curing- fish and meat, 824 ^ 
 Current, electric, 14, 323 
 Cutch, 609 
 
 Cutting 1 isinglass, 753 
 Cyamelide, 702 
 
 Cyanacetate of potassium, 614 
 Cyanamide, 704 
 Cyanethine, 700 
 Cyanetholin, 705 
 Cyanates, 702 
 Cyanic acid, 702 
 Cyanides, 692 
 
 of hydrocarbon radicles, 699 
 Cyanin, 747 
 Cyanines, 767 
 Cyanite, 389 
 Cyan-methine, 699, 769 
 Cyano-benzene, 700 
 Cyanogen, 687 
 
 bromide, 698 
 chloride, 698 
 compounds, 686 
 iodide, 698 
 reactions of, 688 
 sulphide, 704 
 Cyanmuramide, 704 
 Cyanurates, 702 
 Cyanuric acid, 701 
 
 chloride, 698 
 
 Cyclic compounds, 526, 538 
 Cyclohexanes, 539 
 Cylinder-charcoal, 113 
 Cymene, 544 
 Cymogene, 528 
 Cytisine, 783 
 Cytoblast, 755 
 
 DAPHNETIN, 744 
 
 Daphnin, 744 
 
 Daturine, 777 
 
 Davy lamp, 146 
 
 Deacon's chlorine process, 170 
 
 Dead oil of coal-tar, 793 
 
 Decane, 528 
 
 Decay, 119 
 
 Decay after death, 824 
 
 Decolorising' by charcoal, 116 
 
 Decomposition defined, 3 
 
 Deflagrating spoou, 34 
 
 Deflagration, 338 
 
 Dehydracetic acid, 644 
 
 Deliquescence, 53 
 
 Delphinine, 783 
 
 Densimeter, 341 
 
 Density, absolute, 341 
 apparent, 341 
 
 Deodorising- by charcoal, 115 
 chlorine, 176 
 
 Dephlogisticated muriatic acid, 176 
 
 Derbyshire spar, 202 
 
 Dermatol, 610 
 
 Desiccator, 232 
 
 Desilverising lead, 463 
 
 Destructive distillation defined, 112 
 
 Detonating tubes, 186, 647 
 
 Devitrification, 372 
 
 Dextrin, 736 
 
 Dextro-ethylidine lactic acid, 604 
 
 Dextro-rotatory, 542, 619 
 pinene, 557 
 
 Dextrose, 726 
 
 Dextrotartaric acid, 619 
 
 Dhil mastic, 468 
 
 Diabetes, 726 
 
 Diacetyl, 627 
 
 oxide, 593 
 
 Diad elements, n 
 
 Diallyl sulphide, 705 
 
 Dialuramide, 772 
 
 Dialuric acid, 771 
 
 Dialyser, 278 
 
 Dialysis, 277 
 
 of air, 70 
 
 Diamides, 669 
 
 Diamido-azobenzene, 684 
 
 Diamidobenzene, 650, 666 
 
 Diamidothiodipheuylamiue, 645 
 diphenyl, 666 
 
 Diamidogen, 106 
 
 Diamidomiphthalines, 666 
 
 Diamidotriphenylmethane, 722 
 
 Diamines, 658, 665 
 
 Diamond, 108 
 
 black, in 
 combustion of, 109 
 specific heat of, 118 
 
 Diamonds, artificial, no 
 
 Diaspore, 388 
 
 Diastase, 733, 804 
 
 Diathermic, 239 
 
 Diatomic elements, 10 
 
 Diazines, 768 
 
 Diazo-acetamide, 680 
 acetic acid, 680 
 amidobcnzene, 682 
 
 compounds, 682 
 amidonaphthaleue, 666 
 benzene, 680 
 
 butyrate, 68 r 
 chloride, 682 
 compounds, 68 1 
 hydroxide, 68 1 
 nitrate, 680 
 potasso oxide, 68 1 
 sulphonic acid, 683 
 
INDEX. 
 
 841 
 
 Diazo-compounds, 106, 637, 680 
 
 diazoimides, 686 
 
 dyestuffs, 684 
 
 ethane, 680 
 
 methane, 680 
 
 reactions, 106, 68 1 
 Diazonium srilts, 68 1 
 Diazotising-, 681 
 Dibenzofurfurane, 759 
 Dibenzoparadiazine, 769 
 Dibeuzoparathiaziues, 768 
 Dibenzoparoxazine, 768 
 Dibenzopyrrol, 759 
 Dibenzothiophen, 759 
 Dibenzoyl oxide, 601 
 Dibenzyl, 551 
 
 Dibromonitro-aceto-nitrile, 707 
 Dibromo-nitro-phenyl-propionic acid, 764 
 Dibromopropanes, 544 
 Dibutyraldine, 776 
 Dichloracetone, 623 
 
 cyanhydrate, 623 
 Dichloracetonic acid, 623 
 Dichlorethene, 634 
 Dichlorether, 631 
 Dichlorhydrin, 646 
 Dichlorobenzene, 540 
 Dichloromethane, 530 
 Dicinnainene, 550 
 Dicyauimide, 704 
 Dicyauacetonic acid, 623 
 Didymium, 394 
 Diethyl, 653 
 
 amine, 662 
 glycol ether, 631 
 Diethylene-diamine, 666 
 Diethylnitrosamine, 662 
 Diethyloxamide, 669 
 Diffusibility of g- a ses, 25 
 
 law of, 25, 291 
 measurement of, 25 
 Diffusion, 25 
 
 tube, 25 
 Diformin, 647 
 Digallic acid, 610 
 Digestion, 821 
 Digitalin, 745 
 Dihydric alcohols, 555 
 Dihydropyrazoles, 764 
 Dihydroxy anthraquinoline, 768* 
 benzaldehydes, 586 
 benzenes, 712 
 benzoic acid, 609 
 succinic acid, 618 
 toluene, 714 
 Dihydroxyl, 106 
 Diiodopurine, 771 
 Dikakodyl, 656 
 Diketones, 626 
 
 Dimethyl, 530 
 allo 
 
 . Joxantin, 752 
 amido-azobenzene, 683 
 
 benzine sulphouic acid, 683 
 
 pyrimidiue, 769 
 
 toluphenazine, 769 
 amine, 659 
 analine, 664 
 -arsenic acid, 655 
 arsine, 656 
 benzene, 549 
 
 Dimethyl furfurane, 758 
 ketone, 625 
 oxamide, 669 
 oxide, 628 
 parabanic acid, 772 
 Dimethoxyphthalide, 779' 
 Dimorphous, 109, 268 
 Dinaphthyl, 553 
 Dinasfire brickx, 392 
 Dinitraniline, 664 
 Dinitric acid, 96 
 Dinitrobeuzene, 540 
 benzenes, 650 
 phenol, 711 
 Diolefines, 537 
 Dioptase, 485 
 Dioxindol, 760 
 Diphenic acid, 554 
 Diphenyl, 550 
 
 amiiie, 664 
 guanidine, 673 
 ketone (beuzophenone), 626 
 methane, 551 
 methylpyrazole, 764 
 oxide, 631 
 sulphides, 710 
 sulphone, 710 
 -sulphurea, 672 
 urea, 671 
 
 Diphenyleue methane, 551 
 oxide, 764 
 sulphide, 764 
 Diplatinamiue, 508 
 Diplatosamiue, 508 
 Dippel's oil, 753 
 Dipropargyl, 539 
 Dipyrotartracetoue, 619 
 Disaccharides, 731 
 Disacryl, 584 
 Disazo-dyestuffs, 684 
 Discharge in calico printing, 183,694 
 Disinfectant, Cal vert's, 710 
 
 MacDougall's, 710 
 
 Disinfecting by chloride of lime, 184 
 chlorine, 170 
 ferric chloride, 419 
 permanganates, 429 
 fluid, Burnett's, 381 
 Condy's, 428 
 
 Disintegration of rocks, 128 
 Displacement, collection of gas by, 29 
 Dissociation, 301, 312 
 
 effect of pressure on, 301 
 of dissolved molecules, 317 
 sal-ammoniac, 86 
 steam, 48 
 
 vermilion vapour, 504 
 Disthene, 389 
 Distillation, 62 
 
 destructive or dry, 112 
 fractional, 74, 529 
 under diminished pressure, 595 
 Distilled sulphur, 208 
 
 water, 61 
 Diterpene, 555 
 Dithionic acid, 237 
 Dithionous acid, 237 
 Diureides, 771 
 Divalent elements, n 
 Divi-divi, 609 
 
842 
 
 INDEX. 
 
 Dobereiner's lamp, 506 
 Dodecane, 528 
 Dodecatoic acid, 594 
 Dolomite, 373 
 Double salts, 104 
 Dough, 734, 808 
 Dowucast shaft, 88 
 Dowson gas, 163 
 Dragon's blood, 715 
 Drummond light, 48 
 Dryers, 798 
 Drying gases, 46 
 
 in vacuo, 232 
 -oils, 798 
 
 over oil of vitriol, 232 
 Dry rot, 738 
 Ductility of copper, 480 
 Dulcite, 579 
 Dung as manure, 817 
 Dust, 71 
 
 explosions, 148 
 Dutch liquid, 148, 535, 634 
 
 metal, 172 
 Dyeing, 795 
 Dyes, 683 
 
 adjective, 683 
 
 substantive, 683 
 Dyestuffs, acid, 683 
 basic, 683 
 Dynamite, 646 
 Dyslysin, 756 
 
 EARTHENWARE, 392 
 'Earths, alkaline, 372 
 Earth's crust, composition of, 5 
 Eau de Javelte, 184 
 Ebonite, 558 
 Effervescence, 127 
 Efflorescence, 52 
 Egg-shells, 1 20 
 Eikonogeu, 712 
 Elaidic acid, 598, 802 
 Elastine, 677 
 Elaterin, 746 
 Elaterium, 746 
 Elba iron ore, 356 
 Electric arc, 137 
 
 furnace, 138 
 Electrical amalgam, 498 
 pressure, 17 
 quantity, 17 
 tension, 17 
 Electrising, 66 
 Electro-chemical list, 324 
 
 equivalents, 325 
 Electrodes, 14, 118 
 Electro-gilding, 517 
 Electrolysis defined, 15, 323 
 
 of hydrochloric acid, 16 
 of salts, 325 
 
 of sulphuric acid, 15, 324 
 of water, 13.. 
 Electrolytes, 323 
 Electrolytic bleach, 350 
 
 dissociation, 327 
 production of alkali and chlo- 
 rine, 349 
 
 Electro -negative elements, 15 
 plating, 490 
 positive elements, 15 
 
 Electrons, 324 
 
 Element denned, 3 
 
 Elements, groups of, 303 
 
 Elemi-resin, 560 
 
 Ellagic acid, 610 
 
 Embolite, 494 
 
 Emerald, 382 
 
 Emerald green, 271, 485, 592 
 
 Emery, 388 
 
 Emetics, 620 
 
 Emetine, 781 
 
 Empirical formulae, 522 
 
 Ernpyreumatic, 555 
 
 Emulsin, 584 
 
 Enantiomorphous, 621 
 
 Enantiotropes, 315 
 
 Eudosmose, 814 
 
 Endothermic, 96, 305 
 
 Energy, chemical, 304 
 
 Eosins, 723 
 
 Epsom salts, 375 
 
 Equivalent defined, 20 ^ " 
 
 Equivalents of acids and bases, 105 N 
 
 Ergot of rye, 734 S 
 
 Erucic acid, 598 
 
 Erythric acid, 714 
 
 Erythrite, 578 
 
 Erythro-dextrin, 736 
 
 Eserine, 783 
 
 Essence of turpentine, 555 
 
 Essential oils, 555 
 
 extraction of, 555 
 Esters, 640 
 
 sulphuric, 641 
 Ethal, 570 
 Ethane, 524, 530 
 
 constitution of, 527 
 Ethene, 535 
 
 -alcohol, 574 
 -diamines, 666 
 -dibromide, 574, 635 
 -dichloi'ide, 634 
 -di-iodide, 635 
 -naphthalene, 553 
 Ether, 627 
 
 chemical constitution, 628 
 decomposition by heat, 141 
 properties of, 629 
 reactions yielding, 630 
 Ethereal salts, 640, 645 
 Etherification, continuous, 629 
 
 theory of, 629 
 Ethers, 631 
 
 derivation from alcohols, 627 
 mixed, 627 
 
 perfuming and flavouring, 644, 645 
 table of, 628 
 Ethine, 537 
 Ethionic acid, 535, 649 
 
 anhydride, 535 
 Ethoxides, 564 
 Ethoxyl, 654 
 Ethyl, 600 
 
 acetamide, 667 
 acetate, 643 
 aceto-acetate, 644 
 alcohol, 561 
 aldehyde, 583 
 allophanate, 671 
 amine, 662 
 
INDEX. 
 
 843 
 
 Ethylamine hydrochloride, 662 
 
 ethyl thiocarbonate, 706 
 arsenite, 642 
 benzoate, 645 
 borate, 642 
 boric acid, 653 
 bromide, 634 
 butyrate, 644 
 caprate, 644 
 carbamate, 672 
 carbamine, 701 
 carbimide, 705 
 carbinol, 569 
 carbonate, 643 
 chloride, 633 
 cyanide, 699 
 diazo-acetate, 680 
 diethylacetoacetate, 644 
 ether, 628 
 
 ethylacetoacetate, 644 
 fluoride, 634 
 formamide, 701 
 formate, 643 
 hydride, 524, 530 
 iodide, 634 
 isocyanate, 705 
 isocyanide, 701 
 isothiocyanate, 706 
 malonate, 645 
 metaphosphate, 642 
 mustard oil, 706 
 nitrate, 642 
 nitrite, 642 
 nitrosamine, 662 
 orthocarbonate, 643 
 oxalacetate, 645 
 oxalate, 645 
 oxamate, 669 
 oxamide, 669 
 oxysulphide, 573 
 palmitate, 644 
 pelargonate, 644 
 phosphates, 642 
 phosphines, 654 
 phosphinic acids, 654 
 quinol dicarboxylate, 718 
 salicylate, 645 
 silicates, 642 
 sodaceto-acetate, 643 
 sodethylacetoacetate, 644 
 succiuyl succinate, 718 
 sulphates, 641 
 sulphides, 573 
 sulphinic acid, 649 
 sulphite, 648 
 sulphone, 573 
 sulphonic acid, 648 
 sulphuric acid, 628 
 thiocarbimide, 706 
 ureas, 705 
 Ethylates, 564 
 Ethylene, 142, 535 
 
 -diamine, 665, 
 
 bromide, 535, 635 
 
 chloride, 535, 634 
 
 glycol, 574 
 
 hydrate chloride, 631 
 
 iodide, 635 
 
 lactic acid, 607 
 
 oxide, 631 
 
 Ethylene succinic acid, 614 
 Ethylidene chloride, 635 
 
 lactic acid, 603 
 
 succinic acid, 614 
 Ethylsulphuric acid, 641 
 Euchlorine, 188 
 
 -water, 779 
 Eudiometer, Cavendish, 43 
 
 siphon, 44 
 Eudiometric analysis of air, 44 
 
 marsh-gas, 157 
 Eupyrion matches, 188 
 Eurhodines, 769 
 Euxanthic acid, 747 
 Euxanthine, 747 
 Euxanthone, 747 
 
 Evaporation, influence of pressure on, 313 
 Even numbers, law of, 523 
 Evernic acid, 714 
 Everninic acid, 714 
 Exalgin, 668 
 Excretions, 823 
 Exitele, 442 
 Exothermic, 96 
 Explosions, 30, 42 
 
 in coal-mines, 145, 148 
 
 sympathetic, 741 
 Extinguishing fires, 122 
 
 FAGOTING, 407 
 Fallowing, 818 
 Faraday's law, 325 
 Farinose, 735 
 Farm-yard manure, 817 
 Fast colours, 795 
 
 green, 714 
 yellow, 712 
 Fats, 648, 797 
 
 f using-points of, 850 
 Fatty acid series, 587, 588, 644 
 Fehling's test, 619 
 Felspar, 332, 384 
 Fenchene, 557 
 Fenchone, 560 
 Fermentation, 119, 562 
 
 acetous, 590 
 alcoholic, 562 
 arrested, 220, 563 
 viscous, 578 
 Ferrates, 418 
 Ferric acetate, 591 
 
 acid, 418 
 
 ammonio-citrate, 624 
 
 benzoate, 600 
 
 carbonate, 418 
 
 chloride, 419 
 
 citrate, 623 
 
 cyanide, 693 
 
 ferrocyanide, 693 
 
 oxalate, 613 
 
 oxide, 417 
 
 oxychloride, 420 
 
 phosphate, 419 
 
 succiuate, 614 
 
 sulphate, 419 
 Ferricuui, 421 
 Ferricyanides, 695 
 Ferrite, 414 
 Ferrocyanic acid, 687 
 Ferrocyanides, 687 
 
844 
 
 INDEX. 
 
 Ferrocyanogen, 687, 693 
 Ferro-manganese, 403 
 Ferrosoferric oxide, 417 
 Ferrosum, 421 
 Ferrous arsenate, 419 
 chloride, 419 
 carbonate, 418 
 cyanides, 693 
 ferricyanide, 695 
 ferrocyauide, 693 
 hydroxide, 416 
 iodide, 419 
 oxalate, 613 
 oxide, 416 
 phosphate, 419 
 silicate, 419 
 sulphate, 418 
 sulphide, 420 
 Ferrum redactum, 416 
 Ferruretted chyazic acid, 687 
 Fibrin, blood, 751 
 muscle, 751 
 vegetable, 752 
 Fibrinogen, 751 
 Fibroin, 754 
 Filtration, 116 
 Finery cinder, 405 
 Fire-bricks, 392 
 -clay, 384 
 -damp, 144 
 
 indicator, 148 
 Fires, blue flame in, 132 
 coloured, 186 
 gas, 161 
 Fish oils, 799 
 
 shells, 82 
 
 Fittig's reaction, 531, 549 
 Fixing photographic prints, 236 
 Flags, Yorkshire, 365 
 Flake-white, 440 
 Flame, analysis of, siphon, 152 
 blowpipe, 156 
 cause of luminosity in, 152 
 effect of pressure on, 153 
 
 wire gauze on, 151 
 experiments on, 151 
 extinction by gases, 122 
 oxidising and reducing, 156 
 structure of, 148 
 temperature of, 151 
 Flames, simple and compound, 149 
 
 smoky, 154 
 
 Flashing-point of oils, 528 
 Flavin, 745 
 Flavopurpurin, 721 
 Flesh, 814 
 
 juice of, 676, 814 
 sugar of, 716 
 flint, 276 
 
 and steel, 276 
 Flints dissolved, 353 
 Florence flask, 41 
 Floss-hole,- 405 
 Flowers bleached, 220 
 Fluoranthreue, 555 
 Fluorene, 551 
 Fluorescei'n, 714, 724 
 Fluorescence, 724, 781 
 Fluoric acid, 202 
 Fluoride of calcium, 202, 330 
 
 Fluoride of silicon, 203 
 Fluorides', 205 
 Fluorine, 202 
 Fluor spar, 202, 368 
 Flux, 398 
 
 Baume's, 339 
 Fog, 71 
 
 Food, plastic constituents of, 823 
 preservation of, 823 
 respiratory constituents of, 823 
 Forge-iron, 403 
 Formaldehyde, 580 
 Formaline, 580 
 Formamides, 667 
 Formates, 590 
 Formic acid, 589 
 
 aldehyde, 580 
 esters, 643 
 ether, 643 
 thio-aldehyd, 7015 
 Formins, 647 
 Formouitrile. 699 
 Formose, 728 
 
 Formula?, axial symmetrical, 616 
 calculation of, 46, 300 
 empirical, 523 
 graphic, 524 
 molecular, 523 
 plane symmetrical, 616 
 rational, 524 
 structural, 524 
 Formyldiphenylamiue, 768 
 Fouling of guns, 342 
 Foundry iron, 403 
 Fractional distillation, 74, 529 
 
 precipitation, 588 
 Franklinite, 417 
 Fraxin, 744 
 Free-stone, 365 
 Freezing apparatus, 81, 82 
 
 in red-hot crucibles, 219 
 mixtures, 83, 356 
 of water, 63 
 points of solution, 319 
 French chalk, 373 
 Friction-tubes, 445 
 Friedel and Craft's reaction, 549 
 Fructose, 727 
 Fruit essences, 644 
 
 sugar, 727 
 
 Fruits, ripening of, 820 
 Fuchsiue, 722 
 Fucose, 7215 
 Fucusol, 586 
 Fuel, 158 
 
 calorific intensity calculated, 166 
 
 value calculated, 163 
 composition of, 168 
 gaseous, 161 
 Fuller's earth, 384 
 Fulminate of mercury, 706 
 
 silver, 708 
 
 Fulminates, 706, 708 
 Fulminating gold, 518, 697 
 platinum, 507 
 silver, 492 ^ 
 Fulminic acid, 707 
 Fulminurates, 718 
 Fulmiuuric acid, 708 
 Fumanyl dichloride, 640 
 
INDEX. 
 
 845 
 
 Furnaric acid, 615 
 
 Fumarotd structure, 616 
 
 Fumaryl dichloride, 640 
 
 Fumigation with sulphurous acid, 220 
 
 Fuming- sulphuric acid, 224 
 
 Fumitory, 615 
 
 Funnel tube, 22 
 
 Fur in kettles, 57 
 
 Furfural, 586 
 
 Furfuramide, 586 
 
 Furfurane, 622, 758 
 
 Furfuryl alcohol, 586 
 
 Furnace, electric, 138 
 gas, 22 
 
 regenerative, 167 
 reverberatory, 132 
 
 Furnaces, theory of, 167 
 
 waste of heat in, 167 
 
 Furo-azoles, 764 
 
 Fusco-cobalt salts, 423 
 
 Fusel oil, 808 
 
 Fusible alloy, 439 
 
 Fusing-points, 784 
 
 of fats, 800 
 
 Fusion, 277 
 
 Fustic, 715, 747 
 
 Fuze, electric, 487 
 
 percussion, 255 
 
 GADININE, 666 
 Gadolinite, 394 
 Gahnite, 417 
 Galactonic acid, 734 
 Galactose, 727 
 Galbanum, 714 
 Galena, 459 
 Gallein, 715 
 Gallic acid, 609 
 
 synthesis of, 610 
 anhydride, 610 
 Gallium, 392 
 Gall-nuts, 610 
 Gallocyanine, 768 
 Galloflavin, 609 
 
 tannic acid, 610 
 Gallstones, 757 
 Galvanic battery, 14 
 
 cell, 323 
 
 Galvanised iron, 376 
 Gambodic acid, 745 
 Gamboge, 714, 747 
 Gangue, 398 
 Ganister, 407 
 Garlic, essential oil of, 705 
 Garnet, 389 
 Garnierite, 424 
 Gas-burners, 154 
 
 carbon, 792 
 
 composition of, 161, 168 
 
 cylinder, 29 
 
 Dowson, 163 
 
 explosions, 145 
 
 fires, 161 
 
 holder, 135 
 
 jar, 34 
 
 manufacture, 791 
 
 Mond, 163, 168 
 
 producer, 162, 168 
 
 semi-water, 163 
 
 valuation of, 143 
 
 Gas-water, 163, 168 
 Gases, analysis of, 45, 157 
 
 constitution of, 27 
 
 diffusion of, 25 
 
 effect of pressure on, 27 
 
 expansion by heat, 28 
 
 good and bad, 28, 72 
 
 in waters, 54 
 
 solubility of, 315, 316 
 
 effect of heat on, 80 
 
 pressure on, 80 
 Gasolene, 528 
 Gastric juice, 822 
 Gaultheria, oil of, 645 
 Gaylmsite, 364 
 Gedge's metal, 481 
 Geissler tube, 330 
 Gelatin, 753 
 Gelatine dynamite, 647 
 Gelose, 737 
 Gentianin, 745 
 Germanium, 458 
 German silver, 423, 481 
 Germination, 804 
 Germs of disease, 71 
 Geysers, 277 
 Gibbsite, 388 
 Gilding, 517 
 
 porcelain, 392 
 Gin, 808 
 Glass, 370 
 
 Bohemian, 371 
 
 bottle, 371 
 
 coloured, 372 
 
 composition of, 370 
 
 crown, 371 
 
 etched, 204 
 
 flint, 371 
 
 -gall, 370 
 
 of antimony, 445 
 
 plate, 371 
 
 potash, 371 
 
 silvered, 490 
 
 soda, 370 
 
 soluble, 353 
 
 toughened, 372 
 
 window, 370 
 Glauberite, 351 
 Glauber's salt, 351 
 Glaze for earthenware, 391 
 Glazier's diamond, no 
 Gliadin, 753 
 Globulin, 750 
 Glucinum, 382 
 Glucoheptouic acid, 728 
 Glucoheptose, 728 
 Glucol, 715 
 Gluconic acid, 729 
 Glucosan, 726 
 Glucosazone, 728 
 Glucose, 725 
 
 artificial, 726 
 Glucoses, 725 
 
 constitution of, 729 
 synthesis of, 728 
 Glucosides, 743 
 Glucosone, 728 
 Glue, 753 
 
 liquid, 753 
 Glutamic acid, 752 
 
8 4 6 
 
 INDEX. 
 
 Glutaric acid, 615 
 Gluten, 734, 752 
 Glyceric acid, 607 
 
 aldehyde, 584 
 Glycerides, 647 
 Glycerine, 576 
 
 artificial preparation of, 76 
 ether, 631 
 soap, 801 
 Glycerol, 576 
 
 ethereal salts of, 645 
 Glycerose, 584 
 Glyceryl, 636 
 
 arsenite, 647 
 borate, 647 
 phosphate, 647 
 salts, 647 
 tribromide, 636 
 trichloride, 636 
 tricyanide, 623 
 trinitrate, 646 
 Glycocholic acid, 756, 822 
 Glycociamine, 676 
 Glycocine (glycocoll) (glycine), 674 
 
 synthesis of, 654 
 Glycocyamidine, 676 
 Glycogen, 736 
 Glycol, 573, 574 
 
 amide, 668 
 chlorhydrin, 575 
 dialdehyde, 575 
 disodium, 575 
 ethereal salts of, 646 
 ethers, 645 
 monosodium, 575 
 Glycolide, 604 
 Glycollic acid, 602 
 Glycols, secondary, 573 
 
 tertiary, 573 
 Glycosine, 584 
 Glycuronic acid, 607 
 Glycyphillin, 744 
 Glycyrrhizic acid, 746 
 Glyoxal, 584 
 Glyoxalic acid, 607 
 Glyoxalines, 765 
 GlyoxyJic acid, 607 
 Glyoxyl urea, 773 
 Gneiss, 389 
 Gold, 513 
 
 arsenide, 519 
 
 assay by cupellation, 516 
 
 bronze, 436 
 
 chloride, 518 
 
 coin, 515 
 
 crucible, 518 
 
 cyanides, 697 
 
 dissolved, 191 
 
 extracted from silver, 514 
 
 extraction, 513 
 
 fulminating', 518 
 
 identified, 93 
 
 leaf, 517 
 
 oxides, 518 
 
 physical properties of, 517 
 
 refining, 514 
 
 removal of mercury from, 497 
 
 ruby, 254, 517 
 
 salts of, 518 
 
 separated from silver and copper, 233 
 
 Gold, sodium-hyposulphite, 519 
 standard, 515 
 sulphides, 519 
 testing, 516 
 thread, 517 
 Gongs, 452 
 Goose-fat, 648 
 Goulard's extract, 592 
 Grains, brewers', 805 
 Granite, 365 
 
 disintegration of, 365 
 Granitic rocks, 332, 365 
 Granulated zinc, 22 
 Granulose, 735 
 Grape-sugar, 726 
 Grapes, colouring- matter of, 746 
 Graphic formula, 524 
 Graphite, no 
 
 in cast-iron, no, 402 
 Graphitic acid, in 
 Graphitised carbon, 118 
 Green, arsenical, 270 
 
 borate of chromium, 433 
 
 Brunswick, 485 
 
 chrome, 433 
 
 colour of plants, 746 
 
 fire, 186 
 
 flame of barium, 362 
 
 boracic acid, 247 
 copper, 485 
 thallium, 473 
 hydroquinone, 719 
 malachite, 485 
 manuring, 817 
 mineral, 485 
 Kinmann's, 423 
 salt of Magnus, 508 
 vitriol, 418 
 
 Grey antimony ore, 441 
 copper ore, 474 
 iron, 402 
 powder, 497 
 Grinder's waste, 411 
 Gristle, 753 
 Grotto del Cane, 121 
 Groug-h saltpetre, 337 
 Grove's battery, 14 
 Growth of plants, 819 
 Guaiacol, 713 
 Guaiacum, resin, 560, 713 
 Guanidines, 672, 673 
 Guanine, 673, 773 
 Guano, 817 
 Guignet's green, 433 
 Gulose, 727 
 Gum Arabic, 737 
 Bassora, 737 
 British, 736 
 Senegal, 737 
 tragacanth, 737 
 Gums, 737 
 Gum-sugar, 725, 737 
 Gun-cotton, 647, 740 
 
 compared with gunpowder, 742 
 
 composition, 740 
 
 explosion, 741 
 
 manufacture, 740 
 
 products of explosion of, 742 
 
 properties, 742 
 
 pulp, 741 
 
INDEX. 
 
 Gun-cotton, reconversion of, 740 
 Gun-metal, 452, 481 
 Gunpowder, 339 
 
 brown, 340 
 
 composition, 339 
 
 explosion of, 341 
 
 explosion under pressure, 343 
 
 influence of size of grain, 340 
 
 manufacture, 340 
 
 products of explosion, 341 
 
 properties of, 340 
 
 smokeless, 339 
 
 temperature of combustion, 341 
 
 white, 186 
 Gutta-percha, 585 
 Gypsum, 367, 818 
 
 H.^MATEIN, 748 
 
 Haematin, 756 
 Hcematite, 396 
 Hsematoxylin, 748 
 Haemin, 756 
 Haemocyanin, 474 
 Haemoglobin, 755 
 Hair-dye, 237, 493 
 Halogen defined, 205 
 
 derivatives, 632 
 
 from acids, 639 
 from aldehydes, 638 
 of closed-chain hydro- 
 carbons, 637 
 of open-chain hydrocar- 
 bons, 632 
 propylenes, 636 
 Halogens, review of, 205 
 Haloid salts, 205 
 Hammer-slag-, 406 
 Hard metal, 452 
 Hardness, degrees of, 58 
 
 permanent and temporary, 58 
 Hard water, 55 
 Hargreave's soda process, 346 
 Hartshorn, spirit of, 81 
 Hatchett's brown, 694 
 Hauerite, 430 
 Hausmannite, 427 
 Heat and temperature, 163, 164 
 atomic, 296 
 of combustion, 163 
 relation to chemical attraction, 38, 306, 
 
 307 
 
 specific, 296 
 
 units, 44 
 
 Heating- of hay-ricks, 158 
 Heats of formation calculated, 307 
 Heavy metal alkydes, 656, 657 
 Heavy lead ore, 469 
 
 spar, 360 
 Helianthin, 683 
 Helicin, 743 
 Heliotropine, 586 
 Helium, 77 
 Hellebore, 745 
 Helleborein, 745 
 Hemimorphite, 377 
 Hemiterpene, 556 
 Hemlock, 776 
 Henbane, 778 
 Hepatic waters, 61 
 Heptamethylene, 539 
 
 847 
 
 Heptane, 528 
 
 Heptoses, 728 
 
 Heptylic acid, 594 
 
 Herapathite, 781 
 
 Hesperidene, 556 
 
 Hesperidin, 744 
 
 Hesperitin, 744 
 
 Heterocyclic compounds, 757 761: 
 
 Hexacetyl cellulose, 739 ' 
 
 condensed nuclei from, 
 
 759 
 Hexa-chlorobenzene, 540 
 
 dieue, 537 
 
 ethane, 189 
 
 hydric alcohol, 578 
 
 hydropyrazine, 769 
 
 hydropyridine, 766 
 
 hydroxyanthraquinone, 610, 721 
 
 hydro xybenzene, 716 
 
 nitro-diphenylamine, 665 
 Hexagonal crystals, 52 
 Hexoses, 725 
 
 stereo- isomerism of, 730 
 Hexyl alcohol, 570 
 
 fermentation, 570 
 
 butyrate, 570 
 
 carbinol, 570 
 Hexylic acid, 594 
 Hippurates, 675 
 Hippuric acid, 675 
 Holmia, 394 
 Homologous series, 527 
 Honey, 731 
 Hopeite, 382 
 Hop substitute, 711, 745 
 Hops, 805 
 
 essential oil of, 555 
 Hornblende, 389 
 Horn-lead, 471 
 
 quicksilver, 502 
 silver, 493 
 
 Horse-chestnut bark, 744 
 Hot blast, theory of, 399 
 Humic acid, 817 
 Humus, 816 
 Hyacinth, 458 
 Hydantoin, 671 
 Hydramines, 665 
 Hydrargyllite, 388 
 Hydrargyrum cum creti, 497 
 Hydrates, 53 
 Hydraulic cements, 366 
 
 main, 790 
 Hydrazine, 106 
 
 hydrate, 107 
 sulphate, 1 06 
 Hydrazines, 684 
 
 identified, 685 
 Hydrazobenzene, 682 
 Hydrazoic acid, 107 
 Hydrazones, 625 
 Hydrazotoluene, 685 
 Hydrazulmin, 688 
 Hydrides of alcohol radicles, 527 
 Hydrindigotin, 762 
 Hydriodic acid, 200 
 Hydroaromatic hydrocarbons, 550 
 Hydrobenzamide, 585 
 Hydrobenzoin, 575 
 Hydroboracite, 375 
 
8 4 8 
 
 INDEX. 
 
 Hydromic acid, 194 
 Hydrocarbons, 137, 526, 791 
 cracking 1 , 151 
 
 open- and closed-chain, 538 
 Hydrocellulose, 738 
 Hydrochloric acid, 177 
 
 action of, on metals, 179 
 analysis of oxides, 180 
 electrolysis of, 16, 180 
 from alkali works, 178 
 yellow, 178 
 
 Hydrocobalticyanic acid, 692 
 Hydrocoerulignone, 717 
 Hydrocotarnine, 779 
 Hydrocyanic acid, 690 
 
 synthesis of, 690 
 tests for, 691 
 
 Hydrocyanocarbodiphenylimide, 763 
 Hydroferricyanic acid, 695 
 Hydroferrocyanic acid, 693 
 Hydrofluoboric acid, 248 
 Hydrofluoric acid, 202 
 Hydrofluosilicic acid, 284 
 Hydrogel form, 278 
 Hydrogen, 21 
 
 antimonide, 444 
 
 arsenide, 271 
 
 calorific intensity calculated, 166 
 
 value, 163 
 chloride, 177 
 
 synthesis of, 177 
 combustion of, 29, 30 
 dioxide, 63 
 experiments with, 29 
 heat of formation, 172 
 identified, 15 
 liquefaction of, 74 
 nitride, 107 
 peroxide, 63 
 
 tests for, 64 
 persulphide, 217 
 phosphides, 262 
 preparation, 21, 22 
 properties of, 23 
 purification, 46 
 selenietted, 243 
 sulphide, 213 
 Hydrogenium, 49 
 Hydro-isatin, 761 
 Hydrolysis, 265,743 
 
 Hydronaphthalene, 553 
 
 Hydronitroprussic acid, 696 
 
 Hydronitrous acid, 107 
 
 Hydroplatinocyanic acid, 698 
 
 Hydro-potassium tartrate, 619 
 
 Hydropyrrol, 759 
 
 Hydroquinone, 714, 717, 718 
 
 Hydroselenic acid, 243 
 
 Hydrosol form, 278 
 
 Hydrosulphuric acid, 213 
 
 tests for, 216 
 
 use in analysis, 215 
 
 Hydrosulphurous acid, 237 
 
 Hydrotelluric acid, 244 
 
 Hydroterpenes, 551 
 
 Hydroxides. 54 
 
 Hydroxy-acetic acid, 602 
 
 Hydroxy-acids, 570, 601 
 
 authranol, 719 
 
 Hydroxy-acids, azo-eompounds, 684 
 
 benzaldehydes, 585, 586 
 benzenes, 526, 708 
 benzoic acids, 608 
 butyric acids, 607, 644 
 caproicxacid, 607, 677 
 cyanogen compounds, 701 
 ethylajrfine, 666 
 formifc acid, 589 
 indol, 760 
 naalouic acid, 617 
 oleic acid, 607 
 phenyl fatty acids, 611 
 propionic acid, 603 
 pyridines, 766 
 quinoline, 767 ' 
 succinic acid, 618 
 toluenes, 712 
 toluic acids, 609 
 tricarballylic acid, 623 
 
 Hydroxyl, 54, 94 
 
 amine, 103 
 
 Hyoscyamine, 777 
 
 Hypobromous acid, 194 
 
 Hypochlorites, 182 
 
 Hypochlorous acid, 182 
 
 anhydride, 181 
 
 Hyponitrites, 103 
 
 Hyponitrous acid, 103 
 
 Hypophosphites, 260 
 
 Hypophosphorous acid, 260 
 
 Hyposulphite of soda, 236, 352 
 
 Hyposulphuric (dithionic) acid, 237 
 
 Hyposulphurous acid, 235 
 
 Hypoxanthine, 774 
 
 ICE, 63 
 
 Iceland spar, 363 
 Illuminating value, 162 
 Imides, 649, 658 
 Imidogen, 669 
 Incandescent burners, 458 
 Incorporating mill, 340 
 Incrustation on charcoal, 157 
 Incrustations in boilers, 57 
 Indazoles, 765 
 Indian fire, 274 
 
 ink, 748 
 
 India-rubber, 557 
 Indican, 761 
 Indifferent oxides, 38 
 Indigo, 761 
 
 artificial, 762 
 
 blue, 761 
 
 brown, 761 
 
 copper, 487 
 
 gluten, 761 
 
 manufacture of, 763 
 
 red, 761 
 
 reduced, 762 
 
 salt, 764 
 
 vat, preparation, 762 
 
 white, 762 
 Indiglucin, 761 
 Indigo tin, 761 
 
 sulphonic acids, 762 
 Indium, 393 
 Indoaniliue, 718 
 Indole, 759 
 Indolinones, 760 
 
INDEX. 
 
 8 49 
 
 Indophenin, 758 
 Imlophenol, 718 
 Indophor, 760 
 Indoxyl, 760 
 Iiidoxylic acid, 760 
 Induction coil, 17 
 Induliues, 769 
 Ingot iron, 404 
 Ink, 605 
 
 blue, 693 
 
 stains removed, 182 
 Inorganic substances, 6 
 Inosite, 716 
 
 Instantaneous light, 506 
 Intramolecular condensation, 531 
 Intumescence, 353 
 Inulin, 736 
 Invert sugar, 727 
 lodamines, 662 
 lodammonium iodide, 201 
 lodates, 199 
 lodic acid, 199 
 Iodide of nitrogen, 201 
 Iodides, 199 
 Iodine, 195 
 
 bromides, 202 
 chlorides, 202 
 green, 723 
 oxides, 198 
 scarlet, 502 
 test for, 197 
 tincture of, 197 
 Iodised starch-paper, 65 
 lodobenzene, 637 
 lodoform, 636 
 lodopyrrol, 759 
 lodosobenzene, 637 
 lodoxybenzene, 637 
 lonisation, degree of, 326 
 Ions, 323 
 
 IridkKplatinum alloy, 512 
 Iridium, 511 
 Iron, 394 
 
 acetate, 591 
 
 action of acids on, 93, 179, 416 
 
 air on, 376 
 on water, 21 
 
 allotropic, 414 
 
 amalgam, 498 
 
 and carbon, 403 
 
 and oxygen, 34 
 
 atomic weight of, 420 
 
 bar, 407 
 
 carbide, 415 
 
 carbonate, 396 
 
 carbon in, 403, 405 
 
 carbonyls, 420 
 
 cast, 401 
 
 chemical properties of, 416 
 
 chlorides, 419 
 
 cold-short, 408 
 
 critical temperature of, 414 
 
 extraction in the laboratory, 415 
 
 fibre in, 408 
 
 galvanised, 376 
 
 glance, 396 
 
 grey, 402 
 
 group of metals reviewed, 434 
 
 iodide, 419 
 
 magnetic oxide, 417 
 
 Iron, metallurgy of, 396 
 mottled, 402 
 mould, 416, 738 
 nitride, 420 
 ores, 395 
 
 calcining or roasting, 397 
 oxides, 416 
 passive state of, 416 
 perchloride of, 419 
 phosphates, 419 
 phosphorus in, 409 
 plates cleansed, 450 
 puddled, 404 
 
 pure, preparation of, 416. 
 Iron pyrites, 396, 420 
 Iron, pyrophoric, 136 
 red-short, 408 
 refining, 404 
 rusting, 416 
 salts of, 419 
 sand, 396, 456 
 scurf, 392 
 smelting, 398 
 specular, 396 
 sulphates, 418 
 sulphides, 214, 420 
 sulphur in, 401 
 tincture of, 419 
 tinned, 450 
 white, 402 
 wire, 407 
 wrought, 404 
 
 direct extraction, 415 
 manufacture, 404 
 Isatic acid, 679 
 Isatide, 761 
 Isatin, 679, 760 
 
 anilide, 763 
 Isatoic anhydride, 679 
 Iserine, 456 
 
 Isethionic acid, 535, 649 
 chloride, 679 
 Isinglass, 753 
 Isobarbituric acid, 773 
 Iso- butane, 532 
 butylene, 536 
 butyl alcohol, 565, 569 
 cholesterin, 757 
 cumene, 791 
 cyanates, 704 
 cyanides, 760 
 cyanuric acid, 708 
 dialuric acid, 773 
 di-morphism, 442 
 Isomeric alcohols, 567 
 Isomerides, 533 
 Isomerism, 533, 603, 605 
 
 explanation of, 533 
 position, 544 
 Isomorphism, 297 
 Isoparaffins, 533 
 pentane, 533 
 phthalic acid, 617 
 prene, 556 
 propyl alcohol, 568 
 
 benzoic acid, 601 
 carbinol, 568 . 
 
 quinolene, 767 
 Iso-succinic acid, 614 
 uric acid, 773 
 
8 5 
 
 INDEX. 
 
 Isotonic solutions, 318 
 Isoxazole, 765 
 Is ore t, 669 
 Ctaconic acid, 623 
 Ivory, artificial, 742 
 black, 116 
 
 JABORANDINE, 784 
 
 -Jalapin, 745 
 
 Jalapinol, 745 
 
 Jasper, 276 
 
 Jatrophiue, 803 
 
 Jellies, fruit, 820 
 
 Jervine, 783 
 
 Jtt, 160 
 
 Jet for burning' gases, 30 
 
 Jewellers' rouge, 417 
 
 Juniper, essential oil of, 555 
 
 Kainit, 375 
 Kairine, 767 
 Kairolin, 769 
 Kakodyl, 655 
 
 chloride, 655 
 
 compounds, 655 
 
 cyanide, 655 
 
 oxide, 655 ' 
 
 sulphide, 651} 
 
 trichloride, 656 
 Kakodylic acid, 655 
 Kaolin, 384 
 Kassner's process, 469 
 Kekul6's chain, 546 
 Kelp, 195 
 Keratin, 754 
 Kermes mineral, 446 
 Kernel roasting, 486 
 Kerosene, 528 
 Ketodihydropyrazoles, 764 
 Ketols, 626 
 Ketone-acids, 574, 626 
 
 alcohols, 574, 626 
 aldehydes, 574, 626 
 Ketones, 624 
 
 double, 624 
 table of, 624 
 
 Ketonic decomposition, 644 
 Ketoses, 724 
 Ketoximes, 625 
 Kid, 797 
 Kieselguhr, 646 
 Kieserite, 375 
 Kinetic theory of gases, 291 
 
 method of measuring affinity, 312 
 King's yellow, 275 
 Kino, 712, 715 
 Kipp's apparatus, 120 
 Kirschwasser, 8oS 
 Kish, in 
 
 Kjeldahl's method, 521 
 Kola nut, 775, 810 
 Kosine, 746 
 Koumiss, 733 
 Kousso, 746 
 Kreasote, 712 
 Kreatine see, Creatine 
 Kresol, 712 
 Kryolite, 389 
 Kupfernickel, 424 
 Krypton, 77 
 
 Kyanising wood, 820 
 Kyanite, 389 
 
 LAB, 752 
 Lac, 748 
 Lacquer, 748 
 Lacquering-, 482 
 Lactamide, 668 
 Lactams, 678 
 Lactarine, 752 
 Lactates, 604 
 Lactic acid, 603 
 
 anhydride, 603 
 fermentation, 603 
 Lactide, 603 
 Lactims, 679 
 Lactometer, 813 
 Lactones, 627 
 Lactose, 733 
 Lactyl chloride, 639 
 Laevo-rotatory, 542, 621 
 Laevotartaric acid, 621 
 Laevulosan, 728 
 Laevulose, 727 
 Lakes, alumina, 388 
 Lamp-black, in 
 
 without flame, 506 
 Lanarkite, 471 
 
 Landsberger's apparatus, 321 
 Lanolin, 757 
 Lanthanum, 391 
 Lapis lazuli, 389 
 Lard, 648, 799 
 Laudanum, 778 
 Laughing gas, 96 
 Laurel water, 691 
 Laurie acid, 594 
 
 aldehyde, 583 
 Laurite, 511 
 Lauth's violet, 768 
 Lava, 389 
 Law of even numbers, 523 
 
 constant proportions, 7, 286 
 multiple proportions, 286 
 reciprocal proportions, 287 
 periodic, 301 
 thermochemistry, 305 
 Lead, 459 
 
 acetates, 591, 592 
 
 action of acids on, 467 
 on water, 60 
 
 alkides, 656 
 
 applications of, 466 
 
 argentiferous, 463 
 
 arsenate, 471 
 
 calcining, 462 
 
 carbonates, 470, 472 
 
 chlorides, 471 
 
 chlorobromide, 472 
 
 chlorosulphide, 472 
 
 chromates, 432 
 
 coiTosion of, 467 
 
 desilverising process, 463 
 
 dioxide, 469 
 
 extraction in laboratory, 460 
 
 fume, 461 
 
 -glazed earthenware, 468 
 
 hard, 462 
 
 hydroxide, 470 
 
 improving process, 462 
 
INDEX. 
 
 Lead in cider, &c., 467 
 
 in water, 60 
 
 iodide, 199, 472 
 
 nialate, 618 
 
 metallurgy of, 461 
 
 molybdate, 435 
 
 nitrate, 470 
 
 oleate, 598 
 
 ores, 459 
 
 oxides, 467 
 
 in glass, 371 
 
 oxy chlorides, 471 
 
 peroxide, 467 
 
 persulphide of, 472 
 
 phosphate, 471 
 
 plaster, 598 
 
 poisoning, 47I 
 
 propionate, 593 
 
 propylate, 593 
 
 pyrophorus, 467 
 
 selenide, 472 
 
 smelting, 461 
 
 Spanish, 462 
 
 sugar of, 591 
 
 sulphate, 471 
 
 sulphides, 472 
 tartrate, 467 
 
 test for, 6 1 
 tetracetate, 469 
 
 tetramethyl, 656 
 
 tetrethyl, 656 
 thiosulphate, 237 
 tribasic acetate, 592 
 triethyl, 656 
 uses, 466 
 vanadate, 446 
 Lead vitriol, 471 
 Leaden cistern, 60 
 coffins, 467 
 Leadhillite, 471 
 Leather, 797 
 Leaven, 809 
 
 Leblanc alkali process, 345 
 Lecanoric acid, 714 
 Lecithin, 647, 755 
 Legumin, 752 
 Lemery's volcano, 212 
 Lemons, essential oil of, 555 
 Lepidine, 767 
 Lepidolite, 358 
 Leucaniline, 722 
 Leucic acid, 677 
 Leucine, 677 
 Leuco-base, 722 
 Leucoue, 282 
 Leuco-parurosanilme, 722 
 Levulinic acid, 627 
 Libethenite, 485 
 
 Lichens, colouring-matters from, 714 
 Liebermann's reaction, 710 
 Liebig's condenser, 61 
 
 extract, 815 
 Light, action on silver chloride, 236 
 
 carburetted hydrogen, 144 
 
 oil of coal-tar, 539, 793 
 Lignite, 159, 168 
 Ligroin, 528 
 Lime, 363 
 
 action on soils, 818 
 air-slaked, 365 
 
 851 
 
 Lime-burning, 364 
 
 carbonate in waters, 56 
 
 chloride of, 183 
 
 -kilns, 364 
 
 -light, 48 
 
 phosphates, 369 
 
 purifier, 792 
 
 stone, 363 
 
 sulphate, 367 
 
 superphosphate, 369 
 
 water, 365 
 Limonene, 556 
 Linde's machine, 72 
 Linen, 737 
 
 Linoleic acid, 599, 798 
 Linolenic acid, 599 
 Linseed, 737 
 
 oil, 798 
 
 Liquation, 488 
 Liquefaction of air, 73 
 gases, 72 
 
 Liquor ammonia?, 76, bi 
 chlori, 171 
 iodi, 197 
 sanguinis, 814 
 
 sodse chloratae, 184 
 Liquorice root, 746 
 Litharge, 468 
 Lithia, 358 
 Lithia-mica, 358 
 Lithic acid, 769 
 Lithium, 358 
 
 blowpipe test for, 358 
 urate, 770 
 Litmus, 714 
 Loadstone, 396 
 Loam, 384 
 Logwood, 388, 748 
 Looking-glasses silvered, 497 
 Lophin, 765 
 
 Lucifer matches, 254, 255 
 Lugol's solution, 197 
 Luminosity of flames, 149 
 Lunar caustic, 492 
 Lupulin, 805 
 Luteo-cobalt salts, 423 
 Luteolin, 747 
 Lutidine, 766 
 Luting for crucibles, 378 
 
 iron joints, 212 
 Lycopodium, 148 
 Lysidine, 765 
 Lysol, 712 
 
 MACDOUG ALL'S disinfectant, 710 
 Maclurin, 747 
 Madder, 720, 795 
 
 -lakes, 720 
 Magenta, 722, 793 
 
 bronze, 436 
 
 Magic lantern, oil for, 559 
 Magistral, 489 
 Magnesia, 374 
 
 calcined, 375 
 
 citrate, 623 
 Magnesia limestone, 365, 374 
 
 for Duilding. 365 
 Magnesite, 373 
 Magnesium, 373 
 
 action on water, 21 
 
INDEX. 
 
 Magnesium, ammonio- chloride, 376 
 
 phosphate, 375 
 ammonium arsenate, 375 
 borate, 375 
 carbonate, 374 
 chloride, 375 
 citrate, 623 
 fluoride, 205 
 group, review of, 383 
 hydroxide, 374 
 methide, 657 
 nitride, 374 
 phosphates, 375 
 silicates, 373 
 silicide, 282 
 sulphate, 375 
 
 Magnet-fuse composition, 487 
 Magnetic iron ore, 396, 417 
 
 pyrites, 420 
 
 Magnetic rotatory power, 788 
 Magnetite, 417 
 Magnus' green salt, 508 
 Malachite, 474 
 
 green, 722 
 Maleic acid, 615 
 
 Malemoid and fumaroid structure, 616 
 Malic acid, 618 
 Malonic acid, 614 
 
 ether, 645 
 Malonyl urea, 772 
 Malt, 804 
 
 -dust, 804 
 high-dried, 806 
 Malting, 803 
 Maltose, 733 
 Mandelic acid, 609, 744 
 Manganates, 428 
 Manganese, 426 
 
 binoxide, 427 
 Manganese black, 427 
 blende, 430 
 Manganese bronze, 452 
 
 carbonate, 426 
 chlorides, 429 
 dioxide, 426 
 oxalate, 613 
 oxides, 426 
 peroxide, 426 
 recovery, 429 
 separated from iron, 430 
 Manganese spar, 426 
 Manganese sulphate, 430 
 sulphide, 430 
 Manganic acid, 427 
 Manganite, 427 
 Manna, 578 
 
 Australian, 734 
 trehala. 734 
 Mannitane, 579 
 Mannite (mannitol), 578 
 glycertdes, 579 
 Mannose, 579, 727 
 Mannonic acid, 578, 729 
 Mannyl hexanitrate, 578 
 Mantle of flame, 152 
 Mantles for Welsbach burners, 155, 458 
 Manures, 817 
 Manuring, 817 
 Maraschino, 808 
 Marble, 363 
 
 Marcasite (iron pyrites), 420 
 Margaric acid, 596, 798 
 Margarin, 798 
 Margarine, 799 
 Marine glue, 557 
 Marking-ink, 492 
 Marl, 384 
 Marsh -gas, 144, 526 
 
 series, 526 
 
 Marsh's test for arsenic, 272 
 Martensite, 414 
 Martius' yellow, 712 
 Mascagnine, 355 
 Mashing, 805 
 Mass, action of, 310 
 
 active, 310 
 Massicot, 468 
 Matches, 184, 254 
 
 safety, 255 
 
 without phosphorus, 254 
 Mate, 775 
 MatlocTcite, 471 
 Matte, 476 
 Mauve dye, 793 
 Mauveine, 793 
 Meadow-sweet, oil of, 586 
 Meal-powder, 340 
 Meconates, 622 
 Meconic acid, 622 
 Meconine, 779 
 
 hydrocotaruine, 779 
 Meerschaum, 373 
 Melam, 704 
 Melamine, 704 
 Melaniline, 673 
 Mel em, 704 
 Melezitose, 734 
 Melissene, 799 
 Melissyl alcohol, 570 
 
 palmitate, 570, 644 
 Melitose, 734 
 Mellite, 624 
 Mellitic acid, 624 
 Mellone, 704 
 Mellonides, 704 
 Menaccanite, 456 
 Mendeleeffs law, 301 
 Mendipite, 472 
 Menthene, 557 
 Menthol, 557 
 Mercaptan, 572 
 Mercaptides, 572 
 Mercaptol, 626 
 Mercerisation, 738 
 Merchant bar iron, 407 
 
 acetamide, 668 
 Mercuric chloride, 499 
 
 cyanide, 697 
 
 ethide, 657 
 
 fulminate, 706 
 
 iodide, 502 
 
 methide, 656 
 
 nitrate, 499 
 
 oxycyanide, 697 
 
 sulphate, 499 
 
 sulphide, 502 
 
 colloidal, 504 
 
 Mercuroso-mercuric iodide, 502 
 Mercurous acetate, 591 
 chloride, 501 
 
INDEX. 
 
 853 
 
 Mercurous cobalticyanide, 692 
 iodide, 502 
 nitrate, 499 
 sulphate, 499 
 sulphide, 502 
 Mercury, 495 
 
 alkides, 656 
 allyl-hydroxide, 636 
 iodide, 502, 636 
 amido-chloriue, 501 
 ammoniated oxide, 499 
 bichloride, 499 
 chlorosulphide, 503 
 diphenyl, 657 
 ethyl chloride, 657 
 
 hydroxide, 657 
 frozen, 129 
 fulminate, 706 
 metallurgy of, 496 
 methyl chloride, 656 
 nitric oxide of, 498 
 nitride, 499 
 oxides, 498 
 phenyl chloride, 657 
 
 hydroxide, 657 
 protonitrate, 499 
 
 stains removed from gold, 497, 498 
 uses of, 497 
 volatility of, 498 
 yellow oxide, 499 
 Mesaconic acid, 616 
 Mesitylene, 549, 625 
 Mesitylenic acid, 601 
 Mesityl oxide, 625 
 Meso-derivatives, 554 
 Mesotartaric acid, 620 
 Mesoxalic acid, 618, 771 
 Mesoxalyl urea, 771 
 Metabolis, 819 
 Metaboric acid, 246 
 Metacetonic (propylic) acid, 593 
 Metacinnamene, 550 
 Metacresol, 712 
 Metacrolein, 584 
 Metadiazine, 768 
 Metadibroruobenzene, 547 
 Metadihydroxy benzene, 714 
 Metadinitrobenzeue, 650 
 Metatrihydroxy benzene, 715 
 Metal, alkides, 656 
 
 definition of, 38 
 Metaldehyde, 583 
 Metalepsis, 174 
 Meta-diazines, 768 
 Metallic isocyanates, 703 
 
 thiocyanates, 704 
 Metallurgy of copper, 475 
 iron, 396 
 lead, 461 
 tin, 448 
 zinc, 377 
 
 Metals, action on water, 19, 21 
 chemistry of, 332 
 noble, 21 
 
 relations to oxygen, 35 
 Metal-slag (copper), 476 
 Metameric, 533 
 Metantimonic acid, 443 
 Metaphenylinediamine, 666 
 Metaphosphates, 258 
 
 Metaphosphoric acid, 258 
 Metarabin, 737 
 Metarsenic acid, 271 
 Metasilicic acid, 278 
 Metastannic acid, 453 
 Metastyrolene, 550 
 Metatartaric acid, 619 
 Metatoluidine, 665 
 Metaxylene, 549 
 Meteoric iron, 395 
 Methane, 144, 526, 530 
 
 constitution of, 526 
 
 heat of formation, 141 
 
 preparation of, 144, 530 
 Methene di-iodide, 635 
 
 diphenyl, 664 
 Methods of determining molecular weights, 
 
 Methyl, 592 
 
 acetate, 643 
 acrylic acid, 597 
 alcohol, 565 
 aldehyde, 580 
 amine, 659 
 aniline, 664 
 anthranilate, 678 
 arsenic acid, 656 
 arsine, 655 
 benzenes, 548 
 benzoic acid, 601 
 bromide, 633 
 carbamides, 671 
 carbamine, 700 
 
 carbimide, 704 
 
 chloride, 633 
 
 coniine, 776 
 
 cyanate, 704 
 
 cyanide, 668, 699 
 
 cyanurate, 704 
 
 dihydroglyoxaline, 765 
 
 diphenylamine, 664 
 
 ether, 627 
 
 ethylamine, 662 
 
 ethyl amylamine, 662 
 aniline, 664 
 ketone, 626 
 urea, 705 
 
 fluoride, 634 
 
 forinainide, 667 
 
 formate, 643 
 
 formic acid, 590 
 
 glycocines, 674 
 
 glycocyamidine, 676 
 
 glycocyamine, 676 
 
 glycolyl-guanidiue, 676 
 
 guaiacol, 713 
 
 guanidine, 676 
 
 hydantoin, 677 
 
 hydrate, 565 
 
 indol, 760 
 
 indoliu, 760 
 
 iodide, 634 
 
 isocyanate, 704 
 
 isocyanide, 700 
 
 methyl-salicylate, 645 
 
 morphine, 779 
 
 naphthalenes, 553 
 
 nitramiue, 662 
 nonyl ketoue, 626 
 orange, 683 
 
854 
 
 Methyl oxalate, 645 
 
 para-oxy ben zoic acid, 608 
 
 phenol, 709, 712 
 
 phenylamine, 664 
 
 phosphines, 654 
 
 phthalic acid, 758 
 
 propyl carbinol, 560 
 
 protocatechuic acid, 609 
 
 pyrocatechol, 713 
 
 quinolines, 767 
 
 salicylate, 645 
 
 salicylic acid, 645 
 
 succinic acid, 615 
 
 sulphates, 641 
 
 theobromine, 775 
 
 uracyl, 773 
 
 ureas, 705 
 
 violet, 723 
 Methylated ether, 628 
 
 spirit, 565, 628 
 Methylene iodide, 635 
 Metric system, 12 
 Mica, 332, 384 
 Microcosmic salt, 259, 357 
 Mildew, 71 
 Milk, 811 
 
 constituents of, 812 
 of sulphur, 209 
 skimmed, 812 
 sug-ar, 812 
 Mill-cake, 340 
 
 furnace, 407 
 Millon's base, 499 
 
 test, 750 
 
 Millstone grit, 365 
 Mineral cotton, 401 
 
 green, 485 
 
 kermes, 446 
 
 silicates, 280 
 
 waters, 61 
 
 yellow, 472 
 Mines, ventilated, 126 
 Minium, 467 
 Mirbane essence, 540 
 Mirrors, manufacture of, 491, 497 
 Mispickel, 266 
 Mixture defined, 6 
 Moire metallique, 453 
 Molasses, 731 
 
 Molecular formulae, 522, 523 
 heats, 297 
 volumes, 301, 786 
 weight, 292 
 
 determination of, 292, 
 
 2 93 3 J 9> 5 22 
 Molecule, definition, 8 
 Molecules, 8, 286 
 
 velocity of, 25, 290 
 vibrations of, 290, 331 
 Molybdenite, 435 
 Molybdeaum, 435 
 
 glance, 435 
 metallic, 435 
 Molybdic acid, 435 
 
 anhydride, 435 
 ochre, 436 
 oxide, 435 
 Mona copper, 478 
 Monad elements, n 
 Monamides, 667 
 
 INDEX. 
 
 Monamines, 658, 660 
 Monatouiic elements, 12 
 Monazite sand, 458 
 Monethyl glycol ether, 631 
 Mond g-as, 163, 168 
 Monkshood, 783 
 Monobasic acids, 98, 104, 588 
 Mouochloracetamide, 668 
 Monochlorether, 631 
 Monochlorhydrin, 646 
 Monochlorobenzene, 540 
 methane, 633 
 Monoclinic crystals, 52 
 Monoformin, 647 
 Monohydric alcohols, 561, 565 
 Monoses, 728 
 Mordants, 683, 795 
 Morin, 747 
 
 Moritannic acid, 611, 747 
 Morocco leather, 797 
 Morphine, 778 
 
 hydrochloride, 778 
 
 meconate, 778 
 
 periodide, 779 
 Morpholine, 666 
 Mortar for building, 366 
 Mosaic gold, 455 
 Mould, 71 
 
 Mountain-ash berries, 618 
 Mucic acid, 622 
 Mucilage, 737 
 Mucin, 754 
 Muffle, 466 
 
 Mulberry calculus, 613 
 Multiple proportions, 286 
 Mundic (iron pyrites), 420 
 Muntz metal, 481 
 Murexan, 772 
 Murexide, 770 
 Murexoin, 775 
 Muriate of morphia, 778 
 Muriatic acid, 169 
 Muscarine, 666 
 Muscovite, 389 
 Musk, artificial, 757 
 Muslin, uninflammable, 355, 436 
 Mustard, essential oil of, 705 
 oil, reaction of, 706 
 oil test for primary bases, 706 
 Mycose, 734 
 Mydatoxine, 666 
 Mydine, 666 
 Myosin, 751 
 Myricin, 570, 644, 799 
 Myristic aldehyde, 583 
 Myronic acid, 705 
 Myrosin, 705 
 Myrtle, essential oil of, 555 
 
 NAPHTHA, mineral, 528 
 Naphthalene, 551 
 
 chlorides, 552 
 
 chloro -substitution products, 
 
 552 
 
 disulphonic acid, 649 
 heat of combustion of, 165 
 nitro-substitutiou products, 
 
 55 2 > 6 5<> 
 rings, 552 
 sulphonic acid, 649 
 
INDEX. 
 
 Naphthalene, yellow, 712 
 Naphthalic acid, 617 
 Naphthalidine, 665 
 Naphthalines, 528, 539 
 Naphtha zine, 769 
 Naphthendulines, 769 
 Naphthoic acid, 601 
 Naphthol, 708, 712 
 
 yellow, 712 
 
 Naphthoquinolines, 767 
 Naphtlioquinones, 719 
 Naphthohydroquinone, 719 
 Naph'hophenazine, 769 
 Naphthylamine, 665 
 Naphthyleue-diamine, 666 
 Naphthyl-phenyl-ketone, 626 
 Naples yellow, 443 
 Narceine, 780 
 Narcotine, 779 
 Nascent condition, 102 
 Natron, 348 
 Neg-ative change, 310 
 Negative pole, 14 
 Neodyminm, 394 
 Neon, 77 
 
 Neo- paraffins, 533 
 Neo-pentane, 533 
 Neroli oil, 678 
 Nervous substance, 755 
 Nessler's test, 502 
 Nest sugar, 734 
 Neuridine, 666 
 Neurine, 666 
 Neutralisation, 19 
 Newland's law of octaves, 301 
 Nickel, 423 
 
 ammonium sulphate, 425 
 
 arsenical, 424 
 
 arseniosulphide, 424 
 
 blende, 424 
 
 car bony], 425 
 
 cobalticyunide, 692 
 
 cyanide, 692 
 
 glance, 424 
 
 metallurgy of, 424 
 
 oxides, 425 
 
 steel, 415 
 
 sulphate, 425 
 
 sulphides, 425 
 Nicotine, 770 
 
 ethylinm dihydroxide, 777 
 Nicotinic acid, 777 
 Nightshade, 776 
 Nil album, 377 
 Niobium, 447 
 Nitramines, 662 
 Nitranilines, 600, 664 
 Nitrate, 89 
 Nitrates, 95 
 
 as manure, 818 
 formation in nature, 87 
 Nitre, 337, 338 
 
 action on carbon, 339 
 
 cubic, 353 
 
 -heaps, 337 
 purified, 340 
 
 refining, 338 
 Nitric acid, 89 
 
 action on hydrochloric acid, 191 
 metals, 92 
 
 Nitric acid, action on organic bodies, 93 
 
 turpentine, 74 
 composition of, 95 
 formation from uir, 88 
 
 ammonia, 86 
 fuming, 90 
 preparation, 89 
 reduction, products of, 102 
 test of strength, 90 
 anhydride, 96 
 esters, 642 
 ether, 642 
 nitrides, 107 
 oxide, 96 
 peroxide, 100 
 Nitrification, 87 
 Nitrifying organism, 88 
 Nitriles, 699 
 Nitrites, 95, 100 
 Nitro-benzene, 540, 650, 682 
 chloroform, 650 
 cinnamic acid, 764 
 compounds, 649 
 copper, 101 
 erythrite, 578 
 ethene, 650 
 mannite, 578 
 methane, 650 
 naphthalene, 650 
 paraffins, 642, 649 
 phenols, 711 
 
 phenyl-lactomethyl ketone, 764 
 phenylamine, 664 
 phenylpropiolic acid, 761 
 toluenes, 650 
 Nitrogen, 74 
 
 as plant food, 816 
 bromide, 195 
 bulbs, 521 
 
 chemical relations, 75 
 chloride, 90 
 chlorophosphide, 265 
 determination, 521 
 group of elements, 275 
 iodide, 201 
 liquefied, 73 
 oxides, 88 
 preparation, 75 
 properties, 75 
 sulphides, 241 
 
 Nitrogeuised bodies identified, 116 
 Nitroglycerine, 577, 646 
 Nitrolic acid, 567 
 Nitro metals, 100 
 Nitrometer, 93 
 Nitromuriatic acid, 191 
 Nitroprussides, 695 
 Nitrosalicylic acid, 743 
 Nitrosamines, 660 
 Nitroso-phenol, 718 
 
 reaction, 660 
 
 Nitro substitution-products, 94 
 Nitrosulphonic acid, 191 
 sulphuric acid, 191 
 Nitrosyl chloride, 191 
 sulphate, 191 
 Nitrouracyl, 773 
 Nitrous acid, 99, 101 
 
 formed from ammonia, 86 
 anhydride, 98 
 
8 5 6 
 
 INDEX. 
 
 Nitrous ether, 642 
 
 oxide, 96 
 Nitroxyl, 94, 100 
 
 chloride, 192 
 Nitryl chloride, 192 
 Nobel's detonators, 647 
 Nonane, 528 
 
 Non-metallic elements, 3 
 Nonoses, 728 
 Nonylic acid, 594 
 
 alcohol, 565 
 
 Nordhausen oil of vitriol, 224 
 Normal salt defined, 104 
 Normandy's still, 62 
 Nucleal synthesis, 531 
 Nucleiu, 754 
 Nuggets, 513 
 
 Nutmegs, essential oil of, 555 
 Nutrition of animals, 821 
 
 plants, 816 
 Nux vomica, 781 
 
 OCCLUSION of hydrogen, 49 
 Ochres, 384 
 Octane, 528 
 Octoses, 728 
 Octyl acetate, 570 
 
 alcohol, 570 
 Octylic acid, 594 
 CEnanthic acid, 594, 799 
 
 aldehyde, 583, 799 
 ether, 644 
 Oil of cress, 700 
 
 gaultheria, 608 
 
 meadow-sweet, 585 
 
 mignonette root, 705 
 
 mustard, 705 
 
 nasturtium, 700 
 
 rue, 594, 626 
 
 spiraj i, 586 
 
 vitriol, 223 
 
 manufacture, 225 
 
 wine, 641 
 
 winter-green, 608, 645 
 Oils, 798 
 Oleates, 598 
 Olefiant gas, 142, 534 
 Olefine hydrocarbons, general preparation of, 
 
 536 
 Olennes, 534, 536 
 
 structure of, 534 
 Oleic acid, 598 
 Olein, 598, 647, 798 
 Oligist iron ore, 396 
 Olive oil, 648, 798 
 Olivine, 375 
 Onyx, 276 
 
 Oolite limestone, 363 
 Oolitic iron ore, 396 
 Opal, 276 
 
 blue, 723 
 Open- and closed-chain hydrocarbons, 538 
 
 hearth process, 409 
 Opianic acid, 779 
 Opium, 778 
 
 alkaloids, 778 
 Orange chrome, 432 
 Oranges, essential oil of, 555 
 Orcein, 715 
 Orchella weed, 578, 714 
 
 Orcin, or orcinol, 704, 714 
 Ore-furnace, 476 
 Organic acids, 586 
 
 acid radicles, 592 
 analysis, ultimate, 521 
 chemistry, 6, 520 
 compounds, classified, 524, 525 
 matter identified, 108 
 radicles, 524, 592 
 
 Organic compounds, absorption spectra, 788 
 boiling-points of, 785 
 fusing-points of, 784 
 optical properties of, 
 
 787 
 physical properties of, 
 
 784 
 rotatury polarisation 
 
 of, 788 
 
 specific volume?, 786 
 Organo-rnineral compounds, 651 
 Oriental alabaster, 58 
 Orientation of the benzene-ring-, 545 
 Orpiment, red, 274 
 
 yellow, 275 
 Orsellinic acid, 714 
 
 Ortho-, meta-, and para-compounds, 546 
 acetic acid, 643 
 acids, 261 
 boric acitl, 247 
 carbonic aciu, 261 
 cresol, 712 
 
 dibroinobeuzene, 546 
 formic ether, 636 
 phosphates, 258 
 phosphoric acid, 257 
 silicic acid, 278 
 Orthotoluidine, 665 
 Orthoclase, 389 
 Osazones, 728 
 Osmamines, 511 
 Osmazome, 815 
 Osmic acid, 510 
 Osmium, 510 
 Osmosis, 316 
 Osmotic membrane, 317 
 pressure, 316 
 
 law of, 318 
 Osones, 728 
 Oaotriazole, 765 
 Ossein, 766 
 Oswego, 803 
 Oxalates, 613 
 Oxalethylic acid, 645 
 Oxalethyline, 669 
 Oxalic acid, 612 
 
 aldehyde, 584 
 ether, 645 
 Oxalouitrile, 699 
 Oxalovinic acid, 645 
 Oxaluramide, 772 
 Oxaluric acid, 772 
 Oxalyl urea, 772 
 Oxamethane, 669 
 Oxamic acid, 672 
 Oxamide, 669, 672 
 Oxatyl, 587 
 Oxazines, 768 
 Oxazoles, 764 
 Ox- gall, 756 
 Oxidation defined, 32 
 
INDEX. 
 
 857 
 
 Oxidation of tissue products, 823 
 Oxides, 302 
 
 indifferent, 49 
 
 types of, 302 
 Oxidising agent, 91 
 
 Oximes, 625 
 Oxindol, 679 
 Oxindole, 760 
 Oxy-acids, 94 
 Oxycalcium light, 48 
 Oxycellulose, 739 
 Oxygen, 31 
 
 blowpipe flame, 157 
 
 combustion in, 33 
 
 detected, 97 
 
 determined, 44, 521 
 
 extracted from air, 39, 74 
 
 identified, 15 
 
 liquefied, 73 
 
 positive and negative, 67 
 
 preparation, 38, 39 
 
 properties, 31 
 
 purification, 108 
 Oxyhaemoglobin, 755 
 Oxyhydrogen blowpipe, 48 
 Oxymorphiue, 778 
 Oxymuriatic acid, 177 
 Oxynaphthylamine, 665 
 Oxyphenic acid, 713 
 Ozokerite, 529 
 Ozone, 65 
 
 heat of formation, 66 
 Ozonisation by phosphorus, 67 
 Ozonised air, 65 
 
 oxygen, 66 
 Ozonising apparatus, 65 
 
 PAINT, blackened, 216 
 luminous, 368 
 
 Paintings, effect of light and air on, 216 
 Palladamine hydrochloride, 1509 
 Palladium, 509 
 Palmitic acid, 594 
 
 aldehyde, 583 
 Palmitin, 647 
 Palmitolic acid, 599 
 Palm oil, 797 
 Pancreatic juice, 822 
 Papaverine, 780 
 Paper, 737 
 
 action of nitric acid on, 739 
 for photographic printing, 236 
 Parabanic acid, 772 
 Parabin, 737 
 Para-compounds, 546 
 Paraconiine, 776 
 Paracresol, 712 
 Paracyanogen, 687 
 Paradiazine, 769 
 Paraffin, 527 
 
 hydrocarbons, 526 
 
 oil, 527 
 
 series, 526 
 
 wax, 529 
 Paraffins, iso- or secondary, 533 
 
 neo- or tertiary, 533 
 
 normal, 533 
 Paraformaldehyde, 581 
 Paraguay tea, 775 
 
 Paralactic acid, 604 
 Paraldehyde, 583 
 Parainucic acid, 622 
 Paranthracene, 554 
 Paratoluidine, 665 
 Pararosaniline, 723 
 Parchment, 797 
 
 paper, 738 
 
 size, 754 
 
 vegetable, 738 
 Paris yellow, 472 
 Parkes' process, 464 
 Parsley, essential oil of, 555 
 Partial pressures, law of, 314 
 
 saturation, method of, 588 
 Parting of gold, 233 
 Parvoline, 766 
 Passive state, 416 
 Patchouli, oil of, 555 
 Patent yellow, 472 
 Pattinsou's process, 463 
 
 oxy chloride, 471 
 Paviin, 744 
 Paving stones, 365 
 Pea iron ore, 396 
 Peachwood, 748 
 Pear flavouring, 644 
 Pearlash, 333 
 Pearl hardener, 368 
 Pearls, 120 
 Pearl-spar, 375 
 Pearl white, 440 
 Peat-bog, 159 
 Peat, composition of, 168 
 Pectic acid, 820 
 Pectin, 820 
 Pectose, 820 
 Pectosic acid, 820 
 Pelargonic acid, 594 
 
 ether, 644 
 
 Peuicillium glaucum, 621 
 Peutachlorobenzene, 540 
 Pentad elements, n 
 Pentamethylarsiue, 656 
 Pentamethylene, 539 
 
 diainine, 666 
 Pentaue, 533 
 Pentanes, isomeric, 533 
 Peutathionic acid, 238 
 Peutoses, 725 
 
 Pepper, essential oil of, 555 
 Peppermint, essential oil of, 557 
 Pepsin, 750 
 Peptones, 750 
 Perchloracetic ether, 643 
 Perch lorates, 187 
 Perchlorethaue, 189 
 Perchloric acid, 187 
 Perchlorinated ether, 631 
 Perchloronaphthalene, 552 
 Perchrornic acid, 433 
 Percussion cap composition, 707 
 
 fuse, 186, 188 
 Perfume ethers, 644 
 Perfumes, extraction of, 555 
 Periclase, 374 
 Pericline, 389 
 Periodates, 199 
 Periodic acid, 199 
 Periodic law, 301 
 
858 INDEX. 
 
 Periodic law, applications of, 304 
 Perlite, 414 
 Permanent ink, 492 
 
 white, 360 
 Permanganates, 428 
 Permanganic acid, 428 
 Perosmic anhydride, 510 
 Peroivskite, 456 
 Persulphates, 235 
 Persulphocyanic acid, 703 
 Persulphuric acid, 235 
 
 anhydride, 235 
 Perthiocyanogen, 703 
 Per-uranates, 437 
 Peruvian bark, 780 
 
 saltpetre, 337 
 Petalite, 358 
 Petchiney process, 348 
 Petrifying springs, 58 
 Petrol, 528 
 
 Petroleum, 144, 161, 528 
 ether, 528 
 oil, 528 
 spirit, 528 
 Pewter, 452 
 Pharaoh's serpent, 704 
 Phase rule, 315 
 Phellandrene, 556 
 Phenacetine, 711 
 Phenanthraquinone, 721 
 Pheuanthrene, 554 
 Pheuanthridiue, 768 
 Phenanthroline, 767 
 Phenaziue, 769 
 Phenetoi'l, 632 
 Phenic acid, 709 
 Phenol, 708 
 
 aquate, 710 
 
 blue, 718 
 
 properties of, 710 
 
 test for, 710 
 Phenols, 708 
 
 converted into hydrocarbons, 710 
 monohydric, 709 
 Phenolic acids, 608 
 
 general reactions for obtain- 
 ing, 608 
 Phenol-sulphonic acid, 709, 712 
 
 phthalein, 723 
 Phenoxazine, 768 
 Phenyl, 548 
 
 acetate, 644 
 
 acetic acid, 700 
 
 acetonitrile, 700 
 
 acetylene, 550 
 
 acrylic acid, 601 
 
 allyl alcohol, 572 
 
 amine, 662 
 
 aniline, 664 
 
 carbaniine, 701 
 
 carbinol, 571 
 
 chloride, 637 
 
 cyanide, 675, 700 
 
 dimethylpyrazolone, 764 
 
 ethylene, 550 
 
 ethyl ether, 632 
 
 formic acid, 600 
 
 glycocine, 675 
 
 glycollic acid, 609 
 
 glyoxylic acid, 627 
 
 Phenyl hydracrylic acid, 777 
 hydrate, 689, 709 
 hydrazine, 684 
 hydrosulphide, 710 
 imide-amide, 686 
 isocyanide, 701 
 mercaptan, 710 
 methyl ether, 631 
 
 pyrazolone, 764 
 orthophosphate, 710 
 phenol, 710 
 phenyl, 550 
 phosphine oxides, 655 
 phosphinee, 654 
 phosphonium iodides, 654 
 phosphoric acids, 710 
 salicylate, 645 
 sulphuric acid 641 
 Phenylene blue, 719 
 brown, 684 
 diamine, 666 
 Philosopher's wool, 377 
 Phlogistic theory, 176 
 Phlogiston, 176 
 Phloramine, 716 
 Phloretin, 744 
 Phlorizein, 744 
 Phlorizin, 715, 744 
 Phloroglucol, 715 
 Phlorol, 713 
 Phocenin, 799 
 Phorone, 625 
 Phosgene gas, 190 
 Phosphamides, 265 
 Phosphaniline, 654 
 Phosphates, 258 
 Phosphenyl chlorides, 655 
 Phosphenylic acid, 655 
 Phosphenylous acid, 655 
 Phosphides, 254 
 Phosphine, 262, 654 
 Phosphites, 259 
 Phosphobenzene, 655 
 Phosphodiamide, 265 
 
 glyceric acid, 647 
 molybdate of ammonium, 435 
 nitrile, 265 
 
 Phosphonium iodide, 263 
 Phosphor-bronze, 452 
 Phosphorescence, 251 
 Phosphoric acid, 256, 257, 258 
 
 glacial, 257 
 anhydride, 257 
 Phosphorised oil. 251 
 Phosphorite, 249, 256, 369 
 Phosphorous acid, 259 
 
 anhydride, 259 
 Phosphorus, 249 
 
 action of potash on, 262 
 
 of, on other elements, 254 
 allotropic varieties, 252, 253 
 amorphous, 252 
 and oxygen, 32 
 bases, 654 
 bromides, 264 
 burnt under water, 188 
 chlorides, 263 
 cyanide, 704 
 fluoride, 264 
 fuse composition, 255 
 
INDEX. 
 
 859 
 
 Phosphorus iodides, 264 
 
 match-bottle, 251 
 
 oxides, 255 
 
 oxychloride, 264 
 
 pentachloride, 263 
 
 red, 252 
 
 sources of, 249 
 
 suboxide, 260 
 
 sulphides, 264 
 
 sulphochloride, 264 
 
 tetroxide, 259 
 
 trichloride, 263 
 
 vitreous, 252 
 Phosphoryl chloride, 264 
 Phosphotriamide, 265 
 Phosphurets, 254 
 Phosphuretted hydrogen, 262 
 Photographic baths, silver recovered, 494 
 
 printing, 236, 495 
 Photo-reduction, 495 
 
 salts, 494 
 Phthalic acids, 617 
 
 anhydride, 617 
 Phthalide, 779 
 Phthalyl dichloride, 640 
 Phycite, 578 
 Phyllocyanin, 746 
 Phylloxanthiu, 746 
 Physical properties, 12 
 Physostigmiue, 783 
 Phytosterin, 757 
 Picnometer, 81 
 Picolines, 766 
 Picramic acid, 711 
 Picrates, 711 
 Picric acid, 709, 711 
 Picrotoxin, 745 
 Pig- iron, 399, 403 
 Pilocarpine, 783 
 Pimple metal (copper), 478 
 Piuacones, 575 
 Pine-apple flavouring, 644 
 Pinene, 557 
 Pink salt, 455 
 Pins, tinned, 451 
 Pipe clay, 384 
 Piperazine, 666, 769 
 Piperic acid, 611, 776 
 Piperidine, 766 
 Piperine, 766, 776 
 Piperonal, 586 
 Pipette, curved, 130 
 Pit charcoal, 114 
 Pitch-blende, 437 
 Plants, 793 
 
 action of, on carbon dioxide, 119 
 nutrition of, 816 
 Plaster of Paris, 367 
 Plate-powder, 369 
 Platiuamine, 508 
 Platinates, 506 
 Platinic chloride, 506 
 
 hydroxide, 506 
 iodide, 509 
 Platinicyanides, 697 
 Platinised asbestos, 98 
 Platinochlorides, 507 
 Platinocyanides, 697 
 Platinoid metals reviewed, 512 
 Platinous chloride, 508 
 
 Platinum, 504 
 
 amalgam, 498 
 ammonio-chloride, 508 
 arsenide, 509 
 black, 506 
 chlorides, 507 
 corroded, 245, 506 
 crucible heated, 277 
 cyanides, 697 
 fulminating, 507 
 ores, analysis, 512 
 
 treatment of, 504 
 oxides, 506 
 phosphide, 509 
 properties of, 505 
 spongy, 505, 506 
 stills, 228 
 sulphides, 509 
 tetrachloride, 507 
 Platosamine, 508 
 Pleonaste, 417 
 Plumbago, no 
 Plumbite, 467 
 Plumbous oxide, 467 
 Pneumatic trough, 135 
 Poison, cumulative, 471 
 Polarimeter, 543 
 Polarised light, 543, 788 
 Pole, negative and positive, 15 
 Pollux, 359 
 Polonium, 438 
 Polychroite, 747 
 Polyhalite, 375 
 
 Polyhydroxy-monobasic acids, 607 
 Polymeric, 533 
 Polymerides, 533 
 Polymerism, 533 
 Poplar, oil, of, 555 
 Populin, 743 
 Porcelain, 390 
 
 glazed, 391 
 painting, 391 
 Porous cell, 14, 26 
 Porphyry, 365, 389 
 Porter, 806 
 
 Porter-Clark process, 59 
 Portland cement. 366 
 
 stone, 365 
 Port wine crust, 807 
 
 effect of keeping, 807 
 Position-isomerism, 542, 544 
 Positive change, 310 
 
 pole, 14 
 
 Potash-albite, 389 
 Potash, 332 
 
 bichromate, 430 
 bulbs, 521 
 caustic, 333 
 red prussiate, 694 
 Potassamide, 105 
 Potassium, 332, 334 
 
 action on water, 20 
 antimonate, 443 
 autimonyl tartrate, 620 
 antimony oxalate, 613 
 arsenite, 270 
 aurate, 518 
 auricyanide, 697 
 aurocyauide, 697 
 bicarbonate, 333 
 
86o 
 
 INDEX. 
 
 Potassium bichromate, 430 
 bisulphate, 336 
 bitartrate, 333 
 blowpipe, test for, 335 
 bromate, 193 
 bromide, 336 
 
 calcium chromic oxalate, 613 
 carbethylate, 643 
 carbonate, 332 
 carbovinate, 643 
 chlorate, 184, 335 
 
 heat of decomposition, 
 
 186 
 
 chloride, 335 
 chlorochromate, 434 
 chromate, 431 
 chromic oxalate, 613 
 chromcyanide, 696 
 cobaltic nitrite, 422 
 cobalticyauide, 692 
 cobaltocyanide, 692 
 cyanate, 702 
 cyanide, 691 
 dichromate, 430 
 dimetantimonate, 443 
 ferric ferrocyanide, 693 
 ferricyanide, 694 
 ferrocyanide, 689 
 ferrous ferrocyanide, 694 
 ferrous oxalate, 613 
 fluoride, 205, 336 
 fulmiuurate, 708 
 guaiacol, 713 
 hydrate, 333 
 hydride, 335 
 hydroxide, 333 
 iodate, 199, 336 
 iodide, 199, 336 
 isethionate, 679 
 isocyanate, 702 
 isothiocyanate, 703 
 manganate, 428 
 mang-anicyanide, 696 
 manganocyanide, 696 
 metantimonate, 443 
 metastannate, 454 
 myronate, 705 
 nitrate, 337 
 nitrite, 100 
 nitroprusside, 696 
 oleate, 598 
 osmate, 511 
 osmiamate, 511 
 oxalates, 613 
 oxides, 335 
 perchlorate, 335 
 permanganate, 428 
 perosmate, 511 
 peroxide, 335 
 phenol, 710 
 phenyl-sulphate, 641 
 picrate, 711 
 platinochloride, 507 
 platinocyanide, 697 
 pyrosulphate, 337 
 quadroxalate, 613 
 saccharate, 622 
 silicofluoride, 285 
 sulphates, 233, 336 
 sulphides, 336 
 
 Potassium sulphocyanide. 703 
 tannate, 610 
 tartrate, 619 
 tartryl-antimonite, 620 
 test for, 51 
 thio-arsenite, 275 
 thiocyanate, 703 
 trichromate, 432 
 tri-iodide, 336 
 trithionate, 237 
 urate, 770 
 
 Potato, composition of, 803 
 spirit, 569, 808 
 starch, 803 
 
 extraction of, 803 
 Pottery, 390 
 Praseo-dymium, 394 
 
 cobalt salts, 423 
 Press cake, 340 
 Pressure of gases, 27 
 osmotic, 316 
 partial, law of, 314 
 Preston salts, 355 
 Primary compounds, 568 
 Producer, 163 
 Producer-gas, 162 
 Promethean light, 188 
 Proof spirit, 564 
 Propane, 531 
 
 constitution of, 527 
 Propargyl alcohol, 571 
 
 chloride, 637 
 Propene dichloride, 576 
 
 glycerol, 645 
 Propeptone, 750 
 Propine, 538 
 Propinyl alcohol, 571 
 Propiolic acid, 599 
 Propione, 624 
 Propionic acid, 593 
 Propionitrile, 699 
 Propyl alcohols, 569 
 aldehyde, 583 
 benzole acid, 601 
 carbinol, 569 
 hydride, 531 
 
 tetra-hydro-pyridine, 776 
 Propylene, 536 
 Propylic acid, 593 
 ether, 628 
 Protagon, 755 
 Proteids, 748 
 Protein, 748 
 
 Protocatechuic acid, 609 
 Proustite, 266 
 
 Proximate organic analysis, 793 
 Prussian blue, 686, 693 
 
 soluble, 693 
 green, 695 
 
 Prussiate of potash, 134, 689 
 Prussic acid, 687, 690 
 Pseudaconine, 783 
 Pseud aconitine, 783 
 Pseudobutylene, 536 
 Pseudocarbons, in 
 Pseudojervine, 783 
 Pseudonitrol, 569 
 Pseudosulphocyanogen, 703 
 Pseudourea, 671 
 Psilomelane, 426 
 
INDEX. 
 
 861 
 
 Ptomaines, 666, 749 
 Ptyalin, 735, 821 
 Puddled bars, 407 
 steel, 408 
 Puddling-, 404 
 Pulvis fulmiuans, 339 
 Pumice stone, 384 
 Purbeck stone, 366 
 Purine, 771 
 Purple of Cassius, 519 
 Purpureo-cobalt salts, 423 
 Purpurin, 721 
 Purree, 747 
 Pus, 754 
 
 Putrefaction, 119, 825 
 Putrescine, 666 
 Putty powder, 454 
 Pyrazine, 666 
 Pyrazoles, 764 
 Pyrazolidines, 765 
 Pyrazolidones, 765 
 Pyrazolines, 764 
 Pyrazolones, 764 
 Pyrene, 791 
 Pyridine, 766 
 
 bases, 766 
 
 carboxylic acid, 777 
 dicar boxy lie acid, 766 
 series, 777 
 Pyridones, 766 
 Pyrimidines, 768 
 Pyrites, arsenical, 266 
 
 burners, 226 
 
 capillary, 425 
 
 efflorescent, 224 
 
 extraction of sulphur from, 206 
 
 Fahlun, 242 
 
 iron, 396, 420 
 
 magnetic, 420 
 
 oxidation in air, 224 
 
 radiated, 420 
 
 spent, 478 
 
 white, 224, 420 
 Pyroacetic spirit, 625 
 Pyroarsenic acid, 271 
 Pyroboric acid, 246 
 Pyrocatechol, 609, 712 
 Pyrocitric acids, 616 
 Pyrocomenic acid, 622 
 Pyrog-allic acid, 715 
 Pyrogallin, 715 
 Pyrogallol, 610, 708, 715 
 
 -phthalein, 715 
 Pyroligneous acid, 590 
 
 ether, 566 
 Pyrolusite, 426 
 Pyromucic acid, 622 
 
 aldehyde, 586 
 Pyrone, 769 
 Pyrophoric iron, 136 
 Pyrophorus, lead, 467 
 Pyrophosphates, 258 
 Pyrophosphoric acid, 258, 260 
 Pyroracemic acid, 626 
 
 aldehyde, 626 
 Pyrosulphuric acid, 222 
 Pyrosulpimryl chloride, 190 
 Pyrotartaric acid, 615 
 Pyrotritartaric acid, 758 
 Pyroxanthin, 566 
 
 Pyroxylic spirit, 566 
 Pyroxylin, 739 
 Pyrro-azoles, 764 
 
 di:izole, 765 
 
 triazole, 765 
 Pyrrol, 759 
 
 -red, 759 
 Pyrrolidine, 759 
 Pyrrol ine, 759 
 Pyruvic acid, 626 
 
 QUADRATIC crystals, 52 
 Quadrivalent elements, n 
 Quartation of gold, 516 
 Quartz, 383 
 
 artificial, 279 
 Quassia, 745 
 Quassiin, 745 
 Quercetin, 745 
 Quercitannic acid, 611, 797 
 Quercitrin, 745 
 Quercitron, 795 
 Quicklime, 53, 364 
 Quicksilver, 495 
 Quinaldine, 767 
 Quinamine, 780 
 Quinazoline, 769 
 Quince oil, 644 
 Quinhydrone, 718 
 Quinic acid, 611, 717 
 Quinicine, 781 
 Quinidine, 781 
 Quinine, 780 
 
 amorphous, 781 
 sulphates, 781 
 Quinoidine, 781 
 Quinol, 714, 717 
 
 -dicarboxylJc acid, 718 
 Quinoline, 767 
 
 bases, 767 
 
 blue, 767 
 
 cyanine, 767 
 
 red, 767 
 
 yellow, 767 
 Quinolinic acid, 767 
 Quinone, 717 
 
 chlorimidea, 718 
 Quinones, 717 
 Quinonoid structure, 721 
 Quinotannic acid, 611 
 Quinoxaline, 769 
 Quinquivalent elements, n 
 
 RACEMATES, 621 
 
 Racemic acid, 620 
 
 Radiant matter spectroscopy, 330 
 
 Radicles, 94, 168, 524 
 
 alcohol, 568 
 
 alkyl, 593 
 
 aromatic, 548 
 
 basylous, 359 
 
 chlorous, 359 
 
 organic, 524 
 Radium, 438 
 Raffinose, 725 
 Raisins, 726 
 Rancid butter, 799 
 
 oils, 798 
 
 Raoult's method, 319 
 Rape-cake, 817 
 
862 
 
 INDEX. 
 
 Rare earths, 394 
 Rational feeding, 823 
 formulae, 524 
 Reactions, complete, 310 
 reversible, 309 
 Realgar, 274 
 Reaumur's porcelain, 372 
 Reciprocal combustion, 47 
 Rectified coal naphtha, 793 
 Rectified spirit, 564 
 Bed antimony ore, 445 
 
 copper ore, 474 
 
 dyes, 795 
 
 fire, 186 
 
 haematite, 396 
 
 lead, 468 
 
 lead ore, 432 
 
 ochre, 396 
 
 orpiment, 274 
 
 oxide of manganese, 426 
 
 paints, 503 
 
 precipitate, 498 
 
 prussiate of potash, 694 
 
 sanders-wood, 748 
 
 -shortness, 408 
 
 silver ore, 495 
 
 sulphide of antimony, 237, 445 
 
 zinc ore, 379 
 Redonda phosphate, 390 
 Reduced, 39 
 
 Reducing blowpipe flame, 156 
 Reduction by carbonic oxide, 136 
 
 on charcoal, 157 
 Refinery, iron, 404 
 Refraction equivalent, 787 
 of saltpetre, 337 
 Refractive power, 787 
 Refrigerator, Carre's, 81 
 Regenerative cooling, 73 
 
 heating, 167 
 Regular crystals, 52 
 Regulus, 476 
 
 of antimony, 441 
 Rennet, 752, 812 
 Resins, 560 
 
 Resists (calico-priiiting), 796 
 Resorcinol, 713 
 Resorcin-phthalein, 714 
 
 yellow, 684 
 Resorufine, 768 
 Respiration, 223, 821 
 Retene, 554 
 Retort, 6 1 
 
 Reverberatory furnace, 132 
 Reversed condenser, 575 
 Reversible reactions, 309 
 Reverted phosphate, 369 
 Rhamnose, 725 
 Rhamno-hexose, 727 
 Rhigolene, 528 
 Rhodium, 509 * 
 Rhombic crystals, 52 
 Ribose, 725 
 Rice, 803 
 
 Ricinoleic acid, 607, 799 
 Rinmann's green, 423 
 Rising of bread, 809 
 River-water, 54 
 Roasting, chlorinating, 478 
 meat, 815 
 
 Roasting sulphides, 217 
 Rochelle salt, 619 
 Rock crystal, 276 
 
 moss, 714 
 
 oil, 528 
 
 salt, 343 
 
 Roman cement, 366 
 Rosaniline, 722 
 
 acetate, 794 
 salts, 722 
 
 Roseo-cobalt salts, 423 
 Rosette copper, 478 
 Rosewood, oil of, 555 
 Rosiclers, 495 
 Rosin, 560 
 
 soap, 801 
 
 Rosindulenes, 769 
 Rosocyanin, 747 
 Rosolic acid, 723 
 Rotation of crops, 818 
 Rouge, 747 
 Ruberythric acid, 720 
 Rubidine, 766 
 Rubidium, 358 
 Rubijervine, 783 
 Ruby, 388 
 
 glass, 372 
 
 Rue, essential oil of, 594, 626 
 Rufigallic acid, 610, 721 
 Ruhmkorfl's induction-coil, 17 
 Rum, 808 
 Rust, 86, 416 
 
 -joint cement, 212 
 Rusty deposit in waters, 58 
 Ruthenic anhydride, 511 
 Ruthenium, 511 
 Rutic, aldehyde, 583 
 Rutile, 456 
 Rutin, 745 
 Rye-flour, 809 
 
 SACCH ABATES, 622 
 Saccharic acid, 622 
 Saccharides, 724 
 Saccharimeter, 788 
 Saccharine, 668 
 Safety-lamp, Davy's, 146 
 Safflower, 747 
 Saffron, 747 
 
 bronze, 436 
 Safranines, 769 
 Sagapenum, 714 
 Sago, 803 
 Salad oil, 798 
 Sal-alembroth, 500 
 
 ammoniac, 77, 356 
 Sal-gemme, 343 
 Saliciu, 743 
 Salicyl alcohol, 572 
 aldehyde, 585 
 chloride, 639 
 Salicylates, 608 
 Salicylic acid, 608 
 
 aldehyde, 585 
 
 chloride, 639 
 Saligenin, 743 
 Saline waters, 61 
 Salipyrine, 765 
 Saliretin, 743 
 Saliva, 821 
 
INDEX. 
 
 Salol, 645 
 Sal-polychrest, 336 
 prunelle, 338 
 volatile, 356 
 Salt as manure, 818 
 cake, 345 
 common, 343 
 defined, 37 ^ 
 
 electrolysis of, 349 
 -gardens of Marseilles, 344 
 -glazing, 392 
 of lemons, 613 
 of sorrel, 613 
 of tartar, 619 
 Salting of meat, 815 
 Saltpetre, 337 
 
 as manure, 817 
 cubical, ^338 
 -flour, 338 
 impurities in, 338 
 made from sodium nitrate, 337 
 prismatic, 338 
 properties, 338 
 refining, 338 
 tests of purity, 338 
 Salt-radicles, 205 
 Salts, acid, 104 -" 
 basic, 104 
 
 classification of, 104 
 constitution of, 104 
 double, 104 
 
 electrolysis of, 324^^-^" 
 haloid, 205 
 iron of, 419 
 normal, 104 
 Samarskite, 394 
 Sand, 276 
 
 Sandarach resin, 560 
 Sandemeyer's reaction, 681 
 Sandstone, 365 
 
 Cratgleith, 365 
 Santalin, 747 
 Santonic acid, 745 
 Santonin, 745 
 Sap of plants, 819 
 Saponification by steam, 802 
 
 sulphuric acid, 802 
 of ethereal salts, 641 
 theory of, 802 
 Saponin, 745 
 Sappan wood, 748 
 Sapphire, 388 
 Sarcine, 774 
 Sarcolactic acid, 604 
 Sarcosine, 675 
 Sassafras nuts, 594 
 Satin spar, 363 
 Saturated compounds, 136 
 
 hydrocarbons, 526 
 solution, 50 
 
 Savin, essential oil of, 555 
 Saxony blue, 762 
 Scale, boiler, 57 
 Scarnmony, 745 
 Scandium, 394 
 Scarlet dyes, 795 
 Scheele's green, 270, 485 
 Scheelite, 436 
 Schlippe's salt, 446 
 Schultze's pomler, 742 
 
 863 
 
 Schweitzer's reagent 778 
 Scotch pebbles, 27 6 
 Scott's cement, 367 
 Scrubber, 791 
 Scurvy-grass, oil of, 706 
 Seal oil, 799 
 Sea- water, 61 
 
 extraction of salts from, 344 
 weed, 817 
 Sebacic acid, 598 
 Secretion, 823 
 Sedative salt, 245 
 Seeds, composition, 804 
 germination, 804 
 Seignette's salt, 619 
 Sel d'or, 518 
 
 Selective absorption, 780 
 Selenic acid, 243 
 Selenides, 243 
 Selenietted hydrogen, 247 
 Selenite, 367 
 Selenium, 242 
 
 dioxide, 243 
 Selenophen, 758 
 Self-burning gas, 156 
 Self-reduction, 460 
 Sellaite, 205 
 Seltzer water, 61, 120 
 Semidine nigration, 685 
 Semi- water gas, 163 
 Senarmontite, 442 
 Separating funnel, 143 
 Sericin, 754 
 Serin, 754 
 Serpentine, 375 
 Serum, 813 
 
 albumin, 750 
 Sesqui-terpenes, 556 
 Shaft, downcast and upcast, 126 
 Shale oils, 529 
 Shamoying, 797 
 Shear steel, 412 
 
 Sheep-dipping composition, 270 
 Shell-lac, 560, 748 
 Sherry, 808 
 Shoddy, 738 
 Shot, 466 
 
 Sicilian sulphur, 207 
 Side-chains, 550, 551 
 Siderite, 418 
 Siemen's regenerative furnace, 167 
 
 -Martin steel, 409 
 Sienna, 384 
 
 Signal-light composition, 274 
 Silica, 276 
 
 amorphous, 279 
 crystalline, 278 
 
 dissolved by hydrofluoric acid, 293 
 gelatinous, 278 
 Silicated soap, 801 
 Silicates, 280 
 
 aluminium of, 389 
 Silicic acid, 278 
 
 ether, 642 
 Silicium, 281 
 Silico-acetic acid, 654 
 
 acetylene, 282 
 chloroform, 283 
 nonane, 653 
 nonyl-alcohol, 653 
 
864 
 
 INDEX. 
 
 Silico-acetic propionic acid, 654 
 Silicon, 276, 281 
 
 alkides, 653 
 
 amorphous, 281 
 
 carbide, 282 
 
 chloride, 282 
 
 disulphide, 285 
 
 ethide, 653 
 
 ethylates, 653, 654 
 
 fluorides, 283 
 
 graphitoid, 281 
 
 hydride, 282 
 
 methide, 653 
 
 nitride, 282 
 
 organic compounds of, 653 
 
 tetrabromide, 283 
 Silicone, 282 
 Silk-gelatin, 754 
 Silver, 487 
 
 acetamide, 668 
 acetate, 591 ^' 
 acetylide, 140, 537 
 allotropic, 491 
 amalgam, 498 
 amalgamation process, 489 
 ammonio-nitrate, 493 
 arsenate, 495 
 arsenite, 270, 495 
 bromide, 494 
 carbonate, 493 
 chlorides, 493 
 chromates, 432 
 cleaned, 215 
 coin, 489 
 colloidal, 490 
 crucibles, 491 
 cyanide, 696 
 dendritic, 488 
 detected in lead, 464 
 extracted by amalgamation, 488 
 from copper ores, 488 
 
 lead, 463 
 ferricyanide, 695 
 ferrocyanide, 695 
 fluoride, 495 
 frosted, 489 
 fulminate, 708 
 fulminating, 492 
 fusing-point, 491 
 glance, 495 
 hallides, 494 
 hypouitrite, 103, 493 
 hyposulphite, 236 
 iodide, 199, 494 
 meconate, 622 
 metaphosphate, 258 
 native, 488 
 nitrate, 492 
 nitride, 492 
 nitrite, 493 
 ore, red, 495 
 
 orthophosphate, 258, 495 
 oxalate, 613 
 oxides, 492 
 oxidised, 489 
 paracyanide, 696 
 periodate, 199 
 phosphate, 494 
 photo-salts, 494 
 plate, 490 
 
 Silver, pure, preparation of, 491 
 
 pyrophosphate, 258 
 
 refining, 464 
 
 solder, 489 
 
 sprouting of, 491 
 
 standard, 489 
 
 sub-chloride, 493 
 
 sulphantimomite, 495 
 
 sulpharsenite, 495 
 
 sulphates, 495 
 
 sulphide, 495 
 
 sulphite, 495 
 
 tarnished, 215 
 
 tartrate, 620 
 
 thiosulphate, 236 
 
 tree, 498 
 Silvering, 490 
 Simple solution, 49 
 Sinamiue, 705 
 Siphon eudiometer, 44 
 Size, 754 
 Skatole, 760 
 Skraup's method, 767 
 Slag blast-furnace, 400 
 iron -refinery, 405 
 lead-furnace, 461 
 ore-furnace, 476 
 puddling-f urnace, 407 
 refinery (copper), 476 
 roaster (copper), 477 
 Slaked lime, 364 
 Slaking' of lime, 53, 364 
 Slate, 384 
 Slow port fire, 339 
 Smalt, 422 
 Smelling-snlts, 355 
 Smelting tin stone, 448 
 SmitJisonite, 380 
 Smoke, 159 
 Smokeless gas burners, 154 
 
 powder, 339 
 Smut, 485 
 Snow, 63 
 Snuff, 777 
 Soap, 800 
 
 arsenical, 270 
 
 Castile, 801 
 
 glassmaker's, 372 
 
 mottled, 801 
 
 white curd, 596 
 
 yellow, 801 
 Soda, 348 
 
 action on hard waters, 59 
 
 ash, 346 
 
 caustic, 348 
 
 -lime, 521 
 
 -lye, 348 
 
 manufacture, 345 
 
 washing, 348 
 
 -waste, 315 
 
 -water, 127 
 Sodacetic ether, 643 
 Sodamide, 105 
 
 Sedium potassium tartrate, 619 
 Sodium, 343, 350 
 
 acetate, 592 
 acetylide, 537 
 action on water, 20 
 aluminate, 388 
 amalgam, 85 
 
INDEX. 
 
 Sodium, ammonium racemate, 621 
 
 and oxygen, 36 
 
 anthrapurpurate, 720 
 
 antimonites of, 442 
 
 arsenates, 352 
 
 arsenite, 270 
 
 aurocliloride, 518 
 
 bicarbonate, 348 
 
 borate, 352 
 
 carbonates, 348 
 
 Castner's process, 350 
 
 chlorate, 354 
 
 chloride, 351 
 
 dichromate, 431 
 
 equivalent weight, 20 
 
 ethoxide, 564 
 
 extraction, 350 
 
 fluoride, 351 
 
 fulminate, 708 
 
 glycol, 574 
 
 hydride, 351 
 
 hydrosulphite, 237 
 
 hydroxide, 348 
 
 hypochlorite, 184 
 
 hypophosphite, 260 
 hyposulphite, 352 
 line in spectrum, 329 
 man gam te, 428 
 metaphosphate, 259 
 methoxide, 627 
 nitrate, 353 
 nitride, 107 
 nitrite, 353 
 nitromethane, 707 
 nitroprusside, 695 
 oleate, 598 
 oxalate, 613 
 palmitate, 801 
 pentasulphide, 237 
 periodate, 199 
 permanganate, 429 
 peroxide, 351 
 phenol, 710 
 phenoxide, 709 
 phosphate, 352 
 platinate, 507 
 platiuochloride, 507 
 potassium alloy, 350 
 propenoxides, 577 
 pyroborate, 352 
 pyrophcsphate, 352 
 pyrosulphate, 351 
 silicates, 353 
 sodiolactate, 604 
 stannate, 453 
 stannite, 453 
 stearate, 596 
 sulphantimonate, 215 
 sulpharseniate, 215 
 sulphates, 351 
 sulphides, 351 
 sulphite, 221, 351 
 sulphostannate, 217 
 tetrathionate, 237 
 thiochromite, 434 
 thiophosphate, 352 
 thiosulphate, 352 
 tungstate, 436 
 urate, 770 
 zirconate, 458 
 
 865 
 
 Soffioni, 246 
 Softening waters. 59 
 Soft soap, 598, 801 
 
 water, 55 
 
 Soils, absorptive power of, 816 
 carbonic acid in, 81 
 formation of, 817 
 impoverished, 817 
 iron in, 417 
 Solanine, 778 
 Solder, 452 
 
 brazier's, 452 
 silversmith's, 490 
 Soluble glass, 353 
 Solution, 50, 316 
 Solutions, freezing-points of, 320 
 isetonic, 318 
 nature of, 316 
 saline, 321 
 solidified, 451 
 vapour pressure of, 320 
 Solvay's process, 346 
 Sombrerite, 369 
 Soot, 159 
 
 as manure, 818 
 Sorbic acid, 599 
 Sorbitol, 579 
 Sorrel, salt of, 613 
 Sovereign, 515 
 Sozoidol, 712 
 Spanish black, in 
 Sparkling wines, 127 
 Sparteine 777 
 Spathic iron ore, 396, 418 
 Specific gravity of gases, 24, 31, 293 
 liquids, 63, 81 
 solids, 63 
 
 heat and atomic weight, 297 
 refractive power, 787 
 rotatory power, 788 
 volume, 786 
 Spectroscope, 328 
 
 use of, 329 
 Spectroscopy, 328 
 Spectrum analysis, 329 
 Specular iron ore, 417 
 Speculum metal, 452, 481 
 Speiss, 422 
 Spelter, 379 
 Spent oxide, 478, 792 
 Spermaceti, 799 
 Sperm oil, 799 
 Spheroidal state, 219 
 Spices, preservative effect of, 824 
 Spiegeleisen, 403 
 Spinelle, 388 
 Spirit, methylated, 565 
 of hart's horn, 81 
 of salt, 169 
 of turpentine, 555 
 of wine, 563 
 proof, 564 
 Spirits, 807 
 Spiritus rectificatus, 564 
 
 tenuior, 564 
 Spodumene, 358 
 Spongin, 754 
 Spongy platinum, 504 
 Spontaneous combustion, 33 
 Sprengel's pump, 70 
 
 31 
 
866 INDEX. 
 
 Springs, petrifying, 58 
 Spring water, 55, 127 
 Sprouting- of stiver, 491 
 Stalactites and stalagmites, 58 
 Standard gold, 516 
 Stannates, 453 
 Stannic acid, 454 
 
 anhydride, 453 
 arsenate, 456 
 bromide, 455 
 chloride, 455 
 ethide, 657 
 nitrate, 454 
 oxide, 453 
 phosphate, 456 
 sulphate, 456 
 sulphide, 455 
 Stannous chloride, 454 
 ethide, 657 
 nitrate, 454 
 oxide, 453 
 sulphide, 455 
 Star antimony, 441 
 Starch, 734, 803 
 
 animal, 736 
 cellulose, 735 
 commercial, 734 
 extraction, 734 
 iodised, 198 
 manufacture of, 802 
 soluble, 735 
 -sugar, 726 
 varieties of, 735, 803 
 Stassfurtite, 375 
 Stavesacre, 783 
 
 Steam, composition by volume, 45 
 decomposed by c:irbon, 134 
 chlorine, 174 
 electric sparks, 17 
 heat, 1 8 
 
 heat of formation of, 307 
 latent heat of, 307 
 specific gravity calculated, 63 
 Stearates, 596, 644 
 Stearic acid, 595 
 
 aldehyde, 583 
 Stearin, 595. 647 
 
 caudles, 596 
 Stearolic acid, 599 
 Steatite, 373 
 Steel, 397 
 
 annealing, 413 
 Bessemer, 410 
 blistered, 412 
 cast, 413 
 crucible, 413 
 
 distinguished from iron, 41 
 hard, 404, 410 
 hardening, 410 
 influence of impurities, 415 
 manufacture, 410 
 mild, 404, 409 
 properties of, 413 
 shear, 412 
 tempering, 414 
 tungsten in, 415 
 Whitworth's, 413 
 Stereochromy, 353 
 Stereo-isornerides, 605 
 Stereo-isomerism, 604, 620, 730 
 
 Stereotype metal, 439 
 Sterro-metal, 482 
 Stibines, 656 
 Stibiopentamethyl, 656 
 Stibiotriethyl, 656 
 Stibiotrimethyl, 656 
 Stibnite, 441 
 Stilbeue, 551 
 Still, 61 
 
 Stone, artificial, 354 
 -coal, 160 
 decayed, 366 
 preservation of, 366 
 test of durability, 365 
 -ware, 392 
 Storax, 561, 645 
 Stout, 806 
 Straits tin, 449 
 Stramonium, 777 
 Stream tin ore, 447 
 Sti*ontia, 362 
 
 -process for sugar-refining, 731 
 Strontianite, 362 
 Strontium, 362 
 
 carbonate, 362 
 chloride, 362 
 dioxide, 362 
 hydroxide, 362 
 minerals, 362 
 nitrate, 362 
 sulphate. 362 
 sulphide, 362 
 
 Structural formulae, 102, 524 
 Strychnic acid, 782 
 Strychnine, 782 
 
 methylium hydroxide, 782 
 Strychnos alkaloids, y 8 c 
 Stubb, 555 
 Stucco, 367 
 Stupp, 555 
 Styphnic acid, 714 
 Styracin, 645 
 Styrolene, 550 
 Suberic acid, 615 
 Sublimate, corrosive, 499 
 Sublimation, 78 
 Sublimed sulphur, 208 
 Substantive dyes, 683 
 Substitution-products, 527 
 
 rules concerning, 547 
 Succinamic acid, 672 
 Succiuamide, 669 
 Succiuic aciil, 614, 672 
 anhydride, 614 
 series of acids, 570, 611 
 Succiuimide, 669 
 Succino-dialdoxime, 759 
 Succinyl dichloride, 639 
 Succussion, 228 
 Sucrates, 732 
 Sucrose, 731 
 Sucrotetrauitrate, 733 
 Suet, 648, 799 
 Sugar, 731 
 
 artificial, 727 
 barley, 732 
 beetroot, 731 
 -candy, 731 
 cane, 726, 731 
 compounds of, 732 
 
INDEX. 
 
 867 
 
 Sugar extraction, 731 
 -lime, 732 
 loaf, 731 
 maple, 731 
 of flesh, 716 
 of fruits, 725 
 of gelatine, 675 
 of lead, 592 
 of manna, 578 
 of milk, 727, 733, 812 
 refining, 731 
 starch, 726 
 synthesis of, 728 
 uncrystallisable, 731 
 Sugars, 724 
 
 constitution of, 727 
 isomerism among, 730 
 synthesis of, 728 
 Suint, 333, 795 
 Sulphamylic acid, 629 
 Sulphanilic acid, 664 
 Sulphonal, 626 
 Sulpharsenntes, 275 
 Sulphates, 206 
 Sulphethylates, 641 
 Sulphethylic acid, 535, 628, 641 
 Sulphides, 206 
 
 action of air on, 217 
 formation of, 212 
 Sulphindigotic acid, 175, 762 
 Sulphindylic aciJ, 762 
 Sulphines, 573 
 Sulphiuic acids, 648 
 Sulphites, 221 
 Sulpho- See also Thio 
 Sulphobenzide, 710 
 
 carbonates, 240 
 carbonic acid, 240 
 cyanic acid, 703 
 cyanides, 703 
 glyceric acid, 646 
 methylates, 641 
 inetbylic acid, 641 
 palmitic acid, 802 
 phosphotriamide, 265 
 stearic acid, 802 
 urea, 671 
 
 vinic acid, 535, 641 
 Sulpholeic acid, 802 
 Sulphonal, 626 
 Sulphouamides, 668 
 Sulphones, 573 
 Sulphonic acids, 648 
 Sulphur, 206, 479 
 -acids, 217 
 action of alkalies on, 216 
 
 lime on, 217 
 alcohols, 572 
 allotropic states of, 212 
 amorphous or insoluble, 210 
 and oxygen, 34 
 bases, 217 
 chlorides, 241, 242 
 dimorphous, 210 
 dioxide, 218 
 distilled, 208 
 ductile, 210 
 electro-negative, 210 
 positive, 210 
 extraction, 207 
 
 Sulphur, extraction from soda-waste ^7 
 
 flowers of, 208 
 
 iodides, 242 
 
 milk of, 209 
 
 occurrence in nature, 206 
 
 octahedral, 211 
 
 ores, 206 
 
 oxides, 218 
 
 plastic, 210 
 
 prismatic, 211 
 
 properties, 209 
 
 recovered, 347 
 
 refining, 208 
 
 roll, 208 
 
 rough, 208 
 
 -salts, 217 
 
 sesquioxide, 235 
 
 sublimed, 208 
 
 trioxide, 222 
 
 uses, 209 
 
 vapour density, 213 
 Sulphureous waters, 61 
 Sulphuretted hydrogen, 213 
 Sulphuric acid, 223 
 
 action on copper, 218 
 fats, 802 
 metals, 233 
 organic matters, 
 
 anhydro-, 223 
 anhydrous, 222 
 composition of, 233 
 concentration, 228 
 dihydrated, 232 
 diluted, turbidity of, 232 
 distillation of, 228 
 fuming, 223 
 glacial, 232 
 
 heat evolved in diluting, 232 
 manufacture, 225 
 
 by contact pro- 
 cess, 229 
 
 monobydrated, 232 
 Nordhausen, 223 
 solidified, 232 
 anhydride, 222 
 ether, 628 
 
 Sulphuring casks, 220 
 Sulphurous acid, 219 
 
 properties, 219 
 anhydride, 218 
 Sulphuryl, 221 
 
 chloride, 221 
 Sumach, 611, 797 
 Superphosphate of lime, 369 
 Supersaturated solutions, 51 
 Swedish iron ore, 396 
 Sweet oil, 798 
 
 spirit of nitre, 642 
 Syenite, 389 
 Sylvestriue, 556 
 Symbols, 4, 9 
 
 Symmetrical substitution-products, 546 
 Sympathetic ink, 53, 422 
 Synaptase (emulsiu), 584 
 Synthesis, 6 
 
 of acids of the acetic series, 587 
 organic compounds, 141, 539 
 water, 42 
 Syntonin, 750 
 
868 
 
 INDEX. 
 
 TABASHEER, 277 
 Tagilite, 485 
 Talc, 373 
 Tallow, 648, 799 
 Taloses, 727 
 Tank liquor, 349 
 
 waste, 345 
 Tannates, 610 
 Tannic acid, 610 
 Tannin, 611 
 Tanning-, 797 
 Tantalite, 447 
 Tantalum, 447 
 Tap-cinder, 407 
 Tapioca, 803 
 
 coal, 791 
 Tartar, 618 
 
 -emetic, 442, 620 
 salt of, 619 
 Tartaric acid, 619 
 
 anhydride, 619 
 
 properties of, 619 
 
 salts of, 619 
 Tartralic acid, 619 
 Tartrates, 619 
 Tartrazine, 765 
 Tartronic acid, 617 
 Tartronyl urea, 771 
 Tartryl antim onions acid, 620 
 
 antimonites, 620 
 Taurine, 679, 757 
 
 synthesis of, 679 
 Taurocarbamic acid, 679 
 Taurocholic acid, 756, 822 
 Tautomerism, 701 
 Tawing, 797 
 Tea, composition, 810 
 Teeth, artificial, 368 
 Telluretted hydrogen, 244 
 Telluric acid, 244 
 Tellurides, 244 
 Tellurium, 243 
 Tellurous acid, 244 
 Temper spoilt, 414 
 Tempering, colours in, 414 
 Tenacity of iron, 397 
 Tennantite, 266 
 Terbia, 394 
 Terebenthene, 557 
 Terephthalic acid, 617 
 Terne plate, 450 
 Terpenes, 555, 556 
 Terpiuene, 556 
 Terpineol, 559 
 Terpin hydrate, 559 
 Terpinolene, 556 
 Terra japonica, 609 
 Tertiary alcohols, 568 
 
 amines, 658 
 
 benzene ring, 716 
 
 butyl alcohol, 568 
 Test-tube, 40 
 Tetrachlorether, 631 
 Tetrachlorobenzene, 540 
 
 ethylene, 190 
 hydroquinone, 718 
 methane, 530 
 quinone, 718 
 Tetrad elements, 12 
 Tetrahydric alcohols, 577 
 
 Tetrahydropyrazoles, 765 
 
 hydroxy-anthraquinoue, 721 
 Tetramethyl-alloxantin, 775 
 
 -ammonium hydroxide, 661 
 
 iodide, 659 
 arsonium hydroxide, 656 
 
 iodide, 656 
 benzene, 549 
 methane, 533 
 murexide, 775 
 stiboniuin hydroxide, 656 
 thiouine, 768 
 
 Tetramethoxyben zylisoquinoliue, 780 
 Tetramethylenindde, 759 
 Tetrathionic acid, 237 
 Tetratomic molecules, 300 
 Tetrazines, 768 
 Tetrazodiphenyl, 684 
 Tetrazole, 765 
 Tetrethyl ammonium hydroxide, 662 
 
 iodide, 662 
 Tetrethylium hydroxide, 662 
 
 iodides, 662 
 Tetrethyl-phosphouium hydroxide, 654 
 
 iodide, 654 
 Tetrolic acid, 599 
 Tetroses, 725 
 Thalleiochin, 781 
 Thalliue, 767 
 Thallium, 473 
 
 eth oxide, 564 
 Thebaine, 779 
 Thebeuine, 780 
 Theine, 775 
 Thenard's blue, 423 
 Thenardite, 351 
 Theobromine, 754 
 Thennochemical data, 305 
 
 determination of, 306 
 application of, 308 
 Thermochemistry, 305 
 Thiazines, 768 
 Thiazoles, 764 
 Thio-acetic acid, 593 
 -alcohols, 572 
 aldehydes, 583 
 antimonates, 446 
 arsenates, 275 
 arsenites, 275 
 azoles, 764 
 carbamic acid, 672 
 carbamide, 671 
 carbanilide, 672 
 carbimides, 703, 705 
 carbonates, 240 
 chromites, 434 
 cyanic acid, 702 
 cyanates, 703 
 cyanogen compounds, 701 
 diphenylamiue, 768 
 ether, 573 
 ethoxides, 572 
 phenol, 710 
 
 phosphoryl chloride, 264 
 resorcinol, 714 
 sulphates, 235 
 sulphuric acid, 235 
 Thionic acids, 237 
 Thionine, 768 
 Thionyl, 221 
 
INDEX. 
 
 Thionyl chloride, 221 
 Thiophen, 758 
 Thiophosphates, 264 
 Thio-stannates, 456 
 Thio-sulphuric acid, 235 
 Thomas-Gilchrist process, 410 
 
 slag, 818 
 Thoria, 458 
 Thorium, 458 
 Thorite, 458 
 Thulia, 394 
 
 Thyme, essential oil of ccc 
 Thymol, 712 
 Tiglic acid, 597 
 Tile copper, 476 
 Tiles, 392 
 Tin, 447 
 
 alkides, 657 
 alloys of, 451 
 amalgam, 498 
 binoxide, 453 
 bisulphide, 455 
 boiling, 454 
 chlorides of, 454 
 crystals, 454 
 dichloride, 454 
 dimethyl iodide, 657 
 disulphide, 455 
 dropped, 449 
 foil, 449 
 grain, 449 
 grey, 450 
 hexethide, 657 
 impurities, 452 
 metallurgy of, 448 
 nitromuriate. 455 
 ores, 447 
 oxides, 453 
 oxychloride, 454 
 plate, 450 
 properties of, 449 
 protochloride, 454 
 protosulphide, 455 
 protoxide, 453 
 pure, 449 
 
 purification of, 449 
 pyrites, 456 
 salts, 454 
 sesquioxide, 454 
 spots, 452 
 stannate, 454 
 stone, 447 
 sulphides of, 455 
 tetrachloride, 455 
 tetramethide, 657 
 tetrethide, 657 
 -tree, 455 
 
 trimethyl-iodide, 657 
 Tincal, 245, 352 
 Tinned iron, 450 
 Tinning brass, 451 
 
 copper, 450 
 Tinwhite cobalt, 421 
 Titanic acid, 456 
 iron, 396 
 oxide, 456 
 Titanium, 456 
 
 salts, 457 
 Toast, 736 
 Tobacco, 777 
 
 869 
 
 Tokay, 808 
 
 Tolane, 555 
 
 Tolidine, 685 
 
 Tolu, essential oil of, ccc 
 
 Toluene, 549 
 
 Toluic acid, 601 
 
 Toluidines, 665 
 
 Tolusafrauine, 769 
 
 Toluylene, 551 
 
 reds, 760 
 Tolyl, 548 
 
 diphenylmethanc, 722 
 Tolypyrine, 765 
 Tonka- bean. 611 
 Topaz, 205, 388 
 Torbane-hill mineral, 516 
 Touch-paper, 339 
 Touch-stone, 93 
 Toughening steel, 413 
 Tourmaline, 205 
 
 artificial, 781 
 Tous-les-mois, 735 
 Toxiues, 666 
 Transition-point, 315 
 
 of iron, 414 
 Trap-rock, 389 
 Treacle, 731 
 Tree-wax, 799 
 Trehalose, 734 
 Triacetin, 648 
 Triad elements, 12 
 Triallyl melamine, 705 
 Triamidotolydiphenyl carbinol, 721 
 Triamidotriphenylmethane, 722 
 Triamines, 658 
 Triaziues, 768 
 Triazoacetic acid, 680 
 Treborethyl, 653 
 Tribromauilines, 664 
 Tribromhy driu, 636 
 Tribromophenol, 710 
 Tributyrm, 648 
 Tricarballylic acid, 623 
 
 aniline, 664 
 Trichlorhydriu, 636 
 Trichlorobenzene, 540 
 
 hydroquiuone, 718 
 propane, 636 
 puriue, 771 
 pyrogallol, 715 
 quinone 718 
 Triclinic crystals, 52 
 Tricyanhydrin, 623 
 Triethylamine, 662 
 arsine, 273 
 phosphiue, 654 
 stibine, 656 
 
 Triethylene diamine, 666 
 Trigonal crystals, 52 
 Trihydric alcohols, 575 
 Trihydroxy-anthraquinone, 721 
 benzene, 715 
 benzoic acids, 609 
 triphenyl-carbiuol, 723 
 methane, 722 
 Tri-iodo-methane, 636 
 Trilauriu, 648 
 Trimesic acid, 624 
 Trimethylamine, 659, 661 
 arsine, 655 
 
8;o 
 
 INDEX. 
 
 Trimethylstibine, 656 
 
 vinyl ammonium hydroxide, 666 
 Trinitro-cellulose, 724 
 phenol, 711 
 phloroglucol, 716 
 resorcin, 714 
 
 Trinitrosophloroglucol, 716 
 Triolein, 648 
 Trioses, 725 
 Tripalmitin, 648 
 Triphane, 358 
 Triphenylamine, 665 
 Triphenylglyoxaline, 765 
 Triphenylmethane, 551 
 
 carboxylic acid, 722 
 dyestuffs, 721 
 rosaniline, 723 
 Triple phosphate, 375 
 Trithionic acid, 237 
 Trivalent elements, n 
 Trona, 348 
 Tropic acid, 777 
 Tropine, 777 
 Tungstates, 436 
 Tungsten, 436 
 Tungstic acid, 436 
 
 hydrated, 436 
 Tungstoborates, 436 
 Tunicin, 743 
 Turacine, 474 
 
 Turbith or turpeth mineral, 499 
 Turkey red, 795 
 Turmeric, 747 
 
 action of boric acid on, 247 
 Turn bull's blue, 695 
 Turner's yellow, 472 
 Turpentine, 555 
 
 action of nitric acid on, 93 
 hydrocarbons, 555 
 in chlorine, 175 
 Turpethin, 745 
 Turquoise, 390 
 Tuyere pipes, 397 
 Type furniture alloy, 463 
 metal, 399, 453, 466 
 Types of chemical compounds, 168 
 Typical oxides, 302 
 Tyrosin, 678 
 Tyrotoxicon, 68 1 
 
 ULMIC acid, 739, 817 
 Ultramarine, artificial, 390 
 green, 390 
 yellow, 432 
 Unit of heat, 44 
 
 volume and weight, 10, 12 
 Umbelliferone, 714 
 Umber, 384 
 Unsaturated compounds, 136 
 
 hydrocarbons, 534 
 Upcast shaft, 126 
 Urainil, 772 
 Uranium, 437 
 Uranyl, 437 
 U rates, 770 
 Urea, 669 
 
 artificial formation, 670 
 
 derivatives of, 671 
 
 extraction from urine, 670 
 
 hydrochloride, 670 
 
 Urea nitrate, 670 
 oxalate, 670 
 Ureas, compound, 671 
 Ureides, 671, 771 
 Urethane, 672 
 Uric acid, 769 
 
 action of nitric acid on, 771 
 
 synthesis of, 773 
 Urine, composition, 815 
 Uroxanic acid, 773 
 Uvinic acid, 758 
 Uvitic acid, 758 
 
 VACUUM-PANS, 731 
 vessel, 73 
 Valency, n, 297 
 Valentinite, 442 
 Valerian, essential oil of, 555 
 
 root, 594 
 
 Valerianic acid, 594 
 Valeric acid, 594 
 
 aldehyde, 583 
 Valerin, 799 
 Vanadic acid, 446 
 Vanadium, 446 
 Vanillic acid, 609 
 Vanillin, 745 
 Van't Hoff's law, 318 
 Vapour-densities, 292 
 
 density determined, 293 
 
 pressure of solutions, 320 
 Varnishes, 560 
 Vaseline, 529 
 Vegetable brimstone, 148 
 
 colouring-matters, 746 
 parchment, 738 
 Vegetation, chemistry of, 816 
 Velocities of molecules, 25, 291 
 Venetian red, 417 
 Venice turpentine, 555 
 Ventilation, 125 
 Veratralbine, 783 
 Veratric acid, 713 
 Veratrine, 783 
 Veratrol, 713 
 Verdigris, 592 
 Verditer, 484 
 Vermilion, 503 
 Vert de Guignet, 433 
 Vesta matches, 188 
 Victoria orange, 712 
 Victor Meyer's apparatus, 293 
 Vinasses, 66 1 
 Vinegar, composition of, 591 
 
 manufacture, 590, 591 
 Vinyl alcohol, 570 
 chloride, 635 
 Violet bronze, 436 
 
 Lauth's, 768 
 Viridine, 766 
 Viscose, 738 
 
 Viscous fermentation, 737, 806 
 Vitriol, 231 
 
 chambers, 226 
 Vivianite, 419 
 Volcanic ammonia, 352 
 Volt, 325 
 Voltameter, 43 
 Volumes, law of, 289 
 
 standard, 10, 292 
 
INDEX. 
 
 8 7 I 
 
 Vulcanised rubber, 558 
 Vulcanite, 558 
 
 Wad, 426 
 
 Walls, efflorescence on, 392 
 
 Wash leather, 797 
 
 Watch-spring burnt in oxygen, 37 
 
 Water, 42 
 
 action on metals, 21 
 analysis, 60, 73 
 chemical relations of, 49 
 decomposed by battery, 13 
 
 heat, 1 8 
 distilled, 61 
 electrolysis of, 15, 324 
 from natural sources, 54 
 -gas, 134, 506 
 hard, 55 
 
 of constitution, 53, 375 
 crystallisation, 53 
 oxygenated, 63 
 physical properties, 63 
 purified, 60, 6 1 
 soft, 55 
 
 synthesis of, 42, 45, 46 
 tested, 60 
 Waterproof cloth, 557 
 
 felt, 557 
 
 Waters, mineral, 61 
 Water vapour, 63 
 Wavellite, 390 
 Wax, bees', 570, 644, 799 
 bleached, 799 
 Chinese, 590, 799 
 Weld, 747 
 Welding, 409 
 Weldon's chlorine process, 170 
 
 manganese recovery process, 170 
 -Peciiiney process, 348 
 Well-water, 55 
 Welsh coal, 160 
 
 Welsbach incandescent light, 154 
 Wermuth, 745 
 Whale oil, 799 
 Wheat, 803 
 
 sprouted, 804 
 Wheaten flour, 808 
 Whey, 812 
 Whiskey, 808 
 Whit? antimony ore, 442 
 arsenic, 267 
 gunpowder, 186, 339 
 iron, 402 
 lead, 460, 470 
 
 manufacture, 470 
 ore, 460 
 metal, 475 
 of egg, 749 
 precipitate, 500 
 
 fusible, 501 
 White vitriol, 381 
 Whitworth's steel, 413 
 Willesden paper, 738 
 Willow-bark, 743 
 Windows, crystals on, 355 
 Wine, 807 
 
 Wines, alcohol in, 808 
 Winter-green oil, 645 
 Wire-iron, 407 
 Witherite, 359, 360 
 
 Woad, 761 
 Wolfram, 436, 447 
 Wood charcoal, 112 
 
 combustion, in 
 
 composition, 168 
 
 distillation, 112, 566 
 
 for gunpowder-charcoal, 113 
 
 gum, 737 
 
 kre isote, 713 
 
 -naphtha, 566 
 
 preservation of, 820 
 
 -smoke, 824 
 
 -spirit, 566 
 
 -tar, 566 
 Wood's fusible alloy, 439 
 Worm, 6 1 
 Worm-seed, 745 
 Wormwood, 745 
 Wort, 562, 805 
 Wrought-iron, 404 
 Wulfenite, 435 
 
 XANTHATES, 643 
 Xanthic acid, 643 
 Xanthine, 774 
 Xantho-cobalt salts, 423 
 X mthogen persulphide, 643 
 Xanthroproteic acid, 750 
 Xanthosiderite, 272 
 Xenon, 77 
 Xylene, 549 
 Xylidine, 665 
 Xylyl, 548 
 Xylonite, 742 
 Xylose, 725 
 
 YEAST, 562, 805 
 Yellow casscl, 472 
 
 chrome, 432 
 
 dyes, 795 
 
 fast, 683 
 
 fire, 350 
 
 Indian, 747 
 
 ochre, 396 
 
 orpiment, 275 
 
 Paris, 472 
 
 prussiate of potash, 689 
 
 Turner's, 472 
 
 ultramarine, 432 
 Ytterbium, 394 
 Yttrium, 394 
 
 ZAFFRE, 423 
 Zeisel's method, 631 
 Zinc, 376 
 
 acet.ite, 592 
 
 alkides, 651 
 
 amalgam, 498 
 
 amalgamated, 498 
 
 amide, 653 
 
 arsenide, 272 
 
 arsenite, 270 
 
 boiling-point, 377 
 
 carbonate, 380 
 
 chloride, 380 
 
 cyanide, 692 
 
 diamine, 380 
 
 ethoxide, 653 
 
 distilled, 378 
 
8 7 2 
 
 Zinc dust, 380 
 ethide, 651 
 ethyl, 651, 652 
 extraction, 377 
 ferrocyanide, 694 
 granulated, 22 
 hydrosulphite, 23 
 hydroxide, 380 
 impurities in, 379 
 lactate, 604 
 mercaptide, 653 
 metallurgy of, 379 
 methide, 653 
 methyl, 653 
 
 INDEX. 
 
 Zinc nitride, 380 
 
 ores, 377 
 
 oxide, 380 
 
 oxychloride, 377 
 
 phosphate, 382 
 
 removal of lead from, 379 
 
 silicate, 382 
 
 sulphate, 381 
 
 sulphide, 381 
 
 white, 380 
 Zircon, 458 
 Zirconia, 458 
 Zirconium, 458 
 Zymase, 584 
 
 Printed by BALLANTVNE, HANSON & Co. 
 London & Edinburgh 
 

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