John Swett 
 

TEXT-BOOKS OF SCIENCE. 
 
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Text-Books of Science. 
 
 'I 'The first' i S&v&if&x.l-~&)oks of the Series, in order of publication : 
 
 l! THE ELEMENTS ,OF MECHANISM. 
 
 I l ;* Designed for Stutffents o'i Applied Mechanics. By T. M. GOODEVE, M.A. 
 '' .** 33diiwr *af Jtho, JSsrteV JSew Edition, revised ; with '257 Figures on Wood. 
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 ' Hitherto text-books on metallurgical 
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Text-Books of Science. 
 
 THE STUDY OF INORGANIC 
 
 III. INTRODUCTION TO 
 
 CHEMISTRY. 
 
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 V. 
 
 has so explained as to make them rather an 
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 THEORY OF HEAT. 
 By J. CLERK MAXWELL, M.A. LL.D. Edin. F.R.SS. L. & E. Professor of 
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 VI. 
 
 admirable account of the existing state 
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 ledge has been acquired, of its bearing 
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 subject of heat touches the general doc- 
 trines of mechanics.' 
 
 PHILOSOPHICAL MAGAZINE. 
 
 VII. TECHNICAL ARITHMETIC AND MENSURATION. 
 
 By CHARLES W. MERRIFIELD, F.R.S. Barrister-at-Law, Principal of the 
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 mechanics, it would lie hard to name a 
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 ' Notwithstanding that arithmetic has 
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 subject, and to the higher rules that 
 
 gradual induction which is a more 
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 ESGINEEB. 
 
Text-Books of Science, 
 
 The following Text-Books are in active preparation : 
 
 ORGANIC CHEMISTRY. 
 
 By H. E. ARMSTRONG, Ph.D. Professor 6f Chemistry in the London Insti- 
 tution. 
 
 ELECTRICITY AND MAGNETISM. 
 
 By FLEEMING JEXKIN, F.R.SS. L. & E. Professor of Engineering in the 
 University of Edinburgh. 
 
 PRACTICAL AND DESCRIPTIVE GEOMETRY, AND PRIN- 
 CIPLES OF MECHANICAL DRAWING. 
 
 By CHARLES W. MERRIFIELD, F.R.S. Barrister- at-Law, Principal of the 
 Royal School of Naval Architecture and Marine Engineering, Honorary 
 Secretary of the Institution of Naval Architects, and Late an Examiner in 
 the Department of Public Education. 
 
 PRINCIPLES OF MECHANICS. 
 
 By T. M. GOODEVE, M,A. Editor of the Series. 
 
 DESCRIPTIVE MECHANISM, 
 
 Including Descriptions of the Lathes, Planing, Slotting, and Shaping 
 Machines, and the mode of Handling Work in the Engineer's Shop and 
 other Workshops. 
 
 By C. P. B. SHELLEY, Civil Engineer, and Professor of Manufacturing 
 Art and Machinery at King's College, London. 
 
 ECONOMICAL APPLICATIONS OF HEAT, 
 
 Including Combustion, Evaporation, Furnaces, Flues, and Boilers. 
 
 By C. P. B. SHELLEY, Civil Engineer, and Professor of Manufacturing 
 Art and Machinery at King's College, London. 
 
 With a Chapter on the Probable Future Development of the Science of Heat, by 
 C. WILLIAM SIEMENS, F.R.S. 
 
 THE STEAM ENGINE. 
 
 By T. M. GOODEVE, M.A. Editor of the Series. 
 
 SOUND AND LIGHT. 
 
 By G. G. STOKES, M.A. D.C.L. Fellow of Pembroke College, Cambridge ; 
 Lucasian Professor of Mathematics in the University of Cambridge ; and 
 Secretary to the Royal Society. 
 
 STRENGTH OF MATERIALS. 
 
 By JOHN ANDERSON, C.E. Superintendent of Machinery at the Royal 
 Arsenal, Woolwich. 
 
 other Branches of Science. 
 
 London: LONGMANS and CO, Paternoster Kow. 
 
TEXT-BOOKS OF SCIENCE 
 
 ADAPTED FOR THE USE OF 
 
 J 
 
 ARTISANS AND STUDENTS IN PUBLIC AND OTHER SCHOOLS. 
 
 INORGANIC CHEMISTRY. 
 
LONDON : PRINTED BY 
 
 SPOTTISWOODE AND CO., NEW-STREET SQUARS 
 AND PARLIAMENT STREET 
 
INTRODUCTION TO THE STUDY , i 
 
 OF 
 
 INORGANIC CHEMISTRY. 
 
 BY 
 
 WILLIAM ALLEN MILLER, M.D. 
 
 D.C.L. LL.D. 
 
 Late Treasurer and Vice-President of the Royal Society ; Vice-President 
 
 of the Chemical Society ; Professor of Chemistry in King's 
 
 College, London; Fellow of the University of London; 
 
 Honorary Fellow of King's College. 
 
 WITH QUESTIONS FOR EXAMINATION. 
 
 D. APPLETON AND CO. 
 
 NEW YORK. 
 
 1872. 
 
'J 
 
 
PREFACE. 
 
 THIS BOOK is written expressly for beginners. In 
 order that they should really understand the state- 
 ments which it contains, it will be necessary for them 
 to begin at the beginning, and to go straight through 
 it. Among other reasons for adopting this course, it 
 is to be noted that it is impossible to avoid the use 
 of technical terms in discussing a scientific subject ; 
 since we often have to deal with matters for which no 
 expressions are in use in ordinary language. In this 
 book, when a technical term is introduced for the 
 first time, its meaning is explained, but the explana- 
 tion is not afterwards repeated. Processes are also 
 described in detail when first mentioned, but when 
 afterwards referred to, they are simply directed to be 
 followed. 
 
 Most of the experiments described are of a simple 
 kind, and only require such apparatus and materials 
 as may be easily constructed or procured. The 
 student is strongly advised never to omit the per- 
 formance of any experiment which he has the means 
 of making. No useful knowledge of Chemistry can 
 be acquired by any one unless he constantly makes 
 experiments as he proceeds with the study. 
 
 541829 W. A. MILLER. 
 
NOTE. 
 
 MY FRIEND Professor MILLER completed this work, and 
 placed the whole of the MSS., including the Preface, in the 
 hands of the Printers. He was actually engaged in reading 
 the proof sheets up to the time of his visit to the British 
 Association Meeting at Liverpool, when he was seized with 
 a sudden and fatal illness. 
 
 Professor Miller placed the first few sheets of the work in 
 my hands, and requested me to read them and give him my 
 opinion as to the mode of treatment. I accordingly did so, 
 and suggested certain changes in the style and arrangement 
 which, if adopted, might add to the clearness of the book 
 and so far assist the young student in Chemistry. He ap- 
 proved of these suggestions, and in his last illness left a 
 written request that I would see the work through the press. 
 I have to the best of my ability complied with his wishes. 
 
 C. TOMLINSON. 
 
 HlGHGATE, N. 
 
 November 10, 1870. 
 
CONTENTS. 
 
 CHAPTER I. 
 CHEMICAL ELEM ENTS COMBINATION. 
 
 PAGE 
 
 1. Scope and aim of Chemistry i 
 
 2. Chemical Elements : their 
 
 mode of occurrence . . 4 
 
 3. Chemical Notation . . 6 
 
 PAGE 
 
 4. Weights and Measures . 9 
 
 5. Physical States of Matter . 12 
 
 6. Mixture distinguished from 
 
 Combination , IQ 
 
 CHAPTER II. 
 
 A. THE NON-METALS. 
 
 ATMOSPHERIC AIR OXYGEN NITROGEN. 
 
 The Atmosphere not an Ele- 
 ment . . . .15 
 
 Oxygen .... 19 
 
 The Pneumatic Trough 
 Collecting Gases . . 20 
 
 Combustion . . . .24 
 
 10. Measurement of Gases under 
 
 Standard Conditions . 28 
 
 11. Acids, Bases, and Salts . 30 
 
 12. Ozone 34 
 
 13. Nitrogen . . . -36 
 
 14. Air a Mixture of several 
 
 Gases . . . .38 
 
 CHAPTER III. 
 
 WATER HYDROGEN. 
 
 15. Water . 
 
 Decomposition of 
 Freezing and boiling of 
 Evaporation 
 Maximum density 
 Rain Water . 
 Spring Water 
 Hard and Soft Water 
 Tests for 
 
 Mineral Waters . 
 Water of Crystallisation 
 
 42 
 
 45 
 46 
 
 47 
 49 
 5 
 53 
 53 
 55 
 57 
 
 1 6. Hydrogen . . . .58 
 Collecting Gases by displace- 
 ment . . 61 
 The Mixed Gases 62 
 Synthesis of Water 65 
 The Oxyhydrogen Jet 67 
 Diffusion . . 69 
 Atomic Weight of Hydrogen 70 
 Hydrogen the Unit . . 70 
 Monads, Dyads, Triads, &c. 72 
 
Vlll 
 
 Contents. 
 
 CHAPTER IV. 
 
 OXIDES OF CARBON CARBON. 
 
 17. Carbonic Anhydride 
 Sources of . 
 Ventilation . 
 Synthesis of CO a 
 CO* in the Air 
 
 18. Carbon 
 
 The Diamond 
 Graphite 
 Pit Coal 
 
 de 
 
 
 PAGE 
 
 Coke .... 
 
 PAGE 
 
 
 
 79 
 
 82 
 
 83 
 
 84 
 
 84 
 85 
 
 86 
 
 Charcoal 
 Animal Charcoal Filtratior 
 Allotropy . . 
 19. Carbonic Oxide . . 
 Washing of Gases 
 20. Classification of Crystals 
 Isomorphism 
 
 i 90 
 92 
 
 97 
 103 
 
 CHAPTER V. 
 
 OXIDES OF NITROGEN NITRIC ACID AMMONIA. 
 
 21. Nitric Acid .... 104 
 22. Other Oxides of Nitrogen 
 Nitrous Oxide . . .no 
 Nitric Oxide . . .112 
 Nitrous Anhydride , . 113 
 
 Nitrogen Peroxide 
 23. Ammonia . 
 Ammoniacal Gas . 
 Absorption of by Charcoal 
 Solution of Ammonia . 
 
 "4 
 114 
 
 "5 
 117 
 ns 
 
 CHAPTER VI. 
 
 
 SEA SALT HYDROCHLORIC ACID. 
 
 
 24. Chlorine . . 120 
 25. Hydrochloric Acid 123 
 Analysis of . . 125 
 Solution of . . 126 
 26. Oxides of Chlorine 129 
 
 27. Bromine 
 28. Iodine . 
 Hydriodic Acid . 
 29. Fluorine 
 Hydrofluoric Acid 
 
 I 3 2 
 134 
 
 ^37 
 
 III 
 
 CHAPTER VII. 
 
 
 SULPHUR GROUP. 
 
 
 30. Sulphur . . . 141 
 31. Sulphurous Anhydride . 145 
 32. Sulphuric Acid . . 147 
 Nordhausen Acid . 148 
 Sulphuric Acid Chambers 149 
 Salts and Tests . . 151 
 
 33. Hyposulphites 
 34. Sulphuretted Hydrogen 
 Hydrosulphates . . 
 35. Carbon Disulphide . 
 Selenium Tellurium . 
 
 152 
 
 155 
 
 157 
 158 
 
 CHAPTER VIII. 
 
 
 PHOSPHORUS GROUP. 
 
 
 36. Phosphorus .... 159 
 37. Oxides of Phosphorus . . 163 
 
 Sodic Phosphates 
 37 a. Phosphuretted Hydrogen . 
 
 164 
 
 166 
 
Contents. 
 
 IX 
 
 CHAPTER IX. 
 
 SILICON AND BORON. 
 
 38. Silicon . 
 
 39. Silicates : Glass 
 
 PAGE 
 
 . 168 
 . 170 
 
 39 a. Boron 
 
 Boracic Anhydride 
 
 PAGE 
 
 . 174 
 
 CHAPTER X. 
 COAL GAS, AND OTHER COMPOUNDS OF CARBON. 
 
 40. Hydrocarbons 
 Olefiant Gas 
 Marsh Gas . 
 The Safety Lamp 
 Flame . 
 
 Bunsen's Burner . 
 The Blowpipe 
 
 177 
 177 
 179 
 180 
 181 
 182 
 183 
 
 Coal Gas 
 
 41. Cyanogen . 
 
 42. The Atomic Theory 
 Atomic Weights and 
 
 mical Equivalents 
 
 Che- 
 
 185 
 188 
 190 
 
 193 
 
 Atomic Volumes and Mole- 
 cular Volumes . . .195 
 
 43- 
 
 CHAPTER XL 
 B. THE METALS. 
 
 The Metals in General . .198 
 Specific Gravities and Fusing 
 
 Points of Metals . . 199 
 Properties of the Metals . 200 
 
 Metallic Alloys . 
 Native Metals 
 44. Classification of the Metals 
 
 GROUP I. METALS OF THE ALKALIES. 
 
 45. Potassium .... 205 
 Potash .... 206 
 Potassic Chloride, Carbon- 
 ate, &c 207 
 
 Nitre or Saltpetre . . 208 
 Gunpowder .... 209 
 
 46. Sodium .... 210 
 Common Salt . . .210 
 
 Soda 210 
 
 Sodic Chloride, Sulphate, &c. 211 
 Manufacture of Soda . .212 
 Tests for the Alkali Metals in 
 
 Combination . . , .214 
 
 47. Ammonium .... 215 
 
 Its Carbonate . . . 216 
 
 GROUP II. METALS OF THE ALKALINE EARTHS. 
 
 48. Barium 
 Baryta 
 
 The Sulphate 
 
 Tests for Barium Salts 
 
 Strontium . 
 
 49. Calcium 
 
 217 
 217 
 218 
 219 
 219 
 219 
 
 Lime . 
 
 Mortar 
 
 Calcic Chloride . 
 
 Gypsum 
 
 Calcic Carbonate . 
 
 Tests . 
 
 . 220 
 
 . 221 
 
 . 221 
 
 . 221 
 
 . 222 
 
 . 223 
 
Contents. 
 
 CHAPTER XII. 
 GROUP III. METALS OF THE EARTHS. 
 
 50. Aluminum . 
 Alumina 
 The Alums . 
 
 PAGE 
 
 . 223 
 . 224 
 . 226 
 
 PAGE 
 
 Silicates of Alumina Clays . 227 
 Earthenware and China . 228 
 Tests for Aluminum Salts . 229 
 
 GROUP IV. MAGNESIUM METALS. 
 
 51. Magnesium . 
 
 . 229 
 
 52. Zinc ..... 
 
 232 
 
 Magnesia 
 Magnesic Chloride 
 
 . 230 
 . 230 
 
 Salts of Zinc 
 Cadmium .... 
 
 233 
 234 
 
 Sulphate 
 
 . 231 
 
 Indium .... 
 
 234 
 
 Tests . 
 
 . 231 
 
 
 
 CHAPTER XIII. 
 
 
 GROUP 
 
 V. METALS ALLIED TO IRON. 
 
 
 53. Cobalt. 
 
 235 
 
 Ferrous Chloride, Carbonate, 
 
 
 Nickel . 
 
 236 
 
 &c 
 
 243 
 
 Uranium 
 
 my* 
 
 237 
 
 Tests for Iron 
 
 T\J 
 
 243 
 
 54. Iron 
 
 237 
 
 55. Chromium . 
 
 244 
 
 Ores of 
 
 237 
 
 Salts of 
 
 245 
 
 Manufacture of Iron 
 
 238 
 
 Chrome Yellow 
 
 246 
 
 Steel . 
 
 2 39 
 
 Manganese . 
 
 246 
 
 Properties of Iron 
 
 240 
 
 Compounds of Manganese 
 
 247 
 
 Oxides . 
 
 241 
 
 Tests . 
 
 248 
 
 Iron and Sulphur . 
 
 242 
 
 
 
 
 CHAPTER XIV. 
 
 
 GROUP 
 
 VI. TIN AN-D ALLIED METALS. 
 
 
 56. Tin ... 
 
 . 249 
 
 Tests . . . . 
 
 252 
 
 Its Alloys 
 
 . ! 250 
 
 Titanium, Zirconium, Thori- 
 
 
 Its Oxides . 
 
 . 250 
 
 num, Molybdenum 
 
 252 
 
 Compounds of Tin 
 
 . 251 
 
 
 
 CHAPTER XV. 
 
 
 I. ARSENICUM. 2. ANTIMONY. 3. BISMUTH. 
 
 57. Arsenicum . 
 Arsenic 
 
 253 
 255 
 
 58. Antimony . 
 Compounds of Antimony 
 
 a-,8 
 2J9 
 
 Tests for 
 
 . 2sq 
 
 59. Bismuth .... 
 
 2JO 
 
 Arseniuretted Hydrogen . 257 
 
 Compounds of Bismuth 
 
 aSi 
 
Contents. 
 
 XI 
 
 CHAPTER XVI. 
 
 I. COPPER. 2. LEAD. 3. THALLIUM. 
 
 60. Copper 
 Smelting of Copper 
 Oxides 
 
 Salts and Tests . 
 
 61. Lead . 
 
 PAGE 
 26l 
 262 
 263 
 264 
 265 
 
 Action of Water on Lead . 266 
 
 Oxides 267 
 
 Salts 268 
 
 62. Thallium .... 269 
 
 CHAPTER XVII. 
 
 THE NOBLE METALS. 
 
 63. Mercury 
 Its Oxides c/. 
 Its Chlorides 
 Iodide and Tests 
 64. Silver . 
 Its Compounds 
 65. Gold . 
 
 
 
 270 
 272 
 273 
 274 
 
 3 
 
 278 
 
 Its Chloride . . . 279 
 
 Purple of Cassius . . . 280 
 66. Platinum . . . .280 
 Its Chlorides . . .281 
 Palladium, Rhodium, Os- 
 mium, Indium, Ruthenium 282 
 
 QUESTIONS FOR EXAMINATION . 283 
 
INORGANIC CHEMISTRY. 
 
 CHAPTER I. 
 
 CHEMICAL ELEMENTS COMBINATION. 
 
 (i) Scope and aim of Chemistry. Many of the changes 
 in natural objects which are taking place around us every 
 .day some slowly, some quickly are the result of a class of 
 actions which are called chemical. When, for instance, a 
 piece of iron is exposed to the open air and becomes 
 covered with rust, or when a fallen leaf crumbles away, or 
 when milk becomes sour after it has been kept for a few 
 days, the change which has occurred in each case is of a 
 chemical nature : in all of them an alteration in the com- 
 position of the substance has taken place, and new sub- 
 stances, with properties quite different from those of the 
 original material, have been formed. The iron has taken 
 up something from the air which has altered its colour and 
 lessened its strength ; the leaf has furnished new bodies, 
 some of which have passed off unseen into the atmosphere ; 
 while the sugar in the milk has become changed into an 
 acid, and the curd has been separated from the whey. 
 
 It is the business of the chemist to find out what these 
 various substances are made of, as well as the exact nature 
 of the alteration in composition which has occurred in 
 these cases, and the means by which such changes can be 
 
2 1 4 ,,...: Objects of Chemistry. 
 
 forwarded or varied,, or altogether prevented. Chemistry is 
 .,11) 'fact the science .which teaches us the composition of 
 bodies. Whenever, therefore, a new substance is pat into 
 the hands of the chemist, whether it be derived from the 
 mineral, the vegetable, or the animal creation, one of his 
 first questions is, Of what is this body made ? Is it com- 
 posed of one kind of matter or of several kinds ? 
 
 In order to obtain answers to these questions we must 
 learn to observe carefully the changes which are going on 
 around us ; and we must also contrive fresh arrangements, 
 more or less altered, in which the exact circumstances 
 have been planned by ourselves for the purpose of seeing 
 what will happen under these altered conditions. Such 
 planned observations are what are commonly called experi- 
 ments ; and the better they are planned and performed 
 the more we shall be able to learn if we reason accurately 
 upon the result obtained. Chemistry is in the best sense 
 an experimental science, calling into action alternately the 
 head to plan, the hands to perform, and the head again to 
 explain the results of our experiments. 
 
 Various substances may easily be shown to contain more 
 than one kind of matter ; while others have hitherto foiled 
 all the efforts made to separate from them any second sub- 
 stance. For example, from a mass of pure silver nothing 
 can be obtained but silver itself, copper will furnish 
 nothing but copper, and from sulphur the chemist can ex- 
 tract nothing but sulphur. Such bodies have therefore been 
 called undecomposed or simple substances^ or chemical elements. 
 
 On the other hand, such bodies as table salt, iron rust, 
 water, chalk, wood, mercuric oxide, may each by the use of 
 suitable means be made to yield more than one kind of 
 matter. 
 
 Experiment I. Place a scrap of wood in a test-tube, which 
 is a glass tube about the size of the forefinger, and closed at one 
 end. Heat it by holding it just above the flame of a spirit 
 lamp. The wood will become charred and blackened, while 
 
Chemical Elements Combination. 3 
 
 vapours will be given off, and will collect on the cold sides of the 
 glass in the form of a brownish tarry liquid. 
 
 Exp. 2. Place in a test-tube as much mercuric oxide, or red 
 oxide of mercury, as will cover a sixpence, and heat the end 
 of the tube in the flame of a spirit lamp. Oxygen gas will come 
 off as a colourless gas, in which a splinter of wood, previously 
 kindled and introduced into the tube, will burn brilliantly, and 
 drops of metallic mercury will collect on the cold sides of the 
 tube. 
 
 Such bodies as wood and mercuric oxide are said to 
 admit of being decomposed, that is, they may be separated 
 into two or more distinct kinds of material ; and all sub- 
 stances which thus admit of being analysed or pulled 
 asunder into their constituent substances are known chemi- 
 cally as compounds. 
 
 In many cases the chemist can not only separate a com- 
 pound into its elements, but he can, out of those elements, 
 by synthesis, or putting them together again, build up the 
 compound as may easily be done with the iron rusi, 
 and the mercuric oxide just mentioned. When a body 
 can be thus separated into its elements, and can be re- 
 produced by combining those elements again with each 
 other, we possess the most complete proof of its chemical 
 composition, though much remains to be discovered respect- 
 ing the mode in which the different substances are arranged 
 in the compound. We may know, for example, what 
 letters are wanted to spell a particular word, but in order to 
 spell the word correctly we must also know the order in 
 which these letters are to follow one another. Just so it is 
 necessary to discover if possible the arrangement of the 
 elements in a chemical compound before we can be said 
 truly to know its constitution. Every material object with 
 which we are acquainted is, in a chemical point of view, 
 either an element or a compound, or else a mechanical mix- 
 ture of two or more elements or compounds. 
 
 By far the greater number of natural objects are com- 
 
 2 
 
4 Chemical Elements Attraction. 
 
 pounds. These compounds consist of two or more simple 
 substances united according to certain fixed rules or laws. 
 The simple bodies have no more likeness to the com- 
 pounds which they form than the separate letters of the 
 alphabet have to the words which may be made from them. 
 The power which causes the various elements to unite one 
 with another, and which holds them together after they have 
 united, is called chemical attraction. It is much stronger 
 between some elements than others, and is exerted accord- 
 ing to special rules, which will be explained hereafter. 
 
 (2) Chemical Elements : tJieir mode of occurrence. Two of 
 the most important of the elements, .oxygen and nitrogen, 
 form the principal portion of the atmosphere, and they 
 occur in it mixed with each other, but not chemically com- 
 bined. The only other elements of importance which are 
 met with in their separate or native state are sulphur or 
 brimstone, carbon (in the very different forms of black-lead 
 and diamond), iron, copper, bismuth, mercury, silver, gold, 
 and platinum; but some of these are found much more 
 abundantly in combination with other elements than in the 
 separate form. 
 
 The chemical elements are little more than sixty in 
 number. Most of them occur in combination in the strata 
 of the earth. Some, indeed, are found so sparingly that 
 their properties have been but little examined. Others 
 again are extremely abundant, particularly hydrogen, oxygen, 
 nitrogen, and carbon ; two or more of these four elements 
 enter into the formation of most of the objects familiar to us, 
 except the ordinary metals, which are themselves elementary 
 bodies. 
 
 Taking the earth as a whole, so far as man has been able 
 to penetrate into and examine it, more than one-third of it 
 has been found to consist of oxygen either combined or un- 
 combined, and nearly one-fourth consists of silicon in com- 
 bination, for the most part, with oxygen. Besides this, com- 
 pounds of aluminum, calcium, iron, carbon, magnesium. 
 
Chemical Elements Metals Non-metals. 
 
 5 
 
 sodium, potassium, and sulphur, are found in considerable 
 proportion ; some confined to special places, and the others 
 very generally diffused : while, dissolved in sea water, we 
 have, independently of the oxygen and hydrogen of the water, 
 compounds of sodium, chlorine, magnesium, calcium, and 
 potassium, in addition to combinations of about twenty 
 other elements in extremely small proportions. 
 
 For the sake of convenience the elements are divided 
 into the two classes of metals and non-metals, though the 
 two classes run into each other. Fifty of the .elements are 
 commonly reckoned as metallic, and thirteen as non-metallic 
 in their nature. The thirteen elements commonly enume- 
 rated as non-metals are oxygen, nitrogen, hydrogen, carbon, 
 chlorine, bromine, iodine, fluorine, sulphur, selenium, phos- 
 phorus, silicon, and boron. 
 
 In the following list those of the greatest importance are 
 printed in capitals, as OXYGEN. The chemical properties 
 of these we shall examine hereafter; those in ordinary type, 
 as Bromine, will be touched upon less fully; whilst of those 
 in italics, such as Tantalum, owing to their rarity, and the 
 absence of any important application of them in the arts, 
 few will need more than a passing mention. 
 
 ELEMENTS WITH THEIR SYMBOLS AND ATOMIC WEIGHTS. 
 
 Name 
 
 Symbol 
 
 Atomic 
 Weight 
 
 | 
 Name 
 
 Symbol 
 
 Atomic 
 Weight 
 
 ALUMINUM . 
 
 Al 
 
 27-5 
 
 Cerium 
 
 Ce 
 
 92 
 
 Antimony (Stibium) 
 
 Sb 
 
 122 
 
 CHLORINE . 
 
 Cl 
 
 35'5 
 
 Arsenicum 
 
 As 
 
 75 
 
 Chromium 
 
 Cr 
 
 5 2 5 
 
 BARIUM 
 
 Ba 
 
 137 
 
 Cobalt . 
 
 Co 
 
 59 
 
 Bismuth 
 
 Bi 
 
 2IO 
 
 COPPER (Cuprum) 
 
 Cu 
 
 63-5 
 
 Boron . 
 
 B 
 
 II 
 
 Didymium 
 
 D 
 
 96 
 
 Bromine 
 
 Br 
 
 80 
 
 Erbium 
 
 E 
 
 112 
 
 Cadmium 
 
 Cd 
 
 112 
 
 Fluorine 
 
 F 
 
 19 
 
 Ctzsium 
 
 Cs 
 
 !33 
 
 Glucinum 
 
 G 
 
 9'5 
 
 CALCIUM 
 
 Ca 
 
 40 
 
 Gold (Aurum) 
 
 Au 
 
 I 9 7 
 
 CARBON 
 
 C 
 
 12 
 
 HYDROGEN . 
 
 H 
 
 I 
 
6 List of Elements Notation. 
 
 ELEMENTS WITH THEIR SYMBOLS AND ATOMIC WEIGHTS cont. 
 
 Name 
 
 Symbol 
 
 Atomic 
 Weight 
 
 Name 
 
 Symbol 
 
 Atomic 
 Weight 
 
 Indium 
 
 In 
 
 7 6 
 
 Rhodium 
 
 Ro 
 
 104 
 
 Iodine . 
 
 I 
 
 127 
 
 Rubidium 
 
 Rb 
 
 85 
 
 Iridium 
 
 Ir 
 
 I 9 7 
 
 Ruthenium 
 
 Ru 
 
 104 
 
 IRON (Ferrum) 
 
 Fe 
 
 56 
 
 Selenium 
 
 Se 
 
 79'5 
 
 Lanthanum . 
 
 La 
 
 92 
 
 SILICON 
 
 Si 
 
 28 
 
 LEAD (Plumbum) . 
 
 Pb 
 
 207 
 
 SILVER (Argentum) 
 
 Ag 
 
 108 
 
 Lithium 
 
 L 
 
 7 
 
 SODIUM (Natrium) 
 
 Na 
 
 23 
 
 MAGNESIUM . 
 
 Mg 
 
 24 
 
 Strontium 
 
 Sr 
 
 87-5 
 
 MANGANESE. 
 
 Mn 
 
 55 
 
 SULPHUR 
 
 S 
 
 3 2 
 
 MERCURY (Hy- j 
 drargyrum) \ 
 
 Hg 
 
 200 
 
 Tantalum 
 Telhirium 
 
 Ta 
 Te 
 
 182 
 129 
 
 Molybdenum . 
 
 Mo 
 
 96 
 
 Thallium 
 
 Tl 
 
 204 
 
 Nickel . 
 
 Ni 
 
 59 
 
 Thorinum 
 
 Th 
 
 238 
 
 Niobium 
 
 Nb 
 
 94 
 
 Tin (Stannum) 
 
 Sn 
 
 118 
 
 NITROGEN . 
 
 N 
 
 4 
 
 Titanium 
 
 Ti 
 
 50 
 
 Osmium 
 OXYGEN 
 
 Os 
 O 
 
 199 
 16 
 
 Tungsten (Wol- ) 
 f ram him) . \ 
 
 W 
 
 184 
 
 Palladium 
 
 Pd 
 
 106 
 
 Uranium . 
 
 U 
 
 120 
 
 PHOSPHORUS 
 
 P 
 
 3i 
 
 Vanadium 
 
 V 
 
 5 1 
 
 Platinum 
 
 Pt 
 
 197 
 
 Yttrium 
 
 Y 
 
 62 
 
 POTASSIUM (Ka- ) 
 
 
 
 ZINC . 
 
 Zn 
 
 65 
 
 Hum) . . \ 
 
 
 39 
 
 Zirconium 
 
 Zr 89 
 
 (3) Chemical Notation. In the foregoing table it will be 
 seen that opposite to the name of each element is placed its 
 chemical symbol, which consists of the first letter of its Latin 
 name. Where two or more of these names begin with the 
 same letter, a second letter is added to distinguish such 
 symbols from each other. These symbols form a simple 
 and easy kind of shorthand, by means of which chemical 
 changes may be clearly and compactly represented. 
 
 It is important to remark that whenever the symbol of 
 any element is used, it represents not merely the element 
 itself, but a definite quantity of that element. For instance, 
 the symbol O always stands for 16 parts by weight of 
 oxygen ; the symbol H always stands for i part by weight 
 of hydrogen ; and in the table opposite to the symbol of 
 
Chemical Symbols Notation. 7 
 
 each element is placed the number of parts of the element 
 which that symbol represents. To render our ideas precise, 
 we will suppose that H stands for i gram of hydrogen ;* 
 then O will represent, not i gram, but 16 grams of oxygen ; 
 C will represent 12 grams of carbon; S 32 grams of sul- 
 phur, and so on. The reason why these particular numbers 
 are appropriated in the table to their corresponding elements 
 will be explained hereafter. They constitute a very impor- 
 tant series of constants, which, in the case of the more 
 important elements, it will be found highly useful to commit 
 to memory. These numbers represent what chemists have 
 termed the atomic weights of the elements. Every element 
 is supposed to be made up of excessively small particles or 
 atoms exactly of the same size and weight in the same 
 body. If the atom of hydrogen be supposed to weigh i, 
 the number opposite to each element in the table represents 
 the weight of its atom, or smallest particle, compared with 
 that of the atom of hydrogen. 
 
 Compound bodies may also be represented by symbols ; 
 and the proportion as well as the nature of the elements 
 concerned is easily expressed by writing the symbols side by 
 side : HC1, for instance, represents hydrochloric acid, a 
 compound of hydrogen with chlorine, in which the propor- 
 tion of i gram of hydrogen is united with 35*5 grams of 
 chlorine ; H 2 O indicates water, a compound of hydrogen 
 with oxygen, the figure 2 below the symbol H multiplies the 
 quantity of hydrogen by 2, and represents 2 grams of 
 hydrogen combined with 16 grams of oxygen. When two or 
 more chemical symbols are thus written side by side, they 
 constitute a chemical formula. Whenever the sign -f is 
 placed between two formulae, it is employed to show that 
 the two bodies have been mixed with each other. The 
 
 * Another unit of weight might have been taken, such, for instance, as 
 I grain, or I ounce, or I pound; then O would stand for 1 6 grains of 
 oxygen, 1 6 ounces of oxygen, or impounds of oxygen, according as a grain, 
 an ounce, or a pound of hydrogen was the unit chosen for the comparison. 
 
8 Chemical Symbols. 
 
 sign = does not indicate identity or absolute equality, but 
 is usually employed in the sense of the word 'yields;' and 
 when it connects the two halves of a chemical equation, it 
 represents that if the compounds which stand before it are 
 mixed with each other, with due precaution, a chemical 
 change will occur which may be represented by the arrange- 
 ment of the symbols placed after the sign =. For instance, 
 in the chemical equation, 
 
 CaCO 3 + 2HC1 = CaCl 2 + H 2 O + CO 2 , 
 
 CaCO 3 is the chemical formula for calcic carbonate, of 
 which marble is one of the many forms ; and if H represents 
 i gram of hydrogen, CaCO 3 will represent 100 grams of 
 marble, since Ca stands for 40 grams of calcium, C for 12 
 grams of carbon, O 3 for 3 times 1 6 or 48 grams of oxygen, 
 making together 100 grams. HC1 is the chemical symbol 
 for hydrochloric acid ; and since H means i gram of hy- 
 drogen, Cl 35*5 grams of chlorine, 2HC1 will mean twice 
 that quantity, or 73 grams of hydrochloric acid. As soon 
 as the hydrochloric acid is poured on the marble, a chemical 
 change occurs; the marble is dissolved, and an efferves- 
 cence* is produced, the result being the production of 
 calcic chloride, CaCl 2 , containing 40 grams of calcium, 
 twice 35 '5 or 71 grams of chlorine, making together in 
 grams of calcic chloride; H 2 O, 18 grams of water, con- 
 taining 2 grams of hydrogen, and 16 grams of oxygen ; 
 while CO 2 stands for 44 grams of carbonic anhydride 
 (or carbonic acid), containing 12 grams of carbon with twice 
 1 6 or 32 grams of oxygen, and this lias passed off as a gas, 
 and produced the effervescence. 
 
 The whole may be represented as follows, where the 
 figures written under each symbol represent the number of 
 grams of each -element or combination of elements : 
 
 * A body is said to cffei-vesce^ when it gives off gas suddenly with an 
 appearance of boiling. 
 
Weights and Measures. 9 
 
 Calcic Hydrochloric Ca'cic Wot-m Carbonic 
 
 Carbonate Acid . Chloride Anhydride 
 
 CaC0 3 + 2HC1 = CaCl 2 + H 2 O + CO, 
 40 + 12 + 16x3 2(1+35-5) 40 + 355x2 1x2 + 16 12 + 16x2 
 
 100 73 in 18 44 
 
 Or in words : Mix 100 grams of marble with a solution of 
 73 grams of hydrochloric acid : it will yield 1 1 1 grams of calcic 
 chloride, 18 grams of water, and 44 of carbonic anhydride. 
 
 Whenever a chemical compound is formed, the same 
 compound is always found to contain the same elements, 
 united in fixed and invariable proportions ; 100 parts of 
 marble always contain 40 of calcium, 12 of carbon, and 48 
 of oxygen : and in like manner 18 parts, whether grams, 
 pounds, or tons of water, always contain 2 parts of hydro- 
 gen and 1 6 parts of oxygen, be they grams, pounds, or tons. 
 
 (4) Weights and Measures. The weights and measures 
 used in this work are those of the metric system, which, 
 on account of their simplicity and convenience, are now 
 commonly employed by men of science throughout the 
 world. This uniformity of usage does away with the waste 
 of time formerly incurred in converting the weights and 
 measures of one country into those of their neighbours. 
 As, however, most persons in this kingdom have been ac- 
 customed from infancy to a different system in the trans- 
 actions of daily life, it will be necessary to explain the 
 principles of the metrical system. It will be needful to bear 
 in mind that the metre or unit of length is equal to 39*37 
 English inches; and consequently that 10 centimetres re- 
 present very nearly 4 inches, while a millimetre is almost 
 exactly ^th of an inch. The subdivisions of the metre are 
 marked by the Latin prefixes deci, ten, centi, a hundred, and 
 milli, a thousand ; so that the tenth of a metre is called a 
 decimetre, the hundredth of a metre a centimetre, and the 
 thousandth of a metre a millimetre. The higher multiples 
 are indicated by the Greek prefixes deca, ten, hecto, one 
 
IO Weights and Measures. 
 
 hundred, kilo, one thousand ; but the prefix kilo, or multiple 
 by one thousand, is almost the only one used in practice. 
 For instance, the higher multiple, or 1000 metres, is called a 
 kilometre. It is used as a measure of distance by road, and 
 represents about 1094 yards, 16 kilometres being equal to 
 nearly 10 English miles.* 
 
 Fig. i. 
 
 Each side of this square measures 
 
 i Decimetre, or 
 10 Centimetres, or 
 100 Millimetres, or 
 3*937 English inches. 
 
 A litre is a cubic measure of i decimetre in the side, or a cube 
 each side of which has the dimensions of this figure. 
 
 When full of water at 4 C. a litre weighs exactly I kilogram or 
 looo grams, and is equivalent to 1000 cubic centimetres ; or to 
 6ro24 cubic inches, English. 
 
 A gram is the weight of a centimetre cube of distilled water; at 
 4 C. it weighs 15-432 grains. 
 
 isq. 
 Centim. 
 
 4 inches. 
 
 * The metre is a bar of platinum deposited in the archives of France, 
 and when made it was believed to represent exactly the ten-millionth part 
 of a quadrant of a great circle encompassing the globe of the earth on 
 
Metric System. 
 
 II 
 
 " The measures of capacity are connected with those of 
 length by making the unit of capacity in this series a cube 
 of one decimetre, or 3*937 English inches, in the side; this, 
 which is termed a litre, is equal to 17637 imperial pints, or 
 to 6 1 -024 cubic inches. 
 
 Finally, the system of weights is connected with both the 
 preceding systems by taking as its unit the weight of a cubic 
 centimetre of distilled water at 4 C. : it weighs 15*432 
 English grains. The gram, as this quantity is called, is 
 further subdivided into tenths or decigrams, hundredths or 
 centigrams, and thousandths or milligrams, the milligram 
 being equal to about ^ of a grain. 
 
 The higher multiple of 1000 grams constitutes the kilogram. 
 It is the commercial unit of weight, and represents 15,432 
 English grains, or rather less than z\ Ib. avoirdupois. 
 
 The weight of 1000 kilograms, or a cubic metre, of water, 
 is 0-9842 of a ton, which is sufficiently near to a ton weight 
 to allow of its being reckoned as one ton in rough calcu- 
 lations. 
 
 The temperatures given in this book are expressed 
 throughout in degrees of the centigrade thermometer, unless 
 otherwise specified. The following is a short comparative 
 table of the two scales, Centigrade and Fahrenheit. 
 
 c. 
 
 F. 
 
 C. 
 
 F. 
 
 G 
 
 F. 
 
 C. 
 
 F. 
 
 -20 
 
 -4 
 
 15 
 
 59 
 
 45 
 
 113 
 
 75 
 
 I6 7 
 
 -15 
 
 + 5 
 
 20 
 
 68 
 
 50 
 
 122 
 
 80 
 
 176 
 
 IO 
 
 H 
 
 25 
 
 77 
 
 55 
 
 131 
 
 85 
 
 185 
 
 - 5 
 
 23 
 
 3 
 
 86 
 
 60 
 
 I 4 
 
 90 
 
 194 
 
 o 
 
 3 2 
 
 35 
 
 95 
 
 65 
 
 149 
 
 95 
 
 203 
 
 5 
 
 41 
 
 40 
 
 104 
 
 70 
 
 I 5 8 
 
 IOO 
 
 212 
 
 10 
 
 50 
 
 
 
 
 
 
 
 the meridian of Paris. But it has been found by later and more ac- 
 curate measurements that this assumption is erroneous. The metric 
 system is, however, no way dependent upon the accuracy of this 
 assumption, and the actual bar of platinum then made continues not- 
 withstanding to be the unit of the metric system. 
 
1 2 Solids L iquids Gases. 
 
 (5) Physical States of Matter. Most of the simple bodies 
 of the chemist occur as solids at the common temperature 
 of the air ; two only, mercury and bromine, exist as liquids ; 
 while four others, viz. oxygen, hydrogen, nitrogen, and 
 chlorine, are known as gases ; but in one or other of these 
 three forms of solid, liquid, or gaseous every substance exists, 
 whether it be simple or compound. 
 
 Solid bodies, such as a bar of iron or a block of wood, 
 have a definite form, which cannot be altered without the 
 application of some force more or less considerable. 
 
 Liquids, on the contrary, like water, when placed in an 
 open vessel yield to the slightest force : their particles slide 
 easily over each other; they adapt themselves at once to 
 any unevennesses of the bottom or sides of the vessel, and 
 they always present a level surface in an open vessel. They 
 do not become smaller by compression in ctosed vessels to 
 any extent which can be seen by common observation. 
 
 Gases, on the other hand, like air, yield easily to com- 
 pression. In closed vessels, when the pressure upon them is 
 increased, it can be seen that they are forced into a smaller 
 space ; and when the pressure is lessened the space filled by 
 the gas becomes larger. Hence gases are sometimes spoken 
 of as elastic fluids. They are always tending to increase in 
 bulk, and they always completely fill the vessel which con- 
 tains them, no matter ho\v irregular may be its shape. 
 
 Many bodies may be made to assume either of these three 
 states at pleasure, and to pass slowly backwards and for- 
 wards from one condition to the other for any number of 
 times by simply altering the degree of heat to which they 
 are exposed. Ice, water, and steam, for example, are the 
 same chemical substance in three different physical states, 
 and the same quantity of water may be raised into steam, 
 and converted back again into water or into ice as often as 
 may be desired. The alteration of the form of a body does 
 not affect its weight. A gram of ice when changed into 
 steam still weighs a gram although we no longer see it; and 
 
Mixture Chemical Combination. 13 
 
 every litre or other fixed measure of each has a definite 
 weight, as may be easily pro /ed by the use of proper means. 
 
 All the solid elementary bodies except carbon have been 
 melted, though some require a very intense temperature. 
 Some of the metals, such as platinum and a few of the metals 
 which accompany it in its ores, cannot be melted in ordinary 
 furnaces ; but the extreme heat of the voltaic arc or the 
 electric current produced between the poles of the voltaic 
 battery converts all the metals not merely into liquids but 
 even into vapour, and at this exceedingly intense heat all 
 compounds are separated into their elements. On the other 
 hand, most gases may, by the united action of cold and 
 great pressure, be reduced to the liquid state ; among these 
 are chlorine, sulphurous anhydride, carbonic anhydride, and 
 hydrochloric acid ; several of these have also been frozen by 
 intense cold into masses like ice or snow. A few gases, 
 including the elements oxygen, hydrogen, and nitrogen, have 
 never been liquefied, though it can scarcely be doubted that 
 their liquefaction, and even freezing, would be effected could 
 we apply a still more intense degree of cold and pressure 
 combined. 
 
 (6) Mixture distinguished from Combination. When once 
 a chemical compound has been formed its components can- 
 not, as a rule, be separated by merely mechanical methods. 
 A piece of marble, as we have seen (p. 8), consists of three 
 elementary bodies carbon, oxygen, and calcium. It is easy 
 to grind the marble to a powder of extreme fineness, but 
 every fragment of that powder is still marble, and no one by 
 mere grinding could separate the carbon, the ox.ygen, and 
 the calcium from each other. The molecule or minutest par- 
 ticle of marble which can exist separately is still a compound 
 substance formed of still smaller particles or atoms, of the 
 elements carbon, oxygen, and calcium. To accomplish the 
 separation of these atoms, which together form the molecule 
 of marble, we must employ some new power ; and one 
 which the chemist finds his most useful ally in such cases is 
 
14 Difference between Mixture 
 
 heat. If the marble be heated for a time to bright redness 
 it is decomposed. The carbon with part of the oxygen is 
 driven off as a compound gas, and the calcium with the 
 rest of the oxygen remains behind in the form of the solid 
 compound, lime. Still, by this means a partial separation 
 only of the three elements has been effected, two new com- 
 pounds having been formed instead of the original one. 
 
 Again, it seldom happens that by mechanical means alone 
 we can make two bodies unite chemically with each other. 
 In making gunpowder, for example, which is a mixture of 
 sulphur, charcoal, and nitre, the three substances are first 
 ground separately to a fine powder. They are then mingled 
 together, moistened with water, and ground for several 
 hours under edge stones, in order to mix them as intimately 
 as possible : after this they are subjected to intense pres- 
 sure, and finally broken up into grains. But, notwith- 
 standing all this, gunpowder still remains only a mechanical 
 mixture of its three components, nitre, charcoal, and sulphur. 
 The nitre may be washed out of the mixture by means of 
 water ; the sulphur may be dissolved out of the remainder 
 by means of carbon disulphide, and the charcoal will be left. 
 On evaporating the water the nitre may be recovered un- 
 altered ; and on allowing the disulphide to volatilise or 
 escape in vapour, the sulphur will remain behind. But the 
 mixed materials are ready in gunpowder to act chemically 
 upon each other; for if a spark fall upon the powder a 
 sudden change occurs, a flash follows, and a prompt che- 
 mical action takes place, in consequence of which a large 
 volume of gas is produced, while the heap of powder is 
 converted into new substances, several of which are gases, 
 and none have any resemblance to the original materials. 
 
 Mechanical mixture, then, and chemical combination are 
 two very different things ; they ought never to be confounded 
 with each other, although the mistake is often made by 
 beginners. Whilst in every true chemical compound the 
 proportion of its constituents is perfectly fixed, in a 
 
and Chemical Combination. 1 5 
 
 mechanical mixture the proportions of the substances of 
 which it is made may be altered to any extent that may be 
 desired; besides this, the mixture always . preserves proper- 
 ties which are intermediate between those of its compo- 
 nents. A mixture of table salt and sugar, for instance, may 
 be made by grinding the two together, and the quantity of 
 either may be varied at pleasure. Its flavour will par- 
 take of the saline taste of the one, and of the sweetness of 
 the other; the degree of saltness will vary according as the 
 proportion of salt to the sugar is increased or diminished. 
 But each particle of salt and of sugar, however small, still 
 continues a true chemical compound unaffected by the 
 other, and in each of them the quantity of the constituent 
 elements is unchanged. 
 
 Further, in the case of every true chemical compound, not 
 only are the proportions of its constituent elements fixed, 
 but the properties of the compound, for the most part, 
 differ totally from those of the separate elements which form 
 it, as well as from those of the mixture of the two elements 
 before they have become chemically united. The truth cf 
 this we shall see as we proceed, and the first case in which 
 we shall have occasion to observe it is in the chemical pro- 
 perties of the air, which we shall now examine. 
 
 CHAPTER II. 
 
 A. THE NON-METALS. 
 
 ATMOSPHERIC AIR. OXYGEN NITROGEN. 
 
 (7) The Atmosphere not an Element. We are surrounded 
 on all sides by a viewless substance, the air, which though 
 commonly unnoticed, makes itself felt at once in every 
 gust of wind which blows. Every 'empty' vessel, as it is 
 usually called, is really full of air. 
 
16 Atmospheric Air. 
 
 Exp. 3. Take a glass bottle and press it with its mouth 
 downwards into a basin of water. The water will not fill the 
 bottle, for it is already full of air. Now turn the mouth of the 
 bottle upwards, still keeping it under water ; bubbles of air will 
 escape, and when all the air has thus been allowed to pass out 
 the bottle will have become full of water. 
 
 So lately as a hundred years ago the air was thought to 
 
 be an element ; but it may easily be shown that it is truly a 
 
 mixture of several different substances, some of which are 
 
 simple bodies, and others are chemical 
 
 Fi g- 2 - compounds. 
 
 Exp. 4. Fasten a short bit of candle 
 to a flat piece of cork (Fig. 2). Float it on 
 some water in a soup plate ; light the 
 candle, and place a jar full of air with its 
 mouth downwards over it. In a few 
 minutes the candle will burn dimly, and 
 then will go out. 
 
 The air which is left will no longer allow a candle to burn 
 in it ; it has become altered in its properties by the burning 
 of the candle, and has experienced an important chemical 
 change. Other substances besides a burning candle will 
 produce chemical changes in the air. 
 
 Exp. 5. Take a glass jar 6 or 8 centim. in diameter and 
 2.5 cm. high; moisten it upon the inside, and sprinkle over 
 the moistened surface a thick layer of iron filings ; then place it, 
 with its open end downwards, over water in a soup plate, and 
 set it aside in a warm room for a day or two : the iron filings 
 will gradually grow rusty, the bulk of the air in the jar will be- 
 come less, and the water will rise slowly until it stands about 
 5 centim. higher in the jar than it did at first; after this the 
 bulk of the enclosed air will not be further lessened. If a flat 
 plate of glass be now slipped under the open end of the jar, 
 the whole may be lifted out of the water ; and on placing it 
 mouth upwards, and then removing the glass plate, and at once 
 putting into the jar a lighted taper fastened to a wire, as shown 
 in Fig. 3, the taper will immediately cease to burn. 
 
Experiments on Air. 
 
 Fig. 3. 
 
 The iron in rusting has taken away something from the 
 air which enabled the taper to burn in it ; and that some- 
 thing is the elementary gas called 
 oxygen. The remainder of the air 
 in which the taper will not burn 
 consists chiefly of another gaseous 
 element, called nitrogen. 
 
 The candle in burning, Exp. 4, 
 also took oxygen from the air, and it 
 went out as soon as it had taken up 
 a certain quantity of the oxygen con- 
 tained in the air enclosed by the jar. 
 
 Other metals besides iron may be 
 used to remove oxygen from the air, 
 particularly if they are heated with 
 it. If mercury be used for the 
 purpose, it will not only remove 
 
 the oxygen, but it may be afterwards made to give it up again 
 in a separate form. 
 
 Exp. 6. This experiment Fig. 4. 
 
 requires some days to com- 
 plete it, but it is very in- 
 structive, and may be made 
 in the following manner : 
 Into a dry flask provided 
 with a neck 50 centim. or 
 more in length introduce 
 about 40 grams of clean 
 mercury ; then bend the 
 neck of the flask twice 
 upon itself, into the form 
 shown in Fig. 4, and plunge 
 the bend into a small Wedg- 
 wood-ware mortar, contain- 
 ing mercury, so as to leave 
 the open end of the neck 
 projecting above the surface of the metal into a jar containing 
 
 C 
 
1 8 Experiments on Air. 
 
 air, which is to be supported over it. Now apply the heat of a lamp 
 to the flask, and keep the mercury for two or three days at a 
 point just below that necessary to make it boil. Red scales will 
 be formed slowly upon the surface of the mercury in the flask ; 
 and these scales after a time will no longer increase in quantity. 
 If the lamp be then withdrawn, and the whole allowed to cool, 
 the bulk of the air will be found to have become considerably 
 less. The hot mercury has acted chemically on the air both 
 of the flask and of the jar, owing to the free passage of both 
 portions through the neck. 
 
 The gas which is left consists almost entirely of nitrogen. 
 On adding mercury till the height outside and inside the 
 jar is the same, and then withdrawing the stopper and in- 
 troducing a lighted taper, supported on a wire handle, it will 
 be put out. A mouse or other small animal would also soon 
 die if plunged into it. The oxygen is the portion of the air 
 necessary to support the life of animals. If one or two 
 grams of the red scales formed by thus heating mercury in 
 air be placed in a test tube, they may be made to give up 
 the oxygen again by heating them still more strongly. 
 
 Exp. 7. Fit a good cork to the mouth of the tube ; then with- 
 draw the cork, and with a round file bore a hole through it, just 
 
 large enough to 
 
 Fi S- 5- admit a narrow 
 
 glass tube, bent 
 as shown in Fig. 
 5. Heat the 
 tube and the red 
 scales in the 
 flame of a spirit 
 lamp while the 
 
 open end of the narrow tube is dipped under water. Bubbles of 
 gas will soon begin to come off. Next fill two or three narrow jars 
 or wide test tubes with water ; close them with the finger, and in- 
 vert them in the basin ; collect the bubbles of gas in one of them 
 as they escape from the narrow tube. The first jar will be filled 
 chiefly with the air originally in the heated tube ; this may be 
 thrown away ; but if into one of the other tubes, when filled with 
 
Air a Mixture. 19 
 
 the gas, a splinter of wood on the end of which is a glowing 
 spark be plunged, the wood will burst into a flame. 
 
 The mercury used in the flask, Fig. 4, has in fact sepa- 
 rated the atmospheric air into two portions, one of which, 
 the nitrogen, will not allow a candle to burn in it, and is 
 left unacted upon by the metal ; while the portion which is 
 active in supporting flame has combined with the mercury, 
 and converted it into the red scales. . When these scales 
 are heated more strongly, they become separated into 
 metallic mercury, and into the gas which, as we have seen, is 
 highly fitted both for the support of life and for the burning 
 of such bodies as may be kindled in the open air. This gas 
 is called oxygen (the 'acid producer'), because it forms a 
 needful part of many acid bodies. 
 
 A fixed weight of mercury will always unite with a fixed 
 quantity of oxygen. For instance, 400 grams of mercury 
 will combine with exactly 32 grams of oxygen, and will form 
 432 grams of the red oxide. If, again, 432 grams of these 
 red scales of mercuric oxide be decomposed by heat, and 
 proper care be taken to collect the whole of what is given 
 off, 400 grams of liquid metallic mercury would be found, 
 and 32 grams, or about 22*4 litres, of gaseous oxygen. 
 These changes may be represented in symbols as follows; 
 the quantities of each substance are written beneath : 
 
 Mercuric Oxide Mercury Oxygen 
 
 2Hg O = 2Hg + 2 
 
 2(20O + l6) 2 X 200 l6 X 2 
 
 (8) OXYGEN.: Symbol, O; Atomic Weight, 16; Atomic 
 Volume, [_] ; Specific Gravity, 1*10563 ; Relative Weight, 16;* 
 Molecular Weight, O 2 , 32 ; Molecular Volume^ [ |.f 
 
 Exp. 8. There are other means of obtaining oxygen : one of 
 the best is by heating potassic chlorate (KC1O 3 ). This salt may 
 
 * See page 30. 
 
 t* See the chapter on the Atomic Theory for an explanation of these 
 terms. 
 
 C 2. 
 
2O Mode of Collecting Gases. 
 
 be mixed with about its own weight of black manganese oxide 
 in fine powder. This oxide should be first made red hot in a 
 covered clay crucible, and allowed to cool ; it should then be 
 ground up in a clean mortar with the chlorate. The manganese 
 oxide enables the oxygen to pass off from the chlorate at a much 
 lower heat than is needed if the salt is heated alone, although 
 the oxide itself undergoes no permanent change. 30 or 40 
 grams of this mixture may be put into a clean and dry Florence 
 oil flask, provided with a good cork, through which is passed a 
 tolerably wide bent glass tube. The flask is to be placed with 
 the end of the tube dipping under the water in the pnetimatic 
 trough, Fig. 6. If the mixture in the flask is heated over a lamp, 
 gas comes off freely, and may be collected in jars placed for its 
 reception. 
 
 Fig. 6. 
 
 A pneumatic trough for experiments upon gases may be 
 easily made out of a small tub or pan, which is to be nearly 
 filled with water. A shelf must be fixed at one end, so 
 as to be 3 or 4 centim. below the surface of the water, or 
 the glass jar may even be supported on a brick; 3 or 4 
 jars, each holding about a litre, may be used to receive the 
 gas. They should be open below, and one or two may be 
 provided with a glass stopper ground to fit the neck. They 
 
Oxygen Gas. 21 
 
 may be filled with water in the trough, and placed with the 
 bottom downwards on the shelf. As they become filled one 
 after another with the gas, they can be removed by sliding a 
 plate under each, while the mouth is still under water, and 
 then lifting the plate and jar together out of the trough. 
 
 Though the potassic chlorate is more easily decomposed 
 when mixed with manganese oxide than when heated alone, 
 the pure salt may be made to give off oxygen by heating it 
 more strongly by itself. 
 
 Exp. 9. Place about a gram of the salt in a test tube, 
 and heat it over a spirit lamp. The chlorate snaps and 
 flies to pieces, or decrepitates, when first heated. It then 
 melts and forms a clear liquid, which, when heated more 
 strongly, gives off bubbles of pure oxygen gas. The mass gra- 
 dually becomes white and opaque, and ceases to give off oxygen, 
 leaving a white residue, consisting of chlorine and potassium 
 only, and known as potassic chloride. The gas at first often 
 looks cloudy, owing to little particles of the salt which are 
 carried over suspended in it in fine powder, but these gradually 
 become dissolved in the water. 
 
 245 grams of the chlorate would give off 96 grams of 
 oxygen, or about 67*2 litres of the gas. The change may 
 be thus represented : 
 
 Potassic Chlorate Potassic Chloride 
 
 2 K Cl 3 = 2K Cl + 3O 2 
 + i6x3) 2(39 + 35-5) 6 x 16 
 
 245 H9 96 
 
 If the mineral known as black manganese oxide (MnO 2 ) 
 be made red hot, oxygen may also be obtained from it ; but 
 only one-third of its oxygen is thus driven off, or about one- 
 ninth of the weight of the mineral if pure. The ore of 
 manganese, however, always contains impurities, which cause 
 the oxygen gas to be mixed with more or less of other gases. 
 The black oxide when heated becomes converted, with loss 
 
22 Oxygen Mode of Preparing. 
 
 of oxygen, into a reddish-brown oxide of manganese : 261 
 grams of pure black oxide would yield 32 grams of oxygen, 
 or 22' 4 litres of gas. 
 
 Black Oxide Red Oxide Oxygen 
 
 3Mn O a = Mn 3 O 4 
 3(55 + 16x2) 55><3 + i6x4 
 
 261 229 
 
 261 
 
 Exp. 10. Procure a gaspipe or an iron tube 3 or 4 centim. in 
 diameter, 40 or 50 cm. long, closed at one end, and provided at 
 the other with a cork, through which is passed a long piece of 
 pewter or copper tubing ; place 50 or 100 grams of the oxide in 
 small lumps in the tube, and make the closed end of the iron tube 
 red hot : gas will be driven off, and may be collected over water. 
 
 Red lead, nitre, and several other substances, also give off 
 oxygen, more or less pure, when heated ; but either potassic 
 chlorate, or manganese oxide, or the mixture of both, is the 
 substance from which it is usually and most easily obtained. 
 
 Oxygen is a clear, transparent, colourless gas, which has 
 never been liquefied by cold or pressure ; it has no smell or 
 taste. No other gas can be used instead of oxygen for the 
 support of respiration in man and animals ; but it cannot be 
 safely breathed in a pure state for any length of time, as it 
 would over-excite the bodily frame. The nitrogen with 
 which it is mixed in the air is needed to dilute it, so that 
 it may be respired with safety. Oxygen is attracted by a 
 magnet like iron. 
 
 Oxygen is remarkable for its great chemical activity. It 
 will combine with each of the elementary bodies, with the 
 single exception of fluorine. Substances which will burn 
 in air burn in oxygen with much greater energy, as may be 
 further shown by the following experiments : 
 
 Exp. 1 1. Fasten a piece of barky charcoal to a stout wire ; 
 pass the wire through a small flat board or a piece of tinplate. 
 Kindle the charcoal by holding it in a flame ; then hang it in a 
 
Oxygen Properties. 2 3 
 
 jar of oxygen. It will burn away rapidly, with a steady glow, 
 throwing out sparks, or scintillations^ and will produce a new 
 colourless gas, called carbonic anhydride, or carbonic acid 
 (C0 2 ). 
 
 Exp. 12. Place a little sulphur in a small copper spoon on 
 the end of a wire, called a deflagrating spoon ; heat it in the flame 
 of a spirit lamp till it takes fire, and suspend it in like manner in 
 another jar of oxygen. The sulphur will burn with a lilac flame, 
 and on uniting with the gas will form an invisible substance with 
 a pungent odour, called sulphurous anhydride (SO 2 ). 
 
 Exp. 13. Cut off a piece of phosphorus of about the size of 
 a pea from a stick of phosphorus under water.* Dry it care- 
 fully on a bit of blotting-paper, and put it into a copper spoon, 
 also suspended from a wire. Touch it with a hot wire : it will 
 take fire. Plunge it at once into oxygen : it will burn with 
 dazzling brilliancy, and form white fumes of phosphoric 
 anhydride (P 2 O 5 ). 
 
 Many substances which will scarcely burn in air deflagrate, 
 or burn with violence, in oxygen : 
 
 Exp. 14. Heat a piece of watch-spring red hot for a few 
 moments in the fire ; let it cool, and then twist it into a spiral. 
 Heat one end slightly, and dip it into a little powdered 
 sulphur, and pass the other end through a cork. Set fire 
 to the sulphur, and immediately plunge it into a jar of oxygen, 
 supporting it in the neck of the jar by the cork. The 
 burning sulphur will set fire to the steel, which will burn with 
 great splendour, while drops of melted oxide of iron (Fe 3 O 4 ) will 
 run down and fall upon the plate below. 
 
 Exp. 15. Zinc foil cut into the form of a tassel, if it be 
 tipped with sulphur to enable it to take fire, may be kindled and 
 will burn in oxygen with a dazzling white light, forming zinc 
 oxide (ZnO). 
 
 Exp. 1 6. Place a piece of potassium f of the size of a pea in 
 
 * Phosphorus is extremely inflammable ; it must always be kept under 
 water, and should not be handled with the warm hand except under 
 water. 
 
 t Potassium is the metal contained in pearl-ash ; it must always be 
 kept under naphtha, and must not be touched with the fingers, or with 
 anything that is wet. 
 
24 Oxidation Combustion. 
 
 a copper spoon ; heat it in the flame of a spirit lamp till it be- 
 gins to glow ; then introduce it into a jar of oxygen. It will 
 burn, and a quantity of white solid potash (K 2 O) will be formed 
 in the spoon by the union of oxygen with the potassium. 
 
 The compounds which oxygen forms with other elements 
 are called oxides, and the act of combination of any substance 
 with oxygen is called oxidation. The experiments above 
 described are instances of this process, and in each case a 
 compound is produced entirely different in properties both 
 from the oxygen and from the body burned. 
 
 (9) Combustion. Whenever any rapid chemical action 
 takes place, attended with great heat and light, combustion is 
 said to occur. In order to start the process, it is generally 
 necessary to heat the body ; afterwards the heat given out by 
 the chemical change produced is more than enough to carry 
 it on, and the combination goes forward with increasing 
 vigour until it is completed. 
 
 Bodies which are burned, and which disappear from sight 
 as when coal or charcoal is consumed in the fire are in 
 no case actually destroyed. They are only altered in form. 
 A candle, for example, in burning seems to be completely 
 consumed, but the materials of which it consisted are not 
 destroyed. This most important fact may be proved as 
 follows : 
 
 Exp. 17. Take a glass tube 30 or 40 centim. long and 4 cm. 
 in diameter. Thrust a piece of wire gauze half-way down the 
 tube, and fill the upper half with fragments of caustic soda 
 (Fig. 7). To the lower end of the tube a fit a cork pierced with 
 three or four holes for the admission of air, and fasten to it a 
 short piece of wax taper. To the other end of the tube fit a cork 
 through which a short tube of about 8 millimetres in diameter is 
 passed. Now weigh the tube and its contents. By means of a 
 piece of india-rubber tubing, join the short tube at the top with 
 a closed jar filled with water, which is to act as an aspirator. 
 This is easily made from a tinplate 9-litre (2-gallon) oil can b y 
 into the side of which, near the bottom, a small cock is soldered. 
 Open the stop-cock near the bottom of the closed jar, and let 
 
Matter when Burnt not Destroyed. 2$ 
 
 the water flow. The water cannot run out at the stop-cock 
 unless air takes its place ; and since the aspirator is connected 
 by the caoutchouc tubing with the wide glass tube, which is open 
 freely to the outer air at the bottom, a current of air is esta- 
 blished through the wide tube. Now withdraw the cork at the 
 bottom, light the taper, and immediately put it back into the 
 
 Fig. 7. 
 
 tube. In three or four minutes' time close the stop-cock : the 
 taper will at once go out. When the apparatus is cold, slip 
 off the caoutchouc connecting tube, and weigh the wide glass 
 tube. It will be found to have gained in weight by several 
 decigrams. 
 
 The candle in burning combines with a portion of oxygen 
 from the air, forming water and carbonic anhydride. These 
 are both absorbed as they pass over the caustic soda, and 
 hence, though the taper itself looks smaller, and has really 
 lost in weight, the chemical products obtained weigh more 
 than the taper originally did. 
 
 Whether a body be burned quickly or slowly, the quantity 
 of heat which a given weight of it, say i gram, gives out in 
 burning is perfectly fixed, and depends upon the nature of 
 
26 Combustion Quick, Slow. 
 
 the burning body. Nevertheless, the more the oxygen Is 
 diluted by mixture with a gas which does not act chemi- 
 cally upon it, such as nitrogen, the lower is the apparent 
 temperature which is produced at the moment by combus- 
 tion; because not only are fewer particles of oxygen in 
 contact with the burning body, but at the same time the 
 diluting gas carries off part of the heat, since it has its own 
 temperature raised without contributing to the chemical 
 action. And hence, when a body is burned in air, it seems 
 to give out much less heat than when burned in oxygen, and 
 it burns much more slowly. But when we blow a fire with 
 the bellows, or cause a powerful draught of air up the 
 chimney, we quicken the combustion and raise the heat, 
 because we thus bring a larger number of particles of 
 oxygen into contact with the fuel in a given time ; and 
 by the same operation we carry off the gases formed by 
 combustion, which are unable to combine with the burning 
 body, and would prevent its contact with fresh particles of 
 the oxygen of the air. That this is so may be seen by the 
 check to the fire and the reduced consumption of fuel 
 caused by closing the damper or shutting the ashpit door of 
 a furnace. 
 
 Oxygen is the most important and also the most abundant 
 of the elements. We have already seen (Exp. 5), that it 
 forms a little more than a fifth of the bulk of the air ; it 
 also constitutes eight-ninths of the entire weight of water ; 
 while clay, limestone, and siliceous sand contain about half 
 their weight of it. Oxygen is also found largely in various 
 other common substances not of mineral origin, such as 
 sugar, starch, and woody fibre, which contain about half 
 their weight of it ; and many bodies derived from animals, 
 such as muscular tissue, leather, and horn, contain it in 
 large proportion. 
 
 Oxygen may be shaken up with water without experiencing 
 any sensible change in bulk, for it is only slightly soluble in 
 that liquid, 100 cub. centim. of it, at 15 C., dissolving about 
 
Oxygen, Test for it* 
 
 27 
 
 Fig. 8. 
 
 3 c.c. of the gas : but this solubility, slight as it may appear, is 
 essential to the existence of living animals, for it is only in the 
 dissolved state that the gas finds its way into the blood, and 
 effects the chemical changes in the body necessary to life, 
 both in land animals and in those which live in water. 
 A solution of potash may also be shaken up with oxygen with- 
 out sensibly dissolving it ; but if pyrogallic acid be added 
 to the potash solution, the oxygen is rapidly absorbed, and 
 the liquid turns brown. 
 
 Exp. 1 8. Pass a few bubbles of oxygen into a strong tube, 
 graduated to divisions of 0-5 c. c. each, filled with mercury, and 
 placed in a deep glass full of mercury (Fig. 8). Introduce a 
 solution of potash (i part of solid potash in 4 of water) by means 
 of a pipette with a point 
 curved upwards, blowing into 
 the pipette with sufficient 
 force to drive over 8 or 10 
 drops of the solution. Agitate 
 this liquid briskly with the gas 
 by thrusting the tube down 
 quickly into the mercury, and 
 raising it to its former level 
 several times. The oxygen 
 will not alter in volume. Now, 
 with a fresh pipette, intro- 
 duce an equal quantity of a 
 solution of pyrogallic acid 
 (i part of acid and 6 of 
 water). Again agitate the mix- 
 ture. It becomes intensely 
 brown, and the whole of the 
 gas will disappear if pure. 
 If a measured quantity of 
 air be taken, it is easy in 
 
 a few minutes to ascertain roughly the proportion of oxygen 
 present by the absorption effected in this way, because the 
 nitrogen is left unchanged, and may be measured after the 
 absorption of oxygen is over. 
 
28 Measurement of Gases. 
 
 Oxygen is a little heavier than atmospheric air. A 
 measure of air which weighs i gram would, if filled with 
 oxygen at the same temperature, and when the baro- 
 meter stands at the same height, weigh 1*1056 gram ; and a 
 measure of hydrogen which weighs i gram would, when 
 filled with oxygen, weigh exactly 16 grams : so that oxygen 
 is precisely 16 times as heavy as hydrogen. 
 
 (10) Measurement of Gases under Standard Conditions. 
 It is necessary when comparing the weights of gases with 
 each other to attend carefully to the temperature. A quan- 
 tity of any gas which at o C. exactly fills i litre expands so 
 rapidly when heated, that at 273C. it would become dilated 
 to 2 litres. A quantity of any gas which at o C. measures 
 just i litre would, if heated to 100 C. (the temperature of 
 boiling water), become expanded to 1*366 litre. It is now 
 customary to compare gases at the standard temperature of 
 o C. ; or, if they are not actually at this temperature, to re- 
 duce the results to this point by calculation. For instance, 
 if v be the volume of any gas measured at the temperature t 
 in Centigrade degrees, and V be the bulk of the same gas at 
 o C., then 
 
 V - 2 73?' 
 273+* 
 
 It is equally important to compare gases at a fixed baro- 
 metric pressure. At the level of the sea, the average weight 
 of a column of air which reaches to the top of the atmosphere 
 will exactly balance a column of mercury 760 millimetres 
 high, and at o C. But at the top of a mountain of a little 
 more than 5*5 kilometres or nearly 3*4 miles high, the weight 
 of a column of air reaching to the top of the atmosphere 
 would only be able to balance a column of mercury of half 
 this height, or 380 mm. And a quantity of air at the bottom 
 of the mountain which measures i litre while the barometer 
 stands at 760 mm. would, if carried to the top of the moun- 
 tain, expand to 2 litres. But it is not necessary to take the 
 air to the top of the mountain in order to observe this fact : 
 
Measurement of Gases. 29 
 
 for if the pressure upon the gas be by any other suitable 
 means lessened to one-half, the air will immediately become 
 doubled in bulk. If, on the other hand, the pressure be 
 doubled, the air will become reduced in bulk to one-half. 
 Gases, in fact, occupy a space inversely as the pressure to 
 which they are subjected ; and, in order to avoid inaccuracy 
 in measuring them, they are always compared by calculating 
 them as if subjected to a fixed or standard pressure of a 
 column of mercury at o C. of 760 mm. high. 
 
 Suppose v to be the observed volume (after it has been 
 corrected, if necessary, for temperature),/ the pressure at 
 the time of observation, measured by the height of the mer- 
 curial column in the barometer in millimetres, and Fthe 
 volume corrected to the pressure of 760 mm. of mercury, 
 then 
 
 y=P v , 
 
 760' 
 
 In taking the specific gravity of gases, it has been the 
 practice to compare them with an equal bulk of dry air as 
 the standard. When, for instance, it is said that the specific 
 gravity of oxygen is 1-10563, the expression means that if 
 a vessel which holds a certain volume of dry air which 
 weighs exactly i grarn, were filled with dry oxygen gas, 
 at the same temperature and pressure, the weight of this 
 oxygen would be i '10563 gram; the same bulk of dry 
 hydrogen would be only -0691 gram, and the specific gravity 
 of hydrogen is said to be '0691. 
 
 This practice of comparing gases with air is both cus- 
 tomary and convenient; but it has been objected to on the 
 ground that air is a mixture, and not a true chemical com- 
 pound. Now the proportions of the substances in a mixture 
 are liable to variation, while those of a chemical compound 
 are invariable. Fortunately for the accuracy of the data 
 founded on comparison with the air as a standard, the pro- 
 portions of the oxygen and nitrogen in the air do not vary 
 practically to any important amount, but the objection in 
 
3O Measurement of Gases. 
 
 principle remains. Hence it has of late years become the 
 custom further to compare the weights of gases and vapours 
 with the weight of an equal volume of some elementary 
 body ; and the element selected for the purpose is hydrogen, 
 the lightest of all known substances. The result of this 
 comparison with hydrogen will hereafter be spoken of as the 
 relative weight of a gas or vapour. Suppose that, for the 
 purpose of this comparison, we take a vessel which would hold 
 i gram of hydrogen at o C. and 760 mm. barometer ; the 
 capacity of such a vessel would be 1 1 '19 litres. This measure, 
 when filled with oxygen under similar circumstances, would 
 contain 1 6 grams of oxygen; and if filled with nitrogen, it 
 would contain 14 grams of nitrogen. Hence, if the weight of 
 such a bulk of hydrogen be called i, the relative weight of oxy- 
 gen will be 16, the relative weight of nitrogen 14, and so oa 
 
 (u) Acids, Bases , and Salts. The compounds formed by 
 the union of oxygen with the other elements differ from each 
 other very much in properties ; but among them are two im- 
 portant classes of oxides, chemically opposed to each other, 
 one commonly known as acids, the other as bases. Everyone 
 is familiar with the sourness of vinegar or of a lemon, which 
 in both cases is due to the presence of a substance known in 
 chemical language as an add. The acetic acid gives the sour 
 taste to vinegar ; the citric acid is the substance which gives 
 the sharp flavour to the lemon. There are many other well- 
 known substances, like sulphuric, nitric, and phosphoric 
 acids, which when diluted sufficiently to prevent them from 
 injuring the surface of the tongue, possess a sour taste ; and 
 these all belong to the class of acids. 
 
 Again, most persons are acquainted with the nauseous 
 taste of soda, and with the peculiar soapy feeling which it 
 occasions when rubbed upon the skin : this is due to what 
 is called the alkaline property of soda, a property in which 
 it resembles potash and a few other substances. The 
 alkalies are soluble in water, and form one class of a numerous 
 group of chemical agents, known under the name of bases. 
 
A cids and A Ikalics. 3 1 
 
 Many elementary substances, like sulphur and phosphorus, 
 by their combination with oxygen, furnish compounds which 
 are freely soluble in water, and have a sour, and often a 
 burning, taste ; they also turn many vegetable blue colours, 
 such as the blue of an infusion of litmus,* or of purple 
 cabbage, to a bright red. Such oxides are called anhydrides 
 (which means bodies free from hydrogen) to distinguish 
 them from the bodies these same oxides furnish when they 
 are acted upon by water, which all contain hydrogen, and 
 belong to the class of adds. All the non-metallic elements, 
 except hydrogen and fluorine, form with oxygen one 
 or more compounds, which, when dissolved in water, are 
 acids, and often intensely powerful acids. Many of the 
 metals, on the other hand, by their union with oxygen, give 
 rise to bodies of an opposite kind, which have been termed 
 bases. For instance, the white alkaline substance formed by 
 burning potassium in oxygen is dissolved rapidly by water ; 
 it produces a colourless liquid, of a soapy, disagreeable taste, 
 and a peculiar lixivial smell. It corrodes the skin, dissolves 
 oil-paint, restores the blue colour to litmus which has been 
 reddened by an acid, and neutralises the strongest acids. This 
 power which acids and bases have of uniting with each other, 
 and destroying the chemical activity which each has when 
 separate, is the most marked feature of these two classes of 
 substances. The compounds produced by their action upon 
 
 
 * Paper tinged blue with a watery or spirituous infusion of litmus (a 
 colouring matter obtained from certain lichens) is in constant use for 
 showing the .presence of an acid in a liquid, as it immediately becomes 
 reddened by the action of even very small quantities of an acid when 
 uncombined with a base. The same paper, if faintly reddened by means 
 of vinegar or any other acid, is equally valuable as a test for an alkali, 
 which if present uncombined with acids immediately restores the blue 
 colour. The alkalies also turn paper tinged yellow with the colouring 
 matter of turmeric or rhubarb to a reddish-brown hue. 
 
 A test in chemistry simply means a method of trial, and test solutions 
 or test papers, are solutions or papers made for the purpose of trying 
 whether certain substances are present or not, according as the solu- 
 tion or paper does or does not undergo a particular change, which would 
 be produced if the body sought for were there. 
 
32 Acids y Bases y Salts. 
 
 each other constitute what are called salts, and, when 
 freed from the water in which they are dissolved, may often 
 be obtained in crystals. 
 
 Exp. 19. Cut a red cabbage into slices, and boil it with 
 water ; strain off the purplish liquid thus obtained. To a portion 
 of this decoction add a little solution of caustic potash : a green 
 liquid will be produced. To another portion of the cabbage 
 liquor add a few drops of sulphuric acid : the solution will 
 become red. Pour the red acid liquor into the green alkaline 
 solution, and stir the mixture : the red colour at first disappears, 
 and the whole remains green ; but on continuing to add the red 
 liquid cautiously, a point is reached at which the liquid assumes 
 a clear blue colour. There is then no excess either of acid or of 
 alkali in the solution ; and on evaporating the liquid a neutral 
 salt, potassic sulphate, formed by the action of the acid upon the 
 alkali, may be obtained in the form of crystals.* 
 
 Here it is necessary to remark that the same element often 
 forms more than one oxide which when dissolved in water, 
 furnishes an acid. When this is the case, the oxide which 
 contains the largest quantity of oxygen is designated by a 
 name ending in ic, while the compound with the smaller 
 proportion of oxygen is made to end in ous. Sulphur, for 
 example, furnishes both sulphuric acid (H 2 SO 4 ) and sulphur- 
 ous acid (H 2 SO 3 ) ; and both these acids form salts when acted 
 upon by bases. The salts of acids ending in ic are indicated 
 by names which end in ate, while the salts of acids in ous 
 have names ending in ite. For instance, the salts of sul- 
 phuric acid are called sulphates ; of nitric acid, nitrates ; of 
 phosphoric acid, phosphates ; while those of sulphurous 
 
 * The change may be expressed in symbols in this manner : 
 Sulphuric Acid Caustic Potash Potassic Sulphate Water 
 
 H a SO 4 + 2KHO = K 2 SO 4 + 2H 2 O 
 
 2x1 + 32+16x4 2(39+I + l6) 2x39 + 32+16x4 2(lx2+l6) 
 
 from which, by reference to the table of atomic weights (page 5), it 
 may be seen that 98 grams of pure sulphuric acid, with 1 12 grams of 
 caustic potash, would form 1 74 grams of a neutral salt, and wouM set 
 free 36 grams of water. 
 
Names given to Acids and Bases. 33 
 
 acid are called sulphites ; those of nitrous acid, nitrites ; and 
 of phosphorous acid, phosphites. 
 
 The acids are not all soluble in water ; and the insoluble 
 acids have no sour taste. In like manner bases exist, such as 
 zinc oxide and ferric oxide, which are not soluble in water, 
 and then they neither corrode the skin nor exert any sensible 
 effect upon coloured tests ; but they are capable of com- 
 bining chemically with acids, and forming salts. 
 
 Exp. 20. Add zinc oxide to diluted sulphuric acid and stir 
 the two together : it will be readily dissolved, and, on evaporat- 
 ing the liquid, a true salt, zinc sulphate, may be obtained in 
 needle-shaped crystals : 
 
 Sulph. Acid Zinc Oxide Zinc Sulphate Water 
 
 H a SO 4 + ZnO = ZnSO 4 + H a O 
 
 Sometimes the same metal, when combined with different 
 quantities of oxygen, furnishes two different bases, or bodies 
 capable of neutralising acids more or less completely. Iron, 
 for instance, furnishes ferric oxide (Fe 2 O 3 ) and ferrous oxide 
 (FeO) ; mercury also gives mercuric oxide (HgO) and mer- 
 curous oxide (Hg 2 O). The base to which the name ending in 
 ic is given always contains the larger proportion of oxygen. 
 A compound formed by the action of ferrous oxide on sul- 
 phuric acid would be called ferrous sulphate; while that 
 furnished by the action of ferric oxide on sulphuric acid 
 would be known as ferric sulphate. 
 
 Besides the oxides which furnish acids and bases, there is 
 a third set of oxides, which is neither acid nor basic, and is 
 not disposed to enter into combination with either class. 
 Black manganese oxide (MnO 2 ; or, as would be better, by 
 doubling the molecular formula, MnO, MnO 3 ), magnetic 
 iron oxide (FeO, Fe 2 O 3 ), and red lead (2PbO, PbO 2 ), afford 
 instances of this kind. Such oxides appear generally to be 
 formed by the union of two different oxides of the same 
 metal with each other, and are analogous to salts. Indeed, 
 the union of an anhydride with an anhydrous (or water free) 
 
 D 
 
34 Ozone. 
 
 basic oxide furnishes a true salt ; for instance, sulphuric an- 
 hydride (SO 3 ), by uniting with cupric oxide (CuO), furnishes 
 cupric sulphate (CuO,SO 3 , or CuSO 4 , as it is usually written) ; 
 but in such cases no separation of water occurs. 
 
 (12) Ozone. Oxygen in its usual form has no sensible 
 smell, but it may be obtained in a more active condition, 
 and then it has a very peculiar odour. This smell is per- 
 ceived whenever an electrical machine is put in action in the 
 air, and more or less ozone (as it has been called from the 
 Greek ow, I smell) is immediately produced. It is also 
 formed whenever water is decomposed between platinum 
 plates by the voltaic battery (p. 44). A special form of 
 apparatus has been contrived for electrifying a current of 
 air, so as to change part of its oxygen into ozone. Ozone 
 may also be obtained by chemical means. 
 
 Exp. 21. Scrape off the white coating of a stick of phospho- 
 rus under water, and cut the cleansed phosphorus into pieces 
 12 or 15 millirn. long. Place one of these pieces in a wide- 
 mouthed litre bottle full of air, with about a teaspoonful of water 
 at the bottom. Close the mouth of the bottle with a glass 
 plate, and expose the whole for half an hour to a temperature of 
 15 or 20 C. Then invert the neck of the bottle in water, and 
 allow the phosphorus to fall out. Replace the glass plate, and 
 withdraw the bottle and its contents from the water. The 
 phosphorus in this experiment undergoes a slow oxidation, 
 during which a little ozone is formed, and is left mixed with the 
 >r ; but the ozone will be again destroyed if it is left too long 
 with the phosphorus. 
 
 The most delicate test of ozone is potassic iodide (KI), 
 from which it immediately sets iodine free, which can in- 
 stantly be detected by its action on starch. 
 
 Exp. 22. Boil a gram of starch in 50 grams of water, so as 
 to produce a thin mucilage, and add o - i gram of potassic iodide 
 to the mixture. Brush a little of this solution over a slip of 
 clean writing-paper, and plunge the paper into one of the jars in 
 which the phosphorus has been acting on the air. An imme- 
 
Ozone. 3 5 
 
 diate blue stain is produced, owing to the action first of the 
 ozone upon the iodide, and then of the free iodine upon the 
 starch. Paper may be prepared beforehand with this starch 
 paste and iodide, and dried ; in which form it may be kept in a 
 bottle till wanted. 
 
 The ozone displaces iodine from the iodide, though ordi- 
 nary oxygen will not do so. 
 
 The slow oxidation of ether, of oil of turpentine, and of 
 many other substances, is attended with the formation of 
 small quantities of ozone ; and most plants, when growing in 
 the sunshine, give it out in excessively small quantities. 
 Traces of ozone are probably present usually in the air, but 
 the proportion varies. If a piece of the dry iodized paper 
 be exposed for five minutes in the open air of the country, it 
 acquires a bluish tint, the strength of which varies on dif- 
 ferent days, according as the quantity of ozone in the air is 
 greater or less. Sometimes, in damp or foggy weather, no 
 such change occurs, and it is scarcely ever observed in the 
 air of large towns. The effect is most marked on the sea 
 coast, and when the wind blows off the sea. It is not im- 
 probable that these minute quantities of ozone, exert an 
 important purifying effect upon the atmosphere by destroying 
 and oxidising animal effluvia, which would otherwise in- 
 crease in quantity until they produced disease. The ozone 
 is absorbed by these offensive bodies, which it converts into 
 harmless compounds. 
 
 Ozone is not soluble in water, but it at once corrodes 
 caoutchouc, cork, and many other organic matters. It pro- 
 duces a feeling of irritation in the lungs when air strongly 
 charged with it is breathed. It immediately oxidizes the 
 common metals, as well as mercury, when dry, and even 
 silver, if it be moist. It is instantly changed into common 
 oxygen, if passed over manganese oxide, on which, however, 
 it produces no permanent effect. Several other bodies also 
 on which it exerts no sensible action change it into common 
 oxygen ; and if it be heated to a temperature not greater 
 
 D 2 
 
36 Ozone. 
 
 than that of boiling water, a similar change occurs. Ozone 
 is much denser than oxygen gas : probably three measures 
 of oxygen furnish by condensation two measures of ozone. 
 The exact amount of condensation, however, is not certain, 
 because ozone has never been obtained free from admixture 
 with a very large proportion either of air or of oxygen. 
 
 Ozone has a powerful bleaching action. It has been 
 attempted to make ozone by electric action on the air, and 
 to use the product as a bleaching agent. 
 
 Exp. 23. Take a bottle of air which has been ozonised by 
 means of phosphorus, and add to it a few drops of a "very dilute 
 blue solution, formed by dissolving powdered indigo in strong 
 sulphuric acid, and then diluting it with water. If the blue 
 liquid is shaken up with the ozonised air, the colour quickly dis- 
 appears. 
 
 The mode in which electricity and phosphorus, and other 
 agents, act upon oxygen and convert it into ozone is not 
 understood. 
 
 (13) NITROGEN: Symbol N; Atomic Wt. 14; Atomic 
 Vol. Q ; Sp. Gr. 0-971 ; Rd. Wt. 14; Mol. Wt. N 2 , 28 ; 
 Mol. Vol. [""7"]. 
 
 The most abundant constituent of the atmosphere, nitro- 
 gen (the ' generator of nitre,' so called because it is an es- 
 sential component in nitre) is also sometimes called azote, 
 because it is unfit to support life. 
 
 The easiest methods of obtaining nitrogen are founded 
 upon the removal of oxygen from the air. One of these, 
 the exposure of moistened iron filings to air contained in a 
 jar over water, has been already described (Exp. 4). 
 
 Exp. 24. Support a stick of phosphorus upon a wire above 
 the surface of a dish of water, and place a jar of air over it. The 
 phosphorus will, without the aid of heat, gradually remove the 
 oxygen from the air, forming phosphorous anhydride (P 2 O 3 ). 
 which will be dissolved by the water, and in a day or two the 
 gas which is left will be nitrogen nearly pure. 
 
Nitrogen. 37 
 
 Exp. 25. The same change may be effected in a few minutes 
 if the phosphorus is heated. Dry two or three pieces of phos- 
 phorus of the size of a pea upon blotting-paper, and float them 
 in a small porcelain dish upon the water in the trough : kindle the 
 phosphorus by touching it with a hot wire, and cover it at once 
 with a jar full of air. The phosphorus will burn till it has 
 exhausted all the oxygen in the jar, which will become filled with 
 white fumes of phosphoric anhydride (P a O 5 ). These become 
 gradually dissolved by the water, and nearly pure nitrogen is left. 
 
 Oxygen may also be very completely separated from 
 nitrogen by allowing the air to stream very slowly over finely 
 divided copper made red hot. ' 
 
 Nitrogen has neither colour, taste, nor smell. It has 
 ggf been liquefied by cold or pressure. It is a little 
 lighter than air. A measure of hydrogen which would weigh 
 i gram would, when filled with nitrogen at the same tem- 
 perature and pressure, weigh 14 grams. Water dissolves it 
 but sparingly, taking up about one-fiftieth of the bulk of the 
 gas. Nitrogen alone is unfit for the support of life, but it 
 is not a direct poison, and is, indeed, constantly inhaled 
 when mixed with oxygen, the activity of which it serves to 
 moderate. 
 
 Exp. 26. Plunge a -lighted taper into a jar of nitrogen : the 
 gas does not take fire, but the light is put out instantly. 
 
 Nitrogen offers a striking contrast in properties to oxygen. 
 It has scarcely any tendency to unite directly with any of 
 the elements except boron, titanium, and one or two of the 
 rarer metals. Yet it is one of the most widespread forms of 
 matter ; it is found in the free state in the air, as well as in 
 combination in some of the most active and- important com- 
 pounds such, for instance, as in nitric acid, which is obtained 
 from the nitre of commerce, and in ammonia or hartshorn. 
 Though not abundant in plants, it is never quite wanting in 
 them. It also forms part of the strongest vegetable poisons 
 and medicines, such as prussic acid, strychnia, and morphia ; 
 and it is a component of some of the most important 
 
38 Nitrogen Other Components 
 
 articles of food, such as bread, milk, and the flesh of 
 animals. The compounds which nitrogen forms with each 
 of the other elements are called nitrides, and animal sub- 
 stances which contain nitrogen are often spoken of as 
 azotised substances. 
 
 (14) Air a Mixture of Several Gases. 
 
 Exp. 27. Measure off into a jar over water 210 c. c. of oxygen, 
 and add to it 790 c. c. of nitrogen ; then introduce a lighted 
 taper. I twill continue to burn as in ordinary air. 
 
 Such a mixture might be breathed with perfect safety, and 
 would possess most of the properties of the air. The atmo- 
 sphere is in fact a true mixture of several gases, among 
 which nitrogen and oxygen are by far the most abundant. 
 Though these two gases are not chemically united in the 
 atmosphere with each other, yet in the open air they are 
 found to be mixed in very uniform proportions. Careful 
 analyses of numerous specimens of air taken from the most 
 distant parts of the earth furnish results the extremes of 
 which do not vary from one another in the proportion of 
 oxygen more than about i part in 200, and generally the 
 variation is much less. The samples were taken, amongst 
 other places, from Port Bowen, amidst the perpetual ice of 
 the Arctic Circle ; from Vera Cruz, the hotbed of yellow 
 fever ; from the summits of the Andes in the western hemi- 
 sphere, and of the Alps in the eastern ; from the higher 
 regions of the atmosphere in balloons, as well as from the 
 streets of the crowded capitals of Europe, such as London, 
 Paris, Berlin, and Madrid. Supposing all the ingredients 
 of the air except nitrogen and oxygen to have been removed 
 by proper means, it has been found that i litre, or 1000 c. c., 
 of the mixture would contain on the average 209 '5 c. c. of 
 oxygen and 790*5 c. c. of nitrogen. If the quantities be 
 determined by weight, instead of by measure, 1000 grams of 
 the mixture would contain 232*2 grams of oxygen and 
 767*8 grams of nitrogen. 
 
of A tmospheric A ir. 3 9 
 
 But it is easy to show that air always contains other sub- 
 stances besides oxygen and nitrogen. 
 
 Exp, 28. Pour a little clear lime-water into a saucer, and 
 leave it for a few minutes. A white skin or film will gradually 
 be formed upon the surface, and this if shaken will sink to the 
 bottom ; a fresji film will then be formed in its place, and if this 
 be disturbed it- will again be renewed, until the whole of the lime 
 has been separated from its solution in the form of this white 
 substance, which has the chemical composition of chalk, or calcic 
 carbonate. 
 
 In this experiment the lime has taken up from the air one 
 of the less abundant gases which it contains, and to this gas 
 the name of carbonic acid or carbonic anhydride (CO 2 ) has 
 been given. The quantity of this gas is always small. It 
 varies in i litre, or 1000 c. c., of air from 0*3 to 0*6 c. c., so 
 that 10,000 measures of air contain from 3 to 6 measures of 
 this gas. 
 
 Exp. 29. Pour some water into a glass tumbler, taking care 
 to keep the outside dry ; place in the water a lump of ice. In 
 the course of a. few minutes the water will have become cooled 
 by the melting ice, and the cooling effect will extend to the 
 outer surface of the glass, while dew or moisture will be de- 
 posited upon it, owing to the condensation of viewless watery 
 vapour from the air. 
 
 This experiment shows the presence of steam in the atmo- 
 sphere. The proportion of watery vapour, however, varies 
 greatly from time to time, being much less during the frosts 
 of winter than it is in the hot weather of summer. In this 
 climate loooc. c. of air seldom contain more than 20 c. c. 
 of invisible vapour, and the proportion ordinarily found in a 
 litre, or 1000 c. c., may be roughly reckoned at 14 c. c. 
 
 The weight of a litre of dry air free from carbonic anhy- 
 dride, at o C. when the mercury in the barometer stands at 
 760 mm., has been found to be 1^2932 gram. 
 
 It must also be added that variable traces both of am- 
 monia and of nitric acid are found in the air, but the pro- 
 
4O Less abundant Components of Atmospheric Air. 
 
 portions are so minute that they cannot be detected unless" 
 very large quantities of air are examined ; and these sub- 
 stances are more easily found in the rain, which, by falling 
 through large tracts of air, has dissolved them, and brought 
 them down with itself. Minute as the quantity is which is 
 found even then, they have important uses in supplying 
 what is needful for the health of growing plants. 
 
 In large towns small quantities of other gases are likewise 
 occasionally met with, such as sulphurous anhydride (SO 2 ), 
 derived from the pyrites in the coal consumed, and sul- 
 phuretted hydrogen (H 2 S), from the putrefaction of animal 
 refuse. 
 
 Besides these gaseous bodies, minute "particles of solid 
 matter are always suspended in the air; these are of the 
 most varied kinds, and among them are the spores and 
 seeds of minute fungi and plants. These particles are so 
 small that they commonly escape notice ; under favourable 
 "circumstances they may be easily seen, as they form the 
 ' motes ' which appear to be dancing in the sunbeams when 
 they find their way into a darkened room. 
 
 The average composition of a litre, or 1000 c. c., of air 
 may be represented as follows, in measure of each in- 
 gredient : 
 
 Cub. Centim. 
 
 Oxygen 206' I 
 
 Nitrogen 7 79' 5 
 
 Aqueous Vapour (about) . . 14-0 
 
 Carbonic Anhydride ... *4 
 Nitric Acid . . \ 
 
 Ammonia I traces 
 Carburetted Hydrogen ) 
 
 lOOO'O 
 
CHAPTER III. 
 
 WATER HYDROGEN. 
 
 (15) WATER: Symbol, H 2 O ; Atomic and Mol Wt. 18 ; 
 Sp. gr. of liquid at 4 C. rooo; Sp. gr. of ice, 0*918 ; Sp. gr. 
 of steam, 0*622 ; Rel. Wt. 9; Atomic and Mol. Vol. \ \ \. 
 
 Until about a hundred years ago this wonderful and uni- 
 versally diffused liquid was, like the air, supposed to be one 
 of the elements of nature ; but we can now easily prove 
 that it is a compound body, and can both separate it into 
 its elements, and reproduce it from those elements by causing 
 them again to combine together. 
 
 Exp. 30. Throw a small piece of the metal potassium into a 
 saucer containing water, and retreat to a little distance. As the 
 metal is lighter than water, it will rise to the surface, where it 
 will seem to burst into flame, rolling rapidly about until it dis- 
 appears with a slight report. Now place a piece of reddened 
 litmus paper in the water : it will become blue, showing that 
 the potassium has combined with oxygen, which, as we shall 
 see, is derived from the water, and has been by it converted into 
 the alkaline body potash (Exp. 16). 
 
 Exp. 31. Roll upon the end of a cedar pencil a piece of wire 
 gauze about 4 centim. square, and fold up the end of the cylin- 
 der thus formed ; twist a piece of copper bell-wire 25 or 30 
 centim. long round the little cage, so as to form a handle ; then 
 introduce into it one or two small pieces of sodium, the metal 
 contained in common salt, and pass the cage quickly beneath 
 the mouth of a small glass jar filled with water, and inverted in 
 water : bubbles of gas will be formed at once, and will continue 
 to rise into the jar until all the sodium has disappeared. Now 
 close the jar with a glass plate, withdraw it from the water, and 
 apply a light. The gas will take fire, and burn with a pale 
 flame. 
 
 To this substance the name of hydrogen (water-producer) 
 has been given. It is regarded as an elementary body. 
 
Decomposition of Water. 
 
 The results of these experiments may be thus explained : 
 Water is a compound of oxygen and hydrogen. The 
 potassium or the sodium displaces a part of the oxygen from 
 the water, and becomes converted into potash or soda, 
 which is dissolved by the water, while the hydrogen escapes 
 in the gaseous form, as may be explained by the following 
 equation : 
 
 Water Potassium Potash Hydrogen 
 
 2H a O + K z 2KHO + H 3 
 
 2(2xl + l6) 2x39 2(39+1 + 16) 2x1 
 
 112 
 
 114 
 
 114 
 
 Fig. 9. 
 
 When potassium is used, the hydrogen becomes so much 
 heated at the moment when it is set free that it takes fire in 
 the air at once ; but when the sodium is kept under water, 
 the hydrogen is prevented from mixing 
 with the air till it becomes cool, and 
 then it does not burn till a light is 
 applied to it. 
 
 If a small voltaic battery can be had. 
 it is easy to obtain both the oxygen 
 and the hydrogen from the water at 
 the same time. 
 
 Exp* 32. Select two pieces of glass 
 tube of equal diameter, about 12 centim. 
 long and 1 2 mm. wide, and open at both 
 ends. Fit a cork into one end of each, 
 and pass a stout platinum wire, ending in a small plate of 
 platinum, through each cork, so as to reach nearly to the 
 open end of the tube. Then cover each cork neatly with a 
 solution of sealing-wax in spirit of wine, and let it dry. Next 
 fill each tube with water slightly acidulated with sulphuric 
 acid * (about i part of acid in 30 of water), and invert it in 
 
 * Much heat is given out whenever strong sulphuric acid is mixed 
 even with cold water. When this mixture is to be made, the water 
 
Decomposition of Water. 43 
 
 a glass of the same acidulated water (Fig. 9). Connect one 
 of the platinum wires with the wire proceeding from one of 
 the poles of a properly charged voltaic battery, which may 
 consist of three or four cells made on Grove's plan (see treatise 
 on ' Electricity ; ), and connect the other platinum wire with the 
 remaining pole of the battery. Gas will begin at once to rise 
 from both plates, and will collect in the tubes : one of these tubes 
 will receive just twice as much gas in the same time as the other. 
 When sufficient gas has been collected, remove the tube with the 
 smaller quantity of gas, closing it with the thumb before lifting 
 it out of the water. Turn 'it mouth upwards, and introduce a 
 splinter of wood red-hot at the point. It will be rekindled. 
 This we know is a characteristic property of oxygen. Now 
 remove the other tube in a similar manner, and apply a lighted 
 taper. The gas will take fire, and burn with the pale flame pecu 1 - 
 liar to hydrogen. 
 
 In this experiment it is to be noted that for each cubic 
 centimetre of oxygen obtained from the water 2 c. c. of 
 hydrogen have been procured. Further, it may be easily 
 shown that these two gases may be made to combine again 
 chemically in the same proportions, and that they then 
 reproduce water. For this purpose the last experiment must 
 be altered in form as follows : 
 
 E.vp. 33. Fit a good cork to the neck of a bottle which will 
 hold 100 c. c. ; adjust a tube, bent as in Fig. 10, 'to the cork, 
 having its lower end turned upwards, and pass the wires con- 
 nected with the two platinum plates through the cork, taking 
 care that the metals do not touch each other. Nearly fill the 
 bottle with water slightly acidulated with sulphuric acid, and 
 insert the cork with its bent tube and platinum plates. Connect 
 each plate with one of the wires of the voltaic battery, as before ; 
 allow the air in the tube to be displaced by the gas, and then 
 collect the mixed gases, as they rise from both plates, in a strong 
 
 should be placed in a jug or earthenware vessel ; it should be stirred 
 round and round with a glass rod, and the acid should be p&ured into the 
 water (not the water into the acid) in a slender stream, the whole being 
 kept stirred till the mixture is complete. ^ 
 
44 Decomposition of Water. 
 
 dry tube filled with mercury, and supported in a wooden vice, 
 and inverted in a small Wedgwood-ware mortar containing mer- 
 cury. When the tube has become full of gas, close the end of it 
 with the finger, raise it out of the mercury, and apply a light : 
 
 Fig. 10. 
 
 a sharp report will be heard ; the two gases will suddenly unite, 
 and the sides of the tube will become dewed with moisture, 
 showing that water has been formed by the union of the oxygen 
 and hydrogen. 
 
 Another mode of making this important experiment will 
 be described when we come to treat of hydrogen. 
 
 Each litre of oxygen gas unites with exactly two litres of 
 hydrogen ; and if the gases be heated to above 100 C. before 
 causing them to unite, and the heat be kept up to the same 
 point after they have united, exactly two litres of steam or 
 watery vapour will be obtained. Hence, in representing the 
 composition of water by symbols, its formula is written H 2 O, 
 and its combining number is 18. When converted into 
 vapour 9 grams of water furnish a bulk of steam exactly 
 equal to that of i gram of hydrogen at the same temperature 
 and pressure ; so that the relative weight of steam is 9, and 
 the specific gravity of steam is 0*622; or the weight of a 
 quantity of steam, compared with that of a quantity of air 
 which weighs i gram at the same temperature and pressure, 
 is 0-622 gram. It is also convenient to bear in mind that 
 i litre of water will at 100 furnish 1696 litres of steam, of 
 
Freezing and Boiling of Wetter. 45 
 
 an elasticity sufficient to balance the pressure of a column of 
 mercury of 760 millimetres, i cubic inch of water producing 
 nearly a cubic foot of steam. 
 
 Pure water has neither taste nor smell, and it is generally 
 supposed to be colourless, though when seen through a 
 depth of 5 or 6 metres it has a delicate and faint tinge of blue. 
 When cooled sufficiently, it becomes converted into the 
 transparent solid form of ice. The point at which pure ice 
 melts, or the freezing fioint, as it is usually called, always 
 occurs at exactly the same temperature, if the ice is not 
 exposed to pressure. Hence the melting point of ice has 
 been made the starting point or o, the zero, as it is termed, 
 of the centigrade thermometric scale.* Again, if the tem- 
 perature of water be raised sufficiently high, the liquid 
 assumes the form of gas, while bubbles of steam rise through 
 the heated liquid and break upon its surface, passing off as 
 invisible vapour. The water is said to boil, and its vapour 
 is then of an elastic force just sufficient to balance the pres> 
 sure of the air upon its surface, whatever that pressure may 
 be. The temperature at which pure water boils under equal 
 pressures is found to be quite as uniform as its freezing 
 point. This boiling point of water serves, therefore, as a 
 second fixed point upon the thermometric scale, and it has 
 been agreed to call the point at which the mercury stands 
 in boiling water 100 on the centigrade scale; the observa- 
 tion being always made when the pressure of the air upon 
 the surface of the boiling water, as indicated by the baro- 
 meter, is equal to that of a mercurial column 760 mm. long 
 when measured at o C. One degree of the centigrade scale 
 represents the looth part of the apparent expansion of the 
 mercury in the thermometer between the freezing and the 
 boiling points of water, f 
 
 * If the water holds salts dissolved in it, the freezing point is lowered 
 to an extent depending on the quantity and kind of salt. 
 
 t If salts are present in the water, the boiling point may be raised 
 several degrees, the amount varying according to he quantity and kind 
 of salt in solution. 
 
46 Evaporation of Water. 
 
 But water evaporates, or slowly passes off into the air in 
 the invisible form of vapour or steam at all temperatures 
 even from ice itself; and this evaporation is going on 
 more or less actively almost everywhere upon the surface of 
 the earth, so that the air is at all times charged with moisture, 
 the proportion of which is perpetually varying. In dry 
 weather the quantity of vapour found is always less than 
 that which could exist unseen in the air at the time. It is 
 owing to this circumstance that wet bodies, when exposed to 
 the air, become dry in a few hours. By the process of 
 evaporation from the surface of the land, as well as of the 
 ocean, a natural distillation and purification of water, of the 
 utmost importance, is always taking place around us. The 
 water discharged by rivers into the sea returns unperceived 
 into the air. The vapour is at first unseen, but as it rises 
 into the colder regions of the atmosphere it is condensed 
 into masses of visible cloud. These at last become too 
 heavy to stay aloft. High ridges or mountains are especially 
 active in arresting the clouds, which then fall in showers, 
 and supply the high lands with water. This flows down the 
 sides of the hills, collects into rivulets, and these again into 
 rivers ; or else the water sinks into the earth through the 
 porous strata, and passes down until it meets with a bed of 
 clay or some stratum through which water cannot pass. The 
 liquid, when thus stopped, flows along over the face of the 
 imbedded stratum until it reaches the surface of the soil at 
 some lower level in the valley, where it bursts forth in the 
 form of a spring. 
 
 Water exhibits a remarkable exception to the law of con- 
 traction by the removal of heat, which all other bodies obey. 
 When exposed to a falling temperature, it diminishes in 
 bulk regularly till it has become cooled down to 4 C. ; and 
 then, instead of contracting, it begins slowly to expand, and 
 continues to do so until it reaches the freezing point, when 
 the ice which is formed suddenly expands still more. This 
 exceptional expansion of water as it cools is attended with 
 
Maximum Density of Water. 47 
 
 very important consequences to our well being. During the 
 frosts of winter a rapid process of cooling occurs from the 
 surface of all lakes and streams ; the colder water sinks to 
 the bottom until the whole has become reduced to 4 C., 
 but below this point the colder water becomes the lighter, 
 and remains at the top, so that it protects the mass beneath 
 from the winter cold. In this way it prevents such a reduc- 
 tion of temperature in deep pools as would be fatal to fishes 
 and aquatic animals. The ice also floats upon the surface, 
 and thus the bottoms of lakes and rivers are preserved from 
 the accumulation of masses of ice, which, if it sank as fast 
 as it is formed, could never be melted even by the summer's 
 sun. 
 
 The temperature of 4 C. is that at which water is heavier 
 than at any other, and is hence called its point of maximum 
 density. A litre of water at this temperature weighs exactly 
 1000 grams, or i kilogram. Water is 773 times as heavy as 
 air at o C., when the barometer is at 760 mm. In taking 
 the specific gravity of solids and of liquids, they are always 
 compared with the weight of an equal bulk of pure water at 
 4 C. For example, if gold be said to have a specific gravity 
 of 1 9 '34, it is meant that i c. c. of water at 4 weighs i gram, 
 while a cub. centim. of gold at the same temperature weighs 
 19-34 grams. 
 
 In order to obtain pure water for this and various other 
 purposes, it must be distilled. This is usually performed by 
 means of a still and worm-tub ; but if these be not at hand, 
 a small quantity of water may be distilled in the following 
 manner : 
 
 Exp. 34. Procure a clean tinplate Q-litre (or 2-gallon) oil can ; 
 bend a glass tube into the form shown in Fig. 10 ; adapt it to a 
 sound bung which exactly fits the neck of the can, and fill the 
 can about two-thirds full of water. Then adjust the bent tube 
 to the condenser shown in the figure. Place the can upon the 
 fire, and heat it till the water boils steadily, whilst a small 
 stream of cold water is kept running through the outer tube of the 
 
4 8 
 
 Distillation of Water. 
 
 condenser. Allow the water as it distils over from the can tc 
 flow into a flask placed for its reception. Throw away the firsl 
 40 or 50 cub. cm., which are apt to contain a little ammonia and 
 semi-gaseous impurities. Then collect 3 or 4 litres. This will 
 be distilled water ; and if the experiment is performed carefully, 
 
 the liquid so condensed will be pure from all solid substances in 
 solution. A few drops when allowed to evaporate from a slip of 
 clean glass will leave scarcely a perceptible mark behind ; but 
 if a few drops of the water before distillation be so treated, a 
 distinct residue will be obtained. A sufficient condenser may be 
 made without difficulty as follows : Select a piece of glass tube 
 
Rain Water. 49 
 
 of about 80 centim. in length and 2 ccntim. in diameter ; fit it 
 by means of corks into a second tube of glass or of tinplate 
 about 60 centim. in length and 4 centim. in diameter. Into the 
 space between the two tubes pass a bent quill tube through one 
 of the corks, and introduce through the other cork a second 
 similar tube ; cold water is to be supplied through the tube at 
 the lower end, while the hot water runs off at the upper end, as 
 shown in the figure. 
 
 Water, in consequence of its extensive power of dis- 
 solving bodies of various kinds, is not met with naturally 
 in a state of perfect purity. Rain water, collected in the 
 open country after continued wet weather, is nearly pure ; 
 but even this contains the gases of the atmosphere dis- 
 solved in it, usually to the extent of from about 30 to 50 
 c. c. in a litre of water, besides particles of solid suspended 
 matters. 
 
 The presence of air in water is necessary to the life of 
 fishes and aquatic animals generally, for it is by means of 
 the oxygen thus dissolved that they maintain respiration. 
 Its presence may be shown as follows : 
 
 Fig. 12. 
 
 Exp. 35. Fit a quill tube, a (Fig. 12), by means of a sound cork 
 to a Florence flask, having first filled the flask with rain water, 
 or with spring water ; fill the tube also completely with water, 
 and adapt it to a small glass jar, b, also filled with water, and 
 standing in the water-bath. Heat the water in the flask till it 
 
 E 
 
5<D Impurities which occur 
 
 boils briskly ; bubbles of air will gradually be driven out of the 
 water, and may be collected in the glass receiver, b. 
 
 Rain water which falls in mountainous or rocky districts 
 formed of millstone grit, mica slate, and other rocks 
 which contain but little soluble material, generally runs 
 off nearly free from anything except a little vegetable 
 matter and dissolved gases ; but spring water, although it 
 may be perfectly colourless and transparent, contains some 
 salts in solution. The quantity and the kind of these 
 salts varies with the kind of rock or soil in which the spring 
 originates. 
 
 The salts most often found in spring water are sodic 
 chloride or common salt, calcic carbonate from chalk, 
 and calcic sulphate, as well as small amounts of magnesic 
 carbonate and sulphate. The waters of town wells also 
 generally contain traces of ammonia, and more or less of the 
 nitrates and nitrites of calcium or of sodium. The nitric 
 acid in these salts is the result of the gradual oxidation of 
 the drainage from animal refuse, which, though in its recent 
 state one of the most noxious impurities that can be found 
 in water, yet when completely oxidized into nitrates is no 
 longer dangerous to health. Nearly all spring waters 
 contain also a very small quantity of silica in solution. 
 Wholesome waters do not contain in solution more than 
 one gram of saline substances per litre ; and the most 
 highly prized sources contain but a few centigrams only in a 
 litre of water. 
 
 Exp. 36. Select a thin porcelain dish which will hold 60 or 
 80 cub. cm. ; place it in one pan of the balance, and cut a piece of 
 lead till, when placed in the other scale-pan, it counterpoises or 
 exactly balances the dish. Measure off half a litre of spring 
 water, and pour some of this water into the weighed dish ; place 
 it over a very small gas flame, so as to evaporate the water gently 
 without allowing it to boil ; add the rest of me water from time 
 to time until the half litre has been completely evaporated away. 
 Dry the salts thus obtained, and weigh what is left as accurately 
 
in Natural Waters. 51 
 
 as you can. By multiplying this quantity by 2 you will obtain 
 the amount of soluble solid substances per litre which that par- 
 ticular specimen of water contained. 
 
 This is the basis of the plan which, with many additional 
 precautions, is adopted for determining the quantity of salts 
 in the process of analysing waters to be used for drinking or 
 manufacturing purposes. 
 
 River water often holds a smaller proportion of salts dis- 
 solved in it than spring water ; and yet it may be less fit for 
 drinking, for it generally contains a much larger quantity of 
 organic matter ; that is to say, it contains a larger propor- 
 tion of soluble drainage products of a vegetable or animal 
 nature, which have been washed off the surface of the 
 soil by the rain, or which have been emptied from sewers 
 into the stream. 
 
 Such sewerage products should not be allowed to escape 
 into rivers until they have been more or less purified by 
 allowing the liquid to run over cultivated land, which is 
 manured by it in its progress. The liquid afterwards runs 
 away comparatively harmless. 
 
 Happily for mankind, running water is endowed with 
 a considerable amount of purifying power, due to the 
 oxygen of the air which it holds in solution. Vegetable 
 matters consist almost entirely of carbon, oxygen, and 
 hydrogen, with a very small proportion of nitrogen ; whilst 
 animal matters, in addition to carbon, oxygen, and hydro- 
 gen, contain a considerable proportion of nitrogen ; both 
 vegetable and animal matter likewise contain a little sulphur, 
 either as sulphates or in some other form. During putre- 
 faction these organic bodies give out a disgusting odour, 
 and, if swallowed in this state, even when largely diluted with 
 water, may cause serious illness. By the action of the 
 oxygen dissolved in the water, the hydrogen of these com- 
 pounds becomes changed into water, the carbon into car- 
 bonic acid, and most of the nitrogen into nitric acid. The 
 continual motion of the water exposes fresh surfaces to the 
 
 E 2 
 
5 2 Impurities found in Water. 
 
 air; fresh oxygen is in consequence always being absorbed, 
 and the oxidation which takes place is generally sufficient 
 to preserve the stream in a wholesome state. But if the 
 water be overloaded with organic refuse, or if it become 
 stagnant, the whole of the dissolved oxygen may become 
 absorbed by the decaying matter without renewal from the 
 air, and the pool will then emit an offensive odour, and may 
 become a centre of disease. The nitration through the well 
 aerated porous soil which water naturally undergoes before 
 it issues in the form of springs, is attended with an oxidizing 
 and purifying action of the highest importance. 
 
 River water should always be filtered through sand or 
 through a charcoal filter before it is used for drinking. 
 Suspended matters, such as clay, fish spawn, or small 
 animals may be thus removed, but the salts in solution are 
 not sensibly affected by such filtration. 
 
 Exp. 37. Dissolve 0-395 gram of potassic permanganate in 
 
 1 litre of water, and add 3 c. c. of this solution to a mixture of 
 
 2 c. c. of dilute sulphuric acid (40 of water and I of acid) with 
 half a litre of distilled water, in a glass flask, so as to give the 
 liquid a distinct purplish tinge ; little or no change of colour 
 will be seen at the end of three hours, if the mixture be left 
 to itself. Do the same thing with an equal quantity of river 
 water : in three hours' time the tint will have become reddish 
 or brownish, if any considerable quantity of organic matter be 
 dissolved in the water. 
 
 The foregoing result may be thus explained : The sul- 
 phuric acid separates permanganic acid from the salt, and in 
 the presence of organic matter this acid loses a portion of its 
 oxygen, which combines with the constituents of the organic 
 matter, while the permanganic acid becomes converted into 
 a compound of manganese of a different and less intense 
 colour, and containing less oxygen. 
 
 A weak solution of the permanganate, indeed, furnishes 
 a valuable comparative test of the fitness of water for 
 drinking. If the permanganate does not alter sensibly in 
 
Hard and Soft Water. ^,3 
 
 colour in such an experiment, there is no organic impurity 
 to be feared in the water. 
 
 Water is commonly spoken of as hard or soft, according 
 to its action upon soap. Soap is a combination of a fatty 
 or oily acid with soda ; and this compound is readily soluble 
 in pure water. Waters which contain salts of calcium or 
 magnesium cause the soap to curdle, since these metals 
 furnish with the fatty acid of the soap compounds which 
 are not soluble in water. Such waters are said to be hard. 
 Soap which is thus curdled is consumed in waste. In such 
 water soap neither cleanses nor produces a lather until the 
 whole of the earthy salts have been decomposed and an ex- 
 cess of soap is present. Soft waters, on the contrary, do not 
 contain these earthy salts, and they dissolve the soap without 
 difficulty, and without destroying either its cleansing power 
 or its tendency to form a lather. 
 
 Many waters exhibit what is called temporary hardness ; 
 such waters become softer by boiling. The hardness in this 
 case is due to the presence of calcic or magnesic carbonate. 
 These compounds are scarcely soluble at all in pure water, 
 but they become soluble to a considerable extent in water 
 charged with uncombined carbonic acid. When such waters 
 are boiled, the carbonic acid is driven off by the heat, and 
 the calcic and magnesic carbonates which the acid had dis- 
 solved become deposited, and a ' fur' or incrustation takes 
 place on the inside of the boiler, as may be seen by examin- 
 ing a kettle used for boiling such waters. 
 
 Exp. 38. Place half a litre of a water of the kind just referred 
 to, such as that of the Thames or of the New River, in a glass 
 flask, and boil it over a lamp for a quarter of an hour : little 
 crystalline grains of the earthy carbonates which were in solution 
 will gradually be deposited, and the water will be found to 
 be considerably softened. 
 
 Exp. 39. Mix another half litre of such a water before it is 
 boiled with about one-eighth of its bulk of limewater. The 
 liquid will become turbid, and on standing for a few hours, till it 
 is clear, it will be found to be much softer than before. 
 
54 Soap-test for Water. 
 
 The reason of this result is, that the lime in the limewater 
 has combined with the carbonic acid which the river water 
 held dissolved. Chalk is thus formed, and at the same time 
 the chalk previously dissolved by the carbonic acid becomes 
 separated ; so that both the lime of the limewater, if it be 
 not added in too large a proportion, and that originally in 
 the water dissolved as chalk, become precipitated * together, 
 and the water is softened. 
 
 Exp. 40. Prepare a mixture of about equal parts of strong 
 spirit and water, so as to obtain a liquid of sp. gr. 0*920, and in 
 half a litre of this dissolve o'l gram of curd soap. Into a glass 
 bottle fitted with a stopper, and capable of holding about 100 c. c., 
 measure off 50 c. c. of such a hard water ; then add, little by 
 little, some of the spirituous solution of soap. Put the stopper 
 into the bottle, and shake it briskly for a minute : no lather will 
 be formed at first, but the soap will be curdled. Continue to 
 add the solution, shaking briskly between each addition. At 
 length there will be more soap added' than the lime salts can 
 decompose, and as soon as this happens a lather will be formed 
 in the bottle. 
 
 This is the principle upon which Dr. Clark's soap test for 
 determining the hardness of water is based. In applying 
 this test the strength of the soap solution is first carefully 
 ascertained, and then the exact proportion necessary to 
 produce a lather is determined for each particular water ; 
 by means of tables constructed for the purpose, the hardness 
 of the water is then easily calculated. 
 
 Besides this temporary hardness in water, there is a per- 
 manent form of hardness. Indeed, very commonly the same 
 water exhibits hardness of both kinds. The amount of each 
 may be found by applying the soap test to the water before 
 it has been boiled, and again after boiling it for half an hour, 
 
 * When a clear liquid becomes cloudy or milky from the addition of 
 another clear liquid, the chemical change is attended with the formation 
 of some insoluble compound, which is separated, or, in chemical lan- 
 guage, is precipitated from the liquid. The insoluble substance is called 
 a precipitate ', whether it sinks to the bottom or floats in the solution. 
 
Permanent Hardness Mineral Waters. 55 
 
 taking care to add distilled water if necessary to supply the 
 exact quantity which has been boiled away. 
 
 The difference between the hardness of the water before 
 it was boiled and that found afterwards gives the temporary 
 hardness ; while the degree of hardness which remains after 
 the boiling represents the amount of permanent hardness. 
 This permanent hardness is due to the presence of salts of 
 calcium or magnesium other than the carbonates, such as 
 the sulphates or nitrates. 
 
 Waters having this permanent kind of hardness may be 
 softened by a method well known in the laundry ; for by the 
 addition of sodic carbonate, or common washing soda, the 
 calcium or magnesium is precipitated as carbonate, while 
 sodic sulphate or nitrate remains dissolved. For instance, 
 with calcic sulphate the change may be thus represented : 
 
 Calcic Sulphate Sodic Carbonate Sodic Sulphate Calcic Carbonate 
 
 CaSO 4 + Na 2 CO 3 = Na z SO 4 + CaCO 3 
 
 The sodic sulphate which is formed does not curdle the 
 soap. 
 
 Mineral waters hold a much larger quantity of substances 
 in solution than waters used for domestic purposes. If such 
 waters contain iron, they have an inky taste, like some of 
 those at Tunbridge Wells. They are called chalybeate waters, 
 and may be known by the rusty deposit which they form when 
 exposed to the air. Others are strongly effervescent, like 
 seltzer water, owing to the escape of carbonic acid ; while 
 others have a strong sulphuretted odour, like the H arrogate 
 water, owing to the presence of sulphuretted hydrogen. 
 Others, again, are strongly saline, like the springs at Epsom 
 and at Cheltenham ; whilst in some cases in volcanic districts, 
 as in the Geysers of Iceland, the water is actually boiling 
 hot, and holds silica dissolved ; and in the Bath waters the 
 springs, though not boiling, are much hotter than the surface 
 of the soil from which they come forth, owing to the action 
 of subterraneous feat. 
 
5 6 Saturation Crystallisation . 
 
 Sea water is largely loaded with common salt, and with 
 magnesic chloride and sulphate, to which last the bitter taste 
 is due. It contains also a large number of other salts ; 
 among these are small proportions of bromides and iodides. 
 A litre of sea water contains about 37*5 grams of various 
 salts dissolved in it; about 29 grams of these consist of 
 sodic chloride. 
 
 Water dissolves certain bodies, such as common salt, 
 nitre, and Epsom salt, with great ease; but other salts, 
 such as calcic sulphate, are soluble in much smaller pro- 
 portion in the same quantity of water. When water has 
 dissolved as large a proportion of any substance as it can 
 take up, it is said to be saturated with that substance. 
 Some substances, such as silver chloride and siliceous 
 sand, are not soluble in water to any sensible extent. 
 Generally speaking, water, though saturated with any parti- 
 cular salt when cold, will dissolve a larger quantity of the 
 same salt when heated. 
 
 Exp. 41. Grind up in a mortar 50 or 60 grams of sodic sul- 
 p'bate with about twice its weight of water at 15 C. The \vater 
 will dissolve a considerable proportion, but not the whole of the 
 salt. Pour this saturated solution into a flask, and wann it 
 gently; it will now dissolve 50 grams more of the salt without 
 difficulty. Allow the solution to cool down to the temperature 
 of .the air, say 15 C. : long four-sided needles will crystallise 
 from the liquid. Pour off the liquid, and dry the crystals by 
 pressing -them between a few folds of blotting-paper. When 
 they appear to 'be dry, put a small quantity of the crystals into a 
 test-tube, and apply a gentle heat : the salt will liquefy, and on 
 continuing to apply the heat a large quantity of water will be 
 driven off, and a (dry white powder will be left in the tube. 
 
 The water .thus given off was chemically combined with 
 the ,ery stats. Many oth^r salts which appear to be perfectly 
 dry to the touch, give off water when heated, and crumble 
 down to a shapeless mass ; such, for example, as alum, cupric 
 gulphate, and sodie carbonate; but they all lose the dis- 
 
Efflorescent and Deliquescent Salts. 57 
 
 tinctive form of their crystals when the water has been 
 expelled. If the dry residue be again dissolved in water, 
 new crystals similar to the ' original ones are obtained, and 
 they are found also to contain water as before. The quan- 
 tity of water is definite for each salt ; for instance, sodic 
 sulphate contains 10 atoms of water combined with each 
 atom of the salt, and its composition is represented by the 
 formula Na 2 SO 4 , ioH 2 ; cupric sulphate has 5 atoms 
 (CuSO 4 , 5H 2 O), sodic carbonate 10 atoms to each atom of 
 the salt (Na 2 CO 3 , ioH 2 O), and so on. Such water which is 
 necessary to the form of the salt, but which can be driven 
 off without altering its chemical character, is called water 
 of crystallisation. Sometimes mere exposure of the salt 
 to the air is sufficient to get rid of this water of crystal- 
 lisation. 
 
 Exp. 42. Take some of the fresh .crystals of sodic sulphate ; 
 let them lie exposed on a piece of blotting-paper for two or three 
 days. They will gradually lose their water, and crumble down, 
 or effloresce into a white powder. 
 
 Other salts act in the opposite manner. They absorb 
 moisture from the air, and become dissolved in it : they 
 deliquesce. 
 
 Exp. 43. Put a little calcic chloride in a watch-glass, and 
 expose it to the air; do the same with a few decigrams of 
 potassic carbonate ; in two or three days both salts will be 
 found in a liquid state. 
 
 The compounds of water are often called hydrates (from 
 the Greek vdwp, water) ; and when a substance is entirely 
 free from water in combination, it is said to be anhydrous. 
 When a salt is dissolved in water, it is not considered by the 
 act of solution to have entered into true chemical combina- 
 tion ; the water and the salt may be separated from each 
 other unchanged by merely altering the temperature a few 
 degrees. Many other substances besides water dissolve 
 bodies without acting chemically on them. Spirit of wine 
 
58 Hydrogen. 
 
 dissolves camphor, coal naphtha dissolves caoutchouc, 
 and each is left unchanged when the spirit or the naphtha 
 evaporates. 
 
 In a case of true chemical action, the result is different ; 
 the product obtained differs in properties from the original 
 bodies. When potassium is thrown into water, the metal 
 disappears, and seems to dissolve, but it cannot be removed 
 by evaporation. The water has been decomposed, hydrogen 
 escapes, and on evaporation a solid compound of potassium 
 and hydrogen with oxygen, in perfectly definite proportions, 
 is obtained (KHO), and this may be made red hot without 
 being chemically altered. 
 
 ( 1 6) HYDROGEN : Symb. H ; Atomic Wt. i Atomic Vol. 
 Q ; Mol. Wt, H 2J 2 ; Mol. Vol. ["T"1 ; S P- G r - 0-0691 ; Rel. 
 Wt. i. 
 
 We have already found that when sodium or potassium is 
 placed in water an immediate escape of hydrogen occurs, as 
 a colourless inflammable gas. 
 
 Potassium and sodium are among the few bodies which 
 act powerfully upon water at common temperatures : there 
 are some other metals which, when cold, have scarcely any 
 action upon it, though when made red hot they easily 
 decompose it. Iron is one of these metals. 
 
 Exp. 44. Procure an iron gaspipe about 60 centim. long and 
 2 centim. in diameter ; fit a cork and a short piece of glass tube 
 to each end. Introduce some iron filings into the iron tube. 
 To one end attach a quill tube by means of a flexible caoutchouc 
 tubing ; and to the other, also by means of a vulcanised rubber 
 tube, fasten a Florence flask about one-third full of water, fitted 
 with a cork and quill tube. Make a temporary furnace (as 
 shown in Fig. 13) by means of six or eight bricks, with a 
 grating, which may consist simply of a coarse piece of wire 
 gauze ; support the iron tube across the furnace, and make it 
 red hot by surrounding it with burning charcoal. Then cause 
 the water in the flask to boil with such force as to drive the steam 
 
Preparation of Hydrogen. 
 
 59 
 
 through the red-hot pipe over the heated iron filings. Gas will 
 come off at the other end, and may be collected in jars over the 
 
 pneumatic trough. When a light is applied to it, it will burn 
 with a pale yellowish flame. It is, in fact, hydrogen. 
 
 In this process the red-hot iron has removed the oxygen 
 from the vapour of water, and left the hydrogen in a 
 separate form, magnetic oxide of iron being produced. The 
 decomposition may be thus represented : 
 
 Iron Water Magnetic Oxide Hydrogen 
 
 3Fe + 4H 2 O = Fe 3 O 4 
 
 3x56 4(2x1 + 16) 3x56 + 4x16 
 
 168 72 232 
 
 240 
 
 240 
 
 The usual and the most convenient mode of preparing 
 hydrogen is the following : 
 
 Exp. 45. Melt about half a kilogram of zinc in an iron ladle, 
 and pour it in a thin stream from a height of about a metre into 
 a pailful of cold water ; the metal will be obtained in flakes, and 
 is said to ^granulated. Introduce into a bottle which will hold 
 about 300 c. c. about 15 grams of granulated zinc; fit a good 
 cork to the neck of the bottle ; then remove the cork and pierce 
 two holes in it with a round file ; through one hole pass a glass 
 tube funnel, and through the other a tube bent as in Fig. 14. 
 To the bent tube attach another bent glass tube, by means of a 
 
6o 
 
 Formation of Hydrogen. 
 
 piece of vulcanised rubber tubing. Next pour upon the zinc 
 through the funnel about 70 c. c. of diluted sulphuric acid (i mea- 
 sure of strong acid to 7 measures of 
 water). A brisk effervescence will 
 occur, and a colourless gas will come 
 off, which may easily be collected in 
 jars over the pneumatic trough. 
 
 In this case the zinc appears to 
 displace hydrogen from the acid ; 
 a new salt (zinc sulphate) is formed, 
 and becomes dissolved in the water. 
 The reaction is shown in the fol- 
 lowing equation : 
 
 Sulphuric Acid 
 
 H 2 S0 4 
 2x2 + 32 + 4x16 
 
 Zinc 
 
 Zn 
 65 
 
 Zinc Sulphate 
 
 ZnSO 4 
 65 + 32 +4 x 1 6 
 
 Hydrogen 
 
 2X1 
 
 Scraps of iron may be used instead of zinc in this experi- 
 ment ; but the gas then has a disagreeable smell, owing 
 to the presence of carburetted hydrogen derived from the 
 carbon in the iron. Ferrous sulphate (FeSO 4 ) is now formed 
 instead of zinc sulphate. 
 
 Hydrogen is not a poison when breathed, but it cannot 
 support life. It is very slightly soluble in water; 100 c. c. 
 of water dissolve only i "93 c. c. of the gas. 
 
 Hydrogen is a colourless gas ; when pure it is without 
 either taste or odour. It has never been liquefied by cold 
 or pressure. Owing to its lightness it was at one time used 
 for filling balloons ; but coal gas is now substituted for it, as, 
 though not so light as hydrogen, it is more easily obtained 
 in sufficient quantity. 
 
 Exp. 46. Hold a small jar, with its mouth downwards, over 
 the tube of the hydrogen bottle while it is giving off gas freely, 
 as shown in Fig. 15. The hydrogen will gradually displace the 
 heavier air, and may be found in the jar even after the lapse of 
 two or three minutes, if the mouth of the jar be kept downwards, 
 
Properties of Hydrogen. 6 1 
 
 as may be proved by applying a flame, when it will take fire ; but 
 if the mouth be turned upwards, the gas will escape in a few 
 seconds, and no flash will occur 
 on applying a light. 
 
 Hydrogen in burning gives 
 out little light, but much 
 heat ; a jet of the gas burns 
 with a pale yellowish flame. 
 
 All gases which are formed 
 in contact with water neces- 
 sarily contain a certain small 
 amount of moisture in the 
 invisible form ; but they may 
 be freed from this when neces- 
 sary by causing the gas to pass 
 slowly over some salt, which, 
 like calcic chloride, has a 
 strong attraction for moisture. 
 For the purpose of removing this small quantity of moisture 
 from hydrogen, as ordinarily prepared, the following arrange- 
 ment may be made : 
 
 Exp. 47. Fill a tube of about 20 centim. long with calcic 
 chloride broken into pieces about the size of a pea ; plug each 
 end loosely with cotton wool; then fit a cork, pierced with a 
 quill tube 5 centim. long, into each end ; fasten this drying ap- 
 paratus to the hydrogen bottle by means of the caoutchouc tube. 
 The gas as it comes out at the other end of the drying tube will 
 be dry. Now set fire to the dry gas as it escapes, and hold 
 a cold glass jar over the burning jet. The side of the glass 
 will quickly become bedewed with moisture, owing to the union 
 of the burning hydrogen with oxygen obtained from the atmo- 
 sphere. 
 
 Oxygen and hydrogen may be kept mixed together at 
 ordinary temperatures for any length of time without com- 
 bining; but if an electric spark be applied to the mixture, 
 or a lighted or even a glowing match, immediate combination 
 occurs, with a bright flash and a loud report. 
 
62 
 
 The Mixed Gases. 
 
 Exp. 48. Fit a good cork into the neck of a gas jar, and 
 pass a quill tube 5 centim. long through it. Bind a short piece 
 of caoutchouc tube firmly to the quill tube, and close this elastic 
 tube with a small screw vice or tap made for such purposes. 
 Fill the jar with water over the pneumatic trough. Now fill a 
 small jar which will hold about half a litre with oxygen, and 
 transfer it by manipulating, as shown in Fig. 16, without loss to 
 the gas jar. Fill the same jar with hydrogen, and transfer 
 it to the large jar. Repeat the operation with the hydrogen, so 
 as to obtain in the larger jar a mixture of half a litre of oxygen 
 
 Fig. 16. 
 
 and I litre of hydrogen. Having previously softened a thin 
 bladder by soaking it in water, tie into the neck of it a glass 
 quill tube 5 centim. long : then adjust to the projecting portion 
 a piece of vulcanised caoutchouc tubing provided with another 
 screw tap. Press the air out of the bladder ; connect by means 
 of a short piece of glass tubing the two pieces of vulcanised 
 tube ; depress the jar in the pneumatic trough, and then open 
 each screw tap. The gas will now pass into the bladder ; close 
 both screw taps, and remove the bladder. Now place the end 
 of the tube attached to the bladder under some soapsuds, and 
 
Union of Hydrogen and Oxygen. 63 
 
 force out the mixed gas by squeezing the bladder so as to make 
 a lather. Carefully remove the bladder to a distance, and then 
 apply a light to the froth of soapsuds. A loud explosion will 
 immediately follow. 
 
 In this experiment steam is formed; this first expands con- 
 siderably, owing to the heat produced by the combination of 
 the oxygen and hydrogen, and immediately afterwards the 
 steam becomes condensed, the particles of the surrounding 
 air rush in to fill the void, and by striking one against the 
 other produce the report. 
 
 If the hydrogen be mixed with air, instead of pure oxygen, 
 a similar but weaker explosion occurs when a light is applied. 
 In all experiments with hydrogen it is therefore necessary 
 to allow time for the expulsion of the air from the apparatus 
 before setting fire to the gas as it comes out. If the mixture 
 be diluted with a large excess of hydrogen or of air, the 
 explosion becomes less sudden, and less heat is given out ; 
 until, when the dilution reaches a certain point, the mixture 
 only burns quickly without explosion, and, if still more 
 diluted, the combustion only takes place at the spot where 
 heat is applied. 
 
 The proportion of oxygen and hydrogen which unite 
 together is perfectly defined, no matter in what proportion 
 they are mixed. One measure of oxygen invariably unites 
 with exactly two measures of hydrogen. If the gases before 
 firing are heated beyond the temperature of boiling water, 
 and be kept at the same temperature after the explosion,* 
 the three measures of gas which have united will form exactly 
 two measures of steam 
 
 It might be considered that we now have proved the true 
 composition of water, for we have found that water may 
 by analysis be made to yield both oxygen and hydrogen, and 
 
 * This form of the experiment requires special apparatus, and, except 
 in practised hands, is rather difficult of performance. 
 
6 4 
 
 Composition of Water. 
 
 Fig. 17. 
 
 that when oxygen and hydrogen are burned water is formed ; 
 
 but at present we have not shown absolutely that oxygen and 
 
 hydrogen are the only sub- 
 stances which enter into the 
 formation of water. 
 
 The following mode of ex- 
 A i;'.i 1 periment, for which a some- 
 
 what costly form of apparatus 
 is required, proves this fact, 
 however, in a conclusive 
 manner. 
 
 Exp. 49. Fig. 17 repre- 
 sents a strong glass vessel A, 
 through the upper part of 
 which two platinum wires are 
 inserted ; the vessel can be 
 closed by a glass stop-cock c ; 
 by means of a second stop- 
 cock it can be attached to an 
 air-pump, not shown in the 
 figure, and the air exhausted. 
 The stop-cocks having been 
 closed, the vessel is screwed upon the top of a jar, B, containing a 
 mixture of two measures of hydrogen and one measure of oxygen. 
 On opening the stop-cocks a portion of the mixture enters the 
 vessel ; the cocks are then closed, and an electric spark passed 
 through the mixture. A bright flash occurs ; the gases com- 
 bine, and the whole of the two gases become condensed into 
 water, which trickles down the sides of the glass. On again 
 opening the stop-cocks a fresh quantity of gases may be ad- 
 mitted, to supply the place of those just condensed. The spark 
 may be again transmitted, and the process may be repeated 
 until the whole of the gases are consumed and a considerable 
 quantity of water formed. 
 
 If in this experiment oxygen or hydrogen be used in ex- 
 cess, that excess will be found in the vessel unacted on after 
 firing the mixture. 
 
Synthesis of Water. 
 
 Fig. i 8. 
 
 Exp. 50. Provide a stout tube bent into the form shown in 
 
 Fig. 1 8, open at one end and sealed at the other, the sealed 
 limb having been divided into cubic centimetres, or other equal 
 divisions. Into the sides of the tube, near the sealed extremity, 
 two platinum wire-s are fused, with two of the ends inside the 
 tube, nearly touching each other. Fill the tube with mercury ; 
 then introduce a mixture of 4 volumes of oxygen and 2 volumes 
 of hydrogen. The bulk of this gas 
 is to be carefully measured ; say it 
 fills 6 divisions after causing the 
 liquid metal to stand at the same 
 level in both tubes ; this may be 
 easily effected either by adding mer- 
 cury or by drawing it off through 
 the caoutchouc tube and screw-tap 
 near the bottom. The open end of 
 the tube must now be firmly closed 
 with a cork, below which a column 
 of air is included. This air is meant 
 to act as a spring for gradually 
 checking the force of the explosion, 
 which is now to be produced by 
 passing an electric spark either from 
 a Leyden jar or an induction coil 
 between the wires. After the ex- 
 plosion the gas in the closed limb 
 will measure less than before. With- 
 draw the cork, and add mercury until the metal again stands at 
 the same height in both tubes. Suppose the gas filled 6 divisions 
 before the spark was passed ; it fills just 3 divisions afterwards : 
 the 2 volumes of hydrogen which the mixture contained combine 
 with i volume of oxygen, and immediately condense into mois- 
 ture on the cold sides of the tube. The remaining 3 volumes may 
 be shown to be oxygen as follows : Fill up the open limb with 
 mercury; close it with the thumb ; then incline the tube so as 
 to transfer the gas from the sealed to the open limb. A match 
 with a red-hot point will immediately blaze up if introduced into 
 rt (Exp. 7). 
 
 Such an instrument (Fig. 18) is called a eudiomdcr, and 
 is often used for the analysis of mixtures of gases. 
 
66 
 
 Synthesis of Water. 
 
 Pure water may also be formed in considerable quantities 
 by the following method, which rests on this important fact, 
 that when cupric oxide is heated in contact with hydrogen, 
 it gives up its oxygen to the hydrogen, and the two unite to 
 form water, which may not only be collected and weighed, 
 but the proportion by weight of each of its constituents may 
 also be determined. 
 
 Exp. 51. Place a quantity of pure and dry cupric oxide 
 (CaO) in a globe, F (Fig. 19), made of glass of difficult fusibility, 
 and weigh the globe and its contents accurately. Hydrogen is 
 next to be disengaged steadily, by adding small quantities of 
 
 Fig. 19. 
 
 diluted sulphuric acid to granulated zinc contained in the bottle 
 A. Let the gas bubble up through a solution of potash in B, and 
 then pass through the tube c, which is filled with fragments of 
 pumice moistened with a solution of corrosive sublimate (HgCl a ), 
 then through D, which is filled with pieces of fused potash, and 
 lastly through E, which contains fragments of pumice moistened 
 with strong sulphuric acid. The potash and the mercuric salt 
 remove traces of arsenicum, sulphur, and carburetted compounds 
 derived from impurities -in the acid or the zinc, while the tube E 
 deprives the gas of every trace of moisture. In this way pure 
 and dry hydrogen is obtained before it passes into the globe F. 
 When all the air of the apparatus has been displaced, by allow- 
 ing a certain quantity of hydrogen to pass through it to waste. 
 
TJie Oxy-Jiydrogcn Jet. 
 
 67, 
 
 Fig. 20. 
 
 heat is applied to the globe F. The cupric oxide when heated 
 alone is not altered, but when heated with hydrogen it loses 
 oxygen, which converts the hydrogen into water ; this is collected 
 in the receiver G and the bent tube H, which contains pieces of 
 pumice moistened with strong sulphuric acid. When the globe F 
 is cold, pass a current of air through the apparatus, for the 
 purpose of displacing the hydrogen left in it. Weigh the 
 globe with the oxide a second time : the loss shows how much 
 oxygen has been removed. Weigh also the receivers G and H 
 again : the increase in weight shows how much water has been 
 condensed; the difference between the oxygen lost by F and the 
 water gained by G and H is the hydrogen which has combined 
 with the oxygen to form water. 
 
 By numerous careful experiments 
 performed in this way it has been found 
 that 1 6 grams of oxygen combine with 
 exactly 2 grams of hydrogen to form 
 1 8 grams of water. 
 
 Hydrogen, in combining with oxy- 
 gen, gives out a heat surpassing that 
 which any other chemical action pro- 
 duces. By forcing a jet of oxygen 
 through the flame of a spirit lamp, of 
 coal gas, or of hydrogen, a very high 
 temperature is immediately obtained ; 
 but the most intense heat is procured 
 by sending a jet of oxygen into the 
 midst of a jet of hydrogen by means 
 of two concentric tubes, as shown in 
 Fig. 20. The outer tube, provided with 
 the stop-cock H, is connected with a 
 large bladder or bag of hydrogen, placed 
 under a weighted board, which by its 
 pressure drives out the gas, while the 
 inner tube, with its stop-cock o, is connected with another 
 bag, which supplies oxygen. If the mixed gas, as it issues, 
 is kindled, a small feebly luminous but intensely hot jet of 
 
 F 2 
 
68 Synthesis of Water. 
 
 flame is obtained, in which a thick platinum wire may be 
 quickly melted and partially volatilised. Thick iron and steel 
 wires held in this flame are also easily melted, and burn, 
 giving off brilliant sparks. Rock crystal melts in it like 
 glass, and the stem of a tobacco pipe fuses without difficulty. 
 If the jet be directed on a pellet of lime, the earth does not 
 fuse, but becomes white hot, giving out a very pure white 
 light, which, under the name of the ' Drummond light,' 
 has been extensively used for signalling, and, when pro- 
 perly mounted in the focus of a concave mirror, has been 
 seen, from great elevations, at a distance of more than 
 100 miles. 
 
 The combustion of the mixed gases, as the oxygen and 
 hydrogen in proper proportions are termed, produces, as we 
 know, pure water. Water is also formed abundantly when- 
 ever combustible bodies which contain much hydrogen are 
 burned in the open air; such, for instance, as wood, oil, 
 tallow, spirit of wine, and coal gas. A tallow candle, in 
 burning, produces rather more than its own weight of 
 water; and alcohol or spirit of wine yields a still larger 
 amount. 
 
 Exp. 52. Hold a cold glass over a burning candle : it will 
 quickly become bedewed with moisture. 
 
 A similar result may be observed every time a retort or 
 vessel containing cold liquid is heated over the flame of a 
 lamp or of gas : drops of water condense until the vessel 
 becomes sufficiently hot to prevent this effect from oc- 
 curring. 
 
 Hydrogen is rapidly absorbed by many porous bodies, 
 particularly by the metals platinum and palladium. Palla- 
 dium, indeed, can absorb as much as 900 times its bulk of 
 hydrogen gas without losing its brilliant lustre. It retains 
 the gas at ordinary temperatures, but loses it by degrees if 
 the temperature be raised ; and if heated to redness, in a 
 vessel from which the air is exhausted, all the hydrogen may 
 be again extracted. 
 
Diffusion of Hydrogen. 69 
 
 Exp. 53. Fasten a piece of spongy platinum (a form in which 
 the metal may be obtained by heating its compound chloride 
 [2H 4 NC1, PtClJ, as will be explained hereafter) to a thin pla- 
 tinum wire, and hold it in a jet of hydrogen as it escapes into the 
 air. The cold platinum will become red hot, and kindle the gas. 
 
 This effect appears to be due to the condensation of the 
 gas by the platinum, which also condenses oxygen from the 
 air, and the heat attending the condensation is sufficient 
 ultimately to set fire to the mixture of gases. 
 
 Another peculiar property of gases is well exhibited by 
 hydrogen. Whenever two gases are placed in vessels which 
 communicate with each other, the gases become gradually 
 intermingled, although they may not have any tendency to 
 chemical combination; and the greater the difference in 
 density between them, .the more rapidly does this process of 
 diffusion, as it is called, take place. 
 
 Exp. 54. Take a tube of about 20 centim. long and 2 centim 
 wide, open at both ends. Mix a little plaster of Paris with 
 water so as to be of the consistence of thick cream, and im- 
 merse one end of the glass tube in the mixture to the depth of 
 5 mm. In about ten minutes the plaster will have become 
 solid, and on raising the tube out of the mixture its extremity 
 will be closed with a thin plate of plaster ; let it dry in a warm 
 room for a couple of days. Through this . 
 
 porous plug the effects of diffusion may 
 be observed. Fill this diffusion-tube with 
 hydrogen gas by displacement, covering 
 the plug of plaster with a cap of tinfoil 
 when the tube is full of hydrogen. Place 
 it in a tall jar of water (Fig. 21), with the 
 open end downwards, and remove the 
 tinfoil. The water will rise rapidly in the 
 tube, as though it were dissolving the gas, 
 and will soon fill it above two-thirds of its height. 
 
 In this experiment the porous plug favours the diffusion 
 of the hydrogen : about 3-8 measures of hydrogen pass out, 
 while only i measure of air enters ; hence the liquid rises in 
 the tube. 
 
JO Hydrogen the Unit. 
 
 Other gases exhibit a similar tendency to diffusion, though 
 to a less extent, the diffusiveness depending upon the relative 
 density of the two. Its amount admits of exact calculation, 
 supposing the specific gravity of the gas to be known. The 
 rule is to take the square root of the number which re- 
 presents the specific gravity of the gas, and divide i by 
 this number : the fraction thus obtained is the diffusiveness 
 required. 
 
 For example, the numbers which represent the specific 
 gravity of oxygen and hydrogen, i'io57 and 0*0691, are to 
 each other in the proportion of 16 to i. The square root 
 of 1 6 is 4, and the square root of i is i. Now, the rate 
 at which hydrogen diffuses into an atmosphere consisting 
 of pure oxygen is as 4 to i. That is to say, that when proper 
 precaution is used in making the experiment with such a 
 diffusion-tube as that described, while 4 measures of hydro- 
 gen pass out into the oxygen through the plaster, i measure 
 of oxygen would pass into the hydrogen in the opposite 
 direction. The specific gravities of air and hydrogen are 
 
 i and 0-0691, and their rates of diffusion are j= (= i) and 
 
 f , or i and 3-8. In fact, 3 '8 measures of hydrogen 
 \/o'o6gi 
 
 become diffused into the air, while i measure of air is being 
 diffused at the same time into the hydrogen. 
 
 Hydrogen is the lightest substance known ; an equal bulk 
 of oxygen being 16 times as heavy, and an equal bulk of 
 air 14*47 times as heavy as the same bulk of hydrogen under 
 similar circumstances of temperature and pressure. Hydro- 
 gen has also a smaller combining number than any other 
 elementary body ; and this, with its lightness, furnish two of 
 the reasons which have induced chemists to take hydrogen 
 as the unit or standard of comparison both for atomic 
 weights and combining volumes. The atomic weight of 
 hydrogen has been therefore taken as i, or H = i, and its 
 combining volume is also i, or H = [ |. 
 
Hydrogen and Chlorine, Oxygen, &c. 71 
 
 Suppose, then, i gram of hydrogen to be the unit of 
 weight, the space it would occupy at o, under a barometric 
 pressure of 760 mm., would be 11*19 litres. The same 
 volume of oxygen would weigh 16 grams, of nitrogen 
 14 grams, of chlorine 35*5 grams. This volume, 11-19 litres, 
 may, therefore, be regarded as representing i gas volume. 
 For many purposes, however, the litre is a convenient mea- 
 sure ; and i litre of hydrogen, at the temperature of o and 
 760 mm. pressure, weighs 89*6 milligrams. 
 
 The proportion in volume in which a certain fixed volume 
 of each of the elementary gases or vapours combines with 
 hydrogen, and the volume of gas or vapour which such 
 combinations furnish, compared with the space they occupy 
 before combination, affords a character upon which the 
 grouping of the different elements into natural families is 
 founded. 
 
 For example, when a litre of chlorine unites with hydrogen, 
 it does so in the proportion of i litre of hydrogen, and it 
 forms with it 2 litres of a new compound, hydrochloric acid 
 gas; but a litre of oxygen, when it unites with hydrogen, 
 requires not less than 2 litres of hydrogen, though it still 
 forms only 2 litres of the new body, aqueous vapour ; further, 
 if a litre of nitrogen be combined with hydrogen, it will unite 
 with 3 litres of hydrogen, and yet will form only 2 litres of 
 the resulting ammoniacal gas. Consequently, if the hydro- 
 chloric acid be represented by the symbols HC1, it is agreed 
 by chemists to represent the equal bulk of aqueous vapour as 
 H 2 O, and the same bulk of ammonia as H 3 N. 
 
 We see, then, that a single volume of chlorine, of oxygen, 
 and of nitrogen, when uniting severally with hydrogen, 
 requires, respectively, one, two, and three volumes of hydro- 
 gen, while in every one of these cases the compound which 
 is formed measures two volumes, no matter whether the 
 volume used be a cubic centimetre, a litre, a cubic inch, a 
 cubic foot, or any other volume which may be agreed on. 
 
 Further, it is important to remember that the quantity of 
 
72 Monad, Dyad, &c. Elements. 
 
 any compound represented by its formula is spoken of as its 
 molecule ; and when the body is known in the aeriform state, 
 that molecule is always tacitly compared with an equal 
 bulk of hydrogen, which is represented by the formula H 2 ; 
 and this amount of hydrogen is also spoken of as its 
 molecule.* 
 
 In the table which follows, some of the most important 
 gaseous compounds of the different elements are enumerated. 
 In each case the quantity represented by the formula indi- 
 cates 2 volumes, say 2 litres, of the gaseous compound. 
 H = i, being Q i volume or i litre, and H 2 = 2 volumes 
 | I | or 2 litres. 
 
 In the first column all the compounds are represented in 
 their formulae as furnished by the union of single volumes 
 of each element, the two bodies combining volume to volume. 
 Elements which combine in this way are called monads, or 
 wiivalcnt elements. 
 
 In the second column two volumes of hydrogen are repre- 
 sented in combination with a single volume of certain other 
 elements, which, from their power of chemically uniting with 
 two volumes of hydrogen, have been termed dyads, or bi- 
 valent elements. 
 
 In the third column each of the compounds contains 3 
 volumes of hydrogen united with i volume of one of the 
 elements of a natural group known as the triads, or, as they 
 are sometimes called, tervalent elements, f i volume of each 
 of these element requiring 3 volumes of hydrogen to form 
 the compound. 
 
 And, lastly, in the fourth column the compounds repre- 
 sented each contains 4 volumes of hydrogen, united with a 
 fixed quantity of certain elements, which cannot be obtained 
 
 * Some further observations on gaseous molecules will be found in 
 the paragraph on the atomic theory. 
 
 "t* Phosphorus rnd arsenicum are, however, exceptional, since they 
 combine with 3 volumes of Jr drogen in the proportion of \ a volume 
 of their vapour. 
 
Monads, Dyads, Triads, &c. 
 
 73 
 
 separately as gases, but which are distinguished as tetrads, 
 or quadrivalent elements.* 
 
 COMPOUNDS OF 
 MONADS 
 
 COMPOUNDS OF 
 DYADS 
 
 COMPOUNDS OK 
 TRIADS 
 
 COMPOUNDS OF 
 TETRADS 
 
 Hydrochloric 
 Acid 
 
 HC1 
 
 Water 
 H 2 
 
 Ammonia 
 
 H 3 N 
 
 Marsh Gas 
 
 H 4 C 
 
 Hydrobromic 
 Acid 
 
 HBr 
 
 Sulphuretted 
 Hydrogen 
 
 H 2 S 
 
 Phosphuretted 
 Hydrogen 
 
 H 3 P 
 
 Siliciuretted 
 Hydrogen 
 
 H 4 Si 
 
 Hydriodic 
 Acid 
 
 HI 
 
 Seleniuretted 
 Hydrogen 
 
 H 3 Se 
 
 Arseniuretted 
 Hydrogen 
 
 H 3 As 
 
 
 Hydrofluoric 
 Acid 
 
 HF 
 
 Telluretted 
 Hydrogen 
 
 H 2 Te 
 
 Antimoniuretted 
 Hydrogen 
 
 H 3 Sb 
 
 
 The compounds which hydrogen forms when it unites 
 with any other elementary body are known as hydrides. 
 
 CHAPTER IV. 
 
 OXIDES OF CARBON CARBON. 
 
 (17) CARBONIC ANHYDRIDE {Carbon Dioxide, or Car- 
 bonic Acid] : Symbol, CO 2 ; Atomic Weight, 44 ; Atomic 
 and Molecular Volume, P "j ; Specific Gravity, 1*5 29; Re- 
 lative Weight, 22. 
 
 We have already seen that when a saucer containing 
 limewater is exposed to the air for a few minutes, the surface 
 of the limewater becomes covered with a thin insoluble crust 
 
 * The elements which combine with I, with 3, or with an uneven 
 number of volumes of hydrogen are sometimes further distinguished as 
 pcrissad elements ; and those which combine with 2, 4, or an even 
 number of volumes of hydrogen are called arliad elements. 
 
74 Formation of Carbonic Anhydride. 
 
 or pellicle, consisting of chalk, which is formed by the union 
 of carbonic anhydride contained in the atmosphere with the 
 lime, CO 2 -f CaO forming CaCO 3 . Such compounds of 
 carbonic anhydride with bases are called carbonates hence 
 chalk is called calcic carbonate, or often carbonate of lime. 
 When chalk is heated to bright redness, the carbonic anhy- 
 dride is driven off, and the lime is left behind, as in the 
 ordinary process of burning limestone into lime, CaCO 3 
 becoming separated into CaO and CO 2 . 
 
 The carbonic is a very weak acid, and may be displaced 
 from its' compounds by almost every acid which is soluble 
 in water. 
 
 Exp. 55. In a glass bottle, similar to that used for preparing 
 hydrogen (Fig. 14), place 15 or 20 grams of chalk in small 
 lumps, or of marble, which is a crystalline form of the same 
 chemical compound. Pour on it some strong acid, such as the 
 hydrochloric (muriatic), HC1, diluted with 8 or 10 times its bulk 
 of water. 
 
 In this experiment the acid exchanges its hydrogen for 
 the calcium, producing calcic chloride (CaCl 2 ) on the one 
 hand, and carbonic acid (H 2 CO 3 ) on the other. But the 
 carbonic acid is so unstable that it immediately becomes 
 decomposed into water, which remains behind, and into 
 carbonic anhydride,* which comes off as a gas with brisk 
 effervescence. The decomposition may be represented as 
 follows : 
 
 CaCO 3 + 2HC1 = CaCl 2 + H 2 O + CO 2 . 
 
 Limestone (CaCO 3 ), pearlash (K 2 CO 3 ), sodic carbonate 
 (Na 2 CO 3 ), and indeed all the carbonates, may be made to 
 
 * An anhydride is an oxide which, when dissolved in water, furnishes 
 an acid, by uniting with the elements of water ; and it must be dis- 
 tinguished from a true acid, which is always a salt of hydrogen. Some 
 writers are not sufficiently careful to distinguish the two classes of bodies 
 from each other. The gas CO 2 was formerly known as carbonic acid ; 
 but as it is not a salt of hydrogen, it has been found necessary to change 
 its name for the sake of precision, and it is now called carbonic anhy- 
 dride, and sometimes carbon dioxide. 
 
Properties ef Carbonic Anhydride. 75 
 
 furnish carbonic anhydride as easily as marble, when treated 
 with a strong acid. 
 
 Although carbonic anhydride it usually obtained as a 
 heavy transparent gas, without colour, and with a faintly 
 acidulous taste and smell, it can be procured as a colourless 
 transparent liquid, by generating it from materials packed 
 into a small space in a strong closed tube ; but it requires a 
 pressure of 40 or 50 atmospheres to effect this ; and it is not 
 an experiment that can be made with safety by an inex- 
 perienced person. The gas is sometimes liquefied in large 
 quantities for experimental purposes in strong wrought-iron 
 vessels constructed with this object. When a stream of the 
 liquid thus obtained is allowed to escape into the air, one 
 portion of the liquid evaporates so rapidly as to carry off 
 heat so quickly that it freezes the rest into a snow-white 
 solid. If this be collected and mixed with ether, it produces 
 a cold bath or freezing mixture of great intensity, owing to 
 the rapid evaporation of the frozen gas, which carries off 
 heat in large quantity from any substance nearest to it ; a 
 cold estimated at 75 is thus easily attained. 
 
 Exp. 56. Fill three or four small jars with the gas as obtained 
 in Exp. 55. Plunge a lighted candle into one of them : the flame 
 is extinguished, but the gas does not take fire. 
 
 It will be remembered that other gases, such as nitrogen, 
 put out the light. 
 
 Exp. 57. Into another jar of the gas pour two or three table- 
 spoonfuls of limewater. It will at once become milky, owing to 
 the formation of chalk ; two or three drops of any strong acid 
 will immediately redissolve the chalk. 
 
 This action of the gas upon limewater is a very con- 
 venient and characteristic test of its presence, even when it 
 is mixed largely with air or other gases, since these gases do 
 not render limewater turbid. 
 
 Undiluted carbonic anhydride cannot be breathed, be- 
 cause the glottis, or valve at the entrance of the windpipe, 
 closes and prevents it from entering the lungs ; but if the 
 
7 6 
 
 Density of Carbonic A nhydride. 
 
 Fig. 22. 
 
 gas be largely mixed with air ; that is, if it be present in a 
 quantity varying from 3 to 4 per cent of the respired air, it 
 acts as a stupefying or narcotic poison, by preventing the 
 proper action of the air upon the blood as it passes through 
 the lungs, and in this way produces death. Part of the 
 bad effect experienced after remaining in crowded and ill- 
 ventilated rooms is owing to the presence of unusual quan- 
 tities of this gas, the true prevention in such cases being 
 efficient ventilation. 
 
 Carbonic anhydride is more than half as heavy again as 
 air. It is just 22 times as heavy as hydrogen, so that 
 11-19 litres, at o C. and 760 mm. 
 bar., weigh 22 grams, while the same 
 volume of air weighs only 14*47. 
 
 Exp. 58. Allow the gas to pass to 
 the bottom of a small jar, arranged as 
 in Fig. 22 ; when full, the gas, though 
 invisible, may be shown to be there, as 
 it will extinguish a candle lowered into 
 it on a wire. 
 
 Exp. 59. Take a second similar jar 
 full of air, and pour the gas slowly into 
 it from the jar rilled as in Exp. 58, as 
 though it were water. The light will now be extinguished if 
 lowered into the second jar, but will burn if introduced into the 
 first. 
 
 Many amusing experiments may be made upon this gas, 
 owing to the ease with which, from its density, it may be 
 transferred from vessel to vessel. It may be drawn off with 
 a syphon, ladled out with a glass, and so on. 
 
 Water dissolves about its own bulk of carbonic anhydride, 
 forming a solution of carbonic acid, CO 2 + H 2 O becoming 
 H 2 CO 3 . The water may be made to dissolve considerably 
 more than its own bulk of the gas, if it be forced in under 
 pressure. It is in this way that the so-called soda water is 
 made, though the water seldom contains soda, or indeed 
 
Test for Carbonic Anhydride. 77 
 
 anything but the dissolved gas. As soon as the pressure is 
 removed, the gas escapes with effervescence. 
 
 Exp. 60. Cause a stream of the gas to bubble briskly through 
 60 or 100 c. c. of water. To a portion of the solution of the gas 
 thus obtained add a few drops of tincture of litmus : it will be 
 reddened. Now boil the red liquid for a few minutes : the gas 
 will be driven off again, and the litmus will recover its blue 
 colour. 
 
 The solution of carbonic acid exerts slight but important 
 solvent powers upon many rocks and minerals. This action 
 produces changes which, insignificant as the amount may 
 appear at any given moment, yet in the lapse of ages be- 
 comes very considerable, since few natural waters are found 
 which are not charged more or less extensively with carbonic 
 acid. 
 
 Carbonic anhydride is largely produced in a variety of 
 important natural operations. Respiration, or the process 
 of breathing, both in man and animals, is always attended 
 with the formation of a large quantity of the gas. 
 
 Exp. 61. By means of a tube open at both ends blow a 
 little air from the lungs through limewater ; it will speedily 
 become turbid, owing to the formation of calcic carbonate. 
 
 Air which has been breathed once contains from 3^ to 4 
 per cent, of the gas. 
 
 Exp. 62. Pass a little of the air from the lungs, by means of 
 a tube, into a gas jar filled with water, and standing over water. 
 When the water has been displaced by the exhaled air, it may 
 be tried with a lighted candle, which will quickly go out. 
 
 Fermentation is another source of carbonic acid. 
 
 Exp. 63. Dissolve 15 or 20 grams of sugar in ten times its 
 weight of water, at 25 C. Add two teaspoonfuls of brewers' 
 yeast, and introduce the mixture into a Florence flask provided 
 with a cork and bent tube for the escape of gas. In about an 
 hour's time it will begin to give off a gas which puts out a light 
 and makes limewater turbid. 
 
 The briskness of bottled beer and of champagne is due to 
 
78. Sources of Carbonic Anhydride. 
 
 the dissolved carbonic acid which they contain. Accidents 
 have often happened in breweries where fermentation is 
 carried on upon a large scale, owing to the incautious 
 entrance of the workmen into an empty fermenting vat 
 before the heavy gas has had time to escape. The plug at 
 the bottom should be left open after the liquor has run off, 
 to assist the escape. 
 
 Large quantities of carbonic anhydride are also expelled 
 in the process of burning limestone in a limekiln ; and a 
 similar action occurs if limestone is found in volcanic dis- 
 tricts, owing to the action upon it of the heat beneath the 
 surface of the earth, in consequence of which immense 
 volumes of the gas escape from craters and fissures of the 
 soil. The springs of such districts are often lightly charged 
 with carbonic acid, and the gas passes off with effervescence 
 when the water comes to the surface. 
 
 Much of the carbonic acid found in ordinary spring and 
 river water is furnished by the gradual oxidation, in the pores 
 of the soil, of the vegetable and other organic matter with 
 which they had been before contaminated. 
 
 What is called choke damp by miners is also principally 
 composed of this gas. It often accumulates in old pits or 
 wells, and in the abandoned workings of mines. No one 
 ought ever to venture into such places without first trying 
 whether a candle will burn freely in the pit or shaft. If it 
 does it is safe, at least for a short time. 
 
 Whenever charcoal, or any substance which contains car- 
 bon, such as wood, coal, oil, or tallow, is burnt, carbonic 
 anhydride is formed in abundance. 
 
 Exp. 64. Kindle a piece of charcoal, and plunge it into a 
 bottle of oxygen ; it will burn brilliantly. After the combustion 
 is over, shake some limewater with the gas which remains ; the 
 immediate precipitation of chalk shows that carbonic anhydride 
 has been formed abundantly. 
 
 Exp. 65. Hold a glass jar full of air for a few minutes over 
 a piece of burning charcoal ; withdraw the jar, and close the 
 
Ventilation. 
 
 79, 
 
 Fig. 23. 
 
 mouth of it with a glass plate. Add a tablespoonful of lime- 
 water, and shake it up in the jar. Chalk will immediately be 
 formed. The result will be similar if the jar be held over a jet 
 of burning coal gas, over a burning candle, or over the flame of 
 a spirit lamp. 
 
 Two candles of 6 to the pound, in burning, may be 
 reckoned to produce about 38 litres of carbonic anhy- 
 dride per hour, or as much of the gas as would be generated 
 by the respiration of a man of ordinary size in the same 
 time. 
 
 Although pure carbonic anhydride is heavier than air, 
 both the products from a burning candle and air which has 
 been respired are, owing to the heat produced in each case, 
 lighter than the surrounding air, and they accumulate in the 
 upper part of an inhabited room. 
 In ventilating such a room, open- 
 ings should be made in or near 
 the ceiling for the escape of the 
 impure heated air, while the free 
 admission of fresh air should be 
 secured near the floor. 
 
 Exp. 66. Fasten a piece of taper 
 to a bit of cork, and place it in a 
 plate, with a little water. Light the 
 taper; then cover it with a wide- 
 necked gas jar, and over the neck 
 of the jar place a glass gas-chimney, 
 as in Fig. 23. In a few minutes the 
 taper will burn dimly, and would 
 soon go out ; but if the edge of the 
 jar be slightly raised out of the 
 water in the plate, air will enter at 
 the bottom, and the heated impure 
 air will pass off by the chimney. The course of the current may 
 be watched by means of the smoke from a smouldering bit of 
 brown paper, which will follow the movements of the air, if 
 brought near enough. Instead of lifting the edge of the jar, 
 
So Decomposition of Carbonic Anhydride. 
 
 divide the air-way through the chimney by placing a long slip 
 of card down the middle ; a downward current will then be 
 established on one side of the card, and an ascending current 
 on the other, and the taper will burn freely. 
 
 It is on this principle that small mines are often ventilated 
 for a time, the shaft being divided by a wooden partition 
 into a downcast and an upcast shaft. In the best ventilated 
 mines, however, this is done by two separate shafts, sunk at 
 some distance from each other, and in one of these shafts a 
 fire is kept burning, for the purpose of producing an ascend- 
 ing current of hot air. Ventilation by means of fans driven 
 by machinery is, however, both much safer and more effectual 
 in producing the necessary movement of the air. 
 
 Carbon may without difficulty be separated from carbonic 
 anhydride. 
 
 Exp. 67. Cause a current of the gas to pass through a 
 drying-tube containing calcic chloride (Fig. 24), and then through 
 
 Fig. 24. 
 
 a bulb tube containing a small piece of potassium. Heat the 
 potassium in the gas : it will soon take fire, and burn brilliantly. 
 Let the tube cool, and then plunge it into water. 
 
 In this experiment potash is formed in the tube at the 
 expense of oxygen derived from the gas ; the alkali is dis- 
 solved by the water, and black particles of charcoal become 
 diffused through the liquid. 
 
 Exp. 68. Kindle a strip of magnesium foil, by holding it 
 
Synthesis of Carbonic A nhydride. 8 1 
 
 with the tongs in the flame of a spirit lamp; and when burning 
 brightly, introduce it into a jar filled with carbonic anhydride. 
 The metal will continue to burn ; white flakes of magnesia, 
 mixed with black particles of carbon, will be deposited. Add a 
 little dilute nitric acid : this will dissolve the magnesia, and 
 leave the carbon. 
 
 Carbonic anhydride is not only absorbed by limewater, 
 but it is also quickly absorbed by any alkali, such as a solu- 
 tion of potash. 
 
 Exp. 69. Fill a strong graduated test-tube with carbonic an- 
 hydride by displacement, and invert it in a deep glass containing 
 mercury, as shown in Fig 8. Then introduce the curved beak 
 of a pipette, filled with a strong solution of potash, beneath the 
 edge of the tube, and blow from the lungs with just sufficient 
 force to drive a few drops of the liquid into the tube. The solu- 
 tion of potash will quickly absorb the gas, and mercury will 
 rise in the tube. 
 
 A strong solution of potash is in continual use in the 
 laboratory for separating carbonic anhydride from other 
 gases which, like oxygen, nitrogen, and hydrogen, are in- 
 soluble in the potash solution. In this way it is easy to 
 estimate the quantity of carbonic anhydride in respired air. 
 
 We have thus proved by synthetic experiments that when 
 charcoal is burned in air or in oxygen, carbonic anhydride is 
 formed; and we have found by analysis that the gas con- 
 tains both oxygen and charcoal. It may be shown that it 
 contains nothing but carbon and oxygen, and the exact pro- 
 portions may be determined by means of the apparatus 
 shown in Fig. 25. 
 
 A is a gas-holder filled with pure oxygen, B a strong solu- 
 tion of potash, D a tube filled with calcic chloride in lumps, 
 E a sheet-iron furnace containing a tube of hard glass : at F, 
 within the tube, is a platinum tray containing the carbon ; G is 
 a tube containing calcic chloride, H a series of bulbs filled 
 with solution of potash, while I is a tube filled with lumps of 
 potash. 
 
 The platinum tray with the carbon, whether in the form ot 
 
 G 
 
82 Synthesis of Carbonic Anhydride. 
 
 diamond, graphite, or charcoal, is weighed accurately at 
 first. Then the oxygen dried in its passage is allowed to 
 stream slowly through the tube, which is gradually made red 
 hot by placing glowing charcoal round it in the furnace. 
 The carbon in the platinum tray burns brilliantly in the 
 stream of oxygen, and becomes converted into carbonic anhy- 
 dride. The tube should also contain cupric oxide, by which 
 any trace of carbonic oxide which might be formed would be 
 at once converted into the anhydride. This is completely 
 arrested by the potash in the bulb tubes H, no gas but pure 
 
 and dry oxygen escaping into the air. The gain in weight 
 of H and i together shows how much carbonic anhydride has 
 been formed. The loss of weight of the platinum tray F 
 shows how much carbon has been burnt, and the difference 
 between this weight and that of the carbonic anhydride 
 shows how much oxygen has combined with the carbon. 
 No chemical experiment has ever been made with greater 
 care than this for the purpose of arriving at accurate results, 
 since the composition of carbonic anhydride is a fundamental 
 datum in all analyses of organic compounds. It has been 
 found by repeated trials of this process that 12 grams of car- 
 bon require exactly 32 grams of oxygen to convert them into 
 44 grams of carbonic anhydride ; so that, assuming for the 
 present the atomic weight of carbon to be 12, the molecular 
 weight of a carbonic anhydride is 44, and the formula re- 
 presenting its composition is CO 2 . 
 
Carbonic Acid in the Atmosphere. 83 
 
 If carbon be burned in a jar of oxygen over mercury, so 
 as to prevent any loss of the gas, it is found that the gas, 
 when it has cooled down again and is measured with due 
 care, is not altered in bulk. The carbonic anhydride formed 
 occupies the same volume as the oxygen which has entered 
 into its composition, so that the gas contains its own bulk 
 of oxygen. 
 
 Carbonic acid, though a weak one, forms a numerous and 
 important series of salts, called carbonates. Except those of 
 the alkaline metals, they are nearly insoluble in water ; and 
 all, whether soluble in water or not, dissolve with effer- 
 vescence in dilute nitric acid. The gas which comes off 
 is colourless, with scarcely any smell ; and if passed into 
 limewater, it makes it turbid, thus showing it to be carbonic 
 acid. 
 
 Many of the carbonates occur in immense quantities as 
 natural products, 'particularly calcic and magnesic car- 
 bonates. 
 
 The quantity of carbonic anhydride in the atmosphere is 
 tending continually to increase, in consequence of the 
 numerous chemical processes by which it is being produced; 
 and it would accumulate to a serious extent, were it not pre- 
 vented by a remarkable counteracting power possessed by 
 growing plants. The green parts of plants, when in the 
 sun's light, decompose carbonic acid, and lay up the carbon 
 in the wood and other parts, whilst they give back most of 
 the oxygen to the air, thus converting again into fuel that 
 material which has been diffused through the atmosphere, 
 and has, by being burned, lost for the time its chemical 
 activity. The rain as it falls dissolves the carbonic anhy- 
 dride, and carries it down to the earth; and the roots of the 
 plants absorb it, and carry it up into the leaves, where it 
 undergoes the necessary chemical change, so long as the sun's 
 rays fall upon the plant. In the dark, no such removal of 
 carbon from the gas and restoration of oxygen to the air 
 occurs. 
 
 G 2 
 
84 
 
 Varieties of Carbon. 
 
 Exp. 70. Into a small gas jar (Fig. 26) fit a good cork, instead 
 of the stopper, and pass a test-tube tightly through a hole bored 
 through the cork. Place the jar in a large beaker filled with 
 
 p. 
 
 spring water, which has been mixed with 
 a fourth of its bulk of solution of carbonic 
 acid in water. Fill the tube with water, 
 and place it in the neck of the jar, having 
 introduced a few sprigs of mint or the leafy 
 branches of any succulent plant in the 
 jar, and then expose it for an hour or two 
 in direct sunshine. Bubbles of gas will be 
 seen studding the leaves ; and on shaking 
 the jar, these will become detached, and 
 will rise into the test-tube. After a time 
 the cork and tube may be withdrawn, 
 keeping the mouth of the tube beneath 
 the surface of the water ; then close it with 
 the thumb, turn the tube mouth upwards, 
 and test the gas with a glowing splinter. The wood will burst 
 into a blaze, showing that the gas consists mainly of oxygen. 
 
 (18) CARBON: Smyb. C; Atomic Wt. 12; Sp. Gr. as 
 diamond, about 3-4. 
 
 Carbon is an elementary body of the greatest importance, 
 and it occurs in various familiar forms, viz. naturally as 
 diamond, and as graphite or black-lead, as well as less pure 
 in the different artificial substances known as charcoal and 
 coke. It is also abundant in combination : chalk contains 
 not less than an eighth of its entire weight of carbon, and 
 magnesic carbonate more than one-seventh. Carbon also 
 occurs combined with other elements ; for it is the cha- 
 racteristic constituent of those substances which are called 
 organic and are of vegetable or animal origin. 
 
 a. The diamond is the hardest of known substances, and 
 the most valuable of gems. It consists of pure carbon 
 crystallised in forms derived from the regular octahedron and 
 dodecahedron, and often in the form of rolled pebbles, with 
 a dingy exterior, which would cause them often to be over- 
 
Diamond Plumbago. 85 
 
 looked by an unskilled observer. The diamond can only be 
 cut and polished by grinding it with its own powder. Its 
 most important use is familiar to us in the hands of the 
 glazier for cutting sheets of glass. Owing to its rarity, its 
 high refracting power, and brilliant lustre, it has been prized 
 for ornamental purposes from time immemorial. 
 
 Diamond may be burned in oxygen gas, when it con- 
 sumes away almost without residue. Twelve mgrams. of 
 diamond have been found to yield when thus burned exactly 
 44 mgrams. of carbonic anhydride, and no other product. It 
 has never been melted. It is a non-conductor of electricity, 
 though other forms of carbon conduct it well. When heated 
 intensely in the arc of the voltaic battery, as soon as it 
 becomes white hot, it swells up, loses its transparency, 
 acquires the power of conducting electricity, and is con- 
 verted into a black opaque mass resembling coke. 
 
 b. Plumbago, or graphite, frequently from its appearance 
 called black-lead, though it contains no lead, is another form 
 in which carbon is found naturally, but in tolerable quantity. 
 It has a sp. gr. of about 2 '2, and occurs sometimes in crys- 
 talline six-sided plates. It has a leaden-grey lustre, leaves a 
 streak upon paper on which it is rubbed, on which account 
 the finest kind is used in making artists' drawing pencils. It 
 is a good conductor of electricity. When it is burned in 
 oxygen, it always leaves from 2 to 5 per cent, of ash, which, 
 however, is not a necessary part of it. The gas which it 
 furnishes when thus burned in oxygen is pure carbonic 
 anhydride. Owing to its perfect indifference to the action 
 of oxygen at common temperatures, it forms a serviceable 
 coating for the protection of ironwork from rust, as is com- 
 monly practised with fire-grates and stoves. Graphite, when 
 mixed with clay, is often made into crucibles, because they 
 are not liable to crack in the fire. Molten iron dissolves 
 carbon readily ; much of it separates from the iron again if 
 the melted metal is allowed to cool slowly. It is then in the 
 form of graphite. 
 
86 Pit Coal Anthracite. 
 
 Pit Coal This is one of the most important natural sub- 
 stances rich in carbon. It is a material, of vegetable origin, 
 which has become altered during the lapse of ages, while 
 exposed, tinder great pressure in the strata of the earth, to 
 the combined action of water holding in solution oxygen 
 derived from the air, and moderate heat. The composition of 
 pit coal varies greatly according to the length of time during 
 which it has been thus acted on, the older deposits being 
 those which contain the largest proportion of carbon. The 
 elements of which the original vegetation consisted are car- 
 bon in large proportion, oxygen in smaller quantity, still less 
 hydrogen, and a very small proportion of nitrogen; but 
 besides these there is a variable quantity of saline and earthy 
 substances which always occur in vegetable juices ; added 
 to which are earthy impurities derived from the adjacent 
 strata, as well as a portion of iron pyrites (FeS 2 ), which is 
 always gradually formed in the coal. When coal is burned 
 in the open fire, if there be a sufficient supply of air, the 
 carbon becomes carbonic anhydride, the hydrogen burns 
 into water, the nitrogen escapes chiefly as gas, and the ash 
 which remains is composed of the saline and earthy residue. 
 
 Much of the South Wales coal is of the modification called 
 culm or anthracite, which contains upwards of 90 per cent, 
 of carbon, and but little volatile matter. It burns without 
 flame, and with a steady glow. House coal, such as is used 
 in London, is of a different kind. It softens when heated, 
 and forms a pitchy or bituminous mass, which causes the 
 pieces to cake together. Such coal is never burned com- 
 pletely, even in an open fire \ but in the act of burning it 
 gives off a quantity of gaseous or tarry matter, holding finely 
 divided carbon or soot in suspension. When a quantity of 
 fresh coal of this kind is thrown upon a hot fire, it at once 
 begins to be decomposed ; considerable quantities of the 
 compounds of carbon and hydrogen are formed, and pass 
 off in the condition of gas or vapour. A portion of these sub- 
 stances immediately takes fire, and burns with a bright light 
 
Combustion and Distillation of Coal. 87 
 
 and a smoky flame ; but a large portion of them, when they 
 pass over the glowing embers, is more or less completely 
 decomposed ; the carbon and hydrogen become partially 
 separated from each other in a part of the fire where there is 
 but little uncombined oxygen ; the hydrogen, being the more 
 combustible element of the two, seizes upon such oxygen as 
 it finds, or else it escapes unburnt in the form of gas ; while 
 the carbon, still containing a notable proportion of hydro- 
 gen, is carried away in very fine particles, and passes off as 
 smoke, suspended in the heated gases. 
 
 The formation of this black smoke may, however, be pre- 
 vented by throwing the coal upon the fire in small quantities 
 at a time, taking care to keep up a strong steady heat, so as 
 to consume the gases as they are formed ; but this can only 
 be secured by a sufficient supply of atmospheric air, a con- 
 dition not so easily fulfilled in manufacturing furnaces as 
 might be expected, though with proper care it can be done. 
 
 When bituminous coal is heated in long closed iron 
 cylinders, out of contact with air, a large quantity of gas 
 and of tar is formed ; they contain the oxygen, hydrogen, 
 nitrogen, and part of the carbon of the coal, while the 
 greater portion of the carbon is left behind as a porous mass, 
 called coke. Coke resembles graphite in properties, but it 
 retains all the ash and earthy impurities of the coal. It 
 burns with a steady glow, without emitting flame or smoke ; 
 it is less combustible than coal, and requires a brisk current 
 of air to keep it burning. The more highly the coke is heated 
 during its preparation, the more compact does it become, 
 the better does it conduct heat, and the more slowly does it 
 burn. 
 
 Exp. 71. Get a blacksmith to weld up one end of a wrought- 
 iron gas-pipe 25 mm. (i inch) in diameter, and 50 centim. long. 
 Fit a cork and a bent tube to the open end ; put from 50 to 100 
 grams of coarsely broken coal into the iron tube;* heat the 
 
 * A hard glass tube may be used instead of the iron tube, and may 
 be heated in a flame, but it does not yield the gas so easily. 
 
88 Coke Preparation of Charcoal. 
 
 closed end in a common fire, and direct the gas into the pneu- 
 matic trough. Some tarry matter will pass over, and a con- 
 siderable quantity of gas may be collected, which will burn with 
 a bright flame. When all the gas appears to have been driven 
 off. take the tube out of the fire, let it cool, and then, with an 
 iron rod, detach what is left in the inside of the tube. It will be 
 found to be common coke. Put some of this coke in a small 
 open clay crucible, and heat it in the fire : the coke will gra- 
 dually burn away, leaving nothing but a little ash. 
 
 The dense coke required for burning in the powerful draught 
 created under the boiler of a locomotive engine is usually 
 prepared by burning the coke in massive brick ovens, in 
 each of which several tons of coal can be charred in a single 
 operation, the ovens being provided with a sliding door, for 
 regulating the admission of air, which plays over the surface of 
 the heap and burns off the volatile matters, and so chars the 
 whole mass at a very high temperature, each charge requir- 
 ing 48 hours for its conversion into coke. 
 
 If, instead of heating coal in an iron retort, wood be 
 treated in the same way, a still larger quantity of volatile 
 and liquid products will be given off, and what is left behind 
 is a black porous substance, of the same shape as the wood, 
 familiarly called charcoal. Wood tar, vinegar, and wood 
 naphtha are among the liquid products, which redden litmus 
 paper strongly, but the gas has little illuminating power. A 
 more compact charcoal, better suited for use as fuel, is made 
 by burning wood in heaps. A stake is driven into the 
 ground, brushwood is placed round the bottom, and logs of 
 wood are piled up regularly around the stake. The heap thus 
 formed is often 10 metres or more in diameter; it is covered 
 with powdered charcoal, turf, and earth. It is then kindled 
 by introducing lighted fagots at openings left for the pur- 
 pose. Large quantities of moisture are driven off, and the 
 fire spreads gradually through the mass, the admission of air 
 being carefully regulated, so to cause one part of the wood in 
 burning completely to char and drive off the volatile matters 
 
CJiarcoal Carbon Fuel. 89 
 
 from the rest. When gas and vapours cease to come off, the 
 fire is ^extinguished by closing all the openings for the 
 admission of air, and adding a thicker layer of mould and 
 turf. Such a heap takes nearly a month to burn out, and 
 never furnishes more charcoal than a quarter of the weight 
 of the wood used. 
 
 The gas and the liquids which are obtained from the coal 
 and the wood during this process of destructive distilla- 
 tion do not exist ready formed in these substances. They 
 are the result of chemical changes produced under the 
 influence of the heat ; the carbon and hydrogen combine 
 together in new proportions, and thus furnish substances 
 quite different in properties from the original coal and 
 wood. 
 
 Nearly all vegetable and animal matters, when heated out 
 of contact with air, furnish charcoal more or less pure. 
 
 Exp. 72. Put a few pieces of wood into a clay crucible ; 
 cover the wood completely with sand, and heat the whole for 
 20 minutes in a fire. Gas will be given off, and burn. Take 
 the crucible out of the fire, let the whole cool, then empty the 
 crucible : the wood will be found to be converted into charcoal. 
 
 Charcoal gives out more heat in burning than an equal 
 bulk of wood, as the moisture and volatile matters given off 
 by the wood carry away much of the heat in the latent state. 
 But in the economy of fuel it is not sufficient to consider 
 simply the absolute amount of heat which a given weight of 
 it emits in burning. A fuel which burns with flame is 
 necessary where it is desired to communicate an elevated 
 and uniform temperature to objects at a distance from the 
 fire-grate, as in heating glass pots or the contents of a porce- 
 lain kiln ; whilst in heating boilers and objects where direct 
 radiation from the fuel can act fully, coke, charcoal, or 
 anthracite is very valuable; and in an ordinary open fire these 
 same fuels radiate much more heat into the room, though 
 they do not look so cheerful, as the bituminous coal, with its 
 fitful, flickering flame. 
 
QO Lamp-black Bone Charcoal. 
 
 There are other forms of carbon besides coke and char- 
 coal which are manufactured for use in the arts. One of 
 these is lamp-black, the basis of printers' ink, and the most 
 permanent of black pigments. It is obtained by heating in 
 an iron pot vegetable matters, such as rosin and pitch, which 
 are rich in hydrogen and carbon. The vapours are burned 
 in a current of air insufficient for complete combustion ; the 
 hydrogen, which is the more inflammable element, burns 
 first, leaving the carbon in a finely divided state. 
 
 Exp. 73. Set fire to a little rosin in a small iron spoon ; 
 hold a cold white plate in the flame. Abundance of soot will 
 be deposited upon it. The flame of a candle or of an oil lamp 
 will give a similar result. 
 
 Animal charcoal, or ivory black, is prepared by heating 
 bones in iron retorts. It is used largely by the sugar refiners 
 for removing colour from syrups. 
 
 Exp. 74. Place a few pieces of mutton shank or other bone 
 in a clay crucible ; cover them completely with sand, and heat 
 the crucible for half an hour in a common fire. Take it out, and 
 when cold crush the burnt bones to a coarse powder. Dissolve 
 25 grams of coarse brown sugar into 5 or 6 times its weight 01 
 water ; divide the solution into two parts, and pour one half 
 upon about 20 grams of the crushed bone charcoal, and let it 
 stand for an hour; then filter the solution through blotting- 
 paper. In order to prepare this fil'.er, fold a square of paper, as 
 
 shown in Fig. 27, first into half, and then again into a quarter of 
 its first size ; cut off the edges in the direction of the dotted 
 line shown in the left-hand figure, open out the folded paper, 
 and drop it into a funnel a little larger than the paper cone. 
 
A ntiscptic powers of Charcoal. 9 r 
 
 The liquor which runs through will be found, when compared 
 with the original syrup, to have lost most of its brown colour, 
 which is caused by a substance that remains adherent to the 
 charcoal. Wash out the syrup ; then pour a little solution of 
 potash upon the charcoal in the filter. The brown colouring 
 matter will become again dissolved by the alkaline solution as it 
 runs through. 
 
 Port wine, porter, and many other coloured liquids may 
 be deprived of their colour in a similar manner. 
 
 Wood charcoal produces decolourising effects similar to 
 those obtained with animal charcoal, though it is less power- 
 ful. Charcoal, like most porous bodies, condenses many 
 gases and vapours in its pores. 
 
 Exp. 75. Weigh a piece of freshly burned charcoal as soon 
 as it is cold ; leave it exposed to the air for 24 hours, and weigh 
 it again : it will be found to be heavier. Place the charcoal in a 
 glass tube, and heat it over a lamp : a good deal of moisture 
 will be driven off, and will become condensed on the cold sides 
 of the tube. This moisture was absorbed from the air by the 
 charcoal. 
 
 Exp. 76. Place a piece of raw meat in a glass jar, and cover 
 it with a layer of charcoal powder 25 mm. thick, and leave it for 
 several days. No offensive odour will be perceived, even in the 
 height of summer. 
 
 The meat may even become putrid, but the noxious and 
 offensive gases which would otherwise escape are absorbed 
 by the charcoal, and are slowly oxidized within in its pores 
 by the action of the oxygen, condensed by the charcoal from 
 the surrounding air. Shallow trays of wood charcoal are of 
 use in sick rooms, owing to their exerting this absorbent and 
 purifying action upon the atmosphere. They preserve their 
 power for an unlimited time, the carbon of the absorbed 
 organic matter being dissipated as carbonic anhydride, and 
 the hydrogen as water. 
 
 Owing to this absorbent action, charcoal forms a valuable 
 material in the construction of niters for water, as it acts 
 powerfully on many of the organic impurities. 
 
92 Allotropy. 
 
 Exp. 77. Shake up some stagnant water which has been 
 kept till it smells offensively with a little powdered charcoal 
 In an hour it will have lost all its disagreeable odour. 
 
 Carbon is indestructible by exposure, at ordinary tem- 
 peratures, to the air or to water. Hence it is a common 
 practice to char the surface of wooden piles before driving 
 them, and to prepare the interior of casks and water-butts in 
 a similar manner. 
 
 Charcoal and the common varieties of carbon, however, 
 combine rapidly with oxygen at high temperatures ; and their 
 attraction for oxygen is so great that carbon in some form 
 or other is employed to remove oxygen from its combinations 
 with other elements, particularly from the oxides of the 
 metals, which, when heated with carbon, are reduced or brought 
 back to the metallic state. Hence carbon is spoken of as 
 a reducing agent by the metallurgist. This action may be 
 shown as follows : 
 
 Exp, 78. Mix in a mortar 20 grams of litharge or lead oxide 
 (PbO) with 40 grams of common salt and I gram of powdered 
 charcoal ; cover it with a little more salt, and place the mixture 
 in a small clay crucible ; heat it to bright redness in the fire. 
 When the mixture is melted, take the crucible out of the fire and 
 let it cool. When quite cold, break the crucible, and a bead of lead 
 will be found at the bottom, under the melted salt, the carbon 
 having taken the oxygen from the oxide of lead. 
 
 Twelve grams of pure charcoal,* free from ash, when 
 burned in a current of oxygen, yield exactly 44 grams of 
 carbonic anhydride. Equal weights of diamond, plumbago, 
 and charcoal are thus shown, when heated with oxygen, to 
 yield equal weights of carbonic anhydride; and though so 
 different in appearance, they still consist of the same ele- 
 mentary body. Many of the elements have the power of 
 assuming forms which differ in appearance and properties 
 quite as much as these three different conditions of carbon. 
 Such elements are then said to assume different allotropic 
 
 * Common charcoal, however, always retains a little hydrogen. 
 
Carbonic Oxide. 93 
 
 states, which is as much as to say that in each different 
 modification, though all the atoms are alike, yet they are 
 arranged in a different way. The atoms of carbon, for in- 
 stance, which constitute diamond, are arranged very dif- 
 ferently from those which form graphite, and the atoms of 
 carbon in charcoal are differently arranged from those of 
 either diamond or graphite. 
 
 Carbon unites with sulphur if strongly heated with it, and 
 if heated intensely in hydrogen gas a small quantity of 
 acetylene (C 2 H 2 ) is formed ; but it has little tendency to 
 unite with the other non-metals. Some of the compounds 
 of carbon with the metals are important. They are termed 
 Carbides. 
 
 (19) CARBONIC OXIDE: Symb. CO; Atomic and Mol. Wt. 
 28; Sp. Gr. 0-967; Rel. Wt. 14. 
 
 Carbon forms only two compounds with oxygen, so far as 
 is known. One of these is carbonic anhydride ; the other, 
 also a gas, containing just half as much oxygen, is called car- 
 bonic oxide. 
 
 Exp. 79. Fill the iron tube (Fig. 13) with small lumps of 
 charcoal, instead of with iron turnings; make it red hot in the 
 furnace, and drive steam over the ignited charcoal. Collect the 
 gas which is formed : it will burn with a pale blue flame. Shake 
 up a little lime water with another of the jars of gas : it will be 
 rendered milky. 
 
 Three gases, viz. hydrogen, carbonic anhydride, and car- 
 bonic oxide, are formed in this case. These changes may 
 be thus explained : the carbon takes the oxygen from the 
 water, forming a mixture of carbonic oxide and carbonic 
 anhydride, whilst its hydrogen is set at liberty 
 
 H 2 O + C = CO + H 2 ; and 2 H 2 O + C = CO 2 + 2H 2 . 
 
 Exp. 80. Mix some chalk with its own weight of iron filings ; 
 place 40 or 50 grams of the mixture in an iron tube arranged 
 as in Exp. 71. Heat the closed end of the iron tube to redness 
 in the fire : a gas comes off, which may be collected over water. 
 
94 Experiments with Carbonic Oxide, 
 
 The heat expels carbonic anhydride from the chalk, and 
 the iron takes half the oxygen from the carbonic anhydride* 
 and forms carbonic oxide ; CaO, CO 2 + Fe becoming 
 CaO + FeO + CO. 
 
 Exp. 8 1. Plunge a taper into a jar of the gas ; the light will 
 be extinguished, but the gas will burn at the mouth of the jar 
 with a blue flame. 
 
 Carbonic oxide is often formed largely in stoves and 
 furnaces, owing to the manner in which heated carbon acts 
 on carbonic anhydride. When air enters at the bottom of 
 a clear fire, the oxygen burns a part of the carbon at once 
 into carbonic anhydride; and this gas, with the nitrogen of 
 the air, passes through the red-hot embers. The nitrogen 
 undergoes no change, but the carbonic anhydride takes up a 
 further quantity of carbon, and becomes converted into 
 carbonic oxide : C + CO 2 = 2 CO, the carbonic anhydride 
 being exactly doubled in bulk in consequence. This mode 
 of the formation of the gas is important, because, if the 
 supply of air to a furnace is too small, the carbonic oxide 
 passes up the chimney unburnt, and much heat is wasted, 
 which would be saved if the gas were properly consumed. 
 Sometimes we see the carbonic oxide burning on the 
 top of a clear glowing fire, where it again mixes with 
 fresh oxygen of the air while the gas is still hot enough to 
 burn. Furnaces are sometimes made to supply air just 
 above the top of the fire-grate, so as to burn the carbon 
 oxide completely. 
 
 Exp. 82. Make the iron tube and charcoal red hot, as in 
 Exp. 79 ; but instead of sending steam through it, attach to the 
 tube a bottle which is giving off carbonic anhydride steadily. 
 Collect the gas over water as it escapes at the other end : it will 
 burn with the blue flame which distinguishes carbonic oxide. 
 
 Exp. 83. Collect some carbonic oxide in a jar provided with 
 astop-cock at the top, or fitted up in the way directed in Exp. 48 
 (Fig. 16), with a flexible tube and screw-tap. Fasten a glass quill 
 tube to the vulcanised tube ; depress the jar in the pneumatic 
 trough, and allow a little of the gas to escape, by relaxing the 
 
Preparation of Carbonic Oxide. 95 
 
 screw ; set fire to the issuing gas, and hold over it a small gas 
 jar. No water will be condensed on its sides ; but if the jar be 
 closed with a glass plate, and limewater be poured into it, a 
 white precipitate of chalk will be produced. 
 
 The carbonic oxide in burning becomes converted into 
 carbonic anhydride ; 2 litres of carbonic oxide require i 
 litre of oxygen for its complete combustion, and 2 litres of 
 carbonic anhydride are produced : 
 
 2CO + O 2 = 2CO 2 
 
 There are several other ways of preparing carbonic oxide. 
 The best of these consists in drying the yellow salt known 
 as potassic ferrocyanide, K 4 FeC6N6, 3H 2 O (prussiate of 
 potash), till it crumbles down to a white powder. 
 
 Exp. 84. Mix 5 grams of this dry powder with 50 c. c. of oil 
 of vitriol in a Florence flask ; adjust a cork and a wide bent tube 
 to the mouth of the flask, and heat the mixture. When the heat 
 reaches a certain point, the gas will come off very quickly. 
 
 In this experiment the decomposition is complicated,* but 
 the result is, that the whole of the carbon of the salt comes 
 off as pure carbonic oxide, while the whole of its nitrogen 
 remains behind as an ammonium salt with the acid em- 
 ployed. 
 
 Another plan commonly practised for obtaining carbonic 
 oxide is to heat crystals of oxalic acid with about 10 times 
 their weight of oil of vitriol ; but in this case the carbonic 
 oxide is mixed with an equal volume of carbonic anhydride : 
 
 Oxalic Acid Water Carbonic Anhydride Carbonic Oxide 
 
 H 2 C a O 4 H 2 O = CO, + CO 
 
 In this process the oxalic acid is deprived of the elements 
 
 Potassic w . Sulphuric 
 
 Ferrocyanide Acid 
 
 K 4 FeC 6 N 6 + 6H a O -t- 6H 2 SO 4 
 
 Carbonic Potassic Ferrous Ammonic 
 
 Oxide Sulphate Sulphate Sulphate 
 
 6CO + 2K 3 S0 4 + FeS0 4 + 
 
96 Properties of Carbonic Oxide. 
 
 of water by the sulphuric acid, and the remaining carbon 
 and oxygen pass off in the form of equal measures of the 
 two gases. 
 
 The carbonic anhydride may be removed by causing the 
 mixture of gases to pass through a solution of caustic soda ; 
 and the apparatus may be arranged as shown in Fig. 28, in 
 which the gas generated in the flask A is transmitted through 
 
 the tube B, which passes loosely through the wider tube c 
 below the surface of a solution of soda contained in the 
 bottle D. From this bottle the gas passes off, by a tube the 
 end of which is above the solution, into the jar E standing 
 in the pneumatic trough. 
 
 Carbonic oxide is a gas without colour, but with a faint 
 oppressive odour. It is very poisonous when breathed, so 
 small a quantity as i measure of the gas in 100 of air 
 speedily producing a peculiar sensation of oppression and 
 tightness of the head. The fumes of burning charcoal owe 
 their most active poisonous property to the presence of car- 
 bonic oxide, which is always largely mixed with carbonic 
 anhydride in the products of a slowly-burning charcoal fire. 
 This gas has not been liquefied, either by cold or pressure. 
 It is but slightly soluble, 100 c. c. of water dissolving about 
 2 '4 c. c. of the gas. A solution of cupreous chloride (CuCl) 
 in hydrochloric acid dissolves carbonic oxide gas slowly if 
 
On Crystallisation. 97 
 
 agitated with it, but the gas is not soluble in a solution of 
 potash. 
 
 (20) Classification of Crystals, We have had occasion to 
 allude to the crystalline form of the diamond and some other 
 substances, and different varieties of crystals will continually 
 need notice. It will therefore be necessary to acquire some 
 general notions of what is meant when crystals are spoken 
 of, how their different varieties are designated, and what are 
 the principles on which their different forms are classified. 
 
 Exp. 85. Dissolve 250 grams of nitre in half a litre of 
 boiling water, and allow the solution to cool slowly in a basin. 
 Six-sided needles will gradually be formed in the liquid, owing 
 to the separation of part of the salt. 
 
 Exp. 86. Dissolve some common salt by grinding it with 
 about twice its weight of water in a mortar. Pour off the clear 
 liquid, and set it aside for several days in a soup plate or other 
 shallow vessel : the water will gradually evaporate, and little 
 cubes of salt will be formed. 
 
 Exp. 87. Prepare in like manner a solution of alum, and 
 leave it to evaporate slowly, when transparent octahedra will be 
 obtained. 
 
 In most cases, where solid bodies are allowed to separate 
 undisturbed from their solutions, they are found to assume 
 '.he form of some regular geometrical solid, bounded by flat 
 faces, called planes. Each substance has its own peculiar 
 form, and the regular geometrical solids thus obtained are 
 called crystals. By these differences in form many substances 
 may be at once distinguished from each other. The process 
 of crystallisation is commonly used as a means of freeing 
 salts from small quantities of foreign admixture ; as, for 
 instance, for separating nitre from small quantities of com- 
 mon salt. The impure nitre is dissolved in hot water, and 
 the nitre as it cools crystallises, whilst the liquid, or mother 
 liquor, retains in solution the small proportion of common salt. 
 
 The principle upon which the classification of crystals is 
 founded is the symmetry of their form. By symmetry is 
 meant a complex uniformity of figure ; in other words, a 
 
 H 
 
9 8 
 
 Axes of Crystals. 
 
 Fig. 29. 
 
 similar arrangement of two or more corresponding forms 
 round a common centre. This, indeed, is the general law of 
 creation. It is seen in the correspondence of external form 
 of the two sides of the body in animals ; of the two halves 
 of a leaf on either side of its midrib in plants ; in the two 
 halves of most seeds; and still more rigidly in the constitu- 
 tion of every crystal. The imaginary line round which the 
 parts of a crystal are symmetrically disposed is called the 
 axis of symmetry, or, simply, the axis of a crystal. 
 
 Select an octahedral crystal of alum, and place it with one 
 of its angles uppermost ; an imaginary line, a a, Fig. 290, pass- 
 ing through- the middle of the crystal to 
 the opposite angle is an axis of the crys- 
 taf. Each end of this axis is formed by 
 the meeting of four sides or planes of 
 the crystal. Every one of these sides is 
 similar to its fellows, and each is in- 
 clined to the axis at an equal angle. 
 Each of the four faces therefore is sym- 
 metrically disposed around the axis. 
 If any internal force act upon the particles during the 
 formation of the crystal, so as to produce a bevelling of one 
 of the edges of any one of these planes, the same cause 
 will act upon the other corresponding edges, and will pro- 
 duce a corresponding modification of a symmetrical character 
 upon each of the other corresponding edges. This regu- 
 larity is often interfered with mechanically, as when many 
 crystals are formed in the same mass, or by the accident of 
 its position during its formation. 
 
 In describing crystals, several of these imaginary lines are 
 supposed to exist, around which their faces are arranged. 
 Generally speaking, these axes may be reduced to three, all 
 of which intersect each other in the centre of the figure. 
 
 For the purpose of making the direction of these axes 
 more easily understood, let a piece of soap be cut in the 
 fo r m of a cube, or figure of 6 equal square sides, each of 
 
Cleavage of Crystals. 
 
 99 
 
 Fig. 29 a. 
 
 which is 6 or 8 centimetres long ; through the middle of one 
 
 of its sides thrust a piece of wire 18 centimetres long, so 
 
 that it shall pass out in the middle 
 
 of the opposite side," and project 
 
 equally on either side, as shown at 
 
 a a, Fig. 290; do the same through 
 
 two of the other sides, as at bb. 
 
 These two wires will represent the 
 
 direction 'of two out of the three axes 
 
 of the cube which cross each other 
 
 at right angles at its centre. Now 
 
 repeat the process on the remaining 
 
 two sides. The third axis of the cube will be represented by 
 
 this third wire, which will be at right angles to both the others. 
 
 Fig. 30. Fig. 31. Fig. 32. 
 
 Fig- 33- 
 
 Twist a piece of thread round the end of one of the wires, and 
 connect each point of the wires in succession with each of 
 the four points nearest to it, stretching the 
 thread across from one to the other. An 
 outline of the regular octahedron will thus 
 be formed. Take another cube of soap, 
 and pare off each of its 8 corners, as at 
 o 0, Fig. 30, by a plane inclined equally 
 to each of the three adjacent faces of the 
 cube. If these new faces be gradually 
 enlarged by continuing to pare away the corners, as shown in 
 Jfoerigs. 31 and 32, the cube will by degrees be converted 
 into the octahedron (Fig. 36), an 8/sided solid, in which the 
 three axes of the cube, a a, a a, a #; end in the six solid angles 
 of the octahedron. If in another cube of soap the 12 edges 
 
 H 2 
 
100 
 
 First and Second Systems. 
 
 of the cube be pared off so as to form 12 planes, b, b, Fig. 33, 
 sloped equally towards the adjacent faces, the cube will 
 gradually be converted into a regular 1 2-sided figure, the 
 rhombic dodecahedron (Fig. 34), which is also symmetrically 
 
 Fig. 34- 
 
 Fig. 35- 
 
 Fig. 36. 
 
 arranged around the three axes of the cube (Fig. 35). These 
 three forms, the cube, the octahedron, and the rhombic 
 dodecahedron, being formed around a similar set of axes, 
 are said to belong to the same system of crystals; and 
 this particular system is called the regular or cubic system. 
 All the different" known forms of crystals have been ar- 
 ranged in one or other of six such systems or classes, 
 
 i st. The regular or cubic, distinguished by possessing three 
 axes equal in length, crossing each other at right angles. 
 Common salt and fluor spar, which crystallise in cubes, alum 
 in octahedra, and garnet in the rhombic dodecahedron, are 
 examples of this class. 
 
 2nd. The square prismatic or pyramidal. In this system 
 
 Fig. 39- 
 
Third Syst&tn. 
 
 JOI 
 
 there are also three axes, which cross each other at right 
 angles ; two of these axes are equal, but the third or prin- 
 cipal axis is either longer or shorter than the others. The 
 forms of this system are either (i) the octahedron (Fig. 37), 
 
 Fig. 39 a. Fig. 40. Fig. 41. 
 
 such as potassic ferrocyanide, which sometimes loses the 
 pointed terminations and becomes shortened into the form 
 of a table, or flat, plate ; or (2) the square prism, sometimes 
 ending in the faces of the octahedron, as tin-stone (Fig. 40). 
 The base of the octahedron is shown in Fig. 38, with its two 
 equal axes, A A, A A, terminating in the angles ; but there are 
 octahedra in which the two axes terminate in the middle of 
 the sides, as shown in Figs. 39, 390, in which, in Fig. 39, the 
 principal axis, c c, is seen intersecting one*>f the others. 
 
 3rd. The rhombohedral or hexagonal system. There are 
 four axes in this system : three of these are in the same plane 
 or flat surface ; they are equal in length, and cross each other 
 at angles of 60, as shown in Fig. 41 ; while the fourth or 
 
 Fig. 42. 
 
 Fig. 43- 
 
 Fig. 44. 
 
 principal axis crosses the other three at right angles, and 
 may be either longer or shorter than they. The six-sided 
 prism, like beryl (Fig. 42), and the rhombohedron, such as 
 Iceland spar (Fig. 43), are the most important forms, some- 
 
. 1 02 . . ,,,... <Fourth-ttnd Fifth Systems. 
 
 times conjoined with the double six-sided pyramid which 
 usually terminates the crystals of quartz (Fig. 44). 
 4th. The prismatic system. In this there are three axes,. 
 A A, B B, c c, all unequal in length, but they all cross each 
 
 Fig, 45- 
 
 other at right 
 angles. Two of 
 them form a 
 rhombic base 
 for the prism or 
 octahedron, as 
 shown in Figs. 45, 46, 47, the 
 dimensions of the rhomboid 
 varying according to the length 
 of each pair of axes included 
 in the section. 
 
 Fig. 48 represents an octahedron of this system, to which 
 sulphur crystallised in the cold belongs. Fig. 49 represents a 
 tabular prism of this class. 
 
 5th. The oblique system. In this there are three axes, 
 which may all differ in length ; two of them cross each 
 other obliquely, as is shown in the principal section ot 
 the octahedron (Fig. 51), while the other crosses them 
 both perpendicularly, as shown in Fig. 52. 
 The octahedron itself is seen at Fig. 50. 
 The principal forms are the oblique rhombic 
 
 Fig. 48. 
 c 
 
 Fig. 50. 
 
 Fig- 
 
 prism, a modification of which is seen at Fig. 520. Sulphur 
 crystallised after fusion, sodic sulphate, and borax belong to 
 this system. 
 
Sixth System Isomorphism. 
 
 103 
 
 6th. The doubly oblique system. This is the most com- 
 plicated of the whole series. The three axes may all differ 
 in length, and they cross each other obliquely. Cupric 
 
 Fig. 5 2 a. 
 
 sulphate and bismuth nitrate offer good examples of 
 the doubly oblique prism, one modification of which is shown 
 in Fig. 53, while the octahedron is seen in Fig. 54. 
 
 Fig- S3- 
 
 Inorganic bodies which are destitute of crystalline form 
 are said to be amorphous. When, like carbon, they crystallise 
 in forms which belong to two distinct crystalline systems, 
 they are said to be dimorphous ; and when with a similar 
 chemical composition they crystallise in similar forms, as is 
 the case with the arseniates and phosphates of the same 
 metal, or the seleniates and sulphates of the same metal, 
 they are said to be isomorphous. 
 
 NOTE. A prism is a solid, the lateral edges of which are parallel, 
 and the terminal planes of which are also parallel. Prisms which stand 
 perpendicularly when resting on their bases are called right prisms ; those 
 which incline from the perpendicular are called oblique prisms. When 
 the base is a rhomb, or a rhomboid, it is called a rhombic prism ; and 
 a rhombohedron is a six-sided solid, all the sides of which are formed 
 by rhombs, a rhomb being a plane figure with four equal parallel sides, 
 ..hut the angles of which are not right angles, while a rhomboid is a 
 similar figure in which one pair of sides is longer than the other pair. 
 
104 
 
 CHAPTER V. 
 
 OXIDES OF NITROGEN NITRIC ACID AMMONIA. 
 
 (21) NITRIC ACID : Symb. HNO 3 ; Atomic Wt. 63; Sp. gr. 
 cf liquid, i'52; Boiling Pt. 84 '5 C. ; Freezing Pt. about 
 - 40 C. 
 
 The attraction of oxygen for nitrogen is but feeble ; these 
 gases do not easily combine together, and they remain mixed 
 together without change and under great variation of con- 
 ditions in atmospheric air. Nevertheless, true chemical com- 
 pounds may be formed between them, differing entirely in 
 properties from the bland mixture which we breathe at every 
 moment. As in many other cases where the attraction 
 between two elements is weak, nitrogen forms with oxygen 
 several compounds, not fewer than five being known ; they 
 contain i, 2, 3, 4, and 5 volumes of oxygen respectively, 
 uniting in each case with 2 volumes of nitrogen. 
 
 These compounds have been named 
 
 1. Nitrous Oxide . . . N a O 
 
 2. Nitric Oxide . . . N 2 O 2 or NO 
 
 3. Nitrous Anhydride . . N 2 O 3 
 
 4. Nitrogen Peroxide . . N 2 O 4 or NO 2 
 
 5. Nitric Anhydride . . N Z O 5 
 
 The third of these oxides, when dissolved in water, fur- 
 nishes nitrous acid-(HNO 2 ), for 
 
 H 2 + N 2 O 3 = 2HNO 2 ; 
 and the fifth yields nitric acid (HN0 3 ), since 
 
 H 2 O + N 2 O 5 = 2 HNO 3 . 
 
 Nitric acid is one of the most important acids known. It 
 was formerly called aqua-fortis (strong water), from its cor- 
 rosive action and power of dissolving the metals. 
 
 Traces of nitric acid are always formed when a discharge 
 of electricity passes through moist air, so that rain water 
 generally contains a trace of this acid, owing to the action 
 of lightning or atmospheric electricity. But in tropical 
 
Distillation of Nitric Acid. 
 
 105 
 
 climates, particularly in some districts of India, potassic 
 nitrate, and in Chili sodic nitrate, is found as an efflorescence 
 upon the surface of the soil. It is from one of these salts 
 that nitric acid is extracted for use in the arts. The opera- 
 tion may be conducted on a small scale as follows : 
 
 Exp. 88. In a retort, a, Fig. 55, which will hold 2 litres place 
 half a kilogram of sodic nitrate,* and pour over it an equal 
 weight of concentrated sulphuric acid. Adjust the retort to a 
 Liebig's condenser (Fig. n), or even to a long straight tube, as 
 shown at b, and cover the upper part of the retort with a tinplate 
 
 Fig- 55- 
 
 cap, c, for the purpose of keeping the body of the retort hot, 
 and distil the mixture carefully over an Argand gas-burner, 
 collecting the intensely corrosive acid liquid in a flask cooled by 
 immersion in a pan of water. This experiment is best made in an 
 outhouse where there is a free current of air. Red fumes come 
 off, and a straw-coloured liquid distils over, which is concentrated 
 nitric acid, or hydric nitrate, as it is now sometimes called. 
 
 In this distillation the kind of change called ' double 
 
 * In making the acid, smaller quantities may be used, and saltpetre 
 or nitre (the potassic nitrate, KNO 3 ) may be employed instead of sodic 
 nitrate. 
 
IO6 Decomposition of Sodic Nitrate. 
 
 decomposition ^>takes place; part -of the hydrogen of the 
 sulphuric 'acid changes place with a corresponding amount 
 of the sodium of the sodic nitrate, forming hydric sodic 
 sulphate, which, as it is not volatile, remains in the retort, 
 while the more volatile nitric acid distils over when heated. 
 The decomposition may be thus represented : 
 
 Sulphuric Acid Sodic Nitrate Hydric Sodic Sulphate Nitric Acid 
 
 H 2 S0 4 + NaN0 5 = NaHSO 4 + HNO 3 
 
 2 + 32 + 16x4 23 + 14+16x3 23 + 1+32 + 16x4 1 + 14+16x3 
 
 ~~98~ ~~85~~ 120 63 
 
 This plan of obtaining nitric acid from one of its metallic 
 salts affords a good instance of the method adopted generally 
 when volatile acids which can be distilled without suffering 
 decomposition are required. The weaker and more volatile 
 acid is in such cases displaced, like the nitric, by the stronger 
 and less volatile acid, such as the sulphuric; and in the 
 process the hydrogen of the stronger acid changes place 
 with the metal contained in the salt of the acid sought. 
 The ordinary acids, it must be remembered, are always salts 
 of hydrogen. 
 
 When nitric acid is distilled in glass vessels, the quantity 
 of sulphuric acid used -is double that required by the manu- 
 facturer, who employs a large iron cylinder, the upper part 
 of which is lined with fire-clay to protect it from the action 
 of the acid vapours ; but it requires a higher heat to drive 
 off the last portions of the. nitric acid. 
 
 In fact, sulphuric acid forms two different salts with 
 sodium, one of which is an acid sulphate, and the other a 
 7ieutral sulphate ; the neutral sulphate containing twice as 
 much sodium as the other. The acid sulphate, or hydric 
 sodic sulphate (NaHSO 4 ) is very soluble and readily fusible, 
 so that it can be extracted from the glass retort without risk : 
 while the neutral sulphate (Na 2 SO 4 ) is less soluble, and 
 cannot be melted in glass vessels. 
 
 When sodic nitrate and sulphuric acid are mixed in the 
 
Properties of Nitric Acid. 107 
 
 proportion of equal weights, the whole of the nitre is decom- 
 posed in one stage ; the acid salt only is obtained, and nitric 
 acid comes over at a low temperature; half the hydrogen 
 only of the sulphuric acid being displaced by sodium. The 
 change is represented by the equation already given 
 H 2 SO 4 + NaNO 3 = NaHSO 4 + HNO 3 . 
 
 But if the nitrate be mixed with half its weight only of sul- 
 phuric acid, the decomposition takes place in two stages, 
 instead of in one. In the first of these, half the nitre only is 
 decomposed, hydric sodic sulphate being produced at first, 
 as before, and a gentle heat is sufficient to distil over this 
 first half of the nitric acid 
 H 2 SO 4 + 2NaNO 3 = NaHSO 4 + HNO 3 + NaNO 3 . 
 
 As soon as the first half of the nitric acid has come over, the 
 heat must be increased ; the acid sulphate will then begin to 
 act upon th,e undecomposed nitre ; the second half of the 
 nitric acid is now formed, but is partly decomposed, par- 
 ticularly towards the end of the process. The whole of the 
 sodium remains in the retort in the form of disodic sulphate, 
 or the neutral sulphate. This second stage of the distillation 
 may be represented by the following equation 
 
 Sodic Nitrate Hydric Sodic Sulphate Nitric Acid Sodic Sulphate 
 
 NaNO 3 + NaHSO 4 = HNO 3 + Na 2 SO 4 . 
 
 The acid which is distilled in this way has a yellow colour, 
 owing to the presence of one of the lower oxides of nitrogen 
 in solution ; but the pure acid is quite colourless. Its exact 
 analysis cannot easily be made. It is very easily decom- 
 posed. The sun's light causes it to change, and give off 
 oxygen gas, while the acid becomes yellow or brown. It is 
 a fuming intensely corrosive liquid, which stains the skin of 
 a permanent yellow. It freezes at about 40 C, and 
 begins to boil at 85-5 C. 
 
 Nitric acid is a powerful oxidising agent. 
 
 Exp. 89. Place a little warm powdered charcoal in a small 
 saucer, and pour over it about a teaspoonful of the strongest 
 
io8 Action of Nitric Acid on Metals. 
 
 nitric acid from a test-tube fastened to the end of a stick : the 
 charcoal will burn with sparks. 
 
 Exp. 90. Fasten- a test-tube to the end of a stick, and mix in 
 the tube about 2 c. c. of nitric acid with an equal measure of 
 concentrated sulphuric acid. Place about 2 c. c. of oil of tur- 
 pentine in a small cup, under the chimney, and pour the acid 
 into the turpentine at arm's length : the mixture will burst into 
 a blaze. 
 
 Exp. 91. Mix the strong acid with about an equal bulk of 
 water ; pour 2 or 3 c. c. of the mixture upon a few copper turn- 
 ings : dense red fumes will be given off, and the copper will be 
 dissolved, forming a blue solution of cupric nitrate. 
 
 Iron filings, tinfoil, and many other metals, when in a 
 divided state, are acted upon by nitric acid with almost equal 
 violence ; indeed, this acid dissolves or attacks nearly all the 
 common metals, except gold and platinum. The mode of 
 its action varies according to the temperature and the 
 degree of its dilution with water. Usually it acts most 
 powerfully when of a sp. gr. between 1*25 and 1*35, or when 
 the strong acid is mixed with from two-thirds of its bulk to 
 an equal bulk of water. 
 
 When the common metals are presented to any of the 
 stronger acids, a brisk action frequently occurs, accompanied 
 with escape of gas. In explaining this result, it is often 
 stated that the metal first becomes oxidized and then com- 
 bines with the acid. For instance, when copper is put into 
 nitric acid, part of the acid is decomposed : it may be sup- 
 posed that the copper is first oxidized, while gaseous 
 fumes escape, and that the oxide then combines with a 
 portion of the unaltered acid, while water is separated, as 
 follows : 
 
 Copper Nitric Acid Cupric Oxide Nitric Oxide Water 
 
 (1) 3Cu + 2HNO 3 = 3CuO + 2NO + H 4 O 
 
 Cupric Oxide Nitric Acid Cupric Nitrate Water 
 
 (2) 3 CuO + 6HN0 3 = 3(Cu2N0 3 ) + 3H Z O 
 When the acid is one which, like the nitric, is easily 
 
Nitric Acid Nitrates. 109 
 
 decomposed, a part of the acid appears to lose oxygen in 
 this way. 
 
 But the action is different when the acid, like the sul- 
 phuric, is less easily decomposed ; the metal then is also 
 dissolved with effervescence, but in this case the escaping 
 gas consists of hydrogen, and no water is formed; for 
 example : 
 
 Exp. 92. Dissolve a pinch of iron filings in diluted sulphuric 
 acid in a test-tube fitted with a cork and bent tube. Collect 
 the gas : it will burn on the application of a flame. It is 
 hydrogen. 
 
 H 2 SO 4 -f- Fe = FeSO 4 + H 2 . 
 
 On the other hand, when an oxide of a metal is dissolved 
 in an acid, no gas is given off, but water is separated, and a 
 metallic salt is produced, as when zinc oxide is dissolved in 
 sulphuric acid : 
 
 Zinc Oxide Sulphuric Acid Zinc Sulphate Water 
 
 ZnO + H a SO 4 = ZnS0 4 + H a O 
 
 Nitric Anhydride (N 2 O 5 ). It is possible, by decomposing 
 silyer nitrate with chlorine, using special care, to obtain this 
 substance in white crystals, which, however, become decom- 
 posed spontaneously. When dissolved in water, it furnishes 
 nitric acid, N 2 O 5 + H 2 O becoming 2HNO 3 , one molecule of 
 the anhydride and one of water furnishing two molecules of 
 nitric acid. 
 
 When nitric acid is neutralised by bases, it forms the salts 
 called nitrates. They are all freely soluble in water ; when 
 heated, they melt and give off oxygen, accompanied in some 
 cases by red fumes ; and when thrown on red-hot coals, they 
 deflagrate (or burn with violence), owing to the rapidity with 
 which they give up oxygen to the burning embers, as may 
 be seen by throwing a small pinch of nitre into the fire. 
 
 Exp. 93. Dissolve I gram of nitre in 5 grams of water; soak 
 a little blotting-paper in the solution, and allow it to dry. When 
 this paper is burned, it will smoulder away : it forms what is 
 known as 'touch-paper/ 
 
no Nitrous Oxide. 
 
 Exp. 94. Take a small scrap of one of the nitrates ; dissolve 
 it in a test-tube, with a crystal of ferrous sulphate, in a cub. cm. 
 of distilled water. Hold the tube obliquely, and allow an equal 
 bulk of pure oil of vitriol to flow gently down into it. A cha- 
 racteristic brown colour will be formed at the line of contact 
 between the dense acid and the liquid above it. 
 
 In this experiment the sulphuric acid decomposes the 
 nitrate, nitric acid is set free, and this in its turn is decom- 
 posed by the iron salt, the- excess of which dissolves the 
 nitric oxide formed, and gives the characteristic brown 
 colour. This is one of the best tests for the nitrates. 
 
 Exp. 95. Add to a fragment of a nitrate in a test-tube a few 
 scraps of copper, and pour on it 3 or 4 drops of oil of vitriol. 
 Heat the mixture gently : red fumes will be given off, and may 
 be distinguished readily, even when very small in amount, by 
 looking through the tube obliquely over a sheet of white paper. 
 
 The sulphuric acid decomposes the nitrate, setting nitric 
 acid free ; and this in its turn is decomposed by the copper, 
 with formation of the red fumes of nitrogen peroxide. 
 
 (22) Other Oxides of Nitrogen, NITROUS OXIDE (or 
 Nitrogen Protoxide] : Symb. N 2 O ; Atom, and Mol. Wt. 44 ; 
 Mol. Vol. nn ; SP- &' r 5 2 7 j && Wt. 22. 
 
 If pure nitric acid be neutralised by ammonium car- 
 bonate, and the solution be evaporated to dryness, a solid 
 white salt is left, ammonium nitrate (H 4 N, NO 3 ). 
 
 Exp. 96. Heat a small quantity of this salt in a test-tube : it 
 will melt, and, if heated more strongly, will appear to boil, giving 
 off a considerable quantity of steam, and will at length be 
 wholly dissipated. If a cork and bent tube be adjusted to the 
 mouth of the test-tube, a gas may be collected over .water. 
 
 This gas is the compound of nitrogen with the smallest 
 proportion of oxygen. The ammonium nitrate is entirely 
 decomposed by heat into water and nitrous oxide gas, 
 H 4 N, NO 3 becoming 2H 2 O + N 2 O. The whole of the 
 nitrogen, both of the ammonium and the nitrion (NO 3 ), 
 pass off in the state of nitrous oxide, while the whole of 
 
Properties of Nitrous Oxide, I.LI 
 
 the hydrogen appears as water. This gas is colourless and 
 transparent, and has a faint sweetish smell and taste. It is 
 unfit for the support of life, but may be breathed for a time ; 
 and it exerts a remarkable action upon the brain and 
 nerves. If respired in a pure state, it produces transient 
 insensibility, and is in consequence sometimes administered 
 to deaden the pain in surgical operations. If it be mixed 
 with air, and breathed for a few minutes, it occasions a 
 peculiar kind of intoxication, often attended with uncon- 
 trollable laughter : this has given to the compound its popular 
 name of laughing gas \ the effect soon passes off. 
 
 Many bodies burn in nitrous oxide nearly as brightly as 
 in oxygen gas. 
 
 Exp. 97. Fill a small jar with the gas, and thrust into it a 
 splinter of wood of which the end is still glowing brightly : it 
 will burst into flame. 
 
 Exp. 98. Place some sulphuj in a deflagrating spoon ; kindle 
 the sulphur, and when burning briskly introduce it into the gas : 
 it will burn with a pale rose-coloured flame. 
 
 Exp. 99. Half fill a test-tube with gas, over water. Close 
 the tube under water firmly with the thumb, and then agitate 
 the water and gas together. On removing the thumb under 
 water, a considerable rush of water into the tube will occur, as 
 the gas is soluble in about its own volume of cold water. By 
 this circumstance the gas is easily distinguished from oxygen. 
 
 Nitrous oxide contains its own volume of nitrogen united 
 with half its volume of oxygen, the three measures which 
 the two gases occupied when separate becoming condensed 
 into two measures by combining 
 
 |N'N| + fol = ETol. 
 
 If the gas be mixed with its own bulk of hydrogen in a 
 eudiometer, and the electric spark be passed, an explosion 
 will occur, the bulk of the gas will be reduced to exactly one- 
 half, a few drops of water will be formed, and pure nitrogen 
 will be left equal in bulk to the nitrous oxide employed, 
 N 2 O + H 2 becoming N 2 + H 2 O. 
 
i 1 2 Properties of Nitric C Me. 
 
 NITRIC OXIDE : Symb. NO ; Atomic and Mot. Wt. 30 ; 
 Sp. Gr. 1-039; Rd. Wt. 15 ; Atomic and Mot. Vol. [^]. 
 
 Exp. 100. Dilute nitric acid with water until it becomes of 
 the sp. gr. i -2, and pour about 60 cub. centim. of it upon 15 grams 
 of copper clippings, contained in a retort : the retort becomes 
 quickly filled with red fumes, and a colourless gas may be col- 
 lected over water. 
 
 In this experiment 3 molecules of copper and 8 of nitric 
 acid being concerned, whilst as the result, 3 molecules of 
 cupric nitrate, 2 of nitric oxide, and 4 of water are formed, 
 as shown in the equation : 
 
 3 Cu + 8HNO 3 = 3(Cu 2 NO 3 ) + 2 NO + 4H 2 O. 
 
 Other metals, such as mercury, may be substituted for 
 copper in this reaction, and the gas will still be formed. 
 
 Nitric oxide has a strong disagreeable odour ; it cannot be 
 breathed, even in very small Quantity, without producing an 
 instant feeling of suffocation. It is very slightly soluble in 
 water ; but its most remarkable property is its strong ten- 
 dency to combine with oxygen. 
 
 Exp. 10 1. Allow a bubble or two of the colourless gas to 
 escape into the air : dense brownish-red fumes are immediately 
 formed. 
 
 These fumes are always produced when the gas is first 
 prepared in the flask, owing to its action on the oxygen of 
 the air contained in it ; they consist of a mixture of nitrous 
 anhydride and of nitrogen peroxide, and are freely soluble in 
 water, with which they form an acid liquid. This change of 
 colour, produced by mixing nitric oxide with any gas con- 
 taining free oxygen, often affords a convenient means of 
 detecting small quantities of oxygen when present in admix- 
 ture with other gases, such, for instance, as coal gas. 
 
 Exp. 102. Fill a small gas jar with water coloured blue by 
 means of tincture of litmus, and pass up into it sufficient nitric 
 oxide gas to fill about one-third of the jar : the litmus will not 
 change in colour. Now allow a few bubbles of oxygen to pass 
 up into the .nitric oxide : deep red fumes are formed, which are 
 
Properties of Nitric Oxide. 1 1 3 
 
 quickly dissolved, and the blue solution becomes red. If both 
 the oxygen and the nitric oxide be pure, it is possible, by cautiously 
 adding the oxygen, to cause a complete absorption of both gases. 
 
 Many combustible bodies, if strongly heated, burn well in 
 this gas ; but they are extinguished if not heated sufficiently 
 to begin the decomposition of the gas by separating the 
 oxygen from the nitrogen. 
 
 Exp. 103. Place a piece of dried phosphorus in a deflagrating 
 spoon ; kindle it with a hot wire, and instantly introduce the 
 phosphorus into a jar of nitric oxide : it will be extinguished. 
 Again draw it out into the air : it will burst into flame. When 
 burning briskly, again put it into the jar of gas : it will now burn 
 nearly as vividly as in pure oxygen. 
 
 Nitric oxide, in contact with strong nitric acid, is im- 
 mediately dissolved by it. The acid becomes first yellow, 
 and, if more gas be added, ultimately green. It is also quickly 
 dissolved by a solution of ferrous sulphate, forming an intense 
 olive-brown liquid. This fact is often taken advantage of in 
 testing for nitric acid or for nitrates (Exp. 94). 
 
 Nitric oxide contains equal bulks of its component gases : 
 
 1 litre of oxygen, when united with i litre of nitrogen, forms 
 
 2 litres of nitric oxide 
 
 the gases having united without undergoing any change in 
 bulk. 
 
 If potassium or tin be heated in the gas with proper care, ' 
 the metal is oxidized, and exactly half the quantity of the gas 
 employed is left. This residue is found to be pure nitrogen. 
 
 Nitric oxide has never been liquefied. 
 
 Nitrous Anhydride (N 2 O 3 ) is the third in the series of the 
 oxides of nitrogen. It may be formed by mixing 4 measures 
 of nitric oxide with i measure of oxygen, when deep red 
 fumes are produced. These furnish an acid liquid when 
 dissolved in water 
 
 N 2 O 3 + H 2 O = 2 HNO 2 . 
 
 This acid, the nitrous, furnishes, when neutralised by bases, 
 
 I 
 
1 1 4 Sources of A mmonia. 
 
 a series of salts, called nitrites ; but they are of little prac- 
 tical importance. 
 
 Nitrogen Peroxide (NO 2 or N 2 O 4 ) is the fourth term of 
 this remarkable series of oxides. It is most easily procured 
 by heating lead nitrate in a glass tube. Deep red fumes are 
 given off. These fumes may, at a low temperature, be con- 
 densed into a red liquid, and, if quite free from water, may 
 even be obtained in crystals. The lead nitrate yields oxygen 
 and lead oxide, as well as nitrogen peroxide, 2(Pb2N0 3 ) 
 becoming 2?bO -f- 2N 2 O 4 + O 2 . 
 
 (23) AMMONIA: Symb. H 3 N; Atomic Wt. 17; Atomic 
 andMol. Vol. |""7"| ; Sp. Gr. 0-59; Rel. Wt. 8-5. 
 
 Nitrogen and hydrogen cannot be made to unite directly 
 with one another, but they combine indirectly under various 
 circumstances. Only one compound between them can be 
 isolated, and this is the well-known volatile alkali ammonia, 
 or hartshorn. 
 
 Exp. 104. Heat a tuft of hair in a test-tube : it will become 
 brown, and will give off a few drops of an offensively smelling 
 liquid, which will immediately turn a piece of reddened litmus 
 paper blue, owing to the formation of ammonia. 
 
 Shreds of bone, of ivory, of isinglass, of horn, of parchment, 
 of feathers, or of silk, and most other animal bodies which 
 contain nitrogen, when thus decomposed by heat, give off a 
 mixture of various compounds of ill-odour, among which 
 ammonia, in greater or less quantity, is always present. 
 
 It was by the distillation of substances of this kind that 
 ammonia was formerly exclusively procured, but now it is 
 usually obtained from the waste liquors collected during the 
 distillation of coal in the manufacture of gas, since all coal 
 contains small quantities of compounds of nitrogen, which 
 furnish ammonia when distilled at a high temperature. 
 
 Whenever moist animal substances putrefy, ammonia is 
 amongst the products. It is abundant in stale urine, as well 
 as in guano, which is the decomposed e-crement of sea-fowl. 
 
Preparation of A mmonia. 1 1 5. 
 
 Exp. 105, Mix intimately 3 grams of fine iron filings in a 
 mortar with 0-2 gram of caustic potash ; introduce the mixture 
 into a test-tube, to the mouth of which a cork and a bent quill 
 tube are attached. Heat the mixture in a Bunsen gas flame : 
 gas will escape, and may be collected over water in a test-tube. 
 It burns with flame, and consists of hydrogen. 
 
 At a high temperature, the iron displaces hydrogen from 
 the caustic potash 
 
 5Fe + 2KHO = 5FeO + K 2 O + H 2 . 
 
 Exp. 106. Mix 3 grams of iron filings intimately with 0*2 
 gram of nitre. Heat the mixture and collect the gas as before : 
 it will not burn, does not render limewater milky, and is, in fact, 
 nitrogen. 
 
 The iron has combined with the oxygen of the nitre, potash 
 is formed, and nitrogen is liberated 
 
 5Fe + 2 KNO 3 = sFeO.+ K 2 O + N 2 . 
 
 Exp. 107. Mix 6 grams of iron filings with o'2 gram of caustic 
 potash and 0-2 gram of nitre, and heat the mixture in a tube. 
 
 The gas which now comes off has the pungent smell of 
 hartshorn ; it is strongly alkaline, and immediately restores 
 the blue colour of reddened litmus. In the reaction which" 
 takes place, the hydrogen and the nitrogen, at the moment 
 that each is set free, seize one upon the other, and ammonia 
 is formed 
 8Fe + 6KHO + 2KNO 3 = 8FeO + 4 K 2 O + 2H 3 N. 
 
 Traces of ammonia exist in the atmosphere, and are 
 brought down in rain and dews to the surface of the earth. 
 In the rusting of iron, and in almost every other process of 
 oxidation when moisture is present, small quantities of 
 ammonia are formed. 
 
 The common mode of preparing ammonia for experiment 
 consists in heating one of its commercial salts, such as" the 
 sulphate or the hydrochlorate, with a strong base, like lime. 
 The lime combines with the acid, and sets the ammonia at 
 liberty. 
 
 12 
 
Properties of A mmoniacal Gas. 
 
 Exp. 1 08. Powder finely 30 grams of sal ammoniac, and mix 
 it with 20 grams of finely powdered lime : the pungent fumes of 
 Fig. 56. ammonia immediately begin to escape. 
 
 Place the mixture in a flask provided 
 with a cork and a drying tube filled 
 with quicklime and attached to a bent 
 tube ^Fig. 56). Apply a gentle heat, 
 and ammoniacal gas will be liberated. 
 Ammoniacal gas is very soluble in 
 water, which at i5C. dissolves up- 
 wards of 700 times its bulk of the 
 gas ; so that it cannot be collected 
 over water without being absorbed. 
 It may, however, be collected over 
 mercury. 
 
 Exp. 109. Fill a strong test-tube 
 with mercury, close it with the thumb, 
 and invert it in a small basin of 
 mercury over the end of the gas-tube. 
 Bubbles of gas will rise in the tube, and will displace the 
 mercury. 
 
 Ammonia is much lighter than the air ; and this fact may 
 be taken advantage of so as to collect it in a flask or bottle, 
 by upward displacement, as shown in Fig. 56 
 2(H 3 N, HC1) + CaO = CaCl 2 + H 2 O + 2H 3 N. 
 It may easily be ascertained when the bottle is full of the 
 gas by the brown colour given . to a piece of dry turmeric 
 paper brought near to the mouth. 
 
 Ammonia is a gas which has no colour ; it has an intensely 
 pungent odour, and brings tears into the eyes. It has an 
 acrid taste. It is a strong stimulant to the nerves, and, in 
 the form of smelling-salts, is used to check feelings of faint- 
 ness. It is powerfully alkaline. 
 
 Exp. no. Place a little solution of litmus, feebly reddened 
 by the addition of a drop or two of any acid, in a basin ; carefully 
 raise the flask full of ammonia gas from the gas-delivering tube ; 
 close the flask with the thumb, plunge the mouth under the 
 
A bsorption of A mmonia. 117 
 
 solution of litmus, and withdraw the thumb : the liquid will rush 
 rapidly into the flask, the ammonia gas will be absorbed, and 
 the red liquid will become blue. 
 
 Ammonia neutralises the most powerful acids, and forms 
 with them an important series of salts, some of which will be 
 noticed when speaking of the salts of the metals of the 
 alkalies. Any volatile acid, when brought into an atmo- 
 sphere containing ammonia, produces a white cloud, by com- 
 bining with the ammonia and forming a white solid salt. 
 This property is often used to detect small quantities of 
 ammonia. 
 
 Exp. in. Mix common hydrochloric acid with half its bulk 
 of water ; dip a glass rod into the mixture, and hold it near the 
 mouth of the flask which is giving off ammonia. Dense white 
 fumes of sal ammoniac will appear around the rod. 
 
 Gaseous ammonia becomes liquid at a cold of 40 C.. 
 and by a pressure of about 7 atmospheres at 15. It may 
 even be frozen at 75 C. into a transparent solid. 
 
 Exp. 1 1 2. Slip a piece of freshly-burned charcoal under the 
 edge of a long tube previously filled with dry ammonia gas, and 
 standing over mercury. The charcoal will quickly absorb the 
 ammonia ; if pure, the whole of the gas will disappear, and the 
 mercury will fill the tube. 
 
 Charcoal has this power of absorbing all gases to a greater 
 or less extent ; but such gases as are freely soluble in water 
 are more easily absorbed by charcoal than those which are 
 sparingly soluble. One c. c. of boxwood charcoal will take up 
 fully 90 c. c. of ammonia; so that the gas is subjected to a 
 much greater degree of condensation by this absorptive 
 action than would be necessary to liquefy it by pressure. 
 
 A solution of ammonia is in constant use in the laboratory. 
 It may easily be prepared as follows : 
 
 Exp. 113. Mix from 30 to 50 grams of powdered sal ammo- 
 niac with an equal weight of slaked lime, and place the mixture 
 in a flask ; then add 30 or 40 c. c. of water, and let the flask be 
 fitted with a good cork and bent tube, as shown in Fig. 57. 
 Next, by means of a piece of vulcanised tubing, connect the bent 
 
1 1 & Solution of A mmonia. 
 
 tube of the flask with a three-necked bottle containing water, or 
 with a wide-mouthed bottle fitted with a cork and three tubes, 
 two of which are bent at right angles. Neither of these bent 
 tubes must dip into the water. The second bent tube may pass 
 
 Fig. 57- 
 
 into another three-necked bottle containing water, the first bent 
 tube of which passes below it, and the second bent tube into a 
 bottle also containing water, for the purpose of condensing any 
 of the gas which may escape from the first two vessels. 
 
 A bottle of this kind is known as a Woulfes bottle-, and 
 the middle tube, open at both ends and dipping into the 
 liquid, is intended to admit air, if the gas is absorbed by the 
 water faster than it is supplied ; at the same time, none of the 
 gas can escape through it into the atmosphere. By this 
 contrivance air can enter the partial vacuum, and the water 
 in the outermost bottle is prevented from being driven back 
 by atmospheric pressure. 
 
 The solution of ammonia is lighter than water, the specific 
 gravity of the solution diminishing as the quantity of gas 
 contained in it increases. The water also increases in bulk 
 as it dissolves the ammonia ; and when saturated at 1 5, it 
 contains more than a third of its weight of the alkali. It has 
 the intensely pungent odour of ammonia, and, when gently 
 heated, gives off the gas in large quantity. 
 
Analysis of Ammonia Gas. 
 
 Exp. 114. Boil a little of a strong solution of ammonia in a 
 flask provided with a cork and tube, bent as shown in Fig. 58 : 
 the gas will come off freely. p- - g 
 
 Apply a light to the issuing 
 gas : it will not burn readily, 
 but a pale greenish flame 
 will play over the top of the 
 light. Place the tube from 
 which the gas is escaping in 
 a bottle of oxygen, and then 
 apply a light : it will now 
 burn with a green flame. 
 
 Ammonia consists of one 
 measure of nitrogen and three measures of hydrogen, which 
 become condensed into the space of two measures by the 
 act of combining 
 
 Ammonia may be separated into its two constituent gases 
 by passing a series of electric sparks through a quantity of 
 gaseous ammonia confined in a tube over mercury. By 
 degrees the volume of the gas becomes doubled ; and on 
 then causing a little water to pass up into the tube by means 
 of a bent pipette (Fig. 8), the gas^will be found to be no 
 longer soluble in water ; and on applying a lighted match, 
 the hydrogen in the mixture will take fire. The quantity of 
 hydrogen may be ascertained by introducing (say) 8 measures 
 of the gas obtained by the action of the electric sparks upon 
 ammonia into a eudiometer, and then adding 3 measures 
 of oxygen. On firing the mixture by the electric spark, the 
 1 1 measures of gas will become reduced to 2 ; 9 measures 
 of a mixture of oxygen and hydrogen in the proportions to 
 form water will have disappeared in other words, 6 mea- 
 sures of hydrogen will have combined with 3 of oxygen, and 
 become condensed as water. Consequently, 8 measures of 
 the mixed gas from the ammonia must have consisted of 6 
 measures of hydrogen and the 2 of nitrogen which are left. 
 
I2O 
 
 CHAPTER VI. 
 
 SEA SALT HYDROCHLORIC ACID. 
 
 i. CHLORINE. 2. BROMINE. 3. IODINE. 4. FLUORINE. 
 
 (24) The four elementary bodies, chlorine, bromine, iodine, 
 and fluorine, constitute a remarkable group of closely related 
 substances. Characterised by high chemical activity, and 
 by the power of forming with the metals compounds ana- 
 logous to sea salt, they have hence been called halogens, or 
 salt producers, from aXc, sea salt. 
 
 i. CHLORINE: Symb. Cl; Atomic Wf. 35*5; Mol. Wt. 71; 
 Atomic Vol. Q; Sp. Gr. 2-435; *M- Wt. 35-5; Mol. 
 Vol. FT! (C1 2 ). 
 
 Common table salt, or sodic chloride (NaCl), is the most 
 abundant compound of chlorine. It is from this substance 
 almost exclusively that chlorine is obtained ; it is never 
 found uncombined in nature. 
 
 Exp. 115. Mix 32 grams of finely powdered manganese di- 
 oxide with an equal weight of common salt. Introduce them 
 into a flask provided with a cork and bent tube, and pour upon 
 the mixture 84 c. r. of oil of vitriol previously diluted with 
 60 c. c. of water and allowed to cool. On heating the mixture 
 gently, chlorine comes off as a dense greenish-yellow suffocating 
 gas, and may be collected in dry bottles by downward displace- 
 ment.* 
 
 The chemical reactions may be thus shown : 
 
 Manganese Sodic Sulphuric Manganese Hydric Sodic Tir 
 
 Dfoxide Chloride Acid Sulphate Sulphate Water Chlorine 
 
 MnO a + 2NaCl + 3H 8 SO 4 = MnSO 4 + NaHSO 4 + 2 H,O + Cl a 
 
 Owing to the yellow colour of the gas, it can easily be seen 
 when the bottle is full. Each bottle, as it becomes filled 
 
 * The experiment should be made either in an outhouse or under a 
 chimney where there is a strong draught to carry off the irritating 
 
 vapours. 
 
Solution of Chlorine. 1 2 1 
 
 with the gas, should be closed with a ground stopper, the 
 side of which should be greased. If the gas is collected 
 over water, much is wasted, owing to its solubility in this 
 liquid. Chlorine cannot be collected over mercury, as 
 it immediately begins to combine chemically with the metal. 
 Another process for obtaining chlorine is this : 
 Exp. 1 1 6. Place in a flask 50 grams of powdered manganese 
 dioxide, and pour upon it 250 c. c. of common hydrochloric 
 acid previously diluted with one-third of its bulk of water : 
 chlorine comes off freely, on heating the mixture. 
 
 In this case the hydrogen of the acid is wholly converted 
 into water by the oxygen of the manganese oxide ; half the 
 chlorine unites with the manganese, while the other half 
 comes off as gas 
 
 Mn0 2 + 4 HC1 = MnCl 2 + 2H 2 O + C1 2 . 
 
 Cold water dissolves about twice its bulk of chlorine. 
 
 Exp. 1 1 7. Remove the stopper from a bottle of chlorine gas, 
 close the mouth with a glass plate, plunge the mouth of the 
 bottle into water, and remove the plate : a little water will 
 enter. Close the bottle with the plate, and shake the gas and 
 the water together. Again open it under water : more water will 
 enter ; and by repeating the agitation and other operations again 
 two or three times, a solution of the gas in water will be obtained. 
 
 The solution of chlorine must be kept in the dark. If 
 exposed to a strong light, water is decomposed and oxygen 
 is set free. The hydrogen of the decomposed water combines 
 with chlorine to form hydrochloric acid, which dissolves in 
 the liquid, and this will redden litmus, and not bleach it. 
 The reaction may be thus represented : 
 
 2 C1 + 2 H 2 O = 4HC1 + O 2 . 
 
 Exp. 1 1 8. Fill a litre bottle with a strong solution of chlo- 
 rine. Fit a sound cork to the neck ; pass through the cork a quill 
 tube open at both ends, and bent twice at right angles, so that 
 the tube shall reach nearly to the bottom of the bottle. Place 
 it in direct sunshine : gas will rise into the upper part of the 
 bottle, and will displace the solution, which must be allowed 
 
122 Properties of Chlorine. 
 
 to flow over into, a vessel placed for its reception. If the cork 
 be withdrawn when sufficient gas has been formed, and a lighted 
 match be introduced, it will burn briskly in the liberated oxygen. 
 
 This power of decomposing water and of setting oxygen 
 free often renders chlorine an indirect but powerful means of 
 forwarding oxidation. 
 
 The solution of chlorine has the smell and taste of the 
 gas. When cooled down to near the freezing point of water, 
 crystals of chlorine hydrate are formed. If these crystals are 
 put into a strong tube, so as nearly to fill- it, and the tube 
 be carefully sealed, the crystals will melt when the tempera- 
 ture rises, and yellow oily-looking drops of liquid chlorine 
 will separate, and subside through the water. They exert 
 at 15 C. a pressure equal to about 4 atmospheres. 
 
 Chlorine is not inflammable. 
 
 Exp. 119. Plunge a lighted taper into the gas : it burns 
 feebly, with a red smoky flame. 
 
 Chlorine combines at once with many elementary sub- 
 stances with great energy. 
 
 Exp. 1 20. Place a piece of dry phosphorus in a copper de- 
 flagrating spoon ; introduce it into a bottle of chlorine gas : the 
 phosphorus takes fire, and burns with a pale greenish flame, while 
 suffocating fumes of phosphoric chloride (PC1 5 ) are formed. 
 
 Exp. 121. Dip a strip of blotting-paper into oil of tur- 
 pentine ; plunge it into a jar of chlorine gas : it immediately 
 bursts into flame, whilst a dense black smoke is given off. 
 
 In this case the chlorine unites with the hydrogen of the 
 oil of turpentine, and the carbon is separated. 
 
 Exp. 122. Powder some metallic antimony finely in a 
 mortar, and sprinkle a little of it into a jar of chlorine : it takes 
 fire as it falls, giving out fumes of antimonic chloride (SbCl 5 ), 
 which are very irritating. 
 
 Copper leaf, powdered bismuth, and many other metals, 
 when in a sufficiently finely divided state, take fire when 
 introduced into chlorine, forming chlorides by their union 
 with the gas. In all cases where chlorine combines with 
 
Hydrogen and Chlorine. 123 
 
 another elementary body, the new compound is termed a 
 chloride. . 
 
 This energetic action of chlorine renders it of great value 
 as a disinfectant, for it immediately decomposes all animal 
 effluvia with which it comes into contact, and converts them 
 into new and harmless substances. 
 
 Another very important property of chlorine is its bleach- 
 ing power. Many vegetable and animal colours are attacked, 
 when moist, by chlorine, which removes a portion of their 
 hydrogen, while a corresponding quantity of chlorine takes 
 its place, often forming a substance which has little or no 
 colour. In other cases the chlorine acts by removing hydro- 
 gen from water, setting oxygen free, and this, at the moment 
 of its liberation, decomposes the colouring material. 
 
 Exp. 123. Pour a little boiling water upon some chips of 
 logwood, so as to obtain a deep red liquid : add a little of the 
 solution of chlorine, and the red colour will be discharged. 
 
 Common writing-ink, infusions of cochineal, of brazil- 
 wood, of litmus, and of many other colouring matters, will 
 also be bleached by it with facility. Chlorine is very ex- 
 tensively used for bleaching purposes in the manufacture of 
 cotton goods and of paper, as well as in calico printing and 
 in dyeing. 
 
 (25) HYDROCHLORIC ACID : Symb. HC1; Atomic Wt. 36-5; 
 Atomic and MoL Vol. ^^]; S#. Gr. 1*2474; Relative 
 Wt. 18-25. 
 
 Hydrogen and chlorine have a very powerful attraction 
 for each other. If equal measures of the two gases be mixed 
 together, and exposed to direct sunlight, or other strong 
 light, such as that of burning magnesium, they combine 
 instantly, with a powerful explosion ; in diffused daylight they 
 gradually unite, but the mixture may be preserved unaltered 
 if kept in the dark. 
 
 Exp. 124. Wrap up a soda-water bottle in a towel; fill it 
 with water, and invert it in the pneumatic trough. Introduce a 
 
Hydrochloric Acid Gas. 
 
 glass funnel into the neck, and, having filled a jar of 100 c. c. 
 capacity with chlorine, decant the gas into the bottle. Fill the 
 same jar with hydrogen, and decant that into the same bottle ; 
 withdraw the funnel, close the neck with the palm of the hand, 
 Jift the bottle out of the water-bath, give it a shake to mix the 
 gases, and apply a lighted match. A sharp explosion imme- 
 diately follows, and gaseous hydrochloric acid is formed. 
 
 Equal measures of hydrogen and chlorine unite in this 
 way, and the gas produced occupies the same bulk that its 
 components did when separate 
 
 [H] + |a] = |H!CI| ; 
 
 but owing to the action of chlorine on mercury, and its 
 solubility in water, it is not easy to make this experiment 
 with accuracy. 
 
 Hydrochloric acid gas is transparent and colourless; it 
 has a pungent irritating smell, and an intensely acid taste ; 
 it also makes the eyes smart. This acid is not inflammable, 
 and it will not allow a candle to burn in it. It is also 
 injurious to vegetation. It is heavier than air, and is very 
 soluble in water, producing a powerfully acid solution. By 
 a very strong pressure, the gas may be reduced to a liquid, 
 which has never been frozen. 
 
 Exp. 125. Melt 200 or 300 grams of common salt in a clay 
 crucible at a good red heat, and pour out the salt when melted 
 upon a dry stone slab, or into a clean iron shovel. When cold, 
 break up the mass into pieces of the size of a pea, and preserve 
 them in a dry bottle. Introduce 50 grams of the chloride * into a 
 flask provided with a cork and bent tube, having poured over it 
 about twice its weight of oil of vitriol. Hydrochloric acid gas 
 comes off, even in the cold, but it is" extracted still more 
 abundantly when heated. Collect the gas in dry bottles by 
 downward displacement. It may easily be ascertained when 
 the bottle is full, as a lighted taper will be extinguished if in- 
 troduced only into its neck. 
 
 * Other chlorides such as chloride of potassium, ammonium, or 
 calcium might be used ; but common salt, as the cheapest, is always 
 preferred for preparing hydrochloric acid. 
 
A ndlysis of Hydrochloric A cid< '25? 
 
 This gas emits copious whitish fumes as it escapes into 
 the air, owing to its combining with the moisture of the 
 atmosphere, and condensing it into the form of liquid 
 globules, which again slowly evaporate. The reaction which 
 accompanies its formation may be thus represented : 
 NaCl + H 2 SO 4 = HC1 + NaHS0 4 . 
 
 Exp. 126. Fill a flask with the gas by displacement, close 
 the neck with the thumb, and immerse it in a basin containing 
 infusion of litmus ; on removing the thumb, the blue liquid will 
 rush into the flask, and will become red. 
 
 The presence of hydrogen and chlorine in the acid gas, 
 may be proved analytically as follows : 
 
 Exp. 127. Heat two or three globules of sodium of the size 
 of a pea in a copper spoon in the flame of a spirit lamp till they 
 begin to burn ; then 
 plunge them into ajar 
 of hydrochloric acid 
 gas. The sodium will 
 take fire and burn. 
 
 In this experiment 
 the hydrochloric acid 
 is decomposed, the 
 sodium uniting with 
 the chlorine to form 
 common salt, while 
 the hydrogen is set 
 free. 
 
 Hydrochloric acid 
 contains half its bulk 
 of hydrogen, as may 
 be shown by an 
 exact analysis of the 
 gas by means of a so- 
 lution of sodium in mercury, which may be effected in the 
 following manner: Fill a bent tube (Fig. 59) with mer- 
 cury, slip a piece of flexible tube over the end of a quill tube 
 
126 Solution of Hydrochloric Acid. 
 
 connected with a glass flask from which hydrochloric acid gas 
 is being disengaged, and, having passed the flexible tube 
 rpund the bend into the closed limb of the U tube, allow 
 hydrochloric acid to pass until the closed limb is two-thirds 
 full. The displaced mercury must be allowed to escape at the 
 quill tube, on which the screw-tap is relaxed ; then withdraw 
 the flask and tube, and close the screw-tap on the U tube. 
 Pour in mercury until it stands at the same level in both 
 limbs. Now slip a small elastic ring over the sealed tube, 
 so as to mark the height at which the mercury stands ; fill 
 up the open limb with an amalgam of sodium, prepared by 
 dissolving 6 or 8 pieces of sodium the size of a pea in 30 c. c. 
 of mercury. Close the tube with a good cork. Transfer the 
 gas into the limb containing the amalgam, and agitate it 
 briskly: sodic chloride will be formed. Retransfer the gas 
 to the closed limb, allow mercury to run off till it stands at 
 the same level in both limbs : it will be found that the. gas 
 has been reduced to half its original bulk, and that which is 
 left is hydrogen, for it will burn on the approach of a light. 
 
 Exp. 128. Fill a dry bottle with hydrochloric acid gas, and 
 close the mouth with a glass plate. Withdraw the stopper from 
 a bottle of ammoniacal gas of the same size ; invert the jar of 
 hydrochloric acid over the one containing the ammonia, and 
 remove the glass plate. The two invisible gases will suddenly 
 combine, a dense white cloud will be formed, and a solid salt 
 (sal ammoniac, or ammonium chloride) will be produced. 
 
 Equal bulks of the two gases unite and condense each 
 other, HC1 + H 3 N becoming H 4 NC1. The group H 4 N has 
 never been obtained in a separate form ; but many chemists 
 regard it as a compound metal, called ammonium, which com- 
 bines with chlorine, and completely neutralises its activity, 
 just as sodium does in common salt, NaCl resembling 
 (H 4 N)C1 in many important points. 
 
 A solution of hydrochloric acid in water forms an im- 
 portant and powerful chemical agent. It is frequently 
 spoken of as muriatic acid, from the word muria, brine. The 
 
Hydrochloric A cid. 1 2 7 
 
 common commercial acid has often a yellow colour, owing 
 to the presence of a little iron. It is a fuming liquid, of 
 sp. gr. about 1*17, and contains about a third of its weight 
 of the gas. A solution of hydrochloric acid may readily be 
 prepared by connecting a flask charged with a mixture of 
 fused salt and oil of vitriol with an apparatus similar to that 
 employed for obtaining a solution of ammonia (Fig. 5 7). This 
 acid dissolves those metals which decompose steam when 
 passed over them at a red heat, such as zinc, iron, nickel, and 
 tin, with escape of hydrogen, while chlorides of the metals are 
 
 formed : 
 
 Zn + 2 HC1 = ZnCl 2 + H 2 . 
 
 Exp. 129. Dilute a tittle hydrochloric acid with 6 or 8 times 
 its bulk of water, and add caustic soda cautiously, until the 
 liquid is exactly neutral, and neither reddens blue litmus 
 nor restores the blue to red litmus paper. Pour the liquid into 
 a basin, and evaporate it slowly : crystals of common salt will 
 be deposited in cubes. 
 
 In this case the whole of the hydrogen of the acid, in 
 combination with oxygen derived from the soda, will pass 
 off as water, the change being as follows 
 
 HC1 + NaHO =; NaCl 4- H 2 O. 
 
 Exp. 130. Pass a piece of quicklime into a tube filled with 
 hydrochloric acid gas standing over mercury : the gas will be 
 quickly absorbed. 
 
 The change is the following : 
 
 CaO + 2HCI = CaCl 2 + H 2 O, 
 
 calcic chloride and water being formed. 
 
 Most of the chlorides are soluble in water ; and when a 
 solution of a strong base, such as potash, is added to the 
 solution of a chloride of one of the metals which forms an 
 insoluble oxide, the oxide, and not the metal, is pre- 
 cipitated. 
 
 Exp. 131. Add a solution of caustic potash to a diluted solu- 
 tion of cupric chloride. 
 
128 Hydrochloric Acid. 
 
 In this case hydrated cupric oxide is thrown down, of a 
 pale blue colour 
 
 CuCl 2 + 2 KHO = 2KC1 + CuH 2 O 2 . 
 
 If a more complex oxide be acted on, a corresponding 
 chloride is formed, if the formation of such a compound be 
 possible. For instance, ferric oxide may be dissolved by 
 hydrochloric acid, and the change is thus shown 
 Fe 2 O 3 + 6HC1 = Fe 2 Cl 6 + 3H 2 O. 
 But if there be no chloride corresponding to the oxide, part 
 of the chlorine escapes, while a chloride of simpler com- 
 position is formed, as in the common process of obtaining 
 chlorine gas, by acting on manganese dioxide, to which there 
 is no corresponding chloride, MnO 2 -f 4-HC1 becoming 
 MnCl 2 + 2H 2 O -t- C1 2 . 
 
 Hydrochloric acid and the chlorides are easily distin- 
 guished when present in solution by the following tests : 
 
 Exp. 132. Dissolve 0*2 gram of sodic chloride in 100 c. c. 
 of water, and divide it into two portions, (i) To one of these add 
 a few drops of a solution of argentic nitrate : an abundant white 
 cloud of argentic chloride (AgCl) will be formed. Divide this 
 milky liquid into two portions. To one of them add a few drops 
 of nitric acid : no change will be perceptible. To the other add 
 a few drops of ammonia solution : the liquid will become clear, 
 since ammonia dissolves argentic chloride readily. (2) To another 
 portion of the sodic chloride solution add a few drops of a solu- 
 tion of mercurous nitrate : a white precipitate of calomel will 
 appear. Divide this turbid solution into two portions. Add a 
 few drops of nitric acid to one : no change will occur. To the 
 other add ammonia : the precipitate will become black. 
 
 Exp. 133. Boil hydrochloric acid in a test-tube with frag- 
 ments of gold leaf : they will not be dissolved. Now add a 
 drop or two of nitric acid : a yellow solution of auric chloride 
 (AuCl 3 ) will be quickly formed. 
 
 Scraps of platinum are not dissolved by hydrochloric 
 acid, but they enter slowly into solution if nitric acid be 
 added and the mixture be warmed. This mixture of hydro- 
 chloric with nitric acid is often called aqua regicz (royal water), 
 
Compounds of Chlorine and Oxygen. 1^5 
 
 from its power of dissolving gold, which was regarded by tht 
 alchemists as the king of metals. This mixture of acids is 
 often useful for dissolving ores which resist either acid singly. 
 It owes its activity to the chlorine which is set free. IP 
 using the liquid, it should be only gently warmed, because 
 if boiled the chlorine is quickly expelled to waste. Some 
 oxy chlorides of nitrogen are formed at the same time, and 
 pass off in red vapours ; but the chlorine is really the active 
 substance 
 
 2 HC1 + HNO 3 = H 2 O + HNO 2 + Cl a . 
 If the hydrochloric acid be used in excess, chlorides only 
 remain in the liquid, the whole of the nitric acid being de- 
 composed and going off with the gases. 
 
 (26) Oxides of Chlorine. Chlorine does not combine 
 directly with oxygen, but it forms with it three gaseous com- 
 pounds, all of which have a red or yellow colour, a peculiar 
 irritating odour, a corrosive action, and are all so unstable 
 that they are easily decomposed by heat, and explode with 
 violence. These gases are : 
 
 Hypochlorous anhydride . . . C1 2 O 
 Chlorous anhydride .... C1 2 O 3 
 
 Chloric oxide C1O 3 
 
 The first two, when acted on by water, furnish acids; and, 
 in addition, two other acids containing chlorine and oxygen 
 are known. These acids form a regular series, in which the 
 oxygen increases step by step as follows : 
 
 Hypochlorous acid .... HC1O 
 
 Chlorous acid HC1O 2 
 
 Chloric acid HC1O 3 "" 
 
 Perchloric acid HC1O 4 
 
 All these acids are very unstable, and they are seldom 
 prepared. Some of their salts, particularly the hypochlorites 
 and chlorates, are important. 
 
 Some of these salts are formed by acting upon a strong 
 base with chlorine ; but the result varies according to the 
 temperature employed. 
 
1 30 Chlorine A cids. 
 
 Exp. 134. Cause a current of chlorine gas to pass slowly into 
 a dilute solution of potash which is to be kept cool. 
 
 In this case a liquid is obtained which possesses bleaching 
 properties, and in which a mixture of two salts (potassic 
 chloride and potassic hypochlorite) is formed 
 
 C1 2 + 2KHO = KC1 + KC1O + H 2 O.* 
 
 Exp. 135. Repeat the experiment on a stronger solution of 
 potash (i of potash to 3 of water) which is to be heated. 
 
 In this case also the chlorine will be absorbed, but potassic 
 chlorate and potassic chloride will now be formed, and no 
 bleaching liquor will be obtained 
 
 3 C1 2 + 6KHO = 5KC1 + KC10 3 + 3 H 2 O. 
 
 The potassic chlorate is sparingly soluble ; and if the solu- 
 tion be evaporated to a small quantity, and then allowed to 
 cool, flat tables of the salt will crystallise out. If the solu- 
 tion be poured off from these crystals, and they be re- 
 dissolved in a small quantity of boiling water, the second 
 crop of crystals will be nearly pure. This is the salt usually 
 employed for obtaining oxygen by decomposing it at a high 
 temperature. 
 
 Exp. 136. Dissolve a few crystals of the pure chlorate in 
 water, and add a little solution of argentic nitrate. 
 
 In this case no precipitate is formed, because argentic 
 chlorate is soluble. 
 
 Exp. 137. Heat some of the crystals in a test-tube as long 
 as they give off oxygen. When cold, dissolve the white residue 
 in water. 
 
 The solution will now precipitate the argentic nitrate 
 abundantly ; the chlorate has been decomposed into oxygen 
 and potassic chloride, and this salt immediately forms ar- 
 gentic chloride wijh the nitrate 
 
 2 KC1O 3 = 2KC1 + sO 2 . 
 
 * Bleaching powder, or chloride of lime, is a similar compound. It 
 is manufactured on a large scale by passing chlorine gas through boxes 
 containing trays of slaked lime. 
 
Chlorides and Chlorates. 1 3 1 
 
 Chloric acid is very unstable, and is rarely prepared. No 
 attempt must be made to obtain it by distilling potassic 
 chlorate with sulphuric acid, in imitation of the process for 
 nitric acid. 
 
 Exp. 138. Put two drops of oil of vitriol in a test-tube ; throw 
 in a crystal of potassic chlorate of about the size of a split pea, 
 holding the mouth of the tube away from you, and warm the 
 mixture. A dense brownish-yellow gas, of peculiar irritating 
 odour, will come off, and at a heat below that of boiling water 
 a loud cracking sound or small explosion will occur. 
 
 The sulphuric acid in this case decomposes the chlorate, 
 and liberates chloric acid, which immediately breaks up into 
 chloric oxide and potassic pefchlorate, while the chloric oxide 
 when heated is in turn decomposed with explosion. The 
 following equation represents the change : 
 
 Potassic Sulphuric Chloric Potassic Hydric Potassic -, v 
 
 Chlorate Acid Oxide Perchlorate Sulphate 
 
 3KC1O 3 + 2H Z SO 4 = 2C1O, + KC1O 4 + 2KHSO 4 + H a O 
 
 Exp. 139. Put two or three crystals of potassic chlorate into 
 a wineglass, and pour some water upon them. Add a piece of 
 phosphorus of the size of a split pea. Place the glass upon a 
 soup plate, and with a long-necked funnel reaching to the bottom 
 of the glass pour in quietly about a teaspoonful of oil of vitriol. 
 As soon as the acid reaches the bottom a crackling noise is 
 heard, and flashes of a green light are produced, owing to the 
 burning of the phosphorus under water in the chloric oxide as 
 it is formed. 
 
 Exp. 140. Melt a little potassic chlorate in a test-tube, and 
 heat it moderately as long as it gives off gas freely. If the ex- 
 periment be carefully watched, the salt will be seen gradually to 
 become pasty ; when this occurs, remove the tube from the 
 lamp and set it to cool. Treat what is left first with cold water, 
 and then dissolve the sparingly soluble residue in boiling water ; 
 as it cools a new salt, the potassic perchlorate, will crystallise. 
 
 The chlorate in this operation loses one-third only of its 
 oxygen. When heated, it becomes separated into two new 
 salts, potassic chlorite and potassic perchlorate 
 2KC1O 3 = KC1O 2 + KC10 4 ; 
 
 K 2 
 
1 3 2 Sources of Bromine. 
 
 but the chlorite is decomposed, as fast as it is formed, into 
 oxygen gas and potassic chloride 
 
 KC1O 2 = KC1 + O 2 ; 
 
 and the chloride, which is very soluble, is easily separated 
 from the sparingly soluble potassic perchlorate. If the per- 
 ch lorate be heated still more strongly, it in turn is decom- 
 posed into oxygen gas and potassic chloride 
 
 KC10 4 = KC1 + 20 2 . 
 
 (27) 2. BROMINE: Symb. Br ; Atom. Wt. 80; Atom. 
 Vol. Q; Mol. Wt. (Br 2 ) 160; Mol. Vol. |"T"I J &* Wt. 
 80; Sp. gr. of vapour, 5-54 ; of liquid at o C. 3-187 ; Boils 
 at 63 C. ; Freezes at 12-5. 
 
 Bromine is the only element except mercury which is 
 liquid at ordinary temperatures. It is of a deep red colour, 
 and gives off abundant dark red vapours, which have a very 
 irritating effect upon the eyes and the back of the throat, 
 with a peculiar disagreeable odour, whence its name is 
 derived. It is about three times as heavy as water, and is 
 but sparingly soluble in it, but freely so in alcohol and 
 ether. Its chemical properties are similar to those of 
 chlorine, but less active. It forms a gaseous compound with 
 hydrogen, the hydrobromic acid (HBr = 81 ; Sp. Gr. 2731 ; 
 Rel. Wt. 42*5), which fumes in air and is extremely soluble 
 in water ; it is powerfully acid, and much resembles hydro- 
 chloric acid. It may be obtained by decomposing potassic 
 bromide with phosphoric acid. Bromine also forms acids 
 in which oxygen is present ; but only two of them the 
 bromic (HBrO 3 ), corresponding to the chloric, and per- 
 bromic (HBrO 4 ), corresponding to the perchloric have 
 been examined carefully. 
 
 Bromine is contained in sea water, as magnesic bromide 
 (MgBr 2 ), in quantity varying from 4 to 14 mgrams. per litre. 
 
 Sea water is concentrated in large quantities for the sake 
 of its common salt and potassic and magnesic salts ; and 
 when these have been separated by crystallisation, the mother 
 
Formation of Bromine. 133 
 
 liquor, or bittern, is treated for the bromine. Many strong 
 brine springs, such as those of Kreuznach and Kissingen, 
 also contain small quantities of the bromides. The bittern 
 is made to yield its bromine by transmitting into it a current 
 of chlorine gas, avoiding an excess of it. All the bromides 
 of the metals are decomposed by chlorine, which has a more 
 powerful attraction for the metals than bromine has. The 
 liquid acquires a beautiful golden yellow colour, due to the 
 liberated bromine, MgBr 2 + C1 2 becoming MgCl 2 + Br 2 . 
 This yellow liquid is then mixed with ether and shaken up 
 with it. The ether dissolves the bromine ; and if the mixture 
 be placed in a glass globe, provided with a stopper at top 
 and a glass stop-cock at bottom, the ether rises in a yellow 
 layer to the surface, and the mother liquor is easily drawn 
 off from below. The ethereal solution is then shaken up with 
 a solution of caustic potash, by which the yellow colour is 
 immediately destroyed : potassic bromide and bromate are 
 formed, and become dissolved in the water, while the ether 
 rises to the surface, and may again be used in a similar 
 manner with fresh portions of bittern. The action of potash 
 upon bromine resembles that which it exerts upon chlorine, 
 3Br 2 + 6KHO yielding KBrO 3 + sKBr + sH 2 O. When 
 the solution of potash has become neutralised by the action 
 of repeated charges of bromine, the liquid is evaporated to 
 dryness, mixed with a little charcoal, and gently heated, to 
 remove the oxygen from the bromate ; after which the 
 residue, consisting of bromide and the excess of charcoal, is 
 mixed with manganese dioxide and sulphuric acid in a retort. 
 On applying heat, red vapours of bromine pass over 
 
 The reaction resembles that by which chlorine is obtained. 
 
 Exp. 141. Dissolve 2 or 3 decigrams of potassic bromide 
 in 20 c. c. of water. Mix the solution in a long and wide test- 
 tube, with 5 c. c. of solution of chlorine, and add 5 c. c. of ether. 
 Agitate the mixture : a yellow solution of bromine in ether will 
 rise to the surface. Decant this ethereal solution into another 
 
1 34 Iodine. 
 
 tube, and shake it with an equal bulk of a solution of caustic 
 potash. The yellow colour will disappear, and the ether will 
 rise to the top, and form a colourless layer. 
 
 Bromine combines directly with phosphorus, and with 
 many of the metals. The compound formed by the union 
 of bromine with any other element is called a bromide. 
 Argentic bromide is a substance 'of importance to the 
 photographer. 
 
 Exp. 142. Add a little of a solution of argentic nitrate to a 
 weak solution of potassic bromide : a white precipitate is formed. 
 Divide the liquid with the precipitate into three portions. To one 
 of them add a little nitric acid, to another a few drops of a solution 
 of ammonia : no solution occurs in either case. To the third add 
 a little of a solution of sodic hyposulphite : the liquid becomes 
 clear, a double hyposulphite of silver and sodium being formed. 
 
 The bromides also form a white precipitate of mercurous 
 bromide (HgBr) with a solution of mercurous nitrate ; and a 
 white precipitate with lead nitrate, consisting of lead bromide 
 (PbBr 2 ). Chlorine water decomposes both, setting bromine 
 free, and forming a chloride of mercury or of lead. 
 
 (28) 3. IODINE': Symb. I; Atomic Wt. 127; Atomic vol. 
 cf vapour [] ; Mol. Vol. fT~] (I 2 ) ; Rel. Wt. 127; Sp. gr. 
 of vapour, 8716; of solid, 4*947; Melting Ft. 107 C. ; 
 Boiling Pt. 175 C. 
 
 Iodine is a solid, which crystallises in bluish-black scales, 
 resembling plumbago in lustre. It is volatile at ordinary 
 temperatures, and emits a feeble smell, resembling that of 
 chlorine, and sublimes* slowly in the bottles in which it is 
 kept, and is deposited in crystals on the sides. When heated 
 to a little beyond 100 C. it melts, and at a higher tem- 
 perature gives off dense vapours, of a rich violet hue, whence 
 it derives its name. 
 
 * A body which rises in vapour and condenses in the so^id form is 
 said to sublime, in opposition to one which condenses in the liquid 
 form, when it is said to distil. 
 
Tests for Iodine, 1 3 5 
 
 Exp. 143. Place about 0*2 gram of iodine in a flask ; warm it 
 over a lamp. The iodine will melt to a brown liquid ; and if the 
 flask be heated gradually and uniformly, beautiful violet vapours 
 will fill it. When allowed to cool, its interior will be coated 
 over with small crystals of sublimed iodine. 
 
 Iodine stains the skin and most organised substances 
 brown, and gradually corrodes them. Water dissolves it but 
 sparingly, alcohol and ether freely ; solutions of the iodides 
 in water also dissolve it. 
 
 Exp. 144. Take four test-tubes, and place about a decigram 
 of iodine in each. Pour into the first 2 c. c. of water, into 
 the second the same quantity of alcohol, into the third the same 
 quantity of ether, to the fourth add 0*2 gram of potassic iodide, 
 and then a little water. A pale-yellow liquid will be formed in 
 the first tube, and scarcely any iodine will be dissolved, whilst the 
 iodine will be dissolved in each of the other tubes, and wiil form 
 a deep-brown solution. Mix the solution in alcohol with twice 
 its bulk of water : most of the iodine will separate in scales, as 
 it is not soluble in water, and the water immediately separates 
 the alcohol from the iodine. Mix the solution in the fourth tube 
 with water : no precipitation will occur, because the potassic 
 iodide retains the iodide dissolved. 
 
 Exp. 145. Place about 0*3 gram of iodine in a test-tube 
 with a few drops of water, and add about o - i gram of iron 
 filings : a green solution of ferrous iodide will be formed. 
 
 Exp. 146. Let zinc filings be substituted for iron, and a 
 colourless solution of zinc iodide will be obtained. 
 
 When an element combines with iodine, the compound is 
 known as an iodide. 
 
 All the iodides of the metals are readily decomposed by 
 chlorine, and even by bromine, while the iodine is set free. 
 This is taken advantage of in testing for iodine. The most 
 delicate test for free iodine is the intense blue colour which 
 it yields with cold starch paste. 
 
 Exp. 147. Mix i gram of white starch with 10 grams of 
 water, and pour it slowly into 40 or 50 grams of boiling water ; 
 boil for a minute, and allow it to cool. Mix a little of this 
 mucilage with water, and add one or two drops of any of the 
 
1 36 Source of Iodine. 
 
 solutions of iodine prepared as above directed : the intense blue 
 iodide of starch is immediately formed. 
 
 Exp. 148. Mix one or two drops of a solution of potassic 
 iodide with a little of the diluted starch mucilage : no change 
 of colour will occur. Add a single drop of chlorine water to the 
 mixture : an immediate coloration will occur, owing to the com- 
 bination of the chlorine with the potassium, while iodine is set 
 free, and acts upon the starch. Add a little more chlorine 
 water : the colour disappears, owing to the formation of chlorine 
 iodide, which is without action on starch. 
 
 A solution of bleaching powder may be used instead of 
 chlorine water, or, still better, a solution of potassic 
 nitrite, to which a drop or two of acetic acid has been 
 added. An excess of nitrite does not interfere with the blue 
 colour. 
 
 Exp. 149. Heat the blue solution of starch iodide to boiling : 
 the colour fades, and often quite disappears. Cool the solution, 
 and the blue colour returns. 
 
 The cause of this change of colour is not known . 
 
 Other tests for the iodides, though of less delicacy, are the 
 following : A solution of lead salt, when mixed with a soluble 
 iodide, gives beautiful silky yellow scales of lead iodide 
 (PbI 2 ). A silver salt, such as argentic nitrate, gives a pale 
 buff-coloured argentic iodide (Agl), nearly insoluble in am- 
 monia. Mercuric chloride gives a yellow precipitate of 
 mercuric iodide (HgI 2 ), quickly passing into scarlet. 
 
 Exp. 1 50. Divide the last named solution with its precipitate 
 into two portions. To one portion add a little more of the mer- 
 curial solution : the precipitate will be redissolved. To the other 
 portion add an excess of potassic iodide : this also will re- 
 dissolve the precipitate. 
 
 Hence it will be seen that an excess of either salt must be 
 avoided when testing for iodides or for mercury. 
 
 Iodine is contained in minute proportion in sea water, 
 from which it is extracted by the sea-weeds during their 
 growth, and stored in their tissues. In order to obtain the 
 iodine, the weeds are first dried in the sun, and then burned, . 
 
Hydriodic A cid. 137 
 
 at a low temperature, in shallow pits on the shore ; the -ashes 
 forming what is called kelp. The iodine is present in this 
 ash as sodic iodide. The soluble matters are washed out of 
 the ash, and the liquor is evaporated, to allow most of the 
 salts of potassium and sodium to crystallise out. Sulphuric 
 acid is then added to the mother liquor ; and after the effer- 
 vescence due to the escape of carbonic anhydride and gaseous 
 compounds of sulphur is over, the acid liquor is run off into 
 stills, mixed with powdered manganese dioxide, and distilled 
 at a gentle heat 
 2NaI + MnO z + 3H 2 SO 4 = 2NaHSO 4 + MnSO 4 + 2H 2 O+ I z . 
 
 The decomposition which occurs resembles that which 
 attends the liberation of chlorine or of bromine, as already 
 described. Violet vapours of iodine come off, and are 
 condensed in a series of globular receivers. The crude 
 iodine thus obtained is purified by a second sublimation. 
 
 HYDRIODIC ACID : Symb. HI; Atom, and Mol. Wt. 128; 
 Mol. Vol. FT"! ; Sp- Gr. 4-443 ; Rel Wt. 64. 
 
 Exp. 151. Dry a piece of phosphorus of the size of a split 
 pea, and place it on a saucer. Then let a few crystals of iodine 
 fall upon it. In a few moments the two bodies will unite, and 
 so much heat will be given out that the phosphorus will take fire. 
 
 In this experiment one portion of phosphorus burns-in the 
 air, while another portion unites with the iodine to form 
 phosphorous iodide (PI 5 ). 
 
 Exp. 152. Place in a small retort 2 grams of iodine, I c. c. 
 of water, and then add cri gram of phosphorus. 
 
 In this case phosphorous iodide is also formed as before, 
 but it is now decomposed by the water, and phosphoric and 
 hydriodic acids are formed 
 
 PI 5 + 4 H 2 = H 3 P0 4 + sHI. 
 
 On heating the mixture gently, hydriodic acid gas will 
 escape, and may be collected by downward displacement in 
 a wide test-tube. 
 
138 Hydrofluoric A cid. 
 
 Hydriodic acid gas extinguishes a light, and does not 
 itself burn ; it is more than four times as heavy as atmospheric 
 air; it is colourless, but fumes strongly when it escapes, owing 
 to its condensing the moisture present in the air. It is very 
 soluble in water, with which it forms an intensely acid 
 liquid. Chlorine immediately decomposes it, and sets iodine 
 at liberty. Its solution in water, if exposed to the air, 
 gradually absorbs oxygen ; the hydrogen unites with the oxy- 
 gen, and the liquid becomes brown from liberated iodine 
 4HI + O 2 = 2H 2 O + 2l a . 
 
 Iodine forms a white oxide, iodic anhydride (I 2 O 5 ), corre- 
 sponding to nitric anhydride. There are also two acids of 
 iodine containing oxygen, viz. the iodic (HIO 3 ) and the 
 periodic (HIO 4 ) ; but they are not of practical importance. 
 
 (29) 4. FLUORINE: Symb. F; Atom. Wt. 19. 
 
 Many unsuccessful attempts have been made to obtain 
 fluorine in an isolated state, but its chemical activity is so 
 great that it combines with the metal or glass with which it 
 is in contact at the moment that it is set free ; so that no 
 satisfactory knowledge of free fluorine has yet been obtained. 
 Its compounds with other elements are termed fluorides. 
 
 The most important and abundant natural compound of 
 fluorine is calcic fluoride or fluor spar (CaF 2 ), a mineral 
 which is insoluble in water, colourless when pure, but more 
 frequently met with in beautifully-veined blue or green 
 masses, which, when crystallised, occur in cubes, or some 
 forms derived from the cube. 
 
 Cryolite, a fluoride of aluminum and sodium (3NaF, A1F 3 ), 
 is also found abundantly in Greenland. 
 
 No oxides or oxygen acids of fluorine are knowft; but 
 when combined with hydrogen, it furnishes an intensely 
 corrosive acid, the hydrofluoric (HF), which immediately 
 attacks glass, so that it cannot be prepared or preserved in 
 glass vessels. Its fumes are dangerously irritating, and 
 great care must be taken to avoid inhaling them. The acid 
 
Its Action on Glass. 139 
 
 is freely soluble in water, and is often prepared in a diluted 
 form for etching on glass, as, for instance, in engraving 
 thermometer scales, and for similar purposes. This diluted 
 acid may be preserved in silver or leaden bottles, or, as is 
 more usual, in vessels made of gutta percha. 
 
 Exp. 153. Powder a gram of fluor spar finely, and place it 
 in a small shallow leaden cup, 6 or 8 centim. in diameter, and 
 pour over it 2 or 3 grams of oil of vitriol; then place over the 
 leaden cup a plate of glass large enough to cover it, prepared in 
 the following manner : Cover one side of the glass with a thin 
 uniform layer of beeswax, which may be done by warming the 
 glass and rubbing it over with the wax. When the glass is cold, 
 trace a few characters with the point of a knife through the wax, 
 so as to expose the glass beneath. Place the glass with the 
 waxed surface downwards over the leaden dish, and warm it 
 gently, taking care not to melt the wax. Vapours of hydrofluoric 
 acid will be given off, which in a few minutes will corrode the 
 glass where it is exposed, but will not attack the wax. 
 
 The acid acts on the fluor spar in the following manner : 
 
 CaF 2 + HS 2 O 4 = CaSO 4 + 2HF. 
 On cleaning off the beeswax with a little oil of turpentine, 
 the design will be found more or less distinctly etched upon 
 the glass plate. A very small quantity of fluorine compound 
 may be detected in a mixture by proceeding carefully in the 
 same manner. In the enamel of the teeth, and often in 
 fossil bones, fluorine exists in quantity sufficient to be easily 
 detected in this way. 
 
 The hydrofluoric acid attacks the silica of the glass, 
 furnishing water and gaseous silica fluoride 
 
 SiO 2 + 4HF = SiF 4 + 2 H 2 O. 
 
 This action of hydrofluoric acid renders it a valuable agent 
 in the analysis of the silicates in many cases where the 
 ordinary acids do not decompose them. Argentic fluoride 
 is soluble, so that the fluorides give no precipitate with 
 argentic nitrate. The acid unites with potassic fluoride, and 
 forms a crystalline compound (KF, HF), from which the 
 anhydrous hydrofluoric acid has been obtained. 
 
140 Hydrogen and the Halogens. 
 
 All the halogens fluorine, chlorine, bromine, and iodine 
 are regarded as monads, since they are characterised by 
 forming a very soluble powerfully acid gas when united with 
 hydrogen, such as the hydrofluoric, hydrochloric, hydro- 
 'bromic, and hydriodic. No condensation accompanies the 
 combination, for analysis shows that in each case the acid 
 contains half its bulk of hydrogen, the hydrogen being 
 united with its own volume of the halogen, the gaseous acid 
 occupying the same bulk as its component gases of vapours 
 did in their separate form. 
 
 With the exception of fluorine, each of these elements 
 emits a coloured vapour; each, though incombustible in 
 oxygen, yet forms acids with it, the series known being the 
 following : 
 
 HF 
 
 HC1 HC1O HClO a HC1O 3 HC1O 4 
 HRr HBrO? HBrO 3 HBrO 4 
 
 HI HI0 3 HIO 4 
 
 In comparing the halogens with each other, the chemical 
 activity of fluorine, which has the smallest atomic weight, is 
 the most powerful ; next in the order in activity is chlorine, 
 then bromine, and, lastly, iodine, the atomic weight increas- 
 ing as the chemical energy declines. Chlorine is gaseous, 
 bromine liquid, and iodine solid. The specific gravity, the 
 fusing point, and the boiling point, rise as the atomic weight 
 increases. The halogens combine energetically with the 
 metals, and, when united with the same metal, furnish com- 
 pounds which are isomorphous ; that is to say, they all crys- 
 tallise in the same form potassic fluoride, chloride, bromide, 
 and iodide, for example, all crystallise in cubes. 
 
141 
 
 CHAPTER VII. 
 
 SULPHUR GROUP. 
 
 i. SULPHUR. 2. SELENIUM. 3. TELLURIUM. 
 
 (30) i. SULPHUR: Symb. S; Atom. Wt. 32; Melting Pt. 
 115; Boiling Pt. 446 C. 
 
 Sulphur, or brimstone, has been known from time imme- 
 morial, as it is an element found uncombined in considerable 
 quantities in volcanic districts. It is also found in com- 
 bination with many of the metals ; for instance, when united 
 with iron it forms the yellow brassy-looking mineral known 
 as iron pyrites ; with lead it furnishes galena, the principal 
 ore of lead ; and with zinc it gives the brown mineral called 
 blende. In combination with oxygen, it is found forming 
 salts with other metals, known as sulphates, among which 
 those of calcium, magnesium, and barium are of most 
 frequent occurrence. Sulphur also occurs in combination 
 in white of egg, in muscle, and some other animal products. 
 
 Sulphur is a yellow brittle solid, which is not soluble in 
 water, but is soluble in carbon disulphide, oil of turpentine, 
 and in benzol, as well as to a slight extent in hot alcohol. 
 It is highly inflammable, and burns with a blue flame, 
 emitting pungent suffocating vapours of sulphurous anhy- 
 dride. When heated to 115 C. it melts, forming a trans- 
 parent yellow liquid, which undergoes a series of curious 
 changes by the continued application of heat. 
 
 Exp. 1 54. Place a few grams of sulphur in a wide test-tube, 
 and apply the heat of a lamp cautiously. The sulphur melts 
 and forms a pale yellow liquid, which flows easily. Pour part 
 of the melted mass into cold water : a yellow brittle solid is 
 formed. Heat the portion still left in the tube more strongly : 
 it gradually deepens in colour, and becomes thick, assuming a 
 treacly appearance. On heating the sulphur still higher, it again 
 becomes somewhat more fluid. Pour it now in a thin stream 
 into cold water : the sulphur forms into tough, elastic, semi- 
 transparent strings. 
 
142 Crystals of Sulphur. 
 
 The colour of these cooled threads varies from a pale 
 amber to a deep brown, becoming darker in proportion as 
 the heat applied is greater. If kept for a day or two, this 
 elastic sulphur gradually becomes hard, opaque, and brittle. 
 
 Sulphur may easily be obtained in crystals. 
 
 Exp. 155. Melt from a quarter to half a kilogram of sulphur 
 in an earthen pipkin at a low and carefully applied heat. When 
 completely melted, set it aside to cool slowly. Allow it to stand 
 for a short time after it has become solid over the surface ; then, 
 with a hot wire, pierce two holes through the crust near the 
 edge on opposite sides, and pour out the still liquid portion. 
 
 When the mass is cold, remove the solid crust carefully, 
 and the interior will be found to be lined with transparent 
 honey-yellow needles, which, when scratched, or even when 
 left to themselves for a few hours, gradually become opaque. 
 The crystals thus obtained belong to the class known as the 
 oblique prismatic. 
 
 Sulphur may also be obtained in crystals of a different 
 form, the octahedron with a rhombic base. Native sulphur 
 assumes this shape ; and it may be obtained by dissolving 
 sulphur in carbon disulphide, and allowing the solution to 
 evaporate spontaneously. This form has a sp. gr. of 2*05, 
 while the crystals obtained by fusion (Exp. 155) are less 
 dense, being only of sp. gr. 1-98. They also have different 
 fusing points, the octahedral sulphur fusing at 1 1 5, and the 
 prismatic requiring a temperature at 120 C. for its fusion. 
 
 Bodies which, like sulphur, can be obtained in forms 
 which belong to two distinct classes of crystals are said to 
 be dimorphous. 
 
 Sulphur also offers a good instance of allotropy. In these 
 two varieties of crystalline form, and in the elastic threads, 
 or viscous state obtained by sudden cooling from a high 
 temperature, we have three different modifications of the 
 same element. A fourth may also be procured by placing 
 in carbon disulphide the hard mass furnished by keeping the 
 viscous sulphur till it becomes solid. The carbon disulphide 
 
Distillation of Sulphur. 
 
 Fig. 60. 
 
 dissolves all that can be removed from the mass, and a grey 
 amorphous (or non- crystalline) powder is left; this differs 
 from the crystalline varieties in its singular insolubility in 
 carbon disulphide, which dissolves both the crystalline forms 
 readily. 
 
 All these different varieties of sulphur may be distilled by 
 the application of sufficient heat, provided air be excluded, 
 otherwise they would take fire. The distilled sulphur thus 
 obtained exhibits no difference 
 in properties, whichever allo- 
 tropic modification may have 
 been used. 
 
 Exp. 1 56. Place a few pieces 
 of sulphur in a Florence flask. 
 Cut off the neck of a second 
 flask, so as to enable the neck 
 of the first flask to pass into the 
 second, as shown in Fig. 60. 
 Heat the flask containing the 
 sulphur, covering the upper sur- 
 face with a cone of thin sheet 
 iron, to keep it hot. The sul- 
 phur first melts, then boils, and 
 ultimately distils over into the 
 second flask. 
 
 The vapour of sulphur, at 
 temperatures of about 500, is 
 96 times as heavy as that of 
 an equal volume of hydrogen at 
 the same temperature ; but if the sulphur vapour be. heated 
 to 1000 C. it becomes expanded, until its density is only 
 32 times that of hydrogen at the same temperature and 
 pressure. 
 
 Selenium and tellurium show the same curious exceptional 
 effect of heat upon their vapours. 
 
 The compounds which sulphur forms with any of the other 
 elements are termed sulphides, or sometimes sulphurds. 
 
144 Sulphur and Oxygen. 
 
 Advantage is taken of the volatility of sulphur to purify 
 it from earthy matters. It is usually distilled roughly on 
 the spot where it is found, and afterwards purified by a 
 second more careful distillation. The roll sulphur of com- 
 merce is obtained by pouring the melted sulphur into cylin- 
 drical wooden moulds, in which it is allowed to cool. 
 Flowers of sulphur, as they are called, occur in the form of 
 a harsh yellow crystalline powder, which is procured by 
 distilling sulphur slowly into a large brickwork chamber, where 
 the fumes become condensed in this form. If distilled more 
 quickly, the brickwork becomes hot, and then the sulphur 
 melts and runs down the sides, forming a solid mass as it cools. 
 
 Sulphur, from its ready inflammability, is used in the pre- 
 paration of matches. Large quantities are also employed 
 in the manufacture of gunpowder ; but its principal con 
 sumption is in the production of sulphuric acid. 
 
 Sulphur combines directly with many of the metals, and 
 gives out much heat in the process. 
 
 Exp. 157. Mix 3 or 4 grams of copper filings with half their 
 weight of flowers of sulphur, and heat them in a large test-tube. At 
 a temperature a little above the melting-point of sulphur the two 
 bodies will begin to unite, and a bright glow will spread through 
 the mass. When the tube is cold, break it and examine the 
 product. A substance in no way resembling copper or sulphur 
 will be found : it consists of the sulphide of the metal. 
 
 Two compounds of sulphur with oxygen are known, sul- 
 phurous anhydride (SO 2 ) and sulphuric anhydride (SO 3 ), 
 both of which furnish important acids when combined with 
 water. There are also other acids of sulphur containing 
 oxygen : these are known as the polythionic series, in refer- 
 ence to the multiple proportion in which sulphur (delov) enters 
 into their formation. It will be sufficient merely to give their 
 formulae. The series of oxygen-sulphur acids is as follows 
 
 Sulphurous acid H 2 SO 3 
 
 Sulphuric acid H 3 SO 4 
 
 Hyposulphurous acid H 2 S 2 O 3 
 
 Dithionic acid H ? S,O 6 [ 
 
 Trithionic acid H 2 S 3 O 6 
 
 Tetrathionic acid H S S 4 O 6 
 Pentathionic acid H a S 5 O 6 
 
Sulphurous Anhydride. 145 
 
 (31) SULPHUROUS ANHYDRIDE (or Sulphur Dioxide) \ 
 Symb. SO 2 ; Atom, and Mot. Wt. 64 ; Atom, and Mol. Vol. 
 
 ^] ; : Spec. grav. of gas, 2*247 ; Rel. Wt. 32 ; Boiling Pt. 
 -ioC.; Melting Pt. -76. 
 
 Sulphur burns in oxygen with a lilac flame, and produces 
 a permanent gas, which, after it has again become cool, 
 occupies the same bulk as the original oxygen, but it has 
 become doubled in density. Two volumes of oxygen unite 
 with one volume of sulphur vapour, the three volumes be- 
 coming condensed into two 
 
 The gas so produced has a pungent and suffocating odour ; 
 in a concentrated form it cannot be breathed, but in a diluted 
 state it excites the symptoms of a common cold. It is trans- 
 parent and colourless, is not inflammable, and immediately 
 extinguishes the flame of burning bodies. Water dissolves 
 more than 40 times its bulk of the gas, and furnishes sulphur- 
 ous acid HzO + SOz = H 2 SO 3 . 
 
 The solution has the smell and taste of the gas, which 
 readily escapes from the water when heated. 
 
 Sulphurous anhydride is usually obtained by heating sul- 
 phuric acid in contact with a metal, such as copper : sul- 
 phurous anhydride comes off, while water and cupric sulphate 
 is formed 
 
 2H 2 SO 4 + Cu = CuSO 4 + SO 2 + 2H 2 O. 
 
 E.rp. 158. Place about 5 grams of copper clippings in a flask 
 provided with a cork and bent tube, and pour upon _it 30 c. c. 
 of oil of vitriol. Heat the mixture strongly, and collect, by 
 downward displacement, 2 or 3 jars of the gas that is given off. 
 Test one jar with a piece of blue litmus paper : the blue will 
 immediately be reddened. Plunge a lighted taper into another 
 jar : it will be extinguished. 
 
 Exp. 1 59. Suspend a bunch' of violets or a rose in a jar of 
 the gas : they will be bleached completely. Throw the flowers 
 into a very weak solution of ammonia : the colour will first be 
 restored, and will then be changed to green by the alkali. 
 
 L 
 
146 The Sulphites. 
 
 The bleaching action of this gas differs from that of 
 chlorine in not destroying the colour, for this is again 
 restored by the action of an alkali or a stronger acid. 
 
 Flannel, sponge, silken goods, isinglass, and many articles 
 which would be injured by chlorine, are bleached by sus- 
 pending them, in a damp state, in a closed chamber, and 
 then exposing them to the fumes of burning sulphur. 
 
 Sulphurous anhydride is useful as a fumigation for destroy- 
 ing infection. By its action, meat is also preserved from 
 putrefying for a while ; and it is frequently employed to check 
 fermentation in cider and home-made wines, for which pur- 
 pose a little sulphur is burnt in the cask before filling it with 
 the liquor. 
 
 There are various other modes of obtaining the gas. One 
 of these consists in heating a mixture of powdered black 
 manganese oxide with about its own weight of sulphur ; half 
 the sulphur combines with the oxygen, the other half with 
 the manganese 
 
 MnO 2 + S 2 = MnS -f SO 2 . 
 
 If charcoal is boiled with sulphuric acid, a mixture of sul- 
 phurous and carbonic anhydrides are evolved 
 
 C + 2H 2 SO 4 = 2 SO 2 + CO 2 + 2 H 2 O. 
 In the manufacture of sulphuric acid, sulphurous anhydride 
 is supplied simply by burning sulphur or iron pyrites in a 
 current of air. In this way it is obtained mixed with a large 
 bulk of nitrogen. Sulphurous anhydride is also emitted 
 largely from the craters of volcanoes. 
 
 When dissolved in water, the gas furnishes sulphurous 
 acid, and this acid furnishes the salts known as sulphites. 
 The sulphites of the alkalies may be obtained by passing the 
 gas into a solution of potash or soda. It forms two kinds of 
 salts : one of these contains two atoms of the metal, such as 
 the common disodic sulphite (Na 2 SO 3 , ioH 2 O), while the 
 other kind of salt is frequently called a bisulphite, and con- 
 tains but a single atom of the metal. Hydric potassic 
 sulphite (KHSO 3 ) is the best example of this class. 
 
Sulphuric Acid. 147 
 
 The sulphites are easily distinguished by their effervescing 
 when treated with a strong acid, such as the hydrochloric, 
 giving off a colourless gas, with the pungent characteristic 
 odour of sulphurous anhydride. 
 
 Exp. 160. Add a little of a solution of baric chloride to a 
 solution of a sulphite. A white precipitate of baric sulphite 
 (BaSO 3 ) is formed. 
 
 In this case, if the sulphite be free from sulphate, the pre- 
 cipitate will be dissolved on adding a little hydrochloric 
 acid ; but the clear liquid will be rendered milky by the 
 addition of chlorine water, which will convert the sulphurous 
 into sulphuric acid, and this will give a white precipitate of 
 baric sulphate, which is insoluble in acids. 
 
 The chlorine takes hydrogen from the water, forming 
 hydrochloric acid, and the oxygen which is set free converts 
 the sulphurous into sulphuric acid 
 
 H 2 SO 3 + C1 2 + H 2 O = H 2 SO 4 + 2HC1. 
 
 (32) SULPHURIC ACID (Dihydric Sulphate] : Symbol, 
 H 2 SO 4 ; Mol. Wt. 98 ; Sp. grav. of liquid, i '846 ; Melting 
 Pt. 10-5 C; Boiling PL 338. 
 
 This is the most important of the acids, and is the basis 
 of our chemical manufactures. The consumption of it 
 annually in this country considerably exceeds 100,000 tons, 
 or one hundred million kilograms. 
 
 Exp. 161. Dry some of the green crystals of ferrous sulphate 
 (the salt formerly called green vitriol}, and place the dried salt 
 in a test-tube, and heat it nearly to redness. White acid fumes 
 are given off, which condense in oily-looking drops ; they are 
 mixed with the pungent vapours of sulphurous anhydride. 
 When all the acid is expelled, a red powder, consisting of ferric 
 oxide, or colcothar, as it is called, is left in the tube. 
 
 The changes may be thus represented 
 
 2FeSO 4 = Fe 2 O 3 + SO 3 + SO 2 . 
 
 From the oily appearance of the product the old name of 
 oil of vitriol was derived. 
 
 L 2 
 
148 Formation of Sulphuric Anhydride. 
 
 When thus prepared, the distilled liquid consists of 
 a mixture of sulphuric acid with sulphuric anhydride 
 (H 2 SO 4 , S0 3 ). Some sulphuric acid is always formed 
 during the operation, because the ferrous salt cannot in 
 practice be completely freed from water before it is distilled. 
 This water comes away during distillation ; and as soon as 
 the anhydride, which distils off also, becomes mixed with 
 water, combination between the two occurs, and sulphuric 
 acid is formed, SO 3 + H 2 O becoming H 2 SO 4 . 
 
 The distillation of dried sulphate of iron has long been 
 conducted on a considerable scale at the town of Nord- 
 hausen, in Saxony, where it is made for the purpose of dis- 
 solving indigo for the preparation of Saxony blue, and hence 
 the acid so prepared is generally called Nordhausen Sulphuric 
 Acid. When such sulphuric acid, holding sulphuric anhy- 
 dride in solution (H 2 SO 4 , SO 3 ), is heated, the sulphuric 
 anhydride (SO 3 ) comes off in dense white fumes, which, if 
 immediately shut up in a vessel excluded from the moisture 
 of the air, become converted, as it cools, into a silky-looking 
 white fibrous mass. This substance is not acid, though it 
 immediately becomes so when mixed with water. It com- 
 bines with water with the evolution of a very high tempera- 
 ture, emitting a hissing sound, like that produced by 
 quenching a red-hot body in water. After the water has 
 thus combined with the anhydride the two are not separated 
 readily by simple heat If the acid thus obtained be further 
 diluted with water, this additional quantity of water may be 
 removed by evaporation. During this process the boiling 
 point gradually rises till it reaches 338; when this point is 
 attained, the acid has become reduced to the state repre- 
 sented by the formula H 2 SO 4 ; the whole then distils over, 
 and condenses again unaltered. 
 
 The great bulk of the sulphuric acid required in the arts 
 is, however, obtained by a different process from that just 
 described. When sulphur is burned in dry air or in oxygen, 
 the product is always sulphurous anhydride ; it never occurs 
 
Sulphuric Acid Chamber. 149 
 
 as a higher state of oxidation of sulphur, although a higher 
 oxide namely, the sulphuric anhydride may be obtained by 
 indirect means. If sulphurous anhydride be mixed with oxygen 
 in the presence of water, and be presented to nitric oxide, 
 or to any other of the higher oxides of nitrogen, the further 
 oxidation of the sulphur may be effected with great rapidity. 
 Moreover, a small proportion of the oxide of nitrogen will 
 effect the combination of an indefinite amount of sulphurous 
 anhydride and oxygen. Nitric oxide (NO) in the presence 
 of oxygen immediately becomes nitrogen peroxide (NO*), 
 and this, when mixed with sulphurous anhydride and a large 
 quantity of water, furnishes sulphuric acid and nitric oxide. 
 The sulphuric acid remains dissolved in the water, while the 
 nitric oxide, by absorbing oxygen from the air, again becomes 
 nitrogen peroxide ; this combines with fresh sulphurous 
 anhydride, which, when acted on by water, becomes sul- 
 phuric acid, the nitric oxide being again liberated, to go 
 through the same series of changes with fresh portions of 
 oxygen and sulphurous anhydride as long as any remain in 
 presence of each other uncombined, NO 2 + SO 2 + x H 2 O 
 yielding NO + H 2 SO 4 + x -iH 2 O. 
 
 In making sulphuric acid on a large scale, sulphur or iron 
 pyrites is burned in a current of air in furnaces (A A, Fig. 61). 
 In the stream of heated gas is suspended an iron pot (b\ 
 charged with a mixture of sodic nitrate and sulphuric acid. 
 Vapours of nitric acid are thus set free, and these pass on 
 mixed with sulphurous anhydride and excess of atmospheric 
 air. The mingled gases pass into immense chambers (FF), 
 constructed of sheet lead, supported by a framework of 
 timber. A shallow layer of water (d) covers the bottom of 
 the chamber, and the intermixture and chemical action of 
 the gases are further favoured by the injection of jets of 
 steam (eee\ supplied from the boiler (G). The vapours of 
 nitric acid lose part of their oxygen, and are quickly reduced 
 by the sulphurous acid to the state of nitric oxide ; then 
 the changes already described succeed each other rapidly, 
 
ISO 
 
 Properties of Sulphuric Acid. 
 
 leaving ultimately nothing but nitrogen and nitric oxide, 
 which pass off into the atmosphere by a flue (c). 
 
 Fi.-. 61. c 
 
 The sulphuric acid which .collects at the bottom of the 
 chamber is concentrated by evaporation in shallow leaden 
 pans, till it reaches a sp. gr. of 1720, when it forms the 
 brown sulphuric acid of commerce. In this state it is largely 
 employed in making manures, and for converting common 
 salt into sodic sulphate. The further concentration must be 
 completed in glass or platinum stills, as the leaden pans 
 would melt at the heat required. In these it is further 
 evaporated till the boiling point has risen to 338 C., and 
 then nothing but the concentrated acid (H 3 SO 4 ) remains. 
 If the application of heat were continued further, the acid 
 would distil over. 
 
 The oil of vitriol of commerce is a dense oily-looking 
 colourless liquid, without odour, and of sp. gr. 1*842. It is 
 .intensely caustic, and chars almost all organic substances, 
 owing to its powerful attraction for moisture. If exposed in 
 a shallow dish to the air for a few days, it increases in weight 
 considerably, by absorbing watery vapour from the air. This 
 property may be made use of for the purpose of drying 
 gases and various other bodies in the laboratory. When 
 
Salts of Sulphuric Acid. 1 5 1 
 
 mixed with water, it gives out great heat, so that much 
 care is required in diluting the acid. 
 
 Exp. 162. Pour a little of the strong acid into a test-tube. 
 Place a splinter of wood in it : the wood will be blackened in a 
 few minutes. 
 
 Exp. 163. Pour a cub. centim. of the strong acid into a tube 
 containing 3 or 4 c. c. of water : considerable heat will be felt 
 to attend the mixture. Take a little of this diluted acid, and 
 with a feather dipped into it trace a few letters upon writing- 
 paper. Hold the paper near the fire : the water will evaporate, 
 leaving the acid behind ; this will soon blacken the paper. 
 
 It is owing to this kind of action that even a very dilute 
 acid, if left upon linen, will cause it to fall into holes when 
 exposed to the air; the \\ater evaporates, and the acid, 
 which is not volatile, destroys the fibre. 
 
 Tests. The sulphates, when dissolved in water, may be 
 known by producing a white precipitate when mixed with a 
 solution of a salt of barium, such as baric chloride. This 
 precipitate consists of baric sulphate (BaSO 4 ). It is not 
 dissolved by nitric acid. 
 
 The sulphuric belongs to the class of acids known as 
 dibasic ; that is to say, it contains two atoms of hydrogen, 
 which admit of displacement by a metal ; and, like all acids of 
 this class, it furnishes two sets of salts with metals of which 
 the atom, like the sulphides of the alkali-metals, is chemically 
 equivalent to one atom of hydrogen. Such metals are called 
 monads. In one set of these salts one atom only of hydro- 
 gen is displaced by the metal, in the other set both atoms 
 of hydrogen are so displaced. A salt of the first series is 
 often spoken of as an acid salt ; for instance, they may be 
 thus represented, if the formula of sulphuric acid be written 
 as dihydric sulphate (H 2 SO 4 ); then 
 
 Hydric potassic sulphate, or Disulphate, is HKSO 4 ; 
 Dipotassic sulphate, or normal sulphate, K a SO 4 . 
 
 But there are cases in which a single atom of a metal, like 
 calcium, displaces both atoms of the hydrogen, and then 
 
I $ 2 Sodic Hypos ulphite. 
 
 but one salt of such metal can be formed. Copper, lead, and 
 barium are metals of this kind. These metals, of which the 
 atom is thus equivalent chemically to two atoms of hydrogen, 
 are called dyads ; so that we write 
 
 Baric sulphate Ba"SO 4 
 
 Calcic sulphate Ca"SO 4 
 
 Lead sulphate Pb"SO 4 
 
 and so on. The two dashes ("), when used, imply that the 
 metal has supplied the place of two atoms of hydrogen. 
 
 Lead sulphate is nearly as insoluble as baric sulphate, and 
 strontic sulphate is but little less so. Calcic sulphate is 
 more soluble, though still but slightly so ; but most of the 
 other sulphates are freely soluble. The soluble sulphates 
 are often easily formed by dissolving the metal in dilute 
 sulphuric acid ; where this cannot be done, the oxide or the 
 carbonate of the metal may be dissolved in the acid 
 (i)Zn + H 2 SO 4 = ZnS0 4 + H 2 , 
 
 (2) CuO + H 2 SO 4 = CuSO 4 + H 2 O ; or 
 
 (3) MnCO 3 + H 2 SO 4 - MnSO 4 + H 2 O + CO 2 . 
 
 (33) Hyposulphites. Sodic hyposulphite is a salt which 
 is used extensively by the photographer. This use depends 
 upon the fact that the hyposulphite has the power of dis- 
 solving many of the salts of silver which are insoluble in 
 water. 
 
 E.rp. 164. Add a few drops of a solution of argentic nitrate 
 to a weak solution of common salt : argentic chloride will be/ 
 formed ; and on the addition of a small quantity of a solution of 
 sodic hyposulphite, it will be completely dissolved. The solution 
 has a sweet metallic taste. 
 
 Argentic bromide and argentic iodide may also be dis- 
 solved by the hyposulphite, though not so readily. 
 
 When a photograph is washed in water, the excess of 
 soluble argentic nitrate is washed out, but the chloride or 
 iodide remains in the paper. If now this be plunged into a 
 solution of sodic hyposulphite, the portion of unaltered in- 
 soluble silver salt becomes dissolved in the liquid, while the 
 
Sulphuretted Hydrogen. 
 
 153 
 
 part which has been blackened by light is unacted on. If 
 the picture is then thoroughly washed in pure water it is 
 fixed-, that is, it becomes no longer liable to change on 
 exposure to light. 
 
 There are several ways of preparing sodic hyposulphite. 
 One of the simplest consists in digesting a solution of sodic 
 sulphite upon flowers of sulphur 
 
 Na 2 SO 
 
 S = Na 2 S 2 O 3 . 
 
 A colourless solution is obtained, from which, on evapora- 
 tion, large colourless striated crystals of sodic hyposulphite 
 are easily procured (Na 2 S 2 O 3 , 5H 3 O). Many other hypo- 
 sulphites may be obtained, but they are unimportant. The 
 acid cannot be isolated, as it immediately begins to undergo 
 decomposition into sulphur and sulphurous acid. 
 
 Exp. 165. Add to a solution of sodic hyposulphite a little 
 hydrochloric acid. In a few minutes a pungent smell of sul- 
 phurous acid will be perceived, while the liquid becomes milky 
 from the deposition of sulphur 
 
 Na 2 SO 3 + 2HC1 = 2NaCl + H,SO 3 + S. 
 
 (34) SULPHURETTED HYDROGEN : Symb. H 2 S ; Atomic and 
 MoL Wt. 34; Mol. Vol. QI]; S P- Gr > 1*1912; Relative 
 Wt. 17. 
 
 Exp. 1 66. Place 10 or 15 
 grams of ferrous sulphide in 
 small lumps in a gas bottle 
 (Fig. 62), and pour upon it 
 about 100 c. c. of diluted sul- 
 phuric acid (i of acid to 6 of 
 water) : an effervescence, with 
 escape of this offensive gas, 
 immediately occurs 
 H Z SO 4 + FeS = FeS0 4 + H 2 S. 
 
 Other sulphides also furnish 
 the gas sulphide of anti- 
 mony, for example, when heated with hydrochloric acid. 
 This gas is often wanted in the laboratory for the analysis 
 
 Fig. 62. 
 
154 Sulphuretted Hydrogen. 
 
 of ores, and Fig. 62 shows a convenient mode of arranging 
 the apparatus for liberating it. The small bottle contains a 
 little water, through which the gas bubbles, in order to re- 
 move any particles of acid or of iron salt which may have 
 been splashed over by the effervescence, before it is passed 
 into the solution for analysis. 
 
 Sulphuretted hydrogen is colourless and transparent ; it 
 has a disgusting odour of rotten eggs, and is very poisonous 
 if breathed. It is soluble in about one-third of its bulk of 
 water, and the solution, which has the smell of the gas, is a 
 useful test for certain metals. But if the solution be kept in 
 bottles only partially filled, the oxygen of the air combines 
 with the hydrogen of the compound, water is formed, and 
 the liquid becomes milky from deposited sulphur 
 2H 2 S + O 2 = 2H 2 O + S 2 . 
 
 Sulphuretted hydrogen burns in the air with a pale bluish 
 flame, furnishing water and frequent fumes of sulphurous 
 anhydride. It contains its own bulk of hydrogen, and half 
 its volume of the vapour of sulphur 
 
 the three volumes of the constituents becoming condense'd 
 into two volumes, just as, in the analogous case of water, the 
 two volumes of hydrogen and one volume of oxygen furnish 
 two volumes of steam. 
 
 Sulphuretted hydrogen, though, soluble, may be collected 
 over warm water, if the gas be made in a retort or in a flask 
 fitted with a gas tube. 
 
 Exp. 167. Fill two small bottles of 250 or 300 c. c. capacity 
 with the gas; prepare a bottle of sulphurous anhydride of 
 similar size; withdraw the stopper, and close the bottle with a 
 glass plate. Do the same with one of the bottles of sulphuretted 
 hydrogen, and invert the sulphurous anhydride over this bottle. 
 The two gases will immediately, in the presence of the moisture, 
 react on each other ; the oxygen of the sulphurous anhydride 
 uniting with the hydrogen of the sulphuretted hydrogen, while 
 sulphur is deposited. 
 
Hydrosulpkates, 155 
 
 A little pentathionic acid (H 2 S 5 O6) is always formed at 
 the same time 
 
 5H 2 S + 5SO 2 = 58 + 4H 2 O + H 2 S 5 O 6 - 
 Chlorine, iodine and bromine also immediately decompose 
 sulphuretted hydrogen, with separation of sulphur. 
 
 Exp. 1 68. Repeat the experiment above described, substitu- 
 ting a bottle of chlorine for one of sulphurous anhydride : hydro- 
 chloric acid is formed, and sulphur is deposited 
 H 2 S + Cl a = 2HC1 + S. 
 
 Sulphuretted hydrogen is often produced spontaneously 
 under various circumstances. Whenever a soluble sulphate 
 of the metal of one of the alkalies or alkaline earths is kept 
 in contact with decaying organic matter, where air does not 
 find free access, the sulphate becomes reduced to the form 
 of sulphide, so that soluble sulphides become formed, the 
 organic matter removing the oxygen and furnishing water 
 and carbonic acid. The deoxidising action on sodic sul- 
 phate is as follows : 
 
 Na 2 SO 4 - 2O 2 = Na 2 S. 
 
 In this way soluble sulphides are formed in certain 
 springs, such as those of Harrogate and Moffat, giving to 
 them their nauseous odour ; since the sulphuretted hydrogen 
 is liberated by the action of even so feeble an acid as the 
 carbonic 
 
 Na 2 S + H 2 O + CO 2 = Na 2 CO 3 + H 2 S. 
 
 Sulphuretted hydrogen is really a feeble acid, and is often 
 spoken of as hydrosulphuric aci<i. When it acts on bases, 
 it furnishes true salts, the sulphides, sometimes called hydro- 
 sulphates. If the gas be passed into an alkaline solution, it 
 is quickly absorbed ; solution of potash (zKHO + H 2 S) 
 becomes potassic hydrosulphate (K 2 O, H 2 S + H 2 O), though 
 it is usual to regard these compounds as sulphides, analogous 
 to the chlorides, the oxygen of the base being exactly 
 sufficient to form water with the hydrogen, for 
 K 2 O, H 2 S = K 2 S -r H 2 O. 
 
156 Sulphuretted Hydrogen and the Metals. 
 
 A solution of ammonia, when saturated with sulphuretted 
 hydrogen, is a useful test for metals, 2H 3 N + H 2 S yielding 
 (H 4 N) 2 S. 
 
 Metals the atom of which, like potassium, take the place 
 of a single atom of hydrogen usually form two compounds 
 with sulphuretted hydrogen, in one of which a single atom 
 of the hydrogen is displaced by the metal, and in the other 
 both atoms are displaced ; for instance, we have 
 Sulphuretted hydrogen HHS 
 
 Hydric potassic sulphide KHS 
 
 Dipotassic sulphide KKS ; 
 
 wnilst metals of which .the atom, like calcium, displaces two 
 atoms of hydrogen form but a single compound when acted 
 upon by the gas ; as, for example 
 
 Baric sulphide BaS, 
 
 Calcic sulphide CaS ; and so on. 
 
 Certain metals may be precipitated from their acidulated 
 solutions by sulphuretted hydrogen. Among these are silver, 
 bismuth, mercury, lead, copper, gold, platinum, tin, antimony, 
 and arsenicum ; and the precipitate, which is usually in the 
 form of a hydrate, often has a characteristic colour. 
 
 Exp. 169. Prepare a solution of sulphuretted hydrogen in 
 water, by passing a stream of bubbles of the gas through 
 water for a few minutes. Add some of this solution to a dilute 
 solution of tartarised antimony : a beautiful orange-coloured 
 antimony sulphide is separated. With a dilute solution of 
 stannic chloride, a yellow stannic sulphide will be formed ; and 
 with a solution of cupric sulphate, also largely diluted, a 
 brownish-black cupric sulphide will be obtained. 
 
 Other metals are not precipitated from the acidulated 
 solutions of their salts by sulphuretted hydrogen ; among 
 these are the salts of iron, cobalt, nickel, manganese, zinc, 
 aluminum, and chromium. Hence it is customary, in the 
 analysis of minerals, to employ sulphuretted hydrogen as a 
 means of separating those metals above mentioned which 
 are precipitated from their solutions by the action of the 
 gas from those which are unacted upon by it. 
 
Carbon Bisulphide. 157 
 
 In the case of those metals which are not precipitated 
 from their acid solutions by sulphuretted hydrogen, the sul- 
 phide may generally easily be obtained by presenting an 
 alkali metal to the acid radical at the same moment that 
 the sulphur is presented to the metal which is required in 
 the state of insoluble sulphide, and this is done by adding a 
 soluble sulphide to the solution of the metallic salt. Ferrous 
 sulphate, for instance, gives no precipitate with sulphuretted 
 hydrogen, but it yields a black ferrous sulphide as soon as 
 its solution is mixed with one of dipotassic sulphide 
 FeSO 3 + K 2 S, H 2 O = K 2 SO 4 + FeS, H 2 O. 
 
 Many of the sulphides of metals which are precipitated by 
 the gas from the acid solutions of their salts are soluble in 
 the solutions of the alkaline sulphides, owing to their power 
 of forming double sulphides, which are ! soluble in water. 
 Among these are the sulphides of gold, platinum, antimony, 
 arsenicum, and tin, which may be dissolved out and separated 
 from other sulphides such as those of copper, bismuth, lead, 
 silver and mercury, by treating the mixed precipitates with a 
 solution of dipotassic sulphide, in which the metals last 
 enumerated are insoluble. 
 
 The smell of sulphuretted hydrogen is one of its several 
 tests ; very small traces of it may also be recognised by 
 their power of blackening white paper moistened with a 
 solution of acetate or other salt of lead. 
 
 Exp. 170. Place a drop of a solution of lead acetate upon a 
 piece of paper. Hold it for an instant near the open bottle of a 
 solution of sulphuretted hydrogen : a black or brown stain of 
 lead sulphide will immediately be produced. 
 
 (35) CARBON DISULPHIDE : Symb. CS 2 ; Atomic Wt. 76. 
 This is an extremely volatile liquid, usually of very 
 offensive odour, due to some impurity. It exerts a poisonous 
 action upon animals. It boils at 48, giving off a remarkably 
 inflammable vapour. It is considerably heavier than water, 
 and is not soluble in it ; but is very soluble in ether and 
 
158 Selenium and Tellurium. 
 
 alcohol, as well as in the oils. It is one of the best solvents 
 for the oils and fats, and is used largely for their extraction. It 
 also freely dissolves sulphur, iodine, bromine, and phos- 
 phorus. 
 
 Exp. 171. Place a few drops of the disulphide in three or four 
 test-tubes. To one add a little powdered sulphur, to a second a 
 minute scrap of iodine, to a third a fragment of phosphorus, and 
 to a fourth a few drops of water. Notice the beautiful colour 
 produced by the iodine, the solution of the sulphur and phos- 
 phorus, and the insolubility of the liquid in water. 
 
 Carbon disulphide is prepared on a large scale by driving 
 the vapour of sulphur over glowing coke, and condensing 
 that vapour in suitably cooled receivers. It is one of the 
 few liquids which does not freeze at the lowest temperature 
 hitherto obtained. This body combines with the sulphides 
 of the alkali metals, and forms unstable compounds, which 
 are in some respects analogous to the carbonates, but they 
 contain sulphur instead of oxygen ; K 2 CO 3 being the car- 
 bonate, K 2 CS 3 the corresponding sulphocarbonate. 
 
 Sulphur combines with chlorine in two proportions. One 
 of these (S 2 C1 2 ) is a yellow liquid, the other (SC1 2 ) is of a 
 deep red colour, and fumes strongly in the air. Both are 
 decomposed by water. 
 
 2. SELENIUM. 3. TELLURIUM. 
 
 Sulphur belongs to a group of elements of which the other 
 two, selenium and tellurium, are of rare occurrence, and are 
 practically unimportant. All three elements are characterised 
 by forming gaseous fetid compounds with hydrogen, con- 
 taining two atoms of hydrogen to one atom of the charac- 
 teristic element, and in each case ' the gas contains two 
 volumes of hydrogen united with one volumes of the vapour 
 of the other element, the three volumes having become con- 
 densed into the space of two. 
 
 . All the three elements have a strong attraction for oxygen, 
 and they each furnish two oxidized compounds, which in 
 combination with water have acid properties. 
 
The PhospJwnis Group. 159 
 
 Sulphuretted hydro- Sulphurous acid Sulphuric acid 
 
 ' gen (H,S) (H 3 S0 3 ) (H,SO 4 ) 
 
 Seleniuretted hydro- Selenious acid Selenic acid 
 
 gen (H,Se) (H 2 SeO 3 ) (H a SeO 4 ) 
 
 Telluretted hydro- Tellurous acid Telluric acid 
 
 gen (H,Te) (H 3 TeO 3 ) (H 3 TeO 4 ) 
 
 The properties of selenium are intermediate between those 
 of sulphur and tellurium ; and this last has so much resem- 
 blance to the metals that it is usually described among them. 
 Of the three, sulphur has the lowest and tellurium the highest 
 atomic weight ; and the specific gravity, the fusing point, 
 and the boiling point increase in the same order as the 
 atomic weights. 
 
 CHAPTER VIII. 
 
 PHOSPHORUS GROUP. 
 i. PHOSPHORUS. 2. ARSENICUM. 3. ANTIMONY. 4. BISMUTH. 
 
 (36) i. PHOSPHORUS: Symb. P; Atom. Wt. 31; Atom. 
 Vol. j_j ; Sp. gr. of solid, 1*83 ; of vapour, 4-42 ; Rel. Wt. 
 62; Mol. Wt. P 4 , 124; Mol. Vol. rTTTI; Boiling Pt. 
 288; Fusing Pt. 44. 
 
 This remarkable element has considerable resemblance to 
 the metals arsenicum and antimony. All three form fetid, 
 inflammable, gaseous compounds with hydrogen, in which 
 three atoms of hydrogen are united with one atom of the 
 other element. Nitrogen has also a near relation to this 
 group ; but its hydrogen compound, ammonia, is strongly 
 alkaline, while the hydrogen compounds of the other mem- 
 bers of the group are very feebly so. Bismuth, though a 
 member of this group, forms no compound with hydrogen. 
 Each of the five elements is also distinguished by furnishing 
 two compounds with oxygen, which, when combined with 
 water, possess acid properties, except the lower compound 
 
1 66 Sources of Phosphorus. 
 
 with antimony, which is feebly basic, and that of bismuth,, 
 which is more strongly basic. 
 
 Ammonia Nitrous anhydride Nitric anhydride 
 
 ' (NHj) (N 2 3 ) (N 2 5 ) 
 
 Phosphuretted hy- Phosphorous anhy- Phosphoric anhy- 
 
 drogen (PH 3 ) dride (P 2 O 3 ) dride (P 2 O 5 ) 
 
 Arseniuretted hydro- Arsenious anhydride Arsenic anhydride 
 
 gen (AsH 3 ) (As 2 O 3 ) (A2 2 O 5 ) 
 
 Antimoniuretted hy- Antimonious anhy- Antimonic anhy- 
 
 drogen (SbH 3 ) dride (Sb 2 O 3 ) dride (Sb 2 O 5 ) 
 
 Bismuth oxide Bismuthic anhydride 
 
 (Bi 2 3 ) (Bi 2 5 ). 
 
 Arsem'cum, antimony, and bismuth will be described with 
 the metals. 
 
 Phosphorus is never found uncombined in nature. It 
 occurs in small quantities in granite and the older rocks, in 
 the form of tricalcic phosphate, or phosphate of lime. When 
 these rocks crumble down and form soil, they supply phos- 
 phates to plants, which store them up in considerable quantity 
 in their seeds. From the seeds the animals which feed upon 
 them derive a sufficient quantity for their support. Phosphorus 
 collects in the animal system in large quantities, and fur- 
 nishes, as calcic phosphate, the principal earthy component 
 of the bones. Phosphorus is also an essential ingredient in 
 the brain and nervous tissue ; and it passes out of the body 
 constantly, in the form of soluble phosphates in the urine, 
 and in the solid excreta as insoluble earthy phosphates. It 
 is also abundant in guano, the excrement of seafowl. 
 
 Phosphorus is now always extracted from calcic phosphate, 
 which is generally obtained from bones. 
 
 Exp. 172. Burn a few bones in the open fire. They will 
 leave more than half their weight of a white ash. Grind this ash 
 to a fine powder, and mix 30 grams of it with 20 grams of oil of 
 vitriol and 180 or 200 grams of water. After standing for some 
 hours, strain off the acid liquor from the calcic sulphate which is 
 formed. Preserve this liquor for preparing some of the soluble 
 phosphates. 
 
Properties of Phosphorus. 1 6 1 
 
 The change in this experiment consists in the removal of 
 two-thirds of the calcium by the sulphuric acid, in the in- 
 soluble form of calcic sulphates ; the bone earth, which is 
 not soluble in water, becoming converted into a very soluble 
 acid phosphate, as shown by the equation 
 
 Tricalcic Phosphate Sulphuric Acid Acid Phosphate Calcic Sulphate 
 
 Ca 3 2PO 4 + 2H Z SO 4 = CaH 4 2PO 4 + 2CaSO 4 
 If phosphorus is to be made, a solution of the acid phos- 
 phate, or superphosphate of lime, prepared by a similar process, 
 is evaporated down to a syrupy consistence, and mixed with 
 about a third of its weight of powdered charcoal, after which 
 it is heated nearly to redness. It is then placed in an earthen 
 retort, and slowly raised to a full red heat. Phosphorus 
 gradually comes over in vapour, and is condensed in water, 
 while a large quantity of hydrogen and carbonic oxide gases 
 pass off, leaving a considerable residue of bone earth in the 
 retort. The superphosphate when heated with charcoal is 
 decomposed. Its calcium retains sufficient phosphorus and 
 oxygen to reconvert it into tricalcic phosphate, 3(CaH 4 2PO 4 ) 
 becoming Ca 3 , 2PO 4 4- 4H 3 PO 4 ; while the phosphoric acid 
 in the presence of the charcoal breaks up as follows : - 
 
 4 H 3 PO 4 + i6C = P 4 + 6H 2 + i6CO. 
 The phosphorus is purified by melting it under warm 
 water, heating it with chloride of lime, and forcing it, by 
 pressure, through washleather ; it is then moulded, while 
 in the fluid state, by allowing it to flow into tubes, which are 
 next chilled in cold water, and the phosphorus becomes 
 solid. 
 
 Phosphorus is a soft, semi-transparent, waxy-looking sub- 
 stance, which fumes in the air, and forms white vapours, 
 smelling something like garlic. The fumes are feebly lumi- 
 nous in a dark room, and hence its name, which means the 
 'light-bearer/ It has a sp. gr. of 1-83, and melts at 44. 
 It is extremely inflammable, and takes fire just above its 
 melting point. On this account it must always be kept 
 under water, and should not be handled with warm fingers. 
 
 M 
 
1 62 Safety Matches. 
 
 Phosphorus is not soluble in water, but it is slightly 
 so in ether; it is more soluble in benzol, oil of turpentine, 
 and in the fixed oils. 
 
 Phosphorus is also known in two other allotropic forms, 
 viz. white and red. White phosphorus is slowly produced 
 upon the sticks of phosphorus when kept under water. 
 The red form, or amorphous phosphorus, is prepared in 
 large quantities by heating phosphorus for several hours to 
 about 260 C. in closed vessels, filled with nitrogen or with 
 carbonic anhydride. The melted phosphorus gradually 
 becomes solid, opaque, and of a deep red colour, and its sp. 
 gr. becomes increased to 2-14. In this form it is insoluble 
 in carbon disulphide, which may be used to dissolve out the 
 last traces of the common form. When quite free from 
 ordinary phosphorus, red phosphorus may be exposed to the 
 air without danger. It may be heated in the open air be- 
 yond 200 without taking fire ; but if raised to about 288 
 it is changed into the common form, and bursts into a blaze. 
 When heated in vessels full of nitrogen, it may be distilled 
 like common phosphorus, the vapour condensing in clear, 
 colourless drops.* 
 
 Exp. 173. Dissolve I or 2 decigrams of phosphorus in 
 2 c. c. of carbon disulphide in a test-tube; pour a little of the 
 solution upon a piece of filtering-paper, and allow it to dry. The 
 phosphorus will be left in a finely divided form, and will set fire 
 to the paper in a few minutes. 
 
 Red phosphorus is employed in preparing safety matches. 
 The matches are covered with melted parafrme, and tipped 
 with a paste consisting of potassic chlorate, antimonious 
 sulphide, powdered glass, and gum water. When they are 
 to be lighted, they are rubbed upon a surface covered with a 
 mixture of red phosphorus with half its weight of powdered 
 glass. Common lucifer-matches have the phosphorus mixed 
 
 * The vapour of phosphorus has twice as many atoms in its molecule 
 as most elements, 4 atoms of phosphorus instead of 2 being contained 
 in the molecule. Arsenicum resembles phosphorus in this respect. 
 
Oxides of Phosphorus. 163 
 
 up in the paste with which they are tipped, and these take fire 
 when rubbed on any rough surface. The safety matches 
 can only be kindled by friction on the phosphorised surface. 
 
 Exp. 174. Place a bit of phosphorus in a solution of argentic 
 nitrate. In the course of a day or two it will be covered with 
 brilliant crystals of reduced silver. 
 
 Solutions of salts of copper, platinum, or gold will also 
 yield up their metal if used instead of solution of a silver 
 salt, owing to the strong attraction of phosphorus for oxygen. 
 
 Phosphorus combines with many of the metals when 
 heated with them. Such compounds are called phosphides. 
 
 (37) Phosphorus forms two well-marked oxides phos- 
 phoric anhydride (P 2 O 5 ) and phosphorous anhydride (PzC^). 
 They give powerful acids when combined with water, viz. 
 phosphoric acid (H 3 PO 4 ) and phosphorous acid (H 2 PHO 3 ) ; 
 besides which, there is a third acid, the hypophosphorous 
 (HPH 2 O 2 ), with still less oxygen. 
 
 Phosphoric Anhydride (P 2 O 5 ). 
 
 Exp. 175. Dry two or three pieces of phosphorus of the size 
 of a pea upon blotting-paper, and place them upon a small cap- 
 sule in the middle of a plate. Touch the phosphorus with a hot 
 wire, and cover it at once with a dry gas jar. White flakes of 
 the anhydride will be formed, and will settle down upon the 
 plate. 
 
 This anhydride is a snow-white powder, which attracts 
 moisture quickly ; it hisses when a few drops of water are 
 added to it ; it dissolves quickly, except a few flocculi, and 
 produces phosphoric acid, which is intensely sour, but not 
 caustic 
 
 P 2 5 + 3 H 2 = 2 H 3 P0 4 . 
 
 It is easily made in large quantities by burning dry phos- 
 phorus in a dish hung in a large globe supplied with a current 
 of dry air. 
 
 Phosphoric acid may be formed by dissolving phosphorus 
 in about 13 times its weight of diluted nitric acid of sp. gr. 
 i'2O. Concentrated acid must not be used, as it acts with 
 
 M 2 
 
164 Sodic Phosphates. 
 
 great violence. The phosphorus becomes oxidized by the 
 nitric acid, which is decomposed ; and on boiling down the 
 solution the excess of nitric acid is driven off, and pure 
 phosphoric acid is obtained in solution. If the water be 
 driven off as far as possible, the acid is left in a form which 
 fuses at a low red heat, and becomes a clear, glassy-looking 
 solid on cooling. This glass dissolves easily in water. 
 
 There are three different forms of phosphoric acid, each 
 of which possesses the properties of a distinct acid, and 
 forms a distinct set of salts, viz. metaphosphoric acid (HPO 3 ) ; 
 orthophosphoric, or ordinary phosphoric acid (H 3 PO 4 ); and 
 pyrophosphoric acid (H 4 P 2 O 7 ). 
 
 The ordinary phosphoric acid is prepared by dissolving 
 phosphorus in nitric acid, as already described. If the 
 glassy acid thus obtained be boiled with water, and made 
 slightly alkaline with sodic carbonate, a salt is obtained, the 
 disodic hydric phosphate, which on crystallisation gives efflo- 
 rescent rhombic prisms (Na 2 HPO 4 , i2H 2 O). 
 
 Exp. 176. Take the solution of superphosphate of lime pre- 
 pared as directed in Exp. 1 72 ; add sodic carbonate until the 
 liquid is faintly alkaline; filter it from the precipitated calcic 
 phosphate, and evaporate the solution till a drop of it crystallises 
 when allowed to cool on a slip of glass. Then allow the whole 
 solution to cool. Crystals of disodic hydric phosphate will be 
 formed. 
 
 If this disodic hydric phosphate, or rhombic phosphate, as it 
 is sometimes called, be mixed with an excess of caustic soda, 
 a crystallisable salt, formerly called subphosphate of soda, 
 with the formula Na 3 PO 4 , i2H 2 O, or trisodic phosphate, 
 is obtained. If a quantity of phosphoric acid be divided 
 into two equal parts, one of which is just neutralised with 
 sodic carbonate, and then the other half of the acid be 
 added, a third salt is obtained, which crystallises with diffi- 
 culty. It was formerly known as biphosphate of soda. It 
 is the dihydric sodic phosphate (NaH 2 PO 4 , H 2 O). 
 
 Thus iT is possible to form three different sodium salts 
 
Sodic Phosphates. 165 
 
 from the common phosphoric acid, in which the hydrogen 
 
 of the acid is displaced step by step : 
 
 Tribasic phosphoric acid H 3 PO 4 
 
 Dihydric sodic phosphate NaH 2 PO 4 , H 2 O 
 
 Hydric disodic phosphate Na 2 HPO 4 , i2H a O 
 
 Trisodic phosphate Na 3 PO 4 , I2H 2 O 
 
 These salts all give a yellow precipitate with argentic 
 nitrate, or triargentic phosphate (Ag 3 PO 4 ). They also give, 
 when mixed with ammonia and magnesic sulphate, a crystal- 
 line precipitate of ammonic magnesic phosphate (H 4 N, 
 Mg"P0 4 , 6H 2 0). 
 
 Exp. 177. Dry a portion of the disodic hydric phosphate 
 crystals at 1 50 C. They will lose their water of crystallisation, 
 and leave a white mass. 
 
 This consists of Na 2 HPO 4 . If it be redissolved in water, 
 it will furnish the original salt, known by its property of pre- 
 cipitating silver nitrate yellow 
 Na 2 HPO 4 + 3AgNO 3 = Ag 3 PO 4 + 2NaNO 3 + HNO 3 . 
 
 As a triargentic phosphate, the solution will contain nitric 
 acid, and will redden litmus. 
 
 Exp. 178. Take a portion of the same sodium salt, and heat 
 it to redness in a porcelain crucible before redissolving it in water. 
 
 The result will now be different : two molecules of the 
 salt coalesce, and lose a molecule of water, 2Na 2 HPO 4 be- 
 coming Na 4 P 2 O 7 + H 2 O. If the residue be redissolved 
 in water, the salt may be crystallised with ioH 2 O. 
 
 Exp. 179. Add a portion of the solution to one of argentic 
 nitrate, and a white precipitate will be formed, Na 4 P 2 O 7 + 
 4AgNO 3 becoming Ag 4 P 2 O 7 + 4NaNO 3 . 
 
 This white salt is the pyrophosphate, so called because 
 obtained by the action of fire upon the common phosphate. 
 
 Exp. 1 80. Heat a little of the dihydric sodic phosphate to 
 redness : it becomes converted into a glassy mass of sodic ineta- 
 phosphate, the elements of water being expelled 
 NaH s PO 4 , H 8 = NaP0 3 + 2H 3 O. 
 
1 66 Phosphorus and Hydrogen. 
 
 This salt belongs to a class known as the metaphosphates, 
 which are recognised by precipitating argentic nitrate white 
 and gelatinous, and redissolving the precipitate if an excess 
 of the phosphate be used. 
 
 The pyrophosphoric and the metaphosphoric acids may 
 even be obtained in solution in water by decomposing the 
 silver or lead salts of their acids by means of sulphuretted 
 hydrogen. For instance 
 
 Argentic Metaphosphate Metaphosphoric Acid 
 
 ' 2AgPO 3 + H 3 S = 2HPO 3 + Ag z S; 
 
 Argentic Pyrophosphate Pyrophosphoric Acid 
 
 Ag 4 P a 7 + 2H Z S = H 4 P 2 7 + 2Ag z S; 
 
 the silver and the hydrogen changing places. 
 
 The ordinary triargentic phosphate would yield the 
 common form of the acid 
 
 2 Ag 3 PO 4 + 3H 2 S = 2H 3 PO 4 + 3 Ag 2 S. 
 
 Acids which, like the metaphosphoric, contain one atom 
 of hydrogen, capable of displacement by a metal, are called 
 monobasic acids. Those in which there are three atoms of 
 hydrogen which admit of displacement by hydrogen, like the 
 ordinary form of phosphoric acid, are called tribasic acids ; 
 while in such cases as the pyrophosphoric, which contain 
 four atoms of displaceable hydrogen, the acid is said to be 
 tetrabasic. 
 
 The phosphorous and hypophosphorous acids are of little 
 importance. 
 
 (37 a) With hydrogen phosphorus forms three compounds : 
 one solid (HP 2 ) ; one liquid (H 10 P 5 ), the vapour of which 
 inflames immediately on reaching the air; and a gas (H 3 P). 
 This is the only hydride of phosphorus that we shall describe. 
 
 PHOSPHURETTED HYDROGEN : Symb. H 3 P ; Atom, and 
 Mol. Wt. 34 ; Sp. Gr. 1-185 ; && Wt - I 7- 
 
 This is a poisonous gas, with a disgusting odour of garlic, 
 highly inflammable, and liquefiable under pressure. It is 
 decomposed by chlorine, and, though not soluble in water, 
 
Phosphorus and Chlorine. 1 67 
 
 is wholly absorbed by a solution of bleaching-powder. It 
 precipitates the salts of lead and copper black (forming 
 phosphides), and corrosive sublimate yellow. 
 
 Exp. 181. Dissolve 4 grams of caustic potash in 16 grams of 
 water; place it in a small retort of about 50 c. c. capacity, and 
 add 2 or 3 decigrams of phosphorus ; immerse the beak of the 
 retort just below the surface of water in a small capsule, and 
 heat the mixture gently. Bubbles of gas will form in the retort, 
 and will break with a flash and a slight explosion upon the sur- 
 face of the potash solution. By degrees the air of the retort 
 will be deprived of all its oxygen, and then the bubbles of gas, 
 as they escape into the air, will take fire, producing a white 
 wreath of phosphoric anhydride, which forms a number of ring- 
 lets, revolving in vertical planes around the axis of the wreath 
 itself as it ascends. 
 
 In this beautiful experiment, which requires care, lest the 
 retort be broken by the bursting of the bubbles within it, 
 phosphuretted hydrogen gas is formed, accompanied by 
 traces of the vapour of the liquid phosphide, which causes it 
 to take fire as soon as it mixes with the air 
 
 Potash Phosph. Potass. Hypo- 
 
 Hydrogen phosphite 
 
 P 4 + 3H Z + 3KHO = H 3 P + 3 KPH 3 O 3 . 
 
 Pure phosphuretted hydrogen, which does not take fire 
 
 spontaneously, is obtained by heating phosphorous acid, which 
 
 breaks up into phosphoric acidand phosphuretted hydrogen 
 
 4 H 2 PH0 3 = 3H 3 P0 4 + H 3 P. 
 
 Phosphuretted hydrogen is feebly alkaline in its nature, 
 which is in some measure analogous to that of ammonia, to 
 which it corresponds in composition, but it contains only 
 half a volume of phosphorous vapour and three volumes of 
 hydrogen in two volumes of the gas. 
 
 Phosphorus burns when placed in chlorine gas. When 
 the chlorine is in excess, it forms a solid volatile chloride 
 (PC1 5 ), which, when put into water, produces phosphoric 
 and hydrochloric acids 
 
 PC1 5 + 4 H 2 = H 3 P0 4 
 
1 68 Silicon. 
 
 If the phosphorus is in excess, a liquid chloride (PC1 3 ) is 
 formed; and this furnishes with water phosphorous and 
 hydrochloric acids 
 
 PC1 3 + 3 H 2 = H 2 PH0 3 + 3 HC1. 
 There are corresponding bromides of phosphorus. 
 
 CHAPTER IX. 
 
 SILICON AND BORON. 
 
 (38) Silicon, in combination with oxygen as silica or 
 silex, is the most abundant solid material found upon the 
 earth. It forms the essential substance of flint, sea sand, 
 sandstone, quartz, agate, and calcedony, besides entering 
 largely into the composition of clay, and a great number of 
 crystallised minerals, and nearly all the common rocks, 
 except limestone. 
 
 SILICON Symb. Si ; Atom. Wt. 28 ; Sp. Gr. 2*49 is never 
 found uncombined, but is always obtained by chemical 
 means, one method being the heating of sodium in the 
 vapour of silicic chloride (SiCl 4 ), when common salt is 
 formed and silicon is set free. It is a brown powder, which 
 burns when heated strongly in air or oxygen, but which at a 
 very high heat, though below that required for fusing steel, 
 may be melted if excluded from air. It may be obtained 
 crystallised in plates and octahedra, which are hard enough 
 to scratch glass. 
 
 Silicon forms only one oxide, viz. silica (SiO 2 ), and this is 
 found both crystallised and amorphous. Pure crystalline 
 silica has a sp. gr. of 2*642. It occurs in quartz in six-sided 
 prisms, ending in six-sided pyramids. Amethyst is a purple 
 variety of quartz. The amorphous form of silica has a sp. 
 gr. of only 2*2 ; it may be obtained by melting quartz 
 before the oxyhydrogen blowpine. Calcedony is a mechanical 
 
Silica. 169 
 
 mixture of crystalline and amorphous quartz. 4 gate consists 
 of a succession of layers of crystalline and amorphous silica. 
 flint is a form of calcedony chiefly found in the upper chalk ; 
 and opal is a hydrated variety of amorphous silica. 
 
 Silica, when once crystallised, is insoluble in water, and 
 in all acids except the hydrofluoric. 
 
 Silica, in fine powder, looks like a white earth, but it has 
 a strong tendency to unite with bases, a property which may 
 be employed to obtain it in a pure form. 
 
 Exp. 182. Place about 60 grams of a mixture of potassic 
 and sodic carbonates in a clay crucible, and raise it to a red 
 heat ; when fused add 1 5 grams of ground flint or of fine sand to 
 the melted mass : effervescence is produced slowly, due to the 
 escape of carbonic anhydride, and the silica is gradually dis- 
 solved. When the decomposition is over, pour out the mass on 
 a stone slab, and after it has cooled let it digest in water : most 
 of it will dissolve, with the exception of some impurities, such as 
 oxide of iron. 
 
 The solution thus obtained consists of a mixture of sili- 
 cates of potash end soda, with a large excess of the alkalies. 
 
 A smaller proportion of alkali might have been used, but 
 it would have required a stronger heat to melt the silicate, 
 and the product would have been less easily soluble. 
 
 Exp, 183. Add gradually to a portion of this solution dilute 
 hydrochloric acid in excess : the mass becomes partly or wholly 
 redissolved, but on evaporating it the silica separates at first 
 as a jelly-like hydrate, and this, by further drying, becomes con- 
 verted into a white earthy-looking powder, no longer soluble in 
 acids. Wash the dry mass with water as long as anything is 
 dissolved; the soluble chlorides may thus readily be removed, 
 leaving silica in a nearly pure state, in the amorphous form. 
 
 Exp. 184. Heat some common flints to redness in the fire, 
 and suddenly quench them in water : they become very friable, 
 and are easily reduced to a fine powder. Heat this, add hydro- 
 chlorijc acid, and wash thoroughly, and the result is nearly pure 
 silica. 
 
 Exp. 185. To another portion of the solution of silica in the 
 alkalies add hydrochloric acid in excess, so as to redissolve the 
 
1 70 The Silicates. 
 
 whole. Place the clear solution in a shallow tray formed by 
 tying a piece of parchment paper over a hoop of wood or of 
 gutta percha, 10 or 12 cm. in diameter, and float this little 
 vessel in a dish of water. The acid and saline substances are 
 separated by dialysis from the silica, and pass out into the 
 water. If the water in the dish be changed twice a day, the 
 liquid left in the hoop will, in three or four days' time, be found 
 to consist of a solution of pure silica in water, and may be 
 further concentrated by cautious evaporation. 
 
 In this experiment the parchment paper, or dialyser, retains 
 the colloid, or gelatinous form of silica, while it allows the 
 crystalline and acid particles to pass through its pores into 
 the water on the other side. 
 
 The solution of silica is tasteless, limpid, and colourless ; 
 but if the evaporation be carried too far, the silica separates 
 in the form of a jelly. 
 
 Finely divided silica may be gradually dissolved by boil- 
 ing it with the alkalies or their carbonates, and even flints in 
 their unground condition may be dissolved in strong solu- 
 tions of caustic alkali if the solution be digested upon 
 them under pressure. The Geysers, or hot springs of Ice- 
 land, contain large quantities of silica dissolved, and as the 
 liquid cools deposit a considerable portion upon objects 
 exposed in the stream. They are then often said to be 
 ' petrified,' or converted into stone, the silica being deposited 
 in the interstices, and preserving the appearance of the 
 original structure. 
 
 (39) Silicates : Glass. The silicates are very abundant 
 natural productions. Silica combines with bases in several 
 different proportions, and forms a great variety of crystal- 
 lised minerals, many of which are double silicates of complex 
 nature. 
 
 Glass consists of a mixture of several silicates, which, when 
 heated to a particular temperature, are plastic and viscous, 
 and retain their transparency on cooling. The nature and 
 proportions of the silicates present are made to vary accord- 
 ing to the use to which the glass is to be applied. The degree 
 
Varieties of Glass. 171 
 
 of fusibility of the silicates varies widely. Fire-clay, or alumina 
 silicate (A1 2 O 3 , 2SiO 2 ), is nearly infusible in the furnace, 
 and it is the material of which fire-bricks and crucibles are 
 made. Calcic silicate is also very infusible, whereas the 
 ferrous silicate (FeO, 2SiO 2 ) constitutes the 'bull-dog' or 
 fusible slag, of iron refiners. Lead silicate (2PbO, 3SiO 2 ) is 
 still more fusible, and furnishes a clear yellowish glass. The 
 silicates of potash and soda are also very fusible. All these 
 silicates, when mixed with each other, melt at much lower 
 temperatures than they do when separate. Many of them, 
 when thus melted, possess the exceptional property of 
 viscosity, between the point of perfect liquidity and solidifi- 
 cation. It is this viscous condition which enables glass to 
 be moulded into the countless forms required for art or 
 luxury. Good glass also has the valuable property of not 
 crystallising as it cools ; in certain cases some of the silicates, 
 however, do crystallise out, and then the glass becomes 
 opaque, and though the separate silicates of which it con- 
 sists are more or less readily attacked by water and acids, if 
 the proportions of the mixture are properly selected, glass 
 formed from these silicates is no longer soluble. The 
 different varieties of glass are not to be regarded as definite 
 compounds, but as mixtures in varying proportions of their 
 component silicates, which, however, in the best kinds 
 generally approach some simple atomic proportions. 
 
 Much care is requisite in selecting the materials for the 
 finer kinds of glass. Potash is preferred to soda, because 
 the glass made from soda has a bluish green tinge. Soda 
 gives a more fusible glass. The addition of lime increases 
 its hardness and lustre, but diminishes its fusibility. An 
 excess of lime is apt to make it milky-looking. 
 
 i. Window glass, or crown glass, is made of a mixture of 
 silicates of soda and lime. 100 parts of pure white sand, 35 or 
 40 of chalk, 30 of soda ash, and from 50 to 150 of broken glass, 
 or culletj are the proportions often used. The mixture is 
 heated gradually, to prevent it from frothing up, and is after 
 
172 Properties of Glass. 
 
 wards raised to a very intense heat. Plate glass contains the 
 same materials in different proportions. 2. Bottle glass 
 contains a smaller proportion of silica than either window or 
 plate glass, and is made of much coarser materials. It con- 
 sists of a mixture of silicates of soda, lime, alumina, and 
 iron. 3. Bohemian glass, which is very hard and infusible, 
 is a mixture of silicates of potash and lime. It is used for 
 making the combustion tubes employed in the analysis of or- 
 ganic substances, and hence is much prized in the laboratory. 
 4. The ordinary white, or flint glass, consists almost entirely 
 of silicates of potassium and lead. The proportions of ma- 
 terials used are 300 of fine sand, 200 of red lead, 100 of 
 refined pearlash, and about 30 parts of nitre. The oxide of 
 lead renders the glass much heavier and more fusible, giving 
 it a higher refractive and dispersive power upon light, and 
 greater brilliancy, but it makes it softer and more easily 
 tarnished, and it is also liable to be corroded by alkaline 
 solutions. 
 
 Glass, when melted, dissolves many of the metallic oxides 
 without losing its transparency, but becomes coloured with 
 tints varying according to the metallic oxide employed. 
 Cobalt gives a splendid sapphire blue, manganese a violet, 
 uranium a yellow, ferrous oxide a green, ferric oxide a 
 yellow or reddish-brown, cupric oxide a green, and cupreous 
 oxide a ruby-red. 
 
 Well-made glass is not acted on by any acid or mixture 
 of acids, except the hydrofluoric, which last removes its 
 silica ; but it is not quite insoluble. If left long in water, 
 or buried in moist earth, it becomes slowly decomposed. 
 This is often seen in wine-bottles, which exhibit the brilliant 
 colours of thin plates, due to the scaling off from the surface 
 of flakes detached by slow chemical action of moisture. 
 
 Exp. 1 86. Grind a little glass to a fine powder in a mortar ; 
 place it on a piece of moistened turmeric paper : sufficient 
 alkali will be dissolved by the water to tinge the turmeric 
 brown. 
 
Compounds of Silicon. 173 
 
 If glass articles are allowed to cool rapidly by exposing 
 them while red hot to the air, they become inconveniently 
 brittle. The outer surface becomes solid, whilst the inner 
 portion remains dilated by the heat : as the mass cools, the 
 particles within, by their adhesion to the external solid por- 
 tion, are still held in their dilated state. A very slight force, 
 such as a scratch on the surface, or the change of tem- 
 perature from a cold room to a warm one, will often cause 
 them to crack. In order to avoid this inconvenience, the 
 glass is annealed, or placed in a chamber heated nearly to 
 redness, where the material is allowed to cool very slowly, 
 by which means the particles are enabled to assume their 
 natural position with regard to each other. 
 
 Glass, however, is a bad conductor of heat, but dilates 
 considerably when heated, so that even after annealing it is 
 liable to crack when exposed to sudden changes of tem- 
 perature, such as that produced by pouring boiling water into 
 a cold glass, especially if it be thick. 
 
 Exp. 187. Take one of the drops of glass formed by allow- 
 ing melted glass to fall into water, and suddenly nip off the 
 tail : the glass flies to pieces with a kind of explosion, and is 
 reduced almost to powder. 
 
 Exp. 1 88. Grind 3 or 4 grams of fluor spar to fine powder, 
 and mix it with an equal weight of powdered glass or fine sand. 
 Introduce it into a Florence flask previously fitted with a sound 
 cork and a tube bent downwards for delivering gas. Pour upon 
 the mixture about 30 grams of oil of vitriol, insert the cork and 
 tube, and apply a gentle heat: a densely fuming gas is dis- 
 engaged, consisting of silicic fluoride. 
 
 The change that takes place may be thus represented 
 2 CaF 2 + 2 H 2 SO 4 + SiO 2 = SiF 4 + 2CaSO 4 4- 2H 2 O. 
 
 The gas (SiF 4 ) must not be inhaled, as it is very irritating, 
 and produces coughing. When dry, it is colourless and 
 transparent. Water produces a remarkable change in it. 
 
 Exp. 189. Pass the gas into a glass of water. Each bubble 
 as it rises becomes coated with a white opaque film, composed of 
 
1 74 Boron. 
 
 hydrated silica, while the liquid becomes intensely acid, from the 
 formation of a new acid (the hydrofluosilicic), water being de- 
 composed at the same time 
 
 3SiF 4 + 2H 3 O = SiO, + 2(2HF, SiF 4 ). 
 
 It is owing to the strong tendency to the formation of 
 silicic fluoride that hydrofluoric acid corrodes glass so 
 rapidly. 
 
 Silicon also forms a compound with chlorine (SiCl 4 ), and 
 with bromine (SiBr 4 ), both of which are volatile liquids 
 which are decomposed by water. A remarkable gaseous 
 compound with hydrogen (SiH 4 ) is also known. It takes 
 fire as soon as it escapes into the air, and may be procured, 
 mixed with hydrogen, by decomposing a compound of 
 silicon and magnesium by means of hydrochloric acid. 
 
 Silicon belongs to the group of tetrad elements : it has 
 certain points of resemblance with the rare substances 
 titanium and zirconium on the one hand, and with carbon 
 on the other. All these elements form volatile compounds 
 with four atoms of chlorine (CC1 4 , SiCl 4 , TiCl 4 , ZrCl 4 ). 
 These chlorides are colourless liquids, except zirconic 
 chloride, which is solid. 
 
 (39 a] BORON: Symb. B; Atom. Wt. n. 
 
 This is the characteristic element in boracic acid, which 
 enters into the formation of borax, the sodium salt of this 
 acid. It is an olive-brown powder, which may be obtained 
 by fusing 5 parts of boracic acid with 3 of sodium in a 
 covered iron crucible, previously made red hot, covering the 
 mixture with three parts of common salt, previously fused, 
 and broken into coarse powder. An intense action occurs, 
 and the mass becomes melted. It is to be poured in this 
 red-hot condition into a large and deep vessel containing 
 water acidulated with hydrochloric acid. The boron re- 
 mains undissolved. By fusing it with aluminum, in which 
 metal it is dissolved, boron has als) been obtained in 
 crystals, which are transparent, and nearly as hard as 
 
Properties of Borax. 175 
 
 diamond. This element is remarkable for its power of 
 combining directly with nitrogen when heated in the gas, 
 forming a grey powder. When heated with chlorine it 
 burns freely, and combines with it, furnishing a gas (BC1 3 ), 
 which is immediately decomposed by water into boracic and 
 hydrochloric acids 
 
 2 BC1 3 + 4H 2 O = 6HC1 + 2HBO 2 . 
 
 Boracic Anhydride (Symb. B 2 O 3 ) is the only known oxide 
 of boron. It combines with water, and then forms boracic 
 acid, which crystallises in white, pearly-looking scales 
 (HBO 2 , H 2 O) ; for 
 
 B 2 3 + 3 H 2 = 2 (HB0 2 H 2 O). 
 
 The most abundant source of boracic acid is the district 
 called the Maremma, in Tuscany, where it occurs in the un- 
 combined state. It issues in small quantities in the jets of 
 steam called sqffioni, which are produced by volcanic heat. 
 These jets are directed into basins formed of brickwork and 
 filled with water, when the steam is condensed, and a weak 
 solution of boracic acid obtained. This solution is con- 
 centrated in shallow pans by the heat of the jets of steam 
 themselves, directed beneath them, and the acid is finally 
 crystallised out on cooling. 
 
 Borax (Na 2 O, 2B 2 O 3 , ioH 2 O) is the most important salt 
 of the acid. It is a natural production obtained by the 
 drying up of certain lakes of Thibet, and it has lately been 
 found in California and in some other localities. The crude 
 Indian borax is called tincal. Borax is used as a flux in 
 soldering, as it dissolves most metallic oxides and leaves a 
 clean surface of the metal : it is often added to enamels, for 
 the purpose of rendering them more fusible, and is used by 
 the refiner in melting gold and silver, for making his cru- 
 cibles Jess porous, and for rendering the collection of the 
 metal more easy. 
 
 Exp. 190. Bend the end of a piece of thin platinum wire, 8 
 or 10 cm. long, into a small hook; heat the wire to redness, and 
 
1 76 Boracic A cid. 
 
 instantly touch a crystal of borax as large as a split pea with the 
 wire : it will adhere to the wire. Then introduce the wire and 
 crystal into the flame of a spirit lamp. The borax will swell 
 up, become opaque and white, and will then melt into a clear 
 glassy bead. 
 
 Borax dissolves many metallic oxides when melted with 
 them, and hence is often used as a test before the blow- 
 pipe (Fig. 66). 
 
 Exp. 191. Touch the bead just made with a wire moistened 
 with a solution of cobalt nitrate. Then melt the borax again 
 in the flame. A beautiful blue bead is obtained, which is 
 almost opaque if the quantity of cobalt be considerable. If a 
 scarcely visible fragment of manganese oxide be used, a purplish 
 bead is obtained. 
 
 Boracic acid is easily obtained from borax. 
 
 Exp. 192. Dissolve 40 grams of borax in about 4 times its 
 weight of boiling water; add to the hot solution 10 grams of 
 oil of vitriol, previously mixed with its own bulk of water. Sodic 
 sulphate is formed, and remains in solution, while pearly crystals 
 of boracic acid are deposited as the liquid cools. Pour off the 
 solution, dry the crystals by pressure between pieces of blotting- 
 paper. Place a few of them on a slip of platinum foil, and heat 
 them in the flame of a spirit lamp. Water is driven off, and the 
 anhydride which is left melts into a clear glass. 
 
 Exp. 193. Dissolve a few crystals of the boracic acid in a 
 small dish with a teaspoonful of alcohol. Set fire to the spirit: 
 it burns with a green flame, which is a good test for boracic 
 acid. A similar green flame is obtained if a crystal of borax be 
 moistened with sulphuric acid and alcohol added, and kindled 
 as before. 
 
 This green flame, when seen in the spectroscope, contains 
 a series of peculiar green bands. 
 
 Boron forms with fluorine a gaseous trifluoride (BF1 3 ), 
 which is easily obtained by heating boracic anhydride with 
 twice its weight of powdered fluor spar to redness in an 
 iron tube. 
 
 Boron belongs to the class of triad elements, but in many 
 properties it resembles silicon more than any other element. 
 
CHAPTER X. 
 
 COAL GAS, AND OTHER COMPOUNDS OF CARBON. 
 
 (40) The two elements carbon and hydrogen furnish by 
 their union a very numerous series of compounds, of which 
 some are gaseous, some liquid, and some solid. They have 
 received the general name of hydrocarbons ; but the full 
 study of these remarkable substances belongs to the division 
 of chemical science known as organic chemistry, since they 
 are, practically, always derived from the decomposition of 
 bodies of organic origin. 
 
 Many of these bodies consist of absolutely identical pro- 
 portions of the two elements, though they differ widely in 
 properties. When compared together in their gaseous state 
 they differ in density, so that the number of atoms of the 
 elements in the molecule of these compounds must be 
 different, although on analysis they yield the same propor- 
 tions of each element. Let us take, for instance, a few of the 
 many compounds of which 100 parts consist, of 8571 of 
 carbon and 14*29 of hydrogen : 
 
 11*19 litres of olefiant gas (C a H 4 ) weigh 14 grams 
 
 oil gas (C 4 H 8 ) 28 
 naphthene (C 8 H l6 ) 56 
 
 cetylene (C J6 H 3Z ) ,,112 
 
 The density of oil gas is double that of olefiant gas ; whilst 
 that of naphthene is double that of oil gas, and cetylene is 
 double that of naphthene. Such bodies are said to be 
 polymeric. 
 
 OLEFIANT GAS (or Ethylene) : Symb. C 2 H 4 ; Atom, and 
 Mol. Wt. 28; Sp. Gr. 0-978; ReL Wt. 14. 
 
 Exp. 194. Introduce into a retort which will hold a litre 30 
 c. c. of alcohol and 60 c. c. of oil of vitriol. Heat the mixture, and 
 collect the gas over water ; continuing the experiment until the 
 mass blackens and swells up considerably. The gas consists at 
 first chiefly of olefiant gas, mixed with ether vapour; but towards 
 the end it becomes mingled with sulphurous anhydride. 
 
 N 
 
178 Olefiant Gas. 
 
 The production of olefiant gas is due to the removal of 
 the elements of water from the alcohol by the action of the 
 acid. This occurs in two stages; in the first of which 
 ethylsulphuric acid is formed, and in the second stage this 
 body is decomposed 
 
 Alcohol Sulph. Acid Ethylsulph. Acid Water 
 
 (1) C 2 H 6 O + H Z SO 4 = HC 2 H 5 S0 4 + H a O 
 And ethylsulphuric acid, when heated, is decomposed 
 
 (2) HC,H 5 S0 4 
 
 becoming olefiant gas (C 2 H 4 ) and sulphuric acid (H 2 SO 4 ). 
 
 Olefiant gas has no colour, but a faint sweetish smell, as of 
 garlic. It is but little soluble in water. Under great pres- 
 sures it may be liquefied, but has not been frozen. It is 
 combustible, but will not support life. 
 
 Exp. 195. Plunge a lighted taper into a small jar of the gas. 
 The taper will be extinguished, but the gas will burn at the 
 mouth of the jar with a bright smoky flame. 
 
 If mixed with three times its bulk of oxygen, it explodes 
 violently by the action of flame or of the electric spark. If 
 care be taken, the gas may be analysed by this means : steam 
 is formed and immediately condensed, the 4 volumes of the 
 mixture giving 2 volumes of carbonic anhydride 
 C 2 H 4 + 3 2 = 2C0 2 -i- 2H 2 0. 
 
 Exp. 196. Mix half a litre of the gas with the same quantity 
 of chlorine, and let the mixture stand over water : the two gases 
 combine slowly and form drops of a yellowish liquid, which col- 
 lect on the surface of the water, and sink to the bottom as 
 they increase in size. 
 
 The name ohfiant, or ' oil-maker,' gas was derived from 
 this circumstance, and the liquid itself, which was discovered 
 by some Dutch chemists, is called Dutch liquid (C 2 H 4 C1 2 ). 
 
 Exp. 197. Mix half a litre of olefiant gas in a tall jar with a 
 litre of chlorine, and, having closed the jar with a glass plate, 
 mix the gases by agitation ; then apply a light. The mixture 
 will burn quietly, with the formation of a dense black smoke. 
 
Marsh Gas. 1 79 
 
 The chlorine in this case combines with the hydrogen, 
 forming hydrochloric acid, while the whole of the carbon is 
 separated 
 
 C 2 H 4 +. 2C1 2 = 4HC1 + C 2 . 
 
 Olefiant gas is one of the substances found in coal gas, 
 and is among the gases given off when fats and rosin are 
 decomposed by heat. 
 
 MARSH GAS: Symb. CH 4 or Methyl Hydride (CU 3 , H) 
 Atom. andMol. Wt. 16; Sp. Gr. 0-55; ReL Wt. 8. 
 
 This is the simplest of the compounds of carbon with 
 hydrogen. It is easily obtained, in an impure state, mixed 
 with nitrogen and carbonic anhydride, by stirring the mud 
 of stagnant pools, when it rises in bubbles to the surface, as 
 a result of the decomposition of vegetable matter. It is also 
 abundant in coal gas, as it is one of the substances most 
 frequently produced by the distillation of organic matters at 
 a high temperature. It is this gas which escapes from the 
 seams of coal, and which, when mixed with air, fills the 
 workings of the mines with the inflammable material known 
 as fire-damp, and this gives rise to the disastrous explosions 
 which occur from time to time in our collieries. 
 
 Marsh gas may be obtained pure by distilling one of the 
 acetates with a hydrated alkaline base ; for example : 
 
 Sodic Acetate Sodic Hydrate Sodic Carb. Marsh Gas 
 
 NaC z H 3 O a + NaHO = Na a CO 3 + CH 4 . 
 Half the carbon remains behind as carbonate, with the 
 whole of the oxygen in combination with the base; while 
 the other half of the carbon unites with the whole of the 
 hydrogen to form marsh gas. 
 
 Marsh gas has neither colour, odour, nor taste. It does 
 not support life, but is not poisonous if breathed when 
 mixed with air. It is but very slightly soluble in water, and 
 has not been liquefied either by cold or pressure. It burns 
 with a yellowish flame. It requires twice its bulk of oxygen 
 for complete combustion, and then explodes with the forma- 
 
 N 2 
 
1 80 The Safety Lamp. 
 
 tion of its own bulk of carbonic anhydride, the steam which is 
 formed becoming immediately condensed, the three volumes 
 of gas before combustion becoming one afterwards 
 CH 4 + 20 2 = C0 2 + 2H 2 0. 
 
 If a mixture of about 10 volumes of air with i of marsh 
 gas be made, it will contain the quantity of oxygen necessary 
 for complete combustion, and will explode powerfully on 
 the approach of a light ; 8 volumes of nitrogen and i of 
 carbonic anhydride will be produced, while the steam will 
 be immediately condensed. Hence the after-damp, or air 
 left in a mine after an explosion has occurred, is entirely 
 unfit for the support of human life ; so that persons exposed 
 to its influence perish as surely as they do from the direct 
 effects of the flame. 
 
 Marsh gas, mixed with less than between two and three 
 times its bulk of air, does not explode on the application of 
 flame ; and, if diluted with more than 18 or 20 parts of air, it 
 only burns rapidly, but does not explode with sudden violence. 
 
 Sir H. Davy's safety lamp was contrived for the purpose 
 of preventing these calamitous explosions in mines. Marsh 
 gas requires a high temperature to set it on fire ; so that, to 
 kindle it, a substance must be not merely red hot, but nearly 
 white hot. 
 
 Exp. 198. Twist a piece of rather thick platinum wire 5 or 6 
 times round a thin glass rod, so as to form a coil at one end of 
 the wire ; hold this coil in the flame of a spirit lamp until it is red 
 hot, then instantly place it in a jet of coal gas which is not burn- 
 ing, but is allowed to escape into the air. The wire will continue 
 to glow without kindling the gas. 
 
 Exp. 199. Place a sheet of iron or copper wire gauze, con- 
 taining about ico meshes in a square centimetre, over the flame 
 of a spirit lamp : the flame will not pass through the gauze, owing 
 to its being cooled down below its inflaming point. A piece of 
 coarse gauze containing from 4 to 9 meshes in the sq. centim. 
 will not prevent the flame from passing through. 
 
 Sir H. Davy's safety lamp is merely an oil lamp, enclosed 
 
Nature of Flame. 1 8 1 
 
 within a cylinder of fine wire gauze provided with a double 
 top, and with a crooked wire passing up through the body 
 of the lamp to trim the wick. When such a lamp is intro- 
 duced into an atmosphere containing fire-damp, the flame is 
 seen to enlarge until, when the proportion of marsh gas 
 becomes large, it burns on the inner surface of the cylinder. 
 Whenever this pale enlarged flame is seen, the miner must 
 withdraw; for though no explosion can occur while the 
 gauze is sound, yet the metal at that high temperature 
 becomes corroded, and might easily break into holes, and a 
 single large hole would be sufficient to cause an explosion. 
 
 Flame is never produced by a burning body, unless that 
 body is converted into vapour before it burns ; charcoal and 
 iron, for instance, are not volatile, and they do not burn 
 with flame ; but phosphorus, sulphur, and zinc, all of which 
 are volatilised before they take fire, burn with flame. Flame 
 is hollow, and contains unburned combustible matter within, 
 forming in fact a sort of luminous bubble. 
 
 Exp. 200. Support one end of a glass tube, 12 or 14. cm. 
 long and 6 or 8 mm. in diameter, just above the wick in the 
 flame of a lighted candle. Vapours will pass up the tube, and 
 may be burned at the other end. 
 
 The light and heat of flames are not proportioned to each 
 other. The oxyhydrogen jet is the hottest flame known, 
 but it gives out scarcely any light. If, however, a little solid 
 matter, such as a piece of lime or the stem of a tobacco- 
 pipe, be introduced, the light becomes very intense, although 
 the effect of these solids is to lower the temperature of the 
 flame. At high temperatures a solid body, when heated, 
 even though it does not burn, gives out light. At first the 
 light is dull red; as the heat increases it becomes yellow, 
 then full white, and, when extremely intense, it has a tinge of 
 violet. All our common luminous flames contain carbon in 
 the solid state, which, when heated strongly, gives out light. 
 
 Exp. 201. Place a cold saucer in a jet of b'urning coal gas : 
 it is quickly covered with soot. Do the same in a candle flame : 
 
182 
 
 Structure of Flame. 
 
 the saucer is blackened. Try the experiment with the scarcely 
 luminous flame of a spirit lamp : no soot is formed. 
 
 The deposit of soot is occasioned by the decomposition 
 of olefiant gas and marsh gas under the influence of a high 
 temperature ; hydrogen is partially separated from the carbon, 
 and, being more inflammable, burns first, heating the carbon 
 intensely. If the carbon reach the oxygen of the air at this 
 high temperature, it burns away also ; but the cold surface 
 cools it before it enters into combination, and so it is deposited. 
 Exp. 202. Kindle a common Argand gas-burner and place 
 a glass chimney over it. Observe the strong light it gives out. 
 Remove the chimney, blow out the flame, replace the chimney, 
 covering the upper end with a cap of fine wire gauze; then 
 kindle the gas above the gauze. The gas will have become 
 mixed with air ; it will burn quietly above the gauze, but will not 
 give out light, nor will it smoke a cold saucer. 
 
 The air burns the carbon and hydrogen together before 
 they can separate. What is called Bunsen's burner acts upon 
 
 a similar principle ; it con- 
 Flg - 6 * sists of a jet of gas (a, 
 Fig. 63), which is sur- 
 rounded by a tube of metal 
 (c\ at the bottom of which 
 are openings for the admis- 
 sion of air (b); the gas 
 passes up the tube, and 
 becomes mixed with the air 
 which enters at the open- 
 ings near the bottom, and 
 it burns without smoke 
 when kindled at the top. 
 A sufficient supply of gas must be kept 
 up, or else the flame will recede into 
 the tube, and the gas will burn at the bottom. 
 
 The structure of flame may be examined easily in the 
 flame of a candle. It will be seen to consist of several 
 distinct portions, as shown in Fig. 64. 
 
The Blowpipe. 
 
 183 
 
 Fig. 65. 
 
 The flame is maintained by the decomposition of the 
 melted wax or tallow which rises in the wick, where it is 
 converted into gases by the heat. At the lower part of the 
 flame these gases become at once mixed with atmospheric 
 air, no separation of carbon occurs, and they burn with a 
 pale blue light at a. The greater part of the combustible 
 vapours are still unburned ; they rise above the wick, and 
 form the central dark part of the flame b. Here they are 
 decomposed by the heat produced by the combustion of the 
 parts below. This heat causes the separation of solid par- 
 ticles of carbon, which become intensely hot, and give out 
 light chiefly in the part marked c. This carbon itself burns 
 away gradually as it rises to the surface of the flame, where 
 it meets with fresh oxygen, and disappears 
 in the form of transparent carbonic anhy- 
 dride d. 
 
 By directing a jet of air into a flame the 
 combustion may be rendered more active, and may 
 be concentrated into a small space, so as to afford a 
 very high temperature. It is upon this principle that 
 that very useful instrument the mouth blow-pipe 
 acts. Fig. 65 shows a convenient form of it. If by 
 its means a current of air be directed horizontally 
 across the flame a little above the wick, the flame loses 
 its brilliancy, and is thrown to one side in the form of 
 a beautiful pointed cone (Fig. 66), in which three dis- 
 tinct parts are visible. In the centre is a well-marked 
 blue cone ending at a ; outside this is a whiter and 
 more luminous cone, and again outside this brilliant 
 cone, which ends at b, is a third pale yellow flame c. 
 The different parts of the flame vary in the effects which they 
 produce ; the blue cone is produced by the complete com 
 bustion of part of the vapour in the excess of oxygen 
 supplied by the jet of air to that part of the flame. Beyond 
 this the combustible vapour continually rising from the 
 wick forms the luminous portion, which is, very hot, and froia 
 
1 84 Use of the Blowpipe. 
 
 its containing an excess of combustible matter, is ready to 
 take oxygen from any substance which is exposed to it. It 
 is called the reducing flame. At the outer point of the flame 
 the effects are reversed ; atmospheric oxygen is carried for- 
 
 Fig. 66. 
 
 ward by the jet of flame, and becomes heated by it, so that 
 an oxidising action occurs : if a fragment of a metal be ex- 
 posed to the action of this part of the flame, it will be con- 
 verted into oxide. 
 
 Exp. 203. Introduce a small piece of common flint glass 
 tube into the reducing flame, between a and b (Fig. 66), obtained 
 by blowing gently through a candle flame. The glass will be- 
 come opaque and black, because the lead will be reduced from 
 the transparent form of oxide to the opaque condition of metal. 
 When this has happened, place the black portion just in front of 
 the oxidating flame at c. The discolouration will slowly dis- 
 appear, and the lead will recombine with oxygen from the air, 
 and again become transparent. 
 
 In skilful hands the blowpipe enables the observer to 
 obtain quickly results of great value. Many compounds, 
 when heated on a piece of charcoal in the reducing flame, 
 immediately yield up their metallic basis ; and by the colour 
 of the little bead, and its malleability or brittleness, it may 
 easily be known what metal is present. 
 
 Sometimes when the body does not yield a metal readily, a 
 platinum wire, d (Fig. 66), bent into a hook at one end, forms 
 a convenient support for the substance, which should not 
 exceed a mustard seed in bulk. It will easily be ascertained 
 whether the substance melts ; whether it yields a transparent 
 an opaque, or a coloured bead ; whether it changes the 
 
Manufacture of Coal Gas. 185 
 
 colour of the flame, and whether the effect of the reducing 
 flame differs from that of the oxidating flame upon the body 
 under examination. 
 
 A little borax or phosphate of sodium and ammonium, 
 commonly called microcosmic salt, sometimes assists the 
 examination. 
 
 When the substance is placed on charcoal sodic carbonate 
 furnishes a flux which is often very useful. 
 
 Exp. 204. Select a small stick of charcoal, and with the 
 point of a knife make a small cavity of the size of a split pea 
 upon the side near one end. Put a little white lead in the cavity, 
 and heat it before the blowpipe in the reducing flame. A little 
 bead of lead will easily be obtained, surrounded by a border of 
 yellow lead oxide. The lead will flatten under the hammer. 
 
 Exp. 205. Place in a cavity in another piece of charcoal a 
 small fragment of copper oxide, with about its own bulk of sodic 
 carbonate. The metal will require a stronger heat, but may 
 be reduced in like manner. If the little bead be placed between 
 two folds of paper it may be flattened with the hammer, and 
 will show the red colour of copper. 
 
 Coal gas. Certain kinds of coal, such as cannel coal and 
 the bituminiferous house coal used in London, when heated, 
 undergo decomposition, their constituents rearrange them- 
 selves in new forms, and give out a large quantity of gas, 
 which burns with brilliant jets of flame. If such coal, instead 
 of being allowed to burn in the open fire, is heated out of 
 the air in iron or clay retorts provided with an escape-tube, 
 a large quantity of gas may be collected, and may be used 
 for illuminating or heating purposes. This is the common 
 process of making coal gas. The products obtained by 
 heating coal in this manner are very numerous. The solid 
 residue in the retort, after the volatile matters have been 
 driven off, constitutes ' gas coke.' Among the volatile 
 matters are water, along with which condense the sulphide 
 and carbonate of ammonium ; besides this there is a dense 
 black offensive viscid liquid, known as coal tar, which is a 
 
1 86 Analysis of Coal. 
 
 very complex mixture, chiefly consisting of hydrocarbons and 
 carbolic acid ; some portions of these hydrocarbons supply 
 the material from which aniline, the basis of most of the coal- 
 tar dyes, is procured. The gaseous products are also very 
 numerous ; among them are defiant gas, and some other 
 gases of greater density, but of a similar character, which 
 furnish the most important illuminating constituents ; marsh 
 gas, hydrogen, and carbonic oxide are also present; but 
 they have little illuminating power. There are also small 
 quantities of sulphuretted hydrogen, carbonic anhydride, 
 cyanogen, and carbon disulphide, all of which it is the 
 object of the gas-maker to remove. This is done by pass- 
 ing the gas over hydrated ferric oxide and slaked lime ; the 
 iron oxide removes the sulphuretted hydrogen and cyanogen, 
 while the carbonic anhydride is stopped by the lime. The 
 gas, when thus purified, is washed with water to get rid of 
 small quantities of ammonia, and is afterwards stored up in 
 vast iron reservoirs or gas-holders, from which it is dis- 
 tributed for consumption. 
 
 The removal of the sulphur compounds is especially neces- 
 sary ; because, when burned, they furnish sulphurous and 
 sulphuric acids, which are very injurious to furniture, books, 
 and paintings exposed to their action. The other materials 
 furnish only water and carbonic anhydride, when burned 
 with a sufficient supply of air. 
 
 Coal gas has a peculiar offensive odour, due in part to a 
 compound of carbon and hydrogen called acetylene (C 2 H 2 ). 
 If coal gas escape into the atmosphere, it forms an explosive 
 mixture. Hence, if a smell of gas be perceived in a room, 
 no light must be admitted ; the supply of gas should be at 
 once shut off from the main, and the doors and windows 
 thrown open to ventilate the house or the room. After- 
 wards the cause of the escape may be sought. 
 
 Exp. 206. Place 1 5 or 20 grams of coal in small fragments 
 in a tube of Bohemian glass, a (Fig. 67), 18 or 20 centimetres 
 long, and sealed at one end ; to the other end fit a good cork, 
 
Destructive Distillation of Coal. 187 
 
 through which passes a quill tube bent at a right angle, and 
 fitted into a phial (<). In one limb of the bent tube (c) place a 
 piece of reddened litmus paper; in the other (a?), a piece of 
 filtering-paper moistened with a solution of lead acetate. Place 
 a little limewater in the test-tube *?, and collect the gas which 
 comes over in a gas jar (/) provided with a stop-cock. Heat 
 the tube a gradually by placing it in a tray of coarse wire 
 gauze, and surrounding it with lighted charcoal ; let it rise to 
 
 Fig. 67. 
 
 dull redness. Tar will become condensed, mixed with water 
 in b, the red litmus in c will become blue from the ammonia, the 
 lead salt will be blackened by the sulphuretted hydrogen, the lime- 
 water rendered milky by the carbonic acid, while an inflammable 
 gas will be collected in the jar, and may be burned by transferring 
 the jar to the deep part of the trough, depressing it in the water, 
 and 'lighting the gas as it escapes on gradually opening the stop- 
 cock. Coke will be left in the glass tube. 
 
 Exp, 207. Hold a cold wide glass tube, of a metre or more 
 in length, over a jet of burning coal gas : moisture will speedily 
 become condensed on the cold sides of the tube, owing to the 
 formation of water by the burning of the hydrogen. 
 
 Exp. 208. Pour a little limewater into the tube, having closed 
 one end with the hand after withdrawing it from the flame : the 
 limewater will become turbid by absorbing carbonic acid. 
 
 A single jet of coal gas, consuming about 136 litres 
 (5 cubic feet) of gas per hour, will produce nearly a quarter 
 of a litre of water as it burns. 
 
1 88 Cyanogen. 
 
 (41) CYANOGEN: Symb. Cn or Cy; Rel and Atom, Wt. 
 26; Mol. Wt. 52; Mol. Vol. [~y"|, Cy 2 ; S/. Gr. r8o6. 
 
 This is the name given to the compound which carbon 
 forms with nitrogen, the ' blue producer,' owing to its being 
 the characteristic component of Prussian blue. The two 
 elements do not combine directly ; but if nitrogen gas be 
 passed over a red-hot mixture of charcoal and potassic car- 
 bonate, the carbon and nitrogen unite with the potassium, 
 while carbonic oxide escapes 
 
 K 2 CO 3 + 4 C + N 2 = 2 KCN + 3 CO. 
 
 Cyanogen is always one of the products obtained, in small 
 quantities, during the distillation of pit coal ; but its com- 
 pounds are usually obtained from the cyanide of iron and 
 potassium, which crystallises in large yellow tables, and is 
 known as potassic ferrocyanide or prussiate of potash 
 (K 4 FeCy 6 , 3 H 2 0). 
 
 This salt is prepared by heating to dull redness, in a covered 
 iron pot, about 5 parts of parings of horns, hides, hoofs, or 
 other animal refuse, with 2 parts of pearlash and iron filings. 
 The nitrogen and carbon combine at the high temperature, 
 and unite with the iron and a portion of reduced potassium. 
 
 If this salt be dissolved in water and distilled with diluted 
 sulphuric acid, the intensely poisonous prussic or hydro- 
 cyanic acid comes over, and the distilled liquid, if saturated 
 with mercuric oxide, furnishes mercuric cyanide (HgCy 2 ); 
 which, if thoroughly dried, and heated in a test-tube, becomes 
 decomposed into metallic mercury and cyanogen gas 
 HgCy 2 = Hg + Cy 2 . 
 
 Cyanogen is a transparent, colourless gas, with a peculiar 
 penetrating odour. It is very poisonous, and is combustible. 
 If a jet of the gas be kindled, it burns with a characteristic 
 rose-edged purple flame. It is soluble in water and in 
 alcohol. 
 
 The peculiar character of cyanogen is its property, though 
 a compound, of combining with the metals like one of the 
 
Hydrocyanic Acid. 189 
 
 halogens. Potassium when heated in the gas combines 
 with it, and forms potassic' cyanide. This circumstance has 
 given rise to the theory Qi compound radicals? now so exten- 
 sively applied in organic chemistry, cyanogen being the first 
 of these radicals which was obtained. 
 
 Cyanogen forms with hydrogen an acid compound the 
 intensely poisonous hydrocyanic acid (HCy), which, however, 
 cannot be obtained by the direct union of its components. 
 The vapour of this acid contains one volume of hydrogen 
 and one of cyanogen, united without condensation, as in the 
 case of hydrochloric acid, and the hydrogen acids of the 
 other halogens. It is a very volatile liquid, which boils at 
 26-5 C. ; but on account of its poisonous character, it is 
 rarely prepared in a pure state. The vapour is inflammable, 
 and burns with a whiter flame than that of cyanogen, which 
 it resembles in appearance. 
 
 In a diluted state it is obtained by distilling a solution of 
 the cyanide or of the ferrocyanide of potassium with diluted 
 sulphuric acid, taking care that the vapours are carried away 
 at once by a brisk current of air 
 
 KCy + H 2 S0 4 = HCy + KHSO 4 . 
 
 It is better not to make these experiments without the aid of 
 some person of experience. 
 
 The solution of this acid has an odour resembling that of 
 peach-blossoms. Its acid properties are feeble ; it does not 
 neutralise potash perfectly, but dissolves mercuric oxide very 
 readily ; and it gives a white precipitate of argentic cyanide 
 (AgCy) when mixed with a solution of argentic nitrate. A 
 good test of the acid is to add a slight excess of potash, and 
 then a mixture of ferrous and ferric sulphate. A mixed pre- 
 cipitate of ferrous and ferric oxide is thus formed j and this, 
 
 * By the term radical is meant any substance which by uniting with 
 a metal forms a salt, or with hydrogen forms an acid. In NaCl or 
 common salt, chlorine is the simple radical ; in HNO 3 or nitric acid, 
 NO; or nitrion is the compound radical. So in KCN or potassic 
 cyanide, CN is the compound radical. 
 
190 Compounds of Cyanogen. 
 
 on adding hydrochloric acid in slight excess, to redissolve 
 
 the excess of oxides of iron, leaves Prussian blue (Fe 4 , 
 
 Fe 3 Cy l8 ) 
 
 iSKCy + 2FeO, 3Fe 2 O 3 + iSHCl + 9H 2 O + Fe 4 Fe 3 Cy l8 . 
 
 Hydrocyanic acid, mixed with a peculiar essential oil, is 
 obtained by distillation from the kernels of the bitter almond, 
 and many kinds of stone fruit, after they have been crushed 
 and mixed with water. The juice of the tapioca plant also 
 contains it. It is also present in the water distilled off the 
 leaves of the laurel, the peach, and several other shrubs. 
 
 Many cyanides of the common metals are insoluble in 
 water, but are readily dissolved by solutions of the cyanide 
 of potassium or of sodium. The double cyanides thus 
 obtained are numerous, and some of them very remarkable. 
 The simple cyanides are intensely poisonous, and require 
 great care in experimenting with them. 
 
 Exp. 209. Dissolve 3 or 4 decigrams of potassic cyanide in 
 about ten times their weight of water. Add a few drops to a small 
 quantity of a solution of argentic nitrate in a test-tube. At first a 
 copious white precipitate of argentic chloride will be formed 
 
 KCy + AgNO 3 = AgCy + KNO 3 , 
 
 and on further additions of the cyanide the precipitate will be 
 gradually dissolved, AgCy, KCy being formed. 
 
 Exp. 210. Melt 2 grams of potassic cyanide in a small iron 
 spoon, and add a little litharge till the salt becomes slightly 
 yellow. A bead of metallic lead will be formed, and the cyanide 
 will have become converted into cyanate 
 
 PbO + KCy = Pb + KCyO. 
 
 Potassic cyanide, in consequence of this tendency to 
 absorb oxygen, is often used to reduce the metals from their 
 oxides as a test in the laboratory. 
 
 Cyanogen forms a large number of other important com- 
 pounds, but they are properly to be studied among the 
 products of organic chemistry. 
 
 (42) The Atomic theory. In the foregoing pages the 
 terms atom, atomic weight, and molecule have been frequently 
 
The Atomic Theory. 191 
 
 used. It will be necessary now to consider more exactly 
 what these expressions mean. 
 
 Chemists assume that though every visible fragment of 
 any elementary body admits of further division into a vast 
 multitude of minute particles, there is a limit beyond 
 which this process of subdivision cannot be carried by any 
 known method, whether chemical or mechanical. These 
 ultimate or indivisible particles are what are called the 
 atoms of the element. No one has ever seen an atom, 
 since such bodies are far more minute than the smallest 
 fragments visible by the aid of our strongest magnifying 
 glasses. The atoms of any particular element are further 
 supposed to be exactly equal to each other in size and in 
 weight; and when at the same temperature, to be abso- 
 lutely similar one to another in all respects. But the atoms 
 of any single element differ from those of all the other 
 elements in chemical properties as well as in weight. 
 Further, whenever chemical combination takes place be- 
 tween any two chemical elements, it is assumed that union 
 occurs between their separate atoms. This chemical union 
 is far more intimate than that effected by the force of co- 
 hesion which forms them into solids, still more than that 
 mechanical mixture by which they are converted into masses 
 or heaps of powder ; and the difference between combination 
 and mechanical mixture is that the atoms, being in the case 
 of true combination held together by chemical force, cannot 
 be separated by mechanical means ; while such separation 
 is practicable more or less completely when the two bodies 
 are merely mixed mechanically, and therefore imperfectly, 
 and often more or less irregularly. 
 
 These assumptions as to the atomic constitution of matter 
 have been made with a view of explaining the quantitative 
 laws which regulate chemical combination. This theory 
 of the finite and definite divisibility of matter, or divisibility 
 of matter down to a fixed limit, is in fact the only one 
 hitherto conceived by which union in definite proportion is 
 
1 92 Law of Definite and Multiple Proportions, &c. 
 
 accounted for ; and if these suppositions be admitted, the 
 known laws of chemical combination follow from them as a 
 matter of necessity. 
 
 These laws are as follow : 
 
 1. The law of definite proportions. Whenever such com- 
 bination occurs between two elements as to form any given 
 compound, the proportions must be definite, since these 
 proportions are determined by the relative weights of the 
 atoms of the combining elements, and the atom cannot be 
 subdivided. 
 
 2. The law of multiple proportions. When the same 
 pair of elements unite in several different proportions, these 
 proportions must vary according to the terms of a simple 
 series of multiples, since each atom of one element must 
 unite with one, with two, or with three atoms of the other 
 element, or in some other ratio almost equally simple, be- 
 cause the atom does not admit of subdivision. 
 
 3. The law of equivalent proportions. Combination must 
 also occur in equivalent proportions, since the amount of 
 each element which is capable of displacing any of the other 
 elements must be in the proportion of the weight of the 
 atom of the displacing element, or of a simple multiple of 
 that weight, and the atom cannot be subdivided. 
 
 4. The law of molecular weights. In every compound 
 body the molecular weight, or weight of the smallest particle 
 of the compound which can exist, is necessarily that obtained 
 by adding together the weights of all the atoms of the several 
 elements which have united together to form the molecules 
 of the compound body, since none of the atoms of the con- 
 stituent elements can be subdivided. 
 
 Suppose, for example, that each atom of oxygen weigh 
 1 6 times as much as each separate atom of hydrogen ; that 
 the atom of chlorine weighs 35-5 times as much, the atom 
 of nitrogen 14 times -as much, the atom of bromine 80 times 
 as much, the atom of silvet 108 times as much, and the 
 atom of mercury 200 times as much; exactly as is repre- 
 
Chemical Equivalents. 193 
 
 sented in the column headed 'Atomic Weights' in the table 
 at page 198. 
 
 It follows that when chlorine and hydrogen unite to form 
 hydrochloric acid, if one atom of each element enters into 
 the formation of each molecule of the compound (HC1), 
 hydrochloric acid must necessarily and invariably contain in 
 every 36^5 parts by weight, whether it be grams, pounds, or 
 tons, i part of hydrogen and 35*5 parts of chlorine. 
 
 In like manner, if each of the molecules of argentic bro- 
 mide be formed by the union of i atom of silver with i of 
 bromine (AgBr), then 188 parts, by weight of this bromide 
 will necessarily consist of 108 parts of silver and 80 of 
 bromine. 
 
 Again, if each molecule of water consist of 2 atoms of 
 hydrogen and i atom of oxygen (H 2 0), it must happen that 
 1 8 parts by weight of water will always contain 2 parts by 
 weight of hydrogen and 16 parts by weight of oxygen. 
 
 Suppose next that argentic bromide be heated in a stream 
 of chlorine gas; the bromine will be displaced by the 
 chlorine, and argentic chloride will be formed. Now if 
 each molecule of argentic chloride (AgCl) be formed by the 
 union of i atom of silver with i of chlorine, the bromine 
 displaced must be in the proportion of 80 parts of bromine 
 for every 35-5 of chlorine which unite with the silver; that 
 is to say, 35-5 parts of chlorine are equivalent in combination 
 to 80 parts of bromine. 
 
 It was at one time supposed that the chemical equivalent 
 of the elements always represent the relative weights of their 
 atoms, so that the term atomic weight was often used instead 
 of that of chemical equivalent ; but the two terms involve 
 ideas which are essentially distinct. A simple substance 
 can have but one atomic weight, but it may have two or 
 more chemical equivalents ; for instance, mercury forms two 
 compounds with chlorine, viz. calomel and corrosive sub- 
 limate. In calomel 200 grams of mercury are combined 
 with 35-5 grams of chlorine ; whilst in corrosive sublimate 
 
 
 
1 94 Law of Volumes. 
 
 the 200 of mercury are united with 71 grams of chlorine, 
 or twice as much; and this is explained upon the sup- 
 position that the atom of mercury is in calomel united with 
 i atom of chlorine (HgCl), whilst in corrosive sublimate 
 it. is united with 2 atoms (HgCl 2 ). But if we compare the 
 quantity of mercury in each compound with the same weight, 
 35 '5, of chlorine, we find in calomel that 200 parts of 
 mercury are equivalent to 35*5 parts of chlorine ; whilst in 
 corrosive sublimate 100 parts of mercury are equivalent to 
 the same 35*5 parts of chlorine ; consequently mercury has 
 two different equivalents in the two compounds. 
 
 Again, in the five oxides of nitrogen we have an excellent 
 example of multiple proportion. If 2 atoms of nitrogen are 
 supposed in each case to be concerned, we find the com- 
 position of each represented by the following numbers : 
 Citrons oxide contains in every 44 parts 28 parts of nitrogen 
 and 1 6 of oxygen, or 2 atoms of nitrogen and i of oxygen ; 
 nirjdc oxide in every 60 parts contains 28 parts of nitrogen 
 arid 3:2 of oxygen, or 2 atoms of nitrogen and 2 of oxygen ; 
 nitrooas anhydride in every 76 parts contains 28 of nitrogen 
 arid/48 of oxygen, or 2 atoms of nitrogen and 3 of oxygen ; 
 niteogen peroxide in every 92 parts contains 28 of nitrogen 
 andr&4 of oxygen, or 2 atoms of nitrogen and 4 of oxygen ; 
 while: nitric anhydride in every 108 parts contains 28 of 
 nittfGkg'en and 80 of oxygen, or 2 atoms of nitrogen and 5 of 
 oxygen ; the series being represented as N 2 O, N 2 O 2 , N 2 O 3 , 
 
 N 2 O 5 . 
 
 has been ascertained that equal measures or volumes 
 gas and every vapour taken at a sufficient distance 
 frobffii^its boiling point, no matter whether simple or com- 
 p$as8< ^expand equally for an equal rise of temperature, if 
 both mire-compared under equal pressures, and at the same 
 te#Apei&tures. It is also true that all gases and vapours 
 contract equally when equal volumes of the 
 are submitted, at the same temperatures, to 
 diminution or increase of pressure. Hence it 
 
Atomic Weights. 195 
 
 appears to be a necessary conclusion that equal volumes of 
 all gases contain an equal number of molecules, whether 
 those molecules be simple or compound. Further, the 
 molecules of the same substance are all absolutely similar to 
 each other in size, weight, and chemical properties, if com- 
 pared under similar circumstances. 
 
 The term molecular volume is used to signify the space 
 occupied by a molecule of the body in the form of gas or 
 vapour, compared with that of the atom of hydrogen, or the 
 atomic volume of hydrogen. Now the volume of the molecule 
 of a compound body in the aeriform state \ \ \ is exactly 
 double the volume of the atom of hydrogen [H|. 
 
 The atom is denned to be the smallest and chemically 
 indivisible particle of each element which can exist in a 
 compound, united with other particles, either of the same or 
 of different elements, but which is not known in a separate 
 form , and the molecule of an element is defined to be the 
 smallest quantity of that elementary substance supposed to 
 be capable of existing in a separate form. If H, for instance, 
 represent the atom of hydrogen, H 2 will represent its mole- 
 cule. Each molecule of chlorine and of the other allied 
 elements when in the gaseous state appear, for reasons to 
 be explained immediately, to consist of two atoms. When 
 a molecule of hydrogen is made to react chemically upon 
 a molecule of chlorine, two molecules of hydrochloric acid 
 are formed, the half molecule of hydrogen exchanging places 
 with the half molecule of chlorine 
 
 W&\ + |C1C1| becoming [HCl] + JHClJ. 
 
 It will be desirable to develop these considerations a little 
 more fully. The number adopted for the atomic weight of 
 any element is based upon a careful chemical analysis of 
 several compounds of that element. Suppose, for example, 
 the atomic weight of copper to be the subject of experiment, 
 and that a quantity of the pure oxide of the metal has been 
 prepared, and a portion carefully weighed, and heated in 
 
 o a 
 
1 96 Determination of A tomic Weights. 
 
 a stream of pure hydrogen gas. The hydrogen gradually 
 removes all the oxygen in the form of steam, leaving nothing 
 but pure copper behind. On weighing this copper, the 
 quantity of oxygen originally combined with it in the oxide 
 is ascertained by the loss of weight experienced. Then the 
 relative proportions between the combining proportion of 
 copper and oxygen, referred to hydrogen as the unit, can 
 be easily calculated. 
 
 But this determination would not be sufficient to settle 
 the atomic weight if taken alone, even if other analyses of 
 this same oxide and of other compounds of copper gave 
 results which showed that the experiments had been made 
 with exactness. It is necessary also to know the number of 
 atoms in the molecule of the different compounds of the 
 substances analysed; whether, for instance, the number of 
 atoms of copper in the molecule of its oxide be one of 
 copper to one of oxygen, two of copper to one of oxygen, 
 or two of oxygen to one of copper, two of copper to three of 
 oxygen, or any other proportion. In the case of solid 
 bodies, not convertible easily into vapour, this determination 
 is often attended with difficulty and uncertainty. There are, 
 however, various considerations by which this conclusion 
 may be arrived at with more or less probability. One of the 
 best methods consists in comparing together all the com- 
 pounds of the element under examination, for the purpose of 
 finding out the smallest proportion in which that element 
 enters into any compound molecule, for this must repre- 
 sent its atom, by the definition of the word which we have 
 adopted. 
 
 In cases where bodies can be converted into vapour, this 
 task is much facilitated by that very circumstance. For 
 example, a large number of compounds of hydrogen have 
 been analysed. Most of them may be obtained in the form 
 of gas or vapour ; in which case their specific gravities in the 
 aeriform condition may be ascertained by experiment. From 
 these specific gravities the relative weights, or weights com- 
 
Atomic and Molecular Weights. 
 
 197 
 
 pared with that of an equal bulk of hydrogen, and the 
 molecular weights are at once easily obtained. 
 
 Some of the more important of these compounds have 
 been already described, and they are mentioned in the 
 following list : 
 
 Compounds of Hydrogen 
 
 Molecular 
 Volume 
 
 Weights 
 referred to 
 Hydrogen 
 
 Weights of 
 Hydrogen 
 in Molecule 
 
 Hydrochloric Acid 
 
 m 
 
 36-5 
 
 I 
 
 Hydrobromic Acid 
 
 CH 
 
 8ro 
 
 I 
 
 Hydrogen Gas . 
 
 i : i 
 
 2'O 
 
 2 
 
 Water .... 
 
 m 
 
 18-0 
 
 2 
 
 Sulphuretted Hydrogen 
 
 m 
 
 34-0 
 
 2 
 
 Ammonia . . 
 
 CD 
 
 17-0 
 
 3 
 
 Phosphuretted Hydrogen 
 
 a 
 
 34-0 
 
 3 
 
 Olefiant Gas 
 
 m 
 
 28-0 
 
 4 
 
 Marsh Gas. . .' v . 
 
 CD 
 
 i6 - o 
 
 4 
 
 Now if the molecule of hydrogen weigh 2, the smallest 
 weight of hydrogen which is contained in an equal volume 
 of vapour of any of the compounds of hydrogen in this list, 
 and it may be added in any others that are known, is half 
 that amount, or i. Hence chemists have concluded that 
 this quantity of hydrogen is the smallest that can enter into 
 combination, or, according to the supposition with which we 
 began, that it is to be regarded as the atom of hydrogen. 
 Now hydrogen has the smallest combining number of any 
 element known, so that it has been found convenient to 
 take the hydrogen number as i, or the unit of the scale with 
 which the atomic weights of all the other elements are com- 
 pared, as has been done in the table given at page 1 98 ; so 
 
198 
 
 The Metals. 
 
 that supposing the weight of the atom of hydrogen to be 
 known, the atomic weight of any other element would be the 
 number which represents how many times this atom is 
 heavier than the atom of hydrogen. 
 
 The following table contains a list of such of the elemen- 
 tary bodies as have been converted into vapour in such a 
 manner as to admit of determining their specific gravity in 
 that form, and thus of ascertaining the number of atoms in 
 the molecule, on the supposition that equal volumes of every 
 gas or vapour contain an equal number of molecules : 
 
 Element 
 
 Atomic 
 Weights 
 
 Weights of 
 equal 
 Volumes 
 of Vapour 
 
 Atoms in 
 i Molecule 
 
 Specific Gravity of Vapour 
 
 Observed 
 
 Calculated 
 
 Cadmium 
 
 112 
 
 56 
 
 I 
 
 3'94 
 
 3-8690 
 
 Zinc 
 
 65 
 
 32-5 
 
 I 
 
 
 
 Mercury 
 
 2OO 
 
 100 
 
 I 
 
 6-976 
 
 6-9101 
 
 Hydrogen 
 
 I 
 
 I 
 
 2 
 
 0-0692 
 
 0-0691 
 
 Chlorine 
 
 35'5 
 
 35*5 
 
 2 
 
 2-47 
 
 2'453I 
 
 Bromine 
 
 80 
 
 80 
 
 2 
 
 5'54 
 
 5-528I 
 
 Iodine . 
 
 127 
 
 127 
 
 2 
 
 8-716 
 
 8-7560 
 
 Oxygen . 
 
 16 
 
 16 
 
 2 
 
 1-1056 
 
 1-1056 
 
 Sulphur . 
 
 S 2 
 
 32 
 
 2 
 
 2-23 
 
 2-2168 
 
 Selenium 
 
 79*5 
 
 79'5 
 
 2 
 
 5-68 
 
 5-4680 
 
 Tellurium 
 
 129 
 
 129 
 
 2 
 
 9-00 
 
 8-9130 
 
 Nitrogen 
 
 14 
 
 14 
 
 2 
 
 0-9713 
 
 0-9674 
 
 Phosphorus 
 
 3i 
 
 62 
 
 4 
 
 4-42 
 
 4-2840 
 
 Arsenicum 
 
 75 
 
 150 
 
 4 
 
 10-60 
 
 10-1670 
 
 CHAPTER XL 
 B. THE METALS. 
 
 (43) The Metals in General. There is no absolute dis- 
 tinction between the non-metals and the metals, but the 
 subdivision is practically convenient, and it is usual to con- 
 sider a body which has a high lustre, great opacity, and is a 
 
Melting Points of Metals. 
 
 199 
 
 good conductor of heat and electricity, as a metal. But on 
 the one hand, graphite, although it has all these properties, 
 is not reckoned amongst the metals ; and on the other, 
 arsenicum and tellurium, though possessing them, are by 
 some chemists considered as non-metals. 
 
 The metals differ very much in chemical properties ; 
 some, like potassium and sodium, have an intense attraction 
 for oxygen, whilst others, like gold and silver, have but a 
 feeble attraction for it. As a rule, the lighter metals are 
 those which are most easily oxidized. In the following table 
 the lightest metals are placed first. The metals exhibit a 
 very great variation in density. Three of them are light 
 enough to float in water, and lithium is lighter than any 
 known liquid, while platinum is the heaviest of all known 
 substances. 
 
 SPECIFIC GRAVITIES AND FUSING POINTS OF METALS. 
 
 
 Specific 
 Gravity 
 
 Fusing 
 Point 
 
 
 Specific 
 Gravity 
 
 Fusing 
 Point 
 
 Lithium . , . 
 
 o-593 
 
 1 80 
 
 Molybdenum 
 
 8-62 
 
 
 Potassium . 
 
 0-865 
 
 62-5 
 
 Nickel . 
 
 8-82 
 
 
 Sodium . .. 
 
 0-972 
 
 97-6 
 
 Copper 
 
 8'95 
 
 IO9O 
 
 Rubidium . 
 
 1-52 
 
 38-5 
 
 Cobalt 
 
 8-95 
 
 
 Calcium . " . 
 
 I-578 
 
 
 Bismuth . 
 
 9-80 
 
 26 4 
 
 Magnesium 
 
 1-743 
 
 
 Silver 
 
 10-53 
 
 1023 
 
 Glucinium . 
 
 2'I 
 
 
 Lead 
 
 11-36 
 
 325 
 
 Strontium . 
 
 2-54 
 
 
 Ruthenium 
 
 11-4 
 
 
 Aluminum 
 
 2-67 
 
 
 Palladium . 
 
 irS 
 
 
 Arsenicum 
 
 5'95 
 
 
 Thallium . 
 
 11-9 
 
 294 
 
 Tellurium . 
 
 6-25 
 
 
 Rhodium < 
 
 I2'I 
 
 
 Antimony . 
 
 6-71 
 
 450 
 
 Mercury . 
 
 I3-596 
 
 -39 
 
 Chromium 
 
 6-81 
 
 
 Tungsten . 
 
 17-6 
 
 
 Zinc . 
 
 7*15 
 
 412 
 
 Uranium . 
 
 1 8-4 
 
 
 Tin . 
 
 7-29 
 
 228 
 
 Gold . 
 
 1934 
 
 1 102 
 
 Iron . 
 
 7-84 
 
 
 Iridium 
 
 21-15 
 
 
 Manganese 
 
 8-01 
 
 
 Osmium . 
 
 21-4 
 
 
 Cadmium . 
 
 8-69 
 
 228 
 
 Platinum . 
 
 2i-53 
 
 
 The melting points of the metals also vary very widely. In 
 the table the melting points of all the metals, so far as they 
 have been ascertained, are given. Mercury is liquid at all 
 
200 Properties of the Metals. 
 
 ordinary temperatures ; potassium and sodium melt beneath 
 the boiling point of water. Zinc melts below, and copper 
 above, a red heat ; silver, gold, and copper require a very 
 bright red heat to fuse them. Cast iron melts at about 
 1500, and wrought iron not lower than 1800 C. Cobalt, 
 nickel, and wrought iron require the strongest heat of the 
 forge to melt them. Molybdenum, chromium, tungsten, 
 and palladium do not completely melt even at this tempera- 
 ture ; and platinum, rhodium, iridium, vanadium, ruthenium, 
 and osmium cannot be melted but in the heat of the oxy- 
 hydrogen blowpipe, or that of the voltaic arc. 
 
 Some few of the metals may be converted into vapour 
 readily, and are ordinarily purified by distillation. Mer- 
 cury, arsenicum, tellurium, cadmium, zinc, magnesium, potas- 
 sium, sodium, and rubidium are thus purified. Mercury 
 boils at 350 C. Arsenicum is volatilised below redness. 
 Cadmium requires a full red heat (860), at which point it 
 boils, and may be distilled ; and the boiling point of zinc, 
 though as high as 1040, is equally fixed. Potassium, sodium, 
 magnesium, and rubidium require a still higher temperature, 
 which has not been measured. 
 
 Many of the other metals, including silver and gold, may 
 be volatilised by the intense heat of the sun's rays when 
 brought to a focus by a very large convex lens. 
 
 Several of the metals when rubbed give out a character- 
 istic odour, as is the case with iron, tin, and copper. Arse- 
 nicum, when volatilised, emits a strong odour of garlic. 
 The taste of many of the soluble salts of the metals is 
 astringent or acrid, and of the peculiar kind termed 
 metallic. 
 
 The most usual colour exhibited by the metals is a white, 
 of varying shades. It is nearly pure in silver, platinum, 
 cadmium, and magnesium; yellowish in tin ; bluish in zinc 
 and lead ; grey in iron and arsenicum ; and is reddish in 
 bismuth. Calcium is pale yellow, gold full yellow ; and 
 copper is red. 
 
Metallic A Hoys. 201 
 
 Many of the metals show the properties of malleability, or 
 the power of being flattened under the hammer. They may 
 also be extended into ribbon or foil, by passing them be- 
 tween steel rollers : among these are gold, silver, platinum, 
 palladium, copper, iron, aluminum, tin, lead, zinc, and 
 thallium. Gold is the most malleable of the metals, but 
 silver and copper may also be hammered into very thin 
 leaves. The same metals are likewise ductile; that is, they 
 admit of being drawn into wire, often finer than a hair, by 
 drawing them through holes in a hard steel plate, termed a 
 draw-plate ; the holes through which the wire is made to 
 pass being successively smaller and smaller. 
 
 On the other hand, there are metals so brittle that they 
 may be powdered without difficulty: such are arsenicum, 
 antimony, and bismuth. These metals have a crystalline 
 structure, and are very hard. Metals which have a fibrous 
 texture, like bar iron, are, on the contrary, very tough. 
 
 When the metals are combined with each other, the 
 resulting substance is called an alloy. Many of these, such 
 as brass, German silver, bronze, and pewter, are used largely 
 in the arts, on account of advantages which they offer over 
 their constituent metals in increased hardness and elasticity, 
 as well as increased fusibility. Brass is a hard, somewhat 
 fusible alloy, consisting of about two-thirds of copper and 
 one-third of zinc. If bras? be melted with about a fifth of 
 its weight of nickel, it furnishes German silver. Bronze is an 
 alloy of tin and copper, o'l which there are several varieties : 
 with 10 per cent, of tin it forms the tough gun-metal ; with 
 20 per cent, of tin it furnishes the sonorous, elastic bell- 
 metal ; and with 33 per cent of tin the hard, white, brittle 
 metal used for the mirrors of telescopes. 
 
 The white metal used in types for printing is an alloy of 
 about i part of antimony, i of tin, and 2 of lead ; it is 
 fusible, expands on becoming solid, so as to fill the mould, 
 and is hard enough to bear pressure, but will not cut the 
 paper. All the alloys melt at a lower temperature than 
 
2O2 Native Metals. 
 
 that which would be the mean of the fusing points of their 
 components. 
 
 Exp. 211. Heat in a small iron ladle 20 grams of lead ; as 
 soon as it is melted add 40 grams of bismuth and 10 of tin ; they 
 will fuse quickly, and an alloy will be thus obtained known as 
 fusible metal', it melts when thrown into boiling water, although 
 tin, the most fusible of its components, does not melt below 
 228 C. 
 
 A combination of a metal with mercury forms an amalgam. 
 Some amalgams are soft and semi-solid ; others are brittle 
 and crystalline. Alloys and amalgams appear to consist of 
 definite compounds, which are often mixed with, or dissolved 
 by, an excess of one of the metals employed ; for the pro- 
 portion of the metals used in an alloy can be varied within 
 any limits. 
 
 Some few of the metals are found in the native, or uncom- 
 bined, state in the earth. Among these the most important 
 are gold, silver, platinum and a few rare metals which 
 accompany it, mercury, bismuth, and copper. More usually 
 the metals occur united with sulphur, when they preserve 
 their metallic brilliancy, but not their ductility or tenacity. 
 Lead, antimony, mercury, copper, iron, and zinc are often, 
 and some of them almost always, found in the condition of 
 sulphides. Other metals such, for instance, as tin, iron, 
 manganese, and chromium are met with as oxides, under the 
 aspect of dull blackish or earthy bodies. The metals of the 
 earths, and of the alkalies, are generally found in the form of 
 salts, such as sulphates, carbonates, silicates, or chlorides. 
 Further particulars respecting the ores of the metals, their 
 distribution over the surface of the earth, the formation of 
 mineral veins, and the methods employed for extracting the 
 metals for use in the arts, will be found in the text-book on 
 ' Metallurgy.' 
 
 (44) Classification of the Metals. The metals may be 
 divided into 10 groups, founded upon their different degrees 
 of attraction for oxygen, and the properties of the oxides 
 which they form. 
 
Classification of the Metals. 203 
 
 Group i : 5 Metals of the Alkalies, viz. i. Csesium ; 2. 
 Rubidium; 3. Potassium ; 4. Sodium; and 5. Lithium, with 
 which it is convenient to arrange the salts of ammonium, 
 although it is not a simple body. These metals are monads, 
 and displace i atom of hydrogen from the radicals of the 
 acids. They are soft, easily fusible, and volatile at high 
 temperatures. They have an intense attraction for oxygen, 
 and become tarnished as soon as they are exposed to the 
 air. They decompose water instantly at all temperatures, 
 with rapid disengagement of hydrogen, and form a soluble 
 oxide, which is powerfully caustic and alkaline, but which, 
 after it has been dissolved, cannot be again completely 
 deprived of water by heat. They form but one set of salts 
 with the halogens. Though they furnish but a single chloride, 
 they yield several sulphides, all of which are soluble. When 
 exposed to the air their oxides absorb carbonic acid greedily, 
 and form soluble carbonates. Only two of them, potassium 
 and sodium, are sufficiently abundant to require description. 
 Csesium and rubidium are of quite recent discovery, and 
 were found in minute quantity in the water of a mineral 
 spring, of which the saline residue was submitted to exami- 
 nation by the method of spectrum analysis, lately discovered, 
 and they have since been found in minute quantity in the 
 ash of various plants, and in some crystallised minerals. 
 
 Group 2 : 3 Metals of the Alkaline Earths, viz. i. Ba- 
 rium ; 2. Strontium ; and 3. Calcium. These are dyads ; 
 they displace two atoms of hydrogen from the radicals of the 
 acids. When thrown into water they decompose it with 
 avidity, and set hydrogen free. They form powerfully basic 
 oxides, which are soluble in water, though lime is only 
 sparingly so. These oxides absorb carbonic acid rapidly, 
 and form carbonates which are insoluble in water, but some- 
 what soluble in a solution of carbonic acid. Their phos- 
 phates are insoluble in water. 
 
 Group 3 : Metals of the Earths. The only one of prac- 
 tical importance is i. Aluminum; but 2. Glucinium; 3. 
 
204 Classification of the Morals. 
 
 Yttrium ; 4. Erbium ; 5. Cerium ; 6. Lanthanium ; and 7. 
 Didymium, are commonly included in this division. The 
 last six are, however, very rarely met with, and their pro- 
 perties are only imperfectly known. 
 
 Aluminum is a triad : it forms but one oxide ; this is 
 insoluble in water, and is but feebly basic. 
 
 Group 4 : 4 Magnesian Metals, viz. i. Magnesium ; 2. 
 Zinc ; 3. Cadmium ; 4. Indium. These metals are dyads ; 
 they form but a single oxide, which is insoluble in water. 
 They decompose steam at a red heat, but are without action 
 on water at common temperatures. They form a single 
 soluble chloride, and a single nearly insoluble sulphide. 
 
 Groups: 6 Metals allied to Iron, viz. i. Cobalt; 2. 
 Nickel ; 3. Uranium ; 4. Iron ; 5. Chromium ; and 6. Man- 
 ganese. These metals are remarkable as forming two sets 
 of compounds, in one of which the metal is dyad, in the 
 other triad. They furnish several oxides : those which con- 
 tain least oxygen are basic and insoluble ; those which 
 contain most are often soluble, and are then distinctly acid. 
 Several of these metals are magnetic ; they are oxidized by 
 passing steam over them when heated to redness, though 
 they do not decompose water at ordinary temperatures. 
 
 Group 6 : 4 Metals allied to Tin, viz. i. Titanium ; 2. 
 Tin ; 3. Zirconium; and 4. Thorinum. They are all tetrad, 
 or equivalent to 4 atoms of hydrogen. Tin is the only 
 one of practical importance : it furnishes two oxides, both 
 capable of acting as bases ; but the higher oxide is more 
 often acid. 
 
 Group 7 : 2 Metals, Molybdenum and Tungsten, which are 
 hexad, or equivalent to 6 atoms of hydrogen. They yield 
 trioxides, which furnish metallic acids; but we shall not 
 enter into any description of them. 
 
 Group 8 : 6 Metals. They present in their combinations 
 an analogy with phosphorus, viz. i. Niobium; 2. Tantalum; 
 3. Vanadium; 4. Arsenicum; 5. Antimony ;'and 6. Bismuth. 
 They furnish at least two oxides. We shall not enter further 
 
Metals of the Alkalies. 205 
 
 into any description of the first three of these metals, but 
 the last are of practical importance. 
 
 Group 9: 3 Metals, viz. i. Copper; 2. Lead; and 3. 
 Thallium, which are not closely related. 
 
 Group 10 : 9 noble Metals, viz. i. Mercury; 2. Silver; 
 3. Gold ; 4. Platinum, with which are associated 5 other rare 
 metals, viz. 5. Palladium; 6. Rhodium; 7. Ruthenium; 8. 
 Osmium ; and 9. Iridium, which we need not further notice. 
 The first four metals form more than one oxide, but have so 
 slight a tendency to union with oxygen that their oxides are 
 decomposed by exposure to a heat below redness. All the 
 metals of this group are commonly found in the native state ; 
 but mercury and silver also occur as sulphides. Their attrac- 
 tions both for chlorine and for sulphur are much stronger 
 than for oxygen. Each forms more than one chloride; 
 their compounds have a tendency to combine with the 
 chlorides of the alkali-metals to form double salts. 
 
 GROUP I. METALS OF THE ALKALIES. 
 
 i. POTASSIUM. 2. SODIUM. 3. LITHIUM. 4. CESIUM. 
 
 5. RUBIDIUM. (AMMONIUM). 
 
 (45) POTASSIUM : Symb. K; Atom. Wt. 39 ; Sp. Gr. 0-865; 
 Fusing Pt. 6 2 '5. 
 
 This metal was originally obtained by decomposing a 
 fragment of caustic potash by means of a powerful voltaic 
 battery, when globules of potassium were separated at the 
 negative wire. It is now prepared by distilling potassic 
 carbonate mixed with charcoal, at an intense heat, in iron 
 bottles, and condensing the green vapours of potassium in 
 receivers containing naphtha, carbonic oxide being dis- 
 engaged during the process 
 
 K 2 C0 3 + 2 C = K 2 + 3 CO. 
 
 This is a difficult and dangerous operation. Potassium vapour 
 takes fire instantly in the air or on contact with water ; it 
 also absorbs carbonic oxide, and the compound thus formed, 
 if kept, gradually becomes changed into a black, powerfully 
 
206 Potassium Oxides and Hydrate. 
 
 explosive compound. To avoid this danger potassium is 
 always redistilled, immediately after its preparation, in a small 
 iron retort containing naphtha vapour. 
 
 Potassium is a brilliant silver-white metal, soft enough to 
 be spread with a knife. It tarnishes immediately that it is 
 exposed to the air, and decomposes water, evolving hydro- 
 gen as soon as it is thrown into the liquid. (Exp. 30.) The 
 gas takes fire from the heat produced by the action. It is 
 necessary to preserve the metal either in vessels closed so 
 as to prevent access of air, or under some liquid, such as 
 naphtha, which contains no oxygen. It combines imme- 
 diately with chlorine, bromine, iodine, and sulphur, if heated 
 with them. 
 
 Potassium furnishes an important basic oxide (K 2 O), 
 potash ; besides this, there are two other oxides (K 2 O 2 and 
 K 2 O 4 ), which, when thrown into water, give off oxygen, and 
 furnish a solution of potash. The anhydrous potash is 
 difficult to obtain pure, and is seldom prepared ; but its 
 hydrate is a very important substance, and is known as 
 caustic potash, or potassic hydrate (KHO). This, when 
 dissolved in water, furnishes potash ley. It is prepared by 
 mixing a solution of potassic carbonate with slaked lime 
 
 K 2 CO 3 + CaO, H 2 O = 2 KHO + CaCO 3 . 
 
 If the solution is poured off from the calcic carbonate and 
 evaporated down in a silver dish, an intensely caustic solid 
 substance is left, which fuses at a red heat, and may be cast 
 into metallic moulds. It furnishes the hydrate of potash. 
 This substance absorbs both moisture and carbonic acid 
 from the air. Caustic potash, if fused in glass or porcelain 
 dishes, corrodes and dissolves them. It also attacks platinum 
 vessels, but has little action on silver. It is very soluble 
 both in water and in alcohol. The solution decomposes the 
 fats and oils, and converts them into soluble soaps. Ordinary 
 soft soap contains potash as its base. Caustic potash is also 
 a valuable agent in the laboratory, where it is used for the 
 
Salts of Potassium. 207 
 
 purpose of absorbing aeid gases, such as the carbonic. In 
 consequence of its powerful attraction for acids, it readily 
 decomposes the salts of all metals which form oxides in- 
 soluble in water, and it precipitates the oxide of the metal in 
 the form of hydrate, while the radical of the acid forms a 
 potassic salt, which remains in solution ; such a salt, for 
 example, as the cupric sulphate is decomposed as follows : 
 
 CuS0 4 + 2KHO K 2 S0 4 + CuO, H 2 O. 
 
 Potash is found in all fertile soils, generally in the clay 
 derived from the felspar, which, after crumbling down, has 
 become mingled with other substances. Growing plants 
 require potash to aid in forming their tissues. The alkaline 
 salt is dissolved by the rain-water from the soil, absorbed 
 by the roots, and carried by the circulation of the sap into 
 the plant, where it becomes combined with the radical of 
 some vegetable acid. When the plant is burned the salt 
 of the vegetable acid is decomposed, and the potassium 
 remains in the ash, chiefly in the form of carbonate. The 
 more soluble portions of this ash are washed out by the 
 action of water, which when evaporated leaves the potassic 
 carbonate, or potash, of commerce, which is imported largely 
 from North America and Russia. Pearlash is the first pro- 
 duce, refined by a second solution in a very small quantity of 
 water, and evaporation to dryness. 
 
 Potassic chloride has also been found native, in consider- 
 able amount, in the salt beds of Stassfurth, near Magdeburg ; 
 and it is present in sea water in quantity sufficient to render 
 this a very important source of supply. 
 
 Potassium forms five sulphides : K 2 S, K 2 S 2 , K 2 S 3 , K 2 S 4 , 
 and K 2 S 5 . They are all soluble, and have a strongly alkaline 
 reaction. When mixed with an acid, they give off in every 
 case, except with K 2 S, sulphuretted hydrogen and deposit 
 of sulphur. 
 
 Potassic Carbonate (K 2 CO 3 ) is a very soluble salt, which, 
 if exposed to the air, attracts moisture from it, and soon 
 
208 Nitre or Saltpetre. 
 
 becomes liquid. It is strongly alkaline, and restores the blue 
 colour of red litmus paper. 
 
 Exp. 212. Burn some dry brushwood ; collect the ash, and 
 wash it with five or six times its bulk of water. Filter off from 
 the undissolved substances. Test the solution with a piece of 
 reddened litmus paper, which will at once become blue. Eva- 
 porate the solution to dryness in a small porcelain dish. If the 
 dry mass be left exposed to the air for a few hours it will become 
 moist. The potassic carbonate, of which it chiefly consists, 
 attracts moisture rapidly and deliquesces. To a portion of the 
 salt add a few drops of hydrochloric acid : brisk effervescence 
 occurs. 
 
 Exp. 213. Place 30 grams of pearlash in a half-litre bottle, 
 and dissolve it in 250 c. c. of water. Shake 20 grams of quick- 
 lime with five or six times its bulk of boiling water, and add the 
 pasty mixture (about 120 c. c. in bulk) to the solution of pearl- 
 ash. Agitate the mixture, and let it stand till it is clear. Pour 
 off a portion of the liquid : it is a solution of caustic potash. 
 Add to it some hydrochloric acid : no effervescence will occur. 
 Agitate a tablespoonful of olive oil m a small phial with 3 or 
 4 c. c. of the caustic solution diluted with ten times its bulk 
 of water : a milky-looking liquid will be formed, which is the 
 first stage in the making of soap. 
 
 Potassic Hydric Carbonate (KHCO 3 ). If a current of 
 carbonic acid gas be passed through a strong solution of 
 potassic carbonate, it is quickly absorbed, and crystals of a 
 less soluble salt, often called the bicarbonate, are formed 
 K 2 C0 3 + C0 2 + H 2 = 2 KHC0 3 . 
 
 Potassic Nitrate (KNO 3 ). Another important salt, usually 
 called nitre or saltpetre, is found on the surface of the 
 soil in some parts of tropical India. It is also obtained in 
 temperate climates by allowing animal matter mixed with 
 lime rubbish to decay in heaps, which are moistened from 
 time to time, and from which the nitre is at intervals removed 
 by washing. The nitrogen in the animal refuse becomes 
 slowly oxidized into nitric acid, and this combines with the 
 lime and potash present. 
 
Gunpowder. 209 
 
 Nitre has a cooling saline taste, and is soluble in about 
 3^ times its weight of cold water. 
 
 Exp. 214. Dissolve 150 grams of nitre in a quarter of a litre 
 of boiling water, and allow it to cool slowly : six-sided prisms 
 of nitre will crystallise from the liquid. 
 
 Exp. 215. Mix a portion of the solution with three or four 
 times its bulk of water, and dip some strips of filtering-paper 
 into the liquid. When dry the paper, called touch paper, will 
 smoulder if kindled. 
 
 Exp. 216. Throw a little nitre into a clear fire : the embers 
 will burn with brilliant sparks. 
 
 Exp. 217. Put a few dry crystals of nitre into a test-tube, 
 and heat them over a lamp : they will melt to a clear liquid. 
 Heat them more strongly : they will be decomposed, gas will 
 escape, which will rekindle a glowing match, and which at first 
 consists of pure oxygen, potassic nitrite being formed 
 2KNO 3 = 2KNO a + O 4 . 
 
 The principal use of nitre depends upon this readiness to 
 part with oxygen, of which it contains nearly 48 per cent, 
 and which enables it to add great intensity to combustion. 
 
 Gunpowder is a mechanical mixture of about 75 parts of 
 nitre, 15 of charcoal, and 10 of sulphur; the quantities of 
 the ingredients used being nearly in the proportions of i 
 atom of sulphur, 2 of nitre, and 3 of charcoal. An excess 
 of sulphur is to be avoided, as it corrodes the gun. The 
 application of a spark, or even of a temperature of about 
 250 C., produces an instantaneous decomposition of the 
 mixture, attended with an immense production of gas (chiefly 
 carbonic anhydride and nitrogen) at a very high temperature, 
 so that the gases at the moment of firing become expanded 
 to at least 1500 times the bulk of the gunpowder. The 
 chemical change is sometimes roughly represented as 
 follows : 
 
 S + 3C + 2 KNO 3 = 3CO 2 + N 2 + K 2 S ; 
 though it is really much more complex. Gunpowder thus 
 contains within itself the oxygen necessary to enable it to 
 burn in a space excluded from air, or even under water the 
 
 p 
 
2io Sodium and its Compounds.' 
 
 oxygen forming either carbonic oxide or carbonic anhydride, 
 while nitrogen is set free, and the sulphur remains combined 
 with the potassium. 
 
 (46) 2. SODIUM: Symb. Na; Atomic Wt. 23; Sp. Gr. 
 0-972 ; Fusing Pt. 9 7 -6. 
 
 Sodium much resembles potassium. It is obtained from 
 its carbonate, by heating it with charcoal, in a similar 
 way to that followed with potassium, but it is more easily 
 managed. It is made in large quantities as a preparatory 
 process in the extraction of aluminum and magnesium. 
 Sodium gives off a colourless vapour, which burns with a 
 bright yellow flame. When thrown into water it rises to the 
 surface, and disengages hydrogen freely; but the gas does 
 not generally take fire unless the water is heated first, or is 
 small in quantity. 
 
 Common salt, sodic chloride (NaCl), is the great source 
 from which all compounds of sodium are obtained. This is 
 met with in large quantities in sea water, which contains 
 more than a quarter of a pound in a gallon, or about 27 
 parts in 1000. It is also found in extensive deposits in 
 Cheshire, and still more abundantly in the mines of Wielitzka, 
 in Poland. Sodium is also found in Atacama as nitrate, 
 and in many rocks and minerals, as, for instance, in soda 
 felspar or albite, and in cryolite (3NaF, A1F 3 ), a fluoride of 
 sodium and aluminum. 
 
 Sodium forms two oxides, Na 2 O and Na 2 O 2 . The first 
 is the only one of importance. It is the base from which 
 the salts of sodium are derived, but is seldom obtained free 
 from water. 
 
 Caustic Soda, or sodic hydrate (NaHO), is a white solid, 
 very soluble in water, of which it cannot be completely 
 deprived by mere heat. Caustic soda is formed on a large 
 scale in the alkali works, but it is easily prepared by treating 
 a solution of sodic carbonate with slaked lime, in a manner 
 similar to that directed for obtaining caustic potash, which it 
 
Sodium Salts. 21 1 
 
 closely resembles. Soda ley, or the solution of this hydrate 
 in water, is largely used in the manufacture of ordinary hard 
 soaps. 
 
 Sodic Chloride, or common sea salt (NaCl), is often ob- 
 tained from sea water, by allowing it to flow into very shallow 
 pools constructed for the purpose, and called saltpans, or 
 salterns where the water evaporates, and becomes concen- 
 trated in the heat of the sun. The salt crystallises out in 
 cubes, and forms the bay salt of commerce. The mother 
 liquor, or bittern, retains salts of potassium and magnesium, 
 which are extracted ; and it also furnishes the principal source 
 of bromine. In some inland countries brine springs furnish 
 important sources of supply of this chloride. Vast beds of 
 rock salt also occur in several countries, as in Galicia, Canada, 
 Spain, and in several parts of the British Islands, especially 
 in Cheshire. It is a common practice where coal is cheap to 
 allow water to flow down into the bed of salt, and to pump 
 up the liquor when it has become saturated. The brine is 
 then boiled down and crystallised. Our common table salt 
 is obtained in this way. ^/rtvrrut/ 
 
 Sodic chloride in small quantities is essential to life. It 
 is soluble in less than three times its weight of water. When 
 heated suddenly it decrepitates, and may be melted at a 
 bright red heat. Fish and meat are often salted to preserve 
 them from putrefaction ; but when so prepared they are 
 much less nutritious than when fresh, as the salt extracts the 
 nutritive and flavouring juices, which become saturated with 
 it and form brine. Salt is used largely as a manure to land. 
 It is consumed in immense quantities in the alkali works for 
 preparing other compounds of sodium ; and it furnishes the 
 supply of chlorine and hydrochloric acid. 
 
 Sodic Sulphate (Na 2 SO 4 , ioH 2 O) was formerly known as 
 Glauber's salt. It crystallises in four-sided prisms, which 
 crumble down to a white powder, and lose their water when 
 exposed to the air. It is very soluble in water, but more so 
 at 33 C. than either at a higher or lower temperature. Salt 
 
 P 2 
 
212 Sodic Carbonate. 
 
 cake is the name given to the sulphate when prepared by 
 decomposing common salt in a furnace with sulphuric acid, 
 at a high temperature, as a preliminary in the manufacture 
 of soda ash. Immense volumes of hydrochloric acid gas 
 are then given off, and these are condensed by causing 
 the fumes to pass through large towers filled with broken 
 coke or stone, over which a stream of water is kept con- 
 stantly trickling. A solution of hydrochloric acid is thus 
 obtained, while the sodic sulphate is left in the furnace. 
 The decomposition occurs in two stages ; in the first, one 
 half only of the salt is decomposed, hydric sodic sulphate 
 being formed, and the first half of the hydrochloric acid 
 comes off easily. The expulsion of the last half of the acid 
 requires a higher temperature, and is driven off by the action 
 of the fusible hydric sodic sulphate on the other half of the 
 sodic chloride 
 
 (1) NaCl + H a SO 4 - HC1 + NaHSO 4 ; and 
 
 (2) NaCl + NaHSO 4 = HC1 + Na 2 SO 4 . 
 
 Sodic Carbonate (Na 2 CO 3 , ioH 2 O). This salt crystallises 
 in large transparent prisms, which effloresce in the air. It 
 has a soapy disagreeable taste, and restores the blue colour 
 to reddened litmus paper. It is very soluble in water ; and 
 when heated melts in its water of crystallisation, which 
 amounts to 63 per cent, of the salt. The dried residue melts at 
 a bright red heat. The dry salt is made in enormous quan- 
 tities, and sold as soda-ash, which is used in the manufacture 
 of glass, in soap-making, in cleansing calicoes, and for a variety 
 of other important purposes. In order to prepare this carbo- 
 nate, salt cake is mixed with about its own weight of chalk and 
 rather more than half its weight of coal dust. This material 
 is then thrown in charges of about 125 kilog. upon the floor 
 of a hot reverberatory furnace (Fig. 69), divided into two 
 beds : on the more distant bed (B) it is first heated, and then 
 thrust on to the bed A, nearest the fire (c). There it melts, 
 and gives off jets of gas, which take fire, and burn with a 
 yellow flame. As soon as this escape of gas ceases, the 
 
Manufacture of Soda. 
 
 213 
 
 mixture is raked out into an iron trough, the next charge 
 is pushed down to the lower bed, and a fresh charge is in- 
 troduced. The chemical change which occurs in this fusion 
 Fig. 69. 
 
 consists mainly : ist, in reducing the sodic sulphate to sul- 
 phide, while carbonic oxide is formed and escapes, taking 
 fire, and becoming converted into carbonic anhydride 
 
 Na 2 SO 4 + 4 C = Na 2 S + 4CO. 
 
 2nd. The sodic sulphide is immediately decomposed by the 
 chalk into calcic sulphide and sodic carbonate 
 
 Na 2 S 
 
 CaCO = Na 2 CO 
 
 CaS. 
 
 This sodic carbonate is always mixed in the process with 
 quicklime, as it is found necessary to employ chalk in 
 excess, and this chalk becomes lime in the high temperature 
 of the furnace. A certain quantity of coal is also always 
 used in excess, and this likewise remains mixed in the fused 
 mass, technically known as ball soda or black ash. 
 
 This ball soda is now broken up, and placed in water at 
 about 45 C, which dissolves out the sodic carbonate, but 
 leaves the calcic sulphide undissolved. This undissolved 
 residue is the soda waste, so troublesome to the manufac- 
 turers. The solution of soda is next evaporated down, and 
 when calcined furnishes the soda-ash or crude alkali of 
 commerce, which contains from 50 to 56 per cent, of caustic 
 soda (Na 2 O), in the form of carbonate and hydrate. If this 
 soda-ash be dissolved in water, and the liquid allowed to 
 cool slowly in a tank, beautiful transparent crystals of the 
 carbonate (soda crystals] are gradually formed. 
 
2 1 4 Tests for the A Ikalies. 
 
 Hydric Sodic Carbonate (NaHCO 3 ), often called bicar- 
 bonate, is obtained by saturating a solution of the carbonate 
 with carbonic acid. It is deposited in white crystalline 
 grains, and is the substance commonly used for producing 
 an effervescing drink with lemon juice. 
 
 Tests for the Alkali Metals in Combination. The salts of 
 potassium are easily distinguished from those of sodium. 
 
 Exp. 218. To a pretty strong solution of the salt in question 
 add a solution of tartaric acid, and stir the mixture with a glass 
 rod. If potassium be present, white gritty crystals of cream of 
 tartar (KHC 4 H 4 O 6 ) will be deposited, but no such precipitate 
 will occur with salts of sodium. 
 
 Sodium forms salts all of which are soluble in water, so 
 that it does not produce any precipitate with ordinary test 
 solutions. It also gives a yellow colour to a colourless flame, 
 such as that of a spirit lamp or a Bunsen gas burner, whereas 
 potassium gives a violet-coloured flame. 
 
 The alkalies are all well distinguished from each other by 
 the colour which they give to flame, especially if the flame 
 be examined by means of the spectroscope. Potassium is 
 then recognised by a single line in the red and another in 
 the violet ; sodium, by a pair of intense lines, so close that 
 they generally seem but one, in the yellow; lithium, by a 
 single intense crimson line, and sometimes a faint one in the 
 orange if the flame be of a very high temperature ; rubidium, 
 by two lines in the red and two in the blue ; and caesium by 
 two intense lines in not so far on the blue as those of 
 rubidium, though in these two last-mentioned spectra there 
 are other lines of less importance. 
 
 Potassium salts may further be distinguished from 
 sodium by means of platinic chloride, which forms with the 
 chlorides of both metals a double salt ; that with potassium 
 (2KC1, PtCl 4 ) is nearly insoluble, that with sodium 
 (2NaCl, PtCl 4 /4H 2 O) crystallises in long soluble needles. 
 
 Exp. 219. Add to the solution two or three decigrams of po- 
 tassium chloride in a small porcelain dish, a few drops of hydro- 
 
A mmonia. 
 
 21$ 
 
 Fig. 70. 
 
 chloric acid, then an excess of solution of platinic chloride ; 
 evaporate to dryness over a saucepan of boiling water, arranged 
 so as to form a water-bath, a circular disk of tin, large enough 
 to project a little way beyond the edge of the saucepan, being 
 substituted for its lid, and a circular hole a little smaller than 
 the dish having been made in this lid, as shown in Fig. 70. 
 When cold, the residue is to be re- 
 dissolved in a few drops of water, 
 which will remove the soluble ma- 
 terials, and leave the sparingly soluble 
 salt of platinum and potassium in 
 small octahedra. 
 
 Caesium and rubidium also form 
 similar double chlorides with pla- 
 tinum chloride, but they are much 
 less soluble in hot water than the 
 potassium salt, a difference which is 
 sometimes made use of to separate 
 these bases from potassium. 
 
 (47) 3. Ammonium (H 4 N). This 
 is not a metal, nor is it even known 
 in a separate form ; but it is 
 generally considered to be the com- 
 pound quasi metal contained in the salts formed by the 
 action of the volatile alkali ammonia on the acids : such, for 
 instance, as sal ammoniac, the compound obtained by 
 neutralising hydrochloric acid with ammonia; ammonic 
 nitrate, the salt obtained by neutralising nitric acid with 
 ammonia; and ammonic sulphate, the salt obtained by 
 neutralising oil of vitriol with ammonia. All these salts 
 crystallise in the same form as the corresponding salts of 
 potassium with the same acids, and in every case the 
 quantity of hydrogen present in the salt formed from am- 
 monia is sufficient to convert it into the body ammonium, 
 which seems to act as a compound metal, much in the same 
 way as cyanogen is found to act like a compound halogen. 
 For instance : 
 
216 Carbonate of Ammonia. 
 
 Ammonia Ammonium Corresponding to 
 
 Salt Salt Potassium Salt 
 
 Hydrochlorate H 3 N, HC1 = (H 4 N)C1 (K)C1 
 
 Nitrate H 3 N, HNO 3 = (H 4 N)NO 3 (K)NO 3 
 
 Sulphate (H 3 N) a , H a S0 4 = (H 4 N) a SO 4 (K) a SO 4 
 
 A solution of ammonia in water may, in fact, be regarded 
 as ammonium hydrate, just as a solution of potash in water 
 is regarded as potassium hydrate 
 
 HN0 3 + (K)HO = (K)N0 3 + H 2 O. 
 
 Upon this supposition it is easy to explain the diverse 
 position of a metallic salt and the separation of the oxide, on 
 adding to it a solution of ammonia ; as, for instance : 
 Fe a Cl 6 + 6[(H 4 N)HO] = Fe s O 3 , 3H,O + 6[(H 4 N)C1] 
 Fe a Cl 6 + 6[(K)HO] = Fe a O 3 , sH 2 O + 6[(K)C1]. 
 
 Exp. 220. Dissolve a piece of sodium of the size of a pea, 
 in about 2 cub. cm. of pure mercury, in a test-tube : the two 
 metals unite suddenly with flame. When cold, pour the amalgam 
 into a large watch-glass, and cover it with a saturated solution 
 of sal ammoniac : the amalgam will gradually swell up and 
 become pasty, and will often float when thrown into water. 
 
 This appears to be an amalgam of ammonium, which is 
 formed and dissolved in excess of mercury, while common 
 salt is dissolved in the water 
 
 H 4 NC1 + NaHg = H 4 NHg + NaCl. 
 
 The ammonium cannot be obtained in a separate form, 
 as if decomposed by heat, and if the amalgam be thrown 
 into water, hydrogen is disengaged, while ammonia is dis- 
 solved. 
 
 One of the most remarkable of the salts of ammonium is the 
 common smelling-salt, or sesquicarbonate 2[(H 4 N) 2 O], 3CO 2 , 
 which is obtained by heating a mixture of chalk with half 
 its weight of powdered sal ammoniac, and subliming it 
 
 gradually 
 
 6H 4 NC1 + 3CaCO 3 = 
 
 3CaCl a + 2[(H 4 N) a O]3CO a + 2H 3 N + H 3 O. 
 A large quantity of free ammonia escapes in the operation, 
 
Baryta. 217 
 
 and the salt is always losing carbonate of ammonia, which 
 causes its pungent smell ; and a white powder, the bicarbon- 
 ate, or hydric ammonic carbonate, is left, 2[(H 4 N) 2 O], 3CO 2 
 becoming 2 H 4 NHCO 3 + (H 3 N) 2 CO 2 . 
 
 A solution of sal ammoniac gives a yellow nearly insoluble 
 double salt with platinic chloride (2H 4 NC1, PtCl 4 ), which 
 crystallises in cubes or octahedra, like the potassium salt. It 
 is often used for ascertaining the quantity of an ammonium 
 salt in solution. A still more delicate test is that known as 
 Nessler's,* which gives a brown stain when the solution 
 contains less than a millionth of its weight of a salt of 
 ammonium. 
 
 GROUP II. METALS OF THE ALKALINE EARTHS. 
 i. BARIUM. 2. STRONTIUM. 3. CALCIUM. 
 
 (48) i. BARIUM : Symb. Ba ; Atomic Wt. 137. 
 
 This metal is scarcely known in a separate state. When 
 combined with oxygen, it forms Baryta (BaO), and a dioxide 
 (BaO 2 ) ; but the first is the only one which combines with 
 acids, and forms salts. Baryta (BaO) may be obtained by 
 treating baric nitrate in a crucible till the salt, which decrepi- 
 tates and melts, again becomes solid, and finally ceases to 
 give off oxygen at a bright red heat. The baryta is left as a 
 grey porous mass, which absorbs moisture and carbonic acid 
 from the air. If mixed with half its weight of water it slakes, 
 forming a hydrate, whilst great heat is given out. This 
 hydrate is largely soluble in boiling water, and the solution 
 deposits a crystalline hydrate of baryta as it cools. The 
 liquid is strongly alkaline, and becomes milky by the action 
 of carbonic acid. 
 
 The dioxide (BaO 2 ) may be formed by passing oxygen 
 
 * Nessler's test for ammonia is prepared thus : add to a solution of 
 mercuric chloride a solution of potassic iodide till the red precipitate 
 first formed is nearly all dissolved. Then add a large excess of caustic 
 potash ; let the mixture stand in a stoppered bottle for three or four 
 days, and decant when clear. It gives a brown precipitate when added 
 to a solution containing a salt of ammonium. This consists of HgH a NI. 
 
2 1 8 Salts of Barium. 
 
 over anhydrous baryta at a low red heat ; but if the heat be 
 raised to full redness, the second atom of oxygen is given off 
 again, and baryta is reproduced. If this oxide be dissolved 
 at a low temperature in hydrochloric acid, baric chloride is 
 formed, and the remarkable body H 2 O 2 , "hydrogen peroxide, 
 is formed in the liquid 
 
 BaO 2 + 2HC1 = BaCl 2 + H 2 O 2 . 
 
 The most abundant compounds of baryta are the sulphate 
 and the carbonate. 
 
 The sulphate (BaSO 4 ) is a very heavy mineral, sp. gr. 4*6, 
 the name baryta having been given to the earth in allusion 
 to its weight, from fiapvc, 'heavy.' It is found crystallised 
 in right rhombic prisms. It is insoluble in water and in 
 solutions of the acids. It is easily obtained artificially by 
 mixing a solution of a sulphate with one of baric chloride, 
 or any soluble barium salt. This sulphate, although in- 
 soluble, furnishes a sulphide soluble in dilute acids if it be 
 heated with carbon. 
 
 Exp. 221. Grind about 10 grams of the sulphate to a very 
 fine powder ; mix it with an equal weight of flour, and make it 
 into a paste with oil; place this mixture in a crucible, with a 
 little charcoal ; lute on the cover of the crucible with fireclay, 
 and when the lid is dry raise the crucible gradually to an intense 
 heat in a furnace, keeping it up for about an hour : then allow 
 it to cool. 
 
 In this process the sulphate becomes reduced to sulphide, 
 while carbonic oxide escapes 
 
 BaSO 4 + 4C = BaS + 4CO. 
 
 Exp. 222. Treat the residue, when cold, with a large quantity 
 of boiling water. Everything should dissolve except the excess 
 of carbon. 
 
 The sulphide thus obtained, if treated with hydrochloric 
 acid, is dissolved, baric chloride is formed, and sulphuretted 
 hydrogen escapes 
 
 BaS + 2HC1 = BaCl 2 + H 2 S. 
 
Compounds of Calcium. 219 
 
 This chloride is one of the salts most often used for pre- 
 cipitating sulphuric acid from the sulphates. Baric Car- 
 bonate (BaCO 3 ) forms the mineral called Witherite, found 
 occasionally in the lead veins in the north of England. It 
 is insoluble in water; soluble with effervescence in dilute 
 acids ; and is easily obtained in the form of a white powder 
 by mixing a solution of sodic carbonate with one of baric 
 chloride or nitrate. 
 
 This carbonate, and all the soluble barium salts, are 
 strongly poisonous, the best antidote being Epsom salts. 
 
 Tests for Barium Salts. The best test for the barium 
 salts in solution is the formation of a white precipitate, in- 
 soluble in nitric acid, on adding a solution of calcic sulphate. 
 They communicate a green tinge to flame, and form, with 
 a solution of sodic hyposulphite, a white sparingly soluble 
 hyposulphite. This last test is useful as a means of dis- 
 tinguishing them from strontium salts, which, however, give 
 a crimson colour to flame. 
 
 2. STRONTIUM: Symb. Sr; Atomic Wt. 87-5; Sp. Gr. 
 
 2-54- 
 
 This metal occurs chiefly combined as sulphate and 
 carbonate in forms resembling the same compounds of 
 barium, for which it was long mistaken ; but its compounds 
 are much less abundant. Its salts are not poisonous. The 
 nitrate is used to give a red fire in the manufacture of 
 fireworks. Strontic sulphate is rather more soluble than 
 baric sulphate. 
 
 (49) 3- CALCIUM: Symb. Ca; Atomic Wt. 40; Sp. Gr. 
 i'578 : 
 
 This is a malleable metal of a very pale yellow colour. 
 It is seldom prepared, but may be procured by decomposing 
 its fused chloride by the voltaic battery. Calcium tarnishes 
 quickly when exposed to the air. It forms but a single 
 oxide (CaO), the very important substance known as lime, 
 which is extremely abundant, both as carbonate and as 
 
22O Limestone. 
 
 sulphate; the chalk and limestone rocks, as well as the 
 different forms of marble, all consist of carbonate more or 
 less pure. Compounds of calcium are also found in all 
 fertile soils, and they occur in a large number of crystallised 
 minerals, amongst which fluor spar, calcic fluoride, is one of 
 the most important. 
 
 Calcic Oxide. Lime (CaO) : Atomic Wt. 56. This is 
 obtained by heating the pure carbonate for some time to 
 bright redness, carbonic anhydride being expelled 
 CaCO 3 = CaO + CO 2 . 
 
 Exp. 223. Place a few lumps of black marble in the open 
 fire, or in an open crucible, with a hole at the bottom, and heat 
 it strongly for an hour or two. When it is completely con- 
 verted into quicklime, the lumps, when broken across, will be 
 quite white. 
 
 Common lime is made by heating limestone for some 
 days in a large egg-shaped or conical kiln t in which a fire is 
 kindled at the bottom. 
 
 Freshly burnt lime is called quicklime. It is a white in- 
 fusible substance, and if left exposed to the air it swells up 
 gradually and falls to powder. If water be poured upon it 
 great heat is given out, the earth swells up and combines 
 with part of the water, and is said to become slaked. In 
 this process a definite hydrate (CaO, H 2 O) is formed : it is 
 a light dry powder, from which the water may be driven 
 out at a red heat. 
 
 Lime is sparingly soluble in water; the solution forms 
 limewater, which is alkaline, and is often used as a test for 
 the presence of carbonic acid, by which it is immediately 
 rendered turbid. 
 
 Milk of lime is merely slaked lime diffused through water. 
 
 The great consumption of lime is in mortars and cements. 
 Common mortar is made by mixing i part of lime into a 
 thin paste with water, and adding 3 or 4 parts of sharp sand. 
 It hardens slowly in the air, and gradually absorbs carbonic 
 acid. 
 
Plaster of Paris. .221 
 
 Limestones are rocks originally deposited in the form of 
 mud from water, and vary in composition, sometimes being 
 mixed with clay, sometimes with sand, or with other 
 materials which alter their properties when burned. Com- 
 mon mortar is gradually dissolved away by the action of 
 water, but when the limestone contains clay in moderate 
 quantity it furnishes, after burning, a cement which hardens 
 under water. Such lime is called hydraulic lime. It slakes 
 much more slowly than pure lime. 
 
 Lime is moreover largely used as a manure, being especially 
 useful in reclaiming peat or bog land, where it decomposes 
 the excess of vegetable matter and renders the soil more 
 open, while the lime becomes a carbonate. 
 
 Lime is used also in many chemical processes, as in con- 
 verting the carbonate of potassium and sodium into caustic 
 alkalies. It is used by the tanner to loosen the hair on 
 hides by dissolving the outer surface of the skin, and it is 
 employed to remove impurities from coal gas. 
 
 Calcic Chloride (CaCl 2 ) is made by dissolving limestone or 
 chalk in diluted hydrochloric acid, and evaporating the 
 solution. It may be obtained in deliquescent crystals with 
 .6H 2 O ; but when strongly heated it loses 4H 2 O, and leaves 
 a porous mass still retaining 2H 2 O, which absorbs moisture 
 greedily, and is often used for drying gases, which are allowed 
 to pass slowly over it. 
 
 Calcic Sulphate, or gypsum (CaSO 4 , 2HO 2 ), is an abundant 
 and important mineral. When heated to about 500 it loses 
 its water, and crumbles down to a white powder, which is ex- 
 tensively used for finishing the interior of houses, under the 
 name of plaster of Paris. If the dry powder be made into 
 a thin paste with water, the mixture becomes solid in a few 
 minutes, owing to the recombination of the water with the 
 sulphate, and expands slightly, eventually becoming as hard 
 as the original gypsum. If the gypsum has been heated 
 to redness it loses its porosity, and no longer * sets ' with 
 water. 
 
222 Calcic Carbonates. 
 
 Exp. 224. Select a medal suitable for the purpose ; paste a 
 shallow rim of paper round it, so as to make it like the lid of a 
 pill-box, and anoint the surface of the medal very lightly with oil. 
 Mix a little of the dry plaster with water till it becomes of the 
 consistence of thin cream ; apply it carefully with a hair pencil to 
 every part of the surface, so as to exclude air bubbles ; then pour 
 a thicker mixture into the mould. Allow it to remain for an 
 hour. The cast may then be removed : it will be a reversed 
 copy of the medal. 
 
 Gypsum in certain cases forms a valuable manure Calcic 
 sulphate is a common impurity in spring waters. 
 
 Calcic Carbonate (CaCO 3 : Atomic Wt. 100). Besides its 
 occurrence in marble and in Iceland spar, which crystallises 
 in rhombohedra, this carbonate is found in crystals of a 
 different system, the prismatic, forming the mineral arago- 
 nite. It forms the different varieties of limestone, chalk, 
 oolite, and calcareous marl, and is the principal constituent 
 of corals, of the shells of fish, and of egg-shells, besides enter- 
 ing into the composition of the bones of animals in greater 
 or less amount. It also forms a combination with magnesic 
 carbonate, which is known as dolomite or magnesian lime- 
 stone, which is very abundant in certain geological deposits. 
 Many of these compact limestone rocks are highly prized 
 for building. Portland stone is an oolite ; that is, it is formed 
 of little rounded grains, which resemble the hard roe of a fish 
 in aspect. 
 
 Calcic carbonate is scarcely soluble in pure water, but it 
 is freely dissolved by water containing carbonic acid, and is 
 deposited again in crystals as the gas escapes. Enormous 
 masses of the crystallised carbonate are thus formed in the 
 lapse of ages. In the limestone hills of Derbyshire and 
 other places, caverns occur where this process is always going 
 on ; water charged with carbonic acid and calcic carbonate 
 makes its way through the roof of the cavern, where, as the 
 carbonic acid gradually escapes, the carbonate is deposited 
 in hanging columns, like icicles, termed stalactites, whilst the 
 water falling upon the floor deposits a fresh portion of the 
 
Aluminum. 223 
 
 dissolved carbonate, which slowly grows upwards till the 
 stalagmite so formed meets the stalactite depending from the 
 roof, and thus a natural pillar of crystallised calcic carbonate 
 is formed. 
 
 In volcanic districts, where the springs are often highly 
 charged with carbonic acid, this deposition is often very 
 rapid; the spring, as it escapes, deposits a porous material 
 termed tufa, while upon sides of the stream a more compact 
 substance, known as travertine, which is a sort of marble 
 highly prized for building purposes, is formed. 
 
 Tests for Calcium Salts. Solutions of these salts give no 
 precipitate with ammonia, or with ammonic sulphide, but 
 they give a white one of calcic carbonate with sodic or po- 
 tassic carbonate, as do also the salts of barium, and of stron- 
 tium ; from these they may be distinguished by means of a 
 solution of calcic sulphate, with which calcium salts give no 
 precipitate. Ammonia oxalate gives, in neutral or alkaline 
 solutions of calcium salts, a white precipitate of calcic 
 oxalate, soluble in nitric or hydrochloric acid, but not in 
 acetic acid. They give a greenish yellnw tinge to flame. 
 
 CHAPTER XII. 
 GROUP III. METALS OF THE EARTHS. 
 
 (50) i. ALUMINUM : Symb. Al; Atomic Wt. 27; Sp. Gr. 
 2*67. 
 
 This metal derives its name from alum, of which material 
 it constitutes between 5 and 6 per cent. Its compounds 
 are among the most abundant constituents of the rocks, 
 including felspar, hornblende, and slate. Aluminum may be 
 obtained from cryolite (sNaF, A1F 3 ) by fusing it with sodium ; 
 but the method usually practised consists in decomposing 
 sodic aluminic chloride (NaCl, A1C1 3 ) by heating it wi;h 
 
224 Calico Printing. 
 
 sodium ; an intense action occurs, and the aluminum is ob- 
 tained in a melted state under the fused sodic chloride 
 NaClAlCl 3 + sNa = 4 NaCl + Al. 
 
 Aluminum is a white malleable metal, resembling zinc in 
 colour and hardness. It may be rolled into foil, and drawn 
 jnto wire. When struck, it gives a clear musical sound. It 
 melts at a temperature below that needed for the fusion 
 of silver. It preserves its brightness in the air, and is but 
 slowly oxidized at a red heat. Nitric acid attacks it with 
 difficulty, but it is rapidly dissolved by hydrochloric acid, 
 and by solutions of the alkalies, hydrogen being given off. 
 This metal, with about 90 per cent, of copper, forms a golden 
 yellow alloy, called aluminum bronze, well fitted for castings. 
 
 Alumina (A1 2 O 3 ). There is only one oxide of this metal, 
 the earth alumina, which, when crystallised, constitutes the 
 Oriental ruby, the sapphire, and corundum. Emery is an- 
 other form, of less purity. All these minerals are very hard ; 
 their colour is due to small quantities of the oxides of chro- 
 mium, iron, .or manganese. Alumina, combined with silica, 
 forms the different varieties of clay, and is the basis of porce- 
 lain and earthenware. The soluble salts of alumina are 
 of value to the calico printer. Hydrated alumina combines 
 intimately with many vegetable colours, and forms with them 
 pigments, called lakes. 
 
 Exp. 22$. Grind some madder root into a coarse powder, 
 and pour a litre of boiling water upon three or four grams of 
 it. Stir it up occasionally; then let it settle for three or four 
 hours ; pour off the red liquor. Mix it with a solution of 4 grams 
 of alum, and add a solution of 4 grams of sodic carbonate. Let 
 the solution rest in a tall glass jar : a red deposit or lake, con- 
 sisting of the colouring matter combined with the alumina, will 
 be produced. 
 
 If a pattern be stamped on calico with a solution of alum, 
 and be then boiled with a solution of madder, the figures will 
 be permanently dyed, while the colour may be easily washed 
 out of the remainder of the cloth. In this case the alumina 
 
Alumina. 225 
 
 in the alum fixes itself upon the cloth, and acts as a mordant, 
 which ' bites in ' the colour, or attaches it to itself, and thus 
 renders the dye fast. Other oxides, such as those of iron 
 chromium, and tin, are used for the same purpose, but they 
 change the colour of the dye stuff at the same time that they 
 fix it upon the calico. All metallic oxides used for such a 
 purpose are termed mordants by the dyer. 
 
 Alumina may be precipitated from its salts by a solution 
 of potash, but an excess of potash redissolves the precipitate. 
 Ammonia also precipitates the alumina as a bulky jelly-like 
 hydrate, but does not redissolve it. 
 
 This hydrate is freely soluble in diluted acids, but the solu- 
 tion has the property of reddening litmus ; so that, while the 
 hydrate acts the part of a feeble acid towards potash and soda, 
 which dissolve it, it also acts the part of a base towards acids, 
 though it is but a weak base, compared with either potash 
 or soda, or bases which contain, like them, i atom of oxygen 
 with 2 atoms of a monad, or, like calcium, i atom of a dyad 
 metal. Alumina resembles ferric and chromic oxides. It 
 crystallises when united with acids in the same form as these 
 oxides do when acted upon by the same acids, and con- 
 sequently it is regarded as a sesquioxide. 
 
 The different basic oxides may be compared together in 
 this manner : 
 
 MONOXIDES 
 Monads Dyads 
 
 K a O Potash CaO Lime 
 
 Na a O Soda FeO Ferrous Oxide 
 
 Ag a O Argentic Oxide CrO Chromous Oxide 
 
 SESQUIOXIDES 
 
 Al a O 3 Alumina 
 Fe a O 3 Ferric Oxide 
 Cr a O 3 Chromic Oxide 
 
 Alumina forms a yellow chloride (A1 2 C16), which is vola- 
 tile below a red heat. It is obtained by mixing alumina 
 and powdered charcoal into a paste with oil, heating the 
 mixture to redness, and sending a current of dry chlorine 
 gas over it : the chlorine unites with aluminum, and the 
 carbon with the oxygen 
 
 A1 2 3 + 3 C + 3 C1 2 = A1 2 C1 6 
 The chloride is used in extracting the metal. 
 
 Q 
 
226 Alums. 
 
 But the most important salt is the sulphate, which is 
 obtained by treating clay for some days with sulphuric acid, 
 at a heat nearly sufficient to make the acid boil. This sul- 
 phate (A1 2 3S0 4 ) is very soluble ; but if mixed with a due pro- 
 portion of potassic sulphate, it forms a salt, which crystallises 
 in fine octahedra, and is well known as potassium alum 
 (KA1 2 SO 4 , i2H 2 O). 
 
 Alum is a double salt, which is made in vast quantities 
 for the use of the calico printer. Ammonic sulphate is now 
 largely employed instead of the potassic salt. It then pro- 
 duces ammonium alum (H 4 N, Al2SO 4 , i2H 2 O), which crys- 
 tallises quite as readily and in exactly the same form as 
 the potassium salt. The place of the aluminic sulphate 
 may be supplied by ferric sulphate, chromic sulphate, and 
 manganic sulphate. In each case a salt is formed, which is 
 different in colour from true alum, but like it, and crystallises 
 in octahedra, resembling those of alum ; so that there are a 
 number of alums known, some of which may be represented 
 as follows : x 
 
 Ammonium Alum . . (H 4 N)Al2SO 4 , I2H 2 O 
 
 Potassium Alum . . KAl2SO 4 , i2H 2 O 
 
 Iron Alum . . . KFe2SO 4 , I2H 3 O 
 
 Manganese Alum . . KMn2SO 4 , i2H 2 O 
 
 Chrome Alum . . . KCr2SO 4 , I2H 3 O 
 
 Alum has a sweetish, astringent taste. Its solution reddens 
 
 litmus strongly. When heated it melts, first in its water of 
 
 crystallisation, then it froths up, forms a tenacious paste, 
 
 and at last becomes a white, bulky, porous, infusible mass, 
 
 called burnt alum. 
 
 A good deal of alum is made by roasting alum schist (a 
 kind of black bituminous clay, which contains a good deal of 
 pyrites) for some weeks at a low temperature. The pyrites 
 absorbs oxygen, and becomes gradually converted into ferrous 
 sulphate, while the second atom of sulphur in the pyrites 
 combines with oxygen, and the product unites with alumina, 
 forming a mixture of aluminic and ferrous sulphates 
 + O 2 == 2FeS 
 
Clays Varieties of Felspar. 227 
 
 and on adding potassic chloride, alum crystallises out from 
 the mixed sulphate and chloride of iron 
 
 FeSO 4 + A1 2 3SO 4 + 2KC1 = FeCl 2 + 2KAhSO 4 . 
 
 Silicates of Alumina Clays. Alumina forms a great 
 number of silicates. All the varieties of clay consist of 
 aluminic silicate, more or less mixed with other matters 
 derived from the rocks which, as they have crumbled down, 
 have furnished the clay. The best fire clay consists of 
 Al 2 O 3 2SiO 2 , 2H 2 O. It is used in making bricks for lining 
 furnaces, and for crucibles and glass pots, as well as for 
 other purposes where resistance to a high temperature is 
 required. But many kinds of clay contain lime, magnesia, 
 or ferric oxide intermixed, and they greatly increase its 
 fusibility, and diminish its plasticity, or fitness for kneading 
 and moulding while in a moist state, and cause it to be more 
 readily attacked by acids, while an excess of silica renders 
 it less fusible. The more mixed varieties of clay constitute 
 marl and loam. Pure clay forms, before it has been ignited 
 and when kneaded with water, a tenacious plastic insoluble 
 paste, which, when slowly dried and exposed to a high heat, 
 shrinks very much, often splits, and becomes extremely hard, 
 but does not melt in the furnace. Clay is not attacked readily 
 by any acid except-tk*. hydrofluoric. Strong sulphuric acid, 
 when strongly heated with it, gradually decomposes it. 
 
 When breathed upon, or slightly moistened, clay gives out 
 a peculiar odour, and if applied in a dry state to the tongue 
 or lips, it adheres to them strongly, and absorbs the saliva. 
 
 Felspar is a very abundant and important double silicate 
 of aluminum and potassium (K 2 O, A1 2 O 3 , 6SiO 2 ), often 
 called adularia. When it contains sodium it is white, and is 
 termed albite ; and when it contains lithium, the mineral is 
 known as petalite. Felspar is a very abundant constituent 
 of the older rocks. Mixed with mica and quartz, it forms 
 granite and gneiss. Porphyry is a compact felspar with 
 crystals of felspar dispersed through it. Basalt is a dark- 
 
 Q 2 
 
228 Pottery Ware. 
 
 coloured volcanic rock, containing crystals of augite diffused 
 through compact felspar. The porous pumice of volcanoes 
 is chiefly felspar altered by high temperature ; and obsidian 
 is melted pumice. Mica is a more complex silicate of 
 alumina, containing a little fluoride. 
 
 Earthenware and China. The basis of these articles is 
 silicate of alumina, but to diminish the tendency to crack 
 during drying, which it has if used alone, the clay is mixed 
 with ground flints, which, however, lessens its tenacity.* 
 To make up for this defect, it is usual to add some fusible 
 material which, at the temperature required for fusing, be- 
 comes softened, and greatly aids in binding the particles 
 together. The clay thus mixed and tempered is moulded, 
 while moist, upon the potter's wheel, after which the dif- 
 ferent articles are dried in a warm room, and are then fired 
 at a comparatively moderate heat : they are thus obtained in 
 a porous state, called biscuit. The patterns or designs are 
 next applied, the colouring matter consisting usually of some 
 metallic oxide ground up into a paste with turpentine or 
 linseed oil. Blue is generally given by cobalt oxide, green by 
 chromic oxide, brown by a mixture of the oxides of iron and 
 manganese, black by uranium oxide, and so on. The ware, 
 when painted, is much too porous for use ; it is therefore 
 glazed by dipping each article into water containing a fusible 
 mixture, finely ground, in suspension. The porous mass 
 quickly absorbs moisture, leaving a thin uniform layer of 
 glaze upon the surface. The goods are then enclosed in 
 fireclay vessels, and exposed to a furnace heat. The glaze 
 melts, and leaves a smooth surface, so that the material is 
 no longer porous and absorbent. 
 
 Stoneware is glazed differently. The pots are raised to a 
 strong red heat in the furnace, and a quantity of damp salt 
 is thrown in. The material, is rapidly volatilised. The salt 
 is decomposed by the silica and ferric oxide of the clay in 
 
 * In making crucibles and firebricks, old pots, finely powdered, are 
 generally used instead of ground flints, but for the same purpose. 
 
Magnesium. 229 
 
 the presence of steam. Ferric chloride and hydrochloric 
 acid pass off with the excess of salt employed, and form the 
 dense brownish fumes which are seen escaping at intervals 
 from the kilns on glazing days, while sodic silicate fuses on 
 the surface of the ware, and makes it impervious to water, 
 the actions being as follows : 
 
 H 3 O + 2NaCl + SiO 3 = 2HC1 + Na z O, SiO 2 ; and 
 Fe a O 3 + 6NaCl + 3SiO z = Fe^ + 3(Na z O, SiO a ). 
 
 Tests for Aluminum Salts. The solutions have a sweet, 
 astringent taste. Potash gives a white precipitate, soluble 
 in excess of the alkali. Ammonia, a white precipitate, in- 
 soluble in excess of the alkali. Carbonates of the alkalies, 
 a white precipitate, insoluble in excess of the alkaline car- 
 bonate. Ammonic sulphide gives a white precipitate of 
 hydrated alumina. 
 
 Exp. 226. Heat a little alum on a platinum wire, bent into 
 a small hook, in the outer flame of a Bunsen gas-burner. After 
 the salt has been touched with a drop of a solution of cobalt 
 nitrate, a pale blue compound of alumina and cobalt oxide will 
 be formed. It is used as a blowpipe reaction for alumina. 
 
 2. Glucinum is the characteristic ingredient in the beryl 
 and emerald. 3. Yttrium and (4) Erbium are both found 
 only in a few rare minerals. 5. Cerium is met with rather 
 more abundantly, accompanied by two other metals, (6) 
 Lanthanum and (7) Didymium, in a mineral called cerite, 
 but none of these are of sufficiently frequent occurrence to 
 need further notice here. 
 
 GROUP IV. MAGNESIUM METALS. 
 i. MAGNESIUM. 2. ZINC. 3. CADMIUM. 4. INDIUM. 
 
 (51) i. MAGNESIUM: Symbol, Mg ; Atom. Wt. 24-3; 
 Sp.Gr. 174. 
 
 This metal is obtained by decomposing its chloride by 
 means of sodium. It is purified by distilling it at a bright 
 
230 Compounds of Magnesia. 
 
 red heat in a current of hydrogen. Magnesium is a malleable, 
 ductile metal, of the colour of silver. It takes a high polish, 
 which it preserves in a dry air ; but it becomes slowly oxidized 
 in a moist atmosphere. At a moderate red heat it melts. 
 
 Exp. 227. Heat a piece of magnesium wire in dry air or in 
 the flame of a lamp : it takes fire, and becomes oxidized, pro- 
 ducing white fumes of magnesia, giving out an intense white light. 
 
 This light is occasionally used for photographic purposes, 
 or in lighting up the interior of buildings. 
 
 Magnesium is dissolved rapidly by diluted hydrochloric 
 acid, giving off hydrogen ; and it is freely soluble in a solu- 
 tion of sal ammoniac. When heated in chlorine, or in the 
 vapour of bromine, iodine, or sulphur, it burns brilliantly. 
 
 Magnesia (MgO). This is the only known oxide of the 
 metal. It occurs abundantly in combination as dolomite, or 
 magnesic calcic carbonate ; as Epsom salts, or sulphate ; 
 as chloride in sea water ; and as silicate in a variety of 
 forms, both alone, as in talc and serpentine, and in com- 
 bination with the silicates of alumina and other bases, as in 
 augite, hornblende, and asbestos ; so that it is an important 
 and frequent constituent of rocks. Magnesia is a bulky, 
 white, tasteless, and nearly insoluble powder, obtained by 
 strongly heating the carbonate or nitrate of the metal. 
 
 Exp. 228. Place a little magnesia on moistened turmeric 
 paper : it is sufficiently soluble to render the parts moistened, 
 on which it rests, brown. 
 
 Exp. 229. Place a small quantity of magnesic carbonate in a 
 crucible ; put on the cover, and heat the crucible in the fire for 
 an hour. Take it out, and allow it to cool : caustic magnesia 
 will be left When moistened with water, it will not slake ; but 
 if hydrochloric or nitric acid be poured upon the moistened 
 earth, it will dissolve slowly, without effervescence. 
 
 Magnesic Chloride (MgCl 2 ) may be obtained by adding 
 to a solution of one part of magnesia in hydrochloric acid 
 three times its weight of sal ammoniac, evaporating to dry- 
 ness, and heating the mixed salts to redness in a covered 
 
Tests for Magnesium Salts. 231 
 
 crucible : the magnesic salt fuses, while the ammoniacal salt 
 goes off in vapour. This chloride is deliquescent ; but if its 
 solution be evaporated by itself, a good deal of hydrochloric 
 escapes, and magnesia is left. 
 
 Magnesic Sulphate (MgSO 4 , 7H 2 0), familiarly known as 
 Epsom Salts. This is the most important soluble salt of the 
 metal. It crystallises in four-sided solid prisms, which are 
 very soluble, and have a bitter taste. 
 
 Tests for Magnesium Salts : 
 
 Exp. 230. Pour over 25 grains of Epsom salts 50 c. c. of 
 boiling water : the salt dissolves, and part crystallises out as the 
 solution cools. To a portion of the cold solution add a solution 
 of sodic hydric carbonate : no precipitate occurs. Boil this 
 mixture, and a white precipitate (the white magnesic carbonate), 
 mixed with magnesic hydrate, is immediately separated. 
 
 Exp. 231. Add to a solution of magnesic sulphate some 
 ammonic chloride ; then add a solution of hydric disodic phos- 
 phate. Stir the mixture : crystals of ammonic magnesic phosphate 
 are deposited in crystalline grains (MgH 4 N, PO 4 , 6H a O), in- 
 soluble in water, containing ammonia in solution, but appreciably 
 soluble in pure water. This is a very delicate test for mag- 
 nesium salts, but it is readily dissolved by acids. Add a few 
 drops of hydrochloric acid to the neutral solution : the precipi- 
 tate disappears. 
 
 Exp. 232. Collect a little of the crystalline precipitate in a 
 filter ; dry it over a steam bath. Place a few decigrams of the 
 dry salt in a small crucible, cover it, and weigh the whole ; then 
 heat it for ten minutes in a Bunsen gas-flame. Water and am- 
 monia will be expelled. Allow the crucible to cool ; then weigh 
 it a second time : it will be found to have lost weight con- 
 siderably. The salt which is left is magnesic pyrophosphate 
 2(H 4 NMgP0 4 ) = 2 H,N + H 3 + Mg,P s O 7 . 
 
 Exp. 233. Add to a solution of any magnesic salt, such as 
 the sulphate, a solution of potash : a white precipitate of 
 hydrated magnesia is formed. Excess of alkali does not re- 
 dissolve it. Limewater produces a similar precipitate. Am- 
 monic oxalate, if mixed with an excess of solution of sal am- 
 moniac, gives no precipitate with solutions of magnesium salts. 
 
232 Properties of Zinc. 
 
 Exp. 234. Place a little of the magnesium salt on a platinum 
 wire moistened with a solution of cobalt nitrate. A pink residue 
 will be obtained on heating the wire in the outer part of a 
 Bunsen gas-flame. 
 
 (52) 2. ZINC or Spelter-. Symbol, Zn ; Atom. Wt. 65; 
 Sp. Gr. 7*15; Fusing Pt. 412. 
 
 This well-known metal occurs chiefly in the form of sul- 
 phide, constituting blende (ZnS), or in that of carbonate, 
 known to mineralogists as calamme (ZnCO 3 ). In order to 
 extract the metal the sulphide is roasted, or heated mode- 
 rately in a current of air : the sulphur burns off, and leaves 
 the oxide. When calamine is roasted, water and carbonic 
 anhydride are expelled, and zincic oxide is also left. The 
 oxide, in either case, is next mixed with powdered coke, and 
 heated. The carbon removes the oxygen as carbonic oxide, 
 while the zinc, which is volatile at a full red heat, distils over, 
 and may be condensed. 
 
 Zinc is a hard bluish-white metal, which, when a mass of 
 it is broken across, shows a beautiful crystalline fracture. 
 At ordinary temperatures it is rather brittle ; but between 
 100 and 150 it may be rolled, and wrought with ease, 
 though between 200 and 300 it again becomes brittle, and 
 may be powdered. At 412 it melts, and it boils steadily 
 at 1040, and may be distilled at a bright red heat. 
 
 Exp. 235. Heat a crucible to a bright red heat, and throw 
 into it a few fragments of zinc. The metal will melt, and give 
 off vapours which burn with great brilliancy, depositing white 
 clouds of zincic oxide. 
 
 Zinc soon tarnishes in a moist atmosphere ; the thin film 
 of oxide adheres closely to the metal, and protects it from 
 further change. Dilute sulphuric and hydrochloric acids 
 dissolve zinc rapidly, and give off hydrogen. Nitric acid 
 also attacks it powerfully, but the acid itself is at the same 
 time partly decomposed. 
 
 Zinc is often used as a substitute for lead in roofing ; it is 
 lighter -and cheaper, but less durable. It is also used as the 
 
Salts of Zinc. 233 
 
 active metal in the voltaic battery, and becomes dissolved 
 in proportion as the electricity is liberated. Sheet iron is 
 often coated with zinc, to render it less liable to rust ; it 
 then forms what is called galvanised iron. Brass is the most 
 important of the alloys of zinc. It contains about two parts 
 of copper to one of zinc, but the proportions of the two metals 
 may be varied according to the purpose to which the alloy 
 is to be applied. German silver is brass whitened by the 
 addition of nickel. 
 
 Zinc Oxide (ZnO). Zinc forms but one oxide, which is 
 generally obtained in the form of a white flocculent powder 
 by burning the metal in a current of air. When heated, this 
 oxide becomes yellow, but on cooling it recovers its white- 
 ness. It is easily soluble in the acids. If a solution of 
 potash be cautiously added to a solution of a salt of zinc, 
 such as the sulphate, a white gelatinous hydrated oxide is 
 precipitated, but it is redissolved by an excess of potash : 
 ammonia has a similar effect. 
 
 Zinc Sulphate (ZnSO 4 , 7H 2 O) is obtained in the ordinary 
 process of preparing hydrogen by dissolving zinc in diluted 
 sulphuric acid. It crystallises in white soluble prisms, re- 
 sembling those of magnesic sulphate. It produces vomiting 
 if swallowed in quantities, such as one or two grams. 
 
 The zinc salts are colourless ; they have an astringent 
 metallic taste. Sulphuretted hydrogen produces no precipi- 
 tate in their acidulated solutions ; but if mixed with a 
 solution of ammonic sulphide, a white gelatinous zinc sul- 
 phide is formed. A solution of sodic carbonate gives, with 
 zinc salts, a white precipitate of hydrated basic zinc car- 
 bonate, not soluble in excess of the alkaline carbonate ; but if 
 ammonic carbonate be used instead, the precipitate is redis- 
 solved by the addition of the ammonic carbonate in excess. 
 Zinc salts yield, with potassic ferrocyanide, a white pre- 
 cipitate. 
 
 Before the blowpipe, in the reducing flame, on charcoal, 
 the metal is reduced and volatilised, burning into white 
 
234 Cadmium Indium. 
 
 fumes of the oxide. If placed on charcoal, and moistened 
 with a solution of cobalt nitrate, they give, when heated in 
 the oxidating flame, a green infusible residue. 
 
 3. CADMIUM : Symb. Cd ; Atom, Wt. 1 1 2. This is a com- 
 paratively rare white, soft, easily fusible, volatilisable metal, 
 usually found as sulphide, accompanying the ores of zinc in 
 small quantity. Being more volatile than zinc, it comes over 
 in the first portions which distil over during the reduction. 
 It may be separated from zinc by dissolving these portions 
 of the metal in sulphuric acid, and transmitting a stream of 
 sulphuretted hydrogen gas through the solution ; a yellow 
 cadmium sulphide is thus separated. This precipitate may 
 be dissolved in hot hydrochloric acid, precipitated from the 
 solution by the addition of ammonic carbonate, and reduc- 
 ing the carbonate by heating it in an earthen retort with 
 powdered charcoal ; the metal distils over at a red heat. It 
 takes fire when heated strongly in air, and burns, forming a 
 brown oxide. The addition of cadmium to the more fusible 
 metals furnishes alloys of low melting point without destroy- 
 ing their toughness and malleability. 
 
 Cadmium furnishes a single oxide (CdO), which is brown 
 when anhydrous, and white when hydrated. Ammonia dis- 
 solves it easily, but ammonic carbonate does not dissolve it. 
 Chloride and iodide of cadmium are used by the photo- 
 grapher. They crystallise easily. 
 
 4. Indium is a white soft metal, which has been found in 
 small quantity occasionally associated with zinc. It was 
 discovered by its property of furnishing, when heated in a 
 colourless gas-flame, a light which is characterised by two 
 strong lines in the indigo portion of the spectrum. 
 
235 
 
 CHAPTER XIII. 
 
 GROUP V. METALS ALLIED TO IRON. 
 
 i. COBALT. 2. NICKEL. 3. URANIUM. 4. IRON. 5. CHROMIUM. 
 
 6. MANGANESE. 
 
 (53) i. COBALT : Symb. Co ; Atom. Wt. 59 ; Sp. Gr. 8-95. 
 
 This metal is never used in the arts in the metallic state, 
 but it furnishes several compounds which are much valued 
 for their beautiful colour. It generally occurs in combina- 
 tion with arsenicum, and is almost always found associated 
 with nickel. 
 
 Metallic cobalt is obtained with difficulty in a pure state 
 by a complicated process, for details of which some larger 
 works on chemistry should be consulted. It is nearly as 
 infusible as iron, is of a reddish grey colour, hard, ductile, 
 and strongly attracted by a magnet. 
 
 Cobalt furnishes several oxides : two are well known the 
 protoxide (CoO), which, when treated with acids, yields the 
 common salts of the metal, and the sesquioxide (Co 2 O 3 ). 
 These two oxides may be combined with each other in more 
 than one proportion. 
 
 The protoxide is soluble in acids, and forms salts which, 
 when anhydrous or in concentrated solutions, are of a beauti- 
 ful blue colour ; but they become pink in dilution. At a 
 particular stage of dilution they become blue when heated, 
 although when cold the solution is pink. This oxide is 
 largely used for painting on porcelain, to which it imparts a 
 rich blue colour. 
 
 Smalt is a beautiful blue glass coloured with this oxide of 
 cobalt. When finely powdered it forms the stone-blue used 
 by laundresses to correct the yellow tinge in linen. 
 
 Cobalt Nitrate (Co2NO 3 , 6H 2 O) is prepared by dissolving 
 cobalt oxide in nitric acid. Its solution is sometimes em 
 ployed as a test before the blowpipe. A fragment of the 
 compound suspected to contain aluminum, magnesium, or 
 zinc, is supported on charcoal, and touched with a minute 
 
236 Salts of Cobalt Nickel 
 
 quantity of a solution of the nitrate : aluminous compounds 
 give a blue residue if heated in the outer flame, those of 
 magnesium a pink, and those of zinc a green residue. 
 
 Tests for Salts of Cobalt. All the compounds of cobalt 
 are easily distinguished before the blowpipe by the intense 
 blue colour which they impart, even in minute quantity, to 
 a bead of borax when fused with it on a loop of platinum 
 wire. If the quantity of cobalt be large, the colour is so 
 intense that it seems to be black. 
 
 Acid solutions containing cobalt are not precipitated by 
 sulphuretted hydrogen, but ammonic sulphide yields a black 
 sulphide of cobalt. Solution of potash precipitates a rose- 
 coloured hydrated oxide, insoluble in excess of the alkali. 
 Ammonia and its carbonate also give a rose-coloured pre- 
 cipitate, soluble in excess of the alkali, forming a brownish 
 solution, which absorbs oxygen from the air, and becomes 
 red. It forms one of a large series of ammoniacal com- 
 pounds which contain cobalt. 
 
 2. NICKEL : Synib. Ni Atom. Wt. 59 ; Sp. Gr. 8-82. 
 This metal has a remarkable analogy with cobalt. It occurs 
 associated with it in nature, has the same atomic weight, 
 and is, like cobalt, powerfully attracted by the magnet. Its 
 most abundant ore is kupfernickel, the arsenide (NiAs). The 
 mode of its extraction is described in the book on ' Metal- 
 lurgy.' Nickel is a brilliant silver-white, hard, ductile metal, 
 nearly as infusible as iron. Its most important alloy is Ger- 
 man silver, which is a kind of brass whitened by the addition 
 of about 20 per cent, of nickel. 
 
 There are two oxides of nickel, a protoxide (NiO) and 
 a sesquioxide (Ni 2 O 3 ) ; the first is the only one of importance. 
 It is obtained by heating the nitrate or the carbonate to 
 redness. It furnishes an olive-green powder. The hydrated 
 oxide is of a delicate apple-green, and may be precipitated 
 from its salts by the addition of a solution of potash, which 
 does not redissolve it when added in excess. Acids dissolve 
 
Uranium Iron. 237 
 
 it and furnish pale green solutions. Ammonia precipitates 
 the hydrated oxide from these solutions, but, if added in 
 excess, redissolves the precipitate, and furnishes a blue liquid. 
 Ammonic carbonate precipitates a green carbonate of nickel, 
 soluble in excess of the alkaline carbonate. 
 
 3. URANIUM : Symb. U ; Atom. Wt. 120. This metal is 
 scarcely known in its pure state. It occurs chiefly in the 
 form of the black oxide (2UO, U 2 O 3 ), which constitutes 
 about 80 per cent, of the mineral pitchblende. The metal 
 furnishes several oxides. The black oxide just mentioned 
 is used as an intense black for painting on porcelain. The 
 sesquioxide (U 2 O 3 ) combines with the alkalies potash and 
 ammonia, and forms a yellow compound. It is also soluble 
 in acids, such as the nitric and acetic, and forms yellow 
 salts, the solutions of which give a brown precipitate with 
 potassic ferrocyanide, and a yellow precipitate with ammonia, 
 not soluble in excess of the alkali. This oxide is used to 
 communicate a peculiar opalescent yellow colour to glass, 
 which exhibits the optical property of fluorescence in a re- 
 markable degree. 
 
 (54) 4. IRON: Symb. Fe ; Atom. Wt. 56; Sp. Gr. 7-84. 
 This, the most important of the metals, is also very 
 abundant. It is found now and then in the metallic state, 
 associated with nickel, cobalt, and some other elements, in 
 those remarkable masses known as meteorites, which fall in 
 an ignited state from the atmosphere from time to time 
 possibly the fragments of some formerly existing planet. 
 For the supply of the vast demand for iron the ores chiefly 
 wrought are magnetic ironstone, or loadstone (FeO, Fe 2 O 3 ) ; 
 specular iron ore (Fe 2 O 3 ), or red haematite, which is a 
 more abundant form of the same oxide ; brown haematite 
 (2Fe 2 O 3 , 3H 2 O), the hydrated sesquioxide ; and spathic iron, 
 or ferrous carbonate (FeCO 3 ). This last is the material 
 which, when mingled with clay, furnishes the immense de- 
 posits of clay-ironstone which occur in what are called the 
 
238 Ores of Iron Cast Iron. 
 
 coal formations of Great Britain. Where this carbonate 
 contains bituminous matter instead of clay, it constitutes the 
 black-band ironstone of the coal fields on the Clyde. 
 
 In order to obtain iron from the ore, if in the form of clay- 
 ironstone, it is broken up into masses about the size of the two 
 fists, and then roasted in heaps to expel water and carbonic 
 acid, by which process the ore is left in a porous state, highly 
 favourable to its reduction in the blast furnace. These fur- 
 naces are usually about fifteen metres high, and in them a 
 mixture of ore, coal, and limestone is subjected to intense heat, 
 fresh supplies being added at the top as the materials sink 
 down in the furnace. Powerful blowing machines supply 
 air constantly near the bottom, and thus a steady and very 
 powerful heat is maintained. The fuel burns, and is converted 
 first into carbonic anhydride ; and this becomes changed by 
 the excess of carbon into carbonic oxide, which, meeting the 
 descending charge, reduces its oxide to metallic iron. The 
 reduced metal, mixed with the earthy matter of the ore, sinks 
 down into the hotter region ; here the lime, though infusible 
 when heated alone, acts as a flux upon the clay of the ore : 
 the two melt and become converted into an imperfect glass 
 or s/ag, while the minutely divided iron combines with a 
 portion of carbon of the fuel, and forms the comparatively 
 fusible material known as cast iron. The slag and melted 
 iron sink down to the bottom of the furnace ; the iron, being 
 much heavier, collects beneath the slag, and is run off at 
 intervals of twelve or twenty-four hours into moulds formed 
 in the sand of the floor, and, being afterwards separated 
 from each other, form pigs of iron. The slag which collects 
 on the surface of the iron before it is run off flows over 
 continually at the opening left for the purpose on a higher 
 level. 
 
 Cast iron, or pig iron, is brittle, and cannot be forged, 
 though, if run into moulds, it takes impressions even of the 
 finest lines. It never contains more than five per cent, of 
 carbon ; but it is not a pure carbide, for in the intense heat 
 
Iron and Steel. 239 
 
 the carbon of the fuel reduces not only the iron oxide, but 
 also portions of silica, alumina, and lime, as well as phos- 
 phates and sulphates which are present. The cast iron, 
 therefore, varies much in its quality, according as it contains 
 more or less of carbon, silicon, sulphur, phosphorus, and other 
 elements. When melted cast iron is allowed to cool slowly, 
 part of the carbon crystallises out, and remains diffused 
 through the mass in small flakes of graphite. This variety 
 of the metal is known as grey cast iron. The same iron, 
 if cooled rapidly, is crystalline in structure, and contains 
 the carbon chemically combined, forming what is known as 
 white cast iron. 
 
 In order to purify the pig iron, it is melted in a current of 
 heated air, so as gradually to burn off the carbon, silicon, 
 and other impurities, which are more combustible than the 
 iron itself, the carbon escaping as carbonic oxide, the silicon 
 as silica, and the phosphorus as phosphates. The silica, 
 with the phosphates, unite with oxide of iron, and form a 
 slag. The metal is thus rendered less and less fusible : it is 
 collected by the workman into large balls, which are sub- 
 jected while white hot to the blows of a powerful hammer, 
 which squeeze out the melted slag ; and the metal, after 
 being passed through grooved rollers, becomes converted 
 into malleable iron, or wrought iron. 
 
 Iron, when combined with a smaller proportion of carbon 
 than is contained in cast iron, furnishes steel, of which there 
 are several varieties. The quantity of carbon in good steel 
 varies between 07 and 17 per cent. That which possesses 
 the greatest tenacity has been found to contain from i -3 to 
 i -5 per cent, of carbon and about OT of silicon. Fuller 
 details of the mode of making cast iron, wrought iron, and 
 steel, will be found in the text book on ' Metallurgy.' 
 
 Steel is more fusible than iron ; it is brittle, and when 
 broken across shows a fine granular texture; but its most 
 characteristic property is that of becoming almost as hard as 
 diamond when heated to redness and then suddenly cooled 
 
240 Properties of Iron. 
 
 by plunging into water or oil. It is thus rendered extremely 
 brittle and almost perfectly elastic. This extreme hardness 
 and brittleness may be removed by the process of tempering, 
 which consists in reheating the hardened steel moderately, 
 and then allowing it to cool. The higher the temperature to 
 which it is raised in the second heating, the softer is the 
 steel 
 
 Exp. 236. Allow a drop of nitric acid to fall upon a slip of 
 polished steel : a dark grey spot is produced, owing to the solu- 
 tion of the metal in the acid, while the carbon is left. If the 
 acid be dropped upon a slip of iron a green stain is formed. 
 
 Bar iron generally contains about o'2 per cent, of carbon. 
 It is hard, takes a high polish, is tough and fibrous, with a 
 peculiar bluish-grey colour. It has a spec. grav. of 77. 
 It requires the most intense heat of a wind furnace to melt 
 it. It passes through a soft intermediate condition between 
 actual fusion and solidity. This property is of the highest 
 practical importance ; and it is owing to this fact that the 
 smith is enabled, after sprinkling the surface of two white 
 bars with sand, to weld them together so completely that 
 the junction is as tough as any other part. The sand acts 
 as a flux to the layer of oxide which forms upon the surface 
 of the hot metal. A slag is thus formed upon each bar. By 
 the blow of the hammer the film of melted matter is forced 
 out, and the two clean surfaces of the metal become 
 united. 
 
 Iron is susceptible of magnetism to a greater degree than 
 any other known substance. At a high temperature it burns 
 readily, as is seen in the vivid sparks thrown off from it when 
 being forged, and the brilliant combustion exhibited by a coil 
 of watch-spring or of wire, when heated and introduced into 
 oxygen gas (Exp. 14). In dry air polished iron remains 
 unaltered; but if exposed to a moist atmosphere, so that 
 liquid water be deposited on the metal, it quickly becomes 
 rusty, and when once a spot of rust is formed the action 
 proceeds rapidly. Iron may, however, be kept for any 
 
Oxides of Iron. 241 
 
 length of time unchanged in water quite free from air, as 
 well as in limewater, or in water containing a little caustic 
 alkali. If steam be passed over red-hot iron, minute crystals 
 of the magnetic oxide are formed, and hydrogen is given off 
 (Exp. 44, Fig. 13). 
 
 Chlorine, bromine, and iodine combine quickly with iron, 
 and dissolve it easily at common temperatures, as may be 
 easily seen by placing a few drops of bromine under water 
 in a test-tube and allowing a small quantity of iron filings to 
 fall into the bromine. The iron will disappear, with a strong 
 evolution of heat. Diluted sulphuric and hydrochloric acid 
 dissolve the metal with escape of hydrogen (Exp. 45 and 
 p. 60). The metal is rapidly attacked by nitric acid, with 
 abundant escape of nitric oxide. Iron may, however, be 
 kept unaltered in nitric acid of sp. gr. i -45, or upwards ; 
 but if the acid be diluted below 1*35, it dissolves the metal 
 with violence. 
 
 Iron yields four definite oxides : i. The protoxide (FeO), 
 the base of the green or ferrous salts ; 2. The sesquioxide, 
 the base of the red or ferric salts ; 3. The black or magnetic 
 oxide (FeO, Fe 2 O 3 ), a compound of the two preceding 
 oxides, which, when treated with acids, yields a mixture of 
 ferrous and ferric salts, but no distinct saline compounds 
 referable to it in constitution ; and 4. Ferric Acid, an 
 unstable metallic acid, the anhydride of which is unknown, 
 but which forms salts, of which potassic ferrate (K 2 FeO 4 ) is 
 the representative. 
 
 Ferrous Oxide (FeO) is scarcely known in a pure state, it 
 absorbs oxygen so rapidly. It forms a white hydrate ; and if 
 obtained by adding an alkali, such as ammonia, to a solution 
 of ferrous sulphate, the white precipitate becomes green, 
 passing into bluish green, black, and finally ochre-coloured, 
 by the formation of sesquioxide. Ferrous salts, such as the 
 chloride or sulphate, are obtained by dissolving the metal or 
 its sulphide in hydrochloric or sulphuric acid, and allowing 
 the solution to crystallise out of contact with air. These 
 
242 Sulphides of Iron. 
 
 salts have a delicate bluish-green colour, and an astringent, 
 inky taste. If exposed to the air while moist, they become 
 grass green, and slowly absorb oxygen. 
 
 Ferric Oxide (Fe 2 O 3 ) is an abundant ore of iron. When 
 anhydrous and crystallised, it forms specular iron ore. When 
 in masses it furnishes haematite. Brown haematite anhydrate 
 (2F 2 O 3 , 3H 2 O) is another abundant and valuable ore. In 
 this form it is readily dissolved by acids. Jewellers' rouge is 
 a finely-powdered red oxide, obtained by igniting the sulphate, 
 as in the process for preparing the Nordhausen oil of vitriol. 
 
 When a ferric salt in solution, such as the chloride, is 
 mixed with potash or ammonia, a milky reddish-brown 
 hydrated ferric oxide is precipitated. 
 
 Iron combines with sulphur in several proportions. The 
 Protosulphide (FeS) may be obtained as follows : 
 
 Exp. 237. Heat a bar of iron white hot in the fire, and bring 
 it in contact with a roll of sulphur over a pail of cold water. 
 The sulphur and iron immediately unite, and form drops of a 
 reddish-brown colour, which run down into the water. 
 
 This sulphide is used in the laboratory for preparing 
 sulphuretted hydrogen, which is disengaged without heat, 
 by pouring upon it sulphuric acid diluted with 5 or 6 times 
 its bulk of water. 
 
 The Disulphide (FeS 2 ) is an abundant natural product. It 
 forms the yellow brassy-looking mineral known as iron 
 pyrites, often found crystallised in cubes. 
 
 Exp. 238. Place a few fragments of pyrites in a small sealed 
 tube, and heat it to dull redness in a lamp-flame ; sulphur will 
 gradually be sublimed. 
 
 When heated in the air the sulphur burns off, and furnishes 
 sulphurous anhydride, which is largely prepared from it for 
 conversion into sulphuric acid. An impure oxide of iron is 
 theQ left. Iron pyrites is not easily dissolved, except by 
 nitric acid, or, still better, by a mixture of nitric with hydro- 
 chloric acid. Mispickel (FeAsS) is the name given to an 
 arsenic sulphide of iron, which furnishes a good deal of the 
 
Tests for Iron. 243 
 
 arsenic of commerce. When heated in a current of air, it is 
 converted into ferric oxide, while sulphurous and arsenious 
 anhydrides are produced. 
 
 A solution of a ferrous salt, such as the sulphate, when 
 mixed with ammonic sulphide, yields a black hydrated 
 ferrous sulphide, and in a similar way a solution of a ferric 
 salt, such as the chloride, yields a hydrated sesquisulphide 
 FeSO 4 + (H 4 N) 3 S = (H 4 N) 2 SO 4 + FeS ; and 
 Fe 2 Cl 6 + 3[(H 4 N) g S] = 6H 4 NC1 + Fe a S 3 . 
 
 Both these sulphides, when exposed to the air, become 
 converted into hydrated oxide, while the sulphur is separated 
 without undergoing oxidation" 
 
 4 (FeS, H 2 0) + 3 2 = 2(Fe 2 O 3 , H 2 O) + 2 S 2 . 
 
 Ferrous Chloride (FeCl 2 , 4H 2 O) may be obtained by dis- 
 solving the metal in hydrochloric acid, and evaporating the 
 solution till it crystallises. Ferric Chloride, formerly known 
 as sesquichloride (Fe 2 Cl6), may be obtained sublimed in 
 anhydrous brown scales by heating iron wire to redness in 
 a current of dry chlorine gas ; it is very deliquescent. A 
 solution of ferric chloride may also be obtained by passing a 
 current of chlorine gas through a solution of ferrous chloride 
 as long as the gas is absorbed, or it may be procured by dis- 
 solving hydrated ferric oxide in hydrochloric acid. 
 
 Ferrous Carbonate (FeCO 3 ) is found native in immense 
 quantities. When crystallised, it is known ,as spathic iron ore ; 
 when mixed with clay, it forms the clay-ironstone ; and 
 when with bituminous matter, furnishes the blackband iron- 
 stone. Ferrous carbonate is also the salt which is found in 
 chalybeate springs, in \v''nch it is held in solution by free 
 carbonic acid. Mere exposure to air then causes, its sepa- 
 ration : the acid escapes, oxygen is absorbed, and hydrated 
 ferric oxide, mixed with a small quantity of organic matter, 
 subsides, forming the ochry deposits so common around 
 ferruginous springs. 
 
 Tests for Iron. The salts of this metal have an inky and 
 astringent taste. The ferrous salts are known by the deep 
 
 R 2 
 
244 Compounds of Chromium. 
 
 blue precipitate which they give with the red prussiate 
 (potassic ferricyanide) in solution. If one of the ferrous 
 salts be boiled with nitric acid, it is converted into a solution 
 of ferric salt, while one of the lower oxides of nitrogen 
 escapes. Ferric salts in solution are known by the rusty-brown 
 precipitate of hydrated ferric oxide which they give with 
 ammonia, by the blood-red solution produced by potassic 
 sulphocyanide when added to an acid or neutral solution, by 
 the bright Prussian blue precipitate occasioned by a solution 
 of yellow potassic ferrocyanide, and by the bluish-black inky 
 precipitate produced by tincture of galls in neutral solutions. 
 This last is the colouring matter in ordinary writing-ink. 
 Potassic ferricyanide gives no precipitate in ferric solutions, 
 and thus may be used to distinguish them from those of 
 ferrous salts. 
 
 Exp. 239. Add to a solution of a ferric salt, mixed with a little 
 solution of a salt of cobalt, a weak solution of ammonia, drop 
 by drop, stirring the liquid between each addition, until the pre- 
 cipitate just begins no longer to be dissolved. The solution will 
 become of a deeper red or yellow tinge. Dilute the liquid freely 
 with water, and then boil it ; an insoluble basic salt of iron will 
 be formed, and every trace of iron may thus be precipitated, 
 whilst the cobalt will remain dissolved, and may be found by 
 adding a little more of ammonia. 
 
 (55) 5. CHROMIUM (Symb. Cr; At. Wt. 52-5) is never 
 used as a metal, or even as an alloy, but is highly prized for 
 the numerous brilliant-coloured compounds which it forms. 
 The name chromium is derived from xi ^/""? colour. It is a 
 rather rare element, and is most usually found in the chrome 
 ironstone (FeO, Cr,O 3 ). 
 
 The metal is very hard and infusible. It is sometimes 
 obtained by heating chromic chloride with sodium. Chromium 
 forms four well-known oxides : chromous oxide (CrO), which is 
 unimportant ; chromic oxide (Cr 2 O 3 ), the basis of the common 
 green or violet salts of the metal : it is prized as a green 
 pigment for colouring porcelain (these two oxides corre- 
 
Salts of Chromium. 245 
 
 Spond to ferrous and ferric oxide in composition); a brown 
 oxide (CrO, Cr 2 O 3 ), corresponding with the magnetic oxide 
 of iron, but which is unimportant; and a stable metallic 
 anhydride (CrO 3 ) 3 which, when dissolved in water, furnishes 
 an important acid, from which the class of chromates is 
 obtained. 
 
 The chromates are prepared on a large scale by heating 
 chrome ironstone to redness, quenching in cold water to 
 render it friable, then reducing it to an extremely fine 
 powder, and heating to bright redness in a current of air, 
 with a mixture of chalk and potassic carbonate. The mixture 
 absorbs oxygen, and becomes yellow. When cold, it is 
 treated with water, which dissolves out the chromates. 
 Potassic carbonate is added as long as it occasions any pre- 
 cipitate of chalk from the solution of calcic chromate. The 
 yellow solution is drawn off, mixed with nitric acid, and on 
 evaporation potassic dichromate crystallises out in large- red 
 anhydrous prisms (K 2 CrO 4 , CrO 3 ), whilst nitric acid remains 
 in solution. 
 
 This dichromate is the common commercial salt. It is a 
 salt of exceptional composition, being a compound of the 
 chromic anhydride with the mineral potassium salt. If 
 formed in the regular way it would be composed as follows : 
 
 KHCr0 4 , or K 2 CrO 4 , H 2 CrO 4 ; 
 
 but such a salt is not known. The dichromate is soluble 
 in about ten parts of cold water. If 4 measures of the cold 
 saturated solution of this salt be mixed with 5 of oil of 
 vitriol, and the liquid be allowed to cool, chromic anhydride 
 crystallises in crimson needles, which may be drained and 
 dried upon a brick. 
 
 Besides the dichromate, there is a normal chromate of 
 potassium (K 2 CrO 4 ), which is yellow, and does not crystal- 
 lise easily ; and there are also potassic salts known which 
 contain two and three atoms of chromic anhydride combined 
 with one atom of the normal salt. 
 
 Baric chromate is a canary-yellow insoluble powder. 
 
246' Oxides of Manganese. 
 
 Chrome Yellow is the normal lead chromate (PbCrO 4 ). It 
 falls as a bright yellow insoluble powder when a solution 
 of lead acetate or lead nitrate is mixed with one of potassic 
 chromate or dichromate. Argentic chromate (Ag 2 CrO 4 ) is 
 of a dark red colour, and is insoluble. Mercurous chromate 
 (3Hg 2 CrO 4 , Hg 2 O), obtained by adding mercurous nitrate 
 to a solution of a chromate, is orange coloured and nearly in- 
 soluble. The chromates of cadmium and bismuth are yellow. 
 
 If a soluble chromate, such as potassic chromate, be 
 mixed with hydrochloric acid, chromic acid and a chloride 
 of the metal are formed in the solution ; and if a little alcohol 
 or sugar be added, and the liquid be boiled, it becomes 
 green, owing to the reduction of the chromic acid to 
 chromic oxide, which becomes dissolved in the excess of 
 hydrochloric acid. If to this green solution ammonia be 
 added in excess, a pale green hydrated chromic oxide is 
 precipitated. This may serve as a distinctive test for the 
 chromates. 
 
 6. MANGANESE : Symbol, Mn ; Atomic Weight, 55. 
 This is an element which is widely diffused, and enters 
 into the formation of many minerals in small quantity, but 
 its only important and valuable ore is the black oxide, found 
 either in masses or in radiated groups of crystals. 
 
 The metal is not used alone, but it is often present in 
 small quantity in cast iron. It is difficult to obtain manganese 
 in a state of purity, as it possesses a powerful attraction 
 for carbon, so that, if reduced, as it may be without much 
 difficulty, by making the carbonate into a paste with oil, 
 and heating it in a covered crucible lined with charcoal, and 
 keeping it for an hour at the highest heat of a forge, the 
 button of metal is always combined with carbon. It also, 
 like iron, combines with silicon. Manganese is a hard, 
 brittle, greyish-white metal, and is feebly magnetic. It is 
 remarkable for the number of oxides which it forms. Man- 
 ganous oxide (JNInO) is the basis of the common salts of the 
 
Compounds of Manganese. 247 
 
 metal ; the sesquioxide (Mn 2 O 3 ) is unimportant, and does 
 not furnish stable salts. The red oxide (Mn 3 O 4 ) may be 
 regarded as the compound of the two preceding ones ; it 
 corresponds to the magnetic oxide of iron, and furnishes no 
 corresponding salts. The black oxide or dioxide (MnO 2 ) 
 is the most important native compound of the metal ; when 
 treated with acids, it gives off half its oxygen, and furnishes 
 manganous salts 
 
 2MnO2 + 2H 2 SO 4 = 2MnSO 4 + 2H 2 O -f O 2 . 
 
 With hydrochloric acid it yields chlorine and manganous 
 chloride 
 
 MnO 2 + 4HC1 = MnCl 2 + 2H 2 O + C1 2 ; 
 
 and if heated alone, it yields oxygen and the red oxide, 
 giving off one-third of its oxygen 
 
 3MnO 2 = Mn 3 O 4 + O 2 . 
 
 When found native, it is called grey manganese ore, or pyro- 
 lusite. Another variety, in warty masses, is psilomelane, and 
 a hydrated form is called wad. It is often found mixed 
 with earthy carbonates, and other impurities. Besides the 
 above-mentioned oxides, manganese forms two others, which 
 are not known in a separate state (MnO 3 and Mn 2 O 7 ), which, 
 when dissolved in water, furnish manganic and permanganic 
 acids. The manganates are of a green colour. Sodic Man- 
 ganate (Na 2 MnO 4 ) is prepared on a large scale by heating a 
 mixture of caustic soda and finely-powdered manganese to 
 dull redness for several hours in shallow vessels. Its solu- 
 tion forms Condy's green disinfecting liquid. This green 
 substance furnishes an excellent method of distinguishing 
 before the blow-pipe, for if the substance be heated on pla- 
 tinum foil, with a little sodic carbonate, it gives a green 
 colour to the melted mass if a trace of manganese be 
 present. 
 
 Solutions of the manganates part very readily with oxygen : 
 they must not even be filtered through paper. A small 
 quantity of a free acid changes their solution from green to 
 
248 Tests for Manganese. 
 
 red, owing to the formation of a permanganate and of a 
 manganous salt 
 
 5K a MnO 4 + 4H,SO 4 = 
 2K a Mn 2 O 8 + MnSO 4 + 3K 2 SO 4 + 4H,O. 
 
 Potassic Permanganate -(K^MnaOs) may be obtained on a 
 small scale by mixing 40 grams of finely-powdered man- 
 ganese dioxide with 35 grams of potassic chlorate, and 
 adding a solution of 50 grams of caustic potash to the mix- 
 ture, evaporating to dryness, and heating the powdered 
 residue to dull redness in a clay crucible. When cold, the 
 mass is treated with water, and decanted from the insoluble 
 residue ; a splendid purple liquid is obtained, which on 
 evaporation yields needles of the permanganate. A solu- 
 tion of this salt is very readily deoxidised and deprived of 
 colour. It furnishes a valuable test liquid in many cases of 
 volumetric analysis. 
 
 Exp. 240. Dissolve two or three decigrams of iron wire in 
 diluted sulphuric acid ; then add water till the liquid measures 
 about half a litre, Add gradually a solution of the permanganate, 
 and stir the mixture : the colour will disappear until the whole of 
 the iron has passed from the state of ferrous into that of ferric 
 salt. When this point is reached, the pink colour of the per- 
 manganate will remain unchanged. 
 
 The change may be thus represented 
 
 ioFeSO 4 + K a Mn a O 8 + 8H a SO 4 -= 
 5Fe 2 3SO 4 + K 2 SO 4 + 2MnSO 4 + 8H 2 O. 
 
 Tests for Manganese. Manganous chloride is formed in 
 large quantities in the ordinary mode of preparing chlorine. 
 The manganous salts are of a delicate pink colour, and give 
 nearly colourless solutions. They give with ammonia a 
 white hydrated manganous oxide, soluble in excess of the 
 alkali; but the solution quickly absorbs oxygen, and deposits 
 a brown hydrated peroxide. Ammonic sulphide precipi- 
 tates a flesh-coloured hydrated manganous sulphide. Solu- 
 tion of potassic carbonate precipitates a white manganous 
 carbonate. Before the blowpipe they give, with sodic car- 
 
Tin. 249- 
 
 bonate on platinum foil, the characteristic green-coloured 
 manganate ; and they give in the oxidising flame, with a 
 bead of borax, a violet colour, which disappears in the re- 
 ducing flame. 
 
 CHAPTER XIV. 
 
 GROUP VI. TIN AND ALLIED METALS. 
 i. TIN. 2. TITANIUM. 3. ZIRCONIUM. 4. THORINUM. 
 
 (56) TIN: Symb. Sn; Atom. Wt. 118; Sp. Gr. 7-29; 
 Fusing Pt. 228. 
 
 This familiar metal was known in the. early ages of the 
 world. It is not found in many places, Cornwall and 
 Malacca supplying the greatest portion. .The only ore of tin 
 of importance is its dioxide, or tinstone, which is often found 
 crystallised. After the ore has been crushed, and roasted to 
 get rid of arsenicum and sulphur, and washed to remove 
 the oxides of iron and copper which are formed from the 
 pyrites by which it is accompanied, the metal is reduced 
 by heating the residue with powdered anthracite or char- 
 coal. 
 
 Tin is a white metal, with a tinge of yellow, and a high 
 lustre, which it preserves unchanged in the atmosphere. It 
 is rather soft, and very malleable, so that it is easily reduced 
 into sheets of tinfoil, but it is not sufficiently tough to be 
 drawn readily into wire. It melts easily (about 228 C), but 
 is not volatilised in the furnace. It has a considerable 
 tendency to crystallise. 
 
 Exp. 241. Warm a sheet of tinplate over a lamp, and then 
 pour over its surface a mixture of nitric and hydrochloric acids 
 diluted with 8 or 10 parts of water. In a few minutes crystalline 
 flakes will appear. They may be rendered permanent by wash- 
 ing off the acid, drying the plate, and varnishing it. 
 
 If heated to bright redness in the air, tin burns with a white 
 light, and furnishes the dioxide. 
 
250 Oxides of Tin. 
 
 Hydrochloric acid, if heated with tin, dissolves it slowly, 
 with escape of hydrogen, forming stannous chloride (SnCl 2 ), 
 one of its most important salts. Nitric acid of sp. gr. 1-3 
 oxidises it violently, and forms a white hydrated oxide, known 
 as metastannic acid, but does not form a nitrate. Tin also 
 combines easily with sulphur, phosphorus, chlorine, and 
 bromine, when heated with them. 
 
 Tin forms several important alloys. Tinplate consists oC 
 sheet iron which has been cleansed from oxide, and coated 
 with tin by plunging it into a bath of the melted metal, 
 Pewter is an alloy of 4 parts of tin 3nd i of lead. Plumbers 1 
 solder is a fusible alloy of equal parts of tin and lead. 
 Britannia metal is composed of equal parts of brass, tin, 
 antimony, aftd bismuth ; it is much used for making common 
 spoons and teapots. 
 
 Copper and tin form several valuable alloys. Bronze is 
 a combination of copper, tin, and zinc, with 5 or 6 per cent, 
 of tin and 3 or 4 of zinc. Gun metal contains 9 or 10 per 
 cent, of tin, bell metal about 22 per cent., and speculum metal 
 about 33 per cent. Tinfoil, when amalgamated with mer- 
 cury, forms the silvering applied to the backs of mirrors. 
 
 Tin forms two oxides, stannous oxide (SnO) and stannic 
 oxide (SnO 2 ). The Stannous Oxide may be obtained as a 
 white hydrate by adding a solution of sodic carbonate to one 
 of stannous chloride : carbonic anhydride escapes, and the 
 hydrated tin oxide is precipitated. It is soluble in an excess 
 of caustic potash, 'but not in excess of ammonia. This 
 oxide, when moist, absorbs oxygen from the air. It is soluble 
 in acids, and furnishes the stannous salts, of which, how- 
 ever, stannous chloride is the only one of considerable im- 
 portance. 
 
 Stannic oxide, the dioxide (SnO 2 ), constitutes the ore of 
 tin. It is in this form very hard, and is insoluble in acids ; 
 but when powdered and fused with potash or soda, it com- 
 bines with the alkali, and becomes soluble in water. When 
 combined with water, this oxide furnishes a feeble metallic 
 
Compounds of Tin. 251 
 
 acid, which is itself readily soluble in diluted acids, though 
 it furnishes salts called stannates. 
 
 Sodic Stannate (Na 2 O, SnO 2 , 3H 2 O) may be prepared by 
 fusion, as above described ; it is used, under the name of tin- 
 prepare liquor, by the calico printer as a mordant for fixing 
 certain colours. 
 
 Another hydrate of this oxide, possessed of entirely dif- 
 ferent properties, is obtained by treating metallic tin with nitric 
 acid. It is called Metastannic Acid (H 2 O, Sn 5 Oio, 4H 2 O), 
 and is quite insoluble in other acids. It also forms unstable 
 salts, such as potassic metastannate (K 2 O, Sn 5 O 10 , 4H 2 O). 
 When metastannic acid is heated to redness, it loses all its 
 water, and furnishes a pale buff-coloured substance, some- 
 times called putty powder. 
 
 Tin forms two well-marked sulphides. Stannous Sulphide 
 (SnS) is thrown down as a chocolate-brown hydrate when a 
 stream of sulphuretted hydrogen is passed through a solution 
 of stannous chloride or other stannous salt. It is dissolved 
 by a solution of ammonic disulphide. 
 
 Stannic Sulphide (SnS 2 ) may be obtained as a hydrate, of 
 a dingy yellow colour, by transmitting sulphuretted hydrogen 
 through a solution of a stannic salt, such as stannic chloride ; 
 and it is readily dissolved by ammonic sulphide, with which 
 it forms a soluble double sulphide. A similar double salt 
 may be obtained in crystals (2Na 2 S, SnS 2 , i2H 2 O), if sodic 
 sulphide be used as the solvent. 
 
 Stannic sulphide may be obtained in beautiful yellow 
 flakes, forming mosaic gold, by heating an amalgam of tin 
 with sulphur and sal ammoniac ; but the operation requires 
 care. 
 
 Stannous Chloride (SnCl 2 , 2H 2 O), the tin salts of the dyer, 
 may be obtained crystallised in needles by dissolving tin in 
 strong hydrochloric acid, and evaporating the liquid. It has 
 a strong attraction both for chlorine and for oxygen. It 
 therefore acts as a powerful reducing agent 
 
 Exp. 242. Add to a solution of corrosive sublimate a drop 
 
252 Tests for Tin. 
 
 or two of a solution of stannous chloride : a white precipitate of 
 calomel is formed 
 
 2HgCl 2 + SnCl, = 2HgCl + SnCl 4 . 
 
 Now add the tin salt in excess : the precipitate becomes dark 
 grey. It consists of metallic mercury, which may be collected 
 into globules 
 
 2HgCl + SnCl, = 2Hg + SnCl 4 . 
 The calomel loses the whole of its chlorine. 
 
 Stannous chloride is used by the dyer for deoxidising 
 indigo and the peroxides of iron and manganese. 
 
 Stannic Chloride (SnCl 4 ) is a colourless liquid, which emits 
 dense fumes in the air, boiling at 1 15 C, and combining with 
 water greedily, to form a crystalline hydrate, which is soluble 
 in a further quantity, but is decomposed by copious dilution, 
 stannic acid being precipitated, while hydrochloric acid is set 
 free. The precipitate is readily redissolved by an excess of 
 acid. Stannic acid is easily obtained from this chloride by 
 the cautious addition of sodic carbonate to the solution. 
 This chloride is prepared without difficulty by distilling 
 i part of tin filings with 4 parts of corrosive sublimate, 
 2HgCl 2 -r- Sn yielding SnCl 4 + 2Hg. Exposure to the fumes 
 must be carefully avoided. 
 
 Tests for Tin. In addition to reactions mentioned when 
 speaking of stannous oxide and stannous chloride, the stan- 
 nous salts are characterised by giving in a dilute solution, if 
 mixed with a solution of auric chloride, a beautiful purple 
 precipitate, ' the purple of Cassius ' ; but if the tin salt be 
 in excess, a brown precipitate of reduced gold is formed. 
 Before the blowpipe on charcoal, tin salts yield a malleable 
 white bead of the metal. 
 
 Tin belongs to the group of tetrad elements, and presents 
 a certain analogy with silicon in its mode of combination. 
 It is still more closely allied to the rare bodies titanium, zir- 
 conium, and thorinum, which, however, are not of sufficient 
 practical importance to need notice here. 
 
 Molybdenum is found as a sulphide resembling blacklead 
 
Arsenicum. 253 
 
 in appearance ; and tungsten in a heavy, black, hard mineral, 
 called wolfram. It is unnecessary to describe further the 
 compounds of molybdenum and tungsten, or those of colum- 
 bium, tantalum, and vanadium : for particulars respecting 
 them the reader is referred to systematic treatises on 
 Chemistry. 
 
 CHAPTER XV. 
 
 I. ARSENICUM. 2. ANTIMONY. 3. BISMUTH. 
 
 (57) i. ARSENICUM : Symb. As; Atom. Wt. 75; Sp. gr. 
 of solid, 5-95 ; of vapour, io'6 ; Atom. Vol. J, or [] ; MoL Vol. 
 I ! ! I j, As 4 ; Rel. Wt. 150. 
 
 This highly poisonous substance exhibits characters inter- 
 mediate between those of the non-metals and the metals. It 
 conducts electricity in a moderate degree, and possesses 
 high metallic brilliancy ; but it much resembles phosphorus 
 in general properties, including its anomalous vapour density. 
 It is usually found in the form of an alloy with some other 
 metal, especially with iron, cobalt, nickel, or copper. Now 
 and then it is found native, and occasionally in the form of 
 a metallic arseniate. 
 
 In the preparation of the metal native arsenide of iron or 
 of cobalt is roasted, or heated in a current of air. The 
 arsenicum becomes oxidized, and forms arsenious anhydride 
 (As 2 O 3 ), or white arsenic, which is volatilised below a red 
 heat, and becomes condensed again as it cools in the flues, 
 or in chambers constructed to receive it. 
 
 In order to obtain the metal, this white oxide is powdered, 
 mixed with charcoal, and heated in a crucible, upon the top 
 of which a second inverted crucible is luted ; and this is 
 screened from the fire by means of a perforated iron plate. 
 Carbonic oxide is formed, and escapes, while the metal, 
 which is also volatile below redness, sublimes, and is con- 
 densed in the cool inverted crucible. The metal, however, 
 
254 Arsenicum. 
 
 is not often wanted. It is very poisonous, both alone and 
 when in combination, and requires great care in experiment- 
 ing with it. 
 
 Exp. 243. Take a fragment of white arsenic, the size of a 
 pin's head ; crush it to a fine powder, and mix it with 3 or 4 times 
 its bulk of powdered charcoal. Introduce the mixture into a glass 
 quill tube, sealed at one end and 8 or 10 cm. long. Warm the 
 mixture gently, so as to drive off the moisture which the char- 
 coal usually contains. This, when condensed, may be removed 
 from the tube by introducing a small roll of filtering-paper. 
 Then heat the end of the tube containing the mixture to red- 
 ness. A dark steel-grey metallic mirror-like sublimate of reduced 
 arsenicum will be condensed on the cool sides of the tube, and 
 a distinct garlic-like odour will generally be perceived. 
 
 Arsenicum is very brittle; it has a brilliant dark steel- 
 grey lustre, and volatilises before it melts, at a temperature of 
 about 1 80 C. It gives off a colourless vapour, with an op- 
 pressive garlic-like smell. If heated in air, it combines with 
 oxygen, and becomes converted into arsenious anhydride, 
 which condenses upon somewhat warm surfaces in trans- 
 parent brilliant octahedra. 
 
 Exp. 244. Cut off with a triangular file the portion of the 
 tube containing the mirror of arsenicum obtained in the last 
 experiment. Crush the glass and put the fragments into another 
 sealed quill tube, and heat the broken portions gently : the metal 
 will be sublimed, but will combine with the oxygen of the air in 
 the tube, on the cool sides of which, by the aid of a pocket lens, 
 octahedra of arsenious anhydride may be seen condensed. 
 
 Arsenicum takes fire if thrown in powder into chlorine gas, 
 and it combines readily with bromine, iodine, and sulphur, 
 if gently heated with them. Nitric acid oxidises the metal 
 rapidly. Hydrochloric acid has but little action, unless a 
 little nitric acid or nitre be added. 
 
 Arsenicum is alloyed in small quantity with lead, to facili- 
 tate its taking a globular form in the manufacture of shot. 
 It is also used in combination with copper and oxygen in 
 the preparation of certain green pigments ; and orpiment, 
 
Tests for A rscnic. 255 
 
 which is a yellow largely employed, is one of the sulphides of 
 the metal. 
 
 Arsenicum forms two compounds with oxygen (As 2 O 3 and 
 As 2 O 5 ), both of which, when combined with water, act as 
 acids. 
 
 Arsenious anhydride, or White Arsenic (As 2 O 3 ), is obtained 
 usually as an opaque milk-white mass, often containing small 
 portions or layers of the transparent crystalline form of the 
 compound. It is but sparingly soluble in cold water, but 
 more so in boiling water, and still more readily in hydro- 
 chloric acid. Alkaline solutions dissolve it easily, and furnish 
 a solution of arsenite of the metal, which does not crystallise. 
 When heated to about 190 the anhydride softens, and sub- 
 limes before fusing. Its vapour is colourless, extremely 
 dense (of sp. gr. 13 '8), and it contains i volume of the vapour 
 of the metal and 3 of oxygen condensed into i volume, 
 being double the density that its composition would have 
 led us to expect. 
 
 Exp. 245. Boil i gram of arsenious anhydride with 3 of 
 potassic carbonate in 100 c. c. of water till it is dissolved, and 
 add it to a solution of 3 grams of cupric sulphate in 100 c. c. of 
 water: a beautiful green precipitate of S cheek's Green (CuH AsO 3 ) 
 will be obtained. 
 
 Exp. 246. Add a few drops of a solution of arsenious anhy- 
 dride to 200 or 300 c. c. of water, and then 3 or 4 c. c. of hydro- 
 chloric acid; place in the liquid two or three slips of bright 
 copper foil, and boil the whole for a few minutes : the copper 
 foil will become coated with a steel-grey film. Part of the 
 copper becomes dissolved, and displaces the arsenicum, which 
 is thrown down on the undissolved portion. Pour off the water, 
 dry the copper on blotting-paper, and heat the foil in a quill 
 tube, sealed at one end. The arsenicum will be oxidized and 
 will sublime, condensing in minute octahedra on the cold sides 
 of the tube. 
 
 This is ReinscKs test for arsenic. Marsh's test may be 
 made as follows : 
 
 Exp. 247. Into a wide-mouthed flask of the capacity of 150 
 
' ; 2 5 6 A rsenic Compounds. 
 
 ,or 200 c. c., fit a cork provided with a tube funnel passing 
 nearly to the bottom, and with a second bent tube, which may 
 -have a bulb blown upon it, as shown in Fig. 71. This is to be 
 connected by means of a cork with a wider tube loosely filled 
 with calcic chloride. To the end of this drying-tube attach a 
 piece of quill tube, free from lead, drawn out into a capillary 
 end. In the flask place a few fragments of pure zinc, or, better 
 still, of magnesium foil. Then pour on some water, and add 
 a sufficient quantity of pure sulphuric acid to cause a steady 
 Fig. 71. 
 
 formation of hydrogen. When all the air has had time to be 
 displaced, apply the flame of a lamp to the shoulder or begin- 
 ning of the narrowed part of the tube. Add through the funnel 
 two or three drops of a solution of arsenious acid. Immediate 
 voltaic action will occur; the arsenious acid will be deprived of 
 its oxygen, and part of the metal will at the instant combine 
 with hydrogen, forming arseniuretted hydrogen. This gas will 
 be separated into arsenicum and hydrogen as it passes through 
 the heated tube, and the metal will be deposited as a steel-grey 
 ring just beyond the spot at which the heat is applied. 
 
 Arsenic Anhydride (As 2 O 5 ) may be obtained by boiling 
 arsenious anhydride with nitric acid, and evaporating to dry- 
 ness. It is very soluble in water, and forms a powerful 
 tribasic acid, which furnishes salts ; these present a very close 
 resemblance to the tribasic phosphates. When united with 
 the same metal, -the arseniate and phosphate crystallise in 
 
Arseniuretted Hydrogen. 257 
 
 exactly the same form, and with the same number of mole- 
 cules of water of crystallisation. 
 
 The hydric disodic arseniate (Na 2 HAsO 4 , i2H 2 O) is made 
 in large quantity for the calico printer and dyer. The potassic 
 dihydric arseniate (KH 2 AsO 4 ) crystallises in fine octahedra, 
 which are easily obtained by throwing a mixture of equal 
 parts of nitre and arsenious anhydride into a red-hot clay 
 crucible. Allow the mass to cool, dissolving the residue in 
 a small proportion of water, and setting it aside to crys- 
 tallise. 
 
 Arsenicum and sulphur combine in several proportions: 
 the red compound (As 2 S 2 ) is called realgar \ orpiment is 
 As 2 S 3 ; and there is another sulphide, As 2 S 5 ; these two last 
 correspond to arsenious and arsenic anhydride. 
 
 Orpiment is easily made by passing sulphuretted hydrogen 
 through a dilute solution of arsenious acid in hydrochloric 
 acid. Orpiment melts easily : it is soluble in ammonia, as 
 well as in potash and soda, and in a solution of an alkaline 
 sulphide. 
 
 Only one compound of chlorine and arsenicum, the tri- 
 chloride (AsCl 3 ), is known. It is liquid and volatile. Corre- 
 sponding compounds with bromine and iodine are solid. 
 
 Arseniuretted Hydrogen (AsH 3 ). (Mol. and Atomic Wt. 
 78; Sp. Gr. 2-695; Relative Wt. 39; Mol. Vol. |""T"T) 
 Arsenicum forms a remarkable gaseous compound with 
 hydrogen, which is a deadly poison. It is neither acid nor 
 alkaline, but it has a close analogy with phosphuretted 
 hydrogen, and with ammonia. It is nearly insoluble in' 
 water, but is absorbed with decomposition by solutions 
 of cupric sulphate, of corrosive sublimate, and of argentic 
 nitrate. In the last case, metallic silver and arsenic acid are 
 formed 
 
 AsH 3 + 8AgNO 3 + 4H 2 O = 8HNO 3 + H 3 AsO 4 + 4Ag 3 . 
 
 Its decomposition, when heated, is turned to account in 
 Marsh's test for arsenic. 
 
258 Antimony. 
 
 (58) ANTIMONY: Symb. Sb ; Atom. Wt. 122; Sp. Gr. 
 671 ; Fusing Pt. about 620. 
 
 This metal is always extracted from the sesquisulphide, 
 which is a bluish-white lustrous mineral, crystallised in four- 
 sided prisms, striated across their length. This sulphide 
 is brittle, and melts below a red heat, crystallising as it cools. 
 The crude antimony of commerce is the sulphide freed by 
 fusion from its earthy impurities. The metal is easily ob- 
 tained in small quantities by mixing 4 parts of this sulphide 
 with 2 of pearlash and i^ nitre, powdering and mixing them 
 intimately, and throwing the powder in small portions at a 
 time into a crucible kept at a bright red heat. The quan- 
 tity of nitre used is not sufficient to oxidise both the sul- 
 phur and the metal; and as the sulphur is the more com 
 bustible element, it burns, while the metal melts, and collects 
 beneath the melted slag of potassic sulphate. 
 
 Antimony is a brilliant bluish-white metal, crystallising in 
 plates, and is so brittle that it may be easily powdered in a 
 mortar. 
 
 It melts just above a red heat, and burns brilliantly hi a 
 current of air, giving off white fumes, composed chiefly of 
 antimonious oxide. Powdered antimony takes fire when 
 thrown cold into chlorine gas, and it combines energetically 
 both with bromine and with iodine. Nitric acid and aqua 
 regia oxidize it with violence; and if powdered, and boiled 
 with sulphuric acid, it is converted into a sulphate. The 
 metal, in fine powder, digested with a persulphide of one of 
 the alkali metals, is dissolved. 
 
 Antimony is too brittle to be used alone, but it is useful 
 for hardening other metals when alloyed with them. Type 
 metal is an alloy of lead with about one-fourth of antimony, 
 and often about the same quantity of tin is added. 
 
 The oxide, when ground up with linseed oil, furnishes a 
 white pigment, inferior, however, to common white lead; 
 and tartar emetic, a salt of tartaric acid with potassium and 
 antimony 2[K(SbO) C 4 H 4 O6] H 2 O, is a very active medicine. 
 
Compounds of Antimony. 259 
 
 Antimony forms three oxides : Sb 2 O 3 , the sesquioxide, is a 
 feeble base, which is freely soluble in hydrochloric and in 
 tartaric acid ; Sb 2 O 5 is a metallic anhydride ; it furnishes 
 salts with bases called antimoniates ; and Sb 2 O 4 is a com- 
 pound of these two, which is formed by heating either of the 
 other oxides in a current of air. 
 
 Antimony combines with hydrogen, and forms a colourless 
 gas, much resembling arseniuretted hydrogen, but with no 
 special odour. It may be obtained by dissolving an alloy of 
 zinc and antimony in diluted sulphuric acid. When a solu- 
 tion of any antimonious salt is added to a mixture of zinc 
 and sulphuric acid which is giving off hydrogen, the antimonial 
 salt is decomposed, and antimoniuretted hydrogen comes off 
 mixed with the free hydrogen. It is decomposed when 
 passed through a red-hot tube, and a brilliant crust of me- 
 tallic antimony is deposited. When the gas is burned in 
 the air, white clouds of antimonious oxide are formed. 
 
 Antimony forms two sulphides (Sb 2 S 3 and Sb 2 S 5 ), which 
 correspond to the two principal oxides. They are both 
 soluble in the solutions of the sulphides of the alkali metals, 
 and combine with them to form definite crystalline com- 
 pounds, or sulphur salts. 
 
 The sesquisulphide (Sb 2 S 3 ) is the ore of the metal, but it 
 may also be obtained artificially in beautiful orange-coloured 
 flocculi, by sending a current of sulphuretted hydrogen 
 through a solution of tartar emetic, or other soluble antimo- 
 nious salt. The formation of this compound furnishes one 
 of the best tests for antimony. It is soluble with escape of 
 sulphuretted hydrogen in hot hydrochloric acid. 
 
 The metal forms two chlorides (SbCl 3 and SbCl 5 ), which 
 correspond to the oxides and sulphides. The trichloride 
 (SbCl 3 ) is a fusible solid, which is a strong caustic. It is 
 soluble in hydrochloric acid ; but, on dilution, unless the 
 quantity of acid be very large, an insoluble oxy chloride 
 (SbCl 3 , Sb 2 O 3 ) falls as a white powder, readily soluble in 
 tartaric acid. If antimony is heated with chlorine in excess, 
 
 S 2 
 
260 Oxides of Bismuth. 
 
 it forms the pentachloride (SbCl 5 ), a fuming volatile liquid, 
 which is decomposed by a large quantity of water. 
 
 The compounds of antimony are powerful irritant poisons. 
 Antimony is more likely to be mistaken for arsenic than for 
 any other metal. The crust which is formed by decom- 
 posing antimoniuretted hydrogen in Marsh's apparatus does 
 not yield octahedra, when sublimed in a tube with air, but 
 prisms. The metal is also easily soluble in yellow ammo- 
 nium sulphide, which is nearly without effect upon arsenical 
 crusts. 
 
 (59) BISMUTH: Symb. Bi ; Atom. Wt. 210; Sp. Gr. 9-8; 
 Fusing Pt. 264. 
 
 This metal is found but rarely, and is generally met with 
 in the native state in quartz rock, from which it is commonly 
 separated by simple fusion. It is hard, brittle, and of a 
 reddish-white colour. It may be crystallised more readily 
 than any other metal ; and it furnishes large hollow cubes 
 by fusion and slow cooling, pouring off the inner part before 
 the whole has become solid. Bismuth does not become 
 tarnished by exposure to the air at ordinary temperatures, 
 but it is rapidly oxidized in a current of air at a red heat. 
 If thrown in powder into chlorine gas, it takes fire ; and it 
 combines easily with bromine, iodine, and sulphur. Nitric 
 acid is its best solvent. The nitrate crystallises in flat, trans- 
 parent, colourless prisms. 
 
 This metal is not used alone, but it enters into a remark- 
 ably fusible alloy, which may be prepared by melting to- 
 gether 2 parts of bismuth, i of lead, and i of tin. This 
 mixture melts at a little below iooC.; and as it expands in 
 setting, it is valuable to the die-sinker, as it enables him 
 to take sharp and faithful impressions of his work from time 
 to time during its progress. Bismuth forms two principal 
 oxides: Bi 2 O 3 , which is basic, and is easily obtained by 
 heating the nitrate to low redness ; it is yellow, fuses at a 
 red heat, and may be obtained as a white hydrate by 
 
Coffer. 261 
 
 adding ammonia to a solution of one of the bismuth salts . 
 the other oxide (Bi 2 O 5 ) is brown, and furnishes unstable 
 compounds with bases. 
 
 A native sulphide (Bi 2 S 3 ) is occasionally found crystallised 
 in needles, and is formed as a black precipitate when solu- 
 tions of the metal are treated with sulphuretted hydrogen. 
 
 A trichloride (BiCl 3 ) may be obtained as a very fusible, 
 volatile, and deliquescent substance. It is decomposed by 
 water, and a white oxychloride is formed, while hydrochloric 
 acid is set free. 
 
 The Nitrate (Bi3NO 3 , 5H 2 O) is the most important solu- 
 ble salt of this metal. It is soluble in excess of acid, but if 
 largely diluted with water a white basic nitrate (Bi 2 O 3 , 2HNO 3 ) 
 is precipitated, while an acid salt is formed in the liquid 
 3(Bi3NO 3 ) + 3H 2 O = Bi 2 O 3 , 2HNO 3 + BisNCK, 4HNO-. 
 
 Bismuth salts generally become milky when their solutions 
 are diluted with water, owing to the formation of an in- 
 soluble salt containing excess of the oxide. This precipi- 
 tate is easily dissolved by acetic acid. Solutions of the 
 alkalies give a precipitate of the white hydrated oxide, not 
 soluble in excess of the alkali. Solutions of the carbonates 
 and phosphates give a white precipitate with bismuth salts ; 
 but the yellow, with potassic chromate, insoluble in caustic 
 potash, is used to distinguish bismuth from lead, as the lead 
 chromate is dissolved by excess of potash. Before the blow- 
 pipe bismuth salts on charcoal yield a brittle bead of metal, 
 surrounded by a ring of yellow oxide. 
 
 CHAPTER XVI. 
 
 I. COPPER. 2. LEAD. 3. THALLIUM. 
 
 (60) i. COPPER: Symb. CM; Atom. Wt. 63-5. This 
 valuable metal is frequently found native, but its most 
 common ore is the sulphide of copper and iron, known as 
 
262 Properties of Copper. 
 
 copper pyrites (Cu 2 S, Fe 2 S 3 ) ; and other less common ores are 
 the green carbonate, malachite (CuCO 3 , CuO, H 2 O), and the 
 blue carbonate (2CuCO 3 , CuO, H 2 O). 
 
 In the Welsh process of copper smelting, the pyrites is 
 roasted at a dull red heat, to get rid of portions of the sul- 
 phur. The calcined ore is then melted with a siliceous slag, 
 which removes the iron in the form of silicate of the oxide, 
 leaving the copper in the condition of a heavy fusible sub- 
 sulphide. This is separated from the slag, which floats 
 above it, and is then roasted, so as partly to get rid of the 
 sulphur as sulphurous anhydride, and partly to convert the 
 copper into oxide. When this point is reached, the smelter 
 stirs in this oxide, and mixes it with undecomposed cupreous 
 sulphide. The copper, both from the oxide and the sulphide, 
 then becomes reduced to the metallic state, and the sulphur 
 and oxygen pass off together as sulphurous anhydride 
 
 Cu 2 S + 2CuO = 4Cu -4- SO 2 . 
 
 The crude or blistered copper thus obtained is then melted 
 in large quantities in a reverberatory furnace, where it is 
 poled \ that is to say, the trunk of a young tree is thrust into 
 the melted metal, and thus the last portions of oxide are 
 reduced to the metallic state by the combustible gases given 
 off by the wood, and the copper is brought into the pure and 
 tough condition in which it is required for use. 
 
 Copper is a tough, tenacious, and somewhat hard metal, 
 with a well-known red colour. It emits a peculiar odour 
 when rubbed. It may be drawn into very fine wire, can be 
 rolled into foil, and hammered into leaf. It is an excellent 
 conductor of electricity and of heat. When required in a 
 state of perfect purity, it may readily be deposited in sheets 
 from a solution of its sulphate by the current from one or 
 two cells of the voltaic batter}'. It tarnishes when exposed 
 to the atmosphere ; and if heated to redness in the air, a layer 
 of oxide is formed upon the surface, which scales off if it be 
 suddenly quenched in water, leaving the metal bright beneath. 
 
Oxides of Copper. 263 
 
 Nitric acid dissolves copper with violence, giving off red 
 fumes of nitrous anhydride. Sulphuric acid in the cold does 
 not attack the metal ; but if the strong acid be boiled upon 
 it, the copper is dissolved, cupric sulphate is formed, and 
 sulphurous anhydride is set free. 
 
 Copper melts at a bright red heat, or 1090 C. It is 
 extensively used in the manufacture of boilers, kettles, 
 saucepans, and the like ; also for the sheathing of ships ; and 
 it enters into the formation of many useful alloys, brass 
 being a mixture of about 2 parts of copper and i of zinc, 
 and bell metal and bronze, which are alloys of copper and 
 tin. Some of the compounds of copper are used as pigments. 
 
 There are two oxides of copper : the red, or cupreous, 
 oxide (Cu 2 O), and the black, or cupric, oxide (CuO). It is 
 the latter which furnishes the important salts of the metal. 
 The hydrated red oxide is easily obtained by dissolving i 
 part of cupric sulphate and i of grape-sugar in water, adding 
 a solution of potash till the precipitate of hydrated cupric 
 oxide is redissolved, and then boiling the solution. A crys- 
 talline precipitate of cupreous oxide is deposited. This 
 oxide is used for colouring glass of a ruby red. 
 
 Cupreous oxide is soluble in ammonia, and forms a 
 colourless liquid, which turns blue directly that it is exposed 
 to the action of oxygen. 
 
 Exp. 248. To a solution of cupric sulphate add ammonia 
 in excess; introduce the solution into a bottle with some 
 copper turnings. Cork up the bottle securely, and place it 
 in water ; heat it for some hours nearly to boiling. The blue 
 solution will gradually become colourless, and a portion of 
 the copper will be dissolved, the cupric becoming converted 
 into cupreous oxide. When cold, pour a little of the colour- 
 less liquid upon a white plate : it will absorb oxygen instantly, 
 and will become blue. 
 
 Cupric oxide (CuO) may be best obtained pure by dis- 
 solving pure copper in nitric acid, evaporating the blue 
 solution to dryness, and decomposing the nitrate by heating 
 
264 Tests for Copper. 
 
 it to redness in a clay crucible for a considerable time. 
 Nitrogen and oxygen are expelled, and ciipric oxide is left 
 as a black powder. It is soluble in acids, and furnishes the 
 blue and green salts of the metal. A solution of any one 
 of these salts, such as the sulphate, when decomposed by 
 potash, gives a pale blue hydrated cupric oxide, which, when 
 boiled in water, becomes black and anhydrous. Ammonia 
 ^ives a similar precipitate, which is redissolved by an excess 
 of the alkali, furnishing an intensely blue liquid, charac- 
 teristic of copper. 
 
 The sulphate, or blue vitriol (CuSO 4 , 5H 2 O), is its most 
 important salt. It is easily obtained on the large scale by 
 boiling metallic copper with oil of vitriol diluted with half 
 its bulk of water. It crystallises in beautiful blue prisms, 
 which, when heated, lose water, and crumble down to a 
 white powder. 
 
 Cupric chloride (CuCl 2 , 2H 2 O) may be obtained by dis- 
 solving the carbonate or the oxide in hydrochloric acid, and 
 evaporating. Its crystals are green, and form a green solu- 
 tion, which becomes blue on dilution. When heated, it 
 loses water, and then half its chlorine, cupreous chloride 
 (CuCl) being formed. Cupreous chloride is also formed when 
 a solution of cupric chloride in hydrochloric acid is digested 
 on copper in closed vessels ; it crystallises gradually in 
 transparent tetrahedra, insoluble in water, but soluble in 
 excess of hydrochloric acid. 
 
 Cupreous sulphide (Cu 2 S) is occasionally found native, as 
 is also the cupric sulphide (CuS), which is precipitated as a 
 brownish-black hydrate when a solution of a cupric salt is 
 exposed to the action of sulphuretted hydrogen. 
 
 Tests for Copper. In addition to the characteristic blue 
 liquid formed in solutions of cupric salts by the addition of 
 excess of ammonia, they are known by their forming a brown 
 precipitate with potassic ferrocyanide, and by the deposit 
 of metallic copper which is produced on a polished plate of 
 iron, if plunged into a feebly acid solution of a cupric salt. 
 
Properties of Lead. 265 
 
 Before the blowpipe, on charcoal in the reducing flame, com- 
 pounds of copper furnish a red malleable bead of the metal. 
 
 Copper salts produce vomiting when swallowed, and act 
 as powerful irritant poisons. 
 
 (61) 2. LEAD: Syinb. Pb; Atom. Wt. 207. This useful 
 metal occurs tolerably abundantly in the form of sulphide, 
 or galena (PbS), which is its only ore of importance, although 
 it is found both as carbonate and as sulphate, and in one or 
 two other minerals. 
 
 In extracting the metal the sulphide is roasted on the 
 hearth of a reverberatory furnace. Sulphur burns off, and 
 a mixture of oxide and sulphate of lead is formed. These 
 substances are at intervals stirred by the workman into the 
 melted mass of sulphide beneath. The oxide and sulphate, 
 as well as the sulphide, give up their lead in the metallic 
 state, and the sulphur and oxygen pass off as sulphurous 
 anhydride. Galena yields by oxidation 
 
 2PbS + 3O 2 = 2.PbO + 2SO 2 ; and 
 
 PbS + 2O 2 - PbSO 4 ; and then 
 
 2PbO + PbS = sPb + SO 2 ; while 
 PbSO 4 + PbS = 2Pb + 2SO a . 
 
 Lead is a soft, bluish- white, brilliant metal, of little tena- 
 city. It melts at a temperature of 327 C., and may with 
 some difficulty be crystallised by slow cooling. It shrinks 
 as it becomes solid, and hence is not well fitted for castings. 
 If exposed to a damp atmosphere it soon tarnishes, and an 
 adherent layer of oxide forms upon the surface. If heated 
 in a current of air, when melted, the metal oxidises quickly, 
 and furnishes an oxide, which melts at a full red heat. 
 During this operation it emits white fumes, owing to a 
 partial volatilisation at a high temperature. Nitric acid, 
 when somewhat diluted, dissolves the metal rapidly, but 
 sulphuric and hydrochloric acids have but little effect upon 
 it. It is on this account that sulphuric acid is made in 
 chambers lined with lead. 
 
266 Oxides of Lead. 
 
 Lead is extensively used in the construction of cisterns, 
 gutters, and pipes for the storage and distribution of water ; 
 also for roofing. It enters into many valuable alloys, such 
 as pewter, type-metal, and plumbers' solder ; and is used 
 in the form of oxide in making glass. The carbonate, oxy- 
 chloride, and chromate are largely employed as pigments. 
 
 Lead is a dangerous but insidious poison, producing 
 symptoms of colic and partial palsy. It is apt to accumu- 
 late in the body when swallowed in minute quantities ; and 
 as it is largely used in the storage of water, it is important to 
 study the conditions under which lead is liable to be che- 
 mically acted on. 
 
 When lead is exposed to a dry air it does not alter, but 
 pure water in the presence of air corrodes it rapidly. The lead 
 becomes oxidized on the surface; the water dissolves the 
 oxide slightly, and this solution absorbs carbonic acid : an in- 
 soluble hydrated basic carbonate of lead is precipitated, fresh 
 oxide is formed on the metal, is dissolved by the water, fresh 
 carbonic acid is absorbed, a fresh precipitate is formed; and 
 so the process goes on continuously. The presence in the 
 water of small quantities of many soluble salts, such as from 30 
 to 60 mgms. per litre, materially alter this result. The corro- 
 sion is much increased by the presence of chlorides, nitrates, 
 and nitrites; but it is diminished by the sulphates, phosphates, 
 and especially by the carbonates. Lead oxide is scarcely so- 
 luble in water which contains these salts. The water supplied 
 in towns generally holds sufficient calcic carbonate dissolved 
 to prevent it from acting to any injurious extent upon the 
 metal. A film of insoluble basic carbonate is formed upon 
 the surface, and thus the lead beneath is protected from 
 further corrosion. Sometimes, as in the pure lake waters of 
 Scotland, the presence of a little vegetable matter acts as a 
 preservative, by combining with the oxide of lead, and 
 forming an insoluble lining to the cisterns and pipes. Slate 
 cisterns, however, are in all cases to be preferred. 
 
 Lea.d forms four oxides : a black suboxide (Pb 2 O) ; a 
 
Compounds of Lead. 267 
 
 protoxide, the important base (PbO) from which the salts of 
 the metal are derived ; a brown dioxide (PbO 2 ), which is in- 
 soluble in the acids ; and an intermediate oxide (red lead), 
 a compound of one or of two molecules of the protoxide 
 with one of the peroxide (PbO, PbO 2 , or more usually 
 2PbO, PbO 2 ). 
 
 The protoxide , or litharge (PbO), is commonly obtained, by 
 heating the metal in a current of air, as a pale yellow scaly 
 mass. It fuses at a full red heat, and is a valuable flux to 
 the assayer; but it speedily penetrates and destroys the 
 crucibles in which it is melted. A solution of a salt of lead, 
 such as plumbic nitrate, furnishes, on the cautious addition 
 of potash or soda, a white precipitate of the hydrated oxide; 
 it is soluble in excess of the alkali. Lead oxide is a power- 
 ful base. It is readily soluble in the acids, and has a strong 
 tendency to form salts which contain an excess of base. 
 
 Exp. 249. Dissolve 2 or 3 grams of lead acetate in 200 or 
 300 c. c. of water, and boil it with a gram of finely-powdered 
 litharge : the oxide will gradually be dissolved, and the solu- 
 tion will restore the blue colour to reddened litmus. 
 
 Exp. 250. Blow a little air from the lungs through a short 
 quill tube into a little of the solution in a test-tube : the solu- 
 tion will become filled with white silky scales of the hydrated 
 oxycarbonate of lead (PbO, H 2 O. PbCO 3 ). 
 
 This solution consequently furnishes one of the best tests 
 for uncombined carbonic anhydride, whether in air or in water. 
 
 Red lead, or minium, is obtained by heating metallic lead 
 in a current of air below the point at which the litharge 
 fuses. The oxide is ground with water to a fine powder, 
 and the fine particles, after they have settled down from 
 suspension in water, are heated to about 320 C., in iron 
 trays, in a current of air for several hours. The oxygen 
 is slowly absorbed, and a fine red crystalline powder is 
 obtained. If heated to redness, the absorbed oxygen is 
 driven off, and litharge is left. Red lead is largely used in 
 making flint glass. 
 
268 Salts of Lead. 
 
 Exp. 251. Pour a little nitric acid, diluted with 3 or 4 
 times its bulk of water, upon a few decigrams of red ead : 
 the red colour will disappear, and the brown dioxide (PbO 2 ) 
 will be left undissolved, whilst lead nitrate is formed. 
 
 Lead Sulphide (PbS). Lead has a very powerful attrac- 
 tion for sulphur. Galena, the common ore of the metal, 
 is the sulphide ; it has a deep leaden colour, is hard, brittle, 
 and has a high metallic lustre. It fuses at a full red heat, 
 and is oxidized easily, with escape of sulphurous anhydride, 
 in a current of air. 
 
 Exp. 252. Mix 10 grams of powdered galena with 14 of 
 dried sodic carbonate and i gram of powdered charcoal. 
 Place 3 or 4 blacksmith's nails, with their heads downwards, 
 in a Cornish clay crucible; then add the mixture. Cover it 
 with a thin layer of fused and powdered borax. Heat the 
 crucible to full redness for 10 minutes; take out the nails. 
 When cool, break the crucible : a button of lead will be found 
 at the bottom, sulphide of iron being formed, while metallic 
 lead separates. This method is commonly used in the dry 
 assay of a sample of galena. 
 
 All the salts of lead, both soluble and insoluble, become 
 blackened when placed in water containing sulphuretted 
 hydrogen. 
 
 Lead Chloride (PbCl 2 ) is sparingly soluble; it is preci- 
 pitated in crystalline needles on adding hydrochloric acid to 
 a solution of a lead salt. 
 
 Lead Sulphate (PbS0 4 ) is a white insoluble powder pro- 
 duced on adding sodic sulphate or other soluble sulphate to 
 a solution of a lead salt. 
 
 Lead Iodide (PbI 2 ) is yellow and insoluble. It is formed' 
 by adding potassic iodide to a soluble lead salt. The 
 Chromate (PbCrO 4 ) is also yellow and insoluble. 
 
 Lead Nitrate (Pb2NO 3 ) is prepared by dissolving metallic 
 lead in nitric acid, and evaporating ; octahedral white anhy- 
 drous crystals are deposited. Several basic nitrates and 
 nitrites may be formed. 
 
 Lead Carbonate (PbCO 3 ), or white lead, is one of the most 
 
Thallium. 269 
 
 important insoluble compounds of the metal. When ground 
 into a paste with a drying oil (linseed oil being generally 
 used), it forms the basis of our common house paints. 
 
 Lead forms a very large number of insoluble compounds. 
 The sulphate, iodide, chromate, and sulphide are often 
 used as tests of the metal. If a water contain lead, even in 
 minute quantity, its presence is easily ascertained by taking 
 two similar jars of 25 cm. high, of colourless glass, filling 
 both of them with the water, and adding to one of the jars 
 3 or 4 c. c. of a solution of sulphuretted hydrogen. A 
 quantity of lead less than one part in two millions is easily 
 perceived, by the brown tinge occasioned, on looking down 
 upon a sheet of white paper ; the jar to which the test has 
 not been added serving as a standard of comparison. 
 
 Exp. 253. Dissolve 30 grams of lead acetate in a litre of 
 distilled water in a flask, and hang up in the solution a lump 
 of zinc. If the glass is left undisturbed for three or four days, 
 beautiful crystalline plates of lead, forming what is often called 
 the ' lead tree,' will be deposited upon the zinc. Zinc will have 
 been dissolved, while the lead, which has a smaller attraction for 
 the radical of the acid, is separated. 
 
 Before the blowpipe on charcoal the salts of lead yield a 
 soft, white, malleable bead of the metal, surrounded by a 
 yellow ring of oxide. 
 
 (62) 3. THALLIUM : Synib. Tl ; Atom. Wt. 204. This 
 is a metal which accompanies certain kinds of pyrites in 
 small quantity. It was discovered quite recently by the 
 beautiful green colour which it gives to flame ; and this, 
 when viewed by the spectroscope, is found to be concen- 
 trated into a single intense green line. It is a heavy metal, 
 resembling lead in appearance, but it quickly tarnishes in 
 the air. Its principal oxide is soluble in water, and has an 
 alkaline reaction on red litmus. The sulphate, nitrate, 
 and carbonate, are white soluble salts. The sulphide is 
 brownish-black ; the chloride yellowish-white, and sparingly 
 soluble. 
 
2;o 
 CHAPTER XVII. 
 
 THE NOBLE METALS. 
 
 i. MERCURY. 2. SILVER. 3. GOLD. 4. PLATINUM. 5. PALLADIUM. 
 6. RHODIUM. 7. OSMIUM. 8. IRIDIUM. 9. RUTHENIUM. 
 
 (63) i. MERCURY : Symb. Hg ; Atom. Wt. 200 ; Sp. Gr. 
 at o, 13*596; of Vapour, 6-976 ; Melting Pt. 39 ; Boiling 
 Pt. 350; Atom. andMol. Vol. \~*~\ ; * Rel. Wt. 100. 
 
 This remarkable and interesting metal, often called quick- 
 silver, is the only one that is liquid at common temperatures. 
 It is found in but few places, and then usually as sulphide 
 in the red ore known as cinnabar, accompanied by small 
 quantities of the metal itself. It is extracted from this ore 
 by simply roasting it in a current of air, and passing the 
 vapours through long earthen pipes. The mercury condenses, 
 and the sulphurous anhydride passes off into the air. Mer- 
 cury possesses a lustre like that of polished silver. It 
 volatilises slowly at all temperatures above 4 C. ; and when 
 heated, it boils at 350, giving off a heavy transparent 
 vapour, which is 100 times as dense as hydrogen. It freezes 
 at 39, and forms a white malleable mass, which contracts 
 suddenly as it becomes solid. When pure, it is not tarnished 
 by exposure to the air; but if kept at a temperature of 300 
 or 400, it absorbs oxygen slowly, and becomes converted 
 into crystalline scales of the red oxide. The purity of the 
 metal may be judged of by the perfect mobility and spheri- 
 city of its globules, which do not wet non-metallic surfaces. 
 If any other metals, such as zinc, lead, or bismuth, be 
 present, the globules assume an irregular elliptical form, 
 and have a tail-like prolongation as they roll about. 
 
 Exp. 254. Dissolve a fragment of lead of about the size of a 
 mustard seed in 40 or 50 grams of clean mercury. Cork it up 
 in a glass bottle which will hold 200 or 300 c. c. and agitate the 
 
 * The molecule of the vapour of mercury, like that of zinc, cadmium, 
 and other metallic dyads, contains only I atom of the metal. 
 
Properties of Mercury. 2/1 
 
 mercury briskly : a black film will be found over the surface. 
 Withdraw the cork, blow out the air with a pair of bellows, and 
 then renew the shaking. Repeat this three or four times until 
 the black powder ceases to increase. Then pour the mercury 
 into a cone of writing-paper folded like an ordinary filter, but 
 pierced at the point with a pin-hole, and supported in a funnel : 
 the metal will run through, and leave the oxide of lead, mixed 
 with finely divided mercury, adhering to the paper. If a little 
 finely-powdered loaf-sugar be added before agitating the mercury, 
 the process is effected more quickly. 
 
 If a iarge quantity of mercury is to be purified from 
 foreign metals, it is best to place it in a shallow layer on the 
 bottom of a dish, and to cover it with nitric acid diluted 
 with ten or twelve times its bulk of water, leaving it for a 
 few days at ordinary temperatures, frequently stirring the 
 acid and mercury together ; after which it may be washed, 
 and dried with a cloth. 
 
 Mercury is attacked immediately by chlorine and by bro- 
 mine ; more slowly by iodine. It also dissolves most of the 
 metals, except iron and platinum. Gold, silver, and tin 
 amalgams are used in the arts. It also combines readily 
 with lead, bismuth, antimony, zinc, and copper. The 
 amalgamation is immediately effected by cleansing the sur- 
 face of the metal with a solution of mercury in nitric acid, 
 and then placing the metal in the mercury. 
 
 Nitric acid dissolves mercury with great energy and 
 liberation of nitrous fumes. Hydrochloric acid is without 
 action on the metal. Sulphuric acid, when boiled upon it, 
 dissolves mercury, while sulphurous anhydride is given off; 
 but it has no action upon it in the cold. 
 
 Mercury is used in medicine, mixed, by simple grinding 
 with chalk, into a grey powder ; and when incorporated with 
 a proper proportion of conserve, it forms what is well known 
 as blue pill. It acts as a powerful metallic poison. Work- 
 men exposed to its vapours in the operations of gilding 
 suffer from a peculiar tremulous affection, called mercurial 
 palsy ; and it often produces salivation, with ulceration of 
 
272 Compounds of Mercury. 
 
 the mouth and throat. Some of its salts, such as corrosive 
 sublimate, when swallowed, act as immediate and powerful 
 irritants, producing speedy death. 
 
 Mercury is largely used in philosophical enquiries. Its 
 expansion in glass is employed as a measure of temperature 
 in the thermometer ; and it is not only a requisite in the 
 construction of the barometer, but it furnishes an indispen- 
 sable liquid in the apparatus used for the accurate collection 
 and measurement of gases. 
 
 Mercury forms two oxides : the grey or black oxide 
 (Hg 2 O), and the red oxide (HgO) : both of them yield 
 salts when treated with acids. 
 
 Mercurous Oxide (Hg 2 0) is a powerful base, but is unstable 
 when isolated. Exposure to light or to a moderate heat causes 
 it to separate into the metal and the red oxide, Hg 2 O becoming 
 Hg + HgO. It is best obtained by grinding calomel with 
 caustic soda in excess, and washing out the sodic chloride 
 
 2 HgCl + 2 NaHO = Hg 2 O + 2NaCl + H 2 O. 
 
 Mercuric Oxide, or the red oxide (HgO), is obtained 
 slowly, in red scales, by heating mercury to 300 or 400 in 
 an open flask with a long neck for some days ; but it is 
 more conveniently procured by heating the nitrate cautiously 
 till it is converted into a bright scarlet powder. It may also 
 be precipitated as a yellow powder by adding a solution of 
 potash or soda to one of corrosive sublimate. 
 
 The red oxide, when heated, becomes black ; and at a 
 higher temperature is separated into metallic mercury and 
 oxygen, It is easily dissolved by acids. 
 
 Mercury forms two sulphides, Hg 2 S and HgS, the latter, 
 cinnabar, constituting the principal ore of the metal. It is 
 formed artificially by subliming mercury with about a sixth 
 of its weight of sulphur, when it furnishes the beautiful red 
 pigment known as vermilion. This sulphide is also obtained 
 as a black precipitate by decomposing a soluble mercuric 
 salt with sulphuretted hydrogen in excess. 
 
Mercury and Chlorine. 273 
 
 Mercury also forms two chlorides, calomel (HgCl) and 
 corrosive sublimate (HgCl 2 ). 
 
 Calomel, or Mercurous Chloride (HgCl), is a heavy, white, 
 insoluble powder, which may be obtained by mixing a solu- 
 tion of sodic chloride with one of mercurous nitrate ; but it 
 is more commonly obtained by converting 4 parts of mercury 
 into sulphate -by boiling it to dryness with 6 parts of oil 
 of vitriol, and then grinding the dry mass with 4 parts more 
 of mercury and 3 parts of sodic chloride, and heating the 
 mixture. Mercuric sulphate is first obtained 
 
 Hg + 2 H 2 S0 4 = HgS0 4 + 2 H 2 O + S0 2 . 
 This sulphate is then converted, by the additional mercury, 
 into the mercurous sulphate 
 
 Hg + HgS0 4 = H g2 S0 4 ; 
 
 and this, by sublimation with common salt, is converted 
 into calomel and sodic sulphate 
 
 2 NaCl + Hg 2 SO 4 = 2HgCl + Na 2 SO 4 . 
 
 Exp. 255. Heat a little calomel in a test-tube : it will sub- 
 lime without melting, and condense on the cold sides of the tube. 
 
 Exp. 256. Place a small quantity of calomel at the bottom of 
 a short quill tube, cover it with a layer of dried sodic carbonate 
 1 5 mm. thick, heat the sodic carbonate to redness, and gradually 
 sublime the calomel through it : white metallic globules of the 
 metal will condense in the cold part of the tube. 
 
 Corrosive Sublimate, or Mercuric Chloride (HgCl 2 ), is 
 usually prepared by grinding 5 parts of mercuric sulphate 
 with 2 of common salt, and subliming the mixture 
 HgS0 4 + 2NaCl = HgCl 2 + Na,SO 4 . 
 
 Its fumes are very acrid and poisonous. 
 
 Corrosive sublimate melts easily ; and when heated further, 
 boils (at 295), furnishing vapours, which condense in semi- 
 transparent or in white crystals. It is freely soluble in water, 
 alcohol, and ether. It is the most important of the soluble 
 mercuric compounds. It is a strong antiseptic. 
 
 Exp. 257. Whip up the white of an egg with water; strain ft 
 T 
 
Tests for Mercury. 
 
 through muslin. Add a little solution of corrosive sublimate : an 
 immediate coagulation of the white of egg will occur. Such 
 coagulated albumen is not liable to putrefy. 
 
 Wood, cordage, and canvas are sometimes soaked in a 
 solution of the salt, and are thereby rendered less likely to 
 decay. 
 
 Mercuric Iodide (HgI 2 ). Add to a dilute solution of 
 potassic iodide a few drops of a solution of corrosive sub- 
 limate : a yellow precipitate of mercuric iodide, becoming 
 salmon-coloured, and ultimately brilliant scarlet (HgI 2 ), is 
 formed. This iodide is redissolved by an excess of potassic 
 iodide, or by one of corrosive sublimate : with the iodide it 
 forms a soluble double salt (KI, HgI 2 ), and a similar double 
 salt with corrosive sublimate (HgI 2 , 2HgCl 2 ). 
 
 Exp. 258. Heat a little of the mercuric iodide in a dry test- 
 tube : it will melt and sublime, and condense in yellow crystals. 
 Shake out the sublimate upon a piece of paper, and draw a glass 
 rod firmly across the heap of crystals : a scarlet colour will be 
 produced. 
 
 This change is brought about by the conversion of the 
 yellow rhombic plates into a dimorphous red octahedral form 
 by the molecular disturbance occasioned by pressure. 
 
 Tests for Mercury. All the salts of this metal are vola- 
 tilised by heat. They are all reduced to the metallic state, 
 whether soluble or insoluble, by being boiled with an excess 
 of stannous chloride. If a slip of copper be boiled in a 
 solution of a salt of mercury, it becomes coated with a white 
 amalgam \ and if the copper be heated in a small tube to 
 redness, globules of mercury are driven off, and condense 
 upon the sides. Mercurous salts give a black precipitate 
 with sulphuretted hydrogen ; a white, consisting of calomel, 
 with a soluble chloride ; and this white precipitate is black- 
 ened by the addition of ammonia, but is not redissolved by 
 it. It is soluble in chlorine water or in boiling nitric ac-id. 
 Mercuric salts give a yellow precipitate with solution of 
 potash, and a white one with ammonia ; with sulphuretted 
 
Properties of Silver. 275 
 
 hydrogen a white, passing through brownish-red into hdack. 
 Their reactions with potassic iodide have been already 
 noticed. 
 
 (64) 2. SILVER : Symb. Ag ; Atom. Wt. ioS. This 
 beautiful metal has been known and prized from the earliest 
 ages. It is found commonly in the native state, and almost 
 invariably accompanies galena in small quantity, in the form 
 of sulphide. Mercury is used on a large scale for dissolving 
 metallic silver, and separating it from earthy and other im- 
 purities, but the metallurgic processes by which silver is 
 extracted are somewhat elaborate, and are described in the 
 text book on * Metallurgy.' 
 
 Silver has a white colour, with a tinge of red. It pos- 
 sesses considerable tenacity and malleability, so that it may 
 be drawn into very thin wire, and hammered into leaf. It 
 is softer and more fusible than copper, and requires a tem- 
 perature of 1023 C. for its fusion : though it is scarcely 
 volatile in ordinary furnaces, it may even be made to boil 
 under the very intense heat of the oxyhydrogen jet. As a 
 conductor of heat and electricity, it is unsurpassed. It does 
 not become oxidized at any temperature ; but it has a sin- 
 gular power of absorbing oxygen when in a state of fusion, 
 and giving up the gas suddenly when it solidifies. It com- 
 bines slowly with chlorine, bromine, and iodine. Its attrac- 
 tion for sulphur is very considerable ; the brown tarnish that 
 silver acquires by exposure to the air is due to the formation 
 of a thin film of argentic sulphide, in consequence of the 
 action of the metal on the traces of sulphuretted hydrogen 
 occasionally present in the air. This tarnish may be removed 
 by rubbing the surface with a solution of potassic cyanide. 
 Nitric acid is the best solvent for silver ; but it may also be 
 dissolved by boiling sulphuric acid, with escape of sulphurous 
 anhydride. 
 
 Silver is seldom used alone, as it is too soft to resist 
 wear ; but when alloyed with either 7-^- or 10 per cent, 
 
 T 2 
 
276 Experiments on Silver Solutions. 
 
 of copper, it is extensively employed in coinage and in the 
 manufacture of plate. When a thin layer of silver is applied 
 to the surface of copper or of steel articles, it furnishes what 
 are called ' plated goods.' Mirrors for lighthouses are plated, 
 as from its high lustre silver furnishes the best reflecting sur- 
 face for such purposes. 
 
 Exp. 259. Dissolve a sixpenny-piece in nitric acid. The 
 solution has a bluish colour, owing to the presence of the copper 
 which is always added before coining, for the purpose of harden- 
 ing the metal. Dilute the solution with 200 c. c. of water ; then 
 add a solution of common salt so long as it forms a precipitate : 
 white flakes of argentic chloride are formed. Stir the mixture 
 briskly with a glass rod : the precipitate will collect into clots 
 
 AgNO 3 + NaCl = NaNO 3 + AgCL 
 
 Filter the solution. The presence of copper may be proved in 
 the clear liquor by adding ammonia in excess to a portion of the 
 liquid : a blue solution is formed. 
 
 Exp. 260. Place the blade of a knife in another portion of the 
 filtrate: it will become coated with metallic copper. 
 
 Exp. 261. Take the precipitated argentic chloride obtained 
 in Exp. 259, and after having washed it well on a filter, place it 
 in a test-glass with a little water; add two or three drops of 
 sulphuric acid, and then place a slip of zinc in contact with the 
 chloride, and leave it for twenty-four hours. The chloride will 
 be reduced to metallic silver, which will have a grey porous 
 aspect, while zinc chloride will be found in solution. Lift out 
 the piece of zinc carefully ; wash the silver first with water con- 
 taining a little sulphuric acid, then with pure water. Dry the 
 residue. Place a small quantity of it upon an anvil, and strike 
 it a blow with a hammer : a burnished metallic surface will be 
 produced. Place a little of the grey powder upon charcoal, and 
 heat it in the flame of the blowpipe : it will become melted into 
 a brilliant malleable bead. Dissolve another portion in nitric 
 acid : red fumes of nitrogen peroxide escape, and argentic nitrate 
 is obtained in solution. 
 
 Silver belongs to the class of monads ; it forms only one 
 oxide of practical importance (Ag 2 O). It may be obtained 
 as a brown hydrate by adding caustic potash to a solution 
 
Compounds of Silver. 277 
 
 of argentic nitrate. An excess of potash does not redis- 
 solve it ; but it is easily dissolved by an excess of ammonia. 
 Other oxides (Ag 4 O and 2Ag 2 O 2 ) are, however, known. 
 
 The most important soluble salt of silver is the nitrate 
 (AgNO 3 ), which crystallises in colourless anhydrous tables ; 
 it melts at a moderate heat, and when cast into small round 
 sticks forms the ' lunar caustic ' of the surgeon. This salt is 
 readily decomposed by the action of organic matte/, espe- 
 cially when exposed to light ; hence it is used for the pre- 
 paration of ink for marking on linen, as the stain cannot be 
 removed by washing with soap. If it fall upon the skin, it 
 blackens it. A strong solution of potassic iodide, or of the 
 poisonous potassic cyanide, will remove these stains from 
 the skin, or from linen. 
 
 The sulphide (Ag 2 S) often occurs naturally, mixed with 
 lead sulphide in small quantity. It may also be precipitated 
 as a black hydrate when any silver salt, soluble or insoluble, 
 is exposed to a solution of sulphuretted hydrogen. 
 
 The chloride (AgCl) is white, insoluble in water and in 
 nitric acid, even if boiling, but freely soluble in ammonia. 
 If heated to redness, it melts into a horny-looking mass. The 
 precipitated chloride becomes of a dark purple colour when 
 exposed to the light, owing to the formation of a subchloride. 
 
 The bromide (AgBr) is white, insoluble in water and nitric 
 acid, and sparingly soluble in ammonia. 
 
 The iodide (Agl) is of a pale yellow, and is nearly in- 
 soluble in ammonia. 
 
 The chloride, bromide, and iodide of silver may be re- 
 duced to the state of metallic silver by fusing them in a 
 clay crucible with half their weight of dry sodic carbonate. 
 For example 
 
 4AgCl + 2Na 2 CO 3 = 4NaCl + 2Ag 2 + 2GO 2 + O 2 . 
 
 They are all soluble in a solution of sodic hyposulphite, and 
 form an intensely sweet solution with it. When exposed to 
 light in the presence of argentic nitrate and some organic 
 
278 Properties of Gold. 
 
 matter, they undergo chemical changes which form the basis 
 of the common processes of photography. 
 
 The formation of the chloride, bromide, and iodide of 
 silver, and the properties above described of these com- 
 pounds, furnish ready tests for the presence of silver ; but 
 the phosphates, chromates, oxalates, tartrates, and citrates 
 all form insoluble precipitates with salts of silver. Copper 
 placed in a solution of silver nitrate or sulphate separates 
 the silver in crystalline plates; zinc also reduces the salt, 
 as does also a stick of phosphorus ; but the most beautiful 
 effect is produced by adding a few drops of mercury to a 
 solution of silver nitrate containing 5 or 6 per cent, of the 
 salt A beautiful crystallisation, known as the * silver tree/ 
 will be formed in a few days. 
 
 (65) 3. GOLD : Symb. Au ; Atom. Wt. 196-6. This 
 valuable metal has been known from the earliest times, for 
 it is found in small quantity in almost every country, and it 
 always occurs in the native state alloyed with silver, gene- 
 rally in a proportion varying from 4 to 1 2 per cent. Many 
 rivers contain it in their sands. In Australia the gold is 
 associated with quartz and slate, and in California it is 
 found in the detritus of quartz and granite. Gold is ex- 
 tracted by a mechanical process of washing, and afterwards 
 dissolving in mercury such portions of the gold as are in a 
 very finely divided state. The mercury is afterwards dis- 
 tilled off, and condensed again for use. 
 
 Pure gold is of a rich yellow colour and high lustre ; it is 
 nearly as soft as lead. It is very ductile, and is the most 
 malleable of the metals, so that it may be hammered into 
 leaves 11,200 of which would not be thicker than i milli- 
 metre, or 280,000 would not exceed an inch in thickness. 
 A leaf of gold, attached to a pane of glass, and held up 
 between the eye and a light, will allow a green or purple light 
 to pass through. Gold leaf is extensively used for gilding 
 on wood, papier mache, and metal, to the surface of which 
 it is attached by means of an adhesive varnish. 
 
Compounds of Gold. 279 
 
 Gold fuses at about 1 100 C. It is scarcely volatile in the 
 furnace, but in .the intense heat of the oxyhydrogen jet it 
 may be dissipated in purple vapours. Sulphuric acid does 
 not attack it; neither does the nitric or the hydrochloric 
 acid separately, but a mixture of the two liberates chlorine, 
 and this gradually dissolves it, forming a yellow solution. 
 
 Exp. 262. Place a little gold leaf in two test-tubes ; to one 
 add nitric, to the other hydrochloric acid. Even when heated 
 with the acid the gold leaf remains unaffected. Pour the con- 
 tents of one tube into the other : the gold will disappear with 
 effervescence. Evaporate this solution in a small porcelain 
 capsule till the acid is nearly all driven off : auric chloride will 
 be left. 
 
 Exp. 263. Dilute the solution with 3 or 4 c. c. of water. To 
 a portion of this liquid add a solution of ferrous sulphate : a 
 brown precipitate of finely divided reduced gold is obtained, and 
 ferric chloride is formed 
 
 6FeSO 4 + 2AuCl 3 = 2(Fe a 3SO 4 ) + Fe a Q 6 + 2Au. 
 
 This is a common mode of separating gold from its solutions. 
 
 Add to another portion of the auric chloride a solution of sul- 
 phurous acid : on warming the mixture gold will be precipitated 
 
 2AuCl 3 + 3 H 2 + 3H,S0 3 = 6HC1 + 3H a SO 4 + 2Au. 
 A solution of oxalic acid will have a similar effect 
 
 2AuCl 3 + 3H a C 2 O 4 = 2Au + 6HC1 + 6CO 2 , 
 carbonic acid being produced. 
 
 All these liquids look purple when viewed by holding 
 them between the eye and the light, owing to the trans- 
 parency of the finely divided gold. 
 
 Gold in its pure state is too soft to be used for the pur- 
 poses of coin or plate. It is hardened by alloying it with 
 about a tenth or a twelfth of its weight of copper. Gold is 
 usually triad in combination ; it however forms two oxides 
 (Au 2 O and Au 2 O 3 ), but they are seldom prepared. The tri- 
 chloride (AuCl 3 ), obtained by dissolving gold in a mixture of 
 nitric and hydrochloric acids, as above directed, is the most 
 important compound of the metal When heated gradually 
 
280 Platinum. 
 
 to about 175, it loses chlorine and furnishes aurous chloride 
 (AuCl), a pale yellow, sparingly soluble compound ; and by 
 a heat below redness all the chlorine is expelled, and me- 
 tallic gold is left. A solution of the trichloride is easily 
 decomposed by organic matter. It stains the skin and 
 other organic substances, such as white silk, of a purple 
 colour. Its solution is reduced to the metallic state by 
 many metals, such as copper, mercury, iron, and zinc, as 
 well as by phosphorus, and by several other substances. 
 Stannous chloride, if added to its solution in quantity not 
 sufficient to reduce the whole of the gold, gives a fine 
 purple, known as purple of Cassius (Au 2 Sn 3 O6, 4H 2 O). It is 
 used for colouring the ruby glass of Bohemia. 
 
 (66) 4. PLATINUM : Symb. Pt ; Atom. Wt. 197. This is 
 a hard, tough, white metal, a good deal resembling silver in 
 appearance, with which in earlier times it appears to have 
 been confounded. It is the densest substance known, except 
 osmium and iridium, which accompany it in its ores, and are 
 equally dense. It may be drawn into very fine wire, and 
 rolled into thin foil. On account of its great infusibility and 
 its power of resisting all acids except a mixture of the nitric 
 and hydrochloric, it is extremely valuable to the chemist, as 
 it furnishes him with crucibles and other apparatus in which 
 he can in most cases where accuracy is required fuse and 
 heat the various bodies subjected to analysis. It is also used 
 as the negative metal in Grove's voltaic battery. 
 
 Platinum is of comparatively rare occurrence. It is found 
 in metallic grains, sometimes associated with gold, silver, 
 copper, iron, and lead, but it is almost always accompanied by 
 certain other metals, which are never found without it, viz. 
 palladium, osmium, iridium, rhodium, and ruthenium. 
 
 On account of the extreme infusibility of platinum, it re- 
 quires a peculiar and complicated mode of treatment. The 
 ore is treated first with nitric acid, to dissolve out the common 
 metals ; then washed, and treated with hydrochloric acid, 
 
Compounds of Platinum. 281 
 
 and again washed ; after which the residue is digested at a 
 very high temperature in 4 parts of hydrochloric acid, to which 
 about i part of nitric acid is added little by little. When 
 nothing more is dissolved, the acid liquor is decanted, and 
 mixed with a strong solution of sal ammoniac. Most of the 
 platinum is thus precipitated as a yellow double chloride of 
 ammonium and platinum (2H 4 NC1, PtCl 4 ). This is washed 
 and then heated ; the whole of the ammonia and chlorine 
 are expelled, and the platinum is left as a grey porous mass, 
 commonly known as spongy platinum. This is then pressed, 
 and forged at a high heat into bars or plates, which are 
 afterwards hammered into dishes or vessels, rolled into 
 sheets, or drawn into wire. This method is now, however, 
 gradually being displaced by a mode of melting the ore by 
 means of the oxyhydrogen blowpipe. 
 
 Platinum, if heated alone, does not combine with oxygen 
 at any temperature, but it becomes slowly oxidized if heated 
 with the caustic earths or alkalies. It alloys readily if ignited 
 with lead, tin, bismuth, antimony, or any of the more fusible 
 metals, which would melt a hole in a platinum crucible if 
 heated in it. 
 
 Platinum belongs to the group of tetrad metals. It forms 
 two oxides (PtO and PtO 2 ). They both correspond to salts 
 of the metal, but these are seldom prepared. Platinous oxide 
 (PtO) is soluble in a solution of potash, furnishing a dark 
 olive-green liquid ; and the alkalies also combine and dissolve 
 platinic oxide (PtO 2 ). 
 
 There are two chlorides. Platinic Chloride (PtCl 4 ) is the 
 salt obtained by dissolving platinum in a mixture of hydro- 
 chloric and nitric acids, and evaporating the solution to dry- 
 ness at 100 C. It is an orange-coloured deliquescent sub- 
 stance. If heated for some time to about 23 5 C. it loses 
 half its chlorine, and becomes converted into the olive- 
 coloured insoluble platinous chloride (PtCl 2 ). At a heat 
 below redness the whole of the chlorine is driven off, and 
 metallic platinum is left. Platinic chloride forms double 
 salts with the chlorides of the alkali metals ; that with potas- 
 
282 Noble Metals. 
 
 slum (2KC1, PtCl 4 ) forms yellow octahedra, insoluble in 
 alcohol, and nearly so in cold water. The ammonium com- 
 pound (2H 4 NC1, PtCl 4 ) is commonly employed to separate 
 platinum from its solutions. The sodium salt (2NaCl, PtCl 4 , 
 6H 2 O) is soluble, and crystallises in long red needles. All 
 these salts are decomposed at a red heat : metallic platinum 
 is left, and by washing may be obtained free from the alkaline 
 chlorides. 
 
 Solutions of platinic salts are not reduced by ferrous sul- 
 phate, but they are so by mercurous nitrate, which precipitates 
 finely divided metallic platinum. Oxalic acid does not re- 
 duce them, but a solution of a formiate will, if heated with a 
 neutral solution of platinum, cause the metal to be separated 
 in a powder. 
 
 5. Palladium is a white metal, nearly as infusible as pla- 
 tinum. It forms a brown solution when dissolved in nitric 
 acid. 
 
 6. Rhodium is a very hard white metal, very difficult of 
 solution, even in the mixture of nitric and hydrochloric acids. 
 Its salts are of a beautiful rose colour. 
 
 7. Osmium occurs in extremely hard scales alloyed with 
 iridium and ruthenium. When heated in a current of air, it 
 becomes oxidized, and gives off a remarkable volatile oxide 
 (OsO 4 ), which has a peculiar pungent smell, and is freely 
 soluble in water. Osmium is the least fusible of the metals. 
 
 8. Iridium accompanies osmium in the ore of platinum, 
 and is sometimes found native and nearly pure. It is a 
 white, very hard, and brittle metal, which furnishes three 
 oxides. They pass readily one into the other, and furnish 
 salts which differ in tint ; hence the name Iridium, from 
 iris, the rainbow. 
 
 9. Ruthenium is a very hard brittle metal, scarcely fusible 
 before the oxyhydrogen blowpipe. It absorbs oxygen at a 
 red heat, and yields several oxides. 
 
 These metals last mentioned are found, in small quantities, 
 accompanying the ore of platinum ; but they are so rare as 
 not to need further description. 
 
QUESTIONS FOR EXAMINATION. 
 
 THE following questions have been framed in accordance 
 with the Syllabus issued by the Science and Art Department 
 of the Committee of Council on Education, under the head 
 of * Inorganic Chemistry. First Stage or Elementary Course 
 Second Stage or Advanced Course/ pp. 90, 91. 
 
 The student will do well to exercise himself from time to 
 time in answering these questions without reference to the 
 text ; and the general reader will find his knowledge of 
 Chemistry become much improved by adopting the same 
 course. Should he not be able to answer any particular 
 question, he will have to refer to the page of the book as in- 
 dicated in the right-hand column, but he is recommended 
 not to write his answer immediately, but to wait until he has 
 thoroughly mastered the text The answer should as far as 
 possible be given in the student's own language, not in that 
 of the book. 
 
 Teachers who prepare their lectures from this book are 
 recommended to set their pupils a number of these questions 
 the day after each lecture : the answers are to be written in 
 full, and marks given to each paper. Those pupils only who 
 thus acquire a certain number of marks should be allowed 
 
284 Questions for Examination. 
 
 to compete for the prize or prizes at the end of the term 
 or half-year. 
 
 The Teacher can easily frame other questions on the text, 
 and he is recommended to exercise his class in the use of 
 chemical formulae and the numerical statements connected 
 therewith, the measurement of gaseous volumes, the con- 
 version of Fahrenheit into Centigrade degrees, the use of the 
 metric system, &c. 
 
 C. T. 
 
 N0 - OF 
 QUEST. 
 
 1. Give a definition of Chemistry . . . . 2 
 
 2. What is the difference between a simple and a compound 
 
 body? . . . . . . .2-5 
 
 3. What do you mean by the words analysis and synthesis ? . 3 
 
 4. State some of the different modes of chemical action . 4 
 
 5. Write out the symbols of the non -metallic elements with 
 
 their combining weights . . . 5 5 ^ 
 
 6. Do the same for the metals . . . 5, 6 
 
 7. Describe the difference between combining weights and 
 
 volume weights .... 196-8 
 
 8. Explain the equation CaCO 3 + 2HC1 = CaCl 2 + H 2 O + CO 2 
 
 and write out the combining numbers for each element, 
 
 H representing one gram of hydrogen . . -. 'M^\ 
 
 9. What is the length in inches of the French metre, or unit 
 
 of length, the decimetre being 3 -937 inches ? .II 
 
 10. Using the same figures (but adding cyphers where neces- 
 
 sary), write out the value in inches of the decimetre, the 
 centimetre, and the millimetre. Also the decametre, 
 the hectometre, the kilometre, and the myriometre . 9 
 
 11. What is the weight of a gram in grains English? and, if a 
 
 gram be represented by I 'O, how do you write a deci- 
 gram, a centigram, a milligram, a hectogram, a kilo- 
 gram, and a myriogram ? . . . . 1 1 
 
 12. How many cubic inches does the litre contain ? Also how 
 
 many pints ? . . . . IO 
 
Questions for Examination. 285 
 
 , 
 
 13. Using the same figures that express cubic inches or pints, 
 
 give the decalitre, the hectolitre, the kilolitre, and the 
 myriolitre. Also the decilitre, the centilitre, and the 
 millilitre . . . . . 10 
 
 14. What is the weight of a cubic metre of water? . .11 
 
 15. The formula for converting degrees' on Fahrenheit's scale 
 
 to corresponding degrees on the Centigrade scale is 
 |(F. 32) = C. ; and for converting Centigrade to 
 Fahrenheit, |C. + 32 = F.. Convert 1 12, 45, 37, and 
 2i4F., into corresponding degrees on the Centigrade 
 scale ....... 
 
 16. Convert 9, 84, 95 C. into F. . . . . 
 
 17. Convert 7, 45, 39 F. into C. . . . 
 1 8. Convert -i 7, -30,- 8 C. into F. . . . 
 
 19. Give examples of the three states of matter . .12 
 
 20. Which of the elements has never been melted, and what 
 
 gases have never been liquefied ? . . 13 
 
 21. How do you distinguish between mixture and combi- 
 
 nation? . . . . . 13, 14 
 
 22. Is atmospheric air a mixture, or a chemical compound ? 1 5, 38 
 
 23. Write down the symbol, atomic weight, the atomic 
 
 volume, the specific gravity, the relative weight, the 
 molecular weight, and the molecular volume of oxygen . 19 
 
 24. Show how you get from 245 grams of potassic chlorate, 96 
 
 grams of oxygen . . . . .21 
 
 25. How many grams of oxygen are there in 1,000 grams, or 
 
 I kilogram, of potassic chlorate ? . . . 
 
 26. Explain some of the properties of oxygen . 22-28 
 
 27. 50 cubic centimetres of a gas are measured at 10 C. ; how 
 
 much will it measure at 24 C. ? . . .28 
 
 28. 30 cubic centimetres of a gas at o C. are measured at 730 
 
 mm. pressure ; what is its volume at 750 mm. the tem- 
 perature being the same ? . . . 28, 29 
 
 29. I measure 100 cubic centimetres of a gas at 12 C. ; the gas 
 
 is heated until it becomes 145 cubic centimetres. What 
 is the temperature of the gas under these altered con- 
 ditions ? ...... 28 
 
 30. A litre of gas is measured at 20 C. and 730 mm. What is 
 
 its volume at the standard pressure and temperature ? 28, 29 
 
 31. Correct for temperature 50 cubic centimetres of gas mea- 
 
 sured at 5 C. . . . . .28 
 
286 Questions for Examination. 
 
 NO. OF 
 
 QUEST. 
 
 32. Correct for pressure 18 cubic centimetres of a gas at oC. 
 
 and 730 mm. .... 28-29 
 
 33. What is the difference between the specific gravity and the 
 
 relative weight of a gas ? 29-30 
 
 34. What is the difference between an acid and an anhydride ? 31 
 
 35. What is the usual test for an acid ? for an alkali ? 31 
 
 36. What is a base ? . . . . . 31 
 
 37. State the difference between an acid ending in ous and one 
 
 ending in u, and between a salt ending in ite and one 
 ending in ate . . . . 32 
 
 38. Explain this equation : H 2 SO 4 + 2KHO = K 2 SO 4 + 2H 2 O 32 
 
 39. State the difference between ferrous oxide and ferric oxide, 
 
 ferrous sulphate and ferric sulphate . . -33 
 
 40. What is ozone supposed to be ? Name a test for it, and 
 
 describe its properties . . .' , . . 34~3^ 
 
 41. What is the specific gravity, relative weight, and molecular 
 
 weight and volume of nitrogen ? . . .36 
 
 42. How is nitrogen prepared ? and describe its leading pro- 
 
 perties . . . . . -36 
 
 43. When limewater turns milky in the presence of atmospheric 
 
 air, what does that show ? . . . -39 
 
 44. What is the weight of a litre of dry air at the standard 
 
 temperature and pressure ? . . -39 
 
 45. What are the accidental ingredients of the atmosphere ? . 40 
 
 46. What is the symbol of water ; its atomic and molecular 
 
 weights ; its specific gravity at 4 C. ? The specific 
 gravity of ice and steam ? The relative weights of water- 
 gas or vapour, and its atomic and molecular volumes ? 41, 44, 65 
 
 47. State some of the methods by which water is decomposed 
 
 and hydrogen collected, and what becomes of the 
 oxygen . . . . 4 I- 44 
 
 48. How much steam does a litre of water at 100 C. produce ? 44 
 
 49. How are the fixed points in the thermometer determined, 
 
 and what precautions must be taken with respect to the 
 boiling point ? . . . . . -45 
 
 50. Describe some of the physical properties of water . . 45 
 
 51. What takes place during the cooling of water, and what is 
 
 meant by the point of maximum density of water ? . 47 
 
 52. What is the freezing point of water on the C. and F. scales? 
 
 53. What is meant by the specific gravity of a solid gold, for 
 
 example ? . . . . 47 
 
Questions for Examination. 287 
 
 54. How is pure water obtained ? . . . 47 
 
 55. Name some of the impurities that occur in water, and how 
 
 they are detected .... 49~5 2 
 
 56. What is the difference between hard and soft water ? . 53 
 
 How do you distinguish between the temporary and the 
 permanent hardness of water ? . . . 53~54 
 
 58. Describe Clark's soap test . . . . -54 
 
 59. What is meant by a saturated solution ? . . 56 
 
 60. In the formula Na 2 CO 3 , ioH 2 O, what is the ioH 2 O called ? 57 
 
 61. Describe the difference between an efflorescent and a de- 
 
 liquescent salt ; also between a hydrated and an anhy- 
 drous salt . . . . . -57 
 
 62. Describe the processes for obtaining hydrogen as represented 
 
 in the following equations : 
 3Fe + 4H 2 O = Fe 3 O 4 + 4H 2 ; H 2 SO 4 + Zn = ZnSO 4 + H 2 59,60 
 
 63. Describe some of the properties of hydrogen . 60, 6 1 
 
 64. What is meant by collecting a gas by displacement ? .61 
 
 65. How are gases dried ? . . . .61 
 
 66. What is meant by the mixed gases ? . . .61 
 
 67. Describe some of the methods of showing the composition 
 
 of water by synthesis, such as by the use of the 
 Cavendish apparatus, fig. 17, and the Eudiometer, fig. 18. 65 
 
 68. Describe the oxy -hydrogen blow-pipe . . -67 
 
 69. Give some account of diffusion . . . .69 
 
 70. Why is hydrogen selected as the unit or standard of com- 
 
 parison for atomic weights and combining volumes ? 70, 195 
 
 71. What is meant by a gas volume ?. . . 70, 197 
 
 72. The Crith being the weight of I litre of hydrogen at o C. 
 
 and 760 mm. pressure, what is the weight of 10 litres, 
 
 and also of a cubic metre of hydrogen ? . . . 
 
 73. What is the relative weight of oxygen in criths ? of 
 
 chlorine ? of hydrochloric acid ? of ammonia ? . . 
 
 74. What is the weight in criths of 4 cubic metres of hydriodic 
 
 acid, and also of ammonia ? . . . . 
 
 75. What is meant by a monad, a dyad, a triad, and a tetrad ? 
 
 and give examples . . . . 72 
 
 76. Explain the terms univalent, bivalent, tervalent, and quad- 
 
 rivalent elements. Also perissad and artiad elements . 72 
 
 77. What is a hydride ? . . . . -73 
 
288 Questions for Examination. 
 
 NO. OK p .__ 
 
 QUEST. PAGE 
 
 78. Write down the symbol, atomic weight, atomic and 
 
 molecular volume, specific gravity, and relative weight 
 
 of carbonic anhydride . . . . -73 
 
 79. What do you understand by the term carbonate ? . 74 
 
 80. Explain the equation CaCO 3 + 2HC1 = CaCl 2 + H 2 O + CO 2 74 
 
 81. Describe some of the properties of carbonic anhydride . 75 
 
 82. How do you collect this gas by displacement, and how 
 
 does the process differ from that for collecting hydrogen ? 76 
 
 83. Show the composition of carbonic anhydride by synthesis 80-8 1 
 
 84. How is carbonic anhydride disposed of in the atmosphere ? 83 
 
 85. Describe some of the varieties of carbon and their properties 84 
 -86. What is meant by allotropy ? . . 92 
 
 87. How is carbonic oxide prepared ? . . . 93> 95 
 
 88. Write in double columns the different properties of car- 
 
 bonic anhydride and carbonic oxide, such as 
 
 CO 2 is CO is 
 
 non-inflammable inflammable 
 
 and so on . . 73-84, 93-96 
 
 89. What is the axis of a crystal ? . . 98 
 
 90. What are the systems under which crystals are arranged ? 
 
 and give an example of each . . . 100-103 
 
 91. Describe the terms amorphous, dimorphous, and isomor- 
 
 phous . . . 103, 140 
 
 92. Explain the formation of nitric acid from nitre or from 
 
 sodic nitrate . . . . IO 5 
 
 93. Give an example of double decomposition . . . 106 
 
 94. Describe the properties of nitric acid . . .107 
 
 95. What is the difference between N 2 O 5 and HNO 3 ? .109 
 
 96. Describe the process for obtaining nitrous oxide, and state 
 
 some of its properties . .no 
 
 97. Explain 3 Cu + 8HN0 3 = 3 (Cu2N0 3 ) + 2NO + 4H 2 . 112 
 
 98. What is nitric oxide a good test for ? . .112 
 
 99. What is the acid in a nitrite ? and give the formula for it 1 13-1 14 
 
 100. Give a list of the chemical compounds of nitrogen and 
 
 oxygen, and state why atmospheric air is not included 
 
 in this list . . . . 104, 38 
 
 10 1. What is meant by multiple proportion ? . . -194 
 
 102. Write down the symbol, atomic weight, atomic and 
 
 molecular volume, specific gravity, and relative weight 
 
 of ammoniacal gas . . .114 
 
Questions for Examination. 289 
 
 103. Describe the process for collecting and drying ammoniacal 
 
 gas ... . 115-116 
 
 104. Describe some of the properties of ammoniacal gas 116-117 
 
 105. How much of this gas does box- wood charcoal absorb ? . 117 
 
 1 06. At what temperature does ammoniacal gas become liquid ? 
 
 also solid? . . .. . . . 117 
 
 107. What is the difference between liquid ammonia and liquor 
 
 ammoniae? . . . . . . 117 
 
 1 08. What condensation takes place when nitrogen and hydrogen 
 
 combine to form ammoniacal gas ? . . .119 
 
 109. Explain the following equation : MnO 2 + 2NaCl + 3H 2 SO 4 
 
 = MnSO 4 + NaHSO 4 + 2H 2 O + Cl 2 . . .120 
 
 no. Also MnO 2 + 4HCl = MnCl 2 + 2H 2 O + Cl 2 . . 121 
 
 in. Describe some of the leading properties of chlorine, and 
 
 why it is called a halogen . . . 120, 121 
 
 H2. What are the other halogens, and what is their 
 
 atomicity? . . . . . 120, 140 
 
 113. What is the bleaching action of chlorine ? . . .123 
 
 1 14. How is hydrochloric acid directly formed, and what is its 
 
 relative weight ? . . . . .123 
 
 115. Explain NaCl+H 2 SO 4 = HCl + NaHSO 4 . . 125 
 
 1 1 6. What is the analytical method of showing that H and Cl 
 
 are present in hydrochloric acid gas ? . . .125 
 
 117. What tests may be used for the detection of hydrochloric 
 
 acid and the chlorides ?. . . . .128 
 
 1 1 8. Give a list of the compounds of chlorine and oxygen . 129 
 
 119. Show, by means of precipitation, the difference between 
 
 potassic chlorate and potassic chloride . . .130 
 
 1 20. How is bromine obtained ? . - . . .132 
 
 121. Compare hydrobromic with hydrochloric acid . 73, 140 
 
 122. What is the acid in argentic nitrate? and what takes place 
 
 when its solution is added to a weak solution of potassic 
 bromide? ...... 134 
 
 123. Give some numerical data respecting iodine . 134 
 
 124. When a solution of starch is added to one of potassic iodide, 
 
 the characteristic blue colour is not produced : why is 
 this? . . . . . . .136 
 
 125. What is the symbol, atomic and molecular weight, mole- 
 
 cular volume, specific gravity, and relative weight of 
 hydriodic acid ? . . . . 137 
 
 U 
 
290 Questions for Examination. 
 
 NO. OF 
 
 QUEST. PAGE 
 
 126. Explain the equation PI 5 + 4H 2 O = H 3 PO 4 + 5HI . 137 
 
 127. Compare hydriodic acid gas with HC1, HBr, and HF 73, 140 
 
 128. What are the properties of HI? . . . .138 
 
 129. What are the symbols of iodic and periodic acids ? . 138 
 
 130. Why cannot you describe the properties of fluorine ? . 138 
 
 131. Explain this equation : CaF 2 + HS 2 O 4 = CaSO 2 + 2HF . 139 
 
 132. What is the most remarkable property of hydrofluoric acid, 
 
 and how may it be exhibited ? . . . 139, 174 
 
 133. Explain this equation : SiO 2 + 4HF = SiF 4 + 2H 2 O . 139 
 
 134. What is meant by the term dimorphous? and give an ex- 
 
 ample ....... 142 
 
 135. Describe some of the properties of sulphur, and state its 
 
 allotropic modifications, and how they are obtained 141-143 
 
 136. Are roll sulphur and flowers of sulphur allotropic modifica- 
 
 tions? ....... 144 
 
 137. Give some of the leading data respecting sulphurous anhy- 
 
 dride . . . ... . .145 
 
 138. Explain the equation: 2H 2 SO 4 + Cu^CuSO 4 + SO 2 + 2H 2 O 145 
 
 139. Describe some of the properties of sulphurous anhydride 145-7 
 
 140. Why is oil of vitriol so named, and why is Nordhausen 
 
 sulphuric acid so called ? 147, 148 
 
 141. Describe the English process for manufacturing sulphuric 
 
 acid on a large scale . . . . -149 
 
 142. What is the function of nitric oxide in the manufacture of 
 
 sulphuric acid ? . . . . 149 
 
 143. Name some of the properties of sulphuric acid, and the 
 
 test for detecting it . . . . 150,151 
 
 144. What is meant by the term dibasic ? . "-'.. . 151 
 
 145. What is meant by monad metals, and by dyad metals, and 
 
 by what mark are the latter distinguished from the 
 former? . . . . >$.< I S l 
 
 146. What is the difference between a hyposulphite and a sul- 
 
 phite? and explain the use of sodic hyposulphite in 
 photography . . . . . .152 
 
 147. Explain the equation Na 2 SO3 + S = Na 2 S 2 O3 . . 153 
 
 148. What is the difference between a sulphide, a sulphite, and 
 
 a sulphate ? . . . . . 
 
 149. Explain the process for obtaining sulphurettted hydrogen, 
 
 and describe the properties of this gas, and of its aqueous 
 solution ..... *- 
 
Questions for Examination. 29 1 
 
 0ES T F 
 
 1 50. What metals may be precipitated by means of sulphuretted 
 
 hydrogen? ...... 156 
 
 151. Describe the properties of carbon disulphide . 157 
 
 152. What is there peculiar about the atomic and molecular 
 
 volume of phosphorus ? . . . 159, 162 
 
 153. State, in a double column, the chief differences between 
 
 crystalline and amorphous phosphorus . 161 -2 
 
 154. Give the formulae for the chief compounds of phosphorus 
 
 and oxygen ...... 163 
 
 155. What are the three forms of phosphoric acid ? . .164 
 
 156. What is the difference between a phosphate and a pyro- 
 
 phosphate? ...... 165 
 
 157. What is a monobasic, a tribasic, and a tetrabasic acid ? . 166 
 
 158. How is phosphuretted hydrogen prepared? and what are 
 
 its properties ? . . . . . 166-7 
 
 159. Describe some of the crystallised and amorphous forms of 
 
 silica ....... 168 
 
 1 60. How is pure silica obtained ? . . . .169 
 
 161. What do you mean by dialysis ? . . . .170 
 
 162. Give the formulae for fire-clay or alumina silicate, ferrous 
 
 silicate, and lead silicate . . . .171 
 
 163. What is the composition of different kinds of glass ? . 1 71 
 
 164. Explain the equation ; 
 
 2CaF 2 + 2H 2 SO 4 + SiO 2 = SiF 4 + 2CaSO 4 + 2H 2 O . 173 
 
 165. How does boron occur in nature ? . . 175 
 
 1 66. Under what forms has boron been obtained ? . .176 
 
 167. Give the formulae for boracic anhydride, boracic acid, and 
 
 borax . . . , . . . 175 
 
 1 68. What is the atomicity of boron ? . . .176 
 
 169. "What are polymeric bodies ? and give examples . 177 
 
 170. How is olefiant gas prepared, and why is it so named? . 178 
 
 171. What is marsh gas? and give its atomic and molecular 
 
 weights, its specific gravity, and relative weight . 1 79 
 
 172. What is the principle of the Davy lamp ? . 180-1 
 
 173. Describe Bunsen's burner .... 182 
 
 174. Describe the blow-pipe, and distinguish clearly between 
 
 the reducing flame and the oxidising flame . .184 
 
 175 What are the chief products of the destructive distillation 
 
 of coal? ..... 186-7 
 
 U 2 
 
292.; Questions for Examination. 
 
 NO. OF 
 
 QUEST. PAGB 
 
 176. Give the formulae for potassic ferrocyanide, and describe 
 
 . how it is prepared . . . . . 188 
 
 177. What is- the difference between a simple and a compound 
 
 radical ? . . . . . . 189 
 
 178. Which is the radical in NaCl, HNO ? , and also in KCN, 
 
 and which of the three contains a nitrion, and what is it? 189 
 
 1 79. Explain the equation : KCy + H 2 SO 4 = HCy + KHSO 4 . 189 
 
 1 80. Give some account of the atomic theory, and distinguish 
 
 clearly the four laws of chemical combination . 191-2 
 
 181. How do you distinguish between the terms atomic weight 
 
 and chemical equivalent ? 1 93~4 
 
 182. What is meant by the terms atom, molecule, atomic 
 
 , volume, and molecular volume ? . . . 195 
 
 183. How are the atomic weights of the elements determined ? 195-8 
 
 184. What are the general characteristics of the metals ? 198-201 
 
 185. What is the specific gravity of sodium, magnesium, alumi- 
 
 num, antimony, zinc, tin, iron, copper, silver, lead, 
 mercury, gold, and platinum ? and give also their fusing 
 points . . . . . . 199 
 
 186. What is the difference between an alloy and an amalgam ? 201, 202 
 
 187. What is meant by a native metal ? . . . 202 
 
 1 88. Name the metals of the alkalies and their atomicity . 203 
 
 189. What is the atomicity of the metals of the alkaline earths ? 203 
 
 190. What is there peculiar about the atomicity of the six metals 
 
 allied to iron ? . . . . . . 204 
 
 191. Name the nine noble metals .... 205 
 
 192. How is potassium prepared ? .... 205 
 
 193. Explain the term basic oxide . . . . 206 
 
 194. Explain K 2 CO 3 + CaO,H 2 O = 2KHO + CaCO 3 . . 206 
 
 195. Describe some of the properties of potassic carbonate . 207 
 
 196. What is nitre ? and state some of its properties and uses 208-9 
 
 197. What is sea-salt, and how is it obtained ? . .211 
 
 198. Describe briefly the manufacture of soda from sea-salt, and 
 
 explain the terms ball soda, black ash, and soda ash 211-13 
 
 199. How do you distinguish between the salts of potassium and 
 
 those of sodium ? ..... 214 
 
 200. What is Nessler's test ? . . . . .217 
 
 201. How is baryta obtained ? and describe its properties . 217 
 
 202. How is baric sulphate converted into a soluble sulphide? . 218 
 
Questions for Examination- 2 93 
 
 QuksT PAGE 
 
 203. Describe the tests for barium salts . . . - 219 
 
 204. Give a few particulars respecting strontium . . 2ig 
 
 205. How is lime obtained, and what is meant by quick lime " 
 
 and slaked lime ? . . . . . 220 
 
 206. What is plaster of Paris ? . . . . .221 
 
 207. Describe some of the varieties of calcic carbonate . . 222 
 
 208. Name some tests for calcium salts .... 223 
 
 209. How is aluminum obtained, and what are its chief pro- 
 
 perties ? ..... .223-4 
 
 210. What is a lake, and what is a mordant ? . . .224-5 
 
 21 1. State some of the properties of hydrate of alumina . 225 
 
 212. Explain A1 2 O 3 +3C + 3C1 2 ^A1 2 C1 6 + 3CO . . 225 
 
 213. Explain the constitution of the alums . . . 226 
 
 214. What is the formula for the best fire-clay ? . . 227 
 
 215. What is bisc uit ? ...... 228 
 
 216. Describe some of the tests for aluminum salts . . 229 
 
 21 7. Name some of the chief salts of magnesium with their for- 
 
 mulae and tests ...... 230- 1 
 
 218. How is zinc obtained from its ore ? 232 
 
 219. Describe some of the properties of zinc . . . 232 
 
 220. Give some account of the salts of zinc . . . 233 
 
 221. How is cadmium distinguished from zinc ? . . 234 
 
 222. Give some account of cobalt and its oxides . . 235 
 
 223. How are compounds of cobalt distinguished before the 
 
 blow-pipe ? . . . . . 236 
 
 224. ' What is the chief ore of nickel ? . . . . 236 
 
 225. What are the more important ores of iron ? . . 237 
 
 226. How is iron obtained from clay iron-stone ? . . 238 
 
 227. How is cast iron converted into wrought iron ? . . 239 
 
 228. What is steel, and how do you distinguish it from iron ? 239-240 
 
 229. Describe the compounds of iron and oxygen . . 241 
 
 230. How do you distinguish between ferrous and feme salts ? . 243 
 
 231. How are the chromates prepared on a large scale ? . 245 
 
 232. Describe some of the peculiarities of the manganates . 247 
 
 233. How is potassic permanganate prepared ? and give an 
 
 illustration of its use ..... 248 
 
 234. Give some tests for manganese . . . 248 
 
294 Questions for Examination. 
 
 = 
 
 235. Name some of the alloys of tin . . . . 250 
 
 236. How are stannous chloride and stannic chloride prepared ? 251-2 
 
 237. What are the atomic and molecular volumes, and the rela- 
 
 tive weight of arsenicum ? . . . . 253 
 
 238. Describe the two compounds of arsenicum with oxygen . 255 
 
 239. Give an account of Keinsch's test for arsenic ; also of 
 
 Marsh's ..... 255-6 
 
 240. What is Na 2 HAsO 4 , I2H 2 O? . . . .257 
 
 241. Give the molecular and atomic weights, the specific gravity, 
 
 the relative weights, and molecular volume of arseniu- 
 retted hydrogen . . . . . 257 
 
 242. What is the action of a solution of argentic nitrate on this 
 
 gas? . . . . .; . . 257 
 
 243. How is antimony obtained ? ..... 258 
 
 244. Describe the chief properties of antimony . . .258 
 
 245. What are the compounds of aniimony with oxygen, hydro- 
 
 gen, sulphur, and chlorine? .... 259 
 
 246. How do you distinguish in Marsh's test between antimony 
 
 and arsenic ? . . . . . . 260 
 
 247. Describe some of the properties of bismuth . . 260 
 
 248. What is the formula for the basic oxide of bismuth ? . 260 
 
 249. What is the most important soluble salt of bismuth ? . 260 
 
 250. Why do bismuth salts in solution generally become milky 
 
 when diluted? . . . . . .261 
 
 251. Describe briefly the Welsh process of copper-smelting . 262 
 
 252. Describe the more important properties of copper . 262-3 
 
 253. How is cupric oxide obtained ? .... 263 
 
 254. What is the formula for blue vitriol ? . . . 264 
 
 255. Describe the tests for copper . . . . . 264 
 
 256. How is lead obtained from its sulphide ? . s . . 265 
 
 257. What are the chief properties of lead ? .. . . 265 
 
 258. What is the action of pure water on lead ? . 266 
 
 259. What is litharge, and what is minium ? . . . 267 
 
 260. Describe some of the salts of lead .... 268 
 
 261. How is the presence of lead detected in water ? . . 269 
 
 262. Give some of the numerical constants of mercury, such as 
 
 its specific gravity, melting and boiling points, atomic 
 weight, &c. . . . . .270 
 
 263. What is cinnabar, and how is quicksilver obtained from it? 270 
 
Questions for Examination. 295 
 
 NO. OF 
 
 QUEST. PAGE 
 
 264. How may mercury be purified ? . . . 270-1 
 
 265. What is the action of acids on mercury? . . .271 
 
 266. What is vermilion ?..... 272 
 
 267. Describe the chlorides of mercury, and give the formulae . 273 
 
 268. What tests are employed for mercurousand mercuric salts? 274 
 
 269. Write down some of the leading properties of silver . 275 
 
 270. What is the action of common salt on argentic nitrate ? 
 
 and express the reaction in the form of an equation . 276 
 
 271. How are the argentic chloride, bromide, and iodide re- 
 
 duced to metallic silver? . . . . 277 
 
 272. Describe some of the properties of gold . . . 278 
 
 273. What acid dissolves gold, and how does it act ? . .279 
 
 274. How is the purple of Cassius formed ? . . 280 
 
 275. What are the properties of platinum ? . . 280 
 
 276. What is the atomicity of platinum ? . . .281 
 
 277. Describe a few of the salts of platinum . . .281 
 

 
INDEX. 
 
 ACI 
 
 ATM 
 
 BLE 
 
 ACIDS, 30 
 names of, 33 
 
 Analysis, 3 
 Anhydrides, 74 note 
 
 Atmospheric air cont. 
 less abundant compo- 
 
 Adularia, 227 
 After-damp of mines, 180 
 
 Anhydrous substances, 57 
 Aniline, 186 
 
 nents of, 38 
 carbonic acid in the air, 
 
 Agate, 169 
 
 Annealing glass, 171 
 
 83 . 
 
 Albite, 227 
 
 Anthracite, 86 
 
 Atomic theory, the, 190 
 
 Alkalies, 30 
 metals of the, 203, 205 
 
 Antimoniates, 259 
 Antimonic anhydride, 
 
 Atomic weights, 7, 192-196 
 table of, 198 
 
 tests for, in combi- 
 
 160 
 
 Atoms, 191, 195 
 
 nation, 214 
 
 Antimonious anhydride, 
 
 Attraction, chemical, 4 
 
 Allotropy, 92 
 
 160 
 
 Augite, 228, 230 
 
 Alloys, metallic, 201 
 
 Antimoniuretted hydro- 
 
 Azote, 36 
 
 Alum, 226 
 
 gen, 160 
 
 Azotised substances, 38 
 
 various kinds of, 226 
 
 Antimony, 258 
 
 
 properties of, 226 
 
 crude, of commerce, 
 
 
 Alumina, 224 
 
 258 
 
 T3 ALL SODA, or black 
 
 properties of, 224, 225 
 sulphate of, 226 
 silicates of, 171, 227 
 
 oxides of, 259 
 sulphides of, 259 
 chlorides of, 259 
 
 _D ash, 213 
 Baric carbonate, 219 
 chromate, 245 
 
 Aluminum, 223 
 properties of, 22 $ 
 tests for aluminum salts, 
 
 compounds of, 260 
 Antimony sulphide, 156 
 Antiseptic powers of char- 
 
 sulphate, 147, 151, 152 
 sulphite, 147 
 sulphide, 156 
 
 229 
 
 coal, 91 
 
 Barium, 141, 217 
 
 Aluminum bronze, 224 
 
 properties of sulphu- 
 
 salts of, 218 
 
 Amalgam, 202 
 
 rous anhydride, 146 
 
 tests for salts of, 219 
 
 Amethyst, 168 
 
 Aqua-fortis, 104 
 
 Baryta, 217 
 
 Ammonia, 114, 160 
 
 Aragonite, 222 
 
 Basalt, 227 
 
 sources of, 114 
 
 Argentic bromide, 134 
 
 Bases, 31 
 
 preparation of, 115 
 
 chlorate, 130 
 
 names of, 33 
 
 properties of ammonia- 
 
 chloride, 130 
 
 Bell-metal, 201, 250 
 
 cal gas, 116 
 absorption of ammonia, 
 117 
 
 Arsenic, whence obtained, 
 242 
 Arsenic anhydride, 160, 
 
 Beryl, 229 
 Biphosphate of soda, 164 
 Biscuit ware, 228 
 
 solution of, 117, 118 
 
 256, 257 
 
 Bismuth, 260 
 
 analysis of, 1 19 
 
 Arsenic, white, 255 
 
 properties of, 260 
 
 solution of, in water, 216 
 Nessler's test for, 217, 
 
 Arsenicum, 253 
 preparation of, 253 
 
 alloy of, 260 
 oxides of, 160, 260 
 
 note 
 Ammonia oxalate, 223 
 
 properties of, 254 
 alloy of, 254 
 
 sulphide of, 261 
 trichloride of, 261 
 
 Ammonic carbonate, hy- 
 
 compounds of, 255 
 
 nitrate of, 261 
 
 dric, 217 
 
 tests for, 255 
 
 Bismuthic anhydride, 160 
 
 Ammonic magnesic phos- 
 
 Arsenious anhydride, 160, 
 
 Bisulphites, 146 
 
 phate, 165, 231 
 
 254. 2 55 257 
 
 Bittern, or mother liquor, 
 
 Ammonium, 215 
 
 Arseniuretted hydrogen, 
 
 of sea water, 133 
 
 hydrate, 216 
 
 160, 257 
 
 Black-lead, 85 
 
 nitrate, no 
 
 Asbestos, 230 
 
 Bleaching cotton goods 
 
 sulphide and carbonate 
 of, 185 
 
 Atmospheric air, 15 
 not an element, 15 
 
 and paper, 123 
 powder, or chloride of 
 
 Amorphous bodies, 103 
 
 experiments on, 16 
 
 lime, 130, note 
 
 Amorphous phosphorus, 
 
 a mixture of several 
 
 properties of sulphu- 
 
 162 
 
 gases, 38 
 
 rous anhydride, 146 
 
298 
 
 Index. 
 
 BLE 
 
 CHR 
 
 CUL 
 
 Blende, 141, 232 
 
 Carbonate of ammonium, 
 
 Chromium cent. 
 
 Blowpipe, mouth, 183 
 use of the, 184 
 
 185. 
 of lime, 220 
 
 oxides of, 244 
 salts of, 245 
 
 Blue pill, 271 
 
 Carbonates, 74, 83 
 
 Cinnabar, 272 
 
 Bohemian glass, 280 
 Boiling point, 45 
 Bones of animals, prin- 
 
 Carbonic acid, 39, 83 
 Carbonic anhydride, 73 
 formation of, 74 
 
 Clays, 224, 227 
 varieties of, 227 
 Coal gas, 185 
 
 cipal earthy component 
 of, 160 
 Boracic acid, 175, 176 
 Boracic anhydride, 175 
 
 properties of, 75 
 density of, 76 
 test for, 77 
 sources of, 77, 78 
 
 manufacture of, 185 
 products obtained from 
 heating coal, 185, 186 
 purification of, 186 
 
 source of, 175 
 Borax, 175 
 where found, 175 
 
 decomposition of, 80 
 synthesis of, 81 
 carbonic acid in the 
 
 odour of, 1 86 
 Coal, pit, 86 
 Coal tar, 185 
 
 uses and properties of, 
 175, 176 
 
 atmosphere, 83 
 Carbonic oxide, 93 
 
 dyes procured from, 
 1 86 
 
 Boron, 174 
 
 formation and prepara- 
 
 Cobalt, 235 
 
 properties of, 174-176 
 mode of obtaining, 174 
 crystals of, 174 
 
 tion of, 94, 95 
 properties of, 96 
 Cast iron, 238 
 
 oxides of, 235 
 tests for salts of, 236 
 Cobalt nitrate, 235 
 
 compounds of, 175 
 oxide of, 175 
 
 grey and white, 239 
 Cerite, 229 
 
 Coke, 87 
 preparation of, 88 
 
 combination with fluo- 
 
 Cerium, 229 
 
 gas, 185 
 
 rine, 176 
 
 Cetylene, 177 
 
 Colcathar, 147 
 
 Brass, 201 
 Bromide, 134 
 
 Chalybeate waters, 55 
 Charcoal, lamp-black, 90 
 
 Columbium, 253 
 Combination, chemical, i 
 
 of silver, 277 
 
 antiseptic powers of 
 
 mixture distinguished 
 
 Bromine, 132 
 
 charcoal, 91 
 
 from, 13 
 
 properties of, 132 
 
 preparation of, 88 
 
 Combustion, 24 
 
 sources of, 132 
 
 as a fuel, 89 
 
 matter when burnt nat 
 
 formation of, 133 
 
 Charcoal, animal, or ivory 
 
 destroyed, 24. 25 
 
 Bronze, 201, 250 
 
 black, 90 Compound radicals, the- 
 
 ' Bull-dog ' slag, 171 
 
 preparation of, 90 
 
 ory of, 189 
 
 Bunsen's burner, 182 
 
 Chemical formulae, 7 
 Chemistry, scope and aim 
 of, i 
 
 Compounds, 3 
 Condy's green disinfect- 
 ing fluid, 247 
 
 CADMIUM, 234 
 oxide of, 234 
 
 China, basis of, 224, 228 
 Chlorates, 131 
 
 Copper, 261 
 properties of, 262 ~ 
 
 Caesium, 214, 215 
 
 Chloric acid, 129 
 
 smelting, 262 
 
 Calamine, 232 
 Calcedony, 168 
 Calcic carbonate, 222 
 
 preparation of, 131 
 oxide, 129 
 Chloride of lead, 134 
 
 oxides of, 263 
 chloride and sulphides, 
 264 
 
 chloride, 221 
 
 of lime, 130, note 
 
 tests for, 264 
 
 fluoride, 138 
 
 of mercury, 134 
 
 Corrosive sublimate, 273 
 
 phosphate, 160 
 
 of silver, 277 
 
 Corundum, 224 
 
 silicate, 171 
 sulphate, 152, 160, 221 
 
 Chlorides, 123, 130, 167, 
 168^ 
 
 Crucibles, 171 
 Cryolite, whence ob- 
 
 sulphide, 156 
 
 Chlorine, 120 
 
 tained, 138 
 
 Calcium, 141, 219 
 
 mode of obtaining, 120 
 
 Crystals, classification of, 
 
 compounds of, 219, 220' 
 
 solution of, 121 
 
 97 
 
 tests for calcium salts, 
 223 
 
 properties of, 122, 123 
 compounds of chlorine 
 
 symmetry of, 97 
 axes of, 98 
 
 Calico printing, colours 
 
 and oxygen, 129 
 
 cleavage of, 99 
 
 in, 224 
 Calomel, 273 
 
 combination of sulphur 
 with chlorine, 158 
 
 Cubic system of, 99,100 
 square prismatic, or 
 
 Carbides, 93 
 
 Chlorine acids, 130 
 
 pyramidal, system, 100, 
 
 Carbolic acid, 186 
 
 Chlorous acid, 129 
 
 101 
 
 Carbon, 73, 84 
 
 anhydride, 129 
 
 rhombohedral, or hexa- 
 
 varieties of, 84-90 
 properties of, 92 
 compounds of, 177 
 Carbon disulphide, 157 
 
 Choke damp, 78 
 Chromate of bismuth, 246 
 of cadmium, 246 
 Chromates, the, 245, 246 
 
 gonal system, 101 
 prismatic system, 102 
 oblique system, 102 
 doubly oblique system. 
 
 properties of, 157 
 
 Chromic anhydride, 235 
 
 103 
 
 preparation of, 158 
 
 Chromium, 244 
 
 Culm, or anthracite, 86 
 
Index. 299 
 
 CUP GOL HYD 
 
 Cupreous oxide, 263 
 
 FELSPAR, or adu- i Gold cont. 
 
 Cupric chloride, 264 
 
 laria, 227 | properties of, 278, 279 
 
 oxide, 263 
 
 varieties of, 227 
 
 alloy of, 279 
 
 sulphate, 145 
 
 Fermentation, carbonic 
 
 oxides of, 279 
 
 sulphide, 156, 264 
 
 anhydride formed by, 
 
 Granite, 227 
 
 Cyanogen, 188 
 
 77 
 
 Graphite, 85 
 
 preparation of, 188 
 
 mode of checking, 146 
 
 Guano, phosphorus in, 
 
 properties of, 188 
 
 Ferric oxide, 33, 147, 241, 
 
 160 
 
 its property of com- 
 
 242 
 
 Gun-metal, 201, 250 
 
 bining with the metals, 
 
 Ferrous carbonate, 237, 
 
 Gunpowder, 209 
 
 188, 189 
 
 243 
 
 Gypsum, 221 
 
 and with hydrogen, 
 
 chloride, 21, 243 
 
 
 188, 189 
 
 oxide, 33, 241 
 
 
 
 salts, _2 4 3, 244 
 
 HAEMATITE, red, 
 
 
 sulphide, 243 
 
 237 
 
 DAVY'S safety lamp, 
 180,, 181 
 
 Filter, paper, how to 
 make a, 90 
 
 brown, 237 
 Haematite anhydrate, 
 
 Decomposition, 3 
 Destructive distillation, 89 
 
 for water, 91 
 Fire-bricks, 171 
 
 brown, 242 
 Halogens, 140 
 
 Dialysis, 170 
 
 clay, 171 
 
 compounds of the, 1 40 
 
 Diamond, 84 
 
 damp of mines, 179 
 
 compared with each 
 
 Didymium, 229 
 Dihydric sodic phosphate, 
 164, 165 
 Dimorphous bodies, 103, 
 
 Flame, structure and pro- 
 perties of, 181, 182 
 the blowpipe, 184 
 the reducing and the 
 
 other, 140 
 Harrogate water, 155 
 Hartshorn, 114 
 Hornblende, 230 
 
 142 
 Dioxide of barium, 217 
 
 oxidising flames, 184 
 Flint, 169 
 
 Hydrates, 57 
 Hydric disodic arseniate, 
 
 Dipotassic sulphate, or 
 normal sulphate, 151 
 
 Fluorides, 138 
 Fluorine, 138 
 
 disodic phosphate, 1 65 
 
 sulphide, 156 
 Disodic hydric phosphate, 
 
 compound of, with hy- 
 drogen, 140 
 
 nitrate, 105 
 potassic sulphate, or 
 
 formation of, 164 
 
 Fluor spar, 138 
 
 disulphate, 151 
 
 sulphite, 146 
 Distillation, 134 
 destructive, 89 
 
 Foil, of metals, 201 
 Freezing point, 45 
 Fur inside a boiler, 53 
 
 potassic sulphide, 156 
 potassic sulphite, 146 
 Hydride of phosphorus, 
 
 Disulphates, 151 
 
 
 166 
 
 Disulphide of iron, 242 
 
 
 Hydrides, 73 
 
 Dithionic acid, 144 
 
 /^ALENA, 141, 265 
 
 Hydriodic acid, 137, 140 
 
 Dolomite, 230 
 Ductility of metals, 201 
 Dutch liquid, 178 
 
 VT Gas coke, 185 
 Gases, 12 
 experiments with, 20 
 
 properties of, 137 
 Hydrobromic acid, 140 
 Hydrocarbons, 177 
 
 Dyads, or bivalent ele- 
 ments, 72, 73 
 
 measurement of, 29 
 Gaseous compounds of the 
 
 Hydrochloric acid, 120, 
 123, 140, 167, 175 
 
 
 different elements, 72, 
 
 properties of, 124 
 
 EARTHENWARE, 
 
 German silver, 201, 236 
 
 analysis of, 125 
 solution of, 126 
 
 basis of, 224, 228, 
 
 Geysers of Iceland, silica 
 
 Hydrocyanic acid, 188, 
 
 manufacture of, 228 
 
 dissolved in the, 170 
 
 189 
 
 Effervescent waters, 55 
 
 Glass, action of hydro- 
 
 properties of, 189 
 
 Elements, chemical, 6 
 combination, i 
 
 fluoric acid on, 139 
 manufacture of, 170, 
 
 test of, 189 
 sometimes obtained 
 
 mode of occurrence, 4 
 
 171 
 
 from kernels and leaves, 
 
 number of, 4 window glass, or crown 
 
 190 
 
 division into metals and 
 
 glass, 171 
 
 Hydrofluoric acid, 138, 
 
 non-metals, 5 
 list of, with their sym- 
 bols and atomic weights, 
 
 plate glass, 172 
 bottle glass, 172 
 Bohemian glass, 172 
 
 140 
 its action on glass, 138, 
 139 
 
 6 
 
 flint glass, 172 
 
 Hydrogen, 58 
 
 Emerald, 229 
 
 properties of, 172, 173 
 
 mode of preparing, 59 
 
 Emery, 224 
 Epsom salts, 230, 231 
 
 annealing, 173 
 Glaze for stoneware, 228 
 
 properties of, 60, 61 
 union of hydrogen and 
 
 Erbium, 229 
 Ethylsulphuric acid, 178 
 Eudiometer, the, 65 
 
 Glucinum, 229 
 Gneiss, 227 
 Gold, 278 
 
 oxygen, 63 
 diffusion of, 69 
 its atomic weight and 
 
3OO Index. 
 
 HYD MET NOT 
 
 Hydrogen cont. 
 combining volume, the 
 unit or standard of com- 
 
 Lead cont. 
 uses of, 266 
 oxides of, 266 
 
 Metals -cant. 
 sulphides of, 155-157 
 properties of, 199, 200 
 
 parison, 70 
 union with chlorine, 
 
 compounds of, 267, 269 
 salts of, 268 
 
 table of gravities and 
 fusing points of, 199 
 
 oxygen, or nitrogen, 71 
 
 tests for, 269 
 
 malleability of, 201 
 
 gaseous compounds of 
 the different elements, 
 
 Lead carbonate, 268 
 chloride, 268 
 
 alloys, 20 1 
 amalgams, 202 
 
 7 2 > 73 
 
 chromate, 268 
 
 native metals, 202 
 
 salts of, 106 
 
 iodide, 268 
 
 classification of, 202- 
 
 compounds of, with 
 
 nitrate, 268 
 
 205 
 
 phosphorus, 166 
 
 silicate, 171 
 
 Metaphosphates, 166 
 
 Hydrosulphates, 155 
 Hypochlorous acid, 129 
 
 sulphate, 152, 268 
 sulphide, 268 
 
 Metaphosphoric acid, 166 
 Metastannic acid, 251 
 
 Hypochlorous anhydride, 
 
 Lime, 220 
 
 Metric system, 10, n 
 
 129 
 
 hydraulic, 221 
 
 Mica, 228 
 
 Hypophosphorous acid, 
 
 uses of, 221 
 
 Mineral waters, 55 
 
 166 
 Hyposulphites, 152 
 Hyposulphurous acid, 144 
 
 quicklime, 220 
 milk of lime, 220 
 Limestone rocks, 220, 221 
 
 Mines, fire-damp and 
 after-damp of, 179, 180 
 Minium, 267 
 
 
 Liquids, 12 
 
 Mirrors for lighthouses, 
 
 
 Litharge, 267 
 
 276 
 
 TCELAND SPAR, 222 
 
 Litmus-paper, 31, note 
 
 Mispickel, or arsenic sul- 
 
 J. Indium, 234 
 
 Loam, 227 
 
 phide of iron, 242 
 
 lodic acid, 138 
 
 
 Mixture distinguished 
 
 anhydride, 138 
 
 
 from combination, 13 
 
 Iodide of silver, 277 
 Iodides, 135 
 
 MAGNESIA, 230 
 Magnesic chloride, 
 
 MofFat water, 155 
 Molecular weights, 192- 
 
 tests for the, 135, 136 
 
 230 
 
 196 
 
 Iodine, 134 
 
 pyrophosphate, 231 
 
 Molecules, 72, 195 
 
 properties of, 134, 135 
 tests for, 135 
 
 sulphate, 231 
 Magnesium metals, 229 
 
 Molybdenum, 252 
 Monads, or univalent ele- 
 
 source of, 136 
 
 Magnesium, 146, 229 
 
 ments, 72, 73 
 
 Iridium, 282 
 Iron, 237 
 
 properties of, 229, 230 
 oxide of, 230 
 
 Monobasic acids, 166 
 Mordants, in dyeing, 225 
 
 varieties of, 237 
 
 tests f<?r magnesium 
 
 Mosaic gold, 251 
 
 ores of, 238 
 
 salts, 231 
 
 Muriatic acid, 126 
 
 modes of obtaining, 
 
 Manganese, 246 
 
 
 238 
 slag, 238 
 cast or pig iron, 238 
 properties of, 240 
 oxides of, 241 
 
 oxides of, 246, 247 
 compounds of, 247 
 tests for, 247 
 Manganous oxide, 246 
 Maremma, boracic acid 
 
 NAPHTHENE, i 77 
 Nickel, 236 
 ' properties of, 236 
 alloy of, 236 
 
 tests for, 243 
 
 in the, 175 
 
 oxides of, 236 
 
 Ironstone, clay, 237, 238, 
 243 
 black-band, 238 
 
 Marl, 227 
 Marsh gas, 179 
 where found, 179 
 
 Nitrate of bismuth, 261 
 of silver, 277 
 Nitrates, IQQ^ _- 
 
 Isomorphous bodies, 103, 
 140 
 
 properties of, 179 
 Marsh's test for arsenic, 
 
 Nitre, or saltpetre, 208 
 Nitric acid, 104 
 
 Ivory black, 90 
 preparation of, 90 
 
 255 
 Mercurial palsy, 271 
 Mercuric chloride, 273 
 
 distillation of, 105 
 properties of, 107 
 action of, on metals, 
 
 
 cyanide, 188 
 
 108, IOQ 
 
 KELP, 137 
 Kissingen water, 
 
 iodide, 273 
 oxide, 272 
 
 Nitric anhydride, 109, 160 
 oxide, 112 
 
 133 
 
 Mercurous chloride, 273 
 
 Nitrides, 38 
 
 Kreuznach water, 133 
 
 chromate, 246 
 
 Nitrites, 114 
 
 
 oxide, 272 
 
 Nitrogen, 36 
 
 
 Mercury, 270 
 
 methods of obtaining, 
 
 T AMP-BLACK, 90 
 
 properties of, 270, 271 
 
 36 
 
 J/ Lanthanum, 229 
 
 compounds of, 272 
 
 Nitrous acid, 113 
 
 Laughing gas, in 
 
 oxide of, 272 
 
 anhydride, 113, 160 
 
 Lead, 265 _ 
 
 tests for, 274 
 
 oxide, no 
 
 properties, of, afir 
 
 Metals, the, 198 
 
 Notation, chemical 6 
 
Index. 301 
 
 OIL REI SOb 
 
 OIL GAS, 177 
 Olefiant gas, 177 
 production of, 178 
 
 Photography; use of sodic 
 hyposulphite in, 152 
 fixing a picture, 153 
 
 Respiration, carbonic an- 
 hydride produced by, 77 
 Rhodium, 282 
 
 properties of, 178 
 name of, 178 
 
 Pig iron, 238 
 Pitchblende, 237 
 
 Rhombic phosphate, 1 64 - 
 Rouge, jewellers', 242 
 
 Oolite, 222 
 
 Plaster of Paris, 221 
 
 Rubidium, 214, 215 
 
 Opal, 169 
 Ores, analysis of, 154 
 
 ' Plated goods,' 276 
 Platinic chloride, 281 
 
 Ruby, oriental, 224 
 Ruthenium, 282 
 
 Orpiment, 254, 257 
 
 Platinum, 280 
 
 
 Osmium, 282 
 
 properties and uses of, 
 
 
 Oxidation, 24 
 
 280 
 
 SAFETY LAMP, Sir 
 
 Oxides, 24 
 
 compounds of, 281 
 
 H. Davy's, 180, 181 
 
 of carbon, 73 
 
 Plumbago, 85 
 
 matches, manufacture 
 
 of chlorine, 129 
 
 Polyhionic acids, 144 
 
 of, 162 
 
 of iron, 241 
 of nitrogen, 104 
 
 P or tJ> basis of, 224.228 
 manufacture of, 228 
 
 Saline waters, 55 
 Saltpetre, or nitre, 208 
 
 of phosphorus, 163 
 Oxygen, the word, 19 
 
 Porphyry, 227 
 Portland stone, 222 
 
 Salt, bay, 211 
 cake, 211, 212 
 
 mode of preparing 21, 
 
 Potash, caustic, 206 
 
 common, 210, 211 
 
 22 
 
 lye, 206 
 
 rock, 211 
 
 properties of, 22, 23 
 
 of commerce, 207 
 
 table, 211 
 
 abundance of, 26 
 
 Potassic carbonate, 207 
 
 Salts, 31 
 
 test for, 27 
 Oxygen-sulphur acids, 144 
 Oxyhydrogen flame, 181 
 Oxhydrogen jet, the, 65 
 Ozone, 34 
 
 chlorate, 130 
 chloride, 130, 207 
 chlorite, 131 
 cyanide, 189, 190 
 dihyric arseniate, 257 
 
 names of, 32, 33 
 Sapphire, 224 
 Saxony blue, 148 
 Scheele's green, 255 
 Sea water, 56 
 
 test for, 34 
 
 hydric carbonate, 208 
 
 salt, 120 
 
 
 hydrate, 206 
 
 Selenic acid, 159 
 
 
 hypochlorite, 130 
 
 Selenious acid, 159 
 
 PALLADIUM, 282 
 
 nitrate, 208 
 
 Selenium, 158 
 
 Pearl-ash, 207 
 Pentathionic acid, 144 
 
 perchlorate, 131 
 permanganate, 248 
 
 properties of, 158, 159 
 Seleniuretted hydrogen, 
 
 Perchloric acid, 129 
 Periodic acid, 138 
 Petalite, 227 
 
 Potassium, 203, 205 
 mode of obtaining, 205 
 oxides and hydrate of, 
 
 !59. 
 Sesquichloride of iron, 243 
 Sesquisulphide of anti- 
 
 Petrifaction, 170 
 
 206 
 
 mony, 259 
 
 Phosphoric acid, 163, 167 
 
 salts of, 207 
 
 Silica, 168 
 
 formation of, 164 
 
 Precipitate, 54, note 
 
 properties of, 168, 169 
 
 different forms of, 164 
 
 Prism, 103, note 
 
 solution of, 170 
 
 Phosphoric anhydride, 
 160, 163 
 
 Protosulphide of iron, 242 
 Prussic acid, 188 
 
 petrifaction, 170 
 Silicates, 170 
 
 Phosphorous group, 159 
 
 Prussian blue, components 
 
 Silicic fluoride, 171 
 
 Phosphorus, 159 
 
 of, 188 
 
 Silicon, 1 68 
 
 properties of, 159, 161 
 where and how ob- 
 
 formation of, 190 
 Psilomelane, 247 
 
 preparation and pro- 
 perties of, 1 68, 174 
 
 tained, 160, 161 
 
 Pumice, 228 
 
 oxide of, 1 68 
 
 white and red forms 
 
 ' Purple of Cassius, 252, 
 
 compounds of, 173, 174 
 
 of, 162 
 
 280 
 
 Silver, 275 
 
 distillation of, 162 
 
 Putty powder, 251 
 
 properties of, 275 
 
 safety matches, 162 
 
 Pyrites, iron, 242 
 
 oxide of, 276 
 
 oxides of phosphorus, 
 
 Pyrolusite, 247 
 
 compounds of, 277 
 
 163 
 compounds of, with hy- 
 
 Pyrophosphates, 165 
 Pyrophosphoric acid, 166 
 
 tests for, 278 
 ' Silver tree,' 278 
 
 drogen, 1 66 
 
 
 Smalt, 235 
 
 Phosphorous acid, 166 
 
 
 Smelling-salts, 216 
 
 anhydride, 160 
 iodide, 137 
 
 QUARTZ, silica in, 
 z68 
 
 Spathic iron, 237 
 Speculum metal, 250 
 
 Phosphuretted hydrogen, 
 160, 166 
 
 RAIN WATER, 49 
 
 Spring water, 50 
 Soda, caustic, or sodic 
 
 properties of, 166, 167 
 
 Realgar, 257 
 
 hydrate, 210 
 
 formation of, 167 
 
 Red lead, or minium, 267 
 
 manufacture of, 213 
 
 behaviour of in chlo- 
 
 Reinsch's test for arsenic, 
 
 ash, 212, 213 
 
 -?>. 167 
 
 255 
 
 crystals, 213 
 
302 Index. 
 
 SOD TUF ZIR 
 
 Soda water, how made, 76 
 Sodic carbonate, 212 
 
 Sulphuretted waters, 55 
 Sulphuric acid, 147 
 
 Tungsten, 253 
 Type-metal, 201, 258 
 
 carbonate, hydric, 214 
 
 importance ot the 
 
 
 chloride, 211 
 
 manufacture of, 147 
 
 
 hydrate, 210 
 hyposulphite, 152 
 
 mode of preparing, 148 
 manufacture of, on a 
 
 T TRANIUM, 237 
 
 iodide, 137 
 
 large scale, 149, 150 
 
 
 manganate, 247 
 phosphates, 164, 165 
 
 salts of, 151 
 Sulphuric anhydride, for- 
 
 VANADIUM, 253 
 Ventilation of rooms, 
 
 stannate, 251 
 
 mation of, 148 
 
 79 
 
 sulphate, 211 
 
 Sulphurous acid, 144, 145, 
 
 Vermilion, pigment, 272 
 
 Sodium, 210 
 
 146 
 
 Vitriol, blue, 264 
 
 oxides of, 210 
 
 Sulphurous anhydride, 
 
 green, 147 
 
 Solid bodies, 12 
 
 145, 243 
 
 white, 233 
 
 Stalactites, 222 
 
 production of, 145, 146 
 
 oil of, 147, 150 
 
 Stalagmites, 223 
 Stannic acid, 252 
 
 properties of, 145 
 acid and salts, 146 
 
 
 chloride, 251 
 oxide, 250 
 
 Superphosphate of lime, 
 161 
 
 WATER, 41 
 decomposition 
 
 sulphide, 156, 251 
 Stannous chloride,2so,25i 
 
 Symbols, chemical, 6 
 
 of, 42 
 freezing and boiling of, 
 
 oxide, 250 
 sulphide, 251 
 Steel, 239 
 Stone-blue, 235 
 Stoneware, manufacture 
 
 TANTALUM, 253 
 Tartar emetic, 258 
 Telluretted hydrogen, 159 
 Telluric acid, 159 
 
 distillation of, 48 
 rain water, 49 
 presence of air in, 49 
 spring water, 50 
 
 of, 228 
 
 Tellurium, 158 
 
 impurities in natural 
 
 Strontic sulphate, 152, 219 
 Strontium, 219 
 Sublimation, 134 
 Subphosphate of soda, 164 
 
 properties of, 158, 159 
 Tellurous acid, 159 
 Test-papers, 31, note 
 Tests, in chemistry, 31, 
 
 waters, 50-52 
 hard and soft, 53 
 fur inside a boiler, 53 
 soap test for, 54 
 
 Sulphate of barium, 218 
 
 note 
 
 mineral waters, 55 
 
 Sulphates, 141 
 
 Tetrabasic acids, 166 
 
 sea water, 56 
 
 Sulphide of ammonium, 
 
 Tetrads, or quadrivalent 
 
 saturation, 56 
 
 185 
 of barium, 218 
 
 elements, 73 
 Tetrathionic acid, 144 
 
 crystallisation, 58 
 efflorescent and deli- 
 
 of silver, 277 
 
 Thallium, 269 
 
 quescent salts, 57 
 
 Sulphides, 143 
 of metals, 155-157 
 
 properties of, 269 
 Thorinum, 252 
 
 compounds of, 57 
 composition of, 63, 64 
 
 Sulphites, 146 
 properties of the, 147 
 Sulphur group, 141 
 
 Tin, 249 
 alloys of, 250 
 oxides of, 250 
 
 synthesis of, 65 
 the eudiometer, 65 
 Water of crystallisation, 57 
 
 Sulphur, or brimstone, 141 
 
 compounds of, 251 
 
 Water cisterns, lead, 266 
 
 sources of, 141 
 
 tests for, 252 
 
 slate, 266 
 
 properties of, 141 
 
 Tin salts, 251 
 
 Weights and measures, 9 
 
 crystals of, 142 
 
 Tincal, or crude Indian 
 
 Witherite, 219 
 
 distillation of, 143 
 
 borax, 175 
 
 Wolfram, 253 
 
 roll sulphur of com- 
 
 Tinfoil, 249 
 
 Woulfe's bottles, 118 
 
 merce, 144 
 
 Tinstone, 249 
 
 Writing-ink, 224 
 
 flowers of, 144 
 
 Titanium, 252 
 
 
 compounds of, with 
 oxygen, 144 
 
 Touch paper, 209 
 Travertine, 223 
 
 \7TTRIUM, 229 
 
 and with chlorine, 158 
 
 Triads, or tervalent ele- 
 
 Y 
 
 Sulphur salts, 259 
 
 ments, 72, 73 
 
 
 Sulphurets, 143 
 Sulphuretted hydrogen, 
 153, iS9, .242 
 preparation of, 153, 154 
 properties of, 154 
 compounds with metals, 
 156 
 
 Tribasic acids, 166 
 phosphoric acid, 165 
 Tricalcic phosphate, 161 
 Trifluorides, 176 
 Trisodic phosphate, 164, 
 l6 5 
 Trithionic acid, 144 
 
 ZINC, 232 
 properties of, 232 
 alloys of, 233 
 salts of, 233 
 oxide, 233 
 sulphate, 233 
 Zirconic chloride, 174 
 
 tests of, 157 I Tufa, 223 
 
 Zirconium, 252 
 
 Spotiiswoode &> Co., Printers, New-street Square, 
 
CRITICAL OPINIONS of this MANUAL. 
 
 PHARMACEUTICAL JOURNAL. 
 
 ' This introductory treatise relieves us of a difficulty we have 
 often been placed in when requested to recommend an elementary 
 
 book on Chemistry It is a question with some whether 
 
 it is advisable to commence so early the employment of chemical 
 notation. We are, however, of opinion that it is decidedly an 
 advantage to use it, in a simple form, from the very first ; since 
 by doing so the precision which ought to characterise all scientific 
 work is constantly impressed upon the mind. We have much 
 pleasure in cordially recommending this little volume to all who 
 desire to acquire a solid groundwork of general principles.' 
 
 EXAMINER. 
 
 * Another instalment of the admirable series of Scientific 
 Text- Books, edited by Professor GOODEVE, that are intended 
 to serve as a basis for the sound instruction of artisans in the 
 various branches of mechanical and physical science, and for 
 general use in schools. . . . Dr. MILLER'S Inorganic Chemistry 
 certainly fulfils the promise made by the Publishers and Editor, 
 and is by far the best book for beginners in that science that we 
 
CRITICAL OPINIONS. 
 
 have lately seen In the preface Dr. MILLER confesses 
 
 that it is impossible to avoid the use of technical terms in 
 discussing a scientific subject. He has, however, throughout 
 explained every technical term when used for the first time, but 
 the explanation is not repeated. The Author is very successful 
 in explaining clearly and familiarly some of the most difficult 
 parts of the science. We may instance that portion of the first 
 chapter dealing with chemical notation, a subject which fre- 
 quently proves a stumbling-block to young students. Practical 
 experiments, also, are numerous, and will be found to relieve 
 pleasantly the dry study of the text. The apparatus required 
 for these experiments is generally neither complicated nor ex- 
 pensive, and the beginner is urged to repeat every experiment 
 within his power. Dr. MILLER frequently assists the student 
 by informing him how to construct apparatus out of articles of 
 ordinary domestic use, and thus renders the book admirably 
 suited for self-instruction, and for the use of those who cannot 
 attend professorial lectures. .Throughout the volume we find 
 that the practical and useful element predominates over the 
 theoretical. Thus, in the chapter devoted to carbon, the subject 
 of ventilation is treated upon ; while, in another chapter, sewerage 
 and the impurities in natural waters are illustrated and explained 
 In a lucid and familiar manner. The few paragraphs treating of 
 crystallography are thoroughly explanatory and easy of com- 
 prehension, as are also the pages devoted to the discussion of 
 the atomic theory and the laws of chemical combination. The 
 illustrations and diagrams are exceedingly good, and the index 
 is as full and complete as that of every scientific text-book 
 should be.' 
 

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 UNIVERSITY OF CALIFORNIA LIBRARY