GIFT OF 
 MICHAEL REESE 
 
A SYSTEMATIC HANDBOOK 
 
 OF 
 
 VOLUMETRIC ANALYSIS. 
 
SYSTEMATIC HANDBOOK 
 
 OF 
 
 VOLUMETRIC ANALYSIS; 
 
 OR, 
 
 THE QUANTITATIVE ESTIMATION 
 
 OF CHEMICAL SUBSTANCES BY MEASURE, APPLIED TO 
 LIQUIDS, SOLIDS, AND GASES, 
 
 ADAPTED TO THE REQUIREMENTS OF PURE CHEMICAL RESEARCH, 
 PATHOLOGICAL CHEMISTRY, PHARMACY. METALLURGY, MANUFACTURING 
 
 CHEMISTRY, PHOTOGRAPHY, ETC., AND FOR THE VALUATION 
 OF SUBSTANCES USED IN COMMERCE, AGRICULTURE, AND THE ARTS. 
 
 BY 
 
 FRANCIS SUTTON, F.I.C., F.C.S., 
 
 PUBLIC ANALYST FOR THE COUNTY OF NORFOLK: 
 
 LATE ^lEMBER OF OtTUNCIL OF THE SOCIETY OF PUBLIC ANALYSTS ; 
 
 LATE MEMBER OF COUNCIL OF THE PHARMACEUTICAL SOCIETY OF GREAT BRITAIN; 
 
 CO I! RESPONDING MEMBER OF THE IMPERIAL PHARMACEUTICAL SOC. OF ST. PETERSBURG!! ; 
 
 CORRESPONDING MEMBER OF THE AUSTRIAN APOTHEKER VEREIN, VIENNA; 
 
 CONSULTING CHEMIST TO THE NORFOLK CHAMBER OF AGRICULTURE; 
 
 ETC., ETC. 
 
 OF THE 
 
 DIVERSITY 
 
 OF 
 
 SEVENTH EDITION, ENLARGED AND IMPROVED. 
 
 LONDON: 
 
 J. & A. CHURCHILL, 7 GREAT MARLBOROUGH STREET 
 
 (Removed from 11 Neiv Burlington Street), 
 1896. 
 
 [All rights reserrej,'] 
 

OWING to the large edition of this work issued at the end of 
 1890, a rather longer period than usual has occurred 
 between successive issues. The book, however, has been 
 out of print for nearly a year owing to pressure of other 
 matters, and the time required for investigation of new 
 processes or modifications of old ones. 
 
 It will be seen that considerable alterations and additions 
 have been made in various sections, so as to bring the 
 work up to date as closely as possible. 
 
 The sections thus altered, "<aiict> 'pthers entirely new, 
 comprise chiefly the articles on Calibration of Instruments, 
 the Kjeldahl process, Boric Acid, Hydrofluoric Acid and 
 Fluorides, Arsenic, Chromium, Copper, Cyanogen and 
 Cyanides, Iron, Lead, Manganese, Mercury, Nickel, 
 Phosphoric Acid, Sugar, Sulphur and its compounds, 
 
 Tannin, Zinc, Oils and Fats, and Urine. 
 
 - 
 As respects the volumetric method as applied to many 
 
 organic substances, and the action of modern indicators 
 in such work, nothing has been attempted, partly because 
 the results hitherto obtained have not been altogether 
 satisfactory, but mainly because this subject comes 
 specially within the scope of my friend A. H. Allen's 
 well-known work on Organic Analysis, and it cannot in 
 my opinion be left in better hands. 
 
 My thanks are especially due to Mr. W. B. Giles, F.I.C., 
 for his original article on the estimation of Hydrofluoric 
 Acid, and for the benefit of his long practical experience 
 in the examination of Sulphur Compounds and Phosphoric 
 
 Acid. 
 
VI PREFACE. 
 
 Mr. J. W. Westmoreland has also rendered great 
 service in the articles on Copper, Iron, and Manganese. 
 
 Dr. James Edmunds has also favoured me with 
 suggestions on Urinary analysis, which I believe to be of 
 considerable practical value. 
 
 I have availed myself in some instances of the excellent 
 abstracts of original papers now being published in the 
 Analyst, which reflect great credit upon the present 
 management in this department. 
 
 My son, W. L. Sutton, A.I.C., has rendered me help in 
 the general revision of the book and the correction of 
 proof sheets. 
 
 This labour has hitherto been taken, in the five previous 
 editions, by my friend W. Thorp, B.Sc., who would 
 willingly have continued his kind services, but the delay 
 in preparation of the book has necessitated extra rapidity 
 in printing and revision. 
 
 The nomenclature of chemical substances is mainly the 
 same as in previous editions, and inasmuch as the book is 
 largely used by many persons who are practical workers, and 
 not advanced theoretical chemists, I have continued the 
 use of such terms as sodic bicarbonate in place of sodium 
 hydrogen carbonate, and similar modern terms. 
 
 The aim throughout the whole series of editions has 
 been to make the book a guide to practical workers, and to 
 condense the descriptions of processes as much as is 
 possible, without the sacrifice of accuracy or clearness. 
 Notwithstanding, the present edition will be enlarged by 
 more than thirty pages. 
 
 FEANCIS SUTTON. 
 
 NORWICH, 
 August, 1896. 
 
CONTENTS 
 
 PART I. 
 
 Sect. Page 
 
 1. GENERAL PRINCIPLES . . . . .1 
 
 2. The Balance ..... 5 
 
 3. Volumetric Analysis without "Weights . . .5 
 
 4. Volumetric Analysis without Burettes ... 6 
 
 5. The Burette . . . . . .7 
 
 6. The Pipette ... 15 
 
 7. The Measuring Flasks . . . . .15 
 
 8. The Correct Reading of Graduated Instruments . . 17 
 
 9. Calibration of Graduated Apparatus . . .19 
 
 10. The Weights and Measures to be adopted in Volumetric Analysis 23 
 
 11. Preparation of Normal Solutions in General . . 27 
 
 12. Direct and Indirect Processes of Analysis . . .31 
 
 PAET II. 
 
 13. ALKALIMETRY ..... 33 
 
 14. Indicators used in Saturation Analyses . . .33 
 
 15. Normal Alkaline and Acid Solutions ... 44 
 
 16. Correction of Abnormal Solutions . . . .51 
 Table for the Systematic Analysis of Acids, Alkalies, and Alkaline 
 
 Earths ..... 54 
 
 17. Titration of Alkaline Salts . . . .55 
 
 18. Titration of Alkaline Earths .... 69 
 
 19. Ammonia . . . . . .72 
 
 20. ACIDIMETEY ..... 88 
 
 21. Acetic Acid . . . . . .89 
 
 22. Boric Acid and Borates .... 92 
 
 23. Carbonic Acid . . . . . .93 
 
 24. Citric Acid ..... 103 
 
 25. Formic Acid ...... 104 
 
 26. Hydrofluoric Acid ..... 105 
 
 27. Oxalic Acid . . . . . .109 
 
 28. Phosphoric Acid . . . . .109 
 
 29. Sulphuric Anhydride ..... Ill 
 
 30. Tartaric Acid . . . . .112 
 
 31. Estimation of Combined Acids in Neutral Salts . .114 
 
 32. Extension of Alkalimetric Methods 117 
 
Vlll CONTENTS. 
 
 PART III. 
 
 Sect. Page 
 
 33. ANALYSIS BY OXIDATION OR REDUCTION . . . 120 
 
 34. Permanganic Acid and Ferrous Oxide . . . 121 
 
 35. Titration of Ferric Salts by Permanganate . vC . 124 
 
 36. Calculation of Permanganate Analyses . . . 125 
 
 37. Chromic Acid and Ferrous Oxide . . ... . 126 
 
 38. Iodine and Thiosulphate . . . .128 
 
 39. Analysis of Substances by Distillation with Hydrochloric Acid . 132 
 
 40. Arsenious Acid and Iodine - . 136 
 
 PART IV. 
 
 41. ANALYSIS BY PRECIPITATION . . , . 138 
 
 42. Indirect Analyses by Silver and Potassic Chromate . . 140 
 
 43. Silver and Thiocyanic Acid .... ... 142 
 
 44. Precision in Colour Reactions 143 
 
 PART V. 
 
 45. Alumina ...... 145 
 
 46. Antimony . . . . . 147 
 
 47. Arsenic . . . . . . 149 
 
 48. Barium . . . . . .154 
 
 49. Bismuth ...... 154 
 
 50. Bromine . . . . . .156 
 
 51. Cadmium ...... 159 
 
 52. Calcium . . . . . .160 
 
 53. Cerium ...... 162 
 
 54. Chlorine . . . . . .162 
 
 55. Chlorine Gas and Bleach .... 164 
 Chlorates, lodates, and Bromates .... 166 
 
 56. Chromium ...... 167 
 
 57. Cobalt . . . . . .173 
 
 58. Copper . ... 175 
 
 59. Cyanogen . . . . . . 189 
 
 60. Ferro- and Ferri-C3 r anides .... 195 
 Thiocyanates or Sulphocyanides .... 197 
 
 61. Gold . 198 
 
 62. Iodine ...... 199 
 
 63. Ferrous Iron ..... 206 
 
 64. Ferric Iron ...... 210 
 
 65. Iron Ores . . , . . .214 
 
 66. Lead ..... . . 222 
 
 67. Manganese. ..... 226 
 
 68. Mercury . . . . . .238 
 
 69. Nickel 243 
 
CONTENTS. IX 
 
 Sect. 
 
 70. Nitrogen as Nitrates and Nitrites. . . . 245 
 
 71. Oxygen and Hydrogen Peroxide . 269 
 
 72. Phosphoric Acid and Phosphates . . . 284 
 
 73. Silver ..... 297 
 
 74. Sugar .... -305 
 
 75. Sulphur, Sulphides, and Sulphites 
 
 76. Sulphuric Acids and Sulphates . . 325 
 
 77. Sulphuretted Hydrogen .... 329 
 
 78. Tannic Acid . . . . . - 331 
 
 79. Tin . . . 339 
 
 80. Uranium 
 
 81. Vanadium .... 341 
 
 82. Zinc . ... 342 
 
 83. Oils and Pats 
 
 84. Glycerin . -363 
 
 85. Phenol (Carbolic Acid) . . 366 
 
 86. Carbon Bisulphide . 367 
 
 APPENDIX TO PART V. 
 
 Arsenic and Arsenic Acid 
 
 Boric Acid in Milk 
 
 Mixtures of Chlorides, Hypochlorites, and Chlorates 372 
 
 Chloric and Nitric Acids . . 373 
 
 PART VI. 
 
 87. Analysis of Urine ..... 377 
 
 88. Analysis of Potable Waters and Sewage . . . 398 
 
 89. Analytical Processes for Water . . 405 
 
 90. Interpretation of Results of Water Analysis . . 444 
 
 91. Water Analysis without Gas Apparatus . . 455 
 
 92. Reagents and Processes employed .... 463 
 
 93. Oxygen Dissolved in Water .... 474 
 Table for Calculations and Logarithms . . . 476 
 
 PART VII. 
 
 94. Volumetric Analysis of Gases and Construction of Apparatus 480 
 
 95. Gases Estimated Directly and Indirectly . . . 494 
 
 96. H} r drochloric, Hydrobromic, and Hydriodic Acids . 494 
 
 97. Analysis of Air, Carbonic Anhydride, SH 2 , and SO 2 . . 496 
 
 98. Indirect Determinations .... 502 
 
 99. Improvements in Gas Apparatus .... 517 
 
 100. Simpler Methods of Gas Analysis . . .. 547 
 
 101. The Nitrometer, Gasvolumeter, and Gravivolumeter . 557568 
 
Names of Elementary Substances occurring- in Volumetric 
 Methods, with their Symbols and Atomic Weights. 
 
 Name. 
 
 Symbol. 
 
 Exact Atomic 
 Weight 
 as found by 
 the latest 
 researches. 
 
 Atomic Weight 
 adopted in 
 this Edition. 
 
 Aluminium 
 
 Al 
 
 27-3 
 
 27-3 
 
 Antimony 
 Arsenic 
 
 Sb 
 
 As 
 
 119-6 
 74-9 
 
 120-0 
 75-0 
 
 Barium 
 
 Ba 
 
 136-8 
 
 136-8 
 
 Bismuth . 
 
 Bi 
 
 208-0 
 
 208-0 
 
 Bromine 
 
 Br 
 
 79-75 
 
 80-0 
 
 Cadmium . 
 
 Cd 
 
 111-6 
 
 111-6 
 
 Calcium 
 
 Ca 
 
 39-9 
 
 40-0 
 
 Carbon 
 
 C 
 
 11-97 
 
 12-0 
 
 Cerium 
 
 Ce 
 
 141-2 
 
 141'2 
 
 Chlorine . 
 
 Cl 
 
 35-37 
 
 35-37 
 
 Chromium 
 
 Cr 
 
 52-4 
 
 52-4 
 
 Cobalt 
 
 Co 
 
 58-6 
 
 59-0 
 
 Copper 
 Gold 
 
 Cu 
 Au 
 
 63-18 
 196-2 
 
 63-0 
 196-5 
 
 Hydrogen 
 Iodine 
 
 H 
 
 I 
 
 1-0 
 126-86 
 
 1-0 
 127-0 
 
 Iron . 
 
 Fe 
 
 55-88 
 
 56-0 
 
 Lead 
 
 Pb 
 
 206-4 
 
 206-4 
 
 Magnesium 
 Manganese 
 Mercury 
 Molybdenum 
 Nickel 
 
 Mg 
 Mn 
 Hg 
 Mo 
 
 Ni 
 
 23-94 
 55-0 
 199-8 
 95-8 
 58-6 
 
 24-0 
 55-0 
 200-0 
 95-8 
 59-0 
 
 Nitrogen . 
 Oxygen 
 Phosphorus 
 Platinum 
 
 N 
 
 P 
 Pt 
 
 14-01 
 15-96 
 30-96 
 194-3 
 
 14-0 
 16-0 
 31-0 
 194-3 
 
 Potassium 
 
 K 
 
 39-04 
 
 39-0 
 
 Silver . 
 Sodium 
 
 Ag 
 
 Na 
 
 107-66 
 22-99 
 
 107-66 
 23-0 
 
 Strontium 
 
 Sr 
 
 87-2 
 
 87-2 
 
 Sulphur . 
 Tin . 
 
 S 
 Sn 
 
 31-98 
 117-8 
 
 32-0 
 118-0 
 
 Tungsten . 
 Uranium 
 
 w 
 
 Ur 
 
 184-0 
 239-8 
 
 184-0 
 240-0 
 
 Vanadium 
 
 Va 
 
 51-2 
 
 51-2 
 
 Zinc . 
 
 Zn 
 
 64-9 
 
 65-0 
 
[XI] 
 
 Abbreviations and Explanations. 
 
 The formulae are constructed on the basis H=l. = 16 
 H 2 = 18. 
 
 The normal temperature for the preparation and use of standard 
 solutions is 16 C., or about 60 Fahr. 
 
 c.c. denotes cubic centimeter. 
 
 gm. gram = 15-43235 grains English. 
 
 grn. grain. 
 
 dm. decem= 10 fluid grains at 16 C. 
 
 1 liter=1000 c.c. at 16 C. 
 
 1 c.c. = 1 gm. distilled water at 16 C. 
 
 1 dm. = 10 grn. 
 
 Distilled water is to be used in all the processes, unless other- 
 wise expressed. 
 
 Normal Solutions are those which contain one gram atom of 
 reagent (taken as monobasic), or an equivalent in some active 
 constituent (e.r/. oxygen) in the liter (see page 28). 
 
 Decinormal Solutions are one-tenth of that strength = T ^-. 
 Centinormal, one hundredth = -$. 
 
 Empirical Standard Solutions are those which contain no 
 exact atomic proportion of reagent, but are constructed generally so 
 that 1 c.c. = 0'01 gm. (one centigram) of the substance sought. 
 
 A Titrated Solution (from the French word titre, title or 
 power) denotes a solution whose strength or chemical power has 
 been accurately found by experiment. 
 
 When a chemical substance or solution is directed to be titrated, 
 the meaning is, that it is to be quantitatively tested for the amount 
 of pure substance it contains by the help of standard or titrated 
 solutions. The term is used in preference to tested or analyzed, 
 because these expressions may relate equally to qualitative and 
 quantitative examinations, whereas titrations can only apply to 
 quantitative examination. 
 
 J. C. S. denotes Journal of the Chemical Society (Transactions 
 only). 
 
 /. S. C. I. Journal of the Society of Chemical Industry. 
 Z. a. (7. Zeitschrift fiir Analytische Chemie. 
 C. N. Chemical News. 
 
 Other book-references are given in full. 
 
EREATA AND ADDENDA. 
 
 Page 25. Line 15 from top, read 760 in.m. in place of 0'76 m.m. 
 
 Page 139. Line 3 from bottom, read " nitrates " in place of " hydrates." 
 
 Page 149. Line 3 from bottom, omit the words " arsenic obtained as 
 sulphide/' and substitute " arsenical material." 
 
OF THE , 
 
 P"KIVERSITY 
 
 VOLUMETRIC ANALYSIS 
 
 OF 
 
 LIQUIDS AND SOLIDS, 
 
 PART I. 
 
 GENERAL PRINCIPLES. 
 
 1. QUANTITATIVE analysis by weight, or gravimetric analysis, 
 consists in separating out the constituents of any compound, either 
 in a pure state or in the form of some new substance of known 
 composition, and accurately weighing the products. Such opera- 
 tions are frequently very complicated, and occupy a long time, 
 besides requiring in many cases elaborate apparatus, and the exercise 
 of much care and experimental knowledge. Volumetric processes 
 on the other hand, are, as a rule, quickly performed ; in most cases 
 are susceptible of extreme accuracy, and need much simpler 
 apparatus. The leading principle of the method consists in sub- 
 mitting the substance to be estimated to certain characteristic 
 reactions, employing for such reactions solutions of known 
 strength, and from the volume of solution necessary for the pro- 
 duction of such reaction, determining the weight of the substance 
 to be estimated by aid of the known laws of chemical equivalence. 
 
 Volumetric analysis, or quantitative chemical analysis by measure, 
 in the case of liquids and solids, consequently depends upon the 
 following conditions for its successful practice : 
 
 1. A solution of the reagent or test, the chemical power of 
 which is accurately known, called the " standard solution." 
 
 2. A graduated vessel from which portions of it may be 
 accurately delivered, called the " burette." 
 
 3. The decomposition produced by the test solution with any 
 given substance must either in itself or by an indicator be such, 
 that its termination is unmistakable to the eye, and thereby the 
 quantity of the substance with which it has combined accurately 
 calculated. 
 
VOLUMETRIC ANALYSIS. 1. 
 
 Suppose, for instance, that it is desirable to know the quantity of 
 pure silver contained in a shilling. The coin is first dissolved in 
 nitric acid, by which means a bluish solution, containing silver, 
 copper, and probably other metals, is obtained. It is a known fact 
 that chlorine combines with silver in the presence of other metals 
 to form silver chloride, which is insoluble in nitric acid. The pro- 
 portions in which the combination takes place are 35*37 of chlorine 
 to every 107*66 of silver; consequently, if a standard solution of 
 pure sodic chloride is prepared by dissolving in water such a weight 
 of the salt as will be equivalent to 35*37 grains of chlorine ( = 58 -37 
 grains XaCl) and diluting to the measure of 1000 grains; every 
 single grain measure of this solution will combine with 0*10766 grain 
 of pure silver to form silver chloride, which is precipitated to the 
 bottom of the vessel in which the mixture is made. In the process 
 of adding the salt solution to the silver, drop by drop, a point is at 
 last reached when the precipitate ceases to form. Here the process 
 must stop. On looking carefully at the graduated vessel from 
 which the standard solution has been used, the operator sees at 
 once the number of grain measures which has been necessary to 
 produce the complete decomposition. For example, suppose the 
 quantity used was 520 grain measures ; all that is necessary to be 
 done is to multiply 520 by the coefficient for each grain measure, 
 viz. 0*10766, which shows the amount of pure silver present to be 
 55*98 grains. 
 
 This method of determining the quantity of silver in any given 
 solution occupies scarcely a quarter of an hour, whereas the estimation 
 by weighing could not be done in half a day, and even then not so 
 accurately as by the volumetric method. It must be understood 
 that there are certain necessary precautions in conducting the above 
 process which have not been described; those will be found in their 
 proper place; but from this example it will at once be seen that the 
 saving of time and trouble, as compared with the older methods of 
 analysis, is immense ; besides which, in the majority of instances 
 in which it can be applied, it is equally accurate, and in many cases 
 much more so. 
 
 The only conditions on which the volumetric system of analysis 
 are to be carried on successfully are, that great care is taken with 
 respect to the graduation of the measuring instruments, and their 
 agreement with each other, the strength and purity of the standard 
 solutions, and the absence of other matters which would interfere 
 with the accurate estimation of the particular substance sought. 
 
 The fundamental distinction between gravimetric and volumetric 
 analysis is, that in the former method, the substance to be 
 estimated must be completely isolated in the purest possible state 
 or combination, necessitating in many instances very patient and 
 discriminating labour ; whereas, in volumetric processes, such com- 
 plete separation is very seldom required, the processes being so 
 contrived as to admit of the presence of half a dozen or more 
 
$ 1. GENERAL PRINCIPLES. 3 
 
 other substances which have no effect upon the particular chemical 
 reaction required. 
 
 The process just described for instance, the estimation of silver 
 in coin, is a case in point. The alloy consists of silver and copper, 
 with small proportions of lead, antimony-, tin, gold, etc. None of 
 these things affect the amount of salt solution which is chemically 
 required to precipitate the silver, whereas, if the metal had to be 
 determined by weight it would be necessary to first filter the nitric 
 acid solution to free it from insoluble tin, gold, etc. ; then 
 precipitate with a slight excess of sodic chloride; then to bring the 
 precipitate upon a filter, and wash repeatedly with pure water until 
 every trace of copper, sodic chloride, etc., is removed. The pure 
 silver chloride is then carefully dried, ignited separately from the 
 filter, and weighed ; the filter burnt, residue as reduced metallic 
 silver and filter ash allowed for, and thus finally the amount of 
 silver is found by the balance with ordinary weights. 
 
 On the other hand the volumetric process has been purely 
 chemical, the burette or measuring instrument has taken the place 
 of the balance, and theoretical or atomic weights have supplanted 
 ordinary weights. 
 
 The end of the operation in this method of analysis is in all 
 cases made apparent to the eye. In alkalimetry it is the change 
 of colour produced in litmus, turmeric, or other sensitive colouring 
 matter. The formation of a permanent precipitate, as in the 
 estimation of cyanogen. A precipitate ceasing to form, as in 
 chlorine and silver determination. The appearance of a distinct 
 colour, as in iron analysis by permanganate solution, and so on. 
 
 I have adopted the classification of methods used by Mohr and 
 others, namely : 
 
 1. Where the determination of the substance is effected by 
 saturation with another substance of opposite properties generally, 
 understood to include acids and alkalies, or alkaline earths. 
 
 2. Where the determination of a substance is effected by a 
 reducing or oxidizing agent of known power, including most 
 metals, with their oxides and salts ; the principal oxidizing agents 
 being potassic permanganate, potassic bichromate, and iodine; and 
 the corresponding reducing agents, ferrous and stannous compounds, 
 :and sodic thiosulphate. 
 
 3. Where the determination of a substance is effected by 
 precipitating it in some insoluble and definite combination, an 
 example of which occurs in the estimation of silver described 
 above. 
 
 This classification does not rigidly include all the volumetric 
 processes that may be used, but it divides them into convenient 
 sections for describing the peculiarity of the reagents used, and 
 their preparation. If strictly followed out, it would in some cases 
 necessitate the registration of the body to be estimated under two 
 or three heads. Copper, for instance, can be determined residually 
 
 B 2 
 
4 VOLUMETRIC ANALYSIS. 1. 
 
 by potassic permanganate ; it can also be determined by precipitation 
 with sodic sulphide. The estimation of the same metal by potassic 
 cyanide, on the other hand, would not come under any of the 
 heads. 
 
 It will be found, therefore, that liberties have been taken with 
 the arrangement ; and for convenient reference all analytical pro- 
 cesses applicable to a given body are included under its name. 
 
 It may be a matter of surprise to some that several distinct 
 volumetric methods for one and the same substance are given; 
 but a little consideration will show that in many instances greater 
 convenience, and also accuracy, may be gained in this way. The 
 operator may not have one particular reagent at command, or he 
 may have to deal with such a mixture of substance as to preclude 
 the use of some one method; whereas another may be quite 
 free from such objection. The choice in such cases of course 
 requires judgment, and it is of the greatest importance that the 
 operator shall be acquainted with the qualitative composition of the 
 matters with which he is dealing, and that he should ask himself 
 at every step why such and such a thing is done. 
 
 It will be apparent from the foregoing description of the 
 volumetric system, that it may be successfully used in many 
 instances by those who have never been thoroughly trained as 
 analytical chemists ; but we can never look for the scientific 
 development of the system in such hands as these. 
 
 In the preparation of this work an endeavour has been made to 
 describe all the operations and chemical reactions as simply as 
 possible, purposely avoiding abstruse mathematical expressions,, 
 which, though they may be more consonant with the modern study 
 of chemical science, are hardly adapted to the technical operator. 
 
NIVERSIT 
 
 2. INSTRUMENTS. 
 
 THE IKSTBUMENTS AND APPAKATUS. 
 
 THE BALANCE. 
 
 2. STRICTLY speaking, it is necessary to have two balances in 
 order to carry out the volumetric system completely ; one to carry 
 about a kilogram in each pan, and turn when loaded with 
 about five milligrams. This instrument is used for graduating 
 flasks, or for testing them, and for weighing large amounts of pure 
 reagents for standard solutions. The second balance should be 
 light and delicate, and to carry about fifty grams, and turn easily 
 and quickly when loaded with one or two-tenths of a milligram. 
 This instrument serves for weighing small quantities of substances 
 to be tested, many of which are hygroscopic, and need to be 
 weighed quickly and with great accuracy ; it also serves for testing 
 the accuracy of pipettes and burettes. 
 
 For all technical purposes, however, a moderate-sized balance 
 of medium delicacy is quite sufficient, especially if rather large 
 quantities of substances are weighed and brought into solution- 
 then further subdivided by means of measuring flasks and pipettes. 
 
 The operator also requires, besides the balance and the graduated 
 instruments a few beakers, porcelain basins, flasks, funnels, stirring 
 rods, etc., as in gravimetric analysis ; above all he must be 
 practically familiar with proper methods of filtration, washing of 
 precipitates, and the application of heat. 
 
 VOLUMETRIC ANALYSIS WITHOUT WEIGHTS. 
 
 3. THIS is more a matter of curiosity than of value; but, 
 nevertheless, one can imagine circumstances in which it might be 
 useful. In carrying it out, it is necessary only to have (1) a 
 correct balance, (2) a pure specimen of substance to use as a weight, 
 (3) an accurate burette filled with the appropriate solution. It is 
 not necessary that the strength of this should be known ; but the 
 state of concentration should be such as to permit the necessary 
 reaction to occur under the most favourable circumstances. 
 
 If a perfectly pure specimen of substance, say calcic carbonate, 
 be put into one scale of the balance, and be counterpoised with an 
 impure specimen of the same substance, and both titrated with the 
 same, acid, and the number of c.c. used for the pure substance be 
 called 100, the number of c.c. used for the impure substance w r ill 
 correspond to the percentage of pure calcic carbonate in the specimen 
 examined. 
 
 The application of the process is, of course, limited to the use of 
 such substances as are to be had pure, and whose weight is not 
 variable by exposure; but where even a pure substance of one kind 
 cannot be had as a weight, one of another kind may be used as a 
 substitute, and the required result obtained by calculation. For 
 
6 VOLUMETRIC ANALYSIS. 4. 
 
 instance, it is required to ascertain the purity of a specimen of sodic 
 carbonate, and only pure calcic carbonate is at hand to use as a 
 weight; equal weights of the two are taken, and the impure 
 specimen titrated with acid. To arrive at the required answer, it 
 is necessary to find a coefficient or factor by which to convert the 
 number of c.c. required by the sodic carbonate, weighed on the 
 calcic, into that which should be required if weighed on the sodic, 
 basis. A consideration of the relative molecular weights of the 
 two bodies will give the factor thus 
 
 Calcic carbonate 100 
 
 = TTf ; , . w . = 
 
 bodic carbonate lOb 
 
 If, therefore, the c.c. used are multiplied by this number, the 
 percentage of pure sodic carbonate will be obtained. The method 
 may be extended to a number of substances, 011 this principle, with 
 the exercise of a little ingenuity. 
 
 L. de Koningh has communicated to me a similar method 
 devised by himself and Peacock, in which the same end is 
 attained without the aid of a pure substance as standard, thus : 
 Say a specimen of impure common salt is to be examined, a 
 moderate portion is put on the balance and counterpoised with 
 silver nitrate; the latter is then dissolved up to 100 c.c. and placed 
 in a burette. The salt is dissolved in water, a few drops of 
 chromate added and titrated with the silver solution, of which 
 10 c.c. is required; the salt is therefore equal to 10 per cent, 
 of its weight of silver nitrate, then 
 
 16-96 : 58-37 : : 10 = 344 % XaCl 
 
 Or, in the case of an impure soda ash, an equal weight of oxalic- 
 acid is taken and made up to 100 c.c. ; the soda requires, say, 
 50 c.c. for saturation, or 50 per cent., then 
 
 126 : 106 : : 50 = 42 % Na 2 CO :{ 
 
 It may happen that, in some cases, more than one portion of the 
 reagent is required to decompose the substance tested, and to 
 provide against this two or more lots should be weighed in the 
 first instance. 
 
 VOLUMETRIC ANALYSIS WITHOUT BURETTES OR 
 OTHER GRADUATED INSTRUMENTS. 
 
 4. THIS operation consists in weighing the standard solutions 
 on the balance instead of measuring them. The influence of 
 variation in temperature is, of course, here of no consequence. The 
 chief requisite is a delicate flask, fitted with a tube and blowing- 
 ball, as in the burette fig. 7, or an instrument known as 
 Schuster's alkalimeter may be used. A special burette has been 
 devised for this purpose by Casamajor (C. N. xxxv. 98). The 
 
5. 
 
 INSTRUMENTS. 
 
 method is capable of very accurate results, if care be taken in 
 preparing the standard solutions and avoiding any loss in pouring 
 the liquid from the vessel in which it is weighed. It occupies 
 much more time than the usual processes of volumetric analysis, 
 but at great extremes of temperature it is far more accurate. 
 
 THE BURETTE. 
 
 5. THIS instrument is used for the delivery of an accurately 
 measured quantity of any particular standard solution. It invari- 
 ably consists of a long glass tube of even bore, throughout the 
 
 Fig. l. Pig. 2. 
 
 length of which are engraved, by means of hydrofluoric acid, 
 certain divisions corresponding to a known volume of fluid. 
 
8 
 
 VOLUMETRIC ANALYSIS. 
 
 5. 
 
 It may be obtained in a great many forms, under the names of their 
 respective inventors, such as Mohr, Gay Lussac, Links, etc., 
 but as some of these possess a decided superiority over others, it is 
 not quite a matter of indifference which is used, and therefore a 
 slight description of them may not be out of place here. The 
 burette, with india-rubber tube and clip, contrived by Mohr, is 
 shown in figs. 1 and 2, and with stop-cock in fig. 3. "This latter 
 form of instrument is now made and sold at such a moderate price 
 that it has largely displaced the original. 
 
 Fig. 3. 
 
 Fig. 4. 
 
 The advantages possessed by Mohr's burette are, that its fixed 
 upright position enables the operator at once to read off the volume 
 of solution used for any analysis. The quantity of fluid to be 
 delivered can be regulated to the greatest nicety ; and the instru- 
 ment not being held in the hand, there is no chance of increasing 
 the bulk of the fluid by the heat of the body, and thus leading to 
 incorrect measurement, as is the case with Bin ks' or Gay Lussac's 
 
5. 
 
 INSTRUMENTS. 
 
 9 
 
 burette.. The principal disadvantage, however, of these two latter 
 forms is, that a correct reading can only be obtained by placing 
 them in an upright position, and allowing the fluid to find its perfect 
 level. The preference should, therefore, unhesitatingly be given 
 to Mohr's burette. The tap burette may be used not only for 
 solutions affected by the rubber tube, but for all other solutions, 
 and may also be arranged so as to deliver the liquid in drops, 
 leaving both the hands of the operator disengaged. A new 
 
 Pig. 5. 
 
 arrangement is shown in fig. 4, the tap being placed obliquely 
 through the spit, so as to avoid its dropping out of place ; the 
 floats shown are very small thermometers. Owing to the action of 
 caustic alkalies upon glass, tap burettes do not answer well for 
 strong solutions of potash or soda, unless emptied and washed 
 immediately after use. Two convenient forms of stand for Mohr's 
 burettes are shown in figs. 5 and 6 ; in the latter, the arms carrying 
 
10 
 
 VOLUMETRIC ANALYSIS. 
 
 the burettes revolve. A very good modification of this burette, as 
 usually made, is to have the top funnel-shaped, which not only 
 admits of easier filling, but the burette may be slung in a stand by 
 the funnel without other support, so as to be tilted from the 
 vertical when titrating hot solutions. When not in use the dust 
 may be kept out by a greased glass plate. 
 
 Special care should always be taken with Molir's form of 
 burette to fill the delivery point of the instrument and the 
 intervening rubber tube with the liquid, before commencing a 
 titration. This is easily done by filling the burette well above the 
 mark, then rapidly opening the clip wide to expel the air 
 bubbles when this is done the excess of liquid may be quietly 
 run out to the mark. In the tap burette the air space is smaller 
 than with the rubber tube, but the same method should be 
 invariably adopted. 
 
 We are indebted to Mohr for another form of instrument to 
 avoid the contact of permanganate and india-rubber, viz., the foot 
 burette, with elastic ball, shown in fig. 7. 
 
 The flow of liquid from the 
 exit tube ca^n be regulated to 
 a great nicety by pressure 
 upon the ball, which should 
 be large, and have two open- 
 ings, one cemented to the 
 tube with marine glue, and 
 the other at the side, over 
 which the thumb is placed 
 when pressed, and on the 
 removal of which it refills 
 itself with air. 
 
 G a v L u s s a c ' s burette , 
 supported in a wooden foot, 
 may be used instead of the 
 above form, by inserting a 
 good fitting cork into the 
 open end, through which a 
 small tube bent at right 
 angles is passed. If the 
 burette is held in the right 
 hand, slightly inclined to- 
 wards the beaker or flask 
 into which the fluid is to be 
 measured, and the mouth 
 applied to the tube, any 
 portion of the solution may 
 be emptied out by the pressure 
 of the breath, and the disadvantage of holding the instrument in 
 a horizontal position, to the great danger of spilling the contents, 
 
INSTRUMENTS. 
 
 11 
 
 is avoided ; at the same time the beaker or flask can be held 
 in the left hand and shaken so as to mix the fluids, and by 
 this means the end of the operation be more accurately determined 
 (see fig. 8). 
 
 There is an arrangement of Mohr's burette which is extremely 
 serviceable, when a series of titrations of the same character have 
 to be made, such as in alkali works, assay offices, etc. It consists 
 in having a ~J~ piece of glass tube inserted between the lower 
 end of the burette and the spring clip, communicating with 
 
 Fi-. 9. Pig. 10. 
 
 a reservoir of the standard solution, placed above so that the 
 burette may be filled by a syphon, as often as emptied, and in so 
 gradual a manner that no air bubbles occur, as in the case of filling 
 it with a funnel, or pouring in liquid from a bottle ; beside which, 
 this plan prevents evaporation or dust in the standard solution 
 either in the burette or reservoir. 
 
 Figs. 9 and 11 show this arrangement in detail. Connections 
 
12 
 
 VOLUMETRIC ANALYSIS. 
 
 5. 
 
 of this kind may now be had with glass stop-cocks, either of the 
 simple form or the patent two-way cock, made by Greiner and 
 Fried richs, and supplied by most apparatus dealers (fig. 10). 
 
 It sometimes happens that a solution requires titration at a hot or 
 even boiling temperature, such as the estimation of sugar by copper 
 
 -Fig. 11. 
 
 rig. 12. 
 
 solution: here the ordinary arrangement of Mohr's burette will 
 not be available, since the steam rising from the liquid heats the 
 burette and alters the volume of fluid. This may be avoided either 
 by using a special burette, in which the lower end is extended at a 
 right angle with a stop-cock, or by attaching to an ordinary burette 
 
5. INSTRUMENTS. 13 
 
 a much longer piece of india-rubber tube, so that the burette 
 stands at the side of the capsule or beaker being heated, and the 
 elastic tube is brought over its edge ; the pinch-cock is fixed 
 midway ; no heat can then reach the body of fluid in the burette,, 
 since there can be no conduction past the pinch-cock, or a burette- 
 with funnel neck described on p. 10 may be used. 
 
 Gay Lussac's burette is shown in figs. 8 and 12. By using it 
 in the following manner, its natural disadvantages may be overcome 
 to a great extent. Having fixed the burette into the foot securely,, 
 and filled it, take it up by the foot, and resting the uppeu end upon 
 the edge of the beaker containing the solution to be titrated, drop 
 the test fluid from the burette, meanwhile stirring the contents, 
 of the beaker with a glass rod ; by a slight elevation or depression, 
 the flow of test liquid is regulated until the end of the operation is 
 secured, thus avoiding the annoyances which arise from alternately 
 placing the instrument in an upright and horizontal position. 
 
 Pig. 13. 
 
 B inks' burette is well known, and need not be described; it 
 is the least recommendable of all forms, except for very rough 
 estimations. 
 
 It is convenient to have burettes graduated to contain from 
 30 to 50 c.c. in y 1 ^ c.c., and 100 or 110 c.c. in 4 or -J c.c. 
 
 The pinch-cock generally used in Mohr's burette is shown in 
 fig. 1. These are made of brass and are now generally nickel-plated 
 to prevent corrosion ; another form is made of one piece of steel 
 wire, as devised by Hart; the wire is softened by heating and 
 coiled round, as shown in fig. 13. When the proper shape has 
 been attained, the clip is hardened and tempered so as to convert it. 
 into a spring. . 
 
VOLUMETRIC ANALYSIS. 
 
 Another pinch-cock is shown in fig. 13. It may be made of 
 hard wood, horn, or preferably, of flat glass rod. The levers 
 should be long. A small piece of cork, of the same thickness 
 as the elastic tube of the burette when pressed close, should be 
 fastened at the angles of the levers as shown in the engraving. 
 
 50 CC 
 
 10CC 
 
 Pig. 14. 
 
 Pig. 15. 
 
 The use of any kind of pinch-cock may be avoided, and a very 
 ilelicate action obtained, by simply inserting a not too tightly fitting 
 piece of solid glass rod into the elastic tube^ between the end of the 
 burette and the spit ; a firm squeeze being given by the finger and 
 thumb to the elastic tube surrounding the rod, a small canal is 
 opened, and thus the liquid escapes, and of course can be controlled 
 by the operator at will (see fig. 14). 
 
6. INSTRUMENTS. 
 
 THE PIPETTE. 
 
 6. THE pipettes used in volumetric work are of two kinds, 
 viz., those which deliver one certain quantity only, and those which 
 are graduated on the stem, so as to deliver various quantities at the 
 discretion of the analyst. In the former kind, or whole pipette, 
 the graduation should be that in which the fluid runs out by its 
 own weight, but the last few drops empty themselves slowly ; 
 if, however, the lower end of the pipette be touched against the 
 moistened edge of the beaker or the surface of the fluid into 
 which it is emptied, the flow is hastened considerably, and in 
 graduating the pipette, it is preferable to adopt this plan. 
 
 In both the whole and graduated pipettes, the upper end is 
 narrowed to about -J inch, so that the pressure of the finger is 
 sufficient to arrest the flow at any point. 
 
 Pipettes are invariably filled by sucking the upper end with the 
 mouth, unless the liquid is volatile or highly poisonous, in which 
 case it is best to use some other kind of measurement. Beginners 
 invariably find a difficulty in quickly filling the pipette 
 above the mark, and stopping the fluid at the exact 
 point. Practice with pure water is the only method of 
 overcoming this. 
 
 Fig. 15 shows two whole pipettes, one of small and the 
 other of large capacity, and also a graduated pipette of 
 medium size. It must be borne in mind that the pipette 
 graduated throughout the stem is not a reliable in- 
 strument for accurate titration, owing to the difficulty of 
 stopping the flow of liquid at any given point, and 
 reading off the exact measurement. Its chief use is in 
 the approximate estimation of the strength of any 
 standard solution in the course of preparation. 
 
 Fig. 16 shows a very useful form of pipette for 
 measuring strong acids or alkalies, etc., the bulb prevent- 
 ing the entrance of any liquid into the mouth. Pig. 16. 
 
 THE MEASURING- FLASKS. 
 
 7. THESE indispensable instruments are made of various 
 capacities ; they serve to mix up standard solutions to a given 
 volume, and also for the subdivision of the substance to be 
 tested by means of the pipettes. They should be as narrow 
 in the neck as is compatible with pouring in and out, and the 
 graduation line should fall just below the middle of the neck, 
 so to allow room for shaking up the fluid. Convenient sizes 
 are 100, 200, 250, 300, 500, and 1000 c.c., all graduated to 
 contain the respective quantities. If required to deliver these 
 volumes they must have a second higher mark in the neck, 
 obtained by weighing into the wetted and drained flasks the 
 
16 
 
 VOLUMETRIC ANALYSIS. 
 
 respective number of grams of distilled water at 16 C. 
 flask is shown in fig;. 17. 
 
 A liter 
 
 Pig. 17. 
 
 Fisr. 18. 
 
 W. B. Giles lias described a modified flask (C. N. Ixix. 99) 
 shown in fig. 18. It is handy in making up standard solutions 
 where the reagent cannot be weighed in an absolutely pure state, 
 for instance, sulphuric acid, ammonic thiocyanate, or uranic salts. 
 Such a quantity, hoAvever, is taken as will give a solution about 
 a ninth or tenth too strong, and the measure is made up to 1100 c.c. 
 The real strength is then taken by two titrations on 25 or 30 c.c. 
 with a known standard, so that its exact working strength is 
 known ; the remainder of the 100 c.c. is then removed down to the 
 1000 c.c. mark, and a slight calculation will show how much water 
 has to be added to the 1000 c.c. to make a correct solution. If 
 only a liter is made up, an unknown volume is left in the flask, 
 and it must be transferred to a measuring cylinder, where, owing 
 to the large diameter of the vessel, the graduation can never be so 
 accurate as in the narrow neck of . the flask. Should the solution 
 prove to be only about a tenth too strong, the necessary dilution 
 may be made in the flask itself; but if stronger than this, the 
 flask must be emptied into the store bottle and rinsed out with the 
 measured quantity of water required, which is then drained into 
 the store bottle, and the whole carefully mixed. 
 
INSTRUMENTS. 
 
 17 
 
 Besides the measuring flasks 
 it is necessary to have graduated 
 vessels of cylindrical form, 
 for the purpose of preparing 
 standard solutions, etc. 
 
 Fig. 19 shows a stoppered 
 cylinder for this purpose, 
 generally called a test mixer. 
 Wide-mouthed open cylinders, 
 with spouts, are also used of 
 various sizes and graduated 
 like fig. 19. 
 
 ON THE CORRECT 
 
 READING- OF GRADUATED 
 
 INSTRUMENTS. 
 
 8. THE surface of liquids 
 contained in narrow tubes is 
 always curved, in consequence 
 of the capillary attraction 
 exerted by the sides of the 
 tube, and consequently there 
 is a difficulty in obtaining a 
 distinct level in the fluid to 
 be measured. If, however, 
 the lowest point of the curve 
 is made to coincide with the 
 graduation mark, a correct 
 proportional reading is always 
 obtained, hence this method of 
 reading is the most satisfac- 
 tory (see fig. 20). 
 
 The eye may be assisted 
 materially in reading the 
 divisions on a graduated 
 tube by using a piece of 
 white paper or opal glass 
 held at an angle of 30 or 
 40 from the burette and 
 near the surface of the 
 liquid, or a small card, the 
 lower half of which is 
 blackened, the upper re- 
 maining white. If the line 
 of division between the 
 black and white be held 
 about an eighth of an inch below the surface of the liquid, 
 
 Fig. 20. 
 
18 
 
 VOLUMETRIC ANALYSIS. 
 
 and the eye brought on a level with it, the meniscus then can be 
 seen by transmitted light, bounded below by a sharply defined 
 black line. A card of this kind, sliding up and down a support,, 
 is of great use in verifying the graduation of the burettes or 
 pipettes with a cathetometer. Another good method 
 is to use a piece of mirror, upon which are gummed 
 two strips of black paper, half an inch apart ; apply it 
 in contact with the burette so that the eye can be 
 reflected in the open space. The operator may consult 
 with advantage the directions for calibration on the 
 opposite page, and details of graduating and verifying* 
 measuring instruments for the analysis of gases as- 
 described in Part 7. In taking the readings of 
 burettes, pipettes, and flasks, the graduation mark 
 should coincide as nearly as possible with the level of 
 the operator's eye. 
 
 Pig. 21. 
 
 v 
 
 Erdmann's Float. This useful little instrument 
 to accompany Mohr's burette, gives the most accurate 
 reading that can be obtained j one of its forms is 
 shown in fig. 21, another, containing a thermometer, 
 is shown in fig. 4. The latest form is shown in fig. 22, 
 where the ring-mark is made within the bulb, as indeed 
 it is best to be in all -cases. A special form for use with 
 dark-coloured solutions like iodine, permanganate, &c., is 
 to have two bulbs with the ring-mark in the upper bulb, 
 and the instrument is so weighted that the upper bulb 
 stands out of the liquid, and of course may then be read 
 off as easily as if the liquid were transparent. The 
 instrument consists essentially of an elongated glass tube, 
 K rather smaller in diameter than the burette itself, and 
 Pio- 22 weighted at the lower end with a globule of mercury. 
 The actual height of the liquid in the burette is not- 
 regarded, because if the operator begins with the line on 
 the float, opposite the graduation mark on the burette, 
 the same proportional division is always maintained. 
 
 It is essential that the float should move up and down 
 in the burette without wavering, and the line upon it 
 
 should always be parallel to the 
 burette. 
 
 graduations of the 
 
 Filter for ascertaining: the end re-action in certain pro- 
 cesses. This is shown in fig. 23, and the instrument is 
 known as Be ale's filter. It serves well for taking a few 
 drops of clear solution from any liquid in which a pre- ^f* 
 cipitate will not settle readily. To use it, a piece of filter 
 paper is tied over the lower end, arid over that a piece of fine muslin, 
 to keep the paper from being broken. When dipped into a muddy 
 
9. INSTRUMENTS. 19 
 
 mixture, the clear fluid rises and may be poured out of the little 
 spout for testing. If the process in hand is not completed, the 
 contents are washed hack to the bulk, and -the operation repeated 
 as often as may be required. 
 
 THE CALIBRATION OF GRADUATED APPARATUS. 
 
 9. IT is obvious that in the practice of volumetric analysis 
 the absolute correctness of the graduations of the vessels used to 
 a given standard is not necessary, so long as they agree with one 
 another. In the present day there* are many makers of in- 
 struments, some using the liter of 1000 grams of distilled water 
 at 4 C., others at 15'5 C., and again at 17'5 C. Under these 
 circumstances it is conceivable that operators may purchase, from 
 time to time, a mixture of instruments of a heterogeneous 
 character. The German Imperial Standard Commission have, 
 I believe, now made it legal only to use for official purposes the 
 liter and its divisions, containing 1000 grams of pure water at 
 4 C. (p. 23). These instruments for use in that country are all 
 stamped in the same way as commercial measures are stamped by 
 law in this country. If, then, instruments are sent abroad, they 
 Avill not agree with the bulk of those hitherto used. On this 
 account, as well as for general accuracy, it is necessary to calibrate 
 or measure the divisions upon the various instruments by 
 actual experiment, carried on in a room kept at the temperature 
 of 16 C. 
 
 Flasks. The shortest way to get at the true contents of a liter 
 flask, or to correct it for a given temperature by making a fresh 
 mark, is to weigh the contents by substitution, which is done as 
 follows : 
 
 The flask is cleaned and dried, by first rinsing with alcohol, then 
 ether, and the latter blown out with a bellows or driven off by 
 warming, when cool it is placed on a sufficiently large and 
 sensitive balance, together with a kilogram weight, side by side 
 a shallow metal tray is placed on the other pan, and sufficient shot 
 added to exactly balance the flask and weight ; both the latter are 
 then removed, leaving the shot on the other pan. The flask is 
 then placed level, and distilled water at 16 C. poured in up to 
 the mark ; the moisture in the neck is removed after a few 
 minutes by filter paper and the flask placed on the empty pan, if 
 the two pans are in equilibrium the mark is correct, if not, water 
 must be added or removed, with a small pipette, and the mark 
 altered. Smaller flasks are calibrated in the same way. 
 
 To calibrate a flask for delivering an exact liter or less, some 
 water is poured into the empty flask, which is drained for half 
 a minute, and weighed with its stopper ; it is then filled to the 
 neck with pure water, and closed by the glass or rubber stopper, 
 
 c 2 
 
20 VOLUMETRIC ANALYSIS. 9. 
 
 to prevent evaporation, and water added or removed as before. 
 A nick is then made with a diamond, or sharp file, opposite the 
 lowest part of the meniscus, which may be extended to a proper 
 mark after the flask is emptied. Such a flask, when correctly 
 marked, will deliver the volume required at the given temperature, 
 after the contents have been poured out and drained for half 
 a minute. 
 
 Burettes. After firmly fixing in its stand, filling with pure 
 water at 16 C., and getting rid of the air bubbles in the tap or 
 spit, the exact level at the mark is made preferably with aij 
 ErdmaAn float; successive quantities of 5 or 10 c.c. are then run 
 into a small dry tared beaker and rapidly weighed. If great 
 accuracy is required a closed vessel ought to be employed, but this 
 necessitates the drying after each weighing ; a very small beaker 
 can be easily wiped dry, and rapid weighings made without any 
 sensible loss of accuracy. If the weighings have shown reasonable 
 accuracy, say within a milligram or so for each c.c., it will be 
 sufficiently correct ; if otherwise, a table must be constructed, 
 showing the correct contents at any given point. 
 
 An excellent method of calibrating tap burettes is described by 
 Carnegie (C. N. Ixiv. 42), which saves the labour involved in 
 the separate weighings just described, but does not give the weight 
 contents. A small column of CS 2 , saturated with water, and 
 tinted with iodine, is used to measure the spaces between the 
 graduation marks of the instrument. The burette is connected by 
 rubber tube with a reservoir of water like that used for mercury 
 in gas apparatus, and by the pressure of the water in this reservoir 
 5 c.c. or so of the CS 2 may be moved from the bottom upwards, 
 throughout the whole length of the instrument, so as to compare 
 portions of the scale throughout. It is essential that the measure- 
 ment takes place from the bottom, which is done by allowing 
 water to flow in up to the lower mark of the burette, then gently 
 running in the portion of CS 2 from a long fine pipette ; when 
 settled, and the meniscus observed, a cautious opening of the tap 
 will allow of the movement of the column, through the various 
 divisions, up to the top. 
 
 Pipettes. With the instrument made to deliver one quantity 
 only it is generally sufficient to fill it by suction above the mark, 
 then gently release the pressure of the finger, until the exact mark 
 is reached. The contents are then run into a dry tared beaker, 
 drained for half a minute in contact with the sides of the beaker, 
 and the beaker quickly weighed. If not fairly correct, trials must 
 be made by placing a thin strip of gummed paper on the stem, 
 and marking the height of each trial until the correct weight is 
 found, when a permanent mark may be made. 
 
 Graduated pipettes are best calibrated by filling them above the 
 
9. 
 
 PRESERVATION OF SOLUTIONS. 
 
 21 
 
 mark, fixing them in a stand like a burette, closing the top with 
 a stout piece of rubber tube, clamped with a strong clip, then, 
 after adjusting the level, drawing off in quantities of 5 c.c. or so, 
 and weighing in the same way as directed for burettes. 
 
 Cylinders. The only method of calibrating these vessels is to 
 measure into them repeatedly various volumes of water, from 
 delivery pipettes of proved accuracy, taking precautions as to level, 
 meniscus, and the proper drainage of the pipette after each 
 delivery. 
 
 Preservation of Solutions. There are test solutions which, in 
 consequence of their proneness to decomposition, cannot be kept 
 at any particular strength for a length of time ; consequently they 
 must be titrated on every occasion before being used. Stannous 
 chloride and sulphurous acids are examples of such solutions. 
 Special vessels have been devised for keeping solutions liable to 
 alter in strength by access of air, as shown in figs. 24 and 25. 
 
 Pig. 25. 
 
22 
 
 VOLUMETRIC ANALYSIS. 
 
 9. 
 
 Fig. 24 is especially applicable to caustic alkaline solutions, the 
 tube passing through the caoutchouc stopper being filled with dry 
 soda-lime, resting on cotton wool. 
 
 Fig. 25, designed by Mohr, is a considerable improvement 
 upon this, since it allows of the burette being filled with the 
 solution from the store bottle quietly, and without any access of 
 air whatever. The vessel can be used for caustic alkalies, baryta, 
 stannous chloride, permanganate, and sulphurous acids, or any other 
 liquid liable to undergo change by absorbing oxygen. The corks 
 are dried and soaked in melted paraffins ; or, still better, may be 
 substituted by caoutchouc stoppers ; and a thin layer of rectified 
 paraffin oil is poured on the top of the solution, where, of course, 
 owing to its low specific gravity, it always floats, placing an 
 impermeable division between the air and the solution ; and as 
 this body (which should always be as pure as possible) is not 
 affected by these reagents in their diluted state, this form offers 
 great advantages. Solutions not affected chemically by contact 
 with air should nevertheless be kept in bottles, the corks or stoppers 
 of which are perfectly closed, and tied over with india-rubber or 
 bladder to prevent evaporation, and should further be always 
 shaken before use, in case they are not quite full. The influence 
 of bright light upon some solutions is very detrimental to their 
 chemical stability ; hence it is advisable to preserve some solutions 
 not in immediate use in the dark, and 
 at a temperature not exceeding 15 or 
 16 C. 
 
 The apparatus devised by J. C. 
 Chorley, and shown in fig 26, will be 
 found useful for preserving and delivering 
 known volumes of such solutions as 
 alcoholic potash, which are liable to 
 contamination by exposure to air. The 
 wash bottle inserted in the cork of the 
 large store bottle contains a solution of 
 caustic soda, and serves to wash all air 
 entering the large bottle. By means of 
 the three-way stop-cock at the bottom of 
 the apparatus the solution is allowed to 
 fill the pipette and overflow into its upper 
 chamber, the excess being caught in the 
 small side bulb and reservoir ; this solution 
 serves to wash all air entering the pipette 
 when the stop-cock is turned to deliver 
 the solution, which is run off to a mark 
 just above the tap. When full, the side 
 reservoir may be emptied by withdrawing 
 the small ground stopper. Fig. 26. 
 
 ' 
 
10. WEIGHTS AND MEASURES. 2o 
 
 ON THE SYSTEM OF WEIGHTS AND MEASURES 
 TO BE ADOPTED IN VOLUMETRIC ANALYSIS. 
 
 10. IT is mucli to be regretted that the decimal system of 
 weights and measures used on the Continent is not universally 
 adopted, for scientific and general purposes, throughout the civilized 
 world. Its great advantage is its uniformity throughout. The 
 unit of weight is the gram ( = 15-43235 grains troy), and a gram 
 of distilled water at 4 C., or 39 Fahr., measures exactly a cubic 
 centimeter. The kilogram contains 1000 grams, the liter 1000 
 cubic centimeters. 
 
 It may not be out of place here to give a short description of the 
 origin of the French decimal system, now used exclusively for 
 scientific purposes in that country, and also in Prussia, Austria, 
 Holland, Sweden, Denmark, Belgium, and Spain. 
 
 The commission appointed in France for the purpose of instituting 
 a decimal system of weights and measures, founded their standard 
 on the length of the meridian arc between the pole and equator, 
 the ten-millionth part of which' was called the metre ( = 39*3710 
 English inches), although the accuracy of this measurement has 
 been disputed. It would have been preferable, as since proposed, 
 that the length of a pendulum vibrating exactly 86,400 times in 
 twenty-four hours, or one second for each vibration, equivalent to 
 39 '1372 English inches, should have been taken as the standard 
 juttrvj in which case it would have been much easier to verify the 
 standard in case it should be damaged or destroyed. However, the 
 actual mid-re in use is equal to 39 '371 inches, and from this standard 
 its multiples and subdivisions all proceed decimally ; its one-tenth 
 part being the decimetre, one-hundredth the centimetre, and one- 
 thousandth the millimetre. 
 
 In accordance with tins, a cube of distilled water at its greatest 
 density, viz., 4 C., or 39 Fahr., whose side measures one decimeter, 
 has exactly the weight of one kilogram, or 1000 grams, and occupies 
 the volume of one liter, or 1000 cubic centimeters. 
 
 This simple relationship between liquids and solids is of great 
 value in a system of volumetric analysis, and even for ordinary 
 analysis by weight ; for technical purposes it is equally as applicable 
 as the grain system, the results being invariably tabulated in 
 percentages. 
 
 With these brief explanations, therefore, I have only to state 
 that the French decimal system will be mainly used throughout 
 this treatise ; but at the same time, those who may desire to adhere 
 to the ordinary grain weights, can do so without interfering with 
 the accuracy of the processes described. 
 
 As has been before stated, the true cubic centimeter contains 
 one gram of distilled water at its greatest density, viz., 4 C., 
 or 39 Fahr. ; but as this is a degree of temperature at which it 
 is impossible to work for more than a month or two in the year, it 
 is better to take the temperature of 16 C., or about 60 Fahr., as 
 
24 VOLUMETRIC ANALYSIS. W. 
 
 the standard ; because in winter most laboratories or rooms have 
 furnaces or other means of warmth, and in summer the same 
 localities ought not, under ordinary circumstances, to have a much 
 higher degree of heat than 16 C. In order, therefore, that the 
 graduation of instruments on the metrical system may be as- 
 uniform as possible with our own fluid measures, the cubic- 
 centimeter should contain one gram of distilled water at 16 C, 
 The true c.c. (i.e. = 1 gm. at 4 C., or 39 Fahr.) contains only 
 0-999 gm. (strictly 0-998981) at that temperature; but for con- 
 venience of working, and for uniformity with our own standards- 
 of volume, it is better to make the c.c. contain one gram at 16 C. 
 The real difference is one-thousandth part. The operator, there- 
 fore, supposing he desires to graduate his own measuring flasks, 
 must weigh into them 250, 500, or 1000 grams of distilled water 
 at 16 C., or 60 Fahr. 
 
 Fresenius and others have advocated the use of the strict liter 
 by the graduation of instruments, so that they shall contain 
 999 gm. at 16 C. Mohr, on the contrary, uses a 1000 gm., at 
 the temperature of 17 '5, the real difference being T2 c.c. in the 
 liter, or about one eight-hundredth part. 
 
 It will be seen above that I have advocated a middle course on 
 two grounds: (1) That in testing instruments it is much easier 
 to verify them by means of round numbers, such as 5 or 10 gm. 
 (2) That there are many thousands of instruments already in use- 
 varying between the two extremes ; and as these cannot well be 
 annihilated, the adoption of a mean will -give a less probable amount 
 of error between the respective instruments ; and, moreover, the 
 difference between the liter at 4 and 16 being one-thousandth 
 part, it is easy to correct the measurement for the exact liter. 
 
 It matters not which plan is followed, if all the instruments in 
 a particular set coincide with each other ; but it would be 
 manifestly wrong to use one of Mohr's burettes with one of 
 Fresenius' measuring flasks. Operators can, however, without 
 much difficulty re-mark their measuring flasks to agree with their 
 smaller graduated instruments, if they are found to differ to any 
 material extent. 
 
 Variations of Temperature. In the preparation of standard 
 solutions, one thing must especially be borne in mind ; namely, 
 f that saline substances on being dissolved in water have a consider- 
 able effect upon the volume of the resulting liquid. The same is 
 also the case in mixing solutions of various salts or acids with each 
 other (see Gerlach, " Specifische Gewichte der Salzosungen ; " 
 also Gerlach, " Sp. Gewichte von wasserigen Losungen," Z. a C. 
 viii. 245). 
 
 In the case of strong solutions, the condensation in volume is as 
 a rule considerable : and, therefore, in preparing such solutions for 
 volumetric analysis, or in diluting such solutions to a given volume 
 
10. 
 
 INFLUENCE OF TEMPERATURE. 
 
 25 
 
 for the purpose of removing aliquot portions subsequently for 
 examination, sufficient time must be given for liquids to assume 
 their constant volume at the standard temperature. If the strength 
 of a standard solution i-s known for one temperature, the strength 
 corresponding to another temperature can only be calculated if the 
 rate of expansion by heat of the liquid is known. The variation 
 cannot be estimated by the known rule of expansion in distilled 
 water; for Gerlacli has shown that even weak solutions of acids 
 and salts expand far more than water for certain increments of 
 temperature. The rate of expansion for pure water is known, 
 and may be used for the purpose of verifying the graduation of 
 instruments, where extreme accuracy is required. The following 
 short table furnishes the data for correction. 
 
 The weight of 1000 c.c. of water at t C., when determined by 
 means of brass weights in air of t C., and at 0'76 m.ni. pressure, 
 is equal to 1000 x gm. 
 
 Slight variations of atmospheric pressure may be entirely 
 disregarded. 
 
 t* 
 
 10 
 
 11 
 
 12 
 
 13 
 
 14 
 
 15 16 
 
 17 
 
 18 
 
 19 
 
 
 X 
 
 1-34 
 
 1-43 1-52 
 
 1'63 
 
 176 
 
 1-89 2-04 
 
 2'2 
 
 2-37 
 
 2-55 
 
 
 t 
 
 20 
 
 21 
 
 22 
 
 23 
 
 24 
 
 25 26 
 
 27 
 
 28 
 
 29 
 
 30 
 
 X 
 
 274 
 
 2-95 
 
 3-17 
 
 3-39 
 
 3'63 
 
 3-88 4-13 
 
 4-39 
 
 4-67 
 
 4-94 
 
 5-24 
 
 x is the quantity to be subtracted from 1000 to obtain the 
 weight of 1000 c.c. of water at the temperature i. Thus at 20 
 2-74 must be deducted from 1000 = 997*26. 
 
 Bearing the foregoing remarks in mind, therefore, the safest plan 
 in the operations of volumetric analysis, so far as measurement is \ 
 concerned, is to use solutions as dilute as possible. Absolute! 
 accuracy in estimating the strength of standard solutions can only 
 be secured by weight, the ratio of the weight of the solution to the 
 weight of active substance in it being independent of temperature. 
 
 Casamajor (C. N. xxxv. 160) has made use of the 
 data given by Matthiessen in his researches on the expansion 
 of glass, water, and mercury, to construct a table of corrections to 
 be used in case of using any weak standard solution at a different 
 temperature to that at which it was originally standardized. 
 
 The expansion of water is different at different temperatures ; 
 the expansion of glass is known to be constant for all temperatures 
 up to 100. The correction of volume, therefore, in glass burettes, 
 must be the known expansion of each c.c. of water for every 1 C., 
 less the known expansion of glass for the same temperature. 
 
 It is not necessary here to reproduce the entire paper of 
 Casamaj or, but the results are shortly given in the following table. 
 
 * 
 
 UNIVERSITY 
 
26 VOLUMETRIC ANALYSIS. 10. 
 
 The normal temperature is 15 C. ; and the figures given are the 
 relative contractions below, and expansions above, 15 C. 
 
 DC?. C. Deg. C. 
 
 7 _ -Q00612 24 + '001686 
 
 8 _ -000590 25 + '001919 
 
 9 _ -000550 26 + '002159 
 10 _ -000492 ' 27 + '002405 
 
 1 1 -000420 
 
 12 '000334 
 
 28 4- '002657 
 
 29 + -002913 
 
 13 '000236 30 + "003179 
 
 14 '000124 31 + '003453 
 
 15 Normal 32 + "003739 
 
 16 + '000147 33 + -004035 
 
 17 + -000305 34 + -004342 
 
 18 + -000473 35 + '004660 
 
 19 + '000652 36 + '0049S7 
 
 20 + -000841 37 + "005323 
 
 21 + -001039 38 + -005667 
 
 22 + -001246 39 + '006040 
 
 23 + '001462 40 + '000382 
 
 By means of these numbers it is easy to calculate the volume of 
 liquid at 15 C. corresponding to any volume observed at any 
 temperature. If 35 c.c. of solution has been used at 37 C., the 
 table shows that 1 c.c. of water in passing from 15 to 37 is 
 increased to 1 -005323 c.c. ; therefore, by dividing 35 c.c. by 1 "005323 
 is obtained the quotient 34'819 c.c., which represents the volume 
 at 15 corresponding to 35 c.c. at 37 ; or the operation can be 
 simplified by obtaining the factor, thus : 
 
 1^5323 = 0-991705 
 
 A table can thus be easily constructed which would show the 
 factor for each degree of temperature. 
 
 These corrections are useless for concentrated solutions, such as 
 normal alkalies or acids ; with great variations of temperature 
 these solutions should be used by weight. 
 
 Instruments graduated on the Grain System. Burettes, pipettes, 
 and flasks may also be graduated in grains, in which case it is best 
 to take 10,000 grains as the standard of measurement. In order 
 to lessen the number of figures used in the grain system, so far 
 as liquid measures are concerned, I propose that ten fluid grains be 
 called a decem, or for shortness dm. ; this term corresponds to the 
 cubic centimeter, bearing the same proportion to the 10,000 grain 
 measure as the cubic centimeter does to the liter, namely, the 
 one-thousandth part. The use of a term like this will serve to 
 prevent the number of figures, which are unavoidably introduced 
 by the use of a small unit like the grain. 
 
 Its utility is principally apparent in the analysis for percentages, 
 particulars of which will be found hereafter. 
 
11. NORMAL SOLUTIONS. 27 
 
 The 1000 grain burette or pipette will therefore contain 100 
 tlecems, the 10,000 gr. measure 1000 dm., and so on. 
 
 The capacities of the various instruments graduated on the grain 
 system may be as follows : 
 
 Flasks : 10,000, 5000, 2500, and 1000 grs. = 1000, 500, 250, and 
 100 dm. Burettes : 300 grs. in 1-gr. divisions, for very delicate 
 purposes = 30 dm. in y^j-GOO grs. in 2-gr. divisions, or i dm.; 
 1100 grs. in 5-gr. divisions, or J dm. ; 1100 grs. in 10-gr. divisions, 
 or 1 dm. The burettes are graduated above the 500 or 1000 grs. 
 in order to allow of analysis for percentages by the residual method. 
 Whole pipettes to deliver 10, 20, 50, 100, 200, 500, and 1000 grs., 
 graduated ditto, 100 grs. in y 1 ^ dm. ; 500 grs. in ?, dm. ; 1000 grs. 
 in 1 dm. 
 
 Those who may desire to use the decimal systems constructed on 
 the gallon measure = 70,000 grains, will bear in mind that the 
 "septem"of Griffin, or the "decimillem" of Acland are each 
 equal to 7 grs. ; and therefore bear the same relation to the 
 pound = 7000 grs., as the cubic centimeter does to the liter, or the 
 decem to the 10,000 grs. An entirely different set of tables for 
 calculations, etc., is required for these systems ; but the analyst 
 may readily construct them when once the principles contained in 
 this treatise are understood. 
 
 VOLUMETRIC ANALYSIS BASED ON THE SYSTEM OF 
 CHEMICAL EQUIVALENCE AND THE PREPARATION 
 OF NORMAL TITRATED SOLUTIONS. 
 
 11. WHEX analysis by measure first came into use, the test 
 solutions were generally prepared so that each substance to be tested 
 had its own special reagent ; and the strength of the standard 
 solution was so calculated as to give the result in percentages. 
 Consequently, in alkalimetry, a distinct standard acid was used for 
 soda, another for potash, a third for ammonia, and so on, necessi- 
 tating a great variety of standard solutions. 
 
 Griffin and Ure appear to have been the first to suggest the use 
 of standard test solutions based on the atomic system; and folio wing- 
 in their steps Mohr has worked out and verified many methods of 
 analysis, which arc of great value to all who concern themselves 
 with scientific and especially technical chemistry. .Not only has 
 Mohr done this, but in addition to it, he has enriched his 
 processes with so many original investigations, and improved the 
 necessary apparatus to such an extent, that he may with justice 
 be called the father of the volumetric system. 
 
 Normal Solutions. It is of great importance that no misconcep- 
 tion should exist as to what is meant by a normal solution ; but it 
 does unfortunately occur, as may be seen by reference to the 
 chemical journals, also to Muir's translations, of Fleischer's 
 book (see Allen, C. N. xl. 239, also Analyst, xiii. 181). 
 
VOLUMETRIC ANALYSIS. 11. 
 
 Normal solutions as originally devised are prepared so that one 
 liter at 16 C. shall contain the hydrogen equivalent of the active 
 reagent weighed in grams (H=l). Seminormal, quintinormal, 
 clecinormal, and centinormal solutions are also required, and may 
 be shortly designated as J f- -~~ and y^ solutions.* 
 
 In the case of univalent substances, such as silver, iodine, 
 hydrochloric acid, sodium, etc., the equivalent and the atomic 
 (or in the case of salts, molecular) weights are identical ; thus, a 
 normal solution of hydrochloric acid must contain 36*37 grams of 
 the acid in a liter of fluid, and sodic hydrate 40 grams. In the 
 case of bivalent substances, such as lead, calcium, oxalic acid, 
 sulphurous acid, carbonates, etc., the equivalent is one half of the 
 atomic (or in the case of salts, molecular) weight ; thus, a normal 
 solution of oxalic acid would be made by dissolving 63 grams of 
 the crystallized acid in distilled water, and diluting the liquid to 
 the measure of one liter. 
 
 Further, in the case of trivalent substances, such as phosphoric 
 acid, a normal solution of sodic phosphate would be made by 
 weighing -f-= 119*3 grams of the salt, dissolving in distilled 
 water, and diluting to the measure of one liter. 
 
 One important point, however, must not be forgotten, namely, 
 that in preparing solutions for volumetric analysis the value of a 
 reagent as expressed by its equivalent hydrogen-weight must not 
 always be regarded, but rather its particular reaction in any given 
 analysis ; for instance, tin is a quadrivalent metal, but when 
 using stannous chloride as a reducing agent in the analysis of 
 
 * It is much to be regretted that the word "normal," originally based on the 
 equivalent system, should now be appropriated by those who advocate the use of 
 solutions based on molecular weights, because it not only leads to confusion between 
 the two systems, but to utter confusion between the advocates of the change them- 
 selves. In Fleischer's German edition of his Maasanalyse the molecular system 
 is advocated, but, as the old atomic weights are used, the solutions are really, in the 
 main, of the same strength as those based on the equivalent system. Pattiusoii 
 Muir, however, in his translation, has thought proper to use modern atomic weights, 
 and the curious result is that one is directed to prepare a normal solution of caustic 
 potash, with 39 '1 grams K to the liter, while a normal potassic carbonate is to contain 
 138'2 grams K-CO a , or 78'2 grams K, in the same volume of solutions. Again, Muter, 
 in his Manual of Analytical Chemistry, defines a normal solution as having one molecular 
 weight of the reagent in grams per liter; then follows the glaring inconsistency, 
 among others, of directing that a decinormal solution of iodine should contain 12 '7 
 grams of I per liter, whereas, if it was strictly made according to the original definition, 
 it shotild contain 25'4 grams in the liter. Menschutkin's Analytical Chemistry, 
 translated by Locke, recently published by Macmillan & Co., unfortunately adopts 
 the molecular system. 
 
 If the unit H be adopted as the basis or standard, everything is simplified, and 
 actual normal solutions may be made and used; but, on the molecular system, this 
 is, in many cases, not only unadvisable but impossible, besides leading to ridiculous 
 inconsistencies. As Allen points out in the reference above, it is, to say the least 
 of it, highly inconvenient that the nomenclature of a standard solution should be 
 capable of two interpretations. I have given the term systematic to this handbook, 
 and I maintain that the equivalent system used is the only systematic and consistent 
 one ; it was adopted originally by M o h r , followed by Freseuius, and continued 
 by Classen in the new edition of Mohr's Titrirmethode. Allen himself has 
 unhesitatingly preferred to tise it in his Organic Analysis, and these, together with 
 this treatise, being all text-books having a wide circulation, ought to settle definitely 
 the meaning of the term normal as applied to systematic standard solutions. Anyhow, 
 it is to be hoped that those who communicate processes to* the chemical journals, or 
 abstractors of foreign articles for publication, will take care to distinguish between 
 the conflicting systems. 
 
11. NORMAL SOLUTIONS. 29 
 
 iron, the half, and not the fourth, of its molecular weight is 
 required, as is shown by the equation Fe 2 Cl + Sn C1 2 = 2 Fe Cl 2 
 + Sn Cl 4 . 
 
 In the same manner with a solution of potassie permanganate 
 Mn KO 4 when used as an oxidizing agent, it is the available oxygen 
 which has to be taken into account, and hence in constructing a 
 normal solution one-fifth of its molecular weight =J^ = 31*6 grams 
 must be contained in the liter. 
 
 Other instances of a like kind occur, the details of which will 
 be given in the proper place. 
 
 A further illustration may be given in order to show the method 
 of calculating the results of this kind of analysis. 
 
 Each c.c. of ^ silver solution will contain Yy-Jo-Q- of the atomic 
 weight of silver = 0*010766 gin., and will exactly precipitate 
 T _i__ of the atomic weight of chlorine = '003537 gm. from any 
 solution of a chloride. 
 
 In the case of normal oxalic acid each c.c. will contain ^Vo of 
 the molecular weight of the acid = 0*063 gm., and will neutralize 
 __!__ of the molecular weight of sodic monocarbonate = 0*053 gm., 
 or will combine with o-^Vo f the atomic weight of a dyad metal 
 such as lead = 0;1032 gm., or will exactly saturate T oVo- f the 
 molecular weight of sodic hydrate = 0*040 gm., arid so on. 
 
 Where the 1000 grain measure is used as the standard in place 
 of the liter, 63 grains of oxalic acid would be used for the normal 
 .solution;- but as 1000 grains is too small a quantity to make, it is 
 better to weigh 630 grains, and make up the solution to 10,000 
 grain measures = 1000 dm. The solution would then have exactly 
 the same strength as if prepared on the liter system, as it is pro- 
 portionately the same in chemical power ; and either solution may 
 be used indiscriminately for instruments graduated on either scale, 
 bearing in mind that the substance to be tested with a c.c. burette" 
 must be weighed on the gram system, and vice versa, unless it be 
 desired to calculate one system of weights into the other. 
 
 The great convenience of this equivalent system is, that the 
 numbers used as coefficients for calculation in any analysis are 
 familiar, and the solutions agree with each other, volume for 
 volume. We have hitherto, however, looked only at one side of 
 its advantages. For technical purposes the plan allows the use of 
 all solutions of systematic strength, and simply varies the amount 
 .of substance tested according to its equivalent weight. 
 
 Thus, the normal solutions say, are- 
 Crystallized oxalic acid =63 gm. per liter 
 Sulphuric acid =49 gm. 
 Hydrochloric acid -=36.37. gm. 
 Nitric acid =63 gm. 
 Anhydrous sodic carbonate =53 gm. 
 Sodic hydrate =40 gm. 
 Ammonia = 17 gm. 
 
30 VOLUMETRIC ANALYSIS. 11. 
 
 100 c.c of any one of these normal acids should exactly neutralize 
 100 c.c. of any of the normal alkalies, or the corresponding amount 
 of pure substance which the 100 c.c. contain. In commerce we 
 continually meet with substances used in manufactures which, are 
 not pure, and it is necessary to know how much pure substance 
 they contain. 
 
 Let us take, for instance, refined soda ash (sodic carbonate). If 
 it were absolutely pure, 5 '3 gm. of it should require exactly 100 c.c. 
 of any normal acid to saturate it. If we therefore weigh that 
 quantity, dissolve it in water, and deliver into the mixture the 
 normal acid from a burette, the number of c.c. required to saturate 
 it will show the percentage of pure sodic carbonate in the sample. 
 Suppose 90 c.c. are required 90 %. 
 
 Again a manufacturer buys common oil of vitriol, and requires 
 to know the exact percentage of pure hydrated acid in it; 4'9 grams 
 are weighed, diluted with water, and normal alkali delivered in 
 from a burette till saturated; the number of c.c. used will be the 
 percentage of real acid. Suppose 58'5 c.c. are required = 58'5 %. 
 
 On the grain system, in the same way, 53 grains of the sample of 
 soda ash would require 90 dm. of normal- acid, also equal to 90 %. 
 
 Or, suppose the analyst desires to know the equivalent percentage 
 of dry caustic soda, free and combined, contained in the above 
 sample of soda ush, without calculating it from the carbonate found 
 as above, 3'1 gm. is treated as before, and the number of c.c. 
 required is the percentage of sodic oxide. In the same sample 
 52'6 c.c. would be required = 52*6 per cent, of sodic oxide, or 90 
 per cent, of sodic carbonate. 
 
 Method for percentag-e of Purity in Commercial Substances. The 
 rules, therefore, for obtaining the percentage of pure substance in 
 any commercial article, such as alkalies, acids, and various salts, 
 by means of systematic normal solutions such as have been 
 described are these 
 
 1. With normal solutions ^ or (according to its atomicity) 
 of the molecular weight in grams of the substance to be analyzed 
 is to be weighed for titration, and the number of c.c. required to 
 produce the desired reaction is the percentage of the substance 
 whose atomic weight has been used. 
 
 With decinormal solutions -$ or TT of the molecular weight 
 in grams is taken, and the number of c.c. required will, in like 
 manner, give the percentage. 
 
 Where the grain system is used it will be necessary, in the case 
 of titrating with a normal solution, to weigh the whole or half the 
 molecular weight of the substance in grains, and the number of 
 decems required will be the percentage. 
 
 With decinormal solutions, y 1 ^- or J^- of the molecular weight in 
 grains is taken, and the number of decems will be the percentage. 
 
 It now only remains to say, with respect to the system of weights- 
 
12. VOLUMETRIC PROCESSES. 31 
 
 and measures to be used, that the analyst is at liberty to choose his 
 own plan. Both systems are susceptible of equal accuracy, and he 
 must study his own convenience as to which he Avill adopt. The 
 normal solutions prepared on the gram system are equally applicable 
 for that of the grain, and vice versa, so that there is no necessity 
 for having distinct solutions for each system. 
 
 Factors, or Coefficients, for the Calculation of Analyses. It 
 frequently occurs that from the nature of the substance, or from 
 its being in solution, this percentage method cannot be conveniently 
 followed. For instance, suppose the operator has a solution con- 
 taining an unknown quantity of caustic potash, the strength of 
 which he desires to know ; a weighed or measured quantity of it 
 is brought under the acid burette and exactly saturated, 32 c.c. 
 being required. The calculation is as follows : 
 
 The molecular Aveight of potassic hydrate being 56 : 100 c.c. of 
 normal acid will saturate 5*6 gm. ; therefore, as 100 c.c. are to 5*6 srni.* 
 
 so are 32 c.c. to #,' JQQ~~= 1*792 gm. KH.O. 
 
 The simplest way, therefore, to proceed, is to multiply the 
 number of c.c. of test solution required in any analysis, by the 
 TTTO (T ( or T<TO o- ^ bivalent) of tli3 molecular weight of the substance 
 sought, which gives at once the amount of substance present. 
 
 An example may be given 1 gm. of marble or limestone 'is 
 taken for the estimation of pure calcic carbonate, and exactly 
 saturated with standard nitric or hydrochloric acid (sulphuric or 
 oxalic acid are, of course, not admissible) 17 '5 c.c. are required, 
 therefore 17 -5 x 0*050 (the o-oVir f the molecular weight of 
 CaCO 3 ) gives 0'875 gm., and as 1 gm. of substance only was 
 
 taken = 87 "5% of calcic carbonate. 
 
 ON THE DIRECT AND INDIRECT PROCESSES OF 
 ANALYSIS AND THEIR TERMINATION. 
 
 12. THE direct method includes all those analyses where the 
 substance under examination is decomposed by simple contact with 
 a known quantity or equivalent proportion of some other body 
 capable of combining with it, and where the end of the decomposition 
 is manifested in the solution itself. 
 
 It also properly includes those analyses in which the substance 
 reacts upon another body to the expulsion of a representative 
 equivalent of the latter, which is then estimated as a substitute 
 for .the thing required. 
 
 Examples of this method are readily found in the process for 
 the determination of iron by permanganate, where the beautiful 
 rose colour of the permanganate asserts itself as the end of the 
 reaction. 
 
 The testing of acids and alkalies comes, also, under this class, the 
 
32 VOLUMETRIC ANALYSIS. 12. 
 
 great sensitiveness of litmus, or other indicators, allowing the 
 most trifling excess of acid or alkali to alter their colour. 
 
 The indirect method is exemplified in the analysis of manganese 
 ores, and also other peroxides and oxygen acids, by boiling with 
 hydrochloric acid. The chlorine evolved is estimated as the 
 equivalent of the quantity of oxygen which has displaced it. We 
 are indebted to Bun sen for a most accurate and valuable series of 
 processes based on this principle. 
 
 The residual method is such that the substance to be analyzed is 
 not estimated itself, but the excess of some other body added for 
 the purpose of combining with it or of decomposing it ; and the 
 quantity or strength of the body added being known, and the con- 
 ditions under which it enters into combination being also known, 
 by deducting the remainder or excess (which exists free) from the 
 original quantity, it gives at once the proportional quantity of the 
 substance sought. 
 
 An example will make the principle obvious : Suppose that a 
 sample of native calcic or baric carbonate is to be tested. It is not 
 possible to estimate it with standard nitric or hydrochloric acid in 
 the exact quantity it requires for decomposition. There must be 
 an excess of acid and heat applied also to get it into solution ; if, 
 therefore, a known excessive quantity of standard acid be first 
 added and solution obtained, and the liquid then titrated backward 
 with an indicator and standard alkali, the quantity of free acid can 
 be exactly determined, and consequently that which is combined 
 also. 
 
 In some analyses it is necessary to add a substance which shall 
 be an indicator of the end of the process j such, for instance, is 
 litmus or the azo colours in alkalimetry, potassic chromate in silver 
 and chlorine, and starch in iodine estimations. 
 
 There are other processes, the end of which can only be 
 determined by an indicator separate from the solution ; such is 
 the case in the estimation of iron by potassic bichromate, where 
 a drop of the liquid is brought into contact with another drop of 
 solution of red potassic prussiate on a white slab or plate ; when 
 .a blue colour ceases to form by contact of the two liquids, -the end 
 of the process is reached. 
 
14 
 
 INDICATORS. 
 
 33 
 
 PAET II. 
 
 ANALYSIS BY SATURATION. 
 
 ALKALIMETRY. 
 
 13. GAY LUSSAC based his system of alkalimetry upon a 
 standard solution of sodic carbonate, with a corresponding solution 
 of sulphuric acid. It possesses the recommendation, that a pure 
 standard solution of sodic carbonate can be more readily obtained 
 than any other form of alkali. Mohr introduced the use of 
 caustic alkali instead of a carbonate, the strength of which is 
 established by a standard solution of oxalic or sulphuric acid. 
 The advantage in the latter system is, that in titrating acids with 
 a caustic alkali, the well-known interference produced in litmus 
 by carbonic acid is avoided ; this difficulty is now overcome 
 wherever it is desired by the new indicators to be described. 
 
 INDICATORS USED IN ALKALIMETRY. 
 
 14. 1. Litmus Solution. It has 
 been the custom since the introduction 
 of the azo indicator, to regard litmus as 
 old fashioned and of very doubtful 
 sensitiveness. This is a mistake, for if 
 properly prepared, it is, in the absence 
 of carbonic acid, one of the most 
 sensitive of the indicators used for 
 alkalies. The difficulty which occurs 
 when carbonates are titrated may be 
 overcome by boiling off the gas, but 
 this is tedious, and like most of the 
 indicators in use, it is less sensitive in hot 
 than in cold liquids, nevertheless it has 
 excellent qualities, arid will hold its 
 position against many more modern 
 indicators. The litmus of commerce 
 differs considerably in purity and colour, 
 but a careful examination will at once 
 detect a good specimen by the absence 
 of a greyish muddy colour, due to 
 inert matters, both of vegetable and mineral nature. 
 
 A simple solution may be made by treating the cubes with 
 repeated small quantities of hot water; mixing all the extracts, 
 and allowing the liquid to stand in a covered beaker for a day or 
 night. The clear blue liquid is then poured off and placed in the 
 stock bottle, together with two or three drops of chloroform, this 
 
 D 
 
34 VOLUMETRIC ANALYSIS. 14. 
 
 latter agent prevents the development of bacteria, and if the 
 bottle is simply covered with a piece of paper, through which the 
 pipette is passed, the solution will keep for a long period. If the 
 colour is a deep blue it must be modified by a few drops of diluted 
 hydrochloric acid, until it is a faint purple. In course of time it 
 may lose its colour, but this may be restored by simple exposure 
 in a basin. Another method of preparing an extract of litmus in 
 a concentrated form for dilution whenever required is as follows : 
 extract all soluble matters from the solid litmus by repeated 
 quantities of hot w r ater ; evaporate the mixed extracts to a moderate 
 bulk, and add acetic acid in slight excess to decompose carbonates; 
 evaporate to a thick extract, transfer this to a beaker, and add a large 
 proportion of hot 85 per-cent. alcohol or methylated spirit ; by this 
 treatment the blue colour is precipitated, and the alkaline acetates, 
 together with some red colouring matter, remain dissolved; the 
 fluid with precipitate is thrown on a filter, washed with hot spirit, 
 and the pure colouring matter finally evaporated to a paste, which 
 is placed in a wide-mouthed bottle, together with a few drops of 
 chloroform ; this extract will keep for years unchanged. 
 
 Another recent method gives the best results of any. The 
 crushed litmus is extracted with warm distilled water, as before 
 described, and the several extracts mixed, then allowed to stand 
 in a beaker till quite clear this clear extract is poured off, 
 freely acidified with hydrochloric acid, and put into a dialyser, 
 which is surrounded by running water and kept so for about 
 a week. The colouring matter of litmus being a colloid, all the 
 calcium and other salts are removed, and a pure soluble colour in 
 hot distilled water remains, which may be preserved in the 
 manner previously described, or evaporated to a pasty condition 
 and kept for use at any time when required. 
 
 Free carbonic acid interferes considerably with the production of 
 the blue colour, and its interference in titrating acid solutions with 
 alkaline carbonates can only be got rid of by boiling the liquid 
 during the operation, in order to displace the gas from the solution. 
 If this is not done, it is easy to overstep the exact point of neutrality 
 in endeavouring to produce the blue colour. The same difficulty is 
 also found in obtaining the pink-red when acids are used for 
 titrating alkaline carbonates, hence the great value of the caustic 
 alkaline solutions free from carbonic acid when this indicator is used. 
 
 It sometimes occurs that titration by litmus is required at night. 
 Ordinary gas or lamp light is not adapted for showing the reaction 
 in a satisfactory manner ; but a very sharp line of demarcation 
 between red and blue may be found by using a monochromatic 
 light. With the yellow sodium flame the red colour appears 
 perfectly colourless, while the blue or violet appears like a mixture 
 of black ink and water. The transition is very sudden, and even 
 sharper than the change by daylight. 
 
 The operation should be conducted in a perfectly dark room ; 
 
14 INDICATORS. 35 
 
 and the flame may be best obtained by heating a piece of platinum 
 coil sprinkled with salt, or a piece of pumice saturated with a 
 concentrated solution of salt, in the Bunsen flame. 
 
 2. Litmus Paper. Is simply made by dipping strips of 
 calendered unsized paper in the solution and drying them ; the 
 solution used being rendered blue, red, or violet as may be 
 required. 
 
 3. Cochineal Solution. This indicator possesses the advantage 
 over litmus, that it is not so much modified in colour by the presence 
 of carbonic acid, and may be used by gas-light. It may also be used 
 with the best effect with solutions of the alkaline earths, such as 
 lime and baryta water ; the colour with pure alkalies and earths is 
 especially sharp and brilliant. The solution is made by digesting 
 1 part of crushed cochineal with 10 parts of 25 per-cent. alcohol. 
 Its natural colour is yellowish-red, which is turned to violet by 
 alkalies ; mineral acids restore the original colour ; it is not so 
 easily affected by weak organic acids as litmus, and therefore for 
 these acids the latter is preferable. It cannot be used in the 
 presence of even traces of iron or alumina compounds or acetates, 
 which fact limits its use. 
 
 4. Turmeric Paper. Pettenkof er, in his estimation of car- 
 bonic acid by baryta water, prefers turmeric paper as an indicator. 
 For this purpose it is best prepared by digesting pieces of the root, 
 first in repeated small quantities of water to remove a portion of 
 objectionable colouring matter, then in alcohol, and dipping strips 
 of calendered unsized paper into the alcoholic solution, drying and 
 preserving them in the dark. 
 
 Thomson in continuance of his valuable studies on various 
 indicators, found that turmeric paper is of very little use for 
 ammonia, or the alkaline carbonates, or sulphides and sulphites, 
 but he prepared a special paper of a light red-brown colour, by 
 dipping it into the alcoholic tincture of turmeric rendered slightly 
 alkaline by caustic soda. If this paper is wetted with water the 
 colour is intensified to a dark red-brown ; when partly immersed in 
 a very dilute solution of an acid, the wetted portion becomes bright 
 yellow, while immediately above this a moistened dark red-brown 
 band is formed, and the upper dry portion retains its original 
 colour. This appearance only occurs in the titration of a com- 
 paratively large proportion of an acid, when the latter is nearly all 
 neutralized, and thus serves to indicate the near approach to the 
 end-reaction. When neutral or alkaline, the colour of the immersed 
 portion of paper is simply intensified as already described. This 
 intensification is quite as decided as a change of tint. This red- 
 brown paper is equally as sensitive as phenolphthalein for the 
 titration of citric, acetic, tartaric, oxalic and other organic acids by 
 standard soda or potash, and may be used for highly coloured 
 
 D 2 
 
36 VOLUMETRIC ANALYSIS. 14. 
 
 solutions. It is also available, like phenolphthalein, for the 
 estimation of small quantities of acid in strong alcohol. 
 
 Indicators derived from the Azo Colours, etc. 
 
 A great stride has been taken in the application of these 
 modern indicators, and the best thanks of all chemists are due to 
 R. T. Thomson for his valuable researches on them, read before 
 the Chemical Section of the Philosophical Society of Glasgow, and 
 published in their Transactions ; also reprinted (C. A 7 ", xlvii. 123, 
 185; xlix. 32, 119; J. &. C. I. vi. 195). The experiments 
 recorded in these papers are most carefully carried out, and the 
 truthfulness of their results has been verified by Lunge and other 
 practical men as well as by myself. 
 
 Space will only permit here of a record of the results, fuller 
 details being given in the publications to which reference has been 
 made. 
 
 Much discussion has arisen as to the comparative sensitiveness 
 of litmus and methyl orange, but there can be no doubt that in 
 the absence of CO 2 litmus bears the palm, especially with very 
 dilute solutions. In the titration of alkaline carbonates litmus 
 may safely be used, if a considerable excess of standard acid is 
 first added, the CO 2 completely boiled off, the liquid rapidly 
 cooled, then titrated back with standard alkali free from CO' 2 . 
 Where very great delicacy is required, not only must the standard 
 solutions be free from CO 2 but the distilled water used for dilution 
 should have been recently boiled. 
 
 5. Methyl Orang-e, or para-dimethylaniline-azo-benzone-sulphonic 
 acid is prepared by the action of diazotized sulphanilic acid upon 
 dimethylaniline, the commercial product being either an ammonium 
 or sodium salt of the sulphonic acid thus produced. If carefully 
 prepared from the purest materials it possesses a bright orange 
 colour, perfectly soluble in water ; but the commercial product is 
 often of a dull colour, due to slight impurities in the substances 
 from which it is produced, and often not completely soluble in 
 water. These impurities may generally IDC removed by 
 recrystallizatiori from hot alcoholic solution. Complaints have 
 been made by some operators that the commercial article is some- 
 times unreliable as an indicator ; it may be so, but although I have 
 examined many specimens, I have not yet found any in which the- 
 impurities sensibly affected its delicate action when used in the 
 proper manner. The common error is the use of too much of it ; 
 again, there is the personal error of observation, some eyes being- 
 much more sensitive to the change of tint than others. The 
 great value of this indicator is that, unlike litmus and some other 
 agents, it is comparatively unaffected by carbonic acid, sulphuretted 
 hydrogen, hydrocyanic, silicic, boric, arsenious, oleic, stearic,. 
 palmitic, and carbolic acids, etc. It must not be used for the- 
 
1-1. INDICATORS. 37 
 
 organic acids, such as oxalic, acetic, citric, tartaric, etc., since 
 the end-reaction is indefinite ; nor can it be used in the presence 
 of nitrous acid or nitrites, which decompose it. It may safely be 
 used for the estimation of free mineral acids in alum, ferrous 
 sulphate or chloride, zinc sulphate, cupric sulphate or chloride. The 
 acid radical (and consequently -its equivalent metal) in cupric 
 sulphate and similar salts may be estimated with accuracy by pre- 
 cipitating the solution with sulphuretted hydrogen, filtering, and 
 titrating the filtrate at once with normal alkali and methyl orange. 
 
 Methyl orange is especially useful for the accurate standardizing 
 of any of the mineral acids by means of pure sodic carbonate in the 
 cold, the liberated carbonic acid having practically no effect, as is the 
 case with many indicators. Its effect is also excellent with ammonia 
 or its salts. A convenient strength for the indicator is 1 gram of 
 the powder in a liter of distilled water ; a single small drop of the 
 liquid is sufficient for 100 c.c. or more of any colourless solution 
 the colour being faint yellow if alkaline, and pink if acid ; if too 
 much is used the end-reaction is slower and much less definite. 
 All titrations with methyl orange should be carried on at ordinary 
 temperatures if the utmost accuracy is desired. 
 
 There are two other azo-compounds in use, more especially by 
 continental chemists, which possess the same properties and give 
 much the same effect as methyl orange, namely Fischer's 
 dimethylamido-azobenzene and tropoeolin 00. My experience is 
 that these preparations are less sensitive than methyl orange, and 
 wherever they are recommended for any process of titration the 
 latter may be substituted with advantage. 
 
 6. Phenacetolin. This substance is prepared by boiling together 
 for several hours equal molecular proportions of phenol, acetic 
 anhydride, and sulphuric acid. The product is well washed with 
 water to remove excess of acid and dried for use ; it is soluble 
 only in alcohol, and a convenient strength is 2 gm. per liter. The 
 solution is dark brown, which gives a scarcely perceptible yellow 
 with caustic soda or potash, when a few drops are used with the 
 ordinary volumes of liquid. With ammonia and the normal 
 alkaline carbonates it gives a dark pink, with bicarbonate a much 
 more intense pink, and with mineral acids a golden yellow. This 
 indicator may be used to estimate the amount of caustic potash 
 or soda in the presence of their normal carbonates if the proportion 
 of the former is not very small, or of caustic lime in the presence 
 of carbonate. 
 
 Practice however is required with solutions of known composition, 
 so as to acquire knowledge of the exact shades of colour. 
 
 7. Phenolphthalein. This substance is obtained by heating 
 together at 120 C., for ten or twelve hours, five parts of phthalic 
 anhydride, ten of phenol, and four of sulphuric acid j the product 
 
38 VOLUMETRIC ANALYSIS. 14 
 
 is boiled with water, and the residue dissolved in dilute soda and 
 filtered. The nitrate contains the phenolphthalein, which may 
 be precipitated by neutralizing with acetic and hydrochloric acids, 
 and purified by solution in alcohol, boiling with animal charcoal 
 and re-precipitating with boiling water ; it is of a resinous nature, 
 but quite soluble in 50 per-cent. alcohol. A convenient strength 
 is 10 gm. per liter. 
 
 A few drops of the indicator show no colour in the ordinary 
 volumes of neutral or acid liquids ; the faintest excess of caustic 
 alkalies, on the other hand, gives a sudden change to purple-red. 
 
 This indicator is useless for the titration of free ammonia, or its 
 compounds, or for the fixed alkalies when salts of ammonia are- 
 present, except with alcoholic solutions, in which case caustic soda 
 or potash displace the ammonia in equivalent quantities at ordinary 
 temperatures, and the indicator forms no compound with the 
 ammonia. 
 
 It may, however, be used like phenacetoKn for estimating the 
 proportions of hydrate and carbonate of soda or potash in the 
 same sample where the proportion of hydrate is not too small. 
 Unlike methyl orange, this indicator is especially useful in titrating 
 all" varieties of organic acids ; viz., oxalic, acetic, citric, tartaric, 
 etc. 
 
 One great advantage possessed by phenolphthalein is, that it 
 may be used in alcoholic solutions, or mixtures of alcohol and 
 ether,* and therefore many organic acids insoluble in water may 
 be accurately titrated by its help ; in addition to this it may be 
 used to estimate the acid combined with many organic bases, 
 such as morphia, quinia, brucia, etc., the base having no effect 
 on the indicator. 
 
 8. Kosolic Acid is soluble in 50 per-cent. alcohol, and a con- 
 venient strength is 2 gm. per liter. Its colour is pale yellow, 
 unaffected by acids, but turning to violet-red with alkalies. It 
 possesses the advantage over litmus and the other indicators, that 
 it can be relied upon for the neutralization of sulphurous acid 
 with ammonia to normal sulphite (Thomson). Its delicacy- 
 is sensibly affected by salts of ammonia and by carbonic acid. 
 It is excellent for all the mineral, but useless for the organic acids^ 
 excepting oxalic, 
 
 9. Lacmoid. This indicator is a product of resorcin, and is- 
 therefore somewhat allied to litmus ; nevertheless, it differs from it 
 in many respects, and has a pronounced and valuable character of 
 its own, especially when used in the form of paper. It may be 
 
 * H. 1ST. and. C. Draper (C. N. Iv. 143) have shown that this indicator is rapidly 
 decomposed by atmospheric carbonic acid, which is more readily absorbed, by alcohol 
 than by water. Fortunately this is less the case with hot solutions than with cold ; 
 titrations of this kind should therefore be quickly done, and with not too small 
 a quantity of the indicator. 
 
14. INDICATORS. 
 
 prepared by heating gradually to 110 C. a mixture of 100 parts 
 of resorcin, five parts of sodic nitrite, and five parts of water; 
 after the violent reaction moderates, it is heated to 120 C. until 
 evolution of ammonia ceases. The residue is dissolved in warm 
 water, and the lacmoid precipitated therefrom by hydrochloric 
 acid ; it is well washed from free acid and dried for use. Lacmoid 
 is soluble in dilute alcohol, and the indicator is best made by 
 dissolving 2 gm. to the liter. 
 
 10. Lacmoid Paper. This is prepared by dipping slips of 
 calendered unsized paper into the blue or red solution, and drying 
 them. 
 
 Thomson states that, in nearly every particular, lacmoid paper, 
 either blue or red, is an excellent substitute for methyl orange, 
 and may be employed in titrating coloured solutions where the 
 latter would be useless. Solution of lacmoid, on the other hand, 
 is not so valuable as the paper, inasmuch as it is more easily affected 
 by weak acids such as carbonic, boric, etc. 
 
 There are a host of other indicators belonging to the same category 
 as those mentioned above, such as Congo red, Porrier's blue, 
 fluorescin, etc. ; but as they have no special advantages over them, 
 and indeed are practically inferior in delicacy, no description of 
 them will be given here. 
 
 Two or more indicators are sometimes useful in one and the 
 same solution, and will be described as occasion requires. 
 
 Special indicators for certain purposes, such as potassic chromate 
 for silver, ferric sulphate for sulphocyanides, etc., will be described 
 in their proper place. 
 
 Extra Sensitive Indicators. Mylins and Fb'rster (Bericlite, 
 xxiv. 1482 ; also C. N. Ixiv. 228, et seq.) describe a series of 
 experiments on the estimation of minute traces of alkali and the 
 recognition of the neutrality of water by means of an etheieal 
 solution of iodeosin or erythrosin. This body is a derivative of 
 fluorescin, and occurs plentifully in commerce as a dye for fabrics 
 and paper. The commercial material is purified by solution in 
 aqueous ether, and the filtered solution is shaken with dilute 
 caustic soda which removes the colour; the latter is then precipitated 
 with stronger alkali. The salt is then filtered off, washed with 
 spirit . and finally recrystallized from hot alcohol. The indicator 
 used by the operators was made by dissolving 1 decigram 
 of the dry powder in a liter of aqueous pure ether. The 
 ether of commerce is purified and rendered neutral by washing 
 with weak alkali, afterwards with pure water, and keeping 
 the ether over pure water. The indicator so prepared is quite 
 useless for the ordinary titration of acids and alkalies ; its 
 chief use is for the detection and measurement of very minute 
 proportions of alkali such as would occur in water kept in glass 
 
40 VOLUMETRIC ANALYSIS. 14. 
 
 vessels, or the solubility of calcium or other earthy carbonates in 
 water free from carbonic acid, or in the use of millinormal solutions 
 of alkalies and acids, also the neutrality of so-called pure salts 
 or water. The method of using the indicator is that of shaking 
 up say 20 c.c. of the indicator with 100 c.c. of the liquid to 
 be examined, when, if alkali is present, a rose colour will be 
 communicated to the layer of ether which rises to the top. The 
 indicator may be used in conjunction with millinormal standard 
 solutions, or colorimetrically, like the well-known Xessler test. 
 Further details of its use are described in the contributions 
 mentioned. Another similar indicator is mentioned by Ru hem ami 
 (J. C. S. Trans. Ixi. 285), the imide of dicinnamylphenylazimide. 
 This material gives a violet rose colour with the most minute traces 
 of alkali, such, for instance, as would occur from merely heating 
 alcohol in a test tube, the faint trace of alkali thus derived from 
 the glass being sufficient to cause a rapid development of colour. 
 
 SHORT SUMMARY OF THOMSON'S RESULTS WITH 
 INDICATORS AND PURE SALTS OF THE ALKALIES 
 AND ALKALINE EARTHS, 
 
 The whole of the base or acid in the following list of substances 
 may be estimated with delicacy and precision unless otherwise 
 mentioned. 
 
 Litmus Cold. Hydrates of soda, potash, ammonia, lime, baryta, 
 etc. ; arsenites of soda and potash, and silicates of the same bases ; 
 nitric, sulphuric, hydrochloric, and oxalic acids. 
 
 Litmus Boiling. The neutral and acid carbonates of potash, 
 soda, lime, baryta, and magnesia, the sulphides of sodium and 
 potassium, and silicates of the same bases. 
 
 Methyl Orange Cold. The hydrates, carbonates, bicarbonates, 
 sulphides, arsenites, silicates, and borates of soda, potash, ammonia, 
 lime, magnesia, baryta, etc., all the mineral acids, sulphites, half the 
 base in the alkaline and earthy alkaline phosphates and arseniates. 
 
 Rosolic Acid Cold. The whole of the base or acid may be 
 estimated in the hydrates of potash, soda, ammonia, and arsenites 
 of the same ; the mineral and oxalic acids. 
 
 Rosolic Acid Boiling. The alkaline and earthy hydrates and 
 carbonates, bicarbonates, sulphides, arsenites, and silicates. 
 
 Phenacetolin Cold. The hydrates, arsenites, and silicates of the 
 alkalies ; the mineral acids. 
 
 Phenacetolin Boiling. The alkaline and earthy hydrates, car- 
 bonates, bicarbonates, sulphides, arsenites, and silicates. 
 
14. INDICATORS. 41 
 
 Phenolphthalein Cold. -The alkaline hydrates, except ammonia; 
 the mineral acids, oxalic, citric, tartaric, acetic, and other organic 
 acids. 
 
 Phenolphthalein Boiling. The alkaline and earthy hydrates, 
 carbonates, bicarbonates, and sulphides, always excepting ammonia 
 and its salts. 
 
 Lacmoid Cold. The alkaline and earthy hydrates, arsenites and 
 borates, and the mineral acids. Many salts of the metals which are 
 more or less acid to litmus are neutral to lacmoid, such as the 
 sulphates and chlorides of iron, copper, and zinc ; therefore this 
 indicator serves for estimating free acids in such solutions. 
 
 Lacmoid Boiling. The hydrates, carbonates, and bicarbonates of 
 potash, soda, and alkaline earths. 
 
 Lacmoid Paper The alkaline and earthy hydrates, carbonates, 
 bicarbonates, sulphides, arsenites, silicates, and borates ; the mineral 
 acids ; half of the base in sulphites, phosphates, arseniates. 
 
 This indicator reacts alkaline with the chromates of potash or 
 soda, but neutral with the bichromates, so that a mixture of the 
 two, or of bichromates with free chromic acid, may be titrated by 
 its aid, which could also be done with methyl orange were it not 
 for the colour of the solutions. 
 
 The following substances can be determined by standard 
 alcoholic potash, with phenolphthalein as indicator. One c.c. 
 normal caustic potash (1 c.c. = '056 gm. KHO) is equal to 
 (Hehner and Allen) 
 
 088 gm. butyric acid. '1007 gm. tributyrin 
 
 282 ,, oleic acid. '2947 ,, triolein. 
 
 256 ,, palmitic acid '2687 tripalmitin. 
 
 284 ,, stearic acid '2967 ,, tristearin. 
 
 410 ,, cerotic acid. '6760 ,, myricin. 
 
 329 ,, resin acids (ordinary colophony, chiefly sylvic acid). 
 
 General Characteristics of the Foregoing Indicators. 
 
 It is interesting to notice the different degrees of sensitiveness 
 shown by indicators used in testing acids and alkalies. This is well 
 illustrated by Thomson's experiments, where he used solutions 
 of the indicator containing a known weight of the solid material, 
 and so adjusted as to give, as near as could be judged, the same 
 intensity of colour in the reaction. 
 
 It was found that lacmoid, rosolic acid, phenacetolin, and 
 phenolphthalein were capable of showing the change of colour 
 with one-fifth of the quantity of acid or alkali which was required 
 in the case of methyl orange or litmus ; that is to say, in 100 c.c. 
 of liquid, where the latter took 0*5 c.c., the same effect with the 
 former was gained by O'l c.c. 
 
42 VOLUMETRIC ANALYSIS. ' 14 
 
 Another important distinction is shown in their respective 
 behaviour with mineral and organic acids. 
 
 It is true the whole of them are alike serviceable for the 
 mineral acids and fixed alkalies ; but they differ considerably in 
 the case of the organic acids and ammonia. Methyl orange 
 and lacmoid appear to be most sensitive to alkalies, while 
 phenolphthalein is most sensitive to acids ; the others appear to^ 
 occupy a position between these extremes, each showing, however, 
 special peculiarities. The distinction, however, is so marked, that, 
 as Thomson says, it is possible to have a liquid which may be 
 acid to phenolphthalein and alkaline to lacmoid. 
 
 The presence of certain neutral salts has, too, a definite effect 
 on the sensitiveness of certain indicators. Sulphates, nitrates, 
 chlorides, etc., retard the action of methyl orange slightly, while in 
 the case of phenacetolin and phenolphthalein they have no effect. 
 On the other hand, neutral salts of ammonia have such a disturbing 
 influence on the latter as to render it useless, unless with special 
 precautions. 
 
 Nitrous acid alters the composition of methyl orange ; so also 
 do nitrites when existing in any quantity. Forbes Carpenter 
 has noted this effect in testing the exit gases of vitriol chambers 
 (J. S. C. I. v. 287). 
 
 Sulphites of the fixed alkalies and alkaline earths are practically 
 neutral to phenolphthalein, but alkaline to litmus, methyl orange, 
 and phenacetolin. 
 
 Sulphides, again, can be accurately titrated with methyl orange 
 in the cold, and on boiling off the H 2 S a tolerably accurate result can 
 be obtained with litmus and phenacetolin, but with phenolphthalein 
 the neutral point occurs when half the alkali is saturated. The 
 phosphates of the alkalies, arseniates, and arsenites, also vary in 
 their effects on the various indicators. 
 
 Again, boric acid and the borates can be very accurately titrated 
 by help of methyl orange or lacmoid paper, but the other indicators 
 are practically useless, except with the modification on page 44. 
 
 Thomson classifies the usual neutrality indicators into three 
 groups. The methyl orange group, comprising that substance, 
 together with lacmoid, dimethylamidobenzene, cochineal and Congo 
 red ; the phenolphthalein group, consisting of itself and turmeric ; the 
 litmus group, including litmus, rosolic acid, and phenacetolin. The 
 methyl orange group are most susceptible to alkalies, the phen- 
 olphthalein to acids, and the litmus somewhat between the two. 
 This classification has nothing to do with delicacy of reaction, but 
 with the special behaviour of the indicator under the same circum- 
 stances ; for instance, saliva, which is generally neutral to litmus 
 paper, is always strongly alkaline to lacmoid or Congo red, and acid 
 to turmeric paper. Fresh milk reacts very much in the same way. 
 No absolutely hard and fast line can however be drawn. 
 
 Thomson gives the following table as an epitome of the results 
 
14 
 
 INDICATORS. 
 
 obtained with indicators, and 011 which several processes have beert 
 based. The figures refer to the number of atoms of hydrogen 
 displaced by the monatomic metals, sodium or potassium, in the 
 form of hydrates. Where a blank is left it is meant that the end- 
 reaction is obscure. The figures apply also to ammonia, except 
 where phenolphthalein is concerned, and when boiling solutions are 
 used. Calcic and baric hydrates also give similar results, -.except 
 where insoluble compounds are produced. Lacmoid paper acts in 
 every respect like methyl orange, except that it is not affected by 
 nitrous acid or its compounds. Turmeric paper behaves exactly 
 like phenolphthalein with the mineral acids and also with thio- 
 sulphuric and organic acids. 
 
 Acids. 
 
 Methyl Orange. 'Phenolphthalein. 
 
 Litmus. 
 
 Name. 
 
 Formula. 
 
 Cold. 
 
 Cold. 
 
 Boiling. 
 
 Cold. 
 
 Boiling. 
 
 Sulphuric . . 
 
 H 2 SO 4 
 
 2 
 
 2 
 
 2 
 
 2 
 
 2 
 
 Hydrochloric . 
 
 HC1 
 
 I 
 
 1 
 
 1 
 
 1 
 
 1 
 
 Nitric . . . 
 
 HNO 3 
 
 1 
 
 1 
 
 1 
 
 1 
 
 1 
 
 Thiosulpliuric . 
 
 H-'S 2 3 
 
 2 
 
 2 
 
 2 
 
 2 
 
 2 
 
 Carbonic . . 
 
 H 2 C0 3 
 
 
 
 1 dilute! 
 
 - 
 
 
 
 Sulphurous 
 
 H 2 SO :? 
 
 1 
 
 2 
 
 
 
 
 
 Hydrosulphuric 
 
 H 2 S 
 
 
 
 1 dilute 
 
 o 
 
 
 
 Phosphoric 
 
 HAPO 4 
 
 1 
 
 2 
 
 ; 
 
 
 
 
 
 Arsenic . . . 
 
 H 3 AsO 4 
 
 1 
 
 2 
 
 
 
 
 
 
 
 Arsenious . . 
 
 IFAsO 3 
 
 
 
 
 
 
 
 
 
 
 
 Nitrous . . . 
 
 HNO 2 
 
 indicator destroyed * 
 
 
 
 1 
 
 
 
 Silicic . . . 
 
 H 4 Si0 4 
 
 
 
 
 
 
 
 
 
 
 
 Borio . . . 
 
 H 3 B0 3 
 
 
 
 
 
 
 
 
 
 
 
 Chromic . . 
 
 H 2 Cr0 4 
 
 1 
 
 2 
 
 2 
 
 
 
 
 
 Oxalic . . . 
 
 H 2 C 2 4 
 
 
 
 2 
 
 2 
 
 2 
 
 2 
 
 Acetic . . . 
 
 HC 2 H 3 2 
 
 1 
 
 
 
 1 nearly 
 
 
 
 Butyric . . . 
 
 HC 4 H7O 2 
 
 1 
 
 
 
 1 nearly 
 
 
 
 Succiuic . . . 
 
 H 2 C 4 H 4 O 4 
 
 2 
 
 
 
 2 nearly 
 
 
 
 Lactic . . . 
 
 HC 3 H 5 3 
 
 
 
 1 
 
 
 
 1 
 
 
 
 Tartaric . . . 
 
 H 2 C 4 H 4 ( 
 
 . 
 
 2 
 
 . 
 
 2 
 
 
 
 Citric . . . 
 
 H 3 C 6 H 5 0' 
 
 
 
 3 
 
 
 
 
 
 
 
 Allen (Pliarm. Jour., May llth, 1889) clearly points out that 
 the acid which enters into the composition of an indicator must be 
 weaker than the acid which it is required to estimate by its means. 
 The acid of which methyl orange is a salt is a tolerably strong one, 
 since.it is only completely displaced by the mineral acids; the 
 organic acids are not strong enough to overpower it completely, 
 hence the uncertainty of the end-reaction. The still weaker acids, 
 such as carbonic, hydrocyanic, boric, oleic, etc., do not decompose 
 the indicator at all, hence their salts may be titrated by it, just as 
 if the bases only were present. On the other hand the acid of 
 phenolphthalein is extremely weak, hence its salts are easily 
 decomposed by the organic and carbonic acids. A combination of 
 the two indicators is frequently of service ; say, for instance, in a 
 
44 VOLUMETRIC ANALYSIS. 15. 
 
 mixture of normal and acid sodic carbonate, if first titrated with 
 plienolphthalein and standard mineral acid, the rose colour dis- 
 appears exactly at the point when the normal carbonate is saturated, 
 the bicarbonate can then be found by continuing the operation 
 with methyl orange. The study of these new indicators is still 
 imperfect, and requires further elucidation ; more especially if we 
 take into consideration some new aspects of the question mentioned 
 in a paper by K. T. Thomson (/. S. C. I. xii. 432). The 
 experiments there recorded and which are too voluminous to 
 produce here, are of a very interesting character and point to the 
 supposition that molecular condition, viscosity of the liquid or 
 some such influence was at work, so as to modify very considerably 
 the action of the indicator. The irregularities occurring in the cases 
 mentioned are no doubt exceptional, and need not disturb the faith 
 hitherto reposed in well-known and much-used methods of titration. 
 
 The particular indicator whose erratic action was under 
 discussion was phenolphthalein and it was demonstrated, that in 
 using this indicator in the titration of boric acid with soda, no 
 satisfactory end-reaction could be got in a merely aqueous solution, 
 but that by the addition of not less than 30 per cent, of glycerine 
 to the mixture, a perfectly correct determination could be made. 
 Other substances such as starch, glucose, and cane sugar had 
 a similar effect, but not to the same extent as glycerine. 
 
 The result of these investigations, is to give a satisfactory 
 method of estimating volumetrically the boric acid existing in its 
 natural compounds, which has hitherto been a much desired thing. 
 
 PREPARATION OF THE NORMAL ACID AND ALKALINE 
 
 SOLUTIONS. 
 
 15. IT is quite possible to carry out the titration of acids 
 and alkalies with only one standard liquid of each kind; but it 
 frequently happens that standard acids or alkalies are required 
 in other processes of titration beside mere saturation, and it is 
 therefore advisable to have a variety. 
 
 Above all things it is absolutely necessary to have, at least, one 
 standard acid and alkali prepared with the most scrupulous 
 accuracy to use as foundations for all others. 
 
 I prefer sulphuric acid for the normal acid solution, inasmuch as 
 there is no difficulty in getting the purest acid in commerce. The 
 normal acid made with it is totally unaffected by boiling, even 
 when of full strength, which cannot be said of either nitric or 
 hydrochloric acid. Hydrochloric acid is however generally pre- 
 ferred by alkali makers, owing to its giving soluble compounds 
 with lime and similar bases. Nitric and oxalic acids are also 
 sometimes convenient. 
 
 Sodic carbonate, on the other hand, is to be preferred for the 
 standard alkali, because it may readily be prepared in a pure 
 
15. NORMAL SOLUTIONS. 45 
 
 state, or may be easily made from pure- bicarbonate as 
 described further on. Differences of opinion exist among 
 chemists as to the best material to be used as a standard, in 
 preparing the various solutions used in alkalimetry and acidimetry. 
 Some give the preference to borax with methyl orange as indicator 
 for alkalies. Others to potassic quadroxalate for acids with 
 phenolphthalein as indicator. My experience satisfies me, that 
 although many of these modifications may serve very well as 
 controls, there is no more reliable standard than pure sodie 
 carbonate. 
 
 The chief difficulty with sodic carbonate is, that with litmus as 
 indicator, the titration must be carried on at a boiling heat in 
 order to get rid of carbonic acid, which hinders the pure blue 
 colour of the indicator, notwithstanding the alkali may be in 
 great excess. This difficulty is now set aside by the use of methyl 
 orange. In case the operator has not this indicator at hand, litmus- 
 gives perfectly accurate results, if the saturation is first conducted 
 by rapidly boiling the liquid in a thin flask for a minute after each 
 addition of acid until the point is reached when one drop of acid 
 in excess gives a pink-red colour, which is not altered by further 
 boiling. This is used as a preliminary test, but as titrations are 
 usually conducted at ordinary temperatures, the final adjustment 
 should be made by adding in the second trial a moderate excess of 
 the acid, then boiling to get thoroughly rid of the CO 2 , rapidly 
 cooling the liquid in a closed flask, and titrating back with an 
 accurate standard alkali. A slight calculation will then give the 
 figures for adjustment. 
 
 As has been previously said, these two standards must be pre- 
 pared with the utmost care, since upon their correct preparation and 
 preservation depends the verification of other standard solutions. 
 
 It may, however, be remarked, that in place of a standard solution 
 of sodic carbonate, which is of limited use for general purposes, 
 the pure anhydrous salt may be used for the rigid adjustment of 
 normal acid. In this case about 3 grams of pure ^N"a 2 C0 3 or 4 gm. 
 of pure XaHCO 3 are heated to dull redness for ten minutes in a 
 weighed platinum crucible, cooled under an exsiccator, the exact 
 weight quickly taken, then transferred to a flask by means of a 
 funnel, through which it is washed and dissolved - with distilled 
 water, methyl orange added, and the operation completed by 
 running the acid of unknown strength from a burette divided into- 
 -j c.c. into the soda solution in small quantities until exact 
 saturation occurs. 
 
 A second trial should now be made, but preferably with 
 a different weight of the salt. The saturation is carried out 
 precisely as at first. The data for ascertaining the exact strength 
 of the acid solution by calculation are now in hand. 
 
 A strictly normal acid should at 16 C. exactly saturate sodic-. 
 carbonate in the proportion of 100 c.c. to 5 -3 gm. 
 
46 VOLUMETRIC ANALYSIS. 15. 
 
 Suppose that 2'46 gm. sodic carbonate required 41 '5 c.c. of tlie 
 acid in the first experiment, then 
 
 2-46 : 5-3 : : 41'5 : x = 89'4 c.c. 
 
 Again: 2*153 gm. sodic carbonate required 36*32 c.c. of acid, 
 then 
 
 2-153 : 5-3 : : 36'32 : x = S9'4 c.c. 
 
 The acid may now be adjusted by measuring 890 c.c. into the 
 graduated liter cylinder, adding 4 c.c. from the burette, or 
 with a small pipette, and filling to the liter mark with distilled 
 water. 
 
 Finally, the strength of the acid so prepared must be proved by 
 taking a fresh quantity of sodic carbonate, or by titratioii with a 
 strictly normal sodic carbonate solution previously made, and using 
 not less than 50 c.c. for the tit-ration, so as to avoid as much 
 as possible the personal errors of measurement in small quantities. 
 If the measuring instruments all agree, and the operations are 
 .all conducted with due care, a drop or two in excess of either 
 acid or alkali in 50 c.c. should suffice to reverse the colour of 
 the indicator. 
 
 In all alkalimetric titrations it must not be forgotten that some 
 glass vessels yield a notable quantity of alkali to boiling water,. 
 and even more to hot alkaline solutions. The use of vessels made 
 of Jena glass is therefore preferable. 
 
 1. Normal Sodic Carbonate. 
 53 gm. !S T a 2 C0 3 per liter.. 
 
 This solution is made by quickly weighing and dissolving 
 53 gm. of pure sodic monocarboiiate, previously gently ignited and 
 cooled under the exsiccator in hot distilled water, and when cooled 
 diluting to 1 liter at 16 C. Absolutely pure sodic carbonate is 
 -difficult to find in commerce, and even if otherwise pure, is 
 generally contaminated with insoluble dust contracted in the 
 process of drying ; very pure bicarbonate is not difficult to find, 
 but its purity must be proved, the usual impurities are traces of 
 chlorides, sulphates, and occasionally thiosulphate or sulphite. 
 
 To obtain a salt which shall be suitable for a standard, the best 
 white bicarbonate should be selected, and 20 or 30 grams 
 dissolved in about half a liter of hot water. If the solution is 
 free from any sediment or floating particles, a portion is acidified 
 with pure nitric acid in a small beaker and tested with silver 
 nitrate for chlorine, another portion for sulphate with baric 
 chloride ; if either of these are found the salt is freed from them 
 by packing, say half a pound, into a clean funnel, the neck of 
 which is stopped with a plug of cotton wool. Cold distilled water 
 free from any trace of chloride or sulphate is then poured on the 
 .salt in repeated small quantities, and allowed to filter through 
 until the testing shows the absence of these impurities. Of 
 
15. NORMAL SOLUTIONS. 47 
 
 course this means a waste of some bicarbonate, but as the salt is 
 not very soluble in cold water it is of no consequence. When 
 the impurities are found to be removed, the funnel is allowed to 
 drain completely, the contents spread out on a clean flat dish or 
 plate, tied over loosely with porous paper, and placed on the water 
 bath or in some other warm position to dry, finally put into 
 a stoppered bottle for conversion into monocarbonate as required. 
 
 If on the other hand the sample has not dissolved quite clear, 
 another method must be adopted by making a saturated solution 
 of the salt in boiling distilled water, filtering at once through 
 paper in a heated funnel into a clean porcelain dish and keeping 
 the solution stirred until quite cold ; by this means a pure salt 
 deposits in a granular state which, after pouring off the superfluous 
 liquid, may be dried and kept for "use as before described. In 
 using this salt for the standard the procedure is as follows : 
 
 About 85 gm. is heated to dull redness (not to fusion) in a 
 platinum crucible, for fully ten minutes, stirring it occasionally 
 with a platinum wire, then placed under an exsiccator to cool ; 
 when placed upon the balance it will be found that very little 
 more than 53 gm. remains. The excess is removed as quickly as 
 possible, and the contents of the crucible washed into a beaker 
 with hot distilled water; when the salt is dissolved the solution is 
 cooled to a proper temperature, decanted into a liter flask and 
 filled up to the mark with distilled water at 16 C. If cold 
 water is used a hard cake is produced which dissolves very slowly. 
 
 2. Normal Potassic Carbonate. 
 
 69 gm. K 2 C0 3 per liter. 
 
 This solution is sometimes, though rarely, preferable to the soda 
 salt, and is of service for the estimation of combined acids in certain 
 cases, where, by boiling the compound with this agent, an inter- 
 change of acid and base occurs. 
 
 It cannot be prepared by direct weighing of the potassic carbonate, 
 and is therefore best established by titrating a solution of unknown 
 strength with strictly normal acid. 
 
 3. Normal Sulphuric Acid. 
 49 grn. H 2 S0 4 per liter. 
 
 About 30 c.c. of pure sulphuric acid of sp. gr. 1'840, or there- 
 abouts, are mixed with three or four times the volume of distilled 
 water and allowed to cool, then put into the graduated cylinder and 
 diluted up to the liter at the proper temperature. The solution 
 may now be titrated by strictly normal alkali, or with sodic 
 carbonate. 
 
 25 c.c. of the solution, diluted to 250 c.c., may be con- 
 trolled by precipitation with baric chloride at a boiling heat, 
 in which case 100 c.c. should produce as much baric sulphate as is 
 equal to 49 gm. per liter. 
 
48 VOLUMETRIC ANALYSIS. 15. 
 
 In using this control it is best to make two determinations, and 
 preferably with different quantities of the acid, the mean is then 
 taken for basis of calculation. 
 
 4. Normal Oxalic Acid. 
 63 gm. C 2 4 H 2 ,2H 2 0, or 45 gm. C 2 4 H 2 per liter. 
 
 This solution cannot very well be established by direct weighing, 
 owing to uncertain hydration ; hence it must be titrated by normal 
 alkali of known accuracy. 
 
 The solution is apt to deposit some of the acid at low tempera- 
 tures, but keeps well if preserved from direct sunlight, and will 
 bear heating without volatilizing the acid. Very dilute solutions 
 of oxalic acid are very unstable ; therefore, if a decinormal or 
 centinorrnal solution is at any time required, it should be made 
 when wanted. 
 
 5. Normal Hydrochloric Acid. 
 
 36-37 gm. HC1 per liter. 
 
 It has been shown by Roscoe and Dittmar (J. C. S. xii. 128, 
 1860) that a solution of hydrochloric acid containing 20'2 per cent, 
 of the gas when boiled at about 760 m.m. pressure, loses acid and 
 water in the same proportion, and the residue will therefore 
 have the constant composition of 20 "2 per cent., or a specific 
 gravity of 1-10. About 181 gm. of acid of this gravity, diluted 
 to one liter, serves very well to form an approximate normal 
 acid. 
 
 The actual strength may be determined by precipitation with 
 "silver nitrate, or by titration with an exactly weighed quantity of 
 pure sodic monocarbonate. Hydrochloric acid is useful on account 
 of its forming soluble compounds with the alkaline earths, but it has 
 the disadvantage of volatilizing at a boiling heat. Dittmar says 
 that this may be prevented by adding a few grains of sodic sulphate. 
 In many cases this would be inadmissible, for the same reason that 
 sulphuric acid cannot be used. The hydrochloric acid from which 
 standard solutions are made must be free from chlorine gas or 
 metallic chlorides, and should leave no residue when evaporated in 
 a platinum vessel. 
 
 6. Normal Nitric Acid. 
 63 gm. H2x T 3 per liter. 
 
 A rigidly exact normal acid should be established by sodic 
 carbonate, as in the case of normal sulphuric and hydrochloric acids. 
 
 The nitric acid used should be colourless, free from chlorine 
 and nitrous acid, sp. gr. about T3. If coloured from the 
 presence of nitrous or hyponitrous acids, it should be mixed with 
 two volumes of water, and boiled until white. When cold it may 
 be diluted and titrated as previously described for sulphuric acid. 
 
15. NORMAL SOLUTIONS. 49 
 
 7. Normal Caustic Soda or Potash. 
 40 gin. NallO or 56 gm. KHO per liter. 
 
 Pure caustic soda made from metallic sodium may now be readily 
 obtained in commerce, and hence it is easy to prepare a standard 
 solution of exceeding purity, by simply dissolving the substance in 
 distilled water till of about 1*05 sp. gr., or about 50 gm. to the 
 liter, roughly estimating its strength by normal acid and methyl 
 orange or litmus, then finally adjusting the exact strength by 
 titrating 50 c.c. with normal acid. 
 
 However pure caustic soda or potash may otherwise be, they are 
 both in danger of absorbing carbonic acid, and hence in using 
 litmus the titration must be conducted with boiling. Methyl 
 orange permits the use of these solutions at ordinary temperature 
 notwithstanding the presence of CO 2 . 
 
 Soda and potash may both be obtained in commerce sufficiently 
 pure for all ordinary titration purposes, but in case they are not at 
 hand the requisite solutions may be prepared as follows : 
 
 Two parts of pure sodic or potassic carbonate are to be dissolved 
 in twenty parts of distilled water, and boiled in a clean iron pot ; 
 during the boiling, one part of fresh quick-lime, made into a cream 
 with water, is to be added little by little, and the whole boiled until 
 all the carbonic acid is removed, which may be known by the clear 
 solution producing no effervescence on the addition of dilute acid ; 
 the vessel is covered closely and set aside to cool and settle ; when 
 cold, the clear supernatant liquid should be poured or drawn off 
 and titrated by normal acid, and made of the proper strength 
 as directed for sulphuric acid. 
 
 Soda or potash solutions may be freed from traces of chlorine, 
 .sulphuric, silicic, and carbonic acids, by shaking with Mi lion's 
 base, trimercur-ammonium (C. N. xlii. 8). Carbonic acid may be 
 removed by the cautious addition of baric hydrate in solution, 
 shaking well, and then after settling clear ascertaining the exact 
 strength with correct standard acid. 
 
 In preparing these alkaline solutions, they should be exposed as 
 little as possible to the air, and when the strength is finally settled, 
 should be preserved in the bottle shown in fig. 24, or in full bottles 
 having their glass stoppers slightly greased with vaseline. 
 
 8. Semi-normal Ammonia. 
 8-5 gm. NH :3 per liter. 
 
 For some years past I have used this strength of standard 
 ammonia for saturation analyses, and have been fully satisfied with 
 its behaviour ; it is cleanly, does not readily absorb carbonic acid, 
 holds its strength well for two or three months when kept in a cool 
 place and well stoppered ; and can at any time be prepared in a few 
 
50 VOLUMETKIC ANALYSIS. 15. 
 
 minutes, by simply diluting strong solution of ammonia with fresh 
 distilled water. 
 
 A normal solution cannot be used with safety, owing to evapora- 
 tion of the gas at ordinary temperatures. 
 
 It is necessary to add that, even in the case of ~ strength, 
 the solution should be titrated from time to time against correct 
 normal acid. ^ ammonia keeps its strength for a long time 
 in well-closed bottles. 
 
 9. Decinormal Caustic Baryta. 
 
 The solution of caustic baryta is best made from the crystallized 
 hydrate, approximately of ~ strength. This is best done by 
 shaking up in a stoppered bottle powdered crystals of baric 
 hydrate with distilled water, and allowing it to stand a day or 
 two until quite clear ; there should be an excess of the hydrate, 
 in which case the clear solution, when poured off into a stock 
 bottle fitted with CO 2 tube, will be nearly twice the required 
 strength. It is better to dilute still further (after taking its 
 approximate titre with HC1 and phenolphthalein) with freshly 
 boiled and cooled distilled water ; the actual working strength 
 may be checked by evaporating 20 or 25 c.c. to dryness with 
 a slight excess of sulphuric acid, then igniting over a Bun sen 
 flame and weighing the BaSO 4 . The corresponding acid may be 
 either ^ oxalic, nitric, or hydrochloric, and the proper indicator 
 is phenolphthalein. Oxalic acid is recommended byPettenkofer 
 for carbonic acid estimation, because it has no effect upon the 
 baric carbonate suspended in weak solutions; but there is the 
 serious drawback in oxalic acid, that in dilute solution it is liable 
 to rapid decomposition ; and as in my experience ~ hydrochloric 
 acid in very dilute mixtures has no effect upon the suspended 
 baric carbonate, it is preferable to use this acid. 
 
 The baryta solution is subject to constant change by absorption 
 of carbonic acid, but this may be prevented to a great extent by 
 preserving it in the bottle shown in fig. 24. A thin layer of light 
 petroleum oil on the surface of the liquid preserves the baryta at 
 one strength for a long period in the bottle shown in fig. 25. 
 
 The reaction between baryta and yellow turmeric paper is very 
 delicate, so that the merest trace of baryta in excess gives a decided 
 brown tinge to the edge of the spot made by a glass rod on the 
 turmeric paper. If the substance to be titrated is not too highly 
 coloured, phenolphthalein should invariably be used. 
 
 10. Normal Ammonio-Cupric Solution for Acetic Acid and free 
 Acids and Bases in Earthy and Metallic Solutions. 
 
 This acidimetric solution is prepared by dissolving pure cupric 
 sulphate in warm water, and adding to the clear solution liquid 
 ammonia, until the bluish-green precipitate which first appears is- 
 
16. NORMAL SOLUTIONS. 51 
 
 nearly dissolved ; the solution is then filtered into the graduated 
 cylinder, and titrated by allowing it to flow from a pipette graduated 
 in i or y 1 ^- c.c. into 10 or 20 c.c. of normal sulphuric or nitric acid 
 (not oxalic). While the acid remains in excess, the bluish-green 
 precipitate which occurs as the drop falls into the acid rapidly 
 disappears ; but so soon as the exact point of saturation occurs, the 
 previously clear solution is rendered turbid by the precipitate 
 remaining insoluble in the neutral liquid. 
 
 The process is especially serviceable for the estimation of the free 
 acid existing in certain metallic solutions, i.e. mother-liquors, etc., 
 where the neutral compounds of such metals have an acid reaction 
 on litmus such as the oxides of zinc, copper, and magnesia, and 
 the protoxides of iron, manganese, cobalt, and nickel; it is also 
 applicable to acetic and the mineral acids. 
 
 If cupric nitrate be used for preparing the solution instead of 
 sulphate, the presence of barium, or strontium, or metals precipitable 
 by sulphuric acid is of no consequence. The solution is stand- 
 ardized by normal nitric or sulphuric acid ; and as it slightly alters 
 by keeping, a coefficient must be found from time to time by 
 titrating with normal acid, by which to calculate the results 
 systematically. Oxides or carbonates of magnesia, zinc, or other 
 admissible metals, are dissolved in excess of normal nitric acid, 
 and titrated residually with the copper solution. 
 
 Example : 1 gra. of pure zinc oxide was dissolved in 27 c.c. of normal 
 acid, and 2'3 c.c. of normal copper solution required to produce the 
 precipitate ==24*7 c.c. of acid; this multiplied by 0'0405, the coefficient 
 i'or zinc oxide, - I'OOO gm. ' 
 
 ESTIMATION OF THE CORRECT STRENGTH OF STANDARD 
 SOLUTIONS NOT STRICTLY NORMAL OR SYSTEMATIC. 
 
 16. IN discussing the preparation of the foregoing standard 
 solutions, it has been assumed that they shall be strictly and 
 absolutely correct; that is to say, if the same measure be filled 
 first with any alkaline solution, then with an acid solution, and the 
 two mixed together, a perfectly neutral solution shall result, so that 
 a drop or two either way will upset the equilibrium. 
 
 Where it is possible to weigh directly a pure dry substance, this 
 approximation may be very closely reached. Sodic monocarbonate, 
 for instance, admits of being thus accurately weighed. On the 
 other hand, the caustic alkalies cannot be so weighed, nor can 
 the liquid acids.- An approximate quantity, therefore, of these 
 substances must be taken, and the exact power of the solution 
 found by experiment. 
 
 In titrating such solutions it is exceedingly difficult to make them 
 so exact in strength, that the precise quantity, to a drop or two, 
 shall neutralize each other. In technical matters a near approxima- 
 tion may be sufficient, but in scientific investigations it is of the 
 greatest importance that the utmost accuracy should be obtained ; 
 
 E 2 
 
52 VOLUMETRIC ANALYSIS. 16. 
 
 it is therefore advisable to ascertain the actual difference, and to 
 mark it upon the vessels in which the solutions are kept, so that 
 a slight calculation will give the exact result. 
 
 Suppose, for instance, that a standard sulphuric acid is prepared, 
 which does not rigidly agree with the normal sodic carbonate (not 
 at all an uncommon occurrence, as it is exceedingly difficult to hit 
 the precise point) ; in order to find out the exact difference it must 
 be carefully titrated as in 15. Suppose the weight of sodic 
 carbonate to be 1*9 gm., it is then dissolved and titrated with the 
 standard acid, of which 36*1 c.c, are required to reach the exact 
 neutral point. 
 
 If the acid were rigidly exact it should require 35 '85 c.c. ; in 
 order, therefore, to find the factor necessary to bring the quantity 
 of acid used in the analysis to an equivalent quantity of normal 
 strength, the number of c.c. actually used must be taken as the 
 denominator, and the number which should have been used, had 
 the acid been strictly normal, as the numerator, thus 
 
 35 ' 8 - 5 -0-99V 
 36-1 ' 
 
 Q'993 is therefore the factor by which it is necessary to multiply 
 the number of c.c. of that particular acid used in any analysis 
 in order to reduce it to normal strength, and should be marked 
 upon the bottle in which it is kept. 
 
 On the other hand, suppose that the acid is too strong, and that 
 35 '2 c.c. were required instead of 35*85, 
 
 1-0184 is therefore the factor by which it is necessary to multiply 
 the number of c.c. of that particular acid in order to bring it to 
 the normal strength., This plan is much better than dodging about 
 with additions of water or acid. 
 
 Under all circumstances it is safer to prove the strength of any 
 standard solution by experiment, even though its constituent has 
 been accurately weighed in the dry and pure state. 
 
 Further, let us suppose that a solution of caustic soda is to be. 
 made by means of lime as described previously. After pouring off 
 the clear liquid, water is added to the sediment to extract more 
 alkaline solution ; by this means we may obtain two solutions, one 
 of which is stronger than necessary, and the other weaker. Instead, 
 of mixing them in various proportions and repeatedly trying the 
 strength, we may find, by two experiments and a calculation, 
 the proportions of each necessary to give a normal solution, thus : 
 
 The exact actual strength of each solution is first found, by 
 separately running into 10 c.c. of normal acid as much of each 
 alkaline solution as will exactly neutralize it. We have, then, in 
 the case of the stronger solution, a number of c.c. required less 
 than 10. Let us call this number V. 
 
16. NORMAL SOLUTIONS. 53 
 
 In the weaker solution the number of c.c. is greater than 10, 
 represented by v. A volume of the stronger solution x will 
 saturate 10 c.c. of normal acid as often as V is contained in x. 
 
 A volume of the weaker solution = y will, in like manner, saturate 
 
 10 y 10 x 10 ?/, 
 
 - c.c. ot normal acid; both together saturate y -\ -- 
 
 and the volume of the saturated acid is precisely that of the two 
 liquids, thus- 1() x 1Q 
 
 -I 
 
 mence 
 
 = x 
 
 1Q>* + 10 Vy = *.* + Vp y 
 
 v x (10 - Y) = V y (v - 10). 
 
 And lastly, , r / , m 
 
 x_ _ V (v + 10) 
 
 ~y ~ v (10 - V)" 
 
 An example will render this clear. A solution of caustic soda 
 was taken, of which 5*8 c.c. were required to saturate 10 c.c. normal 
 acid; of another solution, 12*7 c.c. were required. The volumes of 
 each necessary to form a normal solution were found as follows : 
 
 5-8 (12-7 -10) = 15-66 
 12-7 (10 -5-8) = 53-34 
 
 Therefore, if the solutions are mixed in the proportion of 15'66 
 c.c. of the stronger with 53 '34 c.c. of the weaker, a correct solution 
 ought to result. The same principle of adjustment is, of course, 
 applicable to standard solutions of every class. 
 
 Again: suppose that a standard solution of sulphuric acid has 
 been made, approximating as nearly as possible to the normal 
 strength, and its exact value found by precipitation with baric 
 chloride, or a standard hydrochloric acid with silver nitrate, and 
 such a solution has been calculated to require the coefficient 0*995 
 to convert it to normal strength, by the help of this solution, 
 though not strictly normal, we may titrate an approximately normal 
 alkaline solution thus : Two trials of the acid and alkaline solu- 
 tions show that 50 c.c. alkali =48'5 c.c. acid, having a coefficient 
 of 0'995 = 48'25 c.c. normal ; then, according to the equation, 
 x 50 := 48'25 is the required coefficient for the alkali. 
 
 = 0-965. 
 
 And here, in the case of the alkaline solution being sodic carbonate, 
 we can bring it to exact normal strength by a calculation based on 
 the equivalent weight of the salt, thus 
 
 1 : 0-965 : : 53 : 5M45. 
 
 The difference between the two latter numbers is 1'855 gm., and 
 this weight of pure sodic carbonate, added to one liter of the 
 solution, will bring it to normal strength. 
 
54 
 
 VOLUMETRIC ANALYSIS. 
 
 TABLE FOR THE SYSTEMATIC ANALYSIS OF ALKALIES, 
 ALKALINE EARTHS AND ACIDS. 
 
 Substance. 
 
 Formula. 
 
 Atomic 
 Weight. - 
 
 Quantity to be 
 weighed so that 1 
 c.c. Normal Solu- 
 tion=l per cent, 
 of substance. 
 
 Normal 
 Factor.* 
 
 Soda 
 
 Na 2 O 
 
 62 
 
 3'1 gm. 
 
 0-031 
 
 Sodic H} T drate . . 
 
 NaHO 
 
 40 
 
 4-0 gm. 
 
 0-040 
 
 Sodic Carbonate . . 
 
 Na 2 C0 3 
 
 106 
 
 5'3 gm. 
 
 0-053 
 
 Sodic Bicarbonate 
 
 NaHCO 3 
 
 84 
 
 8'4 gm. 
 
 0-084 
 
 Potash 
 
 K 2 O 
 
 94 
 
 4' 7 gm. 
 
 0-047 
 
 Potassic Hydrate . . 
 
 KHO 
 
 56 
 
 5'6 gm. 
 
 0-056 
 
 Potassic Carbonate . 
 
 K-CO 3 
 
 138 
 
 6'9 gm. 
 
 0-069 
 
 Potassic Bicarbonate 
 
 KHCO 3 
 
 100 
 
 lO'O gm. 
 
 O'lOO 
 
 Ammonia .... 
 
 NH 3 
 
 17 
 
 1:7 gm. 
 
 0-017 
 
 Ainmonic Carbonate 
 
 (NH 4 ) 2 CO 3 
 
 96 
 
 4'8 gm. 
 
 0-048 
 
 Lime (Calcic Oxide) . 
 
 CaO 
 
 56 
 
 2-8 gm. 
 
 0-028 
 
 Calcic Hydrate . . 
 
 CaH 2 2 
 
 74 
 
 3'7 gm. 
 
 0-037 
 
 Calcic Carbonate . . 
 
 CaCO 3 
 
 100 
 
 5'0 gm. 
 
 O'OoO 
 
 Baric Hvdrate . . 
 
 BaH 2 O 2 
 
 171 
 
 8'55 gm. 
 
 0'0855 
 
 Do. (Crystals) . . 
 
 BaO 2 H 2 (H 2 0) s 
 
 315 
 
 1575 gm. 
 
 0-1575 
 
 Baric Carbonate . . 
 
 BaCO 3 
 
 197 
 
 9-85 gm. 
 
 0-0985 
 
 Strontia 
 
 SrO 
 
 103'5 
 
 5*175 gm. 
 
 0-05175 
 
 Strontic Carbonate . 
 
 SrCO 3 
 
 147'5 
 
 7-375 gm. 
 
 0-07375 ' 
 
 Magnesia .... 
 
 MgO 
 
 40 
 
 2'00 gm. 
 
 0-020 
 
 Magnesic Carbonate. 
 
 MgCO 3 
 
 84 
 
 4'20 gm. 
 
 0-042 
 
 Nitric Acid. . . . 
 
 HNO 3 
 
 63 
 
 6'3 gm. 
 
 0-063 
 
 Hydrochloric Acid . 
 
 HC1 
 
 36-37 
 
 3'637 gm. 
 
 0-03637 
 
 Sulphuric Acid . . 
 
 H 2 SO 4 
 
 98 
 
 4'9 gm. 
 
 0-049 
 
 Oxalic Acid . . . 
 
 C 2 O 4 H 2 (H 2 O) 2 
 
 126 
 
 6'3 gm. 
 
 0-063 
 
 Acetic Acid . . - . 
 
 C 2 O 2 H 4 
 
 60 
 
 6'0 gm. 
 
 0-060 
 
 Tartaric Acid . . . 
 
 C 4 G H r, 
 
 150 
 
 7-5 gin. 
 
 0075 
 
 Citric Acid .... 
 
 C0'H S + H 2 
 
 210 
 
 7-0 gm. 
 
 0-070 
 
 Carbonic Acid . . . 
 
 CO 2 
 
 44 
 
 
 0'022 
 
 * This is the coefficient by which the number of c.c. of normal solution used in 
 any analysis is to be multiplied, in order to obtain the amount of pure substance 
 present in the material examined. 
 
 If grain weights are used instead of grams, the decimal point must be moved 
 one place to the right to give the necessary weight for examination; thus sodic 
 carbonate, instead of 5'3 gm., would be 53 grains, the normal factor in this case would 
 also be altered to 0'53. 
 
17. ALKALINE SALTS. 55 
 
 THE TITRATION OF ALKALINE SALTS. 
 1. Total Alkali in Caustic Soda or Potash, or their Carbonates. 
 
 17. THE necessary quantity of substance being weighed or 
 measured, as the case may be, and mixed with distilled water to a 
 proper state of dilution (say about one per cent, of solid material), 
 an appropriate indicator is added, and the solution is ready for the 
 burette. Xormal acid is then cautiously added from a burette 
 till the change of colour occur. In the case of caustic alkalies 
 free from CO 2 , the end-reaction is very sharp with any of the 
 indicators ; but if CO' 2 is present, the only available indicators in 
 the cold are methyl orange or lacmoid paper. If the other indica- 
 tors are used, the CO 2 must be boiled off after each addition of acid. 
 
 In examining carbonates of potash or soda, or mixtures of caustic 
 and carbonate, where it is only necessary to ascertain the total 
 alkalinity, the same method applies. 
 
 In the examinations of samples of commercial refined soda or 
 potash salts, it is advisable to proceed as follows : 
 
 Powder and mix the sample thoroughly, weigh 10 gm. in a platinum or 
 porcelain crucible, and ignite gently over a spirit or gas lamp, and allow the 
 crucible -to cool under the exsiccator. Weigh again, the loss of weight gives 
 the moisture ; wash the contents of the crucible into a beaker, dissolve and 
 filter if necessary, and dilute to the exact measure of 500 c.c. with distilled 
 water in a half-liter flask ; after mixing it thoroughly take out 50 c.c. 1 gm. 
 of alkali with a pipette, and empty it into a small flask, bring the flask under 
 a burette containing normal acid and graduated to i or T V c.c., allow the acid 
 to flow cautiously as before directed, until the neutral point is reached : the 
 process may then be repeated several times if necessary, in order to be certain 
 of the correctness of the analysis. 
 
 Residual Titration : As the presence of carbonic acid with litmus and the 
 other indicators, except methyl orange, always tends to confuse the exact end 
 of the process, the difficulty is best overcome, in the case of not using methyl 
 orange, by allowing an excess of acid to flow into the alkali, boiling to expel 
 the CO 2 , and then cautiously adding normal caustic alkali, drop by drop, 
 until the liquid suddenly changes colour; by deducting the quantity of 
 caustic alkali from the quantity of acid originally used, the exact volume of 
 acid necessary to saturate the 1 gm. of alkali is ascertained. 
 
 This method of re-titration gives a very sharp end-reaction, as 
 there is 110 carbonic acid present to interfere with the delicacy of 
 the indicator. It is a procedure sometimes necessary in other cases, 
 owing to the interference of impurities dissipated by boiling, e.g. 
 sulphuretted hydrogen, which would otherwise bleach the indicator, 
 except in the case of methyl orange and lacmoid paper, either of 
 which are indifferent to H 2 S in the cold. An example will make 
 the plan clear : - 
 
 Example : 50 c.c. of the solution of alkali prepared as directed, equal to 
 1 gm. of the sample, is put into a flask, and 20 c.c. of normal acid allowed to 
 flow into it ; it is then boiled and shaken till all CO 2 is expelled, and normal 
 caustic alkali added till the neutral point is reached ; the quantity required 
 is 3'4 c.c v which deducted from 20 c.c, of acid leaves 16'6 c.c. The following 
 
56 VOLUMETKIC ANALYSIS. IT. 
 
 calculation, therefore, gives the percentage of real alkali, supposing it to 
 be soda : 31 is the half molecular weight of anhydrous soda (Na-O) and 1 c.c. 
 of the acid is equal to 0'031 gm., therefore 16'6 c.c. is multiplied by 0'031, 
 which gives 5146 ; and as 1 gm. was taken, the decimal point is moved 
 two places to the right, which gives 5T46 per cent, of real alkali ; if calculated 
 as carbonate, the 16'6 would be multiplied by 0'053, which gives 0'8798 gm. 
 = 87'98 per cent. 
 
 2. Mixed Caustic and Carbonated Alkaline Salts. 
 
 The alkaline salts of commerce, and also alkaline lyes used in 
 soap, paper, starch, and other manufactories, consist often of a 
 mixture of caustic and carbonated alkali. If it be desired to 
 ascertain the proportion in which these mixtures occur, the total 
 alkaline power of a weighed or measured quantity of substance (not 
 exceeding 1 or 2 gm.) is ascertained by normal acid and noted; a 
 like quantity is then dissolved in about 150 c.c. of water in a 
 200 c.c. flask, and exactly enough solution of baric chloride added 
 to remove all carbonic acid from the soda or potash. 
 
 Watson Smith has shown (J. S. C. I. i. 85) that whenever an 
 excess of baric chloride is used in this precipitation so as to form 
 baric hydrate, there is an invariable loss of soda : exact precipita- 
 tion is the only way to secure accuracy. 
 
 The flask is now filled up to the 200 c.c. mark with distilled 
 water, securely stoppered, and put aside to settle. When the 
 supernatant liquid is clear, take out 50 c.c. with a pipette, and 
 titrate with normal hydrochloric acid to the neutral point. The 
 number of c.c. multiplied by 4 will be the quantity of acid required 
 for the caustic alkali in the original weight of substance, because 
 only one-fourth was taken for analysis. The difference is calculated 
 as carbonate, or the precipitated baric carbonate may be thrown 
 upon a dry filter, washed well and quickly with boiling water, and 
 titrated with normal acid, instead of the original analysis for the 
 total alkalinity ; or both plans may be adopted as a check upon 
 each other. 
 
 ^--iThe principle of this method is, that when baric chloride is added 
 to a mixture of caustic and carbonated alkali, the carbonic acid of 
 the latter is precipitated as an equivalent of baric carbonate, while 
 the equivalent proportion of caustic alkali remains in solution as 
 baric hydrate. By multiplying the number of c.c. of acid required 
 to saturate this free alkali with the y^Vo atomic weight of caustic 
 potash or soda, according to the alkali present, the quantity of 
 substance originally present in this state will be ascertained. 
 
 As caustic baryta absorbs CO 2 very readily when exposed to the 
 atmosphere, it is preferable to allow the precipitate of baric 
 carbonate to settle in the flask as here described, rather than to 
 filter the solution as recommended by some operators, especially 
 also as the filter obstinately retains some baric hydrate. 
 
 A very slight error, however, occurs in all such cases, in 
 
17. ALKALINE SALTS. 57 
 
 consequence of the volume of the precipitate being included in 
 the measured liquid. 
 
 K. Williams (/. S. C. I. vi. 346) estimates the caustic soda in. 
 soda ash by digesting a weighed quantity in strong alcohol in a 
 tightly stoppered flask with frequent shaking and finally allowing 
 to stand overnight ; the undissolved carbonate is filtered off, 
 washed with alcohol until a drop gives no alkaline reaction 
 the nitrate and washings are then titrated with normal acid and 
 phenolphthalein. 
 
 Peter Hart recommends the following technical method of 
 ascertaining the relative proportions of caustic and carbonated 
 soda in sola ash : 50 grains of the sample are dissolved in 
 10 ounces of water, phenolphthalein added, and the standard 
 acid (1 dm. - 0'5 grn. Na 2 0) slowly run in until the colour- 
 disappears. At this point all the caustic soda and one-naif the 
 carbonate has been neutralized, say 30 dm. has been used. To 
 the same solution (in which the soda now exists as bicarbonate) 
 methyl orange is added, and the titration continued until pink ; 
 the burette now reads 50 dm. Then 50 - 30 = 20 as NaHCO", 
 but as this originally existed in the sample as Na 2 CO :) , this figure 
 must be doubled = 40, which deducted from 50 leaves 10 dm. as 
 representing the caustic soda in the sample. 
 
 3. Estimation of Hydrates of Soda or PotasB. with small 
 proportions of Carbonate. 
 
 This may be accomplished by means of phenacetolin (Lunge, 
 /. & C. I. i. 56). The alkaline solution is coloured a scarcely 
 perceptible yellow with a few drops of the indicator. The standard 
 acid is then run in until the yellow gives place to a pale rose 
 tint; at this point all the caustic alkali is saturated, and the 
 volume of acid used is noted. Further addition of acid now 
 intensifies this red colour until the carbonate is decomposed, when 
 a clear golden yellow results. The neutralization of the NaHO or 
 the KHO is indicated by a rose tint permanent on standing ; that 
 of Xa 2 C0 3 or K 2 C0 3 by the sudden passage from red to yellow. 
 
 Practice is required with solutions of known composition to 
 accustom the eye to the changes of colour. Phenolphthalein may 
 also be employed for the same purpose as follows : 
 
 Add normal acid to the cold alkaline solution till the red colour 
 is discharged, taking care to use a very dilute solution, and keeping 
 the spit of the burette in the liquid so that no CO 2 escapes. The 
 point at which the colour is discharged occurs when all the hydrate 
 is neutralized and the carbonate converted into bicarbonate ; the 
 volume of acid is noted, and the solution heated to boiling, with 
 small additions of acid, till the red colour produced by the decom- 
 position of the bicarbonate is finally destroyed. 
 
 In both these methods it is preferable, after the first stage, to 
 
 E8E LIB, 
 
 OF THE 
 
 UNIVERSITY, 
 
 . m OF 
 
58 VOLUMETRIC ANALYSIS. 17. 
 
 add excess of acid, boil off the CO 2 , and titrate back with normal 
 alkali. The results are quite as accurate as the method of precipi- 
 tation with barium. 
 
 4. Estimation of Alkaline Bicarbonates in presence of 
 Normal Carbonates (Lring-e, J. S. C. I. i. 57). 
 
 To a weighed quantity of the solid bicarbonate, or a measured 
 quantity of a solution, there is added an excess of J ammonia, 
 followed by an excess of solution of baric chloride. The mixture 
 is made in a measuring flask, and the whole diluted with hot 
 distilled water to the mark. 
 
 A portion of the clear settled liquid, or filtered through a dry 
 filter, is then titrated with normal acid : the alkaline strength due 
 to the excess of ammonia, above that required to convert the bicar- 
 bonate into normal carbonate, deducted from the total ammonia 
 added, gives the equivalent of the bicarbonate present. 
 
 Example (Lunge) : 20 gm. sodic bicarbonate in the course of manufac- 
 ture were dissolved to a liter. 50 c.c. of this solution required 12' 1 c.c. 
 normal acid=0'3751 gm. Na 2 O ; 50 c.c. were then mixed with 50 c.c. of 
 standard ammonia (50 ' c.c. =24'3 normal acid) and the whole treated with 
 excess of baric chloride. One half of the clear liquid required 6'25 c.c. 
 of normal acid, 24'3 (6'25 x 2) = 11'8 c.c. : this is, therefore, the equivalent 
 of the CO 2 as bicarbonate. 
 
 ' XaHCO 3 : 11-8 x -084= '9912 gm. 
 Xa-CO 3 : (12-1 11-8) x "053= "0159. 
 
 A simpler plan than the above has been devised by Thomson, 
 which gives good results when carefully carried out. 
 
 To the cold solution of the sample, an excess of normal caustic 
 soda, free from CO 2 , is added, the CO 2 is then precipitated with 
 neutral solution of baric chloride, and the excess of sodic hydrate 
 found by standard acid, using phenolphthalein as indicator. The 
 precipitate of baric carbonate has no effect on the indicator in the 
 cold. The calculation is the same as before. 
 
 5. Estimation of small quantities of Sodic or Potassic 
 Hydrates in presence of Carbonates. 
 
 This method, by Thomson, has just been alluded to, and 
 consists in precipitating the carbonates by neutral solution of baric 
 chloride in the cold : the baric carbonate being neutral to phenol- 
 phthalein, this indicator can be used for the process. When the 
 barium solution is added, a double decomposition occurs, resulting 
 in an equivalent quantity of sodic or potassic chloride, while the 
 baric carbonate is precipitated, and the alkaline hydrate remains in 
 solution. 
 
 Example (Thomson): 2 gm. of pure sodic carbonate were mixed in 
 solution with '02 gm. of sodic hydrate; excess of baric chloride was then 
 
17. ALKALINE SALTS. 
 
 which in three trials an average of 5 c.c. was required ; therefore, 
 5 x '004 = '02 gm. exactly the quantity used. 
 
 In this process the presence of chlorides, sulphates, and sulphites 
 does not interfere ; neither do phosphates, as baric phosphate is 
 neutral to the indicator. With sulphides, half of the base will be 
 estimated ; but if hydrogen peroxide be added, and the mixture 
 allowed to rest for a time, the sulphides are oxidized to sulphates, 
 Avhich have no effect. If silicates or aluminates of alkali are 
 present, the base will of course be recorded as hydrate. 
 
 Thomson further says : 
 
 "The foregoing method can also be applied to the determination 
 of hydrate of sodium or potassium in various other compounds, 
 which give precipitates with baric chloride neutral to phenolph- 
 thalein, such as the normal sulphites and phosphates of the alkali 
 metals. An illustration of the use to which the facts I have 
 stated in this and former papers may be put will be found in the 
 analysis of sulphite of sodium. Of course sulphate, thiosulphate, 
 and chloride are determined as usual, but to estimate sulphite, 
 carbonate and hydrate, or bicarbonate of sodium by methods in 
 ordinary use is rather a tedious operation. To find the proportion 
 of hydrate, all that is necessary is to precipitate with baric chloride 
 and titrate with standard acid, as above described. Then, by 
 simple titration of another portion of the sample in the cold, using 
 phenolphthalein as indicator, the hydrate and half of the carbonate 
 can be found, and finally, by employment of methyl orange as 
 indicator, and further addition of acid, the other half of the 
 carbonate and half of the sulphite can- be estimated. By simple 
 calculations, the respective proportions of these three compounds 
 can be obtained, a result which can be accomplished in a few 
 minutes. It must be borne in mind that if a large quantity of 
 sodic carbonate is in the sample the proportion of that compound 
 found will only be an approximation to the truth, as the 
 end-reaction is only delicate with small proportions of sodic 
 carbonate. If there is no hydrate found, bicarbonate of sodium 
 can be tested for, and determined by Lunge's method described 
 above" ( 17.4). 
 
 6. Estimation of Alkalies in the presence of Sulphites. 
 
 It is not possible to estimate the alkaline compounds in the 
 presence of sulphites by titration with acids, as a certain' quantity 
 of acid is taken up by the sulphite, SO 2 being evolved. This 
 difficulty may be completely overcome by the aid of hydrogen 
 peroxide, which speedily converts the sulphites into sulphates 
 (Grant and Cohen, J. & C. I. ix. 19). These operators proved 
 that neither caustic or carbonate alkali were affected by H 2 2 , nor 
 had the latter any prejudicial effect on methyl orange in the cold. 
 
60 VOLUMETRIC ANALYSIS. 17. 
 
 The quantity of H 2 2 required in any given analysis must depend 
 on the amount of sulphite present ; for instance, the caustic 
 salts of commerce contain about 50 % of sulphite, and it suffices 
 to take 10 o.c. of ordinary 10 vol. H 2 2 for every O'l gm. of the 
 salts in solution. In the case of mixtures containing less or more 
 sulphite the quantity may be varied. 
 
 The Analysis : A measured volume of the peroxide is run into a beaker, 
 and three or four drops of methyl orange added. As the H-O- is invariably 
 faintly acid, the acidity is carefully corrected by adding- drop by drop from a 
 pipette T T caustic soda. The required quantity of salt to be analyzed is 
 then added in solution, and the mixture gently boiled, during the boiling the 
 methyl orange will be bleached. The liquid is then cooled, a drop or two 
 more of methyl orange added, and the titration for the proportion of alkali 
 carried out with normal acid in the usual way. The results are very 
 satisfactory. 
 
 7. Estimation of Caustic Soda, or Potach by standard 
 Bichromate of Potash. 
 
 This process was devised by Richter, or rather the inverse of 
 it, for estimating bichromate with caustic alkali by the aid of 
 phenolphthalein. Exact results may be obtained by it in titrating 
 soda or potash as hydrates, but not ammonia as recommended 
 by Richter. 
 
 For the process there are required a decinormal solution of bichromate con- 
 taining 1474 gm. per liter, and ^ soda or potash solution titrated against 
 sulphuric acid. A comparison liquid containing about 1 gm. of monochro- 
 mate of potash in 150 200 c.c. water is advisable for ascertaining the exact 
 end of the reaction ; 50 c.c. of the alkali being diluted with the same volume 
 of water, is coloured with phenolphthalein, and the bichromate run in from 
 a burette ; the fine red tint changes to reddish yellow, which remains till 
 the neutral point is nearly reached, when the yellow colour of the mono- 
 chromate is produced; the change is not instantaneous as with mineral acids, 
 so that a little time must be allowed for the true colour to declare itself. 
 
 8. Estimation of Potash in Neutral Salts free from Soda. 
 
 Stolba precipitates the potash from a tolerably concentrated solution of 
 the substances with hydrofluosilicic acid and strong alcohol. The method is 
 also applicable to the estimation of potash in potassic platinum chloride. To 
 ensure complete decomposition, it is well to warm the mixture for a little 
 time before adding the alcohol, which must be of about the same volume as 
 the liquid itself. After some hours, when the precipitate has settled, the 
 solution is filtered off, the beaker and precipitate well washed with equal 
 mixtures of alcohol and water, the whole transferred to a white porcelain 
 basin, water rather freely added, and heated to boiling, a few drops of 
 litmus added, and normal or semi-normal alkali run in until exact 
 saturation occurs ; or a known excess of alkali may be added, and the amount 
 found by residual titration with normal acid. The results are generally 
 about 1' too low, owing to the difficulty of fully decomposing the pre- 
 cipitate. 
 
 2 eq. alkali = 1 eq. potash. 
 
 The process is very limited in its use, and is not applicable when 
 
17. ALKALINE SALTS. 61 
 
 sulphates are present, nor in the presence of any great amount of 
 free acid. Sulphuric acid may be previously removed by calcic 
 acetate and alcohol ; other acids by moderate ignition previous to 
 precipitation. Large proportions of ammonia salts must also be 
 removed ; and, of course, all other matters precipitable by hydro- 
 fluosilicic acid, especially soda. 
 
 9. Direct estimation of Potash in tb.e presence of Soda. 
 
 Fleischer recommends the following method; and my own 
 experiments confirm his statements, so far at least as the pure salts 
 are concerned. 
 
 The solution must contain no other bases except the alkalies, nor any acids 
 except nitric, hydrochloric, or acetic. This can almost invariably be easily 
 accomplished. Earthy alkalies are removed by ammonic carbonate or 
 phosphate ; sulphuric, chromic, phosphoric, and arsenic acids by baric 
 chloride, followed by ammonic carbonate. 
 
 The solution should be tolerably concentrated, and the volume about 25 or 
 30 c.c. ; 1015 c.c. of neutral solution of ammonic acetate of sp. gr. 
 T035 are added ; followed by finely powdered pure tartaric acid in sufficient 
 quantity to convert the potash into acid tartrate, with an excess to form some 
 ammonic tartrate, but not enough to decompose the whole. This is the weak 
 part of the method ; however, as a guide, it is not advisable to add more 
 than 5 gm. tartaric acid for 10 c.c. of ammonic acetate. If the quantity of 
 potash is approximately known, it is best to add about one-third more than 
 is sufficient to convert the whole into acid tartrate. 
 
 After adding the tartaric acid the mixture must be well stirred for five or 
 ten minutes, without rubbing the sides of the beaker; a like volume of 95 
 per-cent. alcohol is added, and again well stirred. The precipitate contains 
 the whole of the potash as tartrate, and a portion of ammonium tartrate. 
 After standing half an hour with occasional stirring, the precipitate is 
 collected on a porous filter, and repeatedly washed with alcohol and water in 
 equal parts until clean. 
 
 When the washing is finished the precipitate will be entirely free from 
 soda ; filter and precipitate are transferred to a porcelain basin, treated with 
 sufficient hot water to dissolve the tartrates, then exactly neutralized with 
 normal alkali and litmus, and the volume so used noted. A like volume, or 
 preferably, a larger known volume of normal alkali is now added, and the 
 mixture boiled to expel all ammonia ; the end may be known by holding 
 litmus paper in the steam. The excess of normal alkali is now found by 
 titration with normal acid ; the amount so found must be deducted from that 
 which was added in excess after the exact titration of the tartrate : the 
 difference equals the ammonia volatilized. By deducting this difference 
 from the volume of normal alkali originally required, the volume corre- 
 sponding to potash is found. 
 
 Example : 29'4 c.c. of normal alkali were required in the first instance to 
 neutralize a given precipitate ; 40 c.c. of the same alkali were then added, 
 the boiling accomplished, and 22'5 c.c. normal acid used for the excess ; then 
 40 22-5 = 17-5 c.c., and again 29'4 I7'5 = ir9, which multiplied by the 
 factor for KHO = 0'056 gives 0'6664 gm. 
 
 The soda in the nitrate may be obtained by evaporation with 
 hydrochloric acid as sodic chloride, and estimated as in 42. 
 
62 VOLUMETRIC ANALYSIS. 17. 
 
 10. Mixed Caustic Soda and Potash. 
 
 This process depends upon the fact, that potassic bitartrate is 
 almost insoluble in a solution of sodic bitartrate. 
 
 Add to the solution containing 1 the mixed salts a standard solution of 
 tartaric acid till neutral or faintl} 7 " acid this produces neutral tartrates 
 of the alkalies now add the same volume of standard tartaric acid as before 
 they are now acid tartrates, and the potassio bitartrate separates almost 
 completely, filter off the sodic bitartrate and titrate the filtrate with normal 
 caustic soda ; the quantity required equals the soda originally in the 
 mixture the quantity of tartaric acid required to form bitartrate with the 
 soda subtracted from the total quantity added to the mixture of the two 
 alkalies, gives the quantity required to form potassic bitartrate, and thus 
 the quantity of potash is found. 
 
 This process is only applicable for technical purposes. 
 
 Mixtures of potash and soda in the form of neutral chlorides are 
 estimated by J. T. White as follows (C. N. Ivii. 214) : 20 c.c. of the 
 solution containing about 0'2 gm. of the mixed salts are placed into 
 a 100 c.c. flask, and 5 c.c. of a hot saturated solution of ammoiiic bicarbonate 
 added ; the mixture is cooled, and alcohol added in small quantities, with 
 shaking, until the measure is made up to 100 c.c. After three or four hours, 
 10 c.c. of the clear liquid are removed with a pipette, evaporated and ignited, 
 the residue is moistened with a few drops of ammonic chloride solution 
 and again ignited; the sodic chloride so obtained is then titrated 
 with standard silver solution, 1 c.c. of which represents '001 gm. Cl ; this is 
 calculated to iSaCl and the KC1 found by difference. 
 
 11. Potash as Platino-chloride: 
 
 111 cases where potash exists in combination as a neutral salt, 
 such as kainit or kieserit, etc., or as a constituent of minerals, 
 it has to be first separated as double chloride of potassium and 
 platinum. The method usually adopted is that of collecting the 
 double salt upon a tared filter, when the weight of the dry double 
 salt is obtained, the w r eight of potash is ascertained by calculation. 
 
 It may, however, be arrived at by volumetric means as follows : 
 
 The potash having been converted into double chloride in the usual way 
 is dried, collected, and mixed with about double its weight of pure sodic 
 oxalate, and gently smelted in a platinum crucible ; this operation results in 
 the production of metallic platinum, chlorides of sodium and potassium,, 
 with some carbonate of soda. The quantity of potash present is, however,, 
 solely measured by the chlorine ; in order to arrive at this, the fused mass is 
 lixiviated with water, filtered, nearly neutralized with acetic acid, and the 
 chlorine estimated with -$ silver and chromate, the number of c.c. of silver 
 required is multiplied by the factor 0'00157, which gives at once the weight 
 of potash. This factor is used because 1 molecule of double chloride contains 
 3 atoms chlorine, hence the quantity of ^V silver used is three times as much 
 as in the case of sodic or potassic chloride. 
 
 L. de Koninck (Chem. Zeit. xix. 301) has improved this process 
 materially by the use of formic; acid as a reducing agent. The 
 chloroplatinate is filtered and washed in the usual way, dissolved in boiling 
 water and decomposed by calcic formate free from Cl. The liquid is heated 
 until the platinum is fully separated and the solution colourless; it is 
 neutralized with a small quantity of pure calcic carbonate, filtered, washed, 
 and the chlorine determined by titratiou with & silver solution and 
 chromate. 
 
17. ALKALINE COMPOUNDS. 63 
 
 12. Separation of the Potash as Bitartrate. 
 
 The mixed salts being rendered as nearly neutral as possible, a saturated 
 solution of sodic bitartrate is added in excess, and the whole evaporated to 
 dryness in the water bath. The dry mass is then deprived of the excess of 
 sodic bitartrate by washing it on a filter with a saturated solution of potassic 
 bitartrate ; when all the soda salt has been removed, the potash salt is 
 dissolved in hot water, and titrated with normal alkali, of which 1 c.c. 
 represents 0'039 gm. K. In cases where potash is to be separated as 
 bitartrate, the operator should consult 26, 2 and 3. 
 
 TECHNICAL EXAMINATION OF SOME ALKALINE 
 
 COMPOUNDS FOUND IN COMMERCE OH OCCURRING IN 
 
 COURSE OF MANUFACTURE. 
 
 There is now considerable unanimity among English and foreign 
 manufacturers of alkaline compounds, as to methods of analysis to 
 be adopted either for guidance in manufacture or commercial 
 valuation. Lunge has contributed important papers on the 
 subject (/. S. C. I. i. 12, 16, 55, 92), also in conjunction with 
 Hurter in the Alkali Makers' Pocket Book* which contains 
 valuable tables and processes of analysis. So far as volumetric- 
 methods are concerned, the same processes will be given here with 
 others. 
 
 13. Soda Ash, Black Ash, Mother-liquors, etc. 
 
 Soda Ash or Refined Alkali. 5 or 10 gm. are dissolved in about 150 c.c. 
 of warm distilled water, and any insoluble matter filtered off (German, 
 chemists do not filter), and the volume diluted to \ or 1 liter. 
 
 The total quantity of alkali is determined in 50 c.c. by normal sulphuric, 
 nitric, or hydrochloric acid, as in 17. l.f 
 
 The quantity of caustic alkali present in any sample is determined as 
 in 17. 2 or 5. 
 
 The presence of sulphides is ascertained by the smell of sulphuretted 
 hydrogen when the alkali is saturated with an acid, or by dipping paper, 
 steeped in sodic nitro-prusside into the solution : if the paper turns blue or 
 violet, sulphide is present. 
 
 The quantity of sulphide and sulphite may be determined by saturating 
 a dilute solution of the alkali with a slight excess of acetic acid, adding starch 
 and titrating with /^ iodine solution till the blue colour appears. The 
 quantity of iodine required is the measure of the sulphuretted hydrogen 
 and sulphurous acid present. 
 
 The proportion of sulphide is estimated as follows : 13'820 gm. of pure 
 silver are dissolved in dilute nitric acid, and the solution, together with an 
 excess of liquid ammonia, made up to a liter. Each c.c. 0'005 gm. Na 2 S. 
 
 The Analysis : 100 c.c. of the alkali liquor is heated to boiling, some 
 ammonia added, and the silver solution dropped in from a burette until no 
 further precipitate of Ag-S is produced. Towards the end filtration will be 
 necessary, in order to ascertain the exact point, to which end the Be ales 
 filter is serviceable (fig. 23). The amount of Na 2 S so found is deducted 
 from the total sulphide and sulphite found by iodine. 
 
 Sodic chloride (common salt) may be determined by carefully neutralizing 
 1 gin. of the alkali with nitric acid, and titrating 'with deciuormal silver 
 
 * Bell & Sons, York Street, Covent Garden. 
 
 f This gives a alight error, owing- to traces of aluminat3 of o;li ani lime, which 
 consume acid. 
 
<64= VOLUMETRIC ANALYSIS. 17. 
 
 solution and potassic chromate. Each c.o. represents 0'005837 gm. of 
 common salt. Since the quantity of acid necessary to neutralize the alkali 
 has already been found, the proper measure of T ^ nitric acid may at once 
 ,be added. 
 
 Sodic sulphate is determined, either directly or indirectl}% as in 76. 
 Each cc. of normal baric chloride is equal to 0*071 gm. of dry sodic 
 sulphate. 
 
 Examination of Crude Soda Lyes and Red Liquors. K aim aim 
 andSpiiller (Dingl. polyf. */., 264, 456 459) recommend a process based 
 on the insolubility of baric sulphite and the solubility of baric thiosulphate 
 in alkaline solutions. The estimation is performed in the following 
 manner: 1. The total alkalinity is determined in a measured volume of 
 'the liquor under examination by titration with normal acid, methyl orange 
 being used as indicator. The acid consumed equals sodic carbonate 4- sodio 
 sulphide, + sodic hydroxide, + one-half sodic sulphite (Na 2 SO 3 is alkaline 
 and NaHSO 3 neutral to methyl orange). 2. An equal volume of the 
 liquor is titrated with T \ solution of iodine, the volume consumed corres- 
 ponding with the sodic sulphide + the sodic sulphite, + the sodic 
 thiosulphate. 3. Twice the volume of liquor as that used in (1) and (2) 
 is precipitated with an alkaline zinc solution, and the mixture made up to 
 a certain measure, one-half of which is filtered, acidified, and titrated with 
 yV iodine. The iodine consumed equals sodic sulphite + sodic thiosulphate. 
 4. Three or four times the volume of liquor used in (1) and (2) is treated 
 with an excess of a solution of baric chloride, the mixture made up to 
 a known volume with water, and filtered, (a) One-third or one-fourth 
 (as the case may be) of the filtrate is titrated with normal acid, the amount 
 used corresponding with the sodic hydroxide + the sodic sulphite. 
 (b) A new third or fourth of the filtrate is acidified and titrated with -^ 
 iodine, the iodine consumed being equal to sodic sulphite + sodic thio- 
 .sulphate. The calculation is made as follows : 
 
 2 4i A c.c. ^ iodine corresponding to ... Na 2 SO 3 
 
 2 3 = B c.c. yV iodine corresponding to Na 2 S 
 
 46 (2 3) ... = C c.c. $ iodine corresponding to Na 2 S 2 O 3 
 
 4a r VB = D c.c. normal acid corresponding to ... NaOH 
 
 1 (4a + T V A) =E c.c. normal acid corresponding to ... Na' 2 CO 3 
 
 Black Ash. Digest 50 gm. with warm water in a half-liter flask, fill up to 
 mark, and allow to settle clear. 
 
 (1) Total Alkali existing as carbonate, hydrate, and sulphide, is found 
 by titrating 10 c.c. = l gm. of ash with standard acid and metlryl orange in 
 Ihe cold. 
 
 (2) Caustic Soda. 20 c.c. of the liquid are put into a 100 c.c. flask with 
 10 c.c. of solution of baric chloride of 10 per cent, strength, filled up with 
 hot water, well shaken, and corked after settling a few minutes. The clarified 
 liquid is filtered, and 50 c.c. = 1 gm. ash, titrated with standard acid and 
 metlryl orange ; or it may be titrated without filtration if standard oxalic 
 acid and phenolphthalein are used, this acid having no effect on the baric 
 carbonate. Each c.c. normal acid = 0'031 Na 2 0. This includes sulphides. 
 
 (3) Sodic Sulphide. Put 10 c.c. of liquor into a flask, acidulate with 
 acetic acid, dilute to about 200 c.c. and titrate with T ^ iodine and starch. 
 Each c.c. = 0-0039 Na 2 S, or 0'0031 Na 2 O. 
 
 (4) Sodic Chloride. 10 c.c. are neutralized exactly with normal nitric 
 acid, and boiled till all H-S is evaporated. Any sulphur which may have 
 been precipitated is filtered off, and the filtrate titrated with T N silver and 
 chromate. Each c.c. =0'00 5837 gm. NaCl. 
 
 (5) Sodic Sulphate. This is best estimated by precipitation as baric 
 .sulphate, and weighing, the quantity being small. If, however, volumetric 
 estimation is desired, it may be done as in 76, taking 50 c.c. of liquor. 
 
17. ALKALINE COMPOUNDS. 65 
 
 For other methods of examining the various solid and liquid 
 alkali wastes used for soda and sulphur recovery, etc., the reader is 
 referred to the Alkali Makers' Pocket Book already mentioned. 
 
 14. Salt Cake. 
 
 Is the impure sodic sulphate used in alkali manufacture or left in 
 the retorts in preparing hydrochloric acid from sulphuric acid and 
 salt, or nitric acid from sodic nitrate. It generally contains free 
 sulphuric acid existing as sodic bisulphate, the quantity of which 
 may be ascertained by direct titration with normal alkali. 
 
 The common salt present is estimated by decinormal silver solution and 
 chromate ; having first saturated the free acid with pure sodic carbonate, 
 1 c.c. silver solution is equal to 0'005837 gm. of salt. 
 
 Sulphuric acid, combined with soda, is estimated either directly or 
 indirectly as in 76 ; 1 c.c. of normal barium solution is equal to 0'07l gm. 
 or 0'71 grn. of dry sodic sulphate. 
 
 Iron is precipitated from a filtered solution of the salt cake with amtaonia 
 in excess, the precipitate of ferric, oxide re-dissolved in sulphuric acid, 
 reduced to the ferrous state with zinc and titrated with permanganate. 
 
 Grossman adopts a method suggested by Bohlig (see 32), 
 and has worked out the process in the case of salt cake in careful 
 detail (C. N. xli. 114) as follows : 
 
 The neutral solution of salt cake (3'55 gm.) is put into a 500 c.c. 
 flask, 250 c.c. of a cold saturated solution of baric hydrate added, 
 the flask filled with water, and shaken up. Of the filtered clear liquid 
 250 c.c. are put in an ordinary flask, carbonic acid passed through 
 for about ten minutes, and then the contents of the flask boiled so 
 as to decompose any baric bicarbonate which may be in solution. After 
 cooling, the contents of the flask are again transferred to the 500 c.c. 
 flask, the latter filled up with water to the mark, shaken up, and filtered. 
 250 c.c. of the filtrate i.e., one-fourth of the original quantity used are 
 then titrated with one-fourth normal sulphuric acid. The number of c.c. of 
 one-fourth normal acid used multiplied by two will give the percentage of 
 sodic sulphate. 
 
 There are, however, sources of error in the experimental working of this 
 method which make certain corrections necessary. They arise 
 
 (1) From the impurities of the caustic baryta. 
 
 (2) Prom the precipitate formed in the measured liquid. 
 
 (3) Prom certain constant losses. 
 
 The commercial caustic baryta always contains baric nitrate, and sometimes 
 baric chloride. It is evident that on adding a solution of baric hydrata 
 which contains baric nitrate to a solution of sodic sulphate, a quantity of the 
 latter, equivalent to the quantity of the baric nitrate present, will be 
 converted into sodic nitrate, and thus escape the alkalimetric test, as will be 
 seen by the following equations : 
 
 Ba(N O 3 ) 2 + Na 2 SO 4 =BaSO 4 + 2NaNO 3 . 
 Ba(NO 3 ) 2 +2NaOH + CO 2 =BaCO 3 +2NaN0 3 +H 2 O. 
 
 It is therefore necessary to measure approximately the quantity of baryta 
 solution used, so as to know the amount of baric nitrate introduced into the 
 process. The latter can be easily ascertained by passing carbonic acid in 
 excess through the cold saturated solution of baric hydrate, boiling, filtering, 
 and precipitating tke baryta left in solution by sulphuric acid as usual. 
 
 P 
 
66 VOLUMETRIC ANALYSIS. 17. 
 
 250 c.c. of a baryta solution used for experiment yielded 0*0280 gin. of BaSO 4 , 
 which corresponds to Q'0171 gni. of Na 2 S0 4 , or 0*96 c.c. of one-fourth normal 
 acid ; and it follows that for every 250 c.c. of this baryta solution was found 
 0-0171 gm. of Na 2 SO 4 too little ; or, that there must be added 0'24 c.c. of 
 one-fourth normal acid to the result of the final titration (of one-fourth of 
 the original quantity). If the baryta contain caustic alkali, a corresponding 
 quantity of baric nitrate will be found less by the test ; but it is easily 
 understood, that the calculations will not be influenced as long as the baric 
 nitrate is in excess of the caustic alkali, which is always the case in good 
 commercial baryta. 
 
 The second error arises from the precipitates of baric sulphate and carbonate 
 taking up some space in the 500 c.c. flask, the final results thus being found 
 too high. If it is assumed that a cold saturated solution of baryta contains 
 about 23 gm. of BaO per liter, it will be near enough for all practical purposes 
 if in the experiment, working with 3'55 gm. of Na-SO 4 and 250 c.c, of baryta 
 solution, 0'4 per cent, is subtracted from the final results for this error. 
 
 Three experiments made with 3' 55 gm. of pure ignited sodic sulphate gave 
 the following results : 
 
 Used one-fourth normal acid ... 49'37 c.c. 
 Add for Ba (NO 3 ) 2 0'24 c.c. 
 
 49*61 c.c. 
 =99-22 per cent. Na 2 SO 4 . 
 
 II. 
 
 Used one-fourth normal acid ... 49'21 c.c. 
 Add for Ba(NO 3 ) 2 0'24 c.c. 
 
 49-45 c.c. 
 =98*90 per cent. Na 2 SO 4 . 
 
 III. 
 
 Used one-fourth normal acid ... 49'37 c.c. 
 Add for Ba(NO 3 ) 2 0'24 c.c. 
 
 49-61 c.c. 
 =99'22 per cent. Na 2 SO 4 . 
 
 The average of these three experiments gives 99'1 per cent. ; and if 0"4 
 per cent, be subtracted for the precipitate, the result is 98'7 per cent, instead 
 of 100. 
 
 Grossman states that this loss of 1'3 per cent, in working with 3'55 gm. 
 of sulphate in the given dilution is a constant, and by dividing all results by 
 0'987 correct results are obtained. 
 
 It now remains to show the applicability of this method to the assay of 
 salt cake and like substances. The following is a complete analysis of a 
 sample of salt cake made in the usual way : 
 
 Moisture 0'49 
 
 Insoluble ... 0'29 
 
 Free sulphuric hydrate 0*38 
 
 Aluminium sulphate 0*23 
 
 Ferric sulphate 0'42 
 
 Calcic sulphate 1'17 
 
 Sodic chloride 2'00 
 
 Sodic sulphate (by difference) 95'02 
 
 lOO'OO 
 
17. ALKALINE COMPOUNDS. 67 
 
 In order to make a good analysis of salt cake by weight it is necessary to 
 estimate seven constituents, to find by difference the quantity of actual sodic 
 sulphate, which is the only constituent wanted. 
 
 When baric hydrate is added to a solution of salt cake the free acid is 
 precipitated, so are alumina and iron, and the sulphuric acid combined with 
 them and with lime. The lime is partly thrown down as such, and what is 
 left as lime in solution is precipitated as carbonate in the second operation. 
 Thus, whatever other sulphates be present, only the sodic sulphate is given; 
 and by one simple test we are thus able to get a result which formerly could 
 onh r be attained by a tedious complete analysis. 
 
 The salt cake, of which a complete analysis is given above, was tested by 
 the alkalimetric method. 3"55 gm. required 
 
 One-fourth normal acid 46'95 c.c. 
 
 Add for Ba(NO 3 ) 2 0'24 c.c. 
 
 47'19 c.c. 
 =94-38 per cent. Na 2 SO 4 . 
 
 (94-38 0-40)=93'98. 
 
 93-98 : 0-987=95-2 per cent. 1SVSO 4 . 
 
 Thus, by the alkalimetric test, 95*2 per cent, of JS"a 2 S0 4 occurs, 
 whereas the analysis gives 95 '02 per cent. If it be considered how 
 difficult it is to wash soda salts completely from precipitates, it is 
 not surprising to find the result too low in the complete analysis, 
 as in five precipitates a very minute quantity will make up 0*2 
 per cent. 
 
 It is hardly necessary to point out that none of the figures for 
 the correction of the errors enumerated above can be used by any 
 one else working by this method, but that they must be ascertained 
 in every individual case. It is absolutely necessary to ascertain 
 after the first operation that there is no sulphate, and after the 
 second (before titrating) that there is no baryta in solution. 
 
 15. Raw Salt, Brine, etc. 
 
 Lime may be estimated by precipitation with ammonic oxalate, and the 
 precipitate titrated with permanganate, as in 52. 
 
 Sulphuric acid as in 76. 
 
 Magnesia is precipitated as ammoniacal phosphate, by a solution of sodic 
 phosphate containing ammonia, first removing the lime by ammonic oxalate, 
 the precipitate of double phosphate of magnesia and ammonia is brought on 
 a filter, washed with cold water containing ammonia, then dissolved in acetic 
 acid, and titrated with standard uranium solution, or by the process for 
 P-0 5 ( 24). 
 
 The quantity of real salt in the sample may be ascertained by treating a 
 weighed quantity in solution with caustic baryta, boiling, setting aside that 
 the excess of baryta may precipitate itself as carbonate, or more quickly by 
 udding ammonic carbonate, filtering, evaporating the solution to dryness, and 
 gently igniting the residue is pure salt. The loss of weight between this 
 and the original specimen taken for analysis, will show the percentage of 
 impurities. 
 
 16. Silicates of Soda and Potash. 
 
 A weighed quantity of the substance is gently ignited, until no aqueous 
 vapours are given off, and the residue weighed thus the respective per- 
 centages of water and anhydrous material are obtained. 
 
 F 2 
 
68 VOLUMETRIC ANALYSIS. 17. 
 
 Another portion of the substance is dissolved in hot water, and titrated 
 with litmus and normal acid boiling, or with methyl orange after cooling. The 
 volume of acid is calculated to soda or potash. Solid alkaline silicates require 
 to be finely powdered previous to solution in hot water. 
 
 17. Soap. 
 
 The methods here given are a combination of those published 
 by A. R. Leeds (C. N. xlviii. 166) and C. R. A. Wright (Journ. 
 Soc. Arts, 1885, 1117, also J. S. C. I. iv. 631), and others. 
 
 (1) Moisture and Volatile Matters. 15 gin. are dried to a constant 
 weight, first at 100, then at 110 C. 
 
 (2) Free Fats. Residue of (1) is exhausted in a S o x h 1 e t tube, with light 
 petroleum ether, and the extract, after evaporation of the ether, weighed. 
 
 (3) Fatty Acids, Chlorides, Sulphates, G-lycerine, etc. The residue 
 from (2), w r hich has been treated with ether, represents 15 gm. soap ; it is 
 weighed, and two-thirds of it are dissolved in water, and normal nitric acid 
 added in excess to separate the fatty acids. These are collected on a tared 
 filter, dried, and weighed. The acid filtrate is now titrated with normal soda 
 or potash (free from chlorides or sulphates), with phenolphthalein as indicator ; 
 the difference between the volumes of acid and alkali used gives roughly the 
 total alkali. The residual neutral liquid is divided into two equal parts, in 
 one of which chlorine is estimated with T N ^ silver and chromate, and in the 
 other sulphuric acid by normal baric chloride. If glycerine is present, 
 it may be estimated by Muter's copper test in the absence of sugar. 
 Sugar is, however, often largely used in transparent soaps in place of 
 glycerine; when both are present, the separate estimation is difficult, but 
 "Wright suggests the method of Fehliug for the sugar, first inverting 
 with acid ; the copper retained in solution by the glycerine being estimated 
 colorimetrically, using for comparison a liquid containing both sugar and 
 glycerine to known extents, treated side by side with the sample tested. 
 
 (4) Free and Total Alkali. These are obtained by Wright's alcohol test. 
 Two or three grams of the soap are boiled with 95 per cent, alcohol, the extract 
 filtered off and residue washed with alcohol. The solution so obtained may 
 be either positively alkaline with caustic alkali, or negatively alkaline from 
 the presence of fatty acids or a diacid soap, according to the kind of soap 
 used. Phenolphthalein is added, which shows at once whether free alkali is 
 present, and in accordance with this either standard alcoholic acid or alkali is 
 used for titration. The residue on the filter is then dissolved in water, and 
 titrated Avith normal or decinormal acid ; the alkali so found may include 
 carbonate, silicate, borate, or aluminate of soda or potash, and also any 
 soluble lime. The sum of the two titrations will be the total alkalinity in 
 case both showed an alkaline reaction ; if otherwise, the alkali used to 
 produce a colour in the alcoholic extract is deducted from the volume of acid 
 used in the water extract. This method of taking the alkalinity of a soap 
 is very fairly exact; the error ought never to exceed _+ 0'5 per cent. 
 J. A. Wilson (C. N. lix. 280) states that the estimation of free caustic 
 alkali in high class soaps, containing no free glycerides, by the alcoholic 
 method is correct, but in the case of common commercial soaps it is 
 entirely misleading. 
 
 (5) Combined A IJcali Wilson (C. N. Ixiv. 205) proceeds as follows : 
 1. The alkali, in all forms, is determined by titration with standard acid in the 
 usual manner. 2. Another weighed quantity of the soap is decomposed in an 
 Erlenmeyer flask with a slight excess of dilute H 2 SO 4 , and the flask kept 
 on the water-bath till the fatty acids separate quite clear. The flask is then 
 placed in ice-water to cool, and then filtered. The fatty acids are washed three 
 times successively Avith 250 c.c. of boiling water and allowed to cool each time 
 
18. ALKALINE EARTHS. 69 
 
 uiid filtered. The united filtrates are diluted to 1 liter, and 500 c.c. placed 
 in a clear white beaker and tinted with methyl orange ; T ^ alkali is then 
 dropped in till the liquid acquires the usual colour, after which a little 
 phenolphthalein is added, and the addition of standard alkali continued till 
 a permanent pink is established. The number of c.c. used in the latter 
 titration are due to the soluble acids, and are calculated to caprylic acid. 
 The fatty acids in the flask, and any little on the filter are dried and 
 weighed, and then dissolved in alcohol, and titrated with | alcoholic alkali. 
 The alkali so used, together with that required for neutralization of the 
 soluble acids, and deducted from the total alkali, gives the alkali existing 
 In other forms than as soap. Of course, if desired, the soap may be 
 decomposed with standard H 2 SO 4 , and the alkali required to neutralize the 
 methyl orange noted, which, deducted from the total acid used, would give 
 the acid equivalent to the alkali existing in all forms. 
 
 The method of C. Hope is undoubtedly the quickest and best for the 
 examination of the alcoholic solution of soap. Two grams of soap are dissolved 
 in hot absolute alcohol, a drop of phenolphthalein indicator added, and some 
 bubbles of CO 2 passed through till the colour disappears. The liquid is 
 filtered ; the residue, consisting of total impurities, is washed with hot alcohol, 
 weighed and titrated with r \ acid and methyl orange, which gives the alkali 
 not existing as soap. The alcoholic solution is evaporated to dryness at 
 100 C. and the dry soap weighed. It is then gently ignited, dissolved in 
 water, and titrated with T ^- acid and methyl orange to find the alkali existing 
 as soap. The difference between this and the soap residue, before ignition, 
 gives the fatty anhydrides, which multiplied by 1*03 gives the fatty acids. 
 The water is found by deducting the weights of the impurities arid dry soap 
 from 100. Fuller information on this subject may be found in Allen's 
 Organic Analysis and in Lant Carpenter's treatise on Soap and Candles. 
 
 TITRATION OF AL.KALINE EARTHS. 
 
 18. STANDARD hydrochloric or nitric acid must in all cases be 
 used for the titration of the caustic or carbonated alkaline earths, as 
 these are the only acids yielding soluble compounds, except in the 
 case of magnesia. The hydrates, such as caustic lime, baryta, 
 strontia, or magnesia, may all be estimated by any of the indicators, 
 using the residual method, i.e., adding a known excess of standard 
 acid, boiling to expel any trace of CO 2 , and re-titrating with 
 standard alkali. 
 
 The carbonates of the same bases may of course also be 
 estimated in the same way, bearing in mind, that when methyl 
 orange is used, the liquid is best cooled before re-titration. All 
 heating may be avoided when using methyl orange in titrating 
 mixtures of hydrates and carbonates, or the latter only, unless it is 
 impossible to dissolve the substance in the cold. A good excess 
 of acid is generally sufficient. 
 
 The total amount of base in mixtures of caustic and carbonated 
 alkaline earths is also estimated in the same way. 
 
 (1) Estimation of Mixed Hydrates and Carbonates. This may 
 be done either by phenacetolin or phenolphthalein as indicator. 
 The former has been recommended byDegener and Lunge : the 
 method, however, requires practice in order to mark the 
 change of colour. 
 
70 VOLUMETRIC ANALYSIS. 18. 
 
 The liquid containing the compound in a fine state of division is tinted 
 with the indicator so as to be of a faint 3 T ellow; standard acid is then 
 cautiously added until a permanent pink occurs (at this stage all the hydrate 
 is saturated), more acid is now cautiously added until the colour becomes deep 
 yellow, the volume of acid so used represents the carbonate. 
 
 The method is especially adapted to mixtures of calcic hydrate 
 and carbonate. It is also applicable to barium, but not to 
 magnesium, owing to the great insolubility of magnesic hydrate in 
 dilute acid. If phenolphtlialein is used as indicator, the method 
 is as follows : 
 
 Heat the liquid to boiling, and cautiously add standard acid until the red 
 colour is just discharged. The carbonates of lime and baryta, rendered 
 dense by boiling, are both quite neutral to the indicator. To obtain the 
 whole of the base, excess of standard acid is used, and the mixture re-titrated 
 with standard alkali. 
 
 Magnesia in solution as bicarbonate may be accurately estimated 
 in the cold with methyl orange as indicator. 
 
 (2) Estimation of Calcium, Barium, Magnesium, and Strontium 
 in Neutral Soluble Salts. The amount of base in the chlorides and 
 nitrates of the alkaline earths may be readily estimated as 
 follows : 
 
 The weighed salt is dissolved in water, cautiously neutralized if acid or 
 alkaline, phenolphtlialein added, heated to boiling, and standard sodic 
 carbonate delivered in from time to time with boiling until the red colour 
 is permanent. 
 
 Magnesium salts cannot however be estimated in this way, 
 or even mixtures of lime and magnesia, as magnesic carbonate 
 affects the indicator in a different manner to the other carbonates. 
 
 (3) Precipitation of the Alkaline Earths from their Central Salts as 
 Carbonates. Soluble salts of lime, bar} T ta, and stroutia, such as chlorides, 
 nitrates, etc., are dissolved in water, and the base precipitated as carbonate, 
 with excess of ammonic carbonate and some free ammonia. The mixture is 
 heated to about 60 C. for a few 7 minutes. The precipitated carbonate is then 
 to be filtered, well washed with hot water till all soluble matters, especially 
 ammonia, are removed, and the precipitate with filter titrated with normal 
 acid, as already described. 
 
 Magnesia salts require caustic soda or potash instead of ammonic carbonate ; 
 but the process gives results slightly too low, owing to the slight solubility of 
 magnesic hydrate in the alkaline liquid. 
 
 (4) Lime and Magnesia Carbonates in Waters. The amount of calcic 
 or calcic and magnesic carbonates, dissolved in ordinary non- alkaline waters 
 may be very readily, and with accuracy, found by taking 200 or 300 c.c. 
 of the water, heating to near boiling, adding phenacetolin or lacmoid, and 
 titrating cautiously with T ^- nitric or sulphuric acid. An equally accurate 
 result may be obtained by methyl orange in the cold liquid. 
 
 (5) Magnesia. The magnesia existing in the commercial Stassfurt salts 
 used for manures, etc., and other soluble magnesia salts, may very readily 
 be determined with accuracy by Stolba's method, as given for P 2 O 5 in 
 24.2, or in all cases where separation can be made as ammonio-magnesic 
 
ALKALINE EAKTHS. 71 
 
 phosphate. The precipitation ma} 7 be hastened considerably by precipitating 
 with microcosmic salt, in the presence of a tolerably large proportion of 
 ammonic chloride, accompanied with vigorous stirring. Half an hour quite 
 suffices to bring down the whole of the double phosphate, and its adherence 
 to the sides of the beaker is of no consequence, if the titration is made in 
 the same beaker, and with the same glass rod, using an excess of standard 
 acid, and titrating back with weak standard ammonia and methyl orange. 
 
 The precipitate may also be titrated with standard uranium ( 72). 
 Precht (Z. a, C. 1879, 438) adopts the following method for soluble 
 magnesia salts in kaiuit, kieserit, etc., depending upon the insolubility of 
 magnesic hydrate in weak caustic potash : 
 
 10 gm. of the substance are dissolved, filtered, and mixed with 25 c.c. of 
 normal caustic potash, if it contains less than 50 per cent, of magnesic 
 sulphate ; or 50 c.c. if it contains more than 50 per cent. The mixture is 
 warmed somewhat, transferred to a 500 c.c. flask, and the volume made up 
 with water. After standing at rest for half an hour, 50 c.c. of the clear 
 liquid are withdrawn, and the excess of normal alkali estimated in the usual 
 way with normal acid. Ammonium and metallic salts must be absent. 
 
 1 c.c. normal potash 0'02 gm. MgO. 
 
 (6) Hardness of Water estimated without Soap Solution. As is 
 generally known, the soap-destroying power of a water is ascertained 
 in Clark's process by a standard solution of soap in weak alcohol, 
 titrated against a standard solution of calcic chloride. The 
 valuation is in so-called degrees, each degree being equal to I grain 
 of calcic carbonate, or its equivalent, in the imperial gallon. The 
 process is an old and familiar one, but open to many objections 
 from a scientific point of view. The scale of degrees is arbitrary, 
 and is seriously interfered with by the presence of varying 
 proportions of magnesia.. 
 
 We are indebted, primarily to Mohr, and subsequently to 
 Hehner, for an ingenious method of determining both the 
 temporary and permanent hardness of a water without the use 
 of soap solution. 
 
 The standard solutions required are -^ sodic carbonate and 
 -$ sulphuric acid. Each c.c. of standard acid exactly neutralizes 
 1 m.gm. of CaCO 3 , and each c.c. of the alkali precipitates the like 
 amount of CaCO 3 , or its equivalent in magnesia, in any given 
 water. 
 
 Process : 100 c.c. of the water are tinted with an indicator of suitable 
 character, heated to near boiling, and standard acid cautiously added until 
 the proper change of colour occurs. Hehner recommends phenacetolin ; 
 but my own experiments give the preference to lacmoid, which is also 
 commended by Thomson. Draper (C. N. li. 206) points out the value 
 of lacmoid and carminic acid for such a process, and I fully endorse his 
 opinion with respect to both indicators. Practice is desirable in order 
 to recognize the precise end-reaction. The number of c.c. of acid used 
 represents the number of Clark's degrees of temporary hardness per 100,000. 
 To obtain degrees per gallon, multiply the number of c.c. by 0'7. The 
 permanent hardness is ascertained by taking 100 c.c. of the water and adding 
 to it a rather large known excess of the standard sodic carbonate. The 
 quantity must of course be regulated by the amount of sulphates, chlorides, 
 or nitrates of lime and magnesia present in the water ; as a rule, a volume 
 
72 VOLUMETRIC ANALYSIS. 19. 
 
 equal to the water will more than suffice. Evaporate in a platinum dish to 
 dryness (glass or porcelain will not do, as they affect the hardness), then 
 extract the soluble portion with small quantities of distilled water, through 
 a very small filter, and titrate the filtrate with the standard acid for the 
 excess of sodic carbonate : the difference represents the permanent hardness. 
 
 Some waters contain alkaline carbonates, in which case there is 
 of course no permanent hardness, because the salts to which this is 
 clue are decomposed by the alkaline carbonate. In examining a 
 water of this kind, the temporary hardness will be shown to be 
 greater than it really is, owing to the alkaline carbonate ; and the 
 estimation for permanent hardness will show more sodic carbonate 
 than was actually added. If the difference so found is deducted 
 from the temporary hardness, as first noted, the remainder will be 
 the true temporary hardness. 
 
 AMMONIA. 
 
 19. IN estimating the strength of solutions of free ammonia 
 by the alkalimetric method, it is better to avoid the tedious process 
 of weighing any exact quantity, and to substitute for it the following 
 plan, which is applicable to most liquids for the purpose of 
 ascertaining both their absolute and specific weights. 
 
 Let a small and accurately tared flask, beaker, or other convenient vessel 
 be placed upon the balance, and into it 10 c.c. of the ammoniacal solution 
 delivered from a very accurately graduated 10 c.c. pipette. The weight 
 found is, of course, the absolute weight of the liquid in grams ; suppose it to 
 be 9'65 gm., move the decimal point one place to the left, and the specific 
 weight or gravity is at once given (water being 1), which in this case is 0'965. 
 
 It must be borne in mind that this system can only be used properly with 
 tolerably delicate balances and ver} r accurate pipettes. The latter should 
 invariably be tested by weighing distilled water at 16 C. 
 
 The 10 c.c. weighing 9'65 gm., are now mixed with water and titrated with 
 nesmal acid of which 49 c.c. are required, therefore 49 x 0'017=0'833 gm. NH 3 
 =8'64 per cent, of real ammonia; according to Otto's table 0'965 sp. gr. is 
 equal to 8'50 per cent. Ammonic carbonate, and a mixture of the same with 
 bicarbonate, as it most commonly occurs in commerce, may be titrated direct 
 with normal acid for the percentage of real ammonia, using methyl orange 
 as indicator. The carbonic acid can be determined by precipitating the 
 solution while hot with baric chloride, and when the precipitate is well 
 washed, dissolving it with an excess of normal acid and titrating backward 
 with normal alkali; the number of c.c. of acid used multiplied by 0'022 
 (the i mol. wt. of CO 2 ) will give the weight of carbonic acid present in 
 the sample. 
 
 1. Estimation of Combined Ammonia "by distillation with Alkalies 
 or Alkaline Earths. 
 
 This method allows of the expulsion of ammonia from all its 
 salts. Caustic soda, potash, or lime, may any of them be used 
 where no organic nitrogenous compound exists in the substance ; 
 
19. AMMONIA. 73 
 
 but should such be the case, it is preferable to use freshly ignited 
 magnesia. 
 
 The distilling apparatus may conveniently be arranged by con- 
 necting an ordinary well-stoppered small retort to a small Liebig 
 condenser, and leading the distilled gas into a vessel containing an 
 excess of normal acid. After the operation is ended, the excess 
 of acid is ascertained by residual titration with normal alkali or 
 ammonia, and thus the amount of displaced ammonia is found. 
 
 The retort must be so supported that its neck inclines well 
 upwards, in order that any alkali mechanically carried into it by 
 the spray which occurs during ebullition shall not reach the 
 condenser. An angle of about 30 suffices ; and in order that a 
 convenient connection may be made with the condenser, the end of 
 the retort is bent downward, and the connection securely made with 
 india-rubber tubing. In like manner, the end of the condenser is 
 elongated by a glass tube and india-rubber joint, so that the tube 
 dips into a two-necked bottle or bulb, containing the measured 
 normal acid ; the end of this tube should be cut obliquely, and 
 reach nearly, but not quite, to the surface of the acid. The outlet 
 of the receiver is fitted with a tube containing glass wool, broken 
 glass, or fibrous asbestos, wetted with a portion of the normal 
 acid, so that any traces of ammonia which may possibly escape 
 condensation in the bulk of the acid may be retained. 
 
 The retort containing the ammoniacal compound in solution 
 being securely fixed, and all the apparatus tightly connected, the 
 stopper of the retort is removed, and a strong solution of caustic 
 alkali, or, in case of compounds in which ammonia is quickly 
 released, pieces of solid alkali are rapidly introduced, the stopper 
 inserted, and the distillation forthwith commenced. Lime or 
 magnesia, suspended in water, must be added through a small 
 funnel ; the distillation is continued until the steam has washed all 
 traces of ammonia out of the condenser tube into the normal acid. 
 Cold water is of course run continuously through the condenser as 
 usual. Finally, the tubes connected with the receiver are well 
 washed out into the bulk of normal acid, methyl orange added, and 
 the titration completed with normal alkali or J ammonia. 
 
 Each c.c. of normal acid neutralized by the displaced ammonia 
 represents O'OIT gm. NH 3 . 
 
 The apparatus shown in fig. 28 is of great value in determining 
 accurately all the forms of ammonia which can be displaced by 
 soda, potash, or lime, and the gas so evolved collected in a known 
 volume in excess of normal acid, the excess of acid being after- 
 wards found by residual titration with normal alkali or ammonia. 
 
 Many modifications of this apparatus have been suggested, such 
 as the introduction of a condenser between the two flasks to cool 
 the distillate; another is the use of a (J tube containing some 
 standard acid in place of c. I do not find that any of these 
 modifications are required to secure accuracy, if the apparatus 
 
74 
 
 VOLUMETRIC ANALYSIS. 
 
 is tightly fitted. It is necessary that a bulb should exist in 
 the distilling tube, just above the cork of the distilling flask, 
 otherwise the spray from the boiling liquid is occasionally projected 
 into the tube, and is blown over with the condensed steam. 
 
 Fig. 28. 
 
 Another precaution is advisable where dilute liquids are boiled, 
 and much steam generated, that is, to immerse the condenser flask 
 in cold water. 
 
 The little flask, holding about 200 c.c. and placed upon the wire 
 gauze, contains the ammoniacal substance. The tube d is filled with strong 
 solution of caustic potash or soda. The large flask holds about half a liter, 
 and contains a measured quantity of normal acid, part being contained in 
 the tube c, which is filled with glass wool or broken glass, and through which 
 the normal acid has been poured. The stoppers of the flasks should be 
 caoutchouc, failing which, good corks soaked in > melted paraffin may be 
 used. 
 
 The substance to be examined is weighed or measured, and put into the 
 distilling flask with a little water, the apparatus then being made tight at 
 every part; some of the caustic alkali is allowed to flow in by opening the 
 clip, and the gas or spirit lamp is lighted under it. 
 
19. AMMONIA. 75 
 
 The contents are brought to gentle boiling, taking care that the froth, if 
 any, does not enter the distilling tube. It is well to use a movable gas 
 burner or common spirit lamp held under the flask in the hand ; in case 
 there is any tendency to boil over, the heat can be removed immediately, and 
 the flask blown upon by the breath, which reduces the pressure in a moment. 
 In examining guano and other substances containing ammouiacal salts and 
 organic matter by this means, the tendency to frothing is considerable; and 
 unless the above precautions are taken, the accuracy of the results will be 
 interfered with. A small piece of bee's wax or solid paraffin is very 
 serviceable in allaying the froth. 
 
 The distilling tube has both ends cut obliquely ; and the lower end nearlv, 
 but not quite, reaches to the surface of the acid, to which a little methyl 
 orange may be added. The quantity of normal acid used must, of course, be 
 more than sufficient to combine with the ammonia produced ; the excess is 
 afterwards ascertained by titration with normal alkali or ^ ammonia. 
 
 It is advisable to continue the boiling for say ten or fifteen minutes, 
 waiting a minute or two to allow all the ammonia to be absorbed ; then opening 
 the clip, blow through the pipette so as to force all the remaining gas into 
 the acid flask. The tube c must be thoroughly washed out into the flask 
 with distilled water, so as to carry down the acid with any combined gas which 
 may have reached it. The titration then proceeds as usual. This process 
 is particularly serviceable for testing commercial ammouiacal salts, gas 
 liquor, etc. (see below). The results are extremely accurate. 
 
 2. Indirect Method. 
 
 In the case of tolerably pure ammoniacal salts or liquids, free 
 from acid, or in which the free acid is previously estimated, 
 a simple indirect method can be used, as follows : 
 
 If the ammoniacal salt be boiled in an open vessel with normal caustic 
 alkali, the ammonia is entirely set free, leaving its acid combined with the 
 fixed alkali. If, therefore, the quantity of alkaline solution is known, the 
 excess beyond that, necessary to supplant the ammonia, may be found by 
 titration with standard acid. The boiling of the mixture must be continued 
 till a piece of red litmus paper, held in the steam from the flask, is no longer 
 turned blue. 
 
 Example : 1*5 gm. of purest sublimed ammonic chloride was placed in a 
 wide-mouthed flask with 40 c.c. of normal soda, and boiled till all ammonia 
 was expelled, then titrated back with normal sulphuric acid, of which 
 11'9 c.c. were required; 28'1 c.c. of normal alkali had therefore been 
 neutralized, which multiplied by 0'05337, the factor for ammonic chloride, 
 gave T499 gm., instead of 1'5 gm. originally taken. 
 
 3. Technical Analysis of Gras Liquor, Sulphate of Ammonia, Sal 
 Ammoniac, etc., arranged for the use of Manufacturers. 
 
 This process depends upon the fact, that when ammoniacal salts 
 are heated with caustic soda, potash, or lime, the whole of the 
 ammonia is expelled in a free state, and may by a suitable apparatus 
 (fig. 29) be estimated with extreme accuracy (see 19. 1). 
 
 The set of apparatus here described consists of a distilling flask 
 B, and condensing flask F, fitted together in such a manner, that no 
 loss of free ammonia can occur ; the whole of the ammonia being 
 liberated from the distilling flask into a measured quantity of free 
 
76 VOLUMETRIC ANALYSIS. 19. 
 
 acid contained in the condensing flask, where its amount is after- 
 wards found by the method hereinafter described. 
 
 Analysis of Gas Liquor. This liquid consists of a solution of 
 carbonates, sulphates, hyposulphites, sulphides, cyanides, and other 
 salts of ammonia. The object of the ammonia manufacturer is to 
 get all these out of his liquor into the form of sulphate or chloride 
 as economically as possible. The whole of the ammonia existing 
 as free or carbonate in the liquor, can be distilled off at a steam 
 heat ; the fixed salts, however, require to be heated with soda, 
 potash, or lime (the latter is generally used on a large scale as most 
 economical), in order to liberate the ammonia contained in them. 
 
 The valuation of gas liquor is almost universally made in Great 
 Britain by Twaddle's hydrometer, every degree of which is taken 
 to represent what is technically called "two-ounce strength;" that is 
 to say, a gallon of such liquor should neutralize exactly two ounces by 
 weight of concentrated oil of vitriol thus 5 degrees, Twaddle, is 
 called " ten-ounce " liquor but experiment has clearly proved, that 
 although the hydrometer may be generally a very convenient 
 indicator of the commercial value of gas liquor, it is not accurate 
 enough for the manufacturer who desires to work with the utmost 
 economy. Sometimes the liquor contains a good deal of free 
 ammonia, and in such case the hydrometer would show it to be 
 weaker than it really is ; on the other hand, sometimes, from 
 accidental causes, other solid matters than ammonia salts occur in 
 the liquor, and the hydrometer shows it to be stronger than it really 
 is. The method of saturation, by mixing standard acid with the 
 liquor, is perhaps more correct than the hydrometer; but this 
 system is entirely at fault in the presence of much fixed ammonia, 
 and is, moreover, a very offensive and poisonous operation. 
 
 The apparatus here described is exactly the same on a small 
 scale as is necessary in the actual manufacture of sulphate of 
 ammonia in quantities ; and its use enables any manufacturer to 
 tell to a fraction how much sulphate of ammonia he ought to 
 obtain from any given quantity of gas liquor. It also enables him 
 to tell exactly how much ammonia can be distilled off with heat 
 alone, and how much exists in a fixed condition requiring lime. 
 
 The measures used in this process are on the metrical system ; 
 the use of these may, perhaps, at first sight appear strange to 
 English manufacturers ; but as the only object of the process is to 
 obtain the percentage of ammonia in any given substance, it is 
 a matter of no importance which system of measures or weights is 
 used, as when once the percentage is obtained, the tables will at 
 once show the result in English terms of weight or measure. 
 
 a is a small pipette, holding 10 cubic centimeters to the mark in neck : 
 this is the invariable quantity of liquor used for the analysis, whatever the 
 strength may be. This measure is filled to the mark by suction and 
 transferred, without spilling a drop, to flask B the fittings being previously 
 
UJ 
 
78 VOLUMETRIC ANALYSIS. 19. 
 
 removed the tube C is then filled in the same manner, with strong 
 caustic soda solution from a clean cup or other vessel, in order to do 
 which, the clip at the top must be opened : the cork is then replaced, and 
 the flask B is then securely imbedded in perfectly dry sand, in the sand- 
 bath D. The graduated pipette E is then filled in the same manner to 
 the O mark, with standard acid, and 20, 30, 40, or 50 c.c. (according 
 to the estimated strength of the liquor) allowed to flow into the flask P, 
 through the cup G, which is filled with broken glass placed on a layer of 
 glass wool or fibrous asbestos. The broken glass should be completely 
 wetted with the acid, so that any vapours of ammonia which may escape 
 the acid in the flask shall become absorbed by the acid. The quantity 
 of standard acid to be used is regulated by the approximately known 
 strength of the liquor, which of course can be told by Twaddle's 
 hydrometer: thus, for a liquor of 3 C Twaddle=6-oz. liquor, 20 c.c. 
 8-oz., 25 c.c. 10-oz., 30 c.c. of acid will be sufficient but there must 
 always be an excess. The required quantity can always be approx- 
 imately known, since every 10 c.c. of acid represents 1 per cent, of 
 ammonia. The standard acid having been carefully passed through G, 
 the apparatus is fitted together at H by the elastic tube, and the india-rubber 
 stoppers securely inserted in both flasks; this being done, the lamp is 
 lighted under the sand-bath, and at the same time the spring-clip on C is 
 pressed, so as to allow about two-thirds of the caustic soda to flow into B ; 
 the rest will gradually empty itself during the boiling. The heat is continued 
 to boiling, and allowed to go on till the greater bulk of the liquid in B 
 is boiled away into P. A quarter of an hour is generally sufficient for this 
 purpose, but if the boiling is continued till the liquid in B just covers the 
 bottom of the flask, all the ammonia will have gone over to P; during 
 the whole operation the distilling tube must never dip into the acid in P. 
 In order to get rid of the last traces of ammonia vapour out of B, the lamp 
 is removed, and the mouth being applied to the tube over the spring-clip, 
 the latter is opened, and a good blast of air immediately blown through. 
 The apparatus may then be detached at H ; distilled or good boiled drinking 
 water is then poured repeatedly through G in small quantities, till all traces of 
 acid are removed into flask P. This latter now contains all the ammonia out of 
 the sample of liquor, with an excess of acid, and it is necessar} r now to find out 
 the quantity of acid in excess. This is done by means of the burette I, and 
 the standard solution of soda, w : hich soda is of exactly the same strength as 
 the standard acid. In order to find out how much of the standard acid has been 
 neutralized by the ammonia in the liquor distilled, the burette I is filled to 
 with standard soda, and one drop of methyl orange, or a sufficiency of any 
 other indicator, other than phenolphthalein, being added to the cooled contents 
 of flask P, the soda is slowly dropped into it from the burette, with constant 
 shaking, until the indicator changes colour. The number of c.c. of soda so 
 used, deducted from the number of c.c. of standard acid used, will show 
 the number neutralized by the ammonia in the liquor distilled ; therefore, if 
 the number of c.c. of soda used to destroy the pink colour be deducted 
 from the number of c.c. of standard acid originally used, it will show the 
 number of c.c. of standard acid neutralized by the ammonia, which has been 
 distilled out of the liquor, and the strength of the solutions is so arranged 
 that this is shown without any calculation. The following examples will 
 suffice to show this : Suppose that a liquor is to be examined which marks 
 5 Twiddle, equal to 10-ounce liquor ; 10 c.c. of it are distilled into 30 c.c. 
 of the standard acid, and it has afterwards required 6 c.c. of standard 
 soda to neutralize it ; this leaves 24 c.c. as the volume of acid saturated 
 by the distilled ammonia, and this represents 2'4 per cent. ; and on referring 
 to the table it is found that this number corresponds to a trifle more than 
 11 ounces, the actual figures being 2*384 per cent, for 11 ounce strength. 
 
 The strength of the standard soda and acid solutions is so 
 
19. AMMONIA. 79 
 
 arranged, that when 10 c.c. of liquor are distilled, every 10 c.c. of 
 acid solution represents 1 per cent, of ammonia in the liquor. In. 
 like manner 13 c.c. of acid will represent 1'3 per cent, of ammonia 
 corresponding to 6-ounce liquor. 
 
 The burette is divided into tenths of a cubic centimeter, and 
 those who are familiar with decimal calculations can work out the 
 results to the utmost point of accuracy ; the calculation being, that 
 every 1 per cent, of ammonia requires 4 '61 ounces of concentrated 
 oil of vitriol (sp. gr. 1 *S45) per gallon, to convert it into sulphate : 
 thus, suppose that 10 c.c. of any given liquor have been distilled, 
 and the quantity of acid required amounts to 18 '6 c.c., this is 
 1*86 per cent., and the ounce strength is shown in ounces and 
 decimal parts as follows : 
 
 4-61 
 1-86 
 
 2766 
 3688 
 461 
 
 8 '5746 ounces of oil of vitriol. 
 
 The liquor is therefore a trifle over 8|-ounce strength. 
 
 Spent Liquors. It is frequently necessary to ascertain the 
 percentage of ammonia in spent liquors, to see if the workmen 
 have extracted all the available ammonia. In this case the same 
 measure, 10 c.c. of the spent liquor, is taken, and the operation 
 conducted precisely as in the case of a gas liquor. 
 
 Example : 10 c.c. of a spent liquor were distilled, and found to neutralize 
 3 c.c. of acid : this represents three-tenths of a per-cent. equal to 1-oz. and 
 four-tenths of an ounce, or nearly 1 oz. Such a liquor is too valuable to 
 throw away, and should be worked longer to extract more ammonia. 
 
 Process for Sulphate of Ammonia or Sal Ammoniac : An average 
 sample of the salt being drawn, ten grams are weighed, transferred without 
 loss to a beaker or a flask having a 100 c.c. mark upon it, distilled or boiled 
 drinking water poured on it, and well stirred till dissolved, and finally 
 water added exactly to the mark. The 10 c.c. measure is then filled with 
 the solution, and emptied into the distilling flask B ; 30 c.c. of standard 
 acid are put into flask E and the distillation carried on precisely as in 
 the case of a gas liquor. The number of c.c. of standard acid required 
 shows directly the percentage of ammonia ; thus, if 24*6 c.c. are used in 
 the case of sulphate, it contains 24'6 per cent, of ammonia. 
 
 The liquors when tested must be measured at ordinary tempera- 
 tures, say as near to 60 F. as possible. The standard solutions 
 must be kept closely stoppered and in a cool place. 
 
 The following table is given to avoid calculations ; of course, it 
 will be understood that the figures given are on the assumption 
 that the whole of the ammonia contained in the liquor is extracted 
 
80 
 
 VQLUMETKIC ANALYSIS. 
 
 19. 
 
 in the manufacture as closely as it is in the experiment. With the 
 most perfect arrangement of plant, however, this does not as a rule 
 take place ; but it ought to be very near the mark with proper 
 apparatus, and care on the part of workmen. 
 
 Approxi- 
 mate 
 measure of 
 Standard 
 Acid in c.c. 
 
 Percentage 
 of Ammonia 
 NH3 
 
 Ounce 
 strength 
 pei- 
 gallon. 
 
 Weight of Sulphuric Acid in pounds 
 and decimal parts required for each 
 gallon of liquor. 
 
 Yield of 
 Sulphate 
 per gallon in 
 Ibs. and 
 decimal 
 
 C. O. V. 
 
 T> n \r Chamber 
 U< V- AnirJ 
 
 and tenths. 
 
 
 
 169 Tw. 
 
 144, Tw ACIO. 
 Iw - 120= Tw. 
 
 parts. 
 
 2-2 
 
 2168 
 
 1 
 
 0625 '0781 
 
 0893 
 
 0841 
 
 4'3 
 
 4336 
 
 2 
 
 1250 
 
 1562 
 
 1786 
 
 1682 
 
 6-5 
 
 6504 
 
 3 
 
 1875 
 
 2343 
 
 2679 
 
 2523 
 
 87 '8672 
 
 4 
 
 2500 
 
 3124 
 
 3572 
 
 3364 
 
 lO'l 1-0840 
 
 5 
 
 3125 
 
 3905 
 
 4465 
 
 4205 
 
 13'0 1-3000 
 
 6 
 
 3750 
 
 4686 
 
 '5358 
 
 5046 
 
 15-2 1-5176 
 
 7 
 
 4375 
 
 5467 
 
 6251 
 
 5887 
 
 17-3 
 
 17344 
 
 8 
 
 5000 
 
 6248 
 
 7144 
 
 6728 
 
 19-5 
 
 1-9512 ; 9 
 
 5625 
 
 7029 
 
 8037 
 
 7569 
 
 21-7 
 
 2-1680 
 
 10 
 
 6260 
 
 7810 
 
 8930 
 
 8410 
 
 23-8 
 
 2-3840 
 
 11 
 
 6875 
 
 8591 
 
 9823 
 
 9251 
 
 26-0 
 
 2-6016 
 
 12 
 
 7600 
 
 9372 
 
 1-0716 
 
 1-0092 
 
 28-2 
 
 2-8184 
 
 13 
 
 8125 
 
 1-0153 
 
 1-1609 
 
 1-0933 
 
 30-4 
 
 3-0350 
 
 14 
 
 8750 
 
 1-0934 
 
 1-2502 
 
 1-1774 
 
 32-5 
 
 3-2520 
 
 15 
 
 9375 
 
 1-1715 i 1-3395 
 
 1-2615 
 
 34-7 
 
 3-4688 
 
 16 I'OOOO 
 
 1-2496 1-4288 
 
 1-3456 
 
 36-9 
 
 3-6856 
 
 17 1-0625 
 
 1-3277 
 
 1-5181 
 
 1-4297 
 
 39-0 
 
 3-9024 
 
 18 1-1250 
 
 1-4058 
 
 1-6074 
 
 T5138 
 
 41-2 
 
 4-1192 
 
 19 
 
 T1875 
 
 1-4839 
 
 1-6967 
 
 1-5979 
 
 43'3 
 
 4-3360 
 
 20 
 
 1-2500 
 
 1-5620 ! 1-7860 
 
 1-6820 
 
 The weight of sulphuric acid being given in decimals renders it 
 very easy to arrive at the weight necessary for every thousand 
 gallons of liquor, by simply moving the decimal point ; thus 8-oz. 
 liquor would require 500 Ibs. of concentrated oil of vitriol, 625 Ibs. 
 of brown oil of vitriol, or 714J Ibs. chamber acid for every 1000 
 gallons, and should yield in all cases 672*8 (say 673) Ibs. of 
 sulphate. 
 
 4. Combined Nitrog-en in Organic Substances. 
 
 The old-fashioned process consists in heating the dried substance 
 in a combustion tube with soda lime, by which the nitrogen is con- 
 verted into ammonia; and this latter being led into a measured 
 volume of normal acid contained in a suitable bulb apparatus, 
 combines with its equivalent quantity ; the solution is then 
 titrated resiclually with standard alkali for the excess of acid, 
 and thus the quantity of ammonia found. 
 
 As the combustion tube with its arrangements for organic 
 analysis is well known, and described in any of the standard books 
 on general analysis, it is not necessary to give a description here. 
 
19. AMMONIA. 
 
 5. Kjeldahl's Method. 
 
 This has met with considerable acceptance in lieu of the 
 combustion method, on account of its easy management and 
 accurate results. Unlike the combustion method, the ammonia is 
 obtained free from organic matters or colour, and moreover salts of 
 ammonia and nitrates may be estimated with extreme accuracy. 
 It was first described by Kjeldahl (Z. a. C. xxii. 366), and has 
 since been commented upon by many operators, among whom are 
 Warington (G. N. lii. 162), Pfeiffer and Lehmann (Z. a. C. 
 xxiv. 388), Marcker and others (Z. a. C. xxiii. 553; xxiv. 
 199,393; xxv. 149, 155; xxvi. 92; xxvii. 222, 398); Gunning 
 (idem xxviii. 188); Arnold and Wedermeyer (idem xxxi. 525); 
 and recently by Bernard Dyer (J. C. S. Ixvii.-viii. 811). 
 
 The original process consisted in heating the nitrogenous substance 
 in a flask, with concentrated sulphuric acid, to its boiling point, 
 and when the oxidation through the agency of the acid is nearly 
 completed, adding finely powdered permanganate of potash in small 
 quantities till a green or pink colour remains constant ; the whole 
 of the nitrogen is thus converted into ammonic sulphate. The 
 flask is then cooled, diluted with water somewhat, excess of 
 caustic soda added, the ammonia distilled off' into standard acid, 
 and the amount found by titration in the usual way. 
 
 Some practical difficulties occurred in the process as originally 
 devised; and, moreover, with some organic substances a very 
 long time was required to destroy the carbon set free by the 
 strong acid. 
 
 Another difficulty was, that if nitrates were present in the 
 compound analyzed their reduction to ammonia was not certain nor 
 regular, and unless this difficulty could be overcome the value of 
 the process was limited. 
 
 The experience of many hundreds of operators since this 
 method was first introduced has resulted in rendering it as perfect 
 as need be, and the results of this experience in all essential 
 particulars will -now be described, omitting the details as to some 
 of the special forms of apparatus, and which are not absolutely 
 essential. The method requires the following re-agents and 
 apparatus : 
 
 1 . Standard acid, which may be either sulphuric or hydrochloric ; 
 a convenient strength is semi-normal. 
 
 2. Standard alkali, either ammonia, soda, or potash, of corres- 
 ponding strength to the acid. 
 
 3. Concentrated sulphuric acid free from nitrates and ammonic 
 sulphate.* 
 
 * Commercial oil of vitriol frequently contains ammonia, owing to the fact that 
 makers sometimes add ammonic sulphate during concentration in order to get rid of 
 nitrous compounds. Meldola and Moritz state that any traces of ammonia may be 
 destroyed by digesting the acid for two or three hours at a temperature below boiling 
 
 G 
 
82 VOLUMETRIC ANALYSIS. J 9. 
 
 4. Mercuric oxide prepared in the wet way or metallic 
 mercury. 
 
 5. Powdered potassic sulphate. 
 
 6. Granulated zinc. 
 
 7. Solution of potassic sulphide in water, 40 gm. in the 
 liter. 
 
 8. A saturated solution of caustic soda free from nitrates or 
 nitrites. 
 
 9. An indicator litmus, methyl orange, or cochineal are 
 suitable, but any other except phenolphthalein may be used. 
 
 10. Digestion flasks with long neck and round bottom, holding 
 about 200 250 c.c. These flasks should be well annealed and 
 not too thick, preferably made of Jena glass the neck about 
 -f inch wide, and 3| 4 inches long. 
 
 1 1 . Distillation flasks of hard Bohemian glass and Erlenmeyer 
 pattern, 550 600 c.c. capacity, fitted with a rubber stopper and 
 a bulb above with curved delivery tube, to prevent the spray of 
 the boiling alkaline liquid from being carried over into the 
 condenser tubes. Copper distilling bottles or flasks are used by 
 some operators for technical purposes with good results, but in this 
 case it is advisable to put the soda into the vessel first then add 
 the acid liquid. 
 
 12. The condenser. Owing to the undoubted solubility of 
 glass in fresh distilled water containing ammonia, it is advisable to 
 have the condenser tube made of block tin. This should be about 
 three-eighths of an inch wide externally, and is connected with the 
 bulb tube of the distilling flask with stout pure rubber tube. It is 
 surrounded by either a metal or glass casing, through which 
 cold water is passing in the usual manner. It is very easy to 
 fit up such an arrangement with the condenser tubes made 
 entirely of glass sold by the dealers in chemical apparatus. The 
 end of the condenser tube may be simply inserted into the neck 
 of a flask in an oblique position, containing the standard acid, 
 or it may have a delivery tube connected by rubber leading 
 into a beaker. There is no necessity for dipping the delivery 
 tube into the acid unless the temperature of the place is 
 very high. 
 
 In places where it is difficult to arrange for a flow of water to 
 keep the distilling tube cool the simple apparatus shown in fig. 30 
 may be serviceable, and unless the temperature of the place is 
 exceedingly high there is no loss of ammonia, This arrangement 
 is used by Stutzer, whose results with it compare well 
 
 with sodic or potassic nitrite in the proportion of 0'5 gm. of the salt to 100 c.c. of 
 acid. Lunge objected to this treatment, because of the probable formation of nitro- 
 sulphuric acid. Experiments have since been made by Mori tz which prove that the 
 objection is groundless, provided the digestion is carried on for a period sufficient to 
 expel the nitrous acid (J. S. C. I. ix. 443). The purification of the acid may of course 
 be obviated by ascertaining once for all the amount of ammonia in any given stock of 
 acid, by making a blank experiment with pure sugar and allowing in all cases for the 
 amount of NH-i so found. 
 
19. AMMONIA.. 83 
 
 with others made in condensers surrounded by flowing 
 
 water ; and equally 
 accurate figures 
 have been got in 
 comparison with 
 the ordinary con- 
 denser, using the 
 same quantity of 
 substance for 
 digestion. The 
 explanation of this 
 is, no doubt, the 
 very strong affinity 
 of ammonia for 
 Tig. 30. water, and when 
 
 in very minute 
 
 quantity it is held very tenaciously, even at a tolerably high 
 temperature. The tube should be not less than 3 feet long. 
 Where a large number of estimations are being carried on it is 
 convenient to have a special condenser, which will allow of six 
 or more distillations being worked at the same time. Several 
 forms of such arrangements have been devised, and are obtainable 
 of the apparatus dealers. 
 
 For use in my own laboratory where a large number of agricul- 
 tural samples are examined, the form shown in fig. 31 has been 
 adopted, and has been found to answer well. The body of the 
 condenser consists of an ordinary 10-gallon iron drum filled AA 7 ith 
 water; the block tin distilling tubes run through this at equal 
 distances from each other, and emerge at the bottom of sufficient 
 length to dip into the vessels containing the standard acid. With 
 this arrangement there is no necessity for running water, and six 
 distillations may be carried on simultaneously without fear of 
 losing ammonia ; the body of water is so great that the lower 
 portion is quite cool after the distillations are finished. In case 
 of extremely hot weather or in a very hot laboratory, the cover 
 may be removed and a lump of ice placed in the water, if a large 
 number of distillations are required. 
 
 The distilling flasks are closed with rubber stoppers, and fitted 
 with ball top arrangement shown more plainly in fig. 30.* These 
 are connected with the tin tubes by rubber joints, and supported on 
 an iron frame over which is laid a strip of wire gauze. The Bunsen 
 burners are of Fletcher's make, with nickel gauze tops which 
 give a smokeless flame of any desired size. So well does this 
 arrangement work, that during many hundreds of distillations not 
 one breakage has occurred, due to the heating or the distillation. 
 The tin condensing tubes do not in this case dip into the standard 
 acid, as various experiments have proved it unnecessary. 
 
 *These may be had of Gerhard t, Bonn, and probably of other apparatus dealers. 
 
 G 2 
 
84 
 
 VOLUMETRIC ANALYSIS. 
 
 19. 
 
 Dyer uses a block tin condensing tube rising 15 18 inches 
 vertically from the distilling flask with no condenser, but bent 
 
 Pig. 31. 
 
 downwards and fitting into a pear-shaped adapter (with large 
 expansion to allow of varied pressure), whose narrowed end dips 
 actually into the acid. 
 
 13. " A convenient stand for 
 holding the digestion flasks is shown 
 in fig. 32, and they rest in an 
 oblique position. Heat is supplied 
 by small Buns en burners. With 
 a little care the naked flame can be 
 applied directly to the flask with- 
 out danger. Some operators prefer 
 to close the digestion flasks with 
 a loosely fitting glass stopper 
 elongated to a point, and having 
 a balloon-shaped top. This aids in the condensation of any acid 
 
 rig. 32. 
 
19. AMMONIA. 85 
 
 which may distil, but if the flasks are tolerably long in the neck, 
 there is practically no loss of acid except as SO 2 which occurs in 
 any case. It is almost needless to say that the digestion should be 
 done in a fume closet with good draught. 
 
 The Kjeldahl-Grunning Process : From 05 to 5 gm. of the substance 
 according to its nature is brought into a digestion flask with approximately 
 O'o gm. of mercuric oxide or a small globule of metal and 20 c.c. of 
 sulphuric acid (in case of bulky vegetable substances 30 c.c. or more may 
 be necessary). The flask is placed on wire gauze over a small Bun sen 
 burner in an upright position, or in the frame above described in an inclined 
 position, and heated below the boiling-point of the acid for from five to 
 fifteen minutes, or until frothing has ceased. The heat is then raised till 
 the acid boils briskly, this is continued for about fifteen minutes, when 
 about 10 grams of potassic sulphate are added, and the boiling continued. 
 No further attention is required till the contents of the flask have become 
 a clear liquid, which is colourless, or at least has only a very pale straw 
 colour. The flask is then removed from the frame, and after cooling, the 
 contents are transferred to the distilling flask with repeated quantities of 
 water amounting in all to about 250 c.c., and to this 25 c.c. of potassic 
 sulphide solution are added, 50 c.c. of the soda solution*, or sufficient to 
 make the reaction strongly alkaline, and a few pieces of granulated zinc. 
 The flask is at once connected with the condenser, and the contents are 
 distilled till all ammonia has passed over into the standard acid, and the con- 
 centrated solution can no longer be safely boiled. This operation usually 
 requires from twenty to thirty minutes. The distillate is then titrated with 
 standard alkali. 
 
 The use of mercury or its oxide in this operation greatly shortens the 
 time necessary for digestion, which is rarely over an hour, and in the case 
 of substances most difficult to oxidize, is more commonly less than an 
 hour. Potassic sulphide removes all mercury from solution, and so prevents 
 the formation of mercuro-ammonium compounds which are not completely 
 decomposed by soda solution. The addition of zinc gives rise to an evolution 
 of hydrogen, and prevents violent bumping. Previous to use the stock of 
 reagents should always be tested by a blank experiment; in many cases 
 if potassic sulphate is used there is no necessity for mercury, and therefore 
 no sulphide is required. 
 
 The following modifications must be used for the determination 
 of nitrogen in substances which contain nitrates. 
 
 Estimation of Nitrog-en, including- Nitrates, by the Kjeldahl- 
 Grunning 1 - Jodlbauer Process. 
 
 The requisite quantity of substance to be analyzed is put into the digesting 
 flask together with 1 or 2 gm. of zinc dust. From 20 to 30 c.c. of 
 sulphuric acid containing 2 gm. of salicylic acid are then quickly poured over 
 the mixture so as to cover it at once. The whole is then gently heated till 
 frothing is over, and the process finished with or without the potassic sulphate 
 as before described. 
 
 The following observations by Bernard Dyer are of consider- 
 able importance in connexion with the modified process : 
 " When nitrates are present in addition to organic or ammoniacal 
 
 *Some operators prefer to close the distilling flask with, a caoutchouc stopper, 
 through which in addition to the distilling tube, a funnel with tap is fixed for running 
 in the alkali, this is to guard against possible loss of ammonia. 
 
86 VOLUMETRIC ANALYSIS. 19. 
 
 nitrogen, Jodlbauer's modification (Cliem. Centr. iii., xvii., 433) 
 suffices to determine accurately the total nitrogen. This process 
 consists in previously adding to the sulphuric acid used for 
 oxidation, either phenol or, preferably, salicylic acid generally 
 about 2 grams for a determination. While the contents of the 
 flask are still cold, from 1 to 2 grams of zinc dust are added (as 
 well as a drop of mercury or some oxide) and allowed to dissolve 
 before the flask is heated. The process is then continued exactly 
 as previously described, when the whole of the nitrogen is 
 obtained as ammonia. There is no difficulty whatever in 
 determining the nitrogen in potassium or sodium nitrate in 
 this manner ; but I find that when ammonia salts are present as 
 well as potassium or sodium nitrate, the results are invariably too 
 low, unless the sulphuric acid containing the salicylic acid is 
 poured quickly into the flask out of a beaker, so that the nitrate 
 shall be completely covered by the acid before the lapse of an 
 appreciable interval of time ; this prevents the formation of the 
 lower oxides of nitrogen, and consequent loss. When even 
 ammonium nitrate is treated in this way, the whole of the nitrogen 
 is retained in solution. I allude to this detail, because I have 
 nowhere seen attention drawn to it, and because I think there is 
 a probability of large errors occurring in the analysis of compound 
 fertilisers, including mixtures of ammonia salts and alkali nitrates, 
 if the acid is allowed to flow on to the sample from a pipette in 
 the usual way." The experiments carried on by this chemist, and 
 recorded in the paper already mentioned are extremely valuable. 
 They show that the Kjeldahl process either with the modifications 
 of Gunning and Arnold, or with that of the same and 
 Jodlbauer is capable of accurately estimating the nitrogen in 
 a very large variety of complex substances, and with the 
 expenditure of very little time as compared with older 
 methods. 
 
 As respects the substances available for the accurate estimation 
 of their nitrogen by the Kjeldahl method, Dyer finds that if 
 zinc alone (without the use of phenol or salicylic acid) be used 
 with aromatic nitro-compounds there is loss of nitrogen, as though 
 it were necessary that more carbon should be present. 
 
 The Kjeldahl-Gunning method fails to furnish the calculated 
 quantity of nitrogen in azobenzene or amido-azobenzene. Mere 
 reduction by zinc suffices with amido-azobenzene, but in the case of 
 azobenzene the complete Jodlbauer modification is necessary. 
 With amido-azotoluene the correct amount was obtained by the 
 Kjeldahl-Gunning process supplemented by reduction with 
 zinc and with carbazol by the Kjeldahl-Gunning method 
 alone. 
 
 Hydroxylamine hydrochloride, which contains 20-21 per cent, 
 of nitrogen, yielded only 3 per cent, by the Kjeldahl-Gunning 
 method; by reduction with zinc about 10 per cent, was obtained ; 
 
19. AMMONIA. 87 
 
 by the Kjeldahl-Gunning-Jodlbauer method about 19 per 
 cent, j by reduction with sugar and zinc less than 19 per cent. 
 The Kjeldahl-Gunning-Jodlbauer method with the addition 
 of sugar as well as zinc, however, gave the calculated quantity in 
 each of three separate determinations. Acetaldoxime, by the 
 K j eld a hl-Gu lining method, gave somewhat low results, but with 
 the addition of sugar and zinc furnished correct results. 
 jXaphthoquinone-oxinie yields its full percentage by the Kjeldahl- 
 Guniiing method. 
 
 Potassium cyanide and ethyl cyanide both give nearly correct 
 results by the K j e 1 d a h 1 - G u n n i n g method ; no trace of 
 hydrocyanic acid is evolved if the sulphuric acid used be strong. 
 Potassium ferrocyanide also yields accurate results. Potassium 
 ferricyanide, however, only gives sufficiently accurate results when 
 reduced by the addition of sodium thiosulphate. Sodium 
 nitroprusside failed with any modification of the method to yield 
 all its nitrogen. 
 
 Phenylhydrazine derivatives cannot by any modification of the 
 method tried be made to give correct results ; there is invariably 
 loss of nitrogen, presumably liberated in the free state. 
 
 H. C. Sherman (Jour. Amer. Chem. Soc. xvii. 567) states 
 that no known modification will give accurate results, where large 
 proportions of both chlorides and nitrates exist in the substance 
 digested. 
 
 The Stock Method. A method based on the same principle as 
 that of Kjeldahl has been devised by W. F. K. Stock (Analyst 
 xvii. 109, idem xviii. 58), but the oxidation in this case depends 
 not on the sulphuric acid but on manganic oxide. From 0'5 to 
 1 '0 gm. of the substance is digested at a temperature below boiling, 
 with 10 c.c. of strong sulphuric acid and 5 gm. of finely ground 
 MnO 2 until the black carbonaceous matters are destroyed and 
 a greenish liquid results ; this is distilled in a special apparatus, 
 arranged by the author of the method much in the same way as 
 in Kje Id a hl's process, with excess of soda and titrated in the 
 same way. 
 
 The results obtained by me with organic substances have almost 
 invariably been low in comparison with the Kjeldahl method 
 described above, and this is probably due to the same cause as that 
 existing in the original Kjeldahl method where a lower 
 temperature was used, and the oxidizing influence of permanganate 
 was relied on for completing the decomposition. 
 
 All modern authorities appear to agree in discarding the use of 
 permanganate in the Kjeldahl method as not only useless but 
 even harmful. 
 
 It is only fair to say that very good results have been obtained 
 in the case of certain nitrogen compounds by the Stock method, 
 and further research may result in its being improved. 
 
88 VOLUMETRIC ANALYSIS. 20. 
 
 ACIDIMETRY OB- THE TITRATION OF ACIDS. 
 
 20. THIS operation is simply the reverse of all that has been 
 said of alkalies, and depends upon the same principles as have 
 been explained in alkalimetry. 
 
 With free liquid acids, such as hydrochloric, sulphuric, or nitric, 
 the strength is generally taken by means of the hydrometer or 
 specific-gravity bottle, and the amount of real acid in the sample 
 ascertained by reference to the tables constructed by Otto, 
 Bine an, or lire. The specific gravity may very easily be taken 
 with the pipette, as recommended with ammonia, and of course the 
 real acid may be quickly estimated by normal caustic alkali and an 
 appropriate indicator. 
 
 In the case of titrating concentrated acids of any kind it is 
 preferable in all cases to weigh accurately a small quantity, dilute 
 to a definite volume, and take an aliquot portion for titration. 
 
 Delicate End-reaction in Acidimetry. 
 
 If an alkaline iodate or bromate be added to a solution of an 
 alkaline iodide in the presence of a mineral acid, iodine is set free 
 and remains dissolved in the excess of alkaline iodide, giving the 
 solution the well-known colour of iodine. This reaction has been 
 long observed, and is capable of being used with excellent effect as 
 an indicator for the delicate titration of acids, and therefore of 
 alkalies, by the residual method. Kjeldahl, for instance, uses it 
 in his ammonia process, where the distillate contains necessarily an 
 excess of standard acid. The reaction is definite in character, and 
 may be used in various ways in volumetric processes. For instance, 
 potassic bromate liberates iodine in exact proportion to its contained 
 oxygen in the presence of excess of dilute mineral acid, and the 
 iodine so liberated may be accurately titrated w r ith sodic thiosulphate. 
 In acidimetry, however, the method is simply used for its exceeding 
 delicacy as an end-reaction, one drop of T ^ sulphuric, nitric, or 
 hydrochloric acid being quite sufficient to cause a deep blue colour 
 in the presence of starch. 
 
 The adjustment of the standard liquids is made as follows : 
 2 or 3 c.c. of - acid are run into a flask, diluted somewhat with 
 water, and a crystal or two of potassic iodide thrown in ; 1 or 2 c.c. 
 of a 5 per cent, solution of potassic iodate are then added, which 
 at once produces a brown colour, due to free iodine. A solution 
 of sodic thiosulphate is added from a burette, with constant 
 shaking, until the colour is nearly discharged ; a few drops of clear 
 freshly prepared starch solution are now poured in, and the blue 
 colour removed by the very cautious addition of thiosulphate.. 
 The quantity of thiosulphate used represents the comparative 
 strengths of it and the standard acid, and is used as the basis 
 of calculation in other titrations. The first discharge of the blue- 
 colour must be taken in all cases as the correct ending, because OH 
 
21. ACIDIMETRY. 89 
 
 standing a few minutes the blue colour returns, due to some 
 obscure reaction from the thiosulphate. This has been probably 
 regarded as one of the drawbacks of the process, and another is the 
 instability of the thiosulphate solution ; but these by no means 
 invalidate its accuracy, and it moreover possesses the advantage of 
 being applicable to excessively dilute solutions, and may be used 
 by artificial light. The organic acids cannot be estimated by this 
 method, the action not being regular. Neutral alkaline and 
 alkaline earthy salts have no interference, but salts of the organic 
 acids and borates must be absent. 
 
 ACETIC ACID. 
 
 C 2 H 4 2 = 60. 
 
 21. IN consequence of the anomaly existing between the sp. gr. 
 of strong acetic acid and its actual strength, the hydrometer is not 
 reliable, but the volumetric estimation is now rendered extremely 
 accurate by using phenolphthaleiii as indicator, acetates of the 
 alkalies and alkaline earths having a perfectly neutral behaviour to 
 this indicator. Even coloured vinegars may be titrated when 
 highly diluted. Where, however, the colour is too much for this 
 method to succeed Pettenkofer's plan is the best, and this opinion 
 is endorsed by A. K. Leeds (Jour. Am. Chem. Soc. xvii. 741). 
 The latter takes 50 c.c. of the vinegar and 50 c.c. of water with 
 a drop of phenolphthalein, adds - baryta to slight excess which 
 causes the organic colouring matters to separate either in the cold 
 or on warming, the excess of baryta is then found by titration 
 with -^ acid and turmeric paper. 
 
 Several processes have at various times been suggested for the 
 accurate and ready estimation of acetic acid, among which is that 
 of Greville Williams, by means of a standard solution of lime 
 syrup. The results obtained were very satisfactory. 
 
 C. Mohr's process consists in adding to the acid a known 
 excessive quantity of precipitated neutral and somewhat moist 
 calcic carbonate. When the decomposition is as nearly as possible 
 complete in the cold, the mixture must be heated to expel the CO 2 , 
 and to complete the saturation ; the residual carbonate is then 
 brought upon a filter, washed with boiling water, and titrated with 
 excess of normal acid and back with alkali. 
 
 In testing the impure brown pyroligneous acid of commerce, 
 this method has given fairly accurate results.* 
 
 The titration of acetic acid or vinegar may also be performed by 
 the ammonio-cupric solution described in 15.10. 
 
 *A. E. Leeds (loo. cit.) has not found this method to answer, which I think must 
 be due to using dried calcic carbonate. I have only used it for commercial wood acid, 
 and the figures obtained by me were the highest among several other methods ; but an 
 error has been committed in not mentioning that the CaCQ3 should not be thoroughly 
 dried, and the alkalinity of which is known. 
 
90 VOLUMETRIC ANALYSIS. 21. 
 
 1. Free Mineral Acids in Vineg-ar. Hehlier has devised ail 
 excellent method for this purpose (Analyst i. 105). 
 
 Acetates of the alkalies are always present in commercial vinegar ; 
 and when such vinegar is evaporated to dryness, and the ash ignited, 
 the alkalies are converted into carbonates having a distinct alkaline 
 reaction on litmus; if, however, the ash has a neutral or acid 
 reaction, some free mineral acid must have been present. The 
 alkalinity of the ash is diminished in exact proportion to the 
 amount of mineral acid. added to the vinegar as an adulteration. 
 Hence the following process : 
 
 50 c.c. of the vinegar are mixed with 25 c.c. of -$ soda or potash, 
 evaporated to dryness, and ignited at a low red heat to convert the acetate? 
 into carbonates ; when cooled, 25 c.c. of ^r acid are added ; the mixture 
 heated to expel CO', and filtered ; after washing the residue/the filtrate and 
 washings are exactly titrated with ^ alkali ; the volume so used equals the 
 amount of mineral acid present in the 50 c.c. of vinegar. 
 
 1 c.c. / alkali=0'0049 gra. H 2 SO 4 or 0'003037 gm.liCl. 
 
 If the vinegar contains more than 0'2 per cent, of mineral acid, 
 more than 25 c.c. of ~ alkali must be used to the 50 c.c, vinegar 
 before evaporating and igniting. 
 
 2. Acetates of the Alkalies and Earths. These salts are 
 converted by ignition into carbonates, and can be then residually 
 titrated with normal acid ; no other organic acids must be present, 
 nor must nitrates, or similar compounds decomposable by heat. 
 1 c.c. normal acid^O'06 gm. acetic acid. 
 
 3. Metallic Acetates. Neutral solutions of lead and iron acetates 
 may be precipitated by an excess of normal sodic or potassic carbonate, the 
 precipitate well boiled, filtered, and washed with hot water, the filtrate and 
 washings made up to a definite volume, and an aliquot portion titrated with 
 N or ^ acid ; the difference between the quantity so used and calculated for 
 the original volume of alkali will represent the acetic acid. 
 
 If such solutions contain free acetic or mineral acids, they must 
 be exactly neutralized previous to treatment. 
 
 If other salts than acetates are present, the process must be 
 modified as follows : 
 
 Precipitate with alkaline carbonate in excess, exactly neutralize with 
 hydrochloric acid, evaporate the whole or part to dryuess, ignite to convert 
 the acetates into carbonates, then titrate residually with normal acid. Any 
 other organic acid than acetic will, of course, record itself in terms of acetic 
 acid. 
 
 4. Commercial Acetate of Lime. The methods just described 
 are often valueless in the case of this substance, owing to tarry 
 matters, which readily produce an excess of carbonates. 
 
 Presenius (Z. a. c. xiii. 153) adopts the following process for tolerabl} r 
 pure samples : 5 gm. are weighed and transferred to a 250 c.c. flask, 
 dissolved in about 150 c.c. of water, and 70 c.c. of normal oxalic acid added ; 
 the flask is then well shaken, and filled to the mark, 2 c.c. of water are added 
 
21. ACETIC ACID. 91 
 
 to allow for the volume occupied by the precipitate, the whole is again well 
 shaken, and left to settle. The solution is then filtered through a dry filter 
 into a dry flask : the volume so filtered must exceed 200 c.c. 
 
 100 c.c. are first titrated with normal alkali and litmus ; or, if highly 
 coloured, by help of litmus or turmeric paper ; the volume used multiplied 
 by 2' 5 will give the volume for 5 gm. 
 
 Another 100 c.c. are precipitated with solution of pure calcic acetate in 
 slight excess, warmed gently, the precipitate allowed to settle somewhat, 
 then filtered, well washed, dried, and strongly ignited, in order to convert 
 the oxalate into calcic carbonate or oxide, or a mixture of both. The 
 residue so obtained is then decomposed with excess of normal acid, and 
 titrated residually with normal alkali. By deducting the volume of acid 
 used to neutralize the precipitate from that of the alkali used in the first 
 100 c.c., and multiplying by 2'5, is obtained the volume of alkali expressing 
 the weight of acetic acid in the 5 gm. of acetate. 
 
 In the case of very impure and highly coloured samples of 
 acetate, it is only possible to estimate the acetic acid by repeated 
 distillations with phosphoric acid and water to incipient dryness, 
 and then titrating the acid direct with ~ alkali, each c.c. of which 
 represents 0'006 gm. acetic acid. 
 
 The distillation is best arranged as suggested by Still well and 
 Gladding, or later by Harcourt Phillips (C. N. liii. 181). 
 
 A 100 to 120 c.c. retort, the tubulure of which carries a small funnel 
 fitted in with a caoutchouc stopper, and the neck of the funnel stopped 
 tightly with a glass rod shod with elastic tube, is supported upon a stand in 
 such a way that its neck inclines upwards at about forty-five degrees : the 
 end of the neck is drawn out, and bent so as to fit into the condenser by 
 help of an elastic tube. The greater part of the retort neck is coated with 
 flannel, so as to prevent too much condensation. 
 
 1 gm. of the sample being placed in the retort, 10 c.c. of a 40 per cent, 
 solution of P 2 O 5 are added, together with as much water as will make about 
 50 c.c. A small naked flame is used, and if carefully manipulated, the 
 distillation may be carried on to near dryness without endangering the 
 retort. After the first operation the retort is allowed to cool somewhat, then 
 50 c.c. of hot water added through the funnel, another distillation made as 
 before, and the same repeated a third time, Avhich will suffice to carry 
 over all the acetic acid. The distillate is then titrated with alkali and 
 phenolphthalein. 
 
 By this arrangement the frothing and spirting is of no con- 
 sequence, and the whole process can be completed in less than 
 an hour. The results are excellent for technical purposes. 
 
 Weber (Z, a. C. xxiv. 614) has devised a ready and fairly 
 accurate method of estimating the real acetic acid in samples of 
 acetate of lime, based on the fact that acetate of silver is insoluble 
 in alcohol. 
 
 Process : 10 gm. of the sample in powder are placed in a 250 c.c. flask, 
 a little water added, and heated till all soluble matters are extracted, cooled, 
 and made up to the measure : 25 c.c. are then filtered through a dry filter, 
 put into a beaker, 50 c.c. of absolute alcohol added, and the acetic acid at 
 once precipitated with an alcoholic solution of silver nitrate. The silver 
 acetate, together with any chloride, sulphate, etc., separates free from 
 colour. The precipitate is brought on a filter, well washed with 60 per cent, 
 alcohol till the free silver is removed ; precipitate is then dissolved in weak 
 
92 VOLUMETRIC ANALYSIS. 22. 
 
 nitric acid, and titrated with ^ salt solution. Each c.c. represents O'OOG gm. 
 acetic acid. 
 
 Several trials made in comparison with the distillation method 
 with phosphoric acid gave practically the same results. 
 
 A good technical process has been devised by Grim aha w 
 (Allen's Organic Analysis i. 397). 10 gm. of the sample are treated 
 with water and an excess of sodic bisulphate (ISfaHSO 4 ), the 
 mixture diluted to a definite volume, filtered, and a measured 
 portion of the filtrate titrated with standard alkali ; a similar 
 portipn meanwhile is evaporated to dryness with repeated 
 moistening with water, to drive off all free acetic acid. The 
 residue is dissolved and titrated with standard alkali, when the 
 difference between the volume now required and that used in the 
 original solution will correspond to the acetic acid in the sample. 
 Litmus paper is the proper indicator. 
 
 BORIC ACID AND EQUATES. 
 
 Boric anhydride B 2 3 =70. 
 
 22. THE soda in borax may, according to Thomson, be 
 very accurately estimated by titrating the salt with standard H 2 S0 4 
 and methyl orange or lacmoid paper. Litmus and phenacetolin 
 give very doubtful end-reactions : phenolphthaleiii is utterly useless. 
 
 Example : T683 gm. sodic pyroborate in 50 c.c. of water required in one 
 case 16'7 c.c. normal acid, and in a second 16'65 c.c. The mean of the two 
 represents 0'517 gm. Na 2 O. Theory requires 0'516 gm. 
 
 The estimation of boric acid as such has up to the present time 
 presented great difficulties, and no volumetric method of any 
 value has been available. 
 
 R. T. Thomson has now removed this difficulty by finding 
 a method easy of execution, and of considerable accuracy 
 (J. S.C.I, xii. 432), see also page 44 in this book. 
 
 Process : To determine boric acid in articles of commerce it is 
 necessary to use methyl orange, to which indicator boric acid is perfectly 
 neutral. In the case of boric acid in borax 1 gm. is dissolved in water, 
 metlryl orange added, and then dilute sulphuric acid till the pink colour just 
 appears. Boil for a short time to expel carbonic acid, cool, and add normal 
 or fifth-normal soda till the pink colour of the methyl orange (a little more 
 of which should be added if necessary) just assumes a pure yellow tinge. 
 At this stage all the boric acid will exist in the free state. Add glycerine in 
 such proportion that the total solution after titration will contain 30 per 
 cent, at least, then add a little phenolphthaleiii, and lastly normal or fifth- 
 normal soda from a burette until a permanent pink colour is produced. 
 More glycerine may be added during the estimation if it is found necessary. 
 The proportion of boric acid present is calculated from the number of c.c. of 
 soda consumed. 
 
 1 c.c. normal NaOH=0'0620 gm. H 3 BO 3 
 
 1 c.c. =0-0505 gm. Na 2 B 4 7 
 
 1 c.c. =0-0955 gm. Na 2 B 4 O 7 +10H-O 
 
23. CARBONIC ACID. 93 
 
 In the case of boric acid of commerce, which generally contains salts of 
 ammonium, 1 gin. may be dissolved in hot water, a slight excess of sodic 
 carbonate added, and the solution boiled down to about half its bulk to expel 
 ammonia. Any precipitate which appears may then be filtered off, and the 
 filtrate titrated as already described. 
 
 The method may also be applied to boracite or borate of lime by dissolving 
 1 gm. of either of these minerals in dilute hydrochloric acid with the aid of 
 heat, nearly neutralizing with caustic soda, boiling to expel carbonic 
 acid, cooling, exactly neutralizing to rnetlryl orange, and continuing the 
 determination as in borax. If much iron is present, however, it may be 
 removed by a preliminary treatment with sodic carbonate, and removal of 
 oxide of iron as well as the carbonates of calcium and magnesium ~by 
 nitration. 
 
 Thomson has also attempted to apply the process to the 
 estimation of boric . acid in milk and other foodstuffs. This of 
 course necessitates the removal of phosphoric acid from the ash of 
 the milk, for which purpose a barium salt was found to be 
 a successful precipitant, and if the solution be sufficiently dilute 
 will leave the boric acid in solution. The experiments have not 
 as yet been completely successful. 
 
 CARBONIC ACID AND CARBONATES. 
 
 23. ALL carbonates are decomposed by strong acids ; the 
 carbonic acid which is liberated splits up into water and carbonic 
 anhydride (CO 2 ), which latter escapes in the gaseous form. 
 
 It will be readily seen from what has been said previously as 
 to the estimation of the alkaline earths, that carbonic acid in 
 combination can be estimated volumetrically with a very high 
 degree of accuracy (see 18). 
 
 The carbonic acid to be estimated may be brought into 
 combination with either calcium or barium, these bases admitting 
 of the firmest combination as neutral carbonates. 
 
 If the carbonic acid exist in a soluble form as an alkaline mono- 
 carbonate, the decomposition is effected by the addition of baric or 
 calcic chloride as before directed ; if as bicarbonate, or a compound 
 between the two, ammonia must be added with either of the 
 chlorides. 
 
 As solution of ammonia frequently contains carbonic acid, this 
 must be removed by the aid of baric or calcic chloride, previous 
 to use. 
 
 1. Carbonates Soluble in Water. 
 
 It is necessary to remember, that when calcic chloride is used as 
 the precipitant in the cold, amorphous calcic carbonate is first 
 formed ; and as this compound is sensibly soluble in water, it is 
 necessary to convert it into the crystalline form. In the absence of 
 free ammonia this can be accomplished by boiling. When ammonia 
 is present, the same end is obtained by allowing the mixture to 
 
94 VOLUMETRIC ANALYSIS. 23. 
 
 stand for eight or ten hours in the cold, or by heating for an hour 
 or two to 70 80 C. "With barium the precipitation is regular. 
 
 Another fact is, that when ammonia is present, and the precipi- 
 tation occurs at ordinary temperatures, ammonic carbamate is 
 formed, and the baric or calcic carbonate is only partially precipi- 
 tated. This is overcome by heating the mixture to near boiling for 
 a couple of hours, and is best done by passing the neck of the 
 flask through a retort ring, and immersing the flask in boiling 
 water. 
 
 When caustic alkali is present in the substance to be examined, 
 it is advisable to use barium as the precipitant ; otherwise, for all 
 volumetric estimations of CO 2 calcium is to be preferred, because 
 the precipitate is much more quickly and perfectly washed than 
 the barium compound. 
 
 Example : 1 gra. of pure anhydrous sodic carbonate was dissolved in 
 water, precipitated while hot with baric chloride, the precipitate allowed to 
 settle well, the clear liquid decanted through a moist filter, more hot water 
 containing a few drops of ammonia poured over the precipitate, which was 
 repeatedly done so that the bulk of the precipitate remained in the flask, 
 being washed by decantation through the filter ; when the washings showed 
 no trace of chlorine, the filter was transferred to the flask containing the 
 bulk of the precipitate, and 20 c.c. of normal nitric acid added, then titrated 
 with normal alkali, of which 1/2 c.c. was required=18'8 c.c. of acid ; this 
 multiplied by 0'022, the coefficient for carbonic acid, gave O4136 gin. CO-= 
 41'36 per cent., or multiplied by 053, the coefficient for sodic carbonate, 
 gave 0*9964 gm. instead of 1 gm. 
 
 2. Carbonates Soluble in Acids. 
 
 It sometimes occurs that substances have to be examined for 
 carbonic acid, which do not admit of being treated as above 
 described ; such, for instance, as the carbonates of the metallic 
 oxides (white lead, calamine, etc.), carbonates of magnesia, iron, 
 and copper, the estimation of carbonic acid in cements, mortar, and 
 many other substances. In these cases the carbonic acid must be 
 evolved from the combination by means of a stronger acid, and 
 conducted into an absorption apparatus containing ammonia, then 
 precipitated with calcic chloride, and titrated as before described. 
 
 The following form of apparatus (fig. 33) affords satisfactory 
 results. 
 
 The weighed substance from which the carbonic acid is to be evolved is 
 placed in b with a little water; the tube d contains strong hydrochloric 
 acid, and c broken glass wetted with ammonia free from carbonic acid. 
 The flask is about one-eighth filled with the same ammonia : the bent tube 
 must not enter the liquid. When all is ready and the corks tight, warm the 
 flask a gently so as to fill it with vapour of ammonia, then open the clip and 
 allow the acid to flow circumspectly upon the material, which may be heated 
 until all carbonic acid is apparently driven off ; then by boiling and shaking 
 the last traces can be evolved, and the operation ended. When cool, the 
 apparatus may be opened, the end of the bent tube washed into a, and also 
 a good quantity of boiled distilled water passed through c, so as to carry 
 
23. 
 
 CARBONIC ACID. 
 
 95> 
 
 down any ammonic carbonate that may have formed. Then add solution of 
 calcic chloride, boil, filter, and titrate the precipitate as before described. 
 
 -During- the filtration, and while ammonia is present, there is a great 
 avidity for carbonic acid, therefore boiling water should be used for washin- 
 and the funnel kept covered with a small glass plate. 
 
 In many instances CO 2 may be estimated by its equivalent in 
 chlorine with -- silver and potassic chromate, as in 39. 
 
 Fig. 33. 
 3. Carbonic Acid. G-as in 
 
 etc. 
 
 Waters, 
 
 The carbonic acid existing in waters as neutral carbonates of the 
 alkalies or alkaline earths may very elegantly and readily be titrated 
 directly by ^ acid (see- 18). 
 
 "Well or spring water, and also mineral waters, containing free 
 carbonic acid gas, can be examined by collecting measured quantities 
 of them at their source, in bottles containing a mixture of calcic 
 and ammonic chloride, afterwards heating the mixture in boiling 
 water for one or two hours, and titrating the precipitate as before 
 described. 
 
 Pettenkofer's method with caustic baryta or lime is decidedly 
 preferable to any other. Lime water may be used instead of' 
 
96 VOLUMETRIC ANALYSIS. 23. 
 
 baryta with equally good results, but care must be taken that the 
 precipitate is crystalline. 
 
 The principle of the method is that of removing all the carbonic 
 acid from a solution, or from a water, by excess of baryta or lime 
 water of a known strength ; and, after absorption, finding the 
 excess of baryta or lime by titration with -^ acid and turmeric 
 paper. 
 
 The following is the best method to be pursued for ordinary 
 drinking waters not containing large quantities of carbonic acid : 
 
 100 c.c. of the water are put into a flask with 3 c.c. of strong solution of 
 calcic or baric chloride, and 2 c.c. of saturated solution of ammonic chloride ; 
 45 c.c. of baryta or lime water, the strength of which is previously ascertained 
 by means of decinormal acid, are then added, the flask well corked and put 
 aside to settle ; when the precipitate is f ully subsided, take out 50 c.c. of the 
 clear liquid with a pipette, and let this be titrated with decinormal acid. 
 The quantity required must be multiplied by 3 for the total baryta or lime 
 solution, there being 50 c.c. only taken ; the number of c.c. so found must be 
 deducted from the original quantity required for the baryta solution added ; 
 the remainder multiplied by 0'0022 will give the weight of carbonic acid 
 existing free and as bicarbonate in the 100 c.c. 
 
 The addition of the baric or calcic chloride and ammonic chloride is made 
 to prevent any irregularity which might arise from alkaline carbonates or 
 sulphates, or from magnesia. 
 
 If it be desirable to ascertain the volume of carbonic acid from 
 the weight, 1000 c.c. of gas, at and 0*76 m.m., weigh 
 1 '96663 gm. 100 cubic inches weigh 47'26 grains. 
 
 4. Carbonic Acid in Aerated Beverages, etc. 
 
 For ascertaining the quantity of carbonic acid in bottled aerated 
 waters, such as soda, seltzer, potass, and others, the following 
 .apparatus is useful. 
 
 Fig. 34 is a brass tube made like a cork -borer, about five inches long, having 
 four small holes, two on each side, and about two inches from its cutting end ; 
 the upper end is securely connected with the bent tube from the absorption 
 flask (tig. 35) by means of a vulcanized tube ; the flask contains a tolerable 
 quantity of pure ammonia, into which the delivery tube dips ; the tube 
 a contains broken glass moistened with ammonia. 
 
 Everything being ready the brass tube is greased, and the bottle being 
 -held in the right hand, the tube is screwed a little aslant through the cork 
 by turning the bottle round, until the holes appear below the cork and the 
 gas escapes into the flask. When all visible action has ceased, after the 
 bottle has been well shaken two or three times to evolve all the gas that can 
 i be possibly eliminated, the vessels are quietly disconnected, the tube a washed 
 out into the flask, and the contents of the bottle added also ; the whole is 
 then precipitated with calcic chloride and boiled, and the precipitate titrated 
 as usual. This gives the total carbonic acid free and combined. 
 
 To find the quantity of the latter, another bottle of the same manufacture 
 must be evaporated to dryness, and the residue gently ignited, then titrated 
 with normal acid and alkali ; the amount of carbonic acid in the mono- 
 -carbonate deducted from the total, will give the weight of free gas originally 
 present. 
 

 
 CARBONIC ACID. 
 
 97 
 
 The volume may be found as follows : 1000 c.c. of carbonic acid at 0, 
 and 76 m.m., weigh T96663 gm. Suppose, therefore, that the total weight 
 of carbonic acid found in a bottle of ordinary soda water was 2'8 gm., and 
 the weight combined with alkali 0'42 gm., this leaves 2'38 gm. CO 2 in 
 a free state 
 
 1-96663 : 2'38 
 
 1000 : x = 1210 
 
 If the number of c.c. of carbonic acid found is divided by the 
 number of c.c. of soda water contained in the bottle examined, the 
 quotient will be the volume of gas compared with that of the soda 
 water. The volume of the contents of the bottle is ascertained by 
 marking the height of the fluid previous to making the experiment ; 
 the bottle is afterwards filled to the same mark with water, emptied 
 into a graduated cylinder and measured ; say the volume was 
 292 c.c., therefore 
 
 4-14 vols. CO 2 . 
 
 rig. si. 
 
 5. Carbonic Acid in Air. 
 
 A dry glass globe or bottle capable of being securely closed by 
 a rubber stopper, and holding 4 to 6 liters, is filled with the air 
 to be tested by means of a bellows aspirator ; baryta water is then 
 introduced in. convenient quantity and of known strength as 
 compared with T ~ acid.'" The vessel is securely closed, and the 
 liquid allowed to flow round the sides at intervals during half an 
 hour or more. When absorption is judged to be complete, the 
 
 * Clowes and C o 1 e m a n prefer to use saturated lime water in place of baryta, and 
 have obtained good results : see their Quantitative Analysis, 2nd. edit. p. 416. 
 
 II 
 
98 VOLUMETRIC ANALYSIS. 23. 
 
 baryta is emptied out quickly into a stoppered bottle, and the 
 excess of baryta at once ascertained in a measured portion by T ^y- 
 hydrochloric acid and turmeric paper as described in 15.9. The 
 final calculation is of course made on the total baryta originally 
 used, and upon the exact measurement of the air-collecting vessel. 
 It is above all things necessary to prevent the absorption of CO 2 
 from extraneous sources during the experiment. The error may be 
 reduced to a minimum by carrying on the titration in the vessel 
 itself, which is done by fixing an accurately graduated pipette 
 through the cork or caoutchouc stopper of the air vessel, to the 
 upper end of which is attached a stout piece of elastic tube, closed 
 with a pinch-cock ; and this being filled to the mark with dilute 
 standard acid acts as a burette. The baryta solution tinted with 
 phenolphthaleiii is placed in the air bottle which must be of 
 colourless glass, and after absorption of all CO 2 , the excess of 
 baryta is found by running in the acid until the colour disappears. 
 The cork or stopper must have a second opening to act as 
 ventilator ; a small piece of glass tube does very well. 
 
 If a freshly made solution of oxalic acid is used containing 
 0*2863 gm. per liter, each c.c. represents 1 mgm. CO 2 . The liquid 
 holds its strength correctly for a day, and can be made as required 
 from a strong solution, say 28*636 gm. per liter. 
 
 Another method of calculation is, to convert the volume of 
 baryta solution decomposed into its equivalent volume in ~ acid, 
 1 c.c. of which = 0*0022 gm. CO 2 or by measurement at C. and 
 760 m.m. pressure represents 1*119 c.c. The method above 
 described is a combination of those of Pettenkofer and Dal ton, 
 and though much used, is liable to considerable error from various 
 causes. 
 
 A. H. Gill in a report from the Sanitary and Gas Analysis 
 Laboratory of the Technical Institute at Boston, U.S.A. 
 (Analyst xvii. 184), gives a somewhat modified arrangement of the 
 Pettenkofer method. Ordinary green glass bottles of one or 
 two gallon capacity are measured with water, and the contents in 
 c.c. ascertained preferably by weighing on a good balance. 
 
 The bottles are dried before being used, this may easily be done 
 by rinsing first with alcohol or methylated spirit, draining, then 
 rinsing with ether and after again draining, the bottle is quickly 
 dried by blowing air through it witli the ordinary laboratory bellows. 
 If this plan is not used they must be dried after draining well, in 
 a warm closet. A special form of bellows for filling the bottle 
 with air is used by Gill, but the usual aspirator made on the 
 accordion pattern suffices, or a small fan blower, the driving parts 
 of which are connected by rubber bands to render it noiseless, may 
 be used. 
 
 The bottle is fitted with a rubber stopper carrying a glass tube, 
 closed by a plug of solid rubber. 
 
 The air to be tested is drawn into the bottle by repeated use of 
 
23. CAKBONIC ACID. 99 
 
 the aspirator so as to collect a representative sample, and if the 
 test is made in a room everything should be quiet, and care must 
 be taken to avoid draughts or the proximity of a number of 
 persons. 
 
 Process : 50 c.c. of the standard barium hydrate are run into the 
 bottle rapidly from a burette (the tip passing entirely through the tube in 
 the stopper), the nipple replaced, and the solution spread completely over the 
 sides of the bottle while waiting three minutes for the draining of the 
 burette, before reading, unless it be graduated to deliver 50 c.c. The bottle 
 is now placed upon its side, and shaken at intervals for forty to sixty 
 minutes, taking care that the whole surface of the bottle is moistened with 
 the solution each time. The absorption of the last traces of carbon dioxide 
 is very slow indeed, half an hour in many cases being insufficient. 
 
 At the time at which the barium solution is added, the temperature and 
 pressure should be noted. At the end of the above period, shake well to 
 insure homogeneity of the solution, remove the cap from the tube, and 
 invert the large bottle quickly over a 60 or 70 c.c. glass stoppered bottle, so 
 that the solution shall come in contact with the air as little as possible. With- 
 out waiting for the bottle to drain, withdraw a portion of 15 or 25 c.c. with 
 a narrow-stemmed spherical-bulbed pipette and titrate with sulphuric acid* 
 (1 c.c.=l mgm. CO 2 ), using rosolic acid as an indicator. The difference 
 between the number of c.c. of standard acid required to neutralize the 
 amount of barium hydrate (e.g., 50 c.c.) before and after absorption, gives 
 the number of milligrams of carbon dioxide present in the bottle. 
 
 This is expressed in cubic centimeters under standard conditions, and 
 divided by the capacity of the bottle under standard conditions, and the 
 results reported in parts per 10,000. To reduce the air in the bottle to standard 
 conditions, a hygrometric measurement of the air in the room from which 
 the sample was taken, is necessary. This in ordinary cases is usually 
 omitted, as the object of the investigation is comparative results, as regards 
 the efficiency of ventilation, and the rooms in the same building Avould not 
 vary appreciably in the amount of moisture in the atmosphere. This 
 correction may make a difference of about 0'15 parts per 10,000. 
 
 Another method on the same principle is to attacli a bulb 
 apparatus, containing a measured quantity of baryta or lime 
 water, to an aspirator bottle filled with water; the tap of the 
 "bottle is opened to such an extent as to allow the air to bubble 
 through the test solution at a moderate rate. The process of 
 titration is the same as above. This method takes longer time, 
 and the volume of air, which should not be less than five or six 
 liters, is ascertained by measuring the volume of water allowed to 
 run out of the aspirator, and the rate of flow being regulated so 
 that from two to three hours is required to pass the above volume 
 of air. If a flask, fitted with tubes, is used in place of, the bulb 
 apparatus, the titration may be done without transferring the test 
 solution. 
 
 * Sulphuric acid, in distinction to oxalic acid, enables one to estimate the excess of 
 "barium hydrate in presence of the suspended barium carbonate, and also of caustic 
 alkali, which is a frequent impurity of commercial barium hydrate. Professor 
 Johnson, in the American edition of Fresenius' Quantitative Analysis, calls 
 attention to the fact that the normal alkaline oxalates decompose the alkaline earthy 
 carbonates, so that the reaction continues alkaline if the least trace of soda or potash 
 be present. The sulphuric acid may be prepared by diluting 46*51 c.c. normal sulphuric 
 acid to a liter. 
 
 H 2 
 
100 VOLUMETRIC ANALYSIS. 23, 
 
 6. Sckeibler's Apparatus for the estimation of Carbonic Acid 
 
 by "Volume. 
 
 This apparatus is adapted for the estimation of the CO 2 contained 
 in native carbonates, as well as in artificial products, and has been 
 specially contrived for the purpose of readily estimating the CO 2 
 in the bone-black used in sugar refining. The principle upon, 
 which the apparatus is founded is simply this : That the quantity 
 of CO 2 contained in calcic carbonate can be used as a measure 
 of the quantity of that salt itself ; and instead of determining, as 
 has usually been the case, the quantity of gas by weight, this 
 apparatus admits of its. estimation by volume ; and it is by this 
 means possible to perform, in a few minutes, operations which 
 would otherwise take hours to accomplish, while, moreover, the 
 operator need scarcely possess any knowledge of chemistry. The 
 results obtained by this apparatus are correct enough for technical 
 purposes. 
 
 The apparatus is shown in fig. 36, and consists of the following 
 parts : The glass vessel, A, serves for the decomposition of the 
 material to be tested for CO 2 , which for that purpose is treated 
 with dilute HC1 ; this acid is contained, previous to the experiment,. 
 in the gutta-percha vessel s. The glass stopper of A is perforated, 
 and through it firmly passes a glass tube, to which is fastened the 
 india-rubber tube r, by means of which communication is opened 
 with B, a bottle having three openings in its neck. The central 
 opening of this bottle contains a glass tube (r) firmly fixed, which 
 is in communication, on the one hand, with A, by means of the 
 flexible india-rubber tube already alluded to, and, on the other 
 hand, inside of B, with a very thin india-rubber bladder, K. 
 The neck (</) of the vessel B is shut off during the experiment by 
 means of a piece of india-rubber tubing, kept firmly closed with 
 a spring clamp. The only use of this opening of the bottle B,, 
 arranged as described, is to give access of atmospheric air to the 
 interior of the bottle, if required. The other opening is in 
 communication with the measuring apparatus C, a very accurate 
 cylindrical glass tube of 150 c.c. capacity, divided into 0*5 c.c. ; 
 the lower portion of this tube C is in communication with the 
 tube D, serving the purpose of controlling the pressure of the gas. 
 The lower part of this tube D ends in a glass tube of smaller 
 diameter, to which is fastened the india-rubber tube p, leading 
 to E, but the communication between these parts of the apparatus 
 is closed, as seen at p, by means of a spring clamp. E is a water 
 reservoir, and on removal of the clamp at p, the water contained 
 in C and D runs off towards E ; when it is desired to force the 
 water contained in E into C and I), this can be readily done 
 by blowing with the mouth into V, and opening the clamp 
 at p. 
 
 The main portion of the apparatus above described, with the 
 exception, however, of the vessel A, is fixed by means of brass 
 
23. 
 
 CARBONIC ACID. 
 
 101 
 
 fittings to a wooden board ; a thermometer is also attached. The 
 filling of the apparatus with water is very readily effected by 
 pouring it through a suitable funnel placed in the open end of the 
 tube D, care being taken to remove, or at least to unfasten, the 
 .spring clamp at p ; in this manner the water runs into E, which 
 
 should be almost entirely filled. Distilled water is preferable for 
 this purpose, especially as the filling only requires to be done once, 
 because the water always remains in E as long as the apparatus is 
 intended to be kept ready for use. When it is required to fill the 
 tubes C and I) with water, so as to reach the zero of the scale 
 
102 VOLUMETRIC ANALYSIS. 2S. 
 
 of the instrument, it is best to remove the glass stopper from A. 
 The spring clamp at p is next unfastened, and air is then blown by 
 means of the mouth into the tube V, which communicates with E ; 
 by this operation the water rises up into the tubes C and D, 
 which thus become filled with that liquid to the same height. 
 Care should be taken not to force the water up above the zero* 
 of the scale at C, and especial care should be taken against forcing 
 so much of the fluid up that it would run over into the tube ?/,. 
 and thence find its way to B, whereby a total disconnection of 
 all the parts of the apparatus would become necessary. If by any 
 accident the water should have been forced up above the zero at C,, 
 before the operator had closed the spring clamp at p, this is easily 
 remedied by gently opening that clamp, whereby room is given for 
 the water to run off to E in such quantity as may be required to- 
 adjust the level of that fluid in C precisely with the zero of the scale. 
 The filling of the tube C with water has the effect of forcing the 
 air previously contained in that tube into E, where it causes the 
 compression of the very thin india-rubber ball placed within B. 
 If it should happen that this india-rubber ball has not become 
 sufficiently compressed and flattened, it is necessary to unfasten the 
 spring clamp at q, and to cautiously blow air into B, through 
 the tube q, by which operation the complete exhaustion of the- 
 india-rubber bladder placed within B is readily performed. This- 
 operation is also required only once, because during the subsequent 
 experiments the india-rubber bladder K is emptied spontaneously. 
 It may happen, however, that while the filling of the tubes I) and C 
 with water is being proceeded with, the india-rubber bladder K 
 has become fully exhausted of air before the water in C reaches 
 the zero of the scale. In that case the level of the water in the 
 tubes D and C will not be the same, but will be higher in D : 
 it is evident, however, that this slight defect can be at once 
 remedied by momentarily unfastening the spring clamp at q. 
 
 The apparatus should be placed so as to be out of reach of direct 
 sunlight, and should also be protected against the heat of the 
 operator's body by intervention of a glass screen, and is best placed 
 near a north window, so as to afford sufficient light for reading off 
 the height of the water in the tubes. 
 
 In testing carbonates the method is as follows : 
 
 Put the very finely powdered portion of carbonate into the perfectly dry 
 decomposing glass A, fill the gutta-percha tube with 10 c.c. hydrochloric 
 acid of 1'12 sp. gr., place the tube cautiously in the decomposing glass, and 
 then close the bottle with the well-tallowed stopper. Here the water will 
 sink a little in C and rise in D ; open q for a moment, and the equilibrium 
 Avill be restored. Now note the thermometer and barometer, grasp the bottle 
 with the right hand round the neck to avoid warming, raise it, incline it 
 slightly so that the hydrochloric acid may mix with the substance gradually, 
 and at the same time with the left hand regulate p, so that the water in the 
 two tubes may be kept at exactly the same height ; continue these operations 
 without intermission, till the level of the water in C does not change for 
 a few seconds. Now bring the columns in C and D to exactly the same height, 
 
24. CITRIC ACID. 103 
 
 read off the height of the water, and note whether the temperature has 
 remained constant. If it has, the number of c.c. read off indicates the 
 liberated CO' 2 , but as a small quantity has been dissolved by the hydrochloric 
 acid, it is necessary to make a correction. Scheibler has determined the 
 small amount of carbonic acid which remains dissolved in the 10 c.c. 
 hydrochloric acid at the mean temperature, and he directs to add 0'8 c.c. to 
 the volume of the carbonic acid read off. Warington (C. N. xxxi. 253) 
 states that this is not a constant quantity, but is dependent upon the volume 
 of gas evolved, and this ratio he fixes at 7 per cent, of the gas measured. 
 Lastly, the volume being reduced to 0, 760 m.m., and the dry condition, the 
 weight is found. 
 
 Under no circumstances can the method be considered actually accurate, 
 but for technical purposes it is convenient, as the operation is performed in 
 a very short time, and is specially suitable for comparative examinations 
 of various specimens of the same material. 
 
 If it is desired to dispense with all corrections, each set of 
 experiments may be begun by establishing the relation between 
 the CO 2 obtained in the process (i.e. the CO 2 actually yielded 
 + 0*8 c.c.) and pure calcic carbonate. This relation is, of course, 
 dependent on the temperature and pressure prevailing on the 
 particular day. For example, from 0'2737 gm. calcic carbonate 
 containing 0*1204 gm. CO 2 , 63*8 c.c. were obtained, including 
 the 0*8 c.c. ; and in an analysis of dolomite under the same 
 circumstances from 0'2371 gm. substance, 57*3 c.c. were obtained, 
 including the 0*8 c.c. 
 
 Therefore 63*8 : 57*3 : : 0*1204 : x, or = 0*1082, consequently 
 the dolomite contains 45*62 per cent, of CO 2 . 
 
 For the special procedure in testing bone-black, used in sugar 
 refining, the reader is referred to the printed instructions supplied 
 with the apparatus.* 
 
 "Wigner (Analyst i. 158) has obtained exceedingly good results 
 in the analysis of lead carbonates, etc., with Me Leod's gas 
 apparatus. The nitrometer has also been turned to good account 
 for the same purpose. 
 
 CITRIC ACID. 
 
 C 6 7 H 8 xH 2 = 210. 
 
 24. THIS acid in the free state may readily be titrated 
 with pure normal soda and phenolphthalein. 1 c.c. normal alkali 
 = 0*07.gm. crystallized citric acid. 
 
 1. Citrates of the Alkalies and Earths. These citrates may be 
 treated with neutral solution of lead nitrate or acetate, in the absence of 
 other acids precipitable by lead. The lead citrate is washed with a mixture 
 of equal parts alcohol and water, the precipitate suspended in water, and 
 H 2 S passed into it till all the lead is converted into sulphide; the clear 
 liquid is then boiled to remove IPS, and titrated with normal alkali. 
 
 * It is perhaps almost needless to say that the modern apparatus designed by 
 Hemp el, Lunge, and others, for technical gas analysis, practically supersedes that 
 of Scheibler. The methods are all, however, open to the objection that an uncertain 
 portion of CO- is lost by aqueous absorption. 
 
104 VOLUMETRIC ANALYSIS. 25. 
 
 2. Fruit Juices, etc. If tartaric is present, together with free 
 citric acid, the former is first separated as potassic bitartrate, 
 which can very well be done in the presence of citric acid, as 
 follows : 
 
 A cold saturated proof spirit solution of potassic acetate is added to a 
 somewhat strong solution of the mixed acids in proof spirit, in sufficient 
 quantity to separate all the tartaric acid as bitartrate, which after stirring 
 well is allowed to stand some hours ; the precipitate is then transferred to a 
 filter, and first washed with proof spirit, then rinsed off the filter with a cold 
 saturated solution of potassic bitartrate, and allowed to stand some hours, 
 with occasional stirring; this treatment removes any adhering citrate. The 
 bitartrate is again brought on to a filter, washed once with proof spirit, then 
 dissolved in hot water, and titrated with normal alkali, 1 c.c. of which 
 0'15 gni. tartaric acid. 
 
 The first filtrate may be titrated for the free citric acid present after 
 evaporating the bulk of the alcohol. 
 
 3. Lime and Lemon Juices. The citric acid contained in lemon, 
 lime, and similar juices, may be very fairly estimated by 
 Warington's method (J. C. S. 1875, 934). 
 
 15 or 20 c.c. of ordinary juice, or 34 c.c. of concentrated juice, are first 
 exactly neutralized with pure normal soda, made up, if necessary, to about 
 50 c.c., heated to boiling in a salt bath, and so much solution of calcic 
 chloride added as to be slightly in excess of the organic acids present. The 
 mixture is kept at the boiling point for about half-an-hour, the precipitate 
 collected on a filter and washed with hot water, filtrate and washings concen- 
 trated to about 15 c.c., and a drop of ammonia added ; this will produce a 
 further precipitate, which is collected separately on a very small filter by 
 help of the previous filtrate, then washed with a small quantity of hot water. 
 Both filters, with their precipitates, are then dried, ignited at a low red heat, 
 and the ash titrated with normal_or ^ acid, each c.c. of which represents 
 respectively O'OY or O'OOT gm H 3 Ci + H 2 O. 
 
 FORMIC ACID. 
 
 HCOOH = 4G. 
 
 25. H. C. JONES (Amer. Cliem, Jour. xvii. 539 541) has 
 worked out a method which though not acidimetric may be 
 quoted here. It is based on a' process originally devised by 
 Peau de Saint-Gilles, by titration with potassic permanganate 
 in the presence of an alkaline carbonate. Lieben confirmed 
 this, using a more elaborate process. The method is on the same 
 principle, but the procedure differs from that of Lieben. 
 
 Process : The solution containing the formic acid is made alkaline with 
 Na 2 CO 3 , warmed and an excess of standard permanganate added. All the 
 formic acid is thus oxidized, and a precipitate of manganese hydroxide 
 thrown down. The solution is acidified with H-'SO 4 , and a measured volume 
 of oxalic acid run in until all the precipitate has dissolved and the 
 permanganate disappeared. The excess of oxalic acid is then titrated with 
 standard permanganate. A volume of oxalic acid equal to that taken is also 
 titrated with the permanganate solution, and the difference between the result 
 <md the total permanganate used gives the quantity of permanganate required 
 fco oxidize the formic acid. The experimental results agree well among 
 themselves and with those obtained by other methods. 
 
26. HYDROFLUOKIC ACID. 105 
 
 The author further shows that Saint- Gilles' statement that 
 oxalic acid can be titrated in acid solution in the presence of 
 formic acid is unreliable, since formic acid is also oxidized to some 
 extent by the permanganate under these conditions. 
 
 F. Freyer (Chem, Zeit. xix. 1184), having occasion to determine 
 the formate in a mixture of calcium acetate and formate, has 
 devised the following method. 
 
 Process : The mixed calcium salts are distilled with dilute sulphuric acid 
 in a current of steam until the distillate is no longer acid ; an aliquot portion 
 of the distillate is titrated with alkali to determine the total acid, wiiilst 
 another portion is evaporated, if necessary, with excess of caustic soda to 
 concentrate it, and is treated as follows : 10 to 20 c.c , containing about 
 0'5 gm. of formic acid, are heated for half an hour to an hour with 50 c.c. 
 of a 6 per cent, solution of potassic bichromate and 10 c.c. of concentrated 
 sulphuric acid in a flask provided with an inverted condenser. The liquid is 
 now made up to 200 c.c., and the unaltered chromic acid determined in 
 10 c.c. of it. For this purpose, 1 to 2 gm. of pure potassic iodide, 10 c.c. 
 of a 25 per cent, solution of phosphoric acid, and some water are added ; and 
 after five minutes the solution is diluted to about 100 c.c. with boiled water, 
 and titrated with T ^- thiosulphate solution in the usual manner: The 
 phosphoric acid is added according to Meineke's recommendation, and is 
 for the purpose of rendering the change from the blue colour of the iodide 
 of starch to the green of the chromium salt more visible ; the commercial 
 glacial acid may be dissolved in water, oxidized by potassium permanganate 
 until it has a faint rose colour, and filtered before being used. 
 
 The bichromate solution used for the oxidation is titrated in the same 
 way. One mol. potassic bichromate is equivalent to three mols. formic acid. 
 
 The results quoted by the author show that the method is fairly 
 accurate, both in the absence and in presence of acetic acid. 
 
 HYDROFLUORIC ACID, SILICOFLUORIC ACID, 
 AND FLUORIDES. 
 
 1 c.c. of ^ alkali = 0-02 gm. of HF = 0'024 gm. of H 2 SiF. 
 
 26. COMMERCIAL hydrofluoric acid, which is now a not 
 inconsiderable article of commerce, is as a rule far from pure. It 
 generally contains in addition to hydrofluoric acid, silicofluoric acid, 
 sulphuric acid, sulphurous acid, and frequently traces of iron and 
 lead. Two analyses of commercial acid gave the following 
 figures : 
 
 1. 2. 
 
 Hydrofluoric acid 4S'00 45'80 
 
 Silicofluoric acid 13'05 9'49 
 
 Sulphuric acid 4'07 3'23 
 
 Sulphurous acid 0*49 ...... 1'06 
 
 Left on evaporation 0'16 
 
 Water by difference 34-23 4-0*42 
 
 100-00 100-00 
 
106 VOLUMETRIC ANALYSIS. 26. 
 
 If it is desired to prepare pure acid, the best way is to add to the 
 commercial acid peroxide of hydrogen till it ceases to bleach 
 iodine, and then potassic hydric fluoride sufficient to fix all the 
 silicofluoric and sulphuric acids. Re-distillation in a lead retort 
 with a platinum condenser will then give perfectly pure acid. 
 
 The total amount of free acid may be estimated with normal 
 alkali (preferably potash), using phenolphthalein or litmus, the 
 former is best. Methyl orange and lacmoid do not give 
 good results. In the case of pure acid, each c.c. of ~ alkali 
 indicates 0*02 gm. of HF, and the reaction when phenolphthalein is 
 employed is very sharp, When, however, commercial acid is thus 
 titrated a difference is observed ; the pink colour obtained on 
 adding the alkali only endures for a second or so and then fades 
 away, and this may be repeated for some time till at last 
 a permanent pink is produced. The cause of this is the presence 
 of silicofluoric acid. The first appearance of pink ensues when 
 the reaction H 2 SiF 6 + K 2 = K-'SiF 6 + H 2 occurs. Then another 
 reaction sets in 
 
 K 2 SiF 6 + 2 K 2 = (KF) 6 + SiO 2 , 
 
 but from the slight solubility of the potassium silicofluoricle some 
 time elapses before it is complete. 
 
 The sulphuric and sulphurous acid must also be estimated if the 
 real amount of HF is required. 
 
 Estimation of Sulphuric Acid in Presence of Hydrofluoric Acid 
 (W. B. Giles). Long experience has convinced the author of this new 
 process, that all methods depending upon the supposed solubility of barium 
 fluoride, and the corresponding insolubility of the sulphate in either hot or 
 cold diluted hydrochloric acid give most erroneous results. For instance, 
 a sample of hydrofluoric acid known to contain 4/ of H 2 SO 4 was treated in 
 the way described by Fresenius, using a large volume of hot dilute 
 hydrochloric acid, and' the precipitate was copiously washed with the same 
 weak acid. The barium precipitate obtained was equal to 6'08 / of SO 3 or 
 over 50 / more than was present, and it was found that on repeatedly 
 moistening the precipitate with dilute H-SO 4 , and re-igniting, that the 
 weight increased materially, showing co-precipitation of barium fluoride. 
 The author therefore devised the following process for the estimation of the 
 SO 3 which gives accurate results. Its basis is - 
 
 1. The conversion of HF into H-'SiF, which is easily accomplished. 
 
 2. The precipitation of the SO 3 from this solution by means of lead silico- 
 fluoride. 
 
 3. The total insolubility of PbSO 4 in a solution containing an excess of 
 the said lead salt. 
 
 Process : A convenient weight of the hydrofluoric acid is placed in 
 a platinum dish, about half its volume of water is added, and then 
 precipitated silica in evident excess, and the whole is allowed to stand with 
 occasional stirring for a few hours. It is then filtered, using an ebonite 
 funnel, into another suitable platinum basin, and the excess of silica 
 thoroughly washed, the filtrate and washings are then evaporated to 
 a convenient bulk, and solution of lead silicofluoride is added in excess. If 
 the least trace of sulphuric acid was contained in the acid originally, an 
 almost immediate precipitate of PbSO 4 Avill form, as it is exceedingly 
 
26. HYDROFLUORIC ACID. 107 
 
 insoluble in the presence of the lead silicofluoride. The solution is allowed! 
 to stand an hour or two, and the PbSO 4 separated by nitration, when it can 
 of course be treated in any convenient volumetric way for the estimation of 
 the lead, or it may be weighed direct. 
 
 Lead silicofluoride is easily prepared by saturating commercial HF with 
 coarsely powdered flint in a lead basin, and then agitating with powdered 
 litharge. Its solubility is very great, and the specific gravity of the 
 solution may reach 2'000 or more. 
 
 Example : To 37'89 gm. of chemically pure HF of 1250 sp. gr., there 
 was added 25 c.c. of normal acid=ro gm. SO 3 . The mixture was then 
 treated as described above, and gave PbSO 4 3'782 gm.=l'0002 gm. of SO 3 . 
 
 Estimation of the Silicofluoric Acid. To a convenient quantity of the 
 acid contained in a platinum dish, a solution of potassic acetate in strong 
 methylated spirit is added in excess, and then more spirit is added, so that 
 there may be about equal volumes of liquid and spirit. Allow to stand for 
 several hours, and then filter and wash with a mixture of half spirit and 
 half water. The resulting potassium silicofluoride may then be titrated 
 with normal alkali according to the equation : 
 
 or if the filter was a weighed one, it may be dried at 100 C. and weighed 
 direct. 
 
 Example : 2 gm. of chemically pure precipitated silica were dissolved in 
 a large excess of pure diluted HF. Treated as above described, it yielded 
 7'35 gm. of K 2 SiF which equals 2'004 gm. of silica; 2 gm. of some 
 powdered flint treated in the same way with 50 gm. of pure HF (of 40 / ) 
 gave 7-168 gm. of K 2 SiF 6 =l'958 gm. of silica. 
 
 Sulphurous Acid. This is easily estimated by taking the solution which 
 results from the total acidity determination and titrating with decinormal 
 iodine. Commercial hydrofluoric acid generally contains from 0'5 to 2'0 % 
 
 The amount of each of the impurities being thus known, the 
 percentage of real HF is easily calculated; e.g., 10 gm. of an 
 acid was found to neutralize 276'0 c.c. of normal alkali. It was 
 found to give the following results : 
 
 c c. normal alkali 8'0 = 3 -2 3 SO 3 
 
 39-0= 9-36H 2 SiF 
 276 -4:7 = 229 c.c. x 0'02 = 45-80 % HF. 
 
 41-61% H 2 by difference 
 
 100-00 
 In this instance the amount of SO 2 was not allowed for. 
 
 Bifluorides. -These salts have lately been used to some extent 
 on the Continent by distillers. They may be titrated in the same 
 way as the acid with phenolphthalein. They generally contain 
 some silicofluoride.* 
 
 The estimation of fluorine in soluble fluorides has been done 
 
 * The whole of this section, to this point, is kindly contributed by W. B. Giles, 
 F.I.C., who has had large practical experience on the subjects treated. 
 
108 VOLUMETRIC ANALYSIS. 26. 
 
 volumetrically by Knob loch (Pliarm. Zeitslirift xxxix. 558). 
 The process is based on the following facts : 
 
 "When a solution of ferric chloride is mixed with its equivalent 
 quantity of potassic fluoride the decomposition is complete, and 
 the resulting ferric fluoride solution is colourless. In this state 
 the iron is not detectable by such tests as thiocyanate, salicylic 
 acid, etc. Still more interesting is the fact that ferric fluoride 
 does not liberate iodine from iodides. 
 
 The following standard solutions, &c., are required : 
 
 -A potassic fluoride ; 5 '809 gm. of the pure ignited salt in 
 a liter of water. 
 
 ^j- solution of ferric chloride, which the author prepared by 
 diluting 19 gm. of the officinal ferric chloride of the Prussian 
 pharmacopoeia to a liter. 
 
 ~Q sodic thiosulphate solution. 
 
 Zinc iodide solution, made by mixing 10 gm. of iodine, 5 gm. 
 of zinc powder, and 25 c.c. of water in a flask, and warming till 
 the violent action is over and the solution colourless, then diluting 
 to 40 c.c. and filtering. 
 
 Process: The liquid containing the fluorides in solution is mixed with 
 a known excess of ferric chloride solution, then with excess of zinc iodide, 
 and allowed to remain in a closed vessel at 35 40 C. for half an hour ; the 
 liberated iodine is then titrated with thiosulphate. The volume of the 
 latter used is deducted from that of the ferric chloride the difference is the 
 measure of the fluorine, 1 c.c. thiosulphate = 0'0019 gm. P. 
 
 The author states that calcium and strontium in their soluble 
 salts may also be estimated by the same method by acidifying 
 their solutions with hydrochloric acid, adding equal volumes, first 
 of potassic fluoride and then ferric chloride solutions in excess, 
 excess of zinc iodide is then added, and digested at 35 40 C. 
 and the liberated iodine ascertained as before, 1 c.c. of thiosulphate 
 -0-002 Ca. 
 
 None of these reactions have been verified by me, but the 
 method as given here is novel, and probably capable of being 
 developed by experience. 
 
 A very interesting paper on the acidimetry of hydrofluoric acid 
 is contributed by Hag a and Osaka (J. C. S. xvii. xviii. 251), being 
 the results of independent experiments made by them in the 
 laboratory of the Imperial University, Japan. 
 
 The authors examined the behaviour of the usual indicators in 
 the neutralization of hydrofluoric acid. That its alkali salts blue 
 litmus, and that its avidity number places it among the vegetable 
 acids rather than with the strong mineral acids, appear to be the 
 only two facts yet recorded bearing upon its acidimetry. ' 
 
 To get uniform indications it was found necessary to have not 
 only the acid pure, but the titrating solutions also ; a little silica, 
 alumina, or carbon dioxide affecting the titration more than it 
 would in the case of the ordinary mineral acids. 
 
28. PHOSPHORIC ACID. 
 
 Phenolphthalein is the best indicator, and leaves nothing to be 
 desired when potash or soda is used for the titration. Rosolic acid 
 is almost equal to it, and can be used besides with ammonia. 
 "With both indicators the change of colour has the advantage of 
 being very evident in platinum vessels. Methyl orange is useless. 
 Litmus, lacinoid and phenacetolin are all capable of being made to 
 yield accurate results in the hands of an experienced operator. 
 
 The fact that accurate results can only be obtained with very- 
 pure acid and reagents, militates against the value of any 
 acidimetric process, and therefore the indirect method by Giles, 
 described above, is of greater technical value. 
 
 OXALIC ACID. 
 
 C 2 H 2 4 2H 2 0-126. 
 
 27. THE free acid can be accurately titrated with normal 
 alkali and phenolphthalein. 
 
 In combination with alkalies, the acid can be precipitated with calcic 
 chloride as calcic oxalate, where no other matters occur precipitable by 
 calcium; if acetic acid is present in slight excess it is of no consequence, as 
 it prevents the precipitation of small quantities of sulphates. The precipi- 
 tate is well washed^dried, ignited, and titrated with normal acid, 1 c.c. of 
 which = 0-063 gm. O~. 
 
 Acid oxalates are titrated direct for the amount of free acicL 
 The reaction continues to be acid until alkali is added in such 
 proportion that 1 molecule acid = 2 atoms alkali metal. 
 
 The combined acid may be found by igniting the salt, and 
 titrating the residual alkaline carbonate as above. 
 
 PHOSPHORIC ACID. 
 
 28. FREE tribasic phosphoric acid cannot be titrated directly 
 with normal alkali in the same manner as most free acids, owing ta 
 the fact, that when an alkaline base (soda, for instance) is added to 
 the acid, a combination occurs in which at one and the same time 
 red litmus paper is turned blue and blue red. This fact has been 
 repeatedly noticed in the case of some specimens of urine, also in 
 milk. In order, therefore, to estimate phosphoric acid, or alkaline 
 phosphates, alkalimetrically, it is necessary to prevent the formation 
 of soluble phosphate of alkali, and to bring the acid into a definite 
 compound with an alkaline earth. Such a method gives tolerably 
 good results when carried out as follows : 
 
 The solution of free acid, or its acid or neutral combination with alkali in 
 a somewhat dilute state, is placed in a flask, and a known volume of normal 
 alkali in excess added, in order to convert the whole of the acid into a basic 
 salt; a drop or two of rosolic acid is added, then sufficient neutral baric 
 
110 VOLUMET1MC ANALYSIS. 28. 
 
 chloride poured in to combine with all the phosphoric acid, the mixture is 
 heated nearly to boiling; and, while hot, the excess of alkali is titrated with 
 normal acid. The suspended baric phosphate, together Avith the liquid, 
 possesses a rose-red colour until the last drop or two of acid, after continuous 
 heating, and agitation, gives a permanent Avhite or slightly yellowish, milky 
 appearance, when the process is ended. 
 
 The volume of normal alkali, less the volume of acid, represents the 
 amount of alkali required to convert the phosphoric acid into a chemically 
 neutral salt, e.g. trisodic phosphate. 1 c.c. alkali = 0'02366 gm. P 2 O 5 . In 
 dealing with small quantities of material, it is better to use f or ^ standard 
 solutions. 
 
 Thomson has shown in his researches on the indicators, that 
 phosphoric acid, either in the free state, or in combination with 
 soda or potash, may with very fair accuracy be estimated by the 
 help of methyl orange and phenolphthalein. If, for instance, 
 normal potash be added to a solution of phosphoric acid" until the 
 pink colour of methyl orange is discharged, KH 2 P0 4 is formed 
 (112 KHO-142 P 2 5 ). If now phenolphthalein is added, and 
 the addition of potash continued until a red colour occurs, K 2 HP0 4 
 is formed. (Again 112 KHO = 142 P 2 5 .) On adding standard 
 hydrochloric or sulphuric acid, until the pink colour of methyl 
 orange reappears, the titration with standard potash may be 
 repeated. 
 
 Many attempts have been made to utilize these reactions for the 
 accurate estimation of P 2 5 in manures, etc., but, so far as my 
 own experience goes, without adequate success. 
 
 Titration as Ammonio-magnesian Phosphate- Stolba (Cliem. 
 Gent, 1866, 727, 728) adopts an alkalimetric method, which 
 depends upon the fact, that one molecule of the double salt 
 requires two molecules of a mineral acid for saturation. 
 
 The precipitation is made with magnesia mixture, the precipitate well 
 washed with ammonia, and the latter completely removed by Avashing with 
 alcohol of 50 or 60 per cent. The precipitate is then dissolved in a measured 
 excess of ^ acid, methyl orange added, and the amount of acid required found 
 by titration with ^ alkali. Care must be taken that all free ammonia is 
 removed from the filter and precipitate, and that the whole of the double 
 salt is decomposed by the acid before titration, which may always be insured 
 by using a rather large excess and warming. The titration is carried on cold. 
 
 This method has given me very good results in comparison with 
 the gravimetric method. The same process is applicable to the 
 estimation of arsenic acid, and also of magnesia, 
 
 1 c.c. of T ^ acid -0-00355 gm. P 2 O 
 = 0-00575 gm. As 2 3 
 = 0-002 gm. MgO 
 
 = - 
 
 The reaction in the case of phosphoric acid may be expressed as 
 follows : 
 
 Mg (NEP) PO 4 + 2HC1 - (NH 4 ) H 2 P0 4 + MgCl 2 . 
 
29. SULPHURIC ANHYDRIDE. Ill 
 
 Method for the Determination of Phosphoric Acid in its Pure 
 Solutions E. Segalle (Z.A.C. xxxiv. 3339) has investigated various 
 methods for the above purpose with the following result: 
 
 By far the most accurate results are obtained by Glucksinann's method. 
 In this, the phosphoric acid is precipitated by an excess of " magnesia 
 mixture " of known strength in free ammonia, the precipitate filtered off, 
 and the free ammonia left in solution is titrated by standard acid. From 
 the equation 
 
 H 3 P0 4 + MgSO 4 + 3 NIP - MgNH 4 P0 4 + (NH 4 ) 2 SO 4 
 
 it will be seen that H 3 PO 4 =3NH 3 . 
 
 The following modification is recommended as being more convenient and 
 simple. To the phosphoric acid solution, contained in a graduated flask, an 
 excess of standard ammonia (preferably normal) is added, followed by an 
 excess of a saturated neutral solution of magnesium sulphate. The liquid 
 is then diluted to the mark, well shaken, and filtered, and the residual 
 ammonia titrated in an aliquot part of the filtrate. 
 
 On account of its simplicity, the modified method is well adapted for 
 ascertaining the strength of the solutions of phosphoric acid employed in 
 pharmacy. 
 
 SULPHURIC ANHYDRIDE. 
 
 SO 3 = 80. 
 
 29. NORDHAUSEX or fuming sulphuric acid consists of a 
 mixture of SO 3 and H 2 SO. When it is rich in SO 3 it occurs in 
 a solid form, and being very hygroscopic cannot be weighed in the 
 ordinary manner. Its strength is therefore best taken in the way 
 recommended by Mess el as follows : A very thin, bulb tube with 
 capillary ends is inserted into a bottle of the melted acid. The 
 ends are bent like the letter /, the bulb being in the middle. The 
 bottle should be of such size, that one end of the tube projects out 
 of its mouth. As soon as the bulb is filled, the upper capillary 
 end is sealed, the tube lifted out, wiped, inverted, and the other 
 end sealed ; the tube is then carefully wiped with blotting paper 
 till dry and clean, then weighed. A stoppered bottle, just large 
 enough to allow the tube being placed loosely inside it, is then 
 about one-third filled with water, the tube gently inserted, the 
 stopper replaced, held firmly in by the hand, and a vigorous shake 
 .given so as to break the tube. A sudden vibration occurs from 
 contact of the acid with the water, but no danger is incurred. 
 A white cloud is seen on the sides of the bottle, which disappears 
 on shaking for a few minutes. After the bottle is cooled the 
 contents are emptied into a measuring flask. An aliquot portion 
 is then taken out and titrated with iodine for SO 2 , which is 
 always present in small quantity : another portion is titrated with 
 standard alkali and methyl orange for sulphuric acid. No other 
 indicator is available, and as Lunge has pointed out (Zeii, Angew. 
 Cliem. 1895, 221), neutrality is reached when the acid sulphite is 
 formed, and not when the whole of the SO 2 is neutralized. 
 
112 VOLUMETRIC ANALYSIS. 30. 
 
 TARTARIC ACID. 
 
 C 4 H 6 G =150. 
 
 30. THE free acid may be readily titrated with normal alkali 
 and phenolphthalein. 
 
 1 c.c. alkali = 0*075 gm. tartaric acid. 
 
 The amount of tartaric acid existing in tartaric acid liquors is 
 best estimated by precipitation as potassic bitartrate ; the same is 
 also the case with crude argols, lees, etc. Manufacturers are highly 
 indebted to War in gt on and Grosjean for most exhaustive 
 papers on this subject, to which reference should be made by all 
 who desire to study the nature and analysis of all commercial 
 compounds of citric and tartaric acids (Warington, J. C. S. 1875 r 
 925994; Grosjean, J. C. S. 1879, 341356). 
 
 Without entering into the copious details and explanations given 
 by these authorities, the methods may be summarized as follows : 
 
 1. Commercial Tartrates. 
 
 In the case of good clean tartars, even though they may contain sulphates 
 and carbonates, very accurate results may he obtained by indirect methods. 
 
 (a] The very finely powdered sample is first titrated with normal alkali, 
 and thus the amount of tartaric acid existing as bitartrate is found; another 
 portion of the sample is then calcined at a moderate heat, and the ash 
 titrated. By deducting from the volume of acid so used the volume used 
 for bitartrate, the amount of base corresponding to neutral tart rates is 
 obtained. 
 
 (b) The whole of the tartaric acid is exactly neutralized with caustic 
 soda, evaporated to dryness, calcined, and the ash titrated with normal acid ; 
 the total tartaric acid is then calculated from the volume of standard acid 
 used ; any other organic acid present Avill naturally be included in this 
 amount. In the case of fairly pure tartars, etc., this probable error may he- 
 disregarded. 
 
 Warington's description of the first process is as follows : 
 
 5 gni. of the finely powdered tartar are heated with a little water to 
 dissolve any carbonates that may be present. If it is wished to guard against 
 crystalline carbonates, 5 c.c. of standard HC1 are added in the first instance 1 , 
 and the heating is conducted in a covered beaker. Standard alkali is next 
 added to the extent of about three-fourths of the amount required by a good 
 tartar of the kind examined, plus that equivalent to the acid used, and the 
 whole is brought to boiling; when nearly cold, the titration is finished. 
 From the amount of alkali consumed, minus that required by the HC1, the 
 tartaric acid present as acid tartrate is calculated. 
 
 2 gm. of the powdered tartar are next weighed into a platinum crucible 
 with a well-fitting lid ; the crucible is placed over an argand burner ; heat is 
 first applied very gently to dry the tartar, and then more strongly till 
 inflammable gas ceases to be evolved. The heat should not rise above very 
 low redness. The black ash is next removed with water to a beaker. If the 
 tartar is known to be a good one, 20 c.c. of standard H 2 SO 4 are now run 
 from a pipette into the beaker, a portion of the acid being used to rinse the 
 crucible. The contents of the beaker are now brought to boiling, filtered, 
 and the free acid determined with standard alkali. As the charcoal on the 
 filter under some circumstances retains a little acid, even when well washed,. 
 
.30. TARTARIC ACID. 113 
 
 it is advisable when the titration is completed to transfer the iilter and its 
 contents to the neutralized fluid, and add a further amount of alkali if 
 necessar} r . From the neutralizing power of a gram of burnt tartar is 
 subtracted the acidity of a gram of unburnt tartar, both expressed in c.c. of 
 standard alkali, the difference in the neutralizing power of the bases existing 
 as neutral tartrates, and is then calculated into tartaric acid on this 
 assumption.* 
 
 If the tartar is of low quality, 5 c.c. of solution of hydrogen peroxide 
 (1 volume 10 volumes O) are added to the black ash and water, and 
 immediately afterwards, the standard acid ; the rest of the analysis proceeds 
 .as already described ; the small acidity usually belonging to the peroxide 
 .-solution must, however, be known and allowed for in the calculation. By 
 the use of hydrogen peroxide the sulphides formed during ignition are 
 reconverted into sulphates, and the error of excess which their presence 
 would occasion is avoided. 
 
 The above method does not give the separate amounts of acid 
 and neutral tartrates in the presence of carbonates, but it gives the 
 correct amount of tartaric acid ; it is also correct in cases where 
 free tartaric acid exists, so long as the final results show that some 
 acid existed as neutral salt. Whenever this method shows that 
 the acidity of the original substance is greater than the neutralizing 
 power of the ash, it will be necessary to use the method b, which 
 is the only one capable of giving good results when the sample 
 contains much free tartaric acid. 
 
 Instead of the alkalimetric estimation in both the above methods, 
 equally good results may be got by a carbonic acid determination 
 in the asli with S c he i bier's apparatus ( 23.6), or any of the 
 usual methods. 
 
 2. Tartaric Acid Liquors. 
 
 Old factory liquors contain a great variety of substances gradually 
 accumulated, from which the actual tartaric acid can only be 
 separated as bitartrate by the following process : 
 
 (c) A quantity of liquor containing 24 gm. of tartaric acid, and of 
 30 40 c.c. volume, is treated Avith a saturated solution of neutral potassic 
 citrate, added drop by drop with constant stirring. If free sulphuric acid is 
 present no precipitate is at first produced ; but as soon as the acid is satisfied, 
 the bitartrate begins to appear in streaks on the sides of the vessel. When 
 this is seen, the remainder of the citrate is measured in to avoid an undue 
 excess : 4 c.c. of a saturated solution of potassic citrate will be found 
 sufficient to precipitate the maximum of 4 grams of tartaric acid supposed to 
 be present. If the liquor contain a great deal of sulphuric acid, a fine 
 precipitate of potassic sulphate will precede the formation of bitartrate, but 
 is easily distinguished from it. With liquors rich in sulphuric acid, it is 
 advisable to stir the mixture vigorously at intervals for half an hour, then 
 proceed as in 3 d. 
 
 Grosjean modifies this process by precipitating the liquor with an excess 
 of calcic carbonate, then boiling the mixture with excess of potassic oxalate. 
 
 * It is obvious that the neutralizing power of the ash of an acid tartrate is exactly 
 the same as the acidity of the same tartrate before burning-. In making the calcula- 
 tions, it nmst be remembered that the value of the alkali in tartaric acid is twice as 
 great in the calculation made from the acidity of the unburnt tartar, as in the 
 . calculation of the acid existing as neutral tartrates. 
 
 I 
 
114 VOLUMETRIC ANALYSIS. 31. 
 
 By this means the alumina, iron, phosphoric and sulphuric acids are thrown 
 down with the calcic oxalate, and the precipitate allows of ready nitration. 
 The separation as bitartrate then follows, as in d. 
 
 3. Very impure Lees and Argrols. 
 
 Grosjean (/. C. S. 1879, 341) gives a succinct method for 
 the treatment of these substances, based on War ing ton's original 
 oxalate process, the principle of which is as follows : 
 
 The finely ground sample ( about 2 gm. tartaric acid) is first moistened 
 with a little water, heated to 100 C., then digested for 15 minutes or so with 
 an excess of neutral potassic oxalate (the excess must not be less than 
 1'5 gm.), and nearly neutralized with potash. After repeated stirring, the 
 mixture is transferred to a vacuum filter, and the residue washed; the 
 liquid so obtained contains all the tartaric acid as neutral potassic tartrate ; 
 excess of citric acid is added, which precipitates the whole of the tartaric 
 acid as bitartrate, and the amount is found by titration with standard alkali 
 in the usual way. 
 
 One of the chief difficulties in treating low qualities of material is the 
 filtration of the nearly neutral mixture above mentioned. Grosjean adopts- 
 the principle of Casamajor's filter (C. N. xxxii. 45), using an ordinary 
 funnel with either platinum, lead, or pumice disc ; but whether this, or 
 Bun sen's, or other form of filter is used, the resulting filtrate and washings- 
 (which for 2 gm. tartaric acid should not much exceed 50 c.c.) are ready for 
 the separation of the bitartrate in the following improved way : 
 
 (d) To the 50 c.c. or so of cold solution 5 gm. of powdered potassic- 
 chloride are added, and stirred till dissolved : this renders the subsequent 
 precipitation of bitartrate very complete. A 50 per-cent. solution of citric 
 acid is then mixed with the liquid in such proportion, that for every 2 gm. 
 of tartaric acid an equal, or slightly greater amount of citric acid is present. 
 By continuously stirring, the whole of the bitartrate comes down in ten 
 minutes (Grosjean) ; if the temperature is much above 16, it is preferable 
 to wait half an hour or so before filtering. This operation is best done on 
 the vacuum filter, and the washing is made with a 5 per-cent. solution of 
 potassic chloride, saturated at ordinary temperature with potassic bitartrate ; 
 if great accurac} 7 is required, the exact* acidity of the solution should be 
 found by ^5- alkali, and the washing continued until the washings show no- 
 greater acidity, thus proving the absence of citric acid. Finally, the washed 
 precipitate is gently pressed into a cake to free it from excess of liquid,, 
 transferred to a beaker Avith the filter, hot \vater added, and titrated with 
 standard alkali. 
 
 The troublesome filtration can be avoided in many cases by taking* 
 30 40 gm. of substance, and after decomposition by oxalate, and neutralizing- 
 with potash, making up the volume to 150 or 200 c.c., adding water in 
 corresponding proportion to the bulk of the residue, then taking an aliquot 
 portion for precipitation. A blank experiment made by Grosjean in this 
 way, gave a volume of 3'75 c.c. for the residue in 10 gm. lees. Other things, 
 being equal, therefore, 30 or 40 gm. may respectively be made up to 161 and 
 215 c.c., then 50 c.c. taken for precipitation. > 
 
 ESTIMATION OF COMBINED ACIDS AND BASES IN 
 NEUTRAL SALTS. 
 
 31. THIS comprehensive method of determining the quantity 
 of acid in neutral compounds (but not the nature of the acid), is 
 applicable only in those cases where the base is perfectly precipitated 
 
31. COMBINED ACIDS AND BASES. 115 
 
 by an excess of caustic alkali or its carbonate. The number of 
 bodies capable of being so precipitated is very large, as has been 
 proved by the researches of Langer and "VVawnikiewicz (Ann. 
 Chem. u. Phar. 1861, 239), who seem to have worked out the 
 method very carefully. These gentlemen attribute its origin to 
 Bunsen ; but it does not seem certain who devised it. The best 
 method of procedure is as follows : 
 
 The substance is weighed, dissolved in water in a 300-c.c. flask, heated to 
 boiling or not, as may be desirable ; normal alkali or its carbonate, according 
 to the nature of the base, is then added from a burette, until the whole is 
 decidedly alkaline. It is then diluted to 300 c.c. and put aside to settle, and 
 100 c.c. are taken out and titrated for the excess of alkali ; the remainder 
 multiplied by 3, gives the measure of the acid combined with the original 
 salt, i.e. supposing the precipitation is complete. 
 
 Example : 2 gm. crystals of baric chloride were dissolved in water, heated 
 to boiling, and 20 c.c. normal sodic carbonate added, diluted to 300 c.c. and 
 100 c.c. of the clear liquid titrated with normal nitric acid, of which 1*2 c.c. 
 was required ; altogether, therefore, the 2 gm. required 16'4 c.c. normal 
 alkali ; this multiplied by 0'122 gave 2'0008 gm. Bad 2 2H 2 O instead of 
 2 gm. ; multiplied by the factor for chlorine 0'03537, it yielded 0'58007 gm. 
 Theory requires 0'5809 gm. chlorine. 
 
 The following substances have been submitted to this mode of 
 examination with satisfactory results : 
 
 Salts of the alkaline earths precipitated with an alkaline 
 carbonate while boiling hot. 
 
 Salts of magnesia, with pure or carbonated alkali. 
 
 Alum, with carbonate of alkali. 
 
 Zinc salts, boiling hot, with the same. 
 
 Copper salts, boiling hot, with pure potash. 
 
 Silver salts, with same. 
 
 Bismuth salts, half an hour's boiling, with sodic carbonate. 
 
 Nickel and cobalt salts, with the same. 
 
 Lead salts, with the same. 
 
 Iron salts, boiling hot, with pure or carbonated alkali. 
 
 Mercury salts, with pure alkali. 
 
 Protosalts of manganese, boiling hot, with sodic carbonate. 
 
 Chromium persalts, boiling hot, with pure potash. 
 
 Where the compound under examination contains but one base 
 precipitable by alkali, the determination of the acid gives, of 
 course, the quantity of base also. 
 
 Wolcott Gibbs (C. N. 1868, i. 151) has enunciated a new 
 acidimetric principle applicable in cases where a base is precipitable 
 at a boiling temperature by hydric sulphide, and the acid set free 
 so as to be estimated with standard alkali. Of course the method 
 can only be used where complete separation can be obtained, and 
 where the salt to be analyzed contains a fixed acid which has no 
 effect upon hydric sulphide. A weighed portion is dissolved in 
 
 i 2 
 
116 VOLUMETRIC ANALYSIS. 31. 
 
 water, brought to boiling, and the gas passed in until the metal is 
 completely precipitated ; which is known by testing a drop of the 
 clear liquid upon a porcelain tile with sulphuretted hydrogen 
 water, or any other appropriate agent adapted to the metallic salt 
 under examination. 
 
 The liquid is filtered from the precipitate, and the latter well 
 washed, and the solution made up to a definite measure. An 
 aliquot portion is then titrated with normal alkali as usual, Avith 
 one of the phenol indicators. 
 
 In the case of nitrates or chlorides, where nitric or hydrochloric 
 acid would interfere with the hydric sulphide, it was found that the 
 addition in tolerable quantity of a neutral salt containing an organic 
 acid (e.g. sodic or potassic tartrate, or the double salt) obviated all 
 difficulty. 
 
 The results obtained by Gibbs in the case of copper, lead,, 
 bismuth, and mercury, as sulphate, nitrate, and chloride, agreed 
 very closely with theory. 
 
 Though not strictly belonging to the domain of acidimetry, 
 a method worked out by Neumann (Z. A. C. xxxiv. 454) may here 
 be mentioned for the technical estimation of some of the heavy 
 metals precipitable by sodic sulphide. The strength of the sulphide 
 solution is ascertained by boiling it with a measured excess of 
 standard acid till all the H 2 S is dissipated ; the excess of acid is 
 then found by titration with standard alkali, using phenolphthalein 
 as indicator. Having established the working strength of the 
 sulphide solution, the neutral solution of the metal to be estimated 
 is first precipitated with a known excess of standard sulphide, 
 and the solution containing the suspended sulphide or hydroxide 
 is rendered clear, if necessary, by the addition of strong sodium 
 chloride solution, and diluted to a definite volume at 16 C. 
 An aliquot part of the solution is then filtered off, or removed 
 by means of a pipette, and the excess of sulphide indirectly 
 determined in it. This indirect process is necessary, because the 
 alkaline sulphide destroys the colour of litmus or of phenolphthalein. 
 The estimation of the amounts of metal in the following salts by 
 this method gave excellent results : alum, chrome alum, silver 
 sulphate, copper sulphate, cobalt sulphate, cadmium sulphate, lead 
 nitrate, manganese sulphate, nickel sulphate, ferrous sulphate, 
 ferrous ammonium sulphate, ferric chloride. This method, of course, 
 is not applicable if the solutions contain any free acid. Solutions 
 of chlorides containing free hydrochloric are first evaporated on 
 the water-bath, the residue moistened with alcohol, and again 
 evaporated to dryness. Sulphates are first converted into chlorides 
 by treatment with barium chloride and hydrochloric acid, and 
 the solutions so obtained are treated as before described for the 
 removal of the free HC1. .Nitrates are twice evaporated to dryness 
 with concentrated HC1, excess of the latter being finally removed 
 in the above-mentioned manner. 
 
32, ALKALIMETBIC METHODS. 117 
 
 EXTENSION OF ALKALIMETBIC METHODS. 
 
 32. BOHLIG (Z. a. C. 1870, 310) has described a method 
 for the estimation of sulphuric acid, baryta, chlorine, iodine, and 
 bromine, which appears worthy of some consideration, since the 
 only standard solutions required are an acid and an alkali v 
 
 Alkaline sulphates are known to be partially decomposed, in 
 contact with baric carbonate, into alkaline, carbonates and baric 
 sulphate. The decomposition is complete in the presence of free 
 carbonic anhydride ; acid carbonates of the alkali-metals are left in 
 solution, together with some acid baric carbonate, which can be 
 removed by boiling. The solution is filtered, and the alkaline 
 carbonate determined by means of a standard acid solution, and 
 the amount of sulphuric acid or alkaline sulphate calculated 
 from the amount of normal acid required. This process has been 
 satisfactorily used by Hanbst for sulphates in waters (C. N. 
 xxxvi. 227), and by Grossmann for salt cake (C. N. xli. 114). 
 See also 17.14. 
 
 Neutral chlorides, bromides, and iodides, more especially of the 
 alkali-metals, are most readily decomposed by pure silver oxide 
 into insoluble silver salts, leaving the alkali-metal in solution as 
 hydrate (ammonia salts always excepted), which can then be 
 determined as usual by standard acid. 
 
 The author treats solutions containing sulphates of the heavy 
 metals, of the earths or alkaline earths, and free from acids whose 
 presence would influence the method, viz., phosphoric, arsenic, 
 oxalic, etc., with a solution of potassic carbonate so as to precipitate 
 the bases and leave about double or treble the amount of alkaline 
 carbonate in solution. From 1 to 1J gm. of substance is operated 
 upon in a flask. The solution is made up to 500 c.c., well shaken, 
 and the precipitate allowed to subside. 50 c.c, are then filtered, 
 and titrated with standard acid and methyl orange. Another 100 c.c. 
 are filtered in like manner into a strong quarter-liter flask, and 
 diluted with about 100 c.c. of hot water; the requisite quantity of 
 normal acid is then run in at once from a burette ; the solution 
 diluted to 250 c.c. ; and about a gram of dry baric carbonate 
 (free from alkali) added. The flask is next closed, and the liquid 
 well agitated. The decomposition of the alkaline sulphate is 
 complete in a few minutes. The flask should be opene.d now and 
 then to allow the carbonic anhydride to escape. Finally, about 
 J gm. of pulverized baric hydrate is added, the whole well shaken, 
 and a portion of the rapidly clearing liquid tested qualitatively for 
 barium and sulphuric acid. The result should be a negative one. 
 50 c.c., corresponding to 20 c.c. of the original solution, are then 
 filtered and titrated with normal acid, and the quantity of sulphuric 
 acid (sulphate) calculated as usual. 
 
 The source of carbonic anhydride is thus placed in the liquid 
 itself, provided the quantity of potassic carbonate be not -too small. 
 
118 VOLUMETIIIC ANALYSIS. 32. 
 
 Equivalent quantities of K 2 S0 4 + 2K 2 C0 3 + 2HC1 + BaCO 3 when 
 mixed with sufficient water change into BaSO 4 + 2KHC0 3 + 2KC1, 
 and it is therefore more than sufficient to add twice the quantity 
 of potassic carbonate compared with the alkaline sulphate operated 
 upon. 
 
 Baric hydrate is added with a view of removing any carbonic 
 anhydride left in the liquid after boiling, which would otherwise 
 dissolve some of the excess of baric carbonate contained in the 
 precipitate. 
 
 Any baric hydrate not required to remove CO 2 is acted upon by 
 the acid potassic carbonate, but does not influence the final result. 
 
 Phosphoric and oxalic acids the author proposes to remove by 
 means of calcic chloride ; chromic acid by deoxidizing agents, 
 such as alcohol and hydrochloric acid. Bohlig recommends this 
 method for estimating sulphuric acid in ashes, crude soda, Stassfurth 
 salts, etc, 
 
 Solutions containing baryta are estimated in like manner by 
 precipitation as carbonate, and decomposition with potassic sulphate 
 in a solution containing free carbonic acid. Chlorine is determined 
 in solutions by first precipitating any metallic chloride with potassic 
 carbonate added in moderate excess. The filtrate is made up to 
 250 c.c., and the excess of potassic carbonate determined in 50 c.c. 
 by means of a normal solution of HC1. 125 c.c. of the solution 
 are next treated with excess of silver oxide and made up to 250 c.c., 
 well shaken (out of contact with the light) and filtered. 100 c.c. 
 of the nitrate are titrated with normal hydrochloric acid. The 
 difference between the quantity of acid required in the last and 
 that of the first experiment, multiplied by 5, gives the amount 
 of chlorine contained in the original solution. A portion of the 
 filtrate should be tested for chlorine by means of mercurous nitrate. 
 
 The filtrate is obtained perfectly clear only in the presence of 
 some potassic or sodic carbonate, and by employing argentic oxide 
 free from argentous oxide. A few drops of pure potassic per- 
 manganate added to the argentic oxide preserved in water prevent 
 formation of the latter. The oxide to be employed for each 
 experiment is filtered when required, and thoroughly washed. 
 
 Bromine and iodine are determined in like manner, The author 
 has not been able, however, to estimate the mixtures of the halogen 
 salts ; but Jie has made the interesting observation that potassic 
 iodide, when boiled with potassic permanganate, is completely 
 oxidized into iodate. This facilitates the detection of small 
 quantities of chlorine and bromine, in the presence of much 
 iodide. The greater part of iodate may be separated also by 
 precipitation with baric nitrate before determining chlorine. The 
 standard acid solutions which Bohlig employed contained not more 
 than one-third of the equivalent of HC1 or SO 3 per liter. 
 
 For further particulars the reader is referred to the original 
 paper (Arch. Pharm. 3 cxlv. 113). 
 
32. ALKALIMETRIC METHODS. 119 
 
 Siebold (Year Bool- of Pharmacy, 1878, 518) describes a very- 
 ingenious process, devised by himself, for the titration of caustic 
 and carbonated alkalies by means of prussic acid, the principle of 
 which is explained in 59. The process is useful in the case of 
 carbonates, since CO 2 is no hindrance. 
 
 0'5 to 1 gm. of the alkali or alkaline carbonate is dissolved in about 100 c.c. 
 of water, and an excess of hydrocyanic acid (say 10 or 20 c.c.) of 5 per cent, 
 solution added; then ~ silver solution cautiously added with constant 
 stirring until a faint permanent turbidity occurs. Each c.c. of T ^j- silver 
 = 0-0138 gm. K 2 CO 3 , or 0'0106 gm. Na 2 CO 3 . 
 
 In the case of chlorides being present, their quantity may be 
 determined by boiling down the mixture to about half its volume 
 to expel all free prussic acid, adding a drop or two of potassic 
 chromate as indicator, then titrating with ~$ silver. Any excess 
 .above that required in the first titration will be due to chlorine, 
 and may be calculated accordingly. 
 
120 VjOLUMETKIC ANALYSIS. 33. 
 
 PART III. 
 ANALYSIS BY OXIDATION OR REDUCTION. 
 
 33. THE series of analyses which occur under this system are 
 very extensive in number, and not a few of them possess extreme 
 accuracy, such in fact, as is not possible in any analysis by weight. 
 The completion of the various processes is generally shown by 
 a distinct change of colour ; such, for instance, as the occurrence 
 of the beautiful rose-red permanganate, or the blue iodide of 
 starch ; and as the smallest quantity of these substances will 
 colour distinctly large masses of liquid, the slightest excess of the 
 oxidizing agent is sufficient to produce a distinct effect. 
 
 The principle involved in the process is extremely simple. 
 Substances which will take up oxygen are brought into solution, 
 and titrated with a substance of known oxidizing power ; as, for 
 instance, in the determination of ferrous salts by permanganic- 
 acid. The iron is ready and willing to receive the oxygen, 
 the permanganate is equally willing to part with it ; while the iron 
 is absorbing the oxygen, the permanganate loses its colour almost 
 as soon as it is added, and the whole mixture is colourless ; but 
 immediately the iron is satisfied, the rose colour no longer disappears, 
 there being no more oxidizable iron present. In the case of potassic 
 permanganate the reaction is: lOFeO + 2MnK0 4 = 5Fe 2 :! + 
 2MnO + K-'O. Oxalic acid occupies the same position as the 
 ferrous salts ; its composition is C 2 4 H 2 + 2H-O = 126. If perman- 
 ganate is added to it in acid solution, the oxalic acid is oxidized to 
 carbonic acid, and the manganic reduced to manganous oxide, thus 
 Mn 2 7 + 5C 2 0*H 2 + 2H 2 S0 4 = 10C0 2 + 2MnS0 4 + 7H 2 O. When 
 the oxalic acid is all decomposed, the colour of the permanganate 
 no longer disappears. On the other hand, substances which will 
 give up oxygen are deoxidized by a known excessive quantity of 
 reducing agent, the amount of which excess is afterwards ascertained 
 by residual titration with a standard oxidizing solution; the strength 
 of the reducing solution being known, the quantity required is 
 a measure of the substance which has been reduced by it. 
 
 The oxidizing agents best available are potassic permanganate, 
 iodine, potassic bichromate, and red potassic prussiate. 
 
 The reducing agents are sulphurous acid, sodic hyposulphite,'"" 
 sodic thiosulphate, oxalic acid, ferrous oxide, arsenious anhydride, 
 stannous chloride, yellow potassic prussiate, and zinc or magnesium. 
 
 With this variety of materials a great many combinations may be 
 arranged so as to make this system of analysis very comprehensive; 
 but the following are given as sufficient for almost all purposes, 
 
 :;: S c li il t z e 11 b e r g e r ' s preparation is here meant. 
 
L; 
 
 *r | 
 
 UNIVERSITY 
 
 34. STANDARD PERMANGAN 
 
 and as being susceptible of the greatest amount of purity and 
 stability of material, with exceedingly accurate results: 
 
 1. Permanganate and ferrous salts (with the rose colour as 
 indicator) ; permanganate and oxalic acid (with the rose colour 
 as indicator). 
 
 2. Potassic bichromate and ferrous salts (with cessation of blue 
 colour when brought in contact with red potassic prussiate, as 
 indicator). 
 
 3. Iodine and sodic thiosulphate (with starch as indicator) ; 
 iodine and sodic arsenite (with starch as indicator). 
 
 PREPARATION OF STANDARD SOLUTIONS. 
 
 PERMANGANIC ACID AND FERROUS OXIDE. 
 
 1. Potassic Permang-anate. 
 Mn 2 K 2 8 = 315'6. Decinormal Solution = 3 '156 gm. per liter. 
 
 34. THE solution of this salt is best prepared for analysis by 
 dissolving the pure crystals in fresh distilled water, and should be 
 of such a strength that 17*85 c.c. will oxidize 1 decigram of iron. 
 The solution is then decinormal. If the salt can be had perfectly 
 pure and dry, 3'156 gm. dissolved in a liter of water at 16 C., will 
 give an exactly decinormal solution ; but, nevertheless, it is always 
 well to verify it as described below.* If kept in the light in 
 ordinary bottles it will retain its strength for several months, if in 
 bottles covered with black paper much longer, nevertheless, it 
 should from time to time be verified by titratioii in one of the 
 following ways : 
 
 2. Titration of Permanganate. 
 
 (a) With. Metallic Iron. The purest iron to be obtained is 
 thin annealed binding-wire free from rust, generally known as 
 flower wire.f Its actual percentage of pure iron may be taken 
 as 99-6 
 
 * Very fairly pure permanganate, in large crystals, may now be obtained in commerce, 
 and if this salt is recrystallized twice from hot distilled water and dried thoroughly at 
 1')J J C., it will be found practically pure. 
 
 t Miss C. F. Roberts (Amer. Jour. Sci. 1894, 286, 290) advocates the use of pure 
 iron, prepared by electrolysis, as follows : About 10 gin. -of ferrous-ammonium sulphate 
 are dissolved in 150 c.c. of water. 5 c.c. of a saturated solution of potassic oxalate 
 added, and then heated with a sufficiency of solution of animonic oxalate until clear. 
 A weighed piece of platinum foil, shaped so as to be easily placed into a rather large 
 weighing bottle, is then pvit into a beaker containing the iron solution, and the latter 
 decomposed with a current of about two amperes between two platinum electrodes. In 
 about two hours enough iron will be deposited for a tit-ration. The deposited metal is 
 of course well washed, dried, and weighed in the weighing bottle, then dissolved in 
 dilute acid, precisely as in the case of iron wire. 
 
122 VOLUMETRIC ANALYSIS. 34. 
 
 Process : Fit a tight cork or rubber stopper, with bent delivery tube, into 
 a flask holding about 300 c.c., and clamp it in a retort stand in an inclined 
 position, the tube so bent as to dip into a small beaker containing pure 
 water. Pill the flask one-third with dilute pure sulphuric acid, and add 
 a few grains of sodic carbonate in crystals ; the CO 2 so produced will drive 
 out the air. While this is being done weigh about O'l gram of the wire; 
 put it quickly into the flask when the soda is dissolved, and apply a gentle 
 heat till the iron is completely in solution, a few black specks of carbon are 
 of no 'consequence. The flask is then rapidly cooled under a stream of cold 
 water, diluted if necessary with some recently boiled and cooled water, and 
 the permanganate run in cautiously from a T V c.c. tap burette, Avith constant 
 shaking, until a faint rose-colour is permanent. Instead of this arrange- 
 ment for dissolving the iron the apparatus shown in the section on iron 
 analysis ma}^ be used, 63. 
 
 The decomposition which ensues from titrating ferrous oxide by 
 permanganic acid may be represented as follows : 
 
 lOFeO and Mn 2 7 - 2MnO and 5Fe 2 :) . 
 
 The weight of wire taken, multiplied by 0*996, will give the 
 actual weight of pure iron upon which to calculate the strength of 
 the permanganate. 
 
 Example: Exactly O'l gm. of wire was dissolved and titrated with 
 a permanganate solution, of which the quantity required was 17*6 c.c. 
 The equation O'l : 0'0996 : : 17'85=^ gives 17'45, the permanganate is 
 therefore a trifle too strong, but correct enough for all practical purposes. 
 
 (b) "With Ferrous-ammonium Sulphate. In order to ascertain 
 the strength of the permanganate, it may be titrated with 
 a weighed quantity of this substance instead of metallic iron. 
 
 This salt is a convenient one for titrating the permanganate, as it saves the 
 time and trouble of dissolving the iron, and Avhen perfectly pure, it can be 
 depended on without risk. To prepare it, 139 parts of the purest crystals of 
 ferrous sulphate, and 66 parts of pure crystallized ammonic sulphate are 
 separately dissolved in the least possible quantity of distilled water of about 
 40 C. (if the solutions are not perfectly clear they must be filtered) ; mix 
 them at the same temperature in a porcelain dish, adding a few drops of 
 pure sulphuric acid, and stir till cold. During the stirring the double salt 
 will fall in a finely granulated form. Set aside for a few hours, then pour 
 off the supernatant liquid, and empty the salt into a clean funnel with a little 
 cotton wool stuffed into the neck, so that the mother-liquor may drain away ; 
 the salt may then be quickly and repeatedly pressed between fresh sheets of 
 clean filtering paper. Lastly, place in a current of air to dry thoroughly, 
 so that the small grains adhere no longer to each other, or to the paper in 
 which they are contained, then preserve in a stoppered bottle for use. 
 
 The formula of the salt is Fe (XH 4 )' 2 (SO 4 ) 2 , 6H 2 = 392. 
 Consequently it contains exactly one-seventh of its weight of iron ; 
 therefore 0*7 gm. represents O'l gm. Fe, and this is a convenient 
 quantity to weigh for the purpose of titrating the permanganate. 
 
 Process : 0'7 gm. being brought into "dilute cold solution in a flask or 
 beaker, and 20 c.c. of dilute sulphuric acid (1 to 5) added (the titration of 
 permanganate, or any other substance by it, should always take place in the 
 presence of free acid, and preferably sulphuric), the permanganate is delivered 
 
34 STANDARD PERMANGANATE. 123 
 
 from a burette with glass tap divided in T V c.c., as before described, until 
 a point occurs when the rose colour no longer disappears on shaking. 
 
 (<?) With Oxalic Acid. This is a very quick method of titrating 
 permanganate, if the exact acidimetric value of the solution of pure oxalic 
 acid is known. 10 c.c. of normal solution are brought into a flask with dilute 
 sulphuric acid, as in the case of the iron salt, and considerably diluted with 
 water, then warmed to about 60 C., and the permanganate added from the 
 burette. The colour disappears slowly at first, but afterwards more rarpidly, 
 becoming first brown, then yellow, and so on to colourless. More care must 
 be exercised in this case than in the titration with iron, as the action is not 
 momentary. 100 c.c. should be required to be strictly decinormal. The 
 chemical change which occurs is explained on page 120. 
 
 (d) With Lead Oxalate. Stolba prefers this salt to oxalic acid, for 
 the reasons that it contains no water, is not liable to absorb an}' from 
 exposure, and has a high molecular weight, 1 part of the salt representing 
 0'42799 of oxalic acid, or 63 oxalic acid=147'2 lead oxalate. 
 
 The method of titration is similar to that with oxalic acid, using dilute 
 sulphuric acid, and warming the mixture to ensure the complete decomposi- 
 tion of the salt into lead sulphate and free oxalic acid. Sodic oxalate is 
 also anhydrous and equally serviceable. 
 
 The lead oxalate is prepared by precipitating pure lead acetate with oxalic 
 acid in excess, and washing the precipitate by decantation with warm water 
 till all free acid is removed; the precipitate is then dried at 120 C., and 
 preserved for use. Some operators prefer to use ammonic oxalate in place of 
 oxalic acid or lead oxalate, as being a substance of definite hydration, and 
 easily obtained in a pure state. Its formula is (NH 4 ) 2 C 2 O 4 , H 2 6 - 142=2Fe. 
 The titration is carried on precisely as in the case of oxalic acid. 
 
 0) With Hydrogen Peroxide in the Nitrometer. In a paper on 
 this subject by Lunge ('/. S. C. I. ix. 21) it is shown by very carefully 
 conducted experiments with purest materials and verified apparatus that 
 -exceedingly accurate results may be obtained by the modified nitrometer 
 with patent tap (illustrated at the end of Part VII.). Lunge's experiments 
 were made on a semi-normal solution of permanganate (1 c.a=0'004 gin. O), 
 but whether equally exact results would be obtained with T \ permanganate 
 I cannot say, not having tried it ; but of course an approximately semi-normal 
 solution may be made and reduced to either -| or T ^ strength, if desired, 
 by dilution with fresh distilled water. The exact method of using this 
 instrument will be described under the head of Nitrometer in Part VII. ; 
 but so far as permanganate is concerned it was found that convenient 
 quantities of substances to use were 10 c.c. of permanganate, 15 c.c. 
 of ordinary 10 volume H 2 2 , and 30 c.c. of sulphuric acid 1 : 5. The 
 nitrometer having been charged with water, the mixture was shaken up 
 and allowed to stand ten minutes, shaken again and read off after five 
 minutes. The volume of oxygen so obtained was corrected for temperature 
 and pressure, then calculated into weight. The results of three experiments 
 using the quantities mentioned above were as follows : 
 
 1. Corrected volume of O 55'92 c.c.=0'0040C7 gm. 
 
 2. 55-82 c.c.=0-004000 
 
 3. 55'82 c.c.=0'004000 
 Average 0'004002 gm. of oxygen per c.c. of solution. 
 
 Three experiments with the same permanganate solution gave, when iron 
 wire was used, an average of 0*00399 gm., and with oxalic acid 0'OU3997 gm. 
 of oxygen respectively per c.c. 
 
 Lunge says : *' Wo cannot but infer that standardizing a solution 
 
124 VOLUMETRIC ANALYSIS. 35. 
 
 of permanganate with hydrogen peroxide in the nitrometer when 
 observing the prescribed precautions is one of the most accurate 
 known methods for this purpose, and withal possesses the great 
 advantage that it is carried out within an extremely short time, 
 without requiring a fundamental substance of accurately known 
 composition." 
 
 Many other substances have been proposed for standardizing 
 permanganate, such as potassic ferrocyanate, thiocyanate, vanadic 
 oxide, etc., but they are all inferior in value to those above named. 
 
 3. Precautions in Titrating with Permanganate. 
 
 Tt must be borne in mind that free acid is always necessary in 
 titrating a substance with permanganate, in order to keep the 
 resulting mangaiious oxide in solution. Sulphuric acid, in a dilute 
 form, has no prejudicial effect on the pure permanganate, even at 
 a high temperature. With hydrochloric acid the solution to be 
 titrated must be very dilute and of low temperature, otherwise 
 chlorine will be liberated and the analysis spoiled. This acid acts 
 as a reducing agent on permanganate in concentrated solution, 
 thus 
 
 Mn 2 7 + 14HC1 = 7H 2 + 10C1 + 2MnCK 
 
 The irregularities due to this reaction may be entirely obviated 
 by the addition of a few grams of manganous or magnesic sulphate 
 before titration. 
 
 Organic matter of any kind decomposes the permanganate, and 
 the solution therefore cannot be filtered through paper, nor can it 
 be used in Mohr's burette, because it is decomposed by the 
 india-rubber tube. It may, however, be filtered through gun 
 cotton or glass wool. 
 
 TITRATION OF FERRIC SALTS BY PERMANGANATE. 
 
 35. ALL ferric compounds requiring to be estimated by 
 permanganate must, of course, be reduced to the ferrous state. 
 This is best accomplished by metallic zinc or magnesium in 
 sulphuric acid solution. Hydrochloric may also be used with the 
 precautions mentioned. 
 
 The reduction occurs on simply adding to the warm diluted 
 solution small pieces of zinc (free from iron, or at least with 
 a known quantity present) or coarsely powdered magnesium until 
 colourless ; or until a drop of the solution brought in contact with 
 a drop of potassic thiocyanate produces no red colour. All the 
 zinc or magnesium must be dissolved previous to the titration. 
 
 The reduction may be hastened considerably as shown in 61.3. 
 
 When the reduction is complete, no time should be lost in 
 titrating the solution. 
 
36. STANDARD PERMANGANATE. 125 
 
 CALCULATION OF ANALYSES MADE WITH 
 PERMANGANATE SOLUTION. 
 
 36. THE calculation of analyses with permanganate, if the 
 solution is not strictly decinormal, can be made by ascertaining its 
 coefficient, reducing the number of c.c. used for it to decinormal 
 strength, and multiplying the number of c.c. thus found by -^3^-$ 
 of the equivalent weight of the substance sought ; for instance 
 
 Suppose that 15 c.c. of permanganate solution have been found 
 to equal Ol gm. iron; it is required to reduce the 15 c.c. 
 to decinormal strength, which would require 1000 c.c. of per- 
 manganate to every 5'6 gm. iron, therefore 5*6 : 1000 : : O'l : x = 
 17-85 c.c. ; 17-85 x 0-0056 = 0-09996 gm. iron, which is as near to 
 O'l gm. as can be required. Or the coefficient necessary to reduce 
 the number of c.c. used maybe found as follows: O-'l : 15 : : 
 
 5'6 : .= 84 c.c,, therefore -o-p=-- 1 '19. Consequently 1-19 is the 
 
 coefficient by which to reduce the number of c.c, of that special 
 permanganate used in any analysis to the decinormal strength, from 
 whence the weight of substance sought may be found in the 
 usual way. 
 
 Another plan is to find the quantity of iron or oxalic acid repre- 
 sented by the permanganate used in any given analysis, and this being 
 done the following simple equation gives the required result : 
 
 Fe (56) eq. weight of the weight the weight of 
 
 or : the substance : : of Fe or : substance 
 
 O (63) sought O found sought 
 
 In other words, if the equivalent weight of the substance analyzed 
 be divided by 56 or 63 (the respective equivalent weights of iron or 
 oxalic acid), a coefficient is obtained by which to multiply the 
 weight of iron or oxalic acid, equal to the permanganate used, 
 and the product i the weight of the substance titrated. 
 
 For example : sulphuretted hydrogen is the substance sought, 
 the eq. weight of H' 2 S corresponding to 2 eq. Fe is 17; let this 
 
 17 
 number therefore be divided by 56, -^ = 0-3036, therefore, if the 
 
 quantity of iron represented by the permanganate used in an 
 estimation of H 2 S be multiplied by 0'3036, the product will be 
 the weight of the sulphuretted hydrogen sought. 
 
 Again : in the case of manganic peroxide whose equivalent 
 weight is 43*4. 
 
 5=0.775 
 
 The weight of iron therefore found by permanganate in any analysis 
 multiplied by the coefficient 0*775 will give the amount of manganic 
 peroxide, MnO 2 . Again: if m gm. iron = k c.c. permanganate, 
 
 then 1 c.c permanganate = -r gm. metallic iron. 
 
126 VOLUMETRIC ANALYSIS. 37. 
 
 The equivalents here given are on the hydrogen scale, in 
 accordance with the normal system of solutions adopted ; and thus 
 it is seen that two equivalents of iron are converted from the 
 ferrous to the ferric state by the same quantity of oxygen as 
 suffices to oxidize one equivalent of oxalic acid, sulphuretted 
 hydrogen, or manganic peroxide. 
 
 1 c.c. decinormal permanganate is equivalent to 
 0'0056 gm. Fe estimated in the ferrous state 
 
 0-0072 
 
 FeO 
 
 
 
 0-008 
 
 Fe 2 O 3 
 
 
 0-003733 
 
 Fe 
 
 from' PeS 
 
 0-0059 
 
 Bn 
 
 SnCl 2 
 
 0-00295 
 
 Sn 
 
 SnS 2 
 
 0-00315 
 
 Cu 
 
 CuS 
 
 0-00274 
 
 Mn 
 
 MnS 
 
 0-00315 
 
 Cu 
 
 Cu+Fe 2 CF 
 
 0-0063 
 
 Cu 
 
 CuO+Fe 
 
 0-0017 
 
 H 2 S 
 
 55 35 
 
 0-0008 
 
 
 
 
 0-0063 
 
 CT 
 
 
 0-002 
 
 Ca from 
 
 CaC 2 O 4 
 
 0-0120 
 
 Ur 
 
 UrO, etc., etc. 
 
 When possible the necessary coefficients will be given in the 
 tables preceding any leading substance. 
 
 
 
 CHROMIC ACID AND FERROUS OXIDE. 
 
 37. POTASSIC bichromate, which appears to have been first 
 proposed by Penny, possesses the advantage over permanganate, 
 that it is absolutely permanent in solution, may easily be obtained 
 in a pure state, and its solution may be used in Mohr's burette 
 without undergoing the change peculiar to permanganate : on the 
 other hand, the end of the reaction in the estimation of iron can 
 only be known by an external indicator ; that is to say, a drop of 
 the mixture is brought in contact with a drop of solution of red 
 potassic prussiate (freshly prepared) upon a white slab or plate. 
 While the ferrous oxide is in tolerable excess, a rich blue colour 
 occurs at the point of contact between the drops but as this 
 excess continues to lessen by the addition of the bichromate, the 
 blue becomes somewhat turbid, having first a green, then a grey, 
 and lastly a brown shade. When the greenish-blue tint has all 
 disappeared, the process is finished. This series of changes in the 
 colour admits of tolerably sure reading of the burette, after some 
 little practice is obtained. 
 
 The .Reaction between chromic acid and ferrous oxide may be 
 represented by the formula : 
 
 2Cr0 8 + 6FeO - CrW + 3Fe 2 3 . 
 The decomposition takes place immediately, and at ordinary 
 
STANDARD BICHROMATE. 
 
 temperatures, in the presence of free sulphuric or hydrochloric acid. 
 Xitric acid is of course inadmissible. 
 
 The reduction of ferric compounds to the ferrous state may be 
 accomplished by zinc,""" magnesium, sodic sulphite, ammonic 
 bisulphite, or sulphurous acid; or, instead of these, stannous 
 chloride may be used, which acts very rapidly as a reducing agent 
 upon ferric oxide, the yellow colour of the solution disappearing 
 almost immediately. 
 
 In the analysis of iron ores, reduction by the latter is very rapid 
 and serviceable ; the greatest care, however, is necessary that the 
 stannous chloride is not present in excess, as this would consume 
 the bichromate solution equally with the ferrous oxide, and so 
 lead to false results. 
 
 The discharge of the yellow colour of the iron solution may with 
 care be made a very sure indicator of the exact point of reduction. 
 But in order to obviate the inaccuracy which would be produced 
 by an excess of tin in the state of protosalt, an aqueous solution of 
 mercuric chloride should be added to the mixture in slight excess ; 
 the stannous chloride is then all converted into stannic chloride, 
 and the titration with bichromate may proceed fas usual ; 
 a precipitate of Hg 2 Cl 2 does not interfere. The concentrated 
 hydrochloric solution of iron is heated to gentle boiling, and the 
 moderately dilute tin solution added with a pipette, waiting 
 a moment for each addition till the last traces -of colour have 
 disappeared ; the solution is then poured into a beaker, diluted 
 with boiled and cooled water, mercuric solution added, and titrated 
 with the bichromate as above described. See also 64. 
 
 It is absolutely necessary that the solution of potassic ferri- 
 cyanide used as the indicator with bichromate should be free from 
 f errocyanide ; and as a solution when exposed to air for a short 
 time becomes in some measure converted into the latter, it is 
 necessary to use a freshly prepared liquid. 
 
 1. Preparation of the Decinormal Solution of Bichromate. 
 4 '9 13 gm. per liter. 
 
 The reaction which takes place between potassic bichromate and 
 ferrous oxide is, 
 
 6FeO + Cr 2 K 2 0" - 3Fe 2 3 + Cr 2 3 + K 2 
 
 It is therefore necessary that J eq. in grams should be used for the 
 liter as a normal solution and ^ for the decinormal ; and as it is 
 preferable on many accounts to use a dilute solution, the latter is 
 the more convenient for general purposes. 
 
 Taking the equivalent number of chromium as 52 '4, that of 
 potassic bichromate is 294'S ; if, therefore, /^ of this latter number 
 
 * When zinc is used, the zinc ferricyanide somewhat obscures the critical point in. 
 testing with the indicator. 
 
128 VOLUMETRIC ANALYSIS. 38. 
 
 = 4'913 gm. of the pure \vell dried salt be dissolved in a liter of 
 water, the decinormal solution is obtained. 
 
 1 c.c. of this solution is capable of yielding up y^^ eq. in 
 grams of oxygen, and is therefore equivalent to the yo^jo^ eq. of 
 any substance which takes up 1 equivalent of oxygen. 
 
 2. Solution of Stannous Chloride. 
 
 About 10 gm. of pure tin in thin pieces are put into a large 
 platinum capsule, about 200 c.c. strong pure hydrochloric acid 
 poured over it, and heated till it is dissolved ; or it may be 
 dissolved in a porcelain capsule or glass flask, adding pieces of 
 platinum foil to excite a galvanic current. The solution so 
 obtained is diluted to about a liter with distilled water, and pre- 
 served in the bottle (fig. 24) to which the air can only gain access 
 through a strongly alkaline solution of pyrogallic acid. When 
 kept in this manner, the strength will not alter materially in 
 a month. If not so preserved, the solution varies considerably 
 from day to day, and therefore should always be titrated before 
 use as described in 64 if required for quantitative analysis. 
 
 Examples of Iron Tit ration : 0'7 gm. of pure and dry ammonio-ferrous 
 sulphate=0'l gm. iron, was dissolved in water, and titrated with decinormal 
 bichromate, of which 17'85 c.c. were required; this multiplied by 0'03913 
 gave 0'699 gm. instead of 0'7 gm. 
 
 0'56 gm. of iron wire required 99'8 c.c. =0*5588 gm. ; as it is impossible 
 to obtain iron wire perfectly pure, the. loss is undoubtedly owing to the 
 impurities. 
 
 IODINE AND SODIC THIOSULPHATE. 
 
 38. THE principle of this now beautiful and exact method of 
 analysis was first discovered by Dupasquier, who used a solution 
 of sulphurous acid instead of sodic thiosulphate. Bun sen im- 
 proved his method considerably by ascertaining the sources of 
 failure to which it was liable, which consisted in the use of a too 
 concentrated solution of sulphurous acid. The reaction between 
 iodine and very dilute sulphurous acid may be represented by the 
 formula 
 
 SO 2 + 1 2 + 2H 2 = 2HI + H 2 SO. 
 
 If the Sulphurous acid is more concentrated, i.e. above 4 04 per 
 cent., in a short time the action is reversed, the irregularity of 
 decomposition varying with the quantity of water present, and the 
 rapidity with which the iodine is added.'"" 
 
 Sulphurous acid, however, very rapidly changes by keeping even 
 in the most careful manner, and cannot therefore be used for 
 a standard solution. The substitution of sodic thiosulphate is 
 a great advantage, inasmuch as the salt is easily obtained in 
 
 * Tliis irregularity is now obviated by tie' method of Giles and Shearer ( 75.5), 
 in which solutions of SO 2 or sulphites of any strength may be accurately titrated 
 with iodine, by adding the latter to the former in excess, and when the reaction is 
 complete titrating the excess of iodine with tMosulphate. 
 
38. IODOMETRY. 129 
 
 a pure state, and may be directly weighed for the standard solution. 
 The reaction is as follows : 
 
 2Na 2 S 2 3 + 2I = 2]S 
 
 the result being that thiosulphuric acid takes oxygen from the 
 water, with the production of tetrathionic and hydriodic acids in 
 combination with soda. 
 
 In order to ascertain the end of the reaction in analysis by this 
 method an indicator is necessary, and the most delicate and sensitive 
 for the purpose is starch, which produces with the slightest trace of 
 free iodine in cold solution the well-known blue iodide of starch. 
 Hydriodic or mineral acids and iodides have no influence upon the 
 colour. Caustic alkalies destroy it. 
 
 The principle of this method, namely, the use of iodine as an 
 indirect oxidizing body by its action upon the elements of water, 
 forming hydriodic acid with the hydrogen, and liberating the oxygen 
 in an active state, can be applied to the determination of a great 
 variety of substances with extreme accuracy. 
 
 Bodies which take up oxygen, and decolorize the iodine solution, 
 such as sulphurous acid, sulphites, sulphuretted hydrogen, alkaline 
 thiosulphites and arsenites, stannous chloride, etc., are brought 
 into dilute solution, starch added, and the iodine delivered in 
 with constant shaking or stirring until a point occurs at which 
 a final drop of iodine colours the whole blue a sign that the 
 substance can take up no more iodine, and that the drop in excess 
 has shown its characteristic effect upon the starch. 
 
 Free chlorine, or its active compounds, cannot, however, be 
 titrated with thiosulphate directly, owing to the fact that, instead 
 of tetrathionic acid being produced as with iodine, sulphuric acid 
 occurs, as may be readily seen by testing with baric chloride. 
 In such cases, therefore, the chlorine must be evolved from its 
 compound and passed into an excess of solution of pure potassic 
 iodide, where it at once liberates its equivalent- of iodine, which 
 can then, of course, be estimated with thiosulphate. 
 
 All bodies which contain available oxygen, and which evolve 
 chlorine when boiled with strong hydrochloric acid, such as the 
 chromates, manganates, and all metallic peroxides, can be readily 
 and most accurately estimated by this method. 
 
 1. Preparation of the Decinormal Solution of Iodine. 
 
 I = 127 ; 12 '7 gm. per liter. 
 
 Chemically pure iodine may be obtained by intimately mixing 
 dry commercial iodine with about one-fourth of its weight of 
 potassic iodide, and gently heating the mixture between two large 
 watch-glasses or porcelain capsules ; the lower one being placed 
 upon a heated iron plate, the iodine sublimes in brilliant plates, 
 which, with the exception of a trace of moisture, are pure. 
 
 K 
 
130 VOLUMETRIC ANALYSIS. 38. 
 
 The watch-glass or capsule containing the iodine is placed under 
 the exsiccator to cool, and also to deprive it of any traces of watery 
 vapour; then 12*7 gm. are accurately weighed, and together with 
 about 18 gm. of pure potassic iodide (free from iodate)""' dissolved, 
 in ahout 250 c.c. of water, and diluted to a liter. The flask must 
 not be heated in order to promote solution, and care must be taken 
 that iodine vapours are not lost in the operation. 
 
 The solution is best preserved in stoppered bottles, kept in the 
 dark, and which should be completely filled ; but under any 
 circumstances it does not hold its strength well for any length 
 of time, and consequently should be titrated before use in 
 analysis. 
 
 The verification of the iodine solution may be done in many 
 ways. Pure sodic thiosulphate prepared as described below, or 
 a strictly -f$ solution of it, or again pure arsenious acid or its ^ 
 solution, with the addition of a little sodic bicarbonate, or baric- 
 thiosulphate as proposed by Plimpton and Chorley, may be 
 used; this latter salt possesses a high molecular weight, 267 parts 
 being equivalent to 127 of iodine, but being sparingly soluble in 
 water the titration must be carefully done, inasmuch as the 
 crystalline powder has to be gradually decomposed by the iodine,, 
 and the end-point may easily be overstepped. A weighed quantity 
 of the salt is put into a stoppered bottle with water, and the 
 iodine run in from a burette with continuous shaking, until the 
 salt is nearly dissolved; starch indicator is then added, and the 
 iodine continued with shaking until the blue colour is faintly 
 permanent. 
 
 Pure baric thiosulphate is easily prepared by mixing together 
 a warm solution of 50 gm. of sodic thiosulphate in 300 c.c. of 
 water, and 40 gm. of baric chloride in a like volume of warm 
 w r ater ; after stirring well, the salt soon separates in fine powdery 
 crystals. These are collected in a funnel stopped with glass or 
 cotton wool, repeatedly washed with cold water till all chlorine 
 is removed, then dried at below 30 C. on a glass or porcelain 
 plate until all extraneous moisture is removed ; or the crystals may 
 be treated, after thorough washing with alcohol and ether, as. 
 described below for sodic thiosulphate. 
 
 2. Decinormal Sodic Thiosulphate. 
 ]S T a 2 S 2 3 , 5H 2 = 248-27 = 24*827 gm. per liter. 
 
 It is not difficult either to manufacture or procure pure sodic 
 thiosulphate, but there may be uncertainty as to extraneous water 
 
 * Morse and Burton (Amer. Chem. Jour,, 1888) state that potassic iodide may be 
 completely freed from iodate by boiling a solution of it with zinc amalgam, prepared 
 by shaking zinc dust in good proportion with mercury in presence of tartaric acid, and 
 washing with water. The iodate is completely reduced with formation of zinc hydroxide. 
 The pure solution of iodide is filtered for use through a paper filter saturated with hot 
 water. 
 
38. IODOMETEY. 131 
 
 held within the crystals. In order to avoid this, Me in eke 
 (Gli em. Zeit. xviii. 33) recommends that the otherwise pure crystals 
 be broken to coarse powder, washed first with pure alcohol, then 
 with ether, and lastly dried in a current of dry air at ordinary 
 temperature. The salt so prepared may be weighed directly, and 
 dissolved in a liter of distilled water, and then titrated with the 
 iodine solution and starch indicator ; or it may be checked with 
 j bichromate as recommended by Mohr, by digesting a measured 
 volume of the bichromate with an excess of potassic iodide, and 
 hydrochloric acid, in a well-stoppered flask at moderate heat. 
 When the mixture has cooled, the liberated iodine is measured by 
 the thiosulphate, and the working power of the latter ascertained. 
 It is advisable to preserve the solution in the dark. After a time 
 all solutions of thiosulphate undergo a slight amount of oxidation, 
 and sulphur deposits upon the bottle ; it is therefore always 
 advisable to titrate it previous to use. 
 
 Beside the clecinornial iodine and thiosulphate, it is convenient 
 in some cases to use centinormal solutions, which can readily be 
 prepared by diluting the decinormal solution when required. 
 
 In using the iodine solution Mohr's burette may be employed, 
 but care must be taken that the solution is not left in it for 
 any length of time, as decomposition slowly takes place, and the 
 tube becomes hard ; the tap burette is on this account preferable. 
 
 3. Starch. Indicator; 
 
 One part of clean potato starch, or arrowroot, is first mixed 
 smoothly with cold water into a thin paste, then gradually poured 
 into about 150 or 200 times its weight of boiling water, the boiling 
 continued for a few minutes, then allowed to stand and settle 
 thoroughly ; the clear solution only is to be used as the indicator, 
 of which a few drops only are necessary/' 5 ' The solution may 
 be preserved for some long time by adding to it a few drops of 
 chloroform, and shaking well in a stoppered bottle. 
 
 Lintnar's soluble starch acts well as an indicator, as it gives at 
 once a clear solution in boiling water. It is prepared by steeping 
 potato starch, at ordinary temperature, for a week in dilute hydro- 
 chloric acid, washing out the acid with repeated quantities of cold 
 water,, and drying the starch at a moderate temperature. The 
 colour which occurs with this form of starch is not quite so pure 
 a blue as fresh ordinary starch, owing to the presence of some 
 dextrine produced unavoidably in the preparation, but it is no 
 hindrance to the end-point in practice. 
 
 Concentrated Solution of Starch. This will keep any length of 
 time. Made by rubbing about 5 gm. starch to a smooth emulsion, 
 
 * In iodometric analyses it is always advisable in titrating- the free iodine with thio- 
 sulphate or arsenious solution to delay adding the starch until the iodine colour is nearly- 
 removed j a much more delicate ending may be obtained and with very little starch. 
 
 K 2 
 
132 VOLUMETRIC ANALYSIS. 39. 
 
 with about 50 c.c. water. Then add 25 c.c. of strong solution of 
 caustic potash and shake well, dilute with half a liter of water, 
 boil, and allow to settle. This indicator answers very well in 
 cases where the alkali is of no consequence, but is not available 
 for the delicate acidimetric method by iodic acid unless the alkali 
 is exactly corrected. It answers well, however, with the addition 
 of 2 gm. of potassic iodide as a reagent for nitrites, and keeps 
 perfectly though exposed to light. 
 
 ANALYSIS OF SUBSTANCES BY DISTILLATION WITH 
 HYDROCHLORIC ACID. 
 
 39. THERE are a great variety of substances containing oxygen, 
 which when boiled with hydrochloric acid yield chlorine, equivalent 
 
 to the whole or a part only of the oxygen they contain according to 
 circumstances. Upon this fact are based the variety of analyses 
 which may be accomplished by means of iodine and sodic thio- 
 sulphate, or arsenite ; the chlorine so evolved, however, is not itself 
 estimated, but is conveyed by means of a suitable apparatus into 
 a solution of potassic iodide, thereby liberating an equivalent 
 quantity of iodine. This latter body is then estimated by thio- 
 sulphate ; the quantity so found is, therefore, a measure of the 
 oxygen existing in the original substance, and consequently 
 a measure of the substance itself. Analyses of this class may be 
 made the most exact in the whole range of volumetric analysis, 
 far outstripping any process by weight. 
 
39. 
 
 IODOMETRY. 
 
 The apparatus used for distilling the substances, and conveying 
 the liberated chlorine into the alkaline iodide, may possess a variety 
 of forms, the most serviceable, however, being the three kinds 
 devised respectively by Bun sen, Fresenius, and Mohr. 
 
 Bunsen's arrangement consists of an inverted retort, into the 
 neck of which the tube from the small distilling flask is passed. 
 
 Owing to the great solubility of HC1 in the form of gas, the 
 apparatus must be so constructed that when all Cl is liberated and 
 HC1 begins to distil, the liquid may not rush back to the flask 
 owing to condensation. 
 
 Fig. 38. 
 
 The best preventive of this regurgitation is, however, suggested 
 by Fresenius, and applicable to each kind of apparatus; namely, 
 the addition of a few pieces of pure magnesite. This substance 
 dissolves but slowly in the hydrochloric acid, and so keeps up 
 a constant flow of CO 2 , the pressure of which is sufficient to 
 prevent the return of the liquid. 
 
 The apparatus contrived by Fresenius is shown in fig. 37, and 
 is exceedingly useful as an absorption apparatus for general 
 purposes. 
 
VOLUMETRIC ANALYSIS. 39. 
 
 Mo hr's apparatus is shown in fig. 38 and is, on account of its 
 simplicity of construction, very easy to use. 
 
 The distilling flask is of about 2 oz. capacity, and is fitted with 
 a cork soaked to saturation in melted paraffin ; through the cork 
 the delivery tube containing one bulb passes, and is again passed 
 through a common cork, fitted loosely in a stout tube about 12 or 
 13 inches long and 1 inch wide, closed at one end like a test tube. 
 This tube, containing the alkaline iodide, is placed in an hydrometer 
 glass, about 12 inches high, and surrounded by cold water ; the 
 delivery tube is drawn out to a fine point, and reaches nearly to 
 the bottom of the condenser. No support or clamp is necessary, 
 as the hydrometer glass keeps everything in position. The 
 substance to be distilled is put into the flask and covered with 
 strong hydrochloric acid, the magnesite added, the condenser 
 supplied with a sufficient quantity of iodide solution, and the 
 apparatus put together tightly. Either an argand or common 
 spirit lamp, or gas, may be used for heating the flask, but the 
 flame must be manageable, so that the boiling can be regulated at 
 will. In the case of the common spirit lamp it may be held in the 
 hand, and applied or withdrawn according to the necessities of the 
 case : the argand spirit or gas lamp can, of course, be regulated by 
 the usual arrangements for the purpose. If the iodine liberated 
 by the chlorine evolved should be more than will remain in 
 solution, the cork of the condensing tube must be lifted, and more 
 solution added. "When the operation is judged to be at an end, 
 the apparatus is disconnected, and the delivery tube washed out 
 into the iodide solution, which is then emptied into a beaker or 
 flask and preserved for titration, a little fresh iodide solution is 
 put into the condenser, the apparatus again put together, and 
 a second distillation commenced, and continued for a minute or so, 
 to collect every trace of free chlorine present. This second 
 operation is only necessary as a safeguard in case the first should 
 not have been complete. 
 
 The solutions are then mixed together and titrated in the 
 manner previously described. In all cases the solution must be 
 cooled before adding the thiosulphate, otherwise sulphuric acid 
 might be formed. 
 
 Instead of the large test tube, some operators use a (J tube to 
 contain the potassic iodide, having a bulb in each limb, but the 
 latter is not necessary if magnesite is used. 
 
 The solution of potassic iodide may conveniently be made of 
 such a strength that T 2 ^- eq. or 33 '2 gin. are contained in the liter. 
 1 c.c. will then be sufficient to absorb the quantity of free iodine, 
 representing 1 per cent, of oxygen in the substance analyzed, 
 supposing it to be weighed in the metric system. In examining 
 peroxide of manganese, for instance, 0'436 gm. or 4*36 grn. would 
 be used, and supposing the percentage of peroxide to be about 
 sixty, 60 c.c. or dm. of iodide solution would be sufficient to absorb 
 
IODOMETRY. 
 
 135 
 
 the chlorine and keep in solution the iodine liberated by the 
 process ; it is advisable, however, to have an excess of iodide, and, 
 therefore, in this case, about 70 c.c. or dm. should be used. 
 A solution of indefinite strength will answer as well, so long as 
 enough is used to absorb all the iodine. It may sometimes happen 
 that not enough iodide is present to keep all the liberated iodine in 
 solution, in which case it will separate out in the solid form ; more 
 iodide, however, may be added to dissolve the iodine, and the 
 titration can then be made as usual. 
 
 The process of distillation above described may be avoided in 
 many cases. There are a great number of substances which, by 
 mere digestion with hydrochloric acid and potassic iodide at an 
 elevated temperature, undergo decomposi- | 
 tion quite as completely as by distillation, sjjf 
 For this purpose a strong bottle with 
 a very accurately ground stopper is neces- 
 sary ; and as the ordinary stoppered bottles 
 of commerce are not sufficiently tight, it is 
 better to re-grind the stopper with a little 
 very fine emery and water. It must then 
 be tested by tying the stopper tightly 
 down and immersing in hot water ; if any 
 bubbles of air find their way through the 
 stopper the bottle is useless. The capa- 
 city may vary from 30 to 150 c.c., accord- 
 ing to the necessities of the case. 
 
 The stopper may be secured by fine copper binding-wire, or 
 a kind of clamp contrived by Mohr may be used, as shown in 
 fig. 39 ; by means of the thumb-screws the pressure upon the 
 stopper may be increased to almost any extent. 
 
 The substance to be examined, if in powder, is put into the 
 bottle with pure flint pebbles or small garnets, so as to divide it 
 better, and a sufficient quantity of saturated solution of potassic 
 iodide and pure hydrochloric acid added ; the stopper is then 
 inserted, fastened down, and the bottle suspended in a water 
 bath, and the water is gradually heated to boiling by a gas 
 name or hot plate as may be most convenient. When the 
 decomposition is complete the bottle is removed, allowed to cool 
 someAvhat, then placed in cold water, and, after being shaken, 
 emptied into a beaker, and the liquid diluted by the washings 
 for titration. 
 
 The salts of chloric, iodic, bromic, and chromic acids, together 
 with many other compounds, may be as effectually decomposed by 
 digestion as by distillation ; many of them even at ordinary tem- 
 peratures. Recently precipitated oxides, or the natural oxides, 
 when reduced to fine powder are readily dissolved and de- 
 composed by very weak acid in the presence of potassic iodide 
 (Pickering). 
 
136 VOLUMETRIC ANALYSIS. 40. 
 
 The potassic iodide used in the various analyses must be abso- 
 lutely free from potassic iodate and free iodine, or if otherwise, the 
 effect of the impurity must be known by blank experiment. 
 
 ARSENIOTJS ACID AND IODINE. 
 
 40. THE principle upon which this method of analysis is 
 based is the fact, that when arsenious acid is brought in contact 
 with iodine in the presence of water and free alkali, it is converted 
 into arsenic acid, the reaction being 
 
 AS 2 3 + 41 + 2K' 2 = As 2 5 + 4KI. 
 
 The alkali must be in sufficient quantity to combine with the 
 hydriodic acid set free, and it is necessary that it should exist in 
 the state of bicarbonate, as caustic or monocarbonated alkalies 
 interfere with the colour of the blue iodide of starch used as indicator. 
 
 If, therefore, a solution of arsenious acid containing starch is 
 titrated with a solution of iodine in the presence of an alkaline 
 bicarbonate, the blue colour does not occur until all the arsenious 
 acid is oxidized into arsenic acid. In like manner, a standard 
 solution of arsenious acid may be used for the estimation of iodine 
 or other bodies which possess the power of oxidizing it. 
 
 The chief value, however, of this method is found in the 
 estimation of free chlorine existing in the so-called chloride of 
 lime, chlorine water, hypochlorites of lime, soda, etc., in solution; 
 generally included under the term of chlorimetry. 
 
 Preparation of the ^ Solution of Alkaline Arsenite. 
 As 2 3 = 198 ; 4-95 gm. per liter. 
 
 The iodine solution is the same as described in 38. 
 
 The corresponding solution of alkaline arsenite is prepared by 
 dissolving 4'95 gm. of the purest sublimed arsenious oxide in 
 about 250 c.c. of distilled water in a flask, with about 20 gm. of 
 pure sodic carbonate.'"" It is necessary that the acid should be in 
 powder, and the mixture needs warming and -shaking for some 
 time in order to complete the solution ; when this is accomplished 
 the mixture is diluted somewhat, cooled, then made up to the 
 liter. 
 
 In order to test this solution, 20 c.c. are put into a beaker with 
 a little starch indicator, and the iodine solution allowed to flow in 
 from a burette, graduated in -^ c.c. until the blue colour appears. 
 If exactly 20 c.c. are required, the solution is strictly decinormal ; 
 if otherwise, the necessary factor must be found for converting it 
 to that strength. 
 
 * In the previous edition of this book, the arsenkms solution was recommended to 
 be made with alkaline bicarbonate, but this has, after keeping, been found to give 
 defective results with bleach analyses from some cause not yet understood. 
 
40. . IODOMETRY. 137 
 
 Iodized Starch-paper. Starch solution cannot be used for the 
 direct estimation of free chlorine, consequently resort must be had 
 to an external indicator ; and this is very conveniently found in 
 starch-iodide paper, which is best prepared by mixing a portion of 
 starch solution with a few drops of solution of potassic iodide on 
 a plate, and soaking strips of pure filtering paper therein. The 
 paper so prepared is used in the damp state, and is far more 
 sensitive than when dried. 
 
 Example of Titration : 50 c.c. of chlorine water were mixed with solution 
 of sodic carbonate, and brought under the arsenic burette, and 20 c.c. of 
 solution added ; on touching the prepared paper with the mixture no colour 
 was produced, consequently the quantity used was too great; starch was 
 therefore added, and decinorinal iodine, of which 3"2 c.c. were required to 
 produce the blue colour. This gave 16'8 c.c. of arsenious solution, which 
 multiplied by 0'003537, gave 0*05942 gm. of Cl in the 50 c.c. A second 
 operation with the same water required 16'8 c.c. of arseuious solution direct, 
 before the end of the reaction with iodized starch-paper was reached. 
 
138 VOLUMETRIC ANALYSIS. 41. 
 
 PART IV. 
 ANALYSIS BY PRECIPITATION. 
 
 41. THE general principle of this method of determining the 
 quantity of any given substance is alluded to in 1, and in all 
 instances is such that the body to be estimated forms an insoluble 
 precipitate with a titrated reagent. The end of the reaction is, 
 however, determined in three ways. 
 
 1. By adding the reagent until no further precipitate occurs, 
 as in the determination of chlorine by silver. 
 
 2. By adding the reagent in the presence of an indicator con- 
 tained either in the liquid itself, or brought externally in contact 
 with it, so that the slightest excess of the reagent shall produce 
 a characteristic reaction with the indicator ; as in the estimation 
 of silver with sodic chloride by the aid of potassic chromate, or 
 with thiocyanate and ferric sulphate, or that of phosphoric acid 
 with uranium by yellow potassic prussiate. 
 
 3. By adding the reagent to a clear solution, until a precipitate 
 occurs, as in the estimation of cyanogen by silver. 
 
 The first of these endings can only be applied with great accuracy 
 to silver and chlorine estimations. Very few precipitates have the 
 peculiar quality of chloride of silver ; namely, almost perfect 
 insolubility, and the tendency to curdle closely by shaking, so as to 
 leave the menstruum clear. Some of the most insoluble precipitates, 
 such as baric sulphate and calcic oxalate, are unfortunately excluded 
 from this class, because their finely divided or powdery nature 
 prevents their ready and perfect subsidence. 
 
 In all these cases, therefore, it is necessary to find an indicator, 
 which brings them into class 2. 
 
 The third class comprises only two processes; viz., the deter- 
 mination of cyanogen by silver, and that of chlorine by mercuric 
 nitrate. 
 
 Since the estimation of chlorine by precipitation with silver, 
 and that of silver by thiocyanic acid, can be used in many cases 
 for the indirect estimation of many other substances with great 
 exactness, the preparation of the necessary standard solutions will 
 now be described. 
 
 SILVER AND CHLORINE. 
 I. Decinormal Solution of Silver. 
 
 10-766 gm. Ag or 16-^66 gm. AgXO :! per liter. 
 
 10 '7 6 6 gm. of pure silver are dissolved in pure dilute nitric acid 
 with gentle heat in a flask, into the neck of which a small funnel 
 is dropped to prevent loss of liquid by spirting. T\ r hen solution 
 is complete, the funnel must be washed inside and out with 
 
41. PKECIPITATIOX ANALYSES. 139 
 
 distilled water into the flask, and the liquid diluted to a liter ; but 
 if it be desired to use potassic chromate as indicator in any analysis, 
 the solution must be neutral ; in which case the solution of silver 
 in nitric acid is evaporated to dryness, and the residue dissolved in 
 a liter; or, what is preferable, 16-966 gm. of pure silver nitrate, 
 previously heated to 120 C. for ten minutes, are dissolved in 
 a liter of distilled water. 
 
 2. Decinormal Solution of Salt. s 
 
 5-837 gm. 2s r aCl per liter. 
 
 5-837 gm. of pure sodic chloride are dissolved in distilled water, 
 and the solution made up to a liter. 
 
 There are two methods by which the analysis may be ended : 
 
 (a) By adding silver cautiously, and well shaking after each 
 addition till no further precipitate is produced. For details 
 see 73. 
 
 (/;) By using a few drops of solution of pure potassic rnono- 
 chromate as indicator, as devised by Mohr. If the pure salt is 
 not at hand, some silver nitrate should be added to the solution of 
 the ordinary salt, to remove chlorine, and the clear liquid used. 
 
 The method I is exceedingly serviceable, on the score of saving 
 both time and trouble. The solutions must be neutral, and cold. 
 When, therefore, acid is present in any solution to be examined, it 
 should be neutralized with pure sodic or calcic carbonate in very 
 slight excess.* 
 
 Process : To the neutral or faintly alkaline solution, two or three 
 drops of a cold saturated solution of chromate are added, and the silver 
 solution delivered from the burette until the last drop or two produce 
 a faint blood-red tinge, an evidence that all the chlorine has combined with 
 the silver, and the slight excess has formed a precipitate of silver chromate ; 
 the reaction is very delicate and easily distinguished. The colour reaction 
 is even more easily seen by gas-light than by daylight. It may be rendered 
 more delicate by adopting the plan suggested by I) up re (Analyst v. 123). 
 A glass cell, about 1 centimeter in depth, is filled with water tinted with 
 chromate to the same colour as the solution to be titrated. The operation is 
 performed in a white porcelain basin. The faintest appearance of the red 
 change is at once detected on looking through the coloured cell. Tor the 
 analysis of waters weak in chlorine this method is very serviceable, 
 but contrary to what has been generally accepted, the accuracy of the 
 results are seriously interfered with by great dilution or high temperature 
 (W. G. Young, Analyst xviii. 125). As is the case with most volumetric 
 processes, it is therefore necessary in order to secure a high degree of 
 accuracy to titrate under the same conditions under which the standard was 
 fixed. 
 
 Example: 1 gm. of pure sodic chloride was dissolved in 100 c.c. of water, 
 a few drops of chromate added, and titrated with ^V silver, of which 17'1 c.c. 
 were required to produce the red colour ; multiplied by the T *V factor for 
 sodic chloride = 0'005837 the result was 0'998 gm. NaCl, instead of 1 gm. 
 
 * Silver chromate is sensibly soluble in the presence of alkaline or earthy nitrates, 
 especially at a high temperature ; sodic and calcic hydrates have the least effect ; 
 arninonic, potassic, and inagnesic nitrates the greatest. See also Forbes Carpenter 
 (J. S. C. I. v. 286). 
 
140 VOLUMETRIC ANALYSIS. 42. 
 
 INDIRECT ESTIMATION OF AMMONIA, SODA., POTASH, 
 LIME, AND OTHER ALKALIES AND ALKALIN * EAxtTH ?, 
 WITH THEIR CARBONATES, NITRATES, AND CHLO- 
 RATES, ALSO NITROGEN, BY MEANS OF DECINORMAL 
 SILVER SOLUTION, AND POTASSIC CHROMATE, AS 
 INDICATOR. 
 
 1 CiC . _*_ silver solution = T olyo^ ^. eq. of each substance. 
 
 42. MOHR, with, his characteristic ingenuity has made use 
 of the delicate reaction between chlorine and silver, with potassic 
 chromate as indicator, for the determination of the bodies men- 
 tioned above. All compounds capable of being converted into. 
 neutral chlorides by evaporation to dryness with hydrochloric acid 
 may be determined with great accuracy. The chlorine in a com- 
 bined state is, of course, the only substance actually determined ; 
 but as the laws of chemical combination are exact and well known, 
 the measure of chlorine is also the measure of the base with which 
 it is combined. 
 
 In most cases it is only necessary to slightly supersaturate the 
 alkali, or its carbonate, with pure hydrochloric acid ; evaporate on 
 the water bath to dryness, and heat for a time to 120 C. in the air 
 bath, then dissolve to a given measure, and take a portion for 
 titration ; too great dilution must be avoided. 
 
 Alkalies and Alkaline Earths with organic acids are ignited to 
 convert them into carbonates, then treated with hydrochloric acid, 
 and evaporated as before described. 
 
 Carbonic Acid in combination may be determined by precipita- 
 tion with baric chloride, as in 23. The washed precipitate is 
 dissolved on the filter with hydrochloric acid (covering it with 
 a watch-glass to prevent loss), and then evaporated to dryness 
 repeatedly till all HC1 is driven off. In order to titrate with 
 accuracy by the help of potassic chromate, the baryta must 
 be precipitated by means of a solution of pure sodic or potassic 
 sulphate, in slight excess ; the precipitated baric sulphate does 
 not interfere with the delicacy of the reaction. If this precaution 
 Avere not taken, the yellow baric chromate would mislead. 
 
 Free Carbonic Acid is collected by means of ammonia and baric 
 chloride (as in 23), and the estimation completed as in the case of 
 combined CO 2 . 
 
 Chlorates are converted into chlorides by ignition before titration. 
 
 Nitrates are evaporated with concentrated hydrochloric acid, and 
 the resulting chlorides titrated, as in the previous case. 
 
 Nitrogen. The ammonia evolved from guano, manures, oilcakes, 
 
42. PRECIPITATION ANALYSES. 141 
 
 and sundry other substances, when burned with soda lime or 
 obtained by the Kj el da hi method, is conducted through dilute 
 hydrochloric acid; the liquid is carefully evaporated to dryness 
 before titration. 
 
 In all cases the operator will, of course, take care that no chlorine 
 from extraneous sources other than the hydrochloric acid is present; 
 or if it exists in the bodies themselves as an impurity, its quantity 
 must be first determined. 
 
 Example : 0'25 gm. pure sodic carbonate was dissolved in water, and 
 hydrochloric acid added till in excess ; it was then dried on the water bath 
 till no further vapours of acid were evolved; the resulting white mass was 
 heated for a few minutes to about 150 C., dissolved and made up to 30 c.c. 
 100 c.c. required 15'7 c.c. T ^ silver, this multiplied by 3 gave 47'1 c.c., which 
 multiplied by the T ^ factor for sodic carbonate 0'0053, gave 0'24963 gm. 
 instead of 0*25 gm. 
 
 Indirect Estimation of Potash and Soda existing as Mixed 
 Chlorides. It is a problem of frequent occurrence to determine the 
 relative quantities of potash and soda existing in mixtures of the 
 two alkalies, such as occur, for instance, in urine, manures, soils, 
 waters, etc. The actual separation of potash from soda by means 
 of platinum is tedious, and not always satisfactory. 
 
 The following method of calculation is frequently convenient, 
 since a careful estimation of the chlorine present in the mixture is 
 the only labour required ; and this can most readily be accom- 
 plished by ~Q silver and chromate, as previously described. 
 
 (1) The weight of the mixed pure chlorides is accurately found and noted. 
 
 (2) The chlorides are then dissolved in water, and very carefully titrated 
 with / silver and chromate for the amount of chlorine present, which is 
 also recorded ; the calculation is then as follows : 
 
 The weight of chlorine is multiplied by the factor 2'103 ; from the product 
 so obtained is deducted the weight of the mixed salts found in 1. The 
 remainder multiplied by 3'6288 will give the weight of sodic chloride 
 present in the mixture. 
 
 The weight of sodic chloride deducted from the total as found in 1 will 
 give the weight of potassic chloride. 
 
 Sodic chloride x 0'5302=Soda (Na e O). 
 Potassic chloride x 0'63l7=Potash (K 2 O). 
 
 The principle of the calculation, which is based on the atomic constitution 
 of the individual chlorides, is explained in most of the standard works on 
 general analysis. Indirect methods like this can only give useful results 
 when the atomic weights of the two substances differ considerably, and when 
 the proportions are approximately equal. 
 
 Another method of calculation in the case of mixed potassic and 
 sodic chlorides is as follows : 
 
 The weight of the mixture is first ascertained and noted ; the chlorine is 
 then found by titration with T ^ silver, and calculated to NaCl : the weight 
 so obtained is deducted from the original weight of the mixture, and the 
 remainder multiplied by 2'42857 will give the potassium. 
 
142 VOLUMETRIC ANALYSIS. 43. 
 
 SILVER AND THIOCYANIC ACID. 
 
 43. THIS excellent and most accurate method has been devised 
 "by Volhard and is fully described by the author (Lielig's Ann. cL 
 CJiem. cxc. 1), and has been favourably noticed by Falck (Z. a. C. 
 xiv. 227), Briigelman (Z. a. C. xvi. 7), and Drechsel (Z. a. C. 
 xvi. 351), and many other well known chemists. It differs from 
 Mohr's chromate method in that the silver solutions may contain 
 free nitric acid, which renders it of great service in indirect 
 analyses. 
 
 This method is based on the fact that when solutions of silver 
 and an alkaline thiocyanate are mixed in the presence of a ferric 
 salt, so long as silver is in excess, the thiocyanate of that metal 
 is precipitated, and any brown ferric thiocyanate which may 
 form is at once decomposed. When, however, the thiocyanate is 
 added in the slightest excess, brown ferric thiocyanate is formed, 
 and asserts its colour even in the presence of much free acid. 
 The method may of course be used for the estimation of silver, 
 and by the residual process, for the estimation of substances which 
 are completely precipitated by silver.'"" 
 
 It may be used for the estimation of silver in the presence of 
 copper up to 70 per cent. ; also in presence of antimony, arsenic, 
 iron, zinc, manganese, lead, cadmium, bismuth, and also cobalt and 
 nickel, unless the proportion of these latter metals is such as to 
 interfere by intensity of colour. 
 
 It may further be used for the indirect estimation of chlorine, 
 bromine, and iodine, in presence of each other, existing either in 
 minerals or inorganic compounds, and for copper, manganese, and 
 zinc ; these will be noticed under their respective heads. 
 
 1, Decinormal Ammonic or Potassic Thiocyanate. 
 
 This solution cannot be prepared by weighing the thiocyanate 
 direct, owing to the deliquescent nature of the salts; therefore 
 about 8 gm. of the ammonium, or 10 gm. of the potassium salt 
 may be dissolved in about a liter of water as a basis for getting an 
 exact solution, which must be finally adjusted by a correct 
 decinormal silver solution. 
 
 The standard solution so prepared remains of the- same strength 
 for a very long period if preserved from evaporation. 
 
 2. Decinormal Silver Solution. 
 
 This is the same as described in a preceding section ( 41), and 
 may contain free nitric acid if made direct from metallic silver. 
 
 * In cases where chlorine is precipitated by excess of silver, and the excess has to be 
 found by thiocyanate, experience has proved that it is absolutely necessary to filter off 
 the chloi'ide and titrate the filtrate and washings. If this be not done the solvent 
 effect of the thiocyanate upon the AgCl will give inaccurate results. This fact seems 
 to have been overlooked at the time the method was first introduced. 
 
44. COLOUR REACTIONS. 143 
 
 3. Ferric Indicator. 
 
 This may consist simply of a saturated solution of iron alum ; 
 or may be made by oxidizing ferrous sulphate with nitric acid, 
 evaporating with excess of sulphuric acid to dissipate nitrous 
 fumes, and dissolving the residue in water so that the strength 
 is about 10 per cent. 
 
 5 c.c. of either of these solutions are used for each titration, 
 which must always take place at ordinary temperatures. 
 
 4. Pure Nitric Acid. 
 
 This must be free from the lower oxides of nitrogen, secured by 
 diluting the usual pure acid with about a fourth part of water, 
 and boiling till perfectly colourless. It should then be preserved 
 in the 'dark. 
 
 The quantity of nitric acid used in the titration may vary 
 within wide limits, and seems to. have no effect upon the precision 
 of the method. 
 
 The Process for Silver : 50 c.c. of & silver solution are placed into 
 a flask, diluted somewhat with water, and 5 c.c. of ferric indicator added, 
 together with about 10 c.c. of nitric acid. If the iron solution should 
 cause a yellow colour, the nitric acid will remove it. The thiocyauate is 
 then delivered in from a burette; at first a white precipitate is produced 
 rendering the fluid of a milky appearance, and as each drop of thiooyanate 
 falls in, it produces a reddish-brown cloud which quickly disappears on 
 shaking. As the point of saturation approaches, the precipitate becomes 
 flocculent and settles easily ; finally, a drop or two of thiocyanate produces 
 a faint brown colour which no longer disappears on shaking. If the 
 solutions are correctly balanced, exactly 50 c.c. of thiocyanate should be 
 required to produce this effect. 
 
 The colour is best seen ~by holding the flask so as to catch the reflected 
 light of a white Avail or a suspended sheet of white paper. 
 
 PRECISION IN COLOUR REACTIONS: 
 
 44. DUPRE adopts the following ingenious method for colour 
 titrations (Analyst v. 123) : As is well known, the change from 
 pale yellow to red, in the titration of chlorides by means of silver 
 nitrate with neutral chromate as indicator, is more distinctly 
 perceived by gas-light than by daylight ; and in the case of potable 
 waters, containing from one to two grains of chlorine per gallon, 
 it is absolutely necessary to concentrate by evaporation previous 
 to titration, or else to perform the titration by gas-light. The 
 adoption of the following simple plan enables the operator to 
 perceive the change of colour as sharply, and with as great 
 a certainty, by daylight as by gas-light. Nevertheless, as has 
 been before mentioned, it is impossible to get accurate results 
 with very weak solutions of chlorine unless the silver solution 
 is standardized upon similar solutions. 
 
 The water is placed into a white porcelain dish (100 c.c. are 
 a useful quantity), a moderate amount of neutral chromate is added 
 
144 VOLUMETRIC ANALYSIS. 4-i. 
 
 (sufficient to impart a marked yellow colour to the water), but 
 instead of looking at the water directly, a flat glass cell containing 
 some of the neutral chromate solution is interposed between the 
 eye and the dish. The effect of this is to neutralize the yellow 
 tint of the water ; or, in other words, if the concentration of the 
 solution in the cell is even moderately fairly adjusted to the depth 
 of tint imparted to the water, the appearance of the latter, looked 
 at through the cell, is the same as if the dish were filled with pure 
 water. If now the standard silver solution is run in, still looking 
 through the cell, the first faint appearance of a reel coloration 
 becomes strikingly manifest; and what is more, when once the 
 correct point has been reached the eye is never left in doubt, how- 
 ever long we may be looking at the water. A check experiment 
 in which the water, with just a slight deficiency of silver, or excess 
 of chloride, is used for comparison is therefore unnecessary. 
 
 A similar plan will be found useful in other titrations. Thus, 
 in the case of turmeric, the change from yellow to brown is per- 
 ceived more sharply and with greater certainty when looking 
 through a flat cell containing tincture of turmeric of suitable 
 concentration than with the naked eye. The liquid to be titrated 
 should, as in the former case, be placed into a white porcelain dish. 
 Again, in estimating the amount of carbonate of lime in a water 
 by means of decinormal acid and cochineal, the exact point of 
 neutrality can be more sharply fixed by looking through the 
 cell filled with a cochineal solution. In this case the following 
 plan is found to answer best. The water to be tested about 
 250 c.c. is placed into a flat porcelain evaporating dish, part of 
 which -is covered over with a white porcelain plate. The water is 
 now tinted with cochineal as usual, and the sulphuric acid run in, 
 the operator looking at the dish through the cell containing the 
 neutral cochineal solution. At first the tint of the water and the 
 tint in which the porcelain plate is seen are widely different ; as, 
 however, the carbonate becomes gradually neutralized, the two 
 tints approach each other more and more, and when neutrality is 
 reached they appear identical ; assuming that the strength of the 
 cochineal solution in the cell, and the amount of this solution 
 added to the water, have been fairly well matched. Working in 
 this manner it is not difficult (taking |- liter of water) to come 
 within 0*1 c.c. of decinormal acid in two successive experiments, 
 and the difference need never exceed 0'2 c.c. In the cell employed 
 the two glass plates are a little less than half an inch apart. 
 
 A somewhat similar plan may be found useful in other titrations, 
 or, in fact, in many operations depending on the perceptions of 
 .colour change. 
 
45. ALUMINIUM. 145 
 
 PAET V. 
 
 APPLICATION OF THE FOREGOING PRINCIPLES OF 
 ANALYSIS TO SPECIAL SUBSTANCES. 
 
 AL.TJMINITJM. 
 
 Al = 27-3. 
 
 45. ALUMINIUM salts (the alums and aluminium sulphates 
 used in dyeing and paper-making) may be titrated for alumina 
 in the absence of iron (except in mere traces) by mixing the acid 
 solutions with a tolerable quantity of sodic acetate, then a known 
 volume in excess of y^ phosphate solution (2O9 gm. of ammonio- 
 sodic phosphate per liter), heating to boiling, without filtration; the 
 excess of phosphate is found at once by titration with standard 
 uranium. If iron in any quantity is present, it may be estimated 
 in a separate portion of the substance, and its amount deducted 
 before calculating the alumina. The latter is precipitated as 
 A1P0 4 , and any iron in like manner as FePO 4 . Each c.c. of ~ 
 phosphate = 0*005 13 gm. A1 2 O 3 . Only available for rough purposes. 
 
 Baeyer's Method. As originally proposed, this process for 
 estimating alumina in alums and aluminic sulphates was carried 
 out by two titrations, a measured portion of the solution being first 
 treated with an excess of normal soda in sufficient quantity to 
 dissolve the precipitate of hydrate of alumina first formed. It was 
 then diluted to a definite volume, half being titrated with normal 
 acid and litmus, other half with tropoeolin 00, the difference being 
 calculated to alumina. 
 
 A considerable improvement however has been made by using 
 phenolphthalein as the indicator, one titration only being necessary. 
 The method is based on the fact that, if to a solution of alumina, 
 containing the indicator, normal soda is added in excess, or until 
 the red colour is produced, normal acid be then added until the 
 colour disappears, the volume of acid so required is less than the 
 soda originally added in proportion to the quantity of alumina 
 present. 
 
 The volume of acid which so disappears is in reality the quantity 
 necessary to combine with the alumina set free by the alkali ; and 
 if this deficient measure of acid be multiplied by the factor 
 0-01716 (J mol. wt. of A1 2 3 ), the weight of alumina will be 
 obtained. This factor is given on the assumption that the normal 
 sulphate APS SO 4 is formed. 
 
 The titration must take place in the cold and in dilute solutions. 
 Very fair technical results have been obtained by me with 
 
 L 
 
146 VOLUMETRIC ANALYSIS. 45. 
 
 potash and ammonia alums and the commercial sulphates of 
 alumina. 
 
 Alumina existing as aluminate of alkali in caustic soda, for 
 instance, may be very well estimated by taking advantage of the 
 fact, that such alumina is quite indifferent to methyl orange, but 
 reacts acid with phenolphthalein. This fact has been recorded by 
 Thomson and others, but the priority of discovery appears to be 
 due to Baeyer (Z. a. C. xxiv. 542), who, however, used litmus in 
 the place of phenolphthalein and tropceolin 00 instead of methyl 
 orange. 
 
 Cross and Be van (J. S. C. I. viii. 252) in their examination of 
 caustic soda for alumina, found by experiment, that the mean of 
 the differences between the titration with methyl orange and 
 phenolphthalein required the factor O0205 per c.c. of normal acid 
 for the alumina, pointing to the salt as 2AP0 3 : 5S0 3 . 
 
 The estimation of the alumina in caustic soda has given rise to 
 much discussion between even very experienced operators, notably 
 MM. Cross and Bevan and Lunge, but the former chemists 
 have proved, as far as possible, by various methods, the accuracy 
 of their views that the above-named equation is correct. The 
 method adopted by them consists in boiling the weighed sample 
 with a slight excess of standard acid, allowing to cool and titrating 
 back with standard soda and phenolphthalein. The acid so con- 
 sumed represents the total alkali present. To a similar portion 
 a slight excess of acid is added and titrated back with soda and 
 methyl orange. 
 
 Estimation of free Acid. Alum cakes or aluminic sulphates of 
 various kinds often contain free H 2 S0 4 , and many methods have 
 been proposed for its estimation. Baeyer titrates a 10 per cent, 
 solution of the substance in water with normal soda, and tropceolin 
 00 or methyl orange. 
 
 R. Williams (C. N. Ivi. 194) adopts the -alcohol method by 
 digesting the substance for at least twelve hours with strong 
 alcohol, filtering off and washing with the same agent, and titrating 
 the solution without dilution or evaporation with -$ acid and 
 phenolphthalein. 
 
 Beilsteiii and Grosset (Bull, de I'Academie Imp. des Sciences 
 de St. Petersburg, xiii. 41) have examined with great care all the 
 proposed methods for this purpose, and have devised one which 
 gives very good technical results. 
 
 Process : 1 to 2 gin. of substance is dissolved in 5 c.c. of water, 5 c.c. 
 of a cold saturated neutral solution of ammonic sulphate added, and stirred 
 for a quarter of an hour. 50 c.c. of 95 per cent, alcohol are then added, the 
 mixture thrown on a small filter, and washed with 50 c.c. of the same 
 alcohol. The nitrate is evaporated on the water bath, the residue dissolved 
 in water, and titrated with ^ alkali and litmus. The whole of the neutral 
 aluminic sulphate is precipitated as ammonia alum, the alcohol contains all 
 the free acid. 
 
46. ANTIMONY. 147 
 
 ANTIMONY. 
 
 Sb = 120. 
 
 1. Conversion of Antimonious Acid in Alkaline Solution into 
 Antimonic Acid by Iodine (Mohr). 
 
 46. ANTIMONIOUS oxide, or any of its compounds, is brought 
 into solution as tartrate by tartaric acid and water ; the excess of 
 acid neutralized by sodic carbonate ; then a cold saturated solution 
 of sodic bicarbonate added, in the proportion of 10 c.c. to about 
 O'l gm. Sb 2 3 ; to the clear solution starch is added and 
 iodine until the blue colour occurs. No delay must occur in the 
 titration when the bicarbonate is added, otherwise a portion of the 
 metal is precipitated as antimonious hydrate, upon which the iodine 
 fas little effect.* 
 
 For the estimation of antimonic acid and its salts, G.vonKnorre 
 (Zeit. Angeic. Chem., 1888, 155) gives the following method as 
 accurate : 
 
 The solution of the salt, strongly acidified with hydrochloric acid, is treated 
 in a roomy flask with strong solution of sodic sulphide, added gradually in 
 small portions. It is then vigorously boiled until all SO 2 is expelled, a drop 
 of phenolphthalein is added, then caustic potash until red ; this is in turn 
 removed by a small excess of tartaric acid. Sodic bicarbonate is then added, 
 and the titration with iodine carried out in the usual way. 
 
 The colour disappears after a little time, therefore the first 
 appearance of a permanent blue is accepted as the true measure 
 of iodine required. 
 
 1 c.c. T ^ iodine = 0-0060 gm. Sb. 
 
 Estimation of Antimony in presence of Tin (Type and Britannia 
 metal, etc.). The finely divided alloy is dissolved in strong hydro- 
 chloric acid by heat, adding frequently small quantities of potassic 
 chlorate. The liquid is boiled to remove free chlorine, cooled, 
 a slight excess of strong solution of potassic iodide added, and 
 the liberated iodine estimated by standard thiosulphate. Some 
 operators prefer to collect the liberated iodine in carbon bisulphide 
 previous to titration. 
 
 120 Sb liberate 253 I, and the weight of I found multiplied 
 by 0-47 5 = Sb. 
 
 If iron or other metal capable of liberating iodine be present, 
 treat the alloy with nitric acid, and evaporate to obtain the oxides 
 of antimony and tin wash, boil in hydrochloric acid, and proceed 
 as before described. The rationale is, that antimonic chloride is 
 reduced to antimonious chloride, while stannic chloride is not affected. 
 
 H. Oxidation by Potassic Bichromate or Permanganate (Kessler), 
 Bichromate or permanganate added to a solution of antimonious 
 
 *Dunstaii and Boole (Pharm. Jour., Nov., 1888) have proved that the accurate 
 estimation of the antimony in tartar emetic may be secured by this method, using the 
 precautions above mentioned. 
 
 L 2 
 
148 VOLUMETRIC ANALYSIS. 46. 
 
 chloride, containing not less than J of its volume of hydrochloric 
 acid (sp. gr. 1*12), converts it into antimonic chloride. 
 
 The reaction is uniform only when the minimum quantity of acid 
 indicated above is present, but it ought not to exceed i the volume, 
 and the precautions before given as to the action of hydrochloric 
 acid on permanganate must be taken into account, hence it is 
 preferable to use bichromate. 
 
 Kessler (Poggend. Annal. cxviii. 17) has carefully experimented 
 upon this method and adopts the following processes. 
 
 A standard solution of arsenious acid is prepared containing 
 5 gm. of the pure acid, dissolved by the aid of sodic hydrate, 
 neutralized with hydrochloric acid, 100 c.c. concentrated hydro- 
 chloric acid added, then diluted with water to 1 liter ; each c.c. of 
 this solution contains 0'005 gm. As 2 3 , and represents exactly 
 0-007253 gm. Sb' 2 3 . 
 
 Solutions of potassic bichromate and ferrous sulphate of known 
 strength in relation to each other, are prepared in the usual way ; 
 and a freshly prepared solution of potassic ferricyanide used as 
 indicator. 
 
 The relation between the bichromate and arsenious solution is 
 found by measuring 10 c.c. of the latter into a beaker, 20 c.c. 
 hydrochloric acid of sp. gr. 1*12, and from 80 to 100 c.c. of water 
 (to insure uniformity of action the volume of HC1 must never be 
 less than J or more than J) ; the bichromate solution is then added 
 in excess, the mixture allowed to react for a few minutes, and the 
 ferrous solution added until the indicator shows the blue colour. 
 To find the exact point more closely, J or 1 c.c. bichromate solution 
 may be added, and again iron, until the precise ending is obtained. 
 
 Process : The material, free from organic matter, organic acids, or heavy 
 metals, is dissolved in the proper proportion of HC1, and titrated precisely 
 as just described for the arsenious solution ; the strength of the bichromate 
 solution having been found in relation to As 2 O 3 the calculation as respects 
 Sb 2 O 3 presents no difficulty. Where direct titration is not possible the same 
 course may be adopted as with arsenic ( 47) ; namely precipitation with 
 H 2 S and digestion with mercuric chloride. 
 
 In the case of using permanganate it is equally necessary to have 
 the same proportion of HC1 present in the mixture, and the 
 standard solution must be added till the rose colour is permanent. 
 The permanganate may be safely used with J the volume of HC1, 
 with the addition of some magnesic sulphate, and as the double 
 tartrate of antimony and potassium can readily be obtained pure, 
 and the organic acid exercises no disturbing effect in the titration, 
 it is a convenient material upon which to standardize the solution. 
 
 3. Distillation of Antimonious or Antimonic Sulphide -with. 
 Hydrochloric Acid, and Titration of the evolved Sulphuretted 
 Hydrogen (Schneider). 
 
 When either of the sulphides of antimony is heated with 
 hydrochloric acid in Bunsen's, Fresenius', or Mohr's distilling 
 
47. AKSENIC. 149 
 
 apparatus ( 39), for every 1 eq. of antimony present as sulphide, 
 3 eq. of HAS are liberated. If, therefore, the latter be estimated, 
 the quantity of antimony is ascertained. 
 
 Process : The antimony to be determined is brought into the form of ter- 
 or penta -sulphide (if precipitated from a hydrochloric solution, tartaric acid 
 must be previously added to prevent the precipitate being contaminated with 
 chloride), which, together with the filter containing it, is put into the distilling 
 flask with a tolerable quantity of hydrochloric acid not too concentrated. 
 The absorption tube contains a mixture of caustic soda or potash, with a 
 definite quantity of ^V arsenious acid solution in sufficient excess to retain all 
 the sulphuretted hydrogen evolved. The flask is then heated to boiling, and 
 the operation continued till all evolution of sulphuretted hydrogen has ceased ; 
 the mixture is then poured into a beaker, and acidified with hydrochloric 
 acid, to precipitate all the arseuious sulphide. The whole is then diluted to, 
 say 300 c.c., and 100 c.c. taken with a pipette, neutralized with sodic 
 carbonate, some bicarbonate added, and the titration for excess of arsenious 
 acid performed with ^ iodine and starch, as directed in 40. The separa- 
 tion of antimony may generally be insured by precipitation as sulphide. If 
 arsenic is precipitated at the same time, it may be removed by treatment 
 with ammonic carbonate.- 
 
 ARSENIC. 
 
 As = 75. As 2 3 = 198. As 2 5 ^230. 
 1. Oxidation by Iodine (Mo hr). 
 
 47. THE principle upon which the determination of arsenious 
 acid by iodine is based is explained in 40. 
 
 Experience has shown, that in the 'estimation of arsenious 
 compounds by the method there described, 'it is necessary to use 
 sodic bicarbonate for rendering the solution alkaline as in the case 
 of antimony. 
 
 Process : To a neutral aqueous solution, add about 20 c.c. of saturated 
 solution of sodic bicarbonate to every O'l gm. or so of As 2 O 3 , and then titrate 
 with 3^ iodine and starch. When the solution is acid, the excess may be 
 removed by neutral sodic carbonate, then the necessary quantity of bicar- 
 bonate added, and the titration completed as before. 
 
 Process for Arsenic Acid: This is best done by dissolving the acid in water, 
 and boiling with potassic iodide in the presence of hydrochloric acid in large 
 excess until all iodine vapours are dissipated. The'AsHO 4 is completely 
 reduced to AsHO 3 . The liquid is then cooled, sodic carbonate added to 
 neutrality, then some bicarbonate, and the arsenious acid titrated with 
 iodine in the usual way. Younger (J. 8. C. I. ix. 158) has verified this 
 method and proved that the reduction is complete : he also states that when 
 the boiled solution cools, the liberation of a slight amount of iodine occurs, 
 which may be prevented by using a few c.c. of glycerine. Of course the 
 arsenic acid must contain no nitric acid, nitrates, or similar interfering 
 bodies. 
 
 1 c.c. T \ iodine - 0-00495 gm. As 2 3 , or 0*00575 gm. As 2 5 . 
 
 Arsenic in Copper, Iron, Pyrites, etc. The method generally 
 adopted is the distillation of the arsenic obtained as sulphide, 
 with ferric chloride, and titration of the distillate with iodine as 
 above described, but F. Flatten (J. S. C. I. xvii. 324) has made 
 
150 VOLUMETRIC ANALYSIS. 47. 
 
 use of the discovery, that if As 2 S 3 is simply boiled with pure 
 water for a period of from 1 to 3 hours or until the liquid is 
 quite colourless and all H 2 S dissipated, the whole of the arsenic 
 will exist as As 2 3 , and may be titrated with T f y- iodine direct. 
 The results obtained by this method are as exact as any other, and 
 saves an immense amount of work. 
 
 Titration of Alkaline Arseniates. In a previous edition of this 
 book it was recommended, on the authority of Barnes, to estimate 
 the arsenic acid in commercial arseniates of soda, etc., by reduction 
 with sulphurous acid (passing the gas through the liquid), boiling 
 off the excess of SO' 2 , neutralizing with sodic bicarbonate, and 
 titrating with iodine as described above. This method has not 
 given me satisfactory results. The mere passing the gaseous SO 2 
 through the liquid does not, in all cases, insure the complete 
 reduction to arsenious acid. 
 
 Holthof (Z. a. C. xxii. 378) and McKay (0. N. liii. 221243) 
 have experimented largely on this method of estimating arsenic, 
 which was really originally suggested by Mohr, but never widely 
 adopted, owing to the defect already mentioned. Holthof proved 
 that various forms of arsenic, on being converted into arsenic acid, 
 would bear evaporation to dryness with HC1 without loss, and that 
 arsenic sulphide could be oxidized by strong nitric acid, or with 
 HC1 and KC10 3 to arsenic acid, and reduced to the lower state of 
 oxidation by copious treatment with SO 2 , the method being to add 
 300 or 400 c.c. of strong solution of SO 2 , digest on the water bath 
 for two hours, then boil down to one-half, and when cool add 
 sodic bicarbonate, and titrate with iodine and starch. 
 
 McKay shortens the method considerably by placing the 
 mixture in a well-stoppered bottle, tying down the stopper, and 
 digesting in boiling water for one hour. At the end of that time 
 the bottle is removed and allowed to cool somewhat, then emptied 
 into a boiling flask, diluted with about double its volume of water, 
 and boiled down by help of a platinum spiral to one-half. The 
 liquid is cooled, diluted, and either the whole or an aliquot portion 
 titrated in the usual way. 
 
 For quantities of material representing about 0*1 gm. As, 30 c.c. 
 of saturated solution of SO 2 will suffice, and the reduction may 
 therefore be made in a bottle holding 50 or 60 c.c. (fig. 39). The 
 results are very satisfactory. In the case of titrating commercial 
 alkaline arseniates, which often contain small quantities of 
 arsenious acid, this must be estimated first, and the amount 
 deducted from the total obtained after reduction. 
 
 2. Oxidation by Potassic Bichromate (Kessler). 
 
 This method is exact!}' the same as is fully described in 46 for antimony. 
 
 The arsenious compound is mixed with T \ bichromate in excess in presence 
 of hydrochloric acid and water, in such proportion that at least ^ of the total 
 volume consists of hydrochloric acid (sp. gr. 1'12). 
 
47. ARSENIC. 151 
 
 The excess of bichromate is found by a standard solution of pure iron, or 
 of double iron salt, with potassic ferricyanide as indicator ; the quantity of 
 bichromate reduced is, of course, the measure of the quantity of arsenious 
 converted into arsenic acid. 
 
 1 c.c. T \ bichromate -0-00495 gm. As 2 3 . 
 
 In cases where the direct titration of the hydrochloric acid solution cannot 
 be accomplished, the arsenious acid is precipitated with H' 2 S (with arsenates 
 at 70C.) 5 the precipitate well washed, the filter and the precipitate placed in 
 a stoppered flask, together with a saturated solution of mercuric chloride in 
 hydrochloric acid of 1/12 sp. gr., and digested at a gentle heat until the 
 precipitate is white, then water "added in such proportion that not less than ^ 
 of the volume of liquid consists of concentrated HC1 ; ^V bichromate is then 
 added, and the titration with standard ferrous solution completed as usual. 
 
 3. Indirect Estimation by Distilling- with Chromic and 
 Hydrochloric Acids (B u n s e n) . 
 
 The principle of this very exact method depends upon the fact, 
 that when potassic bichromate is boiled with concentrated hydro- 
 chloric acid, chlorine is liberated in the proportion of 3 eq. to 1 eq. 
 chromic acid. 
 
 If, however, arsenious acid is present, but not in excess, the 
 chlorine evolved is not in the proportion mentioned above, but so 
 much less as is necessary to convert the arsenious into arsenic acid. 
 
 A S 2Q 3 + 4C1 + 2H 2 - As 2 5 + 4HC1. 
 
 Therefore every 4 eq. of chlorine, short of the quantity yielded 
 when bichromate and hydrochloric acid are distilled alone, represent 
 1 eq. arsenious acid. The operation is conducted in the apparatus 
 fig. 37 or 38. 
 
 4. By Precipitation as TJranic Arsenate (Bodeker). 
 
 The arsenic must exist in the state of arsenic acid (As-O 5 ), and the process 
 is in all respects the same as for the estimation of phosphoric acid, devised 
 by N e u b a u e r , P i n c u s , and myself ( 72) . The strength of the uranium 
 solution may be ascertained and fixed by pure sodic or potassic arseuate, or 
 by means of a weighed quantity of pure arsenious acid converted into arsenic 
 acid by evaporation with strong nitric acid, and neutralizing with alkali, then 
 dissolved in acetic acid. The method of testing is precisely the same as with 
 phosphoric acid ; the solution of uranium should be titrated upon a weighed 
 amount of arsenical compound, bearing in mind here, as in the case of P'O , 
 that the titration must take place under precisely similar conditions as to 
 quantity of liquid, the amount of sodic acetate and acetic acid added, and 
 the depth of colour obtained by contact of the fluid under titration with the 
 yellow prussiate solution. 
 
 Bo am ((7. N. Ixi. 219), who has had large experience in the 
 examination of arsenical ores, recommends this method as being 
 rapid and accurate, and carries it out as follows : 
 
 1 to 1-5 gm. of dried and powdered ore is boiled to dryness with 2025 
 c.c. of strong nitric acid ; when cool about 30 c.c. of 30 % caustic soda 
 solution is added and boiled for a few minutes ; then diluted, filtered and 
 
152 VOLUMETRIC ANALYSIS. 47. 
 
 made up to 250 c.c. 25 c.c. of the liquid are acidified with a solution 
 containing 10 per cent, of sodic acetate in 50 per cent, acetic acid, and 
 heated to near boiling, then titrated with the standard uranium as usual. For 
 this latter, the same authority recommends what he terms a fourth normal 
 solution of uranium, containing 17'1 gm. uranic acetate, and 15 c.c. glacial 
 acetic acid made up to 2 liters with water, 1 c.c. being equal to T25 m.gm. 
 As. But if the method has to be considered accurate, this suggestion can 
 scarcely be adopted, since the uranic acetate of commerce is of indefinite 
 hydration; and moreover, to insure exactitude, it is necessary that the 
 titration should be carried out with the same proportions of saline matters, 
 acetic acid, etc., as existed in originally standardizing the uranium. I there- 
 fore unhesitatingly recommend that the uranium should be standardized 
 with a known weight of pure arsenic or arsenate in the presence of the same 
 proportions of sodic hydrate and acetate, acetic acid, etc., as will actually 
 be used in the analysis of an ore. The method may be used for all ores 
 which can be attacked by nitric acid. It is also available for iron pyrites 
 containing tolerable quantities of arsenic ; the ferric arsenate being readily 
 decomposed by excess of NaHO, thus allowing the ferric hydrate to be 
 filtered off free from As. 
 
 The solution of arsenic acid must of course be free from 
 metals liable to give a colour with the indicator and from 
 phosphates. Alkalies, alkaline earths, and zinc are of no con- 
 sequence, but it is advisable to add nearly the required volume of 
 uranium to the liquid before heating. The arsenic acid must be 
 separated from all bases which would yield compounds insoluble 
 in weak acetic acid. 
 
 The AsH 3 evolved from Marsh's apparatus may be passed into 
 fuming HNO 3 , evaporated to dryness, the arsenic acid dissolved in 
 water (antimony if present is insoluble), then titrated cautiously 
 with uranium in presence of free acetic acid and sodic acetate as 
 above described. 
 
 5. By Standard Silver as Arsenate. 
 
 The principle of this method has been adopted by Pearca 
 of the Colorado Smelting Company, and also by McCay (G, N. 
 xlviii. 7). The authors, however, differ in the details of the 
 process. The former prefers to separate the arsenic as silver 
 arsenate, and, estimating the silver so combined, thence calculate 
 the arsenic. The latter nses a known excess of standard silver, 
 and estimates the combined silver residually. 
 
 P e a r c e ' s Process. The finely-powdered substance for analysis is mixed 
 in a large porcelain crucible with from six to ten times its weight of 
 a mixture of equal parts of sodic carbonate and potassic nitrate. The mass 
 is then heated with a gradually increasing temperature to fusion for a few 
 minutes, allowed to cool, and the soluble portion extracted by warming with 
 water in the crucible, and filtering from the insoluble residue. The arsenic 
 is in the filtrate as alkaline arsenate. The solution is acidified with nitric 
 acid and boiled to expel CO" 2 and nitrous fumes. It is then cooled to the 
 ordinary temperature, and almost exactly neutralized as follows : Place 
 a small piece of litmus paper in the liquid: it should show tin acid reaction. 
 Now gradually add strong ammonia till the litmus turns blue, avoiding 
 a great excess. Again make slightly acid with a drop or two of strong nitric 
 
47- ARSENIC. 153 
 
 acid ; and then, by means of very dilute ammonia and nitric acid, added drop 
 by drop, bring the solution to such a condition that the litmus paper, after 
 having previously been reddened, will, in the course of half a minute, 
 begin to show signs of alkalinity. The litmus paper may now be removed 
 and washed, and the solution, if tolerably clear, is ready for the addition of 
 silver nitrate. If the neutralization has caused much of a precipitate 
 (alumina, etc.), it is best to filter it off at once, to render the subsequent 
 filtration and washing of the arsenate of silver easier. 
 
 A solution of silver nitrate (neutral) is now added in slight excess ; and 
 after stirring a moment, to partially coagulate the precipitated arsenate, 
 which is of a brick-red colour, the liquid is filtered, and the precipitate 
 washed with cold water. The filtrate is then tested with silver and dilute 
 ammonia, to see that the precipitation is complete. 
 
 The object is now to determine the amount of silver in the precipitate, 
 and from this to calculate the arsenic. The arsenate of silver is dissolved on 
 the filter with dilute nitric acid (which leaves undissolved any chloride 
 of silver), and the filtrate titrated, after the addition of ferric sulphate, with 
 ammonic thiocyanate ( 43). 
 
 From the formula 3Ag 2 O.As 2 5 , 648 parts Ag-150 parts As, 
 or Ag: As =108: 25. , 
 i 
 
 McCay's Process. The preliminary fusion is the same as in the 
 former method, but after acidulating with nitric acid and boiling 
 off CO 2 , the liquid is evaporated to drynessand heated till no more 
 acid fumes are given off. The residue is taken up with wa-ter, 
 filtered, made up to a definite volume, and the arsenic determined 
 in the following manner : 
 
 The solution of arsenic acid or arsenate is heated to boiling, and excess of 
 standard silver nitrate run in ; the liquid is then stirred briskly until the 
 precipitate begins to settle and the liquid becomes clear, when the beaker is 
 to be removed from the flame and left to cool to about 37 . Dilute ammonia 
 is now carefully added until a cloudiness ceases to form. The solution 
 should be well stirred before each successive addition, so as to obtain a clear 
 liquid in order to observe the cloud formation more distinctly. The silver 
 arsenate is finally filtered off and well washed ; the filtrate is acidulated with 
 nitric acid ; ferric sulphate added ; and the silver titrated with ammonic 
 thiocyanate ( 43). The amount of silver thus found deducted from the 
 quantity taken gives the amount combined with the arsenic ; and from this 
 datum the quantity of arsenic present is calculated. 
 
 Of these two methods the preference must be given to the first 
 on the score of accuracy, there being less probability of error from 
 contaminating substances; both, however, are available for technical 
 purposes. 
 
 Owing to the large amount of arsenate of silver formed from 
 a small quantity of arsenic (nearly six times by weight), it is 
 not at all necessary or even desirable to work with large amounts 
 of substance. 0'5 gm. is usually sufficient for the determination of 
 the smallest quantity of arsenic ; and where the percentage is high, 
 as little as O'l gm. may be taken with advantage. The method 
 has been used with very satisfactory results on the sulphide of 
 arsenic obtained in the ordinary course of analysis. 
 
 Substances such as molybdic and phosphoric acids, which may 
 
154 VOLUMETRIC ANALYSIS. 49. 
 
 behave similarly to arsenic under this treatment, interfere, of course, 
 with the method. Antimony, by forming antimoniate of sodium, 
 remains practically insoluble and without effect. 
 
 The method has been used by Me Cay for the estimation of 
 arsenic in the presence of alkaline earths, as occurring in some 
 minerals, with success. 
 
 BARIUM. 
 Ba = 136-8. 
 
 48. IN a great number of instances the estimation of barium 
 is simply the Converse of the process for sulphuric acid ( 76), 
 using either a standard solution of sulphuric acid or a neutral 
 sulphate in a known excess, and finding the amount by residual 
 titration. 
 
 When barium can be separated as carbonate, the estimation 
 is made as in 18.2. 
 
 Precipitation as Baric Clare-mate. A clecinormal Solution of 
 bichromate for precipitation purposes must differ from that used 
 for oxidation purposes. In the present case the solution is made 
 by dissolving 7 '37 gm. of pure potassic bichromate in water, and 
 diluting to 1 liter. 
 
 The barium compound, which may contain alkalies, magnesia, strontia, 
 and lime, is dissolved in a good quantity of water, ammonia free from 
 carbonate added, heated to 60 or 70 C., and the standard bichromate added 
 cautiously, with shaking, so long as the yellow precipitate of baric chromate 
 is formed, and until the clear supernatant liquid possesses a faint yellow 
 colour. 1 c.c. y^ solution = 0'00684< gm. Ba. 
 
 Titration of the Precipitate with Permanganate. In this case the 
 precipitate of baric chromate is well washed, transferred to a flask, and mixed 
 with an excess of double iron salt ; the amount of iron oxidized by the 
 chromic acid is then estimated by titration with permanganate ; the quantity 
 of iron changed to the ferric state multiplied by the factor 0'8187 = Ba. 
 
 BISMUTH. 
 
 Bi = 208. 
 
 49. THE estimation of this metal or its compounds volume t- 
 rically has occupied the attention of Pa tt ins on Muir, to whom 
 we are indebted for several methods of gaining this end. Two of 
 the best are given here, namely, (1) precipitation of the metal as 
 basic oxalate, and titration with permanganate ; (2) precipitation 
 as phosphate with excess of standard sodic phosphate, and titration 
 of that excess by standard uranic acetate. 
 
 1. Titration as Oxalate. 
 
 Normal bismuth oxalate, produced by adding excess of oxalic 
 acid to a nitric solution of the metal when separated by filtration, 
 
49. BISMUTH. 155 
 
 and boiled with successive quantities of water for three or four 
 times, is transformed into basic oxalate. The method of titratioii 
 is as follows : 
 
 The solution containing bismuth must be free fr om hydrochloric acid, as 
 the basic oxalate is readily soluble in that acid. A large excess of nitric 
 acid must also be avoided. Oxalic acid must be added in considerable 
 excess. If the precipitate be thoroughly shaken up with the liquid, and the 
 vessel be then set aside, the precipitate quickly settles, and the supernatant 
 liquid may be poured off through a filter in a very short time. If the 
 precipitate be boiled for five or "ten minutes with successive quantities of 
 about 50 c.c. of water, it is quickly transformed into the basic salt. So soon 
 as the supernatant liquid ceases to show an acid reaction, the transformation 
 is complete. It is well to employ a solution of permanganate so dilute, that 
 at least 50 c.c. are required for the titration (^ strength suffices). The basic 
 oxalate may be dissolved in dilute sulphuric acid in place of hydrochloric ; 
 it is more soluble, however, in the latter acid. If the solution contains but 
 little hydrochloric acid, there is no danger of chlorine being evolved during 
 the process of titration. 
 
 In applying this process to the estimation of bismuth in a solution 
 containing other metals, it is necessary, if the solution contain substances 
 capable of acting upon, or of being acted on b} 7 permanganate, to separate 
 the bismuth from the other metals present. This is easily done by 
 precipitating in a partially neutralized solution with much warm water and 
 a little ammonic chloride. The precipitate must be dissolved in nitric acid, 
 and the liquid boiled down once or twice with addition of the same acid in 
 order to expel all hydrochloric acid, before precipitating as oxalate. The 
 liquid should contain just sufficient nitric acid to prevent precipitation of 
 the basic nitrate before oxalic acid is added. 1 molecule oxalic acid corresponds 
 to 1 atom bismuth, or 126 = 203. 
 
 A shorter method, based on the same reactions, has been arranged 
 by Muir and Robbs (J. C. S. I. xli. 1). In this case, however, 
 the double oxalate of potassium and bismuth is the compound 
 obtained, the excess of oxalate of potash being determined 
 residually. Reis (Bericlite, xiv. 1172) has shown that when 
 normal potassic oxalate is added to a solution of bismuth nearly 
 free from mineral acid, but containing acetic acid, a double salt of 
 the formula Bi' 2 (C 2 4 ) a , K 2 C 2 4 is precipitated. In applying this 
 process for the estimation of bismuth in mixtures, it is necessary 
 to separate the metal as oxychloride, and that it should be obtained 
 in solution as nitrate with a small excess of nitric acid. This is 
 done by evaporating off the greater part of the free acid, allowing 
 just sufficient to remain that the bismuth may remain in solution 
 while hot. A large excess of acetic acid is then added, it is made 
 up to a definite measure, and an aliquot portion taken for titration. 
 
 The solution of normal potassic oxalate standardized by perman- 
 ganate must not be added in great excess. It is well, therefore, 
 to deliver it into the bismuth liquid from a burette until the 
 precipitation is apparently complete, then add a few extra c.c., and 
 allow to remain for some time with shaking. It is then filtered 
 through a dry filter, a measured portion taken, and the residual 
 oxalic acid found by permanganate. 
 
156 VOLUMETBIC ANALYSIS. 50. 
 
 2. Precipitation as Phosphate. 
 
 The necessary standard solutions are 
 
 (a) Standard sodic phosphate containing 35*8 gin. per liter. 
 1 c.c. -0-0071 gm. P 2 5 . 
 
 (b) Standard uramc acetate, corresponding volume for volume 
 with the above, when titrated with an approximately equal amount 
 of sodic acetate and free acetic acid. 
 
 Success depends very much upon identity of conditions, as is 
 explained in 72. 
 
 The bismuth to be estimated must be dissolved in nitric acid ; bases other 
 than the alkalies and alkaline earths must be absent. The absence of those 
 acids which interfere with the determination of phosphoric acid by the 
 uranium process (non-volatile, and reducing organic acids, sulphuretted 
 hydrogen, hydriodic acid, etc.) must be assured. As bismuth is readily 
 separated from other metals, with the exception of antimony and tin, by 
 addition of much warm water and a little ammonic chloride to feebly acid 
 solutions, a separation of the bismuth from those other metals which are 
 present should precede the process of estimation. If alkalies or alkaline 
 earths be alone present, the separation may be dispensed with. The pre- 
 cipitated bismuth salt is to be washed, dissolved in a little strong nitric acid. 
 and the solution boiled down twice with addition of a little more nitric acid, 
 in order to remove the whole of the hydrochloric acid present. 
 
 Such a quantity of a tolerably concentrated solution of sodic acetate is 
 added as shall insure the neutralization of the nitric acid, and therefore the 
 presence in the liquid of free acetic acid. If a precipitate form, a further 
 addition of sodic acetate must be made. The liquid is heated to boiling ; 
 a measured volume .of the sodic phosphate solution is run in ; the boiling 
 is continued for a few minutes ; the liquid is passed through a ribbed filter. 
 the precipitate being washed repeatedl}" with hot water ; and the excess of 
 phosphoric acid is determined in the filtrate by titration with uranium. 
 If the filtered liquid be received in a measuring flask, which is subsequently 
 filled to the mark with water, and if the inverted uranium method be then 
 employed, the results are exceedingly accurate. This method is especially to 
 be recommended in the estimation of somewhat large quantities of bismuth, 
 since it is possible that in such cases a large amount of sodic acetate will 
 have been used, which, as is well known, has a considerable disturbing effect 
 on the reaction of the indicator. 
 
 If the bismuth solution contain a large excess of nitric acid, it is better to 
 neutralize nearly with sodic carbonate before adding sodic acetate and titrating. 
 
 Fuller details of both the above processes are contained in J. C. S. 
 1877 (p. 674) and 1878 (p. 70). 
 
 BROMINE. 
 
 Br-80. 
 
 50. THIS element, or its unoxidized compounds, can be 
 estimated precisely in the same way as chlorine by -~ silver solution 
 ( 42), or alkalimetrically as in 32, or by thiocyanate ( 43), 
 but these methods are seldom of any avail, since the absence of 
 chlorine or its combinations is a necessary condition of accuracy. 
 
 Bromine in aqueous solution, or as gas, may be estimated by 
 
50. BROMINE. 157 
 
 absorption with solution of potassic iodide, in many cases by mere 
 digestion, and in other cases by distillation, in any of the forms of 
 apparatus given in 39, and the operation is carried out precisely 
 as for chlorine ( 54). 1 eq. I = 1 eq. Br. or I found x O63 = Br. 
 
 A process for the estimation of bromine in presence of chlorine 
 is still much wanted in the case of examining kelp liquors, etc. 
 Heine (Journ. f. pract. Cliem. xxxvi. 184) uses a colour method 
 in which the bromine is liberated by free chlorine, absorbed by 
 ether, and the colour compared with an ethereal solution of bromine 
 of known strength. Fehling states that with care the process 
 gives fairly accurate results. It is of course necessary to have an 
 approximate knowledge of the amount of bromine present in any 
 given solution. 
 
 Reimann (Annal. d. CJiem. u. Pkarm. cxv. 140) adopts the 
 following method, which gives tolerably accurate results, but 
 requires skill and practice. 
 
 The neutral bromine solution is placed in a stoppered vessel, 
 together with a globule of chloroform about the size of a hazel nut. 
 Chlorine water of known strength is then added cautiously from 
 a burette, protected from bright light, in such a way as to insure 
 first the liberation of the bromine, which colours the chloroform 
 orange yellow ; then more chlorine water, until the yellowish white 
 colour of chloride of bromine occurs (KBr + 2C1 = KC1 + BrCl). 
 
 The operation may be assisted by making a w r eak solution of 
 potassic chromate, of the same colour as a solution of chloride of 
 bromine in chloroform, to serve as a standard of comparison. 
 
 The strength of the chlorine water is ascertained by potassic 
 iodide and -^ thiosulphate. 2 eq. Cl.=l eq. Br. 
 
 In examining mother-liquors containing organic matter, they 
 must be evaporated to dryness in presence of free alkali, ignited, 
 extracted with water ; then neutralized with hydrochloric acid 
 before titrating as above. 
 
 Cavazzi (Gazz. Chim. Hal. xiii. 174) gives a method which 
 answers well for estimating bromine in small quantity, when mixed 
 with large proportions of alkaline chlorides. It is based on the 
 fact that, when such a mixture is heated to 100 C. with baric 
 peroxide and sulphuric acid, the whole of the bromine is liberated 
 with a mere trace of chlorine ; the bromine so evolved is absorbed 
 in any convenient apparatus, such as fig. 37. The distillation 
 is made in a 350 c.c. flask with double-bored stopper; one bore 
 contains an open tube reaching to the bottom of the flask, the 
 other carries the delivery tube which is connected with the (J tubes. 
 The first U tu ^ e i g empty; the second contains 20 c.c. of 
 a standard solution of arsenious acid in hydrochloric acid, con- 
 taining 0-005 gm. As 2 3 in each c.c., and is connected with an 
 aspirator. The apparatus is arranged so that the flask and empty 
 (J tube are immersed in boiling water, the vapours of H 2 2 are 
 thus decomposed, and the stream regulated by the aspirator. 
 
158 VOLUMETRIC ANALYSIS. 50. 
 
 The requisites used by the author are 
 
 Baric peroxide, containing 63 % BaO 2 . 
 
 Dilute sulphuric acid 1:2. 
 
 Arsenious acid dissolved in dilute hydrochloric acid, 5 gm. of 
 pure As 2 3 per liter. 
 
 Standard permanganate, 3 '55 gm. per liter. 
 
 It was found that the relative strengths of the arsenic and 
 permanganate solutions, when titrated together, diluted, and boiling, 
 were, 18*2 c.c. of the latter to 20 c.c. of the former. Therefore 
 1 c.c. of permanganate by calculation = 0*00888 gm. Br. 
 
 The author found that treating 2 gm. of KC1 in the apparatus, 
 without bromine, always gave a faint trace of Cl, so that only 
 18 c.c. of permanganate were required for the 20 c.c. of arsenic, 
 instead of 18 '2 c.c. ; and this he regards as a constant for that 
 quantity of material. The examples of analysis with from 
 O'Oo to 0*2 gm. KBr, and all with the correction of 0*2 c.c., are 
 satisfactory. 
 
 Norman McCulloch (C. N. Ix. 259) has described a method, 
 devised by himself, for the rapid and accurate estimation of bromine, 
 in presence of iodine or chlorine, in any of the ordinary commercial 
 forms or chemical combinations, free from oxidizing and reducing 
 agents and metals forming bromides, insoluble in hydrochloric 
 acid. The author's explanation of the principles upon which 
 the method is based is complicated and voluminous, for which the 
 reader is referred to the original article. I have not been able to 
 verify the method, but as the author is . known to have practical 
 experience, as well as theoretical knowledge, a short summary is 
 given here. 
 
 The requisites described by the author are 
 
 Standard permanganate, 31 '9 grains of the salt in 10,000 grains 
 of water (or 3*19 gm. per liter). 
 
 Standard potassic iodide, 82 '78 grains of KI in 10,000 grains of 
 water" (or 8 '2 7 8 gm. per liter.) 
 
 The solutions should agree volume for volume, but it is pre- 
 ferable to verify them by dissolving 3-5 grains of iodine in 
 caustic soda, in a 5-oz. stoppered bottle, adding HC1 in good excess, 
 cooling, then adding the permanganate from a burette, until nearly 
 colourless. A little chloroform as indicator is then added, and the 
 permanganate cautiously run in, with shaking until the violet 
 colour of the iodine is discharged, owing to production of IC1, 
 due to the reaction of Cl liberated by the permanganate from 
 HC1. 
 
 The iodine equivalent of the permanganate is calculated to 
 bromine by the coefficient x 0'6713 and each decem of permanganate 
 should represent about 0*04 grain Br (or each c.c 0*004 gm 
 Br). 
 
 The other reagents are purified chloroform, made by adding 
 some permanganate, then HC1 till colour is discharged, then a little 
 
51. CADMIUM. 159 
 
 KI and the I so liberated again discharged with permanganate, 
 finally the chloroform is washed free from all acid. 
 
 A three per cent, solution of hydrocyanic acid, made by decom- 
 posing a solution of pure potassic cyanide, with excess of HC1, and 
 adding permanganate till a faint pink colour remains. 600 grains 
 of KC1ST in 13 J ounces of water (or 40 gm. in 400 c.c.) with 
 2J- ounces of HC1 (or 70 c.c.) will give such a solution. Owing to 
 its poisonous nature great caution must be used in making this 
 solution, and to avoid as much as possible the evolution of prussic 
 acid the temperature must be kept down by ice, or a freezing 
 mixture of nitre and sal ammoniac. If the cyanide contains, as is 
 often the case, some alkaline carbonate, this should be removed 
 previously by Bad, as otherwise CO 2 will be liberated and a loss 
 of HCX occur, finally the cool solution is rendered faintly pink 
 with some permanganate. 
 
 Solution of manganous chloride, made by dissolving half a pound 
 of MnCl 2 + 4H 2 in 4 oz. of warm water (or 500 gm. in 250 c.c.), 
 This solution is used to prevent the liberation of free chlorine 
 from the HC1 in the analysis. 
 
 Process : The weighed bromide, containing from 1 to 3 grains of Br 
 (0'05 to 0'15 gm.), is dissolved in half an ounce (15 c.c.) of water in a 5 oz. 
 stoppered bottle, and about an ounce (30 c.c.) of the manganese sohition 
 added ; permanganate is then run in excess of the required quantity, and the 
 bottle cooled rapidly to 50 P. (10 C.) by ice or a freezing mixture. When 
 cooled, the bottle is shaken by a rotary motion, and about half an ounce 
 (15 c.c.) of moderately strong HC1 slowly added, with motion of the bottle 
 to dissolve the manganic hydroxide, 3 to 6 dm. (2 4 c.c.) 0f hydro- 
 cyanic solution are then delivered in, the bottle closed and returned to the 
 cooling mixture for about half an hour. The liquid is then titrated with 
 the standard potassic iodide, until nearly decolorized from the decomposition 
 of the manganic chloride, and then slightly coloured from liberation of 
 free I. Lastly, the slight excess of iodide is estimated by adding a little 
 chloroform, and the titration finished with permanganate. The bromine is 
 calculated by taking the difference between the amounts of bromine, 
 represented by total permanganate and iodide used. If iodine is present it 
 is of course recorded as bromine, and its amount, if required, must be 
 ascertained by some other method capable of its estimation in the presence 
 of bromine. 
 
 The author gives several very good results with pure sodic 
 bromide, an example of which may be given. Each measure of 
 permanganate=0-0392 Br. T032 grain Br was taken, and 40 '6 
 measures of permanganate with 14*3 measures of iodide used, then 
 40-6 -14-3=26-3 which multiplied by 0-0392=1-031 Br. 
 
 CADMIUM. 
 
 Cd=lll-6. 
 
 51. THIS metal may be estimated, as is the case with many 
 others, by precipitation as sulphide, and decomposing the sulphide 
 with a ferric salt, the iron being reduced to the ferrous state in 
 proportion to the amount of sulphide present. 
 
160 VOLUMETRIC ANALYSIS. 52. 
 
 Follenius has found that when cadmium is precipitated as 
 sulphide in acid liquids, the precipitate is apt to be contaminated 
 with salts other than sulphide to a small extent. The separation 
 as sulphide is hest made by passing H 2 S into the hot liquid which 
 contains the cadmium, and which should be acidified with 10 per- 
 cent, of concentrated sulphuric acid by volume. . From hydrochloric 
 acid solutions the metal is only completely separated by H 2 S when 
 the hot solution contains not more than 5 per cent, of acid of 
 sp. gr. I'll, or 14 per cent, if the liquid is cold. 
 
 Ferric chloride is to be preferred for the decomposition of the 
 cadmium sulphide, and the titration is carried out precisely as in 
 the case of zinc ( 81). 
 
 P. von Berg (Z. a. C. xxvi. 23) gives a good technical process 
 for the estimation of either cadmium or zinc as sulphides, by 
 means of iodine, as follows : - 
 
 The washed sulphide of zinc or cadmium is allowed to drain upon the 
 filter, and then transferred, together with the filter, to a stoppered flask 
 containing 800 c.c. of water deprived of air by boiling and the passage of 
 carbonic acid gas. The whole is well shaken to break up the precipitate and 
 bring it intfl the most finely divided condition possible, so that the sulphide 
 may not be protected from the action of the iodine by separated sulphur. 
 A moderate quantity of hydrochloric acid is added, there being no necessity 
 to entirely dissolve the sulphide, and then an excess of iodine solution of 
 known strength. The residual free iodine is then titrated with thiosulphate 
 without loss of time. The whole operation, from the transference of the 
 sulphide to the flask to the final titration, occupies about five minutes, and 
 gives results varying between 98'8 and 100'2 per cent. The reaction proceeds 
 according to the equation, ZnS+2HCl+2l = ZnCl 2 +2HI + S. 
 
 Cadmium may also be estimated, when existing as sulphate or 
 nitrate, by precipitation as oxalate, and titration of the washed 
 precipitate by permanganate. The details are carried out precisely 
 as in the case of estimating zinc as oxalate ( 81). 
 
 CALCIUM. 
 
 Ca40. 
 
 1 c.c. y^ permanganate = 0'002S gm. CaO 
 
 - 0-0050 gm. CaCO 3 
 = 0-0086 gm. CaS0 4 + 
 ,, normal oxalic acid 0-0280 gm. CaO 
 
 Cryst. oxalic acid x 0-444 = CaO 
 
 Double iron salt x 0-07143 = CaO 
 
 52. THE estimation of calcium alkalimetrically has already 
 been given ( 18), but that method is of limited application, unless 
 calcic oxalate, in which form Ca is generally separated from other 
 bases, be converted into carbonate or oxide by ignition, and thus 
 determined with normal nitric acid and alkali. This and the 
 following method by Hemp el are as exact in their results as the 
 
52. CALCIUM. 161 
 
 determination by weight ; and where a series of estimations have 
 to be made, the method is very convenient. 
 
 Titration with. Permanganate. The readiness with which calcium 
 can be separated as oxalate facilitates the use of this method, so 
 that it can be applied successfully in a great variety of instances. 
 It is not necessary here to enter into detail as to the method 
 of precipitation ; except to say, that it may occur in either 
 ammoniacal or weak acetic acid solution ; and that it is absolutely 
 necessary to remove all excess of ammonic oxalate from the 
 precipitate by washing with warm water previous to titration. 
 
 Process : When the clean precipitate is obtained, a hole is made in the 
 filter, and the bulk of the precipitate is washed through the funnel into 
 a flask ; the filter is then treated with small quantities of hot dilute sulphuric 
 acid, and again washed into the flask. Hydrochloric acid in moderate 
 quantity may be safely used for the solution of the oxalate, since there is 
 not the danger of liberating free chlorine Avhich exists in the case of iron 
 (Fleischer, Titrirmethode, p. 76), but the sulphuric is better. 
 
 When the precipitate is completely dissolved, the solution is freely diluted 
 with water, and further acidified with sulphuric acid, warmed to 60 or 70, 
 and the standard permanganate cautiously delivered into the liquid with 
 constant agitation until a faint permanent pink tinge occurs, precisely as in 
 the case of standardizing permanganate with oxalic acid ( 34.2c). 
 
 Process for Lime in Blast Furnace Slags : Place about 1 gm. of the very 
 finely-ground slag into a beaker, cover with water, and boil gently, then 
 add gradually strong HC1 until the whole is dissolved, including SiO' 2 . 
 Dilute the liquid, nearly neutralize with ammonia, and add a solution of 
 ammonic acetate. The silica and alumina form a flocculent precipitate 
 which is easily washed on a filter. The filtrate and washings are concen- 
 trated somewhat, and the CaO precipitated with oxalate of ammonia and 
 free ammonia ; the precipitate is dissolved as before described in hot dilute 
 sulphuric acid, and titrated with permanganate. If much manganese is 
 present, the calcic oxalate must be re-dissolved and re-precipitated before 
 the titration is made. 
 
 In all cases where a clean oxalate precipitate can be obtained, 
 such as mineral waters, manures, etc., very exact results are obtain- 
 able ; in fact, quite a,s accurate as by the gravimetric method. 
 Ample testimony on this point is given by Fresenius, Mohr, 
 Hempel, and others. 
 
 Tucker (Iron, ^"ov. 16, 1878) has given the results of many 
 experiments made by him upon mixtures of Ca.with abnormal 
 proportions of iron, magnesia, alumina, etc. ; and even here the 
 numbers obtained did not vary more than 2 to 3 per cent, from the 
 truth. In the case of large proportions of these substances it will 
 be preferable to re-precipitate the oxalate, so as to free it from 
 adhering contaminations previous to titration. 
 
 o 
 
 Indirect Titration. In the case of calcic salts soluble in water and 
 of tolerably pure nature, the estimation by permanganate can be 
 made by adding to the solution a measured excess of normal oxalic 
 acid, neutralizing with ammonia in slight excess, and heating to 
 
 M 
 
162 VOLUMETRIC ANALYSIS. 54 
 
 boiling, so as to rapidly separate the precipitate. The mixture is 
 then cooled, diluted to a measured volume, filtered through a dry 
 filter, and an aliquot portion titrated with permanganate after 
 acidifying with sulphuric acid as usual. A great variety of calcium 
 salts may be converted into oxalic by a short or long treatment 
 with oxalic acid or ammonic oxalate, including calcic sulphate, 
 phosphate, tartrate, citrate, etc. 
 
 CERIUM. 
 
 Ce- 141-2. 
 
 53. THE most exact method of estimating this metal is by 
 precipitating as cerotis oxalate, then drying the precipitate, and 
 strongly igniting in an open crucible, so as to convert it into eerie 
 oxide. 
 
 Stolba (Z. a. C. xix. 194) states that the moist oxalate may be 
 titrated precisely as in the case of calcic oxalate with permanganate, 
 and with accurate results. ~No examples or details, however, are 
 given. 
 
 CHLORINE. 
 
 01=35-37. 
 
 1 c.c. ~ silver solution^O'00^537 gm. Cl. 
 =0-005837 sin. 
 
 54. THE powerful affinity existing between chlorine and silver 
 in solution, and the ready precipitation of the resulting chloride, 
 seem to have led to the earliest important volumetric process in 
 existence, viz., the assay of silver by the w r et method of Gay 
 Lussac. The details of the process are more particularly described 
 under the article relating to the assay of silver ( 73) ; the deter- 
 mination of chlorine is just the converse of the process there 
 described, and the same precautions, and to a certain extent the 
 same apparatus, are required. 
 
 The solutions required, however, are systematic, and for exactness 
 and convenient dilution are of decinormal* strength as described in 
 41. In many cases it is advisable to possess also centinormal 
 solutions, made by diluting 100 c.c. of ~ solution to 1 liter. 
 
 1. Direct Precipitation -with ^Q Silver. 
 
 Very weak solutions of chlorides, such as drinking waters, are not easily 
 examined for chlorine by direct precipitation, unless they are considerably 
 concentrated by evaporation previous to treatment, owing to the fact that, 
 unless a tolerable quantity of chloride can be formed, it Avill not collect 
 together and separate so as to leave the liquid clear enough to tell on the 
 addition of fresh silver whether a distinct formation of chloride occurs. 
 The best effects are produced when the mixture contains chlorine equal to 
 from H to 2 gm. of salt per 100 c.c. Should the proportion be much less 
 
54. . CHLORINE. 163 
 
 than this, the difficulty of precipitation may be overcome by adding a 
 quantity of freshly precipitated chloride, made by mixing 1 equal volumes of 
 -j^r salt and silver solution, shaking vigorously, pouring off the clear liquid, 
 and adding the chloride to the mixture under titration. The best vessel to 
 use for the trial is a well-stoppered round white bottle, holding 100 to 150 
 c.c., and fitting into a paper case, so as to prevent access of strong light 
 during the titration. Supposing, for instance, a neutral solution of potassic 
 chloride requires titration, 20 or 30 c.c. are measured into the shaking 
 bottle, a few drops of strong nitric acid added (free acid must always be 
 present in direct precipitation), and a round number of c.c. of silver solution 
 added from the burette. The bottle is placed in its case, or may be enveloped 
 in a dark cloth and vigorous!} 7 shaken for half a minute, then uncovered, 
 and gently tapped upon a table or book, so as to start the chloride downward 
 from the surface of the liquid \vhere it often swims. A quick clarification 
 indicates excess of silver. The nearer the point of exact counterbalance the 
 more difficult to obtain a clear solution by shaking, but a little practice soon 
 accustoms the eye to distinguish the faintest precipitate. 
 
 In case of overstepping the balance in any trial, it is only 
 necessary to add to the liquid under titration a definite volume of 
 ~ salt solution, and finish the titration in the same liquid, 
 deducting, of course, the same number of c.c. of silver as has been 
 added of salt solution. . 
 
 Fuller details and precautions are given in 73. 
 
 2. Precipitation by Silver in Neutral Solution with Chromate 
 Indicator (see 41, 2 t>). 
 
 3. Titration with ^ Silver and ' Thiocyanate (see 43). 
 
 This method gives very accurate results if, after the chlorine is 
 precipitated with excess of silver, the silver chloride is filtered 
 off, washed well, and the filtrate and washings titrated with 
 thiocyanate for the excess of silver. . 
 
 Process : The material to be titrated, such as water residues, beer ash, or 
 other substances in which the chlorine is to be estimated being brought into 
 clear solution, a known volume of ^ silver in excess is added, having previously 
 acidified the mixture with nitric acid ; the mixture is well stirred, and the 
 supernatant liquid filtered off through a small filter, the chloride well 
 washed, and to the filtrate and washings 5 c.c. of ferric indicator ( 43.3) 
 and the same volume of nitric acid ( 43.4) are added. The flask is then 
 brought under the thiocyanate burette, and the solution delivered in with 
 a constant gentle movement of the liquid until a permanent light-brown 
 colour appears. If the silver chloride is not- removed from the liquid 
 previous to titration a serious error may occur, owing to the read}^ solubility 
 of the chloride in the thiocj-auate solution. 
 
 4. By Distillation and Titration with Thiosulphate or Arsenite. 
 
 In cases where chlorine is evolved direct in the gaseous form or 
 as the representative of some other body (see 39), a very useful 
 absorption apparatus is shown in fig. 37. The little flask a is used 
 as a distilling vessel, connected with the bulb tubes by an india- 
 
 M 2 
 
164 VOLUMETRIC ANALYSIS. 
 
 rubber joint ;* the stoppers for the tubes are also of the same 
 material, the whole of which should be cleansed from sulphur by 
 boiling in weak alkali. A fragment of solid magnesite may with 
 advantage be added to the acid liquid in the distilling flask ; in 
 all other respects the process is conducted exactly as is described 
 in 39. 
 
 This apparatus is equally well adapted to the absorption of 
 ammonia or other gases, and possesses the great recommendation 
 that there is scarcely a possibility of regurgitation. 
 
 Mohr's apparatus (fig. 38) is also serviceable for this method. 
 
 CHLORINE G-AS AND BLEACHING- COMPOUNDS. 
 
 1 c.c. yjj- arsenious or thiosulphate solution=0*003537 gm. CI. 
 1 liter of chlorine at C., and 760 m.m., weighs 3'167 gm. 
 
 55. CHLORINE water may be titrated with thiosulphate by 
 adding a measured quantity of it to a solution of potassic iodide, 
 then delivering the thiosulphate from a burette till the colour of 
 the free iodine has disappeared; or by using an excess of the 
 reducing agent, then starch, and titrating residually with iodine. 
 When arsenious solution is used for titration, the chlorine water is 
 delivered into a solution of sodic carbonate, excess of arsenious 
 solution added, then starch and iodine till the colour appears, 
 or iodized starch-paper may be used. 
 
 Bleaching- Powder. The chief substance of importance among 
 the compounds of hypochlorous acid is the so-called chloride of 
 lime. The estimation of the free chlorine contained in it presents 
 no difficulty when arsenious solution is used for titration. 
 
 Commercial bleaching powder consists of a mixture in variable 
 proportions of calcic hypochlorite (the true bleaching agent), calcic 
 chloride, and hydrate; and in some cases the preparation contains 
 considerable quantities of chlorate, due to imperfect manufacture or 
 age. It is generally valued and sold in this country by its 
 percentage of chlorine. In France it is sold by degrees calculated 
 from the volume of gaseous chlorine: 100 Erench=31 < 78 per 
 cent. English. 
 
 1. Titration by Arsenious Solution (Penot). 
 
 The first thing to be done in determining the value of a sample 
 of bleaching powder is to bring it into solution, which is best 
 managed as follows : 
 
 The sample is well and quickly mixed, and 7'17 gm. weighed, put into 
 a mortar, a little water added, and the mixture rubbed to a smooth cream ; 
 more water is then stirred in with the pestle, allowed to settle a little while, 
 then poured off into a liter flask; the sediment again rubbed with water, 
 
 * India-rubber and specially vulcanized rubber is open to some objection in these 
 analyses, and apparatus is now readily to be had with glass connections. 
 
55. BLEACHING POWDER. 165 
 
 poured off, and so on repeatedly, until the whole of the chloride has been 
 conveyed into the flask without loss, and the mortar washed quite clean. 
 The flask is then filled to the mark with water, well shaken, and 50 c.c. of 
 the milky liquid taken out with a pipette, emptied into a beaker, and the & 
 arsenious solution delivered in from a burette until a drop of the mixture 
 taken out with a glass rod, and brought hi contact with the prepared starch- 
 paper ( 40) gives no blue stain. 
 
 The starch-paper may be dispensed with by adding arsenious solution in 
 excess, then starch, and titrating residually with & iodine till the blue 
 colour appears. The number of c.c. of arsenic used shows direct percentage 
 of available chlorine. 
 
 A more rapid technical method can be adopted in cases where a series of 
 samples has to be tested, as follows : 4'95 gm. of pure arsenious acid are 
 finely powdered and dissolved by the aid of a gentle heat in about 15 c.c. 
 of glycerine, then diluted with water to 1 liter ; 25 c.c. are measured into 
 a flask, and 1 c.c. of indigo solution added. The turbid solution of bleaching 
 powder is poured into a suitable burette, and before it has time to settle is 
 delivered with constant shaking into the blue arsenious solution until the 
 colour is just discharged : the percentage of chlorine is then found by a slight 
 calculation. 
 
 2. Bunsen's Method. 
 
 10 or 20 c.c. of the chloride of lime solution, prepared as above, are 
 measured into a beaker, and an excess of solution of potassic iodide added ; 
 the mixture is then diluted somewhat, acidified with acetic acid, and the 
 liberated iodine titrated with T ^ thiosulphate and starch; 1 eq. iodine so 
 found represents 1 eq. chlorine. 
 
 The presence of chlorate does not affect the result when acetic 
 acid is used. If it be desired to estimate the amount of chlorate 
 in bleach, the following method has been devised by R. Fresenius. 
 It depends on the fact that hypochlorites are decomposed by lead 
 acetate with formation of lead peroxide, whilst the chlorate which 
 may be present is unaffected. 
 
 Process ; 20 gm. of bleaching powder are ground up with water in 
 repeated quantities and made up to a liter; after settling, 50 c.c. 1 gm. of 
 bleach are filtered off through a dry filter, put into a flask, and mixed with 
 a solution of lead acetate in some excess. There is formed at first a white 
 precipitate of lead chloride and lead hydroxide, these being acted on by the 
 hypochlorite become first yellow, then brown, with liberation of chlorine and 
 passing into lead peroxide. After the precipitate has settled, more lead 
 solution is added, to be sure that the conversion is complete. The mixture 
 is allowed to stand in the open flask, with frequent shaking, till all smell of 
 chlorine has disappeared, which occurs in from eight to ten hours. The 
 precipitate is then filtered off and washed till the wash-water is free from 
 acid. ' The washings are evaporated somewhat, added to the filtrate, and the 
 whole mixed with sodic carbonate in slight excess, to precipitate the lead and 
 lime as carbonates these are well Avashed, the filtrate and w r ashings 
 evaporated nearly to dryness, then transferred to either a P r e s e n i u s or 
 Mohr apparatus (fig. 37 or 38) and distilled with HC1 as directed in 39. 
 1 cq. :I-1 eq. Cl-O 5 . 
 
 3. Gasometric Process. 
 
 This method has been devised by Lunge (Bericlde xix. 868, 
 also J. S. C. I. ix. 22) and is both accurate and rapid. The 
 instrument used for the analysis is preferably the improve^ 
 
166 VOLUMETRIC ANALYSIS. 
 
 nitrometer, with patent tap and bulb (see Part VII.), winch permits 
 the use of a larger weight of the sample than the ordinary 50 c.c. 
 nitrometer. In both instruments for this class of analysis ordinary 
 tap water may be used, instead of mercury, with equally accurate 
 results. 
 
 The reagent used for the decomposition of the bleach is 
 hydrogen peroxide, and the reaction is CaOCl 2 + H 2 2 =CaCl 2 + 
 H 2 + O 2 . Lunge's directions are as follows : 
 
 It is not necessary to know the exact composition of the hydrogen peroxide, 
 but as it is desirable not to employ too large an excess of it in this case, it is 
 best to estimate its percentage by a preliminary test occupying but a few 
 minutes, in which a certain yolume of H-O- is decomposed by an excess of 
 bleach solution (the inverse of the titration of the latter). This need be 
 done only quite roughly. For the ana-lysis of chloride of lime the hydrogen 
 peroxide must be diluted before use so as not to give out more than 7 c.c. of 
 oxygen per c.c., and it must be made alkaline by means of caustic soda 
 solution up to the point where a flocculent precipitate appears. The alkaline 
 reaction ought to be quite distinct, but any fjreat excess of alkali should be 
 avoided. It is not necessary to shake much, and the reading ought to be 
 made quickly, say five minutes after mixing the liquids, otherwise the results 
 will be too high owing to the gradual evolution of more oxygen from the 
 alkaline liquid. It might be thought that muddy solutions, such as arc 
 regularly employed in testing commercial bleaching powder, would yield less 
 reliable results, the solid matter favouring the evolution of oxygen from 
 II-O- otherwise than through the action of CaOCl 2 ; but this is not so; 
 muddy solutions can be tested by the nitrometer just as well as clear bleach 
 liquors, provided the time of five minutes is not exceeded. As the reaction 
 does not produce a sensible change of temperature, that time will quite 
 suffice, provided that the operator has avoided raising the temperature of the 
 flask in manipulating it, which he can do by handling it always by the neck 
 with his thumb and forefinger only. 
 
 In order to find the percentage of available chlorine by weight, that is, 
 the English chlorometrical degrees, it should be borne in mind that every 
 c.c, of gas evolved, reduced to and 760 m.m., represents 0'003167 gin. of 
 chlorine. Hence, if the quantity of bleach employed is = 1 gin. (for 
 instance, by dissolving 20 gm. in 500 c.c. of water, and employing 25 c.c. 
 of the solution for each test), each c.c. of gas is = 3167 per cent, of 
 available chlorine in the bleach. This involves the use of a bulb nitrometer 
 holding 140 c.c. If only a 50 c.c. instrument is at hand, it will be necessary 
 to take, say, 5 c.c. of the first-mentioned bleach solution, in which case every 
 c.c. of gas represents 5xO'3167 = l'58 per cent, of chlorine. The most con- 
 venient way is to dissolve 7'917 gm. of bleach in 250 c.c. of water, and 
 emploj'ing 10 c.c. of the solution for each test, when each c.c. of oxygen 
 evolved will directly indicate 1 per cent, of available chlorine, and a 50 c.c. 
 nitrometer should be used. 
 
 The general method of manipulating the nitrometer is described 
 in Part VII. 
 
 CHLORATES, IODATES, AND BROMATES. 
 
 Chloric anhydride, C1 2 5 =150'74. lodic anhydride, I 2 5 =333. 
 Bromic anhydride, Br 2 5 =239'5. 
 
 The compounds of chloric, iodic, and bromic anhydrides may 
 all be determined by distillation or digestion with excess of 
 
56. CHROMIUM. 167 
 
 hydrochloric acid ; with chlorates the quantity of acid must be 
 considerably in excess. 
 
 In. each case 1 eq. of the respective anhydrides taken as 
 monobasic or their compounds, liberates 6 eq. of chlorine, and 
 consequently 6 eq. of iodine when decomposed in the digestion 
 flask. In the case of distillation, however, iodic and bromic acids 
 only set free 4 eq. iodine, while iodous and bromous chlorides 
 remain in the retort. In both these cases digestion is preferable 
 to distillation. 
 
 Example : 0'2043 gm. pure potassic chlorate, equal to the sixth part of 
 r " TJ J inr eq. was decomposed by digestion with potassic iodide and strong 
 hydrochloric acid in the bottle shown in fig. 39. After the reaction was 
 complete, and the bottle cold, the stopper was removed, and the contents 
 washed out into a beaker, starch added, and 103 c.c. T ^ thiosulphate delivered 
 in from the burette ; then again 23'2 c.c. of ^ iodine solution, to reproduce 
 the blue colour ; this latter was therefore equal to 2'32 c.c. T ^- iodine, which 
 deducted from the 103 c.c. thiosulphate gave 100'68 c.c., which multiplied by 
 the factor 0'002043, gave 0'2056 gm., instead of 0'2043 gm. 
 
 CHROMIUM. 
 
 Cr=52-4. 
 1. Ueduction by Iron. 
 
 56. THE estimation of chromates is very simply arid success- 
 fully performed by the aid of ferrous sulphate, being the converse 
 of the process devised by Penny for the estimation of iron 
 (see 37). 
 
 Process : A very small beaker or other convenient vessel is partly or 
 wholly filled, as may be requisite, with perfectly dry and granular double 
 sulphate of iron and ammonia ; the exact weight then taken and noted. 
 The chromium compound is brought into solution, not too dilute, acidified 
 with sulphuric acid, and small quantities of the iron salt added from time to 
 time with a dry spoon, taking care that none is spilled, and stirring with 
 a glass rod, until the mixture becomes green, and the iron is in excess, best 
 known by a small drop being brought in contact with a drop of red'prussiate 
 of potash on a white plate; if a blue colour appears at the point of contact, 
 the iron is in excess. It is necessary to estimate this excess, which is most 
 conveniently done by ^ bichromate being added until the blue colour 
 produced by contact with the red prussiate disappears. The vessel containing 
 the iron salt is again weighed, the loss noted; the quantity of the salt 
 represented by the ^ bichromate deducted from it, and the remainder 
 multiplied by the factor required by the substance sought. A freshly made 
 standard -solution of iron salt, well acidified with sulphuric acid, may be used 
 in place of the dry salt. 
 
 Example : 0'5 gm. pure potassic bichromate was taken for analysis, and to 
 its acid solution 4'15 gm. double iron salt added. 33 c.c. of / bichromate 
 Avere required to oxidize the excess of iron salt ; it was found that 0'7 gm. of 
 the salt= 17'85 c.c. bichromate, consequently 3'3 c.c. of the latter were equal 
 to 0'12985 gm. iron salt; this deducted from the quantity originally used 
 left 4-02015 gm., which multiplied by 01255 gave 0'504 gm. instead of 
 0'5 gm. 
 
168 VOLUMETRIC ANALYSIS. 56. 
 
 In the case of lead chromate being estimated in this way, it is 
 best to mix both the chromate and the iron salt together in 
 a mortar, rubbing them to powder, adding hydrochloric acid, 
 stirring well together, then diluting with water and titrating as 
 before. ...Where 'pure double iron salt is not at hand, a solution of 
 iron wire in sulphuric acid, freshly made, and of ascertained 
 strength, may be used. 
 
 2. Estimation of Chromates by Distillation with Hydrochloric Acid. 
 
 When chromates are boiled with an excess of strong hydrochloric 
 acid in one of the apparatus (fig. 37 or 38), every 1 eq. of chromic 
 acid liberates 3 eq. chlorine. For instance, with potassic bichromate 
 the reaction may be expressed as follows 
 
 K 2 O 2 O r + 14HC1=2KC1 + Cr 2 Cl 6 + 7H 2 + 6C1. 
 
 If the liberated chlorine is conducted into a solution of potassic 
 iodide, 3 eq. of iodine are set free, and can be estimated by 
 arsenite or thiosulphate. 3 eq. of iodine so obtained=379'5 
 represent 1 eq. chromic acid 100 '40. The same decomposition 
 takes place by mere digestion, as described in 39. 
 
 3. Chrome Iron Ore, Ste'el, etc. 
 
 The ore varies in quality, some samples being very rich, while 
 others are very poor, in chromium. In all cases the sample is to 
 be first of all brought into extremely fine powder. About a gram is 
 rubbed tolerably fine in a steel mortar, then finished fractionally 
 in an agate mortar. 
 
 Christomanos recommends that the coarse powder should be 
 ignited for a short time on platinum previous to powdering with 
 the agate mortar ; after that it should be sifted through the finest 
 material that can be used, and the coarser particles returned to the 
 mortar for regrinding. 
 
 Previous to analysis it should be again ignited, and the analysis 
 made on the dry sample. 
 
 O'Neill's Process. The very finely powdered ore is fused with 
 ten times its weight of potassic bisulphate for twenty minutes, taking care 
 that it does not rise over the edge of the platinum crucible ; when the fusion 
 is complete, the molten mass is caused to flow over the sides of the crucible, 
 so as to prevent the formation of a solid lump, and the crucible set aside to 
 cool. The mass is transferred to a porcelain dish, and lixiviated with warm 
 water until entirely dissolved (no black residue must occur, otherwise the 
 ore is not completely decomposed) ; sodic carbonate is then added to the 
 liquid until it is stro'ngly alkaline ; it is then brought on a filter, washed 
 slightly, and the filter dried. When perfectly dry, the precipitate is 
 detached from the filter as much as possible ; the filter burned separately ; 
 the ashes and precipitate mixed with about twelve times the weight of the 
 original ore, of a mixture of two parts potassic chlorate and three parts 
 sodic carbonate, and fused in a platinum crucible for twenty minutes or so ; 
 the resulting mass is then treated with boiling water, filtered, and the filtrate 
 titrated for chromic acid as in 5 56.1. 
 
56. 
 
 CHROMIUM. 169 
 
 The ferric oxide remaining on the filter is titrated, if required, 
 by any of the methods described in 63 and 64. 
 
 Britton's Process. Reduce the mineral to the finest state of 
 division possible in an agate mortar. Weigh off 0'5 gm., and add to it 
 4 gm. of flux, previously prepared, composed of one part potassic chlorate 
 and three parts soda-lime ; thoroughly mix the mass by triturating in a 
 porcelain mortar, and then ignite in a covered platinum crucible at a bright- 
 red heat for an hour and a half or more. 20 minutes is sufficient with 'the 
 gas blowpipe. The mass will not fuse, but when cold can be turned out of 
 the crucible by a few gentle taps, leaving the interior of the vessel clean 
 and bright. Triturate in the mortar again and turn the powder into a tall 
 4-oz. beaker, and add about 20 c.c. of hot water, and boil for two or three 
 minutes ; when cold add 15 c.c. of HC1, and stir with a glass rod, till 
 the solid matter, with the exception probably of a little silica in flakes,' 
 becomes dissolved. Both the iron and chromium will then be in the highest 
 state of oxidation Ee 2 O 3 and Cr' 2 O 3 . Pour the fluid into a white porcelain 
 dish of about 20-oz. capacity, and dilute with washings of the beaker to 
 about 3 oz. Immediately after, also, add cautiously 1 gm. of metallic iron 
 of known purity, or an equivalent quantity of double iron salt, previously 
 dissolved in dilute sulphuric acid, and further dilute with cold water to 
 about 5-oz., to make up the volume in the dish to about 8 oz., then titrate 
 with j permanganate the amount of. ferrous oxide remaining. The 
 difference between the amount of iron found and of the iron weighed will 
 be the amount oxidized to sesquioxide by the chromic acid. Every one part 
 so oxidized will represent 0'320 of Cr"or 0'4663 of sesquioxide, Cr 2 O 3 , in 
 which last condition the substance usually exists in the ore. 
 
 If the amount of iron only in the ore is to be determined, the process is 
 still shorter. After the fluxed mineral has been ignited and reduced to 
 powder, as already directed, dissolve it by adding first, 10 c.c. of hot water 
 and applying a gentle heat, and then 15 c.c. of HC1, continuing the heat to 
 incipient boiling till complete decomposition has been effected; cool by 
 immersing the tube in a bath of cold water, add pieces of pure metallic zinc 
 sufficient to bring the iron to the condition of protoxide and the chromium 
 to sesquioxide, and apply heat till small bubbles of hydrogen cease, and the 
 zinc has become quite dissolved; then nearly fill the tube with cold water, 
 acidulated with one-tenth of sulphuric acid, and pour the contents into the 
 porcelain dish, add cold water to make up the volume to about 8 oz., and 
 complete the operation with standard permanganate or bichromate. 
 
 Sell's Process. This method is described in J. C. S. 1879 
 (p. 292), and is carried out by first. fusing the finely ground ore 
 with a mixture of sodic bisulphate and fluoride in the proportion 
 of I mol. bisulphate, and 2 mol. fluoride, and subsequent titration 
 of the chromic acid by standard thiosulphate and iodine. 
 
 Prom O'l to 0'5 gm. of the ore is placed on the top of ten times its weight 
 of the above-mentioned mixture in a large platinum crucible, and ignited for 
 fifteen minutes ; an equal weight of sodic bisulphate is then added and well 
 incorporated by fusion, and stirring with a platinum wire; then a further 
 like quantity of bisulphate added in the same way. When complete 
 decomposition has occurred, the mass is boiled with water acidulated with 
 sulphuric acid, and the solution diluted to a definite volume according to the 
 quantity of ore originally taken. 
 
 To insure the oxidation of all the chromium and iron previous to titration, 
 a portion, or the whole, of the solution is heated to boiling, and permanganate 
 added until a permanent red colour occurs. Sodic carbonate is then added 
 in slight excess, and sufficient alcohol to destroy the excess of permanganate ; 
 
170 VOLUMETRIC ANALYSIS. 56. 
 
 the manganese precipitate is then filtered off, and the clear solution titrated 
 with T ^j- thiosulphate and iodine. 
 
 The author states that the analysis of an ore by this method 
 may be accomplished in one hour and a half. 
 
 For the oxidation of salts of chromium, the same authority 
 recommends boiling with potash or sodic carbonate (to which 
 a small quantity of hydrogen peroxide is added) for 1 5 minutes. 
 
 For the preliminary fusion and oxidation of chrome iron ore, 
 Dittmar recommends a mixture of two parts borax glass, and one 
 and a half part each of sodic and potassic carbonate. These are 
 fused together in a platinum crucible until all effervescence ceases, 
 then poured out into a large platinum basin or upon a clean iron 
 plate to cool, broken up, and preserved for use. 
 
 Ten parts of this mixture is used for one part of chrome ore, 
 and the fusion made in a platinum crucible, closed for the first five 
 minutes, then opened for about forty minutes, frequently stirring 
 with a platinum wire, and using a powerful Bunsen name. The 
 gas blowpipe hastens this method considerably. 
 
 The above described methods of treating the ores of chromium, 
 so as to obtain complete decomposition, are apparently now super- 
 seded to a great extent by the use of sodic peroxide, but the action 
 of this agent is so energetic upon platinum, gold, silver, nickel, or 
 porcelain that its use requires great care. Many well known 
 authorities on the analysis of chrome ores use a basic mixture 
 such as was first suggested by Clark, but modified by Stead, i.e., 
 magnesia or lime four parts, potassic and sodic carbonates of each 
 one part. Clark's original mixture of magnesia and caustic soda 
 acts on platinum, but Stead's mixture does not. 
 
 The fusion is made by mixing the very finely ground sample with ten 
 times its weight of the basic mixture in a platinum crucible, and heating to 
 bright redness at the back of a gas muffle for about an hour. When the 
 crucible is removed and cool the mass is found sintered together. It is 
 removed to a beaker, and the crucible washed out with water and dilute 
 sulphuric acid. The decomposition i. generally complete, but if any black 
 specks are found they must be separated by filtration, dried, and again fused 
 with some of the basic mixture ; finally the whole is mixed with excess of 
 ferrous salt, and the unoxidized iron titrated with bichromate as before 
 described. 
 
 Hi deal and Rosenblum (J. S. C. 1. xiv. 1017) give a series 
 of experiments on the estimation of chromium in ores, steels, etc., 
 and on the use of sodic peroxide, which latter they find has a 
 most destructive effect 011 all kinds of vessels in which the 
 decomposition is made nickel seems the best material if not 
 exposed to too high a temperature, but they found also that a good 
 deal of nickel was dissolved from the crucibles by the sulphuric 
 acid used to dissolve the melt, and they therefore attach great 
 importance to the filtration of the aqueous solution of the melt, se- 
 as to remove nickel and iron oxides, which otherwise interfere with 
 the titration by masking the colour of the indicator. 
 
56. CHROMIUM. 
 
 Ferroclirome, Ciirommm Steel, etc. S puller and Ivalman 
 (Chein. Zeit. xvii. 880 and 1207) describe a method which gives 
 good results, but is unfortunately tedious in working. 
 
 Process for Ferroclirome. 0'35 gm. of the finely-powdered sample first 
 sifted through linen and then rubbed down in an agate mortar, is mixed 
 with 4 gm. of sodium peroxide and 8 gm. of caustic soda, and heated in 
 a silver dish over a slightly smoky flame. The temperature is gradually 
 raised so that at the end of five minutes the edge of the mixture begins 
 to fuse, and after a further period of ten minutes the whole mass has 
 become liquid. The heating is continued for half an hour over the slightly 
 smoky flame until the bottom of the dish is covered with soot. During the 
 last quarter of an hour the melt is stirred with a silver spatula. The attack 
 of the ferro-chromium is then complete if the heating has been conducted 
 as described, and the sample has been powdered sufficiently fine. The basin 
 Avith its contents is allowed to cool to 40 50 C., freed from soot, and 
 digested, in a large hemispherical porcelain dish, with hot water. The dish 
 is then removed and rinsed into the basin. The loss in weight of a silver 
 dish Aveighing about 38 gm. may be as much as 0'04 0'05 gm. for a single 
 fusion. The aqueous extract of the melt contains sodium manganate and 
 ferrate as well as chromate. Only traces of sodium peroxide remain, as the 
 bulk is decomposed during solution. Sodium manganate and ferrate are 
 removed by the addition of successive small quantities of sodium peroxide, 
 which reduces these salts, itself undergoing simultaneous reduction. A 
 quantity of 0'3 0'6 gm. is usually requisite, and any excess that may be 
 added is got rid of either by allowing the solution to stand while being 
 kept warm for some hours, or preferably by passing CO 2 into the solution 
 for an hour and heating it for fifteen minutes on a water or sand bath. 
 By the latter treatment hydrogen peroxide is liberated from the sodium 
 peroxide, and being unstable in alkaline solution is decomposed on heating. 
 Sodium chromate is not affected by excess of the peroxide in alkaline 
 solution. Clark and E/ideal both find that mere boiling for ten minutes, 
 is sufficient to decompose the excess of peroxide. 
 
 The aqueous solution of the melt is made up to 500 c.c., the contents 
 of the flask allowed to stand and an aliquot portion (?.g. 100 c.c.) filtered 
 from ferric oxide, etc., and the chromium in it determined by a permanganate 
 solution of which 1 c.c. equals about O'OOS gm. of iron, and a solution of 
 ferrous ammonium sulphate containing 7 gm. of the salt in 500 c.c. The 
 chromium solution is diluted with 1 liter of cold Avater which has been 
 previously boiled and acidified with 20 c.c. of sulphuric acid (1 : 5 by volume); 
 100 c.c. of ferrous ammonium sulphate are added, and the mixture titrated 
 back with permanganate. The strength of the ferrous solution is determined 
 by a blank experiment under similar conditions. 
 
 Process for Chromium Steel : The material is dissolved in dilute sulphuric 
 acid, evaporated to dry ness and fused Avith caustic soda and sodium peroxide,, 
 as above described. The mass is digested with Avater, and after removal of 
 any alkaline manganate or ferrate with peroxide and decomposing excess of 
 the latter by CO 12 or by simple boiling,. the' solution is diluted to a definite 
 volume, and aliquot portions titrated as before mentioned. 
 
 Rideal and llosenbluni have obtained excellent results with 
 ferrochrome, by fusion with sodic peroxide alone. The manner of 
 procedure was as follows : 
 
 About 0'5 gm. of a very finely poAvdered ferrochrome was mixed with 
 3 gm. of sodic peroxide and heated very gently in a nickel crucible, until 
 
172 VOLUMETRIC ANALYSIS. 56. 
 
 the mass began to melt, and then to glow by itself. The heating was then 
 continued for ten minutes, and after the mass was partially cooled 1 gm. of 
 sodic peroxide was added and the heating continued for another five minutes. 
 
 The crucible, when still moderately warm, was placed in a suitable 
 porcelain basin, which was then half filled with hot water and covered with 
 a clock glass. The melt easily dissolved in the hot water, the solution 
 obtained being of a deep purple colour, due to sodic ferrate, which is 
 abundantly formed during the fusion. The solution also contained sodic 
 manganate, resulting from the oxidation of the manganese which is present 
 in ferrochrome. 
 
 To decompose both these salts a small quantity of sodic peroxide was 
 ndded, on which the solution immediately lost its purple colour. The 
 solution was then boiled for ten minutes to decompose the excess of sodic 
 peroxide and the insoluble residue of iron, nickel, and manganese oxide was 
 filtered off. An excess of sulphuric acid w r as then added to the solution and 
 after cooling it was titrated in the usual manner. 
 
 Galbraith's method, modified somewhat by Stead (Jour. Iron 
 and Steel Institute, 1893, 153), is considered the most rapid method 
 for the estimation of chromium in irons and steels. 
 
 The sample is dissolved in dilute sulphuric acid, filtered, the solution 
 diluted to about 300 c.c., and heated to boiling. Strong solution of potassic 
 permanganate is now" added until the red colour is permanent for ten 
 minutes, then 80 c.c. of 10 per cent, hydrochloric acid, and the liquid 
 heated until decolorized ; 150 c.c. of water are added, about 100 c.c. boiled 
 off to expel the chlorine; and the chromium is then titrated. The residue 
 insoluble in dilute sulphuric acid is mixed with 0'5 gm. of the basic mixture 
 previously mentioned, and heated to intense redness for half an hour ; the 
 chromium is afterwards titrated in hydrochloric acid solution with ferrous 
 sulphate and bichromate. 
 
 Another process consists in dissolving 2 gm. of the sample in hydrochloric 
 acid ; without filtering, the liquid is nearly neutralized with a 2 per cent, 
 solution of caustic soda, and after diluting to 300 c.c., 10 c.c. of a 5 per cent. 
 -solution of sodic phosphate and 30 gm. of sodic thiosulphate are added. After 
 boiling to expel the SO 2 , 20 c.c. of a saturated solution of sodic acetate 
 are added, and the boiling continued for five minutes ; the precipitated 
 chromium phosphate is then washed with a 2 per cent, solution of ammonium 
 nitrate, dried, calcined, and fused with the basic mixture. The melt, 
 dissolved in 30 c.c. of hydrochloric acid and 150 c.c. of water, is boiled 
 for ten minutes and titrated. The process may be used in presence of 
 vanadium. In this case, the chromium must be titrated by means of ferrous 
 sulphate and permanganate in presence of sulphuric acid. 
 
 E ideal and Rosenbl urn's experiments appear to show that 
 .sodic peroxide, if certain conditions be observed in its use, is 
 .a very valuable agent for the analysis of chrome ore, ferro- 
 chrome, and chrome steel, as it removes the two main defects 
 of former methods, viz., the necessity of repeated fusion to effect 
 complete decomposition and the inconvenient slowness of these 
 processes. The conditions which should be observed are sum- 
 marized by them as follows : 
 
 (1) Great care should be taken to reduce the chrome ore or the ferro- 
 chrome to an almost impalpable powder. This can be done without much 
 difficulty if the ore or the alloy be crushed in a steel mortar until a powder 
 is obtained which will pass through a linen bag. This powder is then 
 
57. COBALT. 
 
 ground in an agate mortar to the required degree of fineness, a little water 
 feeing added to facilitate the grinding. 
 
 (2) The water solution of the melt, before acidulation, must be freed, 
 from an excess of sodic peroxide. Whenever sodium ferrate or sodium 
 manganate is formed during the fusion it must be decomposed in the water 
 solution of the melt. 
 
 (3) As the result of the analysis depends to a large extent upon the 
 titration, and especially upon a clear perception of its final point, it is 
 important that the solution in which the chrome is to be determined should 
 be as free as possible from other metallic salts, as for instance, iron, 
 manganese, and nickel salts. We have also observed that the ferricyanide 
 solution which is used as an indicator is most satisfactory when it contains 
 no more than 1 per cent, of ferricyanide. 
 
 COBALT. 
 
 Co=59. 
 Estimation "by Mercuric Oxide and Permanganate (W inkier). 
 
 57. IF an aqueous solution of cobaltous chloride or sulphate be- 
 treated with moist finely divided mercuric oxide, no decomposition- 
 ensues, but on the addition of permanganate to the mixturej 
 hydrated cobaltic and manganic oxides are precipitated. It is 
 probable that no definite formula can be given for the reaction, 
 and therefore practically the working effect of the permanganate 
 is best established by a standard solution of c'obalt of known 
 strength, say metallic cobalt dissolved as chloride, or neutral 
 cobaltous sulphate. 
 
 Process : The solution, free from any great excess of acid, is placed in 
 a flask, diluted to about 200 c.c., and a tolerable quantity of moist mercuric 
 oxide (precipitated from the nitrate or perchloride by alkali and washed)' 
 added. Permanganate from a burette is then slow T ly added to the cold solution- 
 with constant shaking until the rose colour appears in the clear liquid above 
 the bulky brownish precipitate. 
 
 The appearance of the mixture is somewhat puzzling at the 
 beginning, but as more permanganate is added the precipitate 
 settles more freely, and the end as. it approaches is very easily 
 distinguished. The final ending is when the rose colour is 
 persistent for a minute or two; subsequent bleaching must not 
 be regarded. 
 
 The actual decomposition as between cobaltous sulphate and 
 permanganate may be formulated thus 
 
 GCoSO 4 + 5H 2 + 2MnK0 4 = K 2 S0 4 + 5H 2 S0 4 + 3Co 2 3 + 2Mn0 2 
 but as this exact decomposition cannot be depended upon in all the 
 mixtures occurring, it is not possible to accept systematic .numbers- 
 calculated from normal solutions. 
 
 Solutions containing manganese, phosphorus, arsenic, active 
 chlorine or oxygen compounds, or organic matter, cannot be used 
 in this estimation ; moderate quantities of nickel are of no 
 consequence. 
 
174 VOLTJMET1UC ANALYSIS. 57. 
 
 Norman McCulloch (C. N. lix. 51) has proved that cobaltic 
 oxide, as cobalticyanide, is a stable compound, and makes use of 
 this fact to establish a process which gives very good results, by 
 conversion of cobaltocyanide to the higher state of oxidation, the 
 estimation of the oxygen being the measure of the cobalt itself. 
 The method is exact in the presence of nickel, manganese, lead, 
 arsenic, zinc, antimony, uranium, etc., but not in that of iron or 
 copper. 
 
 The standard solutions required are the ordinary ~ potassic 
 bichromate, 1 c.c. of which represents O0059 gm. of Co, and an 
 acid solution of ammonio-ferrous sulphate, whose strength is known 
 by titration with the bichromate. There is also required a 5 per 
 cent, solution of pure potassic cyanide, and a solution of nickel 
 sulphate. 
 
 The apparatus required may be simply a 12-oz. flask, fitted with 
 two-hole stopper, one for a thistle funnel and the other as an 
 escape for vapour. The mouth of the funnel should be somewhat 
 constricted, and the lower end must dip beneath the surface of the 
 liquid in the flask. 
 
 Process : The standard bichromate and cyanide solutions are conveyed in 
 their proper quantities to the flask above described, a few drops of ammonia 
 added for subsequent neutralization of any free acid in solution to be tested, 
 and the whole diluted, if necessary, to a convenient bulk with Avater. 
 
 The amount of bichromate taken need not greatly exceed the theoretical 
 requirement for the greatest probable quantity of cobalt to be estimated, but, 
 with the cyanide, an allowance is made also for the conversion to soluble 
 double c} r anides of such other metals as may be present. 
 
 The cork and thistle-funnel are now placed in position, and the.solution 
 boiled to expel air from the flask. Tho hot solution to be tested, of con- 
 venient bulk and not too acid, and free, of course, from oxidizing or reducing 
 constituents, is now added, and the ensuing reaction is instantaneously 
 complete. 
 
 After this stage the continued use of the cork and thistle-funnel is 
 necessary only in presence of manganese. 
 
 The contents of the flask are now cautiously treated with excess of 
 a moderately warm concentrated solution of ammonic chloride, and the 
 ebullition sustained for about ten minutes longer to expel volatile cyanide 
 .(an operation conducted in a fume chamber or in a draught of air to carry 
 off poisonous fumes). 
 
 It now remains, preceding the estimation of non-reduced chromic acid 
 with ferrous salt, to throw down soluble cobaltocyanide and decompose 
 potassium-nickel cyanide by the addition of nickel sulphate. This is to 
 prevent the subsequent formation of ferrous cobaltocyanide and double 
 cyanide of iron and nickel respectively compounds difficultly soluble in 
 dilute acid and, consequently, low results. To effect the above precipitation, 
 a weight of nickel is required at least equal to that of the nickel and cobalt 
 'existing in the contents of the flask, but if such acids as arsenic and phosphoric 
 are present more is needed, as their precipitation is involved. Simply, the 
 solution of nickel is added until no further precipitate is formed, or until the 
 precipitate settles in a peculiar manner, to be known by experience ; great 
 -excess of nickel is thus avoided, which would tend to interfere with the 
 !erric3'anide reaction in the subsequent operation. 
 
 The contents of the flask are now poured into excess of a hot aqueous 
 
oS. COPPER. 175 
 
 solution of standard ferrous salt contained in a basin, acidified with a few 
 drops of hydrochloric acid, and titrated with bichromate in usual way. 
 
 The cobalt is calculated by multiplying the difference between the number 
 of c.c. of bichromate taken at the outset of the estimation and that found 
 at the completion, by 0*0059, and correcting- this by a slight allowance for 
 reducing action of the potassic cyanide and its impurities on the chromate. 
 In the author's case this correction was taken from experiment, and it was 
 deemed sufficiently near to accept the reducing action of the cyanide as 
 simp]}' proportionate to the quantity of this reagent used in the estimation, 
 although it is not altogether independent of the proportion and amount 
 of the bichromate, the degree of dilution, length of time of boiling, etc. 
 The result showed that 100 c.c. of the bichromate boiled for a few minutes 
 with its own bulk of the cyanide, and then for about ten minutes more with 
 addition of excess of ammonic chloride, lost in value to the extent of about 
 one c.c., which was deducted from the amount of bichromate reduced by the 
 cobaltocyanide in such estimations, using the above bulk of cyanide, a fifth 
 of this for 25 or 30 c.c., and so on. It is, of course, advisable, where the 
 highest accuracy is desired,. to determine the necessary correction by a blank 
 experiment, and duplicating also the approximate quantity of cobalt. 
 
 It is best to separate iron as well as copper, and in the case of a cobalt ore 
 the author would dissolve the sample in aqua-regia, and evaporate to dryness. 
 The nitric acid would then be destroyed by two or three evaporations to 
 dryness with hydrochloric acid, and the copper precipitated from the solution 
 of the residue by sulphuretted hydrogen. In the filtrate from sulphide 
 the iron would be separated by the acetate of soda method, and the iron 
 precipitate re-dissolved and re-precipitated in a similar way to separate any 
 small portion of cobalt. The combined filtrates from the acetate precipitates 
 would be evaporated to convenient bulk, and the excess of acid neutralized 
 by sodic hydrate or carbonate. The solution so obtained would then be added 
 to suitable amounts of bichromate and cyanide, as described above. 
 
 Examples : 0*114 gm. Co taken and 25*4 c.c. respectively of bichromate 
 and cyanide used. The volume of bichromate reduced, allowing for the 
 correction, was 19 2 c.c.=l*113 gm. Co. Again, 0*114 gm. Co and 0*228 gm. 
 Ni taken, 25 c.c. of bichromate and 50 c.c. of cyanide used, the volume of 
 the former reduced was 19'1 c.c.=0*112 gm. Co. Equally good results were 
 obtained with mixtures of manganese, lead, arsenic, etc. 
 
 COPPER. 
 
 Cu=63. 
 
 1 c.c. ~ soliitioii=0*0063 gm. Cu. 
 Iron x 1-125 =Cu. 
 
 Double Iron Salt x O1607=Cu. 
 
 1. Reduction by Grape Sugar and subsequent titration with Ferric 
 Chloride and Permanganate (Schwarz). 
 
 58. THIS process is based upon the fact that grape sugar 
 precipitates cuprous oxide from an alkaline solution of the metal 
 containing tartaric acid ; the oxide so obtained is collected and 
 mixed with ferric chloride and hydrochloric acid. The result is 
 the following decomposition : 
 
 Cu 2 + Fe 2 Cl 6 + 2HCl=:2CuCl 2 + 2FeCl 2 + H 2 0. 
 Each equivalent of copper reduces one equivalent of ferric to ferrous 
 
176 VOLUMETRIC ANALYSIS. 58. 
 
 chloride, which is estimated by permanganate with due precaution. 
 The iron so obtained is calculated into copper by the requisite factor. 
 
 Process : The weighed substance is brought into solution by nitric or 
 sulphuric acid or water, in a porcelain dish or glass flask, and most of the 
 acid in excess saturated with sodic carbonate ; neutral potassic tartrate is then 
 added in not too large quantity, and the precipitate so produced dissolved to 
 a clear blue liquid by adding caustic potash or soda in excess ; the vessel is 
 next heated cautiously to about. 50 C. in the water bath, and sufficient 
 grape sugar added to precipitate the copper present ; the heating is continued 
 until the precipitate is of a bright red colour, and the upper liquid is 
 brownish at the edges from the action of the alkali on the sugar : the heat 
 must never exceed 90 C. When the mixture has somewhat cleared, the 
 upper fluid is poured through a moistened filter, and afterwards the precipitate 
 brought on the same, and washed with hot water till thoroughly clean ; the 
 precipitate which may adhere to the dish or flask is well washed, and the 
 filter containing the bulk of the protoxide put with it, and an excess of 
 solution of ferric chloride (free from nitric acid or free chlorine) added, 
 together with a little sulphuric acid ; the whole is then warmed and stirred 
 until the cuprous chloride is all dissolved. It is then filtered into a good- 
 sized flask, the old and new filters being both well washed with hot water, to 
 which at first a little free sulphuric acid should be added, in order to be 
 certain of dissolving all the oxide in the folds of the paper. The entire 
 solution is then titrated with permanganate in the usual way. Bichromate 
 ma} 7 ' also be used, but the end of the reaction is not so distinct as usual, from 
 the turbidity produced by the presence of copper. 
 
 2. Reduction by Zinc and subsequent titration with Ferric Chloride 
 and Permang-anate (Fleitmann). 
 
 The metallic solution, free from nitric acid, bismuth, or lead, is 
 precipitated with clean sticks of pure zinc ; the copper collected, 
 washed, and dissolved in a mixture of ferric chloride and hydro- 
 chloric acid : a little sodic carbonate may be added to expel the 
 atmospheric air. The reaction is 
 
 Cu + Fe 2 Cl 6 =:CuCl 2 + 2FeCP. 
 
 When the copper is all dissolved, the solution is diluted and 
 titrated with permanganate; 56 Fe=31'5 Cu. 
 
 If the original solution contains nitric acid, bismuth, or lead, 
 the decomposition by zinc must take place in an ammoniacal 
 solution, from which the precipitates of either of the above metals 
 have been removed by filtration ; the zinc must in this case be 
 finely divided and the mixture warmed. The copper is all 
 precipitated when the colour of the solution has disappeared. It 
 is washed first with hot water, then with weak HC1 and water to 
 remove the zinc, again with water, and then dissolved in the acid, 
 and ferric chloride as before. 
 
 3. Estimation as Cuprous Iodide (E. O. Brown). 
 
 This excellent method is based on the fact that when potassic 
 iodide is mixed with a salt of copper in acid solution, cuprous 
 iodide is precipitated as a dirty white powder, and iodine set free.. 
 
58. COPPER. 
 
 If the latter is then immediately titrated with thiosulphate and 
 starch, the corresponding quantity of copper is found. 
 
 The solution of the metal, if it contain nitric acid, is evaporated 
 with sulphuric acid till the former is expelled, or the nitric acid is 
 neutralized with sodic carhonate, and acetic acid added ; the 
 sulphate solution must be neutral, or only faintly acid ; excess of 
 acetic acid is of no consequence, and therefore it is always 
 necessary to get rid of all free mineral acids and work only Avith 
 free acetic acid. 
 
 J. W. Westmoreland (/. S. C. I. v. 51), who has had very large 
 experience in examining a variety of copper products, strongly 
 recommends this process for the estimation of copper in its various 
 ores, etc. The metal may very conveniently be separated from a hot 
 sulphuric acid solution by sodic thiosulphate : this gives a flocculent 
 precipitate of subsulphide mixed with sulphur, which filters readily, 
 and can be washed with hot water. Arsenic and antimony, if 
 present, are also precipitated ; tin, zinc, iron, nickel, cobalt, and 
 manganese are not precipitated. On igniting the precipitate most 
 of the arsenic and the excess of sulphur is expelled, an impure 
 subsulphide of copper being left. Sulphuretted hydrogen may of 
 course be used instead of the thiosulphate, but its use is objection- 
 able to many operators, beside which, under some circumstances, 
 a small amount of copper remains in the solution, and moreover 
 iron in small quantity is also precipitated with the copper, and 
 cannot be entirely removed by washing. If HAS is used it should 
 be passed for some time, and the precipitate allowed to stand a few 
 hours to settle after nitration and washing the CuS should be 
 redissolved in HXO 3 and reprecipitated with -the gas, it is then quite 
 free from iron. 
 
 Standardizing- the Thiosulphate Solution. This may be done on 
 pure electrotype copper, but this is not always pure, and the safest 
 standard is high conductivity wire, dissolved first in nitric acid, 
 boiling to expel nitrous fumes, diluting, neutralizing with sodic 
 carbonate till a precipitate occurs, then adding acetic acid till clear. 
 The liquid is then made up to a definite volume, and a quantity 
 equal to about 0'5 gm. Cu taken in a flask or beaker, about ten 
 times the copper weight of potassic iodide added, and when 
 dissolved the thiosulphate is run in from a burette until the free 
 iodine is nearly removed, add then some starch, and finish the 
 titration in the usual way. The thiosulphate will of course need 
 to be checked occasionally. 
 
 If strictly - thiosulphate is used, each c.c. =0*0063 gm. Cu. 
 
 Process : For estimating the copper in iron pyrites or burnt ore 5 gm. of 
 the substance should be taken, 2 gm. for 30 40 / mattes or 1 gin. for 
 60 /'o mattes, and with precipitates it is best to dissolve say 5 gm. and dilute 
 to a definite volume, and take as much as would represent from 0'5 to 07 gm. 
 of Cu for titration. The solution is made with nitric acid, to which hydrochloric 
 is also added later on, and then evaporated to dryness with excess of sulphuric 
 
 N 
 
178 VOLUMETRIC ANALYSIS. 58. 
 
 acid to convert the bases into sulphates ; the residue is treated with warm 
 water and any insoluble PbSO 4 , c., filtered off. The filtrate is heated to 
 boiling and precipitated with sodic thiosulphate, this precipitate is filtered 
 off, washed with hot water, dried, and roasted, the resulting copper oxide is 
 then dissolved in nitric acid, and after the excess of acid is chiefly removed 
 by evaporation sodic carbonate is added, so as to precipitate part of the 
 copper and ensure freedom from mineral acid, acetic acid is added till 
 a clear solution is obtained ; about ten parts of potassic iodide to one of 
 copper, supposed to be present, are then added, and the titration carried out in 
 the usual way. 
 
 A modification of this process is adopted in tlie United States 
 (Peters, Eng. and Min. Journ. lix. 124) as follows : 
 
 In the treatment of ores 1 gin. is heated with hot, strong nitric acid, to 
 which is then added strong hydrochloric acid. After boiling, strong- 
 sulphuric acid is added, and the volatile acids evaporated off. After 
 diluting, the PbSO 4 , &c., is filtered off, and the solution, which should not 
 exceed 75 c.c., is run into a beaker, at the bottom of which is a strip of 
 aluminium 3 in. long, 1^ in. wide, and turned up at the ends so that the 
 body of the strip can lie flat. The copper is all precipitated after boiling for 
 six or seven minutes. The liquid is filtered off, and the loose and adherent 
 copper is all dissolved in a little nitric acid. To this is added half a gram 
 of chlorate of potash, to fulty oxidize any arsenic present, and the solution 
 boiled down to small bulk, but not sufficiently low to produce a basic salt 
 of copper. The solution is then neutralized with ammonia, acidified with 
 acetic acid, and titrated in the usual manner. 
 
 This treatment removes all interfering impurities or renders them inert. 
 Zinc is not such a good precipitant for the copper as aluminium, as some 
 iron is also carried down even from strongly acid solutions. When aluminium 
 is used, the precipitation may be effected without boiling by adding a little 
 hydrochloric acid to the solution, but this is not so desirable as the method 
 described. For the success of the titration it is essential that no free nitric 
 acid or nitrate of copper be present. Cold ammonia in excess does not, 
 apparently, entirely decompose the latter, hence the necessity for boiling. 
 Care must be taken that the aluminium contains no copper, or if it does 
 its quantity must be known. 
 
 By either of the above methods there is no interference from 
 arsenic or bismuth, so long as no free mineral acid is present. 
 
 4. Estimation by Potassic Cyanide (P ; 'arkes and C. Itlohr). 
 
 This well-known and much-used, process for estimating copper 
 depends upon the decoloration of an ammoniacal solution of copper 
 by potassic cyanide. The reaction (which is not absolutely uniform 
 with variable quantities of ammonia) is such that a double cyanide 
 of copper and ammonia is formed; cyanogen is also liberated, which 
 reacts on the free ammonia, producing urea, oxalate of urea, 
 ammonic cyanide and formate (Liebig). Owing to the influence 
 exercised by variable quantities of ammonia, or its neutral salts, 
 upon the decoloration of a copper solution by the cyanide, it has 
 been suggested by Beringer to substitute some other alkali for 
 neutralizing the free acid in the copper solution other than 
 ammonia. The suggestion has been adopted by Da vies (C. N. 
 Iviii. 131) and by Eessenden (C. N. Ixi. 131), who both 
 
COPPER. ] 79 
 
 recommend sodic carbonate. My own experiments completely 
 confirm their statement that none of the irregularity common to 
 variable quantities of ammonia or its salts occurs with soda or 
 potash. Suppose for example that copper has been separated as 
 sulphide, and brought into solution by nitric acid, the free nitro- 
 sulphuric acid is neutralized with JX r a 2 C0 3 , and an excess of it 
 added to redissolve tlie precipitate. The cyanide solution is then 
 cautiously ran into the light blue solution until the colour is just 
 discharged. My own experience is, that it is impossible to 
 redissolve the whole of the precipitate without using a very large 
 excess of soda ; but there is no need to add such an excess, as 
 the precipitate easily dissolves when the cyanide is added. 
 I have used a modification of this method, which gives excellent 
 results, viz., to neutralize the acid copper solution either with 
 Na' 2 CO :J or NaHO, add a trifling excess, and then 1 c.c. of 
 ammonia 0'960 sp. gr. ; a deep b^ue clear solution is at once given, 
 which permits of very sharp end-reaction with the cyanide. 
 
 J. J. and C. Beringer (C. N. xlix. iii.) have already adopted 
 the method of neutralizing the acid copper solution with soda, 
 then adding ammonia, but the proportion they recommend is larger 
 than necessary. 
 
 In standardizing the cyanide, it is advisable to arrange so that 
 copper is precipitated with soda exactly as in the titration of 
 a copper ore ; that is to say, free nitric or mtro-sulphuric acid 
 should be added, then neutralized with slight excess of soda, 
 cleared with 1 c.c. of ammonia, then titrated with cyanide. Large 
 quantities of nitrate or sulphate of soda or potash, however, make 
 very little difference in the quantity of cyanide used. 
 
 It lias generally feeen thought that where copper and iron occur together, 
 it is necessary to separate the latter before using the cyanide. P. Field, 
 however, has stated that this is not necessary (C. N. i. 25) ; and I can fully 
 eadorse his statement that the presence of the suspended ferric oxide is no 
 hindrance to the estimation of the copper ; in fact, it is rather an advantage, 
 as it acts as an indicator to the end of the process. 
 
 While the copper is in excess, the oxide possesses a purplish-brown colour, 
 but as this excess lessens, the colour becomes gradually lighter, until it is 
 orange brown. If it be now allowed to settle, which it does very rapidly, the 
 clear liquid above will be found nearly colourless. A little practice is of 
 course necessary to enable the operator to hit the exact point. 
 
 It is. impossible to separate the ferric oxide by filtration without 
 leaving some copper in it, and no amount of washing will remove 
 it. For example, 10 c.c. of a copper solution with 10 c.c. of ferric 
 solution were directly titrated with cyanide after treatment with 
 ]N r aHO in slight excess and 1 c.c. of ammonia: The cyanide 
 required was 12 c.c. Another 10 c.c. of the same copper and iron 
 solutions were then precipitated with soda and ammonia in same 
 proportions. This gave a complete solution of the copper with the 
 ferric oxide suspended in it. The solution was filtered and the 
 ferric oxide well washed with hot water, then the filtrate cooled and 
 
 N 2 
 
180 VOLUMETRIC ANALYSIS. 58. 
 
 titrated with cyanide, 9*5 c.c. only being required. On treating the 
 ferric oxide on the filter with nitric acid, neutralizing with XaHO 
 and NH 8 in proper proportions exactly, 2 '5 c.c. of cyanide were 
 required, showing that the ferric oxide had retained 20 per cent, 
 of the copper. 
 
 I strongly recommend that operators who have to deal with 
 copper determination upon samples containing much iron, should 
 practise the use of the cyanide method in the presence of the iron, 
 and accustom their eyes to the exact colour which the ferric oxide 
 takes when the titration is finished, always, however, with this 
 proviso, that the cyanide solution is standardized upon a known 
 weight of copper in the presence of a moderate amount of iron. 
 
 The solution of potassic cyanide should he titrated afresh at 
 intervals of a few days. Further details of this process are given 
 in 58.8. 
 
 Dulin (Jour. Amer. Cliem. Soc.^vii. 346) advocates the cyanide 
 process for copper ores as follows : 
 
 Process : The ore is treated in the way described in 58.3 to obtain a solution 
 of the copper practically free from silver and lead. The copper is then pre- 
 cipitated upon aluminium foil as there mentioned. Should cadmium be 
 present it is also precipitated to some extent, but only after the copper 
 is thrown down. If care be taken to stop the boiling immediately after 
 the copper is precipitated, which a practised eye will readily detect, the 
 amount of cadmium precipitated is so small as to cause no sensible error. 
 The liquid being decanted from the copper and foil, the latter are washed 
 well with hot water, taking care to lose no metal ; when quite clean, dilute 
 nitric acid is added and boiled till the copper is dissolved, the liquid then 
 neutralized with excess of ammonia, and titrated with cyanide in the 
 usual way. 
 
 5. Estimation as Sulphide (Pelouze). 
 
 It is first necessary to have a solution of pure copper of known 
 strength, which is best made by dissolving 39*523 gm. of pure 
 cupric sulphate in 1 liter of water ; each c.c. will contain 
 0-01 gm. Cu. 
 
 Precipitation in Alkaline Solution. This process is based on the 
 fact that if an ammoniacal solution of copper is heated to from 
 40 to 80 C., and a solution of sodic sulphide added, the whole 
 of the copper is precipitated as oxysulphide, leaving the liquid 
 colourless. The loss of colour indicates, therefore, the end of the 
 process, and this is its weak point. Special practice, however, will 
 enable the operator to hit the exact point closely. 
 
 Example : A measured quantity (say 50 c.c.) of standard solution of copper 
 is freely supersaturated with ammonia, and heated till it begins to boil. 
 The temperature will not be higher than 80 C. in consequence of the 
 presence of the ammonia ; it is always well, however, to use a thermometer. 
 The sodic sulphide is delivered cautiously from a Molar's burette, until the 
 last traces of blue colour have disappeared from the clear liquid above the 
 precipitate. The experiment is repeated, and if the same result is obtained, 
 the number of c.c. required to precipitate the amount of copper contained 
 
58. COPPER. 181 
 
 in 50 c.c. 0'5 gin., is marked upon the alkaline sulphide bottle. As the 
 strength of the solution gradually deteriorates, it must be titrated afresh every 
 day or two. Special regard must be had to the temperature of the precipi- 
 tation, otherwise the accuracy of the process is seriously interfered with. 
 
 Casamajor (0. N. xlv. 167) uses instead of ammonia the alkaline 
 tartrate solution same as for Fehling, adding a slight excess so as 
 to make a clear blue solution. The addition of the sulphide gives 
 an intense black brown precipitate, which is stirred vigorously till 
 clear. The copper sulphide agglomerates into curds, and the 
 reagent is added until no further action occurs with a drop of 
 the sodic sulphide. This modification can also be used for lead. 
 PbSO 4 is easily soluble in the tartrate solution, and can be estimated 
 by the sodic sulphide in the same way as copper. 
 
 The colour of the solution is not regarded, but the clotty 
 precipitate of sulphide, which is easily cleared by vigorous stirring. 
 Very good results may be gained by this modification. 
 
 Copper can also be first separated by glucose, or as thiocyanate 
 (Rivot), then dissolved in HXO 3 , and treated with the tartrate. 
 
 Precipitation in Acid Solution. The copper solution is placed 
 in a tall stoppered flask of tolerable size (400 or 500 c.c.), freely 
 acidified with hydrochloric acid, then diluted with about 200 c.c. 
 of hot water. 
 
 The alkaline sulphide is then delivered in from a burette, 
 the stopper replaced, and the mixture well shaken ; the precipitate 
 of copper sulphide settles readily, leaving the supernatant liquid 
 clear ; fresh sulphide solution is then at intervals added until no 
 more precipitate occurs. The calculation is the same as in the case 
 of alkaline precipitation, but the copper is precipitated as pure 
 sulphide instead of oxysulphide. 
 
 6. Estimation by Staniious Chloride (Weil). 
 
 This process is based on the fact, that a solution of a cupric salt 
 in large excess of hydrochloric acid at a boiling heat shows, even 
 when the smallest trace is present, a greenish-yellow colour. If to 
 such a solution stannous chloride is added in minute excess, a 
 colourless cuprous chloride is produced, and the loss of colour 
 indicates the end of the process. 
 
 2CuCl 2 + SnCl 2 ==Cu 2 Cl 2 + SnCl 4 . 
 
 The change is easily distinguishable to the eye, but should any 
 doubt exist as to whether stannous chloride is in excess, a small 
 portion of the solution may be tested with mercuric chloride. Any 
 precipitate of calomel indicates the presence of stannous chloride. 
 
 The tin solution is prepared as described in 37.2. 
 
 A standard copper solution is made by dissolving pure cupric 
 sulphate in distilled water, in the proportion of 39 '523 gm. per 
 liter=10 gm, of Cu. 
 
182 VOLUMETRIC ANALYSIS. 58. 
 
 Process for Copper alone. 10 c.c. of the copper solution O'l gm. of 
 Cu are put into a Avhite-glass flask, 25 c.c. of pure strong hydrochloric acid 
 added, placed on a sand-bath and brought to boiling heat ; the tin solution is 
 then quickly delivered in from a burette until the colour is nearly destroyed, 
 finally a drop at a time till the liquid is as colourless as distilled water. No 
 oxidation will take place during the boiling, owing to the flask being filled 
 with acid vapours. 
 
 A sample of copper ore is prepared in the usual way by treatment Avith 
 nitric acid, which is afterwards removed by evaporating with sulphuric acid. 
 Silica, lead, tin, silver, or arsenic, are of no consequence, as when the solution 
 is diluted with water to a definite volume, the precipitates of these substances 
 settle to the bottom of the measuring flask, and the clear liquid may 
 be taken out for titration. In case antimonic acid is present it will be 
 reduced with the copper, but on exposing the liquid for a night in an open 
 basin, the copper will be completely re-oxidized but not the antimony ; 
 a second titration will then show the amount of copper. 
 
 Process for Ores containing 1 Copper and Iron. In the case of copper 
 ores where iron is also present, the quantity of tin solution required will of 
 course represent both the iron and the copper. In this case a second titration 
 of the original solution is made with zinc and permanganate, and the quantity 
 so found is deducted from the total quantity; the amount of tin solution 
 corresponding to copper is thus found. 
 
 Example : A solution was prepared from 10 gm. of ore and diluted to 
 250 c.c. : 10 c.c. required 26'75 c.c. of tin solution whose strength was 
 16'2 c.c. for O'l gm. of Cu. 
 
 10 c.c. of ore solution were diluted, warmed, zinc and platinum added till 
 reduction Avas complete, and the solution titrated with permanganate Avhose 
 quantity=0-0809 gm.-of Fe. 
 
 The relative strength of the tin solution to iron is 18'34 c.c.=0'l gm. 
 of Fe : thus : 
 
 63 : 56 =0-1 : 0'0888. 
 
 therefore O'l gm. of Cu=0'0888 gm. of Fe=16'2 c.c. of SnCP 
 whence 0'0888 : 0'1=16'2 :" 18'34 
 thus 0*0809 Fe (found above)=14'837 c.c. of SnCl 2 
 O'l : 0809=18-34 : 14'837 hence 
 
 Iron and copper = 26'750 c.c. SnCl 2 
 
 Subtract for iron = 14'837 
 
 Leaving for copper 1T913 
 
 10 c.c. of ore solution therefore contained 16'2 : O'l : : 11-913=0'0735 gm. 
 of Cu, and as 10 gm. of ore=250 c.c. contained T837 gm. of Cu=18'37 per 
 cent. Aiiatysis by weight as a control gave 18'34 per cent. Cu. 
 Fe voluinetrically 20'25 per cent., by Aveight 20' iO per cent. 
 
 The method is specially adapted for the technical analysis of 
 fahl-ores. 
 
 Process for Ores containing Nickel or Cobalt. The ore is dissolved 
 in nitric or nitre-hydrochloric acid, then nearly neutralized with sodic 
 carbonate, diluted Avith cold water, and freshly precipitated baric carbonate 
 and some ammouic chloride added ; the whole is Avell mixed together, 
 producing a precipitate containing all the copper and iron, AAiiile the nickel 
 or cobalt remains in solution ; the precipitate is first washed by decantation, 
 collected on a filter, well washed, then dissolved in hydrochloric add, and 
 titrated with stannous chloride as before described. 
 
COPPEK. 183 
 
 Method for Copper, Iron, and Antimony. The necessary solutions 
 arc: (I) Standard copper. 19'667 gm. of copper sulphate are dissolved 
 in water to 500 c.c. (2) A similar solution containing 7'867 gin. of copper 
 sulphate. (3) Standard tin solution. 4'5 to 5 gm. of stannous chloride, 
 and 230 gm. of HC1, are made up to 500 c.c. with water. This solution is 
 standardized with No. 1, 10 c.c. of which solution should be mixed with 
 25 c.c. hydrochloric acid, boiled, and the tin solution to be standardized run 
 in until the green colour disappears. 
 
 Estimation of Copper. 5 gm. of substance are dissolved in HC1 or 
 IT 2 S0 4 , and made up to 250 c.c. 10 c.c. of this solution are taken, 25 c.c. 
 HC1 added, and then titrated as above. 
 
 Estimation of Iron. When there are 2 vols. of free HCl to 1 vol. of 
 the ferric solution no indicator is necessary, and the standard tin solution is 
 run in until the iron solution is colourless ; in this way the quantity of iron 
 is obtained in terms of copper. Of solutions containing 2 gm. of the sample 
 in 250 c.c., 10 c.c. are evaporated in a porcelain capsule, with 10 c.c. of the 
 copper solution (No. 2) ; to the concentrated mixed solution large excess 
 (about 75 c.c.) of HC1 is added, and this is titrated with the tin solution as 
 before. Of course the tin required for the copper used must be deducted. 
 The copper is used as an indicator, and is not required with substances 
 containing more than 2 per cent, of iron. 
 
 Estimation of Iron and. Copper. 5 gm. of ore in 250 c.c. Titrate as 
 before directed. In another 10 c.c. of solution, precipitate the copper with 
 zinc, filter, reconvert the ferrous into ferric salt by means of permanganate, 
 and titrate the iron again. 
 
 Estimation of Antimony. In making up the 250 c.c. in this case, it is 
 necessary to use aqueous solution of tartaric acid to prevent precipitation of 
 antimony. The solution of antimonic chloride is mixed with No. 1 copper 
 solution and a large excess of HCl, then titrated; the c.c. of standard tin 
 solution used indicates the sum of the Cu and Sb. If the mixed solution of 
 cuprous and antimonious chloride is allowed to remain some hours the Cu 
 becomes re-oxidized, but the Sb does not, therefore a second titration gives 
 the quantity of Cu only; this is scarcely required when the strength and 
 volume of copper solution added is known. 
 
 Antimony, Copper, and Iron, when together in same sample, are thus 
 determined. 5 gm. substance are dissolved in nitric acid, evaporated down, 
 and filtered. The filtrate contains iron and copper, which are determined as 
 above directed. The precipitate contains all the antimony ; it is dissolved in 
 HCl, treated with permanganate, and the antimonic chloride determined as 
 directed. 
 
 This process depends on the reducing action of stannous chloride. It is 
 therefore necessary to get rid of extraneous oxidizing influences, such as 
 free chlorine, nitric acid, or excess of permanganate, etc., before titration ; 
 this is effected by evaporating to dryness, taking up with hydrochloric acid, 
 and repeating, until the solution or vapour evolved on boiling ceases to turn 
 iodized starch-paper blue. 
 
 All the above described Weil methods must only be taken as 
 approximately accurate, but sufficiently so for technical use. 
 
 7. Volhard's method. 
 
 The necessary standard solutions are described in 43, Each c.c, 
 of ~Q thiocyanate represents 0*0063 gm. Cu, 
 
184 VOLUMETRIC ANALYSIS. 58. 
 
 Process : The copper in sulphuric or nitric acid solution is evaporated to 
 remove excess of acid, or if the acid is small in quantity neutralized with 
 sodic carbonate, washed into a 300 c.c. flask, and enough aqueous solution of 
 SO 2 added to dissolve the traces of basic carbonate and leave a distinct smell 
 of SO 2 . Heat to boiling, and run in from a burette the thiocyanate until the 
 addition produces no change of colour, add 3 or 4 c.c., and note the entire 
 quantit} 7 ", allow to cool, fill to mark, and shake well. 100 c.c. are then filtered 
 through a dry filter, 10 c.c. of ferric indicator with some nitric acid added, 
 then titrated with T ^ silver till colourless : then again thiocyanate till the 
 reddish colour occurs. The volume of silver solution, less the final correction 
 with thiocyanate, deducted from the original thiocyanate, will give the 
 volume of the latter required to precipitate the copper" 
 
 The process is not accurate in presence of Fe, Ag, Hg, Cl, I or Br. 
 
 8. Technical Examination of Copper Ores (Steinbeck's 
 Process): 
 
 In 1867 the Directors of the Mansfield Copper Mines offered 
 a premium for the best method of examining these ores, the chief 
 conditions being tolerable accuracy, simplicity of working, and the 
 possibility of one operator making at least eighteen assays in the day. 
 
 The fortunate competitor was Dr. Steinbeck, whose process 
 satisfied completely the requirements. The whole report is con- 
 tained in Z. a. C. viii. 1, and is also translated in C. JV. xix. 181. 
 The following is a condensed ri'sunu'. of the process, the final 
 titration of the copper being accomplished by potassic cyanide as 
 in 58.4. A very convenient arrangement for filling the burette 
 with standard solution where a series of analyses has to be made, 
 and the burette continually emptied, is shown in fig. 40 ; it may 
 be refilled by simply blowing upon the surface of the liquid. 
 
 (a) The extraction of the Copper from the Ore. 5 gm. of pulverized 
 ore are put into a flask with from 40 to 50 c.c. of hydrochloric acid (specific 
 gravity 1*16), whereb} r all carbonates are converted into chlorides, while 
 carbonic acid is expelled. After a while there is added to the fluid in 
 the flask 6 c.c. of a special nitric acid, prepared by mixing equal bulks of 
 water and pure nitric acid of 1'2 sp. gr. As regards certain ores, however, 
 specially met with in the district of Mansfield, some, having a very high 
 percentage of sulphur and bitumen, have to be roasted previous to being 
 subjected to this process; and others, again, require only 1 c.c. of nitric acid 
 instead of 6. The flask containing the assay is digested on a sand-bath for 
 half an hour, and the contents boiled for about fifteen minutes; after which 
 the whole of the copper occurring in the ore, and all other metals, are in 
 solution as chlorides. The blackish residue, consisting of sand and schist, 
 has been proved by numerous experiments to be either entirely free from 
 copper, or to contain at the most only O'Ol to 0'03 per cent. 
 
 (b) Separation of the Copper. The solution of metallic and earthy 
 chlorides, and some free HC1, obtained as just described, is separated by 
 filtration from the insoluble residue, and the fluid run into a covered beaker 
 of about 400 c.c. capacity. In this beaker a rod of metallic zinc, weighing 
 about 50 gm., has been previously placed, fastened to a piece of stout 
 platinum foil. The zinc to be used for this purpose should be as much as 
 possible free from lead, and at any rate should not contain more than from 
 O'l to 0'3 per cent, of the latter metal. The precipitation of the copper in 
 

 
 COPPER. 
 
 185 
 
 the metallic state sets in already during the nitration of the warm and 
 concentrated fluid, and is, owing especially also to the entire absence of 
 nitric acid, completely finished in from half to three-quarters of an hour after 
 the beginning of the filtration. If the fluid be tested with SH 2 , no trace 
 of copper can or should be detected; the spongy metal partly covers the 
 platinum foil, partly floats about in the liquid, and in case either the ore 
 itself or the zinc applied in the experiment contained lead, small quantities 
 of that metal will accompany the precipitated copper. After the excess of 
 zinc (for an excess must always be employed) has been removed, the metal is 
 repeatedly and carefully washed by decantation with fresh water, and care 
 taken to collect together every particle of the spongy mass. 
 
 Pig. 40. 
 
 (c) Estimation of the precipitated Copper. To the spongy metallic- 
 mass in the beaker glass, wherein the platinum foil is left, since some of the 
 metal adheres to it, 8 c.c. of the special nitric acid are added, and the copper 
 dissolved by the aid of moderate heat in the form of cupric nitrate, which,, 
 in the event of any small quantity of lead being present, will of course be 
 contaminated with lead. 
 
 "VYhen copper ores are dealt with containing above 6 per cent, of copper, 
 which may be approximately estimated from the bulk of the spongy mass off 
 
186 VOLUMETRIC ANALYSIS. 58. 
 
 precipitated metal, 16 c.c. of nitric acid, instead of 8, are applied for 
 dissolving the metal. The solution thus obtained is left to cool, and next 
 mixed, immediately before titration with potassic cyanide, with ]() c.c. of 
 special solution of liquid ammonia, prepared by diluting 1 volume of liquid 
 ammonia (sp. gr. 0'93) with 2 volumes of distilled water. 
 
 The titration with cyanide is conducted as described in 58.4. 
 
 In the case of such ores as } r ield over 6 per cent, of copper, and when a 
 double quantity of nitric acid has consequent!}' been used, the solution i.? 
 diluted with water, and made to occupy a bulk of .100 c.c.; this bulk is then 
 exactly divided into two portions of 50 c.c. each, and each of these separately 
 mixed with 10 c.c. of ammonia, and the copper therein volumetrically 
 determined. The deep blue coloured solution only contains, in addition to 
 the copper compound, ammouic nitrate ; any lead which might have been 
 dissolved having been precipitated as hydrated oxide, which does not interfere 
 with the titration with cyanide. The solution of the last-named salt is so 
 arranged, that 1 c.c. thereof exactly indicates 0'005 gin. of copper (about 
 21 gm. of the pure salt per liter). Since, for every assay, 5 gin. of ore have 
 been taken, 1 c.c. of the titration fluid is equal to 0*1 per cent, of copper, 
 it hence follows that, by multiplying the number of c.c. of cyanide solution 
 used to make the blue colour of the copper solution disappear by O'l, the 
 percentage of copper contained in the ore is immediately ascertained. 
 
 Steinbeck tested tins method specially, in order to see what 
 influence is exercised thereupon by (1) ammonic nitrate, (2) caustic 
 ammonia, (3) lead. The copper used for the experiments for this 
 purpose was pure metal, obtained by galvanic action, and was 
 ignited to destroy any organic matter which might accidentally 
 adhere to it, and next cleaned by placing it in dilute nitric acid. 
 5 gm. of this metal were placed in a liter flask, and dissolved in 
 266*6 c.c. of special nitric acid, the flask gently heated, and, after 
 cooling, the contents diluted with water, and thus brought to a 
 bulk of 1000 c.c. 30 c.c. of this solution were always applied to 
 titrate one and the same solution of cyanide under all circumstances. 
 When 5 gm. of ore, containing on an average 3 per cent, of copper, 
 are taken for assay, that quantity of copper is exactly equal to 
 0*150 gm. of the chemically pure copper. The quantity of nitric 
 acid taken to dissolve 5 gm. of pure copper (266*6 c.c.) was 
 purposely taken, so as to correspond with the quantity of 8 c.c. of 
 special nitric acid which is applied in^ the assay of the copper 
 obtained from the ore, and this quantity of acid is exactly met 
 Avith in 30 c.c. of the solution of pure copper. 
 
 The influence of double quantities of ammonic nitrate and free 
 caustic ammonia (the quantity of copper remaining the same) is 
 shown as follows : 
 
 (a) 30 c.c. of the normal solution of copper, containing exactlj' O'lSO gm. 
 of copper, were rendered alkaline with 10 c.c. of special ammonia, and were 
 found to require, for entire decoloration, 29'8 c.c. of cyanide. A second 
 experiment, again with 30 c.c. of copper solution, and otherwise under 
 identically the same conditions, required 29 9 c.c. of cyanide. The average 
 is 29'85 c.c. 
 
 (6) When to 30 c.c. of the copper solution, first 8 c.c. of special nitric 
 acid are added, and then 20 c.c. of special ammonia instead of only 8, whereby 
 
COPPER. 187 
 
 the quantity of free ammonia and of amraonic nitrate is double what it was 
 in the case of , there is required of the same cyanide 30*0 c.c. to produce 
 decoloration. A repetition of. the experiment,' exactly under the same 
 conditions, gave 30'4 c.c. of the cyanide ; the average is, therefore, 30'35 c.c. 
 The difference amounts to only 0'05 per cent, of copper, which may be 
 allowed for in the final calculation. 
 
 When, however, larger quantities of ammoniacal salts are present 
 in the fluid to be assayed for copper, by means of cyanide, and 
 especially when ammonic carbonate, sulphate, and worse still, 
 chloride are simultaneously present, these salts exert a very dis- 
 turbing influence.* The presence of lead in the copper solution 
 to be assayed has the effect of producing, on the addition of 10 c.c. 
 of normal ammonia, a milkiness with the blue tint ; but this does 
 not at all interfere with the estimation of the copper by means 
 of the cyanide, provided the lead be not in great excess ; and a 
 slight milkiness of the solution even promotes the visibility of the 
 approaching end of the operation. 
 
 Steinbeck purposely made some experiments to test this point, 
 and his results show that a moderate quantity of lead has no 
 influence. 
 
 Experiments were also carefully made to ascertain the influence 
 of zinc, the result of which showed that up to 5 per cent, of the 
 copper present, the zinc had no disturbing action; but a considerable 
 variation occurred as the percentage increased above that proportion. 
 Care must therefore always be taken in washing the spongy copper 
 precipitated from the ore solution by means of zinc. 
 
 The titration must always take place at ordinary temperatures, 
 since heating the ammoniacal solution while under titration to 40 
 or 45 C. considerably reduces the quantity of cyanide required. 
 
 9. Estimation of Copper by Colour Titration. 
 
 This method can be adopted with very accurate results, as in the 
 case of iron, and is available for slags, poor cupreous pyrites, 
 waters, etc. (see Carnelly, C. N. xxxii. 308). 
 
 The reagent used is the same as in the case of iron, viz., potassic 
 ferrocyanide, which gives, a purple-brown colour with very dilute 
 solutions of copper. This reaction, however, is not so delicate as 
 it is with iron, for 1 part of the latter in 13,000,000 parts of water 
 can be detected by means of potassic ferrocyanide ; while 1 part 
 of copper in a neutral solution, containing ammonic nitrate, can 
 only be detected in 2,500,000 parts of water. Of the coloured 
 reactions which copper gives with different reagents, those with 
 sulphuretted hydrogen and potassic ferrocyanide are by far the 
 most delicate, both showing their respective colours in 2,500,000 
 parts of water. 
 
 * I have retained this technical process in its original form, notwithstanding the use 
 of ammonia, because it is systematic, and the results obtained by it are all comparable 
 among themselves. Of course soda or potash may be used in place of ammonia, if the 
 cyanide is standardized with them. 
 
188 VOLUMETRIC ANALYSIS. 58. 
 
 Of the two reagents sulphuretted hydrogen is the more delicate ; 
 but potassic ferrocyanide has a decided advantage over sulphuretted 
 hydrogen in the fact that lead, when not present in too large 
 quantity, does not interfere with the depth of colour obtained, 
 whereas to sulphuretted hydrogen it is, as is well known, very 
 sensitive.'"' 
 
 And though iron if present would, without special precaution 
 being taken, prevent the determination of copper by means of 
 ferrocyanide ; yet, by the method as described below, the amounts 
 of these metals contained together in a solution can be estimated 
 by this reagent. 
 
 Ammonic nitrate renders the reaction much more delicate ; other 
 salts, as ammonic chloride and potassic nitrate, have likewise the 
 same effect. 
 
 The method of analysis consists in the comparison of the 
 purple-brown colours produced by adding to a solution of potassic 
 ferrocyanide first, a solution of copper of known strength ; and, 
 secondly, the solution in which the copper is to be determined. 
 
 The solutions and materials required are as follows : - 
 
 (1) Standard Copper solution. Prepared by dissolvingO'395gm. 
 of pure CuSO 4 , 5H 2 in one liter of water. 1 c.c. = O'l m.gm. Cu. 
 
 (2) Solution of Ammonic nitrate. Made by dissolving 100 gm. 
 of the salt in one liter of water. 
 
 (3) Potassic ferrocyanide solution. 1 : 25. 
 
 (4) Two glass cylinders holding rather more than 150 c.c. each, 
 the point equivalent to that volume being marked on the glass. 
 They must both be of the same tint, and as colourless as possible. 
 
 A burette, graduated to y 1 ^ c.c. for the copper solution; a 5 c.c. 
 pipette for the ammonic nitrate ; and a small tube to deliver the 
 ferrocyanide in drops. 
 
 Process : Five drops of the potassic ferrocyanide are placed in each 
 cylinder, and then a measured quantity of the neutral solution in which 
 the copper is to be determined is placed into one of them, and both filled 
 up to the mark with distilled water, 5 c.c. of the ammonic nitrate solution 
 added to each, and then the standard copper solution ran gradually into 
 the other till the colours in both cylinders are of the same depth, the 
 liquid being well stirred after each addition. The number of c.c. used are 
 then read off. Each c.c. corresponds to O'l m.gm. of copper, from which 
 the amount of copper in the solution in question can be calculated. 
 
 The solution in which the copper is to be estimated must be 
 neutral ; for if it contain free acid the latter lessens the depth of 
 colour, and changes it from a purple-brown to an earthy brown. 
 If it should be acid, it is rendered slightly alkaline with ammonia, 
 and the excess of the latter got rid of by boiling. The solution 
 must not be alkaline, as the brown coloration is soluble in ammonia 
 
 * In colour titrations of this character it is essential that the comparisons be made 
 under the same circumstances as to temperature, dilution, and admixture of foreign 
 substances, otherwise serious errors will arise. 
 
58. CYANOGEN. 189 
 
 and decomposed by potash or soda ; if it be alkaline from ammonia, 
 this is remedied as before by boiling it off; while free potash or 
 soda, should they be present, are, neutralized by an acid, and the 
 latter by ammonia, 
 
 Lead, when present in not too large quantity, has little or no 
 effect on the accuracy of the method. The precipitate obtained on 
 adding potassic ferrocyanide to a lead salt is white ; and this, except 
 when present in comparatively large quantity with respect to the 
 copper, does not interfere with the comparison of the colours. 
 
 When copper is to be estimated in a solution containing iron, 
 the following method is adopted : 
 
 A few drops of nitric acid are added to the solution in order to oxidize the 
 iron, the liquid evaporated to a small bulk, and the iron precipitated by 
 ammonia. Even when very small quantities of iron are present, this can be 
 done easily and completely if there be only a very small quantity of fluid. 
 The precipitate of ferric oxide is then filtered off, washed once, dissolved in 
 nitric acid, and re-precipitated by ammonia, filtered and washed. The iron 
 precipitate is now free from copper, and in it the iron can be estimated by 
 dissolving in nitric acid, making the solution nearly neutral with .ammonia, 
 and determining the iron by the method in 64.4. The filtrate from the 
 iron precipitate is boiled till the ammonia is completely driven off, and the 
 copper estimated in the solution so obtained as already described. 
 
 When the solution containing copper is too dilute to give any 
 coloration directly with ferrocyanide, a measured quantity of it 
 must be evaporated to a small bulk, and filtered if necessary; 
 .and if it contain iron, also treated as already described. 
 
 In the determination of copper and iron in water, for which the 
 method is specially applicable, a measured quantity is evaporated 
 to dryness with a few drops of nitric acid, ignited to get rid of any 
 organic matter that might colour the liquid, dissolved in a little 
 boiling water and a drop or two of nitric acid ; if it is not all 
 soluble it does not matter. Ammonia is next added to precipitate 
 the iron, the latter filtered off, washed, re-dissolved in nitric acid, 
 and again precipitated by ammonia, filtered off, and washed. The 
 filtrate is added to the one previously obtained, the iron estimated 
 in the precipitate, and the copper in the united filtrates. 
 
 CYANOGEN. 
 
 CIS T -=26. 
 
 1 c.c. T ^ silver solution=0'0052 gin. 
 
 Cyanogen. 
 =0-0054 gm. 
 
 Hydrocyanic acid. 
 =0;01302 gm. 
 
 Potassic cyanide. 
 yjj iodine solution=0'003255 gm. 
 
 Potassic cyanide. 
 
190 VOLUMETRIC ANALYSIS. 
 
 1. By Standard Silver Solution (Lie big). 
 
 59. THIS ready and accurate method of estimating cyanogen 
 in prnssic acid, alkaline cyanides, 1 etc., was discovered by Liebig, 
 and is fully described in Ann. der Ghem. und Pliarm. Ixxvii. 102. 
 It is based on the fact, that when a solution of silver nitrate is 
 added to an alkaline solution containing cyanogen, with constant 
 stirring, no permanent precipitate of silver cyanide occurs until all 
 the cyanogen has combined with the alkali and the silver, to form 
 a soluble double salt (in the presence of potash, for example, 
 KCy, AgCy). If the slightest excess of silver, over and above the 
 quantity required to form this combination, be added, a permanent 
 precipitate of silver cyanide occurs, the double compound being 
 destroyed. If, therefore, the silver solution be of known strength, 
 the quantity of cyanogen present is easily found ; 1 eq. of silver 
 in this case being equal to 2 eq. cyanogen. 
 
 So fast is this double combination, that, when sodic chloride is 
 present, no permanent precipitate of silver chloride occurs, until 
 the quantity of silver necessary to form the compound is slightly 
 overstepped. 
 
 Siebold, however, has pointed out that this process, in the case 
 of free hydrocyanic acid, is liable to serious errors unless the 
 following precautions are observed : 
 
 () The solution of sodic or potassic hydrate should be placed in the 
 beaker first, and the hydrocyanic acid added to it from a burette dipping 
 into the alkali. If, instead of this, the acid is placed in the beaker first, 
 and the alkaline hydrate added afterwards, there mny be a slight loss by 
 evaporation, which becomes appreciable whenever there is any delay in the 
 addition of the alkali. 
 
 (5) The mixture of hydrocyanic acid and alkali should be largely diluted 
 with water before the silver nitrate is added. The most suitable proportion 
 of water is from ten to twenty times the volume of the officinal or of 
 Scheele's acid. With such a degree of dilution, the final point of the- 
 reaction can be observed with greater precision. 
 
 (c) The amount of alkali used should be as exactly as possible that 
 required for the conversion of the hydrocyanic acid into alkaline cyanide., 
 as an insufficiency or an excess both affect the accuracy of the result. It is 
 advisable to make first a rough estimation with excess of soda as a guide, 
 then finish with a solution as neutral as possible. 
 
 Caution. In using the pipette for measuring hydrocyanic acid, 
 it is advisable to insert a plug of cotton wool, slightly moistened 
 with silver nitrate, into the upper end, so as to avoid the danger 
 of inhaling any of the acid ; otherwise it is decidedly preferable 
 to weigh it. 
 
 Example ivith Commercial Potassic Cyanide : The quantity of this sub- 
 stance necessary to be taken for analysis, so that each c.c. or dm. shall be 
 equal to 1 per cent, of the pure C3*auide. is 1'30 gm. or 13'0 grn. 13 grains, 
 therefore, of the commercial article were dissolved in water, no further alkali 
 being necessaiy, and 54 dm. yV silver required to produce the permanent 
 turbidity. The sample therefore contained 54 per cent, of real cyanide. 
 
59. CYANOGEN. 191 
 
 2. By Standard Mercuric Chloride (Hannay). 
 
 This convenient method is fully described by the author (/. C. S. 
 1878, 245), and is well adapted for the technical examination of 
 commercial cyanides, etc., giving good results in the presence of 
 cyanates, sulphocyanates, alkaline salts, and compounds of ammonia 
 and silver. 
 
 The standard solution of mercury is made by dissolving 13 '537 
 gm. HgCl 2 in water, and diluting to a liter. Each c.c.=:0'00651 gm. 
 of potassic cyanide or 0*0026 gm. Cy. 
 
 Process : The cyanide is dissolved in water, and the beaker placed upon 
 black paper or velvet ; ammonia is then added in moderate quantity, and 
 the mercuric solution cautiously added with constant stirring until a bluish- 
 white opalescence is permanently produced. With pure substances the 
 reaction is very delicate, but not so accurate with impure mixtures occurring 
 in commerce. 
 
 3. By Iodine (Fordos and Gelis). 
 
 This process, which is principally applicable to alkaline cyanides, 
 depends on the fact, that when a solution of iodine is added to one 
 of potassic cyanide, the iodine loses its colour so long as any 
 imdecomposed cyanide remains. The reaction may be expressed 
 by the following formula : - 
 
 Therefore, 2 eq. iodine represent 1 eq. cyanogen in combination; so 
 that 1 c.c. of -^ iodine expresses the half of T o-Jo-o eq. cyanogen 
 or its compounds. The end of the reaction is known by the 
 yellow colour of the iodine solution becoming permanent. 
 
 Commercial cyanides are, however, generally contaminated with 
 caustic or monocarbonate alkalies, which would equally destroy 
 the colour of the iodine as the cyanide ; consequently these must 
 be converted into bicarbonates, best done by adding carbonic acid 
 water (ordinary soda water). 
 
 Example : 5 gm. of potassio cyanide were weighed and dissolved in 500 c.c. 
 water; then 10 c.c. (=0'1 gni. cyanide) taken with a pipette, diluted with 
 about i liter of water, 100 c.c. of soda water added, then T ^ iodine delivered 
 from the burette until the solution possessed a slight but permanent yellow 
 colour; 25'5 c.c. were required, which multiplied by 0'003255 gave 0'08300 
 gm. instead of O'l gm., or 83 per cent, real cyanide. Sulphides must of 
 course be absent. 
 
 4. By ]-0 Silver and Chromate Indicator. 
 
 Yielhaber (Arch. PJtarm. [3] xiii. 408) has shown that weak 
 solutions of prussic acid, such as bitter-almond water, etc., may be 
 readily titrated by adding magnesic hydrate suspended in water 
 until alkaline, adding a drop or two of cliromate indicator, and 
 delivering in $ silver until the red colour appears, as in 
 
192 VOLUMETRIC ANALYSIS. 59. 
 
 the case of titrating chlorides. 1 c.c. silver solution=0'0027 
 gm. HCy. 
 
 This method may be found serviceable in the examination of 
 opaque solutions of hydrocyanic acid, such as solutions of bitter- 
 almond oil, etc. ; but of course the absence of chlorine must be 
 insured, or, if present, the amount must be allowed for. 
 
 It is preferable to add the HCy solution to a mixture of 
 magnesia and chromate, then immediately titrate with silver. 
 
 5. Cyanides used in Gold Extraction. 
 
 All interesting series of papers on this subject have been 
 contributed by Glenn ell (G. N. Ixxvii. 227, and Eettel, idem 
 286, 298). The experiments carried out by these chemists are 
 far too voluminous to be reproduced here, but a short summary 
 of the results may be acceptable for the technical examination of 
 the original solutions and their nature, after partial decomposition 
 and admixture with zinc and other impurities which naturally 
 occur in the processes of gold extraction. The results of both 
 chemists point to the fact that the estimation of cyanide in the 
 weak solutions used in the MacArthur-Forrest process is much 
 hampered by zinc double cyanide, by thiocyanates, also by ferro and 
 ferricyanides, together with organic matters which occur in the 
 liquors after leaching the ores. According to Glenn ell the presence 
 of ferrocyanides gives too high a result when the silver process of 
 Liebig is used, but is not of much consequence unless the cyanide 
 is relatively small as compared with the ferrocyanide ; with the 
 iodine process the interference of ferrocyanide is much less, and 
 very fair technical results may be obtained in the presence of both 
 ferro and ferri salts by this process. The silver process appears to 
 be fairly serviceable where the quantity of ferrocyanide is not too 
 large ; the reddish precipitate which forms at first from the ferri salt 
 is soluble in the presence of excess of cyanide, and a definite end- 
 reaction can be obtained. Thiocyanates render the silver process 
 useless, but do not interfere with the iodine process. Ammonic 
 carbonate interferes with the silver process unless potassic iodide is 
 added so as to produce silver iodide, which is insoluble in the 
 ammonia salt. Ferrocyanides, in the absence of other reducing 
 .agents, may be accurately estimated, as in 60. 1 ; the presence of 
 cyanides and ferricyanides does not seriously interfere. Ferri- 
 cyanides may be estimated as in 60.2; ferrocyanides do not 
 seriously interfere, but cyanides render the results somewhat low. 
 These remarks apply to solutions not complicated by admixture of 
 zinc or other matters which naturally occur in the cyanide liquors 
 after they have been in contact with the ore. For the actual 
 methods which have been found useful in examining the usual 
 cyanide liquors the following processes, devised by Bettel, are 
 given, not as being absolutely correct, but sufficiently so for 
 technical purposes, and occupying little time in the working : 
 
59. CYANOGEN. 193 
 
 It is necessary to state at the outset that the following remarks have 
 reference to the MacArthur-Forrest working solutions containing zinc, 
 an element which complicates the analysis in a truly surprising manner. 
 Before dealing with the analysis proper, attention is drawn to the peculiarities 
 of a solution of the double c} r anide of zinc and potassium, usually written 
 K 2 ZnCy 4 . As is stated in works on chemistry, this cyanide is alkaline to 
 indicators. Now here lies the peculiarity. To phenolphthalein the alkalinity, 
 as tested by T ^ acid, is equal to 19' 5 parts of cyanide of potassium out of 
 a possible 130'2 parts. "With methyl orange as indicator, the whole of the 
 metallic cyanide may be decomposed by T \ acid, as under : 
 
 K 2 ZnCy 4 +4HCl=ZnCl 2 +2KCl+4HCy. 
 
 On titration with silver nitrate solution the end-reaction is painfully indefinite. 
 If caustic alkali in excess (a few c.c. normal soda) be added to a known 
 quantity of potassic zinc cyanide solution together with a few drops of 
 potassic iodide, and standard silver solution added to opalescence, the reaction 
 will indicate sharply the total cyanogen present in the double cyanide even 
 in presence of ferrocyanides. If to a solution of potassic zinc cyanide 
 be added a small quantity of ferrocyanide of potassium, and the silver 
 solution added, the flocculent precipitate of what is supposed to be normal 
 zinc ferrocyanide (Zn 2 FeCy 6 ) appears, the end-reaction is fairly sharp, and 
 indicates 19' 5 parts of potassic cyanide out of the actual molecular contents 
 of 130'2 KCy. If, however, an excess of ferrocyanide be present, the 
 flocculeut precipitate does not appear, but in its place one gets an opalescence 
 which speedily turns to a finely granular (sometimes slimy) precipitate of 
 potassic zinc ferrocyanide, K 2 Zn 3 Fe 2 Cy 12 . This introduces a personal equation 
 into the analysis of such a solution, for if the silver solution be added 
 rapidly the results are higher than if added drop by drop, as this ferro- 
 cyanide of zinc and potassium separates out slowly in dilute solutions 
 alkaline or neutral to litmus paper. 
 
 For the estimation of free hydrocyanic acid use is made of Sieb old's 
 ingenious method for estimating alkalies in carbonates and bicarbonates, by 
 reversing the process, adding bicarbonate of soda, free from carbonate, to 
 the solution to be titrated for hydrocyanic acid and free cyanide. This is 
 the one instance where hydrocyanic acid turns carbonic acid out of its 
 combinations, and as such is interesting. 
 
 2KHC0 3 +AgN0 3 +2HCy=KAgCy 2 +KN0 3 +2C0 2 +2H 2 0. 
 
 The methods of analysis are as follows : 
 
 1. Free Cyanide. 50 c.c. of solution are taken and titrated with silver 
 nitrate to faint opalescence or first indication of a flocculeut precipitate. 
 This will indicate (if sufficient ferrocyanide be present to form a flocculent 
 precipitate of zinc ferrocyanide) the free cyanide, and cyanide equal to 7'9 
 per cent, of the potassic zinc cyanide present. 
 
 2. Hydrocyanic Acid. To 50 c.c. of the solution add a solution of 
 alkaline bicarbonate, free from carbonate or excess of carbonic acid. Titrate 
 as for free cyanide. Deduct the first from the second result 
 
 =HCy 1 c.c. AgN0 3 ==:0-00829 / HCy. 
 
 3. Double Cyanides: Add excess of normal caustic soda to 50 c.c. of 
 solution and a few drops of a 10 per cent, solution of KI, titrate to opalescence 
 with AgNO 3 . This gives 1, 2, and 3. Deduct 1 and 2=K 2 ZnCy 4 as KCy 
 less 7'9 per cent. 
 
 A correction is here introduced. The KCy found in 3 is calculated to 
 K 2 ZnCy 4 . Factor : KCy (as K 2 ZnCy 4 ) x 0'9493=K ? ZnCy 4 . Add to this 
 7'9 per cent, of total, or for every 92'1 parts of K 2 ZnCy 4 add 7'9 parts. 
 
 
 
194 VOLUMETRIC ANALYSIS. 59. 
 
 If this fraction, calculated back to KCj, be deducted from 1, the true free 
 cyanide (calculated to KCy) is obtained. 
 
 4. Ferro cyanides and Thiocyanates. In absence of organic matters 
 it is found that an acidified solution of a simple cyanide, such as KCy, or 
 a double cyanide (as K'-ZnCy 4 ), i.e., solution of HCy, is not affected by 
 dilute permanganate. On the other hand, acidified solutions of femxryanides 
 and sulphocyanides are rapidly oxidizedthe one to ferrocyanide, the other 
 to H 2 SO 4 +ilCy. 
 
 If, now, the ferroc} r anogen be removed as Prussian blue, by ferric chloride 
 in an acid solution, the filtrate will contain ferric and hydric thiocyanate, 
 both of which are oxidized by permanganate as if iron were not present ; 
 by deducting the smaller from the larger result, we get the permanganate 
 consumed in oxidizing ferrocyanide, the remainder equals the permanganate 
 consumed in oxidizing thiocyanate. 
 
 The method of titratiou is as follows (in presence of zinc) : A burette 
 is filled with the c} r anide solution for analysis, and run into 10 or 20 c.c. 
 rjfo K 2 Mn 2 O 8 strongly acidified with H 2 SO 4 until colour is just discharged. 
 Result noted (a). 
 
 A solution of ferric sulphate or chloride is acidified with H 2 SO 4 and 
 50 c.c. of the cyanide solution poured in. After shaking for about half 
 a minute, the Prussian blue is separated from the liquid by filtration, and 
 the precipitate and filter paper washed. The filtrate is next titrated Avith 
 T^T K 2 Mn 2 8 (b). 
 
 Let c c.c. permanganate required to oxidize ferrocyanide. 
 
 Then ab = c. 
 
 (c) 1 c.c. ^ K 2 Mn 2 8 = 0-003684 gm. K 4 FeCy 6 . 
 
 (*) 1 c.c. y^- K 2 Mn 2 O 8 =0'0001618 gm. KCNS. 
 
 5. Oxidizable Org-anic Matter in Solution. In treating spruit tail- 
 ings, or material containing decaying vegetable matter., the following method 
 is used for testing coloured solutions : 
 
 Prepare a solution of a thiocyanate, so that 1 C.C.T^ K 2 Mn 2 O 8 . 
 
 To 50 c.c. solution add sulphuric acid in excess, and then a large 
 excess of permanganate, y^. Keep at 6070 C. for an hour. Then cool 
 and titrate back with the KCNS solution. 
 
 Result O consumed in oxidizing organic matter. 
 O K'FeCy 6 . 
 
 O KCNS. 
 
 After estimating KCNS and K 4 FeCy 6 , a simple calculation gives the 
 oxygen to oxidize organic matter. This result multiplied by 9 will give 
 approximately the amount of organic matter present. 
 
 In order to clarify such organically charged solutions, they are shaken 
 up with powdered quicklime and filtered ; the solution is then of a faint 
 straw colour, and is in a proper condition for analysis. In such clarified 
 solution the oxidizable organic matter is no longer present, and the 
 estimations are readily performed. 
 
 6. Alkalinity. Potassic cyanide acts as caustic alkali, when neutralized 
 by an acid; the end-reaction, however, is influenced to some extent by 
 the hydrocyanic acid present, and is therefore not sharp. It is possible, 
 however, to estimate 
 
 With phenolphtMeinas indicator. 
 
 }^^ 1 -'*"- '" 
 Ey T ^- acid the K 2 O in ZnK 2 O 2 ... With phenolphthalein as indicator. 
 
59. FERRO- AND FERRI-CYANIDES. 195 
 
 It will be necessary to point out the decompositions which result from 
 adding alkali, or a carbonate of an alkali, to a working solution containing 
 ;zinc. 
 
 K 2 ZnCy 4 + 4KHO=ZnK 2 O 2 + 4KCy . 
 K 2 ZnCy 4 + 4Na 2 CO 3 + 2H 2 O=2KCy + 2NaCy + ZnNa 2 O 2 + 4NaHCO 3 . 
 
 Bicarbonates have no action upon potassic or sodic zinc cyanide. 
 Potassic or sodic zinc oxide (in solution as hydrate) acts as an alkali 
 towards phenolphthalein and methyl orange. 
 
 ZnK 2 O 2 + 4HC1 = 2KC1 + ZnCl 2 + 2H 2 O . 
 
 Calcic and magnesic hydrates decompose the double salt of K 2 ZuCy 4 to 
 some extent, but not completely, so that it is possible to find in one and the 
 same solution a considerable proportion of alkalinity towards phenolphthalein, 
 due to calcic hydrate in presence of K 2 ZnCy 4 . 
 
 The total alkalinity as determined by T ^ acid with methyl orange as 
 indicator gives, in addition to those before mentioned, the bicarbonates. 
 If to a solution containing sodic bicarbonate and potassic zinc cyanide be 
 added lime or lime and magnesia, the percentage of C3 r anide will increase, 
 the zinc remaining in solution as zinc sodic oxide. 
 
 Clennell (C. N. Ixxi. 93) gives a method for the approximate estimation 
 of alkaline hydrates and carbonates in the presence of alkaline cyanides, 
 as follows : 
 
 (1) Estimation of the cyanide by direct titration with silver. 
 
 (2) Estimation of the hydrate and half the carbonate of alkali on adding 
 phenolphthalein to the previous solution (after titration with silver) by 
 ^ hydrochloric acid. 
 
 (3) Estimation of the total alkali by direct titration, in another portion 
 of the solution, with T ^ hydrochloric acid and methyl orange. 
 
 7. Ferricyanide Estimation. This is effected by allowing sodium 
 amalgam to act for fifteen minutes on the solution in a narrow cylinder, 
 then estimating the ferrocyanide formed by permanganate in an acid 
 solution. Deduct from the results obtained the ferrocyauide and thiocyanate 
 previously found, 1 c.c. ^ permanganate^O'003293 gm. K 6 Fe 2 Cy 12 . 
 
 8. Sulphides. It rarely happens that sulphides are present in a cyanide 
 solution ; if present, however, shake up with precipitated carbonate of lead, 
 filter, and titrate with T - - permanganate. The loss over the previous 
 estimation (of 'K 4 FeCy 6 KCNS, &c.) is due to elimination of sulphides. 
 
 1 c.c.' T K 2 Mn 2 O 8 =0'OOOl7 gm. H 2 S, or 0'00055 gm. K 2 S. 
 
 The hydrogen alone being oxidized by dilute permanganate in acid solution 
 where the permanganate is not first of all in excess. 
 
 9. Ammonia. If sufficient silver nitrate be added to a solution (say 
 10 c.c.) to wholly precipitate the cyanogen compounds and a drop or two of 
 f HC1 be added, the Avhole made up to 100 c.c., and filtered ; then 10 c.c. 
 distilled with about 150 c.c. of ammonia free water and Nesslerized in the 
 usual way, the amount of ammonia may be ascertained. 
 
 FERRO- AND FERRI-CYANIDES. 
 
 Potassic Ferrocyanide. 
 
 Metallic iron 7 -541= Crystallized Potassic ferrocyanide. 
 
 Double iron salt x 1*077= 
 
 o 2 
 
196 VOLUMETRIC ANALYSIS. 60. 
 
 1. Oxidation to Ferricyanide by Permanganate (De Ha en). 
 
 60. THIS substance may be estimated by potassic permanga- 
 nate, which acts by converting it into red prussiate. The process 
 is easy of application, and the results accurate. A standard 
 solution of pure ferrocyanide should be used as the basis upon 
 which to work, but may, however, be dispensed with, if the operator 
 chooses to calculate the strength of his permanganate upon iron or its 
 compounds. If the permanganate is decinormal, there is of course 
 very little need for calculation (1 eq.=422 must be used as the 
 systematic number, and therefore 1 c.c. of ^5- permanganate is 
 equal to OO422 gm. of yellow prussiate). The standard solution 
 of pure ferrocyanide contains 20 gm. in the liter : each c.c. will 
 therefore contain 0'02 gm. 
 
 Process : 10 c.c. of the standard prussiate solution are put into a white 
 porcelain dish or beaker standing on white paper, and 250 c.c. or so of water 
 added; it is then acidified pretty strongly with sulphuric acid, and the 
 permanganate delivered from the burette until a pure uranium yellow colour 
 appears ; it is then cautiously added until the faintest pink tinge occurs. 
 
 Ferrocyanides in Alkali waste. Acidulate the solution with 
 HC1, and add strong bleaching powder solution with agitation until 
 a drop of the liquid gives no blue colour with ferric indicator. The 
 liquid is then titrated with a solution of cupric sulphate, standardized 
 on pure potassic ferrocyanide, using dilute ferrous sulphate as 
 indicator; as soon as no more blue or grey colour occurs, but 
 a faint reddening, the process is ended. 
 
 Ferrocyanides in G-as Liquor. 250 c.c. are evaporated to dryness^. 
 dissolved in water, the solution filtered, and the ferrocyanides 
 precipitated as Prussian blue by ferric chloride. The blue is 
 filtered off, w T ashed, and decomposed with caustic soda. The ferric 
 hydroxide so obtained is, after filtering, washing, and dissolving in 
 dilute H 2 S0 4 reduced with zinc, and titrated with permanganate.. 
 Fe x 5-07-=(NH 4 ) 4 FeCy 6 . 
 
 POTASSIC FERRICYANIDE. 
 
 K 6 Cy 12 Fe 2 =658. 
 
 Metallic iron x 5 '88 = Potassic ferricyanide. 
 
 Double iron salt x 1*68 = ,, 
 
 T N o- Thiosulphate x 0-0329 
 
 2. By Iodine and Thiosulphate. 
 
 This salt can be estimated either by reduction to ferrocyanide 
 and titratioii with permanganate or bichromate as above, or by 
 Lenssen's method, which is based upon the fact, that when 
 potassic iodide and ferricyanide are mixed with tolerably concen- 
 trated hydrochloric acid, iodine is set free. 
 
60. THIOCYANATES. 197 
 
 K 6jVCy 12 + 2KI=2K*Cy 6 Fe + 1 2 
 
 the quantity of which can be estimated by -^ thiosulphate and 
 starch. This method does not, however, give the most satis- 
 factory results, owing to the variation produced by working 
 with dilute or concentrated solutions. C. Mohr's modification 
 (see Zinc, 81) is, however, more accurate, and is as follows : 
 The ferricyanide is dissolved in a convenient quantity of water, 
 potassic iodide in crystals added, together with hydrochloric acid 
 in tolerable quantity, then a solution of pure zinc sulphate in 
 excess ; after standing a few minutes to allow the decomposition 
 to perfect itself, the excess of acid is neutralized by sodic carbonate, 
 .so that the latter slightly predominates. 
 
 At this stage all the zinc ferricyanide first formed is converted 
 into the ferrocyanide of that metal, and an equivalent quantity of 
 iodine set free, which can at once be titrated with T ^ thiosulphate 
 and starch, and with very great exactness. 1 c.c. ~ thiosalphate 
 = 0'0329 gm. potassic ferricyanide. 
 
 The mean of five determinations made by Mohr gave 10O21 
 instead of 100. 
 
 Another method consists in boiling with excess of potash, then 
 cooling, and adding H 2 2 till the colour is yellow. The excess of 
 the peroxide is then boiled off, H 2 S0 4 added, and titrated with 
 permanganate. 
 
 3. Reduction of Ferri- to Ferro-cyanide. 
 
 This process is, of course, necessary when the determination by 
 permanganate has to be made, and is best .effected by boiling the 
 weighed ferricyanide with an excess of potash or soda, and adding 
 small quantities of concentrated solution of ferrous sulphate until 
 the precipitate which occurs possesses a blackish colour (signifying 
 that the magnetic oxide is formed). The solution is then diluted 
 to a convenient quantity, say 300 c.c., well mixed and filtered 
 through a dry filter; 50 or 100 c.c. may then be taken, sulphuric 
 acid added, and titrated with permanganate as before described. 
 
 Kassner suggests the use of sodic peroxide for the reduction 
 of ferri- to ferrocyanide (Arch. Pharm. ccxxxii. 226) as being 
 rapid and complete. About 0'5 gm. in 100 c.c. water requires 
 about. 0*06 gm. -of the peroxide ; the mixture is heated till all 
 effervescence is over, acidified with sulphuric acid, cooled, and 
 titrated with permanganate in the usual way. 
 
 THIOCYANATES. 
 
 For the estimation of thiocyanic acid in combination with the 
 alkaline or earthy bases, Barnes and Liddle (/. S. C. I. ii. 122) 
 have devised a method which is easy of application, and gives good 
 technical results. It is not, however, available for gas liquors. 
 
198 VOLUMETRIC ANALYSIS. 61. 
 
 The method depends upon the fact that when a solution of 
 a cupric salt is added to a solution of a thiocyanate in presence 
 of a reducing agent, as sodic bisulphite, the insoluble cuprous salt 
 of thiocyanic acid is precipitated, the end of the reaction being 
 ascertained by a drop of the solution in the flask giving a brown 
 colouration when brought in contact with a drop of ferrocyanide,. 
 The following reactions take place : 
 
 2CuS0 4 + 2KSCX + Xa 2 S0 3 + H 2 = 
 
 and 
 
 2CuS0 4 + Ba(SC^s T ) 2 + !S T a 2 S0 3 + H 2 = 
 Cu 2 S 2 C 2 JS T2 + BaSO 4 + 2 
 
 The following solutions are required : 
 
 1. A standard solution of Cupric sulphate containing 6 '2375 
 gm. per liter, 1 c.c. of which is equivalent to '00 145 gm. SC^N". 
 
 2. A solution of Sodic bisulphite of specific gravity 1*3. 
 
 3. A solution of Potassic ferrocyanide (1 : 20). 
 
 Process: About 3 gm. of the sample are weighed from a stoppered 
 tube into a liter flask, dissolved in water, and made up to the mark. After 
 well mixing, 25 c.c. are measured into a flask, about 3 c.c. of the bisulphite 
 added, and the whole boiled. Whilst this is heating a burette is filled with 
 the copper solution, and a white porcelain slab is dotted over with the 
 ferrocyanide. When the liquid in the flask has reached the boiling point, 
 20 c.c. of the copper solution are run in, well shaken, the precipitate allowed 
 to settle for about a minute, a drop is taken out by means of a glass rod, and 
 brought in contact with a drop of ferrocyanide, and should no brown 
 colouration appear, more of the copper solution is run in, say 1 c.c. at 
 a time, and again tested. This is continued until a drop gives an immediate 
 colour. By this means an approximation to the truth is obtained. It will 
 be observed, during a titration, that the mixed drops, after standing for 
 a minute, or even less, produce a brown tint. It is of the utmost importance 
 that the colouration be immediate. 
 
 A second 25 c.c. of the thiocyanate solution are run into a clean flask, 
 the bisulphite added, and boiled as before. 
 
 Suppose that in the first experiment, after an addition of 27 c.c. of copper 
 solution, no colour was formed with ferrocyanide, but that 28 c.c. gave an 
 immediate colour ; then in the second experiment 27 c.c. are run in at once, 
 and the liquid is again tested, when no colour should appear. The copper 
 solution is then run in drop by drop until there is a slight excess of copper, 
 as proved by the delicate reaction with the ferrocyanide. The second 
 experiment is thus rendered more exact by the experience gained in the first. 
 
 GOLD. 
 
 Au- 196-5. 
 1 c.c. or 1 dm. normal oxalic acid=0'0655 gm. or 0'655 grn. Gold. 
 
 61. THE technical assay of gold for coining purposes is 
 invariably performed by cupellation. Terchloride of gold is, 
 however, largely used in photography and electro-gilding, and 
 
62. IODINE. 199 
 
 therefore it may be necessary sometimes to ascertain the strength 
 of a solution of the chloride, or its value as it occurs in commerce. 
 
 If to a solution of gold in the form of chloride (free from nitric 
 acid) an excess of oxalic acid be added, in the course of from 
 eighteen to twenty-four hours all the gold will be precipitated in 
 the metallic form, while the corresponding quantity of oxalic acid 
 has been dissipated in the form of carbonic acid ; if, therefore, the 
 quantity of oxalic acid originally added be known, and the excess, 
 after complete precipitation of the gold, be found by permanganate, 
 the amount of gold will be obtained. 
 
 Example : A 15-grain tube of the chloride of gold of commerce was 
 dissolved in water, and the solution made up to 300 decems. 20 dm. of 
 normal oxalic acid were then added, and the flask set aside for twenty-four 
 hours in a warm, dark place ; at the end of that time the gold had settled, 
 and the supernatant liquid was clear and colourless. 100 dm. were taken 
 out with a pipette, and titrated with T ^ permanganate, of which 25 dm. were 
 required ; this multiplied by 3 gives 75 dm.=7'5 dm. normal oxalic acid, 
 which deducted from the 20 dm. originally added, left 12'5 dm. ; this 
 multiplied by ^ the equivalent of gold (1 eq. of gold chloride decomposing 
 3 eq. oxalic acid)=0'655 gave 8'195 grn. metallic gold, or multiplied by 101 
 (=1 eq. AuCl 3 ) gave 12'625 grn. ; the result was 84 per cent, of chloride of 
 gold instead of 100. A more rapid method consists in boiling the gold 
 solution with an excess of standard solution of potassic oxalate containing 
 8'3 gm. of the pure salt per liter, and titrating back with a permanganate 
 solution which has the same working strength as the oxalate. Each c.c. 
 of oxalate solution decomposed represents 0'00855 gm. Au. 
 
 IODINE. 
 
 1=127-0. 
 1. By Distillation. 
 
 
 
 in potassic iodide, and titration with starch and -- thiosulphate, 
 as described in 38.* 
 
 Combined iodine in haloid salts, such as the alkaline iodides, 
 must be subjected to distillation with hydrochloric acid, and some 
 other substance capable of assisting in the liberation of free iodine, 
 which is received into a solution of potassic iodide, and then 
 titrated with ~ thiosulphate in the ordinary way. Such a 
 substance presents itself best in the form of ferric oxide, or some 
 of its combinations ; if, therefore, hydriodic acid, or what amounts 
 to the same thing, an alkaline iodide, be mixed with an excess of 
 
 62. FREE iodine is of course very readily estimated by solution 
 
 * I would here again impress upon the operator's notice that it is of great importance 
 to ascertain the exact strength of the standard solutions of iodine and thiosulphate as 
 compared with each other. Both solutions constantly undergo an amount of change 
 depending upon the temperature at which they are kept, their exposure to light, etc., 
 and therefore it is absolutely necessary, to ensure exactness in the multifarious analyses 
 which can be made by the aid of these two reagents, to verify their agreement by 
 weighing a small portion of pure dry iodine at intervals, and titrating it with the 
 standard thiosulphate, or checking the iodine with baric or sodic thiosulphate of 
 known purity. 
 
 OF THE 
 
 UNIVERSITY 
 
 CAI icrikBNliA* 
 
200 VOLUMETRIC ANALYSIS. 62. 
 
 ferric oxide or chloride, and distilled in the apparatus shown in 
 fig. 37 or 38, the following reaction occurs : 
 
 Fe 2 3 + 2IH=2FeO + H 2 + 1 2 . 
 
 The best form in which to use the ferric oxide is iron alum. 
 
 The iodide and iron alum being brought into the little flask (fig. 38), 
 sulphuric acid of about 1 '3 sp. gr. is added, and the cork carrying 
 the still tube inserted. This tube is not carried into the solution 
 of potassic iodide in this special case, but within a short distance 
 of it ; and the end must not be drawn out to a fine point, as there 
 represented, but cut off straight. The reason for this arrangement 
 is, that it is not a chlorine distillation for the purpose of setting 
 iodine free from the iodide solution, as is usually the case, but an 
 actual distillation of iodine, which would speedily choke up the 
 narrow point of the tube, and so prevent the further progress 
 of the operation, 
 
 As the distillation goes on, the steam washes the condensed 
 iodine out of the tube into the solution of iodide, which must be 
 present in sufficient quantity to absorb it all. When no more 
 violet vapours are to be seen in the flask, the operation is ended ; 
 but to make sure, it is well to empty the solution of iodine out 
 of the condensing tube into a beaker, and put a little fresh iodide 
 solution with starch in, then heat the flask again ; the slightest 
 traces of iodine may then be discovered by the occurrence of the 
 blue colour when cooled. In case this occurs the distillation is 
 continued a little while, then both liquids mixed, and titrated 
 with j~ thiosulphate as usual. 
 
 It has been previously stated that the rubber joints to the 
 special apparatus of Fresenius, Bunsen, or Mohr for iodine 
 distillations are objectionable. Topf avoids this by fitting his 
 apparatus together, so that although rubber is used, the reagents 
 do not come in contact with it (Z. a. C. xxvi. 293). 
 
 Another form of apparatus designed by Stortenbeker (Z. a. C. 
 xxix. 273) is shown in fig. 41, in which rubber joints are entirely 
 dispensed with, and glass connections used. The connection 
 between the distilling tube and the absorbing apparatus is a water 
 joint, the tube resting in a socket kept wet with water, the 
 chloride of calcium tube is filled with glass pearls, moistened 
 with concentrated solution of potassic iodide, and the connection 
 with the absorbing apparatus is ground in like an ordinary stopper. 
 The absorbing bulbs are immersed in water to the middle of the 
 bulbs, and the iodide solution filled to the lower end of them. 
 
 Ferric chloride may be used instead of the iron alum, but it 
 must be free from nitric acid or active chlorine (best prepared 
 from dry Fe 2 3 and HC1). 
 
 The iodides of silver, mercury, and copper cannot be accurately 
 analyzed in this way, but must be specially treated. They should 
 be dissolved in the least possible quantity of sodic thiosulphate 
 
62. IODINE. 201 
 
 solution, and precipitated boiling with sodic sulphide, then filtered ; 
 the nitrate contains the whole of the iodine free from metal. The 
 nitrate is evaporated to dryness and ignited, then dissolved in 
 water, and distilled with a good excess of ferric salt (Mensel 
 Z. a. C. xii. 137). 
 
 2. Mixtures of Iodides, Bromides, and Chlorides. 
 
 Don a th (Z. a. C. xix. 19) has shown that iodine may be 
 accurately estimated by distillation in the presence of other halogen 
 salts, by means of a solution containing about 2 to 3 per cent, of 
 chromic acid, free from sulphuric acid. 
 
 In the case of iodides and chlorides together the action is 
 perfectly regular, and the whole of the iodine may be received into 
 potassic iodide without any interference from the chlorine. 
 
 Fig. 41. 
 
 In the case of bromides being present, the chromic solution must 
 be rather more dilute, and the distillation must not be continued 
 more than two or three minutes after ebullition has commenced, 
 otherwise a small amount of bromide is decomposed. 
 
 The reaction in the case of potassic iodide may be expressed 
 thus : 
 
 6KI + 8Cr0 3 = I 6 + Cr 2 3 + 3K 2 OW. 
 
 The distillation may be made in Mohr's appnratus (fig. 38), 
 using about 50 c.c. of chromic solution for about 0'3 gm. I. 
 
 The titration is made with thiosulphate in the usual way. 
 
 A much less troublesome method of estimating iodine in the 
 presence of bromides or chlorides has been worked out by Cook 
 (/. C. S. 1885, 471), and depends on the fact that hydrogen 
 peroxide liberates iodine completely from an alkaline base in the 
 
202 VOLUMETRIC ANALYSIS. 62. 
 
 presence of excess of acetic acid, while neither bromine nor 
 chlorine are affected. 
 
 Hydrogen peroxide alone will only partially liberate iodine from 
 potassic iodide, but with excess of a weak organic acid to combine 
 with the alkaline hydroxide, the liberation is complete. Strong 
 mineral acids must not be used, or bromine and chlorine, if present, 
 would also be set free. 
 
 Process : The solution is strongly acidified with acetic acid, and sufficient 
 hydrogen peroxide added to liberate the .iodine (5 c.c. will suffice for 1 gm. 
 KI). The mixture is allowed to stand from half an hour to an hour; the 
 whole of the iodine separates, some being in the solid state if the quantity 
 is considerable. Chloroform is now added in sufficient volume to dissolve 
 the iodine, the solution syphoned off, and the globule repeatedly washed 
 with small quantities of water to remove excess of peroxide, then titrated 
 with thiosulphate, with or without starch, in the usual way. If the 
 peroxide is not completely removed by washing, it will decompose the sodic 
 iodide produced in the titration, and so liberate traces of iodine. 
 
 The results obtained by Cook in mixtures of bromides, iodides, 
 and chlorides, were about 99 per cent, of the iodine present. 
 
 Gooch and Browning (Ainer. Jour. Science xxxix. March, 
 1890, also C. N. Ixi. 279) publish a method of estimating iodine 
 in halogen salts of the alkalies which gives excellent results, and 
 which is based on the fact that arsenic acid in strongly acid solution 
 liberates iodine, becoming itself reduced to arsenious acid, according 
 to the equation 
 
 IPAsO 4 + 2HI = HMsO 3 + H 2 + 21. 
 
 A very careful series of experiments are detailed in the original 
 paper, the outcome of the whole- being summarized in the following 
 process : 
 
 Process : The substance (which should not contain of chloride more 
 than an amount corresponding to 0'5 gm. of sodic chloride, nor of bromide 
 more than corresponds to 0'5 gm. of potassic bromide, nor of iodide much 
 more than the equivalent of 0'5 gm. of potassic iodide) is dissolved in water 
 in an Erlenmeyer beaker of 300 c.c. capacity, and to the solution are 
 added 2 gm. of potassic binarseniate dissolved in water, and 20 c.c. of a 
 mixture of sulphuric acid and water in equal volumes, and enough water to 
 increase the total volume to 100 c.c. or a little more. A platinum spiral is 
 introduced, a trap made of a straight two-bulb drying tube, cut off short, is 
 hung with the larger end downward in the neck of the flask, and the liquid 
 is boiled until the level reaches a mark put upon the flask to indicate a 
 volume of 35 c.c. Great care should be taken not to press the concentration 
 be}*ond this point on account of the double danger of losing arsenious 
 chloride and setting up reduction of the arseniate by the bromide. On the 
 other hand, though 35 c.c. is the ideal volume to be attained, failure to- 
 concentrate below 40 c.c. introduces no appreciable error. The liquid 
 remaining is cooled and nearly neutralized by sodic hydrate (ammonia is not 
 equally good), neutralization is completed by potassic bicarbonate, an excess 
 of 20 c.c. of the saturated solution of the latter is added, and the arsenious 
 oxide in solution is titrated by standard iodine in the presence of starch. 
 
 With ordinary care the method is rapid, reliable, and easily 
 
62. IODINE. 203 
 
 executed, and the error is small. In analyses requiring extreme 
 accuracy, all but accidental errors may be eliminated from the 
 results by applying the corrections indicated. 
 
 The indicated corrections are based on a long series of ex- 
 periments, which cannot well be given here, but the results may 
 be stated shortly as follows : 
 
 When no chloride or bromide is present the iodine may be 
 estimated with a mean error of 0*2 m.gm. in 0*5 gm. or so of the 
 alkaline iodide. When sodic chloride is present there is a slight 
 deficiency in iodine, which is proportional to the amount of iodide 
 decomposed. For about 0*56 gm. of potassic iodide and 0*5 gm. 
 of sodic chloride the deficiency in iodine amounted to 0*0011 gm. 
 When the iodide is decreased, say to one-tenth or less, the deficiency 
 falls to 0*0002 gm. The presence of potassic bromide liberates 
 traces of bromine, and consequently increases the AsO 3 , and gives 
 apparent excess of iodine, the mean error being 0*0008 gm. for 
 0*5 gm. of bromide. 
 
 The simultaneous action of the chloride and bromide tends of 
 course to neutralize the error due to each. Thus, in a mixture 
 weighing about 1*5 gm. and consisting of sodic chloride, potassic 
 bromide, and potassic iodide in equal parts, the mean error amounts 
 to -0*0003 gm. The largest error in the series is +0*0016 gm., 
 when the bromide was at its maximum, and no chloride was 
 present; and the next largest was - 0*0013 gm., when the chloride 
 was at its maximum and no bromide was present. 
 
 From a series of experiments detailed in the original paper, it 
 was deduced that the amount of iodine to be added, in each case, 
 may be obtained by multiplying the product of the weights in 
 grams of sodic chloride and potassic iodide by the constant 0*004 ; 
 and the amount to be subtracted, by multiplying the weight in 
 grams of potassic bromide by 0*0016; but in order to make use 
 of these corrections, the approximate amounts of these salts must 
 be known. 
 
 3. Titration with -j^ Silver and Thiocyanate. 
 
 The thiocyanate and silver solutions are described in 43. 
 
 The iodide is dissolved in 300 or 400 times its weight of water 
 in a well-stoppered flask, and y^r silver delivered in from the burette 
 with constant shaking until the precipitate coagulates, showing 
 that silver is in excess. Ferric indicator and nitric acid are then 
 added in proper proportion, and the excess of silver estimated 
 by thiocyanate as described in 43. 
 
 4. Oxidation of combined Iodine toy Chlorine (Golfier Besseyre 
 and D u p r e) . 
 
 This wonderfully sharp method of estimating iodine depend3 
 upon its conversion into iodic acid by free chlorine. When a 
 
204 VOLUMETRIC ANALYSIS. 62. 
 
 solution of potassic iodide is treated with successive quantities of 
 chlorine water, first iodine is liberated, then chloride of iodine 
 (IC1) formed. If starch, chloroform, benzole, or -bisulphide of 
 carbon be added, the first will be turned blue, while any of the 
 others will be coloured intense violet. A further addition of chlorine, 
 in sufficient quantity, produces pentachloride of iodine (IC1 5 ), or 
 rather, as water is present, iodic acid (I0 3 H). No colouration of 
 the above substances is produced by these compounds, and the 
 accuracy with which the reaction takes place has been made use of 
 byGolfier Besseyre and Dupre, independently of each other, 
 for the purpose of estimating iodine. The former suggested the use 
 of starch, the latter chloroform or benzole, with very dilute chlorine 
 water. Dupre 's method is preferable on many accounts. 
 
 Example : 30 c.c. of weak chlorine water were put into a beaker with 
 potassic iodide and starch, and then titrated with ^ thiosulphate, of which 
 17 c.c. were required. 
 
 10 c.c. of solution of potassic iodide containing O'OIO gm. of iodine were 
 put into a stoppered bottle, chloroform added, and the same chlorine water as 
 above delivered in from the burette, with constant shaking, until the red 
 colour of the chloroform had disappeared ; the quantity used was 85'8 c.c. 
 The excess of chlorine was then ascertained by adding sodic bicarbonate, 
 potassic iodide, and starch. A slight blue colour occurred ; this was removed 
 by T g- thiosulphate, of which 1*2 c.c. was used. Now, as 30 c.c. of the 
 chlorine solution required 17 c.c., the 85'8 c.c. required 48'62 c.c. of thio- 
 sulphate. From this, however, must be deducted the 1*2 c.c. in excess, 
 leaving 47'42 c.c. T 77 =4'742 c.c. of r ^ solution, which multiplied by 0'00211, 
 the one-sixth of Twinr e Q- (\ e( l- f iodic acid liberating 6 eq. iodine), gave 
 0'010056 gin. iodine instead of O'Ol gm. 
 
 Mohr suggests a modification of this method, which dispenses 
 with the use of chloroform, or other similar agent. 
 
 The weighed iodine compound is brought into a stoppered flask, and 
 chlorine water delivered from a large burette until all yellow colour has 
 disappeared. A drop of the mixture brought in contact with a drop of 
 starch must produce no blue colour ; sodic bicarbonate is then added till 
 the mixture is neutral or slightly alkaline, together with potassic iodide 
 and starch ; the blue colour is then removed by f^ thiosulphate. The 
 strength of the chlorine water being known, the calculation presents no 
 difficulty. 
 
 Mohr obtained by this means 0*010108 gm. iodine, instead of 
 1-01 gm. 
 
 5. Oxidation by Permanganate (Reinig-e). 
 
 This process for estimating iodine in presence of bromides and 
 chlorides gives satisfactory results. 
 
 When potassic iodide and permanganate are mixed, the rose 
 colour of the latter disappears, a brown precipitate of manganic 
 peroxide results, and free potash with potassic iodide remains in. 
 solution. 1 eq. I=l27 reacts on 1 eq. K 2 Mn 2 O s ==316, thus 
 
 KI + K 2 Mn 2 8 ==KIO :5 + K 2 + 2Mn0 2 . 
 
62. IODINE. 205 
 
 Heat accelerates the reaction, and it is advisable, especially with 
 weak solutions, to add a small quantity of potassic carbonate to 
 increase the alkalinity. Xo organic matter must be present. 
 
 The permanganate and thiosulphate solutions required in the 
 process may conveniently be of T ^- strength, but their reaction upon 
 each other must be definitely fixed by experiment as follows : 
 2 c.c. of permanganate solution are freely diluted with water, a few 
 drops of sodic carbonate added, and the thiosulphate added in very 
 small portions until the rose colour is just discharged. The slight 
 turbidity produced by .the precipitation of hydrated manganic 
 oxide need not interfere with the observation of the exact point. 
 
 Process : The iodine compound being dissolved in water, and always 
 existing only in combination with alkaline or earthy bases, is heated to 
 gentle boiling, rendered alkaline with sodic or potassic carbonate, and 
 permanganate added till in distinct excess, best known by removing the 
 liquid from the fire for a minute, when the precipitate will subside, leaving- 
 the upper liquid rose-coloured; the whole may then be poured into a 500-c.c. 
 flask, cooled, diluted to the mark, and 100 c.c. taken out for titration with 
 thiosulphate. The amount so used, being multiplied by 5, will give the 
 proportion required for the whole liquid, whence can be calculated the 
 amount of iodine. To prove the accuracy of the process in a mixture of 
 iodides, bromides, and chlorides, with excess of alkali, the following experi- 
 ment was made. 7 gm. commercial potassic bromide, the same of sodic 
 chloride, with 1 gm. each of potassic hydrate and carbonate, were dissolved 
 in a convenient quantity of water, and heated to boiling ; permanganate was 
 then added cautiously to destroy the traces of iodine and other impurities 
 affecting the permanganate so long as decolouration took place; the slightest 
 excess showed a green colour (manganate). To the mixture was then added 
 0'1246 gm. pure iodine, and the titration continued as described : the result 
 was 0'125 gm. I. 
 
 With systematic solutions of permanganate and thiosulphate- 
 
 the calculation is as follows : 
 
 
 
 1 c.c. solution=0-0127 m. I. 
 
 6. By Nitrous Acid and Carbon Bisulphide (Fresenius). 
 This process requires the following standard solutions : 
 
 (a) Potassic iodide, about 5 gm. per liter. 
 
 (b) Sodic thiosulphate, ^V normal, 12;4 gm. per liter, or there- 
 about. 
 
 (c) Nitrous acid, prepared by passing the gas into tolerably 
 strong sulphuric acid until saturated. 
 
 (d) Pure Carbon bisulphide. 
 
 (e) Solution of Sodic bicarbonate, made by dissolving 5 gm. of 
 the salt in 1 liter of water, and adding 1 c.c. of hydrochloric acid. 
 
 The strength of the sodic thiosulphate in relation to iodine is 
 first ascertained by placing 50 c.c. of the iodide solution into 
 a 500 c.c. stoppered flask, then about 150 c.c. water, 20 c.c. 
 
206 VOLUMETRIC ANALYSIS. 63. 
 
 carbon bisulphide, then dilute sulphuric acid, and lastly, 10 drops 
 of the nitrous solution. The stopper is then replaced, and the 
 whole well shaken, set aside to allow the carbon liquid to settle, 
 and the supernatant liquid poured into another clean flask. The 
 carbon bisulphide is then treated three or four times successively 
 with water in the same way till the free acid is mostly removed, 
 the washings being all mixed in one flask ; 10 c.c. of bisulphide 
 are then added to the washings, well shaken, and if at all coloured, 
 the same process of washing is carried on. Finally, the two 
 quantities of bisulphide are brought upon a moistened filter, 
 washed till free from acid, a hole made in the filter, and the 
 bisulphide which now contains all the iodine in solution allowed 
 to run into a clean small flask, 30 c.c, of the sodic bicarbonate 
 solution added, then brought under the thiosulphate burette, and 
 the solution allowed to flow into the mixture while shaking until 
 the violet colour is entirely discharged. The quantity so used 
 represents the weight of iodine contained in 50 c.c. of the standard 
 potassic iodide, and may be used on that basis to ascertain any 
 unknown weight contained in a similar solution. 
 
 When very small quantities of iodine are to be titrated, weaker 
 solutions and smaller vessels may be used. 
 
 7. By ^5- Silver Solution and Starch Iodide (Pisani). 
 
 The details of this process are given under the head of silver 
 assay ( 73.2), and are of course simply a reversal of the method 
 there given. This method is exceedingly serviceable for estimating 
 small quantities of combined .iodine in the presence of chlorides 
 and bromides, inasmuch as the silver solution does not react upon 
 these bodies until the blue colour is destroyed. 
 
 IRON. 
 
 Fe = 56. 
 Factors. 
 
 1 c.c. ~ permanganate, bichromate, 
 
 or thiosulphate = 0-0056 Fe 
 
 = 0-0072 FeO 
 = 0-0080 FeW 
 
 ESTIMATION IN THE FERROUS STATE. 
 
 1. Verification of the standard solutions of Permanganate or 
 
 Bichromate. 
 
 63. THE estimation of iron in the ferrous state has already 
 been incidentally described in 34, 35, and 37. The present 
 and following sections are an amplification of the methods there 
 given, as applied more distinctly to ores and products of iron 
 manufacture ; but before applying the permanganate or bichromate 
 
63. IRON. 207 
 
 process to these substances, and since many operators prefer, with 
 reason, to standardize such solutions upon metallic iron, especially 
 for use in iron analysis, the following method is given as the 
 Lest : 
 
 A piece of soft iron wire, known as flower wire, is well cleaned with 
 scouring paper, and about 1 gram accurately weighed ; this is placed into 
 a, 250 c.c. boiling flask a, and 100 c.c. of dilute pure sulphuric acid (1 part 
 concentrated acid to 5 of water) poured over it; about a gram of sodic 
 carbonate in crystals is then added, and the apparatus fixed together as 
 in fig. 42, the pinch-cock remaining open. The flask a is closed by a tight- 
 fitting india-rubber stopper, through which is passed the bent tube. The 
 flask c contains 20 or 30 c.c. of pure distilled water; the flask a being 
 supported over a lamp is gently heated to boiling, and kept at this 
 temperature until all the iron is dissolved; meanwhile about 300 c.c. of 
 distilled water are boiled in a separate vessel to remove all air, and allowed to 
 cool. As soon as the iron is dissolved, the lamp is removed, and the pinch- 
 cock closed ; when cooled somewhat, the pinch-cock is opened, and the wash 
 water suffered to flow back together with the boiled water, which is added 
 to it until the flask is filled nearly to the mark. The apparatus is then 
 disconnected, and the flask a securely corked with a solid rubber cork, and 
 suffered to cool to the temperature of the room. Finally, the flask is filled 
 exactly to the mark with the boiled water, and the whole well shaken and 
 mixed. When the small portion of uudissolved carbon has subsided, 
 SO c.c., equal to i the weight of iron taken, may be removed with the pipette 
 for titration with the permanganate or bichromate. 
 
 In the case of permanganate the 50 c.c. are freely diluted with freshly 
 boiled and cooled distilled water, and the standard solution cautiously added 
 from a tap burette, divided into T V c.c., until the rose colour is faintly 
 perceived. 
 
 In the case of bichromate the solution should be less diluted, and the 
 titration conducted precisely as in 37. 
 
 The amount of pure iron contained in the portion weighed for titration is 
 found by the co-efficient 0'996, and from this is calculated the w r orking 
 .strength of the oxidizing solution (see p. 122.) 
 
 Pig. 42. 
 
 Instead of the two flasks, many operators use a single flask, fitted 
 ^vith caoutchouc stopper, through which a straight glass tube is 
 passed, fitted with an india-rubber slit valve (known as Bunsen's 
 valve), which allows gas or vapour to pass out, but closes by 
 atmospheric pressure when the evolution ceases. Another 
 arrangement is described on p. 122. 
 
208 VOLUMETRIC ANALYSIS. 6 
 
 A large number of technical operators do not trouble themselves 
 to arrange any apparatus of the kind described, but simply dissolve 
 a weighed quantity of wire of known ferrous contents in a conical 
 beaker covered with a clock glass. If kept from draughts of cold 
 air while dissolving so as to avoid convection, it is said that 
 practically no oxidation takes place. 
 
 The double iron salt (p. 122) is a most convenient material for 
 adjusting standard solutions, but it must be most carefully made 
 from pure materials, dried perfectly in the granular form, and kept 
 from the light in small dry bottles, well closed. In this state it 
 will keep for years unchanged, and only needs immediate solution 
 in dilute H 2 S0 4 for use. Even in the case of the salt not being 
 strictly free from ferric oxide, due to faulty preparation, if it be 
 once thoroughly dried, and kept as above described, its actual 
 ferrous strength may be found by comparison with metallic iron, 
 and a factor found for weighing it in system. 
 
 It should be borne in mind that ferrous compounds are much 
 more stable in sulphuric than in hydrochloric acid solution, and 
 whenever possible, sulphuric acid should be used as the solvent. 
 When hydrochloric acid must be used, manganous or magnesia 
 sulphate should be added unless the solution is very dilute. 
 
 2. Reduction of Ferric Compounds to the Ferrous State. 
 
 This may be accomplished by metallic zinc OP magnesium, for use with 
 permanganate, or by stannous chloride or an alkaline sulphite for bichromate 
 solution. The magnesium method is elegant and rapid but costty. In the 
 case of zinc being used, the metal must either be free from iron, or if it 
 contain any, the exact quantity must be known and allowed for ; and further, 
 the pieces of zinc used must be entirely dissolved before the solution is- 
 titrated.* The solution to be reduced by zinc should not contain more than 
 0'15 gm. Fe. per 250 c.c., and for this quantity about 10 gin. of Zn. and 
 25 c.c. H 2 SO 4 are advisable ; when the zinc is all dissolved, the whole 
 should be boiled with exclusion of air, then cooled rapidly before titration 
 with the permanganate. In the case of stannous chloride the solution must 
 be clear, and is best made to contain 10 to 15 gm. per liter, as directed 
 in 37.2. The point of exact reduction in the boiling hot and somewhat 
 concentrated acid liquid may be known very closely by the discharge of 
 colour in the ferric solution : but may be made sure by the use of a saturated 
 aqueous solution of mercuric chloride as mentioned p. 127. Some operators 
 use a few drops of solution of platinic chloride in addition to the mercury. 
 
 It is exceedingly difficult to hit the exact point of reduction so- 
 that there shall be neither excess of tin nor unreduced iron, and 
 
 * Many operators now use amalgamated zinc in conjunction with platinum foil for 
 the reduction, but a practical difficulty occurs from the platinum becoming also 
 amalgamated through contact with the zinc and stopping the action. Beebe 
 (C. N. liii. 269) suggests the following convenient arrangement : A strip of thin 
 platinum foil, 1 in. square, is perforated with pin holes all over, then bent into 
 a U form, and the ends connected with platinum wire so as to form a basket. In this 
 is placed a piece of amalgamated zinc, and the whole suspended by a stout platinum 
 wire in the reducing flask. When lowered into the solution, another strip of platinum 
 foil, 2 in. square, is dropped in and leaned against the wire carrying the basket : a very 
 free evolution of hydrogen is then obtained from the foil. When the reduction- 
 is complete, the basket is lifted out and well washed into the beaker containing the 
 liquid to be titrated. 
 
63. IRON. 209 
 
 technical iron analysts now almost universally use mercuric chloride 
 as a precaution against excess of tin solution. The general method 
 of procedure is to dissolve the material in diluted hydrochloric acid 
 (1 acid 2 water) in a conical beaker moderately heated over a rose 
 burner; when solution is complete the sides of the vessel are 
 washed down with hot water, the liquid brought to gentle boiling, 
 and strong tin solution added from a dropping bottle until the 
 colour of the iron solution is nearly discharged, a dilute tin 
 solution is then dropped in until all colour has disappeared, and 
 there is a decided slight excess of tin. Cold air-free water is then 
 washed over the sides of the beaker, the vessel covered with 
 a clock-glass placed in a bowl of cold water and allowed to cool, 
 an excess of the mercuric solution is then added, and the 
 titratioii with bichromate is at once completed in the usual way. 
 
 Some technical operators prefer to use sodic sulphite or ammonic 
 bisulphite for the reduction. In the case of using the sodic 
 sulphite the solution of iron must not be too acid and should 
 be dilute, say a volume of half a liter for J gm. of Fe, the 
 sulphite is added and the flask gently heated till the liquid 
 is colourless. It is then boiled briskly till all SO 2 is dissipated, 
 when cooled it is ready for titration with bichromate. In the case 
 of ores containing titanium it is preferable to avoid the use of zinc 
 for reduction, as it reduces also more or less the titanium ; alkaline 
 sulphite does not. 
 
 The ammonic bisulphite is used as follows : (Atkinson C. N. xlvi. 217). 
 To the acid solution of the ore or metal, diluted and filtered, ammonia 
 is added until a faint precipitate of ferric oxide occurs. This is re-dissolved 
 with a few drops of IIC1, and some strong solution of bisulphite added, in 
 the proportion of about 1 c.c. for each O'l gm. of ore, or 0'05 gm. Fe. The 
 mixture is well stirred, boiling water added, then acidified with dilute 
 sulphuric acid, and boiled for half an hour : it is then ready for titration. 
 
 I). J. Carnegie (J. C. 8. liii. 468) points out the value of zinc dust for 
 the rapid reduction of ferric solutions, and suggests the following method 
 of carrying it out. 
 
 The bottom of a dry and narrow beaker is covered with zinc dust sifted 
 through muslin. A known volume of ferric solution, previously nearly 
 neutralized with ammonia, is placed in the beaker and shaken with the zinc 
 dust ; then a known volume of dilute sulphuric acid is added and shaken for 
 a few moments. The reduction is much more rapid in neutral than in acid 
 solutions, but of course acid in this case must be present in excess to keep 
 the iron in solution. Carnegie withdraws a portion of the reduced 
 solution from the undissolved zinc by help of a filter, such as is described on 
 p. 18, and as measured volumes have been used, an aliquot part taken with 
 a pipette may be at once titrated, and the amount of iron found.* 
 
 * Commercial zinc dust is probably a by-product in zinc manufacture, and cannot 
 therefore be obtained pure. Samples examined by myself, and apparently others also, 
 do not, however, contain much iron, but a good deal of zinc oxide with traces of 
 cadmium and lead. Carnegie states that the oxide maybe removed by repeatedly 
 digesting- with weak acid, and still better, by treatment with ammonic chloride and 
 ammonia, the well-washed dust being 'finally dried on porous tiles in a vacuum. 
 I find that by washing once with strong alcohol after the water, and finally with ether, 
 the dust may be rapidly dried in good condition, and when a quantity of such purified 
 dust is obtained, its amount of iron may easily be estimated once for all, and allowed 
 for in titration. Good zinc dust is undoubtedly a valuable reagent in a laboratory for 
 other purposes beside iron titrations. 
 
 P 
 
210 VOLUMETRIC ANALYSIS. 64. 
 
 Clemens Jones in a paper read before the American Institute of 
 Mining Engineers, and which is reproduced in C. N. Ix. 93, adopts the plan 
 suggested by Carnegie, and has designed a special apparatus for filtering 
 the ferric solution through a column of zinc dust. This arrangement gives 
 complete reduction in a very short period of time, and is serviceable where 
 a large number of titrations have to be carried on. 
 
 ESTIMATION OF IRON IN THE FERRIC STATE. 
 1. Direct Titration of Iron by Stannous Chloride. 
 
 64. THE reduction of iron from the ferric to the ferrous state 
 by this reagent has been previously referred to ; and it will be 
 readily seen that the principle involved in the reaction can be made 
 available for a direct estimation of iron, being, in fact, simply 
 a reversion of the ordinary process by permanganate and 
 bichromate. 
 
 Fresenius has recorded a series of experiments made on the 
 weak points of this process, and gives it as his opinion that, with 
 proper care, the results are quite accurate. The summary of his 
 process is as follows : 
 
 (a) A solution of ferric oxide of known strength is first prepared by 
 dissolving 10*04 gm. of soft iron wire (=10 gm. of pure iron) in pure hydro- 
 chloric acid, adding potassic chlorate to complete oxidation, boiling till the 
 excess of chlorine is removed, and diluting the solution to 1 liter.* 
 
 (6) A clear solution of stannous chloride, of such strength that about one 
 volume of it and two of the iron solution are required for the complete 
 reaction (see 37.2). 
 
 (<?) A solution of iodine in potassic iodide, containing about O'OIO gm. 
 of iodine in 1 c.c. (if the operator has the ordinary decinormal iodine solution 
 at hand, it is equally applicable). The operations are as follows : 
 
 (1) 1 or 2 c.c. of the tin solution are put into a beaker with a little starch, 
 and the iodine solution added from a burette till the blue colour occurs ; 
 the quantity is recorded. 
 
 (2) 50 c.c. of the iron solution (-=0'5 gm. of iron) are put into a small 
 flask with a little hydrochloric acid, and heated to gentle boiling (preferably 
 on a hot plate) ; the tin solution is then allowed to flow in from a burette 
 until the yellow colour of the solution is nearly destroyed ; it is then added 
 drop by drop, waiting after each addition until the colour is completely 
 gone, and the reduction ended. If this is carefully managed, there need be 
 no more tin solution added than is actually required; however, to guard 
 against any error in this respect, the solution is cooled, a little starch 
 added, and the iodine solution added by drops until a permanent blue colour 
 is obtained. As the strength of the iodine solution compared with the tin 
 has been found in 1, the excess of tin solution corresponding to the iodine 
 used is deducted from the original quantity, so that by this means the volume 
 of tin solution corresponding to 0'5 gm. of iron is found. 
 
 The operator is therefore now in a position to estimate any 
 
 * A ferric standard may also be made, as suggested by French (C. N. Ix. 271), by 
 dissolving a weighed amount of double iron salt in dilute sulphuric acid, adding- an 
 excess of hydrogen peroxide, warming up, and finally boiling to dissipate the excess of 
 the peroxide. 
 
64 IRON. 211 
 
 unknown quantity of iron which may exist in a given solution, in 
 the ferric state, by means of the solution of tin.* 
 
 If the iron should exist partly or wholly in the state of ferrous 
 oxide, it must be oxidized by the addition of potassic chlorate, and 
 boiling to dissipate the excess of chlorine, as described in a, or 
 with hydrogen peroxide. 
 
 Example : 50 c.c. of iron solution, containing 0*5 gm. of iron, required 
 25 c.c. of tin solution. 
 
 A solution containing an unknown quantity of iron was then taken for 
 analysis, which required 20 c.c., consequently a rule-of-three sum gave the 
 proportion of iron as follows : 
 
 25 : 0'50 gm. : : 20 : 0'40 gm. 
 
 It must be remembered that the solution of tin is not permanent, conse- 
 quently it must be tested every day afresh. Two conditions are necessary in 
 order to ensure accurate results. 
 
 (1) The iron solution must be tolerably concentrated, since the end of 
 the reduction by loss of colour is more distinct ; and further, the dilution of 
 the liquid to any extent interferes with the quantity of tin solution necessary 
 to effect the reduction. Fresenius found that by diluting the 10 c.c. of 
 iron solution with 30 c.c. of distilled water, O'l c.c. more was required than 
 in the concentrated state. This is, however, always the case with stannous 
 chloride in acid solution, and constitutes the weak point in Streng's method 
 of analysis by its means. 
 
 (2) The addition of the tin solution to the iron must be so regulated, that 
 only a very small quantity of iodine is necessary to estimate the excess ; if 
 this is not done another source of error steps in, namely, the influence which 
 dilution, on the one hand, or the presence of great or small quantities of 
 hydrochloric acid on the other, are known to exercise over this reaction. 
 Practically, it was found that where the addition of tin to the somewhat 
 concentrated iron solution was cautiously made, so that the colour was just 
 discharged, the mixture then rapidly cooled, starch added, and then iodine 
 till it became blue, the estimation was extremely accurate. 
 
 2. Titration by Sodic Thiosulphate. 
 
 Scherer first suggested the direct titration of iron by thio- 
 sulphate, which latter was added to a solution of ferric chloride 
 until no further violet colour was produced. This was found by 
 many to be inexact, but Kremer ( Journ. f. Pract. Chem. Ixxxiv. 
 339) has made a series of practical experiments, the result of which 
 is that the following modified method can be recommended. 
 
 The reaction which takes place is such as to produce ferrous 
 chloride, sodic tetrathionate, and sodic chloride. 2S 2 3 Na 2 + 
 Fe 2 Cl 6 + 2HC1 = S 4 6 H 2 + 4ffaCl + 2FeCl 2 . The thiosulphate, 
 which may conveniently be of T ^- strength, is added in excess, 
 and the excess determined by iodine and starch. 
 
 * F. H.. Morgan (Journ. Anal. Chem. ii. 169) points out a very simple and useful 
 method of finding the end-point in titrating iron solutions with stannous chloride 
 without resorting to an indicator. It consists in using a round bottom white glass 
 flask containing the boiling liquid under titration, fixed over a small bluish-coloured 
 B u n s e n flame at a distance of 13 m.m. in a darkened room or a dark corner. So long 
 as the slightest trace of unreduced iron exists, a distinct green colour appears when 
 looking at the faint blue flame through the solution. It is stated that one part of iron 
 as oxide may be recognized in 1,500,000 parts of solution by this means. 
 
 p 2 
 
212 VOLUMETKIC ANALYSIS. 64V 
 
 Process : The iron solution, containing not more than 1 per cent, of metal, 
 which must exist in the ferric state without any excess of oxidizing material 
 (best obtained by adding excess of hydrogen peroxide, then boiling till the 
 excess is expelled), is moderately acidified with hydrochloric acid, sodic 
 acetate added till the mixture is red, then dilute hydrochloric acid until the 
 red colour disappears ; then diluted till the iron amounts to i or i per cent., 
 and T ^5- thiosulphate added in excess, best known by throwing in a particle of 
 potassic sulphocyanide after the violet colour produced has disappeared ; if 
 any red colour occurs, more thiosulphate must be added. Starch and ^ 
 iodine are then used to ascertain the excess. A mean of several experiments 
 gave 100-06 Fe, instead of 100. 
 
 Oudemanns' Method. A simpler process for the direct titra- 
 tion of iron by thiosulphate has been devised by Oudemanns 
 (Z. a. C. vi. 129 and ix. 342), which gives very good results. 
 
 Process: To the dilute ferric solution, which should not contain more 
 than O'l to 0'2 gm. Fe in 100 c.c. nor much free HC1, 3 c.c. of 1 per cent, 
 solution of cupric sulphate are added, 2 c.c. of concentrated hydrochloric 
 acid, and to about every 100 c.c. of fluid, 1 c.c. of a 1 per cent, solution 
 of potassic thiocyanate. 
 
 The mixture may with advantage be very slightly warmed, and the 
 thiosulphate delivered in from the burette at first pretty freely. The red 
 colour produced by the indicator gradually fades away; as this occurs, the 
 thiosulphate must be added in smaller quantities, constantly agitating the 
 liquid until it becomes as colourless as pure water. If any doubt exists as 
 to the exact ending, a slight excess of thiosulphate may be added, and the- 
 quantity found by T ^- iodine and starch. Greater accuracy will always be 
 insured by this latter method. 
 
 The accuracy of the process is not interfered with by the 1 
 presence of salts of the alkalies, strontia, lime, magnesia, alumina,, 
 or manganous oxide ; neither do salts of nickel, cobalt, or copper,, 
 unless their -quantity is such as to give colour to the solution. 
 
 The process is a rapid one, and with care gives very satisfactory 
 results. 
 
 3. Estimation by Iodine and Sodic Thiosulphate. 
 
 When ferric chloride is digested with potassic iodide in excess,, 
 iodine is liberated, which dissolves in the free potassic iodide 
 
 Fed 3 + KI - Fed 2 + KC1 + L 
 
 Process : The hydrochloric acid solution, which must contain no free- 
 chlorine or nitric acid, and all the iron in the ferric state, is nearh r 
 neutralized with caustic potash or soda, transferred to a well-stoppered flask, 
 and an excess of strong solution of potassic iodide added ; it is then heated 
 to 50 or 60 C. on the water bath, closely stoppered, for about twenty 
 minutes ; the flask is then cooled, starch added, and titrated with thiosulphate 
 till the blue colour disappears. This process gives very satisfactory results 
 in the absence of all substances liable to affect the potassic iodide, such as 
 free chlorine or nitric acid, and is particularly serviceable for estimating. 
 small quantities of iron. 
 
' 64 IRON. 213 
 
 4. Estimation of Iron by Colour Titration. 
 
 These methods, which approach in delicacy the Nessler test 
 for ammonia, are applicable for very minute quantities of iron, 
 such as may occur in the ash of bread when testing for alum, water 
 residues, alloys, and similar cases. 
 
 It is first necessary to have a standard solution of iron in the ferric state, 
 which can be made by dissolving 1*004 gm. of iron wire in nitro-hydrochloric 
 acid, precipitating with ammonia, washing and re-dissolving the ferric oxide 
 in a little hydrochloric acid, then diluting to 1 liter. 1 c.c. of this solution 
 contains 1 milligram of pure iron in the form of ferric chloride. It may be 
 further diluted, when required, so as to contain ^ milligram in a c.c./and 
 this is the best standard to use.* The solution for striking the colour is 
 either potassic ferrocyanide or thiocyanate dissolved in water (1 : 20). 
 
 Example with Ferrocyanide : The material containing a minute unknown 
 quantity of iron, say a w r ater residue, is dissolved in hydrochloric acid, and 
 diluted to 100 c.c., or any other convenient measure. 10 c.c. are placed 
 into a white glass cylinder marked at 100 c.c., 1 c.c. of concentrated nitric 
 acid added (the presence of free acid is always necessary in this process), then 
 diluted to the mark with distilled water, and well stirred. 
 
 1 c.c. of ferrocyanide solution is then added, well mixed, and allowed to 
 stand at rest a few minutes to develop the colour. 
 
 A similar cylinder is then filled with a mixture of, say 1 c.c. of standard 
 iron solution, 1 c.c. nitric acid and distilled water, and 1 c.c. ferrocyanide 
 added ; if this does not approach the colour of the first mixture, other 
 quantities of iron are tried until an exact similarity of colour occurs. The 
 exact strength of , the iron solution being known, it is easy to arrive at the 
 quantity of pure iron present in the substance examined, and to convert 
 it into its state of combination by calculation. 
 
 Carter Bell (J. S. C. I. viii. 175) adopts the following plan in 
 the case of waters : 70 c.c. of the water are evaporated to 
 dryrjess in a platinum dish, and gently ignited to burn off organic 
 matters. 1 c.c. of dilute nitric acid, 50 c.c. of strong acid in 
 a liter, is then poured over the residue from a pipette, and 
 evaporated to dryness in the water bath ; the residue is then 
 dissolved in 1 c.c. of a 10 per cent, hydrochloric acid, 5 or 10 c.c. 
 of distilled water added, and the solution filtered and washed 
 through a small filter, and made up to 50 c.c. in a Messier glass; 
 and finally tested with 1 c.c. each of ferrocyanide solution and 
 nitric acid. 
 
 With Thiocyanate. Thomson (J. C. S. 1885, 493) recom- 
 mends this method as being specially available in the presence of 
 other ordinary metals and organic matters, silver, copper, and 
 cobalt being the only interfering substances. The delicacy is said 
 to be such, that 1 part of iron can be recognized in 50 million parts 
 of water. The presence of free mineral acids greatly adds to the 
 
 * A solution of this strength can also be made by weighing 0'7 gin. of pure ammonio- 
 ferrous sulphate ( 34.2b), dissolving in water, acidifying- with sulphuric acid, adding 
 sufficient permanganate solution to convert the iron exactly into ferric salt, then 
 diluting to 1 liter. Hydrogen peroxide may also be used in place of permanganate, 
 taking care to dissipate the excess by boiling. 
 
214 VOLUMETRIC ANALYSIS. 65. 
 
 sensitiveness. The standard ferric solution may be the same as for 
 ferrocyanide ; and in preparing the material for titration, the 
 weighed quantity is dissolved in an. appropriate acid, evaporated 
 nearly to dryness, taken up with water, converted into the ferric 
 state by cautious addition of permanganate, then diluted with water 
 to a measured volume, and an aliquot portion taken for titration. 
 
 The standard iron used by Thomson y 1 ^ m.gm. per c.c. 
 (0*7 gm. double iron salt [oxidized] per liter). 
 
 Example : Into two colourless glass cylinders marked at 100 c.c. pour 
 5 c.c. of nitric or hydrochloric acid (1 : 5), together with 15 c.c. of 
 thiocyanate, and to one glass a measured volume of the solution to be tested : 
 fill up both glasses to the mark with pure water. If iron be present, a blood 
 red colour more or less intense will be produced. Standard iron is then 
 cautiously added from a burette to the other glass till the colour agrees. 
 The quantity of Pe taken should not require more than 2 or 3 c.c. of the: 
 standard to equal it, or the colour will be too deep for comparison. 
 
 If other metals are present which form two sets of salts, they 
 must be in the higher state of oxidation, or the colour is destroyed. 
 Oxalic acid also destroys it. Examples in the presence of a great 
 variety of metals show very good results. 
 
 IRON ORES. 
 
 65. THE great desideratum in the analysis of iron ores is 
 to get them into the finest possible state of division, and ten 
 minutes' hard work with the agate mortar will often save hours 
 of treatment of the material with acids. The operator of 
 experience can generally tell if the ore to be examined will dissolve- 
 in acids. Some clay iron stones and brown haematites contain 
 organic matters, and they are best first roasted in an open platinum 
 crucible, gradually raising the heat to redness; this course is 
 advisable also when an ore contains pyrites ; this latter is easily 
 converted to Fe 2 3 by roasting. The proportion in iron ores is 
 generally under half a per cent. Some ores give a residue in any 
 case by treatment with HC1, this should be separated by nitration and 
 fused with sodic carbonate which will render all the iron in a soluble 
 state. In the analysis of iron ores it is very often necessary to. 
 determine not only the total amount of iron, but also the state in 
 which it exists; for instance, magnetic iron ore consists of 
 a mixture of the two oxides in tolerably definite proportions, and 
 it is sometimes advisable to know the quantities of each. 
 
 In order to prevent, therefore, in such cases, the further oxidation 
 of the ferrous oxide, the little flask apparatus (fig. 43) adopted by 
 Mohr is recommended, or fig. 42 is equally serviceable. 
 
 The left-hand flask contains the weighed ore in a finely powdered state, to 
 which, tolerably strong hydrochloric acid is added ; the other flask contains- 
 distilled water only, the tube from the first flask entering to the bottom of the 
 second. When the ore is ready in the flask and the tubes fitted, hydrochloric 
 acid is poured in, and a few grains of sodic bicarbonate added to produce 
 
IRON ORES. 
 
 215 
 
 a flow of CO' 2 . The air of the flask is thus dispelled, and as the acid dissolves 
 the ore, the gases evolved drive out in turn the CO-, which is partly absorbed 
 by the water in the second flask. When the ore is all dissolved and the 
 lamp removed, the water immediately rushes out of the second flask into the 
 first, diluting and cooling the solution of ore, so that, in the majority 
 of cases, it is ready for immediate titration. If not sufficiently cool or 
 dilute, a sufficient quantity of boiled and cooled distilled water is added. 
 
 When the total amount of iron present in any sample of ore has 
 to be determined, it is necessary to reduce any peroxide present to- 
 the state of protoxide previous to titration. 
 
 Reduction to the Ferrous state may be done by sodic sulphite 
 in dilute solution, but not so with stannous chloride, the latter 
 must be used in a boiling and concentrated solution strongly 
 acidified with hydrochloric acid. Most technical operators now 
 use the tin method, which, by the help of mercuric chloride as 
 described 63.2, is rendered both rapid and trustworthy. Both 
 with the sulphite and tin method bichromate is the invariable 
 titrating solution. When permanganate is to be used for titration 
 the reduction is always best made with zinc or magnesium in 
 sulphuric or very weak hydrochloric acid solution. With bichro- 
 mate, the best agent is either pure sodic sulphite, ammonic 
 bisulphite, or stannous chloride. 
 
 1. Bed and Brown Haematites. Red haematite consists generally 
 of ferric oxide accompanied with matters insoluble in acids. 
 Sometimes, however, it contains phosphoric acid, manganese, and 
 earthy carbonates. 
 
 Brown haematite contains hydrated ferric oxide, often accompanied 
 
216 VOLUMETRIC ANALYSIS. 65. 
 
 "by small quantities of ferrous oxide, manganese, and alumina ; 
 sometimes traces of copper, zinc, nickel, cobalt, with lime, magnesia 
 and silica ; occasionally also organic matters. 
 
 In cases where the total iron only has to be estimated, it is 
 advisable to ignite gently to destroy organic matters, then treat 
 with strong hydrochloric acid at near boiling heat till all iron is 
 dissolved, and in case ferrous oxide is present add small quantities 
 of potassic chlorate, afterwards evaporating to dryness to dissipate 
 free chlorine ; then dissolve the iron with hot dilute hydrochloric 
 acid, filter, and make up to a given measure for reduction and 
 titration. 
 
 In some instances the insoluble residue persistently retains some 
 iron in an insoluble form; when this occurs, resort must be had to 
 fluxing the residue with sodic carbonate, followed by solution in 
 hydrochloric acid. 
 
 2. Magnetic Iron Ore. The ferrous oxide is determined first by 
 means of the apparatus fig. 42 or 43. The ore is put into the 
 vessel in a state of very fine powder, strong hydrochloric acid 
 added, together with a few grains of sodic bicarbonate, and heat 
 applied gently with the lamp until the ore is dissolved, then 
 diluted if necessary, and titrated with bichromate or permanganate. 
 Technical operators generally use only a covered beaker. 
 
 Example : 0"5 gm. of ore was treated as above, and required 19"5 c.c. of 
 xo- bichromate, which multiplied by 00)56 gave 0-1032 gin. of iron = Q-14D4 
 gm. of ferrous oxide = 28"08 per cent. FeO. 
 
 The ferric oxide was now found by reducing 0'5 gm. of the same ore, and 
 estimating the total iron present: the quantity of bichromate required was 
 59 c.c. T ^=0-3304 gm. total Fe 
 Deduct 0-1092 gm. Fe as FeO 
 
 Leaving 0'2212 gm. Fe as Fe-O 3 
 
 The result of the analysis is therefore 
 
 Ferrous oxide 28'08 per cent. 
 
 Ferric oxide 63'20 
 
 Difference (Gangue, etc.) ... 872 
 
 100-00 
 
 3. Spathose Iron Ore. The total amount of ferrous oxide in 
 this carbonate is ascertained directly by solution in hydrochloric 
 acid ; as the carbonic acid evolved is generally sufficient to expel 
 all air, the tube dipping under water may be dispensed with. If 
 the ore contains pyrites it should be first roasted, but this of course 
 converts the ferrous carbonate into Fe 2 3 . 
 
 As the ore contains, in most cases, the carbonates of manganese, 
 lime, and magnesia, these may all be determined, together with the 
 iron, as follows : 
 
 A weighed portion of ore is brought into solution in hydrochloric acid, 
 after ignition if pyrite is present, and filtered, if necessary, to separate 
 insoluble silicious matter. 
 
Go. IRON ORES. 217 
 
 The solution is then boiled, Avith a few drops of nitric acid to peroxidize 
 the iron, diluted, nearly neutralized with ammonia, and a solution of 
 ummonic acetate added, then boiled for two minutes and allowed to settle. 
 The precipitate is collected on a filter and washed with boiling water, 
 containing a little ammonic acetate. It is then dissolved off the filter in 
 HC1 which also dissolves any A1 2 O 3 or P 2 O 5 which may be present. The 
 liquid is then evaporated, reduced, and titrated as usual. " 
 
 The filtrate from the above is concentrated by evaporation, cooled, 3 or 
 4 c.c. of bromine added, and well mixed by shaking; when most of the 
 bromine is dissolved the liquid is rendered alkaline by ammonia, and gently 
 warmed till the Mn separates in large flocks as hydrated oxide, which is 
 collected and titrated by one of the methods in 67. 
 
 The filtrate from the last is mixed with ammonic oxalate to precipitate the 
 lime, which is estimated by permanganate, as in 52. 
 
 The filtrate from the lime contains the magnesia, which may be precipitated 
 with sodic phosphate and ammonia, and the precipitate weighed as usual, or 
 titrated with uranium solution. 
 
 4. Estimation of Iron in Silicates. Wilbur and Wllittlesey 
 (C. N. xxii. 5) give a series of determinations of iron existing in 
 various silicates, either as mixtures of ferric and ferrous salts or of 
 either separately, which appear very satisfactory. 
 
 The very finely powdered silicate is mixed with rather more than its own 
 weight of powdered fluor-spar or cryolite (free from iron) in a platinum 
 crucible, covered with hydrochloric acid, and heated on the water-bath until 
 the silicate is all dissolved. During the digestion either carbonic acid gas or 
 coal gas free from H 2 S is supplied over the surface of the liquid so as to 
 prevent access of air. When decomposition is complete (the time varying 
 with the nature of the material), the mixture is diluted and titrated with 
 permanganate in the usual way for ferrous oxide ; the ferric oxide can then 
 be reduced by zinc and its proportion found. 
 
 By Hydrofluoric Acid. 2 gm. of the finely powdered silicate are placed 
 in a deep platinum crucible, and 4O c.c. of hydrofluoric acid (containing 
 about 20 per cent. HF) added. The mixture is heated to near the boiling 
 point and occasionally stirred with a platinum wire until the decomposition 
 of the silicate is complete, which occupies usually about ten minutes. 10 c.c. 
 of pure H 2 SO 4 diluted with an equal quantity of water are then added, and 
 the heat continued for a few minutes. The crucible and its contents are 
 then quickly cooled, diluted with fresh boiled water, and the ferrous salt 
 estimated with permanganate or bichromate as usual. 
 
 Leeds (Z. a. C. xvi. 323) recommends that the finely powdered 
 silicate be mixed with a suitable quantity of dilute sulphuric 
 acid, and air excluded by CO 2 during the action of the hydrofluoric 
 acid. The titration may then at once be proceeded with when the 
 decomposition is complete. 
 
 If the hydrofluoric acid has been prepared in leaden vessels, it 
 invariably contains SO 2 ; in such cases it is necessary to add to it, 
 previous to use, some hydrogen peroxide (avoiding excess) so as to 
 oxidize the SO 2 . 
 
 The process is a rapid and satisfactory one, yielding much more 
 accurate results than the method of fusion with alkaline carbonates 
 or acid potassic sulphate. 
 
218 VOLUMETRIC ANALYSIS. 65. 
 
 5. Colorimetric estimation of Carbon in Steel and Iron. The 
 method devised by Eggertz, and largely adopted by chemists, for 
 estimation of combined carbon, is well known, but is open to the 
 objection that minute quantities of carbon cannot be discriminated 
 by it, owing to the colour of the ferric nitrate present. Stead 
 (G. N. xlvii. 285) in order to overcome this difficulty has devised 
 a method described as follows : 
 
 In some careful investigations on the nature of the colouring 
 matter which is produced by the action of dilute nitric acid upon 
 white iron and steel, it was found it had the property of being 
 soluble in potash and soda solutions, and that the alkaline solution 
 had about two and a half times the depth of colour possessed by 
 the acid solution. This being so, it was clear that the colouring 
 matter might readily be separated from the iron, and be obtained 
 in an alkaline solution, by simply adding an excess of sodic 
 hydrate to the nitric acid solution of iron, and that. the coloured 
 solution thus obtained might be used as a means of determining 
 the amount of carbon present. Upon trial this was found to 
 be the case, and that as small a quantity as OO3 per cent, of 
 carbon could be readily determined. 
 
 The solutions required are : 
 
 Standard solution of Nitric acid, 1 '20 sp. gr. 
 
 Standard solution of Sodic hydrate, 1'27 sp. gr. 
 
 Process : One gram of the steel or iron to be tested is weighed off and 
 placed in a 200 c.c. beaker, and after covering with a watch-glass, 12 c.c. 
 of standard nitric acid are added. The beaker and contents are then placed 
 on a warm plate, heated to about 90 to 100 C., and there allowed to remain 
 until dissolved, which does not usually take more than ten minutes. At the 
 same time a standard iron containing a known quantity of carbon is treated 
 in exactly the same way, and when both are dissolved 30 c.c. of hot water 
 are added to each, and 13 c.c. soda solution. 
 
 The contents are now to be well shaken, and then poured into a glass 
 measuring-jar and diluted till they occupy a bulk of 60 c.c. After again 
 well mixing and allowing to stand for ten minutes in a warm place, they are 
 filtered through dry filters, and the filtrates, only a portion of which is used r 
 are compared. This may be done by pouring the two liquids into two 
 separate measuring tubes in such quantity or proportion that upon looking 
 down the tubes the colours appear to be equal. 
 
 Thus if 50 measures of the standard solution are poured into one tube, and if 
 the steel to be tested contains say half as much as the standard, there will be 
 100 measures of its colour solution required to give the same tint. The carbon 
 is therefore inversely proportional to the bulk compared with the standard, 
 and in the above assumed case, if the standard steel contained 0'05 per cent, 
 carbon,, the following simple equation would give the carbon in the sample 
 tested : 
 
 0'05 x 50 
 
 ,,-.,-. = 0'02o per cent. 
 
 J-Ul/ 
 
 The proportions here given must be strictly adhered to in order to insure 
 exactness. The colours from low carbon irons differ in tint from those in 
 high carbon steels, and therefore a low standard specimen must be used for 
 comparison. It is evident that the safest plan to insure absolute comparison 
 
65. IRON. 219 
 
 is to weigh and dissolve a known standard steel or iron for each batch 
 of tests. 
 
 Stead has devised a special colorimeter for the process, but it is 
 evident that any of the usual instruments may be used. 
 
 Arnold (Steel Works Analysts, p. 46) gives the following 
 conditions as necessary for the accurate working of the Eggertz 
 test. 
 
 (a) The standard steel should have been made by the same process as the 
 sample. 
 
 (b) The standard should be in the same physical condition, as far as this 
 can be secured by mechanical means. 
 
 (c) The standard should not differ greatly in the percentage of carbon. 
 
 (d) The solution of the standard and the samples should be made at the 
 same time, and under identical conditions, and the comparisons should be 
 made without delay. 
 
 (e) Above all, the standard should be above suspicion, its carbon contents* 
 having been settled on the mean of several concordant combustions made on 
 different weights of steel from a homogeneous bar. 
 
 6. Estimation of Arsenic in Iron Ores, Steel, and Pig- Iron 
 (J. E. Stead). The best method of separating arsenic from iron 
 solutions is undoubtedly that of distilling with hydrochloric acid 
 and ferrous chloride. 
 
 Stead found after many trials and experiments, that if the 
 distillation is conducted in a special manner, the whole of the 
 arsenic may be obtained in the distillate, unaccompanied with any 
 traces of chloride of iron, and that if the hydrochloric acid is 
 nearly neutralized with ammonia, and finally completely neutralized 
 with bicarbonate of soda, the arsenic can be determined 
 volumetrically with a standard solution of iodine. 
 
 The standard solutions required are : 
 
 Arsenious oxide. O66 gin. (0'5 gm. metallic arsenic) of pure 
 arsenious acid in fine powder is weighed and placed into a flask, 
 with '2 gm. of sodic carbonate and 100 c.c. of boiling distilled 
 water, and the liquid boiled till all the arsenious oxide has 
 dissolved. When cool, 2 gm. of sodic bicarbonate are added 
 and diluted to one liter : 1 c.c. = 0'0005 gm. As. 
 
 Iodine solution. 1*275 gm. of pure iodine is dissolved in 2 gm. 
 of potassic iodide and water, the solution diluted to one liter, then 
 standardized by titrating 20 c.c. of the arsenious solution. If the 
 iodine. has been pure, 20 c.c. of the solution should be required to 
 just produce a permanent blue with starch indicator. 
 
 These solutions keep fairly well without alteration for several 
 months. It is advisable, however, to periodically ascertain the 
 value of the iodine by titrating 20 or 30 c.c. of the arsenic 
 solution. 
 
 Process for Steel: Prom 1 to 50 gm. of the steel in drillings are 
 introduced into a 30-ounce flask, and a sufficient quantity of equal parts of 
 strong hydrochloric acid and water is added to dissolve it. The mouth of the 
 flask is closed with a rubber cork carrying a safety tube, and a tube to 
 
220 VOLUMETRIC ANALYSIS. 65. 
 
 convey the gas evolved into the Winkler's spiral absorption tubes, 
 containing a strong saturated solution of bromine in water. 
 
 The tube is filled to one-third of its length with the solution, and about 
 i c.c. of free bromine is run in to replace the bromine which is consumed or 
 carried out with the passing gas. 
 
 The contents of the flask are now gently heated to such a degree that 
 a steady but not rapid current of gas passes through the bromine solution. 
 
 In about one hour the whole of the steel will be dissolved, and when no 
 more evolution of hydrogen can be observed, the liquid in the flask is w r ell 
 boiled, so as to completely drive all the gas into and through the bromine 
 solution. 
 
 The absorption tube is now disconnected, and the bromine solution 
 containing that part of the arsenic which has passed off as gas is rinsed out 
 into a small 100 c.c. beaker, and the excess of bromine is gently boiled off, 
 and the clear colourless solution is poured into the flask. About 0'5 gm. of 
 .zinc sulphide is now dropped into the iron solution and the contents are 
 violently shaken for about three minutes, by which time the whole of the 
 arsenic will be in the insoluble state, partly as sulphide and partly as a black 
 precipitate of possibly free arsenic and arsenide of iron. 
 
 It has been found that violent agitation for a few minutes is quite as 
 efficacious in effecting the complete separation of arsenic sulphide as by the 
 method of passing a current of CO 2 through the solution to remove the 
 excess of hydric sulphide, or by allowing it to stand ten or twenty hours to 
 settle out. 
 
 The insoluble precipitate is now rapidly filtered through a smooth filter- 
 paper, and the flask is rinsed with cold distilled water. The precipitate 
 usually does not adhere to the filter, and in such cases the paper is spread 
 out flat upon a porcelain slab, and the arsenic compounds are rinsed off with 
 a fine jet of hot water into a small beaker. The precipitate is now dissolved 
 in bromine water, and a drop or two of HC1. 
 
 The bromine solution now containing all the arsenic is gently boiled to 
 expel the bromine, and it is then poured into a 10-ounce retort and is 
 distilled with ferrous chloride and hydrochloric acid. 
 
 The apparatus used consists of an ordinary Liebig's condenser, but the 
 retort has its neck bent to an angle of about 150, and this is attached to the 
 condenser, so that any iron mechanically carried over may run back. By 
 this device, the distillate w r ill never contain more than the very slightest 
 trace of iron. 
 
 The solution containing the arsenic having been run into the retort, the 
 beaker is washed out and the washings are also poured in. If the solution 
 is much above 20 c.c. in bulk, it is advisable to add a strong solution of 
 ferrous chloride containing about 0'5 gm. of iron in the ferrous state, and 
 for this purpose nothing answers so well as a portion of the steel solution 
 remaining after separating the arsenic, which is first well boiled to free it 
 from hydric sulphide, and should contain about 10 per cent, of soluble iron 
 as ferrous chloride. 5 c.c. of this solution will contain the necessary amount 
 of iron to add to the retort. After adding the chloride, it is best to boil 
 down the solution to about 20 c.c. before adding any HC1, taking care, of 
 course, to collect what liquid distils over. When the necessary concentration 
 has been effected, 20 c.c. strong HC1 is run in, and the distillation is 
 continued till all excepting about 10 c.c. has passed over. A further 
 quantity of 20 c.c. mixed with 5 c.c. of water is run in, and this is all 
 distilled over. At this point, as a rule, all the arsenic will have passed into 
 the distillate, but it is advisable to make quite certain, and to add a third portion 
 of acid and w r ater, and to distil it over. If the distillation has not been 
 forced, the distillate will be quite colourless. The arsenic in the distillate 
 will exist as arseaious chloride, accompanied with a large excess of 
 hydrochloric acid. A drop of litmus is put into this solution, and strong 
 
65. 
 
 IRON. 221 
 
 ammonia is run in until alkaline. It is now made slightly acid with a few 
 drops of HC1, and a slight excess of solid bicarbonate of soda is dropped in. 
 The contents of the flask are now cooled by a stream of water, and, after 
 adding a clear solution of starch, the standard iodine is run in from a burette 
 till a deep permanent blue colouration is produced. 
 
 If the steel or iron contains much arsenic, a smaller quantity, say, one or 
 two gm., may be dissolved in nitric acid of T20 specific gravity and the 
 solution evaporated to dryness, the residue being dissolved in hydrochloric 
 acid, and the solution transferred to the retort, and distilled directly with 
 ferrous chloride and hydrochloric acid, care being taken that the distillation 
 is not forced, so as to avoid any of the iron solution passing over into the 
 distillate. 
 
 Process for Pig Iron : In testing pig irons, they may be dissolved in 
 nitric acid and evaporated to dryness, or be treated in a flask with HC1 
 exactly in the manner described above, but it is advisable, if the latter 
 method is adopted, after treating the voluminous mass of silica and 
 graphite, &c., with bromine and hydrochloric acid, to filter off the insoluble 
 matter and distil the clear solution. 
 
 Process for Iron Ores : In testing ores, it is only necessary to place the 
 powdered ore directly into the retort, and distil at once with HC1 and 
 ferrous chloride, taking care to place a few pieces of fire-brick also in the- 
 vessel, to avoid bumping. 
 
 If the ore contains much manganese, it is advisable to dissolve it in 
 a separate vessel to liberate and expel the chlorine, and then to transfer it 
 into the retort. 
 
 The time taken to test iron or steel need not exceed two hours, and for 
 iron or other ores not much more than half an hour. 
 
 It is quite possible to accurately determine as small a quantity as 0'002 
 per cent, of arsenic by this method. 
 
 When dissolving steels in dilute HC1, if there is no rust on the sample or 
 ferric chloride present in the acid, and the presence of air is carefully 
 avoided, as a rule only about one-tenth of the total arsenic present passes off 
 with the gas. 
 
 Platten's method, alluded to on page 149, depends on the fact 
 that when sulphide of arsenic (obtained by treating the arsenical 
 distillate with H 2 S) is boiled with pure water, the gas escapes, and 
 arsenious oxide remains in solution. This solution is then titrated 
 with iodine in the usual way. 
 
 Both methods have been proved to give identical results, when 
 carried out by separate skilled operators on the same samples of 
 material. 
 
 7. Estimation of Phosphorus in Iron and Steel. Dudley and 
 Pease (/. Anal. Cliem. vii. 108) adopt the following method: 
 
 1 gm. of the sample is dissolved in an Erlenmeyer flask, in 75 c.c. of 
 nitric acid of sp. gr. T15 ; when dissolved, it is boiled for a minute and 
 mixed with 10 c.c. of a solution of potassic permanganate, and then again 
 boiled until manganese dioxide begins to separate. The liquid is now 
 cleared by the cautious addition of pure ferrous sulphate, heated to 85 C., 
 and mixed with 75 c.c. of ammonium molybdate solution at 27 C. After 
 shaking for five minutes in a whirling apparatus, the precipitate is washed 
 with solution of ammonic sulphate until the washings give no colouration 
 with ammonic sulphide, and then dissolved in a mixture of 5 c.c. of 
 ammonia and 25 c.c. of water. The solution is now mixed with 10 c.c. of 
 
222 VOLUMETKIC ANALYSIS. 66. 
 
 strong sulphuric acid, diluted to 200 c.c., and reduced with zinc. The 
 solution is then titrated with permanganate. The volume of the latter 
 which represents 1 gm. of Pe equals 0'0172444 gm. of P. 
 
 8. Estimation of Sulphur in Iron and Steel. The necessary 
 solutions for this method are 
 
 Standard iodine, 1 c.c. of which equals 1 m.gm. of S, made by 
 dissolving 7 '9 gm. of pure iodine with 16 gm. of potassic iodide 
 in a liter of water. 
 
 Standard sodic thiosulphate of corresponding strength this 
 solution should also contain about 20 gm. of sodic bicarbonate in 
 the liter. The two solutions are adjusted by titration with starch. 
 
 Solution of caustic soda 280 gm. of good commercial hydrate 
 are dissolved in a liter of water, and as the soda generally contains 
 some substances capable of liberating iodine, a titration must be 
 made for each lot of solution to find the constant for that 
 particular solution. 
 
 Process : 5 gm. of drillings are put into a 20 oz. flask, to which is fitted 
 a rubber stopper with two holes, through one of which is a safety funnel 
 and the other a blank pipette, the upper end of which is bent twice at right 
 angles, and attached by a small rubber stopper to a f-in. bulb \J tube. 
 Into this latter is put 7 c.c. of the caustic soda solution and the apparatus 
 put together. 75 c.c. of dilute HC1 (2 acid 1 water) are poured through the 
 funnel, and the flask placed over a burner and heated moderately until the 
 steel is dissolved. The tube containing the soda solution is disconnected, 
 poured and washed into a beaker containing 15 c.c. of dilute H-SO 4 (1 : 4) 
 mixed with as much iodine solution as will be in excess of the sulphur 
 expected. The mixture is diluted to about 200 c.c. and at once titrated 
 with thiosulphate and starch. The number of c.c. of iodine required, plus 
 the caustic soda constant, multiplied by 20 will give the percentage of 
 sulphur. 
 
 LEAD. 
 
 Pb = 206-4. 
 
 1 c.c. -3^- permanganate =0*01032 gin. Lead. 
 1 c.c. normal oxalic acid = 0'1032 gm. ,, 
 Metallic iron x 1'846= 
 
 Double iron salt x 0'263 = 
 
 66. THE accurate estimation of lead is in most cases better 
 effected by weight than by measure ; th^re are, however, instances 
 in which, the latter may be used with advantage. 
 
 1. As Oxalate (Hem pel). The acetic lead solution, which must contain 
 no other body precipitable by oxalic acid, is put into a 300 c.c. flask, and 
 a measured quantity of normal oxalic acid added in excess, the flask filled to 
 the mark with water, shaken, and put aside to settle ; 100 c.c. of the clear 
 liquid may then be taken, acidified with sulphuric acid, and titrated with 
 
 rmanganate for the excess of oxalic acid. The amount so found multiplied 
 3, and deducted from that originally added, will give the quantity 
 combined with the lead. 
 
 Where the nature of the filtrate is such that permanganate cannot be used 
 
66. LEAD. 223 
 
 for titration, the precipitate must be collected, well washed, dissolved in 
 dilute nitric acid, with a considerable quantity of sodic acetate, sulphuric 
 acid added, and titrated with permanganate. 
 
 In neither case are the results absolutely accurate, owing to the slight 
 solubility of the precipitate, but with careful manipulation the error need 
 not exceed 1 per cent. The error is much increased in the presence of 
 ammoniacal salts. 
 
 The technical analysis of red lead is best made as follows : 
 
 2*064 gm. ( 7 V eq. of Pb) are placed in a 300 c.c. porcelain basin, and 20 or 
 30 c.c. nitric acid sp. gr. 1'2 poured over it, then warmed gently with stirring. 
 In a few minutes the lead oxide is dissolved and the peroxide left insoluble. 
 50 c.c. of oxalic acid are added and the mixture boiled : this decomposes 
 and dissolves the peroxide, leaving undissolved uny adulterant such as baryta, 
 lead sulphate, oxide of iron, gypsum, or sand. While still hot f permanganate 
 is added in moderate portions until the colour is permanent for a few seconds. 
 The volume of permanganate deducted from 50 gives direct the percentage 
 of lead existing as peroxide. 
 
 The total lead may be found in the same solution b}' removing the excess 
 of permanganate with a drop or two of oxalic acid, neutralizing with ammonia, 
 adding a good excess of ammonic or sodic acetate, and titrating with bichro- 
 mate as described in this section. 
 
 Lead acetates in crystals or in solution may readily and with 
 tolerable accuracy be titrated direct with normal oxalic acid. The 
 best effects are obtained however by adding the lead solution 
 (diluted and rendered clear by a little acetic acid) from a burette 
 into the oxalic acid contained in a flask or beaker, warmed by 
 a water-bath. The addition of the lead solution is continued with 
 shaking and warming until no further precipitation takes place. 
 
 Another method for acetates is to precipitate the lead with 
 a slight excess of normal sulphuric acid in a 300 c.c. flask, fill 
 to the mark, estimate the excess of H 2 S0 4 in 100 c.c. by weight, 
 then calculate the combined acid into lead ; then by titrating 
 another portion for acidity with phenolphthalein, the proportion 
 of acetic acid can be obtained by deducting the free H 2 S0 4 from 
 the total acid found. 
 
 2. As Chromate (Schwarz). The lead is precipitated as chromate, 
 <well washed, and digested with a weighed excess of double iron salt and 
 hydrochloric acid; the resulting solution contains ferric and chromic 
 chlorides, together with lead chloride, and undecomposed iron salt. The 
 quantity of the last is found by permanganate, and deducted from the 
 original weight; the remainder, multiplied by the factor 0'263, will give the 
 weight. of lead. 
 
 The difficulty with this method is the end-point, owing to the 
 confusion produced by the yellow chromate. Diehl (Z. a. C. 1880, 
 -306) modified the process by precipitating the lead with excess 
 of bichromate and estimating the excess by thiosulphate, but this 
 again is open to the objection of an indistinct end-point. 
 
 Cushman and Hayes Campbell (Journ. Amer. Chem. Sac. 
 xvii. 901) have, however, modified the process so as to be 
 workable. Their method consists in titrating the solution after 
 
224 VOLUMETRIC ANALYSIS. 66, 
 
 filtering off the precipitated lead chromate, with a standard 
 solution of ammonio-ferrous sulphate, using ferricyanide as an 
 outside indicator, under exactly the same conditions observed in 
 standardizing bichromate solutions. The bichromate solution is 
 made up of convenient empirical strength, and standardized 
 against a weighed amount of pure ammonio-ferrous sulphate. 
 Slightly more than the equivalent weight of the latter salt is then 
 weighed out and dissolved in a liter of water, with the addition 
 of a few drops of sulphuric acid. The solution is transferred to- 
 a stock bottle into which is immediately poured a sufficient 
 quantity of some light paraffin oil to form a layer over the solution r 
 thus protecting it from oxidation. The stock bottle is fitted with 
 a syphon tube and pinch-cock, so that the solution can be drawn 
 out when needed. With this arrangement change in strength 
 of the ammonio-ferrous sulphate solution takes place very slowly,, 
 while, as a few moments only are required to titrate it against the 
 standard bichromate, its exact strength can be easily determined 
 from day to day. 
 
 Process : About 1 gm. of finely pulverized ore is digested in a casserole or 
 evaporating dish with 15 c.c. of a mixture of two parts of nitric acid and 
 one part sulphuric acid, until decomposition is complete. 10 c.c. more 
 of sulphuric acid are now added, and the liquid evaporated until it fumes 
 freely. Cool, dilute with 10 c.c. of dilute sulphuric acid (1 10), and then 
 add gradually 40 c.c. of water. Heat to boiling, filter, and wash by 
 decantation with dilute sulphuric acid (1 10), getting as little of the lead 
 sulphate on the filter as possible. To the residue in the dish add 20 c.c. 
 of strong ammonia, then make slightly acid with acetic acid. Boil until the 
 lead sulphate is dissolved, then pour the liquid through the filter, having first 
 moistened the paper with ammonia. Wash the filter with water containing 
 ammonic acetate in solution, and finally once or twice with hot water. 
 Cool the filtrate, and run in from a burette an excess of standard bichromate 
 solution, stirring until the precipitate settles rapidly and the supernatant 
 liquid has a yellow colour. Allow to settle for a few minutes, then filter, 
 under pressure if possible ; wash a few times, and titrate the filtrate against 
 the standard ammonio-ferrous sulphate. 
 
 After a little practice the method can be carried out as above detailed 
 in about thirty minutes. In case the ore is known to be free from bismuth 
 and antimony, the method can be materially shortened. Instead of bringing 
 the ore into solution with a mixture of nitric and sulphuric acids, nitric acid 
 alone is used. After solution the acid is neutralized with an excess of 
 ammonia, and "then made acid with acetic acid : this dissolves any lead 
 sulphate that has been formed. This solution is then immediately titrated 
 with the bichromate and ammonio-ferrous sulphate solutions exactly as 
 described above. In general it may be said that the results are a trifle low. 
 The mean of the amount of lead recovered in twenty determinations. was 
 99'6 per cent, of that taken. 
 
 3. Alkalimetric Method (M o h r) . The lead is precipitated as carbonate 
 by means of a slight excess of ammonic carbonate, together with free 
 ammonia : the precipitate well washed, and dissolved in a measured excess 
 of normal nitric acid; neutral solution of sodic sulphate is then added 
 to precipitate the lead as sulphate. "Without filtering, the excess of nitric 
 acid is then estimated by normal alkali, each c.c. combined being equal to 
 0'1032 gm. of lead. 
 
66. LEAD. 225 
 
 4. As Sulphide (Casamaj or). The lead, if not in a state convenient 
 for titration, is separated as sulphate, well washed, and while still moist is 
 dissolved in alkaline tartrate solution exactly as in the case of copper (see 
 58.5) ; the precipitated sulphide separates very freely, and if the operation 
 is performed in a white basin the end-point is easy of detection. 
 
 The chief drawback to the method is the instability of the sulphide 
 solution, which necessitates a fresh standardizing with known quantities of 
 metal every day. 
 
 5. Estimation of Lead in presence of Tin. For technical purposes 
 this may be readily done as follows : 
 
 The alloy is treated with nitric acid, by which means the lead is dissolved, 
 and the tin rendered insoluble as stannic acid. The excess of nitric acid is 
 removed by a very faint excess of sodic hydrate, then slightly acidified with 
 acetic acid. The solution is diluted, so that it contains not less than half 
 a per cent, of lead. It is then titrated with a standard solution of potassic 
 ferrocyanide containing 10'2 gm. per liter, Avhich has been standardized 
 against a lead nitrate solution containing 15'987 gm. per liter, using drops 
 of ferric chloride solution on a white plate as indicator. 
 
 6. Colorimetric estimation. Where there is no other metal 
 than lead present, simple addition of freshly made sulphuretted 
 hydrogen water in the presence of weak acetic acid as suggested 
 by Miller gives good results, comparison being made with 
 a standard solution of lead acetate containing 0*1831 gm. per liter. 
 Each c.c. = O'OOOl gm. lead. The estimation is made in colourless 
 glass cylinders in the same way as described for copper or iron 
 58, 64, taking care that the comparative tests are made under 
 precisely the same conditions. 
 
 7. Leadin Citric and Tartaric Acids, etc. Warington has worked 
 out the best method of ascertaining the proportions of lead in 
 these commercial acids, and shows that ammonium sulphydrate 
 is to be preferred to sulphuretted hydrogen for the process, 
 inasmuch as the tint produced is much more uniform throughout 
 a long scale, and very free from turbidity. Warington's 
 description of the method is as follows : 
 
 The depth of tint produced for the same quantity of lead present is far 
 greater in an ammouiacal tartrate or citrate solution than in the same 
 volume of water ; it is quite essential, therefore, if equality of tint is to be 
 interpreted as equality of lead, that all comparisons should be between two 
 citrate and tartrate solutions, and not between one of these and water. 
 
 To carry out the method it is necessary to have solutions of lead-free 
 tartaric and citric acid supersaturated with pure ammonia ; these solutions 
 should develop no colour when treated with ammonium sulphydrate. 
 A convenient strength is 100 gm. of acid in 300 c.c. of final solution.* 
 
 Of the tartaric or citric acid to be examined, 40 gm. are taken and dissolved 
 in a little water ; warm water is most convenient for crystal and cold for 
 powder ; the solution is best prepared in a flask. To the cold solution pure 
 strong ammonia is gradually added till it is in slight excess ; the final point 
 is indicated in the case of tartaric acid by the solution of the acid ammonium 
 
 * Tlie standard lead solutions are made by dissolving T6 gin. of crystallized lead 
 nitrate dried over sulphuric acid in a liter of water, each c.c. =0'001 gm. Pb. A weaker 
 solution is also made by diluting 100 c.c. of this to a liter. 
 
 Q 
 
226 VOLUMETRIC ANALYSIS. 67. 
 
 tart rate first formed ; in the case of citric acid it is conveniently shown by 
 a fragment of turmeric paper floating in the liquid. When an excess 
 of ammonia is reached the liquid is cooled, diluted to 120 c.c., and filtered. 
 
 As a preliminary experiment 10 c.c. are taken, diluted to 50 c.c. in the 
 measuring cylinder, and placed in a Nesslerizing glass, one drop of ammonium 
 sulphydrate solution added, and the whole well stirred ; the colour developed 
 indicates what volume of solution should be taken for the determination, this 
 volume may range from 5 c.c. to 50 c.c. If less than 50 c.c. are taken the 
 volume is brought to 50 c.c. with water, and one drop of ammonium 
 sulphydrate is then added. 
 
 The tint thus adopted has now to be matched with the pure solutions. 
 A volume of the pure ammoniacal tartrate or citrate, identical with that 
 taken of the acid under examination, receives a measured quantity of lead 
 solution from the burette, the -volume is brought to 50 c.c., it is placed 
 in a Nesslerizing glass, and receives one drop of ammonium sulplrydrate ; 
 the experiment is repeated till a match is obtained. As in the previous 
 method, the best comparison of tints is obtained by making finally three 
 simultaneous experiments, one with the acid under examination, the other 
 two with pure acid containing slightly varying amounts of lead, the aim 
 being that the tint given by the acid to bo analyzed shall lie within this 
 narrow scale. In following this method, considerable use has to be made of 
 the weaker of the two lead solutions alread} r mentioned. 
 
 The whole time required for a determination of lead by this method now 
 given is about 1| hour; this time will be somewhat shortened as the 
 operator becomes familiar with the tints produced by varying proportions 
 of lead. If traces of copper or iron are present, any interference on their 
 part may be removed by adding to the alkaline solution a few drops of 
 potassic cyanide solution. 
 
 MANGANESE. 
 
 Mn=55, MnO = 71, Mn0 2 =S7. 
 Factors. 
 
 Metallic iron x 0'63393=MnO. 
 
 x 0-491 =Mn. 
 
 x 0-7768 =Mn0 2 . 
 
 Double iron salt 0-0911 =.MnO. 
 
 Cryst. oxalic acid x 0-6916 =Mn0 2 . 
 
 Double iron salt x 1 1 1 = MnO 2 . 
 
 1 c.c. T ^ solutioii=0-00355 gm. MiiO or=0'00435 gm. MnO 2 . 
 
 67. ALL the oxides of manganese, with the exception of the 
 first or protoxide, when boiled with hydrochloric acid, yield 
 chlorine in the following ratios : 
 
 Mn 2 3 =l eq. 0= 2 eq. Cl. 
 Mn 3 O=r.l eq. 0=2 eq. Cl. 
 Mn 2 =1 eq. 0= 2 eq. Cl. 
 Mn 3 =2 eq. 0= 4 eq. Cl. 
 Mn 2 7 =5 eq. = 10 eq. Cl. 
 
 The chlorine so produced can be allowed to react upon a known 
 weight of ferrous salt; and when the reaction is completed, the 
 
67. M.VXGAXESE. 227 
 
 unchanged amount of iron salt is found by permanganate or 
 bichromate. 
 
 Or, the chlorine may be led by a suitable arrangement into 
 a solution of potassic iodide, there setting free an equivalent 
 quantity of iodine, which is found by the aid of sodic thio- 
 sulphate. 
 
 Or, in the case of manganese ores, the reaction may take place 
 with oxalic acid, resulting in the production of carbonic acid, 
 which can be weighed as in Fresenius' and Wills' method, 
 or the amount of unchanged acid remaining after the action can 
 l)e found by permanganate.""' 
 
 The largely increased use of manganese in the manufacture of 
 steel has now rendered it imperative that some rapid and trust- 
 worthy method of estimation should be devised, and happily this 
 has been done simultaneously by two chemists, Pattinson and 
 Kessler; both have succeeded in finding a method of separating 
 manganese as dioxide, of perfectly definite composition. Pattinson 
 found that the regular precipitation was secured by ferric chloride, 
 and Kessler by zinc chloride. Wright and Menke have 
 experimented on both processes with equally satisfactory results, 
 but give a slight preference to zinc. Pattinson titrates the 
 resulting MnO- with standard bichromate, and Kessler with 
 permanganate. 
 
 Pat tins on's method has been fully described (/. C. S. 1879, 
 -365), and again with slight modifications in J. S. C. I. x. 337. 
 
 1. Precipitation as MnO? and Titration with Bichromate 
 (Pattinson). 
 
 The author's own description of the method is as follows : 
 
 This method depends upon the whole of the manganese being 
 precipitated as hydrated dioxide by calcium carbonate, when 
 chlorine or bromine is added to a solution of manganous salt 
 containing also a persalt of iron or a salt of zinc, and under 
 certain conditions of temperature, &c. We have reason to believe 
 that this method is now adopted by many chemists both in private 
 laboratories and in the laboratories of steel works; and we therefore 
 think that the following description of it in its slightly modified 
 form, as we now use it for determining manganese in manganiferous 
 iron ores, manganese ores, spiegeleisen, ferromanganese, &c., will 
 not be out of -place. 
 
 * The literature of manganese compounds and their estimation has now become very 
 -voluminous. The principal contributions to the subject are as follows : 
 Wright and Menke J. C. JS. 1880, 22-48. 
 
 Morawski and S t i n g 1 Jour. /. pract. Chem. xviii. 96. 
 Volhard Anna! en, cxcviii. 318. 
 
 Guyard Bull. Soc. Chim. [2] i. 88. 
 
 Kessler Z. a. C. 1879, 1-14. 
 
 Pattinson J. C. S. 1879, 365. 
 
 Pattinson J. S. C. I. x. 337. 
 
228 VOLUMETRIC ANALYSIS. 67. 
 
 Process: A quantity of the sample to be analyzed, containing not more 
 than about 4 grains (0'25 gm.) of manganese, is dissolved in hydrochloric 
 acid. In the case of spiegeleisen and ferromanganese, about 50 grains 
 (3 4 c.c.) of nitric acid are afterwards added to oxidize the iron. In the 
 case of manganese ores, ferromanganese, and manganese slags, which do not 
 contain about as much iron as manganese, we add to the solution as much 
 iron, in the form of ferric chloride, as will make the quantities of iron and 
 manganese in the solution about equal. An excess of iron is no draw- 
 back, except that a larger precipitate has afterwards to be filtered and 
 washed. 
 
 The excess of acid in the solution is then neutralized by the addition 
 of calcium carbonate, which is added until a slight reddening of the solution 
 is produced. The solution is then rendered very slightly acid by dropping 
 into it just enough hydrochloric acid to remove the red colour. 
 
 We then add in all cases 1 oz. (30 c.c.) of a solution of zinc chloride 
 containing 7 grains (0'5 gm.) of metallic zinc per ounce. The liquid is then 
 brought to the boiling point, and diluted with boiling water to about 10 oz. 
 (300 c.c.). 
 
 Two oz. (60 c.c.) of a solution of calcium hypochlorite, made by dissolving 
 1500 grains of 35 per cent, bleaching powder in 100 oz. of water (about 33 gm. 
 of bleaching powder per liter) and filtering, are then poured into the 
 manganese solution; but we add to the hypochlorite solution, before pouring 
 it into the manganese solution, just enough hydrochloric acid to give it 
 a faint permanent greenish-fellow colour after gentle agitation. 
 
 The object of this addition of acid is to prevent a precipitate forming 
 when the hypochlorite is added, due to the alkalinity of this solution. 
 When hydrochloric acid is added in this way to the solution of calcium 
 hypochlorite, the manganese solution remains clear on the addition of the 
 calcium hypochlorite, and any possible local precipitation of manganese in 
 a lower state of oxidation than MnO' 2 is obviated. 
 
 Finally, Ave add to the manganese solution about 45 grains (3 gm.) of 
 calcium carbonate diffused in about half an ounce (15 c.c.) of boiling water. 
 After the first evolution of carbonic acid has ceased, during which time the 
 cover is kept on the beaker, the precipitate is stirred to make it collect 
 together, and half a dram (2 c.c.) of methylated spirits of wine is added 
 and it is again stirred. 
 
 The precipitate is then thrown upon a large filter of English filtering paper 
 and washed, at first with cold water until the greater part of the chlorine is 
 removed, and afterwards, to make the washing more rapid, with warm \vater 
 at about 150 P. (65 C.). It is washed until, after draining, a drop shaken 
 down straight from the precipitate, by gently jolting the funnel, shows 
 no indication of chlorine when tested with a strip of iodized starch-paper. 
 As a matter of practice we always give two or three washings after there has 
 ceased to be any indication of chlorine. 
 
 By carrying out the process in the manner here described, the temperature 
 of the liquid, immediately after the precipitation is complete, is about 
 170 3 1\ (77 C.), and we find that the best and most constant results are 
 obtained when the temperature after precipitation is near this point. 
 
 1000 grains of an acidified solution of ferrous sulphate, containing about 
 10 grains of iron 'per 1000 grains of the solution, and made by dissolving 
 crystallized ferrous sulphate in a mixture of one part of monohydrated 
 sulphuric acid and three parts of water, are then accurately measured off by 
 a pipette and run into the beaker in which the precipitation was made. The 
 precipitate, together with the filter paper, are then removed from the funnel 
 and placed in the solution of ferrous sulphate in the beaker. The precipitate 
 readily dissolves even in the cold (sometimes it may be necessary to add 
 a little more acid to dissolve the ferric hydrate completely), the manganese 
 dioxide converting its equivalent of ferrous sulphate into ferric sulphate. 
 
67. MANGANESE. 229 
 
 A sufficient quantity of cold water is now added, and the ferrous sulphate 
 still remaining is titrated with a standard solution of potassium dichromate. 
 
 The exact amount of ferrous sulphate in 1000 grains of the ferrous 
 sulphate solution is determined hy measuring off into a clean beaker another 
 portion of 1000 grains, and titrating with standard dichromate solution. 
 The difference between the amounts of dichromate solution required gives 
 the quantity of ferrous sulphate oxidized by the manganese dioxide, and 
 from this the percentage of manganese in the sample can be calculated. 
 
 The ferrous sulphate solution should be standardized from day to day, as it 
 undergoes slow oxidation on exposure to air. 
 
 A solution of bromine in water may of course be used instead of the 
 hypochlorite solution, in which case no acid is added to the bromine solution. 
 "When using bromine a solution containing about 10 grains of bromine 
 per ounce (about 22 gm. per liter) should be used, and 3 oz. of this solution 
 (90 c.c.) used for precipitating about 4 grains of manganese. 
 
 The unpleasantness of working with bromine may be mitigated, to some 
 extent, by adding to the bromine solution before pouring it into the liquid 
 containing the manganese, a few drops of a solution of sodium hydrate until 
 nearly all, but not quite all, the bromine is taken up. If an excess of 
 sodium hydrate were added to the bromine it would produce a precipitate on 
 pouring it into the manganese solution, and this is to be avoided. 
 
 We prefer to have both zinc and iron in solution with the manganese. 
 When working with either of these alone we obtain all the manganese in 
 the form of dioxide, but with iron alone there is a greater tendency to 
 the formation of permanganate, than when zinc is also present. This point 
 was also noticed by Wright arid Menke (J. C. S. Trans. 1880, 43). 
 When zinc alone is present we have found that the precipitation of the 
 dioxide does not take place so rapidly as when iron is also present. When 
 both iron and zinc are used, there is very seldom any permanganate formed, 
 if care is taken not to use an t unnecessarily large excess of chlorine or 
 bromine, but occasionally there is a small quantity formed, especially if the 
 precipitate is left to stand some considerable time before filtering. We have 
 found that the addition of a very small quantity of alcohol immediately 
 after the precipitation of the manganese is complete, entirely prevents the 
 formation of. permanganate even when a large excess of chlorine has been 
 used, and for this reason we make a practice of adding it. 
 
 We find that when filtering paper has been wetted with the solution 
 containing free chlorine or bromine and afterwards washed clean, it has no 
 reducing action either upon potassium dichromate or upon ferric sulphate. 
 The addition of the filter together with the precipitate to the solution 
 'of ferrous sulphate therefore does not influence the result. 
 
 We must point out that the presence of lead, copper, nickel, cobalt, and 
 chromium in the substances under examination interferes with the accuracy 
 of this method of testing manganese. 
 
 It was found that so large a proportion as 1 per cent, of lead, copper, and 
 nickel does not greatly interfere with the test, but the interference of cobalt 
 and, especially of chromium, is serious. All these substances, except 
 chromium, form, under the conditions of the test, higher oxides insoluble in 
 water, which are precipitated with the manganese dioxide, and which 
 oxidize ferrous sulphate to ferric sulphate ; whilst chromium forms some 
 insoluble chromate which goes down with the manganese dioxide. 
 
 Fortunately these metals rarely, if ever, occur in the ores of manganese 
 or in spiegeleisen and ferromanganese in sufficient quantity to affect the 
 practical accuracy of this test. 
 
 This volumetric method cannot, however, be applied to the determination 
 of manganese in alloys of these metals, such as ferrochrome or in ores 
 containing these metals, without previously separating them from the 
 solution containing the manganese. 
 
230 VOLUMETRIC ANALYSIS. G7. 
 
 The method as above described is undoubtedly one of the best 
 volumetric ones known for the estimation of manganese in various 
 compounds and ores; but Saniter in criticising the method gives 
 it credit for slightly low results, and advocates the standardizing 
 of the bichromate, not upon iron, but upon a manganese oxide of 
 known composition (/. S. C. I. xiii. 112). 
 
 Atkinson ( J, S. C. I. v. 365) gives the following short descrip- 
 tion of the method as practically in daily use in a large steel works. 
 
 Weigh out 0'5 gm. or 0'6 gm. of an ore containing about 20 per cent, 
 manganese, dissolve in 7 or 8 c.c. of strong HC1, and when dissolved, wash 
 the whole, without filtering, into a large narrow-sided beaker. When cold 
 it is neutralized with precipitated calcic carbonate, until the liquid assumes 
 a reddish hue. 40 or 50 c.c. of saturated bromine water are added, and the 
 mixture allowed to stand in the cold for half-an-hour. At the expiration of 
 that time the beaker is nearly filled up with boiling water, and precipitated 
 calcic carbonate added until there is no further effervescence, and part of the 
 carbonate is evidently unacted upon. A small quantity of spirits of wine is 
 then added, the whole well stirred, and the precipitate allowed to settle. The 
 clear liquid is filtered off and fresh boiling water added to the residue in the 
 beaker, a little spirits of wine being used to reduce any permanganate which 
 is formed. The filtration and washing are repeated until the nitrate when 
 cooled no longer turns iodized starch-paper blue. During the washing about 
 1'9 to 2' 5 gm. of pure granular ferrous-ammonium sulphate are weighed 
 out, washed into the beaker in which the precipitation took place, and about 
 30 to 50 c.c. of dilute sulphuric acid added. The filter containing the pre- 
 cipitated MnO 2 is then placed in the beaker, and the latter is quickty dissolved 
 by the oxidation of a portion of the ferrous salt into ferric sulphate. The 
 remaining ferrous iron is then titrated with potassic bichromate in the usual 
 way. The difference in the number of c.c. of bichromate used from the 
 number which the original weight of the ferrous-ammonium sulphate would 
 have required if directly titrated, is a measure of the quantity of MnO- 
 present. For rapidity and simplicity this volumetric process leaves nothing 
 to be desired ; duplicate experiments agree within very narrow limits ; and 
 if the assumption is accepted that the presence of ferric chloride enables the 
 complete oxidation of the manganese to the state of peroxide, no other 
 process can compete with it. 
 
 Pattinson prefers to use bleach solution to bromine, because 
 the formation of permanganate is more easily seen. In any case 
 not more than a trace of permanganate should be formed, and if 
 the first experiment shows this to be the case, another trial must 
 be commenced with less oxidizing material. 
 
 J. "W. Westmoreland, in a communication to me, describes 
 a modified method which is designed to overcome some objections 
 raised against the above processes. 
 
 With ferro-manganese and ores containing about 50 to 60 c of Mn about 
 0*4 gm. is taken ; ores with 40 % ' 5 g m - '> manganiferous iron ores, with 
 say about 20 % each of Fe and Mn, 0'75 gm.; spiegeleisen and silicospiegels, 
 with about 25 % Mn, the same. 
 
 The material having been brought into solution by any of the methods 
 described, is concentrated to a small bulk in a large conical beaker. 
 A solution of ferric chloride, containing about the same amount of iron as 
 there is approximately of Mn, is added, together with a solution of zinc 
 
67. MANGANESE. 231 
 
 chloride, containing about 0'5 gm. of Zn. The excess of acid is then 
 neutralized with caustic potash, so that the bulk of liquid is about 80 c.c., 
 to this is added about 60 c c. of saturated bromine water, more for 
 ferro-manganese, less for manganiferous iron ores, and zinc oxide emulsion * 
 is graduall}' dropped in with shaking, until the Pe and Mn are pre- 
 cipitated, care must be taken to avoid a large excess of zinc oxide, the 
 beaker is then filled up with boiling tap-water, and the clear liquid poured 
 through a filter, previously adding a few drops of alcohol. The beaker is 
 then filled with boiling water five times in succession, the precipitate being 
 stirred up with the hot water each time of washing and allowed to settle. 
 It is then brought on the filter, and again freely washed with boiling 
 distilled water. The filter and contents are then transferred to the beaker, 
 an excess of acid solution of ferrous sulphate added, and when the precipitate 
 is dissolved the liquid is diluted with cold distilled water, and the excess of 
 ferrous iron estimated at once with permanganate. The value of the iron 
 solution in metallic iron is found by titrating the same volume of iron 
 solution as has actually been used for dissolving the Mn precipitate, and the 
 Fe oxidized multiplied by 0'491 = Mn. 
 
 It is absolutely necessary, in order to get accurate results, to 
 wash the precipitate as thoroughly as mentioned. 
 
 2. By Precipitation with Potassic Permanganate (G-uyard). 
 
 If a dilute neutral or faintly acid solution of manganese salt be 
 heated to 80 C. and permanganate added, hydrated MnO 2 is pre- 
 cipitated, and the end of the reaction is known by the occurrence of 
 the usual rose colour of permanganate in excess. The reaction is 
 exact in neutral solutions. Any large excess of either HC1 or H' 2 S0 4 
 causes irregularity, as also do ferric or chromic salts; nickel, cobalt, 
 zinc, alumina, or lime, in moderate quantity are of no consequence. 
 
 This method is of easy execution, and gives good results in cases 
 where it can be properly applied, but such instances are few. 
 
 Process : 1 or 2 gm. of the manganese compound are dissolved in aqua 
 refjia, boiled a few minutes, the excess of acid neutralized with alkali, then 
 diluted largely with boiling water (1 or 2 liters), kept at a temperature 
 of 80 C., arid standard permanganate added so long as a brownish precipitate 
 forms, and until the clear supernatant liquid shows a distinct rose colour. 
 2 eq. of permanganate = 3 eq. of manganese, therefore 1 c.c. of T ^ solution = 
 0-0016542 gm. of Mn. 
 
 Volhard's method. This is now largely used by Continental 
 chemists, the details of the original process being as follows : 
 
 A quantity of material is taken so as to contain from 0'3 to 0'5 gm. Mn, 
 dissolved in hydrochloric or nitric acid, evaporated in porcelain to dryness, 
 first adding a little ammonia nitrate, then heated over the flame to destroy 
 organic matter. The residue is digested with HC1, adding a little strong 
 H-SO 4 , and again evaporated to dryness, first on the water-bath, then with 
 greater heat till vapours of SO 3 occur. It is then washed into a liter flask 
 and neutralized with sodic hydrate or carbonate : sufficient pure zinc oxide, 
 made into a cream, is added to precipitate all the iron. The flask is filled to 
 
 * The emulsion of zinc oxide may, of course, be readily made by rubbing down pure 
 zinc oxide in water so as to be about the consistence of cream. Emmertpn (Trans. 
 Antcr. Inst. Min. Eng. x. 201) suggests the following method of preparing this reagent. 
 Dissolve ordinary zinc white in HC1, add the powder until there remains some 
 
232 VOLUMETRIC ANALYSIS. 67. 
 
 the mark, shaken, and 200 c.c. filtered off into a boiling flask, acidified with 
 2 drops of nitric acid, sp. gr. 1'2, heated to boiling, and titrated with 
 T ^j- permanganate whilst still hot. 
 
 Blair (Chem. Anal. Iron, 2nd edit.) for practical working recommends 
 dissolving the material in HC1 and H 2 S0 4 , evaporate to dryness until fumes 
 of the latter escape; allow to cool, add water, and heat till sulphates are 
 dissolved. Wash into a 300 c.c. flask, add solution of Na 2 CO 3 until the 
 precipitate, which at first forms, dissolves only with difficulty. Then add 
 slowly the zinc oxide emulsion, shaking well after each addition, till the iron 
 precipitate curdles ; after the precipitate has settled, there is left a slightly 
 milky upper liquid. Fill the flask to the mark with water, and agitate well 
 by pouring the contents of the flask back and forward into a dry beaker. 
 Finally filter off 200 c.c. and titrate Avith permanganate as before described, 
 first adding 2 drops of HNO 3 . The permanganate should be added slowly 
 from the burette, shaking after each addition to facilitate the collection 
 of the precipitate and avoid an excess of permanganate. If the solution 
 during the process should cool too much, it should be heated up to near 
 boiling again. 
 
 Saniter recommends that any iron or chromium should be first separated 
 by ammonia and ammonic acetate, and the manganese precipitated with 
 bromine and ammonia. This precipitate is, after ignition, dissolved in 
 hydrochloric acid, and neutralized with zinc oxide suspended in water, any 
 excess of the latter being dissolved by adding nitric acid drop by drop. 
 
 Another variation of this method is given (Jour. Ainer. Chem. 
 Soc. xviii. 228) by G. E. Stone, in some criticisms on a previous 
 paper by M. Auchy. 
 
 The material taken should contain 0'05 to 0'15 Mn. If an alloy, dissolve 
 in HNO 3 (sp.'gr. ri) ; if an ore or cinder, in HC1, and boil with a little 
 KC1O 3 ; use but small excess of acid. Cool and wash into a 500 c.c. flask 
 with cold water, then add zinc emulsion until precipitate curdles ; the 
 change is sharp and distinct. Dilute to mark, shake well and pour into 
 a beaker ; allow to settle ; measure 100 c.c. into a 4-inch casserole, dilute 
 to about 200 c.c., heat nearly to boiling, and titrate with permanganate, 
 1 c.c. of which=0 001 gin. Mn (1'99 gin. K-MnO 4 per liter). The greater part 
 of the permanganate should be added at once with vigorous stirring. The 
 Mn in spiegels is easily obtained in half an hour ; ores somewhat longer, 
 as more difficult to dissolve. 
 
 There are many other volumetric methods in use for estimating 
 manganese either as binoxide or metal, among which may be 
 mentioned that of Chalmers Harvey (C. N. xlvii. 2) by 
 stannous chloride, and that of Williams (Trans. Amer. Inst. of 
 Mining Engineers, x. 100), which consists in separating MnO 2 
 from a nitric solution by potassic chlorate, dissolving in excess of 
 standard oxalic acid, and estimating the excess by permanganate. 
 
 A critical paper on this process, accompanied with the results of 
 experiment, is contributed by Macintosh (C. N. 1. 75). Also 
 another by Hintz (Z. a. C. xxiv. 421 438) reviewing a large 
 number of volumetric methods for manganese, but as none of them 
 
 undissolved, then add a little bromine water; heat the mixture, filter and precipitate 
 the zinc oxide from the filter with the slightest possible excess of ammonia. Wash 
 thoroughly by decantation, and finally wash into an appropriate bottle with enough 
 water to give a proper consistence. By this method a very finely divided oxide is 
 obtained, owing to its not being dried. 
 
67. MANGANESE. 233 
 
 are more accurate or convenient than the methods here given, the 
 details are omitted. 
 
 3. Estimation of Manganese in small quantities (Chatard). 
 
 This method depends upon the production of permanganic acid 
 by the action of nitric acid and lead peroxide, originally used by 
 Crum as a qualitative test. The accuracy of the process as 
 a quantitative one can, however, only be depended on when the 
 quantity of manganese is very small, such as exists in some 
 minerals, soils, etc. 
 
 The material to be examined is dissolved in nitric acid and 
 boiled with lead peroxide, by which means any manganese present 
 is converted to permanganate ; the quantity so produced is then 
 ascertained by a weak freshly made standard solution of oxalic 
 acid or ammonic oxalate. 
 
 The process gives good results in determining manganese in 
 dolomites and limestones, where the proportions amount to from 
 yy to 2 per cent. In larger quantities the total conversion of the 
 manganese cannot be depended on. 
 
 Thorpe and Hambly ( J. C. S. liii. 182) found that the final 
 point in the titration with ammonic oxalate was apt to be obscured 
 by the precipitation of lead carbonate, and they suggest a modifi- 
 cation which consists in using some dilute sulphuric acid with 
 the lead peroxide and nitric acid during the oxidation of the 
 manganese ; no lead then passes into solution, and the filtered 
 liquid remains perfectly clear on titration. These operators found 
 the method quite trustworthy for quantities of manganese below 
 O'Ol gm., and carried out as follows : 
 
 Process : To the manganese solution, which must be free from chlorine 
 and not too dilute, say about 25 c.c., add 5 c.c. of nitric acid (sp. gr. 1'4), 
 2 3 gm. of lead peroxide, and 1020 c.c. of dilute sulphuric acid (1 : 2). 
 Boil gently for about four minutes, wash down the sides of the flask with 
 hot water, and continue the boiling for half a minute. Allow the lead 
 sulphate and peroxide to subside and filter at once (best with filter pump 
 through asbestos, previously ignited and washed with dilute H 2 SO 4 ). Wash 
 the residue in fl-ask with boiling water by decantation, heat the clear filtrate 
 to 60 C., and titrate with T ^ ammonic oxalate. 
 
 Peters avails himself of this method for estimating manganese 
 in pig iron or steel, by weighing O'l gm. of the sample and boiling 
 in 3 or 4 c.c. of nitric acid until solution of the metal is complete, 
 adding O2 or 0'3 gm. PbO 2 , and again boiling for two or three 
 minutes, without filtering off the insoluble graphite, if such should 
 be present. The solution is then cooled, filtered through asbestos 
 into a suitable graduated tube, and the colour compared with 
 a standard solution of permanganate contained in a similar tube. 
 
 The standard permanganate is best made by diluting 1 c.c. of 
 Y^ solution with 109 c.c. of water; each c.c. will then represent 
 '00001 gm. Mn. It has been previously mentioned that accurate 
 
234 VOLUMETRIC ANALYSIS. 67. 
 
 results by this method can only be obtained by using very small 
 quantities of material. Peters finds this to be the case, and hence 
 recommends, that for irons containing from O10 to 0'35 per cent, 
 of Mn Ol gm. should be operated upon ; when from 0~8 to 1 
 per cent, is present, 0*1 gm. of the sample is weighed and one- 
 fourth of the solution only treated with PbO' 2 ; in still richer 
 samples proportionate quantities must be taken. As a guide, it is 
 well to assume, that when the amount of iron taken yields a colour 
 equal to 25 35 c.c. of the standard, the whole of the Mn is 
 oxidized. The actual amount of manganese in any test should not 
 exceed half a milligram (G. N. xxxiii. 35). 
 
 4. Teslinical EXE mination of Manganese Ores used for Bleaching- 
 Purposes, etc. 
 
 The ore, when powdered and dried for analysis, rapidly absorbs 
 moisture on exposing it to the air, and consequently has to be 
 weighed quickly ; it is better to keep the powdered and dried 
 sample in a small light stoppered bottle, the weight of which,, 
 with its contents and stopper, is accurately known. About 1 or 2 
 gm., or any other quantity within a trifle, can be emptied into- 
 the proper vessel for analysis, and the exact quantity found by 
 reweighing the bottle. 
 
 A hardened steel or agate mortar must be used to reduce the- 
 mineral to the finest possible powder, so as to insure its complete 
 and rapid decomposition by the hydrochloric acid. 
 
 Considerable discussion has occurred as to the best processes- 
 for estimating the available oxygen in manganese ores, arising from 
 the fact that many of the ores now occurring in the market contain 
 iron in the ferrous state ; and if such ores be analyzed by the usual 
 iron method with hydrochloric acid, a portion of the chlorine 
 produced is employed in oxidizing the iron contained in the original 
 ore. Such ores, if examined by Fresenius and Wills' method,, 
 show therefore a higher percentage than by the iron method, since- 
 no such consumption of chlorine occurs in the former process. 
 Manufacturers have therefore refused to accept certificates of 
 analysis of such ores when based on Fresenius and "Wills' 
 method. This renders the volumetric processes of more importance,, 
 and hence various experiments have been made to ascertain their 
 possible sources of error. 
 
 The results show that the three following methods give very 
 satisfactory results (see Scherer and Eumpf, C. N. xx. 302; 
 also Pattinson, Hid. xxi. 266; and Paul, xxi. 16). 
 
 5. Direct Analysis by Distillation with Hydrochloric Acid. 
 
 This is the quickest and most accurate method of finding the 
 quantity of available oxygen present in any of the ores of manganese 
 or mixtures of them. It also possesses the recommendation that the 
 
67. MANGANESE. 235 
 
 quantity of chlorine which they liberate is directly expressed in the 
 analysis itself ; and, further, gives an estimate of the quantity of 
 hydrochloric acid required for the decomposition of any particular 
 sample of ore, which is a matter of some moment to the manu- 
 facturer of bleaching powder. 
 
 The apparatus for the operation may be those shown in figs. 
 37 and 38. For precautions in conducting the distillation 
 see 39. 
 
 Process : In order that the percentage of dioxide shall be directly 
 expressed by the number of c.c. of r ^ thiosulphate solution used, 0'436 2:111. 
 of the properly dried and powdered sample is weighed and put into the little 
 flask ; solution of potassic iodide in sufficient quantity to absorb all the 
 iodine set free is put into the large tube (if the solution containing T 2 7 eq. or 
 33'2 gin. in the liter be used, about 70 or 80 c.c. Will in ordinary cases be 
 sufficient) ; very strong hydrochloric acid is then poured into the distilling 
 flask, and the operation conducted as in 39. Each equivalent of iodine 
 liberated represents 1 eq. Cl, also 1 eq. MnO 2 . 
 
 Instead of using a definite weight, it is well to do as before 
 proposed, namely, to pour about the quantity required out of the 
 weighed sample-bottle into the flask, and find the exact weight 
 afterwards. 
 
 Barlow (0. N. liii. 41) records a good method. of separating 
 Mn from the metals of its own group as well as from alkalies and 
 alkaline earths. 
 
 For the quantitative estimation of Fe and Mn in the same 
 solution as chlorides (other metals except Cr and Al may be present, 
 but best absent), solution of iS r H 4 Cl is first added, then strong 
 NH 4 HO in excess, boil, then hydrogen peroxide so long as a 
 precipitate falls, boil for a few minutes, filter, wash with hot water, 
 ignite, and weigh the mixed oxides together as Fe 2 3 + Mn 3 4 . 
 
 The oxides are then distilled with HC1, and the amount of 
 iodine found by thiosulphate. 
 
 The weight of mixed oxides, minus the Mn 3 4 , gives the weight 
 of Fe 2 3 . 
 
 Pickering (/. 0. S. 1880, 128) has pointed out that pure 
 manganese oxides, freshly prepared, or the dry oxides in very 
 fine powder, may be rapidly estimated without distillation by 
 merely adding them to a large excess of potassic iodide solution 
 in a beaker, running in 2 or 3 c.c. of hydrochloric acid, when 
 the oxides are immediately attacked and decomposed; the liberated 
 iodine is then at once titrated with thiosulphate. Impure oxides, 
 containing especially ferric oxide, cannot however be estimated in 
 this way, since the iron would have the same effect as manganic 
 oxide ; hence distillation must be resorted to in the case of all 
 such ores, and it is imperative that the strongest hydrochloric acid 
 should be used. 
 
 Pickering's modified process is well adapted to the examination 
 of the Weldon mud, for its available amount of manganese dioxide. 
 
236 VOLUMETRIC ANALYSIS. 67. 
 
 6. Estimation by Oxalic Acid. 
 
 The very finely powdered ore is mixed with a known volume of 
 normal oxalic acid solution, sulphuric acid added, and the mixture 
 heated and well shaken, to bring the materials into intimate contact 
 and liberate the CO 2 . When the whole of the ore is decomposed, 
 which may be known by the absence of brown or black sediment, 
 the contents of the vessel are made up to a definite volume, say 
 300 c.c., and 100 c.c. of the dirty milky fluid well acidified, 
 diluted, and titrated for the excess of oxalic acid by permanganate. 
 If, in consequence of the impurities of the ore, the mixture be 
 brown or reddish coloured, this would of course interfere with the 
 indication of the permanganate, and consequently the mixture in 
 this case must be filtered ; the 300 c.c, are therefore well shaken 
 and poured upon a large filter. When about 100 c.c. have passed 
 through, that quantity can be taken by the pipette and titrated as 
 in the former case. 
 
 If the solution be not dilute and freely acid, it will be found 
 that the permanganate produces a dirty brown colour instead of its 
 well-known bright rose-red ; if the first few drops of permanganate 
 produce the proper colour immediately they are added, the solution 
 is sufficiently acid and dilute. 
 
 If 4-357 gm. of the ore be weighed for analysis, the number of 
 c.c. of normal oxalic acid will give the percentage of dioxide ; but 
 as that is rather a large quantity, and takes some time to dissolve 
 and decompose, half the quantity may be taken, when the per- 
 centage is obtained by doubling the volume of oxalic acid. 
 
 Example : The permanganate was titrated with normal oxalic acid, and it 
 was found that 1 c.c.=0'25 c.c. of normal oxalic acid. 2'1T8 gm. of a rich 
 sample of commercial manganese (pyrolusite) were treated with 50 c.c. of 
 normal oxalic, together with 5 c.c. of concentrated sulphuric acid, until the 
 decomposition was complete. The resulting solution was milky, but con- 
 tained nothing to obscure the colour of the permanganate, and therefore 
 needed no filtration. It was diluted to 300 c.c., and 100 c.c. taken for titra- 
 tion, which required 6'2 c.c. of permanganate. A second 100 c.c. required 
 G'3, mean 6'25, which multiplied by 3 gave 18'75 c.c.; this multiplied by 
 the factor 0'25 to convert it into oxalic acid gave 4'68 c.c. normal oxalic, 
 and this being deducted from the original 50 c.c. used, left 45'32 c.c.=90'64 
 per cent, of pure manganic dioxide. 
 
 This process possesses an advantage over the following, inasmuch 
 as there is no fear of false results occurring from the presence of 
 air. The analysis may be broken off at any stage, and resumed 
 at the operator's, convenience. 
 
 7. Estimation by Iron. 
 
 The most satisfactory form of iron is soft " flower " wire, which 
 is readily soluble in sulphuric acid. If a perfectly dry and un- 
 oxidized double iron salt be at hand, its use saves time. 1 mol. 
 -of this salt = 392, representing 43 '5 of MnO 2 , consequently, 1 gm. of 
 
67. MANGANESE. 2S7 
 
 the latter requires 9 gm. of the double salt ; or in order that the 
 percentage shall be obtained without calculation,, I'lll gm. of ore 
 may be weighed and digested in the presence of free sulphuric acid, 
 with 10 gm. of double iron salt, the whole of which would be 
 required supposing the sample were pure dioxide. The. undecom- 
 posed iron salt remaining at the end of the reaction is estimated by 
 permanganate or bichromate ; the quantity so found is deducted 
 from the original 10 gm., and if the remainder be multiplied by 10 
 the percentage of dioxide is gained. 
 
 Instead of this plan, which necessitates exact weighing, any 
 convenient quantity may be taken from the tared bottle, as before 
 described, and digested with an excess of double salt, the weight 
 of which is known. After the undecomposed quantity is found by 
 permanganate or bichromate, the remainder is multiplied by the 
 factor O'lll, which gives the proportion of dioxide present, 
 whence the percentage may be calculated. 
 
 The decomposition of the ore may be made in any of the 
 apparatus used for titrating ferrous iron. The ore is first put 
 into the decomposing flask, then the iron salt and \vater, so as to 
 dissolve the salt to some extent before the sulphuric acid is added. 
 Sulphuric acid should be used in considerable excess, arid the 
 flask heated by the spirit lamp till all the ore is decomposed ; 
 the solution is then cooled, diluted, and the whole or part titrated 
 with permanganate or bichromate. 
 
 Example : 1 gin. of double iron salt was titrated with permanganate 
 solution of which 21'4 c.c. were required. 
 
 I'll I gm. of the sample of manganese was accurately weighed and digested 
 with 8 gin. of iron salt, and sulphuric acid. After the decomposition, 8'8 c.c. 
 of permanganate were required to peroxidize the undecomposed iron salt 
 (=0'42 gm.), which deducted from the 8 gm. originally used left 7*58 gin. ; 
 or placing the decimal point one place to the right, 75'8 per cent, of pure 
 dioxide. 
 
 In the case of using -^ bichromate for the titration, the following- 
 plan is convenient : 100 c.c. of ^ bichromate = 3 '92 gm. of double 
 iron salt (supposing it to be perfectly pure), therefore if 0'436 gm. 
 of the sample of ore be boiled with 3 '92 gm. of the double salt 
 and excess of acid, the number of c.c. of bichromate required 
 deducted from 100 will leave the number corresponding to the 
 percentage. 
 
 Example : 0'436 gm. of the same sample as examined before was boiled 
 with 3'92 gm. of double salt, and afterwards required 24 c.c. 'of T ^ bichro- 
 mate, which deducted from 100 leaves 76 per cent, of dioxide, agreeing very 
 closely with the previous examination. 
 
 When using metallic iron for the titration (which in most cases is preferred) 
 Pattinson proceeds as follows: 30 grn. of clean iron wire are placed in 
 a suitable apparatus, with 3 oz. of dilute sulphuric acid, made by adding 
 3 parts of water to one of concentrated acid. When the iron is quite dissolved, 
 30 grn. of the finely powdered and dried sample of manganese ore to be 
 tested are put into the flask, the cork replaced, and the contents again made 
 
238 VOLUMETRIC ANALYSIS. 68. 
 
 to boil gently over a gas flame until it is seen that the whole of the black 
 part of the manganese is dissolved. The Avater in the small flask is then 
 allowed to recede through the bent tube into the larger flask, more distilled 
 Avater is added to rinse out the small flask or beaker and bent tube, the cork 
 well rinsed, and the contents of the flask made up to about 8 or 10 oz. with 
 distilled water. The amount of iron remaining unoxidized in the solution 
 is then ascertained by means of a standard solution of potassic bichromate. 
 The amount indicated by the bichromate deducted from the total amount of 
 iron used, gives the amount of iron which has been oxidized by the manga- 
 nese ore, and from which the percentage of manganic dioxide contained in 
 the ore can be calculated. Thus, supposing it were found that 4 grn. of 
 iron remained unoxidized, then 30426 grn. of iron which have been 
 oxidized by the 30 grn. of ore. Then, as 
 
 5G : 43'5 : : 26 : 20'2 
 
 the amount of dioxide in the 30 gru. of ore. The percentage is therefore 
 67'33. Thus 
 
 30 : 20-2 : : 100 : 67'33 
 
 Grain weights are given in this example, but those who use the 
 .gram system will have no difficulty in arranging the details 
 .accordingly. 
 
 MERCURY. 
 
 Hg = 200. 
 
 1 c.c. T \ solution = 0-0200 gm. Hg. 
 -0-0208 gm. Hg 2 
 = 0-0271 gm. HgCl 2 
 
 Double iron salt x 0*5104 = Hg. 
 
 x 0-6914 = HgCl 2 
 
 1. Precipitation as Mercurous Chloride. 
 
 68. THE solution to be titrated must not be warmed, and 
 must contain the metal only in the form of protosalt. ~ sodic 
 chloride is added in slight excess, the precipitate washed with the 
 least possible quantity of water to ensure the removal of all the 
 sodic chloride to the nitrate a few drops of chromate indicator are 
 added, then pure sodic carbonate till the liquid is of a clear yellow 
 colour, y 1 ^- silver is then delivered in till the red colour occurs. 
 The quantity of sodic chloride so found is deducted from that 
 originally used, and the difference calculated in the usual way. 
 
 2. By Ferrous Oxide and Permanganate (Mohr). 
 
 This process is based on the fact that when mercuric chloride 
 (corrosive sublimate) is brought in contact with an alkaline solution 
 of ferrous oxide in excess, the latter is converted into ferric oxide, 
 while the mercury is reduced to mercurous chloride (calomel). 
 The excess of ferrous oxide is then found by permanganate or 
 ^bichromate 
 
 2HgCl 2 + 2FeCl 2 = Hg 2 Cl 2 + Fe 2 Cl 6 . 
 
68. MERCURY. 239 
 
 It is therefore advisable in all cases to convert tlie mercury to be 
 estimated into the form of sublimate, by evaporating it to dryness 
 with nitro-liydrochloric acid ; this must take place, however, below 
 boiling heat, as vapours of chloride escape with steam at 100 C. 
 (Fresenius). 
 
 Citric acid or free chlorine must be altogether absent during 
 the decomposition with the iron protosalt, otherwise the residual 
 titration will be inexact, and the quantity of the iron salt must be 
 more than sufficient to absorb half the chlorine in the sublimate. 
 
 Example : 1 gm. of pure sublimate was dissolved in warm water, and 
 3 gm. of double iron salt added, then solution of caustic soda till freely 
 ulkaline. The mixture became muddy and dark in colour, and was well 
 shaken for a few minutes, then sodic chloride and sulphuric acid added, con- 
 tinuing the shaking till the colour disappeared and the precipitate of ferric 
 oxide dissolved, leaving the calomel white ; it Avas then diluted to 300 c.c. 
 filtered through a dry filter, and 10D c.c. titrated with ^ permanganate, of 
 which 13'2 c.c. were required 13'2 x 3=39'6, which deducted from 76'5 c.c. 
 (the quantity required .for 3 gm. double iron salt), left 36'9 c.c.=r447 gm. 
 of undecomposed iron salt, which multiplied by the factor 0'6914, gave 
 1-0005 gm. of sublimate, instead of 1 gm., or the 36'9 c.c. may be multiplied 
 by the ^ factor for mercuric chloride, which will give 1 gm. exactly. 
 
 3. By Iodine and Thiosulphate (Hem pel). 
 
 If the mercury exist as a protosalt it is precipitated by sodic 
 chloride, the precipitate well washed and together with its filter 
 pushed through the funnel into a stoppered flask, a sufficient 
 quantity of potassic iodide added, together with ^ iodine solution 
 (to 1 gm. of calomel about 2 '5 gm. of iodide, and 100 c.c. of ~ 
 iodine), the flask closed, and shaken till the precipitate has 
 dissolved 
 
 Hg 2 Cl 2 + 6KI + 21 = 2HgK 2 P + 2KC1. 
 
 The brown solution is then titrated with ^ thiosulphate till 
 colourless, diluted to a definite volume, and a measured portion 
 titrated with ~ iodine and starch for the excess of thiosulphate. 
 1 c.c. T ^- iodine = 0'02 gm. Hg. 
 
 Where the mercurial solution contains nitric acid, or the metal 
 exists as peroxide, it may be converted into protochloride by the 
 reducing action of ferrous sulphate, as in Mohr's method. The 
 solution must contain hydrochloric acid or common salt in sufficient 
 quantity to transform all the mercury into calomel. At least three 
 times the weight of mercury present of ferrous sulphate in solution 
 is to be added, then caustic soda in excess, the muddy liquid well 
 shaken for a few minutes, then dilute sulphuric acid added in 
 excess, and the mixture stirred till the dark-coloured precipitate 
 lias become perfectly white. The calomel so obtained is collected 
 on a filter, well washed, and titrated with T ^- iodine and thiosulphate 
 as above. ' 
 
240 VOLUMETRIC ANALYSIS. 68. 
 
 4. Direct Titration -with Sodic Thiosulphate (Scherer). 
 
 The standard thiosulphate is made by dissolving -^ eq. = 12'4 
 gm. of the salt in 1 liter of water. 
 
 The reaction which takes place with thiosulphate in the case of 
 mercurous nitrate is 
 
 - Hg 2 S + Na 2 SO* + N*0 5 . 
 With mercuric nitrate 
 
 3Hg(N0 3 ) 2 + 2Na 2 S 2 3 - 2HgS.Hg(N0 3 ) 2 + 2Xa 2 80 4 + 23S' 2 5 . 
 "With mercuric chloride 
 
 SHgCl 2 + 2Na 2 S 2 3 + 2H 2 - 2HgS.HGl 2 + 2Xa 2 SO* + 4HC1. 
 
 (a) Mercurous Salts. The solution containing the metal as a pro to- 
 salt only is diluted, gently heated, and the thiosulphate delivered in from the 
 burette at intervals, meanwhile well shaking until the last drop produces no 
 brown colour. The sulphide settles freely, and allows the end of the reaction 
 to be easily seen. 1 c.c. of thiosulphate 0'020 gm. Hg, or 0'0208 gm. 
 Hg 2 0. 
 
 (b) Mercuric Nitrate. The solution is considerably diluted, put into 
 a stoppered flask, nitric acid added, and the thiosulphate cautiously delivered 
 from the burette, vigorously shaken meanwhile, until the last drop produces 
 no further } r ellow precipitate. Scherer recommends that when the greater 
 part of the metal is precipitated, the mixture should be diluted to a definite 
 volume, the precipitate allowed to settle, and a measured quantity of the 
 clear liquid taken for titration ; the analysis may then be checked by a second 
 titration of the clear liquid, if needful. 1 c.c. thiosulphate=0'015 gin. Hg, 
 or 0-0162 gm. HgO. 
 
 (c) Mercuric Chloride. With mercuric chloride (sublimate) the end of 
 the process is not so easily seen. The procedure is as follows : The very 
 dilute solution is acidified with hydrochloric acid, heated nearly to boiling, 
 and the thiosulphate cautiously added so long as a white precipitate is seen 
 to form ; any great excess of the precipitant produces a dirty -looking colour. 
 Filtration is necessary to distinguish the exact ending of the reaction, for 
 which purpose Beale's filter (fig. 23) is useful. 
 
 Liebig's method is the reverse of that used for determining 
 chlorides in urine, sodic phosphate being used as indicator in the 
 estimation of mercury, instead of the urea occurring naturally in 
 urine The method is capable of very slight application. 
 
 5. As Mercuric Iodide (Personne), Compt. Rend. Ivi. 63. 
 
 This process is founded on the fact that if a solution of mercuric 
 chloride be added to one of potassic iodide, in the proportion of 
 1 equivalent of the former to 4 of the latter, red mercuric iodide is 
 formed, which dissolves to a colourless solution until the balance is 
 overstepped, when the brilliant red colour of the iodide appears as 
 a precipitate, which, even in the smallest quantity, communicates- 
 its tint to the liquid. The mercuric solution must always be added 
 
68. MEUCUKY. 241 
 
 to the potassic iodide ; a reversal of the process, though giving 
 eventually the same quantitative reaction, is nevertheless much less 
 speedy and trustworthy. The mercurial compounds to be estimated 
 by this process must invariably be brought into the form of neutral 
 mercuric chloride. 
 
 The standard solutions required are decinormal, made as follows : 
 
 Solution of Potassic iodide. 33*2 gm. of pure salt to 1 liter. 
 1 c .c.=0-01 gin. Hg. or 0-01355 gm. HgCR 
 
 Solution of Mercuric chloride 13 '537 gm. of the salt, with 
 about 30 gm. of pure sodic chloride (to assist solution), are dissolved 
 to 1 liter. 1 c.c. =0*1 gm. Hg. 
 
 The conversion of various forms of mercury into mercuric chloride 
 is, according to Personne, best effected by heating with caustic 
 soda or potash, and passing chlorine gas into the mixture, which 
 is afterwards boiled to expel excess of chlorine (the mercuric 
 chloride is not volatile at boiling temperature when associated with 
 alkaline chloride). The solution is then cooled and diluted to 
 a given volume, placed in a burette, and delivered into a measured 
 volume of the decinormal potassic iodide until the characteristic 
 colour occurs. It is preferable to dilute the mercuric solution con- 
 siderably, and make up to a given measure, say 300 or 500 c.c. ; 
 and as a preliminary trial take 20 c.c. or so of iodide solution, 
 and titrate it with the mercuric solution approximately with 
 a graduated pipette ; the exact strength may then be found by 
 using a burette of sufficient size. 
 
 6. By Potassic Cyanide (Hannay). 
 
 This process is exceedingly valuable for the estimation of almost 
 all the salts of mercury when they occur, or can be separated, in 
 a tolerably pure state. Organic compounds are of no consequence 
 unless they affect the colour of the solution. 
 
 The method depends on the fact that free ammonia produces 
 a precipitate, or (when the quantity of mercury is very small) an 
 opalescence in mercurial solutions, which is removed by a definite 
 amount of potassic cyanide. 
 
 The delicacy of the reaction is interfered with by excessive 
 quantities of ammoniacal salts, or by caustic soda or potash ; but 
 this difficulty is lessened by the modification suggested by Tuson 
 and Xeison (J. C. S. 1877, 679). 
 
 Chapman Jones (/. C. S. Ixi. 364) has further modified the 
 process so as to make it easier to detect the end-point, and says of 
 the method as worked by Tuson and Xeison: "Their general 
 method consists in dissolving the mercury compound in acid, as 
 may be convenient, adding a little ammonium chloride, and then 
 potassic carbonate, until an opalescent precipitate appears. The 
 
242 VOLUMETKIC ANALYSIS. G8. 
 
 cyanide solution is then added. They give experiments showing 
 the trustworthiness of the process as applied to the nitrate, 
 sulphate, acetate, oxalate, sebate, and citrate of mercury ; and 
 state that the presence of nitrates, sulphates, chlorides, acetates, 
 oxalates, citrates, and butyrates of potassium, sodium, calcium, 
 and magnesium, and organic matter as far as tested, does not 
 interfere with the accuracy of the method. 
 
 From my experience, I cannot affirm that these methods of 
 working are satisfactory. There is considerable uncertainty as to 
 the end of the reaction, because less potassic cyanide will effect 
 a clearance if longer time is allowed. 
 
 These difficulties and uncertainties can, I find, be entirely 
 eliminated, and the process reduced to a series of operations which 
 are comparatively simple and rapid, by performing the titration in 
 an entirely different manner from either variation suggested by 
 the authors referred to. I employ a solution of mercuric chloride 
 containing O'Ol gm. of metal per c.c., and a solution of crystallized 
 potassic cyanide made by dissolving 7 gm. to the liter, the exact 
 value of which is found by titrating it against the mercury solution. 
 Strong ammonia diluted to ten times its bulk, and some diluted to 
 fifty or a hundred times its bulk, are convenient. 
 
 Process : If the mercury solution is not fit for titration, the metal is 
 precipitated as sulphide, which, after washing, is washed off the filter and 
 allowed to subside ; the clear water is then decanted off, and aqua regia 
 added to the moist residue. The precipitate, with the paper it is on, might 
 doubtless be treated direct with aqua regia, as Tuson and Neison found 
 that organic matter, so far as ihey tried it, does not influence the result. 
 To avoid the possibility of volatilizing the mercury salt, the aqua regia is 
 allowed to act in the cold. In a few hours, sometimes in far less time, the 
 residue is of a pure ^yellow colour, and the solution may be diluted and 
 filtered. The solution, or an aliquot part of it, is then coloured distinctly 
 with litmus, treated with successive small quantities of powdered potassic 
 carbonate until alkaline, warming but slightly, and then rendered just acid 
 with dilute hydrochloric acid, with subsequent boiling to remove the carbonic- 
 anhydride. The mercury is not precipitated at all, unless the carbonic 
 anhydride is boiled out before acidification. After cooling, the dilutest 
 ammonia mentioned above is added, a drop at a time, until the litmus in the 
 solution shows that the excess of acid is very slight, or in just insufficient 
 quantity to produce a permanent precipitate. A quantity of cyanide 
 solution, which is known to be in excess of that required, is added, and, as 
 a guide for the first titration, the ammonia may be added until a slight 
 precipitate is produced, and cyanide until the solution is cleared. Two or 
 three drops (not more) of the 1 in 10 ammonia are introduced, and then 
 more of the mercury solution is added until the permanent turbidity 
 produced matches that obtained by adding O'l c.c. of the mercury solution 
 to about the same bulk of water as the test, and containing approximately 
 the same amounts of litmus and free ammonia. Each drop of the mercury 
 solution added produces its maximum turbidity in a few seconds, and it can 
 be seen at a glance, if the flasks are properly placed, whether this turbidity 
 is equal to or less than the standard. In a few seconds more it is quite 
 obvious whether the turbidity is permanent or is growing less. Too much 
 free ammonia causes the precipitate to clot together, and so vitiates the 
 result. The presence of the litmus tends, in my experience, to lessen the 
 
G9. NICKEL. 243 
 
 error due to the variation in the state of aggregation of the precipitate 
 when too much ammonia has been added. The turbidities so obtained will 
 remain apparently unchanged for many hours. The (VI c.c. excess of 
 mercury solution is of course allowed for in the calculation." 
 
 NICKEL. 
 
 69. THE estimation of this metal volumetrically has now 
 become satisfactory, and we are indebted to T. Moore (C. N. Ixxii. 
 92) for a much more perfect process than was given by him in the 
 previous edition. The modified process consists in discarding the 
 use of cupric ferrocyanide as the indicator, and substituting silver 
 iodide in its place. Moore's own description of the method is as 
 follows : 
 
 "If to an ammoniacal solution of nickel containing Agl in 
 suspension (silver iodide being almost insoluble in weak ammonia) 
 there is added potassic cyanide, the solution will remain turbid so 
 long as all the nickel is not converted into the double cyanide of 
 nickel and potassium, the slightest excess of cyanide being indicated 
 by the clearing up of the liquid, and, furthermore, this excess 
 may be exactly determined by adding a solution of silver until the 
 turbidity is reproduced. It is a fortunate circumstance that the 
 complicated side-reactions existing in Parke's copper assay do not 
 appear to take place with nickel solutions, at least not when the 
 temperature is kept below 20 C. This is fully borne out by the 
 fact that the potassic cyanide may be standardized on either silver 
 or nickel solutions with equal exactness. In practice it has been 
 found best to proceed in the following manner : 
 
 Standard solution of Silver nitrate, containing about 3 gm. of 
 silver per liter. The strength of this solution must be accurately 
 known. 
 
 Potassic iodide, 10 per cent, solution. 
 
 Potassic cyanide, 22 to 25 gm. per liter. This solution must be 
 tested every few days, owing to its liability to change. 
 
 Standardizing- the Cyanide Solution. This may be accomplished in 
 two ways: (a) on a solution of nickel of known metallic contents, or (6) on 
 the silver solution. 
 
 (a) First accurately establish the relation of the cyanide to the silver 
 solution, by running into a beaker 3 or 4 c.c. of the former; dilute this with 
 about 150 c.c. of water, render slightly alkaline with ammonia, and then add 
 a few drops of the potassic iodide. Now carefully run in the silver solution 
 until a faint permanent opalescence is produced, which is finally caused to 
 disappear b\~ the further addition of a mere trace of cyanide. The 
 respective volumes of the silver and cyanide solutions are then read off, and 
 the equivalent in cyanide of 1 c.c. silver solution calculated. A solution 
 containing a known quantity of nickel is now required. This must have 
 sufficient free acid present to prevent the formation of any precipitate, on 
 the subsequent addition of ammonia to alkaline reaction ; if this is not so, 
 a little anmionic chloride may be added. A carefully measured quantity of 
 the solution is then taken, containing about O'l gm. of nickel, and rendered 
 distinctly alkaline with ammonia, a few drops of potassic iodide added, and 
 
 R 2 
 
244 VOLUMETEIG ANALYSIS. 69. 
 
 the liquid diluted to 150 or 200 c.c. A few drops of the silver solution are 
 now run in, and the solution stirred to produce a uniform turbidity. The 
 solution is now ready to be titrated with the potassic cyanide, which is 
 added slowly and with constant stirring until the precipitate wholly 
 disappears; a few extra drops are added, after which the beaker is placed under 
 the silver nitrate burette, and this solution gently dropped in until a faint 
 permanent turbidity is again visible ; this is now finally caused to dissolve 
 by the mere fraction of a drop of the cyanide. A correction must now be 
 applied for the excess of the cyanide added, by noting the amount of silver 
 emplo^yed, and working out its value in cyanide from the data already 
 found; this excess must then be deducted, the corrected number of c.c. 
 being then noted as equivalent to the amount of nickel employed. 
 
 (b) Having determined the relative value of the cyanide to the silver 
 solution, and knowing accurately the metallic contents of the latter, then 
 Ag x G'27196 gives the nickel equivalent. This method is quite as accurate 
 as the direct titration. 
 
 A modification of the above process, wherein one burette only 
 is necessary, has been found very convenient, and lias given most 
 excellent results. It is as follows : 
 
 When a solution of potassic cyanide, containing a small quantity of 
 silver cyanide dissolved in it, is added to an ammoniacal solution of nickel 
 containing potassic iodide, it is seen that silver iodide is precipitated, and 
 the turbidity thus caused in the solution continues to increase up to the 
 point where the formation of the nickelo-potassic c} r anide is complete ; any 
 further addition after this stage is reached will produce a clearing up of the 
 liquid, until, at last, the addition of a single drop causes the precipitate to 
 vanish. This final disappearance is most distinct, and leaves no room for 
 doubt. Such a solution may be prepared by dissolving 20 to 25 gm. of 
 potassic cyanide in a liter of water, adding to this about 0'25 gm. silver 
 nitrate previously dissolved in a little water. For large quantities of nickel 
 the quantity of silver may advantageously be diminished, and vice versa. 
 The value of the cyanide is best ascertained in the manner already 
 described, on a nickel solution. 
 
 Small quantities of cobalt do not seriously affect the results, but 
 It must be remembered that it will be estimated with the nickel ; 
 its presence is at once detected by the darkening of the solution. 
 Manganese or copper render the process valueless, so also does 
 zinc ; the latter, however, in alkaline pyrophosphate solution 
 exercises no influence. In the presence of alumina, magnesia, or 
 ferric oxide, citric acid, tartaric acid, or pyrophosphate of soda 
 may be employed to keep them in solution. The action of iron is 
 somewhat deceptive, as the solution, once cleared up, often 
 becomes troubled again on standing for a minute ; should this 
 occur, a further addition of cyanide must be given until the liquid 
 is rendered perfectly limpid. The temperature of the solution 
 should never exceed 20 C. : above this the results become 
 irregular. The amount of free ammonia has also a disturbing 
 influence ; a large excess hinders or entirely prevents the reaction ; 
 the liquid should, therefore, be only slightly but very distinctly 
 alkaline. A word of caution must be given regarding the potassic 
 cyanide, as many of the reputed pure samples are very far from 
 
70. NITRATES. 245 
 
 being so. The most hurtful impurity is, however, sulphur, as it 
 gives rise to a darkening of the solution, owing to the formation of 
 the less readily soluble silver sulphide ; to get rid of the sulphur 
 impurity it is necessary to thoroughly agitate the cyanide liquor 
 with oxide of lead, or, what is far preferable, oxide of bismuth. 
 
 As regards the exactness of the methods, it may be said, that, 
 after a prolonged experience, extending over many thousands of 
 estimations, they have been found to be more accurate and reliable 
 than either the electrolytic or gravimetric methods, and when time 
 is a consideration the superiority is still more pronounced. The 
 employment of organic acids or sodic pyrophosphate in the case 
 when iron, zinc, etc., are present, allows the operator to dispense 
 with the tedious separation which their presence otherwise entails-; 
 and this is a matter of considerable importance in the assay of 
 nickel mattes or German silver." 
 
 NITROGEN AS NITRATES AND NITRITES. 
 
 Nitric Anhydride. 
 
 :N T2 5 =108. 
 
 Nitrous Anhydride. 
 
 Normal acid x 0-0540 = ]S T2 5 
 
 Ditto x 0-1011 =KN T 3 
 
 Metallic iron x 0-3750 = HNO 3 
 
 Ditto x 0-601 8 = KN0 3 
 
 Ditto x 0-3214 = N 2 5 
 
 70. THE accurate estimation of nitric acid in combination. 
 presents great difficulties, and can only be secured by indirect 
 means ; the methods here given are sufficient for most purposes. 
 Very few of them can be said to be simple, but it is to be feared 
 that no simple process can ever be obtained for the determination 
 of nitric acid in many of its combinations. 
 
 1. Gay L.US sac's Method modified by Abel (applicable only 
 to Alkaline Nitrates). 
 
 This process depends upon the conversion of potassic or sodic 
 nitrates into carbonates by ignition with carbon, and the titration 
 of the carbonate so obtained by normal acid. The number of c.c. 
 of normal acid required multiplied by O'lOl will give the weight 
 of pure potassic nitrate in grams ; by 0'085, the weight of sodic 
 nitrate in grams. 
 
 The best method of procedure is as follows : 
 
 The sample is finely powdered and dried in an air bath, and 1 gm., or- an 
 equivalent quantity in grains, weighed, introduced into a platinum crucible. 
 
246 VOLUMETRIC ANALYSIS. 
 
 and mixed with a fourth of its weight of pure graphite (prepared by 
 Erodie's process), and four times its weight of pure ignited sodic chloride. 
 The crucible is then covered and heated moderately for twenty minutes over 
 a B un sen's burner, or for eight or ten minutes in a muffle (the heat must 
 not be so great as to volatilize the chloride of sodium to any extent). If 
 sulphates are present they will be reduced to sulphides ; and as these would 
 consume the normal acid, and so lead to false results, it is necessary to 
 sprinkle the fused mass with a little powdered potassic chlorate, and heat 
 again moderately till all effervescence has ceased. The crucible is then set 
 aside to cool, warm water added, the contents brought upon a filter, and 
 washed with hot water till the washings are no longer alkaline. The filtrate 
 is then titrated with normal acid in the ordinary way. 
 
 2. Estimation of Nitrates by Distillation with Sulphuric Acid. 
 
 This method is of very general application, but particularly so 
 with the impure alkaline nitrates of commerce. The process needs 
 careful manipulation, but yields accurate results. 
 
 There are two methods of procedure. 
 
 (a) To bring the weighed nitrate into a small tubulated retort with 
 a cooled mixture of water and strong sulphuric acid, in the proportion of 10 
 c.c. of water and 5 c.c. of sulphuric acid for 1 gin. of nitrate. The neck of 
 the retort is drawn out to a point and bent downward, entering a potash or 
 other convenient bulb apparatus containing normal caustic alkali. The 
 retort is then buried to its neck in the sand-bath, and heated to 170 C. 
 (338 Fahr.) so long as any liquid distils over ; the heat must never exceed 
 175 C. (347 Fahr.), otherwise traces of sulphuric acid will come 1 over with 
 the nitric acid. The quantity of acid distilled over is found by titrating the 
 fluid in the receiver with normal acid as usual. 
 
 (b) Distillation in a Partial Vacuum (Finkener).- By this 
 arrangement there is no danger of contaminating the distillate with 
 sulphuric acid, inasmuch as the operation is conducted in a water 
 bath, and when once set going needs no superintendence. 
 
 The retort is the same as before described, but the neck is not drawn out 
 or bent; the stopper of the tubulure must be well ground. The receiver is 
 a 200-c.c. flask with narrow neck, containing the requisite quantity of normal 
 alkali diluted to about 30 c.c. The receiver is bound, air-tight, to the neck 
 of the retort (which should reach nearly to the middle of the flask) by 
 means of a vulcanized tube; the proportions of acid and water before 
 mentioned are introduced into the retort with a tube funnel. The stopper 
 of the retort is then removed, and the contents, both of the receiver and 
 retort, heated by spirit or gas lamp to boiling, so as to drive out the air ; the 
 weighed nitrate contained in a small tube is then dropped into the retort, 
 the stopper inserted, the lamps removed, and the retort brought into the 
 water bath, while the receiver is kept cool with wet tow, or placed in cold 
 water. The distillate is titrated as before. 1 or 2 gm. of saltpetre require 
 about four hours for the completion of the process. 
 
 Finkener obtained very accurate results by this method. 
 "When chlorides are present in the nitrate, a small quantity of 
 moist oxide of silver is added to the mixture before distillation. 
 
70. 
 
 NITRATES. 
 
 247 
 
 3. Estimation by conversion into Ammonia (Schxilze and 
 Vernon Harcourt). 
 
 The principle of this method is based on the fact that when 
 a nitrate is heated with a strong alkaline solution, and zinc added, 
 
 Fig. 44. 
 
 ammonia is evolved ; when zinc alone is used, however, the 
 quantity of ammonia liberated is not a constant measure of the 
 nitric acid present. Vernon Ha r court and Sie we rt appear to 
 have arrived independently at the result that by using a mixture 
 of zinc and iron the reaction was perfect (/. C. S. 1862, 381 ; An. 
 diem. u. Phar. cxxv. 293). 
 
 A convenient form of apparatus is shown in fig. 44. 
 
 The distilling flask holds about 200 c.c., and is closely connected by a bent 
 tube Avith another smaller flask, in such a manner that both may be placed 
 obliquely upon a sand-bath, the bulb of the smaller flask coming just under 
 the neck of the larger. The oblique direction prevents the spirting of the 
 boiling liquids from entering the exit tubes, but as a further precaution, 
 these latter are in both flasks turned into the form of a hook ; from the second 
 flask, which must be somewhat wide in the mouth, a long tube passes through 
 aLiebig's condenser (which may be made of wide glass tube) into an 
 ordinary tubulated receiver, containing normal sulphuric acid coloured with 
 an indicator. The end of the distilling tube reaches to about the middle of 
 the receiver, through the tubulure of which Harcourt passes a bulb 
 apparatus of peculiar form, containing also coloured normal acid ; instead of 
 this latter, however, a chloride of calcium tube, filled with broken glass, and 
 moistened with acid, will answer the purpose. The distilling tube should be 
 cut at about two inches from the cork of the second flask, and connected by 
 means of a well-fitting vulcanized tube ; by this means water may be passed 
 through the tube when the distillation is over so as to remove any traces of 
 ammonia which may be retained on its sides. All the corks of the apparatus 
 should be soaked in hot paraffine, so as to fill up the pores. 
 
 All being ready, about 50 gm. of finely granulated zinc (best made by 
 pouring molten zinc into a warm iron mortar while the pestle is rapidly 
 being rubbed round) are put into the larger flask with about half the 
 quantity of clean iron filings which have been ignited in a covered crucible 
 (fresh iron and zinc should be used for each analysis) ; the weighed nitrate 
 is then introduced, either in solution, or with water in sufficient quantity to 
 
2-iS VOLUMETRIC ANALYSIS. 70. 
 
 dissolve it, strong solution of caustic potash added, and the flask immediately 
 connected with the apparatus, and placed on a small sand-bath, which can 
 be heated by a gas-burner, a little water being previously put into the 
 second flask. Convenient proportions of material are i gm. nitre, and 
 about 25 c.c. each of water, and solution of potash of spec, grav. .1/3. 
 The mixture should be allowed to remain at ordinary temperature for about 
 an hour (Eder). 
 
 Heat is now applied to that part of the sand-bath immediately beneath 
 the larger flask, and the mixture is gradually raised to the boiling point. 
 "When distillation has actually commenced, the water in the second flask is 
 made to boil gently ; by this arrangement the fluid is twice distilled, and any 
 traces of fixed alkali which may escape the first are sure to be retained in the 
 second flask. The distillation with the quantities above named will occupy 
 about an hour and a half, and is completed when hydrogen is pretty freely 
 liberated as the potash becomes concentrated. The lamp is then removed, 
 and the whole allowed to cool, the distilling tube rinsed into the receiver, 
 also the tube containing broken glass ; the contents of the receiver are then, 
 titrated with ^ caustic potash or soda as usual. 
 
 Eder recommends that an ordinary retort, with its beak set upwards, 
 should be used instead of the flask for holding the nitrate, and that an 
 aspirator should be attached to the exit tube, so that a current of air may be 
 drawn through during and after the distillation. 
 
 Chlorides and sulphates do not interfere with the accuracy 
 of the results. Harcourt, Eder, and many others, including 
 myself, have obtained very satisfactory results by this method. 
 
 Siewert has suggested a modification of this process. The dis- 
 tilling apparatus is a 300 350 c.c. flask with tube leading to two 
 small flasks connected together as wash bottles, and containing 
 standard acid. For 1 gm. of nitre, 4 gm. of iron, and 10 gm. 
 of zinc filings, with 16 gm, of caustic potash, and 100 c.c. of 
 alcohol of sp. gr. 0*825 are necessary. After digesting for half an 
 hour in the cold or in slight warmth, a stronger heat may be 
 applied to drive out all the ammonia into the acid flasks. Finally. 
 10 15 c.c. of fresh alcohol are admitted to the distilling flask, 
 and distilled off to drive over the last traces of ammonia, and the 
 acid solution then titrated residually as usual. The alcohol is 
 used to prevent bumping, but this is also avoided in the original 
 process by adopting the current of air recommended by Eder. 
 
 The copper-zinc couple devised by Gladstone and Tribe has 
 been used by Thorp for the reduction of nitrates and nitrites 
 occurring in water residues, etc. (/. C. S. 1873, 545). The 
 resulting ammonia is distilled into weak hydrochloric acid, and an 
 aliquot portion then JS T esslerized in the usual way. 
 
 M. W. Williams (J, C. S. 1881, 100) has shown that this 
 reduction, in the case of small quantities of nitric or nitrous acids, 
 may be carried on by mere digestion with a properly arranged 
 couple at ordinary temperatures, and may safely be hastened by 
 increasing the temperature to about 25 C. in the presence of 
 certain saline or acid substances ; alkaline substances, on tho 
 contrary, retard the action. The details are further described ii\ 
 Part VI, 
 
TO. NITRATES. 249 
 
 4. By Oxidation of Ferrous Salts (Pelouze). Not available in the 
 presence of Organic Matter. 
 
 The principle upon which this well-known process is based 
 is as follows : 
 
 (a) When a nitrate is brought into contact with a solution of 
 ferrous oxide, mixed with free hydrochloric acid, and heatedj part 
 of the oxygen contained in the nitric acid passes over to the iron, 
 forming a persalt, while the base combines with hydrochloric acid, 
 and nitric oxide (NO 2 ) is set free. 3 eq. iron= 168 are oxidized 
 by 1 eq. nitric acid 63. If, therefore, a weighed quantity of the 
 nitrate be mixed with an acid solution of ferrous chloride or 
 sulphate of known strength, in excess, and the solution boiled, to 
 expel the liberated nitric oxide, then the amount of unoxidized 
 iron remaining in the mixture found by a suitable method of 
 titration, the quantity of iron converted from ferrous into ferric 
 oxide will be the measure of the original nitric acid in the propor- 
 tion of 168 to 63 ; or by dividing 63 by 168, the factor 0'375 is 
 obtained, so that if the amount of iron changed as described be 
 multiplied by this factor, the product will be the amount of nitric 
 acid present. 
 
 This method, though theoretically perfect, is in practice liable to 
 serious errors, owing to the readiness with which a solution of 
 ferrous oxide absorbs oxygen from the atmosphere. On tins- 
 account accurate results are only obtained by conducting hydrogen 
 or carbonic acid gas through the apparatus while the boiling is- 
 carried on. This modification has been adopted by Fresenius 
 with very satisfactory results. 
 
 The boiling vessel may consist of a small tubulated retort, supported 
 in such a manner that its neck inclines upward : a cork is fitted into the 
 tubulure, and through it is passed a small tube connected with a vessel for 
 generating either carbonic acid or hydrogen. If a weighed quantity of pure 
 metallic iron is used for preparing the solution, the washed carbonic acid or 
 hydrogen should be passed through the apparatus while it is being dissolved ; 
 the solution so obtained, or one of double sulphate of iron and ammonia of 
 known strength, being already in the retort, the nitrate is carefully introduced, 
 and the mixture heated gently by a small lamp, or by the water bath, for ten 
 minutes or so, then boiled until the dark-red colour of the liquid disappears,, 
 and gives place to the brownish-yellow of ferric compounds. The retort is 
 then suffered to cool, the current of carbonic acid or hydrogen still being 
 kept up, then the liquid diluted freely, and titrated with & permanganate. 
 
 Owing to the irregularities attending the use of permanganate 
 with hydrochloric acid, it is preferable, in case this acid has been 
 used, to dilute the solution less, and titrate with bichromate. Two 
 grams of pure iron, or its equivalent in double iron salt, 0'5 gm. 
 of saltpetre, and about 60 c.c. of strong hydrochloric acid, are 
 convenient proportions for the analysis. 
 
 Eder (Z. a. C. xvi. 267) has modified Fresenius' improve- 
 ments as follows : 
 
250 VOLUMETRIC ANALYSIS. 
 
 1*5 gm. of very thin iron wire is dissolved in 30 to 40 c.c. of pure fuming 
 hydrochloric acid, placed in a retort of about 200 c.c. capacity ; the beak of 
 the retort points upwards, at a moderately acute angle, and is connected with 
 ti U-tube, which contains water. Solution of the iron is hastened ~by appty- 
 ing a small flame to the retort. Throughout the entire process a stream of 
 CO 2 is passed through the apparatus. When the iron is all dissolved the 
 solution is allowed to cool, the stream of CO 2 being maintained ; the weighed 
 quantity of nitrate contained in a small glass tube (equal to about 0'2 gm. 
 HNO 3 ) is then quickly passed into the retort through the neck ; the heating 
 is continued under the same conditions as before, until the liquid assumes 
 the colour of ferric chloride. The whole is allowed to cool in a stream of 
 CO 2 ; water is added in quantity, and the unoxidized iron is determined l>y 
 titration with permanganate. The results are exceedingly good. 
 
 If the CO 2 be generated in a flask, with a tube passing down- 
 wards for the reception of the acid, air always finds its way into the 
 retort, and the results are unsatisfactory. Eder recommends the 
 use of Kipp's CO 2 apparatus. By carrying out the operation 
 exactly as is now to be described, he has obtained very good results 
 with ferrous sulphate in place of chloride. 
 
 The same apparatus is employed ; the tube through which CO 2 enters the 
 retort passes to the bottom of the liquid therein, and the lower extremity of 
 this tube is drawn out to a fine point. The bubbles of CO 2 are thus reduced 
 in size, and the whole of the nitric acid is removed from the liquid by the 
 passage of these bubbles. The iron wire is dissolved in excess of dilute 
 sulphuric acid (strength 1 : 3 or 1 : 4). When the liquid in the retort has 
 become cold, a small tube containing the nitrate is quickly passed, by means 
 of a piece of platinum wire attached to it, through the tubulus of the retort, 
 and the cork is replaced before the tube has touched the liquid ; CO 2 is again 
 passed through the apparatus for some time, after which, by slightly loosening 
 the cork, the tube containing the nitrate is allowed to fall into the liquid. 
 The Avhole is allowed to remain at the ordinary temperature for about an 
 hour this is essential after which time the contents of the retort are heated 
 to boiling, CO 2 being passed continuously into the retort, and the boiling 
 continued till the liquid assumes the light yellow colour of ferric sulphate. 
 After cooling, water is added (this maybe omitted with bichromate), and the 
 unoxidized iron is determined by permanganate. 
 
 Eder also describes a slight modification of this process, allowing 
 of the use of a flask in place of the retort, and of ammonio-ferrous 
 sulphate in place of iron wire. Although the titration with per- 
 manganate is more trustworthy when sulphuric acid is employed 
 than when hydrochloric acid is used, he nevertheless thinks that the 
 use of ferrous chloride is generally to be recommended in preference 
 to that of ferrous sulphate. When the chloride is employed, no 
 special concentration of acid is necessary ; the nitric oxide is more 
 readily expelled from the liquid, and the process is finished in 
 a shorter time. 
 
 The final point in the titration with permanganate, when the 
 sulphate is employed, is rendered more easy of determination by 
 adding a little potassic sulphate to the liquid. 
 
 & Direct titration of the resulting- Ferric salt by Stanncms 
 
70. NITRATES. 251 
 
 Chloride. Fresenius has adopted the use of stannous chloride for 
 titrating the ferric salt with very good results. 
 
 The following plan of procedure is recommended by the same 
 authority. 
 
 A solution of ferrous sulphate is prepared by 'dissolving 100 gm. of the 
 crystals in 500 c.c. of hydrochloric acid of spec. grav. 1*10 ; when used for 
 the analysis, the small proportion of ferric oxide invariably present in it 
 is found by titrating with stanuous chloride. The nitrate being Aveighed 
 or measured, is brought together with 50 c.c. (more or less, according to the 
 quantity of nitrate) of the iron solution into a long-necked flask, through 
 the cork of which two glass tubes are passed, one connected with a CO' 2 
 apparatus, and reaching to the middle of the flask, the other simply an outlet 
 for the passage of the gas. When the gas has driven out all the air, the flask 
 is at iirst gently heated, and eventually boiled, to dispel all the nitric oxide. 
 The CO 2 tube is then rinsed into the flask, and the liquid, while still boiling 
 hot, titrated for ferric chloride, as in 64.1. 
 
 The liquid must, however, be suffered to cool before titrating 
 with iodine for the excess of stannous chloride. While cooling, 
 the stream of CO 2 should still be continued. The quantity of iron 
 changed into peroxide, multiplied by the factor O375, will give the 
 amount of nitric acid. 
 
 Example : (1) A solution of stannous chloride was used for titrating 
 10 c.c. of solution of pure ferric chloride containing 0*215075 gm. Fe. 
 25'65 c.c. of tin solution were required, therefore that quantity was equal 
 to 0*0807 gm. of HNO 3 , or 0*069131 gm. of N 2 O 5 - 
 
 (2) 50 c.c. of acid ferrous sulphata were titrated with tin solution for 
 ferric oxide, and 0*24 c.c. was required. 
 
 (3) 1 c.c. tin solution=3*3 c.c. iodine solution. 
 
 (4) 0*2177 gm. of pure nitre was boiled, as described, with 50 c.c. of the 
 acid ferrous sulphate, and required 45*03 c.c. tin solution, and 4*7 c.c. iodine 
 
 4*7 c.c. iodine solution =1*42 c.c. SnCl' 2 
 
 The peroxide in the protosulphate solution=0*24 c.c. 
 
 f66 
 
 45-03 1-66=43-37, therefore 25'65 : 0'069131=43'37 : ^,=0*1169 N 2 O 5 
 instead of 0'1163, or 53*69 per cent, instead of 53*41. A mean of this, with 
 three other estimations, using variable proportions of tin and iron solutions, 
 gave exactly 53*41 per cent. The process is therefore entirely satisfactory in 
 the case of pure materials. 
 
 The above process is slightly modified by Eder. About 10 gm. 
 of ammonio-ferrous sulphate are dissolved in a flask, in about 50 c.c. 
 of hydrochloric acid (sp. gr. 1 -07) in a stream of CO 2 . The tube 
 through which the CO 2 enters is drawn to a point ; an exit-tube, 
 somewhat trumpet-shaped, to admit of any liquid that may spirt 
 rinding its way back into the flask passes downwards into water. 
 After solution of the double salt, the nitrate is dropped in with 
 the precautions already detailed, and the liquid is boiled until the 
 nitric oxide is all expelled. The hot liquid is diluted with twice 
 its own volume of water, excess of standard stannous chloride 
 solution is run in, the whole is allowed to cool in a stream of CO 2 , 
 and the excess of tin is determined by means of standard iodine. 
 
 ^JtS 
 
 f OF THE 
 
 (UNIVERSITY 
 V r^,. 
 
9n9 
 
 VOLUMETEIC ANALYSIS. 
 
 (c) Holland's Modification of the 
 Pelouze Process. The arrangement of 
 apparatus shown in fig. 45 obviates the 
 use of an atmosphere of H or CO 2 . A is 
 a long-necked assay flask drawn off at B, so 
 as to form a shoulder, over which is passed 
 a piece of stout pure india-rubber tube, D, 
 about 6 centimeters long, the other end 
 terminating in a glass tube, F, drawn off 
 so as to leave only a small orifice. On 
 the elastic connector D is placed a screw 
 clamp. At c, a distance of 3 centimeters 
 Fig. 45. from the shoulder, is cemented with 
 
 a blow-pipe a piece of glass tube about 
 
 2 centimeters long, surmounted by one of stout elastic tube rather 
 more than twice that length. The elastic tubes must be securely 
 attached to the glass by binding with wire. After binding, it is as 
 well to turn the end of the conductor back, and smear the inner 
 surface with fused caoutchouc, and then replace it to render the 
 joint air-tight. 
 
 Process : A small funnel is inserted into the elastic tube at c, the clamp 
 at D being for the time open ; after the introduction of the solution, 
 followed by a little Avater which washes all into the flask, the funnel is 
 removed, and the flask supported by means of the wooden clamp, in the 
 inclined position it occupies in the figure. The contents are now made to 
 boil so as to expel all air and reduce the volume of the fluid to about 4 or 
 5 c.c. When this point is reached a piece of glass rod is inserted into the 
 elastic tube at c, which causes the water vapour to escape through F. 
 
 Into the small beaker is put about 50 c.c. of a previously boiled solution of 
 ferrous sulphate in hydrochloric acid (the amount of iron already existing 
 as persalt must be known). 
 
 The boiling is still continued for a moment to ensure perfect expulsion of 
 air from F, the lamp is then removed, and the caoutchouc connector slightly 
 compressed with the first finger and thumb of the left hand. As the flask 
 cools the solution of iron is drawn into it ; when the whole has nearly receded 
 the elastic tube is tightly compressed with the fingers, whilst the sides of the 
 beaker are washed with a jet of boiled water, which is also allowed to pass 
 into the flask. The washing may be repeated, taking care not to dilute more 
 than is necessary or admit air. Whilst F is still full of water, the elastic- 
 connector previously compressed with the fingers is now securely closed with 
 the clamp, the screw of which is worked with the right hand. Provided 
 the clamp is a good one, F will remain full of water during the subsequent 
 digestion of the flask. 
 
 After heating in a water bath at 100 for half an hour, the flask is removed 
 from the water bath and cautiously heated with a small flame, the fingers at 
 the same time resting on the elastic connector at the point nearest the 
 shoulder ; as soon as the tube is felt to expand, owing to the pressure from 
 within, the lamp is removed and the screw clamp released, the fingers main- 
 taining a secure hold of the tube, the gas-flame is again replaced, and when 
 the pressure on the tube is again felt, this latter is released altogether, thus 
 admitting of the escape of the nitric oxide through F, -which should be 
 below the surface of water in the beaker whilst these manipulations are 
 performed. The contents of the flask are now boiled until the nitric oxide 
 
NITRATES. 
 
 253 
 
 is entirely expelled, and the solution of iron shows only the brown colour of 
 the perchloride. At the completion of the operation the beaker is first 
 removed, and then the lamp. 
 
 It now only remains to transfer the ferric solution to a suitable vessel, and 
 determine the perchloride with staunous chloride as in b. 
 
 A mean of six experiments for the percentage determination of 
 X-0 5 in pure nitre gave 53'53 per cent, instead of 53*41. The 
 process is easy of execution, and gives satisfactory results. The 
 point chiefly requiring attention is that the apparatus should be 
 air-tight, which is secured by the use of good elastic tubes and 
 clamp. 
 
 5. S chlos in g-'s Method (available in the presence of Organic 
 
 Matter). 
 
 The solution of nitrate is boiled in a flask till all air is expelled, 
 then an acid solution of ferrous chloride drawn in, the mixture 
 boiled, and the nitric oxide gas collected over mercury in a balloon 
 filled with mercury and milk of lime ; the gas is then brought, 
 without loss, in contact with oxygen and water, so as to convert it 
 
 again into nitric acid, then titrated with -f^ alkali as usual. 
 
 This method was devised by Schlosing for the estimation of 
 nitric acid in tobacco, and is especially suitable for that and similar 
 purposes, where the presence of organic matter would interfere with 
 
254 VOLUMETttlC ANALYSIS. 
 
 the direct titration of the iron solution. "Where the quantity of 
 nitric acid is not below O15 gin. the process is fairly accurate, but 
 needs a special and rather complicated arrangement of apparatus, 
 the description of which may be found in the original paper in 
 Annal. de Chim. [3] xl. 479, or in Fresenius' Quant. AnaL, sixth 
 edition. 
 
 An arrangement of apparatus, dispensing with the use of mercury, 
 has been devised by Wildt and Scheibe (Z. a. C. xxiii. 151), 
 which simplifies the analysis and gives accurate results with not 
 less than 0*25 gin. N 2 5 . With smaller quantities the results are 
 too low. Fig. 46 shows the apparatus used. 
 
 A is an Erlenmeyer's flask of 250 c.c. capacity, containing 
 the solution to be analyzed. B is a round-bottomed flask of 
 250 300 c.c. capacity, half filled with caustic soda, to absorb any 
 HC1 which might be carried over from A. C is an Erlenmeyer's 
 flask of 750 c.c. capacity, containing a little water to absorb the 
 nitric acid. D is a tube, containing water to collect any nitric 
 acid not absorbed by the water in C. The tube d is bent, as shown 
 in the diagram, and drawn out to a point, to diminish the size of 
 the bubbles. The tube e is wide, and cut obliquely to prevent 
 water collecting and passing into C. 
 
 Process : The clip b is closed and c opened, and the tube e disconnected 
 from f. The solutions in A and B are then boiled for 20 minutes to remove 
 all oxygen. The tubes e and /are again connected, the clip c is closed, the 
 flame under B increased to prevent the liquid in C from being drawn 
 back, and the clip b is opened. As soon as steam issues from the tube a, it 
 is dipped into a conical glass containing 50 c.c. of ferrous chloride prepared 
 according to Schldsing's directions, and the flume under A is removed. 
 when the ferrous chloride enters the flask. The clip b is regulated with the 
 finger and thumb, so as to prevent the entry of air into the flask. The 
 conical vessel is rinsed two or three times with water, and this is allowed 
 to enter the flask, and the clip b is then closed, and the vessel A heated. 
 The liquid in A turns brown in a short time, and nitric acid is evolved. 
 The clip c is opened slightly from time to time until the pressure is high 
 enough, when it is opened entirely. The flames must be regulated so that 
 a slow current of gas bubbles through the water in C. The hydrochloric 
 acid is removed by the caustic soda in B, and the nitric oxide on coming 
 in contact with the air in C. is oxidized, and the nitric acid absorbed by 
 the water. In case the current of gas is too rapid, the escaping nitric 
 acid is absorbed in I). After an hour the tubes e and / are disconnected, 
 while the solutions in A and B are still boiling, and the nitric acid is 
 titrated with dilute caustic soda (about i normal). The vessel C must 
 be well cooled during the whole experiment, which occupies about an 
 hour and a half. 
 
 Good results were obtained with nitrates of potash and soda, 
 both alone and mixed with ammonium sulphate, superphosphate, 
 and amido compounds. With superphosphate the solution should 
 be made slightly alkaline, to prevent the liberation of nitric acid. 
 
 AVarington (J. C. S. 1880, 468) has made a series of experi- 
 ments on the original Schlosing process, for the purpose of 
 testing its accuracy, when small quantities of nitric acid have to be 
 
70. 
 
 NITRATES. 
 
 determined in the presence of organic substances, such for instance 
 as in soils, the sap of beet-root, etc. ; but instead of converting the 
 nitric oxide back into nitric acid as in the original method, he 
 collected the gas either over caustic soda as recommended by 
 Reich ardt, or over mercury, and ascertained its amount by 
 measurement in Frankland's gas apparatus. The results obtained 
 by AVarington plainly showed that even on the most favourable 
 circumstances the method as usually worked in Germany, either by 
 the alkalimetric titration or by measurement of the gas, invariably 
 gave results much too low, especially if the quantity of nitrate 
 operated on was small, say 5 or 6 centigrams of nitre ; moreover,, 
 
 Fig. 47. 
 
 when sugar or similar organic substance was present the resulting 
 gas was very impure, and the distillates were highly coloured from 
 the presence of some volatile products.. The nitric oxide also 
 suffered considerable diminution of volume, when left for any time 
 in contact with the distillate, especially when over caustic soda. 
 This being the case, the following modification originally recom- 
 mended by Schlosing was adopted, in which CO 2 was employed, 
 both to assist in expelling the air from the apparatus, and to chase 
 out the nitric oxide produced. 
 
 The form of apparatus adopted by Warington is shown in 
 fig. 47. The vessel in which the reaction takes place is a small 
 
256 VOLUMETRIC ANALYSIS. 70. 
 
 tubulated receiver, the tubulure of which has been bent near its 
 extremity to make a convenient junction with the delivery tube, 
 which dips into a trough of mercury on the left. The long supply 
 tube attached to the receiver is of small bore, and is easily filled by 
 a J c.c. of liquid. The short tube to the right is also of small bore, 
 and is connected by a caoutchouc tube and clamp with an apparatus 
 for the continuous production of carbonic acid. 
 
 In using this apparatus the supply tube is first filled with 
 strong HC1, and CO 2 is passed through the apparatus till a portion 
 of the gas collected in a jar over mercury is found to be entirely 
 absorbed by caustic potash. The current of gas is then stopped 
 by closing the clamp to the right. A chloride of calcium bath at 
 140 is next brought under the receiver, which is immersed one- 
 half or more in the hot fluid ; the temperature of the bath is 
 maintained throughout the operation by a gas burner placed beneath 
 it. By allowing a few drops of HC1 to enter the hot receiver, the 
 CO 2 it contains is almost entirely expelled. A jar filled with 
 mercury is then placed over the end of the delivery tube, and all 
 is ready for the commencement of a determination. 
 
 The nitrate, which should be in the form of a dry residue in 
 a small beaker or basin, is dissolved in about 2 c.c.* of strong 
 ferrous chloride solution, 1 c.c. of strong HC1 is added, and the 
 whole is then introduced into the receiver through the supply tube, 
 being followed by successive rinsings with HC1, each rinsing not 
 exceeding a J c.c., as the object is to introduce as small a bulk of 
 liquid as possible. The contents of the receiver are in a few 
 minutes boiled to dryness ; a little CO 2 is admitted before dryness 
 is reached, and again afterwards to drive over all remains, of nitric 
 oxide. If the gas will not be analyzed till next day, it is advisable 
 to use more CO 2 , so as to leave the nitric oxide diluted with several 
 times its volume of that gas. As soon as one operation is concluded 
 the apparatus is ready for another charge. 
 
 This mode of working presents the following advantages : 
 
 (1) The volume of liquid introduced into the apparatus is much 
 diminished, and with this of course the amount of dissolved air 
 contributed from this source. 
 
 (2) By evaporation to dryness a complete reaction of the nitrate 
 .and ferrous chloride, and a perfect expulsion of the nitric oxide 
 formed, is as far as possible attained. 
 
 (3) The nitric oxide in the collecting jar is left in contact with 
 .a much smaller volume of acid distillate, and its liability to 
 absorption is greatly diminished by its dilution with CO-. 
 
 The results obtained with this apparatus by Warington on 
 small quantities of nitre alone, and mixed with variable quantities 
 
 * Supposing the ferrous chloride to contain 2 gm. of iron per 10 c.c., then 1 c.c. of 
 the solution will be nearly equivalent to 0'12 gm. of nitre, or 0'0166 gin. of nitrogen. 
 A considerable excess of iron should, however, always be used. 
 
70. NITRATES. 257 
 
 of ammonic salts and organic substances including sugar, showed 
 a marked improvement upon the method as usually carried out. 
 
 A further improvement has been made in this method by 
 Warington (/. C. S. 1882, 345), and described by him as 
 follows : 
 
 The apparatus now employed is quite similar to that shown in fig. 47, with 
 the only difference that the bulb retort in which the reaction takes place is 
 now only 1 inch in diameter, thus more exactly resembling the. form 
 employed by Sch losing. A bulb of this size is sufficient for the analysis 
 of soil extracts ; for determinations of nitrates in vegetable extracts a larger 
 bulb is required. 
 
 The chief improvement consists in the use of CO 2 as free as possible from 
 oxygen. The generator is formed of two vessels. The lower one consists of 
 a bottle with a tubulurc in the side near the bottom; this bottle is supported 
 in an inverted position, and contains the marble from which the gas is 
 generated. The upper vessel consists of a similar bottle standing upright ; 
 this contains the HC1 required to act on the marble. The two vessels are 
 connected by a glass tube passing from the side tubulure of the upper vessel 
 to the inverted mouth of the lower vessel ; the acid from the upper vessel 
 thus enters below the marble. CO 2 is generated and removed at pleasure by 
 opening a stop-cock attached to the side tubulure of the lower vessel, thus 
 allowing HC1 to descend and come in contact with the marble. The 
 fragments of marble used have been previously boiled in water. The boiling 
 is conducted in a strong flask. After boiling has proceeded some time, 
 a caoutchouc stopper is fixed in the neck of the flask, and the flame removed ; 
 boiling will then continue for some time in a partial vacuum. The lower 
 reservoir is nearly filled with the boiled marble thus prepared. The HC1 
 has been also well boiled, and before it is introduced into the upper reservoir 
 it has dissolved in it a moderate quantity of cuprous chloride. As soon as 
 the acid has been placed in the upper reservoir it is covered by a layer of 
 oil. The apparatus being thus charged is at once set in active work by 
 opening the stop-cock of the marble reservoir ; the acid descends, enters the 
 marble reservoir, and the CO 2 produced drives out the air which is necessarily 
 present at starting. As the acid reservoir is kept on a higher level than the 
 marble reservoir, the latter is always under internal pressure, and leakage of 
 air from without cannot occur. 
 
 The presence of the cuprous chloride in the hydrochloric acid not only 
 ensures the removal of dissolved oxygen, but affords an indication to the eye 
 of the maintenance of this condition. So long as the acid remains of 
 an olive tint, oxygen will be absent ; but should the acid become of a clear 
 blue-green, it is no longer certainly free from oxygen, and more cuprous 
 chloride must be added. 
 
 A further slight improvement adopted consists in the use of freshly-boiled 
 reagents, which are employed in as small a quantity as possible. When 
 boiling the hydrochloric acid it is well to add a few drops of ferrous chloride, 
 in order more certainly to remove any dissolved oxygen. 
 
 The mode of operation is as follows : The apparatus is fitted together, the 
 long funnel tube attached to the bulb retort being filled with water. 
 Connection is made with the glass stop- cock of the CO 2 generator by means 
 of a short stout caoutchouc tube, provided with a pinch-cock. The pinch- 
 cock being opened, the stop-cock is turned till a moderate stream of bubbles 
 rises in the mercury trough ; the stop-cock is left in this position, and the 
 admission of gas is afterwards controlled by the pinch-cock, pressure on 
 which allows a few bubbles to pass at a time. The heated chloride of calcium 
 bath is next raised, so that the bulb retort is almost submerged; the 
 temperature, shown by a thermometer which forms part of the apparatus, 
 
 s 
 
258 VOLUMETRIC ANALYSIS. 70. 
 
 should be 130 140. By boiling small quantities of water or hydrochloric 
 acid in the bulb retort in a stream of CO 2 the air present is expelled; the 
 supply of gas must be stopped before the boiling has ceased, so as to leave 
 little in the retort. Previous to very delicate experiments it is advisable to 
 introduce through the funnel tube a small quantity of nitre, ferrous chloride, 
 and hydrochloric acid, rinsing the tube Avith the latter reagent ; any trace of 
 oxygen remaining in the apparatus is then consumed by the nitric oxide 
 formed, and after boiling to d^ness, and driving out the nitric oxide with 
 CO 2 , the apparatus is in a perfect condition for a quantitative experiment. 
 
 Soil extracts may be used without other preparation than concentration. 
 Vegetable juices, which coagulate when heated, require to be boiled and 
 filtered, or else evaporated to a thin syrup, treated with alcohol and filtered. 
 A clear solution being thus obtained, it is concentrated over a water-bath to 
 the smallest volume, in a beaker of smallest size. As soon as cool, it is mixed 
 with 1 c.c. of a cold saturated solution of ferrous chloride and 1 c.c. HC1, 
 both reagents having been boiled and cooled immediately before use. In 
 mixing with the reagents care must be taken that bubbles of air are not 
 entangled; this is especial^ apt to occur with viscid extracts. The quantity 
 of ferrous chloride mentioned is amply sufficient for most soil extracts, but 
 it is well perhaps to use 2 c.c. in the first experiment of a series; the 
 presence of a considerable excess of ferrous chloride in the retort is thus 
 ensured. With bulky vegetable extracts more ferrous chloride should be 
 employed ; to the syrup from 20 gm. of mangel sap should be added 5 c.c. 
 of ferrous chloride, and 2 c.c. of hydrochloric acid. 
 
 The mixture of the extract with ferrous chloride and HC1 is introduced 
 through the funnel tube, and rinsed in with three or four successive ^ c.c. 
 of HC1. The contents of the retort are then boiled to dry ness, a little CO- 
 being from time to time admitted, and a more considerable quantity used at 
 the end to expel any remaining nitric oxide. The most convenient tem- 
 perature is 140, but in the case of vegetable extracts it is well to commence 
 at 130, as there is some risk of the contents of the retort frothing over. 
 The gas is collected in a small jar over mercury. As soon as one operation 
 is completed, the jar is replaced by another full of mercury, and the 
 apparatus is ready to receive a fresh extract. A series of five determinations, 
 with all the accompanying gas analyses, may be readity performed in one 
 day. The bulb retort becomes encrusted with charcoal when extracts rich 
 in organic matter are the subject of analysis ; it is best cleaned first with 
 water, and then by heating oil of vitriol in it. 
 
 Mercury, contrary to the statement in most text-books, is gradually 
 attacked by hj'drochloric acid in the presence of air ; the mercury in the 
 trough is thus apt to become covered with a grey chloride, and it is quite 
 necessary to keep the store of mercury in contact with sulphuric acid to 
 preserve its mobile condition. 
 
 The gas analysis is of a simple character; the gas is measured after 
 absorption of the CO 2 by potash, and again after absorption of the nitric 
 oxide, the difference giving the amount of this gas. For the absorption of 
 nitric oxide, a saturated solution of ferrous chloride was for some time 
 employed. This method is not, however, perfectly satisfactory when the 
 highest accuracy is required, the nitric oxide being generally rather under- 
 estimated, except the process of absorption is repeated with a fresh portion 
 of ferrous chloride. The error is greater in proportion to the quantity of 
 unabsorbed gas present. ThuSj with a mixture of nitrogen and nitric oxide 
 containing little of the former, absorption of the nitric oxide by successive 
 treatment with oxygen and pyrogallol over potash showed 97' 8 per cent, of 
 nitric oxide ; while the same gas, analyzed by a single absorption with ferrous 
 chloride (after potash), showed 97' 5 per cent, of nitric oxide. With a mixture 
 containing more nitrogen, the oxygen method showed 65'9 per cent, of nitric 
 oxide ; while one absorption with ferrous chloride gave 64'2 per cent., and 
 
70. NITRATES. 259 
 
 a second absorption, in which the ferrous chloride was plainly discoloured, 
 66'2 per cent. The use of ferrous chloride as an absorbent for nitric oxide 
 has now been given up, and the oxygen method substituted. All the 
 measurements of the gas are now made without shifting the laboratory 
 vessel ; the conditions are thus favourable to extreme accuracy^ 
 
 The chief source of error attending the oxygen process lies in the 
 small quantity of carbonic oxide produced during the absorption with 
 pyrogallol ; this error becomes negligible if the oxygen is only used 
 in small excess. The difficulty of using the oxygen in nicely 
 regulated quantity may be removed by the use of Bischof's gas 
 delivery- tube. This may be made of a test-tube, having a small 
 perforation half an inch from the mouth. The tube is partly 
 filled with oxygen over mercury, and its mouth is then closed by 
 a finely-perforated stopper, made from a piece of wide tube, and 
 fitted tightly into the test-tube by means of a covering of 
 caoutchouc. When this tube is inclined, the side perforation 
 being downwards, the oxygen is discharged in small bubbles from 
 the perforated stopper, while mercury enters through the side 
 opening. Using this tube, the supply of oxygen is perfectly 
 under control, and can be stopped as soon as a fresh bubble ceases 
 to produce a red tinge in the laboratory vessel. The trials made 
 with this apparatus have been very satisfactory. If nitrites are to 
 be estimated by this method, it is necessary first to convert them 
 into nitrates, with excess of hydrogen peroxide, which is entirely 
 destroyed by the subsequent evaporation to dryness. 
 
 Technical method for Alkaline Nitrates and Nitrated Manures. 
 
 Wagner uses a simple arrangement of apparatus, which gives 
 fairly good results, and permits of rapid working. 
 
 A 200 c.c. flask is fitted with a two-hole rubber stopper. One hole carries 
 an ordinary gas delivery tube, and the other a thistle funnel, having a stop- 
 cock below the funnel. The end of this tube is narrowed, and does not 
 quite reach the liquid in the flask. 
 
 A solution of 200 gm. of iron wire in hydrochloric acid is made and 
 diluted to 1 liter. 40 c.c. of this solution are placed in the flask, and the air 
 expelled by boiling. 10 c.c. of a standard solution of sodic nitrate, con- 
 taining 33 gm. per liter, are then placed in the funnel, and allowed gradually 
 to drop into the boiling solution of iron. A gas tube graduated to 100 c.c. 
 is filled with boiled and cooled distilled water, and the nitric oxide collected 
 in the usual way. When the nitre solution is nearly all dropped in, the 
 funnel is filled with 20 per cent. HC1, and run down ; this is repeated, the 
 liquid being still kept gently boiling. 10 c.c. of the solution to be tested 
 are now put into the funnel, taking care that not more than 100 c.c. of gas 
 will result. The gas is collected as before in a fresh tube precisely as in the 
 case of the pure nitrate. In this manner five or six estimations can be 
 made with the one and the same ferrous solution. Finally, a fresh test is 
 made with standard nitre solution ; the readings of the tubes are taken, and 
 as they will all be of same temperature and pressure no correction is 
 necessary, all being allowed to cool to the same point. 
 
 s 2 
 
260 VOLUMETRIC ANALYSIS. 
 
 The calculation is easy. Suppose that the pure nitre gave 90c.c. 
 of gas, this volume = 6-33 gm, of XaXO 8 , or 1 c.c. = 0*00366 
 gin. = 0-000604 gm. X. 
 
 Technical use of the Pelouze Process for Manures. Vincent 
 Edwards adopts the following method for manures containing 
 nitrates together with ammonia and other matters (C. N. Ixxi. 307). 
 The solutions required are : 
 
 Standard Potassic bichromate, 14*742 gm. per liter. 1 c.c. = 
 0-0085 gm. XaXO 3 or 0-0101 gm. KXO 3 . 
 
 Ferrous Sulphate. 100 gm. of crystallized salt with 100 c.c. of 
 concentrated H 2 S0 4 per liter. 
 
 The exact working strength of these two solutions in practice, is 
 found by boiling 50 c.c, of the iron solution till it becomes thick 
 in a stout well annealed glass flask, preferably of Jena glass, which 
 is fitted with a Buns en valve, made by cutting the rubber tube 
 with a sharp razor, the glass tube to which it is fitted passing- 
 through a light fitting rubber stopper ; after boiling the flask is set 
 aside to cool, then 100 c.c. or so of water are added, and the 
 titration made with bichromate in the usual way with fresh 
 solution of ferricyanide as indicator. 
 
 Process : 1020 gm. of the nitrated manure, according to its richness, are 
 exhausted with water and the liquid made up to 200 c.c. 
 
 20 c.c. of this solution are placed in the boiling flask together with 50 c.c. 
 of the iron solution, the stopper with valve is then inserted, and the mixture 
 boiled until it becomes thick, and semi-solid drops are splashed against the 
 sides of the flask ; the flask is then enveloped in a cloth, and removed 
 to cool ; when this has occurred, 100 c.c. or so of water are run into the flask, 
 well shaken, then titrated with the bichromate as in the case of the blank 
 experiment. 
 
 Example : The blank titration showed that c.c. of iron solution 
 required 54 c.c. of bichromate. 20 c.c. of the manure solution = 1 gm. 
 manure were treated as above described, and required 31 c.c. of bichromate, 
 therefore 5431 = 23 c.c. which multiplied by 0'0085 = 0'1955 or 19'55 % 
 of XaXO 3 in the manure. The manure was known to be a mixture of 
 20/ of nitrate of soda, of 95'5% strength, with 80 per cent, of an 
 ammouiacal guano. 
 
 This technical process is, of course, chiefly valuable where the 
 nitrate is required to be estimated apart from the ammonia, 
 
 6. By the Kj eldahl Process. 
 
 By the modified method described on page 85, it is now quite 
 possible to estimate the nitrogen in commercial nitrates with great 
 accuracy and very little personal attention. 
 
 7. lodometric Estimation of Nitrates. 
 
 F. A. Goocli and H. Gruener (Amer. J. Sci. xliv. 117) 
 recommend distilling the nitrate (about 0'2 gm.) with 20 c.c. of 
 
70. NITRATES. 261 
 
 a saturated solution of crystallized manganous chloride in strong 
 hydrochloric acid, in a current of CO' 2 . The products of the 
 distillation are passed into a solution of potassic iodide, and the 
 liberated iodine is afterwards titrated by means of sodic thiosulphate. 
 3 mols. of iodine correspond with 2 mols. of nitric acid 
 
 Process : The apparatus employed consists of a bent pipette, serving 
 instead of a retort, which is connected with a Kipp's apparatus evolving 
 CO 2 . The other goose-neck-like end is sealed to a Will and Varrentrap 
 nitrogen bulb, the exit tube of which is drawn out, so that it may be pushed 
 well within the inlet tube of a Will and Varrentrap absorption flask. 
 A third receiver simply acts as a trap to exclude air from the absorption 
 apparatus proper. The titration should be completed immediately after the 
 distillation, during which the nitrogen bulbs should be immersed in cold 
 w r ater; otherwise, traces of dissolved nitric oxide might get oxidized and 
 liberate more iodine. 
 
 Another method worked out by H. Gruener consists in 
 distilling the nitrate with potassic iodide and phosphoric acid 
 (Amer. J. Sd. xlvi., July, 1883.) 
 
 Process : The nitrate, not to exceed in amount 0'05 gm. of potassio nitrate, 
 is introduced into a retort, together with ten times its weight of potassic 
 iodide, and 17 to 20 c.c. of phosphoric acid, of specific gravity 1'43. All 
 water used should be recently boiled. CO 2 is passed from a proper apparatus. 
 The neck of the retort passes into a receiver containing a known amount 
 of TV arsenious oxide, alkaline with a good excess of sodic' bicarbonate, and 
 diluted to a convenient bulk. To this flask is attached for additional safety 
 a simple trap containing water. The solution in the retort is boiled until it 
 is clear that no more iodine remains, when the receiver, after proper washing 
 and addition of the liquid in the trap, is titrated with iodine to find the 
 amount of arsenious oxide still left. This gives the measure of the iodine 
 evolved and consequently of the nitrate present. 
 
 These processes are simply mentioned here, as perhaps being 
 available under particular circumstances, but the author has had 
 no experience of them. The test examples given by the operators 
 are fairly satisfactory, especially the first. 
 
 8. G-asometric estimation as Nitric Oxide. 
 
 This method of estimating nitrogen existing as nitric and nitrous 
 acids, either separately or together, is an exceedingly delicate one, 
 and capable of great accuracy under proper manipulation. 
 
 It is now best known as the Crum-Frankland method, the 
 original idea emanating from Crum, and afterwards improved in 
 detail of manipulation by Frankland and Armstrong, in their 
 well-known method of water analysis. 
 
 So far as the use of the method for water analysis is concerned, 
 the process is given in Part VI., where the shaking tube which is 
 used for the decomposition of the nitrogen compounds by mercury 
 and sulphuric acid is figured, and the details of the process as 
 applied to waters fully described. 
 
262 VOLUMETRIC ANALYSIS. 70. 
 
 The method there given, however, requires the use of a gas 
 apparatus. This method obviates that necessity, and though the 
 results cannot be said to be absolutely as exact, they are very 
 satisfactory for some purposes, such as the examination of nitrous 
 vitriol, raw commercial nitrates, manures, etc. 
 
 The apparatus used is Lunge's nitrometer, a figure of which is 
 given in the section on technical gas analysis, accompanied with 
 a description of the method of using it. The 'application of the 
 instrument to the estimation of nitrous and nitric acids in vitriol 
 and other substances is explained in the same section. 
 
 The volume of the nitric oxide obtained can be read off to -^ c.c. ; 
 it is reduced by Buns en's tables to and 760 m.m., and the 
 percentage of the acid calculated from it. Each c.c. of XO, 
 measured at and 760 m.m., corresponds to 1*343 m.gm. XO, or 
 1-701 m.gm. K 2 :} , or 2-417 m.gm. X 2 5 , or 4-521 KXCF, or 
 3-805 m.gm. K"aN0 3 . By this process, of course, nitric and nitrons 
 acids cannot be distinguished, but are always estimated together. 
 
 The principle of the reaction is explained in the section on Water 
 Analysis (Estimation of titrates and Nitrites), and the satisfactory 
 nature of the method for vitriol-testing has been amply demonstrated 
 by Watts, by Davis (C. N. xxxvii. 45), and many others. The 
 instrument itself has been made in several modified ways, but the 
 principle of its construction is the same. 
 
 Allen (Analyst v. 181) recommends the use of this instrument 
 for the estimation of nitrates and nitrites in water residues ; and 
 to obviate the difficulty in reading the volume Avhich sometimes 
 arises from the mercurial froth, he uses two nitrometers side by 
 side, in one of which is worked a pure standard nitrate solution, 
 and in the other the material for analysis under precisely the same 
 conditions of temperature, pressure, etc. If the apparatus 
 containing the comparative test is free from leakage, it may be 
 retained for a long period for the purpose of comparison. 
 
 9. Colorimetric Methods. 
 
 Phenol Method (Spr eng-el). Both this and the carbazol method 
 are applicable chiefly to waters where only small proportions of 
 nitric acid are to be estimated. The solutions required are 
 
 Standard Potassic nitrate. 0-7215 gm. of IvXO 3 is dissolved 
 in a liter of water. 1 c.c. of this solution = -f^ m.gm. of X, or one 
 part X in 100,000. 100 c.c. of it should be diluted to a liter for 
 use in the actual analysis, and 10 c.c. taken, to avoid the possible 
 error resulting from measuring only 1 c.c. 
 
 Phenol Sulphomc acid. 80 c.c. of liquefied pure phenol are 
 poured into 200 c.c. of pure concentrated sulphuric acid in 
 a flask, and kept on a boiling water bath for eight hours. The 
 mixture is cooled, and 140 c.c. of pure hydrochloric acid with 
 420 c.c. of water added. The solution is then ready for use. 
 
70. NITRATES. 263 
 
 Process : 10 c.c. of the water under examination and 10 c.c. of the 
 standard potassic nitrate are pipetted into two small beakers and placed near 
 the edge of a hot plate. When nearly evaporated they are removed to the 
 top of the water-oven and left there till they are evaporated to complete 
 dryness. As this operation usually takes about an hour and a half, it is 
 better, when time is an object, to evaporate to dryness in a platinum dish 
 over steam. The residue in each case is then treated with 1 c.c. of the 
 phenolsulphuric acid, and the beakers are placed on the top of the water- 
 oven. If the water under examination contain a large quantity of nitrates 
 the liquid speedily assumes a red colour, which, in a good water, will not 
 appear for about ten minutes. After standing for fifteen minutes the beakers 
 are removed, the contents of each washed out successively into a 100 c.c. 
 measuring glass, a slight excess (about 20 c.c. of 0'96) of ammonia added, 
 the 100 c.c. made up by the addition of water, and the yellow liquid 
 transferred to a Nessler glass. The more strongly coloured liquid is then 
 partly transferred to the measuring glass again and the tints compared 
 a second time. In this way the tints are adjusted, and when, as far as 
 possible, matched, the liquid that has been partially removed is made up to 
 the 100 c.c. mark with water, and, after well mixing, finally compared, If 
 not exactly the same, a new liquid can at once be made up, probably of 
 exactly the same tint, as the first experiment gives very nearly the number 
 of c.c. of the one equivalent to the 100 c.c. of the other. A. E. Johnson 
 in his very useful Analyst's Laboratory Companion (p. 50) has given 
 a table for obtaining the nitrogen in parts per 100,000, and also in grains 
 per gallon, by this method. 
 
 In the case of very good waters, 20, 50, or more c.c. should be evaporated 
 to a small bulk, rinsed into a small beaker, and evaporated to dryness and 
 treated as above only 5 c.c. of the standard potassic nitrate ( = 0'5 N in 
 100,000) being taken. In the case of very bad waters, 10 c.c. should be 
 pipetted into a 100 c.c. measuring flask and made up to the mark with 
 distilled water, then 10 c.c. of the well mixed liquid (=1 c.c. original water) 
 withdrawn and treated as above. 
 
 A. II. Gill (Tech. Quarterly vii., 1894, 5562) has studied 
 this method, and says : The phenolsulphonic acid used should be 
 the pure disulphonic acid (C 6 H 3 (OH) S0 3 H 2 ), which, with nitric 
 acid, gives picric acid even in the cold (Kekule, Lehrbucli iii. 236.) 
 To prepare it, 3 gm. of pure phenol and 37 gm. (20 '1 c.c.) of pure 
 sulphuric acid of 1 '84 sp. gr. are mixed in a flask and heated for 
 six hours to 100 in a water bath. The acid, as thus prepared, 
 may crystallize out on standing, but may be brought into solution 
 again by reheating for a short time. 
 
 Process : The author takes 1 or 2 c.c. of the water (diluted if necessary), 
 containing about - 0007 m.gm. of nitrogen as nitrate, and rapidly evaporates 
 over a steam bath, in a 2 inch porcelain dish, the dish being removed as 
 soon as dry, or, preferably, when just a drop remains. With "ground 
 waters/' 10 c.c. of a portion which has been decolourized by alumina in the 
 cold are evaporated. The residue is treated in the dish with enough of the 
 acid to cover it, 10 drops (=0'7 c.c.) being usually sufficient, and by stirring 
 with a glass rod every part of the residue is moistened. Seven c.c. of water 
 are added and stirred, and then ammonia in excess, and the solution again 
 stirred. The colour is compared with the standard, either in a similar dish, 
 or both are poured into tubes If inch deep and f inch internal diameter. 
 
 The standard solution of potassic nitrate is made by dissolving 
 0'720 gm. KNO :s in water, diluting to 1 liter, evaporating 10 c.c. in vacua 
 
264 VOLUMETRIC ANALYSIS. 70. 
 
 over sulphuric acid, treating the residue -with phenolsulphonic acid, as above, 
 and diluting to 1 liter. One c.c. of this solution contains O'OOL m.gm. 
 nitrogen. A measured volume of it is made alkaline with ammonia as 
 required. 
 
 The author concludes from his experiments that : 
 
 1. The pure disulphonic acid gives the best results. 
 
 2. No advantage is gained by treating the water residue with the acid at 
 100, as Sprengel directs; equally good results are obtained in the cold ; 
 but if the temperature be as low as 0, decidedly low results are obtained. 
 
 3. The amount of acid used makes very little difference so long as there is 
 enough used. 
 
 4. There is a loss of nitrogen during evaporation, which is least if the 
 evaporation take place in vacua over sulphuric acid, or rapidly in an open 
 dish at 100 ; slower evaporation, at 65, caused more loss, and the dry 
 residues, if further heated, lose nitrogen. The addition of sodium carbonate 
 does not prevent the loss. 
 
 5. Chlorine does not interfere if less than two parts per 100.000 be 
 present ; if more be present, evaporation should be conducted in vacua ; 
 but if the chlorine exceed seven parts per 100,000 it should be removed 
 by pure silver sulphate before evaporation. 
 
 6. In comparing the colours the most accurate estimations are made 
 when the intensity of the colour does not exceed that produced by 1 c.c. of 
 a water containing about 0'05 part nitrogen per 100,000. The colour 
 produced by O'lO part per 100,000 is very difficult to match accurately. 
 
 7. The process does not estimate the nitrogen as liitrite, as the action of 
 nitrous acid results in the formation of nitrosophenol CH 4 (NO) (OH), 
 which is colourless in dilute solutions. 
 
 The Carbazol Method. The standard potassic nitrate and pure 
 sulphuric acid, as above, are required as well as the following 
 special reagents : 
 
 (a) Silver sulphate solution containing 4 '3945 gm. per liter; 
 1 c.c. will precipitate one part of chlorine per 100,000 from 
 100 c.c. of water. 
 
 (b) Aluminium sulphate solution free from chlorides and iron, 
 5 gm. per liter. 
 
 (c) Carbazol Solution. 0'6 gm. carbazol is dissolved in glacial 
 acetic acid, and the solution made up to 100 c.c. with the glacial 
 acid. For use, 1 c.c. of this solution is withdrawn by a pipette 
 and mixed w r ith 15 c.c. of pure re-distilled sulphuric acid. 
 
 It is advisable to prepare a series of solutions containing - 03, 
 0'05, 0'07, etc., parts of nitrogen per 100,000 from the standard 
 nitrate solution by diluting with water. 
 
 Process : To 100 c.c. of the water, the amount of chlorides in which has 
 first been ascertained, sufficient of the silver sulphate solution is added from 
 a burette to precipitate all the chlorides. To this solution, containing the 
 silver chloride in suspension, 2 c.c. of the aluminium sulphate solution are 
 added, and the whole made up to a convenient bulk, 110 c.c. in the case of 
 waters containing 1 to 6 parts of chlorine per 100,000. The solution is then 
 filtered, and 2 c.c. of this filtrate are then taken for the nitrate estimation, 
 and, of course, the amount found must be calculated from the diluted bulk 
 of the solution. To the 2 c.c. of the filtered water contained in a test-tube, 
 4 c.c. concentrated sulphuric acid are added, and the mixture well cooled, 
 
70. 
 
 NITRITES. 
 
 265 
 
 1 c.c. of the carbazol solution in sulphuric acid as above described is then 
 added, and a bright green colour appears in a few moments if nitrates are 
 present. The amount of nitrate is roughly gauged from the colour 
 produced, and 2 c.c. of the standard nitrate solution, considered to be equal 
 to it, are placed in a second test-tube, and the operation repeated with it and 
 a fresh 2 c.c. of the water under examination at the same time. If the 
 tints are not similar a fresh comparison must be made, and in every case it is 
 necessary to repeat the operation with a fresh quantity of the water, so that 
 the colours may be developed as nearly as possible simultaneously. 
 
 The author states that 0*0008 m.gm.of nitrogen as nitrate maybe detected 
 by the carbazol method. The removal of chlorides is necessary for accurate 
 results, but the nitration does not take much time when aluminium sulphate 
 solution is added as described. 
 
 Other special methods for the estimation of nitrates in water 
 will be given in the section on Water Analysis. 
 
 Fig. 48. 
 
 NITRITES. 
 1, lodometric method. 
 
 Dunstan and Dymond (Pliarm. Journ. 
 [3] xix. 741) have devised a method for the 
 estimation of N 2 3 in organic and inorganic 
 combination which is both simple in operation 
 and accurate in results. The authors point 
 out that although the inorganic nitrites may 
 be accurately analyzed by gasometric methods, 
 or by permanganate 1 , it is impossible to use 
 such methods for the organic compounds or 
 their alcoholic solutions. The reaction upon 
 w T hich the method depends is not new, being 
 based on the following equation 
 
 2HI + 2ffis T 2 m 2H 2 + 2NO + 1 2 . 
 
 The liberated iodine is titrated with - thio- 
 sulphate in the usual way. The chief merit 
 in the process is the simple form of apparatus 
 used, and which is shewn in fig. 48. 
 
 A stout glass flask, having a capacity of 
 about 100 c.c., is closed by a tightly fitting 
 rubber stopper, through which passes a piece of 
 rather wide glass tubing (C), one end of which 
 (that within the flask) is cut. off obliquely, so 
 that liquid may flow freely through it. The 
 other end of the tube is connected by means 
 of a piece of thick rubber tubing with 
 a large glass tube, which forms a lipped funnel 
 (A). A steel screw clamp (B) regulates com- 
 munication between the funnel and the tube, 
 and the short interval of rubber which is not 
 occupied by glass tubing forms a hinge upon 
 
2G6 VOLUMETRIC ANALYSIS. 70. 
 
 which the flask may be moved into a position at right angles to- 
 the funnel, in order to mix by agitation the liquids which are 
 introduced into the apparatus. The absence of any leak in the 
 apparatus is ascertained by boiling about 50 c.c. of water in the 
 flask until steam has continuously issued from the funnel for some 
 few minutes, when the screw clip is quickly closed and simul- 
 taneously the source of heat is removed. A little water is now- 
 placed in the funnel and the flask is cooled by immersion in water. 
 On sharply inverting the flask the " click " of the water against 
 the airless flask should be quite distinct. ]N T o water should be 
 drawn from the funnel or from any of the joints into the flask, 
 and no diminution in the intensity of the " click " should be 
 observed after the apparatus has been standing, neither when the 
 flask is inverted and the funnel empty should any bubbles of air 
 pass through into the liquid. Having thus proved the absence 
 of any leak in the apparatus, it is ready for use. The flask is now 
 free from all but mere traces of oxygen. A conclusive proof of 
 this is obtained by boiling in the flask a solution of potassic 
 iodide, acidified with diluted sulphuric acid, and then, after the 
 closed flask has been cooled, the funnel removed and its place 
 taken by a smaller glass tube filled with air-free water, the 
 apparatus is connected with a reservoir of pure nitric oxide. 
 When the clamp is unscrewed nitric oxide is drawn into the flask,, 
 and should any oxygen be present nitrous acid will be produced, 
 and consequently iodine will be set free. This experiment has 
 often been made by the authors, who have failed to observe any 
 but an insignificant trace of liberated iodine. 
 
 Process : 5 c.c. of a 10 per cent, solution of potassic iodide, 5 c.e. of 
 a 10 per cent, solution of sulphuric acid, and 40 c.c. of water are introduced 
 into the flask, which is securely fitted with the cork carrying the funnel and 
 tube. The screw clip being open, and a free passage left for the escape of 
 steam, the liquid is boiled. After a few minutes, when a,r\y iodine which 
 may have been liberated has been expelled, and the upper part of the flask is 
 completely filled with steam, which is also freely issuing from the funnel, the 
 clip is tightly closed, and at the same moment the source of heat is removed. 
 A little water is now put into the funnel, and also on the rim of the flask, as 
 a safeguard against a possible minute leakage, and the vessel is cooled, by 
 immersion in water. A solution containing a known weight of the nitrite 
 (equivalent to about O'l gm. of nitrous acid) is placed in the funnel, and 
 slowly drawn into the flask by cautiously unscrewing the clip. The liquid 
 which adheres to the funnel is washed into the flask with recently boiled and 
 air-free water, care being taken that during this operation no air is admitted 
 into the flask. When experiments are being made with organic nitrites 
 which are insoluble in water, they are dissolved in alcohol, and alcohol is also 
 used to wash the funnel. When the nitrite is very volatile, a little cold 
 alcohol should be put in the funnel, and the point of the pipette containing 
 the nitrite should be held at the bottom of the funnel beneath the alcohol, 
 and the liquid quickly drawn from the pipette into the flask. The nitrate 
 having been introduced, the flask is well shaken and the liberated iodine is 
 titrated with a standard solution of sodic thiosulphate, small quantities of 
 which are delivered from a burette into the funnel and gradually drawn into- 
 
NITRITES. 267 
 
 the flask ; the screw clip renders it quite easy to admit minute quantities of 
 the solution. As soon as the iodine is decolorized any standard solution 
 remaining in the funnel is returned to the burette. Or the funnel may, 
 before the titration is commenced, be replaced by the burette itself, and the 
 standard solution delivered direct into the flask. Starch may be used as an 
 indicator, but it is usually quite easy to observe the complete disappearance of 
 the yellow colour of the dissolved iodine. From the volume of the standard 
 solution used, the amount of nitrous acid is calculated from the equation 
 before given. 
 
 It is obvious that the apparatus might be improved in several 
 respects, as, for example, by constructing it entirely of glass, with 
 a ground stopper and tap, as well as by the use of a graduated 
 funnel to deliver the standard solution, and also in other ways. 
 
 The authors quote numerous experiments, comparing the method 
 with careful estimations of sodic and ethyl nitrites, gasometrieally 
 shelving excellent results. 
 
 As a further test of the accuracy of the process, experiments 
 were made with various organic nitrites of known purity. In 
 each instance a solution of the nitrite was made by weight, and 
 a weighed quantity was used for the estimation. To prevent any 
 loss of these volatile nitrites the experiments were conducted in 
 the following manner : A well-stoppered bottle half filled with 
 the alcohol corresponding to the nitrite'"' to be estimated was 
 weighed. Sufficient of the nitrite was now introduced by means 
 of a pipette to constitute approximately a 2 per cent, solution, and 
 the liquid again weighed. The exact strength of the solution 
 having been thus determined, the contents of the bottle were well 
 mixed, and the neck and stopper of the bottle dried. The bottle 
 was now re-weighed, and about 2 c.c. of the solution removed by 
 a pipette, care being taken not to wet the neck of the bottle. The 
 liquid having been introduced into the flask without exposure to 
 air, in the manner which has been previously described, the bottle 
 containing the solution was again weighed. The results obtained 
 with ethyl nitrite were : 
 
 Taken. Found. 
 
 O'OSS gin. 0'089 gm. 
 
 0-176 0-179 
 
 0-113 . 0-115 , 
 
 2. Analysis of Alkaline Nitrites by Permanganate. 
 
 Kinnicutt and Xef have experimented on the following 
 method, and obtained very fair results. 
 
 The sample of nitrite is dissolved in cold water in the proportion of about 
 1 to 300 : to this liquid T ^ permanganate is added drop by drop, till it has 
 
 * The corresponding alcohol was employed to prevent loss consequent on the occurrence 
 of a reverse chemical change, which takes place when a lower homologous alcohol is 
 mixed with the nitrite corresponding to a higher homologous alcohol ; for example, 
 a solution of ainyl nitrite in ethyl alcohol soon becomes a solution of ethyl nitrite in 
 amyl alcohol, from which the ethyl nitrite rapidly volatilizes. 
 
268 VOLUMETRIC ANALYSIS. 70. 
 
 a permanent red colour ; then 2 or 3 drops of dilute H-SO 4 , and immediately 
 afterwards a known excess of the permanganate. The liquid, which should 
 now be of a dark red colour, is strongly acidified with pure H-SO 4 , heated 
 to boiling, and the excess of permanganate determined by means of freshly 
 prepared T ^ oxalic acid. 1 c.c. permanganate-=0'0345 gm. ]S T aNO' 2 , or 
 0-0425 gm. KNO 2 . 
 
 Of course there must be no other reducing substance than the 
 nitrite present in the material examined, and, to ensure accuracy, 
 a blank experiment should be made with the like proportions of 
 H 2 S0 4 and oxalic acid. 
 
 3. Gasometric method. 
 
 Percy Frankland (/". C. S. liii. 364) adopts this method for 
 the estimation of nitrous acid in small quantity, but too large for 
 colorimetric estimation, and where also ammonia, organic matters, 
 and nitrates may co-exist. It is based on the fact that when 
 nitrous acid, together with excess of urea, is mixed with sulphuric 
 acid in the cold, the reaction is 
 
 2CO(JS T H 2 ) 2 + X 2 :5 - CO(jS T ETO) 2 + CO 2 + 2X 2 . 
 
 The decomposition is made in the Cr urn-Frank land shaking tube, 
 described and figured in Part VI., and the evolved nitrogen gas 
 measured in the usual gas apparatus. The ordinary nitrometer may 
 also be used for larger quantities of XO 2 by the same method. 
 
 In the case of an ordinary alkali nitrite, the dry substance, or 
 its solution evaporated to dryness, is mixed with excess of 
 crystallized urea, and dissolved in about 2 c.c. of boiling water in 
 a beaker, then transferred, with the rinsings, to the cup of the 
 apparatus, and passed into the tube. A few c.c. of dilute 
 sulphuric acid (1:5) are then passed in. A vigorous evolution of 
 gas takes place, and continues for some five minutes ; the gas is 
 a mixture of nitrogen and carbonic anhydride. The decomposition 
 is complete in fifteen minutes. A solution of pure sodic hydrate 
 (1 : 3) is now added through the cup, and the mixture violently 
 shaken, until the CO 2 is absorbed. The gas and liquid are then 
 transferred, by means of another mercury trough, to the laboratory 
 vessel, and the gas, which is double the volume of the X existing 
 as ]S 2 3 , measured in a gas ajiparatus, and its weight calculated in 
 the usual way. 
 
 Example : A solution of sodic nitrite was made and standardized with 
 permanganate, the result being that 10 c.c.=0'001346 gm. N. 10 c.c. of the 
 same solution were evaporated to dryness in a small beaker, about 0'2 gm. of 
 urea added, the whole dissolved in 2 c.c. of hot water, which, with the 
 rinsings, were transferred through the cup into the tube, treated with 
 sulphuric acid and caustic soda, then transferred to the gas apparatus with 
 the following results: Volume of N, 13'79 c.c.; mercurial pressure, 127'5 
 m.m. ; temperature, 17'7 C. The weight of N thus found, after the 
 necessary corrections, was 0'0013645 gm. 
 
71. OXYGEN. 269 
 
 The Crum -Frank land mercury method, described in the 
 section on Water Analysis, and in which the same shaking tube is 
 used, does not distinguish between nitric and nitrous nitrogen ; 
 but Percy Frank land required a method for the estimation of 
 nitrous acid in a mixture of nitrates, peptones, sugar, and various 
 salts occurring in a solution used for cultivation of micro-organisms, 
 and the experiments carried out by him showed that when such 
 a mixture was evaporated to dryness the loss of HNO 2 was consider- 
 able, and the results came out much too low. Further experiment, 
 however, showed that the addition of a slight excess of caustic 
 potash during evaporation prevented the loss of any HNO 2 ; and 
 on the other hand the addition of a slight excess of ammonic chloride 
 entirely destroyed it. Therefore by a combination of the mercury 
 and the urea methods, the estimation of nitric and nitrous acids 
 may be satisfactorily accomplished, the destruction of the HXO 2 
 on the one hand being effected by excess of NH 4 C1, whilst on the 
 other hand all loss of HJSTO 2 may be avoided by evaporation with 
 caustic alkali. The mode of procedure has the advantage over all 
 differential methods, in that each acid is determined individually 
 and independently of the other. 
 
 4. Mixtures of Alkaline Sulphites, Thiosulphates, and Nitrites. 
 
 Lunge and Smith (J. S. C. I. ii. 465) have shown that the only 
 satisfactory method of completely oxidizing sulphites and thio- 
 sulphates by permanganate is to add to the solution a large excess 
 of permanganate, more than sufficient for complete oxidation, and 
 Avith formation of MnO 2 . Excess of FeSO 4 is then added, and 
 again permanganate till pink. When such a mixture contains 
 nitrites, they will of course be oxidized to nitrates. 
 
 To find the amount of nitrites present, therefore, the following 
 method is adopted : 
 
 The solution of the substance in not too large quantity is 
 exactly oxidized as described, a known volume of standard ferrous 
 sulphate is added, together with a large excess of strong H 2 SO 4 . 
 The mixture is boiled nearly to dryness in a flask with slit valve, 
 diluted, and, when cool, titrated with permanganate. The difference 
 between the volume then required and that required by the original 
 Fe 2 SQ 4 , represents the nitric acid which has been reduced and 
 escaped as NO. 
 
 The exceedingly delicate colorimetric method of estimating 
 nitrites originally devised by Griess, and improved by others, will 
 be described in the section on Water Analysis. 
 
 OXYGEN. 
 
 0=16. 
 
 71. THE volumetric determination of the dissolved oxygen in 
 water, .is an operation of some importance in water analysis. It is. 
 
270 VOLUMETRIC ANALYSIS. 71. 
 
 well known that organic and bacterial contamination generally 
 exist side by side ; the organic matter offering a suitable nidus for 
 the growth of bacterial life. Water thus contaminated is 
 de-oxygenated by the living organisms, which consume oxygen 
 during their growth ; hence the importance of the estimation of 
 dissolved oxygen in water, as a means of ascertaining the 
 co-existence of the two kinds of impurity. 
 
 In brewing also a knowledge of the state of aeration of the wort 
 is sometimes of importance, especially at the fermentation stage of 
 the process. 
 
 Several methods have been proposed for carrying out the 
 estimation. Mo hr's method, depending on the oxidation of ferrous 
 compounds, with subsequent titration by permanganate, has not 
 come greatly into use. Winkler (Bericlite, 1888, 2851) has quite 
 recently proposed to take advantage of the oxidation of manganous 
 hydroxide* by dissolved oxygen, the higher oxide formed being 
 decomposed by sulphuric acid and potassic iodide with liberation 
 of iodine, which is estimated by titration with sodic thiosulphate. 
 This method is disturbed by the presence of nitrites, which also 
 liberate iodine from acidified potassic iodide ; great organic con- 
 tamination also interferes, inasmuch as the impurities present take 
 up a portion of the liberated iodine. 
 
 Schiitzenberger's method,! fully described in the last edition 
 of this book, has received great attention from many operators, 
 some of whom have reported favourably, whilst others find the 
 process unreliable. The reason for the anomalies apparent in the 
 reports of the various experimenters is shown in the results of an 
 interesting critical investigation of the process carried out by 
 Koscoe and Lunt (/. C. S. 1889, 552). They show that an 
 important disturbing influence had been overlooked, and explain 
 many previously ill-understood points in the process. 
 
 Schiitzenberger's original process depends on the reducing 
 action of sodic hyposulphite Na 2 S0 2 , prepared by the action of 
 zinc dust on a saturated solution of sodic bisulphite, containing 
 an excess of sulphurous acid. The estimation was originally 
 carried out in a large "Woullf 's bottle, of about two liters capacity, 
 filled with pure hydrogen. About 20 30 c.c. of water were 
 introduced, and slightly coloured blue by indigo-carmine solution. 
 The blue colour was then cautiously discharged by the careful 
 dropping in of hyposulphite solution. To the yellow reduced 
 liquid thus produced, the water to be examined was added from 
 .a pear-shaped vessel holding about 250 c.c. The dissolved oxygen 
 restored the blue colour by oxidation, and the amount of hypo- 
 . sulphite required to again decolorize the liquid was noted. 
 
 Schiitzenberger showed that when a small amount of indigo 
 
 * Obtained by mixing solutions of a manganous salt and caustic alkali. 
 
 t See Fermentation by P. S c h il t z e u b e r g e r (International Scientific Scries). 
 
71. OXYGEN. 271 
 
 was employed in the estimation, the' yellow colour produced when 
 the titration was completed quickly returned to blue, and this 
 when decolorized again turned blue, and so on for some time, until 
 double the first amount of hyposulphite had been used. He 
 showed also that by using a much larger amount of indigo the 
 double portion of hyposulphite was required at once. 
 
 By titrating an ammoniacal solution of copper sulphate with the 
 hyposulphite used he arrived at a value (though an erroneous one) 
 for the hyposulphite employed in his experiments, and concluded 
 that, at the first yellow colour produced in a titration where 
 a small amount of indigo was used, only half the oxygen actually 
 present had been obtained. The other half he accounted for by 
 saying that the reaction between hyposulphite and dissolved oxygen 
 is such, that one-half the oxygen becomes latent as hydrogen 
 peroxide, which slowly gives up half its oxygen. He thus accounted 
 for the return of the blue colour, as well as his observation that 
 only half the oxygen was at once obtained. To explain the 
 observation, that when a large amount of indigo was employed 
 the wliole, of the dissolved oxygen was found, he assumed that 
 a different reaction takes place, one between dissolved oxygen 
 and reduced indigo, in which the peroxide of hydrogen is not 
 formed. 
 
 Ramsay and Williams (/. C. S. 1886, 751), whilst agreeing 
 with Schiitzenberger and with Dupre,* that the process gives 
 reliable results, throw a doubt on the chemical explanation given 
 of the above experiments. 
 
 Instead of the ratio 1 : 2, they find 3 : 5 to be the ratio 
 between the first and total quantity of hyposulphite required when 
 -a small amount of indigo is employed, but give it only as the mean 
 expression of the varying ratios they obtain, and add, " but it is 
 difficult to devise an equation which will in a rational manner 
 account for this partition of oxygen" into two stages of the 
 process. Eoscoe and Lunt's investigation (J". C. S. 1889, 552) 
 lias thrown a new light on these experiments. They show (1) that 
 a series of fifteen estimations carried out with every care in 
 improved apparatus, and under apparently identical conditions, 
 gave discordant results, varying between 4 '55 and 6*50 c.c. of 
 hyposulphite for the same volume of water, showing a difference 
 of 0'35 per cent, of the moan value. (2) The rapidity of titration 
 has a great influence on the result. The mean of a series of ten 
 estimations carried out drop by drop was 5 '47, whilst ten 
 experiments with the same sample of water gave a mean of 7 '12 
 when the titration was performed quickly. (3) Not only is 
 a low result obtained by a slow titration and a high result by 
 a quick one, but by varying the time of titration still more, extreme 
 variations in the result are obtained; any value between 1 and 100 
 
 * Analyst x. 156. 
 
272 
 
 VOLUMETRIC ANALYSIS. 
 
 71. 
 
 per cent, of the total oxygen- present being shown to be possible. 
 (4) The ratio between the first reading and the total quantity 
 of hyposulphite required is not a constant one, and is shown to 
 be capable of an infinite range of variation. 
 
 Fig. 49. 
 
 The key to the explanation of these remarkable results is given 
 by the authors as follows: "The conclusion" from their experi- 
 ments "was, that when aerated water is introduced into an 
 atmosphere of pure hydrogen, it immediately begins to lose oxygen 
 
71. OXYGEN. 273 
 
 by diffusion into the hydrogen until an equilibrium is established." 
 By the recognition of this disturbing influence, the previous 
 anomalies are easily explainable on the following data. 
 
 (1) Discordant results are obtained from the same water, 
 because the several titrations are not performed in exactly the same 
 time, therefore, varying amounts of oxygen diffuse, and leave 
 a vary ing 'residue for titration. 
 
 (2) The high results of a quick titration are accounted for by 
 the fact that a large amount of oxygen is titrated and fixed before 
 it has had time to diffuse, whilst the slow titration gives a low 
 result, because a large amount of oxygen has already diffused 
 from the liquid before the titration is completed. JS'o greater 
 proof of the rapidity with which the water under examination lost 
 oxygen by the old process need be given than the fact, that 
 Schiitzenberger's results show that half the oxygen had left the 
 liquid by diffusion before the estimation could be completed. 
 
 (3) The return of the blue colour is due to the re-absorption 
 of the diffused oxygen by the sensitive yellow liquid, oxidation by 
 gaseous oxygen producing the blue colour, which is thus not due 
 to a reaction -within the liquid. 
 
 (4) The whole of the oxygen is obtained when a large amount 
 of indigo is used, because when reduced it is capable of at once 
 fixing the whole of the dissolved oxygen and thus prevents 
 diffusion. The use of so large a quantity of indigo, necessary to 
 effect this result, however, so disturbs the end-reaction that " it is 
 difficult to fix the point at which the last trace of blue has been 
 discharged with any degree of accuracy" (Dupre loc. cit.). Hence 
 a new method must be resorted to in which diffusion is eliminated, 
 and Roscoe and Lunt have devised the following method to 
 satisfy the conditions of the case. The apparatus employed by 
 them is shown in fig. 49. 
 
 It consists essentially (1) of an apparatus for the continuous 
 generation and purification of hydrogen, by the action of dilute 
 sulphuric acid on zinc ; (2) a 200 c.c. wide-mouthed bottle, fitted 
 with three burettes with glass taps, inlet and outlet tubes for 
 a current of hydrogen, and an outlet tube for the titrated liquid ; 
 (3) Winchester stock bottles of hyposulphite, indigo (not shown), 
 and water (sample), communicating with their respective burettes 
 by glass* syphons. The hydrogen generated in A passes through 
 two wash-bottles containing caustic potash, thence through two 
 E miner ling's tubes filled with glass beads, moistened with an 
 alkaline solution of potassic pyrogallate, an arrangement being 
 made whereby the beads may be re-moistened with fresh pyrogallate 
 from the bottles beneath, the liquid being forced up by hydrogen 
 pressure. Pure hydrogen is supplied continuously (1) to the 
 
 * India-rubber tubing must not be used for the conveyance of the hyposulphite 
 solution (or the water under examination), as atmospheric oxygen rapidly diffuses 
 through the india-mbber and affects the strength of the solution. 
 
 T 
 
274 VOLUMETKIG ANALYSIS. 71. 
 
 stock bottle of hyposulphite, (2) to the hyposulphite burette, and 
 (3) to the titration bottle. 
 
 Preparation of the Reagents. The reagents required arc 
 Hyposulphite solution. 
 Indigo-carmine solution. 
 Standard aerated distilled water. 
 
 The Hyposulphite solution is prepared by dissolving 125 gm. of 
 sodic bisulphite in 250 c.c. of water, and passing a current of SO 2 
 through the solution until saturation is effected. The solution is 
 poured into a stoppered bottle of about 500 c.c. capacity, containing 
 50 gm. of zinc dust, the bottle is almost filled up with water, and 
 the mixture well shaken for five minutes, after which the bottle is 
 placed beneath a running tap to cool. The mixture is again 
 agitated after a quarter of an hour and left to deposit the excess of 
 zinc. The clear liquid is poured off from the sediment into 
 a Winchester quart bottle half full of water. Milk of lime is 
 added in excess, and the solution made up to fill the bottle almost 
 completely. The mixture is now thoroughly shaken and allowed 
 to stand (best overnight) until clear. 
 
 The solution thus obtained is much too strong for use. 200 c.c. 
 of this may be poured into a "Winchester quart bottle of water 
 (never into a bottle filled with air) and well shaken with as little 
 air as possible. The approximate strength of this dilute solution 
 must now be found by titrating good tap water in the apparatus 
 already described. The strength should be such that 100 c.c. of 
 water require about 5 c.c. of hyposulphite, and the solution should 
 be made up approximately to this value. It slowly loses strength 
 on keeping, even in hydrogen, and its value should be determined 
 daily as required to be used. 
 
 The Indigo-carmine solution is prepared by shaking up 200 gm. 
 of indigo-carmine in a Winchester quart bottle of water, and 
 filtering the blue solution, which must be diluted to such a strength 
 that 20 c.c. require about 5 c.c. of the above hyposulphite solution 
 for decolorization. 
 
 Standard Aerated Distilled "Water. Two Winchester quart bottles 
 half filled with freshly distilled water are vigorously agitated for 
 five minutes, and the air renewed several times by filling up one 
 bottle with the contents of the other, and again dividing into two 
 portions, which are repeatedly shaken with fresh air. Finally, one 
 bottle being filled, the temperature of the water is taken, and also 
 the barometric pressure, after which the bottle is allowed to stand 
 stoppered for half an hour, to get rid of minute air-bubbles. The 
 following table, due to Eoscoe and Lunt, gives the volume of 
 oxygen contained in this standard aerated water, and the results 
 show that Buns en's co-efficients, previously used, are inaccurate. 
 
OXYGEN. 275 
 
 Oxyg-en Dissolved by Distilled Water. 530 C. 
 
 
 
 | . 
 
 
 
 Temp. 
 C. 
 
 c.c. Oxygen 
 N.T.P. 
 per liter Aq. 
 
 Diff. for ' Temp. 
 0'5 C. C. 
 
 c.c. Oxygen 
 N.T.P. 
 per liter Aq. 
 
 Diif. for 
 0-5 C. 
 
 5-0 
 
 8-68 
 
 18'0 
 
 6-54 
 
 0-07 
 
 5-5 
 
 8-58 
 
 o-io 
 
 18'5 
 
 6-47 
 
 0-07 
 
 6-0 
 
 8-49 
 
 0'09 19'0 
 
 6-40 
 
 006 
 
 6-5 
 
 8'40 
 
 0'09 
 
 19-5 
 
 6'34 
 
 0-06 
 
 7-0 
 
 8'31 
 
 0-09 20-0 
 
 6-28 
 
 0-06 
 
 7'5 
 
 8-22 
 
 0-09 
 
 20-5 
 
 6-22 
 
 0-06 
 
 8'0 
 
 8-13 
 
 0-09 21-0 
 
 6-16 
 
 0-06 
 
 8'5 
 
 8-04 
 
 0'09 21-5 
 
 6-10 
 
 0-06 
 
 9-0 
 
 7-95 
 
 0-09 22-0 
 
 6*04 
 
 0-05 
 
 9-5 
 
 7-86 
 
 0'09 
 
 22-5 
 
 5-99 
 
 0-05 
 
 10-0 
 
 777 
 
 0-09 
 
 23-0 
 
 5'94 
 
 0'05 
 
 10-5 
 
 7-68 
 
 0-08 23-5 5-89 
 
 0-05 
 
 ll'O 
 
 7-60 
 
 0-08 24-0 5-84 
 
 O'Ol 
 
 11-5 
 
 7'52 
 
 0-08 
 
 24-5 
 
 5-80 
 
 0-04 
 
 12-0 
 
 744 
 
 0-08 
 
 25'0 
 
 5-76 
 
 0-04 
 
 12'5 
 
 7'36 
 
 0-08 
 
 25'5 5-72 
 
 0-04 
 
 13-0 
 
 7'28 
 
 0'08 
 
 28-0 5'68 
 
 0-04 
 
 13-5 
 
 7-20 
 
 0'08 
 
 26'5 5'64 
 
 0'04 
 
 14-0 
 
 7-12 
 
 0'08 
 
 27'0 5'60 
 
 0'03 
 
 14-5 
 
 7-04 
 
 0-08 
 
 27'5 5'57 
 
 0'03 
 
 15'0 
 
 6-96 
 
 0-08 
 
 28-0 5-54 
 
 0-03 
 
 15-5 
 
 6-89 
 
 0-07 28'5 5-51 
 
 0-03 
 
 16-0 
 
 6-82 
 
 0-07 29-0 5-48 
 
 0-03 
 
 16-5 
 
 675 
 
 0'07 29'5 5-45 
 
 0-02 
 
 17'0 
 
 668 
 
 0'07 30'0 5-43 
 
 
 17'5 
 
 6-61 
 
 0'07 
 
 i 
 
 In this table the results are calculated for aeration at an observed 
 barometric pressure of 760 m.m. When the observed pressure is below 
 760 m.m. T Vth the value must be subtracted for every 10 m.m. diff. The 
 same^value must be added when the pressure is above 760 m.m. 
 
 The Estimation : The burettes having been filled, and a preliminary trial 
 made 
 
 (1) 20 c.c. of the water are introduced into the small bottle and about 
 3 c.c. of indigo solution added. 
 
 (2) A moderite current of hydrogen is passed through the blue liquid by 
 a very fine jet for three minutes to free both water and supernatant gas 
 from free oxygen. 
 
 (3) Hyposulphite is now carefully added, during the flow of hydrogen, 
 until the change from blue to yellow occurs, taking care not to overstep this 
 point. 
 
 (4) A further measured quantity of hyposulphite is now added (say 10 c.c.) 
 sufficient to combine with all the dissolved oxygen in the volume of water 
 (50 100 c.c.) proposed to be used in the estimation. 
 
 (5) The important point is, that the water is now quickly run in from 
 a burette by a capillary tube passing beneath the surface of the liquid to the 
 bottom of the vessel. The water is thus introduced into a liquid which will 
 at once fix the free oxygen and thus prevent its diffusion on coming in 
 contact with the hydrogen, the reduced indigo acting as an indicator for the 
 complete oxidation of the hyposulphite. The liquid is kept in constant 
 motion during the addition of the water, which is shut off the moment 
 a permanent blue colour appears. 
 
 T 2 
 
276 VOLUMETRIC ANALYSIS. 71. 
 
 (6) The blue is decolorized by a further slight addition of hyposulphite. 
 The volume of water used and the total hyposulphite, minus the first 
 addition, are noted and the estimation repeated for confirmation. 
 
 When the water contains very little oxygen the second addition 
 of hyposulphite may be omitted, the reduced indigo-carmine being 
 -sufficient to take up all the dissolved oxygen. In this case, care 
 must be taken that the oxygen added should require not more 
 than half the hyposulphite first added to decolorize the indigo- 
 carmine. 
 
 Standardizing: the Hyposulphite. In order to complete the 
 estimation it is necessary to know the strength of the hyposulphite 
 solution employed, and for this purpose the bottle of standard 
 aerated distilled water is titrated. This method has the great 
 advantage that it is a titration carried out under almost the same 
 conditions as the examination of the sample. The result of an 
 estimation is easily obtained by the following formula 
 
 d x hs x Od 
 
 r~y = # c.c. O per liter of water 
 8 x lid 
 
 where d and s = the volumes of distilled water and sample 
 respectively used, lid and hs the hyposulphite required for the 
 distilled water and sample respectively, arid Od the volume of 
 dissolved oxygen contained in one liter of the standard water. 
 
 Standardizing- the Indigo. When once the hyposulphite has 
 been carefully standardized by distilled water, the rather trouble- 
 some aeration may be avoided by finding the oxygen-value of the 
 indigo-carmine solution. This solution remaining constant may be 
 used for the subsequent standardizing of the hyposulphite. 
 
 It is only necessary to take a suitable quantity of indigo solution, 
 diluted with water if necessary, free it from all dissolved oxygen 
 by a current of pure hydrogen continued for five minutes, then 
 carefully decolorize with hyposulphite, the value of which has 
 been found by using aerated distilled water. 
 
 The authors show that Schutzenberger's method of standard- 
 ization, depending on the decolorization of ammoniacal copper 
 sulphate, gives inaccurate results. 
 
 Free acids or alkalies greatly disturb the process. Bicarbonates 
 have no effect. Of course when other substances than oxygen, 
 which decompose hyposulphite, are present, the accuracy of the 
 method is proportionately disturbed. The authors have applied the 
 process to waters of very varied character, and containing widely 
 different amounts of oxygen, and show that the method is capable 
 of giving good results, compared with the actual volume of oxygen 
 found by extracting the gases by boiling in vacua. 
 
 The delicacy of the reaction is such that one part of oxygen in 
 two million parts of water is easily detected. 
 
71. 
 
 OXYGEN. 
 
 277 
 
 The following numbers were obtained from five different samples 
 of London tap- water collected on five different days. 
 
 
 (1) 
 
 (2) 
 
 (3) 
 
 (4) 
 
 (5) 
 
 Nitrogen 
 
 c.c. 
 13*22 
 5-15 
 
 7'98 
 
 c.c. 
 13-95 
 5-91 
 9-29 
 
 c.c. 
 13-36 
 5-38 
 6-70 
 
 c.c. 
 13-43 
 6-31 
 7-35 
 
 c.c. 
 13-49 
 5-80 
 8-11 
 
 Oxygen 
 
 Carbonic acid 
 Total o-as . . 
 
 26-35 
 
 29-15 
 
 25-44 
 
 27-09 
 
 27-40 
 
 
 Oxygen by the new 
 volumetric method . . . 
 Gas obtained 
 
 5-52 
 5-15 
 
 6-13 
 5-91 
 
 5-64 
 5-38 
 
 6-41 
 6'31 
 
 6-24 
 5-80 
 
 Difference . 
 
 0-37 
 
 0-22 
 
 0-26 
 
 o-io 
 
 0-44 
 
 
 Mean difference 0'28 c.c. oxygen per liter of water. 
 
 The oxygen values obtained by the two methods show close 
 agreement, considering the possible experimental error in so 
 complex a comparison. 
 
 M. A. Adams describes and figures a very convenient arrange- 
 ment for carrying out this process (J. C. S. Ixi. 310), which is 
 well adapted for technical work, and less cumbrous than the 
 apparatus here described. 
 
 lodometric Method. 
 
 A simpler method than the foregoing has been proposed by 
 Thresh (/. C. S. Ivii. 185), which by comparison with Roscoe 
 and Lunt's method appears to give satisfactory results when 
 aerated distilled water was under titration, the differences occurring 
 only in the second decimal place. The author was led to 
 investigate the method by observing the. large amount of iodine 
 which a very minute quantity of a nitrite caused to be liberated, 
 when potassic iodide and dilute sulphuric acid were added to water 
 containing it. The amount of iodine liberated varies with the 
 length of exposure to air. If air is excluded no increase of free 
 iodine occurs after the first few minutes, and if the water is 
 previously boiled and cooled in an air-free space still less iodine is 
 liberated. In this latter case the action is represented by the 
 equation 
 
 2HI + 2HX0 2 = I 2 + 2H 2 + 2X0. 
 
 When oxygen has access to the solution, the nitric oxide acts as 
 a carrier, and more hydrogen iodide is decomposed, the nitric oxid 
 
2/8 VOLUMETRIC ANALYSIS. 71. 
 
 apparently remaining unaffected, and capable of causing the 
 decomposition of an unlimited quantity of the iodide. 
 
 This reaction is the one utilized in the process devised by 
 Thresh for estimating the oxygen dissolved in water. As 16 parts 
 by weight of oxygen will liberate 254 parts of iodine, thus 
 
 and as the latter element admits of being accurately estimated, 
 theoretically the oxygen should be capable of very precise 
 determination. Practically such is the case ; the oxygen dissolved 
 in drinking waters admits of being estimated both rapidly and 
 with precision. It is only necessary to add to a known volume of 
 the water a known quantity, of sodic nitrite, together with excess 
 of potassic iodide and acid, avoiding access of air, and then to 
 determine volumetrically the amount of iodine liberated. After 
 deducting the proportion due to the nitrite used, the remainder 
 represents the oxygen which was dissolved in the water and in the 
 volumetric solution used. 
 
 The following are the reagents required : 
 
 (1) Solution of sodic nitrite and potassic iodide : 
 
 Sodic nitrite 0'5 gm. 
 
 Potassic iodide 20'0 gm. 
 
 Distilled water 100 c.c. 
 
 (2) Dilute sulphuric acid : 
 
 Pure sulphuric acid 1 part. 
 
 Distilled water 3 parts. 
 
 (3) A clear fresh solution of starch. 
 
 (4) A volumetric solution of sodic thiosulphate : 
 
 Pure crystals of thiosulphate, 7 '7 5 gm. 
 
 Distilled water to 1 liter. 
 
 1 c.c. corresponds to 0'25 milligram of oxygen. 
 
 The apparatus required is very simple, and can readily be fitted 
 up. It consists of a wide-mouthed white glass bottle (A, fig. 50) 
 of about 500 c.c. capacity, closed with a caoutchouc stopper having 
 four perforations. Through one passes the tube B, drawn out at 
 its lower extremity to a rather fine point, and connected at the 
 upper end, by means of a few inches of rubber tubing, with the 
 burette C, containing the thiosulphate. Through another opening 
 passes the nozzle of a separatory tube D, having a stopper and 
 stopcock. The capacity of this tube when full to the stopper 
 must be accurately determined. Through the third opening passes 
 a tube E, which can be attached to an ordinary gas supply. Through 
 the last aperture is passed another tube, for the gas exit, and to 
 tin's is attached a sufficient length of rubber tubing to enable the 
 
71. 
 
 OXYGEN. 
 
 279 
 
 cork G at its end to be placed in the neck of the tube D when the 
 stopper is removed. A small piece of glass tube projects through 
 the cork, to allow of the escaping gas being ignited. 
 
 The apparatus is used in the following manner : The bottle A 
 being cleaned and dry, the perforated bung is inserted, the burette 
 charged, and the tube B fixed in its place. E is connected with 
 the gas supply. The tube D is filled to the level of the stopper 
 with the water to be examined, 1 c.c. of the solution of sodic 
 nitrite and potassic iodide added from a I c.c. pipette, then 1 c.c. 
 of the dilute acid, and the stopper instantly fixed in its place, 
 displacing a little of the water, and including no air. If the 
 pipette be held in a vertical position with its tip just under the 
 surface of the water, botli the saline solution and the acid, being 
 much denser than the water, flow in a sharply defined column to 
 the lower part of the tube, so that an infinitesimally small quantity 
 
 (if any) is lost in the water which overflows when the stopper is 
 inserted. The tube is next turned upside down for a few seconds 
 for uniform admixture to take place, and then the nozzle is pushed 
 through the bung of the bottle, and the whole allowed to remain 
 at rest for 15 minutes, to enable the reaction to become complete. 
 A rapid current of coal gas is now passed through the bottle A, 
 until all the air is displaced and the gas burns at G with a full 
 
280 VOLUM ETHIC ANALYSIS. 71. 
 
 luminous flame ; the flame is now extinguished, the stopper of D 
 removed, and the cork G rapidly inserted. On turning the stop- 
 cock, the water flows into the bottle A. The stopcock is turned 
 off, the cork G removed, and the supply of gas regulated so that 
 a small flame only is produced when this gas is ignited at G. 
 Thiosulphate is now run in slowly until the colour of the iodine is 
 nearly discharged. A little solution of starch is then poured into 
 D, and about 1 c.c. allowed to flow into the bottle by turning the 
 stopcock. The titration with thiosulphate is then completed. 
 After the discharge of the blue colour, the latter returns faintly in 
 the course of a few seconds, due to the oxygen dissolved in the 
 volumetric solution ; after standing about two minutes, from 0*05 
 to O'l c.c. of thiosulphate must be added to effect the final 
 discharge. The amount of volumetric solution used must now be 
 noted. This will represent a, the oxygen dissolved in the water 
 examined, + &, the nitrite in the 1 c.c. of solution used, and the 
 oxygen in the acid and starch solution + c, a portion of the dissolved 
 oxygen in the volumetric solution. To find the value of a, it is 
 obvious that I and c must be ascertained. This can be effected in 
 many ways, and once known does not require re-determination 
 unless the conditions are changed. 
 
 To Find the Value of 1>. Probably the best plan is to complete 
 a determination as above described, and then, by means of the 
 stoppered tube, introduce into the bottle in succession 5 c.c. of 
 nitrite solution, dilute acid, and starch solution. After standing 
 a few minutes, titrate. One-fifth of the thiosulphate used will be 
 the value required. 
 
 To Find the Value of c. This correction is a comparatively 
 small one, and admits of determination with sufficient accuracy if 
 it is assumed that the thiosulphate solution normally contains as 
 much dissolved oxygen as distilled water saturated at the same 
 temperature. Complete a determination as above described, then 
 remove the stoppered tube, and insert a tube similar to that 
 attached to the burette, and drop in from it 10 or 20 c.c. of 
 saturated distilled water exactly as the thiosulphate is dropped in. 
 Allow to stand a few minutes and titrate. One-tenth or one- 
 twentieth of the volumetric solution used, according to the 
 number of c.c. of water added, will represent the correction for 
 each c.c. of volumetric solution used. Call this value d. 
 
 Let e be the number of c.c. of thiosulphate used in an actual 
 determination of the amount of oxygen in a sample of water ; 
 
 /= the capacity in c.c. of the tube employed -2 c.c., the volume 
 of reagents added ; 
 
 17 = the amount of oxygen in milligrams dissolved in 1 liter of 
 the water ; 
 
 1000, 7 ,, 
 then V = -. . (e-l- e<?) 
 
71. OXYGEN. 
 
 With a tube made to hold exactly 250 c.c., the most convenient 
 
 quantity to use, becomes unity, and 
 
 In the author's experiments two nitrite solutions were used; 
 in the first l = 2'l c.c., in the second 3'1 c.c. A number of 
 determinations of d were made, at temperatures varying from 
 40 to 60 F. The value of d was found to vary between 0'03 
 and 0*031 5. In all the author's recent experiments d was taken 
 as 0-031. 
 
 When e = 3 c.c. the reaction seems to be complete in five 
 minutes, but, to be on the safe side, it is better to fix the minimum 
 at fifteen minutes. 
 
 The use of coal-gas is recommended by the author without 
 passing it over alkaline pyrogallol or otherwise treating it before 
 allowing it to pass through the apparatus. 
 
 The results obtained, however, can be made to vary, the extreme 
 limit being less than 0'5 milligram of oxygen per liter of water, 
 using 250 c.c. for the estimation. To quote an extreme case. In 
 one experiment (1), after the air had been wholly expelled from 
 the bottle A, no more gas was passed through, and the titration 
 was effected in the closed apparatus, the volumetric solution being 
 run in as rapidly as possible. The end-reaction was not well 
 defined. In the second experiment (2), the volumetric solution 
 was run in very slowly drop by drop, and a brisk current of gas 
 was kept passing through the apparatus. End-reaction well 
 defined. 
 
 Volume of water. Thiosulphate. Oxygen per liter. 
 
 (1) ...... 322 c.c. 15-35 c.c. ' 9 '14 milligrams. 
 
 (2) ...... 322 14-9 8-80 
 
 The difference is probably due to nearly all the oxygen dissolved 
 in thiosulphate being used up in the first case, and being lost by 
 diffusion in the second. 
 
 In the examination of waters from various sources, and making 
 the experiments in pairs, using tubes of different sizes, the author 
 found that exceedingly concordant results could easily be 
 obtained. 
 
 In estimating the oxygen in distilled water saturated with air,. 
 the author found that the results at 25 and 30 C. were higher 
 than those obtained by Roscoe and Lunt, whilst at the lower 
 temperatures they were almost identical, and it occurred to him that 
 the difference was probably due to the mode of saturation. The 
 agitation in a couple of Winchesters was done as directed by 
 them, but the water used had been previously saturated at the 
 lower temperatures, and probably was slightly super-saturated. 
 A further series of experiments were then made with freshly- 
 
282 VOLUMETRIC ANALYSIS. 71. 
 
 distilled water, which was not agitated with air until it had 
 attained the desired temperature. The results proved that this 
 surmise was correct. Probably some such explanation accounts for 
 the uniformly higher results obtained by Dittmar. 
 
 No doubt there will be exceptional cases in which the process 
 cannot be used, and others in which some modification may be 
 required. A water containing nitrites will require the amount of 
 the nitrous acid to be determined if the utmost accuracy is 
 required. (A water containing 1 part of HNO 2 in 1,000,000, will 
 affect the results + '17 milligram of oxygen per liter, 94 parts 
 of the acid corresponding to 16 of oxygen). Where nitrites are 
 present in sufficient quantity to interfere, the amount may be 
 determined by any of the ordinary processes, but the author 
 prefers the following method : 
 
 To 250 c.c. of the water to be examined, rendered faintly 
 alkaline if not already so, add a few drops of strong solution of 
 potassic iodide, and boil vigorously for a few minutes. Then 
 transfer to the bottle A used in the oxygen determination, and 
 allow to get quite cold in a slow current of coal gas. Then add 
 a few drops of dilute sulphuric acid and solution of starch, and 
 titrate with the thiosulphate. The correction to be made in the 
 oxygen determination is thus ascertained. One or two experi- 
 mental results may be quoted. 
 
 Quantity Thiosulphate p.,^ ar -\ Milligrams of 
 of water. used. CoiiectecL oxygen per liter. 
 
 Tap water 232T> 13'2 9'7 10'43 
 
 Tap water + 5 milli- ^ 
 
 grams commercial C 232' 5 15'95 9' 55 10'27 
 
 sodic nitrite ) 
 
 Tap water + 10 milli- ) 000 . K i n-i Q 
 
 1 -j "* <_>_ O Jo O 7 ~rO J-V J-/ 
 
 grams sodic nitrite ) 
 
 In number 2, the thiosulphate used by 250 c.c. of the boiled 
 
 water was 2*8 c.c. 
 
 In number 3, the thiosulphate used by 250 c.c. of the boiled 
 water was 5 '45 c.c. 
 
 The results are fairly satisfactory, even with such large pro- 
 portions of nitrite, proportions far larger than are likely to be met 
 with in practice. 
 
 Nitrates do not interfere, even when present in large quantities ; 
 but fresh urine, when present to the extent of 1 per cent., has 
 a small but very appreciable effect. 
 
 The following is an example of the method at ordinary 
 temperature : 
 
71. HYDROGEN PEROXIDE. 283 
 
 Temperature 15 C. 
 
 Quantity of Thiosulphate | , _ fe _ , d \ Milligrams of Difference 
 
 water taken. used. ' Oxygen per liter, from mean. 
 
 1... 
 
 2... 
 
 322-0 15-45 12-87 9'99 0'04 
 
 322-0 15-55 12-97 10'07 + 0'04 
 
 3... 232-5 11-90 9-43 10'14 +0'11 
 
 4... 232-5 11-70 9-23 9'92 O'll 
 
 Mean... - 10'03 
 
 Barometer reading 30 in. 
 10-03 milligrams=7'02 c.c. at N.P.T. 
 Eoscoe and Lun't found 6'96 Difference + 0'06. 
 
 Hydrog-en Peroxide. 
 IPO 2 =34. 
 
 This substance is now largely used in commerce, and is sold 
 as containing 5, 10, or 20 volumes of oxygen in solution. This 
 should mean that the specified number of volumes can be obtained 
 from the solution itself, but preparations are sent into the market 
 under false pretences. A so-called 10 volume solution gives, it is 
 true, 10 volumes of when decomposed gasometrically with 
 permanganate, but 5 volumes of the comes from the per- 
 manganate itself, and therefore such a solution is really only 5 
 volume. A true 10 volume solution should yield from itself, when 
 fully decomposed, ten times its volume of O, and contain by weight 
 3 '04 per cent, of H 2 2 or 1'43 per cent, by weight of 0. 
 
 Kingzett (J. C. S. 1880, 792) has clearly shown that the best 
 and most rapid estimation of the hydrogen peroxide, contained in 
 .any given solution of it, is made by iodine and thiosulphate in the 
 presence of a tolerably large excess of sulphuric acid, the reaction 
 being 
 
 The function performed by the sulphuric acid is difficult of ex- 
 planation, but the want of uniformity in the reaction experienced 
 by many operators no doubt has arisen from the use of insufficient 
 acid. 
 
 Process : Kingzett's consists in mixing 10 c.c. of the peroxide solution 
 to be examined with about 30 c.c. of dilute sulphuric acid (1 : 2) in a beaker, 
 adding crystals of potassic iodide in sufficient quantity, and after standing 
 five minutes titrating the liberated iodine with ^ thiosulphate and starch. 
 The peroxide solution should not exceed the strength of 2 volumes; if 
 stronger, it must be diluted proportionately before the analysis. 
 
 In the case of a very weak solution it will be advisable to titrate with 
 x-iju- thiosulphate. 
 
 1 c.c. & thiosulphate = 0'0017 gm. H-O 2 or 0*0016 gm. O. 
 
 The estimation of this substance may also be readily made in the 
 
284 VOLUMETRIC ANALYSIS. 72. 
 
 absence of organic or other reducing matters by weak standard per- 
 manganate in the presence of free sulphuric acid, the permanganate 
 being added until a faint rose colour occurs : the reaction is 
 
 2KMn0 4 + 5H 2 2 + 3IPS0 4 = K 2 S0 4 + 2MnS0 4 + 8H 2 + 50 2 . 
 
 Process : To about 500 c.c. of water in a white porcelain dish there is 
 added 5 c.c. of dilute H-SO 4 , and then sufficient permanganate to give 
 a faint persistent pink colour. 5 c.c. of the peroxide solution are then 
 pipetted into the mixture, and standard permanganate containing 2'625 gm. 
 per liter run in until the colour no longer disappears. The number of c.c. 
 used, divided by ten, gives the volume of oxygen liberated by each c.c. of 
 the hydrogen peroxide. 
 
 Carpenter and Nicholson (Analyst ix. 36) report a series 
 of experiments on the analysis of hydrogen peroxide, both by the 
 iodine and permanganate methods. 
 
 The conclusion they arrive at is, that the process of Kingzett 
 is accurate, but in their hands somewhat tedious, owing to slow 
 decomposition towards the end. Kingzett however states that if 
 a volume of strong sulphuric acid equal to the peroxide taken be 
 used, and especially if the dilute solution be slightly wanned, the 
 reaction is complete in a few minutes, and this is my own 
 experience. 
 
 Soclic Peroxide. 
 
 L. Archbutt (Analyst xx. 5) gives the results of some 
 experiments on the estimation of the oxygen contained in this 
 substance, and found that a near approximation to the truth could 
 be obtained by simple titration with permanganate, the peroxide 
 (one or two decigrams) being added to cold water acidified with 
 H 2 S0 4 contained in a white dish, and j permanganate dropped in 
 with stirring, until the colour became permanent ; but a more 
 exact method would be to add a known weight of the peroxide to 
 an excess of ~ permanganate, previously mixed with dilute 
 H 2 S0 4 , and titrate for the excess of permanganate with -f^ oxalic 
 acid. Archbutt, however, prefers to use the nitrometer, and 
 recommends the following procedure : about 0*25 gm. of the 
 substance is placed in the dry tube of the nitrometer flask, and in 
 the flask itself about 5 c.c. of pure water, containing in suspension 
 a few milligrams of precipitated cobalt sesqui-oxide, this latter 
 reagent brings about a rapid and complete decomposition of the 
 peroxide, the volume of oxygen evolved being the available oxygen 
 in the sample. 
 
 PHOSPHORIC ACID AND PHOSPHATES. 
 
 72. THE estimation of phosphoric acid volu metrically may 
 be done with more or less accuracy by a variety of processes, among 
 
72. PHOSPHORIC ACID. 285 
 
 which may be mentioned that of Mohr as lead phosphate, the 
 indirect method as silver phosphate (the excess of silver being found 
 by thiocyanate), by standard uranium nitrate or acetate, by 
 P ember ton's method as phospho-molybdate, or when existing 
 only as monocalcic phosphate, by standard alkali, as recommended 
 by Mo 11 end a or Emm er ling. These processes are mainly useful 
 in the case of manures, or the raw phosphates from which manures 
 are manufactured, and for P 2 5 in urine, etc. For the purpose 
 mentioned, that is to say, when in combination with alkaline or 
 earthy alkaline bases and moderate quantities of iron or alumina, 
 phosphoric acid may be estimated volumetrically with very fair 
 accuracy, and with much greater rapidity than by gravimetric 
 means as usually carried out. This remark, however, can only be 
 applied to uranium or molybdenum methods ; therefore only these 
 will be described. 
 
 1. Precipitation as Uranic Phosphate in Acetic Acid Solution. 
 
 This method is based on the fact that when uranic acetate or 
 nitrate is added to a neutral solution of tribasic phosphoric acid, 
 such, for instance, as sodic orthophosphate, the whole of the 
 phosphoric acid is thrown down as yellow uranic phosphate Ur 2 3 , 
 P 2 5 + Aq. Should the solution, however, contain free mineral 
 acid, it must be neutralized with an alkali, and an alkaline acetate 
 added, together with excess of free acetic acid. In case of using 
 ammonia and ammonic acetate, the whole of the phosphoric acid 
 is thrown down as double phosphate of uranium and ammonia, 
 having a light lemon colour, and the composition Ur 2 :j 
 2(XH 4 0), P 2 5 + Aq. When this precipitate is washed with hot 
 water, dried and burned, the ammonia is entirely dissipated leaving 
 uranic phosphate, which possesses the formula Ur 2 3 , P 2 5 , and 
 contains in 100 parts 80 '09 of uranic oxide and 19*91 of phosphoric 
 acid. In the presence of fixed alkalies, instead of ammonia, the 
 precipitate consists simply of uranic phosphate. By this method 
 phosphoric acid may be completely removed from all the alkalies 
 and alkaline earths ; also, with a slight modification, from iron ; 
 not, however, satisfactorily from alumina when present in any 
 quantity. 
 
 The details of the gravimetric process were fully described by 
 me (C. N. i. 97 122), and immediately after the publication of 
 that article, while employed in further investigation of the subject, 
 I devised the volumetric method now to be described. Since that 
 time it has come to my knowledge that jS'eubauer* and Pincusf 
 had independently of each other and myself arrived at the same 
 process. This is not to be wondered at, if it be considered how 
 easy the step is from the ordinary determination by weight to that 
 
 * Archiv. f&r wissenschuftliclie Heillcunde, iv. 228. 
 f Journal fur Prald. Chem. Ixxvi. 104. 
 
286 VOLUMETRIC ANALYSIS. 7 '2. 
 
 by measure, when the delicate reaction between uranium and 
 potassic ferrocyanide is known. Moreover, the great want of a 
 really good volumetric process for phosphoric acid in place of those 
 hitherto used has been felt by all who have anything to do with it, 
 and consequently the most would be made of any new method 
 possessing so great a claim to accuracy as the gravimetric estimation 
 of phosphoric acid by uranium undoubtedly does. 
 
 Conditions under -which, accxiracy may be insured. Objections 
 have been urged, not without reason, that this process is inaccurate, 
 because varying amounts of saline substances have an influence 
 upon the production of colour with the indicator. Again, that 
 very different shades of colour occur with lapse of time. This 
 is all true, and the analysis is unfortunately one of that class which 
 requires uniform conditions; but when the source of irregularity is 
 known, it is not difficult to obviate them. Therefore it is absolutely 
 essential that the standardizing of the uranium solution should be 
 done under the same conditions as the analysis. For instance, a 
 different volume of uranium will be required to give the colour in 
 the presence of salts of ammonia to that which would be necessary 
 with the salts of the fixed alkalies or alkaline earths. But if the 
 standard solution is purposely adjusted with ammonia salts in about 
 the same proportion, the difficulties all vanish. Fortunately this 
 can be easily done, and as the chief substances requiring analysis 
 are more or less ammoniacal in their composition, such as urine, 
 manures, etc., no practical difficulty need occur. 
 
 Excessive quantities of alkaline or earthy salts modify the colour, 
 but especially is it so with acetate or citrate of ammonia. For this 
 reason it is necessary to ensure the complete washing of the citro- 
 magnesian precipitate, where that method of separating P 2 5 is 
 adopted previous to titration. 
 
 2. Estimation of Phosphoric Acid in combination with Alkaline 
 Bases, or in presence of small quantities of Alkaline Earths. 
 
 The necessary materials are 
 
 (a) A standard solution of Uranium, 1 c.c. 0*005 gm. P 2 5 . 
 
 (&) A standard solution of tribasic Phosphoric acid. 
 
 (c) A solution of Sodic acetate in dilute acetic acid, made by 
 dissolving 100 gm. of sodic acetate in water, adding 50 c.c. of 
 glacial acetic acid, and diluting to 1 liter. Exact quantities are 
 not necessary. 
 
 (d) A freshly prepared solution of Potassic ferrocyanide, or 
 some finely powdered pure crystals of the same salt. 
 
 Standard Solution of Uranium. This solution may consist 
 either of uranic nitrate or acetate. An approximate solution is 
 obtained by using about 35 gm. of either salt to the liter. 
 In using uranic nitrate it is imperative that the sodic acetate 
 
72. PHOSPHORIC ACID. 287 
 
 should be added in order to avoid the possible occurrence of free 
 nitric acid in the solution. With acetate, however, it may be 
 omitted at the discretion of the operator, but it is important 
 that the method used in standardizing the uranium be invariably 
 adhered to in the actual analysis. The solution should be perfectly 
 clear and free from basic salt. Whether made from acetate or 
 nitrate, it is advisable to include about 50 c.c. of pure glacial acetic, 
 or a corresponding quantity of weaker acid to each liter of 
 solution ; exposure to light has then less reducing action. 
 
 My own practice is to use in all cases acetate solution, and 
 dispense entirely with the addition of sodic acetate. 
 
 3. Titration of the Uranium Solution. 
 
 Standard Phosphoric Acid. When the uranium solution is not 
 required for phosphate of lime, it may be titrated upon ammonio- 
 sodic phosphate (microcosmic salt) as follows : 5'886 gm. of the 
 crystallized, non-effloresced salt (previously powdered and pressed 
 between bibulous paper to remove any adhering moisture) are 
 weighed, dissolved in water, and diluted to 1 liter. 50 c.c. of this 
 solution will represent O'l gm. of P-0 5 .* 
 
 Process : 50 c.c. of this solution are measured into a small beaker, 5 c.c. sodic 
 acetate solution added if uranic nitrate is to be used, and the mixture heated to 
 90 or 100 C. The uranium solution is then delivered in from a burette, 
 divided into T V c.c., until a test taken shall show the slight predominance of 
 uranium. This is done by spreading a drop .or two of the hot mixture upon 
 a clean white level plate, and bringing in contact with the middle of the drop 
 a small glass rod moistened with the freshly made solution of f errocyanide, 
 or a dust of the powdered salt. The occurrence of a faint brown tinge shows 
 an excess of uranium, the slightest amount of which produces a brown 
 precipitate of uranic f errocyanide. 
 
 A second or third titration is then made in the same way, so as 
 to arrive exactly at the strength of the uranium solution, which 
 is then diluted and re-titrated, until exactly 20 c.c. are required to 
 produce the necessary reaction with 50 c.c. of phosphate. 
 
 Suppose 18*7 c.c. of the uranium solution have been required to 
 produce the colour with 50 c.c. of phosphate solution, then every 
 18 '7 c.c. will have to be diluted to 20 c.c. in order to be of the 
 proper strength, or 935 to 1000. After dilution, two or three 
 fresh trials must be made to insure accuracy. 
 
 It is of considerable importance that the actual experiment for 
 estimating phosphoric acid by means of the uranium solution 
 should take place with about the same bulk of fluid that has 
 been used in standardizing the solution, and with as nearly as 
 
 * "W. B. Giles, who has had great experience in the determination of phosphoric acid 
 in various forms, has called my attention to dihydric potassic phosphate, KH-'PO 4 , as an 
 excellent form of salt for a standard solution. The sample sent to nie was in beautifully 
 formed crystals which do not alter on exposure to the air, and makes a solution which 
 keeps clear. Every one knows how unsatisfactory sodic phosphate is, both as to its 
 state of hydration and its keeping qualities in solution : the microcosmic salt is better, 
 but is open to objection on the score of indefinite hydration. If the potassium salt ia 
 used, a standard solution of the proper strength is made by dissolving 3'83 gm. in a liter. 
 
288 VOLUMETRIC ANALYSIS. 72. 
 
 possible the same relative amount of sodic acetate, and the 
 production of the same depth of colour in testing. Hence the 
 proportions here recommended have been chosen, so that 50 c.c. of 
 liquid shall contain O'l gm. P 2 5 . 
 
 Standard Phosphoric Acid corresponding- volume for volume with 
 Standard TJianium. This solution is obtained by dissolving 
 14 '7 15 gm. of microcosmic salt in a liter, and is two and a half 
 times the strength of the solution before described ; it is used for 
 residual titration in case the required volume of uranium is over- 
 stepped in any given analysis. 
 
 A little practice enables the operator to tell very quickly the 
 precise point ; but it must be remembered that when the two drops 
 are brought together for the production of the chocolate colour, 
 however faint it seems at first, owing to the retarding action of the 
 sodic acetate and acetic acid upon the formation of uranic 
 ferrocyanide, if left for some little time the colour increases con- 
 siderably ; but this has no effect upon the accuracy of the process, 
 since the original standard of the solution has been based on an 
 experiment conducted in precisely the same way. 
 
 Process : In estimating unknown quantities of P 2 5 , it is necessary to have 
 an approximate knowledge of the amount in any given material, so as to 
 fulfil as nearly as possible the conditions laid down above ; that is to say, 
 50 c.c. of solution shall contain about O'l gm. P 2 O 5 , or whatever other pro- 
 portion may have been used in standardizing the uranium. 
 
 The compound containing the P 2 5 to be estimated is dissolved in water ; 
 if no ammonia is present, 1 c.c. of 10 per cent, solution is dropped in and 
 neutralized with the least possible quantity of acetic acid (also 5 c.c. of sodic 
 acetate if uranic nitrate has to be used), and the volume made up to about 
 50 c.c., then heated to about 90 C. on the water bath, and the uranium 
 solution delivered in cautiously, with frequent testing as above described, 
 until the faint brown tinge appears. 
 
 The first trial will give roughly the amount of solution required, and 
 taking that as a guide, the operator can vary the amount of liquid and sodic 
 acetate for the final titration, should the proportions be fonnd widely 
 differing from those under Avhich the strength of the uranium was 
 originally fixed. 
 
 Each c.c. of uranium solution=0'005 gm. P 2 O 5 . 
 
 . Estimation of Phosphoric Acid in combination with Lime and 
 Magnesia (Bones, Bone Ash, Soluble Phosphates, and other 
 Phosphatic Materials, free from Iron and Alumina). 
 
 The procedure in these cases differs from the foregoing in two 
 Tespects only ; that is to say, the uranium solution is preferably 
 standardized by tribasic calcic phosphate ; and in the process of 
 titration it is necessary to add nearly the full amount of uranium 
 required before heating the mixture, so as to prevent the precipita- 
 tion of calcic phosphate, which is apt to occur in acetic acid 
 solution when heated; or the modification adopted by Fresenius, 
 Xeubauer, and Luck, may be used, which consists in reversing 
 "the process by taking a measured volume of uranium, and delivering 
 
72. PHOSPHORIC ACID. 289 
 
 into it the solution of phosphate until a drop of the mixture ceases 
 to give a brown colour with ferrocyanide. This plan gives, how- 
 ever, much more trouble, and possesses no advantage on the score 
 of accuracy, because in any case at least two titrations must occur, 
 and the first being made somewhat roughly, in the ordinary way, 
 shows within 1 or 2 c.c. the volume of standard urani am required ; 
 and in the final trial it is only necessary to add at once nearly the 
 quantity, then heat the mixture, and finish the titration by adding 
 a drop or two of uranium at a time until the required colour is 
 obtained. 
 
 This reversed process is strongly advocated by many operators, 
 but except in rare instances I fail to see its superiority to the direct 
 method for general use. The best modification to adopt in the 
 reverse process is to use invariably an excess of uranium, and to 
 titrate back with standard phosphate solution till the colour 
 disappears ; this avoids all the trouble of preparing and cleaning 
 a burette for the solution to be analyzed, and if a standard phosphate 
 is made to correspond volume for volume with the uranium, an 
 analysis may always be brought into order at any stage. 
 
 Standard Calcic Phosphate. It is not safe to defend upon the 
 usual preparations of tricalcic phosphate by weighing any given 
 quantity direct, owing to uncertainty as to the state in which the 
 phosphoric acid may exist ; therefore, in order to titrate the 
 uranium solution with calcic phosphate, it is only necessary to 
 take rather more than 5 gin. of precipitated pure tricalcic phosphate 
 such as occurs in commerce, dissolve it in a slight excess of dilute 
 hydrochloric acid, precipitate again with a slight excess of ammonia, 
 re-dissolve in a moderate excess of acetic acid, then dilute to 
 a liter ; by this means is obtained a solution of acid monocalcic 
 phosphate, existing under the same conditions as occur in the 
 actual analysis. In order to ascertain the exact amount of tribasic 
 phosphoric acid present in a given measure of this solution, two 
 portions of 50 c.c. each are placed in two beakers, each holding 
 about half a liter. A slight excess of solution of uranic acetate 
 or nitrate is then added to each, together with about 10 c.c. of the 
 acetic solution of sodic acetate ; they are then heated to actual 
 boiling on a hot-plate or sand-bath, the beakers filled up with 
 boiling distilled water, and then set aside to settle, which occurs 
 very speedily. The supernatant fluid should be faintly yellow 
 from excess of uranium. When perfectly settled, the clear liquid 
 is withdrawn by a syphon or poured off as closely as possible with- 
 out disturbing the precipitate, and the beakers again filled up with 
 boiling water. The same should be done a third time, when the 
 precipitates may be brought on two filters, and need very little 
 further washing. 
 
 "When the filtration is complete, the filters are dried and ignited 
 separate from the precipitate, taking care to burn off all carbon. 
 
 u 
 
290 VOLUMETRIC ANALYSIS. 72. 
 
 Before being weighed, however, the uranic-phosphate must be 
 moistened with strong nitric acid, dried perfectly in the water bath 
 or oven, and again ignited ; at first, very gently, then strongly, so 
 as to leave a residue when cold of a pure light lemon colour. This 
 is uranic phosphate Ur 2 3 , P 2 5 , the percentage composition of 
 which is 80 '09 of uranic oxide, and 19 '91 of phosphoric acid. 
 
 The two precipitates are accurately weighed, and should agree to 
 within a trifle. If they differ, the mean is taken to represent the 
 amount of P 2 0. 5 in the given quantity of tricalcic phosphate, from 
 which may be calculated the strength of the solution to be used as 
 a standard. Of course any other accurate method of determining 
 the P 2 5 may be used in place of this. 
 
 The actual standard required is 5 gm. of pure tricalcic phosphate 
 per liter ; and it should be adjusted to this strength by dilution, 
 after the actual strength has been found. In this way is obtained 
 a standard which agrees exactly with the analysis of a super- 
 phosphate or other similar manure. 
 
 Standard Uranium Solution. This is best adjusted to such 
 strength that 25 c.c. are required to give the faint chocolate colour 
 with ferrocyaiiide, when 50 c.c. of the standard acetic solution of 
 calcic phosphate are taken for titration. Working in this manner 
 each c.c. of uranium solution represents 1 per cent, of soluble 
 tricalcic phosphate, when 1 gm. of manure is taken for analysis, 
 because 50 c.c. of the calcic phosphate will contain monocalcic 
 phosphate equal to 0'25 gm. of Ca :j P 2 8 and will require 25 c.c. 
 of uranium solution to balance it. 
 
 These standards are given as convenient for manures, but they 
 may be modified to suit any particular purpose. 
 
 Process in case of Superphosphate free from Fe and Al, except 
 in mere traces : 10 gm. of the substance are weighed, placed in a small glass 
 mortar and gently broken down by the pestle, coid water being used to bring 
 it to a smooth cream. The material should not be ground or rubbed hard, 
 which might cause the solution of some insoluble phosphate in the 
 concentrated mixture. The creamy substance is washed gradually without 
 loss into a measuring flask marked at 503'5 c.c., the 3'5 c.c. being the space 
 occupied by the insoluble matters in an ordinary 25 to 30 per cent, 
 superphosphate. The flask is filled to the mark with cold water, and shaken 
 every few minutes during about half-an-honr. A portion is then filtered 
 through a dry filter into a dry beaker, and 50 c.c.==i gm. of manure 
 measured into a beaker holding about 100 c.c. Sufficient 10 per cent, ammonia 
 is then added to precipitate the monocalcic phosphate in the form of 
 Ca 3 P 2 O 8 (in all ordinary superphosphates there is enough Ca present as 
 sulphate to ensure this, and four or five drops of ammonia generally suffice 
 to effect the precipitation). Acetic acid is then added in just sufficient 
 quantity to render the liquid clear. Should traces of gelatinous A1PO 4 or 
 FePO 4 occur at this stage, the liquid will be slightly opalescent ; but this 
 may be disregarded if only slight, as the subsequent heating will enable the 
 uranium to decompose it. If more than traces occur, the method will not 
 be accurate, and recourse must be had to separation by the citro-magnesic 
 solution. 
 
 While the liquid is still cold, a measured volume of the standard uranium 
 
72. PHOSPHORIC ACID. 291 
 
 is run in with stirring, and occasional drops are taken out with a glass rod, 
 and put in contact with some ferrocyanide indicator sprinkled on a white 
 plate until a faint colour occurs. The beaker is then placed in the water- 
 bath for a few minutes, and again the mixture tested with the indicator : 
 ufter heating in this way the testing ought to show no colour. More 
 uranium is then added with stirring, and drop by drop till the proper reaction 
 occurs. This titration is only a guide for a second, which maybe made more 
 accurate by running in at once very nearh r the requisite volume of uranium. 
 
 This operation may be reversed, if so desired, by making the 
 clear solution of phosphate up to a definite volume (say 60 c.c.), 
 and running it into a measured volume of uranium until a test 
 taken shows no colour. 
 
 5. Estimation of Phosphoric Acid in Minerals or other substances 
 containing- Iron, Alumina, or other disturbing- matters. 
 
 In order to make use of any volumetric process for this purpose, 
 the phosphoric acid must be separated. As has been already 
 described, this may be ^lone either by the molybdic precipitation 
 followed by solution in !N"H 3 , again precipitated with ordinary 
 magnesia mixture, or direct separation by the citro-magnesia 
 mixture described below. In either case the ammonio-magnesic 
 salt is dissolved in the least possible quantity of nitric or 
 hydrochloric acid, neutralized with ammonia, acidified with acetic 
 acid, and the titration with uranium carried out as before described. 
 
 6. Joulie's Method. 
 
 This differs somewhat from the foregoing, and may be summarized 
 as follows (Munro, C.N. Hi. 85). 
 
 Joulie applies the citro-magnesia method to all phosphates, 
 whether containing iron and alumina or not, and prefers nitrate to 
 acetate of uranium. 
 
 1 to 10 gm. of the sample are dissolved in HC1. Some chemists use 
 nitric acid with a view of leaving as much ferric oxide as possible undissolved. 
 This course is condemned by the author, because the presence of ferric salts 
 in no way interferes with the process, and because HC1 is a much better 
 solvent of mineral phosphates than nitric acid, and leaves a residue free from 
 iron, by the whiteness of which one may judge of the completeness of the 
 attack. In the case of phosphates containing a little pyrites, nitric acid 
 should be used in conjunction with hydrochloric. The removal of silica by 
 evaporation to dry ness is necessary only in those cases where the sample 
 contains silicates decomposable by HC1, with separation of gelatinous silica. 
 The sample is boiled with the acid in a measuring flask until the residue is 
 perfectly white, the contents are cooled, made up to the mark with cold 
 water, mixed, filtered through a dry filter, and such a fraction of the filtrate 
 withdrawn by a pipette as contains about 50 m.gm. of P-0 5 . The sample 
 being delivered from the pipette into a small beaker, 10 c.c. of citro-magnesic 
 solution are added, and then a large excess of ammonia. If this quantity 
 of citro-magnesic solution is sufficient, no precipitate will form until the lapse 
 of a few moments ; should an immediate precipitate form, it is iron or 
 aluminium phosphate. In this case a fresh sample must be pipetted off, and 
 20 c.c. of citro-rnagnesic solution are added ; it is of no use adding another 10 c.c. 
 
 u 2 
 
292 VOLUMETRIC ANALYSIS. 72. 
 
 of the citric solution to the original sample, as the precipitated phosphates 
 of iron and aluminium do not readily redissolve when once formed. 
 
 Citro-Magnesic Solution. 27 gm. of pure maguesic carbonate are added 
 by degrees to a solution of 270 gm. of citric acid in 350 c.c. of warm water ; 
 when all effervescence is over and the liquid cool, about 400 c.c. of solution 
 of ammonia are added, containing 10 per cent, of NH 3 (about 0'96 sp. gr.), 
 or if other strength is used, enough to ensure decided excess of NH 3 :" the 
 whole is then diluted to a liter, and preserved in a well-stoppered bottle. 
 
 The old plan of adding first citric acid and then " magnesia mixture " to 
 the solution under analysis frequently leads to incomplete precipitation of 
 the phosphoric acid, because . the ammonio-magnesic phosphate is slightly 
 soluble in ammonic citrate unless a sufficient excess of magnesium salt is 
 present, and therefore the quantity of magnesium salt should be increased 
 pari passu with the citric acid required, which is best done when they are in 
 solution together. The liquid after precipitation is allowed to stand from 2 
 to 12 hours (covered to prevent evaporation of ammonia), and then decanted 
 through a small filter. The precipitate remaining in the beaker is washed 
 Avith weak ammonia by decantation, and then on the filter until the filtrate 
 gives no precipitate with sodic phosphate. Dilute nitric acid is next poured 
 into the beaker to dissolve the precipitate adhering to the glass, thence on to 
 the precipitate on the filter. The nitric solution is received in a beaker 
 holding about 150 c.c. and marked at 77 c.c. After two or three washings 
 with acidulated water the filter itself is detached from the funnel and added 
 to the contents of the beaker, as the paper is found to retain traces of P-O 5 
 even after many washings. Dilute ammonia is next added until a slight 
 turbidity is produced, which is removed by the addition of one or two drops 
 of dilute nitric acid, the liquid is heated to boiling, 5 c.c. of the sodic acetate 
 solution added ( 72.2c.), and the titration Avith uranic nitrate immediately 
 proceeded with. 
 
 The Standard Uranic Nitrate is made by dissolving about 40 gm. of the 
 pure crj^stals in 800 c.c. water, adding a few drops of ammonia to produce 
 a slight turbidity, then acetic acid until cleared, and diluting to 1 liter. 
 Acetate of uranium should not be used, as it impairs the sensibility of the 
 end-reaction. The uranium solution is titrated with 10 c.c. of a standard 
 solution of acid ammonic phosphate containing 8'10 gm. of the pure dry salt 
 per liter (1 c.c.=0'005 gm. P-O 5 ). The ammonic phosphate solution is- 
 verified by evaporating a measured quantity (say 50 c.c.) of it to dryness 
 with a measured quantity of a solution of pure ferric nitrate containing an 
 excess of ferric oxide, and calcining the residue. The difference in weight 
 between this calcined residue and that from an equal volume of ferric nitrate 
 solution evaporated alone, is the weight of phosphoric anhydride contained 
 in the 50 c.c. of ammonic phosphate solution. The actual verification of the 
 uranic nitrate is performed by measuring accurately 10 c.c. of the ammonic 
 phosphate into a beaker marked at 75 c.c., adding 5 c.c. of the sodic- 
 acetate, making up with water to about 30 c.c., and heating to boiling. 
 9 c.c. uranium are then run in from a burette, and the liquid tested in the 
 usual way with ferrocyanide. From, this point the uranium is added two or 
 three drops at a time, until the end-reaction just appears, the burette being 
 read off at each testing. As soon as the faintest colouration appears, 
 the beaker is immediately filled to the mark with boiling distilled Avater, 
 and another test made. If the operation has been properly conducted no 
 brown colour will be detected, owing to the dilution of the liquid, and one 
 or two drops more of the uranium solution must be added before the colour 
 becomes evident, and the burette is finally read off. A constant correction is 
 subtracted from all readings obtained in this way : it is the quantity of 
 uranium "found necessary to give the end-reaction Avith 5 c.c. of the sodic 
 acetate solution alone, diluted to 75 c.c. Avith boiling Avater as above described. 
 The end-point must always be verified by adding three or four drops o 
 
8 72. PHOSPHORIC ACID. 293 
 
 o 
 
 uranium in excess, and testing again, when a strongly marked colour should 
 be produced. The standard uranium is made of the same strength as the 
 standard ammonic phosphate, in order to eliminate the error caused by 
 changes in the temperature of the laboratory. The actual analysis is made 
 in the same way as the titration of the standard uranium, except that 
 a slight error is introduced by the number of tests that have to be made 
 abstracting a small fraction of the assay. To correct this, a second estimation 
 should always be made, and nearly the whole of the uranium found 
 necessary in the first trial should be added at once. Tests are then made at 
 intervals of two or three drops, and the final and correct result should 
 slightly exceed that obtained in the first trial. 
 
 7. Pemberton's Original Molybdic Method. 
 
 This process, with all the steps that led to its adoption, and the 
 difficulties involved, is described in a paper read before the chemical 
 section of the Franklin Institute in 1882 (C. N. xlvi. 4). 
 
 The process is based on the fact that, if a standard aqueous 
 solution of ammonic molybdate be added to one of phosphoric 
 acid, in the presence of a large proportion of ammonic nitrate, 
 accompanied with a small excess of nitric acid, and heat applied to 
 the mixture, the whole of the P 2 5 is immediately and completely 
 carried down as phospho-molybdate quite free from MoO 3 . A small 
 excess of the precipitant renders the supernatant liquid clear and 
 colourless, and the ratio of molybdic trioxide to phosphoric 
 anhydride is always the same. 
 
 The weak part of the method is the difficulty in finding the 
 exact point at which the precipitation is ended, because the 
 yellow precipitate does not settle in clots like silver chloride, 
 and hence filtration is necessary, in order to obtain a portion of 
 clear liquid for testing with a drop of the molybdate. Very good 
 results may be obtained with some little patience and practice by 
 using the Bcale filter (fig. 23). When the precipitation is thought 
 to be nearly complete, the filter is dipped into the hot liquid, so 
 as to obtain 2 c.c. or so in a clear condition : this is transferred 
 to a clean test tube or small short beaker, and a drop or two 
 of the precipitant added, then heated in the bath to see if a yellow 
 colour occurs ; if it does, the filter and beaker are washed again 
 into the bulk with hot water in very small quantities from a small 
 wash-bottle. A second titration ought to result in "a very near 
 approximation, and a third will be exact. A convenient small 
 suction asbestos filter is figured and described by Professor 
 C a Id well as well adapted to this process (C. N. xlviii. 61). 
 As each titration can be made in a very short time, the process 
 may be made valuable for technical purposes in the absence of 
 either iron or alumina except in mere traces. , 
 
 It is, however, imperative here, as it is in the usual molybdic 
 process, to avoid the presence of soluble silica, organic matter, and 
 organic acids, also iron and alumina. Chlorides in moderate 
 quantity do not interfere. 
 
294 VOLUMETRIC ANALYSIS. 72. 
 
 The necessary solutions and reagents are 
 
 Standard Ammonic molybdate. 89'543 gin. of the pure crystallized 
 salt are dissolved in about 900 c.c. of water ; if not quite clear, 
 a very few drops of ammonia may be added to ensure perfect 
 solution ; the flask is then filled to the liter mark. The weight of 
 salt used is based on the proportion of 24 MoO :J to 1 of P 2 5 , and 
 each c.c. precipitates 3 m.gm. P 2 5 . If any doubt exists as to the 
 purity of the molybdate, the solution should be standardized with 
 a solution of P 2 5 of known strength. In any case this is to be 
 recommended. 
 
 Ammonic nitrate in granular form and neutral. 
 
 Nitric acid, sp. gr. not less than 1'4; or if of less strength, 
 a proportionate increase must be used in the titration. 
 
 Process : The phosphate to be titrated is taken in quantity containing not 
 over O'l gm. P 2 5 or 0'15 gm. at the utmost. If silica is present, the 
 solution is evaporated to dryness. In presence of organic matter ignite 
 gently and evaporate to dryness twice with HNO 3 . There is no advantage 
 in filtering off the SiO' 2 . The solution is transferred to a beaker of 100 to 
 125 c.c., using as little water as possible to prevent unnecessary dilution 
 and is just neutralized with NH 4 HO, i.e., until a slight precipitate is 
 formed. 
 
 If much iron is present the ammonia is added until the yellow colour 
 begins to change to a darker shade. 2 c.c. of nitric acid are added. Care 
 must be taken that the sp. gr. of the acid is not less than T4, otherwise more 
 must be added. 10 gm. of granular nitrate of ammonia are now added. 
 After a little experience the quantity can be judged with sufficient accuracy 
 by the eye without the trouble of weighing. The solution is now heated to 
 140 P. or over and the molybdate solution run in (most conveniently from 
 a Gay Lussac burette), meanwhile stirring the liquid. The beaker is now 
 left undisturbed for about a minute on the water-bath or hot plate until the 
 precipitate settles, leaving the supernatant liquid not clear but containing 
 widely disseminated particles, in which the yellow cloud can easily be seen 
 on the further addition of the molybdate. This addition is continued as 
 long as the precipitate is thick and of a deep colour. But as soon as it 
 becomes rather faint and thin, a little of the solution, about 2 to 3 c.c., after 
 settling of the precipitate, is filtered into a very small beuker, and this is 
 heated on a hot plate and 4 or 5 drops of the molybdate added. If 
 a precipitate is produced, the whole is poured back into the large beaker, and 
 a further addition of the molybdate (1, 2, or 3 c.c.) added, according to the 
 quantity of the precipitate in the small beaker. After stirring and settling, 
 another small quantity is filtered and again tested. If the mark has been 
 overstepped and too much molybdate added, a measured quantity of P-O" 
 solution of known strength is added, and the corresponding amount of 
 P 2 O 5 deducted. The results may be checked by adding 1 c.c. of standard 
 P 2 O 5 solution, and then again testing. This can be repeated as often as 
 desired. The portion that finally produces a cloud is the end-point ; from 
 this is deducted 0'5 c.c. (for neutralizing the solvent action of the nitric 
 acid), the remainder multiplied by 3 gives the weight of P 2 5 in milligrams. 
 O'l gm. of P 2 5 gives about 275 gm. of the yellow precipitate, and the 
 accuracy of the method is largely due to the low percentage of P 2 O 5 . 
 
 8. P ember ton's new Molybiic Method. 
 
 This method, a full description of which is given in Jour. 
 jimer. Cliem. Soc. 1894, 278, is one which requires great delicacy 
 
72. PHOSPHOEIC ACID. 295 
 
 of manipulation, but gives excellent results with all the alkaline 
 or earthy phosphates, but unfortunately is practically useless with 
 the phosphates of iron or alumina, or with materials containing 
 more than mere traces of these substances. For superphosphates 
 it is available, unless the amount of iron or alumina or both exist 
 in more than ordinary proportion, and also for the raw phosphates 
 from which they are made. One great recommendation of the 
 method is that it occupies little time, the whole operation may be 
 performed in less than an hour in the case of a raw phosphate of 
 lime. With superphosphates there has of course to be the extraction 
 of the soluble phosphate, but once this is done the determination 
 of the soluble P 2 5 may readily be done in half-an-hour, and 
 moreover two or three determinations may be carried on simul- 
 taneously with the expenditure of very little extra time. 
 
 The method is based on the fact, which has been proved by 
 numerous experiments, that if a pure yellow phospho-molybdate 
 be titrated with alkali and a proper indicator, so much of it as 
 contains one molecule of P 2 5 will exactly represent 23 molecules 
 of XjiHO. Of course it is of the greatest importance that in the 
 method a pure phosphomolybdate should be obtained, and hence 
 the difficulty where such bases as iron or alumina are present, as it 
 seems impossible to prevent their being carried down with the 
 yellow precipitate even in presence of much nitric acid. As 
 has been already said, the process is one of great delicacy of 
 treatment, and cannot be satisfactorily used by inexperienced 
 operators. The most suitable alkali for the standard is caustic 
 potash which should be free from CO 2 , and the most delicate 
 indicator is phenolphthalein. Further, the quantity of material 
 taken for the titration must be very small, preferably containing not 
 more than Ol gin. of P 2 5 . It will readily be seen that if an 
 error is made it becomes a serious matter, when results are 
 calculated into percentages. 
 
 The solutions required are : 
 
 Ammonic molybdate. 1 c.c. of which will precipitate 3 m.gm. 
 of P 2 5 . This is made by dissolving 90 gm. of the pure salt in 
 about 700 c.c. of water, and allowing to stand a few hours, if 
 then quite clear it may be diluted at once to a liter, but if a slight 
 precipitate of molybdic acid occurs the clear liquid is decanted, 
 the precipitate dissolved in a few drops of ammonia, and the 
 whole made up to the liter. The strength of this solution need 
 not be absolutely exact. 
 
 Standard Caustic Potash. Made by diluting 323 '7 c.c. of 
 strictly normal solution (free from CO 2 ) to a liter. 
 
 Standard Sulphuric Acid. Made to correspond exactly with 
 the standard alkali, using phenolphthalein as the indicator in the 
 cold. The phenolphthalein solution is the same as described on 
 page 37, and not less than 0'5 c.c. should be used for each titration. 
 
296 VOLUMETRIC ANALYSIS. 72. 
 
 There are also required a saturated aqueous solution of ammonic 
 nitrate and nitric acid of about 1*4 sp. gr. 
 
 Process for raw Phosphates of Lime : 1 gm. of the phosphate is dissolved 
 in nitric acid, an excess of which can be used with impunity, and the 
 solution filtered into a 250 c.c. flask and made up to the mark. The solution 
 can even be poured into the flask without filtering, since the presence of 
 a little insoluble matter does not interfere in the least with the titration. 
 Moreover, since most phosphate rocks seldom contain over 10 per cent, 
 of insoluble matter, and as this has the specific gravity of, at least, 2, it 
 occupies a volume of about 0'05 c.c., an amount so small that it may be 
 neglected. 
 
 After the clear solution has been poured off, it is well to treat the 
 sand, etc., at the bottom of the beaker, with a c.c. or so of HC1, in the 
 warmth, to insure complete solution. 
 
 It is not necessary to evaporate to dryness. Isbert and Stutzer have 
 shown (Z. A. C. xxvi. 584), that when the yellow precipitate is washed with 
 water, the soluble silica is removed, and that evaporation (to render the 
 silica insoluble) is superfluous. In the event of its being desirable to 
 remove silica by evaporation for any purpose, the evaporation should be 
 performed over a water-bath, or, if on an iron plate, with great care, since, 
 otherwise, meta- or pyrophosphates are formed, with results that are 
 correspondingly low. 
 
 25 c.c. of the solution (equal to O'l gm.) are now measured out and 
 delivered into a beaker holding not more than 100 to 125 c.c. A large 
 beaker requires unnecessary washing to remove the free acid in washing the 
 yelloAV precipitate. The solution is neutralized with ammonia until 
 a precipitate just begins to form and 5 c.c. of nitric acid of sp. gr. 1*4 
 added ; 10 c.c. of the ammonic nitrate solution are poured in, and the entire 
 bulk of the mixture made up to 60 or 70 c.c. by adding water. 
 
 Heat is now applied, and the solution brought to a full boil. It is then 
 removed from the lamp, no more heat being applied, and treated at once 
 with. 5 c.c. of the aqueous solution of ammonium molybdate, which is run into 
 it slowly from a 5 c.c. pipette, the solution being stirred as the precipitate is 
 added. The beaker is now allowed to rest quietly for about one minute, 
 during which time the precipitate settles almost completely. The 5 c.c. 
 pipette is filled with the molybdate solution, and a part of its contents 
 allowed to drop in, holding the beaker up to the light. If a formation of 
 a yellow cloud takes place it is at once perceptible in which case the 
 remainder of the pipetteful is run in, the solution stirred and allowed to 
 settle. A third pipetteful is now added as before. Should it cause no 
 further cloud, only about one-half of its contents are added. 
 
 It is seldom that more than 15 c.c. of the molybdate have to be added. 
 Since each c.c. precipitates 3 m.gm. of P 2 O 5 , 15 c.c. will precipitate 45 m.gm. 
 of P 2 O 5 . This is equivalent to 45 per cent, on the O'l gm. taken for 
 analysis, and it is not often that any material to be examined contains over 
 this percentage. This is not strictly true, for the reason that a small 
 quantity (something over 1 c.c.) of the molybdate is required to neutralize 
 the solvent action of the nitric acid. Therefore, in very high grade 
 phosphates a fourth 5 c.c. pipetteful may be required. In this process the 
 point at Avhich sufficient of the precipitant has been added is easily seen. 
 No molybdic acid separates, because, in the first place, no great excess of 
 molybdate is added; and because, in the second place, the solution is 
 filtered immediately, or as soon as it has settled, which requires only 
 a minute or two. The time required from the first addition of the molybdate 
 to the beginning of the filtration is never over ten minutes, and is generally 
 less. The filtrate and washings from the precipitate when treated with 
 additional molybdate solution, give, on standing on a hot plate for an hour 
 
72. SILVER. 297 
 
 or so, a snow-white precipitate of molybdic acid, showing that all of the 
 phosphoric acid has been precipitated. 
 
 The yellow precipitate is now filtered through a filter 7 c.m. in diameter, 
 decanting the clear solution only. This is repeated three or four times, 
 washing down the sides of the beaker, stirring up the precipitate, and 
 washing the filter and sides of the funnel above the filter each time. The 
 precipitate is then transferred to the filter and washed there. When the 
 precipitate is large it cannot be churned up by the wash water, and cannot 
 be washed down to the apex of the filter. This is generally the case when 
 there is over 10 to 15 per cent, of phosphoric acid present in the substance 
 analyzed. In such an event, the precipitate is washed back into the beaker, 
 and the funnel tilled with water above the level of the filter, this being done 
 two or three times, then the precipitate washed back into the filter. It is 
 not necessary to transfer to the filter the precipitate adhering to the sides of 
 the beaker. 
 
 During the washing no ammonia must be present in the atmosphere of 
 the laboratory. Inasmuch as the beaker, funnel, filter and precipitate are 
 small, the washing does not take long to perform. It requires, in fact, from 
 ten to fifteen minutes, even when large precipitates (=30 to 40 per cent. 
 P-O 5 ) are handled. The precipitate and filter are now transferred together 
 to the beaker. The standard alkali is run in until the precipitate has 
 dissolved, phenolphthalein then added, and the acid run in without delay 
 until the pearly colour disappears and the solution is colourless. The 
 presence of the filter paper does not interfere in the least. The reaction of 
 the indicator is not so sharp as when only acid and alkali are used, but it is 
 easy to tell with certainty the difference caused by one drop of either acid 
 or alkali. After deducting the volume of acid used from that of the alkali, 
 the remainder gives the percentage of P-O 5 directly, each c.c. being equal to 
 1 per cent. P 2 O 5 . Thus, if there are 28'3 c.c. of alkali consumed, the 
 material contains 28'3 per cent. P 2 O 5 when one decigram is taken for 
 analysis. From the time the 25 c.c. are measured out until the result is 
 obtained, from thirty to forty minutes are required. 
 
 Process for soluble P 2 5 in Superphosphates : A measured portion of the 
 clear aqueous solution of the material according to its grade, and representing 
 not more than 0'05 gm. P 2 O 5 , are pipetted into a small beaker and treated 
 exactly as described above. 
 
 B. W. Kilgore (Jour. Amer. Cliem. Soc. 1894, 765) states that 
 good results in general were obtained by him in using this method, 
 but that occasionally too high figures for P 2 5 were obtained. 
 This is also stated by other operators. The variations in this 
 direction are generally caused by the deposition of molybdic acid, 
 but .they may, of course, be also caused by imperfect washing of 
 the precipitate. Kilgore prefers to use the ordinary official acid 
 molybdic solution, and to precipitate at 50 or 60 C. instead of 100 
 C. The official molybdic solution is made by dissolving 100 gm. 
 of molybdic acid in 417 c.c. of ammonia, sp. gr. 0*96, and 
 pouring this into 1250 c.c. of nitric acid, sp. gr. 1*2, then filtering 
 before use. 
 
 SILVER. 
 
 Ag=: 107-66. 
 
 1 c.c. or 1 dm. - sodic chloride- 0'010766 gm. or 0'10766 grn. 
 Silver; also 0*016966 gm. or 0*16966 grn. Silver nitiate. 
 
298 VOLUMETRIC ANALYSIS. 73. 
 
 3. Precipitation with ^ Sodic Chloride. 
 
 73. THE determination of silver is precisely the converse of 
 tl;e operations described under chlorine ( 54, 1 and 2), and the 
 process may either be concluded by adding the sodic chloride till 
 no further precipitate is produced, or potassic chromate may be 
 used as an indicator. In the latter case, however, it is advisable 
 to add the salt solution in excess, then a drop or two of chromate, 
 and titrate residually with silver, till the red colour is produced, 
 for the excess of sodic chloride. 
 
 2. By Ammonic Sulphocyanate (Thiocyanate) . 
 
 The principle of this method is fully described in 43, and 
 need not further he alluded to here. The author of the method 
 (Volhard) states, that comparative tests made by this method 
 and that of Gay Lussac gave equally exact results, both being 
 controlled by cupellation, but claims for this process that the end 
 of the reaction is more easily distinguished, and that there is no 
 labour of shaking, or danger of decomposition by light, as in the 
 case of chloride. My own experience fully confirms this. 
 
 3. Estimation of Silver, in Ores and Alloys, by Starch Iodide 
 (Method of Pisani and P. Field). 
 
 If a solution of blue starch-iodide be added to a neutral solution 
 of silver nitrate, while any of the latter is in excess, the blue colour 
 disappears, the iodine entering into combination with the silver ; 
 as soon as all the silver is thus saturated, the blue colour remains- 
 permanent, and marks the end of the process. The reaction is 
 very delicate, and the process is more especially applicable to the 
 analysis of ores and alloys of silver containing lead and copper, but 
 not mercury, tin, iron, manganese, antimony, arsenic, or gold in 
 solution. 
 
 The solution of starch iodide, devised by Pisani, is made by 
 rubbing together in a mortar 2 gm. of iodine with 15 gm. of starch 
 and about 6 or 8 drops of water, putting the moist mixture into 
 a stoppered flask, and digesting in a water bath for about an hour, or 
 until it has assumed a dark bluish-grey colour ; water is then added 
 till all is dissolved. The strength of the solution is then ascertained 
 by titrating it with 10 c.c. of a solution of silver containing 1 gm. 
 in the liter, to which a portion of pure precipitated calcic carbonate 
 is added; the addition. of this latter removes all excess of acid, and 
 at the same time enables the operator to distinguish the end of the 
 reaction more accurately. The starch iodide solution should be of 
 such a strength that about 50 c.c. are required for 10 c.c. of the 
 silver solution ( = O'Ol gm. silver). 
 
 F. Field (C. N. ii. 17), who discovered the principle of this 
 method simultaneously with Pisani, uses a solution of iodine in 
 potassic iodide with starch. Those who desire to make use of 
 
73. SILVER. 299 
 
 this plan can use the T ^ and T gy solutions of iodine described 
 in 38. 
 
 In the analysis of silver containing copper, the solution must be 
 considerably diluted in order to weaken the colour of the copper ; 
 a small measured portion is then taken, calcic carbonate added, and 
 starch iodide till the colour is permanent. It is best to operate 
 with about from 60 to 100 c.c., containing not more than 0'02 gni. 
 silver; when the quantity is much greater than this, it is preferable 
 to precipitate the greater portion with sodic chloride, and to 
 complete with starch iodide after filtering off the chloride. When 
 lead is present with silver in the nitric acid solution, add sulphuric 
 acid, and filter off the lead sulphate, then add calcic carbonate to 
 neutralize excess of acid, filter again if necessary, then add fresh 
 carbonate and titrate as described above. 
 
 4. Assay of Commercial Silver (Plate, Bullion, Coin, etc.). Gray 
 Lussac's Method modified by J. G-. Mulder. 
 
 For more than thirty years Gay Lussac's method of estimating 
 silver in its alloys has been practised intact, at all the European 
 mints, under the name of the " humid method," in place of the old 
 system of cupellation. During that time it has been regarded as one 
 of the most exact methods of quantitative analysis. The researches 
 of Mulder, however, into the innermost details of the process 
 have shown that it is capable of even greater accuracy than has 
 hitherto been gained by it. 
 
 The principle of the process is the same as described in 41, 
 depending on the affinity which chlorine has for silver in preference 
 to all other substances, and resulting in the formation of chloride 
 of silver, a compound insoluble in dilute acids, and which readily 
 separates itself from the liquid in which it is suspended. 
 
 The plan originally devised by the illustrious inventor of the 
 process for assaying silver, and which is still followed, is to consider 
 the weight of alloy taken for examination to consist of 1000 parts, 
 and the question is to find how many of these parts are pure silver. 
 This empirical system was arranged for the convenience of commerce, 
 and being now thoroughly established, it is the best plan of 
 procedure. If, therefore, a standard solution of salt be made of 
 such strength that 100 c.c. will exactly precipitate 1 gm. of silver, 
 it is manifest that each yy c.c, will precipitate 1 in.gm. or y^cr 
 part of the gram taken ; and consequently in the analysis of 
 1 gm. of any alloy containing silver, the number of y 1 ^ c.c. 
 required to precipitate all the silver out of it would be the number 
 of thousandths of pure silver contained in the specimen. 
 
 In practice, however, it would not do to follow this plan precisely, 
 inasmuch as neither the measurement of the standard solution nor 
 the ending of the process would be gained in the most exact 
 manner ; consequently, a decimal solution of salt, one-tenth the 
 strength of the standard solution, is prepared, so that. 1000 c.c. 
 
SOO VOLUMETRIC ANALYSIS. 73. 
 
 will exactly precipitate 1 gm. of silver, and, therefore, 1 c.c. 
 1 m.gm. 
 
 The silver alloy to be examined (the composition of which must 
 be approximately known) is weighed so that about 1 gm. of pure 
 silver is present ; it is then dissolved in pure nitric acid by the aid 
 of a gentle heat, and 100 c.c. of standard solution of salt added 
 from a pipette in order to precipitate exactly 1 gm. of silver ; the 
 bottle containing the mixture is then well shaken until the chloride 
 of silver has curdled, leaA^ing the liquid clear. 
 
 The question is now : Which is in excess, salt or silver ? A drop 
 of decimal salt solution is added, and if a precipitate be produced 
 1 c.c. is delivered in, and after clearing, another, and so on as long 
 as a precipitate is produced. If on the other hand the one drop of 
 salt produced no precipitate, showing that the pure silver present 
 was less than 1 gm., a decimal solution of silver is used, prepared 
 by dissolving 1 gm. pure silver in pure nitric acid and diluting to 
 1 liter. This solution is added after the same manner as the salt 
 solution just described, until no further precipitate occurs; in either 
 case the quantity of decimal solution used is noted, and the results 
 calculated in thousandths for 1 gm. of the alloy. 
 
 The process thus shortly described is that originally devised by 
 Gay Lussac, and it was taken for granted that when equivalent 
 hemical proportions of silver and sodic chloride were brought thus 
 in contact, that every trace of the metal was precipitated from the 
 solution, leaving sodic nitrate and free nitric acid only in solution. 
 The researches of Mulder, however, go to prove that this is not 
 strictly the case, but that when the most exact chemical proportions 
 of silver and salt are made to react on each other, and the chloride 
 has subsided, a few drops more of either salt or silver solution will 
 produce a further precipitate, indicating the presence of both silver 
 nitrate and sodic chloride in a state of equilibrium, which is upset 
 on the addition of either salt or silver. Mulder decides, and no 
 doubt rightly, that this peculiarity is owing to the presence of sodic 
 nitrate, and varies somewhat with the temperature and state of 
 dilution of the liquid. 
 
 It therefore follows that when a silver solution is carefully 
 precipitated, first by concentrated and then by dilute salt solution, 
 until no further precipitate appears, the clear liquid will at this 
 point give a precipitate with dilute silver solution ; and if it be 
 added till no further cloudiness is produced, it will again be 
 precipitable by dilute salt solution. 
 
 Example : Suppose that in a given silver analysis the decimal salt solution 
 has been added so long as a precipitate is produced, and that 1 c.c. (=20 drops 
 of Mulder's dropping apparatus) of decimal silver is in turn required to 
 precipitate the apparent excess, it would be found that when this had been 
 done, 1 c.c. more of salt solution would be wanted to reach the point at which 
 110 further cloudiness is produced by it, and so the changes might be rung 
 time after time ; if, however, instead of the last 1 c.c. (=20 drops) of salt, 
 half the quantity be added, that is to say 10 drops (=| c.c.), Mulder's 
 
73. SILVEB. 301 
 
 so-called neutral point is reached ; namely, that i n which, if the liquid be 
 divided in half, both salt and silver will produce the same amount of 
 precipitate. At this stage the solution contains silver chloride dissolved 
 in sodic nitrate, and the addition of either salt or silver expels it from* 
 solution. 
 
 A silver analysis may therefore be concluded in three ways 
 
 (1) By adding decimal salt solution until it just ceases 1x> 
 produce a cloudiness. 
 
 (2) By adding a slight excess of salt, and then decimal silver; 
 till no more precipitate occurs. 
 
 (3) By finding the neutral point. 
 
 According to Mulder the latter is the only correct method, and 
 preserves its accuracy at all temperatures up to 56 C. ( = 133 
 Fahr.), while the difference between 1 and 3 amounts to | a m.gm., 
 and that between 1 and 2 to 1 m.gm. on 1 gm. of silver at, 
 16 C. (= 60 Fahr.), and is seriously increased by variation of 
 temperature. 
 
 It will readily be seen that much more trouble and care is 
 required by Mulder's method than by that of Gay Lussac, but,, 
 as a compensation, much greater accuracy is obtained. 
 
 On the whole it appears to me preferable to weigh the alloy so, 
 that slightly more than 1 gm. of silver is present, and to choose the- 
 ending No. 1, adding drop by drop the decimal salt solution until 
 just a trace of the precipitate is seen, and which, after some practice, 
 is known by the operator to be final. It will be found that the- 
 quantity of salt solution used will slightly exceed that required by 
 chemical computation; say lOO'l c.c. are found equal to 1 gm. of 
 silver, the operator has only to calculate that quantity of the salt 
 solution in question for every 1 gm. of silver he assays in the form 
 of alloy, and the error produced by the solubility of silver chloride 
 in sodic nitrate is removed. 
 
 If the decimal solution has been cautiously added, and the 
 temperature not higher than 17 C. (62 Fahr.), this method of 
 conclusion is as reliable as No. 3, and free from the possible errors^ 
 of experiment ; for it requires a great expenditure of time and 
 patience to reverse an assay two or three times, each time 
 cautiously adding the solutions drop by drop, then shaking and' 
 waiting for the liquid to clear, besides the risk of discolouring the 
 chloride of silver, which would at once vitiate the results. 
 
 The decimal silver solution, according to this arrangement, would, 
 seldom be required ; if the salt has been incautiously added, or the 
 quantity of alloy too little to contain 1 gm. pure silver, then it is 
 best to add once for all 2, 3, or 5 c.c., according to circumstances, 
 and finish with decimal salt as iNo. 1, deducting the silver added. 
 
 The Standard Solutions and Apparatus. 
 
 () Standard Salt Solution. Pure sodic chloride is prepared by treating;- 
 a concentrated solution of the whitest table-salt first with a solution of 
 
VOLUMETRIC ANALYSIS, 73. 
 
 caustic baryta to remove sulphuric acid and magnesia, then with a slight 
 excess of bodic carbonate to remove baryta and lime, warming and allowing 
 the precipitates to subside, then evaporating to a small bulk that crystals 
 may form ; these are separated by a filter, and slightly washed with cold 
 distilled water, dried, removed from the filter, and heated to dull redness, 
 and when cold preserved in a well-closed bottle for use. The mother-liquor 
 is thrown away, or used for other purposes. Of the salt so prepared, or of 
 chemically pure rock-salt (Steinsalz, a substance to be obtained freely in 
 Germany), 5'4145 gui. are to be weighed and dissolved in 1 liter of distilled 
 water at 16 C. 100 c.c. of this solution will precipitate exactly 1 gm. of 
 silver. It is preserved in a well-stoppered bottle, and shaken before use. 
 
 (b) Decimal Salt Solution. 100 c.c. of the above solution are diluted to 
 exactly 1 liter with distilled water at 16 C. 1 c.c. will precipitate O'OOl gm. 
 of silver. 
 
 (c) Decimal Silver Solution; Pure metallic silver is best prepared by 
 galvanic action from pure chloride ; and as clean and seeure a method as any 
 is to wrap a lump of clean zinc, into which a silver wire is melted, with 
 a piece of wetted bladder or calico, so as to keep any particles of impurity 
 contained in the zinc from the silver. The chloride is placed at the bottom 
 of a porcelain dish, covered with dilute sulphuric acid, and the zinc laid in 
 the middle ; the silver wire is bent over so as to be immersed in the chloride. 
 As soon as the acid begins to act upon the zinc the reduction commences in 
 the chloride, and grows gradually all over the mass ; the resulting finely- 
 divided silver is well washed, first with dilute acid, then with hot water, till 
 all acid and soluble zinc are removed. 
 
 The moist metal is then mixed with a little sodic carbonate, saltpetre, 
 and borax, say about an eighth part of each, dried perfectly, then melted. 
 Mulder recommends that the melting should be done in a porcelain crucible 
 immersed in sand contained in a common earthen crucible; borax is sprinkled 
 over the surface of the sand so that it may be somewhat vitrified, that in 
 pouring out the silver when nielted no particles of dirt or sand may fall into 
 it. If the quantity of metal be small it may be melted in a porcelain crucible 
 over a gas blowpipe. 
 
 The molten metal obtained in either case can be poured into cold water 
 and so granulated, or upon a slab of pipe-clay, into which a glass plate has 
 been pressed when soft so as to form a shallow mould. The metal is then 
 washed well with boiling water to remove accidental surface impurities, and 
 rolled into thin strips by a goldsmith's mill, in order that it may be readily 
 cut for weighing. The granulated metal is, of course, ready for use at once 
 without any rolling. 
 
 1 gm. of this silver is dissolved in pure dilute nitric acid, and 
 diluted to 1 liter; each c.c. contains O'OOl gm. of silver. It should 
 be kept from the light. 
 
 (<i) Dropping- Apparatus for Concluding- the Assay.- Mulder 
 constructs a special affair for this purpose, consisting of a pear- 
 shaped vessel fixed in a stand, with special arrangements for 
 preventing any continued flow of liquid. The delivery tube has an 
 opening of such size that 20 drops measure exactly 1 c.c. The 
 vessel itself is not graduated. As this arrangement is of more 
 service to assay than to general laboratories, it need not be further 
 described here. A small burette divided in -^ c.c. with a conve- 
 nient dropping tube, will answer every purpose, and possesses the 
 further advantage of recording the actual volume of fluid delivered. 
 
73. SILVEE. 303 
 
 The 100-c.c. pipette, for delivering the concentrated salt solution, 
 must be accurately graduated, and should deliver exactly 100 gm. 
 of distilled water at 16 C. 
 
 The test bottles, holding about 200 c.c., should have their 
 stoppers well ground and brought to a point, and should be fitted 
 into japanned tin tubes reaching as high as the neck, so as to pre- 
 serve the precipitated chloride from the action of light, and, when 
 shaken, a piece of black cloth should be covered over the stopper. 
 
 (e) Titration of the Standard Salt Solution. From what has 
 been said previously as to the principle of this method, it will be 
 seen that it is not possible to rely absolutely upon a standard 
 solution of salt containing 5 '4 145 gm. per liter, although this is 
 chemically correct in its strength. The real working power must 
 be found by experiment. From 1*002 to 1*004 gm. of absolutely 
 pure silver is weighed on the assay balance, put into a test bottle 
 with about 5 c.c. of pure nitric acid, of about 1'2 sp. gr., and gently 
 heated in the water or sand bath till it is all dissolved, The 
 nitrous vapours are then blown from the bottle, and it is set aside 
 to cool down to about 16 C. or 60 Fahr. 
 
 The 100 c.c. pipette, which should be securely fixed in a support, 
 is then carefully filled with the salt solution, and delivered into 
 the test bottle contained in its case, the moistened stopper inserted, 
 covered over with the black velvet or cloth, and shaken con- 
 tinuously till the chloride has clotted, and the liquid becomes clear ; 
 the stopper is then slightly lifted, and its point touched against the 
 neck of the bottle to remove excess of liquid, again inserted, and 
 any particles of chloride washed down from the top of the bottle 
 by carefully shaking the clear liquid over them. The bottle is 
 then brought under the decimal salt burette, and J c.c. added, the 
 mixture shaken, cleared, another | c.c. put in, and the bottle lifted 
 partly out of its case to see if the precipitate is considerable * 
 lastly, 2 or 3 drops only of the solution are added at a time until 
 no further opacity is produced by the final drop. Suppose, for 
 instance, that in titrating the salt solution it is found that 1 *003 gm. 
 of silver require 100 c.c. concentrated, and 4 c.c. decimal solution, 
 altogether equal to 100 '4 c.c. concentrated, then 
 
 .1-003 silver : 100*4 salt : : 1*000 : x. =100*0999. 
 
 The result is within -jo-J^yo" ^ 100*1, which is near enough for the 
 purpose, and may be more conveniently used. The operator 
 therefore knows that 100*1 c.c. of the concentrated salt solution 
 at 16 C. will exactly precipitate 1 gm. silver, and calculates 
 accordingly in his examination of alloys. 
 
 In the assay of coin and plate of the English standard, namely, 
 11*1 silver and 0*9 copper, the weight corresponding to 1 gm. of 
 silver is 1*081 gm., therefore in examining this alloy 1*085 gm. 
 may be weighed. 
 
304 \ 7 OLUMET11IC ANALYSIS. 73. 
 
 When the quantity of silver is not approximately known, 
 a preliminary analysis is necessary, which is best made by 
 dissolving J or 1 gm. of the alloy in nitric acid, and precipitating 
 very carefully with the concentrated salt solution from a ^ c.c. 
 burette. Suppose that in this manner 1 gm. of alloy required 
 45 c.c. salt solution, 
 
 100-1 salt : 1-000 silver : : 45 : x. = 0-4495. 
 Again 0-4495 : 1 : : 1-003 : x = 2'23l. 
 
 r> 
 
 2'231 gm. of this particular alloy are therefore taken for the 
 assay. 
 
 Where alloys of silver contain sulphur or gold, with small 
 quantities of tin, lead, or antimony, they are first treated with 
 a small quantity of nitric acid so long as red vapours are disengaged., 
 then boiled with concentrated sulphuric acid till the gold has 
 become compact, set aside to cool, diluted with water, and titrated 
 as above. 
 
 Assaying- on the Grain System. 
 
 It will be readily seen that the process just described may quite 
 as conveniently be arranged on the grain system by substituting 10 
 grains of silver as the unit in place of the gram ; each decem of 
 concentrated salt solution would then be equal to ~ of a grain 
 of silver, and each decem of decimal solution to -$ of a grain. 
 
 5. Analysis of the Silver Solutions used in Photography. 
 
 The silver bath solutions for sensitizing collodion and paper 
 frequently require examination, as their strength is constantly 
 lessening. To save calculation, it is better to use an empirical 
 solution of salt than the systematic one described above. 
 
 This is best prepared by dissolving 43 grains of pure sodic 
 chloride in 10,000 grains of distilled water. Each decem ( = 10 grn.) 
 of this solution will precipitate 0-125 grn. (i.e, \ grn.) of pure 
 silver nitrate ; therefore, if one fluid drachm of any silver solution 
 be taken for examination, the number of decems of salt solution 
 required to precipitate all the silver Avill be the number of grains 
 of silver nitrate in each ounce of the solution. 
 
 Example : One fluid drachm of an old nitrate bath was carefully measured 
 into a stoppered bottle, 10 or 15 drops of pure nitric acid and a little 
 distilled water added ; the salt solution was then cautiously added, shaking- 
 well after each addition until no further precipitate was produced. The 
 quantity required was 26'5 dm. 26| grains of silver nitrate in each ounce 
 of solution. 
 
 Crystals of silver nitrate may also be examined in the same way, 
 by dissolving say 30 or 40 grn. in an ounce of water, taking one 
 drachm of the fluid and titrating as above. 
 
74 SUGAR. 305 
 
 In consequence of the rapidity and accuracy with which silver 
 may be determined, when potassic chromate is used as indicator, 
 some may prefer to use that method. It is then necessary to have 
 a standard solution of silver, of the same chemical power as the 
 salt solution : this is made by dissolving 125 grains of pure and 
 dry neutral silver nitrate in 1000 dm. of distilled water; both 
 solutions will then be equal, volume for volume. 
 
 Suppose, therefore, it is necessary to examine a silver solution 
 used for sensitizing paper. One drachm is measured, and 
 if any free acid be present, cautiously neutralized with a weak 
 solution- of sodic carbonate ; 100 dm. of salt solution are then 
 added with a pipette. If the solution is under 100 grn. to 
 the ounce, the quantity will be sufficient. 3 or 4 drops of 
 chromate solution are then added, and the silver solution delivered 
 from the burette until the red colour of silver chromate is just 
 visible. If 25'5 dm. have been required, that number is deducted 
 from the 100 dm. of salt solution, which leaves 74'5 dm., or 
 74J- grains to the ounce. 
 
 This method is- much more likely to give exact results in the 
 hands of persons not expert in analysis than the ordinary plan by 
 precipitation, inasmuch as, with collodion baths, containing as they 
 always do silver iodide, it is almost impossible to get the supernatant 
 liquid clear enough to distinguish the exact end of the analysis. 
 
 SUGAR. 
 
 74. SUGARS belong to the large class of organic bodies known 
 as " carbo-hydrates," of which there are three main classes, viz. : 
 
 (1) The Glucoses, C 6 H 12 0, the principal members of which 
 are glucose, dextrose, or grape sugar, occurring in the urine in 
 Diabetes mellitus, and with levulose in most sweet fruits and in 
 honey ; levulose or fruit sugar ; galactose. 
 
 (2) The Di-saccharides, C 12 H 22 O n , the chief members of which 
 are cane sugar or sucrose, occurring in the juice of the sugar 
 cane, beet root, and maple ; milk sugar or lactose, occurring in the 
 milk of mammals and in various pathological secretions ; malt 
 sugar or maltose, formed by the action of malt diastase upon 
 starch. 
 
 (3) The Poly-saccharides, or starches and gums (C 6 H 10 5 X of 
 which the most important members are starch, glycogen (found in 
 the liver), dextrine, and cellulose or wood-fibre. 
 
 The di- and poly-saccharides are "inverted" or " hydrolyzed " 
 by being boiled with dilute acids, or by the action of unorganized 
 ferments like diastase and pepsin, and those contained in yeast 
 and saliva ; i.e., they become converted into glucoses. Cane sugar 
 on inversion yields equal parts of dextrose and levulose (invert 
 sugar), milk sugar yields dextrose and galactose, maltose yields 
 
 x 
 
306 VOLUMETRIC ANALYSIS. 74 
 
 dextrose ; starch, glycogen, dextrose, and cellulose all yield dextrose 
 as the final product. 
 
 The methods in general use for the quantitative estimation of 
 the various kinds of sugar are the fermentation method, 
 estimating the final density of the saccharine solution, and 
 the amount of CO 2 evolved; the optical method, by the polarimeter ; 
 gravimetrically, by the reduction of an alkaline copper solution ; 
 volumetrically, by reduction of copper or mercury solutions. 
 
 All the glucoses reduce the alkaline copper solution, known as 
 Fehling's, more or less readily; maltose and lactose reduce it in 
 a less degree ; starch, cane sugar, dextrine, and cellulose rrot at all. 
 Other substances besides sugars reduce Fell ling's solution, e.g., 
 chloroform, salicylic and uric acids, creatinine and phenyl- 
 hyclrazine. 
 
 The volumetric method of estimating glucose by Fehl ing's 
 copper solution has for a long time been thought open to question 
 on the score of accuracy, and the extensive and elaborate experi- 
 ments of Soxhlet have clearly shown, that only under identical 
 conditions of dilution, etc., can concordant results be obtained. 
 The high official position of this chemist, together with the evident 
 care shown in his methods, leave no doubt as to the general 
 accuracy of his conclusions. His rather sweeping statement, how- 
 ever, that the accurate gravimetric estimation of glucose by 
 Fehling's solution is impossible, is strongly controverted by 
 Brown and Heron, whose large experience leads them to 
 a different conclusion. It is probable, however, that both 
 authorities are right from their own points of view, and that 
 Brown and Heron do obtain concordant results when working in 
 precisely the same way; whereas Soxhlet is equally correct in 
 stating that the gravimetric estimation, as usually performed under 
 varying conditions, is open to serious errors. 
 
 Kjeldahl maintains that Fehling's solution, however pure its 
 constituents, always undergoes a slight reduction on prolonged 
 heating, especially in strong solution, and he fixes the limit of 
 time for which the liquid should be exposed to the temperature of 
 boiling water at twenty minutes. 
 
 The Solution of Sugar. For all the processes of titration this 
 must be so diluted as to contain J or at most 1 per cent, of sugar : 
 if on trial it is found to be stronger than this, it must be further 
 diluted with a measured quantity of distilled water. 
 
 If the sugar solution to be examined is of dark colour, or likely 
 to contain extractive matters which might interfere with the 
 distinct ending of the reaction, it is advisable to heat a measured 
 quantity to boiling, and add a few drops of milk of lime, allow the 
 precipitate to settle, then filter through purified animal charcoal, 
 and dilute with the washings to a definite volume. In some 
 instances cream of alumina or basic lead acetate may be used to 
 
74. SUGAR. 307 
 
 clarify highly coloured or impure solution, Imt no lead must be 
 left in the solution.'* 
 
 From thick mucilaginous liquids, or those which contain a large 
 proportion of albuminous or extractive matters, the sugar is best 
 extracted by Graham's dialyser. 
 
 The Fell ling method may be applied directly to fresh diabetic 
 urine (see Analysis of Urine), as also to brewer's wort or distiller's 
 mash. Dextrine does not interfere, unless the boiling of the 
 liquid under titration is long continued. 
 
 ]. Inversion of Various Sugars into Glucose. 
 
 Ordinary cane sugar is best inverted by heating to about 70 C. 
 a dilute solution (in no case should the concentration exceed 25 per 
 cent.) of the sugar with 10 per cent, of fuming hydrochloric acid 
 for 15 minutes. Dilute sulphuric acid is preferred by some 
 operators. If the mixture is boiled, the inversion occurs in from 
 5 to 10 minutes. The inversion of milk sugar takes longer time 
 than cane sugar. 
 
 Maltose or malt sugar takes a much longer time than milk 
 sugar, but may be done by the addition of 3 c.c. of concentrated 
 sulphuric acid to 100 c.c. of wort, and heating for 3 hours in 
 a boiling water bath ; if dextrine is present, it is also inverted at 
 the same time. 
 
 The inversion of the slowly changing sugars may be hastened 
 considerably by heating at increased atmospheric pressure, although 
 some authorities condemn the process. 0' Sullivan however 
 states that a good result with maltose or dextrine is obtained by 
 heating 30 gm. of the substance in 100 c.c. of water containing 
 1 c.c. of H 2 S0 4 for 20 minutes, at a pressure of one additional 
 atmosphere (Allen's Organic Analysis i. 217). 
 
 Allen also gives a handy means of carrying out this method, 
 which consists in using a soda water bottle with rubber stopper 
 through which passes a long glass tube bent at right angles, and 
 immersed to a depth of 30 inches in mercury contained in 
 a vertical tube of glass or metal. The rubber stopper must be 
 secured by wire, and the bottle heated to boiling in a saturated 
 solution of sodic nitrate, which gives a temperature corresponding 
 to an extra atmosphere. Of course in all cases where acid has 
 been used for the inversion of sugar, it must be neutralized before 
 the copper titration takes place ; this may be done either with 
 sodic or potassic hydrates or carbonates, or calcic carbonate may be 
 used. 
 
 * Although traces of lead are of no great consequence when clarifying sugars for the 
 polariscope, it is of great importance to remove all lead in the volumetric method. In 
 order to do this it is best to treat a measured quantity of the sugar solution which has 
 been clarified by lead with a strong solution of sulphurous acid until no further 
 precipitate occurs, then add a few drops of alumina hydrate suspended in water, 
 dilute to a definite volume and filter. In many cases concentrated solution of sodic 
 carbonate will suffice to remove all lead. These methods of clarification are highly 
 necessary in the case of albuminous or gelatinous liquids, as otherwise the copper oxide 
 will not settle readily, and it becomes difficult to tell when the end-reaction occurs. 
 
 x 2 
 
308 VOLUMETEIC ANALYSIS. 74. 
 
 Starch from various sources may be inverted in the same way 
 as the sugars, but it needs a prolonged heating with acid. For 
 approximate purposes 1 gm. of starch should be mixed to a smooth 
 cream w r ith about 30 c.c. of cold water, then 1 c.c. of strong 
 hydrochloric acid added, and the mixture kept at a boiling 
 temperature in an obliquely fixed flask for 8 or 10 hours, replacing 
 the evaporated water from time to time to avoid charring the 
 sugar, and testing with iodine to ascertain when the inversion is 
 complete. The product is glucose. 
 
 For the estimation of the starch itself a number of processes 
 were tried by Ost (Cliem. Zeit. 1895, xix. 1501), the one which 
 was found to answer best being that of Sachsse (Cliem. CentralM. 
 viii. 732), slightly modified. In this modification 3 gm. of the 
 starch are heated with 200 c.c. of water and 20 c.c. of hydrochloric 
 acid, specific gravity 1'125 ( - 5*600 gm. of HC1), for two to three 
 hours in a boiling water bath, using the factor 0*925 to calculate 
 the glucose found in the starch. Longer heating gives results too 
 low, and two hours on the water bath are not sufficient. Slightly 
 higher yields of glucose (89*8 instead of 89*5 per cent.) can be 
 obtained by heating for a much longer period with less starch and 
 acid, but there is no advantage to be gained by the alteration. 
 Oxalic acid gives no better results. Dextrine may be determined 
 in the same manner also maltose, if 1 gm. of the latter be heated 
 for five hours with 100 c.c, of 1 to 2 per cent, hydrochloric acid 
 as before. 
 
 100 parts of grape sugar, found by Fehling's process, represent 
 90 parts of starch or dextrine. When dextrine is present with 
 grape sugar, care must be taken not to boil the mixture too long 
 with the alkaline copper solution, as it has been found that a small 
 portion of the copper is precipitated by the dextrine (Rumpf and 
 Heintzerling, Z. a. C. ix. 358). 
 
 An inversion of starch may be produced more rapidly, and at 
 lower temperature, by using some form of diastase in place of 
 acid. An infusion of malt is best suited to the purpose, but the 
 temperature must not exceed 71 C. (160 Fahr.). The digestion 
 may vary from fifteen minutes to as many hours. The presence of 
 unchanged starch may be found by occasionally testing with iodine. 
 If the digestion is carried beyond half an hour, a like quantity of 
 the same malt solution must be digested alone, at the same 
 temperature, and for the same time, then titrated for its amount of 
 sugar, which is deducted from the total quantity found in the 
 mixture. O'Sullivan (J. C. S. 1872, 579) has, however, clearly 
 shown that the effect of the so-called diastase is to produce maltose, 
 which has only the power of reducing the copper solution to the 
 extent of about three-fifths that of dextrose or true grape sugar, 
 the rest being probably various grades of dextrine. Brown and 
 Heron's experiments clearly demonstrate that no dextrose is 
 produced from starch by even prolonged treatment with malt 
 
74 SUGAR. 309 
 
 extract ; the only product is maltose. Sulphuric or other similar 
 acids cause complete inversion. 
 
 For the exact estimation of starch in grain of various kinds 
 O'Sullivan gives very elaborate directions, involving the treat- 
 ment of the substance with alcohol and ether, to remove fatty and 
 other constituents previous to digestion with diastase. The same 
 authority also gives special directions for the preparation of the 
 proper kind of diastase, all of which may be found in J. C. S. 
 xlv. 1. 
 
 2. Estimation of Glucose by Fehling's Solution. 
 
 Preparation of the Standard Solutions. Fehling's Standard 
 Copper Solution. Crystals of pure cupric sulphate are powdered 
 and pressed between unsized paper to remove adhering moisture ; 
 69 '28 gm. are weighed, dissolved in water, about 1 c.c. of pure 
 sulphuric acid added, and the solution diluted to 1 liter. 
 
 Alkaline Tartrate Solution.- 350 gm. of Rochelle salt (sodio- 
 potassic tartrate) are dissolved in about 700 c.c. of water, and the 
 solution filtered, if not already clear ; there is then added to it 
 a clear solution of 100 gm. of caustic soda (prepared by alcohol) 
 in about 200 c.c. of water. The volume is made up to 1 liter. 
 
 These solutions are prepared separately, and when mixed in 
 exactly equal proportions form the original Fell ling solution, 
 each c.c. of which should contain 0*03464 gm. of cupric sulphate, 
 and represents 0*005 gm. of pure anhydrous grape sugar, if the 
 conditions of titration laid down below are adhered to.'" The 
 method is based on the fact that although Fehling's solution 
 may be heated to boiling without change, the introduction into it 
 of the smallest quantity of grape sugar, at a boiling temperature, 
 at once produces a precipitate of cuprous oxide, the ratio of 
 reduction being uniform if the conditions of experiment are 
 always the same. 
 
 The Titration of Glucose with Fehling's Solution. 5 c.c. each of 
 standard copper and alkaline tartrate solutions are accurately measured into 
 a thin white porcelain basin, 40 c.c. of water added, and the basin quickly 
 heated to boiling on a sand-bath or by a small flame. No reduction or 
 change of colour should occur; it' it does, the alkaline tartrate solution 
 is probably defective from age. This may probably be remedied by the 
 addition of a little fresh caustic alkali on second trial, but it is advisable to 
 use a new solution. The % or 1 per cent, sugar solution is then delivered in 
 from a burettef in small quantities at a time, with subsequent boiling, unti 
 
 * If pure cupric sulphate has been used, and the solutions mixed only at the time of 
 titration, there need be very little fear of inaccuracy ; nevertheless it is advisable to 
 verify the mixed solutions from time to time. This may be done by weighing and 
 dissolving 0'95 gm. of pure cane sugar in about 500 c.c. of water, adding 2 c.c. of. 
 hydrochloric acid, and heating to 70 C. for ten minutes. The acid is then neutralized 
 with sodic carbonate and diluted to a liter. 50 c.c. of this liquid should exactly 
 reduce the copper in 10 c.c. of Fell ling's solution. A standard solution of inverted 
 sugar, which will keep good for many months, may be made in the foregoing manner : 
 it should be of aboiit 20 per cent, strength, and rendered strongly alkaline with soda or 
 potash. 
 
 t The instrument should be arranged as described on page 12. 
 
310 VOLUMETRIC ANALYSIS. 74. 
 
 the blue colour of the copper solution is just discharged, a point which is 
 readily detected by inclining the basin, so that the colour of the clear 
 supernatant fluid may be observed against the white sides of the basin. 
 Some operators use a small thin boiling flask instead of the basin. 
 
 It is almost impossible to hit the exact point of reduction in the 
 first tit ration, but it affords a very good guide for a more rapid and 
 exact addition of the sugar solution in a second trial, when the 
 sugar may be added with more boldness, and the time of exposure 
 of the copper solution to the air lessened, which is a matter of 
 great importance, since prolonged boiling has undoubtedly a 
 prejudicial effect on the accuracy of the process.'"' 
 
 When the exact point of reduction is obtained, it is assumed 
 that the volume of sugar solution used represents O05 gm. of 
 grape sugar or glucose, for 10 c.c. Feh ling's solution contain 
 O'll gm. cupric oxide, and 5 molecules CuO (396) are reduced 
 to cuprous oxide by 1 molecule of glucose (180), therefore 
 396 : 180 = 0*11 : 0'05, i.e. 0*05 gm. glucose exactly reduces 
 10 c.c. Feh ling's solution. 
 
 With this assumption, however, Soxhlet does not agree, but 
 maintains from the results of his experiments on carefully prepared 
 standard sugars, that the accuracy of the reaction is interfered 
 with by varying concentration of the solutions, duration of the 
 experiment, and the character of the sugar. 
 
 For example, he found that the reducing power of glucose, 
 invert sugar, and galactose was in each case lowered by dilution of 
 the Fehling's solution, whilst that of maltose was raised, and that 
 of milk sugar was not affected. 
 
 The remarks which Soxhlet appends to his experiments are 
 thus classified : 
 
 (1) The reducing power of inverted sugar, for alkaline copper solution, is 
 importantly influenced by the concentration of the solutions : a smaller 
 quantity of sugar being required to decompose Fehling's solution in the 
 undiluted state than when it is diluted Avith 1, 2, 3, or 4 volumes of water. 
 It is immaterial whether the sugar solution be added to the cold or boiling 
 copper reagent. 
 
 (2) If inverted sugar acts on a larger quantity of copper solution than it 
 is just able to reduce, its reducing power will be increased, the increment 
 var}dng according to the amount of copper in excess and the concentration 
 of the cupric liquid ; in the previous experiments the equivalents varied 
 from 1 : 97 to 1 : 12*6, these numbers being by no means the limit of 
 possible variation. 
 
 (3) In a volumetric estimation of inverted sugar by means of Fehling's 
 solution, the amount of copper reduced by each successive addition of sugar 
 solution is a decreasing quantity ; the results obtained are therefore perfectly 
 empirical, and are only true of that particular set of conditions. 
 
 (4) The statement that 1 equivalent of inverted sugar reduces 10 
 
 * It has been proposed to use an excess of copper, and to estimate the excess 
 iodometrically or with cyanide ( 58) in view of the alleged uncertain ending in the 
 ordinary Fehling process. My experiments with these methods show that the 
 errors are g reater than the one they are siipposed to cure. Moreover, in practised 
 hands the true ending presents no difficulty. 
 
74. SUGAR. 311 
 
 equivalents of cupric oxide is not true, the hypothesis that 0'5 gm. inverted 
 sugar reduces 100 c.c. of Fehling's solution being shown to be incorrect; 
 the real amount under the conditions laid down by Fehling (1 volume of 
 alkaline copper solution. 4 volumes of water, sugar solution fc 1 per cent.) 
 being 97 c.c., the results obtained under this hypothesis are, therefore, 3 per 
 cent, too low. Where, however, the above conditions have been fulfilled, the 
 results, although not absolutely, are relatively correct; not so, however, those 
 obtained by gravimetric processes, since the interference of concentration 
 and excess has not been previously recognized. 
 
 These facts, however, do not vitiate the process as carried out 
 under the well recognized conditions insisted on in the directions 
 for titration that were given above. If these are adhered to it is 
 found the sugars have the following reducing powers 
 
 10 c.c. Feh ling solution are completely reduced by 
 O05 gm. glucose, levulose, galactose 
 0'0475 gm. cane sugar (after inversion) 
 O067S gm. milk sugar 
 0*0807. gm. maltose 
 0'045 gm. starch (after inversion). 
 
 Lowe, and more recently Haines, have advocated the sub- 
 stitution of an alkaline solution of glycerine for the alkaline tartrate 
 in F,e hi ing's solution. This solution is said to keep indefinitely, 
 but it is riot so delicate a test as Fehling's. 
 
 3. Estimation of Glucose by Mercury. 
 
 Knapp's Standard Mercuric cyanide. 10 gm. of pure dry 
 mercuric cyanide are dissolved in about 600 c.c. of water ; 100 c.c. 
 of caustic soda solution (sp. gr. 1'145) are added, and the liquid 
 diluted to 1 liter. 
 
 Sachsse's Standard Mercuric iodide. 18 gm. of pure dry 
 mercuric iodide and 25 gm. of potassic iodide are dissolved in 
 water, and to the liquid is added a solution of 80 gm. of caustic 
 potash ; the mixture is finally diluted to 1 liter. 
 
 These solutions, if well preserved, will hold their strength 
 unaltered for a long period. 
 
 These solutions are very nearly, but not quite, the same in 
 mercurial strength, Knapp's containing 7'9365 gm. Hg in the 
 liter, Sachsse's 7 '92 95 gm. 100 c.c. of the former are equal to 
 100-1 c.c. of the latter. 
 
 Indicators for the Mercurial Solutions. In the case of Fehling's 
 solution, the absence of blue colour acts as a sufficient indicator, 
 but with mercury solutions the end of reaction must be found by 
 an external indicator. In the case of Knapp's solution the end 
 of the reaction is found by placing a drop of the clear yellowish 
 liquid above the precipitate on pure white Swedish filter paper, 
 then holding it first over a bottle of fuming HC1, then over strong 
 sulphuretted hydrogen water ; the slightest trace of free mercury 
 shows a light brown or yellowish-brown stain. The indicator best 
 
312 VOLUMETEIC ANALYSIS. 74 
 
 adapted for Sachsse's solution is a strongly alkaline solution of 
 stannous chloride spotted on a porcelain tile. An excess of 
 mercury gives a brown colour. 
 
 The Titration : 40 c.c. of either solution are placed in a porcelain basin 
 or a flask, diluted with an equal bulk of water, and heated to boiling. The 
 solution of sugar of i per cent, strength is then delivered in until all the 
 mercur} 7 - is precipitated, the theory being in either case that 40 c.c. should 
 be reduced by O'l gm. of dextrose. 
 
 The results of Soxhlet's experiments show that this estimate 
 is entirely wrong""" ; nevertheless, it does not follow that these 
 mercurial solutions are uselessi It is found that, using them l>y 
 comparison with Feh ling's solution, it is possible to define to 
 some extent the nature of mixed sugars, on the principle of indirect 
 analysis. 
 
 Knapp's solution is strongly recommended by good authorities 
 for the estimation of diabetic sugar in urine. The method of using 
 it is described in the section on Urinary Analysis. 
 
 The behaviour of the sugars with alkaline mercury solutions was tested 
 by Soxhlet both with Knapp's solution and Sachsse's solution. 
 
 He found that different results are obtained from Knapp's solutions, 
 according as the sugar solution is added gradually, or all at once ; when 
 gradually added more sugar being required; with Sachsse's, however, the 
 reverse is the case. 
 
 To get comparable results the sugar must be added all at once, the solution 
 boiled for two or three minutes, and the liquid tested for mercury, always 
 using the same indicator ; in using the alkaline tin solution as indicator, 
 0'200 0'202 gm. of grape sugar was always required for 100 c.c. Knapp, 
 in a large number of experiments. It is remarkable that these two solutions, 
 although containing almost exactly the same amount of mercury, require 
 very different quantities of sugar to reduce equal volumes of 'them. This is 
 shown to be due, to a great extent, to the different amounts of alkali present 
 in them. 
 
 The various sugars have different reducing powers for the 
 alkaline mercury solutions, and there is no definite relation between 
 the amount of Knapp's and Sachsse's solutions required by 
 them; the amount of Sachsse's solution, to which 100 c.c. 
 Knapp's correspond, varying from 54*7 c.c. in the case of galactose, 
 to 7 4 '8 c.c. in the case of invert sugar. 
 
 The two mercury methods have no advantage in point of 
 accuracy or convenience over Fehlin g's method, the latter having 
 the preference on account of the great certainty of the point at 
 which the reduction is finished. 
 
 The mercury methods are, however, of great importance, both 
 for the identification of a sugar and for the estimation of two 
 sugars in presence of each other, as proposed by Sachsse. 
 For instance, in the estimation of grape and invert sugars in 
 presence of each other, there are the two equations: ax + by = ~F,, 
 ex + dy = S. 
 
 * Careful experiment shows that 40 c.c. of Sachsse's solution is redrc3d by 0'1342. 
 gin. dextrose or 0'1072 gm. invert sugar. 
 
74. 
 
 SUGAR. 
 
 313 
 
 Where 
 a number of 1 c.c. Fehling, reduced by 1 gm. grape sugar. 
 
 
 Saclisse 
 
 invert sugar. 
 
 ,, grape sugar. 
 
 d ,, ,, ,, invert sugar. 
 
 F ,, Fehling, used for 1 vol. sugar solution. 
 
 S = Saclisse 
 
 x amount of grape sugar in gms. in 1 vol. of the solution. 
 y= invert sugar 
 
 It need hardly be mentioned that the above, like all other indirect 
 methods, leaves room for increased accuracy ; but nevertheless the 
 combination of a mercury method with a copper method in the 
 determination of a sugar whose nature is not exactly known, gives 
 a more serviceable result than the hitherto adopted plan, by which 
 a solution that reduced 10 c.c. .Fehling was said to contain 
 0-05 gm. of sugar (J. C. S. Abstracts, 1880, 758). 
 
 Taking the reducing power of grape- sugar =100, the reducing 
 powers of the other sugars are : 
 
 Fehling (undiluted). Knapp. Sachsse. 
 
 Grape sugar ............. , ..... 100 100 100 
 
 Invert sugar .................. 96'2 99'0 124-5 
 
 Levulose (calculated) ......... 92*4 102*2 148-6 
 
 Milk sugar ..................... 70-3 64-9 70'9 
 
 Galactose ..................... 93'2 83*0 74'8 
 
 Inverted milk sugar ... ...... 96'2 90'0 85*5 
 
 Maltose .. 61 -0 63'8 65-0 
 
 4. Sidersky's Method. 
 
 
 
 This process has found great favour among French sugar experts, 
 and is based on the use of Soldaini's cupric solution, which was 
 devised to remedy the faults common to Fehling and other 
 copper solutions containing tartrated and caustic or carbonated 
 alkalies. 
 
 This liquid is prepared, according to Degener, in the following 
 manner : 40 gm. of cupric sulphate are dissolved in water, and, in 
 another vessel, 40 gm. of sodic carbonate are also dissolved in water. 
 The two solutions are mixed, and the copper precipitated in the 
 state of hydrobasic carbonate. The precipitate is washed with 
 cold water and dried. This precipitate is added to a very con- 
 centrated and boiling solution of bicarbonate of potash (about 
 415 gm.) and agitated until the whole is completely or nearly 
 dissolved, water is added to form a volume of 1400 c.c., and the 
 whole mass heated for two hours upon a water-bath. The insoluble 
 matter is filtered, and the filtrate, after cooling, is of a deep blue 
 colour. The sensibility of this liquid is so great that it gives 
 
3J4 VOLUMETRIC ANALYSIS. 74. 
 
 a decided reaction with 0*0014 gm. of invert sugar. The presence 
 of sucrose in the solution increases this sensibility still more. 
 
 Sidersky has recently offered a new volumetric method, based 
 upon the use of Soldaini's solution. With .sugars the same 
 method as is now in use with Fehling's solution can easily be 
 followed, watching the disappearance of the blue colour, and 
 testing the end with ferrocyanide and acetic acid. This process 
 offers no serious objections common to Fehling's solution, but is 
 inapplicable to coloured sugar solutions, such as molasses, etc. For 
 the last the following is recommended : 25 gm. of molasses are 
 dissolved in 100 c.c. of water and sub-acetate of lead added in 
 sufficient quantities to precipitate the impurities, and the volume 
 raised to 200 c.c. and filtered. To 100 c.c. of the filtrate are 
 added 25 c.c. of concentrated solution of carbonate of soda, 
 agitated, and filtered again. 100 c.c. of the second filtrate with 
 excess of lead removed are taken for analysis. On the other hand, 
 100 c.c. of Soldaini's solution are placed in a flask and heated five 
 minutes over an open flame. The sugar solution is now added 
 little by little, and the heating continued for five minutes. Finally, 
 the heat is withdrawn and cooled by turning in 100 c.c. of cold 
 water, and filtered through a Swedish filter, washed with hot 
 water, letting each washing run off before another addition. Three 
 or four washings will generally remove completely the alkaline 
 reaction. The precipitate is then washed through a hole in the 
 filter into a flask, removing the last trace of copper. 25 c.c. of 
 normal sulphuric acid are added with two or three crystals of 
 chlorate of potash, and the whole gently heated to dissolve com- 
 pletely the oxide of copper, which is transformed into copper 
 sulphate. The excess of sulphuric acid is determined by a 
 standard ammonia solution (semi-normal), of which the best 
 indicator is the sulphate of copper itself. When the deep blue 
 colour gives place to a greenish tinge the titration is completed. 
 The method of titration is performed as follows : Having cooled 
 the contents of the flask, a quantity of ammonia equivalent to 
 25 c.c. of normal sulphuric acid is added. From a burette 
 graduated into one-tenth c.c. standard sulphuric acid is dropped 
 in drop by drop, agitating after each addition. The blue colour 
 disappears with each addition to reappear after shaking. When 
 the last trace of ammonia is saturated the titration is complete, 
 which is known by a very feeble greenish tinge. The number of 
 .c. is read from the burette, which is equivalent to the copper 
 precipitated. The equivalent of copper being taken at 31 '7, the 
 normal acid equivalent is 0'0317 of copper. Multiplying the 
 topper found by 3546 the invert sugar is found. A blank titration 
 is needed to accurately determine the slight excess which gives 
 the pale green tinge.'" 
 
 * Report of Proceedings of Fifth Animal Co-.ivcn'iou of the Ameiicui Association 
 of Official Agricultural Che nists (188S). 
 
74 SUGAR. 315 
 
 5. Pavy's modified Fehling; Process. 
 
 This method consists in adding ammonia to the ordinary 
 Fehling solution, by which means the precipitation of cuprous 
 oxide is entirely prevented, the end of the reaction being shown by 
 the disappearance of the blue colour in a perfectly clear solution 
 (C. N. xL 77). 
 
 The solution recommended by Pavy is made by mixing 120 c.c. 
 ordinary Fehling solution* (see p. 309) with 300 c.c. of strong 
 ammonia (sp. gr. 0*880), adding 100 c.c. of a 10 per cent, caustic 
 soda solution or of a 14 per cent, solution of potash, and diluting 
 to a liter. If Fehling's solution is not available, Pavy's solution 
 may be made directly by adding a cooled solution of 21 '6 gm. 
 Eochelle salt and 1S ! 4 gm. of soda (or 25 '8 gm. of potash) to 
 a solution of 4'157 gm. pure cupric sulphate, adding 300 c.c. 
 of strong ammonia, and making up to a liter. 100 c.c. 
 Pavy's solution =10 c.c. Fehling's solution = 0*05 gm. of 
 glucose. 
 
 As ammoniacal cuprous solutions are readily oxidized, it is 
 important to exclude air from the liquid during titration. The 
 titratioii should be made in a small boiling flask, through the 
 cork of which the elongated end of the burette is passed. A small 
 escape tube, preferably with a valve, also passes through the same 
 cork, and leads into a vessel containing water or weak acid, to 
 condense the ammonia. Allen has found a layer of paraffin over 
 the liquid an effective means of excluding air. 
 
 In carrying out the titration (100 c.c. of the Pavy's solution is 
 a convenient quantity to take) a few pieces of pumice or pipe- 
 stem are added, the liquid brought to boiling, and kept boiling 
 whilst the sugar solution is gradually run in. The end-point is 
 very sharp. Whilst rapid manipulation is desirable, the solution 
 must not be run in too quickly, because reduction takes place 
 more slowly than with Fehling's solution. 
 
 The method is well adapted for the examination of diabetic 
 urine and milk, also mixtures of milk and cane sugars, and 
 certainly has the advantage over the ordinary Fehling method 
 by its definite end-point. 
 
 Z. Peska gives the following method for the volumetric 
 estimation of sugar by means of ammoniacal copper solution 
 (Chem. Zeit. Rep. 1895, 257). In order to avoid the oxidation of 
 the copper oxide in solution, a layer of vaseline is used instead of 
 the usual current of hydrogen. Two solutions are prepared : 
 6 -927 gin. of the purest crystallized copper sulphate are dissolved 
 in water, 160 c.c. of 25 per cent, ammonia added, and the whole 
 made up to 500 c.c. ; 3 4 '5 gm. of Rochelle salt and 10 gm. of 
 caustic soda are also dissolved and diluted to 500 c.c. 
 
 * In ammoniacal solution only 5 molecules CuO are reduced by 1 molecule glucose 
 instead of 6 CuO, as in Fehling's solution, hence 120 c.c. of the latter are used in 
 making Pavy's solution, and not 100 c.c. 
 
316 
 
 VOLUMETRIC ANALYSIS. 
 
 74 
 
 Process : A mixture of 50 c.c. of each liquid is heated in a beaker under 
 a layer of vaseline oil 5 m.m. thick, to a temperature of 80 C. ' The sugar 
 solution is run in 1 c.c. at a time for the first test, but on a repetition the 
 whole amount may be added at once. Towards the end of the titration, the 
 temperature must be raised to 85, and the heating continued for two minutes 
 when working on either glucose or invert sugar, four minutes for maltose, 
 and six minutes for milk sugar. Dextrine increases the reducing power of 
 the sugar in this solution less than in the one prepared with potash, and as 
 the ammonia has no injurious action, the whole process is both exact and 
 convenient. When saccharose is present, 1 gm. of it has a reducing action 
 equivalent to 0'026 gm. of invert sugar. In the determination of lactose in 
 milk the albuminoids should be precipitated with lead acetate and the excess, 
 of lead removed by sodium sulphate. The following table gives directly the 
 number of milligrams of each sugar in 100 c.c. of solution. 
 
 c.c.'s Glucose. 
 
 Invert 
 
 Milk 
 
 Maltose. c.c. 
 
 's Glucose. 
 
 Invert 
 
 Milk 
 
 Maltose. 
 
 used. 
 
 
 sugar. 
 
 sugar. 
 
 used. 
 
 sugar. 
 
 sugar. 
 
 . 
 
 8 
 
 997-8 
 
 1049-2 
 
 
 50 
 
 163-0 
 
 173-2 
 
 318-1 
 
 360-0 
 
 9 
 
 889-4 
 
 935-1 
 
 
 
 
 
 51 
 
 159-8 
 
 169-8 
 
 311-9 
 
 353-0 
 
 10 
 
 802'3 
 
 844-6 
 
 
 
 
 
 52 
 
 156-8 
 
 166-5 
 
 306-0 
 
 346-3 
 
 11 
 
 730-7 
 
 770-0 
 
 
 
 
 
 53 
 
 153-9 
 
 163-4 
 
 300-3 
 
 339-9 
 
 12 
 
 670-8 
 
 707-6 
 
 
 
 _ 
 
 54 
 
 151-1 
 
 160-4 
 
 294-8 
 
 333-8 
 
 13 
 
 620*0 
 
 654-5 
 
 
 
 
 
 55 
 
 148'4 
 
 157-5 
 
 289-4 
 
 327-9 
 
 14 
 
 576-3 
 
 608-7 
 
 . . 
 
 
 
 56 
 
 145-7 
 
 154-7 
 
 284-2 
 
 322-2 
 
 15 
 
 538-4 
 
 568-9 
 
 1033*9 
 
 
 
 57 
 
 143-1 
 
 152-0 
 
 279-3 
 
 316-7 
 
 16 
 
 505-2 
 
 534-2 
 
 971-4 
 
 58 
 
 140-6 
 
 149-4 
 
 274-5 
 
 311-4 
 
 17 
 
 475-8 
 
 503-3 
 
 916*0 
 
 1023-0 59 
 
 138-2 
 
 146-9 
 
 269-9 
 
 306-3 
 
 18 
 
 449-7 
 
 475-7 
 
 866-5 
 
 968-8 60 
 
 135-9 
 
 144-5 
 
 265-4 
 
 301-3 
 
 19 
 
 426-3 
 
 451-2 
 
 822-3 
 
 920-3 61 
 
 133-7 
 
 142-2 
 
 261-1 
 
 296-4 
 
 20 
 
 405-2 
 
 429-0 
 
 782-4 
 
 876-3 62 
 
 131-5 
 
 139-9 
 
 256-9 
 
 291-6 
 
 21 
 
 386-0 
 
 408-8 
 
 746-0 
 
 836-4 63 
 
 129-4 
 
 137-7 
 
 252-9 
 
 287-0 
 
 22 
 
 368-7 
 
 390-6 
 
 713-0 
 
 800-0 64 
 
 127-4 
 
 135-5 
 
 249-0 
 
 282-6 
 
 23 
 
 352-8 
 
 373-8 
 
 682-7 
 
 766-5 65 
 
 125-4 
 
 133-4 
 
 245-2 
 
 278-3 
 
 24 
 
 338-2 
 
 358-4 
 
 654-8 
 
 735-8 66 
 
 123-5 
 
 131-4 
 
 241-5 
 
 274-1 
 
 25 
 
 324-8 
 
 344-3 
 
 629-2 
 
 707-5 67 
 
 121-7 
 
 129-5 
 
 237'9 
 
 270'0 
 
 26 
 
 312-4 
 
 331-2 
 
 605-5 
 
 681-3 68 
 
 119-9 
 
 127-6 
 
 234-4 
 
 266-1 
 
 27 
 
 300-9 
 
 319-3 
 
 583-5 
 
 656-8 69 
 
 118-2 
 
 125-7 
 
 231-0 
 
 262-3 
 
 28 
 
 290-3 
 
 307-8 
 
 563-1 
 
 634-1 70 
 
 116-5 
 
 123-9 
 
 227-7 
 
 258-6 
 
 29 
 
 280-3 
 
 297-3 
 
 544-1 
 
 613-0 71 
 
 114-9 
 
 122-2 
 
 224-6 
 
 255-0 
 
 30 
 
 271-1 
 
 287*5 
 
 526-2 
 
 593-2 i 72 
 
 113-3 
 
 120-5 
 
 221-5 
 
 251-5 
 
 31 
 
 262-4 
 
 278-2 
 
 509-5 
 
 574-5 73 
 
 111-8 
 
 118-9 
 
 218-5 
 
 248-1 
 
 32 
 
 254-2 
 
 269-6 
 
 493-8 
 
 557'1 
 
 74 
 
 110*3 
 
 117-3 
 
 215-6 
 
 244-8 
 
 33 
 
 246-6 
 
 261-6 
 
 479-1 
 
 540-8 
 
 75 
 
 108-8 
 
 115-8 
 
 212-8 
 
 241-6 
 
 34 
 
 239-3 
 
 253-9 
 
 465-3 
 
 525-3 
 
 76 
 
 107-4 
 
 114-3 
 
 210-0 
 
 238-4 
 
 35 
 
 232-6 
 
 246-7 
 
 452-2 
 
 510-7 
 
 77 
 
 106-0 
 
 112-8 
 
 207-3 
 
 235-3 
 
 36 
 
 226-1 
 
 240-0 
 
 439-8 
 
 496-8 
 
 78 
 
 104-6 
 
 111-4 
 
 204-7 
 
 232-3 
 
 37 
 
 220-0 
 
 233-5 
 
 428-1 
 
 483-7 
 
 79 
 
 103-3 
 
 110-0 
 
 202-1 
 
 229-4 
 
 38 
 
 214-3 
 
 227-4 
 
 417*0 
 
 471-3 
 
 80 
 
 102-0 
 
 108-6 
 
 199-6 
 
 226-6 
 
 39 
 
 208-8 
 
 221-7 
 
 406-5 
 
 459*5 
 
 81 
 
 100-8 
 
 107-2 
 
 
 
 223-9 
 
 40 
 
 203-6 
 
 216-2 
 
 396-5 
 
 448*3 
 
 82 
 
 99-6 
 
 105-9 
 
 
 
 221-2 
 
 41 
 
 198-7 
 
 211-0 
 
 387-0 
 
 437-6 
 
 83 
 
 
 
 104-6 
 
 
 
 218-6 
 
 42 
 
 194-1 
 
 206-0 
 
 377-8 
 
 427-4 
 
 84 
 
 , 
 
 103-4 
 
 
 
 216-0' 
 
 43 
 
 189-7 
 
 201-3 
 
 369-2 
 
 417-7 
 
 85 
 
 
 
 102-2 
 
 
 
 213-5 
 
 44 
 
 185-4 
 
 198-7 
 
 360-9 
 
 408*4 
 
 86 
 
 
 
 101-1 
 
 
 
 211-1 
 
 45 
 
 181-2 
 
 192-3 
 
 353-0 
 
 399-5 
 
 87 
 
 
 
 
 
 
 
 208-7 
 
 46 
 
 177-3 
 
 188-1 
 
 345-4 
 
 391-0 
 
 88 
 
 
 
 
 
 
 
 206-4 
 
 47 
 
 173-5 
 
 184-1 
 
 338-1 
 
 382-8 
 
 89 
 
 
 
 
 
 
 
 204-1 
 
 43 
 
 169-9 
 
 180-3 
 
 331-2 
 
 374' 9 90 
 
 
 
 
 
 
 
 201-9 
 
 49 
 
 166-4 
 
 176-7 
 
 324-5 
 
 367-3 ; 91 
 
 
 
 
 
 
 
 199-7 
 
74. SUGAB. 317 
 
 6. Gerrard's Cyano-cupric Process. 
 
 This process (Year Book Pharm. 1892, 400), as improved by 
 Gerrard and A. H. Allen, promises to prove a valuable addition 
 to the processes of titration based on the reducing power of glucose. . 
 It has the advantage over Pavy's method in causing no evolution 
 of ammonia ; moreover, the reduced solution is reoxidized so slowly 
 that titration may even be conducted in an open dish with reason- 
 able expedition. The process is based on the following facts : - 
 When a solution of potassium cyanide is added to a solution of 
 copper sulphate a colourless stable double cyanide of copper and 
 potassium is formed, thus : 
 
 CuSO* + 4KCy = CuCy 2 ,2KCy + K 2 SO*. 
 
 This salt is not decomposed by alkalies, hydrogen sulphide, or 
 ammonium sulphide. If potassium cyanide be added to Feh ling's 
 solution the latter is decolourized, the above double salt being 
 formed at the same time, and if the colourless solution be boiled 
 with glucose no cuprous oxide is precipitated. If there be present 
 -excess of Feh ling's solution over the amount capable of being 
 decolourized by the potassium cyanide, the mixture is blue, and when 
 it is boiled with a reducing sugar the extra portion is reduced, but 
 no cuprous oxide is precipitated, the progress of the reduction 
 being marked by the gradual and final disappearance of the colour 
 of the solution, just as in Pavy's process. 
 
 Process of Titration. 10 c.c. of fresh Pehling's solution, or 5 c.c. of 
 each of the constituent solutions are diluted with 40 c.c. of water in 
 a porcelain dish and heated to boiling. An approximately 5 per cent, 
 solution of potassium cyanide is added very cautiously from a "burette or 
 pipette to the still boiling and "well agitated blue liquid, till the colour is 
 just about to disappear. Excess of cyanide must be carefully avoided.* 
 
 10 c.c. of Fehling solution are now accurately measured into the dish, 
 and the sugar solution (of about \ per cent, strength glucose) run in slowly 
 from a burette with constant stirring and ebullition, till the blue colour 
 disappears. Only the second measure of Fehling's solution suffers 
 reduction. The volume of sugar solution run in contains 0'05 gin. of 
 glucose. 
 
 Some technical applications of these Solutions to mixtures of 
 various Sugars. 
 
 It cannot be claimed for these estimations that they are 
 absolutely exact ; but with care and practice, accompanied with 
 uniform conditions, they are probably capable of the best possible 
 results whatever methods may be used. 
 
 Cane Sugar, Grape Sugar, and Dextrine (Biard and Pellet, 
 Z. a. C. xxiv. 275). The solution containing these three forms is first 
 titrated with the usual Fehling solution for grape sugar. A second portion 
 
 * As the double cyanide solution keeps for some time, a stock may be made up, so 
 that 59 c.c. contain 10 c.c. of Fehling' s solution, and that volume taken for each 
 titration, instead of going through the process of exact decolonization every time. 
 
318 VOLUMET1UC ANALYSIS. 75. 
 
 is boiled with acetic acid (which only inverts cane sugar) and titrated. 
 Finally, a third portion is completely inverted with sulphuric acid and 
 titrated. The difference of the first and second titrations gives the cane 
 sugar, and that of the second and third the dextrine. 
 
 Milk and Cane Sug-ar. If the estimation of milk sugar is alone re- 
 quired, and by the usual Fehling solution, the casein and albumen must 
 be first removed. Acidify the liquid with a few drops of acetic acid, warm 
 until coagulation is effected, and filter. Boil the filtrate to coagulate the 
 albumen. Filter again, and neutralize with soda previous to treatment for 
 sugar by the copper test. The number of c.c. of Fehling's solution 
 required, multiplied by 0'0067S6, will give the weight of milk sugar in 
 grams. Direct estimation by Pa vy-F eh ling is preferable to this method. 
 Cane sugar in presence of milk sugar may be estimated as follows : Dilute 
 the milk to ten times its bulk, having previously coagulated it with a little 
 citric acid, filter, and make up to a definite volume, titrate a portion with 
 Pavy-Fehling solution, and note the result. Then take 100 c.c. of the 
 filtrate, add 2 gm. of citric acid, and boil for 10 minutes, cool, neutralize, 
 make up to 200 c.c., and titrate with copper solution as before. The difference 
 between the reducing powers of the solutions before and after conversion is 
 due to the cane sugar, the milk sugar not being affected ~by citric acid. 
 
 Stokes and Bodmer (Analyst x. 62) have experimented largely on this 
 method, and with satisfactory results. The plan adopted by them is to use 
 40 c.c. of Pavy-Fehling liquid ( = 0'02 gm. glucose), and to dilute the 
 sugar solution (without previous coagulation), so that from 6 to 12 c.c. are 
 required for reduction. By using a screw-clamp on the rubber burette tube, 
 the sugar solution is allowed to drop into the boiling liquid at a moderate 
 rate. If Cu 2 O should be precipitated before the colour disappears, a fresh 
 trial must be made, adding the bulk of the sugar at once, then finishing by 
 drops. If, on the other hand, the sugar has been run in to excess, which 
 owing to the rather slow reaction is easily done, fresh trial must be again 
 made until the proper point is reached : this gives the milk sugar. Mean- 
 while a portion of the mixed sugar solution is boiled with 2 per cent, of 
 citric acid, neutralized with NH 3 , made up to double its original volume, 
 and titrated as before. 
 
 These operators have determined the reducing action of milk, 
 cane, and grape sugar on the Pavy-Fehling liquid, the result 
 being that 100 lactose represents respectively 52 glucose, or 49 '4 
 sucrose. 
 
 The Pavy-Fehling liquid is admirably adapted for the esti- 
 mation of lactose in milk direct after dilution, no coagulation being 
 necessary. 
 
 SULPHUR. 
 
 Estimation in Pyrites, Ores, Residues, etc. 
 1. Alkalimetric Method (Pelouze). 
 
 75. THIS process, designed for the rapid estimation of sulphur 
 in iron and copper pyrites, has hitherto been thought tolerably 
 accurate, but experience lias shown that it cannot be relied upon 
 except for rough, technical purposes. 
 
75. SULPHUR, 319 
 
 The process is based on tlie fact, that when a sulphide is ignited 
 with potassic chlorate and sodic carbonate, the sulphur is converted 
 entirely into sulphuric acid, which expels its equivalent proportion 
 of carbonic acid from the soda, forming neutral sodic sulphate ; if 
 therefore, an accurately weighed quantity of the substance be 
 fused with a known weight of pure sodic carbonate in excess, and 
 the resulting mass titrated with normal acid, to find the quantity 
 of unaltered carbonate, the proportion of sulphur is readily 
 calculated from the difference between the volume of normal acid 
 required to saturate the original carbonate, and that actually 
 required after the ignition. 
 
 It is advisable to take 1 gm. of the finely levigated pyrites, and 
 5 '3 gm. of pure sodic carbonate for each assay; and as 5*3 gm. of 
 sodic carbonate represent 100 c.c. of normal sulphuric acid, it is 
 only necessary to subtract the number of c.c. used after the ignition 
 from 100, and multiply the remainder by 0'016, in order to arrive 
 at the weight of sulphur in the 1 gm. of pyrites, and by moving 
 the decimal point two places to the right, the percentage is obtained. 
 
 Example : 1 gm. of finely ground FeS 3 was mixed intimately with 5'3 gm. 
 sodic carbonate, and about 7 gm. each of potassic chlorate, and decrepitated 
 sodic chloride, in powder ; then introduced into a platinum crucible, and 
 gradually exposed to a dull red heat for ten minutes ; the crucible suffered 
 to cool, and warm water added ; the solution so obtained was brought on 
 a moistened filter, the residue emptied into a beaker and boiled with a large 
 quantity of water, brought on the filter, and washed with boiling water till 
 all soluble matter was removed ; the filtrate coloured with methyl orange^ 
 and titrated. 67 c.c. of normal acid were required, which deducted from 100, 
 left 33 c.c. ; this multiplied by 0*016 gave 0'528 gm. or 52*8 per cent. S. 
 
 Burnt Pyrites. The only satisfactory volumetric method of 
 estimating the sulphur in the residual ores of pyrites, is that 
 described by Watson (J. S. C. I. yii. 305), and which is in daily 
 use in large alkali works. In order to avoid calculation, Watson 
 adepts the following method : 
 
 Standard Hydrochloric Acid. 1 c.c. =0*02 gm. ^Na 2 O. 
 
 Sodic bicarbonate. This may be the ordinary commercial salt, 
 but its exact alkalinity must be ascertained by the standard acid. 
 Where a number of analyses are being made, a good quantity of 
 the salt should be well mixed, and kept in a stoppered bottle. Its 
 exact alkalinity having been once determined it will not alter, 
 though daily opened. 
 
 Process: 2 gm. of bicarbonate is placed in a crucible which may be 
 either of platinum, porcelain, or nickel, and to it is added 5'16 gm. of the 
 finely powdered ore, then intimately mixed with a flattened glass rod. 
 Heat gently over a Bunsen burner for 5 or 10 minutes, and break up the 
 mass with a stout copper wire. After stirring, the heat is increased and 
 continued for 10 or 15 minutes. The crucible is then washed out with hot 
 water into a beaker. The mixture is boiled for 15 minutes, filtered into 
 a flask, the residue washed repeatedly with hot water, then cooled and 
 titrated with the standard acid, using methyl orange as indicator. 
 
320 VOLUMETRIC ANALYSIS. 75. 
 
 Example : 2 gm. of the bicarbonate originally required 37' 5 c.c. of acid. 
 After ignition with the ore, 28 c.c. were required = 9'5 c.c., this divided by 
 5 will give 1'9, which is the percentage of total sulphur in the ore. 
 
 This total sulphur includes that which exists as soluble sulphide, 
 and which is not available for acid making. In order to find 
 the amount of this soluble sulphur, Watson boils 5*16 gm. of the 
 ore with 5 c.c. of standard sodic carbonate (1 c.c. = 0*05 gm. ]N"a 2 0) 
 diluted with water, for 15 minutes. After filtering and washing, 
 the filtrate is titrated with the standard hydrochloric acid, and the 
 difference between the volume used and that which was originally 
 required for 5 c.c. of the soda solution is divided by 5, as in the 
 ase of the former process, which gives at once the percentage of 
 sulphur existing in the ore in a soluble form. The results are not 
 absolutely exact, but quite near enough to guide a manufacturer in 
 the working of the furnaces. 
 
 This method is not available for unburnt pyrites. 
 
 2. Estimation of Sulphur in Coal Gas. 
 
 A most convenient and accurate process for this estimation is 
 that of Wildenstein ( 76.2). The liquid produced by burning 
 the measured gas in a Lethe by or Tern on Ha re our t apparatus 
 is well mixed, and brought to a definite volume ; a portion repre- 
 senting a known number of cubic feet of gas is then poured into 
 a glass, porcelain, or platinum basin, acidified slightly with HC1, 
 heated to boiling, and a measured excess of standard baric chloride 
 added ; the excess of acid is then cautiously neutralized with 
 rammonia (free from carbonate), and the excess of barium ascer- 
 tained by standard potassic chromate exactly as described in 
 76.2. 
 
 The usual method of stating results is in grains of sulphur per 
 100 cubic feet of gas. This may be done very readily by using 
 semi-normal solutions of baric chloride and potassic chromate on 
 the metric system, and multiplying the number of c.c. of baric 
 solution required with the factor 0*1234, which at once gives the 
 .amount of sulphur in grains. 
 
 3. Estimation of Sulphur in Sulphides decomposable by 
 Hydrochloric or Sulphuric Acids (Weil). 
 
 This process, communicated to me by M. Weil, is based on the 
 fact that, in the case of sulphides where the whole of the sulphur 
 is given off as H 2 S by heating with HC1 or H 2 S0 4 , the IPS may 
 "be evolved into an excess of a standard alkaline copper solution. 
 After the action is complete, the amount of Cu left unreduced is 
 estimated by standard .stannous chloride. The method is available 
 for the sulphides of lead, antimony, zinc, iron, etc. Operators 
 
75. SULPHUR. 321 
 
 should consult and practise the methods described in 58.6, in 
 order to become accustomed to the special reaction involved. 
 
 Process : Prom 1 to 10 gm. of material (according to its richness in 
 sulphur) in the finest state of division, are put into a long-necked flask of 
 about 200 c.c. capacity, to which is fitted a bent delivery tube, so arranged as 
 to dip to the bottom of a tall cylinder, containing 50 or 100 c.c. of standard 
 copper solution made by dissolving 39'523 gm. of cupric sulphate, 200 gm. 
 of Eochelle salt and 125 gm. of pure caustic soda in water, and diluting to 
 1 liter (10 c.c. = O'l gm. Cu). When this is ready, a few r pieces of granulated 
 zinc are added to the sulphide. 75 c.c. of strong HC1 are then poured over 
 them, the cork with delivery tube immediately inserted, connected with the 
 copper solution, and the flask heated on a sand-bath until all evolution of 
 H 2 S is ended. The blue solution and black precipitate are then brought on 
 a filter, filtrate and washings collected in a 200 or 250 c.c. flask, and diluted 
 to the mark ; 20 c.c. of the clear blue liquid are then measured into a boiling 
 flask, and evaporated to 10 or 15 c.c. 25 to 50 c.c. of strong HC1 are then 
 added, and the standard tin solution dropped in while boiling, until the blue 
 gives place to a clear pure yellow. 
 
 Each c.c. of standard copper solution represents 0*50393 gm. 
 of sulphur. The addition of the granulated zinc facilitates the 
 liberation of the H 2 S, and sweeps it out of the flask ; moreover, 
 in the case of dealing with lead sulphide, which forms insoluble 
 lead chloride, it materially assists the decomposition. Alkaline 
 tartrate solution of copper may be used in place of ammoniacal 
 solution if so desired. 
 
 Examples (Weil) : 1 gm. of galena was taken, and the gas delivered into 
 50 c.c. of standard copper solution (=0'5 gm. Cu). After complete pre- 
 cipitation the blue liquid was diluted to 200 c.c. 20 c.c. of this required 
 12'5 c.c. of stannous chloride, the titre of which was 16'5 c.c. for 0'04 gm. 
 Cu. Therefore lf/5 : 0'04 : : 12'5 : 0'0303. Thus 200 c.c. (= 1 gm. galena) 
 represent 0'303 gm. Cu. Then 0'5 gm. Cu, less 0'303 = 0'197 gm. for 1 gm. 
 galena or 197 for 100 gm. Consequently 197 x 0'50393 = 9'92 per cent. S. 
 Estimation by weight gave 9'85 per cent. Again, 1 gm. zinc sulphide was 
 taken with 100 c.c. copper solution and made up to 250 c.c., 25 c.c. of which 
 required 14'3 c.c. of same stannous chloride, or 143 c.c. for the 1 gm. 
 sulphide. This represents 0'347 gm. Cu. Thus 1 0'347 0'653 gm. Cu 
 (precipitated as CuS) or 65'3 per 100. Consequently 65'3 x 0'50393 = 32'9 
 per cent. S. Control estimation by weight gave 33 per cent. 
 
 The process has given me good technical results with Sb 2 S 3 , but 
 the proportion of sulphur to copper is too great to expect strict 
 accuracy. 
 
 4. Estimation of Alkaline Sulphides by Standard Zinc Solution. 
 
 This method, which is simply a counterpart of 82.3, is 
 -especially applicable for the technical determination of alkaline 
 rsulphides in impure alkalies, mother-liquors, etc. 
 
 If the zinc solution be made by dissolving 3 '253 gm. of pure 
 metallic zinc in hydrochloric acid, supersaturating with ammonia, 
 .and diluting to 1 liter, 1 c.c. will respectively indicate 
 
322 VOLUMETRIC ANALYSIS. 75. 
 
 0-0016 gin. Sulphur 
 0-0039 Sodic sulphide 
 0-00551 Potassic sulphide 
 0*0034 Ammonic sulphide. 
 
 The zinc solution is added from a burette until no dark colour is 
 shown when a drop is brought in contact with solution of nickel 
 sulphate spread in drops on a white porcelain tile. 
 
 5. Sulphurous Acid and Sulphites: 
 
 The difficulties formerly presented in the iodometric analyses of 
 these substances are now fortunately quite overcome by the 
 modification devised by Giles and Shearer (J. S. C. I. iii. 197 
 and iv. 303). A valuable series of experiments on the estimation 
 of SO 2 , either free or combined, are detailed in these papers. The 
 modification is both simple and exact, and consists in adding the 
 weighed SO 2 or the sulphite in powder to a measured excess 
 of J^. iodine without dilution with water, and when the decomposi- 
 tion is complete, titrating back with ^ thiosulphate. Yery con- 
 centrated solutions of SO 2 are cooled by a freezing mixture, and 
 enclosed in thin bulbs, which can be broken under the iodine- 
 solution : this is, however, not required with the ordinary pre- 
 parations. Sulphites and bisulphites of the alkalies and alkaline 
 earths, also zinc and aluminium, may all be titrated in this way 
 with accuracy ; the less soluble salts, of course, requiring more 
 time and agitation to ensure their decomposition. A preliminary 
 titration is first made with a considerable excess of iodine, and 
 a second with a more moderate excess as indicated by the first 
 trial. 1 c.c. T ^ iodine = 0-0032 gm. SO 2 . 
 
 The authors found that when perfectly pure iodine and neutral 
 potassic iodide were used for the standard solution, its strength 
 remained intact for a long period ; and the same with the 
 thiosulphate, if the addition of about 2 gm. of potassic bicarbonate 
 to the liter was made, and the stock solution kept in the dark. 
 
 From a large number of experiments, they also deduced the 
 simple law of the ratio between any given percentage of SO 2 
 in aqueous solution at 15-4 and 760 m.m., and its specific gravity ;. 
 namely, the percentage found by titration multiplied by OO05' 
 and added to unity gives the sp. gr. 
 
 In cases where the iodine method may not be suitable, W. B. 
 Giles recommends the use of a standard ammoniacal silver nitrate. 
 This process is applicable alike to SO 2 , sulphites and bisulphites. 
 The silver solution may conveniently be of ~ strength, but before 
 use ammonia is added in sufficient quantity, first to produce 
 a precipitate of silver oxide, then to dissolve it to a clear solution. 
 A known excess of this solution is digested in a closed bottle. 
 with the substance, in a water-bath for some hours, the result of 
 
75. SULPHUR. 323 
 
 which is the reduction of the silver as a bright mirror on the 
 sides of the vessel. The filtered liquid and washings may then 
 be titrated by thiocyanate for the excess of silver, or the mirror 
 together with any collected on the filter after washing and burning 
 to ash may be dissolved in nitric acid and estimated by the same 
 process ( 43). 1 c.c. T ^ silver=0'0032 gm. of SO 2 . 
 
 Example : 0'1974 gm. of chemically pure potassium metasulphite was 
 weighed out and treated as above described, the mirror of silver and a little 
 on the filter estimated gave 0'1918 gm. of metallic silver, which multiplied 
 by the factor T028 gives 0'19717 of metasulphite or 99'9 %. 
 
 This method is very useful in determining the percentage of the 
 SO 2 in liquefied sulphurous acid, which is now found in large 
 quantities in commerce. By cooling down this substance to 
 a point where it has no tension, small bulbs can be filled with 
 facility and sealed up. After weighing they are introduced into 
 a -we/Z-stoppered bottle containing an excess of the ammoniacal 
 silver, and the stopper firmly secured by a clamp. By shaking the 
 bottle vigorously the bulb is broken, and the estimation is then 
 conducted as above described. 
 
 A 2 ON 2 5 + SO 2 + xNH 3 = As 2 + SO 3 + WO 5 + xNH 3 . 
 
 6. Estimation of Mixtures of Alkaline Sulphides, Sulphites, 
 Thiosulphates, and Sulphates. 
 
 No method up to the present has apparently been successfully 
 devised for the estimation of the above-mentioned substances 
 when existing together in any given solution. Richardson and 
 Aykroyd (J. S. C. 1. xv. 171) have, however, now published 
 a method which seems to give fairly accurate results. 
 
 The estimation of the SO 3 in such a mixture cannot be done 
 volumetrically, but by the addition of about 5 gm. of tartaric acid to 
 such a quantity of solution of mixed thiosulphate, sulphate, and 
 sulphite as would be usually taken for analysis, the SO 3 may 
 readily be precipitated with baric chloride in the cold. The 
 precipitate of BaSO 4 contains some baric sulphite, but this is 
 easily removed by hot dilute HC1 and boiling water. The 
 thiosulphate produces no SO 3 whatever under these circumstances, 
 whereas in the presence of a mineral acid sulphate is always 
 produced. 
 
 The sulphides are estimated by standard ammoniacal zinc 
 solution, which may conveniently be of such strength that 
 1 c.c. = 0'0016 of S, using nickel sulphate solution as an external 
 indicator. 
 
 The zinc solution is easily made from pure metallic zinc 
 dissolved in HC1, and the precipitate which is formed by adding 
 ammonia, is brought into clear solution by a moderate excess of 
 the same re-agent. 
 
 Y 2 
 
324 VOLUMETRIC ANALYSIS. 75. 
 
 This zinc solution is also used for removing sulphides from 
 a mixture of these with thiosulphates, sulphites, and sulphates 
 prior to the estimation of the latter bodies. In this case it is 
 only necessary to add a slight excess of the zinc solution, and 
 filter off the precipitated sulphide. 
 
 The authors of this method after pointing out the value of 
 Giles and Shearer's method of estimating sulphites by iodine, 
 described in this section (par. 5), mention a method devised by 
 themselves, which they believe enables them to estimate not only 
 sulphites but free SO 2 , not only in a pure state but in mixtures 
 with sulphates, thiosulphates, and sulphides. They avail them- 
 selves of the well-known reaction, that when iodine is added to 
 a neutral sulphite, neutral sulphate and an equivalent amount of 
 hydriodic acid are formed 
 
 H 2 - Na 2 S0 4 + 2HI, 
 
 and the acidity of the solution may be accurately measured by 
 standard alkali and methyl orange. 
 
 The authors proceed to state that the best plan is to convert all 
 sulphites to bisulphites, i.e., to the hydrogen sulphite of the base : 
 this is necessary because a sulphite may be alkaline, or it may be 
 exclusively acid. Sodic bisulphite is quite neutral to methyl 
 orange, and by titrating the solution of a neutral sulphite with 
 decinormal sulphuric acid, using methyl orange, we arrive exactly 
 at a point when all the sulphite is converted into the acid sulphite. 
 The reason for this is patent when the reaction which takes place 
 when an acid sulphite acts upon iodine is considered 
 
 KaH.S0 8 + OH 2 + 1 2 - NaH.SO* + 2HL 
 
 Here is a new factor, inasmuch as the titration with alkali and 
 with methyl orange as indicator is concerned ; although the acid 
 sulphite of soda is neutral to methyl orange, the acid sulphate of 
 soda is acid to the full and exact extent of its combining power. 
 
 Thus one molecule of sodic bisulphite, on titration with - iodine, 
 liberates acid equivalent to three molecules of sodic or potassic 
 hydrate. 
 
 A solution containing 1'62 per cent, of Na 2 SO 3 .7Aq was titrated. Iodine 
 solution equivalent to 9'5 c.c. T \ I ; 29'9 c.c. were required; the mixture 
 required 14'6 c.c. of ^ NaHO. Now 9'5 c.c. T \ I and 14'6 c.c. T ^ NaHO 
 are in the ratio of 2 : 3 almost exactly; by using 0'0126 as the factor for 
 the c.c. of T \ I and 0'084 for the ^ NaHO, both results give T64 per cent. 
 of Na 2 SO 3 .7Aq. (Of course the sulphite solution had been previously 
 titrated with ^ T H 2 SO 4 in the presence of methyl orange.) 
 
 As the details of calculation may be somewhat obscure to those who have 
 not experimented in this direction, the working out of an actual analysis 
 may be of interest. A solution containing 1 per cent, of pure sodic 
 tine-sulphate, and 0'78 per cent, of sodic sulphite, was titrated upon 20 c.c. 
 of iodine ; 19'3 c c. were required to decolorize ; to neutralize with methyl 
 orange as indicator 17*9 c.c. of 5- soda were required ; therefore ICO c.c. of 
 
76. SULPHURIC ACID. 325 
 
 the mixture required 103'6 c.c. iodine and 92 - 7 c.c. of T \ soda respectively ; 
 the c.c. of soda x 0'0084 give 0'7787 as the percentage of Na 2 SO 3 .7Aq, and 
 this figure-:- 0*0126 (the factor for 1 c.c. iodine in Na 2 SO 3 .7Aq) gives 61'8 c.c., 
 and this subtracted from 103'6 c.c. of total iodine required gives 41'8 c.c., 
 and this x 0'0248 gives T036 instead of 1 per cent, of Na 2 S 2 O 3 .5Aq. 
 
 The immense advantage of this method is better seen in the 
 case of a complex mixture, where one must remove sulphides or 
 other bodies by the addition of an alkaline solution of zinc or 
 other precipitating agent. The alkaline filtrate is speedily brought 
 into a suitable condition for iodimetric and alkalimetric titration 
 'by the method proposed. 
 
 Example : A solution of known amounts of sodic thiosulphate and 
 sulphite was treated with 10 c.c. of a strongly ammoniacal zinc-chloride 
 solution, and the mixture was titrated with it until it gave a neutral 
 reaction with methyl orange; it was now made to 1000 c.c., and was titrated 
 upon a known volume of f$ iodine, using starch to find the end-reaction 
 (which is otherwise somewhat obscured by the methyl orange). The 
 disappearance of the blue colour and the appearance of the pinkish-purple 
 of the acidified methyl orange is both interesting and striking. Titration 
 with /TJ- NaHO was now easily accomplished. The results were exact in the 
 case of thiosulphate, and very slightly in excess in the case of sulphite. 
 
 After the sulphite and thiosulphate solution has been titrated 
 upon a known volume of y^- iodine, the sulphate formed is 
 estimated by barium at a boiling heat in the presence of a little 
 dilute HC1. Any sulphate in the original solution is, of course, 
 estimated by the tartaric acid method and deducted from the 
 result. Ammonic tartrate must be avoided in the process, owing 
 to its solvent action on barium sulphate. 
 
 SULPHURIC ACID AND SULPHATES. 
 Monohydrated Sulphuric Acid. 
 
 H 2 S0 4 = 98. 
 
 Sulphuric Anhydride. 
 
 SO 3 = 80. 
 
 I. Mohr's Method. 
 
 76. THE indirect process devised by C. Mohr (Ann. der 
 Chem. u. Pharm. xc. 165) consists in adding a known volume of 
 baric solution to the compound, more than sufficient to precipitate 
 the SO 3 . The excess of barium is converted into carbonate, and 
 titrated with normal acid and alkali. 
 
 formal Baric chloride is made by dissolving 12177 gm. of 
 pure crystals of baric chloride in the liter ; this solution likewise 
 suffices for the determination of SO 3 by the direct method. 
 
 Process : If the substance contains a considerable quantity of free acid, 
 it must be brought near to neutrality by pure sodic carbonate ; if alkaline, 
 
326 VOLUMETRIC ANALYSIS. 76. 
 
 slightly acidified with hydrochloric acid ; a round number of c.c. of baric 
 solution in excess is then added, and the whole digested in a warm place for 
 some minutes; the excess of barium is precipitated by a mixture of 
 carbonate and caustic ammonia in slight excess ; if a piece of litmus paper 
 be thrown into the mixture, a great excess may readily be avoided. The 
 precipitate containing both sulphate and carbonate is now to be collected on 
 a filter, thoroughly washed with boiling water, and titrated. 
 
 The difference between the number of c.c. of baric solution 
 added, and that of normal acid required for the carbonate, will be 
 the measure of the sulphuric acid present ; each c.c. of baric 
 solution is equal to 0*040 gm. SO 3 . 
 
 Example : 2 gm. of pure and dry baric nitrate, and 1 gm. of pure potassic 
 sulphate were dissolved, mixed, and precipitated hot with carbonate and 
 caustic ammonia ; the precipitate, after being thoroughly washed, gave 
 T002 gm. potassic sulphate, instead of 1 gm. 
 
 For technical purposes this process may be considerably shortened 
 by the following modification, which dispenses with the washing of 
 the precipitate. 
 
 The solution containing the sulphates or sulphuric acid is first rendered 
 neutral ; normal baric chloride is then added in excess, then normal sodic 
 carbonate in excess of the baric chloride, and the volume of both solutions 
 noted ; the liquid is then made up to 200 or 300 c.c. in a flask, and an aliquot 
 portion filtered off and titrated with normal acid. The difference between 
 the baric chloride and sodic carbonate gives the sulphuric acid. 
 
 The solution must of course contain no substance precipitable by 
 sodic carbonate except barium (or if so, it must be previously 
 removed) ; nor must it contain any substance precipitable by 
 barium, such as phosphoric or oxalic acid, etc. 
 
 2. Titration by Baric Chloride and Potassic Chroxnate 
 (Wildenstein). 
 
 To the hot solution containing the SO 3 to be estimated (which 
 must be neutral, or if acid, neutralized with caustic ammonia, free 
 from carbonate), a standard solution of baric chloride is added in 
 slight excess, then a solution of potassic chromate of known 
 strength is cautiously added to precipitate the excess of barium. 
 So long as any barium remains in excess, the supernatant liquid is 
 colourless ; when it is all precipitated the liquid is yellow, from the 
 free chromate ; a few drops only of the chromate solution are 
 necessary to produce a distinct colour. 
 
 Wildenstein uses a baric solution, of which 1 c.c. = 0*015 
 gm. of SO 3 , and chromate 1 c.c. = 0*010 gm. of SO 3 . I prefer 
 to use I- solutions, so that 1 c.c. of each is equal to 0*02 gm. 
 of SO 3 . If the chromate solution is made equal to the baric 
 chloride, the operator has simply to deduct the one from the other, 
 in order to obtain the quantity of baric solution really required to 
 precipitate all the SO 3 . 
 
76. SULPHURIC ACID. 327 
 
 Process : The substance or solution containing SO 3 is brought into a small 
 flask, diluted to about 50 c.c., acidified if necessary with HC1, heated to 
 boiling, and precipitated with a slight excess of standard baric chloride 
 delivered from the burette. As the precipitate rapidly settles from a boiling 
 solution, it is easy to avoid any great excess of barium, which would prevent 
 the liquid from clearing so speedily. The mixture is then cautiously 
 neutralized with ammonia free from carbonic acid (to be certain of this, it is 
 well to add to it two or three drops of calcic chloride or acetate solution). 
 
 The flask is then heated to boiling, and the chromate solution added 
 in i c.c. or so, each time removing the flask from the heat and allowing to 
 settle, until the liquid is of a light yellow colour ; the quantity of chromate 
 is then deducted from the barium solution, and the remainder calculated 
 for SO 3 . 
 
 Or the mixture with barium in excess may be diluted to 100 or 150 c.c. 
 the precipitate allowed to settle thoroughly, and 25 or 50 c.c. of the clear 
 liquid heated to boiling, after neutralizing, and precipitated with chromate 
 until all the barium is carried down as baric chromate, leaving the liquid of 
 a light yellow colour; the analysis should be checked by a second titration. 
 The process has yielded me very satisfactor} 7 results in comparison with the 
 barium method by weight ; it is peculiarly adapted for estimating sulphur in 
 gas when burnt hi the Letheby sulphur apparatus, details of which will be 
 found on page 320. 
 
 The presence of alkaline and earthy salts is of no consequence 
 Zn and Cd do not interfere Xi, Co, and Cu give coloured 
 solutions which prevent the yellow chromate being seen, but this 
 difficulty can be overcome by the use of an external indicator for 
 the excess of chromate. This indicator is an ammoniacal lead 
 solution, made b^ mixing together, at the time required, one 
 volume of pure ammonia and four volumes of lead acetate solution 
 (1 : 20). The liquid has an opalescent appearance. To use the 
 indicator, a large drop is spread upon a white porcelain plate, and 
 one or two drops of the liquid under titration added; if the 
 reddish-yellow colour of lead chromate is produced, there is an 
 excess of chromate, which can be cautiously reduced by adding 
 more barium until the exact balance occurs. 
 
 3. Direct Precipitation -with. Normal Baric Chloride. 
 
 Yery good results may be obtained by this method when 
 carefully performed. 
 
 Process : The substance in solution is to be acidified with hydrochloric 
 acid, heated to boiling, and the baric solution allowed to flow cautiously in 
 from the burette until no further precipitation occurs. The end of the 
 process can only be determined by filtering a portion of the liquid, and 
 testing with a drop of the baric solution. Beale's filter (shown in fig. 23) 
 is a good aid in this case. A few drops of clear liquid are poured into a test 
 tube and a drop of baric solution added from the burette ; if a cloudiness 
 occurs, the contents of the tubes must be emptied back again, washed out 
 into the liquid, and more baric solution added until all the SO 3 is precipitated. 
 It is advisable to use r \ solution towards the end of the process. 
 
 Instead of the test tube for finding whether barium or sulphuric 
 acid is in excess, a plate of black glass may be used, on which a drop 
 
328 VOLUMETRIC ANALYSIS. 76. 
 
 of the clear solution is placed and tested by either a drop of baric 
 chloride or sodic sulphate, these testing solutions are preferably 
 kept in two small bottles with elongated stoppers. A still better 
 plan is to spot the liquids on a small mirror, as suggested by 
 Haddock (C. N. xxxix. 156); the faintest reaction can then be 
 seen, although the liquid may be highly coloured. 
 
 Wildenstein "has arranged another method for 
 direct precipitation, especially useful where a con- 
 stant series of estimations have to be made. The 
 apparatus is shown in fig. 51. A is a bottle of 
 900 or 1000 c.c. capacity, with the bottom removed, 
 and made of well-annealed glass so as to stand 
 heating ; B a thistle funnel bent round, as in the 
 figure, and this syphon filter is put into action by 
 opening the pinch-cock below the cork. The mouth 
 of the funnel is first tied over with a piece of fine 
 cotton cloth, then two thicknesses of Swedish filter 
 _, paper, and again with a piece of cotton cloth, the 
 
 whole being securely tied with waxed thread. 
 In precipitating SO 3 by baric chloride, there occurs a point 
 similar to the so-called neutral point in silver assay, when in one 
 and the same solution both barium and sulphuric acid after a 
 minute or two produce a cloudiness. Owing to this circumstance, 
 the barium solution must not be reckoned exactly by its amount 
 of Bad 2 , but by its working effect; that is to say, the process 
 must be considered ended when the addition of a drop or two of 
 barium solution gives no cloudiness after the lapse of two minutes. 
 
 Process : The solution containing the SO 3 being prepared, and preferably 
 in HC1, the vessel A is filled with warm distilled water, and the pinch-cock 
 opened so as to fill the filter to the bend C ; the cock is then opened and 
 shut a few times so as to bring the water further down into the tube, but 
 not to fill it entirely ; the water is then emptied out of A, and about 400 c.c. 
 of boiled distilled water poured in together with the SO 3 solution, then, if 
 necessary, a small quantity of HC1 added, and the baric chloride added in 
 moderate quantity from a burette. After mixing well, and waiting a few 
 minutes, a portion is drawn off into a small beaker, and poured back without 
 loss into A ; a small quantit} 7 is then drawn off into a test tube, and two 
 drops of baric chloride added. So long as a precipitate occurs, the liquid is 
 returned to A, and more barium added until a test is taken which shows no 
 distinct cloudiness; the few drops added to produce this effect are deducted. 
 If a distinct excess has been used, the analysis must be corrected with 
 a solution of SO 3 corresponding in strength to the barium solution. 
 
 A simpler and even more serviceable arrangement of apparatus 
 on the above plan may be made, by using as the boiling and 
 precipitating vessel an ordinary beaker standing on wire gauze or 
 a hot plate. The filter is made by taking a small thistle funnel, tied 
 over as described, with about two inches of its tube, over which is 
 tightly slipped about four or five inches of elastic tubing, terminating 
 with a short piece of glass tube drawn out to a small orifice like 
 
77. SULPHURETTED HYDROGEN. 329 
 
 a pipette ; a small pinch-cock is placed across the elastic tube just 
 above the pipette end, so that when hung over the edge of the 
 beaker with the funnel below the surface of the liquid, the 
 apparatus will act as a syphon. It may readily be filled with warm 
 distilled water by gentle suction, then transferred to the liquid 
 under titration. By its means much smaller and more concentrated 
 liquids may be used for the analysis, and consequently a more 
 distinct evidence of the reaction obtained. 
 
 SULPHURETTED HYDROGEN. 
 IPS = 34. 
 
 1 c.c. -fjj arsenious solution = O00255 gm. IPS. 
 1. By Arsenious Acid (Mohr). 
 
 77. THIS residual process is far preferable to the direct titration 
 of sulphuretted hydrogen by iodine. The principle is based on the 
 fact, that when H 2 S is brought into contact with an excess of 
 arsenious acid in hydrochloric acid solution, arsenic sulphide is- 
 formed ; 1 eq. of arsenious acid and 3 eq. of sulphuretted hydrogen 
 produce 1 cq. of arsenic sulphide and 3 eq. of water, 
 
 As 2 3 + 3H 2 S = As 2 S 3 + 3H 2 0. 
 
 The excess of arsenious acid used is found by iodine and starch y 
 as in 40. In estimating the strength of sulphuretted hydrogen 
 water, the following plan may be pursued. 
 
 Process : A measured quantity, say 10 c.c. of ^ arsenious solution, is put 
 into a 300 c.c. flask, and 20 c.c. of sulphuretted hydrogen water added, well 
 mixed, and sufficient HC1 added to produce a distinct acid reaction ; this- 
 produces a precipitate of arsenic sulphide, and the liquid itself is colourless. 
 The whole is then diluted to 300 c c., filtered through a dry filter into a dry 
 vessel, 100 c.c. of the filtrate taken out and neutralized with sodic- 
 bicarbonate, then titrated with T ^ iodine and starch. The quantity of 
 arsenious acid so found is deducted from the original 10 c.c., and the 
 remainder multiplied by the requisite factor for H 2 S. 
 
 The estimation of IPS contained in coal gas, may by this 
 method be made very accurately by leading the gas very slowly 
 through the arsenious solution, or still better, through a dilute 
 solution of caustic alkali, then adding arsenious solution, and 
 titrating as before described. The apparatus devised by Mohr for 
 this purpose is arranged as follows : 
 
 The gas from a common burner is led by means of a vulcanized tube into- 
 two successive small wash-bottles, containing the Alkaline solution; from the 
 last of these it is led into a large Woulf f's bottle filled with water. The 
 bottle has two necks, and a tap at the bottom ; one of the necks contains 
 the cork through which the tube carrying the gas is passed; the other, 
 a cork through which a good-sized funnel with a tube reaching to the bottom 
 
"330 VOLUMETRIC ANALYSIS. 77. 
 
 of the bottle is passed. When the gas begins to bubble through the flask, 
 the tap is opened so as to allow the water to drop rapidly ; if the pressure of 
 gas is strong, the funnel tube acts as a safety valve, and allows the water to 
 rise up into the cup of the funnel. "When a sufficient quantit}' of gas has 
 passed into the bottle, say six or eight pints, the water which has issued from 
 the tap into some convenient vessel is measured into cubic inches or liters, 
 and gives the quantity of gas which has displaced it. In order to insure 
 accurate measurement, all parts of the apparatus must be tight. 
 
 The flasks are then separated, and into the second 5 c.c. of arsenious 
 solution placed, and. acidified slightly with HC1. If any traces of a 
 precipitate occur it is set aside for titration with the contents of the first 
 flask, into which 10 c.c. or so of arsenious solution are put, acidified as 
 before, both mixed together, diluted to a given measure, filtered, and a 
 measured quantity titrated as before described. 
 
 This method does not answer for very crude gas containing large 
 quantities of H 2 S unless the absorbing surface is largely increased. 
 
 2. By Permang-anate (Moh.r). 
 
 If a solution of H 2 S is added to a dilute solution of ferric 
 .sulphate, the ferric salt is reduced to the ferrous state, and free 
 sulphur separates. The ferrous salt so produced may be measured 
 accurately by permanganate without removing the separated 
 .sulphur. Ferric sulphate, free from ferrous compounds, in 
 sulphuric acid solution, is placed in a stoppered flask, and the 
 solution of H 2 S added to it with a pipette ; the mixture is allowed 
 to stand half an hour or so, then diluted considerably, and per- 
 manganate added until the rose colour appears. 
 
 56 Fe=17 H 2 S 
 
 or each c.c. of -^ permanganate represents O0017 gm. of IPS. 
 The process is considerably hastened by placing the stoppered llask 
 containing the acid ferric liquid into hot water previous to the 
 addition of H 2 S, and excluding air as much as possible. 
 
 3. By Iodine. 
 
 Sulphuretted hydrogen in mineral waters may be accurately 
 estimated by iodine in the following manner : 
 
 Process : 10 c.c or any other necessary volume of T V iodine solution are 
 measured into a 500 c.c. flask, and the water to be examined added until the 
 colour disappears. 5 c.c. of starch indicator are then added, and T y iodine 
 until the blue colour appears ; the flask is then filled to the mark with pure 
 distilled water. The respective volumes of iodine and starch solution, 
 together with the added water, deducted from the 500 c.c., will show the 
 volume of water actually titrated by the iodine. A correction should be 
 made for the excess of iodine necessary to produce the blue colour. 
 
 Fresenius examined the sulphur water of the Grindbrunnen, 
 in Frankfurt a. M. (Z. a. C. xiv. 321), both volume trically and 
 
78. TANNIC ACID. 331 
 
 by weight for H 2 S with very concordant results. 361*44 gm. of 
 water (correction for blue colour being allowed) required 20*14 c.c. 
 of iodine, 20*52 c.c. of which contained '02 527 of free iodine 
 = H 2 S 0*009194 gm. per million. 444'65 gm. of the same water 
 required, under the same conditions, 25 '05 c.c. of the same iodine 
 solution = H 2 S 0-009244 gm. per million. By weight the H 2 S 
 was found to be 0*009377 gm. per million. 
 
 TANNIC ACID. 
 
 78. THE estimation of tannin in the materials used for 
 tanning is by no means of the most satisfactory character. Many 
 methods have been proposed, and given up as practically useless. 
 In the previous editions of this book LowenthaPs method 
 as then perfected was given but it is still somewhat deficient 
 in accuracy or constancy of results, although much ingenuity and 
 intelligence have been expended on it. 
 
 One difficulty is still urisurmounted, and i^hat is, the preparation 
 of a pure tannic acid to serve as standard. The various tannins in 
 existence are still very imperfectly understood,* but so far as the 
 comparative analysis of tanning materials among themselves is 
 concerned, the method in question is theoretically the best. 
 
 The principle of the method depends on the oxidation of the 
 tannic acid, together with other glucosides and easily oxidizable 
 substances by permanganate, regulated by the presence of soluble 
 indigo-carmine, which also acts as an indicator to the end of the 
 reaction. The total amount of such substances being found and 
 expressed by a known volume of permanganate, the actual available 
 tannin is then removed by gelatine, arid the second titration is 
 made upon the solution so obtained in order to find the amount of 
 oxidizable matters other than tannin. 
 
 The volume of permanganate so used, deducted from the volume 
 used originally, shows the amount of tannin actually available for 
 tanning purposes expressed in terms of permanganate. 
 
 It will be at once seen that this method is essentially a practical 
 one, because it is only the particular tannin capable of combining 
 with organic tissue which is estimated. It has been critically 
 examined with approbation by good authorities, among whom may 
 be mentioned, Procter (C. N. xxxvi. 59 ; ibid, xxxvii. 256), 
 Kathreiner (Z. a. C. xviii. 112), (Diiigler's Polyt. Jour. 
 cxxvii. 481), and Hewitt (Tanner's Jour., May, 1877, 93). My 
 
 *Von Schroder, whose suggestions have been adopted by the German Association 
 of Tanners, selects a commercial pure tannic acid for use as a standard by dissolving 
 2 gm. in a liter of water. 10 c.c. of this is titrated with permanganate as described. 
 50 c.c. are then digested twenty hours with 3 gm. moistened hide powder. 10 c.c. of 
 the filtrate from this is then titrated, and if the permanganate consumed amounts to 
 less than 10 per cent, of the total consumed by the tannin, it is suitable for a standard. 
 1000 parts being considered equivalent in reducing power to 1048 parts of tannin pre- 
 cipitable by hide, according to Hammer's experiments, therefore Von Schroder, 
 after titrating as described, calculates the dry matter, and multiplies by the round 
 number 1 '05 to obtain the value in actual tannin precipitable by hide. 
 
332 VOLUMETRIC ANALYSIS. 78. 
 
 own experiments have shown that for all materials containing, 
 tannin, even catechu, it is the best process yet discovered, but 
 requires patient practice to ensure concordant results. Lowenthal's- 
 description of the method is given in Z. a. C. xvi. 33. 
 
 The extraction of the tannic acid from the raw material is best 
 performed by boiling it in a large flask with about a liter of 
 distilled water for half an hour, then straining, and diluting when 
 cold to 1 liter. Portions are filtered if necessary. Concentrated 
 extracts are dissolved before titration by adding them to boiling 
 water, then cooling and diluting to the measure. In the case of 
 strong materials such as sumach or valonia 10 gm., or oak-bark 
 20 gm., are used. 
 
 The quantity of these extracts to be used for titration must be 
 regulated to some extent by the amount of permanganate required 
 to oxidize the tannic and gallic acids present. Practice and 
 experience will enable the operator to judge of the proper propor- 
 tions to use in dealing with the various materials, bearing in mind 
 that volumetric processes are largely dependent upon identity of 
 conditions for securing concordant results. 
 
 Procter, who is probably one of the best authorities on this 
 .subject, has modified to some extent the details of this process 
 (/. S. C. I. iii. 82, and ibid. v. 79), and these modifications are 
 embodied here. 
 
 Standard Solutions and Re-agents. 
 
 Standard Potassic permanganate. Kathreiner recommends 
 that this solution should contain not more than 1*333 gm. of 
 the pure salt per liter (better only about 1 gm.) ; therefore, if 
 the operator is accustomed to use the decinormal solution, a very 
 convenient strength is made by diluting one volume of it with 
 two of water, thus obtaining a solution of -$ strength ( = 1 '052 gm. 
 per liter). 
 
 This standard is the more advisable because it enables the 
 operator to calculate its value into oxalic acid, and so arrive at the 
 theoretical standards adopted by Neubauer and Oser; namely, 
 that 0*063 gm. of oxalic acid represents 0'04157 gm. of gallo-tannic 
 acid (gall-nut tannin), or 0*062355 gm. of querci-tannic acid (oak 
 bark tannin). These coefficients for calculation are now largely 
 adopted, and are certainly preferable to standardizing the perman- 
 ganate upon any specimen of so-called pure tannin. 
 
 30 c.c. of -jf^j- permanganate will therefore represent 0'063 gm. 
 of oxalic acid or the weights of tannin above mentioned. 
 
 Solution of Indigo Carmine. This should be a clear solution of 
 about 5 gm. to the liter with about 50 c.c. of pure H 2 S0 4 . 
 
 Solution of Gelatine. This solution is used to precipitate the 
 available tannin in any given solution after its total oxidizable 
 matters have been determined by the indigo and permanganate. It 
 
78. TANNIC ACID. 333 
 
 should be made fresh for each series of titrations, by dissolving 
 2 gm. of Nelson's gelatine in 100 c.c. of water and filtering. 
 Dilute Sulphuric Acid. MO. 
 
 Processes of Tit-ration : The first thing to be done is to ascertain the 
 relationship between the permanganate and indigo solutions (it is assumed 
 that the permanganate is correct as regards its relation to oxalic acid), and 
 therefore 10 or 20 c.c. of the indigo are measured into a white porcelain basin, 
 and diluted to f of a liter with distilled w r ater, or good ordinary water free 
 from organic matter or other substances capable of reducing permanganate. 
 10 c.c. of the dilute acid are measured in, and the permanganate delivered 
 in with a hand-pipette in drops, with constant stirring, until the colour is 
 just discharged, leaving a clear faint yellow tint, with just a shade of pink 
 at the rim. 
 
 This experiment will act as a guide to the final adjustment of the indigo 
 with an accurate 30 c.c. burette in $, which should be of such dilution that 
 about 20 c.c. correspond to about 15 c.c. of permanganate. 
 
 Titration of the Tanning Material : It is very important, in order to 
 avoid uncertainty in the end-point of the reaction,' that only so much 
 material shall be used as shall consume about 7 or 8 c.c. of permanganate of 
 -5^5- strength above that point which is required for the indigo. 
 
 Procter and Kathreiner both insist upon these proportions, and the 
 general method adopted by them is to add 20 c.c. of indigo with 10 c.c. of 
 dilute acid to about i of a liter of water, in a porcelain dish, followed by 5 c.c. 
 of tannin solution. The permanganate is then delivered in very slowly, with 
 constant stirring, until a faint rose colour appears round the edges of the 
 liquid. The time allowed for the titration is also very important. " 
 
 Von Schroder, representing the Association of German Tanners, 
 prefers to add the permanganate 1 c.c. at a time with vigorous 
 stirring, until the colour of the liquid indicates that a few drops 
 only are required to end the titration. Procter, on the other 
 hand, prefers the rapid drop method for the commencement, and 
 until near the end. He also finds that the method of stirring 
 influences the result in no very slight degree. Whatever plan the 
 operator adopts, it is advisable to keep consistently to it in order 
 that the results may be comparatively the same. 
 
 It must be remembered that neither by this nor any other 
 method is it possible to accurately estimate the tannin, but only as 
 a means of comparing two samples of the same material. 
 
 Precipitation of the Tannin, and subsequent Titration of Substances 
 other than Tannin. Procter's procedure is to take 50 c.c. of the tannin 
 infusion (5 c.c. of which has been titrated), and add to it 28'6 c.c. of gelatine 
 solution in a flask holding about 150 c c. The mixture is well shaken, then 
 saturated with clean table salt, and 10 c.c. of the dilute acid added, together 
 with a teaspoonful of kaolin : the whole is vigorously shaken, then filtered, 
 and made up to exactly 100 c.c. 10 c.c. of this liquid, representing 5 c.c. of 
 the tannin decoction, are then titrated in precisely the same manner as before. 
 The calculation of percentage is then made as follows : Let the first titration 
 (two of which should be made for security) be called a ; the second, also in 
 duplicate, b. If further, c be the quantity of permanganate required to 
 oxidize 10 c.c. of ^V oxalic acid, and 10 gm. of substance have been employed 
 for 1 liter of decoction, then c : (a b) : : 6'3 : x, where x is the percentage 
 of tannin expressed in terms of oxalic acid. 
 
334 VOLUMETRIC ANALYSIS. 78. 
 
 Hunt, who is also an undoubted authority on tannin estimation, 
 differs from Procter on the question of saturating the liquid for 
 final titration with salt (J. C. S. I. iv. 263), on the ground that, in 
 the case of material containing much gallic acid, some of it is 
 precipitated with the tannin, thus leading to higher results. This 
 he has proved by experiment, and therefore prefers to act as- 
 follows : 
 
 50 c.c. of the tannin solution are run into a small dry flask, to this 25 c.c. 
 of the fresh filtered gelatine solution are added, and the flask shaken. 25 c.c. 
 of a saturated solution of salt, containing 50 c.c. of strong H' 2 SO 4 per liter, 
 are now added, and about a teaspoonful of kaolin, or baric sulphate. The 
 flask is thoroughly shaken for a feAV minutes, after which a clear bright 
 filtrate may be obtained. 
 
 For materials containing over 45 per cent, tannin, it is advisable 
 to take 25 c.c. instead of 50, and to use 50 c.c. of salt, the amount 
 of gelatine solution. being the same. The same authority also states 
 that, for gambler and its allies, the method of titration as above 
 described does not give accurate results, inasmuch as the gelatine 
 and salt do not remove all the substances of tanning value from the 
 liquid. In such case it is necessary to digest the liquid for at least 
 twelve hours with pure hide powder. The mixture is then filtered 
 and titrated in the usual way. 
 
 It is impossible to give here the opinions held by various 
 authorities on this subject, therefore the reader who desires fuller 
 information should consult the papers to which reference has been 
 made. 
 
 The table on next page by Hunt is appended, as the result of 
 careful working, and as a guide to the nature of various tanning 
 materials : 
 
 The " total extract " in the table was determined by evaporating 
 a portion of the tannin solution to dryness in a small porcelain 
 basin and drying the residue at 110 C. The "insoluble matter" 
 was also dried at 110 C. 
 
 The hide powder process for tannin not being a volumetric one 
 is not described here. 
 
 Tannin in Tea. The extract in this substance is made upon 
 10 gm. of the tea, by boiling it with repeated quantities of distilled 
 water, filtering and diluting the liquid when cool to a liter. The 
 percentage varies from about 12 in black tea to 18 or 20 in green. 
 
78. 
 
 TANNIC ACID. 
 
 335> 
 
 Total 
 matters 
 
 NAME or MATERIAL. ^g^. 
 g-auate, as 
 i Oxalic Ac. 
 
 Tannin, as 
 Oxalic Ac, 
 (Procter) 
 
 Tannin, as 
 Oxalic Ac. 
 (H u n t) 
 
 Total 
 Extract. 
 
 Insoluble. 
 
 
 per cent. 
 
 per cent. 
 
 per cent. 
 
 per cent. 
 
 per cent. 
 
 English Oak Bark ... 1570 
 
 13-54 
 
 11-97 
 
 18-38 
 
 66-15 
 
 CanadianHemlockBark 9'03 
 
 7-46 
 
 7-08 
 
 13-96 
 
 75-25 
 
 Larch Bark 
 
 8-20 
 
 7-17 
 
 6-15 
 
 20-64 
 
 60'80 
 
 Mangrove Bark 
 
 31-35 
 
 29-71 
 
 28-48 
 
 26-60 
 
 49-70 
 
 Alder Bark 
 
 8'27 
 
 6-15 
 
 5-73 
 
 19-36 
 
 68-00 
 
 Blue Gum Bark 
 
 10-18 
 
 8-91 
 
 8-91 
 
 11-76 
 
 74-65 
 
 Valonia 
 
 37-41 
 
 35-24 
 
 30-50 
 
 38-50 
 
 46-05 
 
 Myrabolans 
 
 48-23 
 
 38-43 
 
 38-00 
 
 42-80 
 
 
 
 Sumach 
 
 42-53 
 
 34-30 
 
 31-46 
 
 44-10 
 
 47-77 
 
 BetelNut 
 
 15-91 
 
 13-87 
 
 13-79 
 
 17-94 
 
 67-00 
 
 Turkish Blue Galls ... 
 
 73-38 
 
 65-83 
 
 59-96 
 
 48*40 
 
 36-35 
 
 Aleppo Galls 
 
 98-85 
 
 87-82 
 
 83-05 
 
 68-80 
 
 1432 
 
 Wild Galls 
 
 26-21 
 
 18-75 
 
 16-56 
 
 31-70 
 
 54-17 
 
 Divi-Divi 
 
 66-98 
 
 62-62 
 
 61-22 
 
 54-38 
 
 29-90 
 
 Balsamocarpon (poor 
 
 
 
 
 
 
 and old sample) ... 
 
 50-49 
 
 37-76 
 
 32-88 
 
 57-14 
 
 28-25 
 
 Pomegranate Rind . . . 
 
 27-58 
 
 21-18 
 
 23-12 
 
 41-00 
 
 49-50 
 
 Tormentil Root 
 
 22-27 
 
 20-98 
 
 20-68 
 
 1970 
 
 67-95 
 
 Rhatany Root 
 
 22-27 
 
 20-15 
 
 19-30 
 
 18-80 
 
 66-00 
 
 Pure Indian Tea 
 
 23-06 
 
 18-65 
 
 17-40 
 
 34-46 
 
 53-40 
 
 Pure China Tea 
 
 1 8-03 
 
 14-21 
 
 14-09 
 
 24-50 
 
 62'6'0 
 
 Cutch 
 
 57"65 
 
 51-95 
 
 44-24 
 
 61-60 
 
 4-75 
 
 Gum Kino 
 
 66-39 
 
 59-55 
 
 51-55 
 
 7930 
 
 i-oo 
 
 Hemlock Extract ... 
 
 35-16 
 
 33-17 
 
 30*98 
 
 48-78 
 
 i 
 
 Oak wood Extract ... 
 
 33-49 
 
 26-90 
 
 23*86 
 
 37-78 
 
 
 
 Chestnut Extract ... 
 
 39-77 
 
 32-63 
 
 28'88 
 
 50-28 
 
 
 
 Quebracho Extract ... 
 
 48-22 
 
 44-45 
 
 40-84 
 
 49-00 
 
 
 
 "Pure Tannin" 
 
 135-76 
 
 122-44 
 
 121-93 
 
 
 
 . 
 
 TanLiquor,sp. gr.1'030 
 
 4-84 
 
 3-14 
 
 2-10 
 
 6-01 
 
 
 
 Spent Tan Liquor, sp. 
 
 
 
 
 
 
 gr. 1'0165 
 
 1-40 
 
 0-37 
 
 0-25 
 
 3-10 
 
 
 
 
 
 
 Absorbed 
 
 
 
 
 
 
 by Dry 
 
 
 
 
 
 
 Pure Skin. 
 
 
 
 Gambier, Cube 
 
 70-12 
 
 . 
 
 51-07 
 
 74-40 
 
 5-31 
 
 Sarawak . . . 
 
 63-13 
 
 
 
 47-09 
 
 70-70 
 
 3-67 
 
 Bale 
 
 56-00 
 
 
 
 43-70 
 
 63'54 
 
 1'40 
 
 Tannin in Wine, Cider, etc. The method now generally adopted 
 for this estimation is that of treating a known volume of the 
 wine, etc., with catgut (violin strings which have not been oiled, 
 and which have been purified by washing in dilute alcohol acid 
 and water, until they have no reducing action on permanganate in 
 the cold). The digestion is carried on at ordinary temperature for 
 a week, in a closely stoppered bottle. The original substance, and 
 that from which the tannin has been removed, are then titrated 
 with permanganate, and the difference calculated to tannin. 
 
 Another method consists in mixing equal parts of an eight per 
 
.336 VOLUMETRIC ANALYSIS. 78. 
 
 cent, solution of alum and the wine, collecting the precipitate on 
 .a filter, washing slightly with cold water, transferring the precipitate 
 *by a stream of water from a wash-bottle to a beaker, then acidifying 
 with H 2 S0 4 and titrating with indigo and permanganate as usual. 
 
 Dreaper's Copper Process for Tannic and Gallic Acids. This 
 as described in a paper contributed to /. C. S. I. xii. 412, from 
 which the following abstract is taken. 
 
 The methods hitherto proposed for the estimation of tannin may 
 IDC divided into two classes, viz. : 
 
 (1) Those which act by precipitating the tannic acid as an 
 insoluble compound. 
 
 (2) Those which act by oxidation. 
 
 To the former class belongs the well-known hide powder process, 
 .and to the latter Lowenthal's permanganate method, which has 
 been modified by Procter and others. These fairly represent the 
 two classes, and are the only ones in general use at the present 
 -day. 
 
 Dreaper, however, has adopted a modified form of Darton's 
 method, the novelty of which consists in precipitating the tannic 
 .acid by means of an ammonio-copper sulphate solution, after 
 a preliminary treatment with sulphuric acid to remove the ellagic 
 acid, and then a treatment with ammonia, filtering after each 
 treatment. Procter states that this preliminary treatment is 
 unnecessary in the case of some extracts, but Dreaper has never 
 found any precipitation to take place in the case of the so-called 
 pure tannic acids, probably owing to the removal of the impurities 
 during the process of purification. The original solution and the 
 (filtrate are titrated with permanganate as in Lowenthal's method, 
 the difference in the two results being due to the tannic acid 
 present. The copper compound may be dried at 110 C. and 
 weighed, or else ignited and weighed as copper oxide. Fleck 
 states that the tannic acid can be calculated from this by multi- 
 plying by the factor 1 "034. 
 
 The standard copper solution used by the author contained 
 ."30 gm. of pure crystallized copper sulphate in a liter of water. 
 Baric carbonate is also required, which should be free from calcic 
 .-salts. 
 
 The process is based on the direct precipitation of the gallic and tannic 
 acids by means of a copper salt, using as outside indicator potassic ferro- 
 cyanide. If a standard solution of copper sulphate be run into a solution 
 of the mixed acids, a certain amount of copper tannate and gallate will be 
 precipitated, depending on the dilution of the solution and the amount of 
 acid set free from the copper sulphate. The precipitate is, under these 
 circumstances, of a bulky nature and ill adapted to any separation by quick 
 filtration, so necessary in a process of this description. It was found that 
 when a solution of copper sulphate was added to a solution of the mixed 
 acids in the presence of baric carbonate, the precipitation proceeds with the 
 utmost regularity. The carbonate immediately forms insoluble sulphate 
 -with the free acid, and also helps to consolidate the precipitated copper salts, 
 
78. 
 
 TANNIC ACID. 
 
 so that towards the end of the reaction they fall rapidly to the bottom of 
 the vessel, leaving the supernatant liquid clear. This separation is a good 
 indication that the end of the titration is near, and is supplemented hy the 
 ferrocyanide test. 
 
 A modified method of testing for the excess of copper in the solution 
 is as follows : Pieces of stout Swedish filter-paper one inch square are folded 
 across the middle, and a drop of the liquid to be tested taken up on a glass 
 rod and gently dropped on to the top surface. The liquid will percolate 
 through to the under fold, leaving the precipitate on the upper one. It 
 is then only necessary to unfold the sheet and apply a drop of ferrocyanide 
 to the under surface. If the reaction is complete a faint pink colouration 
 will take place, which is perhaps more easily recognized by transmitted light. 
 
 The results obtained by duplicate experiments tend to show that the copper 
 salts are perfectly constant in composition when precipitated in this manner, 
 and the results equal in accuracy any obtained with other processes. 
 
 About 1 gin. of baric carbonate was added in each case and the solution 
 heated up to 90 C. before titration. The temperature at the end of the 
 titration should not be less than 30 C. 
 
 The precipitation by copper is done say on 25 c.c. of the solution of the 
 sample, and the results noted. 50 c.c. of the same sample are then mixed 
 with the usual proportions of gelatine, salt, acid, and baric sulphate ; diluted 
 to 100 c.c., then filtered through a dry filter and 50 c.c. ( = 25 c.c. of the 
 original liquid) titrated with copper solution as before, the difference being 
 calculated to available tannin. 
 
 The experiments show that the separation of the tannic acid by means of 
 an acid solution of gelatine and salt will not affect the general results 
 obtained, and this method for want of a better was used in the experiments, 
 Procter's modification being considered the most accurate, and therefore 
 adopted. 
 
 The following table was prepared from experiments, showing the error 
 due to the indicator in c.c. of standard solution added to different quantities 
 of water: 
 
 c.c. of Water. 
 
 c.c. of Standard Solution 
 required. 
 
 20 
 
 0-3 
 
 30 
 
 0-4 
 
 60 
 
 07 
 
 100 
 
 1-0 
 
 150 
 
 1-5 
 
 The above correction should be made in all cases. 
 
 A sample of so-called pure tannic acid gave the following results 
 
 Weight taken. 
 
 c.c. required. 
 
 Gni. 
 
 
 O'o 
 
 25-0 
 
 0-5 
 
 25-2 
 
 0-5 
 
 25-2 
 
 Slightly lower results were obtained when the operation was conducted in 
 the cold, probably owing to the slower action of the carbonate on the free 
 
 z 
 
338 
 
 VOLUMETEIC ANALYSIS. 
 
 78. 
 
 acid ; but the rate of running in of the solution had no appreciable effect 
 on the quantity required. 
 
 A sample of the purest gallic acid that could be obtained gave the 
 following figures : 
 
 Weight taken. 
 
 c.c. required. 
 
 GUI. 
 
 
 0-5 
 
 45'0 
 
 0-5 
 
 448 
 
 Allowing that the acid was of 90 per cent, purity, these results would give 
 a value for each c.c. of O'Olll gm. This figure must of course only be 
 taken as approximate. It will be seen that more solution is required to 
 precipitate the gallic than the tannic acid. This is also noticed in 
 Lowenthal's method. 
 
 The chief advantages claimed by the author of this method over 
 Lowenthal's are as follows : 
 
 (1) Both the tannic and gallic acids are estimated. 
 
 (2) Rapidity of estimation where a simple assay is sufficient. 
 
 (3) The results are expressed in terms of the copper oxide 
 precipitated. 
 
 (4) The standard solution keeps well, and there is no correction 
 necessary for indigo-carmine solution or gelatine. 
 
 (5) Larger quantities of the solution can be titrated, thus 
 reducing the working error. 
 
 It seems to be possible to use this method for substances other 
 than tannic or gallic acids, e.g. Fustic. 
 
 The following results were obtained with a sample of pure 
 Fustic extract 51 Tw. 
 
 0*5 gin. taken required 11 '5 c.c. of standard solution. 
 
 0'5 gm. taken required 11*6 c.c. of standard solution. 
 
 The end of the reaction was sharp when the titration was 
 carried on at the boiling-point and the precipitate settled well. 
 
 Other Methods of Estimating- Tannin. 
 
 Direct Precipitation by Gelatine. The difficulty existing with 
 this method is that of getting the precipitate to settle, so that it 
 may be clearly seen when enough gelatine has been added. 
 
 Tolerably good results may sometimes be obtained by using 
 a strong solution of sal ammoniac or chrome alum as an adjunct. 
 The best aid is probably barium sulphate, 2 or 3 gm. of which 
 should be added to each portion of liquid used for titration. 
 
 The Standard Solution of Gelatine should contain 1*33 gm. of 
 dry gelatine per liter, in which is also mixed a few drops of 
 chloroform or a small quantity of thymol to preserve it. 45 c.c. 
 = 0'05 gm. tannin (Carles). This method is adapted only for 
 rough technical purposes, as also the following. 
 
' 79. TIN. 
 
 Direct Precipitation by Antimony. This method is still in 
 favour with some operators ; but, like the gelatine process, is beset 
 with the difficulty of getting the precipitate to settle. 
 
 The Standard Antimony solution is made by dissolving 2*611 
 .gm. of crystals of emetic tartar dried at 100 C. in a liter. I c.c. = 
 '0*005 gm. tannin. This liquid may also be kept from decomposition 
 by a few grains of thymol. 50 c.c. of the tannin solution may be 
 taken for titration, to which is added 1 or 2 gm. of sal ammoniac, 
 :and the antimonial solution run in until no further cloudiness is 
 produced. 
 
 In both the above methods the final tests must either be made 
 by repeatedly filtering small portions to ascertain whether the 
 precipitation is complete, or by bringing drops of each liquid 
 together on black glass or a small mirror. 
 
 TIN. 
 
 Sn = 118. 
 
 Metallic iron 1*0536 =Tin. 
 
 Double iron salt 0*1505= 
 
 Factor for T ^- iodine 
 
 or permanganate 
 
 solution 0*0059 
 
 79. THE method, originally devised by Streng, for the 
 direct estimation of tin by potassic bichromate, or other oxidizing 
 agents in acid solution, has been found most unsatisfactory, from 
 the fact that variable quantities of water or acid seriously interfere 
 with the accuracy of the results. The cause is not fully under- 
 stood, but that it is owing partly to the oxygen mechanically 
 contained in the water reacting on the very sensitive stannous 
 chloride there can be very little doubt, as the variations are 
 considerably lessened by the use of water recently boiled and 
 cooled in closed vessels. These difficulties are set aside by the 
 processes of Lenssen, Lowenthal, Stromeyer, and others, now 
 to be described, and which are found fairly satisfactory. 
 
 1. Direct Titration by Iodine in Alkaline Solution (Lenssen). 
 
 Metallic tin or its protosalt, if not already in solution, is 
 dissolved in hydrochloric acid, and a tolerable quantity of Rochelle 
 salt added, together with sodic bicarbonate in excess. If 
 enough tartrate be present, the solution will be clear ; starch is 
 then added, and the mixture titrated with ~ iodine. Metallic tin 
 is best dissolved in HC1 by placing a platinum crucible or cover in 
 contact with it, so as to form a galvanic circuit. 
 
 Benas (Cliem. Gentr-blatt. li. 957) points out that the chief 
 error in the estimation as above arises from oxygen dissolved in 
 
 z 2 
 
340 VOLUMETRIC ANALYSIS. 79. 
 
 the liquid, or absorbed during the operation. In order to obtain 
 constant results, it is necessary to dissolve the tin compound 
 in HC1, dilute with oxygen-free water, and add at once excess of 
 standard iodine, which excess is found by residual titration with 
 standard thiosulphate. 
 
 2. Indirect Titration by Ferric Chloride and Permanganate 
 (Lbwenthal, Stromeyer, etc.). 
 
 This method owes its value to the fact, that when stannous 
 chloride is brought into contact with ferric or cupric chloride, it 
 acts as a reducing agent, in the most exact manner, upon these 
 compounds, stannic chloride being formed, together with a pro- 
 portionate quantity of ferrous or cuprous salt, as the case may be. 
 If either of the latter be then titrated with permanganate, the 
 original quantity of tin may be found, the reaction being, in the 
 case of iron, 
 
 SnCl 2 + Fe 2 Cl 6 =SnCl 4 + 2FeCl 2 . 
 
 56 iron=59 tin. If decinormal permanganate, or the factor 
 necessary to convert it to that strength, be used, the calculation by 
 means of iron is not necessary. 
 
 Process: The solution of stannous chloride, or other protosalt of tin in 
 HC1, or the granulated metal, is mixed with pure ferric chloride, which, 
 if tolerably concentrated, dissolves metallic tin readily, and Avithout evolution 
 of hydrogen, then diluted with distilled water, and titrated with perman- 
 ganate as usual. To obtain the most exact results, it is necessary to make an 
 experiment with the same permanganate upon a like quantity of water, 
 to which ferric chloride is added; the quantity required to produce the 
 same rose colour is deducted from the total permanganate, and the remainder 
 calculated as tin. 
 
 Stannic salts, also tin compounds 'containing iron, are dissolved in water, 
 HC1 added, and a plate of clean zinc introduced for ten or twelve hours ; 
 the tin so precipitated is carefully collected and washed, then dissolved 
 in HC1, and titrated as ahove; or the finely divided metal may at once 
 be mixed with an excess of ferric chloride, a little HC1 added, and when 
 solution is complete, titrated with permanganate. 4 eq. of Iron ( = 224) 
 occurring in the form of ferrous chloride represent 1 eq. ( = 118) of tin. 
 
 Tin may also be precipitated from slightly acid peroxide solution 
 as sulphide by H 2 S, the sulphide well washed, and mixed with 
 ferric chloride, the mixture gently warmed, the sulphur filtered 
 off, and the filtrate then titrated with permanganate as above. 
 4 eq. of iron=l eq. of tin. 
 
 Tin Ore. In the case of analysis of cassiterite, Arnold (C. N. 
 xxxvi. 238) recommends that 1 gm. of the very finely powdered 
 mineral be heated to low redness for two hours in a porcelain boat 
 in a glass tube with a brisk current of dry and pure hydrogen gas, 
 by which means the metal is reduced to the metallic state. It is 
 then dissolved in acid ferric chloride, and titrated with perman- 
 ganate or bichromate in the usual way. 
 
80. VANADIUM. 341 
 
 URANIUM. 
 
 Ur = 240. 
 
 80. THE estimation of uranium may be conducted with great 
 accuracy by permanganate, in precisely the same way as ferrous 
 salts ( 63). The metal must be in solution either as acetate, 
 sulphate, or chloride, but not nitrate. In the latter case it is 
 necessary to evaporate to dryness with excess of sulphuric or 
 hydrochloric acid, or to precipitate with alkali, wash and redissolve 
 in acetic acid. 
 
 The reduction to the ura nous state is made with zinc, but as the 
 end of reduction cannot, like iron, be known by the colour, it is 
 necessary to continue the action for a certain time ; in the case of 
 small quantities a quarter, larger half an hour, at a temperature of 
 50 to 60 C., and in the presence of excess of sulphuric acid; 
 all the zinc must be dissolved before titration. The solution is 
 then freely diluted with boiled water, sulphuric acid added if 
 necessary, and then permanganate until the rose colour is faintly 
 permanent. The ending is distinct if the solution be well diluted, 
 and the reaction is precisely the same as in the case of ferrous 
 salts ; namely, 2 eq. of uranium existing in the uranous state 
 require 1 eq. of oxygen to convert them to the uranic state ; hence 
 56 Fe = 120 Ur, consequently the strength of any permanganate 
 solution in relation to iron being known, it is easy to find the 
 amount of uranium. 
 
 VANADIUM. 
 
 ' 81. VANADIUM salts, or the oxides of this element, may be 
 very satisfactorily titrated by reduction with a standard ferrous 
 solution ; thus 
 
 2FeO + VO 3 = Fe 2 3 + VO. 
 
 1 gm. of Fe represents 1 "630357 gm. of vanadic pentoxide. 
 
 Lindemann (Z. a. C. xviii. 99) recommends the use of a 
 solution of ferrous ammonio-sulphate (double iron salt) standardized 
 by y 1 ^ potassic bichromate. 
 
 Of course it is necessary that the vanadium compound should be 
 in the highest state of oxidation, preferably in pure sulphuric acid 
 solution. The blue colour of the tetroxide in the dilute liquid has 
 no misleading effect in testing with ferridcyanide. 
 
 With hydrochloric acid great care must be taken to insure 
 absence of free Cl or other impurities. The end-point in the case 
 -of this acid is different from that with sulphuric acid, owing to the 
 colour of the ferric chloride, the mixture becoming clear green. 
 
 The accuracy of the reaction is not interfered with by ferric or 
 chromic salts, alumina, fixed alkalies, or salts of ammonia. 
 
342 VOLUMETRIC ANALYSIS. 82. 
 
 Vanadic solutions being exceedingly sensitive to the action of 
 
 reducing agents, great care must be exercised to exclude dust 
 or other carbonaceous matters, alcohol, etc. 
 
 ZINC. 
 Zn = 65. 
 
 1 c.c. T ^ solution =0-003 2 5 gm. Zinc. 
 Metallic iron x 0*5809 = Zinc. 
 
 ,, x 0-724 = Zinc oxide. 
 
 Double iron salt x 0-08298 = Zinc. 
 
 x 0-1034 = Zinc oxide. 
 
 1. Indirect Method (Mann). 
 
 82. THIS process gives exceedingly good results, and consists 
 in precipitating the zinc as hydrated sulphide, decomposing the 
 sulphide with moist silver chloride, then estimating the zinc 
 chloride so formed with ammonic thiocyanate as in Volhard's 
 method ( 43). 
 
 The requisite materials are 
 
 Silver chloride. Well washed and preserved from the light- 
 under water. 
 
 Standard Silver nitrate. 33'18 gm. of pure silver, dissolved in 
 nitric acid and made up to 1 liter, or 52'3 gm. silver nitrate per 
 liter. If made direct from silver, the solution must be well boiled 
 to dissipate nitrous acid. 1 c.c. = 0*01 gm. of zinc. 
 
 Ammonic thiocyanate. Of such strength that exactly 3 c.c.. 
 suffice to precipitate 1 c.c. of the silver solution. 
 
 Ferric Indicator and Pure Citric Acid (see 43.3 and 4). 
 
 Process: 0'5 to 1 gm. of the zinc ore is dissolved in nitric acid. Heavy 
 metals are removed by H 2 S, iron and alumina by double precipitation 
 with ammonia. The united filtrates are acidified with acetic acid, and H 2 S 
 passed into the liquid until all zinc is precipitated as sulphide. Excess of 
 H'-S is removed by rapid boiling, so that a drop or two of the filtered liquid 
 gives no further stain on lead paper. The precipitate is then allowed to settle, 
 decanted while hot, the precipitate brought on a filter with a little hot water, 
 and without further washing, the filter with its contents is transferred to 
 a small beaker, 30 50 c.c. of hot water added, well stirred, and so much 
 moist silver chloride added as is judged necessary to decompose the sulphide, 
 leaving an excess of silver. The mixture is now boiled till it shows signs of 
 settling clear ; 5 or 6 drops of dilute sulphuric acid (1 : 5) are added to the 
 hot mixture, and in a few minutes the whole of the zinc sulphide will be 
 converted into zinc chloride. The free sulphur and excess of silver chloride 
 are now filtered off, washed, and the chloride in the mixed filtrate and 
 washings estimated as follows : 
 
 To the cool liquid, measuring 200 or 300 c.c., are added o c.c. of ferric 
 indicator, and so much pure nitric acid as is necessary to remove the yellow 
 colour of the iron. A measured excess of the standard silver solution is then 
 
82. ZINC. 343 
 
 delivered in with the pipette, and without filtering off the silver chloride, or 
 much agitation, so as to clot the precipitate, the thiocyanate is cautiously 
 added, with a gentle movement after each addition, until a permanent light 
 brown colour appears. 
 
 The volume of silver solution represented by the thiocyanate 
 being deducted from that originally used, will give the volume to 
 be calculated to zinc, each c.c. being equal to 0*01 gm. Zn. 
 
 2. Precipitation as Sulphide and subsequent titration with. Ferric 
 Salts and Permang-anate (Schwarz). 
 
 The principle of this method is based on the fact, that when zinc 
 sulphide is mixed with ferric chloride and hydrochloric acid, or 
 better still, with ferric sulphate and sulphuric acid, ferrous or zinc 
 chloride, or sulphates respectively, and free sulphur are produced. 
 If the ferrous salt so produced is estimated with permanganate or 
 bichromate, the proportional quantity of zinc present is ascertained. 
 2 eq. Fe represent 1 eq. Zn. 
 
 Preparation of the Ammpniacal Zinc Solution. In the case of rich 
 ores 1 gm., and poorer qualities 2 gm., of the finely powdered material are 
 placed into a small wide-mouthed flask, and treated with HC1, to which 
 a little nitric acid is added, the mixture is warmed to promote solution, and 
 when this has occurred the excess of acid is evaporated by continued heat. 
 If lead is present, a few drops of concentrated sulphuric acid are added 
 previous to complete dryness, in order to render the lead insoluble ; the 
 residue is then extracted 'with water and filtered. Should metals of the fifth 
 or sixth group be present, they must be removed by H 2 S previous to the 
 following treatment. The solution will contain iron, and in some cases 
 manganese. If the iron is not already fully oxidized, the solution must be 
 boiled with nitric acid ; if only traces of manganese are present, a few drops 
 of bromized HC1 should be added. When cold, the solution may be further 
 diluted if necessary, and then super-saturated with ammonia to precipitate 
 the iron ; if the proportion of this metal is small, it will suffice to filter off 
 and wash the oxide with ammoniacal warm water, till the washings give no 
 precipitate of zinc on adding ammonic sulphide. Owing to the fact that 
 this iron precipitate tenaciously holds about a fifth of its weight of zinc, it 
 will be necessary when the proportion is large to redissolve the partly washed 
 precipitate in HC1, and reprecipitate (best as basic acetate) ; the filtrate from 
 this second precipitate is added to the original zinc filtrate, and the whole 
 made up to a liter. 
 
 Process : The ammouiacal zinc solution (prepared as described above) is 
 heated, and the zinc precipitated in a tall beaker, with a slight excess of 
 sodic or ammonic sulphide, then covered closely with a glass plate, and set 
 aside in a warm place for a few hours. The clear liquid is removed by 
 a syphon, and hot water containing some ammonia again poured over the 
 precipitate, allowed to settle, and again removed, and the washing by 
 decantation repeated three or four times ; finally, the precipitate is brought 
 upon a tolerably large and porous filter, and well washed with warm water 
 containing ammonia, till the washings no longer discolour an alkaline lead 
 solution. The filter pump may be used here with great advantage. 
 
 The filter with its contents is then pushed through the funnel into a large 
 flask containing a sufficient quantity of ferric sulphate mixed with sulphuric 
 acid, immediately well stopped or corked, gently shaken, and put into a warm 
 place ; after some time it should be again well shaken, and set aside quietly 
 
344 VOLUMETRIC ANALYSIS. 82. 
 
 for about ten minutes. After the action is all over the mixture should 
 possess a yellow colour from the presence of undecomposed ferric salt ; when 
 the cork or stopper is lifted there should be no odour of H 2 S. The flask is 
 then nearly filled with cold distilled water, if necessarj- some dilute 
 sulphuric acid added, and the contents of the flask titrated with permanganate 
 or bichromate as usual. 
 
 The free sulphur and filter will have no reducing effect 
 upon the permanganate if the solution be cool and very dilute. 
 
 3. Precipitation by Standard Sodic Sulphide, with Alkaline Lead 
 Solution as Indicator (applicable to most Zinc Ores and Products). 
 
 The Ammoniacal Solution of Zinc is prepared just as previously 
 described in Schwarz's method. 
 
 Standard Sodic sulphide. A portion of caustic soda solution is 
 saturated with H 2 S, sufficient soda added to remove the odour of 
 the free gas, and the whole diluted to a convenient strength for 
 titrating. 
 
 Standard Zinc Solution. 44*12 gin. of pure zinc sulphate are 
 dissolved to the liter. 1 c.c. will then contain 0*01 gm. of 
 metallic zinc, and upon this solution, or one prepared from pure 
 metallic zinc of the same strength, the sulphide solution must be 
 titrated. 
 
 Alkaline Lead Indicator. Is made by heating together lead 
 acetate, tartaric acid, and caustic soda solution in excess, until 
 a clear solution is produced. It is preferable to mix the tartaric 
 acid and soda solution first, so as to produce sodic tartrate ; or if 
 the latter salt is at hand, it may be used instead of tartaric acid. 
 Some operators use sodic nitroprusside instead of lead. 
 
 Process: 50 c.c. of zinc solution (=0*5 gm. Zn) are put into a beaker, 
 a mixture of solutions of ammonia and ammonic carbonate (3 of the former 
 to about 1 of the latter) added in sufficient quantity to redissolve the 
 precipitate which first forms. A few drops of the lead solution are then, by 
 means of a glass rod, placed at some distance from each other, on filtering 
 paper, laid upon a slab or plate. 
 
 The solution of sodic sulphide contained in an ordinary Mohr' s burette 
 is then suffered to flow into the zinc solution until, on bringing a drop from 
 the mixture and placing it upon the filtering paper, so that it may expand 
 and run into the drop of lead solution, a black line occurs at the point of 
 contact ; the reaction is very delicate. At first it will be difficult, probably, 
 to hit the exact point, but a second trial with 25 or 50 c.c. of zinc solution 
 will enable the operator to be certain of the corresponding strength of the 
 sulphide solution. As this latter is always undergoing a slight change, it is 
 necessary to titrate occasionally. 
 
 Direct titration with pure zinc solution gave 99'6 and 100'2, instead of 100. 
 
 Groll recommends the use of nickel protochloride as indicator, 
 instead of sodic nitroprusside or lead. The drops are allowed to 
 now together on a porcelain plate ; while the point of contact shows 
 a blue or green colour the zinc is not all precipitated by the sodic 
 sulphide, therefore the latter must be added until a greyish black 
 colour appears at contact. 
 
82. ZINC. 345 
 
 4. Precipitation as Sulphide with Ferric Indicator (Schaffner) . 
 
 Schaffner's modification of this process, and which is used 
 constantly at the laboratory of the Vieille Montagne and the 
 Rhenish Zinc Works, is conducted as follows : For ores containing 
 over 35 per cent, zinc, 0*5 gm. is taken ; for poorer ones, 1 gm. to 
 2 gm. Silicates, carbonates, or oxides, are treated with hydro- 
 chloric acid, adding a small proportion of nitric acid at boiling heat 
 to peroxidize the iron. Sulphur ores are treated with aqua regia, 
 evaporated to dryness, and the zinc afterwards extracted by hydro- 
 chloric acid ; the final ammoniacal solution is then prepared as 
 described on page 343. 
 
 Process : The titration is made with a solution of sodio sulphide, 1 c.c. of 
 which should equal about O'Ol gm. Zn. The Vieille Montagne laboratory 
 uses ferric chloride as an indicator, according to Schaffner's method. 
 For this purpose a single drop or some few drops of this chloride are let fall 
 into the ammoniacal solution of zinc. The iron which has been added is at 
 once converted into red flakes of hydrated ferric oxide, which float at the 
 bottom of the flask. If sodic sulphide be dropped from a burette into the 
 solution of zinc, a white precipitate of zinc sulphide is at once thrown down, 
 and the change in the colour of the flakes of iron from red to black shows 
 the moment when all the zinc is sulphuretted, and the titration is ended. It 
 is advisable to keep the solution for titration at from 40 to 60 C. Titration 
 carried out under exactly equal conditions, with a known and carefully 
 weighed proportion of zinc, gives comparative data for calculation, and thus 
 for the determination of the contents of any zinc solution by means of 
 a simple equation. If, for example, 30'45 c.c. of sodic sulphide have been 
 used to precipitate 0'25 gm. of zinc, 1 c.c. of it will precipitate 8'21 m.gm. 
 of zinc (30'45 : 0'25 -1 : x, and therefore #=0-00821). 
 
 The following method is adopted in the laboratory of a well- 
 known copper works in Wales : 
 
 Reduce the sample to fine powder, and dry at a temperature of about 
 105 C. Dissolve 0'5 gm. of the sample thus prepared in aqua regia, 
 evaporate nearly to dryness, take up with hot water, add 20 c.c. of 
 ammonia and 10 c.c. of a solution of ammonic carbonate (1 to 10), then 
 a few drops of solution of permanganate to precipitate lead and manganese. 
 Now heat nearly to boiling-point and filter into a larger flask, wash the 
 precipitate well with hot water containing ammonia until a drop of the 
 washings shows no reaction with sodic sulphide. The volume of the filtrate 
 and washings should be about 250 c.c., and the temperature about 50 C. Now 
 titrate with a standard solution of sodic sulphide. The most convenient 
 strength is 70 c.c. = 0'5 gm. of pure zinc, heat the sample liquid almost to 
 boiling-point, and add not quite enough sulphide solution to precipitate the 
 whole of the zinc. Now take a drop of a dilute solution of ferric chloride, 
 and let it fall into a small beaker containing a few drops of dilute ammonia, 
 wash the whole contents of the beaker into the assay, and continue titrating 
 slowly and cautiously, at last adding the sulphide solution by O'l c.c. at 
 a time, while continually agitating the flask until the ferric oxide at the 
 bottom of the flask begins to turn black, when the assay is finished. 
 
 The number of c.c. of sulphide solution used is noted. In order to 
 determine the strength of the sulphide solution, weigh 0'5 gm. pure zinc, 
 place this in a flask, dissolve in 10 c.c. of HC1, and add some hot water, 20 
 c.c. of ammonia, and 10 c.c. of ammonic carbonate as above, and fill up with 
 hot water to about 250 c.c. Then titrate with the sulphide solution 
 
346 VOLUMETRIC ANALYSIS. 82. 
 
 as described. From the number of c.c. used for the O'o gm. pure zinc 
 (standard), and the number used for the sample, the zinc contents of the 
 latter can be easily calculated. 
 
 The copper present in blendes and calamines does not usually exceed 0'5 
 per cent. It may be estimated colori metrically, and the amount deducted 
 from the total produced. 
 
 If any considerable amount of copper or other impurities be present,, 
 they must be separated by the ordinary well-known methods. In order to 
 obtain greater accuracy a correction is made by measuring the volume of 
 the liquid after the assay is finished, and deducting 0'6 c.c. from the 
 sulphide solution used for every 100 c.c. of the volume of the assay : this 
 correction is equally applied to the standard. Experiments have shown that 
 oxide of iron prepared as described above placed in 100 c.c. of distilled 
 water containing ammonia, requires 0'6 c.c. of a sulphide solution of the 
 above strength to turn distinctly black. 
 
 The essential point in this volumetric process practised at the 
 Vieille Montagne is the perfect uniformity of working adopted in 
 the assays with reference to the volume of the solutions and 
 reagents used and the colour of the indicator. In titrating,. 
 the same quantities of ferric chloride, hydrochloric acid and 
 ammonia are steadily used. Work is done always at one tem- 
 perature and in the same time, particularly at the end of the 
 operation, when the iron begins to take on that characteristic 
 colour which the flakes take at the edges points which should 
 not he overlooked. As a further precaution, the titrating 
 apparatus is provided in duplicate, two assays being always made. 
 It permits the execution of several titrations without the necessity 
 of a too frequent renewal of sodic sulphide, which is stored in 
 a yellow flask of large capacity supplying two Mohr's burettes, 
 under which the beakers can be placed and warmed. A mirror 
 shows by reflection the iron flakes which settle down after shaking 
 the liquid. 
 
 Too much stress cannot be laid upon the necessity of standard- 
 izing the sodic sulphide under the same conditions as to volume of 
 fluid, proportions of NH y and HC1, and colour of the indicator, as 
 will actually occur in the analysis. 
 
 5. Estimation as Ferrocyanide. 
 
 In Acetic Acid Solution (Galetti). When ores containing zinc 
 and iron are dissolved in acid, and the iron precipitated with 
 ammonia, the ferric oxide invariably carries down with it 
 a portion of zinc, and it is only by repeated precipitation that the 
 complete separation can be made. In this process the zinc is 
 converted into soluble acetate, and titrated by a standard solution 
 of potassic ferrocyanide in the presence of insoluble ferric acetate. 
 
 The Standard Solution of Potassic ferrocyanide, as used by 
 Galetti, contains 41 '250 gm. per liter. 1 c.c. = O'Ol gm. Zn, but 
 its actual working power must be fixed by experiment. 
 
 Standard Zinc Solution, 10 gm. of pure metallic zinc per liter 
 dissolved in hydrochloric acid. 
 
82. ZINC. 347 
 
 The process is available in the presence of moderate quantities of 
 iron and lead, but copper, manganese, nickel, and cobalt must be 
 absent. 
 
 The adjustment of the ferrocyanide solution (which should be 
 freshly prepared at short intervals) must be made in precisely the 
 same way, and with the same volume of liquid as the actual 
 analysis of ores, and is best done as follows : - 
 
 25 c.c. of zinc solution are measured into a beaker, 15 c.c. of liquid 
 ammonia of sp. gr. 0'900 added to render the solution alkaline, then very 
 cautiously acidified with acetic acid, and 50 c.c. of acid ammonic acetate 
 (made by adding together 20 c.c. of ammonia of sp. gr. 0'900, 15 c.c. of 
 concentrated acetic acid and 65 c.c. of distilled water), which is poured into 
 the mixture, then dilated to 250 c.c., and warmed to about 50 C. The 
 titration is then made with the ferrocyanide solution by adding it from 
 a burette until- the whole of the zinc is precipitated. Galetti judges the 
 ending of the process from the first change of colour from white to ash grey y 
 which occurs when the ferrocyanide is in excess ; but it is best to ascertain 
 the ending by taking drops from the solution, and bringing them in contact 
 with solution of uranic acetate on a wiiite plate until a faint brown colour 
 appears. The ferroc} r anide solution should be of such strength that 
 measure for measure it agrees with the standard zinc solution. In the 
 present case 25 c.c. would be required. 
 
 In examining ores of zinc, such as calamine and blende, Galetti takes 
 0'5 gm. for the analysis, and makes the solution up to 500 c.c. Calamine 
 is at once treated with HOI in sufficient quantity to bring it into solution. 
 Blende is treated with aqua regia, and evaporated with excess of HC1 to- 
 remove nitric acid. The solutions of zinc so obtained invariably contain 
 iron, which together with the zinc is kept in solution by the HC1, but to 
 insure the peroxidation of the iron, it is always advisable to add a little 
 potassic chlorate at a boiling heat during the extraction of the ore. The 
 hydrochloric solution is then diluted to about 100 c.c., 30 c.c. of ammonia 
 added, heated to boiling, exactly neutralized with acetic acid, 100 c.c. of the 
 acid ammonic acetate poured in, and diluted to about 500 c.c. The mixture 
 as prepared will contain all the zinc in solution, and the iron will be 
 precipitated as acetate. The titration may at once be proceeded with at 
 a temperature of about 50 to 60 C. by adding the ferrocyanide until the 
 necessary reaction with uranium is obtained. As before mentioned, 
 Galetti takes the change of colour as the ending of the process, and when 
 iron is present this is quite distinguishable, but it requires considerable 
 practice, to rely upon, and it is therefore safer to use the uranium indicator. 
 When using the uranium, however, it is better to dilute the zinc solution less, 
 both in the adjustment of the standard ferrocyanide and the analysis of 
 ores. The dilution is necessaiy with Galetti's method of ending the 
 process, but half the volume of liquid, or even less, is better with the 
 external indicator. 
 
 in Hydrochloric Acid Solution (Fahlberg and Maxwell Ly te). 
 This method is not available in the presence of iron, copper, nickel, 
 cobalt, or manganese. 
 
 The Standard Solution of Ferrocyanide. 1 c.c. = 0*01 gm. of 
 zinc. Lyte finds that this is obtained by dissolving 43 '2 gm. of 
 pure potassic ferrocyanide and diluting to 1 liter. This corresponds 
 volume for volume with a solution of 10 gm. of pure zinc in excess 
 of hydrochloric acid diluted to 1 liter. My experiments confirm 
 
348 VOLUMETllIC ANALYSIS. 82. 
 
 this, but each operator is advised to adjust his solutions by 
 experiment, always using the same quantities of reagents and 
 volume of liquid. The end of the reaction between the zinc and 
 ferrocyanide is found by uranium. 
 
 Process : If a solution of zinc freely acidified with HCl is heated to nearly 
 boiling-point, two or three drops of uranic acetate or nitrate solution added, 
 and the ferrocyanide delivered into the mixture from a burette, white zinc 
 ferrocyanide immediately precipitates, and as the drops of ferrocyanide fall 
 into the mixture, a brown spot of uranic ferrocyanide appears, but dis- 
 appears again on stirring so long as free zinc exists in solution. The 
 moment all the zinc is converted into ferrocyanide, the addition of test 
 solution tinges the whole liquid brown. This addition of uranium to the 
 liquid may be used as a guide to the final testing on a porcelain plate, since 
 as the precipitation approaches completion, the tinge of brown disappears 
 more slowly. The actual ending, however, is always ascertained by spreading 
 a drop or two of the liquid upon the plate, bringing into contact with it 
 a glass rod moistened with uranic solution ; when the same shade of colour 
 is produced as occurred in the original titration of the ferrocyanide 
 solution, the process is ended. 
 
 Ly te gives the following method of treating a blende containing 
 lead, copper, and iron (C. N. xxi. 222) : 
 
 2 gm. of finely powdered ore were boiled with strong HCl and a little 
 KC1O 3 , the insoluble matter again treated in like manner, the solutions 
 mixed and evaporated somewhat, washed into a beaker, cooled, and moist 
 baric carbonate added to precipitate iron, allowed to stand a few hours, then 
 filtered into a 200 c.c. flask containing 10 c.c. of strong HCl, and washed 
 until the exact measure was obtained. 20 c.c. ( = 0'2 gm.) of blende were 
 measured into a small beaker, diluted with the same quantity of water, 
 3 drops of uranic solution added, and the ferrocyanide delivered in from 
 a burette. When 70 c.c. were added the brown tinge disappeared slowly ; 
 the testing on a white plate was then resorted to, and the ferrocyanide 
 added drop by drop, until the proper effect occurred at 73 c.c. As a slight 
 excess of ferrocyanide was necessary to produce the brown colour, 0'2 c.c. 
 was deducted, leaving 72'8 c.c. as the quantity necessary to precipitate all 
 the zinc. The 0'2 gm. of blende therefore contained 0'0728 gm. of Zn or 
 36'4 per cent. 
 
 The sample in question contained about 2*7 per cent, of copper, 
 but this was precipitated with the iron by the baric carbonate ; had 
 it contained a larger quantity, the process would not have been 
 available unless the copper was removed by other means. 
 
 Mahon (Amer. Chem. Journ. iv. 53) uses the ferrocyanide 
 method much in the same way as above described, but finds that 
 Mn must be absent to ensure good results. In the presence of 
 Mil he separates the Zn from a strong acetic solution with H 2 S. 
 The sulphide is then dissolved in HCl and titrated as before. 
 
 A modification of the ferrocyanide method so as to be available 
 for the estimation of both zinc and manganese in the presence of 
 each other has been devised by G. C. Stone (Jour. Amer. Cliem. 
 Soc. xvii. 437). 
 
 The standard solutions required are : 
 
82. ZINC. 349 
 
 Potassic ferrocyanide, about 30 gm. per liter. Its actual working 
 strength is found by titrating it upon a known weight of either 
 zinc or manganese in slightly acid solution, using a very dilute 
 solution of cobalt nitrate as outside indicator. A correction is 
 made in all cases for the amount of ferrocyanide required to give 
 the reaction with the indicator, and may be taken as 0*5 c.c. for 
 every 100 c.c. of the solution titrated. 
 
 Potassic permanganate, 1*99 gm. of the pure salt per liter, 1 c.c. 
 = 1 m.gm. of Mn. 
 
 The end-point of reaction with the indicator is found by placing 
 drops of the cobalt solution on a white tile, and bringing a drop of 
 the liquid under titration in contact with it, but not actually 
 mixing. The occurrence of an immediate faint green line at the 
 junction of the drops is accepted as the correct reading. 
 
 Process : The ore is dissolved in HC1 with the addition of KC1O 3 as an 
 oxidizer, and care must be taken to have sufficient acid to keep all the 
 manganese in solution. 
 
 Lead alone need not be separated ; copper can be precipitated by lead ; or 
 lead and copper can both be precipitated by aluminium. Cadmium should 
 be precipitated by H 2 S, and the nitrate oxidized. Iron and aluminium are 
 best separated by baric carbonate, but the latter must be free from alkaline 
 carbonates and hydroxides, baric hydroxide and ammonium salts. A salt 
 sufficiently pure for the purpose may be obtained by suspending the ordinary 
 pure carbonate (first proved free from ammonium salts) in warm water for 
 several hours with 2 or 3 per cent, of its weight of baric chloride. 
 
 The well oxidized solution of the ore is put into a 500 c.c. flask, and baric 
 carbonate suspended in water added until the precipitate coagulates. The 
 Avhole is then poured into a beaker, well mixed, allowed to settle, and the 
 clear liquid decanted through a dry filter, and diluted to 500 c.c. Portions 
 of 50, 100, or 200 c.c. of the filtrate are used for each titration. One portion, 
 which should contain between O'Ol and 0'04 gm. of manganese, is diluted to 
 200 c.c., heated nearly to boiling in a porcelain dish, and titrated rapidly 
 with permanganate with vigorous stirring. 
 
 A second portion is made slightly acid with hydrochloric acid, the 
 zinc and manganese are titrated together in the cold with ferroc} 7 anide ; the 
 dark colour of the precipitate suddenly changes to light yellowish green 
 shortly before the end of the reaction. It is not necessary to test with the 
 cobalt solution until 1 or 2 c.c. of the ferrocyanide have been added after 
 the lightening of the precipitate. 
 
 Example : 1 c.c. of the ferrocyanide solution equalled 0'00606 gm. of 
 zinc, or 0'00384 of manganese; 1 c.c. of the permanganate equalled O'OOl 
 gm. of manganese. 2^ gm. of the ore were dissolved, and the iron 
 precipitated and filtered out. 50 c.c. of the solution were diluted, heated, 
 and titrated with permanganate, requiring 18'45 c.c. = 7'38 per cent, of 
 manganese. 100 c.c. titrated with ferrocyanide required 27'85 c.c., of which 
 9'6l c.c. would be used by the manganese present. Deducting this, 18'24 
 c.c. was left for the zinc, equal to 0'11053 gm., or 22'11 per cent. The 
 amounts of zinc and manganese as determined gravimetrically were 22 05 
 and 7' 58 per cent, respectively. 
 
 Von Schulz and Low's Method (Eng. and Min. Jour. 1892, 178). 
 Prepare a solution of potassic ferroc} r anide by dissolving 44 gm. of the pure 
 salt in distilled water and diluting to 1 liter. Then prepare a standard 
 solution as follows : Dissolve 200 m.gm. of pure zinc oxide in 10 c.c. of pure-, 
 
350 VOLUMETRIC ANALYSIS. 82. 
 
 strong hydrochloric acid. Add 7 gm. of chemically pure ammonic chloride 
 (free from copper) and about 100 c.c. of boiling water. Titrate the clear 
 liquid with the ferrocyanide solution until a drop tested on a porcelain plate 
 with a drop of a strong aqueous solution of uranic acetate shows a brown 
 tinge. About 16 c.c. of ferrocyanide solution are required. When the brown 
 tinge is obtained, see if any of the previous tests subsequently develop 
 a similar colour, and, if so, correct the burette reading accordingly. Usually 
 the correction for two previous drops has to be made. One c.c. of this 
 solution equals about O'Ol gm. of zinc. 
 
 In the test take exactly 1 gm. of ore and treat it in a 3^-in. porcelain 
 crucible with 25 c.c. of a saturated solution of chlorate of potash in nitric 
 acid. Do not cover the vessel at first, but warm gently until any violent 
 action is over and greenish vapours have ceased to come off. Then cover 
 with a Avatch-glass and boil rapidly to complete dryness, but avoid over- 
 heating and baking. A drop of nitric acid adhering to the cover does no 
 harm. Cool sufficiently and add 7 gm. of ammonic chloride, 15 c.c. of 
 strong ammonia, and 25 c.c. of hot water. Cover and boil for one minute, 
 and thea, with a rubber-tipped glass rod, see that all solid matter on the 
 cover, sides, and bottom of the crucible is either dissolved or disintegrated. 
 Filter into a beaker and wash several times with hot ammonic chloride 
 solution (10 gm. to the liter). A blue-coloured filtrate indicates the 
 presence of copper. In that case add 25 c.c. of strong pure hydrochloric 
 acid and about 40 gm. of granulated test lead. Stir the lead about in the 
 beaker until the liquid has become perfectly colourless, and continue the 
 stirring for a short time, to make sure that the copper is all precipitated. 
 The solution, which should still be quite hot, is now read}' for filtration. 
 In the absence of copper the lead is omitted and only the acid added. 
 
 About one-third of the solution is now set aside, and the main portion is 
 titrated rapidly with the ferrocyanide until the end-point is passed, using 
 the uranium indicator as in the standardization. The greater part of 
 the reserved portion is now added, and the titration continued with more 
 caution until the end-point is again passed. Then add the remainder of 
 the reserved portion and finish the titration carefully, by additions of 
 two drops of ferrocyanide at a time. Make corrections for the final reading 
 of the burette as in the standardization. In this process cadmium behaves 
 like zinc, and must be separated, if necessary, by some other method. 
 
 Technical process for Ores containing- Iron. Voigt (Zeit. ang. Chem. 
 1889, 307, 308). The solution of the substance in hydrochloric acid is 
 oxidized with nitric acid and diluted to about 100 c.c. Sufficient potassic 
 tartrate to keep the iron in solution is added, and then ammonia to feeble 
 alkalinity, and the liquid is further diluted to about 250 c.c. Standard 
 solution of potassic ferrocyanide is then run in, until a drop of the mixture 
 brought in contact with strong acetic acid develops a permanent blue. The 
 ferrocyanide is of suitable strength if 1 c.c. is equal to O'Ol gm. of zinc. 
 About 46 gm. of the salt are dissolved to a liter, and the solution is standard- 
 ized against one of zinc made by dissolving 12'461 gm. of zinc oxide in 
 hydrochloric acid and diluting to a liter; 10 c.c. of this solution are mixed 
 with 5 gin. of potassic tartrate, a few drops of ferric chloride, ammonia, and 
 water to 250 c.c., and should require 10 c.c. of the ferrocyanide. An essential 
 condition is that the excess of ammonia should be as small as possible. 
 Incorrect results are obtained when much manganese is present ; lead is not 
 injurious. 
 
 6. Estimation of Zinc as Oxalate. 
 
 This method is based on the fact that all the metals of the 
 magnesia group are precipitated in the absence of alkaline salts by 
 
82. ZINC. 351 
 
 oxalic acid, with the addition of alcohol. The cases are very few 
 in which such a method can be made available, but the process as 
 described by W. G. Leison (Silliman's Journ. Sept. 1870) 
 is here given. 
 
 The zinc compound is obtained, preferably as sulphate, in neutral solution, 
 and strong solution of oxalic acid and a tolerable quantity of strong alcohol 
 are added. Zinc oxalate quickly separates in a fine crystalline powder, which 
 when washed by alcohol from excess of oxalic acid and dried, can be dissolved 
 in hot dilate sulphuric acid, and titrated with permanganate ; the amount 
 of zinc is calculated from the weight of oxalic acid so found. If the zinc 
 oxalate be washed on a paper filter, it cannot be separated from the paper 
 without contamination with fibres of that material, which would of course 
 affect to some extent the permanganate solution. Hence it is advisable to 
 filter through very clean sand, best done by a special funnel ground conical 
 at the throat ; into this is dropped a pear-shaped stopper with a long stem, 
 the pear-shaped stopper fitting the funnel throat tightly enough to prevent 
 sand but not liquids from passing; a layer of sand being placed upon the 
 globular end of the stopper and packed closely, the liquid containing the 
 oxalate is brought upon it and so washed ; finally the stopper is lifted, the 
 sand and oxalate washed through with dilute acid into a clean flask, and the 
 titratiou completed. 
 
 7. Zinc Dust. 
 
 The value of this substance depends upon the amount of metallic 
 .zinc contained in it ; but as it generally contains a large proportion 
 of zinc oxide, the foregoing methods are not available for its 
 valuation. The volume of hydrogen yielded by it on treatment 
 with acids appears to be the most accurate, as suggested by 
 Presenius or by Barnes (/". S. C. I. v. 145). This may very 
 well be done in the nitrometer with decomposing flask, and 
 comparing the volume of gas yielded by pure zinc and the sample 
 of dust under examination. 
 
 "Weil decomposes a known volume of standard solution of 
 copper by digesting 0'4 gm. of the zinc dust in a platinum capsule, 
 with 50 c.c. of copper solution containing 0*5 gm. Cu. The zinc- 
 precipitates metallic copper equivalent for equivalent. After 
 removing the zinc refuse and metallic copper by filtration and 
 washing, an aliquot portion of the filtrate is titrated with standard 
 tin solution for the excess of copper as described in 58.6. The 
 amount, of Cu precipitated, when multiplied by the factor 1'0236, 
 will give the Zn in the 0'4 gm. of dust. 
 
 Many other methods have been proposed for the valuation of 
 this substance. The best is that of Klemp (Z. a. C. xxix. 253), 
 which consists in treating the dust with an excess of caustic 
 potash and potassic iodate ; the latter is reduced in definite pro- 
 portion by the metallic zinc to potassic iodide, and the latter 
 estimated by distillation in the iodometric apparatus, figs. 37 or 
 38. The solutions of potash and iodate must be somewhat con- 
 centrated, and the mixture with the zinc dust must be intimate, 
 which may be best secured by shaking the whole together in 
 
352 VOLUMETEIC ANALYSIS. 83. 
 
 a well-stoppered 200 c c. flask with glass beads. A 5 per cent, 
 solution of iodate should be used, and the potash solution should 
 be about 40 per cent. For 1 gin. of the dust, 30 c.c. of the iodate 
 and so much of the potash solution should be used as to measure 
 130 c.c. The weighed substance, together with the beads, being 
 already in the flask, the solutions are added, the stopper greased 
 with vaseline, tied down and shaken for five minutes, then heated 
 on the water bath, with occasional shaking, for one hour. 
 (Digestion without heat gives practically the same results.) The 
 flask is then cooled and the contents diluted to 250 or 500 c.c., and 
 50 or 100 c.c. placed in the distilling flask, acidified with sulphuric 
 acid, and the iodine so set free distilled into solution of potassic 
 iodide, and titrated with thiosulphate in the usual way. Each 
 0*2 gm. of iodine so found = 0*25644 gm. Zn or 1 part of Zn should 
 theoretically liberate 07799 part of I. 
 
 8. Zinc Oxide and Carbonate. 
 
 Benedikt and Cantor (Zeit. angew. CJiem. 1888, 236, 237) 
 shew that zinc oxide and carbonate can be accurately titrated with 
 standard acid and alkali, using methyl orange as indicator, and 
 other zinc salts, using phenolphthalein. The oxide or carbonate is 
 dissolved in excess of acid, and the excess titrated back by soda 
 solution. Zinc salts are dissolved in water (50 c.c. to O'l gm. ZnO), 
 phenolphthalein is added, and then standard soda solution to intense 
 red colour. A few more c.c. of soda are then added, the mixture 
 is boiled for some minutes, and the excess of soda titrated, If 
 either free acid or zinc oxide is present in the zinc salt, it is 
 neutralized in presence of methyl orange by alkali or acid, as the 
 case may be. 
 
 OILS AND FATS. 
 
 83. THE examination of fatty matters by titration of their 
 soluble or volatile and total fatty acids has of late assumed very 
 considerable importance, in view of furnishing results which aid 
 in determining the amount of adulteration to which they are 
 subject. It has been found especially serviceable in the case of 
 butter, and two methods are in vogue, both of which give good 
 results. The same methods are more or less available for the 
 examination of fats other than butter ; and further experiments 
 by various operators have rendered the methods of value for 
 differentiating various fatty bodies. The titration methods, more 
 especially for butter, were originated by Koettstorf er (Z. a. C. 
 xix. 199) and Keichert (Z. a. (7. xviii. 68): this latter method 
 has been considerably improved by the suggestions of Wollny, 
 based on a long series of experiments (Bied. Centr. 699, also 
 Analyst xii. 203), and is now known commonly as the Reichert- 
 Wollny method. 
 
83. OILS AND FATS. 353 
 
 Another interesting method of examining the nature and 
 composition of various fats, is by the power they possess of 
 absorbing bromine or iodine. This method, as regards bromine, 
 has been worked out with considerable diligence and ability by 
 Mills and Snod grass (J. S. C. /, ii. 435 and ibid iii. 366), also 
 by Allen (ibid v. 68, and also in his well-known treatise on 
 Organic Analysis). The iodine method of Hubl is described in 
 /. $. G. I. iii. 641. These various methods have been most 
 voluminously discussed in their chemical and practical aspects, so 
 that it must suffice here to give shortly the methods of analysis. 
 It is only perhaps necessary to say that Hubl's iodine method is 
 now generally adopted in preference to the absorption by bromine 
 except in the case of Hehner's gravimetric bromine method. 
 The literature on this subject is extremely voluminous and cannot 
 be quoted here. An excellent digest of the Various methods and 
 opinions is given in Allen's Organic Analysis, also by Droop 
 Kichmond (Analyst xvii. 171). 
 
 Butter. 
 
 Bei chert's Method. This method is based on the fact, that 
 butter fat in a genuine state never contains less than 4 per cent, 
 of volatile fatty acids, whereas other fats contain either none at all 
 or very much less than butter. The process consists in saponifying 
 the fat to be examined by an alkali, separating the fixed acids by 
 neutralizing the alkali, and distilling off the volatile acids (chiefly 
 butyric and caproic) for titration with standard acid. In this and 
 Koettstorfer's method, where also alcoholic solution of caustic 
 alkali is used, it is essential to avoid absorption of CO 2 by long 
 exposure. 
 
 The necessary solutions are : 
 
 1. Standard Baric hydrate. -~ strength is most convenient, 
 but any solution approximating to that strength may be used, and 
 a factor found to convert it to that strength in calculating the 
 results of titration. It must be carefully preserved from CO 2 by 
 any of the usual arrangements, and where a constant series of 
 titrations are carried on, it is best to have a store bottle and 
 burette fitted, as shown p. 12, fig. 11. 
 
 2. Phenol phthalein, see p. 37. 
 
 3. Alcohol of about 95 per cent, strength, recently distilled from 
 caustic soda. 
 
 4. Solution of caustic soda. Made by dissolving 100 gm. of good 
 sodic hydrate in 100 c.c. of distilled water which has been recently 
 well boiled and cooled ; this solution will not be contaminated with 
 CO 2 to any extent, since any JSTa 2 C0 3 which might be formed is 
 quite insoluble in the strong solution ; it must be allowed to 
 stand until quite clear, then poured off and well preserved. 
 
 Leffmann and Beam advocate the use of alkali-glycerol in 
 
 A A 
 
VOLUMETRIC ANALYSIS. 
 
 83. 
 
 place of alcoholic alkali in saponifying the fat, and the 
 re-agent is made by mixing 25 c.c. of the 50 per cent, 
 caustic soda described above with 125 c.c. of pure glycerine. 
 10 c.c. of this solution will perfectly saponify 5 gm. of 
 butter fat when the two are heated carefully over a Buns en flame 
 in a small flask for five minutes with shaking. The operation of 
 evaporating off the alcohol together with the risks of absorption 
 of CO 2 is thus obviated. After complete saponification, the soap is 
 dissolved in about 100 c.c. of water added, at first, drop by drop, 
 and the distillation carried on as usual. 
 
 5. Dilute sulphuric acid for separating the fatty acids, is made 
 by diluting 25 c.c. of strongest H 2 S0 4 to a liter. 
 
 6. The apparatus for digestion and distillation are shown in 
 fig. 52, the same Erlenmeyer flask being used for the digestion 
 and for the distillation. The distilled liquid drops into a small 
 
 Tig. 52. 
 
 funnel containing a small porous filter for separating any scum 
 which may pass over with the distillate ; the receiver holding the 
 funnel is marked at 50 c.c. and 100 c.c., so as to be available for 
 either 2 '5 gm. or 5 gm. of butter fat. 
 
 The following method of manipulation as drawn up by the 
 Association of Official Agricultural Chemists, U.S.A., is recom- 
 mended as being all that is required to ensure accuracy, and 
 applies to the treatment of approximately 5 gm. of fat for each 
 operation. Many operators prefer to take about half that 
 quantity, which saves time, and need not be any the less accurate. 
 
 Process, Weighing the Fat : The butter or fat to be examined should be 
 melted and kept in a dry warm place at about 60 C. for two or three hours 
 until the moisture and curd have entirely settled out. The clean supernatant 
 fat is poured off and filtered through a dry filter paper in a jacketed filter 
 containing boiling water, to remove all foreign matter and any traces of 
 
83. OILS AND FATS. 355 
 
 moisture. Should the filtered fat in a fused state not be perfectly clear the 
 treatment above mentioned must be repeated. 
 
 The sapoiiific-ition flasks are prepared by having them thoroughly washed 
 with water, alcohol, and ether, wiped perfectly dry on the outside, and 
 heated for one hour to 100 C. The flasks should then be placed in a tray 
 by the side of the balance and covered with a silk handkerchief until they 
 are perfectly cool. They must not be wiped with a silk handkerchief within 
 fifteen or twenty minutes of the time they are weighed. The weight of 
 each flask is determined accurately, using a flask for a counterbalance or not, 
 as may be convenient. The weight of the flasks having been accurately 
 determined they are charged with the melted fat in the following way: 
 
 A pipette with a long stem marked to deliver 5'75 c.c. is warmed to 
 a temperature of about 50 C. The fat having been poured back and forth 
 once or twice into a dry beaker in order to thoroughly mix it, it is taken up 
 in the pipette, the nozzle of the pipette carried to near the bottom of the 
 flask, it having been previously wiped to remove any adhering fat. The 
 5'75 c.c. of fat are allowed to flow into the flask and the pipette is removed. 
 After the flasks have been charged in this way they should be re-covered 
 with the silk handkerchief and allowed to stand fifteen or twenty minutes, 
 when they are again weighed to ascertain the exact amount of fat. 
 
 The Saponificati.on : 10 c.c. of 95 per cent, alcohol re-distilled from caustic 
 soda are added to the fat in the flask, 2 c.c. of the concentrated soda solution are 
 udded, a soft cork stopper inserted in the flask, and tied down with a piece of 
 twine. The saponification is then completed by placing the flasks upon the 
 water or steam bath. The flasks during the saponification, which should last 
 for one hour, should be gently rotated from time to time, being careful not 
 to project the soap for an} r distance up the sides of the flask. At the end of 
 an hour the flasks, after having been cooled to near the room temperature, 
 are opened. 
 
 Removal of the Alcohol : The stoppers having been laid loosely in the 
 mouth of the flasks the alcohol is removed by dipping the flasks 
 into a steam bath. The steam should cover the whole of the 
 flask except the neck. After the alcohol is nearly removed, frothing 
 nriy be noticed in the soap, and to avoid any loss from this cause, or any 
 creeping of the soap up the sides of the flask, it should be taken from the 
 bath and shaken to and fro until the frothing disappears. The last traces 
 of alcohol vapour may be removed from the flask by waving it briskly, 
 mouth down, to and fro. Complete removal of the alcohol with the pre- 
 cautions above noted should take about forty-five minutes. 
 
 Dissolving the Soap : After the removal of the alcohol the soap should 
 be dissolved by adding 100 c.c. of recently boiled distilled water, and warmed on 
 the steam bath with occasional shaking until the soap is completely dissolved. 
 
 Setting Free the Fatty Acids : When the soap solution has cooled to 
 about 60 or 70 C., the fatty acids are separated by adding 40 c.c. of the 
 dilute sulphuric acid mentioned above. 
 
 MMing the Fatty Acids: The flasks should now be re-stoppered as in the 
 first instance, and the fatty acids melted by replacing the flasks on the steam 
 bath. According to the nature of the fat examined the time required for 
 the fusion of the fatty acids may vary from a few minutes to hours. 
 
 The Distillation : After the fatty acids are completely melted, which can 
 be determined by their forming a transparent oily layer on the surface of 
 the water, the flasks are cooled to room temperature and a few pieces of 
 pumice stone added. The pumice stone is prepared by throwing it, at white 
 heat, into distilled water, and keeping it under water until used. The flask 
 is now connected with the condenser, slowly heated with a naked flame until 
 ebullition begins, and then the distillation continued by regulating the flame 
 in such a way as to collect 100 c.c. of the distillate in as nearly as possible 
 thirty minutes. 
 
 A A 2 
 
356 VOLUMETRIC ANALYSIS. 83. 
 
 Titration of the Volatile Acids: The 100 c.c. of the filtered distillate are 
 poured into a beaker holding from 200 250 c.c., 0'5 c.c. of phenolphthalein 
 solution added, and decinormal baric hydrate run in until a red colour is 
 produced. The contents of the beaker are then returned to the measuring- 
 flask to remove any acid remaining therein, poured again into the beaker, 
 and the titration continued until the red colour produced remains 
 apparently unchanged for two or three minutes. 
 
 It must be borne in mind that this method is not one of strict 
 chemical accuracy, but the experience of the author and a host of 
 other very competent operators, clearly show that the distillate 
 from 5 gm. of genuine normal butter fat when carried out as 
 described, should require not less than 25 c.c. of ~j alkali to 
 neutralize the volatile acids present. It is true that butters known 
 to be genuine have occasionally been found to give lower figures 
 from some unexplained causes, one of which seems to be due to 
 milk taken from cows towards the end of their period of lactation. 
 The figure may also rise to 32 or 33 c.c. of alkali. This is often 
 the case with butters produced in warmer climates than Great 
 Britain. The general average for butters taken from the mixed 
 milk of a number of cows will be between 27 and 28 c.c., whereas 
 margarine will rarely require more than 0'5 c.c., beef fat and 
 lard about the same, while cocoa-nut fat, which gives the highest 
 figures, requires about 7 c.c. 
 
 It may therefore be concluded that any sample of butter fat, 
 which requires less than 25 c.c. of ~ alkali must be looked upon 
 with suspicion. 
 
 Koettstorfer's Method. This operation estimates the saponi- 
 fying equivalent of any fatty substance, but is allowed on all 
 hands to be less satisfactory in discriminating mixtures of other 
 fats with butter, although extremely useful. In this method the 
 whole of the acids existing in the fat are estimated. The solutions 
 required are the following : 
 
 Standard Hydrochloric Acid. Semi-normal strength, i.e., 18*185 
 gm. per liter. 
 
 Standard Solution of Caustic Potash in Alcohol. Methylated 
 spirit, previously digested with permanganate, dehydrated with dry 
 potassic carbonate, then distilled, rejecting the first portions, may 
 be used in place of pure alcohol. In any case the strength should 
 not be less than 90 per cent., and the solution should be freshly 
 made to avoid any deep colouration likely to interfere with the 
 indicator. As it rapidly changes in strength, it is not possible to 
 rely upon its being semi-normal, but it should be roughly adjusted 
 at about that strength with absolutely accurate hydrochloric acid, 
 and a blank experiment made side by side with each titration of 
 fat. The excess of potash used in the fat titration is thus expressed 
 in terms of acid, and to arrive at the percentage of potash each 
 c.c. is multiplied by 0'02805. The saponification equivalent of 
 the fat or oil is found by dividing the weight in milligrams of the 
 
83. 
 
 OILS AND FATS. 
 
 357 
 
 sample by the number of c.c. of normal (not ^) acid corresponding 
 to the alkali neutralized by the oil. If the percentage of potash 
 is known, the saponifying equivalent may be found l}y dividing 
 this percentage into 5610, or if j^aHO is the alkali used, 
 into 4000. 
 
 Process : From 2 to 2'5 gm. of the fat, previously purified by melting and 
 filtration, are carefully weighed into a flask fitted with vertical tube. 25 c.c. 
 of standard potash are then added, the mixture heated on the water bath to 
 gentle boiling, with occasional agitation, until a. perfectly clear solution is 
 obtained. Koettstorfer recommends heating for fifteen minutes ; but in 
 the case of butters this is generally more than sufficient ; with other 
 fats twenty minutes to half an hour may be required. At the end of the 
 saponification the flasks are removed from the bath, a definite and not too 
 small a quantity of phenolphthalein added, and the titration carried out with 
 as little exposure to the air as is possible. 
 
 The method of calculation adopted by Koettstorfer is to 
 ascertain the number of milligrams of KHO required to saturate 
 the acids contained in 1 gm. of fat, or, in other words, parts 
 per 1000. He found that, operating in this way, pure butters 
 required from 221*5 to 232 '4 m.gm. of KHO for 1 gm., whereas 
 the fats usually mixed with butter, such as beef, mutton, and pork 
 fat, required a maximum of 197 m.gm. for 1 gm., and other oils 
 and fats much less. 
 
 Practically this means that the amount of KHO required for 
 genuine butters ranges from 23*24 to 22'15 per cent., the latter 
 being the inferior limit. If caustic soda is used instead of potash, 
 other numbers must of course be used. 
 
 My experience, and, I believe, also that of others, shows that 
 the method cannot be depended upon in the case of old re-melted 
 butters, although perfectly genuine. 
 
 The following list shows the parts of KHO required per 1000 
 of fat ; the first four being calculated from their known equivalents, 
 the rest obtained experimentally by Koettstorfer, Allen, 
 Stoddart, or Archbutt: 
 
 Tripalinitin 208'8 Linseed - 189 195 
 
 Tristearin - - - 189 1 Cotton Seed - - 191196 
 
 Trioleiii - - - 190'4 Whale - - - 190191 
 
 Tributyr-in - - - 557'3 Seal - 191196 
 
 Cocoamit Oil - - 270-0 Colza and Rape - - 175179 
 
 Dripping - - - 197'0 Cod Oil 182187 
 
 Lard - 195'6 Pilchard - - - 186187 
 
 Horse Fat - - - 199'4 Castor - - - 176178 
 
 Lard Oil - - - 191196 Sperm - - - 130134 
 
 Olive Oil - - - 191196 Shark 84'5 
 
 Niger Oil - - - 189191 
 
 A further application of this method may be made in estimating 
 separately the amounts of alkali required for saturating the free 
 fatty acids and saponifying the neutral glycerides or other ethers 
 of any given sample of fat, oil, or wax (see Allen^ Organic 
 Analysis ii. 45, 76), 
 
358 VOLUMETRIC ANALYSIS. 83. 
 
 Titration of Miscellaneous Oils and Fats with Bromine or Iodine. 
 
 The best method of carrying out this examination as regards 
 bromine, appears to be that of Mills and Snodgrass, to which 
 reference has previously been made. The idea of using bromine 
 is by no means new. Cailletet in 1857 adopted such a method ; 
 but the difficulty then, and up to the time when the task was 
 undertaken by the operators mentioned, was the accurate measure- 
 ment of the excess of bromine used, and the adaptation of such 
 a solvent for both the fats and the bromine as would exclude the 
 presence of water, and the tendency to form substitution products 
 of variable and unknown character in preference to merely additive 
 products. 
 
 Our knowledge of the exact composition of the great family of 
 fats and oils is at present limited, and it is not possible to make 
 this reaction possess any strict chemical valency ; but experiment 
 has shown that there are certain well-defined fats which absorb 
 within a very narrow limit the same amount of the halogen under 
 the same conditions, and hence the method may be made highly 
 suggestive as to mixtures of various fats whose absorption powers 
 have been observed. 
 
 In the first instance the common solvent used for the fat 
 and the bromine was carbon disulphide ; but although very good 
 results were obtained, compared with solvents previously tried by 
 other operators, there were the drawbacks of its offensive smell, 
 and .the solutions of bromine in it did not possess much stability. 
 Finally, Dr. Mills adopted carbon tetrachloride as. the medium 
 with the happiest effects ; and it was found that the bromide 
 solution could be preserved for at least three months without 
 diminution of standard. On the other hand, by using this 
 medium, there is the necessity of working with greater delicacy, 
 since the presence of the merest trace of water has more effect in 
 producing substitution compounds than in the case of the disulphide. 
 The accurate estimation of the excess of bromine, after the absorp- 
 tion is complete, is necessarily a matter of great importance ; and 
 this can be done either by comparison of colour with bromine solu- 
 tion of known strength (the least effective method) ; or by titration 
 with thiosulphate, using starch and potassic iodide as the indicator, 
 which is better. But, best of all, the operators after long research 
 found that by using j3 naphthol (a substance which is readily and 
 cheaply obtainable, and which forms in the presence of carbon 
 tetrachloride a mono-bromo derivative) they could construct 
 a solution of corresponding strength to the standard bromine, and 
 thus titrate back in the same way as is commonly practised in 
 alkalimetry. Very fair results were obtained colorimetrically by 
 adopting the device of interposing a stratum of pctassic chromate 
 solution, so as to neutralize the yellow colour produced with 
 some of the fish oils, and which tended to mask the red colour of 
 
83. 
 
 OILS AND FATS. 
 
 359 
 
 the bromine. Experiments showed that, using a bromine solution 
 having a mean standard of 0*00644 grn. per c.c., the average 
 probable error per cent, in a single result, when adopting the colour 
 method or the thiosulphate and iodine was 0*62, whereas with 
 /3 naphthol it was reduced to 0*46. But it is hardly necessary to 
 say that, using such a small portion of material as is absolutely 
 necessary in order to avoid secondary results, considerable care 
 and practice are required. The sample of oil or fat must be dried 
 as completely as possible, by heating and subsequent filtering 
 through dry scraps of bibulous paper, or through dry double filters, 
 before being weighed. 
 
 Process: O'l to 0'2 gm. of the fat is dissolved in 50 c.c. of the tetra- 
 chloride and standard bromine added, until at the end of 15 minutes there 
 is a permanent red colour. If the colorimetric method is used 50 c.c. of 
 tetrachloride is tinted with standard bromine to correspond. If the iodine 
 re-action, the solution of brominated material is added to potassic iodide and 
 starch, and T ^ sodic thiosulphate delivered in from a burette till the colour is. 
 discharged. If, on the other hand, the standard naphthol solution is used, 
 it is also cautiously added from a burette until the colour is removed. It is 
 imperative that the operations in all cases be carried on out of direct sunlight. 
 If the operator is unable to use carbon tetrachloride, the disulphide may be 
 used; but the solution of bromine in this medium is less stable, and must 
 be checked more frequently. Somewhat larger portions of oil or fat may 
 however be used for the analysis. 
 
 * 
 
 It may be of service to give some few of the results obtained 
 by Mills and Snodgrass. 
 
 Absorption per cent. 
 
 OILS. 
 
 FATS. 
 
 WAXES. 
 
 Almond (from Beef 
 
 35-01 
 
 Beeswax - 
 
 o-oo 
 
 bitter fruit) 26'27 
 
 Butter (fresh) - 
 
 27-93 
 
 Carnauba 
 
 33-50 
 
 Do. (from sweet) 53'74 
 
 Do. (commercial) 
 
 25-0 
 
 Japan (1) 
 
 2-33 
 
 Cod - - - 83-00 
 
 Butterine Scotch 
 
 36-32 
 
 Do. (2) 
 
 1-53 
 
 Nut - - - 30-24 
 
 Do. (French) - 
 
 39-71 
 
 Myrtle - 
 
 6-34 
 
 Ling Liver - 82'44 
 
 Cocoanut - 
 
 570 
 
 
 
 Mustard - - 46' 15 
 
 Vaseline - 
 
 5-55 
 
 
 
 Neatsfoot - - 38'33 
 
 Stearic Acid 
 
 o-oo 
 
 
 
 Olive - - 60-61 
 
 Lard 
 
 37-29 
 
 
 
 Palm - - 35-00 
 
 O 1 *' *T.O 4 
 
 
 
 
 
 Seal - - - o7 34 
 Whale - - 30-92 
 
 
 X 
 
 NIVERSITY) 
 
 Linseed - - 76'09 
 Mineral Oil - 30'31 
 
 
 (u 
 
 Shale Oil ) 
 
 
 X 
 
 according to > 22 to 12 
 
 
 
 sp. gr. ) 
 Aniline - - 169'8 
 
 
 
 Turpentine (dry) 236'0 
 
 
 
360 VOLUMETRIC ANALYSIS. 83.' 
 
 The same operators determined the percentage absorption by 
 pure anhydrous turpentine, aniline and olive oil purified by 
 filtration after long standing at low temperature. The calculated 
 values are based on the known ratios 
 
 C io H i6 . Bl 4 C 6 H 7 ^ : Br 2 and (C 3 H 5 ) (C 18 H 83 2 ) 3 : Br. 
 
 The mean of three estimations each in turpentine and aniline were 
 236*0 and 169*8 per cent., five estimations in olive oil (triolein) 
 54 per cent. The percentage by calculation is respectively 235'3, 
 172, and 54-3. 
 
 The Iodine Method. This has been worked out by Hubl 
 and others, but is not nearly so expeditious as the method just 
 described; though, as before stated, it has to a large extent replaced 
 it, owing mainly to the fact that less trouble is required, and the 
 reactions involved are less delicate while equally accurate. 
 The Standard Iodine Solution. This is made by dissolving 
 respectively 5 gm. of iodine and 6 gm. of mercuric chloride in 
 separate portions of strongest alcohol, of 100 c.c. each, then mixing 
 the two liquids, and allowing to stand for 12 hours before taking 
 the standard with thiosulphate and starch. This solution must 
 always be standardized before use, and it is advisable not to mix 
 a large quantity unless, it can be consumed at once. 
 
 Process : 0'2 to 0'5 gm. of the fat or oil is dissolved in 10 c.c. of purest 
 chloroform in a well-stoppered wide-mouthed bottle, and 20 c.c. of the iodine 
 solution added. After not less than two hours' digestion the mixture 
 should possess a dark brown tint ; under any circumstances it is necessary 
 to have a considerable excess of iodine (at least double the amount 
 absorbed ought to be present), and the digestion should be from six 
 to eight hours. At tli3 end of that time the liquid is transferred to 
 a beaker, the bottle rinsed out with some solution of potassic iodide, the 
 rinsings added to the beaker, then more of the iodide solution added until all 
 free iodine is dissolved, the whole is then diluted with 150 c.c. of water, 
 and y^- thiosulphate delivered in till the colour is nearly discharged. 
 Starch is then added, and the titration finished in the usual way. 
 
 If after standing, say two hours, the amount of iodine is insufficient, it is 
 "best to make a fresh experiment with either less fat or more iodine. 
 
 The numbers obtained by Hubl are given in /. S. C. /. iii. 642. 
 
 A blank experiment should in every case be made side by side 
 with the sample, using the same proportions of chloroform and 
 iodine solution. 
 
 Example with pure Lard (E. TT. T. Jones): About 20 drops of the 
 melted lard were dropped into a carefully weighed dry bottle, the weight of 
 fat taken, the bottle then placed on the water bath so as to melt the fat, and 
 then before quite cold the 10 c.c. of chloroform added and mixed. "When 
 quite cold 20 c.c. of the iodine mixture were measured in and the whole 
 allowed to stand the required time. The thiosulphate was not of strict f^- 
 strength, but a careful titration showed that each c.c. =0'0127678 gm. 1. 
 The amount of fat taken was 0'5C6 gm., and after digestion with 20 c.c. of 
 the Hubl solution required 9'4 c.c. of thiosulphate. The 20 c.c. of Hubl 
 
83. OILS AND FATS. 361 
 
 originally required 35'6 c.c. of thiosulphate, hence 35'6 9'4 26*2 x 
 
 -I ,\r\ 
 
 O'O 127678 x ~- ^ = 59'1 % of iodine. 
 O'obb 
 
 Allen states that, in both the bromine and iodine methods of 
 titration, the amount of halogen taken up may be considered as 
 a measure of the unsaturated fatty acids (or their glycerides) 
 present. Thus, the acids of the acetic or stearic series exhibit no 
 tendency to combine with bromine or iodine under the conditions 
 of the experiments, while the acids of the acrylic or oleic series 
 assimilate two, and the acids of the linoleic series four atoms of 
 the halogen. 
 
 We are indebted to K. T. Thompson and H. Ballantyne 
 (/. S. C. I. ix. 588) for a very careful revision of the constants 
 required in the analysis of Oils and Fats, the results of which are 
 given in the following table.""" The lards operated upon were 
 rendered by themselves and are therefore genuine. The fact is 
 brought out that for each O'l increase in specific gravity, there is 
 an increase of 1 '3 per cent, of iodine absorption, and beef fat seems 
 to follow the same rule. Cotton seed oil shows only about half 
 that proportion. 
 
 In using the iodine absorption method these operators found 
 that some oils required fully eight hours for complete absorption, 
 and they recommend, as a rule, to start the digestion in the evening 
 and titrate the solutions on the following morning. 
 
 * Since the figures in the following table were published, the authors have revised 
 them by further experiments (.T. >. o'. JT. x. 233), and compared them with results 
 obtained by other chemists. The conclusion is that in the case of Olive oils, the 
 figures may vary for iodine absorption from 79 % in Gioja to 88'9 in Mogadore oil; 
 slight variations also occur in the potash neutralizing power, the numbers being 
 generally too low. 
 
362 VOLUMETRIC ANALYSIS. S3. 
 
 Table of Constants in the Analysis of Oils. 
 
 Nature of Oil or Fat. 
 
 Sp. Gr. 
 at 15-5 C. 
 
 Sp. Gr. 
 at 99 J C. 
 
 Iodine 
 Absorptn. 
 
 KOH 
 
 Neutrlizd. 
 
 Free Acid. 
 
 
 
 
 per cent. 
 
 per cent. 
 
 per cent. 
 
 Olive (Gioja) 
 
 915-6 
 
 
 
 79-0 
 
 19-07 
 
 9-42 
 
 Olive (Gioja) after re- 
 
 
 
 
 
 
 moval of free acid ... 
 
 915-2 
 
 
 
 79-0 
 
 19-07 
 
 None. 
 
 Olive 
 
 914-8 
 
 _'_ 
 
 83-2 
 
 18-93 
 
 3-86 
 
 'Olive 
 
 9147 
 
 
 
 80-0 
 
 
 
 23-78 
 
 Olive 
 
 916'8 
 
 ___ 
 
 83'1 
 
 19-00 
 
 5'19 
 
 Olive 
 
 916-0 
 
 
 
 81-6 
 
 
 19-83 
 
 Olive (for dyeing) 
 
 915-4 
 
 
 
 78-9 
 
 19-00 
 
 9-67 
 
 Olive 
 
 914-5 
 
 
 
 86-4 
 
 18-90 
 
 11-28 
 
 Olive (for cooking) 
 
 915-1 
 
 
 
 83-1 
 
 19-20 
 
 4-15 
 
 Olive (for cooking) 
 
 916-2 
 
 
 
 81-2 
 
 1921 
 
 Not done 
 
 Lard (from omentum) ... 
 
 
 
 859-8 
 
 52-1 
 
 
 
 
 
 Lard (from leg) 
 
 
 
 860-5 
 
 61-3 
 
 
 
 
 
 Lard (from ribs) 
 
 
 
 860-6 
 
 62-5 
 
 
 
 
 
 Beef fat (from suet) ... 
 
 
 
 857-2 
 
 34-0 
 
 
 
 
 
 Beef fat (oleomargarine) 
 
 
 
 858-2 
 
 462 
 
 
 
 
 
 Pat from marrow of ox... 
 
 
 
 858'5 
 
 45-1 
 
 19-70 
 
 
 
 Fat from bone of ox ... 
 
 
 
 859-2 
 
 47'0 
 
 19-77 
 
 
 
 Cotton seed 
 
 923-6 
 
 8C8-4 
 
 110-1 
 
 
 
 
 
 Cotton seed 
 
 922-5 
 
 . . 
 
 106-8 
 
 19-35 
 
 027 
 
 Linseed (Baltic) 
 
 934-5 
 
 
 
 187-7 
 
 19-28 
 
 
 
 Linseed (East India) ... 
 
 931-5 
 
 
 
 178-8 
 
 19-28 
 
 
 
 Linseed (Eiver Plate) ... 
 
 932-5 
 
 
 
 175*5 
 
 19-07 
 
 
 
 Linseed 
 
 932-5 
 
 
 
 173-5 
 
 19-00 
 
 0'76 
 
 Linseed 
 
 931-2 
 
 
 
 168-0 
 
 19-00 
 
 
 
 Rape 
 
 916-8 
 
 
 
 105-6 
 
 17-53 
 
 243 
 
 Rape 
 
 913-1 
 
 
 
 100'7 
 
 17-33 
 
 . . 
 
 Rape 
 
 914"5 
 
 
 104'1 
 
 17-06 
 
 2-53 
 
 Rape 
 
 915-0 
 
 
 
 104-5 
 
 17-19 
 
 3-10 
 
 Rape 
 
 914-1 
 
 
 
 100-5 
 
 17-39 
 
 
 
 Castor (commercial) 
 
 967-9 
 
 
 
 83-6 
 
 18-02 
 
 2-16 
 
 Castor (commercial) 
 
 965-3 
 
 
 
 
 
 17*86 
 
 
 
 Castor (medicinal) 
 
 963-7 
 
 
 
 
 
 17-71 
 
 
 
 Arachis (commercial) ... 
 
 920-9 
 
 
 
 987 
 
 1921 
 
 6-20 
 
 Arachis (French refined) 
 
 917-1 
 
 
 
 98-4 
 
 IS'93 
 
 0-62 
 
 Lard oil (prime) 
 
 917-0 
 
 
 
 76-2 
 
 
 
 
 
 Southern sperm 
 
 880-8 
 
 
 
 81-3 
 
 13-25 
 
 
 
 Arctic sperm (bottle-nose) 
 
 879-9 
 
 . 
 
 82-1 
 
 13-04 
 
 
 
 Whale (crude Norwegian) 
 
 920-8 
 
 
 
 109-2 
 
 
 
 
 
 Whale (pale) 
 
 919-3 
 
 
 
 110-1 
 
 
 
 
 
 Seal (Norwegian) 
 
 925-8 
 
 
 
 152-1 
 
 
 
 
 
 Seal (cold drawn, pale) . . . 
 
 926-1 
 
 
 
 145-8 
 
 19-28 
 
 
 
 Seal (steamed, pale) 
 
 924-4 
 
 
 
 142-2 
 
 18-93 
 
 
 
 Seal (tinged) 
 
 925-7 
 
 
 
 152-4 
 
 
 
 
 
 Seal (boiled) 
 
 923-7 
 
 
 
 142-8 
 
 
 
 
 
 Menhaden 
 
 931-1 
 
 
 
 160-0 
 
 18-93 
 
 
 
 Newfoundland cod 
 
 924-9 
 
 
 
 1600 
 
 
 
 
 
 Scotch cod 
 
 925-0 
 
 
 
 158-7 
 
 
 
 
 
 Cod liver (medicinal) . . . 
 
 926-5 
 
 
 
 166-6 
 
 18-51 
 
 0-36 
 
 Mineral ,. 
 
 873-6 
 
 
 
 12-8 
 
 - 
 
 
 
 Mineral 
 
 886-0 
 
 
 
 26-1 
 
 
 
 
 
 Rosin 
 
 986-0 
 
 
 
 67-9 
 
 
 
 
8-4. GLYCERIN. 365 
 
 GLYCERIN (GL.YCEROL,). 
 
 C :J H 8 3 = 92. 
 
 84. UP to a very recent time no satisfactory method of 
 determining glycerin had been devised, but the problem has now 
 been solved in a tolerably satisfactory manner. The permanganate 
 method appears to have been originally suggested by Wanklyn, 
 improved by him and Fox, and further elaborated by Eenedikt 
 and Zsigmondy (CJiem. Zeit. ix. 975). It depends on the 
 saponification of the fat, and oxidation of the resultant glycerin 
 by permanganate in alkaline solution, with formation of oxalic 
 acid, carbon dioxide, and water, thus 
 
 C 3 H 8 8 + 30 2 = C 2 H 2 4 + CO 2 + 3H 2 0. 
 
 Aqueous solutions of glycerin may of course be submitted to 
 the method very easily. 
 
 The excess of permanganate is destroyed by a sulphite, the 
 liquid filtered from the manganese precipitate, the oxalic acid then 
 precipitated by a soluble calcium salt in acetic solution, and the 
 precipitated calcic oxalate, after ignition to convert it into carbonate, 
 titrated with standard acid in the usual way, or the oxalic 
 precipitate titrated with permanganate. The oxalic solution may be 
 titrated direct after addition of H' 2 S0 4 with permanganate ; but 
 Allen and Belcher have found this method faulty, probably 
 from the formation of a dithionate, due to the sulphite. On the 
 other hand, they have obtained very satisfactory results by the 
 alkalimetric or the permanganate titration, on known weights of 
 pure oxalic acid and glycerin. 
 
 These operators have also shown that, in the case of dealing with 
 fats, where it has been recommended by Wanklyn and Fox to 
 use ordinary alcohol as the solvent, and by Benedikt methyl 
 alcohol, both these media, especially ethylic alcohol, produce in 
 themselves a variable quantity of oxalic acid when treated with 
 alkaline permanganate, and hence vitiate the process. Again, if it 
 be attempted to avoid this by boiling off the alcohols, there is 
 a danger of losing glycerin.* 
 
 Allen's method with oils and fats is as follows : 
 
 10 gm. of the fat or oil are placed in a strong small bottle, together with 
 4 gm. of pure KH.O dissolved in 25 c.c . of water. A solid rubber stopper is 
 then used to close the bottle, and tied down firmly with wire. It is then 
 placed in boiling water, or in a water oven, and heated, with occasional 
 shaking, from 6 to 10 hours, or until the contents are homogeneous, and all 
 oil}" globules have disappeared. "When saponification is complete, the bottle 
 is emptied into a beaker and diluted with hot water which should give a clear 
 solution, the fatty acids are then separated by dilute acid, filtered, and the 
 filtrate made up to a given volume. 
 
 * In dealing- with waxes or similar bodies including 1 sperm oil, potash dissolved in 
 methyl alcohol must be used for the saponitication, as it is almost impossible to do it 
 with aqueous potash. 
 
364 VOLUMETRIC ANALYSIS. 84. 
 
 This solution, which will usually contain from 0'2 to 0'5 of glycerol, 
 according to its origin, is transferred to a porcelain basin and diluted with 
 cold water to about 400 c c. From 10 to 12 gm. of caustic potash should 
 next be added, and then a saturated aqueous solution of potassic permanganate 
 until the liquid' is no longer green but blue or blackish. An excess does no 
 harm. The liquid is then heated and boiled for about an hour, when a strong 
 solution of sodic sulphite should be added to the boiling liquid until all 
 violet or green colour is destroyed. The liquid containing the precipitated 
 oxide of manganese is then poured into a 500 c.c. flask, and hot water 
 added to 15 c.c. above the mark, the excess being an allowance for the 
 volume of the precipitate and for the increased measure of the hot liquid. 
 The solution is then passed through a dry filter, and, when cool, 400 c.c. of 
 the filtrate should be measured off, acidified with acetic acid, and precipitated 
 with calcic chloride. The solution is kept warm for three hours, or until 
 the deposition of the calcic oxalate is complete, and is then filtered, the 
 precipitate being washed with hot water. The precipitate consists mainly of 
 calcic oxalate, but is liable to be contaminated more or less with calcic; 
 sulphate, silicate, and other impurities, and hence should not be directly 
 weighed. It may be ignited, and the amount of oxalate previously present 
 deduced from the volume of normal acid neutralized by the residual calcic, 
 carbonate, but a preferable plan is to titrate the oxalate by standard 
 permanganate. For this purpose, the filter should be pierced and the 
 precipitate rinsed into a porcelain basin. The neck of the funnel is then 
 plugged, and the filter filled with dilute sulphuric acid. After standing 
 for five or ten minutes this is allowed to run into the basin and the filter 
 washed with water. Acid is added to the contents of the basin in quantity 
 sufficient to bring the total amount used to 10 c.c. of concentrated acid, the 
 liquid diluted to about 200 c.c., brought to a temperature of about 60 C., 
 and decinormal permanganate added gradually till a distinct pink colouration 
 remains after stirring. Each c.c. of permanganate used corresponds to 
 O'0045 gm. of anhydrous oxalic acid, or to 0'004y gm. of gl.ycerin. Operating 
 in the way described, the volume of permanganate solution required will 
 generally range between 70 and 100 c.c. 
 
 C. Mangold '(Zeit. f. angew. Chem. 1891, p. 400) advocates 
 the reduction of the excess of permanganate by hydrogen peroxide 
 in preference to sodic sulphite as used by Allen. The author 
 simplifies the method by carrying out the oxidation in the cold. 
 
 Process : 0'2 to 0'4 gm. of glycerin is dissolved in about 300 c.c. of water, 
 10 gm. potassic hydrate and so much 5 per cent, solution of permanganate 
 is added, that for each part of glycerin about seven parts of permanganate 
 are present. The mixture is allowed to stand at ordinary temperature for 
 half an hour. Hydrogen peroxide is then added until the liquid is 
 colourless, well shaken, filled up to one liter, 500 c.c. are filtered off through 
 a dry filter, boiled for half an hour to destro} r the excess of peroxide, 
 allowed to cool to about 80 C., and after acidulation with dilute sulphuric 
 acid, the oxalic acid titrated with standard permanganate. 
 
 Otto Hehner has experimented largely on the estimation of 
 glycerol in soap leys and crude glycerins, the results of which are 
 given in /. S. C. I. viii. 4. The volumetric methods recommended 
 in preference to the permanganate are the oxidation Avith potassic 
 bichromate or the conversion of the glycerol into triacetin. 
 
 The Bichromate Method.: One part of glycerol is completely 
 
84 GLYCERIN. 365 
 
 converted into carbonic acid by 7 '486 parts of bichromate in the 
 presence of sulphuric acid. The solutions required are : 
 
 Standard Potassic bichromate. 74*86 gm. of pure potassic 
 bichromate is dissolved in water. 1 50 c.c. of concentrated sulphuric 
 acid added, and when cold diluted to a liter. 1 c.c. =0'01 gm. 
 glycerol. 
 
 A weaker solution is also made by diluting 100 c.c. of the strong 
 solution to a liter. 
 
 These solutions should be controlled by a ferrous solution 
 of known strength, if there is any doubt about the purity of the 
 bichromate. 
 
 Solution of double Iron salt. 240 gm. of ferrous ammonium 
 sulphate is dissolved with 50 c.c. of concentrated sulphuric acid to 
 a liter, and its relation to the standard bichromate must be 
 accurately found from time to time by titration with the latter, 
 using the ferricyanide indicator ( 37, p. 127). 
 
 Process : With concentrated or tolerably pure samples of glycerin it is 
 only necessary to take a small weighed portion, say 0'2 gm. or so, dilute 
 moderately, add 10 or 15 c.c. of concentrated sulphuric acid and 30 or 40 c.c. 
 of the stronger bichromate, place the beaker covered with a watch glass in 
 a water bath and digest for two hours; the excess of bichromate is then 
 found by titration with the standard iron solution. The weaker bichromate 
 is useful in completing the titration where accuracy is required. As the 
 stronger bichromate and the iron solution are both concentrated, they must 
 be used at a- temperature as near 16 C. as possible. In the case of crude 
 glycerin it must be purified from chlorine or aldehyde compounds as 
 follows: About 1"5 gm. of the diluted sample is placed in a 100 c.c. flask, 
 some moist silver oxide added, and allowed to stand 10 minutes. Basic lead 
 acetate i's then added in slight excess, the measure made up to 100 c.c., 
 filtered through a dry filter, and 25 c.c. or so digested with excess of 
 bichromate, and titrated as before described. 
 
 The Acetin Method. This method is due to Benedikt and 
 Cantor (Monatsheft ix. 521), and recommends itself by its 
 simplicity and rapidity as compared with other methods. Hehner 
 lias pointed out the precautions necessary to insure accuracy as 
 follows : 
 
 Procfss : About 1'5 gm. of the crude glycerin is placed in a round- 
 bottomed flask, together with 7 gm. of acetic anhydride and 3 gm. of 
 perfectly anhydrous sodic acetate; an upright condenser is attached to the 
 flask, and the contents are heated to gentle boiling for one hour and a half. 
 After cooling, 50 c.c. of water are added, and the mixture heated until all 
 triacetin has dissolved. The solution is then filtered into a large flask, the 
 residue or filter well washed, the liquid cooled, some phenolphthalein added, 
 and the acidity exactly neutralized by a dilute solution of caustic soda. The 
 triacetin is then saponified by adding 25 c.c. of an approximately 10 per 
 cent, solution of pure caustic soda standardized on normal sulphuric or 
 hydrochloric acid, and boiling for 10 minutes, taking care to attach a reflux 
 condenser to the flask. The excess of alkali is then titrated back with 
 normal acid, each c.c. of which represents 0'03067 gm. of glycerin. 
 
 It is essential that the processes of analysis should be rapid and 
 continuous, and especially that the free acetic acid in the first process be,- 
 
-"366 VOLUMETRIC ANALYSIS. 85. 
 
 .neutralized very cautiously, and with constant agitation to avoid the local 
 action of alkali. 
 
 Weak soap lyes should be concentrated to 50 per cent, of 
 glycerin if estimated by the acetin method ; if not the bichromate 
 method must be used. 
 
 For fats and soaps about 3 gm. should be saponified with 
 alcoholic potash, diluted with 200 c.c. of water, the fatty acids 
 .-separated and filtered off. The filtrate and washings are then 
 .rapidly boiled to one-half and titrated with bichromate. 
 
 PHENOL, (CARBOLIC ACID). 
 
 C 6 H 5 OH=94. 
 
 85. THE only method claiming accuracy for the estimation of 
 rthis substance volumetrically was originated' by Ivoppeschaar 
 (Z. a. C. xvi. 233), and consists in precipitating the phenol from 
 dts aqueous or dilute alcoholic solution with bromine water in the 
 form of tribromphenol. 
 
 The strength of the bromine water was established by 
 IKoppeschaar, by titratioii with thiosulphate and potassic iodide 
 with starch. 
 
 Allen modifies the process as follows : 
 
 A certain weight of the sample is dissolved in water: as much as 
 corresponds to O'l gm. of phenol is taken out and put into a stoppered bottle 
 
 ^holding 250 c.c. Further, to 7 c.c. of normal soda solution ( = 0'04 gm. 
 TsaOH per c.c.) bromine is gradually added till a yellow colour appears and 
 
 remains ; the liquid is then boiled till it has become colourless again. It 
 now contains 5 molecules of sodic bromide and 1 of sodic bromate. When 
 completely cooled, it is put into the phenol solution, after which 5 c.c. con- 
 centrated hydrochloric acid are at once added, and the bottle stoppered and 
 
 shaken for some time. The reactions are : 
 
 II. C li H (i O + 6Br - C 6 H 3 Br 3 O + 3HBr. 
 
 The bromine set free in the first, and not fixed by phenol in the second 
 reaction, must be still free, and is estimated by adding potassic iodide and 
 titrating the iodine liberated, by -*$ thiosulphate : 
 
 III. 2KI + Br 2 = 2KBr+2L 
 
 IV. F+2Na 2 S 2 3 = Na 2 S 4 6 +2NaI. 
 
 For this purpose the bottle is allowed to stand for 15 or 20 minutes ; 
 
 : a solution of about 1'25 gm. potassic iodide (free from iodate) is added, the 
 bottle is stoppered, shaken up, and allowed to rest. Its contents are now 
 poured into a beaker ; the bottle is rinsed out, a little starch solution is added, 
 
 - and thiosulphate is run in from a burette till the blue colour is gone. (It 
 will be best not to add the starch till the colour of the liquid has diminished 
 to light yellow.) The calculation is made as follows : 7 c.c. of normal soda 
 solution neutralize 0'56 gm. of bromine, all of which is liberated by HC1. 
 O'l gm. phenol would require 0'4068 and leave a surplus of 0'1532 gm. ; the 
 latter would liberate enough iodine to saturate 19'5 c.c. of ^ thiosulphate. 
 Every c.c. of thiosulphate used over and above this indicates 0'00197 gm. 
 
 :, impurities in O'l gm. of the sample that is, T27 per cent. 
 
86. CARBON BISULPHIDE. 367 
 
 If a number of estimations liave to be made at one time, it 
 would seem decidedly preferable to adopt Koppeschaar's original 
 method, rather than to prepare special bromine solution as above. 
 For the estimation of phenol in raw products, Toth (Z. a. C. 
 xxv. 160) modifies the bromine process as follows : 
 
 20 c.c. of the impure carbolic acid are placed in a beaker with 20 c.c. of 
 caustic potash solution of 1/3 sp. gr., well shaken, and allowed to stand for 
 half an hour, then diluted to about i liter with water. By this treatment 
 the foreign impurities are set free, and may mostly be removed by filtration ; 
 the filter is washed with warm water, until all alkali is removed. The 
 filtrate and washings are acidulated slightly with HC1, and diluted to 3 liters. 
 50 c.c. are then mixed with 150 c.c. of standard bromine solution, and then 
 5 c.c. concentrated HC1. After twenty minutes, with frequent shaking, 
 10 c.c. of iodide solution are added, mixed, and allowed to rest three to five 
 minutes, then starch, and the titration with thiosulphate carried out as usual. 
 
 Example : 20 c.c. raw carbolic oil were treated as above described. 50 c.c. 
 of the solution, with 150 c.c. bromine solution (made by dissolving 2'04 gin. 
 sodic bromate and 6'959 gm. sodic bromide to the liter), then 5 c.c. of HC1, 
 required 17'8 c.c. of thiosulphate for titration. The 150 c.c. bromide 
 = 0'237 gm. Br. The 17'8 c.c. thiosulphate required for residual titration 
 = 0'052 gm. Br, leaving 0'185 gm. Br for combination with the phenol. 
 According to the equation 
 
 2 ^ 3HBr+C G H 2 OHBrl 
 
 One mol. phenol = 3 mol. Br, hence the percentage of phenol was 10'86. 
 
 Ivle inert (Zt. a. C. xxxiii. 1) suggests, and his experiments 
 appear to prove, that in titrating acid creosote oil by Koppeschaar's 
 method for phenol, a serious error occurs in virtue of such oil 
 containing substances of higher boiling-point than phenol, which 
 are soluble in water, and behave with bromine in the same manner 
 as true phenol. 
 
 Meissinger and Wortmann (Pharm. Z&it. f. Russland 
 xxix. 759) describe a method of estimating phenol based on the 
 fact, that iodine combines with phenol in alkaline solution, in 
 the proportion of 6 atoms I to 1 mol. phenol. 
 
 Process : 2 to 3 gm. phenol are dissolved in caustic soda solution (3 eq. 
 NaHO to 1 eq. phenol) and made up to 500 c.c. with water; 10 c.c. of t,his 
 are placed in a flask, warmed to 60 C., and /^ iodine added until the solution 
 is faintly yellow, with formation of a red precipitate. When cold, the 
 solution is acidified with dilute H 2 SO 4 , made up to 500 c.o. and filtered. In 
 100 c.c. of the filtrate, the excess of I is titrated with ^ thiosulphate ; this 
 amount, deducted from the total I used, gives the amount absorbed by 
 phenol, which, when multiplied by 0'123518, gives amount of phenol in the 
 sample. 
 
 CARBON DISU-LPHIDE AND THIOCABBONATES. 
 
 CS 2 =76. 
 
 86. FOR the purpose of estimating carbon disulphide in 
 the air of soils, gases, or in thiocarbonates, Gas tine has devised 
 the following process (Oompt. Rend, xcviii. 1588) : 
 
368 VOLUMETRIC ANALYSIS. 86. 
 
 The gas or vapour to be tested is carefully dried, and then passed through 
 a concentrated solution of recently fused potassic hydroxide in absolute 
 alcohol. The presence of even traces of water seriously diminishes the 
 delicacy of the reaction. The alcoholic solution is afterwards neutralized 
 with acetic acid, diluted with water, and tested for xanthic acid by adding 
 copper sulphate. 
 
 In order to determine the distribution of carbon bisulphide introduced 
 into the soil, 250 c.c. of the air in the soil is drawn by means of an aspirator 
 through sulphuric acid, and then through bulbs containing the alcoholic 
 potash. For quantitative determinations, a larger quantity of air must be 
 used, and the xanthic acid formed is estimated by means of the reaction 
 2C 3 H G OS 2 +I 2 = 2C 3 H 5 OS 2 + 2HI. The alkaline solution is slightly acidified 
 with acetic acid, mixed with excess of sodic bicarbonate, and titrated in the 
 usual way with a solution of iodine containing T68 gm. per liter, 1 c.c. of 
 which is equivalent to 1 m.gm. of carbon bisulphide. 
 
 To apply this method to thiocarbonates, about 1 gm. of the substance, 
 together with about 10 c.c. of water, is introduced into a small flask and 
 decomposed by a solution of zinc or copper sulphate, the flask being heated 
 on a water bath, and the evolved carbon bisulphide passed, first through 
 sulphuric acid, and then into alcoholic potash. In the case of gaseous 
 mixtures of carbon bisulphide, nitrogen, hydrogen sulphide, carbonic 
 anhydride, carbonic oxide, and water-vapour, the gas is passed through 
 a strong aqueous solution of potash, then into sulphuric acid, and finally into 
 alcoholic potash. The thiocarbonate formed in the first flask is decomposed 
 by treatment with copper or zinc sulphate as above, and the xanthic acid 
 obtained is added to that formed in the third flask, and the whole titrated 
 with iodine. 
 
 Another method available for technical purposes, such as the 
 comparative estimation of CS 2 in coal gas, or in comparing 
 samples of thiocarbonates, is as follows : 
 
 The liquid or other substance containing the disulphido is added to 
 strong alcoholic potash, or gas containing the CS 2 is passed slowly through 
 the alkaline absorbent. The disulphide unites with the potassic ethylate to 
 form potassic xanthate. The liquid is neutralized with acetic acid and the 
 xanthate is then estimated by titrating with a standard solution of cupric 
 sulphate (12'47 gm. per liter), until an excess of copper is found by potassic 
 ferroc3 r anide used as an external indicator. Each c.c. of copper solution 
 represents 0'0076 gm. CS 2 . 
 
BORIC AND ARSENIC ACIDS. 309 
 
 APPENDIX TO PART V. 
 
 Addition to 22. 
 
 Boric Acid in Milk. R. T. Thomson (Glasgow City Anal. Soc. 
 Repts., 1895, p. 3). One to two gm. of sodic hydrate are added to 
 100 c.c. of milk, and the whole evaporated to dryness in a platinum 
 dish. The residue is thoroughly charred, heated with 20 c.c. of 
 water, and hydrochloric acid added drop by drop until all but the 
 carbon is dissolved. The whole is transferred to a 100 c.c. flask, 
 the bulk not being allowed to get above 50 or 60 c.c., and 0'5 gm. 
 dry calcium chloride added. To this mixture a few drops of 
 phenolphthalein solution are added, then a 10 per cent, solution of 
 caustic soda, till a permanent slight pink colour is perceptible, and 
 finally 25 c.c. of lime-water. In this way all the P 2 5 is 
 precipitated as calcic phosphate. The mixture is made up to 100 
 c.c., thoroughly mixed and filtered through a dry filter. To 50 c.c. 
 of the nitrate (equal to 50 gm. of the milk) normal sulphuric acid 
 is added till the pink colour is gone, then methyl orange, and the 
 addition of the acid continued until the yellow is just changed to 
 pink. caustic soda is now added till the liquid assumes the 
 yellow tinge, excess of soda being avoided. At this stage all acids 
 likely to be present exist as salts neutral to phenolphthalein, except 
 boric acid (which, being neutral to methyl orange, exists in the 
 free condition), and a little carbonic acid, which is expelled by 
 boiling for a few minutes. The solution is cooled, a little 
 phenolphthalein added, and as much glycerin as will give at least 
 30 per cent, of that substance in the solution, and titrated with -J 
 caustic soda till a distinct permanent pink colour is produced ; each 
 c.c. of the soda is equal to 0*0124 gm. crystallized boric acid. 
 A series of experiments with this process showed that no boric 
 acid was precipitated along with the phosphate of lime so long as 
 the solution operated upon did not contain more than 0'2 per cent, 
 of crystallized boric acid, but when stronger solutions were tested, 
 irregular results were obtained. The charring of the milk is apt 
 to drive off boric acid, but by carefully carrying the incineration 
 only so far as is necessary to secure a residue which will yield 
 .a colourless solution, no appreciable loss occurs. 
 
 Addition to 47. 
 
 The Estimation of Arsenic Acid in Arsenates. A. Williamson 
 (Journal of the Society of Dyers and Colourists, May, 1896) has 
 devised the following ready method as being applicable to 
 commercial arsenates, and has made use of the reaction which 
 takes place between arsenic and hydriodic acids in strong acid 
 
 B B 
 
370 VOLUMETRIC ANALYSIS. 
 
 solution. Under these circumstances arsenic acid is quantitatively 
 reduced with liberation of iodine. The reaction is 
 
 As 2 5 + 4HI = As 2 8 + 2H 2 + 41. 
 
 It was found that the reduction is only complete in strongly acid 
 solution, and if such a solution be diluted the reverse reaction 
 takes place to a certain extent, a portion of the arsenious becoming 
 oxidized to arsenic acid. The iodine may, however, be estimated 
 before dilution, by means of thiosulphate, and in the absence of 
 other bodies capable of liberating iodine it may be taken as 
 a measure of the arsenic acid. The acid solution may then be 
 neutralized, and the arsenite titrated with iodine. This serves as 
 a check on the thiosulphate titration. 
 
 The reduction may be effected either in hydrochloric or sulphuric 
 acid solution, but in either case a considerable excess of acid must 
 be present, otherwise the reduction is incomplete. 
 
 Example: A. standard solution of arsenate of soda was prepared by 
 oxidizing 4'95 gm. of arsenious oxide with nitric acid, evaporating to dryness 
 on the water bath, neutralizing with sodic carbonate, and diluting to one 
 liter. 25 c.c. of this standard were then treated with 3 gra. potassic iodide 
 and 25 c.c. of hydrochloric acid, sp. gr. 1*16, and the liberated iodine titrated 
 with thiosulphate.* 
 
 The decolorized solution was then neutralized with sodic carbonate, and 
 after the addition of bicarbonate, was titrated with iodine. The arsenic 
 acid calculated from the thiosulphate was 99'6, and from the iodine 100'2, 
 instead of 100. To ensure complete reduction in the cold, the solution must 
 contain one-half its volume of hydrochloric acid and the quantity of potassic 
 iodide- mentioned. With less quantities than these, there is a danger of the 
 reduction not being immediately complete. The amount of thiosulphate 
 consumed agrees very well with the arsenite found in the neutralized 
 solution by titration with iodine. 
 
 As commercial sodic arsenate usually contains some nitrate, 
 experiments were made to ascertain whether the presence of this 
 salt interferes with the accuracy of the thiosulphate titration. 
 A pure solution of arsenate was prepared as before, and 1 gm. of 
 sodic nitrate added. 25 c.c. of this solution were then treated 
 with potassic iodide and hydrochloric acid, and the iodine titrated 
 with thiosulphate, as before. The arsenic acid calculated from the 
 thiosulphate consumed was 100*3, instead of 100. It is evident 
 that the presence of nitrate causes little or no liberation of iodine 
 in the cold, but if the arsenate is digested with hydrochloric acid 
 and potassic iodide in a closed bottle immersed in boiling water, 
 the iodine liberated is considerably in excess of that corresponding 
 
 * A brown precipitate falls on adding this quantity of acid, but it dissolves as the 
 solution becomes diluted by titration with thiosulphate. The amount of thiosulphate 
 required to decolorize the small quantity of iodine liberated by mixing the same weight 
 of potassium iodide and hydrochloric acid under the same conditions was subtracted. 
 It is advisable not to have the solution of arsenate stronger than decinormal, or the 
 dilution consequent on titrating with thiosulphate may cause the reverse reaction to 
 take place to a slight extent, and the result would come out too low. The solution 
 should be quite cold before titrating the iodine. 
 
AKSENATES. 371 
 
 to the arsenic acid. In this case, the quantity of thiosulphate 
 consumed is of no value. The arsenic can, however, be accurately 
 estimated by titrating the arsenite after the iodine has been 
 decolorized. 
 
 Instead of hydrochloric acid, 15 c.c. of a mixture of sulphuric 
 acid and water, in equal volumes, may be used. Since the 
 addition of sulphuric acid causes the solution to become slightly 
 heated, it is cooled before titrating the iodine. The results are 
 practically the same as with hydrochloric acid. 
 
 Xot less than 3 gm. potassic iodide should be added, or complete 
 reduction is not immediately effected. The presence of small 
 quantities of nitrate does not interfere with the accuracy of the 
 thiosulphate titration. Complete reduction can be brought about 
 with 2 gm. potassic iodide and 10 c.c. of sulphuric acid, if the 
 solution is heated for five minutes on the steam bath. A portion 
 of the iodine volatilizes, but no arsenic is lost. The iodine is 
 exactly decolorized with thiosulphate, the solution neutralized and 
 titrated with iodine in the ordinary manner. 
 
 Process with Commercial Arsenate of Soda : 10 gm. are dissolved to 1 
 liter, and the arsenic acid in 25 c.c. estimated by one of the methods given 
 above. The thiosulphate titration only records the arsenic previously 
 existing as arsenic acid. The small proportion of As 2 O 3 which usually exists 
 is ascertained by direct titration. When this is calculated to arsenic acid, and 
 added to that found by thiosulphate, the results approximate very closely to 
 those found by titrating the arsenite. 
 
 Estimation of Arsenic in presence of Tin. If both these elements 
 are present in the lower state of oxidation, the tin may be oxidized 
 with iodine in strong acid solution, the arsenic being unaffected. 
 Rochelle salt is then added, the solution neutralized, and the 
 arsenite titrated with iodine. 
 
 Example: 25 c.c. of -*-$ sodic arsenite were mixed with 25 c.c. of hydro- 
 chloric acid, and 3 gm. stannous chloride added. The tin was then exactly 
 oxidized with standard iodine, and the arsenic titrated in the alkaline 
 solution, 24'9 c.c. of T ^- iodine were required. 
 
 If they are present in the highest state of oxidation, the arsenic 
 may be reduced by one of the methods given under the estimation 
 of arsenic acid. The stannic salt is not affected. 
 
 It is thus possible to estimate the arsenic in a mixture of 
 arsenate and stannate of soda. In presence of a considerable 
 quantity of tin, however, the complete reduction of the arsenic 
 acid is not effected quite as readily as when tin is absent. The 
 following method has given good results : 
 
 4 or 5 gm. of the mixture are dissolved in as small a quantity of HC1 as 
 possible, an equal weight of tartaric acid is dissolved in the solution, which 
 is then diluted to 250 c.c. (If the tartaric acid is not added a precipitate 
 forms on dilution which contains both tin and arsenic). 25 c.c. of this 
 solution are then mixed with 3 gm. potassic iodide and 25 c.c. HC1, sp. gr. 
 
 B B 2 
 
372 VOLUMETFJC ANALYSIS. 
 
 1'16, and the solution heated on the steam bath for two or three minutes to 
 ensure the complete reduction of the arsenic acid. The liberated iodine is 
 exactly decolorized with thiosulphate, and the arsenic estimated by titration 
 with iodine in the neutralized solution. A mixture of arsenate and stannate 
 in equal quantities and containing a known percentage of arsenic gave 
 28'57 instead of 28'75 per cent, of arsenic acid. 
 
 Addition to 54, 55. 
 
 Mixtures of Chlorides, Hypochlorites, and Chlorates. It is 
 known that chlorine acting upon alkaline and alkaline-earthy 
 hydrates gives rise to chlorides, and at the same time to chlorates, 
 or to hypochlorites, according as the temperature and the con- 
 centration are higher or lower. In average conditions the three 
 kinds of salts are formed simultaneously. 
 
 A mixture of the same salts is produced if solutions of sodic 
 chloride are submitted to electrolysis, according to the processes 
 recently tried for the manufacture of free chlorine and of caustic 
 soda, or of chlorates or hypochlorites. 
 
 In these various cases it is of great industrial importance to 
 determine easily the proportion of each of the salts present. 
 
 For the analysis of such a mixture of salts, the subjoined 
 method is recommended as at once expeditious and accurate. All 
 the determinations are performed successively upon one and the 
 same specimen of the saline solution (A. Garnet, Compt. Rend. 
 cxxii. 449). 
 
 Process: 1. The mixture of hypochlorite, chlorate, and chloride taken 
 from the solution of electrolyzed sodic chloride, or from the liquid obtained 
 on lixiviating chloride of lime, is poured into a test-glass. There is then run 
 into it from a burette a standard solution of alkaline arsenite, prepared as 
 usual, until the bypochlorite is completely reduced. To find the exact 
 moment when the reduction is completed, a drop of the liquid is placed 
 upon a porcelain plate in contact with a drop of solution of potassic iodide 
 and starch. 
 
 On the mixture of the two drops there appears a blue colour as long as 
 there remains any hypochlorite not reduced. As soon as the mixture ceases 
 to become coloured, the volume of the arsenite liquid is noted, and the 
 proportion of hypochlorite or hypochlorous acid w r hich has transformed it 
 into arsenic acid is obtained ; or, consequently, that of the corresponding 
 chlorine. 
 
 As 2 O 3 + CaCl-O 2 = As 2 O 5 + CaCl 2 , 
 or 
 
 As 2 O 3 +2NaC10 = As 2 5 +2NaCl. 
 
 2. The liquid (which now contains merely chlorate and chloride) is 
 slightly acidified with sulphuric acid, and a quantity of ammonium-ferrous 
 sulphate added, at least twenty times of that of the supposed chlorates. 
 Heat to about 100, adding in small successive quantities 5 c.c. of 
 sulphuric acid diluted with 15 c.c. of water. It is best to use 
 a tap-funnel, letting the acid fall in drop by drop. After having stoppered 
 the vessel, to avoid contact of air, it is allowed to cool for a short time, and 
 the excess of ferrous salt is then titrated with permanganate. As the 
 quantity of ferrous salt which was introduced, is known, by difference the 
 
CHLORIDES, HYPOCHLORITES, CHLORATES, NITRATES. 373 
 
 quantity which has been peroxidized at the expense of the chlorate reduced 
 to the state of chloride is found. 
 
 NaC10 3 +GFeO = NaCl+Pe-O 3 . 
 
 It is thus easy to calculate the proportion of chlorate or of chloric acid, 
 or the corresponding quantity of chlorine. 
 
 3. The total chlorine, which is now entirely present in the state of 
 chloride, is determined as follows : The rose tint produced by the 
 permanganate is removed by adding a trace of ferrous sulphate, crystallized 
 or in solution. Then add a measured volume of silver nitrate, more than 
 enough to precipitate all the chlorine, and determine the excess of the 
 silver salt by means of standard thiocyanate ( 43). The ferric salt 
 previously formed by the peroxidation of the ferrous salt serves as an 
 indicator, by producing a permanent red colouration as soon as there is no 
 more silver salt to precipitate. The arsenic acid produced in the first 
 operation does not interfere in the least. 
 
 In order to avoid the use of too large a quantity of silver nitrate, which 
 would be necessary on account of the large proportion of chlorine to be 
 precipitated, an aliquot part of the solution may be taken. 
 
 The chlorine found in the state of a chloride in the original liquid is 
 easily calculated by deducting from the total chlorine just determined the 
 two quantities already found in the state of hypochlorite and of chlorate. 
 
 The three operations succeed each other without interruption, and with- 
 out separate preparation, and are completed in a short time. 
 
 In a number of experiments with mixtures, the discrepancies found 
 between the experimental results and the calculated numbers rarely reached 
 1 m.gm. when operating upon from 250 to 500 m.gm. 
 
 Additions to 54 and 70. 
 
 The lodometric Estimation, of Chloric and Nitric Acids. The 
 following methods by McGowan (/. G. S. Ixix. 530, and /. C. S. 
 Ixi. 87) depend on the principle that, when a fairly concentrated 
 solution of a nitrate or chlorate is warmed with an excess of pure, 
 strong hydrochloric acid, a nitrate is completely decomposed, and 
 the production of nitrosyl chloride and chlorine is quantitative, 
 the reaction being 
 
 HXO 3 + 3HC1=XOC1 + Cl 2 + 2IPO. 
 
 If the operation is conducted in an atmosphere of carbonic acid, 
 and the escaping gases are passed through a solution of potassic 
 iodide, an amount of iodine is liberated exactly equivalent to the 
 whole of the chlorine present (free and combined), nitric oxide 
 escaping. 1 mol. of nitric acid thus yields 3 atoms of chlorine 
 or iodine. The iodine can then be titrated in the usual manner 
 with thiosulphate. With chlorates only chlorine is evolved. 
 De Koninck and Nihoul (Zeit. fiir ancjew. Chem. August 15, 
 1890) give details of a process depending upon the same principle. 
 
 Process for Nitrates. It is, of course, absolutely essential that air should 
 be completely excluded from the apparatus, as, if any were present, the 
 escaping nitric oxide would be re-oxidized to nitrogen trioxide or tetroxide, 
 and this w r ould in its turn liberate a further quantity of iodine from the 
 iodide solution. 
 
374 
 
 VOLUMETRIC ANALYSIS. 
 
 The apparatus required is very simple, and can readily be made by any 
 one moderately expert at glass-blowing. The main point to be attended to 
 is to have no corks or rubber stoppers, &c., for the escaping chlorine to act 
 upon. Fig. 53 is a sketch of the apparatus ; the condensing arrangement 
 for the chlorine does its work perfectly, and may therefore be used Avith 
 advantage, not only for this, but also for other similar methods in Avhich 
 iodine is set free. The measurements given are those of the apparatus as 
 used by the author. 
 
 A is a small, round-bottomed flask, into the neck of which a glass stopper, 
 x, is accurately ground (with fine emery and oil). The capacity of the 
 bulb is about 46 c.c., and the length of the neck, from x to y, 90 m.in. 
 The first condenser is a simple tube, slightly enlarged at the foot into two 
 
 small bulbs. The length from a to I is 300 m.m., from b to c 180 m.m., and 
 from e to f 30 m.m. The capacity of the bulb J? is 25 c.c., and the total 
 capacity of the two bulbs and tube, up to the top of C, 41 c.c. This 
 condenser is immersed, up to the le\ r el of c, in a beaker of Avater. D is 
 a Geissler bulb apparatus, and E a chloride of calcium tube, filled with 
 broken glass, Avhich acts as a tower, g is a small funnel, attached by rubber 
 and clip to the branch tube li. Between the tube i and the Avash-bottle 
 for the carbonic acid is placed a short piece of glass tubing, *. containing 
 a strip of filter paper, slightly moistened with iodide of starch solution. 
 This tube s is really hardly necessary, as no chlorine escapes backAvards 
 if a moderate current of carbonic acid is kept passing, but it serves as 
 a check. The joints p and q are of narroAV rubber tubing. The joint o 
 is made by grinding one tube into the other, k is the outlet tuba. 
 
 The operation is performed in the following manner: The evolution 
 flask is Avashed and thoroughly dried, and the nitrate (say about 0'25 gin. 
 of potassic nitrate) is tapped into it from the weighing tube. 1 to 2 c.c. 
 
NITRATES AND CHLORATES. 375 
 
 of water are now added, and the bulb is gently warmed, so as to bring the 
 nitrate into solution, after which the stopper of the flask is firmly inserted 
 into it. About 15 c.c., or so, of a solution of potassic iodide (1 in 4) are 
 run into the first condensing tube, any iodide adhering to the upper portion 
 of the tube being washed down with a little water, and 5 c.c. of the same 
 solution, mixed with 8 to 10 c.c. of water, are sucked into the Geissler 
 bulbs, whilst the glass in tower E is also thoroughly moistened with the 
 iodide. The Geissler bulbs should be so arranged that gas only bubbles 
 through the last of them, the liquid in the others remaining quiescent. 
 
 All the joints having been made tight, the CO 2 is turned on briskly, and 
 passed through the apparatus until a small tubeful collected at I, over caustic 
 potash solution, shows that no appreciable amount of air is left in it. The 
 small outlet tube I is now replaced by a chloride of calcium tube, filled with 
 broken glass which has been moistened with the above iodide solution, and 
 closed by a cork through which an outlet tube passes, the object of this 
 "trap" tube being to prevent any air getting back into the apparatus; 
 and the brisk current of CO- is continued for a minute or two longer, so 
 as to practically expel all the air from this last tube. The stream of gas is 
 now stopped for an instant, and about 15 c.c. of pure concentrated hydro- 
 chloric acid, free from chlorine, run into A through the funnel g (into the 
 tube of which it is well to have run a few drops of water before beginning to 
 expel the air from the apparatus), and A is shaken so as to mix its contents 
 thorouglil}'. A slow current of CO- is now again turned on (1 to 2 bubbles 
 through the wash-bottle per second), and A is gently warmed over a burner. 
 It is a distinct advantage that the reaction does not begin until the mixed 
 solutions are warmed, when the liquid becomes orange-coloured, the colour 
 again disappearing after the nitrosyl chloride and chlorine have been expelled. 
 The warming should be very gentle at first, in order to make sure of the 
 conversion of all the nitric acid, and also because the first escaping vapours 
 are relatively very rich in chlorine ; afterwards the liquid in A is briskly 
 boiled. A very little practice enables the operator to judge as to the proper 
 rate of warming. When the volume of liquid in A has been reduced to 
 about 7 c.c., or so (by which time it is again colourless), the stream of CO 2 
 is slightly quickened, and the apparatus allowed to cool down a little. The 
 burner is now set aside for a few minutes, and 2 c.c., or so, more of hydro- 
 chloric acid, previously warmed in a test-tube, run in gently through <j ; 
 there is no fear either of the iodide solution running back, or of any bubbles 
 of air escaping through y, if this is done carefully. This is a precautionary 
 measure, in case a trace of the liberated chlorine might have lodged in the 
 comparatively cool liquid in tube li. The CO 2 is once more turned on 
 slowly, and the liquid in A is boiled again until it is reduced to about 5 c.c. 
 It is now only necessary to allow the apparatus to cool down, passing CO 2 
 all the time, after which the contents of the condensers are transferred to 
 a flask and titrated with thiosulphate. At the end of a properly conducted 
 experiment, the glass in the upper part of tower E should be quite colourless, 
 and there should only be a mere trace of iodine showing in the lower part 
 of the tower, while the liquid in the last bulb of the Geissler apparatus 
 ought to be only pale yellow. During the operation, the stopper of A and 
 the various joints can be tested for tightness from time to time by means 
 of a piece of iodide of starch paper, and, before disjointing, it is well to 
 test the escaping gas (say, at m) in the same wa}*, to make sure that all 
 nitric oxide has been thoroughly expelled. 
 
 Example: 0'2627 gm. of pure KNO 3 was taken. The liberated iodine 
 required 38'56 c.c. of thiosulphate (of which 1 c.c. =0*003805 gm. KNO 3 ) 
 for conversion. This gave 0'2624 gm. nitrate found, or 99'89 per cent. 
 
 Process for Chlorates. The apparatus employed is the same as for nitrates, 
 but since it is unnecessary in this estimation to previously expel the air 
 
376 VOLUMETRIC ANALYSTS. 
 
 present by a current of CO 2 , those tubes which come after the tower E are 
 dispensed with. The details of the operation are also practically the same 
 as in the case of a nitrate, only simpler. Comparatively dilute hydrochloric 
 acid may be employed, and the CO' is required merely to ensure a regular 
 passage of the vapours through the iodine solution, and to prevent any 
 chlorine escaping backwards. This is tested, as before, by the small piece 
 of iodide of starch paper in tube s, which should be so placed as never to 
 get warm. 
 
 The chlorate is weighed out into the dry evolution flask A, then dissolved 
 in 8 to 10 c.c. of w\ater, and, after all the necessary connections have been 
 made, 8 to 10 c.c. of pure concentrated hydrochloric acid are run in through 
 the funnel g. Since the reaction begins in the cold, the CO' 2 must be 
 turned on immediately, and kept passing at the rate of about four bubbles 
 per second. Care should be taken to heat very gently at first, until the 
 bulk of the chlorine has come over, after which the lamp flame may be 
 gradually turned up and the liquid boiled, exactly as in the case of the 
 nitrate ; this ensures that no chlorine escapes backwards. And, as before, 
 after all the chlorine has been apparently driven out, and the solution has 
 become colourless, a second quantity of warm hydrochloric acid (1 in 2) 
 is run in, and the boiling repeated for a few minutes. 
 
87. URIXF, 377 
 
 PART VI. 
 
 SPECIAL APPLICATIONS OF THE VOLUMETRIC 
 
 SYSTEM TO THE ANALYSIS OF URINE, POTABLE 
 
 WATERS, SEWAGE, ETC. 
 
 ANALYSIS OF URINE. 
 
 87. THE complete and accurate determination of the normal 
 and abnormal constituents of urine presents mere than ordinary 
 difficulty to even experienced chemists, and is a hopeless task in 
 the hands of any other than such. Fortunately, however, the 
 most important matters, such as urea, sugar, phosphates, sulphates, 
 and chlorides, can all be determined volumetrically with accuracy 
 by ordinary operators, or by medical men who cannot devote 
 much time to practical chemistry. The researches of Liebig, 
 Neubauer, Bence Jones, Vogel, Beale, Hassall, Pavy, 
 and others, during the last few years, have resulted in a truer 
 knowledge of this important secretion ; and to the two first 
 mentioned chemists we are mainly indebted for the simplest 
 and most accurate methods of estimating its constituents. With 
 the relation which the proportion of these constituents bear 
 to health or disease the present treatise has nothing to do, its 
 aim being simply to point out the readiest and most useful 
 methods of determining them quantitatively. Their pathological 
 importance is very fully treated by some of the authorities just 
 mentioned, among the works of which Neubauer and Vogel's 
 Anal i i se des Hams, Be ale's Urine, Urinary Deposits, and Calculi, 
 and M elm's Traite de Cliiinie Medicale, are most prominent and 
 exhaustive ; and we now have the collected experience of all 
 the best authorities in the world in The Pathological Handbook 
 of Drs. Lander Brunton, Klein, Foster, and Burdon 
 Sanderson (Churchill), and in Allen's Chemistry of Urine 
 (Churchill). 
 
 The gram system of weights and measures will be adopted 
 throughout this section, while those who desire to use the grain 
 system will have no difficulty in working, when once the simple 
 relation between them is understood* (see 10 p. 26). The question 
 of weights and measures is, however, of very little consequence, if 
 the analyst considers that he is dealing with relative parts or pro- 
 portions only ; and as urine is generally described as containing so 
 
 * In a word, whenever c.c. occurs, dm. may be substituted ; and in case of using 1 
 grains for grains, move the decimal point one place to the right ; thus 7*0 grams would 
 be changed to 70 grains. Of course it is understood that where grains are taken c.c. 
 must be measured, and with grains dm., the standard solution being the same for both 
 systems. 
 
378 VOLUMETRIC ANALYSIS. 87. 
 
 many parts of urea, chlorides, or phosphates, per 1000, the absolute 
 weight may be left out of the question. The grain system is more 
 readily calculated into English ounces and pints, and therefore is 
 generally more familiar to the medical profession of this country. 
 
 One thing, however, is necessary as a preliminary to the exami- 
 nation of urine, and which has not generally been sufficiently 
 considered ; that is to say, the relation between the quantity of 
 secretion passed in a given time, and the amount of solid matters 
 found in it by analysis. In a medical point of view it is a mere 
 waste of time, generally speaking, to estimate the constituents in 
 half-a-pint or so of urine passed at any particular hour of the day 
 or night, without ascertaining the relation which that quantity, 
 with its constituents, bears to the whole quantity passed during, 
 say, 24 hours ; and this is the more necessary, as the amount of 
 fluid secreted varies very considerably in healthy persons ; besides 
 this, the analyst should register the colour, peculiarity of smell (if 
 any), consistence, presence or absence of a deposit (if the former, 
 it should be collected for separate analysis, filtered urine only 
 being used in such cases for examination), and lastly its reaction to 
 litmus should be observed. 
 
 1. Specific Gravity. 
 
 This maybe taken by measuring 10 c.c. with an accurate pipette 
 into a tared beaker or flask. The observed weight say is 10*265 
 gm. ; therefore 1026*5 will be the specific gravity, water being 1000. 
 Where an accurate balance, pipette, or weights are not at hand, 
 a good uririometer may be used. These instruments are now to be 
 had with enclosed thermometer and of accurate graduation. 
 
 2. Estimation of Chlorides (calculated as Sodic Chloride). 
 
 This may be done in several ways, and I have placed the 
 methods in the order in which I consider they ought to be ranked 
 as regards accuracy. Liebig's method is by far the simplest, but 
 the end-point is generally so obscure that the liability to error is 
 very great. Mohr's method I have modified by the use of 
 ammonic in place of potassic nitrate, owing to 'the solvent effect 
 which the latter has been found to produce on silver chroinate. 
 By ignition the ammonia salt is destroyed. 
 
 (a) By Silver Nitrate (Mohr). 10 c.c. of the urine are 
 measured into a thin porcelain capsule, and 1 gm. of pure ammonic 
 nitrate in ponder added ; the whole is then evaporated to dryness, 
 and gradually heated over a small spirit lamp to low redness till 
 all vapours are dissipated and the residue becomes white'" ; it is 
 
 *Dr. Edmunds has called my attention to the fact, that there is great danger of 
 losing chlorine if the ignition is made at a high temperature, and there is no doubt he 
 is right. He prefers to char the urinary residue thoroughly over a spirit lamp, and 
 wash out the chlorides with hot water, the filtered liquid is then available for direct 
 estimation v/ith silver and chroinate or by the V o 1 h ar d method. 
 
87. URINE. 379 
 
 then dissolved in a small quantity of water, and the carbonates 
 produced by the combustion of the organic matter neutralized by 
 dilute acetic acid ; a few grains of pure calcic carbonate to remove 
 all free acid are then added, and one or two drops of solution of 
 potassic chromate. 
 
 The mixture is then titrated with ~ silver, as in 41.2 (/;). 
 
 Each c.c. of silver solution represents 0*005837 gm. of salt, 
 consequently if 12 '5 c.c. have been used, the weight of salt in the 
 10 c.c. of urine is 0*07296 gm., and as 10 c.c. only were taken, 
 the weight multiplied by 10, or what amounts to the same thing, 
 the decimal point moved two places to the right, gives 7*296 gm. 
 of salt for 1000 c.c. of urine. 
 
 If 5'9 c.c. of the urine are taken for titration, the number of c.c. of T V 
 silver used will represent the number of parts of salt in 1000 parts of urine. 
 
 (1) By Volhard's Method. This is a direct estimation of 
 Cl by excess of silver and the excess found by ammonic or potassic 
 thiocyanate ( 43), which gives very good results in the absence of 
 much organic matter, and is carried out as follows : 
 
 10 c.c. of urine are placed in a 100 c.c. flask and diluted to about 60 c.c. 
 2 c.c. of pure nitric acid and 15 c.c. of standard silver solution (1 c.c. =0*01 
 gm. NaCJ) are then added ; the closed flasked is well shaken, and the measure 
 made up to 100 c c. with distilled water. 
 
 The mixture is then passed through a dry filter, and about 70 or 80 c.c. of 
 the clear fluid titrated with standard thiocyanate for the excess of silver, 
 using the ferric indicator described on page 143. The relative strength of 
 the silver and thiocyanate being known, the measure of the former required 
 to combine with the chlorine in the 7 or 8 c.c. of urine is found and 
 calculated into NaCl. 
 
 Arnold (Pflilger' 1 s Arcldv. xxxv. 541) carries out this process 
 as follows : 
 
 10 c.c. of urine are mixed with 10 to 20 drops of nitric acid sp. gr. 1*2, 
 2 c.c. of ferric indicator, and 10 to 15 drops of solution of permanganate to 
 oxidize organic matter. The liquid is then filtered and titrated as described 
 above. 
 
 Dr. James Edmunds, of Dover Street, Piccadilly, who is not 
 only a prominent London physician but also an excellent chemist, 
 has kindly contributed his special way of carrying out the estimation 
 of chlorides in urine by this process. 
 
 " In determining the chlorides of urine, and other organic liquids, by 
 desiccation and ignition, I find the results generally too low. It seems 
 impracticable to prevent the fume of charring from mechanically carrying 
 off chlorides, and the heat of ignition from volatilizing a further portion. 
 By careful charring at a low temperature, breaking up the char, and 
 washing out the soluble salts, the loss of chlorides is minimized. On the 
 other hand, I know of no measurement which is more entirely satisfactory 
 than the determination of chlorides by the beautiful process devised by 
 Volhard. The organic matters of urine open up the way to two fallacies. 
 
880 VOLUMETRIC ANALYSIS. 87. 
 
 1. The reduction of nitric acid and the production of a red shade due to 
 the lower oxides of nitrogen. But this never amounts to the full red which 
 is given, in cases of doubt, by running in a further portion of the 
 thiocyanate, and then titrating back with the silver until the red is about to 
 fade out. In that way the true end-point of the reaction is made sharp 
 and unequivocal. 2. The second possible fallac} r is the reduction of the 
 ferric indicator to the ferrous condition. But this does not prevent the 
 end-point from showing, unless the whole of the ferric has been reduced to 
 ferrous oxide, and, if a full measure of a good ferric indicator is used, this 
 cannot happen. In case of any uncertainty the addition of a fresh c.c. of 
 the ferric indicator, at the moment when the titration seems to be 
 complete, is decisive as to the true end-point. In some cases it may be 
 necessary to get rid of oxalic acid, or other active reducers by previous 
 treatment with potassic permanganate free from chlorine, until a slight rose 
 tint persists, and this may be perfectly removed by passing the liquid 
 through a filter paper. 
 
 " The indicator which I use is a very simple and convenient one. It is 
 made by dissolving 2'8 gm. of clean soft iron wire in nitric acid of about 
 1250 sp. gr., boiling off the red fumes, and then making up to 100 c.c. 
 with pure nitric acid and water so that the solution has a sp. gr. of about 
 1 385, and is well below the fuming point at ordinary temperatures. To 
 remove the last traces of the nitrogen oxides, I then put the solution into 
 a tall jar, and blow air through it by means of a glass tube attached to 
 a rubber-ball bellows. The solution which is thus obtained is a pale 
 greenish yellow ; it is a pure ferric nitrate in slightly diluted nitric acid ; 
 and it keeps well. This gives, at one addition, the ferric indicator and the 
 nitric acid which is needed for the process. It cannot be sucked up into 
 a pipette without serious risk of causing pneumonia, and it should be 
 poured out into a 10 c.c. tubular measure. For ordinary liquid, where no 
 organic matter is present, this solution may be reduced to ten times its 
 volume with additional pure nitric acid and water, and, if its colour goes 
 wrong, air must again be blown through it, or it must be heated until, 
 when cold, it is a pale greenish yellow. 
 
 " In the analysis, I dilute the urine to 10 volumes with distilled water 
 which reduces its colour and dilutes its organic matter, and I use 
 solutions of thiocyanate and of silver, which are the chlorine-reciprocals 
 of normal solutions ; i.e., normal solutions diluted to 35'37 volumes, and of 
 which 1 c.c. is equal each to O'OOl Cl. These solutions may be marked 
 K Ij7~~ or 35^jT They are very convenient and eliminate all calculation. 
 In fact, this method of calculating and marking various standard solutions 
 is very useful. Placing 10 c.c. of the diluted urine into a beaker on white 
 paper, I add 10 c.c. of the ferric indicator, and at once run in 1 c.c. of the 
 thiocyanate, so as to get a sharp red colour, and stir thoroughly. I then run 
 in the silver with continuous stirring until the red colour begins to 
 distinctly fade. From this point onwards continuous stirring, and the slow 
 addition of the last drops of silver gives a sharp and unquestionable end- 
 point. If overdone by accident, I add another c.c. of thioc} r anate, and 
 repeat the silver more cautiously as the end-point approaches, stirring very 
 actively. The titration should commence Avith the burettes at 0, and then 
 a simple reading of the burettes at the end of the operation gives both 
 quantities used, however often the titration backwards and forwards may 
 have been done. The silver c.c., minus the thiocyauate c.c., give the milligrams 
 of chlorine in 1 c.c. of urine. It is necessary to use a small very accurately 
 graduated burette, say 20 c.c. in T V : it' the tube is narrow it is possible to 
 have very distinct readings. 
 
 " It cannot be possible to get an easier, quicker, or more precise 
 determination of chlorides in urines, milk serums, and other organic liquids 
 than this." 
 
87. URINE. 381 
 
 (/) By Mercuric Nitrate (LieMg). The principle of this 
 method is as follows : If a solution of mercuric nitrate, free from 
 any excess of acid, is added to a solution of urea, a white gelatinous 
 precipitate is produced, containing urea and mercuric oxide in the 
 proportions of 1 eq. of the former to 4 eq. of the latter (4HgO + 
 Ur). When sodic chloride, however, is present in the solution, 
 this precipitate does not occur until all the sodic chloride is 
 converted by double decomposition into mercuric chloride (sub- 
 limate) and sodic nitrate, the solution remaining clear ; if the 
 exact point be overstepped, the excess of mercury immediately 
 produces the precipitate above described, so that the urea present 
 acts as an indicator of the end of the process. It is therefore 
 possible to ascertain the proportion of chlorides in any given 
 sample of urine by this method, if the strength of the mercurial 
 solution is known, since 1 eq. of mercuric oxide converts 1 eq. of 
 sodic chloride into 1 eq. each of corrosive sublimate and sodic 
 nitrate. 
 
 Standard Solution of Mercuric nitrate. It is of great im- 
 portance that the solution be pure, for if the mercury from which 
 it is made be contaminated with traces of other metals, such as 
 bismuth, silver, or lead, they will produce a cloudiness in the 
 liquid while under titration, which may possibly obscure the exact 
 ending of the reaction ; therefore 18 '42 gm. of the purest precipi- 
 tated mercuric oxide are put into a beaker, with a sufficiency of 
 pure nitric acid of about 1'20 spec. grav. to dissolve it by the 
 aid of a gentle heat ; the clear solution so obtained is evaporated 
 on the water bath to remove any excess of free acid. When the 
 liquid is dense and sirupy in consistence, it may be transferred to 
 the graduated cylinder or flask and diluted to a liter. 1 c.c. of the 
 solution so prepared is equal to 0*01 gm. of sodic chloride, or 
 0-006059 gm. of chlorine. 
 
 If pure mercuric oxide is not at hand, the solution is best made ~by 
 weighing 25 gm. of mercuric chloride, which is dissolved in about a liter of 
 water and the oxide precipitated with a slight excess of caustic potash or 
 soda. The precipitate of yellow oxide is allowed to settle clear and the 
 liquid decanted. It is repeatedly washed in this manner Avith warm 
 distilled water until the washings show no amount of alkali or alkaline 
 chloride ; the precipitate is then dissolved in the smallest quantit}^ of pure 
 nitric acid, and diluted to about 950 c.c. If any great excess of nitric acid is 
 present, it may be cautiously neutralized by pure sodic hydrate or carbonate. 
 
 Verification of the Mercuric Solution. This is carried out by 
 the help of the following solutions : 
 
 Pure Sodic chloride. 20 gm. per liter. 
 
 Solution of Urea. 4 gm. of pure urea in 100 c.c. 
 
 Solution of pure Sodic sulphate. Saturated at ordinary tem- 
 peratures. This is used to regulate the action of the free acid 
 which is liberated in the reaction. In the case of natural urine it 
 is not necessary. 
 
382 VOLUMETRIC ANALYSIS. 87. 
 
 Process of Tilration : 10 c.c. of the standard sodic chloride ( = 0'2 gm. 
 NaCl) are placed iu a small beaker, together with 3 c.c. of the urea solution, 
 and 5 c.c. of sodic sulphate. The mercuric solution is then delivered in from 
 the burette, with constant stirring, until a decided permanent white pre- 
 cipitate is seen to form. A mere opalescence may occur even at the beginning, 
 arising from slight impurities in the mercury, but this may be disregarded. 
 If the mercuric solution has been made from weighed pure oxide, exactly 20 
 c.c. should be required ; if, on the contrary, it has been made from the fresh 
 umveighed oxide, somewhat less than 20 c.c. should be required. Say that 
 18' 5 c.c. have been found to give the necessary reaction, then the solution 
 must be diluted with distilled water in the proportion of 1'5 c.c. to every 
 18'5, or 925 c.c. made up to a liter. 
 
 (d) Baryta Solution for removing- Phosphoric and Sulphuric 
 Acids. Before urine can be submitted to titration by the mercurial 
 solution, it is necessary to remove the phosphoric acid, and the 
 proper agent for this purpose is a mixture composed of 1 vol. of 
 cold saturated solution of baric nitrate and 2 vols. of saturated 
 baric hydrate ; the same agent is used previous to the estimation 
 of urea, and may be simply designated Baryta solution. 
 
 Process : 40 c.c. of the clear urine are mixed with 20 c.c. of baryta 
 solution, and the thick mixture poured upon a small dry filter; when 
 sufficient clear liquid has passed through, 15 c.c. ( = 10 c.c. of urine) are 
 taken with a pipette and just neutralized, if necessary, with a drop or two of 
 nitric acid. If not alkaline, the probability is that sufficient baryta solution 
 has not been added to precipitate all the phosphoric and sulphuric acids. 
 This may be known by adding a drop or so of the baryta solution to the 
 filtrate ; if any precipitate is produced, it will be necessary to mix a fresh 
 quantity of urine with three-fourths or an equal quantity of baryta, in which 
 case I7i or 20 c.c. must be taken to represent 10 c.c. of urine ; the excess in 
 either case of baryta must be cautiously neutralized with nitric acid. 
 
 The vessel containing the fluid is then brought under a Mo hr's burette 
 containing the mercurial solution, and small portions delivered in with 
 stirring, until a distinct permanent precipitate is produced. The volume of 
 solution used is then read off and calculated for 1000 parts of urine. 
 
 'Example : 15 c.c. of the liquid prepared with a sample of urine, as 
 described above ( = 10 c.c. of urine), required 6'2 c.c. of mercurial solution : 
 the quantity of salt present was therefore 0'062 gm., or 6'2 parts in 1000 
 parts of urine. 
 
 3. Estimation of Urea (Lie big). 
 
 The combination between urea and mercuric oxide in neutral or 
 alkaline solutions has been alluded to in the foregoing article on 
 chlorides ; it will therefore probably be only necessary to say that 
 the determination of urea in nrine is based on that reaction ; and 
 as the precipitate so produced is insoluble in water or Aveak alkaline 
 solutions, it is only necessary to prepare a standard solution of 
 mercury of convenient strength, and to find an indicator by which 
 to detect the point when all the urea has entered into combination 
 with the mercury, and the latter slightly predominates. This 
 indicator is sodic carbonate. Liebig's instructions are, that when 
 in the course of adding the mercurial solution from the burette to 
 
87. URINE. 38l> 
 
 the urine, a drop of the mixture is taken from time to time and 
 brought in contact with a few drops of solution of sodic carbonate 
 on a glass plate or in a watch-glass, no change of colour is 
 produced at the point of contact until the free urea is all removed ; 
 when this is the case, and the mercury is slightly in excess,, 
 a yellow colour is produced, owing to the formation of hydrated 
 mercuric oxide. 
 
 The compound of urea and mercury consists, according to 
 Liebig's analysis, of 1 eq. of the former to 4 eq. of the latter; 
 that is to say, if the nitric acid set free by the mixture is 
 neutralized from time to time with sodic carbonate or other 
 suitable alkali. If this be not done, the precipitate first formed 
 alters in character, and eventually consists only of 3 eq. of mercury 
 with 1 of urea. In order to produce the yellow colour with 
 sodic carbonate, there must be an excess of mercurial solution. 
 Theoretically, 100 parts of urea should require 720 parts of 
 mercuric oxide ; but practically, 772 parts of the latter are- 
 necessary to remove all the urea, and at the same time" show 
 the yellow colour with alkali ; consequently the solution of 
 mercuric nitrate must be of empirical strength, in order to give- 
 accurate results. 
 
 Preparation of the Mercuric Solution. 77 '2 gin. of red mercuric- 
 oxide, or 71 '5 gm. of the metal itself, are treated with nitric acid,, 
 as described in the previous article on chlorides, and in either case 
 diluted to 1 liter : 1 c.c. of the solution is then equal to O'Ol gm. 
 of urea. (The extreme care required to remove traces of foreign 
 metals from the mercury is not so necessary here as in the foregoing 
 instance, but no large amount of free acid, must be present.) 
 Dragendorff prefers to use mercuric chloride in the preparation 
 of the standard solution, by weighing 96*855 gm. of the pure salt,, 
 which is dissolved in water, then precipitated with dilute caustic 
 soda, the precipitate well washed by decantation until free from 
 chlorine, then dissolved in a slight excess of nitric acid, and the 
 solution diluted to 1 liter. 
 
 Process : Two volumes of the urine are mixed with one of baryta solution 
 as before described in the case of chlorides (reserving the precipitate for the 
 determination of phosphoric acid, if necessarj 7 ), and 15 c.c. (=10 c.c. of 
 urine) taken in a small beaker for titration ; it is brought under the burette 
 containing the mercurial solution (without neutralizing the excess of baryta,, 
 as in the case of chlorides), and the solution added in small quantities so 
 long as a distinct precipitate is seen to form. A plate of glass laid over 
 dark paper is previously sprinkled with a few drops of solution of sodic 
 carbonate, and a drop of the mixture must be brought from time to time, by 
 means of a small glass rod, in contact with the soda. So long as the colour 
 remains white, free urea is present in the mixture ; when the yellow colour 
 is distinctly apparent, the addition of mercury is discontinued, and the 
 quantity used calculated for the amount of urea. It is always advisable to 
 repeat the analysis, taking the first titration as a guide for a more accurate 
 estimation by the second. 
 
384 VOLUMETRIC ANALYSIS. 87. 
 
 Example : 15 c.c. of urine deprived of phosphates ( = 10 c.c. of the original 
 urine) were titrated as described, and required 17'6 c.c. of mercurial solution : 
 consequently there was 0'176 gm. of urea present in the 10 c.c., or 17'6 parts 
 in the 1000 of urine. 
 
 The experiments of Rautenberg (Ann. d. Chem. u. Pit arm. 
 cxxxiii. 55) and Pfliiger (Z. a. C. xix. 375) show, however, that 
 the method, as devised byLiebig, is open to serious errors, due to 
 the uncertainty in the point of neutralization. 
 
 Pfliiger's researches are very complete, and lead to the follow- 
 ing modification of the process. 
 
 A solution of pure urea is prepared containing 2 gm. in 100 c.c. 
 10 c.c. of this solution is placed in a beaker, and 20 c.c. of the 
 mercury solution ran into it in a continuous stream ; the mixture is 
 then immediately brought under a burette containing normal sodic 
 carbonate, and this solution is added with constant agitation until 
 a permanent yellow colour appears. The volume of soda solution 
 so used is noted as that which is necessary to neutralize the acidity 
 produced by 20 c.c. of the mercury solution in the presence of urea. 
 Pfliiger found that by titrating 10 c.c. of the urea solution by 
 small additions of the mercury, and occasional neutralization, the 
 end of the reaction occurred generally at from 17 '2 to 17 '8 c.c. of 
 mercury ; but w r hen he ran in boldly 19 '7 c.c. of mercury, followed 
 immediately by normal sodic carbonate to near neutrality, then 
 alternately a drop or two of first mercury, then soda, the exact 
 point was reached at 20 c.c. of mercury ; and when 10 c.c. of the 
 mercury solution w r hich gave this reaction were analyzed as 
 sulphide by weight, a mean of several determinations gave '0 '7726 
 gm. of HgO, which agrees very closely with Liebig's number. 
 
 In the case of titrating urine, the following method is adopted : 
 
 A plate of colourless glass is laid upon black cloth, and some drops of 
 a thick mixture of sodic bicarbonate (free from carbonate) and water placed 
 upon it at convenient distances. The mercury solution is added to the urine 
 in such volume as is judged appropriate, and from time to time a drop of the 
 white mixture is placed" beside the bicarbonate so as to touch, but not mix 
 completely. At first the urine mixture remains snow-white, but with 
 further additions of mercury a point at last occurs when the white gives 
 place to yellow. "When the colour has developed itself, both drops are rubbed 
 quickly together with a glass rod : the colour should disappear. Further 
 addition of mercury is made cautiously until a faint yellow is permanent. 
 Now is the time to neutralize by the addition of the normal soda to near the 
 volume which has been found necessary to completely neutralize a given 
 volume of mercury solution. If the time has not been too long in reaching 
 this point, it will be found that a few tenths of a c.c. will suffice to complete 
 the reaction. If, however, much time has been consumed, it may occur that, 
 notwithstanding the mixture is distinctly acid, the addition of soda produces 
 a more or less yellow colour : in this case, nothing is left but to go over the 
 analysis again, taking the first trial as a guide for the quantities of mercury 
 and soda solutions, Vhich should be delivered in one after the other as 
 speedily as possible until the exact end is reached. 
 
 It is absolutely necessary, with this modified process, to render 
 
OF THE 
 
 UNIVERSITY 
 
 335 
 
 tlie urine perfectly neutral, after it is freed from phosphates and 
 sulphates by baryta solution. 
 
 Corrections and Modifications (Liebig). In certain cases the results 
 obtained by the above methods are not strictly correct, owing to the variable 
 state of dilution of the liquid, or the presence of matters which affect the 
 mercury solution. The errors are, however, generally so slight as not to 
 need correction. Without entering into a full description of their origin, 
 I shall simply record the facts, and give the modifications necessary to be 
 made where thought desirable. 
 
 The Urine contains more than 2 per cent, of Urea, i.e., more 
 than 20 parts per 1000. This quantity of urea would necessitate 20 c.c. 
 of mercurial solution for 10 c.c. of urine. All that is necessary to .be done 
 when the first titration has shown that over 2 per cent, is present, is to add 
 half as much water to the urine in the second titration as has been needed of 
 the mercurial solution above 20 c.c. Suppose that 28 c.c. have been used at 
 first, the excess is 8 c.c., therefore 4 c.c. of water are added to the fluid before 
 the second experiment is made. 
 
 The Urine contains less than 2 per cent, of Urea. In this case, 
 for every 4 c.c. of mercurial solution less than 20, O'l c.c. must be deducted, 
 before calculating the quantity of urea ; so that if 16 c.c. have been required 
 to produce the yellow colour with 10 c.c. urine, 15'9 is to be considered the 
 correct quantity. 
 
 The Urine contains more than 1 per cent, of Sodic Chloride, 
 i.e., more than 10 parts per 1000. In this case 2 c.c. must be deducted from 
 the quantity of mercurial solution actually required to produce the yellow 
 colour with 10 c.c. of urine. 
 
 The Urine contains Albumen. In this case 50 c.c. of the urine are 
 boiled with 2 drops of strong acetic acid to coagulate the albumen, the 
 precipitate allowed to settle thoroughly, and 30 c.c. of the clear liquid mixed 
 with 15 c.c. of baryta solution, filtered, and titrated for both chlorides and 
 urea, as previously described. 
 
 The Urine contains Ammonic Carbonate. The presence of this 
 substance is brought about by the decomposition of urea, and it may 
 sometimes be of interest to know the quantity thus produced, so as to 
 calculate it into urea. 
 
 As its presence interferes with the correct estimation of urea direct, by 
 mercurial solution, a portion of the urine is precipitated with baryta as 
 usual, and a quantity, representing 10 c.c. of urine, evaporated to dryuess in 
 the water bath to expel the ammonia, the residue then dissolved in a little 
 water, arid the urea estimated in the ordinary way. On the other hand, 
 50 or 100 c.c. of the urine, not precipitated with baryta, are titrated with 
 normal sulphuric acid and litmus paper, each c.c. of acid representing 
 0'017 gm. of ammonia, or 0*03 gm. of urea. 
 
 Pfl tiger's correction for concentration of the urea differs from 
 Liebig's, his rule being as follows : 
 
 Given the volume of urea solution + the volume of NaCO 3 required + the 
 volume of any other fluid free from urea which may be added, and call this 
 V 1 ; the volume of mercury solution is V 2 ; the correction, C, is then 
 
 C= (V 1 Y 2 )x0'08. 
 
 This formula holds good for cases where the total mixture is less than three 
 times the volume of mercury used. 
 
 With more concentrated solutions this formula gives results too high. 
 
 C C 
 
386 VOLUMETRIC ANALYSIS. 87. 
 
 Pfeiffer (Zeit. f. Biol. xx. 540) has made a careful comparison 
 of Liebig's (as modified by Pfliiger)and Rautenberg's methods 
 of estimating urea. The essential difference of Rautenberg's 
 method consists in maintaining the urea solution neutral throughout 
 by successive additions of calcic carbonate ; under these conditions, 
 the composition of the precipitate differs from that formed when 
 the titration is made according to Pfliiger's process, a fact which, 
 accounts for the diminished consumption of mercuric nitrate in the 
 former method. The general conclusions from his observations 
 may be summarized as follows : (1) In estimating the correction 
 for sodic chloride, the amount of free acid should be as small as 
 possible, and O'l c.c. should be subtracted from every c.c. of 
 mercuric nitrate used, but in human urine it is preferable to 
 precipitate the chlorine with silver nitrate, as a slight excess of the 
 latter does not influence the result. (2) The coefficient for 
 dilution should be determined afresh for every new standard 
 solution. 
 
 4. Estimation of Urea by its conversion into Nitrogen Gas. 
 
 If a solution of urea is mingled with an alkaline solution of 
 hypochlorite or hypobromite, the urea is rapidly decomposed and 
 nitrogen evolved, which can be collected and measured in any of 
 the usual forms of gas apparatus described in the section on 
 analysis of gases. 
 
 Test experiments with pure urea have shown, that the whole of 
 the nitrogen contained in it is eliminated in this process, with the 
 exception of a constant deficit of 8 per cent. In the case of urine 
 there are other nitrogenous constituents present, such as uric acid, 
 hippuric acid, and creatinine, which render up a small proportion 
 of their nitrogen in the process, but the quantity so obtained is 
 insignificant, and may be disregarded. Consequently, for all 
 medical purposes, this method of estimating urea in urine is 
 sufficiently exact. 
 
 In the case of diabetic urines, 'however, Menu and others have 
 pointed out that this deficiency is diminished, and if, in addition 
 to the glucose present, cane sugar be also added, it will almost 
 entirely disappear. Mehu therefore recommends that in the 
 analysis of saccharine urines cane sugar be added to ten times the 
 amount of urea present, when the difference between the actual 
 and theoretical yield of nitrogen will not exceed 1 per cent. (Bull. 
 Soc. Chim. [2] xxxiii. 410). 
 
 Russell and West (/. C. S, [2] xii. 749) have described a 
 very convenient apparatus for working the process, and which gives 
 very good results in a short space of time. This method has given 
 rise to endless forms of apparatus devised by various operators, 
 including Mehu, Yvon, Dupre, Apjohn, Maxwell Simpson, 
 Dor emus, O'Keefe, etc., etc. ; the principles of construction are 
 
87. 
 
 URINE. 
 
 387 
 
 all, however, the same. Those who may wish to construct simple 
 forms of apparatus from ordinary laboratory appliances, will do 
 well to refer to the arrangements of Dupre (J. C. S. 1877, 534) 
 or Maxw'ell Simpson (ibid. 538). The nitrometer, with side 
 flask, and using mercury, is perhaps the best of all for the 
 gasometric estimation of urea. Each c.c. of X produced, after 
 correction for temperature, pressure, and moisture, being equal to 
 0'002952 gm. of urea on the assumption that 92 % is evolved. 
 
 The apparatus devised by Russell and West is shown in 
 fig. 54, and may be described as follows : 
 
 The tube for decomposing the urine 
 is about 9 inches long, and about half 
 an inch inside diameter. At 2 inches 
 from its closed end it is narrowed, and 
 an elongated bulb is blown, leaving the 
 orifice at its neck f of an inch in 
 diameter; the bulb should hold about 
 12 c.c. The mouth of this tube is 
 fixed into the bottom of a tin tray 
 abouir If inch deep, which acts as a 
 pneumatic trough ; the tray is supported 
 on legs long enough to allow of a 
 small spirit lamp being held under the 
 bulb tube. The measuring tube for 
 collecting the nitrogen is graduated into 
 cubic centimeters, and of such size as 
 to fit over the mouth of the decom- 
 posing tube ; one holding about 40 c.c. 
 is a convenient size. Russell and West 
 have fixed by experiment the propor- 
 tions, so as to obviate the necessity for 
 correction of pressure and temperature, namely, 37'1 c.c. = Ol gm. 
 -of urea, since they found that 5 c.c. of a 2 per cent, solution of 
 urea constantly gave 37*1 c.c. of nitrogen at ordinary temperatures 
 .and pressures. The entire apparatus can be purchased of most 
 operative chemists for a moderate sum. 
 
 Hypobromite Solution. This is best prepared by dissolving 
 100 gm. of caustic soda in 250 c.c. of water and at the time 
 required 25 c.c. of the solution are mixed with 2*5 c.c. of bromine ; 
 this mixture gives a rapid and complete decomposition of the 
 urea. Strong solution of sodic or calcic hypochlorite answers 
 equally well. 
 
 Process : 5 c.c. of the urine are measured into the bulb-tube, fixed in 
 its proper position, and the sides of the tube washed down with distilled 
 water so that the bulb is filled up to its constriction. A glass rod, having 
 .a thin band of india-rubber on its end, is then passed down into the tube so 
 as to plug up the narrow opening of the bulb. The hypobromite solution is 
 then poured into the upper part of the tube until it is full, and the trough 
 is afterwards half filled with water. 
 
 C C 2 
 
 Fig. 54. 
 
388 VOLUMETRIC ANALYSIS. 87. 
 
 The graduated tube is filled with water, the thumb placed on the opeiu 
 end, and the tube is inverted in the trough. The glass rod is then pulled 
 out, and the graduated tube slipped over the mouth of the bulb-tube. 
 
 The reaction commences immediately, and a torrent of gas rises into the- 
 measuring tube. To prevent any of the gas being forced out by the reaction,, 
 the upper part of the bulb-tube is slightly narrowed, so that the gas is directed 
 to the centre of the graduated tube. With the strength of Irypobromite- 
 solution above described, the reaction is complete in the cold in about ten or 
 fifteen minutes ; but in order to expedite it, the bulb is slightly warmed. 
 This causes the mixing to take place more rapidly, and the reaction is then 
 complete in five minutes. The reaction will be rapid and complete only 
 when there is considerable excess of the hypobromite present. After the 
 reaction the liquid should still have the characteristic colour of the- 
 hypobromite solution. 
 
 The amount of constriction in the tube is by no means a matter 
 of indifference, as the rapidity with which the reaction takes place 
 depends upon it. If the liquids mix too quickly, the evolution of 
 the gas is so rapid that loss may occur. On the other hand, if the 
 tube is too much constricted, the reaction takes place too slowly. 
 
 The simplest means of supporting the measuring tube is to have 
 the bulb-tube corked into a well, wfcich projects from the bottom of 
 the trough about one inch downwards. The graduated tube stands- 
 over the bulb-tube, and rests upon the cork in the bottom of the 
 well. It is convenient to have, at the other end ctf ihe trough, 
 another well, which will form a support for the measuring tube- 
 when not in use. 
 
 To avoid all calculations, the measuring tube is graduated so that 
 the amount of gas read off expresses at once what may be called 
 the percentage amount of urea in the urine experimented upon :: 
 i.e. the number of grams in 100 c.c., 5 c.c. being the quantity of 
 urine taken in each case. The gas collected is nitrogen saturated 
 with aqueous vapour, and the bulk will obviously be more or less- 
 affected by temperature and pressure. Alterations of the barometer 
 produce so small an alteration in the volume of the gas, that it 
 may be generally neglected ; e.g. if there are 30 c.c. of nitrogen,, 
 the quantity preferred, an alteration of one inch in the height of 
 barometer would* produce an error in the amount of urea of about 
 0*003 ; but for more exact experiments, the correction for pressure 
 should be introduced. 
 
 In the wards of hospitals, and in rooms where the experiments 
 are most likely to be made, the temperature will not vary much 
 from 65 F., and a fortunate compensation of errors occurs with 
 this form of apparatus under these -circumstances. The tension of 
 the aqueous vapour, together with the expansion of the gas at this 
 temperature, almost exactly counterbalances the loss of nitrogen 
 in the reaction. 
 
 The authors found from experience that 5 c.c. of urine is the 
 most advantageous quantity to employ, as it usually evolves a con- 
 venient bulk of gas to experiment with, i.e. about 30 c.c. They 
 
. 87. URINE. 389 
 
 have shown that 5 c.c. of a standard solution containing 2 per cent, 
 of urea evolve 37'1 c.c. of nitrogen, and have consequently taken 
 this as the basis of the ^raduation of the measuring tube. This 
 bulk of gas is read off at once as 2 per cent, of urea, and in the 
 same way the other graduations on the tube represent percentage 
 amounts of urea. 
 
 If the urine experimented with is very rich in urea, so that the 
 5 c.c. evolve a much larger volume of gas tMIn 30 c.c., then it is 
 best at once to dilute tllfe urine with its own bulk of water ; take 
 5 c.c. of this diluted urine, and multiply the volume of gas obtained 
 by two. 
 
 If the urine contains much albumen, this interferes with the, 
 process so far that it takes a long ^me for the bubbles of gas to 
 subside, before the volume of gas obtained can be accurately read 
 off. It is therefore better in such cases to remove as much as 
 possible of the albumen by heating the urine with two or three 
 drops of acetic acid, filtering, and then using the nitrate in the 
 usual manner. 
 
 Hamburger (Zeit.f. JBioL xx. 286) describes a method founded 
 on Quinquand's (Monit. Scien. 1882, 2), in which the decom- 
 position of ureaby hypobromite is supposed to take place thus : 
 
 CO(XH 2 ) 2 + 3XaBrO=3NaBr + 2H 2 + CO 2 + N*. 
 
 This reaction requires the proportion of bromine, sodic hydrate, and 
 water to be exactly balanced or incorrect results will be obtained. 
 The author claims for his method that it will yield correct results, 
 no matter in what proportions these reagents are present. It 
 consists essentially in adding an excess of an alkaline solution 
 of sodic hypobromite (of known strength in relation to standard 
 alkaline arsenite) to the liquid containing urea, then destroying 
 the excess oiWiypobromite with an excess of standard arsenite 
 ( 19 '8 gin. As 2 3 per liter), and finally determining the amount 
 of arsenite remaining unoxidized, by titration with standard iodine, 
 the amount of urea then being readily calculated from the amount 
 of arsenite remaining unoxidized. The author's experiments as to 
 the accuracy of the method, show that a certain quantity of urea 
 always requires the same amount of hypobromite, and that the 
 dilution of the solution of urea has no ^effect on the quantity of 
 hypobromite employed. 
 
 To decide on the applicability of the method to natural urine, 
 great pains were taken, the urea being determined as described, the 
 effect of its dilution with water studied, pure urea added, and the 
 whole estimated, and lastly sodic hypobromite of various degrees of 
 concentration, employed; the results of "the experiments are given 
 very fully and tabulated. On the whole, they are very satisfactory, 
 the differences falling well within the limits of errors of observa- 
 tion and manipulation ; the method may therefore be considered 
 applicable to the determination of urea in urine. 
 
390 VOLUMETRIC ANALYSIS. 87. 
 
 5. Estimation of Phosphoric Acid (see also 72). 
 
 The principle of this method is fully described at page 285. 
 The following solutions are required : 
 
 (1) Standard Uranic acetate or nitrate. 1 c.c. =0*005 gm. 
 P 2 5 (see p. 286). 
 
 (2) Standard Phosphoric acid (see p. 287). 
 
 (3) Solution of Sodic acetate (see p. 286). 
 
 (4) Solution of Potassic ferrocyanide. About 1 part to 20 
 of water, freshly prepared. 
 
 Process : 50 c.c. of the clear urine are measured into a small beaker r 
 together w^th 5 c.c. of the solution of sodic acetate (if uranic nitrate is used). 
 The mixture is then warm^ in the water bath, or otherwise, and the uranium 
 solution delivered in from the burette, with constant stirring, as long as a 
 precipitate is seen to occur. A small portion of the mixture is then removed 
 with a glass rod and tested as described (p. 286) ; so long as no brown colour 
 is produced, the addition of uranium may be continued ; when the faintest- 
 indication of this reaction is seen, the process must be stopped, and the 
 amount of colour observed. If it coincides with the original testing of the 
 uranium solution with a similar quantity of fluid, the result is satisfactory., 
 and the quantity of solution used may be calculated for the total phosphoric 
 afrid contained in the 50 c.c. of urine ^ if the uranium has been used 
 accidentally in too great quantity, 10 or 20 c.c. of the same urine may be 
 added, and the testing concluded more cautiously. Suppose, for example, 
 that the solution has been added in the right proportion, and 19'2 c.c. used, 
 the 50 c.c. will have contained 0'096 gm. phosphoric acid (=1/92 per 100). 
 With care and some little practice the results are very satisfactor}'. 
 
 Earthy Phosphates. The above determination gives the total amount 
 of phosphoric acid, but it may sometimes be of interest to know how much of 
 i^is combined with lime and magnesia. To this end 100 or 200 c.c. of the 
 urine are measured into a baker, and rendered freely alkaline with ammonia ; 
 the vessel is then set aside for ten or twelve hours, for the precipitate of 
 earthy phosphates to settle : the clear fluid is then decanted through a filter, 
 the precipitate brought upon it and washed with ammoniacal water ; a hole 
 is then made in the filter and the precipitate washed through ; the paper 
 moistened with a little acetic acid, and washed into the vessel containing 
 the precipitate, which latter is dissolved in acetic acid, some sodic acetate 
 added, and the mixture diluted to about 50 c.c. and titrated as before 
 described ; the quantity of phosphoric acid so found is deducted from the 
 total previously estimated, and the remainder gives the quantity existing in 
 
 combination with alkalies. 
 
 
 
 6. Estimation of Sulphuric Acid. 
 
 Standard Baric chloride. A quantity of crystallized baric 
 chloride is to be powdered, and dried between folds of blotting- 
 paper. Of this, 30*5 gm. are dissolved in distilled water, and the 
 liquid made up to a liter. 1 c.c. =0*01 gm. of SO 3 . 
 
 Solution of Sodic sulphate. 1 part to 10 of water. 
 
 Process : 100 c.c. of the urine are poured into a beaker, a little hydro- 
 chloric acid added, and the whole placed on a small sand bath, to which heat 
 
87. URINE. 391 
 
 is applied. When the solution boils, the baric chloride is allowed to flow 
 in very gradually as long as the precipitate is seen distinctly to increase. 
 The heat is removed, and the vessel allowed to stand still, so that the 
 precipitate may subside. Another drop or two is then added, and so on, 
 until the whole of the SO 3 is precipitated. Much time, however, is saved 
 by using Be ale's filter, represented in fig. 23. A little of the fluid is thus 
 filtered clear, poured into a test-tube, and tested with a drop from the 
 burette; this is afterwards returned to the beaker, and more of the test 
 solution added, if necessary. The operation is repeated until the precipita- 
 tion is complete. In order to be sure that too much of the baryta solution 
 has not been added, a drop of the clear fluid is added to the solution of sodic 
 sulphate placed in a test-tube or upon a small mirror (see p. 328). If no 
 precipitate occurs, more baryta must be added ; if a slight cloudiness takes 
 place, the analysis is finished ; but if much precipitate is produced, too large. 
 a quantity of the test has been used, and the analysis must be repeated. 
 
 For instance, suppose that 18'5 c.c. have been added, and there 
 is still a slight cloudiness produced which no longer increases after 
 the addition of another J c.c., we know that between 18^ and 
 19 c.c. of solution have been required to precipitate the whole of 
 the sulphuric acid present, and that accordingly the 100 c.c. of 
 urine contain between 0*185 and 0*19 gm. of SO 3 . 
 
 7. Estimation of Sugar. 
 
 Feh ling's original method is precisely the same as described 
 in 74, but the most suitable methods for urine are Gerrard's 
 (p. 317) or the Pavy-Fehling (p. 315). 
 
 Process for the Ct/ano-cupric Solution .- 10 c.c. of the clear urine are diluted 
 by means of a measuring flask to 200 c.c. with water, and a large burette 
 filled with the fluid. To 10 c.c. of the copper solution prepared as directed 
 (p. 317) are then measured another 10 c.c. of copper and the liquid, the 
 vessel brought to boiling ; the diluted urine is then delivered in cautiously 
 from the burette while still boiling, and with constant stirring, until the 
 bluish colour has nearly disappeared. The addition of the urine must then 
 be continued more carefully, until the colour is all removed, the burette 
 is then read off, and the quantity of sugar in the urine calculated as 
 follows : 
 
 Suppose that 40 c.c. of the diluted urine have been required to reduce 
 the 10 c.c, of copper solution, that quantity will have contained 0'05 gm. of 
 sugar; but, the urine being diluted 20 times, the 40 c.c. represent only 2 c.c. 
 of the original urine; therefore 2 c.c. of it contain 0'05 gm. of sugar, or 
 25 parts per 1000. 
 
 If the Pavy-Fehling solution is used it is prepared as described 
 in 74 (p. 315). 
 
 Process : 10 c.c. of clear urine are diluted as just described, and delivered 
 cautiously from the burette into 50 or 100 c.c. of the Pavy-Fehling 
 liquid (previously heated to boiling) until the colour is discharged. The 
 calculation is the same as before. 100 c.c. of Pavy-Fehling solution 
 =0'05 gm. glucose. 
 
 The ammoniacal fumes are best absorbed by leading an elastic tube 
 from the reduction flask into a beaker of water ; the end of the tube should 
 be plugged with a piece of solid glass rod, and a transverse slit made in the 
 
392 VOLUMETRIC ANALYSIS. 87. 
 
 elastic tube just above the plug. This valve allows the vapours to escape, 
 but prevents the return of the liquid in case of a vacuum. 
 
 Dr. Edmunds communicates the following colorimetric method 
 for Sugar in Urine. 
 
 A ready preliminary test for sugar in urine is essential for medical 
 practitioners at the bedside or in the consulting room. An excellent and 
 handy test is that of picric acid, as recommended by Sir George Johnson, 
 but which has not come into general use because of the complexity of the 
 process ; the two solutions and the urine being added together in different 
 portions. I simplify the proceeding by substituting soda for potash, which 
 gives a soluble salt ; and then making the solution up so that it and the 
 , imne are always added together in equal volumes : on boiling the depth of 
 colour at once displays the presence of sugar, unless only questionable traces 
 are present, a question to decide which the ordinary laboratory processes 
 must be resortod to. 
 
 For the ready test I take a solution containing 0'5 % of pure picric acid 
 and 1 % of pure caustic soda, made up with freshly boiled distilled water to 
 volume. Any convenient quantity of the urine is poured into a test tube, 
 and to it is added about an equal volume of the picrate solution. On boiling 
 the mixture for one minute the presence of an opaque red-brown colour at 
 once appears if there be as much as 1 % of sugar in the urine. Normal 
 urine gives a full transparent blood-red colour, as can be seen at once by 
 testing any normal urine. This red colour is due to the kreatinine in the 
 urine, which, reduces the picric to picramic acid, precisely as is done by 
 glucose. The standard of colour can also be precisely realized by using 
 a 0'2 / solution of pure dextrose in distilled water. 
 
 It is most convenient to pour 10 c.c. of this solution of dextrose into an 
 ordinary 25 c.c. hand-measure, and then to fill up to 20 c.c. with the sodium 
 picrate solution. On boiling this mixture in a test -tube for one minute, 
 a deep transparent blood-red solution is obtained which represents the 
 reducing power of the kreatinine in normal urine. If, on testing a urine, 
 an opaque red-brown liquid be obtained, the urine should then be diluted 
 with distilled water to ten times its volume, and the test reapplied to the 
 diluted urine in equal volumes as at first. If this gives still an opaque-red, 
 the urine must be further diluted, and again used in equal measured volumes 
 with the test solution. On the other hand, if the resulting mixture is too 
 pale the dilution must be less, and the dilution factor multiplied with 0'2 / 
 gives the percentage of glucose in the urine. For precise colorimetric work 
 the mixture should be poured into standard tubes of equal diameter as 
 recommended by Allen, and then viewed side by side with the decoction 
 obtained by using a 0'2 / solution of pure dextrose in distilled water. 
 
 The solution above described keeps perfectly, and the process is as handy 
 as that of estimating albumen in urine by boiling and acidulating with 
 normal acetic acid. 
 
 8. Estimation of Uric Acid. 
 
 A method for the accurate estimation of this constituent of 
 urine has, up to the present, not been found. The difficulty is 
 caused by the complicated character of the urine itself, and how- 
 ever accurate the process may be with the acid in a separate pure 
 state, it becomes far less reliable when such method is applied to 
 normal or abnormal urine. The precipitation of the acid in 
 combination with some metal, such as silver or copper, carries 
 
87. UIUXE. 393 
 
 with it also the so-called alloxuric bases, and the separation by 
 hydrochloric acid contaminates the precipitate with colouring and 
 other matters which militate against its accurate estimation with 
 permanganate. I am, however, of the opinion that the latter 
 method is even now the best for a rapid comparative estimation 
 of this constituent. 
 
 Process : 200 c.c. of the urine are put into an evaporating basin with 
 a few drops of concentrated hydrochloric acid, and evaporated on the water 
 bath to about half the volume ; it is then transferred to a closely-stoppered 
 flask, together with any slight precipitate which may have formed. 5 c.c. 
 of concentrated hydrochloric acid are then added, and the mixture violently 
 shaken for a few minutes. It is then allowed to settle for half an hour and 
 the liquid passed through a small filter of smooth, hard texture, taking care 
 to pass as little as possible of the sediment to the filter. About 20 c.c. of 
 cold water are then added to the precipitate in the flask, which is in turn 
 passed through the filter. The filter is then also washed with about the 
 same quantity of water; a hole is then made at its apex, and the small 
 quantity of adhering precipitate washed into the original flask. Finally 
 about 10 c.c. of concentrated solution of caustic potash (1 : 10) are added 
 to the contents of the flask and slightly warmed until a clear solution is 
 obtained. The mixture is then diluted with about 100 c.c. of cold water, 
 20 c.c. of dilute sulphuric acid added (1 : 5), and the titration with T ^ 
 permanganate carried out in the usual manner. 
 
 Xo absolute weight of uric acid can be calculated from the 
 results, but Mohr assumes that each c.c. of ~ permanganate 
 = 0'0075 gm. of uric acid;'"" the process may, however, be made 
 available for pathological purposes by comparing the results from 
 time to time with the urine from the same person. 
 
 The following recent method has, in my opinion, a better claim 
 to accuracy as respects the actual amount of uric acid present in 
 any given specimen of urine than any other. It is based on the 
 fact that an alkaline solution of uric acid reduces Fehling 
 solution in the same way as glucose. The method is worked 
 out by E. Eiegler (Z. a. C. 1896, 31), who found that an average 
 of many experiments gave 0*8 gin. of reduced copper for 1 gm. 
 of uric acid. The acid is first separated from the urine under 
 examination as ammonic urate in the following manner : 
 
 Process : 200 c.c. of urine are mixed with 10 c.c. of a saturated solution 
 of sodic carbonate, allowed to stand for half an hour, and filtered from the 
 precipitated phosphates. The precipitate is washed with 50 c.c. of hot 
 water, and to the filtrate and wash-water 20 c.c. of a saturated solution of 
 ammonic chloride added. The liquid is well stirred, and after five hours 
 filtered, preferably through a Schleicher and S chilli filter, No. 597, 
 11 c.m. The precipitate is washed with 50 c.c. of water, and then introduced 
 by means of a jet from a washing-bottle into a 300 c.c. beaker. Several 
 drops of potash are added to clear the liquid, then 60 c.c. of Fell ling's 
 solution, and the whole well stirred. The beaker is then heated on a wire 
 gauze until the liquid boils, the boiling being continued for five minutes. 
 
 * This figaire has been verified by F. G. Hopkins (Allen's Chemistry of Urine, 
 ]?. 171). 
 
394 VOLUMETRIC ANALYSIS. 87. 
 
 AVhen the precipitate has subsided, the liquid is filtered through a small 
 tough filter (Schleicher and S chilli, No. 590, 9 c.m.), the precipitate 
 well washed, and dissolved in 20 c.c. of nitric acid (sp. gr. I'l), the filter 
 being washed with 60 c.c. of water. 
 
 To this solution dry powdered sodic carbonate is added little by little 
 until there is a permanent turbidity. The liquid is then cleared by the 
 cautious addition of dilute sulphuric acid, and made up to 100 c.c. 25 c.c. 
 of this are placed in a 100 c.c. flask, 1 gm. of potassic iodide in 10 c.c. of 
 water added, allowed to stand for ten minutes, then titrated with standard 
 thiosulphate solution (1 c.c. = 0'002 gm. uric acid), using starch as the 
 indicator. To the total amount of uric acid found in the 200 c.c. of urine, 
 an additional 0'030 gm. should be added to allow for the solubility of the 
 ammonic urate in urine. 
 
 The standard thiosulphate solution is made by diluting 126 c.c. 
 of y^- solution to 500 c.c. The reaction is : 
 
 2Cu(ST0 3 ) 2 + 4KI =Cu 2 ! 2 + 4KN0 3 + 1 2 . 
 
 The reduced cuprous oxide may also be weighed directly or reduced 
 to metallic copper, as in the estimation of sugar. In the latter 
 case the amount of copper, multiplied by the factor 1*25, gives 
 the corresponding amount of uric acid. 
 
 Dr. Edmunds sends me the following pertinent remarks as to 
 the estimation of Uric Acid. 
 
 1. Chemical uric acid differs entirely in its habitudes from urinary uric 
 acid. Its crystalline form is always uniform as chemical uric acid colour- 
 less and quite different from urinary uric acid, which, as got from urine, is 
 always coloured yellow-brown, and is protean in its crystalline forms. 
 
 2. The problem of titrating chemical uric acid or pure uric acid is 
 not quite the same as that of titrating the uric acid in urine. I am not 
 yet able to say in what the difference consists, and I have often crystallized 
 pure uric acid out of iron and other solutions, but have never been able to 
 colour uric acid, nor to get it to crystallize again like urinary uric acid. 
 The only way in which I have succeeded is to add an alkaline solution of 
 chemical urate of potash to a urine out of which I had precipitated all its- 
 uric acid with HC1. In that way I found that the uric acid took up from 
 the urine something which gave it the colouration and the protean crystalline 
 form of urinary uric acid. I have thought that urinary uric acid is really 
 a combination of chemical uric acid with some animal base or colourant 
 of urine. 
 
 3. To purify urinary uric acid it should be dissolved (and thrown out by 
 dilution) in H 2 SO 4 three successive times. In titrating this with per- 
 manganate I am not prepared to give you the reaction, but the practical 
 point is that, as the permanganate goes in by drops, it is instantly decolour- 
 ized as long as there is any uric acid present, and the end-point is marked 
 quite distinctly (if you are on the look out for it) by a certain hang or 
 hesitation in the decolonization of the permanganate. 
 
 4. Fokker's process, as modified by Hopkins, is, I think, the best. 
 The saturation with absolutely pure NH 4 C1 of an acid urine (which should 
 be freshly passed and filtered at 120) throws out all the uric acid as ammonic 
 urate. This is well set out in Allen's Chemistry of Urine, p. 168, et seq. 
 But much of the work does not say whether the processes have been worked 
 out on the chemical uric acid or on the real "uric acid," as we call it, 
 
87. uniXE. 395 
 
 freshly obtained from urine. "What we have to deal with in medicine is that 
 coloured protean crystalline . substance which comes out constantly from 
 urines on adding pure strong HC1 and setting aside for forty-eight hours. 
 That is what we get in the uric acid diathesis, in gout, and in calculi. 
 
 For the estimation of uric acid I set aside 100 c.c. of fresh urine, filtered 
 at about 120 F., and acidify it with 5 / of pure strong hydrochloric acid. 
 At the end of forty-eight hours a deposit of uric acid will be seen at the 
 bottom of the tube, and from this a very good idea is gained of the uric 
 acid in the urine. If closer quantification be wanted, the uric acid is 
 collected on a small fine filter paper, washed with a few centimeters of ice- 
 cold distilled water, then dried and weighed, with deduction for the filter 
 paper, and with addition for the uric acid dissolved in the 105 c.c. of acid 
 urinar}'" mother-liquor. The amount of uric acid contained in the 105 c.c, 
 of liquid would depend upon the temperature before and at the time of 
 filtration. At 33 F. it would contain only some 2 m.gm., at 68 F. it would 
 contain 6 m.gm., at 212 F. it would contain 62'5 m.gm. 
 
 9. Estimation of Lime and Mag-nesia. 
 
 Process: 100 c.c. of the urine are precipitated with ammonia, the 
 precipitate re-dissolved in acetic acid, and sufficient ammonic oxalate added 
 to precipitate all the lime present as oxalate. The precipitate is allowed to 
 settle in a warm place, then the clear liquid passed through a small filter, 
 the precipitate brought upon it, washed with hot water, the filtrate and 
 washings set aside, then the precipitate, together with the filter, pushed 
 through the funnel into a flask, some sulphuric acid added, the liquid freely 
 diluted, and titrated with permanganate, precisely as in 52; each c.c. of 
 jV permanganate required represents 0'0028 gin. of CaO. 
 
 Or the following method may be adopted : 
 
 The precipitate of calcic oxalate, after being washed, is dried and, together 
 with the filter, ignited in a platinum or porcelain crucible, by which means 
 it is converted into a mixture of calcic oxide and carbonate. It is then 
 transferred to a flask by the aid of the washing-bottle, and an excess of $ 
 nitric acid delivered in with a pipette. The amount of acid, over and above 
 what is required to saturate the lime, is found by T \ caustic alkali, each c.c. 
 of acid being equal to 0'0028 gm. of CaO. 
 
 In examining urinary sediment or calculi for calcic oxalate, it is 
 first treated with caustic potash to remove uric acid and organic 
 matter, then dissolved in sulphuric acid, freely diluted, and titrated 
 with permanganate ; each c.c. of ~ solution represents 0'0054 gm. 
 of calcic oxalate. 
 
 Mag-nesia. The filtrate and washings from the precipitate of 
 calcic oxalate are evaporated on the water bath to a small bulk, 
 then made alkaline w r ith ammonia, sodic phosphate added, and set 
 aside for 8 or 10 hours in a cool place, that the magnesia may 
 separate as ammonio-magnesic phosphate. The supernatant liquid 
 is then passed through a small filter, the precipitate brought upon 
 it, washed with ammoniacal water in the cold, and dissolved in 
 acetic acid, then titrated with uranium solution, as in 72 ; each 
 c.c. of solution required represents 0*002815 gm. of magnesia. 
 
396 VOLUMETRIC ANALYSIS. 87. 
 
 10. Ammonia. 
 
 The only method hitherto applied to the determination of 
 .ammonia in urine is that of 8 ch losing, which consists in placing 
 a measured quantity of the urine, to which milk of lime is 
 previously added, under an air-tight hell-glass, together with an 
 open vessel containing a measured quantity of titrated acid. In 
 the course of from 24 to 36 hours all the ammonia will have 
 passed out of the urine into the acid, which is then titrated with 
 standard alkali to find the amount of ammonia absorbed. 
 
 One great objection to this method is the length of time required, 
 .since no heating must be allowed, urea being decomposed into free 
 ammonia, when heated with alkali. There is also the uncertainty 
 as to the completion of the process ; and if the vessel be opened 
 before the absorption is perfect, the analysis is spoiled. The 
 following plan is recommended as in most cases suitable : When 
 a solution containing salts of ammonia is mixed with a measured 
 quantity of free fixed alkali of known strength, and boiled until 
 ammoniacal gas ceases to be evolved, it is found that the resulting 
 liquid has lost so much of the free alkali as corresponds to the 
 ammonia evolved ( 19) ; that is to say, the acid which existed in 
 combination with the ammonia in the original liquid has simply 
 changed places, taking so much of the fixed alkali (potash or soda) 
 as is equivalent to the ammonia it has left to go free. In the case 
 of urine being treated in this way, the urea will also be decomposed 
 into free ammonia, but happily in such a way as not to interfere 
 with the estimation of the original amount of ammoniacal salts. 
 The decomposition is such that, while free ammonia is evolved from 
 the splitting up of the urea, carbonate of fixed alkali (say potash) 
 is formed in the boiling liquid, arid as this reacts equally as alkaline 
 as though it were free potash, it does not interfere in the slightest 
 degree with the estimation of the original ammonia. 
 
 Process : 100 c.c. of the urine are exactly neutralized with ^ soda or 
 potash, as for the estimation of free acid ; it is then put into a flask capable 
 of holding five or six times the quantity, 10 c.c. of normal alkali added, and 
 the whole brought to boiling, taking care that the bladders of froth which 
 at first form do not boil over. After a few minutes these subside, and the 
 boiling proceeds quietly. When all ammoniacal fames are dissipated, the 
 lamp is removed, and the flask allowed to cool slightly ; the contents then 
 emptied into a beaker, and normal nitric acid delivered in from the burette 
 with constant stirring, until a fine glass rod or small feather dipped in the 
 mixture and brought in contact with violet-coloured litmus paper produces 
 neither a blue nor a red spot. The number of c.c. of normal acid are 
 deducted from the 10 c.c. of alkali, and the rest calculated as ammonia. 
 1 c.c. of alkali = 0'017 gm. of ammonia. 
 
 Example : 100 c.c. of urine were taken, and required 7 c.c. of -^f alkali 
 to saturate its free acid ; 10 c.c. of normal alkali were then added, and the 
 mixture boiled until a piece of moistened red litmus paper was not turned 
 blue when held in the steam ; 4'5 c.c. of normal acid were afterwards required 
 to saturate the free alkali ; the quantity of ammonia was therefore equal to 
 5'5 c.c., which, multiplied by O'OIT, gave 0'0935 gm. in 1000 of urine. 
 
87. UIUXE. 397 
 
 It must be borne in mind, that the plan just described is not applicable to 
 urine which has already suffered decomposition by age or other circumstances 
 so as to contain carbonate of ammonia ; in this case it would be preferable to 
 adopt Schl 6 sing's method; or where no other free alkali is present, direct 
 titratiou with normal acid may be adopted. 
 
 11. Estimation of Free Acid. 
 
 The acidity of urine is doubtless owing to variable substances,, 
 among the most prominent of which appear to be acid sodic phos- 
 phate and lactic acid. Other free organic acids are probably in 
 many cases present. Under these circumstances, the degree of 
 acidity cannot be placed to the account of any particular body ;. 
 nevertheless, it is frequently desirable to ascertain its amount, 
 which is best done as follows : 
 
 100 c.c. of urine are measured into a beaker, and ^ alkali delivered in 
 from a small burette, until a thin glass rod or feather, moistened with the- 
 mixture and streaked across some well-prepared violet litmus paper, produces 
 no change of colour ; the degree of acidity is then registered as being equal 
 to the quantity of ^V alkali used. 
 
 12. Estimation of Albumen. 
 
 Bodeker has worked out a method of titration which gives 
 approximate results when the quantity of albumen is not too 
 small, say not less than 2 per cent. The principle is based on the 
 fact that, potassic ferrocyanide completely precipitates albumen 
 from an acetic acid solution in the atomic proportions of 211 
 ferrocyanide to 1612 albumen. 
 
 Standard Solution of Ferrocyanide. 1*309 gm. of the pure- 
 salt in a liter of distilled water. 1 c.c. of the solution precipitates 
 O01 gm. of albumen. It must be freshly prepared. 
 
 Process : 50 c.c. of the clear filtered urine are mixed with 50 c.c. of 
 ordinary commercial acetic acid, and the fluid put into a burette. Pive or 
 six small niters are then chosen, of close texture, and put into as many 
 funnels, then moistened with a few drops of acetic acid, and filled up with 
 boiling water ; by this means the subsequent clear filtration of the mixture 
 is considerably facilitated. 10 c.c. of the ferrocyanide solution are then 
 measured into a beaker, and 10 c.c. of the urinary fluid from the burette 
 added, well shaken, and poured upon filter No. 1. If the fluid which 
 passes through is bright and clear with yellowish colour, the ferrocyanide 
 will be in excess, and a drop of the urine added to it will produce a cloudiness. 
 On the other hand, if not enough ferrocyanide has been added, the filtrate 
 will be turbid, and pass through very slowl} r ; in this case, frequently both 
 the ferrocyanide and the urine will produce a turbidity when added. In 
 testing the filtrate for excess of ferrocyanide, care must be taken not to add 
 too much of the urine, lest the precipitate of hydroferrocyanide of albumen 
 should dissolve in the excess of albumen. 
 
 According to the results obtained from the first filter, a second trial is 
 made, increasing the quantity of urine or ferrocyanide half or as much 
 again, and so until it is found that the solution first shown to be in excess is 
 reversed. A trial of the mean between this quantity and the previous one 
 will bring the estimation closer, so that a final test may be decisive. 
 
398 VOLUMETRIC ANALYSIS. 88. 
 
 Example: 50 c.c. of urine passed by a patient suffering from B right's 
 disease were mixed with the like quantity of acetic acid, and tested as 
 follows: 
 
 In filtrate 
 
 Urine. Ferrocyanide. Urine Ferrocyanide 
 
 gave 
 
 1. 10 c.c. ' 10 c.c. prec. 
 
 2. 10 20 prec. 
 
 3. 10 15 prec. 
 
 4. 10 17-5 ., faint prec. 
 
 5. 10 18 
 
 Therefore the 10 c.c. of diluted urine ( = 5 c.c. of the original 
 secretion) contained P 18 gm. albumen, or 36 parts per 1000. 
 
 13. Estimation of Soda and Potash.. 
 
 50 c.c. of urine are mixed with the same quantity of baryta solution, 
 allowed to stand a short time, and filtered ; then 80 c.c. ( = 40 c.c. urine) 
 measured into a platinum dish and evaporated to dryness in the water bath ; 
 the residue is then ignited to destroy all organic matter, and when cold 
 dissolved in a small quantity of hot water, ammonic carbonate added so long 
 as a precipitate, occurs, filtered through a small filter, the precipitate washed, 
 the filtrate acidified with hydrochloric acid and evaporated to dr}mess, then 
 cautiously heated to expel all ammoniacal salts. The residue is then treated 
 with a little water and a few drops each of ammonia and ammonic carbonate, 
 filtered, the filter thoroughly washed, the filtrate and washings received into 
 a tared platinum dish, then evaporated to dryness, ignited, cooled, and 
 weighed. 
 
 By this means the total amount of mixed sodic and potassic 
 chlorides is obtained. The proportion of each is found by titrating 
 for the chlorine as in 41, and calculating as directed on page 141. 
 
 14. Estimation of Total Nitrogen. 
 
 This can now be easily accomplished by Kjeldahl's method 
 ( 19.5) and is especially serviceable, since it has been found that 
 the results of the titration method for urea by Lie big's process, 
 either in its original way or by subsequent modifications, cannot 
 give the true data for calculating the nitrogen in any given specimen 
 of urine. 
 
 Process : 5 c.c. of urine of average concentration are measured into 
 a flask holding about 300 c.c., together with 20 c.c. of sulphuric acid, then 
 heated to boiling, and the heat continued until all vapour and gases are 
 given off and the fluid possesses a clear yellow tint. 25 to 30 minutes 
 generally suffices. The flask is then suffered to cool, the liquid diluted, and 
 distilled with caustic soda and zinc as described on page 85. 
 
 ANALYSIS OF NATURAL WATERS AND SEWAGE. 
 
 88. THE analysis of natural waters and sewage has for a long 
 period received the attention of chemists, but until lately no methods 
 of examination have been produced which could be said to satisfy 
 the demands of those who have been interested in the subject 
 
88. WATER ANALYSIS. 399 
 
 from various points of view. The researches of Frank land, and 
 Armstrong, Miller, "Wanklyn, Tidy, Bischof, Warington, 
 and others, have, however, now brought the whole subject into 
 a more satisfactory form, so that it may fairly be said that, as regards 
 accuracy of chemical processes, or interpretation of results from 
 a chemical and sanitary point of view, very little addition is 
 required. Considerable space will be devoted to the matter here ; 
 and as most of the processes are now volumetric, and admit of 
 ready and accurate results, the general subject naturally falls with- 
 in the scope of this work. Care has been taken to render the 
 treatment of the matter practical and trustworthy. 
 
 The following processes mainly originated by Frankland and 
 Armstrong necessitate the use of peculiar materials and 
 apparatus : the preparation and arrangement of these will be 
 described at some length previous to the introduction of the 
 general subject. 
 
 THE PREPARATION OF REAGENTS. 
 
 A. Reagents required for the Estimation of Nitrogen present as 
 
 Ammonia. 
 
 (a) Xessler's Solution. Dissolve 62*5 gm. of potassic iodide 
 in about 250 c.c. of distilled water, set aside a few c.c,, and add 
 gradually to the larger part a cold saturated solution of corrosive 
 sublimate until the mercuric iodide precipitated ceases to be 
 redissolved on stirring. When a permanent precipitate is obtained, 
 restore the reserved potassic iodide so as to redissolve it, and 
 continue adding corrosive sublimate very gradually until a slight 
 precipitate remains undissolved. (The small quantity of potassic 
 iodide is set aside merely to enable the mixture to be made rapidly 
 without danger of adding an excess of corrosive sublimate.) 
 
 ^N"ext dissolve 150 gm. of solid potassic hydrate (that usually 
 sold in sticks or cakes) in 150 c.c. of distilled water, allow the 
 solution to cool, add it gradually to the above solution, and make 
 up with distilled water to one liter. 
 
 On standing, a brown precipitate is deposited, and the solution 
 becomes clear, and of a pale greenish-yellow colour. It is ready 
 for use as soon as it is perfectly clear, and should be decanted into 
 a smaller bottle as required. 
 
 (/3) Standard Solution of Ammonic chloride. Dissolve 1'9107 
 gm. of pure dry ammonic chloride in a liter of distilled water ; of 
 this take 100 c.c., and make up to a liter with distilled water. 
 The latter solution will contain ammonic chloride corresponding to 
 0'00005 gm. of nitrogen in each c.c. In use it should be measured 
 from a narrow burette of 10 c.c. capacity divided into tenths. 
 
 [If it is desired to estimate " ammonia " rather than " nitrogen as 
 ammonia," take T5735 gm. of ammonic chloride instead of 1'9107 gm. 
 1 c.c. will then correspond to O'OOOOS gm. of ammonia (NH 3 ).] 
 
400 VOLUMETRIC ANALYSIS. 88. 
 
 (y) Sodic carbonate. Heat anhydrous sodic carbonate to 
 redness in a platinum crucible for about an hour, taking care not 
 to fuse it. While still warm rub it in a clean mortar so as to 
 break any lumps which may have been formed, and transfer to 
 a clean dry wide-mouthed stoppered bottle. 
 
 (3) Water free from Ammonia. If, when 1 c.c. of !N"essler's 
 solution (A. a) is added to 100 c.c. of distilled water in a glass 
 cylinder, standing on a white surface (see Estimation of Ammonia), 
 no trace of a yellow tint is visible after five minutes, the water is 
 sufficiently pure for use. As, however, this is rarely the case, the 
 following process must usually be adopted. Distil from a large 
 glass retort (or better, from a copper or tin vessel holding 15 20 
 liters) ordinary distilled water which has been rendered distinctly 
 alkaline by addition of sodic carbonate. A glass Liebig's 
 condenser, or a clean tin worm should be used to condense the 
 vapour ; it should be connected to the still by a short india-rubber 
 joint. Test the distillate from time to time with jSTessler's 
 solution, as above described, and when free from ammonia collect 
 the remainder for use. The distillation must not be carried to 
 dryness. Ordinary water may be used instead of distilled water, 
 but it occasionally continues for some time to give off traces of 
 ammonia by the slow decomposition of the organic matter present 
 in it. 
 
 B. Reagents required for the Estimation of Organic Carbon and 
 
 Nitrogen. 
 
 (a) Water free from Ammonia and Organic Matter. Distilled 
 water, to which 1 gm. of potassic hydrate and 0'2 gm. of potassic 
 permanganate per liter have been added, is boiled gently for about 
 twenty-four hours in a similar vessel to that used in preparing 
 water free from ammonia (A. ), an inverted condenser being so 
 arranged as to return the condensed water. At the end of that 
 time the condenser is adjusted in the usual way, and the water 
 carefully distilled, the distillate being tested at intervals for 
 ammonia, as in. preparing A. 3. When ammonia is no longer 
 found the remainder of the distillate may be collected, taking care 
 to stop short of dryness. The neck of the retort or still should 
 point slightly upwards, so that the joint which connects it with 
 the condenser is the highest point. Any particles carried up 
 mechanically will then run back to the still, and not contaminate 
 the distillate. The wate"r thus obtained should then be rendered 
 slightly acid with sulphuric acid, and re-distilled from a clean 
 vessel for use, again stopping short of dryness. 
 
 (/3) Solution of Sulphurous acid. Sulphurous anhydride is 
 prepared by the action of pure sulphuric acid upon cuttings of 
 clean metallic copper which have been digested in the cold with 
 
88. WATER ANALYSIS. 401 
 
 concentrated sulphuric acid for twenty-four hours, and then washed 
 with water. The gas is made to bubble through water to remove 
 mechanical impurities, and then conducted into water free from 
 ammonia and organic matter (B. a) until a saturated solution is 
 obtained. 
 
 (y) Solution of Hydric sodic sulphite. Sulphurous anhydride, 
 prepared and washed as above, is passed into a solution of sodic 
 carbonate made by dissolving ignited sodic carbonate (A. y) in 
 water free from ammonia and organic matter (B. a). The gas is 
 passed until carbonic anhydride ceases to be evolved. 
 
 (o) Solution of Ferrous chloride. Pure crystallized ferrous 
 sulphate is dissolved in water, precipitated by sodic hydrate, the 
 precipitate well washed (using pure water B. a for the last 
 washings), and dissolved in the smallest possible quantity of pure 
 hydrochloric acid. Two or three drops must not contain an 
 appreciable quantity of ammonia. It is convenient to keep the 
 solution in a bottle with a ground glass cap instead of a stopper, 
 so that a small dropping tube may be kept in it always ready 
 for use. 
 
 (e) Cupric oxide. Prepared by heating to redness with free 
 access of air, on the hearth of a reverberatory furnace, or in 
 a muffle, copper wire cut into short pieces, or copper sheets cut into 
 strips. That which has been made by calcining the nitrate cannot 
 be used, as it appears to be impossible to expel the last traces of 
 nitrogen. After use, the oxide should be extracted by breaking 
 the combustion tube, rejecting the portion which was mixed with 
 the substance examined. As soon as a sufficient quantity has been 
 recovered, it should be recalcined. This is most conveniently 
 done in an iron tube about 30 m.m. in internal diameter, and about 
 the same length as the combustion furnace. One end should be 
 closed with a cork, the cupric oxide poured in, the tube placed in 
 the combustion furnace (which is tilted at an angle of about 15, 
 so as to produce a current of air), the cork removed, and the tube 
 Icept at a red heat for about two hours. In a Hofmann's gas 
 furnace, with five rows of burners, two such tubes may be heated 
 at the same time if long clay burners are placed in the outer rows, 
 and short ones in the three inner rows. If the furnace has but 
 three rows of burners, a rather smaller iron tube must be used. 
 "When cold, the oxide can easily be extracted, if the heat has not 
 "been excessive, by means of a stout iron wire, and should be kept 
 in a clean dry stoppered bottle. Each parcel thus calcined should 
 invariably be assayed by filling with it a combustion tube of the 
 usual size, and treating it in every respect as an ordinary combustion. 
 It should yield only a very minute bubble of gas, which should be 
 almost wholly absorbed by potassic hydrate. (The quantity of 
 CO 2 found should not correspond to more than 0-00005 gm. of C, 
 
 D D 
 
402 VOLUMETRIC ANALYSIS. 88. 
 
 otherwise the oxide must be recalcined). The finer portions of the 
 oxide should, after calcining, he sifted out by means of a sieve of 
 clean copper gauze, and reserved for use as described hereafter. 
 
 New cupric oxide as obtained from the reverberatory furnace 
 should be assayed, and if not sufficiently pure, as is most likely the 
 case, calcined as above described, and assayed again. 
 
 () Metallic Copper. Fine copper gauze is cut into strips 
 about 80 m.m. wide, and rolled up as tightly as possible on 
 a copper wire so as to form a compact cylinder 80 m.m. long. This 
 is next covered with a tight case of moderately thin sheet copper, 
 the edges of which meet without overlapping. The length of the 
 strip of gauze, and the consequent diameter of the cylinder, must 
 be regulated so that it will fit easily, but not too loosely in the 
 combustion tubes. A sufficient number of these cylinders being- 
 prepared, a piece of combustion tube is filled with them, and they 
 are heated to redness in the furnace, a current of atmospheric air 
 being passed through them for a few minutes in order to burn off 
 organic impurity, and coat the copper gauze superficially with 
 oxide. A current of hydrogen, dried by passing through strong 
 sulphuric acid, is then substituted for the air, and a red heat 
 maintained until hydrogen issues freely from the end of the tube. 
 It is then allowed to cool, the current of hydrogen being continued, 
 and when cold the copper cylinders are removed, and kept in 
 a stoppered bottle. After being used several times they must be 
 heated in a stream of hydrogen as before, and are then again ready 
 for use. The heating in air need not be repeated. 
 
 (rj) Solution of Potassic bichromate. This is used as a test 
 for and to absorb sulphurous anhydride which may be present in 
 the gas obtained by combustion of the water residue. It should 
 be saturated, and does not require any special attention. The 
 yellow neutral chromate may also be used, but must be rendered 
 slightly acid, lest it should absorb carbonic as well as sulphurous 
 anhydride, 
 
 (6) Solution of Potassic hydrate. A cold saturated solution, 
 made by dissolving solid potassic hydrate in distilled water. 
 
 (t) Solution of Pyrogallic acid. A cold saturated solution, 
 made by dissolving in distilled water solid pyrogallic acid obtained 
 by sublimation. 
 
 (K) Solution of Cuprous chloride. A saturated solution of 
 cupric chloride is rendered strongly acid with hydrochloric acid, 
 a quantity of metallic copper introduced in the form of wire or 
 turnings, and the whole allowed to stand in a closely stoppered 
 bottle until the solution becomes colourless. 
 
 (X) Oxygen. Blow a bulb of about 30 c.c. capacity at the end 
 of a piece of combustion tube, and draw out the tube so that its 
 internal diameter for a length of about 30 m.m. is about 3 m.m. 
 
 
88. WATER ANALYSIS. 403 
 
 This is done in order that the capacity of the apparatus apart from 
 the bulb may be as small as possible. Cut the tube at the wide 
 part about 10 m.m. from the point at which the narrow tube 
 commences, thus leaving a small funnel-shaped mouth. Then 
 introduce, a little at a time, dried, coarsely powdered, potassic 
 chlorate until the bulb is full. Cut off the funnel, and, at 
 a distance of 100 m.m. from the bulb, bend the tube at an angle 
 of 45, and at 10 m.m. from the end bend it at right angles in the 
 opposite direction. It then forms a retort and delivery tube in 
 one piece, and must be adjusted in a mercury trough in the usual 
 manner, taking care that the end does not dip deeper than about 
 20 m.m. below the surface, as otherwise the pressure of so great 
 a column of mercury might destroy the bulb when softened by 
 heat. On gently heating, the potassic chlorate fuses and evolves 
 oxygen. The escaping gas is collected in test tubes about 150 m.m. 
 long and 20 m.m. in diameter, rejecting the first 60 or 80 c.c., 
 which contain the nitrogen of the air originally in the bulb retort, 
 l^ive or more of these tubes, according to the quantity of oxygen 
 required, are collected and removed from the mercury trough, in 
 very small beakers, the mercury in which should be about 10 m.m. 
 above the end of the test tube. Oxygen may be kept in this way 
 for any desired length of time, care being taken, if the temperature 
 falls considerably, that there is sufficient mercury in the beaker to 
 keep the mouth of the test tube covered. About 10 c.c. of 
 the gas in the first tube collected is transferred by decantation in 
 a mercury trough to another tube, and treated with potassic hydrate 
 and pyrogallic acid, when, if after a few minutes it is absorbed, 
 with the exception of a very small bubble, the gas in that and the 
 remaining tubes may be considered pure. If not, the first tube is 
 rejected, and the second tested in the same way, and so on. 
 
 (n) Hydric metaphosphate. The glacial hydric metaphosphato, 
 usually sold in sticks, is generally free from ammonia, or very 
 nearly so. A solution should be made containing about 100 gm. 
 in a liter. It should be so far free from ammonia as that 10 c.c. 
 do not contain an appreciable quantity. 
 
 (v) Calcic phosphate. Prepared by precipitating common 
 disodic phosphate with calcic chloride, washing the precipitate 
 with water by decantation, drying, and heating to redness for 
 an hour. 
 
 C. Reagents required for the Estimation of Nitrogen present as 
 Nitrates and Nitrites (drum's process). 
 
 (a) Concentrated Sulphuric acid. This must be free from 
 nitrates and nitrites. 
 
 (/3) Potassic permanganate. Dissolve about 10 gm. of crys- 
 tallized potassic permanganate in a liter of distilled water. 
 
 D D 2 
 
404 VOLUMETRIC ANALYSIS. 88. 
 
 (y) Sodic carbonate. Dissolve about 10 gm. of dry, or an 
 equivalent quantity of crystallized sodic carbonate free from 
 
 nitrates, in a liter of distilled water. 
 
 For the Estimation of Nitrogen as Nitrates and Nitrites in Waters 
 containing 1 a very large quantity of Soluble Matter, but little 
 Organic Nitrogen. 
 
 (c) Metallic Aluminium. As thin foil. 
 
 (f) Solution of Sodic hydrate. Dissolve 100 gm. of solid 
 sodic hydrate in a liter of distilled water ; when cold, put it in 
 a tall glass cylinder, and introduce about 100 sq. cm. of aluminium 
 foil, which must be kept at the bottom of the solution by means of 
 a glass rod. When the aluminium is dissolved, boil the solution 
 briskly in a porcelain basin until about one-third of its volume has 
 been evaporated, allow to cool, and make up to its original volume 
 with water free from ammonia. The absence of nitrates is thus 
 ensured. 
 
 () Broken Pumice. Clean pumice is broken in pieces of the 
 size of small peas, sifted free from dust, heated to redness for 
 about an hour, and kept in a closely stoppered bottle. 
 
 (rj) Hydrochloric acid free from Ammonia. If the ordinary 
 pure acid is not free from ammonia, it should be rectified from 
 sulphuric acid. As only two or three drops are used in each 
 experiment, it will be sufficient if that quantity does not contain 
 an appreciable proportion of ammonia. 
 
 For the Estimation of Nitrites by G-riess's Process. 
 
 (6} Meta-phenylene-diamine. A half per cent, solution of the 
 base in very dilute sulphuric or hydrochloric acid. The base alone 
 is not permanent. If too highly coloured, it may be bleached by 
 pure animal charcoal. 
 
 (i) Dilute Sulphuric acid. One volume of acid to two of 
 water. 
 
 (K) Standard Potassic or Sodic nitrite. Dissolve 0*406 gm. 
 of pure silver nitrite in boiling distilled water, and add pure 
 potassic or sodic chloride till no further precipitate of silver 
 chloride occurs. Make up to a liter ; let the silver chloride settle, 
 and dilute 100 c.c. of the clear liquid to a liter. It should be kept 
 in small stoppered bottles completely filled, and in the dark. 
 
 1 c.c. -O'Ol m.gm. X 2 :! . 
 
 The colour produced by the reaction of nitrous acid on meta- 
 phenylene-diamine is triamidoazo-benzene, or " Bismarck brown." 
 
89. WATER ANALYSIS. 405 
 
 D. Reag-ents required for the Estimation of Chlorine present as 
 
 Chloride. 
 
 (a) Standard Solution of Silver nitrate. Dissolve 2 '3944 
 gni. of pure recrystallized silver nitrate in distilled water, and 
 make up to a liter. In use it is convenient to measure it from 
 a burette which holds 10 c.c. and is divided into tenths. 
 
 ((3) Solution of Potassic chromate. A strong solution of pure 
 neutral potassic chromate free from chlorine. It is most con- 
 veniently kept in a bottle similar to that used for the solution of 
 ferrous chloride (B. <)). 
 
 E. Reagents required for determination of Hardness. 
 
 (a) Standard Solution of Calcic chloride. Dissolve in dilute 
 hydric chloride, in a platinum dish, 0'2 gin. of pure crystallized 
 calcite, adding the acid gradually, and having the dish covered 
 with a glass plate, to prevent loss by spirting. When all is 
 dissolved, evaporate to dryness on a water bath, add a little distilled 
 water, and again evaporate to dryness. Repeat the evaporation 
 several times to ensure complete expulsion of hydric chloride. 
 Lastly, dissolve the calcic chloride in distilled water, and make up 
 to one liter. 
 
 (/3) Standard Solution of Potassic soap. Rub together in 
 a mortar 150 parts of lead plaster (Emplast. Plumbi of the 
 druggists) and 40 parts of dry potassic carbonate. ' When they are 
 fairly mixed, add a little methylated spirit, and continue triturating 
 until an uniform creamy mixture is obtained. Allow to stand for 
 some hours, then throw on to a filter, and wash several times with 
 methylated spirit. The strong solution of soap thus obtained 
 must be diluted with a mixture of one volume of distilled water 
 and two volumes of methylated spirit (considering the soap solution 
 as spirit), until exactly 14'25 c.c. are required to form a permanent 
 lather with 50 c.c. of the standard calcic chloride (E. a), the 
 experiment being performed precisely as in determining the hardness 
 of a water. A preliminary assay should be made with a small 
 quantity of the strong soap solution to ascertain its strength. 
 After making the solution approximately of the right strength, 
 allow it to stand twenty-four hours ; and then, if necessary, filter 
 it, and afterwards adjust its strength accurately. It is better to 
 make the solution a little too strong at first, and dilute it to the 
 exact strength required, as it is easier to add alcohol accurately 
 than strong soap solution. 
 
 THE ANALYTICAL PROCESSES. 
 
 89. To form, for sanitary purposes, an opinion of the character 
 of a natural water or sewage, it will in most cases suffice to 
 determine the nitrogen as ammonia, organic carbon, organic nitrogen, 
 
406 VOLUMETRIC ANALYSIS. 89. 
 
 total solid matter, nitrogen as nitrates and nitrites, suspended 
 matter, chlorine, and hardness ; and in the following pages the 
 estimation of these will be considered in detail, and then, more 
 briefly, that of other impurities. 
 
 The method of estimating nitrogen as ammonia is substantially 
 that described by the late W. A. Miller (/. C. S. [2] iii. 125), 
 and that for estimating organic carbon and nitrogen was devised 
 by Frank land and Armstrong, and described by them in the 
 same journal ([2] vi. 77 et seq.). 
 
 1. Collection of Samples. The points to be considered under 
 this head are, the vessel to be used, the quantity of water required, 
 and the method of ensuring a truly representative sample. 
 
 Stoneware bottles should be avoided, as they are apt to affect the 
 hardness of the water, and are more difficult to clean than glass. 
 Stoppered glass bottles should be used if possible ; those known 
 as " Winchester Quarts," which hold about two and a half liters 
 each, are very convenient and easy to procure. One of these will 
 contain sufficient for the general analysis of sewage and largely 
 polluted rivers, two for well waters and ordinary rivers and streams, 
 and three for lakes, and mountain springs. If a more detailed 
 analysis is required, of course a larger quantity must be taken. 
 
 If corks must be used, they should be neic, and well washed 
 with the water at the time of collection. 
 
 In collecting from a well, river, or tank, plunge the bottle itself, 
 if possible, below the surface ; but if an intermediate vessel must 
 be used, see that it is thoroughly clean and well rinsed with the 
 water. Avoid the surface water and also any deposit at the 
 bottom. 
 
 If the sample is taken from a pump or tap, take care to let the 
 water which has been standing in the pump or pipe run off before 
 collecting, then allow the stream to flow directly into the bottle. 
 If it is to represent a town water-supply, take it from the service 
 pipe communicating directly with the street main, and not from 
 a cistern. 
 
 In every case, first fill the bottle completely with the water thus 
 expelling all gases and vapours, empty it again, rinse once or twice 
 carefully with the water, and then fill it nearly to the stopper, and 
 tie down tightly. 
 
 At the time of collection note the source of the sample, whether 
 from a deep or shallow well, a river or spring, and also its local 
 name so that it may be clearly identified. 
 
 If it is from a well, ascertain the nature of the soil, subsoil, and 
 water-bearing stratum ; the depth and diameter of the well, its 
 distance from neighbouring cesspools, drains, or other sources 
 of pollution ; whether it passes through an impervious stratum 
 before entering the water-bearing stratum, and if so, whether the 
 sides of the well above this are, or are not, water-tight. 
 
89. WATER ANALYSIS. 407 
 
 If the sample is from a river, ascertain the distance from the 
 source to the point of collection ; whether any pollution takes 
 place above that point, and the geological nature of the district 
 through which it flows. 
 
 If it is from a spring, take note of the stratum from which it 
 issues. 
 
 2. Preliminary Observations. In order to ensure uniformity, 
 the bottle should invariably be well shaken before taking out 
 a portion of the sample for any purpose. The colour should be 
 observed as seen in a tall, narrow cylinder standing upon a white 
 surface. It is well to compare it Avith distilled water in a similar 
 vessel. The taste and odour are most easily detected when the 
 water is heated to 30 35 C. 
 
 Before commencing the quantitative analysis, it is necessary to 
 decide whether the water shall be filtered or not before analysis. 
 This must depend on the purpose for which the examination is 
 undertaken. As a general rule, if the suspended matter is to be 
 determined, the water should be filtered before the estimation of 
 organic carbon and nitrogen, nitrogen as ammonia, and total solid 
 residue ; if otherwise, it should merely be shaken up. If the 
 suspended matter is not determined, the appearance of the water, 
 as w r hether it is clear or turbid, should be noted. This is 
 conveniently done when measuring out the quantity to be used for 
 the estimation of organic carbon and nitrogen. If the measuring 
 flask be held between the eye and a good source of light, but with 
 an opaque object, such as a window bar, in the line drawn from 
 the eye through the centre of the flask, any suspended particles 
 will be seen well illuminated on a dark ground. 
 
 Water derived from a newly sunk well, or which has been 
 rendered turbid by the introduction of innocuous mineral matter 
 from some temporary and exceptional cause should be filtered, but 
 the suspended matter in most such cases need not be determined. 
 The introduction of organic matter of any kind Avould almost 
 always render the sample useless. 
 
 3. Estimation of Nitrogen as Ammonia. Place about 50 C.C. of 
 the water in a glass cylinder about 150 m.m. high, and of about 
 70 c.c. capacity, standing upon a white glazed tile or white paper. 
 Add about 1 c.c. of ^sessler's solution (A. a), stir with a clean 
 glass rod, and allow to stand for a minute or so. If the colour 
 then seen does not exceed in intensity that produced when O'l c.c. 
 of the standard ammonic chloride (A. /5) is added to 50 c.c. of 
 water free from ammonia (A. ), and treated in the same way, 
 half a liter of the water should be used for the estimation. If 
 the colour be darker, a proportionately smaller quantity should be 
 taken ; but it is not convenient to use less than 20 or 25 c.c. 
 
 If it has been decided that the water should be filtered before 
 analysis, care must be taken, should it contain only a small quantity. 
 
408 VOLUMETRIC ANALYSIS. 89. 
 
 of ammonia, that the filter paper is free from ammonia. If it is 
 not, it must be steeped in water free from ammonia for a day or so, 
 and when used, the first portion of the filtrate rejected. Wasliimj 
 with water, even if many times repeated, is generally ineffectual. 
 When a large quantity of ammonia is present, as in highly polluted 
 water and sewage, any ammonia in the filter paper may be' neglected. 
 A moderate quantity of suspended matter may also generally be 
 neglected with safety, even if the water is to be filtered in 
 estimating organic carbon and nitrogen and total solid matter. 
 
 The water, filtered or unfiltered as the case may be, should be 
 carefully measured and introduced into a capacious retort, connected 
 by an india-rubber joint with a Liebig's condenser, the volume 
 being if necessary, made up to about 400 c.c. with water free from 
 ammonia. Add about 1 gni. of sodic carbonate (A. y), and distil 
 rapidly, applying the lamp flame directly to the retort, and collect 
 the distillate in a small glass cylinder, such as is described above. 
 When about 50 c.c. have distilled into the first cylinder, put it aside 
 and collect a second 50 c.c., and as soon as that is over remove the 
 lamp, and add to the second distillate about 1 c.c. of Messier 's 
 solution, stir with a clean glass rod, and allow to stand on a white 
 tile or sheet of paper for five minutes. To estimate the ammonia 
 present, measure into a similar cylinder as much of the standard 
 ammonic chloride solution as you judge by the colour to be present 
 in the distillate ; make it up with water free from ammonia to the 
 same volume, and treat with I^essler's solution in precisely the 
 same way. If, on standing, the intensity of colour in the two 
 cylinders is equal, the quantity of ammonia is also equal, and this 
 is known in the trial cylinder. If it is not equal, another trial 
 must be made with a greater or less quantity of ammonic chloride. 
 The ammonic chloride must not be added after the JSTessler's 
 solution, or a turbidity will be produced which entirely prevents 
 accurate comparison. If the ammonia in the second distillate does 
 not exceed that in 0*2 c.c. of the standard ammonic chloride, the 
 distillation need not be proceeded with any further, but if otherwise, 
 successive quantities must be distilled and tested until ammonia 
 ceases to be found. If the ammonia in the second distillate 
 corresponds to 0*4 c.c. or less of the ammonic chloride, that in the 
 first may be estimated in the same way ; but if the second contains 
 a greater quantity of ammonia, the first must be measured, and an 
 aliquot part taken and diluted to about 50 c.c. with water free from 
 ammonia, as it is likely to contain so much ammonia as to give 
 a colour too intense to admit of easy comparison. A colour produced 
 by more than 2 c.c. of ammonic chloride cannot be conveniently 
 employed.'"" When, as in the case of sewage, a large quantity of 
 
 * In order to insure absolute accuracy in Nesslerizing it is necessary that the distillate 
 should be of the same temperature as the standard liquid made by mixing the ammonic 
 chloride with distilled water. Hazen and Clark (Amer. Cliem. Jour. xii. 425) found 
 that the water Nesslerized from a metal condenser, immediately after collection, gave 
 a, lower figure than when the two liquids were allowed to assume the same temperature. 
 
89. WATER ANALYSIS. 409 
 
 ammonia is known to be present, it saves trouble to distil about 
 100 c.c. at first, and at once take an aliquot part of that, as above 
 described. If the liquid spirts in distilling, arrange the retort so 
 that the joint between the retort and condenser is the highest point; 
 the distillation will proceed rather more slowly, but anything 
 carried up mechanically will be returned to the retort. When the 
 ammonia has been estimated in all the distillates, add together the 
 corresponding volumes of ammonic chloride solution ; then, if 500 
 c.c. have been employed for the experiment, the number of c.c. of 
 ammonic chloride used divided by 100 will give the quantity of 
 nitrogen as ammonia in 100,000 parts of the water; if less than 
 that, say y c.c. have been used, multiply the volume of ammonic 
 chloride by 5 and divide by y. 
 
 Eefore commencing this operation, ascertain that the retort and 
 condenser are free from ammonia by distilling a little common 
 water or distilled water with sodic carbonate until the distillate is 
 free from ammonia. Remove the residue then, and after each 
 estimation, by means of a glass syphon, without disconnecting the 
 retort. If a small quantity of water is to be distilled, the residue 
 or part of it from a previous experiment may be left in the retort, 
 instead of adding water free from ammonia, care being taken that 
 the previous distillation was continued until ammonia ceased to be 
 evolved. 
 
 When urea is present the evolution of ammonia is long continued, 
 owing to the decomposition of the urea. In such cases, collect tbe 
 distillate in similar quantities, and as soon as the first rapid 
 diminution in the amount of ammonia has ceased, neglect the 
 remainder, as this would be due almost wholly to decomposition of 
 the urea. 
 
 4. Estimation of Org-anic Carbon and Nitrogen. This should be 
 commenced as soon as the nitrogen as ammonia has been determined. 
 If that is less than 0'05 part per 100,000, a liter should be used ; 
 if more than 0'05, and less than 0'2, half a liter; if more than 
 0'2 and less than I'O, a quarter of a liter; if more than 1*0, 
 a hundred c.c. or less. These quantities are given as a guide in 
 dealing with ordinary waters and sewage, but subject to variation 
 in exceptional cases. A quantity which is too large should be 
 avoided as entailing needless trouble in evaporation, and an 
 inconveniently bulky residue and resulting gas. If it is to be 
 filtered before analysis, the same precaution as to filter paper must 
 be taken as for estimation of nitrogen as ammonia, the same filter 
 being generally used. 
 
 Having measured the quantity to be used, add to it in a capacious 
 flask 15 c.c. of the solution of sulphurous acid (B. /3), and boil 
 briskly for a few seconds, in order to decompose the carbonates 
 present. Evaporate to dryness in a hemispherical glass dish, about 
 a decimeter in diameter, and preferably without a lip, supported in 
 
410 VOLUMETRIC ANALYSIS. 89. 
 
 a copper dish with a flange (fig. 56 d e). The flange has a diameter 
 of about 14 centimeters, is sloped slightly towards the centre, and 
 has a rim of about 5 m.m. turned up on its edge, except at one 
 point, where a small lip is provided. The concave portion is made 
 to fit the contour of the outside of the glass dishes, and is of such 
 a depth as to allow the edge of the dish to rise about 15 m.m. 
 above the flange. The diameter of the concavity at / is about 
 90 m.m., and the depth at fj about 30 m.m. A thin glass shade, 
 such as is used to protect statuettes, about 30 centimeters high, 
 stands on the flange of the copper dish, its diameter being such as 
 to fit without difficulty on the flange, and leave a sufficient space 
 between its interior surface and the edge of the glass dish. The 
 copper dish is supported on a steam or water bath, and the water 
 as it evaporates is condensed on the interior of the glass shade, runs 
 down into the copper dish, filling the space between it and the 
 glass dish, and then passes off by the lip at the edge of the flange, 
 a piece of tape held by the edge of the glass shade, and hanging 
 over the lip, guiding it into a vessel placed to receive it. 
 
 We are indebted to Bischof for an improved apparatus for 
 evaporation, which by keeping the dish always full by a self-acting 
 contrivance, permits the operation to proceed without attention 
 during the night, and thus greatly reduces the time required. 
 This form of apparatus is shown in fig. 56. The glass dish d is 
 supported by a copper dish e as described above, and resting on 
 the latter is a stout copper ring Jt which is slightly conical, being 
 115 m.m. in diameter at the top and 130 at the bottom. At the top 
 is a narrow flange of about 10 m.m. with a vertical rim of about 
 5 m.m. The diameter across this flange is the same as the diameter 
 of the dish e, so that the glass shade i will fit securely either on k 
 or e. The height of the conical ring is about 80 m.m. 
 
 The automatic supply is accomplished on the well-known prin- 
 ciple of the bird fountain, by means of a delivery tube I, the upper 
 end of which is enlarged to receive the neck of the flask a con- 
 taining the water to be evaporated, the joint being carefully ground 
 so as to be water-tight. The upper vertical part of />, including 
 this enlargement, is about 80 m.m. in length, and the sloping part 
 about 260 m.m. with a diameter of 13 m.m. The lower end 
 which goes into the dish is again vertical for about 85 m.m., and 
 carries a side tube c of about 3 m.m. internal diameter, by which 
 air enters the delivery tube whenever the level of the water in the 
 dish falls below the point at which the side tube joins the delivery 
 tube. The distance from this point to the end of the tube which 
 rests on the bottom of the dish at g, and is there somewhat con- 
 tricted, is about 30 m.m. The side tube c should not be attached 
 on the side next the flask, as if so the inclined part of I passes 
 over its mouth and renders it very difficult to clean. Mills 
 prevents circulation of liquid in the sloping part of the tube by 
 bending it into a slightly undulating form, so that permanent 
 
89. 
 
 WATER ANALYSIS. 
 
 411 
 
 bubbles of air are caught and detained at two points in it. The 
 flask a should hold about 1200 c.c. and have a rather narrow neck 
 about 20 m.m. and a flat bottom. A small slot is cut in the 
 upper edge of the copper ring li to accommodate the delivery tube, 
 as shown in fig. 55. Its size and shape should be such that the 
 tube does not touch the edge of the glass shade i, lest water 
 running down the inner surface of the shade should find its way 
 down the outside of the delivery tube into the dish. This being 
 
 Fig. 55. 
 
 Pig. 56. 
 
 avoided, the opening should be as closely adjusted to the size of the 
 delivery tube as can be. The copper dish e should rest on a steam 
 or water bath, so that only the spherical part is exposed to the 
 heat. 
 
 After the addition of the 15 c.c. of sulphuric acid, the water 
 may either be boiled in the flask a, or in another more capacious 
 one, and then transferred to a. It should be allowed to cool 
 before the delivery tube is adjusted, otherwise the joint between 
 the two is liable to become loose by expansion of the cold socket 
 
412 VOLUMETRIC ANALYSIS. 89. 
 
 of the delivery tube, after being placed over the hot neck of 
 the flask. 
 
 The glass dish having been placed on the copper dish e, the 
 conical ring It is fitted on, and the flask with the delivery tube 
 attached inverted, as shown in fig. 56, a b. This should not be 
 done too hurriedly, and with a little care ther? is no risk of loss. 
 The flask is supported either by a large wooden filtering stand, the 
 ring of which has had a slot cut in it to allow the neck of the flask 
 to pass, or by a clamp applied to the upper end of the delivery 
 tube where the neck of the flask fits in. The delivery tube having- 
 been placed in the slot made to receive it, the glass shade is fitted 
 on, and the evaporation allowed to proceed. When all the water 
 has passed from the flask into the dish, the flask and delivery tube,, 
 and the conical ring h may be removed, and the glass shade placed 
 directly on the dish e until the evaporation is complete. If the 
 water is expected to contain a large quantity of nitrates, two or 
 three drops of chloride of iron (B. ) should be added to the first 
 dishful ; and if it contains little or no carbonate, one or two c.c. 
 of hydric sodic sulphide (B. 7). The former facilitates the destruc- 
 tion of nitrates and nitrites, and the latter furnishes base for the 
 sulphuric acid produced by oxidation of the sulphurous acid, and 
 which would, if free, decompose the organic matter when concen- 
 trated by evaporation. An estimate of the quantity of carbonate 
 present, sufficiently accurate for this purpose, may generally be 
 made by observing the quantity of precipitate thrown down 011 
 addition of sodic carbonate in the determination of nitrogen as- 
 ammonia. 
 
 With sewages and very impure waters (containing upwards of Ol 
 part of nitrogen as ammonia per 100,000 for example) such great 
 precaution is hardly necessary, and the quantity to evaporate being 
 small, the evaporation may be conducted in a glass dish placed 
 directly over a steam bath, and covered with a drum or disc of filter 
 paper made by stretching the paper by means of two hoops of light 
 split cane, one^ thrust into the other, the paper being between them, 
 in the way often employed in making dialysers. This protects the 
 contents of the dish from dust, and also to a great extent, from 
 ammonia which may be in the atmosphere, and which would impair 
 the accuracy of the results. As a glass dish would be in some danger 
 of breaking by the introduction of cold water, the flask containing 
 the water being evaporated in this or in the first described manner, 
 must be kept on a hot plate or sand bath at a temperature of about 
 60 or 70 C., and should be covered with a watch-glass. This 
 precaution is not necessary when Bischof's apparatus is used. 
 If, at any time, the water in the flask ceases to smell strongly of 
 sulphurous acid, more should be added. The preliminary boiling 
 may be omitted when less than 250 c.c. is used. When the 
 nitrogen as nitrates and nitrites exceeds 0'5 part, the dish, after 
 the evaporation has been carried to dryness, should be filled with 
 
89. WATER ANALYSIS. 
 
 distilled water containing ten per cent, of saturated sulphurous 
 acid solution, and the evaporation again carried to dryness. If it 
 exceeds I'O part, a quarter of a liter of this solution should be 
 evaporated on the residue ; if 2'0 parts, half a liter ; and if 5 parts, 
 a liter. If less than a liter has been evaporated, a proportionally 
 smaller volume of this solution may be used. The estimation of 
 nitrogen as nitrates and nitrites will usually be accomplished before 
 this stage of the evaporation is reached. 
 
 M. W. Williams proposes to avoid the use of sulphurous acid, 
 with its acknowledged disadvantages and defects, by removing 
 the nitric and nitrous acids with the zinc-copper couple and 
 converting them into ammonia. If the amount is large, it is best 
 distilled from a retort into weak acid ; if small, into an empty 
 Messier tube. The amount so found is calculated into nitrogen 
 as nitrates and nitrites, if the latter are found in the water. The 
 residue, when free from ammonia is further concentrated, the 
 separated carbonates re-dissolved in phosphoric or sulphurous 
 acid, in just, sufficient quantity, then transferred to a glass 
 basin for evaporation to dryness as usual ready for combustion 
 (J. 0. S. 1881, 144). 
 
 In the case of sewage, however, it is advisable to employ hydric 
 metaphosphate in the pJace of sulphurous acid, as the ammonic 
 phosphate is even less volatile than the sulphite. This can only 
 be employed for sewage and similar liquids, which are free from 
 nitrates and nitrites. To the measured quantity of liquid to be 
 evaporated add, in the glass dish, 10 c.c. of the hydric metaphos- 
 phate (B. fj.), and, in order to render the residue more convenient 
 to detach from the dish, about half a gram of calcic phosphate 
 (B. v), and proceed as usual. No chloride of iron, sulphurous 
 acid, or sodic sulphite is required ; nor is it necessary to boil 
 before commencing the evaporation. 
 
 The next operation is the combustion of the residue. The 
 combustion tube should be of hard, difficultly fusible glass, with 
 an internal diameter of about 10 m.m. Cut it in lengths of about 
 430 m.m., and heat one end of each in the blowpipe flame to round 
 the edge. Wash well with water, brushing the interior carefully 
 Avith a tube brush introduced at the end whose edge has been 
 rounded, rinse with distilled water, and dry in an oven. When 
 dry, draw off and close, at the blowpipe, the end whose edge has 
 been left sharp. The tube is then ready for use. 
 
 Pour on to the perfectly dry residue in the glass dish, standing 
 on a sheet of white glazed paper, a little of the fine cupric oxide 
 (B. e), and with the aid of a small elastic . steel spatula (about 100 
 m.m. long and 15 m.m. wide) .carefully detach the residue from the 
 glass and rub it down with the cupric oxide. The spatula readily 
 accommodates itself to the curvature of the dish, and effectually 
 scrapes its surface. When the contents of the dish are fairly 
 mixed, fill about 30 m.m. of the length of the combustion tube 
 
414 
 
 VOLUMETEIC ANALYSIS. 
 
 89. 
 
 with granulated cupric oxide (B. e), and transfer the mixture in the 
 dish to the tube. This is done in the usual way by a scooping 
 motion of the end of the tube in the dish, the last portions being 
 
 7 
 
 Fig. 57. 
 
 transferred by the help of a bent card or a piece of clean and smooth 
 platinum foil. Kinse the dish twice with a little fine cupric oxide, 
 rubbing it well round each time with the spatula, and transfer to 
 
89. WATER ANALYSIS. 415 
 
 the tube as before. Any particles scattered on the paper are also 
 to be put in. Fill up to a distance of 270 m.m. from the closed 
 end with granular cupric oxide, put in a cylinder of metallic copper 
 (B. ), and then again 20 m.rn. of granular cupric oxide. This last 
 is to oxidize any traces of carbonic oxide which might be formed 
 from carbonic anhydride by the reducing action of iron or other 
 impurity in the metallic copper. 2sow draw out the end of the 
 tube so as to form a neck about 100 m.m. long and 4 m.m. in 
 diameter, fuse the end of this to avoid injury to the india-rubber 
 connector, and bend it at right angles. It is now ready to be 
 placed in the combustion furnace and attached to the Sprengel 
 pump. 
 
 The most convenient form of this instrument for the purpose is 
 shown in fig. 57. The glass funnel a is kept supplied with mercury, 
 and is connected by a caoutchouc joint with a long narrow glass 
 tube which passes down nearly to the bottom of a wider tube d, 
 900 m.m. long, and 10 m.m. in internal diameter. The upper end 
 of d is cemented into the throat of a glass funnel c from which 
 the neck has been removed. A screw clamp b regulates the flow of 
 mercury down the narrow tube. A piece of ordinary glass tube / g, 
 about 6 m.m. in diameter and 600 m.m. in length, is attached at g 
 to a tube g h /, about 6 m.m. in diameter, 1500 m.m. long, with 
 a bore of 1 m.m. This is bent sharply on itself at h, the part h k 
 being 1300 m.m. long, and the two limbs are firmly lashed together 
 with copper wire at two points, the tubes being preserved from 
 injury by short sheaths of caoutchouc tube. The end 7: is recurved 
 for the delivery of gas. At the top of the bend at h, a piece of 
 ordinary tube k I, about 120 m.m. long, and 5 m.m. in diameter, is 
 sealed on. The whole I Jc is kept in a vertical position by a loose 
 support or guide, near its upper part, the whole of its weight resting 
 on the end A; so that it is comparatively free to move. It is 
 connected at / with the lower end of d, by means of a piece of caout- 
 chouc tube covered with tape, and furnished with a screw clamp e. 
 At I it is connected with the combustion tube o, by the connecting 
 tube I m n, which is made of tube similar to that used for 7* 7r. A 
 cork slides on h I, which is fitted into the lower end of a short 
 piece of tube of a width sufficient to pass easily over the caoutchouc 
 joint connecting the tubes at I. After the joint has been arranged 
 (the ends of the tubes just touching) and bound with wire, the 
 cork and wide tube are pushed over it and filled with glycerine. 
 The joint at n is of exactly the same kind, but as it has to be fre- 
 quently disconnected, water is used instead of glycerine, and the 
 caoutchouc is not bound on to the combustion tube with wire. It 
 will be seen that the joint at I is introduced chiefly to give flexi- 
 bility to the apparatus. At m is a small bulb blown on the tube 
 for the purpose of receiving water produced in the combustion. 
 This is immersed in a small water trough x. The tube h k stands in 
 a mercury trough p, which is shown in plan on a larger scale at B. 
 
416 VOLUMETRIC ANALYSIS. 89. 
 
 This trough should be cut out of a solid piece of mahogany, as it 
 is extremely difficult to make joints to resist the pressure of such 
 .a depth of mercury. It is 200 m.m. long, 155 m.m. wide, and 
 100 m.m. deep, outside measurement. The edge r r is 13 m.m. 
 wide, and the shelf s 65 m.m. wide, 174 m.m. long, and 50 m.m. 
 deep from the top of the trough. The channel t is 25 m.m. wide, 
 and 75 m.m. deep, having at one end a circular well w, 42 m.m. in 
 diameter, and 90 m.m. deep. The recesses u u are to receive the 
 ends of two Sprengel pumps. They are each 40 m.m. long, 
 25 m.m. wide, and of the same depth as the channel t. A short- 
 iron wire v, turning on a small staple, and resting at the other end 
 against an iron pin, stretches across each of these, and serves as 
 : a kind of gate to support the test tube, in which the gas delivered 
 by the pump is collected. The trough stands upon four legs, 75 
 m.m. high, and is provided at the side with a tube and screw 
 clamp q, by which the mercury may be drawn off to the level of 
 the shelf s. 
 
 The combustion tube being placed in the furnace, protected from 
 the direct action of the flame by a sheet-iron trough lined with 
 asbestos, and the water joint at n adjusted, the gas is lighted at 
 the front part of furnace so as to heat the whole of the metallic 
 copper and part of the cupric oxide. A small screen of sheet 
 iron is adjusted astride of the combustion tube to protect the 
 part beyond the point up to which the gas is burning from the 
 heat. 
 
 At the same time a stream of mercury is allowed to flow from the 
 funnel , which fills the tubes d and/' until it reaches h, when it 
 falls in a series of pellets down the narrow tube li /', each carrying 
 before it a quantity of air drawn from the combustion tube. The 
 flow of mercury must be controlled by means of the clamps I) and e, 
 so as not to be too rapid to admit of the formation of these separate 
 pistons, and especially, care should be taken not to permit it to go 
 so fast as to mount into the connecting tube I m n, as it cannot be 
 removed thence except by disconnecting the tube. During the 
 exhaustion, the trough x is filled with hot water to expel from the 
 bulb in any water condensed from a previous operation. In about 
 ten minutes the mercury will fall in the tube li It with a loud, sharp, 
 clicking sound, showing that the vacuum is complete. As soon as 
 this occurs, the pump may be stopped, a test tube filled with mercury 
 inverted over the delivery end of the tube A', cold water substituted 
 for hot in the trough x, the iron screen- removed, and combustion 
 proceeded with in the usual way. This will take from fifty to sixty 
 minutes. As soon as the whole of the tube is heated to redness, 
 the gas is turned off, and the tube immediately exhausted, the 
 gases produced being transferred to the tube placed to receive them. 
 When the exhaustion is complete, the test tube of gas may be 
 removed in a small beaker, and transferred to the gas analysis 
 apparatus. 
 
89. 
 
 WATER ANALYSIS. 
 
 This gas collected consists of carbonic anhydride, nitric oxide, 
 nitrogen, and (very rarely) carbonic oxide, which can readily be 
 separated and estimated by the ordinary methods of gas analysis. 
 
 Pig. 58. 
 
 This is rapidly accomplished with the apparatus, shown in the 
 accompanying diagram, which, whilst it does not permit of analysis 
 by explosion, leaves nothing to be desired for this particular 
 
 E E 
 
 OF THE 
 
418 VOLUMETRIC ANALYSIS. 89. 
 
 operation. It is essentially that described by Frankland (J. O. S. 
 [2] vi. 109), but is slightly modified in arrangement. In the 
 diagram, a c d is a measuring tube, of which the cylindrical 
 portion a is 370 m.m. long, and 18 m.m. in internal diameter, the 
 part c 40 m.m. long, and 7 m.m. in diameter, and the part d 175 
 m.m. long, and 2*5 m.m. in diameter. To the upper end of d 
 a tube, with a capillary bore and stop-cock /, is attached, and bent 
 at right angles. Allowing 20 m.m. for each of the conical portions 
 at the joints between a and c, and c and d, and 25 m.m. for the 
 vertical part of the capillary tube, the vertical measurement of 
 the entire tube is 650 m.m. It is graduated carefully from below 
 upward, at intervals of 10 m.m., the zero being about 100 m.m. 
 from the end, as about that length of it is hidden by its support, 
 and therefore unavailable. The topmost 10 m.m. of d should be 
 divided into single millimeters. At the free end of the capillary 
 tube a small steel cap, shown in fig. 59, B, is cemented gas-tight. 
 
 .A 
 
 Pig. 59. 
 
 The lower end of a is drawn out to a diameter of 5 m.m. The 
 tube I) is about 1*2 meter long, and 6 m.m. internal diameter, is 
 drawn out like a at the lower end, and graduated in millimeters 
 from below upward, the zero being about 100 m.m. from the end.""' 
 The tubes a c d and b pass through a caoutchouc stopper 0, which 
 fits into the lower end of a glass cylinder n n, intended to contain 
 water to give a definite temperature to the gas in measuring. The 
 zeros of the graduations should be about 10 m.m. above this 
 stopper. Immediately below this the tubes are firmly clasped by 
 the wooden clamp p (shown in end elevation and plan at fig. 58, 
 B, C), the two parts of which are drawn together by screws, the 
 tubes being protected from injury by a piece of caoutchouc tube 
 fitted over each. The clamp is supported on an upright piece of 
 wood, screwed firmly to the base A. If the stopper o is carefully 
 fitted, and the tubes tightly clamped, no other support than p will 
 be necessary. The tubes below the clamp are connected by joints 
 of caoutchouc covered with tape, and strongly bound with wire, to 
 the vertical legs of the union piece q, to the horizontal leg of 
 which is attached a long caoutchouc tube of about 2 m.m. internal 
 diameter, which passes to the glass reservoir t. This tube must 
 be covered with strong tape, or (less conveniently) have a lining of 
 canvas between two layers of caoutchouc, as it will be exposed to 
 
 * The graduation is not shown in the diagram. 
 
89. WATER ANALYSIS. 419 
 
 considerable pressure. In its course it passes through the double 
 screw steel pinch-cock r, the lower bar of which is fixed to the side 
 of the clamp p. It is essential that the screws of the pinch-cock 
 should have smooth collars like that shown in fig. 59 A, and that 
 the upper surface of the upper bar of the pinch-cock should be 
 quite flat, the surfaces between which the tube is passed being 
 cylindrical. 
 
 Franklaiid has introduced a form of joint by which the steel 
 caps and clamp are dispensed with. The capillary tube at the 
 upper end of a c d is expanded into a small cup or funnel, and the 
 capillary tube of the laboratory vessel bent twice at right 
 angles, the end being drawn out in a conical form to fit into the 
 neck of the above-named cup. The opposed surfaces are fitted 
 by grinding or by covering the conical end of the laboratory 
 vessel with thin sheet caoutchouc. The joint is kept tight by 
 an elastic band attached at one end to the stand, and at the other 
 to a hook on the horizontal tube of the laboratory vessel, and the 
 cup is filled with mercury. 
 
 In the base A is fixed a stout iron rod, 1'4 meter long, with 
 
 2> 
 
 Fig. 60. Fig. 61. 
 
 a short horizontal arm at its upper end, containing two grooved 
 pulleys. The reservoir t is suspended by a cord passing over these 
 pulleys, and attached to an eye u in the iron rod, the length of the 
 cord being such that, when at full stretch, the bottom of the 
 reservoir is level with the bottom of the clamp p. A loop is made 
 on the cord, which can be secured by a hook v on the rod, so that 
 when thus suspended, the bottom of t is about 100 m.m. above the 
 stop-cock /. A stout elastic band fitted round t at its largest 
 diameter acts usefully as a fender to protect it from an accidental 
 blow against the iron rod. A thermometer <?, suspended by a wire 
 hook from the edge of the cylinder n n, gives the temperature of 
 'the contained water, the uniformity of which may be insured 
 .(though it is scarcely necessary) by passing a slow succession of 
 bubbles of air through it, or by moving up and down in it a wire 
 with its end bent into the form of a ring. The jar k is called the 
 laboratory vessel, arid is 100 m.m. high, and 38 m.m. in internal 
 diameter, having a capillary tube, glass stop-cock, and steel cap c/ h 
 exactly like / y. The mercury trough I is shown in figs. 60 and 
 61. It is of solid mahogany, 265 m.m. long, 80 m.m. broad, and 
 90 m.m. deep, outside measurement. The rim a a a a is 8 m.m. 
 Inroad, and 15 m.m. deep. The excavation l> is 230 m.m. long, 
 
 E E 2 
 
420 VOLUMETKIC ANALYSIS. 89. 
 
 26 m.m. broad, and 65 m.m. deep, with a circular cavity to receive 
 the laboratory vessel sunk at one end, 45 m.m. in diameter, and 
 20 m.m. in depth below the top of the excavation. Two small 
 lateral indentations c c (fig. 61) near the other end accommodate 
 a capsule for transferring to the trough tubes containing gas. This 
 trough rests upon a telescope table, which can be fixed at any 
 height by means of a screw, and is supported on three feet. It 
 must be arranged, so that when the laboratory vessel is in its place 
 in the trough, the two steel caps exactly correspond face to face. 
 
 The difference of level of the mercury in the tubes b and a c d, 
 caused by capillary action, when both are freely open to the air, 
 must be ascertained by taking several careful observations. This 
 will be different for each of the portions a c and d, and must be 
 added to or deducted from the observed pressure, as the mercury 
 when thus freely exposed in both tubes to the atmospheric pressure 
 stands in a c or d above or below that in &. This correction will 
 include also any that may be necessary for difference of level of 
 the zeros of the graduations of the two tubes, and, if the relative 
 positions of these be altered, it must be redetermined. A small 
 telescope, sliding on a vertical rod, should be used in these and all 
 other readings of the level of mercury. 
 
 The capacity of the measuring tube a c d at each graduation 
 must now be determined. This is readily done by first filling the 
 whole apparatus with mercury, so that it drips from the cap g. 
 The stop-cock / is then closed, a piece of caoutchouc tube slipped 
 over the cap, and attached to a funnel supplied with distilled 
 water. The reservoir t being lowered, the clamp r and the stop- 
 cock / are opened, so that the mercury returns to the reservoir, 
 water entering through the capillary tube. As soon as it is below 
 the zero of the graduation, the stop-cock / is closed, the funnel and 
 caoutchouc tube removed from the cap, and the face of the last 
 slightly greased in order that water may pass over it without 
 adhering. Now raise the reservoir, open the stop-cock /, and allow 
 the water -to flow gently out until the top of the convex surface of 
 the mercury in a just coincides with the zero of the graduation. 
 The mercury should be controlled by the clamp i; so that the water 
 issues under very slight pressure, l^ote the temperature of the 
 water in the water-jacket, and proceed with the expulsion of the 
 water, collecting it as it drops from the steel cap in a small carefully 
 weighed glass flask. When the mercury has risen through 100 m.m. 
 stop the flow of water, and weigh the flask. The weight of water 
 which was contained between the graduations and 100 on the 
 tube is then known, and if the temperature be 4 C., the weight in 
 grams will express the capacity of that part of the tube in cubic 
 centimeters. If the temperature be other than 4 C., the volume 
 must be calculated by the aid of the co-efficient of expansion of 
 water by heat. In a similar way the capacity of the tube at 
 successive graduations about 100 m.m. apart is ascertained, the 
 
89. WATER ANALYSIS. 421 
 
 last determination in a being at the highest, and the first in c at 
 the lowest graduation on the cylindrical part of each tube ; the 
 tube between these points and similar points on c and d being so 
 distorted by the glass blower that observations could not well 
 be made. The capacity at a sufficient number of points being 
 ascertained, that at each of the intermediate graduations may be 
 calculated, and a table arranged with the capacity marked against 
 each graduation. As the calculations in the analysis are made by 
 the aid of logarithms, it is convenient to enter on this table the 
 logarithms of the capacities instead of the natural numbers. 
 
 In using the apparatus, the stop-cocks on the measuring tube 
 and laboratory vessel should be slightly greased with a mixture of 
 resin cerate and oil, or vaseline, the Avhole apparatus carefully filled 
 with mercury, and the stop-cock/ closed ; next place the laboratory 
 vessel in position in the mercury trough, and suck out the air. 
 This is readily and rapidly done by the aid of a short piece of 
 caoutchouc tube, placed in the vessel just before it is put into the 
 mercury trough, and drawn away as soon as the air is removed. 
 Suck out any small bubbles of air still left through the capillary 
 tube, and as soon as the vessel is entirely free from air close the 
 stop-cock. Slightly grease the face of both caps with resin cerate 
 (to which a little oil should be added if very stiff), and clamp them 
 tightly together. On opening both stop-cocks mercury should now 
 freely through the capillary communication thus formed, and the 
 whole should be quite free from air. To ascertain if the joints are 
 all in good order, close the stop-cock It, and lower the reservoir t to 
 its lowest position ; the joints and stop-cocks will thus be subjected 
 to a pressure of nearly half an atmosphere, and any leakage would 
 speedily be detected. If all be right, restore the reservoir to its 
 upper position. 
 
 Transfer the tube containing the gas to be analyzed to an 
 ordinary porcelain mercury trough ; exchange the beaker in which 
 it has been standing for a small porcelain capsule, and transfer it 
 to the mercury trough I, the capsule finding ample room where the 
 trough is widened by the recess D. 
 
 Carefully decant the gas to the laboratory vessel, and add a drop 
 or two of potassic bichromate solution (B. 77) from a small pipette 
 with a bent capillary delivery tube, to ascertain if the gas contains 
 any sulphurous anhydride. If so, the yellow solution will 
 immediately become green from the formation of a chromic salt, 
 and the gas must be allowed to stand over the chromate for four or 
 five minutes, a little more of the solution being added if necessary. 
 The absorption may be greatly accelerated by gently shaking from 
 time to time the stand on which the mercury trough rests, so as to 
 cause the solution to wet the sides of the vessel. With care this 
 may be done without danger to the apparatus. Mercury should be 
 allowed to pass slowly into the laboratory vessel during the whole 
 time, as the drops falling tend to maintain a circulation both in 
 
422 VOLUMETRIC ANALYSIS. 
 
 the gas and in the absorbing liquid. The absence of sulphurous 
 anhydride being ascertained, both stop-cocks are set fully open, the 
 reservoir t lowered, and the gas transferred to the measuring tube. 
 The stop-cock h should be closed as soon as the liquid from the 
 laboratory vessel is within about 10 m.m. of it. The bore of the 
 capillary tube is so fine, that the quantity of gas contained in it is 
 too small to affect the result. ]S r ext bring the top of the meniscus 
 of mercury seen through the telescope exactly to coincide with one 
 of the graduations on the measuring tube, the passage of mercury 
 to or from the reservoir being readily controlled by the pinch-cock r. 
 jSbte the position of the mercury in the measuring tube and in the 
 pressure tube ?>, the temperature of the water-jacket, and the height 
 of the barometer, the level of the mercury in the pressure tube and 
 barometer being read to the tenth of a m.m. and the thermometer 
 to 0*1 C. This done, introduce into the laboratory vessel from 
 a pipette with a bent point, a few drops of potassic hydrate solution 
 (B. 6), and return the gas to the laboratory vessel. The absorption 
 of carbonic anhydride will be complete in about three to five 
 minutes, and if the volume of the gas is large, may be much 
 accelerated by gently shaking the stand from time to time, so as to 
 throw up the liquid on the sides of the vessel. If the small 
 pipettes used to introduce the various solutions are removed from 
 the mercury trough gently, they will always contain a little mercury 
 in the bend, which will suffice to keep the solution from flowing 
 out, and they maybe kept in readiness for use standing upright in 
 glass cylinders or other convenient supports. At the end of five 
 minutes the gas, which now consists of nitrogen and nitric oxide, 
 is again transferred to the measuring tube, and the operation of 
 measuring repeated ; the barometer, however, need not be observed, 
 under ordinary circumstances, more than once for each analysis, 
 as the atmospheric pressure w r ill not materially vary during the 
 twenty-five to thirty minutes required. JS T ext pass into the 
 laboratory vessel a few drops of saturated solution of pyrogallic 
 acid (B. t), and return the gas upon it. The object of adding the 
 pyrogallic acid at this stage is to ascertain if oxygen is present, as 
 sometimes happens when the total quantity of gas is very small, 
 and the vacuum during the combustion but slightly impaired. 
 Under such circumstances, traces of oxygen are given off by the 
 cupric oxide, and pass so rapidly over the metallic copper, as to 
 escape absorption. This necessarily involves the loss of any nitric 
 oxide which also escapes the copper, but this is such a very small 
 proportion of an already small quantity that its loss will not 
 appreciably affect the result. If oxygen be present, allow the gas 
 to remain exposed to the action of the pyrogallate until the liquid 
 when thrown up the sides of the laboratory vessel runs off without 
 leaving a dark red stain. If oxygen be not present, a few bubbles 
 of that gas (B. X) are introduced to oxidize the nitric oxide to 
 pernitric oxide, which is absorbed by the potassic hydrate. The 
 
89. 
 
 WATER ANALYSIS. 
 
 423 
 
 oxygen may be very conveniently added from the gas pipette shown 
 
 in fig. 62, where a b are glass 
 bulbs of about 50 m.m. dia- 
 meter, connected by a glass 
 tube, the bore of which is 
 constricted at c, so as to allow 
 mercury to pass but slowly 
 from one bull) to the other, 
 and thus control the passage 
 Q2 f g as through the narrow 
 
 delivery tube d. The other 
 end e is provided with a short piece of caoutchouc tube, by blowing 
 through which any desired quantity of gas may be readily delivered. 
 Care must be taken after use that the delivery tube is not removed 
 from the trough till the angle d is filled with mercury. 
 
 To replenish the pipette with oxygen, fill the bulb b and the 
 tubes c and d with mercury ; introduce the point of d into a tube 
 of oxygen standing in the mercury trough, and draw air from the 
 tube e. The gas in b is confined between the mercury in c and 
 that in d. 
 
 When the excess of oxygen has been absorbed a"s above described, 
 the residual gas, which consists of nitrogen, is measured, and the 
 analysis is complete.* 
 
 There are thus obtained, three sets of observations, from which, 
 by the usual methods, we may calculate A the total volume, B the 
 volume of nitric oxide and nitrogen, and C the volume of nitrogen, 
 all reduced to C. and 760 m.m. pressure ; from these may be 
 obtained 
 
 A - B = vol. of CO 2 , 
 
 and hence the weight of carbon and nitrogen can be readily 
 found. 
 
 It is much less trouble, however, to assume that the gas in all 
 three stages consists wholly of nitrogen ; then, if A be the weight 
 of the total gas, B its weight after treatment with potassic hydrate, 
 and C after treatment with pyrogallate, the weight of carbon will 
 
 be (A - B) i. and the weight of nitrogen ^ for the weights 
 of carbon and nitrogen in equal volumes of carbonic anhydride and 
 
 *When the quantity of carbon is very large indeed, traces of carbonic oxide are- 
 occasionally present in the gas, and will remain with the nitrogen after treatment with 
 alkaline pyrogallate. When such excessive quantities of carbon are found, the stop- 
 cock / should be closed when the last measurement is made, the laboratory vessel 
 detached, washed, and replaced filled with mercury. Introduce then a little solution 
 of cuprous chloride (B. K), and return the gas upon it. Any carbonic oxide will be 
 absorbed, and after about five minutes the remaining nitrogen may be measured. In 
 more than twenty consecutive analyses of waters of very varying kinds, not a trace of 
 carbonic oxide was found in any of the gases obtained on combustion. 
 
424 
 
 VOLUMETRIC ANALYSIS. 
 
 
 
 nitrogen, at the same temperature and pressure, are as 6 : 14 ; and 
 the weights of nitrogen in equal volumes of nitrogen and nitric 
 oxide are as 2 : 1. 
 
 The weight of 1 c.c. of nitrogen at C. and 760 m.m. is 0-0012562 
 
 , ,, , * iv - T- 'i *- 0-001 2562 x y x p 
 
 mi.. and the formula tor the calculation is u- = -^. A A AO^^\ ^/n> 
 
 (1 + m 006bit) i bO 
 
 in which w the weight of nitrogen, v the volume, p the pressure 
 corrected for tension of aqueous vapour, and t the temperature in 
 degrees centigrade. To facilitate this calculation, there is given in 
 
 0-0012562 
 Table 2 the logarithmic value of the expression ,, j-O-OOSfP/^ ^60 
 
 for each tenth of a degree from to 29 '9 C., and in Table 1 the 
 tension of aqueous vapour in millimeters of mercury. As the 
 measuring tube is always kept moist with water, the gas when 
 measured is always saturated with aqueous vapour. 
 
 The following example will show the precise mode of calcu- 
 lation : 
 
 Volume of gas .... 
 
 A B 
 
 m 4. i After absorption 
 Total. Qf C02 i 
 
 4-4888 c.c. 0-26227 c.c. 
 13-5 13-6 
 m.m. m.m. 
 310 480-0 
 193-5 343-5 
 
 C 
 Nitrogen. 
 
 0-26227 c.c. 
 13-7 
 m.m. 
 480-0 
 328-2 
 
 Height of mercury in a, c, d 
 ,, ,, b 
 
 Difference 
 Plus tension of aqueous vapour . 
 
 Deduct correction for capillarity. 
 
 Deduct this from height of bar . 
 Tension of dry gas 
 
 Logarithm of volume of gas 
 0-0012562 
 
 116-5 
 11-5 
 
 136-5 
 11-6 
 
 151-8 
 11-7 
 
 128-0 
 0-9 
 
 Add for 7 . 2 
 capillarity ) " ^ 
 
 2-2 
 
 127-1 
 
 769-8 
 127-1 
 
 150-3 
 
 769-8 
 150-3 
 
 165-7 
 
 769-8 
 165-7 
 
 642-7 
 0-65213 
 
 619-5 
 1-41875 
 
 604-1 
 T41875 
 
 (l+0'00367t)760 
 ,, ,, tension of dry gas . 
 
 Logarithm of weight of gas calcu- 
 lated as N 
 
 6-19724 
 
 2-80801 
 
 6-19709 
 2-79204 
 
 6-19694 
 2-78111 
 
 3-65738 
 0-0045434 
 
 440788 
 0-0002558 
 
 4-3968G 
 0-0002494 gm. 
 
 
 From these weights, those of carbon and of nitrogen are obtained 
 by the use of the formulae above mentioned. Thus 
 
 A- B = 0-0042876 B + C = 0-0005052 
 
 x 3 ^2 
 
 -f- 7)0-0128628 Weight of nitrogen, Q-Q002526 
 Weight of carbon, Q-Q01837 
 
 When carbonic oxide is found, the corresponding weight of 
 nitrogen may be found in a similar manner, and should be added 
 to that corresponding to the carbonic anhydride before multiplying 
 
89. WATER ANALYSIS. 425 
 
 o 
 
 by ^, and must be deducted from the weight corresponding to the 
 
 volume after absorption of carbonic anhydride. 
 
 As it is impossible to attain to absolute perfection of manipulation 
 and materials, each analyst should make several blank experiments 
 by evaporating a liter of pure distilled water (B. a) with the usual 
 quantities of sulphurous acid and ferrous chloride, and, in addition, 
 O'l gin. of freshly ignited sodic chloride (in order to furnish 
 a tangible residue). The residue should be burnt and the resulting 
 gas analyzed in the usual way, and the average amounts of carbon 
 and nitrogen thus obtained deducted from the results of all 
 analyses. This correction, which may be about O'OOOl gm. of C, 
 and 0*00005 gm. of X, includes the errors due to the imperfection 
 of the vacuum produced by the 8pr.en.gel pump, nitrogen retained 
 in the cupric oxide, ammonia absorbed from the atmosphere during 
 evaporation, etc. 
 
 When the quantity of nitrogen as ammonia exceeds O'OOT part 
 per 100,000, there is a certain amount of loss of nitrogen during 
 the evaporation by dissipation of ammonia. This appears to be 
 very constant, and is given in Table 3, which is calculated from 
 Table 5, which has been kindly furnished by Dr. Frankland. 
 The number in this table corresponding to the quantity of nitrogen 
 as ammonia present in the water analyzed should be added to the 
 amount of nitrogen found by combustion. The number thus 
 obtained includes the nitrogen as ammonia, and this must be 
 deducted to ascertain the organic nitrogen. If "ammonia" is 
 determined instead of " nitrogen as ammonia," Table 5 may be used. 
 
 When, in operating upon sewage, hydric metaphosphate has 
 been employed, Tables 4 or 6 should be used. 
 
 Rules for Converting- Parts per 100,000 into Grains per Gallon, 
 or the reverse. 
 
 To convert parts per 100,000 into grains per gallon, multiply 
 by 0-7. 
 
 To convert grains per gallon into parts per 100,000, divide 
 by 07. . 
 
 To convert grams per liter into grains per gallon, multiply 
 by 70. 
 
 
426 VOLUMETRIC ANALYSIS. 89. 
 
 TABLE 1. 
 
 Elasticity of Aqueous "Vapour for each jLth degree centigrade 
 from to 30 C. (Reg-nault). 
 
 
 all? 
 
 
 s !*? 
 
 
 .2 1& 
 
 
 *16 
 
 
 Ss 
 
 Temp. 
 
 Ill 
 
 Temp. 
 
 
 Tom p. 
 
 o? I 
 
 Temp. 
 
 
 Temp. 
 
 ||| 
 
 C. 
 
 'ia^ 
 
 C. 
 
 las 
 
 C. 
 
 'i^^ 
 
 C. 
 
 aSa 
 
 C. 
 
 2 5 iS 
 
 
 |j| 
 
 
 l|<s 
 
 
 H|< 
 
 
 , .,_, F-4 
 
 
 p|2 
 
 
 
 4-6 
 
 6-0 
 
 7'0 
 
 12-0 
 
 10-5 
 
 18-0 
 
 15-4 
 
 24-0 
 
 22-2 
 
 1 
 
 4-6 
 
 1 
 
 7-0 
 
 1 
 
 10-5 
 
 1 
 
 15-5 
 
 1 
 
 22-3 
 
 '2 
 
 4'7 
 
 2 
 
 
 2 
 
 10-6 
 
 2 
 
 15-6 
 
 2 
 
 22-5 
 
 "3 
 
 47 
 
 3 
 
 7-1 
 
 3 
 
 107 
 
 3 
 
 157 
 
 3 
 
 22-6 
 
 4 
 
 47 
 
 4 
 
 7-2 
 
 4 
 
 107 
 
 4 
 
 157 
 
 4 
 
 227 
 
 *5 
 
 4-8 
 
 '5 
 
 7-2 
 
 5 
 
 10-8 
 
 5 
 
 15-8 
 
 5 
 
 22'9 
 
 6 
 
 4'8 
 
 6 
 
 7-3 
 
 6 
 
 10-9 
 
 6 
 
 15-9 
 
 6 
 
 23'0 
 
 *7 
 
 4-8 
 
 7 
 
 7'3 
 
 7 
 
 10-9 
 
 7 
 
 16-0 
 
 7 
 
 231 
 
 8 
 
 4-9 
 
 8 
 
 7'4 
 
 8 
 
 11-0 
 
 8 
 
 161 
 
 8 
 
 23-3 
 
 9 
 
 4'9 
 
 9 
 
 7-4 
 
 9 
 
 111 
 
 9 
 
 1G-2 
 
 9 
 
 23'4 
 
 1-0 
 
 4'9 
 
 7'0 
 
 7'5 
 
 13-0 
 
 11-2 
 
 19-0 
 
 16-3 
 
 25-0 
 
 23-5 
 
 1 
 
 5-0 
 
 1 
 
 7*5 
 
 1 
 
 11-2 
 
 1 
 
 16-4 
 
 1 
 
 237 
 
 *2 
 
 5-0 
 
 2 
 
 7-0 
 
 2 
 
 11*3 
 
 2 
 
 16-6 
 
 "2 
 
 23-8 
 
 "3 
 
 5-0 
 
 3 
 
 
 3 
 
 11-4 
 
 3 
 
 167 
 
 3 
 
 24-0 
 
 4 
 
 5-1 
 
 '4 
 
 77 
 
 4 
 
 11-5 
 
 4 
 
 16-8 
 
 4 
 
 241 
 
 5 
 
 51 
 
 5 
 
 7-8 
 
 5 
 
 11-5 
 
 5 
 
 IG'9 
 
 '5 
 
 24-3 
 
 6 
 
 5-2 
 
 6 
 
 7'8 
 
 6 
 
 11-6 
 
 P 6 
 
 17-0 
 
 6 
 
 24-4 
 
 7 
 
 5'2 
 
 7 
 
 7-9 
 
 7 
 
 117 
 
 7 
 
 171 
 
 7 
 
 24'6 
 
 8 
 
 5 '2 
 
 8 
 
 7'9 
 
 8 
 
 11-8 
 
 8 
 
 17-2 
 
 8 
 
 247 
 
 9 
 
 5-3 
 
 9 
 
 8-0 
 
 9 
 
 11-8 
 
 9 
 
 17-3 
 
 9 
 
 24-8 
 
 2-0 
 
 5'3 
 
 8-0 
 
 8-0 
 
 14-0 
 
 11-9 
 
 20-0 
 
 17-4 
 
 26-0 
 
 25'0 
 
 1 
 
 5'3 
 
 1 
 
 81 
 
 1 
 
 12-0 
 
 1 
 
 17-5 
 
 1 
 
 251 
 
 2 
 
 5'4 
 
 2 
 
 81 
 
 2 
 
 12-1 
 
 '2 
 
 17-6 
 
 '2 
 
 253 
 
 3 
 
 5*4 
 
 3 
 
 8-2 
 
 3 
 
 121 
 
 3 
 
 177 
 
 3 
 
 25-4 
 
 4 
 
 5-5 
 
 4 
 
 8-2 
 
 4 
 
 12-2 
 
 4 
 
 17-8 
 
 4 
 
 25-6 
 
 5 
 
 5-5 
 
 5 
 
 8-3 
 
 5 
 
 12-3 
 
 5 
 
 17'9 
 
 5 
 
 257 
 
 6 
 
 5-5 
 
 '6 
 
 8'3 
 
 6 
 
 12-4 
 
 6 
 
 18-0 
 
 6 
 
 25-9 
 
 7 
 
 5-6 
 
 7 
 
 8'4 
 
 7 
 
 12-5 
 
 7 
 
 18'2 
 
 7 
 
 26-0 
 
 8 
 
 5'6 
 
 8 
 
 8-5 
 
 8 
 
 12-5 
 
 8 
 
 18-3 
 
 8 
 
 26'2 
 
 9 
 
 5-6 
 
 9 
 
 8-5 
 
 9 
 
 12-6 
 
 9 
 
 18'4 -9 
 
 26-4 
 
 3-0 
 
 57 
 
 9-0 
 
 8-6 
 
 15-0 
 
 12-7 
 
 21-0 
 
 1S'5 
 
 27-0 
 
 26'5 
 
 1 
 
 57 
 
 1 
 
 8-6 
 
 1 
 
 12-8 
 
 1 
 
 18-6 
 
 1 
 
 267 
 
 2 
 
 5'8 
 
 2 
 
 87 
 
 2 
 
 12-9 
 
 '2 
 
 187 
 
 '2 
 
 26'8 
 
 3 
 
 5-8 
 
 '3 
 
 87 
 
 3 
 
 12-9 
 
 3 
 
 18-8 
 
 3 
 
 27'0 
 
 4 
 
 5-8 
 
 4 
 
 8'8 
 
 4 
 
 13-0 
 
 4 
 
 19'0 
 
 4 
 
 271 
 
 5 
 
 5-9 
 
 *5 
 
 8'9 
 
 5 
 
 131 
 
 5 
 
 191 
 
 5 
 
 27-3 
 
 6 
 
 5-9 
 
 6 
 
 8-9 
 
 6 
 
 13-2 
 
 6 
 
 19'2 
 
 6 
 
 27-5 
 
 7 
 
 G-0 
 
 7 
 
 9-0 
 
 7 
 
 13-3 
 
 7 
 
 19-3 
 
 7 
 
 27'G 
 
 8 
 
 6-0 
 
 8 
 
 9-0 
 
 8 
 
 13-4 
 
 8 
 
 19-4 
 
 8 
 
 27-8 
 
 9 
 
 6-1 
 
 9 
 
 91 
 
 9 
 
 13-5 
 
 9 
 
 19-5 
 
 9 
 
 27-9 
 
 4-0 
 
 6-1 
 
 10-0 
 
 9'2 
 
 16-0 
 
 13-5 
 
 22-0 
 
 197 
 
 28-0 
 
 281 
 
 1 
 
 6-1 
 
 1 
 
 9-2 
 
 1 
 
 13-6 
 
 1 
 
 19-8 
 
 1 
 
 28-3 
 
 2 
 
 6-2 
 
 2 
 
 9-3 
 
 2 
 
 137 
 
 '2 
 
 19-9 
 
 2 
 
 28-4 
 
 3 
 
 6-2 
 
 3 
 
 9-3 
 
 3 
 
 13-8 
 
 3 
 
 20-0 
 
 3 
 
 28'6 
 
 4 
 
 6-3 
 
 4 
 
 9-4 
 
 4 
 
 13-9 
 
 4 
 
 201 
 
 4 
 
 28-8 
 
 5 
 
 6-3 
 
 5 
 
 9-5 
 
 5 
 
 14-0 
 
 '5 
 
 20-3 
 
 '5 
 
 28-9 
 
 6 
 
 6-4 
 
 6 
 
 9-5 
 
 6 
 
 141 
 
 6 
 
 20-4 
 
 G 
 
 291 
 
 7 
 
 6-4 
 
 7 
 
 9-6 
 
 7 
 
 14-2 
 
 7 
 
 20'5 
 
 7 
 
 29'3 
 
 8 
 
 6-4 
 
 8 
 
 97 
 
 8 
 
 14-2 
 
 8 
 
 20 -6 
 
 8 
 
 09-4 
 
 9 
 
 6-5 
 
 9 
 
 97 
 
 9 
 
 14-3 
 
 9 
 
 20-8 
 
 9 
 
 29-6 
 
 5-0 
 
 6-5 
 
 11-0 
 
 9-8 
 
 17-0 
 
 14-4 
 
 23-0 
 
 20'9 
 
 29-0 
 
 29-8 
 
 1 
 
 6-6 
 
 1 
 
 9-9 
 
 1 
 
 14-5 
 
 1 
 
 21-0 
 
 1 
 
 30-0 
 
 2 
 
 G-6 
 
 "2 
 
 9-9 
 
 2 
 
 14-6 
 
 '2 
 
 211 
 
 2 
 
 301 ! 
 
 3 
 
 6-7 
 
 3 
 
 10-0 
 
 3 
 
 147 
 
 3 
 
 21'3 
 
 3 
 
 30-3 
 
 4 
 
 6-7 
 
 4 
 
 101 
 
 4 
 
 14-8 
 
 4 
 
 21-4 
 
 4 
 
 30-5 1 
 
 "5 
 
 6-8 
 
 "5 
 
 101 
 
 5 
 
 14-9 
 
 5 
 
 21'5 
 
 5 
 
 307 
 
 6 
 
 6-8 
 
 6 
 
 10-2 
 
 6 
 
 15-0 
 
 6 
 
 217 
 
 6 
 
 30-8 1 
 
 7 
 
 6-9 
 
 7 
 
 10-3 
 
 7 
 
 151 
 
 7 
 
 21-8 
 
 7 
 
 31-0 
 
 8 
 
 6-9 
 
 8 
 
 10-3 
 
 8 
 
 15-2 
 
 8 
 
 21-9 
 
 8 
 
 31-2 1 
 
 9 
 
 7-0 
 
 9 
 
 10-4 
 
 9 
 
 15-3 
 
 9 
 
 221 
 
 9 
 
 31-4 
 
89. 
 
 WATER ANALYSIS. 
 
 427 
 
 TABLE 2. 
 
 Baduction of Cubic Centimeters of Nitrogen to Grams. 
 
 A'AAI OXf!> 
 
 Lo. 
 
 0-00367)760 
 
 from to 30 
 
 t.c. 
 
 o-o 
 
 O'l 
 
 0-2 
 
 0-3 
 
 0-4 
 
 0-5 
 
 0-6 
 
 0-7 
 
 0-8 
 
 0-9 
 
 
 
 "6-21824 
 
 808 
 
 793 
 
 777 
 
 761 
 
 745 
 
 729 
 
 713 
 
 697 
 
 681 
 
 1 
 
 665 
 
 649 
 
 633 
 
 617 
 
 601 
 
 586 
 
 570 
 
 554 
 
 538 
 
 522 
 
 2 
 
 507 
 
 491 
 
 475 
 
 459 
 
 443 
 
 427 
 
 412 
 
 396 
 
 380 
 
 364 
 
 3 
 
 349 
 
 333 
 
 318 
 
 302 
 
 286 
 
 270 
 
 255 
 
 239 
 
 223 
 
 208 
 
 4 
 
 192 
 
 177 
 
 161 
 
 145 
 
 130 
 
 114 
 
 098 
 
 083 
 
 067 
 
 051 
 
 5 
 
 035 
 
 020 
 
 004 
 
 *989 
 
 *973 
 
 *957 
 
 *942 
 
 -926 
 
 *911 
 
 *895 
 
 6 
 
 6-20S79 
 
 864 
 
 848 
 
 833 
 
 817 
 
 801 
 
 786 
 
 770 
 
 755 
 
 739 
 
 7 
 
 723 
 
 708 
 
 692 
 
 676 
 
 661 
 
 645 
 
 629 
 
 614 
 
 598 
 
 583 
 
 8 
 
 567 
 
 552 
 
 536 
 
 521 
 
 505 
 
 490 
 
 474 
 
 459 
 
 443 
 
 428 
 
 
 
 413 
 
 397 
 
 382 
 
 366 
 
 351 
 
 335 
 
 320 
 
 304 
 
 289 
 
 274 
 
 10 
 
 259 
 
 244 
 
 228 
 
 213 
 
 198 
 
 182 
 
 167 
 
 151 
 
 136 
 
 121 
 
 11 
 
 106 
 
 090 
 
 075 
 
 060 
 
 015 
 
 029 
 
 014 
 
 *999 
 
 *984 
 
 *969 
 
 
 
 
 
 
 
 
 
 
 
 
 12 
 
 619953 
 
 93S 
 
 923 
 
 907 
 
 892 
 
 877 
 
 862 
 
 846 
 
 831 
 
 816 
 
 13 
 
 800 
 
 785 
 
 770 
 
 755 
 
 740 
 
 724 
 
 709 
 
 694 
 
 679 
 
 664 
 
 14 
 
 648 
 
 633 
 
 618 
 
 603 
 
 588 
 
 573 
 
 558 
 
 543 
 
 528 
 
 513 
 
 15 
 
 497 
 
 482 
 
 467 
 
 452 
 
 437 
 
 422 
 
 407 
 
 392 
 
 377 
 
 362 
 
 16 
 
 346 
 
 331 
 
 316 
 
 301 
 
 286 
 
 271 
 
 256 
 
 241 
 
 226 
 
 211 
 
 17 
 
 196 
 
 181 
 
 166 
 
 151 
 
 136 
 
 121 
 
 106 
 
 091 
 
 076 
 
 061 
 
 IS 
 
 046 
 
 031 
 
 016 
 
 001 
 
 *986 
 
 *971 
 
 *956 
 
 *941 
 
 *926 
 
 *911 
 
 19 
 
 6-18897 
 
 882 
 
 887 
 
 852 
 
 837 
 
 822 
 
 807 
 
 792 
 
 777 
 
 762 
 
 20 
 
 748 
 
 733 
 
 718 
 
 703 
 
 688 
 
 673 
 
 659 
 
 644 
 
 629 
 
 614 
 
 21 
 
 600 
 
 585 
 
 570 
 
 555 
 
 540 
 
 526 
 
 511 
 
 496 
 
 481 
 
 466 
 
 22 
 
 452 
 
 437 
 
 422 
 
 408 
 
 393 
 
 378 
 
 363 
 
 349 
 
 334 
 
 319 
 
 23 
 
 . 305 
 
 290 
 
 275 
 
 261 
 
 246 
 
 231 
 
 216 
 
 202 
 
 187 
 
 172 
 
 24 
 
 158 
 
 143 
 
 128 
 
 114 
 
 099 
 
 084 
 
 070 
 
 055 
 
 041 
 
 026 
 
 25 
 
 012 
 
 *997 
 
 *982 
 
 *968 
 
 *953 
 
 *938 
 
 *924 
 
 *909 
 
 *895 
 
 *8SO 
 
 26 
 
 "6-17866 
 
 851 
 
 837 
 
 822 
 
 808 
 
 793 
 
 779 
 
 764 
 
 750 
 
 735 
 
 27 
 
 721 
 
 706 
 
 692 
 
 677 
 
 663 
 
 648 
 
 634 
 
 619 
 
 605 
 
 590 
 
 28 
 
 576 
 
 561 
 
 547 
 
 532 
 
 518 
 
 503 
 
 489 
 
 475 
 
 460 
 
 446 
 
 29 
 
 432 
 
 417 
 
 403 
 
 388 
 
 374 
 
 360 
 
 345 
 
 331 
 
 316 
 
 302 
 
 
 
 
 
 
 
 
 
 
 
 
428 
 
 VOLUMETRIC ANALYSIS. 
 
 89. 
 
 TABLE 3. 
 
 Loss of Nitrogen by Evaporation of NH3. 
 With Sulphurous Acid. 
 
 Parts per 100,000. 
 
 Nas 
 
 Loss 
 
 Nas 
 
 Loss 
 
 Nag 
 
 Loss 
 
 Nas 
 
 Loss 
 
 Nas 
 
 Loss 
 
 Nas 
 
 Loss 
 
 NH3. 
 
 of N. 
 
 NH3. 
 
 of N. 
 
 NH3. 
 
 of N. 
 
 NH3. 
 
 of N. 
 
 NH3. 
 
 of N. 
 
 NH3. 
 
 of N. 
 
 5-0 
 
 1-741 
 
 3'9 
 
 1-425 
 
 2-8 
 
 898 
 
 17 
 
 370 
 
 6 
 
 145 
 
 04 
 
 009 
 
 4-9 
 
 1-717 
 
 3'8 
 
 1-378 
 
 27 
 
 850 
 
 1-6 
 
 338 
 
 5 
 
 109 
 
 03 
 
 007 
 
 4'8 
 
 1-693 
 
 3-7 
 
 1-330 
 
 2-6 
 
 802 
 
 1-5 
 
 324 
 
 4 
 
 075 
 
 02 
 
 005 
 
 47 
 
 1-669 
 
 3-6 
 
 1-282 
 
 2-5 
 
 754 
 
 1-4 
 
 309 
 
 3 
 
 057 
 
 01 
 
 003 
 
 4'6 
 
 1-645 
 
 3-5 
 
 1-234 
 
 2-4 
 
 706 
 
 1-3 
 
 295 
 
 2 
 
 038 
 
 008 
 
 002 
 
 4-5 
 
 1-621 
 
 3-4 
 
 1-186 
 
 2-3 
 
 658 
 
 1-2 
 
 280 
 
 1 
 
 020 
 
 007 
 
 001 
 
 4'4 
 
 1-598 
 
 3-3 
 
 1-138 
 
 2-2 
 
 610 
 
 1-1 
 
 266 
 
 09 
 
 018 
 
 
 
 4-3 
 
 1-574 
 
 3-2 
 
 1-090 
 
 2-1 
 
 562 
 
 i-o 
 
 252 
 
 08 
 
 017 
 
 
 
 4-2 
 
 1-550 
 
 3-1 
 
 1-042 
 
 2-0 
 
 514 
 
 9 
 
 237 
 
 07 
 
 015 
 
 
 
 4-1 
 
 1-521 
 
 3-0 
 
 994 
 
 1-9 
 
 466 
 
 8 
 
 217 
 
 06 
 
 013 
 
 
 
 4-0 
 
 1-473 
 
 2-9 
 
 946 
 
 1-8 
 
 418 
 
 7 
 
 181 
 
 05 
 
 on 
 
 
 
 TABLE 4. 
 
 Loss of Nitrogen by Evaporation of NIP. 
 With Hydric Metaphosphate. 
 
 Parts per 100,000. 
 
 3 
 
 H 
 
 a 
 
 # 
 
 1 
 
 s 
 
 fe 
 
 5! 
 
 a 
 
 fe 
 
 i 
 
 co" 
 
 *' 
 
 11 
 
 
 "o 
 
 3 g 
 
 
 "o 
 
 11 
 
 & 
 
 o 
 
 C3 
 
 & 
 
 "o 
 
 *o ^ 
 
 tw 
 
 % 
 
 'o ^ 
 
 C/l 
 
 
 'o ^ 
 
 22 
 
 co 
 
 *o S, 
 
 Jl 
 
 cc 
 
 *s 
 
 fc 
 
 
 o 
 
 " 
 
 
 o> 
 
 Of 
 
 1 
 
 
 & 
 
 3 
 
 100 c.c. 
 
 8'2 
 
 482 
 
 100 c.c. 
 
 5-9 
 
 385 
 
 100 c.c. 
 
 3'6 
 
 28 L 
 
 100 c.c. 
 
 1-3 
 
 142 
 
 
 8-1 
 
 477 
 
 
 5-8 
 
 381 
 
 
 3-5 
 
 277 
 
 
 1'2 
 
 136 
 
 
 8-0 
 
 473 
 
 
 5-7 
 
 377 
 
 
 3-4 
 
 272 
 
 
 1-1 
 
 129 
 
 
 7-9 
 
 469 
 
 
 5-6 
 
 373 
 
 
 3-3 
 
 267 
 
 
 i-o 
 
 123 
 
 
 7-8 
 
 465 
 
 
 5'5 
 
 368 
 
 
 3-2 
 
 261 
 
 
 9 
 
 117 
 
 .. 
 
 7'7 
 
 461 
 
 
 5'4 
 
 364 
 
 
 
 255 
 
 
 8 
 
 111 
 
 
 7'6 
 
 456 
 
 
 5'3 
 
 360 
 
 
 30 
 
 249 
 
 250 c.c. 
 
 "7 
 
 088 
 
 
 75 
 
 452 
 
 
 5-2 
 
 356 
 
 
 2-9 
 
 242 
 
 
 6 
 
 073 
 
 
 7'4 
 
 448 
 
 
 5-1 
 
 352 
 
 
 2-8 
 
 236 
 
 
 "5 
 
 061 
 
 
 7'3 
 
 444 
 
 
 5-0 
 
 347 
 
 
 27 
 
 230 
 
 SOOc.c. 
 
 4 
 
 049 
 
 
 7-2 
 
 440 
 
 
 4'9 
 
 343 
 
 
 2-6 
 
 223 
 
 
 3 
 
 036 
 
 .. 
 
 7-1 
 
 435 
 
 
 4'S 
 
 338 
 
 
 2-5 
 
 217 
 
 1000 c.c. 
 
 '2 
 
 024 
 
 
 7-0 
 
 431 
 
 
 4-7 
 
 334 
 
 
 2-4 
 
 211 
 
 
 1 
 
 012 
 
 
 6-9 
 
 427 
 
 
 4-G 
 
 329 
 
 
 2-3 
 
 205 
 
 
 09 
 
 on 
 
 
 68 
 
 423 
 
 
 4-5 
 
 324 
 
 ' 
 
 2-2 
 
 198 
 
 
 08 
 
 010 
 
 
 6'7 
 
 419 
 
 
 4-4 
 
 319 
 
 
 21 
 
 192 
 
 
 07 
 
 008 
 
 
 6-6 
 
 414 
 
 
 4'3 
 
 '315 
 
 
 2-0 
 
 186 
 
 
 05 
 
 007 
 
 
 6-5 
 
 410 
 
 
 4'2 
 
 310 
 
 
 1-9 
 
 180 
 
 
 05 
 
 006 
 
 
 6-4 
 
 403 
 
 ... 
 
 4-1 
 
 305 
 
 
 1-8 
 
 173 
 
 
 04 
 
 005 
 
 
 6-3 
 
 402 
 
 
 4-0 
 
 301 
 
 
 17 
 
 167 
 
 
 03 
 
 004 
 
 .. 
 
 62 
 
 398 
 
 ... 
 
 3-9 
 
 296 
 
 
 1-6 
 
 161 
 
 
 02 
 
 002 
 
 
 6-1 
 
 394 
 
 
 3'8 
 
 291 
 
 
 1-5 
 
 154 
 
 
 01 
 
 001 
 
 
 
 6-0 
 
 389 
 
 
 3-7 
 
 286 
 
 
 1-4 
 
 118 
 
 
 
 
89. WATER ANALYSIS. 
 
 TABLE 5. 
 
 Loss of Nitrogen l>y Evaporation 
 With Sulplmrous Acid. 
 
 Parts per 100,000. 
 
 429 
 
 NH3. 
 
 Loss 
 of N. 
 
 NH3. 
 
 Loss 
 of N. 
 
 NH3. 
 
 Loss 
 of N. 
 
 NH3. 
 
 Loss 
 of N. 
 
 NH3. 
 
 Loss 
 of N. 
 
 NH3. 
 
 Loss 
 of N. 
 
 6-0 
 
 1727 
 
 4-8 
 
 1-451 
 
 3-6 
 
 977 
 
 2 "4 
 
 503 
 
 1-2 
 
 250 
 
 09 
 
 014 
 
 5-9 
 
 1707 
 
 47 
 
 1-411 
 
 3-5 
 
 937 
 
 2-3 
 
 463 
 
 1-1 
 
 238 
 
 08 
 
 013 
 
 5-8 
 
 1-688 
 
 4-6 
 
 1-372 
 
 3-4 
 
 898 
 
 2-2 
 
 424 
 
 i-o 
 
 226 
 
 07 
 
 012 
 
 57 
 
 1-668 
 
 4-5 
 
 1-332 
 
 3-3 
 
 858 
 
 2'JL 
 
 38 1 
 
 9 
 
 196 
 
 05 
 
 010 
 
 5-6 
 
 1-648 
 
 4'4 
 
 1-293 
 
 32 
 
 819 
 
 2-0 
 
 345 
 
 8 
 
 166 
 
 05 
 
 009 
 
 5-5 
 
 1-628 
 
 4-3 
 
 1-253 
 
 31 
 
 779 
 
 1-9 
 
 333 
 
 7 
 
 136 
 
 04 
 
 007 
 
 5-4 
 
 1-609 
 
 4-2 
 
 1-214 
 
 SO 
 
 740 
 
 1-8 
 
 321 
 
 6 
 
 106 
 
 03 
 
 006 
 
 5'3 
 
 1-589 
 
 4-1 
 
 1-174 
 
 2-9 
 
 700 
 
 1-7 
 
 309 
 
 5 
 
 077 
 
 02 
 
 004 
 
 52 
 
 1-569 
 
 4-0 
 
 1-135 
 
 2-8 
 
 661 
 
 1-6 
 
 297 
 
 4 
 
 062 
 
 01 
 
 ors 
 
 5-1 
 
 1-549 
 
 3-9 
 
 1-095 
 
 2-7 
 
 621 
 
 1-5 
 
 285 
 
 3 
 
 04-7 
 
 009 
 
 001 
 
 5-0 
 
 1-530 
 
 3-8 
 
 1-056 
 
 2-G 
 
 582 
 
 1-4 
 
 274 
 
 2 
 
 032 
 
 
 
 4-9 
 
 1-490 
 
 37 
 
 1-016 
 
 2-5 
 
 542 
 
 1-3 
 
 262 
 
 1 
 
 017 
 
 
 
 TABLE 6. 
 
 Loas of Nitrogen by Evaporation of NHX 
 With Hydric Metaphosphate. 
 
 Parts per ICO, COO. 
 
 i 
 
 
 ft 
 
 2*2 
 
 
 ft' 
 
 .1 
 
 
 ft 
 
 8*8 
 
 
 ft 
 
 I~H 
 
 hH 
 
 "8 
 
 || 
 
 3 
 
 'o 
 
 II 
 
 w 
 
 "o 
 
 " 
 
 w 
 
 
 
 'o 2 
 
 ft 
 
 3 
 
 
 ft 
 
 s 
 
 eg, 
 
 ft 
 
 05 
 
 H 
 
 ll 
 
 
 
 > 
 o 
 
 
 ? 
 
 > l 
 
 
 o 
 
 1 
 
 
 
 Hi 
 
 0) 
 
 
 
 100 c.c. 
 
 10-0 
 
 483 
 
 100 c.c. 
 
 7-2 
 
 386 
 
 100 c.c. 
 
 4-4 
 
 283 
 
 100 c.c. 
 
 1-6 
 
 143 
 
 
 9'9 
 
 480 
 
 
 7-1 
 
 383 
 
 
 4'3 
 
 279 
 
 
 1-5 
 
 137 
 
 
 9-8 
 
 476 
 
 
 7'0 
 
 379 
 
 
 4'2 
 
 275 
 
 
 1-4 
 
 132 
 
 
 97 
 
 473 
 
 
 6'9 
 
 375 
 
 
 4-1 
 
 271 
 
 
 1-3 
 
 127 
 
 
 9-6 
 
 469 
 
 
 6'8 
 
 372 
 
 
 4'0 
 
 267 
 
 
 1-2 
 
 122 
 
 
 9'5 
 
 466 
 
 
 67 
 
 368 
 
 
 3-9 
 
 262 
 
 
 1-1 
 
 117 
 
 
 9'4 
 
 462 
 
 
 6'6 
 
 365 
 
 
 3-8 
 
 257 
 
 
 i-o 
 
 112 
 
 
 9'3 
 
 459 
 
 
 6'5 
 
 361 
 
 
 37 
 
 252 
 
 253 c.c. 
 
 9 
 
 096 
 
 
 9'2 
 
 455 
 
 
 6'4 
 
 358 
 
 
 36 
 
 247 
 
 
 8 
 
 080 
 
 
 9.1 
 
 452 
 
 
 6'3 
 
 354 
 
 ... 
 
 3-5 
 
 242 
 
 
 7 
 
 070 
 
 
 9'0 
 
 448 
 
 
 6'2 
 
 351 
 
 
 3'4 
 
 236 
 
 
 6 
 
 060 
 
 
 8-9 
 
 445 
 
 
 6-1 
 
 348 
 
 
 3*3 
 
 231 
 
 500 c.c. 
 
 5 
 
 050 
 
 
 8'8 
 
 441 
 
 
 6"0 
 
 345 
 
 
 3'2 
 
 226 
 
 
 4 
 
 040 
 
 
 87 
 
 438 
 
 
 5'9 
 
 341 
 
 
 3-1 
 
 221 
 
 
 3 
 
 030 
 
 
 8'6 
 
 434 
 
 
 5-8 
 
 337 
 
 
 3-0 
 
 216 
 
 1000 c.c. 
 
 2 
 
 020 
 
 
 8'5 
 
 431 
 
 
 57 
 
 333 
 
 
 29 
 
 211 
 
 
 1 
 
 010 
 
 
 8-4 
 
 428 
 
 
 5-6 
 
 330 
 
 
 28 
 
 205 
 
 
 09 
 
 009 
 
 
 8-3 
 
 424 
 
 
 
 326 
 
 
 2-7 
 
 200 
 
 
 08 
 
 008 
 
 
 8-2 
 
 421 
 
 
 5-4 
 
 322 
 
 
 2-6 
 
 195 
 
 
 07 
 
 007 
 
 
 8-1 
 
 417 
 
 
 53 
 
 318 
 
 
 2-5 
 
 190 
 
 
 06 
 
 006 
 
 
 8'0 
 
 414 
 
 
 52 
 
 314 
 
 
 2'4 
 
 184 
 
 
 05 
 
 005 
 
 
 7'9 
 
 410 
 
 
 5'1 
 
 310 
 
 
 2'3 
 
 179 
 
 
 04 
 
 004 
 
 
 7'8 
 
 407 
 
 
 5-0 
 
 306 
 
 
 2'2 
 
 174 
 
 
 03 
 
 003 
 
 
 7-7 
 
 403 
 
 
 4-9 
 
 302 
 
 
 2-1 
 
 169 
 
 
 02 
 
 002 
 
 
 7-6 
 
 400 
 
 
 4'8 
 
 298 
 
 
 2'0 
 
 164 
 
 
 01 
 
 001 
 
 
 7'5 
 
 396 
 
 
 4-7 
 
 204 
 
 
 1-9 
 
 158 
 
 
 
 
 
 7'4 
 
 393 
 
 
 46 
 
 291 
 
 
 1-8 
 
 153 
 
 
 
 
 
 7-3 
 
 389 
 
 
 4-5 
 
 287 
 
 
 1-7 
 
 148 
 
 
 
 
430 VQLUMETHIC ANALYSIS. 89. 
 
 5. Estimation of Total Solid Matter. Evaporate over a steam 
 or water bath half a liter or a less quantity of the water in a platinum 
 dish which has been heated to redness and carefully weighed. 
 The water should be filtered or unfiltered, according to the decision 
 made in that respect at the commencement of the analysis. The 
 quantity to be taken is regulated chiefly by the amount of nitrate 
 present, as the residue from this operation is, with certain exceptions, 
 employed for the determination of the nitrogen as nitrates and 
 nitrites. As a general rule, for water supplies and river water 
 half a liter should be used ; for shallow well waters, a quarter 
 of a liter. Of sewages, 100 c.c., and of waters containing more 
 than 0'08 part of nitrogen as ammonia per 100,000, a quarter of 
 a liter will generally be convenient, as in these cases the residue 
 will not be used for the estimation of nitrogen as nitrates and 
 nitrites ; and the only point to lie considered is to have a quantity 
 of residue suitable to weigh. It is desirable to support the platinum 
 dish during evaporation in a glass ring with a flange, shaped like 
 the top of a beaker,- the cylindrical part being about 20 m.m. deep. 
 This is dropped into the metal ring on the water bath, and thus 
 lines the metal with glass, and keeps the dish clean. A glass 
 disc with a hole in it to receive the dish is not satisfactory, as 
 drops of water conveying solid matter find their way across the 
 under surface from the metal vessel to the dish, and thus soil 
 it. As soon as the evaporation is complete, the dish with the 
 residue -is removed, its outer side wiped dry with a cloth, and 
 it is dried in a water or steam oven for about three hours. It 
 is then removed to a desiccator, allowed to cool, weighed as rapidly 
 as possible, returned to the oven, and weighed at intervals of an 
 hour, until between two successive weighings it has lost less than 
 0-001 gm. 
 
 6. Estimation of Nitrogen as Nitrates and Nitrites. The residue 
 obtained in the preceding operation may be used for this estimation. 
 Treat it with about 30 c.c. of hot distilled w^ater, taking care to 
 submit the whole of the residue to its action. To ensure this it 
 is advisable to rub the dish gently with the finger, so as to detach 
 the solid matter as far as possible, and facilitate the solution of 
 the soluble matters. The finger may be covered by a caoutchouc 
 finger-stall. Then filter through a very small filter of Swedish 
 paper, washing the dish several times with small quantities of hot 
 distilled water. 
 
 The filtrate must be evaporated in a very small beaker, over 
 a steam bath, until reduced to about 1 c.c,, or even to clryness. 
 This concentrated solution is introduced into the glass tube shown 
 in fig. 63, standing in the porcelain mercury trough, rilled up to 
 the stop-cock with mercury. (If the nitrometer of Lunge is 
 used in place of Cr urn's tul3e, the use of the laboratory tube and 
 gas apparatus is avoided.) The tube is 210 m.m. in total length, 
 
89. WATER ANALYSIS. 431 
 
 and 15 m.m. in internal diameter. By pouring the liquid 
 into the cup at the top, and then cautiously opening the 
 stop-cock, it may he run into the tuhe without admitting 
 any air. The beaker is rinsed once with a very little hot 
 distilled water, and then two or three times with strong 
 sulphuric acid (c. a.), the volume of acid being to that of 
 the aqueous solution about as 3 : 2. The total volume of 
 acid and water should be about 6 c.c. Should any air by 
 chance be admitted at this stage, it may readily be removed 
 by suction, the lips being applied to the cup. With care 
 there is but little danger of getting acid into the mouth. 
 
 In a few cases carbonic anhydride is given off on 
 addition of sulphuric acid, and must be sucked out before 
 proceeding. 
 
 Now grasp the tube firmly in the hand, closing the open 
 end by the thumb, which should be first moistened ; 
 withdraw it from the trough, incline it at an angle of about 
 45, the cup pointing from you, and shake it briskly with 
 a rapid motion in the direction of its length, so as to 
 throw the mercury up towards the stop-cock. After 
 Fig. 63. a very little practice there is no danger of the acid finding- 
 its way down to the thumb, the mixture of acid and. 
 mercury being confined to a comparatively small portion of the 
 tube. In a few seconds some of the mercury becomes very finely 
 divided \ and if nitrates be present, in about a minute" or less 
 nitric oxide is evolved, exerting a strong pressure on the thumb. 
 Mercury is allowed to escape as the reaction proceeds, by partially, 
 but not wholly, relaxing the pressure of the thumb. A slight 
 excess of pressure should be maintained within the tube to prevent 
 entrance of air during the agitation, which must be continued 
 until no more gas is evolved. 
 
 "When the quantity of nitrate is very large, the mercury, on 
 shaking, breaks up into irregular masses, which adhere to one 
 another as if alloyed with lead or tin, and the whole forms a stiff 
 dark-coloured paste, which it is sometimes very difficult to shake ; 
 but nitric oxide is not evolved for a considerable time, then comes 
 off slo\yly, and afterwards with very great rapidity. To have room 
 for the gas evolved, the operator should endeavour to shake the 
 tube so as to employ as little as possible of the contained mercury 
 in the reaction. At the close of the operation the finely divided 
 mercury will consist for the most part of minute spheres, the alloyed 
 appearance being entirely gone. An experiment with a large 
 quantity of nitrate may often be saved from loss by firmly resisting 
 the escape of mercury, shaking until it is judged by the appearance 
 of the contents of the tube that the reaction is complete, and then 
 on restoring the tube to the mercury trough, allowing the finely- 
 divided mercury also to escape in part. If the gas evolved be not 
 more than the tube will hold, and there be no odour of pernitric 
 
432 VOLUMETPJC ANALYSIS. 89. 
 
 oxide from the escaped finely-divided mercury, the operation may 
 be considered successful. If the amount of nitrate be too large, 
 a smaller quantity of the water must be evaporated and the operation 
 repeated. When no nitrate is present, the mercury usually 
 manifests very little tendency to become divided, that which does 
 so remains bright, and the acid liquid does not become so turbid as 
 it does in other cases. 
 
 The reaction completed, the tube is taken up closed by the 
 thumb, and the gas is decanted into the laboratory vessel, and 
 measured in the usual way in the gas apparatus. The nitric acid 
 tube is of such a length, that when the cup is in contact with the 
 end of the mercury trough, the open end is just under the centre 
 of the laboratory vessel. If any acid has been expelled from the 
 tube at the close of the shaking operation, the end of the tube and 
 the thumb should be washed with water before introducing into 
 the mercury trough of the gas apparatus, so as to remove any acid 
 which may be adhering, which would destroy the wood of the 
 trough. Before passing the gas into the measuring tube of the gas 
 apparatus, a little mercury should be allowed to run over into the 
 laboratory vessel to remove the acid from the entrance to the 
 capillary tube, 
 
 As nitric, oxide contains half its volume of nitrogen, if half 
 a liter of water has been employed, the volume of nitric oxide 
 obtained will be equal to the volume of nitrogen present as nitrates 
 and nitrites in one liter of the water, and the weight of the 
 nitrogen may be calculated as directed in the paragraph on the 
 estimation of organic carbon and nitrogen. 
 
 When more than O'OS part of nitrogen as ammonia is present in 
 100,000 parts of liquid, there is danger of loss of -nitrogen by 
 decomposition of ammonic nitrite on evaporation ; and therefore 
 the residue from the estimation of total solid matter cannot be 
 used. In such cases acidify a fresh quantity of the liquid with 
 dilute hydric sulphate, add solution of potassic permanganate, 
 a little at a time, until the pink colour remains for about a minute, 
 and render the liquid just alkaline to litmus paper with sodic 
 carbonate. The nitrites present will then be converted into 
 nitrates and may be evaporated without fear of loss. Use as little 
 of each reagent as possible. Sewage may be examined in this 
 way ; but it is hardly necessary to attempt the determination, 
 as sewage is almost invariably free from nitrates and nitrites. 
 Out of several hundred specimens, the writer only found two 
 or three which contained any, and even then only in very 
 small quantity. 
 
 7. Estimation of Nitrogen as Nitrates and Nitrites in Waters 
 containing- a very large quantity of Soluble Matter, with but little 
 Ammonia or Organic Nitrogen. When the quantity of soluble 
 matter is excessive, as, for example, in sea-water, the preceding 
 method is inapplicable, as the solution to be employed cannot be 
 
89. WATER ANALYSIS. 433 
 
 reduced to a sufficiently small bulk to go into the shaking tube. 
 If the quantity of organic nitrogen be less than (H part in 100,000, 
 the nitrogen as nitrates and nitrites may generally l>e determined 
 by the following modification of Schulze's method devised by 
 E. T. Chapman. To 200 c.c. of the'water add 10 c.c. of sodic 
 hydrate solution (c. e), and boil briskly in an open porcelain dish 
 until it is reduced to about 70 c.c. When cold pour the residue 
 into a tall glass cylinder of about 120 c.c. capacity, and rinse the 
 dish with water free from ammonia. Add a piece of aluminium 
 foil of about 15 sq. centim. area, loading it with a piece of clean 
 glass rod to keep it from floating. Close the mouth of the cylinder 
 with a cork, bearing a small tube filled with pumice (C. ), moistened 
 with hydric chloride free from ammonia (C. 77). 
 
 Hydrogen will speedily be given off from the surface of the 
 aluminium, and in five or six hours the whole of the nitrogen as 
 nitrates and nitrites will be converted into ammonia. Transfer to 
 a small retort the contents of the cylinder, together with the 
 pumice, washing the whole apparatus with a little water free from 
 ammonia. Distil, and estimate ammonia in the usual way with 
 lS T essler solution. It appears impossible wholly to exclude ammonia 
 from the reagents and apparatus, and therefore some blank experi- 
 ments should be made to ascertain the correction to be applied for 
 this. This correction is very small, and appears to be nearly constant. 
 
 8. Estimation of Nitrogen as Nitrates and Nitrites "by the Indig-o 
 Process. This method will be described further on. 
 
 9. Estimation of Nitrates as Ammonia by the Copper-zinc 
 Couple. It is well known that when zinc is immersed in copper 
 sulphate solution it becomes covered with a spongy deposit of 
 precipitated copper. If the solution of copper sulphate be 
 sufficiently dilute, this deposit of copper is black in colour and 
 firmly adherent to the zinc. It is, however, not so generally 
 known that the zinc upon which copper has thus been deposited 
 possesses the power of decomposing pure distilled water at the 
 ordinary temperature, and that it is capable of effecting many 
 other decompositions which zinc alone cannot. Among these is 
 the decomposition of nitrates, and the transformation of the nitric 
 acid into ammonia, Gladstone and Tribe have shown that 
 the action of the " copper-zinc couple " (as they call the conjoined 
 metals) upon a nitre solution consists in the electrolysis of the 
 nitre, resulting in the liberation of hydrogen and the formation 
 of zinc oxide. This hydrogen is liberated upon and occluded 
 by the spongy copper, and when thus occluded, it is capable of 
 reducing the nitre solution in its vicinity. The nitrate is first 
 reduced to nitrite, and the nitrous acid is subsequently trans- 
 formed into ammonia by the further action of the hydrogen. 
 M. W. Williams has shown (J. C. S. 1881, 100) that even in 
 very dilute solutions of nitre the nitric acid can be completely 
 
 F F 
 
434 VOLUMETRIC ANALYSIS. 
 
 converted into ammonia in tins manner with considerable rapidity ; 
 and further, that the reaction may be greatly hastened by taking- 
 advantage of the influence of temperature, acids, and certain 
 neutral salts, which increase the electrolytic action of the couple. 
 His experiments prove that carbonic acid feeble acid as it is 
 suffices to treble the speed of the reaction, and that traces of sodic 
 chloride (0*1 per cent.) accelerated it nearly as much as carbonic 
 acid. A rise of a few degrees in temperature was also found to 
 hasten the reaction in a very marked degree. The presence of 
 alkalies, alkaline earths, and salts having an alkaline reaction, was 
 found to retard the speed of the reduction. 
 
 Williams has, upon those experiments, founded a simple and 
 expeditious process for estimating the nitric and nitrous acid in 
 water analysis, which, when used with skill, may be applied to by 
 far the greater number of waters with which the analyst is usually 
 called upon to deal (Analyst, 1881, 36). The requisite copper-zinc 
 couple is prepared in the following manner : The zinc employed 
 should be clean, and for the sake of convenience should be in the 
 form of foil or very thin sheet, It should be introduced into 
 a flask or bottle, and covered with a solution of copper sulphate, 
 containing about 3 per cent, of the crystallized salt, which should 
 be allowed to remain upon it until a copious, firmly adherent coating, 
 of black copper has been deposited. This deposition should not 
 be pushed too far, or the copper will be so easily detached that the 
 couple cannot be washed without impairing its activity. When 
 sufficient copper has been deposited the solution should be poured 
 off, and the conjoined metals washed with distilled water. The 
 wet couple is then ready for use. 
 
 To use it for the estimation of nitrates it should be made in 
 a wide-mouthed stoppered bottle. After washing, it is soaked with 
 distilled water ; to displace this, it is first washed with some of the- 
 water to be analyzed, and the bottle filled up with a further 
 quantity of the water. The stopper is then inserted, and the bottle- 
 allowed to digest in a warm place for a few hours. If the bottle 
 be well filled and stoppered, the temperature may be- raised to- 
 30 C., or even higher, without any fear of losing ammonia. The- 
 reaction will then proceed very rapidly ; but if it be desired to> 
 hasten the reaction still more, a little salt should be added (about 
 O'l gm. to every 100 c.c.), or if there be any objection to this, the 
 water may have carbonic acid passed throtigh it for a few minutes 
 before it is poured upon the couple. In the case of calcareous 
 waters, the same hastening effect may be obtained, and the lime 
 may at the same time be removed by adding a very little pure 
 oxalic- acid to the water before digesting it upon the couple. 
 Williams has shown that nitrous acid always remained in the 
 solution until the reaction was finished. By testing for nitrous 
 acid the completeness of the reaction may be ascertained with 
 certainty, and perhaps the- most delicate test that can, be applied for 
 
89. WATER ANALYSIS. 435 
 
 this purpose is that of Gricss, in which metaphenylene-diamine 
 is the reagent employed. When a solution of this substance is 
 added to a portion of the fluid, and acidified with sulphuric 
 acid, a yellow colouration is produced in about half an hour if 
 the least trace of a nitrite be present. The reaction easily detects 
 one part of nitrous acid in ten millions of water. When no 
 nitrous acid is found, the water is poured off the couple into 
 a stoppered bottle, and, if turbid, allowed to subside. A portion 
 of the clear fluid, more or less according to the concentration of 
 the nitrates in the water, is put into a Kessler glass, diluted if 
 necessary, and titrated with Xessler's reagent in the ordinary way. 
 
 This process may be used for the majority of ordinary waters 
 for those that are coloured, and those that contain magnesium or 
 other substances sufficient to interfere with the JSTessler reagent, 
 a portion of the fluid poured off the couple should be put into 
 a small retort, and distilled with a little pure lime or sodic 
 carbonate, and the titration of the ammonia performed upon the 
 distillates. 
 
 About one square decimeter of zinc should be used for every 
 200 c.c. of a water containing five parts or less of nitric acid in 
 100,000. A large proportion should be used with waters richer 
 in nitrates. The couple, after washing, may be used for two or 
 three waters more. When either carbonic or oxalic or any other 
 acid has been added to the water, a larger proportion of Messier 
 reagent should be employed in titrating it than it is usual to add. 
 3 c.c. to 100 of the water are sufficient in almost all cases. 
 
 Blunt (Analyst vi. 202) points out that the above process may 
 be used without distillation, and with accuracy, in the case of any 
 water, by adding oxalic acid to a double quantity of the sample, 
 dividing, and using one portion (clarified completely by subsidence 
 in a closely stoppered bottle) as a comparison liquid for testing 
 against the other, which has been treated with the copper-zinc 
 couple. When dilution is used it must be done in both portions 
 equally. This plan possesses the advantages that an equal turbidity 
 is produced by Messier in both portions, and any traces of 
 ammonia contained in the oxalic acid will have the error due to it 
 corrected. 
 
 In calculating the amount of nitric acid contained in a water 
 from the amount of ammonia obtained in this process, deductions 
 must of course be' made for any ammonia pre-existing in the water, 
 as well as for that derived from any nitrous acid present. 
 
 10. Estimation of Nitrites toy Griess's Method. 100 c.c. of 
 the water are placed in a J^essler glass, and 1 c.c. each of 
 metaphenylene-diamine and dilute acid (p. 404) added. If colour 
 is rapidly produced the water must be diluted with distilled water 
 free from 2x T2 3 , and other trials made. The dilution is sufficient 
 when colour is plainly seen at the end of one minute. The weak 
 
 F F 2 
 
436 VOLUMETRIC ANALYSIS. 89. 
 
 point of the process is that the colour is progressively developed ; 
 however, this is of little consequence if the comparison with 
 standard nitrite is made under the same conditions of temperature, 
 dilution, and duration of experiment. Twenty minutes is a 
 sufficient time for allowing the colours to develop before final 
 comparison. 
 
 M. AV. Williams obviates the uncertainty of the comparison 
 tests by using colourless Xessler tubes, 30 m.m. wide and 
 200 m.m. long, graduated into millimeters. They are used as 
 follows : The comparison of the water to be examined with the 
 standard nitrite is roughly ascertained ; the glasses are then filled 
 to the same height, and the test added, and allowed to stand a few 
 minutes. Usually one will be somewhat deeper than the? other. 
 The height of the deeper-coloured liquid is read off on the scale, 
 and a portion removed with a pipette, until the colours correspond. 
 The amount of N 2 3 in the shortened column is taken as equal to 
 the other, when a simple calculation will show the amount sought. 
 
 11. Estimation of Nitrites by Naphthylamine. "Waringtoii 
 (J. C. S. 1881, 231) has drawn attention to this test, originally 
 devised by Griess, and which is of such extreme delicacy, that 
 by its means it is possible to detect one part of X 2 3 in a thousand 
 millions of water. 
 
 Ilosvay has improved this test by using acetic acid instead of 
 a mineral acid. The colour is more intense and more rapidly 
 developed. He dissolves (1) 0'5 gm. of sulphanilic acid in 150 
 c.c. of dilute acetic acid, (2) boils O'l gm. of a-naphthylamine 
 with 20 c.c. of water, pours off the colourless solution, and mixes 
 it with 150 c.c. of dilute acetic acid. These two solutions are 
 mixed, thus gaining the advantage of having a single reagent 
 instead of two, and one which indicates by its colour whether it 
 has become contaminated by nitrous acid derived from the air. The 
 mixture is not affected by light, but should be protected from the 
 air. Should it, however, become coloured by absorption of nitrous 
 acid, it may be shaken with zinc-dust and filtered. 
 
 This test is almost too delicate to be used quantitatively, but is 
 evidently very serviceable as a quantitative test for very minute 
 quantities of nitrous acid. By its means "Warington has detected 
 nitrous acid in the atmosphere of various places by exposing water 
 containing a few drops of the requisite solutions to the air in a basin 
 for a few hours ; the like mixture kept in a closed flask or cylinder 
 at the same time undergoing no change of colour. 
 
 12. Estimation of Nitrites by Potassic Iodide and Starch. Ekin 
 has pointed out (Pharm. Trans. 1881, 286) that this well-known 
 test will give the blue colour with nitrous acid in a few minutes, 
 when the proportion is one part in ten millions ; in twelve hours 
 when one part in a hundred millions ; and in forty-eight hours 
 when one in a thousand millions. Experience has proved that 
 
89. WATER ANALYSIS. 437 
 
 waters charged with much organic matter must be clarified by the 
 addition of a little pure alum, then well agitated and filtered 
 before testing. 
 
 Ekin used acetic acid for acidifying the water to be tested, and 
 blank experiments with pure water were simultaneously carried on. 
 Sulphuric or hydrochloric acid will, no doubt, give a sharper 
 reaction, but both these acids are more liable to contain impurities 
 affecting the reaction than is the case with pure acetic acid. Owing 
 to the instability of alkaline iodides, zinc iodide, however, is not 
 open to this objection, and is now generally used. 
 
 13. Estimation of Suspended Matter. Filters of Swedish paper, 
 about 110 m.m. in diameter, are packed one inside another, about 
 15 or 20 together, so that water will pass through the whole group, 
 moistened with dilute hydrochloric acid, washed with hot distilled 
 water until the washings cease to contain chlorine, and dried. The 
 ash of the paper is thus reduced by about 60 per cent., and must 
 be determined for each parcel of filter paper by incinerating 10 
 filters, and weighing the ash. For use in estimating suspended 
 matter, these washed filters must be dried for several hours at 
 120 130 C., and each one then weighed at intervals of an hour 
 until the weight ceases to diminish, or at least until the loss of 
 weight between two consecutive weighings does not exceed 0*0003 
 (fm. It is most convenient to enclose the filter during weighing in 
 two short tubes, fitting closely one into the other. The closed ends 
 of test tubes, 50 m.m. long, cut off by leading a crack round with 
 the aid of a pastille or very small gas jet, the sharp edges being 
 afterwards fused at the blow-pipe, answer perfectly. Each pair of 
 tubes should have a distinctive number, which is marked with 
 a diamond on both tubes. In the air bath they should rest in. 
 grooves formed by a folded sheet of paper, the tubes being drawn 
 apart, and the filter almost, but not quite, out of the smaller tube. 
 They can then be shut up whilst hot by gently pushing the tubes 
 together, being guided by the grooved paper. They require to 
 remain about twenty minutes in a desiccator to cool before weighing. 
 Filtration will be much accelerated if the filters be ribbed before 
 drying. As a general rule, it will be sufficient to filter a quarter 
 of a liter of a sewage, half a liter of a highly polluted river, arid 
 a liter of a less polluted water ; but this must be frequently varied 
 to suit individual cases. Filtration is hastened, and trouble 
 diminished, by putting the liquid to be filtered into a narrow- 
 necked flask, which is inverted into the filter, being supported by 
 a funnel-stand, the ring of which has a slot cut through it to allow 
 the neck of the flask to pass. With practice the inversion may 
 be accomplished without loss, and without previously closing the 
 mouth of the flask. When all has passed through, the flask should 
 be rinsed out with distilled water, and the rinsings added to the 
 filter. Thus any particles of solid matter left in the flask are 
 
48 VOLUMETRIC ANALYSIS. 89. 
 
 secured, and the liquid adhering to the suspended matter and filter 
 is displaced. The filtrate from the washings should not be added 
 to the previous filtrate, which may be employed for determination 
 of total solid matter, chlorine, hardness, etc. 
 
 Thus washed, the filter with the matter upon it is dried at 
 100 C., then transferred from the funnel to the same pair of tubes 
 in which it was previously weighed, and the operation of drying at 
 120 - 130 C. and weighed until constant repeated. The weight 
 thus obtained, minus the weight of the empty filter and tubes, 
 gives the weight of the total suspended matter dried at 120 130 C. 
 
 To ascertain the quantity of mineral matter in this, the filter 
 with its contents is incinerated in a platinum crucible, and the 
 total ash thus determined, minus the ash of the filter alone, gives 
 the weight of the mineral suspended matter. 
 
 14. Estimation of Chlorine present as Chloride. -To 50 c.c. of 
 the water add two or three drops of solution of potassic eliminate 
 (D. /3), so as to give it a faint tinge of yellow, and add gradually 
 from a burette standard solution of silver nitrate (D. a), until the 
 red silver chromate which forms after each addition of the 
 nitrate ceases to disappear on shaking. The number of c.c. of 
 silver solution employed will express the chlorine present as 
 chloride in parts in 100,000. If this amount be much more than 
 10, it is advisable to take' a smaller quantity of water. 
 
 If extreme accuracy be necessary, after completing a determination, 
 destroy the slight red tint by an excess of a soluble chloride, and 
 repeat the estimation on a fresh quantity of the water in a similar 
 flask placed by the side of the former. By comparing the contents 
 of the flasks, the first tinge of red in the second flask may be 
 detected with great accuracy. It is absolutely necessary that the 
 liquid examined should not be acid, unless with carbonic acid, nor 
 more than very slightly alkaline. It must also be colourless, or 
 nearly so. These conditions are generally found in waters, but, if 
 not, they may be brought about in most cases by rendering the 
 liquid just alkaline with lime water (free from chlorine), passing- 
 carbonic anhydride to saturation, boiling, and filtering. The calcic 
 carbonate has a powerful clarifying action, and the excess of alkali 
 is exactly neutralized by the carbonic anhydride. If this is not 
 successful, the water must be rendered alkaline, evaporated to 
 dryness, and the residue gently heated to destroy organic matter. 
 The chlorine may then be extracted with water, and estimated in 
 the ordinary way, either gravimetrically or volumetrically. 
 
 15. Estimation of Hardness. The following method, devised by 
 tile late Dr. Thomas Clark, of Aberdeen, is in general use ; and 
 from its ease and rapidity is of some value, though it can hardly 
 be called accurate. (For estimating the hardness of waters 
 without soap solution see page 71.) 
 
 Uniformity in conducting it is of great importance ; especially 
 
89. HARDNESS OF WATERS. 439 
 
 the titration of the soap solution, and the estimation of the hardness 
 of waters, should be performed in precisely similar ways. 
 
 Measure 50 c.c. of the water into a well-stoppered bottle of about 
 250 c.c. capacity, shake briskly for a few seconds, and suck the 
 air from the bottle by means of a glass tube, in order to remove 
 any carbonic anhydride which may have been liberated from the 
 water. Add standard soap solution (E. j3) from a burette, one c.c. 
 at a time at first, and smaller quantities towards the end of the 
 operation, shaking well after each addition, until a soft lather is 
 obtained, which, if the bottle is placed at rest on its side, remains 
 continuous over the whole surface for five minutes. The soap 
 should not be added in larger quantities at a time, even when the 
 volume required is approximately known. This is very important. 
 
 When more than 16 c.c. of soap solution are required by 50 c.c. 
 of the water, a less quantity (as 25 or 10 c.c.) of the latter should 
 be taken, and made up to 50 c.c. with recently boiled and cooled 
 distilled water, so that less than 16 c.c. of soap solution will suffice, 
 and the number expressing the hardness of the diluted water 
 multiplied by 2 or 5, as the case may be. 
 
 When the water contains much magnesium, which may be 
 known by the lather having a peculiar curdy appearance, it should 
 be diluted, if necessary, with distilled water, until less than 7 c.c. 
 are required by 50 c.c. 
 
 The volume of standard soap solution required for 50 c.c. of the 
 water being known, the weight of calcic carbonate (CaCO 3 ) corres- 
 ponding to this may be ascertained from the following Table 7* : 
 
 * The table is calculated from that originally constructed by Dr. Clark, which is 
 ilS follows : 
 
 Degree of Hardness. Measures of Differences for the 
 
 Soap Solution. next 1 of hardness. 
 
 (Distilled water) ... 1'4 ... 1'8 
 
 1 ... ... 3-2 ... 2-2 
 
 5-4 2-2 
 
 7-6 ... ... 2-0 
 
 9-6 ... 2-0 
 
 11-6 2-0 
 
 13-6 ... 2-0 
 
 15-6 ... ... 1-9 
 
 17-5 1-9 
 
 19-4 
 21-3 
 23-1 
 
 1-9 
 
 1-8 
 1-8 
 1-8 
 
 24-9 
 
 13 26-7 1-8 
 
 14 ... ... 23-5 ... . . 1-8 
 
 15 30-3 1-7 
 
 16 32-0 
 
 Each "measure" being 10 grains, the volume of water employed 1000 grains, and each 
 " degree " 1 grain of calcic carbonate in a gallon. 
 
 If the old weights and measures, grains and gallons, be preferred, this table may be 
 used, the process being exactly as above described, but 1000 grains of water taken 
 instead of 50 c.c., and the soap solution measured in 10-graiu measures instead of cubic 
 centimeters. If the volume of soap solution used be found exactly in the second column 
 of the table, the hardness will, of course, be that shown on the same line in the first 
 column. But if it be not, deduct from it the next lower number in the second column, 
 when the corresponding degree of hardness in the first column will give the integral 
 part of the resiilt ; divide the remainder by the difference on the same line in the third 
 column, and the quotient will give the fractional part. For example, if 1000 grains of 
 water require 16 " measures " of soap, the calculation will be as follows : 
 
440 
 
 VOLUMETRIC ANALYSIS. 
 
 89>. 
 
 TABLE 7. 
 
 Table of Hardness, Parts in 100,000. 
 
 16-0 
 15-6 (=7 hardness). 
 
 Ill 
 
 !" 
 
 *o ^ 
 2 cu 3 
 
 Jl^ 
 
 ll 
 
 ^-2 
 2 JS 
 
 8 
 
 8S~ 
 
 loj 
 
 = 11 
 
 
 
 ft O 
 
 o o 
 > m 
 
 S 
 
 ^& 
 
 fe 
 
 A 
 
 % 
 
 > CQ 
 
 s> 
 
 c.c. 
 
 
 c.o. 
 
 
 C.C. 
 
 
 C.C. 
 
 
 
 
 4-0 
 
 4-57 
 
 8-0 
 
 10-30 
 
 12-0 
 
 16-43 
 
 
 
 1 
 
 71 
 
 1 
 
 45 
 
 1 
 
 59 
 
 
 
 2 
 
 86 
 
 2 
 
 60 
 
 2 
 
 75 
 
 
 
 3 
 
 5-00 
 
 3 
 
 75 
 
 3 
 
 90 
 
 
 
 4 
 
 14 
 
 4 
 
 90 
 
 4 
 
 17'06 
 
 
 
 5 
 
 29 
 
 5 
 
 11-05 
 
 5 
 
 22 
 
 
 
 6 
 
 43 
 
 6 
 
 20 
 
 6 
 
 38 
 
 0-7 
 
 oo 
 
 7 
 
 57 
 
 7 
 
 35 
 
 7 
 
 54 
 
 0-8 
 
 16 
 
 8 
 
 71 
 
 8 
 
 50 
 
 8 
 
 70 
 
 0-9 
 
 32 
 
 9 
 
 86 
 
 9 
 
 65 
 
 9 
 
 86 
 
 i-o 
 
 48 
 
 5-0 
 
 6-00 
 
 9-0 
 
 80 
 
 13-0 
 
 18-02 
 
 1 
 
 63 
 
 1 
 
 14 
 
 i 
 
 95 
 
 1 
 
 17 
 
 2 
 
 79 
 
 2 
 
 29 
 
 2 
 
 12-11 
 
 2 
 
 33 
 
 8 
 
 95 
 
 3 
 
 43 
 
 3 
 
 26 
 
 3 
 
 49 
 
 4: 
 
 I'll 
 
 4 
 
 57 
 
 4 
 
 41 
 
 4 
 
 65 
 
 5 
 
 27 
 
 5 
 
 71 
 
 5 
 
 56 
 
 5 
 
 81 
 
 6 
 
 43 
 
 6 
 
 85 
 
 6 
 
 71 
 
 6 
 
 97 
 
 7 
 
 56 
 
 7 
 
 7-00 
 
 7 
 
 86 
 
 7 
 
 19-13 
 
 8 
 
 69 
 
 8 
 
 14 
 
 8 
 
 13-01 
 
 8 
 
 29 
 
 9 
 
 82 
 
 9 
 
 29 
 
 9 
 
 16 
 
 9 
 
 44 
 
 1 2-0 
 
 95 
 
 6-0 
 
 43 
 
 10-0 
 
 31 
 
 14-0 
 
 60 
 
 1 
 
 2-08 
 
 1 
 
 57 
 
 1 
 
 46 
 
 1 
 
 76 
 
 2 
 
 21 
 
 2 
 
 71 
 
 2 
 
 61 
 
 2 
 
 92 
 
 3 
 
 34 
 
 3 
 
 86 
 
 3 
 
 76 
 
 3 
 
 20-08 
 
 4 
 
 47 
 
 4 
 
 8-00 
 
 4 
 
 91 
 
 4 
 
 24 
 
 5 
 
 60 
 
 5 
 
 14 
 
 5 
 
 14-06 
 
 5 
 
 40 
 
 6 
 
 73 
 
 6 
 
 29 
 
 6 
 
 21 
 
 6 
 
 56 
 
 7 
 
 86 
 
 7 
 
 43 
 
 7 
 
 37 
 
 7 
 
 71 
 
 8 
 
 99 
 
 8 
 
 57 
 
 8 
 
 52 
 
 8 
 
 87 
 
 9 
 
 3-12 
 
 9 
 
 71 
 
 9 
 
 68 
 
 9 
 
 21-03 
 
 3-0 
 
 25 
 
 7-0 
 
 86 
 
 ! 11-0 
 
 84 
 
 15-0 
 
 19 
 
 1 
 
 38 
 
 1 
 
 9-00 
 
 i 
 
 15-00 
 
 1 
 
 35 
 
 2 
 
 51 
 
 2 
 
 14 
 
 2 
 
 16 
 
 2 
 
 51 
 
 3 
 
 64 
 
 3 
 
 29 
 
 3 
 
 32 
 
 3 
 
 68 
 
 4 
 
 77 
 
 4 
 
 43 
 
 4 
 
 48 
 
 4 
 
 85 
 
 5 
 
 90 
 
 5 
 
 57 
 
 5 
 
 63 
 
 5 
 
 22-02 
 
 6 
 
 4-03 
 
 fi 
 
 71 
 
 6 
 
 79 
 
 6 
 
 18 
 
 7 
 
 16 
 
 7 
 
 g-> 
 
 7 
 
 95 
 
 7 
 
 35 
 
 8 
 
 29 
 
 8 
 
 10-00 
 
 8 
 
 16-11 
 
 8 
 
 52 
 
 3-9 
 
 43 
 
 7-9 
 
 15 
 
 i 11-9 
 
 27 
 
 9 
 
 69 
 
 
 
 I 
 
 
 j 
 
 
 16-0 
 
 86 
 
 (Difference =) (l'9)/4 
 
 21 
 
 therefore the hardness is 7'21 grains of CaCO 3 per gallon. The water must be diluted 
 with distilled water if necessary, so that the quantity of soap required does not exceed. 
 32 measures in ordinary waters, and 14 measures in water containing much magnesia.. 
 
89. MINERALS AND METALS IN WATERS. 441 
 
 When water containing calcic and magnesic carbonates, held 
 in solution by carbonic acid, is boiled, carbonic anhydride is 
 expelled, and the carbonates precipitated. The hardness due to 
 these is said to be temporary, whilst that due to sulphates,, 
 chlorides, etc., and to the amount of carbonates soluble in pure 
 water (the last-named being about three parts per 100,000) is 
 called permanent. 
 
 To estimate permanent hardness, a known quantity of the water 
 is boiled gently for half an hour in a flask, the mouth of which 
 is freely open. At the end of the boiling, the water should be 
 allowed to cool, and the original weight made up by adding 
 recently boiled distilled water. 
 
 Milch trouble may be avoided by using flasks of about the same 
 weight, and taking so much water in each as will make up the 
 same uniform weight. Thus if all the flasks employed weigh 
 less than 50 gm. each, let each flask with its contents be made to 
 weigh 200 gm. 
 
 After boiling and making up to the original weight, filter the 
 water, and determine the hardness in the usual way. The hardness 
 thus found, deducted from that of the unboiled water, will give 
 the temporary hardness. 
 
 16. Mineral Constituents and Metals. The quantities of the 
 following substances which may be present in a sample of water 
 are subject to such great variations, that no definite directions can 
 be given as to the volume of water to be used. The analyst must 
 judge in each case from a preliminary experiment what will be 
 a convenient quantity to take. 
 
 Sulphuric Acid. Acidify a liter or less of the water with 
 hydrochloric acid, concentrated on the water bath to about 100c.c. r 
 and while still hot add a slight excess of baric chloride. Filter, 
 wash, ignite, and weigh as baric sulphate, or estimate volumetrically y 
 as in 76. 
 
 Sulphuretted Hydrogen. Titrate with a standard solution of 
 iodine, as in 77.3. 
 
 Phosphoric Acid. This substance may be determined in the 
 solid residue obtained by evaporation, by moistening it with nitric 
 acid, and again drying to render silica insoluble ; the residue is 
 again treated with dilute nitric acid, filtered, molybdic solution 
 (p. 297) added, and set aside for twelve hours in a warm place ; 
 filter, dissolve the precipitate in ammonia, precipitate with magnesia 
 mixture, and weigh as magnesic pyrophosphate, or estimate volu- 
 metrically as in 72. 
 
 Another method is to add to 500 c.c. of the sample about 10 c.c. 
 of solution of alum, then a few drops of ammonia, lastly acidify 
 slightly with acetic acid, and set aside to allow the precipitated 
 A1P 2 4 to settle. The clear liquid may then be poured off, the- 
 
442 VOLUMETRIC ANALYSIS. 89. 
 
 precipitate dissolved in nitric acid and estimated with molybdic 
 solution. 
 
 These estimations are only available in cases where the P-0 5 
 is very large. In most waters it is simply necessary to record 
 whether the molybdic precipitate is in heavy or minute traces. 
 
 Silicic Acid. Acidify a liter or more of the water with 
 hydrochloric acid, evaporate, and dry the residue thoroughly. 
 Then moisten with hydrochloric acid, dilute with hot water, and 
 filter off, wash, ignite, and weigh the separated silica. 
 
 Iron. To the nitrate from the estimation of silicic acid add a few 
 drops of nitric acid, dilute to about 100 c.c., and estimate by colour 
 titration, as in 64.4 ; or where the amount is large, add excess of 
 ammonia, and heat gently for a short time. Filter off the precipitate 
 and estimate the iron in the washed precipitate colorimetrically, 
 as in 64. 
 
 Calcium. To the filtrate from the iron estimation add excess of 
 ammonic oxalate, filter off the calcic oxalate, ignite and weigh 
 as calcic carbonate, or estimate volumetrically with permanganate, 
 as in 52. 
 
 Magnesium. To the concentrated filtrate from the calcium 
 estimation add sodic phosphate (or, if alkalies are to be determined 
 in the filtrate, ammonic phosphate), and allow to stand for twelve 
 hours in a warm place. Filter, ignite the precipitate, and weigh 
 as magnesic pyrophosphate, or, without ignition, titrate with 
 uranium. 
 
 Barium. Is best detected in a water by acidifying with 
 hydrochloric acid, filtering perfectly clear if necessary, then 
 add a clear solution of calcic sulphate, and set aside in a warm 
 place. Any white precipitate which forms is due to barium. 
 
 Potassium and Sodium. These are generally determined jointly, 
 and for this purpose the filtrate from the magnesium estimation 
 may be used. Evaporate to dryness, and heat gently to expel 
 ammonium salts, remove phosphoric acid with plumbic acetate, and 
 the excess of lead in the hot solution by ammonia and ammonic 
 carbonate. Filter, evaporate to dryness, heat to expel ammonium 
 salts, and weigh the alkalies as chlorides. 
 
 It is, however, generally less trouble to employ a separate 
 portion of water. Add to a liter or less of the water enough pure 
 baric chloride to precipitate the sulphuric acid, boil with pure milk 
 of lime, filter, concentrate, and remove the excess of lime with 
 ammonic carbonate and a little oxalate. Filter, evaporate, and 
 weigh the alkaline chlorides in the filtrate. If the water contains 
 but little sulphate, the baric chloride may be omitted, and a little 
 ammonic chloride added to the solution of alkaline chlorides. 
 
89. MINERALS AND METALS IN WATERS. 443 
 
 If potassium and sodium must each be estimated, separate them 
 by means of platinic chloride ; or, after weighing the mixed 
 chlorides, determine the chlorine present in them, and calculate the 
 amounts of potassium and sodium by the following formula : 
 Calculate all the chlorine present as potassic chloride ; deduct this 
 from the weight of the mixed chlorides, and call the difference d. 
 Then as 16'1 : 58'37 : : d : XaCl present. (See also 42.) 
 
 Lead. May be estimated by the method proposed by Miller. 
 Acidulate the water with two or three drops of acetic acid, and 
 add -i- of its bulk of saturated aqueous solution of sulphuretted 
 hydrogen. Compare the colour thus produced in the colorimeter 
 or a convenient cylinder, with that obtained with a known quantity 
 of a standard solution of a lead salt, in a manner similar to that 
 described for the estimation of iron ( 64.4). The lead solution 
 should contain 0'1831 gin. of normal crystallized plumbic acetate in 
 a liter of distilled water, and therefore each c.c. contains 0*0001 gm. 
 of metallic lead. 
 
 It is obvious that in the presence of copper or other heavy metals 
 the colour produced by the above method will all be ascribed 
 to lead ; it is preferable, therefore, to adopt the method of Harvey 
 (Analyst vi. 146), in which the lead is precipitated as chromate. 
 The results, however, are not absolute as to quantity, except so 
 far as the eye may be able to measure the amount of precipitate. 
 
 The standard lead solution is the same as in the previous 
 method. The precipitating agent is pure potassic bichromate, 
 in fine crystals or powder. 
 
 250 c.c. or so of the water is placed in a Phillips' jar with 
 a drop or two of acetic acid, and a few grains of the reagent added, 
 and agitated by shaking. One part of lead in a million parts of 
 water will show a distinct turbidity in five minutes or less. In six 
 or eight hours the precipitate will have completely settled, and the 
 yellow clear liquid may be poured off without disturbing the 
 sediment, which may then be shaken up with a little distilled 
 water, and its quantity judged by comparison with a similar 
 experiment made with the standard lead solution. 
 
 Copper. Estimate by colour titration, as in 58.9. 
 
 Arsenic. Add to half a liter or more of the water enough 
 sodic hydrate, free from arsenic, to render it slightly alkaline, 
 evaporate to dryness, and extract with a little concentrated 
 hydrochloric acid. Introduce this solution into the generating 
 flask of a small Marsh's apparatus, and pass the evolved hydrogen, 
 first through a U-tube filled with pumice, moistened with plumbic 
 acetate, and then through a piece of hard glass tube about 150 m.m. 
 in length, and 3 m.m. in diameter (made by drawing out combustion 
 tube). At about its middle, this tube is heated to redness for 
 a length of about 20 m.m. by the flame of a small Bun sen burner, 
 
444 VOLUMETRIC ANALYSIS. 90. 
 
 and here the arsenetted hydrogen is decomposed, arsenic "being 
 deposited as a mirror on the cold part of the tube. The mirror 
 obtained after the gas has passed slowly for an hour is compared 
 with a series of standard mirrors obtained in a similar way from 
 known quantities of arsenic. Care must be taken to ascertain in 
 each experiment that the hydrochloric acid, zinc, and whole apparatus 
 are free from arsenic, by passing the hydrogen slowly through the 
 heated tube before introducing the solution to be tested. 
 
 Zinc. This metal exists in waters as bicarbonate, and on 
 exposure of such waters in open vessels a film of zinc carbonate 
 forms on the surface ; this is collected on a platinum knife or foil 
 and ignited. The residue is of a yellow colour when hot, and 
 turns white on cooling. The reaction is exceedingly delicate. 
 
 THE INTERPRETATION OF THE RESULTS OF ANALYSIS. 
 
 90. THE primary form of natural water is rain, the chief impurities in 
 which are traces of organic matter, ammonia, and ammouic nitrate derived 
 from the atmosphere. On reaching the ground it becomes more or less 
 charged with the soluble constituents of the soil, such as calcic and magnesic 
 carbonates, potassic and sodic chlorides, and other salts, Avhich are dissolved, 
 some by a simple solvent action, others by the agency of carbonic acid in 
 solution. Draining off from the land, it will speedily find its way to a stream 
 which, in the earlier part of its course, will probably be free from pollution by 
 animal matter, except that derived from any manure which may have been 
 applied to the land on which the rain fell. Thus comparatively pure, it will 
 furnish to the inhabitants on its banks a supply of water which, after use, 
 will be returned to the stream in the form of sewage charged with impurity 
 derived from animal excreta, soap, household refuse, etc., the pollution being 
 perhaps lessened by submitting the sewage to some purifying process, such as 
 irrigation of land, filtration, or clarification. The stream in its subsequent 
 course to the sea will be in some measure purified by slow oxidation of the 
 organic matter, and by the absorbent action of vegetation. Some of the 
 rain will not, however, go directly to a stream, but sink through the soil to 
 a well. If this be shallow, it may be considered as merely a pit for the 
 accumulation of drainage from the immediately surrounding soil, which, as 
 the well is in most cases close to a dwelling, will be almost inevitably 
 charged with excretal and other refuse ; so that the water when it reaches 
 the well will be contaminated with soluble impurities thence derived, and 
 with nitrites and nitrates resulting from their oxidation. After use the 
 Avater from the well will, like the river water, form sewage, and find its 
 w r ay to a river, or again to the soil, according to circumstance-. 
 
 In the case of a deep well, from which the surface water is excluded, the 
 conditions are different. The shaft will usually pass through an impervious 
 stratum, so that the water entering it will not be derived from the rain 
 w r hich falls on the area immediately surrounding its mouth, but from that 
 which falls on the outcrop of the pervious stratum below the impervious one 
 just mentioned; and if this outcrop be in a district which is uninhabited 
 and uncultivated, the water of the well will probably be entirely free from 
 organic impurity or products of decomposition. But even if the water be 
 polluted at its source, still it must pass through a very extensive filter before 
 it reaches the well, and its organic matter will probably be in great measure 
 converted by oxidation into bodies in themselves innocuous. 
 
 This is very briefly the general history of natural waters, and the problem 
 presented to the analyst is to ascertain, as far. as possible, from the nature 
 
90. INTERPRETATION OF RESULTS. 445 
 
 and quantity of the impurities present, the previous history of the water, 
 and its present condition and fitness for the purpose for which it is to 
 be used. 
 
 It is impossible to give any fixed rule by which the results obtained by the 
 foregoing method of analysis should be interpreted. The analyst must form 
 an independent opinion for each sample from a consideration of all the results 
 he has obtained. Nevertheless, the following remarks, illustrated by reference 
 to the examples given in the accompanying table, which may be considered 
 as fairly typical, will probably be of service. (See Table 8.) 
 
 Total Solid Matter. 
 
 Waters which leave a large residue on evaporation are, as a rule, less suited 
 for general domestic purposes than those which contain less matter in solution, 
 and are unfit for many manufacturing purposes. The amount of residue is 
 also of primary importance as regards the use of the water for steam boilers, 
 as the quantity of incrustation produced will chiefly depend upon it. It may 
 vary cousiderabh r , apart from any unnatural pollution of the water, as it 
 depends principally on the nature of the soil through or over which the 
 water passes. River water, when but slightly polluted, contains generally 
 from 10 to 40 parts. Shallow well water varies greatly, containing from 30 
 to 150 parts, or even more, as in examples X. and XIII., the proportion 
 here depending less on the nature of the soil than on the original pollution 
 of the water. Deep well water also varies considerably; it usually contains 
 from 20 to 70 parts, but this range is frequently overstepped, the quantity 
 depending largely upon the nature of the strata from which the w r ater is 
 obtained. Example XV. being in the New E-ed Sandstone, has a small pro- 
 portion but XVII. and XVIII. in the Chalk have a much larger quantity. 
 Spring waters closely resemble those from deep wells. Sewage contains 
 generally from 50 to 100 parts, but occasionally less, and frequently much 
 more, as in example XXXIV. The total solid matter, as a rule, exceeds the 
 sum of the constituents determined ; the nitrogen, as nitrates and nitrites, 
 being calculated as potassic nitrate, and the chlorine as sodic chloride ; but 
 occasionally this is not the case, owing, it is likely, to the presence of some 
 of the calcium as calcic nitrate or chloride. 
 
 Organic Carbon or Nitrogen. 
 
 The existing condition of the sample, as far as organic contamination is 
 concerned, must be inferred from the amount of these two constituents. In 
 a good water, suitable for domestic supply, the former should not, under 
 ordinary circumstances, exceed 0'2 and the latter 0'02 part. 
 
 Waters from districts containing much peat are often coloured more or 
 less brown, and contain an unusual quantity of organic carbon, but this 
 peaty matter is probably innocuous unless the quantity be extreme. The 
 large proportion of organic carbon and nitrogen given in the average for 
 unpolluted upland surface water in Table- 8 (XXVIII.) is chiefly due to the 
 fact that upland gathering grounds are very frequently peaty. The examples 
 given (I. to V.) may be taken as fairly representative of the character of 
 upland surface waters free from any large amount of peaty matter. In 
 surface waters from cultivated areas the quantity of organic carbon and 
 nitrogen is greater, owing to increased density of population, the use of 
 organic manures, etc., the proportion being about 0'25 to 0'3 part of organic 
 carbon, and 0'04 to 0'05 part of organic nitrogen. The water from shallow 
 wells varies so widely in its character that it islmpossible to give any useful 
 average. In many cases, as for example in XIII. and XIV., the amount is 
 comparatively small, although the original pollution, as shoAvn by the total 
 inorganic nitrogen and the chlorides, was very large ; the organic matter in 
 
446 
 
 TABLE 8. 
 
 VOLUMETRIC ANALYSIS. 90. 
 
 Results of Analysis expressed 
 
 of 
 
 Sample. 
 
 DESCRIPTION. 
 
 REMARKS. 
 
 I. 
 
 II. 
 
 III. 
 
 IV. 
 
 V. 
 
 VI. 
 VII. 
 
 VIII. 
 
 IX. 
 
 X. 
 
 XI. 
 
 XII. 
 XIII. 
 XIV. 
 
 XV. 
 XVI. 
 
 XVII. 
 XVIII. 
 
 XXI. 
 
 XXII. 
 
 XXIII. 
 
 XXIV. 
 
 XXV. 
 
 XXVI. 
 
 Upland Surface Waters. 
 
 The Dee above Balmoral, March 9th, 1872 
 Glasgow Water supply from Loch Katrine average of ") 
 monthly analyses during five years, 1876 81 > 
 
 Liverpool Watersupply from RivingtonPike,June4th,1869 
 Manchester Water supply, May 9th, 1874 
 Cardiff Water supply, Oct. 18th, 1872 
 
 Surface Water from Cultivated Land. 
 Dundee Water supply, March 12th, 1872 
 Norwich Water supply, June 18th, 1872 
 
 Shallow Wells. 
 
 Cirencester, Market Plnce, Nov. 4th, 1870 
 Marlborough, College Yard, Aug. 22nd, 1873 ... 
 Birmingham, Hurst Street, Sept. 18th, 1873 ... 
 
 Sheffield, Well near, Sept. 27th, 1870 
 
 London, Aldgate Pump, June 5th, 1872 
 London, Wellclose Square, June 5th, 1872 
 Leigh, Essex, Churchyard Well, Nov. 28th, 1871 
 
 Deep Wells. 
 
 Birmingham, Short Heath Well, May 16th, 1873 
 Caterham, Water Works Well, Feb. 14th, 1873 
 Ditto, Softened (Water supply) ..." 
 
 London, Albert Hall, May, 1872 
 Gravesend, Kail way Station, Jan. 17th, 1873 ... 
 
 Spring-s. 
 
 Dartmouth Water supply, Jan. 8th, 1873 
 Grantham Water supply, July llth, 1873 
 
 Clear 
 
 Clear; very pale 1 
 
 Clear ... ' 
 
 Turbid 
 
 Clear 
 
 Turbid ; brownish 3 
 Slightly turbid... 
 
 Slightly turbid... 
 
 Clear 
 
 Clear; strong saline 
 
 C Very turbid & off 
 sive. Swarm 
 
 (. with bacteria, 
 Clear ... 
 Slightly turbid; salii 
 Slightly turbid... 
 
 Clear 
 
 Clear 
 
 Slightly turbid... 
 Clear 
 
 Turbid 
 Clear 
 
 London Water supply average monthly analyses dur ing 21 years, 1869 
 
 From the Thames ... 
 
 From the Lea 
 
 From Deep Chalk Wells (Kent Company) 
 
 Ditto (Colne Valley Co.) softened thirteen years, 187789 
 
 Ditto (Tottenham) thirteen years, 1877 89... ... I 
 
 Birmingham Water supply average monthly analyses, 18751880. 
 
 Average Composition of Unpolluted 
 Bain Water 
 Upland Surface Water 
 
 Deep Well Water 
 
 Spring Water 
 Sea Water 
 
 Water. 
 
 39 samples 
 
 195 
 
 157 
 
 198 
 
 23 
 
 Sewage. 
 
 Average from 15 "Midden" Towns, 37 analyses 
 Average from 16 "Water Closet" Towns, 50 analyses .. 
 Salford, Wooden Street Sewer, March 15th, 1869 
 Merthyr Tydfil, average 10 a.m. to 5 p.m., Oct. 20th, 1871 
 
 (after treatment with lime) 
 Ditto, Effluent Water ... 
 
EXAMPLES OF WATER AND SEWAGE ANALYSES. 447 
 
 in parts per 100, CCO. 
 
 TABLE 8. 
 
 i 
 i 
 
 Organic 
 Carbon. 
 
 Organic 
 Nitro- 
 gen. 
 
 f 
 
 Z 
 
 o 
 
 Nitro- 
 gen !IS 
 Am- 
 monia. 
 
 Nitrogen 
 as 
 Nitrates 
 and 
 Nitrites. 
 
 Total 
 Inorganic 
 Nitrogen 
 
 Total 
 Combined 
 
 Nitrogen 
 
 L Chlorine. 
 
 Hardness. 
 
 Tem- 
 porary. 
 
 Perma- 
 nent. 
 
 Total. 
 
 fa 
 
 132 
 
 014 
 
 9-4 
 
 
 
 
 
 
 
 014 
 
 50 
 
 
 
 1-5 
 
 1-5 
 
 ii. 
 
 148 
 
 016 
 
 9-2 
 
 
 
 005 
 
 005 
 
 022 
 
 64 
 
 
 
 
 
 9 
 
 ;; 
 
 210 
 
 029 
 
 7'2 
 
 002 
 
 
 
 002 
 
 C31 
 
 1-53 
 
 3 
 
 3-7 
 
 4-0 
 
 )o 
 
 132 
 
 031 
 
 41 
 
 002 
 
 
 
 002 
 
 033 
 
 90 
 
 
 
 2-7 
 
 2-7 
 
 >0 
 
 212 
 
 031 
 
 6-8 
 
 
 
 034 
 
 034 
 
 065 
 
 1-40 
 
 7-1 
 
 129 
 
 20'0 
 
 .6 
 
 418 
 
 059 
 
 7-1 
 
 001 
 
 081 
 
 082 
 
 141 
 
 1-75 
 
 
 
 6-0 
 
 6-0 
 
 e 
 
 432 
 
 080 
 
 5-4 
 
 012 
 
 036 
 
 048 
 
 128 
 
 3-10 
 
 21-3 
 
 5-3 
 
 26-6 
 
 )0 
 
 041 
 
 008 
 
 5-1 
 
 
 
 362 
 
 362 
 
 -370 
 
 1-GO 
 
 18-4 
 
 4-6 
 
 23-0 
 
 8 -049 
 
 015 
 
 3-3 
 
 
 
 613 
 
 613 
 
 628 1-90 
 
 15-6 
 
 101 
 
 25-7 
 
 -340 
 
 105 
 
 3'2 
 
 511 
 
 14-717 
 
 15-228 
 
 15'33o 
 
 36-50 
 
 27-5 
 
 99-6 
 
 127-1 
 
 j 1-200 
 
 126 
 
 9-5 
 
 091 
 
 
 
 091 
 
 217 
 
 2'20 
 
 2-0 
 
 1-4 
 
 34 
 
 1 '144 
 
 141 
 
 i-o 
 
 181 
 
 6-851 
 
 7-032 
 
 7-173 
 
 12-85 
 
 37-1 
 
 40-0 
 
 77-1 
 
 -278 
 
 087 
 
 3'2 
 
 
 
 25-8:10 
 
 25-840 
 
 25-927 
 
 34-60 
 
 26'7 
 
 164-3 
 
 191-0 
 
 2 
 
 210 
 
 065 
 
 32 
 
 
 
 5-047 
 
 5-047 
 
 5-112 
 
 13 ; 75 
 
 14-3 
 
 45-7 
 
 60-0 
 
 8 
 
 C09 
 
 004 
 
 2-2 
 
 
 
 447 
 
 447 
 
 451 
 
 1-30 
 
 4-6 
 
 5-1 
 
 9-7 
 
 6 
 
 028 
 
 009 
 
 3-1 
 
 
 
 021 
 
 021 
 
 030 
 
 1-55 
 
 15-2 
 
 6-0 
 
 21-2 
 
 o 
 
 015 
 
 003 
 
 5-0 
 
 
 
 . 
 
 
 
 . 
 
 
 
 
 
 
 
 4-4 
 
 s 
 
 168 
 
 042 
 
 4-0 
 
 007 
 
 066 
 
 073 
 
 115 
 
 15-10 
 
 3-4 
 
 22 
 
 5-6 
 
 >L) 
 
 127 
 
 029 
 
 4'4 
 
 063 
 
 2-937 
 
 3-000 
 
 3-029 
 
 5-40 
 
 27-9 
 
 14-5 
 
 42-4 
 
 6 
 
 060 
 
 016 
 
 37 
 
 
 
 330 
 
 330 
 
 346 
 
 2-45 
 
 1-6 
 
 10-0 
 
 11-G 
 
 
 
 048 
 
 018 
 
 2-7 
 
 
 
 833 
 
 833 
 
 851 
 
 2-05 
 
 17-1 
 
 6-5 
 
 23-6 
 
 2 
 
 191 
 
 033 
 
 5-8 
 
 
 
 210 
 
 210 
 
 243 
 
 1'68 
 
 _ 
 
 _ 
 
 20-1 
 
 9 
 
 -134 
 
 025 
 
 5'4 
 
 
 
 226 
 
 226 -251 1-76 
 
 
 
 
 
 20-9 
 
 
 
 049 
 
 on 
 
 4'5 
 
 
 
 446 
 
 446 
 
 458 2-47 
 
 . 
 
 
 
 28-5 
 
 
 
 059 
 
 014 
 
 4'2 
 
 003 
 
 367 
 
 370 
 
 384 1 1-70 
 
 
 
 6-0 
 
 9 
 
 068 
 
 016 
 
 4'2 
 
 054 
 
 143 
 
 196 
 
 196 
 
 2-85 
 
 
 
 
 
 23-3 
 
 1 
 
 245 
 
 054 
 
 4-6 
 
 002 
 
 231 
 
 233 
 
 287 
 
 1-73 
 
 7'7 
 
 8-8 
 
 16'5 
 
 5 
 
 '070 
 
 015 
 
 4-7 
 
 024 
 
 003 
 
 027 
 
 042 
 
 22 
 
 
 
 3 
 
 7 
 
 322 
 
 032 
 
 10-1 
 
 002 
 
 009 
 
 on 
 
 043 
 
 1-13 
 
 1-5 
 
 4-3 
 
 5-4 
 
 8 
 
 061 
 
 018 
 
 3-4 
 
 010 
 
 495 
 
 505 
 
 523 
 
 5-11 
 
 15-8 
 
 9-2 
 
 25-0 
 
 
 
 056 
 
 013 
 
 4-3 
 
 001 
 
 383 
 
 381- 
 
 397 
 
 2'49 
 
 11-0 
 
 7-5 
 
 18-5 
 
 7 
 
 278 
 
 165 
 
 1'7 
 
 005 
 
 033 
 
 038 
 
 203 
 
 1975-6 
 
 48-9 
 
 748-0 
 
 796-9 
 
 
 
 
 
 
 
 
 
 
 Suspended Matter. 
 
 
 
 
 
 
 
 
 
 
 Mineral. Organic. Total. 
 
 4 
 
 4-181 
 
 1-975 
 
 2-1 
 
 4-476 
 
 
 
 4-476 
 
 6-451 
 
 11-54 
 
 17-81 
 
 21-30 
 
 39-11 
 
 2 
 
 4-696 
 
 2-205 
 
 2-1 
 
 .5-520 
 
 003 
 
 5-523 
 
 7-728 
 
 10-66 
 
 24-18 
 
 20-51 
 
 44-69 
 
 6 
 
 11-012 
 
 7-634 
 
 T4 
 
 5-468 
 
 
 
 5-468 
 
 13-102 
 
 20-50 
 
 18-88 
 
 26-44 
 
 45-32 
 
 
 
 1-282 
 
 952 
 
 1-3 
 
 1-054 
 
 052 
 
 1-106 
 
 2-058 
 
 5-25 
 
 7-88 
 
 6-56 
 
 14-44 
 
 8 
 
 123 
 
 031 
 
 4-0 
 
 048 
 
 300 
 
 348 
 
 379 
 
 2-60 
 
 
 Trace. 
 
 
448 VOLUMETEIC ANALYSIS. 
 
 -these cases having heen almost entirely destroyed hy powerful oxidation. In 
 VIII. and IX. the original pollution was slight ; and oxidation being active, 
 the organic carhon and nitrogen have been reduced to extremely small 
 quantities. On the other hand, in XI. the proportion of organic matter is 
 enormous, the oxidizing action of the surrounding soil being utterly 
 insufficient to deal with the pollution. The danger attending the use of 
 shallow well waters, which contain when anatyzed very small quantities of 
 organic matter, arises chiefly from the liability of the conditions to variation. 
 Change of weather and many other circumstances may at any time prevent 
 the purification of .the water, which at the time of the analysis appeared to 
 be efficient. Moreover, it is by no means certain, that an oxidizing action 
 which would be sufficient to reduce the organic matter in a water to a very 
 small proportion, would be equally competent to remove the specific poison 
 of disease. Hence the greater the impurity of the source of a water the 
 greater the risk attending its use. 
 
 In deep well waters the quantity of organic carbon and nitrogen also 
 extends through a wide range, but is generally low, the average being 
 about 06 part carbon and 0'02 part nitrogen (XXIX). Here the conditions 
 are usually very constant, and if surface drainage be excluded, the source of 
 the water is of less importance. Springs in this, as in most other respects, 
 resemble deep wells ; the water from them being generally, however, some- 
 what purer. In sewage great variations are met with. On the average it 
 contains about four parts of organic carbon and two parts of organic nitrogen 
 -(XXXII. and XXXIII.), but the range is very great. In the table, XXXIV. 
 is a very strong sample, and XXXV. a weak one. The effluent Avater from 
 land irrigated with sewage is usually analogous to waters from shallow wells, 
 and its quality varies greatly according to the character of the sewage and 
 ,the conditions of the irrigation. 
 
 Ratio of Organic Carbon to Organic Nitrogen. 
 
 The ratio of the organic carbon to the organic nitrogen given in the 
 .seventh column of the table (which shows the fourth term of the proportion 
 organic nitrogen : organic carbon : : 1 x), is of great importance as 
 furnishing a valuable indication of the nature of the organic matter present. 
 When this is of vegetable origin, the ratio is very high, and when of animal 
 -origin ven r low. This statement must, however, be qualified, on account of 
 the different effect of oxidation on animal and vegetable substances. It is 
 found that when organic matter of vegetable origin, with a high ratio of 
 carbon to nitrogen, is oxidized, it loses carbon more rapidly than nitrogen, 
 so that the ratio is reduced. Thus unoxidized peaty waters exhibit a ratio^ 
 varying from about 8 to 20 or even more, the average being about 12 ; 
 whereas, the ratio in spring water originally containing peaty matter, varies 
 from about 2 to 5, the average being about 3'2. When the organic matter 
 is of animal origin the action is reversed, the ratio being increased by 
 .oxidation. In unpolluted upland surface waters the ratio varies from about 
 6 to 12, but in peaty waters it may amount to 20 or more. In surface \\ater 
 from cultivated land it ranges from about 4 to 10, averaging about 6. In 
 water from shallow wells it varies from about 2 to 8, with an average of 
 about 4, but instances beyond this range in both directions are very frequent. 
 In water from deep wells and springs, the ratio varies from about 2 to 6, 
 with an average of 4, being low on account, probably, of the prolonged 
 oxidation to which it has been subjected, which, as has been stated above, 
 removes carbon more rapidly than nitrogen. In sea water this action 
 reaches a maximum, the time being indefinitely prolonged, and the ratio is 
 on the average about 1'7. This is probably complicated by. the presence, in 
 some cases, of multitudes of minute living organisms.. In sewage the ratio 
 /ranges from about 1 to 3, with an average of about 2. 
 
90. INTERPRETATION OF RESULTS^- 44.9 
 
 _ When, in the case of a water containing much nitrogen as nitrates and 
 nitrites, this ratio is unusually low, incomplete destruction of nitrates during 
 the evaporation may be suspected, and the estimation should be repeated. 
 To provide for this contingency, if a water contain any considerable quantity 
 of ammonia, it is well, when commencing the evaporation in the first 
 instance, to set aside a quantity sufficient for this repetition, adding to it the 
 usual proportion of sulphurous acid. 
 
 Nitrogen as Ammonia. 
 
 The ammonia in natural waters is derived almost exclusively from animal 
 contamination, and its quantity varies between very wide limits. In upland 
 surface waters it seldom exceeds O'OOS part, the average being about 0'002 
 part. In water from cultivated land the average is about 0'005, and the 
 range is greater, being from nil to 0'025 part, or even more. In water from 
 shallow wells the variation is so great that it would be useless to attempt to 
 state an average, all proportions from nil to as much as 2*5 parts having 
 been observed. In waters from deep wells a very considerable proportion is 
 often found, amounting to O'l part or even more, the average being O'Ol 
 part, and the variations considerable. In spring water it is seldom that 
 more than O'Ol part of nitrogen as ammonia occurs, the average being only 
 O'OOl part. Sewage usually contains from 2 to 6 parts, but occasionally as 
 much as 9 or 10 parts, the average being about five. Ammonia is readily 
 oxidized to nitrates and nitrites, and hence its presence, in considerable 
 quantity, usually indicates the absence of oxidation, and is generally 
 coincident with the presence of organic matter. That sometimes found in 
 waters from very deep wells is, however, probably due to subsequent 
 decomposition of nitrates. 
 
 Nitrogen as Nitrates and Nitrites. 
 
 Nitrates and nitrites are produced by the oxidation of nitrogenous 
 organic matter, and almost always from animal matter. In upland surface 
 waters the proportion varies from nil to 0'05 part or very rarely more, but 
 the majority of samples contain none or mere traces (I. to V.), the average 
 being about 0'009 part. In surface waters from cultivated land the quantity 
 is much greater, varying from nil, which seldom occurs, to 1 part, the 
 average being about 0'25 part. The proportion in shallow wells is usually 
 much greater still, ranging from nil, which very rarely occurs, to as much 
 as 25 parts. It would be probably useless to attempt to state an average, 
 but quantities of from 2 to 5 parts occur most frequently. In water from 
 deep wells the range is from nil to about 3 parts, and occasionally more, the 
 average being about 0'5 part. In spring water the range is about the same 
 as in deep well water, but the average is somewhat lower. 
 
 It sometimes happens that, when the supply of atmospheric oxygen is 
 deficient, the organic matter in water is oxidized at the expense of the 
 nitrates present ; and occasionally, if the quantities happen to be suitably 
 proportioned, they are mutually destroyed, leaving no evidence of pollution. 
 This reduction of nitrates often occurs in deep well water, as for example, 
 in that from wells in the Chalk beneath London Clay, where the nitrates are 
 often totally destroyed. In sewages, putrefaction speedily sets in, and 
 during this condition the nitrates are rapidly destroyed, arid so completely 
 and uniformly that it is probably needless to attempt their estimation, 
 except in sewages which are very weak, or for other special reasons 
 abnormal. Out of a large number of samples, only a very few have been 
 found which contained any nitrates, and those only very small quantities. 
 
 Nitrites occurring in deep springs or wells no doubt arise from the 
 deoxidation of nitrates by ferrous oxide, or certain forms of organic matter 
 
 G G 
 
450 VOLUMETRIC ANALYSIS. 
 
 of a harmless nature ; but whenever they occur in shallow wells or river 
 water, they may be of much greater significance. Their presence in such 
 cases is most probably due to recent sewage contamination, and such waters 
 must be looked upon with great suspicion. 
 
 Total Inorganic Nitrogen. 
 
 When organic matter is oxidized it is ultimately resolved into inorganic 
 substances. Its carbon appears as carbonic acid, its hydrogen as water, and 
 its nitrogen as ammonia, nitrous acid, or nitric acid; the last two combining 
 with the bases always present in water to form nitrites and nitrates. The 
 carbon and hydrogen are thus clearly beyond the reach of the analyst ; but 
 the nitrogen compounds, as has been shown, can be accurately determined, 
 and furnish us with a means of estimating the amount of organic matter 
 which was formerly present in the water, but w r hich has already undergone 
 decomposition. 
 
 The sum of the amounts of nitrogen found in these three forms con- 
 stitutes then a distinct and valuable term in the analysis, the organic 
 nitrogen relating to the present, and the total inorganic nitrogen to the 
 past condition of the water. Since ammonia, nitrites and nitrates are quite 
 innocuous, the total inorganic nitrogen does not indicate actual evil like 
 the organic nitrogen, but potential evil, as it is evident that the innocuous 
 character of a water which contains much nitrogen in these forms depends 
 wholly on the permanence of the conditions of temperature, aeration, 
 nitration through soil, etc., which have broken up the original organic 
 matter; if these should at any time fail, the past contamination would 
 become present, the nitrogen appearing in the organic form, the water being 
 loaded in all likelihood with putrescent and contagious matter. 
 
 In upland surface waters which have not been contaminated to any 
 extent by animal pollution the total inorganic nitrogen rarely exceeds 0'03 
 part. In water from cultivated districts the amount is greater, ranging as 
 high as 1 part, the average of a large number of samples being about 0'22 part. 
 It is useless to attempt any generalization for shallow wells, as the pro- 
 portion depends upon local circumstances. The amount is usually large and 
 may reach, as seen in Examples XIII., the enormous quantity of twenty-five 
 parts per 100,000. Waters containing from one to five parts are very commonly 
 met with. In water from deep wells and springs, quantities ranging up to 
 3' 5 parts have been observed, the average on a large series of analyses being 
 0'5 part for deep wells and about 0'4 part for springs. It must be re- 
 membered that the conditions attending deep wells and springs are 
 remarkably permanent, and the amount of filtration which the water under- 
 goes before reaching the well itself, or issuing from the spring is enormous. 
 Meteorological changes here have either no effect, or one so small and slow 
 as not to interfere with any purifying actions which ma}'- be taking place. 
 All other sources of water, and especially shallow wells,' are on the other 
 hand subject to considerable changes. A sudden storm after drought will 
 wash large quantities of polluting matter into the water-course ; or dissolve 
 the filth which has been concentrating in the pores of the soil during the 
 dry season, and carry it into the well. Small indications therefore of a 
 polluted origin are very serious in surface waters and shallow well waters, 
 but are of less moment in water from deep wells and springs; the present 
 character of these being of chief importance, since whatever degree of 
 purification may be observed, may usually be trusted as permanent. The 
 term "total inorganic nitrogen" has been chosen chiefly because it is 
 based on actual results of analysis without the introduction of any theory 
 whatever. It will be seen that it corresponds very nearly with the term 
 "previous sewage or animal contamination," which was introduced by Dr. 
 Prankland, and which was employed in the second edition of this work. 
 
90. INTERPRETATION OF RESULTS. 451 
 
 Perhaps few terms have been more wonderfully misunderstood and mis- 
 represented than that phrase, and it is hoped that the new term will be less 
 liable to misconception. It will be remembered that the "previous sewage 
 contamination " of a water was calculated by multiplying the sum of the 
 quantities of nitrogen present as ammonia, nitrates, aiid nitrites, by 10,000 
 and deducting 320 from the product, the number thus obtained representing 
 the previous animal contamination of the water in terms of average filtered 
 London sewage. It was purely conventional, for the proportion of organic 
 nitrogen present in such sewage was assumed to be 10 parts per 100,000, 
 whereas in the year 1857 it was actually 8'4 parts, and in 1869 only 7 parts. 
 The deduction of 320 was made to correct for the average amount of 
 inorganic nitrogen in rain water, and this is omitted in calculating "total 
 inorganic nitrogen " for the following reasons : The quantity is small, 
 and the variations in composition of rain water at different times and under 
 different circumstances very considerable, and it appears to obscure the 
 significance of the results of analysis of very pure waters to deduct from 
 all the same fixed amount. As, too, the average amount of total inorganic 
 nitrogen in unpolluted surface waters is only O'Oll part (XXVIII.), it 
 cannot be desirable to apply a correction amounting to nearly three times 
 that average, and so place a water which contains 0'032 part of total 
 inorganic nitrogen on the same level as one which contains no trace of any 
 previous pollution. 
 
 Chlorine. 
 
 This is usually present as sodic chloride, but occasional!}^ as has been 
 mentioned before, it is most likely as a calcic salt. It is derived, in some 
 cases, from the soil, but more usually from animal excreta (human urine 
 contains about 500 parts per 100,000), and is therefore of considerable 
 importance in forming a judgment as to the character of a water. Un- 
 polluted river and spring waters usually contain less than one part; average 
 town sewage about eleven parts. Shallow well water may contain any 
 quantity from a mere trace up to fifty parts or even more. Its amount is 
 scarcely affected by any degree of filtration through soil : thus, the effluent 
 water from land irrigated with sewage contains the same proportion of 
 chlorine as the .sewage, unless it has been diluted by subsoil water or con- 
 centrated by evaporation. Of course, attention should be given to the 
 geological nature of the district from which the water comes, the distance 
 from the sea or other source of chlorine, etc., in order to decide on the 
 origin of the chlorine. Under ordinary circumstance, a water containing 
 more than three or four parts of chlorine should be regarded with suspicion. 
 
 Hardness. 
 
 This is chiefly of importance as regards the use of the water for cleansing 
 and manufacturing purposes, and for steam boilers. It is still a moot point 
 as to whether hard or soft water is better as an article of food. The 
 temporary hardness is often said to be that due to carbonates held in solution 
 by carbonic acid, but this is not quite correct; for even after prolonged 
 boiling, water will still retain about three parts of carbonate in solution, 
 and therefore when the total hardness, exceeds three parts, that amount 
 should be deducted from the permanent hardness and added to the temporary, 
 in order to get the quantity of carbonate in solution. But the term 
 "temporary" hardness properly applies to the amount of hardness which 
 may be removed by boiling, and hence, if the total hardness be less than 
 three parts, there is usually no temporary. As the hardness depends 
 chiefly on the nature of the soil through and over which the water passes, 
 the variations in it are very great; that from igneous strata has least 
 liardness, followed in approximate order by that from Metamorphic, 
 
 G G 2 
 
452 VOLUMETRIC ANALYSIS. 90. 
 
 Cambrian, Silurian and Devonian rocks, Millstone Grit, London Clay, 
 Bagshot Beds, New Eed Sandstone, Coal Measures, Mountain Limestone, 
 Oolite, Chalk, Lias, and Dolomite, the average in the case of the first 
 being 2'4 parts, and of the last 41 parts. As animal excreta contain u 
 considerable quantity of lime, highly polluted waters are usually extremely 
 hard. Water from shallow wells contains varying proportions up to nearly 
 200 parts of total hardness (XIII.). No generalization can be made as to 
 the proportion of permanent to temporary hardness. 
 
 Suspended Matter. 
 
 This is of a less degree of importance than the matters hitherto considered. 
 Prom a sanitary point of view it is of minor interest, because it may be in 
 most cases readily and completely removed by filtration. Mineral suspended 
 matter is, however, of considerable mechanical importance as regards the 
 formation of impediments in the river bed by its gradual deposition, and 
 as regards the choking of the sand filters in water-Avorks ; and organic- 
 suspended matter is at times positively injurious, and always favours the 
 growth of minute organisms. 
 
 From the determinations which have been described, it is believed that 
 a sound judgment as to the character of a water may be made, and the 
 analyst should hardly be content with a less complete examination. If, 
 however, from lack of time or other cause, so much cannot be done, 
 a tolerably safe opinion may be formed, omitting the determination of total 
 solid matter, and organic carbon and nitrogen. But it must not be forgotten 
 that by so doing the inquiry is limited as regards organic impurity, to. the 
 determination of that which was formerly present, but has already been 
 converted into inorganic substances. If still less must suffice, the estimation 
 of nitrogen as nitrates and nitrites may be omitted, its place being to> 
 a certain extent supplied by that of chlorine, but especial care must then be 
 taken to ascertain the source of the latter by examination of the district. 
 If it be in any degree of mineral origin, no opinion can be formed from it 
 as to the likelihood of organic pollution. At best, so slight an examination 
 must be of but little value, and considering the rapidity with which the 
 nitrogen as nitrates can be determined b^y the indigo process ( 92), the saving; 
 of time would be very small. 
 
 General Considerations. 
 
 In judging of the character of a sample of water, due attention must 
 of course be paid to the purpose for which it is proposed to be used. The 
 analyst frequently has only to decide broadly whether the water is good or 
 bad ; as, for example, in cases of the domestic supply to isolated houses or of 
 existing town supplies. "Water which would be fairly well suited for the 
 former might be very objectionable for the latter, where it would be 
 required to a certain extent for manufacturing purposes. Water which 
 would be dangerous for drinking or cooking may be used for certain kinds- 
 of cleansing operations; but it must not be forgotten, that unless great care 
 and watchfulness are exercised there is considerable danger of this restriction 
 being neglected, and especially if the objectionable water is nearer at hand 
 than the purer supply. There would for this reason, probably, be some 
 danger attending a double supply on a large scale in a town, even if the 
 cost of a double service of mains, etc., were not prohibitive. 
 
 It is often required to decide between several proposed sources of supply, 
 and here great care is necessary, especially if the differences between the 
 samples are not great. If possible, samples should be examined at various 
 seasons of the year ; and care should be taken that the samples of the several 
 waters are collected as nearly as possible simultaneously and in a normal 
 condition. The general character of a water is most satisfactorily shown by 
 
90. GENERAL CONSIDERATIONS. 453 
 
 the average of a systematic series of analyses ; and for this reason the average 
 analysis of the water supplies of London, taken from the Reports of Dr. 
 Frankland to the Registrar General, of Glasgow by Dr. Mills, and of 
 Birmingham by Dr. Hill, are included in the table. River waters should, 
 as a rule, not be examined immediately after a heavy rain when they are in 
 flood. A sudden rainfall after a dry season w r ill often foul a river more 
 than a much heavier and more prolonged downfall after average Aveather. 
 Similarly the sewage discharged from a town at the beginning of a heavy 
 rainstorm is usually extremely foul, the solid matter which has been 
 accumulating on the sides of the sewers, and in corners and recesses, being 
 rapidly washed out by the increased stream. 
 
 The possibility of improvement in quality must also be considered. A 
 turbid water may generally be rendered clear by filtration, and this will 
 often also effect some slight reduction in the quantity of organic matter; 
 but while somewhat rapid filtration through sand or similar material will 
 usually remove all solid suspended matter, it is generally necessary to pass 
 the water very slowly through a more efficient material to destroy any large 
 proportion of the organic matter in solution. Very fine sand, animal 
 charcoal, and spongy iron are all in use for this purpose. The quantity 
 of available oxygen must not be neglected in considering the question of 
 filtration. If the water contains only a small quantity of organic matter 
 and is well aerated, the quantity of oxygen in solution may be sufficient, 
 and the filtration may then be continuous; but in many instances this 
 is not the case, and it is then necessary that the filtration should be 
 intermittent, the water being allowed at intervals to drain off from the 
 filtering material in order that the latter may be well aerated, after which 
 it is again fit for work. 
 
 Softening water by Clark's process generally removes a large quantity 
 of organic matter (see Table 8, XVI.) from solution, it being carried down 
 with the calcic carbonate precipitate. 
 
 It is evident that no very definite distinction can be drawn between deep 
 and shallow wells. In the foregoing pages, deep wells generally mean such 
 as are more than 100 feet deep, but there are many considerations which 
 qualify this definition. A deep well may be considered essentially as one 
 the water in which has filtered through a considerable thickness of porous 
 material, and whether the shaft of such a well is deep or shallow will depend 
 on circumstances. If the shaft passes through a bed of clay or other 
 impervious stratum, and the surface water above that is rigidly excluded, the 
 well should be classed as " deep," even if the shaft is only a few feet in 
 depth, because the water in it must have passed for a considerable distance 
 below the clay. On the other hand, however deep the shaft of a well, it 
 must be considered as "shallow" if water can enter the shaft near the 
 surface, or if large cracks or fissures give free passage for surface water 
 through the soil in which the well is sunk. With these principles in view, 
 the water from wells may often be improved. Every care should be taken 
 to exclude surface water from deep wells; that is to say, all water from 
 strata within about 100 feet from the surface or above the first impervious 
 bed. In very deep wells which pass through several such beds, it is desirable 
 to examine the water from each group of pervious strata, as this often varies 
 in quality, and if the supply is sufficient, exclude all but the best. 
 
 In shallow wells much may occasionally be accomplished in a similar 
 manner by making the upper part of the shaft water-tight. It is also 
 desirable that the surface for some distance round the well should be puddled 
 with clay, concreted, or otherwise rendered impervious, so as to increase the 
 thickness of -the soil through which the water has to pass. Drains passing 
 near the well should be, if possible, diverted ; and of course cesspools should 
 t>e either abolished, or, if that is impracticable, removed to as great 
 a distance from the well as is possible, and in addition made perfectly 
 
454 VOLUMETRIC ANALYSIS. 90. 
 
 water-tight. Changes such as these tend to diminish the uncertainty of the 
 conditions attending a shallow well, but in most cases such a source of 
 supply should, if possible, be abandoned as dangerous at best. 
 
 Clark's Process for Softening- Hard Water. 
 
 The patent right of this process having expired, the public are free to use it. 
 
 This method of softening consists in adding lime to the hard water. It is 
 only applicable to water which owes its hardness entirely, or chiefly, to the 
 calcic and magnesic carbonates held in solution by carbonic acid (temporary 
 hardness). Water which owes its hardness to calcic or magnesic sulphate 
 (permanent hardness} cannot be thus softened ; but an}" water which softens 
 on boiling for half an hour will be softened to an equal extent by Clark's 
 process. The hard water derived from chalk, limestone, or oolite districts, 
 is generally well adapted for this operation. 
 
 To soften 700 gallons of water, about one ounce of quicklime is required 
 for each part of temporary hardness in 100,000 parts of water. The quantity 
 of quicklime required is thoroughly slaked in a pailful of water. Stir up 
 the milk of lime thus obtained, and pour it immediately into the cistern 
 containing at least 50 gallons of the water to be softened, taking care to- 
 leave in the pail any heavy sediment that may have settled to the bottom in 
 the few seconds that intervened between the stirring and pouring. Pill the 
 pail again with water, and stir and pour as before. The remainder of the 
 700 gallons of water must then be added, or allowed to run into the cistern 
 from the supply pipe. If the rush of the water does not thoroughly mix 
 the contents of the cistern, this must be accomplished lay stirring with 
 a suitable wooden paddle. The water will now appear very milky, owing to- 
 the precipitation of the chalk which it previously contained in solution 
 together with an equal quantity of chalk which is formed from the quick- 
 lime added. 
 
 After standing for three hours the water will be sufficiently clear to use 
 for washing ; but to render it clear enough for drinking, at least twelve 
 hours' settlement is required. This process not only softens water, but it 
 removes to a great extent objectionable organic matter present. 
 
 The proportion of lime to water may be more accurately adjusted during 
 the running in of the hard water, by taking a little water from the cistern 
 at intervals in a small white cup, and adding to it a drop or two of solution 
 of nitrate of silver, which will produce a yellow or brownish colouration as 
 long as there is lime present in excess. As soon as this becomes very faint, 
 and just about to disappear, the flow of water must be stopped. The 
 carbonate may be removed b} r filtration in a very short time after the addition 
 of lime, and on the large scale this may be done with great rapiditj r by 
 means of a filter press, as in Porter's process. This latter method of 
 rapidly softening and purifying water is the invention of the late 
 J. Henderson Porter, C.E., Queen Victoria Street, London, Avhose 
 apparatus is largely in use for public water supplies, and for softening waters 
 used in manufacturing processes, and the prevention of boiler incrustations, 
 etc. The chief objections to the original Clark process are, the large space 
 required for mixing and settling tanks, and the time required for subsidence 
 of the precipitate. On the contrary, in Porter's process, the space 
 occupied is small, and the clarification immediate. The results are 
 admirable, and are achieved at a very moderate cost. 
 
 Another apparatus devised by M.M. Gaillet and Hiiet, of Lille, consists- 
 of a lofty tank containing a series of sloping troughs. The water after 
 mixing with the due proportion of lime water passes slowly downwards- 
 through the tank and deposits all the carbonate precipitate in^the troughs, 
 from which it can be run off as mud. The process is thus continuous and 
 very convenient in dealing with large volumes of water. 
 
91. WATER ANALYSIS. 455 
 
 METHODS OF ESTIMATING- THE ORGANIC IMPURITIES IN 
 WATER WITHOUT GAS APPARATUS. 
 
 91. THE foregoing methods of estimating the organic 
 impurities in potable waters, though very comprehensive and 
 trustworthy, yet possess the disadvantage of occupying a good deal 
 of time, and necessitate the use of a complicated and expensive set 
 of apparatus, which may not always be within the reach of the 
 operator. 
 
 ISTo information of a strictly reliable character as to the nature of the 
 organic matter or its quantity can be gained from the use of standard 
 permanganate solution as originally devised by Forschammer, 
 and the same remark applies to the loss on ignition of the residue, 
 both of which have been in past time largely used. 
 
 The For sc hammer or oxygen process, however, as improved by 
 Letheby, and further elaborated by Tidy, may be considered as 
 worthy of considerable confidence in determining the amount of 
 organic substances contained in a water. 
 
 The Oxygren Process. 
 
 This process depends upon the estimation of the amount of 
 oxygen required to oxidize the organic and other oxidizable matters 
 in a known volume of water, slightly acidified with pure sulphuric 
 acid. For this purpose, a standard solution of potassic permanganate 
 is employed in excess. The amount of unchanged permanganate, 
 after a given time, is ascertained by means of a solution of sodic 
 thiosulphate, by the help of the iodine and starch reaction. 
 
 Tidy and Frank land in all cases make a blank experiment 
 with pure distilled water, side by side with the sample. 
 
 As regards the time during which the sample of water should be 
 exposed to the action of the permanganate, authorities somewhat 
 differ. It is manifest that, if the water contains certain reducing 
 agents such as nitrites, ferrous salts, or sulphuretted hydrogen, an 
 immediate reduction of the reagent will occur, and Tidy is 
 disposed to register the reduction which occurs in three minutes, in 
 the known absence of iron and sulphuretted hydrogen, as due to 
 nitrites. The same authority adopts the plan of making two 
 observations, one at the end of one hour and another at the end of 
 three hours, at the ordinary temperature of the laboratory (say 60 
 Fahr. or 16C.). 
 
 Frankland admits this process to be the best volumetric 
 method in existence for the estimation of organic matters, but is 
 content with one experiment lasting three hours (also at ordinary 
 temperature). 
 
 The Water Committee of the Society of Public Analysts of 
 Great Britain and Ireland have adopted the periods of fifteen 
 
456 VOLUMETEIC ANALYSIS. 91. 
 
 minutes and four hours for the duration of the experiment, at the 
 fixed temperature of 80 Fahr. or 27 C.* 
 
 Dupre has carried out experiments (Analyst vii. 1), the 
 Jesuits of which are in favour of the modifications adopted by the 
 Committee. The chief conclusions arrived at are : 
 
 (1) That, practically, no decomposition of permanganate takes 
 place during four hours when digested in a closed vessel at 80 
 with perfectly pure water and the usual proportion of pure 
 sulphuric acid. 
 
 By adopting the closed vessel, all dust or reducing atmospheric 
 influence is avoided. 
 
 (2) The standardizing of the thiosulphate and permanganate, 
 originally and from time to time, must be made in a closed vessel 
 in the same manner as the analysis of a water, since it has been 
 found that when the titration is made slowly in an open beaker 
 less thiosulphate is required than in a stoppered bottle. This is 
 probably due to a trifling loss of iodine by evaporation. 
 
 (3) That with very pure waters no practical difference is 
 produced by a rise or fall of temperature, the same results being 
 obtained at 32 F. as at 80 F. On the other hand, with polluted 
 waters, the greater the organic pollution, the greater the difference 
 in the amount of oxygen absorbed according to temperature. 
 
 (4) As to time, it appears that very little difference occurs in 
 good waters between three and four hours' digestion; but with bad 
 waters there is often a very considerable increase in the extra hour ; 
 and thus Dupre doubts whether even four hours' digestion suffices 
 for very impure waters. 
 
 The necessary standard solutions for working the process will be 
 described further on. 
 
 *Dupre in further comment on the temperature at which it is advisable to carry 
 out this method ( Analyst x. 118), and also as to the reactions involved, points out one 
 feature which has in all probability impressed itself upon other operators, that is to 
 say, the effect of chlorides when present in any quantity. It is evident that if in this 
 case the permanganate is used at a high temperature and in open vessels, chlorine will 
 be liberated ; part escaping into the air, and the rest nullifying the reducing effect of 
 any organic matter present on the permanganate. If, however, the experiment be 
 conducted at high temperature in a closed vessel, the probable error is eliminated, 
 because the chlorine is retained, and subsequently, when cool and the potassic iodide 
 added, the free Cl liberates exactly the same amount of iodine as would have been set 
 free by the permanganate from which it was produced. It thus becomes possible to 
 estimate the amount of oxidizable organic matter, even in sea water. In order, how- 
 ever, to reduce the probable error from the presence of chlorides, Dupre prefers to 
 carry on the experiment at a very low temperature, in fact, as near C. or 32 F. as 
 possible, and uses phosphoric acid in place of sulphuric (250 gm. glacial acid to the 
 liter; 10 c.c. of which is used for each ouarter or half liter of water). The sample is 
 cooled, the reagent added in a stoppered bottle, and kept in an ordinary refrigerator 
 for twenty-four hours. The same operator very rightly condemns the pi-actice adopted 
 by some chemists, especially those of Germany, of boiling a water with permanganate 
 arid sulphuric acid. The presence of chlorides in varying proportions must in such 
 case totally vitiate the results. 
 
91. 
 
 OXYGEN PROCESS FOR WATER. 
 
 457 
 
 Comparison of the Results of this Process -with the Combustion 
 Method. I cannot do better than quote Dr. Frank land's remarks 
 on this subject, as contained in his treatise on Water Analysis: 
 
 " The objections to the oxygen process are first, that its indications are 
 only comparative, and not absolute ; and, second, that its comparisons are 
 only true when the organic matter compared is substantially identical in 
 composition. 
 
 " For many years, indeed, after this process was first introduced, the action 
 of the permanganate was tacitly assumed to extend to the complete oxidation 
 of the organic matter in the water, and, therefore, the result of the 
 experiment was generally stated as ' the amount of oxygen required to 
 oxidize the organic matter ; ' whilst some chemists even employed the number 
 so obtained to calculate the actual weight of organic matter in the water on 
 the assumption that equal weights of all kinds of organic matter required 
 the same weight of oxygen for their complete oxidation. 
 
 "Both these assumptions have been conclusively proved to be entirely 
 fallacious, for it has been experimentally demonstrated by operating upon 
 known quantities of organic substances dissolved in water, that there is no 
 relation either between the absolute or relative weight of different organic, 
 matters and the oxygen which such matters abstract from permanganate. 
 
 "Nevertheless, in the periodical examination of waters from the same 
 source, I have noticed a remarkable parallelism between the proportions of 
 organic carbon and of oxygen abstracted from permanganate. Thus, for 
 many years past, I have seen in the monthly examination of the waters of 
 the Thames and Lea supplied to London such a parallelism between the 
 numbers given by Dr. Tidy, expressing 'oxygen consumed,' and those 
 obtained by myself in the determination of ' organic carbon.' 
 
 " This remarkable agreement of the two processes, extending as it did to 
 1,418 out of 1,686 samples, encouraged me to hope that a constant multiplier 
 might be found, by which the 'oxygen consumed' of the For sc hammer 
 process could be translated into the 'organic carbon' of the combustion 
 method of analysis. To test the possibility of such a conversion, my pupil, 
 Mr. Woodland Toms made, at my suggestion, the comparative experi- 
 ments recorded in the following tables : 
 
 I. River Water. 
 
 Sovirce of Sample. 
 
 Oxygen C Organic 
 consumed, X ; *%& 
 
 Chelsea Company's supply ... 
 
 G'098 x 2'6 = 0-256 
 
 West Middlesex Co.'s 
 
 0-116 x 2-5 = 
 
 0-291 
 
 Lambeth Co.'s ,, 
 
 0-119 x 2-43 = 
 
 0-282 
 
 Southwark Co/s 
 
 0-121 x 222 = 
 
 0-269 
 
 New River Co.'s 
 
 0076 x 2-4 = 
 
 0183 
 
 Chelsea Co.'s second sample ... 
 
 0-070 x 2-69 = 
 
 0-188 
 
 Lambeth Co.'s 
 
 0-119 x 1-99 = 
 
 0-234 
 
 New River Co.'s 
 
 0-107 x 2-25 = 
 
 0-221 
 
 "As the result of these experiments the average multiplier is 2'38, and 
 the maximum errors incurred by its use would be 0'02L part of organic 
 carbon in the case of the second sample of the Chelsea Company's water, 
 and +0*049 part in that of the second sample of the Lambeth Company's 
 water. These errors would practically have little or no influence upon the 
 
458 
 
 VOLUMETRIC ANALYSIS. 
 
 91. 
 
 analyst's opinion of the quality of the water. It is desirable that this 
 comparison should be extended to the water of other moderately polluted 
 rivers. 
 
 II. Deep "Well Water. 
 
 Source of Sample. 
 
 Oxygen 
 consumed. 
 
 X 
 
 c 
 o 
 
 Organic 
 carbon by 
 combustion. 
 
 Kent Company's supply 
 
 0-015 
 
 X 
 
 5'1 == 
 
 0-077 
 
 Colne Valley Co.'s 
 
 0-0133 
 
 x 
 
 6-9 == 
 
 0-094 
 
 Hodgson's Brewer} r well ... ... 1 0*03 
 
 X 
 
 5-3 = 
 
 0-158 
 
 " The relation between ' oxygen consumed ' and ' organic carbon ' in the 
 case of deep well waters is thus very different from that Avhich obtains in the 
 case of river waters, and the average multiplier deduced from the foregoing 
 examples is 5' 8, with maximum errors of +0'01 of organic carbon in the case 
 of the Kent Company's water, and 015 in that of the Colne Valley 
 water. Such slight errors are quite unimportant. 
 
 "Similar comparative experiments made with shallow well and upland 
 surface waters showed amongst themselves a wider divergence, but pointed 
 to an average multiplier of 2'28 for shallow well water, approximately the 
 same as that found for moderately polluted river water, and 1'8 for upland 
 surface water. 
 
 " In the interpretation of the results obtained, either by the P o r s c h a m m e r 
 or combustion process, the adoption of a scale of organic purity is often useful 
 to the analyst, although a classification according to such a scale may require 
 to be modified by considerations derived from the other analytical data. It 
 is indeed necessary to have a separate and more liberal scale for upland surface 
 water, the organic matter of which is usually of a very innocent nature, and 
 derived from sources precluding its infection by zymotic poisons. 
 
 "Subject to modification by the other analytical data, the following scale of 
 classification has been suggested by Dr. Tidy and myself: 
 
 Section I. Upland Surface Water. 
 
 " Class I. Water of great organic purity, absorbing from permanganate 
 not more than O'l part of oxygen per 100,000 parts of water, or 0'07 grain 
 per gallon. 
 
 "Class II. Water of medium purity, absorbing from O'l to 0'3 part of 
 oxygen per 100,000 parts of water, or 0*07 to 0'21 grain per gallon. 
 
 "Class III. Water of doubtful purity, absorbing from 0'3 to 0'4 part 
 per 100,000, or 0'21 to 0'28 grain per gallon. 
 
 "Class IV. Impure water, absorbing more than 0:4 part per 100,000,, 
 or 0'28 grain per gallon. 
 
 Section II. Water other than Upland Surface. 
 
 " Class I. Water of great organic purity, absorbing from permanganate 
 not more than 0'05 part of oxygen per 100,000 parts of water, or 0'035 grain 
 per gallon. 
 
91. OXYGEN PROCESS FOR WATER. 459 
 
 "Class II. Water of medium purity, absorbing from 0*05 to 0'15 part 
 of oxygen per 100,000, or 0*035 to O'l grain per gallon. 
 
 "Class III. Water of doubtful purity., absorbing from 0'15 to 0'2 part 
 of oxygen per 100,000, or O'l to 0'15 grain per gallon. 
 
 "Class IV. Impure water, absorbing more than 0'2 part of oxygen 
 per 100,000, or 0'15 grain per gallon." 
 
 Dr. James Edmunds, Public Analyst for St. James's, London, 
 in a communication to the author, writes as follows : 
 
 Medical practitioners who wish to use permanganate as a ready indicator 
 for organic matter in drinking waters, may be glad of some farther detail as 
 to the significance of the decolourization which permanganate undergoes 
 when in contact with organic, and other reducing matters. 
 
 Two molecules of potassic permanganate (2KMnO 4 = 316) contain five atoms 
 of separable nascent oxygen. Five atoms of oxygen are equivalent to ten 
 atoms of hydrogen, arid, the hydrogen-equivalent being the base of 
 volumetric analysis, it follows that 31'6 gm. KMnO 4 with distilled 
 water to 1000 c.c. will constitute the normal solution, while 3*16 per 1000 
 c.c. will constitute the decinormal solution. Of tbis *-$ permanganate, each 
 c.c. yields O'OOOS of nascent oxygen, and, under proper conditions, will 
 oxidize O'OOOl of hydrogen. So long as the separable nascent oxygen only 
 is regarded, the above solutions constitute the true an d *-$ permanganate. 
 But, under certain conditions, other reactions intervene ; and, in view of 
 these, we require also to consider the hydrogen-equivalent of the 
 permanganate as regards its potassium, and as regards its manganese. On 
 reckoning out these latter equivalences, it will be seen that the decinormal 
 permanganate, while ^ as to its separable oxygen, is ^/TT a $ to its potash, 
 and ^THT as to its manganese. It therefore follows that, to precisely 
 neutralize the potash of the permanganate, and also to dissolve its manganese 
 as a manganous salt, there would be required --$ H' 2 SO 4 equal in volume 
 to the / F permanganate used. 
 
 It must be recollected that the decolouration which permanganate under- 
 goes, is in no sense a measure of the organic, or other reducing matter. It 
 is a measure only of the oxygen-absorbing power of the particular reducing 
 matters under a particular set of conditions. This fact is fundamental in 
 studying the action of permanganate. With a given quantity of the same kind 
 of organic or other reducing matter, the decolourization of permanganate is, 
 doubtless, a perfectly constant quantity so long as the conditions of the 
 reaction are identical. But if the conditions are not identical, new factors 
 come in and vary the results. The practical point therefore is to secure 
 identical conditions for each operation, so as to make the results comparable 
 and reliable as a measure of the oxygen-absorbing power of a particular 
 water. 
 
 Now 3' 160 gm. KMnO 4 breaks up into 
 
 K-O 0-940) 
 MnO T420 =3-160 
 Separable as nascent O 0*800 ) 
 
 Each c.c. of the -^ permanganate will therefore contain ^Vrr of the above 
 quantities. But O'OOOS of nascent oxygen from each c.c. of this 
 permanganate is obtainable only under properly adjusted conditions. 
 Under other conditions the Mn 2 O 7 is not reduced to 2MnO, but only to 
 2MnO 2 . In the latter case, each c.c. yields only 0'00048 of nascent oxygen 
 
460 VOLUMETRIC ANALYSIS. 91. 
 
 instead of O'OOOSO, and the significance of the decolonization varies 
 accordingly. If either of the above conditions, or a definite combination of 
 the two sets of conditions, could be uniformly secured ; or. if the amount of 
 MnO 2 which comes out could afterwards be conveniently determined, there 
 would be no difficulty in calculating the significance of the decolourization. 
 The problem therefore, is, to secure a definite basis for calculation, when 
 we use the decolourization as marking our end-point. 
 
 In order that all the separable oxygen may come out in the nascent 
 condition, so as to combine with the reducing matters whose ox} r geu- 
 absorbing powers are to be measured, w r e must have the following 
 conditions : 
 
 1. The titrate (i.e., the solution about to be titrated by the permanganate) 
 must contain H 2 SO 4 in such excess as will neutralize the potash, and also 
 will instantly seize and draw into solution the MnO which has to be 
 separated from the available ox3 r gen. It has already been seen that, as 
 regards the aggregated potash and manganese, the permanganate is really 
 a y^\ solution, although yV as regards its separable oxygen. Therefore, 
 6 c.c. of T^j- H 2 SO 4 would, in the end, neutralize the potash, and take up the 
 manganese, of 1 c.c. of the ^ permanganate. In practice, however, a very 
 large excess of H 2 SO 4 must be on hand in the solution in order to secure 
 the complete reduction of the manganese to the mauganous condition, and 
 the withdrawal of this into solution in the form of MnSO 4 . Otherwise, the 
 nascent moment of part of the oxygen is lost, the hydrated peroxide of 
 manganese comes out, and we get a muddy brown liquid whose turbidity 
 and colour obscure the end-point. Practically the MnO 2 which thus 
 conies out cannot be got back again into solution, nor can it be easily 
 quantified. Any precipitation of black oxide consequently spoils the 
 titration. 
 
 2. The titrate should in each case be made up to the same volume, and 
 its dilution should bear a reasonable relation to the volume of permanganate 
 \vhich it may require. 
 
 3. The temperature at which the reaction is conducted must be the same 
 for the Avhole series of titrations, and the time during which the action 
 proceeds must be the same. Otherwise, the reaction must be so prolonged 
 as to reduce the maximum possible volume of the permanganate, and yield 
 a water-white or clear pink solution. 
 
 4. The dropping in of the permanganate should closely follow up the 
 disappearance of the colour, and as the decolourizatiou halts, the dropping 
 in of the permanganate should be checked. 
 
 5. If the permanganate be crowded in, under conditions where the 
 chemical potential is on the balance, it becomes easier to reduce a surplus of 
 Mn 2 O 7 one stage to 2MnO 2 , than to reduce the minimum quantity of Mn 2 O 7 
 two stages down to 2MnO. In this case crowding the permanganate in will 
 bring out the hydrated peroxide and spoil the titration. 
 
 6. The operations should be conducted in glass-stoppered white bottles. 
 8-oz. bottles are convenient. In routine titrations the white basin is 
 preferable. 
 
 It must be recollected that, under similar conditions, different substances 
 have a very different chemical potential in their reducing action upon 
 permanganate. In some the chemical potential is so great that they are 
 adequately active at all temperatures, while others cannot be titrated with 
 permanganate unless at an elevated temperature. Thus an acid solution of 
 a ferrous salt reduces permanganate instantly at all temperatures. 
 Oxalic acid at C., or even at the ordinary temperature of the laboratory, 
 reduces permanganate so slowly that it cannot be conveniently titrated. Yet 
 
91. ACTION OF PERMANGANATE. 461 
 
 the oxalic acid titrate when heated to 60 C reduces the permanganate 
 rapidly, and, if not overcrowded, gives a beautifully sharp end-point. 
 Matters not really in solution such as bacterial organisms in water, 
 epithelium and other organic debris in urine react slowl) r and variously 
 with permanganate, and cannot be accurately titrated. On the other hand, 
 fresh normal urine, filtered warm, makes a useful titrate. By its means the 
 decolourization of permanganate with organic matter, under various per- 
 centages of acidity and at various temperatures, may be studied conveniently. 
 The filtered urine should be diluted to ten times its volume with pure distilled 
 water. Of this diluted urine 10 c.c. are taken for each titrate, and made up 
 to 100 c.c. with various percentages of f H 2 SO 4 and distilled water. Each 
 such titrate contains 1 c.c. of filtered urine. The experiments may be made 
 in glass-stoppered white 8-oz. bottles, at the ordinary temperature of the 
 laboratory, and the bottles should be open only while the permanganate is 
 dropped in. 
 
 In working the permanganate into the titrate, several elemental results 
 come out often more or less mixed. Those results may be summarized as 
 follows : 
 
 1. Bleaching continuously out to water-white without turbidity, without 
 brown film in bottle, and without brown precipitate. Here the Mn 2 O 7 is 
 reduced to 2MnO, and a perfectly sharp pink colour is obtained as the end- 
 point. A transient yellowing sometimes occurs. Five atoms of nascent 
 oxygen are set free. 
 
 2. As the oxygen-absorbing power of the titrate is exhausted there 
 comes a halt, and the decolourization is no longer instantaneous. In some 
 titratious, as that for uric acid, this first halt in the decolourization should 
 be taken as the end-point. In other cases the halt marks the exhaustion 
 only of the most active reducers in a complex titrate, and should be noted 
 as a useful datum. In that case, further additions of permanganate require 
 a longer time, or a higher temperature in order to raise the potential and 
 quicken the reduction. So soon as the titration is completed, one drop of 
 permanganate in excess gives a clear permanent faint pink colour. 
 
 3. Sometimes the permanganate forms a ruby-red compound, the tint of 
 which is quite distinct from the purple-pink. On standing, this ruby-red 
 generally yellows or browns out to a turbid liquid, ultimately depositing 
 a brown precipitate of hydrated peroxide of manganese, and leaving a water- 
 white supernatant liquid. 
 
 4. A distinct smokiness, or a yellowing or browning out of the purple 
 sometimes occurs. On standing, MnO 2 comes out. This may appear as 
 a brown film which, on tilting the bottle, contrasts well with the water- 
 white liquid; as a brown sediment ; or as a fine smoky turbidity which takes 
 hours, or even days, to come out as a deposit of MnO" 2 . 
 
 If titrates be made up (A) of 100 c.c. of pure distilled water; (B) of 
 100 c.c. of H 2 SO 4 ; (C) of 1 gm. of MnSO 4 in 100 c.c. of distilled water ; 
 (D) of 1 gm. of MnSO 4 in 100 c.c. of H 2 SO 4 a series of control titrates 
 are obtained. On adding 1 c.c. of permanganate to each titrate, A and B 
 will remain for many days a full colour practically unchanged, though 
 A will at once assume the rub}^-red colouration ; while B will retain the tint 
 of the purple permanganate. On the other hand, the titrates C and D, 
 containing the manganous sulphate, will instantly reduce the permanganate and 
 throw out a brown precipitate which subsides much more rapidly in C than in 
 D. This shows that, apart altogether from the presence of organic or other 
 reducing matters, the accumulation of manganous sulphate in the titrate 
 upsets the balance of the subsequently added permanganate, and throws out 
 hydrated peroxide. 
 
 Another series of titrates may each contain 1 c.c. of filtered urine, with 
 
462 VOLUMETRIC ANALYSIS. 91. 
 
 H 2 SO 4 Y in a series of proportions, and in each case made up with H 2 O to 
 100 c.c. Ten such titrates containing of sulphuric acid 90, 80, 70, 60, 50, 40, 
 30, 20, 10, and / , will show that, on adding to each of the series 1 c.c. 
 TV permanganate, and repeating the addition from time to time till 5 c.c. 
 permanganate have been added, the titrates break up into characteristic 
 groups according to the percentage of sulphuric acid present, and that the 
 groupings will again vary according to the temperatures at which the 
 reactions are conducted, or according to the times for which the titrates are 
 allowed to stand over in their bottles. A comparison of the results shown 
 in ten such titrates 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10, with the results seen 
 in the control titrates A B C 1), will illustrate the complexity of the considera- 
 tions which are involved in measuring the oxygen-absorbing power of 
 organic and other reducing matters, by means of permanganate. As has 
 already been indicated, the action of the permanganate does not quantify 
 the organic or other reducing matters which may be in the titrate ; it merely 
 indicates the oxygen-absorbing powers of those titrates under specific 
 conditions. 
 
 The Albuminoid Ammonia Process. 
 
 Wanklyn, Chapman, and Smith are the authors of this well- 
 known method of estimating the quantity of nitrogenous organic 
 matter in water, which depends upon the conversion of the nitrogen 
 in such organic matter into ammonia, when distilled with an alkaline 
 solution of potassic permanganate (/. C. S. 1867, 591). 
 
 The authors have given the term "Albuminoid ammonia" to 
 the NH 3 produced from nitrogenous matter by the action of the 
 permanganate, doubtless because the first experiments made in 
 the process were made with albuminous substances ; but the authors 
 also proved that ammonia may be obtained in a similar way from, 
 a great variety of nitrogenous organic substances, such as hippuric 
 acid, narcotine, strychnine, morphine, creatine, gelatine, casein, etc. 
 Unfortunately, however, although the proportion of nitrogen 
 yielded by any one substance when treated with boiling alkaline 
 permanganate appears to be definite, yet different substances give 
 different proportions of their nitrogen. Thus hippuric acid and 
 narcotine yield the whole, but strychnine and morphine only one- 
 half of their known proportion of nitrogen. Hence the value of the 
 numerical results thus obtained depends entirely on the assumption 
 that the nitrogenous organic matter in water is uniform in its 
 nature, and the authors say that in a river polluted mainly by 
 sewage "the disintegrating animal refuse would be pretty fairly 
 measured by ten times the albuminoid ammonia which it yields." 
 
 It is stated by the authors that the albuminoid ammonia from a 
 really good drinking water should not exceed O'OOS part in 100,000. 
 The average of fifteen samples of Thames water supplied to London 
 by the various Water Companies in 1867 was 0'0089, and in five 
 samples supplied by the JSVsv River Company 0*0068 part per 
 100,000. 
 
 The necessary standard solutions and directions for working the 
 process will be described further on (page 465). 
 
92. WATER ANALYSIS WITHOUT GAS APPARATUS. 463 
 
 PREPARATION OF THE REAGENTS FOR THE SANITARY 
 ANALYSIS OF WATERS WITHOUT GAS APPARATUS. 
 
 92. THE Water Committee of the Society of Public Analysts 
 of Great Britain and Ireland have drawn up some very concise 
 directions for the practice of water analysis for sanitary purposes, 
 based upon well-known processes, the essential parts of which 
 .are given below. There are some slight modifications, such as the 
 use of the decem or 10-grain measure instead of the grain, etc. 
 The insertion here of these directions in full, or nearly so, necessarily 
 repeats some processes which have been already described in 88 
 and 89, but it avoids cross-references and at the same time gives 
 some slight practical modifications which, to some operators, 
 may seem desirable." The Committee recommend the results to be 
 recorded in grains per imperial gallon ; but whatever system of 
 weights and measures the individual "analyst may use, a slight 
 calculation will enable him to state the results in any required way. 
 
 Reagents for the Estimation of Chlorine. 
 
 Standard Solution of Silver nitrate. -Dissolve 4 '7887 parts of 
 pure recrystallized silver nitrate in distilled water, and make the 
 solution up to 1000 parts. The solution is to be standardized 
 against the standard solution of sodic chloride, and adjusted if 
 necessary. 1 c.c. O'OOl gm. of chlorine, or 1 dm. = O'Ol grn. of 
 chlorine. 
 
 Standard Solution of Sodic chloride. Dissolve 1'648 part of 
 pure dry sodic chloride in distilled water, and make the solution 
 up to 1000 parts. 1 c.c. contains O'OOl gm. chlorine, or 1 dm. = 
 O'Ol grn. of chlorine. 
 
 Potassic monochromate. 50 parts of potassic monochromate 
 are dissolved in 1000 parts of distilled water. A solution of 
 silver nitrate is added, until a permanent red precipitate is 
 produced, which is allowed to settle. This removes any accidental 
 chlorine in the salt. 
 
 Reagent for the Estimation of Phosphoric Acid. 
 
 Molybdic Solution. One part pure molybdic acid is dissolved 
 in 4 parts of ammonia, sp. gr. 0-960. This solution, after nitration, 
 is poured with constant stirring into 15 parts of nitric acid of T20 
 sp. gr. It should be kept in the dark, and carefully decanted 
 from any precipitate which may form. 
 
 Reagents for the Estimation of Nitrogen in Nitrates. 
 Concentrated Sulphuric acid. In order to ensure freedom from 
 
464 VOLUMETRIC ANALYSIS. 92. 
 
 oxides of nitrogen, this should be kept in a bottle containing 
 mercury, and agitated from time to time, which will ensure their 
 absence. 
 
 Metallic Aluminium. As thin foil. 
 
 Solution of Sodic hydrate. Dissolve 100 parts of solid sodic 
 hydrate in 1000 parts of distilled water. When cold, introduce 
 a strip of about 100 square c.m., say fifteen square inches, of 
 aluminium foil, previously heated just short of redness, wrapped 
 round a glass rod. When the aluminium is dissolved, boil the 
 solution briskly in a porcelain basin until about one-third of its 
 volume has been evaporated, allow it to cool, and make it up to 
 its original volume with water free from ammonia. The solution 
 must be tested by a blank experiment to prove the absence of 
 nitrates. 
 
 Broken Pumice. Clean pumice, broken into pieces of the size 
 of small peas, sifted free from dust, heated to redness, and kept 
 in a closely stoppered bottle. 
 
 Hydrochloric acid free from Ammonia. If the ordinary pure 
 acid is not free from ammonia, it should be distilled. As only two 
 or three drops are used in each experiment, it will be sufficient 
 if that quantity does not contain an appreciable proportion of 
 ammonia. 
 
 Copper sulphate Solution. Dissolve 30 parts of pure copper 
 sulphate in 1000 parts of distilled water. 
 
 Metallic Zinc. As thin foil. This should be kept in a dry 
 atmosphere, so as to be preserved as far as possible from oxidation. 
 
 Standard Solution of Ammonic chloride (see below), 
 ^essler's Solution (see below). 
 
 Standard Potassic nitrate of y^y- strength, made by dissolving 
 O'lOll gm. KNO 3 in a liter of water free from nitrates or nitrites. 
 
 Indigo Carmine. A good quality of this substance (sodic 
 sulphindylate) should be selected, such as will not give a very 
 dark brown when oxidized with nitric acid, and about a gram 
 dissolved in half a liter of dilute pure sulphuric acid (1 to 20). 
 This solution keeps in the dark for months without diminution of 
 strength. 
 
 Pure Sulphuric Acid. This must be free from nitric or nitrous 
 compounds, and of not less sp. gr. than 1*843. 
 
92. WATER ANALYSES WITHOUT GAS APPARATUS. 465 
 
 Reagents for the Estimation of Nitrogen as Ammonia and 
 Albuminoid Ammonia. 
 
 Concentrated Standard Solution of Ammonic chloride. Dissolve 
 3 '15 parts of pure ammonic chloride in 1000 parts of distilled water 
 free from ammonia. 
 
 Standard Solution of Ammonic chloride. Dilute the above 
 with pure distilled water to 100 times its bulk. This solution is 
 used for comparison in Xesslerizing, and contains one part of 
 ammonia (NH ;5 ) in 100,000, or ~^ m.gm. in each c.c. 
 
 Xessler Solution. Dissolve 35 parts of potassic iodide in 
 100 parts of water. Dissolve 17 parts of mercuric chloride in 
 300 parts of water. The liquids may be heated to aid solution, 
 but if so must be cooled. Add the latter solution to the former 
 until a permanent precipitate is produced. Then dilute with 
 a 20 per cent, solution of sodic or potassic hydrate to 1000 parts ; 
 add mercuric chloride solution until a permanent precipitate again 
 forms ; allow to stand till settled, and decant off the clear solution. 
 The bulk should be kept in an accurately stoppered bottle, and 
 a quantity transferred from time to time to a small bottle for use. 
 The solution improves by keeping. It will be noticed that this 
 solution is only about half the strength of the one given on page 
 399 ; of course a larger volume has to be used in testing. 
 
 Sodic carbonate. A 20 per cent, solution of recently ignited 
 pure sodic carbonate. 
 
 Alkaline Permanganate Solution. Dissolve 200 parts of potassic 
 hydrate and eight parts of pure potassic permanganate in 1100 parts 
 of distilled water, and boil the solution rapidly till concentrated to 
 1000 parts. 
 
 Distilled Water free from Ammonia (see page 400). 
 
 Reagents for the Estimation of Oxygen absorbed. 
 
 Standard Solution of Potassic permanganate. Dissolve 0*395 
 part of pure potassic permanganate in 1000 of water. Each c.c. 
 contains O'OOOl gm. of available oxygen, and each dm. contains 
 0-001 grn. 
 
 Potassic iodide Solution. One part of the pure salt dissolved 
 in ten parts of distilled water. 
 
 Dilute Sulphuric acid. One part by volume of pure sulphuric 
 .acid is mixed with three parts by volume of distilled water, and 
 solution of potassic permanganate dropped in until the whole 
 retains a very faint pink tint, after warming to 80 F. for four 
 iiours. 
 
 H H 
 
466 VOLUMETRIC ANALYSIS. 92. 
 
 Sodic thiosulphate. One part of the pure crystallized salt 
 dissolved in 1000 parts of water. 
 
 Starch Indicator. The best form in which to use this is the 
 alkaline solution, page 131. 
 
 Reag-ents for the Estimation of Hardness. 
 
 Concentrated Standard Solution of Calcic chloride. Dissolve 
 1*144 gm. of pure crystallized calc-spar in dilute hydrochloric acid 
 (with the precautions given on page 405), then dissolve in water, 
 and make up to a liter. On the grain system, a solution of the same- 
 strength is made by dissolving 11*44 grn. of calc-spar in 1000 dm. 
 
 Standard Water of 8 Hardness. This is made by diluting the 
 foregoing concentrated solution to ten times its volume with 
 freshly boiled and cooled distilled water. 
 
 Standard Soap Solution (is made precisely as directed on page 
 405). It should be of such strength as just to form a permanent 
 lather, when 18 c.c. or dm. measures are shaken with 100 c.c. or 
 dm. of water of 8 hardness. The following table will then give 
 the degrees of hardness corresponding to the number of c.c. or dm. 
 measures employed. 
 
 c.c. or dm. c.c. or dm. 
 
 Hardness. Measures. Hardness. Measures. 
 
 0-9 . 5 12-0 
 
 1 2-9 6 14-0 
 
 2 5-4 7 16-0 
 
 3 7-7 8 18-0 
 
 4 9-9 
 
 After which one degree = 2 c.c. or dm. measures. This is the 
 last solution recommended by Dr. Clark, and differs slightly 
 from the scale given on page 439 ; the variation, however, is very 
 insignificant, except in the first two stages of the table. 
 
 The Analytical Processes. 
 Collection of Samples. The same as directed on page 406. 
 
 Appearance in Two-foot Tube. The colour or tint of the water must 
 be ascertained, by examination, in a tube two feet long and two inches in 
 diameter. This tube should be made of glass as nearly colourless as may be, 
 and should be covered at each end with a disc of perfectly colourless glass, 
 cemented on, an opening being left for filling and emptying the tube. This 
 opening may be made, either by cutting a half-segment off' the glass disc at 
 one end, or by cutting a small segmental section out of the tube itself, before 
 the disc is cemented on. These tubes are most conveniently kept on hooks 
 in a horizontal position to prevent the entrance of dust. 
 
 The tube must be about half-filled with the water to be examined, brought 
 
92. ANALYTICAL PROCESSES FOR WATEU. 467 
 
 into a horizontal position level with the eye, and directed towards a well- 
 illuminated white surface. The comparison of tint has to be made between 
 the lower half of the tube containing the water under examination, and the 
 upper half containing atmospheric air only. 
 
 Smell. Put not less than three or four ounces of the water into a clean 
 eight-ounce wide-mouthed stoppered glass bottle, which has been previously 
 rinsed with the same water. Insert the stopper, and warm the water in a 
 water bath to 100 F. (38 C.). Remove the bottle from the water bath, rinse 
 it outside with good water perfectly free from odour, and shake it rapidly 
 for a few seconds ; remove the stopper, and immediately observe if the water 
 has any smell. Insert the stopper again, and repeat this test. 
 
 "When the water has a distinct odour of any known or recognized polluting 
 matter, such as peat or sewage, it should be so described ; when this is not 
 the case, the smell must be reported simply as none, very slight, slight, or 
 marked, as the case may be. 
 
 Chlorine. Titrate at least 100 c.c. or dm. of the water with the standard 
 silver nitrate solution, either in a white porcelain basin or in a glass vessel 
 standing on a porcelain slab, using potassic chromate as an indicator. The 
 titration is conducted as follows : The sample of water is measured into the 
 basin or beaker, and 1 c.c. or 1 dm. of potassic chromate solution added. 
 The standard silver nitrate solution is then run in cautiously from a burette, 
 until the red colour of the precipitated silver chromate, which is always 
 observed at the point where the silver solution drops in, is no longer entirely 
 discharged on stirring. The burette is then read off. It is best to repeat 
 the experiment, as follows : Add a few drops of dilute sodic chloride solution 
 to the water last titrated, which will discharge the red colour. Measure out 
 a fresh portion of the w r ater to be titrated into another basin, and repeat the 
 titration, keeping the first sample, the colour of which has been discharged, 
 side by side with the second, so as to observe the first permanent indication 
 of difference of colour. If the quantity of chlorine be so small that still 
 greater accuracy is necessary, the titration may be conducted in the same way 
 as last described, but instead of the operator looking directly at the water 
 containing the chromate solution, he may place between the basin containing 
 the water and his eye, a flat glass cell containing some water tinted with the 
 chromate solution to the same tint as the water which is being tested, or may 
 look through a glass coated with a gelatine film coloured with the same salt 
 (see 44) . Care must always be taken that the water is as nearly neutral 
 as possible before titration. If originally acid, it should be neutralized with 
 precipitated carbonate of lime. If the proportion of chlorine be less than 
 0*5 grain per gallon, it is desirable to take a larger quantity of the water, say 
 250 c.c. or 350 dm., for the estimation, and to concentrate this quantity on 
 the water bath before titrating it, so as to bring it to about 100 c.c. or 
 150 dm. This titration may be performed by gas-light. 
 
 Phosphoric Acid. The ignited total residue, obtained as hereafter 
 directed, is to be treated with a few drops of nitric acid, and the silica 
 rendered insoluble by evaporation to dryness. The residue is then taken 
 up with a few drops of dilute nitric acid, some water is added, and the 
 solution is filtered through a filter previously washed with dilute nitric 
 acid. The filtrate, which should measure 3 c.c. (or 5 dm.) is mixed with 
 3 c.c. of inolybdic solution, gently warmed, and set aside for fifteen minutes, 
 at a temperature of 80 F. The result is reported as "traces," "heavy 
 traces," or " very heavy traces," when a colour, turbidity, or definite 
 precipitate, are respectively produced, after standing for fifteen minutes. 
 Another method is given on page 441. 
 
 H H 2 
 
468 VOLUMETRIC ANALYSIS. 92. 
 
 Nitrogen in Nitrates. This may be determined by one of the following 
 processes: viz., Crum, Copper-zinc, Aluminium, or Indigo. Analysts should 
 report which process is employed. 
 
 Crum Process. This is described on page 430, or it may be carried out in 
 a Lunge's nitrometer as follows: 250 c.c. or dm. of the water must be 
 concentrated in a basin to 2 c.c. or. 3 dm. measure. A Lunge's nitrometer 
 is charged with mercury, and the three-way stop-cock closed, both to measuring 
 tube and waste pipe. The concentrated filtrate is poured into the cup at the 
 top of the measuring tube, and the vessel which contained it rinsed with 1 c.c. 
 of water, and the contents added. The stop-cock is opened to the measuring 
 tube, and, by lowering the pressure tube, the liquid is drawn out of the cup 
 into the tube. The basin is again rinsed with 5 c.c. of pure strong sulphuric 
 acid, and this is also transferred to the cup and drawn into the measuring 
 tube. The stop-cock is once more closed, and 12 c.c. more sulphuric acid put 
 into the cup, and the stop-cock opened to the measuring tube until 10 c.c. of 
 acid have passed in. The excess of acid is discharged, and the cup and waste 
 pipe rinsed with w r ater. Any gas which has collected in the measuring tube 
 is expelled by opening the stop-cock and raising the pressure tube, taking 
 care no liquid escapes. The stop-cock is closed, the measuring tube taken 
 from its clamp and shaken by bringing it slowly to a nearly horizontal 
 position, and then suddenly raising it to a vertical one. This shaking is 
 continued until no more gas is given off, the operation being, as a rule, 
 complete in fifteen minutes. Now prepare a mixture of one part of water 
 with five parts of sulphuric acid, and let it stand to cool. After an hour, 
 pour enough of this mixture into the pressure tube to equal the length 
 of the column of acidulated water in the working tube, bring the two tubes 
 side by side, raise or lower the pressure tube until the mercury is of the same 
 level in both tubes, and read off the volume of nitric oxide (for calculation 
 of nitrogen see page 262). This volume, expressed in c.c.'s and corrected to 
 normal temperature and pressure, gives, when multiplied by 0'175, the 
 nitrogen in nitrates, in grains per gallon, if 250 c.c. of the water have 
 been used. 
 
 Copper-zinc Process (already described on page 433). 
 
 Aluminium Process. This is carried out as follows: 50 c.c. or 100 dm. 
 of the water are introduced into a retort, and 50 c.c. or 100 dm. of a 10 per 
 cent, solution of caustic soda, free from nitrates, added. If necessary, the 
 contents of the retort should be distilled until the sample is free from 
 ammonia. The retort is then cooled, and a piece of aluminium foil 
 introduced into it. The neck of the retort is inclined upwards, and its 
 mouth closed with a perforated cork, through which passes the narrow end 
 of a small chloride of calcium tube filled with powdered pumice or glass 
 beads wetted with very dilute hydrochloric acid free from ammonia. This 
 tube is connected with a second tube containing pumice stone moistened 
 with strong sulphuric acid, which serves to prevent any ammonia from the 
 air entering the apparatus, which is allowed to stand in this way for a few 
 hours or overnight. The contents of the first absorption tube that next 
 the retort are washed into the retort with a little distilled water free from 
 ammonia, and the retort adapted to a condenser. The contents of the retort 
 are distilled to about half their original volume. The distillate is collected, 
 and an aliquot part Nesslerized; and, if necessary, the rest of the distillate 
 is diluted, and an aliquot part again Nesslerized as hereafter directed. 
 
 Indigo Process. An elaborate series of experiments made by "War in gt on 
 upon this method were described in a former edition of this book; but 
 experience has shown that the only method by which it can be made 
 serviceable in the case of waters is to have a solution of indigo carmine of 
 
92. ANALYTICAL PROCESSES FOE WATER. 469 
 
 good quality, which is standardized upon a very weak solution of potassic 
 nitrate. A definite volume of indigo must be used invariably, and the 
 water to be examined varied in quantity according to its contents of N 2 O 5 . 
 In this manner very excellent results may be obtained, but it must always 
 be remembered that the process is only accurate with moderate proportions 
 of nitrates, because any error is enormously multiplied when calculated 
 upon a liter or a gallon of water. 
 
 The process now to be described was in constant use in the laboratory of 
 the late Dr. Meymott Tidy, and Mr. J. E. Skelton, F.I.C., his chief 
 assistant for some years, has kindly given me several details of the process 
 as worked by him under Dr. Tidy's direction. I have also found this 
 modification very serviceable for the rapid estimation of nitrates in ordinary 
 potable Avaters. 
 
 Standardizing the Indigo. 10 c.c. of the standard nitrate (p. 464) are run 
 into a thin flask holding about 150 c.c., then 10 c.c. of indigo. 20 c.c. of 
 sulphuric acid are then quickly added from a graduated measure, and a rotary 
 motion given to the flask to mix the liquids the flask is then quickly held 
 over a spirit lamp or small rose gas burner to maintain the heat. 
 
 If the indigo is at once decolorized, more is run in with constant heating, 
 until, after heating for about thirty seconds, a persistent greenish colour is 
 noted. From the number of c.c. of indigo decolorized the necessary degree 
 of dilution is calculated, and must always be made with the five per cent, 
 sulphuric acid, and not with plain water. Fresh trials are made in the same 
 manner until the strength of the indigo is accurately determined. 
 
 Process for Nitrates in water. A trial titration is first made by taking 
 10 c.c. of the water, adding indigo, then strong sulphuric acid in volume 
 equal to the united volumes of indigo and water, and heating exactly as in 
 standardizing the indigo. This first titration will show how much the water 
 under examination must be diluted, so that it may contain nitric acid 
 approximately equal to the roW potassic nitrate. After the water has been 
 diluted with distilled water free from nitrates or nitrites, fresh titrations are 
 made as before described until the exact number of c.c. of indigo decolorized 
 by 10 c.c. of the diluted water is known. In all cases it is important to 
 work to the same shade of greenish colour, after heating for thirty seconds, 
 as was obtained in the original standardizing of the indigo. The colour of 
 the oxidized indigo by itself should be a clear yellow. 
 
 Ammonia, Free and Saline. The estimation of ammonia present in 
 the water in a free or saline form, and of that }delded by the nitrogenous 
 matter present in the water (commonly called albuminoid ammonia), is to be 
 made on the same portion of the sample to be analyzed. 
 
 Take not less than 500 c.c. or 700 dm. (one deci-gallon) of the water for 
 these determinations, and distil in a 40-oz. stoppered retort, which is large 
 enough to prevent the probability of portions of the water being spirted 
 over into the condenser. The neck of the retort should be small enough to 
 pass three or four inches into the internal glass tube of a Liebig's 
 condenser. If the fit between the retort and the inside tube of the 
 condenser is good, the joint may be made by wrapping a small piece of 
 washed tinfoil round the retort tube so as to pass just inside the mouth of 
 the condenser tube. Many analysts prefer, however, to work with a retort 
 fitting loosely into the condenser ; and, in such cases, the joint between the 
 two may be made in one of the two following ways: (1) Either by an 
 ordinary india-rubber ring such as those used for the top of umbrellas 
 which has been previously soaked in a dilute solution of soda or potash 
 being stretched over the retort tube in such a position, that when the retort 
 tube is inserted in the condenser it shall fit fairly tightly within the mouth 
 
470 VOLUMETRIC ANALYSIS. 92. 
 
 of the tube, about half-an-inch from the end : (2) Preferably, when the 
 shape of the large end of the condenser admits of it, by a short length, say 
 not more than two inches, of large size india-rubber tubing, which has been 
 previously soaked in a dilute solution of soda or potash, being stretched 
 outside both retort tube and condenser tube, so as to couple them together, 
 so that the tube of the retort still projects some inches into that of the 
 condenser. It is very desirable to have a constant stream of water round 
 the condenser, whenever it can be obtained. Before distillation, a portion 
 of the water must be tested with cochineal, in order to ascertain if it shows 
 an alkaline reaction. The portion so tested must, of course, be rejected, 
 and not put into the retort. If the water does not show an alkaline 
 reaction, a sufficient quantity of ignited sodic carbonate, to render the water 
 distinctly alkaline, must be added. The distillation should then be com- 
 menced, and not less than 100 c.c. or 150 dm. distilled over. The receiver 
 should fit closely, but not air-tight, on the condenser. The distillation 
 should be conducted as rapidly as is compatible with a certainty that no 
 spirting takes place. After 100 c.c. or 150 dm. have been distilled over, the 
 receiver should be changed, that containing the distillate being stoppered to 
 preserve it from access of ammoniacal fumes. 100 c.c. measuring flasks 
 make convenient receivers. The distillation must be continued until 50 c.c., 
 or say 75 dm. more, are distilled over ; and this second portion of the 
 distillate must be tested with Nessler's reagent, to ascertain if it contains 
 any ammonia. If it does not, the distillation for free or saline ammonia 
 may be discontinued, and this last distillate rejected ; but if it does contain 
 any, the distillation must be continued still longer, until a portion of 50 c.c., 
 or 75 dm., when collected, shows no colouration with the Nessler test. 
 The whole of the distillates must be Nesslerized as follows : The standard 
 solution of ammonia for comparison is that given on page 465. The 
 distillate is transferred to a clean Nessler glass, and one-twentieth of its 
 volume of Nessler solution added. No turbidity must ensue on the 
 addition of the Nessler solution to the water, as such turbidity Avould 
 be a proof that the distillate was contaminated by reason of spirting, and 
 must, therefore, be rejected, and the determination repeated. 
 
 After thoroughly mixing the water and Nessler solution in the glass, an 
 approximate estimate can be formed of the amount of ammonia present, by 
 the amount of colouration produced in the solution. It will now be neces- 
 sary to mix one or more standard solutions with which to compare the tint 
 thus obtained. These solutions must be made by mixing the standard 
 solution of ammonic chloride with distilled water absolutely free from 
 ammonia, and subsequently adding some of the same Nessler solution as 
 was previously added to the distillate. This precaution is essential, because 
 the tint given by different samples of Nessler solution varies. 
 
 Albuminoid Ammonia. As soon as the distillation of the free ammonia 
 has been started, the alkaline solution of permanganate should be measured 
 out into a flask, ready for addition to the water under examination, for the 
 distillation of the albuminoid ammonia. The volume of the alkaline 
 permanganate solution to be taken must be at least one-tenth of that of the 
 water which is being distilled ; and should not exceed that proportion unless 
 the water is of very bad quality, and the solution must be made in 
 accordance with the directions contained in these instructions. This 
 solution must be diluted with four times its own volume of water, and must 
 be placed in a flask and boiled during the whole time that the distillation 
 of the sample for free ammonia is being carried on, care being taken that 
 the concentration does not proceed to too great an extent. There must be 
 enough of this boiled and diluted alkaline permanganate solution to make 
 up the residue in the retort to about 500 c.c. or 700 dm. When the 
 distillation of the sample of water for free and saline ammonia is completed, 
 
92. ANALYTICAL PROCESSES FOR WATER. 471 
 
 the alkaline permanganate solution, which has been thus diluted and 
 boiled, will be ready for use, and the distillation for albuminoid ammonia 
 may be proceeded with, as follows : 
 
 To the residue left in the retort from which the free ammonia has been 
 distilled, add the alkaline permanganate solution to make it up again to 
 a volume of at least 500 c.c., or say 700 dm., and the lamp being replaced, 
 the distillation must be continued, and successive portions of the distillate 
 again collected in precisely the same way as during the process of distillation 
 for free ammonia. 
 
 After 200 c.c. or 300 dm., say two-fifths of the volume contained in the 
 retort, have been distilled over, the receiver should be changed, and further 
 portions of 50 c.c. or 75 dm. collected separately, until the distillate is 
 practically free from ammonia. The distillate must then be mixed, and 
 Nesslerized in the same way as previously directed for free ammonia. The 
 result so obtained must be calculated to ammonia in grams per liter or 
 grains per gallon, and returned as albuminoid ammonia. 
 
 Special care must be taken that the atmosphere of the room in which, 
 these distillations are performed is kept free from ammoniacal vapours, and 
 that the receivers fit close, but not air-tight, to the end of the Liebig's 
 condenser. It is also specially necessary to observe that the colour of the 
 distillate deepens gradually after the addition of the Nessler reagent, and 
 that it is not possible to read off the amount of colour correctly until the 
 Nesslerized liquor has stood for at least three minutes, and been intimately 
 mixed with the Nessler solution (see also note, page 408). 
 
 Special care must be taken that the retort, condensers, receivers, funnels, 
 Nessler glasses, etc., used are all rendered perfectly free from ammonia 
 before use'. Where the water in use in the laboratory is good, this ma} r be 
 used to thoroughly rinse the apparatus two or three times, draining out the 
 adhering water ; otherwise pure distilled water must be used. These 
 ammonia and albuminoid ammonia determinations should be made as soon 
 as possible after the water has been received for analysis. 
 
 Oxygen Absorbed. Two separate determinations have to be made, viz., 
 the amount of oxygen absorbed during fifteen minutes, and that absorbed 
 during four hours. Both are to be made at a temperature of 80 E. (27 C.). 
 It is most convenient to make these determinations in 12-oz. stoppered flasks, 
 which have been rinsed with sulphuric acid and then with water. Put 
 250 c.c. or dm. into each flask, which must be stoppered and immersed in 
 a water bath or suitable air bath until the temperature rises to 80 P. Now 
 add to each flask 10 c.c. or 10 dm. of the dilute sulphuric acid, and then 
 10 c.c. or 10 dm. of the standard permanganate solution. Fifteen minutes 
 after the addition of the permanganate, one of the flasks must be removed 
 from the bath and two or three drops of the solution of potassic iodide added 
 to remove the pink colour. After thorough admixture, run from a burette 
 the standard solution of thiosulphate, until the yellow colour is nearly 
 destroyed, then add a few drops of starch indicator, and continue the 
 addition of the thiosulphate until the blue colour is just discharged. If the 
 titration has been properly conducted, the addition of one drop of 
 permanganate will restore the blue colour. At the end of four hours 
 remove the other flask, add potassic iodide, and titrate with thiosulphate, as 
 just described. Should the pink colour of the water in the flask diminish 
 rapidly during the four hours, further measured quantities of the standard 
 solution of permanganate must be added from time to time so as to keep it 
 markedly pink. 
 
 The thiosulphate solution must be standardized, not only at first, but 
 (since it is liable to change) from time to time in the following way : To 
 250 c.c. or dm. of pure redistilled water add two or three drops of the solution 
 of potassic iodide, and then 10 c.c. or dm. of the standardized solution of 
 
472 VOLUMETRIC ANALYSIS. 92. 
 
 permanganate. Titrate with the thiosulphate solution as above described. 
 The quantity used will be the amount of thiosulphate solution corresponding 
 to 10 c.c. or 10 dm., as may be, of the standardized permanganate, and the 
 factor so found must be used in calculating the results of the thiosulphate 
 titrations to show the amount of the standard permanganate solution used y 
 and thence the amount of oxygen absorbed. 
 
 Great care should be taken that absolutely pure and fresh distilled water 
 is used in standardizing the solution, which should also be kept in the dark 
 and cool. It suffices to compare the solution, if kept in this way, once in 
 three or four days. 
 
 The amount of thiosulphate solution thus found to be required to combine 
 with the iodine liberated by the permanganate left undecomposed in th& 
 water is noted down, and the calculation made as follows : Let A = amount 
 of thiosulphate used in distilled water, and B = that used for water under 
 examination. Then A expresses the amount of permanganate added to the water 
 under examination, and B the amount of permanganate in excess of that which 
 the organic matter in the water has destroyed. Therefore A B is the amount 
 actually consumed. If the amount of available oxygen in the quantity of 
 permanganate originally added be a, the oxygen required to oxidize the 
 
 organic matter in the water operated on would be --*. "^ ut a ( ava ^ a ^ e 
 
 oxygen in the 10 c.c. of standard permanganate used) =0'001. Therefore, 
 A B x 001 A B x 0-4 
 
 T = oxygen for 250 c.c.; or, r = parts of oxygen 
 
 required for 100,000 parts of water. Or, in other words, the difference 
 between the quantity of thiosulphate used in the blank experiment and 
 that used in the titration of the samples of water multiplied by the amount 
 of available oxygen contained in the permanganate added, and the product 
 divided by the volume of thiosulphate corresponding to the latter, is equal 
 to the amount of oxygen absorbed by the water. 
 
 Hardness before and after Boiling-. Place 100 c.c. or 100 dm. of the- 
 water in an accurately stoppered 8-oz. flask. Run in the soap solution from 
 a burette in small quantities at a time. If the water be soft, not more than 
 ^ c.c. or dm. at a time ; if hard, in quantities of 1 c.c. at first. After each 
 addition, shake the flask vigorously for about a quarter of a minute. As 
 soon as a lather is produced, lay the flask on its side after each addition, and 
 observe if the lather remains permanent for five minutes. To ascertain this, 
 at the end of five minutes roll the flask half-wa} r round ; if the lather breaks, 
 instead of covering the whole surface of the water, it is not permanent ; if 
 it still covers the whole surface it is permanent ; now read the burette. 
 
 Repeat the experiment, adding gradually the quantity of soap solution 
 employed in the first experiment, less about 2 c.c. or 2 dm. ; shake as before, 
 add soap solution very gradually till the permanent lather is formed : read 
 the burette, and take out the corresponding hardness from the table. If 
 magnesian salts are present in the water the character of the lather will be 
 very much modified, and a kind of scum (simulating a lather) will be seen 
 in the water before the reaction is completed. The character of this scum 
 must be carefully watched, and the soap test added more carefully, with an 
 increased amount of shaking between each addition. With this precaution 
 it will be comparatively easy to distinguish the point when the false lather 
 due to the magnesian salts ceases, and the true persistent lather is produced- 
 
 If the water is of more than 16 of hardness, mix 50 c.c. or dm. of the 
 sample with an equal volume of recently boiled distilled water which has- 
 been cooled in a closed vessel, and make the determination on this mixture 
 of the sample and distilled water. In this case it will, of course, be- 
 necessary to multiply the figures obtained from the table by 2. 
 
 To determine the hardness after boiling, boil a measured quantity of tk* 
 
92. REPORTING RESULTS OF WATER ANALYSIS. 473 
 
 water in a flask briskly for half an hour, adding distilled water from time to 
 time to make up for loss by evaporation. It is not desirable to boil the water 
 under a vertical condenser, as the dissolved carbonic acid is not so freely 
 liberated. At the end of half an hour, allow the water to cool, the mouth 
 of the flask being closed ; make the water up to its original volume with 
 recently boiled distilled water, and, if possible, decant the quantity necessary 
 for testing. If this cannot be done quite clear, it must be filtered. Conduct 
 the test in the same manner as described above. 
 
 The hardness is to be returned in each case to the nearest half-degree. 
 
 Total Solid Matters. Evaporate 250 c.c. or ^th of a gallon, in 
 a weighed platinum dish on a water bath ; dry the residue at 220 I\ 
 (104 C.), and cool under a desiccator. Weigh the dish containing the 
 residue accurately, and note its colour and appearance, and especially 
 whether it rapidly increases in weight. Return to the water bath for 
 half an hour and re-weigh until it ceases to lose weight, then graduallj' 
 heat it to redness, and note the changes which take place during this 
 ignition. Especially among these changes should be observed the smell,. 
 scintillation, change of colour, separation of more or less carbon, and partial 
 fusion, if any. The ignited residue is to be used for the estimation of 
 phosphoric acid, as before directed. 
 
 Microscopical Examination of Deposit The most convenient plan 
 of collecting the deposit is to place a circular microscopical covering glass at 
 the bottom of a large conical glass holding about 20 oz. The glass should 
 have no spout, and should be ground smooth on the top. After shaking up 
 the sample, this vessel is filled with the water, covered with a plate of ground 
 glass, and set aside to settle. After settling, the supernatant water is drawn 
 off by a fine syphon, and the glass bearing the deposit lifted out, either by 
 means of a platinum wire (which should have been previously passed under 
 it), or in some other convenient way, and inverted on to an ordinary 
 microscopical slide for examination. It is desirable to examine the deposit 
 first by a |th and then bya^th objective. The examination should be made 
 as soon as the water has stood overnight. If the water be allowed to stand 
 longer, organisms peculiar to stagnant water may be developed and mislead 
 the observer. Particular notice should be taken of bacteria, infusoria, ciliata 
 or flagellata, disintegrated fibres of cotton, or linen, or epithelial debris. 
 
 It is particularly desirable to report clearly on this microscopical 
 examination ; not merely giving the general fact that organisms were 
 present, but stating as specifically as possible the names or classes of the 
 organisms, so that more data may be obtained for the application of the 
 examination of this deposit to the characters of potable waters. 
 
 It is also desirable to examine the residue left on a glass slide by the 
 evaporation of a single drop of the water. This residue is generally most 
 conveniently examined without a covering glass. The special appearances 
 to be noticed are the presence or absence of particles of organic matter, or 
 organized structure, contained in the crystallized forms which may be seen ; 
 and also whether any part of the residue left, especially at the edges, is 
 tinted more or less with green, brown, or yellow. 
 
 Reporting: the Results of Water Analysis. The Report of the 
 Committee appointed by the British Association to confer with the Committee 
 of the American Association with a view of forming a uniform system of 
 recording results of Water Anatysis, B. A. Meeting, 1889 (Chem. News. 
 60, 203204) is as follows: The committee recommend a system of 
 statement for a complete analysis of which the following is an epitome. 
 Results to be expressed in parts per 10(),COO. In a potable water, the numbers- 
 to be given in the following order : Total solid matters (a) in suspension,. 
 (b) in solution ; organic carbon ; organic nitrogen ; oxygen consumed, as- 
 
474 VOLUMETRIC ANALYSIS. 93. 
 
 indicated by decoloration of permanganate ; ammonia expelled on boiling 
 with sodic carbonate; ammonia expelled on boiling with alkaline perman- 
 ganate ; nitrogen as nitrates and nitrites ; chlorine ; hardness- temporary, 
 permanent, total. In a mineral Avater carbonate of lime; carbonate of 
 magnesia ; carbonate of soda (calculated from residual alkalinity after 
 boiling and filtering off precipitated CaCO 3 and MgCO 3 ) ; total of each 
 of the following elements calcium, magnesium, potassium, sodium, iron 
 (ferrous), iron (ferric), and each of the following radicles sulphuric (SO 4 ), 
 nitric (NO 3 ), nitrous (NO 2 ), phosphoric (PO 4 ), silicic (SiO 3 ) ; then each of 
 the elements chlorine, bromine, and iodine, and of sulphur as sulphide. 
 Dissolved gases : c.c. at C. and 760 m.m. in 1 liter of water. Carbonic 
 anhydride (CO 2 ) ; oxygen ; nitrogen ; sulphuretted hydrogen. 
 
 They consider that this uniform method should be adopted in all cases 
 where communications come before learned bodies and Avhenever possible in 
 professional practice ; that the decimal numerical notation is to be preferred ; 
 that the different scales for potable and mineral waters suggested by the 
 American Committee are undesirable ; that all results obtained by calculation 
 should be sharply distinguished from those obtained by direct determination ; 
 that a statement of mineral constituents combined as salts is not to be 
 approved of unless the analytical data upon which it is based are clearly 
 stated ; that the American Committee's suggestion of recording the proportion 
 of each element of binary compounds, and recording all the oxygen in 
 oxy-compounds in combination with the negative element, as indicated 
 above, is the most convenient for all purposes of calculation, although the 
 want of a name for these negative groups and the custom of quoting 
 metallic elements as bases are objections to this system ; finall} r , that volumes 
 of dissolved gases may be given as above, or in volumes of gas per 100 
 volumes of water. 
 
 OXYGEN DISSOLVED IN WATERS. 
 
 93. The necessary apparatus and standard solutions for 
 carrying out this estimation are described in 71 (page 269), 
 together with the methods of manipulation. 
 
 The interpretation of the results as regards polluted waters, as 
 given by Dupre, may be summarized as follows : 
 
 The method depends on the fact that, if a perfectly pure water is 
 once fully aerated, and then kept in a bottle so that it could neither 
 lose nor gain oxygen, it would remain fully aerated for any length 
 of time ; but, on the other hand, if the water contained living 
 organic matters capable of absorbing oxygen, such water would after 
 a period of time contain less oxygen, the loss so found being taken 
 as the measure of impurity. The method is really another form of 
 ascertaining the presence of germs and their amount in contrast to 
 the method of cultivation by gelatine and microscopic analysis. 
 
 The practical results from various experiments made by Dupre, 
 and reported by him to the Medical Department of the Local 
 Government Board, 1884, are as follows : 
 
 (1) A water which does not diminish in its degree of aeration during 
 a given period of time, may or may not contain organic matter, but 
 presumably does not contain growing organisms. Such organic matter 
 therefore as it may be found to contain by chemical analysis (permanganate 
 or otherwise) need~ not be considered as dangerous impurity. 
 
 (2) A water which by itself, or after the addition of gelatine or other 
 
93. OXYGEN IN WATEKS. 475 
 
 appropriate cultivating matter, consumes oxygen from the dissolved air at 
 lower temperatures, but does not consume any after heating for say three 
 hours at 60 C., may be regarded as having contained living organisms, but 
 none of a kind able to survive exposure to that temperature. 
 
 (3) A water which by itself, or after addition of gelatine or the like, 
 continues to absorb oxygen from its contained air after heating to 60 C.,may 
 be taken as containing spores or germs able to survive that temperature. 
 
 The exact nature of organisms differing in this way is of course 
 not revealed by the method. D up re's conclusion is, that in the 
 vast majority of cases the consumption of oxygen from the dissolved 
 air of a natural water is due to growing organisms, and that in the 
 complete absence of such . organisms little or no oxygen would 
 be then consumed. 
 
 The paper is accompanied by tables of results of analysis by this 
 and other methods, which are too voluminous to insert here. 
 
 Principle of the method. Dupre states that a water, fully aerated, 
 contains at 20 C. and 760 m.m. pressure 0'594 grain of oxygen per gallon, 
 or 0'04158 gm. per liter.* The proportion varies with the temperature and 
 pressure. The formula given by Bunsen is adopted in this method 
 
 a=2'0225 j8 ; and j8=0 ; 020346 - 0'00052887^+p-000011156^ ; 
 \vhere a is the co-efficient of absorption of oxygen in cubic centimeters, 
 ,/3 the co-efficient for absorption of nitrogen, and t the temperature. 
 
 The variation due to atmospheric pressure is so slight that it 
 may practically be disregarded. The composition of air is taken as 
 2 1 volumes oxygen and 7 9 nitrogen. Dupre adopts the temperature 
 of 20 C. for all waters under experiment; and as a rule the 
 samples were all placed in an appropriate bottle, and kept at 
 a constant temperature of 20 C. for ten days previous to the 
 estimation of the oxygen. 
 
 The maximum degree of oxygen which a pure water should 
 contain at this temperature is called 100, and any less degree found 
 on analysis is recorded as a percentage of this maximum. 
 
 Process: The sample of water is placed in an ordinary bottle, and 
 vigorously shaken to ensure full aeration ; after standing the requisite time 
 it is poured into the experimental bottle, and the estimation of oxygen 
 carried out as described in 71. 
 
 * R o s c o e and L u n t , and also D i 1 1 in a r , show by their experiments that these 
 figures are too low. 
 
476 VOLUMETRIC ANALYSIS. 93. 
 
 Calculation of the Results of Water Analysis. 
 
 Substance estimated. 
 
 Measure of water 
 taken. 
 
 Volume or weight 
 obtained or used. 
 
 Factor for grains per 
 gallon. 
 
 Cl 
 
 100 c.c. or dm. . 
 
 f c.c. or dm. stan- ) 
 ( dard AgNO 3 ) 
 
 x 0-7 =C1 
 
 ... 
 
 140 dm. (-^-gal.) 
 
 dm. 
 
 x 0-5 =C1 
 
 N as HNO 3 ( 
 (Crum) J 
 
 250 c.c. . 
 250 dm. . 
 
 c.c. of NO 
 
 55 J5 
 
 55 5> 
 
 x 0-175 =N 
 x 0'27 =N 
 x 0-193 =N 
 
 f 
 
 100 c.c.' w '. 
 
 grams of NH 3 
 
 x 576-45 =N 
 
 NH 3 copper-zinc N 
 
 50 c.c. . 
 
 yy 39 
 
 x 1152-9 =N 
 
 or aluminium 1 
 
 150 dm. . 
 
 grains of NH 3 
 
 x 38-43 =N 
 
 (_ 
 
 100 dm. . 
 
 55 55 
 
 x 57-64 =N 
 
 Free or Alb. NH 3 
 
 500 c.c. . 
 
 f c.c. standard ") 
 I NH 4 C1 ) 
 
 x 00014=NH 3 
 
 55 }> 55 
 
 700 dm. . 
 
 dm. 
 
 x OO'l =NH 3 
 
 O absorbed . 
 
 250 c c. . 
 
 C 10, 15, or 20 c.c. ) 
 ( permanganate ) 
 
 ( x 0'28(lorl-5or 
 ) 2-#' -0 
 
 
 350 dm. 
 
 f 10, 15, or 20 dm. } 
 
 C x 0'02 (lor 1-5 or 
 
 55 5> 55 
 
 
 ^ permanganate ) 
 
 / 2 *) = O 
 
 Total solids . 
 
 250 c.c. . 
 
 grams 
 
 x 280-0 
 
 
 
 350 dm. . 
 
 grains 
 
 x 20-0 
 
 Coefficients and Logarithms for Volumetric Analysis. 
 
 Coefficients. 
 
 Logarithms. 
 
 Normal H-SO 4 1 c.c.=0'049 gm. H 2 S0 4 
 
 ... 2-6901961 
 
 =0-048 SO 4 
 
 ... 2-6812412 
 
 0-040 SO 3 
 
 ... 2-6020600 
 
 Normal HC1 1 c.c.=0'0365 HC1 
 
 ... 2-5622929 
 
 =0-0355 Cl 
 
 ... 2-5502284 
 
 Normal HNO 3 1 c.c.=0'063 HNO 3 
 
 ... 2-7993405 
 
 =0-062 NO 5 
 
 ... 5-7923917 
 
 =-0-054 N 2 O 5 
 
 ... 2-7323938 
 
 Normal H 2 C 2 4 1 c.c.=0'063 H 2 C 2 O 4 , 20H 2 
 
 ... 2-7993405 
 
 0-045 , H 2 C 2 O 4 
 
 ... 2-6532125 
 
 Normal Acid 1 c.c.=0'0l7 
 
 , NH 3 
 
 ... 2-2304489 
 
 =0-035 
 
 , NH 4 HO .. 
 
 ... 2-5440680 
 
 
 =0-J91 
 
 , Na 2 B 2 O'10H-O 
 
 ... 1-2810334 
 
 
 =0-037 , 
 
 , Oa2HO 
 
 ... 2-5682017 
 
 
 =0-028 
 
 , CaO 
 
 ... 2-4471580 
 
 
 =0-05 
 
 , CaCO 3 
 
 ... 2-6989700 
 
 
 =0-0855 
 
 , BaH-0 2 ... 
 
 ... 2-9319661 
 
 
 =0-1575 
 
 , BaH 2 O 2 8H 2 O 
 
 ... 1-1972806 
 
 
 =0-0985 
 
 , BaCO 3 
 
 ... 2-9934362 
 
 
 =0-02 
 
 , MgO 
 
 ... 2-3010300 
 
 
 =0-042 
 
 , MgCO 3 
 
 ... 2-6232493 
 
 ' =0-056 
 
 , KHO 
 
 ... 2-748188O 
 
 =0-069 
 
 , K 2 CO 3 
 
 ... 2-8388491 
 
 =0-188 
 
 , KHC 4 H 4 O fi ... 
 
 ... 1-2741578 
 
 * A c.c. or dm. of tniosulphate solution corresponding to 10 c.c. or dm. of perman- 
 ganute. B=c.c. or dm. of thiosulpbate solution used after the time of reaction is 
 complete. 
 
93. 
 
 COEFFICIENTS. 
 
 Normal Acid 
 
 Normal NaHO 
 Normal KHO 
 Normal Na 2 C0 3 
 
 Normal Alkali 
 
 Silver 
 
 i^j- Iodine 
 
 Bichromate 
 
 i o 
 
 Thiosulphate 
 
 gm. 
 
 KC 2 H 3 2 ... 
 
 KNaC 4 H 4 O 6 
 
 NaHO 
 
 Na 2 C0 3 
 
 Na 2 C0 3 10H 2 O 
 
 NaHCO 3 ... 
 
 NaHO 
 
 Na 2 O 
 
 KHO 
 
 K 2 
 
 Na 2 CO 3 
 
 CO 3 
 
 CO 2 
 
 IIC 2 H 3 O 2 ... 
 
 H 3 C 6 H 5 O 7 H 2 O 
 
 HC1 
 
 HB 2 ...... 
 
 HI 
 
 HNO 3 
 
 H 2 S0 4 
 
 Coefficients. 
 1 c .c.=0-102 
 
 M =0-098 
 
 =0-141 
 
 =0-04 
 
 =0-053 
 
 -0-143 
 
 =0-084 
 1 c.c.=0'040 
 
 =0-031 
 1 c.c.=0'056 
 
 =0-047 
 1 c.c.=0'053 
 
 =0-030 
 
 =0-022 
 1 c .c.=0-06 
 
 =0-07 
 
 =0-0365 
 
 }} =0-0808 
 
 =0-0128 
 
 =0-063 
 
 =0-049 
 
 =0-075 
 1 c.c.=0'0108 
 
 =0-017 
 
 =0-00355 
 
 =0-00535 
 
 =0-00745 
 
 =0-0119 
 
 =0-0103 
 
 =0-0064 
 1 c.c.=0'0032 
 
 =0-0041 
 
 =0-00495 
 
 =0-0248 
 
 =0-0126 
 
 =0-0097 
 1 c.c.=0'0456 
 
 =0-051 
 
 =0-0849 
 
 =0-0348 
 
 =0-0696 
 
 =0-0216 
 1 c.c.=0'0248 
 
 =0-0127 
 
 =0-00355 
 
 =0-0080 
 CALCIUM (Ca=40) 
 
 1 c.c. yV permanganate=0'0028 gm. CaO 
 
 =0-0050 gm. CaCO 3 ... 
 =0-0086 gm. CaSO 4 , 2OH 2 
 normal oxalic acid=0'0280 gm. CaO ... 
 
 Cryst. oxalic acid x G'444 =CaO 
 
 Double iron salt xO'07143=CaO 
 
 Ag ...... 
 
 AgNO 3 
 
 Cl ...... 
 
 NH 4 C1 
 
 KC1 ...... 
 
 KBr ...... 
 
 NaBr 
 
 Na 2 HAs0 4 ... 
 SO 2 ...... 
 
 H 2 S0 3 
 
 As 2 3 
 
 Na 2 S 2 O 3 5H 2 O 
 
 Na 2 S0 3 7H 2 
 
 K 2 S0 3 2H 2 
 
 FeSO 4 
 
 Fc 2 S0 4 H 2 0... 
 
 FeSO 4 7H 2 O... 
 
 FeCO 3 
 
 Fe 3 4 
 
 FeO ...... 
 
 Sodic thiosulphate 
 
 Cl 
 Br 
 
 477 
 
 Logarithms. 
 1-0086002 
 2-9912261 
 1-1492191 
 2-6020600 
 2-7242759 
 1-1553660 
 2-9242793 
 2-6020600 
 2-4913617 
 27481880 
 2-6720979 
 2-7242759 
 2-4771213 
 2-3424227 
 2-7781513 
 2-8450980 
 2-5622929 
 2-9074114 
 1-1072100 
 2-7993405 
 2-6901961 
 2-8750613 
 2-0334238 
 2-2304489 
 3-5502284 
 3-7283538 
 3-8721563 
 2-0755470 
 2-0128372 
 3-8061800 
 3-5051500 
 3-6127839 
 3-6946052 
 2-3944517 
 2-1003705 
 3-9867717 
 2-6589648 
 2-7075702 
 2-9289077 
 2-5415792 
 2-8426092 
 2-3344538 
 2-3944517 
 2-1038037 
 3-5502284 
 3-9030900 
 
 3-4471580 
 3-6989700 
 3-9344985 
 2-4471580 
 1-6473830 
 2-8538807 
 
 CHLOEINE (Cl=35'37) 
 
 1 c.c. T ^ silver solution=0'003537 gm. Cl 
 
 =0-005837 gm. NaCl 
 
 arsenious or thiosulphate solutiou=0'003537 gm. Cl. 
 
 3-5486351 
 3-7661897 
 3-5486351 
 
478 
 
 VOLUMETRIC ANALYSIS. 
 
 93. 
 
 CHROMIUM (Cr=52'4) Logarithms. 
 
 Metallic iron x 0'3123 =Cr 1-4945720 
 
 xO'5981=CrO 3 1*7767738 
 
 x 0'8784=K 2 Cr 2 O 7 1'9436923 
 
 x 1-926 =PbCrO 4 0-2846563 
 
 Double iron salt x 0'0446=Cr 2'6493349 
 
 xO'0854=CrO 3 2'9314579 
 
 x 0-1255=K 2 Cr 2 O" 1-0986437 
 
 x 0-275 =PbCrO 4 1'4393327 
 
 1 c.c. tV solution=0'003349 gm. CrO 3 S'5249151 
 
 =0-00492 gm. K-Cr 2 7 3'6919651 
 
 COPPER (Cu=63) 
 
 1 c.c. T \ solution=0'0063 gm. Cu 3"'7993405 
 
 Ironx T125=copper 0'0511525 
 
 Double iron salt xO'1607=copper 1-2060159 
 
 CYANOGEN (CN=26) 
 
 1 c.c. T N 7 silver solution=0'0052 gm. CN 
 
 =0-0054 gm. HCN 
 
 =0-01302 gm. KCN 
 
 i^ iodine =0'003255 gm. KCN 
 
 POTASSIC FERROCYANIDE (K 4 FeCy 6 , 30H 2 =422) 
 
 Metallic iron x 7'541=cryst. potassic ferroc} r auide ... 
 Double iron salt x 1-077= 
 
 POTASSIC FERBICYANIDE (K 6 Fe 2 Cy 12 =658) 
 
 Metallic iron x 5'88 =potassic ferricyanide 
 
 Double iron salt x 1*68 = 
 
 :nj- thiosulphate xO'0329= 
 
 GOLD (Au=196-5) 
 
 1 c.c. normal oxalic acid=0"0655 gm. gold 
 
 IODINE (1=127) 
 
 1 c.c. *f thiosulphate=0-0127 gm. iodine 
 
 IRON (Fe=56) 
 
 1 c.c. T ^ permanganate, bichromate,, or thiosulphate 
 
 =0-0056 Fe 
 
 ,, =0-0072 FeO 
 
 =0-0080 Fe 2 a 
 
 LEAD (Pb=206'4) 
 
 1 c.c. YT5- permanganate =0'01032 gm. lead 
 1 c.c. normal oxalic acid=0'1032 gm. lead 
 
 Metallic iron x l'842=lead 
 
 Double iron salt x 0'263=lead 
 
 3-7160033 
 3-7323938 
 2-1146110 
 3-5125510 
 
 0-8774289 
 0-0322157 
 
 0-7693773 
 0-2253093 
 2-5171959 
 
 2-8162413 
 2-1020905 
 
 3-7481880 
 3-8573325 
 3-9030900 
 
 2-0136797 
 1-0136797 
 0-2652896 
 1-4199557 
 
 MANGANESE (Mn=55) 
 
 MnO=7l. Mn0 2 =87. 
 
 Metallic iron x 0-491 =Mn 1*6910815 
 
 xO'63393=MnO 1-8020413 
 
 x 0-7768 =MnO 2 1-8903092 
 
 Double iron salt x 0-09 11 =MnO 2-9595184 
 
 x O'lll =MnO 2 1-0453230 
 
 Cryst, oxalic acid x 0'6916=MnO 2 1-8398550 
 
 1 c.c. ^5- solution=0'00355 gm. MnO 3-5502284- 
 
 =0-00435 gm. MiiO- 3'6384893 
 
93. COEFFICIENTS. 479 
 
 MERCURY (Hg=200) Logarithms. 
 
 Double iron salt xO'5104=Hg 17079107 
 
 x 0'6914=HgCl 2 1-8397294 
 
 1 c.c. & solution=0-0200 gm. Hg 2-3010300- 
 
 =0-0208 gm. Hg 2 O 2-3180633- 
 
 =0-0271 gm. HgCl 2 2-4329693 
 
 NITROGEN AS NITRATES AND NITRITES (N 2 O 5 =108. N 2 O 3 =76) 
 
 Normal acidxO'0540=N 2 O 5 2'7323938 
 
 xO'1011=KNO 3 1-0047512 
 
 Metallic iron xO-3750=HNO 3 1-5740313 
 
 xO-6018=KNO 3 1-7794522 
 
 xO'3214=N 2 O 5 1-5070459 
 
 SILVER (Ag=107-66) 
 
 1 c.c. T N NaCl=0'010766 gm. Ag 2*0320544 
 
 =0-016966 gm. AgNO 3 , 2'2295795- 
 
 SULPHURETTED HYDROGEN (H 2 S=34) 
 
 1 c.c. ^3- arsenious solution=0'00255 gm. H 2 S S'4065402 
 
 TIN (Sn=118) 
 
 Metallic iron x r0536=tin 0'0226758- 
 
 Double iron salt xO'1505=tin T1775365 
 
 Pactor for T ^ iodine or permanganate solution 0'0059... ... 3-7708520- 
 
 ZINC (Zn=65) 
 
 Metallic iron x 0'5809=Zn 1-7641014 
 
 x 0*724 =ZnO ... 1-8597386 
 
 Double iron salt x 0'08298=Zn 2'9189734 
 
 x 0-1034 =ZnO T0145205 
 
 1 c.c. T N ^ solution=0'00325 gni. Zn 3'511883-i 
 
480 VOLUMETRIC ANALYSIS. 8 94 
 
 PART VII. 
 VOLUMETRIC ANALYSIS OF GASES. 
 
 Description of the necessary Apparatus, with Instructions for 
 Preparing-, Etching-, Graduating-, etc. 
 
 94. THIS branch of chemical analysis, on account of its 
 extreme accuracy, and in consequence of the possibility of its 
 application to the analysis of carbonates, and of many other bodies 
 from which gases may be obtained, deserves more attention than 
 it has generally received, in this country at least. It will therefore 
 be advisable to devote some considerable space to the consideration 
 ..of the subject. 
 
 Eor an historical sketch of the progress of gas analysis, the 
 reader is referred to Dr. Frank land's article in the 
 Hand'wdrterlmch der CJiemie, and more complete details 
 of the process than it will be necessary to give here will 
 be found in that article; also in Bun sen's Gasometry 
 and in Dr. Russell's contributions to Watt's Chemical 
 Dictionary. 
 
 The apparatus employed by Bun sen, who was the first 
 successfully to work out the processes of gas analysis, is 
 very simple. Two tubes, the absorption tube and the 
 eudiometer, are used, in which the measurement and 
 analysis of the gases are performed. The first of these 
 tubes is about 250 m.m. long and 20 m.m. in diameter, 
 closed at one end, and with a lip at one side of the open 
 extremity, to facilitate the transference of the gas from the 
 absorption tube (fig. 64) to the eudiometer (fig. 65). The 
 eudiometer has a length of from 500 to 800 m.m., and 
 a diameter of 20 m.m. Into the closed end two platinum 
 wires are sealed, so as to enable the operator to pass an 
 electric spark through any gas which the tube may contain. 
 The mode of sealing in the platinum wires is as follows: 
 ^ken * ne en( * ^ ^ ie tu ^ e i g c l se d, an( l while still hot, 
 ' ' a finely pointed blowpipe flame is directed against the 
 side of the tube at the base of the hemispherical end. 
 When the glass is soft, a piece of white-hot platinum wire is 
 pressed against it and rapidly drawn away. By this means 
 a small conical tube is produced. This operation is then repeated 
 on the opposite side (fig. 66). One of the conical tubes is next 
 cut off near to the eudiometer, so as to leave a small orifice (fig. 67), 
 
94 APPARATUS FOR ANALYSIS OF GASES. 481 
 
 through which a piece of the moderately thin platinum wire, reaching 
 about two-thirds across the tube, is passed. The fine blow-pipe 
 flame is now brought to play on the wire at the point where it enters 
 the tube ; the glass rapidly fuses round the wire, making a perfectly 
 gas-tight joint. If it should be observed that the tube 
 has any tendency to collapse during the heating, it will 
 be necessary to blow gently into the open end of the tube. 
 This may be conveniently done by means of a long piece 
 of caoutchouc connector, attached to the eudiometer, 
 which enables the operator to watch the effect of the 
 blowing more easily than if the mouth were applied 
 directly to the tube. When a perfect fusion of the glass 
 round the wire has been effected, the point on the opposite 
 side is cut off, and a second wire sealed in in the same 
 manner (fig. 68). The end of the tube must be allowed 
 to cool very slowly ; if proper attention is not paid to 
 this, fracture is very liable to ensue. When perfectly 
 cold, a piece of wood with a rounded end is passed 
 up the eudiometer, and the two wires carefully pressed 
 against the end of the tube, so as to lie in contact with 
 the glass, with a space of 1 or 2 m.m. between their 
 points (fig. 69). It is for this purpose that the wires, 
 when sealed in, are made to reach so far across the tube. 
 The ends of the wires projecting outside the tube are 
 then bent into loops. These loops must be carefully 
 treated, for if frequently bent they are very apt to break 
 off close to the glass ; besides this, the bending of the 
 wire sometimes causes a minute crack in the glass, which 
 may spread and endanger the safety of the tube. These 
 difficulties may be overcome by cutting off the wire close 
 to the glass, and carefully smoothing the ends by rubbing 
 them with a piece of ground glass until they are level 
 with the surface of the tube (fig. 70). In order to make 
 contact with the induction coil, a wooden American paper- 
 clip, lined with platinum foil, is made to grasp the tube; 
 the foil is connected with two strong loops of platinum 
 wires, and to these the wires from the coil are attached 
 (fig. 71). In this way no strain is put on the eudiometer 
 wires by the weight of the wires from the coil, and 
 perfect contact is ensured between the foil and platinum 
 wires. It is also easy to clean the outside of the 
 eudiometer without fear of injuring the instrument. 
 
 It will now be necessary to examine if the glass is perfectly 
 fused to the wires. For this purpose the eudiometer is Fig. 65. 
 filled with mercury, and inverted in the trough. If the 
 tube has 800 m.m. divisions, a vacuous space will be formed in the 
 upper end. Note the height of the mercury, and if this remains 
 constant for a while the wires are properly sealed. Should the 
 
 i i 
 
482 
 
 VOLUMETRIC ANALYSIS. 
 
 94 
 
 eudiometer be short, hold it in the hands, and bring it down with 
 a quick movement upon the edge of the india-rubber cushion at 
 the bottom of the trough, taking care that the force of impact is 
 slight, else the mercury may fracture the sealed end of the tube. 
 By jerking the eudiometer thus, a momentary vacuum is formed, 
 and 'if there is any leakage, small bubbles of air will arise from the 
 junction of the wires with the glass. 
 
 Fig. 66. 
 
 Tig. 67. 
 
 Kg. 68. 
 
 Tig. 69. 
 
 Pig. 70. 
 
 The tubes are graduated by the following processes : A cork 
 is fitted into the end of the tube, and a piece of stick, a file, or 
 anything that will make a convenient handle, is thrust into the 
 cork. The tube is heated over a charcoal fire or combustion furnace, 
 and coated with melted wax by means of a earners-hair brush. 
 Sometimes a few drops of turpentine are mixed with the wax to 
 
94 
 
 APPARATUS FOR ANALYSIS OF GASES. 
 
 483 
 
 1 11! | 
 
 render it less brittle, but this is not always necessary. 
 
 cooling it should be found that 
 
 the layer of wax is not uniform, 
 
 the tube may be placed in 
 
 a perpendicular position before 
 
 n fire and slowly rotated so as 
 
 to heat it evenly. The wax will 
 
 then be evenly distributed on 
 
 the surface of the glass, the 
 
 excess flowing off. The tube 
 
 must not be raised to too high 
 
 a temperature, or the wax may 
 
 become too thin ; but all thick 
 
 masses should be avoided, as 
 
 they may prove troublesome in 
 
 the subsequent operation. 
 
 The best and most accurate 
 mode of marking the millimeter 
 divisions on the wax is by 
 a graduating machine; but the 
 more usual process is to copy 
 the graduations from another 
 tube in ihe following manner. 
 A hard glass tube, on which 
 millimeter divisions have al- 1 
 ready been deeply etched, is 
 fixed in a groove in the gra- P 
 duating table, a straight-edge 
 of brass being screwed down 
 on the tube and covering the 
 ends of the lines. The standard 
 tube is shown in the figure at 
 the right-hand end of the 
 apparatus (fig. 72). The 
 waxed tube is secured at the 
 other end of the same groove, 
 and above it are fixed two 
 brass plates, one with a straight- 
 edge, and the other with 
 notches at intervals of 5 m.m., 
 the alternate notches being 
 longer than the intermediate 
 ones (fig. 73). A stout rod of 
 wood provided with a sharp 
 steel point near one end, and 
 a penknife blade at the other 
 (fig. 74), is held so that the 
 steel point rests in one of the 
 
 i i 2 
 
 If, 
 
 on 
 
 
484 VOLUMETRIC ANALYSIS. 94. 
 
 divisions of the graduated tube, being gently pressed at the same 
 time against the edge of the brass plate ; the point of the knife- 
 blade is then moved by the operator's right hand across the portion 
 of the waxed tube which lies exposed between the two 'brass plates. 
 When the line has been scratched on the wax, the point is moved 
 along the tube until it falls into the next division ; another line is 
 now scratched on the wax, and so on. At every fifth division the 
 knife-blade will enter the notches in the brass plate, making 
 a longer line on the tube. After a little practice it will be found 
 easy to do fifty or sixty divisions in a minute, and with perfect 
 regularity. Before the tube is removed from the apparatus, it must 
 be carefully examined to see if any mistake has been made. It 
 may have happened that during the graduation the steel point 
 slipped out of one of the divisions in the standard tube ; if 
 this has taken place, it will be found that the distance between 
 the line made at that time and those on each side of it will 
 not be equal, or a crooked or double line may have been produced. 
 This is easily obliterated by touching the wax with a piece of heated 
 platinum wire, after which another line is marked. The tube is 
 now taken out of the table, and once more examined. If any 
 portions of wax have been scraped off by the edges of the apparatus, 
 
 Fig. 75. 
 
 or by the screws, the coating must be repaired with the hot 
 platinum wire. Numbers have next to be marked opposite each 
 tenth division, beginning from the closed end of the tube, the 
 first division, which should be about 10 m.m. from the end, being 
 marked 10 (see fig. 69). The figures may be well made with 
 a steel pen. This has the .advantage of producing a double line 
 when the nib is pressed against the tube in making a down-stroke. 
 The date, the name of the maker of the tube, or its number, 
 may now be written on the tube. 
 
 The etching by gaseous hydrofluoric acid is performed by 
 supporting the tube by two pieces of wire over a long narrow 
 leaden trough containing sulphuric acid and powdered fluor-spar 
 fig. 75), and the whole covered with a cloth or sheet of paper, 
 f course it is necessary to leave the cork in the end of the tube 
 to prevent the access of hydrofluoric acid to the interior, which 
 might cause the tube to lose its transparency to a considerable 
 extent. The time required for the action of the gas varies with 
 the kind of glass employed. With ordinary flint glass from ten 
 minutes to half an hour is quite sufficient ; if the leaden trough is 
 heated, the action may take place even still more rapidly. The 
 

 
 APPARATUS FOR ANALYSIS OF GASES. 
 
 485 
 
 tube is removed from time to time, and a small portion of the 
 wax scraped off from a part of one of the lines ; and if the division 
 can be felt with the finger-nail or the point of a knife, the 
 operation is finished ; if not, the wax must be replaced, and the 
 tube restored to the trough. When sufficiently etched, the tube 
 is washed with water, heated before a fire, and the wax wiped 
 off with a warm cloth. 
 
 The etching may also be effected with liquid hydrofluoric acid, 
 by applying it to the divisions on the waxed tube with a brush, 
 or by placing the eudiometer in a gutta-percha tube closed at one 
 end, and containing some of the liquid. 
 
 Pig. 76. 
 
 Fig. 77. 
 
 As all glass tubes are liable to certain irregularities of diameter, 
 it follows that equal lengths of a graduated glass tube will not 
 contain exactly equal volumes ; hence it is, of course, impossible 
 to obtain by measurement of length the capacity of the closed end 
 of the tube. 
 
 In order to provide for this, the tube must be carefully calibrated. 
 For this purpose it is supported vertically (fig. 76), and successive 
 quantities of mercury poured in from a measure. This measure 
 should contain about as much mercury as ten or twenty divisions 
 of the eudiometer, and is made of a piece of thick glass tube, 
 closed at one end, and with the edges of the open end ground 
 perfectly flat. The tube is fixed into a piece of wood in order to 
 
486 
 
 VOLUMETRIC ANALYSIS. 
 
 94 
 
 avoid heating its contents during the manipulation. The measure 
 may be filled with mercury from a vessel closed with a stop-cock 
 terminating in a narrow vertical tube, which is passed to the bottom 
 of the measure (fig. 77). On carefully opening the stop cock the 
 mercury flows into the measure without leaving any air-bubbles 
 adhering to the sides. A glass plate is now pressed on the ground 
 edges of the tube, which expels the excess of mercury and leaves 
 the measure entirely filled. The mercury may be introduced into 
 the measure in a manner which is simpler and as effectual, though 
 perhaps not quite so convenient, by first closing it with a glass 
 plate, and depressing it in the mercurial trough, removing the plate 
 from the tube, and again replacing it before raising the measure 
 above the surface of the mercury. After pouring each measured 
 quantity of mercury into the eudiometer, the air-bubbles are 
 carefully detached from the sides by means of a thin wooden rod 
 or piece of w r halebone, and the level of the mercury at the highest 
 part of the curved surface carefully observed. 
 
 In all measurements 
 in gas analysis it is, of 
 course, essential that the 
 eye should be exactly on 
 a level with the surface 
 of the mercury, for the 
 parallax ensuing if this 
 were not the case would 
 produce grave errors 
 in the readings. The 
 placing of the eye in the 
 proper position may be 
 ensured in two ways. A 
 small piece of looking- 
 glass (the back of which 
 is painted, or covered 
 with paper to prevent the 
 accidental soiling of the 
 mercury in the trough) is 
 placed behind, and in contact with the eudiometer. The head is 
 now placed in such a position that the reflection of the pupil of 
 the eye is precisely on a level with the surface of the mercury in 
 the tube, and the measurement made. As this process necessitates 
 the hand of the operator being placed near the eudiometer, which, 
 might cause the warming of the tube, it is preferable to read off 
 with a telescope placed at a distance of from two to six feet from 
 the eudiometer. The telescope is fixed on a stand in a horizontal 
 position, and the support is made to slide on a vertical rod. The- 
 image of the surface of the mercury is brought to the centre of 
 the field of the telescope, indicated by the cross. wires in the eye- 
 piece, and the reading taken. The telescope has the advantage of 
 
94 
 
 CALIBRATION OF INSTRUMENTS. 
 
 487 
 
 magnifying the graduations, and thus facilitating the estimation 
 by the eye of tenths of the divisions. Fig. 78 represents the 
 appearance of the tube and mercury as seen by an inverting 
 telescope. 
 
 By this method the capacity of the tube at different parts of its 
 length is determined. If the tube were of uniform bore, each 
 measure of mercury would occupy the same length in the tube ; 
 but as this is never the case, the value of the divisions at all parts 
 of the tube will not be found to be the same. 
 
 From the data obtained by measuring the space in the tube 
 which is occupied by equal volumes of mercury, a table is con- 
 structed by which the comparative values of each millimeter of the 
 tube can be found. The following results were obtained in the 
 calibration of a short absorption eudiometer : 
 
 On the introduction of the 3rd volume of mercury, the reading was 12'8 m.m. 
 4th 18-4 
 
 Thus, he standard 
 
 5th 
 6th 
 7th 
 
 8th 
 
 24-0 
 
 35-2 
 41-0 
 
 volumes occupied 5'6 ni.in., hetween 12'8 and 18'4 
 
 5-6 
 
 5-8 
 
 5'8 
 
 18'4 24'Q 
 
 24-0 29-8 
 
 29-8 35-2 
 
 35-2 41-0 
 
 If we assume the measure of mercury to contain 5 '8 volumes 
 (the greatest difference between two consecutive readings on the 
 tube), the volume at the six points above given will be as follows : 
 
 At 12-8 it will be 174 or 5-8 x 3 
 
 184 
 24-0 
 29-8 
 35-2 
 41-0 
 
 23-2 
 29-0 
 34-8 
 40-6 
 464 
 
 5-8x4 
 5-8x5 
 5-8x6 
 5-8x7 
 
 5-8x8 
 
 Between the first and second readings these 5*8 volumes are con- 
 tained in 5'6 divisions, consequently each millimeter corresponds to 
 
 v- = 1 -0357 vol. This is also the value of the divisions between the 
 
 O'O 
 
 second and third readings. Between the third and fourth 1 m.m. 
 contains 1 vol. ; between the fourth and fifth, 1 m.m. contains 
 
 =1-0741 vol. ; and between the fifth and sixth m.m. = l vol. 
 
 D - 
 
 From these data the value of each millimeter on the tube can 
 readily be calculated. Thus 13 will contain the value of 12 '8 + 
 the value of 0*2 of a division at this part of the tube, or 174 + 
 (1-0357 x 0'2) = 17-60714. There is, however, no need to go 
 beyond the second place of decimals, and, for all practical purposes, 
 the first place is sufficient. Thus, by adding or subtracting the 
 necessary volumes from the experimental numbers, we find the 
 
488 
 
 VOLUMETRIC ANALYSIS. 
 
 94. 
 
 values of the divisions nearest to the six points at which the 
 readings were taken to be 
 
 13=17-61 or 17-6 
 18=22-79 22-8 
 24=29-00 29-0 
 30=35-00 35-0 
 35=40-38 40-4 
 41=46-40 46-4 
 
 In a precisely similar manner the values of the intermediate 
 divisions are calculated, and we thus obtain the following table : 
 
 I 
 
 
 1 
 
 
 
 
 
 
 Values. 
 
 1 
 
 Values. i ; 
 
 Values. 
 
 K 
 
 
 K 
 
 1 W 
 
 
 
 
 
 li 
 
 
 10 
 
 14-50 
 
 14-5 
 
 21 
 
 25-89 
 
 25-9 
 
 32 
 
 37-15 
 
 37-1 
 
 11 
 
 15-54 
 
 15-5 
 
 22 26-93 
 
 26-9 
 
 33 
 
 38-22 
 
 38-2 
 
 12 
 
 16-57 
 
 16-6 
 
 23 
 
 27-96 
 
 28-0 
 
 34 
 
 39-30 
 
 39-3 
 
 13 
 
 17-61 
 
 17-6 
 
 24 
 
 29-00 
 
 29-0 
 
 35 
 
 40-38 
 
 40-4 
 
 14 
 
 18-65 
 
 18-6 
 
 25 
 
 30-00 
 
 30-0 
 
 36 
 
 41-40 
 
 41-4 
 
 15 
 
 19-68 
 
 19-7 
 
 26 
 
 31-00 
 
 31-0 
 
 37 
 
 42-40 
 
 42-4 
 
 16 
 
 20-71 
 
 20-7 
 
 27 
 
 32-00 
 
 32-0 
 
 38 
 
 43-40 
 
 43-4 
 
 17 
 
 21-75 
 
 21-8 
 
 28 
 
 33-00 
 
 33-0 
 
 39 
 
 44-40 
 
 44-4 
 
 18 
 
 22-79 
 
 22-8 
 
 29 
 
 34-00 
 
 34-0 
 
 40 
 
 45-40 
 
 45-4 
 
 19 
 
 23-82 
 
 23-8 
 
 30 
 
 35-00 
 
 35-0 
 
 41 
 
 46-40 
 
 46-4 
 
 20 
 
 24-86 
 
 24-9 
 
 31 
 
 36-07 
 
 36-1 
 
 &c. 
 
 &c. 
 
 &c. 
 
 If it be desired to obtain the capacity of the tube in cubic 
 centimeters, it is only necessary to determine the weight of the 
 quantity of mercury the measure delivers, and the temperature at 
 which the calibration was made, and to calculate the contents by 
 the following formula : 
 
 0x (1+0-0001815*) 
 13-596V 
 
 in which g represents the weight of the mercury contained in the 
 measure, t the temperature at which the calibration is made, 
 0-0001815 being the coefficient of expansion of mercury for each 
 degree centigrade, V the volume read off in the eudiometer, and C 
 the number of cubic centimeters required. 
 
 A correction has to be made to every number in the table on 
 account of the surface of the mercury assuming a convex form in 
 the tube. During the calibration, the convexity of the mercury is 
 turned towards the open end of the tube (fig. 79), whilst in the 
 
CALIBRATION OF INSTRUMENTS. 
 
 489 
 
 measurement of a gas the convexity will be in tne opposite direction 
 (fig. 80). It is obvious that the quantity of mercury measured 
 during the calibration, while the eudiometer is inverted, will be 
 less than a volume of gas contained in the tube when the mercury 
 stands at the same division, while the eudiometer is erect. The 
 necessary amount of correction is determined by observing the 
 position of the top of the meniscus, and then introducing a faw 
 drops of a solution of corrosive sublimate, which will immediately 
 cause the surface of the mercury to become horizontal (fig. 81), and 
 again measuring. 
 
 It will be observed that in fig. 79 the top of the meniscus was 
 at the division 39, whereas in fig. 81, after the addition of corrosive 
 sublimate, the horizontal surface of the mercury stands at 38*7, 
 giving a depression of 0*3 m.m. If the tube were now placed 
 erect, and gas introduced so that the top of the meniscus was at 39, 
 
 *Eig. 79. 
 
 *Fig. 80. 
 
 Fig. 81. 
 
 and if it were now possible to overcome the capillarity, the horizontal 
 surface would stand at 39 '3. The small cylinder of gas between 
 38-7 and 39'3, or 0'6 division, would thus escape measurement. 
 This number 0'6 is therefore called the error of meniscus, and must 
 be added to all readings of gas in the eudiometer. The difference, 
 therefore, between the two readings is multiplied by two, and the 
 volume represented by the product obtained the error of meniscus 
 is added to the measurements before finding the corresponding 
 capacities by the table. In the case of the tube, of which the 
 calibration is given above, the difference between the two readings 
 was 0'4 m.m., making the error of meniscus 0'8. 
 
 All experiments on gas analysis, with the apparatus described, 
 
 * In these the mercury shovll just torch 
 
 CFTHE 
 
 UNIVERSITY 
 
490 
 
 VOLUMETRIC ANALYSIS. 
 
 94 
 
 should be conducted in a room set apart for the purpose, with the 
 window facing the north, so that the sun's rays cannot penetrate 
 into it, and carefully protected from flues or any source of heat 
 which might cause a change of temperature of the atmosphere. 
 The mercury employed should be purified, as far as possible, from 
 lead and tin, which may be done 
 by leaving it in contact with dilute 
 nitric acid in a shallow vessel for 
 some time, or by keeping it when 
 out of use under concentrated 
 sulphuric acid, to which some mer- 
 curous sulphate has been added. 
 This mercury reservoir may con- 
 veniently be made of a glass globe 
 with a neck at the top and a 
 stop-cock at the bottom (fig. 82), 
 and which is not filled more than 
 one-half, so as to maintain as large 
 a surface as possible in contact 
 with the sulphuric acid. Any 
 foreign metals (with the exception 
 of silver, gold, and platinum) 
 which may be present are removed 
 by the mercurous sulphate, an 
 equivalent quantity of mercury 
 being precipitated. This process, 
 which w r as originated by M. 
 Deville, has been in use for 
 many years with very satisfactory 
 results, the mercury being always 
 clean and dry when drawn from 
 the stop-cock at the bottom of the 
 globe. The mouth of the globe 
 should be kept close to prevent 
 the absorption of water by the 
 sulphuric acid. 
 
 In all cases, where practicable, 
 gases should be measured when 
 completely saturated with aqueous 
 vapour : to ensure this, the top 
 of the eudiometer and absorption 
 tubes should be moistened before 
 the introduction of the mercury. 
 This may be done by dipping the end of a piece of iron wire 
 into w r ater, and touching the interior of the closed extremity of 
 the tube with the point of the wire. 
 
 In filling the eudiometer, the greatest care must of course be- 
 taken to exclude all air-bubbles from the tubes. This may be 
 
 Fig. 82. 
 
94 
 
 THE EUDIOMETER. 
 
 491 
 
 effected in several ways : the eudiometer may be held in an inverted 
 or inclined position, and the mercury introduced through a narrow 
 glass tube which passes to the end of the eudiometer and com- 
 municates, with the intervention of a stop-cock, with a reservoir 
 of mercury (fig. 83). On carefully opening the stop-cock, the 
 mercury slowly flows into the eudiometer, entirely displacing the air. 
 The same result may be obtained by placing the eudiometer nearly 
 in a horizontal position, and carefully introducing the mercury 
 from a test-tube without a rim (fig. 84). Any minute bubbles 
 adhering to the side may generally be removed by closing the 
 mouth of the tube with the thumb, and allowing a small air-bubble 
 to rise in the tube, and thus to wash it out. After filling the 
 eudiometer entirely with mercury, and inverting it over the trough, 
 it will generally be found that the air-bubbles have been removed. 
 
 For the introduction of the gases, the eudiometer should be 
 placed in a slightly inclined position, being held by a support 
 attached to the mercurial trough (fig. 85), and the gas transferred 
 
 rig. S3. 
 
 from the tube in which it has been collected. The eudiometer is 
 now put in an absolutely vertical position, determined by a 
 plumb-line placed near it, and a thermometer suspended in close 
 proximity. It must then be left for at least half an hour, no one 
 being allowed to enter the room in the meantime. After the 
 expiration of this period, the operator enters the room, and, by 
 means of the telescope placed several feet from the mercury table, 
 carefully observes the height of the mercury in the tube, estimating 
 the tenths of a division with the eye, which can readily be done 
 after a' little practice. He next reads the thermometer with the 
 telescope, and finally the height of the mercury in the trough is read 
 off on the tube, for which purpose the trough must have glass sides. 
 The difference between these two numbers is- the length of the 
 column of mercury in the eudiometer, and has to be subtracted 
 from the reading of the barometer. It only remains to take the 
 height of the barometer. The most convenient form of instrument 
 for gas analysis is the syphon barometer, with the divisions etched 
 
492 
 
 VOLUMETRIC ANALYSIS. 
 
 94. 
 
 on the tube. This is placed on the mercury table, so that it may 
 be read by the telescope immediately after the measurements 
 in the eudiometer. There are two methods of numbering the 
 divisions on the barometer : in one the zero point is at or 
 near the bend of the tube, in which case the height of the 
 lower column must be subtracted 
 from that of the higher; in the other 
 the zero is placed near the middle of 
 the tube, so that the numbers have to 
 be added to obtain the actual height. 
 In cases of extreme accuracy, a correction 
 must be made for the temperature of the 
 barometer, which is determined by a ther- 
 mometer suspended in the open limb of the 
 instrument, and passing through a plug of 
 cotton wool. Just before observing the 
 height of the barometer, the bulb of the 
 thermometer is depressed for a moment 
 into the mercury in the open limb, thus 
 causing a movement of the mercurial 
 column, which overcomes any tendency 
 that it may have to adhere to the glass. 
 
 In every case the volume observed must 
 be reduced to the normal temperature and 
 pressure, in order to render the results 
 comparable. If the absolute volume is 
 required, the normal pressure of 760 in.m. 
 must be employed : but when comparative 
 volumes only are desired, the pressure of 
 1000 m.m. is generally adopted, as it 
 somewhat simplifies the calculation. In 
 the following formula for correction of the 
 volume of gases 
 
 V 1 = the correct volume. 
 
 V = the volume found in the table, and 
 corresponding to the observed height of 
 the mercury in the eudiometer, the error 
 of meniscus being, of course, included. 
 
 B = the height of the barometer (cor- 
 rected for temperature, if necessary) at 
 the time of measurement. 
 
 b = the difference between the height of the mercury in the 
 trough and in the eudiometer. 
 
 t = the temperature in centigrade degrees. 
 
 T = the tension of aqueous vapour in millimeters of mercury 
 at t. This number is, of course, only employed when the gas is 
 saturated with moisture at the time of measurement. 
 
94. CORRECTIONS FOR TEMPERATURE AND PRESSURE. 493 
 
 Then 
 
 vl= Yx(E-ft-T) 
 760 x (1 + 0-003665^)' 
 
 when the pressure of 760 m.m. is considered the normal one ; or, 
 
 yi= Yx(B-fr-T) 
 
 1000x(l+0-003665f)' 
 
 when the normal pressure of 1 meter is adopted. 
 
 In cases where the temperature at measurement is below 
 (which rarely happens), the factor 1 - 0'003665 must be used. 
 
 Tables have been constructed containing the values of T; of 
 1000 x (1+0-0036650, and of 760 y (1+0-003665^), which 
 very much facilitate the numerous calculations required in this 
 branch of analysis* These will be found at the end of the book. 
 
 iiiiipiiipiiiiii'. 
 
 We shall now be in a position to examine the methods employed 
 in gas analysis. Some gases may be estimated directly ; that is, 
 they may be absorbed by certain reagents, the diminution of the 
 volume indicating the quantity of the gas present. Some are 
 determined indirectly; that is, by exploding them with other 
 gases, and measuring the quantities of the products. Some gases 
 may be estimated either directly or indirectly, according to the 
 circumstances under which they are found. 
 
 * Mr. Sutton will forward a copy of these Tables, printed separately for laboratory 
 use, to any one desiring them, on receipt of the necessary address. 
 
494 VOLUMETRIC ANALYSIS. 96. 
 
 95. 
 
 1. G-ASES ESTIMATED DIRECTLY. 
 
 A. Gases Absorbed by Crystallized Sodic Phosphate and Potassic 
 
 Hydrate : 
 
 Hydrochloric acid, 
 Hydrobromic acid, 
 Hydriodic acid. 
 
 B. Gases Absorbed by Potassic Hydrate, and not by Crystallized 
 
 Sodic Phosphate: 
 
 Carbonic anhydride, 
 Sulphurous anhydride, 
 Hydrosulphuric acid. 
 
 C. Gases Absorbed by neither Crystallized Sodic Phosphate nor 
 
 Potassic Hydrate: 
 
 Oxygen, 
 Xitric oxide, 
 Carbonic oxide, 
 
 Hydrocarbons of the composition Cn H 2 n, 
 Hydrocarbons of the formula (Cn H 2 n+l) 2 , 
 Hydrocarbons of the formula Cn H 2 n-i-2, 
 except Marsh gas. 
 
 2. GASES ESTIMATED INDIRECTLY. 
 
 Hydrogen, 
 Carbonic oxide, 
 Marsh gas, 
 Methyl, 
 
 Ethylic hydride, 
 Ethyl, 
 
 Propylic hydride, 
 Butylic hydride, 
 Nitrogen. 
 
 DIRECT ESTIMATIONS. 
 
 Group A, containing- Hydrochloric, Hydrobromic, and 
 Hydriodic Acids. 
 
 96. IN Bun sen's method the reagents for absorption are 
 generally used in the solid form, in the shape of bullets. To make 
 the bullets of sodic phosphate, the end of a piece of platinum wire, 
 of about one foot in length, is coiled up and fixed in the centre of 
 a, pistol-bullet mould. It is well to bend the handles of the mould, 
 
96. DIRECT ESTIMATIONS. 495 
 
 so that when it is closed the handles are in contact, and may be 
 fastened together by a piece of copper wire (tig. 86). The usual 
 practice is to place the platinum wire in the hole through which the 
 mould is filled ; but it is more convenient to file a small notch in 
 one of the faces of the open mould, and place the wire in the notch 
 before the mould is closed. In this manner the wire is not in the 
 way during the casting, and it is subsequently more easy to trim 
 the bullet. Some ordinary crystallized sodic phosphate is fused in 
 a platinum crucible (or better, in a small piece of wide glass tube, 
 closed at one end, and with a spout at the other, and held by 
 a copper-wire handle), and poured into the bullet mould (fig. 87). 
 When quite cold, the mould is first gently warmed in a gas-flame, 
 opened, and the bullet removed. If the warming of the mould is 
 omitted, the bullet is frequently broken in consequence of its 
 adhering to the metal. Some chemists recommend the use of sodic 
 sulphate instead of phosphate, which may be made into balls by 
 dipping the coiled end of a piece of platinum wire into the salt 
 
 ig. 86. Fig. 87. 
 
 fused in its water of crystallization. On removing the wire, 
 a small quantity of the salt will remain attached to the wire. 
 When this has solidified, it is again introduced for a moment 
 and a larger quantity will collect ; and this is repeated until the 
 ball is sufficiently large. The balls must be quite smooth, in 
 order to prevent the introduction of any air into the eudiometer. 
 When the bullets are made in a mould, it is necessary to remove 
 the short cylinder which is produced by the orifice through which 
 the fused salt has been poured. 
 
 In the estimation of these gases, it is necessary 'that they should 
 be perfectly dry. This may be attained by introducing a bullet of 
 fused calcic chloride. After the lapse of about an hour, the bullet 
 may be removed, the absorption tube placed in a vertical position, 
 with thermometer, etc., arranged for the reading, and left for 
 half an hour to assume the temperature of the air. When the 
 reading has been taken, one of the bullets of sodic phosphate or 
 sodic sulphate is depressed in the trough, wiped with the fingers 
 
496 
 
 VOLUMETPJC ANALYSIS. 
 
 97. 
 
 while under the mercury in order to remove any air that it might 
 have carried down with it, and introduced into the absorption tube, 
 which for this purpose is inclined and held in one hand, while 
 the bullet is passed into the tube with the other. Care must be 
 taken that the whole of the platinum wire is covered with mercury 
 while the bullet remains in the gas, otherwise there is a risk of 
 air entering the tube between the mercury and the wire (fig. 88). 
 
 After standing for an hour, the bullet is withdrawn from the 
 absorption tube. This must be done with some precaution, so as 
 to prevent any gas being removed from the tube. It is best done 
 by drawing down the bullet by a brisk movement of the wire, the 
 gas being detached from the bullet during the rapid descent of the 
 latter into the mercury. The bullet may then be more slowly 
 removed from the tube. As sodic phosphate and sodic sulphate 
 contain water of crystallization, and a corresponding proportion 
 of this is liberated for every equivalent of sodic chloride formed, 
 care must be taken that the 
 bullets are not too small, else 
 the water set free will soil the 
 sides of the eudiometer, especially 
 if there is a large volume of gas 
 to be absorbed. As a further 
 precaution, drive off some of the 
 water of crystallization before 
 casting the bullet. When the 
 bullet has been removed, the gas 
 must be dried as before with 
 calcic chloride and again measured. 
 If two or more of the gases are 
 present in the mixture to be 
 analyzed, the sodic phosphate ball 
 must be dissolved in water, and 
 the chlorine, bromine, and iodine 
 determined by the ordinary ana- 
 lytical methods. If this has to 
 be done, care must be taken 
 that the sodic phosphate employed is free from chlorine. 
 
 88. 
 
 Group B. Gases absorbed by Potassic Hydrate, but not by 
 Sodic Phosphate. 
 
 Carbonic anhydride, sulphuretted hydrogen, and 
 sulphurous anhydride. 
 
 97. IF the gases occur singly, they are determined by means 
 of a bullet of caustic potash made in the same manner as the sodic 
 phosphate balls. The caustic potash employed should contain 
 sufficient water to render the bullets so soft that they may be 
 
POTASH ABSORPTIONS. 497 
 
 marked with the nail when cold. Before use the balls must be 
 slightly moistened with water ; and if large quantities of gas have 
 to be absorbed, the bullet must be removed after some hours, 
 washed with water, and returned to the absorption tube. The 
 absorption may extend over twelve or eighteen hours. In order to 
 ascertain if it is completed, the potash ball is removed, washed, 
 again introduced, arid allowed to remain in contact with the gas 
 for about an hour. If no diminution of volume is observed the 
 operation is finished. 
 
 The following analysis of a mixture of air and carbonic anhydride 
 will serve to show the mode of recording the observations and the 
 methods of calculation required. 
 
 Analysis of a Mixture of Air and Carbonic Anhydride. 
 
 1. Gas Saturated with Moisture. 
 
 Height of mercury in trough . 171*8 m.m. 
 
 Height of mercury in absorption eudio- 
 meter . . . 89*0 m.m. 
 
 Column of mercury in tube, to be sub- 
 
 tracted from the height of barometer = b = 82-8 m.m. 
 
 Height of mercury in eudiometer 89 '0 m.m. 
 
 Correction for error of meniscus 0'8 m.m. 
 
 " 89*8m.m. 
 
 "Volume in table corresponding to 89 -8 
 
 m.m. . . . = V = 96-4 
 
 Temperature at which the reading was 
 
 made . . . = t = 12*2 
 
 Height of barometer at time of obser- 
 vation . . . =B = 765-25 m.m. 
 Tension of aqueous vapour at 12 -2 = T = 10'6 m.m. 
 
 Vx(B-fr-T) 
 1000x(l + 0-003665/ ( ) 
 96-4 x (765-25 -82-8 -10-6) = 
 1000 x [1 + (0 003665 x 12*2)] ~ 
 
 96-4x671-85 
 1000 x 1-044713" 
 
 log. 96-4 -1-98408 
 log. 671-85 = 2-82727 
 
 4-81135 
 
 log. (1000 x 1-044713) = 3-01900 
 
 1-79235 = log. 61-994 = V 1 
 Corrected volume of aTF~and CO 2 = V 1 = 61*994. 
 
 K K 
 
498 VOLUMETRIC ANALYSIS. 97. 
 
 After absorption of carbonic anhydride by bullet of 
 potassic hydrate. 
 
 Gas Dry. 
 
 Height of mercury in trough . 172'0 m.m. 
 
 Height of mercury in absorption eudio- 
 meter . . . 6 2 -5 m.m. 
 
 Column of mercury in eudiometer = I = 109 '5 m.m. 
 
 Height of mercury in eudiometer 62 '5 m.m. 
 
 Correction for error of meniscus 0*8 m.m. 
 
 63-3 m.m. 
 
 Volume in table corresponding to 6 3 '3 
 
 m.m. . . = V - 69-35 
 
 Temperature . . . = t = 10 '8 
 
 Barometer . . . = B = 766*0 m.m. 
 
 yl= Vx(B-J) 
 
 1000 x (1+0-003665^) 
 
 69-35 x (766-0- 109-5) 
 1000 x [1 + (0-003665 x 10-8)] 
 
 69-35x656-5 
 
 1000x1-039582 
 
 log. 69-35 = 1-84105 
 log. 656-5 -2-81723 
 
 4-65828 
 log. (1000 x 1-039582) = 3-01686 
 
 1-64142= log. 43-795 = V 1 
 
 Corrected volume of air = 43'795 
 Air + CO 2 = 61 -994 
 Air =43-795 
 
 C0 2 = 18-199 
 
 61-994 : 18-199 : : 100 : x = percentage of CO 2 
 
 _ 18-199 x 100 _ 
 61-995 
 
 Percentage of CO 2 in mixture of air and gas = 29 -355. 
 
97. POTASH ABSOEPTIONS. 499 
 
 Gas Moist. 
 
 Height of mercury in trough . 174*0 m.m. 
 
 Height of mercury in eudiometer 98*0 m.rn. 
 
 Column of mercury in tube . = b= 76*0 m.m. 
 
 Height of mercury in eudiometer 98 '0 m.m. 
 
 Correction for error of meniscus 0*8 m.m. 
 
 98-8 m.m. 
 
 Volume in table, corresponding to 98 '8 
 
 m.m. . . . =V= 105-6 
 
 Temperature . . . = t = 12 '5 
 
 Barometer . . . = B = 738*0 m.m, 
 
 Tension of aqueous vapour at 12 '5 = T = 10 '8 m.m. 
 Corrected volume of air and carbonic 
 
 anhydride . . . 65 '754 
 
 After absorption of CO 2 . 
 Gas Dry, 
 
 Height of mercury in trough . 173*0 m.rn. 
 
 Height of mercury in absorption eudio- 
 meter ... 70-3 m.m. 
 
 Column of mercury in tube . =1= 102*7 m.m. 
 
 Height of mercury in eudiometer 70*3 m.m. 
 
 Correction for error of meniscus 0*8 m.m., 
 
 71*1 m.m. 
 
 Volume in table corresponding to 71*1 
 
 m.m. . . . =V= 77*4 
 
 Temperature . . . ==14*1 
 
 Barometer . . . =B = 733*5 m.m. 
 
 Corrected volume of air = 46*425 
 
 Air + CO 2 = 65*754 
 
 Air = 46-425 
 
 CO 2 = 19*329 
 65*754 : 19*329 :: 100 : 22*396. 
 
 i. n. 
 
 Percentage of CO 2 in mixture of air and gas 29*335 25'396 
 
 If either sulphurous anhydride or sulphuretted hydrogen occurs 
 together with carbonic anhydride, one or two modes of operation 
 may be followed. Sulphuretted hydrogen and sulphurous anhydride 
 are absorbed by manganic peroxide and by ferric oxide, which 
 may be formed into bullets in the following manner. The oxides 
 
 K K 2 
 
500 VOLUMETRIC ANALYSIS. 97. 
 
 are made into a paste with water, and introduced into a bullet 
 mould, the interior of which has been oiled, and containing the 
 coiled end of a piece of platinum wire ; the mould is then placed 
 on a sand bath till the ball is dry. The oxides will now be left in 
 a porous condition, which would be inadmissible for the purpose 
 to which they are to be applied ; the balls are therefore moistened 
 several times with a sirupy solution of phosphoric acid, care being 
 taken that they do not become too soft, so as to render it difficult 
 to introduce them into the eudiometer. After the sulphuretted 
 hydrogen or sulphurous anhydride has been removed, the gas 
 should be dried by means of calcic chloride. 'the carbonic 
 anhydride can now be determined by means of the bullet of 
 potassic hydrate. 
 
 The second method is to absorb the two gases by means of 
 a ball of potassic hydrate containing water, but not moistened on 
 the exterior, then to dissolve the bullet in dilute acetic acid which 
 has been previously boiled and allowed to cool without access of 
 air, and to determine the amount of sulphuretted hydrogen or 
 sulphurous anhydride by means of a standard solution of iodine. 
 This process is especially applicable when rather small quantities of 
 sulphuretted hydrogen have to be estimated. 
 
 Group C. This group contains the gases not absorbed by Potassic 
 Hydrate or Sodic Phosphate, and consists of Oxygen, Nitric 
 Oxide, Carbonic Oxide*, Hydrocarbons of the formulae CnH?n 
 (Cn 2 H-n+l)2, and CnH'2n+', except Marsh gas. 
 
 Oxygen was formerly determined by means of a ball of 
 phosphorus, but it is difficult subsequently to free the gas from 
 the phosphorous acid produced, and which exerts some tension, and 
 so vitiates the results ; besides which, the presence of some gases 
 interferes with the absorption of oxygen by phosphorus ; and if 
 any potassic hydrate remains on the side of the tube, from the 
 previous absorption of carbonic anhydride, there is a possibility of 
 the formation of phosphoretted hydrogen, which would, of course, 
 vitiate the analysis. A more convenient reagent is a freshly 
 prepared alkaline solution of potassic pyrogallate introduced into 
 the gas in a bullet of papier-mache. The balls of papier-mache 
 are made by macerating filter-paper in water, and forcing as much 
 of it as possible into a bullet mould into which the end of a piece 
 of platinum wire has been introduced. In order to keep the mould 
 from opening while it is being filled, it is well to tie the handles 
 together with a piece of string or wire, and when charged it is 
 placed on a sand bath. After the mass is dry the mould may be 
 Opened, when a large absorbent bullet will have been produced. 
 The absorption of oxygen by the alkaline pyrogallate is not very 
 rapid, and it may be necessary to remove the ball once or twice 
 during the operation, and to charge it freshly. 
 
97. OXYGEN ABSORPTION. 501 
 
 Nitric oxide cannot be readily absorbed in an ordinary 
 absorption tube ; it may, however, be converted into nitrous 
 anhydride and nitric peroxide by addition of excess of oxygen, 
 absorbing the oxygen compounds with potassic hydrate, and the 
 excess of oxygen by potassic pyrogallate. The diminution of the 
 volume will give the quantity of nitric oxide. This process is 
 quite successful when the nitric oxide is mixed with olefiant gas 
 and ethylic hydride, but it is possible that other hydrocarbons 
 might be acted on by the nitrous compounds. 
 
 Carbonic oxide may be absorbed by two reagents. If carbonic 
 anhydride and oxygen be present they must be absorbed in the 
 usual manner, and afterwards a papier-mache ball saturated with 
 a concentrated solution of cuprous chloride in dilute hydrochloric 
 acid introduced. A ball of caustic potash is subsequently employed 
 to remove the hydrochloric acid given off by the previous reagent, 
 and to dry the ' gas. Carbonic oxide may also be absorbed by 
 introducing a ball of potassic hydrate, placing the absorption tube 
 in a beaker of mercury, and heating the whole in a water bath to 
 100 for 60 hours. The carbonic oxide is thus converted into 
 potassic formate and entirely absorbed. 
 
 Olefiant Gas and other Hydrocarbons of the formula 
 CnH 2 n are absorbed by Nordhausen sulphuric acid, to which an 
 additional quantity of sulphuric anhydride has been added. Such 
 an acid may be obtained by heating some Nordhausen acid in 
 a retort connected with a receiver containing a small quantity of 
 the same acid. This liquid is introduced into the gas by means of 
 a dry coke bullet. These bullets are made by filling the mould, 
 into which the usual platinum wire has been placed, with a mixture 
 of equal weights of finely powdered coke and bituminous coal. 
 The mould is then heated as rapidly as possible to a bright red 
 heat, and opened after cooling ; a hard porous ball will have been 
 produced, which may be employed for many different reagents. 
 It is sometimes difficult to obtain the proper mixture of coal and 
 coke, but when once prepared, the bullets may be made with the 
 greatest ease and rapidity. The olefiant gas will be absorbed by the 
 sulphuric acid in about an hour, though they may be left in contact 
 for about two hours with advantage. If, on removing the bullet, 
 it still fumes strongly in the air, it may be assumed that the 
 absorption is complete. The gas now contains sulphurous, sulphuric, 
 and perhaps carbonic anhydrides ; these may be removed by 
 a manganic peroxide ball, followed by one of potassic hydrate, or 
 the former may be omitted, the caustic potash alone being used. 
 The various members of the CnH 2 n group cannot be separated 
 directly, but by the indirect method of analysis their relative 
 quantities in a mixture may be determined. 
 
 The hydrocarbons (CnH 2 n + 1 ) 2 and CnH 2 n + 2 may be absorbed 
 by absolute alcohol, some of which is introduced into the 
 absorption tube, and agitated for a short time with the gas. 
 
502 VOLUMETRIC ANALYSIS. 98. 
 
 Correction lias then to be made for the weight of the column of 
 alcohol on the surface of the mercury, and for the tension of the 
 alcohol vapour. This method only gives approximate results, and 
 can only be employed in the presence of gases very slightly soluble 
 in alcohol. 
 
 The time required in the different processes of absorption just 
 described is considerable ; perhaps it might be shortened by 
 surrounding the absorption eudiometer with a wider tube, similar 
 to the external tube of a Liebig's condenser, and through which 
 a current of water is maintained. By means of a thermometer in 
 the space between the tubes the temperature of the gas would be 
 known, and the readings might be taken two or three minutes 
 after the withdrawal of the reagents. Besides this advantage, the 
 great precaution necessary for maintaining a constant temperature 
 in the room might be dispensed with. A few -experiments made 
 some years ago in this direction gave satisfactory results. 
 
 INDIRECT DETERMINATIONS. 
 
 98. GASES which are not absorbed by any reagents that are 
 applicable in eudiometers over mercury, must be determined in an 
 indirect manner, by exploding them with other gases, and noting 
 either the change of volume or the quantity of their products 
 of decomposition; or lastly, as is most frequently the case, by 
 a combination of these two methods. Thus, for example, oxygen 
 may be determined by exploding with excess of hydrogen, and 
 observing the contraction ; hydrogen may be estimated by exploding 
 with excess of oxygen, and measuring the contraction ; and marsh 
 gas by exploding with oxygen, measuring the contraction, and also 
 the quantity of carbonic anhydride generated. 
 
 The operation is conducted in the following manner : -The long 
 eudiometer furnished with explosive wires is filled with mercury 
 (after a drop of water has been placed at the top of the tube by 
 means of an iron wire, as before described), and some of the gas to 
 be analyzed is introduced from the absorption eudiometer. This 
 gas is then measured with the usual precautions, and an excess of 
 oxygen or hydrogen (as the case may be) introduced. These gases 
 may be passed into the eudiometer directly from the apparatus in 
 which they are prepared ; or they may be previously collected in 
 lipped tubes of the form of absorption tubes, so as to be always 
 ready for use. 
 
 For the preparation of the oxygen a bulb is used, which is blown 
 at the closed end of a piece of combustion tube. The bulb is about 
 half filled with dry powdered potassic chlorate, the neck drawn out, 
 and bent to form a delivery tube. The chlorate is fused, and the 
 gas allowed to escape for some time to ensure the expulsion of the 
 atmospheric air; the end of the delivery tube is then brought 
 under the orifice of the eudiometer, and the necessary quantity of 
 
98. 
 
 INDIRECT DETERMINATIONS. 
 
 503 
 
 gas admitted. When it is desired to prepare the oxygen beforehand, 
 it may be collected directly from the bulb ; or, another method to 
 obtain the gas free from air may be adopted by those who are 
 provided with the necessary appliances. This is, to connect a bulb 
 containing potassic chlorate with a Sprengel's mercurial air-pump, 
 and, after heating the chlorate to fusion, to produce a vacuum in 
 the apparatus. The chlorate may be again heated until oxygen 
 begins to pass through the mercury at the end of the Sprengel, the 
 heat then withdrawn, and a vacuum again obtained. The chlorate 
 is once more heated, and the oxygen collected at the bottom of 
 the Sprengel. Of course the usual precautions for obtaning an 
 air-tight joint between the bulb and the Sprengel must be taken, 
 such as surrounding the caoutchouc connector with a tube filled 
 with mercury. 
 
 The hydrogen for these 
 experiments must be pre- 
 pared by electrolysis, since 
 that from other sources is 
 liable to contamination with 
 impurities which would 
 vitiate the analysis. The 
 apparatus employed by 
 Bunsen for this purpose 
 (fig. 89) consists of a glass 
 tube, closed at the lower 
 end, and with a funnel at 
 the other, into which a de- 
 livery tube is ground, the 
 funnel acting as a water- 
 joint. A platinum wire is 
 sealed into the lower part of 
 the tube ; and near the 
 upper end another wire, 
 with a platinum plate at- 
 tached, is fused into the 
 glass. Some amalgam of 
 zinc is placed into the tube 
 so as to cover the lower 
 platinum wire, and the ap- 
 paratus filled nearly to the neck with water, acidulated with 
 sulphuric acid. On connecting the platinum wires with a battery 
 of two or three cells, the upper wire being made the negative 
 electrode, pure hydrogen is evolved from the platinum plate, and, 
 after the expulsion of the air, may be at once passed into the 
 eudiometer, or, if preferred, collected in tubes for future use, 
 Unfortunately, in this form of apparatus, the zinc amalgam soon 
 becomes covered with a saturated solution of zinc sulphate, which 
 puts a stop to the electrolysis. In order to remove this layer, 
 
 Fig. 89. 
 
504 
 
 VOLUMETRIC ANALYSIS. 
 
 93. 
 
 Bunsen has a tube fused into the apparatus at the surface of the 
 amalgam ; this is bent upwards parallel to the larger tube, and 
 curved downwards just below the level of the funnel. The end 
 of the tube is closed with a caoutchouc stopper. On removing the 
 stopper, and pouring fresh acid into the funnel, the saturated liquid 
 is expelled. 
 
 Another form of apparatus for preparing electrolytic hydrogen 
 may readily be constructed. A six-ounce wide-mouth bottle is 
 fitted with a good cork, or better, with a caoutchouc stopper. In 
 the stopper four tubes are fitted (fig. 90). The first is a delivery 
 tube, provided with a U-tube, containing broken glass and sulphuric 
 acid, to conduct the hydrogen to the mercurial trough. The second 
 tube, about 5 centimeters long, and filled with mercury, has fused 
 into its lower end a piece of platinum wire carrying a strip of 
 
 foil, or the wire may be 
 simply flattened. The third 
 tube passes nearly to the 
 bottom of the bottle, the 
 portion above the cork is 
 bent twice at right angles, 
 and cut off, so that the 
 open end is a little above 
 the level of the shoulder 
 of the bottle ; a piece of 
 caoutchouc tube, closed by 
 a compression cock, is fitted 
 to the end of the tube. 
 The fourth tube is a piece 
 of combustion tube about 
 30 centimeters in length, 
 and which may with ad- 
 vantage be formed into a 
 funnel at the top. This 
 tube reaches about one-third 
 down the bottle, and inside 
 it is placed a narrower glass 
 tube, attached at its lower 
 end by a piece of caoutchouc 
 connector to a rod of amalgamated zinc. The tube is filled with 
 mercury to enable the operator readily to connect the zinc with 
 the battery ; some zinc amalgam is placed at the bottom of the 
 bottle ; and dilute sulphuric acid is poured in through the wide- 
 tube until the bottle is nearly filled with liquid. To use the 
 apparatus, the delivery tube is dipped into mercury, the wire from 
 the positive pole of the battery placed into the mercury in the 
 tube to which the zinc is attached, and the negative pole connected 
 by means of mercury with the platinum plate. The current, 
 instead of passing between the amalgam at the bottom of the 
 
 fig. 90. 
 
98. 
 
 EXPLOSION OF GASES. 
 
 505 
 
 vessel and the platinum plate, as in Bun sen's apparatus, travels 
 from the rod of amalgamated zinc to the platinum, consequently 
 the current continues to pass until nearly the whole of the liquid 
 in the bottle has become saturated with zinc sulphate. As soon as 
 the hydrogen is evolved, of course a column of acid is raised in 
 the funnel until the pressure is sufficient to force the gas through 
 the mercury in which the delivery tube is placed. Care must be 
 taken that the quantity of acid in the bottle is sufficient to prevent 
 escape of gas through the funnel tube, and also that the delivery 
 tube does not pass too deeply into the mercury so as to cause the 
 overflow of the acid. When the acid is exhausted, the compression 
 cock on the bent tube is opened and fresh acid poured into the 
 funnel ; the dense zinc sulphate solution is thus replaced by the 
 lighter liquid, and the apparatus is again ready for use. 
 
 A very convenient apparatus for transferring oxygen and 
 hydrogen into eudiometers is a gas pipette, figured and described 
 (fig. 62, page 423). 
 
 It is necessary in all cases to add an excess of the oxygen 
 or hydrogen before exploding, and it is well to be able to measure 
 approximately the amount added without going through the whole 
 of the calculations. This may be conveniently done by making 
 a rough calibration of the eudiometer in the following manner : 
 The tube is filled with mercury, a volume of air introduced into 
 it from a small tube, and the amount of the depression of the 
 mercury noted; a second volume is now passed up, a further 
 depression will be produced, but less in extent than the previous 
 one, in consequence of the shorter column of mercury in the tube. 
 This is repeated until the eudiometer is filled, and by means of a 
 table constructed from these observations, but without taking any 
 notice of the variations of thermometer or barometer, the operator 
 can introduce the requisite quantity of gas. It may be convenient 
 to make this calibration when the eudiometer is inclined in the 
 support, and also when placed perpendicularly, so that the gas 
 may be introduced when the tube is in either position. A table 
 like the following is thus obtained : 
 
 Measures. 
 1 
 
 2 
 3 
 4 
 5 
 
 6 
 
 7 
 &c. 
 
 DIVISIONS. 
 
 Tube 
 Inclined. 
 
 27 
 
 45 
 
 61 
 
 75 
 
 88 
 100 
 109 
 &c. 
 
 Tube 
 Perpendicular. 
 
 45 
 
 69 
 
 87 
 102 
 116 
 
 128 
 138 
 &c. 
 
 In explosions of hydrocarbons with oxygen, it is necessary to 
 
506 VOLUMETRIC ANALYSIS. 98. 
 
 have a considerable excess of the latter gas in order to moderate 
 the violence of the explosion. The same object may be attained 
 by diluting the gas with atmospheric air, but it is found that 
 sufficient oxygen serves equally well. If the gas contains nitrogen, 
 it is necessary subsequently to explode the residual gas with 
 hydrogen ; and if oxygen only has been used for diluting the 
 gas, a very large quantity of hydrogen must be added, which 
 may augment the volume in the eudiometer to an inconvenient 
 extent. When atmospheric air has been employed, this incon- 
 venience is avoided. After the introduction of the oxygen, the 
 eudiometer is restored to its vertical position, allowed to stand 
 for an hour, and the volume read off. 
 
 The determination of the quantity of oxygen which must be 
 added to combustible gases so as to prevent the explosion from being 
 too violent, and at the same time to ensure complete combustion, 
 has been made the subject of experiment. When the gases 
 before explosion are under a pressure equal to about half that 
 of the atmosphere, the following proportions of the gases must 
 be employed : 
 
 Volume of Volume of 
 
 Combustible Gas. Oxygen. 
 
 Hydrogen .... 1 T5 
 
 Carbonic oxide ... 1 1-5 
 
 Marsh gas .... 1 5 
 
 Gases containing two atoms of 
 
 carbon in the molecule, as 
 
 Methyl, C 2 H 6 ... 1 10 
 
 Gases containing three atoms of 
 
 carbon in the molecule, as 
 
 Propylic hydride, C 3 H 8 .1 18 
 
 Gases containing four atoms of 
 
 carbon in the molecule, as 
 
 Ethyl, OH 10 ... 1 25 
 
 In cases of mixtures of two or more combustible gases, 
 proportionate quantities of oxygen must be introduced. 
 
 At the time of the explosion, it is necessary that the 
 eudiometer should be carefully closed to prevent the loss 
 of gas by the sudden expansion. For this purpose a 
 thick plate of caoutchouc, three or four centimeters wide, is 
 cemented on a piece of cork by means of marine glue, or some 
 similar substance, and the lower surface of the cork cut so as to lie 
 firmly at the bottom of the mercurial trough (fig. 91). It is, how- 
 ever, preferable to have the caoutchouc firmly fixed in the trough. 
 As the mercury does not adhere to the caoutchouc, there is 
 some risk of air entering the eudiometer after the explosion ; 
 this is obviated by rubbing the plate with some solution of 
 corrosive sublimate before introducing it into the mercury, which 
 
98. 
 
 EXPLOSION OF GASES. 
 
 507 
 
 causes the metal to wet the caoutchouc and removes all air from 
 its surface. When the caoutchouc is not fixed in the trough, the 
 treatment with the corrosive sublimate has to be repeated before 
 every experiment, and this soils the surface of the mercury to an 
 inconvenient extent. The cushion is next depressed to the bottom 
 of the trough, and the eudiometer placed on it and firmly held 
 down (fig. 92). If this is done with the hands, the tube must 
 be held by that portion containing the mercury, for it is found 
 that when eudiometers burst (which, however, only happens when 
 some precaution has been neglected) 
 they invariably give way just at the 
 level of the mercury within the tube, 
 and serious accidents might occur if 
 the hands were at this point. The 
 cause of the fracture at this point is 
 the following : Though the gas is at 
 a pressure below that of the atmosphere 
 before the explosion, yet at the instant 
 of the passage of the spark, the ex- 
 pansion of the gas at the top of the 
 tube condenses the layer just below it ; 
 this 011 exploding increases the density 
 of the gas further down the tube, and 
 by the time the ignition is communicated 
 to the lowest quantity of gas, it may 
 be at a pressure far above that of the 
 atmosphere. It may be thought that 
 the explosion is so instantaneous that 
 this explanation is merely theoretical ; 
 but on exploding along column of gas, the 
 time required for the complete ignition 
 is quite perceptible, and sometimes the 
 flash may be observed to be more 
 brilliant at the surface of the mercury. 
 Some experimenters prefer to fix the 
 eudiometer by means of an arm from 
 a vertical stand, the arm being hollowed 
 out on the under side, and the cavity 
 lined with cork. 
 
 If. a large quantity of incombustible 
 gas is present, the inflammability of 
 
 the mixture may be so much reduced that either the explosion 
 does not take place at all, or, what may be worse, only a partial 
 combustion ensues. To obviate this, some explosive mixture of 
 oxygen and hydrogen, obtained by the electrolysis of water, 
 must be introduced. The apparatus used by Bun sen for this 
 purpose is shown in fig. 93. The tube in which the electrolysis 
 takes place is surrounded by a cylinder containing alcohol, in order 
 
 Fig. 92. 
 
508 
 
 VOLUMETRIC ANALYSIS. 
 
 98. 
 
 to prevent the heating of the liquid. A convenient apparatus- 
 for the preparation of this gas is made by blowing a bulb of 
 about four centimeters in diameter on the end of a piece of narrow 
 glass tube, sealing two pieces of flattened platinum wire into 
 opposite sides of the globe, and bending the tube so as to form 
 a delivery tube. Dilute sulphuric acid, containing about one volume- 
 of acid to twenty of water, is introduced into the globe, either 
 before bending the tube, by means of a funnel with a fine long; 
 stem, or, after the bending, by warming the apparatus, and 
 
 plunging the tube into- 
 the acid. Care must be 
 taken that the acid is- 
 dilute, and that the 
 battery is not too strong, 
 in order to avoid the 
 formation of ozone, which 
 would attack the mer- 
 cury, causing the sides 
 of the eudiometer to be 
 soiled, at the same time 
 producing a gas too rich 
 in hydrogen. 
 
 The spark necessary 
 to effect the explosion 
 may be obtained from 
 several sources. An ordi- 
 nary electrical machine 
 or electrophorus may be 
 used, but these are liable 
 to get out of order by 
 damp. Bunsen uses a 
 porcelain tube, which is 
 rubbed with a silk rub- 
 ber, coated with electrical 
 amalgam ; by means of 
 Fig. 93. this a small Leyden jar- 
 
 is charged. A still more 
 
 convenient apparatus is an induction coil large enough to produce 
 a spark of half an inch in length. 
 
 After the explosion, the eudiometer is slightly raised from the 
 caoutchouc plate to allow the entrance of mercury. When no more 
 mercury rushes in, the tube is removed from the caoutchouc plate, 
 placed in a perpendicular position, and allowed to remain for at 
 least an hour before reading. After measuring the contraction, it is- 
 generally necessary to absorb the carbonic anhydride formed by the 
 combustion by means of a potash ball, in the way previously 
 described. In some rare instances the amount of water produced 
 in the explosion with oxygen must be measured. If this has to be 
 

 
 METHODS OF CALCULATION. 
 
 509 
 
 done, the eudiometer, the mercury, the original gas, and the oxygen 
 must all be carefully dried. After the explosion, the eudiometer 
 is transferred to a circular glass vessel containing mercury, and 
 attached to an iron-wire support, by which the entire arrangement 
 can be suspended in a glass tube adapted to the top of an iron 
 boiler, from which a rapid current of steam may be passed through 
 the glass tube, so as to heat the eudiometer and mercury to an 
 uniform temperature of 100. From the measurements obtained at 
 this temperature the amount of water produced may be calculated. 
 If three combustible gases are present, the only data required for 
 calculation are, the original volume of the gas, the contraction on 
 explosion, and the amount of carbonic anhydride generated. When 
 the original gas contains nitrogen, the residue after explosion with 
 excess of oxygen consists of a mixture of oxygen and nitrogen. To 
 this an excess of hydrogen is added, and the mixture exploded ; the 
 contraction thus produced divided by 3 gives the amount of oxygen 
 in the residual gas, and the nitrogen is found by difference. 
 
 It is obvious that, by subtracting the quantity of residual oxygen, 
 thus determined by explosion with hydrogen, from the amount 
 added, in the first instance, to the combustible gas, the volume of 
 oxygen consumed in the explosion may be obtained. Some chemists 
 prefer to employ this number instead of the contraction as one of 
 the data for the calculation. 
 
 We must now glance at the mode of calculation to be employed 
 for obtaining the percentage composition of a gas from the numbers 
 arrived at by the experimental observations. 
 
 The following table shows the relations existing between the 
 volume of the more important combustible gases and the products 
 of the explosion : - 
 
 Name of Gas. 
 
 Volume of 
 Combustible 
 Gas. 
 
 Volume of 
 Oxygen 
 Consumed. 
 
 Contraction 
 after 
 Explosion. 
 
 "o S'St* 
 
 ill! 
 
 2<31& 
 
 Hydrogen, H 
 
 
 0-5 
 
 1-5 
 
 
 
 Carbonic Oxide, CO 
 
 
 0-5 
 
 0-5 
 
 i 
 
 Methylic Hydride, CH 3 H . 
 
 
 2 
 
 2 
 
 i 
 
 Acetylene, C 2 H 2 . 
 
 
 2-5 
 
 1-5 
 
 2 
 
 Olefiant Gas, C 2 H 4 . ' . 
 
 
 3 
 
 2 
 
 2 
 
 Methyl, CH 3 , CH 3 
 
 
 3-5 
 
 2-5 
 
 2 
 
 Ethylic Hydride, C 2 rf 5 H 
 
 
 3-5 
 
 2-5 
 
 2 
 
 Propylene, C 3 H 6 . 
 
 
 4-5 
 
 2-5 
 
 3 
 
 Propylic Hydride, C 3 H 7 H . 
 
 
 5 
 
 3 
 
 3 
 
 Butylene, C 4 H 8 . 
 
 
 6 
 
 3 
 
 4 
 
 Ethyl, C 2 H 5 , C 2 H 5 
 
 
 6-5 
 
 3-5 
 
 4 
 
 Butylic Hydride, C 4 H 9 H 
 
 1 
 
 6-5 
 
 3-5 
 
 4 
 
510 VOLUMETRIC ANALYSIS. 98. 
 
 As an example, we may take a mixture of hydrogen, carbonic 
 oxide, and marsh gas, which gases may be designated by x, y, and z 
 respectively. The original volume of gas may be represented by A, 
 the contraction by C, and the amount of carbonic anhydride by D. 
 
 A will, of course, be made up of the three components, or 
 
 A = x + y + z. 
 
 C will be composed as follows : When a mixture of hydrogen and 
 oxygen is exploded, the gas entirely disappears. One volume of 
 hydrogen combining with half a volume of oxygen, the contraction 
 will be 1J times the quantity "of hydrogen present, or 1 J.r. In the 
 case of carbonic oxide, 1 volume of this gas uniting with half its 
 volume of oxygen produces 1 volume of carbonic anhydride, so 
 the contraction due to the carbonic oxide will be half its volume, 
 or Jv/. Lastly, 1 volume of marsh gas combining with 2 volumes of 
 oxygen generates 1 volume of carbonic anhydride, so the contraction 
 in this case will be twice its volume, or 2z. Thus we have 
 
 Since carbonic oxide on combustion forms its own volume of 
 carbonic anhydride, the amount produced by the quantity present 
 in the mixture will be y. Marsh gas also generates its own volume 
 of carbonic anhydride, so the quantity corresponding to the marsh 
 gas in the mixture will be z. Therefore 
 
 i>=y+z. 
 
 It now remains to calculate the values of x, y, and z from the 
 experimental numbers A, C, and D, which is done by the help 
 of the following equations : 
 
 To find x 
 
 x+y+z= A ,. 
 
 x = A - P . 
 
 For y we have ^ + 4 , == 4I) ? 
 
 = 3 A - 3D , 
 
 3A-2C + D ' 
 
 y = - 
 
 The value of z is thus found 
 
 3A-2C + D 
 
 ~3 ' r 
 
 2C-3A + 2D m 
 
98. METHODS OF CALCULATION. 511 
 
 By replacing the letters A, C, and D by the numbers obtained 
 by experiment, the quantities of the three constituents in the 
 volume A may easily be calculated by the three formulae 
 
 x = A D = hydrogen , 
 
 3A-2C + D 
 
 2/= - o *" = carbonic oxide , 
 
 2C-3A + 2D 
 z o = marsh gas . 
 
 The percentage composition is, of course, obtained by the simple 
 proportions 
 
 A : x : : 100 : per-cent. of hydrogen , 
 
 A : y : : 100 : per-cent. of carbonic oxide, 
 
 A : z : : 100 : per-cent. of marsh gas . 
 
 If the gas had contained nitrogen, it would have been determined 
 by exploding the residual gas, after the removal of the carbonic 
 anhydride, with excess of hydrogen. The contraction observed r 
 divided by 3, would give the volume of oxygen in the residue, and 
 this deducted from the residue, would give the amount of nitrogen. 
 If A again represents the original gas, and n the amount of nitrogen 
 it contains, the expression A n would have to be substituted for 
 A in the above equations. 
 
 It may be as well to develop the formula for obtaining the same 
 results by observing the volume of oxygen consumed instead of the 
 contraction. If B represent the quantity of oxygen, we shall have 
 
 the values of A and D remaining as before, x = A - D. 
 z is thus found 
 
 3z = 2B - A , or 
 
 x + y + z = 
 
 2B-A 
 
 For y 
 
 ? _3D-2B + A 
 
512 VOLUMETEIC ANALYSIS. 98. 
 
 Thus we have 
 
 x = A-D 
 
 3D-2B + A 
 
 y= 3 
 
 2B-A 
 
 Having thus shown the mode of calculation of the formulae, it 
 will be well to give some examples of the formulae employed in 
 some of the cases which most frequently present themselves in gas 
 analysis. In all cases 
 
 A = original mixture , 
 
 C =sz contraction , 
 
 D = carbonic anhydride produced. 
 
 1. Hydrogen and Nitrogen. 
 
 Excess of oxygen is added, and the contraction on explosion 
 -observed : 
 
 _2C 
 = 3 ' 
 
 3A-2C 
 
 y = - - , or A - x . 
 
 2. Carbonic Oxide and Nitrogen. 
 
 The gas is exploded with excess of oxygen, and the amount of 
 .carbonic anhydride produced is estimated : 
 
 3. Hydrogen, Carbonic Oxide, and Nitrogen. 
 
 In this case the contraction and the quantity of carbonic 
 .anhydride are measured : 
 
 2C-D 
 
 3A-2C-2D 
 
98. METHODS OF CALCULATION. 513 
 
 4. Hydrogen, Marsh Gas, and Nitrogen. 
 
 2C-4D 
 -- 
 
 3A-2C + D 
 
 -- ~ 
 
 Carbonic Oxide, Marsh Gas, and Nitrogen, 
 4D-2C 
 
 3 
 2C-D 
 
 
 C. Hydrogen, Methyl (or Ethylic Hydride), and 
 Xitrogen. 
 
 H = ar; C 2 H 6 = y ; N-=& 
 4C-5D 
 
 3A-2C + D 
 3 
 
 7. Carbonic Oxide, Methyl (or Ethylic Hydride), 
 and Nitrogen. 
 
 5D - 4C 
 
 2C-D 
 
 3A - 4D + 2G 
 3 
 
 L L 
 
514 VOLUMETRIC ANALYSIS. 98. 
 
 8. Hydrogen, Carbonic Oxide, and Marsh Gas. 
 
 3A-2C + D 
 
 2C-3A + 2D 
 
 9. Hydrogen, Carbonic Oxide, and Ethylic Hydride 
 (or Methyl). 
 
 3A + 2C-4D 
 
 ~~6~ 
 3A-2C + D 
 
 10. Carbonic Oxide, Marsh Gas, and Ethylic Hydride 
 (or Methyl). 
 
 C0=ar; CH 4 = // ; C 2 H 6 = ::. 
 
 3A-2C + D 
 x=- -5- 
 
 3A + 2C-4D 
 
 11. Hydrogen, Marsh Gas, and Acetylene. 
 H = x CH 4 = y ; C 2 H 2 = ::. 
 
 5A-2C -D 
 
 a?= - g - ' 
 
 ?/ = 2C-3A, 
 D-2C + 3A 
 2 ' 
 
 12. Hydrogen, Marsh Gas, and Ethylic Hydride 
 
 (or Methyl). 
 H = x CH 4 = y ; C 2 H G = z. 
 
 This mixture cannot be analyzed by indirect determination, since 
 a mixture of two volumes of hydrogen with two volumes of ethylic 
 
98. METHODS OF CALCULATION. 515 
 
 hydride (or methyl) has the same composition as four volumes of 
 marsh as 
 
 and, consequently, would give rise to the same products on 
 combustion with oxygen as pure marsh gas 
 
 C2H + H 2 + s = 2C0 2 + 40H 2 ; 
 
 In this case it is necessary to estimate by direct determination the 
 ethylic hydride (or methyl) in a separate portion of the gas by 
 absorption with alcohol, another quantity of the mixture being 
 exploded with oxygen, and the amount of carbonic anhydride pro- 
 duced and measured. If the quantity absorbed by alcohol =E, then 
 
 x = A - 1) + E , 
 
 13. Hydrogen, Carbonic Oxide, Propylic Hydride, 
 
 3A + 4C-5D 
 9 
 
 3A-2C + D 
 
 ?/= 3 > 
 
 2C-3A + 2D 
 
 ~9~ ~- 
 
 14. Carbonic Oxide, Marsh Gas, and Propylic Hydride, 
 
 3A-2C + D 
 3A + 4C-5D 
 _Dj-A 
 
 15. Carbonic Oxide, Ethylic Hydride (or Methyl), 
 
 and Propylic Hydride. 
 CO = x ; C 2 H 6 = y ; C 3 H S = z. 
 3A-2C + D 
 
 x= ~ 3 ' 
 
 3A + 4C-5D 
 
 y- -3 ' 
 
 4D-3A - 2C 
 
 L L 2 
 
516 VOLUMETRIC ANALYSIS. 98. 
 
 16. Marsh Gas, Ethylic Hydride (or Methyl), and 
 Propylic Hydride. 
 
 = x ; C 2 H = y ; C 3 H 8 = z. 
 
 As a mixture of two volumes of marsh gas and two of propylic 
 hydride has the same composition as four of ethylic hydride (or 
 methyl) 
 
 CH 4 + C 3 H 8 = 2C 2 H 6 , 
 
 the volume absorbed by alcohol, and which consists of ethylic 
 hydride (or methyl) and propylic hydride, must be determined, 
 and another portion of the gas exploded, and the contraction 
 measured. If E represents the volume absorbed 
 
 a; = A-E, 
 
 y = 4A - 2C + 2E , 
 &W2C-4A-E. 
 
 17. Hydrogen, Carbonic Oxide, and Ethyl (or Butylic 
 
 Hydride). 
 
 A + 2C-2D 
 
 -v -' 
 
 3A-2C+D 
 
 y= -y- -, 
 
 2C + 2D-3A 
 
 18. Nitrogen, Hydrogen, Carbonic Oxide, Ethylic 
 Hydride (or Methyl), and Butylic Hy-dride (or Ethyl). 
 
 N = ; !! = ;; C0=>; C 2 H 5 = // ; C 4 H 10 = :. 
 
 In one portion of the gas the ethylic hydride (or methyl) and 
 the butylic hydride (or ethyl) are absorbed by alcohol ; the amount 
 absorbed = E. 
 
 A second portion of the original gas is mixed with oxygen and 
 exploded, the amount of contraction and of carbonic anhydride 
 being measured. 
 
 The residue now r contains the nitrogen and the excess of oxygen; 
 to this an excess of hydrogen is added, the mixture exploded, and 
 the contraction measured. From this the quantity of nitrogen is 
 thus obtained. *Let 
 
 G = excess of oxygen and nitrogen, 
 v = excess of oxygen, 
 u - nitrogen, 
 C' = contraction on explosion with hydrogen. 
 
99. IMPROVED GAS APPARATUS. 517 
 
 Then 
 
 G = v + n , 
 
 3G-C' 
 
 3 "' 
 
 From these data the composition of the mixture can be 
 determined 
 
 2C - D - 3E 
 
 W = 
 
 
 3 
 _3A-2C-2D + 12E-3n 
 
 _ 2C - 3A + '2P-6E + 3K 
 6 
 
 MODIFICATIONS AND IMPROVEMENTS UPON THE 
 FOREGOING^ PROCESSES. 
 
 99. IN the method of gas analysis that we have been consider- 
 ing, the calculations of results are somewhat lengthy, as will be 
 seen by a reference to the example given of the analysis of a 
 mixture of air and carbonic anhydride (page 497). Besides this, the 
 operations must be conducted in a room of uniform temperature, 
 and considerable time allowed to elapse between the manipulation 
 and the readings in order to allow the eudiometers to acquire the 
 temperature of the surrounding air ; and, lastly, the absorption of 
 gases by solid reagents is slow. These disadvantages are to a 
 great extent counterbalanced by the simplicity of the apparatus, 
 and of the manipulation. 
 
 From time to time various chemists have proposed methods by 
 which the operations are much hastened and facilitated, and the 
 calculations shortened. It will be necessary to mention a few of 
 these processes, which, however, require special forms of apparatus. 
 
 Williamson and Russell have described (Proceeding* of the 
 Royal Society, ix. 218) an apparatus, by means of which the 
 gases in the eudiometers are measured under a constant pressure,,, 
 the correction for temperature being eliminated by varying the 
 column of mercury in the tube so as to compensate for the alteration 
 of volume observed in a tube containing a standard volume of moist 
 air. In this case solid reagents were employed in the eudiometers. 
 
518 VOLUMETRIC ANALYSIS. 99. 
 
 In 1864 they published (/. C. S. xvii. 238) a further develop- 
 ment of this method, in which the absorptions were conducted in 
 a separate laboratory vessel, by which means the reagents could be 
 employed in a pasty condition and extended over a large surface. 
 
 And in 1868 Russell improved the apparatus, so that liquid 
 reagents could be used in the eudiometers, and the analysis rapidly 
 executed. A description of this last form of instrument may be 
 found in /. 0. S. xxi. 128. 
 
 The gutta-percha mercury trough employed is provided with 
 a deep well, into which the eudiometer can be depressed to any 
 required extent, and on the surface of the mercury a wide glass 
 cylinder, open at both ends and filled with water, is placed. The 
 eudiometer containing the gas to be examined is suspended within 
 the cylinder of water by means of a steel rod passing through 
 a socket attached to a stout standard firmly fixed to the table. In 
 a similar manner, a tube containing moist air is placed by the side 
 ef the eudiometer. The clamp supporting this latter tube is 
 provided with two horizontal plates of steel, at which the column 
 of the mercury is read off. When a volume of gas has to be 
 measured, the pressure tube containing the moist air is raised or 
 lowered, by means of an ingeniously .contrived fine adjustment, 
 until the mercury stands very nearly at the level of one of the 
 horizontal steel plates. The eudiometer is next raised or lowered 
 until the column of mercury within it is at the same level. The 
 final adjustment to bring the top of the meniscus exactly to the 
 lower edge of the steel bar is effected by sliding a closed wide glass 
 tube into the mercury trough. Thus we have two volumes of gas 
 under the same pressure and temperature, and both saturated with 
 moisture. If the temperature of the water in the cylinder increased, 
 there would be a depression of the columns in both tubes ; but by 
 lowering the tubes, and thus increasing the pressure until the 
 volume of air in the pressure tube was the same as before, it would 
 be found that the gas in the eudiometer Avas restored to the original 
 volume. Again, if the barometric pressure increased, the volumes 
 of the gases would be diminished ; but, by raising the tubes to the 
 necessary extent, the previous volumes would be obtained. There- 
 fore, in an analysis, it is only necessary to measure the gas at 
 a pressure equal to that which is required to maintain the volume 
 of moist air in the pressure tube constant. The reagents are 
 introduced into the eudiometer in the liquid state by means of 
 a small syringe made of a piece of glass tube about one-eighth of 
 an inch in diameter. For this purpose the eudiometer is raised 
 until its open end is just below the surface of the mercury, and 
 the syringe, which is curved upwards at the point, is depressed in 
 the trough, passed below the edge of the water-cylinder, and the 
 extremity of the syringe introduced into the eudiometer. When 
 a sufficient quantity of the liquid has been injected, the eudiometer 
 is lowered and again raised, so as to moisten the sides of the tube 
 

 with the liquid, and thus hasten the absorption. Ten minutes was 
 found to be a sufficient time for the absorption of carlxmic 
 anhydride when mixed with air. 
 
 To remove the liquid reagent, a ball of moistened cotton wool is 
 employed. The ball is made in the following manner : A piece 
 of steel wire is bent into a loop at one end, and some cotton wool 
 tightly wrapped round it. It is then dipped in water and squeezed 
 with the hand under the liquid until the air is removed. The end 
 of the steel wire is next passed through a piece of glass tube, 
 curved near one end, and the cotton ball drawn against the curved 
 extremity of the tube. The ball, saturated with water, is now 
 depressed in the mercury trough, and, after as much of the water 
 as possible has been squeezed out of it, it is passed below the 
 eudiometer, and, by pushing the wire, the ball is brought to the 
 surface of the mercury in the eudiometer and rapidly absorbs all 
 the liquid reagent, leaving the meniscus clean. The ball is removed 
 with a slight jerk, and gas is thus prevented from adhering to it. 
 It is found that this mode of removing the liquid can be used 
 without fear of altering the volume of the gas in the eudiometer. 
 
 Carbonic anhydride may be absorbed by a solution of potassic 
 hydrate, and oxygen by mfans of potassic hydrate and pyrogallic 
 acid. The determination of ethylene is best effected by means of 
 fuming sulphuric acid on a coke ball, water and dilute potassic 
 hydrate being subsequently introduced and removed by the ball of 
 cotton wool. 
 
 Doubtless this mode of using the liquid reagents might be 
 employed with advantage in the ordinary process of analysis to 
 diminish the time necessary for the absorption of the gases. By 
 this process of Russell's the calculations are much shortened 
 and facilitated, the volumes read off being comparable among 
 themselves ; this will be seen by an example, taken from the 
 original memoir, of the determination of oxygen in air 
 
 Volume in Table 
 
 corresponding 
 
 to reading. 
 
 Volume of air taken . . . ISO'S 132 '15 
 
 Volume after absorption of oxygenl 
 
 by potassic hydrate and pyro- - 103-5 104*46 
 gallic acid . . . . j 
 132-15 
 104-46 
 
 '2 1 -6 9 volumes of oxygen in 132 '15 of air. 
 132*15 : 27'69 : : 100 : 20 '953 percentage of oxygen in air. 
 
 Russell has also employed his apparatus for the analysis of 
 carbonates (/. C. S. [x.s.] vi. 310). For this purpose he adapted 
 a graduated tube, open at both ends, to a glass flask by means of 
 a thick piece of caoutchouc tube. Into the flask a weighed 
 quantity of a carbonate was placed, together with a vessel 
 
520 
 
 VOLUMETRIC ANALYSIS. 
 
 20. 
 
 containing dilute acid. The position of the mercury in the 
 graduated tube was first read off, after which the flask was shaken 
 so as to bring the acid and carbonate in contact, and the increase in 
 volume was due to the carbonic anhydride evolved. The results 
 thus obtained are extremely concordant. 
 
 In eight experiments with sodic carbonate the percentage of 
 carbonic anhydride found varied from 41*484 to 41 -GOT, theory 
 requiring 41 '509. 
 
 Thirteen experiments with calc-spar gave from 43 '520 to 43*858, 
 the theoretical percentage being 44*0; and in nine other analyses 
 from 43-581 to 43*901 were obtained. 
 
 Two experiments were 
 made with manganic per- 
 oxide, oxalic acid and sul- 
 phuric acid, and gave 58*156 
 and 58*101 per cent, of 
 carbonic anhydride. 
 
 Some determinations of 
 the purity of magnesium 
 were also performed by dis- 
 solving the metal in hydro- 
 chloric acid and measuring 
 the resulting hydrogen. 
 Four operations gave num- 
 bers varying between 8*255 
 and 8*282. The metal 
 should yield 8*333. 
 
 Russell has also em- 
 ployed this process for the 
 determination of the com- 
 bining proportions of nickel 
 and cobalt (/. C. S. [N.S.] 
 vii. 294). 
 
 Eegnault and Reiset 
 described (Jinn. Cldm. PJn/s. 
 [3] xxvi. 333) an appara- 
 tus by which absorptions 
 could be rapidly conducted 
 by means of liquid reagents 
 brought in contact with the 
 gases in a laboratory tube. 
 
 The measurements are made 
 
 Pig. P4. 
 
 in a graduated tube, which can be placed in communication with 
 the laboratory tube by means of fine capillary tubes provided with 
 stop-cocks, the lower end of the measuring tube being connected by 
 an iron socket and stop-cock with another graduated tube in which 
 the pressure to which the gas is subjected is measured. The 
 measuring and pressure tubes are surrounded by a cylinder of water. 
 
FIIANKLAND AND WATID'S APPARATUS. 521 
 
 An apparatus similar in principle to this lias recently been 
 constructed by Frank land, and is fully described in the section 
 on Water Analysis ( 89, page 417). 
 
 Frankland and Ward (/. C. S. vi. 197) made several 
 important improvements in the apparatus of Regnault and 
 Keiset. They introduced a third tube (fig. 94), closed at the top 
 with a stopper, and which is made to act as a barometer, to indicate 
 the tension of the gas in the measuring tube, thus rendering the 
 operation entirely independent of variations of atmospheric pressure. 
 The correction for aqueous vapour is also eliminated, by introducing 
 a drop of water into the barometer as well as into the measuring 
 tube, the pressures produced by the aqueous vapour in the two 
 tubes thus counterbalancing one another, so that the difference of 
 level of the mercury gives at once the tension of the dry gas. The 
 measuring tube is divided into ten equal divisions (which, for some 
 purposes, require to be calibrated), and in one analysis it is 
 convenient to make all the measurements at the same division, or 
 to calculate the tension which would be exerted by the gas if 
 measured at the tenth division. Frankland and Ward also 
 adapted an iron tube more than 760 m.m. long at the bottom of 
 the apparatus, which enables the operator to expand the gas to any 
 required extent, and thus diminish the violence of the explosions 
 which are performed in the measuring tube. During the operation 
 a constant stream of water is kept flowing through the cylinder, 
 which maintains an uniform temperature. 
 
 By the use of this form of apparatus the calculations of analyses 
 are much simplified. . An example of an analysis of atmospheric 
 air will indicate the method of using the instrument. 
 
 Volume of Air used. Determined at 5th Division on 
 the Measuring Tube. 
 
 m.m. 
 
 Observed height of mercury in barometer . 673*0 
 
 Height of 5 th division . . . . 383-Q 
 
 Tension 01 gas 
 
 Corrected tension of gas at 10th division 
 
 Volume after Admission of Hydrogen. Determined 
 at 6th Division. 
 
 m.m. 
 
 Observed height of mercury in barometer . 772'3 
 
 Height of 6th division . . 304-Q 
 
 TeLsion of gas . 468'3 
 0-6 
 Corrected tension at 10th division . 280 98 
 
522 VOLUMETRIC ANALYSIS. 99. 
 
 Volume after Explosion. Determined at 5th Division. 
 
 m.m. 
 
 Observed height of mercury in barometer . 763*3 
 
 Height of 5th division .... 383*0 
 
 Tension of gas . 3 80 '3 
 0-5 
 
 Corrected tension at 10th division . . 190*15 
 
 Tension of air with hydrogen . . .280*98 
 
 Tension of gas after explosion . . .190*15 
 
 Contraction on explosion . . . 90*83 
 of which one-third is oxygen. 
 
 90*83 
 
 0^ = 30*276 = volumes of oxygen in 145*0 volumes of air 
 
 145*0 : 30*276 : : 100 : x 
 
 30*276x100 _ Q 
 . x= j~jV7A = 20 *8b = percentage ot oxygen in air. 
 
 If all the measurements had been made at the same division, no 
 correction to the tenth division would have been necessary, as the 
 numbers would have been comparable among themselves. 
 
 Another modification of Frank land and "Ward's, or 
 Kegnault's apparatus has been designed by McLeod (/. C. >S Y . 
 [N.S.] vii. 313), in which the original pressure tube of Regnault's 
 apparatus, or the filling tube of Frank land and Ward, is 
 dispensed with, the mercury being admitted to the apparatus 
 through the stop-cocks at the bottom. 
 
 The measuring tube A (fig. 95) is 900 m.m. in length, and about 
 20 m.m. in internal diameter. It is marked with ten divisions, the 
 first at 25 m.m. from the top, the second at 50, the third at 100, 
 and the remaining ones at intervals of 100 m.m. In the upper 
 part of the tube, platinum wires are sealed, and it is terminated by 
 a capillary tube and fine glass stop-cock, a, the capillary tube being 
 bent at right angles at 50 m.m. above the junction. At the bottom 
 of the tube, a wide glass stop-cock b is sealed, which communicates, 
 by means of a caoutchouc joint surrounded with tape and well 
 wired to the tubes, with a branch from the barometer tube B. 
 This latter tube is 5 m.m. in width, and about 1200 m.m. long, 
 and is graduated in millimeters from bottom to top. At the upper 
 extremity a glass stop-cock d is joined, the lower end being curved 
 and connected by caoutchouc with a stop-cock and tube C, 
 descending through the table to a distance of 900 m.m. below the 
 joint. It is advisable to place washers of leather at the end of the 
 plugs of the stop-cocks c and &, as the pressure of the mercury 
 which is afterwards to be introduced has a tendency to force them 
 out if this should happen, the washers prevent any great escape 
 of mercury. 
 
99. 
 
 C LEOD S APPARATUS. 
 
 523 
 
 lig. 95. 
 
524 VOLUMETRIC ANALYSIS. 99. 
 
 The two tubes are firmly held by a clamp D, on which rests 
 a wide cylinder E, about 55 m.m. in diameter, surrounding the 
 tubes, and adapted to them by a water-tight caoutchouc cork F. 
 The cylinder is maintained in an upright position by a support at 
 its upper end G, sliding on the same rod as the clamp. Around 
 the upper part of the barometer tube a syphon H is fixed by means 
 of a perforated cork, through which the stop-cock d passes. A small 
 bulb-tube e, containing some mercury, is also fitted in this cork, so 
 as to allow of the air being entirely removed from the syphon. The 
 syphon descends about 100 m.m. within the cylinder, and has 
 a branch at the top communicating by caoutchouc with a bent tube 
 contained in a wider one J affixed to the support. A constant 
 current of water is supplied to the cylinder through a glass tube, 
 which passes to the bottom, and escapes through the syphon and 
 tubes to the drain. 
 
 To the end of the narrow tube C is fastened a long piece of 
 caoutchouc tube K, covered with tape, by which a communication 
 is established with the mercurial reservoir L, suspended by a cord 
 so that by means of the winch M, it may be raised above the level 
 of the top of the barometer tube. As the mercury frequently forces 
 its way through the pores of the caoutchouc tube, it is advisable 
 to surround the lower part with a piece of wide flexible tube ; this 
 prevents the scattering of the mercury, which collects in a tray 
 placed on the floor. Into the bottom of the tray a screw must be 
 put, to which the end of the glass tube is firmly attached by wire. 
 The capillary stop-cock a is provided with a steel cap, by means of 
 which it may be adapted to a short and wide laboratory tube 
 capable of holding about 150 c.c., and identical in form with, 
 the one described in the section on Water Analysis ( 89). The 
 mercurial trough for the laboratory tube is provided with a stand 
 with rings, for the purpose of holding two tubes containing gases 
 that may be required. 
 
 The apparatus is used in the same way as Frank land and 
 Ward's, except that the mercury is raised and lowered in the tubes 
 by the movement in the reservoir L, instead of by pouring it into 
 the centre supply-tube. 
 
 To arrange the apparatus for use, the reservoir L is lowered to the 
 ground, and mercury poured into it. The laboratory tube being 
 removed, the stop-cocks are all opened, and the reservoir gradually 
 raised. When the tube A is filled, the stop-cock a is closed, and 
 the reservoir eleA'ated until mercury flows through the stop-cock d at 
 the top of the barometer. It is convenient to have the end of 
 the tube above the stop-cock so bent that a vessel can be placed 
 below to receive the mercury. This bend must, of course, be so 
 short that, when the plug of the stop-cock is removed, the syphon 
 will pass readily over. When the air is expelled from the barometer 
 tube, the stop-cock is closed. A few drops of water must next be 
 introduced into the barometer : this is accomplished by lowering 
 
99. MC LEOD'S GAS APPARATUS. 525 
 
 the reservoir to a short distance below the top of the barometer, and 
 gently opening the stop-cock d, while a small pipette, from which 
 water is dropping, is held against the orifice, the stop-cock being 
 closed when a sufficient amount of water has penetrated into the 
 tube. In the same manner, a small quantity of water is passed into 
 the measuring tube. In order to get rid of any bubbles of air which 
 may still linger in the tubes, the reservoir is lowered to the ground 
 so as to produce a vacuum in the apparatus ; in this manner the 
 interior surfaces of the tubes become moistened. The reservoir is 
 now gently raised, thus refilling the tubes with mercury. Great 
 care must be taken that the mercury does not rush suddenly against 
 the tops of the measuring and barometer tubes, which might cause 
 their destruction. This may be avoided by regulating the flow of 
 mercury by means of the stop-cock c, which may be conveniently 
 turned by a long key of wood, resting against the upper table of 
 the sliding stand of the mercurial trough. When the reservoir 
 has again been elevated abcve the top of the barometer, the 
 stop-cocks of the measuring and barometer tubes are opened, and 
 the air and water which have collected allowed to escape. 
 
 The heights of the mercurial columns in the barometer, corre- 
 sponding to the different divisions of the measuring tube, have now 
 to be determined. This is done by running out all the mercury 
 from the tub?-s, and slowly readmitting it until the meniscus of the 
 mercury just touches the lowest division in the measuring tube. 
 This may be very conveniently managed by observing the division 
 through a small telescope of short focus, and sufficiently close to the 
 apparatus to permit of the key of the stop-cock c being turned, while 
 the eye is still at the telescope. When a reading is taken, the 
 black screen behind the apparatus must be moved by means of 
 the winch P, until its lower edge is about a millimeter above the 
 division. The telescope is now directed to the barometer tube, and 
 the position of the mercury carefully noted. As the tubes only 
 contain aqueous vapour, and are both of the same temperature, the 
 columns in the two tubes are those which exactly counterbalance 
 one another, and any difference of level that may be noticed is due 
 to capillarity. 
 
 The same operation is now repeated at each division of the tube. 
 The measuring tube next requires calibration, an operation performed 
 in a manner perfectly similar to that described in. 89 (page 420), 
 namely, by filling the measuring tube with water, and weighing the 
 quantities contained between every two divisions. The eudiometer 
 being filled with water, and the stop-cock b closed, the reservoir is 
 raised and the mercury allowed to rise to the top of the barometer. 
 The capillary stop-cock a having been opened, the cock b is gently 
 turned, and the water allowed to flow out until the mercury reaches 
 the lowest division of the tube. A carefully weighed flask is now 
 supported just below the steel cap, the stop-cock b again opened, 
 until the next division is reached, and the quantity of water is 
 
526 VOLUMETRIC ANALYSIS. 99. 
 
 -weighed, the temperature of the water in the wide cylinder being 
 observed. The same operation is repeated at each division, and by 
 calculation the exact contents of the tube in cubic centimeters may 
 be found. 
 
 In this manner, a table, such as the following, is obtained : 
 
 Division 
 on 
 measuring 
 tube. 
 
 Height of Mercury in 
 Barometer tube 
 corresponding to 
 
 division. 
 
 Contents. 
 Cubic Centimeters. 
 
 Log. 
 
 1 
 
 756-9 
 
 8-6892 
 
 
 
 9389S14 
 
 2 
 
 706-7 
 
 18-1621 
 
 1 
 
 2591664 
 
 3 
 
 606-8 
 
 36-9307 
 
 
 5673880 
 
 4 
 
 506-5 
 
 55-7344 
 
 1 
 
 7461232 
 
 5 
 
 406-8 
 
 74-4299 
 
 1-8717477 
 
 6 
 
 306-8 
 
 93-3306 
 
 1 
 
 9700244 
 
 7 
 
 206-9 
 
 112-4165 
 
 o 
 
 0508303 
 
 8 
 
 107-0 
 
 131-6335 
 
 2 
 
 1193666 
 
 9 
 
 7-1 
 
 151-1623 
 
 f) 
 
 1794435 
 
 AVhen a gas is to be analyzed, the laboratory tube is filled with 
 mercury, either by sucking the air out through the capillary 
 stop-cock, while the open end of the tube stands in the trough, or 
 much more conveniently, by exhausting the air through a piece of 
 flexible tube passed under the mercury to the top of the laboratory 
 tube, the small quantity of air remaining in the stop-cock and at 
 the top of the wide tube being afterwards very readily withdrawn. 
 The face of one of the steel pieces is greased with a small miantity 
 of resin cerate, and, the measuring apparatus being full of mercury, 
 the clamp is adjusted. 
 
 Before the introduction of the gas, it is advisable to ascertain if 
 the capillary tubes are clear, as a stoppage may arise from the 
 admission of a small quantity of grease into one of them. For 
 this purpose the globe L is raised above the level of the top of the 
 measuring tube, and the capillary stop-cocks opened ; if a free 
 passage exists, the mercury will be seen to flow through the tubes. 
 The stop-cock of the laboratory tube is now closed. When all is 
 properly arranged, the gas is transferred into the laboratory tube, 
 and the stop-cock opened, admitting a stream of mercury. The 
 cock c is gently turned, so as just to arrest the flow of mercury 
 through the apparatus, and the reservoir lowered to about the level 
 of the table, which is usually sufficient. By carefully opening the 
 cock c, the gas is drawn over into the measuring tube, and when 
 the mercury has reached a point in the capillary tube of the 
 laboratory tube, about midway between the bend and the stop-cock, 
 the latter is quickly closed. It is necessary that this stop-cock 
 should 1)0 very perfect. This is attained by grinding the plug into 
 
99. MC LEOD'B GAS APPARATUS. 527 
 
 the socket with fine levigated rouge and solution of sodic or potassic 
 hydrate. By this means the plug and socket may be polished so 
 that a very small quantity of resin cerate and a drop of oil renders 
 it perfectly gas-tight. In grinding, care must be taken that the 
 operation is not carried on too long, otherwise the hole in the plug 
 may not coincide with the tubes. If this stop-cock is in sufficiently 
 good order, it is unnecessary to close the stop-cock a during an analysis. 
 
 The mercury is allowed to flow out of the apparatus until its 
 surface is a short distance below the division at which the measure- 
 ments are to be made. The selection of the division depends on 
 the quantity of gas and the kind of experiment to be performed 
 with it. A saving of calculation is effected if all the measurements 
 in one analysis are carried on at the same division. When the 
 mercury has descended below the division, the cock c is closed, the 
 reservoir raised, and the black screen moved until its lower edge is 
 about a millimeter above the division, and the telescope placed so- 
 that the image of the division coincides with the cross-wires in the 
 eye-piece. The stop-cock c is now gently opened until the meniscus 
 just touches the division ; the cock is closed and the height of the- 
 mercury in the barometer is measured by means of the telescope. 
 The difference between the reading of the barometer, and the 
 number in the table corresponding to the division at which the 
 measurement is taken, gives in millimeters the tension of the gas. 
 The volume of the gas is found in the same table, and with the 
 temperature which is read off at the same time as the pressure, all 
 the data required for the calculation of the volume of the gas at 
 Q and 760 m.m. are obtained. ISfo correction is required for 
 tension of aqueous vapour ; the measuring tube and barometer tube 
 being both moist, the tensions in the tubes are counterbalanced. 
 Absorptions are performed with liquid reagents by introducing a few 
 drops of the liquid into the laboratory tube, transferring the gas 
 into it, and allowing the mercury to drop slowly through the gas for 
 about five minutes. The gas is then passed over into the measuring 
 tube, and the difference of tension observed corresponds to the 
 amount of gas absorbed. It is scarcely necessary to add, that the 
 greatest care must be taken to prevent any trace of the reagent 
 passing the stop-cock. If such an accident should occur, the 
 measuring tube must be washed out several times with distilled 
 water at the conclusion of the analysis. If the reagent is a solution 
 of potassic hydrate it may be got rid of by introducing into the tube 
 some . distilled water, to which a drop of sulphuric acid has been 
 added. If this liquid is found to be acid on removing it from the 
 tube, it may be presumed that all the alkali has been neutralized. 
 
 "When explosions are to be performed in the apparatus, the 
 gas is first measured and then returned to the laboratory tube. 
 A quantity of oxygen or hydrogen, as the case may be, which is 
 judged to be the proper volume, is transferred into the laboratory 
 tube, and some mercury is allowed to stream through the gases so- 
 
o2S VOLUMETRIC ANALYSIS. 99. 
 
 as to mix them thoroughly. The mixture is next passed into the 
 eudiometer and measured. If a sufficient quantity of the second 
 gas has not been added, more can readily be introduced. After 
 the measurement, it may be advisable to expand the mixture, in 
 order to diminish the force of the explosion. This is done by 
 allowing mercury to flow out from the tube into the reservoir. 
 When the proper amount of expansion has been reached, the 
 stop-cocks a and b are closed. To enable the electric spark to pass 
 between the wires, it is necessary to lower the level of the water in 
 the cylinder. For this purpose, the bent glass tube at the extremity 
 of the syphon is made to slide easily through the cork which closes 
 the top of the wide tube J. Ly depressing the bent tube, the 
 water flows out more rapidly than before, and the level consequently 
 falls. When the surface is below the eudiometer wires, a spark 
 from an induction-coil is passed, exploding the gas. The syphon 
 ;tube is immediately raised, and, when the water in the cylinder has 
 reached its original level, the gas is cool enough for measurement. 
 900 c.c. of mercury are amply sufficient for the whole apparatus; 
 and as there is no cement used to fasten the wide tubes into iron 
 sockets, a great difficulty in the original apparatus is avoided. 
 
 The following details of an analysis, in which absorptions only 
 Avere performed, will show the method employed. The gas was 
 .a mixture of nitrogen, oxygen, and carbonic anhydride, and the 
 measurements were all made at division Xo. 1 on the eudiometer, 
 which has been found to contain 8 '6892 c.c. 
 
 Original Gas. 
 
 m.m. 
 
 'Temperature of water in cylinder, 15'4. 
 
 Height of mercury in barometer tube .... 980 '5 
 
 ,, ,, corresponding to Division Xo. 1 (see 
 Table) 756'9 
 
 Pressure of the gas ........ 223'6 
 
 After absorption of the carbonic anhydride by solution 
 
 of potassic hydrate 
 Height of mercury in barometer tube 
 
 ,, ,, corresponding to Division Xo. 1 
 
 Pressure of the gas after removal of carbonic anhydride 
 
 Pressure of original gas ...... 
 
 ,, gas after removal of carbonic anhydride . 
 
 Tension of carbonic anhydride ..... 
 
 After absorption of the oxygen by potassic pyrogallate 
 Height of mercury in barometer tube .... 8854 
 ,, corresponding to Division Xo. 1 . 756 !) 
 
 Pressure of nitrogen ....... 128'5 
 
CALCULATIONS, 
 
 529 
 
 Pressure of oxygen and nitrogen 
 nitrogen . 
 
 Pressure of nitrogen 
 
 . 184-8 
 . 128-5 
 
 oxygen 56*3 
 
 These measurements, therefore, give us the following numbers : 
 
 m.m. 
 
 128-5 
 
 56-3 
 
 38-8 
 
 oxygen . 
 
 carbonic anhydride . 
 
 original gas 
 
 223-6 
 
 If the percentage composition of the gas is required, it is readily 
 obtained by a simple proportion, the temperature having remained 
 constant during the experiment : 
 
 m.m. m.m. m.m. 
 
 223-6 : 128-5 : : 100 
 223-6 : 56-3 : : 100 
 
 38-8 : : 100 
 
 223-6 
 
 57-469 per cent. N 
 25-179 per cent. 
 17-352 per cent. CO 2 
 100,000 
 
 If, however, it is necessary to calculate the number of cubic 
 centimeters of the gases at and 760 m.m., it is done by the 
 following formulae : 
 
 8-6892 x 128-5 
 
 7~60 x [1 +(0-003665 x 15'4)~ 
 8-6892 x 56-3 
 
 = 1'3906 c.c. of nitrogen. 
 
 = 0-6093 c.c. of oxygen. 
 
 760 x[l + (0-003665 x 15'4)J 
 
 8-6892x38-8 , , . 
 
 n nAO/? K IK A\-\ = 0'4199 c.c. of carbonic anhydride 
 760 x [1 + (0-00366o x 15'4)J 
 
 8-6892x223-6 ,, . . , 
 
 7607rr + ^QQ3665x 15-4)] = 8 *'' f the ri * mal ^ 
 
 If many of the calculations are to be done, they may be very 
 much simplified by constructing a table containing the logarithms 
 of the quotients obtained by dividing the contents, of each division 
 of the tube by 760 x (1 +0'003665^). The following is a very 
 short extract from such a table : 
 
 T. 
 
 Division No. 1. 
 
 Lc~ 8 ' 6892 
 
 Division No. 2. 
 T 18-1621 
 
 "760x(l + 5t). 
 
 8 760x(l+8t). 
 
 15-0 
 
 2-03492 
 
 2-35511 
 
 1 
 
 2-03477 
 
 2-35496 
 
 2 
 
 2-03462 
 
 2-35481 
 
 3 
 
 2-03447 
 
 2-35466 
 
 4 
 
 2-03432 
 
 2"-34451 
 
 M M 
 
530 
 
 VOLUMETRIC ANALYSIS. 
 
 99. 
 
 By adding the logarithms of the tensions of the gases to those 
 in the above table, the logarithms of the quantities of gases are 
 obtained ; thus : 
 
 Log. corresponding to Division Xo. 1, 
 and 15-4 ..... 
 
 Log. 128*5 = pressure of nitrogen . 
 
 Log. of quantity of nitrogen . 
 Volume of nitrogen at and 
 760 m.m. 
 
 Log. 56 '3 = pressure of oxygen 
 
 Log. of quantity of oxygen 
 
 Volume of oxygen at and 
 760 m.m. 
 
 Log. 38 - 8 = pressure of carbonic anhy- 
 dride ...... 
 
 Log. of quantity of carbonic anhy- 
 dride ...... 
 
 Volume of carbonic anhydride at 
 and 760 m.m. 
 
 Log. 2 23 '6 = pressure of original gas 
 Log. of quantity of original gas 
 Volume of original gas at and 
 760 m.m. 
 
 2-03432 
 200890 
 
 7 14322 = log. 1-3906 
 
 1-3906 c.c. 
 
 2-03432 
 
 1-75051 
 
 T-78483 = log. 0-6093 
 
 0-6093 c.c. 
 2-03432 
 
 T-58883 
 
 1-62315 = log. 0-4199 
 
 0-4199 c.c. 
 
 2-03432 
 2-34947 
 
 0-38379 = log. 2-4198 
 
 2-4198 c.c. 
 
 Nitrogen 
 Oxygen 
 
 Carbonic anhydride 
 Total 
 
 1-3906 
 0-6093 
 0-4199 
 
 or 
 or 
 or 
 or 
 
 1-391 c.c. 
 0-609 c.c. 
 0-420 c.c. 
 2-420 c.c. 
 
 The following example of an analysis of coal gas will show the 
 mode of working with this apparatus, and the various operations to 
 be performed in order to determine the carbonic anhydride, oxygen, 
 hydrocarbons absorbed by Xordhauseii sulphuric acid, hydrogen, 
 marsh gas, carbonic oxide, and nitrogen. 
 
 The measuring tube and laboratory tube were first filled with 
 mercury, some of the gas introduced into the laboratory tube, and 
 passed into the apparatus. 
 
 The gas was measured at the second division. 
 
 Height of mercury in the barometer tube . 989 '0 
 
 measuring tube . 706 -8 
 
 Pressure of the gas at 16 -6 282'2 
 
99. MEASUREMENT OF GASES. 531 
 
 Two or three drops of a solution of potassic hydrate were 
 now placed in the laboratory tube, and the gas passed from the 
 measuring tube, the mercury being allowed to drop through the 
 gas for ten minutes. On measuring again 
 
 Height of mercury in barometer . . . 984*0 
 
 Some saturated solution of pyrogallic acid was introduced into 
 the laboratory tube, and the gas left in contact with the liquid for 
 ten minutes. On measuring 
 
 Height of mercury in barometer 
 Height of mercury when measuring original gas . 
 ,, ,, after absorption of CO 2 
 
 Pressure of CO 2 
 
 ,, after absorption of CO 2 
 
 ,, ,, after absorption of . 
 
 Pressure of 0'4 
 
 The volume of the. gases being proportional to their pressures, it 
 is simple to obtain the percentages of carbonic anhydride and 
 oxygen in the original gas. 
 
 Original s;as. CO- 
 
 282-2 : 5-0 :: 100 : 1*772 per cent. CO 2 
 
 Original gas. O 
 
 282*2 : 0-4 : : 100 : 0*142 per cent. 
 
 By subtracting 1'914 from 100, we obtain the remainder, 
 98'086, consisting of the hydrocarbons absorbed by Xordhausen 
 sulphuric acid, hydrogen, carbonic oxide, marsh gas, and nitrogen ; 
 
 thus : 
 
 Original gas . . . . . . . lOO'OOO 
 
 and CO 2 1*914 
 
 CnH%. H. CO. CH 4 . X. . . . 98-086 
 
 While the gas remains in the measuring tube, the laboratory tube 
 is removed, washed, dried, filled with mercury, and again attached 
 to the apparatus. Much time is saved by replacing the laboratory 
 tube by a second, which was previously ready. As a minute 
 quantity of gas is lost in this operation, in .consequence of the 
 amount between the stop-cocks being replaced by mercury, it is 
 advisable to pass the gas into the laboratory tube, then transfer it 
 to the eudiometer, and measure again. 
 
 On remeasuring, the mercury in the barometer 
 
 stood at t 983*3 
 
 The mercury in the measuring tube . . . 706 -8 
 
 Pressure of CnH-n. H. CO. CH 4 . X. "276^ 
 
 M M 2 
 
532 VOLUMETRIC ANALYSIS. 99. 
 
 The gas is again passed into the laboratory tube, and a coke ball, 
 soaked in faming sulphuric acid, left in contact with the gas for 
 an hour ; the bullet is then withdrawn, and some potassic hydrate 
 introduced and left in the tube for ten minutes, in order to remover 
 the vapours of sulphuric anhydride, and the sulphurous and 
 carbonic anhydrides formed during the action of the Xordhausen 
 acid on the gas. The gas is now measured again. 
 
 Height of mercury in barometer tube . . 969 '3 
 ,, ,, ,, before absorbing 
 
 CnH 2 n 983-3 
 
 after . . 969'3 
 
 Pressure of CnH 2 n 14-Q 
 
 The percentage of these hydrocarbons is thus found : 
 Gas containing CnH 2 n. H. CO. CH 4 . K 
 
 CnH^n. 
 
 276-5 : 14-0 :: 98-086 : 4-966 per cent. CnH-n 
 
 It now remains to determine the hydrogen, carbonic oxide, marsh 
 gas, and nitrogen in a portion of the residual gas. The laboratory 
 tube is therefore removed, some of the gas allowed to escape, and 
 another laboratory tube adapted to the apparatus. The portion of 
 gas remaining is expanded to a lower ring (in this special case to 
 the third division), and the tension measured: 
 
 Height of mercury in the barometer tube . . 042 "2 
 
 ,, measuring tube . . 606*7 
 
 Pressure of residue 35-5 
 
 An excess of oxygen has now to be added. For this purpose 
 the gas is passed into the laboratory tube, and about five times its 
 volume of oxygen introduced from a test tube or gas pipette. The 
 necessary quantity of oxygen is conveniently estimated by the aid 
 of rough graduations on the laboratory tube, which are made by 
 introducing successive quantities of air from a small tube in the 
 manner previously described for the calibration of the eudiometers. 
 
 After the introduction of the oxygen, the mixed gases are passed 
 into the eudiometer and measured. 
 
 Height of mercury in the eudiometer after 
 
 addition of 789-5 
 
 The mixture has now to be exploded, and when the pressure is 
 considerable, it is advisable to expand the gas so as to moderate the 
 violence of the explosion. When sufficiently dilated, the stop-cock 
 at the bottom of the eudiometer is closed, the level of the water 
 lowered beneath the platinum; wires by depressing the syphon, and 
 the spark passed. The- explosion should be so powerful that it 
 should be audible, and the flash visible in not too bright daylight. 
 
99. MEASUREMENT OF GASES. 533 
 
 The stop-cock at the bottom of the eudiometer is now opened, 
 and the gas measured. 
 
 Height of mercury in barometer after explosion . 732 '5 
 
 The difference between this reading and tlrj previous one gives 
 the contraction produced by the explosion : 
 
 Height of mercury in barometer before explosion 789 '5 
 
 after 7 32 -5 
 
 Contraction =C 57 '0 
 
 It is now necessary to estimate the amount of carbonic anhydride 
 formed. This is done by absorbing with potassic hydrate as before 
 described. 
 
 Height of mercury in barometer tube after 
 
 absorbing CO' 2 715*8 
 
 This number deducted from the last reading gives the carbonic 
 anhydride. 
 
 Height of mercury in barometer after exploding 732 '5 
 
 ,, ,, after absorbing CO 2 715*8 
 
 Carbonic anhydride =D 16'7 
 
 It now remains to determine the quantity of oxygen which was 
 riot consumed in the explosion, and which excess now exists mingled 
 with the nitrogen. For this purpose, a volume of hydrogen about 
 three times as great as that of the residual gas is added, in the same 
 way as the oxygen was. previously introduced, and the pressure of 
 the mixture determined. 
 
 Height of mercury in barometer after adding H 1031 '3 
 
 This mixture is exploded and another reading taken. 
 
 Height of mercury in barometer after exploding 
 
 with H 706-7 
 
 This number subtracted from the former, and the difference 
 divided by 3, gives the excess of oxygen. 
 
 Height of mercury in barometer before exploding 
 
 withH 1031-3 
 
 Height of mercury in barometer after exploding 
 
 with H 706-7 
 
 3; 324-6 
 Excess of oxygen 108 '2 
 
 In order to obtain the quantity of nitrogen in the gas analyzed, 
 this number has to be deducted from the volume of gas remaining 
 after the explosion with oxygen and the removal of the carbonic 
 anhydride. 
 
534 VOLUMETRIC ANALYSIS. 99. 
 
 Height of mercury in barometer after absorbing 
 
 CO' . . ...... 715-8 
 
 ,, in eudiometer at division ]S"o. 3 606 '7 
 
 Xitrogen and excess of oxygen . . . 109*1 
 
 Excess of oxygen . . . . . 108 '2 
 
 Nitrogen 0*9 
 
 TTe have now all the data necessary for the calculation of the 
 composition of the coal gas. It is first requisite to calculate the 
 proportion of the combustible gas present in the coal gas, which is 
 done by deducting the sum of the percentages of gas determined 
 by absorption from 100. 
 
 Percentage of carbonic anhydride . . . 1*772 
 
 oxygen ..... 0'142 
 
 CnH 2 n ..... 4-966 
 
 CO 2 . 0. CnH'-'n ~ 6-880 
 
 Original gas ....... 100-000 
 
 CO 2 . 0. CnH 2 ii ...... 6-880 
 
 H. CO. CH 4 . X 93-120 
 
 The formulae for the calculation of the analysis of a mixture of 
 hydrogen, carbonic oxide, and marsh gas, are (see page 510) 
 
 Hydrogen .>: = A D 
 
 3A-2C + D 
 
 Carbonic oxide =//= - o 
 
 2C-3A + 2D 
 
 Marsh gas =::=. Q 
 
 o 
 
 A=35-5 - 0-9 = 34-6 
 C=57-0 
 D = 16-7 
 A=n 34-6 
 L>= J.6-7 
 
 1 7 -9 = a-= Hydrogen in 35 -5 of the gas exploded 
 
 with oxygen. 
 
 A== 34-6 C= 57-0 
 
 3 _2 
 
 3A= 103-8 2C= '114-0 
 
 D= 16-7 
 = 120-5 
 
 3) 6-5=3A + D-2C 
 
 o \ , ~i\ _^ 9p __ 
 
 o ' = 2-167=v/=Carbonic oxide in 35'5 of the gas. 
 
99. ESTIMATION OF HYDROCARBONS. 535 
 
 D= 167 
 
 o 
 
 2D 33-4 
 
 2C = 114-0 
 
 2.D + 2C = 1474 
 
 3A = LOS 
 
 2D + 2C-3A 
 
 = 14*533 = 2 = Marsh gas in 35*5 of the gas. 
 
 These numbers are readily transformed into percentages, thus : 
 
 35-5 : 17-9 : : 93*12 : 46*952 per cent, of Hydrogen. 
 
 35-5 : 2-167 : : 93-12 : 5*684 per cent, of Carbonic oxide. 
 
 35-5 : 14-533 : : 93-12 : 38*122 per cent, of Marsh gas. 
 
 35-5 : 0*9 : : 93*12 : 2*361 per cent, of Xitrogen. 
 
 This completes the calculations, the results of which are as 
 follows : 
 
 Hydrogen . . . .46*952 
 
 Marsh gas . . . .38*122 
 CnH 2 n .... 4*966 
 
 Carbonic oxide . . . 5*684 
 
 Carbonic anhydride . . 1772 
 
 Oxygen . ' . . . 0*142 
 
 o-en 2*361 
 
 99*999 
 
 It is obvious that this analysis is not quite complete, since it 
 does not give any notion of the composition of the hydrocarbons 
 absorbed by the Nordhausen acid. To determine this, some of 
 the original gas, after the removal of carbonic anhydride and oxygen, 
 is exploded with oxygen, and the contraction and carbonic anhy- 
 dride produced are measured. The foregoing experiments have 
 shown the effect due to the hydrogen, carbonic oxide, and marsh 
 gas, the excess obtained in the last explosion being obviously caused 
 by the hydrocarbons dissolved by the sulphuric acid, and from 
 these data the composition of the gas may be calculated. 
 
 It may be remarked that analyses of this kind were performed 
 with the apparatus at the rate of two a day when working for 
 seven hours. 
 
 It may be useful to show how this analysis appears in the 
 laboratory note-book : 
 
5S6 
 
 VOLUMETRIC ANALYSIS. 
 
 99. 
 
 Analysis of Coal Gas. 
 
 989-0^ 
 706-8 I 
 
 original 
 
 282-2 j as 
 
 934-0 Aft. absorb. CO 2 
 
 983-6 Aft. absorb. 
 983-3 Remeasured 
 
 969-3 Aft. Absorb. CnH 2 i 
 
 642 -2 N 
 
 606-7 (portion of 
 
 ~i^j Residue 
 
 789-5 with 
 
 732-5 Aft. expl. 
 715-8 Aft. absorb. CO 2 
 
 1031-3 withH 
 706-7 Aft. expl. 
 
 CO = y = 
 
 ' 2C 
 
 9890 
 984-0 
 
 984-0 
 983-6 
 
 0-4 = < 
 
 282-2 :5-0 : : 100 : 1772 CO 2 
 282-2 : 0-4 : : 100 : 0-142 
 
 1-914 
 
 100-000 
 
 1-914 CO 2 . O 
 
 93-086 CnH 2 n. H. CO. CH*. N 
 
 983-3 
 
 706-8 
 
 983-3 
 969-3 
 
 276-5 140 CnH 2 n 
 
 276-5 : 14-0 : : 9S'OS6 : 4-966 CnH 2 n 
 
 35-5 = H. CO. OH*. N 
 0-9= N 
 
 J34-6 = 11. CO. CH-i=A 
 
 789-5 
 732-5 
 
 = 0-142 
 
 6-880 
 
 32-5 
 
 15-8 
 
 57-0 = contraction = C 167 = CO 2 = D 
 
 1031-3 
 
 7067 
 
 3) 324-6 
 108 r 2 = 
 
 = 17-9 
 
 715-8 
 606-7 
 
 109-1 = 
 108j2=0 
 0-9 = N 
 
 CH4 = z - 
 
 2C - 3A +2D 
 
 
 
 
 
 34-600 
 
 34-6 = 
 16-7 = 
 
 A 
 D 
 
 x = H 
 C 
 
 34-6 
 3 
 
 = A 
 
 =-3A 
 = D 
 
 = 3A H 
 = 2C 
 
 -6 
 
 17-9 = 
 
 57-0 = 
 2 
 
 103-8 
 167 
 
 120-5 
 114-0 
 
 16-7 - D 
 
 33-4 = 2D 
 
 114-0 =2C 
 
 147-4 =2C + 2D 
 103-8 = 3 A 
 
 114-0 = 20 
 
 3) 6-5 =3A + D-2C 
 
 3) 43-6 =2D + 2C-3A 
 
 100-000 
 6-880 CO. 0. CnH'-'n 
 
 93-120 H. CO. CH-*. N 
 
 35 5 : 17-9 : : 93-12 
 
 35-5 : 2-167 : : 93-12 
 
 35-5 : 14-533 : : 93-12 
 
 35-5 : 0-9 : : 93'12 
 
 46-952 H 
 5-684 CO 
 
 38 -122 CH< 
 2-361 N 
 
THOMAS'S GAS APPARATUS. 537 
 
 H = 46-952 
 
 CH 4 - 38-] 22 
 
 CnH-n = 4-966 
 
 CO = 5684 
 
 CO^ = 1-772 
 
 = 0-142 
 
 N = 2-361 
 
 "99-999 
 
 It is assumed in the above example, that the temperature of the 
 water in the cylinder remained constant throughout the period 
 occupied in performing the analysis. As this very rarely happens, 
 the temperature should be carefully read off after every measure- 
 ment of the gas and noted, in order that due correction be made for 
 any increase or decrease of volume which may result in consequence. 
 
 THOMAS'S IMPROVED GAS APPARATUS. 
 
 In the Chemical Societies Journal for May, 1879, Thomas 
 described an apparatus for gas analysis (fig. 96) which has the 
 closed pressure tube of Frankland and "Ward, and is supplied 
 with mercury by means of the flexible caoutchouc tube arrangement 
 of Me Leod. The manner in which this apparatus is filled with 
 mercury and got into order for working is so similar to that already 
 described, that no further reference need be made thereto. 
 
 The eudiometer is only 450 m.m. long from .shoulder to shoulder, 
 and the laboratory tube and mercury trough are under the command 
 of the operator from the floor level. The eudiometer has divisions 
 20 m.m. apart, excepting the uppermost, which is placed as close 
 beneath the platinum wires as is convenient to obtain a reading. 
 The method explained in sequel of exploding combustible gases 
 under reduced pressure, without adding excess of gas to modify the 
 force of the explosion, permits the shortening of the eudiometer as 
 above, and enables the apparatus to be so erected, that a long 
 column of the barometer tube shall stand above the summit of the 
 eudiometer. By means of such an arrangement a volume of gas 
 may be measured under nearly atmospheric pressure, and as this 
 pressure is equal to more than 700 m.m., plus aqueous tension, the 
 sensitiveness of the apparatus is considerably augmented. The 
 barometer tube is 1000 m.m. in length, having about 700 m.m. 
 lines above Division 2 on the eudiometer. The steel clamp and 
 facets forming the connections between the eudiometer and detach- 
 able laboratory tube of the apparatus previously described are 
 dispensed with, as in this form the eudiometer and laboratory 
 vessels are united by a continuous capillary tube, 12 m.m. (outside) 
 diameter, and one three-way glass tap is employed in lieu of the 
 two stop-cocks. The arrangement is simple, The glass tap is 
 hollow in the centre, and through this hollow a communication is 
 made with the capillary, by means of which either the laboratory 
 
538 VOLUMETRIC ANALYSIS. 99. 
 
 tube or the eudiometer can be washed out. As the laboratory 
 vessel is not disconnected for the removal of the reagent used in 
 an absorption, it is supported by a clamp, as shown in the drawing ; 
 and when it requires washing out the mercury trough is turned 
 aside, in order that an enema syringe may be used for injecting a 
 stream -of water. A few drops of water are let fall into the hollow 
 of the tap, and blown through the capillary tube three times in 
 succession, so as to get rid of the absorbent remaining in the 
 capillary, then the syringe is brought into play once more, the 
 excess of water removed by wiping, and the trough turned back 
 into position. The laboratory tube may be refilled with mercury 
 as described on page 526 : but it will be found much more serviceable 
 if a double-acting syringe, connected to a bulb appaiatus (to catch 
 any mercury that may come over), and then to the orifice of the 
 hollow in the tap by a ground perforated stopper, be used, as this 
 will obviate the destructive effect of heavy suction upon the gums 
 and teeth. The mercury trough is supported upon a guide which 
 travels over the upright U, and is turned aside for the purpose of 
 washing out the laboratory vessel in the following manner : The 
 spiral spring is depressed by means of the tension rods until the 
 sloe is brought below the stud fixed in the upright U ; and the top 
 ferrule holding the guide rods being movable, the trough can lie 
 turned round out of the way, but is prevented from coming in 
 contact with the glass water-cylinder by an arrangement in the top 
 of the guide, which comes against the stud in the upright. The 
 height of the trough can be accurately adjusted by the screw in the 
 top of the lever guide. When the trough is in position, the clamp 
 holding the laboratory vessel may be loosed when necessary. 
 
 The eudiometer and barometer tubes pass through an india- 
 rubber cork, as in Me Leod's apparatus, but are not supported by 
 the clamp C, which here simply bears the water-cylinder. Xo 
 glass stop-cocks are used, or glass-work of any kind employed in 
 the construction of the lower portion of the apparatus. The lower- 
 end of the eudiometer has a neck of the same outside diameter as 
 the barometer tube (9*5 m.m.), and both tubes are fixed into the 
 steel block X, without rigidity, by the usual steam cylinder-gland 
 arrangement, small india-rubber rings being used to form the 
 packing. The steel block is fixed to the table by a nut screwed 
 upon the f-inch hydraulic iron tube, which runs to the bottom of 
 the table. The tap in the steel block is so devised that it first cuts 
 off connection with the barometer tube, in order that the gas may 
 he drawn over from the laboratory vessel into the eudiometer with- 
 out risking the fracture of the upper end of the barometer tube by 
 any sudden action of the mercury. This precaution is necessary, as 
 during the transferring of the gas the mercury in the barometer 
 tube is on the point of lowering, to leave a vacuous space in the 
 summit of the tube. By moving the handle a little further on 
 the quadrant a communication is made with both tubes and the 
 
THOMAS S GAS APPARATUS. 
 
 539 
 
 reservoir for the purpose of bringing the gas interposition, so as to 
 take a reading; then the handle is drawn a little further to cut off 
 
 Fig. 90. 
 
 the reservoir supply, whilst there is a way still left between the 
 eudiometer and barometer tubes, and if the handle be drawn 
 
540 VOLUMETRIC ANALYSIS. 99. 
 
 forward a little more, all communication is cut off for the purpose 
 of exploding. 
 
 The windlass B, for raising and lowering the mercury reservoir L, 
 is placed beneath the table, in order that it may be under command 
 from a position opposite the laboratory vessel, and it is furnished 
 with a spring ratchet motion, so as to be worked by one hand. The 
 water-cylinder should be four inches in diameter, and the casing tube 
 of the barometer as wide as practicable, so that the temperature of 
 the apparatus may be maintained as constant as possible. To attain 
 an accurate result it is as essential to keep the barometer tube 
 of uniform temperature as the eudiometer, since the tension of 
 aqueous vapour varies proportionally. The stream of water from 
 the service main is run into the casing tube at the upper end of 
 the barometer, and, whilst the water-cylinder is filling, the tap at 
 the bottom is opened slightly, so that water may run out very 
 slowly. When the water-cylinder is full, the upright tube G acts 
 as a syphon, and sucks out the excess of water from the top of the 
 cylinder, thus keeping up the circulation at the point where it is 
 most required. For a further detailed description of the apparatus 
 see /. C. S., May, 1879. 
 
 There are only tw r o working taps upon this apparatus the 
 three-way glass tap between the eudiometer and laboratory tube, 
 and the steel tap at the lower ends of the barometer and eudiometer. 
 The steel tap is greased with a little beef-tallow (made from clean 
 baef-suet), or with real Russian tallow ; it will last for twelve 
 months without further attention. A moderately thick washer of 
 india-rubber, placed between the steel washer and the nut at the 
 end of the steel tap, adds greatly to the steady working of the 
 needle on the quadrant. Moderately soft resin cerate is best for 
 the glass tap. 
 
 When filling the laboratory vessel with mercury, suction is 
 maintained until the mercury has reached some height in the 
 hollow of the three-way tap. The remainder of the hollow space 
 is replenished by pouring the mercury from a small crucible ; any 
 water that may be present is then removed, and the small stopper 
 inserted. When the laboratory vessel has to be washed out after 
 an absorption, the gas is transferred to the eudiometer until the 
 absorbent gets within a quarter of an inch of the stop-cock. The 
 mechanical arrangement should be so manageable that this nicety 
 of adjustment can be accomplished with ease. Much depends, of 
 course, upon the care bestowed in cerating the tap, so that the 
 capillary is not carelessly blocked up. As soon as the gas has 
 passed over to the extent required, turn the three-way tap until the 
 through-way is at right angles to the capillary, and the way to the 
 hollow of the tap is in communication with the laboratory vessel, 
 then take out the little stopper from the hollow, so that the mercury 
 shall flow out, and allow the laboratory vessel to become emptied 
 whilst the reading of the volume of the gas is being taken. The 
 
99. 
 
 THOMAS 8 GAS APPARATUS. 
 
 541 
 
 best arrangement for washing out the laboratory tube is a " syphon 
 enema" (Dr. Higginson's principle, which maybe obtained of 
 any druggist), adapting in the place of the usual nozzle a bent glass- 
 tube. This syringe is constant in its action, as it fills itself when 
 the pressure is released, if the tube at the lower end is placed in 
 a vessel of water. The laboratory vessel can be washed out and 
 refilled in a very little time, as it is already connected, and for all 
 ordinary absorptions it is sufficient to wipe the vessel out once by 
 passing up a fine towel twisted on a round stick. When CnH 2 ii 
 gases are to be absorbed by fuming sulphuric acid, the water should 
 be carefully blown out of the capillary tube into the laboratory 
 vessel, which must be repeatedly dried. A few drops of strong, 
 sulphuric acid were at first run into the hollow of the tap and then 
 through the capillary whilst the labora- 
 tory vessel was full of mercury, in order 
 to remove any moisture remaining, but 
 it has since been found unnecessary, as 
 the drying can be performed thoroughly 
 without. 
 
 To calibrate the eudiometer with 
 water, introduce the quantity required 
 through the hollow in the stopper, then 
 remove the latter, and collect the water 
 in a light flask from the bottom of the 
 tap-socket. 
 
 In the same paper (J. C. S., May, 
 1879), Thomas pointed out that it was 
 not essential to add excess of either 
 oxygen or hydrogen for the purpose of 
 modifying the force of the explosion 
 when combustible gases were under 
 analysis, and it is necessary to take 
 advantage of this when working with so 
 short an eudiometer. The method is 
 however, applicable to all gas apparatus 
 having a reasonable length of barometer 
 column above the eudiometer ; in fact, 
 the exploding pressures were first worked 
 
 out and employed in an apparatus onMcLeod's model. AVhen the 
 percentage of oxygen in a sample of air has to be determined by 
 explosion, only one-half its volume of hydrogen is required, and the- 
 pressure need not be reduced below 400 m.m. If much more than 
 one-half volume of hydrogen has been added by accident, explode 
 under atmospheric pressure. When the excess of oxygen used in an- 
 analysis has to be determined, add 2 '5 times its volume of hydrogen, 
 and reduce the pressure to 180 m.m. of mercury before exploding. 
 After adding the hydrogen and the reading has been taken, the gas 
 is expanded by lowering the mercurial reservoir until a column of 
 
 Tig. 97. 
 
542 
 
 VOLUMETRIC ANALYSIS. 
 
 mercury, measuring 
 
 the number of m.m.'s in length just referred to 
 
 and in the following table, stands above the meniscus of the mercury 
 in the eudiometer. This column can be read off quite near enough by 
 the eye, as there is no risk of breaking the apparatus by the force of 
 the explosion if the pressure is 20 m.m. greater than that given ; 
 but if the gas under analysis is all combustible, it is better to 
 explode at a slightly less pressure than to exceed that recommended. 
 
 si 
 
 e*-j 
 
 o bii 
 
 
 01 '- 
 
 Q 
 
 gggj 
 
 Name of Gas. 
 
 IJ 
 
 1 | 
 
 g ^ o 'd 
 
 
 "o 3 
 
 "o t^ 
 
 8 IF 
 
 i ^6 
 
 ^0 
 
 ^ 
 
 Hydrogen - 
 
 1 
 
 1 
 
 200 m.m. 
 
 Carbonic Oxide - 
 
 1 
 
 1 
 
 200 m.m. 
 
 Marsh Gas 
 
 1 
 
 2-5 
 
 170 m.m. 
 
 Acetylene - 
 
 1 
 
 3 
 
 150 m.m. 
 
 Olefiant Gas 1 
 
 3-5 
 
 145 m.m. 
 
 Methyl and Hydride of Ethyl 1 
 
 4 
 
 140 m.m. 
 
 Propyl 
 
 1 
 
 5 
 
 135 m.m. 
 
 Hydride of Propyl 
 
 1 
 
 5-5 
 
 130 m.m. 
 
 Butyl 
 
 1 
 
 6 
 
 125 m.m. 
 
 Ethyl and Hydride of Butyl 
 
 1 
 
 7 
 
 120 m.m. 
 
 It follows, naturally, that the exploding pressure will depend upon 
 the proportion of combustible gas introduced ; and experience 
 alone can enable one to determine with any degree of exactness 
 what that pressure must be, as no general law can be laid down. 
 For instance, if more than three volumes of hydrogen were added 
 to one of oxygen, the exploding pressure should exceed 200 m.m. ; 
 and if much nitrogen or other gas were present that did not take 
 .a part in the reaction, the pressure should be still more increased. 
 As a consequence, the same experience is necessary when dealing 
 with explosive gases by the other method, because the addition 
 of too much inert gas, with a view to modify the force of the 
 explosion, may lead to imperfect combustion, inasmuch as the 
 cooling effect of the tube and gas can reduce the temperature 
 below that required. In all instances, when the approximate com- 
 position of the gas is known, it is not difficult to determine the 
 quantity of oxygen or hydrogen, as the case may be, which is 
 required for explosion, or the pressure under which the gas should 
 be exploded. In order to do this systematically, it is always well 
 to remember certain points observed during the stages of the 
 -analysis. The gas in the laboratory vessel, before being transferred 
 to the eudiometer, occupies a certain volume in a position between 
 (or otherwise) the calibration divisions. After transferring and 
 reading off, bear in mind the number of m.ni.'s which the volume 
 
99. REISER'S GAS APPARATUS. 543 
 
 represents ; and calculate, as the gas is being re-transferred to the 
 laboratory vessel to be mixed with that employed in the explosion, 
 the height at which the mercury should stand in the barometer 
 tube when measuring the mixed gases, and how much of the 
 laboratory vessel was occupied on a previous occasion when a similar 
 reading was obtained. If this is done, one can realize at once, after 
 reading off the volume of the mixed gases, the proportion of com- 
 bustible gas added, and the pressure under which the gas has been 
 measured. Another glance at the volume which the gas occupies in 
 the eudiometer, with a comparison of the pressure recorded upon 
 the barometer tube, enables one, after a little practice, to at once 
 expand the mixture to the point at which it will explode with 
 satisf actor v results. It is not expedient to place too much reliance 
 upon the marks showing equal volumes upon the laboratory vessel, 
 especially when dealing with small quantities of gas ; and 
 a comparison of the volumes obtained in reading before and after the 
 addition of oxygen or hydrogen is always prudent, in order to see 
 that sufficient gas has been added, as well as to enable one to judge 
 the pressure under which the gas should be exploded. 
 
 NOTE. Meyer and Seubert (Z. a. C. xxiy. 414) have designed a gas apparatiis 
 similar in many respects to that of McLeod and Thomas, but of simpler con- 
 struction, and especially adapted for explosions under diminished pressure. 
 
 K e i s e r ' s Portable Gas Apparatus. 
 
 This apparatus is based on the principle of determining the 
 volume of a gas from the weight of mercury which it may be made 
 to displace at a known temperature and pressure. It dispenses 
 entirely with the long graduated tubes and other vessels common to 
 the apparatus previously described, without any sacrifice of accuracy. 
 
 The following description occurs in the Amer. Chem. Journ., 1886 
 (but is reproduced here from The Analyst, xi. 106) : 
 
 Fig. 98 shows the construction of the measuring apparatus arid 
 the absorption pipette. A is the measuring apparatus, B is the 
 absorption pipette; a and l> are glass bulbs of about 150 c.c. 
 capacity. They are connected at the bottom by a glass tube of 
 1 m. m. bore, carrying the three-way stop-cock d. The construction 
 of the key of the stop-cock is shown in the margin. One hole is 
 drilled straight through the key, and by means of this the vessels 
 a and b may be made to communicate. Another opening is drilled at 
 right angles to the first, which communicates with an opening 
 extending through the handle, but does not communicate with the 
 first opening. By means of this, mercury contained in either a or b 
 may be allowed to flow out through the handle d into a cup placed 
 beneath. The bulb b is contracted at the top to an opening 20 m.m. 
 in diameter. This is closed by a rubber stopper carrying a bent 
 glass tube, to which is attached the rubber pump e. To a second 
 glass tube passing through the stopper, a short piece of rubber 
 
544 
 
 VOLUMETRIC ANALYSIS. 
 
 99. 
 
 tubing with a pinch-cock is attached. By means of the pump e air 
 may be forced into or withdrawn from /;, as one or the other end of 
 the pump is attached to the glass tube. The bulb a terminates at 
 the top in a narrow glass tube, to which is fused the three-way stop- 
 cock c. The construc- 
 tion of the key of this 
 stop-cock is also shown 
 in the cut. By means 
 of it the vessel a may 
 be allowed to com- 
 municate with the 
 outside air, or with 
 the tube passing to 
 the absorption pipette, 
 or with the gauge y. 
 The gauge rj is a glass 
 tube having a bore 
 1 m.m. in diameter 
 and bent, as shown in 
 the figure. By pouring 
 a few drops of water 
 
 into the open end of 
 Fig. 98. ., . , , l , _c 
 
 this tube a column 01 
 
 water several centimeters high in both limbs of the tube is obtained. 
 This serves as a manometer, and enables the operator to know when 
 the pressure of the gas equals the atmospheric pressure. To secure 
 a uniform temperature, the bulbs a and b are surrounded by water 
 contained in a glass vessel! This vessel for holding water is merely 
 an inverted bottle of clear glass from which the bottom has been 
 removed. The handle of the stop-cock d passes through a rubber 
 stopper in the neck of the bottle. A thermometer graduated to i 
 is placed in the water near the bulb a. The whole apparatus is 
 supported upon a vertical wooden stand. 
 
 The absorption pipette B consists of two nearly spherical glass 
 bulbs of about 300 c.c. capacity. They communicate at the bottom 
 by means of a glass tube, 3 m.m. inside diameter, c is a two-way 
 stop-cock. The holes in the key are drilled at right angles, so that 
 the tube which connects with the measuring apparatus may be put 
 in communication either with the funnel or with the absorption 
 bulb. The funnel is of service in removing air from the tube which 
 connects the measuring apparatus with the absorption pipette. By 
 pouring mercury or water into the funnel and turning the stop- 
 cocks c and c in the proper directions all the air is readily removed. 
 / is a rubber pump used in transferring gas from B to A. The 
 lower part of the pipette contains mercury, which protects the 
 reagent from the action of the air. 
 
 To measure the volume of a gas, the vessel a is filled completely 
 with pure mercury. This is easily accomplished by pouring the 
 
99. REISER'S GAS APPARATUS. 545 
 
 mercury into b, and then, after turning c until a communicates with 
 the outside air, forcing it into a by means of the pump e. Any 
 excess of mercury in b is then allowed to flow out through the stop- 
 cock d. When a and b are now placed into communication the 
 mercury will flow from a to &, and gas will be drawn in through the 
 stop-cock c. The volume of mercury which flows into It is equal to 
 the volume of gas drawn into a. When the mercury no longer 
 rises in b, and it is desired to draw in still more gas into a, then it 
 is only necessary to exhaust the air in b by means of the pump e. 
 After the desired quantity of gas has been drawn into a the stop- 
 cock c is closed. After standing a few minutes the temperature of 
 the gas becomes the same as that of the water surrounding a. 
 The pressure of the gas is then made approximately equal to atmos- 
 pheric pressure by allowing the mercury to flow out of b into a 
 weighed beaker placed beneath the stop-cock d until it stands at 
 nearly the same level in both a and b. Communication is now 
 established between a and //, and by means of the pump e the 
 pressure can be adjusted with the utmost delicacy until it is exactly 
 equal to atmospheric pressure. The stop-cock d is then closed, and 
 the remainder of the mercury in b is allowed to flow out into the 
 beaker. The weight of the mercury displaced by the gas divided 
 by the specific gravity of mercury at the observed temperature gives 
 the volume of the gas in cubic centimeters. 
 
 If it is desired to remove any constituent of the gas by absorption, 
 a pipette B, containing the appropriate reagent, is attached to the 
 measuring apparatus. All the air in the connecting tube is expelled 
 by pouring mercury into the funnel and turning the stop-cocks 
 <' and c so that the mercury flows out through c. A little more 
 than enough mercury to expel the gas in the vessel a is poured into b. 
 The small quantity of air which is confined in the tube connecting b 
 with the stop-cock is removed by allowing a few drops of mercury 
 to run out through b. Then a and b are placed in communication. 
 The stop-cocks c and e are turned so that the gas may pass into the 
 pipette, the mercury which filled the connecting tube passes into the 
 absorbing reagent and unites with that which is already at the 
 bottom of the pipette. The transfer is facilitated by the pump e. 
 After absorption the residual volume is measured in the same way 
 that the original volume was measured, a is completely filled with 
 mercury from the upper to the lower stop-cock, and all the mercury 
 in b is allowed to run out ; the gas is then drawn back into the 
 measuring apparatus, the last portion remaining in the connecting 
 tube being displaced, by means of mercury from the funnel. The 
 volume is then determined as before. 
 
 The calculation of the results of an analysis is very simple. If 
 the temperature and pressure remain the same during an analysis, as 
 is frequently the case, then the weights of mercury obtained are in 
 direct proportion to the gas volumes, and the percentage composition 
 is at once obtained by a simple proportion. 
 
 N N 
 
546 VOLUMETRIC ANALYSIS. 99. 
 
 If the temperature and pressure are different when, the 
 measurements are made, it is necessary to reduce the volumes to 
 and 760 m.m. The following formula is then used : 
 
 - 
 ~ 
 
 D (1+ 0-00367 x^) 760' 
 in which 
 
 W weight of mercury obtained (in grams), 
 D = specific gravity of mercury at t, 
 
 t == temperature at which the gas is measured, 
 H= height of the barometer, 
 h = tension of aqueous vapour, 
 T'' = reduced gas volume (in cubic centimeters). 
 In all the measurements made with the apparatus the gas is 
 saturated with aqueous vapour, because it comes in contact with 
 the water in the manometer //. 
 
 The following experiments were made to test the accuracy of the 
 instrument. A quantity of air was drawn into the measuring bulb 
 and its volume determined. The air was then transferred to an 
 absorption pipette which contained only mercury and no reagent. 
 It was then brought back again into the measuring apparatus and 
 its volume redetermined. The following results were obtained : 
 
 I. 
 
 Volume at 763 in. in. 
 Volume of air taken ... ... ... 57'55S c.c. 
 
 after first transfer ... ... 57'567 
 
 second transfer ... ... 57'570 
 
 II.. 
 
 At 760 m.m. 
 Volume taken ... ... ... ... 93'216 c.c. 
 
 after transferring 93'229 
 
 III. 
 
 At 760 m.m. 
 
 Volume taken ... ... ... ... 133-473 c.c. 
 
 after transferring ... 133'490 
 
 IV. 
 
 At 760 m.m. 
 Volume taken ... ... ... ... 92'275 c.c. 
 
 after transferring ... ... 92'260 
 
 v. 
 
 At 760 in. in. 
 Volume taken ... ... ... 109'025 c.c. 
 
 after transferring ... ... 109'020 
 
 VI. 
 
 At s 750 m.m. 
 Volume taken ... ... ... ... 103'970 c.c. 
 
 after first transfer ... ... 103'955 
 
 second transfer ... ... 103*980 
 
 The apparatus was also tested by making analyses of atmospheric 
 air. It has been shown both by Winkler and Hempel that the 
 composition of the air varies from day to day. This variation is 
 
100. 
 
 SIMPLER METHODS OF GAS ANALYSIS. 
 
 547 
 
 sometimes as much as 0*5 per cent. The causes which produce 
 these fluctuations in the composition of the atmosphere are at 
 present but imperfectly understood. It is therefore desirable to 
 have some simple instrument by means of which the composition 
 of the air may be determined rapidly and yet with great accuracy. 
 The following analyses show that the apparatus here described 
 is well adapted to this purpose. The reagent used to absorb the 
 oxygen and carbon dioxide was an alkaline solution of pyrogallol, 
 prepared by mixing one volume of a 25 per cent, solution of 
 pyrogallol with six volumes of a GO per cent, solution of potassic 
 hydrate. 
 
 Analysis of Air taTcen from the Laboratory. 
 
 W 
 
 Air taken 1738'53 
 
 Vol. of nitrogen 1377'62 
 
 1376-40 
 
 I. 
 
 H 
 
 743-37 
 74337 
 743-55 
 
 t 
 
 15-8 
 15-8 
 15-75 
 
 Per cent, of O aud CO' 2 , 20'765. 
 
 "Per cent. 
 V 0+CO,'. 
 
 116-435 c.c. 
 92-264. 20-760 
 92-255 20-771 
 
 Vol. of air 170S'01 
 
 nitrogen 1356'04 
 
 II. 
 
 H 
 
 748-08 
 74733 
 
 t 
 
 15-0 
 15-2 
 
 Per cent. 
 
 v o+co-'. 
 
 11 5-545 C.C. 
 91-564 20-755 
 
 Per cent, of O and CO 2 found, 20755. 
 
 The following analyses were made with a sample of atmospheric air 
 collected on a subsequent day : 
 
 W 
 
 Vol. of air 1704'81 
 
 nitrogen 1348'33 
 
 1344-71 
 
 I. 
 
 H 
 754-92 
 
 754-78 
 755-92 
 
 t 
 
 12'2 
 12-08 
 11-7 
 
 Per cent. 
 V 0+CO,'. 
 
 117:814 c.c. 
 93-216 20-877 
 93-229 20-868 
 
 Per cent, of O and CO-, 20'872. 
 
 W 
 
 Vol. of air 1669*39 
 
 nitrogen 1323'24 
 
 1322-38 
 
 II. 
 
 H 
 
 756-30 
 755-49 
 755-30 
 
 t 
 
 10-15 
 10-05 
 
 10-00 
 
 Per cent, of O and CO 2 , 20'86G. 
 
 Per cent. 
 
 V O+CO- 1 . 
 
 116-584 C.C. 
 92-260 20-863 
 92-252 20*870 
 
 The apparatus described in the preceding pages was made for the author, 
 ost excellent manner, by Mr. Emil Griener, 79, Nassau Street, New York. 
 
 in most exc 
 
 SIMPLER METHODS OF GAS ANALYSIS. 
 
 100. ALL the sets of apparatus previously described are adapted 
 to secure the greatest amount of accuracy, regardless of speed or the 
 time occupied in carrying out the various intricate processes involved. 
 
 For industrial and technical purposes the demand for something 
 requiring less time and care, even at the sacrifice of some accuracy, 
 has been met by a large number of designs for apparatus of a 
 simpler class, among which may be mentioned those of Orsat, 
 
 XTNIVERSITT 
 
548 VOLUMETRIC ANALYSIS. 100. 
 
 Bunte, Wink el, Hempel, Stead, Lunge, etc. Many of these 
 are arranged to suit the convenience of special industries, and will 
 not be described here. 
 
 The most useful apparatus for general purposes is either that of 
 Hempel or Lunge, both of which will be shortly described. 
 Fuller details as to these and other special kinds of apparatus are 
 contained in Winkler's Handbook of Technical Gas Analysis, 
 translated by Lunge.'"" 
 
 The general principles upon which these various sets of apparatus 
 are based, and the calculation of results, are the same as have been 
 described in preceding pages ; and of course due regard must be 
 had to tolerable equality of temperature and pressure, and the effects 
 of cold or warm draughts of air upon the apparatus whilst the 
 manipulations are carried on. If the operator is not already 
 familiar with methods of gas analysis, a study of the foregoing 
 sections will be of great assistance in manipulating the apparatus 
 now to be described. 
 
 Simple Titration of Gases. Many instances occur in which an 
 absorbable gas can be passed through a solution of known standard 
 in excess, and the measure of the gas being known either by 
 emptying an aspirator of water containing a known volume, or by 
 the use of a gas-meter. The amount of gas absorbed may be found 
 by titration of the standard absorbent residually. Such instances 
 occur in the exit gases of vitriol and chlorine chambers. In the case 
 of vitriol exits the gases are drawn through a standard solution of 
 soda or other alkali contained in T odd's absorption tubes or some 
 similar arrangement, to which is attached a vessel containing 
 a known volume, say exactly T V of a cubic foot of water. A tap 
 is fixed at the bottom of this vessel, so that when all is tightly 
 fitted and the tap partially opened, a small flow of water is 
 induced, which draws the gases through the absorbent. When the 
 aspirator is empty the flow of gases ceases, and of course the volume 
 of water so run out represents that of the gases passed. 
 
 Another way of measuring the gases is to use an india-rubber 
 vessel, which can be compressed by the hand, known as a finger- 
 pump. The volume contents being known by measurement with 
 water or air, the aspirations made by it may be calculated ; the 
 aspirated gases are then drawn slowly through the absorbent liquid. 
 In the case of chlorine exits the gases are passed through a solution 
 of potassic iodide in excess, and the amount of liberated iodine 
 subsequently found by titration with standard sodic arsenite. A 
 most convenient vessel is the revolving double glass aspirator, 
 known as Dancer's or Muencke's. 
 
 The standard solutions used in these cases are generally so 
 arranged as to avoid calculations, and the result found for legal 
 purposes in England is given in grains per cubic foot, in order to 
 
 * Van Voorst, 1885. 
 
TOO. NORMAL SOLUTIONS FOR GAS ANALYSIS. 549 
 
 comply '\vith the conditions of the Noxious Vapours Act, which 
 enjoins that not more than 4 grains of SO 3 , or 2^ grains of Cl, in 
 one cubic foot shall be allowed to pass into the atmosphere. 
 
 Sometimes a gas may be estimated by the reaction which takes 
 place when brought in contact with a chemical absorbent, such as 
 the formation of a precipitate, or the change of colour AA r hich it 
 produces in an indicator. The gas in this case can be measured 
 by a graduated aspirator, the flow of which is stopped when the 
 peculiar reaction ceases or is manifested. 
 
 Normal Solutions for Gas Analysis. In the titration of gases by 
 these methods, particularly on the Continent, the custom is to use 
 special normal solutions, 1 c.c. of which represents 1 c.c. of the 
 absorbable gas in a dry condition, and at 760 m.m. pressure and 
 0C. temperature. These solutions must not be confounded with 
 the usual normal solutions used in volumetric analysis of liquids or 
 solids. For instance, a normal gas solution for chlorine Avould be 
 made by dissolving 4*4288 gm. of As 2 3 , with a feAv grams of sodic 
 carbonate to the liter, and a corresponding solution of iodine 
 containing 11 '3396 gm. per liter, in order that 1 c.c. of either 
 should correspond to 1 c.c. of chlorine gas. 1 c.c. of the same 
 iodine solution would also represent 1 c.c. of dry SO 2 , and so on. 
 
 A very convenient bottle for the titration of certain gases is 
 adopted by Hesse. It is made in a conical form, like an 
 Erlenmeyer's flask, and has a mark in the short neck, down to 
 which is exactly fitted a caoutchouc stopper having two holes, 
 which will either admit the spit of a burette or pipette, or may be 
 securely closed by solid glass rods. The exact contents of the vessel 
 up to the stopper is ascertained, and a conA T enient size is about 500 
 or 600 c.c. The exact volume is marked upon the vessel. 
 
 In the case of gases not affected by Avater, the bottle is filled Avith 
 that liquid and a portion displaced by the gas, and the stopper Avith 
 its closed holes inserted. If water cannot be used, the gas is dra\vn 
 into the empty bottle by means of tubes Avith an elastic pump. 
 The absorbable constituent of the gas is then estimated Avith an 
 excess of the standard solution run in from a pipette or burette. 
 During this a volume of the gas escapes equal to the volume of 
 standard solution added, Avhich must of course be deducted from 
 the contents of the absorbing vessel. The gas and liquid are left to 
 react w.itli gentle shaking until complete. The excess of standard 
 solution is then found residually by another corresponding standard 
 solution; and in the case of using gas normal solutions, the difference 
 found corresponds to the volume of the absorbed constituent of the 
 gas in c.c. ; and from this, and from the total volume of gas employed, 
 may be calculated the percentage, alloAving for the correction men- 
 tioned. This arrangement may be used for CO 2 in air, using normal 
 gas baric hydrate and a corresponding normal gas oxalic acid with 
 phenolphthalein. The normal oxalic acid should contain 5*6314 gm. 
 
550 
 
 VOLUMETRIC ANALYSIS. 
 
 100. 
 
 per liter, in order that 1 c,e. may represent 1 c.c. of CO 2 . The baryta 
 solution must correspond, or its relation thereto found by blank 
 experiment at the time. The arrangement is also available for HC1 
 in gases, using a normal gas silver solution containing 4*8233 gm. 
 Ag per liter, as absorbent, with a corresponding solution of 
 thiocyanate ( 43) and ferric indicator ; or the HC1 may be absorbed 
 "by potash, then acidified with HXO 3 , 
 and the titration carried out by the 
 
 same process ; or again, 
 
 an alkaline 
 
 earbonate may be used, and the titration 
 made with a normal gas silver solution 
 using the chromate indicator (41, 2&). 
 
 Hem pel's Gas Burette. This consists 
 ef two tubes of glass on feet, one of which 
 is graduated to 100 c.c. in i c.c. (the 
 burette proper), and the other plain (the 
 level tube). They are connected at the 
 feet by an elastic tube, much in the 
 same way as Lunge's nitrometer. The 
 arrangement is shown in fig. 99. 
 
 The illustration shows the burette with 
 three-way stop-cock at bottom, which is 
 necessary in the case of gases soluble in 
 water, or where any of the constituents 
 are affected thereby. If this is not the 
 case, a burette without such stop-cock 
 is substituted (fig. 100). The elastic tube 
 should not be in one piece, but con- 
 nected in the middle by a shoit length 
 of glass tube to admit of ready dis- 
 connection. 
 
 Fig. 100 will illustrate not only the original He m pel burette 
 with level tube, but also the method of connection with the gas 
 pipette, and also the way in which the elastic tube is joined by the 
 intervening glass tube.* 
 
 Hempel, with great ingenuity, has devised special pipettes to 
 Be used in connection with the burette, and which render the 
 instrument very serviceable for general gas analysis. The pipette 
 shown in fig. 100 is known as the simple absorption pipette, and 
 serves for submitting the gas originally in the burette to the action 
 of some special absorbent. With a series of these pipettes the gas 
 
 * Tlie same chemist has since designed a gas burette which has the advantage of 
 being unaffected by the fluctuating temperature and pressure of the atmosphere. This 
 fs effected by connecting the measuring apparatus with a space free from air, but 
 saturated with aqueous vapour. A figure showing the arrangement is given in 
 C. N. Ivi. 264. These simpler forms of gas apparatus in great variety, including variovis 
 forms of the nitrometer, are kept in stock by Messrs. Townson and Mercer, 89 Bishops- 
 g-ate Street Within, London, E.G., and probably by most of the dealers in apparatus in 
 the kingdom. 
 
100. 
 
 HEMPEL'S BURETTE AND PIPETTES. 
 
 551 
 
 is submitted to the action of special absorbents, one after another, 
 until the entire composition is ascertained. The connections must 
 in all cases be made of best stout rubber, and bound with wire. 
 
 Fig. 100. 
 
 Collection and measurement of the Gas over Water. Both tubes 
 are filled completely with water (preferably already saturated 
 mechanically with the gas), care being taken that all air is driven 
 out of the elastic tube. The clip is then closed at the top of the 
 burette, and the bulk of the water poured out of the level tube, the 
 elastic tube being pinched meanwhile with the finger and thumb to 
 prevent air entering the burette. The latter is then connected by 
 a smal] glass tube with the source of the gas to be examined, when, 
 
552 
 
 VOLUMETRIC ANALYSIS. 
 
 100. 
 
 by lowering the level tube, the gas flows in and displaces the water 
 from the burette into the level tube. The pressure is then regulated 
 by raising or lowering either of the tubes until both are level, when 
 the volume of gas is read off. It is convenient of course to take 
 exactly 100 c.c. of gas to save calculation. 
 
 Collection and measurement of the Gas without Water. In this 
 case the three-way tap burette (fig. 99) is dried thoroughly by first 
 washing with alcohol, then ether, and drawing air through it. The 
 three-way tap is then closed, the upper tube connected with the gas 
 supply, and the burette filled either by the pressure of the gas, or 
 by using a small pump attached to the three-way cock to draw out 
 the air and fill the burette with the gas. When full the taps are- 
 turned off, and connection made with the level tube, which is then 
 filled with water, the tap opened so that the water may flow into 
 the burette and absorb the soluble gases present. As the burette 
 holds exactly 100 c.c. between the three-way tap and the upper clip,, 
 the percentage of soluble gas is shown directly on the graduation. 
 
 The method of Absorption. In the case of the simple pipette 
 fig. 100, a is filled with the absorbing liquid, which reaches into the 
 syphon bend of the capillary tube ; the bulb b remains nearly 
 empty. In order to fill the instrument, the liquid is poured into /^ 
 and the air sucked out of a by the capillary tube. It is convenient 
 to keep a number of these pipettes filled with various absorbents,, 
 well corked, and labelled. 
 
 Another pipette of similar char- 
 acter is shown in fig. 101, and i& 
 adapted for solid reagents, such as 
 stick phosphorus in water. The 
 instrument has an opening at the 
 bottom, which can be closed with 
 a caoutchouc stopper. This pipette 
 is also used for absorbing CO 2 by 
 filling it with plugs of wire gauze 
 and caustic potash solution, so as 
 to expose a large active surface 
 when the liquid is displaced by 
 the gas. 
 
 To make an absorption, the 
 capillary U-tube is connected with 
 the burette containing the mea- 
 sured gas by a small capillary 
 
 Fig. 101. 
 
 tube (fig. 101), the pinchcock of course being open, then by raisin 
 the level tube, the gas is driven over into the cylindrical bulb,, 
 where it displaces a portion of the liquid into the globular bulb. 
 When the whole of the gas is transferred, the pinchcock is closed f 
 and the absorption promoted by shaking the gas with the reagent. 
 When the action is ended, communication with the burette is 
 
100. HEMPEL'S PIPETTES 553 
 
 restored, and the gas syphoned back with the level tube into the 
 burette to be measured. 
 
 The double absorption Pipette shown in fig. 102 is of great utility 
 in preserving absorbents which would be acted on by the air, such 
 for instance as alkaline pyrogallol, cuprous chloride, etc. The bulb 
 next the syphon tube is filled with the absorbent, the next is empty, 
 the third contains water, and the fourth is empty. When the gas 
 is passed in, the intermediate water passes on to the last bulb 
 to make room for the gas, thus shutting off all contact with the 
 atmosphere, except the small amount in the second bulb. An 
 arrangement is also made for the use of solid reagents, by sub- 
 stituting for the globe next the U capillary tube a cylindrical bulb 
 as in fig. 101. 
 
 Hydrogen Pipette. The hydrogen gas necessary for explosions 
 or combustions is produced from a hollow rod of zinc fixed over 
 a glass rod passed through the rubber stopper (fig. 101). The bulb 
 being filled with dilute acid, gas is generated, and as it accumulates 
 the acid is driven into the next bulb and the action ceases. 
 
 Explosion Pipette. Another arrangement provides for explosions 
 by the introduction into a thicker bulb, measured volumes of the 
 gas, of air, and of hydrogen. The bulb being shut off with 
 a stop-cock, a spark is passed through wires sealed into the upper 
 portion of the bulb. 
 
 Pipette with Capillary Combustion Tube. This simple arrange- 
 ment consists of a short glass capillary tube bent at each end in 
 a right angle, into which an asbestos fibre impregnated with finely 
 divided palladium is placed, so as to allow of the passage of the gas.'"' 
 The gas being mixed with a definite volume of air in the burette, 
 and the measure ascertained (not more. than 25 c.c. of gas 'and 60 
 or 70 c.c. of air), the asbestos tube is heated gently with a small gas 
 flame or spirit lamp, and the pinchcocks being opened, the mixture 
 is slowly passed through the asbestos and back again, the operation 
 being repeated so long as any combustible gas remains. Xo 
 
 * To prepare palladium asbestos, dissolve about 1 gin. palladium in aqua regia, 
 evaporate to dryness on water bath to expel all acid. Dissolve in a very small quantity 
 of water, and add 5 or 6 c.c. of saturated solution of sodic formate, then sodic carbonate 
 until strongly alkaline. Introduce into the liquid about 1 gin. soft, long-fibred asbestos, 
 which should absorb the whole liquid. The fibre is then dried at a gentle heat, and 
 finally in the water bath till perfectly dry it is then soaked in a little warm water, put 
 into a glass funnel, and all adhering salts washed out carefully without disturbing the 
 palladium deposit. The asbestos so prepared contains about 50 per cent. Pd, and in 
 a perfectly dry state is capable of causing the combination of H and O at ordinary 
 temperature, but when used in the capillary tube it is preferable to use heat as mentioned. 
 The capillary combustion tubes are about 1 m.m. bore and 5 m.m. outside diameter, 
 with a length of abotit 15 c.m. The fibre is placed into them before bending the angles 
 as follows : Lay a few loose fibres, about 4 c.m. long, side by side on smooth filter 
 
 Eaper, moisten with a drop or two of water, then by sliding the finger over them twisted 
 ito a kind of thread about the thickness cf darning cotton. The thread is taken 
 carefully up with pincers and dropped into the tube held vertically, then by aid of 
 water and gentle shaking moved into position in the middle of the tube. The tube is 
 then dried in a warm place, and finally the ends bent at right angle for a length of 3| to 
 4 c.m. Platinum asbestos may be prepared in the same way, using, however, only from 
 half to one-fourth the qiiantity of metal. 
 
554 
 
 VOLUMETKIC ANALYSIS. 
 
 100. 
 
 explosion need be feared. The residue of gas ultimately obtained 
 is then measured, and the contraction found ; from this the volume 
 of gas burned is ascertained either directly, or by the previous 
 removal of CO 2 formed by the combustion with the potash pipette. 
 H is very easily burned, CO less easily. Ethylene, benzine, and 
 acetylene require a greater heat and longer time. CH 4 is not 
 affected by the method, even though mixed with a large excess of 
 combustible gases. 
 
 Fig. 102. 
 
 In order to illustrate the working of the whole set of apparatus, the 
 analysis of a mixture containing most or all of the gases likely to be met 
 with in actual testing is given from a paper contributed by Dr. W. Bott 
 (J. S. C. I. iv. 163). The mixture of gases consists of CO-, O, CO, C-H 4 , 
 CH 4 , H and N. A sample of this gas say 100 c.c. is collected and 
 measured in the gas burette. The CO" 2 is next absorbed by passing the gas 
 into a pipette (fig. 100) containing a solution of 1 part of KHO in 
 2 parts of water. To ensure a more rapid absorption, the bulb shown 
 in fig. 101 containing the caustic potash may be partly filled with plugs 
 of wire gauze. The absorption of the CO- is almost instantaneous. It is 
 only necessary to pass the gas into the apparatus and syphon it back again 
 to be measured. The contraction produced gives directly the percentage 
 of CO'-, since 100 c.c. were used at starting. The remaining gas contains 
 O, CO, H, C 2 H 4 , CH 4 , N. The oxygen is next absorbed. This may be 
 effected in two ways by means of moist phosphorus or by an alkaline 
 solution of pyrogallic acid. The former method is by far the more elegant of 
 the two, but not universally applicable. The absorption is done in a pipette 
 (fig. 101), the corked bulb of which is filled with thin sticks of yellow phosphorus 
 surrounded by water. The gas to be tested is introduced in the usual manner, 
 and by displacing the water comes into contact with the moist surface of the 
 phosphorus, which speedily absorbs all the oxygen from it. The absorption 
 proceeds best at about 1520 C., and is complete in ten minutes. The small 
 quantity of P 2 O 3 formed by the absorption dissolves in the water present, and 
 thus the surface of the phosphorus always remains bright and active. This 
 neat and accurate method is not however universally applicable ; the following 
 are the conditions under which it can be used : The oxygen in the gas must 
 
100. HEMPEL'S METHODS OF GAS ANALYSIS. 555 
 
 not be more tluiu 50 per cent., and the gas must be free from ammonia, C-II 4 
 and other hydrocarbons, vapour of alcohol, ether and essential oils. In the 
 instance chosen, the phosphorus method would hence not be applicable, as the 
 mixture contains C' 2 H 4 ; therefore pyrogallic acid must be used. The absorption 
 is carried out in the compound absorption pipette (fig. 102), the bulb of which 
 is completely filled with an alkaline solution of pyrogallol made by dissolving 
 1 part (by volume) of a 25 per cent, pyrogallic acid solution in 6 parts of 
 a 60 per cent, solution of caustic potash. The absorption is complete in about 
 live minutes, but mav r be hastened by shaking. The remainder of the gas 
 now contains C-H 4 , CO, CH 4 , H, N, arid the next step is to absorb the C-H 4 by 
 means of fuming SO 3 , the CH 4 being subsequently determined by explosion. 
 In choosing the latter method a portion, say half, of the residual gas is taken 
 for the estimation of hydrogen. The absorption of the hydrogen is based on 
 the fact that palladium black is capable of completely burning hydrogen 
 when mixed with excess of air, and slowly passed over the metal at the 
 ordinarj r temperature. About 1 gm. of palladium black are placed in a small 
 U-tube plunged into a small beaker of cold water, and the gas, mixed with an 
 excess of air (which, of course, must be accurately measured), is passed slowly 
 through the tube two or three times,* the tube at the time being connected 
 with an ordinary absorption pipette filled with water or else with the KOH 
 pipette, which in this case, of course, simply serves as a kind of receiver. 
 .Finally the gas is syphoned back into the burette and measured two-thirds 
 of the contraction correspond to the amount of H originally present in the 
 mixture of gas and air. The CH 4 is not attacked by ordinary '30 per cent. SO 3 
 Xordhausen acid during the absorption of the C' 2 H 4 . The acid is contained 
 in an absorption pipette (fig. 101), the bulb of which is filled with pieces of 
 broken glass so as to offer a larger absorbing surface to the gas. The 
 absorption is complete in a few minutes, but the remaining gas previous to 
 measuring should be passed into the KOH pipette and back again, so as to 
 free it from fumes of SO 3 . Residual gas : CO, CH 4 , H, N. The CO is next 
 absorbed by means of an ammoniacal solution of cuprous chloride in a com- 
 pound absorption pipette. The gas has to be shaken with the absorbent for 
 about three minutes. It must be borne in mind that Cu 2 Cl 2 solution also 
 absorbs oxygen, and, according to Hempel, considerable quantities of C' 2 H 4 , 
 hence these gases must be removed previously. Residue : CH. 4 , H, N. Both 
 CH 4 and II may now be estimated either by exploding with an excess of air 
 in the explosion pipette and measuring (1) the contraction produced, and (2) 
 the amount of CO" formed (by means of the KOH pipette) ; or, according to 
 Hempel, absorb the hydrogen first of all as described above provided the 
 U-tube be kept well cooled with water, inasmuch as that at about 200 C. 
 a mixture of air and CH 4 is also acted upon by palladium. The presence of 
 CO, vapours of alcohol, benzine and hydrochloric acid also interfere with 
 the absorption by palladium. 
 
 The palladium may be used for many consecutive experiments, but must 
 be kept as dry as possible. After it has been used for several absorptions it 
 may be regenerated by plunging the tube into hot water and passing 
 a current of dry air through it. 
 
 Having estimated the hydrogen, the CH 4 in the remaining portion of the 
 gas has to be determined. This contains CH 4 , N and H, the amount of the 
 latter being kno vvn from the previous experiment. The gas is mixed with the 
 requisite quantity of air and hydrogen, introduced into the explosion pipette 
 and fired by means of a spark. The water resulting from the combustion 
 Condenses in the bulb of the pipette, whilst the CO' 2 formed is absorbed by the 
 KOH solution present. Hence the total contraction produced corresponds to: 
 
 a. The hydrogen present in the original gas + i its vol. of O (the quantity 
 requisite for complete combustion). 
 
 *Instead of this the H may le binned in the tube containing the palladium asbestos 
 fib.-e previously described. 
 
556 
 
 VOLUMETRIC ANALYSIS. 
 
 100. 
 
 I. The known quantity of hydrogen added + i its vol. of O. 
 c. The CEL 4 present + 2 vols. of O requisite for its combustion. 
 CH 4 + O 4 = (CO 2 + 2H 2 O) 
 
 2 4 disappears. 
 
 Since a and b are known, or can be readily calculated from the previous data r 
 by subtracting (a + k) from the total contraction it is possible to obtain C 
 (a + b) = c contraction due to CH 4 alone, and one-third of this is equal to the 
 volume of CH 4 present, as will be readily seen from the above equation. 
 The remaining nitrogen is estimated by difference. 
 
 storing- and 
 an arrange- 
 
 In work- 
 gas to E, 
 
 Improved arrangement of Hempel's Pipettes for 
 using- absorbents. P. P. Beds on has designed 
 ment of pipettes which he uses in connection with a Dittmar's 
 measuring apparatus, hut which may of course be used with 
 other forms of gas apparatus, by suitable connections. The 
 pipettes are shown in fig. 103, and their use may be described 
 as follows : A capillary tube with a three-way cock A is soldered 
 
 to the Hem pel pipette the 
 capillary is drawn out and bent 
 so as to pass into the mercury 
 trough. The tap A can be 
 /D placed in connection with C, to 
 which is attached a movable 
 mercury reservoir D. 
 ing, e.s/., transferring 
 the absorbent fills E and the 
 capillary of tap A. By raising 
 D the vessel C and capillary B 
 are entirely filled with mercury. 
 B, of course, is immersed in 
 the mercury trough. Having 
 filled B with mercury, the test 
 tube containing the gas to be 
 examined is brought over the 
 end of B and some gas drawn 
 into C by depressing D. The 
 tap is then turned to put the 
 tube in connection with E, and 
 the gas forced into E by 
 By raising and lowering the tube 
 
 the gas can be brought into intimate contact with the absorbent 
 and absorption thus promoted. To bring all the gas into E, D is 
 again used and the remainder of gas drawn into C by depressing D ; 
 then by turning the tap round the gas from C can be forced 
 into E ; the tap is then turned so as to put the capillary and 
 E in connection, and the gas flows into E with a small portion 
 in capillary B, retained by the column cf mercury filling the 
 bent limb. 
 
 103. 
 
 depressing the tube in trough. 
 
101. . THE NITROMETER. 557 
 
 The gas may be left thus for some hours ; and to transfer it to 
 the tube, C and E are placed in connection by suitably turning the 
 tap ; then by depressing 1) some gas is drawn into C and the tap 
 turned so as to put C and the tube in connection. 
 
 By carefully raising D the mercury is washed out of B and some 
 of the gas passes into the tube. With B clear of mercury and 
 filled with gas, the tube and E are placed in connection and the 
 gas flows out of E into the tube. When the liquid from E has 
 risen so as to fill the vessel up to the tap (the capillary of the tap 
 being also filled), the tap is turned to put C and B in connection ; 
 then by raising D all gas is washed out of C and capillary into the 
 tube used for its collection and transferred to the measuring tube. 
 
 Professor Beds on also attaches to the measuring apparatus 
 a vessel containing a known volume of air at known temperature 
 and pressure, as recommended by Lunge, so as to dispense with 
 the otherwise necessary corrections. Further details as to the 
 various uses to which II em pel's gas pipettes and other simple 
 forms of gas apparatus may be adapted, will be found in Hem pel's 
 Gas Analysis (Macmillan, 1892). 
 
 THE NITROMETER. 
 
 101. THIS instrument has been incidentally alluded to in 70 
 (page 262) as being useful for the estimation of nitric acid 'in the 
 form of nitric oxide. It was indeed for this purpose that the 
 instrument was originally contrived, more especially for ascertaining 
 the proportion of nitrogen acids in vitriol. 
 
 The instrument has been found extremely useful also for general 
 technical gas analysis, and for the rapid testing of such substances 
 as manganese peroxide, hydrogen peroxide, bleaching powder, urea, 
 etc. The apparatus in its simplest form is shown in fig. 104, and 
 consists of a graduated measuring tube fitted at the top with 
 a three-way stop-cock, and a glass cup or funnel ; the graduation 
 extends from the tap downwards to 50 c.c. usually, and is divided 
 into -~ c.c. The plain tube, known as the pressure or level tube, 
 is about the same size as the burette, and is connected with the 
 latter by means of stout elastic tubing bound securely with wire. 
 Both tubes are held in clamps on a stand, and it is advisable to fix 
 the burette itself into a strong spring clamp, so that it may be 
 removed and replaced quickly. 
 
 One great advantage over many other kinds of technical gas 
 apparatus which pertains to this instrument is, that it is adapted 
 for the use of mercury, thus insuring more accurate measurements, 
 and enabling gases soluble in water, etc., to be examined. 
 
 Another form of the same instrument is designed by Lunge 
 for the estimation of the nitric acid in saltpetre and nitrate of 
 soda, where a larger volume of nitric oxide is dealt with than 
 occurs in many other cases. In this instrument a bulb is blown 
 on. the burette just below the tap, and the volume contents of this 
 
558 
 
 VOLUMETRIC ANALYSIS. 
 
 101. 
 
 bulb being found, the graduation showing its contents begins on the 
 tube at the point where the bulb ends, and thence to the bottom ; 
 the level tube also has a bulb at bottom to contain the mercury 
 displaced from the burette. Illustrations of this form of nitrometer 
 will be found further on. 
 
 The following description of the 
 manipulation required for the estima- 
 tion of nitrogen acids in vitriol applies 
 to the ordinary nitrometer, and applies 
 equally to the estimation of nitrates 
 in water residues and the like (see 
 page 468) : 
 
 The burette a is filled with mercury in 
 such quantity that, on raising b and keeping 
 the tap open to the burette, the mercury 
 stands quite in the tuphole, and about tuo 
 inches up the tube I. The tap is now closed 
 completely, and from O'o to 5 c.c. of the 
 nitrous vitriol (according to strength) poured 
 into the cup. b is then lowered and the tap 
 cautiously opened to the burette, and shut 
 quickly when all the acid except a mere 
 drop has run in, carefully avoiding the 
 passage of any air. 3 c.c. of strong pure 
 H-SO 4 are then placed in the cup and drawn 
 in as before, then a further 2 or 3 c.c. of 
 acid to rinse all traces of the sample out of 
 the cup. a is then taken out of its clamp, 
 and the evolution of gas started by inclining 
 itseveral times almost toahorizontal position 
 and suddenly righting it again, so that the 
 mercury and acid are well mixed and shaken 
 for a minute or two, until no further gas is 
 evolved. The tubes are so placed that the 
 mercury in b is as much higher than that in 
 a as is required to balance the acid in a ; 
 this takes about one measure of mercury fur 
 65 measures of acid. "When the gas has 
 assumed the temperature of the room, and 
 all froth subsided, the volume is read off, 
 and also the temperature and pressure from 
 a thermometer and barometer near the place 
 of operation. The level should be checked 
 by opening the tap, when the mercury level 
 ought not to change. If it rises, too much 
 pressure has been given, and the reading 
 must be increased a trifle. If it sinks, thy 
 reversa. A good plan is to put a little acid 
 into the cup before opening the tap : this 
 will be drawn in if pressure is too low, or 
 blown up if too high. These indications Avill cerve for a correct repetition 
 of the experiment. 
 
 To empty the apparatus ready for another trial, lower a and open the tap, 
 then raise b so as to force both gas and acid into the cup ; by opening the tap 
 then outwards, the bulk of the acid can be collected in a beaker, the last 
 
10.1. 
 
 THE NITROMETER. 
 
 559 1 
 
 drops being wiped out with blotting-paper. It is hardly necessary to say that 
 the tap must be thoroughly tight, and kept so by the use of a little vaseline, 
 taking care that none gets into the bore-hole. 
 
 The calculations for nitrogen are given on page 262. 
 
 It is evident that the nitrometer can be made to replace Hempel's 
 burette if so required, by attaching to the side opening of the three- 
 way tap the various pipettes previously described, or smaller pipettes 
 of the same kind to be used with mercury, as described by Lunge- 
 (Bericlite, xiv. 14, 92), 
 
 The instrument may also be very well employed for collecting, 
 measuring, and analyzing the gases dissolved in water or other 
 liquids. An illustration of this method is given by Lunge and 
 Schmidt (Z. a. C. xxv. 309) in the examination of a sample of 
 water from the hot spring at Leuk in Switzerland. 
 
 Pig. 306. 
 
 The determination of the dissolved gases was made in the nitre- 
 meter, arranged as shown in figs. 105 and 106 : 
 
 The flask A is complete!}' filled with the water ; an indiarubber plug with 
 a capillary tube () passing through it is then inserted in the flask, and the 
 tube is thereby completely filled with water. The whole is then weighed, 
 and the difference between this and the weight of the empty flask and tube 
 gives the amount of water taken. The end of the capillary tube is then 
 connected to the side tube of the nitrometer by the tube b. The nitrometer 
 is then completely filled with mercury, and when the tubes are quiet, the flask 
 and measuring tube of the nitrometer are quickly placed in connection, with- 
 out the introduction of the slightest trace of air. The water in the flask is- 
 
560 
 
 VOLUMETRIC ANALYSIS. 
 
 101. 
 
 then slowly heated to boiling. Some water as well as the dissolved gases 
 collect in the measuring tube of the nitrometer. The tube N of the nitro- 
 meter should be lowered in order that the boiling may take place under 
 reduced pressure. After boiling for five to ten minutes, the stop-cock is 
 quickly turned through 180, so that the flask is placed in combination with 
 the cup B containing mercury, and the flame removed. Since the mercury 
 
 Tig. 107. 
 
 Fig. 109. 
 
 stands lower in N than in M, it is not possible for any loss of gas to take 
 place at the moment of turning the tap. It is also impossible for any gas or 
 steam to escape through the mercury cup, since the pressure is inward. 
 A small bubble of gas always remains under the stopper; this is brought into 
 M by lowering the tube N as much as possible, and then turning the stop- 
 
101. LUNGE'S IMPROVED NITROMETER. 561 
 
 cock so that the flask and measuring tube are again placed in connection, and 
 when the bubble has passed over, quickly reversing the tap again. 
 
 When the whole of the gas is collected in the nitrometer, it is connected 
 with a second instrument P, quite full of mercury. The gas is then 
 transferred by placing the tap in such a position that it is closed in all 
 directions, and the tube M is heated by passing steam through the tube B. 
 When it is quite hot the tube N is lowered, causing the water in M to boil, 
 in order to expel every trace of dissolved gas. The taps are then placed in 
 connection and the gas passes over. It can then be cooled, measured, and 
 submitted to analysis. Two experiments gave 505 grn. water taken, gas 
 evolved 5'OG c.c.,= 10'02 per 1000 gm. ; 502 gm. water taken, gas evolved 
 4'94 c.c.,^9'84 per 1000 gm. 
 
 Lunge's Improved Nitrometer for the Gas-Volumetric Analyses 
 of Permanganate, Chloride of Lime, Manganese, Peroxide, etc. 
 
 Lunge in describing this instrument (/. C. S. I. ix. 21) says: 
 
 " In a paper published in the ChemiscJie Industrie, 1885, 161, I described 
 the manifold uses to which the nitrometer can be put as an apparatus for 
 gas analysis proper, as an absorptiometer, and especially for gas-volumetric 
 analyses. To fit it for the last-mentioned object, I added to it a flask, 
 provided with an inner tube fused on to its bottom, and suspended from 
 the side tube of the nitrometer, as shown in fig. 107, which at the same 
 time exhibits the Greiner and Priedrich's patent tap. This shows 
 how any ordinary nitrometer, such as are now found in most chemical 
 laboratories, can be applied to the before-mentioned uses. Where, however, 
 the methods concerned are to be employed not merely occasionally, but 
 regularly, it will be preferable to get a nitrometer specially adapted to this 
 use, of which figs. 108 and 109 show various forms. They liave no cup at the 
 top, which is quite unnecessary for this purpose, but merely a short outlet 
 tube for air. Fig. 108 shows an instrument provided with one of the new 
 patent taps, which are certainty very handy, and cause a much smaller 
 number of spoiled tests than the ordinary three-way tap, as shown in fig. 109, 
 which at the same time exhibits the form of nitrometer intended for large 
 quantities of gas, the upper part being widened into a bulb, below which the 
 graduation begins with either 60 or 100 c.c., ending at 100 or 140 c.c. 
 respectively. There are also various shapes of flasks shown in these 
 instruments, but it is unnecessary to say that these, as well as the bulb 
 arrangements, can be applied to any other form of the instrument. The 
 nitrometers used for gas-volumetric analyses are best graduated in such 
 manner that the zero point is about a centimeter below the tap, whilst 
 ordinary nitrometers have their zero point at the tap itself. I will say at 
 once that for all estimations of oxygen in permanganate, bleach or manganese 
 (see pages 123, 105), it is quite unnecessary to employ mercury for filling the 
 instruments, since identical results are obtained with ordinary tap water; 
 but it is decidedly advisable to place this instrument, like any ordinary 
 nitrometer or any other apparatus in which gases are to be measured, in 
 a room where there are as few changes of temperature by cold draughts or 
 gas-burners and so forth as possible. 
 
 " It may be as well to give here a general description of the mode of 
 procedure for manipulating gas-volumetric analysis with the nitrometer, 
 common to all analyses according to this method. Pill the nitrometer with 
 water or mercury by raising the level tube till the level of the liquid in the 
 graduated tube is at zero (in the case of instruments bearing the zero-mark 
 a little below the tap, as in figs. 108 and 109), or at TO c.c. (in the case of 
 ordinary nitrometers beginning their graduation at the tap itself). It is 
 unnecessary to say that in the latter case all readings must be diminished by 
 1 c.c. Close the glass tap. Put the substance to be tested into the outer 
 space of the flask, together with any other reagent apart from the H 2 O 2 (in the 
 
 O o 
 
562 VOLUMETRIC ANALYSIS. 101. 
 
 case of bleaching-powder nothing but the bleach liquor, in that of perman- 
 ganate the 30 c.c. of sulphuric acid, etc.). Now put the H-O 2 into the inner 
 tube of the flask, after having, in the case of testing for chlorine, made it 
 alkaline in the previously described way. Put the india-rubber cork, still 
 hanging from the tap, on to the flask, without warming the latter as above 
 described. As this produces a compression of the air within the flask, 
 remove this by taking out the key of the tap in figs. ]07, 108, or 109, 
 turning it for a moment so as to communicate with the short outlet tube. 
 Now turn the tap back, mix the liquids by inclining the flask, shake up and 
 alloAv the action to proceed. As the gas passes over into the graduated tube, 
 lower the level tube, so as to produce no undue pressure ; at last bring the 
 liquid in both tubes to an exact level and read off. 
 
 " In the case of bleach analysis all the oxygen of the chloride of lime is 
 given off, together with exactly as much oxygen of the H-O-. The total is 
 just equal to the volume of chlorine gas which would be given off by the 
 chloride of lime, and thus immediately represents the French or Gay-Lussac 
 ehlorometric degrees, of course after reducing the volume to and 700 m.m. 
 pressure. (The reading of the barometer must be corrected by deducting 
 the tension, of aqueous vapour for the temperature observed as well as the 
 expansion of mercury, according to the tables found everywhere.) These 
 reductions can easily be performed by the tables contained in the " Alkali- 
 Makers' Pocket-book" (pages 28 to 39), which I had calculated a number of 
 years ago, just in order to facilitate the use of the nitrometer." 
 
 Lunge's Gasvolumeter is an apparatus for dispensing with 
 seduction calculations in measuring gas volumes (described by 
 Lunge in Zeitsclirift /. angeic. Chem. 1890, 139 144, and here 
 quoted from J. S. C. I. ix. 547). 
 
 In technical gas analysis a considerable amount of time is taken 
 up by calculations for reducing gas volumes to standard temperature 
 and pressure, In pure gas analysis the inconvenience is not so 
 great ; for technical purposes the initial and end temperature and 
 pressure may be taken as the same, owing to the short duration of 
 the experiment, and for more accurate purpose " compensators " 
 have been devised. Where, however, the gas to be measured is 
 evolved from a weighed quantity of a liquid or solid (so that 
 volume and weight have finally to be connected) the matter is 
 different, and readings of thermometer and barometer have' to be 
 made, and then the necessary calculations are to be gone through. 
 Tables of reduction have certainly been compiled for reduction of 
 gases at various temperatures and pressures, but still readings of 
 thermometer and barometer have to be made, and part of the time 
 only is saved. To further reduce the time occupied and to render 
 the technical chemist in this department to a great extent 
 independent of temperature and atmospheric pressure the present 
 apparatus has been constructed. 
 
 By means of a T-tube, D (fig. 110), and thick-walled rubber tubing, 
 are connected the three tubes A, B, C. A is for measuring the gas ; it 
 .nay be any form of nitrometer, a Bunte's burette or other convenient 
 ourette. B is the " reduction tube," which has at its upper end a spherical 
 or cylindrical bulb. The volume to the first mark is 100 c.c , the remaining 
 narrow portion of the tube being calibrated up to 130140 c.c. in divisions 
 representing 1^- c.c. This '' reduction tube " is set once for all at the 
 
101. 
 
 LUXGE S GASVOLUMETEE. 
 
 beginning of work by observing tliermometer and barometer, calculating the 
 volume which 100 c.c. of perfectly dry air, measured at C. and 760 m.m., 
 would occupy under the existing conditions. This quantity of air is then 
 introduced, and the tube closed by means of the stop-cock shown, or by 
 fusing up the inlet (having in place of the inlet tube shown in the figure 
 a tube of capillary bore) . If it be necessary to measure the gas moist a drop 
 of water is introduced into this tube, and of course in the calculation 
 necessary the barometric pressure must be reduced by the vapour tension of 
 water ; if the gases are to be measured perfectly dry (as, for instance, when 
 using the nitrometer with sulphuric acid), a drop of sulphuric acid takes the 
 place of the water. 
 
 C is the pressure or levelling tube. 
 If necessary for the purpose of 
 
 regulating the temperature A and B 
 may be surrounded with water-jackets. 
 A, B, and C are supported by spring 
 clamps. It is easily seen that when by 
 
 raising C the level of the mercury in 
 
 B has been forced up to the mark 
 
 100, exactly the amount of pressure is 
 
 exerted by C as will compress the gas 
 
 in B to its volume under standard 
 
 conditions. 
 
 In taking a reading A and B must be 
 
 levelled andthemercurylevelin B must 
 
 have been brought up to 100. The 
 
 volume shown on A is then the volume 
 
 reduced to standard temperature and 
 
 pressure. In cases where the gas is 
 
 generated in A itself, or where the gas 
 
 Is transferred to A, this is all that 
 
 need be done. If, however, the gas is 
 
 generated in a side apparatus, as shown 
 
 in fig. 110, A and C must first be 
 
 levelled and the stop-cock of A then 
 
 closed so that the gas in A is collected 
 
 at atmospheric pressure. After this 
 
 reduction may be effected as already 
 
 explained. 
 
 In nitrogen determinations by 
 
 Dumas' method, A contains caustic 
 
 potash as well as mercury; this is 
 
 compensated by "having on the reduc- 
 tion tube, B, a mark at a distance 
 
 below the 100 mark equal to one-tenth 
 
 of the height of the caustic potash 
 
 column (sp. gr. of the caustic potash 
 
 equals one-tenth sp. gr. of mercury) ; 
 
 when taking a reading the mercury in 
 
 B must be at 100, and that in A must 
 
 be on a level with this new lower mark 
 
 of B. Similar allowance may be made 
 
 in nitrometric determinations, but the 
 
 case is here more difficult, owing to 
 
 the variations in the quality and specific 
 
 gravity of the sulphuric acid used. It 
 
 is better in such cases to liberate the gas in a separate vessel and transfer 
 
 subsequently to the burette for reduction and measurement. Pig. Ill 
 
 Pig. 110. 
 
 O O 2 
 
564 
 
 VOLUMETKIC ANALYSIS. 
 
 101. 
 
 shows a convenient form of apparatus. Of course the working part E, F 
 need not be graduated. Before beginning the operation the mercury is 
 made to fill E with the side tube a, which side tube is then capped with 
 a caoutchouc stopper to prevent escape of the mercury during subsequent 
 shaking. A, with its side tube e, is also completely filled with mercury. 
 The substance under examination, and subsequently the acid, are added 
 through C as usual. To transfer the gas from E to A, the cap b is removed 
 and a is fitted to e by means of the rubber connection d. F is then raised 
 and C lowered, the taps are carefully opened, and transference effected until, 
 the acid in E just fills e. 
 
 Fig. 111. 
 
 A further saving of time may be effected in works, where the 
 instrument is to be used for always one and the same object, by 
 marking on the gas burette or nitrometer the weight in milligrams 
 corresponding to certain volumes ; this may be done either instead 
 
101. 
 
 JAPP S GRAVIYOLUMETER. 
 
 565 
 
 of or alongside the c.c. divisions; or by using a fixed quantity of 
 substance, percentages may be marked off directly. For nitrogen 
 determinations by Dumas' method 1 c.c. of nitrogen under normal 
 conditions weighs 1/254 m.gm. In the case of azotometric deter- 
 minations of ammoniacal nitrogen (by sodic hypobromite) the 
 graduations may be made to represent ammonia. Correction must 
 he made in graduating, however, for the incompleteness of the 
 reaction. Tables giving the corrections have been introduced, but 
 the author has shown (Chem. Ind. 1885, 165) that these may be 
 dispensed with, and that it is sufficient to make a correction of 2 '5 
 per cent. For urea, however, the correction is 9 per cent. 
 
 The following table shows substances for which gasometric 
 methods are used : 
 
 Substance. 
 
 Basis to which 
 Percentages are 
 Calculated. 
 
 Method 
 Employed. 
 
 Gas 
 Evolved. 
 
 1 c.c. of Gas 
 =m.gm. of Basis, 
 (Col. II.) 
 
 Organic substances 
 
 Nitrogen 
 
 Dumas' 
 
 N 
 
 1-254 
 
 Ammonia salts ... 
 
 3j 
 
 Hypobrmte. 
 
 N 
 
 1-285* 
 
 ?? ?J 
 
 Ammonia 
 
 J5 
 
 N 
 
 1-561* 
 
 Urine 
 
 Urea 
 
 
 N 
 
 2'952* 
 
 ; Bone-charcoal, etc. 
 
 Carbon dioxide 
 
 Decomposed 
 with HC1 
 
 CO 2 
 
 1-966 
 
 
 Calcic carbonate 
 
 
 CO 2 
 
 4-468 
 
 Pyrolusite 
 Bleaching powder 
 
 Manganese dioxide 
 Chlorine 
 
 By H 2 2 
 
 
 
 o 
 
 3-882 
 1-5835 
 
 Potassic perman- 
 ganate . . . 
 
 Oxygen 
 
 
 
 o 
 
 G'715 
 
 Chili saltpetre ... 
 
 Sodic nitrate 
 
 Nitrometer 
 
 NO 
 
 3805 
 
 Nitrous bodies .. 
 
 N 2 O 3 
 
 } 
 
 NO 
 
 1-701 
 
 
 HNO 3 
 
 
 NO 
 
 2-820 
 
 
 Nitric acid 36 B. 
 
 
 NO 
 
 5330 
 
 ', 
 
 Sodic nitrate 
 
 5> 
 
 NO 
 
 3805 
 
 Nitroglycerol, dy- 
 namite, etc 
 
 Trinit rogly cerol 
 
 
 NO 
 
 3-387 
 
 ) 
 
 Nitrogen 
 
 5J 
 
 NO 
 
 0-6267 
 
 Nitrocellulose, py- 
 rox}'lin 
 
 i 
 
 " 
 
 
 NO 
 
 06267 
 
 * The corrections above referred to have here already been made. 
 
 Professor Japp (J. C. S. lix. 894) describes a modification of 
 Lunge's gasvolumeter, by means of which with accurately 
 graduated ordinary 50 c.c. gas burettes any required single gas 
 may, without observation of temperature or pressure, and without 
 calculation, be measured under such conditions that each c.c. 
 represents a milligram of the gas. The name "gravi volumeter" 
 is appropriately given to this instrument, and it undoubtedly 
 possesses this advantage over Lunge's instrument, that it obviates 
 the necessity of having a number of different gasvolumeters for 
 different substances, and moreover its manufacture involves no 
 
566 
 
 VOLUMETRIC ANALYSIS. 
 
 101. 
 
 large amount of skill, as the ordinary graduation in c.c. in y 1 ^- or ~ 
 is all that is required. 
 
 The apparatus is represented in fig. 112. It consists of two gas burettes, 
 of 50 c.c. capacity each, both furnished with obliquely bored taps. One of 
 these burettes, A, w r hich has a three-way tap, is the gas measuring 
 tube; the other, B, \vhich need only have a single tap, performs 
 the function of the regulator in Lunge's gasvolumeter, and may 
 be termed the "regulator tube." As in Lunge's instrument, both 
 tubes are moistened internally with a drop of water, in order that the gases 
 they contain may be saturated with aqueous vapour, and both are connected, 
 by means of stout, flexible tubing and a "["-piece, with the same movable 
 
 Pig. 112. 
 
 reservoir of mercury, C. And since, in certain determinations, the level of 
 the mercury reservoir is considerably below the lower end of the two 
 burettes, and an inward leakage of air might thus occur at the junctions of 
 the burettes with the india-rubber tubing, these junctions are surrounded 
 with pieces of wider india-rubber tubing, D, D, tied round the bottom and 
 open at the top, and filled with water, so as to form a w r ater joint. 
 
 The 25 c.c. division of the regulator tube is taken as the starting point in 
 calculating what may be termed the " gravivolumetric values " of the 
 different gases to be measured. Thus in the case of nitrogen it is necessary 
 
101. JAPP'S GRAVIVOLUMETEE. 567 
 
 to calculate to what volume 25 c.c. of standard dry nitrogen must be 
 brought in order that 1 c.c. may correspond with 1 m.gm. of the gas ; that 
 is to say, 25 c.c. of standard dry nitrogen weigh 0'001256 x 25=0'0314 gm. ; 
 and, therefore, these 31'4 m.gm. must be brought to the volume of 31'4 c.c. 
 The division 31*4 on the regulator tube is marked N 2 . Corresponding points 
 are in like manner determined for the various other gases which it is desired 
 to measure, and these points are marked O 2 , CO 2 , &c., as the case may be, on 
 the regulator tube. Finally, the thermometer and barometer are read 
 (a process onl}' necessary once for all in setting the regulator), the volume 
 which 25 c.c. of standard dry air would occupy if measured moist at the 
 observed temperature and pressure is calculated, and this calculated volume 
 of air is admitted at atmospheric temperature and pressure into the regulator 
 tube and the tap closed. The instrument is now ready for use. 
 
 Suppose it is desired to ascertain the weight of a quantit} r of nitrogen 
 contained in the measuring tube. The mercury reservoir is raised or 
 lowered until the mercur} r in the regulator tube stand at the nitrogen mark, 
 31'4, at the same time adjusting the regulator tube itself by raising or 
 lowering it bodily, so that the mercury level in the measuring tube and the 
 regulator tube may be the same. Under these circumstances each cubic 
 centimeter of gas in the measuring tube represents 1 m.gm. of nitrogen. For 
 since in the regulator tube 25 c.c. of standard dry air have been made to 
 occupy the volume of 31'4 c.c., and since the gases in the two tubes are 
 under the same conditions as regards temperature, pressure, and saturation 
 with aqueous vapour, therefore, in tlie measuring tube, every 25 c.c. of 
 standard dry nitrogen have also been made to occupy the volume of 31:4 c.c. 
 But 25 c.c. of standard dry nitrogen weigh, as we have seen, 31*4 m.gm. ; so 
 that the problem is solved, and the cubic centimeters and tenths of cubic 
 centimeters give directly the weight of the gas in milligrams and tenths of 
 milligrams. 
 
 The various other single (i.e., unmixed) gases may be weighed in like 
 manner by bringing the me re my in the regulator tube to the " gravi- 
 volumetric mark" of the gas in question, and adjusting the levels as before. 
 An exception would be made in the case of hydrogen, which would be 
 brought to such a volume that the cubic centimeter would contain a tenth 
 of a milligram. 
 
 Mixtures of gases may also be weighed, provided that the density of the 
 mixture is known. 
 
 Lastly, if the mercury in the regulator tube be brought to the mark 25 
 and the levels adjusted, a gas or mixture of gases in the measuring tube 
 will have the volume which it would occupy in the standard dry state. In 
 this form the instrument is merely a gasvolumeter, as described by Lunge, 
 and may be used for ordinary gas analysis. 
 
 The experiments made by Japp with the view of ascertaining 
 the degree of accuracy of which the apparatus is capable were 
 very satisfactory, details being given in the paper mentioned. The 
 substances experimented on were Methane, with a gravivolumetric 
 value- of 17'9; Nitrogen, 31-4; Air, 32'35; and Carbon dioxide, 
 49-3. 
 
 The measuring tube and regulator tube were held by a double clamp, the 
 arms of which could be moved horizontally, so as to admit of bringing the 
 tubes close together when necessary. The two tubes were so arranged that, 
 after adjusting the levels and ascertaining that the mercury in the regulator 
 tube was at the gravivolumetric mark, it was possible to read both levels 
 without moving the position of the eye. The object of this was that any 
 possible error of parallax might occur equally and in the same direction in 
 
568 VOLUMETRIC ANALYSIS. 101. 
 
 both tubes, in which case the two errors would tend to neutralize one another 
 in the final result.* The mercury reservoir was held by a clamp attached to 
 a separate stand, so that in the case of extreme differences of pressure the 
 entire stand could be placed on a different level from the rest of the 
 apparatus. 
 
 Assuming the graduation of a gravivolumeter to be correct, or the defects 
 of graduation to be eliminated by calibration, the sources of error in such 
 an instrument are, broadly speaking, four in number, and are to be found in 
 imperfections (1) in filling the regulator, (2) in adjusting the levels, (3) in 
 reading the regulator, and (4) in reading the measuring tube. The first of 
 these operations, that of filling the regulator, is performed once for all with 
 very great care, and may, for all practical purposes, be disregarded as a source 
 of error. Again, in adjusting the levels, the two tubes can be brought, by 
 means of the double clamp, within such a short distance of one another that 
 the adjustment is also practical!}' accurate. The real sources of error lie in the 
 two last operations. The burettes are divided into tenths of cubic centi- 
 meters, and can be read with the eye alone accurately to -^V c.c. Calculating 
 this error on 25 c.c. as the average volume of gas contained in the regulator 
 tube and measuring tube respectively, we have l/(20x 25)=-^ as the error 
 for each tube. But as the error in the regulator repeats itself in exact 
 proportion in the altered volume of gas in the measuring tube, we must add 
 the error of the regulator to the independent error of the measuring tube, 
 in order to ascertain the maximum error, which would thus be ^ ; and 
 this, calculated as assumed, upon 25 c.c. of gas, would be equal to an error 
 of reading O'l c.c. in the final result. An inspection of the foregoing 
 experimental results, however, discloses the fact that the maximum error is 
 only half this amount, or 0'05 c.c. ; and this the author attributes to the 
 fact that, owing to the method of reading employed, the errors of reading 
 in the regulator and measuring tube are not, as assumed in the foregoing 
 calculation, independent, but tend to neutralize one another. 
 
 This error of 0'05 c.c. is, however, the error of reading of any gas burette 
 which is read with the eye alone ; and the gravivolumeter ma} r , therefore, 
 claim to possess the same degree of accuracy as instruments of this class 
 generally. 
 
 * Suppose the eye in reading to be too high, the mercury in the regulator would stand 
 below the gravivolumetric mark, and the gas in the ineasiiring tube would consequently 
 be expanded beyond its proper volume. But owing to the eye being too high, this too 
 great volume in the measuring tube would be read off as smaller than it actually is. 
 In the case of equal volumes of gas in regulator and measuring tube, there would thus 
 be a total correction of the error committed (since the two tubes are of equal bore) ., 
 and in every case a diminution. 
 
101. 
 
 VOLUMETRIC ANALYSIS. 
 
 569 
 
 TABLE for Correction of Volumes of Gases for Temperature, 
 according to the Formula 
 
 1 
 
 760 x (1 + 5 1) 
 5 t from to 30. 5 = 0'003665. 
 
 t 1 + 5t 
 
 Log. (1 + 51) 
 
 t 
 
 1 + St Log. (1 + 5 1) 
 
 t 
 
 1 + 5t 
 
 Log. (1 + 5 i) 
 
 O'O I'OOOOOOO 
 
 1 1-0003665 
 
 O'OOO 0000 
 1591 
 
 5-0 1-0183250J 0-007 88G4 
 11-0186915 0-008 0427 
 
 16-0 
 
 ] 
 
 1-0366500 
 T0370165 
 
 0-015 6321 
 
 7857 
 
 2 1-0007330 
 
 3182 
 
 21-0190580 
 
 1989 
 
 "2 
 
 T0373830 
 
 9391 
 
 3 1-0010095 
 
 4772 
 
 3I1-0194245 
 
 4551 
 
 3 
 
 1-0377495 
 
 0-016 0925 
 
 41-0014660 
 
 G362 
 
 41-0197910 
 
 5112 
 
 4 
 
 L'0381160 
 
 2459 
 
 0-r> 1-0018325 
 
 7951 
 
 5-51.-0201575 
 
 6672 
 
 10-5 
 
 1-0384825 
 
 3992 
 
 6 1-0021990 
 
 9540 
 
 61-0205240 
 
 8232 
 
 6 
 
 T038S490 
 
 5524 
 
 7 1-00:2 30 5 5 
 
 0-001 1128 
 
 71-0208905 
 
 9791 
 
 7 
 
 1-0392155 
 
 7056 
 
 81-0029320 
 
 2715 
 
 81-0212570 
 
 0-009 1350 
 
 8 
 
 1-0395820 
 
 8588 
 
 91-0032985 
 
 4302 
 
 5-91-0216235 
 
 2909 
 
 10-9 
 
 1-0399485 
 
 0-017 0118 
 
 ] -01-0036650 
 
 O'OOl 5888 
 
 G-0 1-0219900 
 
 0-009 4466 
 
 11-0 
 
 T0403150 
 
 0-017 1648 
 
 1 1-0040315 
 
 7473 
 
 1 
 
 1-0223565 
 
 6024 
 
 1 
 
 1-0406815 
 
 3178 
 
 21-0043980 
 
 9058 
 
 2 1-0227230 
 
 7580 
 
 2 
 
 1-0410480 
 
 4708 
 
 3 1-0047645 
 
 0-002 0643 
 
 31-02308^5 
 
 9136 
 
 3 
 
 L'0414145 
 
 6236 
 
 41-0051310 
 
 2227 
 
 4 1-0234560 
 
 0-010 0692 
 
 4 
 
 1-0417810 
 
 7764 
 
 1-51-0054975 
 
 3810 
 
 C-5 1-0238225 
 
 2247 
 
 11-5 
 
 1-0421475) 9292 
 
 61-0058640 
 
 5393 
 
 Gjl'0241890 
 
 3801 
 
 6 
 
 1-0425140' 0-018 0819 
 
 71-0062305 
 
 6974 
 
 7lr0245555 
 
 5355 
 
 "7 
 
 1-0428805 2346 
 
 8 1-0065970 
 
 8556 
 
 81-0249220 
 
 6908 
 
 8 
 
 1-0432470 3871 
 
 1-91-0069635 
 
 0-003 0137 
 
 6-9 
 
 1-0252885 
 
 8461 
 
 11-9 
 
 1-0436135 5397 
 
 2-01-0073300 
 
 0-003 1718 
 
 7-0 
 
 1-0256550 
 
 0-011 0013 
 
 12-0 
 
 1-0439800 0-018 0922 
 
 ill -0076965 
 
 3298 
 
 1 
 
 1-0260215 
 
 1565 
 
 ] 
 
 T0443465 
 
 8446 
 
 21*0080680 
 
 4877 
 
 2 
 
 1-0263880 
 
 3116 
 
 2 
 
 1-0447130 
 
 9970 
 
 31-0084295 
 
 6455 
 
 3 
 
 1-0267545 
 
 4G6G 
 
 3 
 
 1-0450795 
 
 0-019 1493 
 
 4J1-0087960 
 
 8033 
 
 ' 4 
 
 1-0271210 
 
 6216 
 
 41-0454460 
 
 3016 
 
 2-5 1-0091625 
 
 9611 
 
 7-5 
 
 1-0274875 
 
 7765 
 
 12-5 
 
 L-0458125 
 
 4538 
 
 6 1-0095290 
 
 Q'004 1188 
 
 6 
 
 1-0278540 
 
 9314 
 
 6 
 
 1-0461790 
 
 6060 
 
 7 1-0098955 
 
 2764 
 
 7 
 
 1-0282205 
 
 0-012 0863 
 
 '/ 
 
 1'0465455 
 
 7581 
 
 81-0102620 
 
 4340 
 
 8 
 
 1-0285870 
 
 2410 
 
 8 
 
 1-0469120 
 
 9102 
 
 2-91-0106285 
 
 5916 
 
 7-9 
 
 1-0289535 
 
 3957 
 
 12-9 
 
 L'0472785 
 
 0-020 0622 
 
 3-01-0109950 
 
 0-004 7490 
 
 8-0 
 
 1-0293200 
 
 0'012 5504 
 
 13'0 
 
 T0476450 
 
 0-020 2141 
 
 11-0113615 
 
 9064 
 
 1 
 
 1-0296865 
 
 7050 
 
 1 
 
 1-0480115 
 
 3660 
 
 2J1-0117280 
 
 0-005 0638 
 
 "2 
 
 1-03C 0330 
 
 8596 
 
 2 
 
 1-0483780 
 
 5179 
 
 31-0120945 
 
 2211 
 
 3 
 
 1-0304195 
 
 0-013 0141 
 
 3 
 
 1-0187445 
 
 6697 
 
 4 1-0124610 
 
 3783 
 
 41-0307860 
 
 1685 
 
 4 
 
 1-0491110 
 
 8214 
 
 3-51-0128275 
 61-0131940 
 71-0135605 
 
 5355 
 
 6926 
 
 8497 
 
 8-51-0311525 
 G 1-0315190 
 71-0318855 
 
 3229 
 4772 
 6315 
 
 13-5 
 
 6 
 
 '7 
 
 1-0494775 9731 
 1-04984400-021 1248 
 L'0502105 2764 
 
 8J1-0139270 
 
 0-OOG 0037 
 
 81-0322520 
 
 7857 
 
 8 
 
 1-0505770 4279 
 
 3-91-0142935 
 
 1636 
 
 8-91-0326185 
 
 9399 
 
 13-9 
 
 1-0509435 5794 
 
 4-01-0146600 
 
 0-OOG 3205 
 
 9'0'r0329850 
 
 0-014 0940 
 
 14-0 
 
 1-0513100 0-021 7308 
 
 11-0150265 
 
 4774 
 
 11-0333515 
 
 2-181 
 
 1 
 
 L'0516765 
 
 8822 
 
 21-0153930 
 
 6342 
 
 21-0337180 
 
 4021 
 
 2 
 
 1-0520430 
 
 0-022 0335 
 
 3 1-0157595 
 
 7909 
 
 3 ! r0340S45 
 
 5560 
 
 3 
 
 1-0524095 
 
 1848 
 
 4 1-0161260 
 
 9476 
 
 41-0344510 
 
 7099 
 
 4 
 
 1-0527760 
 
 3360 
 
 4'5 1-0164925 
 
 0-007 1042 
 
 9'5 L'0348175 
 
 8638 
 
 14-5 
 
 1-0531425 
 
 4871 
 
 6 1-0168590 
 
 2607 
 
 6J1-0351840 
 
 0-015 0175 
 
 6 
 
 1-0535090 
 
 6382 
 
 7 1-0172255 
 
 4172 
 
 '71-0355505 
 
 1713 
 
 '7 
 
 1-0538755 
 
 7893 
 
 '81-0175920 5737 
 
 81-0359170 
 
 3250 
 
 8 
 
 1-0542420 9403 
 
 4-91-01795851 7301 
 
 9-9,1-0362835 
 
 4786 
 
 14'9 
 
 1-0546085 0-023 0193 
 
570 TABLES. 101. 
 
 TABLE for Correction of Volumes of Gases continued. 
 
 t 
 
 l+St 
 
 Log. a + 5 o 
 
 t 
 
 1 +8t 
 
 Log. (1 + 5 t) 
 
 t 
 
 1 + 5t 
 
 Log. (1+5 1) 
 
 15'0 r0549750 0'023 24-22 
 
 20'0r0730000 
 
 0-030 7211 
 
 25-0 1*0916250 
 
 0-038 0734 
 
 lil'0553415 
 
 3930 
 
 1 ! 1-0736665 
 
 8694 
 
 11-0919915 
 
 2192 
 
 21-0557080 
 
 5438 
 
 21-0740330 
 
 0'C31 0176 
 
 2U-0923580 
 
 3650 
 
 3 1-0560745 
 
 6946 
 
 31-0743995 
 
 1658 
 
 31-0927245 
 
 5107 
 
 41-0564410 
 
 8452 
 
 4 
 
 r074766i 
 
 3139 
 
 4:1-0930910 6563 
 
 15-5 
 
 1-0568075 
 
 9959 
 
 20-5 
 
 1-0751325 
 
 4620 
 
 25-51-0934575 8020 
 
 6 
 
 1-0571740 
 
 0-024 1465 
 
 6 
 
 1-0754990 
 
 eioo 
 
 6 1-0938240 9474 
 
 7 
 
 1-0575405 
 
 2970 
 
 "7 
 
 1-0758655 
 
 7580 
 
 7 1-0941905 
 
 U'039 0929 
 
 81-0579070 
 
 4475 
 
 8 
 
 1-0762320 
 
 9059 
 
 8 1-0945570 
 
 2384 
 
 15-91-0582735 
 
 5979 
 
 20-9 
 
 1-0765985 
 
 0*032 0538 
 
 91-0949235 
 
 3838 
 
 
 
 
 
 
 
 
 
 16-01-0586400 
 
 0-024 7483 
 
 21-0 
 
 1-0769650 
 
 0-032 2016 
 
 26-01-0952900 
 
 0-039 5291 
 
 11-0590065 
 
 8986 
 
 1 
 
 1-0773315 
 
 3493 
 
 11-0956565 
 
 6745 
 
 2J1-0593730 
 
 0-025 0489 
 
 2 
 
 1-0776980 
 
 4971 
 
 2|l-096023U 
 
 8197 
 
 '31-0597395 
 
 1991 
 
 3 
 
 1-0780645 
 
 6447 
 
 .0 
 
 1-0903395 
 
 9649 
 
 41-0601060 
 
 3493 
 
 4 
 
 1-0781310 
 
 7924 
 
 4 
 
 1-0967560 
 
 0'040 1101 
 
 16-5 
 
 1-0604725 
 
 4994 
 
 21-5 
 
 1-0787975 
 
 9399 
 
 26'5 
 
 1-0971225 
 
 2551 
 
 6 1-0608390 
 
 6495 
 
 6 
 
 1-0791640 
 
 0-033 0874 
 
 6 
 
 1-0974890 
 
 4002 l 
 
 7 
 
 1-0612055 
 
 7995 
 
 7 
 
 1-0795305 
 
 2349 
 
 *7 
 
 1-0978555 
 
 5452 i 
 
 81-0615720 
 
 9495 
 
 8 
 
 1-0798970 
 
 3823 
 
 8 
 
 1-0982220 
 
 6901 
 
 16-9jl-0619385 
 
 0-026 0994 
 
 21-9 
 
 1-0802635 
 
 5298 
 
 9 
 
 1*0985885 
 
 8351 
 
 17-0 
 
 1-0623050 
 
 0-026 2492 
 
 22'0 
 
 1-0806300 
 
 0-033 6771 
 
 27-0 
 
 1-0989550 
 
 0-040 9800 i 
 
 1 
 
 1-0626715 
 
 3990 
 
 1 
 
 1-0809965 
 
 8243 
 
 1 
 
 1-099321 5 
 
 0-041 1247 
 
 21-0630380 
 
 5488 
 
 2 
 
 1-0813630 
 
 9715 
 
 "2 
 
 1-0996880 
 
 2695 
 
 3!l'0634045 
 
 6935 
 
 3 
 
 1-0817295 
 
 0-034 1186 
 
 3 
 
 1-1000545 
 
 4143 
 
 4 
 
 1-0637710 
 
 8482 
 
 41-0820960 
 
 2658 
 
 4 
 
 1-1004210 
 
 5589 
 
 17-5 
 
 1-0641375 
 
 9978 
 
 22-5 
 
 1-0824625 
 
 4129 
 
 27-5 
 
 1-1007875 
 
 7036 
 
 6 
 
 1-0645040 
 
 0*027 1473 
 
 6 
 
 1-0828290 
 
 5598 
 
 6 
 
 T1011540 
 
 8481 
 
 7 
 
 1-0648705 
 
 2968 
 
 "7 
 
 1-0831955 
 
 7069 
 
 - 
 
 T1015205 
 
 9926 
 
 8 
 
 1-0652370 
 
 4462 
 
 8 
 
 1-0835620 
 
 8538 
 
 "8 
 
 1-1018870 
 
 0-042 1371 
 
 17-9 
 
 1-0656035 
 
 5956 
 
 22-9 
 
 1-0839285 
 
 0-035 0006 
 
 9 
 
 1-1022535 
 
 2815 
 
 18-0 
 
 1-0659700 
 
 0-027 7450 
 
 23-0 
 
 1-0842950 
 
 0'035 1475 
 
 28-0 
 
 1-1026200 
 
 0-042 4259 
 
 1 
 
 1-0663365 8943 
 
 1 
 
 1-0846615 
 
 2942 
 
 1 
 
 1-1029865 
 
 5703 
 
 2 
 
 1-0667030 
 
 0-028 0435 
 
 2 
 
 1-0850280 
 
 4409 
 
 2 
 
 1-1033530 
 
 7145 
 
 3 
 
 1-0670695 
 
 1927 
 
 3 
 
 1-0853945 
 
 5876 
 
 3 
 
 1-1037195 
 
 8587 
 
 4 
 
 1-0674360 
 
 3418 
 
 4 
 
 1-0857610 
 
 7342 
 
 41-1040860 
 
 0-043 0029 
 
 18.5 
 
 1-0678025 
 
 4909 
 
 23-51-0861275 
 
 8808 
 
 28-5 T1044525 
 
 1471 
 
 6 
 
 1.0681690 
 
 6400 
 
 61-0864940 
 
 0-036 0273 
 
 6 
 
 1-1048190 
 
 2911 
 
 71-0685355 
 
 7889 
 
 71-0868605 
 
 1738 
 
 71-1051855 
 
 4352 
 
 81-0689020 
 
 9379 
 
 810872270 
 
 3202 
 
 81-1055520 
 
 5792 
 
 18-91-0692685 0'029 0868 
 
 23-91-0875935 
 
 4666 
 
 91-1059185 
 
 7231 
 
 19-01-0696350 0'029 2356 
 
 24-01-0879600 
 
 0-036 6129 
 
 29-01-1062850 
 
 0-043 8671 
 
 11-0700015 3844 
 
 H'0883265 
 
 7592 
 
 11-1066515 
 
 0-044 0109 
 
 2l'0703680l 5331 
 
 21-0886930 
 
 9054 
 
 2;1-1070180 
 
 1546 
 
 3 1-0707345] 6818 
 
 3 1-0800595 
 
 0-037 0517 
 
 31-1073845 2985 
 
 41-0711010- 8304 
 
 41-0894260 
 
 1978 
 
 4 1-10775 101 4422 
 
 19-51-0714675 
 
 9790 
 
 24'5 ! 1-0897925 
 
 3438 
 
 29-51-1081175 5858 
 
 6 
 
 1-0718340 
 
 O'CSO 1275 
 
 61-0901590 
 
 4899 
 
 611-1084840 7295 
 
 '7 
 
 1-0722005 
 
 2760 
 
 71-0905255 
 
 6359 
 
 7 1-1088505 8730 
 
 81-0725670 
 
 4244 
 
 81-0908920 
 
 7817 
 
 8 1-1092170 0-045 0165 
 
 19-91-0729335 
 
 5728 
 
 91-0912585 
 
 9277 
 
 9,1-1095835 1600 
 
 
 
 
 
 
 30'0 1-1099500 G'045 3035 
 
101. 
 
 VOLUMETPJC ANALYSIS. 
 
 571 
 
 TABLE for Correction of Volumes of Gases for 
 Temperature, giving the Divisor for the Formula 
 
 V x 
 
 76O x (1 -f 
 
 t 
 
 760 x 
 (! + *}. 
 
 Log. [760 x 
 (l + St)]. 
 
 t 
 
 760 x 
 (1 + 5;). 
 
 Log. [760 x 
 (1-f 8t)]. 
 
 760 x 
 (!+*>. 
 
 Log. [760 x 
 (1 + 01. 
 
 O'O 760*0000 
 
 2-880 8136 
 
 4-0 
 
 771-1 1162-887 1341 
 
 8-0782-28322-893 3640 
 
 1 
 
 760-2785 9727 
 
 I 771-4201 
 
 2910 
 
 1 7*2-56171 5186 
 
 2 760-5571 2-831] 319 
 
 2 771-6987 
 
 4478 
 
 2782-8403 6732 
 
 3760-8356 2908 
 
 :; 771-9772 
 
 6044 
 
 3783-1188 8276 
 
 4761-1142 4498 
 
 4772-2558 
 
 7611 
 
 4783-3974 9821 
 
 
 
 
 
 
 
 
 0-5 
 
 761-3927 
 
 6087 
 
 4'5 772'53 43 
 
 9178 
 
 s-5 7*3-6759 2-894 1365 
 
 0761-6712 
 
 7676' 
 
 6 772-8128 
 
 2-888 0743 
 
 6J783-9544 
 
 2908 
 
 7 761-9498 
 
 9264 
 
 7773-0914 
 
 2309 
 
 7 784-2330 
 
 4452 
 
 8 
 9 
 
 762-2283:2-882 0851 
 762-5061' 2437 
 
 S 773-3699 
 '.' 773-6485 
 
 3872 
 5437 
 
 > 784 5115 
 9784-7901 
 
 5994 
 7536 
 
 
 
 
 
 
 
 
 1-0 762-7854 2-882 4024. 
 
 5-C 773-9270 
 
 2*888 7000 
 
 9-0785-0686 
 
 2-894 9076 
 
 i 
 
 763-0639! 5610 
 
 1774-2055 
 
 8563 
 
 1785-3471 
 
 2-895 0617 
 
 2 703-34251 7194 
 
 2774-4841 
 
 2-8890125 
 
 2 785-6257 
 
 2157 
 
 3 763-6210 8779 
 
 3 774-7626 
 
 1686 
 
 3 785-9042 
 
 3696 
 
 4 763-89968-883 0362 
 
 4775-0412 
 
 3248 
 
 4786-1828 
 
 5235 
 
 1-5 
 
 764-1781 
 
 1017 
 
 5" 5 
 
 775-3197 
 
 4808 
 
 9-5786-4613 
 
 6774 
 
 ' '764-4566 
 
 3528 
 
 6 
 
 775*5982 
 
 6368 
 
 '6786-7398 
 
 8311 
 
 7764-7352 
 
 5111 
 
 7 
 
 775-8768 
 
 7927 
 
 7 787-0184 
 
 9849 
 
 W65*0137 
 
 6692 
 
 s 
 
 776-1553 
 
 9487 
 
 8787*2969 
 
 2-896 1385 
 
 9765-2923 
 
 8273 
 
 9 
 
 776-4339 
 
 2-890 1044 
 
 9787-5755 
 
 2923 
 
 2T> 765-570S 2-883 9854 
 
 6-0 
 
 776*7124 
 
 2'890 2602 
 
 10-0787-8540 
 
 2*896 4457 
 
 -1 765-84932-8841433 
 
 1 
 
 776-9909 
 
 4159 
 
 1788-1325 
 
 5993 
 
 .. 
 
 766-1279 
 
 3013 
 
 2 777-2695 
 
 5716 
 
 *2 788-4111 
 
 7528 
 
 3 766-40:; 4 
 
 4591 
 
 3777*5480 
 
 7272 
 
 3788-6896 
 
 9061 
 
 4766-6850 
 
 6170 
 
 4 
 
 777-8266 
 
 8828 
 
 4788-9682 
 
 2-8970595 
 
 
 
 
 
 
 
 
 
 2*5 
 
 766-9635 
 
 7747 
 
 6'5 
 
 778-1051 
 
 2-891 C383 
 
 10-5789-2467 
 
 2128 
 
 V, 
 
 767-2420 
 
 9323 
 
 6 
 
 778-3836 
 
 1937 
 
 6789-5252 
 
 3660 
 
 ~ 
 
 767*5206 
 
 2-885 0900 
 
 *7 
 
 778-6622 
 
 3491 
 
 '7789-8038 
 
 5192 
 
 8f767'7991 
 
 2476 
 
 *8 
 
 778-9407 
 
 5044 
 
 8790-0823 
 
 6724 
 
 1) 768-0777 
 
 4052 
 
 *9 
 
 779-2193 
 
 6597 
 
 9 790-3609 
 
 8255 
 
 
 
 
 
 
 
 
 
 :ru 768-3562 2-885 5626 
 
 7 '> 7 79-4978 
 
 2-891 8149 
 
 H-0790'6394 
 
 2-897 9785 
 
 1768-fi347i 7200 
 
 1 7797763 
 
 9701 
 
 1790-9179 
 
 2-898 1315 
 
 2768-9133J 8772 
 :J769-1918'2-8860347 
 
 2780-05492-892 1251 
 3 780-3334 2802 
 
 2791-1965 
 3791-4750 
 
 2844 
 4373 
 
 4769-4704 1919 
 
 4780-6120 4352 
 
 4791-7536 
 
 5901 
 
 
 
 
 1 
 
 . 
 
 
 3-5769-7489 
 
 3491 
 
 7 :> 780-8905 5901 
 
 H-5792'0321 
 
 7428 
 
 6770-0274 
 
 5061 
 
 0781-1690 
 
 7450 
 
 6792-31061 8954 
 
 '7 
 
 770-3060 
 
 6633 
 
 '7781-4476 
 
 8998 
 
 779258922-8990482 
 
 8770-5845 
 
 8203 
 
 8781-7261 
 
 2'S93 0547 
 
 8792-8677 2008 
 
 9770-8631; 9773 
 
 ".'782*0047 
 
 2094 
 
 9793-1463I 3534 
 
TABLES. 
 
 101, 
 
 TABLE for Correction of Volumes of Gases continued. 
 
 760 x 
 (l+5t). 
 
 Log. [760 x 
 (l+8t)]. 
 
 t 
 
 760 x 
 (1 + 5t). 
 
 Log. [760 x 
 (1+ 5t)]. 
 
 t 
 
 760 x 
 
 a + sy. 
 
 Log. [760 x 
 
 (i + Sty]. 
 
 12-0793-42482 899 5057 
 
 16-5 
 
 805-9591 
 
 2-90G 3131 
 
 21-0 
 
 818-4934 
 
 2-9130152 
 
 1793-7033 
 
 6583 
 
 6 
 
 806-2376 
 
 4630 
 
 1818-7719 
 
 1629 
 
 2793-9819 
 
 8106 
 
 "7 
 
 806-5162 
 
 6131 
 
 218 19-0505 
 
 3107 
 
 3 794-2604 
 
 9629 
 
 '8 
 
 806-7947 
 
 7631 
 
 3819-3290 
 
 4584 
 
 4794-5390 
 
 2-900 1153 
 
 9 
 
 807-0733 
 
 9130 
 
 4819-6076 
 
 6059 
 
 12-5794-8175 
 0795-0960 
 
 2674 
 4196 
 
 iw 
 
 807-3518 
 807-6303 
 
 2-907 0627 
 2126 
 
 21-5 | 819-8S61 
 
 6820-1646 
 
 7535 
 
 9010 
 
 71795-3746 
 
 5717 
 
 - -21807-9089 
 
 3624 
 
 71820-4432 
 
 2-914 0485 
 
 8795-6531 
 
 7238 
 
 .Q 
 
 808-1874 
 
 5121 
 
 8820-7217 
 
 1959 
 
 9J795-9317 
 
 8758 
 
 
 808-4660 
 
 6617 
 
 21-9 821-01)03 
 
 3434 
 
 
 
 
 
 
 
 
 
 13-0796-2102 
 
 2-901 0277 
 
 17-5 
 
 808-7445 
 
 8114 
 
 22-0 
 
 821-2788 
 
 2-9144906 
 
 l'796-4SS7 
 
 1796 
 
 6809-0230 
 
 9609 
 
 1 
 
 821-5573 
 
 6379 
 
 2:796-7673 
 
 3316 
 
 '7 809'30] 6 
 
 2-9081103 
 
 2 
 
 821-8359 
 
 7852 
 
 3797-0458 
 
 4833 
 
 8809-5801 
 
 2599 
 
 3 
 
 822-1141 
 
 9322 
 
 4:797-3244 
 
 6351 
 
 9 
 
 309-8587 
 
 4092 
 
 4 
 
 822-3930 
 
 2-9150794 
 
 13-5797-6029 
 
 7867 
 
 18-0 
 
 SlO'13722-9085586 
 
 22'5 
 
 822-0715 
 
 2265 
 
 6J797-S814 
 
 9383 
 
 1|810-4157 
 
 . 7079 
 
 '6 
 
 822-9500 
 
 3734 
 
 7798-16002-9020900 
 
 2810-6943 
 
 8572 
 
 *7 
 
 823-2286 
 
 5204 
 
 8798-4385 2415 
 
 3,810-9728 
 
 2-909 0063 
 
 8823-5071 
 
 0074 
 
 9798-71711 3931 
 
 4 
 
 811-2514 
 
 1554 
 
 9823-7857 
 
 8143 
 
 14-0 798-9956 2-902 5444 
 
 18'5 
 
 811-5299 
 
 3046 
 
 23-0824-0642 
 
 2-9159610 
 
 ] 709-2741 
 
 6958 
 
 GJ811-80S4 
 
 4535 
 
 1824-3427 
 
 2-916 1078 
 
 2:799-5527 
 
 8471 
 
 7:812-0870 
 
 6026 
 
 2824-0213 
 
 2546 
 
 3799-8312 
 4800-1098 
 
 9983 
 2-903 1496 
 
 "8 
 9 
 
 812-3655 
 812-6441 
 
 7515 
 
 9004 
 
 3,824-8998 
 4825-1784 
 
 4012 
 
 5478 
 
 14-5800-3883 
 6800-6668 
 
 3008 
 4518 
 
 190,812-9226 
 l!813-2011 
 
 2-910 0492 
 1980 
 
 23-5 
 6 
 
 825-4569 
 825-7354 
 
 6944 
 8409 
 
 7J800-9454 6029 
 8801-2239 7539 
 
 2813-4797 
 3J813-7582 
 
 3468 
 4953 
 
 7:826-0140 
 8826-2925 
 
 9874 
 
 2-917 1339 
 
 9801-5025 9049 
 
 4814-0368 
 
 6440 
 
 9826-5711 
 
 2802 
 
 15-0 SOl'7810 2-904 0557 
 1 802-0595! 2067 
 
 19-5814-3153 
 
 6 ; 814-5938 
 
 7927 
 9411 
 
 24-0826-8496 
 1827-1281 
 
 2-917 4265 
 
 5728 
 
 2802-338l| 3574 
 
 7814-87242-9110896 
 
 2:827-4067 
 
 7191 
 
 3 802-6166 5081 
 
 8;815-1500 2380 
 
 3 ! 827'6852 
 
 8652 
 
 4802 8952 
 
 6589 
 
 '9 
 
 815-4295 
 
 3865 
 
 4'S27'9638 
 
 2-918 0114 
 
 15-5803-1737 
 
 8095 
 
 20-0815-7080 
 
 2-911 5347 
 
 24-5j828'2423 
 
 1574 
 
 6J803-4522 9601 
 
 1815-9865 
 
 6830 
 
 6828-5208 
 
 3034 
 
 7803-7308 
 
 2-905 1106 
 
 2816-2651 
 
 8313 
 
 7828-7994 
 
 4495 
 
 81804-0093 
 
 2612 
 
 3816-5436 
 
 9794 
 
 8829-0779 
 
 5953 
 
 9804-2879 
 
 4116 
 
 4816-8222 
 
 2-912 1276 
 
 249829-3565 
 
 7413 
 
 16-0804-5664 
 
 2-905 5618 
 
 20-5817-1007 
 
 2756 
 
 25-OJ829-6350 
 
 2*918 8871 
 
 1 804-8449 
 
 7122 
 
 6817-3792 
 
 4236 
 
 1829-9135 
 
 2-919 0329 
 
 2^805-1235 
 
 8625 
 
 "7 
 
 817-6578 
 
 5716 
 
 2:830-1921 
 
 1786 
 
 3805-4020 
 
 2-206 0127 
 
 8817-93(13 
 
 7195 
 
 3830-4706 
 
 3242 
 
 4805-6806 
 
 1629 
 
 '9 
 
 SIS'2149 
 
 8674 
 
 4830-7492 
 
 4699 
 
101. VOLUMETRIC ANALYSIS. 573 
 
 TABLE for Correction of Volumes of Gases continued. 
 
 t 
 
 760 x 
 (1 + 5f). 
 
 Log. [760 X 
 
 (l + St)]. 
 
 t 
 
 760 x 
 (1 + SO 
 
 Log. [760 X 
 (1 + St]. 
 
 t 
 
 760 x 
 (1+50- 
 
 Log. [760 x 
 (! + &)]. 
 
 25-5831-027712-919 6155 
 
 27-0 
 
 835-20582-921 7935 
 
 28'5 839-3839 2-923 9607 
 
 6831-3062! 7610 
 
 1 
 
 835-4843 
 
 9384 
 
 6839-66242-9241047 
 
 7:831-58481 9065 
 
 2835-76292-9220831 
 
 7!839'9410| 2488 
 
 8 
 25'9 
 
 831-86332-9200520 
 8321419 1974 
 
 3 
 
 4 
 
 836-0414 2279 
 836-3200 3725 
 
 8840-2195 
 28 9 840-4981 
 
 3928 
 
 5368 
 
 26'0 
 
 832-4204 2-920 3427 
 
 27-5 
 
 836-5985 
 
 5172 
 
 29-0840-7766 
 
 2-924 6806 
 
 1 
 
 832-6939 4880 
 
 6 836-8770 
 
 6616 
 
 1841-0551 8245 
 
 2 
 
 832-9775 6333 
 
 7837-1556 
 
 8062 
 
 2:841-3337 9683 
 
 3 
 
 833-25601 7784 
 
 8837-4341 
 
 9507 
 
 3 841-6122^-925 1120 
 
 4 
 
 833-534^ 
 
 9236 
 
 27-9 
 
 8377127 
 
 2-923 0951 
 
 4 
 
 841-8908 
 
 2558 
 
 26-5 
 
 833-8131 
 
 2-921 0688 
 
 28-0 
 
 837-9912 
 
 2*923 2394 
 
 29'5 ! 842-1693 
 
 3995 
 
 6 
 
 834-0916 
 
 2137 
 
 -L 
 
 838-2697 
 
 3838 
 
 6)842-4478 5431 
 
 7 
 
 834-3702! 3588 
 
 2838-5483 
 
 5281 
 
 '7812-7264 6836 
 
 8 
 
 834-6487 
 
 5038 
 
 3838-8268 
 
 6723 
 
 8843-0049 8301 
 
 26-9 
 
 834-9273 
 
 6487 
 
 4 
 
 839-1054 
 
 8165 
 
 29'9|843'2835 
 
 9737 
 
 
 
 
 
 
 
 30-0843-56202-926 1170 
 
 * 
 
 
 
 
 1 
 
TABLES. 
 
 101. 
 
 Pressure of Aqueous Vapour in Millimeters of Mercury, 
 from-9'9 to + 35 C. 
 
 
 111 .in. 
 
 
 in. in. 
 
 
 in. m. 
 
 m.m. 
 
 HI .ni. 
 
 in. in. 
 
 -9-0 
 
 2-096 
 
 -5'4 
 
 3-034 
 
 -6-9 
 
 4-299 
 
 3-5 5-889 
 
 8'0 8-017 
 
 12'5 LO'804 
 
 8 
 
 114 
 
 3 
 
 058 
 
 8 
 
 331 
 
 6 
 
 930 
 
 1 
 
 072 
 
 c| '875 
 
 '7 
 
 132 
 
 '2 
 
 082 
 
 "7 
 
 364 
 
 "7 
 
 972 
 
 2 
 
 126 
 
 71 '947 
 
 '6 
 
 150 
 
 1 
 
 106 
 
 '6 
 
 397 
 
 '8 
 
 G'014 
 
 3 '181 
 
 811-019 
 
 '5 
 
 168 
 
 -5-0 
 
 131 
 
 '5 
 
 430 
 
 3-9 
 
 '055 
 
 4 '236 
 
 12'9 
 
 090 
 
 -9-4 
 
 186 
 
 -4'9 
 
 3-156 
 
 -0-4 
 
 463 
 
 4-0 
 
 6-097 
 
 8-5 '291 
 
 13-0 
 
 Ll-162 
 
 3 
 
 204 
 
 '8 
 
 181 
 
 "3 
 
 497 
 
 1 
 
 140 
 
 (j '347 
 
 1 
 
 23a 
 
 2 
 
 223 
 
 7 
 
 206 
 
 "2 
 
 531 
 
 2 
 
 183 
 
 7i '404 
 
 2 
 
 309 
 
 1 
 
 242 
 
 '6 
 
 231 
 
 3 
 
 565 
 
 3 
 
 226 
 
 8' '461 
 
 3 
 
 383 
 
 -9-0 
 
 261 
 
 5 
 
 257 
 
 -o-o 
 
 4'600 
 
 4 
 
 270 
 
 8-9 
 
 517 
 
 4 
 
 456 
 
 -8-9 
 
 2'280 
 
 -44 
 
 283 
 
 + O'f 
 
 4-600 
 
 4.5 
 
 313 
 
 9-0 
 
 8-574 
 
 13-5 
 
 530 
 
 '8 
 
 299 
 
 3 
 
 309 
 
 1 
 
 633 
 
 '6 
 
 '357 
 
 1 
 
 632 
 
 '6 
 
 '605 
 
 "7 
 
 318 
 
 "2 
 
 335 
 
 '2 
 
 667 
 
 7 
 
 '401 
 
 "2 
 
 690 
 
 '/ 
 
 681 
 
 6 
 
 337 
 
 'i 
 
 361 
 
 3 
 
 700 
 
 8 
 
 445 
 
 3 
 
 748 
 
 8 
 
 757 
 
 "5 
 
 356 
 
 -4-0 
 
 387 
 
 4 
 
 733 
 
 4-9 
 
 490 
 
 4 
 
 807 
 
 1 'Q 
 
 832 
 
 - 8-4 
 
 376 
 
 -3'P 
 
 3-414 
 
 0-5 
 
 767 
 
 5-0 
 
 6-534 
 
 9-5 
 
 865 
 
 14'0 
 
 11-908 
 
 3 
 
 396 
 
 '8 
 
 441 
 
 '6 
 
 801 
 
 1 
 
 580 
 
 6 
 
 925 
 
 1 
 
 986 
 
 2 
 
 416 
 
 "7 
 
 468 
 
 '7 
 
 836 
 
 2 
 
 625 
 
 "7 
 
 985 
 
 
 12-064 
 
 1 
 
 436 
 
 '6 
 
 '495 
 
 8 
 
 871 
 
 3 
 
 671 
 
 8 
 
 9-045 
 
 'o 
 
 142 
 
 -8-0 
 
 456 
 
 '5 
 
 522 
 
 0'9 
 
 905 
 
 4 
 
 717 
 
 9'9 
 
 105 
 
 4 
 
 220 
 
 -7-9 
 
 2-477 
 
 -3-4 
 
 550 
 
 i-o 
 
 4-940 
 
 5-5 
 
 763 
 
 10-0 
 
 9-165 
 
 14'5 
 
 298 
 
 8 
 
 498 
 
 3 
 
 '578 
 
 1 -975 
 
 6 
 
 810 
 
 1 
 
 227 
 
 6 
 
 378 
 
 7 
 
 519 
 
 9 
 
 '606 
 
 2 5*011 
 
 "7 
 
 857 
 
 9 
 
 288 
 
 "7 
 
 458 
 
 6 
 
 540 
 
 1 
 
 634 
 
 3 1 '047 
 
 8 
 
 904 
 
 3 
 
 350 
 
 8 
 
 538 
 
 5 
 
 561 
 
 -3'U 
 
 '662 
 
 4 '082 
 
 5-9 
 
 951 
 
 4 
 
 412 
 
 14-9 
 
 619 
 
 -7'4 
 
 582 
 
 -2-9 
 
 3-691 
 
 1-5 
 
 118 
 
 6-0 
 
 6-998 
 
 10-5 
 
 474 
 
 15'0 
 
 12-699 
 
 3 
 
 603 
 
 8 
 
 720 
 
 f 
 
 155 
 
 1 
 
 7-047 
 
 6 
 
 537 
 
 1 
 
 781 
 
 2 
 
 624 
 
 " i 
 
 749 
 
 ' i 
 
 191 
 
 2 
 
 095 
 
 "7 
 
 601 
 
 2 
 
 864 
 
 1 
 
 645 
 
 'b 
 
 778 
 
 '8 
 
 228 
 
 3 
 
 144 
 
 8 
 
 665 
 
 3 
 
 947 
 
 -7-o 
 
 666 
 
 "5 
 
 807 
 
 1-9 
 
 265 
 
 4 
 
 193 
 
 10-9 
 
 728 
 
 4 
 
 13-029 
 
 -6-9 
 
 2-688 
 
 -2-4 
 
 836 
 
 2-0 
 
 5-302 
 
 6-5 
 
 242 
 
 ll'O 
 
 9-792 
 
 15'5 
 
 112 
 
 '8 
 
 710 
 
 3 
 
 865 
 
 '] 
 
 340 
 
 6 
 
 292 
 
 1 
 
 '857 
 
 6 
 
 197 
 
 7 
 
 732 
 
 9 
 
 895 
 
 "2 
 
 378 
 
 "7 
 
 342 
 
 "2 
 
 923 
 
 7 
 
 281 
 
 6 
 
 754 
 
 1 
 
 925 
 
 3 
 
 416 
 
 8 
 
 392 
 
 3 
 
 989 
 
 8 
 
 366 
 
 '5 
 
 '776 
 
 -2-0 
 
 955 
 
 '4 
 
 454 
 
 6-9 
 
 442 
 
 4 
 
 10-054 
 
 15-9 
 
 451 
 
 - 6-4 
 
 798 
 
 -1-9 
 
 3-985 
 
 2-5 
 
 491 
 
 7-0 
 
 7'492 
 
 11-5 
 
 120 
 
 16'0 
 
 13'536 
 
 3 
 
 821 
 
 8 
 
 4-016 
 
 6 
 
 530 
 
 1 
 
 544 
 
 6 
 
 187 
 
 1 
 
 623 
 
 9 
 
 844 
 
 7 
 
 047 
 
 "7 
 
 '569 
 
 2 
 
 595 
 
 ' / 
 
 '255 
 
 '2 
 
 710 
 
 1 
 
 867 
 
 6 
 
 078 
 
 8 
 
 608 
 
 3 
 
 647 
 
 8 
 
 322 
 
 3 
 
 797 
 
 -6-0 
 
 &90 
 
 *5 
 
 109 
 
 2.9 
 
 647 
 
 4 
 
 699 
 
 11-9 
 
 389 
 
 4 
 
 885 
 
 -5-9 
 
 2-914 
 
 -1-4 
 
 140 
 
 3-0 
 
 5'687 
 
 7'5 
 
 751 
 
 12-0 
 
 10-457 
 
 16-5 
 
 972 
 
 8 
 
 938 
 
 3 
 
 171 
 
 1 
 
 727 
 
 6 
 
 804 
 
 1 
 
 526 
 
 6 
 
 14-062 
 
 '7 
 
 962 
 
 9 
 
 203 
 
 "2 
 
 767 
 
 '7 
 
 857 
 
 "2 
 
 596 
 
 "7 
 
 151 
 
 6 
 
 986 
 
 1 
 
 235 
 
 3 
 
 807 
 
 3 
 
 910 
 
 3 
 
 665 
 
 3 
 
 241 
 
 '5 
 
 3-010 
 
 i-o 
 
 267 
 
 4 
 
 848 
 
 7-9 
 
 964 
 
 "4 
 
 734 
 
 16-9 
 
 331 
 
 
 
 
 
 
 
 
 
 
 
 
101. 
 
 VOLUMETIUC ANALYSIS. 
 
 0/0 
 
 Pressure of Aqueous Vapour continued. 
 
 
 
 1 
 
 
 
 
 
 
 in. in. 
 
 t 
 
 ni.ru. 
 
 m.m. 
 
 m.m. 
 
 
 m.m. 
 
 
 m.m. 
 
 17-0 
 
 14-421 
 
 20-0 
 
 17-391 
 
 23-0 20-888 
 
 26-0 
 
 24-988 
 
 29-0 
 
 29-782 
 
 32-0 
 
 35-359 
 
 I 
 
 513 
 
 1 
 
 500 
 
 J 
 
 21'OIG 
 
 1 
 
 25-138 
 
 1 
 
 956 
 
 1 
 
 559 
 
 2 
 
 605 
 
 2 
 
 008 
 
 9 
 
 144 
 
 2 
 
 288 
 
 2 
 
 30-131 
 
 "2 
 
 760 
 
 3 
 
 697 
 
 3 
 
 717 
 
 3 
 
 272 
 
 3 
 
 438 
 
 3 
 
 305 
 
 3 
 
 962 
 
 '4 
 
 790 
 
 4 
 
 826 
 
 4 
 
 400 
 
 4 
 
 588 
 
 4 
 
 479 
 
 4 
 
 36-165 
 
 17-5 
 
 882 
 
 20-5 
 
 935 
 
 23-5 
 
 528 
 
 26-5 
 
 738 
 
 29-5 
 
 654 
 
 32-5 
 
 370 
 
 6 
 
 977 
 
 6 
 
 18-047 
 
 6 
 
 659 
 
 6 
 
 891 
 
 6 
 
 833 
 
 6 
 
 576 
 
 7 
 
 15-072 
 
 "7 
 
 159 
 
 "7 
 
 790 
 
 ' / 
 
 20-045 
 
 "7 
 
 31-011 
 
 "7 
 
 783 
 
 8 
 
 167 
 
 8 
 
 271 
 
 8 
 
 921 
 
 8 
 
 198 
 
 8 
 
 190 
 
 8 
 
 '991 
 
 17'9 
 
 202 
 
 20-9 
 
 383 
 
 23-9 
 
 22-053 
 
 26-9 
 
 351 
 
 29'9 
 
 369 
 
 32'9 
 
 37-200 
 
 IS'O 
 
 15-357 
 
 21-0 
 
 18-495 
 
 24'C 
 
 22-184 
 
 27-0 
 
 26-505 
 
 30-0 
 
 31/548 
 
 33'0 
 
 37*410 
 
 1 
 
 454 
 
 1 
 
 610 
 
 1 
 
 319 
 
 1 
 
 663 
 
 J 
 
 729 
 
 1 
 
 621 
 
 "2 
 
 552 
 
 2 
 
 724 
 
 2 
 
 453 
 
 "2 
 
 820 
 
 2| '911 
 
 2 
 
 832 
 
 3 
 
 650 
 
 3 
 
 839 
 
 3 
 
 588 
 
 "3 
 
 978 
 
 3 
 
 32-094 
 
 
 O 
 
 38-045 
 
 4 
 
 747 
 
 4 
 
 954 
 
 4 
 
 723 
 
 4 
 
 27-136 
 
 4 
 
 278 
 
 4 
 
 258 
 
 18-5 
 
 845 
 
 21-5 
 
 19-069 
 
 24-5 
 
 '858 
 
 27-5 
 
 294 
 
 30-5 
 
 463 
 
 33'5 
 
 473 
 
 '6 
 
 945 
 
 6 
 
 187 
 
 e 
 
 996 
 
 6 
 
 455 
 
 6 
 
 650 
 
 6 
 
 689 
 
 '7 
 
 IC'045 
 
 '7 
 
 305 
 
 7 
 
 23-135 
 
 7 
 
 617 
 
 "/ 
 
 837 
 
 '7 
 
 906 
 
 8 
 
 145 
 
 '8 
 
 423 
 
 8 
 
 273 
 
 '8 
 
 778 
 
 8 
 
 33-026 
 
 8 
 
 39124 
 
 18-9 
 
 246 
 
 21-9 
 
 541 
 
 24'9 
 
 411 
 
 27-9 
 
 939 
 
 30-9 
 
 215 
 
 33-9 
 
 344 
 
 19-0 
 
 16-346 
 
 22'0 
 
 .19-659 
 
 250 
 
 23-550 
 
 28-0 
 
 28-101 
 
 31-0 
 
 33*405 
 
 34-0 
 
 39*565 
 
 1 
 
 449 
 
 1 
 
 780 
 
 1 
 
 692 
 
 1 
 
 267 
 
 1 
 
 596 
 
 1 
 
 786 
 
 "2 
 
 552 
 
 "2 
 
 901 
 
 "2 
 
 834 
 
 "2 
 
 433 
 
 2 
 
 787 
 
 "2 
 
 40-007 
 
 3 
 
 655 
 
 3 
 
 20-022 
 
 3 
 
 976 
 
 3 
 
 599 
 
 3 
 
 980 
 
 '3 
 
 230 
 
 4 
 
 758 
 
 4 
 
 143 
 
 4 
 
 24119 
 
 4 
 
 765 
 
 4 
 
 34-174 
 
 4 
 
 455 
 
 19'5 
 
 861 
 
 22-5 
 
 265 
 
 25-5 
 
 261 
 
 28'5 
 
 931 
 
 31-5 
 
 368 
 
 34-5 
 
 680 
 
 6 
 
 967 
 
 '6 
 
 389 
 
 6 
 
 406 
 
 6 
 
 29-101 
 
 6 
 
 564 
 
 6 
 
 907 
 
 7 
 
 17-073 
 
 '7 
 
 514 
 
 7 
 
 552 
 
 7 
 
 271 
 
 '7 
 
 761 
 
 7 
 
 41-135 
 
 8 
 
 179 
 
 8 
 
 639 
 
 8 
 
 697 
 
 8 
 
 441 
 
 8 
 
 959 
 
 '8 
 
 364 
 
 19-9 
 
 285 
 
 22-9 
 
 763 
 
 25-9 
 
 842 
 
 28'9 
 
 612 
 
 31-9 
 
 35-159 
 
 34-9 
 
 595 
 
 
 
 
 
 
 
 
 
 
 
 35-0 
 
 827 
 
 
 
 
 1 
 
 
 
 
 
 
INDEX. 
 
 Absorption apparatus, Mohr's, 133 
 Absorption apparatus, Fresenius', 
 
 132 
 Absorption equivalents shown by oils 
 
 and fats for bromine, 359 
 Acetates, alkaline and earthy, titration 
 
 of, 90 
 
 Acetate of lime, analysis of, 90 
 Acetates, metallic, 90 
 Acidimetry, 88 
 Acidimetry, delicate end-reaction for, 
 
 88 
 
 Acid, acetic, titration of, 89 
 Acid, arsenic, titration of, 151, 152, 153 
 Acid, carbolic, titration of, 366 
 Acid, carbonic, estimation of, 93 
 Acid, chromic, titration of iron with, 
 
 126 
 
 Acid, citric, estimation of lead in, 225 
 Acid, citric, titration of, 103 
 Acid, formic estimation of, 104 
 Acid liquors, tartaric, 113 
 Acid, nitric, pure for titrations, 48 
 Acid, oxalic, titration of, 109 
 Acid, phosphoric, titration of, 109, 284 
 Acid, tannic, titration of, 331 
 Acid, tartaric, estimation of lead in, 
 
 225 
 
 Acid, tartaric, titration of, 112 
 Acid, uric, estimation of, 392 
 Acids and bases combined in neutral 
 
 salts, 114 
 
 Acids, mineral, in vinegar, 90 
 Acids, titration of, 88 
 Acids, titration of by iodine and thio- 
 
 sulphate, 88 
 A e'rated distilled water, preparation of, 
 
 274 
 Air and carbonic anhydride gas, analysis 
 
 of, 497 
 
 Air, carbonic acid in, titration of, 97 
 Albumen in urine, estimation of, 397 
 Albuminoid ammonia process for water, 
 
 Alkalies, caustic and carbonated, titra- 
 tion of, 56 
 
 Alkalies, caustic, titration of, by potas- 
 sic bichromate, 60 
 
 Alkalies, indirect estimation of; 140 
 
 Alkalies in presence of sulphites, titra- 
 
 of, 59 
 
 Alkalimeter, Schuster's, 6 
 Alkalimetric estimation of various me- 
 tallic salts, 117 
 
 Alkalimetric methods, extension of, 117 
 Alkalimetry, 33, 55 
 Alkalimetry, GayLussac's, 33 
 Alkaline carbonates, titration of, 55 
 Alkaline compounds, commercial, 63 
 Alkaline earths, indirect estimation of, 
 
 140 
 
 Alkaline earths, titration of, 69 
 Alkaline earths, titration of mixed 
 
 hydrates and carbonates, 69 
 Alkaline tartrate solution, for sugar 
 
 estimation, 309 
 
 Alkaline permanganate, for water ana- 
 lysis, 465 
 
 Alkaline salts, titration of, 55 
 Alkaline silicates, titration of, 67 
 Alkaline sulphides, titration of, 64, 321 
 Alloys of silver, assay of, 298 
 Alumina, estimation of, 145 
 Alumina in caustic soda, etc., estima- 
 tion of, 146 
 Aluminic sulphates, estimation of free 
 
 acid in, 146 
 Ammonia, albuminoid process, for 
 
 water, 462 
 
 Ammonia, combined, estimation of, 72 
 Ammonia, estimation of, 72 
 Ammonia, indirect titration of, 75 
 Ammonia in urine, estimation of, 396 
 Ammonia in water, estimation of, 407 
 Ammonia., semi-normal, 49 
 Ammonia, sulphate and chloride of, 
 
 estimation of, 79 
 
 Ammonia, technical estimation of, 75 
 Ammoniacal liquor, table showing tho 
 amount of sulphate obtainable 
 from, 80 
 
 A mmonic molybdate, standard, 294, 295 
 Ammonio-cupric solution, normal, 50 
 Analyses, saturation, 33 
 Analysis by oxidation or reduction, 120 
 Analysis by precipitation, 138 
 Analysis, factors for calculation, 54 
 Analysis, gas, simple methods of, 547 
 
578 
 
 INDEX. 
 
 Analysis of substances by distillation 
 with hydrochloric acid, 132 
 
 Analysis, volumetric and gravimetric, 
 distinction between, 2 
 
 Analysis, volumetric and gravimetric, 
 fundamental distinction between, 2 
 
 Analysis, volumetric, general princi- 
 ples, 1 
 
 Analysis, volumetric, methods of classi- 
 fication, 3 
 
 Analysis, volumetric, systematic, 27 
 
 Analysis, volumetric, without burettes, 6 
 
 Analysis, volumetric, without weights, 5 
 
 Analysis, water, reagents for 399, 463 
 
 Antimony, estimation of, as sulphide, 
 148 
 
 Antimony, estimation of, by bichro- 
 mate, 147 
 
 Antimony ^ estimation of, by iodine, 147 
 
 Antimony, estimation of, by perman- 
 ganate, 147 
 
 Aiatimony in presence of tin, estimation 
 of, 147 
 
 Antimony, titration of, by stannous 
 chloride, 183 
 
 Apparatus, absorption, Fresenius', 
 132 
 
 Apparatus, absorption, Mohr's, 133 
 
 Apparatus, Bischof's, for evapora- 
 tion, 411 
 
 Apparatus for iodine distillation, 
 Stortenbek&r's, 201 
 
 Apparatus for chlorine distillation, 
 132, 133 
 
 Apparatus for CO 2 , Scheibler's, 
 101 
 
 Apparatus for gas analysis (Bunsen's 
 method), 480 
 
 Argol, titration of, 114 
 
 Arseniates, estimation of, by iodine, 
 149, 370 
 
 Arseniates, estimation of, by silver, 152 
 
 Arseniates, estimation of, by uranium, 
 151 
 
 Arsenic acid, titration of, 150, 151, 369 
 
 Arsenic, estimation of, by bichromate, 
 150 
 
 Arsenic, estimation of, by distillation, 
 151 
 
 Arsenic, estimation of, by iodine, 149, 
 370 
 
 Arsenic, estimation of, by silver, 152 
 
 Arsenic, estimation of, by uranium, 
 151 
 
 Arsenic, estimation of, in presence of 
 tin, 371 
 
 Arsenical ores, analysis of, 149, 151 
 
 Arsenious acid and iodine analyses, 136 
 
 Asbestos, palladium, 553 
 
 Ash, black, titration of, 64 
 
 Backward or residual titration, 32, 55 
 Balance, the, 5 
 
 Baric chloride, preparation of normal, 
 325 
 
 Baric thiosulphate as standard, 130 
 
 Barium in neutral salts, 70 
 
 Barium, estimation of, as chromate, 154 
 
 Barium, titration of, by permanganate, 
 154 
 
 Baryta solution for removing phos- 
 phates and sulphates from urine, 
 382 
 
 Baryta solution, standard, 50 
 
 Base, M i 1 1 o n ' s , use of, 49 
 
 Beal's filter, 18 
 
 Beverages, carbonic acid in, 96 
 
 Bicarbonates in presence of carbonates, 
 titration of, 58 
 
 Bichromate, standard solution of, 127 
 
 Bifluorides, titration of. 107 
 
 Bischof's apparatus for evaporation, 
 411 
 
 Bismuth, estimation of, as oxalate, 154 
 
 Bismuth, estimation of, as phosphate, 
 156 
 
 Bleaching compounds, titration of, 164 
 
 Bleaching powder, gasometric estima- 
 tion of, 165 
 
 Bleaching powder, titration of, by 
 arsenious solution, 164 
 
 Bleaching powder, titration of, by 
 iodine, 165 
 
 Boric acid and borates, titration of, 92 
 
 Boric acid in milk, estimation of, 369 
 
 Bottle for digestion in iodine estima- 
 tions, 135 
 
 Bromates, titration of, by iodine, 166 
 
 Bromine, absorption of, by oils and 
 fats, 358 
 
 Bromine, colour method of estimation, 
 157 
 
 Bromine, estimation of, by digestion, 
 157 
 
 Bromine, estimation of, by distillation, 
 156 
 
 Bromine, estimation of, by Cavazzi's 
 method, 157 
 
 Bromine, estimation of, by McCul- 
 loch's method, 158 
 
 Bromine, iodine, and chlorine together, 
 201 
 
 Bullets for gas analysis, how made, 467 
 
 Burette, B inks', 13 
 
 Burette clips, 13 
 
 Burette for hot titrations, 12 
 
 Burette, Gay Lussac's, 12 
 
 Burette, Mohr's, 8 
 
 Burette, Mohr's, advantages of, 8 
 
 Burette, the, 7 
 
 Burette, the blowing, 10 
 
 Burette, the foot, 10 
 
 Burette, the tap, 8, 11 
 
 Burette, without pinchcock, 14 
 
 Burette with enclosed thermometer 
 float, figure of, 8 
 
 Burette, with reservoir, 12 
 
 Burette, with oblique tap, 8 
 
 Burettes and pipettes, calibration of, 19 
 
 Butter, titration of, 353 
 
INDEX. 
 
 579 
 
 Butter, Reichert's method for, 353 
 Butter, Koettstorfer's method, 
 
 356 
 Butylic hydride gas, estimation of, 466 
 
 Cadmium, estimation of, as oxalate, 
 160 
 
 Cadmium, estimation of, as sulphate, 
 160. 
 
 Calcium, estimation of, as oxalate, 160 
 
 Calcium, estimation of, as perman- 
 ganate, 161 
 
 Calcium, estimation of, in slags and 
 mixtures, 161 
 
 Calcium, in neutral salts, 70 
 
 Calibration of gas apparatus for water 
 analysis. 420 
 
 Carbolic acid, titration of, 366 
 
 Carbon disulphide, titration of, 367 
 
 Carbon in iron and steel, estimation 
 of, 218 
 
 Carbon tetrachloride, use of, for titra- 
 
 ti^'of fats, 358 
 Carbonates, Pet 
 
 'ettenkofer's method 
 
 for, 95 
 
 Carbonates, alkaline, titration of, 55 
 Carbonates, analysis of, 93 
 Carbonates, indirect estimation of, 95 
 Carbonates soluble in acids, 94 
 Carbonates soluble in water, 93 
 Carbonates, titration of, in presence 
 
 of bicarbonates, 58 
 Carbonic acid in air, titration of, 97 
 Carbonic acid in beverages, 96 
 Carbonic acid in waters, 95 
 Carbonic anhydride gas, estimation of, 
 
 in gas apparatus, 497 
 Carbonic acid gas, estimation of, 95 
 Cathetometer, the, 18 
 Caustic alkalies, titration of, by potassic 
 
 bichromates, 60 
 
 Caustic and carbonated alkalies, titra- 
 tion of, 56 
 
 Caustic soda or potash, titration of, 56 
 Centimeter, cubic, the, 23 
 Cerium, estimation of, 162 
 Chlorates, indirect estimation of, 140 
 Chlorates, titration of, by iodine, 167, 
 
 373 
 Chlorates, chlorides, and hypochlorites, 
 
 mixtures of, 372 
 Chloric and nitric acids, estimation of, 
 
 373 
 
 Chloride of lime, titration of, 164 
 Chlorine and silver analyses, 138 
 Chlorine, bromine, and iodine together, 
 
 estimation of, 201 
 Chlorine, direct precipitation with 
 
 silver, 162 
 Chlorine, estimation of, by distillation. 
 
 163 
 
 Chlorine estimations, indirect, 140 
 Chlorine, estimation of, by silver and 
 
 chromate indicator, 139 
 Chlorine gas, titration of, 164 
 
 Chlorine, indirect estimation of, by 
 
 silver and thiocyanate, 163 
 Chlorine in waters, estimation of, 162 
 
 Chlorine water, titration of, 164 
 Chorley's apparatus for preserving 
 solutions, 22 
 
 Chromate indicator for silver, 139 
 
 Chromates, estimation of by distilla- 
 tion, 168 
 
 Chrome iron ore, analysis of, 168 
 
 Chromic acid in iron titration, 126, 
 206 
 
 Chromium, titration of by iron, 167 
 
 Chromium steel, titration of, 171 
 
 Citrates, titration of, 103 
 
 Citro-magnesic solution for phosphates. 
 292 
 
 Clark's process for softening water, 
 454 
 
 Clips for burettes, 13 
 
 Coal gas, analysis of, 536 
 
 Coal gas, estimation of sulphuretted 
 hydrogen in, 329 
 
 Coal gas, estimation of sulphur in, 320 
 
 Cobalt, estimation of, by permanganate, 
 173 
 
 Cobalt, estimation of, as cyanide, 174 
 
 Cochineal indicator, 35 
 
 Colour reactions, device for seeing, 
 139, 143 
 
 Colour reactions, precision in, 143 
 
 Commercial alkaline compounds, tech- 
 nical analysis of, 63 
 
 Condenser for Kjeldahl method, 82, 
 83 
 
 Constants used in the analysis of oils 
 and fats, 362 
 
 Copper and iron, titration of, in same 
 liquid, 182, 183 
 
 Copper, iron, and^ntimony, estimation 
 of, in same liquid, 183 
 
 Copper, extraction from ores, 177, 184 
 
 Copper, estimation of, as iodide, 176 
 
 Copper, estimation of, as sulphide, 180 
 
 Copper, estimation of, by colour titra- 
 tion, 187 
 
 Copper, indirect estimation of, by 
 silver, 184 
 
 Copper ores, technical analysis of, 184 
 
 Copper, separation of, by electrolysis, 
 176 
 
 Copper in presence of iron, titration 
 of, 182 
 
 Copper solution for sugar, F e h 1 i n g ' s , 
 309 
 
 Copper solution, Pavy's, for sugar, 
 315 
 
 Copper, titration of, by cyanide, 178, 
 184 
 
 Copper, titration of, by permanganate, 
 176 
 
 Copper, titration of, by stannous 
 chloride, 181 
 
 Correct reading of graduated instru- 
 ments, 17 
 
 p p 2 
 
580 
 
 INDEX. 
 
 Corrections for temperature of solu- 
 tions, 25 
 
 Cubic centimeter, the, 23 
 Cupric oxide for combustions, 401 
 Cuprous chloride for water analysis, 402 
 Cyanides, alkaline, titration of, by 
 
 silver, 190 
 Cyanides used in gold extraction, 
 
 estimation of, 192 
 
 Cyanogen, titration of, by iodine, 191 
 Cyanogen, titration of, by mercury, 
 
 191 
 
 Cyanogen, titration of, by silver, 191 
 Cylinders, graduated, calibration of, 21 
 
 Decem, the, 26 
 
 Decimal system, origin of, 23 
 
 Decimillem, the, 27 
 
 Decinormal bichromate solution, 127 
 
 Decinormal iodine, preparation of, 129 
 
 Decinormal permanganate solution, 121 
 
 Decinormal salt solution, 139 
 
 Decinormal silver solution, 138 
 
 Decinormal sodic arsenite, 136 
 
 Decinormal sodic chloride, 139 
 
 Decinormal thiocyanate, 142 
 
 Dextrine, inversion of, 308 
 
 Dextrose, 305 
 
 Digesting bottle for iodine estimation. 
 
 135 
 
 Direct and indirect processes, 31 
 Disaccharides, nature of, 305 
 Dissolved oxygen in waters, 269, 474 
 Dropping appai*atus for silver assay, 302 
 
 Earths, alkaline, titration of, 69 
 Erdmann's float, 18 
 Erdmann's float, newest form, 18 
 Estimations, indirect, by means of 
 
 silver and chromate, 140 
 Ethyl gas, estimation of, 513 
 Ethylic hydride gas, estimation of, 513 
 Eudiometer, B u 11 s e n ' s, calibration 
 
 of, 482 
 
 Explosion of gases, 502, 527 
 Extension of alkalimetric methods, 117 
 
 Factors for calculation of analyses, 31 
 Fats and oilp, titration equivalents of, 
 
 with potash, 352 
 Fats and oils, titration of, with bromine 
 
 or iodine, 358 
 
 F e h 1 i n g ' s copper solution, 309 
 Ferric compounds, reduction of, 208 
 Ferric indicator for analyses by thio- 
 cyanate, 143 
 Ferric iron, titration of, by stannous 
 
 chloride, 210 
 
 Ferric standard, to prepare, 210 
 Ferri cyanides, titration of, 196 
 Ferrochrome titration of, 171 
 Ferrocyanides in alkali waste, 196 
 Ferrocyanides in gas liquor, 196 
 Ferrocyanides in gold extraction, 194 
 Ferrocyanides, titration of, 195 
 
 Ferro-Manganese, estimation of man- 
 ganese in, 227, 229, 230 
 Ferrous iron, how obtained for titration, 
 
 215 
 
 Filter, Beale's. 18 
 Filter, Porter-Clark, 454 
 Filter for baric sulphate, Wilden- 
 
 stein's, 328 
 Flasks, measuring, 16 
 1 Flasks, verification of, 19 
 Float, Erdmann's, 18 
 Float, with thermometer, 8 
 Fluoric acid, estimation of, 105 
 Fluorides, estimation of, 105 
 Fluorescin, 39 
 
 ; Foraiic acid, estimation of, 104 
 | Frankland's and Ward's gas 
 
 apparatus, 520 
 : F r a n k 1 a n d ' s j oint for gas apparatu s, 
 
 419 
 
 Free acid in urine, estimation of, 397 
 Free ammonia in water, 407 
 F r e s e n i u s ' absorption apparatus, 132 
 Fruit juices, titration of, 104 
 
 , Galactose, 305, 313 
 
 i Gas analysis, B u n s e n ' s apparatus 
 
 for, 480 
 
 i Gas analysis, calculations for, 508, 517 
 Gas analysis, normal solutions for, 549 
 j Gas analysis, simple methods of, 547 
 Gas apparatus, etching of, 480 
 Gas apparatus, Frankland's, for 
 
 water analysis, 417 
 
 ! Gas apparatus, K e i s e r ' s portable, 54 4 
 ; Gas burette, H e m p e 1 ' s , 550 
 
 Gas liquor, analysis of, 75 
 1 Gas liquor, spent, analysis of, 79 
 Gas liquor, table showing the amount 
 of sulphate of ammonia to be 
 obtained from, 80 . 
 
 Gas pipettes, B e d s o n ' s modified, 556 
 Gas pipettes, II e m p e 1' s , 552 
 Gasvolumeter, Lunge's, 563 
 Gases, analysis of, 480 
 Gases, explosion of, 502, 507 
 Gases, indirect estimation of, 502 
 Gases, simple titration of, 547 
 Gases soluble in water, estimation of, 
 
 by the nitrometer, 559 
 Glucose or grape sugar, 305, 307 
 Glucose, constitution of, 305 
 i Glycerin, titration of, 363 
 Glycerin, estimation of, by per- 
 manganate, 363 
 Glycerin, estimation of, by bichromate, 
 
 364 
 j Glycerin, estimation of, by the acetin 
 
 method, 365 
 Gold, estimation of, 198 
 Graduated instruments, correct reading 
 
 of, 17 
 
 Grain measures, 26 
 Grains, fluid, 26 
 Gravi volumeter, J a p p ' s , 566 
 
INDEX. 
 
 581 
 
 Haematites, analysis of, 215 
 
 Hardness of water estimated without 
 
 soap solution, 71 
 Hardness of water, soap solution for, 
 
 405 
 
 Hardness in waters, estimation of, 438 
 Hardness in waters, tables of, 439466 
 Hardness in waters, Frankland's 
 
 table for, 439 
 
 H e m;p el's gas burette, 550 
 II e m p e 1 ' s gas pipettes, 552 
 Hot titration s, burette for, 12 
 Hydrobromic acid gas, estimation of, 
 
 494 
 
 Hydrocarbon gases, estimation of, 501 
 Hydrochloric acid, analysis of sub- 
 stances by distillation with, 132 
 Hydrochloric acid, normal, 48 
 Hydrocyanic acid, titration of, by 
 
 silver, 190 
 
 Hydriodic acid gas, estimation of, 494 
 Hydrochloric acid gas, estimatipn of, 
 
 494 
 
 Hydrofluoric acid, estimation of, 105 
 Hydrofluoric acid, cammercial composi- 
 tion of, 105 
 Hydrofluoric acid, H a g a and s a k e 's 
 
 experiments on, 108 
 Hydrosulphuric acid gas, estimation 
 
 of, 494 
 
 Hydrogen apparatus, B u n s e n ' s 503 
 Hydrogen peroxide, titration of, 283 
 Hydrogen sulphuretted, titration of, 
 
 329 
 
 Hypobromite solution for urea, 387 
 Hyposulphite of soda, Schutzen- 
 berger's solution of, 274 
 
 Improved gas apparatus, 517 
 Indicator, ferric, for analyses by 
 
 thiocyanate, 143 
 
 Indicator, starch, preparation of, 131 
 Indicator, chromate, for silver, 139 . 
 Indicator for mercuric solutions in 
 
 sugar analysis, 311 
 Indicators, 33 
 
 Indicators, extra sensitive, 39 
 Indicators, azo, 36 
 Indicators, combination of, 43 
 Indicators, external and internal, 32 
 Indicators, various effects of heat and 
 
 cold on, 40 
 Indicators, Thompson's results 
 
 with, 40 
 Indicators, general characteristics of. 
 
 41 
 
 Indicators, table of results with, 43 
 Indigo solution, standard, 464, 469 
 Instruments graduated, correct reading 
 
 of, 17 
 Instruments graduated, verification of, 
 
 19 
 Todate, how to remove from alkaline 
 
 iodides, 130 
 lodates, titratFon of, 166 
 
 I lodeosin, a new indicator, 39 
 Iodine, absorption of, by oils and fats, 
 
 358-360 
 I Iodine, estimation of, by distillation, 
 
 199 
 Iodine, estimation of, byGrooch and 
 
 Browning's method, 202 
 Iodine, bromine, and chloi-ine, mixed, 
 
 estimation of, 201 
 
 Iodine, estimation of, by chlorine, 203 
 I Iodine, estimation of, by nitrous acid 
 
 and carbon bisulphide, 205 
 Iodine, estimation of, by permanganate 
 
 and thiosulphate, 204 
 Iodine solution, decinormal, verifica- 
 tion of, 130 
 Iodine, titration of, by thiocyanate and 
 
 silver, 203 
 Iodine, titration of, by silver and 
 
 starch iodide, 206 
 
 i Iodine solution, decinormal, prepara- 
 tion of, 129 
 j Iodine and thiosulphate, titrations by, 
 
 128 
 
 i Iodine and arsenious acid analyses, 136 
 j Iodized starch-paper, 137 
 { Iron compounds, reduction of, for 
 
 titration, 208 
 1 Iron, estimation of, with bichromate, 
 
 206 
 Iron, estimation of, with permanganate, 
 
 206 
 Iron, estimation of, by colour titration, 
 
 213 
 
 Iron, estimation of, in ferric state, 210 
 : Iron, estimation of, in ferrous state, 206 
 Jron ore, magnetic, analysis of, 216 
 Iron ore, spathose, analysis of, 216 
 Iron ores, analysis of, 214 
 Iron ores, to render soluble, 214 
 Iron in silicates, estimation of, 217 
 Iron, titration of, by thiosulphate, 212 
 Iron, titration in ferrous state, 206 
 Iron and steel, estimation of, arsenic 
 
 in, 219 
 Iron and steel, estimation of, carbon 
 
 in, 218 
 
 Iron and steel, estimation of phos- 
 phorus in, 221 
 
 Iron and steel, estimation of, sulphur 
 in, 222 
 
 Reiser's gas apparatus, 544 
 
 Kjeldahl's method for nitrogen , 81 
 
 E j e I da hi' s method, new condenser 
 for, 84 
 
 Kjeldahl method, substances in 
 which their nitrogen may be 
 estimated by, 86 
 
 Kjeldahl method, modification of 
 for nitrates, 85 
 
 Kjeldahl method, Dyer's experi- 
 ments on, 85 
 
 Kjeldahl method, apparatus and 
 solutions for, 81, 82 
 
582 
 
 INDEX. 
 
 Knapp's standard mercuric cyanide 
 for sugar, 311 
 
 Lacmoid paper, 39 
 
 Lacmoid, preparation of, 38 
 
 Lacmoid solution, 39 
 
 Lead acetates, titration of, 223 
 
 Lead, as carbonate, estimation of, 224 
 
 Lead in citric and tartaric acids, 225 
 
 Lead, as sulphide, estimation of, 225 
 
 Lead, estimated as oxalate, 222 
 
 Lead in presence of tin. estimation of, 
 
 225 
 
 Lead, estimation of, as chromate, 223 
 Lead, red, titration of, 223 
 Lees, tartaric, titration of, 114 
 Lemon juice, titration of, 104 
 Levulose, 305, 311 
 Lime acetate, analysis of, 90 
 Lime and magnesia in urine, 395 
 Lime and magnesia in waters, 70 
 Lime, chloride of, gasometric estima- 
 tion, 165 
 
 Lime, estimation of (see Calcium), 160 
 Lime juice, titration of, 104 
 Liquors, red, examination of, 64 
 Litmus indicator, 33 
 Litmus, interference in, by carbonic 
 
 acid, 33 
 
 Litmus paper, 35 
 Litnms, pure extract of, 34 
 Litmus, preparation of, 33 
 Litmus, preservation of, 34 
 Litmus, xise of, by artificial light, 34 
 Logarithms for use in volumetric 
 
 analysis, 476 
 
 L u n g e ' s nitrometer, 123, 262, 468 
 Lyes, soda, examination of, 64 
 
 Magnesia and lime in urine, 395 
 
 Magnesia and lime in waters, 70 
 
 Magnesia, estimation of, 70 
 
 Magnesia, titration of, 70 
 
 Magnesic-citrate solution for phos- 
 phates, 292 
 
 Magnesite, use of, for preventing re- 
 gurgitation in distilling chlorine, 
 133 
 
 Magnetic iron ore, analysis of, 216 
 
 Magnesium as reducing agent for ferric 
 salts, 208 
 
 Maltose or malt sugar, 305, 307, 308, 
 311 
 
 Manganese, estimation of, by distilla- 
 tion with hydrochloric acid, 234 
 
 Manganese, estimation of, by iron, 
 236 
 
 Manganese, estimation of, by oxalic 
 acid, 236 
 
 Manganese, Westmoreland's 
 process for, 230 
 
 Manganese, Volhard's process for, 
 231 
 
 Manganese, estimation by Pattin son's 
 method, 227 
 
 Manganese in small quantities, estima- 
 tion of, 233 
 Manganese ores, analysis of, 227, 230, 
 
 Manganese ores, moisture in, 234 
 Manganese oxides, nature of, 226 
 Manganese, precipitation as dioxide, 
 
 227 
 
 Manganese, precipitation of, by per- 
 manganate, 231 
 
 Manganese, technical method of esti- 
 mating, 230 
 
 Marsh gas, estimation of, 466 
 M c L e o d ' s gas apparatus, 523 
 Measuring flasks, 16 
 Mercurial trough, 416 
 Mercuric cyanide, standard for sugar, 
 
 311 
 
 Mercuric iodide for sugar, 311 
 Mercury, estimation, as chloride, 238' 
 Mercury, estimation of, as iodide, 240 
 Mercury, estimation of, by cyanogen, 
 
 241 
 
 Mercury, preservation of, for gas appa- 
 ratus, 462 
 
 Mercury solution for urea, 383 
 Mercury, titration of, by thiosulphate, 
 
 240 
 Metallic salts of all kinds, alkalimetric 
 
 titration of, 117 
 Metals, heavy titration of, 116 
 Metals and minerals in waters, estima- 
 tion of, 441 
 
 Method for percentages, 30 
 Methyl gas, estimation of, 466 
 Methyl orange, 36 
 
 Methyl orange, the proper use of, 36 
 M ethyl orange, commercial, the defects 
 
 of, 36 
 
 Mill on 's base, use of, 49 
 Milk sugar, inversion of, 307 
 Mineral acids in vinegar, 90 
 Mirror for detecting precipitates, 328 
 Mixer, test, 17 
 
 Mixtures of sugars, titration of, 317 
 Mohr Dr. F., father of the volumetric 
 
 system, 27 
 
 M o h r ' s burette, advantages of, 8 
 Molybdenum solution for precipitating 
 
 phosphoric acid, 297 
 Molybdenum solution, Pern be r ton's 
 standard, 294, 225 
 
 Napthol /J, for titrating bromine, 358 
 Nessler's solution, preparation of, 
 
 399, 465 
 
 Nickel, estimation of, 243 
 Nitrate baths for photography, assay 
 
 of, 304 
 Nitrates, colorimetric estimation of, 
 
 262 
 Nitrates, estimation of, by ferrous salts, 
 
 249258, 260 
 Nitrates, estimation of, by nitrometer 
 
 262 
 
INDEX. 
 
 583 
 
 Nitrates, indirect estimation of, 140 
 Nitrates in water, aluminium process 
 
 for, 433, 468 
 Nitrates in water, estimation of, in 
 
 nitrometer, 468 
 
 Nitrates by K j eldahl method, 85 
 Nitrates in manures, technical method 
 
 of titration 259, 260 
 Nitric acid, estimation of, by distilla- 
 tion, 246 
 Nitric and chloric acids, estimation of, 
 
 373 
 Nitric acid, estimation of, by indigo, 
 
 469 
 Nitric acid, estimation of, by 
 
 Schlo's ing's method, 253 
 Nitric acid, estimation of, Pelouze 
 
 method, 249, 260 
 Nitric acid, estimation of, in absence 
 
 of organic matter, 249 
 Nitric acid, estimation of, in presence 
 
 of organic matter, 253 
 Nitric acid, normal, 48 
 Nitric acid, pure, for titrations, 143 
 Nitric oxide gas, estimation of, 494, 501 
 Nitrite, standard solution of, for water 
 
 analysis, 404 
 
 Nitrites alkaline, titration of, 267 
 Nitrites, colorimetric titration of, 248 
 Nitrites, estimation by iodometric 
 
 method, 265 
 
 Nitrites, estimated gasometrically, 268 
 Nitrites, sulphites and thiosulphates, 
 
 analysis of mixtures thereof, 269 
 Nitrogen as nitrates and nitrites, 
 
 factors for, 245 
 Nitrogen as nitrate, estimation of, by 
 
 copper-zinc couple, 248, 430 
 Nitrogen combined in organic sub- 
 stances, 80 
 Nitrogen, estimation of, as nitric oxide, 
 
 2tfl 
 
 Nitrogen gas, estimation of, 466 
 Nitrogen in alkaline nitrates, 245, 259 
 Nitrogen, indirect estimation of, 140 
 Nitrogen, Kjeldahl's method for, 
 
 81 
 Nitrogen, total in urine, estimation of, 
 
 398 
 
 Nitrometer, general uses of, 533 
 Nitrometer, Lunge's, 529537 
 Normal acid and alkaline solutions, 
 
 preparation of, 44 
 Normal acid solutions, verification of, 
 
 45 
 
 Normal ammonio-cupric solution, 50 
 Normal baric chloride, preparation of, 
 
 325 
 
 Normal hydrochloric acid, 48 
 Normal nitric acid, 48 
 Normal oxalic acid, 48 
 Normal potash solution, 49 
 Normal potassic carbonate, 47 
 Normal soda solution, 49 
 Normal sodi$ carbonate, 46 
 
 Normal solutions, 27 
 
 Normal solutions, definition of, 28 
 
 Normal solutions, based on molecular 
 
 weights, 28 
 
 Normal solution for gases, 521 
 Normal sulphuric acid, 47 
 
 Oils and fats, titration equivalents of, 
 
 with potash, 357 
 Oils and fats, titration of, with bromine 
 
 or iodine, 358 
 Oils and fats, titration of, by iodine, 
 
 360 
 
 Olefiant gas, estimation of, 473 
 Orange, methyl, the proper use of, 36 
 Orange, methyl, 36 
 Ore, tin, titration of, 340 
 Ores, arsenical, analysis of, 151, 152 
 Ores, copper, technical analysis of, 
 
 184 
 
 Ores, iron, analysis of, 214 
 Ores, iron, to render soluble, 214 
 Organic carbon and nitrogen in waters, 
 
 409 _ 
 Organic impurities in water, estimation 
 
 of, without gas apparatus, 445 
 Organic nitrogen and carbon in waters, 
 
 409, 445 
 
 Oxalates, titration of, 109 
 Oxalic acid, normal, 48 
 Oxidation and reduction analyses, 120 
 Oxidizing agents, 120 
 Oxygen dissolved in waters, 269, 474 
 Oxygen dissolved in water at various 
 
 temperatures, 275 
 Oxygen gas, estimation of, 500 
 Oxygen in water, estimation of, 269, 
 
 474 
 
 Oxygen in water, Adam's method, 277 
 Oxygen in waters, Mohr's method of 
 
 estimating, 270 
 Oxygen in waters, W i n k 1 e r ' s method 
 
 of estimating, 270 
 Oxygen in waters.Schiitzenberger's 
 
 method of estimating, 270 
 Oxygen in waters, Koscoe and 
 
 Lunt's method of estimating, 
 
 270, 271 
 Oxygen in waters, iodometric method 
 
 of estimating, 277 
 Oxygen process for water, comparison 
 
 with combustion methods, 457 
 Oxygen process for water, 455, 471 
 
 Palladium asbestos for gases, 553 
 
 Paper, iodized starch, 137 
 
 Paper, lacmoid, 39 
 
 Paper, litmus, 35 
 
 Paper, turmeric, 35 
 
 Paper, turmeric, alkaline, 35 
 
 Pavy's copper solution for sugars, 
 
 315 
 
 Percentages, method for, 30 
 Permanganate, alkaline, for water 
 
 analysis, 465 
 
584 
 
 INDEX. 
 
 Permanganate analyses, calculation of, 
 
 125 
 Permanganate for oxygen process in 
 
 water analysis, 465 
 Permanganate of potash, gasometric 
 
 titration of, 123 
 Permanganate, precautions in using, 
 
 124 
 
 Permanganate, preparation of stan- 
 dard solution, 121 
 Permanganate, titration with double 
 
 iron salt, 122 
 
 Permanganate, titration with iron, 121 
 Permanganate, titration of ferric salts 
 
 by, 124 
 Permanganate, titration of, with lead 
 
 oxalate, 123 
 Permanganate, titration of, with oxalic 
 
 acid, 123 
 Permanganate, titration of, with 
 
 hydrogen peroxide, 123 
 Permanganate, verification of standard 
 
 solution, 121 
 Permanganate, verification of standard 
 
 solution by hydrogen peroxide, 123 
 Phenacetolin, 37 
 Phenacetolin, preparation of, 37 
 Phenol, titration of, 366 
 Phenolphthalein, 37 
 Phenolphthalein, preparation of, 37 
 Phenolphthalein, disadvantages in 
 
 using, 38 
 
 Phosphates, earthy, in urine, 390 
 Phosphates of alkalies in urine, 390 
 Phosphates of lime, titration of, 288 
 Phosphoric acid, alkalimetric titration 
 
 of, 110 
 Phosphoric acid in combination with 
 
 alkaline bases, estimation of, 286 
 Phosphoric acid in minerals, estimation 
 
 of, 291 
 Phosphoric acid, Pemberton's 
 
 methods for, 293, 294 
 Phosphoric acid, titration of by molyb- 
 
 date, 293, 294. 
 Phosphoric acid, uranium method for, 
 
 285 
 
 Pinchcocks for burettes, 13 
 Pipette, the, 15 
 Pipette the, calibration of, 19 
 Plate, silver, assay of, 299 
 Poly-soccharides, nature of, 305 
 Porter-Clark process for softening 
 
 water, 454 
 Potash and soda, caustic, titration of, 
 
 55 
 Potash and soda, indirect estimation 
 
 of, 140 
 
 Potash and soda, mixed, 56 
 Potash and soda in urine, 398 
 Potash, estimation of, 60, 61 
 Potash, estimation of in neutral salts, 
 
 free from soda, 60 
 Potash, estimation of in presence of 
 
 soda, 61 
 
 ! Potash solution, normal, 49 
 Potash in waters, estimation of, 442 
 Potassic carbonate, normal, 47 
 Potassic ferri cyanide as indicator, 127 
 Potassic iodide, how to free from 
 
 iodate, 130 
 Potassic permanganate, preparation of 
 
 standard solution, 121 
 Potassic permanganate, titration of 
 
 standard solution, 121 
 Preservation of solutions, 21 
 Preservation of solutions, Chorley's 
 
 apparatus for, 22 
 Pressure and temperature in gas 
 
 analysis, 492 
 
 Processes, direct and indirect, 31 
 Processes, titration, termination of, 
 
 32 
 Propylic hydride gas, estimation of, 
 
 Pump, S p r e n g e 1 , for water analysis, 
 
 414 
 
 Pyrites, burnt, analysis of, 319 
 Pyrites, estimation of sulphur in, 318 
 
 Red liquors, examination of, 64 
 Reduction and oxidation analyses, 120 
 Reduction agents. 120 
 Regnault and R e i s e t ' s gas appara- 
 tus, 520 
 
 Residual titration, 55 
 Residues, water, combustion of, 413 
 Rosolic acid or corallin, 38 
 
 Sachsse's mercuric iodide for sugar, 
 
 311 
 
 Sal ammoniac, analysis of, 79 
 Salt cake, 65 
 Salt raw, analysis of, 67 
 Salt solution, decinormal, 139 
 Salt, standard, for silver assay, 301 
 Salts, alkaline, titration of, 55 
 Salts, metallic, various, titration of, 
 
 alkalimetrically, 115 
 Samples of water, collection of, 406 
 Scheibler's apparatus for CO 2 , 101 
 Schiitzenberger's method of estima- 
 ting oxygen in waters, 270 
 Septem, the, 27 
 
 Silicates, iron estimated in, 217 
 Silicates of potash and soda, titration 
 
 of, 67 
 
 Silico-fluoric acid, estimation of, 105 
 Silver and chlorine analyses, 138 
 Silver and thiocyanic acid, 142 
 Silver assay, Mulder's improved 
 
 method, 300 
 Silver, assay of, by Gay Lussac's 
 
 method, 299 
 
 Silver, alloys, assay of, 298, 299 
 Silver chromate, solubility of, 139 
 Silver, estimation of, by standard sodic 
 
 chloride, 298, 299 
 Silver plate, assay of, 299 
 Silver solution, decinormal, 138 
 
INDEX. 
 
 585 
 
 Silver solutions used in photography, 
 
 assay of, 304 
 Silver, titration of, by starch iodide, 
 
 298 
 Silver, titration of, by thiocyanate, 142, 
 
 298 
 
 Slags, manganese in. 228 
 Soap, analysis of, 68 
 Soap solution for water hardness, 405, 
 
 466 
 Soda and potash, indirect estimation 
 
 of, 141 
 
 Soda and potash in urine, 398 
 Soda and potash, mixed, estimation 
 
 of, G2 
 Soda and potash solutions, purification 
 
 of, 49 
 
 Soda ash, titration of, 63 
 Soda lyes, examination of, 64 
 Soda solution, normal, 49 
 Sodic carbonate, normal, 46 
 Sodic chloride, decinormal, 139 
 Sodic hyposulphite, Schittzenber- 
 
 ger's, 120, 270 
 Sodic peroxide, titration of, 284 
 Sodic peroxide, use of, as flux, 170 
 Sodic sulphide, titration of, 64 
 Sodic thiosulphate solution, decinormal, 
 
 preparation of, 130 
 S ol d a i n i ' s copper solution for sugar, 
 
 314 
 Solids, total in water, estimation of, 
 
 430 
 
 Solutions, alkaline and acid, prepara- 
 tion of, 44 
 Solutions, correction of volume for 
 
 temperature, 25, 26 
 Solutions, metallic acid, titration of, by 
 
 copper, 51 
 
 Solutions, normal, 27, 44 
 Solutions, normal, definition of, 28 
 Solutions, normal, based on molecular 
 
 weights, 29 
 
 Solutions, preservation of, 21 
 Solutions, standard, correction of, 51 
 Solutions, standard, factors for, 52, 
 
 54 
 Solutions, standard, used by weight, 
 
 6,21 
 Soxhlet's critical experiments on 
 
 sugar titration, 310 
 Spiegeleisen, estimation of manganese 
 
 in, 227232 
 S p r e n g e 1 pump for water analysis, 
 
 Standard alkaline nitrite for water 
 
 analysis, 404 
 
 Standard ammonic molybdate, 294, 295 
 Standard ammonic phosphate, 288 
 Standard baryta solution, 50 
 Standard calcic phosphate, 289 
 Standard copper solution for sugar, 
 
 Fehling's, 309 
 Standard copper solution for sugar, 
 
 Pavy's,315 
 
 Standard copper solution for sugar, 
 
 Gerrard's, 317 
 Standard indigo solution, 464, 469 
 Standard potassic phosphate, 287 
 Standard salt solution for silver assay, 
 
 301 
 Standard silver solution for water, 405, 
 
 463 
 Standard soap solution for hardness, 
 
 405, 466 
 
 Standard solutions, correction of, 51 
 Standard solutions, factors for, 31, 54 
 Standard solutions used by weight, 6, 
 
 21 
 Standard water for hardness (Clark's), 
 
 405, 466 
 Stannous chloride solution, preparation 
 
 of, 128 
 Starch and potassic iodide, permanent 
 
 solution of, 132 
 
 Starch, concentrated solution of, 131 
 Starch indicator, preparation of, 131 
 Starch, inversion of, 308 
 Starch solution, preparation of, 131 
 i Starch paper iodized, 137 
 Steel, estimation of manganese in, 
 
 227232 
 
 ! Stock method for organic nitrogen, 87 
 Strontium in neutral salts, 70 
 Sugar, grape or glucose, 305 317 
 i Sugar in urine, estimation of, 391 
 Sugar in urine, colorimetric method 
 
 for, 392 
 
 Sugar, malt or maltose, 307 
 Sugar, modifications of, 307, 308 
 Sugar of milk, inversion of, 307 
 Sugar solutions, classification of, for 
 
 analysis, 305 
 Sugars, titration of, by S id er sky's 
 
 method, 313 
 Sugar, titration of, by Gerrard's 
 
 process, 317 
 
 Sugar, titration of, by Pe ska's pro- 
 cess, 315 
 
 Sugar, varieties of, 305 
 Sugars, critical experiments on the 
 
 analysis of, 3]0 
 
 Sugars, inverted by acid, 305, 307 
 Sugars, mixed, titration of, 317 
 Sugars, various ratios of reduction, 
 
 with Fehling's solution, 313, 316 
 Sugars, various, inversion into glucose, 
 
 307 
 
 Sulphates in urine, 390 
 Sulphides, alkaline, titration of, 64, 
 
 320, 323 
 
 Sulphides in alkali, detection of, 63 
 Sulphides, sulphites, and thiosulphates 
 
 in same solution, estimation of, 323 
 Sulphides, estimation of sulphur in, 
 
 '320 
 
 Sulphites, alkaline titration of, 64, 322 
 Sulphites in presence of alkalies, 
 
 destruction of, 59 
 Sulphites, titration of, 32^ 
 
586 
 
 INDEX. 
 
 Sulphocarbonates, titration of, 368 
 Sulphur in coal gas, estimation of, 320 
 Sulphur in pyrites, estimation of, 318 
 Sulphur in sulphides, estimation of, 320 
 Sulphuric acid, normal, 47 
 Sulphuric acid, combined, titration of, 
 
 325 
 
 Sulphuric acid in presence of hydro- 
 fluoric acid, estimation of, 100 
 Sulphuric anhydride, titration of, HI 
 Sulphurous acid, ratio of, in solution, 
 
 to specific gravity, 322 
 Sulphurous acid, titration of, 107, 322 
 Sulphurous acid in 'hydrofluoric acid, 
 
 estimation of, 107 
 Sulphurous anhydride gas, estimation 
 
 of, 466 
 Sulphuretted hydrogen in coal gas, 
 
 estimation of, 329 
 
 Sulphuretted hydrogen in water, esti- 
 mation of, 330 
 Sulphuretted hydrogen, titration of, 
 
 329 
 
 Superphosphates, titration of, 290 
 Syringe for cleaning gas apparatus, 541 
 System, decimal, origin of, 23 
 System of weights and measures for 
 volumetry, 23 
 
 Tannic acid, titration of, 331 
 
 Tannin, estimation of, by antimony, 
 
 339 
 Tannin, estimation of, by gelatine, 
 
 338 
 Tannin, titration of, Lowenthal's 
 
 process, 331 
 
 Tannin, titration of, Dreaper's pro- 
 cess, 336 
 Tanning materials, percentage of tannin 
 
 in, 335 
 Tanning materials, preparation of for 
 
 titration, 332 
 
 Tartar emetic, titration of, 147 
 Tartrate solution, alkaline, for sugar, 
 
 309 
 
 Tartrates, titration of, 112 
 Temperature and pressure in gas 
 
 analysis, 492 
 Temperature, variations, influence of 
 
 on solutions, 24, 25 
 Test mixer, 17 
 
 Thiocarbonates, titration of, 368 
 Thiocyanate, clecinormal, 142 
 Thiocyanates, estimation of, 197 
 Thiocyanic acid and silver, 142 
 Thiosulphate and iodine, titration by, 
 
 128 
 Thiosulphate solution, preparation of, 
 
 130 
 Thiosulphates, sulphides, and sulphites, 
 
 mixtures of, 323 
 Thomas's gas apparatus, 537 
 Tin, titration of, 339 
 Tin ore, titration of, 340 
 Titrated solutions, preservation of, 21 
 
 Titration, backward, 32, 55 
 Titration, residual, 32, 55 
 Turmeric paper, alkaline, 35 
 Turmeric paper, 35 
 
 Two-foot tube for water examination, 
 466 
 
 Uranium method for phosphoric acid, 
 
 285 
 
 Uranium method, Joulie's, 291 
 Uranium, standard solution of, 290 
 Uranium, titration of, 341 
 Urea, titration of, by hypobromite and 
 
 sodic arsenite, 386, 389 
 Urea estimation, apparatus for, 387 
 Urea estimation, corrections for, 385 
 Urea, estimation of, by hypobromite, 
 
 386 
 
 Urea, estimation of, by mercury, 382 
 Urea estimations, experiments on, 384 
 Urea, Liebig's method of titration. 
 
 382 
 
 Uric acid, estimation of, 392 
 Urine, albumen in, estimation of, 397 
 Urine, analysis of, 377 
 Urine, baryta solution, for removing 
 
 phosphates and sulphates from, 
 
 382 
 Urine, estimation of chlorides in, 
 
 378382 
 
 Urine, free acid in, 397 
 Urine, potash and soda in, 398 
 Urine, estimation of total nitrogen in, 
 
 Vanadium, titration of, 341 
 Variations of temperature, influence 
 
 of, on solutions, 24 
 Vinegar, estimation of mineral acids 
 
 in, 90 
 Vinegar, titration of, by copper 
 
 solution, 51, 89 
 
 Volumetric analysis, general prin- 
 ciples, 1 
 Volumetric and gravimetric analysis, 
 
 distinction between, 2 
 Volumetric analysis without weights, 
 
 5,6 
 
 Volumetric methods, classification of, 3 
 Volumetric methods, various, reasons 
 
 for, 4 
 
 Water analysis, calculation of results, 
 476 
 
 Water analysis, interpretation of results 
 of, 444 
 
 Water analysis, reagents for, 399, 463 
 
 Water free from ammonia, preparation 
 of, 400 
 
 Water free from ammonia and organic 
 matter, 400 
 
 Water, hardness of, estimated without 
 soap solution, 71 
 
 Water deposits, microscopical examina- 
 tion of, 473 
 
INDEX. 
 
 587 
 
 Water residues, combustion of, 413 
 Water, softening by Clark's process, 
 
 454 
 Water, esitmation of, total solids in, 
 
 430, 473 
 
 Waters, carbonic acid in, 95 
 Waters potable, analysis of, 398, 463 
 Weighing standard solutions instead of 
 
 measuring, 6 
 Weights and measures, systematic, for 
 
 volumetry, 23 
 Wildenstein's filter,' 328 
 Williamson and Russell's gas 
 
 apparatus, 489 
 
 Zinc, ammoniacal solution, preparation 
 of, 343 
 
 Zinc containing iron, analysis of, 347, 
 350 
 
 Zinc dust, analysis of, 351 
 
 Zinc dust for reducing ferric com- 
 pounds, 209 
 
 Zinc dust, purification of, for reducing 
 purposes, 209 
 
 Zinc dust, titration of, 351 
 
 Zinc, as ferrocyanide, estimation of, 
 346 
 
 Zinc ores, analysis of by Vieille 
 Montagne method, 345 
 
 Zinc, as oxalate, estimation of, 350 
 
 Zinc, as sulphide, titration of, 344, 345 
 
 Zinc oxide and carbonate, analysis of, 
 352 
 
 Zinc, titration of, 342352 
 
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