CHEMICAL ANALYSIS SELECT METHODS IN CHEMICAL ANALYSIS (CHIEFLY INORGANIC) BY WILLIAM CROOKES, F.R.S., f.P.C.S., P.P.lNST.E.E EDITOR OF ' THE CHEMICAL NEWS THIRD EDITION, REWRITTEN AND ENLARGED LLUSTRATED WITH 67 WOODCUTS UNIVERSITY LONDON LONGMANS, GEEEN, AND CO. AND NEW YORK : 15 EAST 16 th STREET 1894 All riyhts reserved BIOLOGY IJBF LRY C7 BIOLOGY LIBRARY PBEFACE TO THE THIED EDITION A THIRD EDITION of * Select Methods in Chemical Analysis ' having been called for, advantage has been taken to go over the whole work and remove some of the processes to make room for others which have been proposed and found to be successful during the eight years which have elapsed since the Second Edition was published. It must, however, not be assumed that the processes so discarded are of little value. Indeed, some are at the present time in constant use, having taken their position as regular laboratory processes, and have only been removed from these pages because their value is now too well known to make it advisable to retain them in a book which the Author wishes to be looked upon as mainly a collection of novel or little- known processes. As soon as a new process takes its place among ordinary laboratory processes, there is no reason for its retention here. Other processes have been omitted because further experience with them has shown the Author that they are not so trustworthy as other newer processes which have taken their place. Others, again, have been omitted to prevent the book becoming of an unwieldy size. Thus, most volumetric operations have been omitted, as there are now several standard works which are devoted to this branch of analysis. Then, mere detections which are not separations, and processes of only technical importance, have to a great extent been left out ; the latter are well provided for in the technical literature. It has also Vi PREFACE TO THE THIRD EDITION been thought advisable to omit many purely assaying and furnace operations, as not exactly coming within the scope of the book, and being more fully treated in special works on assaying, such as ' Mitchell's Manual of Practical Assaying.' The space gained by these omissions has been partly filled up by new processes which the Author has considered worth intro- ducing ; but chiefly it has been utilised in giving to the chemical world a series of electrical separations and other processes from the standard work of Dr. Classen. The Author here desires to offer his thanks to Dr. Classen for his great kindness in not only permitting him to make use of a considerable portion of his book, ' Quantitative Chemical Analyses by Electrolysis,' but also for the woodcuts which are used to illustrate the operations. The Author wishes to point out that this book is not to be looked upon as an encyclopaedia of chemical analysis, in which is laid down every good method for the qualitative and quantitative examination of every known substance under every possible com- bination of circumstances. The Author has merely given such methods as have been proved in his own laboratory. Others possibly no less efficient have been passed over because he cannot vouch personally for their value. A main object has been to bring into notice a number of little-known expedients and precautions which prevent mistakes, insure accuracy, or economise time. The arrangement of the book has been adopted, not without careful consideration, as the one which necessitated the smallest number of back references. LONDON: Jure 1894. PBEFACE TO THE FIEST EDITION IT will be perceived from the title of this work that the Author has not intended to provide the student with a complete text -book of analysis, but rather with a laboratory companion, containing in- formation not usually found in ordinary \vorks on analysis. The Author has tested most of the new processes which have appeared during the last twelve years in the ' Chemical News ' ; and as some of these have proved to be of great value, it was thought that a service would be rendered to analytical chemistry if these trustworthy methods of analysis were systematically arranged in a convenient form for laboratory use. In some instances the descriptions are given in the language of the original writer, but in all cases where the Author has improved the processes the necessary modifications have been introduced. It is strange that modern works on analysis should ignore about twenty of the elements. Even Fresenius gives only a separate form for their detection. Were investigators more in the habit of looking for the ' rare ' elements, they would no doubt turn up unexpectedly in many minerals. In the present work equal prominence is given both to the rare and to the ordinary elements. The order in which the analytical separation of the metals is carried out will be readily understood. Take, for instance, the case of copper. After giving the best method for the detection and quantitative estimation of this metal, comes a description of the processes for separating it from those metals which have been Vlll PREFACE TO THE FIRST EDITION previously passed under review, as mercury, silver, and zinc ; but no attention is paid to the separation of copper from such metals as lead, tin, &c., which have not previously been treated of. Under the respective headings ' Lead ' and ' Tin ' the separation of these metals from copper is described. A complete list of separations has not been attempted. Where no process of separation or estimation is given, it may be inferred that the Author has had no experience in any but the well-known methods employed in most laboratories ; and to have introduced these ordinary processes into the work, simply for the sake of filling up gaps, would have largely increased its bulk without add- ing materially to its value. To save space, the description of a process is frequently discontinued at the point where the sub- stances under separation are brought to such a state that the concluding steps are obvious. No special system of weights and measures has been employed ; many of the descriptions having been condensed from the original memoirs, it was thought better to retain the system therein adopted, so as to have simple numbers to deal with, instead of having to convert them to one common scale and to introduce decimals. Thus, when an author says, take 8 grains of a sub- stance, O51816 gramme has not been substituted ; and where 10 grammes are mentioned, he has not put 154-3840 grains. When not otherwise expressed, all degrees are according to the Centigrade scale. Formulae have been avoided as far as practicable. The. names of discoverers of really novel or valuable processes are mentioned; but the introduction in a laboratory guide-book of the name of everyone who has contributed some trifling modifica- tion of a process would materially interfere with the concise description of the various methods, and, as a rule, such names have been omitted. Some processes of great historic interest, as Professor Stas's method for the preparation of pure silver by distillation and other- wise, have been given in considerable detail ; for this the Author thinks no apology is necessary, for it is always well for the student to have before him the highest models, in order that he may strive to attain a like perfection. CONTENTS CHAPTEK I POTASSIUM, SODIUM, LITHIUM, CAESIUM, RUBIDIUM (AMMONIUM) Potassium Test for potassium, 1. Estimation of potassium, 1. Precht's method, 3. Com- mittee appointed by Chemical Section of British Association, 3. Mr. Tatlock's method, 4. Process employed at Leopold's-hall and Stassfurt, 5. MM. Coren- winder and G. Coutamine's method, 5. Dr. F. Mohr's method, 6. M. H. L. de Koninck's process, 6. Estimation of potassium sulphate Dr. West's method, 6. Process used at Stassfurt, 6. Estimation of potassium by means of perchloric acid Armand Bertrand's method, 7. M. A. Carnot's method, 7. Volumetric estimation of potassium E. Burcker's process, 9. Marchand's modification, 9. Precipitation of potassium as fluosilicate Drs. Knop and Wolf's method, 9. Sodium Analysis of salt-cake Dr. C. B. A. Wright's method, 10. W. Tate's method, 12. Another method, 12. Black-ash, 12. Valuation of soda-ash M. Jean's method, 16. Estimation of soluble sulphides in commercial soda and soda-ash H. Lestelle's method, 17. Analysis of mixtures of alkaline mono- and bi-carbonates A. Mebus's process, 18. Separation of potassium from sodium Finkener's process, 18. Estimation of small quantities of sodium chloride in presence of potassium chloride F. Kottger and H. Precht's method, 19. Indirect estimation of potassium and sodium, 19. Kapid estimation, 20. Jean's method, 20. Maxwell Lyte's method, 21. Estimation of potash and soda in minerals W. Knop and J. Hazard's method, 22. Lithium, Ccesium, and Rubidium Extraction of lithium, caesium, and rubidium from lepidolite, 22. Estimation of lithia by sodium phosphate, 23. Extraction of caesium and rubidium from mineral waters, 23. From lepidolite, 24. Dr. Oscar D. Allen's method, 24. Separation of potassium, sodium, and lithium, 25. Antimony chloride as reagent for the caesium salts Charples's and Stolba's observations, 25. Separa- tion of caesium from rubidium Dr. Allen's plan, 26. Bunsen's method, 26. Separation of alkalies from silicates not soluble in acids Dr. Lawrence Smith's method, 26. Deville's process, 28. Decomposition of silicates by ignition with calcium carbonate and sal-ammoniac, 28. Sal-ammoniac, 28. Vessels for pro- ducing the decomposition, 29. Manner of heating the crucible, 29. Method of analysis, 29. Bemoval of the sal-ammoniac unavoidably accumulated in the process of analysis, 32. Conversion of the sulphates of the alkalies into chlo- rides, 34. Substitution of ammonium chloride for calcium fluoride to mix with calcium carbonate for decomposing the silicates, 34. Speedy method of separating the alkalies directly from the lime-fusion, for both qualitative and quantitative determination, 35. Special arrangement for heating the crucibles by gas, 37. Estimation of alkalies in fire-clays and other insoluble silicates Mr. Gore's method, 39. X CONTENTS Ammonia Nessler's test for ammonia Various modifications, 39. Estimation of ammonia in gas liquor Mr. T. E. Davis's method, 42. Ammonium chloride in analysis, 42. CHAPTER II BARIUM, STEONTIUM, CALCIUM, MAGNESIUM Barium, Strontium, and Calcium Indirect estimation of barium, strontium, and calcium, 43. Estimation of cal- cium Dr. A. Cossa's method, 45. Mr. Scott's method, 45. Calcium phosphate Professor F. Wohler's method, 46. Separation of calcium from strontium- Stromeyer's process, 47. Detection of calcium in the presence of strontium C. L. Bloxam's method, 47. Separation of calcium from barium and strontium P. E. Browning's process, 48. R. Fresenius's method, 48. Separa- tion of strontium from barium, 48. Magnesium Applications of metallic magnesium, 49. Determination of magnesium as pyro- phosphate Dr. Gibbs's process, 49. Mr. L. Briant's process, 49. Separation of magnesium from calcium Scheerer's method, 50. Dr. A. Cossa's method, 51. Mr. E. Sonstadt's method, 51. Another method, 52. Dr. Mohr's method, 53. H. Hager's method, 54. Separation of magnesium from potassium and sodium, 54. A. Reynoso's method, 55. CHAPTER III CERIUM, LANTHANUM, DIDYMIUM, SAMARIUM, THORIUM, GLUCINUM, THE YTTRIUM METALS, TITANIUM, ZIRCONIUM Cerium, Lanthanum, Didymium, Samarium, and Thorium Separation and estimation of the cerium metals together, 56. Separation of cerium from didymium and lanthanum Messrs. Pattison and Clarke's method, 5(5. Wolcott Gibbs's process, 57. Another method, 58. M. H. Debray's method, 58. Separation of lanthanum from didymium MM. Damour and Deville's process, 59. C. Winckler's process, 60. Volumetric determination of cerium F. Stolba's method, 60. Analysis of cerite, 61. Separation of cerium, didymium, samarium, and lanthanum, 61. Separation of thorium from other earthy metals Professor L. Smith's method, 63. Glucinum Preparation of pure glucina, 63. Dr. W. Gibbs's process, 63. Separation of glucinum from the cerium metals, 64. The Yttrium Metals Analysis of the natural tantalates containing the yttrium metals Professor J. L. Smith's method, 64. Separation of the yttrium metals from glucinum, 65. From those of cerium, 65. Detection and Wide Distribution of Yttrium Introduction, 65. Citron-band spectrum, 66. Examination of calcium compounds, 67. Citron band not due to calcium, 69. Experiments with calcium sulphate, 71. Wide distribution of the citron band-forming body, 71. Examination of zircon for the citron band, 71. Of cerite for the citron band, 73. Of thorite and orangite, 74. Chemical facts connected with the citron body, 76. Sought - for body one of the yttrium family, 78. Has no absorption spectrum, 80. Analysis of samarskite, 81. Preparation of pure terbia, 84. Preparation of mixed erbia, holmia, and thulia, free from other earths, 85. Philippia, 85. Mosandra, 86. Separation of terbia and yttria from erbia, holmia, and thulia, 86. Separation of terbia and yttria, 86. Ytterbia, 87. Purification of yttria, CONTENTS xi 88. Phosphorescent spectrum of yttria, 90. Circumstances modifying the yttria spectrum, 91. Occurrence of yttria in nature, 92. Indications of other spectrum-yielding elements, 94. Samarium, 94. Mixed ' citron ' and ' orange ' spectra, 95. Chemistry of the 'orange-band' forming body, 96. X from samarskite, 97. Thorite and orangite, 98. Perofskite, 98. Calcite, 98. Dolomite, 99. Coral, 99. Sea-water, 99. X in strontium minerals, 100. Is X a mixture ? 100. Explanation of foregoing anomalies, 103. X in cerite, 103. Analysis of cerite, 104. Separation of ceria, lanthana, didymia, and samaria, 105. Purification of lanthana, 106. Of didymia, 107. Of samaria, 109. Phosphorescent spectrum of samarium, 111. Titanium Decomposition of titanium minerals Mr. J. Jones's method, 119. Detection and estimation of titanium Mr. R. Apjohn's method, 120. E. Jackson's method, 120. Preparation of pure titanic acid Professor Wohler's method, 120. Another, 120. Professor Dunnington's method, 121. Zirconium Preparation of pure zirconia Messrs. Tessie du Motay and Co.'s patent, 121. Separation from titanium Messrs. Streit and Franz's method, 122. Dr. G. H. Bailey's method, 122. F. Pisani's method, 123. Oother methods, 123, 124. CHAPTER IV CHROMIUM, URANIUM, VANADIUM, TUNGSTEN, MOLYBDENUM Chromium Estimation of chromium Professor Storer's method, 125. Mr. E. J. Stoddart's experience, 125. Mr. A. H. Pearson's method, 125. Rose's plan, 126. Three more methods, 126. Detection of bichromate and free chromic acid, 127. Estimation of chromium as phosphate, 127. Volumetric estimation of chro- mium, 128. Of chromic acid, 128. C. Zulkowsky's plan, 128. Mr. W. J. Sell's plan, 128. Separation of chromium from aluminium A. Carnot's method, 129. * Uranium Estimation of uranium H. Rose's method, 129. Patera's process, 129. Volu- metric estimation of uranium Guyard's process, 130. Separation from the cerium metals W. Gibbs's method, 131. From chromium, 131. From most heavy metals H. Rose's method, 132. A. Remele's method, 132. Alibegoff's method, 132. Separation from phosphoric acid M. Reichardt's plan, 133. A modification, 133. Vanadium Detection of vanadium R. Apjohn's process, 133. Dr. B. W. Gerland's method, 134. Estimation by titration with permanganate, 136. Detection in iron ores, 136. Boettger's plan, 136. Preparation of vanadic acid from lead vanadate Professor Wohler's method, 137. Sir H. Roscoe's method, 137. Another method, 138. Purification of vanadic acid from phosphorus Sir H. Roscoe's method, 138. Detection and estimation of vanadium and titanium in basalts Mr. G. Roussel's method, 138. Tungsten Preparation of tungstic acid from wolfram Professor Wohler's process, 139. Molybdenum Detection of molybdic acid 0. Maschke's improved plan, 140. Estimation, 140. T. M. ChataixTs process, 140. Separation of molybdic acid from phosphoric acid E. Reichardt's method, 140. xii CONTENTS CHAPTER V ZINC, ALUMINIUM, GALLIUM, IRON Zinc Precipitation of metallic zinc, 141. Electrolytic determination of zinc Classen's method, 141. Von Miller and Kiliani's method, 142. Beilstein and Jawein's method, 142. Parodi and Mescezzini's method, 142. Eiche's method, 142. F. Riidorff's plan, 142. A. Beard's plan, 142. G. Vortmann's process, 142. Picte's method, 143. Volumetric estimation of zinc--M. Renard's process, 143. M. Galetti's method, 143. C. Mann's method, 145. F. Maxwell Lyte's method, 145. M. C. Fahlberg's process, 145. Estimation as oxalate M. Gould Leison's method, 146. Estimation as sulphide J. H. Talbot's plan, 146. As ammonio-phosphate H. Tamm's method, 147. Estimating the value of zinc powder V. Drewsen's method, 148. Fresenius's plan, 149. J. Barnes's plan, 149. Separation of zinc from uranium, 149. From chromium, 149. Aluminium Detection of alumina M. Beckmann's method, 150. Precipitation M. Classen's method, 150. Precipitation and washing of alumina Messrs. S. L. Penfold and D. N. Harper's method, 151. Volumetric estimation in caustic soda Gatenby's method, 152. Assay of clays for alum making M. G. Pouchet's process, 153. Separation of aluminium from zinc, 153. From uranium, 153. From chromium Wohler's plan, 153. From zirconium Mr. J. T. Davis's plan, 154. From glucinum Dr. W. Gibbs's plan, 154. Another, 154. Messrs. S. L. Penfold and D. N. Harper's method, 154. Another, 155. From the cerium metals, 155. From magnesium Dr. W. Gibbs's plan, 155. Wohler's plan, 155. From calcium H. Rose's plan, 156. Gallium Detection of gallium, 156. Separation from zirconium, 157. From uranium (yellow uranic salts) four methods, 157. From z-inc two methods, 158. From aluminium and chromium, 159. Iron Preparation of pure iron, 160. Plan of the British Association Committee, 160. Another, 160. Electrolytic determination of iron Classen's method, 161-163. Another, 162. F. Riidorff's method, 162. A. Baand's method, 162. E. F. Smith's method, 162. Estimation as ferric oxide S. Kern's method, 163. To dissolve ignited ferric oxide A. Classen's method, 163. Estimation of iron protoxide in the presence of peroxide Avery's plan, 163. A. H. Allen's plan, 165. Reduction of sesqui-salts of iron to proto-salts Mr. Reynolds's method, 165. Gravimetric estimation of iron Mr. C. F. Cross's observations, 166. Volumetric estimation by sodium thiosulphate M. Mohr's method, 166. Volu- metric estimation with copper subchloride Dr. Winkler's plan, 167. With potassium permanganate J. Krutwig and A. Cocheteux's method, 168. M. Moyaux's method, 168. E. Hart's method, 169. T. N. Drown's method, 169. Another method, 170. Messrs. Stock and Jack's method, 170. M. A. Eilmann's method, 171. Immediate analysis of meteoric iron M. Stanislas Meunier's method, 172. Nickeliferous iron, 172. Carburetted iron, 174. Sulphuretted iron, 174. Schreibersite, 176. Graphite, 177. External crust, 177. Stony grains, 178. Gases, 179. Rare substances, 179. Preservation of iron proto- salts, 180. Separation of iron from aluminium Wohler's process, 180. R. T. Thomson's process, 180. Vignon's process, 180. F. Beilstein and R. Luther's process, 181. Another, 181. Separation of iron from zinc Three processes, 182. Electrolytic separation of iron from zinc A. Classen's process, 183. Separation from uranium, 184. From chromium, 184. From manganese, nickel, zinc, and aluminium G. Von Knorre's process, 185. From chromium and uranium, 185. From zirconium, 186. From glucinum A. Classen's process, 186. Electrolytic separation of iron from glucinum and aluminium, CONTENTS Xlll 187. From zirconium, 187. From vanadium, 187. Separation of iron from titanium, 187. From cerium, 187. From magnesium Dr. Calvert's process, 188. From calcium, 18S. CHAPTER VI MANGANESE, NICKEL, COBALT Manganese Electrolytic separation of manganese A. Classen's method, 180. F. Riidorff s method, 190. A. Braand's method, 190. Estimation of manganese Dr. W. Gibbs's method, 191. A. Guyard's (Hugo Tamm's) method, 192. Mr. J. Pattin- son's method, 193. M. A. Guyard's method, 194. Deteetion of manganese in ashes E. Campani's process, 194. Separation of manganese from zinc, nickel, and cobalt, 194. Electrolytic separation of manganese from iron A. Classen's method, 195. Separation from iron Various methods, 197. L. Blum's method, 198. From iron when phosphoric acid is present, 198. Separation of manganese, iron, and aluminium from phosphoric acid A. Classen's method, 198. Separatien of manganese, iron, and sulphuric acid A. Classen's method, 199. From aluminium, 199. From zinc Messrs. Jannasch and Niederhofheim's process, 200. From uranium, 201. From cerium, 201. From magnesium, 201. From barium, calcium, magnesium, and alkalies A. Classen's process, 201. Nickel Preparation of metallic nickel, 201. Electrolytic precipitation of nickel Classen's method, 202. Fresenius and Bergmann's process, 202. Brand's process, 202. Riidorff's process, 202. Estimation of nickel Forbes's process. 202. Leison's process, 203. A. A. Julien's process, 203. Another process, 204. Separation from iron Mr. Thomas's process, 205. From zinc, 205. H. Alt and J. Schulze's process, 206. Cobalt Metallic cobalt, 206. Electrolytic determination of cobalt Classen's process, 206. Riidorff's process, 207. A. Brand's process, 207. Gravimetric estimation of cobalt Leison's process, 207. Mr. Forbes's process, 207. Tests for cobalt, 208. Mr. Skey's process, 208. F. Reichel's process, 208. A. H. Allen's process, .208. R. H. Davies's process, 208. G. Papasogli's process, 209. Separation of cobalt from nickel Liebig's process, 210. W. Gibbs's process, 210. T. H. Henry's process, 211. Dr. Phipson's process, 211. A. Jorissen's process, 211. G. Delvaux's process, 212. P. Dirvell's process, 212. W. Gibbs's process, 214. A. Guyard's process, 214. Separation of nickel and cobalt from their ores and from one another Mr. Hadow's process, 215. Fresenius's process, 221. Method I., 223. Method II., 223. Separation of nickel and cobalt from manganese -W. Gibbs's process, 224. Separation from iron T. Moore's process, 225. Electrolytic separation of cobalt and iron Classen's method, 225. Of nickel and iron, 226. Classen's method, 226. Of cobalt and nickel from iron, 226. G. A. Le Roy's method, 226. F. Field's method, 226. T. Moore's method, 228. Separation of nickel from iron T. Moore's method, 228. Of cobalt from zinc Wohler's method, 228. Separation of nickel, cobalt, and iron from zinc P. Von Berg's method, 229. Electrolytic separa- tion of Cobalt and zinc from manganese Classen's method, 229. Of cobalt, nickel, zinc, and iron from aluminium Classen's method, 230. From manga- nese and aluminium, 231. From chromium, 231. From chromium and alu- miniumClassen's method, 232. From manganese, chromium, and aluminium .Classen's method, 232. From uranium Classen's method, 232. From chro- mium and uranium Classen's method, 232. From aluminium, magnesium, and uranium A. Brand's method, 233. Separation of nickel or cobalt from uranium Dr. Gibbs's method, 233. From manganese, iron, zinc, and uranium Clemens Zimmermann's method, 233. siv CONTENTS CHAPTEE VII SILVER, MERCURY, COPPER Silver Preparation of pure silver M. Stas's method, 236. Preparation of silver from silver chloride, 236. By Liebig's process, 237. By electrolysis, 238. By precipi- tation with phosphorus, 238. By reduction of the chloride in the wet way, 239. By reduction of its ammoniacal solutions, 240. Purification of silver M. Stas's method, 241. Distillation of silver, 243. Ascertaining the purity M. Stas's plan, 244. Dr. Classen's plan, 244. Electrolytic separation of silver Dr. Classen's method, 245. F. Kiidorff's method, 245. Fresenius and Berg- mann's method, 245. Volumetric estimation of silver M. Stas's modification of Gay-Lussac process, 246. J. Volhard's process, 249. Separation of silver chloride and iodide Cyanogen, 250. Extraction of silver from burnt pyrites, 250. Detection of alkalies in silver nitrate M. Stolba's plan, 252. Mercury Test for mercurial vapours, 252. Merget's plan, 252. Blowpipe test for mercury, 252. T. Charlton's plan, 252. Electrolytic separation of mercury Dr. Classen's method, 253. F. Biidorff's method, 253. A. Brand's method, 253. G. Vortmann's method, 253. E. F. Smith's method, 254. Estimation of mer- cury by distillation H. Rose's method, 254. Detection of mercury in minerals, 256. Detection of very minute quantities of mercury, 256. Electrolytic detec- tion of mercury, 256. Dr. C. A. Kohn's method, 256. Wolff's method, 257. Assay of mercury ores A. Eschka's method, 257. Electrolytic estimation of mercury F. W. Clarke's method, 258. In the form of protochloride M. de Bonsdorff's plan, 258. Electrolytic separation of mercury from silver, 259. Separation of mercury (persalts) from silver, 259. From zinc, 259. Electrolytic separation of mercury from iron, cobalt, nickel, zinc, manganese, chromium, and aluminium Classen's method, 259. Copper Detection of traces of copper Drs. Endemann and Prochazka's method, 259. B. C. Woodcock's method, 260. Electrolytic reduction of copper Classen's plan, 260. Luckow's plan, 261. liudorff s plan, 261. Electrolytic detection of copper C. A. Kohn's plan, 262. Precipitation of metallic copper in quanti- tative analyses MM. Millon and Commaille's plan, 263. Th. Weyl's method, 263. Precipitation of copper D. Forbes's method, 263. Estimation of copper as sulphocyanide A. Guyard's method, 264. In bar copper and in native copper, 265. In brass, bronze, and German silver, 265. In pyrites and other < copper ores, and in slags, 266. Volumetric estimation of copper - Fleck's method, 266. With potassium ferrocyanide M. Galetti's method, 267. With sodium sulphide C. Kunsel's method, 268. F. Weil's method, 269. Prepara- tion and keeping of the solution of tin protochloride, 270. Titration of tin protochloride, 270. Of any compound of copper not containing either iron or nickel, 271. Of a compound of copper which also contains iron, 271. Which contains nickel M. P. Casamajor's method, 272. T. Carnelley's method, 273. With sulphuretted hydrogen, 274. With potassium ferrocyanide, 274. Assay of copper pyrites F. P. Pearson's method, 276. T. C. Oxland's method, 277. The Mansfeld processes for estimating copper in ores, 278. Dr. Steinbeck's process, 280. M. C. Luckow's process, 285. Detection of minute traces of copper in iron pyrites and other bodies, 291. E. Chapman's method, 291. Estimation of copper suboxide in metallic copper, 292. C. Aubel's method, 292. Separation of copper from lead, cadmium, manganese, mercury, zinc, &C.G. Von Knorre's process, 292. From uranium S. Kern's method, 293. From mercury, 293. Electrolytic separation, 293. E. F. Smith and L. K. Frankel's method, 293. Separation from silver, 293. Electrolytic separation from silver-- E. F. Smith's method, 294. Separation from nickel or cobalt, 294. M. Dewilde's method, "295. From zinc, 295. Electrolytic separation CONTENTS XV from iron, cobalt, nickel, zinc, manganese, chromium, aluminium, and phos- phoric acid Classen's method, 296. From barium, strontium, calcium, potas- sium, sodium, and lithium Classen's method, 296. CHAPTEE VIII CADMIUM, GALLIUM, LEAD, THALLIUM, INDIUM, BISMUTH Cadmium Electrolytic precipitation of cadmium Classen's- method, 297. Smith and Luckow's method, 297. Eliesberg's method, 297. Beilstein and Garvein's method, 297. F. Riidorff's method, 298. A. Brand's method, 298. G. Vort- mann's method, 298. Estimation of cadmium Leison's process, 298. A. Orlowski's process, 299. Separation i'rom copper Wohler's method, 299. G. Vortmann's method, 300. Dr. Wells's process, 300. E. Donath and J. Mayrhofer's process, 300. Electrolytic detection of cadmium Dr. C. A. Kohn's method, 300. Separation of cadmium from copper Classen's method, 300. E. F. Smith's method, 300. From mercury, 301. From zinc Eliesberg's method, 301. A. Yver's method, 301. E. F. Smith and Lee K. Frankel's method, 302. From copper and zinc in alloys H. N. Warren's method, 302. Electrolytic separation of cadmium, copper, mercury, and manganese Classen's method, 303. Detection of cadmium in presence of zinc before the blowpipe E. J. Chapman's method, 303. T. Bayley's method, 304. Gallium Separation of gallium from cadmium, 304. From copper, 305. From mercury, 306. From silver, 306. From cobalt, 306. From nickel, 307. From manganese M. Lecoq de Boisbaudran's methods, 308. From uranium (yellow uranic salts), 310. Lead Preparation of pure lead M. Stas's method, 311. Preparation by reducing the carbonate with potassium cyanide, 311. By reducing the carbonate by black flux, 312. By reducing the chloride, 313. Electrolytic detection of lead C. A. Kohn's method, 313. Precipitation of lead as sulphate M. Level's method, 314. H. C. Debbits's method, 315. S. Eovera's method, 315. Estimation of lead as carbonate, 315. As iodate C. A. Cameron's process, 316. Electrolytic separation of lead Classen's method, 316. G. Vortmann's method, 317. J. Messinger's process, 317. Detection and estimation of small quantities of lead in the presence of other metals, 318. Assay of galena in the wet way F. H. Storer's method, 320. F. Mohr's method, 321. Estimation of lead in ores Mr. Lowe's method, 322. Detection of lead peroxide in litharge, 322. Esti- mation of the value of lead peroxide H. Fleck's method, 322. Detection of lead in the tin linings of vessels M. Forpoz's method, 322. In tin paper Kopp's method, 323. Electrolytic separation of lead from copper Classen's method, 323. Separation of lead from copper, 324. From mercury Rose's method, 324. From silver E. Benedict and L. Gaus's method, 324. D. Forbes's improvements in process, 325. Concentration of silver-lead, 327. Cupellation, 329. Estimation of the weight of the silver globule, 331. Harkort's scale, 331. Mr. Forbes's table, 332. Cupellation loss, 333. Modification of Plattner's table, 334. Metallic alloys, 334. Electrolytic separation of lead from silver, 335. From mercury, 335. Separation of lead from zinc F. M. Lyte's method, 336. Electrolytic separation of lead from cadmium Classen's method, 336. Separation of lead from barium when in the form of sulphates, 336. White lead G. Tissandier's method of analysis, 336. Analysis of minium or red lead T. P. Blunt's process, 337. Iron, 337. Copper, 338. Metallic lead, 339. Silver, 339. Separation of lead from gallium, 340. Volumetric estimation of small quantities of lead in the presence of free hydrochloric acid Mr. A. P. Laurie's method, 341. Electrolytic separation of lead from iron, cobalt, nickel, zinc, chromium, and aluminium Classen's method, 342. ^^aJaaiiDnf com- mercial lead peroxide H. Fleck's method, 342. XVI CONTENTS Thallium Detection of thallium in minerals, 343. Preparation of thallium from the flue- dust of pyrites-burners, 344. From iron pyrites, 347. From sulphur or pyrites in the wet way, 348. From the saline residues of the salt-works at Neuenheim, 348. From commercial hydrochloric acid, 348. From the mother-liquors of the zinc sulphate works at Goslar, 348. Preparation of chemically pure ' thallium, 349. Purification by fusion in lime, 351. Detection by the blow- pipe, 351. Electrolytic separation of thallium Classen's method, 352. G. Neumann's method, 352. Estimation of thallium as platino-chloride, 353. As iodide, 353. As sulphide, 354. Volumetric estimation of thallium, 354. Separation of thallium from lead, 355. Detection and estimation of thallium in presence of lead Mr. E. A. Werner's method, 356. Separation of thallium from cadmium, 356. From copper, 357. From mercury, 357. From silver, 357. From nickel, cobalt, or manganese, 358. From iron, 358. From zinc, 359. From chromium, 359. From gallium, 359. Indium Preparation of indium from commercial zinc, 360. From blende, 361. Purifica- tion of indium, 361. Separation of gallium from indium, 362. Bismuth Detection of small quantities M. M. P. Muir's process, 363. Detection of minute traces of bismuth in copper F. Abel and F. Field's process, 363. By the blow- pipe Von Kobell's method, 364. Cornwall's method, 365. Estimation of bismuth Mr. M. M. P. Muir's process, 365. Messrs. Muir and Robbs's method, 366. Purification of bismuth, 366. Electrolytic separation of bismuth Classen's method, 367. A. Brand's method, 367. Eiidorff's method, 367. G. Vortmann's method, 368. Detection of calcium phosphate in bismuth subnitrate, 368. Separation of bismuth from thallium, 368. From gallium, 369. From lead, 370. Estimation of bismuth in lead alloys, 371. Separation of bismuth from cadmium P. Jannasch and P. Etz's method, 372. Electro- lytic separation from copper E. F. Smith's process, 373. E. Matthey's pro- cess, 373. From mercury, 374. Detection of copper, bismuth, and cadmium when simultaneously present M. Iles's method, 374. CHAPTER IX ANTIMONY, TIN, ARSENIC, TELLURIUM, SELENIUM Antimony Electrolytic deposition of antimony Classen's method, 375. H. Nissenson's method, 377. G. Vortmann's method, 377. Dr. C. A. Kohn's method, 377. Estimation of antimony Wohler's method, 378. Mr. Sharples's method, 378. Rapid detection of antimony in minerals Dr. E. Chapman's method, 379. Dr. Weller's method, 380. Estimation of antimony in native antimony sulphide, 380. In antimony sulphide obtained in analysis, 381. Separation of antimony from mercury, 382. From copper, 382. Tin Electrolytic separation of tin Classen's method, 382. Estimation of tin binoxide Mr. A. H. Allen's process, 384. Assay of tin ores J. S. C. Wells's process, 385. J. W. B. Hallett's process, 385. M. Moissenet's process, 386. P. Hart's process, 386. A. E. Arnold's process, 387. Separation of tin from antimony F. W. Clarke's process, 387. M. Ad. Carnot's process, 389. Electrolytic separation of antimony from tin Classen's method, 390. Detection of tin in presence of antimony M. M. P. Muir's process, 392. Separation from bismuth, 392. From thallium, 392. From lead, 392. From copper, 392. (Analysis of gun and bell metals, containing besides traces of lead, zinc, and iron) Process at Ecole Normale, 393. From tungsten J. H. Talbott's method, 395. From CONTENTS xvii titanium H. Haas's method, 396. Commercial analysis of tin ware MM. Millon and Morin's process, 397. Separation of tin from phosphoric acid- Classen's method, 400. Arsenic Purification of metallic arsenic, 400. Detection by Marsh's test, 400. Improve- ment in Marsh's apparatus, 402. Detection of arsenic in either organic or in- organic matter MM. Mayencon and Bergeret's process, 402. In the colours of paper hangings M. Hager's method, 402. Keinsch's test for arsenic, 403. Identification of arsenious acid by crystallisation F. W. Griffin's method, 403. Electrolytic deposition of arsenic Classen's method, 404. Estimation of arsenious acid in presence of arsenic acid M. L. Mayer's process, 404. Silver nitrate test for arsenic acid Mr. Every's process, 405. E. Salkowski's process, 405. Detection of arsenic in commercial hydrochloric acid, 405. Separation of arsenic from other metals E. Fischer's process, 406. Estimation of arsenic as magnesium pyro-arseniate Dr. F. Eeichel's process, 406. C. Kammelsberg's process, 406. Separation of arsenic from gallium, 407. Volumetric estimation of small quantities of arsenic and antimony A. Houzeau's process, 407. Indirect process, 407. Estimation of arsenic in arsenic tersulphide M. Graebe's process, 408. In arsenic pentasulphide Lenssen's process, 408. In ores Mr. ParnelPs process, 408. MM. de Clermont and Frommel's method, 409. Separation of arsenic from tin, 409. Solution of arsenical and antimonial com- pounds Kammelsberg's method, 410. Separation of arsenic from antimony R. Bunsen's method, 411. Separation of tin from antimony and arsenic M. Carnot's method, 412. Detection of arsenic in tartar emetic Dr. Von Ankum's method, 414. Electrolytic separation of arsenic from antimony Classen's method, 414. Separation of arsenic, antimony, and tin Classen's method, 415. E. Fischer and Hufschmidt's method, 415. Detection of arsenic in bismuth, 416. Separation of arsenic from copper Mr. E. W. Parnell's method, 417. Detection of arsenic in copper, 418. In commercial copper Dr. W. Odling's method, 420. Electrolytic separation of arsenic from antimony and copper Classen's method, 420. E. F. Smith's method, 421. Separation of arsenic from mercury and palladium Classen's method, 422. Estimation of small quantities of arsenic in sulphur H. Schseppi's method, 422. Tellurium and Selenium Separation of tellurium from selenium and sulphur Dr. Oppenheim's method, 422. Mr. E. Donath's method, 423. M. V. Schroetter's process, 424. G. Kustel's process, 424. Estimation of selenium H. Eose's process, 425. Separation of selenium from metals, 426. Preparation from seleniferous flue-dust, 426. Detection of sulphur in selenium, 426. Preparation of selenious acid, 427. Of selenic acid Wohler's process, 427. CHAPTER X GOLD, PLATINUM, PALLADIUM, IRIDIUM, OSMIUM, RHODIUM, RUTHENIUM Gold Detection of minute traces of gold in minerals Mr. Skey's method, 428. Sergius Kern's method, 430. Colonel Ross's method, 430. Mr. Blossom's method, 430. Estimation of gold in pyrites, 431. Separation of gold by quartation with zinc Balling's modification of Jiiptner's process, 433. Cabell Whitehead's process, 433. Employment of cadmium in cupellation, 433. Electrolytic separation of gold from other metals E. F. Smith's process, 435. Classen's process, 435. Platinum Detection of small quantities of platinum F. Field's method, 436. Purification Stas's method, 436. Mr. Sonstadt's method, 436. Analysis of platinum ores MM. Deville and Debray's method, 437. Bunsen's method, 440. C. Lea's process, 445. Dr. Wolcott Gibbs's process, 449. Electrolytic precipitation of platinum Classen's method, 452. E. F. Smith's method, 452. Preparation of platinum chloride from residues, 453. Mending platinum crucibles T. Garoide's method, 453. XVlll CONTENTS Palladium Test for the presence of palladium C. Lea's process, 453. Electrolytic separation of palladium Classen's method, 454. E. F. Smith's method, 454. Separation of palladium from copper, 454. Rhodium Separation of rhodium from platinum Wolcott Gibbs's plan, 454. Iridium Separation of iridium from platinum Wolcott Gibbs's method, 455. Electrolytic separation of iridium from platinum Classen's method, 456. Separation from rhodium Claus's method, 456. Osmium Reduction of osmic acid, 457. Separation from iridium (analysis of osmiridium) Wohlers method, 458. Fritzsche and Struve's process, 458. Claus's method, 458. Dr. Wolcott Gibbs's process, 459. Ruthenium Preparation of ruthenium from iridium osmide (osmiridium) Claus's method, 461. Gibbs's process, 462. Estimation of ruthenium, 462. Detection of ruthenium in the presence of iridium C. Lea's process, 463. Wolcott Gibbs's, 463. Dr. Claus's, 464. Separation of ruthenium from iridium Dr. Gibbs's process, 465. Separation of ruthenium from rhodium, 466. From platinum Dr. Gibbs's process, 467. CHAPTER XI SULPHUR, PHOSPHORUS, NITROGEN Sulphur Estimation of sulphur in pyrites In the dry way, 469. D. S. Price's method, 469. P. Holland's process, 471. In the wet way C. R. A. Wright's process, 472. A. H. Pearson's process, 473. R. Fresenius's method, 475. G. Lunge's method, 475. P. Waage's method, 475. Reichardt's process, 476. Messrs. Glendenning and Edgar's process, 476. Estimation of sulphur in iron, steel, and iron ores C. H. Piesse's process, 476. M. Koppmayer's process, 477. T. J. MorrelPs process, 477. Estimation in vermilion, 478. In mineral waters F. Maxwell Lyte's process, 478. W. J. Land's process, 479. Detection of sulphur by means of sodium or magnesium Dr. Schonn's process, 480. Reagent for sulphur Dr. Schlossberger's method, 480. Mr. Brunner's method, 480. Obtaining sul- phuretted hydrogen in the laboratory E. Divers and T. Schimidzu's process, 481. Anomalies in the detection of sulphuric acid Mr. Spiller's method, 481. Of free sulphuric acid in vinegar, 482. Quantitative determination of sulphur Don Klobulow's process, 482. Estimating free sulphuric acid in superphos- phates R. C. Moffat's method, 484. Precautions in precipitating barium sul- phate Fresenius's precautions, 485. Purification of sulphuric acid from arsenic MM. Bussy and Buignet's method, 485. M. Blondlot's method, 485. Maxwell Lyte's process, 485. Detection of gaseous impurities in sulphuric acid Mr. R. Warrington's method, 485. Analysis of sulphuric anhydride and fuming sulphuric acid 0. Clar and J. Gaier's process, 487. Detection of sul- phurous and thiosulphuric acid Dr. Reichardt's process, 488. Estimation of sulphides and hydrosulphites B. Proskauer's process, 488. Phosphorus Detection of phosphorus Modification of Mitscherlich's process, 488. Detection of arsenic in commercial phosphorus C. J. Rademaker's process, 489. Phos- phorus holder, by E. Kernan, 490. Preparation of phosphuretted hydrogen, 490. Distinction between phosphates and arseniates A. H. Allen's observa- tions, 490. Estimation of phosphoric acid By the modified tin process CONTENTS XIX (Keynoso's), 491. By the magnesium process, 492. M. G. Villc's process, 494. T. B. Ogilvie's process, 496. Professor Tollens's process, 496. M. Joulie's process, 497. C. Mohr's method, 497. By the uranium process Mr. Button's method, 499. Special precautions to be taken when iron is present, 500. Preparation of uranium protochloride, 501. A. Kitchin's remarks, 502. F. Jean's method, 502. Carl Mohr's method, 502. Estimation by the bismuth process, 503. A. Adriaanzs's method, 504. By the lead process Mr. Warington's method, 504. By mercury, 506. By iron, 506. By the molybdic acid process, 506. K. Finkener's method, 508. Champion and Pellet's method, 508. Kecovery of molybdic acid Drs. Stunkel and Wetzke and Professor Wagner's method, 509. E. Richters' method, 510. K. Finkener's method, 511. A. Attarberg's method, 512. Estimation by means of oxalic acid B. W. Gerland's method, 512. As calcium phosphate, 513. Estimation of ' reduced ' phosphates in calcium super- phosphate Mr. Sibson's method, 515. Grupe and Tollens's method, 515. M. P. Chastaigne's method, 516. Separation of phosphoric acid from aluminium, 516. From chromium, 516. From bases in general, 517. From iron A. E. Haswell's method, 517. E. Agthe's method, 517. Sir F. Abel's process, 519. Spiller's process, 519. W. Flight's process, 520. M. A. Esilman's process, 520. Separation from silica and fluorine Dr. Gilbert's process, 521. Pre- paration of phosphorous acid, 522. Detection, 522. Estimation MM. Prinz- horn and Precht's process, 522. Nitrogen Estimation by weight Dr. W. Gibbs's method, 523. Detection of 'nitric acid Mr. Blunt's test, 524. M. F. Bucherer's test, 525. Electrolytic determination of nitric acid in nitrates Classen's method, 525. Luckow's method, 525. G. Vort- mann's method, 525. Estimation of nitric acid by the oxidation of an iron proto- salt Pelouze's method, 526. Mr. Holland's modification, 526. Schlcesing's process, 528. J. Boyd Kinnear's process, 529. Estimation in commercial nitrates F. Jean's process, 530. When in the free state, 530. When com- bined with heavy metals, 531. When combined with any base, 531. By fusion or calcination, 532. Detection of nitrous acid T. M. Chatard's method, 532. Dr. A. Jorissen's test, 533. Estimation of nitrites When a considerable quantity is present Mr. Tichborne's processes, 533. When minute quanti- ties only are present Dr. Angus Smith's process, 535. Mr. P. Holland's process, 535. Kolb's process, 537. G. E. Davis's process, 537. Modification of W. Crum's process, 538. Mr. Davis's apparatus, 538. The Tennant nitrometer, 538. CHAPTEE XII IODINE, BROMINE, CHLORINE, FLUORINE (CYANOGEN) Iodine Purification by sublimation, 539. Assay of commercial iodine M. A. Bobierre's method, 539. Detection of minute quantities of iodine C. Lea's process, 540. In sea-water, &c. M. A. Chatin's process, 542. Sergius Kern's process, 543. Estimation of iodine inorganic liquids M. Kraut's process, 543. Reinige's process, 543. Bromine Detection of bromine M. Fresenius's process, 544. Detection of bromides in potassium iodide Dr. E. van Melckebeke's process, 544. Solution of bromine as a reagent M. L. de Koninck's process, 545. Detection of chlorine, iodine, and bromine in organic matter C. Neubauer's process, 545. Estimation of bromine and iodine in presence of chlorine, 545. Mr. Tatlock's method, 546. Application of the foregoing method to the analysis of kelp, 548. Detection of bromine in presence of chlorides, 549. Of chloride in potassium bromide, 549. M. Baudrimont's process, 550. Detection of iodine in potassium bromide, 550. XX CONTENTS Chlorine Estimation of chlorine with the aid of Gooch's method of nitration D. Lindo's method, 551. Professor A. R. Leeds's method, 552. Detection and estimation of chlorine in presence of bromine and iodine G. Vortmann's method, 552. In presence of bromine and chlorine E. Donath's method, 553. Estimation of chlorine in bleaching powder, 553. C. R. A. Wright's method, 554. Of chlorate in bleaching chlorides M. E. Dreyfus's process, 555. Preparation of the sample of chloride of lime, 556. Detection of arsenic in hydrochloric acid, 556. Purification from arsenic Purification of weak acid, 557. Preparation of fuming acid, 557. Detection of hydrochloric acid in solutions of ferric chloride Professor N. Eease's method. 558. By sulphuric acid and acid potassium chromate H. W. Wiley's method, 558. Valuation of potassium chlorate, 551). Fluorine Detection in water, 560. Estimation A. Liversidge's process, 560. Mr. Chap- man's process, 561. Volumetric estimation of fluorine S. L. Penfield's method, 561. CHAPTER XIII CARBON, BORON, SILICON Carbon Assay of animal charcoal Dr. Wallace's process, 564. Estimation of the decolour- ising power of animal charcoal Mr. Arnot's precautions, 565. Volumetric estimation of carbonic acid in animal charcoal Dr. Scheibler's process, 567. Modification of Scheibler's apparatus By E. Nicholson, 574. By R. Warington, 576. Proximate analysis of coal, 576. Professor G. Hinrichs's process, 577. Estimation of the volatile matter, 577. Influence of drying the coal before ignition, 578. Of cooling after ignition over the Bunsen burner, and before ignition over the blast-flame, 579. Of repeated heating, 579. Of protracted heating, 580. Of the degree of heat, 580. Result, 580. Estimation of the moisture, 581. Of hygroscopic water, 581. Of carbon and hydrogen, 581. Calculation of the calorific power, 582. On the slow oxidation of coal, 582. Estimation of ash, 583. Dr. F. Muck's method, 583. Determination of specific gravity, 585. Calculation of results, 585. Assay of coal before the blowpipe, 585. B. S. Lyman's method, 586. Estimation of sulphur in coal and coke Mr. Crossley's method, 587. Dr. T. M. Drown's method, 587. M. A. Eschka's method, 588. Valuation of coal for the production of illuminating gas, 589. Coal gas Detection of air in coal gas, 589. Estimation of sulphuretted hydrogen in coal gas Dr. Wagner's apparatus, 590. Detection of carbon disulphide in coal gas Dr. Herzog's method, 593. Of sulphur, 594. Estima- ation of the total amount of sulphur in coal gas Dr. Letheby's method, 594. Mr. A. Ellissen's method, 595. Valentin's process, 596. Carbonic Acid Estimation in natural water M. Lory's process, 598. In artificial mineral waters Mr. H. N. Draper's process, 599. In solid carbonates Sir C. Cameron's apparatus, 601. Estimation of carbonic acid Mr. T. S. Wadding's apparatus, 601. Boron Detection in minerals Professor Wohler's process, 602. Dr. M. W. Iles's process, 603. Estimation of boracic acid Professor Wohler's process, 603. A. Ditte's method, 603. Analysis of borates and fluoborates Marignac's method, 604. Silicon Decomposition of silicates in the wet way, 605. By means of a fluoride and acid C. E. Avery's method, 605. Of hydrofluoric acid N. S. Maskelyne's method, 606. Decomposition of silicates in the dry way, 607. By hydrofluoric acid at a red heat M. F. Kuhlmann's method, 607. By fusion with caustic alkali CONTENTS XXI Mr. Iles's method, 608. Mr. W. Bettell's method, 608. With baryta M. A. Terrell's method, 609. With a fluoride F. W. Clarke's method, 609. With lead oxide G. Bong's method, 609. With bismuth subm'trate W. Hempel's method, 609. Separation of silica in the analysis of limestones, iron ores, &c. Dr. Percy's process, 611. H. Rocholl's process, 611. Estimation of ferrous oxide in silicates W. Earl's process, 613. W. Knop's method, 613. Separa- tion of crystalline silicic acid, especially quartz, when mixed with silicates E. Laufer's process, 615. Estimation of clay in arable soils Th. Schlo3sing's method, 615. CHAPTEE XIV ELECTROLYTIC ANALYSIS, GAS ANALYSIS Electrolytic Analysis . A. Classen's method, 617. The performance of the analysis, 619. Notes on the work, by Dr. T. O'Connor Sloane, 626. Gas Analysis Analysis of a mixture of oxygen, carbonic acid, and nitrogen In the cold, 628. With heat, 629. Vogt's apparatus, 629. Mixture of oxygen, hydrogen, and nitrogen, 630. Of hydrogen, marsh gas, and nitrogen, 630. Of sulphuretted hydrogen, carbonic acid, and nitrogen Bunsen's method, 631. Of hydro- chloric acid, sulphuretted hydrogen, carbonic acid, and nitrogen, 631. Of sulphurous acid, carbonic acid, oxygen, and nitrogen, 632. Sulphuretted hydro- gen, carbonic acid, hydrogen, and nitrogen, 632. Carbonic acid, carbonic oxide, hydrogen, and nitrogen, 632. Carbonic acid, carbonic oxide, hydrogen, marsh gas, and nitrogen, 633. And olefiant gas, 633. Rapid analysis of mixtures of gases C. Stammer's apparatus, 634. F. M. Raoult's modification, 634. Wilkinson's modification, 635. A. H. Elliott's apparatus, 635. T. M. Morgan's apparatus, 638. C. Winkler's apparatus, 639. Estimation of aqueous vapour, 642. Carbonic acid, 642. Nitrogen, 642. Sulphurous acid, 643. Nitric oxide and nitrous acid, 644. Chlorine, 644. Hydrochloric acid, 644. Ammonia, 644. Sulphuretted hydrogen, 644. Carbonic oxide, 645. Nitrous oxide A. Wagner's method, 645. Of free oxygen in water- -C. C. Hutchinson's modi- fication of Schiitzenberger's process, 646. CHAPTER XV MISCELLANEOUS PROCESSES AND GENERAL METHODS OF MANIPULATION Sensitive reagent for gaseous ammonia - G. Kroupa's method, 649. Standard soda solution Gerresheim's process, 649. New form of burette by P. Casamajor, 649. Ammonia-free water D. B. Bisbee's method, 652. Simple method of estimating the temporary hardness of water M. V. Wartha's method, 652. New tests for reducing agents E. Smith's method, 653. Improved methods of oxidation Professor Storer's method, 653. Blowpipe analysis Employment of silver chloride H. Gericke's process, 654. Quantitative spectral analysis M. Hiifner's method, 656. M. Vierordt's method, 657. New method of quan- titative chemical analysis, 657. H. Carmichaers apparatus, 658. An im- proved mode of filtration Bunsen's method, 663. I. B. Cooke's method, 664. Separation and subsequent treatment of precipitates F. A. Gooch's method, 666. New method of filtration by means of easily soluble and easily volatile filters F. A. Gooch's method, 669. Rapid separation of slimy precipitates K. Zulkowsky's process, 671. Separation of minerals for analysis E. Sonstadt's method, 671. Incineration of filters, 671. Indicators for alkalinity R. T. Thomson's method, 672. Dr. Lunge's method, 673. Ultramarine test- paper, 674. Application of hydrogen peroxide in chemical analysis, 675. Preservation of platinum crucibles Erdmann's observations, 676. His experiments with Pettenkofer, 677. Analysis of the gold and platinum salts of organic bases M. C. Scheibler's process, 678. To prevent the bumping of boiling liquids H. Miiller's method, 678. On the correct adjustment of chemical weights W. Crookes's method, 679. XX11 CONTENTS CHAPTEE XVI Useful Tables Conversion of Centigrade and Fahrenheit degrees, 686. Mutual conversion of French and English weights and measures, 687. Eelative value of French and English weights and measures, 690. Baum6's hydrometer, 692. Table for liquids heavier than water, 693. For liquids lighter than water, 693. TwaddelPs hydrometer, 694. Percentage of soda in aqueous solutions of various specific gravities, 694. Of caustic potash in aqueous solutions of various specific gravities, 694. Of ammonia in aqueous solutions of various specific gravities, 695. Of nitric acid in aqueous solutions of various specific gravities, 695. Of sulphuric acid in aqueous solutions of various specific gravities, 696. Of hydrochloric acid in aqueous solutions of various specific gravities, 696. Table of atomic weights, 697. INDEX 699 SELECT METHODS CHEMICAL ANALYSIS CHAPTER I POTASSIUM, SODIUM, LITHIUM, C.ESIUM, KUBIDIUM (AMMONIUM) POTASSIUM Test for Potassium M. L. DE KONINCK finds that if a 10 per cent, solution of sodium nitrite is mixed with cobalt chloride and acetic acid, the liquid forms a reagent for the detection of potassium much more sensitive than platinum chloride. An immediate yellow precipitate is obtained in a solution containing one part potassium chloride in 100 parts of water. It is still perceptible if diluted to 1 : 1000, but in the proportion of 1 : 2000 a precipitate is no longer obtained. Ammonia gives a simi- lar but much less sensitive reaction ; sodium, magnesium, calcium, barium, strontium, iron, aluminium, and zinc salts are not precipitated by this reagent. Estimation of Potassium (A) Whenever possible, potassium should be estimated in the form of platinum salt. The results are exact and unvarying, and they are attended with the great advantage that, owing to the high atomic weight of platinum, any errors of manipulation, unless beyond the limits of probability, affect but slightly the percentage result of potassium. To obtain trustworthy results several precautions have to be attended to ; these have been fully described by Messrs. F. T. Teschemacher and J. Denham Smith, and the following process, which the author has verified on many occasions, is condensed from their description (C7iemica News, xvii. 244). It is assumed that the salt under examination is a sample of com- mercial potassium chloride, or that the alkalies exist in such a condition 2 SELECT METHODS IX CHEMICAL AXALYSIS that, by the addition of hydrochloric acid in excess, they will be con- verted into chlorides. Take 500 grains of the salt, previously care- fully ground and mixed, and dissolve it in water, filtering if requisite, and washing the insoluble portion till solution and washings measure 5000 grains. Mix this solution by pouring from one glass to another, and take 500 measured grains of the liquid (measured accurately, always at one level of the eye and one level of liquid and line of measurement), dilute these 500 grains till they measure 5000 liquid grains, and mix ; 1000 measured grains of this solution contain 10 grains of the original salt. Now, to 1000 measured grains of this solution, add excess, say 50 grains, of hydrochloric acid, if the alkalies are not present as chlorides, and pour into a shallow porcelain dish, making, with the rinsings of the measure, &c., some 1500 grains of solution. Heat the dish and contents nearly to ebullition, and add to the hot liquid so much solution of platinum chloride as is equal to 20 grains of the metal. Evaporate this mixture on the water-bath nearly to dryness ; that is, to the point when the thick syrupy liquid, on the momentary removal of the dish from the bath, passes into an orange-coloured pasty mass. At this point remove the dish from the bath, and at the same instant and before the dish and its contents have had time to cool, drench it with 500 to 600 grains of rectified methylated spirit, containing about 15 per cent, of water and 85 of alcohol ; mix rapidly by imparting a rotatory motion to the contents of the dish ; then cover it and allow it to digest for five minutes. Have a filter ready, not too- small, of 400 to 500 grains capacity, in a funnel with a cover : wash the filter first with hot water, and then with spirit, and after a short digestion pour the alcoholic solution of the platinum salts on to the filter, draining the crystalline solid scales of the potassium salt as dry as possible, and again drench, agitate, and digest the insoluble salt . with spirit ; repeat this a third time, when the spirit will come away nearly colourless. Now collect the light orange crystalline scales of the potassium platino- chloride on the filter, by means of a wash-bottle, and, if need be, wash with spirit till it passes perfectly colourless. It is very advisable to wash the potassium platiiio-chloride by decanta- tion, and finally by a stream of spirit from a wash-bottle, to avoid the use of stirrers so as to prevent the scales being broken down, and to keep both dish and funnel lightly covered till the washing is completed. There is now nothing more to be done than to dry and weigh the potassium platino -chloride, and to ignite and weigh the filter and add this to the weight of the salt. Owing, however, to the crystalline nature of the salt thus obtained, but a slight stain adheres to the filter, so that the loss by ignition is very minute and does not affect the result. As this crystalline precipitate is not hygrometric, its weight is easily and accurately determined. ESTIMATION OF POTASSIUM 3 Tn this process the following points must be chiefly attended to : I. Strength of solutions. II. Use of platinum chloride in large excess, about 20 grains of metallic platinum to 10 grains of the salt examined. III. Heating of solutions, and evaporation so conducted as to obtain the potassium salt in a crystalline scale-like condition. IV. Evaporation on water-bath to a pasty condition no further. V. Drenching with spirit whilst the salt and dish are hot, and instantly on removal from water-bath. VI. Washing by decantation, and avoiding breaking down of the crystalline precipitate. In practice, the process is a rapid one, from beginning to end requiring about two hours less time, indeed, than is frequently expended in merely washing the dense pulverulent precipitate which is obtained by the usual mode of manipulation. The results are very accurate. The authors take 244-20 as the equivalent of the potassium platino-chloride. (B) Precht conducts the determination of potassium as follows : The sulphuric acid is removed by barium chloride in a solution con- taining 0'5 of hydrochloric acid to 1 of the salt. The clear liquid should contain neither barium chloride nor sulphuric acid. Traces of the latter may be removed in the measuring vessel by finely pulverised barium chloride. Small quantities of sulphuric acid are admissible if the solution with platinum chloride is not evaporated quite to dryness. In acid solutions the objection to the removal of sulphuric acid by means of barium chloride, viz. that alkalies are carried down along with the barium sulphate, has little weight. In neutral solutions so much potassium sulphate is thrown down that an error of 1 per cent, may be occasioned. In evaporating down with platinum chloride care should be taken that large crystals of sodium platino-chloride are not formed which would interfere with washing. The latter process is best performed with hot alcohol, there being no danger of the reduction of the platinum. A mixture of alcohol and ether is not to be recommended, nor an addition of glycerine. For the determination of small quantities of potassium chloride along with an excess of sodium chloride, Precht evaporates 10 to 100 grammes along with a solution of sodium platino-chloride of known strength. The potassic salts are thus thrown dow.n, the excess of the sodium compound is washed away with the absolute alcohol, and the platinum reduced on the filter and weighed. (C) The committee appointed by the chemical section of the British Association reports that (1) potassium in the form of pure chloride can be determined with great accuracy by precipitation as platino-chloride. If a large excess of platinum solution be employed, and alcohol only used for washing the precipitate, the results have a tendency to exceed the truth. By avoiding the use of a large excess of platinum solution B 2 4 SELECT METHODS IN CHEMICAL ANALYSIS more accurate results are obtained. If a small volume of platinum solution be employed in the first instance for washing the precipitate (as recommended by Tatlock), and the washing then completed with alcohol in the usual way, the results are accurate. Potassium platino- chloride appears to be practically insoluble in a concentrated solution of platinum chloride. (2) In presence of a considerable proportion of sodium chloride, washing the precipitate with alcohol alone tends to give results in excess of the truth. If the precipitate be first treated with platinum solution, the results are somewhat low, apparently owing to the solu- bility of the precipitate in solutions of sodium platino-chloride ; the error increases with the amount of sodium, but is never very large, and a correction may be applied if desired. (3) If Tatlock's method be employed, there is no occasion to separate sulphates, nitrates, or magnesium ; but if the amount of chloride present is insufficient for the existence of all the potassium as potassium chloride, the deficiency must be supplied by the addition of sodium chloride or hydrochloric acid. The results obtained are in many cases accurate, but have a tendency to be somewhat below the truth. (4) There is practically no advantage in drying potassium platino- chloride at 130 C. rather than at 100 C. ; the loss at the higher temperature was found to exceed 0'07 per cent, of the weight of the precipitate, but is probably governed by the conditions of precipitation. (5) The committee is of opinion that a preliminary washing of the precipitate of potassium with a solution of platinum chloride is a valuable modification of the usual process. As the method so modified is capable of direct application to commercial potassium salts, and does not necessitate the removal of sulphates, nitrates, or magnesium, the committee considers that it deserves to be generally applied to the determination of potassium in commercial products containing it. (D) Mr. E. Tatlock's modification of the platinum process above referred to is as follows : Dissolve 35 grammes of the sample in water, filter if necessary, and make up the bulk to 500 c.c. Deliver 10 c.c. of the solution into a small porcelain basin, add 20 c.c. of water, stir, and then add 30 c.c. of a solution of platinum chloride containing 7 grammes of metallic platinum in every 100 c.c. Evaporate on a water-bath, but not to perfect dryness. Add a few drops of water, and evaporate again ; remove the basin and stir the precipitate well with 2 c.c. of the platinum solution ; then wash the precipitate on the filter with 1 c.c. more. Now wash the basin and filter and contents with the smallest possible quantity of alcohol of 95 per cent. Dry the filter containing the precipitate on the water-bath ; remove the pre- cipitate as completely as possible into a small platinum capsule ; dry at 100 C. and weigh. Ignite the 'filter with trace of adhering ESTIMATION OF POTASSIUM 5 precipitate ; weigh the residue which is left ; calculate its weight of 2(KCl)PtCl 4 , and add the weight to that of the precipitate already obtained. (E) The process employed at Leopold's-hall and Stassfurtis described by Drs. Zuckschwerdt and West as follows : 10 grammes of a well- mixed sample are dissolved in a 500 c.c. flask filled up to the mark, shaken, an aliquot part filtered, and 20 c.c. (= 0-4 gramme) measured off. This is mixed in a porcelain capsule with 7 c.c. of a solution of platinum chloride, containing 10 grammes of platinum in 100 c.c. As commercial samples rarely contain more than 20 per cent, of sodium chloride, whilst the above quantity of platinum would suffice for 0*4 gramme of sodium chloride at 100 per cent., there is always a considerable excess of platinum chloride present. The contents of the capsule are then evaporated on the water-bath with frequent stirring, to the consistency of syrup, so that when cold the mass appears dry. The free hydrochloric acid is thus chiefly expelled. When cold the mass is covered with 10 c.c. of alcohol at 95 per cent., well rubbed up with a glass rod, and the washings poured upon a tared filter. Alcohol is again spirted on in smaller quantity ; the mass is again rubbed up, the washings poured off, and the operation is repeated once more. As a rule, at the second decantation the colour of the washings, and consequently the proportion of the platinum double salt, will be very slight, and in the third operation it disappears altogether ; otherwise the operation must be repeated once more. The precipitate, which now consists of perfectly pure potassium platino-chloride, is brought upon the filter by means of the alcohol washing-bottle ; and after drying for half an hour at 110 to 115, it is weighed under the same conditions as it had been when empty. The total quantity of alcohol consumed is in general 50 c.c. The errors fall within the narrowest limits of permissible experimental errors, and could scarcely be removed or avoided by greater complication. (F) MM. Coren winder and G. Coutamine add to the portion taken for analysis a slight excess of hydrochloric acid, and then, without taking any notice of the possible presence of sulphuric acid, silica, or phosphoric acid, they evaporate on the water-bath, after having added a sufficiency of platinum chloride. The potassium platino-chloride thus obtained is digested with alcohol at 95 mixed with ether, and washed in the ordinary way with the same liquid. When this opera- tion is complete, boiling water is poured upon the filter by means of a pipette, till the platino-chloride is entirely dissolved, and the filtered liquid is collected. Water containing sodium formate is then heated, and whilst it is boiling the preceding solution of potassium platino- chloride is carefully poured into it by degrees. In a few moments the platinum is thrown down as a black powder, which merely needs to be washed, dried, heated to redness, and weighed in order to find the quantity of potassium present in the sample. 6 SELECT METHODS IN CHEMICAL ANALYSIS (G) Dr. F. Mohr estimates potassium by titrating the chlorine con- tained in the platino-chloride. He decomposes this salt by fusing it in a platinum crucible, with twice its weight of sodium oxalate. After lixiviation the chlorine is determined by a decinorinal silver solution. (-ZJ) M. L. de Koninck throws down potassium with the ordinary precautions by platinum chloride ; the precipitate is collected on a filter, washed in alcohol, and immediately dissolved in boiling water. The solution is reduced hot by magnesium. All the chlorine of the platino-chloride is obtained in the form of a soluble chloride and a black precipitate of reduced platinum. At the same time the magne- sium decomposes the water, yielding hydrated magnesia with an escape of hydrogen. When the reduction is complete the mixture is filtered, and in the neutral solution the chlorine is determined in the usual manner with a standard solution of silver nitrate, using potassium chromate as indicator. The following processes are based upon different reactions : Estimation of Potassium Sulphate (A) Dr. West finds that the ordinary method of removing the sul- phuric acid by means of barium chloride and converting the excess of the latter into barium carbonate by evaporation and ignition with oxalic acid, is open to a double objection. Barium sulphate retains much potassium chloride, even in an acid solution, and during the ignition a further quantity of barium chloride is lost by volatilisation. (B) At Stassfurt the following method is in use : 10 grammes of the salt in question are placed in a 500 c.c. flask with 350 to 400 c.c. of water and 25 c.c. of hydrochloric acid at 25 per cent., and a solution of barium chloride (almost saturated and containing 50 c.c. aqueous hydrochloric acid per litre) is gradually added, boiling up each time till the sulphuric acid is entirely thrown down, a point easily reached with practice. A very small excess of sulphuric acid has no effect upon the result, whilst an excess of barium chloride increases the result : or the sulphuric acid in the salt may be determined volu- metrically in a separate portion with barium chloride and potassium chromate, and the quantity of barium chloride thus found is added to the potassium salt in an acid solution. In evaporating, care must be taken that the free hydrochloric acid is entirely expelled (which is not easy in presence of much magnesia), otherwise an error may arise of 0'5 per cent. The correction for the potassium chloride retained by the barium sulphate is as follows : in 10 grammes of potassium sulphate there are 4'59 sulphuric anhydride=13'79 grammes barium sulphate, which occupy the space of 3 c.c. Each c.c. of the precipitate contains as much potassium as 6 c.c. of the solution. ESTIMATION OF POTASSIUM 7 Estimation of Potassium by Means of Perchloric Acid (A) Armand Bertrand finds that if the substance in question con- tains an ammoniacal salt the ammonia must be expelled by boiling with a little caustic lime. The solution should be perfectly clear. The filtered solution of the sample is evaporated on the water-bath in a small porcelain capsule with 5 c.c. of perchloric acid at 45 B., until the volume of the liquid is reduced to about 10 c.c. The capsule is taken off the water-bath, alcohol at 95 per cent, is added : it is cooled, and the potassium perchlorate is collected on a small filter. The precipitate is washed with alcohol at 95 per cent., containing 10 per which is near enough for all practical purposes. The result obtained deducted from 100, the remainder will be the percentage of potassium sulphate, and from these results the quan- tities of each of the alkalies sought may be calculated. Of THE [UilTiKSXTT] 22 SELECT METHODS IN CHEMICAL ANALYSIS Estimation of Potash, and Soda in Minerals , W. Knop and J. Hazard dissolve in hydrofluoric acid, evaporate, and drench the residue with concentrated sulphuric acid, thus removing the bulk of the silicon fluoride. The sulphuric acid is then evaporated off, the dry residue moistened with five or six drops of concentrated sulphuric acid, heated, drenched with 150 c.c. water, and barium hydrate added till red litmus-paper is turned distinctly blue. The mixture of barium sulphate, silica, alumina, magnesia, and ferric oxide is then filtered off and well washed. The filtrate is evaporated to (kyness, adding, when it is concentrated down to about 200 c.c., a few grammes of dry ammonium sesquicarbonate. When perfectly dry the residue of barium and calcium carbonates is extracted successively fifteen times, each time with 20 c.c. water, the liquid being each time filtered through a small filter of 3 to 4 c.m. diameter into a platinum capsule, and evaporated to dryness. The residue is drenched again with 20 c.c. water, the water is decanted through a similar fresh filter, and the solution, after it has deposited a little barium carbonate with some alumina and iron, is collected along with the washing 1 ; in a fresh platinum capsule. The alkaline carbonate, to which a few more granules of ammonium carbonate have been added, is again dissolved in 20 c.c. water, observing that no residue remains. The liquid is then neutralised with hydrochloric acid, evaporated, the chlorides dried strongly, and the potassium and sodium separated by means of platinum chloride. LITHIUM, CESIUM, AND RUBIDIUM Extraction of Lithium, Caesium, and Rubidium, from Lepidolite The following process has been found to answer well on a large scale : Fuse the mineral at a red heat, pour it into cold water, pul- verise and wash it, and treat the washed mass with twice its weight of hydrochloric acid. After several hours boiling, separate the greater part of the silica, add nitric acid to peroxidise the iron, and precipi- tate by sodium carbonate, the solution being made so weak that the lithium carbonate will not be thrown down. After evaporation in this way in an iron vessel, to separate more magnesium carbonate, saturate with hydrochloric acid and add the proper quantity of potas- sium platino-chloride to precipitate all the rubidium and caesium. The filtered liquid, containing an excess of platinum and lithium, is treated with sulphuretted hydrogen to separate the platinum, then concentrated and mixed with sodium carbonate to precipitate the lithium carbonate. By this method 1000 parts of lepidolite will give LITHIUM, CAESIUM, AND RUBIDIUM 23 78 parts of lithium carbonate, 6'5 parts of rubidium and caesium chlorides, supposing the operation to be continuous. The advantage of this process consists in the direct fusion of the mineral, and it may be applied to all lithian micas. If thallium is present, which is frequently the case, it will be precipitated as thallium platino-chloride along with the rubidium and caesium. Estimation of Lithia by Sodium Phosphate Berzelius detected lithia in Carlsbad water by evaporating the solution of the alkalies with phosphoric acid and sodium carbonate. On treating the whole with water, an insoluble sodium and lithium phosphate remained. This double salt has been shown by C. Kam- melsberg to be a variable mixture of the two phosphates. Mayer, however, contradicted these results and denied the existence of a double phosphate, and contended that the above residue was pure lithium phosphate. C. Rammelsberg has repeated his former experi- ments and, completely confirmed them, preparing synthetically double salts having sodium to lithium as 1 to 3, or 9 to 2, and therefore he concludes that lithium cannot be determined by Mayer's method, which is also recommended by FreseniuS'. The employment of this process for the estimation of lithium in micas has led to too high a percentage of lithium. Lithium and sodium chlorides may be separated by treatment with ether and alcohol. Extraction of Caesium and Rubidium from Mineral Waters Compounds of these rarer alkali metals may be separated in the following manner from saline mother-liquors derived from the evapo- ration of some mineral waters. A boiling dilute solution of platinum chloride added to a boiling, rather dilute solution, containing potas- sium, rubidium, and caesium, will precipitate the latter metals with but a very small proportion of the first. The platinum being removed from this precipitate by means of sulphuretted hydrogen, the alkaline metals are again brought into dilute solution as chlorides ; the solu- tion is heated to boiling, and once more a dilute solution of platinum chloride is added in two portions. After each addition the liquor is filtered, while boiling, through a water-bath filter, and the precipitate is washed in hot water ; the solution is then allowed to cool and deposit. In this way three precipitates are obtained ; the first contains nearly all the caesium, the second almost all the rubidium, and the third, deposited on cooling, is, for the most part, the potassium compound. By repeating these precipitations the compounds may be almost completely separated. The caesium and rubidium may be finally separated from each other by one of the methods subsequently described (page 26). 24 SELECT METHODS IX CHEMICAL ANALYSIS Extraction of Caesium and Rubidium from Lepidolite Dr. Oscar D. Allen, of Yale College, has shown that the lepidolite' occurring at Hebron, in Maine, U.S., contains these metals in con- parative abundance, and he has recommended the following process for their extraction from this mineral. The process used is based upon that employed by Professor J. Lawrence Smith, for the deter- mination of alkalies in silicates (for this process, see page 26). Ten parts of the pulverised lepidolite are first mixed with 40 parts of coarsely powdered quicklime ; a mixture of enough water to slake the quicklime, with hydrochloric acid sufficient to form from 6 to 7 parts of calcium chloride, is next made ready ; the two mixtures are then united and stirred vigorously during the process of slaking, thus intimately blending the mineral with suitable proportions of dry hydrate of lime and calcium chloride. Practically as good results are obtained when the lepidolite is powdered sufficiently fine to pass through a sieve of twenty holes to the linear inch, as when it is more finely pulverised ; the fact being that the foliated structure of the mineral exposes a large surface to the decomposing agency of the lime mixture. This mixture is heated to redness for six or eight hours in Hessian crucibles. Care must be taken to avoid a heat much above redness, as otherwise alkaline chlorides volatilise in dense clouds, and the mass fusing is absorbed to a considerable extent into the crucible and lost. The agglomerated product obtained from the ignition of this mix- ture is detached from the crucible, boiled with water from a quarter to half an hour, and washed till all but a trace of the chlorides are removed. The solution thus procured, containing calcium chloride and the chlorides of the alkali metals, is evaporated till crystals begin to form ; then sulphuric acid is added as long as calcium sulphate separates, taking care to avoid excess : and the whole mass is evapo- rated to dryness and strongly heated to expel free hydrochloric acid. The residue is treated with water, and the small quantity of calcium sulphate which goes into solution is precipitated with ammonium car- bonate. The filtered solution is again evaporated to dryness and ignited. In this manner is obtained a mixture of salts, consisting of the chlorides with a small admixture of sodium, potassium, lithium, rubidium, and caesium sulphates. By treating this by the process of fractional precipitation with platinum chloride, a mixture of the caesium and rubidium platino-chlorides is obtained, in which no potassium can be detected with the spectroscope. The platinum salts are to be gently heated in a current of hydrogen, until a complete reduc- tion of the platinum takes place, when the alkaline chlorides may be extracted with water. By working in the above manner Dr. Allen obtained from 10J kilo- CJESIUM 25 grammes of lepidolite 2169 grammes of crude alkaline chlorides, which yielded 172 grammes of mixed caesium and rubidium platino-chlorides,. equivalent to a yield of about J per cent, of the two metals from the lepidolite. In separating the caesium and rubidium platinum salts from that of potassium, a not inconsiderable amount of these metals goes into solu- tion with the potassium salt, thus materially diminishing the quantity obtained ; much the larger proportion of this loss is rubidium, due to the greater solubility of its platinum salt. This can in great measure be recovered by a repetition of the treatment. Separation of Potassium, Sodium, and Lithium If potassium, sodium, and lithium are present in the same solution,, convert the three into platino-chlorides, extract the sodium and lithium salts with a mixture of alcohol and ether containing a little hydro- chloric acid, and wash with a mixture of absolute alcohol 6 volumes,, ether 1 volume ; the residue is pure potassium platino-chloride. Direct experiments show that the above method is not vitiated in any degree by the presence of hydrochloric, nitric, phosphoric, arsenic, or boric acids, or salts of magnesium, zinc, manganese, iron (ferrous or ferric),, aluminium, nickel, or copper. Antimony Chloride as Reagent for the Caesium Salts (A) If the solution of caesium salt, not too dilute, is mixed with a solution of antimony chloride in concentrated hydrochloric acid, a white crystalline precipitate is at once formed which, according to E. Godeffroy, does not disappear on the addition of hydrochloric acid. The solutions of the other alkali metals yield no precipitate if similarly treated. The precipitate may be filtered, washed with concentrated hydrochloric acid, and re-dissolved in the same acid much diluted. The solution yields on evaporation well -developed, hard, permanent crys- tals belonging to the hexagonal system. They may be obtained pure by repeated solution in dilute hydrochloric acid, and recrystallisation. They contain 33-419 per cent, of chlorine, and of antimony 30-531 per cent., corresponding to the formula SbCl 3 CsCl. This salt is decom- posed on the application of heat, and on treatment with water. It is completely soluble in dilute acids. (B) Charples and Stolba observed a similar reaction of the caesium salts with stannic chloride. The rubidium salts, however, give with tin chloride a precipitate which is very sparingly soluble. The pre- sence of ammonia in the liquid contaminates the double caesium and tin chloride with ' pink salt.' The reaction with antimony chloride is not interfered with either by ammonia or rubidium. The liquid must be strongly acid to prevent the precipitation of^ antimony oxychloride. 'Of THS^ TJBriVERSITY; 26 SELECT METHODS IN CHEMICAL ANALYSIS Separation of Caesium from Rubidium (A) The plan recommended by Dr. Allen for separating these metals depends upon the fact that bitartrate of rubidium requires about eight times as much water for its solution as the caesium bitartrate, and hence they are easily separated by crystallisation. The mixed chlorides are converted into carbonates by first con- verting them into sulphates, separating the sulphuric acid by caustic baryta, and removing the excess of baryta by carbonic acid. To the alkaline solution thus obtained twice as much tartaric acid is added as is necessary to neutralise it. This solution is concentrated until it is nearly saturated at 100 C. The crystals, which deposit on cooling, show the rubidium lines more intensely than did the original mixture, whilst the caesium lines are much fainter. This product is dissolved and recrystallised from hot saturated solutions three times. The caesium reaction in these successive crops diminishes until, in the fourth, it disappears, leaving the rubidium spectrum in entire purity. The solution from which the first crystals have been removed is concentrated to nearly one-half its original volume, when, on cooling, a very small quantity of salts of the two alkalies is deposited. On repeating this operation three times, a portion of the solution, evapo- rated to dryness and examined by the spectroscope, gives only the lines belonging to caesium. The several intermediate products contain- ing both alkalies are then united, and another portion of each salt is separated from them in the same manner. By repeating this process of fractional crystallisation four times, about 90 per cent, of a mixture of these alkalies may be separated in a perfectly pure state. It re- quires no great expenditure of time, since the solutions employed can be concentrated at high temperatures, and, on cooling, immediately deposit well-formed crystals. (B) Bunsen's recent method for the separation of caesium and rubi- dium is somewhat similar to the above, but it has the advantage that it can be effected when working on less material. It is as follows : In a mixture of pure caesium and rubidium chlorides the chlorine is determined, and from its amount that of rubidium is calculated. The chlorides are converted into carbonates, and to the latter salts a little more tartaric acid is added than is necessary to produce neutral caesium tartrate and rubidium bitartrate. The mixture, dried and pulverised, is brought upon a funnel, whose neck is stopped by a small filter, and the whole is placed in an atmosphere saturated with moisture. The neutral caesium salt deliquesces, and passes the filter, while the acid rubidium salt remains behind. Separation of the Alkalies from Silicates not Soluble in Acids One of the best processes for separating the alkalies from silicates is the one devised by Professor J. Lawrence Smith, M.D. It is ALKALJKS IN INSOLUBLE SILICATES 27 sufficiently accurate to be available for their quantitative estimation. This process has scarcely received the attention it deserves, and as it appears to be almost unknown in England, it is considered advisable to give the description mainly in Dr. Smith's own words rather than in a condensed abstract. 1. ' In this description of separating and determining the alkalies, it is my intention to give the minutest details, although it may be thought useless by some ; but numerous analyses have given me the experience here detailed ; and I am convinced that analytical chemists, if they follow them out, will never resort to any other known method after a few trials ; and if. there be a better method, it is yet to be dis- covered. The presence of boracic, hydrofluoric, and phosphoric acids in the minerals in no way interferes with the process. Even in silicates soluble in acids, I prefer this method, in common with other analysts, for its ease and accuracy. 2. ' During the latter part of 1852 I made the researches, the de- tails of which were published early in 1853. 1 Since that time I have employed the process many hundreds of times with the greatest satis- faction, most accurate results, and ready manipulation ; some minor points were not completed satisfactorily until several years after the first notice of the method ; these have been subsequently perfected, and in my mind there is nothing further now to be desired. I might state that many analytical chemists have for years constantly used this process to the exclusion of all others. 3. ' The purpose of this article is to give all the perfections, and a minute detail of the manipulations, with whatever precautions are necessary, all of which are simple and easily executed. In the two articles on the subject of alkali determination in minerals, published in 1853, the whole subject was reviewed, which it is needless to recur to now. I then reviewed the process by caustic baryta and its salts, by hydrofluoric acid, also detailing some experiments on the separation of the different alkalies from each other, microscopic examinations of the same, &c. It was shown that after the caustic alkalies, the most powerful agent to attack silicates at a high temperature is caustic lime, a fact not new to chemists, for as early as 1847 I used this process for attacking silicates, and others had done the same prior to that period. But for the purpose of arriving conveniently at a quantitative determi- nation of the alkalies in silicates, certain methods of manipulation, quantity of material, admixture, &c., had to be discovered, and in them resides the success of my process converting the most difficult parts of the analysis of a silicate into the easiest. 4. ' The methods of analysis of the silicates by caustic baryta and 1 'Shortly after my first publication, M. St. Claire Deville made known his method of analysing the silicates by fusion with lime ; but the nature of his process and the objects to be arrived at were quite different from those attained by the process under consideration. 28 SELECT METHODS IN CHEMICAL ANALYSIS its carbonate are well known ; but for various reasons fully detailed by Kose, in his " Analytical Chemistry," are now no longer used. The method still employed extensively is the one proposed by Berzelius, with hydrofluoric acid, and when applied with numerous precautions, it seems to decompose all silicates ; still, according to Rose, there are siliceous compounds that cannot be completely decomposed by hydro- fluoric acid. 1 Dismissing all criticism, I at once proceed to the method which is the subject of this article. 5. * Decomposition of Silicates by Ignition with Calcium Carbonate and Sal- Ammoniac. This mixture of calcium carbonate and sal-ammoniac is used simply for the purpose of bringing in a most thorough manner caustic lime to act upon the silicates at a red heat. 2 The first step in the process is to have pure carbonate of lime. 6. ' This is made in my laboratory as follows : Take as good marble as can be conveniently found (not dolomitic), or calc spar, and dissolve in hydrochloric acid. It is not necessary that the acid be perfectly pure. Add an excess of the marble and warm the solution : to it add lime-water or some milk of lime, made from pure or nearly pure lime, until the solution is alkaline to test-paper; the lime is added to precipitate any magnesia, phosphate of lime, &c., that may have been in the marble. Filter this solution, and after heating it to at least 160 F., precipitate with ammonium carbonate. 3 The calcium car- bonate thus precipitated is to be thrown on a filter and well washed with pure rain-water or with distilled water. 7. * Thus prepared, the calcium carbonate is a dense powder and perfectly pure : or, if it contain any impurity, it will be a trace of barium or strontium carbonate which in no way interferes with the use of the calcium carbonate. 8. ' Sal- Ammoniac. To give to this reagent the most convenient form, take fragments of clean sublimed sal-ammoniac, dissolve them in water over a gentle fire, filter, evaporate the filtered solution over a steam-bath, or on a sand-bath, or any other convenient gentle heat, and as the small crystals deposit themselves, stir the solution to keep the crystals small ; when one-half or two-thirds of the sal-ammoniac 1 ' The process used by Deville in fusing with lime is in most cases better than that by hydrofluoric acid, and one that I should use in preference to all others, except the one now being described. 2 ' Calcium chloride at a red heat will dissolve more or less caustic lime. 3 ' This precaution must not be overlooked, as it is desirable to obtain the pre- cipitated calcium carbonate as dense as possible. If the ammonium carbonate be added to the cold solution, the precipitate, at first gelatinous, will ultimately become much more dense and settle readily ; the same is true if the mixture be heated after the addition of the ammonium carbonate ; but in neither case will it be as dense as when the carbonate is added to the hot solution of calcium chloride. The reaction in this process of analysis is in no way affected by the form of the calcium carbonate ; but by using the denser form, the mixture occupies less space in the crucible in which it is heated. ANALYSIS OF SILICATES 29 is deposited, pour off the liquid without waiting for it to cool, throw on a cotton filter, and dry the crystals at the temperature of the atmosphere. In this way, sal-ammoniac is furnished that is easily pulverised. 9. ' Vessels for Producing the Decomposition. The ordinary platinum crucible can be employed for this purpose, and is now most commonly used, and for many years was used by myself. It was, how- ever, found that, while this method exceeds in precision and ease all other known methods for alkali determinations in silicates, there was yet a very minute quantity of alkalies lost by volatilisation, and while the method gave satisfaction to those who used it, I yet continued my researches to overcome even this small loss. This has been success- fully accomplished, and for some time I have been in the constant habit of using an improved form. Instead of the ordinary platinum crucible, I use an elongated one, which may be made of various dimen- sions. The one employed, with from ^ to 1 gramme of silicate, is of the following form and dimensions. 10. ' An elongated slightly conical crucible with rounded bottom, and having a cover with or without a central wire to hold the cover ; its length is 95 millimetres ; diameter of opening 22 millimetres ; dia- meter of small end, just at the turn of the bottom, 16 millimetres ; and weight about 35 or 40 grammes. It can be made lighter, but experi- ence has shown that it is better if stiff and solid. Messrs. Johnson and Matthey, Hatton Garden, London, have made a number for me, and they have my drawings and directions. It is thus made for the purpose of having that portion of the crucible containing the mixture heated strongly, while the upper portion is below a red heat. 11. ' Manner of Heating the Crucible. If the ordinary crucible be used, it is heated in the manner usually employed for the fusion of silicates. If the new form of crucible be employed, then the upper part may be grasped by a convenient metallic clamp in a slightly in- clined position, and a moderate blast from the table blowpipe made to play upon it for about 25 or 30 minutes. But now gas is to be found in every well-mounted laboratory, Bunsen burners of all dimensions are used, and when properly applied, can be made to give gradations of heat, from the mildest to that sufficient to melt cast-iron. A simple, cheap, and convenient furnace, with a properly arranged draught, can be made to accomplish all silicate fusions without the aid of any manual labour, and therefore I employ such an apparatus, of which a descrip- tion will be given at the end of this article. 12. ' Method of Analysis. We have now the pure calcium car- bonate, granular sal-ammoniac, and the proper crucible. The silicate is to be well pulverised in an agate mortar ; l for the analysis I take 1 ' While in all mineral analyses, thorough pulverisation of the mineral is usually essential, still it is a singular fact that very good analyses can be made with this method, even when the powder is tolerably coarse, and in some experiments with 30 SELECT METHODS IX CHEMICAL ANALYSIS \ or 1 gramme, the former is most commonly used, as being sufficient, and best manipulated in the crucible ; a gramme, however, may be conveniently employed. The weighed mineral is placed in a large agate mortar, or better in a glazed porcelain mortar of $ to 1 pint ca- pacity. Weigh out an equal quantity of the granular sal-ammoniac (a centigramme more or less is of no consequence), put it in the mortar with the mineral, rub the two together intimately ; after which add 8 parts of calcium carbonate in three or four portions, and mix inti- mately after each addition ; empty the contents of the mortar com- pletely upon a piece of glazed paper, that ought always to be under the mortar, and introduce into the crucible. The crucible is tapped gently upon the table and the contents settled down. 13. ' It is then clasped by a metallic clamp in an inclined position, or it is placed in the support referred to in the latter part of this article, leaving outside about ^ or inch ; a small Bunsen burner is now placed beneath the crucible, and the heat brought to bear just about the top of the mixture, and gradually carried toward the lower part, until the sal-ammoniac is completely decomposed, which takes about 4 or 5 minutes ; heat is then applied in the manner suggested, either with the blast or with the burners referred to, acting by its own draught, and the whole kept up to a bright red heat, for from 40 to 60 minutes. It is well to avoid too intense a heat, as it may vitrify the mass too much. 14. * The crucible is now allowed to cool, and, when cold, the con- tents will be found to be more or less agglomerated in the form of a semi-fused mass ; a glass rod or blunt steel point will most commonly detach the mass, which is to be dropped into a platinum or porcelain capsule of about 150 c.c. capacity, and 60 or 80 c.c. of distilled water is added. In the course of a longer or shorter space of time, the mass will slake and crumble after the manner of lime ; still better, this may be hastened by bringing the contents of the capsule to the boiling- point, either over a lamp or a water-bath. At the same time, water is put into the crucible to slake out any small particles that may adhere to it, and subsequently this is added to that from the capsule, washing off the cover of the crucible also. 15. ' After the mass is completely slaked, the analysis may be pro- ceeded with, although, as a general rule, I prefer to allow the digestion to continue for six or eight hours ; this, however, is not necessary. If the contents of the crucible are not easily detached, do not use unnecessary force, as the crucible may be injured by it, but fill the crucible to about two-thirds of its capacity with water, bring almost to the boiling-point and lay it in the capsule, with the upper portion resting on the edge ; the lime will slake in the crucible, and then may lepidolite, powder was used with much of it in particles from ^ to ^ of an inch in size, giving good results. Notwithstanding this, thorough trituvation of the mineral is recommended. ANALYSIS OF SILICATES 31 bo washed thoroughly into the dish, and, as before, the cover is to be washed off. 16. ' We have now by this treatment with water the excess of lime slaked into a hydrate, and some of the lime, combined with the silica and other ingredients of the silicate, in an impalpable form ; in solution there is the excess of the calcium chloride formed in the operation, and all the alkalies originally contained in the mineral as chlorides, and all that now remains to be done is to filter, separate the lime as carbonate, and we have nothing left but the chlorides of the alkalies. To do this, I proceed as follows : 17. ' Throw the contents of the capsule on a filter (the size preferred for the quantity above specified is one 3 to 3^ inches in diameter), wash well, to do which requires about 200 c.c. of water ; the washing is executed rapidly. The contents of the filter (except in those cases where the amount of the mineral is very small, and there is no more for the estimation of the other constituents) are of no use, unless it be desired to heat again, first adding a little sal-ammoniac to see if any alkali still remains in it, a precaution I find unnecessary. The filtrate contains in solution all the alkalies of the mineral, together with some calcium chloride and caustic lime ; to this solution, after it has been placed in a platinum or porcelain capsule, is added a solution of pure ammonium carbonate (about H gramme is required). 18. ' This precipitates all the lime as carbonate ; it is not, however, filtered immediately, but is evaporated over a water-bath to about 40 c.c., and to this we add again a little ammonium carbonate and a few drops of caustic ammonia to precipitate a little lime that is redissolved by the action of the sal-ammoniac on the carbonate of lime. Filter on a small filter (2 inches), which is readily and thoroughly washed with but little water, and allow the filtrate to run into a small glass beaker. In this filtrate are all the alkalies as chlorides and a little sal-ammoniac ; add a drop of a solution of am- monium carbonate to make sure that no lime is present. Evaporate over a water-bath in a tared platinum dish, in which the alkalies are to be weighed ; the capsule used holds about 30 to 60 c.c., and during the evaporation is never filled to more than two-thirds its capacity. 19. ' After the filtrate has been evaporated over the water-bath to dryness, the bottom of the dish is dried, and on a proper support heated very gently by a Bunsen flame to drive off the little sal- ammoniac. It is well to cover the capsule with a piece of thin platinum to prevent any possible loss by the spitting of the salt after the sal- ammoniac has been driven off. Gradually increasing the heat, the temperature of the dish is brought to a point a little below redness, the cover being off (the cover can be cleansed from any sal-ammoniac that may have condensed by heating it over a lamp). The capsule is again covered, and when sufficiently cool, before becoming quite cold> 32 SELECT METHODS IN CHEMICAL ANALYSIS is placed on the balance and weighed. This weight gives as chlorides the amount of alkalies contained in the mineral. 20. ' If lithium chloride be present, it is necessary to weigh quickly, for the salt being very deliquescent attracts moisture rapidly. * It not unfrequently occurs that the chlorides at the end of the analysis are more or less coloured with a small amount of carbon, arising from certain constituents in ammonium carbonate ; the quantity is usually very minute, and in no way affects the accuracy of the analysis. In selecting pure ammonium carbonate for analytical pur- poses, it is well to select specimens that are not coloured by the action of the light. 21. 'It only now remains to separate the alkali by the known methods. ' The Removal of the Sal- Ammoniac unavoidably Accumu- lated in the Process of Analysis. This is probably one of the greatest annoyances to the analyst in his examination of minerals : (1st) from the manner in which the salt creeps up the sides of the vessel in which the evaporation to dryness is carried on ; and (2nd) from the great difficulty of preventing loss of the chlorides of the fixed alkalies mixed with sal-ammoniac. Owing to these difficulties, which my experience has often led me to contend with, the method about to be mentioned was contrived. It recommends itself both on account of its simplicity and certainty of operation. * Having some time back noticed the decomposing effect produced by heating sal-ammoniac with nitric acid, the result of the investigation was that the sal-ammoniac could be completely decomposed at a low temperature into gaseous products, and it was immediately adopted in my analytical process, giving the greatest satisfaction, both as to accuracy of results as well as economy of labour. ' The manner of proceeding is as follows : To the filtrate and wash- ings concentrated in the way mentioned above, and still remaining in the flask, pure nitric acid is added, about 3 grammes of it to every gramme of sal-ammoniac supposed to exist in the liquid ; a little ex- perience will suffice to guide one in adding the nitric acid, as even a large excess has no effect on the accuracy of the analysis. * The flask is now warmed very gently, and before it reaches the boiling-point of water a gaseous decomposition will take place with great rapidity. This is caused by the decomposition of the sal- ammoniac. It is no great advantage to push the decomposition with too great rapidity ; a moderately warm place on the sand-bath is best adapted for this purpose. With proper precautions the heat can be continued, and the contents of the flask evaporated to dryness in that vessel ; but it is more judicious to pour the contents of the flask after the liquid has been reduced to | an ounce into a porcelain capsule (always preferring one of Berlin porcelain) of about 3 ^ to 4 inches diameter, inverting a clean funnel of small diameter over it, and evaporating to SEPARATION OF THE ALKALIES FROM SILICATES 33 dryness on the sand-bath or over a lamp. I prefer the latter, as at the end of the operation the heat can be increased to 400 or 500. ' By this operation, which requires no superintendence, 100 grammes of sal-ammoniac might be separated as easily and safely as 1 gramme from 5 milligrammes of alkalies, and no loss of the latter be experienced. What remains in the capsule occupies a very small bulk ; this is now dissolved in the capsule with a little water (the funnel must be washed with a little water), small quantities of a solution of ammonium car- bonate added, and the solution gently evaporated nearly to dryness. This is done to separate what little lime may have escaped the first action of the ammonium carbonate, or may have passed through the filter in solution in carbonic acid. If any of the earths soluble in ammonium carbonate existed in the mineral, they now become separated along with the lime. ' A little more water is now added to the contents of the capsule, and the whole thrown on a small filter ; the filtrate as well as washings are received in,a small porcelain capsule. The liquid contains only the alkalies (as chlorides and nitrates) mixed with a minute quantity of sal-ammoniac. This is evaporated to dryness over a water-bath, and then heated cautiously over the lamp, to drive off what sal-ammoniac may have formed, which is exceedingly minute if the process as pointed out be closely adhered to. It is not absolutely necessary to heat the capsule over the lamp to get rid of the sal-ammoniac, for the little ammonium sulphate which may be formed in the next step is easily removed in the final heating in a platinum vessel. ' On the contents of the capsule, as taken either from the water-bath or after being treated over the lamp, pure dilute sulphuric acid is poured (1 part acid, 2 water), and the contents boiled for a little time, when all the nitric acid and chlorine in combination with the alkalies will be expelled ; the acid solution of the alkalies is now poured into a platinum capsule or crucible, evaporated to dryness, and ignited. In order to ensure complete reduction of the bisulphates to the neutral sulphates, the usual method must be adopted of throwing some pulver- ised ammonium carbonate in the platinum capsule or crucible, and covering it up so as to have an ammoniacal atmosphere around the salt, which will ensure the volatilisation of the last traces of free sulphuric acid. The alkalies are now in the state of pure sulphates, and may be weighed as such. ' Thus far, the mineral has been supposed to contain no magnesia. If this alkaline earth be present, take the residue as found in the capsule, dissolve it in a little water, then add sufficient pure lime-water l to render the solution alkaline, boil and filter ; the magnesia will, in this simple way, be separated from the alkalies. The solution which has 1 ' If lime-water is made, it is well to make it of lime of the best quality, and the first two or three portions of distilled water shaken up should be thrown away, as containing the small amount of alkalies sometimes presen in lime. D 34 SELECT METHODS IN CHEMICAL ANALYSIS passed through the filter is treated with ammonium carbonate in the manner already alluded to on the previous page, and the process continued and completed as described. * Conversion of the Sulphates of the Alkalies into Chlorides. The method ordinarily adopted to accomplish this change is to precipitate the sulphuric acid by means of barium chloride, care being taken to avoid the slightest excess of the latter. The annoyance attendant upon this exact precipitation is familiar to all who may have had occasion to make the trial. ' Instead of barium chloride lead acetate is used ; a solution of this salt is poured in excess upon the solution of sulphates ; warming the latter slightly, the lead sulphate readily separates ; the whole can be immediately thrown on a filter and washed ; a drop or two of the lead acetate should be added to the filtrate to ensure there being an excess of the lead salt. ' The filtrate is then warmed and sulphuretted hydrogen added ; care must be taken to see that there is an excess of sulphuretted hydrogen, a test most readily performed by means of a piece of lead-paper. The liquid is thrown on a filter to separate the lead sulphide ; the filtrate containing the alkalies as acetates is evaporated, and, when nearly dry, an excess of hydrochloric acid is added, and the whole evaporated to dryness, over a water-bath, and finally heated to above 250. A hot solution of the lead chloride can be used instead of the acetate, rendering the addition of hydrochloric acid unnecessary. * It needs but little experience to convince one of the superiority of this method over that by the barium chloride for converting the sulphates into the chlorides, its principal recommendation being the indifference with which an excess of the lead salt can be added to- precipitate the sulphuric acid, and the subsequent facility with which that excess of lead can be got rid of. It may be well to state that experiments were made to prove the perfect precipitation of the sul- phuric acid from the sulphates of the alkalies by lead salts, and it is only after numerous comparative results that it is now recommended. ' Substitution of Ammonium Chloride for Calcium Fluoride to mix with Calcium Carbonate for Decomposing the Silicates. It is mentioned above (page 28) on this subject how calcium car- bonate could be rendered as powerful in its decomposing agency on the silicates as caustic potash, the effect being due to the use of a flux, fluoride or calcium chloride being used for that purpose. I have since tested more carefully the merits of the calcium chloride, and for various reasons prefer it to the exclusion of the fluoride. In the first place, it introduces chlorine instead of fluorine into the analysis ; and secondly, the fused mass is more easily detached from the crucible, and dissolved by hydrochloric acid. * The manner of introducing the calcium chloride into the mixture of mineral and calcium carbonate was a point of some little importance, SEPARATION OF THE ALKALIES FROM SILICATES 35 as from the deliquescent nature of that compound it was inconvenient to weigh and mix it with the calcium carbonate and mineral ; these difficulties are obviated by employing ammonium chloride to form indirectly the calcium chloride. * The process, which appears to leave hardly anything to be desired, is to take 1 part of the finely pulverised mineral, 5 to 6 of calcium carbonate, and \to f of ammonium chloride ; l mix them intimately in a glazed mortar, place the mixture in a platinum crucible, and heat to bright redness in a furnace 2 from 30 to 40 minutes. ' There is no silicate which, after having undergone this process, is not easily dissolved by hydrochloric acid. For the action of the lime to have been complete, it is not necessary that the mass should have settled down in perfect fusion. The contents of the crucible are dissolved, and the analysis continued as pointed out in the preceding pages. ' This method ensures the obtaining of every particle of the alkalies in the mineral examined, requiring no more precaution than any good analyst is expected to take in the simplest of his processes : and not the least of the advantages is the ready method of separating all the other ingredients, and the small accumulation of water arising from the little washing necessary. (A) ' A Speedy Method of Separating the Alkalies directly from the Lime-Fusion, for both Qualitative and Quantitative Determination. As soon as the fusion with calcium carbonate and sal-ammoniac gave evidence of the mineral being so thoroughly attacked, the question naturally arose as to the condition the alkalies were in after the fusion, and the possibility of dissolving them out by the agency of water alone, at least for the purpose of qualitative determina- tion. Experiments directed to this object soon made it evident that the alkalies might be obtained from any silicate, without resorting to the use of acid as a solvent for the fusion. * The mass as it comes from the crucible is placed in a capsule with water, and then heated in a sand-bath or over a lamp for two or three hours, renewing the water from time to time as it evaporates. The mass disintegrates very shortly after being placed in the water. The contents of the capsule are next thrown on a filter, and the water passes through, containing the chloride of the alkali, a little calcium 1 ' The ammonium chloride is best obtained in a pulverulent condition by dissolving some of the salt in hot water, and evaporating rapidly ; the greater portion of the ammonium chloride will deposit itself in a pulverulent condition, the water is poured off, and the salt, thrown on bibulous paper, allowed to dry, the final desiccation being effected on a water-bath, or in any other way with a corresponding temperature. 2 ' An ordinary portable furnace with a conical sheet-iron cap of from 2 to 3 feet high answers the purpose perfectly well, all the requisite heat being afforded by it. 36 SELECT METHODS IN CHEMICAL ANALYSIS chloride and caustic lime ; all else that the mineral may have contained remains on the filter, except baryta and strontia, if they be present in the mineral ; but as these oxides are of rare occurrence in silicates, no allusion will be made to them here. ' To the filtrate add ammonium carbonate, and boil for some time, when all the calcium will be precipitated as carbonate ; add a few drops of a solution of ammonium carbonate to the hot solution to be sure that all the calcium is precipitated ; should this be the case, filter ; the filtrate will contain the chlorides of the alkalies and ammonium chloride ; it is evaporated to dryness over a water-bath in a small platinum capsule; the capsule is carefully heated to expel the sal- ammoniac, and finally heated to about 400 ; it is then weighed with its contents, and the chlorides, if mixed, separated in any convenient manner. The amount of sal-ammoniac to be expelled is quite small, not equalling the weight of mineral originally employed. ' Nothing in analysis can be simpler or more speedy than this pro- cess. Its constant accuracy still lacked something to render it perfect, as usually an amount of alkali remained behind amounting to from 0-2 to 1 per cent, of the mineral used, certainly a small quantity, but still too much to be omitted in an accurate analysis. This also must be arrived air, and it can be accomplished in the following manner : ' After the fused mass has been treated with water, filtered, and washed as above, the filter and its contents are dried ; the latter are detached from the filter and rubbed up in a glazed mortar with an amount of sal-ammoniac equal to one-half the weight of the mineral and reheated in a platinum crucible exactly as in the first instance, treated with water, thrown on a filter and washed, the filtrate added to that from the first fusion, the whole treated with ammonium carbonate and completed as above described. . * This second fusion complicates the method but little, as the residue on the filter readily dries in a water-bath into a powder that is easily detached from the filter, and the small portion adhering to the latter may be disregarded, as the alkalies remaining rarely exceed more than gfa of the whole mass, and, in most instances, not more than ToVo. In many analyses made, one fusion sufficed for the entire extraction of the alkalies ; but as a few tenths would occasionally remain behind, we preferred the additional fusion to get at that small quantity, and to entitle it to rank as a method by which all but the merest trace of the alkalies could be extracted from the insoluble silicates. ' The proportion of sal-ammoniac added to the calcium carbonate as here recommended was arrived at after numerous experiments. By increasing the sal-ammoniac, and thereby augmenting the amount of calcium chloride formed, the mass fuses more thoroughly, but the water does not disintegrate it as completely as when the ammoniacal salt is less an object not to be disregarded. SEPARATION OF THE ALKALIES FROM SILICATES 37 ' The advantage of thus estimating the alkalies in insoluble silicates is obvious ; the long routine of separating silica, alumina, lime, &c., is done away with ; the accumulation of ammonium chloride is very trifling ; and lastly, the alkalies are obtained directly in the form of chlorides. The method will vie in accuracy with any other, including the one already mentioned in the first part of this description, and at the same time it is unequalled in simplicity, speed of execution, and constancy of results. * In examining for alkalies qualitatively, one fusion will of course be all that is necessary, and the action of the heat need not be continued for more than 30 minutes before filtering. This method will not answer when boracic acid is present in the silicate.' For methods of proceeding in such a case, see the chapter on Boron. 'In a recent note on the subject of alkalies in silicates Professor Lawrence Smith gives some interesting particulars respecting the presence of rare alkalies in the mineral leucite : 1 The specimens of leucite examined came from four localities Vesuvius, Andernach, Borghetta, and Frascati. They were about as good specimens as are obtained from those localities, although all of them were not equally pure. The alkalies found in each, calculated as potash, were Vesuvius 21-85 Andernach 20-06 Borghetta 20-68 Frascati 20-38 'Although they are said to be "calculated as potash," there is a notable quantity of rubidium and caesium present in all the specimens above mentioned. In fact, by the method adopted in testing for these alkalies, abundant indications are obtained of the presence of rubidium and caesium (the last not so readily), even when operating on but ^ a gramme of the mineral. The quantity of these alkalies in leucite is found to be about 0'9 per cent, of the entire mineral. Of course it is not at all remarkable that the amount of potash in the different specimens of leucite should be the same : but it is a matter of interest to know that, from whatsoever locality it comes, this minute quantity of rubidium and caesium occurs with it. 22. ' A Special Arrangement for Heating the Crucibles by Gas. The support and burner, where gas is to be had (as it is in almost all analytical laboratories), are simple in their .character, and have been arrived at after a great variety of experiments with gas furnaces. The figure here given illustrates the stand, burner, crucible, &c., and is about one-sixth the natural size. H is the stand with its rod, G. D is a brass clamp, with two holes at right angles to each other ; having two binding screws, it slides on the rod, G ; the second hole is for a round arm attached to B, the binding screw, E, fixing it in any position. 38 SELECT METHODS IN CHEMICAL ANALYSIS B is a plate of cast-iron, 5 to 6 millimetres thick, 10 to 11 centimetres long, and 4J centimetres broad, having a hole in its centre large enough to admit the crucible to within about 15 millimetres of the cover without binding. A is the cru- cible already referred to, which is made to incline a few degrees down- wards, by turning the plate of iron that supports it. c is a chimney of sheet iron, 8 to 9 centimetres long, 10 centimetres high, the width at the bottom being about 4 centimetres at one end and about 3 centimetres at the other end. It is made with the sides straight for about 4 centimetres, then inclines towards the top, so as to leave the width of the opening at the top about 1 centimetre. A piece is cut out of the front of the chimney of the width of the diameter of the hole in the iron support, and about 4 centimetres in length, being semi- circular at the top, fitting over the platinum crucible. Just above this part of the chimney is rivetted a piece of sheet iron in the form of a flattened hook, N, which holds the chimney in place by being slipped over the top of the crucible support ; it serves as a protection to the crucible against the cooling effects of the currents of air. F is the burner, which has been described in an article on flame heat in the American Journal of Science, November, 1870, p. 341, the upper opening of which is a slit from 1^ to 2 millimetres in width, and from 3 to 4 centimetres long, and when used it is brought within about 2 centimetres of the lowest point of the crucible, the end of the flame just playing around the lower end of the crucible. The gas enters the lower part of the burner by two small holes of ^\- of an inch, furnishing at 1 inch pressure about 5^ cubic feet of gas per hour. The precaution must be observed, already referred to, of heating the crucible at first gently. 23. 'It is surprising to see the effect produced by this simple burner as here used ; 8 grammes of precipitated calcium carbonate can be de- composed to within 2 or 3 per cent, in one hour, and when mixed with silica or a silicate, in a very much shorter space of time, although in my analyses I employ one hour, as it requires no attention after the FIG. I. 1 1 These burners and stands, as well as the platinum crucibles, made according to Professor Lawrence Smith's pattern, can be obtained of Messrs. Johnson and Matthey, Hatton Garden. NESSLEK'S TEST FOR AMMONIA 39 operation is once started. This form of furnace and crucible is found to be convenient for other operations. 24. 'Although the details given here are lengthy, the time occupied in the analysis is short and the precautions necessary are of a simple character, so much so that results obtained by students beginning chemical analysis have been found by me reliable, and less variable on the alkalies of the silicates than of any of the other constituents of this class of bodies. I have often made good alkali determinations in three hours from the commencement of the operations, hastening the evaporations by more direct application of heat, which, of course, requires close watching. 25. ' It is a common practice, when a silicate comes under my examination that is not easily made out by its physical properties, to make at once an alkali determination, which often indicates at once what it is if it be a known silicate. If not, the alkali determination serves as one step in its examination.' Estimation of Alkalies in Tire-Clays and other Insoluble Silicates Mr. G. Gore, F.R.S., has described a modification of the hydro- fluoric process of treating silicates, which has been found useful when only the alkalies are required. An intimate mixture of the finely powdered fire-clay, barium nitrate, and barium fluoride is projected into a heated crucible ; when all the mixture has been thrown in, the crucible is covered and gradually heated in a furnace until the contents are completely melted; the mixture is poured into a cast-iron vessel, and immediately covered over. The resulting fused mass is finely powdered, digested with sulphuric acid, evaporated to dryness, and afterwards treated in the usual manner. The results of analyses made in this manner agree with those obtained by the hydrofluoric acid process. In the Chapter on Silicates will be found other methods of analysis by which the alkalies may be separated and estimated ; but the pro- cesses being mostly devised for the simultaneous estimation of many other substances, are not so simple as those here given. AMMONIA Nessler's Test for Ammonia. This test is of great value in water analyses and other cases where the ammonia is present in minute quantities only. Mr. Hadow, Dr. W. A. Miller, Professor Frankland and Dr. Armstrong have introduced useful modifications into the original process. The following process, which has been found to answer perfectly, is based upon the descriptions of the above chemists. Make a concentrated solution of an ounce or more of corrosive 40 SELECT METHODS IN CHEMICAL ANALYSIS sublimate ; having dissolved 2^ ounces of potassium iodide in about 10 ounces of water, add to this the mercurial solution until the mercury iodide ceases to be dissolved on agitation ; next dissolve 6 ounces of solid potassium hydrate in its own weight of water, and add it gradually to the iodised mercurial solution, stirring whilst the mixture is being made ; then dilute the liquid with distilled water till it measures one quart. When first prepared it usually has a brown colour of greater or less intensity, owing to the presence of a little ammonia ; but if set aside for a day or two it becomes clear and nearly colourless ; the clear liquid may then be decanted for use. For a litre of the test liquid of equal strength 62-5 grammes of potassium iodide and 150 grammes of solid caustic potash will be required. About 50 grains (3 c.c.) of this solution are drawn oif by a marked pipette and added to one-half of a solution or distillate to be tested for ammonia ; if no ammonia be present the mixture remains colourless, but if ammonia be present the liquid will assume a yellowish tinge of greater or less intensity. The liquid will remain clear if the ammonia does not exceed -^ of a grain in the 5 ounces, or about 0*25 milligramme, in 125 grammes of the distillate. The quantity of ammonia in such a case may be very accurately estimated in the following manner : A solution of sal- ammoniac is prepared, containing 3*17 grains of the salt in 10,000 grains of water (or 0-316 gramme of salt per litre), which is equivalent to TOOOO f a grain of ammonia in each grain of this solution, or O'l gramme in 1 litre. Suppose that a tint is obtained in the distilled liquid, which experience leads the observer to estimate, say, at TTHTO of a grain ; 50 grains of the standard sal-ammoniac solution are placed in a beaker similar in size to that used for the distillate under trial, then diluted with 5 ounces of distilled water previously ascertained to be free from ammonia (an impurity not unfrequently met with in the first portions of water which come over in distillation) ; lastly, 50 grains of the mercurial test liquor are added. If the tint coincides in intensity with that furnished by the distillate which has received an equal quantity of the mercurial test, the amount of ammonia may be considered to correspond with that taken in the liquid for comparison. If the distillate appears to have a deeper or a paler tint, a second approximative trial with a larger or a smaller quantity of sal-ammoniac must be made, and so on until the operator is satisfied that the tints coincide. On multiplying the number of grains of sal-ammoniac solution employed by 8, the product will give in 10 j >00 ths of a grain the quantity of ammonia per gallon in the water under examination. Suppose that the observer estimates the amount of ammonia in the 125 c.c. on which he is operating, at 0'25 milligramme he takes 2'5 c.c. of the sal-ammoniac solution, and dilutes it with dis- tilled water to 125 c.c. ; he then adds 3 c.c. of the mercurial liquor and compares it with the tint produced in the distillate by a like addition of the mercurial test. If the two tints correspond, multiply by 2 the NESSLEK'S TEST FOE AMMONIA 41 number of c.c. of sal-ammoniac solution required, and the number obtained will give the proportion of ammonia per litre in tenths of a milligramme. When the quantity of ammonia exceeds the -$ of a grain per gallon, or 0-6 milligramme per litre, it is necessary to deter- mine the amount by neutralisation. Unless the amount of ammonia obtained by distillation alone, or with sodium carbonate, be considerable (about O'Ol part in 100,000 parts of water) this modification of Nessler's process is all that could be desired for its accurate determination. But if a larger proportion than this be obtained in a potable water, the presence of urea may be suspected, and it becomes necessary to make the Nessler ammonia test directly in the original water, without the intervention of distillation. For this purpose, however, the water should be colourless, and free from calcium and magnesium carbonates. Any tint which is appreciable in a stratum 6 or 8 inches thick would obviously vitiate the result of a colour test, whilst, if calcium or magnesium carbonate be present, the addition of the Nessler solution will infallibly produce turbidity ; more- over, we find that the slightest opalescence in the water, under these circumstances, is absolutely incompatible with an accurate determination* Both these difficulties may be effectually removed by adding to the water first a few drops either of ferric perchloride or of aluminium chloride in solution, and then a few drops of a solution of sodium carbonate, so as to precipitate iron sesquioxide or alumina. The precipitate com- pletely decolourises the water, and no turbidity is caused by the sub- sequent addition of the Nessler solution ; but, unfortunately, the precipitate carries down with it an amount of ammonia which, in the case of the iron sesquioxide, sometimes amounts to one-third of the total quantity present. Remembering the beautiful blue-green tint the natural colour of absolutely pure water which is presented by a reservoir of water that has been softened by Clarke's process, Messrs. Frankland and Armstrong tried upon peaty water the effect of pre- cipitating in it calcium .carbonate, and found that the decolouration was as complete as could be desired, and that no appreciable amount of ammonia was carried down with the precipitate. The amount of calcium carbonate present in a coloured water is rarely sufficient to enable the operator to carry out this reaction with sufficient rapidity and completeness ; it is therefore best in all cases to add a few drops of a concentrated solution of calcium chloride to half a litre of the water. The subsequent addition of a slight excess of sodium carbonate then produces a copious precipitate of calcium carbonate, which should be allowed to subside for half an hour before filtration. 100 c.c. of the filtrate is a convenient quantity to take for the direct Nessler determi- nation of ammonia. To this volume of the filtrate 1 c.c. of the Nessler solution is added, and the colour observed as above described. By this direct process, the ammonia in fresh urine can be readily estimated ; for this purpose 5 c.c. of the urine should be diluted with 95 c.c. of 42 SELECT METHODS IN CHEMICAL ANALYSIS water free from ammonia. Known quantities of ammonia, added in the form of ammonium chloride to urine, can be determined with great accuracy. The colour observations of the Nessler determination are best made in narrow glass cylinders, of such a diameter that 100 c.c. of the water to be tested form a stratum about 7 inches deep. The depth of tint is best observed by placing these cylinders upon a sheet of white paper near a window, and looking at the surface of the liquid obliquely. Estimation of Ammonia in Gas Liquor Mr. T. E. Davis considers that the direct titration of liquor with normal sulphuric acid and calculation into ammonia would be a test sufficient to base a contract upon ; and for the guidance of a manu- facturer, and for all practical purposes, it may be looked upon as correct. Moreover, each test does not take five minutes, whereas the distillation process takes the best part of an hour. The titration method of testing is as follows : Into a flask of about 300 c.c. capacity, 10 c.c. of the sample to be tested are run in, and into this 15 c.c. of normal sulphuric acid. The contents of the flask are then raised to boiling over a naked flame, a few drops of litmus added and titrated back with normal soda. The number of c.c. of soda used is deducted from the 15 c.c. of acid employed, the result multiplied by 17 and divided by the specific gravity of the liquor. The result thus obtained represents the percentage of ammonia contained in the liquor. An example will make this clear : 10 c.c. of a liquor at 5 T. (sp. gr.=1025), boiled with 15 c.c. normal acid, require 5 c.c. normal soda to neutralise it, consequently the sample contains 1'658 per cent. NH 3 : thus Now as to the valuation. Suppose we consider 10s. per unit of NH 3 per ton to be fair value, then the above sample would be worth 1-66 x 105 = 17s. 5d. per ton. Such a system would induce gas managers to make the liquor as strong as possible, and ammonia manufacturers would do well if they were to refuse a contract for liquor containing less than 1 per cent, of NH 3 ; for if below this unless the liquor were given them they would barely clear expenses of manufacture. Ammonium Chloride in Analysis. For the best method of removing the ammonium chloride which unavoidably accumulates in the process of analysis, see ante, page 32. 43 CHAPTER II BARIUM, STEONTIUM, CALCIUM, MAGNESIUM Indirect Estimation of Barium, Strontium, and Calcium THE estimation of these three earthy metals is generally effected after they are separated from each other. These separations can be dispensed with if an indirect method be employed, thereby avoiding the loss attendant upon different separations, and materially hastening and simplifying the whole estimation. The following indirect method, which is very successful for the estimation of these three metals, may also be employed in the presence of magnesium. In the first place, the calcium, strontium, and barium must be precipitated as carbonates, by . means of ammonium carbonate and hydrate. It must be borne in mind that in a liquid containing much sal-ammoniac or ammonium nitrate neither calcium, strontium, nor barium can be completely precipitated by ammonium carbonate, so that, after filtering, it is possible, by means of sulphuric acid or ammonium oxalate, to recognise a more or less considerable quantity. The cause of this is, that ammoniacal .salts of strong acids have a solvent action upon calcium carbonate, and this action is still stronger upon the strontium and barium carbonates. Should, on the other hand, ammonium acetate or carbonate be used, instead of sal-am- moniac or ammonium nitrate in solution, the precipitation of the three bases by ammonium carbonate will be so complete that it will be im- possible to discover in the filtrate, by means of the before-mentioned reagents, any traces of calcium, strontium, or barium. In order to have in solution no other ammoniacal salts than acetate and carbonate, it will suffice to add to the tolerably neutral solution as much sodium acetate as there is supposed to be sal-ammoniac or ammonium nitrate held in solution, and then to supersaturate with ammonia and ammonium carbonate and, after a short digestion, to cool the solution ; the carbonated alkaline earths which have in this manner been completely precipitated are now filtered off. Digestion is not absolutely necessary here ; it only serves to render those deposits granular which would otherwise be voluminous. On the other hand, in order to obtain complete precipitation, it will be necessary to reduce the whole to the ordinary temperature before filtering, because hot ammonium acetate has a solvent action upon 44 SELECT METHODS IN CHEMICAL ANALYSIS carbonated alkaline earths, although in a far less degree than sal- ammoniac. A certain degree of dilution of the ammoniacal salt is to be recom-* mended ; in any case, the solution must not be more concentrated than in the proportion of one part of salt to twenty of water. Sodium carbonate may be substituted for the acetate, in order to decompose the sal-ammoniac ; but if, at the same time, magnesium be held in solution, the presence of a large quantity of an ammonium salt of stronger acid than carbonic will be necessary, in order that it may not be deposited with the alkaline earths. For this purpose, the addition of sodium acetate is eminently suitable, because the ammonium acetate thus formed (as with oxygenated ammonium salts generally) prevents the precipitation of the magnesium much more than sal- ammoniac does, without, as before remarked, dissolving barium, strontium, or calcium. In the presence of magnesium, a too great excess of ammonium ca.rbonate must be avoided as a reagent, in order to hinder the forma- tion of ammoniacal magnesium carbonate, which is difficult to dissolve. After these precautionary measures, the barium, strontium, and calcium having been separated, the precipitate is washed, filtered, dried, heated, and weighed ; it is then dissolved in a measured quantity of normal hydrochloric acid and titrated. This is done (after removing the carbonic acid by heat from the diluted solution, which is coloured with litmus) by estimating with normal standard ammonia solution the amount of hydrochloric acid which had been required to transform the three carbonates into chlorides. The solution is now mixed with a known amount of potassium bichromate, caustic ammonia being added in excess, to precipitate all the barium, so that no trace of it may be detected in the acidulated filtrate, by potassium fluosilicate and alcohol. 1 The barium chromate is filtered off and washed until lead acetate ceases to give a yellow precipitate in the filtrate ; in the solution tbe excess of chromic acid is determined according to the usual process, with a standard solution of iron protosulphate ; and the amount of baryta is then obtained, according to the formula Chromic acid x 1*527 = Baryta, or Chromic acid x 1'964 = Barium carbonate. If, on the one hand, the amount of barium carbonate thus obtained be deducted from the weight of the three carbonates, and, on the other, the amount of hydrochloric acid answering to the baryta be calculated, the difference between this amount of hydrochloric acid and the amount found, will be the quantity of hydrochloric acid which corresponds to 1 Pure barium chloride solution produces no turbidity when, after the pre- cipitation of baryta by potassium chromate and ammonia, the nitrate is mixed with sulphuric acid. It is, of course, assumed that the reagents employed in precipitation are quite free from sulphuric acid. ESTIMATION OF CALCIl'M 45 the united weight of the calcium and strontium carbonates, which has just been calculated. The amount of calcium and strontium carbonates is obtained as follows : Calculate the amount of calcium carbonate (which is equiva- lent to the known quantity of hydrochloric acid) contained in the excess of calcium and strontium carbonates, deduct this from the weight of the two carbonates, multiply the remainder by the constant factor 3 T V, and the product will then be the required quantity of strontium car- bonate ; this, when again subtracted from the united weight of both salts, yields, as its remainder, the quantity of calcium carbonate. The constant factor, 3 T ^, is obtained by the following calculation : Calcium carbonate = 100 Strontium carbonate = 148 Calcium and strontium carbonates = 248 hence 2 eqs. of calcium carbonate = 200 and this subtracted from the equivalent of strontium carbonate leaves 48, and 148 divided by 48 =3 r J 5 . This method of estimating these three earthy metals always yields satisfactory results. It is quickly carried out, and is very exact, because the precipitations are all perfect, and the two volumetric estimations involved in the method admit of great accuracy. More- over the troublesome and somewhat uncertain separation of the stron- tium and calcium with a concentrated solution of ammonium sulphate, which is very inconvenient in estimating the calcium, is avoided. In the absence of strontium, either precipitate the calcium and barium as carbonates, estimating the precipitate alkalimetrically ; or precipitate the barium as sulphate, and the calcium as carbonate, by digesting the solutions of both with a mixture of three parts of potas- sium sulphate and one part of potassium carbonate ; weigh the dried and ignited precipitate, and estimate the calcium carbonate alkali- metrically. Estimation of Calcium (A) Dr. A. Cossa has determined the accuracy of estimating calcium as quicklime or caustic lime, instead of weighing it as calcium carbonate. The experiments were made (1) with pure calcium oxalate previously dried at 100 ; (2) with calcium carbonate precipitated from a solution of pure calcium chloride by means of pure sodium carbonate ; (3) with pure native calcium carbonate. The result of an average of three experiments with No. 1 is 0'07 per cent, too low ; with No. 2, 0-35 per cent, too low ; with No. 3, 0-27 per cent, too high. (B) To avoid the inaccuracy and loss of time nearly always resulting from the ordinary method of determining calcium, viz. by strongly heating the precipitate of calcium oxalate, and converting the same into carbonate by repeatedly moistening with solution of ammonium carbonate, Mr. Scott recommends weighing the precipitate as sul- 46 SELECT METHODS IN CHEMICAL ANALYSIS phate instead. The addition of sulphuric acid, or even of ammonium sulphate alone, to caustic lime is hardly a safe operation from an analy- tical point of view, if the mass in the crucible is at all bulky, but by using the following solution no inconvenience is experienced. Three parts of pure liquor ammonia of the ordinary strength should be just neutralised with pure sulphuric acid (previously diluted with its bulk of water), and two parts of the ammonia solution added. In each ounce of the fluid thus obtained 10 grains of ammonium chloride must be dissolved : the whole may then be filtered into a small reagent bottle and appropriately labelled. It must, of course, entirely volatilise when heated on platinum foil. In this manner the calcium is weighed as sulphate, which may be strongly ignited without change, one weighing therefore being sufficient. Calcium Phosphates The commercial estimation of superphosphates is given in the chapter on Phosphoric Acid. The following process, recommended by Professor F. Wohler for the analysis of apatite and similar phosphates, will be found to be one of the most trustworthy : Dissolve the mineral in nitric acid in a capsule, and then add pure mercury in such quantity that when the acid is saturated with it there still remains a portion of mercury undissolved. Evaporate the mixture on the water- bath to complete dryness. If a slight odour of nitric acid is still dis- engaged, add more water, and evaporate again to dryness, so as to get rid of it completely ; then extract with water, place it on the smallest possible filter, and well wash the residue, which contains all the phos- phoric acid. Besides the excess of mercury the filtrate contains all the calcium. With hydrochloric acid precipitate the mercury proto-salt. As a little mercuric binoxide may have been formed, precipitate the solution with ammonia. If the mineral contains iron or other bases precipitable with ammonia, these remain after calcining the last precipitate. The solution is rapidly filtered, with as little exposure to the air as possible, and the calcium in it precipitated with ammonium oxalate. The filter, which, besides the excess of mercury, contains phos- phoric acid, is well dried, and the whole is placed in a platinum crucible and mixed with potassium and sodium carbonates. The crucible is then heated to a temperature below redness, under a chimney with a good draught, until all the mercury is volatilised, after which it may be heated to redness and the contents fused. Then dissolve in water, add an excess of hydrochloric acid, and precipitate the phosphoric acid with ammonia and magnesium sulphate. To estimate the chlorine, dissolve a known weight of the mineral in dilute nitric acid, 1 and precipitate the chlorine with silver nitrate. 1 Certain brown apatites leave as a residue a small quantity of a crystalline powder, which is cryptolite (cerous phosphate). DETECTION OF CALCIUM IN PRESENCE OF STRONTIUM 47 Some kinds of apatite contain a small quantity of fluorine. When it is desired to ascertain the presence of this body, finely powder the mineral and then mix it in a platinum crucible with concentrated sul- phuric acid ; cover the crucible with a piece of glass coated with wax and having characters traced on it with the point of a needle. Then heat the crucible, taking care not to melt the wax. If fluorine is present, the characters will be found engraved on the glass when the wax is removed. The amount of fluorine present may be deduced from the loss of weight obtained in the complete analysis. Separation of Calcium from Strontium (A) The best process is that originally devised by Stromeyer, based upon the solubility of calcium nitrate in absolute alcohol and the in- solubility therein of strontium nitrate, but adding an equal volume of ether to the alcohol. A mixture of alcohol and ether does not dissolve more than -^ -J-^ part of strontium nitrate, whilst it dissolves calcium nitrate perfectly. (B) A similar separation may be effected by ammonium sulphate, in which calcium sulphate is soluble, whilst strontium sulphate remains unaffected. The proportions to employ are : 50 parts of ammonium sulphate and 200 parts of water to 1 strontium sulphate. There is then formed a soluble double salt, which resembles potassio-gypsite (calcium and potassium sulphate). This process is, however, less delicate than that of Stromeyer. Detection of Calcium in the Presence of Strontium C. L. Bloxam has devised a very delicate method of detecting cal- cium in the presence of strontium. If a solution of calcium sulphate be mixed with ammonia and a little solution of arsenic acid, it yields on stirring with a glass rod a highly crystalline precipitate of ammo- nium-calcium arseniate which is deposited very strongly on the lines where the glass rod has rubbed the tube. This precipitate is nearly as insoluble as calcium oxalate, whilst it is far more crystalline. When strontium chloride is precipitated by excess of sulphuric acid the minute quantity of strontium left in the solution is not precipitated by ammonia in excess and arsenic acid. A solution containing one part (0*0381 grains) of calcium and 50 parts of strontium, acidulated with hydrochloric acid, precipitated by sul- phuric acid, filtered, mixed with excess of ammonia, cooled, and stirred withalittle solution of arsenic acid, gave a copious crystalline precipitate. With 1 part (0'019 grain) of calcium and 100 parts of strontium the precipitate appeared after two or three minutes. With the same weight of calcium and 500 parts of strontium, the filtrate from the strontium sulphate was evaporated to a small bulk, mixed with excess of ammonia, filtered from a further deposit of stron- 48 SELECT METHODS IN CHEMICAL ANALYSIS tium sulphate and stirred with arsenic acid ; in a few seconds the precipitate of ammonium 1 calcium arseniate was deposited on the lines of friction and identified by the microscope. Samples of strontium nitrate and carbonate, purchased as pure, were found to contain much calcium when examined in this way. Separation of Calcium from Barium and Strontium (A) P. E. Browning has found that when in the form of nitrates, boil- ing amyl alcohol dissolves the calcium salt while it has no action on the barium or strontium salt. For details of the operations the reader is referred to the author's papers in the American Journal of Science, vol. xliii., 1892. (B) B. Fresenius sums up the results of a prolonged investigation on the separation of strontium from barium as follows : 1. Barium chromate is not soluble in water containing acetic acid if so much ammonium chromate is present that the liquid contains only alkaline acetate and bichromate. 2. Barium chromate dried at 110 is not anhydrous (as formerly assumed), but contains about 0'5 per cent, of moisture. 3. Barium chromate is not decomposed on gentle ignition, and if adhering to a filter it may be weighed without loss by cautiously in- cinerating the filter and gently igniting the residue. 4. The determination of barium by precipitation with ammonium chromate gives results which are perfectly satisfactory. 5. The complete separation of barium from strontium by a single precipitation of the former as a chromate is not successful under any circumstances. The most favourable results obtained in this manner depend on the accidental compensation of errors of a conflicting nature. 6. A complete separation of barium and strontium and an absolutely satisfactory result in the determination of both bases can be obtained only by a twice repeated precipitation of the barium in an acetate solution with an excess of ammonium chromate ; the strontium can then be thrown down as strontium carbonate, which is then purified by conversion into sulphate. Separation of Strontium from Barium When in the form of sulphates, prolonged digestion with a cold solution of ammonium carbonate will convert the strontium into car- bonate, whilst it has no action on the barium. Boiling the solution or employing sodium carbonate is not so effectual. Finely pulverise the mixed salts, wash thoroughly with water, and treat with nitric acid. The strontium will dissolve as nitrate and leave the residue of the barium sulphate. Barium and calcium may be separated in a similar manner. DETERMINATION OF MAGNESIUM 49 MAGNESIUM Applications of Metallic Magnesium. The magnesium which is now met with in commerce in the form of ribbon, wire, and rod, possesses properties which render it of great value in some chemical operations. When magnesium is added to a slightly acid solution of iron, zinc, cobalt, or nickel salt, an evolution of hydrogen takes place, and these metals are respectively precipitated in the metallic state. When washed, dried, and compressed, the precipitated metals possess great brilliancy and dissolve completely in acids. The iron, cobalt, and nickel so obtained are highly magnetic. Besides these metals, mag- nesium precipitates gold, silver, platinum, bismuth, tin, mercury, copper, lead, cadmium, and thallium. When magnesium is put into water containing a little common salt, sal-ammoniac, or dilute acid, very pure and inodorous hydrogen gas is evolved. Owing to the high electromotive force of magnesium and its low equivalent, it would be decidedly the best positive element for galvanic batteries could it be produced at a cheap rate. When magnesium is introduced into an acid solution containing arsenic or antimony, these metals are not precipitated, but combine with the evolved hydrogen, and pass off as arseniuretted or antimoniuretted hydrogen. Owing to the great purity of the distilled magnesium of commerce, and its freedom from silicmm and poisonous metals, it is invaluable to the toxicologist, and should always be used in Marsh's apparatus instead of zinc, for the evolution of hydrogen. Further particulars as to the special employment of magnesium for this purpose will be found in the chapter on Arsenic. Determination of Magnesium as Pyrophosphate (A) Mr. K. W. Emerson Mclvor strongly recommends the process of Dr. Gibbs, who substitutes microcosmic salt for ordinary sodium phosphate. He heats the mixed solution of magnesium sulphate and ammonium chloride to the boiling point, and precipitates the magne- sium from the boiling liquid by adding the ammonium phosphate solution. After having been allowed to cool, ammonium hydrate is added, and the whole allowed to stand for twenty-four hours. The precipitate of magnesium ammonio-phosphate is then collected upon a filter, dried at 100 C., ignited, and weighed as magnesium pyro- phosphate in the usual manner. As magnesium is a substance which analysts have frequent occasion to estimate, Dr. Gibbs's suggestions are well worthy of their consideration. (B) Experiments have been conducted by Mr. Lawrence Briant to determine whether the well-known accelerative action of agitation 50 SELECT METHODS IN CHEMICAL ANALYSIS could not be applied to the precipitation of magnesia, so as to shorten the duration of the experiment. The mode of procedure was as follows : Comparative determinations were made in which the quantity of magnesia in given solutions was estimated by three ways. First, precipitation in the ordinary manner,, allowing the liquid to stand in the cold for twenty-four hours ; second, after twelve hours ; and third, after violently shaking in a stoppered glass jar for ten minutes, at once throwing the liquid on to a filter. The volume of liquid was in each experiment the same, viz. 155 c.c., whilst the precipitate was washed with 100 c.c. of dilute ammonia (1 to 3), divided into three different washings, between each of which the filter was allowed to drain completely. The precipitate in the case of the experiments in which the liquid was violently shaken was very granular, and was without difficulty transferred to the filter. The results are as follows : MgO Treatment found grin. MgO present grm. 1 stood twenty-four hours 2 twelve 3 shaken ten minutes 4 5 6 stood twenty-four hours 7 twelve 8 shaken ten minutes 9 0-050 0-049 0-051 0-050 0-050 0-022 | 0-022 0-021 0-020 0-002 0-003 '; 0-002 0-0017 0-050 0-050 0-050 0-050 0-050 0-022 0-022 0-022 0-022 0-002 0-002 0-002 0-0015 10 stood twenty-four hours 11 twelve ,, 12 shaken ten minutes 1 '-i These experiments seem to prove that whilst the method recom- mended vastly shortens the length of time occupied in making a deter- mination of magnesia, it in no wise impairs its accuracy. Separation of Magnesium from Calcium (A) The method of separating calcium and magnesium by means of ammonium oxalate does not succeed when only a very small quantity of calcium is present. In such a case the calcium is either not pre- cipitated at all, or but very incompletely. Free ammonia also tends to hinder the precipitation, and, when it has evaporated, crystals are obtained, which consist of calcium oxalate with magnesium oxalate, and the liquid still contains calcium. (B) A better result, Scheerer says, is obtained by converting the alkaline earths into neutral sulphates, and adding alcohol to the aqueous solution until a persistent cloudiness is produced. Alter some hours all the calcium sulphate is deposited. When too much alcohol has been used, some of the magnesium sulphate is deposited as well ; it is MAGNESIUM FKOM CALCIUM * 51 sufficient then to redissolve the sulphates in water and precipitate a second time with alcohol, or the calcium may now be thrown down by the ammonium oxalate. The magnesium, not being in excess, no longer hinders the precipitation. (C) With regard to the analysis of dolomite, Dr. A. Cossa states, that when care is not taken to redissolve the precipitate of calcium oxa- late first obtained, and precipitate this a second time, it is always so contaminated with magnesium oxalate or magnesium ammonio-oxalate, that the quantity of calcium found as carbonate may be O62 per cent, in excess of what it ought to be, while the loss of magnesium carbonate may even be as high as 0'78 per cent. When, in the ordinary course of qualitative analysis, ammonium carbonate is used to separate calcium from magnesium, unless the former metal is present in notable proportion to the latter, a very in- soluble double magnesium and ammonium carbonate always accom- panies the calcium carbonate, if this is allowed sufficient time to form. If much magnesium and no calcium be present, the magnesium pre- cipitate still falls after a while. Both metals are precipitated by this reagent, the only difference being that the calcium precipitate forms somewhat earlier than the magnesium precipitate. Calcium, there- fore, can only be separated from magnesium by this reagent by frac- tional precipitation, which necessarily involves loss of substance ; and, in qualitative examination, the method is sure to mislead when the proportion of calcium present is small, unless it is controlled by other methods. The same remarks apply, in substance, to the method of precipitation by ammonium oxalate. Within a trace the whole of the magnesium present, in a considerable quantity of solution of magnesium chloride, can be precipitated simply by successive additions of ammonium oxalate : the solution being concentrated to its original bulk after the last addition of the reagent. Yet, in working with this reagent, the rule is, that enough of it must always be added to transform all the magnesium salt into oxalate, since calcium oxalate is soluble in solu- tion of magnesium chloride. That some magnesium salt must pre- cipitate with the calcium salt under such conditions is obvious : and that it does so is well known, and is, though incompletely, provided for by the direction being given to repeat the process upon the pre- cipitate first obtained. This process, therefore, is also one of frac- tional precipitation, and for it to approach success, the operator must know pretty nearly beforehand how much calcium, in proportion to the magnesium present, he has to deal with. (D) Mr. Edward Sonstadt has discovered that in sodium tung- state we possess a test for calcium which is probably equal in delicacy and in certainty to that of chlorine for silver, or of sulphuric acid for barium, and on this discovery he has based an excellent method for the separation of magnesium from calcium. Mr. Sonstadt gives the following details respecting the manipula- 52 SELECT METHODS IN CHEMICAL ANALYSIS tion required in separating calcium from magnesium by sodium tung- state, that experience has shown to be necessary. It is convenient to have the solution of the magnesium and calcium salts made somewhat alkaline by ammonia, but a very large quantity of this, as well as of ammoniacal salt, is to be avoided. The beaker in which the precipita- tion is to be effected should, while perfectly dry and warm, be rubbed within by chamois leather on which a drop or two of fine oil (such as is used for oiling balances) has been put. If this precaution be not taken it will be found impossible to detach the precipitate of calcium tungstate from the sides and bottom of the vessel. A considerable excess of the reagent is not necessary, but, if it occur, is not material. If, on the addition of the reagent, a white flocculent precipitate forms im- mediately, it is well to add a few drops of ammonia, when the flocculent precipitate will redissolve ; but, if it does not redissolve after warming, there is some other element present, which, if ordinary Epsom salts are used, will probably be manganese. The calcium tungstate precipi- tate is very dense ; it forms slowly in very dilute solutions, and, in all cases, several hours should be allowed for it to form. The solution should be warmed meanwhile, but must not be allowed to boil. The precipitate must be washed till the filtrate shows no cloudiness on standing with silver nitrate when the salts are chlorides ; or, if they are sulphates, till barium chloride gives no cloudiness. The precipitate must then be further washed with dilute solution of ammonia, but these washings need not be saved. The filter should be burnt sepa- rately, after the precipitate is cleared from it as much as possible. After the ignited precipitate is weighed, a little strong solution of ammonia should be poured upon it, and allowed to stand for a while, when the ammonia is decanted, and supersaturated with acid. If a precipitate falls after a time, the calcium tungstate precipitate should (without being removed from the crucible) be allowed to stand for some hours with more ammonia ; it is then washed by decantation, again ignited, and weighed. The ignited precipitate should be perfectly white. The filtrate containing the magnesium salt and sodium tungstaie may be at once precipitated by sodium phosphate in the usual way ; but if this i done much washing is required to get rid of the little tungstic acid that adheres obstinately to the precipitate. It is better, especially when a great excess of the reagent has been used, to first precipitate the tungstic acid by a considerable excess of hydrochloric acid, and boil until the precipitate becomes dense and intensely yellow. The solution is then filtered, supersaturated with ammonia, and the magnesium precipitated in the usual way ; but, even in this case, it is better to wash lastly with stronger ammonia solution than ordinary. (E) Mr. E. Sonstadt also separates calcium and magnesium in the following manner. He finds that calcium iodate is not sensibly soluble MAGNESIUM FROM CALCIUM 53 in a saturated solution of potassium iodate, whereas magnesium iodate is not precipitated from solution in any degree by potassium iodate. If to 10 or 12 c.c. of a saturated solution of potassium iodate a few drops are added of solution of calcium sulphate, and after two hours the liquid is filtered and ammonium oxalate added to the nitrate, a slight opalescence appears after a while, due to the presence of a trace of calcium. But if the potassium iodate solution to which the calcium salt was added, is allowed to stand twenty hours, and is then filtered and ammonium oxalate added to the filtrate, not the slightest opales- cence appears, even after many hours. A slight crystallisation takes place, owing to a diminution of the solubility of the potassium iodate by the presence of ammonium oxalate, but the crystals entirely disap- pear, leaving the solution perfectly limpid on addition of a very small proportion of water. The precipitation of calcium by saturation of the solution with potassium iodate does not appear to be affected by the presence of alkali and magnesium salts, in whatever proportion these may be present. If, for instance, a small quantity, such as a decigramme, of ordinary Epsom salts is dissolved in the least possible quantity of water, and four or five times its bulk of a saturated solution of potas- sium iodate is added, after a few hours a crystalline precipitate forms, which may be collected on a filter, washed with solution of potassium iodate, dissolved off the filter with dilute hydrochloric acid, and minute as the quantity of calcium present is, it may be shown immediately by the precipitate falling on addition of ammonia and ammonium oxalate to the strongly acid filtrate. In separating calcium from magnesium by precipitation of the former by potassium iodate it is obviously important, in view of the subsequent determination of the magnesium, to know if the presence of potassium iodate hinders the precipitation of magnesium as mag- nesium-ammonium phosphate. So far from this being the case, it is found that the double phosphate is even less soluble in a saturated solution of potassium iodate containing some free ammonia than it is in a mixture of two parts ordinary ' liquor ammonias ' with one part of water. Thus the addition of solution of potassium iodate to the ordi- nary liquid containing phosphate of an alkali and much free ammonia, over precipitated magnesium ammonium phosphate, renders the fluid at once opalescent, and occasions an additional precipitation of magne- sium salt. Mr. Sonstadt says that he has never met with a specimen of any magnesia or magnesium salt in commerce, although sold as chemically pure, that did not contain a very sensible portion of calcium. The only available source of a magnesium salt free from calcium is distilled magnesium. (F) Dr. Mohr also uses microcosmic salt in precipitating magnesia after lime from an ammoniacal solution which has been kept clear by means of sal-ammoniac. 54 SELECT METHODS IN CHEMICAL ANALYSIS (G) In separating magnesium salts from lime, ferric oxide, and the alkalies, H. Hager mixes the finely powdered sample with 10 parts of glycerine and a little water, and adds 40 to 50 parts of solution of oxalic acid at 5 per cent. Calcium and magnesium oxalates are both formed, the former remaining undissolved, whilst the magnesium salt passes into solution. After standing for half an hour the calcium oxalate is collected upon a filter, washed, and determined as usual. The filtrate is boiled in a flask for five to eight minutes, filtered boiling, and the precipitate is dried, and weighed as magnesia. In a solution containing calcium and magnesium salts the liquid is first mixed with glycerine, a sufficiency of ammonium oxalate is added, the liquid is strongly acidified with oxalic acid, and the process is completed as above. Magnesium can also be precipitated as an oxalate in presence of ferric oxide by adding glycerine, ammonium oxalate, and oxalic acid, and then boiling. In order to determine the ferric oxide in the filtrate it is heated to a boil along with ammonium carbonate, evaporated to dryness, the glycerine extracted with alcohol, the insoluble residue treated with hot ammoniacal water, and the ferric hydroxide collected upon a filter. For separating magnesia from the alkalies the hydrochloric solution is boiled with ammonium oxalate and oxalic acid, and filtered at a boil. (H) The following method shows whether in calcined magnesia or magnesium carbonate the proportion of lime exceeds a certain limit : 0-1 gramme of calcined magnesia or 0-25 gramme of the carbonate must be well shaken up in a test-tube with a solution of oxalic acid at 5 or 10 per cent. Perfectly pure preparations dissolve in the first minute, and the solution remains clear for five minutes ; in presence of lime the solution is turbid. In the latter case the agitated turbid liquid is poured into a test-tube 1*25 centimetre wide, and an ink-line upon paper 1 millimetre in breadth is examined through the column of liquid. If the line is perceptible, the preparation of lime in the calcined magnesia does not exceed 0-25 per cent., and that in the carbonate O'l per cent. Separation of Magnesium from Potassium and Sodium In the following method phosphoric acid can be employed under all circumstances, since its ill effects are neutralised by the complete elimination of any excess of it. Acidulate the liquid with nitric acid, and then add excess of am- monia. To the filtered liquid add ammonium phosphate, or simply phosphoric acid, and collect the ammonio-magnesium phosphate pre- cipitate. To get rid of the ammoniacal salts, filter, evaporate, and calcine ; this causes the greater part, or even the whole, of the hydro- MAGNESIUM FKOM ALKALIES 05 chloric acid to be eliminated, when that acid is present, and the two bases remain united with phosphoric acid only. However, to make certain, treat the residue two or three times with concentrated nitric acid and calcine, when the whole of the hydrochloric acid being thus eliminated, only phosphoric acid, potash, and soda remain. The residue is collected in a flask and treated by a large excess of tin and nitric acid ; the phosphoric acid being thus rendered insoluble, the liquid is filtered and concentrated. The residue, composed of potas- sium and sodium nitrates, is calcined till completely decomposed, and as soon as the capsule is cooled the caustic alkalies are transformed into carbonates, after which they are converted into chlorides, then into sulphates, and finally ammonium carbonate is added to decom- pose the potassium bisulphate. With these combined elements it is possible to determine the quantity of each alkali indirectly. The exactness of this process consists in the method of removing the phosphoric acid a method founded on the property (discovered by A. Eeyiioso) possessed by stannic acid of forming a combination with phosphoric acid completely insoluble in water and in nitric acid. To render this process accurate, the hydrochloric acid must be eliminated an object easily effected. 56 SELECT METHODS IN CHEMICAL ANALYSIS CHAPTER III CERIUM, LANTHANUM, DIDYMIUM, SAMARIUM, THOKIUM, GLUCINUM r THE YTTRIUM METALS, TITANIUM, ZIRCONIUM CERIUM, LANTHANUM, DIDYMIUM, SAMARIUM, AND THORIUM Separation and Estimation of the Cerium Metals together THE precipitation of the cerium metals in the form of oxalates from a slightly acid solution is, unquestionably, the most satisfactory method of separating these oxides. The estimation of the oxalates upon a weighed filter is accompanied with the usual trouble and loss of time in perfectly drying the filter before and after collecting the precipitate upon it. By the following mode of proceeding Dr. W. Gibbs com- pletely avoids these difficulties. The usual mixture of cerium, lantha- num, didymium, and samarium, when neutral, is to be rendered slightly acid by sulphuric or hydrochloric acid, and then largely diluted with water. Half a litre of water for every estimated gramme of oxide is a good working proportion. The solution is then to be boiled, and a hot solution of oxalic acid or ammonium oxalate added. On cooling, especially when the solution has been well stirred with a glass rod, or shaken, the oxalates separate in large crystalline grains of a pale rose- violet colour. The precipitate is to be filtered off and well washed with boiling water, the washing being extremely easy in consequence of the coarse granular character of the precipitate. The filter is then to be pierced and the oxalates carefully washed down into a crucible ; after which the water in the crucible may easily be removed by evapo- ration, and the oxalates dried at a temperature of 100. The equiva- lents of lanthanum and didymium are so near to that of cerium, that no very sensible error is committed by considering the mixed oxalates as consisting simply of cerium oxalate with three equivalents of water. Separation of Cerium from Didymium and Lanthanum (A) The following method, which we owe to the researches of Messrs. Pattison and Clarke, has been found to be very effective for the separation of cerium from didymium and lanthanum. It is based upon the fact that when cerium chromate is evaporated to dryness and heated SEPARATION OF CERIUM 57 to about 110, it is decomposed, and the cerium oxide remains as an insoluble powder, whilst the didymium and lanthanum chromates, when subjected to the same treatment, remain unchanged. The mixed cerium, didymium, and lanthanum oxides are subjected to the action of an aqueous solution of chromic acid, aided by heat till solution is complete. The chromic acid need not be entirely free from sulphuric acid. The solution obtained is evaporated to dryness, and the residue heated to about 110. Hot water is then added, which dissolves the lanthanum and didymium chromates and leaves the cerium oxide, which is then separated by filtering. Thus obtained, the cerium oxide is a yellowish-white powder which is almost completely insoluble in acids, but is rendered soluble by fusion with the acid potassium sulphate. This process may also be employed for the quantitative determina- tion of cerium, as it has been found, by careful trial, that not a trace of cerium can be detected by the best known processes in the solution after its separation as above described. (B) Dr. Wolcott Gibbs has found that when a mixed cerium, lan- thanum, and didymium salt is boiled with dilute nitric acid, and lead peroxide added to the solution, the cerium is quickly, and under some circumstances completely, oxidised, the solution becoming more or less deeply orange-yellow. This process affords an extremely simple and delicate test for cerium ; it succeeds with all the salts which are soluble in nitric acid, though, of course, when the mixed oxalates are tested the oxalic acid is oxidised to carbonic acid before the characteristic cerium yellow appears. For the purpose of testing, it is sufficient to dissolve the salt to be examined in nitric acid diluted with its own volume of water, to add a small quantity of pure lead peroxide and boil for a few minutes, when the smallest trace of cerium can be detected by the yellow colour of the solution. When a solution containing a cerium salt dissolved in strong nitric acid is boiled for a short time with a large excess of lead peroxide, oxygen gas is copiously evolved, and, at the same time, the cerium sesquioxide formed at first is completely reduced to protoxide, the solution becoming perfectly colourless. The remarkable reaction which occurs in this case appears to be connected with the formation of lead nitrate, since, when the solution of cerium protoxide contains a large excess of this salt, the cerium is not peroxidised by boiling with nitric acid and the peroxide. When a solution of cerium, didymium, and lanthanum is treated with nitric acid and lead peroxide in the manner pointed out above, the deep orange-coloured liquid evaporated to dryness, and heated for a short time to a temperature sufficiently high to expel a portion of the acid, it will be found that boiling water acidulated with nitric acid dissolves only the lanthanum and didymium salts, leaving the whole of the cerium in the form of a basic nitrate insoluble in water. The insoluble matter is to be filtered off and thoroughly washed. A 58 SELECT METHODS IN CHEMICAL ANALYSIS current of sulphuretted hydrogen passed into the filtrate removes the lead, after which the lanthanum and didymium may be precipi- tated together as oxalates, which, if the process has been carefully performed, are perfectly free from cerium. The mass on the filter is readily dissolved by fuming nitric acid. Sulphuretted hydrogen is then to be passed through the solution, sufficiently diluted with water, until the lead is completely precipitated. The cerium may then be thrown down by oxalic acid, ignited, and weighed as ceroso-ceric oxide or converted into sulphate and weighed as such. Cerium proto-nitrate obtained by this process gives, when tested by the spectroscope with transmitted light, even in very thick layers, a scarcely perceptible indication of didymium. (C) Another very good method of separating the cerium from lantha- num and didymium is to precipitate the three metals in the state of gelatinous hydrates by adding an excess of caustic potash to their solution. These oxides are washed several times by decantation, and then a concentrated solution of caustic potash is added, and the whole submitted to a current of chlorine. The alkaline liquid being thus saturated with chlorine, the lanthanum and didymium oxides are re- dissolved, lemon-coloured insoluble eerie oxide remaining. This sub- stance is washed on a filter, then re-dissolved, while still moist, in hydrochloric acid, precipitated by ammonium oxalate, and strongly calcined ; the cerous oxalate is thus transformed into very light rose- coloured ceroso-ceric oxide. The chlorinated liquid contains lanthanum and didymium oxides, which may be precipitated together by adding ammonium oxalate. (_D) For the separation of cerium from didymium and lanthanum, as in cerite, M. H. Debray melts the mixed nitrates with 8 or 10 parts of potassium nitrate in a porcelain capsule, and the fused mass is kept between 300 and 850 by means of a gas furnace. Cerium nitrate is decomposed, forming a yellowish powder of cerium oxide, which retains a little nitric acid, but didymium and lanthanum nitrates, when melted with nitre, are not appreciably decomposed, even at 350. A thermo- meter, plunged into the bath of nitrate, indicates its temperature. When the escape of nitrous fumes ceases, which requires several hours, the operation is stopped. "When cold the melted mass is easily detached from the capsule, and the cerium oxide is found collected at the lower part. It is dissolved in water, and there remains a powder, yellowish if it contains mere traces of didymium, but reddish if it contains more. It is well to wash with a little weak nitric acid, which dissolves a little didymium subnitrate, produced at the same time as the cerium oxide if the capsule is too strongly heated at certain points. This is of little consequence, as the cerium oxide obtained in the first operation always requires to be purified. It may be entirely freed from didymium by transforming it into nitrate, which is melted a second time with 8 or 10 parts of potassium ' LANTHANUM FKOM DIDYMIUM 59 nitrate. For this purpose the oxide is treated with sulphuric acid diluted with an equal volume of water, when everything dissolves if the liquid is sufficiently acid. The yellow ceroso-ceric sulphate thus obtained is reduced with sulphurous acid, and the cerous sulphate is precipitated with oxalic acid. The cerous oxalate is then readily converted into nitrate by boiling with nitric acid. This second treatment gives a yellow powder, which contains neither didyinium nor lanthanum, as the nitrate of the latter earth is still more stable than that of didymium. If it is transformed into colourless cerous sulphate the spectroscope does not detect the least trace of this body, which is always easy to recognise by its absorption- spectrum. The didymium and lanthanum nitrates, which remain mixed with a large excess of potassium nitrate, are evaporated and remelted, the temperature being between 350 and 450. The remaining trace of cerium nitrate which has escaped decomposition in the former operation is completely destroyed, and there is even formed a small quantity of didymium subnitrate. But the bulk of the didymium remains with the lanthanum in the state of a soluble nitrate. We have thus a certain and rapid method of obtaining cerium oxide free from didymium and lanthanum, or, on the other hand, a mixture of these two oxides absolutely free from cerium. Separation of Lanthanum from Didymium (A] The nitric acid solution of lanthanum and didymium is evapor- ated to dryness in a flat-bottomed capsule. The dried mass is of a pale rose tint. By exposing the capsule for a few minutes to a temperature of 400 or 500 the saline mass will be fused, with disengagement of nitrous vapours. The capsule is withdrawn from the fire before the decomposition is complete, and hot water must be poured in. Lan- thanum nitrate dissolves and didymium subnitrate remains insoluble in the form of greyish-white flakes. The whole is left to stand for a few hours, then boiled and filtered ; if the liquid still retains a feeble rose tint, the same operation must be repeated until a colourless liquid is obtained, containing lanthanum nitrate, free from didymium subnitrate. Lanthanum oxide is obtained by evaporating this liquid and strongly calcining the residue. The didymium oxide may also be estimated after the calcination of the subnitrate thus obtained. This process, which was first devised by MM. Daniour and De- ville, is founded on the fact that didymium nitrate decomposes before lanthanum nitrate, and that the first of these salts changes to the state of subnitrate. Several precautions must be observed. The bottom of the capsule containing the mixture of the two salts must not be too much heated, nor must too large quantities of material be used, as in that case it forms a thick layer at the bottom of the capsule and decomposes unequally. It is better to recommence the operation 60 SELECT METHODS IN CHEMICAL ANALYSIS several times than to heat too strongly in attempting to separate the two oxides at the same time. The first portions of didymium oxide ob- tained in this way give, with sulphuric acid, reddish-violet crystals, with traces of white needle-shaped ones, which belong to the lanthanum sulphate. The last portions give a sulphate less coloured, but, like the preceding, with the same crystalline form derived from the oblique rhomboidal prisms ; the needles of lanthanum sulphate are rather more numerous. Finally, the above-described colourless solution gives, with sulphuric acid, colourless crystals derived from the right rhomboidal prism, characteristic of lanthanum sulphate. By following this method, the estimation of didymium comes out rather too high, and consequently, that of lanthanum rather too low. (B) Dr. C. Winckler has ascertained that when cerium is separated from its solutions by mercury binoxide and potassium permanganate the cerium is not merely precipitated in the state of a peroxide, but is accompanied by didymium, whilst; the lanthanum remains in solution. This is an excellent method for separating didymium from lanthanum. To obtain the didymium which accompanies the cerium in its pre- cipitation by potassium permanganate, redissolve the precipitate in hydrochloric acid. After having well calcined it to free it from the mercuric oxide, evaporate the hydrochloric solution to dryness in the presence of sulphuric acid ; dissolve the residue of sulphate in water, and add potassium sulphate to it. In twenty-four hours a triple cerium, didymium, and potassium sulphate separates, insoluble in potassium sulphate. The precipitate must then be dissolved in water, and the sulphates changed to oxalates, which are calcined to obtain the cerium and didymium oxides ; these are then separated in the usual way. The lanthanum in the filtered liquid may be obtained thus : First treat the filtered liquid with sulphuretted hydrogen, to separate the mercuric oxide, then precipitate the lanthanum as an oxalate, and calcine it. The lanthanum oxide then contains very little didymium. Lanthanum and didymium may also be separated by taking advan- tage of the different solubilities of their sulphates. By digesting a mixture of the dry salts in cold water (5), a saturated solution may be obtained, which, upon being heated to 30, deposits lanthanum sulphate, whilst didymium sulphate remains dissolved. The salts may be obtained quite pure by repeating this operation two or three times. Lanthanum sulphate is colourless, whilst didymium sulphate is of a beautiful rose-red. Volumetric Determination of Cerium. Franz Stolba deter- mines eerie oxalate volumetrically by means of potassium permanganate. Pure eerie sulphate, carefully dehydrated, is dissolved to the volume of a litre, and measured portions of the solution are precipitated with ammonium oxalate, the latter being determined in the known manner ANALYSIS OF CERITE 61 with standard permanganate, the solution of the latter being standard- ised by means of lead oxalate. On the other hand, portions of the solution are taken for determination as cerium oxide. Using the atomic weight Ce=141'27, the quantity of cerous oxide is ascertained from the quantities of standard permanganate consumed. The results are concordant, and where differences appear they fall within the inevitable errors of observation. Hence, cerium, when freed from lanthanum and didymium, and separated as oxalate, may be conveniently and accurately determined as such. A corresponding quantity of sulphuric acid must be employed in titratioii, and warm water used. During the process, the quantity of undissolved matter diminishes, and the change of colour at the conclusion is distinctly marked. Analysis of Cerite. Separation of Cerium, Didymium, Samarium, and. Lanthanum. The mineral cerite is a hydrated cerium silicate with lanthanum, didymium, samarium, and iron ; traces of some of the other rare earths are also present, as yttria, terbia, &c. As quantitative methods of any exactness for the separation of some of these earths are not yet know^n, the true composition of the mineral is only known approximately, and in its structure it is anything but homogeneous. Its composition agrees with the formula for the ortho- silicates, R 2 Si0 4 + aq., and it contains from 55 to 60 per cent, of cerium oxide, about 8 per cent, of the lanthanum, didymium, and samarium oxides, 20 per cent, of silica, and 6 per cent, of water. (A) To disintegrate the mineral it is finely ground, made into a thick paste with strong sulphuric acid, and heated to drive off excess of acid. The mass becomes of a white or pale grey colour. This is digested in cold water, filtered, and the residue well washed with cold water. It should be remembered that the sulphates of the cerium earths are much less soluble in hot than in cold water. To the filtrate oxalic acid is added, which precipitates all the earths, with any lime and bismuth that may be present, as oxalates. It is sometimes advisable to ignite the oxalates so obtained and boil the residue in dilute nitric acid, by which means the didymium, samarium, and lanthanum oxides are dissolved, leaving the greater part of the cerium oxide insoluble ; this method is objectionable, how- ever, as the cerium oxide retains obstinately much didymium, and probably also lanthanum and samarium. A better plan is to heat the dried oxalates with strong nitric acid till all dissolves, and allow to cool, or dilute, when a mixture of oxalates separates out rich in didymium and samarium, the solution containing much cerium and lanthanum oxalates. (jB) For the general method of separating the earths, however, it is well to proceed as follows : The dried oxalates are boiled with .stiong nitric acid till completely decomposed, evaporated to dryness, 62 SELECT METHODS IN CHEMICAL ANALYSIS and fused at the lowest temperature at which nitrous fumes come off, the residue digested in water, filtered, and washed. The insoluble residue, of a pale yellow colour, consists of cerium oxide and basic cerium nitrate, with a little didymium, whilst the filtrate contains the lanthanum, didymium, and samarium. The operation of fusing must be repeated on the filtrate many times to throw out all the cerium, whilst the cerium oxide, or basic nitrate obtained, is freed from any didymium by retreatment with nitric acid and fusion as above ; the presence of didymium in it being indicated by its brown colour or by the absorption spectrum of the solution. To free the didymium and other nitrates from the last traces of cerium it is necessary to fuse them with three or four times their weight of potassium nitrate, very gently, at a temperature just sufficient to cause slight decomposition. The separation of lanthanum, didymium, and samarium from each other is a most laborious process, and the amount of these earths, obtainable in anything like a pure state, small, compared with the mass of material worked up. The solution of the nitrates of these elements is made perfectly neutral, diluted to such a strength as to contain about 1 per cent, of the oxides and a very dilute solution of ammonia added, about ! gramme NH 3 in 500 cubic centimetres ; the precipitation being conducted in large vessels, such as ordinary Winchester quart bottles. The first precipitates formed are rich in samarium and con- tain much didymium ; these are followed by didymium, with some lanthanum and samarium ; and the final precipitates consist almost wholly of lanthanum. By this method there are obtained three portions of hydrates, which must be again worked up separately by precipita- tion as above ; the first for samarium, the second for didymium, and the third for lanthanum, the process of fractional precipitation being repeated on each portion fifty or a hundred times. The separation of the last traces of didymium from the samarium can only be accomplished by fractional precipitation, an operation so tedious that few chemists will probably be inclined to undertake it. The second portion of hydrates, consisting chiefly of didymium, is purified from the small quantities of samarium and lanthanum it contains by fusing with potassic nitrate for the samarium, as explained above for the traces of cerium ; whilst to separate the lanthanum the oxalates are dis- solved in warm strong nitric acid and allowed to cool, when didymium oxalate nearly free from lanthanum is obtained ; repeated several times, the last trace of lanthanum remains in the solution. To separate the small quantity of didymium from the lanthanum obtained as the final precipitate with ammonia, the only method is by a continuation of the process of fractionation ; the lanthanum oxide finally obtained should be pure white, any trace of a yellowish tinge indicating that didymium is still present. As cerite contains small quantities of the yttria earths, these may be separated from cerium, didymium, &c., by making a cold solution PREPARATION OF PURE OLUCINA 6& of the sulphate and adding finely powdered potassium sulphate in quantity more than sufficient to saturate the solution ; it is then allowed to stand (with frequent agitations) for a few days and filtered, washing the precipitate with a saturated solution of potassium sulphate. The fil- trate contains the yttria earths, and for their complete separation it is advisable to repeat the operation with potassium sulphate three or four times. The insoluble residue, consisting of a double sulphate of potassium, cerium, didyniium, &c., is boiled with sodium hydrate, filtered, well washed, redissolved in nitric acid, precipitated with oxalic acid, and the oxalates ignited, leaving the earths lanthana of a pure white colour, didymia of a deep chocolate brown, and samaria of a pale brown colour. Separation of Thorium from other Earthy Metals Prof. L. Smith has discovered an exact method for separating thoria from the other earths. It consists, like the method employed for separating cerium from didymium and lanthanum, in suspending the oxides recently precipitated in water containing four to five times their weight of caustic potash or soda, and in passing a current of chlorine into the liquid. All the oxides are dissolved, save those of cerium and thorium, the residue being a gelatinous precipitate, like alumina. He has also employed fractional precipitation with ammonia for separating the greater part of the thoria in operations on a large scale ; the thoria comes down first, but the separation is not sufficiently exact for analy- tical purposes. GLUCINUM Preparation of Pure Glucina The simplest way to prepare a chemically pure glucinum salt is to make use of the process devised by Dr. W. Gibbs. The crude glucina obtained in the ordinary manner from beryl, but still contaminated with alumina, iron, &c., is fused with twice its weight of acid potas- sium fluoride, and the fused mass treated with boiling water, to which a small quantity of hydrofluoric acid has been added. On filtering, a notable quantity of the insoluble aluminium and potassium fluoride almost always remains upon the filter, even when the separation -of glucina has been carefully executed by means of ammonium carbonate. The filtrate, on cooling, deposits colourless transparent crusts of the double glucinum and potassium fluoride, which are easily purified by recrystallisation. Glucina may be prepared direct from beryl by this process, but as beryl only contains 13 or 14 per cent, of glucinum, it will be more economical to separate the other oxides, as far as possible, by the ordinary methods, and then to purify the crude glucina by the above process. From the aqueous solution of the double fluoride, pure glucina may be precipitated directly by ammonia. 64 SELECT METHODS IN CHEMICAL ANALYSIS Separation of G-lucinum from the Cerium Metals The separation may best be effected in the following way : Convert the salts into sulphates, and dissolve in the smallest quantity of water. If iron be present, reduce it to the state of protosulphate, by passing a stream of sulphuretted hydrogen through the hot solution ; if this precaution is not taken, the precipitated double sulphates will contain iron. Then add a saturated solution of sodium sulphate (which Dr. W. Gibbs has shown to be greatly superior to potassium sulphate for this purpose), and sufficient dry sodium sulphate in powder to saturate the water of solution. It is most advantageous to use hot solutions. The insoluble double sulphates of sodium and the cerium metals separate immediately as a white, highly crystalline powder, which is thrown upon a filter and washed thoroughly with a hot saturated solution of sodium sulphate. After washing, the double sulphates on the filter are .to be dissolved in hot dilute hydrochloric acid, the solution largely diluted with water, and the cerium metals precipitated by ammonium oxalate. From the filtrate the glucinum may be precipitated at once by ammonium hydrate. THE YTTRIUM METALS Analysis of the Natural Tantalates containing the Yttrium Metals. Prof. J. L. Smith calls attention to the use made for their solution of concentrated hydrofluoric acid, whose action, es- pecially upon the samarskite and euxenite of North Carolina, is as rapid and energetic as that of hydrochloric acid upon calcareous spar. If finely powdered samarskite is taken, moistened with its own weight of water, and treated with twice its weight of fuming commercial hy- drofluoric acid, the attack takes place in the cold in a few seconds, the mass heats with a slight effervescence, and the decomposition is effected in from five to ten minutes. If needful, the action may be assisted by exposure to the heat of the water-bath for a few moments. The cap- sule is then kept at the temperature of boiling water long enough to expel the excess of acid. The contents of the capsule are then treated with 30 to 40 grammes of water (to 5 grammes of mineral) thrown upon a filter and carefully washed, adding, if needful, one or two drops of hydrofluoric acid. The mineral is thus separated into two portions ; the filtrate, containing all the metallic acids and the iron and man- ganese oxides, and the insoluble precipitate, containing all the earths and uranic oxide. The difficulty of the attack increases with the pro- portion of tantalic acid in the minerals. The most interesting con- stituents of samarskite are the earths. In the description already published of the North Carolina variety, the author merely arranged the earths in two classes the yttria group and the cerium group DISTRIBUTION OF YTTRIUM 65 remarking that the latter probably did not contain cerium oxide, and that the thoria detected in the variety from the Urals was present in too small quantity to be recognised in a satisfactory manner, fie has since found that the earths of the yttria group consist of about two- thirds yttria and one- third erbia. t Separation of the Yttrium Metals from G-lucinum These metals may be separated by mixing the precipitated hydrated oxides with sugar, drying, and then heating to redness in a covered crucible. The black carbonised mass is then introduced into a piece of combustion-tubing, and heated to redness, whilst a slow current of dry chlorine is passed over. The chlorides of the yttrium metals are non-volatile, whilst glucinum chloride volatilises and may be collected in any appropriate condenser. Separation of the Yttrium Metals from those of Cerium The yttrium metals behave the same as glucinum, in respect to sodium sulphate. The double sulphates of sodium and the yttrium metals, being readily soluble in sodium sulphate solution, may be separated from cerium, lanthanum, and didymium in the way detailed on the previous page. ON THE DETECTION AND WIDE DISTRIBUTION OF YTTRIUM > Introduction 1 . ' In March, 1881, 1 sent to the Eoyal Society a preliminary notice of some results I had obtained when working on the molecular discharge in high vacua. 2 When the spark from a good induction coil traverses a tube having a flat aluminium pole at each end, the appearance changes according to the degree of exhaustion. Supposing atmospheric air to be the gas under exhaustion, at a pressure of about 7 millimetres a narrow black space is seen to separate the luminous glow from the aluminium pole connected with the negative pole of the induction coil. As the exhaustion proceeds this dark space increases in thickness, until, at a pressure of about 0'02 millimetre (between 20 and 30 M.), 3 the dark spark has swollen out till it nearly fills the tube. The luminous cloud showing the presence of residual gas has almost dis- appeared, and the molecular discharge from the negative pole begins to excite phosphorescence on the glass where it strikes the side. There- is a great difference in the degree of exhaustion at which various sub- 1 ' The Bakerian Lecture, by William Crookes, F.B.S. Delivered before the Eoyal Society, May 31, 1883. - ' Proceedings of the Royal Society, No. 213, 1881. :i ' M = one-millionth of an atmosphere. 06 SELECT METHODS IN CHEMICAL ANALYSIS stances begin to phosphoresce. Some refuse to glow until the ex- haustion is so great that the vacuum is nearly non-conducting, whilst others begin to show luminosity when the gauge is 5 or 10 millimetres below the barometric level. The majority of bodies, however, do not phosphoresce till they are well within the negative dark space. This phosphorogemc phenomenon is at its maximum at about 1 M., and unless otherwise stated, the experiments now about to be described were all tried at this high degree of exhaustion. ' Under the influence of this discharge, which I have ventured to call radiant matter, a large number of substances emit phosphorescent light, some faintly and others with great intensity. On examining the emitted light in the spectroscope, most bodies give a faint continuous spectrum, with a more or less decided concentration in one part of the spectrum, the superficial colour of the phosphorescing substance being governed by this preponderating emission in one or other part of the spectrum. ' Sometimes, but more rarely, the spectrum of the phosphorescent light is discontinuous, and it is to bodies manifesting this phenomenon that my attention has been specially directed for some years past, considerable interest attaching to a solid body whose molecules vibrate in a few directions only, giving rise to spectrum lines or bands on a dark background. The Citron-Band Spectrum 2. * For a long time past I have been haunted by a bright citron- coloured band or line appearing in these phosphorescent spectra, sometimes as a sharp line, at others as a broader nebulous band, but having always a characteristic appearance and occurring uniformly in the same spot. This band I first saw in the summer of 1879, and from that date down to a comparatively short time ago all my efforts to clear up the mystery proved vain. By chemical means it was not difficult to effect a partial separation of a certain mineral or earthy body into two parts, one giving little or no citron-band, the other giving one stronger than the original band; and by again treating this latter portion by appropriate chemical means, the citron-band forming body could frequently be still more concentrated ; but further than this for a long time it seemed impossible to go. I soon came to the conclusion that the substance I was in search of was an earth, but on attempting to determine its chemical properties I was baffled. A more Proteus-like substance a chemist never had to deal with. In my preliminary note, above referred to, speaking of the possibility that some of these spectrum-forming bodies might be new chemical elements, I said : " The chemist must be on his guard against certain pitfalls which catch the unwary. I allude to the profound modification which the presence of fluorine, phosphorus, boron, &c., causes in the chemical reactions of many elements, and to the interfering action of DISTRIBUTION OF YTTRIUM 67 a large quantity of one body on the chemical properties of another which maybe present in small quantities." 3. * This warning was not unnecessary. No Will-o'-the-Wisp ever led the unwary traveller into so many pitfalls and sloughs of despond as the hunt for this phantom band has entrapped me. I have started with a large quantity of substance which, from preliminary observa- tions, promised to be a rich mine of the desired body, and have worked it up chemically to a certain point, when the citron band vanished, and could not be again detected in either precipitate or nitrate. Half-a-dozen times in the last four years the research has been given up as hopeless, and only a feeling of humiliation at the thought of a chemist being beaten by any number of anomalies made me renew each time the attack. Likewise, the tedious character of the research made a long continuance of failures very disheartening. To perform a spectrum test, the body under examination must be put in a tube and exhausted to a very high point before the spectroscope can be brought to bear on it. Instead of a few minutes, many hours are occupied in each operation, and the tentative gropings in the dark, pre-eminently characteristic of this kind of research, have to be extended over a long period of time. 4. ' I soon found that the best way to bring out the band was to treat the substance under examination with strong sulphuric acid, drive off excess of acid by heat, and finally to raise the temperature to dull redness (10). The anhydrous sulphate thus left frequently showed the citron band in the radiant matter tube, when before this treatment the original substance showed nothing (75). * Examination of Calcium Compounds 5. ' My first idea was that the band might be due to a compound of lime. Much chemical evidence tended to support this view. I have already explained that the chemical extraction was rendered very difficult by the fact of the citron band so frequently turning up both in the precipitate and the filtrate. By neglecting the portion showing the least citron band, and removing all the elements present which gave little or none, I could generally concentrate the citron band into a solution which according to our present knowledge of analytical chemistry should contain little else than the earths, alkaline earths, and alkalies. Ammonia added to this solution would precipitate an earth (11, 14), and in the filtrate from this oxalic acid would precipitate an insoluble oxalate (7, 13). 'The citron band hovered between these two precipitates, being sometimes stronger in one and sometimes in the other. It was also to be detected, but more faintly, in the residue left after evaporating to dryness and igniting the filtrate from the oxalate. * I frequently obtained no precipitate with ammonia, and then the F 2 68 SELECT METHODS IN CHEMICAL ANALYSIS oxalate gave the band brilliantly ; and occasionally the ammonia pre- cipitate when formed gave little or no citron band. I was, however, generally sure to find it in the insoluble oxalate, and sometimes it was very brilliant, being accompanied by two bright green bands and a fainter red band. 6. ' At this time one of the minerals which showed the citron band most strongly was a phosphorescent apatite from Ireland ; and know- ing the difficulties of separating the last traces of phosphoric acid from the earths, I explained the foregoing facts by the presence of small quantities of phosphoric acid, which gave rise to the ammonia precipi- tate ; the bulk of the citron body not being precipitated by ammonia, but coming down as oxalate ; whilst a little of this oxalate would remain dissolved in the ammoniacal salts present, and so appear with the alkalies. * I tested this hypothesis in every imaginable way, by mixing small quantities of phosphoric acid with salts of lime and other earths, in the endeavour to imitate the conditions occurring in the native minerals, and so educe the citron band ; but I was unable to get any precipitate giving the citron band when I started with materials which did not originally give it. 7. * A sufficient quantity of precipitated oxalate (5) having in course of time been accumulated, I attempted its purification. It was ignited, dissolved in dilute hydrochloric acid, and rendered slightly alkaline with ammonia and ammonium sulphide. The liquid was boiled to a small bulk, keeping it alkaline, and was then set aside in a warm place : a slight flocculent precipitate formed. This was filtered, and the filtrate reconcentrated. The clear strong solution should now contain nothing but barium, strontium, and calcium, with traces of elements from previous groups which might be soluble in the precipi- tants employed or in the ammoniacal salts present (for we know that the word insoluble applied to a precipitate is not an absolute term, and in minute analysis allowance must be made not only for the slight solubility of precipitates in the reagents present, but also for the power possessed by most precipitates of carrying down with them traces of soluble metallic salts from solution). Besides these, it was possible that a hitherto unrecognised element might be present, to which the citron band was due. By the ordinary process of analysis I could, however, only detect the presence of calcium and strontium. 8. * The concentrated ammoniacal solution was added to an excess of a boiling solution of ammonium sulphate, and the whole was set aside for twenty-four hours ; the precipitate which had formed was filtered off and washed with a saturated solution of ammonium sulphate. The precipitate was found to consist of strontium sulphate. On testing this in a radiant matter tube the citron band was very decided, although much fainter than in the original oxalate. The filtrate was diluted largely, heated, and precipitated with a hot solution of ammonium DISTRIBUTION OF YTTEIUM 69 oxalate ; it was then allowed to stand for some time, when a bulky white calcium oxalate came down. This was filtered and washed. Tested in the radiant matter tube, after ignition and treatment with sulphuric acid, it gave the citron band, far exceeding in brightness the spectrum of the original oxalate. 9. ' So far all the chemical evidence went to show that the band- forming substance was calcium, and further tests tried with the puri- fied oxalate confirmed this inference. Every analytical test to which it was subjected showed lime, and nothing but lime; all the salts which were prepared from it resembled those of lime, both physically and chemically ; the flame spectrum gave the calcium lines with extraordinary purity and brilliancy ; and finally, the atomic weight, taken with great care, came out almost the same as that of calcium, 39 '9 as against Ca 40. 10. ' I now sought for the citron band amongst other calcium minerals. The preliminary testing was simple. The finely powdered mineral was moistened with strong sulphuric acid, the action being assisted by heat, and the mass was raised to dull redness (4). It was then put into a radiant matter tube and the induction spark passed through after the exhaustion had been pushed to the required degree. ' Treated in this manner most native compounds of lime gave the citron band. A perfectly clear and colourless crystal of Iceland spar converted into sulphate gave it strongly, native calcic phosphate less strongly, and a crystal of arragonite much more brightly. A stalac- tite of calcium carbonate from the Gibraltar caves gave the band almost as well as calcite, as also did cinnamon stone (lime alumina garnet), iron slag from a blast furnace, commercial plaster of Paris, and most specimens of ordinary burnt lime. ' The Citron Band not due to Calcium 11. 'Evidence stronger than this in favour of the view that the citron band was an inherent characteristic of calcium could scarcely be ; but, on the other hand, there was evidence equally conclusive that the band was not essential to calcium. The ammonia precipitate (5) sometimes gave the citron band with great strength and purny. and although I had not yet obtained this in quantities sufficient for a detailed examination, it was easy to decide that it contained no phos- phoric, silicic, or boric acid, fluorine, or other body likely to cause the precipitation of lime in this group. This precipitate must therefore be an earth, and the more carefully I purified it from lime and other substances, the more brilliantly shone out the citron band, and the more intense became the green and red bands. 1 Another stubborn fact was this : Starting with a lime compound which showed the citron band, I could always obtain a calcium oxalate 70 SELECT METHODS IN CHEMICAL ANALYSIS which gave the band stronger than the original substance ; but if I started with a lime compound which originally gave no citron band, I could never by any means, chemical or physical, constrain the lime or the earthy precipitate to yield a citron band. 12. ' Among the minerals tried was eudialyte, a zirconium, iron, calcium, and sodium silicate, containing about 10 per cent, of lime. No citron band could be detected on testing the original mineral or any of the constituents separated from it on analysis. This and a lump of common whiting (levigated chalk) were for some time my only sources of lime which gave no citron band. 18. ' The only explanation that I could see for this anomaly was that the elusive citron band was caused by some element precipitated with the calcic oxalate, but present in a quantity too small to be detected by ordinary chemical means. I then thought that were I to fractionally precipitate the solution of lime, the band-forming body might be concentrated in one or the other portion. Accordingly the calcium oxalate (7, 8, 9) was ignited and dissolved in hydrochloric acid, and fractionally precipitated in three portions with ammonium oxalate, the first and third portions being comparatively small. They were dried, ignited with sulphuric acid, and tested in the radiant matter tube. All three portions showed the citron band, but the portion which came down first gave the band decidedly the strongest, and the third portion precipitated showed it weakest. This therefore pointed to a difference between calcium and the body sought for. The process, however, was not satisfactory, and I was driven to seek some other method. 14. * A portion of an ammonia precipitate, found to give the citron band very well (5, 11), was dissolved in dilute sulphuric acid, and the solution evaporated down. Crystals were formed which were difficultly soluble in hot water, but appeared more soluble than calcic sulphate. 1 A large quantity of the calcic oxalate (7, 8, 9) was ignited with sulphuric acid at a dull red heat, and the resulting calcium sulphate was finely ground and then boiled in a very small quantity of water not sufficient to dissolve the one-hundredth part of it. The mass was thrown on a filter, and a small quantity of clear liquid which came through was precipitated with ammonium oxalate. The resulting white precipitate was ignited with sulphuric acid, and tested in the radiant matter tube. For the sake of comparison a portion of the calcium sulphate remaining on the filter was also put in a radiant matter tube. The sulphate from the aqueous extract gave the citron band far more brilliantly than the calcium sulphate from the filter. I found, however, that it was impossible, by any amount of washing or boiling out, to deprive the calcium sulphate of all power of giving the citron band, although it was possible in this way to weaken its intensity con- siderably. DISTRIBUTION OF YTTRIUM 71 4 Experiments with Calcium Sulphate 15. ' Supposing that the substance giving the citron band formed a sulphate more soluble in water than calcium sulphate, it was antici- pated that repeated washings with cold water would extract some of it, which might then be detected more easily. About 4 Ibs. weight of commercial plaster of Paris, which showed very faint traces of the citron band, were mixed with water and rapidly poured on a large filter. Before the mass solidified a slight saucerlike depression was made in the upper part, and a few ounces of water were poured on. This ran through slowly, and it was then poured back and the exhaustion repeated several times. The aqueous extract was then evaporated to dryness, ignited with sulphuric acid, ground in a mortar with small successive quantities of water, the liquid boiled, filtered, and precipitated first with ammonia, and the filtrate with ammonium oxalate. These precipitates both showed the citron band very fairly, far more intensely than it was seen in the original calcium sulphate. The green and red bands were also visible. ' The same mass of plaster of Paris was then washed, as before, with a little dilute hydrochloric acid passed through several times, and this extract was treated in the same way by evaporation and extraction with water, and the filtrate precipitated, first with ammonia, and then with ammonium oxalate. In these precipitates the citron band, together with the green and red bands, were much more brightly manifest than in the precipitates from the aqueous extract. . 4 Wide Distribution of the Citron Band-forming Body 16. ' These experiments are conclusive in proving that the citron band is not due to calcium, but to some other element, probably one of the earthy metals, occurring in very minute quantities, but widely distributed along with calcium, and I at once commenced experiments to find a more abundant supply of the body sought for. Amongst other substances tested I may note the following as giving a more or less decided citron band in the spectrum when treated with sul- phuric acid in the manner indicated above (10) : Crystallised barium chlorate, heavy spar, common limestone, strontium nitrate, native strontium carbonate, crystallised uranium nitrate, commercial magne- sium sulphate, commercial potassium sulphate, Wagnerite (magnesium phosphate and fluoride), zircon, cerite, and commercial cerium oxalate. ' Examination of Zircon for the Citron Band 17. ' Some specimens of zircon treated in the above manner ap- peared sufficiently rich to make it probable that here might be found an available source of the citron-band-yielding body. I found it in crystals from Green Kiver, North Carolina, from Ceylon, from 72 SELECT METHODS IN CHEMICAL ANALYSIS Espailly, from Miask (Oural), and from Brevig, and having a good supply of North Carolina zircons I started working up these in the following manner : 1 The finely powdered zircons were fused with sodium fluoride, and the melted mass powdered, boiled with sulphuric acid, and filtered. The solution was precipitated with excess of ammonia, the precipitate well washed and dissolved in hydrochloric acid, and the solution made nearly neutral. A little zirconium oxychloride sometimes separated on evaporation ; this was filtered off. An excess of sodium thiosulphate was now added, and the whole boiled for some time until a portion of the filtrate gave no further precipitate on boiling again with sodic thio- sulphate. The precipitated zirconium thiosulphate was worked up for zirconia ; it was found to be quite free from the substance giving the citron band. The solution filtered from the zirconium thiosulphate was precipitated with ammonia, and the brown gelatinous precipitate was well washed. The filtrate was precipitated with ammonium oxalate, which brought down much calcium oxalate. This showed the citron band, but not strongly. The brown gelatinous precipitate was dissolved in nitric acid. Silver nitrate was added to separate chlorine, and the filtrate from the silver chloride was boiled down with nitric acid and excess of metallic tin to separate phosphoric acid. The clear solu- tion, separated from the stannic oxide, phosphate, &c., was boiled down with hydrochloric acid to remove nitric acid, and then saturated with hydric sulphide to separate silver and tin. 18. ' The filtrate from the sulphides was freed from hydric sulphide by boiling, and was then mixed with tartaric acid and excess of ammonia, to precipitate any yttria that might be present, together with Forbes's zirconia j3 (jargonia?). 1 On standing for some hours this gave a small quantity of a precipitate, which was separated by filtra- tion ; it was tested in the radiant matter tube, and found not to give the citron-band spectrum (44). To the filtrate ammonium sulphide was added to precipitate the iron. The black precipitate was filtered off and the filtrate evaporated to dryness, and ignited to destroy the organic matter. The residue, heated with sulphuric acid and ignited, gave the citron spectrum very brightly. This would probably be the earth which Forbes calls zirconia y. 2 19. c For many years chemists have suspected that what is known as zirconia might be a compound. Svanberg 3 found that zircons from different localities varied in specific gravity, and the earth or earths obtained by fractional precipitation with oxalic acid had not the same properties, the hydrogen equivalents of the metals of the earths of the different fractions varying from 17'01 to 27'3, the metal of the earth hitherto recognised as zirconia being 22'4. 4 He considered zirconia 1 Par. 98, and ' Chemical News, vol. xix. p. 277. 2 Par. 98, and ' Loc. cit. 3 ' Poggend* Annal. vol. Ixv. p. 317. Svanberg's numbers for these earths are 938 to 1320 (M,0 3 ), the earth DISTRIBUTION OF YTTEIUM 7B- to contain two different earths, the oxalate of one being less soluble in acid than that of the other, and their sulphates differing in crystal- line form and solubility. He proposed the name " noria " for one of the earths, retaining that of zirconia for the other. The researches of Berlin, on the other hand, seem to disprove this. 20. * Kemembering the remarkable result produced in the absorption spectrum of some jargons by the presence of a minute trace of ura- nium, 1 I tried numerous experiments with this metal, adding small quantities of it to zirconia, lime, thoria, ceria, &c., but in no case could I produce the citron-band spectrum by this means. ' I may condense a year's work on zircon more than 10 Ib. weight of crystals from North Carolina having been worked up by stating that the result was comprised in about 300 grains of an earthy residue (18), and about two ounces of oxalate, chiefly calcium ; the former gave the citron band very well. The process as detailed above is given, since by this means a very large quantity of zircons was worked up, affording me the material which ultimately enabled me to solve the problem, which at one time seemed almost hopeless. ' The zirconia prepared from these zircons when tested sometimes showed the citron band, especially after precipitation as an oxychloride. Zirconia precipitated as thiosulphate did not yield the citron band (28). A zirconia rich in citron band, fractionally precipitated by ammonia, yielded precipitates of increasing richness, the last fraction showing the citron band strongly. 21. * The calcium oxalate obtained from zircon gave unsatisfactory results, so attention was directed to the earthy residue (18). This was found to be of highly complex character, containing thoria (which had escaped precipitation as thiosulphate), ceria, lanthana, didymia, yttria, and probably some of the newly discovered rarer earths. ' Examination of Cerite for the Citron Band 22. ' The position of the citron band in the spectrum falls exactly on the strongest absorption band of didymium, so that a piece of didymium glass or a cell of solution of the nitrate entirely obliterates the citron band. This naturally suggested that the band was due to didymium. ' Cerite was accordingly the next mineral experimented on. The powdered mineral tested in the tube in the original way, gave a good citron band. It was made into a paste with sulphuric acid, and after all action had ceased it was extracted with cold water. The earths hitherto recognised as zirconia being 1140 ; oxygen being 100. For the sake of uniformity I have recalculated his equivalents for the metals on the = 16 scale, taking the formula as M.O (see note 1, par. 40). 1 ' Chemical Neics, vol. xix. pp. 121, 142, 205, 277 ; vol. xx. pp. .7, 104 ; vol. xxi. p. 73. 74 SELECT METHODS IN CHEMICAL ANALYSIS were then precipitated with ammonium oxalate, and the oxalate ignited. The fawn-coloured powder was then converted into sulphate, dissolved in water, and the cerium metals precipitated by long digestion with excess of potassium sulphate. When no didymium bands could be detected in a considerable thickness of the supernatant liquor, it was assumed that all the cerium metals were down, and the liquid was filtered. 23. * The precipitated double sulphates were dissolved in hydro- chloric acid, and the earths precipitated as oxalates. After ignition and treatment with sulphuric acid, the mixed ceria, lanthana, and didymia were tested in the radiant matter tube, but the merest trace only of citron band was visible. 24. ' This experiment proved the inadequacy of the didymium ex- planation (22), and further tests showed that not only could I get no citron band in pure didymium compounds, but the spectrum entirely failed to detect didymium in many solutions of the earth which gave the citron band brilliantly. 25. * Attention was now turned to the solution filtered from the insoluble double sulphates from cerite (22). Potash in excess was added to the filtrate, and the flocculent precipitate was filtered off, and after well washing was converted into sulphate, and tested in a radiant matter tube. The spectrum, of extraordinary brilliancy, was far brighter than any I had hitherto obtained. Unfortunately, however, the quantity was too small to be subjected to very searching chemical analysis. ' Examination of Thorite and Orangite 26. * Search was next made amongst other minerals rich in the rarer earths. Thorite, another disputed mineral, was finely powdered, treated with sulphuric acid, and tested in the radiant matter tube. It gave the citron spectrum most brilliantly equal, in fact, to the mixture of earths obtained from zircons (18, 21) at so great an expenditure of time and trouble. Orangite treated in the same manner gave almost as good a spectrum. Pure thorium sulphate prepared by myself was found not to give the citron band, but three specimens prepared and given to me by friends all gave it ; so it was not unlikely that in thorite and orangite might at last be found a good source of the long-sought element that in fact the body I was hunting for, if not thorium, might possibly be Bahr's hypothetical wasium. Having obtained about 2 Ibs. of orangite and thorite, they were worked up as follows : 27. ' The finely powdered mineral was heated for some time with strong hydrochloric acid, and when fully gelatinised and all action had ceased, it was evaporated to dryness to render the silica insoluble ; then extracted with water slightly acidulated with hydrochloric acid, boiled, and filtered. Hydric sulphide was passed through the filtrate for some time. The flask then corked was set aside for twenty-four THORITE AND OEANGITE 75 hours and filtered. The filtrate was evaporated to a small bulk, nearly neutralised with ammonia, and then boiled for some time with excess of sodium thiosulphate. This precipitated the thoria, alumina, zirconia, and titanic acid, whilst it left in solution the metals of -the cerium and yttrium groups. The filtrate was boiled down to a small bulk, when a further precipitation took place : this was filtered off and added to the first thiosulphate precipitate. To the clear filtrate excess of ammonium oxalate was added, and the whole allowed to rest twenty-four hours. The precipitated oxalates were filtered, washed, ignited, dissolved in hydrochloric acid, and the excess of acid evaporated off. The aqueous solution was then mixed with a large excess of freshly precipitated barium carbonate, and set aside for twenty-four hours with frequent shaking (29). This would precipitate much of the cerium, and any iron or alumina which might have escaped previous treatment. The liquid was filtered from the precipitate by barium carbonate, and the clear solution, which would contain nothing but barium, and some of the yttrium and cerium metals, was treated as described farther on (30). 28. ' The thiosulphate precipitate tested in the radiant matter tube gave no citron band, nor did it seem possible to detect this band on testing the purified thoria obtained from this precipitate nor from the alumina or zirconia from the same precipitate. This confirmed the results obtained when working up zircons, that sodium thiosulphate did not precipitate the citron-band-forming body. 29. ' The barium precipitate (27) was dissolved in hydrochloric acid, the baryta separated with sulphuric acid, and the solution precipitated with ammonium oxalate. The ignited precipitate, which amounted to 0-223 per cent, of the mineral taken, contained the cerium metals. On testing in a radiant matter tube it gave the citron band only moderately well not nearly so strong as the original thorite and orangite. The iron and alumina in the filtrate from the cerium oxalates were likewise precipitated and tested ; they showed a faint trace of citron band. 30. ' The solution (27) filtered from the barium precipitate was freed from baryta by sulphuric acid, precipitated with ammonium oxa- late, and the precipitate washed and ignited ; it amounted to only 0'125 of the mineral taken. Tested in the radiant matter tube, it showed the citron band about as well as the corresponding earth from the barium precipitate. ' This was disheartening, for after having started with a mineral which gave the citron band well, and having hunted the citron band, as it were, into a corner, the only result was two trifling precipitates showing the citron band less intensely than did the raw material itself. The experiment, however, proved one thing : the band-forming sub- stance was not thoria. The occurrence of this spectrum must there- fore be due to some other element present in small quantity in thorite and orangite. 31. ' The two mixtures of earth the one from the barium precipi- 76 SELECT METHODS IN CHEMICAL ANALYSIS tate (29) and the other from the barium filtrate (30) which showed the citron line moderately well, were dissolved in sulphuric acid, the solution neutralised as nearly as possible with potash and digested for several days with excess of potassium sulphate. The solution, which at first showed the didymium bands, was then found to be free from didymiurn. 32. ' The insoluble double sulphates were filtered and washed with a cold saturated solution of potassium sulphate. The precipitate was boiled for some time in ammonia, filtered, dissolved in hydrochloric acid, and precipitated with ammonium oxalate. This precipitate was ignited and tested in the radiant matter tube. It gave scarcely a trace of citron band (23). The earth was further purified by the potash and chlorine method, and was found to consist principally of cerium oxide. 33. The solution filtered from the insoluble potassio-cerium sul- phate (31) was boiled with ammonia and ammonium sulphide. A small quantity of a white flocculent earth came down too small a quantity to weigh. Tested in a radiant matter tube, it gave the citron band better than either of the above precipitates, showing that by this treatment the body had been concentrated (25). 34. ' It seemed possible that the earth sought for might be present in larger quantity in the thorite, but that it had been gradually carried down mechanically or by mass-action rather than chemically, by the numerous operations it had undergone before getting it to the final stage. Therefore a fresh quantity of thorite was extracted with hydrochloric acid. The solution was precipitated with potassium sul- phate, taking the usual precautions to secure complete precipitation. A bulky precipitate ensued, which contained the thoria and cerium earths. These were separated and tested, and found to give only a faint citron band. 35. ' The solution of earthy sulphates soluble in potassium sulphate was precipitated with ammonium oxalate. The precipitate ignited with sulphuric acid, and tested in a radiant matter tube, gave the citron spectrum with great brilliancy (25, 33). Chemical Facts connected with the Citron Body 36. ' Certain chemical facts concerning the behaviour of the sought- for element which came out during the course of the tentative trials already described had considerably narrowed the list amongst which it might probably be found. All the evidence tended to show that it belongs to the group of earthy metals, consisting of aluminium, glu- cinum, thorium, zirconium, cerium, lanthanum, didymium, and the yttrium family, together with titanium, tantalum, and niobium. The sought-for earth is insoluble in excess of potash (25) ; this excludes aluminium and glucinum. It is not precipitated by continued boiling THE CITKON-BAND-FORMING- BODY 77 with sodium thiosulphate (17, 27) ; this excludes aluminium, thorium, iiiul zirconium. Fused with acid potassium sulphate, the resulting compound is readily soluble in cold water ; this excludes tantalum and niobium. Evaporating to dryness with hydrochloric acid and heating for some time does not render the body insoluble in water (27) ; this excludes titanium and silicium. It is easily soluble in an excess of a saturated solution of potassium sulphate (25, 33, 34) ; this excludes thorium, the cerium group, some of the numerous members of the yttrium group, and zirconium. The only remaining elements among which this elusive body would probably be found are those mem- bers of the yttrium family which are not precipitated by potassium sulphate. 37. ' On the other hand, the body giving the citron -band spectrum did not behave like one of the known earths. A rich residue was fused with sodium carbonate, and the mass extracted with water. The inso- luble residue, on testing in the usual way, was rich in citron band, but subsequent treatment of the aqueous solution gave me an earth which also gave the citron band strongly. ' An acid solution of the citron body was precipitated by ammonia and ammonium chloride. The earth was not completely precipitated, but after a long boiling some remained in solution. (I have since ascertained that the detection of the citron-band body in solution under these circumstances is only owing to the marvellous delicacy of the test, which carries our powers of recognition far beyond the resources of ordinary chemistry.) 38. ' Besides obtaining indirect evidence that the citron band was not due to certain elements, I tried special experiments with each sub- stance, brought to the highest possible state of purity. In many cases I detected more or less traces of citron band ; but I had come to the conclusion, abundantly warranted by facts, that this citron band was an extraordinarily sensitive test of the presence of the element causing it ; and the minute chemistry of many of these earthy metals being insufficiently known, it was not surprising that traces of one of them should adhere to another in spite of repeated attempts to purify it out. With each successive fractional precipitation the citron band became fainter, showing that with perseverance the last trace would probably disappear. The time this process would have occupied, in my opinion, seemed not worth the little additional evidence it would have afforded. 39. 'Taking into consideration the extremely small quantity of phosphorescent material which had so far been obtained, all these experiments justified me in assuming that the body sought for not only belonged to the group of earths, but also most probably to the sub- group, not precipitated by potassium sulphate, to which yttria belongs. As, however, the number of these metals has increased so much within the last few years, and as the quantity of material which I had up to the present at my disposal was too small to admit of a satisfactory 78 SELECT METHODS IN CHEMICAL ANALYSIS chemical examination being made of it, search was commenced among other sources known to be rich in these metals. Besides, not only did the majority of the substances I had up till now obtained in anything like quantity indicate the citron-band earth to belong to the yttria group (33, 34, 36), but also that either the earth itself showed an absorption baud in the spectroscope, or was invariably accompanied by one which did. On the other hand, I had a certain amount of evidence that the earth sought for did not show a band in the spectroscope (24) ; but remembering the extremely small quantity of very impure sub- stance experimented with, the evidence on this point was not at all conclusive. 1 The Sought-for Body one of the Yttrium Family 40. ' The yttria earths form a somewhat numerous family. Fortu- nately for chemists, a mineral rich in yttria earths samarskite has been found in large quantity in Mitchell County, North Carolina, and to this mineral I accordingly now directed my attention. ' The annexed list of elements of the yttrium and its allied families, said to occur in samarskite and similar minerals, may be considered complete to the present time. Name. Absorp- tion Hydrogen equivalent of Metal. 1 ^ ame - Spec- trum. (Type of Oxide ' M,0.) Cerium No 47-1' Samarium . Columbiuin :i Yes Scandium . Decipium Yes 57-0 4 Terbium Didymium . Yes 48-5 5 Thorium Didymium j8 Yes 47-0 a ' Thulium Erbium Yes 55-3 7 ! Ytterbium . Holmium 8 . . Yes 54-0 9 I Yttrium Lanthanum . No 46-0 lo : Yttrium a . Mosandrum . No 51-2 " Yttrium . Philippium '- No Zirconium . Bogerium 13 . Yes Absorp- tion Hydrogen equivalent of Spec- trum. Metal. 1 (Type of Oxide M a O) Yes 50-0 u No 14-7 l5 No 49-5 l6 No 58-4 Yes 56-5 17 No 57-9 ' No 29-7 19 No 52-2 > Yes 49-7 - l No 22-5 1 ' As it is at present doubtful whether the oxides of several of the metals in this table belong to the type M 2 O, M 2 3 , or MO, I have, for the sake of uniformity and simplicity, in calculating the values from the composition of their salts, by which these metals are chiefly discriminated, taken the type of oxide to be M 2 0. 2 ' Biihrig, J. Pr. Chem. ser. 2, vol. xii. p. 209. 3 ' Dr. J. Lawrence Smith, in a paper read before the United States National Academy of Sciences in 1879, announced the discovery in samarskite of two new elements, which he named Columbium and Bogerium (Nature, vol. xxi. p. 146). I have failed to find any further notice of these elements. This columbium must not be confounded with the well-known columbium, sometimes called tantalum. 4 ' Delafontaine, Comptes Rendus, vol. Ixxxvii. p. 632, vol. xciii. p. 63. Chemical News, vol. xxxviii. p. 223, vol. xliv. p. 67. 5 ' Cleve, Bull. Soc. Chim. ser. 2, vol. xxi. p. 246. Brauner, Comptes Rendus> vol. xciv. p. 1718 : Chemical News, vol. xlvii. . 175. THE YTTKIUM GKOUP 79 41. ' Some of these claimants will certainly not stand the test of further scrutiny. Thus samarium and yttrium fi are in all probability identical ; and I should scarcely have included philippium, as Eoscoe l has conclusively proved that this is a mixture of terbium and yttrium, and my own results (61) confirm those of Roscoe. Moreover, others 6 ' Cleve, Comptes Rendus, vol. xciv. p. 1528 ; Chemical News, vol. xiv. p. 273. Brauner, Comptes Rendus, xciv. p. 1718 ; Chemical News, vol. xlvi. p. 16. 7 ' Cleve, Comptes Rendus, vol. xci. p. 381 ; Chemical News, vol. xlii. p. 199. Lecoq de Boisbaudran, Comptes Rendus, vol. Ixxxix. p. 516 ; Chemical News, vol. xl. p. 147. 8 ' Called by Soret, the first discoverer, X. Subsequently Cleve discovered the same metal and called it holmium. Soret has now adopted Cleve' s name. Comptes Rendus, vol. Ixxxix. p. 708, and vol. xci. p. 378 ; Chemical Neius, vol. xl. p. 224, and vol. xlii. p. 199. Lecoq de Boisbaudran, Comptes Rendus, vol. Ixxxix. p. 516 ; Chemical News, vol. xl. p. 147. 9 ' Cleve, Comptes Rendus, vol. Ixxxix. p. 478; Chemical News, vol. xl. p. 125. 10 ' Brauner, Comptes Rendus, vol. xciv. p. 1718 ; Chemical News, vol. xlvi. p. 16. 11 ' Lawrence Smith, Comptes Rendus, vol. Ixxxvii. pp. 145, 146, 148. Marignac, ibid. vol. Ixxxvii. p. 281. Delafontaine, in October 1878 (ibid, vok Ixxxvii. p. 600), considers mosandrum a mixture of terbium, yttrium, erbium, didymium, and philippium. Subsequently, however, Lawrence Smith, in November 1878 (ibid. vol. Ixxxvii. p. 831), adduces chemical and other reasons to show that his mosandrum is not a mixture, but a true element. A year later, September 1, 1879 (ibid. vol. Ixxxix. p. 480), Lawrence Smith repeats the claim for mosan- drum to be classed with the elements. ' 2 ' Delafontaine, Comptes Rendus, vol. Ixxxvii. p. 559 ; Chemical News, vol. xxxviii. p. 202 ; Journ. Chem, Soc. vol. xxxvi. p. 116. 13 ' See note 3 to columbium, ante. 14 ' Lecoq de Boisbaudran, Comptes Rendus, vol. Ixxxviii. p. 322, and vol. Ixxxix. p. 212 ; Chemical News, vol. xxxix. p. 115, and vol. xl. p. 99. Brauner, Chemical News, vol. xlvii. p. 175. Cleve, Comptes Rendus, vol. xcvii. p. 94 ; Chemical News, vol. xlviii. p. 39. 15 'Nilson, Comptes Rendus, vol. xci. p. 118; Chemical News, vol. xlii. p. 83. Cleve, Comptes Rendus, vol. Ixxxix. p. 419 ; Chemical News, vol. xl. p. 159. 16 ' Marignac, Ann. Chim. et Phys. ser. 5, vol. xiv. p. 247 ; Journ. Qhem. Soc. vol. xxxvi. p. 113. Delafontaine, Ann. Chim. et Phys. ser. 5, vol. xiv. p. 238. Journ. Chem. Soc. vol. xxxvi. p. 114. 17 ' Cleve, Comptes Rendus, vol. Ixxxix. p. 478, and vol. xci. p. 328 ; Chemical News, vol. xl. p. 125, and vol. xlii. p. 182. Thalen, Comptes Rendus, vol. xci. p. 376 ; Chemical News, vol. xlii. p. 197. 18 ' Marignac, Comptes Rendus, vol. Ixxxvii. p. 578 ; Chemical News, vol. xxxviii. p. 213. Nilson, Comptes Rendus, vol. Ixxxviii. p. 642, vol. xci. p. 56 ; Chemical News, vol. xlii. p. 61. 19 Cleve, Comptes Rendus, vol. xcv. p. 1225 ; Chemical News, vol. xlvii. p. 4 ; Bull. Soc. Chim. vol. xxxix. p. 120 ; Chemical News, vol. xlvii. p. 143. 80 ' Marignac, Comptes Rendus, vol. xc. p. 899 ; Chemical News, vol. xli. p. 250. - 1 ' This is almost certainly identical with Lecoq de Boisbaudran's samarium. See Marignac, Comptes Rendus, vol. xc. p. 899 ; Chemical News, vol. xli. p. 250 ; Soret, Comptes Rendus, vol. xci. p. 378 ; Chemical News, vol. xlii. p. 199. 1 Journ. Chem. Soc. vol. xli. p. 277. 80 SELECT METHODS IN CHEMICAL ANALYSIS of these so-called elements will probably turn out to be mixtures of known elements. But in the confessedly very imperfect state of our knowledge of the chemistry of these metals it is not safe for me in this research to assume that any one of them will surely not survive. The complete list as it stands will therefore be taken to contain all hitherto claimed as new, although it is almost certain to include too many. ' The Sought-for Body has no Absorption Spectrum 42. ' In the second column, p. 78, " Yes " or " No "indicates whether the solutions give an absorption spectrum when examined by transmitted light. Now, could I definitely settle whether solutions of the citron- band body gave an absorption spectrum or not, I could at once eliminate a whole class of elements. ' This was not difficult to determine. I have already said (22, 24) that spectroscopie examination entirely failed to detect didymium in many solutions of the earth which gave the citron band strongly. This was not always the case. -In the early days of this research I frequently obtained absorption bands innumerable when the citron-band body was known to be present ; but as I became better acquainted with the chemi- cal reactions of the new earth I gradually succeeded in eliminating one after the other those metals yielding absorption spectra. The earth from zircons (18, 21) gave the most satisfactory results in this respect. This, after removing the little didymium present, gave but a trace of an absorption spectrum, which from its general appearance was probably due to erbia. The earth obtained from cerite (25), which gave the citron spectrum with great brilliancy, on the other hand yielded no absorption spectrum ; and generally I may say that, when- ever I started with a sufficient quantity of an earth giving both citron- band spectrum and absorption spectrum, I could, by appropriate chemical means, always separate it into three portions one which gave the citron-band spectrum with great brilliancy, and showed in concentrated solution a very faint absorption spectrum, and frequently none at all ; another which gave very little citron-band spectrum, but a good absorption spectrum ; and a third intermediate portion about four-fifths of the whole which gave both citron-band and absorption spectrum. This portion, by repetition of the treatment, could again be split up in the same way, and the operation repeated as often as the stock of the material held out. 43. ' Having definitely settled the question that the element giving the citron-band spectrum was not one of those giving an absorption spectrum, the possible elements become materially narrowed to the following list : Cerium, lanthanum, mosandrum, scandium, terbium, thorium, ytterbium, yttrium, yttrium , and zirconium. ' Of these the potassium sulphate reaction (36) excludes cerium, lanthanum, scandium, thorium, yttrium a, and zirconium, so there are left only the following : ANALYSIS OF SAMARSKITE 81 Mosandrum, Terbium, Ytterbium, Yttrium 44. ' Certain chemical reactions for a long time made me dismiss yttrium from the list of likely bodies. In my analysis of zircons (18), towards the latter part of the process, I used the following process to separate the iron : The solution, mixed with tartaric acid and excess of ammonia, was allowed to stand for some time. A small quantity of a precipitate gradually formed, which was filtered off, and it was this nitrate, after separating the iron with ammonium sulphide, that yielded the greatest quantity of substance giving the citron band. Now one of the methods of separating yttria from alumina, glucina, thoria, and zirconia, is to precipitate it as tartrate in the presence of excess of ammonia, the other earths remaining in solution. Fresenius says : " The precipitation ensues only after some time, but it is complete." ' The precipitate thus obtained with tartaric acid and ammonia should therefore contain all the yttria : it gave no citron band whatever in the radiant matter tube ; whilst the residue, which should be free from yttria (18), proved for a long time the only source of material wherewith to investigate the chemical properties of the body giving the citron-band spectrum. 45. 'Another reason which made me, at this stage of the research, pass over yttria was that I had already tested this earth in the radiant matter tube. In a paper on " Discontinuous Phosphorescent Spectra in High Vacua," read before the Koyal Society, May 19, 1881, r I said, " Yttria shows a dull greenish light giving a continuous spectrum " (75). ' For these reasons I for a long time omitted yttria from my list of possible bodies, and considered that the earth, if not a new one, might turn out to be either mosandra, terbia, or ytterbia. ' Analysis of Samarskite 46. ' A very large quantity (about 15 Ibs. weight altogether) of samarskite was worked up, partly by the hydrofluoric-acid method of Lawrence Smith, 2 and partly by fusion with potassium bisulphate. The niobic and tantalic acids after purification were found to give no citron-band spectrum. 4 These methods both gave as a result a large quantity of mixed earths containing most, if not all, of the bodies enumerated in par. 40. Tested in the radiant matter tube, this material gave the citron spectrum very brilliantly. It was dissolved in hydrochloric acid, neutralised as nearly as possible with ammonia, and boiled with sodium thiosulphate. This precipitated the thoria, zirconia, and alumina. In this precipitate some of the scandia might also be found 1 ' Proc. Roy. Soc. No. 213, 1881. >J ' Conqrtcs Rendus, vol. Ixxxvii. p. 1-46. 82 SELECT METHODS IN CHEMICAL ANALYSIS if present in quantity, but as scandium thiosulphate is not completely precipitated, and the earth is present only in minute traces, not much scandia, it is probable, was thus carried down. ' This thiosulphate precipitate, treated in the usual way with sul- phuric acid, gave no citron band in the radiant matter tube. 47. * The nitrate from the thiosulphate was precipitated hot with excess of ammonia, and the precipitate after washing treated with sul- phuric acid, dried, and heated till fumes of sulphuric acid disappeared. The sulphate, whitish with a very pale rose tint, was finely ground, and dissolved with frequent agitation in the smallest possible quantity of cold water an operation which required much time. The solution was then precipitated with potassium sulphate, taking all necessary pre- cautions to keep the liquid well saturated with potassium sulphate. This operation was allowed to go on for about ten days, when the precipitated double sulphates were filtered off and slightly washed with a saturated solution of potassium sulphate. The precipitate contained cerium, lanthanum, didymium, didymium /?, decipium, samarium, scandium, yttrium a, yttrium ft, together with any thorium and zirconium which might have escaped the thiosulphate treatment. 48. ' The filtrate from the double sulphates was precipitated hot with ammonia, which brought down the erbia, holmia, mosandra, terbia, thulia, ytterbia, and yttria. The small quantity of manganese in solution was in this operation completely thrown out. 49. ' The insoluble double sulphates (45) were dissolved in hydro- chloric acid, precipitated hot with ammonia, washed till free from potassium salts, redissolved, precipitated as oxalates, ignited, and set aside for further examination. On testing in the radiant matter tube this mixture of oxides was found to be practically free from citron band. 50. ' The ammonia precipitate rom the sulphates soluble in potas- sium sulphate (46) was well washed till free from potassium salts, and dissolved in excess of nitric acid. The concentrated solution gave an absorption spectrum showing lines belonging to erbium and allied metals. Having already proved that the body sought was not one of those metals which gave an absorption spectrum (42, 43), my first object was to find some method by which I could roughly separate this mixture of earths into two portions, one giving absorption bands, and the other having no action on the transmitted spectrum. This was found to be possible by taking advantage of the different solubility of the oxalates in nitric acid. 51. * The highly acid solution of the nitrates was fractionally precipitated in the following manner : ' To the boiling liquid a solution of ammonium oxalate was added drop by drop. The precipitate at first formed redissolved on stirring. The cautious addition of ammonium oxalate was repeated until the precipitate refused to dissolve entirely, but left the hot liquid some- ANALYSIS OF SAMARSKITE 83 what milky. It was then rapidly cooled with constant stirring, which brought down a heavy crystalline oxalate. This was filtered off, and called oxalate A. The filtrate, again heated to boiling, was precipi- tated in exactly the same way with a further quantity of ammonium oxalate till the hot liquid became opalescent. On cooling and stirring a further quantity of oxalate came down. The nitrations and precipi- tations were repeated until no more precipitate could be obtained. Usually I could get twelve or thirteen fractionations in this manner ; towards the end the solution did not get milky, and it had to stand sometimes twenty-four hours before much oxalate came down. 52. ' The fractions first precipitated by oxalic acid gave very strong absorption bands when the concentrated solutions of the oxides were examined by transmitted light. The fractions last precipitated showed the absorption bands only faintly. 53. ' These operations gave me oxalates from A to L. These, ignited, with free access of air, were then each dissolved in nitric acid, and again separately fractionated as oxalates. The result was about 150 precipitates, ranging from A t A 2 . . . A 12 , Bj B 2 . . . B 12 , to L, L 2 . . . L 12 . ' These, after ignition, were separated into five lots according to order of colour, and the fractionation of each of the five lots repeated as already described ; the series of operations now closely resembling those of Pattinson's process for desilvering lead. This gave me about sixty lots. This time the hydrogen equivalent of the metal of each lot was taken by converting the oxalate into sulphate and estimating the sulphuric acid, assuming M 2 to be the type of oxide (40, note 1). The result was a series of earths having hydrogen equivalents (M) ranging from about 48 to 33. The earths were now sorted into high, low, and intermediate, those giving intermediate H equivalents being re-fractionated with repeated H equivalent estimation, the highest and lowest being each time separated and added to the former high and low lots. 54. ' The ultimate result of about five hundred fractional precipita- tions gave me a mixture of earths having an H equivalent M=48, and showing a strong absorption spectrum (56) ; a mixture having an H equivalent M=33, having no absorption spectrum (65) ; and inter- mediate earths. * In the radiant matter tube all these fractions gave the citron-band spectrum well, but that of the earth of lowest equivalent was much the brightest, and that of the highest equivalent the least intense. 55. * Three methods are available for the partial separation of these earths and for the complete purification of any one of them. The formic-acid process (56, 57) is best for separating terbia, as terbic formate is difficultly soluble in water, the other formates being easily soluble. ' Fractional precipitation with oxalic acid (63, 64, 65) separates first 2 84 SELECT METHODS IN CHEMICAL ANALYSIS erbia, holmia, and thulia, then terbia, and lastly yttria. This is the only method which is applicable for the separation of small quantities of terbia from yttria. ' Fusing the nitrates (60, 68, 69) separates ytterbia, erbia, holmia, and thulia from yttria. It is not so applicable when terbia is present,, and is most useful in purifying the gadolinite earths. This process is the only one known for separating ytterbia from yttria. * Selection must be made of these methods according to the mix- ture of earths under treatment, changing the method as one earth or the other becomes concentrated on one side or thrown out on the other. Each operation must be repeated many times before even approximate purity is attained. The operations are more analogous to the sepa- ration of members of homologous series of hydrocarbons by fractional distillation than to the separations in mineral chemistry as ordinarily adopted in the laboratory. * Preparation of Pure Terbia 56. ' The mixture of high equivalent earths (54) richest in terbia r erbia, holmia, and thulia was treated as follows : ' The earths were dissolved in dilute formic acid, and the solution heated for some time. A white powder of terbium formate separated. This was filtered off, the solution containing the more easily soluble formates evaporated to dryness, and ignited. In this way the M=48 earths were separated into two lots, one rich in terbia and the other rich in erbia, &c. The treatment with formic acid was again repeated on both lots, and the crude terbia finally purified as follows : 57. ' The crude terbia from all the operations was systematically treated by the formic-acid process, keeping the liquid so dilute that only a portion of the terbium formate separated out each time. The syrupy solution of formates was treated as described further on (60). The hydrogen equivalent of the terbium was taken each time ; latterly it kept pretty constant at 49*5. The terbia was also tested in the radiant matter tube. At first the citron spectrum was very strong ; gradually, however, it got fainter and fainter under the repeated formic treatment, until finally the spectrum became so weak as to satisfy me that it was due only to impurity in the terbia, and that, had the material been sufficient to stand against the extravagant process of purification adopted, I should finally have got a terbia giving no citron- band spectrum. (Subsequent examination (87) showed me that this terbia did not contain more than ^Vff P art f yttria.) 58. * A concentrated solution of the purest terbia obtained in this way, when examined by the spectroscope, showed no absorption lines whatever : proving the absence of erbium, holmium, and thulium. 59. ' The hydrogen equivalent (49*5) would not definitely show the absence of ytterbium (57*9) and yttrium (29'7) ; but these would have ANALYSIS OF SAMARSK1TE 85 teen separated by the formic-acid treatment, terbium formate requiring 30 parts of water for its solution, whilst yttrium and ytterbium formates dissolve in less than their own weight of water. Moreover, it was not probable that the terbia contained an appreciable quantity of any of these earths as an impurity, for neither the oxalic acid, the fusing nitrate, nor the formic-acid process of fractionation produced any change in the atomic weight, 49'5. Preparation of Mixed Erbia, Holmia, and Thulia, free from other Earths 60. ' The filtrate from the terbium formate (57), rich in erbia, and -containing besides terbia, holmia, thulia, and yttria, was now treated by converting it into nitrates, evaporating to dryness, and submitting the mass to careful fusion, stopping the operation when the liquid mass began to evolve nitrous fumes. The erbium, holmium, and thulium nitrates decomposing before the yttrium nitrate, extraction with water gave an insoluble residue rich in erbia, holmia, and thulia, and a filtrate rich in yttria. The insoluble residue was dissolved in nitric acid, again evaporated to dryness, and fused. These operations were repeated eight or ten times, with the result of raising the H equivalent of the erbium metals to about 56*8, but the citron-band spectrum remained strong for some time after. It, however, ultimately disappeared. A concentrated solution of this erbium, &c., nitrate showed a beautiful and intense absorption spectrum. I did not attempt any separation of erbium, holmium, and thulium from each other, as the evidence here obtained was sufficient to show that the element giving the citron-band spectrum is not one of these three metals. Likewise I had far too little material to enable me to enter on a work of such difficulty with -any prospect of success. ' Philippia 61. ' The so-called philippia was sought for in the portion of earths intermediate between the terbia and yttria (54). These were dissolved in dilute formic acid, and the solution, filtered from some terbium formate which would not dissolve, was carefully evaporated down to a small bulk, filtering off the terbium or other difficultly soluble formates as they deposited. The clear concentrated solution was then set aside over sulphuric acid to crystallise. In the course of a few days brilliant rhombic prisms crystallised out, having exactly the appearance de scribed by Delafontaine. 1 The finest of these crystals were picked out, dried on blotting-paper, and analysed. The hydrogen equivalent was found to be M= 38- 2. The citron -band spectrum in the radiant matter tube was very brilliant. The solution decanted from these crystals 1 ' Comptes Ftcndus, vol. Ixxxvii. p. 599 ; Chemical Neivs, vol. xxxviii. p. 202 ; Journ. Chem. Soc. vol. xxxvi. p. 116. 86 SELECT METHODS IN CHEMICAL ANALYSIS was evaporated to a syrupy consistency, filtered from insoluble terbium formate which deposited, and treated for yttria (65). 1 Some of the best rhombic crystals were added to cold water acidu- lated with formic acid, and gently heated, but all attempts to dissolve and recrystallise them failed. A large quantity of an insoluble formate separated, and the mother-liquor on concentration again deposited shining rhomboidal crystals. On attempting to recrystallise these, they again deposited an insoluble white powder. The mother-liquor was found to contain a large quantity of yttria, and the white insoluble formate on ignition gave an earth having the atomic weight and chemical behaviour of terbia. This entirely corroborates Professor Eoscoe's conclusions, 1 that Delafontaine's philippia is nothing but a mixture of yttria and terbia. ' Mosandra 62. 'The chemical characters of this earth are so little known that I could not attempt to search for it. But as the citron-band-forming earth always appeared concentrated amongst those whose double sulphates were most soluble in potassium sulphate and, of these, amongst those having the palest colour and lowest atomic weight it was scarcely conceivable that the earth I was in search of should ultimately prove to be one whose properties did not in any case corre- spond to these one of a dark orange-yellow colour, forming a difficultly soluble double potassium sulphate, and having the very high equivalent of M=51*2 : these being the properties ascribed to mosandra by the discoverer, Professor Lawrence Smith. 'Separation of Terbia and Yttria from Erbia, Holmia, and Thulia 63. * The mother-liquors, from which as much terbium formate as possible had been separated by the process above described (56, 57), were now evaporated down with nitric acid till all the formates were decomposed, and the highly acid solutions of nitrates were fractionally precipitated with oxalic acid (51, 52, 53). 64. ' The erbium, holmium, and thulium oxalates come down first ; then the terbium oxalate ; lastly, the yttrium oxalate (53). After re- peated fractional precipitations I at last succeeded in obtaining a mix- ture of yttria and terbia of a golden colour, which gave a very brilliant phosphorescent spectrum in the radiant matter tube, but showed no trace of absorption band when the concentrated solution of the nitrates was examined in the spectroscope. ' Separation of Terbia and Yttria 65. ' The crude yttria was now added to the mixture of earths (54) having a hydrogen equivalent to M=33, and the whole submitted 1 ' Journ. Chem. Soc. vol. xli. p. 277. ANALYSIS OF GADOLINITE 87 again to fractionation with oxalic acid in a somewhat modified manner. ' An excess of strong nitric acid was added to the solution of mixed terbium and yttrium nitrates, and the solution was heated to the boil- ing-point. Strong oxalic-acid solution was added drop by drop till a faint permanent precipitate was produced. Strong nitric acid was now added, a drop at a time, till the solution again became clear, and the whole was allowed to cool very slowly without agitation. On cooling, an oxalate crystallised out in brilliant prisms. These contained nearly all the terbia with some of the yttria whilst the mother-liquor con- tained most of the yttria with a little terbia. The filtrate was treated with more oxalic acid, a fresh crop of crystals being produced, when the crystals were ignited, and the resulting earths re-treated with nitric acid and oxalic acid. After repeated fractionations I finally obtained in this manner a perfectly white yttria, and a terbia containing a small quantity of yttria. This terbia was added to the crude terbia from previous operations, and purified as already described (57). ' These operations gave me two earths yttria and terbia which, from the constancy of their H equivalents, were taken to be pure. The earths giving absorption spectra and having H equivalents other than 29'7 and 49'5 include erbia, holmia, and thulia. This portion was not further examined for the purposes of this investigation. * Ytterbia 66. * Before considering it finally proved that the substance forming the citron -band spectrum was yttria, it was necessary to prepare ytterbia and ascertain its behaviour in the radiant matter tube, this earth and yttria being the only remaining earths to which the citron spectrum could possibly belong. * The two metals have hydrogen equivalents ytterbium 57'9 and yttrium 29*7. The chemical reactions are also sufficiently different to render their separation a matter of no very great difficulty. 67. ' Gadolinite is said by Nilson to contain most ytterbia, so this mineral was chosen in preference to samarskite. The crude earths were first purified from all the earths whose sulphates are difficultly soluble in potassium sulphate (22, 25, 31 to 36), then by the formic-acid process from terbia (56, 57), and lastly by fractional precipitation with oxalic acid from the erbia earths (65). There remained an almost white yttria, which gave the citron-band spectrum very brilliantly. Now, gadolinite contains only about O'l per cent, of ytterbia, and about 35 per cent, of yttria ; therefore the ytterbia to yttria in this mixture was somewhat in the proportion of 1 to 350, and it gave the citron - band spectrum as brilliantly as I had ever seen it. The probability was that the earth forming nearly the whole was the one giving the spectrum. 88 SELECT METHODS IN CHEMICAL ANALYSIS 68. ' Ytterbium nitrate decomposes on fusion almost as easily as erbium nitrate (60), whilst yttrium nitrate resists decomposition much more energetically. 1 Fusion of the nitrates is also the best process for throwing out the erbia, holmia, and thulia, and is therefore the best for purifying gadolinite yttria, as this mineral is rich in the erbia earths and contains little terbia. ' The gadolinite yttria was converted into nitrate, fused for a short time, and extracted with water. The portions soluble and insoluble in water were again separately submitted to this treatment, until at last a colourless earth was obtained, the nitrate of which decomposed easily on fusion, and another whose nitrate resisted decomposition when exposed for a long time to nearly a red heat (70). ' The earth from the easily decomposed nitrate gave at first a faint citron-band spectrum, evidently due to impurity. On repeating the operation several times I at last succeeded in obtaining a white earth which gave only the merest trace of citron-band spectrum. Its hydrogen equivalent, 58'0, and its chemical properties showed that it was probably Marignac's ytterbia. Subsequent experiments satisfied me that this earth did not contain more than y^j-J-^^- part of yttria (84, 87). The extreme tediousness of the chemical operations neces- sary to obtain this high degree of purity, and the long time they require, prevented me from pushing these results beyond what was necessary to prove the special point at issue. ' Purification of Yttria 69. * The white earth obtained in the operation described at par. 05 might still contain traces of terbia, together with erbia, holmia, and thulia. I had relied on the absence of absorption spectrum as proving the absence of erbia, holmia, and thulia, but this test is not a very delicate one, and a final purification was therefore attempted. The decomposition of the fused nitrates was now the process relied on for this final purification, the yttrium nitrate resisting nearly a red heat without decomposition, whilst the erbium, holmium, and thulium nitrates are decomposed at a much lower temperature. The operation was carried on as described at par. 60. ' The yttrium nitrate left undecomposed, after repeated fusions, was now fused at a higher temperature, extracted with water, filtered from insoluble residue, and the operation repeated on the filtrate. After several such operations the H equivalent of the yttria was taken at every succeeding operation, and the spectral appearance in the radiant matter tube was also examined. The equivalent gradually got down to 81*0, but the spectra did not vary very much ; that from the earth of lowest equivalent being, however, the most brilliant. 70. '* The yttrium nitrate, prepared from gadolinite and freed from 1 ' Marignac, Comptes Rendus, vol. xc. p. 902. PHOSPHORESCENT SPECTRA OF YTTRIA 89 90 SELECT METHODS IN CHEMICAL ANALYSIS ytterbia by the fusion of the nitrates (68), was converted into oxalate and ignited. The resulting yttria was quite white, and on testing in the radiant matter tube gave a spectrum absolutely identical with that given by the zircon (18), cerite (25), thorite and orangite (33, 34), and samarskite (64, 69),yttrias. Pure yttria was also prepared fromyttro- tantalite, euxenite, allanite, tyrite, and also from plaster of Paris (15) and common limestone. In no case could I detect any difference in the position or intensity of the lines shown by their phosphorescent spectra. ' The Phosphorescent Spectrum of Yttria 71. * The spectrum shown by pure ignited yttrium sulphate in a radiant matter tube is one of the most beautiful objects in the whole range of spectroscopy. The lines are not so sharp as those given by spark spectra, but are more like the flame spectra of the alkaline earths. The spectrum is best seen under low dispersion and not too narrow a slit. The accompanying cut gives an accurate map of the spectrum. I have given in line No. 1 the position of the principal Frauenhofer lines for comparison of position. Line No. 2 gives the position of the bands, and No. 3 the relative intensities represented by the heights of the ordinates. The numbers along the top refer to a scale of squared oscillation frequencies, or of the squared reciprocals of wave- lengths. 72. * Commencing at the red end, two narrow faint bands are seen at 2245 and 2275, followed by a stronger and broader red band extend- ing between 2355 and 2415. Another faint band occurs between 2577 and 2610, followed after a very narrow black interval by a stronger reddish- orange band extending to 2627. Another faint orange band occurs at about 2800, with edges too indistinct for measurement. At about 2940 a faint yellow band appears, extending to about 3025. The strong citron-coloured band follows closely from 3028 to 3049 ; and a little farther on, between 3100 and 3120, a much fainter citron band is seen. Two characteristic green bands follow after a dark interval : the first, very bright, extending between 3312 and 3320, but shading off each side ; the second somewhat fainter, but more sharply denned than the first, extending from 3420 to 3440 ; there is also a third faint green band, between 3460 and 3467. At 3730 is the centre of a narrow and faint bluish-green band ; at 4110 to 4125 is a blue band ; and at 4296 another blue band commences, and, extending a short distance, fades away so gradually as to render measurement of the farther side im- possible. At 5052 and 5351 are two violet lines, but they are not sufficiently sharp to enable accurate measurements to be taken. ' I have carefully compared the spark spectrum given by yttrium chloride with the phosphorescent spectrum, and have not found any similarity between them, neither have I detected any discontinuity of spectrum on examining the faint light shown by yttrium compounds in Becquerel's phosphoroscope. PHOSPHORESCENT SPECTRA OF YTTRIA 91 78. ' The above description applies to the spectrum shown either by pure yttria or by an earth tolerably rich in yttria. When traces are present the citron band only is seen. A little more yttria brings out the first and then the second green band, and finally, as the proportion of yttria increases, the red and blue bands appear (80 to 86). ' Circumstances modifying the Yttria Spectrum 74. 'In the early days of this investigation I frequently found that an earthy mixture which by one mode of treatment gave no spectrum would give a good citron band by a modification of the treatment, and I gradually found that I was most likely to get the spectrum when the body had been treated with sulphuric acid and then ignited to dull red- ness (4). Not knowing the circumstances governing the appearance of the citron band, it would not then have been safe to have altered this mode of treatment. Now, however, having ascertained the earth to which the spectrum was due, and having a considerable quantity at my disposal, experiments were tried on other methods of treating yttria before exposing it in the radiant matter tube. 75. ' Pure yttria precipitated by ammonia from the sulphate was dried at a temperature below redness and tested. It did not phos- phoresce in the slightest degree, and, necessarily, no citron-band spectrum was to be seen. The yttria was removed from the tube, con- verted into sulphate, heated to redness, and again tested. It now gave the citron band magnificently. This shows what apparently trivial circumstances will alter the whole course of an investigation. In 1881, when searching for discontinuous phosphorescent spectra, I tried a similar experiment with pure precipitated yttria (45), and entirely missed its citron-band spectrum. Had I first treated the yttria with sulphuric acid, instead of testing the earth itself in the radiant matter tube, the results would have been very different, and this research would probably have never been undertaken. 76. ' Yttria was now prepared by igniting the precipitated oxalate at a red heat. On testing in the radiant matter tube it phosphoresced with feeble intensity, the light being about one-twentieth of that given by the ignited sulphate under similar conditions. The citron band was almost as sharp as the sodium line, and was shifted one division towards the blue end, now occupying the position 3050 to 3060, its former place 3028 to 3049 being quite dark. The appearance is shown in line No. 4. On superposing this spectrum and that from the ignited sulphate the displacement of the citron bands was clearly observed ; with a very narrow slit the two bands were seen not to touch. The two green bands were visible, but very hazy and indistinct, and only ta be resolved into bands with difficulty. The yttria was now removed from the tube, ignited to a bright red heat, and re-tested. The spectrum was a little stronger than that given by the yttria ignited at 92 SELECT METHODS IN CHEMICAL ANALYSIS a lower temperature, but in other respects the general appearance and measurements were unchanged. No alteration was caused by subse- quent ignition to a white heat. 77. ' Pure yttrium sulphate ignited to a bright white heat gave a spectrum corresponding to the oxide (76) ; the sulphate having been decomposed by the high temperature. 78. ' Yttrium phosphate was precipitated, washed, and dried at a heat below redness, and introduced into the radiant matter tube. It phosphoresced faintly, giving the citron band hazy and faint, extending from about 3010 to 3060. The red bands were faint, and the green bands, especially the first one, were stronger than usual. The salt was now removed from the tube and heated to redness. It became of a grey colour, and now phosphoresced with a beautiful green light. The citron band was still broad and faint, but the green bands were very bright and distinct, and the red band between 2610 and 2627 was .also stronger. The spectrum No. 5 shows the appearance. ' Heating the phosphate before the blowpipe made little change in the character of the phosphorescence. It was moistened with sulphuric acid, heated to a dull redness, and then tested, but no further change was produced in the spectrum. This experiment shows that the citron- band test for yttrium is far less delicate in the presence of phosphoric -acid than in its absence. ' Occurrence of Yttria in Nature 79. ' It is an old and probably a true saying that every element could IOQ detected everywhere had we sufficiently delicate tests for it. Early observations (10, 16) had prepared me for the wide distribution of the element giving the citron band, and no sooner had the exquisite sensi- tiveness of this spectrum test forced itself on my notice than I sought for yttrium in other minerals. Facts which I had noticed in connec- tion with the variation of the appearance of the citron spectrum, according to the quantity of yttrium present, showed that it might be possible to devise a process for the rough quantitative estimation of jttrium, and after several experiments this was ultimately carried out in the following manner : ' Some calcium carbonate which was found to give no citron band (12) was boiled in a quantity of nitric acid insufficient to dissolve it. The solution was filtered from the insoluble residue, diluted to a convenient bulk, and standardised : 14-91 grains of solution contained 1 grain of calcium. This operation was performed in a room in which had been no yttria compound, and the chemicals and apparatus were new, and had not been taken into the general laboratory. A portion of the standard solution was precipitated with ammonium oxalate, and the calcium oxalate ignited and treated with sulphuric acid. Tested in the radiant matter tube it gave no citron band. OCCURRENCE OF YTTRIUM IN NATURE 9$ ' Pure yttrium sulphate was dissolved in water to such a strength that 8000 grains of solution contained 1 grain of yttrium. 80. * The solutions were mixed together in the proportion of 1 of yttrium to 100 of calcium, evaporated to dryness, and ignited with sulphuric acid, and the residue tested in a radiant matter tube. The spectrum was bright, the citron band, the two green bands, the blue and the red bands showed distinctly. 81. * A mixture was now prepared in the proportion of 1 of yttrium to 500 of calcium, and tested as above. The citron band was strong,, but the green bands were fainter ; the blue bands were still visible. 82. ' A mixture containing 1 of yttrium to 1000 of calcium was next prepared. In the radiant matter tube the citron band was almost a& strong as in the last experiment, but the edges were not so sharp, the blue bands were faint, and the green bands had disappeared. 83. ' A mixture containing 1 of yttrium to 5000 of calcium tested in the radiant matter tube showed the citron band still very bright,, but hazy about the edges. No other bands were seen. Parts. Pink coral (one particular specimen) One part of yttrium in 200 Strontianite One 500 Stilbite One 500 Hydrodolomite, from Vesuvius . . One , 500 Witherite One 1000 Arragonite ..... One 2000 Chrondrodite (Humite) from Vesuvius One 4000 Egyptian syenite (Cleopatra's Needle) One 7000 Calcite One 10,000 Natrolite One 10,000 Ox bone ' One 10,000 Meionite (Vesuvius) .... One 10,000 Meteorite (Alfianello, Feb. 16, 1883) One 100,000 Brevicite | One 200,000 Prehnite One 500,000 Thomsonite One 500,000 Vesbine, mixed with lava, from Vesuvius One 700,000 Dolomite One 1,000,000 Tobacco ash One 1,000,000 Leucite, from Vesuvius . . . Less than one 1,000,000 Nepheline, from Vesuvius . . None Meteorite (Dhurmsala, 1860) . . None Analcite None Phenakite None Chrysolite None 1 Haiiynite I None Turquoise None 84. ' A mixture of 1 of yttrium and 10,000 of calcium was now tried. The citron band was still decided, but not at all sharp. 85. ' One of yttrium to 100,000 of calcium was next prepared and tested. The citron band was faint, but easily seen. It could not, however, be obtained at all sharp, and appeared broader than usual. 94 SELECT METHODS IN CHEMICAL ANALYSIS 86. * A mixture of 1 of yttrium and 1,000,000 of calcium was lastly prepared, and tested in the radiant matter tube. The citron band was very faint, but there was no mistaking its presence, and with care I have no doubt a smaller quantity than 1 in 1,000,000 could be detected. This, however, appears to be near the limit of the test. 87. ' These seven tubes were mounted on a board, so that connection with the induction coil could rapidly be made to either of them ; and various minerals, &c., were prepared and tested in radiant matter tubes (10). By comparing their spectra with those of the standard tubes I could, after a little practice, determine roughly the proportion of yttrium present, supposing the test not to be interfered with by the presence of phosphoric acid (78). 88. 'In the table given on the preceding page are some of the most interesting results obtained in this way. Indications of other Spectrum-yielding Elements 89. ' Throughout the course of this paper I have devoted myself only to the citron-band spectrum. I do not, however, wish it to be thought that no other spectra were obtained. On the contrary, I have repeatedly seen indications of another very beautiful spectrum charac- terised by a strong red and a double orange band, and, more rarely, of a third spectrum distinct from the other two. These I am investigating, but not yet having obtained definite results I forbear from saying any more about them. I hope that they may bear sufficiently good fruit to be worthy of presentation at some future time to the Royal Society.' Samarium l 90. ' In the concluding sentence of the Bakerian Lecture which I had the honour to deliver before the Royal Society, May 31, 1883, I said that the new method of radiant matter spectroscopy there de- scribed had given me not only spectrum indications of the presence of yttrium as an almost invariable, though very minute, constituent of a large number of minerals, but had likewise revealed signs of another spectrum-yielding element. I stated that I had repeatedly seen indi- cations of another very beautiful spectrum characterised by a strong red and a double orange band. That this second spectrum was not then new to me is shown by a paper sent to the Royal Society in 1881, 2 in which I described a double orange band occurring in the phosphorescent spectrum of an earth less frequently met with than the " pale yellowish coloured earth" (since identified as yttria) which gave me the " red, orange, citron, and green bands." 91. ' The method adopted to bring out the orange band is to treat 1 Extracts from a paper read before the Koyal Society, June 18, 1885, by William Crookes, F.R.S. 1 Proc. Boy. Soc., vol. xxxii. (1881), p. 206. THE ORANGE-BAND SPECTRUM 95 the substance under examination with strong sulphuric acid, drive off excess of acid by heat, and finally to raise the temperature to dull redness. It is then put into a radiant matter tube, of the form shown FIG. 3. in fig. 3, and the induction spark is passed through it after the exhaus- tion has been pushed to the, required degree. The anhydrous sulphate thus left frequently shows the orange band in the radiant matter tube, though before this treatment the original substance shows nothing. ' Mixed " Citron " and " Orange " Spectra 90. * Since the date of my last paper I have devoted myself to the task of solving the problem presented by the double orange band first observed in 1881. With the yttrium experience as a guide it might be thought this would not be a difficult task, but in truth it helped me little beyond increasing my confidence that the new, like the old spec- trum, was characteristic of an element. The extreme sensitiveness of the test is a drawback rather than a help. To the inexperienced eye one part of " orange band " substance in ten thousand gives as good an indication as one part in ten, and by far the greater part of the chemi- cal work undertaken in the hunt for the spectrum-forming element has been performed upon material which later knowledge shows does not contain sufficient to respond to any known chemical test. It is as if the element sodium were to occur in ponderable quantity only in a few rare minerals seldom seen out of the collector's cabinet. With only the yellow line to guide, and seeing the brilliancy with which an imponderable trace of sodium in a mineral declares its presence in the spectrum, I venture to think that a chemist would have about as stiff a hunt before he caught his yellow line as I had to bring my orange and citron bands to earth. ' Chemistry, except in few instances, as water-analysis and the de- tection of poisons, where necessity has stimulated minute research, takes little account of " traces " ; and when an analysis adds up to 99*99, the odd 0*01 per cent, is conveniently put down to " impurities," " loss," or "errors of analysis." When, however, the 99'99 per cent, constitutes the impurity and this exiguous O'Ol is the precious material 96 SELECT METHODS IN CHEMICAL ANALYSIS to be extracted, and when, moreover, its chemistry is absolute!} unknown, the difficulties of the problem become enormously enhanced. Insolubility as ordinarily understood is a fiction, and separation by precipitation is nearly impossible. A new chemistry has to be slowly built up, taking for data uncertain and deceptive indications, marred by the interfering power of mass in withdrawing soluble salts from a solution, and the solubility of nearly all precipitates in water or in ammoniacal salts when present in traces only. What is here meant by " traces " will be better understood if I give an instance. After six months' work I obtained the earth didymia in a state which most chemists would call absolutely pure, for it contained not more than one part of impurity in five hundred thousand parts of didymia (131). But this one part in half a million profoundly altered the character of didymia from a radiant-matter-spectroscopic point of view, and the persistence of this very minute quantity of interfering impurity entailed another six months' extra labour to eliminate these final " traces " and to ascertain the real reaction of didymia pure and simple (131). 1 For a long time the " citron-band " and the " orange-band " spectra were confounded. That they were due to two different states or kinds of matter was not easily decided, since in all the early experiments I was dealing with a mixture ; consequently the spectra obtained were not only mixed but differed considerably in the relative intensities and faintness of the different lines (146). 97. ' At last, having separated yttria and obtained its spectrum pure (71), the characteristic lines in the other spectrum or spectra could be provisionally mapped out by difference, and a systematic hunt was instituted for the new " orange band" substance, which, to avoid peri- phrasis, was termed x. Naturally my thoughts turned to samarskite and the yttria earths. A wide, prolonged survey over every available substance had convinced me that the number of bodies giving a dis- continuous phosphorescent spectrum is extremely limited, and to be counted on the fingers of one hand ; and having satisfactorily mated one of these spectra to yttria it became in the highest degree probable that the twin spectrum should belong to one of the nearest chemical associates of yttria. * Chemistry of the " Orange-band " Forming Body 98. 'At first it was necessary to take stock, as it were, of all the facts regarding x which had turned up during the search for the orange band. In the first place x is almost as widely distributed as yttria, generally occurring with the latter earth. Sometimes, however, the orange band was strong where the citron band was almost or quite absent. It is almost certainly one of the earthy metals, as it occurs in the insoluble oxalates, in the insoluble double sulphates, and in the precipitate with ammonia. It is not precipitated by sodic thiosul- phate, and moreover it must be present in very minute quantities, since X FROM SAMARSKITE 97 the ammonia precipitate is always extremely small, and as a rule x is not found in the nitrate from this precipitate. 99. ' At this stage of the inquiry the chemical reactions of x were much more puzzling than with yttria. At the outset an anomaly presented itself. The orange band was prone to vanish in a mysterious manner. Frequently an accumulation of precipitates tolerably rich in x was worked up for purposes of concentration, when the spectrum reaction suddenly disappeared, showing itself neither in precipitate nor filtrate (3, 101, 108, 115) ; whilst on other occasions, when following apparently the same procedure, the orange band became intensified and concentrated with no apparent loss. The behaviour of the sulphate to water was also very contradictory ; on some occasions it appeared to be almost insoluble, whilst occasionally it dissolved in water readily (115). 100. ' For some time I debated whether the orange-band spectrum might not be merely a modification of the yttrium spectrum induced by the presence of some extraneous body. We know that yttria per se has little or no phosphorescence (75), that this power chiefly resides in the ignited sulphate. Might it not happen that some other earth with molecules peculiarly sensitive to the longer vibrations would confer upon yttria some of its sensitiveness to the red end of the spectrum ? ' It would be too much like a repetition of my paper on the yttrium spectrum quest were I to detail the numerous experiments and false starts with samarskite, orangite, thorite, strontianite, crelestine, perofskite, cerite, coral, &c. ; but I may be permitted to extract from an enormous mass of chronicles which must remain unpublished some few experiments which will usefully emphasize what I may call the nodal points in this research. ' X from Samarskite 101. ' It was to be expected that samarskite would contain x. It occurred, however, very little in the yttria group, but was found with the decipia residues (47, 49) or the earths forming, with potassium, insoluble double sulphates ceria, lanthana, didymia, decipia, samaria, together with a little thoria and zirconia. These residues were dissolved in hydrochloric acid, precipitated with ammonia, washed till free from potassic salts, re-dissolved, and precipitated as oxalates. The filtrate was set aside in Winchester quart bottles, and after standing for some weeks a further quantity of insoluble oxalates was found deposited at the bottom of the bottles. These were collected and appeared to be very rich in x ; but on attempting to work them up vexatious anomalies constantly started up : suddenly the orange-band would disappear, and after being lost sight of for a week or two, would return in a manner equally unaccountable (3, 99, 108, 115). 98 SELECT METHODS IN CHEMICAL ANALYSIS ' Thorite and Orangite 102. ' Early in my research thorite and orangite (26) had given a brilliant spectrum, afterwards identified with that of yttria (70). When hunting for x some of the insoluble double sulphates from these minerals (32) were treated like the samarskite double sulphates to remove potassium (101), and examined in the radiant matter tube. Here also was found the orange-band spectrum, quite different from the yttrium spectrum of the soluble sulphates ; but, as usual, it behaved in a most capricious manner. ' Perofskite 103. ' An American friend, Mr. George F. Kunz, with great kindness sent me some pounds weight of the rare mineral perofskite (calcic titanate), in fine crystals, from Magnet Cove, Arkansas, together with a large number of specimens of associated minerals from the same locality. The perofskite was found to be richer in x than any mineral yet examined. At great sacrifice of material a small portion of an earthy body was obtained giving the orange-band spectrum more brilliantly than I ever had seen it before. Analysis failed to detect anything in it but lime (5, 9), the flame spectrum showed lime, and the atomic weight came out BO =55-3, CaO being 56. ' Calcite 104. ' Mr. Lettsom, understanding I was engaged in quest of an un- known body supposed to be associated with calcium, most kindly sent me specimens of rare and curious minerals ; and through his good offices Professor Albin Weisbach presented me with an extensive set of calcites ; these, prior to the invention of the spectroscope, had been measured by Professor A. Breithaupt, who, owing to discordant measurements, held what is known as " calcium " to consist of two or more allied elements, which as yet chemists were unable to separate. * These calcites were treated as usual and examined most carefully in the radiant matter tube. In one of them only was a trace of yttria found, but the orange -band spectrum was very faintly seen in six of the thirteen specimens. The others shone with the usual greenish- blue phosphorescence of calcic sulphate, giving no lines or bands in the spectrum. ' I am also indebted to Mr. Lettsom for a specimen of calcite from Branchville, S. Carolina, which when heated has the curious property of glowing strongly with a golden-yellow light showing a faint continu- ous spectrum. In the radiant matter tube the phosphorescence was very brilliant, but there was no discontinuity in the spectrum, only a concentration of light in the red portion. A' IN COEAL AND SEA WATER 99 * Dolomite 105. ' Another curious mineral, for which I am also indebted GO Mr. Lettsom, is a granular dolomite from Utah. When scratched with a knife or struck with a pick it emits so strong a phosphorescent red light that the miners call it " hell-fire rock," By itself in the radiant matter tube it brightly phosphoresces with a reddish light, showing no bands, but a concentration of light in the red. Treated with sulphuric acid in the usual manner, and then examined in a vacuum tube, a similar con- tinuous spectrum is observed. Chemical analysis showed that it was a nearly pure double calcic and magnesic carbonate, with a little iron, alumina, and phosphoric acid. ' Amongst other minerals found to give the orange-band spectrum I may mention zircon, euxenite, tyrite, fergusonite, rhabdophane, ceruss- ite, apatite, galliferous blende, argentiferous galena, anglesite, harmo- tome, allanite ; cerite, magnesite, oolite from Bath, &c. ' Coral 106. ' In my former paper (88) I mentioned that a specimen of pink coral contained about a half per cent, of yttria, judging from the very strong yttrium spectrum it gave in the vacuum tube. Professor Martin Duncan has identified this specimen as a G-orgonia of the genus Meli- tli&ci. Another recent coral, Mussa sinuosa, gave equally strong indica- tions of yttrium. By the kindness of Professor Duncan I have since been enabled to submit a large number of corals to spectrum examina- tion in the radiant matter tube. Nearly all showed more or less discontinuity in their phosphorescent spectra, but as in the yttrium spectrum research I obtained only two specimens giving a brilliant yttrium spectrum, so in the present quest I have found only two corals giving a strong orange-band spectrum. One is a Pocillopora dami- cornis, from Singapore and most of the Pacific Islands which have reefs, one of the old group of tabulate corals. A fragment of this coral, treated with sulphuric acid and examined in the radiant matter tube, gave as brilliant an orange-band spectrum as I had ever seen. The other is of the species Symphyllia, close to Mussa, a reef-builder from the same locality as the Mussa which gave so much yttria. ' Sea- water 107. ' These results induced me next to try sea-water. Ammonic oxalate and hydrate gave a white precipitate, which was filtered off and washed. The oxalate was then ignited, dissolved in nitric acid, and the solution supersaturated with ammonia and boiled. The resulting precipitate, tested in the radiant matter tube, showed the orange-band spectrum very well. H2 100 SELECT METHODS IN CHEMICAL ANALYSIS * X in Strontium Minerals 108. t The orange-band spectrum in the radiant matter tube at first sight bore a close resemblance in the red region to the flame spectrum of strontium ; the two spectra therefore were examined together, and on comparing them a near coincidence was observed between two lines in the orange. Was it possible that the sought-for element was strontium ? * This led to an examination of the strontic nitrate used in the flame reaction. When converted into sulphate and tested in the radiant matter tube the experiment succeeded only too well. The orange-band spectrum came out brilliantly. ' Other commercial strontium compounds were now tested. Yttria was found almost universally, but the orange band was capricious ; the nitrate generally showed it well, caustic strontia sometimes, chloride as a rule not at all. These were from different makers. The source was inquired for, and in a few weeks my laboratory was filled with large specimens of Gloucestershire, Italian, and Sicilian coalestine, and Scotch, Italian, and German strontianite, together with waste products, mother-liquors, and every commercial salt of strontium. The kindness of the manufacturers was great, and I regret that the outcome was not more notable. * Italian coslestine showed a good orange-band spectrum when crushed and examined in the tube without any chemical treatment. After getting the mineral into solution by fusion with sodic carbonate, &c., the x could be concentrated by fractionally precipitating with alka- line carbonates (coming down in the first fractions). The sulphate produced from this precipitate also showed the desired spectrum. 1 This sulphate was digested for some time in warm ammonic carbo- nate, and now the old distressing anomalies re-commenced. On most occasions, when working roughly on a scale of a few grammes, all the x was found in the filtrate on evaporation and ignition. When, how- ever, I took identically the same material, and worked it up more care- fully, in pounds or hundredweights, it sometimes gave nothing at all, sometimes only a ridiculus mus on the smallest sized filter, got from a mountain of raw material. This was at first accounted for by the want of homogeneity of the mineral. The real explanation, however, was not discovered till long after (115). ' A quantitative estimation was attempted of the amount of x sub- stance got from Italian coalestine. 620 grammes gave 1*525 gramme, or 0*24 per cent. Analysis showed this to be chiefly strontic sulphate, and the atomic weight of the metal was close to that of strontium. ' Is X a Mixture ? 109. ' For a considerable time strontium minerals and salts only were worked upon, these being considered the cheapest and most fruit- IS X A MIXTURE ? 101 ful sources of x. A considerable quantity of material was thus accumulated, showing the desired spectrum with great brilliancy. When, however, attempts were made to separate the spectrum-forming body from the accompanying elements, as strontium, calcium, &c., all the foregoing anomalies were displayed. Ultimately two portions of substance were produced a precipitate (113) containing the supposed new element, and a filtrate, containing the strontium, calcium, and other impurities. Neither the precipitate nor filtrate tested in the usual manner showed the orange band anything like so well as the material before such separation, and indeed at this stage of the experiments it frequently vanished altogether. 1 Some of the filtrate and precipitate were now mixed together, treated with sulphuric acid, and tested as before : they gave the orange-band spectrum as brightly as did the original substance. The ammonia precipitate was too small for analysis, but judging from its origin it might contain any or all of the rare earths. Chemical analysis showed nothing but a calcium salt in the filtrate. 110. ' Could it be that the union of two bodies was necessary to give this spectrum, and that calcium was one of these ? Could the other constituent be of the nature of an acid such as boric, or a halogen like fluorine ? ' Many experiments were tried to test this hypothesis. Pure Iceland spar was dissolved in acid, a little of the above-described precipitate added, and the mixture tested in the usual way. The orange band appeared again. 1 Every conceivable mixture was now made of lime with other bodies, but whilst I frequently obtained faint indications of orange band there was never sufficient to satisfy me that I had artificially formed the spectrum-bearing body ; the traces observed were evidently due to the all-pervading presence of the sought-for body. ' So far all had been contradictory and disheartening. Analogy with the yttrium results failed to throw light to guide through the gloom. The hypothesis that the body sought was an earth, widely diffused in minute quantities only, and that its anhydrous sulphate gave a phos- phorescent spectrum in the radiant matter tube, had guided me a cer- tain distance and then led me widely astray. A new factor must now be taken into account the presence of a calcium compound appeared to be necessary. An earthy body which, when treated and tested in the usual manner, fails to show the faintest glow of an orange-band spectrum, can by admixture with calcic sulphate be made to yield a pure and brilliant spectrum, rivalling in clearness and beauty that given by yttric sulphate. 111. 'Of the two components of the phosphorescing body calcium and x which is the necessary and which is the variable factor ? ' This question did not appear difficult to answer. In the first case 102 SELECT METHODS IN CHEMICAL ANALYSIS the calcium must be kept the constant, and x be made the variable quantity. 4 A piece of pure colourless Iceland spar the sulphate from which had been proved to phosphoresce normally with a greenish-blue light, without bands or concentration in any part of the spectrum (164) -was dissolved in hydrochloric acid, and mixed with about 10 per cent, of various metallic sulphates. Sulphuric acid was added, the mixture evaporated to dryness, ignited, and tested in a radiant matter tube. The bodies thus used to replace x, in addition to the more common earths, were the earths from samarskite enumerated in the first part of this paper (40) in as pure a state as I could get them, together with various earthy precipitates, oxalates, &c., obtained from different minerals during the preceding operations. ' These experiments resulted in an embarras des richesses. "Whereas, hitherto, I had considered the orange-band-forming body rare and sparsely distributed, I now found it sharing with yttrium the attribute of ubiquity. The answer to my question was too full, and left me again in doubt as to whether calcium or x was the variable quantity. ' The yttrium spectrum turned up in this series of experiments about as frequently as the orange-band Spectrum. I knew that in such cases yttrium was present as an impurity ; might it not be that the almost universal occurrence of the orange-band spectrum was equally caused by a minute but varying quantity of x in the earths under test ? 112. 'I took them one by one and submitted them to further severe chemical treatment, fractionally precipitating them, in cold dilute solution, with weak ammonia, or fractionally crystallising their oxalates from nitric acid. As the purification progressed the orange-band spectrum generally lessened in intensity till in the case of many earths it faded out altogether, and in most of them it gave evident indications of being extraneous to the earth itself. In some instances, however, the spectrum increased in intensity ; moreover, when the purified earth showed any diminution of the orange band the eliminated impurity always showed the orange band in an exalted degree. I drew from these experiments the inference that x was a definite element, as widely distributed, or nearly so, as yttrium, but requiring admixture with a calcium compound to bring out its phosphorescent properties. 113. * Next I had to ascertain if the calcium could be replaced by any analogous body. In this case, therefore, the x was kept constant whilst the calcium was replaced. An ammonia precipitate (109) from a rich accumulation of orange band substance was chosen as the x. Tested in the usual manner, by itself, it showed nothing, but mixed with lime it gave the orange-band spectrum very bright and pure. ' The metals used to mix with it were in the form of sulphates strontium, barium, glucinum, zirconium, thorium, magnesium, zinc, cadmium, lead, copper, silver, cerium, lanthanum, didymium, alu- minium, manganese, tin, bismuth, antimony ; also silicic, titanic, KXPLANATJOX OF THE ANOMALIES OF X 103 tantalic, tungstic, molybdic, and niobic acids. More than half of these bodies possessed the property of conferring " orange-band " phosphores- cence on the precipitate under examination, although by themselves they evinced no power of giving a phosphorescent spectrum. ' Explanation of foregoing Anomalies 114. ' In this manner the remarkable fact was established, that the x I sought was an earth which of itself could give little or no phosphor- escent spectrum in the radiant matter tube, but became, immediately endowed with this property by admixture with some other substance, which substance likewise by itself had no power of phosphorescing with a discontinuous spectrum. ' Of the great number of bodies used to mix with the earth x in these experiments, which acted best ? It was not easy to try comparative experiments at this early stage ; ultimately I came to the conclusion that lime, if not the best, was as good as any. 115. ' These results afford a full explanation of the anomalies which had so long hampered my endeavours to repeat on a large scale experi- ments which, when working with small quantities, had given good results (99, 101, 108). The preliminary experiments were intended to ascertain whether the desired orange band was present or not. Natural impatience led to hurried operations and defective washing of precipi- tates, and thus some of the necessary lime was left with the phosphor- escing body. The subsequent larger operations were performed in a more systematic manner with the object of securing as large a yield of substance as possible. The precipitates were thoroughly washed, the lime was more completely thrown out, and the sought-for earth, although obtained, refused to reveal itself by the spectroscope and radiant matter tube. ' The contradictory behaviour of the sulphate to water (99) was now easily explained. The insoluble crystals, which from the brilliancy of their phosphorescent spectrum I had at first mistaken for the nearly pure sulphate of x, were merely calcic or strontic sulphate contaminated with perhaps not more than the one ten-thousandth part of x sulphate which it had carried down with them on crystallising. '^in Cerite 116. 'In the corresponding yttrium research I was aided materially by the fact that the sought-for earth did not give an absorption spectrum (42). This enabled me to throw out a large number of obscurely known elements, and I therefore early endeavoured to ascertain whether the supposed new earth, x, did or did not give an absorption spectrum. At first I could not decide one way or the other. I frequently obtained a good orange-band spectrum when the solutions gave no trace of absorption spectrum, whilst on other occasions the 104 SELECT METHODS IN CHEMICAL ANALYSIS solution showed good didymium and other bands. Gradually, how- ever, it was noticed that whenever the didymium absorption bands, were strong the orange-band spectrum was also particularly brilliant. Moreover, amongst the earths enumerated in par. 113 as mixed with lime in the quest for x, I have mentioned that some of them gave the orange-band spectrum with increased intensity ; the earths of the cerium group were the most noteworthy, and these considerations made it probable that here would be found the location of x. 117. ' On a former occasion, when searching for the citron-band- yielding earth, and examining cerite (22 to 25), I made use of the potassic-sulphate method of separating the two great sub-groups, viz. the cerium and the yttrium earths ; the former giving insoluble, and the latter soluble, double sulphates. I said (23) : ' " The precipitated double sulphates were dissolved in hydrochloric acid, and the earths precipitated as oxalates. After ignition and treat- ment with sulphuric acid, the mixed ceria, lanthana, and didymia were- tested in the radiant matter tube, but the merest trace only of citron band was visible." ' A repetition of the above experiment produced similar results. The contents of the tube were now removed, mixed with lime and excess of sulphuric acid, ignited, and again tested in the tube. This time the orange-band spectrum came out very brilliantly, showing in a striking manner the necessity of supplementing x with some other earth to- bring out its phosphorescing properties. 1 The cerium group, to which x was now almost certainly traced, consists of cerium, lanthanum, didymium, samarium, and perhaps yttrium-a (136). The other metals, enumerated in par. 101 as being precipitated by potassic sulphate, were found not to phosphoresce with a discontinuous spectrum, either alone or when mixed with lime. ' Analysis of Cerite 118. ' The first necessity was to get the earths ceria, lanthana, and the mixture hitherto called didymia in a pure state, for my so-called pure earths of this group all showed the orange band in more or less- degree. ' About 14 Ibs. of cerite were finely ground, made into a thick paste with strong sulphuric acid, and heated to drive off excess of acid. The mass became of a white or pale grey colour. This was digested in cold water, filtered, and the residue well washed with cold water. 1 To the filtrate oxalic acid was added, which precipitated all the earths, with any lime, &c., that might be present, as oxalates. It saves time at first only to aim at a partial separation of the mixed earths, and for this purpose it is well to proceed as follows : The dried oxalates are boiled with strong nitric acid till completely decom- posed, the nitrates are evaporated to dryness, mixed with three times SEPARATION OF CERIA FROM ALLIED EARTHS 105 their weight of nitre, and fused at the lowest temperature at which nitrous fumes come off; the residue is digested in water, filtered, and washed. The insoluble residue, of a pale yellow colour, consists of eerie oxide and basic eerie nitrate, with a little of the other oxides, whilst the filtrate contains the bulk of the lanthanum, didymium, and samarium. ' Separation of Ceria, Lanthana, Didymia, and Samaria 119. ' To free the lanthanic, didymic, and samaric nitrates from the last traces of cerium, it is necessary to fuse them again very gently with three or four times their weight of potassic nitrate, at a temperature just sufficient to cause slight decomposition. The operation of fusing must be repeated on the evaporated filtrate many times to throw out all the cerium. ' The eerie oxide or basic nitrate obtained is freed from any didy- mium by re-treatment with nitric acid and fusion as above ; the presence of didymium being indicated by its brown colour or by the absorption spectrum of the solution. 120. ' The separation from each other of lanthana, didymia, and samaria is a most laborious process, and the amounts of these earths, obtainable in anything like a pure state, is small compared with the mass of material worked up. The solution of the nitrates of these elements is made perfectly neutral, diluted to such a strength as to contain about 1 per cent, of the oxides, and a very dilute solution of ammonia is added, about 0*1 gramme NH 3 in 500 cubic centimetres, the precipitation being conducted in large vessels, as ordinary Win- chester quart bottles. The first precipitates formed are rich in sama- rium, and also contain much didymium ; these are followed by didymium, with some lanthanum and samarium ; and the final precipitates consist almost wholly of lanthanum. By this method there are obtained three portions of hydrates, which must be again worked up separately by precipitation ; the first for samarium (133), the second for didymium (127), and the third for lanthanum (125), the process of fractional pre- cipitation being repeated on each portion fifty or a hundred times. 121. ' The separation of the last traces of didymium from the sama- rium can be accomplished only by fractional precipitation, an operation so tedious that probably few chemists will be inclined to undertake it. The second portion of hydrates, consisting chiefly of didymium, is purified from the small quantities of samarium and lanthanum by fusing with potassic nitrate, as explained above for the traces of cerium (118) ; to separate the lanthanum the oxalates are dissolved in warm strong nitric acid and allowed to cool, when didymic oxalate nearly free from lanthanum is obtained ; after repeating several times, the last trace of lanthanum remains in the solution. 122. ' To separate the small quantity of didymium from the lanthanum obtained in the final precipitates with ammonia, the only 106 SELECT METHODS IN CHEMICAL ANALYSIS method is to continue the process of fractionation ; the lanthanic oxide finally obtained should be pure white, any trace of yellow showing that didymiu is still present. 123. ' As cerite contains small quantities of the yttria earths, these must be separated from cerium, didymium, &c., by making a cold solution of the sulphates arid adding finely powdered potassic sulphate in quantity more than sufficient to saturate the solution, allowing the mixture to stand (with frequent agitation) for a few days ; filtering, and washing the filtrate with a saturated solution of potassic sulphate. The filtrate contains the yttria earths, and for their complete separa- tion it is advisable to repeat the operation with potassic sulphate three or four times. The insoluble residues, consisting of a double potassic sulphate with either cerium, didymium, or other member of this group, are boiled with sodic hydrate, filtered, well washed, re-dissolved in nitric acid, precipitated with oxalic acid, and the oxalates ignited, leaving the earths lanthana, didymia, or samaria to be finally purified as described further on. 124. ' The eerie oxide obtained in the manner just described was white. A considerable thickness of a strong solution did not show a trace of absorption spectrum. The atomic weight of the metal was taken and yielded the number . . . . . . . = 141*1 The number given by BiJHRiG 1 .... =141-2 ROBINSON 2 . . . = 140-2 ' Many older determinations 3 range from 138 to 139. ' This eerie oxide gave no orange -band spectrum in the radiant matter tube, either with or without the addition of lime. * Purification of Lanthana 125. * The lanthana obtained in the manner described above (120, 122) was more difficult to purify than ceria. Long after the lanthana appeared pure, it gave in the radiant matter tube a good orange-band spectrum when mixed with lime and treated as usual, although with- out lime it gave no spectrum. ' So long as the lanthana showed the didymium absorption bands I could not be certain whether the orange-band spectrum belonged to it or to didymium, therefore the tedious process of fractionation with very weak ammonia in cold dilute solutions was repeated for some weeks. The first precipitates were lanthana containing most of the didymia, whilst the final precipitates were lanthana almost if not quite free from didymia, according to the quantity originally present. After 1 Journ. prakt. Chem. (2), xii. 209. 2 Chemical News, vol. 1. p. 251, Nov. 28, 1884. 3 Ibid., vol. xlix. p. 282, June 27, 1884. PURIFICATION OF DIDYMIA 107 several hundred fractional precipitations repeated over and over again, a little lanthana was got which failed to show the didymium absorption bands. As the purification progressed the phosphorescent orange-band spectrum became fainter, until finally a lanthana was obtained which, mixed with lime and treated in the usual manner, gave no orange-band spectrum whatever. This lanthana was snow-white, and had an atomic weight of 138-3. MABIGNAC gives for lanthana 138-6, BBAUNEB 138-28, CLEVE 138-22. ' Purification of Didymia 120. ' The earth formerly called didymia is now known to be a mixture of didymia and samaria. The didymia which I prepared by the method described above, when mixed with lime and sulphuric acid and tested in the radiant matter tube, gave the orange-band spectrum as brightly as I had ever seen it. It was not, however, quite free from the accompanying samaria, and systematic operations were now com- menced with the object of obtaining the didymia and the samaria in a state of purity that is to say, in such a condition that one of them should show no orange-band spectrum at all, whilst the other should give the spectrum in its highest degree of intensity. ' I did not attempt the two purifications simultaneously on the same material. One earth only was taken in hand at a time, and by repeated fractionations and the most profuse sacrifice of material I was at last enabled to obtain a little of the desired earth quite free from admixture. 127. * I took didymia first. About 1000 grammes of the earth, par- tially purified as described (120, 121), were dissolved in a large excess of strong nitric acid. To the nearly boiling liquid a hot saturated solution of oxalic acid was carefully added, and constantly stirred, until the precipitate, which at first rapidly disappeared, just refused to dissolve. A drop or two of nitric acid was now added to render the solution clear, and the liquid set aside to cool, when brilliant pink-coloured prisms of didymic oxalate (containing nitric acid) crystallised out. These crystals contained nearly all the didymium and samarium, whilst the mother- liquor contained the greater part of the lanthanum, reserved for the preparation of pure lanthana (125). ' The crystals of didymic oxalate were ignited and again converted into nitrate, and the above-described partial crystallisation as oxalate repeated five or six times, in each case rejecting the mother-liquor as contaminated with lanthanum. 128. ' The final oxalates the ultimate accumulation of the portions least soluble in nitric acid were next converted into nitrates, and the excess of acid driven off. The anhydrous salt was dissolved in fifty times its weight of water, and fractionally precipitated by ammonia in the following manner : A large quantity of ammonia was first pre- pared of the dilution (1 to 5000) used in the previous fractionatioii (120), and 500 c.c. of this were gradually added, with constant stirring, 108 SELECT METHODS IN CHEMICAL ANALYSIS to Winchester quarts about three-fourths full of the dilute didymic nitrate. In about half an hour another 500 c.c. of ammonia were again added, and this operation was repeated at intervals till the Winchester quarts were full. The bulk of the samaria comes down in the first precipitates, which are filtered off and set aside for the pre- paration of pure samaria (133). ' To the filtrate, containing didymium, with a little samarium and lanthanum, ten successive quantities of about 200 c.c. each of dilute ammonia were added to each Winchester quart at intervals of about an hour, and after violent agitation allowed to subside. The clear super- natant liquid was now poured off, evaporated to about half its bulk, and then, when cold, again poured back into the precipitate, and the operation of precipitating with dilute ammonia was likewise repeated. By this means the greater portion of the samarium present was obtained in the precipitate, whilst the didymium left in solution contained a less proportion of samarium. . 129. ' After a time a balance seemed to be established between the affinities at work, when the earths would appear in the same proportion in the precipitate and the solution. At this stage they were thrown down by ammonia, and the precipitated earths set aside to be worked up by the fusion of their anhydrous nitrates so as to alter the ratio between them, when fractionation by ammonia could be again em- ployed. ' Samaric nitrate decomposes by heat before didymic nitrate. The nitrates were mixed with four times their weight of potassic nitrate, and the whole kept fused in a crucible till about three-fourths of the earthy nitrates were decomposed. The cooled mass was then dissolved in water, filtered, and the solution evaporated to dryness, and again submitted to fusion. This was repeated several times. ' The basic nitrates insoluble in water were dissolved in nitric acid, and put through the operation of fractional precipitation with ammonia for samaria (133), in the manner just described above (128). 130. ' To remove the last traces of samarium which might have sur- vived this treatment, the solution of nitrates which had longest resisted decomposition by fusion was now mixed with excess of potassic sulphate. The precipitated double sulphates were subjected to long washing with a saturated solution of potassic sulphate, in which the samarium salt is more soluble than the didymium salt. They were then reconverted into nitrates, and the precipitation and washing with potassic sulphate repeated several times. Finally, the didymium salt was converted into oxalate, and re-crystallised many times from nitric acid, to eliminate any trace of lanthanum that might still contaminate it. Pure didymia is of a very deep chocolate-brown colour. 1 These proceedings are tedious enough even in their narration, but no mere words can enable the reader to realise the wearisome character PURIFICATION OF SAMARIA 109 of these operations when repeated day by day, month after month, on long rows of Winchester quart bottles. 131. 'I commenced the purification of didymia in the latter part of the year 1883, and the operations have been going on since almost daily in my laboratory. 1 At intervals of some weeks the didymia in the then stage of purification was tested in the radiant matter tube, a little lime having previously been added to bring out the discontinuous phosphorescence. During the first month the intensity of the orange- band spectrum scarcely diminished. After this it began to fade, but the last traces of orange band were very stubborn, and not till the last few weeks could I obtain a didymia to show no trace of the orange- band spectrum ; and this result has not been accomplished without sacrifice. 'My 1,000 grammes have dwindled away bit by bit, till now less than half a gramme represents all my store. 132. * Whilst in the midst of the operations of purifying didymium and samarium I had the pleasure of receiving a visit from Prof essor Cleve, to whom we owe so much of our knowledge of the chemistry of the samarskite and cerite metals, and especially of didymium and samarium. He gave me not only most valuable information, and suggestions respecting the work I was then engaged upon, but on his return to Upsala he munificently presented me with specimens of lanthana, didymia, samaria, yttria, and erbia specimens at that time considered to represent a state of purity. According to any chemical tests these earths would be deemed absolutely pure, but the test of the phospho- rescent spectrum proved too severe a trial, and the didymia, lanthana, and samaria all showed the orange band the lanthana faintly, the didymia more strongly, and the samaria brightest of all. A subsequent lot of " samarium-free " didymia, sent by Professor Cleve, also gave a strong orange-band spectrum, though the samarium present probably did not amount to more than the one hundred thousandth part of the didymium. ' Purification of Samaria 133. ' The foregoing experiments left little doubt that x, the orange- band-forming body, was samarium ; the last problem was, therefore, to get this earth in a pure state. The general plan of operations was the same as I adopted in getting didymium free from samarium, only atten- tion was now directed to the portions richest in samarium which had been formerly set aside (128, 129). On fractionation in highly dilute solu- tions with very weak ammonia the first precipitates are richer in samaria than the last. These first precipitates were re-converted into nitrates, and fractionation again proceeded with. 4 Fusion of the nitrates with potassic nitrate (129), or precipitation by, and washing with, potassic sulphate (130), is of no use in the final purification of samarium. When the object is to separate .a little 1 This was written in 1885. The experiments on the rare earths are still going on.-[W. C. Jan. 1894]. 110 SELECT METHODS IN CHEMICAL ANALYSIS samarium from a large quantity of didymium, fusing the nitrates will effect the purpose, but I have not found the converse to hold good. The potassic sulphate method cannot separate the last traces of didy- mium from samarium, for the diclymic double sulphate, not being quite insoluble, would wash out along with the first portions of the samaric salt. I have found no method better than fractionation with ammonia, and Professor Cleve tells me that is his experience. ' Towards the end of the operations, when the samaria is getting pure, it is useful to precipitate it as a double sulphate with potassic sulphate, and wash it well for some time, to remove any traces of earths of the yttria and other groups which might have been present and become accumulated with the samaria (123). 134. ' During fractional precipitation with ammonia an experienced eye can judge roughly what is the preponderating earth present, by the appearance of the precipitate as it comes down. When much samaria is present, with but little didymia and lanthana, the precipitate forms immediately. When there is much didymia, and little samaria and lanthana, the precipitate forms as quickly as in the first case, but does not settle so rapidly. With much didymia, and a fair quantity of lanthana, the precipitate forms more slowly than before and settles slug- gishly. When there is much lanthana and little didymia the precipitate takes a long time to settle, the liquid remaining opalescent for days. These peculiarities are due in great measure to the varying basicity of the elements, samarium being the least basic and lanthanum being the most basic, didymium occupying an intermediate position. ' In freeing samarium from the last portions of didymium the only test available to detect the presence of the latter metal is the absorp- tion spectrum. The best plan is to provide a strong solution of the samaric nitrate in a flask, to act as a lens, and to concentrate the light of a gas-flame by its means on to the slit of a low dispersion spectro- scope. Long after the light colour of the ignited oxide shows that the didymium is getting small in quantity, its absorption bands will be so strong as almost to obliterate the fainter samarium spectrum. 135. ' The fractionation should be persevered in till no didymium bands are seen in the absorption spectrum. After this point is reached I prefer to keep on fractionating for some time longer, if the material will hold out, so as to make assurance doubly sure. The colour of samaria, as pure as I have been able to prepare it, is w r hite with the faintest possible tinge of yellow. The absorption spectrum of samarium salts is much more feeble than the spectrum of didymium salts. ' The accompanying drawing (fig. 4) shows the absorption spectra of solutions of didymic and of samaric nitrates. It will be observed that the strongest bands of the samarium absorption spectrum are almost covered by strong absorption bands of didymium. Unless, therefore, the samarium is decidedly in excess, it will be difficult for any but a very practised observer to detect its presence. Fortunately the mar- PHOSPHORESCENT SPECTRUM OF SAMARIA 111 vellous delicacy of the phosphorescent spectrum of samarium renders any other spectrum test of less value. 136. 'I have already mentioned (117) that the cerite earths are sup- posed to contain a fifth member, which has been provisionally called Ya. 1 Not much is known respecting the properties of this earth, but from the little I can glean it would appear to become concentrated with the samarium, from which a partial sepa- ration may be effected either by con- tinuing the operation of fractional precipitation or by taking advantage of the different solubilities of their double potassic sulphates in potassic sulphate ; the potassio-samaric sul- phate being almost insoluble in a saturated solution of potassic sul- phate, whilst the corresponding salt of Ya is soluble in 100 to 200 volumes of the same solution. By persevering in this mode of treatment I ulti- mately obtained a small quantity of a white earth which gave no sa- marium spectrum in the radiant matter tube. Whether or no it was Ya I cannot say, as the quantity obtained was insufficient to enable me to determine its atomic weight. ' The Phosphorescent Spectrum of Samarium 137. * Pure samaric sulphate by itself gives a very feeble spectrum. Some of the pure salt was heated to redness, 2 sealed in a radiant matter tube, and carefully exhausted. The coil was adjusted so as to give a powerful spark ; the room was well 1 Marignac, Comptes Rendus, vol. xc. p. 899 ; Chemical News, vol. xli. p. 250. 3 Samaric sulphate is not decomposed at the temperature employed. 112 SELECT METHODS IN CHEMICAL ANALYSIS darkened, and the eye kept shielded from extraneous light. It was difficult to hit the exact moment of exhaustion between the dis- appearance of gas and non-conductivity, but by careful watching at the spectroscope a point was reached at which the phosphorescence appeared. The spectrum consists of a faint band in the red, then a sharp orange line (146, 165), next a wide ill-defined orange band, and finally an equally ill-defined green band. 138. ' When, however, the samaria is mixed with lime (114) before examination in the radiant matter tube, the change is very striking, and the spectrum is, if anything, more beautiful than that of yttrium. The bands are not so numerous, but the contrasts are sharper. Ex- amined with a somewhat broad slit, and disregarding the fainter bands, which require care to bring them out, the spectrum is seen to consist of three bright bands red, orange, and green, nearly equidistant, the orange being the brightest. With a narrower slit the orange and green bands are seen to be double, and on closer examination faint wings are seen, like shadows to the orange and green bands. In this spectrum the sharp orange -coloured line (137) of pure samaric sulphate is absent. 139. ' The bands are best seen in a spectroscope of low dispersion, and with not too narrow a slit. In appearance they are more analo- gous to the absorption bands seen in solutions of didymium than to the lines given by spark spectra. Examined with a high magnifying power all appearance of sharpness generally disappears ; the scale measure- ments given below must therefore be looked upon as approximate only ; the centre of each band may be taken as accurately determined within the unavoidable errors of experiment, but it is impossible to define their edges with much precision. 140. ' The accompanying cut (fig. 5) gives as good an idea of the spectrum of samarium-calcium as is possible in black and white. The numbers along the top are the squared reciprocals of wave-lengths, and are on the same scale as the diagram of the yttrium spectrum (71) given in my Bakerian Lecture already quoted. The phosphorescing mixture in the tube consisted of 20 parts of pure samaria and 80 parts of lime. They were converted into nitrates in a platinum capsule, and then decomposed by excess of sulphuric acid and ignited at a dull red heat. If sulphuric acid is added in the first instance there is a diffi- culty in getting the earths completely converted. ' The least refrangible band seen is a very faint red, which extends from -i 2310 to 2400. Here a much stronger red band begins, extend- ing to 2494. The first component of the bright orange band begins at 2739 and ends at 2762. Between 2762 and 2798 is a dark interval, And then the second component of the orange band is seen extending from 2798 to 2818. This band is stronger and more sharply defined than the preceding band. A faint yellow wing extends from the second PHOSPHORESCENT SPECTRUM OF SAMARIUM 113 orange band to 2942. There is now an intensely black interval reaching to 3025 ; here a faint yellowish-green light is seen extending to 3149, where the green band commences and extends to 3164. Here a fainter green wing begins, and extends to 3270. On this wing a very narrow faint green band is seen, having its centre at 3190. There is then another dark space, after which three ill-defined blue and violet bands are seen, too faint to measure accurately. 141. ' Preliminary experiments (114) had shown me that lime was one of the best materials to mix with samaria in order to bring out its phosphorescent spectrum, but it was by no means the only body which would have the desired effect. More accurate observations were now taken with pure materials mixed together in definite quantities. The i 114 SELECT METHODS IN CHEMICAL ANALYSIS bodies employed were those enumerated in par. 113. Of these the- following induced no phosphorescence : zirconium, cerium, didymium, copper, silver, manganese, and tin ; silicic, titanic, tungstic, molybdic, niobic, and tantalic acids. 142. * The other substances which I tried caused the samarium to give good phosphorescence with a discontinuous spectrum. They are strontia, baryta, beryllia, thoria, magnesia, zinc oxide, cadmium oxide, lead oxide, lanthana, alumina, bismuth oxide, and antimony oxide. There is a general resemblance between these spectra, but nearly all of them differ one from another in details. 145. * The samarium spectra, modified by other metals as above described, may be divided into three groups. The first group com- prises the spectra given when glucinum, magnesium, zinc, cadmium, lanthanum, bismuth, or antimony is mixed with the samarium. It consists simply of three coloured bands, red, orange, and green ; as a typical illustration I will select the lanthanum-samarium spectrum (fig. 6). The centres of the bands are red 2429, orange 2808, and green 3177. ' The second type of spectrum gives a single red and orange, and a, double green band. This is produced when barium, strontium, thorium or lead are mixed with samarium. The lead- samarium spectrum (fig. 7) illustrates this type. The centres of the bands of this spectrum are red 2437, orange 2830, green 3133 and 3199. * The third kind of spectrum is given by calcium mixed with samarium. Here the red and green are single, and the orange double. Aluminium would also fall into this class were it not that the broad ill-defined green band is also doubled. The calcium-samarium spec- trum, already illustrated in fig. 5 (140), is a good illustration of this type. 156. ' The foregoing observations had prepared me for the exceeding delicacy of this spectroscopic test for samarium. I have already shown (86) that one part of yttrium can be detected spectroscopically in the presence of a million parts of calcium, and the reaction is almost as sensitive if other earths are taken instead of lime. The spectrum test for samarium is, if possible, even more delicate. Experiments were now commenced with the object of getting some approach to a quantitative estimate of how small a quantity of samarium could be detected. ' A solution of specially purified calcic nitrate (79), which was found to contain neither yttrium nor samarium by the radiant matter test, was standardised, so that one part of calcium was contained in fifty parts of solution. 157. 'A standard solution of samaric nitrate was made containing one part of samarium in 100,000 parts of solution. ' These solutions were mixed in the proportion of 1 part samarium to 100 parts of calcium. The spectrum (fig. 8) was very brilliant, PHOSPHORESCENT SPECTRUM OF SAMARIUM 115 and but little inferior in sharpness to the spectrum given by a 50 per cent, mixture. 158. 'A mixture was now prepared containing 1 part of samarium to 1000 parts of calcium. Very little difference could be detected between the spectrum of this mixture and that of the last. The bands were, however, a little less sharp. Fig. 9 shows the appearance of this spectrum. 159. 'A mixture containing 1 part of samarium to 10,000 parts of calcium. The resulting spectrum is shown in fig. 10. The bands are now getting fainter, the second green band is fading out, and the continuous spectrum of calcic sulphate is getting brighter. 160. ' The next mixture tried contained 1 part of samarium in 100,000 i2 116 SELECT METHODS IN CHEMICAL ANALYSIS parts of calcium. The appearance of the spectrum is shown in fig. 11. Here the green is almost gone, being overshadowed by the continuous spectrum of calcium which has spread over it. The red band has likewise almost disappeared in the greater brightness of the continu- ous red of the calcic spectrum. The double orange band is still very prominent, and the black space, 2942, between it and the green is very marked. 161. * The next mixture, 1 part of samarium to 500,000 parts of cal- cium, gives a spectrum which is fainter than the last, but the orange bands are still distinctly visible. The black space between the yellow and green is strongly marked, but narrower than before. Fig. 12 shows the appearance of this spectrum. PHOSPHORESCENT SPECTRUM OF SAMARIUM 117 162. * A mixture of 1 part of samarium in 1,000,000 parts of calcium was next subjected to experiment. In this the samarium spectrum is very feeble, and the orange bands are only to be seen with difficulty. Now the most striking characteristic of this spectrum is the black space which still cuts out the greater portion of the yellow. Fig. 18 represents this spectrum. 163. < A mixture of one of samarium in 2,500,000 parts of calcium was now taken. In the spectrum shown by this mixture the bands of samarium have entirely gone, and its presence now is apparent only by the darkening in the yellow portion of what otherwise would be a continuous spectrum. Fig. 14 shows this appearance. 164. ' Finally the calcium spectrum by itself was examined. It is continuous, with no break, lines, or bands in it. 118 SELECT METHODS IN CHEMICAL ANALYSIS 167. * In this and the former paper on Radiant Matter Spectro- scopy much stress has been laid on the sensitiveness of the radiant matter test for indicating the presence of samarium and yttrium ; but it might be argued, from the anomalies that arise when both these elements occur together, that in reality the radiant matter test, however delicate, is one not to be depended upon. For instance, it might reasonably be asked what inference is to be drawn in the case of certain minerals treated with sulphuric acid and tested in the vacuum tube, and found to give only a feeble spectrum ? Does this prove the absence of all but traces of either samarium or yttrium, or does it show the presence of both these earths in considerable quantity ? The answer is simple. In spite of the perplexing anomalies that have come to light, and are described in this paper, regarding the influence of these two phosphor- escing earths on each other, no single instance has occurred during the work connected with this subject in which, with the experience now gained, brilliant phosphorescence and a characteristic spectrum could not be evolved from any mixture containing both or either of the earths samaria and yttria. If, after treatment with sulphuric acid and ignition, the earthy mixture gives a pure spectrum of either yttria or samaria, and the line 2693 is absent, it is pretty safe to assume that the particular earth indicated is alone present. If, however, the spec- trum is not quite characteristic, or the anomalous line 2693 is present, it is not sufficient to test the unknown mineral or mixture direct in the vacuum tube. It must first be treated chemically to separate the samaria and yttria (123, 133), and lime must be added before testing in the radiant matter tube (138), when the spectrum immediately makes its appearance if either of these earths be present in the smallest quantity. Although I say lime is to be added, many other substances perform the same office of eliciting the spectrum, such as baryta, lead, &c. (142 145) ; but my chief experience has been with lime, and I have always found it to give uniform results under varied conditions. * One important lesson taught by the many anomalies unearthed in these researches is, that inferences drawn from spectrum analysis per sc are liable to grave doubt, unless at every step the spectroscopist goes hand in hand with the chemist. Spectroscopy may give valuable indications, but chemistry must after all be the court of final appeal. 168. ' Chemistry, however, by itself would have been helpless to solve the difficulties had it not been possible to appeal at every step to the radiant matter tube and to the spectroscope.* The problems to be solved are so new as to be entirely outside the experience of laboratory work. A double orange-coloured band shows itself in a faint emission spectrum obtained under novel circumstances. On further examination the band, or one not far from it, is seen to occur in minerals of very divergent kinds and apparently irrespective of their chemical constitu- TITANIUM tion or locality, as well as in laboratory reagents and chemicals ot assured purity. This band is sometimes accompanied by bands in other parts of the spectrum, and occasionally shifts its place to the right or to the left. Frequently the orange band disappears and a citron- coloured band takes its place. Chemical research continued for a longer time than most chemical researches require fails to throw any light on the subject. These being the conditions of the problem, the very last explanation likely to occur to the inquirer would be that these elusive shifting bands were due to the presence of two elements almost uni- versally distributed, and that these two elements should be yttrium and samarium, yttrium one of the rarest of known elements, and samarium, almost unknown at the time its spectrum reaction was first discerned.' TITANIUM Decomposition of Titanium Minerals In attempting to conduct the analysis of a very refractory mineral containing titanium, magnesium, chromium, &c. according to the method given by Chatard, it was found very difficult to secure complete decomposition of the mineral by the use of hydrofluoric and sulphuric acids as detailed. Kepeated fusions with potassium pyrosulphate while decomposing the mineral introduced large quantities of salts, and was -very tedious. These difficulties led Mr. Jesse Jones to seek some method that would give more satisfactory results. The following was finally adopted : 2 grammes of the mineral were placed in a pressure bottle, to which was added 20 c.c. of water and 20 c.c. strong sulphuric acid. The ground-glass stopper not fitting air-tight, a small sheet of pure rubber was interposed. The bottle and contents were placed in an ordinary air-bath, and kept at 200 C. for two hours. The residue weighed O'OIS gramme and was mainly silica. On treatment with hydrofluoric acid, but 0-002 gramme of residue remained. A tempera- ture of 200 C. was found to melt the rubber somewhat, but a longer exposure at a lower temperature gave equally good results. As the re- sulting solution showed a tendency to gelatinise, water was added to it, taking care not to allow it to touch the heated sides of the bottle. The refractory nature of the rock may be judged from the fact that it contained over 7 per cent, magnesia, 14 per cent, alumina, and consider- able amounts of titanium and chromium. By using ammonium salts in the subsequent operations, they can be expelled by nitric acid, and potash and soda if present in the mineral can be determined. If a pressure bottle is not at hand, one can easily be improvised. The writer found an old bromine bottle sufficiently strong. 120 SELECT METHODS IN CHEMICAL ANALYSIS Detection and Estimation of Titanium (A) Mr. E. Apjohn proceeds as follows : Twelve grammes of the finely powdered rock are fluxed with six times their weight of acid potassium sulphate, and the heat is continued ui:til the greater part of the free sulphuric acid is driven off. The cooled mass is reduced to a fine powder, extracted with cold water, and the aqueous solution, largely diluted, is boiled with acid sodium sulphate. As soon as the precipitation is complete, the contents of the flask are allowed to cool,, and a little sulphurous acid is added to re-dissolve any iron or alumi- nium which might have been precipitated. This precipitate of titanic acid is converted into the potassium titano-fluoride in the usual manner,, and the salt thus obtained is collected on a weighed filter, washed with a few drops of cold water, dried, and weighed ; and from this weight the amount of titanic acid is reduced. (B) For the detection of small quantities of titanium, especially when mixed with iron, alumina, and silica, E. Jackson adds hydrogen per- oxide to the acid (hydrochloric or nitric) solution. A fine yellow or orange colour appears. Ferric chloride should not be present. An excess of hydrofluoric acid prevents the appearance of the colour unless a larger excess of hydrochloric acid is added. Ammonium molybdate in nitric acid gives a similar colouration, but the two are readily distinguished by means of the spectroscope. The titanium solutions show no blue or green in strong solutions, only orange and red remaining, whilst with ammonium molybdate the shade of the green and some of the blue are visible. Preparation of Pure Titanic Acid (A) The following is Wohler's plan for preparing pure titanic acid : Fuse the rutile or titaniferous iron with an excess of potassium carbonate at a high temperature, in a fire-clay crucible. Pour the fused mass out on to a piece of sheet-iron, so as to form, on cooling,, a thin cake ; next, grind this to powder, thoroughly extract with water, which leaves the greater part of the iron undissolved, and saturate the filtrate with hydrofluoric acid. A formation of potassium fluotitanate soon occurs in white scaly crystals resembling boracic acid. These may be rendered quite free from iron and silicium by a few crystallisa- tions from hot water, and ammonia will then precipitate pure titanic acid from their hot aqueous solution. (B) Another method for the preparation of pure titanic acid is to fuse the rutile or titaniferous iron with potassium carbonate, and extract the fused mass with water in the manner above described. After filter- ing from the insoluble portion, the liquid is slightly supersaturated with hydrochloric acid added in the cold ; it is then filtered if necessary. Acetic acid and dilute sulphuric acid are now added, and a brisk current. ZIKCONIUM 121 of steam is passed in for several hours, the liquid being kept boiling all the time. Pure titanic acid will be precipitated. (C) Professor Dunnington has improved Weller's method for the estimation of titanium, depending upon the production of a compound of intense yellow colour by the addition of hydrogen peroxide to the solution of titanium. The solution of the melt obtained by fusion with acid sodium sulphate, when made with dilute sulphuric acid of 5 or more per cent., gives constant results, which tally with those made gravimetrically ; but when water only or very dilute acid is employed, one may obtain lower results. Upon one occasion a colouration was obtained which corresponded to only about one -third of the titanium which was after- wards found to be present. Moreover, if we take a slightly acid solution of titanium sulphate, dilute it, and heat until it is partially precipitated, cool, re-dissolve with sulphuric acid and then add hydrogen peroxide, the yellow colouration will correspond to only a portion of the titanium present. An explanation of these facts is found in the forma- tion of some meta-titanic acid. It appears probable that after the fusion of titanic oxide with acid sodium sulphate, if the melt is digested in water only, the solution of the free acid may occasion sufficient heat to form some meta-titanic acid, which when re-dissolved by the further admixture of acid would not be coloured by the hydrogen dioxide. It is therefore concluded that in making the estimation of titanium the melt, after cooling, is to be digested in dilute sulphuric acid of such strength as will prevent the formation of a precipitate even in warm solutions of titanic sulphate ; for this purpose 5 per cent, acid is found to answer. ZIRCONIUM Preparation of Pure Zirconia (A) The zircon is first broken up in a diamond mortar, and next reduced to a powder in an agate mortar. It is then mixed with acid potassium fluoride, and the mixture fused. In this manner a perfect resolution of the mineral is easily obtained. The potassium fluozir- conate is then dissolved out from the insoluble fluosilicate by means of hot water acidulated with hydrofluoric acid. From this solution zirconia may be precipitated by ammonia. (B) In Messrs. Tessie du Motay and Co.'s patent for improvements in preparing zircoma for purposes of oxyhydrogen illumination, the fol- lowing process is given. The zirconia is extracted from its native ores by transforming, by the action of chlorine, in the presence of charcoal, the zirconium silicate into the zirconium and silicium chlorides. The silicium chloride, which is more volatile than the 122 SELECT METHODS IN CHEMICAL ANALYSIS zirconium chloride, is separated from the latter by the action of heat ; the zirconium chloride remaining is afterwards converted to the state of oxide by any of the methods now used in chemistry. The zirconia thus obtained is first calcined, then moistened, and submitted in moulds to the action of a press with or without the intervention of agglutinant substances, such as borax, boracic acid, or clay. The sticks, cylinders, discs, or other forms thus agglomerated, are brought to a high temperature, and thus receive a kind of tempering or pre- paring, the effect of which is to increase their density and molecular compactness. Of all the known earthy oxides zirconia is the only one which remains entirely unaltered when submitted to the action of a blowpipe fed by oxygen and hydrogen. Zirconia is also, of all these earthy oxides, that which, when introduced into an oxyhydrogen flame, develops the most intense and the most fixed light. Separation of Zirconium from Titanium Titanic acid and zirconia, which separately may be estimated with the greatest accuracy, when together present such properties that it might be said one of these two bodies had partly destroyed the indi- viduality of the other, since the reactions they possess when separate they no longer possess together, whilst in some cases they act quite differently. Thus, it is well known that titanic acid in the state of sulphate is completely precipitated by boiling in a diluted solution ; but that when in presence of zirconia there may be, according to the pro- portions of the two bodies, either incomplete precipitation or none at all. Moreover, the precipitated titanic acid always retains zirconia, although the greater part remains in solution with the rest of the titanium. (A) Messrs. G. Streit and B. Franz say that when titanic acid is precipitated from a solution containing zirconia, by boiling with dilute sulphuric and acetic acids, the precipitated titanic acid is free from zirconia. The boiling should be performed by the aid of steam, and be continued for eight or ten hours. They experimented with a solu- tion containing 4-23 grammes 1 of titanic acid, and added thereto the sulphuric acid solution of 0*613 gramme of zirconia. To the solution was then added its own bulk of acetic acid, and the liquid boiled ; all the titanic acid was thereby precipitated, while zirconia remained in solution. From the filtrate the latter substance was precipitated by ammonia, and, after having been collected upon a filter, washed, dried, ignited, and weighed. The quantity obtained was very near the amount required by theory. (B) According to Dr. G. H. Bailey hydrogen peroxide supplies a means of separating zirconium from its associated earths. Very dilute solutions of hydrogen peroxide produce no precipitate, but with a SEPAEATION OF ZIRCONIUM FROM TITANIUM 123 moderately concentrated solution the precipitation is perfect. Cleve has already shown that it does not throw down iron and alumina. Titanium occasions a colouration from which the formation of a higher oxide may be inferred, but there is no precipitation. From a solution containing titanium salts zirconium may, therefore, be thrown down quite free from titanium. Niobium and tantalum seem likewise to form no precipitates with hydrogen peroxide, as is also the case with tin and silicium. The above-mentioned elements are those which gene- rally occur together with zirconium, and are difficult to separate according to the ordinary method. Hydrogen peroxide of such a strength that it yields 120 vols. oxygen throws down zirconia at once, and completely separates it from a solution of zirconium in excess of sulphuric acid. (C) F. Pisani adds metallic zinc to a mixed solution of titanic acid and zirconia in sulphuric or hydrochloric acid, until the titanium is reduced to the state of titanium sesquioxide, giving the liquid a more or less intense violet colour. Titanic acid and zirconia are, under ordinary circumstances, precipitated equally by potassium sulphate ; but if the titanium is previously reduced in this manner only the zirconia is precipitated. Add excess of potassium sulphate to the violet liquid, which should be small in quantity and not too acid, the zinc being still slowly attacked ; leave the whole to stand for some time, then filter quickly and wash the precipitate with a solution of potassium sulphate ; afterwards extract the zirconia by the usual processes. Upon dissolving this zirconia in hydrochloric acid, and adding zinc, it will be found that only a trace of titanium remains. Unfortunately, this process is not quite accurate, and cannot be used for quantitative separation. (D) Titanic acid may be estimated in the presence of zirconia volu- metrically. The above -described violet solution of titanium is a powerful reducing agent. On pouring potassium permanganate into this liquid, titanic acid is formed, and the solution gradually loses its colour, until it becomes of a rose tint. According to the quantity of potassium per- manganate it is found necessary to add, may be calculated the quantity of titanic acid, taking for each equivalent of iron to which the permanga- nate corresponds one equivalent of titanic acid. The following is the mode of operating as described by Pisani, to whom this process is due : Titanic acid in solution in hydrochloric acid is best, because if in the state of sulphate, it is liable to be partially precipitated by the rising of the temperature before its complete reduction has been effected. The reduction should be effected in a flask, to which has been adapted a cork with a tube drawn out to a point, so as to keep the liquid from contact with the air. The quantity of liquid should not be great, and should be acidified until the disengagement of hydrogen becomes regular ; then heat gently to accelerate the reduc- tion, and when the colour of the liquid ceases to increase in intensity, leave it to get quite cold, and dilute the liquid with cold water which 124 SELECT METHODS IN CHEMICAL ANALYSIS, has been previously boiled to free it from air, as it would otherwise oxidise the titanium. As soon as the liquid is diluted, decant it into a glass without taking the zinc with it, wash the flask once or twice, and then rapidly pour in the potassium permanganate. The combined weight of titanic acid and zirconia being previously known, and the titanium being estimated volumetrically, the difference gives the quantity of zirconia. The permanganate should be previously stan- dardised by means of iron by Margueritte's process. If potassium fluotitanate or titanic acid in hydrochloric acid to which an alkaline fluoride has been added, is reduced by zinc, the liquid is no longer violet, but greenish, probably because a titanium sesqui- fluoride is then formed instead of a sesquichloride. The results of the estimation by permanganate are, however, the same in each case. (E) Zirconia may be detected in titanic acid by taking advantage of its reaction on turmeric paper. A solution of zirconia in hydrochloric acid colours turmeric paper orange, especially after it has been left to dry, but titanic acid, under the same circumstances, colours it brown, 'which prevents zirconia from being recognised. The difficulty may be overcome by reducing the titanium by zinc, as in the state of sesqui- oxide titanium does not colour turmeric paper, leaving the colour of the zirconia to appear alone. The paper must not, however, be left too long to dry in the air, or the titanium, passing into the state of titanic acid, would in its turn colour the paper brown. 125 CHAPTER IV CHBOMIUM, URANIUM, VANADIUM, TUNGSTEN, MOLYBDENUM CHROMIUM Estimation of Chromium (.4) PROFESSOR STORER has shown that chromic oxide is quickly changed to chromic acid when boiled with a mixture of concentrated nitric acid and potassium chlorate. All the chromium in J gramme of chromium oxide, or of any of the ordinary chromium salts, can in this way be converted into chromic acid in a few moments ; and even com- pounds as refractory as chrome -iron ore, or chromium oxide, which has been strongly ignited, can be oxidised in less time than would be required to complete their oxidation by the process of fusion ordinarily employed. (B) Mr. E. J. Stoddart, working under the direction of Prof. E. T. Thorpe, finds this method unsatisfactory for chrome-iron ores, a part of the mineral remaining unoxidised even after boiling for an hour. (C) Mr. A. H. Pearson, experimenting on this process, finds that the chromic acid thus formed in the wet way can be readily and accurately estimated in the form of barium chromate, if care be taken to wash the precipitated chromium with ammonium acetate, or some other saline solution in which barium chromate is insoluble. Anhydrous chromic oxide is placed in an evaporating dish, together with a quantity of nitric acid and some potassium chlorate, and covered with an inverted funnel with a bent stem. The acid is heated, and fragments of potas- sium chlorate are added to it from time to time, until the chromic oxide has completely disappeared. This result is attained in the course of half an hour. The acid solution is diluted with water, then neutralised with ammonia, and the ammoniacal solution in its turn treated with enough acetic acid to make it slightly acid. After the acidulated solu- tion has become cold a solution of barium chloride is added to it in slight excess, and the mixture is left at rest for ten or twelve hours. The precipitated barium chromate is washed by decantation with a cold solution of ammonium acetate, then collected on a filter, rinsed with water, dried, heated in a crucible to expel the last traces of water and of the ammonium-salt, and weighed. The precipitate of barium chromate must be allowed to stand for some time before filtering, lest it pass through the pores of the filter 126 SELECT METHODS IN CHEMICAL ANALYSIS and render the nitrate cloudy. The ammonium acetate employed for washing serves to dissolve any barium nitrate or barium chloride which may have been precipitated with the chromate ; it has the further advantage of dissolving less of the barium chromate than pure water would. Experiments on various compounds of chromium show that this process is tolerably exact. Estimations of chromium in different speci- mens of sesquioxide gave 68'31, 68-65, 68'60, 68'31 per cent. Theory requires 68' 62 per cent. Chromic acid may also be estimated by adding mercurous nitrate to its quite cold solution, neutralised with sodium carbonate or with nitric acid ; the orange-red precipitate of mercury chromate should be allowed to stand for some hours before filtering, and after being washed with a weak solution of mercurous nitrate, and dried, is heated to redness in a platinum crucible, when it leaves pure green chromium sesquioxide. (D) Kose strongly recommends the method of Berzelius, which consists in precipitating the chromic acid by mercurous nitrate, and washing with a dilute solution of the same salt. The precipitated chro- mate is voluminous, and has a brown-red colour when the precipitation takes place in the cold. A better result is obtained by precipitating at a boiling heat, when the mercurous chromate almost immediately becomes highly crystalline, its colour changing to a bright scarlet. It may then be washed with the greatest ease, and ignited in the usual manner. It is absolutely necessary, in applying this method, that the mercurous nitrate used should be perfectly free from nitrous acid. Hot solutions must not be employed, on account of the reduction of chromic acid by mercurous nitrate. This reduction is not due to the tempera- ture, but to the presence of a small quantity of nitrous acid in the mercurous nitrate employed. It is easy to avoid this source of error by dissolving the mercury in nitric acid in an open vessel, and crystal- lising the nitrate two or three times, using for solution dilute nitric acid which has been perfectly freed from nitrous acid by a current of air or carbonic acid. We arrive more quickly at our object when we precipitate at once at the boiling-point, and then wash with a hot dilute solution of the nitrate. (E) In several works on analytical chemistry it is recommended to precipitate chromic acid from its solutions by lead acetate, and to weigh the resulting lead chromate. It is, however, next to impossible to prevent the precipitated lead chromate from passing more or less through the filter so as to render the filtrate turbid. (F) Very accurate results may be obtained by precipitation with barium acetate at a boiling heat, adding a small quantity of strong alcohol to the liquid, washing with water containing alcohol, and igniting. The wash-water need not contain more than T V of its volume of alcohol. The precipitated chromate must, before filtering, be allowed to settle ESTIMATION OF CHKOMIUM 127 completely, leaving the supernatant liquid perfectly clear. The filtrate never becomes turbid, even after all the soluble salts are washed out. Finally, it is not necessary to weigh the barium chromate upon a weighed filter. A very small quantity of the chromic acid is always reduced by the carbon of the filter in igniting, but the loss of weight is inappreciable. This method is much shorter than that which is usually employed, as the filtration and washing may be executed almost immediately after precipitation. (G) For the quantitative separation of uranium and chromium, in a first series of experiments, weighed quantities of potassium bichromate were mixed with much larger, but undetermined, quantities of uranium nitrate. The chromic acid was then precipitated by mercurous nitrate from the boiling solutions. The mean of the analyses was 51*73 per cent., which is precisely the percentage required by the formula. Detection of Bichromate and Free Chromic Acid To detect a monochromate along with a bichromate, add to a few c.c. of the boiling solution a drop of a moderately concentrated solution of manganese sulphate. In presence of monochromate a blackish-brown precipitate is formed. Bichromate in monochromate is detected by adding to a boiling solution of sodium thiosulphate an equal volume of a hot solution of the chromate in question. A brown precipitate or a distinct turbidity proves the presence of bichromate. The precipitate is chromic oxide. Free chromic acid in a solution of bichromate is detected by adding a solution of potassium iodide and shaking with carbon disulphide, which is coloured a deep purple by the liberated iodine. Estimation of Chromium as Phosphate Chromium may be exactly determined as phosphate, and this method is often convenient. On boiling a solution of a chromium salt slightly acidified, to which has been added an alkaline phosphate and sodium acetate, the whole of the chromium is precipitated as phosphate. This method succeeds both with the green and the violet salts, chlorides and sulphates, and with the acetates, but not with the oxalates. It is also suitable for alkaline chromates, but in this case the action of the phosphoric acid must be combined with that of sodium thiosulphate, which acts as a reducing agent. The solution of chromate, to which is added a sufficient quantity of phosphoric acid, or of a phosphate, then of acetate, and lastly of thiosulphate, and which has been slightly acidified, is boiled for about an hour : it deposits all the chromium as phosphate, with a little sulphur derived from the thio- sulphate. The phosphate precipitated is a green hydrate. It may be washed with boiling water, or preferably with hot solutions, first, of ammonium acetate, followed by ammonium nitrate. On calcination 128 SELECT METHODS IN CHEMICAL ANALYSIS it turns grey, and contains chromic oxide in the proportion of 51-86 per cent. Volumetric Estimation of Chromium in the Presence of Ferric Oxide and Alumina If a solution of permanganate is made strongly alkaline with sodium carbonate and a little caustic soda, heated to a boil, and a neutral solution of chromic oxide is run in, the chromic oxide is at once converted into chromic acid, whilst manganese peroxide is separated out. The process is completed when the supernatant fluid has the pure yellow tint of alkaline chromates without the slightest reddish tinge, which may be recognised with sufficient distinctness. The presence even of considerable quantities of ferric oxide and alumina in the solution containing chromium does not prevent the completion of the reaction from being distinguished, since these oxides, if precipitated in a hot solution, are rapidly deposited along with the manganese peroxide. If the approximate relation of the alkaline per- manganate to the chromium solution in question has been determined by a preliminary experiment, on further titration the end of the reaction can be observed with sufficient accuracy. In fact the volumetric determination of chromium is in this manner rendered possible without the previous separation of iron and alumina. Volumetric Estimation of Chromic Acid (A] Add to the chromic-acid solution a sufficient quantity of potas- sium iodide, free from iodate, and pure hydrochloric acid. This mixture is left quietly standing for from half an hour to a few hours according to the degree of concentration of the solution, for in no case is the reduction of the chromic acid by means of the hydriodic acid instantaneous. When the reduction is complete, which may be learned from the pure green colour the liquid has assumed, a small quantity of thin starch paste is added, and the quantity of iodine which has been set at liberty is estimated by titration with a solution of sodium thiosulphate. This plan, first proposed by C. Zulkowsky, gives sufficiently accurate results, and in some cases may be found useful ; but it requires care, and is inferior to gravimetrical estimation. (B) Another method has been devised by Mr. W. J. Sell, and yields rapid and accurate results. The solution, containing chromium acidi- fied with sulphuric acid, is boiled and a dilute solution of permanganate added to the boiling liquid until a purplish tint remains after boiling for three minutes. The solution is then rendered slightly alkaline with sodium carbonate, alcohol is added, and the manganese filtered off. The chromic acid in the filtrate is estimated by titration with iodine and sodium thiosulphate. For the valuation of chrome iron ores, see Iron. ESTIMATION OF URANIUM 129 Separation of Chromium from Aluminium A. Carnot has shown that aluminium can be exactly separated from chromium by converting the latter into an alkaline chromate, acidifying the solution slightly with acetic acid, and adding an excess of sodium phosphate. The mixture is boiled and filtered to separate the alumi- nium phosphate. When this is done, it is easy to determine the chromium by pouring into the liquid, sodium thiosulphate, and if needed a further quantity of alkaline phosphate, and boiling. The precipitate of chromium phosphate is then washed, ignited, and weighed. URANIUM Estimation of Uranium (A] H. Eose l recommends the employment of ammonium sulphide as a precipitant for uranium, as it completely separates this metal from its solutions, provided they are previously saturated with ammonia. No inconvenience attends the presence of a quantity of ammoniacal salts in the solution, excepting, of course, ammonium carbonate and alkaline carbonates in general. The precipitate is black, but with a large excess of sulphide it may be reddish-brown. It is to be washed with water containing a little ammonium sulphide. The precipitate contains no uranium sulphide, but consists essentially of uranium protoxide. After desiccation it is roasted, to expel any sulphur which may adhere to it ; it is then calcined at a high temperature in a current of hydrogen, and left to cool. Pure uranium protoxide is thus obtained. Should the solution contain much potassium salts, or other strong non-volatile base, the precipitate may retain a little of them. (B) If a rapid process is required for the estimation of the com- mercial value of uranium, the following process of Patera's will give sufficiently accurate results, although it is not so trustworthy as the one just described. A weighed quantity of the mineral is dissolved in nitric acid, taking care not to employ a large excess of acid. The solution is diluted with water, and, without filtering, supersaturated with sodium carbonate. It is now boiled to complete the solution of the uranium, and to promote the separation of the iron, lime, &c., carbonates. The filtered solution of uranium oxide in sodium carbonate now contains only traces of foreign substances, and the uranium will be precipitated in the form of sodium uranate with an excess of acid, on the addition of caustic soda. The orange-yellow precipitate is collected on a filter, washed for a short time, and then dried. It is then removed from the filter and heated to redness in a platinum crucible, the ashes of the 1 Pogg. Ann. cxvi. 352. 130 SELECT METHODS IN CHEMICAL ANALYSIS filter, burnt apart, being added to the precipitate. The mixed residues are now placed on another filter arid again washed, dried, and ignited, as before. The residuum of this second calcination is acid sodium uranate, from the weight of which the amount of uranoso-uranic oxide in the mineral may be calculated. 100 parts of the sodium uranate represent 83 parts of uranoso-uranic oxide. Volumetric Estimation of Uranium The author prefers Guyard's process for this estimation, which de- pends on the precipitation of an insoluble triple ammonium, uranium, and manganese phosphate, when an acid solution of manganese phos- phate is added to an acid solution of uranium and ammonium acetate. The test solution of manganese phosphate is prepared as follows : Phosphoric acid solution of a syrupy consistency is heated in a platinum dish, and manganese sesquioxide in fine powder is added by degrees, stirring frequently. The mixture is then heated for some time, and when the fused mass assumes a blue tint, and the phosphoric acid begins to volatilise, it is allowed to cool. It then becomes purple, and if dissolved in water it forms a purple solution resembling that of a permanganate. This solution is diluted, so that 30 c.c, shall represent 1 gramme of metal. The tinctorial power of manganese phosphate is very weak. To titrate this solution use a known quantity of pure uranium ses- quioxide in the form of acetate. The precipitate appears white with a yellowish shade. As soon as the precipitation is complete the precipi- tate has a rose colour. It must be remembered that the presence of ammonium oxalate interferes with the reaction. To apply this process to ores, &c., dissolve a gramme or more of the substance in nitric or hydrochloric acid, or a mixture of the two. The solution is then supersaturated with ammonium carbonate, which separates uranium sesquioxide from the metallic oxides which so often accompany it. In many cases this operation suffices ; but if the ore contains phosphorus or arsenic, or an oxide soluble in ammonium carbonate, the uranium must be precipitated by ammonia and ammo- nium sulphide in the state of protoxide, as already described, and filtered off. The precipitate is dissolved in ammonium carbonate, and then transformed into the acetate of the sesquioxide. In any case the uranium must be brought into this state before estimation ; but oxalic acid must be absent. The solution is now diluted with about a litre of cold water, and then the standard solution of manganese phosphate is gradually added from a burette until the whitish precipitate of uranium, manganese, 'and ammonium phosphates appears rose-coloured. This process is Very rapid, and with a little practice is accurate. In testing for uranium with potassium ferrocyanide, it must be SEPARATION OF URANIUM FROM CHROMIUM 131 borne in mind that the presence of ammonium oxalate prevents the formation of the red precipitate. i Separation of Uranium from the Cerium Metals Wolcott Gibbs's method of precipitating the cerium metals with sodium sulphate in the form of double sodium sulphates with cerium, lanthanum, and didymium will effect this separation perfectly. These double sulphates are insoluble in a saturated solution of sodium sulphate, whilst the double sulphate of sodium and uranium sesquioxide is readily soluble, and may be easily washed out from the highly crystalline insoluble double sulphates of the cerium group. Separation of Uranium from Chromium The author's analyses show that mercurous nitrate gives very accurate results. The employment of this salt in separating chromium from uranium is indicated only in those cases where the chromium exists as chromic acid, where relatively small quantities of chlorine or sulphuric acid are present, and when no other acid is present which, like phosphoric acid, gives an insoluble mercurous salt not completely volatilised by ignition. In the presence of chlorine, sul- phuric acid, &c., the following process may be very advantageously employed. The solution is to be boiled for a few minutes with a small excess of sodium hydrate, the precipitate of sodium uranate filtered off and washed with hot water containing a little sodium hydrate, until the washings no longer give any turbidity with a solution of mercurous nitrate. The sodium uranate in the filter is then to be dissolved in hydrochloric acid and the uranium determined in the usual manner. The filtrate contains all the chromium. After adding hydrochloric acid in excess, the chromic acid may be most conveniently reduced to chromic oxide by adding a solution of potassium or sodium nitrite and boiling for a few minutes, after which the oxide may be pre- cipitated by ammonia in the usual manner. An alkaline nitrite is a better reducing agent than alcohol, as the chromic oxide may be precipitated immediately after the reduction. It remains to consider the case in which chromic and uranic oxides occur together in solution. A solution of sodium hydrate in small excess is to be added, and the whole heated to boiling. To the hot liquid, bromine-water is to be added. Chromium oxide is almost in- stantly oxidised to chromic acid, which remains in solution, while sodium uranate, with a small percentage of uranic chromate, remains undissolved. After washing with hot water containing a little sodium hydrate, the precipitate, which has a deep orange colour, is to be dissolved in hot nitrous acid, the solution boiled for a few minutes to expel any traces of nitric acid, mercurous nitrate added, and the .whole allowed to stand until the small quantity of mercurous chromate K 2 132 SELECT METHODS IN CHEMICAL ANALYSIS has settled. This, after washing, may be ignited in the same crucible with the chromic oxide obtained as above from the sodium chromate in the nitrate. The filtrate is free from uranium. Separation of Uranium from most Heavy Metals (A) Uranium may be easily separated by H. Kose's method from metals which are precipitated from their solutions by ammonium sul- phide, in the following manner: Add to the solution an excess of ammonium carbonate mixed with sulphide. All the oxides which the sulphide trans formsanto sulphides are precipitated, while the uranium protoxide is dissolved in the ammonium carbonate. Leave it to deposit in a closed vessel, wash the precipitate by decantation in water containing ammonium carbonate and sulphide, and filter. Gently heat the filtered liquid to expel most of the carbonate, decompose the sul- phide by hydrochloric acid, oxidise the uranium protoxide with nitric acid, and precipitate the uranium oxide by ammonia. If the operation is quantitative, it should, before weighing, be calcined in a current of hydrogen. (B) A. Kemele recommends ammonium sulphide as the best reagent for the separation of uranium from alkaline earths and alkalies, except in case of barium. Foullon and Alibegoff find that uranium and calcium cannot be separated in this manner. Foullon recommends in this case the use of' ammonium oxalate in a solution previously rendered alkaline by ammonium carbonate. He first mixes the hydrochloric solution with a little ammonium oxalate, and then adds ammonium carbonate until all the uranium oxide is re-dissolved ; ammonium oxalate is then added in excess, and the precipitate allowed to deposit in the absence of strong light. (C) Alibegoff, working in this manner, obtained better results than with ammonium sulphide, but the calcium oxalate was always more or less contaminated with uranium. He therefore adds to a solution of uranium chloride some elutriated mercury oxide, when the uranium is completely deposited on boiling, and the supernatant liquid has quite lost the colour of the uranium salts. In case of uranium solutions in the oxygen acids, a solution of ammonium or sodium chloride is added. A very dilute solution of ammonium chloride is used for washing, as the precipitate, a mixture of uranyl hydroxide and basic mercury uranate, is slightly soluble in water. In carrying out this method the author adds to the solution of uran-oxychloride a few drops of ammonium chloride solution, and heats to a boil. He then adds the pure elutriated mercuric oxide, care- fully avoiding excess. After again boiling and shaking round (in pre- ference to stirring) allow it to cool, when the precipitate settles quickly, and the liquid becomes colourless. Decant a few times, pour it upon the filter, and wash in cold water containing ammonium chloride. The DETECTION OF VANADIUM 133 precipitate along with the filter is heated in a platinum crucible, care- fully at first, then in the uncovered crucible with a gradually increasing heat, and lastly over a blast. The product is weighed as the olive- green uranous-uranic oxide. In presence of calcium the process is the same. If the alkaline earths are in large proportion, their partial precipitation may be avoided by boiling up once more after decantation with water con- taining ammonium chloride. In the filtrate the strontium and calcium are determined in the usual manner after removing the mercury with ammonium sulphide. Uranium may be separated from magnesium by boiling with a sufficiency of ammonium chloride and then precipitating with mercuric oxide as above. Separation of Uranium from Phosphoric Acid (A) In laboratories where the estimation of phosphoric acid by the uranium process is frequently practised, it occasionally becomes advis- able to effect the separation of uranium from the acid. M. Keichardt describes the following plan, which has proved very successful in the author's laboratory : Dissolve the uranium phosphate in hydrochloric or nitric acid, apply heat, add excess of iron perchloride, and next, excess of solution of sodium carbonate, wherein, aided especially by the large quantity of carbonic acid which is thus set free, the uranium oxide is readily dissolved, while the phosphoric acid is combined in an insoluble form with the iron oxide. The solution of uranium oxide in sodium carbonate is acidified with hydrochloric acid, boiled to expel carbonic acid, and the uranium oxide finally precipitated with ammonia. (_B) He has since proposed the following modification : He dis- solves the uranium phosphate in sodium carbonate, and precipitates with a magnesium salt. If the precipitate of uranium phosphate is old, it is necessary to dissolve it first in hot concentrated hydrochloric acid, adding nitric acid to peroxidise any iron present. The solution is then heated and soda added in excess. After filtration the phosphoric acid is thrown down by adding ammonia and magnesium chloride. After twenty-four hours the liquid is separated from the ammonio-magnesium phosphate. It is acidified with hydrochloric acid, heated, and the uranium oxide precipitated by ammonia, avoiding excess. VANADIUM Detection of Vanadium (A) Mr. Richard Apjohn uses the following process: 8 grammes of the finely powdered mineral is fluxed with four times its weight of sodium carbonate. The fused mass is allowed to cool, and a small 134 SELECT METHODS IN CHEMICAL ANALYSIS quantity of nitre added. It is now heated over a Buiisen lamp, taking- care that the crucible does not attain more than a dull red heat. The mass is lixiviated with water, and the aqueous solution boiled with ammonium carbonate and filtered to remove silicic acid. The nitrate is evaporated with hydrochloric acid, and sulphuretted hydrogen passed in to precipitate any metals of the lead group which might be present. The filtered solution is then heated with an equal volume of very concentrated solution of ammonia, and sulphuretted hydrogen is passed in till all the free ammonia is saturated. The solution assumes a beautiful intense cherry-red colour, a sure indication of vanadium. This coloured liquid is filtered off and saturated with hydrochloric acid ; the precipitate, containing sulphur and vanadium sulphide, is dried and ignited, and the residue melted with nitre. From the potassium vanadate thus formed the charac- teristic blowpipe reactions are obtained. (J5) For the analysis of vanadium sulphates Dr. B. W. Gerland proceeds as follows : To estimate the sulphuric acid, vanadium and alkalies, the weighed sample is dissolved in water, according to circum- stances, with the aid of nitric acid or ammonia, or both. After cooling, the clear solution is acidulated with nitric acid, mixed with lead acetate and alcohol until all sulphuric acid is precipitated. After a few hours' rest, when the lead sulphate has settled, it is filtered and washed with dilute alcohol. No difficulty is experienced if the vanadium is present as tetroxide, but with the pentoxide it often hap- pens that lead vanadate is mixed with the sulphate, recognisable by the intense yellow colour of the latter. In that case only the clear liquor is poured off and passed through a small filter, the pre- cipitate treated with a little nitric acid, if necessary heated in a water- bath, then mixed with water and afterwards with alcohol, and allowed to stand for a few hours. The vanadate is generally dissolved by this- treatment, and the lead sulphate appears perfectly white ; it is now thrown on the same filter and treated as before. But it does happen, particularly when the precipitation has taken place at a higher temperature, that the sulphate still retains a small amount of vanadate. Ammonium carbonate is the most efficient means for separating this- small residuum. The solution of this reagent scarcely acts upon the pure lead vanadate ; but if the latter is mixed with lead sulphate the former is left intact, whilst the sulphate is rapidly converted into lead carbonate. The solution, therefore, contains all the sulphuric acid, and only inappreciable traces of vanadium ; it is treated with barium chloride in the usual way, and the barium sulphate weighed. The insoluble part, after washing, is heated with acetic acid to dissolve the lead carbonate, and the remaining vanadate is thrown upon the filter already used, washed, and united to the main vanadium precipitate. The solution from the lead sulphate is neutralised with ammonia, acidulated with acetic acid, and precipitated with lead acetate in small DETECTION OF VANADIUM 135 excess. If vanadium tetroxide is present, as shown by the dark colour of the precipitate, it is necessary to oxidise it, and this is readily effected by the addition of bromine water. The precipitate will now be of a bright orange or yellow colour, and very bulky ; but heating, assisted by agitation, causes it to contract to a heavy curdy mass. In this condition it can be easily filtered and washed on a Bunsen filter under a low pressure. It is of advantage to add a small amount of lead acetate to the wash-water. The precipitate is dissolved in nitric acid, the solution treated with sulphuric acid and alcohol, and after a few hours' rest separated from the lead sulphate, which after washing is free from vanadium, as Roscoe has already pointed out. The filtrate containing the vanadium is evaporated in a porcelain basin, at a very low temperature (the water-bath at boiling-heat would cause a very lively evolution of gas, and loss, particularly when sulphuric acid is added in great excess), the residuum transferred to a platinum dish, is again evaporated, and the sulphuric acid driven off by carefully raising the temperature. All the vanadium sulphates (those of the trioxide, tetroxide, and pentoxide) leave vanadium pentoxide at red heat. But this is readily reduced at that temperature by dust, and even by the gases from the lamp ; it is therefore necessary to cover the capsule well, and prevent the access of fire gases, which is best accomplished by the use of a Rose's tube. The heat is then increased to a bright red, which again causes an evolution of gas, and leaves a pure pentoxide, whose weight is taken. (If the vanadium sulphates are decomposed at a dark-red heat, until gas-bubbles cease to appear, the pentoxide gives off gas again, when the heat is raised and loses weight amounting to about O f 5 per cent.) The platinum vessel suffers in shape by this operation. A dish which was used very often had originally a flat bottom, but now the latter is pressed out by the vanadium pent- oxide, so that the form is hemispherical, and at least 3 millimetres deeper. The filtrate from the lead vanadate contains, besides the alkalies, a small amount of vanadium. Vanadium solutions behave, as I have ascertained, similarly to those of cobalt under the influence of sulphu- retted hydrogen ; a dilute acetic solution with small excess of free acid, particularly in presence of an alkaline acetate, is slowly acted upon by that gas, and the vanadium precipitated as vanadyl sulphide. If the filtrate, therefore, is treated with sulphuretted hydrogen, according to Roscoe 's direction, the vanadium which it contains will be separated with the lead sulphide ; it is on that account preferable to use sulphuric acid and alcohol for the elimination of the lead. The filtrate from this lead sulphate is evaporated, and the residuum heated until the ammonium salts are driven off. The remaining alkalies- are dissolved, treated with acetic acid, and once more submitted to the described process for the separation of the small quantity of vanadium with lead acetate. The filtrate from this lead vanadate precipitate is 136 SELECT METHODS IN CHEMICAL ANALYSIS most expeditiously treated with ammonia and ammonium sulphide at boiling-heat, and the solution separated from the lead sulphide is worked up for the estimation of the alkalies. The Estimation of Vanadium by Titration with Permanganate. The first condition is the conversion of vanadium to a certain stage of oxidation. Aqueous sulphurous acid converts vanadium pentoxide in solution to tetroxide, which is perfectly unchangeable in acid liquors, so that these can be boiled for the expulsion of the excess of sulphur dioxide. The tetroxide solutions undergo a further reduction, which, if not guarded against, might make the test fallacious. I shall shortly be able to refer more fully to this process, but I mention here briefly that the tetroxide in solution, containing an excess of sulphuric acid, is converted into vanadium trioxide by carbonaceous matter (which is introduced by alcohol or with dust), and by sulphur at a temperature of 120, and that at higher temperatures (about 150) the acid vana- dium sulphate separates in the form of insoluble needles, and at about 200 the yellow vanadium sulphate appears as a heavy amorphous sediment mixed with the former. If such conditions are apprehended, it is necessary to add permanganate until the test-solution remains pink after boiling, as proof that all vanadium is oxidised to the pent- oxide, then to treat with sulphurous acid, and, after expelling the excess, titrate again with permanganate. The colouration obtained by the permanganate generally dis- appears after a short time, and is reproduced by the first drop of this solution, to bleach again, and so on, until, after a large quantity (up to 20 per cent, of what was used to produce the first pink) has been added, the solution becomes opaque by the separation of manganic peroxide. In every case the first appearance of the pink colour is the indication that all vanadium is converted into the pentoxide, and the quantity of permanganate used corresponds exactly with that required by an equivalent quantity of oxalic acid. In hot solutions the first appearance of pink is permanent. The reaction of the permanganate solution takes place instantaneously ; the colour changes from blue, through green, to yellow and pink, indicating at every stage the quantity of the standard solution required. The titration of vanadium with a standard solution of permanganate is in fact one of the most elegant, expeditious, and accurate methods of volumetric analysis. Detection of Vanadium in Iron Ores R. Boettger heats the finely powdered ore to redness for a long time with nitre and sodium carbonate. He lixiviates with boiling water and almost neutralises with nitric acid, free from the lower oxides of nitrogen, leaving the solution slightly alkaline. The bulk of PREPARATION OF VANADIC ACID 137 the alumina and silica falls down. The nitrate is treated with barium nitrate, when barium vanadate is thrown down, from which vanadic acid is easily separated. Preparation of Vanadic Acid from Lead Vanadate (A) For the following method the author is indebted to the late Professor Wohler : Finely pulverise the mineral and attack it with a mixture of concentrated hydrochloric acid and alcohol ; wash the precipitated lead chloride with alcohol, and drive off the hydrochloric acid by means of heat from the blue solution of vanadium chloride. This solution, treated with excess of caustic soda, deposits vanadium oxide, which may be converted into vanadic acid by a current of chlorine. (B) For the following method of preparing vanadic acid on the large scale from the cobalt bed sandstone at Mottram, we are in- debted to Sir Henry Roscoe, whose researches on the chemistry of this metal l have afforded so great an insight into the properties of this remarkable element. The sandstone possesses a light colour, and contains from 0*1 to 0'3 per cent, of the cobalt, nickel, and copper oxides. These metals are extracted commercially by the Alderley Edge Copper Mining Com- pany ; the ore is crushed and digested with hydrochloric acid ; bleaching liquor and milk of lime are then added to alkaline reaction ; a portion of the copper, together with the whole of the nickel and cobalt, re- mains in solution, whilst the small portion of vanadium which the ore contains falls down in the precipitate. It was from this precipitate that Sir H. Roscoe was fortunate enough to secure a plentiful supply of this rare metal. A rough analysis of the crude lime precipitate showed that it contained about 2 per cent, of vanadium, together with lead, arsenic, iron, lime, and sulphuric and phosphoric acids. In order to prepare pure vanadium compounds in quantity from this material, 3 cwt. were dried and then finely ground with four times its weight of coal, and the mixture well mrnaced with closed doors for several days until the greater part of the arsenic had been driven off. The coal having been thus burnt off, the mass was then ground up with one quarter of its weight of soda-ash, and well roasted in a reverberatory furnace with open doors for tw r o days to oxidise the vanadium to a soluble vanadate ; the mass was then lixiviated, and the solution drawn off from insoluble matters ; the liquid was acidified with hydrochloric acid, and sulphurous acid was then passed into the solution to reduce the arseniates, when the remaining arsenic was pre- cipitated by sulphuretted hydrogen. The deep-blue solution thus obtained was carefully neutralised by ammonia (an excess causes much of the vanadium to pass into solution), the precipitated vanadium oxide 1 Phil. Trans. 1808, p. 1, and 1869, p. 679. 138 SELECT METHODS IN CHEMICAL ANALYSIS washed on cloth filters, oxidised by nitric acid, and evaporated to dryness. The well-dried crude vanadic acid was then boiled out with a saturated solution of ammonium carbonate, which left iron oxide, calcium sulphate, and aluminium sulphate insoluble, and the nitrate evaporated until the insoluble ammonium vanadate separated out. This crude vanadate was then washed with sal-ammoniac solution to free it from sodium salts, and recrystallised. In order to prepare pure vanadic acid from this salt, it was roasted in the air, and the powdery acid obtained was suspended in water into which ammonia gas was passed ; the dissolved ammonium vanadate was separated by filtration from a residue containing silica, phosphates, &c., and was crystallised by evaporation in platinum. (C) Another method of preparing pure vanadic acid is to obtain the pure oxy chloride, and decompose this by water, when vanadic acid is yielded as a fine orange-coloured powder. The oxychloride is prepared by intimately mixing sugar charcoal with crude vanadic acid, and heating the mixture to redness in a current of hydrogen. After cooling in hydrogen, the mixture of trioxide and carbon is removed to a hard glass retort heated by a large Bunsen's lamp, and a current of dry chlorine gas passed in. The crude oxychloride comes off as a reddish- yellow liquid, which is purified by distillation in a current of carbonic acid, and afterwards rectified several times over clean sodium. It is a yellow-lemon liquid, boiling at 126'7 C. Purification of Vanadic Acid from Phosphorus Sir H. Koscoe has found that phosphorus is very difficult to separate from vanadium. The action of even traces of phosphoric acid on vanadic acid is most remarkable ; if present in quantities exceeding 1 per cent, of the weight of the vanadium, it altogether prevents the crystallisation of the vanadic acid, and the fused mass possesses a glassy fracture and a black vitreous lustre. If much phosphorus is contained with the vanadium, the method which has proved most effectual for its removal is to deflagrate the finely divided impure acid with its own weight of sodium in a well-covered wrought-iron crucible, and wash the resulting mixture of vanadium oxides by decantation until the wash- water ceases to give an alkaline reaction ; frequently this operation has to be repeated three times before the molybdenum test ceases to indicate phosphorus. Detection and Estimation of Vanadium and Titanium in Basalts Mr. G. Roussel proposes the following process : The samples, in fine powder, are fused with thrice their weight of sodium carbonate ; the mass, when cold, is powdered, and treated with water acidulated with hydrochloric acid ; it is evaporated to dryness, heated for twenty- TUNGSTEN four hours on the water-bath, treated again with acidulated water, and then filtered. The silica eliminated is, after calcination, set to digest for twelve to eighteen hours in hot concentrated sulphuric acid, treated after cooling with an excess of cold water, and filtered. This operation is repeated, and the total liquid is mixed with ammonia, which throws down titanic acid. It is filtered, washed, and ignited. The liquid separated from the silica also contains titanic acid. To separate it, it is treated with sodium sulphite, sulphurous acid, and sodium thio- sulphate, boiled for twenty minutes, and there is left the mixed pre- cipitate of sulphur, alumina, and titanic acid. The sulphur is driven off by gentle heating, and the residue is mixed with the former precipitate, and digested in a sealed tube with pure hot concentrated hydrochloric acid, in order to eliminate the alumina. After this series of operations, the titanic acid is pure, and may be dried and weighed. The same basalts contain vanadium, but in a far smaller proportion. To obtain a ponderable quantity, it is necessary to operate upon a sample twenty times larger than is required for the detection of titanium. The basalt is melted with sodium carbonate and the mass oxidised with a little saltpetre. After cooling, the pulverised mass is treated with a. large quantity of boiling water, filtered, and washed perfectly. The liquid is evaporated, boiled with ammonium carbonate and filtered, treated with ammonium sulphide, and left to settle for two or three days. If the solution contains vanadium, at this moment the fine red colour of vanadium sulphide, when dissolved in an alkaline sulphide, appears in the liquid. It is filtered, and hydrochloric acid is poured into the liquid, which throws down vanadium sulphide mixed with sulphur. The latter disappears on careful heating, when the vanadium sulphide, VS 2 , is weighed. The largest percentage of titanium was 2*378, and that of ^anadium 0*023. TUNGSTEN Preparation of Tungstic Acid from Wolfram The following process, due to Professor Wohler, has been found to answer very well : Reduce the wolfram (an iron and manganese tung- state) to fine powder, and digest at a gentle heat in a mixture of four parts strong hydrochloric and one part nitric acid, till yellow pulverulent tungstic acid is left behind. Wash this by decantation, dissolve in ammonia, and evaporate the solution to the crystallising-point. The resulting ammonium tungstate calcined in the air leaves pure yellow tungstic acid. When the impure tungstic acid is dissolved in ammonia, a residue will be left which contains, besides undecomposed wolfram, small white grains composed of silica and niobic acid, and constituting about 2 per cent, of the wolfram. 140 SELECT METHODS IN CHEMICAL ANALYSIS MOLYBDENUM Detsction of Molybdic Acid M. 0. Maschke has improved the process of Schoenn. According to the latter, traces of molybdic acid and its compounds may be dis- covered by the blue colouration produced on heating it with concen- trated sulphuric acid in a porcelain capsule. This test is rendered exceedingly convenient and much more certain by the following modi- fication : A little concentrated sulphuric acid is applied to a piece of platinum foil, bent so as to form a slight depression ; upon the acid is placed a little of the substance in powder, and the foil is heated till vapours escape in abundance ; it is then allowed to cool, and repeatedly moistened with the breath. When, after cooling, only minute spots are visible, the sulphuric acid, after being breathed upon, takes an intense blue colouration. On heating the platinum foil, the blue colour vanishes, but reappears on cooling. It is completely decolourised if a considerable quantity of water is added. Estimation of Molybdic Acid T. M. Chatard proceeds as follows : Add to the boiling solution of the molybdate, lead acetate in slight excess. Boil for a few minutes ; the precipitate, at first milky, will become granular and will subside easily, leaving a perfectly clear supernatant liquid. Care must be taken in boiling, as the thick milky fluid is very apt to boil over. A ribbed filter is to be used, and the precipitate is to be washed with hot water. The washing proceeds with great ease and thoroughness, and not the slightest milkiness should be apparent in the filtrate. The precipitate is dried at 100, separated from the filter, and ignited in a porcelain crucible. The process gives very good quantitative results and is both easy and expeditious. The precipitated molybdate separates easily from the filter, and can be heated to low redness without decomposition. Separation of Molybdic Acid from Phosphoric Acid E . Eeichardt dissolves the phospho-molybdic compound in sodium carbonate, and precipitates by means of magnesia mixture ; the solu- tion is treated with aqua regia, and evaporated to dryness to expel excess of acid. The residue is then treated with water, which leaves the molybdic acid undissolved. 141 CHAPTEK V ZINC, ALUMINIUM, IKON ZINC Precipitation of Metallic Zinc WHEN metallic magnesium, as met with in commerce, is introduced into a slightly acidulated solution of zinc sulphate (or other zinc salt), hydrogen is evolved, and a precipitation of a spongy bulky mass of metallic zinc occurs. If this sponge is washed till free from soluble salts, then dried and pressed in a steel crushing-mortar between the jaws of a powerful vice, a brilliant solid lump of zinc is produced. Electrolytic Determination of Zinc ' (A) According to Classen, 2 zinc is separated from the solution of the zinc ammonium double salt easily and rapidly by the electrolytic method. The reduced metal has a bluish- white colour, and adheres suffi- ciently well to the negative electrode, though not as finely as iron, cobalt, or nickel. For reduction we take the cold solution, pass a current equal to 5 or 6 c.c. detonating gas per minute, and ascertain the end of the decomposition with potassium ferrocyanide, applying heat. The metal deposited, which is purified by washing with water and alcohol, adheres so firmly to the capsule when dry, that it can only be dis- solved with difficulty by heating with acids. There generally results a dark coating of platinum black which can be removed only by igniting the capsule, and again treating the residue with an acid. Hence it is recommended to deposit on the capsule, before weighing, a layer of copper, tin, or, by preference, of silver. For cpppering the platinum capsule we decompose a solution of copper sulphate, acidified with nitric acid, with a current of 2 to 3 c.c. detonating gas, and interrupt it after some hours. The deposit of copper is washed with water and alcohol, and the capsule is dried for a short tim in the air-bath at from 90 to 100. A coating of tin is obtained from the solution of the acid double oxalate (see Tin), and one of silver from the solution in potassium cyanide (see Silver). 1 Por details of the operation see chapter on Electrolytic Analysis. 142 SELECT METHODS IN CHEMICAL ANALYSIS (B) According to Von Miller and Kiliani, 4 grammes potassium oxa- late and 3 grammes potassium sulphate are dissolved in water, a carefully neutralised solution of zinc sulphate or nitrate is added not containing more than 0*3 gramme zinc as a maximum, and electrolysed without heat with a current of normal density 100=0-3 0'5 ampere. The reduction is completed in two or three hours. (C) Beilstein and Jawein precipitate the zinc from a solution of potassium zinc cyanide. For this purpose the liquid is mixed with soda-lye until a precipitate is formed, and potassium cyanide is added until it is re-dissolved. Four Bunsen elements are required for reduc- tion. As the liquid is very strongly heated by the powerful current, the authors recommend that it should be refrigerated. (D) Parodi and Mescezzini for the determination of zinc mix the solution containing it as sulphate with sodium acetate, and acidify with citric acid. The liquid, diluted with water to about 175 c.c., is exposed to the action of a current of 4 to 5 c.c. detonating gas per minute. When the precipitation is complete, the liquid is drawn off by means of a syphon. (E) According to Kiche, zinc is deposited from an acetic solution -containing an excess of ammonium acetate obtained by supersaturating with ammonia and acidulation with acetic acid. (F) F. Riidorff gives the following instructions : To the solution containing at most 0'25 gramme zinc, there are added 20 c.c. of a 25 per- cent, solution of sodium acetate and three drops of dilute acetic acid (50 per cent.). The mixture is diluted with so much water that a copper edging of from 1 to 2 c.m. remains unmoistened in the coppered platinum -capsule. The electrolysis is effected with a battery of 5 to 6 Meidinger elements. In order to prevent the zinc from re-dissolving the capsule must be cleaned as rapidly as possible. For drying the capsule the temperature of the air-bath must not exceed 60. Only solutions which contain the zinc as sulphate are suitable for treatment by the above-described method. (G) A. Beard deposits the zinc from a solution containing sodium pyro-phosnhate in excess (see Iron). After the double salt has been formed the solution is rendered strongly alkaline with ammonium carbonate, and the decomposition is effected with a current of from 5 to 10 c.c. of detonating gas per minute. For the complete separation of the zinc, the current is finally strengthened to from 15 to 20 c.c. detonating gas. (H) G. Vortmann has made experiments on the separation of metals as amalgams. Zinc was determined as an amalgam by C. Luckow as early as 1885. Vortmann effects the separation of zinc as an amalgam either from the double ammonium oxalate or from an ammoniacal solution. In the solution of the zinc salt to be electro- lysed there is dissolved a weighed quantity of mercuric chloride, and from 3 to 5 grammes ammonium oxalate. It is diluted with water and ESTIMATION OF ZINC 143 electrolysed. A current of G to 8 c.c. detonating gas is first passed through the liquid for some minutes, it is then reduced to one half, and is gradually raised to its original strength. As regards the addition of mercury, care must be taken that the proportion is '2 to 3 parts of mercury to 1 part of zinc. The amal- gam obtained is washed with water, alcohol and ether, and dried in the desiccator until the weight is constant. For separating the amalgam from an ammoniacal solution it is mixed with tartaric acid and ammonia in excess. The weight of the mercury in this case must be at least three times that of the zinc. (I) In the separation of zinc from the solution of the double oxalate according to the method of Picte, the determination of the metal as an amalgam presents no practical advantages. Volumetric Estimation of Zinc (A } When a solution of a zinc salt is added to a known quantity of solution of potassium ferrocyanide, there is formed a precipitate of zinc ferrocyanide, insoluble in ammonia. By estimating the amount of potassium ferrocyanide remaining in solution by means of potassium permanganate, the amount of zinc present can be readily calculated. Upon this reaction M. Renard has based the following process : Dissolve a known weight (1 or 2 grammes) of the substance to be assayed for zinc in aqua regia, add excess of ammonia, filter from the precipitate, and wash well. To the filtrate 25 c.c. of a solution of potassium ferrocyanide (150 grammes to the litre) are added ; the solution is made up to 250 c.c., and filtered ; 100 c.c. of the filtrate are measured into a glass vessel, and neutralised with pure hydrochloric acid free from chlorine and sulphurous acid. Afterwards the solution is rendered strongly acid with about 30 c.c. of the same acid, and titrated permanganate solution added until the whole of the yellow prussiate is transformed into red prussiate. By calculation the amount of zinc contained in the substance is arrived at. None of the metals commonly present in minerals, such as iron, aluminium, manganese, lead, &c., influence the process. Either they are precipitated by the ammonia, or they are not precipitated by potassium ferrocyanide. Oopper is an exception, and, if present, interferes with the process. (B) A good method for volumetrically estimating the amount of zinc in ores is given in the Zeitschrift fur analytische Chemie for 1869, by Maurizio Galetti, Chief Assayer at the Royal Assay Office, Genoa. The following is a description of the process : Supposing zinc sulphide (blende) is to be assayed, about half a gramme of the finely pulverised ore is to be treated with concentrated nitric acid, and boiled to incipient dryness, until the sulphur left undissolved does not contain any particles of undissolved ore. Then add strong hydrochloric acid, and boil again until no nitric acid is left. Calamine (zinc carbonate) should at once 144 SELECT METHODS IN CHEMICAL ANALYSIS be acted upon with hydrochloric acid ; but, in order to make sure of the complete oxidation of all the iron the ore may happen to contain, it is best to add to the acid a few decigrammes of pure potassium chlorate. After having boiled this solution for a few minutes, it is diluted with distilled water ; a large excess of ammonia is added to the solution, which is then boiled and slightly acidified with acetic acid. After brisk agitation, boil again for a few minutes, and then supersaturate with ammonia. The liquid is then poured out of the flask into a suit- able glass vessel, and the flask is rinsed out with a sufficient quantity of distilled water to bring the bulk of the fluid up to half a litre. This having been done, the fluid is very cautiously and gradually acidified with dilute acetic acid, one part acid sp. gr. 1-07, to 10 of distilled water. Any large excess of this should be avoided, as the solution should only be very slightly acid. As soon as the basic iron acetate has subsided, the precipitation of the zinc by means of a standard solution of potassium ferrocyanide may be proceeded with. The ferrocyanide solution is made by dissolving 41-25 grammes of the salt in as much distilled water as will make the solution weigh exactly one kilogramme. The presence of lead compounds (as, for instance, lead carbonate, sulphate, or sulphide) occurring along with the ores of zinc, does not interfere with the completeness of the precipitation of zinc as zinc ferrocyanide. This even holds good up to 10 per cent, of metallic lead. Since some zinc ores, especially calamine, often contain manganese, it is best to add to the ammoniacal solution, before any acetic acid is added, a few drops (from 2 to 4) of bromine, in order to convert the manganese protoxide into proto-sesquioxide, leaving the solution stand- ing for twenty-four hours after the addition of the bromine. The ammoniacal solution of zinc chloride being colourless, there should be added to it, previous to cautious acidification by means of dilute acetic acid, a few drops of tincture of litmus, in order to more readily hit the precise point of sufficient acidification, which is known by the blue colouration changing to a rose-red. The zinc ferrocyanide which is mixed with iron oxide preserves its naturally white colour as long as the liquid contains free zinc, but its colour changes to a greyish-white as soon as a very slight excess of the standard ferrocyanide solution is present ; the liquid also then becomes turbid, and the precipitate settles very slowly. By these characteristic signs the end of the operation may be always recognised. In order to make sure, the liquid should be touched with a glass rod which has been just previously moistened with a dilute solution of ammoniacal copper nitrate ; this will have the effect of indicating any excess of the ferrocyanide solution, by producing the more or less intense colour characteristic of copper ferrocyanide. The zinc solution should be at a temperature of from 40 to 50, whereby the rapid subsidence of the zinc ferrocyanide is promoted. ESTIMATION Ol< ZINC 145 Filtration is not necessary, as the presence of the gelatinous silica (due to the decomposition of zinc silicates occurring in the ores of that metal) does not interfere with the correctness of this method of esti- mating zinc quantitatively. (C) C. Mann converts the zinc into chloride and mixes with a few drops of a concentrated solution of iron-ammonium alum, and with an excess of standard silver nitrate. By titrating back with ammonium sulphocyanide till a faint redness is remarked, the excess of silver is ascertained, and consequently the quantity of silver used to precipitate the chlorine, and by reducing the latter to zinc the amount of this metal is known. The zinc is converted into chloride as follows : It is dissolved in nitric acid, mixed with ammonium acetate, sulphuretted hydrogen gas is passed through the solution, and the precipitate, after boiling and twice decanting, is filtered. The precipitate, along with the filter, is placed in a beaker, mixed with about 50 c.c. of water and an excess of well-washed silver chloride, and boiled till the liquid becomes perfectly clear. The precipitate, a mixture of silver sulphide and excess of silver chloride, is easily washed. When this is complete the filtrate is acidulated with nitric acid and treated as above. (D) Mr. F. Maxwell Lyte considers that an advantage will be found by the employment of a uranium salt as an indicator in the estimation of zinc volumetrically by means of ferrocyanide. The zinc should be in solution, in hydrochloric acid by preference, and the solution should be pretty strongly acid. Iron or copper should not be present, nor should nickel or cobalt. , When a solution of zinc in hydrochloric acid is heated to 80 or 100 C., rendered pretty strongly acid, and a drop or two of uranium acetate added, and then a solution of potassium ferrocyanide run in from a burette, a brown spot of uranic ferrocyanide forms where the potassium ferrocyanide falls,, but disappears on stirring, so long as a trace of zinc remains unprecipitated ; but the moment all the zinc has become converted into ferrocyanide, the next drop or so of potassium ferrocyanide tinges the whole liquid brown. Mr. Lyte prefers, in practice, not only adding a trace of uranium acetate to the zinc solution, but at the same time at the end of the operation trying a drop of the zinc solution on a white porcelain plate, with a glass rod moistened with the uranium salt. The reaction seems in this case slightly more delicate, while the operator is warned of the approach of the termina- tion by the fact that the brown colour in the liquid disappears rather more slowly towards the end of the operation. (E) Mr. C. Fahlberg also proposes to titrate zinc in a hydrochloric solution with potassium ferrocyanide, and uses as indicator a solution of uranium nitrate, which, as soon as an excess of ferrocyanide appears in the solution, gives a brown precipitate, or at least a brown coloura- tion. Manganese and alumina do not interfere. After dissolving the 146 SELECT METHODS IN CHEMICAL ANALYSIS ore in aqua regia, all metals precipi table by sulphuretted hydrogen and also iron, are removed by the ordinary methods. The ammoniacal solution containing the zinc is neutralised with hydrochloric acid, and then acidulated with 10 to 15 c.c. of the same acid at sp. gr. 1'12. This solution is titrated with a solution of ferrocyanide, of which 1 c.c. represents 0*01 gramme of zinc ; the final reaction is performed on a porcelain plate upon which a series of drops of a solution of uranium nitrate have been placed. The results are exact to 0'2 or 0'3 per cent. Estimation of Zinc as Oxalate An ingenious method of estimating zinc as well as other metals, and one which, in the author's hands, has proved very accurate, has been worked out by Mr. W. Gould Leison, of the Lawrence Scientific School. The process is as follows : The zinc compound is obtained in the form of a sulphate, and to a neutral solution of this salt oxalic acid and then a large quantity of strong alcohol are added. Zinc oxalate precipitates in the form of an extremely fine powder. This is filtered through sand, thus : A slight funnel is ground conical near the throat. A little pear-shaped piece of glass with a long stem is then dropped into the funnel, stem upwards, so as to form a valve, im- passable to sand laid upon the ball of the glass, but allowing liquids to pass freely. By means of the stem the valve can be lifted from its seat, and the sand and zinc oxalate, after washing with alcohol and careful drying, are washed together into a flask with hot dilute sulphuric acid. A few c.c. of strong sulphuric acid are then added, and the solution titrated with potassium permanganate. From the amount of oxalic acid thus found the quantity of zinc can readily be calculated. Estimation of Zinc as Sulphide All who have experienced the difficulty of filtering and thoroughly washing the light, slimy precipitate of zinc sulphide, as ordinarily obtained, will be glad to know of a modification of the usual mode of precipitation (due to Mr. J. H. Talbot, of the Lawrence Scientific School), whereby this- difficulty is avoided. The solution of zinc, if acid, is to be neutralised as nearly as possible by sodium or ammonium carbonate. To the boiling solution, sodium or ammonium sulphide is to be added, a large excess being very carefully avoided. The white precipitate, on continued boiling, soon becomes granular, and settles readily. The supernatant clear liquid is then to be tested with a drop of the alkaline sulphide, to be sure of complete precipitation, and the sulphide then washed with hot water. The filtrate is perfectly clear and quite free from zinc ; the washing is easy and rapid. The zinc sulphide is next to be partially dried with the filter, brought into a porcelain crucible, and ignited at first gently and afterwards strongly, ESTIMATION OF ZINC 147 with free access of air. The expulsion of the last traces of sulphuric acid is much facilitated by occasionally dropping fragments of ammo- nium carbonate into the crucible. Pure zinc oxide finally remains, the ignition being continued until a constant weight is obtained. The results in this way are very accurate. Estimation of Zinc as Ammonio-phosphate According to Hugo Tamm, when a solution of zinc in any mineral or volatile organic acid is supersaturated by ammonia until all the zinc oxide is dissolved, and when this solution is re-saturated by hydro- chloric acid until litmus-paper indicates a feeble acid reaction, a double .zinc and ammonium chloride exists in the liquor. If a solution of ordinary crystallised sodium phosphate is added, a voluminous white precipitate of zinc phosphate is formed, which, if left for a few minutes at a temperature near the boiling-point of the liquor, soon combines with ammonium phosphate, and suddenly comes down as a dense white precipitate, which settles very rapidly. This precipitate of ammonio-zinc phosphate, collected on a filter, can be washed with the utmost facility, in fact, as fast as water can be poured upon it, and it never passes through filters, a most important property. It retains the sodium phosphate and ammonium chloride in the midst of which it has been precipitated, with some strength, and several successive washings are absolutely required to free it from these salts, but eventually the washing is complete. To ascertain this, silver nitrate acidulated with nitric acid must be used, because the double phosphate retains chlorides with more strength than phosphates. After drying at 100 C., the ammonio-zinc phosphate contains exactly 36'49 per cent, of metallic zinc. Calcined over a gas-lamp, the double phosphate leaves a residue of y.inc pyrophosphate. It might be supposed that zinc could be estimated with accuracy in this salt ; but this is not the case, as a loss of zinc is always incurred during the calcination of the ammonio-zinc phosphate. On the contrary, the composition of the zinc and ammonium phosphate, well washed and dried at 100 C., can always be relied upon, and it is from the weight of this salt that the amount of zinc must be calculated. The precipitation of zinc is complete when the supernatant liquid, mixed with a little excess of sodium phosphate, does not show any precipitate of zinc phosphate ; but it is advisable to add at once to the zinc solution a quantity of sodium phosphate sufficient to turn red litmus-paper blue. The liquor is only momentarily alkaline, and it reassumes its slightly acid or neutral reaction as soon as the double phosphate has come down, so that the precipitation actually takes place in a slightly acid or neutral liquor a gratifying result. Should a very accurate estimation of zinc be required, the liquor i. 2 148 SELECT METHODS IN CHEMICAL ANALYSIS should be left in a warm place for some ten or twelve hours, when the precipitation of the zinc will be very complete, as might be proved by adding ammonium sulphide to the filtered liquor, or sulphuretted hydrogen to the filtrate previously saturated by ammonia, and reacidu- lated by acetic acid. In general a trace of zinc is precipitated, for the double phosphate is not absolutely insoluble. For most practical pur- poses, it is quite sufficient to allow the precipitated double phosphate to rest for about an hour ; a very small quantity of zinc will remain in the liquor, from which it can be separated by ammonium sulphide,, but this quantity of zinc never amounts to more than ^1^ of the quantity of zinc precipitated by sodium phosphate, so that it can be neglected, especially if a simple assay of zinc is all that is required. One of the chief defects of the double phosphate is its propensity of adhering firmly to the side of the flask in which the precipitation takes- place. A thin film of this salt coats the glass, and it can be removed only with some difficulty. A glass stirrer, covered at one end with 1 inch or 1^ inch of indiarubber tubing, can be advantageously em- ployed for this purpose. But it is best, after the bulk of the precipitate has been removed on the filter, to dissolve the adhering film in dilute hydrochloric acid, to neutralise by ammonia, to add a few drops of sodium phosphate, to boil, and then add the slight precipitate obtained to the main portion already placed on the double filter. It is sometimes possible to avoid the coating of the glass with ammonio-zinc phosphate, by heating the solution almost to boiling- point before adding sodium phosphate : the precipitation in this case is- very rapid, and, by taking this precaution, further trouble is avoided. But the chief defect of this mode of estimating zinc is undoubtedly the use of sodium phosphate, a fixed salt, difficult of separation from most substances. Unfortunately, with zinc, there is no choice of precipitat- ing reagents, and sodium phosphate, which must be considered as a very perfect assay reagent, is, from its very nature, a defective one in analytical researches. Estimating the Value of Zinc Powder (A) V. Drewsen prepares two solutions ; the one of pure fused potassium bichromate say 40 grammes per 1000 c.c. and the other of crystalline ferrous sulphate, about 200 grammes in 1000 c.c. The iron solution must be strongly acidulated with sulphuric acid, to prevent oxidation. In order to find the respective value of the two liquids, 10 c.c. of the iron solution are measured into a beaker, a little sulphuric acid is added, and the other solution is dropped in from a burette until a drop of the mixture is no longer turned blue by potassium ferricyanide. About 1 gramme of the zinc powder is then weighed, placed in a beaker with 100 c.c. of the chromic solution, 10 c.c. of dilute sulphuric acid are added, the whole is well stirred, 10 c.c. more of the sulphuric SEPARATION OF ZINC FROM CHROMIUM 149 acid are added, and allowed to act for about a quarter of an hour with diligent stirring. When everything is dissolved except a small insoluble residue, an excess of sulphuric acid is added, and 50 c.c. of the iron solution in order to reduce the greater part of the excess of chromate ; more of the iron solution is then added from a burette till a drop displays a distinct blue reaction with ferricyanide, and the mixture is then titrated back with chromate till this reaction disappears. From the total number of c.c. of the iron solution consumed the quantity is deducted which corresponds to the ferrous solution employed. The chromate contained in the remainder, if multiplied by 0*6611, shows the metallic zinc contained in the powder. (B) To determine the metallic zinc present the only valuable constituent Fresenius mixes about 3 grammes of the powder in a flask with sulphuric acid, and passes the hydrogen gas evolved through refrigerating and desiccating tubes into a combustion-tube filled with cupric oxide. The water formed is absorbed in a U-tube two-thirds full of broken glass and containing 12 c.c. pure concentrated sulphuric acid. Nine parts of water correspond to 32*53 parts of metallic zinc. (C) J. Barnes estimates the value of the zinc powder by the amount of hydrogen evolved. The hydrogen is measured by the quantity of water which it displaces. The gauge consists essentially of a narrow graduated tube placed in mercury ; 011 the upper end of the tube a bulb is blown. The value of the graduations is determined. On exposing this bulb to the temperature and pressure at which the gas is being measured, reading off the division at which the mercury inside and outside is level, and referring to a table, a number is obtained. The observed volume of the gas is divided by this number, and the corrected volume at once obtained. Separation of Zinc from Uranium To a nearly neutral and somewhat dilute solution of the two metals add sodium acetate in excess, boil, and pass sulphuretted hydrogen through the boiling solution till all the zinc is precipitated as sulphide. Filter quickly, wash, and finish as described at page 147. Separation of Zinc from Chromium Obtain the zinc and chromium sesquioxide in the form of a nearly neutral solution, by the addition, if necessary, of sodium carbonate, then add excess of sodium acetate, and oxidise the chromium to the state of chromic acid by a current of chlorine, or (if it be present in small quantity only) by addition of chlorine water, or bromine. The solution should be kept hot and as neutral as possible by the cautious addition of sodium carbonate. When the oxidation is complete, expel the excess of chlorine or bromine by heat, and add barium acetate, which will precipitate the whole of the chromium present in the form 150 SELECT METHODS IN CHEMICAL ANALYSIS of barium chrornate, taking the precautions already described at page 125. The oxidation of the chromium to the state of chromic acid may also be effected by Professor Storer's method, with nitric acid and potassium chlorate, as described at page 125. Separate the excess of barium from the solution by addition of sulphuric acid, and then precipitate the zinc with sodium carbonate ; or the acid solution may be supersaturated with ammonia so as to re- dissolve the zinc oxide, filtered, if necessary, to remove iron, &c., and the zinc precipitated by sulphuretted hydrogen. When barium sulphate and chromate are thrown down together, the chromic acid may be reduced to sesquioxide by boiling with concentrated hydrochloric acid and alcohol, after which the barium may be precipitated by sulphuric acid, and the chromium sesquioxide thrown down in the filtrate by boiling with ammonia in the usual manner. As the reduction of ba- rium chromate by means of hydrochloric acid and alcohol does not take place very readily, it is better to boil the chromate with an excess of potassium or sodium carbonate, to filter off the barium carbonate, and determine the chromic acid by means of mercurous nitrate, as explained at page 127, or by reduction to chromium oxide and precipitation with ammonia in the usual manner. ALUMINIUM Detection of Alumina Mr. Beckmann recommends baryta-water in preference to the caustic alkalies, as not being contaminated with alumina and silica. Solution of ammonium chloride is afterwards added as usual. Precipitation of Alumina (A] Ammonium sulphide is a more complete precipitant for alumina thar caustic ammonia or ammonium carbonate, and should always be employed In preference when practicable. The small quantity of free sulphur which will be generally precipitated at the same time is driven off on ignition. It must be remembered that oxalic acid and its salts possess in a slight degree the property of most non-volatile organic acids, of impeding certain reactions of alumina ; therefore, when ammonium oxalate is present in great excess, alumina is not imme- diately precipitated by ammonia and ammonium sulphide ; although, in the course of a little time, according to its proportion, alumina is precipitated, especially if the solution be heated. (B) M. Classen l finds that if aluminium-ammonium oxalate, dis- solved with an excess of ammonium oxalate, is submitted to the action of an electric current, in proportion as the ammonium oxalate is converted into ammonium carbonate the aluminium is deposited in the state of 1 For details of operations see chapter on Electrolytic Analysis. KST1MATION OF ALUMINA 151 hydroxide. When the oxalic acid is oxidised, the liquid is boiled until it smells faintly of ammonia, filtered, washed with water, and the hydroxide is converted into alumina by ignition. Precipitation and Washing of Alumina Messrs. S. L. Penfold and D. N. Harper have experimented on the precipitation and handling of alumina precipitates. A standard solu- tion of aluminium chloride was first made, containing 0*1002 gramme alumina and 1 c.c. pure concentrated hydrochloric acid in every 50 c.c. The precipitation of the alumina was in all cases made in a volume of about 300 c.c. by neutralising the solution with ammonia till the odour of ammonia could be distinctly obtained from the hot solution ; the beaker was then placed upon a lamp-stand, and the solution brought to boiling, which was not continued more than one minute. The precipitates were in all cases washed without a pump, but suction- tubes 7 inches long were attached to the funnels, which caused a gentle suction, and, if the filter-papers were carefully fitted to the funnels, very materially hastened the filtration. The following facts were observed : That precipitates which were made in solutions containing large quantities of acid, either hydro- chloric or nitric, filtered as well as or better than those from solutions containing little ammonia salts, but on washing with boiling water the precipitates from solutions containing large quantities of ammonia salts became very sticky, washed slowly so that it was almost impos- sible to free them from the last traces of ammonium chloride ; and that very perceptible quantities of alumina settled out from the filtrates and washings, on adding a few drops of ammonia and allowing the beaker to stand in a warm place. Further, that all of the alumina which ran through did so during the washing. The precipitates, after they had become slimy and sticky, seemed either to be quite soluble in the hot water, or else got into such a condition that they readily passed through the pores of the paper and stopped them up, thus hindering the filtration. To make a successful precipitation and washing of alumina, it is quite essential not to have very much ammonia salts present, and even with the greatest care it is found that if the filtrates and washings are set away in a warm place, slight precipitates will almost invariably settle out. The above holds good for solutions containing ammonium chloride and nitrate. The fact that alumina passed through the filter only during the washing, suggested that if the precipitate could be washed with a saline solution which would be completely volatile and do no harm to the precipitate, the passage of the alumina through the filter might be avoided, and it might also hinder the packing of the precipitate. Ammonium nitrate suggested itself as a salt which would be volatile on ignition and do no harm, and experiments with it have 152 SELECT METHODS IN CHEMICAL ANALYSIS been very satisfactory. The following strength of ammonium nitrate was used in all the experiments : 2 c.c. of pure concentrated nitric acid neutralised with ammonia and diluted to 100 c.c. with water ; this strength has proved quite satisfactory. Using this hot saline wash instead of hot water, the precipitation can be made in solutions containing large or small quantities of ammo- nium salts, and no very great care is needed in adding the ammonia. The precipitates from solutions containing a goodly quantity of ammo- nium salts, resulting from 4 to 8 c.c. of pure concentrated hydrochloric or nitric acid, filter and wash better than precipitates from solutions containing less saline matter. After having made a large number of precipitations, the authors can say that only in one or two cases have they found a trace of alumina in either the filtrate or washings, and that unless the precipitate becomes too dry and packs too firmly upon the sides of the funnel, the washing goes on as well at the end as at the beginning, and there is no difficulty in washing the precipitate free from all traces of chlorine. Volumetric Estimation of Alumina in Caustic Soda Gatenby estimates first the amount of caustic soda present with normal hydrochloric acid and phenol-phthalein as indicator. When the phenol-phthalein is decolourised, we have the amount of caustic soda present. Then put into it a few drops of methyl orange solution and again add normal hydrochloric acid, stirring well (not heating), until a pink colour is obtained which does not vanish by stirring for a few seconds. The number of c.c. of normal hydrochloric acid required by the second titration equals the amount of alumina and alkaline soda salts present. Then add litmus solution and titrate back with normal caustic soda until a decided blue colour appears. Each c.c. of normal caustic soda requires 0*0257 of alumina. A sample of caustic soda bottoms from 70 per cent, white caustic soda, called by the trade 68 per cent, bottoms, tested as follows : Na 2 57-1 H.O 16-5 Na 2 C0 3 , &c 2-4 AL0 3 . 11-3 Insoluble Fe 2 3 , &c. . 12-5 99-8 This process is said to be very rapid, and accurate enough for tech- nical use. It is an interesting fact that alumina is alkaline to methyl orange, and acid to litmus solution. Assay of Clays for Alum Making Mr. G. Pouchet proceeds as follows : A mean ' sample of 50 grammes is taken and placed in a tared platinum or porcelain capsule. SEPA EAT 1 N OF A L UM J Nil M 153 It is submitted to a moderate calcination. When it has attained a dull redness, the capsule is withdrawn, allowed to cool, and weighed. The loss indicates the proportion of moisture and of volatile matters (com- bined water and organic matter). Upon the calcined clay are then poured 100 grammes of sulphuric acid at 60 B. ; the whole is well mixed with a glass rod, and heated till it becomes solid. It is then lixiviated with boiling water, and the alumina is determined in the ordinary manner in a known part of the solution. Separation of Aluminium from, Zinc The metals should preferably be in the form of chlorides. Dilute the solution considerably, render it neutral or nearly so, add sodium acetate in excess, and then boil for a short time, adding a drop of free acetic acid occasionally ; the whole of the aluminium will be precipi^- tated in the form of basic acetate. Filter rapidly through a ribbed iilter, and keep the liquid as near the boiling-point as possible during nitration. If an absolutely complete separation is necessary, redissolve the precipitate in dilute hydrochloric acid and repeat the operation. From the solution the zinc is completely precipitated by sulphuretted hydrogen. Separation of Aluminium from Uranium The separation of these two metals may be effected in the same manner as that of aluminium and zinc above described. Separation of Aluminium from Chromium (A) To a strong solution containing these two metals add potassium chlorate and concentrated nitric acid ; the chromium is quickly oxidised to chromic acid. Or, the same thing may be effected by means of chlorine or bromine, as described at page 150. The chromic acid is then precipitated with barium chloride, taking the precautions described at page 125. With care, this process gives very accurate results. (B) Another, and, under some circumstances, a better plan, is the following, for which the author is indebted to Professor Wohler. Pass chlorine through the solution of the chromium and aluminium sesqui- oxides in caustic potash, until all the chromium is oxidised to chromate. The aluminium will then be in the form of precipitated hydrate, with the exception of a small quantity, which is readily precipitated by digestion with ammonium carbonate. Filter the solution of potassium chromate from the alumina, and to the nitrate add alcohol and excess of hydrochloric acid, and heat till the reduction to chromium sesqui- oxide is complete. Add ammonia to the warm solution, when the whole of the chromium will be precipitated as sesquioxide. 154 SELECT METHODS IN CHEMICAL ANALYSIS Separation of Aluminium from Zirconium To separate these two metals Mr. J. Thomas Davis proceeds as follows : Their solution in hydrochloric acid is treated with sodium carbonate until a permanent precipitate is formed. This precipitate is dissolved in the smallest possible quantity of dilute hydrochloric acid, and sodium iodate is added in excess. The solution is heated for about fifteen minutes. It is then allowed to stand twelve hours, filtered, washed down with boiling water, dissolved in hydrochloric acid, and finally precipitated with ammonia, ignited and weighed. Three analyses of the zirconium salt proved it to be an oxy-iodate of variable composition. Several attempts were made to separate iron both in the ferrous and ferric state, but without success. This metal must be removed from the mixture of aluminium and zirconium previous to their treatment with sodium iodate. Separation of Aluminium from Grlucinum (A) Dr. Wolcott Gibbs adds a solution of sodium fluoride to the one of aluminium and glucinum, when the whole of the aluminium is- thrown down in the form of cryolite, while the glucinum remains in solution. From this solution ammonia precipitates the glucina. (B) When sodium thiosulphate is added to a nearly neutral dilute solution containing aluminium and glucinum, and the liquid is boiled until no more sulphurous acid is disengaged, alumina is precipitated (together with some sulphur), whilst the glucinum remains in the solution. The following methods are not satisfactory : precipitation of the alumina as basic acetate, some glucinum being also precipitated ; precipitation of the alumina with barium carbonate ; solution of the glucinum in a boiling solution of ammonium chloride ; by long boiling of a solution of ammonium chloride the solution becomes slightly acid, and some alumina is dissolved, while Genth found that the glucinum was not completely dissolved. Solution of the glucinum in, and preci- pitation of the alumina with ammonium carbonate gives unreliable results. (C) Messrs. S. L. Penfold and D. N. Harper have improved upon Genth ? s process of dissolving the mixed chlorides in the least possible excess of caustic soda, diluting the solution largely, and precipitating the glucina by boiling. The method is as follows : 50 c.c. of each solution were measured into a platinum dish and evaporated to dryness, the chlorides were dissolved in the least possible quantity of water, and a rather strong solution of pure soda, made from metallic sodium, was cautiously added until the precipitate which at first formed was completely dissolved. The contents of the dish were then rinsed with cold water into a beaker containing about 800 c.c. of boiling water, and the contents of the SEPARATION OF ALUMINIUM 155 beaker boiled for one hour, replacing from time to time the water which evaporated. The glucinum separates out as a granular precipi- tate, which is easy to filter and wash. After acidifying and concentra- ting the nitrate, the alumina was precipitated with ammonia. The best results are obtained by dissolving the dried chlorides in the least possible quantity of water, and using as little soda as possible for dis- solving the aluminium and glucinum. (D) When phosphoric acid is present the same authors separate alumina from, glucinum by boiling the solution of the mixed chlorides with barium hydroxide. The alumina goes readily into solution, while the precipitate containing the barium phosphate and glucinum is easy to filter and wash. After dissolving the precipitate and separating the barium with sulphuric acid, a glucinum phosphate can be precipi- tated with ammonia. After weighing this, the phosphoric acid may be determined by means of ammonium molybdate, and the glucinum by difference ; or the precipitate may be fused with sodium carbonate, and the fusion soaked out with water, which gives almost a complete separation of phosphoric acid from glucinum. If phosphoric acid is also to be determined, it must be borne in mind that very perceptible quantities of it will be found in the barium sulphate precipitate. Separation of Aluminium from the Cerium Metals Bring the metals to the form of sulphates dissolved in a small quantity of water, and add sufficient powdered sodium sulphate to form a saturated solution. The cerium metals immediately separate in the form of double sulphates with sodium sulphate, as a white highly crystalline powder. Filter off and wash with a saturated solution of sodium sulphate. Precipitate the aluminium from the filtrate by addition of ammonia and ammonium sulphide, and dissolve the double sodium and cerium sulphates, &c., in dilute hydrochloric acid, and precipitate with ammonium oxalate. Separation of Aluminium from Magnesium (A) These, when in solution together, may be separated by Dr. Gibbs's plan, viz. boiling the dilute solutions with excess of sodium acetate and a little acetic acid, whereby the aluminium is precipitated as basic acetate. The details of the operation are conducted as in the Separation of Aluminium from Zinc (page 153). (B) Insoluble mixtures containing aluminium and magnesium, such as spinel (magnesium aluminate), are best analysed by the process given by Wohler. Fuse the finely levigated mineral with six times its weight of potassium bisulphate, and keep the mass fused at a red heat till sulphuric acid is no longer disengaged. Dissolve the fused mass in water acidified with hydrochloric acid, and decompose it with sal- ammoniac, which precipitates the alumina. To prevent any magnesia, 156 SELECT METHODS IN CHEMICAL ANALYSIS Doming down with the alumina, care must be taken to keep the liquid boiling till no more free ammonia is given off. The gelatinous alumina, which the boiling liquid deposits, is filtered, but as it is almost impos- sible to wash in this state, it must be allowed to half dry on the filter, when it can be washed perfectly. The magnesium is precipitated from the filtrate by ammonia and sodium phosphate. Separation of Aluminium from Calcium The method of separating calcium from aluminium by means of ammonia has been improved by H. Rose. Instead of being careful to employ ammonia free from carbonic acid, and avoiding the presence of this gas, he heats to gentle ebullition the liquid in which the alumina has been precipitated by excess of ammonia. When the evolution of ammonia ceases, all the aluminium is in the precipitate, and may be separated by filtration without requiring any special pre- caution, for the simple reason that in the presence of ammoniacal salts the calcium carbonate is decomposed, the calcium entering into solution. A little sal-ammoniac may even be added, if there is a chance of there not being sufficient to favour this decomposition. When the calcium is present in small quantities only, tartaric acid may be added, and the solution then supersaturated with ammonia. The calcium is precipitated in the form of tartrate if there is only a little aluminium present ; otherwise, much remains in solution. In either case, however, ammonium oxalate will separate it perfectly in the form of calcium oxalate. GALLIUM Detection of Gallium To test for gallium in a blende the mineral is attacked by nitro- hydrochloric acid, excess of acid expelled by boiling, and the solution treated with pure zinc in the cold. The solution is filtered while there is still a notable evolution of hydrogen, and the filtrate boiled with zinc. The precipitate that is formed is washed, dissolved in hydrochloric acid, and the solution, as concentrated as possible, is tested spectroscopically. If necessary, the operation of boiling with zinc is repeated on the first white deposit formed. For a blende containing the average amount of gallium, 10 grammes of the mineral are sufficient to obtain distinctly the principal ray of gallium. Compounds of gallium the chloride in particular give in the spec- troscope two very characteristic rays, one of which especially is suffi- ciently brilliant to reveal feeble traces of this element. The hydrated chloride produces in the gas flame but a very feeble and fugitive spectrum. SEPARATION OF GALLIUM 157 In order to obtain a sensitive reaction it is necessary to have recourse to the induction snark which is taken oft' the surface of the- solution, employing a spark of 1'5 to 2 millimetres long. The characteristic bands in wave lengths are : 509' . . A nebulous band of moderate intensity, only seen with concentrated solutions of Ga,Cl G . 417* . Sharp, intense. 403-1 . . Distinct, but much less intense than 417. Separation of Gallium from Zirconium The boiling solution is treated with excess of solution of potash. The precipitate of zirconia requires prolonged washings, and retains traces of gallia, which are extracted by re-solution in hydrochloric acid and reprecipitation by potash. Two or three treatments with boiling potash generally suffice. The gallium oxide is freed from potassium salts by supersaturation, first with hydrochloric acid, and then with ammonia and prolonged boiling, or more accurately by means of cupric hydrate. Only feeble traces of zirconia pass into the alkaline solution ; these are separated from gallium by potash at the end of the analysis. Ferrocyanide cannot be used, as it gives a canary-yellow precipi- tate in solutions of zirconium, even if very acid and very dilute. Ebul- lition even does not effect the solution of the precipitate in a liquid containing two-thirds of its bulk of concentrated hydrochloric acid. This fact is mentioned because some chemical treatises assert that potassium ferrocyanide gives a precipitate in neutral solutions of zirconium, but not in such as are acid. Separation of Gallium from Uranium (Yellow Uranic Salts) The four following methods are suitable for exact analyses : (A) The hydrochloric solution, slightly acid, is treated at a boil with an excess of cupric hydrate. The deposit contains all the gallium as well as a very sensible portion of uranium. It is redissolved in hydrochloric acid, diluted with water, and boiled in presence of a large excess of cupric hydrate. With from 10 to 15 parts of uranium to 1 of gallium four successive precipitations are required. The uranium is then entirely contained in the liquids, which are acidified, and are then traversed by a current of sulphuretted hydrogen. Copper sul- phide is deposited, and the uranium salt is obtained on evaporating the filtrate. (B) If there is iron to remove along with uranium, it is first reduced by heat with metallic copper, and then boiled with an excess of cuprous oxide. Four successive operations suffice to separate com- pletely 1 part gallium from 10 to 15 parts uranium. The presence of very considerable quantities of alkaline salts does not interfere with 158 SELECT METHODS IN CHEMICAL ANALYSIS the execution of the two methods just described, which may serve for the analysis of a mixture of gallium and of an alkaline uranate. (C) The hydrochloric solution, slightly acid, is mixed with an excess of ammonium acetate, as also a certain quantity of zinc free from gallium, and is then treated with a current of sulphuretted hydrogen. The zinc sulphide carries down the gallium, whilst the uranium re- mains in solution. Only the zinc sulphide, being very difficult to wash, ought to be redissolved in hydrochloric acid and reprecipitated in an acetic solution. The gallium is separated from the zinc, as described below. The uranium is separated by evaporating the liquids with an excess of hydrochloric acid to expel acetic acid, and then destroying the ammoniacal salts with aqua regia. It is essential to add to the liquid so much zinc chloride that the zinc sulphide may carry down all the gallium. Some drops of zinc chloride should be added to the filtered sulphuretted liquids to ascertain the absence of gallium in this last zinc sulphide. Alkaline salts do not interfere with the separation of uranium and gallium by means of zinc sulphide. The present process is suitable for the detection of small traces of gallium in large masses of uranic compounds, especially in presence of metals such as aluminium. But in ordinary cases it is better to make use of the reactions of copper hydrate, or of metallic copper and cuprous oxide. (D) Uranium may be precipitated by a slight excess of caustic potash as an alkaline uranate, scarcely retaining a slight trace of gallium, which may be entirely removed by redissolving in hydro- chloric acid and reprecipitating with potash. The alkaline liquids collected contain all the gallium and traces of uranium. These liquids are slightly supersaturated with hydrochloric acid, mixed with an excess of cupric hydrate and raised to a boil, when the gallium is completely precipitated. In the filtrate, copper, uranium, and potassium are separated by known methods. When the potash employed con- tains a little carbonate (a frequent case), the proportion of uranium not precipitated is sensibly increased. This is without inconvenience, since the separation of the gallium and of the dissolved uranium is effected afterwards by the action of cupric hydrate. Separation of Gallium from Zinc (A) The hydrochloric solution, very strongly acid, is supersaturated with ammonia and boiled till it reddens litmus, the water driven off being replaced. Care must be taken that the liquid when cold does not cease to redden litmus, which will happen if traces of zinc oxide remain unattacked. If the gallium oxide retains a little zinc oxide it is redis- solved by hydrochloric acid in excess, and the boiling with ammonia is repeated. Cupric hydrate separates gallium accurately from zinc. The process is conducted with the aid of heat on principles already SKPARATION OF GALLIUM 159 laid down. In case of need the operation is repeated. When in addition to zinc iron is present in the solution, it is better to reduce with metallic copper and precipitate with cuprous oxide. The separa- tion is as exact as with cupric hydrate. The zinc being much more readily eliminated than the iron, the latter metal is the chief object of concern. (J3) Barium and calcium carbonates precipitate gallium oxide in the cold, but the deposits contain considerable quantities of zinc oxide, especially if barium carbonate has been used. These two reagents can only be employed when it is required to concentrate gallium into a small volume, and cannot, be admitted in an exact analysis. The same observation applies to the precipitation of gallium by calcium carbonate at a boil after sulphurous reduction. There is much zinc in the deposit, however short the boiling has been, especially if the excess of calcium carbonate is considerable. The treatment with calcium carbonate in heat, after reduction with sulphurous acid, though not vsuitable for analysis, is very advantageous for the extraction of gallium from its ores, since by repeating the process two or three times we may eliminate almost all the zinc, the greater part of the iron and many other bodies. Separation of Gallium from Aluminium and Chromium The most convenient process is to precipitate the gallium with ferrocyanide from a very acid hydrochloric solution, containing at least from a fourth to a third of its bulk of concentrated acid. When the gallium is in small proportions (less than Tuinroir)? it must be allowed to stand one or two days for the precipitate to form. It is then received on a filter, and washed with water containing a fourth to a third of its bulk of hydrochloric acid. The filter is dried at a gentle heat and ignited. The result is a mixture of the gallium and iron oxides, which are separated as will be explained subsequently. The almost inevitable formation of a little Prussian blue in the highly acid liquid presents no inconvenience, and merely increases the proportion of ferric oxide to be afterwards separated from the gallium oxide. Ferrocyanide enables us to separate and determine gallium mixed with 2,000 times its weight of aluminium or chromic oxide. Nevertheless, slight traces of gallium diffused among enormous masses of alumina or chromic oxide may escape the action of the ferrocyanide. They are then collected by entanglement in metallic sulphides (those of zinc, arsenic, or manganese) formed in alkaline or acetic solutions. Pre- cipitation with sulphuretted hydrogen in a solution containing ammo- nium acetate, free acetic acid, and arsenious acid seems preferable. The galliferous arsenic sulphide, previously washed with sulphuretted hydrogen water containing a little acid ammonium acetate, is treated with aqua regia, and evaporated almost to dryness in presence of an excess of hydrochloric acid to expel nitric acid. The arsenic acid is 160 SELECT METHODS IN CHEMICAL ANALYSIS then reduced by sulphurous acid or an alkaline sulphite, diluted with water strongly charged with hydrochloric acid, and treated with sulphuretted hydrogen. The precipitated arsenious sulphide is washed with sulphuretted hydrogen water containing hydrochloric acid. The gallium remains in the liquid, and is separated by concentration to a small bulk and boiling, after supersaturation with ammonia. IRON Preparation of Pare Iron (A) The preparation of metallic iron in an absolutely pure state is a problem of enormous difficulty. The British Association appointed a committee, consisting of Sir F. A. Abel, Dr. Forbes, and Dr. Matthiessen, to investigate the subject. The plan finally adopted by the committee was as follows : Pure dried iron protosulphate and pure dried sodium sulphate are mixed in nearly equal propor- tions, and introduced gradually into a red-hot platinum crucible. The mass is kept in fusion until the evolution of sulphurous acid gas ceases. The crucible is then allowed to cool, and the fused mass is extracted with water. If the heat be properly regulated, the whole of the iron is left as a very fine crystalline oxide. This oxide is thoroughly washed by decantation, to remove every trace of the sodium sulphate, and, after being dried, is reduced by hydrogen in a platinum crucible ; the spongy iron thus obtained is pressed into solid buttons by means of a strong coining-press and a diamond mortar, and then melted in lime crucibles, the lime having been previously burnt, slaked, and reburnt, thus forming a fine impalpable powder, which is compressed in the crucible mould. The best method of fusion has been found to be as follows : The lime crucible is placed in a slanting position on a piece of lime. A large oxyhydrogen blowpipe plays on the outside of the crucible, whilst the flame of another is directed inside. When white-hot a cylinder of the compressed iron is thrown into it. It quickly melts, but at the expense of a large quantity of the iron which is oxidised, the amount so lost varying between 25 and 50 per cent. In order to obtain a good solid button of melted iron, it is necessary to cool it in an atmosphere of hydrogen, which is easily obtained by turning off the oxygen from the blowpipe playing inside the crucible. On analysis it was found that buttons so prepared, weighing about 15 grammes each, were free from phosphorus, silicon, and calcium, and only contained sulphur to the extent of from 0-00025 to 0-0007 per cent. (B] Metallic magnesium put into a solution of a proto- or sesqui- salt of iron, causes an evolution of hydrogen, and a precipitation of metallic iron in the pulverulent state. When freed from the saline solution by washing, then dried and compressed, this metallic sponge possesses great brilliancy, and dissolves in acids without leaving any ELECTKOLYTIC DETEKM1NATION OF IKON 161 residue, and without communicating any odour to the hydrogen. As the distilled magnesium of commerce is almost chemically pure, and as ferrous salts of iron can readily be freed from impurities by crystallisa- tion or other means, this affords a good method for obtaining pure iron. The compressed metallic sponge is consolidated, as above described, by heating in lime crucibles before the oxyhydrogen blowpipe. The Electrolytic Determination of Iron l (A) Professor Classen finds that if we mix the solution of a ferrous salt with potassium or ammonium oxalate, there appears a precipitate of ferrous oxalate of an intense yellowish-red colour, soluble in an excess of the reagent with the formation of a yellowish-red double salt. For this operation sulphates are most suitable, chlorides less convenient, whilst nitrates are quite excluded. Ferric salts are not precipitated by the above-named oxalates, but if they are present in sufficient quantity there is formed a solution of a ferric double salt of a more or less distinct green colour. If its solu- tion is submitted to electrolysis, there is first formed a ferrous double salt which is further decomposed with deposition of metallic iron, the green solution becoming first red and then colourless. Hence the de- termination of iron can be effected more rapidly in ferrous, than in ferric solutions. The potassium iron double salt is not adapted for electrolysis because the potassium carbonate formed on the decom- position of the oxalate occasions a precipitate of iron carbonate, in con- sequence of which a complete reduction is impossible. The electrolysis of the ammonium-iron double salt takes place quite smoothly in presence of a sufficient excess of ammonium oxalate without any separation of an iron compound. If the iron solution contains free hydrochloric acid, it is advisable to expel it by evaporation on the water-bath. Free sulphuric acid can be neutralised with ammonia, as the ammonium sulphate formed increases the conductivity of the liquid. Nitrates are converted into sulphates or chlorides by evapora- tion with sulphuric acid or repeated evaporation with hydrochloric acid. For the determination, supposing that 1 gramme iron may be pre- sent in the liquid to be heated, we dissolve about 6 grammes am- monium oxalate in a minimum of water in a platinum capsule with the aid of heat, and add the iron solution gradually whilst stirring. It is not advisable to add the ammonium oxalate to a ferrous solution, as a sparingly soluble ferrous oxalate is deposited which must be con- verted into the soluble double salt by prolonged heating. If there is a ferric salt in solution, it is indifferent whether the ammonium oxalate is dissolved in it, as no precipitate is formed. We dilute with water 1 For details of the manipulation see subsequent chapter. >* 102 SELECT METHODS IN CHEMICAL ANALYSIS to 150-175 c.c. and submit the warm solution to electrolysis. The decomposition is effected with a current of 8 to 10 c.c. detonating gas per minute, increasing it towards the end of the process to 12 or 15 c.c. to promote the separation of the last traces. If a red flocculent ferric precipitate is formed during the electrolysis, we add oxalic acid drop by drop until it is redissolved. For detecting the end of the reaction we take out of the capsule a minute quantity of the decolourised liquid by means of a capillary tube, supersaturate it with hydrochloric acid, and test with potassium sulpho- cyanide. After the completion of the reaction the positive electrode is taken out of the liquid, which is at once poured off, rinsing the capsule three times with 5 c.c. cold water and three times with pure absolute alcohol. The capsule is dried for a few minutes in the air-bath at from 70 to 90 and weighed when cold. The deposit of iron has a shining steel-grey colour, adheres very firmly to the capsule, and may be exposed to the air for days without the occurrence of oxidation. (B) According to experiments in the Munich Laboratory, the solution containing 8 grammes ammonium oxalate, and suitably diluted with water, is electrolysed with a normal density of current (ND 100=0-5 to 1-0 ampere). (C) F. Eiidorff has laid down the conditions under which the precipi- tation of iron is effected from the double ammonium oxalate with Meidinger elements. The solution must not contain more than 0'3 gramme iron. In presence of free acid we add, after previous neutra- lisation with ammonia, 60 c.c. of ammonium oxalate saturated at the ordinary temperature, dilute with water to 120 c.c., and electrolyse with a battery consisting of frcm 6 to 8 elements. As electrodes Riidorff uses a crucible -shaped platinum capsule (CO mm. in height, 75 mm. in diameter at the top, about 40 grammes in weight, and capable of containing 170 c.c. of water). As the positive electrode he uses a thick platinum wire coiled partly in a spiral. The quantitative deposition takes about 14 hours as compared with 4 hours by the former process. (D) According to the experiments of A. Baand the electrolytic precipitation of iron may be effected in a solution containing an excess of sodium pyrosulphate. Ferric salts are precipitated white by this reagent, and give a colourless solution in presence of an excess. Fer- rous salts yield a pale green solution. The solution is rendered alka- line with ammonium carbonate and electrolysed with a current giving from 20 to 33 c.c. of mixed gases per minute. The completion of the reaction is tested with ammonium sulphide. It is necessary to wash without interrupting, as otherwise iron passes into solution. (E) Edgar F. Smith precipitates the iron with a current of 6 to ESTIMATION OF IRON 163 15 c.c. of detonating gas per minute from a solution containing sodium citrate and a few drops of citric acid. (F) According to experiments which Professor Classen made years ago for the separation of iron from the other metals with citric and tartaric acids, metals containing carbon are always obtained in presence of fixed organic acids. Estimation of Iron as Ferric Oxide In most laboratories the flocculent precipitate of hydrated ferric oxide is collected on paper filters a very tiresome operation. In order to collect this precipitate Sergius Kern used a thin platinum funnel. The tube of the funnel is closed by asbestos-wool previously ignited and weighed. The solution is next filtered and the precipitate washed. The funnel is then placed on a sand-bath, and when the precipitate is dry the bottom part of the funnel tube is closed by means of a pla- tinum stopper, and the whole is next ignited and weighed. Knowing the weight of the asbestos and of the funnel, the weight of the ferric oxide may be calculated. In this way the weight of many flocculent precipitates in a dry state may be estimated in a quick and convenient manner. . To dissolve Ignited Ferric Oxide Instead of fusing insoluble ferric oxide with sodium bisulphate, A. Classen prefers to boil it with dilute caustic potash. As soon as the previously pulverulent mass becomes flocculent, the alkaline liquid is decanted off and the oxide dissolved in concentrated hydrochloric acid. Estimation of Iron Protoxide in the Presence of Peroxide (A) Messrs. Wilbur and Whittlesey have carried out a suggestion of A very, 1 and applied it very successfully to the estimation of ferrous and ferric oxides in silicates. Avery found that silica and many silicates can be readily and completely dissolved by a mixture of some normal fluoride with almost any of the stronger acids, whether concentrated or dilute. These chemists have applied this observation to the estimation of ihe two iron oxides, and have obtained such satisfactory results that their process deserves to be generally adopted for the estimation of iron in silicates. The method is as follows: A quantity of the finely powdered silicate to be examined is weighed in a platinum crucible ; as much, or rather more than as much, powdered fluor spar (or pow- dered cryolite), free from iron, is poured into the crucible ; the powders are thoroughly mixed by stirring with a glass rod ; the rod is wiped clean upon a fresh portion of the powdered fluoride ; and the latter is thrown upon the mixture in the crucible. Strong hydrochloric acid iu 1 Chemical News, xix. 270. 164 SELECT METHODS IN CHEMICAL ANALYSIS then poured into the crucible, until the powder is thoroughly drenched and the crucible about two-thirds filled with the liquid. The crucible is set upon a water-bath, and heated until the iron has all dissolved ; the proportion of iron is finally determined by titrating with a standard solution of potassium permanganate. To protect the mineral from the air during the process of solution, the crucible must be kept full of. some non-oxidising gas, which can be either carbonic acid or coal gas y as may suit the convenience of the operator. If carbonic acid be used, it is sufficient to cover the crucible with a bit of sheet-lead, perforated with two holes, through one of which is thrust a glass tube communicating with a gas -bottle in which the carbonic acid is generated, while the other serves as an outlet for the escape of carbonic acid and acid vapours. The crucible is, in this case, simply set upon an ordinary water-bath. When coal-gas is used (and this agent is to be preferred on the whole), the apparatus may be arranged as follows : Set the charged platinum crucible upon a glass or leaden tripod, inside a wide beaker, in the bottom of which there is about an inch of water. Invert a narrower beaker within the first, so that its mouth shall be sealed by the water and the crucible be enclosed in a transparent chamber. Coal-gas is led into the chamber through a bent glass tube, which passes down between the side of the upright and that of the inverted beaker, and delivers the gas near the top of the chamber. The surplus gas escapes through another tube similarly bent, which starts from a point below the crucible, and is burned in the outer air. To facili- tate the passage of the glass tubes, the mouth of the inverted beaker may be made to rest upon three or four bits of stone or metal, or an orifice large enough to admit the tubes may be made upon the rim of the beaker. During the process of solution, the upright beaker is kept immersed in water, at or near the temperature of boiling. In case the coal-gas should contain any sulphuretted hydrogen, it would be well to purify it by means of a potash-tube. An hour and a half is ample for the solution of the iron in 0'5 1 gramme of finely powdered trap rock. Fifteen minutes, on the other hand, will suffice for the solution of 0'2 gramme of iron wire. Instead of hydrochloric acid, sulphuric acid may be used to act upon the mixture of fluor spar and mineral. The calcium sulphate frequently formed is objectionable, from its liability to envelope portions of the mineral and so protect the iron from being dissolved, rather than from any tendency to inter- fere with the actual titration. Experiments have shown that the presence of iron sesquioxide does not interfere in any way with the estimation of the protoxide. Com- mercial iron-alum, which of itself has no decolourising action on potas- sium permanganate, has none after it has been heated with cryolite and hydrochloric acid. It is found, also, by acting upon weighed quantities of iron wire mixed with cryolite and iron-alum, that the ESTIMATION OF IRON 165 iron can be estimated as well in the presence of the alum as in its absence, provided only that the metallic iron be dissolved in hydro- chloric acid, with the necessary precautions to prevent oxidation, before adding the other ingredients of the mixture. If the iron wire, cryolite, and ferric alum were treated all at once with acid, some of the hydrogen generated by the solution of the metallic iron would reduce a part of the ferric salt ; so that, in the final titration, more iron would be found than was introduced into the mixture in the form of wire. If time enough be allowed, finely powdered iron sesquioxide.can be dissolved in this way, even after intense ignition. To estimate iron sesquioxide in a silicate, a separate portion of the mineral may be treated with fluor spar and acid, the solution reduced by zinc in a small flask in the usual way, and the total amount of iron determined with permanganate. Or, if the mineral contains only a small proportion of ferric oxide, it will be sufficient to put a bit of ziiiG into the crucible with the mixture of mineral, fluor spar, and acid. The difference between the total iron and that determined as protoxide is calculated as peroxide. (B) A. H. Allen has pointed out bhat a little irregularity in the results of the above process arises from the employment of hydrochloric acid as a solvent. It has been repeatedly shown that the presence of hydrochloric acid interferes appreciably with the estimation of iron by permanganate, while it does not affect Penny's bichromate process. If the former oxidising agent be employed, the solution should be effected by means of sulphuric acid. Mr. Allen effects solution of difficultly soluble ores by heating with hydrochloric acid under pressure. This method has been used very successfully in the analysis of various titanic iron ores and sands. About a gramme of the finely powdered mineral is heated in a sealed piece of combustion-tubing, half full of fuming hydrochloric acid. At first the heat of a water-bath is sufficient, but after a few hours the temperature is gradually raised to 140 or 150 (X The ore is completely decomposed in four or five hours, and after the tube has cooled the end may be broken under v ater, and the ferrous oxide at once estimated by bichromate. The same method will yield a solution suitable for the determination of the other constituents of the ore. Reduction of Sesqui-Salts of Iron to Proto-Salts Sulphurous acid or metallic zinc is the reducing agent usually employed, but a much more effectual and rapid agent has been pro- posed, in sulphuretted hydrogen, by Mr. Reynolds. This answers much better than either zinc or sulphurous acid. The reduction, even in a strongly acid solution, takes place immediately, and on boiling until the sulphuretted hydrogen is expelled, the sulphur separated coagulates completely ; so that, after allowing the solution to cool in the flask in 166 SELECT METHODS IX CHEMICAL ANALYSIS which it has been boiled, a cork being placed in the neck during the cooling, filtration may be effected so rapidly that no oxidation need be feared, and the determination may then be effected with permanganate,, as usual. It is better to add a considerable quantity of water to the solution before reduction, to avoid the oxidation which would afterwards ensue in the filtration of a concentrated solution of iron protoxide. Gravimetric Estimation of Iron Mr. C. F. Cross calls attention to the following facts in connection with this subject : (1) That ferric oxide, when precipitated in presence of salts of the fixed alkalies, removes a certain quantity of the latter from solutions, this quantity being within certain limits independent of the amount of alkaline salt present in solution, but varying with the temperature of the solution at the time of precipitation, being much greater in the case of cold than of hot solutions. (2) That the error due to the retention of alkaline salt may, by persistent washing with boiling water, be reduced to a minimum, but not completely eliminated. (3) That the error is very much greater when the oxide is precipi- tated by excess of alkali in presence of salts of the alkaline earths ; but that the latter may be effectually separated from iron by preci- pitating this metal in the form of the basic acetate. (4) That ferrous sulphide does not exert this adhesive action upon salts in solution, and is, therefore, where the circumstances of the analysis permit, the best form in which to separate iron from the other metals which accompany it. Volumetric Estimation of Iron by Sodium Thiosulphate M. Mohr has shown that the direct estimation of iron perchloride, by means of a solution of sodium thiosulphate, does not give satisfactory results. The cause of error lies chiefly in the decomposing action exercised by free hydrochloric on thiosulphuric acid. By using sufficiently dilutedv acetic instead of hydrochloric acid, or by treating the weak hydrochloric solution with sodium acetate, it will be found that the thiosulphuric acid is not decomposed, even after some length of time. Consequently, a solution of iron perchloride may be estimated by means of a thiosulphate solution, taking care to add previously sufficient sodium acetate to make apparent the red colour of the ferric acetate, and then sufficient weak hydrochloric acid to make this colour again disappear. Then pour into the solution a known quantity of thiosulphate, and estimate the excess of this re- agent, which colours the liquid a deep violet, by means of starch paste and iodine solution. Very exact results are obtained in this way ; but care must be taken VOLUMETRIC ESTIMATION OF IKON 167 to use liquids not too much diluted ; 0'00012 gramme is the minimum amount of iron which should be contained in 1 c.c. One equivalent of iron perchloride decomposes exactly two equiva- lents of sodium thiosulphate. Volumetric Estimation of Iron with Copper Subchloride Copper subchloride has been found by Dr. Winkler to be a very powerful reducing agent for iron sesquioxide, analogous to tin proto- chloride in its effects. But whilst tin protochloride causes but a partial reduction in a cold solution, copper subchloride acts directly with theoretical accuracy at the lowest temperature, and at any dilu- tion. It is, therefore, particularly adapted for the volumetric deter- mination of iron. The completion of the reduction may be ascertained with certainty by the addition of a few drops of potassium sulphocyanide to the solution to be tested, when the well-known deep-red colour appears. When the subchloride solution is dropped into one of iron so coloured, the red colour becomes lighter and lighter, and finally dis- appears entirely. After the solution is bleached, the reduction of the iron is complete, and the next drop of copper solution causes a preci- pitation of copper subsulphocyanide. This gives a double indication of the end of the reduction, namely, the bleaching of the red colour of the iron sulphocyanido, and the cloudiness produced by the insoluble copper salt. The rapidity and simplicity of the process, as well as- the few accessories required, especially recommend this method to technical laboratories, where the want of a short and accurate process has long been felt. The solution of copper subchloride is made by dissolving sheet - copper in nitric acid ; evaporate to drive off the excess of nitric acid, and dissolve the residue in water containing hydrochloric acid. This solution is put into a flask, and a quantity of common salt equal in weight to the residue of dry copper-salt is added, in order to prevent the separation of a precipitate of copper subchloride during the subse- quent reduction. Several pieces of sheet-copper are put in the flask, and the liquid is then heated to boiling. This is continued until the solution is nearly colourless, and all the copper chloride has been changed to subchloride. The flask is then corked, and allowed to- cool ; the solution is then diluted with water containing hydrochloric acid, until 1 c.c. corresponds to 6 milligrammes of iron. In order to keep this solution without change for further use, it should be poured into a bottle, to which is fitted an air-tight stopper, and containing a spiral of thick copper wire reaching from .the bottom to nearly the neck. This completely protects the copper subchloride from oxidation, so that the strength of the solution remains nearly always the same. It is, however, best to determine the strength of the standard from time to time, since this requires but a few minutes. For this purpose, 168 SELECT METHODS IN CHEMICAL ANALYSIS there is needed a solution of iron sesquichloride of known strength. This may be made, according to Fresenius, by dissolving in hydro- chloric acid and potassium chlorate 10*03 grammes of piano -wire, corresponding to lO'O grammes of pure iron, and diluting to 1 litre. For each test of the standard 10 c.c. of this solution are taken, con- taining 100 milligrammes of iron. In performing this volumetric determination of iron, there are but few rules to be observed. It is advisable that the solution to be treated be decidedly acid, and very dilute, before it is brought under the burette. A solution that contains from 100 to 200 milligrammes of iron should be diltited^to 500 c.e. or more. In looting the end of the reduction, though it is not necessary that the solution of potassium sulphocyanide should contain a known amount of this salt, yet it will be found better to use about the same strength at all times, since the presence of too much sulphocyanide makes the reaction less marked. In adding the sulphocyanide, care must also be taken ; for, if too much is added to the iron solution, although a deeper blood-red will be obtained, yet a difficultly soluble copper subsulphocyanide may separate, clouding the solution and redissolving with trouble. Four or five drops of solution are quite sufficient to be added. Then, by dropping in the copper solution, the bleaching takes place with extraordinary sharpness, and only when all the iron has become a protoxide does the next drop cause a permanent cloudiness. The presence of coloured metallic compounds (such as cobalt, nickel, and copper salts) does not in the least hinder the recognition of the reactions, if the solution is properly dilute. Neither does the presence of arsenic acid affect the process, since this is not reduced by copper subchloride. This process, therefore, is important to the metallurgist, who is often compelled to determine quickly and correctly the amount of iron contained in a matt, or speiss, or other product. By the above process this is possible in an hour. Volumetric Estimation of Iron with Potassium Permanganate (A) J. Krutwig and A. Cocheteux find that the permanganate pro- cess (Margueritte's) may be safely used in presence of hydrochloric acid if the following precautions are observed : 1. If possible, dissolve the ore in very little sulphuric acid. 2 Reduce by means of zinc in the hydrochloric solution. 3. Add a quantity of sulphuric acid twice as great as that of the hydrochloric acid. 4. Dilute the solution to about 300 c.c. 5. Use dilute permanganate in titration. (B) To ensure accuracy in this estimation, M. Moyaux has drawn up certain memoranda which deserve attention in order to secure uni- VOLUMETRIC ESTIMATION OF IKON 109 formity of result. The titration of the permanganate solution can only be properly made by means of metallic iron, and, when the latter metal, in a sufficiently pure state for this purpose, is not at hand, oxalic acid should be employed. The use of iron ammonio-sulphate for obtaining the standard should be rejected. Unless the precise composition of this salt is repeatedly ascertained, it is not to be relied on, and this testing is a loss of time. The evaporation of solutions of iron containing hydrochloric or other volatile acids, after the addition of sulphuric acid, always impairs the result of the titration. The reduction of solutions of iron per-salts to proto-salts, after driving off excess of hydrochloric acid, is best effected by amalgamated zinc if zinc is used at all, but this last metal is to be rejected when a solution of iron happens to contain, at the same time, a proto- and a per-salt. When 0-3 gramme of ore is taken for assay, in case the ore contains more than 40 per cent, of metallic iron (or, when less than that quan - tity, 0'5 gramme is taken for assay;, the quantity of fluid best suited to yield accurate results should not, in either of these cases, respectively exceed -J or a litre. (C) Mr. E. Hart considers that by far the best method of estimat- ing iron volumetrically is by potassium permanganate after previous reduction of the ferric to a ferrous compound. The difficulty en- countered is how to perform this reduction in the best, quickest, and cheapest manner. The best and most complete method of reduction is that by hydrogen, in a porcelain tube, at a red heat. To make the reduction complete it is necessary to pass the gas over the heated ore lor three hours. Not more than 0'3 gramme of the ore should be taken, otherwise at the end of the time specified the reduction will be found to be incomplete. The ore is weighed out in platinum boats, four of which may be placed in the tube and reduced at once. The tube is allowed to cool while the hydrogen is still passing, the boats removed, and carefully dropped into flasks containing hot dilute sul- phuric acid. The flasks are closed with doubly perforated corks, and a current of hydrogen is passed into them while the iron is dissolving. When the solution is complete the flasks are plunged into cold water (hydrogen being still passed into them) and allowed to cool completely, and are then titrated in the usual way. Coal-gas cannot be used in place of the hydrogen, as some of its constituents dissolve in the hot acid and exercise a reducing action on the permanganate. With a great many ores, especially limonites, the reduced iron dissolves with great difficulty, sometimes not at all. (D) This difficulty has been overcome by Dr. T. N. Drown, who passes oxygen or air over the heated ore for half an hour before reducing. The carbonaceous matter is in this way destroyed, and the reduced iron is found to dissolve with the greatest ease. Almost all the magnetites when dissolved in acid leave a resi- due containing iron. The iron in this residue is not reduced by the 170 SELECT METHODS IN CHEMICAL ANALYSIS hydrogen when the iron is determined as above. In this respect, how- ever, the process is neither better nor worse than those ordinarily used. There are only two valid objections against this method. The first is, the gas consumed, which makes it costly; the second, the time required from four to six hours. (E) To estimate iron very rapidly, with a reasonable degree of accu- racy, no process has given better results than that by the reduction of the hydrochloric solution of the ore by stannous chloride. The ore is dissolved in hydrochloric acid in a beaker, and evaporated nearly to dryness. The solution is then diluted with a little water, and an excess of stannous chloride run in from a burette. After the fluid has lost colour a little starch solution is added, and iodine solution run in from another burette until the blue iodide of starch remains permanent. It is found best to have the iron solution rather concentrated and warm. One c.c. of the stannous chloride solution is equivalent to about O012 metallic iron and 3 c.c. of iodine solution. The stannous chloride works best when freshly prepared. Four samples have been weighed, dissolved, reduced, and titrated in an hour and twenty minutes. In a second trial, with four more samples, the same time was taken. In both cases the solutions were standardised while the ore was dissolving. This gives an average of twenty minutes required for one determination, which is all that could be desired. It is best to standardise the stannous chloride solu- tion by means of metallic iron. This is dissolved in hydrochloric acid and a few pieces of potassium chlorate added ; after which the solution is evaporated nearly to dryness. By this means every trace of free chlorine seems to be expelled. A solution of ferric chloride, when freshly prepared, is reduced almost immediately upon the addition of the stannous chloride. After standing some time, however, it is more slowly reduced, and seems to require less tin solution. (F) Messrs. W. F. Stock and W. E. Jack make the following remarks on the working of the stannous chloride process. They find certain objections presenting themselves viz. the liability to add excess of stannous salt, and the want of suitable means to prevent such excessive addition ; but by the method given below, these objections no longer hold good. In this process 1 gramme of ore is dissolved in 30 c.c. of strong hydrochloric acid, and, if not decomposed by hydrochloric acid, it is first fused with an alkaline carbonate, and brought into hydrochloric acid solution ; in either case, the solution is made up to 500 c.c. with dis- tilled water and caused to boil. The stannous chloride may now be added in small portions at a time, but it must be in dilute clear acid solution, a convenient strength containing 10 grammes of tin per litre. The colour of the ferric solution is a fair guide to the addition of the tin-salt within certain limits ; but when the colour becomes faint some other indicator must be used, and this we find in a dilute, recently pre- VOLUMETRIC ESTIMATION OF IRON 171 pared solution of potassium sulphocyanide, which is disposed in drops- over the surface of a white tile. Special care must be taken to add the trial drops of iron solution quickly to those on the tile, and to have the beaker containing the solution in pretty close proximity to the tile, so- as to guard against oxidation of solution on the glass rod with which the test drops are added. The reduction is carried so far that only a, faint tinge of pink is produced when the last addition of tin-salt has- been made and allowed to boil for a few moments. The next step is the titration with potassium bichromate ; and, as a vital part of the process, make the preliminary addition of three drops of bichromate (standard solution 1 c.c.=O01 gramme iron), then test with potassium sulphocyanate. A distinct access of colour in this test, as compared with the last test made in reducing, is accepted as proof of the absence of stannous salt, and it only remains to complete the assay in the usual manner. (G) M. A. Eilmann points out that coaly matter and iron sulphide act during the estimation like iron proto- salts and cause high results. Massive iron pyrites is only slightly decomposed, but it is very pro- bable that the form of pyrites occurring in iron ores, similar to coal brasses, is attacked by acid solutions of iron perchloride at the boiling temperature. All alkaline and earthy sulphides, most varieties of iron sulphide, zinc, lead, cadmium, &c. sulphides, and, difficultly, copper sulphides are decomposed in this manner. If we boil the finely powdered ironstone with dilute hydrochloric acid, invariably filter off the insoluble matter, and determine the iron by the bichromate method in a solution, warm, and not boiling, all difficulties vanish. A fresh portion, calcined, and fused with potassium bisulphate, gives the total iron in a form soluble in hydrochloric acid. It is invariably found that fusion with bisulphate is capable of freeing siliceous matters from iron in less time and at lower temperatures than fusion with alkaline carbonates. Reduction of iron peroxide by stannous chloride seems objection- able where there is organic matter present. In the first place it must be done in a highly concentrated acid solution, when each drop taken out to ascertain the progress of the reduction represents a notable quantity of the substance under examination ; and secondly, it is diffi- cult to remove excess of the reducer. A much more preferable plan is the addition of ammonia and ammonium sulphide in excess, then ebullition with excess of hydrochloric acid to expel the sulphuretted hydrogen, then filtration from sulphur. This does not take a long time, and is very exact. Titration of the iron by bichromate at the boiling temperature is quite unnecessary if a little time is allowed for the reaction ; if the temperature be not high, the oxidation seems to take an appreciable time, and may therefore lead to a false estimation. A cold solution may indeed be used, if the final reactions be not too hurriedly noted, 172 SELECT METHODS IX CHEMICAL ANALYSIS while at a warm temperature the organic matter dissolved from the coaly matter of an ironstone does not interfere. Immediate Analysis of Meteoric Iron The numerous researches hitherto made with regard to the com- position of meteoric irons have demonstrated the existence of the following compounds in these extra-terrestrial bodies : 1. The general mass, which is formed by the union of several alloys in which iron and nickel are predominant, and which we will designate under the name of nickehferous iron. Among the substances com- prised in this mass, kamacite, tcenite, and plessite are specially notice- able. 2. The carburetted iron, comprising campbellite and chalypite, recognisable by the carboniferous deposit which they give under the action of acids. 3. Sulphuretted iron, or troilite, which appears in nodules and in veins. 4. Iron and nickel phosphide, or Schreibersite. 5. Graphite. 6. External crust. 7. Stony particles, or crystals. 8. Gases retained by occlusion. 9. Several compounds which are only met with exceptionally, as chromite and iron protochloride. (The last may indeed have a terrestrial origin, according to the opinion of Mr. Shepard.) M. Stanislas Meunier, Aide-Naturaliste at the Museum of Paris, has tried to separate these different substances, and has submitted each of them to a special examination. His experiments, which have resulted in fixing their chemical formulae, were communicated to the Chemical News, and are given in abstract in the following pages. I. Nickeliferous Iron, The first problem to be solved is the separation of the different alloys which are mixed in the general mass of meteoric irons ; but it is necessary first of all to prepare that general mass free from other substances already named. For this end, the iron being reduced to powder by means of a hard file, the metal is thrown into pure potash, in a state of fusion, in a silver crucible. Instan- taneously the alkali, hitherto limpid, becomes turbid, owing to the presence of little grey flakes, which consist of iron oxide, and are the result of decomposition of troilite, schreibersite, stony matters, &c. When this decomposition of foreign substances is complete, the alkaline mass is cooled and treated with water. All the potash is washed away with the greater part of the iron oxide. The remainder of this oxide is easily dissolved by strong nitric acid, in which the metallic iron becomes passive. The metallic powder is then well washed and dried ; ANALYSIS OF METEORIC IRON 173 it is formed exclusively of nickeliferous iron, containing, however, in certain cases, a small proportion of carburetted iron. Chemical methods have not yet completely succeeded in separating the alloys mixed in the nickeliferous iron, and, after several attempts, M. Meunier was obliged to have recourse to physical processes. His experiments have been made with the meteoric irons of Caille (France),. and of Charcas (Mexico). It was necessary, first of all, to estimate with accuracy the number of constituent compounds contained in the nickeliferous iron of these masses. For this purpose a small polished plate of the iron of Caille was carefully and uniformly heated. This operation, of which the first idea is due to Widmanstatten, drew, by the unequal oxidation of the different immediate principles, a yellow net upon a blue ground. There were also several portions of an intermediate colour, clearly limited like the others, and occupying the spaces bounded by the crossing of the yellow lines. An attentive examination showed that the three metallic compounds were reducible to two ; the third being formed by the mixture of the others, reduced to alternate thin sheets. The blue colouration is formed by kamacite, and the yellow by taenite. Their separation was very difficult, on account of the analogy of the chemical properties of the two minerals. Although it is true that kamacite is more soluble than taenite (and this is proved by the experi- ments of Widmanstatten), this difference is too small to permit of a separation. When all the kamacite is dissolved, only a very small proportion of taenite remains, the greatest part being dissolved also. To effect the separation, some metallic powder was heated upon a glass plate. The particles formed by kamacite became blue, whilst the particles of tsenite were yellow. The two sorts of grains were then separated with pincers. After about fifteen operations, 2 grammes of kamacite and 0-5 gramme of tsenite were collected fit for chemical examination. The Charcas iron gave the same results. The specific gravity of taBnite is 7'38. Its analysis yielded the: following numbers : Iron . . ... ... . . . .... . 85-0 Nickel . ."..,.. ... :'. ... :. ;.. : . s ... . '..-. . . 14-0 99-0 which agree with the formula Fe 6 Ni. Kamacite has a specific gravity of 7'652, and its composition was found to be Iron 91-9 Nickel 7-0 98-9 agreeing with the formula Fe 14 Ni. On this subject it will be remarked that, admitting, according to> 174 SELECT METHODS IN CHEMICAL ANALYSIS the numbers given above, that the Cattle iron contains 80 per cent, of Itamacite, and 20 per cent, of tsenite, its elementary formula will be expressed by Fe 6 Ni + 4(Fe 14 Ni)=Fe 62 Ni 5 , which gives numbers very near those which M. Eivot obtained in the elementary analysis of that mass. The above formula gives Iron 91-4 Nickel 8-6 100-0 "Whilst M. Rivot found, in two analyses Iron 92-3 . . . 92-7 Nickel 6-3 ... 5-6 98-6 98-3 All meteoric irons are not so simple as those of Cattle and of Oharcas. There are some which contain, with kamacite and taenite, a certain quantity of other metallic alloys. One of the most important of these is plessite, which abounds, for example, in irons of Jewell Hill (North Carolina) and of Oldham (Kentucky). This has been isolated by the same method which served for the preceding substances. Plessite has a density of 7*85, and its composition appears to be satisfactorily represented by the formula Fe 10 Ni. Amongst the other alloys of iron and nickel may be mentioned cctibbehite, whose composition is exceedingly remarkable, owing to the large proportion of nickel (59*6 per cent.) it contains. Its density is only equal to 6'854. The meteoric iron of Octibbeha (Mississippi) seems to be entirely formed of that alloy, according to the researches of Mr. Taylor. II. Carburetted Iron. Several meteoric irons give, by the action of acid, a black deposit, more or less abundant, consisting of carbon. This carbon comes from a compound whose position is analogous to that of steel. In this point of view, the meteoric iron of Campbell (Tennessee) may be specially mentioned. It gives, on analysis, a metallic substance, formed by the union of 1-5 per cent, of carbon with 97*54 per cent, of iron. For it the name of campbellilj may be proposed ; its density is 7*05. Mr. Shepard gives the name of chalupite to an iron carbids which Forchhammer has detected in the meteoric iron of Niakornak (Greenland), and of which the formula is CFe 2 . III. Sulphuretted Iron. To obtain the sulphuretted iron, or troilite, in a complete state of purity, we may have recourse to the metallic powder. This powder is placed for a quarter of an hour in a boiling concentrated solution of copper sulphate. All the nickeliferous iron is dissolved, and, by decanting and washing, a mixture of metallic ANALYSIS OF METEORIC IRON 175 copper, troilite, schreibersite, graphite, and stony matter may be obtained. A small quantity of concentrated nitric acid dissolves the copper. The magnet, acting under water, is the best means to separate troilite and schreibersite (which are magnetic) from graphite and stony matter. Finally, lixiviation can be employed to separate troilite from schreibersite. When the iron under experiment contains only a small quantity of troilite, it is preferable not to use nitric acid, which always dissolves a little of the desired substance. In such cases the nickeliferous iron may be dissolved by means of mercury bichloride. The mercury proto- chloride is carried off by a solution of chlorine, and it is easy to separate the metallic mercury. It is, however, always better, when possible, not to extract troilite from the iron, but from the cylindroid nodules in which the substance has concentrated. In these, sulphuretted iron contains only some graphite and stony matter, which can be got rid of by the action of the magnet. There is no doubt that this troilite is one of the most characteristic principles of meteoric iron. Notwithstanding this, its crystalline form has not yet been recognised, and there is some doubt about its chemical composition. The first chemists who examined it considered it as a variety of Breithaupt's pyrrhotine, and gave to it the formula Fe 7 S 8 . But Professor Lawrence Smith concluded from his estimations of the sulphur in the iron of Tazewell, that it had the com- position of a protosulphide, FeS. Notwithstanding this, he continued to give it the name of pyrrhotine, and thus a great confusion was intro- duced into science. Moreover, Professor Smith rested both upon the results of his own experiments and upon those obtained by several chemists in the examination of other samples of troilite ; his conclusion was not admitted, and the existence of true crystalline magnetic pyrites in meteorites will increase the difficulties. The distinction between the troilite (or Professor Smith's pyrrhotine) and Breithaupt's pyrrho- tine, is not so clear as would appear at first sight. The difference of composition is very slight, and the physical properties are very similar. M. Meunier has lately had occasion to analyse several specimens of troilite taken from the meteoric irons of Charcas and of Toluca (Mexico), and the numbers which he has obtained have given him reason to think that the mineral in question is nearer to magnetic pyrites than to iron protosulphide. Before giving the results of these analyses, we may call attention to a reaction which seems calculated to permit in all cases of the distinguishing of the iron protosulphide from magnetic pyrites, and, d fortiori, from compounds which are still richer in sulphur. When iron protosulphide is placed in a solution of copper, it precipitates this metal almost like iron itself; pyrrhotine, on the contrary, produces no such precipitation. The protosulphide obtained by the action of 176 SELECT METHODS IN CHEMICAL ANALYSIS ammonium sulphide upon iron salts produces the same effect as the sulphide of exactly the same composition prepared by igneous means. This being well established, several samples of troilite were put into a solution of copper, and no precipitation could be observed ; troilite, therefore, is very like magnetic pyrites in this respect, and we may draw the same conclusion as to its chemical composition. In fact, Professor Smith has based the formula FeS upon his analysis of Tazewell's troilite, which gave him Iron 62-38 Nickel .... ...'... 0-62 Copper trace Lime 0-08 Silica 0-56 Sulphur 35-67 99-31 But these numbers show that the substance employed in his experi- ments was very impure. Troilite purified by the process described above yielded a substance of which the specific gravity was 4-799. Its colour was bronze, and its analysis gave Iron . . . . . 59-01 Nickel ... 0-14 Copper . trace Sulphur . 40-03 99-18 The formula Fe 7 S 8 requires Iron 60-4 Sulphur . 39-6 100-0 The Charcas troilite, previously purified, yielded Iron 56-29 Nickel 3-10 Sulphur 39-21 98-60 Its density is 4 '78. The normal presence of nickel makes troilite a species distinct from pyrrjiotine, and its true formula becomes (FeNi) 7 S 8 . IV. Schreibersite. Schreibersite, or iron and nickel phosphide, may be prepared by the same method as troilite. It is, besides, always preferable to select the schreibersite in the places where it is naturally concentrated. It is a yellowish, or almost white, metallic- looking substance. Its specific gravity is 7'10B, and it contains ANALYSIS OF METEOKITES 177 Iron . 57-11 Nickel 28-35 Cobalt trace Magnesium . . . trace Phosphorus 15-01 100-47 numbers which lead to the formula Fe 4 Ni 2 P. Schreibersite is mag- netic, and takes permanent polarity by contact with a magnet. It is brittle. Hydrochloric acid has no action upon it. Its crystalline form has not yet been observed. V. Graphite. Graphite may be isolated by the following method : A few grammes of metallic powder are projected into fused potash, and thus a mixture of nickeliferous iron and graphite is obtained. This mixture may be treated in several ways. 1st. The iron is dissolved in hydrochloric acid, which leaves the almost pure graphite as residue. 2nd. The graphite is separated by lixiviation. This process presents the advantage of giving both graphite and nickeliferous iron ; but the separation is never complete. 3rd. When the graphite is abundant the magnet may be employed ; in other cases it is drawn up with the metal. In all cases the residue is washed by hydrochloric acid to dissolve foreign matters, such as troilite and schreibersite, or what is left after attacking with fused alkali. The graphite extracted from the Caille iron has a specific gravity of 1*715. Its analysis gave Carbon 97'3 Iron . ' . . 2-4 Nickel . . . ... " . . . . trace 99-7 The graphite of the Charcas iron has a density of 1-309, and yielded on analysis- Carbon 98-0 Iron 0-9 98-9 The graphite is remarkable on account of its great unalterability. VI. External Crust. Those portions of meteoric iron upon which is a crust, being separated by means of a saw, are placed^in a concentrated solution of mercury bichloride. After a sufficient time all metallic particles are dissolved, and the oxides, amongst which is the crust, remain alone. The crust is, however, still mixed with foreign matters. It usually contains with it the products of its alteration by atmospheric agents, N 178 SELECT METHODS IN CHEMICAL ANALYSIS and particularly limonite. Some schreibersite, troilite, and stony grains may also be mixed with the principal substance, and their separation is very difficult. Weak hydrochloric acid carries away limonite and troilite ; earthy particles remain as residue after the action of the magnet ; lixiviation permits of the purification of the crust from schreibersite. These operations may, however, be simplified by choosing those portions of the crust that seem almost pure. They frequently detach themselves from the subjacent metallic matter. Very few chemists have analysed the external crust of meteoric irons. The analyses given by Pugh, as showing the composition of the crust of the Toluca iron, were evidently executed on an impure portion. These are Pugh's results : Metallic iron 18-717 1 Iron protoxide 19'309 Iron sesquioxide ......... 32-750 Nickel and cobalt protoxides 5*751 Chalk trace Silicates . . . . 10-203 Water 13-270 Chlorine trace 100-000 The metallic iron, silicates, and water are evidently not essential elements of the crust, and must be considered as impurities. Having purified as much as possible by the method above described the crust of the Toluca meteoric iron, M. Meunier found it possessed a density of 4-89, and the following composition : Iron sesquioxide 68-93 Iron protoxide 28-12 Nickel protoxide . 2'00 Cobalt protoxide trace 99-05 These numbers agree with the formula Fe 2 3 , (FeNi) 0, which docjs not differ from that of magnetite, except by. the substitution of a small portion of nickel for a corresponding quantity of the iron of the protoxide. If in Pugh's analysis we only consider iron sesquioxide, iron protoxide, and nickel and cobalt protoxide, we arrive at numbers very near to those required by the above formula. VII. Stony Grains. Several of the operations described above evidently yield the stony grains in a state of purity. But when it is especially intended to obtain these grains, they should be separated in the following way : The meteoric iron in the form of lumps is left protected from the contact of the air in a concentrated solution of mercury bichloride, and frequently stirred. After a sufficient time the metal disappears, and ANALYSIS OF METEOEITES 179 the liquid contains the stony particles mixed with mercury proto- chloride, and generally with a small quantity of metallic mercury, besides troilite, schreibersite, and graphite. A solution of chlorine carries off the calomel, and the magnet removes the schreibersite and the troilite ; lixiviation may be employed to get rid of the graphite. These grains are of different composition, and it appears that there exists a certain relation between their composition and their situation. Some are localised in the iron ; others are situated in the troilite, or, perhaps, in the graphite which surrounds this sulphide. The grains of the first category may be found in meteoric irons of Tazewell and of Tuczon. They consist of peridot, and this is con- firmed by the analyses published by Mr. Lawrence Smith. Their density is equal to 3'35. The grains of the second category are yielded by the troilite of the Caille iron. Submitted to blowpipe assay, they only exhibit the reaction of silica. The troilite of Charcas iron gave analogous results. VIII. Gases. Gases have been recognised in the meteoric iron of Lenarto, by Mr. Graham and by M. Boussingault. M. Meunier has sought for the same bodies in another iron of the same origin by effecting the solution of those masses in concentrated mercury bichloride. As, however, he was not aware that the occluded hydrogen would be all absorbed by the solution of mercury bichloride, reducing it to the state of calomel or metal, he erroneously considered that the absence of visible gas proved that there was no gas occluded. The mass of Krasnoyarsk (Siberia) gave a small bubble of gas, having the composition of atmospheric air ; but it must be remarked that this iron was cracked: IX. Rare Substances. In concluding this enumeration, chromite and iron protochloride must be mentioned as having been found in certain irons. Their separation is evidently easy, and their composi- tion is identical with that of analogous terrestrial compounds. After having described the methods which have permitted him to separate in a state of complete purity the immediate principles of meteoric irons, M. Meunier remarks that these methods can be employed to estimate the relative quantity of the substances in question. He has, for instance, submitted to a quantitative immediate analysis the meteoric iron discovered in 1784, at Xiquipilco, in the valley of Toluca (Mexico), and has found in it Nickeliferous Iron . ,.. - . . . '. 96-301 Graphite . . . ... . ... . M76 Troilite . . . . . . . . . t . . ' . T482 Schreibersite 1-232 100-191 N2 180 SELECT METHODS IN CHEMICAL ANALYSIS Preservation of Iron Proto- Salts Iron protosulphate may be preserved from oxidation by placing with it a piece of camphor wrapped in clean dry paper. Iron protochloride may be obtained pure by evaporating the fresh solution almost to dryness, and adding powdered iron and strong hydro- chloric acid in the proportion of one part of the former to five of the latter ; the mixture is then evaporated to dryness with continual stir- ring by an iron spatula. The nascent hydrogen evolved effectually reduces all the sesqui- to the proto-chloride, and the dry salt will keep for a considerable time. Separation of Iron from Aluminmm (A) Wohler's process, which we have used with success for many years, is to neutralise the very dilute solution of these two bases with sodium carbonate, then add sodium thiosulphate, and, finally, heat till no more sulphurous acid is disengaged. In this manner al] the alumina collects together into a precipitate, which may be calcined. The iron remains in a liquor, which should be concentrated and then decom- posed with potassium chlorate and hydrochloric acid. After filtration to remove sulphur, precipitate the iron sesquioxide by ammonia. (B) When the iron is in large excess, sodium thiosulphate does not completely precipitate the aluminium. E. T. Thomson finds that when the iron and the aluminium are in the proportion of 100 to 1, only about 90 per cent, of the aluminium is precipitated by thio- sulphate. (C) M. Vignon adds to the dilute solution an excess of trimethyl- amine, and filters after twenty-four hours. All the ferric oxide remains on the filter, whilst the alumina passes into solution. Chromium oxide may be separated from iron in the same manner. (D) Add to the cold, strong and slightly acid solution an excess of sodium hydrocarbonate in such quantity that after stirring, a little remains undissolved, and the iron and alumina both appear to be thrown dow r n. Now add potassium cyanide until the precipitate dissolves, and heat gently until the pale yellow colour of the ferrocyanide is produced. Now add a few drops of potassium hydrate to the some- what turbid yellow solution until it becomes perfectly clear ; then boil with the addition of ammonium chloride, when the alumina will be precipitated free from iron. The potassium hydrate and cyanide, as well as the sodium hydrocarbonate for this separation, should be tested for alumina and silica, impurities almost invariably present. (E) Another excellent plan to separate iron and aluminium is to put the calcined precipitate of the two oxides in a porcelain boat, and introduce it into a tube of the same material, heat to bright redness, and pass a current of dry hydrogen, which is kept up whilst the tube is cooling. The hydrogen is then replaced by a current of gaseous SEPARATION OF IRON FROM ALUMINIUM 181 hydrochloric acid, and the tube being reheated the iron, reduced by the hydrogen, is converted into a volatile chloride, whilst the alumina is left behind and may be weighed. The method of weighing the two oxides together, and then sepa- rating the alumina by fusion with caustic soda and subsequent treat- ment with water, is accurate but troublesome. The plan of effecting the separation of the iron by means of ammonium sulphide from the ammonio-citrate solution of the oxides does not give perfectly accurate results, since the ammonium sulphide has the power of holding up small quantities of iron in solution ; this may be proved by letting the perfectly clear nitrate stand a few days, when small flakes of iron sulphide will be deposited. (F) The process of F. Beilstein and K. Luther depends on the unequal solubility in water of the basic ferric nitrates and those of aluminium. The precipitated oxides are dissolved in nitric acid, the solution is evaporated on the water-bath, and the residue is allowed to stand on the bath until acid vapours cease to escape. For their detection a test tube filled with snow or with a freezing mixture is held over the capsule, and the reaction of the water condensed on its sides is examined. The contents of the capsule are covered with hot water, the solid residue is duly crushed up in the water, and (if a small capsule were used) the whole is rinsed into a beaker, in which the mixture is boiled for ten minutes. It is then allowed to cool, 2 or 3 c.c. of a 10-per-cerit. solution of ammonia are added, and, after deposit- ing the basic iron nitrate, is filtered off. As this salt very readily clogs the filter, it is better not to suck the precipitate dry with the water- air pump, but to collect it upon a double filter or pass through a layer of asbestos placed upon a platinum cone. The precipitate is washed (preferably first by decantation) with a cold dilute solution of ammonium nitrate, and finally with a similar hot solution. As it is never practicable to scrape off the precipitate quantitatively from the capsule, the adhering parts are dissolved in dilute hydrochloric acid and reprecipitated with ammonia, The liquid which first passes through, often contains a little ferric oxide, although it is perfectly clear and colourless. The detection of iron is easy if we first acidulate the filtrate with hydrochloric acid and then add potassium sulpho- cyanide. The subsequent portions of the filtrate, however, give no reactions for iron. The first portion of the filtrate (about 100 c.c.) is once more passed through the same filter, when it is found perfectly free from iron. (Gr) Neither the thiosulphate nor the caustic alkali process succeeds when only traces of aluminium are present with the iron. In this case Eobert T. Thomson proceeds as follows : The iron, if in the ferric state, is first reduced to the ferrous condition by passing a current of sulphurous acid through the solution. The excess of sulphurous acid is boiled off, the mixture cooled, and at least as much phosphoric acid. 182 SELECT METHODS IN CHEMICAL ANALYSIS or ammonium or sodium phosphate, added as will be equivalent to the aluminium present. It is advisable to use a large excess of phosphoric acid, as the aluminium may not be completely precipitated if it has not at least its own equivalent of the former. One drawback to the unlimited use of phosphoric acid is that if manganese is present it will be thrown down, but if the quantity of the former is limited the latter will remain in solution. Ammonia is now added until a faint permanent cloudiness is formed ; then excess of ammonium acetate, which throws down the aluminium as phosphate. The precipitate always contains some ferric phosphate, which forms from any traces- of ferric -iron salt which may have escaped reduction, and from the oxidising action of the air during filtration. The great bulk of the iron, however, remains in solution in the ferrous condition. The precipitate is now collected on a filter, washed two or three times with water, and dissolved by passing dilute warm hydrochloric acid through the filter. If it does not seem sufficiently free from iron, the solution thus obtained should be put through the same process as has just been described, beginning at reduction with sulphurous acid. It is well to reduce the iron as much as possible. After obtaining a satisfactory precipitate it is dissolved in hydro- chloric acid, boiled with a little nitric acid to oxidise any proto-salt of iron, nearly neutralised with pure caustic soda, and added to a consider- able excess of the latter in a nickel basin. The mixture is boiled for a short time, filtered, the filtrate acidified with hydrochloric acid, and a large excess of phosphoric acid or phosphate of ammonia or soda added. The presence of at least two equivalents of phosphoric acid to one of alumina is necessary to give rise to the normal aluminium phosphate. The latter is now precipitated by adding ammonia till a slight cloudiness is produced, and then excess of ammonium acetate. The aluminium phosphate is now collected in a filter, washed thoroughly with a hot 1-per-cent. solution of ammonium nitrate containing about 0*1 gramme of the di-acid ammonium phosphate per litre, dried, ignited, and weighed. If the aluminium phosphate is washed with water, it partially loses its gelatinous form, and becomes tedious to filter. But, besides this, the precipitate is decomposed to a considerable extent, and a portion of the phosphoric acid passes into solution. For these reasons the precipitate must be washed in the manner described, when pure aluminium phosphate is weighed, and may be calculated to alumina or aluminium as required. The presence of titanium is not injurious in the above process, as only slight traces of titanic acid are dissolved by strong caustic soda. Separation of Iron from Zinc (A] If the presence of barium is not objectionable, add barium car- bonate to the nearly neutral solution of zinc and iron sesquioxide. The SEPARATION OF IRON FROM ZINC 183 whole of the iron sesquioxide will be precipitated, leaving all the zinc in solution. Nearly neutralise the solution with sodium carbonate, and after sodium acetate is added in excess, brisk ebullition will bring down all the iron as basic acetate. From the filtrate, acidified with acetic acid, a stream of sulphuretted hydrogen will precipitate the zinc. (B) The solution is first brought to such a degree of dilution that it contains at most 0*1 gramme zinc in 100 c. c. ; it is then saturated with a solution of sodium- carbonate until there appears a slight permanent precipitate, which is re-dissolved in a few drops of dilute hydrochloric acid. A current of sulphuretted hydrogen is then passed into the cold liquid, when the greater part of the zinc is precipitated with sulphur, derived from the reduction of the ferric salt ; a large excess of a solu- tion of sodium hyposulphate (di-thionate) is then added, and the current of sulphuretted hydrogen is continued. The last remains of the zinc are precipitated, but the iron remains in solution. An excess of hypo- sulphate is not injurious. For these determinations it is convenient to prepare a solution of known strength and to pour in double the theo- retical quantity as approximately calculated for the double decomposition with the zinc and iron. If after the precipitation of the zinc it is proposed to determine the iron by means of ammonia, as ferric oxide always carries down some proportion of alkaline salts, it is preferable to use ammonium hypo- sulphate, which is now an article of commerce. The initial saturation of the free acid in the solutions is effected, not with sodium carbonate, but with ammonia or ammonium carbonate, until the yellow colouration of the solution containing iron passes to orange, the colour of the neutral or basic salts of this metal. The same method admits of the exact separation of zinc from manganese ; zinc sulphide carries down merely imponderable quantities of manganese. (C) Add sodium hydrocarbonate and then potassium cyanide as recommended for the separation of iron from aluminium. To the clear pale yellow solution of the cyanides add excess of colourless ammonic sulphide and boil, until the steam is neutral to test-paper. The zinc is wholly precipitated as sulphide quite free from iron (or nickel and cobalt if present), and in a granular condition, and it may be filtered and washed with the utmost ease. Electrolytic Separation of Iron from Zinc ' M. Classen finds that when double iron and zinc oxalates are sub- mitted to electrolysis there is not deposited at the negative pole an alloy of both metals, but, in the first place, zinc with a little iron. The electrolysis proceeds quite smoothly, and the sum of both metals may be easily ascertained if the proportion of zinc is less than one-third of the 1 For details of operation see chapter on Electrolytic Analysis. 184 SELECT METHODS IN CHEMICAL ANALYSIS iron. If the proportion of zinc is higher as the electrolysis proceeds the zinc is re-dissolved with a thick development of gas, whilst at the same time ferric oxide is deposited. For larger proportions of zinc it is merely needful to dissolve a weighed quantity of a pure salt of iron (e.g. iron-ammonium sul- phate which contains one-seventh of its weight of iron) in the liquid to be electrolysed in order to effect the determination of both metals in all cases. Separation of Iron from Uranium When, as is generally the case, ammonium carbonate is employed for this separation, it is well known that some of the iron is always dissolved with the uranium. The following is, however, a method for rendering the separation complete : As uranium oxide in solution in ammonium carbonate is not precipitated by ammonium sulphide, add to the liquid, separated by filtration from the bulk of the iron oxide, a few drops of ammonium sulphide to eliminate from it, in the state of sulphide, the small quantity of iron which has been dissolved. After filtering again, a solution is obtained containing all the uranium without any trace of iron. Separation of Iron from Chromium (A) When the iron is in very large excess, the following is a good method for separating the chromium : Treat the metal or ore by the ordinary processes, to separate the silica, and obtain a liquid containing all the metals in solution, the iron being at its maximum of oxidation ; then precipitate the liquid by an excess of a strong solution of potash, and pour, drop by drop, into the solution containing the precipitate (and heated to 80 or 90) a dilute solution of potassium permanganate until the permanganate loses its colour ; the reaction is terminated when the liquid takes a greenish tinge, owing to the presence of potas- sium manganate. Then filter, and saturate the filtered liquid with acetic acid, which immediately reduces the small quantity of potassium manganate that gave to the solution its green colour. Into the liquid, which frequently has a yellow tinge, pour lead acetate, which pro- duces a yellow precipitate of lead chromate, if the least trace of chromium be present. (B) Another method is to nearly neutralise the solution, containing chromium and iron peroxide, with sodium carbonate, and add sodium acetate in excess. A current of chlorine gas or addition of chlorine wa'ter then readily converts the whole of the chromium present into chromic acid. Upon now boiling the solution, the excess of chlorine is expelled, whilst, at the same time, the iron is precipitated as basic acetate. The chromic acid in the filtrate may either be reduced with alcohol and hydrochloric acid and the chromium sesquioxide precipi- IKOS FHOM CHROMIUM AND UKANIUM 185 tated with ammonia, or lead acetate may be added and the lead chromate collected. If it is not desired to precipitate the iron as basic acetate, it may be precipitated with ammonia ; all the chromium will remain in solution as chromic acid. Separation of Iron from Manganese, Nickel, Zinc, and. Aluminium According to G. Von Knorre, in neutral and faintly acid solutions of ferric salts, iron is precipitated by nitroso-naphthol quantitatively as ferri-nitroao-naphthol. In this manner iron can be separated from manganese, nickel, zinc, and aluminium. To about Ol gramme of iron present at least 1 gramme of nitroso-naphthol should be used. If con- siderable quantities of free acid are present, ammonia is added until a precipitate begins to appear, which is then redissolved in a few drops of hydrochloric acid. The weight taken for analysis must be so small that not more than O8 gramme iron is present, as otherwise the bulk of the ferri-nitroso-naphthol is too considerable. The separation of iron from manganese gives very good results. In order to determine the manganese in the nitrate the liquid is concen- trated by evaporation, rinsed into a capacious Erlenmeyer flask, and mixed with ammonium chloride and ammonia in large excess. The manganese is then precipitated by means of a current of air charged with bromine. It falls as hydrated peroxide. The washings retain to the end a slight yellowish colour, but the results are not affected. The separation of iron from zinc and from nickel presents no diffi- culty. In the nitrates zinc is precipitated with sodium carbonate, nickel with bromine-water, and pure potash-lye as nickel sesqui- hydroxide. In precipitating iron by means of nitroso-naphthol it is accompanied not only by copper and cobalt, if present, but also by phosphoric acid. Separation of Iron from Chromium and Uranium According to M. A. Ditte, the separation of these oxides may be effected with great accuracy by operating 'in the manner proposed by M. Sainte-Claire Deville for the separation of iron and alumina. The metals are brought to the state of sesqui- salts ; all metals whose sul- phides are insoluble in dilute acids are removed by known methods, and the ferric, chromic, and uranic oxides are then precipitated together by an excess of ammonia. Care must be taken to drive off by ebullition any free ammonia which might dissolve a little uranium. The oxides are well washed, calcined, placed in a porcelain tube, and heated to redness in a current of pure hydrogen. The ferric oxide becomes metallic iron, the uranic oxide is reduced to uranous oxide, while the chromic oxide remains unaltered. This mixture of iron, 186 SELECT METHODS IN CHEMICAL ANALYSIS uranium, and chromium oxides is weighed, returned to the tube, and submitted to the action of a current of gaseous hydrochloric acid at a red heat. The uranium and chromium oxides remain entirely unattacked by the acid, and their weight suffers no variation. As for the iron, it is entirely volatilised as ferrous chloride, and deposited in white crystals in a cooler part of the tube. After an hour or an hour and a half the tube is allowed to cool in a current of hydrogen, to drive out the hydrochloric acid/ and the mixture of chromic oxide and uranous oxide is weighed and treated with pure nitric acid. The uranium protoxide, which remains in the form of a brown amorphous powder, is at once attacked, even in the cold, with evolution of nitrous fumes and formation of uranium nitrate. It is well, however, to heat for a few moments, in order to be certain that the chromic oxide retains no traces of uranium ; the solution is then filtered off, and the residue calcined and weighed. Separation of Iron from Zirconium Bender the solution nearly neutral with sodium carbonate, and add excess of sodium thiosulphate. Boil the liquid for a short time, and all the zirconia will be precipitated, with a little sulphur, but perfectly free from iron, which will all be in solution. The solution containing zirconium and iron may also be boiled with nitric acid to peroxidise the iron, and then precipitated with excess of ammonia. The precipitate is then digested with excess of oxalic acid, which dissolves the whole of the iron, together with a trace of zirconia, but leaves the greater part of the zirconia in the form of an insoluble oxalate. Or, the mixed precipitate of iron sesquioxide and zirconia may be digested in ammonium sulphide until the whole of the iron is in the state of sulphide. Decant the supernatant liquid and digest the black precipitate in a dilute solution of sulphurous acid. This dissolves the iron sulphide and leaves the zirconia quite colourless. The process given on page 121 for the preparation of pure zirconia, &c., may also be used to separate iron and zirconium. Separation of Iron from G-lucimim ' According to Classen, the electrolytic separation of these metals does not present the slightest difficulty if we prepare soluble double compounds by means of ammonium oxalate (without potassium oxa- late)> taking care to have an excess of ammonium oxalate, and separa- ting the iron by a current of 10 to 12 c.c. of detonating gas per minute. More powerful currents are not applicable, as the liquid would become heated, and the ammonium hydrocarbonate, being formed by the electrolysis, on keeping the glucinum in solution would be decomposed. 1 For details of operation see chapter on Electrolytic Analysis. SEPARATION OF IRON FROM CERIUM 187 It is then possible that the glucinum hydroxide is precipitated before the iron is reduced by the current. The determination of glucinum in the liquid decanted from the iron is very simple : the solution is- boiled for the decomposition of the acid ammonium carbonate, and the application of heat is continued until the liquid has only a faint smell of ammonia ; the glucinum hydroxide is filtered off, washed with hot water, and converted into glucina by ignition in a platinum crucible. Electrolytic Separation of Iron from Glucinum and Aluminium When the iron is reduced the liquid is poured into a platinum cap- sule, and electrolysis is effected with a current of 10 to 12 c.c. detona- ting gas per minute until all the oxalic acid is decomposed and the aluminium precipitated as hydroxide. In the filtrate the glucinum is precipitated as hydroxide by boiling. It is admissible to re-dissolve the aluminium hydroxide, and to- repeat the electrolysis after previous conversion into a double ammo- nium salt. Electrolytic Separation of Iron from Zirconium The separation and determination of zirconium are effected exactly as that of glucinum. Electrolytic Separation of Iron from Vanadium This separation proceeds as smoothly as that of iron from glucinum. Separation of Iron from Titanium (A) When iron sesquioxide and titanic acid are together in dilute solution, they can be separated by ebullition with sodium thiosul- phate, as in the case of iron and zirconium. The titanic acid pre- cipitates whilst the iron remains in solution. Or, add ammonia in excess to the solution, digest the mixed precipitate of titanic acid and iron sesquioxide with ammonium sulphide, and then dissolve out the iron with sulphurous acid. (B) Other methods of separating iron and titanium may be found under the heading Titanium (page 119). Separation of Iron from Cerium The metals must be in solution in the form of sulphates. Reduce the iron completely to the form of protosulphate by means of a current of sulphuretted hydrogen passed into the hot solution. To the solution, which should be concentrated, add a saturated solution of sodium sulphate, together with a sufficient quantity of the dry sulphate in powder to saturate the water of solution. It is most advantageous to use hot solutions. The insoluble double sodium sulphates and the cerium metals separate immediately as a white, highly crystalline powder, which is to be thrown upon a filter and thoroughly washed 188 SELECT METHODS IN CHEMICAL ANALYSIS with a saturated solution of sodium sulphate. After washing, the double sulphates upon the filter are to be dissolved in hot dilute hydro- chloric acid, the solution largely diluted with water, and the cerium metals precipitated by ammonium oxalate in the manner already pointed out (page 56). From the filtrate the iron may be precipitated at once as sesquioxide by ammonia, after peroxidising it by means of chlorine water, and rendering the solution slightly acid with hydrochloric or sulphuric acid. Separation of Iron from Magnesium (A) When iron sesquioxide is precipitated by means of ammonia from a solution containing magnesium, some magnesium is always carried down with it in spite of the presence of an excess of ammo- niacal salts. They may, however, be perfectly separated in this manner : Dilute the solution considerably, neutralise with sodium carbonate, then add acetic acid and sodium acetate to the cold solution. Boil for a short time, when the whole of the iron will be precipitated as basic acetate. Filter hot, and wash quickly with hot water. All the magnesium will be in the solution. (B) Dr. Calvert dissolves the oxides in hydrochloric and a little nitric acid, nearly neutralises with ammonia, and precipitates the iron with ammonium succinate. The succinate of iron sesquioxide is rapidly filtered off and washed with cold water. The filtrate will contain the whole of the magnesium. Separation of Iron from Calcium When iron sesquioxide is precipitated in the ordinary manner with ammonia, in the presence of excess of ammoniacal salts, it always carries down a considerable quantity of calcium if present, and the larger the proportion of iron as compared with that of calcium, the greater is the proportion of calcium carried down by the iron. This error can be avoided by precipitating the iron as succinate, or by throwing. the iron down as basic acetate as just described (Separation of Iron from Magnesium). In either case the whole of the calcium will remain in the solution. Iron sesquioxide may be safely precipitated by ammonia if the precaution is taken to boil until all smell of ammonia has gone off, before filtering ; the iron does not now retain any calcium. If much calcium be present, a little ammonium chloride may be added to make sure of getting all into solution. As the solution no longer contains free ammonia, it can be filtered without there being danger of the calcium coming down as carbonate by absorption of carbonic acid from the atmosphere. The filtrate may be concentrated by evaporation, and the calcium precipitated as oxalate. 189 CHAPTER VI MANGANESE, NICKEL, COBALT MANGANESE CHEOMIUM and manganese may be distinguished before the blowpipe as follows, according to Professor E. J. Chapman : When a mineral is expected to contain manganese, it is commonly tested by fusion with sodium carbonate. But chromium compounds form with that reagent a green enamel, much resembling that formed by manganese com- pounds. The sodium chromate enamel is yellowish green after exposure to the oxidising flame, and never exhibits any tinge of blue. The sodium manganate enamel is greenish blue when quite cold. To prevent mistakes, the bead may be saturated with vitrified boracic acid until all the carbonic acid is expelled and a clear glass is obtained. The chrome glass will retain its green colour, whilst the manganese glass will become amethystine or violet. In place of boracic acid, silica may be used if more convenient. In this case the reaction is assisted by the addition of a very small amount of borax. Electrolytic Separation of Manganese ! (A) Classen finds that manganese ranks among those metals which are oxidised by the current to peroxide and separated out as such at the positive electrode. The quantitative separation as peroxide can be effected from the solution of the potassium manganese oxalate (the precipitation from the double ammonium oxalate is not complete) or from the solution of any manganese salt containing free nitric or sulphuric acid. For the execution of the former method the solution of the manganese salt is mixed with the potassium oxalate in slight excess, diluted with water, and electrolysed with a current of 9 to 12 c.c. detonating gas per minute. Small quantities of peroxide adhere sufficiently fast to the positive electrode, so that after previous washing with water they may be converted into mangano-inanganic oxide by igniting the electrode, which must have been previously weighed. For larger quantities it is admissible to use the platinum capsule as a positive electrode, and to try after the completion of the precipitation 2 to 1 For details- of operation see chapter on Electrolytic Analysis. 2 To ascertain the end of the reaction ammonium sulphide is quite unsuitable, 190 SELECT METHODS IN CHEMICAL ANALYSIS convert (without filtration) the deposit of peroxide into mangano- manganic cxide by ignition. If this is not practicable the preci- pitate is filtered off, washed with hot water, and the manganese is converted either into mangano-manganic oxide or sulphate. The above-described method, as will be further explained, admits of the separation of manganese from a considerable number of metals .and their simultaneous determination. The deposition of manganese in an acid solution is practicable in presence of free nitric or sulphuric acid. For the execution of the former method the solution of manganese nitrate (containing at most 05 gramme manganese) is acidified with nitric acid, the platinum capsule is taken as the positive electrode, and a platinum spiral is immersed as a negative electrode ; the liquid is continuously heated to about 30 in the water- bath and electrolysed with a current of about 0'03 c.c. detonating gas per minute. As the nitric acid is transformed into ammonia, we ascertain from time to time if the, liquid has still an acid reaction. If not, nitric acid is -added until an acid reaction is obtained. The coating of manganese peroxide is carefully washed off with water, and the capsule is dried until the weight is constant, either in the air-bath at 60 or over sulphuric acid in the air-bath. The deposit has the composition Mn0. 2 + H 2 0. On ignition Mn0. 2 is converted into Mn 3 4 , the weight of which may be determined. (B) If the manganese exists in solution as sulphate, F. Eiidcrff acidifies the solution with 3 drops of dilute sulphuric acid, dilutes with water to 100 c.c., and electrolyses with a battery of two Meidinger elements. The maximum quantity of manganese which may be present in solution is 0*04 gramme. The deposition is complete in from 12 to 14 hours, and the end is ascertained by testing with ammonium sulphide. For removing the manganese peroxide from the capsule we use strongly diluted sulphuric acid with the addition of hydrogen. (C) For depositing the manganese as peroxide from a solution of the double pyrophosphate, A. Brand mixes the solution with as much sodium pyrophosphate as is amply sufficient for forming the double salt and adds ammonia until the precipitate has been re-dissolved. If the quantity of manganese is not more than about 0'02 in 100 c.c., he electrolyses with a current of 0*1 c.c. per minute. If the quantity of manganese is greater, the decomposition is begun with a current of only 0-01 c.c. of detonating gas, which, towards the end of the operation, is increased to about 0-4 c.c. Brand washes the peroxide only with water, as on an addition of alcohol the coating easily shells off ; or he as oxalic acid greatly retards the precipitation of the manganese as sulphide. It is best to evaporate a small portion upon the platinum cover, and fuse it with potassium carbonate. ESTIMATION OF MANGANESE 191 converts the Mn0 2 into Mn 3 4 by ignition over the blast. If we use the platinum capsule as a positive electrode, we can, according to Brand, obtain from 150 c.c. of liquid 0*2 gramme manganese as firmly adhering superoxide. Estimation of Manganese Under many circumstances manganese can be estimated with great accuracy by precipitation as ammonio-phosphate, and weighing as pyrophosphate, like magnesium. This salt, from its highly crystalline structure, the facility with which it is formed, and its insolubility, appears well adapted to the quantitative estimation of manganese. (A) Dr. Wolcott Gibbs, who has worked out this method, recommends that to the solution of manganese, which may contain salts of ammonium or of the alkaline metals, di-sodic ortho-phosphate be added in large excess above the quantity required to precipitate the manganese as ortho- phosphate. The white precipitate is then to be re-dissolved in excess of sulphuric or hydrochloric acid, heated to the boiling-point, and ammonia added in excess. A white or semi-gelatinous precipitate is produced, which, on boiling or standing for some time, even in the cold, gradually becomes crystalline, and finally is completely converted into beautiful talcose scales which have a pearly lustre and a pale rose colour. It is best to precipitate each time in a platinum vessel, in which the ammonio-phosphate may be boiled for 10 or 15 minutes, and to allow the salt to remain at a temperature near the boiling-point of the liquid for an hour after it has become crystalline. The ammonio- phosphate may then be filtered off and washed with hot water. The washing takes place with extraordinary facility on account of the crystalline character of the salt. The ortho-phosphate, after drying and ignition, yields manganese pyrophosphate as a nearly white powder. The advantage of this method over that commonly employed for the estimation of %ianganese is that the process admits of the metal being weighed in the form of a perfectly definite compound, and not as an oxide which cannot be safely assumed to be manganoso-manganic oxide. When manganese is associated with the alkaline earths, it is, of course, first to be separated as sulphide, or as a hydrate of the sesquioxide. The ammonio-phosphate is almost absolutely insoluble in boiling water, in ammonia, and in solutions of ammonium salts. The salt is nearly white, but sometimes becomes a little more red upon the filter. If it assumes a rather deep dull red colour, the whole of the manganese phosphate has not been converted into ammonio-phosphate. The pre- cipitate is then to be re-dissolved in dilute hydrochloric acid, more sodium phosphate added, and then ammonia in excess, after which the boiling is to be repeated. This repetition is very rarely necessary, a little practice enabling the analyst to judge when the conversion from the flocky gelatinous to" the crystalline condition is complete. The filtrate from the crystalline salt is perfectly free from manganese. This 192 SELECT METHODS IN CHEMICAL ANALYSIS process will not give accurate results in the presence of copper, or of metals which form precipitates with phosphates. Phosphoric acid cannot be estimated in this way by precipitation as manganese ammo- nio-phosphate, because the crystalline character of the salt upon which the success of the process depends is only produced by digestion with an excess of phosphate. (B) Manganese may be estimated by precipitation as oxalate, and subsequent titration with potassium permanganate (see page 146, Lei- son's process for the estimation of zinc). To a soluble manganese salt add oxalic acid, and then a large excess of strong alcohol ; manganese oxalate is completely precipitated. The subsequent nitration and titration with potassium permanganate is conducted as described at page 146. From the amount of oxalic acid thus found the quantity of manganese may be calculated. (C) A. Guyard estimates manganese by precipitation with potassium permanganate, which forms, with salts of manganese protoxide, a pre- cipitate of permanganate of manganese protoxide, insoluble in water and dilute inorganic acids. All the other metals whose protoxides react on potassium permanganate are found in the state of peroxide in the same liquor in which the manganese exists as protoxide ; conse- quently, these foreign metals, whatever they may be, do not interfere with the results. As long as there is manganese in the liquor it is precipitated, and the potassium permanganate is decolourised ; but as soon as the reaction is ended a drop of the permanganate communi- cates a persistent rose tint to the solution. The operation is best performed in the following manner : 1 or 2 grammes of the manganese salt to be assayed are dissolved in aqua regia. The solution is boiled for some time to transform all the manganese into a protoxide salt ; the solution is then very nearly neutralised by an alkali ; that done, it is diluted with a large quantity of boiling water, and the whole is kept at a temperature boiling water is added, and the capsule is left on the water-bath, adding water from time to time to compensate for the loss by evaporation until the liquid has become colourless or pale yellow, when the iodine is expelled. The silver iodide is then weighed. The authors collect it in a small glass tube filled with glass wool, dry at 110, and weigh. Wash it first with hot water containing nitric acid, and then with a few c.c. of hot water, dry at 110, and weigh. The presence of other metals of the same group, with the excep- tion of mercury, does not interfere. Cuprous iodide, bismuth, and cadmium iodide behave with nitric acid like lead iodide ; on the other hand, mercurous iodide is converted into red iodide, which is not further attacked. In the examination of alloys of lead and silver proceed in the same manner. Dissolve in nitric acid, dilute, precipitate with potassium iodide, and heat on the water-bath. For determining silver in impure leads, from 10 to 50 grms. of the same, according to the proportion of silver, is dissolved in dilute nitric acid containing tartaric acid. To 10 grms. of the sample, use 10 c.c. nitric acid free from chlorine, and an equal quantity of a satu- rated solution of tartaric acid. The presence of the latter effects much more rapid and complete solution. The solution is heated until the oxidation is completed, diluted with boiling water, filtered into a glass capsule, diluted to from 300 to 500 c.c., allowed to cool, 10 c.c. of a 10 per cent, solution of potassium iodide are added, and it is heated on the water -bath. The excess of the nitric acid added for solution is generally sufficient for oxidising the lead iodide ; if the development of iodine vapours and the brown colour do not appear, a little more dilute nitric acid must be added. The proportion of silver in galena may be determined in the same manner. It is oxidised with nitric acid with the addition of tartaric acid. It is most convenient to use equal volumes of nitric acid, solu- tion of tartaric acid, and water. After the oxidation is completed, the liquid diluted with hot water, filtered, and well washed with boiling water, the filtrate is allowed to cool. The process is then completed as above. (B) This is, perhaps, the most appropriate place to describe the valuable improvements which the late Mr. D. Forbes made in the separation of silver and lead before the blowpipe. This assay process is in all cases based upon the reduction to a metallic state of all the silver contained in the compound in question along with more or less metallic lead, which latter metal, when not already present in sufficient quantity in the substance itself under examination, is added in the state of granulated lead to the assay previous to its reduction. The globule of silver-lead thus obtained is soft and free from such elements 326 SELECT METHODS IN CHEMICAL ANALYSIS as would interfere with its treatment upon the cupel, and may then be at once cupelled before the blowpipe until the pure silver alone remains upon the bone-ash surface of the cupel ; but if not, it is previously submitted to a scorifying or oxidising treatment upon charcoal until all such substances are either slagged off or volatilised, and the resulting silver-lead globule cupelled as before. As, therefore, the final operation in all silver assays is invariably that of cupelling the silver-lead alloy obtained from the previous reduc- tion of the substance, effected by methods differing according 10 the nature of the argentiferous ore or compound under examination, it is here considered advisable to introduce the description of the silver assay by an explanation of this process. In the ordinary process of cupellation in the muffle, bone-ash or other cupels are employed, of a size large enough to absorb the whole of the litharge produced from the oxidation of the lead in the assay. This, however, should not be the case when using the blowpipe ; for, as the heating powers of that instrument are limited, it is found in practice much better to accomplish this result by two distinct opera- tionsthe first being a concentration of the silver-lead, in which the greater part of the lead is converted by oxidation into litharge, remain- ing upon, but not, or only very slightly, absorbed by the bone-ash cupel ; the second consisting in cupelling the small concentrated metallic bead so obtained upon a fresh cupel until the remaining lead is totally absorbed by the cupel and the silver left behind in a pure state. By this means a much larger weight of the silver-lead alloy can be submitted to assay, and, for reasons hereafter to be explained, much more exact results are obtained than would be the case when the cupellation is conducted at one operation in the ordinary manner. The apparatus used by the late Mr. Forbes for these operations are shown to a scale of one-half their real size in the woodcut (fig. 19, a to d). In fig. 19, a, is represented in section a [a small cylindrical mould of iron, 0*7 of an inch in diameter and about 0*4 high, in which is turned a cup-shaped, nearly hemispherical depression, 0'2 of an inch deep in centre, the inner surface of which is left rough, or marked with minute ridges and furrows for the purpose of enabling it to retain more firmly the bone- ash lining, which is stamped into it by means of the polished bolt also shown in the figure. This mould rests upon the stand, d, having for this purpose a small central socket in its base, into which the central pivot of the stand enters. The socket is seen in the ground-plan, b, of the base of the mould, which shows likewise CONCENTRATION OF SILVER LEAD 327 three small grooves or slots made in it to enable a steady hold to be taken of it, when hot, by the forceps. The stand itself is composed of a small turned ivory or wood base, fixed into a short piece of strong glass tubing, which, from its non-conducting powers, serves as an excellent handle. In the centre of the base a slight iron rod rising above the level of the glass outer tube serves as a support for the cupel mould, into the socket in the base of which it enters. Bone-ash is best prepared by burning bones which have been previously boiled several times, so as to extract all animal matter. The best bone-ash is made from the core-bone of the horns of cattle well boiled out and burned. The ash from this is more uniform than from the other bones, which have in general a very compact enamel- like exterior surface, whilst the interior is of a much softer nature. Concentration of the Silver-Lead. A cupel is prepared by filling the above-described cupel mould with bone-ash powder not finer than will pass through a sieve containing from 40 to 50 holes in the linear inch ; it should be well dried and kept in an air-tight bottle, and when used, the whole must be pressed down with the bolt, using a few taps of the hammer. It is then heated strongly in the oxidising blowpipe flame, in order to drive off any hygroscopic mois- ture. The bone-ash surface of the cupel, after heating, should be smooth, and pres3iit no cracks ; if the reverse, these may be removed by using the bolt again and re-heating. 1 The silver-lead, beaten on the anvil into the form of a cube, is placed gently upon the surface of the bone-ash, and, directing a pretty strong oxidising flame on to its surface, it is fused, and quickly attains a bright metallic appearance, and commences to oxidise with a rapid rotatory movement. (Occa- sionally, when the assay is large, and much copper or nickel present, the globule may, under this operation, cover itself with a crust of lead oxide, or solidify ; in such cases direct the blue point of a strong flame steadily on to one spot on the surface of the lead-globule until it commences oxidising and rotating. In some cases, where much nickel is present, an infusible scale, impeding or even preventing this action, may form, but will disapear on adding more lead say from 3 to 6 grains, according to the thickness of this scale or crust.) When this occurs the cupel is slightly inclined from the lamp, a fine blue point is obtained by placing the blowpipe nozzle deeper into the lamp, and the flame is directed at about an angle of 30 on to the globule not, however, so near as to touch it with the blue point, but only with the outer flame, so moderating it as to keep the assay at a gentle red heat, and not allowing the rotation to become too violent. This oxidising fusion should be carried on at the lowest tempera- ture sufficient to keep up the rotatory movement, and to prevent a 1 These precautions are very important, as the slightest trace of moisture in the substance of the bone-ash would inevitably cause a spirting of the metal during the operation. 328 SELECT METHODS IN CHEMICAL ANALYSIS crust of litharge accumulating upon the surface of the globule, but still sufficiently high to hinder the metallic globule from solidifying. Should this, however, happen, a stronger flame must be employed for a moment until the metal is again in rotation ; such interruptions should, however, be avoided. The proper temperature can only be learned by practice, a too high temperature is still more injurious, causing the lead to volatilise, and, if rich in silver, carry some of that metal mechanically along with it. The litharge, also, instead of .remaining on the cupel would be absorbed by the bone-ash, and as the surface of the metallic globule is covered by a too thin coating of fused litharge, some silver may be absorbed along with the litharge. In this operation, in order to avoid loss of silver, the fused globule should be always kept in contact with the melted litharge. By the above treatment the air has free access to the assay, and the oxidation of the lead and associated foreign metals goes on rapidly. The surface of the melted globule, when poor in silver, shows a bril- liant play of iridescent colours, which does not take place when very rich in silver. The litharge is driven to the edge of the globule, heaping itself up and solidifying behind and around it. When the globule becomes so hemmed in by the litharge as to present too small a surface for oxidation, the cupel is moved so as to be more horizontal (having been previously kept in an inclined position), thus causing the lead-globule to slide by its own weight on one side and expose a fresh surface to the oxidising action. When the lead is pure, the litharge formed has a reddish-yellow colour, but, if copper is present, is nearly black. In concentrating silver-lead, it must be remembered that an alloy of lead and silver, if in the proportion of about 86 per cent, silver along with 14 per cent, lead, when cooled slowly in the litharge behaves in a manner analogous to the spitting of pure silver, throwing out a whitish-grey pulverulent excrescence rich in silver. For this reason, therefore, the concentration above described should be stopped when the globule is supposed to contain about 6 parts silver along with 1 part in weight of lead. In case, however, this limit should have been exceeded, it is advisable at once to push the concentration still further until the silver globule contains but very little lead. In practice, with poor ores, it is usual to concentrate the lead until the globule is re- duced to the size of a small mustard seed, or in rich ores to some two or three times that size. Upon arriving at this point, the cupel is withdrawn very gradually from the flame, so that the cooling shall take place as slowly as possible until the globule has solidified in its envelope of litharge. If cooled too quickly, the litharge, contracting suddenly, would throw out the globule, or even cause it to spirt ; in such case it should be touched by the point of the blue flame so as to reform it into a round globule, which is cooled slowly as before described. CUPELLATION 329 The globule is now reserved for the next operation, for which purpose it is, when quite cold, extracted from the litharge surrounding it. Cupellation. The bone-ash required for this process should be of the best quality and in the most impalpable powder, prepared by elutriating finely ground bone-ash and drying the product before use. The cupel, still hot from the last operation, is placed upon the anvil, and the crust of litharge, with its enclosed metallic bead, gently re- moved, leaving the hot coarse bone-ash beneath it in the mould ; upon this a small quantity of the elutriated bone-ash is placed, so as to fill up the cavity, and the whole whilst hot stamped down by the bolt, previously slightly warmed, with a few taps of the hammer. The cupel thus formed is heated strongly in the oxidising flame, which should leave the surface perfectly smooth, and free from any fissures or scales ; if such appear, the bolt must again be used, and the cupel re-heated. In this process it is very important that the cupel should possess 'as smooth a surface as possible, whilst at the same time the substancp of the cupel beneath should not be too compact, so as thereby to permit the litharge to filter through and be readily absorbed, leaving the silver bead upon the smooth upper surface. The bead of silver-lead obtained from the last operation is taken out of the litharge in which it is embedded, and, after removing any trace of adherent bone-ash or litharge, is slightly flattened to prevent its rolling about upon the surface of the cupel. It is now put into the cupel prepared as before described, placing it on the side farthest from the lamp and a little above the centre of the cupel, which is now inclined slightly towards the lamp, and is heated by the oxidising flame directed downwards upon it, thus causing the globule when fused and oxidising to move of itself into the centre of the cupel. The cupel is now brought into a horizontal position, and the flame, directed on to it at an angle of about 45 degrees, is made to play upon the bone-ash surface immediately surrounding the globule, without, however, touching it ; so as to keep this part of the cupel at a red heat sufficiently strong to ensure the globule being in constant oxidising fusion, and at the same time to cause the perfect ab- sorption of the litharge, and prevent any scales of litharge forming upon the surface of the cupel under the globule, which would impede the oxidation, as well as prevent the silver bead being easily detached at the conclusion of the operation. Should the heat at any time be too low and the globule solidify, it must be touched for an instant with the point of the flame and proceeded with as before. Should (in consequence of the bone-ash not having been sufficiently heated to absorb the litharge perfectly) a little litharge adhere pertinaciously to the globule, or a particle of the bone-ash cupel attach itself, the cupel should be slightly inclined, so as to allow the globule to move by its own weight on to another and clean part of the cupel, leaving the litharge or bone-ash behind it ; but, if not sufficiently heavy to do so, 330 SELECT METHODS IN CHEMICAL ANALYSIS a small piece of pure lead may be fused to it in order to increase its weight, and so allow of the same proceeding being adopted. By slightly inclining the cupel stand, and moving it so as to pre- sent in turn all parts of the surface surrounding the globule to the action of the flame, the cupellation proceeds rapidly. If, however, the assay contains very little silver, it will be found necessary to move the globule from one spot to another on the cupel, in order to present a fresh surface for absorbing the litharge formed; this is done by simply inclining the cupel stand, remembering that the bone-ash sur- rounding the globule must always be kept at a red heat, without ever touching the globule itself by the flame. In assays rich in silver a play of iridescent colours appears some seconds before the ' -brightening,' which disappears the moment the silver becomes pure ; as soon as this is observed the cupel should be moved in a circular manner, so that the globule is nearly touched all round by the point of the blue flame, and this is continued until the surface of the melted silver is seen to be quite free from any litharge, upon which it is very gradually withdrawn from the flame, so as to cool the assay by degrees very slowly, in order to prevent ' spitting.' When the silver-lead is very poor, this play of colours is not apparent, and as soon as the rotatory movement of the globule ceases, the heat must be increased for an instant in order to remove the last thin but pertinacious film or scale of litharge, and subsequently the assay is cooled gradually ; when cold it should, whilst still upon the cupel, be examined by a lens to see whether the bead possesses a pure silver colour, as if not it must be re-heated. Frequently, when the ' brightening ' takes place, the silver globule is found to spread out, and, after cooling, although of a white colour, is found to appear somewhat less spherical or more flattened in shape than a corresponding globule of pure silver would be. This arises from the presence of copper still remaining in the silver, and in such cases a small piece of pure lead (about from 0*5 grain to 1*5 grain in weight, according to size of assay) should be fused on the cupel along with the silver, and the cupellation of the whole conducted as before on another part of the cupel, when the silver globule will be obtained pure and nearly spherical in shape. Sometimes the silver globule in ' brightening ' may still remain covered with a thin film of litharge, although otherwise pure ; this arises from too little heat having been employed in the last stage of the operation, and con- sequently the bead should be re-heated in a strong oxidising flame until this litharge is absorbed, and the globule, after slow cooling, appears pure. If the instructions here given be strictly attended to, it will be found, after some practice, that very accurate results may be obtained in the blowpipe assay for silver, and that no difficulty will be found in detecting the presence and estimating the amount of silver present, IIAKKORT'S SCALE 331 even when in as small a quantity as 0'5 ounce to the ton. When sub- stances containing very little silver, or less than that amount, are examined, several assays should be made, and the silver-lea^ obtained concentrated separately, after which the various globules should be united and cupelled together in one operation. It is hardly necessary to remark that the lead employed in assaying should be free from silver, or, if not, its actual contents in silver should be estimated, and subtracted from the amount found in the assay. Assay lead containing less than 0*25 ounce to the ton of lead can readily be obtained, or can be made by precipitating a solution of lead acetate by metallic zinc, rejecting the first portion of lead thrown down. In all cases the lead should be fused and granulated finely the granulated lead for use in these assays being previously passed through a sieve containing 40 holes to the linear inch. It is also useful to have some lead in the form of wire, as being very con- venient for adding in small portions to assays when on the cupel. Estimation of the Weight of the Silver Globule obtained on Cupellation. As the amount of lead which can, by the method above described, be conveniently cupelled before the blowpipe is necessarily limited, the silver globule which remains upon the bone- ash surface of the cupel at the end of the operation is, when sub- stances poor in silver have been examined, frequently so very minute that its weight could not be determined with correctness by the most delicate balances in general use. Globules of silver of far less weight than T1J V be distinguished at first sight from silver chloride. When boiled in water it, however, dissolves like lead chloride, and separates again on cooling ; the crystals, however, are much smaller and less brilliant than those of lead chloride. One part of the chloride dissolves in 283*4 parts of water at 60 F., and in 52-5 parts of boiling water. When boiled in nitric acid or aqua regia, it is converted into the sesquichlo- ride, which separates, on cooling, in yellow crystalline scales. It is soluble in 380*1 times its weight of water at 60 F., and. in 52*9 parts of boiling water. Pure water produces a slight decomposition into teroxide and protochloride, which, however, may be prevented by the addition of a drop of nitric or hydrochloric acid. From the slight solu- bility of the chlorides, in even boiling water, it is evident that this method of separating thallium from silver is tedious, and is very liable to leave thallium behind. (C) The best method of separating silver and thallium, when to- gether as chlorides or iodides, consists in reducing the metals by the addition of a rod of pure zinc to the mixture. When the reaction is complete, remove the zinc, and wash with hot water till the washing waters are free from chlorine. Then heat with dilute sulphuric acid, which dissolves the thallium and leaves the silver. Separation of Thallium from Nickel, Cobalt, or Manganese Add sodium sulphite in excess to the solution, so as to be certain that all the thallium is in the state of proto-salt, then add excess of sodium carbonate and boil. The thallium will remain in solution, whilst the other metals will be precipitated. Filter off and add potas- sium iodide to the filtrate ; this will precipitate insoluble thallium iodide in the form of a yellow powder. When the thallium is present in traces only, it is better to add potassium iodide direct to the liquid, without separating the other metals with sodium carbonate. Separation of Thallium from Iron Certain kinds of iron pyrites constitute the richest natural source of thallium. At page 344 the methods of separating thallium from thalli- ferous pyrites on the large scale are fully described. Thallium may be readily detected in thalliferous pyrites in the following manner : Dis- solve the finely powdered mineral in nitro-hydrochloric acid ; evaporate with excess of sulphuric acid until the nitric acid is evolved ; dissolve in water, and add sodium sulphite to reduce the iron and thallium to the state of proto-salts. On adding potassium iodide, and allowing the SEPARATION OF THALLIUM 359 liquid to stand for some time, a bright yellow precipitate of thallium iodide will separate. This test is sufficiently delicate to show thallium in a few grains of a pyrites which does not contain more than 1 part in 10,000. If the iron only is in the state of peroxide (as in the case of thallium-iron alum) the separation may be effected by ammonia, which precipitates the iron sesquioxide and leaves the thallium in solution. Separation of Thallium from Zinc Thallium is present in many specimens of blende and calamine, especially from Nouvelle Montagne and the neighbourhood of Spa, in Belgium. In such cases it accompanies the zinc in most of its prepa- rations, and may, therefore, be frequently detected in the commercial metal. By proceeding in the following manner, the black residue which is left behind when zinc is dissolved in sulphuric acid will gene- rally be found to contain thallium. Dissolve the residue in nitric acid ; evaporate the solution with excess of sulphuric acid ; dissolve the residue in a small quantity of water ; filter the liquid from lead sulphate and add sodium sulphite. Upon adding potassium iodide to the solution the thallium will be precipitated. When thallium is present in larger quantities, precipitate the zinc with sodium carbonate, which has no action on thallium. Separation of Thallium from Chromium The thallium chromates are insoluble in water, but readily soluble in hydrochloric acid, chlorine being evolved and a soluble perchloride being produced. When boiled with hydrochloric acid and alcohol, these chromates are quickly decomposed, thallium protochloride being precipitated, whilst chromium sesquichloride remains in solution. Filter off and wash with alcohol, in which thallium protochloride is insoluble. Separation of Thallium from Gallium This separation is not effected satisfactorily by precipitating the alcoholic solution with potassium iodide, as thallium remains in the ni- trate and sensible traces of gallium in the deposit. It is not more advantageous to reduce the thallium to the metallic state by means of a sheet of zinc. There are thus introduced into the analysis the im- purities so frequently contained in zinc, and the thallium carries down gallium, unless the liquid is kept sufficiently acid, and then the precipi- tation of the thallium is incomplete. The following processes may be recommended, though in different degrees : (.4) Boiling after super saturation with ammonia gives good results with thallium sulphate, chloride, or nitrate, if slightly acid. The salts 360 SELECT METHODS IN CHEMICAL ANALYSIS must previously be reduced to the lowest stage of oxidation by the addi- tion of a few drops of a solution of sulphurous acid. If slight traces of thallium remain in the precipitate they are entirely eliminated by repeating the boiling with ammonia ; the gallium oxide obtained then gives no spectroscopic indication of thallium. (B) Calcium and barium carbonates precipitate gallium in the cold without rendering the thallium insoluble beyond slight traces, which disappear entirely during the operations for removing the lime or baryta. Before adding the carbonates the liquid is reduced by means of sulphurous acid. (C) Calcium carbonate may be used in heat after reduction by means of sulphurous acid. There are sensible traces of thallium in the precipitate, but they are subsequently eliminated along with the lime. (D) Cupric hydrate, as also metallic copper and cuprous oxide, are the best reagents, for the gallium is totally precipitated without carrying down a trace of thallium. If cupric hydrate is employed, the thallium salts must previously be reduced to the lowest stage of oxida- tion by means of sulphurous acid. (E) If the quantity of thallium is not too considerable, so that its chloride remains dissolved, gallium may be precipitated by potassium ferrocyanide in a very acid solution and at a temperature of 70. Traces of thallium contaminate the deposit, which is redissolved in a small excess of potash ; there are added to the liquid a few drops of ammonium sulphide recently prepared, and the whole is filtered to separate thallium sulphide. The clear solution is evaporated to a small bulk, supersaturated with a large excess of hydrochloric acid, and mixed with a little ferrocyanide. The slight traces of gallium carried down by the small quantity of thallium sulphide may generally be neglected. If needful, they may be separated by known methods. (F) Thallium may be thrown down by platinum chloride from an alcoholic solution, acidified with hydrochloric acid. A prolonged cur- rent of sulphuretted hydrogen removes the platinum contained in the liquid, from which is afterwards obtained gallium containing merely traces of thallium. The chloro-platinate, suspended in water acidified with hydrochloric acid, is treated with hydrogen sulphide, which renders the platinum insoluble. The thallium salt obtained does not contain sensible traces of gallium. INDIUM Preparation of Indium from Commercial Zinc Zinc from the Freiburg mines contains, besides a small quantity of lead, iron, arsenic, and cadmium, 0-0448 per cent, of indium. To separate the indium the zinc is dissolved in dilute sulphuric or hydro- PURIFICATION OF INDIUM 361 chloric acid, and boiled until the evolution of gas ceases. The metallic precipitate left, when the precaution is taken to leave a little zinc un- dissolved, contains all the indium, together with the lead, &c. In the case of a solution containing indium such as zinc chloride the separation may be effected by means of sodium acetate, indium having the property, like iron, of forming an insoluble basic salt. A little dilute sulphuric acid is first added to the solution containing indium, and sodium carbonate is next added until, after stirring, a slight cloudi- ness remains ; sodium acetate is then added, and the mixture is boiled. In this way a basic indium sulphate, containing a little iron and zinc, is precipitated. It is best to wash the precipitate by decantation, as the gelatinous precipitate rapidly clogs up the pores of filtering- paper. From a hydrochloric or nitric solution of indium the separation may be effected by barium carbonate, which perfectly precipitates the oxide in the cold. The precipitate usually contains some iron, but no zinc. Preparation of Indium from Blende Roast the indiferous blende and boil in dilute sulphuric acid ; filter, nearly neutralise with sodium carbonate, and then put clean plates of zinc into the solution. Scrape the reduced metals from time to time from the zinc, and preserve the precipitates separately. The purifica- tion of the indium is then easier, in consequence of this fractional precipitation. Purification of Indium To obtain the indium pure, the precipitate containing it is dissolved in nitric acid. Most of the lead is first removed by means of sulphuric acid ; sulphuretted hydrogen is then passed through the liquor until the remainder of the lead, with the arsenic, cadmium, &c., is precipi- tated. The excess of sulphuretted hydrogen is then got rid of by boiling, and the liquor is next oxidised by means of potassium chlorate and precipitated by excess of ammonia. In this way a good deal of the zinc present passes into solution ; a small quantity, however, remains with the precipitated iron and indium oxides. The precipitate is now dissolved in dilute acetic acid, and again precipitated by sulphuretted hydrogen. A little zinc and iron still go down with the indium, and will after six precipitations ; so, for the perfect purification, an addi- tional operation is necessary. The mixed sulphides are dissolved in hydrochloric acid ; in this solution the ferric chloride is reduced to ferrous chloride by the evolution of sulphuretted hydrogen. Barium carbonate is now added, and then after twelve or twenty-four hours all the indium is found in the precipitate, free from all impurities but barium. To obtain the metal, the oxide is carefully heated in a stream of hydrogen. In consequence of the volatility, the heat at first must not 362 SELECT METHODS IN CHEMICAL ANALYSIS be great, and the stream of gas must be passed slowly. After tne reduction the metal will be found in small silver-looking buttons, which can be fused together under potassium cyanide. Separation of Gallium from Indium (A) Indium ferrocyanide, being relatively very soluble (especially at 60 to 70) in a hydrochloric liquid containing from one-third to one- half of the concentrated acid, potassium ferrocyanide may be used for ex- tracting moderate quantities of indium mixed with much gallium. Yet, gallium ferrocyanide retains sensible traces of indium, and the operation needs to be repeated if we wish to obtain an exact separation. This inconvenience, and that of introducing iron into' the analysis, render the process somewhat long and difficult. It is only to be recommended when we wish to separate other metals, such as aluminium and chromium, along with a little indium. (B) Of all the methods tried, the following is the only one which effects a prompt and accurate separation : The solution, suitably con- centrated, is treated with a slight excess of boiling potash. The boiling is kept up for some minutes, for in the cold indium oxide is not immediately thrown down by potash. The precipitate retains merely very slight traces of gallium, which are entirely eliminated by one, or at most two, repetitions of the same treatment. The potassic solutions contain merely slight traces of indium, which may be neglected in weight if the masses of gallium and indium are small, and consequently the volume of the alkaline liquids is moderate. To extract these traces of indium the solution is supersaturated with a very slight excess of hydrochloric acid, and the gallium and indium are precipitated together by slowly boiling the liquid after supersatura- tion with ammonia, or, better still, by means of cupric hydrate. The gallium and indium chlorides are transformed into slightly acid sul- phates ; a quantity of ammonium sulphate is added, slightly larger than what is necessary to transform all the gallium sulphate into gallium alum, and the liquid is then concentrated to a very small volume. After cooling, whether crystals of alum are already formed or not, the solution is mixed with four to five times its volume of alcohol at 70 per cent. The agitation causes the deposit of gallium-ammonium alum in a crystalline powder, which is washed once or twice with alcohol at 70 per cent. The alum is then taken up in a little hot water containing a trace of sulphuric acid, and the operation is re- peated several times. By far the larger quantity of the gallium is in this manner transformed into ammonium alum free from indium. The alcoholic solutions containing a small quantity of indium and gallium are concentrated down to a small bulk. The oxides are thrown down by boiling with ammonia, or by means of cupric hydrate ; they are dis- solved in hydrochloric acid, and are then treated with boiling potash. BISMUTH 363 We obtain thus a small supplementary quantity of indium free from gallium. As very little potash suffices, the slight traces of indium in the alkaline solution are absolutely unimportant, though the last residue of gallium may be separated as alum if its quantity is note- worthy. Generally the traces of indium carried by the potash along with the gallium are entirely eliminated after four alcoholic crystallisa- tions of the gallium-ammonium alum. With gallium containing 4 per cent, of indium seven or eight recrystallisations are necessary. These operations are performed very rapidly and easily with the salt derived from less than O'Ol gramme of gallium. BISMUTH For the detection of small quantities of bismuth, Mr. M. M. Pattison Muir recommends Schneider's test liquid prepared as follows : 12 grammes crystalline tartaric acid and 4 grammes stannous chloride are dissolved in caustic potash so as to produce a clear liquid having a dis- tinctly alkaline reaction ; it must remain clear at 60-70 C. To the liquid to be tested is added a considerable quantity of tartaric acid. It is warmed and made alkaline with caustic potash. A few c.c. of the test liquid are now added, and the mixture is heated for a few minutes to 60-70. If bismuth is present a brownish -black colour is pro- duced. One part bismuth may thus be detected in 210,000 parts of liquid. Mercury must be absent ; copper and manganese interfere slightly ; lead, arsenic, antimony, iron, cobalt, nickel, and chromium not at all. Detection of Minute Traces of Bismuth in Copper Sir F. Abel and Mr. F. Field proceed as follows : About 100 grains of the copper to be examined are dissolved in nitric acid, a solu- tion of lead nitrate, equal to about 5 grains of the salt, is added, and subsequently ammonia and ammonium carbonate. The precipitate is washed with ammoniacal water and dissolved in warm acetic acid. Considerable excess of potassium iodide is introduced, and the liquid is warmed until the precipitate disappears. On cooling, the crystalline scales will show by their colour the presence or absence of bismuth. If the least trace of bismuth is present, the precipitated scales are no longer yellow, but assume a dark orange or crimson tint, varying in intensity of colour according to the amount of bismuth present. This test is of such extraordinary delicacy that 0*00025 of a grain of bismuth may be detected in copper with the greatest ease, the lead iodide becoming dark orange, while O'OOl grain imparts a reddish- brown tinge and O'Ol grain a bright crimson, the scales resembling silver chromate in appearance. 364 SELECT METHODS IN CHEMICAL ANALYSIS Detection of Bismuth by the Blowpipe (A) The mixture of equal parts of potassium iodide and sulphur re- commended by Von Kobell for this excellent test has the great dis- advantage of being very deliquescent ; even if kept in closely stoppered bottles it sooner or later becomes pasty, and indeed almost liquid, if the bottles are often opened for use. As it is a great advantage to be able tc- have such mixtures ready for use, and, where possible, to keep them in little wooden boxes in the portable blowpipe apparatus, Mr. W. M. Hutchings replaces the potassium iodide by cuprous iodide, and finds that, in addition to the advantage of being non-deliquescent, the mixture so made is in other respects superior for use with the test. Von Kobell's mixture has another disadvantage, viz., that it itself yields a copious ivhite sublimate, the brilliant red sublimate obtained when it is used with a substance containing a good deal of bismuth being caused by the mixture of this white with the dark brownish-red given by bismuth iodide alone. When very little bismuth is present and a good deal of the mixture is used, the white frequently overpowers the red almost completely, and when other metals are present which also give white or light-coloured sublimates, it greatly assists in concealing the bismuth colour. This disadvantage is also got rid of by using cuprous iodide and sulphur. The precipitated cuprous iodide is washed free from all trace of potassium salts, dried perfectly, and then ground up to an intimate mixture with an equal volume, or rather more, of flour of sulphur. This proportion is the best ; when less sulphur is used, there is more or less white sublimate of cuprous iodide obtained, and also the forma- tion of bismuth iodide is not as copious. For testing pyrites or other sulphides, less sulphur, or even none at all, would be required ; but it is best to have a mixture which is equally applicable to all bismuth combinations. This mixture can be kept rammed tight into little wooden boxes, and is always ready for use. On aluminium plate it is decidedly more delicate as a reagent 'than the potassium iodide mixture, using in each case 2 volumes of reagent to 1 volume of the powdered substance to be tested, intimately mixing to a paste and heating gently on a charcoal slip. The merest trace of the dark brownish -red bismuth iodide is very conspicuous on the clean aluminium. The plate should be made pretty hot by blowing the flame upon it some distance above the ledge before commencing to heat the test mixture, in o'rder to prevent the settling of a sublimate of iodine, or any condensation of moisture, which latter destroys the red bismuth sublimate. This precaution is particularly necessary when very little bismuth is present. On ordinary charcoal or a blackened porcelain support, the dark- coloured bismuth iodide is not nearly so conspicuous as on aluminium, and does not show so well as the brighter red obtained by using potas- BLOWPIPE DETECTION OF BISMUTH 365 slum iodide. But a few tests with a substance containing very little bis- muth will convince anybody that the aluminium plate, with the cuprous oxide mixture, is very much preferable to charcoal and potassium iodide. Substances containing mercury, when treated with the iodide mixture on aluminium plate, give a sublimate of mercuric iodide which is partly red and partly yellow, the relative quantities of the two colours varying much in sublimates from the same substance. The red is much lighter and brighter than that obtained from bismuth from the cuprous iodide mixture. It might possibly be taken for the bismuth sublimate mixed with that of lead ; but as the number of minerals containing mercury is so limited, and the presence of that metal is so easily proved by other tests, no mistake is likely to arise from this cause. The value of this test of Von Kobell's is very great ; it deserves to rank as one of the best in some cases the best test for bismuth. As little as 0-2 or O'l per cent, can be safely detected by it in many cases, and with great rapidity. In pyritous ores which fuse to a regulus, or in smelted regulus, a considerable amount of bismuth might be present and not be detected by the ordinary sublimate of bismuth oxide, which is frequently very difficult to obtain from such combinations. But a fraction of a per cent, can be found by this test without resorting to the wet way. (B) Substances containing lead give a copious light yellow subli- mate when heated with the iodide and sulphur mixture, and when lead is present beyond certain limits this yellow overpowers the bismuth reaction. According to Cornwall when lead oxide was mixed with 5 per cent, bismuth oxide, and tested on charcoal by Von Kobell's mixture, the bismuth could only just be detected, and not with distinctness. But when lead oxide containing only 1 per cent, bismuth oxide is tested with the cuprous iodide mixture on an aluminium plate, a very fine brownish-red sublimate is always obtained by heating very gently and observing after a few seconds. Later on the yellow covers this up ; but the bismuth iodide always comes off first, and can be seen if observed in time. In all cases sublimates must be allowed to get quite cold before judging them ; lead iodide is reddish when hot, but pure light yellow when cold. Cornwall's tests in open glass tubes which will detect bismuth when present in such small quantity with lead and antimony that the above method fails, can be better applied with the cuprous iodide mixture than with potassium iodide, and so much sulphur as he recommends (5 volumes) does not require to be added. Estimation of Bismuth. (A) Mr. M. M. P. Muir estimates the metal by precipitating a nearly neutral solution of the nitrate by potassium chromate or bi- 366 SELECT METHODS IN CHEMICAL ANALYSIS cliromate in a manner similar to that proposed by Pearson, but lie ascertains the critical point by testing the clear solution from time to time with argentic nitrate until red argentic chromate is produced ; the chromium solution being previously titrated with a solution of bismuth of known strength. The presence of chlorine, sulphuric acid, calcium, copper, or arsenic interferes seriously with the results obtained by this method. (B) Very accurate results are obtained by another process devised by the same author. The nitric acid solution of bismuth is mixed with an excess of sodium acetate, a measured volume excess of standardised sodium phosphate is added, the liquid boiled and filtered, the precipitate is well washed with hot water, and the excess of phos- phoric acid estimated in the filtrate by titration with a standard solution of uranium acetate. (C) Another method also due to Mr. Muir is as follows : An excess of saturated solution of oxalic acid is added to the solution containing bismuth, the precipitate allowed to settle, the supernatant liquid poured off, and the precipitate boiled with water until free from acid. The residue is now dissolved in dilute hydrochloric acid and titrated with permanganate. The absence of free hydrochloric acid must be secured before precipitating. The results are accurate, and the method is generally applicable. (D) Lastly, in a method proposed by Messrs. Muir and Robbs, the bismuth oxide is dissolved in a minimum quantity of nitric acid, the solution freed from excess of nitric acid by evaporation, and a large excess of acetic acid added. An excess of standard potassium oxalate is added in a measuring-flask, and the double bismuth and potassium oxalate, and allowed to settle. An aliquot portion of the clear solution ip drawn off and titrated with permanganate. Purification of Bismuth A simple plan to purify bismuth is based on the fact that when a large quantity of water is added to its solution mixed with hydrochloric acid a completely insoluble precipitate of bismuth oxychloride is obtained. Dissolve the metal in nitric acid and evaporate down with excess of hydrochloric acid ; the residue consists of bismuth chloride. Add concentrated hydrochloric acid and heat till the residue is dissolved ; filter if necessary through a sand filter. Now pour the solution in a thin stream, with constant stirring, into a large quantity of cold distilled water. A white precipitate of oxychloride is produced, which may either be weighed as such or reduced to the metallic state by fusion with potassium cyanide. ELECTEOLYTIC SEPARATION OF BISMUTH 367 Electrolytic Separation of Bismuth l (A) According to Classen, the electrolysis of bismuth presents diffi- culties in so far as it is not practicable to deposit considerable quantities of the metal upon platinum as a dense adhesive mass. Bismuth is always obtained in the same state whether it is deposited from an acid solution from the double ammonium oxalate, or from a solution mixed with potassium tartrate. If a sufficiently large surface is provided, if the capsule used as a negative electrode is filled to the edge, then, if the quantity of bismuth is not large, the washing out with water and alcohol may be effected without loss. But if the particles of metal are detached from the capsule they must be collected upon a weighed filter and determined separately. For the execution of the electrolysis the solution is mixed with a large excess of ammonium oxalate and reduced in the cold with a current of about 0*02 detonating gas per minute. During the decom- position we observe at the positive electrode a separation of peroxide, which again gradually disappears. In order to protect the reduced metal from oxidation, it is necessary to remove the last traces of water by a plentiful washing with absolute alcohol. (B) Good results may be obtained, according to A. Brand, if we mix the acid dilute solution of bismuth with four or five times the quantity of sodium pyrophosphate required for the formation of the double salt, render it exactly alkaline with ammonium carbonate, and dissolve in this liquid from 3 to 5 grammes ammonium oxalate. The solution is diluted to about 200 c.c., and there is then passed a current of from O'l to 0-5 c.c., which is gradually intensified until it reaches 2 to 3 c.c. of detona- ting gas per minute. If we begin with a current of 0*5 c.c. we may, according to Brand's experiments, reduce 0'25 grammes bismuth within twelve hours. If a slight veil of bismuth peroxide is deposited upon the positive electrode, it is removed towards the end of the precipitation with a few drops of oxalic acid. The end of the reaction is recognised by means of sulphuretted hydrogen water. Instead of determining the weight of the deposited metal, which is apt to become slightly oxidised, Brand proposes to convert it into oxide (Bi 2 3 ), which is effected by dissolving in nitric acid and igniting the dried nitrate. (C) Riidorff proposes the following combined method for the deter- mination of bismuth. On the assumption that the quantity of the metal in solution amounts as a maximum to 0*1 gramme he adds to the slightly nitric acid solution so much sodium pyrophosphate that the precipitate is re-dissolved, and then adds 20 c.c. of a saturated solu- tion of potassium oxalate and an equal quantity of potassium sulphate. The liquid diluted to 120 c.c. is decomposed with the current of four 1 For details of operation see chapter on Electrolytic Analysis. 368 SELECT METHODS IN CHEMICAL ANALYSIS Meidinger elements. The reduction requires at least twenty hours. The bismuth obtained is washed and then dried at 60 in the air-bath. (D) G. Vortmann effects the separation of bismuth as an amalgam (see Zinc). The compound of bismuth, dissolved in a minimum of hydrochloric acid, is mixed with a weighed quantity of mercuric chloride, and so much potassium iodide is added that the precipitate produced at first is re-dissolved. After dilution with water he proceeds as directed for zinc. During the electrolysis the iodine is deposited on the surface of the liquid in the form of a mass of bubbles. When the reduction is completed, which is ascertained by means of ammonia and ammonium sulphide, Vortmann, without interrupting the current, adds a little concentrated soda-lye and accelerates the solution by stirring up the liquid with the positive electrode. If the intensified current is then allowed to act for an additional hour, the separation is complete. This is ascertained by adding sodium sulphite and ammonium sul- phite to a small portion of the liquid. The amalgam is heated as described under Zinc. (E) The use of potassium iodide may be avoided if the deposition of the amalgam is effected from a hydrochloric solution mixed with alcohol. For this purpose the bismuth compound and the weighed quantity of mercuric chloride are dissolved in hydrochloric acid, and there are added about 50 c.c. of alcohol at 96 per cent. By degrees the liquid is diluted with so much water that the surface of the solu- tion reaches to 1 c. from the edge of the capsule, and electrolysed as usual. Vortmann especially recommends the last method for the separation of larger quantities of bismuth. Detection of Calcium Phosphate in Bismuth Subnitrate Calcium phosphate is sometimes met with in bismuth subnitrate as an adulterant. It may easily be detected in the following way : To 1 part of the bismuth salt dissolved in weak nitric acid add 2 parts of citric acid ; dissolve with the aid of a little water ; add an excess of solution of ammonia and boil. Any phosphate present will be thrown down by continuous boiling of the solution. Separation of Bismuth from Thallium These elements frequently occur together in minerals containing bismuth, and thallium may frequently be detected in medicinal pre- parations of bismuth, especially the carbonate. The bismuth com- pound is to be first obtained in the form of a dilute solution, any convenient acid being used for this purpose. A slight excess of sodium carbonate is now added, and then a little potassium cyanide free from sulphide. The mixture is to be gently warmed and allowed to SEPARATION OF BISMUTH FROM GALLIUM 369 stand for ten minutes, then filtered, and a few drops of ammonium sulphide added to the clear liquid. If the slightest trace of thallium were originally present in the bismuth compound, it will now be precipitated as a sulphide, which, upon gently heating the liquid (not to the boiling-point), gradually collects together in deep brown, almost black, flakes, after the characteristic manner of thallium sulphide. This process is one of extreme delicacy. By means of it 1 part of thallium can be detected in the presence of more than 10,000 parts of bismuth. In some cases, the thallium is present in so small a quantity as to occasion only a slight darkening of the liquid when the ammonium sulphide is added. Upon allowing this to digest at a gentle heat, it will generally collect in the form of a few flakes at the bottom. These may be collected together on a small filter, washed to the apex, and tested in the spectroscope. When the precipitate is only present in sufficient quantity to produce a faint dark stain on the filter-paper, the latter may be partially dried by pressure between blotting-paper, opened, and the stained surface scraped up with a knife. The dark fibres are now to be twisted up in a platinum wire loop and held in the flame of the spectroscope, when they will give abundant indications of the presence of thallium. Separation of Bismuth from Gallium Three methods are to be recommended : (A) The distinctly acid hydrochloric solution is saturated with hydrogen sulphide. All the bismuth is obtained as sulphide, which retains no gallium. The operation succeeds even when the liquid has been rendered turbid by a previous dilution. (B) The bismuth may be reduced by zinc in a solution which is kept distinctly acid, but it is better to use copper, which does not introduce impurities like zinc, and the ulterior separation of which from gallium is easy. The acid hydrochloric solution is treated for from twelve to eighteen hours with an excess of finely divided copper. The liquid is kept at a gentle heat all the time, which hastens the deposition of the bismuth. We find no bismuth in the liquid or gallium in the deposit. The formation of insoluble cuprous chloride is not an inconvenience. (C) In a solution containing one-third of its volume of concentrated hydrochloric acid, and in presence of bismuth, gallium chloride is precipi- tated by potassium ferrocyanide, either in the cold or at 60 to 70. The gallium ferrocyanide, well washed with hydrochloric water, retains no bismuth. It is to be remarked that, contrary to the statements of the chemical text-books, the precipitate formed by ferrocyanide with bismuth chloride is readily soluble in hydrochloric acid, even if dilute. Boiling potash does not effect the exact separation of gallium from bismuth. The precipitated oxide is free from gallium, but the B B 370 SELECT METHODS IN CHEMICAL ANALYSIS alkaline liquid retains a notable quantity of bismuth. It is generally, but erroneously, assumed that in analysis bismuth oxide is completely precipitated by potash. Separation of Bismuth from Lead (A) Add to the concentrated solution just enough hydrochloric acid to precipitate all the lead chloride, but so that a few drops of water do not render the liquid turbid. Then add dilute sulphuric acid, the slow action of which is hastened by occasional agitation ; finally, after having added alcohol and well mixed the whole by renewed agitation, allow the lead sulphate to deposit. This precipitate is to be filtered and washed, first with alcohol containing a few drops of hydrochloric acid, and then with pure alcohol. The bismuth may be precipitated in the filtrate by dilution with a large quantity of water. (B) There is no difficulty in volatilising bismuth in presence of lead by merely heating their sulphides in a glass tube in a current of bromi- ferous air, with a gas flame one and -a half inches in height. The mixed precipitated sulphides are dried at 100, placed in a porcelain boat which has been previously weighed, and heated in a current of air and bromine vapour. Bismuth bromide distils over completely, whilst lead bromide remains in the boat sufficiently pure for weighing. The receivers for the bismuth bromide should contain very dilute nitric acid. For success the following precautions are absolutely necessary. The sulphides obtained must not be allowed to stand a long time, either in the liquid or in the funnel, &c., but the operation must be proceeded with as soon as possible. A too prolonged action of the air upon the mixed sulphides is decidedly injurious, and sometimes may lead to results which are completely worthless. Such preparations when sub- sequently heated in the current of bromine vapour do not yield simply pure bromides, but simultaneously basic compounds, a circumstance which more or less interferes with the complete volatilisation of the bismuth. Messrs. P. Jannasch and P. Etz make the following arrange- ment. In the evening the solution is placed ready for the introduc- tion of the sulphuretted hydrogen, so that the precipitation may be effected without loss of time the next morning. The filter is carefully lifted out of the funnel and dried, first on a flat porcelain capsule, and then in the funnel, so that in the afternoon, after the commencement of the analysis, they are able to undertake the heating in a current of bromine vapour. The expulsion of the bismuth by bromine suc- ceeds best when a somewhat abundant quantity of sulphur is mixed with the precipitated sulphides. Hence it is advantageous to add to the hydrochloric solution of the metals a few drops of red, fuming nitric acid, prior to the introduction of the current of sulphuretted hydrogen. SEPARATION OF BISMUTH FROM LEAD 371 The mixed sulphides in the porcelain boat, before their introduction into the glass tube, should be duly comminuted by means of a platinum rod, in order, on the one hand, to admit of a rapid and thorough action of the bromine, and on the other to prevent the projection of particles, which is apt to occur if the mass consists of large fragments. The current of bromine from the very commencement of the opera- tion should be rather rapid (about 300 gas bubbles per minute from a glass tube of 6 m.m. in width), since a deficiency of bromine may inter- fere with the formation of the volatile bismuth tribromide, and may also allow of sublimation in the wrong direction. At the end of the operation, and whilst the tube is cooling, the current may be moderated accordingly. As it is found disadvantageous to leave the mixed sulphides in the drying-closet at 100 too long, it is better to put an end to the desicca- tion as soon as the loss of weight of the substance does not exceed a few m.grms. in a quarter of an hour. Hence it appears necessary before commencing the bromine treatment to pass first a current of dry air over the substance in the boat at a very gentle heat, so that the moisture still present may be carried over into the receiver. In the treatment with bromine an unnecessarily strong heat must be avoided. A Bunsen flame of 8 c.m. in height is sufficient. The tube is first heated in front of the boat, waving the flame to and fro, and then the boat itself is gradually heated until the residual lead bro- mide melts. When all the bismuth has been driven as far forward as possible the flame is brought back to the boat, its contents being again heated to fusion. This is repeated two or three times, and when nothing further passes over, the heat must not be increased, but the contents of the tube are allowed to cool quietly in the current of bromine. The lead is weighed first as bromide in the boat and finally as sul- phate, into which state it is converted by heating the bromide with saturated chlorine water and precipitating the solution of lead chloride with sulphuric acid. The solution of bismuth nitrate in the receivers is concentrated, precipitated at the temperature of ebullition with ammonium carbonate, and weighed as bismuth oxide. The ignited oxide is covered with solution of ammonium carbonate, evaporated on the water-bath, heated more strongly in an air-bath, and fully ignited to expel any traces of sulphuric acid. Estimation of Bismuth in Lead Alloys. The alloys are dissolved in nitric acid, the solution diluted with water, and the bis- muth precipitated by a strip of pure lead. The precipitated bismuth, black in colour and in the state of powder, is quickly washed off the lead, and the solution of lead decanted ; the bismuth is then washed first with water and then with alcohol, filtered on a weighed filter, dried, and weighed. B B 2 372 SELECT METHODS IN CHEMICAL ANALYSIS Separation of Bismuth from Cadmium In the separation of certain metals of the sulphuretted hydrogen group, such as lead, bismuth, cadmium, and tin, according to the cus- tomary methods, Messrs. P. Jannasch and P. Etz not seldom en- countered unexpected difficulties which seriously affect the accuracy of the results. Separations in a current of chlorine are evidently more trustworthy, and most of these have already been studied. The decided advantages which bromine permits in its use, as well as the observation that the temperatures of volatilisation of the metallic bromides differ more widely among themselves than those of the cor- responding chlorides, suggested the re-examination of the analyses which were effected some years ago with bromine vapour, and to ex- tend the method. The first examination of this kind was so favour- able that they could hope by means of the new process to enrich quantitative analysis with a series of exceedingly simple and accurate metallic separations. The procedure is as follows : As initial materials they used cad- mium sulphate and metallic bismuth, of the purity of which they were satisfied by special analyses. These substances are dissolved in nitric acid, the solution evaporated down on the water-bath, and the residue taken up with as much hydrochloric acid as is neces- sary to prevent the deposition of basic bismuth chloride on the addi- tion of about 100 c.c. of water. From the solution in hydrochloric acid, which is heated to ebullition, the metals are thrown down as sulphides by means of a current of sulphuretted hydrogen collected upon a filter, dried and weighed at 100, washed with hot sulphuretted hydrogen water, and then completely dried in an air-bath and weighed. The desiccated mixture of sulphides is placed in a porcelain boat in a dried tube of potash glass, and a brisk current of air, which has traversed a cylinder containing bromine, is passed over it from a gaso- meter. The bromine acts upon the substance even in the cold, but the reaction must be assisted and completed by moderate heating with a gas flame 1^ inches high, kept in a wavering motion, during which the occasional appearance of a russet-yellow flame may be observed in the tube. After about half an hour, all the bismuth has been carried into the receivers, which have been charged with weak nitric acid, whilst all the cadmium remains behind in the boat as a bromide. This bromide is dissolved in a little dilute hydrochloric acid, heated to ebullition, and precipitated with sodium carbonate. The solution of bismuth taken from the receivers is evaporated down, and the bismuth is finally separated by boiling with a mixture of ordinary ammonium carbonate and a little ammonia. ELECTROLYTIC SEPARATION OF BISMUTH 373 The complete separation of the bismuth is evident on the careful examination of cadmium. No trace of a brown precipitate appears on passing sulphuretted hydrogen into the hydrochloric solution. The precipitate is a pure yellow from the first. Moreover, the solution of cadmium, copiously diluted with water, gives no milky turbidity of bismuth oxychloride. The mixed sulphides must be perfectly free from water when ex- posed to the action of the current of vapour of bromine. Electrolytic Separation of Bismuth from Copper l (A) A separation of both metals cannot be effected in the solution of double oxalates ; they are always precipitated together. The separa- tion succeeds, however, in a solution containing free nitric acid. Pro- ceed as directed for the determination of copper, and precipitate the bismuth in the filtrate after the removal of the nitric acid and conver- sion into sulphate. (B) E. F. Smith adds citric acid for the separation of the two metals (3 grammes to 0*2 gramme of both), renders the solution alkaline with potash-lye, and adds a slight excess of potassium cyanide. The liquid must become clear after this addition, or more citric acid and potash- lye must be added. The solution is diluted to about 200 c.c. and electrolysed with a current giving 1 c.c. of detonating gas per minute. (C) In the reduction of bismuth from its ores, and its subsequent refining, Mr. Edward Matthey has frequently found this metal to contain a small proportion of copper, an element most detrimental even in small traces, and hitherto only eliminated by a wet process, costly in practice and tedious in operation, it being necessary by such method to dissolve up the whole of the alloy and precipitate the bismuth in the usual manner ; a bulky operation, and one requiring a considerable amount of time. It became therefore advisable, in order to treat cupreous bismuth rapidly and upon a commercial scale, to effect this separation, if possible, by means of a dry process. Mr. E. Matthey having observed, in conducting experiments with bismuth and its sulphides, that bismuth sulphide is very easily im- pregnated with copper, made the simple experiment of fusing the cupreous bismuth with bismuth sulphide, and found it possible by this means to remove every trace of copper, the sulphur readily combining with the metallic copper. In this absorption a proportion of bismuth is reduced equivalent to the amount of copper taken up in the operation. The residual bismuth and copper sulphides thus produced amount to but a small proportion in comparison with the quantity of alloy treated, and the bismuth readily recovered by subsequent reduction and refusion. Large quantities of alloy can be treated at one operation, 1 For details of operation see chapter on Electrolytic Analysis 374 SELECT METHODS IN CHEMICAL ANALYSIS and the bismuth so freed from copper is available for commercial pur- poses. It is better when bismuth is associated with other metals, such as arsenic, antimony, lead, tellurium, &c., as well as with copper, to separate all these metals before attempting to remove the copper by the foregoing method. The operation has been conducted successfully upon many thou- sands of pounds of similar alloy, and the whole of the copper and bis- muth, within a. small fraction, is accounted for, the latter being ob- tained as commercially pure bismuth and wholly free from copper. The first separation frees 90 per cent, of the bismuth at once from the copper associated with it. Mr. E. Matthey has effected complete separation with bismuth con- taining proportions of copper varying from O'l per cent, to 1 per cent, by the above process. Separation of Bismuth from Mercury To the solution containing the bismuth and mercury (as per- salt) add a large excess of hydrochloric acid to prevent the precipitation of bismuth oxychloride, and then add phosphorous acid. On standing, the mercury will be precipitated in the form of protochloride. After the separation of the mercury add a large quantity of water, which precipitates the bismuth as oxychloride. Reduce this to the metallic state by fusion with potassium cyanide. Detection of Copper, Bismuth, and Cadmium when simultaneously present M. lies adds to the slightly acid solution of the three metals, potas- sium ferrocyanide in slight excess, when all three are thrown down as ferrocyanides. Potassium cyanide is added in excess and the mixture is gently heated. The copper and cadmium compounds dissolve, whilst the bismuth remains as a white flocculent hydroxide. The filtrate is divided into two portions ; the one is tested for copper with hydrochloric acid, which occasions a brown-red precipitate of copper ferrocyanide, whilst to the other is added a little ammonia and ammo- nium sulphide. On the application of a gentle heat, yellow cadmium sulphide is precipitated. 375 CHAPTEK IX ANTIMONY, TIN, ARSENIC, TELLURIUM, SELENIUM ANTIMONY Electrolytic Deposition of Antimony ' (A) Classen finds that from a hydrochloric solution antimony is deposited as a metal, but is not firmly adhesive. If potassium oxalate is added to the solution of the antimony, the reduction is very easy, but the metal adheres even less firmly than in the former case. A firmly adherent metallic deposit is obtained by an addition of potassium tar- trate, but the deposition then proceeds too slowly. The precipitation of antimony succeeds very well from the solutions of its sulpho-salts. If ammonium sulphide is used for the formation of the double salt, it must contain neither free ammonia nor poly-sul- phides. It is therefore advantageous to use ammonium hydro-sulphate, which is preserved in small quantities in well-fitting bottles. For the deposition a cold solution and a feeble current musb be used, preferably one which gives off at the voltameter from 1*5 to 2 c.c. of detonating gas per minute. In the electrolysis of a solution of antimony mixed with ammonium sulphide, sulphur is deposited on the capsule above the metal, and cannot be removed by rinsing with water. If the metal is subsequently rinsed with ammonia, we may remove the thin film of sulphur by rubbing with the finger, or with a handkerchief moistened with alcohol, without the risk of losing antimony. The use of antimony sulphide is open to an objection, since, when several determinations are executed simultaneously, the smell is un- bearable. A series of experiments were therefore made with sodium monosulphide, potassium monosulphide, and also sodium and potassium hydro-sulphides, which proves that antimony may be successfully separated from their double salts. Among the above-named alkaline sulphides, sodium sulphide (Na 2 S) offers the greatest advantage for the separation of antimony from tin and arsenic. Hence the subsequent details refer exclusively to the use of the salt in question. The preparation of sodium sulphide is best effected as follows : 1 For details of operation see chapter on Electrolytic Analysis. 376 SELECT METHODS IN CHEMICAL ANALYSIS Pure sodium hydroxide is dissolved in so much water that the solution has the specific gravity of about T25. The liquid is divided into two equal parts, and the one half is saturated in the absence of air with the purest hydrogen sulphide procurable, until no further increase of volume can be observed. The hydrogen sulphide is passed for purification through a washing-bottle filled with water, and then through several glass tubes filled with cotton or wadding. After thorough precipitation the solution is filtered to remove the precipitate, and mixed with the other half of the solution. Hydrogen sulphide is again passed into the mixed liquid, in the absence of air, until perfect saturation is obtained, and the filtration is again repeated. The pale- coloured filtrate is evaporated down as rapidly as possible in a capa- cious basin of platinum or thin porcelain over a brisk, open fire. The liquid boils without bumping if a platinum spiral is inserted. As soon as a thin crystalline film is observed the ebullition is interrupted, and the liquid, while still hot, poured into small bottles fitted with glass stoppers accurately ground. The exclusion of air must be rendered complete by means of melted paraffin. The solution must have a sp. gr. of 1*22 to 1*225 for separating antimony from tin. In the electrolysis of the antimony sulpho-salt, the reaction is pro- bably as follows : The current first decomposes the water 3H 2 0=6H + 30. There is formed at the cathode and at the anode =3NaS In the precipitation of antimony from its solution in sodium sul- phide, it must be remembered that in presence of the sodium poly- sulphides the separation of antimony is either not quantitative or may be entirely prevented. As the determination of antimony is generally preceded by a separation from the metals of the sulphuretted hydrogen group (which separation is effected either by digestion or fusion with the alkaline poly sulphides), the quantitative determination of antimony in the electrolytic way can be applicable only if the antimony sulphide, separated from the sulpho-salts by means of an acid, is first freed from the accompanying sulphur. It does not require special mention that in such cases electrolysis would present no advantages. M. Classen has elsewhere pointed out the energetic oxidising action of hydrogen peroxide, and has pointed out that it converts the alkaline monosulphides into sulphates, without any separation of sulphur. With the alkaline polysulphides its behaviour is analogous. ANTIMONY 377 The method of determining antimony in the solutions of alka- line polysulphides is very simple. Add to the solution in question an excess of hydrogen peroxide, and apply heat until the liquid is colourless. If a large excess of hydrogen peroxide is used, it may happen that the alkaline sulphide is completely decomposed and anti- mony sulphide is liberated. "If the solution is entirely decolourised, or if a precipitate of antimony sulphide has already been formed, add, after it has become cold, about 10 c.c. of a saturated solution of sodium monosulphide, and electrolyse the cold solution, which should amount to 150 to 175 c.c., by means of a current corresponding to 1'5 to 2 c.c. detonating gas per minute. If the electrolysis is initiated in the even- ing, we find the antimony quantitatively deposited the next morning (ten to twelve hours). If the quantity of the antimony does not exceed 0'16 gramme, the metal forms a greyish -white deposit, adhering firmly to the capsule. The capsule with the antimonial deposit is treated in the usual manner with water and perfectly pure, absolute alcohol, dried for a short time in the air-bath at from 80 to 90, and weighed. A Meidinger battery of from 4 to 6 elements may serve to yield a constant current of 1 '5 to 2 c.c. detonating gas per minute. (B) H. Nissenson adds to a solution of antimony containing not more than 0*18 gramme antimony, 50 c.c. of a saturated solution of sodium sulphide. This solution is obtained by covering the commer- cial quality with water, and allowing it to stand with the air excluded until the liquid above the undissolved residue is colourless. The hot solution is electrolysed in a platinum capsule with a current of 0*5 to 1 ampere. About 0*15 gramme of antimony is deposited in the course of one hour. (C) F. Riidorff mixes the solution of antimony with about 30 c.c. of a 10 per cent, solution of sodium monosulphide, and electrolyses with 2 or 3 Meidinger elements. The conclusion of the reaction is ascertained by means of acetic acid, which liberates orange-red anti- mony sulphide, if present. (D) For depositing antimony as an amalgam, G. Vortmann mixes the solution containing the antimony as pentoxide (peroxidised if need- ful with bromine-water) with a weighed quantity of mercuric chloride (to 1 part of antimony at least 2 parts of mercury), and adds the solu- tion proposed by Classen for separating antimony from arsenic (a mix- ture of sodium sulphide and hydroxide) until the solution appears perfectly clear. It is diluted with water to about 175 c.c., and electro- lysed in the manner directed for amalgam. For preparing the mixture 60 c.c. of solution of sodium sulphide (sp. gr. 1;22 to 1-225) are mixed with so much of a concentrated solution of pure sodium hydroxide that the liquid may contain about 1 gramme NaOH. (E) Dr. C. A. Kohn dissolves the precipitated sulphide in potas- sium sulphide, and the resulting solution, after warming with a little 378 SELECT METHODS IN CHEMICAL ANALYSIS hydrogen peroxide to decolourise any polysulphides that may be present, is electrolysed with a current of 1-5 to 2 c.c. of electrolytic gas per minute (10-436 c.c. at and 760m.m.=l ampere), when the antimony is deposited as metal upon the negative electrode. One part of anti- mony (as metal) in 1,500,000 parts of solution may be thus detected a reaction thirty times more delicate than the deposition by means of zinc and platinum. The stain on the cathode, which latter is best used in the form of a piece of platinum foil about 1 c.m. in diameter, is distinct even with a solution containing -^ m. grm. of antimony, and by carefully evaporating a little ammonium sulphide on the foil, or by dissolving the stain in hot hydrochloric acid and then passing a few bubbles of sulphuretted hydrogen gas into the solution, the orange- coloured sulphide is obtained as a satisfactory confirmatory test. The detection of O'OOOl gramme of metal can be fully relied on under all conditions, and one hour is sufficient to completely precipitate such small quantities. Estimation of Antimony (A) When antimony is precipitated in the form of sulphide, instead of weighing it as such, Wohler advises that it be converted into anti- moniate of antimony oxide (Sb. 2 3 ,Sb 2 5 ), by complete oxidation with fuming nitric acid in a weighed porcelain crucible. To avoid ignition, the substance must be moistened with a few drops of dilute acid before adding the fuming acid. A prolonged digestion effects the complete solution of the pulverulent precipitate of sulphur. The excess of acid is then evaporated off carefully, and the residue calcined. (B) Mr. Sharpies employs the following process in the precipita- tion of antimoiiious sulphide : Into the solution, containing, as usual, tartaric and free hydrochloric acids, a current of sulphuretted hydrogen is to be passed, the liquid being, during the passage of the gas, gradu- ally heated to the boiling-point. The boiling is then to be continued for fifteen or twenty minutes, the current of gas passing uninterruptedly until the voluminous sulphide has become a dense granular powder occupying but a small portion of the original volume of the sulphide. The sulphide may then be washed with great facility, and dried upon a sand filter at 200 or 300 C. All the estimations of antimony made in the laboratory of the Lawrence Scientific School for some years have been executed in this manner, the results leaving nothing to be desired. Arsenious sulphide does not become granular and dense under the same circumstances. Rapid Detection of Antimony in Minerals (A) Minerals which contain antimony, when heated alone before the blowpipe on charcoal, or with the addition of three or four parts of fusion mixture (K 2 C03 + Na 2 C0 3 ), yield dense white fumes of anti- RAPID DETECTION OF ANTIMONY 379 monious oxide, 1 which in great measure escape into the atmosphere, but which also in part become deposited on the charcoal support, forming a well-marked white sublimate, or incrustation of the oxide. Those results, though certainly in most cases very useful indications, do not furnish to the satisfaction of the mineralogist sound, conclusive evidence of the presence of antimony in the mineral tested, seeing that several other bodies occurring in the mineral world give, when heated before the blowpipe, exactly the same or nearly similar reactions. As a consequence of the hitherto inconclusive blowpipe evidence, mine- ralogists have usually considered it essential when engaged in correct work to supplement those indications by means of the accurate but tedious method of the ordinary wet way qualitative chemical analysis. With a view to remove the necessity of consuming so much valuable time over the certain identification of antimony, Mr. Alexander John- stone proposes the following exceedingly simple test, which he discovered and successfully applied whilst working amongst the various metallic ores of antimony. To the white coat which will invariably form on the charcoal if the mineral containing antimony be properly treated and heated before the blowpipe, add, by means of a narrow glass tube, a single drop of am- monium sulphide. If the white sublimate is composed of antimonious oxide, then the portion touched by the drop (or the part touched by the edge of the drop) will immediately become converted into the well- known and highly characteristic reddish or orange antimony sulphide. As no other white coat producible on charcoal by heating a mineral in the blowpipe flame becomes reddish or distinctly orange in. colour when treated as above with ammonium sulphide, the value of this easily applied test must at once be apparent. (B) In the examination of mineral bodies for antimony, the test substance is often roasted in an open tube for the production of a white sublimate. Dr. E. Chapman, Professor of Mineralogy at Toronto, re- commends for the detection of antimony in this substance the following process : a method more especially available when the operator has only a portable blowpipe-case at his command : The portion of the tube to which the chief part of the sublimate is attached is to be cut off by a triangular file, and dropped into a test-tube containing some tartaric acid dissolved in water. This being warmed or gently boiled, a part at least of the sublimate will be dissolved. Some potassium bisulphate either alone, or mixed with some sodium carbonate and a little borax, the latter to prevent absorption is then to be fused on charcoal in a reducing flame ; and the alkaline sulphide thus produced is to be removed by the point of the knife-blade and placed in a small porcelain capsule. The hepatic mass is most easily separated from 1 Not altogether antimoniotis oxide (Sb./) 3 ), according to Dittmar. That chemical authority asserts that a small portion of the coat is composed of the amor- phous antimony tetroxide (Sb.OJ. 380 SELECT METHODS IN CHEMICAL ANALYSIS the charcoal by removing it before it has time to solidify. Some of the tartaric acid solution is then to be dropped upon it, when the well-known orange-coloured precipitate of antimony sulphide will at once result. In performing this test, it is as well to employ a somewhat large fragment of the test substance, so as to obtain a thick deposit in the tube. It is advisable also to hold the tube in not too inclined a position, in order to allow but a moderate current of air to pass through it ; and care should be taken not to expose the sublimate to the action of the flame, otherwise it might be converted almost wholly into a compound of antimoiiious and antimonic acids, the greater part of which would remain undissolved in the tartaric acid. A sublimate of arsenious acid, treated in this manner, would, of course, yield a yellow pre- cipitate, easily distinguishable by its colour, however, from the deep orange antimonial sulphide. The crystalline character, &c., of this sublimate would also effectually prevent any chance of misconception. (C) Dr. A. Weller proceeds as follows for the estimation of anti- mony : Antimonic acid and antimonic oxide, and in like manner antimony penta- and trichloride, can be most easily distinguished from each other by their different behaviour with potassium iodide. The property of the former, when in hydrochloric solution, of separating two atoms of iodine from potassium iodide for each atom of antimony, can be used for the qualitative estimation of antimony. In order to verify the method, weighed quantities of finely pulverised pure metallic antimony are oxidised in a flask at a gentle heat with potassium chlorate and hydrochloric acid, and the excess of chlorine is expelled by strong heating. The solution of antimony pentachloride thus ob- tained is introduced into the flask of Bunsen's chlorine distillation apparatus by means of hydrochloric acid, considerably diluted, and mixed with a sufficiency of perfectly pure potassium iodide, avoiding too great an excess. The liberated iodine is distilled into dilute solution of potassium iodide, observing all the precautions laid down by Bunsen, and especially cooling the retort well in flowing water. When cold the distillate is titrated in the usual manner by means of very dilute sulphurous acid and an iodine solution of known strength. The distillation-flask has the capacity of about 120 c.c. The distilla- tion requires from five to ten minutes. Particularly important is the fact that stannic acid and stannic chloride in acid solutions do not decom- pose potassium iodide. This behaviour renders it possible to estimate antimony in presence of tin, as in alloys, easily and accurately. The tin is calculated as difference. Estimation of Antimony in Native Antimony Sulphide The estimation of antimony in this mineral is very easily effected by means of gallic acid, and its complete and accurate analysis is rendered simple by the gallic-acid process. ESTIMATION OF ANTIMONY 381 Twenty grains of the powdered mineral are treated by a slight ex- cess of hydrochloric acid, and the mixture is gently heated until the whole of the sulphuretted hydrogen disengaged is thoroughly evolved. The solution is then filtered, the filter and matrix are washed with dilute hydrochloric acid, and the solution is slowly evaporated in the flask until it is conveniently concentrated and freed from the excess of hydrochloric acid. In this solution the whole of the antimony exists in the state of terchloride, a slight excess of a recently prepared solution of gallic acid is added, with the precautions already indicated. Hot water is then added, and the precipitate of antimony bi-gallate is washed, dried, and weighed, as has already been stated. Antimony may also be estimated as sulphide after having been separated as bi-gallate. Twenty grains of this mineral are quite sufficient for the estimation of antimony, but in the complete analysis it would be inconvenient to operate upon more than 50 grains, as the precipitated antimony bi-gallate is very bulky. Antimony being separated as above, iron, lead, copper, silver, arsenic, and sometimes zinc, cobalt, and other metals remain in solution. Arsenic exists much less frequently than is generally supposed. Copper is very often present. It can be estimated here with the greatest accuracy, as the whole of it exists, or may be made to exist, in the filtrate. The analysis of the filtrate is proceeded with as that of an ordinary liquid containing the metals mentioned. The only metal which can- not be properly estimated in this liquor is iron, the presence of gallic acid preventing its precipitation, even by means of ammonium sul- phide, but its complete separation from antimony is so simple by the known methods that this fact need only be mentioned. Estimation of Antimony in the Antimony Sulphide obtained in the Course of Analysis In the course of a complicated analysis, it is often absolutely neces- sary to obtain antimony first in the state of a sulphide mixed with a large quantity of sulphur, and contaminated with copper, arsenic, or tin sulphides. The gallic-acid process affords a simple means of carrying out a careful analysis in this part of the operation, and of estimating anti- mony by a direct process. For this purpose the collected mixture of sulphur, antimony sulphide, ** 0? THE *"^^i 442 SELECT METHODS IN CHEMICAL ANALYSIS The mother-liquid from which all this platinum and palladium have been obtained may contain some indium and rhodium ; it is, therefore, evaporated to dryness with a little potassium iodide, whereby a mixture of the rhodium and iridium iodides separates. This can either be dissolved in aqua regia and the two metals separated (as will hereafter be described) by sodium bisulphite, or it can be united with the next portion from which these metals will be obtained. Ruthenium, Rhodium, and Iridium. The residue from the original material which remains, after treatment with ammonium chloride and nitric acid, is treated as follows, to get the metals in a form adapted to further chemical treatment. The method depends upon the behaviour of zinc chloride to zinc. If a piece of zinc be melted, it rapidly covers itself with a stratum of oxide. If to the melted metal a metal like iridium be added, the oxide stratum hinders the latter from coming into contact with the zinc, even though it be pushed beneath the surface. If, however, a few grains of ammonium chloride be added to it, ammonia, hydrogen, and zinc chloride will be formed, which last dissolves the oxide stratum to basic zinc chloride. The zinc below resembles mercury in lustre and mobility. As soon as the chloride has dissolved as much of the oxide as possible, the oxide stratum again forms, and is instantly removed again by the addition of more ammonium chloride. The melted zinc, strewn with ammonium chloride, also possesses, like mercury, the property of attacking other metals, if the affinity exists of forming alloys with them. By strewing ammonium chloride upon the melted zinc, a quiet surging is kept up, as the ammonia and hydro- gen are given off. Many oxides and chlorides (among which are those of the platinum metals), when they come into contact with this atmo- sphere of reducing gases, and with the basic zinc chloride, are instantly reduced and dissolved by the zinc. In making the solution, the zinc, in a porcelain capsule, should be constantly rotated : the gangue remains in the basic chloride. The regulus, immediately upon solidifying, should be taken from the capsule, out of the yet liquid basic chloride, and washed off with acetic acid until all the basic chloride is dissolved away. The gangue can be quantitatively estimated by filtration and weighing. If the regulus is not immediately removed, the containing vessel will be broken, owing to the unequal expansion of the porcelain and the metal. The best proportions for a quantitative separation are, to 1 part of the platinum metals, from 20 to 30 parts of zinc. For an ordinary separation, 7 parts of zinc are sufficient. For the extraction of the residues remaining after the treatment with nitric acid this method is admirably adapted. By fusing only once with zinc for 2 or 3 hours, all the platinum metals are extracted. The operation is the following : From 3 to 3*5 kilogrammes of commercial zinc are fused in a 2-litre BUNSEN'S METHOD OF ANALYSING PLATINUM 443 Hessian crucible, ammonium chloride from time to time strewn upon it ; 400 grammes of residue, previously heated to faint glowing with ammonium chloride, are added, and the temperature kept, for 2 or 3 hours, just above the fusing-point of the alloy, by adding, whenever the mass threatens to solidify, some ammonium chloride. The mass is divided into three strata after solidification has taken place. The outer stratum, easily broken away by a blow from a hammer, contains no platinum metals. The next contains some particles of the zinc and platinum alloy, imbedded in the basic zinc chloride ; it is porous, and not very thick. The inner stratum consists of a beautiful crystalline regulus. To obtain the alloy from the middle stratum, it is only necessary to wash repeatedly with water ; and the alloy gained is, of course, to be added to the regulus. To obtain this regulus as pure as possible, it is again fused with 500 grammes of zinc and some ammonium chloride, then granulated in water, and the granules dissolved in fuming hydrochloric acid. The acid attacks the regulus with the greatest energy, and the solution is complete in less than an hour. The zinc chloride can be used for the next operation. The platinum metals are found at the bottom of the vessel, in the form of a finely divided black powder, which is contaminated with zinc, and with traces of iron, copper, &c. from the latter. It cannot be purified with nitric acid, nor with aqua regia, for part of the platinum metals will thereby be dissolved, or, at best, so suspended in the liquid that filtration is impossible. If, however, the powder is treated with hydrochloric acid, singularly enough, all the impurities are dissolved ; not only zinc and iron, but also lead and copper, dissolve readily, with the generation of hydrogen. The explanation is readily found in electrical currents produced by the contact of the metals, the stream passing from the positive zinc, iron, &c. to the negative platinum metals, hydrogen being given off on the latter and chlorine on the former, and uniting with them. The metallic powder, after thorough washing, possesses the property, upon being gently heated, of exploding weakly, and, when highly heated, with violence, the explosion being accompanied with the evolution of light ; thereby neither hydrogen, nor chlorine, nor nitrogen, nor aqueous vapour is given off ; and, as these are the only elements which it is possible that the metallic powder could have taken up, it must be assumed these metals are, by this treatment, converted into an allotropic con- dition, and that, upon heating, they return, with more or less energy, to their original condition. The powder contains, mainly, rhodium and iridium ; but there are traces present of platinum, palladium, lead, copper, iron, and zinc. It is intimately mixed with about 3 or 4 times its weight of con- pletely anhydrous barium chloride, and a stream of chlorine gas led over it at a tolerably high temperature. The operation is concluded 444 SELECT METHODS IX CHEMICAL ANALYSIS when particles of iron sesquichloride show themselves on the neck of the flasks containing the powder. These are carefully brushed away with filter-paper. Some water is now added, and the mass of the platinum metals dissolved with the evolution of heat. There remains behind insoluble matter, which, upon reduction with hydrogen, alloy- ing with zinc, and treatment with hydrochloric acid, furnishes ru- thenium. From the solution all the barium chloride is removed by careful addition of sulphuric acid. The platinum metals are now completely freed from all other metals by reduction with hydrogen, the temperature being, throughout the operation, maintained at nearly 100 C. by means of a constant water-bath. Platinum and palladium chiefly separate first ; then mainly rhodium ; and the last portions consist almost entirely of iridium. It is best to break off the opera- tion when the liquid has assumed a greenish-yellow colour. The last portions of iridium (obtained by evaporating the solution to dryness, fusing with sodium carbonate, and treatment with aqua regia) are added to the portion, afterwards to be again rendered workable by renewed treatment with barium chloride. The operation of reduction is hastened by concentrating the liquid, in doing which care must be taken to guard against explosion, on account of the hydrogen. The separated metals are treated with aqua regia, and the platinum and palladium thus dissolved separated from each other, as already described. The traces of rhodium and iridium in the mother-liquid can be removed entirely by continued boiling with potassium iodide (whereby they are precipitated as iodides) ; they are then dissolved in aqua regia and added to the insoluble portion. This insoluble and partly oxidised portion is now again reduced in hydrogen gas, treated, as before described, with barium chloride, and, after the removal of the barium, the last traces of platinum and pal- ladium removed by boiling with caustic soda. Rhodium and iridium now alone remain to be separated. The brown-red liquid is, for this purpose, evaporated with hydro- chloric acid, and, after filtration, treated with sodium bisulphite in great excess, and the whole allowed to remain quietly in the cold for several days. The double rhodium and sodium sulphide sepa- rates slowly, giving a lemon-yellow precipitate. The solution be- comes lighter and lighter, and finally almost colourless. The colour of the precipitate changes with that of the liquid, becoming, with it, lighter. This precipitate, upon washing, contains the rhodium almost pure. Upon heating the liquid gently, a yellow-white precipitate separates, which consists mainly of rhodium, but contains, also, some iridium. After filtering off this precipitate, the solution, upon being concentrated to a small volume, gives yet two precipitates 1. A curdy, slowly separating, yellowish- white precipitate, con- LEA'S PROCESS FOR ANALYSING PLATINUM ORES 445 taining nearly chemically pure indium, with but the faintest traces of rhodium. 2. A heavy, crystalline powder, quickly separating, which is readily freed from the first hy decantation. Upon testing, it gives all the re- actions for iridium, but likewise some peculiar reactions not shown by the latter. It may possibly contain a new metal. The complete separation of rhodium from iridium is accomplished by treating the yellow precipitates with concentrated sulphuric acid. They are brought in small portions into the acid, heated in a porce- lain capsule until all the sulphurous acid has escaped, and then left upon the sand-bath until the free sulphuric acid has been driven off and the sodium sulphate formed. Upon boiling the mass in water, all the iridium dissolves as sulphate, with a chrome-green colour; while the rhodium remains behind as a flesh-coloured double sodium and rhodium salt. The latter is boiled in aqua regia, and washed by decantation. It is insoluble in water, hydrochloric or nitric acids, and in aqua regia. The rhodium and iridium are now completely separated. The first yellow precipitate obtained in the cold by the sodium bisulphate gives, by this treatment, the rhodium quite pure. The second and third precipitates, containing much iridium, give a very fine rhodium, but still slightly contaminated with iridium. The products, therefore, obtained by this treatment with sulphuric acid (which betray their contamination with iridium by their somewhat brownish colour), are collected for themselves, the rhodium separated therefrom by glowing, treated again with barium chloride, and the operation of separation repeated. The green solution, containing only iridium, is gradually heated over an ordinary burner, in a porcelain cap- sule, and, afterwards, upon the sand-bath, to remove the excess of sul- phuric acid ; and, finally, the capsule and its contents are highly heated in a Hessian crucible. There are formed thereby sodium sulphate and iridium sesquioxide. Upon boiling the mass with water, the last re- mains behind as a black, insoluble powder, which is readily washed by decantation. (C) C. Lea's Process for Analysing Platinum Ores. The ores on which these analyses were performed contained chiefly iridium, to- gether with ruthenium, osmium, rhodium, and platinum. It was a Californian osmiridium which had already undergone a preliminary fusion with nitre and caustic potash. This material is boiled with aqua regia to extract all the soluble portions, the residue then ignited with nitre and caustic soda, 1 and the 1 Attention is necessary to the order in which these substances are employed. If the caustic soda is melted first, it attacks the iron vessel strongly, and may even go through. If added last it causes sudden and violent effervescence, with danger of boiling over. Therefore, place the nitre first in the vessel, and when it is fused add the caustic soda. When a red heat is obtained add the osmiridium by degrees. 446 SELECT METHODS IN CHEMICAL ANALYSIS fused mass heated with water. From the resulting solution small portions of potassium osmite crystallise out. The metallic oxides are next precipitated, and this precipitate, together with the portions insoluble in water, is boiled again with aqua regia, ignited, &c. These ignitions still leave a small portion of unattacked residue. The boiling with aqua regia is continued for a long time, in order to get rid as thoroughly as possible of the osmic acid. Even after 200 hours' boiling, osmium is still left in the solution in easily recognisable but comparatively small quantity. The greatest ad- vantage is found throughout the whole of this part of the operation from the use of a blowing apparatus, with the aid of which all incon- venience from the fumes of osmic acid is avoided. The apparatus is constantly swept clear by a powerful air current, and the osmic acid is removed as fast as it is volatilised. As the ignition of the ore with alkaline nitrate and caustic alkali scarcely drives off any osmium, and as almost all inconvenience in manipulating the resulting solutions can be avoided by throwing down the metals with alcohol from the hot alkaline solution, in place of using acid, it is clear that the diffi- culties arising from the noxious effects of osmic acid can be almost wholly removed from each of the various stages of the process. A very prolonged treatment with aqua regia is found to have the great advantage of converting nearly the whole of the ruthenium into bichloride. The separation of ruthenium in this form from the other metals is so easy in comparison with the difficulties presented by the separation of the sesquichloride, that this advantage cannot be looked upon as other than a very material one. Sal-ammoniac is next added to the mixed solution in quantity suffi- cient to saturate it. The sandy crystalline precipitate (A) is thoroughly washed out, first with saturated and then with dilute sal-ammoniac solution. The saturated solution of ammonium salt carries through with it nearly the whole of the ruthenium as bichloride (B) ; the dilute solution is found to contain small quantities of iridium, rhodium, and ruthenium (c). Over (A), water acidulated with hydrochloric acid is placed, and allowed to stand for some days. This is treated with ammonia and boiled. The precipitate, when treated with hydrochloric acid, furnishes green osmium chloride, with traces of ruthenium. In these preliminary steps Claus's process has been followed, which undoubtedly offers advantages over any other, and best brings the metals into a convenient state for separation, varying it only by pro- longing the treatment with aqua regia, and converting the ruthenium principally into bichloride instead of sesquichloride. We have now 8 portions of material : (A), consisting of ammo- nium iridiochloride, containing also ruthenium, osmium, rhodium, and platinum in small quantities. (The ore under examination con- tained no palladium, which metal, if present, has ^always its own LEA'S PROCESS FOR ANALYSING PLATINUM ORES 447 peculiar mode of separation, and does not enhance the difficulties of operation.) (B), containing ruthenium bichloride, together with iron in quantity, copper, and other base metals which may be present. Finally, (c), containing chiefly ruthenium bichloride, mixed with small quantities of iridium and rhodium. The next step in the process is to introduce the ammonium iridio- chloride (A) into a large flask with 20 to 25 times its weight of water, and apply heat until the solution is brought to the boiling-point ; the whole of the ammonium iridiochloride should be brought into solution in order that the reduction to be effected may not occupy too long a time, as otherwise the platinum and ruthenium salts, if any be present, might likewise be attacked. Crystals of oxalic acid are thrown in as soon as the solution actually boils, whereupon a lively effervescence takes place, and the iridium salt is rapidly reduced. As fast as the effervescence subsides, more oxalic acid is added, until further addi- tions cease to produce any effect. When this is the case, the liquid is allowed to boil for 2 or 3 minutes longer, not more ; the heat is to be removed, and the flask plunged into cold water. By this treatment any platinum present is unaffected. Sal-ammo- niac in crystals is added, about half enough to saturate the quantity of water present. The sal-ammoniac may be added immediately before the flask is removed from the fire. After cooling, the solution should be left for a few days in a shallow basin, whereby the ammonium platinochloride will separate out as a yellow, a reddish, or even (especially if the quantity of water used was insufficient) as a black crystalline powder, according to the quantity of iridium which it may contain. The mother-liquor is to be again placed in a flask and boiled with aqua regia. On cooling, the ammonium iridiochloride crystallises out, and any traces of rhodium and ruthenium which may be present re- main in solution. The iridium salt is to be washed with a mixture of 2 parts of saturated solution of sal-ammoniac and 3 parts of water, and may then be regarded as pure. The treatment by oxalic acid affords iridium free from all traces of ruthenium. The detection of very small quantities of ruthenium in presence of much iridium has been hitherto an impossibility, or could only be effected by Claus's method of allowing a small quantity of water acidulated by hydrochloric acid to remain in contact with the ammonium iridiochloride for some days. The ruthenium salt, by its superior solubility, tended to dissolve first ; hence the acidulated water, after standing, contained ruthenium in larger relative proportion than the original crystals ; the ruthenium reactions were more marked, and if it was present, and in sufficient quantity, it could be detected by potassium sulphocyanide, or, better, to an experienced eye, by lead acetate. The objections to this method are sufficiently obvious. The treatment of solutions (B) and (c) presents no difficulty. With 448 SELECT METHODS IN CHEMICAL ANALYSIS (B) the best plan is to place the solution aside in a beaker covered with filter-paper for some time. Treated in this way, the bichloride gra- dually crystallises out, and by recrystallisations may be obtained in a state of perfect purity. Solution (c) is to be evaporated to dryness, and reduced to an impalpable powder. It is then to be thrown upon a filter, and tho- roughly washed with a perfectly saturated solution of sal-ammoniac. The ruthenium bichloride is thus carried through, with perhaps a trace of rhodium sesquichloride, from which, however, it is easily freed by crystallisation. From the residue, the rhodium and ammonium ses- quichloride is removed by a dilute solution of sal-ammoniac. It is perfectly free from the indium, which is left behind. In connection with this separation, Mr. Lea makes a remark which, though of special reference to this particular case, is also applicable to all those cases in which the double chlorides of the platinum metals are to be separated by their various solubilities in solution of sal- ammoniac. This most valuable process, for which we are indebted, as for so much else, to Glaus, whose untiring labours have made him the father of this department of chemistry, requires to be applied with some attention to minutiae. The crystalline matter must be reduced to the finest powder, and after being thrown upon the filter, it must be washed continuously until the separation is effected. Any interruption of the washing is followed by more or less crystallisation of sal-ammoniac through the material, which precludes an effectual separation. The same material which in a state of coarse pow r der will hardly yield up enough ruthe- nium bichloride to colour the sal-ammoniac solution, w r ill, when thoroughly pulverised, give an almost opaque blood-red filtrate. Solution (c) may be subjected to a different treatment from the foregoing, and oxalic acid may be used to effect the separation. The solution is to be brought to the boiling-point, and oxalic acid added as long as effervescence is produced. The iridium bichloride is thereby reduced, the ruthenium bichloride and the rhodium sesquichloride are not affected. Sal-ammoniac is then to be dissolved in the solution to thorough saturation. By standing and repose the double rhodium and ammonium chloride separates out. The solution is then reoxidised by boiling with aqua regia ; by standing for some days in a cool place, the ammonium iridiochloride crystallises out, and the supernatant solution contains the double ammonium chloride and ruthenium bi- chloride, which may be rendered pure by several recrystallisations. For purifying the double iridium and ammonium chloride, the oxalic process is decidedly the best. It is simpler and easier, and there is the further advantage that the platinum is left in the condi- tion of double chloride, whereas when the usual method of treating with aqueous sulphuretted hydrogen is used, the platinum is apt to be converted partly into sulphide, together with any traces of rhodium DR. GIBBS'S PROCESS FOR ANALYSING PLATINUM ORES 449 and ruthenium which may be present. When oxalic acid is used, the platinum remains behind as a reddish powder, containing some iridium, from which it may be freed in the ordinary manner, if it is present in quantity sufficient to be worth working. For treating a mixture such as that which is here designated as (c), containing no platinum, and only ruthenium present in the form of ammonium rutheniochloride, it is unnecessary to apply reducing agents, and the first method described is the best. But if it be pro- posed to effect the separation by the reduction of the iridium compound, the method here described is preferable to that based on the use of sulphuretted hydrogen even in this case. The action of oxalic acid on the platinum metals is interesting ; its reducing effect upon iridium bichloride at the boiling-point is imme- diate. On ruthenium bichloride it seems to have no effect whatever, and they may be boiled together for a length of time without sensible result. In a trial made with ruthenium and ammonium sesquichloride, the oxalic acid was boiled with the metallic salt for a considerable time without any apparent effect becoming visible, but by long-continued boiling a gradual precipitation took place. When ammonium platino- chloride was boiled with oxalic acid, no effect was produced for a con- siderable time, but gradually the platinum salt diminished in quantity, and the liquid acquired a stronger yellow colour, perhaps owing to for- mation of soluble platinic oxalate. This process will not, however, furnish an easy and convenient method of purifying commercial plati- num from the iridium always found in it, as the reduction of very small quantities of double iridium and ammonium chloride in the presence of a large proportion of the corresponding platinum salt is difficult and slow, and the platinum salt itself is evidently attacked. (D) Dr. Wolcott Gibbs's Process for the analysis of platinum ore is as follows : The metals are first obtained in a nitro-hydro- chloric solution, and the liquid is then evaporated to dryness with an excess of sodium chloride. The mass of double chlorides obtained as already mentioned is to be rubbed to a fine powder, introduced into a deep porcelain evaporating-dish, and mixed with 4 or 5 times its volume of boiling water. A solution of sodium nitrite is then to be added in small quantities at a time, the solution being continually stirred, and occasionally neutralised by addition of sodium carbonate. The liquid soon becomes olive-green, and the greater part of the mass dissolves ; it is advantageous, when the quantity of the mixed chlorides is large, to pour off the liquid as soon as it appears saturated, and to repeat the operation with a fresh quantity of water. The un- dissolved mass, which consists chiefly of the impurities of the ore, when these have not been removed before the process of oxidation, is then to be thrown upon a filter and washed with boiling water until the washings are colourless. By keeping the solution somewhat alka- line, the whole of the iron remains upon the filter as sesquioxide, with G G 450 SELECT METHODS IN CHEMICAL ANALYSIS other impurities. The filtrate contains iridium and rhodium as ses- quichlorides, ruthenium partly as bichloride and partly as protochlo- ride, platinum as bichloride. When the operations already mentioned have been well performed, no determiriable quantities of osmium and palladium are present. On cooling, the greater part of the platinum is deposited as potassium platinochloride mixed with a little of the corresponding iridium salt, and is to be separated by pouring off the olive-green supernatant liquid. The quantity of the alkaline nitrite to be added in this process need not exceed half of the weight of the mass of double chlorides, but with a little experience it will be found unnecessary to weigh the nitrite added, the process of the reduction of the potassium iridiochloride being evident to the eye. To the filtrate a solution of sodium nitrite is to be added, and the whole boiled until the liquid assumes a clear orange-colour. Sodium nitrite should be used in this process, because the resulting double iridium and sodium nitrite is easily decomposed by boiling with hydro- chloric acid, which is not the case with the potassium salt. When potassium nitrite is used, a small quantity of the white insoluble double salt already mentioned is usually formed and renders the solution turbid. To the clear yellow, or orange -yellow, boiling solution, sodium sulphide is to be added until a portion of the dark brown precipitate of the ruthenium, rhodium, and platinum sulphides is dissolved with a brown-yellow colour, and an excess of the alkaline sulphide is, conse- quently, present. The liquid is then to be allowed to cool, and treated with dilute hydrochloric acid, until a distinctly acid reaction is pro- duced. In this manner the whole of the platinum, ruthenium, and rhodium present in the solution are thrown down as insoluble sul- phides. After complete subsidence, the sulphides are to be thrown on a double filter and thoroughly and continuously washed with boiling water. When the operation is carefully performed, the filtrate and washings contain only iridium. It is best to neutralise this solution with sodium carbonate, boil a second time with a little additional sodium nitrite, and treat as before with sodium sulphide and hydro- chloric acid. In this manner very small additional quantities of the platinum, ruthenium, and rhodium sulphides may sometimes be separated. The filtrate is to be evaporated and boiled with an excess of strong hydrochloric acid, which completely decomposes the double iridium and sodium nitrite, yielding the sodium iridiochloride, which is very soluble in water. An excess of a pure and strong solution of am- monium chloride is then to be added, the whole evaporated to dryness, and the dry mass washed with cold water, and then with a cold and strong solution of sal-ammoniac. There remains a mass of pure am- monium iridiochloride, which may be advantageously rubbed to a fine powder, dissolved in boiling water, and allowed to crystallise. The DR. WOLCOTT GIBBS'S PROCESS 451 resulting salt is chemically pure, and the crystals possess an extra- ordinary beauty and lustre. The mass of mixed sulphides, together with the filter, are to be treated with strong hydrochloric acid, and nitric acid added in small portions at a time. By the aid of a gentle heat the sulphides are readily oxidised and dissolved. After sufficient dilution, the liquid is to be filtered, the pulp of undestroyed filter-paper washed, the filtrate evaporated to dryness, the dry mass digested with concentrated hydrochloric acid, and again evaporated to dryness. The dry mass of chlorides and sulphates is to be redissolved in water, and the platinum, ruthenium, and rhodium precipitated by metallic zinc, after addition of hydrochloric acid. The finely divided metals, after filtration, washing, and drying, are then to be mixed with potassium chloride, and treated with dry chlorine at a low red heat. In this manner the metals are again brought into the form of double chlorides, and the difficulties which arise from the presence of the sulphates are avoided. The mixed double chlorides are to be boiled with potassium nitrite, evaporated to dryness, and the soluble ruthenium and potassium nitrites dissolved out with absolute alcohol in the manner described in speak- ing of the separation of platinum from ruthenium (page 467, B). The ruthenium may then be obtained pure by converting it into the double mercury and ruthendiamin chloride (page 468). The mass undissolved by alcohol consists of potassium platino- chloride mixed with both the soluble and the insoluble double rhodium and potassium nitrites. It is to be boiled with dilute hydrochloric acid, neutralised with potassium carbonate, again evaporated to dry- ness after the addition of potassium nitrite, and again boiled with absolute alcohol, which sometimes dissolves a trace of ruthenium. The undissolved mass is then to be treated with hot water, and again evaporated to dryness, and this process repeated two or three times, so as to convert the whole of the soluble rhodium salt into the insoluble salt. The potassium platinochloride may then, after reducing the mass to fine powder, be dissolved out by boiling water, when the rhodium salt remains pure, as a fine orange-yellow crystalline powder. This may be dissolved in hot hydrochloric acid, evaporated to dryness with an excess of pure ammonium chloride, and ignited in a clean porcelain crucible, when pure metallic rhodium remains as a porous mass mixed with potassium chloride. When the process above described has been carefully conducted, and especially when the quantity of sodium nitrite added is sufficient, the mixed sulphides will be found to contain only platinum, rhodium, and ruthenium, and to be free from iridium. If, however, after con- verting the sulphides into double chlorides in the manner pointed out, iridium is found to be present, the process to be pursued is still the same so far as regards the separation of the ruthenium ; the remain- ing mass is then to be dissolved in water with addition of hydrochloric G G 2 452 SELECT METHODS IN CHEMICAL ANALYSIS acid, the solution nearly neutralised with ammonia, the platinum and rhodium separated as sulphides in the manner already pointed out, brought into the form of double chlorides, and then separated by potassium nitrite as before. For the complete success of this method it is absolutely necessary that the mass of mixed double chlorides be freed from osmium as com- pletely as possible. This may be done in the usual manner by repeated evaporation with nitrohydrochloric acid. Electrolytic Precipitation of Platinum * (^t) Classen finds that the compounds of platinum are very easily decomposed by the galvanic current, when the metal is deposited at the negative electrode. If the current of two Bunsen elements arranged parallel are used for electrolysis, the reduction is so rapid that the plati- num is thrown down as platinum black, in which state it cannot be determined. If a single Bunsen element is used, the metal is separated in so dense a state that it cannot be distinguished from forged platinum. In this manner it is easily practicable to deposit uniformly large quan- tities of platinum upon the platinum capsule used as a negative elec- trode, without altering its external appearance. For the determination of platinum in its salts, the solution may be either slightly acidulated with hydrochloric or sulphuric acid, or mixed with ammonium or potassium oxalate, and electrolysed at a gentle heat. The deposition of the platinum is effected in a relatively short time ; e.g. 0*5 gramme platinum was deposited in 5 hours from a solution of platinum chloride diluted to 200 c.c. and containing 0'6 gramme platinum. (B) If the quantity of platinum to be deposited amounts to about 0-4 gramme, according to the results reached in the Munich laboratory, the solution of the platinum salt mixed with 2 per cent, by volume of dilute sulphuric acid (1:5) is heated and electrolysed with a current of ND 100=0'01 to 0-03. The deposition is completed in about 5 hours. (C) E. F. Smith adds to the solution of platinum 30 c.c. of sodium diphosphate, 5 c.c. phosphoric acid, and dilutes with water to 150 c.c. With a current giving 0'2 to 0'8 c.c. (maximum) of detonating gas per minute the platinum is deposited upon a platinum cone previously coated with copper. Iridium is not reduced from its solutions by the current of a Bunsen element. This behaviour may be applied to the quantitative separation of platinum from iridium. Preparation of Platinum Chloride from Residues The concentrated alcoholic solutions are reduced, at a boiling temperature, by a mixture of soda solution and glycerine or sugar. 1 For details of operation see chapter on Electrolytic Analysis. TEST FOR PALLADIUM 453 Platino-potassium chloride is also completely reduced if gradually added to the boiling mixture, and if sufficient soda is present. The pre- cipitate of platinum black is washed by decantation in a porcelain capsule till all the sulphuric acid and potassium are eliminated, dried, ignited and digested at a gentle heat in hydrochloric acid to extract iron, c., and then sufficient nitric acid is gradually added. The solution is evaporated down at a gentle heat ; the platinous chloride is converted into platinic chloride by the addition of fuming hydrochloric acid and a little nitric acid ; the excess of the latter is expelled by the repeated addition of water and hydrochloric acid, and evaporation. The presence of platinous chloride is detrimental for the estima- tion of potassium, rendering the results too high, whilst nitric acid occasions an error in the contrary direction. Traces of iridium have little effect on the accuracy of the analysis. The solubility of platino- potassic chloride in alcohol is 1 part in 42,600 absolute, 1 part in 37,300 at 96 per cent., and 1 in 26,400 at 80 per cent. Platino-sodium chloride is soluble in boiling water in almost every proportion. Platino- barium chloride has the important property of being more or less com- pletely decomposed into platinum chloride and barium chloride. Mending Platinum Crucibles. Mr. T. Garoide gives the follow- ing simple method : Some months ago I had a platinum dish, which had a small hole on the side, near the bottom, and the dish was con- sequently useless for most purposes. I was about to consign it to the old platinum, when it struck me that this metal being * weldable ' I might manage to repair it. Having already a mould for this dish, made of plaster of Paris, and not of wood, this served admirably as an anvil. I then cut a piece of moderately thin platinum foil, about 3 millimetres diameter, and rubbed this and the part of the dish where the hole was with sea-sand until perfectly bright and clean. Having fixed the dish and its mould in an upright position, I laid the platinum foil over the hole, and directed the flame from a table blowpipe upon the spot. A pair of scissors served as a hammer, and by gently tapping with these the two pieces of platinum united perfectly, and made so neat a joint that one would scarcely observe it unless one's attention was called to it. I have used the dish for all kinds of purposes since, and the union is as good as ever. In the above operation the plaster- of-Paris mould, although very dry, was split and cracked by the heat in all directions, nevertheless it had sufficient cohesion to last until the operation was concluded. I find that platinum wires are very easily joined in this way. PALLADIUM Test for the Presence of Palladium Carey Lea proposes sodium thiosulphate as a delicate test for many of the platinum metals. For detecting the presence of palladium he proceeds as follows : Place a solution of sodium thiosulphate in a 454 SELECT METHODS IN CHEMICAL ANALYSIS test-tube with a little liquid ammonia, and add a drop of the palladium solution, so that it shall communicate a pale lemon colour only to the liquid. By boiling, this rapidly darkens to a wine-brown shade, in- creasing in intensity until it finally appears black. Dilution, however, shows that this results from its intensity only ; the diluted liquid is free from turbidity and has a warm-brown tint. Electrolytic Separation of Palladium l (A) The determination of palladium is effected by Classen in a manner analogous to that of platinum. If we use the current of a single Bunsen element, we obtain the palladium in a fine metallic state. (B) According to E. F. Smith, palladium can be determined in the manner directed for platinum. Separation of Palladium from Copper Saturate the solution containing these metals with sulphurous acid gas and add a solution of potassium sulphocyanide. This has no action on the palladium, whilst it completely precipitates the copper in the form of a white sub -sulphocyanide. RHODIUM Separation of Rhodium from Platinum (A) The usual method of approximately separating these metals is, to convert them into their potassium or ammonium double chlorides, and then to carefully wash out the rhodium salt by small successive portions of cold water, or, better, by a moderately concentrated solution of potassium or ammonium chloride. By recrystallising the platinum and rhodium salts respectively, they may be obtained in a state of purity, since they are not isomorphous. (B) To obtain rhodium absolutely free from platinum, Dr. Wolcott Gibbs advises to convert the two metals into the ammonium double chlorides, separate the rhodium salt as completely as possible by wash- ing with a solution of sal-ammoniac, and then evaporate the double rhodium and ammonium chloride with a solution of ammonia. In this manner the rhodium is converted into the chloride of the ammonia - rhodium base, discovered by Glaus, while the platinum forms no well- defined or crystallisable compound. The chloride of Claus's base may then be purified by repeated crystallisation. 1 For details of operation see chapter on Electrolytic Analysis. IRIDIUM 455 IRIDIUM Separation of Iridium from Platinum (A) The following process for separating these metals was proposed by Dr. Wolcott Gibbs : The iridium is, in the first place, to be brought into the form of bichloride, by means of a current of chlorine or by nitric acid, and the two metals are then to be precipitated together as potassium double chlorides, by the addition of a concentrated solution of potassium chloride. The colour of the mixed salts varies from orange to almost black, according to the quantity of iridium present. The mass of crystals is to be rubbed fine in an unglazed porcelain mortar, and boiling water added in the proportion of three volumes of water to one of salt. A dilute solution of potassium nitrite is then to be added until the liquid becomes deep olive-green, sodium carbonate being thrown in from time to time in quantity sufficient to prevent the solution from becoming strongly acid. The iridium is instantly re- duced to sesquichloride, while the platinum salt remains as a reddish- orange powder. The deep olive -green solution is to be poured off, and the undissolved mass treated a second time with hot water and nitrite. This process must be repeated as long as the liquid remains olive-green. The mixed solutions on cooling, or after evaporation, deposit a beautiful mass of crystals of the double potassium chloride and iridium sesqui- chloride. By re-solution and repeated crystallisation, the iridium salt may be obtained perfectly free from platinum. The undissolved mass and the mother-liquors from the iridium salt contain a large quantity of platinum with a comparatively small quantity of iridium. When the absolute quantity of platinum salt is not very large, it may be dis- solved in boiling water, a small quantity of alkaline nitrite added, and the solution allowed to crystallise ; the resulting potassium chloroplati- nate contains only a trace of iridium. This process gives satisfactory results when carefully executed, but requires attention to two points. In the first place the alkaline nitrite must be added in quantity just sufficient to reduce the iridium from bichloride to sesquichloride, but not so as to produce further chemical changes by the formation of the double iridium and potassium nitrite or sodium ; with a very little experience this is easily managed. In consequence of the facility with which the double iridium and sodium nitrite is decomposed by boiling with hydrochloric acid into the double chloride, IrCl 2 ,NaCl, it is better to use sodium nitrite in the above pro- cess, because, in case an excess of nitrite is used, the mixed solution of double chloride and double nitrite can easily be brought to the form of the double chloride, Ir 2 Cl3,3ISIaCl, by boiling with hydrochloric acid, neutralising with sodium carbonate, and then reducing the iridium to sesquichloride by cautiously adding a very dilute solution of sodium nitrite. 456 SELECT METHODS IN CHEMICAL ANALYSIS In the second place, it may happen, as in working with crude platinum solutions obtained not from osmiridium but from platinum ores, that the quantity of platinum is very large when compared with that of iridium. The process applies equally well to this case as far as the iridium is concerned, but it is difficult and troublesome to recrystal- lise large quantities of a salt so insoluble as potassium platinochloride, and small quantities of the corresponding iridium salt are difficult to remove. (B) The following process can be recommended for giving chemi- cally pure iridium when platinum is the only other metal present : The greater portion of the platinum is first to be separated in the man- ner above pointed out. The solution of double iridium and sodium chloride, Ir 2 Cl 3 ,3NaCl, is then-to be filtered, an excess of sodium nitrite added, and the solution boiled until it assumes a clear orange-yellow colour. To the boiling solution sodium sulphide is added drop by drop as long as this produces a cloudiness, and until a small quantity of the precipitated platinum sulphide is redissolved. Dilute hydrochloric acid is then to be added cautiously until the liquid, previously allowed to become cold, is distinctly though faintly acid, when it is to be filtered and the platinum sulphide in the filter washed continuously with hot water. The filtrate is then to be boiled with hydrochloric acid in excess, and the resulting sodium iridiochloride evaporated, precipitated by a cold and strong solution of sal-ammoniac, and washed with the same. This salt, on ignition, yields pure iridium if the operation has been well conducted. It is, however, in all cases well, after separating the platinum sulphide by filtration, to neutralise the filtrate with sodium carbonate, boil a second time with a little additional sodium nilrite, and then add sodium sulphide and proceed as before. In this manner every trace of platinum is removed, and the resulting iridium salt is chemically pure. Electrolytic Separation of Iridium from Platinum * According to Classen, platinum can be deposited as such by means of a very weak current in a solution acidified with hydrochloric acid. This behaviour serves for its separation from iridium. If in the circuit of a battery consisting of 2 or 3 Meidiiiger elements or of a single Bunsen element we introduce the acidified solution of platinum and iridium, the platinum is deposited without any trace of iridium. Separation of Iridium from Rhodium (A) Iridium may be approximately separated from rhodium by the process recommended by Glaus, which consists in taking advantage of the solubility of the double rhodium and ammonium chloride, Eh 2 Cl 3 ,3NH 4 Cl, in moderately strong solutions of ammonium chloride, 1 For details of operation see chapter on Electrolytic Analysis. OSMIUM 457 in which the ammonium iridiochloride is nearly insoluble. This method is difficult of application when the quantity of rhodium is small, and is at best tedious and unsatisfactory. (B) A better method is the following : To the solution containing the two metals, sodium nitrite is to be added in excess, together with a sufficient quantity of sodium carbonate to keep the liquid neutral or alkaline ; the whole is then to be boiled until the solution assumes a clear orange-yellow or orange colour. If a green tint should be per- ceptible, more sodium nitrite must be added and the solution again boiled. Both iridium and rhodium are converted into soluble double nitrites. A solution of sodium sulphide is then to be added in slight excess, the liquid rendered slightly acid, filtered, and the dark brown rhodium sulphide thoroughly washed. The filtrate is perfectly free from rhodium. This is boiled with excess of hydrochloric acid, evapo- rated, precipitated with sal-ammoniac, and treated as described in the method of preparing pure iridium given above. The rhodium sulphide, together with the filter, is to be treated with strong hydrochloric acid, and sal-ammoniac added in quantity sufficient to form ammonium rhodiochloride. Nitric acid is to be added from time to time in small quantities, until, with the aid of heat, the whole of the rhodium sul- phide is oxidised and dissolved. The liquid is then to be filtered, the filter well washed, and the filtrate and washings evaporated to dryness on a water-bath, when, after washing out the soluble salts with a strong solution of sal-ammoniac, the double rhodium and ammonium chloride, Eh 2 Cl 3 ,NH 4 Cl, is left behind. This is insoluble in a cold saturated solution of sal-ammoniac, in which it may be washed once or twice to remove alkaline salts and any traces of iridium which may be present as sulphate. The rhodium salt is then to be purified by crystallisation, or converted into the chloride of Claus's rhodium-ammonium base by evaporation on a water-bath with a solution of ammonia. Iridium sulphate does not give a basic compound under these circumstances. The chloride, 5NH 3 ,Rh 2 01 3 , is then to be further purified by crystal- lisation. OSMIUM Reduction of Osmic Acid A solution of osmic acid on addition of potassium nitrite is reduced to osmious acid, which unites with the alkali, forming the well-known beautiful red salt. The solution may be evaporated to dryness without decomposition. The nitrite may, therefore, be added with great ad- vantage when solutions containing free osmic acid are to be evapo- rated, or even transferred from one vessel to another. No other re- ducing agent answers the same purpose, as the osmium is obtained at once in a very convenient form for preservation. When a solution of osmic acid, to which potassium nitrite has been added, is evaporated 458 SELECT METHODS IN CHEMICAL ANALYSIS sufficiently and then allowed to cool, beautiful garnet-red octahedral crystals of potassium osmite separate. These should be dried over sulphuric acid, and not in contact with paper or organic matter, which partly reduces the osmious acid to the brown osmium sesquioxide. Potassium nitrite exerts no sensible action when boiled with a solution of potassium osmiochloride ; any salt which may be formed is very soluble in water. Separation of Osmium from Iridium (Analysis of Osmiridium) (A) "Wohler's Method of resolving osmiridium consists in passing moist chlorine over the ore mixed with common salt and heated to low redness in a glass or porcelain tube. This method is invaluable in analysis, and gives excellent results in, working the ore upon a small scale. In all cases, however, several repetitions of the process are necessary for complete resolution or reduction to a soluble form. On the other hand, it can scarcely be doubted that this method could be advantageously employed upon the large scale, if vessels of porcelain of large size and of a proper shape could be obtained. Such vessels might be constructed in the form of long and flattened ellipsoids, furnished at each extremity with wide tubes several inches in length, and would be of great utility in various chemical processes. No process of fusion with oxidising agents compares with Wohler's method in point of elegance, as no iron or other impurities afterwards to be removed are introduced by the process itself. (B) Fritzsche and Struve's Process is to treat the ore with a mixture of equal parts of potassium hydrate and chlorate, by which a more or less complete oxidation is effected, without any sensible evolu- tion of osmic acid. The temperature required in this process is not high, but large vessels must be employed, as the mixture froths very much at first. This process does not appear to possess any sensible advantage over that of Glaus, which is, moreover, less expensive, and can be carried out with smaller vessels. (C) Claus's Method of resolving the ore consists in fusing for an hour, at a red heat, a mixture of 1 part of ore with 1 part of caustic potash and 2 of saltpetre. The fused mass is to be poured out upon a stone, allowed to cool, broken into small pieces or powdered, and then introduced into a flask, which is to be filled with cold water and allowed to stand for 24 hours. The clear deep orange-red solu- tion of potassium osmiate and rutheniate is then to be drawn off by means of a syphon, and the black mass remaining again washed in the same manner. The finely divided oxidised portion of the insoluble matter may now be separated from the unattacked ore by diffusion in water and pouring off, after the subsidence of the heavier ore. The unattacked ore is then to be fused a second time with potash and saltpetre and treated as before. Glaus asserts that he has been able ANALYSIS OF OSMIRIDIUM 459 in this manner to resolve the Siberian osmiridium completely in two operations. (D) Dr. Wolcott Gibbs, to whom the chemistry of the platinum metals is so greatly indebted, recommends the following process for the analysis of osmiridium : The ore, which is usually very impure, is in the first place to be fused with 3 times its weight of dry sodium carbonate. The fused mass after cooling is to be treated with hot water, to remove all the soluble portions, and then the lighter por- tions are to be separated by washing from the heavy unattacked ore. In this manner the greater part of the silica and other impurities present may be removed. A previous purification of this kind is not indispensable, and may be omitted altogether when the ore is in plates or large grains, but it is very desirable when the ore is in fine powder, and greatly facilitates the subsequent action of the oxidising mixture. By cutting off the top of a mercury bottle a wrought-iron crucible is obtained, in which 600 grammes of osmiridium may be fused at one operation with potash and saltpetre as above. There is usually little or no foaming, and if any occur it may easily be checked by stirring with an iron rod. No sensible quantity of osmic acid is given off during the process, which with a little care is entirely free from danger. In this manner 1,500 grammes of ore have been worked up in a few hours in three successive operations. The fused mass is to be broken into pieces with a hammer, and put into a clean iron pot. Boiling water, containing about T L O f its volume of strong alcohol, is then to be added, and the whole is to be boiled over an open fire until the fused mass is completely disintegrated. The potassium osmiate is, in this manner, reduced to osmite, while the potassium rutheniate is completely decomposed, the ruthenium being precipitated as a black powder. It is advantageous, after boiling for some time, to pour off the super- natant liquid with the lighter portions of the oxides, and boil a second time with a fresh mixture of alcohol and water. In this manner we obtain a solution of potassium osmite, a large quantity of black oxides, and a heavy black and coarse powder. This last consists chiefly of un- decomposed ore, mixed with a small quantity of the iridium oxides, &c. f with scales of iron oxide from the crucible, and, if the ore has not been previously purified, with the impurities of the ore itself. The greater specific gravity of this residual mass renders it very easy to pour off from it the mixture of black oxides with the solution of potas- sium osmite and alkaline salts. This solution with the suspended powder is to be poured into a beaker and allowed to settle. The heavy black powder remaining in the iron pot is then to be perfectly dried over the fire, and fused a second time with potash and saltpetre as before. The fused mass is to be treated exactly as after the first fusion. The heavy portions remaining after this operation may be fused a third time with the oxidising mixture. When, however, the ore has been previously purified by fusion with sodium carbonate or when 460 SELECT METHODS IN CHEMICAL ANALYSIS it was originally in the form of clean scales, the heavy portion remaining after two successive oxidations will be found to consist chiefly of scales of iron oxide. The solutions containing potassium osmite and alkaline salts are to be carefully drawn off by a syphon from the black oxides which have settled to the bottom of the containing vessels. The oxides may then be washed with hot water containing a little alcohol, and intro- duced into a capacious retort. By this process, when carefully executed, no trace of osmic acid escapes an advantage not to be despised, as the deleterious effects of this body upon the lungs have not been exaggerated, and too much care cannot be taken to avoid inhaling it. The solution of alkaline salts contains only a portion of the osmium in the ore. The other portion exists in the mixture of oxide, and must be separated by distillation. For this purpose the retort should be provided with a safety-tube, passing through the tubulure, and with a receiver kept cool, and connected by a wide bent tube with a series of two or three two-necked bottles containing a strong solution of caustic potash with a little alcohol, and also kept cold. All the tubulures and connections must be made perfectly tight. Strong hydrochloric acid is then to be cautiously poured into the retort, through the safety-tube, in small portions at a time. The reaction which ensues is often violent ; great heat is evolved, and a portion of the osmic acid distils over immediately, and condenses in the receiver in the form of colour- less needles. When a large excess of acid has been added, the action has entirely ceased, and the retort has become cold, heat may be applied by means of a sand-bath. The osmic acid gradually distils over, and condenses in the receiver and in the two-necked bottles. Especial care must be taken that the neck of the retort is not too small at the extremity, as it may otherwise become completely stopped up with the condensed osmic acid. The same applies to the tubes con- necting the receivers and two-necked bottles. The distillation should be continued for some time after osmic acid ceases to appear in the neck of the retort ; when this has once become hot, the acid condenses and passes into the receiver in the form of oily drops. When the distillation is finished, the retort is to be allowed to cool, and- then separated from the receiver, which is to be immediately closed with a cork. By gently heating the receiver in a water-bath, the con- tained osmic acid may be driven over into the two-necked bottles, where it condenses in the alkaline solution, and is reduced by the alcohol to potassium osmite. The solution thus obtained maybe added to that obtained directly from the fused mass of ore, and on evaporation in a water-bath and cooling, will yield crystals of potassium osmite, the salt being but slightly soluble in strong saline solutions. The mother-liquor from the crystals contains only traces of osmium, and may be thrown away as worthless. RUTHENIUM 461 The dissolved portions drawn off from the retort have a very dark brown-red colour. The solution is to be evaporated to dryness, redis- solved in hot water and again evaporated, after adding a little hydro- chloric acid, and this process repeated till no smell of osmic acid can be perceived. A cold and saturated solution of potassium chloride is then to be added in large excess. This dissolves the iron and palladium chlorides which may be present, leaving platinum, iridium, rhodium, and ruthenium as double chlorides, insoluble in a strong solution of the alkaline chloride. The undissolved mass is to be well washed with a saturated solu- tion of potassium chloride, which is preferable to sal-ammoniac. In this manner nearly the whole of the iron and palladium may be removed, while any insoluble impurities contained in the ore remain with the mixed double chlorides. For the separation of osmium from the other metals of the group, the best plan seems to be the one which is universally employed, namely, the volatilisation of the osmium in the form of osmic acid. RUTHENIUM Preparation of Ruthenium from Iridium Osmide (Osmiridium) (A) Osmiridium almost always contains ruthenium, the amount of the latter metal increasing as that of the iridium decreases. The fol- lowing process is the one recommended by Dr. Glaus, the discoverer of ruthenium, for preparing this metal. Osmiridium is melted in the ordinary way with nitre and caustic potash, and moistened with water ; then nearly neutralise with sul- phuric acid, in order to precipitate the metallic acids in solution, always leaving the liquid with a slight alkaline reaction ; add alcohol and boil. Throw the mixture on a filter, and carefully wash in order to free it as far as possible from potassium salts. The black metallic powder thus obtained still contains sufficient potassium in the state of acid potassium iridiate to convert the greater portion of the iridium into double iridic chloride during the subsequent solution of the metallic powder. For this reason evaporate to a considerable extent the aqua regia solution separated from the powder until all the osmium is dis- engaged as osmic acid ; then, if left to cool, most of the iridium is deposited in the state of potassium iridiochloride, and the liquid contains all the ruthenium in a much greater degree of concentration, although always associated with some iridium. Afterwards filter and add powdered sal-ammoniac, which causes the deposition of yet more iridium as a black crystalline precipitate. The solution generally contains ruthenium so concentrated as to be sepa- rable from the iridium by precipitation. Now evaporate again and add 462 SELECT METHODS IN CHEMICAL ANALYSIS more sal-ammoniac until the liquid begins to lose its colour, and most of the platinum metals are deposited as double salts. Then leave it for several days, collect the residue on a filter and wash it with water containing sal-ammoniac in solution, which completely eliminates iron and copper, and does not affect the ruthenium. In this way there is obtained a residue of iridium salts containing ruthenium, which, dis- solved and boiled with the addition of a little ammonia, yields a pre- cipitate of ruthenium sesquioxide. (J5) Commenting on the above process, Dr. Gibbs says that this method of treating the fused mass to separate ruthenium and osmium is liable to two sources of inconvenience. In the first place, the quantity of water required to dissolve out the soluble portions is very large, and the subsequent treatment of such bulky solutions by distil- lation with acids is tedious, very large retorts being necessary. In the next place, it is impossible in this way to avoid exposure to the vapour of osmic acid, especially in transferring the solutions from one vessel to another. He therefore recommends the process which we have given at page 459. Estimation of Ruthenium When it is necessary to estimate ruthenium precisely, the osmium must not be expelled previously by means of aqua regia, otherwise there would be some loss of ruthenium. For the estimation of ruthenium, a larger quantity of the alloy than is generally used is required that is to say, at least 10 grammes, which must all be reserved for the search for ruthenium, disregarding all the other con- stituents. Melt the pulverised ore with potash and saltpetre, dissolve it in water, carefully neutralise it with an acid, and, adding some alcohol, heat it ; then carefully wash the precipitate, which is a black metallic powder, in water, to eliminate the saltpetre and other potas- sium salts. Dissolve this powder in hydrochloric acid, heat it in a retort with potassium chlorate and hydrochloric acid, and collect the volatile products in condensers containing alcohol. By this means ruthenium and osmium are obtained together, but their separation can be effected by alcohol, which instantly decomposes the ruthenic acid, though it takes some time to reduce the osmic acid ; or the two metals may be precipitated from their solution by sulphuretted hydrogen, and the sulphides thus obtained heated in a small platinum vessel, in an oxygen current, which disengages sulphur and osmium as acids, while the ruthenium remains as ruthenic oxide. There is no appreciable loss in melting ruthenium with caustic potash and saltpetre. A piece of paper soaked with alcohol does not blacken if held even for a long time over the heated mixture, and no smell of ruthenic acid is observable, though during the solution of the mixture a feeble odour of it is always given off. If ruthenious ses- quioxide, which is obtained by treating this solution with alcohol, is DETECTION OF RUTHENIUM 463 dissolved in hydrochloric acid, the solution takes place without forming a volatile ruthenic combination ; but there is some likelihood of loss if aqua regia is used as a solvent, for ruthenium is then placed under cir- cumstances similar to those produced by the simultaneous action of potassium chlorate and hydrochloric acid. Detection of Ruthenium in the Presence of Iridium, &c. (A) The reactions of ruthenium are remarkably affected by the presence of iridium ; and in proportion as this last-named metal is present in larger quantity, the indications afforded by most of the tests hitherto proposed grow less and less decided, and some lose all efficacy. Mr. C. Lea has discovered in sodium thiosulphate a very delicate test for ruthenium. When a solution of sodium thiosulphate is mixed with ammonia, and a few drops of solution of ruthenium sesquichloride are added, and the whole boiled, a magnificent red-purple liquid is produced, which, unless the solutions are very dilute, is black by transmitted light. The colouration is permanent, and the liquid may be exposed to the air without alteration. This reaction is obtained with great ease and certainty, and, in the opinion of the discoverer, is far superior to any known test for ruthenium. In order to determine the limits of the sensibility of this reagent, experiments were made with ruthenium solutions of different strengths. The following results were obtained: With 5-oVfr f ruthenium sesquichloride, bright rose-purple. With solotf and - s ^^ fine rose colour. With 5-oiroo> paler, but still perfectly distinct. With ioo'ooo? the colour, though very pale, was still unmistakably present. Where the solutions are so very dilute as these last, the boiling must be continued for some minutes. When the presence of ruthenium in very small quantity, or in very dilute solution, is suspected, it is often advisable to boil the solution with a little hydrochloric acid, previous to the application of the thio- sulphate test. The acidulated solution must be rendered alkaline by addition of ammonia before heating with thiosulphate. This reagent is the best test that is capable of detecting ruthenium in the presence of any excess of iridium. No precautions are neces- sary, and the reaction is always obtained with the greatest facility. The iridium solution is to be rendered alkaline with ammonia, a crystal of sodium thiosulphate is dropped into it, and the whole is boiled for 2 or 3 minutes. If no indication of a red-purple tint appears (or, in case of small quantities of ruthenium, a rose colour), the iridium solution may be pronounced free from ruthenium. (B) Dr. Wolcott Gibbs has discovered another delicate test for ruthenium, which likewise can be employed in the presence of other 464 SELECT METHODS IN CHEMICAL ANALYSIS platinum metals. When a solution of potassium nitrite is added in excess to ruthenium sesquichloride, either free, or in combination with potassium or ammonium chloride, a yellow or orange -yellow colour is produced, but no precipitate is formed. A precisely similar change occurs when the ruthenium is in the form of bichloride ; but in this case the change of colour is produced more slowly, and usually requires heating or even boiling. The change of colour is due in both cases to the formation of an orange -yellow ruthenium and potassium double salt, which is very soluble in water and alcohol ; its relations to alcohol in particular enable us to distinguish ruthenium from the other platinum metals more perfectly than has hitherto been possible. When a few drops of ammonium sulphide are added to a solution of this double salt, a magnificent crimson colour is produced. This reaction furnishes a characteristic test of the greatest value, since it is not materially affected by the presence of the other metals of the same group. The test may be most advantageously applied as follows : The liquid supposed to contain ruthenium is first to be rendered alkaline by the addition of sodium or potassium carbonate. Potassium nitrite in solution is then to be added, the liquid boiled for an instant, allowed to become perfectly cold, and a drop or two of colourless ammonium sulphide added. On shaking, the colour appears, and rapidly deepens to the finest red. When the quantity of ruthenium present is very small, or when large quantities of the other platinum metals are also present, it is better, after adding the alkaline carbonate and nitrite, to evaporate the whole to perfect dryness on a water-bath, and treat the dry and powdered mass with a small quantity of absolute alcohol. The alcoholic solution is then to be filtered off, and tested directly with ammonium sulphide. In this way the smallest trace of ruthenium may be detected even in the presence of very large quantities of the other platinum metals. (C) Dr. Glaus detects ruthenium qualitatively in the presence of iridium by making use of the following reactions : A solution of pure iridium, containing no ruthenium, is instantly decolourised by the addition of excess of caustic potash or ammonia. It remains thus for a long time perfectly transparent, and then, after several days, takes a beautiful blue colour. But if the iridium contains traces of ruthenium, the colour of the solution becomes fainter during the reaction, but does not disappear ; it passes to a yellow-brown or reddish hue, and does not become decolourised for some time, at which point the solution becomes turbid, and a slight brown or yellow precipitate is formed. If the iridium contains more ruthenium, yet not sufficient to produce a visible precipitate, its presence is betrayed by the intense red-purple colour assumed by the liquid, especially if potash is used. SEPARATION OF RUTHENIUM FROM IRIDIUM 465 Separation of Ruthenium from Iridium The quantitative separation of ruthenium from iridium is much more difficult than the mere detection of ruthenium in the presence of iridium. Their separation cannot be effected by igniting them with a mixture of saltpetre and caustic potash. The following is an accurate means of separating the two metals, based upon Dr. Gibbs's discovery of the reaction of alkaline nitrites on ruthenium salts, already described : (A) To the solution containing the two metals, sodium nitrite is to be added in excess, together with sufficient sodium carbonate to keep the liquid neutral or alkaline. The whole is to be boiled until the solution assumes a clear orange-yellow or orange colour. If a green tint should be perceptible, more sodium nitrite must be added, and the solution again boiled. Both ruthenium and iridium are converted into soluble double nitrites. A solution of sodium sulphide is then to be added, in small quantities at a time, until a little of the precipitated ruthenium sulphide is dissolved in the excess of alkaline sulphide. The first addition of the sulphide gives the characteristic crimson tint due to the presence of ruthenium, but this quickly disappears and gives place to a bright chocolate-coloured precipitate. The solution is then boiled for a few minutes, allowed to become perfectly cold, and then dilute hydrochloric acid added cautiously until the dissolved ruthenium sulphide is precipitated and the reaction is just perceptibly acid. The solution is then to be filtered through a double filter, and the ruthenium sulphide washed continuously and thoroughly with boiling water. The filtrate is perfectly free from ruthenium ; it is to be evaporated with hydrochloric acid, and treated with sal-ammoniac in the manner already pointed out in speaking of the separation of iridium from pla- tinum (page 455, A). The washed ruthenium sulphide is to be treated, together with the filter, with strong hydrochloric acid, and ammonium chloride added in sufficient quantity to form ammonium ruthenio- chloride. Nitric acid is to be added from time to time, in small quantities, until, with the aid of heat, the whole of the ruthenium sulphide is oxidised and dissolved. The liquid is then to be filtered, the filter well washed, and the filtrate and washings evaporated to dryness on a water-bath, when, after washing out the soluble salt with strong solution of ammonium chloride, the ammonium rutheniochloride remains almost chemically pure. It is to be dissolved and converted into the compound of mercury and ruthendiamin chloride (see Sepa- ration of Euthenium from Platinum). From this salt chemically pure ruthenium may be obtained by ignition, which is best effected in an atmosphere of hydrogen, as the reduced metal is easily oxidised in the air. It may happen that the precipitated ruthenium sulphide contains traces of iridium. This can only arise from imperfect washing or want H H 466 SELECT METHODS IN CHEMICAL ANALYSIS of proper care in precipitating with sodium sulphide. In this case, the washings from the ammonium rutheniochloride are yellow, and contain iridium sulphate. The quantity of iridium in such cases is too small to be worth the trouble of separate treatment. (B) When a solution contains iridium and ruthenium in the form of bichlorides, the ruthenium may be easily and completely separated by boiling the solution with potassium nitrite in excess, adding, at the same time, enough potassium carbonate to give an alkaline reaction, evaporating to dryness, and dissolving out the double ruthenium and potassium nitrite by means of absolute alcohol. The undissolved mass in this case contains two double iridium and potassium nitrites. By adding a strong solution of ammonium chloride, evaporating to dry- ness, igniting the dry mass in a porcelain crucible, and dissolving out the soluble salts, metallic iridium remains in a state of purity. This method may be used for quantitative separation of iridium from ruthenium ; but when the object is simply to prepare both metals in a state of chemical purity, the separation by means of sodium sul- phide is preferable. Separation of Ruthenium from Rhodium The separation of ruthenium from rhodium is best effected by means of potassium nitrite. The mixed solution of the two metals is to be boiled for a short time with an excess of the nitrite, together with a little potassium carbonate to keep the solution neutral or slightly alkaline. The yellow or orange-yellow solution is then to be evaporated to dryness upon a water-bath, the dry mass rubbed to fine powder and then treated in a flask with absolute alcohol in the manner pointed out for the separation of ruthenium from platinum. After filtration and washing with absolute alcohol, the rhodium remains undissolved in the form of a mixture of the two double rhodium and potassium nitrites. These may be ignited with a large excess of sal-ammoniac, so as to yield, after washing, metallic rhodium ; or the nitrites may be dissolved in hot hydrochloric acid, ammonia added, and the rhodium precipitated as sulphide, which is then treated in the manner already pointed out (page 456, A), so as to convert the rhodium into the double rhodium and ammonium chloride. To remove the last traces of ruthenium the rhodium salt may be a second time treated with potassium nitrite, as above, and again washed with alcohol. The presence of the least trace of ruthenium is easily detected by adding a drop of colourless ammonium sulphide to the alcoholic solution. The method of obtain- ing pure ruthenium from the double ruthenium and potassium nitrite has already been given. Separation of Ruthenium from Platinum (A) The approximate separation of ruthenium from platinum may be effected by precipitating the two metals with potassium chloride and SEPARATION OF RUTHENIUM FROM PLATINUM 467 washing out the potassium rutheniochloride with cold water, in which it is readily soluble. The mixed solutions should be evaporated to dry- ness with an excess of the alkaline chloride, and the dry mass rubbed to a fine powder in a mortar, after which almost the whole of the ruthe- nium may be washed out with water, or with a cold and moderately strong solution of potassium chloride. The undissolved platinum salt may then be purified by crystallisation, but it usually contains traces of ruthenium. The rose-red solution of the ruthenium salt contains a small quantity of platinum, from which it cannot be wholly freed by the difference in solubility of the two salts. Ammonium chloride may be employed in this process in place of potassium chloride. (B) To obtain a complete separation, Dr. W. Gibbs's process may be followed with advantage : The potassium rutheniochloride, sepa- rated as far as possible from the platinum salt, is to be heated with a solution of potassium nitrite in quantity sufficient to convert the whole of the ruthenium into the soluble yellow double ruthenium and potassium nitrite, potassium carbonate being added in small quantities so as to keep the solution neutral or alkaline. The yellow or orange solution is to be evaporated to dryness in a water-bath, the dry mass reduced to powder and boiled with absolute alcohol until the ruthenium salt is completely dissolved. This is best effected in a flask furnished with a condensing-tube bent upwards, so that the alcohol vapours may be condensed and flow back into the flask. The boiling need not be continued for a very long time, as the ruthenium salt is readily soluble in alcohol. The solution is then to be filtered off from the un- dissolved salts, and these are to be washed with absolute alcohol until the washings are colourless, or until they no longer give the character- istic ruthenium reaction with ammonium sulphide. The filtrate and washings may then be distilled, to separate and save the alcohol, water being added in small quantity. The residue in the retort or flask is then to be evaporated with hydrochloric acid, which readily decomposes the double nitrite, and yields a fine deep rose-red solution of the potas- sium rutheniochloride, containing at most only a trace of platinum. The mass of salts undissolved by the alcohol contains nearly all the platinum in the form of potassium platinochloride, which is easily sepa- rated. The solution of the potassium rutheniochloride is now so pure that it gives the reactions of a chemically pure salt. To obtain the ruthenium in a state of absolute purity, the solution is to be evaporated to dryness with a saturated solution of sal-ammo- niac in excess, redissolved, again evaporated, and the dry mass washed with a little cold water to remove the alkaline chlorides. The potas- sium rutheniochloride is in this manner, for the most part at least, converted into the corresponding ammonium salt. This salt is then to be dissolved in hot water, a solution of ammonia added, and the liquid boiled until it assumes a clear yellow or orange-yellow colour, after which it is to be evaporated to dryness on a water-bath. In this H H 2 468 SELECT METHODS IN CHEMICAL ANALYSIS manner the ruthenium is converted into ruthendiamin chloride, dis- covered by Glaus. The yellow mass is to be dissolved in boiling water, and a solution of mercury chloride added. A beautiful yellow crystal- line double salt is precipitated, and the mother-liquor, when cold, contains only traces of ruthenium and platinum. The double mercury and ruthendiamin chloride is almost insoluble in cold water, but is soluble in boiling water, and is easily rendered absolutely pure by re- crystallisation. On ignition, this salt yields chemically pure metallic ruthenium as a silver-white porous mass. When, in a mixture of solutions of ruthenium and platinum, the ruthenium is present either partly or wholly as sesquichloride, the liquid is to be boiled with potassium nitrite and carbonate as above, evaporated to dryness, boiled with excess of hydrochloric acid to con- vert the double ruthenium and potassium nitrite into potassium rutheniochloride, and the resulting solution treated by the process already described. 469 CHAPTER XI SULPHUR, PHOSPHORUS, NITROGEN SULPHUR Estimation of Sulphur in Pyrites 1. Estimation of Sulphur in the Dry Way. (A) Fuse the weighed ore with a weighed quantity of anhydrous sodium carbonate, twice as much potassium chlorate as ore, and from 12 to 20 times as much sodium chloride (added to moderate the action) ; carbonic acid is expelled, potassium chloride formed, and all the sulphur converted into sodium sulphate ; by dissolving the residue in water and estimating alkali - metrically the unaltered sodium carbonate by a standard acid solution, the portion converted into sulphate, and hence the sulphur in the ore, is known. Besides the difficulty of preventing loss by deflagration, this method is open to the small errors caused by reckoning all the arsenic present as sulphur : this, however, is usually of no moment for com- mercial purposes ; any calcium carbonate in the ore may, if required, be previously dissolved out by dilute hydrochloric acid. (B) In performing fusions of sulphur compounds with nitre or potassium chlorate, the operator must bear in mind a source of error, first pointed out by Dr. David S. Price, in consequence of sulphur com- pounds being contained in the coal-gas which frequently serves as fuel in these experiments. By exposing a small quantity of melted nitre, on the outside of a platinum capsule, to the flame of a Bunsen gas- burner for three-quarters of an hour, Dr. Price succeeded in detecting the presence of sulphuric acid to an amount equivalent to 12 milli- grammes of sulphur. This sulphuric acid had been formed by the oxidation of the sulphur in the coal-gas, and, when dissolved in water, gave an immediate precipitate with barium chloride. By making a similar experiment with the use of a spirit-lamp as the source of heat, no trace of potassium sulphate was formed ; nor was any appreciable amount of sulphuric acid generated in another trial made by fusing a small quantity of nitre inside a platinum capsule heated over gas ; but whenever the fused salt crept over the edges of the capsule, some of the sulphate was sure to be formed. This observation may become a matter of importance when the amount of sulphur in pig-iron is estimated by fusion with pure nitre, for the author has remarked that 470 SELECT METHODS IN CHEMICAL ANALYSIS samples containing much manganese are especially liable to impart to the fused salt a tendency to creep up and escape over the sides of the crucible. (6 T ) The following process obviates some of the difficulties just men- tioned : One gramme pyrites is mixed in a large covered crucible with 8 grammes of a mixture of equal parts of potassium chlorate, sodium carbonate, and sodium chloride. The crucible is heated at first gently so as to dry the contents, which are afterwards melted at a high tem- perature. The mass when cold is treated with boiling water, and the solution, together with the deposit, is introduced into a measuring flask of 200 c.c. filled up, filtered, and the sulphuric acid is estimated in aliquot parts, say 50 c.c. The insoluble residue does not retain any sulphuric acid. In this manner the use of nitric acid is avoided. The decomposition of the potassium chlorate is complete. (D) The following is a useful modification of the potassium chlorate method : Half a gramme of finely ground pyrites (sifting is not abso- lutely necessary) is mixed in a large platinum capsule with the well- known mixture of 6 parts sodium carbonate and 1 part potassium chlorate. The mixing is effected with a platinum spatula, and is then made more complete by gentle rubbing with an agate pestle fixed to a wooden handle. The whole is then fused over the blow-lamp. The aqueous solution of the melt is first poured into a beaker to avoid spirting, and then into another tall beaker containing an excess of hydrochloric acid. The filtered solution is heated and precipitated with hot barium chloride, heated gently upon the sand-bath for a time, until the liquid standing above the precipitate has become clear, and is filtered at once. The burnt ores in sulphuric acid works have been for a long time assayed for sulphur by this process. From 20 to 25 grammes of chlorate mixture are required for 2 grammes of burnt ore- If sulphur is fused with a sufficient excess of alkali, it is converted entirely into sulphite, and not into a mixture of thiosulphate and sul- phide, and if still more alkali is present, the result is a mixture of sulphite and sulphate. To oxidise the sulphite to sulphate, bromine is used. This analytical principle may be successfully applied to organic sulphur compounds, to free sulphur, and metallic sulphides. The fusion of sulphur or a metallic sulphide with potash yields a sulphide without any loss ; it is then oxidised by means of bromine and hydrochloric acid, forming sulphuric acid, which is estimated in the ordinary manner. Where metallic oxides are separated after the fusion, in an insoluble state, they are removed by filtration before the bromine and hydrochloric acid are added. Arsenic, antimony, zinc, &c. sulphides all yield, after melting, a fusible mass, whilst in the case of iron and copper sulphides these metals are left behind in the state of oxides. Even in pyritic silicates the sulphur can be accurately estimated in this manner. Care must be taken that not less than 25 grammes pure caustic potash are taken to every O'l gramme of sulphur supposed to ESTIMATION OF SULPHUR 471 be present. The operation is performed in a silver crucible, and the fusion is continued till all the mixture becomes tranquil say from 15 to 20 minutes or till the vapours of alkali begin to condense along the upper part of the crucible, which after use shows a clean surface if sufficient alkali has been used. When cold the mass is dissolved in cold water, freed from oxides, &c. by nitration, mixed with from 75 to 100 c.c. bromine-water, and hydrochloric acid added tih 1 a distinctly acid reaction is obtained. Heat is then applied till the liquid is colour- less. The pyrites may also be burnt in a current of oxygen, and the pro- ducts of combustion titrated. The operation is carried on in a tube of green glass, placed in a furnace for organic analysis. One end of the tube is sealed, and to the other is fitted a stopper with two holes. One of these serves for the escape of the gaseous products of combustion, which are received in a Liebig's bulb apparatus containing standard caustic soda. Through the other hole passes a long narrow tube which conveys oxygen, free from water and carbonic acid, to a small platinum boat placed near the closed end of the combustion- tube, and containing ^ gramme of the pyrites spread out in a thin layer. A plug of asbestos is placed about the middle of the tube, to avoid pro- jections. Heat is first applied towards the open end of the tube, and as it approaches redness it is gradually extended towards the closed end. The current of oxygen is regulated so as to be always in excess. The disappearance of the white vapours formed in the bulb-tube during the operation is a sign that the sulphurous acid is expelled from the combustion-tube. The open end of the tube and the stopper are then washed, and the washings are added to the liquid in the bulb-tube, the sulphurous acid in which is then estimated in the usual manner. If the pyrites contain carbonates, standard solutions cannot be used. It is then necessary to oxidise the sulphurous acid and estimate the sulphuric acid formed. (E) The following process, due to Mr. P. Holland, will be useful in laboratories which do not possess large platinum crucibles. A test- tube or piece of sealed combustion-tube, about 6 inches long and ^ inch internal width, is fitted with a cork and delivery-tube, the latter bent at a right angle and long enough to reach to the bottom of the flask in which it is intended to make the titration. The fusion mixture consists of equal parts of nitre and ignited acid sodium carbonate both free from sulphur, dry, and in fine powder. 9 to 10 grammes are taken in an operation, together with one of pyrites, the latter must be in exceedingly fine powder ; the two are mixed in a warm porcelain dish, or agate mortar, and transferred to the tube without loss. The delivery- tube is then inserted with its extremity dipping into the flask. A channel is made on the surface of the mixture, and the tube, suit- ably supported, is heated in small portions at a time with a Bunsen gas-flame, commencing as usual with the anterior portion. When the 472 SELECT METHODS IN CHEMICAL ANALYSIS operation is progressing favourably, the deflagration proceeds for a few seconds after removing the flame. There is no danger to be apprehended, and with proper care the tube does not crack or blow out. When the tube has been heated throughout, and the deflagration has ceased, it is then more strongly heated with a Herapath or powerful gas-flame. It is a good plan at this stage to slip a coil of wire gauze over the tube, which helps to accumulate the heat. It is not, however, necessary that the contents should be fused a second time. The sulphur ores examined yielded their sulphur readily. The gaseous products of the combustion which mechanically carry over with them small quantities of sulphates or sulphuric acid, being heavier than air, collect in the flask, and are washed by shaking with a little water, closing the flask with the palm of the hand. The delivery-tube is also washed. That containing the fused mass is care- fully broken and put in the flask, together with sufficient hydrochloric acid to dissolve nearly the whole of the oxide ; then ammonia is added until a precipitate of oxide reappears, and, lastly, as much free hydro- chloric acid and water as are necessary to bring the liquid to the con- ditions which were obtained when the barium solution was standardised : 2 c.c. of free acid may be used when the total volume of solution is 200 c.c. 2. Estimation of Sulphur in the Wet Way. (A] Dr. C. R. A. Wright rec'ommends the following process as being the one best adapted for commercial purposes : A known weight of the ore reduced to fine powder is oxidised (best in a small flask with a funnel placed in the mouth to avoid loss by spirting, and heated on a sand-bath) either by strong nitric acid or aqua regia perfectly free from sulphuric acid ; after the oxidation is complete the liquid is evaporated down as far as possible to expel the majority of the remaining nitric or hydrochloric acid ; the residue is boiled with a little water, and almost but not quite neutralised by ammonia ; a solution of barium chloride of known strength is then added until no further precipitate is produced, the exact point being found by filtering off a little of the liquid after each addition of barium chloride, and adding to it a few more drops of the standard solution, care being always taken, in case of a further precipi- tate being thus produced, to add this filtrate to the original solution, and mix well before filtering a second time. In case of overstepping the mark, it is convenient to have at hand a solution of sodium sul- phate of strength precisely equal to that of the barium chloride ; this solution may then be cautiously added, with repeated filtration and examination of the filtrate with the sulphate solution, until the point is just reached when addition of sulphate solution produces no further precipitate ; by subtracting the volume of sulphate solution thus used from the total volume of barium solution added, the exact quantity of this latter consumed is known. If 1 gramme of sulphur ore be taken, PEARSON'S METHOD OF ESTIMATING SULPHUR 473 and 82-5 grammes of pure anhydrous barium chloride be dissolved to a litre of liquid, each cubic centimetre of barium solution used will represent \ per cent, of sulphur in the ore examined ; 22-19 grammes of anhydrous sodium sulphate being dissolved to a litre for the second solution. In case of lead being contained in the ore, an error is intro- duced from the formation of insoluble lead sulphate ; as lead, however, rarely occurs in any perceptible quantity, this error is negligible, the process only giving approximate results. (B) Where greater accuracy is required, it is advisable to precipi- tate the sulphuric acid formed from the original liquid (filtered from in- soluble residue) by barium chloride or nitrate, and to weigh the barium sulphate produced. Instead of oxidising by acids, the powdered ore may be suspended in caustic potash (free from sulphate), and oxidised by passing washed chlorine into the liquid ; lead, being converted into dioxide, is thus rendered non-injurious ; the alkaline liquid obtained is acidified and precipitated by barium chloride as before. In the volu- metric estimation usually pursued, a curious circumstance is occasion- ally observable when much free acid exists in the solution viz. that a point may be reached when the filtered liquid is clear, and remains so even on standing for a short time, but yields a cloud, or even a precipi- tate, on the addition either of barium solution or sulphate solution : this source of error is mostly avoidable by nearly neutralising the free acid with ammonia. ( C) Instead of chlorine, hypochlorous acid may be used to trans- form the pyrites sulphur into sulphuric acid, which is then estimated by barium. Finely pulverise the mineral and suspend it in water, through which a current of gaseous hypochlorous acid, or, better still, hypo- chloric acid, is passed ; this entirely dissolves the pyrites. Hypochloric acid is prepared by heating a milk of calcium carbonate through which a current of chlorine is passed to saturation. Hypochloric acid is also obtained by heating in a water-bath a tube, supplied with a cork and delivery-tube, and containing a mixture of 9 equivalents of oxalic acid and 1 equivalent of potassium chlorate. (D) Mr. A. H. Pearson gives the following very accurate method of estimating sulphur in pyrites : Weigh out 1 gramme or less of the powdered ore, place the powder in a porcelain dish together with a small quantity of potassium chlorate, pour upon it some 50 c.c. of pure nitric acid of 39 B., and cover the mixture with an inverted glass fun- nel with bent stem ; set the dish upon a water-bath, and heat the water to boiling. From time to time throw crystals of potassium chlorate into the hot acid. By adding rather large crystals of the chlorate at frequent intervals, it is easy to oxidise the whole of the sul- phide in half an hour ; but, since the solution obtained in that case is highly charged with saline matter, it will usually be found more advan- tageous to use less of the potassium chlorate and to allow a somewhat longer time for the process of oxidation. 474 SELECT METHODS IN CHEMICAL ANALYSIS When all the sulphur has been oxidised, rinse the funnel with water and remove it from the dish. Evaporate the liquid to a small bulk, then add to it a little concentrated hydrochloric acid, and again evaporate to absolute dryness, in order to render silicic acid insoluble. Moisten the residue with concentrated hydrochloric acid, mix it with water, and filter to separate silicic acid and gangue. To the filtrate from the silicic acid add a quantity of solid tartaric acid, about as large as that of the pyrites originally taken ; heat the liquid almost to boiling, and add to it an excess of barium chloride, to precipitate the sulphuric acid. After the barium sulphate has been allowed to subside, wash it thoroughly by decantation, first with hot water and afterwards with a dilute solution of ammonium acetate (the latter may be prepared at the moment of using by mixing ammonia- water and acetic acid). The purpose of the ammonium acetate is to dissolve any barium nitrate which may adhere to the sulphate ; that of the tartaric acid is to prevent the precipitation of iron compounds together with the barium sulphate. In an experiment where 0*7 gramme of pyrites was oxidised with potassium chlorate and nitric acid, and the filtrate from silica was acidulated with hydrochloric acid without the addition of tartaric acid, there was thrown down, on the addition of barium chloride, a bright yellow precipitate, which became darker coloured when the solution was boiled. It was not only found to be impossible to wash out the iron with which this precipitate was contaminated, but the consistency of the precipitate was such that it was a difficult matter even to wash away the saline liquor in which it was formed. In another experiment the attempt was made to remove the iron in the filtrate from silica, before adding the barium salt to throw down the sulphuric acid ; but in that case a considerable portion of the sul- phuric acid was dragged down as potassium sulphate by the iron precipi- tate, and so lost. The precipitation of the iron was effected, in this experiment, by adding an excess of ammonia-water to the acidulated filtrate from silica, and washing the precipitate for a long time by de- cantation with boiling water. To prove that the iron precipitate really retained sulphuric acid, a quantity of the precipitate was dried, ignited, and powdered, and the powder boiled with water. The clear liquid thus obtained was acidulated with hydrochloric acid, and tested with barium chloride. An abundant precipitate of barium sulphate was at once thrown down. Errors of 1*5 to 4 per cent, are often made if the nitric acid em- ployed in oxidising the sulphur is not driven off by the subsequent application of an excess of hydrochloric acid. If this precaution is omitted, the barium sulphate thrown down in presence of free nitric acid is somewhat soluble, and, if abundantly washed, the result is too low. If, on the other hand, the washing is but slight, a quantity of ESTIMATION OF SULPHUR 475 barium nitrate may remain mechanically mixed with the sulphate, and the result is too high. (E) R. Fresenius shows that the precipitation of barium sulphate in boiling solutions does not take place instantaneously. Appreciable quantities remain at first in solution. If the solution contains ferric chloride, this has, on the one hand, a solvent action upon the barium sulphate, which, on the other hand, always appears red after ignition, and the ferric oxide producing this colour cannot be removed by treat- ment with hot hydrochloric acid. These two sources of error act in opposite directions, but the solvent action of the hydrochloric acid and the ferric chloride preponderates. In an examination of Lunge's pro- cess (precipitation of the boiling liquid containing ferric chloride, and some hydrochloric acid, with boiling barium chloride and immediate filtration), Fresenius has obtained deficiencies of 1 to 1'7 per cent, in a pyrites containing 43*8 per cent, of sulphur, as ascertained by his own method. (F) On the other hand, G. Lunge maintains that his process, though yielding results less absolutely accurate than those obtained by the method of Fresenius, is yet preferable for use in chemical works where time is the first object. He thinks that the larger proportion of sulphur obtained by the process of Fresenius is partly due to the fact that both galena and heavy spar bodies frequently found in pyrites are attacked by the dry process. Lead sulphide, and lead and copper ores in which it occurs, cannot be dissolved in nitric acid without the deposition of lead sulphate, which contains, also, lead antimoniate, if antimony is present. The estimation of the metals in such cases is easy if the compound is dissolved by boiling in hydrochloric acid. Even ores rich in copper dissolve completely. The hot solution is finally allowed to flow into dilute sulphuric acid, to prevent the deposition of lead chloride. (G) P. Waage calls attention to the drawbacks of nitric acid, chlorine, and potassium chlorate with hydrochloric acid, and recom- mends bromine, which he has used with success for two and a half years for sulphur, magnetic pyrites, copper pyrites, mispickel, nickel mattes, and precipitated sulphides, both for the estimation of sulphuric acid and the metals. Sulphur, shaken with bromine and water, is easily converted into hydrobromic and sulphuric acids, if for every atom of sulphur 8 of bromine are present, or 15 by weight of bromine to 1 of sulphur. If sulphur has to be estimated in this way, it is best to add all the bro- mine at once, so that no bromine sulphide can be formed. In the treatment of pyrites no necessity will exist for pulverising them very finely, as they are oxidised by bromine quite easily even in larger pieces ; but it is best to add water first, and then bromine with constant stirring, that the action may not become too violent. Bromine-water is the most convenient material for the destruction 476 SELECT METHODS IN CHEMICAL ANALYSIS of hydrosulphuric acid. A few drops of it added to a filtrate from a metallic sulphide will immediately produce a separation of sulphur, which will as quickly be dissolved by a further addition of a few drops of bromine-water. In dissolving precipitated metallic sulphides proceed in the follow- ing manner : Perforate the filter-paper and wash as much of the precipitate as possible into a beaker. Then pour some of the bromine- water into the funnel, and cover the latter with a watch-glass, when after a few minutes the rest of the sulphide may be washed into the same beaker, and a further addition of bromine-water readily oxidises the rest of the sulphide. We thus get rid altogether of the trouble of burning the filter-paper. (H) Reichardt, however, states that iron pyrites requires to be very finely pulverised, and a prolonged action is required. Copper pyrites is dissolved very rapidly if an excess of bromine is used, which is easily expelled by a gentle heat. The sample is placed in a small flask, covered with a little water, and the bromine is added. A gentle heat is sometimes necessary towards the end. In a direct volumetric estimation of the sulphuric acid resulting from the oxidation of pyrites by the wet method, Mr. Philip Holland finds that it is desirable to titrate in presence of but little free hydro- chloric acid in the entire absence of nitric acid, and to standardise the barium chloride by iron sulphate as nearly as possible under the condi- tions which will prevail in a pyrites assay so far as the amount of free acid and the volume of liquid are concerned. (I) Messrs. Glendenning and Edgar call attention to the inaccuracy introduced in the analysis of pyrites by the use of Wedgwood and por- celain mortars. The percentage of silica is in some cases doubled, and the sulphur necessarily diminished. They recommend that the sample be broken up in a steel mortar and pulverised in an agate mortar. Estimation of Sulphur in Iron, Steel, and Iron Ores (A) According to C. H. Piesse, a simple and ready method of esti- mating the sulphur in pig-irons and steels, and one requiring but little attention, is as follows : Place in a beaker of about 300 c.c. capacity about 3' 5 to 4 grammes of the sample in drillings (weighed to within O'Ol gramme will be sufficiently accurate), and pour upon them 35 to 40 c.c. of aqua regia, maintaining the proportion of 10 c.c. of the mixed acids for every gramme of the metal, keeping the beaker covered as well as possible with a watch-glass. After the first violence of the action has subsided, boil the liquid for a few moments until the whole of the iron is dissolved, then transfer the solution with as little washing as possible to a porcelain basin, and evaporate nearly to dryriess on a water-bath. Treat the residue with some concentrated hydrochloric acid, add about an equal bulk of water, and then filter. To the filtrate ESTIMATION OF SULPHUR IN IRON 477 add a considerable excess of barium chloride solution, allow to stand for about 12 hours, filter, and weigh the precipitated barium sulphate with the usual precautions. (B) M. Koppmayer introduces 10 grammes of iron, finely powdered and sifted, into a bottle holding from ^ to J litre. The stopper has three holes. Through one of these passes a funnel with a ground- glass tap, its neck reaching to the bottom of the bottle. Through the second passes the tube at right angles, fitted with a tap, and reaching also to the bottom of the bottle. Through the third hole passes the delivery-tube, connecting the bottle to the condensing apparatus. This latter consists of a series of bulbs arranged like a staircase, so as to permit the gas to come into the greatest possible contact with the standard solution of iodine in potassium iodide with which the condenser is filled. This solution ought not to be exposed to light. When the apparatus is arranged as above, the air is first driven out of the bottle by means of a current of hydrogen gas introduced by the tube bent at tight angles. When it is considered that the air is entirely expelled, the tap of this tube is closed. The funnel is now filled with hydro- chloric acid, its tap is opened, and by means of the application of heat the acid is allowed to run down upon the iron without allowing any air to enter. Hydrogen and sulphuretted hydrogen are formed, which pass into the condenser. Acid is thus added until all disengage- ment of gas ceases. The bottle is then heated until its contents boil, a little water having been first added by means of the funnel. After these operations hydrogen is again allowed to enter so as to sweep out all remaining gases. The iodised solution is then poured in, care being taken to rinse the bulb-tube thoroughly, and titrated with sodium thiosulphate, so as to find the remaining proportion of free iodine. The difference between the original amount of iodine present in the solution and the amount thus found shows the proportion of iodine which has been converted into hydriodic acid, and which is proportional to the sulphur contained in the sample under examination. (C) The common method of estimating sulphur in iron and steel consists in acting on the metal with sulphuric or hydrochloric acid, and precipitating some metallic sulphide by the evolved sulphuretted hydrogen. It would be a desideratum, in point of time, if this sulphide could be directly weighed. (D) Mr. T. J. Morrell passes the evolved gases through an ammo- niacal solution of cadmium oxide (or a solution of sulphate to which an excess of ammonia has been added) ; a precipitate of cadmium sulphide is obtained, which can be at once collected upon a small filter, dried at 212 F., and weighed. The phosphuretted hydrogen, evolved in a solution of the metal together with the sulphuretted hydrogen, causes no precipitate in the solution. The presence of ammoniacal salts would also prevent any precipi- 478 SELECT METHODS IN CHEMICAL ANALYSIS tation of cadmium carbonate by the traces of carbonic acid in the air, drawn through the apparatus by the aspirator after the metal is dissolved. However, the aspirated air could easily be passed through potash solution, to remove its carbonic acid. To prevent the precipitation of cadmium oxide on the filter, the precipitate should be washed with distilled water containing diminishing quantities of ammonia. If in very accurate analyses it is necessary to estimate the minute quantity of sulphur left in the solution and residue of the metal, this can be done as usual and added to that found as above. Estimation of Sulphur in Vermilion A mixture of nitric acid and potassium chlorate is the best means of oxidising the sulphur in this mineral to sulphuric acid, as no trace of free sulphur is ever seen in the liquid, whilst when hydrochloric acid is used to decompose the chlorate, globules of sulphur float about and entirely resist solution. About 0'5 or O6 of a gramme of the vermilion is placed in a small glass flask, set in an inclined position upon a wire- gauze support above a lamp. A quantity of nitric acid of 89 Beaume is poured into the flask, a small quantity of potassium chlorate then added, and the mixture heated. From time to time crystals of potas- sium chlorate are thrown into the flask, tbe contents of which are maintained near the boiling-point until all the sulphur has dissolved. It sometimes happens, when the proportion of nitric acid is small, that a considerable quantity of saline matter crystallises in the flask ; enough water to redissolve this precipitate may, however, be added to the mix- ture, without impairing to any material extent the oxidising power of the chlorate subsequently added. The acid liquor resulting from the action of nitric acid and potas- sium chlorate upon the vermilion is evaporated to dryness on a water- bath, and the residue treated with strong hydrochloric acid, in order to destroy most of the nitric acid before proceeding to precipitate the sulphuric acid with barium chloride. Before adding the hydrochloric acid to the residue, the latter must be allowed to become perfectly cold, lest the mixture froth violently and portions of it be thrown out of the flask. After the acid has once been added, however, the mixture may be heated gently without risk of loss. The solution must at last be largely diluted with water before adding the barium chloride. Estimation of Sulphur in Mineral Waters (A) Mr. F. Maxwell Lyte has devised an ingenious method of esti- mating free sulphuretted hydrogen in a mineral water when accom- panied by iron protosulphate, the presence of which interferes with the usual tests. Some lead sulphate is prepared by precipitation from ESTIMATION OF SULPHUR IN WATERS 479 boiling solutions, and is well washed with boiling distilled water, and, while still fresh and moist, successive portions are added to the mineral water till the brownish black colour of the precipitate first formed turns to a decided grey, showing that the sulphuretted hydrogen has all been removed from the solution, and that some undecomposed lead salt remains in excess. The supernatant liquid is decanted from the precipitate, which quickly settles down, and the latter is rapidly washed on a filter with boiling distilled water, and subsequently with hot solu- tion of ammonium acetate to dissolve out the excess of lead sulphate, till the washings are no longer coloured by the addition of an alkaline sulphide. The filter is now carefully incinerated, and the lead sulphide oxidised by an addition of a little nitric acid, and evaporated with a little sulphuric acid until heavy fumes of the latter begin to be evolved. Subsequent dilution with water gives a precipitate of lead sulphate, which is separated by deca.ntation and weighed ; from this may be calculated the amount of sulphuretted hydrogen which has been present in the water. (J5) For the estimation of hydrosulphuric acid in mineral waters, Mr. W. J. Land gives the following directions : In an apartment free from direct sunlight, preferably a room lighted by non-actinic rays, prepare a moist precipitate of pure silver carbonate, by dissolving 8" 5 grammes of pure silver nitrate in J litre of distilled water ; also 2'7 grammes of chemically pure dry sodium carbonate in an equal volume of distilled water previously heated to about 180 F. Mix the solutions gradually, simultaneously stirring them with a glass rod. Allow the precipitate to subside, decant the supernatant liquid with a pipette or small syphon, wash with hot distilled water, decanting and washing successively five or six times to obtain a comparatively clean precipitate of silver carbonate, in which substance we have a most excellent reagent for removing every trace of hydrosulphuric acid, small quantities of alkaline sulphides and haloids, from their solution in water. Add to a definite quantity of the water to be operated upon (say 1 litre if strongly impregnated, and 10 litres if weakly impregnated with gas) the still moist precipitate of silver carbonate, until the precipitate, at first black in colour, becomes brown or greyish brown, thus indicating an excess (as desired) of the silver salt. Shake or stir well, warm gently, and allow the precipitate to subside perfectly. Decant the greater part of the liquid, transfer the remainder of the liquid with every trace of the precipitate to a small beaker, and digest the latter with pure dilute nitric acid (1 of acid to about 4 of water), thus removing the excess of silver carbonate. Decant and wash well with distilled water. Transfer to a weighed filter, wash with a moderately dilute solution of ammonia (to remove silver haloids), testing the ammoniacal filtrate occasionally with ammonium sulphide, or other suitable reagent, to discover the presence or absence of the silver haloids in the washings ; when all traces of these have disappeared, 480 SELECT METHODS IN CHEMICAL ANALYSIS wash well with distilled water, lastly with pure 95-per-cent. alcohol ; dry on a water-bath. Kemove the dried silver sulphide from the filter, ignite the latter in a small porcelain crucible with a grain or two of sulphur, heating to incipient redness- (to expel excess of sulphur), add the ignited product to the larger quantity of the precipitate, transfer to a desiccator, afterwards weigh. 124 parts of the sulphide correspond to 17 of hydrosulphuric acid sought. Detection of Sulphur by Means of Sodium or Magnesium Dr. Schonn recommends the use of either of these two metals for ascertaining the presence of sulphur in the oxidised or non-oxidised state in compounds. The substance to be tested (for instance, calcium or barium sulphate) is thoroughly mixed, previously reduced to powder, and next heated to redness with the metal in a test-tube made of thin hard glass. After the reaction is over, the contents of the tube are, when quite cold, treated with distilled water and tested with sodium nitro-prusside. Care should be taken that only small quantities of substance are operated upon in this manner, especially as substances like realgar, orpiment, and others containing sulphur and arsenic at the same time, detonate violently when ignited with sodium. As regards liquids containing sulphur, the author states that a drop of sulphuric acid when brought into contact with sodium yields, among the products of the reaction, sodium sulphide ; with magne- sium, this reaction does not take place unless heat be applied. Carbon disulphide and essential oil of mustard may be readily proved to con- tain sulphur by application of the same test. For detecting sulphur in organic substances, especially of animal origin, the same process is available. Hair and feathers, dry skin and nails, may be at once submitted to ignition with the metal. White of egg, emulsin, saliva, or muscle should first be calcined on a piece of platinum, and the animal charcoal so obtained be ignited along with sodium or magnesium. In most cases of this kind sodium nitro-prusside will be required to make the presence of sulphur distinctly evident. Reagent for Sulphur (A) According to Dr. Schlossberger, a solution of ammonium molybdate in hydrochloric acid, diluted with water, possesses the property of becoming coloured blue if traces of sulphur are present. By this means the presence of sulphur even in a single hair is easily recog- nisable after it is rendered soluble by the method just given. (B] Mr. Brunner mixes the substance under examination with strong potash lye, and adds a few drops of nitro-benzol and alcohol, and allows the mixture to stand at the common temperature. After some time, if sulphur or alkaline sulphides are present, there appears ANOMALIES IN DETECTING SULPHURIC ACID 481 a red colouration from the reduction of nitro-benzol. The inverse re- action can be used for the detection of nitro-benzol. Obtaining Sulphuretted Hydrogen in the Laboratory E. Divers and Tetsukichi Schimidzu obtain a regular stream of pure hydrogen sulphide by gently heating a solution of magnesium hydrosulphide. Ordinary hydrogen sulphide (from ferrous sulphide and hydrochloric acid) is passed into water containing magnesia in suspension. The gas is absorbed, and the magnesia dissolves. The decanted solution is colourless, and when heated to 60 or 65 evolves a steady steam of hydrogen sulphide, free from hydrogen and hydro- gen arsenide. The magnesia which is precipitated during the evolution of the gas can be re-converted by cooling and passing hydrogen sulphide into it. Anomalies in the Detection of Sulphuric Acid In testing for sulphuric acid in the presence of phosphoric acid, attention must be directed to a remarkable case of interference which appears to have escaped observation until it was pointed out by Mr. Spiller. If to an aqueous solution of glacial phosphoric acid a small pro- portion of sulphuric acid be added, the mixed liquid does not give the usual indication of a precipitate on adding a few drops of barium chloride, but requires a liberal addition of the last-named reagent in order to induce the formation of the sulphate. By adding dilute hydrochloric acid, or by raising the temperature of the clear barytic solution, the formation of a precipitate is determined ; but continued ebullition fails, in many instances, to separate the whole of the barium sulphate. When, however, by the action of heat and of hydrochloric acid conjointly, the white precipitate makes its appearance, it is always found to be markedly different in physical character from the product usually obtained, being thrown down in the form of a semi-transparent flocculent precipitate, very like that obtained through the intervention of an alkaline citrate, as described in Mr. Spiller 's paper, entitled ' On the Influence of Citric Acid on Chemical Reactions,' l read before the Chemical Society. This remarkable property of obscuring the indication of sulphuric acid appears to be possessed only by the glacial modification of phos- phoric acid ; for, if the white flakes of phosphoric anhydride (as obtained by the combustion of phosphorus) be dissolved in water, no such result is apparent ; nor do the hydrochloric acid solutions oi bone-ash and of the ordinary sodium phosphate mask, in any appre- ciable degree, the presence of sulphuric acid. But if by heat the ordi- nary crystals of sodium phosphate be converted into pyrophosphato 1 See the Chemical News, vol. viii. p. 280. 482 SELECT METHODS IN CHEMICAL ANALYSIS and then dissolved in dilute hydrochloric acid, a solution is obtained which in this particular exactly resembles the glacial modification of phosphoric acid. Detection of Free Sulphuric Acid in Vinegar Boil about 50 c.c. of the acid to be tested in a retort with a very small quantity of starch, until half the liquid is distilled ; after it has cooled add a drop of tincture of iodine. If, under these circumstances, a blue colouration be produced, no sulphuric acid is present. If the blue colour does not appear, it may be concluded that sulphuric acid is present, which, by reacting on the starch, will have transformed it into glucose. With tincture of iodine, glucose gives no particular colouration. Quantitative Determination of Sulphur Don Klobulow has devised the following process for the volumetric determination of the total quantity of sulphur in all such of its com- pounds as are capable of being decomposed by acids. The products of such decompositions are hydrogen sulphide, sulphurous acid, free sulphur, and, in certain special cases, sulphuric acid. The author finds that, under certain conditions, nascent hydrogen converts not only sulphuric acid, but even the sulphur liberated from some com- pounds quantitatively into hydrogen sulphide. Hence the principle of the method consists in the reduction of the decomposition products of sulphur compounds by acids (always excepting sulphuric acid, which if present, is determined in the ordinary manner) to hydrogen sulphide and its subsequent iodometric determination. The conditions of the reactions are as follows : Sulphurous acid in solutions of a moderate degree of concentration is completely converted into hydrogen sulphide by nascent hydrogen at ordinary temperatures, or, better still, at a gentle heat, if air be excluded, and without any formation of sulphuric acid. The sulphur liberated on the decomposition of some sulphur compounds by dilute mineral acids is completely reduced to hydrogen sulphide in solutions of a moderate concentration, air being excluded, either at ordinary temperatures or, preferably, with slight refrigeration. In the author's method the sulphur compound in question is decomposed in a closed vessel in presence of zinc and hydrochloric acid. The sulphuric acid, which in some cases appears as a final product of the decomposition, remains in the apparatus, and is determined as barium sulphate along with any sulphuric acid pre-existing in the original sample ; whilst the hydrogen sulphide, which always appears as the other final product, passes into suitable absorption apparatus, filled with the titrated solu- tion of iodine, the excess of which is titrated back after the operation. The apparatus used is as follows : QUANTITATIVE ESTIMATION OF SULPHUR 483 A capacious flask, holding about 500 c.c., in which the decomposi- tion of the substance is effected, is connected, on the one hand, with the absorption apparatus, and on the other (by means of a tube reach- ing to the bottom) with a hydrogen apparatus. A ball funnel, fitted with a glass cock, permits the introduction of the hydrochloric acid required for decomposition. The absorption apparatus consists of the following parts, arranged in the order mentioned : A large flask in which the gas delivery pipe from the decomposition flask reaches to the bottom, containing the bulk of the standard solution of iodine ; a Liebig's potash apparatus, also filled with standard iodine solution ; a second potash apparatus, filled with a solution of potassium iodide, in which any iodine vapour carried along from the former apparatus is absorbed. In carrying out the process a quantity of granulated zinc, free from sulphur and arsenic, is introduced into the decomposition flask along with the weighed substance in question or its solution, and diluted with a sufficiency of water. The flask is then closed, connected with the other pieces of apparatus, and hydrogen is passed in for about ten minutes to expel air, when the decomposition may be commenced. The zinc must be in excess, though too large a quantity makes the operation more tedious. The following cases must be distinguished : 1. If there appears as decomposition product, besides hydrogen sulphide, free sulphur alone or along with sulphurous acid the decomposition flask is placed either in a dish of cold water or in a vessel with a continual flow of water, and the decomposition is con- ducted as slowly as possible. Supposing the solution to be originally clear, it becomes milky in consequence of the liberation of sulphur, but this turbidity gradually disappears, and the liquid grows clear again. When the process has reached this stage, which occurs in twenty to twenty-five minutes, the cooling arrangement is removed, more acid is added, and the solution of the residual zinc is promoted by a gentle heat. When the zinc is completely dissolved the flask is heated for a time to 70 to 80. The current of hydrogen (which does not need to be very strong as long as zinc is still present) is reinforced, and the liquid in the decomposition flask is thus kept in brisk motion, which, on the one hand, hastens the removal of the last traces of hydrogen sulphide from the liquid, and prevents a reflux of the absorptive liquid into the decomposition flask as the latter cools. 2. If, in the decomposition of the substance in question, there ap- pears no sulphur, but merely sulphurous acid and hydrogen sulphide, any refrigeration is superfluous ; the decomposition is begun at the ordinary temperature, and afterwards quickened by a gentle heat. In other respects the process is conducted as in Case 1. Before breaking off the experiment it is well to ascertain, by means of lead-paper, if the sulphuretted hydrogen has been entirely removed n2 484 SELECT METHODS IN CHEMICAL ANALYSIS from the flask. This test is best applied at the joint between the gas delivery-tube and the first absorption apparatus. The duration of the entire process is one and a half to two hours ; after its completion the absorbent vessels are emptied into one common vessel, and the excess of the iodine solution is titrated back with sodium thiosulphate. The liquid in the decomposition flask contains all the sulphuric acid which has been formed during the decomposition, as well as that if any pre-existing in the substance. Its determination is effected in the ordinary manner. The solutions used are decinormal iodine and sodium thiosulphate standardised to each other. The hydro- chloric acid used is of the strength 1*1. Estimating Free Sulphuric Acid in Superphosphates The following method is recommended by Dr. R. Carter Moffat as being very accurate : An aqueous solution of the superphosphate being made, evaporate slowly until a small quantity only is leit ; add about 7 volumes of concentrated alcohol, and allow it to settle in the cold for some hours. This precipitates all sulphates, and leaves in .solution, besides phosphates, the free sulphuric acid. Filter^ wash with alcohol, add a large amount of water to the solution, carefully evaporate off the spirit, and estimate the acid in the usual manner by precipitation with barium chloride. The soluble phosphates do not in any way interfere. Should a more ready, though less accurate, process be required, an aqueous solution of the superphosphate treated with a very dilute normal solution of ammonia gives tolerably fair results. Precautions in Precipitating Barium Sulphate (A) It is well known that precipitated barium sulphate may retain alkaline salts in quantities of from 1-5 to 2 per cent., which cannot be removed by the most careful washing. Stolba obtains the barium sulphate pure by digesting it (after washing until the wash-waters no longer show the reaction of barium) with 40 to 50 c.c. of a cold saturated solution of neutral copper acetate and some acetic acid, at nearly a boiling- heat for 10 or 15 minutes. During the digestion enough acetic acid must be present to prevent the formation of basic salt on boiling. Should basic salt form, which may be readily perceived at the bottom of the vessel, more acetic acid must be added, and the digestion must be renewed for 10 or 15 minutes. During the process the vessel containing the precipitate should be constantly agitated. The alkaline salts retained by the barium sulphate undergo double decomposition with copper acetate, and the resulting products all admit of entire separa- tion from the precipitate by means of hot water. The precipitate is washed until no reaction for copper is manifested on testing the PURIFICATION OF SULPHURIC ACID 485 washings with potassium ferrocyanide. This method is also satis- factory for the estimation of sulphuric acid in presence of a large excess of barium nitrate and chloride. (B) The commercial crystallised copper acetate is purified from sulphuric acid, and at the same time saturated with barium sulphate, by adding to its boiling solution a slight excess of barium chloride and acetic acid, and filtering from the precipitate. (C) Fresenius describes a number of very important experiments concerning the influence of various acids and salts on the precipitation of barium sulphate, and the admixtures of foreign salts with the pre- cipitate. His conclusions are : (1) Barium sulphate does not require 43,000 parts of water for solution, as usually stated, but upwards of 400,000 parts, even in presence of hydrochloric acid, which slightly raises its solubility. (2) Sodium chloride, potassium chloride, and barium nitrate do not increase its solubility very perceptibly, but the alkaline nitrates do so. (3) Hydrochloric acid does the same, and it must therefore be evaporated or partially neutralised before the precipitation. (4) Sodium chloride does not produce any foreign admixture in the precipitate. (5) Potassium chlorate does cause such admixture in a high degree. The precipitate can, however, be purified by digesting with hot hydrochloric acid, evaporating the same, and washing with water. (6) Sodium, potassium, and barium nitrate cause a very impure precipitate, which cannot be purified by washing with hydrochloric acid", but only by fusion with sodium carbonate, and estimating the sulphates in the aqueous solution of the fused mass. Purification of Sulphuric Acid from Arsenic Arsenic almost always exists in commercial sulphuric acid in the form of arsenious acid, which, being volatile, distils over with the sulphuric acid, and prevents its purification by rectification. (A) MM. Bussy and Buignet recommend that a sulphuric acid which contains arsenious acid should be boiled with nitric acid, to oxidise arsenious acid to arsenic acid, then mixed with a little am- monium sulphate to destro/ the excess of nitrous compounds, and distilled with precautions to prevent any particles being carried over by projection. The distillate will be free from arsenic. (J5) As there is some theoretical danger that the ammonium sulphate might reduce the arsenic acid to arsenious, which would pass over as before, M. Blondlot recommends that manganese peroxide should be used to oxidise the arsenious acid. The way he proceeds is as follows : Manganese peroxide is added in the proportion of 4 to 5 grammes to the kilogramme cf sulphuric acid, and the mixture heated to boiling in a porcelain dish, stirring all the time. It is allowed to cool, and is then transferred to a retort and distilled. (C) Maxwell Lyte employs a different mode of purification, chiefly 486 SELECT METHODS IN CHEMICAL ANALYSIS with a view to insuring the complete absence of all nitrous products, and obtaining a pure acid from the very first, and of thereby obviating the necessity of changing the receiver a most dangerous operation when distilling sulphuric acid. If the acid contains nitrous compounds, heat it in a porcelain capsule to a temperature of about 110 C., with a small portion of oxalic acid, till the latter is completely decomposed and all effervescence has ceased ; about O26 to 0'5 per cent, is amply sufficient for nearly all samples of commercial acid. It is best to add the oxalic acid before heating, and to stir constantly till the reaction is completed. Now allow the acid to cool down to about 100 C., and add to it a solution of potassium bichromate in sulphuric acid, or some of the salt itself in fine powder, until the pure green colour at first produced by the formation of chromium sesquioxide is replaced by a yellowish green, indicating an admixture of chromic acid in the free state. The acid so prepared, being now distilled, passes from the first perfectly free from all impurity. The addition of the bichromate has another advantage, viz. that if it be first of all applied to a small sample of the commercial acid, it indicates the presence of free sul- phurous acid as well as of arsenious acid, and either of these being present, we may presume on the absence of nitrous compounds. No doubt permanganates would answer equally well ; but the potassium bichromate, which is cheap and easily procured, is so convenient as to leave nothing to be desired. Detection of Gaseous Impurities in Sulphuric Acid It is essential for some purposes that oil of vitriol should contain neither sulphurous acid nor any of the lower nitrogen oxides ; both of these impurities are met with in some commercial samples of oil of vitriol. Mr. E. Warington gives the following method for testing for the presence of sulphurous acid and nitrogen oxides : About 2 pounds of the oil of vitriol are placed in a bottle, which the liquid half fills ; the bottle is then stoppered and violently shaken for a minute or two. The gases contained in the oil of vitriol are thus washed out by the atmospheric air contained in the bottle. Sulphurous acid is then tested for by introducing into the air-space of the bottle a slip of paper coloured blue by iodine and starch ; the paper is con- veniently held in the bottle by means of a wire and a cork. The bleaching of the paper gives evidence of the presence of sulphurous acid. The test-paper is best prepared from Swedish filter-paper ; this is first passed through a well-made solution of starch and then dried. A slip of this paper is next placed in a weak aqueous solution of iodine, where it remains till it has acquired a distinct blue colour. It is then removed, pressed between blotting-paper, and is now ready for use. The paper thus prepared gradually loses its colour by exposure to DETECTION OF SULPHUEOUS ACID 487 air ; it should therefore be used as soon as made ; for the same reason its exposure to the gas in the bottle should not exceed 2 or 3 minutes ; no perceptible change of colour will occur in this time if no sul- phurous acid be present. The colour of the paper is also at once destroyed by heat ; it cannot therefore be used for testing the gases given off by hot liquids. The nitric oxides are detected by substituting for the first test- paper one imbued with potassium iodide and starch. N 2 2 forming N 2 4 on contact with air, and N 2 3 producing the same compound on contact with air and moisture, the presence of any one of these three oxides will suffice to liberate iodine on the moist test-paper and colour the starch. Since sulphurous acid destroys the blue starch iodide, the presence of an excess of this gas will prevent the detection of the nitric oxide. The nitric oxide is, on the other hand, without effect on the test-paper employed for the sulphurous acid. If, therefore, the sul- phurous acid is not in excess, it is quite possible to obtain the reactions of both gases from the same sample of oil of vitriol, and this is no uncommon occurrence with oil of vitriol which has been imperfectly boiled. In using the reaction here described for the purposes of general testing, it is to be remembered that sulphuretted hydrogen produces the same effect as sulphurous acid. Analysis of Sulphuric Anhydride and Fuming Sulphuric Acid 0. Clar and J. Gaier weigh the fuming acid in thin glass bulbs of 20 millimetres in diameter, provided with two long capillary points opposite to each other. The bulbs are half filled with the acid by suction, and are then sealed up at both ends. After weighing, a point is broken off under water. The anhydride is weighed in small glass bottles 58 millimetres high, 17 millimetres wide, with high ground stoppers, enlarged conically above, and with a small aperture in its summit closed with a minute glass plug. The interior of the stopper is filled with glass wool, slightly moistened. The bottle when charged and weighed is allowed to glide in an inverted position into a 2-litre flask held in a sloping position, and containing about 500 c.c. water at 50 to 60. After mixture has taken place through the small aperture in the stopper, the liquid is made up to 1 litre, and a portion of 100 c.c. is titrated with 5-normal soda. Detection of Sulphurous and Thiosulphuric Acid (A) Instead of employing hydrochloric acid and zinc, aluminium and hydrochloric acid are preferable. Zinc may be contaminated with sulphur compounds, while aluminium is always pure in this respect ; the latter metal, moreover, dissolves very slowly in dilute hydrochloric 488 SELECT METHODS IN CHEMICAL ANALYSIS acid, and therefore the same piece of aluminium may serve for many testings. (B) Dr. Reichardt has distinctly detected the sulphuretted hydrogen when a solution of 1 part of sulphurous acid in water, diluted with 500,000 parts of water, was treated with hydrochloric acid and aluminium. Estimation of Sulphides and Hydrosulphites (A) If both salts are present together in solution, it is necessary to- find the quantity of iodine which a part of the liquid requires if mixed with acetic acid, and the quantity of barium sulphate which an equal part of the solution yields after complete oxidation with bromine. Two equations are thus obtained with two. unknown quantities. If a sulphate is also present its quantity is ascertained by adding to the liquid sodium bicarbonate, passing a current of carbonic acid through the liquid, heating after expulsion of the air, and, after the addition of hydrochloric acid in excess, concentrating to a quarter its volume. The sulphurous acid being thus expelled, the sulphur is filtered off, and the sulphuric acid in the filtrate is estimated in the ordinary manner. (B) For the estimation of sulphurous acid in air, B. Proskauer passes a known volume of air through 50 or 75 c.c. of a solution of permanganate containing 15 grammes of the crystalline salt per litre, and 2 or 3 c.c. of hydrochloric acid. The solution is placed in a, Bunsen bulb-tube. PHOSPHORUS Detection of Phosphorus When previously well-dried (previous ignition is often required) inorganic combinations of phosphorus are ignited in a pulverised state in a test-tube with small quantities of magnesium wire, ribbon, or powder, there is formed magnesium phosphide. After cooling, the fused mass, on being moistened with water, will disengage phos- phuretted hydrogen gas, which, in many instances, will be found to be the spontaneously inflammable variety. Phosphorus may be detected in the same way in organic substances as, for instance, brains, muscle, &c. but these should be previously calcined, and the dry animal char- coal so obtained submitted to the experiment. For the detection of phosphorus in organic liquids, the following modification of Mitscherlich's process will be found to answer well. It consists of an ordinary flask, connected with a receiving-bottle by means of a glass tube, which passes about 18 inches through a glass cylinder filled with cold water. A long straight tube conducts the gaseous products from the bottle. The lamp and flask, and about DETECTION OF PHOSPHORUS 489 three-fourths of the glass cylinder, are surrounded with dark paper. The operation is best performed in a dark room. The phosphorescence of the liquid increases in intensity with the consistence of the liquid and the quantity of the phosphorus. The gas-bubbles are luminous, rise in the mixture, and apparently burn upon its surface with a bright flame. With the temperature the light increases ; a photosphere fills the flask, rises in the tube, and moves up and down within the cooled part. Sometimes only a column or a luminous ring appears stationary at the point where the vapours are cooled, and a luminous fog or sparks gradually sink into the receiver, or a sudden, frequently repeated flash of light is observed. If the heat is raised too high, or the cooling is insufficient, the phosphorescence passes through the long gas-tube, at the mouth of which the gases take fire, if the volatile oils from CrucifercR (mustard, &c.) have been present. Coffee, mustard, smoked meat, highly seasoned food and beverages, and medicines containing odorous gum-resins, volatile oils, musk, cam- phor, chlorine, &c., have the property of covering the odour of a small portion of phosphorus. The reaction is not interfered with by the presence of ipecacuanha, tartar emetic, magnesia, hydrated iron oxide, musk, castor, opium, albu- men, neutral acid or basic salts and double salts, volatile organic acids, chlorides, iodides and sulphides, and free acids ; but iodine, and mer- cury chloride and bichloride in considerable proportion, and metallic sulphides in the presence of free sulphuric acid, and particularly oleum cin<% (Artimisice), interfere with or prevent the reaction. Numerous experiments, by distilling the brain of various animals, blood, albumen, casein, fibrin, legumin, and other protein compounds, with dilute sulphuric acid, have not yielded the least phosphoric reaction. Detection of Arsenic in Commercial Phosphorus In preparing dilute phosphoric acid by the oxidation of commercial phosphorus, the precaution should be taken to pass a current of sul- phuretted hydrogen through the solution, in order to free it from all substances precipitable by that agent from acid solutions ; by this operation arsenic sulphide is frequently thrown down. In order to estimate the amount, Dr. C. J. Bademaker oxidises 100 grammes of phosphorus with nitric acid, dilutes the solution and precipitates the arsenic as sulphide, by means of sulphuretted hydrogen ; the solution is allowed to rest for six days, after which the precipitate is collected on a filter and washed, transferred to a small evaporating-dish, oxidised with nitric acid, reduced by means of sulphurous acid to arsenious acid, and again precipitated by means of sulphuretted hydrogen ; the precipitate is digested with ammonia to free it from adhering sulphur, the solution filtered, evaporated, dried, and weighed, when the sample 490 SELECT METHODS IN CHEMICAL ANALYSIS under examination was found to amount to nearly 1 gramme of arsenic sulphide. Phosphorus Holder. Mr. E. Kernan gives the following in- genious method of making a phosphorus crayon which is perfectly safe in the hand for lecture experiments in luminous writing, &c. : A few inches of lead tube, J- in. bore, are contracted to an open cone at one end. As much phosphorus as one may choose is put into the cone of the tube ; the phosphorus is made to project slightly from the cone ; the upper part of the tube is filled with water and corked. To put in the phosphorus, as much as may be required is melted in a conical glass, or test-tube, the cone of which is larger than that of the lead tube. This is put standing in the melted phosphorus, which fills the cone and tube to its own outside level. When cold, there is a nice project- ing crayon, from the form of the glass. Any phosphorus outside the lead tube may be melted off. To renew the writing-point, a test-tube, conical below, is fitted to the cone of the lead ; the whole is held in warm water for a minute, when sufficient phosphorus flows out to form a new point. Preparation of Phosphuretted Hydrogen Prepare zinc phosphide by mixing together amorphous phosphorus with half its weight of powdered zinc, and gently heating the mixture in a hard glass tube through which a current of dry hydrogen or coal- gas passes. The tube and contents- must be cooled in the current of gas. From the zinc phosphide so prepared phosphuretted hydrogen may be readily obtained by means of dilute sulphuric acid or by boiling with caustic potash. The gas is, however, the n on- spontaneously com- bustible kind. The spontaneously combustible gas maybe obtained by taking a larger quantity of zinc phosphide and dissolving it in warm dilute sulphuric acid. Distinction between Phosphates and Arseniates Mr. A. H. Allen remarks that it is well known that the difference in colour between silver phosphate and silver arseniate furnishes the most simple means of distinguishing between the two classes of salts. The presence of free nitric acid or ammonia interfering with the re- action, it is necessary to apply the test to a neutral solution, in which case many other salt radicles may be precipitated. If the phosphate or arseniate be first separated as the ammonio-magnesium salt, it is usual to dissolve this precipitate in nitric or acetic acid before adding silver nitrate. This is quite unnecessary, the characteristic yellow phosphate or brown arseniate being immediately produced on addition of silver nitrate to the crystalline precipitate. This modification ren- ders the test more delicate as the reaction takes place in a neutral liquid. A few streaks on a test-tube show the reaction very distinctly, hardly changing colour if due to phosphate, but turning quite brown if caused ESTIMATION OF PHOSPHORIC ACID 491 by arseniate, in each case becoming soluble in ammonia. On this account the ammonio-magnesium salt must be washed free from ammo- nia, which would either prevent the reaction or lead to confusion by precipitating brown silver oxide. Acetic acid dissolves both silver phosphate and arseniate, the former far more readily than the latter. If, therefore, acetic acid be gradually added to a mixed precipitate of silver phosphate and arseniate, the phosphate dissolves first, and the brown colour of the arseniate becomes more apparent. If, after the addition of a moderate quantity of acetic acid, the liquid be filtered, the dissolved phosphate may often be detected by cautious neutralisation with ammonia, when the yellow silver phosphate is thrown down ; but this reaction is uncertain, as both silver phosphate and rseniate are soluble in ammonium acetate, the phosphate more readily than the arseniate. Estimation of Phosphoric Acid 1. By the Modified Tin Process (Reynoso's). (A) This method depends upon the fact that, when metallic tin is added in ex- cess to a solution of a phosphate in nitric acid, the stannic acid formed by the oxidation of the metal combines with the phosphoric acid and completely removes it from solution. On filtering, therefore, we at once separate the bases which remain in solution from the insoluble combination of stannic and phosphoric acids. In order to estimate the amount of phosphoric acid contained in the tin oxide, the compound is dissolved in a small quantity of concentrated potash solution, when the two acids dissolve as metastannate and potassium phosphate ; the liquid is now saturated with sulphuretted hydrogen, a small quantity of ammonium pentasulphide added, and, lastly, a slight excess of acetic acid. The tin sulphide is then separated by filtration ; all the phos- phoric acid is contained in the filtrate, and its amount may be esti- mated by the ordinary method as magnesium ammonio-phosphate. Two very good modifications of this method have been given. (B) Modification 1. According to the first the substance is dis- solved in nitric acid. When there are any difficulties in getting it into solution, dissolve it first in any convenient reagent, then add excess of ammonia to the solution, which precipitates all the phosphoric acid, with most of the bases ; well wash the precipitate ; it will then be readily soluble in nitric acid. If, for instance, a specimen of cast-iron is being analysed, it must be dissolved in aqua regia ; if a refractory mineral, it must be attacked by alkalies, &c. The nitric solution having been obtained (which should be free from chlorides), throw into it an indefinite quantity of pure tin ; about four or five times the supposed weight of the phosphoric acid present may be employed. This tin passing to the state of stannic acid, under the influence of the nitric acid, carries down with it all the phosphoric 492 SELECT METHODS IN CHEMICAL ANALYSIS acid, as well as a great portion of the iron and a little aluminium ; wash at first by decantation and then on a filter, and place on one side the nitric solution, which is free from tin, but contains all the bases minus a portion of iron and aluminium. Then redissolve the precipitate in a small quantity of aqua regia, and, without troubling about the filaments of filter-paper, or the small portions of tin phos- phate which may remain undissolved, supersaturate with ammonia, and then add an excess of ammonium sulphide. The stannic acid and tin phosphate immediately dissolve, leaving a black precipitate of iron sulphide containing aluminium ; allow it to stand for an hour or two, and then filter, taking care to wash the precipitate with ammo- nium sulphide to remove the last traces of tin. It is then only neces- sary to add magnesium sulphate to the filtered liquid to obtain the characteristic precipitate of magnesium ammonio-phosphate. Collect this on a filter, wash it first with ammonium sulphide, then with ammoniacal water, and afterwards calcine in the ordinary manner. The filter containing the iron sulphide and aluminium is redis- solved in nitric acid, and .the filtered liquid is added to the original solution of the bases, which may then be separated in the ordinary way. This method is both simple and rapid ; it enables one to estimate the phosphoric acid contained in the most complicated mixtures, and then admits of the accurate separation of the bases. (C) Modification 2. Obtain the phosphate in solution in nitric acid, as described above. Concentrate the solution and add the strongest nitric acid (boiling at 86 C.). The nitric acid solution is now in the highest possible state of concentration : on throwing a small quantity of tin into this solution, the metal is rapidly oxidised to stannic acid, and the supernatant liquid remains perfectly clear. The preliminary heating of the solution is indispensable, since in the cold the metal is apt to become passive, when it completely resists the action of the acid. The precipitate is now dissolved in a small quantity of caustic potash, and saturated with sulphuretted hydrogen ; 011 adding acetic acid in slight excess the tin sulphide is precipitated. The precipitate is then separated by means of the Bunsen filter-pump, and the whole of the phosphoric acid is contained in the filtrate. After concen- trating the solution, and again filtering from a minute precipitate of tin sulphide, which invariably separates out (tin sulphide being slightly soluble in solutions containing sulphuretted hydrogen), the phosphoric acid may be precipitated as the magnesium-ammonio salt, and weighed as pyrophosphate. The amount of tin need not exceed four times the weight of the phosphoric acid present. This, however, is the minimum quantity that can be used with safety. 2. Estimation of Phosphoric Acid by the Magnesium Pro- cess. (A) The estimation of phosphoric acid in minerals containing ESTIMATION OF PHOSPHORIC ACID 493 fluorine, iron, and aluminium is a matter of considerable difficulty. After dissolving in mineral acids, most authorities advise that the acid solution should be brought to dryness before proceeding to separate the calcium. Some analysts, however, neglect this part of the process, from the impression that it has no influence on the estimation of the phosphoric acid, and that it is only necessary when the siliceous matter is required for a full analysis. Mr. T. K. Ogilvie has instituted several experiments to show that this impression is an erroneous one. From them the following are selected : (1) A gramme of Cambridge coprolites was dissolved in moderately strong hydrochloric acid, evaporated to dryness, the residue again dis- solved in acid, the calcium separated with ammonium oxalate, citric acid added to hold up iron and aluminium, the solution made alkaline with ammonia, and the phosphoric acid precipitated with magnesia- mixture.' A perfectly granular precipitate was obtained, which, after standing for twelve hours, was washed, dried, ignited, and weighed, and found to be equivalent to 47*44 per cent, tricalcic phosphate. (2) Another gramme of the same coprolites was treated in exactly the same way, with the exception that the acid solution was not brought to dryness. The magnesium ammonio-phosphate, as it gradually formed, presented the usual appearance ; but, when stirred up after a few minutes, a white flocculent body was also observed. After standing for the usual time, the whole precipitate was collected, washed, dried, ignited, and weighed, and gave 53*04 per cent, calcium phosphate. (3) A third gramme was treated as in (2), with the difference that, after the addition of citric acid, the solution was made alkaline with ammonia, and allowed to stand. In a short time a white flocculent precipitate formed, which was filtered, washed, dried, ignited, and weighed. To the clear ammoniacal nitrate, ' magnesia-mixture ' was added ; and a granular precipitate, free from any flocculent matter, was obtained, equivalent to 47*2 per cent, calcium phosphate. This closely corresponds with the result (viz. 47*44 per cent.) obtained in (1) after evaporating to dryness. The flocculent precipitate got by ammonia weighed 4*05 per cent. Had it not been removed, it would have been taken as magnesium ammonio-phosphate, and, as such, been equivalent to 5*66 per cent, calcium phosphate ; this, added to 47*2 per cent., gives 52*86 per cent., against 53*04 per cent, found in (2) by weighing the flocculent precipi- tate along with the magnesium ammonio-phosphate. In these experiments, care was taken that the calcium was perfectly separated, and that sufficient citric acid was present to hold up iron and aluminium. The precipitate which forms on the addition of ammonia to the the test will be none the less exact, as at the time of performing it the relation of a given weight of pure iodine to the arsenite will also be estimated. A somewhat concentrated solution of sodium bi- carbonate is also to be prepared. The analysis is best effected hi a small stoppered flask. Into this are put 10 c.c. of the sodium arsenite, to which must be added 5 c.c. of alkaline bicarbonate solution ; the whole then receives a further addition of about 4 c.c. of perfectly colourless benzol. 540 SELECT METHODS IN CHEMICAL ANALYSIS Weigh a certain quantity of pure iodine between two watch-glasses ; dissolve this in the concentrated solution of potassium iodide prepared beforehand, and which must be of the same strength in all the various estimations which may be made ; with this coloured solution fill a flask containing 100 c.c., shake it, and pour the contents into a graduated burette. On allowing the iodised solution to fall into the arsenite drop by drop, and stirring it quickly, the brown colour will be seen to dis- appear instantaneously ; but scarcely will all the arsenite have been changed to arseniate, when the addition of iodine will produce a double reaction ; in the first place, the benzol will turn red ; secondly, the aqueous liquid, which was perfectly colourless at the beginning of the operation, assumes a very sensibly yellowish tinge. The significant character of this is the more surprising when we remember the very small quantity of iodine which causes it. A second experiment is now to be performed upon the iodine to be estimated, and the same weight being used, its standard is at once shown, since the volume of solution requisite to destroy the alkaline arsenite is in inverse proportion to the quantity of real iodine to be estimated. Detection of Minute Quantities of Iodine (A) Make a mixture of water, 100 grammes ; starch, 1 gramme ; potassium nitrite, 1 gramme : boil this for 5 minutes ; it will then keep for years without deterioration. When required for use, take 10 c.c., and add to it one drop of hydrochloric acid. Take a piece as large as a pin's head of the dry salt to be tested for iodine, place it in a clean porcelain capsule, and add a drop of the test liquid. When no iodine is present, no colouration ensues ; but the least trace of iodine gives rise to the formation of a well-defined blue colour. (B) Carey Lea makes use of the oxidising properties of chromic acid to liberate iodine from its hydrogen and metallic combinations and thereby bring about the starch reaction. If, for example, we take an extremely dilute solution of potassium iodide, such that the addition of nitric acid and starch produces no perceptible effect, the further addition of a single drop of very dilute solution of potassium bichromate will instantly bring about the charac- teristic reaction. When hydrochloric acid is substituted for nitric, the effect of the bichromate is still more marked. The test has, then, the full delicacy at least of the chlorine test, with this great advantage, that an excess of the reagent does not prevent the reaction. As to the delicacy of this test, the following observations have been made : With solutions of potassium iodide up to IOO I OO Q- the precipitate is abundant, becoming less blue and more tawny as the dilution in- creases. Beyond this point the distinctness rapidly falls off. The in- dications are observable at ?Tn i ffTn j.. With a solution of s - -oVoo it is DETECTION OF IODINE 541 doubtful whether any effect is evident. The experiment can be made in two ways, according to the result desired. In employing the reagent in the search for iodine, add the starch to the liquid to be tested, stir it up, add a drop of dilute solution of potassium bichromate, enough to communicate a pale yellow colour, and finally add a few drops of hydrochloric acid. The test is then the production of the characteristic precipitate, or in case of great dilution, approaching to a half -millionth, merely the tawny shade given to the solution. If a very great excess of acid is used, and too much bichromate taken, the starch may be made to reduce the bichromate. Even this, however, cannot deceive, for a bluish-green solution is thereby pro- duced, whereas the indications of iodide are in the order of their strength blue precipitate, tawny precipitate, tawny solution. Unless in the case of very exceptional dilution above spoken of, a well-marked blue precipitate is always obtained. (C) The method of estimating iodine by the thiosulphate process is best conducted as follows : Prepare a normal standard solution containing, for each litre of water, about 40 grammes of sodium thiosulphate, so that 50 c.c. of this solution will completely decolourise 1 gramme of iodine. Then take 10 c.c. of the iodised liquid to be tested, diluted with water if it be very concentrated or rich in iodine ; then add carefully, after it has been acidulated with hydrochloric acid, some drops of hyponitric acid. When it becomes yellow, shake it with benzol or petroleum, which will immediately turn rose or violet. Separate the iodised benzol from the acid liquid, and repeat the operation until the solvent liquid ceases to become coloured. Collect the iodised benzol resulting from these treatments, and wash it with distilled water, which will remove all traces of chlorated or bromated compounds without removing any appreciable quantity of iodine. Then, with constant stirring, add, by means of a burette graduated to tenths of a c.c., the standard thiosulphate liquid until all colour is destroyed ; each cubic half -centimetre of the normal liquid will correspond to one centigramme of iodine contained in the liquids assayed. It is always necessary to desulphurise solutions containing sulphides, sulphites, or thiosulphates, by boiling them with nitric, sulphuric, or hydrochloric acid. To ascertain the purity of commercial iodines, dissolve about 50 centigrammes in diluted alcohol, and operate as above. To ascertain the quantity of iodine in dry or wet sea plants, cut them into small pieces ; dry them, place them in a porcelain capsule and cover them with alcohol; set fire to the alcohol, carefully stir the mass with a glass rod, and the carbon will be obtained without loss of iodine ; then well wash the latter, and act on the solution as above described. 542 SELECT METHODS IN CHEMICAL ANALYSIS Detection of Small Quantities of Iodine in Sea-water, etc. (.4) The liquid to be tested is placed in a test-tube along with carbon disulphide, and a very few drops of dilute sulphuric acid. Hereupon the vapour of red fuming nitric acid is allowed to fall for a moment into the tube. After strong agitation, the carbon disulphide is coloured rose if the slightest trace of iodine is present. (B) M. A. Chatin points out certain causes of failure in the detec- tion of minute quantities of iodine in potable waters, &c. It is needful to precipitate the soluble calcium and magnesium salts with an excess of pure potassium carbonate. The iodine being thus fixed will be found in the residue after evaporation, which is slightly ignited to destroy organic matter. The liquid must be separated by decantation from the earthy carbonates, which will be deposited during the first quarter of the evaporation. Towards the end of this process the heat must be diminished to avoid any loss of the soluble residue by spirting. This last point is important, as the iodide is among the last drops evaporated. The excess of carbonate remaining after the precipitation of the calcio-magnesium salts should be the larger the more organic matter is present. We may ascertain that this excess has been sufficient, either by the residue appearing colourless after calcination, or by the circumstance that although coloured it forms a paste if treated with alcohol at 90 per cent. If the alkaline carbonate has been insufficient, the residue will be divided in the alcohol, like a powder ; the iodine then escapes in great part or entirely during calcination. The alkaline residue left on the evaporation of the water must be treated three times with alcohol, and the solutions are mixed together in a capsule capable of holding at least four times the quantity. Before proceeding to evaporate, which must be done at a low temperature, the alcohol is mixed with about half its volume of pure distilled water. The water should have been distilled after an admixture with potassium carbonate. Frequent agitation is useful. Slight calcination is again needed to destroy a certain quantity of organic matter which has escaped the former ignition, and the presence of which would mask the character of traces of iodine. The residue at the bottom of the cap- sule should be colourless and scarcely perceptible. If it is very appre- ciable in quantity too much alkaline salt is present, and it must be redissolved in alcohol. The last condition is that this residue must be dissolved in a minimum of water, 2 drops, or even a single drop, which must be led over the bottom of the capsule with a glass rod, so as to dissolve all the iodide present. With the end of the stirrer this liquid is divided into three or four portions, one of them which will give the most distinct reaction being left in the bottom of the capsule, the others being placed on fragments of porcelain. One of these little drops is mixed with palladium chloride ; the others, having first re- ESTIMATION OF IODINE 543 ceived a trace of recently made starch-paste, are carefully touched, the one with nitric acid, the other with commercial sulphuric acid ; chlorine water only gives the blue colouration if the quantities are more consider- able. A common cause of failure is the use of chlorine water, and of too dilute solutions. Earths, ores, metals, sulphur, &c., are first finely divided, and then boiled in a solution of potassium carbonate, which is then treated as above. It is well to make blank experiments in researches of this kind. (C) M. Sergius Kern recommends that palladium salts should be very carefully used in analysis for the detection of iodine, because in presence of potassium ferrocyanide or potassium ferricyanide the iodine is not detected, and cannot be separated from bromine or chlorine by palladium chloride. So as gold salts also give, with potassium ferro- cyanide, a green colouration, this reagent may give faulty results, as it was remarked that palladium salts give the same colouration. If palladium salts are used as a reagent for iodine, the preliminary analysis must be very carefully executed, in order to be quite convinced of the absence of double potassium ferrocyanides and other cyanides. In presence of alkaline sulphocyanides iodine is not precipitated by palladium nitrate or chloride. Estimation of Iodine in Organic Liquids (A) There are met with in commerce mother-liquors which are utilised for the manufacture of iodine, and containing, besides this metalloid, sensible quantities of alkaline arseniates and arsenites, as well as organic matter. These liquids occur in the manufacture of aniline colours, and their value depends upon the amount of iodine they con- tain. The following is the best process to adopt for estimating this : 10 grammes of liquid are treated with 2 grammes of concentrated solution of caustic potash ; the mixture is then evaporated to dryness under a chimney with a good draught, or in the open air, on account of the cacodylic products occasionally evolved ; it is ultimately ignited. The aqueous solution of the residue is diluted with water and treated with a mixture of sulphuric and hyponitric acids. The iodine is separated by agitating with carbon disulphide, and this carbon disul- phide solution agitated with water until the washings no longer affect litmus -paper ; when this is attained, a titration of the iodine present is made with sodium thiosulphate or arsenite. (B) To estimate the iodine contained in organic hydriodates, M. Kraut proposes that their solution be digested for some time with a known weight of recently -precipitated silver chloride ; the chlorine is replaced by iodine, and from the increase in weight of the silver chloride the amount of iodine may be calculated. This method has the advantage of not altering the substance beyond removing its iodine, which is replaced by chlorine. (C) Reinige describes a very interesting method for the estimation 544 SELECT METHODS IN CHEMICAL ANALYSIS of iodine, viz. by means of potassium permanganate. 2 equivalents of the latter and 1 equivalent of potassium iodide produce 1 of potassium iodate, 2 of free potash, and 4 of manganese peroxide. The decomposition is assisted by boiling the solution, and if the latter is very dilute, a little potassium carbonate is added to induce the com- mencement of the reaction. As bromine and chlorine are not in the least acted upon under the same circumstances, this reaction is, per- haps, the most convenient for the estimation of iodine. The latter must be combined with potassium, and the solution rendered nearly neutral, but still slightly alkaline. It is heated till it boils gently, and a solution of 2*5 grammes potassium permanganate in 497' 5 grammes water is gradually added, removing the beaker from the lamp each time for a few moments, to allow the precipitated peroxide to deposit, but heating it again to the boiling-point before adding another portion of permanganate. When the solution, after the precipitate has sub- sided, shows a distinctly reddish tint, all potassium iodide is decom- posed. The small excess of permanganate is estimated by sodium thiosulphate, and the remainder shows exactly 2 milligrammes of iodine for each c.c. of the permanganate solution used. The results are very accurate. BROMINE Detection of Bromine The best solvent for bromine just displaced by chlorine is carbon disulphide, a substance long used in France for detecting iodine. M. Fresenius, who has verified this fact with his usual care, insists on the necessity of avoiding excess of chlorine, and of employing carbon disulphide free from sulphurous and sulphuric acid. His preference for carbon disulphide over ether and chloroform is founded on a series of direct experiments with standard solutions con- taining various proportions of bromides. Solutions containing only -siRnnr f bromine in the state of potassium bromide, when treated with the requisite quantity of chlorine, do not communicate the least colour to ether or chloroform, while carbon disulphide acquires a decided yellow tint. Moreover, being heavier than water, it sinks to the bottom of the liquid with the bromine it has dissolved, and there remains. If the bromide is accompanied by an iodide, the iodine must be previously eliminated by adding a little hyponitric acid and a drop of carbon disulphide, which takes away the displaced iodine. After this the separation of the bromine may be proceeded with. Detection of Bromides in Potassium Iodide Dr. E. van Melckebeke finds that if to a saturated solution of potassium bromide a small quantity of pure potassium iodide is added ESTIMATION OF BROMINE AND IODINE 545 it will completely dissolve, but if the iodide is contaminated with potas- sium bromide this impurity will remain undissolved ; 100 parts of water (distilled), at 16, dissolves 140-1 parts of potassium iodide, and the same quantity of water, at the same temperature, dissolves 63*39 of potassium bromide : 100 parts of water saturated with bromide dis- solve only 13-15 parts of potassium iodide, and if more of that salt be added bromide is precipitated. As the solution of the salts in water causes a very sensible lowering of temperature, for testing, the author recommends to dissolve pure potassium bromide in warm water, to let this solution cool, and decant from the crystalline deposit. To 10 c.c. of this solution 10 drops of water are added in a test-tube, and after- wards in small quantities, and, constantly shaking, 1 gramme of the suspected iodide in coarse powder ; if free from bromide it will dissolve almost instantly, while if bromide is present it will remain undis- solved. Solution of Bromine as a Reagent M. L. de Koninck has for three years successfully used the solution of bromine in a 10 per cent, solution of potassium bromide. The author recommends it for the precipitation of manganese from an acetic solution, for the conversion of arsenious into arsenic acid, and for the detection of nickel in presence of cobalt in a potassium cyanide solution. Detection of Chlorine, Iodine, and Bromine in Organic Matter C. Neubauer introduces a little copper oxide into the loop of a platinum wire, and heats till it adheres. It is then dipped into the substance, or a little of the latter if dry is sprinkled upon it. The loop is then brought into the flame of a gas-burner moderately opened, near the lower and inner margin of the flame. The carbon burns first, and the flame becomes luminous, followed by the characteristic blue or green colour. Estimation of Bromine and Iodine in the Presence of Chlorine (A) This process is of special use for the assay of mother-liquors from saltpetre and kelp. A measured quantity of the liquor is intro- duced into a long tube with 20 alkalimeter measures of carbon disul- phide ; and nitrous sulphuric acid (prepared by passing nitrous acid through sulphuric acid) is added, drop by drop, till iodine ceases to be liberated. The tube is inverted several times after the addition of each drop of acid, in order that the iodine may at once be dissolved by the carbon disulphide, to which it gives a violet colour, varying in intensity with the amount of iodine in solution. The quantity of the iodine is estimated by comparing the degree of the colour with that N N 546 SELECT METHODS IN CHEMICAL ANALYSIS which results when a standard solution of potassium iodide is used in the same way. The delicacy of the reaction is such that O01 gramme will communicate a distinct rose tint to the carbon disulphide. When the amount of iodine exceeds 0'2 gramme of iodine in the quantity operated on, a difficulty occurs, as the violet colour becomes so deep that the various shades cannot be distinguished with accuracy. When all the iodine is separated by the carbon disulphide, the solution con- taining the bromine is introduced into another tube, and the bromine is liberated by chlorine water in the usual way, and taken up by a fresh quantity of carbon disulphide. In this case, an orange colour is the result, and the amount of bromine may be estimated by comparing the colour with that resulting when a solution of potassium bromide is used of known strength. (J3) Colour tests being always liable to much uncertainty in their indications if any great accuracy is desired, the following process may be found preferable. It is devised by Mr. Tatlock, and is based upon the wide difference between the equivalents of iodine, bromine, and chlorine. The mode of procedure depends upon the displacement of iodine by bromine, and of iodine and bromine by chlorine. The solution containing the iodide, bromide, and chloride, prefer- ably in combination with an alkali metal, is divided into 3 equal por- tions, or, at any rate, 3 equal portions of it are drawn off. To the one, solution of silver nitrate is added in excess, to precipitate the whole of the iodine, bromine, and chlorine. The liquid is then feebly acidified with pure nitric acid, warmed, and agitated till the precipitate settles. This is collected on a small weighed filter, washed with hot water, dried as far as possible at 100 C., removed from the filter, dried perfectly by heating to incipient fusion, and weighed, the weight of the small portion adhering to the filter being added, and the weight of the whole noted as Agl + AgBr + AgCl. Another portion of the solution is transferred to a small basin, and a quantity of pure bromine water added. The mixture is then care- fully evaporated on an open water-bath, more bromine water being- added from time to time, till the escaping vapours no longer turn starch -paper blue on a fresh addition showing that all the liberated iodine has escaped. To ensure excess, a little more bromine water is added, and the solution evaporated to complete dryness. The dry residue is then drenched with water, and the result heated till again dry ; this operation is repeated two or three times, to ensure the com- plete expulsion of any hydrobromic acid that may have been present in the bromine water. The residue, which now consists solely of alkaline bromide and chloride, is dissolved in water, silver nitrate added in excess, the solution acidified, and the precipitate collected and weighed in the usual way. It is noted as AgBr + AgBr + AgCl. ESTIMATION OF BKOMINE AND IODINE 547 The last portion of the solution is brought into a small basin, and a quantity of strong chlorine water added, to effect the liberation of the iodine and bromine. The mixture is then evaporated till all colour is gone, and some more chlorine water added. If the solution remains colourless, the whole of the iodine and bromine has been expelled, and the alkali metal will exist entirely as chloride. The solution is then brought completely to dryness, after which it is evaporated with a few drops of water two or three times, to expel any hydrochloric or hydro- bromic acid. The dry residue is dissolved in water, the solution acidi- fied with pure nitric acid, silver nitrate added in excess as before, and the silver chloride collected as usual. Its weight is noted as AgCl + AgCl + AgCl. It is obvious that we have now data from which we can calculate the amounts of iodine, bromine, and chlorine present ; for, as the equivalent of bromine is less than that of iodine, in the proportion of 80 to 127, the second precipitate, in which the iodine is replaced by "bromine, must weigh proportionately less than the first ; and, as the equivalent of chlorine is less than, that of either iodine or bromine, in the ratio of 35-5 to 127 in the one case, and to 80 in the other, the last precipitate must weigh still less than the second, and we can thus, from the observed differences, deduce the exact quantities of the three elements present. Example : 1. Agl + AgBr + AgCl weighed 15-57 2. AgBr + AgBr + AgCl 14-69 3. AgCl + AgCl + AgCl 12-20 Then j-j- Observed difference. 14-09 = 0-88 Loss for Observed 1 equiv. I. loss. 1 equiv. I. I present. 47 I 0-88 :: 127 : 2-378 I. III. Observed difference. 15-57 - 12-20 = 3-37 But, as a portion of this loss is caused by the replacement of iodine by chlorine, namely Equiv. of I. Loss in replacing i found . Loss accounted 1 equiv. I by Cl. for by I present. 127 : 91-5^ :: 2-378 : 1-713 Observed Loss accounted Difference loss. for by I present. for Br. 3-37 1-713 = 1-657 Loss for Observed loss on 1 equiv. Br. account of Br. 1 equiv. Br. Br found. 44-5 : 1-657 :: 80 : 2-978 N N 2 548 SELECT METHODS IN CHEMICAL ANALYSIS Then, as the proportion of iodine and bromine are already known, it will be an easy matter to calculate them to iodide and silver bromide, and deduct their weight from precipitate 1, calculating the remainder (silver chloride) to chlorine, thus : I. Agl. I present. AgT. 127 : 235 :: 2-378 : 4-400 And Br. AgBr. Br present. AgBr. 80 : 188 :: 2-978 : 6-998 Then Agl 4-400 AgBr . . . . . . .' 6-998 11-398 Then 15-57 11-398 = 4-172 Then AgCl. Cl. AgCl. 01. 143-5 : 35-5 :: 4-172 : 1-032 There were, therefore, present in the solution Iodine 2-378 Bromine 2-978 Chlorine 1-032 The bromine water may be easily obtained free from chlorine by distilling potassium bromide in solution with less potassium bichromate than is necessary to expel the whole of the bromine, using, of course, a little hydrochloric acid. (C) Application of the foregoing Method to the Analysis of Kelp. It is quite obvious that this process cannot be directly applied to sub- stances containing iodine, bromine, and chlorine, in very different proportions, and consequently it cannot be used for the estimation of these elements in kelp immediately. The following method of treat- ment will be found to equalise as nearly as necessary the proportions of the three : 2,000 grammes of the kelp are digested in hot water, the solution allowed to settle, and the clear liquor filtered. The residue is boiled two or three times with water, the liquid being filtered in each case, and the residue finally brought on a filter and washed with boiling water. The filtrates and washings are neutralised as nearly as possible with hydrochloric acid, and chlorine gas passed into the solution till the latter becomes of a distinct orange colour, due to the liberation of iodine and bromine. The liquid is then shaken up with about J of its bulk of carbon disul- phide, which takes up the liberated iodine and bromine, and carries them in solution to the bottom of the vessel, provided the sp. gr. of the kelp solution be not higher than that of the carbon disulphide. ANALYSIS OF KELP 549 When this is not the case, the solution of kelp may be diluted till the carbon disulphide sinks. The bottom liquid, containing the iodine and bromine, is then drawn off by a fine syphon, and shaken up with an equal volume of water and some zinc filings. The solution is soon decolourised, on account of the formation of zinc iodide and zinc bromide, which pass into the water ; and we have thus an aqueous solution of the two latter salts above, and colourless carbon disulphide at the bottom. The latter is drawn off by a syphon, and restored to the kelp solution, to which some more chlorine water is added ; and, if a further quantity of iodine and bromine be liberated, the above operations are repeated till the liquor is quite exhausted. It only now remains to evaporate the solution of zinc salts, divide into 3 equal portions, and determine iodine, bromine, and chlorine, as before described. Detection of Bromides in the Presence of Chlorides When gold chloride is added to a faintly acid solution of an alkaline bromide, a colouration is produced ranging from dark orange red to light straw colour according to the strength of the solution. Iodides must not be present ; chlorides, however, do not interfere. The best mode of proceeding is as follows : Remove the iodides, if present, by means of palladium, and after getting rid of excess of palladium by sulphuretted hydrogen, concentrate the solution, to about 25 c.c. Select two test-tubes of the same size and shape and colour of glass ; into one pour the solution suspected to contain bromine, and into the other pour pure water containing a trace of potassium chloride. Add to each tube one drop of hydrochloric acid, and one drop of gold chlo- ride solution. On now comparing the two tubes, particularly in the direction of their length, a yellow colour will be observed in the tube containing the bromide, which will be rendered very manifest by comparison with the other tube. The mixed chloride and bromide should be brought to the state of alkaline salts if necessary, by precipitating with silver nitrate, tho- roughly washing and fusing with potassium carbonate. If sodium carbonate is used for this purpose the subsequent reaction with the gold test is not so decided. Detection of Chloride in Potassium Bromide (A) The bromide to be examined is first tested for iodine. For this purpose a small quantity of the salt is dissolved in water in a test- tube, and an equal volume of carbon disulphide added. Upon the addition of a few drops of bromine water, the carbon disulphide becomes coloured violet, under the influence of iodine, if this be present. When the test shows the presence of iodine, it is necessary 550 SELECT METHODS IN CHEMICAL ANALYSIS to remove the whole of this element from the sample. This is effected by dissolving about 10 grammes of the salt in distilled water, adding bromine water until violet vapours are no longer visible upon boiling, and then testing for iodine in the manner first described. Afterwards the solution is evaporated to dryness to remove the excess of bromine,, and thus is obtained a potassium bromide free from iodide, but which may contain chloride. The remainder of the process depends upon the fact that a given weight of potassium chloride requires, for complete precipitation, a much greater amount of a standard solution of silver nitrate than the same weight of potassium bromide. While the bromide for the com- plete precipitation of 1 gramme requires 1*428 gramme of silver nitrate, 1 gramme of the chloride requires 2*278 grammes. A standard solu- tion of silver nitrate is first prepared by dissolving 10 grammes of the pure salt in a litre of water, each ^ c.c. corresponding to 1 milli- - gramme of silver nitrate ; 1 gramme of the bromide to be examined, freed as above from iodine, is dissolved in 100 c.c. of distilled water ; 10 c.c. of this solution, representing 0*1 gramme of potassium bromide, would require, if pure, 14*2 c.c. of the silver solution ; potassium chloride would require 22*7 c.c. (B) M. Baudrimont has proposed a method of making the final re- action more delicate, by adding a few drops of solution of potassium chromate to the bromide examined ; the silver nitrate added at first combines with the whole of the bromine and chlorine in preference, and the complete precipitation is marked by the production of the red precipitate of silver chromate. It is obvious that the bromide con- tains more or less chloride, according as the number of burette divisions (divided into T V c.c.) of the silver salt required exceeds 142. With a salt containing T L of its weight of potassium chloride 151 divisions are required, and with a mixture of equal weights of chloride and bromide, 185. The same method may be employed to recognise the degree of purity of several compounds. Operating as before that is to say, dis- solving 1 gramme of the material to be examined in 100 c.c. of distilled water, and taking 10 c.c. of the solution the following numbers of T V c.c. divisions required will show the purity for at least a con- siderable number of salts : 102 for pure potassium iodide, 257 for potassium cyanide, 246 for dry potassium carbonate, 290 for sodium chloride, 119 for sodium carbonate + 10 equivalents of water, 47 for sodium phosphate + 24 equivalents of water, and 54 for sodium arseniate + 14 equivalents of water. Detection of Iodine in Potassium Bromide (A) When potassium bromide is suspected to be adulterated, or mixed with potassium iodide, place a few grains of the salt in question on paper previously impregnated with starch-paste, moisten it, and admit ESTIMATION OF CHLORINE 551 a small quantity of chlorine gas, whereby the iodine is set free and the paper coloured blue. (B) A better test is the use of bromine water added to the salt after it has been placed in benzol ; if the latter becomes red-coloured, iodine is present. CHLORINE Estimation of Chlorine with, the aid of Gooch's Method of Filtration (-4) Mr. David Lindo remarks that it is generally considered that chlorine can be estimated with great exactness by the gravimetric method. Silver chloride being slightly soluble in water, especially in hot water, a small minus error may occur if the latter is employed to wash with, but this can be prevented by adding a little silver nitrate to the water, as recommended by J. P. Cooke. 1 On the other hand, the precipitate retains occluded matters with great force. Error from not completely removing these often more than compensates for slight loss occasioned by the use of hot water alone, or merely acidulated with nitric acid, or by the manipulations necessary when paper niters are employed. According to Fresenius, 2 we can, with great care, always obtain by this method 99-9 to lOO'l for 100 parts of chlorine taken. It is presumed Fresenius means when using paper niters, in which case the time required to make an estimate is generally six hours. The limits of error here laid down are often reached when paper niters are employed, and no silver nitrate added to the wash water. Though sufficiently near for most purposes, greater accuracy in chlorine estimates may sometimes be desired. By adopting Gooch's method of nitration and Cooke's suggestion, with a few other simple precautions, a much higher degree of accuracy can be attained with less manipulation and expenditure of time than by the usual method. Method : Weigh the solution in a light glass stoppered bottle, and turn it into a deep porcelain capsule, about 4^ ounces capacity, pro- vided with a well-formed lip and handle. Einse the bottle with 25 c.c. distilled water. Add solution of silver nitrate in about the proportion of 25 c.c. to 0-5 gramme potassium chloride, and 2 c.c. pure nitrie acid, sp. gr. 1-2. Heat to boiling-point, and keep at this temperature for some minutes without allowing violent ebullition, and with con- stant stirring, until the precipitate assumes the granular form. Allow to cool somewhat, and then pass the liquid through asbestos in a 1 Chemical News, vol. xliv. p. 235. 2 Quantitative Analysis, Seventh Edition, p. 170. 552 SELECT METHODS IN CHEMICAL ANALYSIS Gooch crucible. Wash the precipitate by decantation with 200 c.c. of very hot water, to which has been added 8 c.c. nitric acid and 2 c.c. dilute solution of silver nitrate containing 1 gramme of the salt in 100 c.c. of water. The washing by decantation is performed by adding the hot mixture in small quantities at a time, and stirring up the precipitate well with a thin glass rod after each addition. The pump is kept in action all the time, but to keep out dust during the washing, the cover is only removed from the crucible when the liquid is to be added. Put the capsule and precipitate aside, return the washings once through the asbestos so as to obtain them quite clear, remove them from the filter, and set aside to recover excess of silver. Rinse the receiver and complete the washing of the precipitate with about 200 c.c. of cold water. Half of this is used to wash by decantation, and the remainder to transfer the precipitate to the crucible with the aid of a trimmed feather. Finish washing in the crucible, the lumps of silver chloride being broken down with the glass rod. Remove the second filtrate from the receiver, and pass about 20 c.c. of alcohol at 98 per cent, through the precipitate. Dry at 140 to 150. Exposure for half an hour is found more than sufficient, at this temperature, -to dry the precipitate thoroughly. (B) In the volumetric estimation of chlorine, with a standard solu- tion of silver and potassium chromate as an indicator, Professor A. R. Leeds points out that the chromate employed is more or less contami- nated with alkaline chlorides. Hence it is necessary to estimate the number of tenths of a c.c. of the silver solution which correspond to the number of drops used of the particular chromate solution. Detection and Estimation of Chlorine in presence of Bromine and Iodine G. Vortmann has discovered a method by means of which even small quantities of chlorine along with the other halogens can be easily and quickly detected. It depends on the different behaviour of the chlorides, bromides, and iodides with manganese and lead peroxides in presence of acetic acid. Iodides are partially decomposed by the above-mentioned peroxides, even in neutral solutions, and if they are boiled with the addition of acetic acid the iodine is completely eliminated. Lead peroxide oxidises a part of the iodine to iodic acid, but with manganese peroxide no iodic acid is formed. In a neutral solution bromides are not decomposed either by manganese or lead peroxide. In an acetic solution the lead peroxide only acts ; bromine escapes ; but bromic acid is formed only if bromides are present in considerable quantities. Manganese peroxide has no action in the acetic solution, even on prolonged heating. Chlorides are not attacked by either of the peroxides in presence of ESTIMATION OF CHLORINE 553 acetic acid. In testing for chlorides in presence of bromides or iodides it is sufficient to boil the substance in an acetic solution with lead peroxide till the liquid on settling is colourless and has not the slightest odour of bromine or iodine. The bromine and a part of the iodine escape as such ; the remainder of the iodine remains as lead iodate along with the excess of the lead peroxide. On filtering and washing the precipitate, all the chlorine is found in the filtrate free from bromine and iodine. In this manner the chlorine may be esti- mated quantitatively. If the quantity of chlorine accompanying the iodine is considerable, manganese peroxide is preferable to lead per- oxide, as otherwise the liquid must be largely diluted with water to prevent lead chloride from depositing. In estimating large quantities of chlorine in presence of bromine, it is well to add along with the lead peroxide some potassium sulphate so that all the chlorine may be found in the filtrate combined with potassium. In order to expel the liberated bromine and iodine more rapidly a moderate current of air may be passed through the solution on the water-bath. Detection and Estimation of Iodine in presence of Bromine and Chlorine E. Donath remarks that whilst potassium bichromate occasions in solutions of potassium iodide no separation of iodine, this result is at once produced by chromic acid. An estimation of the liberated iodine is not possible on account of the action of the excess of chromic acid upon sodium thiosulphate. The iodide of starch is precipitated by solutions of chromic acid as an almost black precipitate. Hence, starch-paste cannot serve as an indicator. The iodine is therefore dis- tilled off, and is estimated in the distillate by means of sodium thiosul- phate. The alkaline bromides and chlorides are not decomposed by concentrated solutions of chromic acid at common temperatures, and the chlorides not even on boiling. Dilute solutions of chromic acid decompose the bromides only to a very small extent at the boiling heat, but the proportion increases with increasing concentration. The method is therefore suitable for accurate estimations of iodine in presence of chlorine, but not when it occurs along with bromine. The solution of chromic acid employed contains from 2J to 3 per cent., and is freed from traces of sulphuric acid by boiling with pure barium chromate. Estimation of Chlorine in Bleaching Powder (A) The commercial estimation of bleaching powder only extends to the estimation of the hypochlorite contained therein ; the result being, however, calculated as so much per cent, of ' available chlorine.' Of the numerous methods proposed for the estimation of the hypo- chlorite, the one usually employed in the trade is that depending on 554 SELECT METHODS IN CHEMICAL ANALYSIS the amount of ferrous salt oxidised by a given weight of bleaching powder. It frequently happens, however, that instead of a perfectly pure ferrous salt (such as the ammonio- sulphate precipitated by alcohol), the ordinary iron protosulphate of the druggists is used, discoloured crystals being of course rejected. This substance is, how- ever, rarely pure, and hence errors are frequently introduced, less chlorine being required to peroxidise a given weight of impure than of pure substance. Again, some analysts neglect to add an acid to the ferrous solution used, and hence the precipitated ferric hydrate is liable to carry down perceptible quantities of ferrous hydrate, again making the apparent amount of chlorine required less than that really requisite. When acid is added, an error is liable to be introduced by the peroxidation of part of the iron by chlorine compounds derived from chlorate that may be present. Direct experiments have shown that acid ferrous solutions are perceptibly oxidised by the presence of chlorate in small quantities in the course of a very few minutes, even at the ordinary temperature, although the peroxidation due to the whole of the chlorate is not manifest until after standing sometime at 20 C., or till after heating to ebullition. Lastly, the equivalent of chlorine is frequently taken to be 36 instead of 35*46 (Stas). All these sources of error tend to make the percentage of chlorine found higher than that really present ; accordingly it frequently happens that analyses of the same sample by different analysts differ by 1, 2, or 3 per cent. of available chlorine. This error becomes of serious importance, it frequently happening that the analysts employed by the seller and purchaser differ in their reports, thus causing much annoyance, and possibly the rejection of the goods as not being of contract strength. (B) As regards the error introduced by the presence of chlorate in the sample analysed, Dr. C. E. A. Wright has made many careful experiments on the subject, which have yielded the following re- sults : 1. Acid ferrous solutions are peroxidised by addition of a chlorate, at a rate depending on the strength of the solutions, the amount of free acid, and the temperature, the reaction taking place completely after heating to ebullition for a minute, and almost as completely after standing for upwards of half an hour at 20 C., time being, however, required for any temperature short of ebullition. 2. Acid solutions of arsenious acid, where a large excess of free acid is present, are scarcely affected by chlorate at 20 C. until after stand- ing some hours ; the reaction ensues completely on heating to ebullition for a minute, and completely in a few minutes' heating on a water-bath. 3. Alkaline solutions of arsenious acid (containing sodium car- bonate and free carbonic acid) are wholly unaffected by chlorate, either cold or boiling, even after several hours. 4. Acid solutions of potassium iodide (free from iodate). Iodine ESTIMATION OF CHLORINE 555 begins to separate even at 20 C. in a very few moments on addition of very little chlorate, and after some time much separates. Heated to 100 on the water-bath, the whole of the chlorate becomes completely decomposed, after five minutes, in presence of sufficient free acid. 5. Alkaline solutions of potassium iodide are unaffected by chlorates even on long standing or long boiling. Where the hypochlorite contained in a sample of bleaching powder, which may also contain chlorate, is to be estimated, the only safe and convenient method is that of Penot, i.e. by the use of an alkaline solution of arsenious acid. When the chlorate likewise is to be esti- mated, it may be expeditiously done by heating the sample with a known quantity of the same arsenite solution, and addition of hydro- chloric acid ; from the difference between the quantities of arsenite peroxidised in the two instances the chlorate is readily known. Dr. Wright has found the bleaching powder of commerce to contain several per cents, of calcium chlorate, even when newly made ; in older samples the chlorate has been occasionally found to represent as much as 10 per cent, of available chlorine, or fully J- of the amount originally present ; thus indicating overheating either in the process of manufacture or subsequently. (C) 2 grammes of the bleaching powder to be tested are well mixed with water, and the liquid so obtained mixed with a solution of iron protochloride freshly made by dissolving 0*6 gramme of pure iron wire in pure hydrochloric acid. Pure hydrochloric acid in excess is next added, and the liquid boiled in a flask, after previous addition of a piece of rather thick, perfectly clean, and polished sheet copper, of a weight of about 4 grammes. The boiling is continued until the colour of the liquid, at first darkish, has become bright green ; the copper is then removed from the flask, washed with distilled water, dried, and weighed. A loss in the weight of copper of 63*4 parts (=2Cu) is equal to 85*5 parts of chlorine in the bleaching powder. This method is based on the fact that, under the conditions described, the chlorine of the bleaching powder first changes the iron protochloride into per- chloride, which in its turn is again reduced to protochloride by the metallic copper, whereby some of the latter becomes dissolved. Every 2 equivalents of copper dissolved in this way are equal to 1 equivalent of chlorine in the bleaching powder. Estimation of Chlorate in Bleaching Chlorides M. E. Dreyfus bases a process on the property of cupric oxide, in a strongly hydrochloric solution, of being reduced to cuprous oxide by the action of stannous chloride at a boil. The end of the operation is marked by the decolouration of the liquid, which from yellow becomes colourless. For the process are required : 1. A solution of copper made by dissolving copper sulphate in 556 SELECT METHODS IN CHEMICAL ANALYSIS distilled water, so as to make up a litre, of which 10 c.c. represent about O'l gramme of metallic copper. 2. An acid solution of stannous chloride made by dissolving 15 grammes of this body in 200 c.c. of hydrochloric acid, and making up to a litre with distilled water. 3. A solution of potassium chlorate. 5-917 grammes of this salt are dissolved in a litre of distilled water. 10 c.c. of this liquid are exactly equal to 0'05 gramme calcium chlorate. To find the value of the cupric solution in comparison with that of potassium chlorate, 10 c.c. of the solution of copper (O'l gramme of copper) are poured into a flask or a conical colourless glass holding 150 c.c., and 50 c.c. of hydrochloric acid are then added. The mixture is heated to an incipient boil, and titrated with the standard liquid till decolourised. To the colourless liquid are added 5 c.c. of the potassium chlorate, which oxidise a corresponding quantity of cuprous chloride. This quantity is estimated again by titrating with stannous chloride. By this titration is found the relation between the cupric and the chlo- rate solutions. When this relation is once found it does not vary as long as the solution lasts. Preparation of the Sample of Chloride of Lime. Ten grammes are stirred up in 100 c.c. of water and saturated with ammo- nia, which is added by small quantities till there is a slight excess. It is then boiled till the odour disappears, and the liquid, with the preci- pitate, is poured into a flask marked at 500 c.c. The liquid is allowed to settle, depositing a precipitate which contains a little ferric oxide. The introduction of a little potash into the chloride after it has been saturated with ammonia much facilitates the settlement of the deposit. When the solution of the chloride is thus prepared we pro- ceed to titrate ; 10 c.c. of the cupric solution are raised to a boil with 50 c.c. of hydrochloric acid, and titrated to decolouration with the stannous chloride. Then 50 c.c. of the solution of settled chloride are added ; the mixture is boiled, and the copper which has been oxidised is titrated again. This method is applicable also to liquid chlorides. Detection of Arsenic in Hydrochloric Acid Take a thoroughly clean and dry test-tube, of not too narrow a bore ; put into it as much pure tin protochloride as can be placed on the point of a knife ; next add from 4 to 6 c.c. of the hydrochloric acid to be tested ; add, after this, gradually from 2 to 3 c.c. of pure con- centrated sulphuric acid, taking care to move the test-tube very gently. If a white precipitate ensues, the addition of a few drops of the hydro- chloric acid will be required to restore the liquid to perfect limpidity. If no arsenic is present, the liquid remains clear and colourless, even after standing for a time ; but if even a trace of arsenic is present, the liquid becomes at first yellowish, next brownish coloured, and at PURIFICATION OF HYDROCHLORIC ACID 557 last the metallic arsenic is deposited as a deep greyish-brown floccu- lent substance. Even with only ^1/0 iro- part of arsenious acid a colouration ensues. It is essential that when the sulphuric acid is added the liquid should become hot ; if, therefore, that acid is too dilute to cause heating, the test-tube and contents should be warmed over a spirit-flame. Purification of Hydrochloric Acid from Arsenic (A) 1. Preparation of Weak Acid. In the preparation of weak acid it is only necessary to boil the commercial arseniferous acid in a flat- bottomed dish until the acid is reduced to two-thirds its original volume. By allowing the hydrochloric gas to escape without collecting it, all the arsenic is taken with it in the form of terchloride, and the liquid remaining in the dish is no longer arseniferous ; 8 litres of commercial acid, treated in this way, furnish in less than three hours 2 litres of acid free from arsenic. 2. Preparation of Fuming Acid. Into a flat -bottomed vessel of 6 litres capacity, first pour 3 litres of the arseniferous acid, and add 0*3 gramme of powdered potassium chlorate (0*1 gramme per litre). Then adapt to the mouth of the flask a cork pierced with two holes, into one of which fit a straight and strong safety- tube ; and into the other a larger tube, of the diameter used in organic analyses, 0*5 metre long, and serving, so to speak, as a vertical elongation. This lengthened tube should be very little tapered at its low T er part ; fill it with about 100 grammes of red copper turnings well beaten down to within 0-07 metre of its upper orifice, and then fill almost up with asbestos or broken glass. Pass the greater part of this tube through the neck of the flask, so that as much as possible of the surface may be heated by the hydrochloric vapour. Then furnish the upper part of the elongated tube with a tube to carry the gas into a receiver. In traversing the column of copper the acid gas is deprived of its chlorine, and arrives in a pure state in the water destined to dissolve it. The mode of operation is very easily comprehended. By boiling the acid the transformation of the arsenic chloride into fixed arsenic acid is completed by the decomposition of potassium chlorate ; the excess of chlorine is taken with the moist hydrochloric gas into the copper, which most readily absorbs it, in preference to the acid, for which its affinity is much less. The copper chloride returns to the flask in the form of a solution, while the gaseous hydrochloric acid condenses in the distilled water. But as it is important that there should always be in the boiling acid a slight excess of chlorine, to prevent the reduction of the arsenic acid, a constant current of hydrochloric acid, to each litre of which 0-1 gramme of potassium chlorate has been added, should arrive through the safety- tube (which should not dip more than from 3 to 5 c.c. into the liquid) so as always to maintain 558 SELECT METHODS IN CHEMICAL ANALYSIS a small excess of chlorine, and at the same time to replenish the flask with hydrochloric acid to be purified. Generally the proportion of liquid acid thus added should be greater than is required for distillation, otherwise there might be an insufficiency of chlorine. When the experiment has been successfully performed the hydrochloric acid contains neither arsenic nor chlorine. By this apparatus pure hydrochloric acid may be constantly obtained without any sensible loss of acid, and the process may thus be applied commercially. (B) Into the crude acid to be purified pass a current of sulphuretted hydrogen until all the arsenic is precipitated. Separate the arsenic sulphide either by subsidence and decantation, or by filtering it through a funnel packed with asbestos. Remove the excess of sulphuretted hydrogen from the filtered liquid by the addition of a concentrated solution of iron sesquichloride, which destroys the sulphuretted hydro- gen, being reduced to protochloride. Finally, rectify the acid from fixed matters. See also the chapter on Arsenic, p. 405. Detection of Free Hydrochloric Acid in Solutions of Ferric Chloride Professor Nicola Rease finds that a solution of ordinary phenol treated with ferric chloride takes an amethyst colouration, turning to a brown. But if a drop of hydrochloric acid is added to the solution, the liquid either assumes no colouration at all or takes a greenish tint. He proceeds as follows : 1 gramme of the crystalline phenol of commerce is heated in 100 c.c. of pure water. He then pours 1 c.c. of the liquid ferric chloride into 50 c.c. of pure water. This solution being in a small test-beaker set on a sheet of white paper, the solu- tion of phenol is added drop by drop. The first drop, if the solution is slightly acid, produces a fugitive colouration, but if it is strongly acid no colour appears. On continuing to add the phenol solution the colour becomes permanent and gradually darkens. From the volume of the phenol solution consumed an approximate idea of the quantity of acid present may be formed. On the Detection of Hydrochloric Acid by Sulphuric Acid and Acid Potassium Chromate Mr. H. W. Wiley finds that this well-known test is more con- veniently applied in the following way than by distillation in a retort as usually directed. Two small beakers are taken, of different sizes, the smaller of which will fit into the larger, leaving a space of two or three centimetres between the two bottoms. The chloride and chro- mate are well rubbed together, and placed in the larger beaker, care being taken that none of the particles touch the sides of the vessel. A VALUATION OF POTASSIUM CHLORATE 559 few drops of oil of vitriol are added, and the smaller beaker then put in place. A lump of ice and if necessary a little salt, are then placed in the inner beaker. The chlorochromic acid is given off at a very gentle heat much below the boiling point, and is readily condensed on the cold surface of the beaker. If there is more than a mere trace of chloride, a watch-glass can be substituted for the smaller beaker. After the reaction has ceased the inner beaker is removed. With a stirring-rod a very little oil of vitriol is placed on a white porcelain surface, and near it a minute crystal of strychnine. The end of the stirring rod is then moistened with the chlorochromic acid and brought into contact with the sulphuric acid and strychnine. The colour test for strychnine is developed with even greater brilliancy than with potassium chromate : the merest trace of a chloride is most un- mistakably revealed by this test. If bromides are present, they do not at all interfere with the above reaction. Bromine itself with strych- nine and sulphuric acid gives no play of colours. Bromides, moreover, when present, can usually be detected at the same time with the chlorides. The bromine formed is readily condensed, and forms either distinct globules or imparts a deeper colour to the chlorochromic acid. With iodides the case is quite different. In many cases no trace of chlorochromic acid has been found, when both chlorides and iodides were present. At other times, the iodine which is set free seems to be dissolved in the chlorochromic acid. In such cases, on adding ammonia to the reddish -yellow distillate, the whole turns black, from the formation of nitrogen iodide. Valuation of Potassium Chlorate After having proved the absence of heavy metals, those of the alkaline earths, and sodium, a certain quantity of the chlorate to be valued is dissolved in water. Some dilute sulphuric acid is then added to the solution, and a piece of zinc is placed in the mixture. The nascent hydrogen immediately transforms the dilute chloric acid into hydrochloric acid. In about half an hour the undissolved zinc is with- drawn from the liquor, the sulphuric acid is precipitated by barium nitrate, and the zinc and excess of barium by means of sodium car- bonate. The hydrochloric acid in the filtered solution is then esti- mated volumetrically by a standard solution of silver nitrate. A convenient solution is made by dissolving 1'387 gramme of silver nitrate in a litre of water, each c.c. of which solution will correspond to 1 milligramme of potassium chlorate. If the chlorate contains chloride, this chlorine is first precipitated by silver nitrate, any excess of silver being removed from the filtered solution by sulphuretted hydrogen. The liquor filtered from the silver sulphide may then be treated with zinc and sulphuric acid, as described above. 560 SELECT METHODS IN CHEMICAL ANALYSIS FLUORINE Detection of Fluorine in Water Treat the solid residue of a large quantity of the water with an excess of concentrated sulphuric acid, and pass the gaseous products into slightly ainmoniacal water. If fluorine is present in the water, gelatinous silica is precipitated in the liquid, resulting from the decomposition of the silicon fluoride which was disengaged from the residue. Estimation of Fluorine (A) For estimating fluorine in combinations easily attacked by sul- phuric acid proceed as follows : Cover the platinum capsule in which the decomposition takes place with a funnel, resting with the capsule on a platinum basin, on which it is fastened with wet plaster ; ascer- tain the weight of the funnel and the composition of the glass of which it is made. Heat the whole until most of the sulphuric acid has been expelled ; then raise the funnel, wash it carefully, dry and weigh it ; the decrease in its weight is owing to a portion of the glass having been attacked ; and as its composition was first ascertained, the weight of silica which has been attacked may be calculated from the decrease in weight, and, consequently, the quantity of hydrofluoric acid which has been disengaged. This method has given very satisfactory results with triplite of Limoges, and with zivieselite, and other analogous phosphates of Schlaggenwald. With calcium fluoride and cryolite too little fluorine is found, because the decomposition of these minerals is complete only when the mixture is properly shaken, which is difficult with the apparatus described above. The same funnel may be used many times, and is even better after it has been corroded. If the substance to be analysed contains silica, the quantity must be ascertained and added to that of the glass attacked, to obtain the weight of fluorine. (J5) Place the substance to be analysed in a rather deep platinum crucible, and cover it with 3 or 4 times its weight of silica ; add a few drops of sulphuric acid, and heat gently for half an hour ; then gradually increase the heat until most of the sulphuric acid is expelled. Then treat the whole with hydrochloric acid, add some water, and leave it to deposit ; collect the deposit, calcine, and weigh it, and the loss of silica will indicate the amount of fluorine con- tained in the substance analysed (38 of fluorine correspond to 30 of silica). (C) For the estimation of fluorine, Professor A. Liversidge de- composes the fluoride by concentrated sulphuric acid in presence of silica, and passes the silicon fluoride formed into ammonia, the quantity ESTIMATION OF FLUORINE 561 of silica carried over being then estimated and the fluorine calculated therefrom. The powdered mineral is introduced into a platinum retort together with the needful quantity of sulphuric acid and finely- divided silica. It is heated first in the water-bath and then at 160 C., the gaseous silicon fluoride formed being decomposed by passing it through a solution of ammonia. The last traces of the gas are carried over by drawing a current of air through the apparatus. The ammonia solution is gently evaporated in a platinum dish till the gelatinous silica passes entirely into solution, and it can then be pre- cipitated as potassium silicofluoride by the addition of potassium chloride and alcohol. (D) Mr. Chapman gives the following processes for the estimation of fluorine, especially applicable to commercial phosphates. The method depends on the fact that aqjd ammonium acetate (i.e. ammonia more than neutralised by acetic acid) precipitates calcium fluoride, but not calcium phosphate, from solution in acids. 2-5 grammes are ignited in a platinum crucible for a short time (this ignition prevents ferric and aluminium phosphates from dissolving in dilute hydrochloric acid), transferred to a mortar, and ground up with repeated small quantities of 10 per cent, hydrochloric acid, filtered, and washed. The filtrate and washings are made up to 250 c.c. 100 c.c. of this are taken and added to the acid ammonium acetate, the calcium fluoride is precipitated, and calcium phosphate remains in solution. The calcium fluoride is filtered off, washed, dried, ignited, and weighed as usual. If the substance be not ignited, the calcium fluoride comes down mixed with ferric and aluminium phosphates, from which the amount of calcium fluoride can be obtained by subtracting the amount of ferric and aluminium phosphates. This second method is not so accurate, as, even without ignition, all the ferric and aluminium phosphates do not dissolve up. Volumetric Estimation of Fluorine Mr. S. L. Penfield has made the well-known reaction 3SiF 4 + 2H 2 0=2H 2 SiF 6 + Si0 2 the basis of a volumetric estimation of fluorine, estimating the quantity of hydrofluosilicic acid formed from a given weight of fluoride by means of a standard alkali solution. It is impossible to titrate the hydrofluosilicic acid directly, because as soon as an alkaline reaction is reached the silicofluoride is decom- posed and a further acid reaction is indicated, which change goes on slowly. But when barium chloride and an equal volume of alcohol are added to the solution, barium silicofluoride is precipitated from the solution, and an equivalent amount of hydrochloric acid is liberated, o o 562 SELECT METHODS IN CHEMICAL ANALYSIS which can be titrated ; by this means, using litmus as an indicator, very satisfactory results have been obtained, but the turbidity caused by the barium silicofluoride interferes with the change of colour of the litmus. It has been found that potassium chloride possesses some advantages over barium chloride. On adding potassium chloride and an equal volume of alcohol, potassium silicofluoride is precipitated from the solution, and an equivalent of hydrochloric acid is liberated, but the potassium silicofluoride is a very transparent precipitate, and does not interfere with the change of colour of the indicators. It is necessary that alcohol shall make up at least one-half the volume of the liquid to be titrated, so as to precipitate the potassium silicofluoride as completely as possible. The apparatus needed is very simple, and consists of a gasometer of 10 or more litres capacity, a few flasks of about 150 c.c. capacity, a few large plain U -tubes 18 centimetres long and 2J centimetres dia- meter, made without any narrowing in the bend, and a heavy iron plate supported properly, so that it may be heated with a lamp. The fluoride is weighed out accurately into one of the flasks ; unless it is a silicate, 10 grammes of powdered and ignited quartz are added, with 2 or 3 pieces of quartz about the size of kidney-beans. These last facilitate mixing up the powder when the flask is shaken. The con- tents of the flask are then drenched with from 30 to 40 c.c. of sulphuric acid which has been previously heated and allowed to cool. The flask is tightly closed with a doubly-perforated cork ; from the gasometer dry air is passed into the flask by means of a glass tube which reaches nearly to the bottom. The silicon fluoride mixed with air passes from the decomposing flask first through a small U-tube, made from ordinary glass tubing, 5 millimetres in diameter, and kept cool by being placed in a beaker of cold water, then into one of the large U -tubes intended for decomposing the silicon fluoride and absorbing the hydrofluosilicic acid. The U-tube contains a solution of potassium chloride mixed with an equal volume of alcohol ; the escaping gas is made to bubble through this, and to ensure complete decomposition a second smaller U-tube is attached to the first : the first tube absorbs nearly all the acid, the second contains only traces. The decomposing flask is supported on the iron plate ; by its side is placed a second flask containing sulphuric acid and a thermometer supported so that its bulb dips into the acid ; the lamp heating the plate is placed midway between the flasks, and the heat is regulated so that the temperature of the acid remains between 150 and 160 C. The decomposition is continued 2 hours in ordinary cases, and during that time a continuous current of air is forced through the apparatus, amounting to from 5 to 6 litres for the 2 hours, while the contents of the decomposing flask are frequently agitated by shaking. After the decomposition and aspiration are completed, the contents ESTIMATION OF FLUORINE 563 of the U -tubes are titrated. For this purpose they may be transferred to a beaker, the tubes being rinsed with alcohol and water, or better, the acid may be titrated directly in the U -tubes. In order that the alcohol may make up one-half the volume of the liquid after the titra-' tion is completed, add a few c.c. of alcohol before titrating, or where 15 or more c.c. are to be added use a standard alkali one-half of whose volume is alcohol. As the separated silicic acid sticks to the sides of the U-tube, it is necessary to have prepared a glass rod bent a little at one end to scrape off and break up this silica. A simple dry U -tube between the decomposing flask and absorbing tube is sufficient to condense any sulphuric acid that may go over from the heated acid. When the fluorine is to be estimated in a mineral containing chlorine, as in the case of an apatite, substitute for the empty U-tube one filled with fragments of pumice impregnated with perfectly anhy- drous copper sulphate. This will intercept any hydrochloric acid, and will also serve to condense any sulphuric acid vapour that may go over from the heated acid. The calculation is very simple. Each equiva- lent of sodium carbonate equals 1 equivalent of hydrofluosilicic acid or 6 of fluorine. The qualitative search for fluorine in substances free from silica is easily made, with small quantities of matter, in a platinum crucible furnished with a lid with a small circular hole pierced in the centre, above which a disc of glass is placed. For the detection and estimation of fluorine in apatite, see p. 47. o o 2 564 SELECT METHODS IN CHEMICAL ANALYSIS CHAPTEE XIII CARBON, BORON, SILICON CARBON Assay of Animal Charcoal THE points of greatest importance in an analysis of animal charcoal are the carbon, the carbonates, and the iron ; the decolouriser, the neutraliser, and the destroyer. Under certain circumstances sulphates may be included, and in the case of unused charcoal the salts soluble in water should also be carefully estimated. The amount of phosphates is comparatively unimportant. The following is the process recom- . mended by Dr. Wallace ; it was frequently verified during the progress of the author's work on Beet-root Sugar and the chemistry of sugar- refining. 1 Carbon. Five grammes of animal charcoal are dried at 220 F. in a hot-air bath or paraffin-bath ; the loss of weight gives the moisture, which, subtracted from the loss by calcination, furnishes the proportion of carbon. Calcium Carbonate. This can be quickly and accurately estimated by well-known processes. Iron. After some little practice the iron can be safely estimated by Penny's process, using a very dilute solution of bichromate. The iron is always in a state of protoxide, faint traces of peroxide excepted, owing to the reducing action of the carbon in the re -burning. Soluble Salts. Fifty grammes of animal black are weighed and thrown into a little stoppered flask containing about 50 c.c. of distilled water ; this is well shaken for a few minutes, and then filtered. Tbe insoluble residue is re-digested in a fresh quantity of water ; and this is repeated several times, so as to eliminate the whole of the soluble salts. The filtered liquid is evaporated over the sand-bath in a little porcelain capsule ; the dry residue is weighed, and its weight gives the proportion of soluble salts. These salts consist of alkaline chlo- rides, sulphates, and carbonates ; they also contain traces of calcium sulphate and sulphide. 1 The Manufacture of Beet- Boot Sugar in England and Ireland, by William Crookes. London : Longmans and Co., 1870. ASSAY OF ANIMAL CHAKCOAL 565 Estimation of the Decolourising Power of Animal Charcoal In these estimations the object is to carry out the operation in such a manner as to obtain, as nearly as possible, the same results on the small scale in the laboratory as in the manufacturing operations ; and it is because many little precautionary measures which tend towards the attainment of that equality are usually omitted in the laboratory that such conflicting and apparently inexplicable results are recorded. Mr. Arnot gives the following precautions to be observed so as to obtain trustworthy results : 1. It must be decided what the results are to express : whether the relative decolourative power of equal bulks or equal weights of the charcoals, irrespective of size and proportion of grain, of the chars uniformly freed from dust, say by a 50-mesh sieve ; or of equal weights of equal grains. 2. According as either of these alternatives is decided upon, the various samples must be thoroughly and intimately mixed, and, if necessary, brought to a uniform dryness and temperature. It is always safest to have them thoroughly dry, and at the temperature of the surrounding air. 3. The various samples are next to be put into glass tubes (tin may be used, but they preclude observations of a very important kind) provided with perforated false bottoms, covered with layers of cloth, and with taps capable of being accurately regulated. The tubes ought to be about 2 inches wide and 2 feet long, as nearly of the same diameter as possible. The best method of filling them is by passing the charcoal through a funnel, keeping the spout of the funnel moving constantly in a circular direction, so as to have the large and small grains equally diffused throughout. To allow the charcoal to run down either at one side, or, to a less degree, in the middle, is to cause to a certainty a separation of the larger grains from the smaller, and thus to create channels through which the liquor has too easy access. 4. See that no one tube is touched or shaken more than the others, after the charcoal has been put in. 5. Sufficient brown sugar liquor, of say 24 B., must be prepared, either by diluting raw filtered liquor from the sugar-house to that gravity, or by dissolving as much of an average quality of raw material as will make sufficient liquor for the whole experiment. In the case of preparing it on the small scale, albumen must be liberally used, and the liquor passed through paper filters coarse French paper answers best. The albumen should not be added till all the sugar has been dissolved, and the temperature at, say, 160 F. An equal quantity of the prepared liquor, as nearly 180 F. as possible, must now be poured uniformly upon the charcoal in each tube. The rapidity with which the liquor passes through the charcoal in 566 SELECT METHODS IN CHEMICAL ANALYSIS each case may be noted. Care must be taken to have the top of the charcoal always covered with liquor, and the taps below open. As soon as the liquor begins to drop at the taps they are closed. 6. The tubes being fully charged with liquor (there should be as much left on the top of the charcoal as will serve to force out the liquor in the charcoal), they are put into a cistern of water at 140 F., the water in which will rise to about 1 inch from the mouths of the tubes ; the time is noted, and the cisterns, which ought to be felted, are covered. 7. At the end of not less than 1 hour (longer than 1 hour is some- times advantageous, particularly if the raw liquor was very brown) the tubes are withdrawn, placed in their stands, and about 2 ounces of liquor run off each ; this may be rejected, as the portion between the false bottom and taps is often turbid, and in addition has not been in contact with the charcoal for a sufficient length of time. The remain- der of the liquor, i.e. so much as has actually been in contact with the charcoal, may now be run off in three successive quantities for comparison. The results may be compared with any set of standard colours, and recorded accordingly. 8. If these results are not sufficiently conclusive, a further quantity of raw liquor may be run on each tube, and the whole transferred as before to the water-bath, which, if felted, will still be hot enough. The second quantity of liquor will be run off with the same precau- tions as the first, and the results will show the isl&iivQ persistency of the charcoal under trial. If the taps are large the liquor will be likely to run off too rapidly, and, in that case, they had better be partially and uniformly closed. If it is found that the liquor runs through one sample particularly slowly, and through another particularly fast, it is quite admissible to assist the one by suction, and to check the other by closing the taps ; but this should not be done unless in extreme cases, and the fact of having so assisted or retarded the process should always be noted. It is scarcely necessary to mention the several points wherein the foregoing differs from the course usually pursued in testing charcoal, and yet it may be useful briefly to indicate some of these. Too little care is usually bestowed upon the selection and preparation of the samples. The tubes are, as a rule, too small : the charcoal cannot be run so uniformly into small tubes as large ones. The samples once charged with liquor are not usually kept warm : it is essential that they should be. Some charcoals act powerfully at low temperatures, while others require a considerable amount of heat to bring out their maximum decolourative power. Care must, however, be taken that the temperature employed does not exceed that attained on the large scale in the refining process. One sample of charcoal, known to be of very inferior decolourative power on the working scale, persistently gave results, by the usual method of testing in the laboratory, equal to the CAKBONIC ACID IN ANIMAL CHARCOAL 567 very finest charcoal obtainable, but when kept at an elevated tem- perature, along with the finer samples, in the manner indicated above, its inferiority was at once manifest. The facts in this case were that the inferior charcoal readily yielded all its decolourative power at the low temperature, while the finer samples required the influence of heat to call their whole power into action. Volumetric Estimation of Carbonic Acid in Animal Char- coal. Dr. Scheibler has devised a very perfect instrument which is adapted for the estimation of the quantity of carbonic acid contained in native carbonates, as well as in artificial products, and has been specially contrived for the purpose of readily estimating the quantity of carbonic acid contained in animal charcoal. The principle upon which the apparatus is founded is simply this that the quantity of carbonic acid contained in calcium carbonate can, according to well- known stoechiometrical rules, be used as a measure of the quantity of that salt itself; and instead of estimating, as has been usually the case, the quantity of carbonic acid by weight, this apparatus admits of its estimation by volume. It is by this means possible to perform, in a few minutes, operations which would otherwise take hours to accomplish. The analytical results obtained by means of this apparatus are very correct, provided care be taken to use the needful precautions. The apparatus is shown in the annexed woodcut, and consists of the following parts : The glass vessel A, serving for the decompo- sition of the material to be tested for carbonic acid, which, for that purpose, is treated with dilute hydrochloric acid ; this acid is contained, previous to the beginning of 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 indiarubber tube r, by means of which communication is opened with a three-necked tubulated bottle, B. The central neck of this bottle contains a glass tube firmly fixed, which is in communication, on the one hand, with A, by means of the flexible indiarubber tube already alluded to, and on the other hand, inside of B, with a very thin indiarubber bladder (similar, as regards thinness, to the very light and well-known inflated indiarubber balloons sold as toys). The neck, q, of the vessel B is shut off during the experiment by means of a piece of indiarubber tubing, kept firmly closed with a spring clamp ; the only use of this neck 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 communi- cation 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 568 SELECT METHODS IN CHEMICAL ANALYSIS 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 D, this can readily be done by blowing with the mouth into v, and opening the clamp at p. The following apparatus and reagents are also necessary : A small FIG. 24. and very accurate weight for weighing off the substances to be tested ; a thermometer ; hydrochloric acid ; a solution of ammonium carbonate ; and several small porcelain basins. The main portion of the apparatus above described, with the ex- ception, however, of the vessel A, is properly fixed by means of brass fittings to a wooden board, as represented in the woodcut. The filling CARBONIC ACID IN ANIMAL CHARCOAL 569 of the apparatus with water is very readily effected by pouring it through a suitable funnel placed in the open end of 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 should be used for this purpose, as the filling only requires to be done once, the water always remaining in B as long as the apparatus is intended to be kept ready for use. When it is required to fill the tubes c and D with water, so as to reach the zero of the scale of the instrument, remove the glass stopper from A ; the spring clamp at p is next unfastened, the 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 above the zero of the scale at c, and especial care should be taken against forcing so much of the liquid up that it would run over into the tube u, and thence find its way to B, as in this case 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 the water is allowed to run off to E in such quantity as may be required to adjust the level of the liquid 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 B, where it causes the compres- sion of the very thin indiarubber ball placed within B. If it should happen that this indiarubber ball has not become sufficiently com- pressed 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 indiarubber bladder placed within B is readily performed. This operation is also required only once, because during the subsequent experiments the indiarubber bladder K is emptied spontaneously. It may happen, however, that while the filling of the tubes D and c with water is being proceeded with, the indiarubber 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 artificial heat and sudden changes of temperature ; the instrument is best placed near a north window, so as to afford sufficient light for reading off the height of the water in the tubes. Hydrochloric Acid. The acid required for the decomposition of the animal charcoal is poured into the vessel s for use during experi- ments. This acid need not be pure ; the crude acid of commerce 570 SELECT METHODS IN CHEMICAL ANALYSIS answers the purpose, provided it be diluted to a specific gravity of 1'12 at 17 C. For practical purposes it is sufficient to mix 2 parts by bulk of water with 1 part by bulk of commercial hydrochloric acid. Ammonium Carbonate. In order to prepare the solution of this salt of the necessary, strength, 1 part by weight of the ordinary ammonium carbonate of commerce is dissolved in 4 parts of water, and to this 1 part of liquid ammonia is added. The salt is first coarsely pulver- ised and immediately after placed in a bottle provided with a well- fitting glass stopper ; the mixture of water and ammonia is next poured over the salt, and the solution of the salt promoted by frequently shaking the bottle. This solution of ammonium carbonate is used for the purpose of converting into calcium carbonate any caustic lime which might be present in the materials to be submitted to analysis. Mode of Operating. (A) It is of the greatest importance that a good average sample, really representing the entire bulk of animal charcoal, be taken for investigation. This can be readily obtained by taking small samples, say a few ounces, from the filter (in sugar works) or from a cask, at various depths of the vessels containing the material, or, better still, if there be room, the charcoal should be placed in a heap on a large sheet of stout canvas, and well mixed together, and samples taken from various parts of the heap. These, if wet (as will be the case with charcoal just removed from the filters), should be dried by suitable means, and afterwards the whole sample should be coarsely ground and thoroughly mixed, and a portion taken for the purpose of being ground up to a very finely-divided powder, to serve the purpose of weighing a sample from. It is essential that the char- coal should be ground to a very fine powder, because this greatly promotes the decomposition by the acid. There is supplied with the apparatus a metallic weight to serve as normal weight. This weight is placed in one of the pans of the balance (any balance, provided it be sensitive to from ^ to T V of a grain, will answer the purpose) ; in the same pan a small porcelain basin is placed, and equilibrium is restored by means of small lead shot. As soon as the equilibrium is restored the normal or standard weight is removed from the pan of the balance, and there is placed in the small porcelain capsule remaining in the pan as much of the sample of bone-black to be tested as is required to restore the equilibrium. When several ex- periments have to be made consecutively, it is better to arrange before- hand the joint tare weight of the normal weight and of a watch-glass of suitable size, and to weigh off upon the latter the several samples. (B) Dr. Scheibler recommends the transference of these weighed quantities to a porcelain capsule, because, according to his plan, the samples, after having been weighed, have to be thoroughly moistened with the solution of ammonium carbonate already referred to, in order to convert any caustic lime which might happen to be present in the CARBONIC ACID IN ANIMAL CHARCOAL 571 material into calcium carbonate ; but it is a decided improvement jbo moisten gently with the solution of ammonium carbonate a sufficient quantity of the sample to be tested previous to weighing, to dry it, and to employ at last, for a few moments, a stronger heat short of redness (an air or fusible metal bath, heated to 240 C.), so as to obviate the chance of either an excess of ammonium carbonate or of water being present, while, at the same time, the decomposition of the calcium carbonate is guarded against. After the samples are quite cold, they are to be transferred to the flask or bottle A. Recent researches have shown that animal charcoal which has been once used for filtering purposes in sugar works no longer contains caustic lime, and the treat- ment with ammonium carbonate can therefore be dispensed with in that case, and need only be employed with samples freshly made. (C) The experiment for the estimation of the carbonic acid is carried out in the following manner : First, the water in the tube c is made to stand exactly at the zero (0) of the scale ; next, the weighed sample of the bone-black to be tested is transferred, with great care and with- out loss, to the bottom of the bottle A, which should be perfectly dry inside and quite clean. This having been done, the gutta-percha vessel s, which should also be previously well cleaned, is filled with the hydro- chloric acid above referred to, to within from ^ to f inch from the top, care being taken not to drop any hydrochloric acid on the outside of the vessel ; the gutta-percha vessel is next placed within the bottle A in a slanting direction, as shown in the woodcut ; after this the glass stopper is replaced at A, care being taken to slightly grease it and the inside of the neck of A, so as to secure a better air-tight fitting. The closing of A will (if all parts of the apparatus are properly tight) have the effect of slightly lowering the level of the water in c below the zero of the scale, while the water will rise just as much higher in D ; by loosening, for a moment, the spring clamp at q, the normal height is properly restored. The operator should very carefully guard against handling or touching A after it has been once closed, because, by so doing, the warmth cf his hand will cause the expansion of the air in A, and thereby affect the proper action of the apparatus. In order to cause the hydrochloric acid contained in the gutta-percha vessel placed inside A to run on to the animal charcoal, placed on the bottom of A, as described, the flask or bottle A is held by the neck, as shown in the woodcut. As soon as the acid comes into contact with the animal charcoal, the evolution of carbonic acid begins, and simultaneously the expansion of the very thin indiarubber bladder K, while the water in the tube c sinks, and correspondingly rises in D. While the bottle A is held in the right hand, as already indicated, and gently moved about so as to promote as much as possible the contact between the acid and the charcoal, the left hand is employed to gently open the spring clamp p, in such a manner as to run off towards E just as much water as is required to keep the level in the tubes c and D at the same height. 572 SELECT METHODS IN CHEMICAL ANALYSIS Both these manipulations should be continued as long as any sinking of the level of the water in c is perceptible : in other words, as long as any carbonic acid is given off. After this has quite ceased, and no change is perceptible, or any motion of the water in the tubes just alluded to has taken place, the operation may be considered at an end, care being taken, however, to keep the levels in the tubes c and D at precisely the same height. This having been done, the next step is to read off the height of the water at the scale on c, and simultaneously the thermometer. Correction of the Volume Bead off. The Table on the following page contains in the first column the figures 1 to 25, which correspond with the numbers on the scale fixed to c ; the next 19 vertical columns con- tain the figures indicating the percentage of calcium carbonate sought at temperatures from 12 to 30 C. If, for instance, the experiment has been made at a temperature of 16, and the reading of the scale at c corresponded to 9, this indicates a quantity of calcium carbonate of 9*03 per cent. Since, however, every degree at c is divided into 10 parts, it is quite possible to read off tenths of a degree, and the corre- sponding quantity of calcium carbonate is also found by the aid of the table referred to, under the first 9 figures of the column, by simply altering from the right to the left hand the decimal point ; for instance, we have found at 14 C. 7*8 at the scale c ; we therefore have for 7 units 7*09 per cent., and for T % 0*81 (because 8=8'11), making together, for 7*8, 7*9 per cent, calcium carbonate. Illustrative Examples. 9'4 read off at c, at a temperature of 19 =9*289 per cent, of calcium carbonate. 14*9 read off at c, at a temperature of 13 = 15*056 per cent, of calcium carbonate. 12-3 read off at c, at a temperature of 24=11'799 per cent, of calcium carbonate. 11-7 read off at c, at a temperature of 16 =11*702 per cent, of calcium carbonate. It is, however, for all practical purposes, quite sufficient to make round numbers of the figures following the decimal point, and instead of 9*289 to read 9*3 ; for 15*056 to read 15*06 ; for 11*799 to read 11*8 ; and for 11*702 to read 11*7. The calcimeter is invaluable in cases where the frequent estimation of carbonic acid is required. With a little practice, 12 or 14 estima- tions may easily be made in an hour ; and these, if upon the same finely-powdered sample, will, with ordinary care, be found to agree almost absolutely. The saving of time by this process over the most expeditious of the ordinary gravimetric methods will be found to be very great. Starting, in each case, with the sample in powder, the difference in time is such as easily to repay the first cost of the instru- ment by a few hours' work. As the instrument is supplied with a CAHBONIC ACID IN ANIMAL CHARCOAL 573 COfMrHCOlOrHCOCiCO^lOOt^OlOrHlMCOlOCOC^COOrHOl ; l>I>l>^;pCp>p^^epI>0OTjb co t- db ci o rH CN oq -*- *---- 574 SELECT METHODS IN CHEMICAL ANALYSIS normal weight and tables of calculated results, no time is lost in after- calculations. The volume of carbonic acid and the temperature indi- cated by the instrument are referred to the tables, where the percent- age quantity of carbonic acid or calcium carbonate is at once found. One great advantage of such an expeditious method as this is that there is no temptation to be satisfied with first results, as a few minutes suffice to repeat the process. Volumetric Estimation of Carbonic Acid by a Modification of Scheibler's Apparatus (A) Mr. E. Nicholson recommends the apparatus figured on the following page. For the second graduated tube of Scheibler's apparatus, with its outlet pipe, reservoir bottle, and blowing-tube, Mr. E . Nichol- son substitutes a reservoir which can be lowered as the pressure of gas forces down the column of water in the graduated tube. He dispenses with the diaphragm formed by the indiarubber bladder, relying on the impossibility of diffusion taking place beyond the double bulb during the short time which the operation requires. If the graduated tube be of 130 c.c., a quantity of gas equivalent to 0'5 gramme of calcium car- bonate will not be beyond its capacity, at least in most European laboratories. The reservoir should be able to contain within its per- fectly cylindrical part somewhat more than the quantity of water for which the tube is graduated. To set the apparatus in working order, raise the reservoir (by means of the cord and counterpoise) until its lower end is 1^ inch, or 1 inch below the zero of the graduated tube, and then pour in distilled water until the column rises to that point. Note the lower level of the water in the reservoir, consequent on the smaller calibre of the graduated tube : this difference for capillarity should be maintained at all readings of the column of water. When the column is under pressure, as at the end of an operation, the difference can, if necessary, be accurately adjusted by means of a scale corresponding to that of the graduated tube, and marked on the frame, or by a sliding pointer ; but this is really unnecessary, for the allowance can be made with sufficient accuracy by the eye. Considering that the height of the column is only affected by less than one-tenth of the amount of error in the adjustment of the reservoir-level, the possible error in an ad- justment by the eye is trivial. An error of a whole centimetre of height in the adjustment would affect the reading to the extent of 0-06 c.c. only. Even with a reservoir of varying calibre, the greatest possible error arising from defective adjustment for capillarity is well within O'l c.c. Mode of Operating. -Into the flask or bottle used for the reac- tion, a weighed quantity of powdered carbonate is introduced, together with a glass or gutta-percha tube containing either 5 c.c. or 10 c.c. of VOLUMETRIC ESTIMATION OF CARBONIC ACID 575 diluted hydrochloric acid. The flask being connected with the appa- ratus, adjust the level of the water to zero, and then close the air-cock at the top of the bulb-tube. Holding the flask by the neck with the right hand, allow the acid to flow on to the carbonate while the left hand, on the cord of the counterpoise, lowers the reservoir as the gas forces the water down in the graduated tube. Agitate the flask as the action slackens, and when the column remains fixed, read off the height, the level of the reservoir being adjusted for capillarity. The operation being finished, disconnect the flask ; raise the reservoir in order to drive carbonic dioxide out of the apparatus, and then open the air-cock ; it may be left open until the next operation. In the apparatus shown in Fig. 25 there is no air-cock, and the level of the water-column, being depressed by the act of closing the flask, cannot be brought to zero ; the reservoir must therefore be lowered to the proper level, the height of the column read off, and the number deducted from that found after the operation. The sources of pos- sible error in estimations by this apparatus are : 1. From expansion of the gas disengaged in consequence of the heat produced during reaction. 2. From the absorp- FlG . 2 5. FIG. 2G. tion, or rather retention, of gas by the acid used for decomposition of the carbonate. The first appears to be quite unimportant, except when the sub- stance operated on contains much free base, as in the case of a partially carbonated lime ; when operating on such a substance, the flask should be immersed in air-warm water during the reaction. The second error can be ascertained and allowed for ; Dr. Scheibler sets it down at 0-8 c.c. for 10 c.c. of acid, sp. gr. T12. It is better for each operator to ascertain the error for the acid he uses : let him make two sets of experiments with the same quantities of calcium carbonate, decomposing this in one set by 5 c.c., in the other by 10 c.c. of acid. 576 SELECT METHODS IX CHEMICAL ANALYSIS 1 c.c. for 5 c.c. of dilute acid (diluted with its bulk of water) is a good allowance ; it is, if anything, slightly under the mark. The volume of gas obtained being corrected for absorption, the result may be cal- culated in two ways, as when the original apparatus is used. Either the experiment may be succeeded by a standard experiment on the same quantity of pure calcium carbonate (in this case there is no correction excepting for absorption, and a simple proportion gives the percentage), or the regular calculation may be applied. (B) Mr. B. Warington considers that Scheibler's apparatus is one of great practical value, as very speedy results, of fair accuracy, can be obtained by its use. The mode of calculating the results described by Scheibler must, however, be abandoned so far as the use of a fixed correction for the retention of gas in the liquid and the employment of Table I. are concerned. By substituting a correction proportional to the volume of gas obtained, and reducing the volume of gas into terms of the carbonate sought by means of Scheibler's Tables III. VI., the errors hitherto made will be avoided. It is not at all pretended that the proportional corrections there given will be found to hold good at all temperatures ; they are probably strictly true only for the tem- perature of the experiment. A far more complete series of observa- tions is required. There are one or two points connected with the use of the apparatus which may be briefly mentioned. Any rise of temperature during the experiment entails a notable error, as the final reading is increased by the expansion of the whole volume of gas in the apparatus. A small rise in temperature is sure to take place if the operator stands before the instrument for 2 or 3 minutes while shaking the generating bottle. This may be avoided by placing a narrow glazed screen between the instrument and the operator. The generating-bottle should also be wrapped in paper during the agitation. Bone charcoal, and many other substances in which carbonic acid has to be estimated, contain small quantities of sulphides ; to prevent sulphuretted hydrogen being evolved, a small quantity of mercuric chloride may be dissolved in the hydrochloric acid used. Proximate Analysis of Coal An elementary analysis of coal teaches little with regard to the nature or practical value of the combustible. A proximate analysis, on the contrary, enables us to learn something in regard to' the real nature of the coal. The moisture and ash are not only diluents of the fuel, but are in themselves obstacles to its effectiveness ; the vapourisation of the moisture causes a serious loss of heat, whilst the ashes, by hindering complete combustion, and by the heat they con- tain when dropped through the grate, constitute another loss. By further estimating the total amount of volatile matter we learn both the percentage of coke in the fuel and the amount of carbon (fixed PKOXIMATE ANALYSIS OF COAL 577 combustible) and bitumen (volatile combustible matter). Although neither of these two products can be considered as simple chemical compounds, it is nevertheless of the utmost practical importance to know these two quantities, because of the great value of coke and gas in manufactures. (A) The proximate analysis of coals has been worked out very fully by Professor G. Hinrichs. Before he instituted his researches no investigation as to its accuracy, nor the best method of conducting the work, was known. In Europe reliance was placed almost exclusively on elementary analysis, whilst in the Government Surveys of the United States proximate analyses seem to have been almost as ex- clusively practised. But while the former may readily be turned into approximate estimations of the heating effects of the fuel, the latter have never been used for such purposes, nor until Professor Hinrichs 's researches was it at all apparent that they ever could be thus made useful. It is evident that the useful applications of coal demand such an analysis, and it was therefore necessary for a rather extensive and thorough search into the method itself to be instituted in order to study its exact value. (B) It is easily seen that the following data will modify the result of the amount of volatile matter driven off from a sample of coal contained in a covered platinum crucible : Weight of coal and of crucible ; degree and duration of heat ; condition of coal. But not- withstanding all these considerations this estimation admits of an accuracy of T T (T of a per cent., equal to that of weighing a gramme exact to the milligramme. The sample of coal used in these preliminary experiments was not selected, but taken at random. From this sample a very pure piece, free from any visible admixture of either gypsum or pyrites, was selected. Its specific gravity was found to be 1*328. Estimation of the Volatile Matter. A common Bunsen burner is used for producing a red heat, and also a gas-burner with six jets, surmounted by a French soufflet cylindrique, for obtaining a white heat, care being taken to keep the gas-cock in the same position by means of an arm of 10 inches in length. These two sources of heat are denoted respectively * BB ' and ' Blast.' The time is measured by means of a small sand-glass, running exactly three and a-half minutes ; this duration is denoted by t. Thus BB, t, means that the crucible was exposed to the constant flame of the Bunsen burner during three and a half minutes. Influence of Quantity of Coal. 1. Coal, pulverised, not dried ; heat BB, t ; cooled and weighed ; then blast, t ; then weighed again. 1 1 Weight = coal taken in grammes; crucible = weight of the same. Deviation per cent, from the mean given. These quantities are given in the same order in all subsequent tables, unless stated otherwise. P P 578 SELECT METHODS IX CHEMICAL ANALYSIS No. of Exper. Weight Volatile matter, per ct. Deviation Crucible d 5-360 48-24 -1-14 19-2 n 1-910 49-58 +0-20 19-2 e 1-147 49-87 +0-49 11-6 o 1-031 49-85 T-0-47 9-4 Mean 49-33 2. Coal in small fragments ; heat as in 1. No. of Exper. Weight Volatile matter, per ct. Deviation Crucible h 3-743 48-30 -0'94 19-2 g 1-130 50-18 +0-94 9-4 Mean 49-24 For the same heat, the amount volatilised is greater as the mass heated is smaller ; whether the coal is in small fragments or pulverised hardly makes any difference ; but since the bitumen passes off more regularly when the coal is pulverised, while, when in fragments, slight explosions sometimes occur, the coal should be pulverised for the estimation of the bitumen. 3. Coal, pulverised, between 1 and 2 grammes ; heat as above. No. of Exper. Weight Volatile matter, per ct. Deviation Crucible n 1-910 49-58 -0-19 19-2 e 1-147 49-87 +0-10 11-6 o 1-031 49-85 +0-08 9-4 Mean 49'77 giving as probable error of a single estimation only 0-108 per cent., or only 1 milligramme for 1 gramme of coal. This is not greater than that of the weighing itself, in which fractions of a milligramme were usually neglected. 4. Coal, pulverised (new portion), and between 1 and 2 grammes ; heat, BB, t ; immediately thereafter, blast, t, without cooling. No. of Exper. Weight Volatile matter, per ct. Deviation Crucible a' 1-16 50-86 +0-14 9-4 n' 1-04 50-58 -0-14 11-0 Mean 50-72 From 3 and 4 it is concluded that if the substance taken is from 1 to 2 grammes, the result will be constant for the same mode of heating. Influence of Drying the Coal before Ignition. 5. Coal fragments ; heat, BB, t ; not cooled ; blast, t, with the probable error of one single estimation, 0'45. No. of Exper. Weight Volatile matter, per ct. Deviation t 1-361 48-49 +0-76 u 1-060 47-26 -0-47 v 1-030 47-43 -0-30 Mean 47-73 PROXIMATE ANALYSIS OF COAL 579 Comparing this with 4 (same heating), it appears that about 8 per cent, less is volatilised by previous drying, and also that the accuracy of 'one estimation is four times less than when the coal is ignited without previous drying. In the arts, coal is not artificially dried before coking. For all these reasons, the amount of volatile matter is best estimated on undried coal. 6. In general, it was found, as means 4 dried coal gave 47*97 per cent, volatile matter 10 undried 49-87 confirming the above. Influence of Cooling after the Ignition over the Bunsen Burner, and before the Ignition over the Blast- flame. 7. Coal, pulverised, not dried ; heat, BB, t ; then blast, t, without cooling. No. of Exper. Weight Volatile matter, per ct. Deviation x 1-314 49-01 -0-02 y 1-156 49-05 +0-02 Mean 49'03 which, compared with the corresponding case, 3, giving the mean 49*77 and maximum deviation 0-19, shows that by the intermediate cooling about f per cent, more is volatilised. This probably is due to the fact that the crucible upon cooling is filled with atmospheric air, which, upon renewed ignition, must burn a corresponding amount of coal. Influence of Repeated Heating, the Crucible being after each Igni- tion Cooled and Weighed. 8. Coal=r= 1*628, in crucible 19*2, was dried, then ignited (BB, t), and lost 41 '77 per cent. Being ignited again in the same way, it lost 2*76 per cent., or, in all, 44-53. Being successively ignited seven times, BB each time for six minutes, the total loss was 52-39, or, on the average for each of these six-minute BB ignitions, 1-12 (two of the estimations nearest this average were 1-06 per cent.). Hereafter the same was exposed to the blast five times for three and a half minutes ; the volatile matter passed off amounted to 57*31, giving for each of these last ignitions the average loss of 0-98 per cent. It now had been ignited fourteen times, each time having been cooled and weighed ; and we have fourteen ignitions, 57*31 volatile first ignition, 41*77 volatile ; hence, average for each of the thirteen ignitions, 1*195, or 1*2 per cent. This series of experiments shows that it is impossible to heat coal until no further loss is sustained ; for it is apparent that each heating, after complete cooling, produces, on the average, more than the addi- tional volatilisation of 1. On 1 gramme of coal taken, 1 per cent, carbon burnt requires about 30 milligrammes, or 20 c.c. of oxygen. p p 2 580 SELECT METHODS IN CHEMICAL ANALYSIS We may, therefore, consider these excesses almost equal losses due to a real combustion. Influence of protracted Heating. 9. Coal, pulverised, not dried ; heat, always first BB, t\ and then immediately, without cooling, transferred to blast-lamp. Difference No. Weight Blast Volatile matter Difference per minute a' + n' (mean) 3 min. 50-72 0-57 0-19 c' 6 51-29 1-04 0-35 V 9 52-33 1-95 0-65 d' 12 54-28 2-93 0-16 &' 30 57-21 By comparing each with the first mean, we obtain for each minute's blast after the first three, respectively 0-24 0-39 0-27 0-2 showing less difference than the above. The volatilisation, after the first three minutes blast, is therefore increasing \ to f per cent, for six minutes, and then very slowly de- creasing to about i per cent, for half-an-hour. At this rate the loss is 12 per hour. It is apparent that the loss is less than when cooled in the inter- vals, but it proves that a slight current of air must get at the coal in the covered crucible. At any rate it is demonstrated that the rule which is sometimes given, to heat until no further loss is sustained, demands an impos- sibility. Influence of the Degree of Heat. 10. Coal, pulverised, not dried ; heat, BB, t ; cooled and weighed ; then blast, t ; cooled and weighed again. After BB. No. of Exper. Weight Volatile matter, per ct. Deviation n 1-910 48-08 +0-42 e 1-147 47-69 +0-03 o 1-031 47-23 +0-43 Mean . . 47'66 Prob. error 0-284 After Blast. No. of Exper. Volatile matter, per ct. Deviation n 49-58 -0-18 e 49-87 +0-11 o 49-85 + 0-09 Mean . . 49-76 Prob. error . 0-108 Showing that the higher temperature gives the most accurate results. . -From these experiments it is concluded that MOISTURE IN COAL 581 The total volatile matter of coal is estimated with accuracy (1 milli- gramme on 1 gramme coal), by taking 1 to 2 grammes of undried, pulverised coal, heating it for three and a half minutes over a Bunsen burner (bright red heat), and then immediately, without cooling, for the same length of time over a blast gas- lamp (white heat). Estimation of the Moisture. (A) A flat-bottomed iron pan, of 20 centimetres in diameter, is filled evenly to the depth of 1^ centi- metre with sand, and the latter is covered with a copper plate, on which the watch-glass containing the coal is placed. A thermometer (scale to 370 C.) is, by means of an indiarubber stopper, inserted in an iron arm of the tripod supporting the iron pan, and held with its bulb about half a centimetre above the copper plate. By means of a Bunsen burner it is found very easy to keep the thermometer perfectly constant at 115 C. This apparatus is a good substitute for Fresenius's iron plate. The coal to be dried is finely pulverised, direct experiments having shown that the employment of fragments is not only very much! 'slower, but also erroneous, on account of the peculiar property of bituminous coal treated of below. These results show that the loss (called moisture) decreases regu- larly after the first hour of drying ; that is to say, while the coal loses in weight during the first hour, it steadily gains in weight thereafter. It appears, furthermore, that the accuracy of an estimation, expressed in the smallness of the deviations from the mean, is greatest at the end of the first hour of drying, least after about three hours of drying, and thereafter increases again. On account of these peculiar properties of bituminous coal, Pro- fessor Hinrichs advises that the loss in weight of the finely-pulverised coal after one hour's drying at a temperature between 105 and 110 C., should be put down as moisture. (B) For the analysis of coal and peat M. Sergius Kern gives a method well adapted for the laboratories of iron works, &c. Estimation of Hygroscopic Water. Three grammes of the substance in a finely-divided state are dried in a porcelain crucible placed in a beaker with a small quantity of sand on the bottom of it. The beaker is covered with a watch-glass, and the whole is placed on a sand-bath and heated for about 3 hours to a temperature of 110. The end of the operation is easily known by the dryness of the watch-glass. The substance when dried is weighed, and the percentage of loss is next calculated. Estimation of Carbon and Hydrogen. The best process was found to be Liebig's : the ignition of 1 gramme of coal or peat with lead chromate in a tube of hard glass 0-25 metre long. The resulting carbonic acid, water, and sulphuric acid are passed through a potash apparatus containing caustic potash (1 part of potassic hydrate dis- solved in 2 parts of water), and 2 U- tubes, the first containing ignited 582 SELECT METHODS IN CHEMICAL ANALYSIS calcium chloride, the second a solution of lead nitrate. The increase in the weight of the potash apparatus and of the first U-tube will show the quantity of carbonic acid and water obtained. Knowing that carbonic acid contains 27'2 per cent, of carbon, and water 11-1 per cent, of hydrogen, the percentage of carbon and hydrogen may be easily calculated. Calculation of the Calorific Power. As 1 part of carbon in burning yields 8,080 calorific units, and 1 part of hydrogen in burning 34,460 calorific units, the calorific power of the coal may be quickly found. Example. Coal from Donetz mountains, near the village of Grouchevka, South of Eussia : Per cent. Carbon . 58-0 Hydrogen 11-0 Sulphur 1-0 Ash 23-0 Hygroscopic water . . . . . 6-0 99-0 For calculating the amount of calorific units in this coal proceed as follows : For carbon 0'58 x 8080 = 4686 For hydrogen 0-11x34460 = 3790 Total calorific units in the analysed specimen .... 8476 On the Slow Oxidation of Coal. An increase in weight after the first hour's drying is found in all Iowa coals. It was also found to occur in a sample of coal (Steinkohle) from Beuthen, Silesia, which showed a loss of 3- 62 per cent, at the close of one hour, and in four hours' further drying gained again 0-42 per cent. It was not noticed in brown coal from Bilin, Bohemia, nor in anthracite from Penn- sylvania. It is therefore probable that it is a property peculiar to pit coal. Pyrites might well be the cause of this phenomenon : the red ashes obtained in many cases may be ascribed to pyrites disseminated through the coal in invisible particles. From an examination of a large series of analyses, it has been found that the more ferruginous ash does correspond to a slightly greater increase in weight ; but it is noticed also that this difference is very small as compared to the total amount of increase, being only -I to -^ of the whole. Arranging these coals in the order of this hourly in- crease, it is found that the colours of the ashes do not at all form a regular series from white to red, as ought to be the case if this increase mainly depended upon the oxidation of the pyrites. The greater increase of the pyritic coals is accounted for by the ASH IN COAL 583 oxidation of the pyrites they contain ; the comparatively great increase of coals giving a pure white ash seems to force the conclusion upon us that the bitumen of the coal itself oxidises, and that to this oxidation the main increase of all these bituminous coals must be ascribed. Bearing in mind the behaviour of bituminous coal from Silesia, anthracite from Pennsylvania, and brown coal from Bohemia, it seems not unlikely that this is another characteristic chemical difference between bituminous coal and other fossil coals. Estimation of Ash. (A) Incineration and an accurate estima- tion of ash are, in many substances, attended with not inconsiderable difficulties. These may arise from the sparingly combustible nature of the bodies, as in the case of anthracite or graphite ; from the presence of certain mineral substances which impede incineration, as silicic acid, phosphates, and fusible salts ; from a tendency to decrepi- tation observed in many vegetable matters, and in all coals ; from the partial volatility of various constituents of the ash, and from the chemical changes which the ash may undergo according to the degree and duration of the heat and the supply of air. The first two of these difficulties affect principally the rapid execu- tion of the process, whilst the remaining affect the composition of the ash and the accurate estimation of its weight. Peat and lignite require no special precautions ; they are readily inflammable, and rarely cake together, often smouldering away like tinder. In true coal all the above-mentioned difficulties may occur. All varieties of coal decrepitate more or less. The losses thus occasioned may be obviated by conducting the incineration at first in covered crucibles. This, however, is inconvenient where a great number of ash estimations have to be performed simultaneously. The incinerations are some- times performed in porcelain crucibles, where unburnt coal is rarely projected over the edge. In general, flat platinum vessels are to be pre- ferred ; in these the process is more rapid, but the chance of loss much greater. To prevent this source of error, it is advisable to reduce the coal to a very fine powder, and, above all, to heat very gradually. The latter precaution, especially in case of caking coal, prevents the formation of coke, the incineration of which requires a much higher temperature, and a very considerable outlay of time. Every ' caking ' coal loses this property completely if very gently heated for a moderate time, and may then be almost completely incinerated at a temperature little above the melting-point of lead. (B) Not every ash can be at once assumed quite free from carbon, and unburnt particles cannot be readily detected by stirring with a needle. Dr. F. Muck advises the use of alcohol for this purpose, when any unburnt portions are detected not merely by their colour, but by floating on the surface. Moistening with alcohol has the additional advantage that the ash, which lies very loose, adheres afterwards more closely to the sides of the crucible, and the complete incineration is 584 SELECT METHODS IN CHEMICAL ANALYSIS thus accelerated. Unburnt carbonaceous particles escape the eye most readily when the coal contains very little ash. When sulphur and iron are present in large proportions, prolonged and repeated ignition is often necessary to reach a constant result. The question remains how the weight of the ash may be affected by the presence of a large proportion of lime. Lime may be present in the coal itself as silicate, as sulphate, as sulphide, and as carbonate. The ash of coal (Westphalian at least) hardly ever effervesces with acids, and when this occurs to the slightest extent, it is partially due to sulphuretted hydrogen. Ash containing much ferric oxide may be not at all, or but slightly red if much lime is simultaneously present, for calcium ferric silicate is colourless or yellowish, but not red. The following is the composi- tion of a pale reddish coal-ash, which, if strongly ignited with the coal in question, melts to a vitreous slag. The ash scarcely effervesced with acids, and after being moistened with sulphuric acid and re-ignited it became red. Silica 32-17 Alumina 17-87 Ferric oxide 17-42 Lime . 17-83 Magnesia 6-97 Sulphuric acid (saturating 4-018 lime) .... 5-94 Matter not estimated 2-00 1*049 gramme of this ash moistened with alcohol, and then ignited for a considerable time in the muffle at a white heat, decreased to 1-0465 gramme. On treatment with ammonium carbonate, and gentle re- heating, the ash weighed 1-056 gramme. The ash effervesced a very little more with acids ; a trace of calcium carbonate had been decom- posed during incineration. The practical results of Dr. Muck's experiments may be stated as follows : 1. The chemical changes during the incineration of coal can only^ serve in rare and especial cases as an explanation of great differences in the estimation of ashes : for instance, when coal contains very much sulphur, and at the same time very little lime. In presence of much lime the combustion-products of the sulphur are more or less completely retained, whilst if little lime is present variable amounts of sulphur are driven off. 2. In case of a thoroughly homogeneous material, i.e. a finely powdered and well-mixed average sample accurately and carefully analysed, the estimations of ash may be expected to agree to within 0-1 to 0-2 per cent. Larger differences, except in the peculiar cases just referred to, must be ascribed to defective work or great difference of the samples. It is understood that the proportion of moisture must be taken BLOWPIPE ASSAY OF COAL 585 into consideration. In a thoroughly air-dry coal not lignite the highest limit of moisture is from 1 to 2 per cent. The platinum crucible, according to the position of the flame, may be coated with soot. This coating may be easily burnt away, but care must be taken not to wipe a sooty place nor a place that has been sooty, without carefully checking the weight of the crucible after weighing the ash. In the places where soot has been formed by the dissociation of the hydrocarbons, the platinum becomes disaggregated and is coated with a black-grey deposit of finely pulverulent metal, which is easily lubbed off. The author has observed variations ex- ceeding 8 milligrammes produced in this manner. Determination of Specific Gravity. Coarse fragments, freed by means of a sieve from all small particles, and averaging -^ c.c. in volume, are introduced into a 50- gramme flask provided with a thermometer stopper. The contents for this flask for temperatures varying from 50 to 80 F. are previously carefully estimated. The given specific gravity corresponds to the coal perfectly soaked, so that all its pores are filled with water. That requires, on the average, 12 hours, permitting two estimates per day, one in the morning, another in the evening. That this precaution is important may be seen from the following example : 2*76 grammes coal gave the sp. gr. 1*309 at 64 F., immediately after filling the flask with water ; after about 12 hours soaking, the sp. gr. had increased to 1*328 for the same temperature. According to this latter estimation, a cubic foot of this coal would weigh 82*76 Ib. ; according to the former, only 81*58, or 1*18 Ib. less. This shows a considerable degree of porosity of the coal, and indicates the absurdity of giving the weight in pounds of a cubic foot of coal with four decimals, although no statement in regard to temperature or time of weighing is made. Calculation of Results. It may be sufficient here to state that, besides the percentage composition of the coal, it is proper to reduce the composition to the combustible =100, in order to obtain a proper comparative estimate of the character of the fuel itself (in regard to the proportion of bitumen a,nd carbon), and of the amount and quality of the impurities (ashes and moisture). It has also been shown that, for considerable areas of the coal-field, the sum of the constituents on the scale of combustible = 100 is the proper caloric equivalent, and that the percentage of the combustible in the fuel gives a proper estimate of its value. Assay of Coal before the Blowpipe The blowpipe method is well adapted to the assaying of coal. Not only does the portability of the apparatus make it very convenient for use away from home, wherever the balance can be set up ; but its 2 ^, 0* TH* 588 SELECT METHODS IN CHEMICAL ANALYSIS use at home is quite as satisfactory on the score of exactness as the assay with the muffle or retort, or large platinum crucible and large balance. Mr. B. S. Lyman gives the following directions for carrying out this assay : Besides the ordinary pieces of the blowpipe apparatus, as made at Freiburg, all that needs to be made expressly for the coal assay is a small covered platinum crucible of the same size and shape as the clay crucibles of that apparatus ; and there must be a little ring for the crucible to stand on, of German silver, about $ of an inch across and half that in Height. Such a crucible cover and ring weigh about 2 grammes more than the ordinary metallic cup that rests on the pan of the balance ; the crucible and ring without the cover weigh about 2 grammes more than the cup. If it be desired to estimate the. amount of hygroscopic moisture in the coal, a small drying bath must be made too ; but the hygroscopic water in ordinarily well-dried coals (not brown coals) is of little importance. The size of the crucible allows the coking of 200 to 600 or more milligrammes of coal, according to the dryness of the coal and the extent of its swelling up when heated ; and as the blowpipe balance weighs within y 1 ^ of a milligramme, it is easy to weigh within much less than -^ of one per cent, of the amount of coal assayed, much nearer, in fact, than the exactness of the coke assay in other respects. In this point, indeed, the blowpipe assay is quite as good as the assay with the larger balance, especially the muffle assay, where the coal must be brushed into a clay receptacle after weighing, and the coke or ash brushed off from it before weighing ; whilst here the crucible is weighed each time without removal of its contents, and without danger, therefore, of losing anything or adding any dust. It may be objected that the smallness of the amount of coal that can be assayed with the blowpipe makes it a less trustworthy indicator of the general composition of the coal than a larger assay ; but the size of the lumps or powder assayed may be made finer accordingly, so that when mixed up an equally just sample of the whole mass would be got, for the small assay as for the large. Anyone who has a little experience both in the use of the blow- pipe and in the ordinary muffle assay of coal will scarcely need any further teaching for the coal assay with the blowpipe. For others, it is worth while to say that the coal may be assayed either in a fine powder or in little lumps, and either with a slowly-increasing or with a quickly-increasing heat. A quick heat will give less coke by several per cents., but will often make a dry coal cake together that would not cake with a slow heat. The cover of the crucible should be left open a very little way for the easy escape of the gas, but covered enough to prevent any loss of solid material. The heat should increase to redness, and as soon as the escaping gas stops burning the heat should be stopped. As some coals part with their gas more quickly than SULPHUR IN COAL AND COKE 587 others, of course no definite time can be fixed for heating all coals ; but the burning of the gas is a sufficiently good sign. Care should be taken not to let the coke take up moisture from the air before weigh- ing, as it will quickly do if it has a chance. Of course, owing to the different effect of quick or slow heat, a certain uniformity of result, even with perfectly uniform samples of coal, can only be got, without error, by practice and by mechanical skill, by reproducing with nicety the same conditions in successive assays. After the coke has been weighed it can be heated again with very free access of air, say with the crucible tilted to one side, with the cover off, until everything is thoroughly burnt to ashes ; and these should be re-heated until no change for the less is made in the weight. With free-burning, soft (semi-bituminous) coals this calcination is very slow, so that it is very fatiguing or even impossible to carry it out with the blowpipe ; but in that case the crucible may be heated over a Bunsen gas-burner or an alcohol lamp, and left to glow for hour after hour. The coking is far more conveniently done in the same way than by blowing with the mouth. As an illustration of the degree of accuracy which this method may be expected to give, the author adduces a pair of blowpipe assays, made five years ago, of some West Virginia asphaltum, that seemed itself to be much more uniform in composition than coal from different benches in one bed is apt to be : Volatile Matter Coke Ash No. 1 . 47'29 per cent. 52-71 per cent. 1-65 per cent. No. 2 . 46-93 53-07 1-81 Mean . 47'11 52-89 1-73 Estimation of Sulphur in Coal and Coke (A) Mr. Crossley has drawn attention to the fact that the process of estimating sulphur in coke, &c., by boiling in nitric acid gives results much below the truth. In the same sample he found the process of fusion with nitre, sodium chloride, and potassium carbonate gave 0*603 per cent., whilst boiling with nitric acid yielded only 0*477 ; whilst in another sample fusion gave 1*23 per cent., and boiling with nitric acid 0*93 per cent. He has arrived at the conclusion that the cause of this loss is, not that some of the sulphur escapes oxidation, but that a portion is driven off by evaporation to dryness. Upon adding a little potassium nitrate to the nitric acid, for the purpose of fixing the sulphuric acid formed and thus preventing its volatilisation on evaporation to dryness, the results appear to be as accurate as those yielded by the fusion process. (B) Dr. T. M. Drown uses bromine as an oxidising agent. He finds it especially valuable in the analysis of coal. By the treatment of coal as here described results are obtained which agree very closely. 588 SELECT METHODS IN CHEMICAL ANALYSIS The coal, as such, is not attacked, and the sulphur obtained therefore represents that existing in the coal as pyrites, and also as soluble sul- phates. The residue left by this treatment has been subjected again to the same process, and yields no more sulphur. On combustion, however, or by complete oxidation, either by oxidising acids or by fusion, additional sulphur may be obtained, which must represent that combined organically with the coal. In comparing the bromine method with others it was found that the treatment with hydrochloric acid and potassium chlorate gave with coals containing but little sulphur in the form of pyrites the same results, while with coals containing much pyrites the results were decidedly lower than by the bromine method. The action of nitric acid and potassium chlorate depends upon the nature of the coal. Some coals are converted partly into a brown unmanageable solution, and others are oxidised completely to a clear solution. In the latter case, of course, the total sulphur could be obtained. As was said above, the sulphur obtained by the bromine method represents both the sulphides and sulphates in the coal. The methods ordinarily given for the separate estimation of calcium sulphate are faulty. Sodium carbonate readily attacks pyrites, and dilute hydrochloric acid and even water, when heated for some time in con- tact with pyrites, with access of air, contain notable quantities of sul- phuric acid. It would seem, therefore, necessary to dissolve out the calcium sulphate by means of water, with the careful exclusion of air. (C) The estimation of the total sulphur in coal by means of fusion with alkaline carbonates and nitrates, or chlorates, is unsatisfactory, owing to the large amount of salts in the solution in which barium sulphate is precipitated. A much better method is to burn the coal in a platinum boat placed in a glass tube in a current of oxygen. The products of combustion may be absorbed by a solution of bromine in hydrochloric acid, or by a dilute solution of potassium permanganate. The latter gives equally good results with the bromine. It is abso- lutely necessary in this process, as originally pointed out by Muck, that the combustion tube should be washed out with water after the completion of the combustion, since sulphuric anhydride condenses in considerable quantity in the tube beyond the boat. It is further necessary, of course, to fuse the residual ash with alkaline carbonates to estimate the sulphur which has not been volatilised by the com- bustion. (D) M. A. Eschka directs to powder as finely as possible 1 gramme of the sample, and mix intimately with 1 gramme of calcined magnesia and 0'5 gramme of anhydrous sodium carbonate. Heat over the lamp in an open platinum crucible, inclined so that only its lower half may be brought to a red heat. The ignition requires from forty-five to sixty minutes, and the mixture should be stirred every five minutes with a platinum wire. The process is complete when the ash becomes ANALYSIS OF COAL GAS 589 yellowish or brownish. Let it become quite cold, and mix intimately with the ash, by means of a glass rod, to 1 gramme of ammonium nitrate, and heat to redness for five to ten minutes, the crucible being covered with its lid. The residue is then placed in a precipitating glass and covered with water. The residue adhering to the crucible is detached by heating with the liquid, and the washings are added to the solution in the glass. The sulphuric acid is then estimated in the usual manner. Valuation of Coal for the Production of Illuminating Gas Take 100 grammes of the coal in small lumps, so that they may be readily introduced into a rather wide combustion-tube. This is drawn out at its open end (after the coal has been put in) so as to form a narrow tube, which is to be bent at right angles ; this narrower open end is to be placed in a wider glass tube, fitted tight into a cork fastened into the neck of a somewhat wide-mouthed bottle serving as tar vessel (hydraulic main of the gasworks). The cork alluded to is perforated with another opening, wherein is fixed a glass tube, bent at right angles, for conveying the gas, first through a calcium chloride tube, next through Liebig's potash bulbs containing a solution of caustic potash, having lead oxide dissolved in it. Next follows another tube, partly filled with dry caustic potash, and partly with calcium chloride ; from this last tube a gas-delivery tube leads to a graduated glass jar standing over a pneumatic trough, and acting as gas-holder. Before the ignition of the tube containing the coal is proceeded with, all the portions of the apparatus are carefully weighed, and next joined by means of indiarubber tubing. After the com- bustion is finished, which should be carefully conducted so as to pre- vent the bursting or blowing out of the tube, the different pieces of the apparatus are disconnected and weighed again. The combustion- tube has to be weighed with the coal after it has been drawn out at its open end, and with the coke after the end of the combustion when it is again cold, and for that reason care is required in managing it. We thus get the quantity of tar, ammoniacal water, carbonic acid, and sulphuretted hydrogen (as lead sulphide). The gas is measured by immersing the jar in water, causing it to be at the same level inside and out. Empty the Liebig's bulbs into a beaker, and separate the lead sulphide by filtration, wash carefully, dry at 100 C., and weigh. From the lead sulphide the sulphuretted hydrogen present is calculated. This process, devised by the late Dr. T. Richardson of Newcastle-on- Tyiie, was found by him to yield very trustworthy results, so as to be suitable for stating what quantity of gas a ton of coal thus analysed would yield. Coal Gas Detection of Air in Coal Gas. Ten parts by weight of an- hydrous manganous sulphate are put into a two-necked Woulfs 590 SELECT METHODS IN CHEMICAL ANALYSIS bottle, and 20 parts of warm water then added to dissolve it. To this mixture is immediately added a solution of 10 parts by weight of Rochelle salt, dissolved in GO parts of water ; the thorough mixing of the liquids is promoted by well shaking the bottle, after this a quantity of a solution of caustic potash is added, sufficient to render the liquid quite clear. Immediately after this, perforated corks fitted with very tightly-fitting glass tubes are placed in the necks of the bottle, which should be entirely filled with the mixed liquid just alluded to. One of the glass tubes the inlet tube for the gas to be tested should just dip a little under the upper level of the liquid ; the outlet tube, on the other hand, should only reach half-way to the perforation of the cork. A very slow current of gas is now made to pass through the liquid, and is kept going for at least a quarter of an hour, and at most one full hour. In case the gas is quite free from atmospheric air, the liquid in the bottle will remain quite clear ; if traces even of air are present, a faint colouration of the liquid will soon become apparent : with a larger proportion of air present in the gas, the liquid will soon be coloured, first light brown and afterwards intensely black. Since these changes of colour are due to the oxidation of the manganese, it is evident that every care must be taken to avoid the presence or access of accidental air ; the liquid in the Woulf's bottle should reach the cork. It is best to cool the bottle during the experiment with ice if at hand, otherwise with very cold water ; the current of gas must be slow. Estimation of Sulphuretted Hydrogen in Coal Gas An apparatus contrived by Dr. Wagner is used at the Munich Gas- works, to indicate the amount of sulphuretted hydrogen contained in crude gas. The following description is from the ' Journal of Gas- lighting ' i :- The apparatus consists of two glass flasks, E and A, a glass pipe, B, fixed upon a stand, and an aspirator. The first flask, E, contains a little acetic acid, for the absorption of the ammonia contained in the gas, and for the reception of the tar. The inlet pipe, a, is bent at an obtuse angle, to allow the condensed tar to flow into the flask, and after passing through an indiarubber stopper, the pipe descends to near the bottom of the flask, and dips into the acetic acid. The outlet- pipe, b, on the contrary, does not penetrate further than to within a short distance below the inner surface of the stopper, and is connected with the second flask, A, into which it enters, descending to nearly the bottom of it, by two bends and proper inclines. The second flask is about half-filled with a solution of lead acetate, made acid by acetic acid. The outlet-pipe, c, of this flask is at its upper end bent down- wards, and is connected by an indiarubber tube with another smaller 1 See also the Chemical News, March 8, 1867, vol. xv. p. 112. SULPHURETTED HYDROGEN IN COAL GAS 591 glass-pipe, d, which passes through an indiarubber stopper, e, and penetrates into the pipe B to its lowest point, terminating in a fine end, so as to prevent the gas coming out otherwise than by a very narrow passage and in small bubbles. The pipe is about 1 metre long, and, as shown in the woodcut, is also filled with a solution of lead acetate. While the left extremity of this pipe is closed by the stopper e, its right has a globe, /, at the end, for the deposit of any liquid that may have been carried over ; and in continuation therewith is a glass tube through which the gas takes its course to the aspirator, c. This 592 SELECT METHODS IN CHEMICAL ANALYSIS aspirator, which in this instance has a capacity of 12 litres, is closed by means of an indiarubber stopper, through which passes the inlet- pipe, #, bent at the top, the extreme end of which, going, downwards, is connected with the glass tube near the globe / by an indiarubber tube. At the bottom of the aspirator a small lateral pipe is inserted, with an indiarubber tube, the latter being provided with a pressure - cock, together with a thumbscrew, for the purpose of discharging the water. When the apparatus is used, the gas is admitted by a connecting pipe between the hydraulic main and the condenser nearest, however, to the former. The cast-iron pipe is drilled at the upper part, and the |-inch outlet lead pipe is carried upwards about 2 feet perpendicularly to convey back into the cast-iron pipe a portion of the tar carried onward by the warm gas, but which soon becomes condensed: The lead pipe is then bent downwards, and carried about 10 feet in length to the experimental table, where it terminates with a stopcock. A short indiarubber tube is drawn over this cock so as to allow of its being connected afterwards with the apparatus. Before an experiment takes place gas is allowed to flow freely for at least half an hour through the supply pipe, in order that the inner surfaces of the same may become completely covered with tar, thus insuring that the lead of the pipe does not decompose the sulphuretted hydrogen of the gas. After filling both the flasks and the pipe in the manner before described with the absorbing liquids, and completely filling the aspirator with water, and making tight all the connections of the apparatus the water is allowed, by opening the pressure-cock, h, to flow out of the aspirator until atmospheric air in the form of bubbles is sucked up by the apparatus, and until the level of the water corresponds exactly with one of the marked lines of the aspirator. The cock h is then again shut for a short time, and the loose end of the indiarubber tube fastened to the supply pipe is then drawn over the glass pipe a. It is of course premised that the pressure of the gas in the supply pipe is = 0, as is the case in establishments where exhausters are used. Upon the connection being restored between the apparatus and the supply pipe, the pressure cock is again slightly opened and the gas allowed to pass gently say about 20 litres per hour until the water- level in the aspirator has descended to the line marked 1. The flow of the gas is kept up as uniformly as possible by the regulating screw of the pressure-cock. As at each experiment from 40 to 50 litres pass each time, it is necessary that the above experiment should be re- peated several times. The pressure-cock and the cock of the supply pipe being again shut, the stopper of the aspirator is loosened, the aspirator again filled with water, and the entire operation repeated in the manner above described. Where no exhausters exist, and where there is a pressure of several CARBON DISULPHIDE IN COAL GAS 593 inches in the gas supply pipe, no aspirators are required, but a gas- meter is used instead. In the first flask, E, filled with acetic acid, is collected the greatest portion of the tar ; no absorption of sulphuretted hydrogen takes place here, aa the crude gas enters it at a high temperature. In the second flask, A, and also very slightly in the pipe B, a black precipitate is formed, composed partly of lead sulphide, partly of tar. The latter,' however, is apt to carry down with it a considerable quantity of the solution of lead employed. In order to bring the precipitate thus formed into a condition to be weighed, it is first filtered, then well washed, and dried at a temperature of about 100 C., and put into a small porcelain dish. Fuming nitric acid is then repeatedly poured over it, also at a temperature of about 100 C., and this is continued until the black mass has become quite white. When this has taken place, the residue of the nitric acid is driven off by evaporation at 100. By the above operation the lead sulphide is converted into lead sulphate, the tar is destroyed, and the lead carried down by the tar is changed into lead nitrate. Lead nitrate, on the contrary, is readily soluble. For this reason the white mass is washed with water in a porcelain dish, and the soluble nitrate separated by filtration from the insoluble lead sulphate. The latter, after being properly washed and dried, is heated in a crucible and weighed as lead sulphate, from which the sulphuretted hydrogen is readily calculated. Detection of Carbon Bisulphide in Coal Gas. Dr. Herzog detects this body in the following manner : A solution is prepared by saturating absolute alcohol with ammonia gas. Then a concentrated aqueous solution of lead acetate is made, and, to insure saturation, a small portion of the solid salt is left in contact. Both these liquids must be preserved in well-stoppered bottles. The gas to be tested may be conveniently delivered from a length of vulcanised indiarubber tubing, to the end of which is adapted a narrow glass tube about 5 or 6 inches long. 5 drops of the lead acetate solution are then mixed in a test-tube, with about 60 or 70 drops of the alcoholic ammonia. No precipitate will be formed pro- viding the latter solution has not been allowed to absorb any carbonic acid. The glass tube delivering the supply of coal gas is now immersed in the mixed solution to a depth just sufficient to allow the gas to be forced out by the existing pressure, and to escape in small bubbles. In the event of carbon disulphide being present, the liquid becomes gradu- ally coloured, and soon afterwards a yellowish-red precipitate is formed, which by longer action assumes a brownish colour. If carbonic acid exists in the gas, then a white precipitate is thrown down, which im- parts to the yellow-red a somewhat lighter colour. As a confirmatory experiment, the gas may be first passed through the alcoholic ammonia alone, and the lead solution subsequently added, QQ 594 SELECT METHODS IN CHEMICAL ANALYSIS when an orange-coloured precipitate, appearing either immediately or very shortly afterwards, will be formed if carbon disulphide be present. In order to meet the objection that sulphuretted hydrogen may perhaps have occasioned this reaction, let some of the gas be first passed through a small quantity of the simple lead solution. The smallest trace of sulphuretted hydrogen causes the blackening of the liquid, whereas carbon disulphide does not alter it in the slightest degree. It should be mentioned that if the yellow-red precipitate be allowed to remain under the liquid, it gradually changes colour, and becomes white after the lapse of about 24 hours. If, however, the precipitate be filtered immediately, slightly washed, and dried, it becomes a dark brown. With regard tolthe explanation of the chemical reactions which occur in this process, the observations made by MM. Zeise and Debus may be considered to prove that, by the action of carbon disulphide on ammonia, according to the concentration and temperature of the liquids and the proportion borne by the ammonia to the sulphide, so will the relative amounts of the products of decomposition vary. In concentrated solutions, and when ammonia is in excess, ammonium sulphocarbonate and ammonium sulphocyanide are formed ; in dilute solutions and when carbon disulphide is in excess, ammonium xantho- nate. Therefore, by this experiment one or other product will prepon- derate according to circumstances, dependent upon the larger or smaller quantity of carbon disulphide contained in the gas. In any case, lead compounds are formed corresponding to the ammonia compounds, which possess at first an orange-red and afterwards a golden-yellow colour. Notwithstanding the complicated nature of the chemical reactions involved in the testing of gas by this process, its adoption is to be recom- mended on account of the practical simplicity which has attended the working of a great number of comparative experiments. Detection of Sulphur in Coal Gas. On forcing, by an ordinary blowpipe, the flame of coal gas for about a minute on to distilled water containing a little acid barium chloride, barium sulphate is formed, and the presence of sulphur in the gas thus proved. Estimation of the Total Amount of Sulphur in Coal Gas. (A) We have employed a contrivance of Dr. Letheby, which is a most simple and effectual means for estimating sulphur in gas. The objects are to effect the combustion of the gas in a strongly ammoniacal atmo- sphere, by which means the sulphurous acid is fixed by the ammonia as soon as formed, and condensed as ammonium sulphite. These ob- jects are accomplished in the following way : After passing the meter, the gas goes through a bottle filled with pebbles moistened with dilute sulphuric acid, for the purpose of estimating any ammonia the gas may contain. The inlet-pipe to this bottle is allowed to pass only 1 inch through the cork ; the outlet-pipe passes to the bottom of the bottle. SULPHUR IN COAL GAS 595 The gas is thus forced through the pebbles / rom the top, prevent- ing any accumulation of salt about the inlet- pipe. In place of this bottle, a tube about 6 inches long, H inch in diameter, and drawn out at each end, may be used. It is filled, of course, with pebbles, moistened with sulphuric acid like the bottle, and may be placed horizontally. The gas thus purified from ammonia is consumed at the rate of about half a foot per hour in a Leslie's burner, which is placed under a long funnel-shaped tube. This tube is connected to one end of a large glass cylinder similar to those used for electrical machines, the other end of which is furnished with a piece of glass tube about 4 feet long, joined in such a manner that any products of combustion condensed in it will flow back into the large cylinder. The means by which ammonia is supplied to the burner are the following : A wide-mouthed bottle filled with the strongest liquid ammonia is placed immediately beneath the burner, and a funnel, with a short tin tube attached to it, is placed over the bottle in an inverted position. This short tube passes through the centre of the burner, so that the end of it is about 2 inches above the top of the flame. The draught produced through the whole apparatus, when the burner is alight, is sufficient to evaporate the ammonia in the bottle, which is discharged through the tube into the centre of the receiving tube over the burner, and about 2 inches above the flame. Immediate combi- nation then ensues between the ammonia and the sulphur products of the consumed gas, and the resulting ammonium sulphite is condensed, along with the water formed, in the large cylinder. After pouring out the solution, and rinsing out the cylinder and tubes, the sulphite is converted into ammonium sulphate, and the sulphuric acid estimated as barium sulphate in the usual way. With this apparatus it is only necessary to observe two precautions to burn the gas very slowly and to keep up the supply of ammonia. The latter is of the utmost importance. (B) Mr. Albert Ellissen speaks of this apparatus as follows : In it the gas is consumed with a Leslie's burner under the best practical con- ditions for a good oxidation of the sulphur contained in the gas. The consumption with that burner is so slow, that certainly during the ordinary burning of gas so perfect a combustion does not take place, and it may be made similar to the blue flame necessary in heating apparatus a mode of consumption which should be taken into consi- deration in the use of gas for domestic purposes. The condensation of the sulphur products (sulphurous and sulphuric acids) in the glass cylinder is complete ; experiments having proved that a sensibly greater amount of sulphur is not obtained by increasing the number of those vessels, nor by filling them with ammonia. The apparatus of Dr. Letheby has the additional advantage that the experiments may be made on the average quality of the gas manu- factured during the day of 24 hours, and does not require the least Q Q 2 596 SELECT METHODS IN CHEMICAL ANALYSIS superintendence. An interval of a few seconds is sufficient to empty the liquor collected in the cylinder, the quantity of which affords a valuable check on the correctness of the progress of the experiment, and a fresh experiment may be immediately commenced by merely opening the stopcock for the gas. Valentin's Process for the Estimation of the Total Amount of Sulphur in Coal Gas. Valentin has found that by passing a mix- ture of coal gas and air over spongy platinum, and then over a layer of soda-lime, both at a red heat, every trace of the sulphur is absorbed and arrested. He employs a platinum tube, MN, fig. 28 (J size), 13 inches in length, which is heated on a small Hoffmann's combustion- furnace. The portion of the platinum tube marked a b, 5 inches in length and f ths of an inch in diameter, is charged with a cage con- structed of a double roll of fine platinum gauze and filled with spongy platinum. The wider portion of the tube, b c, 4 inches in length and f ths of an inch in diameter, contains the soda-lime. The air requisite to completely burn the gas enters through a narrow glass tube, con- nected by means of a small cork at M with the wide end of the platinum r~ C FIG. 28. tube. A cap of an alloy of silver and copper soldered to this part of the tube strengthens it sufficiently to prevent the thin platinum from being injured by a tightly fitting cork. The supply of gas to the tube passes through the narrow tube 4 inches long and ^ths of an inch in diameter, likewise capped, which is seen to branch off at a right angle from the portion of the main tube next to the anterior part of the platinum cage containing the spongy platinum. The products of com- bustion are allowed to escape at N, through the narrow platinum tube, c N. Connections for supplying gas and air are made by narrow non- vulcanised black indiarubber tubing. The air is most conveniently supplied under slight pressure by means of a gas-holder, from which the air is expelled by displacement with water. Such gas-holders are found in most gas-works. A Low's motive-power meter may also be employed with great advantage, as it is capable of being regulated so as to give a supply of air sufficient for one experiment, whilst a small gas-holder would require to be refilled with air once or twice during an experiment. The pressure from the gas-mains is at all times sufficient to send the gas through the platinum VALENTIN'S PROCESS 597 tube. The respective proportions of gas and air are best regulated by means of meters, when the presure-gauge must of course show the same heights of water column ; or the air may also be adjusted without having to pass through a meter merely by using a compression-cock on the narrow indiarubber tube. Preparatory to an experiment the platinum tube is charged with pure soda-lime, by dropping in a lump sufficiently large to easily block up the narrow exit-tube ; the whole of the wide portion of the tube, b c, is then gradually filled with loose pieces of soda-lime, of a size to enable the operator speedily to shake out the charge of soda-lime when the combustion is over. By gently tapping the platinum tube, held in an upright position whilst it is charged, the layer of soda-lime shakes down pretty completely, and is yet sufficiently porous to allow of a free and easy passage for the gaseous products of the combustion. The cage of spongy platinum is next introduced, and pushed down past the narrow branch tube. The gas and air connections are then made, and the platinum tube is placed upon a small combustion furnace, and heat applied to it from a to c by turning on the required number of gas- burners at once. The platinum tube is best protected from the action of the gas -flames by being kept imbedded in asbestos loosely spread in a thin layer along a trough made of tinned sheet iron. The supply of gas to the clay gas -burners should at no time be so great as to cause flames to shoot up above the burners or the tiles which cover the fur- nace. A dull red heat is sufficient, especially as much heat is generated inside the platinum tube by the combustion of the gas and air within the pores of the spongy platinum. From 0*5 to 1 cubic foot of gas can conveniently be burned per hour, requiring from 5 to 10 cubic feet of air for its complete combustion. An experiment can thus be done in 3 to 4 hours, since as a rule 2 to 4 cubic feet of gas, burned in the manner described, yield sufficient sulphuric acid for an accurate weighing in the form of barium sul- phate. The experiment over, the tube is allowed to cool in a slow current of air alone. The two ends are disconnected, and the cage of spongy platinum is drawn out by means of a copper wire having a little hook at one end. A stout bit of platinum wire in the form of a loop or ring may also be attached to the cage, for the more ready removal of the platinum cage. The latter is placed into a good-sized test-tube, and treated repeatedly with boiling distilled water, acidulated in the test- tube with a little dilute hydrochloric acid, in order to remove a little sulphuric acid which the spongy platinum retains. The soda-lime is next shaken out into a high beaker, and the tube washed out with hot dilute hydrochloric acid. This is most conveniently done by moving the platinum tube, held in a horizontal position, with its contents of dilute acid backwards and forwards in a small Bunsen gas-flame. The rinsings are poured over the solid soda-lime contained in the beaker. 593 SELECT METHODS IN CHEMICAL ANALYSIS- Loss from spirting must be guarded against by rapidly covering the beaker with a large watch-glass after each addition of hydrochloric acid, as long as effervescence takes place. The soda-lime is completely dissolved by the application of gentle heat, and the carbonic acid must be entirely driven off before the sulphuric acid can be precipitated by means of a solution of barium chloride. On gently warming for some time, the precipitate falls down readily and completely, and may be filtered off after standing for a short time, and ignited and weighed as barium sulphate. The sulphuric acid can also be estimated volumetrically by means of a standard solution of barium chloride. The following are said by Valentin to be the advantages of this method of estimating sulphur in coal gas : 1. Perfect combustion of the gas in a close vessel, at a very high temperature. 2. Complete and easy absorption of the sulphuric acid generated by the oxidation of the carbon disulphide, in the same vessel in which it was generated. 3. No loss from imperfect condensation. 4. Possibility of completing an experiment in a few hours' time, or, as seems most desirable, during the time of the evening when the greatest consumption of gas occurs. Carbonic Acid Estimation of Carbonic Acid in Natural Water. M. Lory employs copper phosphate dissolved in a very slight excess of hydro- chloric acid. The copper phosphate is obtained by precipitating a solution of copper chloride with ordinary sodium phosphate ; the pre- cipitate is collected on a filter, well washed, and, after having been removed from the filter, it is suspended in water and dissolved by the addition of a few drops of hydrochloric acid. When this reagent is added to any water containing alkaline or earthy metals in the state of carbonates or bicarbonates, the result is at first the formation of a bluish-coloured cloudiness, or turbidity. By the addition of a larger quantity of the reagent, this turbidity disappears, and the liquid be- comes clear again. This point having been reached, the quantity of the reagent employed will be proportional to the total equivalent of the bases present, and consequently to the carbonic acid which was combined with these bases. In order to titrate the reagent, dissolve 0'265 gramme (equal to sJ-tf of an equivalent) of perfectly pure and dry sodium carbonate in water, and saturate this solution with carbonic acid in order to con- vert it into bicarbonate ; excess of carbonic acid does not at all affect the reagent. 4'4 c.c. of this solution in 1 decilitre of pure water should produce, by the addition of the copper liquor, the reaction already ESTIMATION OF CARBONIC ACID IX WATERS 599 alluded to, and these 4*4 c.c. correspond to 0*29 gramme of carbonic acid. This reagent is unchangeable and easily prepared, and is effectual no matter what quantity of chlorides, sulphates, &c., be contained in the water ; it may even be employed for the alkalimetrical estimation of very dilute liquids ; but it should be remarked that the reaction is much more exact with bicarbonates than when the bases exist as neutral carbonates or free alkalies. By combining this quick and simple test with the test by the standard solution of soap, both in the natural water and also in the same water after boiling, the most important elements for the appreciation of its ordinary and hygienic qualities will be ob- tained. Estimation of Carbonic Acid in Artificial Mineral Waters. In these waters the W I k* gas is present under considerable pressure. Mr. H. Napier Draper has devised the following ap- paratus by means of which the c entire quantity of gas is easily and simply estimated. 1 is a tube of strong brass B 15^ "SB furnished at A with, a screw, I ** and tipped at B with a sharp ^ steel ferrule. This tube is open at both ends, and is pierced at c with two small holes. 2 is an accurately ground stopcock, which can be screwed on to A, No. 1. FlG . 29. 3 is a handle like that of a gimlet, screwing on to the other end of the stopcock. 4 represents an air-pump syphon-gauge of stout glass tube, securely cemented into a short brass tube, which is also provided with a screw, the thread of which coincides with those of the stopcock and the tube No. 1. Mercury is poured into this tube and adjusted to the level E E'. The space E' F is then graduated, as shown in the figure, by first dividing it into two equal portions and marking the point of division 2. The lower space is then subdivided in the same manner, and the sepa- rating line marked H. The mark 4 is similarly obtained by dividing the upper space, and the 3 is placed at a point equidistant from 2 to 4. There are two methods of using this apparatus. The first is more suitable in cases where great accuracy is required ; the second is more 600 SELECT METHODS IN CHEMICAL ANALYSIS practically applicable where an approximate knowledge of the gaseous contents of water is required, and where it is certain that these consist wholly of carbonic acid. In the first case an ammoniacal solution of barium chloride is prepared by mixing a saturated solution of the salt with half its volume of strong solution of ammonia, and allowing the mixture to become clear by subsidence. The estimation is then proceeded with in the following manner : A glass flask, capable of holding half as much more liquid than is contained in the bottle experimented upon, is fitted with a cork through which a glass tube passes nearly to the bottom of the flask. About 2 fluid ounces of strong solution of ammonia are now poured into the flask and mixed with 4 ounces of distilled water. The stopcock being adjusted to the tube at A, the handle is now screwed on to the free extremity of the former, and by its aid the steel point is made to penetrate the cork of the bottle to be ex- perimented on until the orifices appear below its under surface. It is used, in fact, precisely as an ordinary cork-borer. The handle is now removed and the stopcock connected with the glass tube which passes into the flask, by means of a piece of vulcanised tubing about G inches long. The stopcock is next turned on just so much as will allow the gas to bubble slowly through the solution of ammonia. The whole is left in this position for 12 hours, by which time all the gas not held in solution at the ordinary pressure will have been absorbed. That which is still retained by the liquid may either be expelled by heating the bottle placed in water, or the entire liquid may be mixed with the contents of the flask. The carbonic acid can now, of course, be estimated by mixing the solution from the flask with about an ounce of the ammoniacal barium solution above mentioned, gently heating, separating by filtration, drying and igniting the precipitated barium carbonate as usual. If the whole of the aerated water has been transferred to the flask, and if it contain carbonates or sulphates, or any earthy or metallic base, the weight of these must be deducted from that of the precipitate. Approximate and Rapid Method of Estimation with this Apparatus. This method of estimation cannot be considered as giving absolutely correct results ; but from the facility with which it can be performed, it will be found useful where great accuracy is not required. It must be premised, however, that the necessary correction for temperature must be made ; when this is done the results coincide very closely with those obtained by the first-described method. In this case the stopcock, instead of being connected with the flask, is screwed into the mercury tube, 4, and gradually turned until fully open. Now, as water dissolves at the ordinary pressure of 30 inches its own volume of carbonic acid, and as the quantity dissolved at other pressures is directly proportional to the pressure exerted, it is clear that if we know the amount of this pressure and the volume of GLADDING'S METHOD 601 the water in which the gas is dissolved, we can, knowing also the weight of an equal volume of carbonic acid, estimate by weight the quantity of the latter held in solution. Or, without knowing this latter number, we can express, as is most usual, the quantity of gas in cubic inches. Now it is also clear that as the volume of a gas is inversely as the pressure to which it is subjected, the mercury tube,, graduated as in the figure, will show at a glance the number of atmospheres under which the carbonic acid is held dissolved. Estimation of Carbonic Acid, in Solid Carbonates. Sir C. Cameron employs an apparatus shown in fig. 30. It consists of a light bottle, of the capacity of 75 cubic centimetres. The lower part is divided into two compartments, in one of which the carbonate is placed, in the other the acid. By inclining the bottle, the acid may be -p allowed to flow over on the carbonate as gradually as the operator pleases. One or two calcium -chloride tubes are inserted through the cork. The use of anhydrous copper sulphate jointly with fused calcium chloride is preferable as a dryer in case hydrochloric acid is used in the analysis. Estimation of Carbonic Acid Mr. T. S. Gladding uses an apparatus for the estimation of carbonic acid by absorption. It has been used in the author's laboratory for several years, and has proved itself indispensable on account of its great convenience and accuracy. It consists of the ordinary generating flask, followed by an empty U-tube to retain condensed water vapour ; this is succeeded by four potash bulbs of the Geissler form. The first of these contains con- centrated sulphuric acid to dry the gas. The next two contain potash solution, of sp. gr. 1*27, for absorbing the carbonic acid ; the last con- tains concentrated sulphuric acid to absorb the moisture taken up from the potash solution. Then comes a U-tube containing soda-lime, and serving as a guard. The last three Geissler bulbs constitute the weighable portion of the apparatus. Perfectly dry air plus carbonic acid enters these, and perfectly dry air alone escapes. The increase in weight gives the amount of carbonic acid. The advantages of this apparatus are : 1. The superiority of concentrated sulphuric acid over calcium chloride as a drying agent on account of (a) its greater thoroughness ; (b) its non-absorption of carbonic acid, as is the case with calcium chloride, requiring its previous saturation by a current of the gas ; and 602 SELECT METHODS IN CHEMICAL ANALYSIS (c) its greater cleanliness and simplicity of renewal, which takes but a moment, and is necessary only at long intervals. 2. The rapidity with which an analysis may be ma,de. The bubbles of gas may pass at the rate of five per second with perfect safety, and an analysis including all weighings, and a final aspiration of 4 or 5 litres of air, be completed in less than 2 hours. 3. The large quantities of substance that may be used, and the con- sequent increase of accuracy obtained. 5 grammes of sodium bicar- bonate may be used as readily as 1 gramme in the old form, and duplicates easily agree within a few hundredths of a per cent. An analysis of Iceland spar, taking 5 grammes, gave 48'97 per cent. A strong aspiration must be maintained from the beginning of the analysis, the flow of gas being regulated by a screw clamp placed before the generating flask. 100 c.c. of water are added to the carbonate, and then normal hydrochloric acid to slight excess. Not a trace of hydro- chloric acid is carried over on boiling. All the corks are of soft rubber, and black rubber tubing is employed for connections. BORON Detection of Boron in Minerals (A) After estimating the water of crystallisation, Professor Wohler dissolves the mineral (tinkalcite) in hydrochloric acid, and after neutra- lising with ammonia, precipitates the calcium with ammonium oxalate, concentrates the filtrate, and estimates the boracic acid in the state of double boron and potassium. In the case of minerals like tourmaline, which contain fluorine and boron, the question is not so simple. The volatile matters may be estimated by a process analogous to that employed in the case of silicon fluoride, the boron fluoride being changed into a mixture of calcium fluoride and boracic acid. Unfortunately we do not know a method of estimating boron directly in mineral substances, especially if associated with fluorine and silicon ; so that if we have boron fluoride, silicon fluoride, and alkaline fluorides, we can estimate the alkalies, but not the boron, silicon, and fluorine. In the absence of a quanti- tative method for estimating boron, we have an excessively delicate qualitative test. (-B) The best method of recognising the presence of boron, if no fluorine is present, is to mix the substance with a small quantity of calcium fluoride and potassium bisulphate, having previously ascer- tained that the two reagents do not contain boron ; two experiments must therefore be made, one on the reagents, and the other on the substance mixed with the reagents. The mixture is slightly moistened, and held on the extremity of a perfectly clean platinum wire. Direct the reducing flame of the blowpipe on to the paste ; at the moment ESTIMATION OF BOKACIC ACID 603 when the mixture appears to boil the flame assumes a vivid green colour, characteristic of boron. When but little boron is present, this must not be tried in full daylight, and it should be viewed against a dead black background ; the colour of the flame will then be easily detected. (C) Dr. M. W. lies finds that borax moistened with glycerine gives before the blowpipe a blue flame which soon changes into a deep green. In subsequent experiments he found it was best first to calcine the mineral, powder, and moisten with sulphuric acid, heat to expel the acid, then to moisten with glycerine and allow it to take fire. Thinking that the carbon exerted some action upon the borate, finely divided charcoal and a borax bead were tried, but they gave negative results. Glycerine and a sodium carbonate bead gave simply a yellow flame. Various metallic bases in a sodium carbonate bead and glycerine also .gave negative results in regard to flame. A ' salt of phosphorus ' bead and glycerine gave the light green phosphoric acid flame, but of less in- tensity than that noticed when a potassium chlorate match is burned. A large number of bases and acids were also experimented upon in connection with glycerine, using different beads ; also substances were treated on charcoal with glycerine, with various results, some of which were without doubt sufficiently characteristic for qualitative reactions. Estimation of Boracic Acid (A) In order to estimate directly the boracic acid contained in dato- lite, a calcium borosilicate, Professor Wohler proceeds as follows : Place the mineral in a small tubulated retort, decompose it with hydro - chloric acid, and distil the mixture to dryness ; pour on to the residue the distillate (which contains boracic acid), and allow it to digest to separate the silica. In the liquid, precipitate the calcium by means of potassium oxalate, taking care not to add it in too great excess. Then, after filtration and concentration, precipitate the boracic acid in the form of double boron and potassium fluoride. For this purpose add a little potash to the material in a platinum capsule, then pour over the mixture a slight excess of hydrofluoric acid, and evaporate the solution to dryness. To remove the other salts it suffices to treat the mass with a moderately concentrated solution of potassium acetate ; then allow it to digest, and throw on to a filter the residual double boron and potas- sium fluoride, and wash it with the same solution of acetate. Then wash with dilute alcohol to remove the potassium acetate. The double fluoride is dried at 100 C., and weighed. (B) If it be required to estimate boracic acid contained in a solution in which it is contained alone, or in combination with alkaline oxides, A. Ditte proposes to add a little ammonia to the liquid in order to neutra- lise any free acid, and then an excess of a saturated solution of pure 604 SELECT METHODS IN CHEMICAL ANALYSIS calcium chloride. All the boracic acid is then found as calcium borate,. in the form of a gelatinous precipitate, soluble in heat in calcium chloride in excess. The matter introduced into a platinum capsule may then be evaporated to dryness without the least trace of boracic acid being volatilised. When dry, the crucible is filled with a mixture in equal equivalents of pure crystalline sodium and potassium chlorides and heated moderately at first, and then to fusion. The calcium borate, much less fusible, collects at the bottom of the crucible in a spongy mass- more or less agglomerated, and dissolves partially in the melting saline mass. If at the bottom of the crucible a temperature is maintained higher than in the upper part, the dissolved calcium borate crystallises. on the surface of the liquid, and forms a ring, which rises along the side of the crucible, just above the surface. Soon all the borate is con* veyed into this ring, and nothing remains at the bottom of the crucible. The crystals are insoluble both in hot and cold water. A cold concen- trated solution of alkaline chlorides does not affect them ; if hot it dissolves a very small quantity. The matter, when cold, is separated from the crucible, and treated with cold water, when the chlorides dis- solve. The crystals are washed on the filter, dried, detached from the filter, and weighed. Care must be taken not to fuse the amorphous calcium borate which occupies the bottom of the crucible in an early stage of the operation. The temperature of the bottom of the crucible should be kept as high as possible short of such fusion. The crucible cannot be sufficiently heated with a Bunsen burner. On approaching the point at which the calcium borate is fused, the volatilisation of the alkaline chlorides becomes visible. There should be 1 part of pure dried cal- cium chloride for 3 parts of the mixture of alkaline chlorides. Analysis of Borates and Fluob orates In solutions which contain only boracic acid and alkalies, Marignac estimates the former as follows : The solution is neutralised with hydrochloric acid, and magnesium chloride, or preferably the double magnesium and ammonium chloride, is added in such quantity that to 1 part of boracic acid at least 2 parts of magnesia are present. The liquid is now made ammoniacal, and finally is evaporated to dryness in a weighed platinum vessel. Should the addition of ammonia cause a precipitate which does not readily disappear on warming, sal- ammoniac must be added until the liquid becomes clear. During the evaporation it is well to add a few drops of ammonia from time to time. When the mass is dry it is heated to redness, then treated with boiling water ; the residue is collected on a filter, and washed with hot water until the washings are not in the slightest degree affected by silver nitrate. The first residue contains, together with excess of magnesia, the larger part of the boracic acid. A small amount of the latter always- SILICON 605 goes into solution. The filtrate and washings are treated with ammo- nia and again evaporated, ignited, and washed as before. The second filtrate and washings are once more treated in the same manner, when .great accuracy is required. The three residues are ignited together in an open crucible as strongly as possible, and sufficiently long to decompose the traces of magnesium chloride which they may contain. When they are weighed, it only remains to estimate the magnesia in them to find by difference the quantity of boracio acid. This can be done either by dissolving in an acid and precipitating magnesium ammonio-phosphate, or more rapidly by dissolving in a known volume of standard sulphuric acid it a foiling heat and estimating the excess of acid by means of a standard alkaline solution. Should an insoluble, heavy, grey residue remain on treating with acid, it must be collected and its weight deducted from that of the magnesium borate ; it will be platinum. From insoluble compounds the boracic acid is obtained in solution by fusing with three times their weight of sodium carbonate, and exhausting the mass with water. In case of silicates the alkaline solution is digested with ammonium chloride to precipitate silica. When operating with a fluoborate, the solution of the sodium car- bonate fusion is digested with sal-ammoniac to decompose a good pro- portion, but not all, of the sodium carbonate, and is then precipitated with a neutral or ammoniacal solution of calcium chloride. The pre- cipitate of calcium fluoride and carbonate is washed a matter easily accomplished dried, gently ignited, treated with acetic acid, evapo- rated to dryness, and the pure calcium fluoride collected, washed, and weighed. The filtrate, after removing calcium by addition of carbo- nate and a few drops of ammonium oxalate, may be treated as before described for the estimation of boracic acid. SILICON Decomposition of Silicates in the Wet Way (^4) By means of a Fluoride and Acid. Mr. C. E. Avery finds that silica and silicates, such as felspar and glass, may be completely dissolved in the cold by a mixture of some normal fluoride with almost any of the stronger acids, whether concentrated or dilute. When mixed with the sodium, barium, aluminium, and lead fluorides, or the double fluorides of these metals, the silicates in ques- tion can be readily decomposed by nitric, hydrochloric, or sulphuric acid, either concentrated or diluted with four volumes of water. If strong sulphuric acid is used, a part of the silicon passes off as gas : if the dilute acid is used, portions of many silicates remain un- dissolved as insoluble sulphates. 606 SELECT METHODS IN CHEMICAL ANALYSIS The same decomposition of the silicates is effected, though less easily, by the action of oxalic, acetic, tartaric, and like acids, on the mixed fluoride and silicate. Carbonic acid, even as dilute as it is in the air, does the same, but less rapidly. Strong nitric acid gives a perfect solution and acts rapidly, dis- solving a moderately fine powder of felspar or quartz in a few hours,. even in the cold. The loss of silica is very slight if the experiment is properly conducted ; hence, all the constituents of a siliceous mineral can be estimated in the solution produced. In analysing silicates in this way, it is best to use the fluoride of some metal which is not to be estimated in the analysis ; since if we use a fluoride whose metal is present in the mineral, we must know the weight of fluoride taken. Of the various fluorides those of barium and lead seem to be the most promising. An objection to the use of ammonium fluoride is that, as usually made, it contains ammonium sulphate, so that insoluble sulphates might be formed and solution retarded. If sodium fluoride, as made from cryolite, were not so hard to purify, it would be well fitted for the analysis of silicates free from sodium. (B) By means of Hydrofluoric Acid. Professor N. S. Maske- lyne employs hydrofluoric acid for the analysis of refractory silicates. The process is conducted in an apparatus of the following construc- tion : A platinum retort, 80 c.c. in capacity, is fitted with a tubulated stopper of the same material, which reaches nearly to the bottom ; a small tube, entering the vertical tube of the stopper at an angle above the neck of the retort, conveys hydrogen to its interior. The vertical tube can be closed, either by a stopper of platinum or by a funnel of that metal, stopped in like manner at the top, and having a fine orifice at its lower extremity. To the side of the retort, just below its neck, a straight delivery- tube is fixed, which in its turn fits into another platinum tube that, after taking a curve into a vertical position, is enlarged into a cylinder which passes a considerable distance down a test-tube. The latter, into which the delivery-tube is fitted with a cork, holds 7'5 c.c., or 6'6 grammes of strong ammonia of the sp. gr. O f 88. The gas delivery-tube inserted in the side of this receiver dips into some more ammonia in a second test-tube. The pounded mineral, from 0'2 to 0'5 gramme in quantity, and a- small platinum ball, are placed in the retort, and the stopper luted to it with gutta-percha, and cemented air-tight in its place with caou- tchouc and gutta-percha varnish. The funnel, filled with perfectly pure hydrofluoric acid, is now introduced into the tubulure of the stopper, the tap opened, and the acid allowed to run down into the retort. This acid contains about 82 per cent, of absolute hydrofluoric acid that is to say, a funnel full of this reagent contains 1*12 gramme DECOMPOSITION OF SILICATES 607 of acid, capable of rendering gaseous 0-84 gramme of silica, and of neutralising O95 gramme of ammonia. The funnel is now replaced by a little platinum stopper, and the orifice secured air-tight with gutta-percha varnish. Pure hydrogen is then allowed slowly to traverse the entire apparatus ; the retort is placed in a water-bath at 100 C. for two hours, and occasionally slightly shaken to set the ball rotating. During the operation, a trace only of silicon fluoride passes over. The retort is next transferred to a paraffin bath, and the tempera- ture is cautiously raised. At first hydrofluoric acid passes over, and at this point of the process the flow of hydrogen requires some atten- tion to prevent regurgitation of ammonia. At about 130 C. the silica first becomes visible in fine flocks in the ammonia of the receiver, and in another minute the whole is cloudy. In eight minutes the rise of the thermometer to 145 C. has brought over so much silicon fluoride that the contents of the tube are semi-solid, and nearly the whole of it has passed over. The tem- perature is then raised to 150 C., and the retort allowed to cool. The process is next repeated with a fresh charge of acid and ammonia. If no more than O2 gramme of silicate be taken, twice charging of the retort is sufficient ; but with 0'5 gramme, three or four repetitions of the process are required. In short, the operation is continued, with fresh reagents, till no more flocks of silica form in the receiver. Finally, 0*75 c.c. of sulphuric acid is introduced into the retort, and the temperature again raised to 160 C., the stream of hydrogen being continued as before. The several ammoniacal charges are poured into a platinum dish, together with the washings of the delivery-tube and the two test-tubes, and slowly evaporated in a water-bath with continued stirring. At a point in the evaporation, just before the solution becomes neutral and the ammonium fluoride begins to turn acid, the entire silica in the dish will have been dissolved by the fluoride. The pro- cess is gradual, but the moment when the solution is complete is easily determined. Then, the dish being removed, potassium chloride is added in slight excess, together with absolute alcohol equal in volume to the contents of the platinum vessel. Potassium fluosilicate precipitates, and after the lapse of 24 hours it is filtered, washed with a mixture of equal volumes of absolute alcohol and water, dried, and weighed. The results are accurate. In the retort are the bases in the form of sulphates, the treatment of which calls for no further remark. Decomposition of Silicates in the Dry Way For Professor J. Lawrence Smith's process for the decomposition of alkaline silicates, see ante, p. 26. By Hydrofluoric Acid at a Red Heat. M. F. Kuhlmann treats 608 SELECT METHODS IN CHEMICAL ANALYSIS rsilicates at a dull red heat with a current of hydrofluoric acid. The apparatus for this process consists of a platinum retort, of which the body may be of lead ; the acid is produced in it by means of sulphuric .acid and white cryolite, or pure calcium fluoride. The neck of the retort fits tightly into a tube of platinum, which contains, in boats of the same metal, the matter to be analysed ; this tube, by means of .a short adapter, also of platinum, communicates with a condensing or absorbing apparatus ; this apparatus may be of vulcanised indiarubber. -One hour's heating suffices for the treatment of 10 grammes of mineral, Imt not more than 2 grammes should be employed. By Fusion with Caustic Alkali. (A) Mr. lies heats from 45 to 50 grammes pure potash in a large silver crucible until the mass has assumed a quiet fusion. (Capacity of crucible 70 c.c.) Upon the surface of the cooled mass 1 gramme finely powdered silicate is introduced, and the heat is gently applied, increasing the heat towards the end of the fusion, which rarely exceeds 30 minutes. Potassium manganate, silicate, and aluminate will be found, and the iron will remain as sesquioxide ; in short, much the same chemical reactions will ensue as when fusion is made in a platinum crucible with carbonates of the alkalies. There is, however, a marked difference in the time required for the performance of the process, and the rapidity of the disintegration of the fused mass when treated with water. The lead will not attack the silver crucible in the slightest degree ; this is not the case when platinum vessels are used, as has already been indicated. After the fusion has been completed, the crucible is allowed to cool and is introduced into a vessel containing just sufficient water to cover it, and the mass allowed to dissolve. The silicic acid is then separated as usual. It must be remembered, however, that fused potash or soda will slightly attack silver vessels, and one must take the precaution to wash the silicic acid with some one of the well- known solvents for silver chloride, as strong ammonia or sodium thio- sulphate. This, however, is rapidly and completely performed. The above mode of procedure has the following advantages : 1. Kapidity of execution. 2. Complete decomposition. 3. Obviating the use of gas. 4. Replacing the expensive platinum crucibles by less expensive silver ones. 5. Less liability to loss in the performance of the operation ; since by dehydrating the potash before beginning the operation, it continues quietly to its completion. (B) Mr. W. Bettell cautions chemists who use the process above given that silver crucibles are seriously attacked. He finds a platinum crucible lined with gold preferable, not merely for this operation, but for oxidation with nitre, fusions with alkaline bisulphates, and DECOMPOSITION OF SILICATES 609 fluorides, &c., provided the temperature is below the melting-point of gold. By Fusion with Baryta. M. A. Terreil attacks silicates with perfectly pure barium hydrate, fused and pulverised, using 7 to 8 parts to 1 of the silicate. The operation is performed in a silver crucible at 350, the temperature being raised a little when the fused mass has again solidified, but not so as to reach dull redness. The mass, after cooling, is boiled in pure water in the crucible, and the filtrate is treated with a current of well-washed carbonic acid, raised to a boil and filtered. The alkalies will be found in the filtrate. By Fusion with a Fluoride. Dr. F. W. Clarke l recommends that 1 part of the very finely powdered mineral should be mixed with 8 parts of sodium fluoride, and that this mixture, after having been placed in a platinum crucible, should be covered with 12 parts of powdered potassium bisulphate, and the whole raised to a red heat. Not only are silicates readily decomposed in this manner, but such minerals as chrome-iron ore, red haematite, tin ores, rutile, corundum, &c., are very readily brought to fusion and disintegrated by this flux, even with no more heat than that obtained from a good Bunsen gas- burner. By Fusion with Lead Oxide. Gaston Bong has proposed to open up silicates with lead oxide, decomposing the unstable compounds formed with nitric acid, and after eliminating the lead by means of sulphuretted hydrogen, proceeding with the analysis in the ordinary manner. This method offers great advantages, since melting lead oxide quickly decomposes the most refractory silicates, even if not in the finest state of mechanical division. By Fusion with Bismuth Subnitrate. W. Hempel in con- junction with Dr. Koch has made a number of experiments with this agent, and found it very difficult to prepare a chemically pure lead oxide. The red lead and the litharge of commerce were found always to contain silica along with other impurities. The preparation of chemically pure lead oxide from metallic lead by dissolving it in nitric acid and igniting the nitrate thus formed, involves great mechanical difficulties, since the lead nitrate melts before decomposing, and froths strongly, so that small quantities only can be obtained in each opera- tion. All these difficulties are overcome by substituting bismuth oxide for lead oxide, simply igniting the silicate in question with bismuth subnitrate. This compound is easily obtained in a state of the utmost chemi- cal purity, and it has the further advantage that it does not melt at its temperature of decomposition. The opening up can be per- formed in the smallest platinum crucibles, as the hyponitric acid liberated fumes slowly away and does not carry with it any of the substance. The resulting melt is dissolved in hydrochloric acid, whilst 1 Chemical News, vol. xvi. p. 232. B R 610 SELECT METHODS IN CHEMICAL ANALYSIS in the lead process nitric acid is required, which must be afterwards expelled. Repeated experiments have shown that it is advisable to work with a large excess of bismuth oxide, so as to have a very basic melt, which is easily decomposed by means of hydrochloric acid. The operation succeeds easily if \ gramme of a silicate is heated gently with 10 grammes of bismuth subnitrate till red fumes no longer escape, and is iinally kept in fusion for about ten minutes. The melt is poured as far as possible whilst still liquid into a platinum capsule floating upon cold water, and the mass thus obtained and the crucible are treated with concentrated hydrochloric acid. The solution thus obtained is evaporated to dryness for the elimination of silica ; the residue is taken up with hydrochloric acid ; the silica filtered off and washed with water acidulated with hydrochloric acid. On diluting the filtrate with water the greater part of the bismuth is precipitated as oxychloride. It is filtered off, washed, and from this second filtrate the remainder of the bismuth is precipitated by means of sulphuretted hydrogen. The further treatment of the filtrate is effected in the ordinary manner. In order to throw a light upon a possible error due to the volati- lisation of the alkalies at the melting temperature of bismuth oxide, a felspar was decomposed by this method, and by the hydrofluoric process. The results were : With bismuth Potash 7-60, 7'70 Soda 471, 4-72 With hydrofluoric acid Potash 7-86, 7'77 Soda 4-70, 4-84 The operation can be safely conducted in a platinum crucible if care be taken that it is not in a reducing atmosphere. If reducing gases are present, metallic bismuth is formed, which destroys the crucible. Silicates which contain organic matter must first be ignited with access of air. A number of meltings have been performed in the same crucible, which suffered no injury. As bismuth is a costly metal, it is prudent to work up all the preci- pitates into subnitrate. This may be conveniently done by melting the residues and the filters along with soda in a Hessian crucible, dissolving in nitric acid the metallic bismuth thus obtained, and precipitating the solution with water as a basic nitrate. The decomposition of silicates should be effected under a draught- hood, as the bismuth oxidises slightly at the melting-point, and the vapours seem to be very poisonous. Separation of Silica in the Analysis of Limestones, Iron Ores, &c. (A) The .mineral is decomposed by hydrochloric acid, evapo- DECOMPOSITION OF SILICATES 611 rated to dryness, and then treated with hydrochloric acid and water. Silica in the insoluble condition, and the bases as soluble chlorides, are thus obtained/ and these are separated by nitration. Many silicates, however, do not yield to this treatment, prominent among them being clay. This aluminium silicate is hardly ever ab- sent as a more or less intimate admixture in such samples of limestones, iron, and manganese ores, and other minerals, as are used for manufac- turing processes. Consequently, if silica be present in the form of clay, or any other non-decomposable silicate, the insoluble residue referred to above is not pure silica, but contains alumina or other bodies. (B) Dr. Percy, in the analyses of British iron ores which were made in his laboratory, and are given in his ' Metallurgy of Iron,' examined separately the soluble and the insoluble part of the samples. On referring to these tables, it will be found that the insoluble residue is, with one exception, never pure silica, but contains alumina, and mostly also other bases. If the quantity of insoluble substance be small, say below 2 per cent., and iron and certain rarer bodies are known to be absent, we may safely, unless absolute accuracy is re- quired, treat it with hydrofluoric and sulphuric acids, ignite, and assume the difference to be silica, the residue being alumina. If the appear- ance of the insoluble matter be that of pure quartz, we may take it to be all silica. (C) For more accurate analysis, however, and when the insoluble residue is considerable in quantity, either the whole of the sample under treatment, or the insoluble part, must be fused with sodium carbonate, or some other basic flux, in 'order to obtain a more basic compound, which is readily decomposed by hydrochloric acid. This way of pro- ceeding has two drawbacks, which, whenever possible, are eschewed by the analyst, viz. considerable expenditure of time, and the introduc- tion of a large quantity of foreign matter into the substance under examination. (D) Mr. H. Rocholl proposes to utilise as flux the bases present in the mineral itself. He prepares by mere ignition, a basic silicate decomposable by hydrochloric acid. As regards limestones, specimens have been successfully treated containing up to 21*2 per cent, silica and 6'5 alumina, care being taken to prove the purity of the silica obtained. In this case the same por- tion of the finely powdered sample which has served for the estima- tion of water and carbonic acid by ignition in a platinum crucible is utilised. It is transferred into a dry basin, and carefully treated with a little water ; the lime left in the crucible is then washed into the basin with water and hydrochloric acid, and more acid is added until solution has taken place. The evaporation to dryness is then quickly effected, as only small quantities of liquid have to be employed. The silica obtained is perfectly pure. E R 2 612 SELECT METHODS IN CHEMICAL ANALYSIS (E) For the analysis of ores a somewhat more circuitous procedure is necessary, as the sample after ignition has to be re-weighed and re- powdered. Weigh out into a tared platinum crucible a quantity of the finely powdered sample, something more than what is required for actual analysis : then ignite, at first gently, afterwards for about 20 minutes, to nearly a white heat, either in a good muffle or within a clay jacket over a strong blowpipe flame. An incipient fusion should take place. Weigh and carefully detach as much as possible from the crucible : this will be effected easily if the substance before ignition had been pressed into one corner of the crucible, and not spread over the bottom. The mass will be found exceedingly hard, and is best treated by being at first roughly powdered in a steel mortar and then finished in an agate or wedgewood mortar. In weighing out a portion for analysis, an allowance may be made in proportion to the loss sustained in the ignition, so that subsequently calculations may be made on the weight usually taken for analysis. The powder is then digested in a porcelain dish with strong hydrochloric acid. If the treatment has been successful, a clear jelly or solution will readily form, and the analysis can be proceeded with in the ordinary way. (F) The ignited silica may still contain certain impurities in small quantities. Titanic acid has to be looked for in certain iron ores, and barium sulphate in manganiferous ores ; indeed, Mr. H. Bocholl says he has met with a red hematite which contained 19 per cent, of the latter body. It is advisable, in the presence of baryta, to precipitate it completely as sulphate before filtering the silica. The ignited resi- due, on treatment with hydrofluoric and sulphuric acids, will leave the whole of it, the difference being silica. The residue may be examined for titanic acid by the known methods. The applicability of this method is limited by the percentage of silica. It was successful with ores containing up to 25 per cent, silica^ but not with an ore containing 31 per cent. The latter was a magnetic ore, containing 41 per cent, of iron ; the gangue consisted of quartz, greenstone, and garnet. In order to try if the want of success was merely owing to the excessive amount of silica, and not to the nature of the compounds in which it occurred, to a fresh portion 50 per cent. of ferric oxide was added, so bringing the silica down to about 21 per cent. After ignition, a mass was obtained which was readily decom- posed, even in rough lumps. Calcined Cleveland ore, a very heterogeneous mixture of numerous compounds, which does not even yield the whole of its iron to hydro- chloric acid, is readily decomposed after semi-fusion of the finely powdered sample. The platinum crucible, after use, is best cleaned by fusing some sodium carbonate in it. Although hydrochloric acid slowly dissolves FERROUS OXIDE IN SILICATES 613 whatever adheres to the sides, its use is better avoided on account of the possible presence of manganese. The idea of letting the base contained in the mineral act as a flux for its impurities seems so readily to suggest itself, that other chemists may have been employing it, particularly for limestones, where its advantages are greatest. Estimation of Ferrous Oxide in Silicates. (A) W. Earl pro- ceeds as follows : About 2 grammes of the finely powdered mineral are placed in a deep platinum crucible, and 40 c.c. of hydrofluoric acid (containing about 20 per cent.) are added. The whole is heated to near the boiling- point, and occasionally stirred with a platinum wire until the disinte- gration of the silicate is complete, which usually takes place in about ten minutes. 10 c.c. of sulphuric acid diluted with an equal volume of water are now added, and the heat is continued for a few minutes. The crucible and its contents are then quickly cooled, diluted with water which has been freed from oxygen by previous boiling, and the ferrous salt present is estimated by titration with potassium perman- ganate or bichromate. It may be remarked that hydrofluoric acid which has been prepared in a leaden vessel invariably contains sulphurous acid. In order to render such acid fit for use, potassium permanganate must be added until the colour just ceases to be discharged. In the analysis of a large number of trap-rocks, it was found that in every case a far larger percentage of ferrous oxide was obtained by dissolving the mineral in hydrofluoric acid than by fluxing it with sodium and potassium carbonate. Thus, in the analysis of a trap-rock which contained 1*2 per cent, of manganous oxide, 5*73 per cent, of ferrous oxide was obtained by solution in hydrofluoric acid, whereas the method of fluxing only yielded 1*3 per cent. (B) W. Knop gives the following method for separating the alkalies in silicates from ferric oxide, alumina, lime, and magnesia. If in dissolving a siliceous mineral we employ a mixture of fuming hydrochloric acid and hydrofluoric acid, everything dissolves during evaporation to a clear liquid, but on further concentration hydrochloric acid escapes, and the alkaline silicofluorides reappear along with the iron, aluminium, calcium, and magnesium chlorides. If a silicate contains a quantity of silica equal to its proportion of alkaline metals, or if, supposing the silica to be insufficient or totally wanting, we dissolve the substance in 10 to 20 c.c. of water and a few c.c. of hydrochloric acid, and add a corresponding quantity of silica, we can convert its alkali metals completely into silicofluorides, by adding the requisite quantity of fuming hydrofluoric acid and evaporating. The alkaline silicofluorides are absolutely insoluble in a mixture of ether and absolute alcohol strongly acidified with hydrochloric acid. 614 SELECT METHODS IN CHEMICAL ANALYSIS Hence the alkaline silicofluorides may be precipitated from a hydro- chloric solution in the form of a crystalline deposit by the addition of ether and absolute alcohol. But if the hydrochloric solution contains also iron, aluminium, calcium, and magnesium chlorides, the alka- line silicofluorides are deposited, not in a pure state, but in combina- tion with small quantities of the above-mentioned metals, the bulk of which, however, remain in solution as chlorides. The process is carried out as follows : The weighed substance is mixed in a platinum crucible with a few c.c. of water, and in case of need with a corresponding quantity of silica. A sufficiency of hydro- fluoric acid is then added and all the liquid is evaporated off. The dry residue is covered with 2 to 3 c.c. of fuming hydrochloric acid, upon which it is readily detached from the crucible. It is washed into a beaker by means of an alcohol washing-bottle, using 25 or at most 50 c.c. of absolute alcohol for washing out the crucible ; the acid liquid is allowed to act for some time upon the precipitate. 100 c.c. of ether are then added, and the whole is allowed to stand for 12 hours. The ethereal liquid is poured off from the precipitate, and the alka- line silicofluorides are brought upon a filter by means of an alcohol washing-bottle. The use of a feather is admissible only at the begin- ning ; a glass rod is objectionable because it makes the precipitate adhere again to the inside of the glass. The precipitate may be trans- ferred easily if the beaker is held in a sloping position over the filter, and a few c.c. of alcohol are ejected behind the precipitate so as to wash it into the filter. The filter is then washed slightly with alcohol, so as to remove the ether ; it is then dried, the precipitate removed, the paper is burnt completely in a platinum capsule ; the precipitate is added to the ash, mixed with concentrated sulphuric acid, allowed to stand for some time until the silicofluoric gas has chiefly escaped, and then ignited so long and at so low a temperature that the alkalies may remain behind as acid sulphates and be unable to react upon the silica liberated. The residue in the capsule is drenched with 10 to 20 c.c. of am- monia and evaporated to dryness, or at least to a paste-like condition. The mass takes again an acid condition by the loss of ammonia, and strong ammonia is therefore added drop by drop until the reaction is again alkaline. The mixture is then allowed to stand for an hour to allow of the complete separation of the ferric oxide and the alumina. Upon the pasty mass is then poured about 20 c.c. of a solution of ammonium monocarbonate (prepared by mixing 180 c.c. ammonia, sp. gr. 0*92, with 230 grammes ammonium sesquicarbonate and water enough to make up 1 litre), and allowed to stand for 12 hours in the covered platinum capsule. The quantities of ferric oxide, alumina, lime, and magnesia thus separated are so small that the entire precipitate may be collected upon ESTIMATION OF CLAY 615 a very small filter. It is washed with the smallest possible quantity of the above-mentioned ammonium carbonate. The filtrate is now exposed first for some time to a very gentle heat, a quantity of ammonium bitartrate corresponding to the ammonium sulphate present in the solution is added, the liquid is evaporated to dryness, and the residue is heated for some time in the air-bath to a temperature above 100. The object of adding ammonium bitartrate is to prevent spirting during the ignition of the ammonium sulphate. The residue is ignited till perfectly white, and weighed. It is then re- dissolved in hot water, mixed with 2 to 3 drops of the solution of ammonium monocarbonate, and set aside to see if any further deposit of iron oxide and alumina takes place. If this is the case the liquid is again evaporated to dryness. These supplemental deposits generally attach themselves so firmly to the platinum that a clear solution is obtained on drenching the residue with 10 to 20 c.c. of boiling water. This solution is decanted into a second platinum capsule in which the solution is evaporated to dryness and the capsule is again strongly ignited and weighed. It is recom- mended to add a few drops of sulphuric acid during the second, evaporation. Separation of Crystalline Silicic Acid, especially Quartz, when mixed with Silicates. E. Laufer takes advantage of the property of phosphorous salt to dissolve metallic oxides at a melting heat, and to isolate silicic acid from silicates without attacking quartz. To the finely powdered material weighed in a platinum capsule, phosphorous salt is added in a larger quantity than is required for the solution of the silicates supposed to be present, the crucible not being more than half full. It is gradually and cautiously heated in the air- bath, then melted, the heat being finally urged with the blast till the mixture is in tranquil fusion. The cold mass is easily separated from the crucible, and is then boiled for a length of time with dilute hydro- chloric acid, washed by decantation, and filtered, the silicic acid being then extracted from the residue with boiling soda. Estimation of Clay in Arable Soils. Th. Schhesing states that the separation of clay, sand, and calcareous matter by levigation is deceptive, since the last lot, supposed to contain the clay, includes in reality whatever is of extreme tenuity, whether sand, lime, or true clay. Two soils which give the same result by levigation may be exceedingly unlike if the last lot in the one consists of clay, and in the other of a mixture in which an extremely fine sand predominates. The author takes a sample of 5 grammes, previously freed from stones and organic matter, made up into a paste with a little water, and rubbed with the finger in a capsule. More and more water is gradually added, and the suspended matter is poured off. By constantly adding water and rubbing, nothing remains in the capsule but sand, which is rubbed until it yields nothing more to water, and is then thrown into the 616 SELECT METHODS IN CHEMICAL ANALYSIS vessel in which all the washings and decantations have been united. The coarse sand is now separated in the ordinary manner by decanta- tion and washing, dried, weighed, and the calcareous sand and organic particles estimated in the ordinary manner. The fine sand, calcareous matter, and clay are now found suspended in 300 or 400 c.c. of water. Nitric acid is now added in small successive quantities, stirring re- peatedly on each addition until the lime is dissolved and the liquid remains clear. The clay is, in fact, coagulated by the calcium salts formed, but the same clearness is noticed when the soil is quite de- prived of calcareous matter. It is due to the presence of free acid. Traces of hydrochloric, nitric, or sulphuric acid have the power of coagulating clay as decidedly as calcium or magnesium salts. After this treatment with acid, the mixture of clay and fine sand is filtered and washed. As soon as the calcareous salts and the free acid are eliminated, the filtrate passes turbid, and filtration becomes difficult. The clay has then resumed its property of diffusion in pure water. The whole is then washed out of the filter into a precipitating-glass of '2 litres capacity. Upon the mixture we pour 1 to 2 c.c. of liquid ammonia and digest for 1 hour. The glass is then filled up with pure water, stirred, and set aside for 24 hours. After this time the amount of fine sand remaining suspended is unimportant. The clay- liquid may be then drawn off by means of a syphon. The residue is washed into a capsule, weighed, and dried. It is fine sand, but is generally confounded with clay. On its surface there is generally found a brown coating, which contracts as it dries and separates from the sand. It consists of organic matter rich in iron oxide. The argillaceous liquid is coloured by a compound ammonium, iron and aluminium humate. On neutralising the ammonia and acidifying slightly, the clay and the organic matter fall together. To separate these two colloids as far as possible, a few grammes of sal-ammoniac are dissolved in the alkaline liquid. The clay coagulates whilst the humate remains suspended. When the liquid has become clarified by standing, it is decanted as far as possible ; the rest, along with the clay, is thrown on a tared filter, dried at 100, and washed. 617 CHAPTER XIV ELECTROLYTIC ANALYSIS 1 FOE measuring the strength of an electric current, the spring gal- vanometer of Kohlrausch is especially adapted. In the laboratory of the Technical High School at Aix-la-Chapelle, instruments are used with a scale graduated from to 2 amperes, enabling the subdivisions of the ampere to be read off. Hitherto most chemists who have been engaged in electrolytic work have expressed the strength of currents in chemical terms, i.e. in c.c. of detonating gas ; and for measurement, they have made almost exclu- sive use of the voltameter. It is a known fact that the detonating-gas voltameter is quite use- less for scientific measurements, because among other things it requires for itself a considerable tension which, under some circumstances, may be much greater than that required for the experiment. Comparable results with detonating-gas voltameters are possible only when the platinum plates are both the same size and are placed at equal distances from each other, and when the concentration of the acid is the same. Further, the statements hitherto to be found in the literature of the subject relate exclusively to the measurement of the current before the introduction of the decomposition-cell, and not to a simultaneous intro- duction into the circuit of the voltameter (or galvanometer) and the decomposition-cell. If, in my experimental work described below, I have retained this manner of measuring the strength of the current, it has been done on account of its simple execution, and especially as a knowledge of the strength of the current obtained as above is fully sufficient for the purposes of quantitative analysis. As it will appear below, for the performance of a quantitative determination or sepa- ration, a quite definite strength of current is not required ; it always fluctuates within certain limits, so that in the majority of methods of determination several c.c. of detonating gas more or less per minute is 1 The contents of this section, on Electrolytic Analysis, are taken from the last German edition of Dr. Alexander Classen's Quantitative Chemical Analyses by Electrolysis, by kind permission of the author. 618 SELECT METHODS IN CHEMICAL ANALYSIS not of importance. It is only thus possible for electrolytic analyses to be effected without further difficulties. The indications or strength of currents given below are, of course, trustworthy, only on the assumption that the repetition of the experi- ments takes place under conditions as similar as possible (equal size and shape of the electrodes, equal respective distances, approximate concentration, &c.). If we wish to be independent of the shape of the electrodes, in addi- tion to a knowledge of the strength of the current, a knowledge is required of its density (i.e. the proportion of the strength of current to the polar surface on which the electrolysis takes place). If we call the density of the current D, the strength of the current I, and the polar surface of the electrode on which the metal is to be precipitated 0, then D =^' In this case the surface must be approximately determined. If we always use one and the same form of electrode, e.g. a platinum capsule as a negative electrode, it is convenient to know its surface, 011 filling it with liquid up to different heights. For the platinum capsule here figured and described below, there exists the following approximate proportion between surface (expressed in square centimetres) and contents (given in c.c.). Surface. Contents. Surface. Contents, square cm. c.c. square cm. c.c. 63 50 113 150 92 100 124 175 In the laboratory of the Munich High School, the proportion of the strength of current to the sur- face of the electrodes has been de- termined for a number of metals. The normal density of current to be used in each case is indicated as N.D 100 , referred to 100 square centi- metres of the polar surface upon FIG 31 which the metal is to be precipi- tated. For a surface of the size 0, the corresponding strength of current can be derived from the formula, I = (N.D 100 ) - n . luu If, e.g., for the separation of iron from a solution of the ammonium double oxalate N.D 100 = 0-5 ampere, then, if = 180 square centi- 1 ftO metres, the strength of the current in amperes = 0'5 x -=- Aft = 0'9. j.\J\J All the statements of the Munich laboratory refer, of course, to a simultaneous introduction of the ammeter and the decomposition-cell into the circuit. ELECTROLYTIC ANALYSIS 619 The Performance of the Analysis The performance of a quantitative analysis by electrolysis demands, above all things, the utmost cleanliness. As little as it is possible in galvano-plastic to produce any metallic coating upon an object if the latter before immersion in the bath has not been most care- fully cleaned, just as little can we carry out successfully a quanti- tative electrolysis if the metallic surface serving as cathode has not been previously rendered faultlessly clean and free from grease. The same precaution extends also to the metallic contacts of the elements, to the supports used in the introduction of the current, as otherwise an interruption or enfeebling of the current is unavoidable. From the nature of the case, it appears advantageous to make the surface of the cathode as large as possible, so that the metal deposited may adhere the better. If any metal separates from a solvent in a dense form as is the case in the electrolysis of double oxalates the increased possibility of oxidation of the metal by an enlargement of the cathode is unimportant. In the deposition of peroxides (i.e. lead or manganese peroxide), which altogether adhere badly, the size of the electrodes upon which the deposition is to take place plays a great part. To use platinum crucibles for electrolytic deposition is, therefore, admissible only where it is required to separate a few milligrammes, since, independently of the small surface of the cathode, the distance of the two electrodes from each other is not sufficient to allow of the separation of the metal in a dense form. On this account I use as negative electrode a platinum capsule (fig. 31) wrought out thin, about 35 to 37 grammes in weight, of 9 cm. in diameter, 4-2 cm. "deep, and containing about 200 c.c. The capsule is shown in the figure, half its true size. Capsules which in the course of time have become rough internally, scratched, or bent, cannot be used for electrolysis. Several metals are not deposited as well in hammered capsules as in such as are smooth and polished on the lathe. If, e.g., we use hammered capsules for the reduction of zinc from the double oxalate, there remains, after dissolving the zinc in acid, always a grey shade of platinum black, which cannot be readily removed even by melting potassium hydrosulphate, and interferes with future determinations in the capsule. On the latter account it is recommended to use for elec- trolysis capsules which are polished faultlessly smooth, and which are, above all things, thoroughly clean, and to reserve them exclusively for the purpose in question. As anode or positive electrode, I use moderately thick sheet platinum of about 4*5 cm. in diameter, which is fixed conductively to a rather stout platinum wire. It is desirable, in order, during the 620 SELECT METHODS IN CHEMICAL ANALYSIS electrolysis, so as to facilitate intermixture of the solution, to perforate the sheet platinum by means of a cork-borer. If this is omitted, it is found that by the union of a number of small gas-bubbles a larger bubble is formed beneath the anode, and bursts at the edge of the capsule, projecting out a certain quantity of the solution, which may possibly occasion slight losses. Quite recently I have used a positive electrode of the shape of the platinum capsule shown in fig. 32, 50 mm. in diameter and 20 mm. in depth. In order to secure a better circulation of the liquid and a more expeditious reduction, the electrode is perforated in five places. This form ' of electrode is especially suited for the determination of those FIG. 32. FIG. 33. metals which, under certain conditions, are disposed to deposit in a spongy form, as, for instance, cadmium and bismuth. For the reception of the anode and cathode there were formerly used, as suggested elsewhere, two special supports. I have combined these into a single stand (fig. 33) provided with a metal ring for receiv- ing the platinum capsule, and to which there are riveted three short contact rods of platinum, and an insulated arm, a, of glass intended to secure the positive electrode. The use of this stand has, however, the disadvantage that the brass support to which the ring and the glass arm are secured is strongly attacked by the fumes in the laboratory, which may occasion intermp- ELECTROLYTIC ANALYSIS 621 tion of contact during electrolysis. For some time the stand (fig. 84) has proved very serviceable. The ring and arm are fixed moveably FIG. 35. to the glass rod G ; n is connected with the negative, and p with the positive pole. The positive electrode itself is secured at e. If it is FIG. 36. FIG. 37. desired to use, instead of a platinum capsule, a platinum cone for the separation of a metal, we fix on the glass rod two arms, as is shown in fig. 35. 622 SELECT METHODS IN CHEMICAL ANALYSIS This arrangement is suitable if it is required to separate metals from acid solutions : the support, with the electrodes, is quickly lifted out of the liquid, immediately immersed in a glass filled with water, and the water is then removed from the negative electrode by washing with alcohol. If a platinum capsule is used, we may place it upon a metal tri- angle, and this again upon a beaker ; and after the decomposition is completed, the acid may be removed from the capsule by means of a stream of water. FIG. 38. FIG. 39. The electrodes proposed by the managers of the mines and furnaces at Mansfeld, and almost exclusively used there for the deter- mination of copper, are shown in figs. 36 to 41. According as larger or smaller quantities of a metal have to be determined, there is used either the cylinder of sheet platinum or the conical platinum jacket shown in figs.- 36, 37, both one-third their natural size. As a positive electrode, there is used either a thick platinum wire, coiled spirally as in fig. 38, or the electrode shown in fig. 39. The arrangement of the several parts, when two stands are used ELECTROLYTIC ANALYSIS 623 instead of the support described, can readily be understood from figs. 40 and 41. Herpin uses, in the execution of electrolyses, the apparatus shown FIG. 40. in fig. 42. The platinum capsule P, resting on the tripod F, is con- nected with the negative pole, and the platinum spiral, S (shown separately in fig. 43), is connected with the positive pole. In FIG. 41. order to prevent loss by spirting, the capsule is covered with the glass funnel T. Riche uses, as a cathode, a platinum cone of the form of a crucible open at both ends and provided with a handle. In order to facilitate a uniform concentration of liquid, longitudinal openings are cut in the cone. It is then immersed in a platinum crucible so that the distance 624 SELECT METHODS IN CHEMICAL ANALYSIS from the sides is from 2 to 4 mm. The entire arrangement is shown in figs. 44, 45. FIG. 42. As for the performance of electrolysis, sulphates are best adapted for conversion into double oxalates, chlorides are less suitable, and nitrates are quite unfit. If chlorides have been used, and if a smell of chlorine is detected during electrolysis, we must gradually dissolve ammonium oxalate in the liquid until the odour disappears. For forming the double salts, there is used sometimes potas- sium oxalate, sometimes ammonium oxalate,. and sometimes a mixture of both salts. As hot liquids conduct the current better, the liquid is often heated before being submitted to electrolysis. In some cases, however, the execution of the process requires a liquid of the ordinary temperature. For the performance of some determinations and separations it- is advisable to heat the liquid to be acted upon continually to a tem- perature not exceeding 50. The following experiments show the in- fluence of heat on the duration of the electrolysis. Approximately equal quantities of iron and of nickel were precipitated under closely similar FIG. 43. ELECTROLYTIC ANALYSIS 625 conditions (strength of current, concentration, &c.), in one case from a solution of about 50, and in another from a solution of about 15. FIG. 44. FIG. 45. IRON Taken Found Strength of Current Time required li. m I. ( 0-2385 1 0-2345 gramme )) FeA (cold) . (hot) . 0-2384 grm. FeA 0-2342 11 c.c. . 11 . 4 20 2 10 II. f 0-2246 1 0-2369 H (cold) . (hot) . 0.2244 0-2369 10 . 10 . 4 10 2 15 NICKEL Taken Found Strength of Current Time required 1 h. m. ; T f 0-2660 ' i 0-2660 gramme Ni (cold) . 0-2660 gramme Ni (hot) . 0'2659 13 c.c. . 13 . 7 25 2 20 TT f 0-2660 > (cold) . 0-2661 13 . 7 30 1 0-2660 J (hot) 0-2660 13 . 2 20 From the above experiments, it appears that when using hot solu- tions the strength of the current may be considerably reduced when an acceleration of the process is not essential. s s 626 SELECT METHODS IN CHEMICAL ANALYSIS The instructions here given refer to solutions at the ordinary tem- perature, unless the contrary is stated. For heating the liquid to about 50 (the temperature must not, under any circumstances, be raised to that of ebullition, as otherwise the reduced metal would exfoliate from the platinum capsule, and consequently could not be determined) we use burners of the accom- panying form. Or the tube of a Bunsen bur- ner may be unscrewed and the luminous gas-flame burning out of the zigzag-shaped cutting is to be reduced to the height of a few mm. and used for heating the liquid. The distance of the capsule from the burner must be about 15 cm. In order to effect a uniform separation of the metal to be reduced, at all points of the capsule, the platinum surface should be uniformly heated. This may best be effected by means of a layer of thin asbestos paper, so cut out that the platinum contacts of the stand supporting the capsule may remain free. The use of asbestos paper also prevents the liquid from reaching ebullition. On a prolonged action of the current, the evaporation of a small quantity of the liquid cannot be avoided. In consequence, a part of the reduced metal is exposed to the action of watery vapour and air, To avoid the oxidation of the metal thus exposed, we pour from time to time a little water upon the glass covering the capsule, so that the metal is always covered by the liquid. When the precipitation is completed, the liquid in the capsule is poured, without loss, into a beaker ; the capsule is rinsed three times successively with about 5 c.c. of cold water, and then three times with pure absolute alcohol. The capsule is dried for 5 minutes in the air- bath at 70 to 90, allowed to cool completely in the desiccator, and its weight is then determined. Eeferring to Dr. Classen's work on Electrolytic Analysis, the following notes have been written by Dr. T. O'Connor Sloane : In Classen's work upon the subject, the voltage of the circuit is duly con- sidered, and an elaborate rheostat for regulating the voltage within somewhat crude limits (^ volt) is described. This is in one of the in- troductory chapters. The rheostat is for use with a 600 watt dynamo. But the author also mentions batteries, and describes his method of ELECTROLYTIC ANALYSIS 627 conducting determinations with these sources of electro-motive force. The current strength is then the standard, and it is determined by the volume of oxy-hydrogen gas which the current can liberate in a definite time. In other words, the amperage of the current alone receives direct attention. By using the same-sized electrodes, the author states, the conditions are kept sensibly the same. Here we have an indirect recognition of the influence of electro-motive force. But the attempted maintenance of the most uniform conditions is a poor reliance. The conditions will inevitably vary, and the temperature of the room and gradual change of the nature of the solution operated on will cause variations in resistance that will affect the difference of potential. To show how little regard is paid to voltage, we are directed in iron de- terminations to use two and sometimes three Bunsen cells. Any change in the number of cells in series would cause great variations in the voltage, in the case cited about 50 per cent. If the cells were kept in parallel, and any resistance, such as that of a voltameter, were in series with the decomposing apparatus, a great variation in voltage would even then ensue by changes in the number of cells. The object of these notes is to plead for a greater recognition of the influence of difference of electric potential in analytical work. The facts of the case are these : For the decomposition of every solution a definite and absolutely fixed voltage is required. The strength of cur- rent affects only the condition of the deposit. Thus a current of any number of amperes might be passed through acidulated water without decomposing it until the voltage passed a fixed point, when decomposi- tion would at once begin. A single gravity cell, large or small (sul- phate of copper, zinc-copper couple), cannot decompose water because its voltage is too low. The minutest bichromate cell will at once begin to decompose it, because its voltage is high enough. Again, the amperage of the current should not be broadly stated without reference to absolutely fixed conditions of electrodes. The proper way would be to state it as referred to unit area of cathode and anode. Probably the cathode reference would be all that is needed. As ordinarily put, the cathode is supposed to be a platinum dish of more or less definite size, filled with a variable depth of liquid, and the electrolytic gas set free in one or more minutes is given. All this tells nothing. It would seem obvious that a definite and absolutely fixed differ- ence of potential being required for the decomposition of each compound, the voltage could be made the basis for analytical work. It would be possible to effect successive separation of metals from the same solu- tion by modifying the voltage, starting, of course, with the lowest. How far the precipitation of mixed metals, so called alloys, would inter- fere with such attempts is not definitely recorded. It amounts to nothing to state, as is done, that a weaker current than is required for iron or some other metals, will precipitate copper. The strength of the s s 2 628 SELECT METHODS IN CHEMICAL ANALYSIS current has nothing to do with it. It is the difference of potential that affects the result. The varying of such difference corresponding in a general way with the strength of the current, as the operations were conducted, has doubtless occasioned the confusion. In stating the results of, or giving directions for, conducting electro- lytic separations, two factors should always be stated. One is the difference of potential, the other the amperage per unit area of cathode. Then something definite would be known. It seems probable that by working on these lines, some exceedingly interesting results in the way of double decompositions, as well as of separations, might be ob- tained. Should any such result be obtained as the determining of a series of potential differences available for separations of metals from single solutions, it would be highly interesting. The heat of combination of a vast number of compounds has been obtained and is readily reduced to volts, but such reduction is theoretical and does not accurately hold for all cases. The principal trouble would lie in the regulation of the voltage. But, at the least, there seems ground for research in the direction here suggested. GAS ANALYSIS 1 Analysis of a Mixture of Oxygen, Carbonic Acid, and Nitrogen (A) Introduce a portion of the mixture into a graduated tube over mercury, and note accurately the volume. To estimate the carbonic acid, pass into the tube, by means of a curved pipette, a small quantity of a concentrated solution of potash, and agitate several times until there is no further variation in the level of the liquid ; the carbonic acid will be absorbed by the potash. To obtain the volume very accurately, transfer the gas to a vessel of water so as to allow the alkali to fall out ; then retransfer the gas to another tube and estimate its volume, saturated with moisture. To estimate the oxygen, first introduce into the tube a concentrated solution of potash, then a little pyrogallic acid. Upon agitation, the oxygen is absorbed, and the nitrogen remains. The bulk of the latter gas may be obtained by taking the same precautions as in the former instance. After having removed the carbonic acid, phosphorus may also be employed to absorb the oxygen. The experiment may be performed in two ways : a. In the Cold. In the tube containing the gas (over mercury) pass up a long stick of moist phosphorus, the sides of the tube being 1 These methods are principally founded on instructions given by Drs. Gran- deau and Troost. GAS ANALYSIS 629 at the same time moistened. The oxygen combines with the phos- phorus, giving phosphorous acid, which dissolves in the water. At the end of an hour the absorption is completed. It may be known by the absence of white fumes on the stick of phosphorus. Kemove the latter, dry the gas, and measure its volume ; it will be nitrogen. b. With Heat. The analysis is effected much more rapidly in the following manner : In a curved tube containing the mixture of oxygen and nitrogen standing over water, introduce by means of an iron wire a small piece of phosphorus, so that it rests in the upper curved portion of the tube ; then remove the iron wire and heat the phosphorus, at first carefully, to volatilise the water which remains in the bend of the tube, and then rapidly, so as to inflame the vapour of phosphorus. A greenish flame will be seen to advance, gradually absorbing the oxygen of the air. When it has descended to the level of the liquid it dis- appears, and the experiment is terminated. Allow it to cool, and estimate the volume of the residual nitrogen. (B) The analysis of a mixture of carbonic acid, oxygen, and nitrogen may be effected with a little more accuracy in the following manner : The dry mixture being contained in a graduated tube standing over mercury, introduce a piece of caustic potash fixed to the extremity of a platinum wire, and slightly moistened. When the carbonic acid is absorbed, withdraw the piece of potash, and a simple observation gives the residual volume of the mixed oxygen and nitrogen perfectly dry. The residue is introduced into a mercurial eudiometer. Add to the mixture double its volume of hydrogen, and pass the electric spark. Water will be produced by the combination of the hydrogen and oxygen in the proportion of 2 volumes of the former to 1 volume of the latter. One-third of the diminution in volume, therefore, represents the volume of oxygen. The volume of nitrogen is obtained by difference ; it will be the excess of the original volume of the mixture over the sum of the volumes of oxygen and carbonic acid. The estimation of oxygen by the eudiometer is not exact unless this gas is present in tolerable quantity in the mixture. If there is only a very small proportion, it is necessary, in order to ensure complete com- bustion, to take the precaution to introduce into the mixture a suf- ficiently large quantity of oxyhydrogen gas, obtained by decomposing acidulated water with 3 or 4 Bun sen's elements. The gas should be passed through concentrated sulphuric acid in order to dry it. (C) For the estimation of oxygen in the gases escaping from the lead chambers Vogt uses an apparatus by which a known volume of the gas is collected after passing through a solution of potassium chro- mate and caustic lye contained in Liebig's bulb-tubes. He then adds to the gas a solution of ammonium- ferrous sulphate and ammonia enough to throw down all the ferrous oxide, by which the oxygen of the gaseous mixture is entirely absorbed. Water is then allowed to re- enter the apparatus, when the quantity absorbed indicates the volume 61)0 SELECT METHODS IN CHEMICAL ANALYSIS of oxygen which has disappeared. Or the precipitate of oxide may be redissolved in sulphuric acid and titrated with permanganate. The apparatus consists of an aspirator flask filled with water recently boiled. This aspirator is connected with the gas to be examined, and the water is allowed to escape. The apparatus is filled with the gas, which has been previously freed by a passage through the bulb-tubes from all gases except oxygen and nitrogen. There is a tube with a tap fixed to the flask for the introduction of the reagents. Mixture of Oxygen, Hydrogen, and Nitrogen (A) After having measured the volume of the mixture, absorb the oxygen by potash and pyrogallic a,cid, or by phosphorus, as already described at p. 628. Pass the remainder into a curved tube over mercury, and introduce into it a piece of compact copper oxide, 1 and heat it for about 20 minutes ; all the hydrogen is then absorbed ; the residue will be nitrogen ; it may be transferred to a graduated tube, and its volume- measured. After the absorption of the oxygen the hydrogen may be estimated by introducing it into the eudiometer with half its volume of oxygen. Two-thirds of the diminution of volume occasioned by the passage of the spark represents the volume of hydrogen. The nitrogen is given by difference. (B) The analysis may also be effected entirely by the eudiometer. Introduce the original mixture into the eudiometer, with twice its volume of hydrogen, and pass the spark. The volume of hydrogen which enters into combination will be two-thirds the diminution of volume, the oxygen being represented by the other third. This first experiment will therefore give the amount of oxygen. In order to ascertain the amount of hydrogen in the mixture, add to the residue of the first explosion half its volume of oxygen, and pass the spark a second time. Two-thirds of the diminution of volume will be hydro- gen. The excess of the sum of the volumes of hydrogen burnt in these two experiments over the volume of this gas introduced into the eudiometer represents the volume of hydrogen found in the original mixture. The nitrogen will still be given by difference. Mixture of Hydrogen, Marsh Gas, and Nitrogen Introduce the mixture into a mercurial eudiometer, with twice its volume of oxygen, and pass the spark. The free hydrogen and that in the marsh gas combine with the oxygen to form aqueous vapour, ' This oxide is prepared by fusing two parts of copper oxide with one part of lead oxide. The fused mass is run on to a plate of copper, then broken into pieces and preserved in bottles. GAS ANALYSIS 631 which condenses. The carbon becomes carbonic acid. The residue is therefore a mixture of nitrogen, oxygen, and carbonic acid. Pass these gases into a graduated tube, and after having observed the volume, absorb the carbonic acid with potash. The diminution of volume gives the volume of carbonic acid, which will be equal to the volume of the carburetted hydrogen originally present. If a little pyrogallic acid is then introduced into the potash, the rest of the oxygen is absorbed, and the volume of nitrogen is obtained as a residue. The amount of the hydrogen which existed in the free state in the original mixture is obtained by taking the excess of the volume of the original mixture over the sum of the volumes of nitrogen and marsh gas. Mixture of Sulphuretted Hydrogen, Carbonic Acid, and Nitrogen (A) The mixture is measured into a graduated tube standing over mercury. Introduce a solution of copper sulphate and agitate. The diminution of volume represents the amount of sulphuretted hydrogen present. (B) Bunsen recommends in preference for the absorption of the sul- phuretted hydrogen a ball of manganese binoxide impregnated with phosphoric acid. To obtain a ball of manganese binoxide which does not tend by reason of its porosity to absorb other gases besides sulphuretted hydrogen, Bunsen prepares by levigation a fine powder which is formed into a thick paste by a little water. This paste is then pressed into a mould round a platinum wire, the extremity of which is twisted into a spiral. The mould is then dried at a gentle heat, when the ball of binoxide is readily detached ; for greater pre- caution, the sides of the mould may be smeared with a little oil. The ball is then moistened several times with a syrupy solution of phos- phoric acid. The remaining gas, transferred to an appropriate tube, is then sub- mitted to the action of caustic potash, which absorbs the carbonic acid. The residue is nitrogen. Mixture of Hydrochloric Acid, Sulphuretted Hydrogen, Carbonic Acid, and Nitrogen When the exact volume of the mixture has been measured in a tube over the mercury, the hydrochloric acid is absorbed by a fragment of hydrated sodium sulphate fixed to the extremity of a platinum wire. To obtain these fragments fuse ordinary sodium sulphate in its water "of crystallisation, and dip the end of the platinum wire in several times. There adheres to the wire a small lump of the sulphate, which aug- ments in volume with each fresh immersion. 632 SELECT METHODS IN CHEMICAL ANALYSIS Then remove the sodium sulphate and measure the volume again. The diminution observed will represent the volume of hydrochloric acid gas. The sulphuretted hydrogen is absorbed by a ball of manganese binoxide soaked in phosphoric acid, and the carbonic acid is after- wards absorbed by potash. The residue gives the nitrogen. Mixture of Sulphurous Acid, Carbonic Acid, Oxygen, and Nitrogen (Gas issuing from Craters of Solfataras) The volume of the mixture being measured dry in a graduated tube over mercury, the sulphurous acid is absorbed by a ball of man- ganese binoxide impregnated with phosphoric acid. After having removed this ball and noted the diminution of volume, a fragment of potash is introduced to absorb the carbonic acid. The second dimi- nution of volume will give the carbonic acid. The oxygen can then be absorbed by potash and pyrogallic acid, or it may be estimated eudiometrically, as described at p. 628. The nitrogen will remain as residue. Sulphuretted Hydrogen, Carbonic Acid, Hydrogen, and Nitrogen (Fumeroles of Volcanoes) Commence by absorbing the sulphuretted hydrogen by introducing into the mixture a ball of manganese binoxide impregnated with phos- phoric acid. The absorption of the carbonic acid is then effected by means of a fragment of moist caustic potash. The hydrogen is then estimated as at p. 628, either by the eudio- meter, or by passing the mixture of hydrogen and nitrogen into a curved tube and introducing compact copper oxide into the upper part of the bend. By heating the part of the tube containing this oxide for a quarter of an hour, the complete absorption of the hydrogen is effected. The nitrogen will form the residue. Carbonic Acid, Carbonic Oxide, Hydrogen, and Nitrogen (Gas from Blast Furnaces where Wood is used) (A) After having accurately measured the volume of the mixture over mercury, absorb the carbonic acid with a fragment of caustic potash. Then estimate the carbonic oxide by introducing into the graduated tube a solution of copper subchloride in hydrochloric acid, agitate, and the absorption will be complete. (B) Instead of introducing the liquid itself, it will be better, as GAS ANALYSIS 683 Bunsen advises, to introduce a ball of papier-mache impregnated with this acid solution of copper subchloride. This experiment should be made over another separate mercurial trough, for the copper subchloride attacks and fouls the mercury. In withdrawing the ball impregnated with chloride, before reading off the volume, it is necessary to remove the hydrochloric acid vapours given off by the chloride. The estimation of the hydrogen can then be effected as already described, either by the eudiometer or by absorption with copper oxide. The nitrogen remains as a residue. Carbonic Acid, Carbonic Oxide, Hydrogen, Marsh Gas, and Nitrogen (Gas from the Mud of a Pond) First estimate the carbonic acid by means of potash, then with a ball of papier-mache introduce into the mixture a concentrated solu- tion of copper subchloride in hydrochloric acid. After the absorption has terminated, withdraw the ball of chloride and replace it by a ball of potash to remove the vapours of hydrochloric acid given off by the acid chloride. If the mixture which contains carbonic oxide also contains oxygen, the latter gas is estimated first by pyrogallic acid and potash. The estimation of the hydrogen and marsh gas is then effected eudiometrically, as already shown at p. 630. Sulphuretted Hydrogen, Carbonic Acid, Carbonic Oxide, Oleflant G-as, Marsh Gas, Hydrogen, and Nitrogen (Coal Gas) The mixture is first accurately measured in a graduated tube standing over mercury. The sulphuretted hydrogen is then estimated by means of a ball of manganese binoxide impregnated with phos- phoric acid. After removing the manganese binoxide and measuring the re- maining volume, introduce a ball of caustic potash, which absorbs carbonic acid. The carbonic oxide is estimated by means of acid copper sub- chloride. To estimate the olefiant gas introduce into the residue a frag- ment of coke soaked in a concentrated solution of anhydrous sulphuric acid in monohydrated sulphuric acid. The absorption of the olefiant gas takes place very rapidly ; the coke is then withdrawn and the acid vapours absorbed by potash. The estimation of the hydrogen and marsh gas is then performed as described at p. 630. The nitrogen remains as a residue. The olefiant gas, as well as the marsh gas and the hydrogen, may 631 SELECT METHODS IN CHEMICAL ANALYSIS also be estimated by the eudiometer. To effect this pass the mixture of these three gases and the nitrogen into the eudiometer with three times its volume of oxygen, and pass the spark. The free hydrogen, as well as that of the carburets, combines with oxygen to form water, whilst the carbon becomes carbonic acid. Then pass the residue of the combustion into a graduated tube, and estimate the carbonic acid with potash, and the excess of oxygen with potash and pyrogallic acid. The residue left after this double absorption gives the nitrogen. The volumes of olefiant gas, marsh gas, and hydrogen may then be obtained by a simple calculation. The reactions which take place show : 1. That the combustion of olefiant gas requires thrice its volume of oxygen, that of marsh gas double its volume, and that of hydrogen half only. 2. That the olefiant gas produces double its volume of carbonic acid, and the marsh gas its own volume exactly. Therefore, calling x, y, z the volumes of the olefiant gas, the marsh gas, and the free hydrogen, of which the sum is known and represented by c, we have 3x + 2y + - =a "2x + y = b x + y + z = c a and b are the volumes of oxygen employed, and of the carbonic acid produced volumes which have been determined by experiment. To find the values of x, y, and z, subtracting the first equation from the sum of the two others, we find c + b~ a; whence z- 2(6 + c a). Then subtracting the last from the second, we find x-2(b + c a) = b-c ; whence x = 3b + c-2a. The second equation then gives 7/ = 4a 56 2c. Rapid Analysis of Mixtures of Gases. In gas works and also in many iron and steel works, it often becomes necessary to make a number of analyses of mixtures of gases daily, which, of course, is only possible with simple apparatus. (4) The earliest and simplest form of apparatus was a tube for the estimation of carbonic acid, very much like an inverted burette, used by C. Stammer. (J5) This tube was further modified by F. M. Kaoult, who used two stopcocks, one above and the other below ; and to the upper stopcock- was attached a funnel, which serves to introduce the chemicals in solution for treating the gas. After treating the gas, Raoult washed out the chemicals used with water introduced through the funnel, and RAPID ANALYSIS OF GASES 635 the gas was measured by bringing the tube to a nearly horizontal position and allowing water to run in through the funnel. (C) Wilkinson modified this tube of Raoult by placing it in a wider tube having a stopcock below, and omitting the stopcock upon the lower end of the measuring tube. By this means he could adjust the pressure upon the gas by adding water to or drawing it from the exterior tube. But the difficulty with these methods is the necessity of washing out the chemicals used to absorb the various gases. For example, after treating a gas mixture with potassium pyrogallate, it is necessary to wash out all the pyrogallate before adding bromine to absorb the illu- minants ; otherwise the bromine is absorbed by the alkali before it can act upon the gas. (D) To obviate this difficulty and one or two others, Mr. Arthur H. Elliott uses the apparatus shown in fig. 47, next page. The tube A is of about 125 c.c. capacity, whilst B, although of the same length, holds only 100 c.c. from the mark D, or zero, to the mark on the capillary tube at c, and is carefully graduated into ^ c.c. The attach- ments to these tubes below are seen from the drawing, except that the stopcock i is three-way, with a delivery through its stem. The bottles x and L hold about one pint each. The tubes A and B are connected above with one another and with the funnel M, by capillary tubing about 1 millimetre in internal diameter. There is a stopcock at G and another at F, while the funnel M, holding about 60 c.c., is ground to fit over the end of F above. At E is a piece of rubber tubing uniting the ends of the capillary tubes, which are ground off square to make them fit as close as possible. In beginning the analysis of a mixture of gases, the stem exit of the three-way cock i is closed by turning it so that L and A are connected through the rubber tubing; the stopcocks F and G are opened, and water is allowed to fill the apparatus from the bottles K and L, which have been previously supplied. When the water rises in the funnel M, and all air-bubbles have been forced out of the tubes, the stopcocks F and G are closed, the funnel M removed, and the tube delivering the gas to be tested attached in its place. By now lowering the bottle L slowly, and simultaneously opening the stopcock F, the tube A is nearly filled with gas, and the stopcock F is closed. The tube delivering the gas is now removed, the funnel M replaced, the bottle L raised, the bottle K lowered, and by opening the stopcock G the gas is transferred to the graduated tube B. By placing the bottle L on a stand at about the level of the water in A, the level in B and in the bottle K can be adjusted to the zero point, and the stopcock G is closed. The excess of gas in A is expelled by opening the stopcock F and raising the bottle L. The gas remaining in the capillary tube between c and the vertical part is disregarded, or in very careful work it may be measured and an allowance made in not filling the tube B 636 SELECT METHODS IX CHEMICAL ANALYSIS quite to the zero mark, but usually it is too small to be worth notice. Having measured the gas to be tested, it is now transferred by means of the bottles K and L into the tube A, and the liquid chemicals- added by placing them in the funnel M and allowing them to flow i r ._, down the sides of the / \ I M / \ tubes slowly, care being taken never to let the liquids run below the level of the top of the vertical tube in the funnel. It is best to have a mark on the outside of the funnel at least J of an inch above the top of the level of the vertical tube, and never to draw the liquid down below this point. Having treated the gas with the reagent, it is transferred by means of the bottles to the tube B, to be measured. If the reagent gets into- the horizontal capillary tube, the passage of a little water from the bottle K will remove it r before transferring the gas. When the gas residue is in B, and the liquid in A has been adjusted at the mark c on the horizontal tube, the stopcock G is closed, the bottle K is lowered till the level of the water in it and that in the tube B are the same, and the reading is then made. The tube A is now filled with the reagent just used, and water. By turning the stem of the three-way cock i, so that it communicates with A, and also opening the stop-cock F, the contents of the tube can be run out, and water run through the funnel M to clean the tube for a new absorption. When the tube is clean, by turning the stopcock i, so that A and L communicate, the water is forced into A, and the whole is ready to receive the gas for fresh treatment. By this means the gas is removed from the action of the EAPID ANALYSIS OF GAS 637 water used to wash out the chemicals, and the chemicals are com- pletely removed from any interference with each other when treating a mixture of gases. In using this apparatus the solutions are added in the following order : 1. Potassic hydrate, to absorb carbonic acid (also sulphuretted hydrogen and sulphurous acid if present). 2. Potassium pyrogallate, to absorb oxygen. 3. Bromine, to absorb illuminants, like olefiant gas and acetylene ; and after the absorption is complete, and the bromine vapours cause an expansion, a little potassium hydrate is added, to absorb these vapours before the gas is transferred and measured. 4. Copper subchloride in concentrated hydrochloric acid solu- tion, to absorb carbonic oxide. After this absorption is complete the gas is transferred to the measuring tube, the contents of the tube A run out, the tube washed, and filled with water from the bottle L. The gas is now transferred to A, and treated with potassium hydrate solution to absorb hydrochloric acid vapours before the final reading is made in B. The treatment up to this point takes from 20 to 30 minutes, ac- cording to the amount of practice the operator has had with the apparatus. The gas residue still contains marsh gas, hydrogen, and nitrogen. By removing the funnel M, and attaching in its place a rubber tube communicating with an explosion eudiometer in a deep cylinder of water (both eudiometer and rubber tube being drawn full of water), a portion of the gas residue can be mixed with oxygen, exploded, and the contraction and the carbonic acid estimated, the marsh gas and hydrogen being calculated by the usual formula. The nitrogen is found by the difference of the addition of the other con- stituents and one hundred. The explosion tube is simply a tube like A without the lower attachment and the lateral capillary tube above, the funnel M being retained ; the two platinum wires are fused into the glass near the top to give the spark for ignition. It is only necessary to clamp this tube down upon a piece of cork in a vessel of water during explosion, and adjust the water-level in a tall cylinder of water when making the readings of contraction and absorption of carbonic dioxide. The whole analysis can be readily completed in 45 minutes, and with due care gives results that are practically correct. The great advantage of this apparatus over the single tube method is, that the gas is not submitted to the action of the water used to wash out the chemicals, which is found to reduce the volume of the illuminants by 2 per cent. Of course this method will not compare with the methods of Bunsen and others, where very delicate readings and nice precautions are taken, but it gives very good results for rapid work, and answers every purpose in everyday practice in a gas or metallurgical works. 638 SELECT METHODS IN CHEMICAL ANALYSIS The water used in the apparatus should be of the same temperature as the room in which the analysis is made, and by careful handling little or no chemicals get* into the bottle L. When working in a warm place the tube B should be surrounded with a water-jacket to prevent change of volume in the gas while under treatment. (E) Thomas M. Morgan has designed an apparatus which is simple in construction, and requires but a small supply of mercury. The eudio- meter tube A B (fig. 48) is drawn out at B until it has a diameter of 5 or 6 millimetres ; c D, a shorter piece of the same tubing, is sealed on at one side in the manner shown in the figure, and both tubes have corresponding millimetre scales etched upon them. The capacity of the divisions on A B must be known, and can be estimated by Bunsen's method. The same tube has platinum wires at A, and to B a piece of strong caoutchouc tubing is firmly secured and provided with a clamp, E, The apparatus is filled with mercury through F or c ; in the former case c must be closed with the cork, in the latter B F is compressed by the clamp E. If c D be kept closed with a cork, the gas may be introduced by a small funnel at F, when the apparatus is held obliquely over the mercury trough, with c D undermost ; or a delivery-tube may pass down c, while E is opened sufficiently to allow the displaced mercury to escape ; or should the gas be in a sealed tube, the latter is attached to F, E is opened for the expulsion of enclosed air, and the point is then broken off; if the gas is under pressure its admission may be regulated by stopping the end c with the thumb. Before measuring, the mercury in the short limb is brought to a proper level by allowing a sufficient quantity to flow out at B ; and that a known temperature may be quickly arrived at, the apparatus is placed vertically in a cylinder of water, the short limb being fitted with a long tube as shown in the figure ; the volume, temperature, and pressure are then read off. Any absorbent to which the gas may have to be submitted is placed in the short limb and caused to pass into the long one by allowing mercury to run out below until a sufficient quantity has entered ; the short limb is then filled up with mercury, closed, and by agitation the absorbable constituent is removed, or the apparatus may be allowed to stand the requisite time. c f? A D IT" cfe -f- 1 r ' s ^_ r= Nt ^B __X73I -| p a Jf H ^2. _tt2n!lP^^ FIG. 48. WINKLER'S APPARATUS 639 The absorbent is removed by means of a stout glass tube, G H, 1 millimetre internal diameter, and considerably longer than the eudio- meter ; one end has a strong caoutchouc tube and clamp attached to it ; the other, after being rubbed with a little grease, is inserted at F and tied sufficiently tight to prevent escape of mercury, and yet to allow of freedom of motion up and down. By gradually opening the clamp E, the air is carried out of this tube, and it is left filled with mercury. The clamp H is then closed, that at E is opened to its fullest extent, and the tube is thrust up until within 2 millimetres of the absorbent ; then, as a slow stream of mercury is allowed to descend, it is alternately raised into the liquid and pulled down below it. Portions of absorbent and mercury thus follow each other down the tube, but it is evident that if a proper propor- tion of the latter be not drawn in, the current will cease. After one or two trials it is not difficult to leave a meniscus free from liquid ; should any of the gas enter, it may be expelled again by quickly compressing the tube at the bottom. In order to obtain the residual gas saturated with aque- ous vapour of normal tension, a little pure water may be introduced and removed in the manner de- scribed. An estimation of nitrates and nitrites by Frankland's method may be made in this apparatus, and it can also be used in an organic analysis by Schulze's method. 1 The apparatus may be strengthened and made more convenient for manipulation by attaching it to a light wooden frame. (F) Clemens Winkler proposes the following apparatus. It con- sists of a two-limbed tube, fig. 49, one limb of which, A, can be closed air-tight by two slightly greased glass taps, a and b. This shut-off portion of the tube contains about 100 c.c., and it is once for all carefully measured, and the amount inscribed upon the glass. This tube, which we may call the measuring-tube, is graduated from tap to FIG. 49. 1 Watts' s Dictionary, 1st suppl. p. 143. 640 SELECT METHODS IN CHEMICAL ANALYSIS tap into cubic centimetres and decimal parts thereof, the divisions being carried out on the narrower parts of the tube close to the taps. The measuring- tube serves for the reception of the gas in question, and is filled with it by opening both taps, and drawing the gas through by means of an aspirator, until it is certain that all atmospheric air is expelled. The tap communicating with the aspirator is then first closed, and afterwards the one through which the gas enters. If the filling of the tube is not effected by means of an aspirator, but by connection with an apparatus in which the gas is generated, or with a gasometer, or under the pressure of a column of liquid, the outlet-tap of the measuring-tube is likewise closed first, and the entrance-tap last. The extra pressure is then got rid of by momentarily opening one of the taps, and the gas is thus brought in equilibrium with the external air. We have also to be satisfied that the gas to be examined is saturated with watery vapour ; this is effected by allowing it, before entering the measuring-tube, to pass through wet cotton-wool, which serves also to remove mechanical impurities, such as soot, flue-dust, &c. When the tube A has been filled, with the above-mentioned pre- cautions, the next step is the estimation of the several gaseous constituents by an absorptio -metric process. The limb B serves for the reception of the absorbing liquid ; it is selected wider or narrower as the case requires, and it is connected with the limb A by means of a piece of caoutchouc tubing. On pouring the absorbing liquid into the tube B, there is formed under the tap a, affixed to the measuring- tube, a collection of air, which must first be removed. For this purpose the tap is provided with two perforations ; the one is the ordinary transverse aperture, and serves to place both limbs of the tube in connection ; the other goes in the direction of the tap-handle, which terminates in a pointed tube, which again can be closed by means of a piece of caoutchouc tube and a pinch -cock. In this man- ner it is practicable to let out the included air through the longitudinal aperture of the tap a, and, when this has taken place, to prevent the liquid from escaping by means of the pinch-cock. This construction of the tap also enables the measuring-tube to be placed in direct com- munication with the external air. The different positions which may be given to the tap a are seen in fig. 50. Position a connects both limbs of the tube, position b connects B with the external air, and position c places the latter in connection with the measuring-tube A. After filling the measuring-tube with the gaseous mixture, the tap a is in the position b, and a cautious open- ing of the pinch- cock releases the enclosed air through the liquid in B. The gas and the liquid are now only separated by the tap a ; by turn- ing this round 90, it takes the position a, fig. 50. A communication between both limbs is thus effected, and absorption begins, aided by the pressure of the column of liquid. To expedite it, however, the support bearing the tubes is so arranged that they can be alternately WINKLER'S APPARATUS 641 placed either horizontally or vertically. Before being placed in a horizontal position, the tap a is placed in the position b, fig. 50, and the tube e, bent at right angles, is connected with the limb B, in order to prevent the escape of the liquid when the tube is inclined. In the horizontal position of the tubes the absorption is very active, as may be perceived if the tube be replaced in the vertical position, and the tap a reopened ; immediately a fresh quantity of liquid forces its way into the measuring- tube. This alternating inclination of the tubes, the tap a being closed each time, is continued until no further entrance of the liquid into the measuring-tube can be per- ceived a result which is mostly effected in a few minutes. It is now necessary to bring the liquid in the two connected tubes to the same level, which is effected by the exit-tap c, fig. 50. The volume of liquid which has entered into A represents the number of c.c. of absorbed gas, and when it is multiplied by 100, and divided by the total capacity of the measur- ing-tube, the percentage of the absorbed constituent is found. From the above it appears that only one gaseous consti- tuent, or the sum of several, can be estimated at once. If a complete analysis is required, as many apparatus can be used at once as there x are gaseous constituents to be estimated. The measuring- tubes are connected together with caoutchouc tubes and filled at once. The analyst has thus the advantage of operating upon a set of portions filled under the same conditions of temperature and atmospheric pressure, and equally saturated with watery vapour, so that the customary corrections for temperature may be dispensed with. The estimations take so little time that an alteration of the volume of the gas from a change of temperature is not to be feared. Care must be taken that the various absorption liquids have all the same tempera- ture. To regulate the temperature of the gaseous mixture, it is T T FIG. 50. 642 SELECT METHODS IN CHEMICAL ANALYSIS allowed to pass through a bottle of mercury, which is kept along with the absorbents. If it is required to estimate relatively small amounts of a gaseous constituent, a somewhat modified construction of the measuring-tube is needful. The lower part nearest to the tap a is made narrower, so as to admit of a more accurate graduation, say to ^ of a c.c. In this case the graduation need not be continued for the whole length of the tube. 1. Aqueous Vapour. All gases are saturated with aqueous vapour prior to measurement. The estimation of the water present is not necessary in every case. If it is required to find the amount of aqueous vapour in a gaseous mixture, concentrated sulphuric acid is used as the absorbent liquid. By inclining the tubes a few times, the gas is dried completely. Before reading off, the sulphuric acid is allowed to stand for a few minutes. If the gas under examination contains originally a certain amount of water, without being saturated, two estimations are required. One apparatus is filled direct with the gaseous mixture, without allowing it to pass through the tube filled with wet cotton-wool ; whilst another is filled with gas which has been thus saturated. The differ- ence which appears between the two subsequent measurements with sulphuric acid corresponds to the volume of aqueous vapour which the gas took up in passing through the damp cotton-wool. 108-7 c.c. air, treated direct with sulphuric acid, required O9 c.c. =0'82 volume -percentage of water. 106'8 c.c. air, saturated with aqueous vapour, required 2-3 c.c. sul- phuric acid =2' 11 volume-percentages of water. The water taken up for saturation amounted, therefore, to 2-11 0'82=1'29 volume-percentages. The estimation of oxygen in the air saturated with aqueous vapour yielded 20'44 per cent. ; consequently, the original unsaturated gas 100-2-11 : 100-0-82 = 20-44 : x x = 20-7 per cent, (measure) oxygen. Hence it follows that the air in question contained Oxygen 20-70 Nitrogen 78-48 Aqueous vapour 0-82 2. Carbonic Acid. The estimation of carbonic acid is not only very rapid, but yields results which, in point of accuracy, leave nothing to be desired. A moderately concentrated solution of the potassium hydrate is used as absorbent. 8. Nitrogen. The direct estimation of nitrogen has not hitherto been found possible. It is estimated from the difference, and, as a matter of course, the residue, representing nitrogen, is burdened with every error in the whole analysis. ESTIMATION OF SULPHUROUS ACID 643 4. Sulphurous Acid. The method employed for carbonic acid can be used in many cases where it is needful to ascertain the amount of sulphurous acid present in a gaseous mixture. The absence of carbonic acid and of other gases soluble in alkaline solutions must, of course, be ascertained with certainty ; otherwise the result would be found too high. For certain furnace gases produced without the use of fuel, e.g. by roasting pyrites in kilns, the potash process is directly applicable, since the error occasioned by the trace of carbonic acid present in the air supporting the combustion is too trifling to be appreciated. If, in a gaseous mixture under examination, the other gases absorb- able by potash -lye are present in addition to sulphurous acid, a solution of iodine in potassium iodide is used as absorbent, of the strength of the deci-normal solution used in volumetric analysis. It must be remembered that this liquid is also not quite without action upon carbonic acid, which it dissolves mechanically to some extent, as water does. This difficulty is got over by using a solution through which a current of carbonic acid has been passed for some hours. When the iodine solution penetrates into the measuring-tube, it is immediately decolourised, and it is only after repeated inclinations that an excess of iodine becomes perceptible within the tube. This excess must be present if the estimation is to be correct. If the liquid remains colourless, it is a sign that the solution of iodine employed is not sufficiently concentrated, and that in consequence a part of the sulphurous acid is not oxidised, but mechanically dissolved. The volumetric estimation of oxygen in gaseous mixtures is effected by means of a solution of pyrogallic acid in potash-lye. The liquid is prepared specially for each estimation by dissolving 1 to 2 grammes of pyrogallic acid in a little water, and adding about 100 c.c. of a tolerably concentrated potash-lye. The absorption is rapicj at first, but becomes slow towards the end. Hence it is prudent, after the action is apparently over, to leave the liquid still for some minutes in contact with the gas, turning the tubes occasionally. Before read- ing off it is necessary to wait till the brown froth has subsided. An estimation requires about 10 minutes. If, in a mixture containing oxygen, gases are present which are absorbable by alkaline liquids, such gases are naturally absorbed by the potassium pyrogallate. This is the case if carbonic acid is present. Under such circumstances, the carbonic acid present is estimated separately in one apparatus by absorption with potash-lye, and in a second the joint amount of oxygen and carbonic acid is absorbed by potassium pyrogallate, and the net volume of oxygen is then found by subtraction. If, in addition to oxygen, nitrogen, and carbonic acid, sulphurous acid be also present, we estimate : ,T2 />. ear ^* 644 SELECT METHODS IN CHEMICAL ANALYSIS By potassium pyrogallate, + C0 2 + S(X By potash-lye, C0 2 + S0 2 By iodine solution, SO., The residue is nitrogen. 5. Nitric Oxide and Nitrous Acid. The volumetric estima- tion of the lower nitrogen oxides is a matter of great importance. A saturated solution of green vitriol seems to have a sufficient ab- sorptive power for the volumetric estimation of nitric oxide, though the numbers obtained are not, so far, as constant as might be desired. The absorption of nitrous acid can be effected by means of concen- trated sulphuric acid. Whilst, however, we may assume with toler- able certainty that nitrous acid may be absorbed by means of sulphuric acid in gaseous mixtures containing nitric oxide, it is questionable whether, conversely, nitric oxide can be estimated by green vitriol in presence of nitrous acid. It appears that green vitriol absorbs nitrous acid also in not inconsiderable amount, whether by simple solution or by some chemical change being not yet decided. If this is confirmed, then in all cases where the two gases are jointly present, it will be requisite to estimate the nitrous acid direct in one apparatus by sulphuric acid, whilst the nitrous acid must be withdrawn from the gaseous mixture as a preliminary to the estimation of the nitric oxide by green vitriol in a second apparatus. This would be effected by passing the mixed gases through a washing-bottle filled with sul- phuric acid, previous to their admission into the measuring-tube. 6. Chlorine. The estimation of chlorine can be effected in most cases by means of a moderately concentrated solution of the potassium hydrate. The process is rapid, and can be recommended when no other gas capable of absorption by alkalies is present along with the chlorine. An admixture of such gases, especially of carbonic acid, is found when chlorine gas is evolved from a calciferous manga- nese. In such cases the chlorine must be absorbed by a liquid which has no action upon carbonic acid. A solution of iron protochloride, mixed with hydrochloric acid, answers the purpose satisfactorily ; it must, however, be previously saturated with carbonic acid, by passing that gas slowly through it for some hours. 7. Hydrochloric Acid. Potash-lye is employed with satisfac- tory results. If carbonic acid is simultaneously present, hydrochloric acid gas might possibly be absorbed by water previously saturated with carbonic acid. 8. Ammonia. The absorption of ammonia is most readily effected by means of dilute sulphuric acid. 9. Sulphuretted Hydrogen. A solution of potassium hydrate absorbs this gas rapidly and completely. If carbonic acid is simul- taneously present, the case is not free from difficulties. Pass the gaseous mixture through a washing-bottle filled with a concentrated solution of iodine previously saturated with carbonic acid ; in this the ESTIMATION OF CARBONIC OXIDE 645 sulphuretted hydrogen is oxidised and the sulphur deposited. The remaining gases, including the carbonic acid, pass on into the measur- ing-tube. The carbonic acid is then estimated in one apparatus, in the portion of gas thus freed from sulphuretted hydrogen, by means of potash-lye. A second apparatus is filled with the gas in its original condition, and carbonic acid plus sulphuretted hydrogen. It may here be remarked that sulphuretted hydrogen is advantageously col- lected over petroleum, by which it is not at all absorbed. 10. Carbonic Oxide. The discovery of a simple and accurate method of estimating carbonic oxide in a gaseous mixture is of the utmost importance for the right management of combustion under a variety of circumstances. The absorbent used is a solution of copper subchloride in hydrochloric acid. The subchloride for this purpose is obtained by precipitating cupric chloride with stannous chloride. The white crystalline precipitate is first repeatedly washed with cold water by decantation, then twice washed with strong alcohol, and finally once with ether. It is then dried at 80 to 90 C. in a current of carbonic acid. The white salt is preserved in air-tight bottles. It is easily and plentifully dissolved in hydrochloric acid, and if a spiral of copper wire is kept in the liquid, reaching from the bottom to the neck of the bottle, the latter being carefully stoppered, it may be pre- served for a long time free from change. The solution should not be too concentrated. A solution suitable for the purpose is obtained by saturating hydro- chloric acid at sp. gr. 1*11 with copper subchloride. The liquid absorbs the gas very greedily. The estimation of carbonic oxide in gaseous mixtures whose other constituents act neither chemically nor mechanically upon the copper subchloride offers no difficulties. Less easy is the estimation when other absorbable gases are present. The error which might arise from the presence of carbonic acid may be evaded by saturating the solution of copper subchloride previously with carbonic acid. Oxygen has a very disturbing influence, and must be removed before the estimation of the carbonic acid. This is effected by allowing the gaseous mixture, before its entrance into the measuring-tube, to pass through a Liebig's potash apparatus filled with the solution of pyrogallic acid in potash-lye. In this manner oxygen, carbonic acid, &c., are absorbed, and only carbonic oxide, hydrogen, and nitrogen passed on into the measuring-tube. The amount of carbonic oxide is then estimated in the gas so treated, while the oxygen, carbonic acid, &c., are estimated in separate portions of the original gas. Estimation of Nitrous Oxide A. Wagner has examined whether nitrous oxide could be estimated by means of its oxidising action upon an ignited mixture of chromium 646 SELECT METHODS IN CHEMICAL ANALYSIS sesquioxide and sodium carbonate in the absence of air, and was com- pletely successful. The nitrous oxide decomposed can be estimated either by the volume of the nitrogen liberated or by the quantity of sodium chromate formed, since 1 volume nitrous oxide yields 1 volume nitro- gen, and 1 part chromium oxide requires 0-3136 oxygen for conver- sion into chromic acid. The author found by special experiments that by heat alone, in the absence of the mixture of sodium carbonate and chromium sesquioxide, only 28'2 per cent, of the nitrous oxide is decomposed. A mixture of equal volumes nitrous and nitric oxide is entirely decomposed under the same conditions, giving up all its oxygen, whilst any excess of nitric oxide escapes unchanged. Estimation of Free Oxygen in Water Mr. C. C. Hutchinson gives the following account of a modifica- tion of Schiitzenberger's process. The reducing agent is sodium hydrosulphite prepared as follows : A concentrated solution of caustic soda, sp. gr. 1*4, is taken ; sulphurous anhydride is passed through it till the liquid is thoroughly saturated and smells strongly of the gas. The yellow liquid (which is kept cool during the process of saturation by immersion in cold water) is sodium bisulphite ; it in- creases slightly in bulk, and is reduced to the sp. gr. of about T34. 100 grammes (75 c.c.) of this solution are then briskly agitated in a flask with 6 grammes of powdered zinc, air being excluded ; a rise of temperature occurs, the bisulphite being converted partly into the hydrosulphite, together with the formation of sodium sulphite and zinc sulphite. After agitation for about five minutes, the liquid is allowed to cool ; 400 c.c. of water recently boiled are added ; 35 c.c. of milk of lime, containing 200 grammes of calcium oxide per litre, are also added, and the mixture allowed to stand until clear, when it is decanted into well-stoppered bottles and kept in the dark. The lime solution not only precipitates the zinc salt, but also renders the solution less ab- sorbent of free oxygen, although it acts very rapidly upon dissolved oxygen. Before use this is further diluted with three times its bulk of distilled water recently boiled. The liquid recommended by which the change of colour detects the completion of the process is either sodium sulphindigotate, or Coupier's aniline blue ; 10 grammes of the extract of indigo are recommended to be dissolved in one litre of water, the product being kept in well- stoppered bottles, also in the dark. An ammoniacal solution of pure copper sulphate is also recom- mended to be made, containing 4'46 grammes (or more correctly, 4'471 grammes) of the crystallised salt per litre. This is to be used for the standardisation of the above two solutions. Since the reducing agent is so sensitive to the presence of oxygen, it is necessary to make the estimations in an atmosphere of pure FEEE OXYGEN IN WATER 647 hydrogen. To insure the purity of the hydrogen, it is passed through a solution of silver nitrate, in addition to the sulphuric acid and the tube containing pieces of caustic potash. We begin by finding the volume relation between the indigo and hydrosulphite. The burettes of the apparatus are filled, one with indigo carmine solution, the other with hydrosulphite ; a rapid current of hydrogen is passed through the apparatus, a small quantity of warm distilled water added, coloured by the addition of a small quantity of indigo. We now add cautiously the hydrosulphite ; the blue solution turns first green, and finally to a clear yellow tint. If the whole of the air has been expelled from the apparatus, the yellow tint will remain unchanged ; the slightest trace of oxygen causes the surface of the liquid to become blue. A known volume of indigo (25 c.c.) is now added, and the hydrosulphite solution again run in until the yellow tint appears, indicative of the reduction of the whole of the indigo. The colour change is exceedingly sharp, one drop being sufficient to change the colour from green to yellow. If the solution be acid, the blue colour changes first to red, and finally the yellow tint appears. We next require to find the reducing power of the hydrosulphite in terms of oxygen, finding from this the amount of oxygen any volume of the indigo will yield. This being a stable solution, the hydro- sulphite (being liable to change) can be readily standardised at any future time. This reducing power can be found by finding the quan- tity necessary to reduce the ammonia copper solution, i.e. the amount which brings the blue solution to a colourless state, by the reduction of the cupric to cuprous oxide ; 10 c.c. of this solution yield 1 c.c. of oxygen (0 C. 760 millimetres pressure) to the reducer. 25 c.c. are operated on in a smaller apparatus similar to the one used for the water estimations. It was found, however, that the colour change in this plan is so indefinite and difficult, even to the practised eye, to detect, that the exact point cannot be determined with any degree of certainty. The method for the estimation of oxygen contained in a water is as follows. Owing to the change which the hydrosulphite under- goes, it is necessary that a comparison between it and the indigo should be made each day. After this has been done and the apparatus freed from air by means of the hydrogen, 200 c.c. of warm water (tem- perature about 50 C.) are then added ; 50 c.c. of indigo are now run in. This is usually effected in portions of about 15 c.c. at a time, decolour- ising each portion by means of the hydrosulphite, thus utilising this step for the comparison of the two reagents ; effecting thereby a saving of time and material. The liquid in the apparatus being now brought to the yellow neutral tint, a measured volume of the water under experiment is added 75 c.c. is a convenient quantity taking care that no air is admitted at the same time. The bleached indigo will now become re- oxidised, turning from yellow to blue, in proper- 048 SELECT METHODS IX CHEMICAL ANALYSIS tion to the amount of oxygen present in the water. The hydrosulphite is now cautiously added until we again arrive at the yellow tint, free from green ; a single drop of the reagent is sufficient to effect the colour change at the proper point. From the quantity used we find the amount of oxygen present in the 75 c.c. of water. The operation can be repeated over again on another volume of the water until the apparatus becomes inconveniently full. The temperature of the apparatus must be kept at about 50 C. by the addition of warm water at intervals ; the amount of hydrosulphite required becomes gradually less as the apparatus cools, giving the results too low. 649 CHAPTER XV MISCELLANEOUS PROCESSES AND GENERAL METHODS OF MANIPULATION Sensitive Reagent for Gaseous Ammonia Gustav Kroupa dissolves magenta in water, and adds dilute sul- phuric acid until the yellowish colour passes into a yellowish -brown. Unsized paper is saturated with this solution, and then appears yellow, hut if exposed to the vapour of ammonia it takes a crimson colour. The paper must be preserved in stoppered bottles. Standard Soda Solution Gerresheim has published an article on ammoniacal mercury com- pounds, wherein he calls attention to the pronounced basic properties of the so-called Millon's base, which is obtained by the action of am- monia upon mercuric oxide. He states that a soda solution to which hydrochloric and sulphuric acid, &c., have been added can be freed from these by shaking with Millon's base. Mercury is not found in the solution. This method has been employed in order to obtain a chemically pure standard soda solution from the ordinary so-called pure caustic soda, and we have found all that the author claims verified. The soda contained large quantities of chlorine, sulphuric acid, and also silicic acid, and carbonic acid. For 2 litres soda solu- tion about 80 grammes of Millon's base are employed. The chlorine disappears first, then carbonic acid, silicic acid, and sulphuric acid. The process is complete after about one week's standing, the mixture being shaken about once or twice each day. Allow the Millon's base to settle in the solution, and draw off with a syphon as required. Shaking from time to time removes any carbonic acid which in the course of time may be absorbed by the soda. Millon's base absorbs carbonic acid from. the air rapidly, and is also not easily filtered and washed. It is therefore not completely washed free from the last traces of ammonia, as it is preferable to remove these by the addition of a small quantity of mercuric oxide when the Millon's base is brought into the soda solution. New Form of Burette. Mr. P. Casamajor has been led to adopt 650 SELECT METHODS IN CHEMICAL ANALYSIS an entirely new form of burette, which is represented in figs. 51 and 52. It consists of a cylindrical tube closed at the bottom, and inserted in a stand or foot made of japanned tin. The cylindrical portion of this tin stand is only partially soldered on to the flat part, to allow the portion left free to act as a spring in hold- ing the glass cylinder tightly. The upper portion of the glass tube has the shape shown in fig. 51, to prevent the liquid from running out when the tube is inclined. Immediately under the curved portion of the burette is a beak, from which the liquid drops when the instrument is inclined and pro- perly turned. By making a trans- verse section through this beak we obtain figs. 53 and 54, which show the shape of the beak, and its posi- tion in relation to the stem for two positions of the tube. To allow the liquid to drop from the burette, it is inclined as in fig. 53, in which position the curved portion at the upper end prevents the liquid from pouring out. Keep- ing the tube inclined as in this FIG. 52. figure, we may either prevent the outflow of its contents or allow it to run with more or less rapidity. To effect this it is merely necessary to turn the instrument round its own axis, so that the beak may be either raised or lowered, as shown in figs. 53 and 54. When the beak is allowed to take the position shown in fig. 53, the liquid in the tube does not run out, while in the position shown in fig. 54 the drops run out quite rapidly. At some intermediate point it will be found .TIG. 54. . .. that the liquid runs out slowly in drops, which may be accelerated or retarded by turning the tube round its axis, but without changing the inclination of this axis. The motion imparted to the burette by holding it in the hand and simply turning it round its axis is an easy one for the operator, who is not obliged to watch the liquid in the instrument with any FIG. 51. NEW FORM OF BURETTE 651 degree of attention. As the liquid runs out of the burette it becomes necessary to incline its axis more and more, to keep a supply of liquid near the beak ; but there is no difficulty connected with this, as the liquid runs out with equal ease when the instrument is full to the mark as when it is nearly empty. When the changes which occur in the liquid under examination indicate that the operation is nearly ended, the liquid may very easily be made to fall in single drops by turning the beak down gradually, and raising it again with a sudden motion. This is easily learnt by a little practice, and does not require a close watch on the contents of the burette. The most convenient position for the operator is to hold the tube almost horizontally and to let the foot roll on a block of proper height, while the necessary motions are given to the instrument by holding it with one hand near its open end. This presents the additional advantage that the por- tion which becomes heated by the hand is not in contact with the liquid contents of the tube. Whenever it becomes necessary to lift the instrument, the beak should be previously raised by turning the tube, as otherwise a drop of liquid may escape and run down the side of the tube. After the operation is ended, the burette should be left in a vertical position for some minuies, to allow the liquid to run down before reading the indication of the scale. As the beak holds by capillarity a certain quantity of test liquor, it will be found convenient to keep it full when- ever the indications of the scale are observed. This beak usually becomes filled of itself at the time of filling the instrument with test-liquor. The open end of the burette may be provided with a lip on the side opposite to the beak, as shown in fig. 52. This is to allow the test-liquor to run out faster. Many chemists are unwilling to trust to volumetric analysis, for fear of the changes of volume which are due to changes of tempera- ture. They are, however, willing to use the solutions of this method of analysis, and they have adopted a gravimetric system, which consists of weighing instead of measuring their test liquors. For this manner of using test solutions the gravimetric burette represented in fig. 56 may be used. The manner of using this burette is precisely the same 652 SELECT METHODS IN CHEMICAL ANALYSIS as for the volumetric instrument, and it does not require any further explanation. The weight of test-solution used in an analysis is best determined by double weighing. The flask or gravimetric burette, containing a greater quantity of test-solution than will be required by the analysis, is placed on the scales and counterbalanced with shot or any other material. After the operation is ended, the flask should be replaced on the same pan of the scale and be made to counterbalance the original quantity of shot by adding weights, which represent the weight of test-solution that has been used. A common balance weighing iiOO grammes and turning to 1 centigramme is sufficient for this method of testing. Ammonia-free Water D. B. Bisbee has described a very easy way of obtaining ammonia- free water. It is to acidulate the water, before distilling, with sulphu- ric acid. The acid holds all ammonia in the retort, the first portions- even of the distillate being ammonia-free. But this acidulation natu- rally causes the nitric acid and nitrous acids in the water to distil over. For some purposes, however, nitrates are not objectionable. When it is desired to obtain chemically pure water for any use, take distilled water, which is nitrate-free, acidulate with sulphuric acid, and distil, at once getting pure water. Simple Method of estimating the Temporary Hardness of Water M. V. Wartha, in order to ascertain the alkalinity of spring waters on the spot, with samples not exceeding 10 c.c., and with a single reagent, makes use of a tube of 30 to 40 centimetres long, closed at the bottom,, and with a mark showing the capacity of 10 c.c. From this mark upwards the tube is graduated into O'l c.c. To estimate the tem- porary hardness the tube is filled to the lowest mark with the water in question, and a little piece of filter-paper, which has been previously steeped in extract of logwood and dried, is thrown in, thus giving the water a violet colour. Centinonnal hydrochloric acid is then added from a dropping bottle till the colour of the liquid inclines to orange. The tube is then closed with the thumb and well shaken. The greater part of the carbonic acid escapes, and the liquid becomes- red again. Acid is again added, and the shaking repeated until the next drop of the acid turns the liquid to a pure lemon-yellow, a point which with a little practice is easily reached. The amount of acid used is read off on the tube itself. The author proposes to express the alkalinity of a water by the number of centimetres of centinormal acid needed to neutralise 10 c.c. He thinks that this method will be found useful both for sanitary and geological purposes. NEW TESTS AND METHODS 653 New Test for Reducing Agents Mr. Edwin Smith has published a method of illustrating the de- oxidising property of sulphurous acid, by exposing a slip of bibulous paper, dipped in a mixed solution of iron sesquisulphate and potas- sium ferricyanide, to the vapour rising from a bit of sulphur burning in air. The iron persalt being reduced to a protosalt by giving up an equivalent of oxygen to the sulphurous acid, a blue reaction takes place with the potassium ferricyanide present in the solution. A solution of sulphurous acid, or of a sulphite or thiosulphate, gives the same result ; while only a very slight greenish tinge is imparted to the mixture by a sulphate, except in the case of iron protosulphate. With this exception, a useful test seems to be afforded between sul- phites and sulphates. The same test will discriminate a nitrite from a nitrate. To the mixed solution of iron sesquisulphate and potassium ferri- cyanide add a few drops of nitric acid ; then add a little of the solu- tion to be tested. If the latter contains a nitrite, a greenish-blue precipitate will begin to fall, and quickly increase ; if a nitrate, only a slight greenish tinge will be imparted to the test. Nitric oxide or nitric trioxide passed into the mixed solution throws down the same characteristic precipitate which is produced by the decomposition of a nitrite in the previous case. Carbonic oxide will act in the same way, and if a slip of paper dipped in the test- mixture be held over the clear part of a bright coal fire, it turns blue with the carbonic oxide or sul- phurous acid there given off. Again, if a bit of phosphorus is dropped into a little of the test-mixture in a porcelain dish, the phosphorus immediately becomes coloured a greenish blue, and on stirring about, gradually imparts the same tinge to the solution. Phosphorous acid may be discriminated from phosphoric acid, just as sulphurous acid is distinguished from sulphuric acid by the blue reaction. Phosphites are also distinguished from phosphates. A solution of phosphorous acid shows the reaction readily on being shaken up with the test- mixture. Lastly, if copper turnings are boiled in the mixed solution for a few minutes, a greenish-blue tint is imparted to it, which becomes gradually deeper with the oxidation of the copper and the consequent reduction of the iron persalt to the state of a protosalt. Improved Methods of Oxidation Professor Storer points out the superior oxidising power of a mix- ture of ordinary nitric acid and potassium chlorate over that of the mixtures of potassium chlorate and hydrochloric or sulphuric acid commonly used in analysis. 654 SELECT METHODS IN CHEMICAL ANALYSIS Blowpipe Analysis. Employment of Silver Chloride Amongst the phenomena which characterise different bodies before the blowpipe, and serve for their distinction, the colour of the flame is of no small importance, especially when the eye observations are supplemented by the use of a spectroscope. This power of colouring the blowpipe flame is not, however, exhibited by all bodies with suffi- cient intensity to enable them to be distinguished by it with certainty, and certain substances, such as hydrochloric acid, are consequently usually employed with barium, strontium, and calcium compounds, partly to form and partly to set free volatile compounds. By this means, however, although the intensity of the colouration is heightened, its duration is not increased, as the acid evaporates, for the most part, before it has acted sufficiently, so that the colouration lasts only for a, few moments. Dr. H. Gericke overcomes this difficulty by the employment, in- stead of the volatile hydrochloric acid, of a chloride which will retain the chlorine at a high temperature, so that it may only be set free by degrees in small quantities, whilst the body forming its base may be without action upon the colouring power of the body under investiga- tion. For this purpose silver chloride appears to be the best, especially as it may readily be prepared in a state of purity. The best plan is to stir it with water into a thick paste, and keep it in a bottle. In regard to the action of silver chloride upon the colouration of the blowpipe flame, the author has investigated several compounds of potassium, sodium, lithium, calcium, barium, strontium, copper, molybdenum, arsenic, antimony, and lead, and mixtures of these sub- stances. Silver chloride has no action upon borates and phosphates. Platinum wire does not answer well as a support, as it is soon alloyed by the metallic silver which separates, and is thus rendered useless. Silver wire is too readily fusible, and also is difficult to obtain free from copper, which may give rise to errors when in contact with the silver chloride. Iron wire is best fitted for experiments with silver chloride, as, from its cheapness, a new piece may be employed for each experiment, whilst the silver may be readily recovered in the form of chloride from the broken pieces. The results obtained by the employment of silver chloride in com- parison with those obtained without this reagent are as follows : With potassium compounds, such as saltpetre, potash, &c., the flame is decidedly of a darker colour with silver chloride ; and even with potassium ferrocyanide, which, when treated by itself with the blowpipe, colours the flame blue, the addition of silver chloride pro- duces a distinct potassium colouration. The action of silver chloride upon sodium salts is not so marked, although with some, such as sodium nitrate, common soda, and labra- BLOWPIPE ANALYSIS 655 dorite, the flame acquires a more intense yellow colour by the addition of silver chloride. This reagent produces no observable difference with other sodium compounds, such as sodium sulphate and analcime. This also applies to the lithium compounds, some of which give a finer purple-red colour 011 the addition of silver chloride, whilst upon others it has no such effect. With calcium compounds silver chloride acts favourably upon the colouring power. Thus, the addition of silver chloride to calcareous spar or gypsum (in the reduction-flame) gives the flame a more dis- tinct yellowish-red colour; but stilbite gives no calcium colouration either with or without silver chloride. With fluor-spar the coloura- tion cannot well be observed, as it decrepitates too violently under the blowpipe. The action of silver chloride upon barium and strontium compounds is decidedly advantageous, as both the intensity of the colouration and its duration leave nothing to be desired. Sicilian crelestine, which when heated by itself in the forceps scarcely colours the flame, immediately produces a permanent red colouration when heated with silver chloride. Although it appears from the preceding statements that the em- ployment of silver chloride presents no advantage with some sub- stances, it may be used with good results in the treatment of mixtures of alkalies and earths. Thus, with petalite alone, the lithium coloura- tion is first produced ; a slight sodium colouration is afterwards obtained ; whilst, with silver chloride, the sodium colouration appears very distinctly after that of lithium. With lithion-mica alone a very distinct lithium colouration is presented, but in the presence of silver chloride a colour is first produced, which may lead to the conclusion that potassium is present but the lithium colouration is weakened. Ehyacolite, heated by itself in the blowpipe flame, only gives a distinct sodium colouration ; but with silver chloride a slight potassium colouration is first produced, and the colouration of sodium then appears very distinctly ; the calcium contained in it cannot, however, be detected by the colouration of the flame, although evident in the spectroscope. Silver chloride may be employed with still greater advantage with the following metals, but in these cases it is particularly necessary that the operator should become familiar with the colour as well as the spectrum produced by each individual substance. With copper compounds, such as red copper ore, malachite, copper pyrites, copper sulphate, &c., when contained in other minerals so as to be unrecognisable by the eye, the employment of silver chloride may be of great service, as the smallest quantities of copper, when treated with silver chloride under the blowpipe, give a continuous and beautiful blue colour to the flame. With silver chloride, the presence of copper may be distinctly ascertained by the blowpipe, even in a 656 SELECT METHODS IN CHEMICAL ANALYSIS solution which is no longer coloured blue by the addition of am- monia. The employment of silver chloride will be equally advantageous with molybdenum, as in this case also the flame gains greatly in intensity. Arsenic, lead, and antimony are already sufficiently cha- racterised, the former by its odour, the two latter by their fumes ; but even with these metals silver chloride may be employed with advantage to render their reactions still more distinct. It is only necessary to observe that the greenish-blue flame of antimony appears greener and more like that of molybdenum under the influence of silver chloride. Silver chloride may also be employed with compounds containing several of the above-mentioned metals. If bournonite be heated in the oxidising flame of the blowpipe, a fine blue flame is first produced, which indicates lead with certainty ; if silver chloride be now applied, copper is also readily shown. The antimony contained in bournonite cannot be ascertained by the colouration of the flame ; but this may be easily detected upon charcoal or in a glass tube open at both ends. Native lead molybdate without silver chloride only gives a blue colour to the blowpipe flame ; with silver chloride this blue colouration of lead conies out more distinctly, but at the same time the tip of the flame, particularly when the reduction-flame is employed, appears of a beautiful yellowish-green colour from molybdenum. With mixtures of arsenic and copper, or antimony and copper, the flame first appears a greyish-blue or greenish-blue colour, from the oxidation of the arsenic or antimony ; the copper may be then very easily detected by silver chloride. This applies also to mixtures of arsenic and molyb- denum, or antimony and molybdenum ; with silver chloride the yellowish-green flame of molybdenum appears distinctly. It will be more difficult to analyse mixtures of arsenic and lead, or antimony and lead, in this manner, and if a compound contains both arsenic and antimony, .these two bodies are not to be distinguished with silver chloride under the blowpipe. Silver chloride is particularly to be recommended in testing metallic alloys for copper. Thus, to test silver for copper, silver chloride may be applied to the ends of silver wires, and on the application of heat the smallest quantity of copper will furnish a distinct reaction. This is as sensitive as any of the known copper reactions, and may be performed quickly and easily. In testing metallic alloys for traces of copper, it may be advisable to submit those which contain antimony, zinc, lead, and other volatile metals, to roasting, so as to drive off these metals before the addition of the silver chloride. Quantitative Spectral Analysis (A) M. Hiifner illuminates the two halves of the slit of the spectro- scope by two pencils of rays, one of which traverses the absorbent, NEW METHODS OF ANALYSIS 657 whilst the other can be darkened at pleasure. As a source of light a petroleum lamp is employed, placed in the focus of a lens ; half of the pencil of rays falls at the angle of polarisation upon a mirror, which throws it back upon a parallel mirror not tinned, placed before the upper portion of the slit ; a Nicol's prism fixed before the eyepiece serves to decrease the polarised pencil without acting upon the other. Before the lower part of the slit is fixed a double prism formed of a prism of transparent glass and one of smoked glass. It is rendered equal with the Nicol's prism, and the absorption corresponding with a given rotation is deduced once for all. This instrument gives very precise chemical indications. (B) M. Vierordt in 1871 proposed to divide in two the slit of the spectroscope ; the plates of the one portion of the slit being set in motion by micrometer screws, which rendered it possible to equalise the spectrum of a light viewed directly through the narrow portion, and the spectrum of the light after its passage through an absorbent transmitted by the other portion. The intensity of the light within the limits of experiment is proportional to the width of the slit. At present he substitutes for this arrangement two others ; in one the four plates of the slit are separately movable ; in the other, two of the plates are regulated by a screw, and move in opposite directions ; the two others are separately movable. The errors of measurement are very trifling. A New Method of Quantitative Chemical Analysis In comparing together the results of a large number of chemical analyses it is seen that the numbers obtained vary between 99-17 and 100-67, giving a difference of about 1-5 per cent., or, supposing a quantity of 1*5 gramme of substance has been taken and the weighings carried to O'OOOl gramme, a difference of 225 units. The analyses here alluded to are by no means those which would be called bad or indifferent, but are such as have been made and published by eminent chemists. It ought further to be remembered that very many analyses yield results varying from 97 to 102 per cent, instead of 100, whilst the really bad ones never see the light at all. Under ordinary circumstances slight differences do not usually affect the result of an analysis, but if it is desired to employ the sum of the substances found to control the results, an incorrect total fails to serve this purpose, as there is no means of knowing upon which of the substances the error really falls. Moreover, in many instances, only small quantities of material are available. A more accurate and improved method of analysis would admit of the employment of smaller quantities, as well as effect a great saving of time and labour. It would appear that neither the methods and processes in use nor the impurities of reagents are greatly at fault, because it is found that when the same substance is analysed under exactly the same u u 658 SELECT METHODS IN CHEMICAL ANALYSIS conditions the results often differ. It would therefore appear that accuracy depends chiefly upon the manipulations, among the most dangerous of which may be mentioned decantation, the removal of substances from a filter, the ignition of the filter-paper, and the calcu- lation of the ash ; the employment of a great number of vessels may either add something to solutions or withdraw something therefrom. Dr. H. Carmichael has proposed a very ingenious apparatus for overcoming these difficulties. His apparatus is represented in the accompanying figures. Fig. 57 (represented one-fourth of its natural size) consists of a doubly bent glass tube, with a funnel-shaped expansion at one of its ends, the wider part being perforated with a large number of small holes ; the other bend of the glass tube is fitted in the T-shaped tube BC D, closed air-tight at B by means of a vulcanised indiarubber ring ; the tube is fastened in the glass plate E F, and fitted air- tight by means of a similar contrivance to the one just mentioned ; E F is covered with a cap made of vul- canised caoutchouc, while between B and c a tube is fitted laterally, bent at D, at right angles (this part is not represented in full in the cut) and fitted with a small-bore vulcanised indiarubber tube closed by a spring clamp. The cap and the ring, B, should be touched with some grease. The .edges of a beaker can be readily rubbed on a piece of fine-grained and thoroughly smooth and level sandstone, to take off the vitreous glaze, so that a plate of ground glass may fit quite tight thereon ; this having been done, the cover E F (a ground-glass plate) may be fitted so tightly that it is possible to keep in the interior of the beaker-glass as good a vacuum as in the receiver of an air-pump. The filtering-bulb, A (fig. 57), being the most essential portion of this apparatus, its construction requires the greatest possible attention, and should be managed as follows : Take a glass tube having an inner bore of 2 millimetres, blow at one end a thick bulb (see A, fig. 58), flatten the bulb at the bottom, keep this bulb so hot that the glass is only slightly soft, and while in that condition make holes in it by means of a white-hot steel wire ; these holes should be close together. FIG. 57. NEW METHODS OF ANALYSIS 659 and not larger than 0'7 millimetre. The width of the edge, a b (fig. 58), differs according to the kind of filtering-paper which it is intended to use. For ordinary filtering-paper the width should be 3 millimetres, for Swedish paper a width of 2 millimetres is sufficient ; the perforated glass knob thus obtained is also ground slightly on sandstone. The tube to which the bulb is blown should be so bent as to make the leg B somewhat longer than the leg A ; the height of the bulb must not be great ; that is to say, it should be sufficiently Flo 58 flat to carry along with the air at the end of the filtration all the liquid into the beaker. The most suitable diameter of the bulb for general use is 2' 5 centimetres ; the number of holes ought to be 50, but a smaller number will do when the holes are connected together by means of small channels cut in the glass with hydrofluoric acid. The apparatus is connected with an air-pump by a strong india- rubber tube. The best air-pump is formed by the human lips, but direct experiments have proved that the power of suction of men varies from 10 to 695 centimetres of mercury, that is to say, from ^ to of an atmospheric vacuum. When the operator cannot suck above ^ atmosphere, or when disagreeable gases a,re to be worked with, the Sprengel pump or the aspirator should be used. Even when full atmospheric pressure is on, the thinnest filtering-paper will not be broken. In order to use the apparatus the air is pumped out, water being poured simultaneously on A. The rapidity of the current thus called into play effectually removes all impurities, and the water serves also to clean the beaker. This having been done, a circularly cut piece of filtering-paper, of the same diameter as A, is pressed against A. It remains fixed there, even when the apparatus is blown into ; a vacuum is again made while the filtering-disc is placed in the solution of the substance to be analysed, care being taken not to let the disc touch the bottom of the vessel in which that solu- tion is contained ; as soon as the solution is filtered off from the sediment, some pure water is added, the vacuum being still main- tained, after which the apparatus, with the precipitate adhering to it, is removed from the vessel in which the solution was con- ,, 9 tained, while any sediment therein remaining is transferred by careful manipulation into a previously tared crucible. Fig. 59 exhibits the mode of the connection of the apparatus with the air-pump. The bulb is placed in the vessel, and distilled water added for the purpose of washing the sediment thoroughly, the water running into the beaker (the vacuum being kept on) for the purpose of drying the precipitate by the current of air. This may be carried so u u 2 660 SELECT METHODS IN CHEMICAL ANALYSIS FIG. GO. far as to cause even gelatinous precipitates to shrink together. The spring clamp now being opened, air is admitted to the beaker, and the filtering-tube removed from the crucible as well as from the cover, E p. If the operation has been properly managed, the disc of filtering-paper remains on the top of the precipitate, the upper surface of the bulb remains clean, while only a very thin and small ring of the substance adheres to the lower edge of the bulb ; this sub- stance is removed by carefully holding a piece of filtering-paper flat in the hand and pressing it gently against the bulb ; turn the latter gently so as to rub all the substance on the paper, which, with the substance thus fastened to it, is thrown into the crucible. This having been done, the crucible, covered with its lid, is placed in an air-bath and heated to 105. At this temperature the precipitate becomes readily and rapidly dry, without any danger of spirting ; after which the crucible is ignited, first without the cover, until the very small quantity of paper is consumed, and afterwards with the lid on. Although a bulb of the size above named is sufficiently large for many substances, it is preferable to have another bulb of 3'5 centi- metres diameter for use with such gelatinous precipitates as alumina and iron peroxide. Instead of the platinum crucibles in ordinary use, it is for this purpose pre- ferable, though not indis- pensable, to use a platinum dish and cover, shaped as shown in fig. GO, and weigh- ing about 28 grammes. As the rapidity of the operations by this method makes it desirable to heat several crucibles at a time to 105, and since this re- quires an air-bath with a really good gas-regulator, those hitherto contrived being either of no use or somewhat expensive and too complicated, Dr. Car- michael has contrived the apparatus shown in fig. 61. Any one who has acquired some practice in glass-blowing may make it for his own use. Take a glass tube 40 centimetres long and 0'6 centimetre interior diameter, bend it as shown in the woodcut so as to admit of two of the bends being placed below the false bottom of the air-bath, and the third, the vertical bend, to pass through an opening out of the FIG. Gl. NEW METHODS OF ANALYSIS 661 bath, but so as not to touch the metal the bath is made of ; at a a glass tube of 2 millimetres interior diameter is melted on the wider tube, and shaped as shown at c ; this narrower tube is branched off into 2 parts, each so bent as to be on a level together. At d and e holes are made in these branches in such a manner as to form small nipples towards the outside, which are next nearly closed, and then connected together by means of an indiarubber tube ; the lower end of the wide glass tube is sealed, and the top opening closed with a cork, into which, through a carefully made hole, a thin and long gla? s rod is fitted ; the cork should extend to a b, so as to exclude air. This contrivance is entirely filled with mercury, and next freed from any adhering air and moisture by heating over a spirit-flame ; one of the open tubes at h and g is in connection with a gas supply-pipe fitted with a tap, the other open glass tube with a burner, while the openings at d and e are so small that the gas which may pass through them is too minute in quantity to heat the bath to any extent, whilst, at the same time, these openings serve to prevent the sudden extinguishing of the flame by the rapid expansion of the mercury. The apparatus is used in the following manner : The bath is heated by a gas-burner, until the thermometer connected with the bath indicates nearly the requisite temperature ; this having been reached, the glass rod, /, is pressed down into the mercury contained in the wider tube, until the mercury at a nearly touches the part c, which should be made as straight (not rounded) as possible. The sensitiveness of this contrivance depends, of course, upon the quantity of the mercury and its adjustment of surface ; but if the apparatus is made with care, according to the directions just described, the bath remains to a fraction of a degree at a constant temperature, even in a draught of air or with a change of pressure of gas. The cooling of the mercury in the narrow tubes prevents oxidation of the metal any- where in the tube. The following advantages are obtained by the use of the filtering- bulb : 1. The decantation of liquids is avoided. 2. The washing, ignition, and allowance for the weight of the filter- ash are entirely dispensed with. For, since the quantity of ash contained in a filter made of the best paper, and of 12 centimetres diameter, amounts to O0005 gramme, the ash contained in a disc of filtering- paper, as used with this apparatus, would only weigh 0*00002 gramme, and even if the paper were of a commoner quality it would make no difference. 3. The velocity of filtration is very great ; the water flowing into the beaker in so uninterrupted a current that it appears as if no paper disc were present. When precipitates are to be filtered off, the velocity is somewhat less ; but it is then far more rapid than by the ordinary plan, and not less rapid than by Bunsen's method. 662 SELECT METHODS IN CHEMICAL ANALYSIS 4. Since the filtering-tube dips under the liquid, no air can pass through the precipitate until it has been completely washed. 5. When a mineral has been dissolved, or when two substances have to be separated from each other, instead of, as is done by the ordinary method, placing them in a beaker to be further treated, the precipitate by this method remains in the crucible, and can be ignited directly after filtration. 6. This apparatus serves as a filtering-stand, and also as a syphon and pipette. 7. The whole apparatus may be readily kept free from dust, and, if required, any gas can be readily admitted to protect a liquid to be filtered from contact with air, while a boiling solution can also be readily filtered. 8. Even so small a quantity of substance as a couple of milli- grammes is sufficient for analysis. With so small quantities the entire precipitate remains fixed to the filtering-disc, and may be burnt on the lid of a crucible, while any other very small portion of the substance which may adhere to any part of the apparatus may be readily removed and estimated. 9. The use of this apparatus, and the employment of small quantities of substance for analysis, occupy only about one-third of the time as compared with that required for analyses done by the ordinary plan. As an instance of the advantage of employing this method of analysis, the author quotes the following : A mixture was taken of magnesia, potassium chloride, and common salt, adding thereto some hydrochloric acid so as to convert the magnesia into chloride, expelling any excess of that acid by a gentle heat. The dry saline mass was redissolved in water, and mercury oxide added. The mass was next gently heated in a covered crucible, until all the mercury was vola- tilised, and the dry residue again treated with water and filtered by means of the filtering-tube above described, by which operation the magnesia was left behind in the crucible. It was then dried in the air-bath and ignited. The solution of the alkalies was next treated in the usual manner with platinum chloride and alcohol, and the potassium platino -chloride, after having been separated from the liquid by the filtering- tube, dried at 105. The small filtering-paper disc, to which hardly a particle of the salt adhered, was removed, and the potassium platino-chloride, first ignited by itself alone, and afterwards with the addition of the paper disc ; the result being that the organic matter of the paper was sufficiently large to cause the reduction of the platinum to the metallic state. The materials left in the crucible were washed with hydrochloric acid to remove any trace of magnesia, and again ignited ; the platinum in the filtrate was also reduced to metal, and the sodium chloride present estimated in the usual way, care being taken to remove and estimate the very small quan- tity of magnesia by means of sodium phosphate, and to deduct the IMPROVED MODE OF FILTRATION 663 weight of the magnesia thus estimated from the weight of the sodium chloride. The results were as follows : Quantities taken Quantities found Magnesia . . . 0-0690 grm. . . 0-0688 grm. Potassium chloride . 0-1873 . . 0-1852 Sodium chloride . . 0-0876 . 0-0900 0-3439 0-3440 It appears that the magnesium chloride was completely converted into magnesia again, notwithstanding the small loss of this substance due to the solubility of some of it in the alkalies present ; that the quantity of the potassium salt found was deficient is accounted for by the fact that the salt was only washed with dilute alcohol, without any addition of ether to lessen the solubility of the potassium platino- chloride. The author twice analysed a portion of a mineral, skolezite, from Scotland, taking in the first case 0'985 gramme of substance, and in the other 0-0807 gramme, the result being that the percentage composition of the substance was found to be : i. ii. Silica . . , . 46-20 . . 46-35 Alumina . . . 26-28 . . 26-21 Lime . . . , 9-22 . . 9-17 Soda .: . . . 6-16 . . 5-10 Water 13-25 13-45 100-11 100-28 In reference to the difference of the quantity of water, the author observes that the substance had been kept for several months under a desiccator. It is clear that the principle of the apparatus above de- scribed may be applied to qualitative analysis, and also in technology on a larger scale, for which purpose a porcelain plate perforated with small holes may be used with a disc of filtering-paper. An Improved Mode of Filtration (^4) The method of filtering, in which Bunsen has availed himself of Sprengel's water-air pump, is a great improvement upon the simple paper system. But the pump is a comparatively costly apparatus, and not always suited to the position and circumstances of a private laboratory ; and as the same, or nearly the same, effects can be pro- duced by means which are in every chemist's hands, the plan here proposed may be convenient for some. The needs of chemists have caused the manufacture of a special paper fitted for most of their filtering operations. But in some cases the texture is too coarse, and in some too fine. When a large-sized filter is used, the ash is too uncertain, and too great for accurate quantitative 664 SELECT METHODS IN CHEMICAL ANALYSIS operations. A small size requires constant and long-continued attention in order to pass through it even a reasonably small quantity of filtrate, together with the requisite washings. (B] In a process described by Mr. Isaac B. Cooke, a quantity of carded cotton-wool, so small that the ash in commercial analyses may be generally neglected, will suffice for any ordinary filtration ; and a little experience enables the operator, by tight or loose packing, to adapt it to the coarsest or finest precipitate. A glass flask, of not more than about 800 c.c. contents, is fitted with a rubber stopper of soft and smooth surface, and of conical shape, so that the small end easily enters the neck of the flask ; but the larger end cannot be forced in even under considerable pressure. Through the centre of the stopper a hole is bored to admit of a glass tube of about -j3 ff inch internal diameter. The tube to be inserted should be about 6 inches long ; one end being fused to a very small opening, and the other slightly enlarged in funnel form. About 1 inch of the nearly closed end of the tube is passed through the stopper, fitting tightly ; and if an inch traverse the stopper 4 inches will be left out- side when the stopper is in its place. Into the funnel-shaped mouth of the tube a small quantity of the carded cotton-wool is packed with the tapering end of a wire not having too sharp a point. The cotton- wool should be lightly pressed in at first until it occupies a length of about J to | inch of the tube, and then may be pressed more tightly at the mouth according to the quality of the precipitate to be filtered off, leaving a spreading brush of about inch length projecting from the end. To put the instrument into operation a small quantity of distilled water is poured into the flask, sufficient, but not more than sufficient, to quite cover the inner convexity of the bottom. The flask is then placed over the lamp till the water boils freely, and all air is expelled from the flask by steam. During the boiling the stopper should be placed in an inclined position, the short end of the tube resting against the inside of the neck of the flask, so as partially to close it, but leaving space for the air and steam to rush out. Unless the mouth of the flask is thus partially closed during the boiling, a much longer time is required to drive out the air ; as if quite open a circulation takes place, cold air passing in at one side as steam is driven out at the other. When steam issues freely past the sides of the stopper, the flask may be taken from the lamp, and the stopper immediately pressed into its place and kept there by pressure until condensation begins. The flask is meantime inverted, and the tube with its brush of cotton- wool plunged into the liquid to be filtered, taking care that the wool is wholly submerged ; as if any portion be left dry protruding from the liquid, air will be drawn through it into the flask. As soon as the liquid is seen to be rising up the tube, the apparatus may be reared against a corner and left to itself. IMPROVED MODE OF FILTRATION 665 The filtration will proceed with more or less rapidity in proportion as the cotton-wool is packed lightly or solidly into the tube. When all the liquid has been drawn up, and the air is about to follow, a stream of distilled water from the wash-bottle may be driven upon the precipi- tate to wash it ; and as the last portion of this also passes up the washing can be repeated, and again as often as it is thought necessary. Lastly, the air following will leave the precipitate and the cotton- wool in a condition almost dry. The contracted orifice of the inner end of the tube secures it also free from liquid. It is generally advantageous to perform the filtration from a small porcelain evaporating basin of about 2^ inches diameter, supported on a cork ring. The liquid and precipitate can be gradually poured and washed into the basin as the process goes on. When it is completed the flask may be reversed, the stopper gently loosened, and the inner end washed by a stream from the wash-bottle into the flask. The cotton plug must now be carefully taken out by forceps over the evaporating basin, partially wiping the end of the tube in doing so with the clean portion of the plug, and the whole added to the precipitate. The forceps should be carefully wiped with a very small piece of cotton- wool, which may be further used with the forceps to complete the cleaning of the tube, and then also added to the precipitate. The basin, after being rapidly dried over the lamp, is ready for ignition. The precipitate cannot well be separated from the plug without loss ; but there are few cases in which it will be injured by being ignited with the same quantity of cotton of which the plug consists, or, at least, in which that injury cannot be remedied by re -ignition after treatment with nitric or sulphuric acid. On cooling, the basin and its contents can be weighed, and, after brush- ing out the ash, the basin alone ; the difference of course being the weight of the ignited ash. A flask of 100 to 150 c.c. capacity is usually sufficient for a filtra- tion ; but it is not safe to use one larger than 300 c.c. unless it be of a spherical shape without the flat or concave bottom, as larger ones are not always proof against the pressure. A spherical flask would be better also in respect of requiring a smaller quantity of water to drive out the air, and, therefore, also a shorter time to prepare it. In this case, however, if only a small part of the surface of the bottom is covered with liquid, care is required not to crack the flask during the boiling. If the stopper be pliable, smooth, and well-fitting, no air will pass FIG. 62. 666 SELECT METHODS IN CHEMICAL ANALYSIS between it and the neck of the flask during the operation. But the appearance of such leakage is simulated by the renewed boiling of the liquid in the flask in consequence of the diminished pressure. Unless the liquid has been boiled immediately before filtration, bubbles of air will constantly ascend the tube during the process. Yet the vacuum caused by the initial boiling will be so nearly completed that the filtration and washing may be continued if necessary till the body of the flask is nearly filled with liquid, and on reversion only a portion of the neck will be occupied with air. When a flask is found unexpectedly not to be large enough to con- tain all the liquid required by the washing, it is better to suspend the filtration before the flask is full, raising it out of the liquid to allow air to pass up the tube before reverting. The plug will then be in a dry state, and no portion of the liquid will run down the outside of the tube and be lost. Another flask in which the same stopper fits may be prepared by boiling, the tube inserted, and the filtration completed. Separation and Subsequent Treatment of Precipitates Mr. F. A. Gooch, impressed with the desirability of further im- provement in those processes of quantitative analysis which involve the use of dried filters, or the separation of filter and precipitate before ignition, has had the good fortune to succeed in devising and pre- paring a felt of anhydrous asbestos, which is capable of filtering liquids with a rapidity and efficiency at least as great as may be obtained by the use of good filter paper. It is light, compact, incombustible at the highest temperatures used in analytical processes ; is not acted upon by acids (excepting hydrofluoric acid) or alkalies ; is sufficiently coherent to resist entirely the disintegrating action of a liquid forced through it under the pressure of the Bunsen pump, and may, more- over, be prepared by a very simple process ; it is, in short, a filtering material which makes it possible to reach a high degree of accuracy in many analytical processes which hitherto have been none of the best, and to add to those already known new methods which previously have been impracticable. The mode of preparing and using the asbestos felt is as follows : First. White, silky, anhydrous asbestos is scraped to a fine short down with an ordinary knife-blade, boiled with hydrochloric acid to remove traces of iron or other soluble matter, washed by decantation, and set aside for use. Secondly. A platinum crucible of ordinary size, preferably of the broad low pattern (fig. 63), is chosen, and the bottom (fig. 65) perforated with fine holes (the more numerous and the finer the better) by means of a steel point ; or, better still, the bottom may be made of fine platinum gauze. Next a Bunsen funnel of the proper size is selected, and following Munroe's plan for holding his porous cones TKEATMENT OF PKECIPITATES 667 FIG. 64. over the top a short piece of rubber tubing is stretched and drawn down until the portion above the funnel arranges itself at right angles to the direction of the stem. Within the opening in the rubber the perforated crucible is fit- ted as shown in fig. 64, and the funnel is connected with the receiver of a Bunsen pump \ / or other exhausting apparatus V / in the ordinary manner. FlG 65 To make the asbestos felt, the pressure of the pump is applied and a little of the as- bestos prepared as described, and, suspended in water, is poured into the crucible. The rubber and the crucible are lield together by the pressure of the vacuum pump with FIG. 65. sufficient force to make an air-tight joint ; the water is drawn through, ancHhe asbestos is deposited almost instantly in a close compact layer upon the perforated bottom ; more asbestos (if necessary), in suspension as before, being poured upon the first until the layer becomes sufficiently thick for the purpose for which it is intended. Finally, a little distilled water is drawn through the apparatus to wash away any filaments that might cling to the under side, and the filter is ready for use : the whole process occupying scarcely more time than is necessary to fold and fit an ordinary paper filter to a funnel. To prepare the filter for the estimation of a precipitate, the crucible, with the felt undisturbed, is removed from the funnel and ignited. In case the precipitate to be subsequently collected must be heated to a very high temperature for a long time, it is better to enclose the per- forated crucible with its felt within another crucible ; because in such cases asbestos felt is apt to curl at the edges, and without such pre- caution some of the precipitate might drop through the perforations and be lost. For drying at low temperatures, however, and even for ordinary ignitions, a second crucible is unnecessary ; but during the ignition of an easily reducible substance care must be taken to prevent the contact of unburnt gas with the perforated bottom. To perform the filtration, the crucible is replaced in the funnel, the pressure applied, and the process conducted precisely as in an ordinary filtration by the Bunsen pump. It is necessary to observe that the vacuum pump is to be started before pouring the liquid upon the filter. The final drying or ignition, as the case may be, of precipitate and filter is made without difficulty or need of extra precaution. When turbid liquids are to be filtered, or gelatinous precipitates 668 SELECT METHODS IN CHEMICAL ANALYSIS FIG. 66. FIG. 67. separated, instead of the perforated crucible it is better to use a. platinum cone (figs. 66 and 67), the upper part of foil (to make a tight joint with the rubber fitting of the funnel), the lower of gauze. The method of cover- ing the gauze with felt is identical with that described above. By reason of the larger filtering surface of this apparatus, the tendency to become clogged is, of course,, very much diminished. When subjected to prolonged igni- tion, the gauze cone is enclosed within a crucible or a cone of platinum foil. In operations in which platinum is liable to receive injury, a porcelain crucible with a perforated bottom may be used ; but recourse to this is rarely necessary, particularly when one may use the gauze cone, protected as it is by asbestos felt ; moreover, the perforation of porcelain with numerous fine holes is a matter of con- siderable difficulty and expense. Asbestos felt may be also used in the process of reverse filtering,. it being merely necessary to dip the platinum rose into the asbestos- mixture, after starting the vacuum pump, in order to make the felt. The rose, with the felt attached, and the vessel in which the precipi- tate is collected are to be weighed together, both before and after filtration. Nothing can be simpler than the whole method of preparation and use of the apparatus which has been described, and its efficiency is extremely great. Clean water may, under the pressure of a Bunseii pump, be passed through a gauze cone coated with asbestos felt, which exposes a filtering surface of 24 square centimetres (nearly the same as that of a paper filter, 8 centimetres in diameter, when folded in the ordinary manner) with ease at the rate of a litre per minute. When the filtering surface is less, the rapidity of filtration is, of course, somewhat diminished, but always exceeds that of paper of the same dimensions. When the felt is deposited upon gauze, the layer may be surprisingly thin, and yet be efficient enough for all ordinary purposes. If the layer of felt be thick, the filtrate from barium sul- phate freshly precipitated in the cold may be made to pass through clear. But the great superiority of asbestos felt lies in its constancy of weight, whether dried at high or low temperatures, the rapidity with which it may be safely and completely dried, and its refractoriness as- regards acids (excepting hydrofluoric acid) and alkalies. NEW METHOD OF FILTRATION 669 A Method of Filtration by Means of Easily Soluble and Easily Volatile Filters The processes of analysis, in which it is desirable to re-dissolve pre- cipitates from the filter after washing, or to separate a mixed precipitate into parts by the action of appropriate solvents, are many. When a complete solution is the object, and the precipitate yields easily to solvents which do not affect paper injuriously, the use of the ordinary filter offers no difficulty. When, however, precipitates are to be treated with reagents which disintegrate paper filters, the case is otherwise, and the attempt to remove by solvents any individual part of a mixed heterogeneous mass upon a filter is always an uncertain matter. As examples of cases of this sort, difficult to deal with, we may take the solution of acid sodic titanate in strong hydrochloric acid ; or the purification of baric sulphate from included salts by digestion in strong hydrochloric acid ; or the separation of sulphides which are soluble from those which are insoluble in alkaline sulphides ; or the washing out of free sulphur from precipitated sulphides by means of carbon disulphide ; or the separation of calcic and baric sulphates by the action of sodium hyposulphite. In cases of this nature it is often convenient to make use of the asbestos filter already described, but this sometimes has disadvantages. Thus, to recur to the examples just cited, acid sodium titanate may be filtered and washed upon an asbestos filter, and felt and precipitate treated together with hydro- chloric acid, but it will be impossible to determine when solution is effected, because of the floating asbestos ; and in separating the sul- phides it would be necessary to know the weight of the asbestos felt, since it must be weighed finally with the insoluble sulphides, unless removed by a special treatment which involves the solution, filtra- tion, and re-precipitation of the latter. It is to meet cases like these that Mr. F. A. Gooch has sought for a filter which, in the reversal of the ordinary mode of separating filter and precipitate, should dissolve easily in solvents which do not affect the ordinary precipitates met with in analysis. The material which seems best suited to the case light and fluffy, capable of making secure filters of any desirable degree of porosity, sufficiently insoluble in water and aqueous solution of salts, alkalies, and acids (except strong sul- phuric, strong nitric, and glacial acetic acids), easily soluble in naphtha, benzol, carbon disulphide, ether, boiling alcohol, and essential oils, and not too costly is anthracene. The mode of preparing and using the filter is simple. Anthracene is slightly moistened with alcohol to make it miscible with water, diluted to the right consistency, and applied to the same apparatus, and in the same way as the emulsion of asbestos which is employed in making asbestos felts ; that is to say, enough of the emulsion in water 670 SELECT METHODS IN CHEMICAL ANALYSIS to form a layer of the proper thickness is poured into a perforated crucible, which is held tightly in a packing of rubber-tubing stretched over a funnel fitted in the usual manner to a vacuum flask or receiver. After washing with water the filter is ready for use. If the felt happens to be too coarse for the use of the moment, it may be made as close as need be by coating the felt first deposited with a finer emulsion, made by dissolving anthracene in hot alcohol and precipitating with water. When voluminous precipitates are to be filtered, the large perforated cone already described may be substituted with advantage for the crucible ; or Cooke's improved form * of Carmichael's process of reverse filtration may prove most useful. In using the cone it is well to apply the anthracene in a thick layer. To remove the anthracene filter from a precipitate it is only necessary to act with the proper solvent. It is usually convenient to stand the crucible containing precipitate and felt in a small beaker, add enough of the solvent, and gently warm until the anthracene dissolves. On the addition of water, or the reagent to work upon the precipitate, the solution of anthracene floats, and nothing remains to obstruct or obscure the action. If the precipitate dissolves entirely, the solution of anthracene may be separated from the aqueous solution by simply pouring the liquid upon a filter previously moistened with water, when the solution in water runs through, and the anthracene and its solvent remain and may be washed indefinitely with water. If, on the other hand, the case is one of the division of precipitates, the anthracene and its solvent may be made to pass the filter, after the water has run through, by adding a little alcohol to overcome the repulsion between the solution and the water which fills the pores of the filter, the precipitate which stays behind being washed first with a solvent of anthracene, and then, if necessary, with alcohol followed by water ; or, if the vacuum filter be used (either paper or asbestos, accord- ing to the circumstances of the case), both liquids leave the precipitate and traverse the filter together. In general, Dr. Gooch prefers benzol as the solvent for anthracene, but some advantage may be gained in special cases by a proper choice of solvents. Thus, in removing intermixed sulphur from precipitated sulphides, both the anthracene and the sulphur may be dissolved in carbon disulphide in a single operation. The ready volatility of anthracene, at a temperature very near its melting-point, 213 C., makes it easily separable in cases when to re- move it by a solvent is not advisable. The treatment of a solution of anthracene, for example, with strong sulphuric or nitric acid is apt to produce carbonaceous or gummy residues. In such cases it is well either to heat the precipitate and filter directly, or to first remove them from the crucible by means of a solvent for anthracene, then evaporate this, and raise the heat gently until the anthracene has vanished. The 1 Proceedings of the American Academy, xii. 124. INCINERATION OF FILTERS 671 purification of precipitated baric sulphate, by dissolving it in hot, strong sulphuric acid, and re-precipitating by dilution, is a case in point, and one, too, in which the reversed filter maybe used with great advantage. It may be remarked, in passing, that if one does not happen to possess a platinum rose and does happen to have at disposal a perforated crucible, a very fair reversed filter may be improvised with the crucible, a piece of glass tubing, and a rubber stopper, the last being fitted to the crucible, and the tube passed through nearly to the perforated bottom. Rapid Separation of Slimy Precipitates K. Zulkowsky effects this in many cases by shaking up the liquid containing the precipitate with ^ volume of ether. The ether entangles the precipitate and carries it to the surface, so that the clear aqueous solution can be withdrawn. The precipitate is then obtained on allow- ing the ether to evaporate. Separation of Minerals for Analysis Mr. E. Sonstadt avails himself for this purpose of their different specific gravities. He prepares a heavy liquid (sp. gr. 3'01) with a solution of mercuric iodide in potassium iodide, by adding alternately those salts in a dry state to the solution, until no more of either is dissolved. The free iodine which sometimes colours it is then removed by means of a crystal or two of sodium thiosulphate, and the liquid, which possesses a very high density, then presents a light straw colour. The roughly crushed mineral is thrown into the solution, when any ingredients heavier than 3*01 sink, whilst the lighter ones float. The solution may be diluted if required. Each class can thus be collected separately, and requires merely to be washed in distilled water. On the Incineration of Filters A previous complete drying of the precipitate is not merely a loss of time, but a disadvantage, whilst introducing the still moist pre- cipitate into the crucible requires the application of a very gentle heat at the outset, and thus ensures the most favourable conditions for the easy and complete incineration of the filter-paper. Precipitates not washed upon the filter-pump can be readily brought to a sufficient degree of dryness if laid for a short time upon blotting-paper or un- glazed earthenware. Dry filters may be also much better incinerated after previous charring at the lowest possible temperature than by rapid carbonisa- tion or direct ignition in the flame. How advantageous it is to char previously very slowly may best be seen on incinerating filters, whose contents impede the complete combustion of the paper by the old 72 SELECT METHODS IN CHEMICAL ANALYSIS process e.g., silicic acid, magnesium -ammonio phosphate, &c. Charred paper obtained by rapid heating is deep black and of a silky lustre, whilst if slowly carbonised it is brownish black, dull, and smoulders away like tinder. Charred paper of the first kind appears under the microscope perfectly amorphous, whilst the other displays the carbona- 'Ceous skeleton of the fibre. A careful removal of precipitates from the filter with the excep- tion of cases like zinc and cadmium, where volatile reduction-products may be formed is quite useless, since the errors which it was hoped to obviate are not really avoided. On incineration with the filter, wet or dry, an error due to reduction may be easily corrected e.y., in barium sulphate with sulphuric acid ; in lead sulphate with nitric and sulphuric 'acids ; in iron and copper oxides with nitric acid ; in silver chloride with nitric and hydrochloric acids, &c. Indicators for Alkalinity (A) The comparative sensitiveness of litmus, methyl- orange, phen- acetoline and phenol-phthaleine has been carefully studied by Mr. K. T. Thomson. In the absence of all interfering agents, litmus and methyl-orange are equally sensitive ; phenacetoline and phenol-phtha- leine about five times more sensitive. If soda exists as hydrate along with sodium carbonate, phenace- toline and phenol-phthaleine are not suitable, if the proportion of carbonate is large. For ammonia phenol-phthaleine is useless, as it does not distinctly indicate the end of the reaction. In the estimation of alkalies existing as carbonates and bicar- bonates, the well-known fact is mentioned that litmus cannot be used for the estimation of ammonia in the commercial carbonate without adding excess of acid, boiling to expel carbonic acid, and titrating back with an alkali. The same holds good for phenacetoline. Methyl- orange appears to have given an apparent excess of ammonia. Phenol- phthaleine is useless for ammonium carbonate, and requires tedious boiling with the carbonates of the fixed alkalies. In presence of alkaline sulphates, nitrates, and chlorides, litmus and phenacetoline are as delicate as in their absence. With methyl- orange a greater quantity of normal acid is needed to bring out the full pink colour than if distilled water only were present. Phenol- phthaleine is unaffected by the above-named salts in case of potash and soda, but ammonia and its salts must be carefully excluded if this indicator is to be used. If the alkaline sulphites are present, the results given by all the indicators are vitiated. Sodium thiosulphate is neutral to all the indicators. With sodium sulphide, litmus, methyl-orange, and phenacetoline INDICATORS FOR ALKALINITY 673 gave accordant results ; phenol- phthaleine showed one half too little Na 2 S, unless boiled, when it approached the truth. If alkaline phosphates were present, methyl- orange gave results slightly higher and nearer the truth than litmus, the end of the re- action being more distinct. Phenol-phthaleine cannot be depended upon. If phenacetoline is used, the normal acid must be added until a permanent colour is produced, when the results agree with those obtained with litmus. If sodium silicate is present, litmus, methyl-orange and phenace- toline give results which do not materially differ. With phenacetoline the end reaction is indistinct. Phenol-phthaleine gives results con- siderably too low. With sodium aluminate litmus gives too high a result, and an indistinct termination : with methyl-orange the result is much too high, whilst phenacetoline and phenol-phthaleine give a correct estimation. Potassium nitrite is neutral to litmus, phenacetoline, and phenol- phthaleine ; methyl-orange is not admissible. For the estimation of soda in borax, methyl-orange shows a correct result, and the end of the reaction is quite distinct. With litmus and phenacetoline the end is indistinct, and phenol-phthaleine is utterly useless. On the estimation of the mineral acids with a caustic alkali, it need only be said that ammonia must not be used with phenol-phthaleine. Sodium carbonate can be used in the cold with methyl- orange. If phenacetoline is to be employed, a little carbonate must be used along with the caustic alkali. For free oxalic acid, litmus and phenol-phthaleine give distinct and concordant results, whilst methyl-orange and phenacetoline cannot be recommended. For free acetic acid, methyl-orange and phenacetoline are not well adapted. With litmus the end of the reaction is not easily recognised. Phenol-phthaleine works admirably. For tartaric acid the results are similar, phenol-phthaleine showing the most distinct reaction. With citric acid, limejuice, &c., the case is similar, methyl-orange and phenacetoline being useless, and phenol-phthaleine giving a sharper end reaction than litmus. (B) For estimating caustic alkalies in presence of alkaline car- bonates, and quicklime in presence of calcium carbonate, Dr. Lunge recommends a method first suggested by Degener. The solution of lime is coloured with phenacetoline, and normal acid is dropped in as long as the yellowness produced by each drop at once gives place to redness. If this change does not occur for a few seconds, the burette is read off, and two more drops of acid are added. If the liquid remains yellow, the former reading was correct, but if x x 674 SELECT METHODS IN CHEMICAL ANALYSIS it becomes red, the addition of the acid must be continued until a permanent yellow colouration is established. The estimation of caustic soda is effected directly by titration with acid, using phenacetoline as indicator. As soon as the liquid remains of a faint rose colour all the sodium hydroxide is saturated, and only the carbonate remains. If more acid is added, the yellowish-red colouration changes suddenly to a golden yellow. At this point the carbonate also is saturated. The process is most suitable for caustic lyes which contain moderately large proportions of carbonate. Am- monia behaves differently from caustic soda, and is at once reddened by phenacetoline. Dr. Lunge recommends practice with this indicator with liquids of known composition, so as to acquire a knowledge of the correct shade of colour. Ultramarine Test-Paper. The great sensitiveness of artificially made ultramarine for even very weak acids has been turned to account by applying that pigment to prepare a test-paper especially suited for the rapid detection of the presence of free acids in such salts as alu- minium sulphate, alum, and other similar compounds. The ultra- marine intended for this use should be that known commercially as No. 1 ; it should first be mixed with some water, collected on a filter, and then thoroughly washed with some boiling distilled water, and afterwards incorporated with a mucilage made of 1 part of selected Irish moss, previously washed with cold water, boiled with about 80 parts of distilled water ; the pigment thus obtained is uniformly painted over best filtering-paper, and, after drying, cut up into strips, as is usual for litmus-paper, and preserved in a glass-stoppered bottle. In order to test the ultramarine, it is necessary to prepare a perfectly neutral alum in the following manner. Alum of commerce, by pre- ference potash alum, is dissolved in from 8 to 10 times its weight of boiling water, and this solution is poured into twice its bulk of alcohol at 80 per cent. The alum separated after complete cooling is collected, redissolved in boiling water, and the solution again poured into the same quantity of fresh alcohol of the same strength ; the alum which separates on cooling is collected on a filter, and, after having been washed with alcohol, dissolved in water ; a drop or two of this solution should not discolour the ultramarine, while its almost instantaneous discolouration should follow on its being touched with a drop or two of very dilute sulphuric acid, 1 part of strong acid to from 50 to 60 parts of distilled water. Application of Hydrogen Peroxide in Chemical Analysis The behaviour of hydrogen peroxide with ammonium sulphide, or of hydrogen sulphide with ammoniacal hydrogen peroxide, may be used qualitatively for the detection of these compounds, and quan- titatively for estimating hydrogen sulphide, whether gaseous or in APPLICATION OF HYDROGEN PEROXIDE 675 solution, and for estimating the sulphur or the metal in metallic sul- phides. In cases where the sulphide can be decomposed by the direct action of hydrogen peroxide in presence of ammonia, it takes place in this manner ; in other cases, as in the sulphides which on heating with hydrochloric acid evolve definite quantities of hydrosulphuric acid, it takes place by conversion into sulphuric acid or barium sulphate. Just as hydrogen sulphide or metallic sulphides are oxidised to sulphuric acid or to sulphates, sulphurous acid and sulphites are oxidised to sul- phuric acid or sulphates. These reactions may be utilised in various directions. Several metallic sulphides are completely oxidised by ammoniacal hydrogen peroxide without the formation of precipitates, as the arsenic, copper, zinc, and thallium sulphides. After the expulsion of the ammonia all the copper is deposited by a copper solution as a dirty green precipitate, not changed by ignition. From the zinc solution only a part of the zinc is separated as a white deposit. On the action of hydrogen peroxide upon antimony trisulphide a part of the antimony separates as a white precipitate, whilst the liquid contains all the sul- phur as sulphuric acid. Tin sulphide is decomposed in a similar manner, oxide being deposited and the sulphur oxidised to sulphuric acid. With the other metallic sulphides the behaviour of hydrogen peroxide is very various. It attacks mercury sulphide, which is scarcely affected by nitric acid, very energetically. After the expulsion of the mercury there remains a spongy precipitate which settles quickly, dissolves in hydrochloric acid, and is converted into a white powder by the action of nitric acid. After the conversion of mercury sulphide by the action of hydrogen peroxide, no mercury can be detected in the filtrate. Cadmium sulphide is decomposed with formation of a yellowish-white precipitate, easily soluble in hydrochloric acid. When the oxidation is completed a part of the cadmium remains in the filtrate as sulphate. Certain metallic sulphides, the solutions of which in acids are pre- cipitable by ammonia, are decomposed by hydrogen peroxide with forma- tion of sulphuric acid and separation of hydroxides ; thus iron sulphide, which is oxidised as just mentioned, and manganese sulphide, which is quickly and completely decomposed with formation of sulphuric acid and separation of a mixture of hydrated peroxide and oxide. On heating cobalt sulphide with ammoniacal hydrogen peroxide there is first formed soluble cobalt sulphate, which on prolonged heating is further attacked, with formation of a dirty brown precipitate. Nickel sulphide is decomposed in the same manner, with formation of a green precipitate which does not contain all the nickel. Silver and bismuth sulphides are not attacked by ammoniacal hydrogen peroxide ; lead sulphide is readily converted into sulphate. The property of hydrogen peroxide in alkaline solution, of easily and completely oxidising hydrogen sulphide to sulphuric acid, may be used, in the first place, for the estimation of hydrochloric, hydrobromic, xx2 676 SELECT METHODS IN CHEMICAL ANALYSIS and hydriodic acids in liquids containing hydrogen sulphide. These estimations have occasioned much trouble to analysts. From the estimation of hydrochloric acid along with hydrogen sulphide an ammoniacal solution of hydrogen peroxide is added, and the mixture is boiled until no more bubbles of oxygen rise up. Nitric acid and silver nitrate are then added, and the silver chloride is esti- mated in the usual manner. For hydriodic acid in presence of hydrogen sulphide the procedure is similar, but the hydrogen peroxide is used mixed not with ammo- nia, but with sodium carbonate. The mixture is boiled as before, and silver nitrate is added, and nitric acid until a faintly acid reaction is produced. In estimating hydrobromic acid under similar circumstances the process is exactly the same as for hydriodic acid. In the metallic sulphides capable of direct oxidation by hydrogen peroxide the quantity of metal can be calculated from the sulphuric acid formed. This method is applicable to the sulphur compounds of arsenic, antimony, zinc, copper, and cobalt. The sulphide is dissolved in ammonia, treated with sufficient hydrogen peroxide, boiled to expel excess, the liquid is acidulated with hydrochloric acid, and the sulphuric acid precipitated with barium chloride. Antimony trisulphide is treated exactly like arsenic trisulphide. Antimony pentasulphide is incompletely oxidised by hydrogen per- oxide. Sulphides which dissolve by boiling with hydrochloric acid, with liberation of hydrogen sulphide, can be readily and accurately estimated by converting the latter compound into sulphuric acid. Sodium thiosulphate is decomposed on boiling with hydrochloric acid, sulphur being deposited and sulphur dioxide formed. This method permits of the estimation of sodium thiosulphate, sulphite, and sulphate, when occurring together. The weighed substance is decom- posed in the apparatus by means of hydrochloric acid, the sulphur dioxide corresponding to the sulphite and thiosulphate is estimated, the sulphur remaining in the flask is weighed on a tared filter, and the sulphuric acid in the filtrate is precipitated as barium sulphate. From the quantity of the sulphur, that of the thiosulphate is calculated. On the Preservation of Platinum Crucibles In connection with some sensible remarks upon the use of sand in cleaning platinum crucibles a practice which, with Berzelius, 1 he heartily commends, urging that it should be employed every time that a crucible is used Erdmann explains the cause of the grey coating which forms upon platinum crucibles whenever they are ignited in the flame of a Bunsen gas-burner. 1 Lehrbuch der Chemie, 1841, 4th Aufl., p. 516. PLATINUM CRUCIBLES 677 This coating has given rise to much annoyance and solicitude among chemists. Indeed, it has often been asserted that the use of Bunsen's burner is unadvisable in quantitative analysis, since by means of it the weight of platinum crucibles is altered and the cru- cibles themselves injured. The coating is produced most rapidly when the crucible is placed in the inner cone of the flame, and the more readily in proportion as the pressure under which the gas is burned is higher. Having found it advantageous to maintain, by means of a special small gas-holder, a pressure of 4 or 5 inches upon the gas used in his own laboratory, Erdmann has observed that the strong gas- flame thus afforded immediately occasions the formation of a dull ring upon the polished metal placed in the inner flame, this ring being especially conspicuous when the crucible becomes red-hot ; it increases continually, so that after long-continued ignition the whole of the bottom of the crucible will be found to be grey and with its lustre dimmed. This ring is caused neither by sulphur, as some have believed, nor by a coating of inorganic matter, but is simply a superficial loosening of the texture of the platinum in consequence of the strong heat ; whence it first of all appears in the hottest part of the flame. In conjunction with Pettenkofer, Erdmann instituted several ex- periments which have left but little doubt that the phenomenon depends upon a molecular alteration of the surface of the metal. If a weighed polished crucible be ignited for a long time over a Bunsen's lamp, the position of the crucible being changed from time to time in order that the greatest possible portion of its surface shall be covered with the grey coating, and its weight be then estimated anew, it will be found that this has not increased. The coating cannot be removed either by melting with potassium bisulphate or with sodium carbonate. It disappears, however, when the metal is polished with sand ; the loss of weight which the crucible undergoes being exceedingly insig- nificant, a crucible weighing 25 grammes having lost hardly ^ a milli- gramme. When the grey coating of the crucible is examined under the microscope it may be clearly seen that the metal has acquired a rough, almost warty surface, which disappears when it is polished with sand. Platinum wires which are frequently ignited in the gas-flame for example, the triangles which are used to support crucibles become, as is known, grey and brittle. Under the microscope they exhibit a multitude of fine longitudinal cracks, which, as the original superficial alteration penetrates deeper, become more open, or as it were spongy, until, finally, the wire breaks. If such a wire is strongly and perseveringly rubbed with sand, the cracks disappear, and the wire becomes smooth and polished ; for the grains of sand, acting like burnishers, restore the original tenacity of the metal, very little of its substance being rubbed off meanwhile. The loosening effect of a strong heat upon metals is beautifully exhibited 678 SELECT METHODS IN CHEMICAL ANALYSIS when silver is ignited in the gas flame, a thick polished sheet of silver immediately becoming dull white when thus heated. Under the micro- scope the metal appears swollen and warty. Where it has been ex- posed to the action of the inner flame along its circumference, this warty condition is visible to the naked eye. A stroke with the bur- nishing-stone, however, presses down the loosened particles and re- produces the original polish. This peculiar condition which the sur- face of silver assumes when it is ignited is well known to silversmiths ; it cannot be replaced by any etching with acids ; and it must be remembered that what is dull white in silver appears grey in plati- num. If each commencement of this loosening is again destroyed, the crucibles will be preserved unaltered ; otherwise they must gradually become brittle. Crucibles of the alloy of platinum and iridium are altered like those of platinum when they are ignited. It is, however, somewhat more difficult to reproduce the original polish of the metal by means of sand, as might be expected from the greater hardness of the alloy. The sand used should be well worn. When examined under the microscope no grain of it should exhibit sharp edges or corners ; all the angles should be obtuse. (See page 453.) Analysis of the Gold and Platinum Salts of Organic Bases M. C. Scheibler dissolves a weighed quantity of the acid or platinum salt in water, or, if it does not happen to be readily soluble, keeps it suspended therein, and places it in contact with metallic magnesium, whereby the metals gold and platinum are separated, and hydrogen is at the same time evolved. This operation is carried on at the ordinary temperature, or, if the salts are difficultly soluble, on a water-bath ; the liquid may be acidified, but not with hydrochloric acid, since the object often may be to estimate chlorine also. The ribbon-like mag- nesium wire met with in commerce is sufficiently pure for this purpose. The gold and platinum separated during this operation are, by means of careful decantation, freed from the liquid wherein they are immersed, and next transferred to a filter and washed, first with distilled water and next, after the filtrates intended for the estimation of chlorine have been set aside, with dilute hydrochloric acid, in order thereby to remove any excess of magnesium or any magnesia which might remain mixed with or adherent to these metals ; after having been well puri- fied and dried the metals are ignited and weighed. The results ob- tained by this method are very correct. To prevent the Bumping of Boiling Liquids (A) In cases where the introduction of any foreign matter into the liquid about to be distilled is undesirable, Dr. Hugo Miiller, F.K.S., ADJUSTMENT OF WEIGHTS 679 introduces through the cork in the tubulure of the retort a glass tube, which is drawn out to a long capillary tube and pressed tightly to the bottom of the retort. The upper end of the glass tube is connected, by means of an india-rubber tube, with a generator of carbonic acid, or hydrogen, or a gas-holder containing air, and whilst the distillation is going on, one of these gases is passed in a slow but continuous current through the liquid. Under these conditions all bumping is avoided, and the distillation proceeds with the utmost facility. (B) For ordinary purposes, however, it is still more convenient to introduce into the liquid about to be distilled a small fragment of sodium amalgam or, in cases where the liquid is acid, a small piece of sodium-tin. Methylic alcohol is well known to be one of the most difficult liquids to distil ; yet, on the introduction of a minute piece of sodium amalgam or sodium-tin, it can be distilled without the slightest inconvenience. On one occasion Dr. Miiller found that more than 400 grammes of methylic alcohol distilled over with perfect steadiness, and without exhausting the activity of a fragment of sodium-tin weighing not more than 0'06 gramme. It is, perhaps, hardly necessary to mention that the action of sodium amalgam and sodium-tin is due to a minute but continuous disengagement of hydrogen taking place during the process of dis- tillation. On the Correct Adjustment of Chemical Weights The following description of the method adopted for adjusting a set of platinum weights is taken from the author's Memoir on the Atomic Weight of Thallium. 1 A set of weights as ordinarily supplied by even the best instrument- makers is never absolutely exact ; however carefully they may be ad- justed, the pieces of metal which respectively represent 1000 grains, 100 grains, 10 grains, &c., are only more or less approximations to the true weights. In most chemical analyses the error arising from such inaccuracies in the weights used is so small, in comparison to errors of manipulation or to imperfections inherent in the chemical processes adopted, that it may generally be disregarded ; but when the chemist has for his object the estimation of an atomic weight, or is engaged in other researches demanding the highest refinement of accuracy which chemistry and physics can supply, then he is bound to neglect no correction which will increase the precision of the results. That chemists whose well-trained reasoning powers allow them to take for granted nothing which is not capable of experimental verification, and who insist upon the utmost attainable precision in their balances, should, as a rule, neglect the probable errors which the inaccuracies of their weights may introduce, is somewhat incon- sistent. J Phil Trans. 1873, p. 277. 680 SELECT METHODS IN CHEMICAL ANALYSIS The weights employed in the experiments were of platinum. The platinum was quite pure ; it was fused, cast, and then well hammered. The weights were adjusted by myself during May, June, July, and August, 1864 : they were first roughly adjusted, and then the specific gravity of each weight was taken. The weights were heated to red- ness in a bath of magnesia previous to ascertaining their specific gravity. The density of the larger weights was ascertained to the second place of decimals, and that of the smaller ones to the first place. The record of the final adjustment of these weights will be sufficient to show the method adopted. In taking the specific gravity of the weights, the distilled water was contained in a glass beaker of about 250 cubic inches capacity. Each weight was suspended by a fine platinum wire to be attached to the pan of the balance. With this wire affixed the weight was introduced into a small glass vessel filled with water, and heated over a spirit- lamp to the boiling-point. When all the air-bubbles had been expelled by this process, the small jar containing the weight was lowered into the water in the beaker, the weight, on removing the small jar, being perfectly free from any adhering bubbles of air. After the tempera- ture had sunk to the proper point, the specific gravity was taken. The 1000-grain weight was selected as the standard ; for in nearly every process in which weights are used in chemistry, the object is not to ascertain the absolute weight of a substance in terms of a grain or gramme, but to estimate its relative weight in comparison with that which it possessed at some other time before it was submitted to cer- tain analytical or synthetical operations. If the weighings are per- formed with the same weights, it does not at all matter whether the weights are absolutely of the value which they profess to be ; but it is very important that they should bear a known proportion to each other. This must be understood as referring only to ordinary chemical re- search in synthesis or analysis. In many physical investigations it is of great importance that the 1000-grain weight should really represent 1000 normal grains, or that its deviation from that value should be accurately estimated ; but I confess I do not know where a standard weight suitable for such a comparison is to be met with. The weights at first tried were far from accurate among themselves. I accordingly ascertained their errors by the method described below, and then ad- justed them myself according to the corrections thus found necessary. The residual errors in the weights were then finally taken in the following manner. The balance being brought into equilibrium and the temperature and barometrical pressure carefully noted, the 1000-grain weight was placed in the left pan, and in the right the 600, the 300, and the 100 grain weights. It was now found that, to bring the balance back to equilibrium, a slight additional weight had to be placed on the right side to supplement the three weights already in that pan. This was ADJUSTMENT OF WEIGHTS 681 noted. The weights were then removed to the opposite sides, the 1000-grains being on the right and the three smaller weights on the left. It was now found that a small weight had to be subtracted from the side carrying the three weights in order to produce equilibrium. The weights were removed and interchanged in this manner ten times, so as to eliminate, as far as possible, the errors arising from observa- tion, or the unequal expansion by heat of the arms of the balance ; and by applying the method of least squares to the results obtained, the following equation was arrived at : (1000) = (600) + (300) + (100) + 0-01 ... a, the figures within parentheses representing the nominal value of the actual pieces of platinum stamped 1000, 600, 100 grams, &c. In a similar manner the values of the remaining weights were ascertained ; thus : (600) = (300) + (200) + (100) + 0-00777 . b. (300) = (200) + (100) + 0-00991 . c. (200) = (100)+ (60)+ (30) + (10) + 0-01577 . d. (100)= (60)+ (30)+ (10) - 0-00030 . e. (60)= (30)+ (20)+ (10)j 0-00522 . /. (30)= (20)+ (10) + 0-00154 . g. (20)= (10)+ (6)+ (3)+ (1) + 0-00355 . . . h. (10)= (6)+ (3)+ (1) + 0-00052 . i. (6)= (3)+ (2)+ (1) 0-00102 . . . j. (3)= (2)+ (1) + 0-00165 . k. (2)= (1)+ (-6)+ (-3)+(-l) 0-00312 . Z. (1)= (-6)+ (-3)+ (-1) 0-00508 . m. (6)= (-3)+ (-2)+ (-1) - 0-00260 . n. (-3)= (-2)+ (-1) + 0-00225 ... o. (-2)= (!)+ (-06)+ (-03) + ('01) - 0-00100 . . p. (-1) = (-06) + (-03) + (-01) - 0-00802 . q. (-06) = (-03) + (-02) + (-01) - 0-00607 . r. (08) = (-02) + (-01) - 0-00642 . s. (02) = (-01) + (-Olr") 1 - 0-OOllSr' . t. (01) = ("Olr") + 0-00413/ . u. (01)= (-Olr f ) + 0-00410r". . . v. We have now the data for ascertaining the absolute values of the weights in terms of the (1000) weight taken as standard. Adding the equations a and b gives (1000) = 2(300) + (200) + 2(100) + 0-01777. Multiplying equation c by 2 gives 2(300) = 2(200) + 2(100) + 0-01982. Subtracting e from d gives (200) = 2(100) + 0-01607. 1 r', r" represent riders, two of which were adjusted in this manner. 682 SELECT METHODS IN CHEMICAL ANALYSIS Now by (a + b) + 2c + 3(d-e) we get (1000) = 10(100) + 0-01777 + 0-01982 + 0-04827 ; .'. (1000) - 10(100) + 0-0858 ; .-. (IJgo) = (100) + 0-00858 ; /. (100)= 100 -0-00858; /. (100) = 99-991420 grains . . .A. 1 Substituting this value for the (100) weight, we get from equation e t 99-991420 = (60) + (30) + (10) - 0-00030 ; /. (60) + (30) + (10) = 99-991720 . . B. From equation d we therefore get (200) = 99-99142 + 99-99172 + 0-01577 ; /. (200) = 199-99891 C. From equation c we get (300) = 199-998910 + 99-991420 + 0-00991 ; /. (300) = 300-000240 . D. From equation b we get (600) = 300-000240 + 199-998910 + 99-991420 + 0-00777 ; /. (600) =599-998340 . E. Again, adding e and /, (100) = 2(30) + (20) + 2(10) - 0-00552 ; .-. from A, 99-991420 = 2(30) + (20) + 2(10) - 0-00552. Multiplying g by 2, 2(30) = 2(20) + 2(10) + 0-00308. Subtracting i from h, (20) = 2(10) + 0-00303. By adding e,f, twice g, and thrice the last equation, we get 99-99142 = 10(10) + 0-000665 ; /. (10) = 9-998477 F. From equation i we get 9-998477 = (6) + (3) + (1) + 0-00052 ; /. (6) + (3) + (1)- 9-997957 . . . G-. Substituting these values in h, we get (20) = 9-998477 + 9-997957 + 0-00355 ; /. (20) = 19-999984 H. 1 Although these decimals are carried to the sixth place, the balance would not indicate beyond the fourth place. By taking the mean of ten interchanged weigh- ings, I could obtain a fifth place. The calculated values of the weights were carried to a sixth decimal, in order to avoid inaccuracy in the fourth and fifth places when several values were summed. ADJUSTMENT OF WEIGHTS 683 From g we get (30) = 19-999984 + 9-998477 + 0-00154 ; /. (30) = 29 -999991 . From / we get (60) = 29-999991 + 19-999984 + 9-998477-0-00522 ; /. (60) = 59-993232 Again, adding i and /, (10) = 2(3) + (2) + 2(1) - 0-00050. Multiplying k by 2, 2(3) = 2(2) + 2(1) + 0-00330. Subtracting m from Z, (2) = 2(1) + 0-001960. Then (i+j) + 2k + 8(l-m) gives (10) + 10(1) + 0-00868 ; /. 9-998477 = (10)1 + 0-00868 ; /. 0-9998477 = (1) + 0-000868 ; /.(I) = 0-9989797 . . . . K. From equation m we have 0-9989797 = (-6) + (-3) + (-1) - 0-00508 ; /. (-6) + (-3) + (!)- 1-0040597 . . - L. From I, (2) = 0-9989797 + 1-0040597 - 0-00312 ; .-.(2) = 1-9998394 ..... M. From k, (3) = 1-9998394 + 0-9989797 + 0-00165 ; /. (3) = 3-0004691 ...... N. From j, (6) = 3-0004691 + 1-9998394 + 0-9989797 - 0-00102 ; .-. (6) = 5-9982682 ..... 0. Again, adding m and n, (1) = 2(-3) + (-2) + 2(-l) -0-00768. Multiplying o by 2, we get 2(-3) = 2(-2)+2(-l) + 0-0045. Subtracting q from p, (-2) = 2(-l) + 0-00702. Then (m+ri) + 2o + 3(p-q) gives (1) = 10 (-1) + 0-01788; .-. 0-9989797 =10(-1) + 0-01788 ; /. 0-09989797= (-1) + 0-001788; /. (-1) = 0-09810997 .- '--. ' -.. : P. 84 SELECT METHODS IN CHEMICAL ANALYSIS From q we get 0-09810997 = (-06) + (-03) + (-01) -0-00802 ; .'.(06) + (-03) + (-01) -0-10612997 . . Q. From p, (-2) + 0-09810997 + 0-10612997 - 0-0010 ; /. (-2) = 0-20323994 E. From o, (-3) = 0-20323994 + 0-09810997 -f 0-00225 ; /. (-3) -0-30359991 S. From n we get (-6) = 0-30359991 + 0-20323994 + 0-09810997 - 0-0026 ; /. (-6) = 0-60234982 T. Again, adding q and r, (-1) - 2(-03) + (-02) + 2(-01) - 0-01409. Multiplying s by 2, we get 2(-03) = 2(-02) + 2(-01) - 0-01284. Subtracting u from t, (-2) = 2(-01) -0-00531. Then (q + r) + 2s + 3(t-u) gives (1) = 10(-01)- 0-04286, /.0-09810997 = 10(-01)- 0-04286, /. 0-009810997 = (-01) -0-004286, /. (-01) = 0-014096997 . . . . U. From u we get 0-014096997= (-Olr") -e 0-00413, /. (-Olr") = 0-009966997 . V. From t we get (-02) = 0-014096997 + 0-009966997 - 0-00118, /. (-02) = 0-022883994 . . . . W. From s we get (-03) = 0-022883994 + 0-014096997 - 0-00642, /.(03) = 0-030560991 . X. From r we get (06) = 0-030560991 + 0-22883994 + 0-014096997 - 0-00607, .'. (-06) = 0-061471982 . Y. From v we get 0-014096997 = (-01/) + 0-0041, /. (-Olr')= 0-009996997 . . . . Z. The value of the weights thus given was, however, their weight in air of the ordinary pressure ; it became therefore necessary to ascertain their value in a vacuum. All bodies displace a bulk of air equal to their own volume, and the weight of this air is of course greater as their ADJUSTMENT OF WEIGHTS 685 specific gravity diminishes. In delicate investigations this loss of weight is important. The reduction of the platinum weights to their true value in vacuo was calculated by the following formula : Let W = weight in air, w= water, a = specific gravity of air as compared with water ; then where x, or weight in vacuo, = a = 0-001225, and l-a = 0-998775. l-a The following Table shows the final results of these adjustments : Nominal Value of Weights True Value in Air at 30 in. 1 62 F. Weight of Air displaced Volume in Water of Maximum Density grs. grs. &r- grs. 1000-00 1000-000000 0-058271 47-5100 600-00 599-998340 0-035533 28-9700 300-00 300-000240 0-017501 14-2700 200-00 199-998910 0-011664 9-5100 100-00 99-991420 0-005887 4-8000 60-00 59-993232 0-003483 2-8400 30-00 29-999991 0-001668 1-3600 20-00 19-999984 0-001104 0-9000 10-00 9-998477 0-000490 0-4000 6-00 5-998268 0-000355 0-2900 3-00 3-000469 0-000171 0-1400 2-00 1-999839 0-000113 0-1000 1-00 0-998980 0-000055 0-0400 0-60 0-602350 0-000035 0-0300 0-30 0-303600 0-000017 0-0200 0-20 0-203240 0-000011 0-0100 0-10 0-098110 0-000005 0-0040 0-06 0-061472 0-000003 0-0030 0-03 0-030561 0-000002 0-0020 0-02 0-022884 o-oooooi 0-0010 0-01 0-014097 0-000001 0-0004 0-01' 0-009997 0-000001 0-0004 0-01" 0-009967 0-000001 0-0004 The value of each weight in air, plus the weight of air displaced, is- the weight in vacuo. Having ascertained their true value, the weights were carefully preserved; and as, being of platinum, there is no accumulation of tarnish on their surface, and as they are lifted with ivory-tipped for- ceps to prevent wear, they have shown up to the present time, when- ever compared, absolutely no alteration. 1 The cistern of the barometer was 115 feet above the approximate mean water-level at Somerset House. 686 SELECT METHODS IN CHEMICAL ANALYSIS CHAPTER XVI USEFUL TABLES Conversion of Centigrade and Fahrenheit Degrees 1 C. = 1-8 F. = f F. 1 C. x | = 1 F. 1 F. x | = 1 C. To convert Fahrenheit into Centigrade Subtract 32 from the original number, and divide the remainder by 1'8, thus: 176 F. 32 -f- 1-8 = 80 Cent. To convert Centigrade into Fahrenheit, multiply by 1'8, add 32 to the product, thus : 80 Cent, x 1-8 + 32 = 176 F. With the aid of a scale like the accompanying one, 1 thermometric degrees may be converted from one to the other with the greatest accu- racy without making any calculations. A simple inspection of the diagram will suffice to show the principle upon which the scale is constructed. Each degree Fahrenheit is divided into 5 parts, and each degree Centigrade into 9 parts, which are intended to represent fractions of a degree ; the degrees themselves being numbered consecutively from the freezing-point of each ther- mometer upwards. A few examples will best explain the use of this scale. Suppose the temperature of a body to be 40 F. and it is required to know what degree that is on the Centigrade scale. By looking for the next degree Centigrade above 40 F. on the scale, it is found to be 4, and 4 of the small divisions after it ; 40 F. are therefore equivalent to 4'4 C., or, repeating the decimal figure for greater accuracy, 4*44 C. When Centigrade degrees have to be reduced to degrees of Fahren- heit, the decimal figures of the latter must be doubled to obtain the correct answer. For example, it is required to represent 3 C. by their Fahrenheit equivalent ; referring to the scale we find the next degree Fahrenheit above 3 C. to be 37'2, and doubling the decimal figure we have the correct answer 37*4 F. Again, taking the outer columns of figures at the same place, we find 43 C. corresponding to 109-4 F. 1 By Mr. Birney. CONVERSION OF WEIGHTS AND MEASURES 687 FAHRENHEIT. CENTIGRADE OR CELSIUS. 20 40 60 21 41 61 22 42 62 23 43 63 24 44 64 25 45 65 - 6 26 46 66 7 27 47 67 - 8 28 48 68 29 49 69 10 30 50 70 31 51 71 12 32 52 72 13 33 53 73 ^S~ - 14 34 54 74 15 35 55 75 36 56 76 : -17 37 57 77 18 38 58 78 19 39 59 79 Tables for the Mutual Conversion of French and English Weights and Measures The equivalents in one system of the weights and measures of the other system can readily be found by means of the following tables. By changing the position of the decimal point, the tables are available for all decimal multiples and subdivisions of these quantities ; for instance, in order to find the part of a gramme which corresponds to 0-1, 0-01, 0-001, &c., of a grain, it is necessary to advance the decimal point one, two, or three places to the left. In the same manner it is advanced to the right for the purpose of finding the grammes corre- sponding to 10, 100, 1000, &c., grains. 140 104 68 32 141 105 69 33 142 106 70 34 143 107 71 35 144 108 72 36 145 109 73 37 146 110 74 38 147 111 75 39 148 112 76 40 - 149 113 77 41 150 114 78 42 151 115 79 43 152 116 80 44 153 117 81 45 154 118 82 46 155 119 83 47 156 120 84 48 -: 157 121 85 49 158 122 86 50 159 123 87 51 160 124 88 52 161 125 89 53 162 126 90 54 - 163 127 91 55 164 128 92 56 165 129 93 57 -: 166 130 94 58 _ 167 131 95 59 168 132 96 60 - 169 133 97 61 170 134 98 62 171 135 99 63 172 136 100 64 173 137 101 65 174 138 102 66 _: 175 139 103 67 - 688 SELECT METHODS IN CHEMICAL ANALYSIS For example : In the table for the conversion of grammes into* grains, it is required to find the equivalent in grains of 6'4431 grammes. From number 6 (without altering the place of the decimal point) 92-6304 1 From number 4 (advancing the decimal point one place to the left) 6-1753 ^rom number 4 (advancing the decimal point two places to the left) 0-6175 1 From number 3 (advancing the decimal point three places to the left) 0-0463 1 From number 1 (advancing the decimal point four places to the left) 0-0015 Therefore 6-4431 grammes are equal to . 99-4710 grains. Grammes into Grains. Grammes 1 = 2 = Grains 15-4384 30-8768 46-3152 Grammes Grains Grammes 4 = 61-7536 7 = 5 = 77-1920 8 = 6 = 92-6304 9 = Grains 108-0688 123-5072 138-9456 Grains into Grammes. Grains 1 = 2 = 3 = Grammes 0-06477 0-12954 0-19431 Grains Grammes Grains 4 = 0-25908 7 = 5 = 0-32385 8 = 6 = 0-38862 9 = Grammes 0-45339 0-51816 0-58293 Pounds into Kilogrammes. Pounds 1 2 = 3 = Kilogrammes Pounds Kilogrammes Pounds 0-4534148 4 = 1-8136592 7 = 0-9068296 5 = 2-2670740 8 = 1-3602444 6 = 2-7204888 9 = Kilogrammes 3-1739036 3-6273184 4-0807332 Kilogrammes into Pounds. Kilogrammes 1 = 2 = 3 = Pounds 2-205486 4-410972 6-616458 Kilogrammes Pounds Kilogrammes 4 = 8-821944 7 = 5 = 11-027430 8 = 6 = 13-232916 9 = Pounds 15-438402 17-643888 19-849374 Inches into Centimetres. Inches 1 = 2 = 3 = Centimetres 2-539954 5-079900 7-619900 Inches Centimetres Inches 4 = 10-1598 7 = 5 = 12-6998 8 = 6 = 15-2397 9 = Centimetres 17-7797 20-3196 22-8596 1 In almost every case when the decimal point is moved to the left, the last figures may be omitted without introducing any appreciable error. CONVERSION OF WEIGHTS AND MEASUEES 689 Centimetres into Inches. Centimetres 1 = 2 = 3 = Inches 0-3937079 0-7874158 1-1811237 Centimetres Inches Centimetres 4 = 1-5748316 7 = 5 = 1-9685395 8 = 6 = 2-3622474 9 = IiK-hes 2-7559553 3-1496632 3-5433711 Feet into Metres. Feet 1 = 2 = 3 = Metres 0-3047945 0-6095890 0-9143835 Feet Metres 4 = 1-2197680 5 = 1-5239724 6 = 1-8287669 Feet 7 = 8 = 9 = Metres 2-1335614 2-4383559 2-7431504 Metres into Feet. Metres 1 = 2 = 3 = Feet 3-2808992 6-5617984 9-8426976 Metres Feet 4 = 13-1235968 5 = 16-4044960 6 = 19-6853952 Metres 7 = 8 = 9 = Feet 22-9662944 26-2471936 29-5280928 Miles into Kilometres, Miles 1 = 2 = 3 - Kilometres 1-6093 3-2186 4-8279 Miles Kilometres 4 = 6-4373 5 = 8-0466 6 = 9-6559 Miles 7 = 8 = 9 = Kilometres 11-2652 12-8745 14-4838 Kilometres into Miles, Kilometres 1 = 2 = 3 = Miles 0-62138 1-24276 1-86414 Kilometres Miles 4 = 2-48552 5 = 3-10690 6 = 3-72828 Kilometres 7 = 8 = 9 = Miles 4-34966 4-97104 5-59242 Square Feet into Square Metres. Sq. Feet 1 - 2 = 3 = Sq. Metres 0-0929 0-1858 0-2787 Sq. Feet Sq. Metres 4 = 0-3716 5 = 0-4645 6 = 0-5574 Sq. Feet 7 = 8 = 9 = Sq. Metres 0-6503 0-7432 0-8361 Square Metres into Square Feet. Sq. Metres 1 = 2 = 3 = Sq. Feet 10-7698 21-5396 32-3094 Sq, Metres Sq. Feet 4 = 43-0792 5 = 53-8490 6 = 64-6188 Sq. Metres 7 - 8 = 9 = Sq. Feet 75-3886 86-1584 96-9282 Cubic Feet into Cubic Metres. Cub. Feet 1 = 2 = 3 = Cub. Metres 0-028314 0-056628 0-084942 Cub. Feet Cub. Metres 4 = 0-113256 5 - 0-141570 6 = 0-169884 Cub. Feet 7 = 8 = 9 = Cub. Metres 0-198198 0-226512 0-254826 Y Y 690 SELECT METHODS IN CHEMICAL ANALYSIS Cubic Metres into Cubic Feet. Cub. Metres Cub. Feet 1 = 35-3171 2 - 70-6342 3 = 105-9513 Cub. Metres Cub. Feet 4 = 141-2684 5 = 176-5855 6 = 211-9026 Cub. Metres Cub. Feet 7 - 247-2197 8 = 282-5368 9 = 317-8539 Long Tons Long Tons into Tonnes of 1000 Kilos. Tonnes of 1000 Kilos. 1-015649 2-031298 3-046947 Long Tons 4 = O =: Tonnes of 1000 Kilos. 4-062596 5-078245 6-093894 Long Tons 7 - Tonues of 1000 Kilos. 7-109543 8-125192 9-140841 Pounds per Square Inch into Kilogrammes per Square Centimetre. Pounds per Kilos, per Sq. Inch Sq. Centim. 1 = 0-0702774 2 = 0-1405548 3 = 0-2108322 Pounds per Kilos, per Sq. Inch Sq. Centim. 4 = 0-2811096 Pounds per Sq. Inch 7 = Kilos, per Sq. Ceutim. 0-4919418 5 = 0-3513870 8 = 0-5622192 6 = 0-4216644 9 = 0-6324966 Kilogrammes per Square Millimetre into Pounds per Square Inch. Kilos, per Sq. Millim. 1 = 2 = 3 = Pounds per Sq. Inch 1425-45 2850-90 4276-35 Kilos, per Pounds per Sq. Millim. Sq. Inch 4 = 5701-80 Kilos, per Sq. Millim. 7 = Pounds per Sq. Inch 6978-15 5 = 7127-25 8 = 11403-60 6 = 8552-70 9 = 12829-05 Relative Values of French and English Weights and Measures. WEIGHTS. Milligramme Centigramme Decigramme Gramme . . = 0-015438395 . = 0-15438395 . = 1-5438395 . = 15-438395 . = 0-643 0-03216 troy grain 55 55 pennyweight oz. troy = 0-03527 oz. avoirdupois Decagramme Hectogramme . Kilogramme Myriagramme . Quintal metrique Tonne .... . = 154-38395 . = 5-64 . = 3-2154 . = 3-527 . = 2-6803 . = 2-205486 . = 26-803 . = 22-05486 . = 100 kilos. = . = 1000 troy grains drams avoirdupois ozs. troy ozs. avoirdupois Ibs. troy Ibs. avoirdupois Ibs. troy Ibs. avoirdupois 220-5486 Ibs. avoir. 2205-486 WEIGHTS AND MEASURES 691 Different authors give the following values for the gramme : Gramme = 15-44402 troy grains = 15-44242 = 15-4402 = 15-43839 = 15-433159 = 15-43235 Avoirdupois. Long ton = 20 cwt. = 2240 Ibs. - 1015-649 kilogrammes Short ton (2000 Ibs.) . . = 906-8296 Hundredweight (112 Ibs.) . = 50-78245 Quarter (28 Ibs.) . . . = 12-6956144 Pound = 16 ozs. = 7000 grs. = 453-4148 Ounce = 16 drams = 437'5 grs. = 28-3375 Dram = 27'344 grains = 1-77108 Grain . . = 0-064773 grammes gramme Troy (Precious Metals). Pound = 12 ozs. = 5760 grs. = 373-096 grammes Ounce = 20 dwts. = 480 = 31-0913 Pennyweight . . = 24 = 1-55457 gramme Grain = 0-064773 Ounce Dram Scruple Troy (Pharmacy). = 8 drams = 480 grs. = 31-0913 gramme - 3 scruples = 60 ., - 3-8869 . = 20 = 1-29546 gramme Inch (th yard) Foot (^rd yard) . Yard. Mile (1760 yards) MEASURES OF LENGTH. Millimetre = 0-03937 inch Centimetre 0-393708 Decimetre = 3-937079 inches Metre 39-37079 3-2808992 feet = 1-093633 yard rf) . . . = 2-539954 centimetres f; . . . = 3-0479449 decimetres . = 0-91438348 metre ,rds) . = 1609-3149 metres SUPERFICIAL MEASURES. Square millimetre > ,, centimetre decimetre metre or centiare j^th of a square inch 0-00155 0-155086 15-5086 inches 0-10769 foot 1550-86 inches 10-7698 feet 1-196033 yard 692 SELECT METHODS IN CHEMICAL ANALYSIS Are Hectare Square inch foot yard Acre (4840 square yards) 1076-98 feet 119-6033 yards 0-098845 rood 11960-33 yards 2-471143 acres 645-109201 millimetres 6-45109 centimetres 9-2903 decimetres 0-836097 metre 0-404671 hectare MEASURES OF CAPACITY. Cubic millimetre . . = 0-000061029 cubic inch centimetre . . = 0-061029 10 cubic centimetres . = 0-61029 100 . = 6-10295 ., inches 1000 or litre . . = 61-0295688 " . = 1-760773 imperial pint M > . = 0-2200967 gallon Decalitre . = 610-295688 cubic inches ,, . . 2-2009668 imp. gallons Hectolitre . - 3-5317 cubic feet ... . = 22-009668 imp. gallons Cubic metre . . = 1-308 cubic yard . - 35-3171 feet Cubic inch = 16-3855 cubic centimetres foot = 28-3159 decimetres yard = 0-764520696 metre BRITISH IMPERIAL MEASURES. Pint (i gallon) Quart (i ) Imperial gallon = 0-567932 litre - 1-135864 - 4-54345797 litres WEIGHT OF WATER, &c. 1 cubic inch 252-45 grs. 1 pint ( = 34-65 cubic inches) .... 1-25 Ib. 1 cubic foot ( = 6-25 galls., or 1000 ozs.) . 62-50 Ibs. 1 gallon ( = 277-274 cubic inches) . . . 10-00 Ibs. 1-8 cubic foot 1 cwt. 35-84 cubic feet 1 ton. 11-20 gallons 1 cwt. 224-0 1 ton. A cubic inch of mercury = 3425-25 grains. Baum's Hydrometer The following tables give the comparison of the degrees of Baume's hydrometer with the specific gravity : SPECIFIC GKAVITY TABLES 693 Table for Liquids Heavier than Water. Degrees ! Specific Baume Gravity Degrees Baume Specific Gravity Degrees Baume Specific Gravity 1-000 26 1-206 52 1-520 1 1-007 27 1-216 53 1-535 2 1-013 28 1-226 54 1-551 3 1-020 29 1-236 55 1-567 4 1-027 30 1-246 56 1-583 5 1-034 31 1-256 57 1-600 6 1-041 32 1-267 58 1-617 7 1-048 33 1-277 59 1-634 8 1-056 34 1-288 60 1-652 9 1-063 35 1-299 61 1-670 10 1-070 36 1-310 62 1-689 11 1-078 37 1-322 63 1-708 12 1-086 38 1-333 64 1-727 13 1-094 39 1-345 65 1-747 14 1-101 40 1-357 66 1-767 15 1-109 41 1-369 67 1-788 16 1-118 42 1-382 68 1-809 17 1-126 43 1-395 69 1-831 18 1-134 44 1-407 70 1-854 19 1-143 45 1-421 71 1-877 20 1-152 46 1-434 72 1-900 21 1-160 47 1-448 73 1-924 22 1-169 48 1-462 74 1-949 23 1-178 49 1-476 75 1-974 24 1-188 50 1-490 76 2-000 25 1-197 51 1-505 Table for Liquids Lighter than Water. Degrees Baume Specific Gravity Degrees Specific Baume Gravity Degrees Baume Specific Gravity 10 1-000 27 0-896 44 0-811 11 0-993 28 0-890 45 0-807 12 0-986 29 0-885 46 0-802 13 0-980 30 0-880 47 0-798 14 0-973 31 0-874 48 0-794 15 0-967 32 0-869 49 0-789 16 0-960 33 0-864 50 0-785 17 0-954 34 0-859 51 0-781 18 0-948 35 0-854 52 0-777 19 0-942 36 0-849 53 0-773 20 0-936 37 0-844 54 0-768 21 0-930 38 0-839 55 0-764 22 0-924 39 0-834 56 0-760 23 0-918 40 0-830 57 0-757 24 0-913 41 0-825 58 0-753 25 0-907 42 0-820 59 0-749 26 0-901 43 0-816 60 0-745 694 SELECT METHODS IN CHEMICAL ANALYSIS Twaddell's Hydrometer To convert degrees of Twaddell's hydrometer into specific gravity, multiply the number by 5, and add 1000 to the product. Example. 25 Twaddell x 5 + 1000 = 1125 specific gravity. To reduce specific gravity into degrees Twaddell, deduct 1000 from the number, and divide the remainder by 5. Example. Specific gravity 1125-1000-^5 = 25 Twaddell. Percentage of Soda in Aqueous Solutions of Various Specific Gravities. Temp. 15. Specific Gravity Na a O p.c. Specific Gravity Na 2 p.c. 1 1 Specific Gravity Na 2 p.c. 1-015 1 1-190 13 1-355 25 1-020 2 1-203 14 1-369 26 1-043 3 1-219 15 1-381 27 1-058 4 1-233 16 1-395 28 1-074 5 1-245 17 1-410 29 1-089 6 1-258 18 1-422 30 1-104 7 1-270 19 1-488 35 1-119 8 1-285 20 1-558 40 1-132 9 1-300 21 1-623 45 1-145 10 1-315 22 1-690 50 1-160 11 1-329 23 1-760 55 1-175 12 1-341 24 1-830 60 Percentage of Caustic Potash in Aqueous Solutions of Various Specific Gravities. Temp. 15. Specific Gravity K 2 p.c. Specific Gravity K 2 p.c. Specific Gravity K 2 0p.c. 1-0050 0-5658 1-1182 11-882 1-30 29-34 1-0153 1-6970 1-1437 14-145 1-34 32-14 1-0260 2-8290 1-1702 16-408 1-38 34-74 1-0369 3-9610 1-1979 18-671 1-42 37-97 1-0478 5-0020 1-2268 | 20-935 1-46 42-31 1-0589 6-2240 1-2493 I 22-632 1-50 46-45 1-0703 7-3550 1-2805 26-895 1-54 50-09 1-0819 8-4870 1-3131 27-158 1-58 53-06 1-0938 9-6190 SPECIFIC GRAVITY TABLES 695 Percentage of Ammonia in Aqueous Solutions of Various Specific Gravities. Temp. 14. Specific Gravity NH 3 p.c. Specific Gravity NH, p.c. ' Specific Gravity NH 3 p.c. ! 8844 36 9133 24 9520 12 8864 35 9162 23 9556 11 8885 34 9191 22 9593 10 8907 33 9221 21 9631 9 8929 32 9251 20 9670 8 8953 31 9283 19 9709 7 8976 30 9314 18 9749 6 9001 29 9347 17 9790 5 9026 28 9380 16 9831 4 9052 27 9414 15 9873 3 9078 26 9449 14 9915 2 9106 25 9484 13 9959 1 Percentage of Nitric Acid in Aqueous Solutions of Various Specific Gravities. Temp. 15. Specific Gravity HN0 3 p.c. Specific Gravity HN0 3 p.c. Specific Gravity HN0 3 p.c. 1-010 2-00 1-225 36-00 1-429 71-24 1-022 4-00 1-251 40-00 1-438 74-01 1-045 7-22 1-274 43-53 1-451 77-66 1-067 11-41 1-298 47-18 1-463 80-96 1-077 13-00 1-323 50-99 1-474 84-00 1-089 15-00 || 1-339 53-81 1-482 86-17 1-105 17-47 |! 1-353 56-10 1-494 89-56 1-120 20-00 1-372 59-59 1-506 93-01 1-138 23-00 1-381 61-21 1-514 95-27 1-166 27-00 1-400 ! 65-07 1-523 97-89 1-185 30-00 1-410 67-00 1-530 99-72 1-211 33-86 1-419 69-20 1-530 100-00 696 SELECT METHODS IN CHEMICAL ANALYSIS Percentage of Sulphuric Acid in Aqueous Solutions of Various Specific Gravities. Temp. 15. Specific Gravity H 2 S0 4 p.c. .Specific Gravity 1-0064 1 1-1060 1-0130 2 1-1136 1-0190 3 1-1210 1-0256 4 1-1290 1-0320 5 1-1360 1-0390 6 1-1440 1-0464 7 1-1590 1-0536 8 1-1740 1-0610 9 1-1900 1-0680 10 1-2066 1-0756 11 1-2230 1-0830 12 1-2390 1-0910 13 1-2560 1-0980 14 1-2720 2 SO,p.c. Specific Gravity H 2 S0 4 p.c. 15 1-2890 38 16 1-3060 40 17 1-3510 45 18 1-3980 50 19 1-4480 55 20 1-5010 60 22 1-5570 65 24 1-6150 70 26 1-6750 75 28 1-7340 80 30 1-7860 85 32 1-8220 90 34 1-8376 95 36 1-8426 100 Percentage of Hydrochloric Acid in Aqueous Solutions of Various Specific Gravities. Temp. 15. Specific Gravity HCl p.c. Specific Gravity HCl p.c. Specific Gravity HCl p.c. 1-0020 0-408 1-0637 13-049 1-1802 36-292 1-0040 0-816 1-0738 15-087 1-1846 37-108 1-0060 1-124 1-0818 16-718 1-1857 37-516 1-0100 2-039 1-0899 18-349 1-1875 37-923 1-0140 2-854 1-1000 20-388 1-1893 38-330 1-0180 3-o70 1-1143 23-242 1-1910 38-738 1-0220 4-486 ; 1-1287 26-098 1-1928 39-146 1-0279 5-709 ! 1-1410 28-544 1-1946 39-554 1-0337 6-932 1-1515 30-582 1-1964 39-961 1-0397 8-155 1-1641 33-029 1-1982 40-369 1-0457 9-379. 1-1741 35-068 1-2000 40-777 1-0557 11-418 ATOMIC WEIGHTS 697 Table of Atomic Weights. This table represents the latest and most trustworthy results, reduced to a uniform basis of comparison, with oxygen =16 as starting-point of the system.* Name Symbol Atomic Weight Nam* Symbol Atomic Weight Aluminium . . Al 27- Neodymium . . Nd 140'5 Antimony . . Sb 12O ! Nickel . . . Ni 58-7 Arsenic ... As 75- Nitrogen. . . X 14-03 Barium Ba 137-43 Osmium ... Os 190-8 Bismuth . . . , Bi 208-9 Oxygen 4 . . 16-000 Boron . . . ; B 11- Palladium . . Pd 106-6 Bromine Br 79-95 Phosphorus . .IP 31- Cadmium . . Cd 112- Platinum . . Pt 195- Cagsium . . . Cs 132-9 Potassium K 39-11 Calcium . . . Ca 40-0 Praseodymium Pr 143-5 Carbon . . . C 12- Ehodium Bh 103- Cerium Ce 140-2 Bubidium . . Kb 85-5 Chlorine Cl 35-45 Ruthenium . . Bu 101-6 Chromium . . Cr 52-1 Samarium . . Srn 150- Cobalt ... Co 59- Scandium Sc 44. Columbium ' . . - Cb 94- Selenium Se 79-0 Copper . . . Cu Didymium '-' . . Di 63-6 142-12 Silicon . Silver Si Ag 28-4 107-92 Erbium . . . Er 166-3 Sodium . Na 23-05 Fluorine. . . F 19- Strontium Sr 87-6 Gadolinium . . Gd 156-1 Sulphur . S 32-06 Gallium . . Ga 69- Tantalum Ta 182-6 Germanium . . j Ge 72-3 Tellurium Te 125- Glucinum " . j Gl 9- Terbium . Tb 160- Gold . . .An 197-3 Thallium Tl 204-18 Hydrogen . . | H 1-008 !| Thorium. Th 232-6 Indium . . . \ In 113-7 Thulium . Tu 170-7 Iodine ... I 126-85 Tin . . . Sn 119- Iridium ... Ir 193-1 Titanium Ti 48- Iron . . . . Fe 56-0 Tungsten W 184- Lanthanum . . La 138-2 I Uranium U 249-6 Lead Pb 206-95 Vanadium V 51-4 Lithium . , . . Li 7-02 Ytterbium Yb 173- Magnesium . . Mg 24-3 Yttrium . Y 89-1 Manganese . . Mn 55- Zinc Zn 65-3 Mercury . . . Hg 200' '. Zirconium Zr 90-6 Molybdenum . . | Mo ! 96- ' Has priority over niobium. Has priority over beryllium. Now split into neo- and praseo-dymium. Standard, or basis of the system. Chemical News, Vol. 69, p. 209. INDEX ABEL, Sir F. A., separation of phos- phorus from iron, 519 and Field, F., detection of bismuth in copper, 363 Forbes, Mr., and Matthiessen, preparation of pure iron, 160 Acid, arsenic, test for, 405 arsenious, estimation of, 404 identification of, 403 - boracic, estimation of, 603 carbonic, estimation of, 598. 601 in animal charcoal, 567, 574 - in gas, 642 chromic, estimation of, 128 free chromic, detection of, 127 hydrochloric, detection of, 558 of arsenic in, 405 estimation of, 644 purification of, 557 molybdic, detection and estima- tion of, 140 process for phosphoric acid, 506 recovery of, 509 nitric, detection of, 524 estimation of, 526 nitrous, detection of, 532 and nitric oxide, estimation of, 644 osmic, reduction of, 457 - oxalic, process for phosphoric acid, 512 perchloric, for estimating potas- sium, 7 - phosphoric, &c., electrolytic separation of copper from, 296 estimation of, 491 separation from various me- tals, 516 of manganese from iron in presence of, 198 of tin from, 400 of uranium from, 133 - phosphorous, preparation, detec- tion, and estimation of, 522 preparation of pure titanic, 120 Acid, selenic, preparation of, 427 selenious, preparation of, 427 sulphuric, anomalies in detecting, 481 detection of free, 484 of impurities, 486 purification of, 485 separation of manganese, iron, and, 199 sulphurous, detection of, 487 in gas, 643 tungstic, from wolfram, prepara- tion of, 139 vanadic, preparation of, 137 Adriaanzs, A., estimation of phos- phoric acid, 504 Agthe, M. E., separation of phos- phorus from iron, 517 Air in coal gas, detection of, 589 Alibegoff, M., separation of uranium from most heavy metals, 132 Alkali manufacture, examination of the commercial products of, 10 Alkalies, estimation in fire-clays, &c., 39 from silicates, separation of, 26 in silver nitrate, detection of, 252 Alkaline carbonates, analysis of, 18 Alkalinity, indicators for, 672 Allen, A. H., distinction between phosphates and arseniates, 490 estimation of iron, 165 of tin binoxide, 384 tests for cobalt, 208 Allen, 0. D., separation of cassium from rubidium, 26 - extraction of caasium and rubi- dium from lepidolite, 24 Alloys of lead, estimation of bismuth in, 371 Alt, H., and Schulze, J., separation of nickel from zinc, 206 Alum making, assay of clays for, 152 Alumina, detection and estimation, 150 700 SELECT METHODS IN CHEMICAL ANALYSIS Alumina, precipitation of, 150 Aluminium, 150 electrolytic separation of cobalt, nickel, zinc, and iron from, 230 separation of, 153 of chromium from, 129 of iron from, 180 of manganese from, 199 of phosphoric acid from, 516 and chromium, electrolytic sepa- ration of nickel, cobalt, &c., from, 232 from gallium, separation of, 159 iron, and manganese, separation from phosphoric acid, 198 Ammonia, 39 estimation of, 644 in gas liquor, 42 -free water, 652 reagent for gaseous, 649 Ammoniacal solutions, preparation of silver by reduction of its, 240 Ammonio-phosphate, estimation of zinc as, 147 Ammonium chloride in analysis, 42 Analyses, quantitative, precipitation of metallic copper in, 263 Analysis, ammonium chloride in, 42 blowpipe, (554 chemical, application of hydrogen peroxide in, 674 electrolytic, 617 estimation of antimony in the antimony sulphide obtained in, 381 new methods of, 657 of borates and rluoborates, 604 of cerite, 61, 104 of coal, 576 of coal gas 589, 633 of coal and peat, 681 of gadolinite, 87 of gas from blast furnaces where wood is used, 632 of gas from the mud of a pond, 633 of gold and platinum salts of organic bases, 678 of gun and bell metals, 393 - of kelp, 548 of limestones. &c., 610 of meteoric iron, immediate, 172 of meteorites, 177 of minium or red lead, 337 of mixtures of alkaline mono- and bi-carbonates, 18 of natural tantalates, 64 of nickel and cobalt ores, 221 of platinum ores, 437 of salt-cake, 10, 12 of samarskite, 81 Analysis, of silicates, 2D of sulphuric anhydride, 487 of tin ware, 397 of vanadium sulphates, 134 of various mixtures of gases, 628, 634 quantitative spectral, 656 separation of minerals for, 671 Animal charcoal, assay of, 5(54 estimation of the decolourising power of, 565 Antimony, 375 and arsenic, estimation of, 407 electrolytic separation of arsenic from, 414 estimation of, 378, 380 - from tin, electrolytic separation of, 390 in minerals, rapid detection of, 378 separation from arsenic, 410 from mercury and copper, 382 of tin from, 387 - tin, and arsenic, separation of, 412, 415 Apatite, analysis of, 46 Apjohn, E., detection of titanium, 120 detection of vanadium, 133 Aqueous vapour in gas, estimation of, 642 Arnold, A. E., assay of tin ores, 387 Arnot, M., estimating the decolour- ising power of animal charcoal, 565 Arseniates and phosphates, distinc- tion between, 490 Arsenic, 400 acid, estimation of arsenious acid in presence of, 404 and antimony, estimation of, 407 detection in various substances, 402 detection of, 400 electrolytic deposition of, 404 estimation in ores, 408 from copper, separation of, 417 - in commercial phosphorus, de- tection of, 489 in copper, detection of, 418 in hydrochloric acid, detection of, 556 - purification of sulphuric acid from, 485 in sulphur, estimation of, 422 in tartar emetic, detection of, 414 separation from other metals, 406 tersulphide, estimation of arsenic in, 408 tin, and antimony, separation of, 412, 415 INDEX 701 Arsenical and antimonial com- pounds, solution of, 410 Arsenious acid, estimation of, 404 identification of, 403 Assay of animal charcoal, 504 of clays for alum making, 152 of coal, 585 of commercial iodine, 539 of copper pyrites, 276 of galena in the wet way, 320 of mercury ores, 257 of silver, volumetric, 248 of tin ores, 385 Atomic weights table, 697 Attarberg, A., estimation of phos- phoric acid, 512 Aubel, C., estimation of copper sub- oxide, 292 Avery, C. E., decomposition of sili- cates, 605 BAAXD, A., electrolytic determination of iron, 162 Bailey, G. H., separation of zirco- nium from titanium, 122 Balling, Mr., modification of Jiipt- ner's process for the separation of gold, 433 Barium and strontium, separation of calcium from, 48 separation of lead from, 336 of manganese from, 201 of strontium from, 48 strontium, and calcium, indirect estimation of, 43 sulphate, precautions in precipi- tating, 484 Barnes, J., estimating the value of zinc powder, 149 Base, estimation of nitric acid when combined with any, 531 Bases in general, separation of phos- phoric acid from, 517 Baudrirnont, M., detection of chlo- rine, 550 Baume's hydrometer, 692 Bayley, T., detection of cadmium, 304 Beckmann, M., detection of alumina, 150 Beilstein, F., and Garvein, M., pre- cipitation of cadmium, 297 and Jawein, M., electrolytic determination of zinc, 142 and Luther, K., separation of iron from aluminium, 181 Bell and gun metals, analysis of, 393 Benedict, R., and Gaus, L., separa- tion of lead from silver, 324 Bergeret and Mayencon, MM., de- tection of arsenic, 402 Bergmann and Fresenius, MM., elec- trolytic separation of silver, 245 Bertrand, A., estimation of potas- sium, 7 Berzelius, M., detection of lithia, 23 Bettell, W., decomposition of sili- cates, 608 Bichromate and free chromic acid, detection of, 127 Binoxide of tin, estimation of, 384 Bisbee, D. B., ammonia-free water, 652 Bismuth, 363 copper, and cadmium, separation of, 374 detection by the blowpipe, 364 of arsenic in, 416 electrolytic separation of, 367 estimation of, 365, 371 in copper, detection of, 363 process for phosphoric acid, 503 purification of, 366 - separation from various metals, 368 of tin from, 392 subnitrate, detection of calcium phosphate in, 368 Black-ash, 12 Blast furnace where wood is used, analysis of gas from, 632 Bleaching powder, estimation of chlorine in, 553 Blende, preparation of indium from, 361 Blondlot, M., purification of sul- phuric acid, 485 Blossom, Mr., detection of traces of gold, 430 Blowpipe analysis, 654 assay of coal, 585 Bloxam, C. L., detection of calcium in presence of strontium, 47 Blum, L., separation of manganese from iron, 198 Blunt, T. P., analysis of red lead, 337 detection of nitric acid, 524 Boettger, R., detention of vanadium in iron ores, 136 Bong, G., decomposition of silicates, 609 Boracic acid, estimation of, 603 Borates, analysis of, 604 Boron, detection of, 602 Brand, A., electrolytic determination of cobalt, 207 precipitation of cadmium, 298 separation of bismuth, 367 of manganese, 190 of mercury, 253 of nickel, cobalt, Joulie, M., estimation of phosphoric acid, 497 Julien, A. A., estimation of nickel, 203 KELP, analysis of, 548 Kern, S., detection of iodine, 543 of traces of gold, 430 INDEX 709 Kern, S., analysis of coal and peat, 581 Kernan, E., phosphorus holder, 490 Kiliani and Von Miller, Messrs., elec- trolytic determination of zinc, 142 Kinnear, J. B., estimation of nitric acid, 529 Kitchin, A., estimation of phosphoric acid, 502 Knop, W., estimation of ferrous oxide in silicates, 613 and Hazard, J., estimation of potash and soda, 22 and Wolf, Messrs., precipitation of potassium, 9 Kohn, C. A., detection of cadmium, 300 detection of lead, 313 electrolytic deposition of anti- mony, 377 detection of copper, 26 of mercury, 256 Kolb, M., estimation of nitrites, 537 Kopp, M., detection of lead in tin paper, 323 Koppmayer,M., estimation of sulphur in iron, &c., 477 Kraut, M., estimation of iodine, 543 Kroupa, G., reagent for gaseous ammonia, 649 Kruting, J., electrolytic separation of silver, 245 and Cocheteux, A., volumetric estimation of iron, 168 Kuhlmann, M. F., decomposition of silicates, 607 Kunsel, C., estimation of copper, 268 Kustel, G., separation of tellurium from selenium and sulphur, 424 LAND, W. J., estimation of hydro- sulphuric acid in mineral waters, 479 Lanthana, purification of, 106 Lanthanum from didymium, separa- tion of, 59 Laufer, E., separation of quartz from silicates, 615 Laurie, A. P., volumetric estimation of lead, 341 Lea, C., analysis of platinum ores, 445 detection of iodine, 540 of ruthenium, 463 test for the presence of palladium, 453 Lead, 311 alloys, estimation of bismuth in, 371 cadmium, Ac., separation of cop- per from, 292 Lead, detection of, 313, 318 estimation of, 315, 318 from gallium, separation of, 340 in ores, estimation of, 322 in the tin linings of vessels, 322 peroxide, detection and estimation of, 322 valuation of commercial, 342 precipitation of, 314 preparation of pure, 312 process for phosphoric acid, 504 red, analysis of, 337 separation of, 316 - from barium and cadmium, 336 from silver, 324 from zinc, 335 of bismuth from, 370 of, from various metals, 323 of thallium from, 355 of tin from, 392 volumetric estimation of, 341 white, 336 Leeds, A. E., estimation of chlorine, 552 Leiscn, W. G. determination of cobalt," 207 estimation of cadmium, 298 of nickel, 203 of zinc, 146 Lepidolite, extraction of caesium, lithium, and rubidium from, 22 Le Eoy, G. A., electrolytic separation of cobalt and nickel from iron, 226 Lestelle, H., estimation of soluble sulphides in commercial soda and soda-ash, 17 Letheby, M., estimation of sulphur in coal gas, 594 Levol, M., precipitation of lead, 314 preparation of silver by reduction of the chloride in the wet way, 239 Liebig, M., separation of cobalt from nickel, 210 Liebig's process for preparing silver, 237 Lime, purification of thallium by fusion in, 351 Lindo, D., estimation of chlorine, 551 Liquids, to prevent the bumping of boiling, 678 Lithia, estimation of, 23 Lithium, ctesium, and rubidium, ex- traction from lepidolite, 22 sodium, and potassium, separa- tion of, 25 Liversidge, A., estimation of fluorine, 560 Lory, M., estimation of carbonic acid in waters, 598 710 SELECT METHODS IN CHEMICAL ANALYSIS Lowe, M., estimation of lead in ores, 322 Luckow, M., electrolytic determina- tion of nitric acid, 525 estimation of copper, 291 reduction of copper, 261 separation of lead, 317 Luckow's process for estimating copper in Mansfeld ores, 285 Lunge, G., estimation of sulphur, 475 Luther, E., and Beilstein, F., sepa- ration of iron from aluminium, 181 Lyman, B. S., blowpipe assay of coal, 586 Lyte, F. M., determination of potash and soda, 21 estimation of sulphur in mineral waters, 478 of zinc, 145 purification of sulphuric acid, 485 - separation of lead, zinc, and silver, 336 MACKINTOSH, J. B., electrolytic esti- mation of copper, 290 Magnesium, application of metallic, 49 barium, calcium, and alkalies, separation of manganese from, 201 determination of, 49 from calcium, separation of, 50 from potassium and sodium, separation of, 54 - process for the estimation of phosphoric acid, 492 pyro-arseniate, estimation of ar- senic as, 406 - separation of aluminium from, 155 of iron from, 188 of manganese from, 201 Manganese, 189 chromium, and aluminium, elec- trolytic separation of cobalt, nickel, &c., from, 232 detection of, 194 estimation of, 191 nickel, &c., separation of iron from, 185 separation from various metals, 197 of gallium from, 308 of nickel and cobalt from, 224 - and aluminium, electrolytic separation of cobalt, nickel, zinc, and iron from, 231 Mann, C., estimation of zinc, 145 Mansfeld processes for estimating copper in ores, 278 Marchand, M., volumetric estimation of potassium, 9 Marignac, M., analysis of borates and fluoborates, 604 Marsh's apparatus for the detection of arsenic, improvement in, 402 test for the detection of arsenic, 400 Maschke, 0., and Schoenn, M., detec- tion of molybdic acid, 140 Maskelyne, N. S., decomposition of silicates, 606 Matthey, E., electrolytic separation of bismuth, 373 Matthiessen, M., Abel, Sir F. A., and Forbes, Mr., preparation of pure iron, 160 Mayencon and Bergeret, MM., detection of arsenic, 402 Mayer, M. L., estimation of arsenious. acid, 404 Mayrhofer, J., and Donath, E., sepa- ration of cadmium from copper, 300 Mclvor, K. W. E., and Gibbs, W., determination of magnesium, 49 Measures and weights, mutual con- version of French and English, 687 relative values of French and English, 690 Mebus, A., analysis of alkaline mono- and bi-carbonates, 18 Mercurial vapours, test for, 252 Mercury, 252 blowpipe test for, 252 detection of, 256 electrolytic estimation of, 258 estimation of, 258 - by distillation, 254 ores, assay of, 257 process for phosphoric acid, 506 separation of, 259 of antimony from, 382 of bismuth from, 374 of cadmium from, 301 of copper from, 293 of gallium from, 306 of lead from, 324 of thallium from, 357 and palladium, separation of arsenic from, 422 Merget, M., test for mercurial va- pours, 252 Mescezzini and Parodi, Messrs., electrolytic determination of zinc, 142 Messinger, J., separation of lead, 317 Metallic arsenic, purification of, 400 INDEX 711 Metallic cobalt, 206 nickel, preparation of, 201 zinc, precipitation of, 141 Metals, cerium, separation and esti- mation of, 56 separation of uranium from, 131 detection and estimation of lead in the presence of other. 318 estimation of nitric acid when combined with heavy, 531 separation of selenium from, 426 of uranium from most heavy, 132 Meteoric iron, immediate analysis of, 172 Meteorites, analysis of, 177 Meunier, M. S., analysis of meteoric irons, 172 Millon and Commaille, MM., pre- cipitation of metallic copper, 263 Millon and Morin, MM., analysis of tin ware, 397 Mineral waters, estimation of sul- phur in, 478 Minerals, detection of gold in, 42^ of mercury in, 256 of thallium in, 343 estimation of potash and soda in, 22 for analysis, separation of, 671 Minium, analysis of, 339 Moffat, K. C., estimating free sul- phuric acid, 484 Mohr; C., estimation of phosphoric acid, 497, 502 Mohr, F., assay of galena, 321 estimation of potassium, 6 Mohr, M., separation of magnesium from calcium, 53 volumetric estimation of copper, 266 of iron, 166 Moissenet, M., assay of tin ores, 386 Molybdenum, 140 Molybdic acid, detection and estima- tion of, 140 process for phosphoric acid, 506 recovery of, 509 Moore, T., separation of nickel from iron, 225, 228 Morgan, T. M., rapid analysis of gases, 638 Morin and Millon, MM., analysis of tin ware, 397 Morrell, T. J., estimation of sulphur in iron, &c. t 477 Mosandra, 86 Moyaux, M., estimation of iron, 168 Muck, F., ash in coal, 583 Muir, M. M. P., detection of bismuth, 363 detection of tin, 392 estimation of bismuth, 365 Miiller, H., to prevent the bumping of boiling liquids, 678 NESSLEK'S test for ammonia, 39 Neubauer, C., detection of iodine chlorine, and bromine, 545 Neumann, G., electrolytic separation of thallium, 352 Nicholson, E., volumetric estima- tion of carbonic acid by a modi- fication of Scheibler's apparatus, 574 Nickel, 201 estimation of, 202 from iron, separation of, 225, 228 separation from various metals, 205, 226 of gallium from, 307 and cobalt ores, analysis of, 221 from manganese, separation of, 224 and iron from cobalt, separation of, 226 cobalt, and iron from zinc, sepa- ration of, 229 - or manganese, separation of thallium from, 358 manganese, &c., separation of iron from, 185 - or cobalt, separation of copper from, 294 - separation from various metals, 233 Niederhofheim M., and Jannasch, P., separation of manganese from zinc, 200 Nissenson, H., electrolytic deposition of antimony, 377 Nitrate of silver test for arsenic acid, 405 Nitrates, electrolytic determination of nitric acid in, 525 estimation of nitric acid in com- mercial, 530 Nitric acid, detection of, 524 estimation of, 526 oxide and nitrous acid, estima- tion of, 644 Nitrites, estimation of, 533 Nitrogen by weight, estimation of, 523 in gas, 642 Nitrous acid, detection of, 532 oxide, estimation of, 645 712 SELECT METHODS IN CHEMICAL ANALYSIS ODLING, W., detection of arsenic in commercial copper, 419 Ogilvie, T. B., estimation of phos- phoric acid, 493 Oppenheim, M., separation of tellu- rium and selenium, 422 Orangite and thorite, examination of, 74, 98 Ores, analysis of platinum, 437 assay of mercury, 257 estimation of arsenic in, 408 separation of nickel and cobalt from their, 214 Organic liquids, estimation of iodine in, 543 or inorganic matter, detection of arsenic in, 402 Orlowski, A., estimation of cadmium, 299 Osmic acid, reduction of, 457 Osmiridium, analysis of, 458 Osmium, 457 from iridium, separation of, 458 Oxalate, estimation of zinc as, 146 Oxalic acid process for phosphoric acid, 512 Oxidation, improved methods? of, 653 Oxide, estimation of carbonic, 645 of nitrous, 645 Oxland, T. C., assay of copper pyrites, 277 Oxygen in water, estimation of, 646 PALLADIUM, 453 separation of, 454 test for the presence of, 453 and mercury, separation of ar- senic from, 422 Papasogli, G., tests for cobalt, 209 Paper hangings, detection of arsenic in, 402 Parnell, E. W., estimation of arsenic in ores, 408 separation of arsenic from copper, 417 Parodi and Mescezzini, Messrs., electrolytic determination of zinc, 142 Patera, M., estimation of uranium, 129 Pattinson J., estimation of man- ganese, 193 Pattison and Clarke, Messrs., separa- tion of cerium, 56 Pearson, A. H., estimation of chro- mium, 125 estimation of sulphur, 473 Pearson, F. P., assay of copper pyrites, 276 Peat and coal, analysis of, 581 Pellet and Champion, Messrs., esti rnation of phosphoric acid, 508 Pelouze's method for the estimation of nitric acid, 526 Penfield, S. L., volumetric estimation of fluorine, 561 Penfolcl, S. L., and Harper, D. N., precipitation and washing of alumina, 151 separation of aluminium, 154 Pentasulphide and tersulphide of arsenic, estimation of arsenic in, 408 Perchloric acid for estimating potas- sium, 7 Percy, Dr., analysis of British iron ores, 611 Perofskite, 98 Philippia, 85 Phipson, Dr., separation of cobalt from nickel, 210 Phosphate, detection of chromium as, 127 Phosphates and arseniates, distinc- tion between, 490 ' reduced,' estimation of, 514 Phosphoric acid, &c., electrolytic separation of copper from, 296 estimation of, 491 separation from various me- tals, 516 of manganese from iron in presence of, 198 of tin from, 400 of uranium from, 133 Phosphorous acid, preparation, de- tection, and estimation of, 522 / Phosphorus, detection of, 488 r holder, 490 preparation of silver by precipita- tion with, 238 purification of vanadic acid from, 138 separation of, 517 Piesse, C. H., estimation of sulphur in iron, steel, and iron ores, 476 Pisani, F., separation of zirconium from titanium, 123 Platino-chloride, estimation of thal- lium as, 353 Platinum, 436 chloride, preparation of, 452 crucibles, mending, 453 preservation of, 676 detection of, 436 electrolytic precipitation of, 452 ores, analysis of, 437 purification of, 436 separation of iridium from, 455 of rhodium from, 454 of ruthenium from, 466 and gold salts of organic base i analysis of, 678 INDEX 713 Potash and soda in minerals, estima- tion of, 22 Potassium, 1 chlorate, valuation of, 559 - estimation of, 1 ferrocyanide, estimation of copper with, 267 from sodium, separation of, 18 iodide, detection of bromides in, 544 sulphate, estimation of, 6 and sodium, estimation of, 19 separation of magnesium from, 54 - sodium, and lithium, separation of, 25 Pouchet, G., assay of clays for alum making, 152 Precht, M. H., estimation of potas- sium, 3 and Prinzhorn, M., estimation of phosphorous acid, 522 and Eottger, F., estimation of small quantities of sodium chlor- ide, 19 Precipitates, separation of slimy, 671 - treatment of, 666 Price, D. S., estimation of sulphur in pyrites, 469 Prinzhorn and Precht, MM., esti- mation of phosphorous acid, 522 Prochazka and Endemann, MM., detection of traces of copper, 259 Proskauer, B., estimation of sulphur- ous acid in air, 488 Protochloride, estimation of mercury as, 258 Pyrites, assay of copper, 276 estimation of gold in, 431 of sulphur in, 469 etc., estimation of copper in, 266 extraction of silver from, 250 iron, detection of copper in, 291 QUARTZ, separation from silicates, 615 EADEMAKER, C. J., detection of ar- senic in commercial phosphorus, 489 Eammelsberg, C., estimation of ar- senic as magnesium pyro-arseni- ate, 406 Eaoult, F. M., rapid analysis of mixtures of gases, 634 Eease, N., detection ot free hydro- chloric acid, 558 Eeducing agents, new test for, 653 Eeichardt, M., detection of sulphur- ous acid, 488 estimation of sulphur, 476 separation of molybdic acid, 140 of uranium from phosphoric acid, 133 Eeichel, F., estimation of arsenic as magnesium pyro-arseniate, 406 tests for cobalt, 208 Eeinige, M., estimation of iodine, 543 Eeinsch's test for arsenic, 403, 419 Eemel6, A., separation of uranium from most heavy metals, 132 Eenard, M., volumetric estimation of zinc, 143 Eeynolds, M., reduction of sesqui- salts of iron, 165 Eeynoso's process for the estimation of phosphoric acid, 491 Ehodium, 454 separation of iridium from, 456 of ruthenium from, 466 Eiche, M., electrolytic determination of zinc, 142 Eiche' s apparatus for electrolytic analysis, 623 Eichters, E., recovery of molybdic acid, 510 Eivot's process for the estimation of copper, 273 Eobbs, M., and Muir, M. M. P., esti- mation of bismuth, 366 Eocholl, H., decomposition of sili- cates, 611 Eoscoe, Sir H., preparation and puri- fication of vanadic acid, 137 Eose, H., estimation of chromium, 126 of mercury, 254 of selenium, 424 of uranium, 129 separation of aluminium, 156 of lead from mercury, 324 of uranium from most heavy metals, 132 Eoss, Mr., detection of traces of gold, 430 Eottger, F., and Precht, H., estima- tion of small quantities of sodium chloride, 19 Eoussel, G., detection and estimation of vanadium and titanium, 138 Eovera, S., precipitation of lead, 315 Eubidium and caesium, extraction from mineral waters, 23 lithium, and caesium, extraction from lepidolite, 22 Eudorff, F., electrolytic deposition of antimony, 377 determination of cobalt, 207 714 SELECT METHODS IN CHEMICAL ANALYSIS Budorff, F., electrolytic determina- tion of iron, 162 of zinc, 142 reduction of copper, 261 separation of bismuth, 367 of manganese, 190 of mercury, 253 of silver, z45 precipitation of cadmium, 298 of nickel, 202 Euthenium, 461 detection of, 463 estimation of, 462 separation of, 465 SALKOWSKI, E., test for arsenic ac 405 Salt-cake, analysis of, 10, 12 Samaria, phosphorescent spectrum of, 111 purification of, 109 Samarium, 94 Samarskite, analysis of, 81 Scheeppi, H., estimation of arsenic in sulphur, 422 Scheerer, M., separation of magne- sium from calcium, 50 Scheibler, M. C., analysis of gold and platinum salts of organic bases, 678 carbonic acid in animal charcoal, 567 Scheibler's apparatus (modification of) for the volumetric estimation of carbonic acid, 574 Schimidzu, T., and Divers, E., obtain- ing sulphuretted hydrogen in the laboratory, 481 Schloesing, T., estimation of clay, 615 estimation of nitric acid, 528 Schlossberger, M., reagent for sul- phur, 480 Schoenn, M., and Maschke, 0.. detec- tion of molybdic acid, 140 Schonn, M., detection of sulphur, 480 Schroetter, M. V., separation of tellurium and selenium and sul- phur, 424 Schulze J., and Alt, H., separation of nickel from zinc, 206 Schiitzenberger, M., estimation of free oxygen in water, 646 Scott, Mr., estimation of calcium, 45 Sea-water, 99 (fee., detection of iodine in, 542 Selenic acid, preparation of, 427 Seleniferous flue-dust, preparation of selenium from, 426 Selenious acid, preparation of, 427 Selenium, detection of sulphur in 426 estimation of, 424 from seleniferous flue-dust, pre- paration of, 426 -- and -tellurium, 422 Sell, W. J., estimation of chromic acid, 128 Sesqui-salts of iron, reduction of, 165 Sharpies, M., estimation of anti- mony, 378 Sibson, M., estimation of ' reduced ' phosphates, 515 Silica and fluorine, separation of phosphoric acid from, 521 separation of, 610 Silicates, alkalies in insoluble, 26 analysis of, 29 decomposition of, 28, 605 estimation of ferrous oxide in r 613 separation of quartz from, 615 Silicon, 605 Silver, 236 ascertaining the purity of, 244 chloride and iodide, separation of, 250 employment in blowpipe analysis, 654 preparation of silver from, 236 electrolytic separation of, 245 extraction from burnt pyrites, 250 German, estimation of copper in, 265 lead, concentration of, 327 nitrate, detection of alkalies in r 252 test for arsenic acid, 405 preparation by Liebig's process , 237 purification of, 241 separation of copper from, 293 of gallium from, 306 - of lead from, 324 of mercury from, 259 of thallium from, 357 volumetric assay of, 248 estimation of, 246 Skey, M., detection of traces of gold, 428 tests for cobalt, 208 Sloane, T. O'C., note on Classen's electrolytic analysis, 626 Smith, A., estimation of nitrites, 535 Smith, E. F., electrolytic determina- tion of iron, 162 precipitation of platinum, 452 separation of arsenic, 421 of bismuth, 373 INDEX 715 Smith, E. F., electrolytic separa- tion of cadmium from copper, 300 of copper from silver, 294 of gold, 435 of mercury, 254 new test for reducing agents, 653 and Frankel, L. K., electrolytic separation of cadmium from zinc, 302 electrolytic separation of copper from mercury, 293 Smith, J. D., and Teschemacher, F. T., estimation of potassium, 1 Smith, J. L., analysis of natural tantalates, 64 separation of alkalies from sili- cates, 26 Smith, L., separation of thorium from other earthy metals, 63 Soda and potash in minerals, estima- tion of, 22 Soda-ash, 15 analysis, 16 solution, standard, 649 Sodium, 10 lithium, and potassium, separa- tion of, 25 sulphate, estimation of copper with, 268 and potassium, estimation of, 19 separation of magnesium from, 54 separation of potassium from, 18 Sonstadt, E,, purification of plati- num, 436 separation of magnesium from calcium, 51 of minerals for analysis, 671 Specific gravity of coal, 585 tables, 693 Spectra of yttria, 89 Spectral analysis, quantitative, 656 Spectrum, ' orange-band,' 95 Spiller, J., anomalies in detecting sulphuric acid, 481 Spiller 's process for separating phos- phorus from iron, 519 Stammer, C., rapid analysis of mix- tures of gases, 634 Stas, M., ascertaining the purity of silver, 244 improvements in the Gay-Lussac process for the volumetric estima- tion of silver, 246 preparation of pure lead, 311 of pure metallic silver, 236 purification of platinum, 436 of silver by distillation, 241 volumetric assay of silver, 248 Steel, iron, &c., estimation of sul- phur in, 476 Steinbeck's process for estimating copper in ores, 280 Stock, W. F., and Jack, W. E., esti- mation of iron, 170 Stolba, F., detection of alkalies in silver nitrates, 252 determination of cerium, 60 and Charples, MM., reagent for caesium salts, 25 Storer, F. H., assay of galena, 320 estimation of chromium, 125 improved methods of oxidation, 653 Streit, G., and Franz, B., separation of zirconium from titanium, 122 Stromeyer, M., separation of calcium from strontium, 47 Strontium, calcium, and barium, in- direct estimation of, 43 from barium, separation of, 48 separation of calcium from, 47 Struve and Fritzsche, MM., analysis of osmiridium, 458 Stunkel, Dr., Wetzke, Dr., and Wag- ner, Prof., recovery of molybdic acid, 509 Sulphate of barium, precautions in precipitating, 484 precipitation of lead as, 314 Sulphide, estimation of thallium as, 354 of zinc as, 146 of antimony, estimation of anti- mony in native, 380 precipitation of copper as, 263 Sulphides, estimation of soluble, in commercial soda and soda-ash, 17 Sulphocyanide, estimation of copper as, 264 Sulphur, detection of. 480 determination of, 482 estimation of, 469 in coal and coke, estimation of 587 in coal gas, 594 in selenium, detection of, 426 reagent for, 480 separation of tellurium and sele- nium from, 422 Sulphuretted hydrogen, estimation of, 644 in coal gas, 590 to obtain, 481 Sulphuric acid, anomalies in detect- ing, 481 detection of free, 484 of impurities in7 486 purification of, 485 separation of manganese, iron, and, 199 anhydride, analysis of, 487 Sulphurous acid, detection of, 487 716 SELECT METHODS IN CHEMICAL ANALYSIS Sulphurous acid in gas, 643 Button, M., estimation of phosphoric acid, 499 TABLE of atomic weights, 697 Tables, specific gravity, 693 useful, 686 Talbott, J. H., estimation of zinc, 146 separating tin from tungsten, 395 Tamm, H., estimation of zinc, 146 Tantalates, analysis of natural, 64 Tartar emetic, detection of arsenic in, 414 Tate, W., analysis of salt-cake, 12 Tatlock, R., estimation of iodine and bromine, 546 of potassium, 4 Tellurium and selenium, 422 . Tennant's nitrometer, 538 Terbia, preparation of, 84 Terreil, M. A., decomposition of sili- cates, 609 Teschemacher, F. T., and Smith, J. D., estimation of potassium, 1 Test-paper, ultramarine, 674 Thallium, 343 detection and estimation of, 351, 356 electrolytic separation of, 352 estimation of, 353 preparation of, 344 of chemically pure, 349 purification of, 351 separation of bismuth .from, 368 of tin from, 392 from various metals, 355 volumetric estimation of, 354 Thomas, Mr., separation of nickel from iron, 205 Thomson, K. T., indicators for alka- linity, 672 separation of iron from aluminium, 180 Thorite and orangite, examination of, 74, 98 Thorium, separation from other earthy metals, 63 Tichborne, Mr., estimation of nitrites, 533 Tin, 382 binoxide, estimation of, 384 detection of, 392 from antimony and arsenic, sepa- ration of, 412, 415 - linings of vessels, detection of lead in, 322 ores, assay of, 385 paper, detection of lead in, 323 - process for the estimation of phosphoric acid, 491 Tin protochloride, titration of, 270 separation from various metals, 387 of arsenic from, 409 ware, analysis of, 397 Tissandier, G-., white lead, 336 Titanium, 119 minerals, decomposition of, 119 separation of iron from, 187 of tin from, 396 of zirconium from, 122 and vanadium, detection and es- timation of, 138 Tollens, M., estimation of phosphoric acid, 496 and Grupe, M., estimation of ' reduced ' phosphates, 515 Tungsten, 139 separation of tin from, 394 Tungstic acid from wolfram, pre- paration of, 139 ULTRAMARINE TEST-PAPER, 674 Uranium, 129 - electrolytic separation of cobalt, nickel, &c., from, 232 process for estimating phosphoric acid, 499 protochloride, preparation of, 501 separation of, 131, 234 of copper from, 293 of gallium from, 157, 310 of iron from, 184 of nickel or cobalt from, 233 of zinc from, 149 volumetric estimation of, 130 and cerium, separation of man- ganese from, 201 and chromium, separation of iron from, 185 VALENTIN'S process for estimating sulphur in coal gas, 596 Vanadic acid, preparation of, 137 purification of, 138 Vanadium, 133 detection of, 134 estimation of, 136 sulphates, analysis of 134 and titanium, detection and esti- mation of, 138 and zirconium, electrolytic separa- tion of iron from, 187 Van Melckebeke, E., detection of ' bromides, 544 Vermilion, estimation of sulphur in, 478 Vierordt, M., quantitative spectral analysis, 657 INDEX 717 Vignon, M., separation of iron from aluminium, 180 Ville's process for the estimation of phosphoric acid, 494 Vinegar, detection of free sulphuric acid in, 482 Vogt's apparatus for gas analysis, 629 Volcanoes, fumeroles of, 632 Volhard, J., volumetric assay of silver, 249 Von Ankum, M., detection of arsenic in tartar emetic, 414 Von Berg, P., separation of nickel, cobalt, and iron from zinc, 229 Von Klobulow, M., determination of sulphur, 482 Von Knorre, G-., separation of copper from lead, cadmium, &c., 292 separation of iron from manganese, nickel, &c., 185 Von Kobell, M., detection of bismuth by the blowpipe, 364 Von Miller, M., and Kiliani, electro- lytic determination of zinc, 142 Vortmann, G., electrolytic deposition of antimony, 377 determination of nitric acid, 525 of zinc, 142 precipitation of cadmium, 298 separation of bismuth, 368 of mercury, 253 estimation of chlorine, 552 separation of cadmium from cop- per, 300 of lead, 317 WAAGE, P., estimation of sulphur, 475 Wagner, A., estimation of nitrous oxide, 645 of sulphuretted hydrogen in coal gas, 590 Wagner, Prof., Wetzke, Dr., and Stunkel, Dr., recovery of molybdic acid, 509 Warington, K., detection of impuri- ties in sulphuric acid, 486 estimation of phosphoric acid, 504 volumetric estimation of carbonic acid, 576 Warren, H. N., separation of cad- mium from copper and zinc alloys, 302 Wartha, M. V., estimating the hard- ness of water, 652 Water, ammonia-free, 652 detection of fluorine in, 560 estimating the hardness of, 652 estimation of free oxygen in, 646 Waters, mineral, estimation of sul- phur in, 478 Waters, estimation of carbonic acid in, 599 Weights, atomic, table of, 697 correct adjustment of chemical 679 and measures, mutual conversion of French and English, 687 relative values of French and English, 690 Weil, F., estimation of copper, 269 Weiler, A., rapid detection of anti- mony, 380 Wells, J. S. C., separation of cadmium from copper, 300 assay of tin ores, 385 Werner, E. A., detection and estima- tion of thallium, 356 West, Mr., estimation of potassium sulphate, 6 and Zuckschwerdt, Messrs. t estimation of potassium, 5 Wetzke, Dr., Stunkel, Dr., and Wag- ner, Prof., recovery of molybdic acid, 509 Weyl, Th., precipitation of metallic copper, 263 Whitehead, C., separation of gold by quartation with zinc, 433 Wilbur and Whittlesey, Messrs., esti- mation of iron protoxide, 163 Wiley, H. W., detection of hydro- chloric acid, 558 Wilkinson, Mr., rapid analysis of gases, 635 Winckler, C., separation of lantha- num from didymium, 60 Winkler, C., estimation of iron, 167 rapid analysis of gases, 639 Wohler, F., analysis of apatite, 46 of osmiridium, 458 detection of boron. 602 estimation of antimony, 378 of boracic acid, 603 preparation of pure titanic acid, 120 of selenic acid, 427 of tungstic acid, 139 of vanadic acid, 137 separation of aluminium from chromium, 153 of aluminium from magnesium, 155 of cadmium from copper, 299 of iron from aluminium, 180 of nickel or cobalt from zinc, 228 Wolf and Knop, Messrs., precipita- tion of potassium, 9 Wolff, Mr., electrolytic detection of mercury, 256 Woodcock, K. C., detection of traces, of copper, 260 718 SELECT METHODS IN CHEMICAL ANALYSIS Wright, C. B. 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