GIFT OF A SYSTEM OF INSTRUCTION QUANTITATIVE CHEMICAL ANALYSIS. SYSTEM OF INSTEUCTION ra QUANTITATIVE CHEMICAL ANALYSIS. BY DK. C. KEMIGIUS FBESENIUS, PBOFERSOB OF CHEMISTRY AND NATURAL PHILOSOPHY, WIESBADEN, jfrom tt* last HSngltsft anfc (Ktrman HSMtion*. EDITED BY SAMUEL W. JOHNSON, M.A., PROFESSOR OF ANALYTICAL AND AGRICULTURAL CHEMISTRY IN THE SHEFFIELD SCDENTIFIO SCHOOL, YALE COLLEGE. NEW YORK : JOHN WILEY & SON, 15 ASTOB, PLACE. 1874. Entered according to Act of Congress, in the year 1870, by JOHN WILEY, la the Clerk's Office of the District Court of the United States for the Souther* District of New York. JOHN F. TROW & SON, PRINTERS, 25-213 EAST i2TH ST., NEW YORK. EDITORS PEEFAOE. IN preparing this edition of Fresenius' Quantitative Chemical Analysis, the editor has sought by various changes to adapt it to the wants of the American student. The foreign editions have attained such encyclopedic dimensions as to occasion the beginner no little confusion and embarrassment. For this reason the bulk of the work has been considerably re- duced. A few processes which the editor's experience has con- vinced him are untrustworthy, and many more that can well be spared because they are tedious or unnecessary, have been omit- ted. The entire chapter on Analysis of Mineral Waters, excellent as it is, has been suppressed on account of its length, and because the few who have occasion to make detailed investigations in that direction have access to the original sources of information. The section on Organic Analysis has been reduced from sixty to thirty pages, mainly by the omission of processes which from their antiquity or inferiority are more curious than useful. The chap- ters on Acidimetry and Alkalimetry have been likewise greatly condensed, and all that especially relates to Soils and Ashes of Plants has been left out. The recent appearance of an excellent special treatise on "Agricultural Chemical Analysis," by Profes- sor Caldwell, of Cornell University, justifies the last-named omission. On the other hand, some important matter has been added. Bunsen's invaluable new methods of treating precipitates are de- scribed in his own (translated) words. Yarious new methods of estimation and separation are incorporated in their proper places. The editor thankfully acknowledges his indebtedness to several gentlemen for special contributions to this work; viz.: To Dr. J. Lawrence Smith, who has kindly furnished a manuscript account of his admirable method of fluxing silicates for the estimation of alkalies. To O. D. Allen, Esq., late chemist to the Freedom Iron 385213 Works, Lewistown, Pennsylvania, for copious notes of his exten- sive experience in the analyses of steel, iron, and iron ores, which have been freely employed in 229. To Mr. Wm. G. Mixter, chief assistant in the Sheffield Laboratory, for the account of the gold and silver assay. To Professor Brush, of Yale College, Pro- fessor Collier, of Yermont University, and B. S. Burton, Esq., of Philadelphia, for various important facts and suggestions. Just before going to press, Dr. Wolcott Gibbs has communicated an account of his new method of finding at once the total correction for temperature, pressure and moisture in absolute determinations of nitrogen or other gases, which, from its simplicity, convenience, and accuracy must prove of the highest service to chemistry. It will be found, with some other matters,* in an appendix, p. 619. The additions which have been made to the methods of exam- ining ores, it is believed, adapt the work to meet all the ordinary requirements of the metallurgical and mining student. The editor's additions are distinguished, in all important cases, by enclosure in brackets, [ ]. While fully recognizing the necessity of teaching the new notation and nomenclature of chemistry, the editor has in this book retained the old system, because it is identified with the chemical literature of the century, and cannot be speedily for- gotten by practical men. At a time when the most elementary text-books are framed on the "modern " system, it is important to keep the student exercised in the language of the old masters of the science, which is still, and must for some time remain, a part of the vernacular of the physician, the apothecary, the metallurgist, and the manufacturer. SAMUEL W. JOHNSON. SHEFFIELD LABORATORY OF YALE COLLEGE, Dec., 1869. * Viz., assay of chrome iron, and separation of phosphoric acid from lime, almnina, and iron. CONTENTS. PAGH INTRODUCTION ...................................................... 1 PART I. DIVISION I. EXECUTION OP ANALYSIS. SECTION I. Operations, 1 ....................................................... 9 I. Determination of quantity, 2 .................................. 9 1. Weighing, 3 ............................................. 9 a. The balance ........................ . ............... 9 Accuracy, 4 ................................... 10 Sensibility, 5 ................................. 11 Testing, 6 and 7 ............................. 12 b. The weights, 8 ................................... 14 c. The process of weighing, 9 ......................... 15 Rules, 10 ..................................... 17 2. Measuring, 11 .......................................... 18 a. The measuring of gases, 12 ........................ 19 Correct reading-off, 13 ......................... 20 Influence of temperature, 14 .................... 21 Influence of pressure, 15 ....................... 21 Influence of moisture, 16 ...................... 22 b. The measuring of fluids, 17 ........................ 23 a. Measuring vessels graduated to hold certain volumes of fluid. aa. Vessels serving to measure out one definite volume of fluid. 1. Measuring flasks, 18 ....................... 22 lib. Vessels serving to measure out different volumes of fluid. 2. The graduated cylinder, 19 ................. 24 6. Measuring vessels graduated to deliver certain volumes of fluid. aa. Vessels serving to measure out one definite volume of fluid. 3. The graduated pipette, 20 .................. 24 bb. Vessels serving to measure out different volumes of fluid. 4. The Burette. I. Mohr's burette, 21 ..................... 26 II. Gay-Lussac's burette, 22 ............... 30 III. Geissler's burette, 23 .................. 31 viii CONTENTS. PAQK II. Preliminary operations. Preparation of substances for the processes of quantitative analysis. 1. Selection of the sample, 24 2. Mechanical division, 25 3. Desiccation, 26 B4 Desiccators, 27 Water-baths, 28 Air-baths, 29 ^ Paraffine-baths, 30 40 III. General procedure in quantitative analysis, 32 40 1. Weighing the substance, 33 41 2. Estimation of water, 34 42 a. Estimation of water by loss of weight, 35 43 b. Estimation of water by direct weighing, 36 44 3. Solution of substances, 37 46 a. Direct solution, 38 47 b. Decomposition by fluxing, 39 48 4. Conversion of the dissolved substance into a weighable form, 40 48 a. Evaporation, 41 49 Weighing of residues, 42 52 b. Precipitation, 43 53 a. Separation of precipitates by decantation, 44. . 55 13. Separation of precipitates by nitration, 45 55 aa. Filtering apparatus 56 bb. Rules to be observed in the process of nitra- tion, 46 58 cc. Washing of precipitates, 47 59 y. Separation of precipitates by decantation and fil- tration combined, 48 60 Further treatment of precipitates preparatory to weighing,. 49 61 aa. Drying of precipitates, 50 61 bb. Ignition of precipitates, 51 62 First method, 52 64 Second method, 53 65 Bunsen's method of rapid filtration, 53, a 66 Bunsen's treatment of precipitates, 53, b 77 Advantages of Bunsen's new method, 53, c 77 Bunsen's simple exhausting apparatus, 53, d 79 5. Volumetric analysis, 54 80 SECTION II. A. Reagents for gravimetric analysis in the wet way. I. Simple solvents, 56 83 II. Acids and halogens. a. Oxygen acids, 57 84 b. Hydrogen acids and halogens, 58 84 c. Sulpho-acids 85 III. Bases and metals. a. Oxygen bases and metals. a. Alkalies, and 0. Alkaline earths, 59 86 y. Heavy metals and oxides of heavy metals, 60. ... 86 b. Sulpho-bases 87 CONTENTS. IX PACK IV. Salts. a. Salts of the alkalies, 61 87 5. Salts of the alkaline earths, 62 88 c. Salts of the oxides of the heavy metals, 63 89 B. Reagents for gravimetric analysis in the dry way, 64 90 C. Reagents for volumetric analysis, 65 91 D. Reagents for organic analysis, 66 96 SECTION III. Forms and combinations in which substances are separated from each other, or weighed, 67 101 A. BASES. FIRST GROUP. 1. Potassa, 68. . 102 2. Soda, 69 103 3. Ammonia, 70 105 SECOND GROUP. 1. Baryta, 71 106 2. Strontia, 72 107 3. Lime, 73 108 4. Magnesia, 74 110 THIRD GROUP. 1. Alumina, 75 112 2. Sesquioxide of chromium, 76 114 FOURTH GROUP. 1. Oxide of zinc, 77 114 2. Protoxide of manganese, 78 116 3. Protoxide of nickel, 79 118 4. Protoxide of cobalt, 80 119 5. Protoxide ; and 6. Sesquioxide of iron, 81 121 FIFTH GROUP. 1. Oxide of silver, 82 124 2. Oxide of lead, 83 125 3. Suboxide ; and 4. Oxide of mercury, 84 127 5. Oxide of copper, 85 129 6. Teroxide of bismuth, 86 131 7. Oxide of cadmium, 87 133 SIXTH GROUP. 1. Teroxide of gold, 88 134 2. Binoxide of platinum, 89 134 3. Teroxide of antimony, 90 135 4. Peroxide of tin; and 5. Binoxide of tin, 91 136 6. Arsenious acid ; and 7. Arsenic acid, 92 137 B. ACIDS. FIRST GROUP. 93. 1. Arsenious and arsenic acids. 2. Chromic acid 139 3. Sulphuric acid 140 X CONTENTS. PACTS 4. Phosphoric acid 140 5. Boracic acid 144 G. Oxalic acid 144 7. Hydrofluoric acid 144 8. Carbonic acid 145 9. Silicic acid 145 SECOND GROUP. 94. 1. Hydrochloric acid 146 2. Hydrobromic acid 146 3. Hydriodic acid 147 4. Hydrocyanic acid 148 5. Hydrosulphuric acid 148 THIRD GROUP. 95. 1 . Nitric acid 148 2. Chloric acid. 148 SECTION IV. Determination of bodies, 96 149 I. Estimation of the bases. FIRST GROUP. 1. Potassa, 97 151 2. Soda, 98 154 3. Ammonia, 99 156 Supplement to first group, 100. 4. Lithia 161 SECOND GROUP. 1. Baryta, 101 164 2. Strontia, 102 166 3. Lime, 103 168 4. Magnesia, 104 171 THIRD GROUP. 1. Alumina, 105 174 2. Sesquioxide of chromium, 106 176 Supplement to third group, 107. 3. Titanic acid 178 FOURTH GROUP. t Oxide of zinc, 108. 179 2. Protoxide of manganese, 109 182 3. Protoxide of nickel, 110 187 4. Protoxide of cobalt, 111 189 5. Protoxide of iron, 112 192 6. Sesquioxide of iron, 113 : 199 Supplement to fourth group, 114. 7. Sesquioxide of uranium 205 FIFTH GROUP. 1. Oxide of silver, 115. . 205 2. Oxide of lead, 116 216 3. Suboxide of mercury, 117 220 CONTENTS. Xl PAGE 4. Oxide of mercury, 118 220 5. Oxide of copper, 119 ' , 225 6. Teroxide of bismuth, 120 232 7. Oxide of cadmium, 121 235 Supplement to fifth group, 122. 8. Protoxide of palladium 236 SIXTH GKOUP. 1. Teroxide of gold, 123 237 2. Binoxide of platinum, 124 239 3. Teroxide of antimony, 125 241 4. Protoxide of tin ; and 5. Binoxide of tin, 126 245 6. Arsenious acid; and 7. Arsenic acid, 127 249 Supplement to sixth group, 128. 8, Molybdic acid 255 II. Estimation of the acids. FIRST GROUP. First Division. 1. Arsenious and arsenic acids, 129 256 2. Chromic acid, 130 257 Supplement* 131. 1. Selenious acid 261 2. Sulphurous acid 262 3. Hyposulphurous acid 263 4. lodic acid 263 5. Nitrous acid 263 Second Division. Sulphurous acid, 132 264 Supplement, 133. Hydrofluosilicic acid 269 Third Division. 1. Phosphoric acid. I. Determination, 134 269 II. Separation from the bases, 135 275 2. Boracic acid, 136 279 3. Oxalic acid, 137 282 4. Hydrofluoric acid, 138 284 Fourth Division. 1. Carbonic acid, 139 285 2. Silicic acid, 140 299 SECOND GROUP. 1. Hydrochloric acid, 141 304 Supplement : free chlorine, 142 307 2. Hydrobromic acid, 143 309 Supplement : free bromine. 144 311 3. Hydriodic acid, 145 '. 311 Supplement : free iodine, 146 313 4. Hydrocyanic acid, 147 316 5. Hydrosulphuric acid, 148 321 THIRD GROUP. 1. Nitric acid, 149 328 2. Chloric acid, 150 335 Xll CONTENTS. SECTION V. PAGB Separation of bodies, 151 ........................................ 337 I. SEPARATION OF BASES FROM EACH OTHER. FIRST GROUP. Separation of the alkalies from each other, 152 ................... 339 SECOND GROUP. I. Separation of the oxides of the second group from those of the first, 153 ....................................................... 343 II. Separation of the oxides of the second group from each other, 154. . 346 THIRD GROUP. I. Separation of the oxides of the third group from the alkalies, 155. . 350 II. Separation of the oxides of the third group from the alkaline earths, 156 ....................................................... 351 III. Separation of the oxides of the third group from each other, 157. . . 354 FOURTH GROUP. I. Separation of the oxides of the fourth group from the alkalies, 158 ....................................................... 355 II. Separation of the oxides of the fourth group from the alkaline earths, 159 ................................. . ................ 356 III. Separation of the oxides of the fourth group from those of the third and from each other, 160 .................................... 358 IV. Separation of sesquioxide of iron, alumina, protoxide of manganese, lime, magnesia, potassa, and soda, 161 ........................ 370 Separation of sesquioxide of uranium from the oxides of groups I. IV. 373 FIFTH GROUP. J. Separation of the oxides of the fifth group from those of the preceding four groups, 162 ............................................ 375 II. Separation of the oxides of the fifth group from each other, 163. . . . 379 SIXTH GROUP. I. Separation of the oxides of the sixth group from those of the first five groups, 164 ................................................ 387 II. Separation of the oxides of the sixth group from each other. 165 . . . 397 II. SEPARATION OF ACIDS FROM EACH OTHER. FIRST GROUP. Separation of the acids of the first group from each other, 166 402 SECOND GROUP. I. Separation of the acids of the second group from those of the first, 167 "... 409 Supplement. Analysis of compounds containing sulphides of the alkali metals, carbonates, sulphates, and hyposulphites, 168 411 II. Separation of the acids of the second group from each other, 169. . 412 CONTENTS. Xlll THIRD GROUP. PAGE I. Separation of the acids of the third group from those of the two first groups, 170 '. 418 II. Separation of the acids of the third group from each other 419 < SECTION VI. Ultimate analysis of organic bodies, 171 42C I. Qualitative, 172 421 II. Quantitative, 173 423 A. Substances consisting of carbon and hydrogen, or of carbon, hydro- gen, and oxygen. a. Solid bodies. Combustion with oxide of copper, 174 424 Completion of the combustion by oxygen gas, 176 431 Combustion with chromate of lead (and bichromate of potash), 177 431 Combustion with oxide of copper and oxygen gas, 178 432 Volatile bodies, or bodies undergoing alteration at 100, 179 435 b. Liquid bodies. a. Volatile bodies, 180 435 /?. Non- volatile bodies, 181 437 /Supplement to A. Modified apparatus for absorption of carbonic acid, 182 438 B. Substances consisting of carbon, hydrogen, oxygen, and nitrogen. a. Estimation of carbon and hydrogen, 183 439 b. Estimation of nitrogen. . From the volume, 184 440 /?. By conversion into ammonia, after Varrentrapp and Will, 185 4i2 C. Analysis of bodies containing sulphur, 186 445 D. Estimation of phosphorus in organic bodies, 187 448 E Analysis of substances containing chlorine, bromine, or iodine, 188 449 F. Analysis of organic substances containing inorganic bodies, 189 . . 451 III. Determination of the equivalent of organic bodies. 1. From their combining proportions with other bodies, 190 452 2. From their vapor-density, 191 453 3. From their products of decomposition, 192 457 DIVISION II. Calculation of analyses 458 I. Calculation of the constituent sought from the compound produced, and exhibition of the results in per-cents, 193 458 1. When the substance sought has been separated in the free state. a. Solid bodies, liquids, or gases, which have been determined by weight, 194 458 b. Gases which have been measured, 195 459 2. When the substance sought has been separated in combination with another, 196 462 3 Calculation of indirect analyses, 197 464 Supplement to I. Remarks on loss and excess, and on taking the average, 198 466 II. Deduction of empirical formulae, 199 468 III. Deduction of rational f ormulaa. 200 471 IV. Calculation of the density of vapors, 201 475 CONTENTS. PART II. PAGB 1. Analysis of fresh water, 202 ...................................... 483 2. Acidimetry. A. Estimation by specific gravity, 203 ............................ 487 B. Determination of the acid by saturation with an alkaline fluid of known strength, 204 ...................................... 487 Kiefer's modification of the process, 205 .................. 496 3. Alkalimetry. A. Estimation of potassa, soda, or ammonia, from the density of their solutions, 206 ............................................ 498 B. Estimation of the amount of caustic and carbonated alkali in com- mercial alkalies ................................ ............ 498 Method of Descroizilles and Gay-Lussac, 207 ............ 499 Modification by Mohr, 208 ............................ 500 C. Estimation of caustic alkali in the presence of carbonates, 209. . 502 D. Estimation of carbonate of soda in presence of carbonate of potassa .......... . ........................................ 502 4. Estimation of alkaline earths by the alkalimetric method, 210 ........ 503 5. Chlorimetry, 211 ................................................. 504 Preparation of the solution of chloride of lime ..................... 504 A. Penot's method, 212 ....................................... 505 B. Otto's method, 213 ........................................ 506 Modification. . ............................................ 507 C. Bunsen's method ............................................ 508 . Valuation of manganese, 214 ...................................... 508 I. Drying the sample ........................................... 508 II. Estimation of the binoxide of manganese, 215 ................. 509 A. Fresenius and Will's method .............................. 509 B. Bunsen's method ........................................ 512 C. Method by means of iron ................................ 512 III. Estimation of moisture in manganese, 216 .................... 513 IV. Estimation of the amount of hydrochloric acid required for the complete decomposition of a manganese, 217 ............... 513 7. Analysis of common salt, 218 .................................... 514 8. Analysis of gunpowder, 219 ................................. . ____ 514 9. Analysis of native silicates, 220 ................................... 516 10. Analysis of limestones', dolomites, marls, &c ......................... 518 A. Method of complete analysis, 221 ........................... 519 B. Volumetric determination of carbonate of lime, 222 .......... 523 11. Analysis of Iron ores, 223 ........................................ 524 A. Estimation of iron ........................................... 524 B. Estimation of iron, manganese, silica, and phosphoric acid ...... 524 C. Estimation of sulphur ....................................... 525 D. Estimation of titanium ...................................... 525 12. Assay of copper ores. 224 ..................................... ... 525 A. Mohr's method for oxides, &c ................................. 525 B. Gibbs' method for sulphides ........................... . ...... 526 C. Storer and Pearson's method for sulphides ..................... 526 13. Analysis of galena, 225 .......................................... 527 14. Silver assay, 226 .......... ...................................... 528 A. Assay of poor ores ........................................... 528 B. Assay of rich ores ........................................... 531 C. Bullion assay ............................................... 531 15. Gold assay, 227 ................................................. 531 A. Ores of the first class ......... . .............................. 531 B. Ores of the second class (sulphides) ............................ 532 16. Assay of zinc ores, 228 .......................................... 534 CONTENTS. yV PAGE 17. Analysis of iron and steel, 229 535 18. Analysis of manures, 231 543 A. General process, 232 543 B. Analysis of guano, 233 545 C. Analysis of bone dust, 234 547 D. Analysis of superphosphate of lime, 235 548 Abridged analysis of superphosphates, 236 550 E. Analysis of bone black, 237 551 Estimation of the carbonate of lime, 238 551 19. Analysis of coal and peat, 239 552 20. Analysis of atmospheric air, 240 553 A. Determination of the water and carbonic acid, 241 553 B. Determination of the nitrogen and oxygen, 242 658 PART III. Exercises for practice 664 APPENDIX Analytical experiments 581 Tables for the calculation of analyses 603 620 I. Equivalents of the elements 603 II. Composition of bases and oxygen acids 604 IIL Reduction of compounds found to constituents sought by simple multiplication or division 608 IV. Amount of constituent sought for each number of compound found 610 V. Specific gravity and absolute weight of several gases 620 VI. Comparison of degrees of mercurial thermometer with those of air thermometer. . 620 EDITOR'S APPENDIX. Dr. Gibbs' method of correcting volume of gases 621 Assay of chromic iron 621 Separation of phosphoric acid from lime, alumina, and iron 622 CHEMICAL 1STOTA.TION AND NOMENCLATURE, OLD AND NEW. BEGINNERS in Chemistry are liable to much confusion and em- barrassment from the fact that there are now in use two distinct systems of Chemical Notation and several forms of Nomenclature. The older chemistry the chemistry generally in vogue up' to 1860, and still employed in all the best treatises on technical, an- alytical, physiological arid pharmaceutical chemistry differs from the " modern chemistry," primarily, in so far as notation is con- cerned, in the use of different atomic weights for certain elements. The older atomic weights employed by English writers were de- cided upon from narrow grounds, and somewhat arbitrarily. It having been found, for example, that water contains one part by weight of hydrogen to eight parts by weight of oxygen, the atomic weight of oxygen was assumed to be eight times that of hydrogen, and water was assumed to consist of one atom of each element, and had the symbol HO assigned to it. Carbonic oxide was found to contain six weights of carbon to. eight weights of oxy- gen, and being the oxygen compound in which the least quantity of carbon exists, was therefore assumed to contain one atom of each of its elements, and six became accordingly the atomic weight of carbon. Carbonic acid, with double the proportion of oxygen, was considered to contain two atoms of oxygen and was written CO a . As discovery revealed the composition of bodies, their atomic weights were agreed upon with reference only to ap- parent simplicity and harmony to what had been previously as- sumed, in the absence of any other and more philosophical crite- rion or guide. The atomic theory of Dalton was and still is philosophical, be- cause it gives, in a certain sense, a reason for the laws of definite and multiple combination ; but the atomic weights he and his sue- cessors adopted were open to revision,* the simplicity which was relied upon in selecting them being often more apparent than real. Thus the atomic weight of carbon was taken to be the smallest quantity of that element which would unite with oxy- gen. Had it happened that carbonic oxide was then unknown, and that carbonic acid was believed to be the lowest oxide of carbon, the atomic weight of carbon would have been fixed at 3, oxygen being 8. Or, if the atomic weight of carbon had been measured directly by hydrogen, in the lowest hydride of carbon, marsh gas, assumed to be OH 2 , the result would also have been 3. We see, then, evidently, that the formerly received atomic weights of those elements, which form multiple combinations, were liable to be multiples or divisors of the true f atomic weights, and were, of necessity, thus far arbitrarily chosen. The discovery that the volumes in which gases unite bear sim pie ratios to one another, was regarded as a clue which might point with certainty to the real atomic relations. When two volumes of water vapor are decomposed, there result two volumes of hydrogen and one volume of oxygen. Berzelius did nut hesi- tate to declare his belief that the number of volumes repre- sent the number of atoms ; that, accordingly, water is a com- pound ct two atoms of hydrogen with one atom of oxygen ; that its formula is, therefore, H 2 O ; and that the atomic weight of hydrogen being one, that of oxygen must be sixteen, or double what Dalton assumed. The progress of science has gradually brought the minds of chemists to the conviction that the greater number of the old atomic weights must be doubled, and that certain formulae must be changed accordingly. To this result not only the "law of vol- umes," but a comparison of the specific heats of the elements and other physical considerations have contributed, while purely chem- ical reasons furnish the most conclusive arguments in favor of the change. The fact that the older atomic weights and nomenclature have been so long in use among druggists, physicians, and manufac- turers, and that so vast a mass of chemical literature has been written in accordance with them, has properly enough prevented their sudden abandonment. The greater truth of the modern chemistry must ultimately compel its adoption with more or less modifications. For the present it is important that the student become familiar with both. This familiarity can readily be ac- quired by practice in translating the older symbols into the newer, and the reverse, by aid of the rules to be found below. In modern chemistry the idea of quantivalence or atom-fixing power serves a very important part. Those elements which, like chlorine, unite with hydrogen, volume for volume, i.e., atom foi * Independently of errors in their determination as combining weights. { Assuming the Atomic Theory to be an expression of fact. atom, have been termed monads, or have been characterized as univalent (one-value) elements. Those elements which, like oxysren, combine with twice their volume (or two atoms) of hydrogen or other monad radical, are dyads, and are spoken of as bivalent (two-value) radicals. Triads, tetrads, pentads, and hexads are elements (or radicals) which unite respectively with three, four, five, and six times their (gaseous) volume of hydrogen or analogous monads, and to which apply respectively the adjectives trivalent, quadrivalent, quinquivalent, and sexivalent. Those elements whose quantivalence is expressed by an odd number, 1, 3, 5 or 7, are collectively termed perissads, and those which unite with an even number of atoms of hydrogen or chlorine are designated artiads* The following table gives the two systems of atomic weights, the older following the symbol printed in Roman type, and the newer that printed in Ital/cs. PEBJSSADS. ARTIADS. OLD AND NEW OLD NEW MONADS. ATOMIC WEIGHTS. DYADS. AT. WTS. AT. WTS. Hydrogen, H = 1 Oxygen, 8 - 16 Chlorine, Cl = 35.5 Sulphur, s 16 8 32 Bromine, Br = 80 Selenium, Se 39.5 Se 79 Iodine, I 127 Tellurium, Te 64 Te rr 128 Fluorine, F = 19 Calcium, Ca 20 Ca 40 Lithium, Li = 7 Strontium, Sr 43.75 8f 87.5 Sodium, Na = 23 Barium, Ba - 68.5 Ba 137 Potassium, K = 39 Mercury, Hg- 100 Hg 200 Rubidium, Rb = 85.4 Copper, Cu 31.7 Cu 63.4 Caesium, Cs = 133 Lead, Pb 103.5 Pb rrr 207 Thallium, Tl = 203 Cadmium, Cd 56 Cd 112 Silver, Ag = 108 Zinc, Zn 32.5 Zn 65 TRIADS. Magnesium, Mg == (2 Mg rz: 24 Boron, B = 11 TETRADS. Gold, Au = 196 Carbon, C 6 C 12 Silicon Si 14 81 28 PENTADS. Titanium, Ti 25 Ti 50 Nitrogen, N = 14 Tin, Sn 59 Sn 118 Phosphorus, P = 31 Aluminium, Al 13.75 Al 27.5 Arsenic, As = 75 Platinum, Pt = 98.94 Pt 197.88 Antimony, Sb = 122 Palladium, Pd 53 Pd 106 Bismuth, Bi = 210 Vanadium. V = 51.3 HEXADS. Chromium, Cr 26.25 Cr - 52.5 Manganese, Mn 27.5 Mn 55 Iron, Fe 28 Fe 56 Nickel, Ni 29.5 Ni 59 Cobalt, Co 9.5 Co = 59 Uranium, U 59.4 U 118.8 Molybdenum, Mo ~ 46 Mo = 92 * Chemists are not agreed as to the quannvalence of various elements. Some regard sulphur as a hexad, and others put down iron, cobalt, and some other metals as dyads. Wanklyn considers sodium to be a triad. The distinction be- tween perissads and artiads is more absolute, but certain elements, especially Vanadium and Uranium, may be J>UL in both groups. It will be seen from the above table that the atomic weights ol the so-called perissad elements, including the monads hydrogen, chlorine, and the members of its group, the alkali metals, thallium and silver, the triads boron and gold, and the pentads nitrogen, etc., including bismuth, have the same atomic weights in the newer chemistry as have been so long used in the older. On the contrary, the artiad elements, viz., the dyads oxygen, sulphur, selenium, tellurium, and the alkali earth-metals ; the tetrads carbon, silicon, titanium, tin, and the remaining metallic elements which are dyads, tetrads, or hexads, have double the atomic weights in the new system which they had in the old. To convert the old-system formulae into corresponding values of the new, the following rules are indicated : 1. Compounds of perissad elements. The symbols of compounds of perissad elements are ordinarily alike in both systems, and their values, expressed by the atomic weights of the old system, or by the molecular weights of the new system, are the same in both, viz. : ATOMIC WEIGHT. MOLECULAR WEIGHT. OLD SYSTEM. NEW SYSTEM. SYMBOLS. * """ HC1 36.5 NH 3 17 PC1 5 208.5 BF S 68 If the newer symbols are unlike the old, the latter and their values are multiplied to make the new. Some chemists change the symbols of the liquid and solid phosphides of hydrogen, viz.: GAS. AT. WT. LIQUID. AT. WT. SOLID. AT. WT. Old system. H 3 P 34 : H 2 P 33 : HP 2 63 MOL. WT. MOL. WT. MOL. WT. New system. H 3 P 34 : H 4 P 2 66 : H 2 P 4 126 2. Compounds of artiad elements. The symbols of compounds of artiad elements are commonly alike in both systems, but in the new system the values are double those of the old. ATOMIC WEIGHT. MOLECULAR WEIGHT. SYMBOLS. OLD SYSTEM. NEW SYSTEM. S0 a 32 64 CO 14 28 C0 2 22 44 BaO 76.5 153 FeS 44 88 A1 2 8 51.5 103 BaO,S0 8 =BaS0 4 116.5 233 3. Compounds of perissad with artiad elements. The symbols of compounds of perissad with artiad elements are converted from the old into the new system, generally, by halving the number of artiad atoms, in which case the values are the Bame in both systems, viz. : SYMBOLS. VALUES. OLD SYSTEM. NEW SYSTEM. AND ^^ MOL NaOHO NaHO 40 Cr 2 3 ,3 SO S , KOS0 3 ,24HO Cr(S0 4 ) 2 K12H 2 O* 499.5 HON0 5 HN0 3 63 KOCO 2 , HOC0 2 KHCO 3 100 C 102 H 96 J2 (C 3 H 6 ) (C 16 H 31 2 ) 3 t 806 When the number of artiad atoms cannot be halved, and in some other cases, the number of perissad atoms is doubled, the values being doubled at the same time, viz. : SYMBOLS. VALUES. OLD SYSTEM. NEW SYSTEM. OLD AT. WT. NEW MOL. WT. N0 5 N 2 5 54 108 HO H 2 9 18 CaCl CaCl 2 55.5 111 HgoCl Hg 2 Cl 2 235.5 771 HgCl HgCl 2 135.5 271 BaO,HO BaH 2 O 2 85.5 171 Cr 2 O 3 ,3S0 3 ,KO,S0 3 K 2 Cr 2 O 8 (S0 2 ) 4 24HO 24H a Ot 499.5 999 The form and arrangement of the symbols of complicated com- pounds is very various, and can only be learned by study of the masters who lead usage. As regards nomenclature the "modern" chemists are by no means agreed. The departures from traditional English usage are, however, with few exceptions, simple changes of verbal form, such as zinc sulphate or zincic sulphate instead of sulphate of zinc, lead nitrite or plumbic nitrite instead of nitrite of lead, silver chloride or argentic chloride instead of chloride of silver. In case of the oxygen compounds of the alkali and alkali-earth metals, the name of the metal itself and not that of the oxide is used, viz. : calcium sulphate or calcic sulphate instead of sulphate of lime, sodium borate or sodic borate instead of borate of soda, barium nitrate or baric nitrate rather than nitrate of baryta. In case of the metals which have two basic oxides, these and the corresponding salts are distinguished by the particles ous and io affixed to the name of the metal used adjectively ; thus, protoxide of iron and sesquioxide or peroxide of iron are respectively ferrous and ferric oxide, hydrated protoxide is ferrous hydrate, sesqui- eulphate is ferric sulphate. Similarly, we have cuprous acetate, cupric oxide, mercurous nitrate, and mercuric phosphate. Sc aluminic sulphate (by analogy), nickelous oxalate, bisniuthic bro- mide, &c. * Chrome alum, WATTS. f Tripalmitine. J Chrome Alum, COOKB. 6 It has long been conceded that the traditional acids CO a , SO 91 PO 6 (P 2 6> 6 ), 'SO t (N^O t ) &c., are no acids (i.e., sour bodies) at all, but yield acids by their combination with the elements of water. They were therefore termed anhydrous acids. Later they have been classed together as anhydrides and designated individually as carbonic anhydride, sulphuric anhydride, phosphoric anhy- dride, &c., and this nomenclature is now employed by many chemists, especially by Odling and Frankland. Others, fol- lowing Williamson, insist that CO^ SO^ &c., are acids in the sense of the old nomenclature, and retain for them the old names, while the sour (hydrated) acids are designated as hydrogen or hydric salts, viz. : U^SO^lijdrie sulphate, ./?,/> 4 =h'ydric phos- phate or phosphoric hydrate. Still other chemists prefer to fall back upon numeral prefixes in case of the anhydrides and other related oxides, viz. : Watts gives to CO,CO^ and Cl t 4 the names carbon monoxide, carbon dioxide, and chlorine tetroxide. Roscoe makes CO carbonic oxide, CO Z carbonic dioxide, and Cl^O^ chlo- ric tetroxide. In case of bodies of more complicated composition, especially those belonging to organic chemistry, the assumption of compound radicals or other peculiar views of rational constitution have led chemists to construct various new form ales and corresponding new names, which are to be learned in the writings where they are propounded. INTRODUCTION. As we have already seen in the " Manual of Qualitative Analysis," to which the present work may be regarded as the sequel, Chemical Analysis comprises two branches, viz. : qualitative analysis and quanti- tative analysis, the object of the former being to ascertain the nature, that of the latter to determine the amount, of the several component parts of any compound. By QUALITATIVE ANALYSIS we convert the unknown constituents of a body into certain known forms or combinations ; and we are thus en- abled to draw correct inferences respecting the nature of these unknown constituents. Quantitative analysis attains its object, according to cir- cumstances, often by very different ways ; the two methods most widely differing from each other, are analysis by weight, or gravimetric analysis, and analysis by measure, or volumetric analysis. GRAVIMETRIC ANALYSIS has for its object to convert the known con- stituents of a substance into forms or combinations which will admit of the most exact determination of their weight, and of which, moreover, the composition is accurately known. These new forms or combinations may be either educts from the analyzed substance, or they may be products. In the former case the ascertained weight of the eliminated substance is the direct expression of the amount in which it existed in the compound under examination ; whilst in the latter case, that is, when we have to^ deal with products, the quantity in which the eliminated constituent was : originally present in the analyzed compound, has to be deduced by calculation from the quantity in which it exists in its new combination. The following example will serve to illustrate these points : Suppose- we wish to determine the quantity of mercury contained in the chloride of that metal ; now, we may do this, either by precipitating the metallic mercury from the solution of the chloride, say by means of protochloride of tin; or we may attain our object by precipitating the solution by sul- phuretted hydrogen, and weighing the precipitated sulphide of mercury. 100 parts of chloride of mercury consist of 73'82 of mercury and 26'18- of chlorine; consequently, if the process is conducted with absolute accuracy, the precipitation of 100 parts of chloride of mercury by proto- chloride of tin will yield 73'82 parts of metallic mercury. With equally exact manipulation the other method yields 85'634 parts of sulphide of mercury. * Now, in the former case we find the number 73*82 directly ; in the- utter case we have to deduce it by calculation : (100 parts of sulphide of mercury contain 86-207 parts of mercury ; how much mercury do 85*634 parts contain ?) 100 : 85-634 : : 86-207 : x x=73-82. As already hinted, it is absolutely indispensable that the forms into which bodies are converted for the purpose of estimation by weight should fulfil two conditions : first, they must be capable of being weighed exactly ; secondly, they must be of known composition, for it is quite obvious, on the one hand, that accurate quantitative analysis must be altogether im- possible if the substance the quantity of which it is intended to ascertain, does not admit of correct weighing ; and on the other hand, it is equally evident that if we do v not know the exact composition of a new product, we lack the necessary basis of our calculation. VOLUMETKIC ANALYSIS is based upon a very different principle from that of gravimetric analysis ; viz., it affects the quantitative determination of a body, by converting it from a certain definite state to another equally definite state, by means of a fluid of accurately known power of action, and under circumstances which permit the analyst to mark with rigorous precision the exact point when the conversion is accomplished. The fol- lowing example will serve to illustrate the principle of this method : Permanganate of potassa added to a solution of sulphate of protoxide of iron, acidified with sulphuric acid, immediately converts the protoxide of iron to sesquioxide ; the permanganic acid, which is characterized by its intense colour, yielding up oxygen and changing to protoxide of manga- nese, which combines with the sulphuric acid present, to colorless sulphate of protoxide of manganese. If, therefore, to an acidified fluid containing protoxide of iron, we add, drop by drop, a solution of permanganate of potassa, its red color continues for some time to disappear upon stirring ; but at last a point is reached when the coloration imparted to the fluid by the last drop added remains : this point marks the termination of the conversion of the protoxide of iron to sesquioxide. Now, by accurately determining the strength or power of action of the solution of permanganate of potassa which is done simply by making it act upon a known quantity of protoxide of iron in solution, and correctly noting how much of it is required to effect the conversion of that pro- toxide to the state of sesquioxide we are now able with this solution to determine the exact amount of protoxide of iron present in any solution. Thus, we will assume, for instance, that we have found it takes exactly 1 00 parts of our solution of permanganate of potassa to oxidize 2 parts of protoxide of iron ; if now, in testing, with this standard solution of per- manganate of potassa, any solution containing an unknown quantity of protoxide of iron, we find that 100 parts of our standard fluid are required to oxidize the iron, we know at once that the examined fluid contained exactly 2 parts of protoxide of iron ; if 50 parts are required, we know that 1 part of protoxide of iron was present, &c. &c. Accordingly, by simply measuring the quantity used of our standard solution of perman- ganate of potassa, we arrive at once at an accurate knowledge of the amount of protoxide of iron. As the process of measuring is mostly adopted, in preference to that of weighing, for determining the quantity used of the standard naid, we give to this analytical method the name of " analysis by measure." It generally leads to the attainment of the object in view with much greater expedition than is the case with analysis by weight. INTRODUCTION. 3 To this brief intimation of the general purport and object of quantita- tive analysis, and the general mode of proceeding in analytical re searches, I have to add that certain qualifications are essential to those who would devote themselves successfully to the pursuit of this branch. These qualifications are, 1, theoretical knowledge ; 2, skill in manipula- tion ; and 3, strict conscientiousness. The preliminary knowledge required consists in an acquaintance with qualitative analysis, the stoichiometric laws, and simple arithmetic. Thus prepared, we shall understand the method by which bodies are separated and determined, and we shall be in a position to perform our calcu- lations, by which, on the one hand, the formulae of compounds are deduced from the analytical results, and, on the other hand, the correct- ness of the adopted methods is tested, and the results obtained are con- trolled. To this knowledge must be joined the ability of performing the necessary practical operations. This axiom generally holds good for all applied sciences, but if it is true of one more than another, quantitative analysis is that one. The most extensive and solid theoretical acquire- ments will not enable us, for instance, to determine the amount of com- mon salt present in a solution, if we are without the requisite dexterity to transfer a fluid from one vessel to another without the smallest loss by spirting, running down the side, &c. The various operations of quantitative analysis demand great aptitude and manual skill, which can be acquired only by practice. But even the possession of the greatest practical skill in manipulation, joined to a thorough theoretical know- ledge, will still prove insufficent to insure a successful pursuit of quanti- tative researches, unless also combined with a sincere love of truth, and a firm determination to accept none but thoroughly confirmed results. Every one who has been engaged in quantitative analysis knows that cases will sometimes occur, especially when commencing the study, in which doubts may be entertained as to whether the result will turn out correct, or in which even the operator is positively convinced that it cannot be quite correct. Thus, for instance, a small portion of the sub- stance under investigation may be spilled ; or some of it lost by decrepi- tation ; or the analyst may have reason to doubt the accuracy of his weighing ; or it may happen that two analyses of the same substance do not exactly agree. In all such cases it is indispensable that the operator should be conscientious enough to repeat the whole process over again. He who is not possessed of this self-command who shirks trouble where truth is at stake who would be satisfied with mere assumptions and guesswork, where the attainment of positive certainty is the object, must be pronounced just as deficient in the necessary qualifications for quantitative analytical researches as he who is wanting in knowledge or skill. He, therefore, who cannot fully trust his work who cannot swear to the correctness of his results, may indeed occupy himself with quanti- tative analysis by way of practice, but he ought on no account to publish or use his results as if they were positive, since such proceeding could not conduce to his own advantage, and would certainly be mischievous as regards the science. The domain of quantitative analysis may be said to extend over all matter that is, in other words, anything corporeal may become the object of quantitative investigation. The present work, however, is in- tended to embrace only the substances used in pharmacy, arts, trades, and agriculture. 4 INTRODUCTION. Quantitative analysis may be subdivided into two branches, viz., ana lysis of mixtures, and analysis of chemical compounds. This division may appear at first sight of very small moment, yet it is necessary that we should establish and maintain it, if we would form a clear conception of the value and utility of quantitative research. The quantitative analy- sis of mixtures, too, has not the same aim as that of chemical com pounds ; and the method applied to secure the correctness of the results in the former case is different from that adopted in the latter. The quantitative analysis of chemical compounds also rather subserves the purposes of the science, whilst that of mixtures belongs to the practical purposes of life. If, for instance, I analyze the salt of an acid, the result of the analysis will give me the constitution of that acid, its combining proportion, saturating capacity, &c. ; or, in other words, the results ob- tained will enable me to answer a series of questions of which the solu- tion is important for the theory of chemical science : but if, on the other- hand, I analyze gunpowder, alloys, medicinal mixtures, ashes of plants, &c., &c., I have a very different object in view ; I do not want in such cases to apply the results which I may obtain to the solution of any the- oretical question in chemistry, but I want to render a practical service either to the arts and industries, or to some other science. If in the analysis of a chemical compound I wish to control the results obtained, I may do this in most cases by means of calculations based on stoi'chio- metric data, but in the case of a mixture a second analysis is necessary to confirm the coiTectness of the results afforded by the first. The preceding remarks clearly show the immense importance of quan- titative analysis. It may, indeed, be averred that chemistry owes to this branch its elevation to the rank of a science, since quantitative researches have led us to discover and determine the laws which govern the combinations and transpositions of the elements. Stoichiometry is entirely based upon the results of quantitative investigations ; all rational views respecting the constitution of compounds rest upon them as the only safe and solid basis. Quantitative analysis, therefore, forms the strongest and most powerful lever for chemistry as a science, and not less so for chemistry in its applications to the practical purposes of life, to trades, arts, manufac- tures, and likewise in its application to other sciences. It teaches the mineralogist the true nature of minerals, and suggests to him principles and -rules for their recognition and classification. It is an indispen- sable auxiliary to the physiologist ; and agriculture has already derived much benefit from it ; but far greater benefits may be predicted. We need not expatiate here upon the advantages which medicine, pharmacy, and every branch of industry derive, either directly or indirectly, from the practical application of its results. On the other hand, the benefit thus bestowed by quantitative analysis upon the various sciences, arts, &c., has been in a measure reciprocated by some of them. Thus whilst stoichiometry owes its establishment to quantitative analysis, the sto'ichio- metric laws afford us the means of controlling the results of our analyses so accurately as to justify the reliance which we now generally place on them. Again, whilst quantitative analysis has advanced the progress of arts and industry, our manufacturers in return supply us with the most perfect platinum, glass, and porcelain vessels, and with articles of india-rubbber, without which it would be next to impossible to conduct our analytical operations with the minuteness and accuracy which we have now attained. INTRODUCTION. 5 Although the aid which quantitative analysis thus derives from &toi- chiometry, and the arts and manufactures, greatly facilitates its practice, and although many determinations are considerably abbreviated by volu- metric analysis, it must be admitted, notwithstanding, that the pursuit of this branch of chemistry requires considerable expenditure of time. This remark applies especially to those who are commencing the study, for they must not allow their attention to be divided upon many things at one time, otherwise the accuracy of their results will be more or less injured. I would therefore advise every one desirous of becoming an analytical chemist to arm himself with a considerable share of patience, reminding him that it is not at one bound, but gradually, and step by step, that the student may hope to attain the necessary certainty in his work, the indispensable self-reliance which can alone be founded on one's own results. However mechanical, protracted, and tedious the opera- tions of quantitative analysis may appear to be, the attainment of accuracy will amply compensate for the time and labor bestowed upon them; whilst, on the other hand, nothing can be more disagreeable than to find, after a long and laborious process, that our results are incorrect or uncertain. Let him, therefore, who would render the study of quan- titative analysis agreeable to himself, from the very outset endeavor, by strict, nay, scrupulous adherence to the conditions laid down, to attain correct results, at any sacrifice of time. I scarcely know a better and more immediate reward of labor than that which springs from the at- tainment of accurate results and perfectly corresponding analyses. The satisfaction enjoyed at the success of our efforts is surely in itself a sufficient motive for the necessary expenditure of time and labor, even without looking to the practical benefits which we may derive from our operations. The following are the substances treated of in this work : I. METALLOIDS, or NON-METALLIC ELEMENTS. Oxygen, Hydrogen, Sulphur, [Selenium,~\ Phosphorus, Chlorine, Iodine, Bromine, Fluorine, Nitrogen, Boron, Silicon, Carbon. II. METALS. Potassium, Sodium, [Lithium,] Barium, Strontium, Calcium, Magnesium, Aluminium, Chromium, [ Titanium^ Zinc, Manganese, Nickel, Cobalt, Iron, [ Uranium,'] Silver, Mercury, Lead, Copper, Bis- muth, Cadmium, [Palladium,] Gold, Platinum, Tin, Antimony, Arsenic, [Molybdenum]. (The elements enclosed within brackets are considered in supplement- ary paragraphs, and more briefly than the rest.) I have divided my subject into three parts. In the first, I treat of quantitative analysis generally; describing, 1st, the execution of analy- sis ; and, 2d, the calculation of the results obtained. In the second, I give a detailed description of several special analytical processes. And in the third, a number of carefully selected examples, which may serve as exercises for the groundwork of the study of quantitati ve analysis. 6 INTRODUCTION. The following table will afford the reader a clear and definite notion of the contents of the whole work : I. GENERAL PART. A EXECUTION OF ANALYSIS. 1. Operations. 2. Reagents. 3. Forms and combinations in which bodies are separated from others, or in which their weight is determined. 4. Determination of bodies in simple compounds. 5. Separation of bodies. 6. Organic elementary analysis. B CALCULATION OF THE RESULTS. II. SPECIAL PART. 1. Analysis of waters. 2. Analysis of such minerals and technical products as are most fre- quently brought under the notice of the chemist ; including methods foi ascertaining their commercial value. 3. Analysis of atmospheric air. III. EXERCISES FOR PRACTICE. APPENDIX. 1. Analytical experiments. 2. Tables for the calculation of analytical results. PART I. GENERAL PART. DIVISION I. THE EXECUTION OF ANALYSIS. SECTION I. OPERATIONS. MOST of the operations performed in quantitative research are the same as in qualitative analysis, and have been accordingly described in my t work on that branch of analytical science. With respect to such opera- tions I shall, i.herefore, confine myself here to pointing out any modifica- tions they iaay require to adapt them for application in the quantitative branch ; but I shall, of course, give a full description of such as are resorted to exclusively in quantitative investigations. Operations form- ing merely part of certain specific processes will be found described in the proper place, under the head of such processes. I. DETERMINATION OF QUANTITY. The quantity of solids is usually determined by weight / the quantity of gases and fluids, in many cases by measure upon the care and accu- racy with which these operations are performed, depends the value of all our results ; I shall therefore dwell minutely upon them. 3. 1. WEIGHING. To enable us to determine with precision the correct weight of a substance, it is indispensable that we should possess, 1st, a good BALANCE, and 2d, accurate WEIGHTS. a. THE BALANCE. Fig. 1 represents a form of balance well adapted for analytical pur- poses. There are several points respecting the construction and proper- ties of a good balance, which it is absolutely necessary for every chemist to understand. The usefulness of this instrument depends upon two points : 1st, its accuracy, and 2d, its sensibility or delicacy. 10 OPERATIONS. 18*- The ACCURACY of a balance depends upon the following conditions : a. The fulcrum or the point on which the beam rests must lie above the centre of gravity of the balance. Fig. 1. This is in fact a condition essential to every balance. If the fulcrum were placed in the centre of gravity of the balance, the beam would not oscillate, but remain in any position in which it is placed, assuming the scales to be equally loaded. If the fulcrum be placed below the centre of gravity, the balance will be overset by the slightest impulse. "When the fulcrum is above the centre of gravity the balance represents a pendulum, the length of which is equal to that of the line uniting the fulcrum with the centre of gravity, and this line forms right angles with the beam, in whatever position the latter may be placed. Now if we impart an impetus to a ball suspended by a thread, the ball, after having terminated its vibrations, will invariably rest in its original perpendicular position under the point of suspension. It is the same with a properly adjusted balance impart an impetus to it, and it will oscillate for some time, but it will invariably return to its original position ; in other words, its centre of gravity will finally fall back into its perpendicular position under the fulcrum, and the beam must consequently reassume the horizontal position. But to judge correctly of the force with which this is accomplished, it must be borne in mind that a balance is not a simple pendulum, but a compound one, i. e. 9 a pendulum in which not one, but many material points move round the turning point. The inert mass to be moved is accordingly equal to the sum of these points, and the moving force is equal to the excess of the material points below, over those above the fulcrum. /3. The points of suspension of the scales must be on an exact level with the fulcrum. If the fulcrum be placed below the line joining the points of suspension, increased loading of the scales will continually tend to raise the centre of gravity of the whole system, so as to bring it nearer and nearer the fulcrum ; the weight which presses upon the scales com- bining in the relatively high-placed points of suspension ; at last, when the scales have been loaded to a certain degree, the centre of gravity 5.] WEIGHING. 11 wall shift altogether to the fulcrum, and the balance will consequently cease to vibrate any further addition of weight will finally overset the beam by placing the centre of gravity above the fulcrum. If, on the other hand, the fulcrum be placed above the line joining the points of suspension, the centre of gravity will become more and more depressed in proportion as the loading of the scales is increased ; the line of the pendulum will consequently be lengthened, and a greater force will be required to produce an equal turn ; in other words, the balance will grow less sensitive the greater the load. But when the three edges are in one plane, increased loading of the scales will, indeed, continually tend to raise the centre of gravity towards the fulcrum, but the former can in this case never entirely reach the latter, and consequently the balance will never altogether cease to vibrate upon the further addition of weight, nor will its sensibility be lessened ; on the contrary speak- ing theoretically a greater degree of sensibility is imparted to it. This increase of sensibility is, however, compensated for by other circum- stances. (See 5.) r y. The beam must be sufficiently rigid to bear without bending the greatest weight that the construction of the balance admits of ' since the bending of the beam would of course depress the points of suspension so as to place them below the fulcrum, and this would, as we have just seen, tend to diminish the sensibility of the balance in proportion to the increase of the load. It is, therefore, necessary to avoid this fault by a proper construction of the beam. The form best adapted for beams is that of an isosceles obtuse-angled triangle, or of a rhombus. $. The arms of the balance must be of equal length, i. e., the points of suspension must be equidistant from the fulcrum, for if the arms are of unequal length the balance will not be in equilibrium, supposing the scales to be loaded with equal weights, but there will be preponderance on the side of the longer arm. The SENSIBILITY of a balance depends principally upon the three fol- lowing conditions : a. The friction of the edges upon their supports must be as slight as possible. The greater or less friction of the edges upon their supports depends upon both the form and material of those parts of the balance. The edges must be made of good steel, the supports may be made of the same material ; it is better, however, that the centre edge at least should rest upon an agate plane. To form a clear conception of how necessary it is that even the end edges should have as little friction as possible, we need simply reflect upon what would happen were we to fix the scales immovably to the beam by means of rigid rods. Such a contrivance would at once altogether annihilate the sensibility of a balance, for if a weight were placed upon one scale, this certainly would have a tendency to sink ; but at the same time the connecting rods being compelled to form constantly a right angle with the beam, the weighted scale would incline inwards, whilst the other scale would turn outwards, and thus the arms would become unequal, the shorter arm being on the side of the weighted scale, whereby the tendency of the latter to sink would be immediately compensated for. The more considerable the friction becomes at the end edges of a balance, the more the latter approaches the state just now described, and consequently the more is its sensibility impaired. 12 OPERATIONS. [ G. (B. The centre of gravity must be as near as possible to the fulcrum The nearer the centre of gravity approaches the fulcrum, the shorter becomes the pendulum. If we take two balls, the one suspended by a short and the other by a long thread, and impart the same impetus to both, the former will naturally swing at a far greater angle from its per pendicular position than the latter. The same must of course happen with a balance ; the same weight will cause the scale upon which it is placed to turn the more rapidly and completely, the shorter the distance between the centre of gravity and the fulcrum. We have seen above, that in a balance where the three edges are on a level with each other, increased loading of the scales will continually tend to raise the centre of gravity towards the fulcrum. A good balance will therefore become more delicate in proportion to the increase of weights placed upon its scales ; but, on the other hand, its sensibility will be diminished in about the same proportion by the increment of the mass to be moved, and by the increased friction attendant upon the increase of load ; in other words, the delicacy of a good balance will remain the same, whatever may be the load placed upon it. The nearer the centre of gravity lies to the fulcrum, the slower are the oscillations of the balance. Hence in regulating the position of the centre of gravity we must not go too far, for if it approaches the fulcrum too nearly, the operation of weigh- ing will take too much time. y. The beam must be as light as %)ossible. The remarks which we have just now made will likewise show how far the weight of the beam may influence the sensibility of a balance. We have seen that if a balance is not actually to become less delicate on increased loading, it must on the one hand have a tendency to become more delicate by the continual approach of the centre of gravity to the fulcrum. Now it is evident, that the more considerable the weight of the beam is, the less will an equal load placed upon both scales alter the centre of gravity of the whole system, the more slowly will the centre of gravity approach the fulcrum, the less will the increased friction be neutralized, and conse- quently the less sensibility will the balance possess. Another point to be taken into account here is, that the moving forces being equal, a lesser mass or weight is more readily moved than a greater. ( 4 a). 6. We will now proceed, first, to give the student a few general rules to guide him in the purchase of a balance intended for the purposes of quantitative analysis ; and, secondly, to point out the best method of testing the accuracy and sensibility of a balance. 1. A balance able to bear 70 or 80 grammes in each scale, suffices for most purposes. 2. The balance must be enclosed in a glass case to protect it from dust. This case ought to be sufficiently large, and, more especially, its sides should not approach too near the sdales. It must be constructed in a manner to admit of its being opened and closed with facility, and thus to allow the operation of weighing to be effected without any disturbing influence from currents of air. Therefore, either the front part of the case should consist of three parts, viz., a fixed centre part and two lateral parts, opening like doors ; or, if the front part happens to be made of one piece, and arranged as a sliding-door, the two sides of the case must be provided each with a door. 7.J WEIGHING. 15 3. The balance must be provided with a proper contrivance to render it immovable whilst the weights are being placed upon the scale. This is most commonly effected by an arrangement which enables the operator to lift up the beam and thus to remove the middle edge from its support, whilst the scales remain suspended. It is highly advisable to have the case of the balance so arranged that the contrivances for lifting the beam and fixing the scales can be worked while the case remains closed, and consequently from without. 4. It is necessary that the balance should be provided with an index to mark its oscillations ; this index is appropriately placed at the bottom of the balance. 5. The balance must be provided with a spirit level, to enable the operator to place the three edges on an exactly horizontal level ; it is best also for this purpose that the case should rest upon three screws. 6. It is very desirable that the beam should be graduated into tenths, so as to enable the operator to weigh the milligramme and its fractions with a centigramme " rider." * 7. The balance must be provided with a screw to regulate the centre of gravity, and likewise with two screws to regulate the equality of the arms, and finally with screws to restore the equilibrium of the scales, should this have been disturbed. The following experiments serve to test the accuracy and sensibility of a balance. 1. The balance is, in the first place, accurately adjusted, if necessary, either by the regulating screws, or by means of tinfoil, and a milligramme weight is then placed in one of the scales. A good and practically useful balance must turn very distinctly with this weight ; a delicate chemical balance should indicate the y 1 ^ of a milligramme with perfect distinctness. 2. Both scales are loaded with the maximum weight the construction of the balance will admit of the balance is then accurately adjusted, and a milligramme added to the weight in ,the one scale. This ought to cause the balance to turn to the same extent as in 1. In most balances, how- ever, it shows somewhat less on the index. It follows from 5/3 that the balance will oscillate more slowly in this than in the first experiment. 3. The balance is accurately adjusted, (should it be necessary to esta- blish a perfect equilibrium between the scales by loading the one with a minute portion of tinfoil, this tinfoil must be left remaining upon the scale during the experiment) ; both scales are then equally loaded, say, with fifty grammes each, and, if necessary, the balance is again adjusted (by the addition of small weights). The load of the two scales is then interchanged, so as to transfer that of the right scale to the left, and vice versd. A balance with perfectly equal arms must maintain its absolute equilibrium upon this interchange of the weights of the two scales. 4. The balance is accurately adjusted ; it is then arrested and again set in motion ; the same process should be repeated several times. A good balance must invariably reassume its original equilibrium. A balance the end edges of which afford too much play to the hook resting upon * [Becker's later balances have beams graduated to twelfths, and a rider weigh- ing 12 mgrs. This enables the operator to use nearly the whole of the gradua- tion. ] 14 OPERATIONS. [ 8. them, so as to allow the latter slightly to alter its position, will show per- ceptible differences in different trials. This fault, however, is possible only with balances of defective construction. A balance to be practically useful for the purposes of quantitative ana- lysis must stand the first, second, and last of these tests. A slight in- equality of the arms is of no great consequence, as the error that it would occasion may be completely prevented by the manner of weighing. As the sensibility of a balance will speedily decrease if the steel edges are allowed to get rusty, delicate balances should never be kept in the laboratory, but always in a separate room. It is also advisable to place within the case of the balance a vessel half filled with calcined carbonate of potassa, to keep the air dry. I need hardly add that this salt must be re-calcined as soon as it gets moist. 8. b. THE WEIGHTS. 1. The French gramme is the best standard for calculation. A set of weights ranging from fifty grammes to one milligramme may be considered sufiicient for all practical purposes. With regard to the set of weights, it is generally a matter of indifference for scientific purposes whether the gramme, its multiples and fractions, are really and perfectly equal to the accurately adjusted normal weights of the corresponding denominations ; * but it is absolutely necessary that they should agree perfectly with each other, i.e., the centigramme weight must be exactly the one hundredth part of the gramme weight of the set, &c. etc. 2. The whole of the set of weights should be kept in a suitable, well- closing box ; and it is desirable likewise that a distinct compartment be appropriated to every one even of the smaller weights. 3. As to the shape best adapted for weights, I think that of short frusta of cones inverted, with a handle at the top, the most convenient and prac- tical form for the large weights ; square pieces of foil, turned up at one corner, are best adapted for the small weights. The foil used for this pur- pose should not be too thin, and the compartments adapted for the recep- tion of the several smaller weights in the box, should be large enough to admit of their contents being taken out of them with facility, or else the smaller weights will soon get cracked, bruised, and indistinct. Every one of the weights (with the exception of the milligramme) should be distinctly marked. 4. With respect to -the material most suitable for the manufacture of weights, we commonly rest satisfied with having the smaller weights only, from 1 or 0*5 gramme downwards, made of platinum or aluminium foil, using brass weights for all the higher denominations. Brass weights must be carefully shielded from the contact of acid or other vapor. s, or their correctness will be impaired ; nor should they ever be touched with the fingers, but always with small pincers. But it is an erroneous no- tion to suppose that weights slightly tarnished are unfit for use. It is, * Still it would be desirable that mechanicians who make gramme -weights in- tended for the use of the chemist, should endeavor to procure normal weights. It is very inconvenient, in many cases, to find notable differences between weights of the same denomination, but coming from different makers ; as I myself have often had occasion to discover. 9.J WEIGHING. Ip indeed, hardly possible to prevent weights for any very great length of time from getting slightly tarnished. I have carefully examined many weights of this description, and have found them as exactly corresponding with one another in their relative proportions as they were when first used. The tarnishing coat, or incrustation, is so extremely thin, that even a very delicate balance will generally fail to point out any per- ceptible difference in the weight. The following is the proper way of testing the weights : One scale of a delicate balance is loaded with a one-gramme weight, and the balance is then completely equipoised by taring with small pieces of brass, and finally tinfoil (not paper, since this absorbs moisture). The weight is then removed, and replaced successively by the other gramme weights, and afterwards by the same amount of weight in pieces of lower denominations. The balance is carefully scrutinized each time, and any deviation from the exact equilibrium marked. In the same way it is seen whether the two-gramme piece weighs the same as two single grammes, the five- gramme piece the same as three single grammes and the two-gramme piece, &c. In the comparison of the smaller weights thus among them- selves, they must not show the least difference on a balance turning with Y'-Q- of a milligramme. In comparing the larger weights with all the small ones, differences of T 1 ^ to T 2 -g- of a milligramme may be passed over. If you wish them to be more accurate, you must adjust them yourself. In the purchase of weights chemists ought always to bear in mind that an accurate weight is truly valuable, whilst an inaccurate one is absolutely worthless. It is the safest way for the chemist to test every weight he purchases, no matter how high the reputation of the maker. 9. c. THE PROCESS OF WEIGHING. We have two different methods of determining the weight of substan- ces ; the one might be termed direct weighing, the other is called weigli- ing by substitution. In direct weighing, the substance is placed upon one scale, and the weight upon the other. If we possess a balance, the arms of which are of equal length, and the scales in a perfect state of equilibrium, it is in- different upon which scale the substance is placed in the several weigh- ings required during an analytical process ; i.e., we may weigh upon the right or upon the left side, and change sides at pleasure, without en- dangering the accuracy of our results. But if, on the contrary, the arms of our balance are not perfectly equal, or if the scales are not in a state of perfect equilibrium, we are compelled to weigh invariably upon the same scale, otherwise the correctness of our results will be more or less materially impaired. Suppose we want to weigh one gramme of a substance, and to divide this amount subsequently into two equal parts. Let us assume our balance to be in a state of perfect equilibrium, but with unequal arms, the left being 99 millimetres, the right 100 millimetres long; we place a gramme weight upon the left scale, and against this, on the right scale, as much of the substance to be weighed as will restore the equilibrium of the balance. According to the axiom, " masses are in equilibrium upon a lever, if 16 OPERATIONS. [ 9 the products of their weights into their distances from the fulcrum are equal," we have consequently upon the right scale 0*99 grm. of substance, since 99 X 1*00=100 X 0*99. If we now, for the purpose of weighing one half the quantity, remove the whole weight from the left scale, substitu- ting a 0*5 grm. weight for it, and then take off part of the substance from the right scale, until the balance recovers its equilibrium, there will remain 0*495 grm. ; and this is exactly the amount we have removed from the scale : we have consequently accomplished our object with re- spect to the relative weight ; and, as we have already remarked, the absolute weight is not generally of so much importance in scientific work. But if we attempted to halve the substance which we have on the right scale, by first removing both the weight and the substance from the scales, and placing subsequently a 0*5 grm. weight upon the right scale, and part of the substance upon the left, until the balance recovers its equilibrium, we should have 0*505 of substance upon the left scale, since 100 X 0'500=99 X 0*505 ; and consequently, instead of exact halves, we should have one part of the substance amounting to 0*505, the other only to 0*485. Jf the scales of our balance are not in a state of absolute equilibrium, we are obliged to weigh our substances in vessels to insure accurate re- sults (although the arms of the balance be perfectly equal). It is self- evident that the weights in this case must likewise be invariably placed upon one and the same scale, and that the difference between the two scales must not undergo the slightest variation during the whole course of a series of experiments. From these remarks result the two following rules : 1. It is, under all circumstances, advisable to place the substance in- variably upon one and the same scale most conveniently upon the left. 2. If the operator happens to possess a balance for his own private and exclusive use, there is no need that he should adjust it at the commence- ment of every analysis ; but if the balance be used in common by several persons, it is absolutely necessary to ascertain, before every operation, whether the state of absolute equilibrium may not have been disturbed. Weighing by substitution yields not only relatively, but also absolutely accurate results ; no matter whether the arms of the balance be of exactly equal lengths or not, or whether the scales be in perfect equipoise or not. The process is conducted as follows: the material to be weighed say a platinum crucible is placed upon one scale, and the other scale is accurately counterpoised against it. The platinum crucible is then re- moved, and the equilibrium of the balance restored by substituting weights for the removed crucible. It is perfectly obvious that the sub- stituted weights will invariably express the real weight of the crucible with absolute accuracy. We weigh by substitution whenever we require the greatest possible accuracy ; as, for instance, in the determination of atomic weights. The process may be materially shortened by first placing a tare (which must of course be heavier than the substance to be weighed) upon one scale, say the left, and loading the other scale with weights until equilibrium is produced. This tare is always retained on the left scale. The weights after being noted are removed. The sub- stance is placed on the right scale, together with the smaller weights re- quisite to restore the equilibrium of the balance. The sum of the weights added is then subtracted from the noted weight of the counter- poise : the remainder will at once indicate the absolute weight of the sub- 10.] WEIGHING. 17 stance. Let us suppose, for instance, we have on the left scale a tare requiring a weight of fifty grammes to counterpoise it. We place a platinum crucible on the right scale, and find that it requires an addition of weight to the extent of 10 grammes to counterpoise the tare on the left. Accordingly, the crucible weighs 50 minus 10=40 grammes. 10. The following rules will be found useful in performing the process of weighing : 1. The safest and most expeditious way of ascertaining the exact weight of a substance, is to avoid trying weights at random ; instead of this, a strictly systematic course ought to be pursued in counterpoising substances on the balance. Suppose, for instance, we want to weigh a crucible, the weight of which subsequently turns out to be 6'627 gram- mes ; well, we place 10 grammes on the other scale against it, and we find this is too much ; we place the weight next in succession, i. e., 5 grammes, and find this too little ; next 7, too much ; 6, too little ; 6*5, too little; 6*7, too much; 6'6, too little; 6*65, too much; 6*62, too little; 6-63, too much ; 6'625, too little; 6'627, right. I have selected here, for the sake of illustration, a most complicated case ; but this systematic way of laying on the weights will in most in- stances lead to the desired end, in half the time required when weights are tried at random. After a little practice a few minutes will suffice to ascertain the weight of a substance to within the ^ of a milligramme, provided the balance does not oscillate too slowly. 2. The milligrammes and fractions of milligrammes are determined by a centigramme rider (to be placed on or between the divisions on the beam) far more expeditiously and conveniently than by the use of the weights themselves, and at the same time with equal accuracy. 3. Particular care and attention should be bestowed on entering the weights in the book. The best way is to write down the weights first by inference from the blanks, or gaps in the weight box, and to control the entry subsequently by removing the weights from the scale, and re- placing them in their respective compartments in the box. The student should from the commencement make it a rule to enter the number to be deducted in the lower line y thus, in the upper line, the weight of the crucible -f the substance ; in the lower line, the weight of the empty crucible. 4. The balance ought to be arrested every time any change is contem- plated, such as removing weights, substituting one weight for another, &c. &c., or it will soon get spoiled. 5. Substances (except, perhaps, pieces of metal, or some other bodies of the kind) must never be placed directly upon the scales, but ought to be weighed in appropriate vessels of platinum, silver, glass, porcelain, &c., never on paper or card, since these, being liable to attract moisture, are apt to alter in weight. The most common method is to weigh in the first instance the vessel by itself, and to introduce subsequently the substance into it ; to weigh again, and subtract the former weight from the latter. In many instances, and more especially where several por- tions of the same substance are to be weighed, the united weight of the vessel and of its contents is first ascertained ; a portion of the contents is then shaken out, and the vessel weighed again; the loss of weight expresses the amount of the portion taken out of the vessel. 2 18 OPERATIONS. [ 11. 6. Substances liable to attract moisture from the air, must be weighed invariably in closed vessels (in covered crucibles, for instance, or between two watch-glasses, or in a closed glass tube) ; fluids are to be weighed in small bottles closed with glass stoppers. 7. A vessel ought never to be weighed whilst warm, since it will in that case invariably weigh lighter than it really is. This is owing to two circumstances. In the first place, every body condenses upon its surface a certain amount of air and moisture, the quantity of which depends upon the temperature and hygroscopic state of the air, and likewise on its own temperature. Now suppose a crucible has been weighed cold at the commencement of the operation, and is subsequently weighed again whilst hot, together with the substance it contains, and the weight of which we wish to determine. If we subtract for this purpose the weight of the cold crucible, ascertained in the former instance, from the weight found in the latter, we shall subtract too much, and conse- quently we shall set down less than the real weight for the substance. In the second place, bodies at a high temperature are constantly com- municating heat to the air immediately around them ; the heated air expands and ascends, and the denser and colder air, flowing towards the space which the former leaves, produces a current which tends to raise the scale, making it thus appear lighter than it really is. 8. If we suspend from the end edges of a correct balance respectively 10 grammes of platinum and 10 grammes of glass, by wires of equal weight, the balance will assume a state of equilibrium ; but if we sub- sequently immerse the platinum and glass completely in water, this equilibrium will at once cease, owing to the different specific gravity of the two substances ; since, as is well known, substances immersed in water lose of their weight a quantity equal to the weight of their own bulk of water. If this be borne in mind, it must be obvious to every one that weighing in the air is likewise defective, inasmuch as the bulk of the substance weighed is not the same with that of the weight. This defect, however, is so very insignificant, owing to the trifling specific gravity of the air in proportion to that of solid substances, that we may generally disregard it altogether in analytical experiments. In cases, however, where absolutely accurate results are required, the bulk both of the substance examined, and of the weight, must be taken into ac- count, and the weight of the corresponding volume of air added respec- tively to that of the substance and of the weight, making thus the pro- cess equivalent to weighing in vacua. 2. MEASURING. The process of measuring is confined in analytical researches mostly to gases and liquids. The method of measuring gases has been brought to such perfection that it may be said to equal in accuracy the method of weighing. However, such accurate measurements demand an expendi- ture of time and care, which can be bestowed only on the nicest and most delicate scientific investigations.* * [The student who will practise the accurate measurement of gases in any but the simplest cases, must refer for all details to Bunsen's " Gasometry " (trans- lated by Roscoe), and Russell, Jour. Chem. Soc., 1868 p. 128, as the subject ia too extensive for the limits of this volume.] 12.] MEASURING. 19 The measuring of liquids in analytical investigations was resorted to first by DESCROIZILLES (" Alkalimeter," 1806). GAY-LUSSAC materially improved the process, and indeed brought it to the highest degree of perfection (measuring of the solution of chloride of sodium in the assay of silver in the wet way). More recently F. MOHR* has bestowed much caie and ingenuity upon the production of appropriate and convenient measuring apparatus, and has added to our store the eminently practical compression stop-cock burette. The process is now resorted to even in most accurate scientific investigations, since it requires much less time than the process of weighing. The accuracy of all measurings depends upon the proper construction of the measuring vessels, and also upon the manner in which the process is conducted. a. THE MEASURING OF GASES. We use for the measuring of gases graduated tubes of greater or less capacity, made of strong glass, and closed by fusion at one end, which should be rounded. The following tubes will be found sufficient for all the processes of gas measuring required in organic elementary analyses. 1. A bell-glass capable of holding from 150 to 250 c. c., and about 4 centimetres in diameter ; divided into cubic centimetres. 2. Five or six glass tubes, about 12 to 15 millimetres in diameter in the clear, and capable of holding from 30 to 40 c. c. each, divided into k c. c. The sides of these tubes should be pretty thick, otherwise they will be liable to break, especially when used to measure over mercury. The sides of the bell-glass should be about 3, of the tubes about 2 millimetres thick. The most important point, however, in connection with measuring in- struments is that they be correctly graduated, since upon this of course depends the accuracy of the results. For the method of graduating I refer to GREVILLE WILLIAMS' " Chemical Manipulation." f In testing the measuring tubes we have to consider three things. 1. Do the divisions of a tube correspond with each other? 2. Do the divisions of each tube correspond with those of the other tubes? 3. Do the volumes expressed by the graduation lines correspond with the weights used by the analyst ? These three questions are answered by the following experiments : a. The tube which it is intended to examine is placed in a perpendicu- lar position, and filled gradually with accurately measured small quanti- ties of mercury, care being taken to ascertain with the utmost precision whether the graduation of the tube is proportionate to the equal vol- umes of mercury poured in. The measuring-off of the mercury is effected by means of a small glass tube, sealed at one end, and ground perfectly even and smooth at the other. This tube is filled to overflowing by im- mersion under mercury, care being taken to allow no air bubbles to * " Lehrbuch der Titrirmethode," by Dr. Fr. Mohr. Brunswick, 1855. f [See also Gary Lea, Am. Jour. Sci. and Arts, 2d ser., vol. 42, p. 375.] 20 OPERATIONS. [ 13. remain in it ; the excess of mercury is then removed by pressing a small glass plate down on the smooth edge of the tube.* b. Different quantities of mercury are successively measured off in one of the smaller tubes, and then transferred into the other tubes. The tubes may be considered in perfect accordance with each other, if the mer- cury reaches invariably the same divisional point in every one of them. Such tubes as are intended simply to determine the relative volume of different gases, need only pass these two experiments ; but in cases where we want to calculate the weight of a gas from its volume, it is necessary also to obtain an answer to the third question. For this purpose c. One of the tubes is accurately weighed and then filled with distilled water of a temperature of 16 to the last mark of the graduated scale; the weight of the water is then accurately determined. If the tube agrees with the weights, every 100 c. c. of water of 16 must weigh 99'9 grm. But should it not agree, no matter whether the error lie in the graduation of the tube or in the adjustment of the weights, we must ap- ply a correction to the volume observed before calculating the weight of a gas therefrom. Let us suppose, for instance, that we find 100 c. c. to weigh only 99*6 grm. : assuming our weights to be correct, the c. c. of our scale are accordingly too small ; and to convert 100 of these c.c. into normal c. c. we say : 99-9 : 99-6 : : 100 : x. In the measuring of gases we must have regard to the folloiving 1. Correct reading-off. 2. The temperature of the gas. 3. The degree of pressure operating upon it. And 4. The circumstance whether it is dry or moist. The three latter points will be readily understood, if it be borne in mind that any alteration in the temperature of a gas, or in the pressure acting upon it, or in the tension of the admixed aqueous vapor, involves likewise a considerable alteration in its volume. 1. CORRECT READING-OFF. This is rather difficult, since mercury in a cylinder has a convex sur- face (especially observable with a narrow tube), owing to its own cohe- sion ; whilst water, on the other hand, under the same circumstances has a concave surface, owing to the attraction which the walls of the tube exercise upon it. The cylinder should invariably be placed in a perfectly perpendicular position, and the eye of the operator brought to a level with the surface of the fluid. In reading-off over water, the middle of the dark zone formed by that portion of the liquid that is drawn up around the inner walls of the tube, is assumed to be the real surface ; whilst when operating with mercury, we have to place the real surface in a plane exactly in the middle between the highest point of the surface of the mercury, and the points at which the latter is in actual contact with the walls of the tube. However, the results obtained in this way are only approximate. Absolutely accurate results cannot be arrived at, in measuring over * As warming 1 the metal is to be carefully avoided in this process, it is advi- sable not to hold the tube with the hand in immersing it in the mercury, but to fasten it in a small wooden holder. 14, 15.] MEASURING OF GASES. 21 water or any other fluid that adheres to glass. But over mercury they may be arrived at if the error of the meniscus be determined and the mercury be read off at the highest point. The determination of the erroi of the meniscus is performed for each tube, once for all, in the following manner : some mercury is poured into the tube, and its height read-off right on a level with the top of the convex surface exhibited by it ; a few drops of solution of chloride of mercury are then poured on the top of the metal ; this causes the convexity to disappear ; the height of the mercury in the tube is now read-off again and the difference noted. In the process of graduation, the tube stands upright, in that of measuring gases, it is placed upside down; the difference observed must accordingly be doubled, and the sum added to each volume of gas read off. 14. 2. INFLUENCE OF TEMPERATURE. The temperature of gases to be measured is determined either by making it correspond with that of the confining fluid, and ascertaining the latter, or by suspending a. delicate thermometer by the side of the gas to be measured, and noting the degree which it indicates. If the construction of the pneumatic apparatus permits the total im- mersion of the cylinder in the confining fluid, uniformity of tempe- rature between the latter and the gas which it is intended to measure, is most readily and speedily obtained ; but in the reverse case, the operator must always, after every manipulation, allow half an hour or, in operations combined with much heating, even an entire hour to elapse, before proceeding to observe the state of the mercury in the cylinder, and in the thermometer. Proper care must also be taken, after the temperature of the gas has been duly adjusted, to prevent re-expansion during the reading-off ; all injurious influences in this respect must accordingly be carefully guarded against, and the operator should, more especially, avoid laying hold of the tube with his hand (in pressing it down, for instance, into the con- fining fluid) ; making use, instead, of a wooden holder. 15 - 3. INFLUENCE OF PRESSURE. "With regard to the third point, the gas is under the actual pressure of the atmosphere if the confining fluid stands on an exact level both in and outside the cylinder ; the degree of pressure exerted upon it may therefore at once be ascertained by consulting the barometer. But if the confining fluid stands higher in the cylinder than outside, the gas is under less pressure, if lower, it is under greater pressure than that of the atmo- sphere ; in the latter case, the perfect level of the fluid inside and outside the cylinder may readily be restored by raising the tube ; if the fluid stands higher in the cylinder than outside, the level may be restored by depressing the tube ; this however can only be done in cases where we have a trough of sufficient depth. When operating over water, the level may in most cases be readily adjusted ; when operating over mercury, it is, more especially with wide tubes, often impossible to bring the fluid to a perfect level inside and outside the cylinder. OPERATIONS. [ 16, 17, 18. 4. INFLUENCE OF MOISTURE. In measuring gases saturated with aqueous vapor, it must be taker into account that the t vapor, by virtue of its tension, exerts a pressure upon the confining fluid. The necessary correction is simple, since we know the respective tension of aqueous vapor for the various degrees of temperature. But before this correction can be applied, it is, of course, necessary that the gas should be actually saturated with the vapor. It is, therefore, indispensable in measuring gases to take care to have the gas thoroughly saturated with aqueous vapor, or else absolutely dry. It is quite obvious from the preceding remarks, that volumes of gases can be compared only if measured at the same temperature, under the same pressure, and in the same hygroscopic state. They are generally reduced to 0, 0*76 met. barometer, and absolute dryness. How this is effected, as well as the manner in which we deduce the weight of gases from their volume, will be found in the chapter on the calculation of analyses. 17. b. THE MEASURING OF FLUIDS. In consequence of the vast development which volumetric analysis has of late acquired, the measuring of fluids has become an operation of very frequent occurrence. According to the different objects in view, various kinds of measuring vessels are employed. The operator must, in the case of every measuring vessel, carefully distinguish whether it is graduated for holding or for delivering the exact number of c. c. marked on it. If you have made use of a vessel of the former description in measuring off 100 c. c. of a fluid, and wish to transfer the latter com- pletely to another vessel, you must, after emptying your measuring vessel, rinse it, and add the rinsings to the fluid transferred ; whereas, if you have made use of a measuring vessel of the latter description, there must be no rinsing. a. MEASURING VESSELS GRADUATED FOR HOLDING THE EXACT MEASURE OF FLUID MARKED ON THEM. aa. Measuring vessels which serve to measure out one definite quantity of fluid. "We use for this purpose 1. Measuring Flasks. Fig. 2 represents a measuring flask of the most practical and con- venient form. Measuring flasks of various sizes are sold in the shops, holding respectively 200, 250, 500, 1000, 2000, &c., c. c. As a general rule, they have no ground-glass stoppers ; it is, however, very desirable, in certain cases, to have measuring flasks with ground stoppers. The flasks must be made of well-annealed glass of uniform thickness, so that fluids may g 18.] MEASURING OF FLUIDS. 23 be heated in them. The line-mark should be placed within the lowei third, or at least within the lower half, of the neck. Measuring flasks, before they can properly be employed in analytical operations, must first be carefully tested. The best and simplest way of effecting this is to proceed thus : Put the flask, perfectly dry inside and outside, on the one scale of a sufficiently delicate balance, together with a weight of 1000 grm. in the case of a litre flask, 500 grm. in the case of a half-litre flask, &c., restore the equilibrium by placing the requisite quantity of shot and tinfoil on the other scale, then remove the flask and the weight from the balance, put the flask on a perfectly level surface, and pour in distilled water of 16,* until the lower border of the dark zone formed by the top of the water around the inner walls corresponds with the line-mark. After having thoroughly dried the neck of the flask above the mark, replace it upon the scale : if this restores the perfect equilibrium of the balance, the water in the flask weighs, in the case of a litre- measure, exactly 1000 grm. If the scale bearing the Fj 2 ^ flask sinks, the water in it weighs as much above 1000 grm. as the additional weights amount to which you have to put in the other scale to restore the equilibrium ; if it rises, on the other hand, the water weighs as much less as the weights amount to which you have to put in the scale with the flask to eflect the same end. If the water in the litre-measure weighs 999 grm.,f in the half-litre measure, 499*5 grm., f the water con- 30.] ESTIMATION OF WATER. 43 tained in a substance is, therefore, one of the most important, as well as most frequently occurring operations of quantitative analysis. The pro- portion of water contained in a substance may be determined in two ways, viz., a, from the diminution of weight consequent upon the expul- sion of the water ; b, by weighing the amount of water expelled. 35. a. ESTIMATION OF THE WATER FROM THE Loss OF WEIGHT. This method, on account of its simplicity, is most frequently employed. The modus operandi depends upon the nature of the substance under examination. a. The Substance hears ignition without losing other Constituents besides Water, and without absorbing Oxygen. The substance is weighed in a platinum or porcelain crucible, and placed over the gas or spirit lamp ; the heat should be very gentle at first, and gradually increased. When the crucible has been maintained some time at a red heat, it is allowed to cool a little, put still warm under the desiccator, and finally weighed when cold. The ignition is then repeated, and the weight again ascertained. If no further diminu- tion of weight has taken place, the process is at an end, the desired ob- ject being fully attained. But if the weight is less than after the first heating, the operation must be repeated until the weight remains constant. In the case of silicates, the heat must be raised to a very high degree, since many of them (e.g. talc, steatite, nephrite) only begin at a red heat to give off water, and require a yellow heat for the complete expulsion of that constituent. (Tn. SCHEERER.*) Such bodies are therefore ignited over a blast lamp. In the case of substances that have a tendency to puff off, or to spirt, a small flask or retort may sometimes be advantageously substituted for the critcible. Care must be taken to remove the last traces of aqueous vapor from the vessel, by suction through a glass tube. Decrepitating salts (chloride of sodium, for instance) are put finely pulverized, if possible in a small covered platinum crucible, which is then placed in a large one, also covered ; the whole is weighed, then heated, gently at first for some time, then more strongly ; finally, after cooling, weighed again. (3. The substance loses on ignition other Constituents besides "Water (JBoracic Acid, Sulphuric, Acid, Fluoride of Silicon, &c.~). Here the analyst has to consider, in the first place, whether the water may not be expelled at a lower degree of heat, which does not involve the loss of other constituents. If this may be done, the substance is heated either in the water-bath, or where a higher temperature is re- quired, in the air-bath or oil-bath, the temperature being regulated by the thermometer. The expulsion of the water may be promoted by the co-operation of a current of air (compare 29 and 30) ; or by the addition of pure dry sand to the substance, to keep it porous, f The * Jahresber. von Liebig- u. Kopp, 1851, 610. f Ann. d. Chera. u. Pharm. , 53, 233. 44 OPERATIONS. [ 36. process must be continued under these circumstances also, until the weight remains constant. In cases where, for some reason or other, such gentle heating is insuf- ficient, the analyst has to consider whether the desired end may not b* attained at a red heat, by adding some substance that will retain the volatile constituent whose loss is apprehended. Thus, for instance, the crystallized sulphate of alumina loses at a red heat, besides water, also sulphuric acid ; now, the loss of the latter constituent may be guarded against by adding to the sulphate an excess (about six times the quan- tity) of finely pulverized, recently ignited, pure oxide of lead. But the addition of this substance will not prevent the escape of fluoride of silicon from silicates when exposed to a red heat (LIST *). Thus again, the amount of water in commercial iodine may be deter- mined by triturating the iodine together with eight times the quantity of mercury, and drying the mixture at 100 (BoLLEYf ). y. The Substance contains several differently combined quantities of Water which require different Degrees of Temperature for Expulsion. Substances of this nature are heated first in the water-bath, until their weight remains constant ; they are then exposed in the oil- or air-bath to 150, 200, or 250, &c., and finally, when practicable, ignited over a gas- or spirit-lamp. [In such experiments, it is best to proceed as de- scribed, 29, p. 39, viz., to heat in a current of dried air, hydrogen, or car- bonic acid.] In this mariner differently combined quantities of water may be dis- tinguished, and their respective amounts correctly estimated. Thus, for instance, crystallized sulphate of copper contains 28'87 per cent, of water, which escapes at a temperature below 140, and 7*22 per cent., which escapes only at a temperature between 220 and 260. S. When the substance has a tendency to absorb oxygen (from the pre- sence of protoxide of iron, for instance) the water is better determined in the direct way, than by the loss. ( 36.) 36. b. ESTIMATION OF WATER BY DIRECT WEIGHING. This method is resorted to byway of control, or in the case of substances which, upon ignition, lose, besides water, other constituents, which cannot be retained even by the addition of some other substance (e.g., carbonic acid, oxygen), or in the case of substances containing bodies inclined to oxidation ( t 05 28-4 14-2 0-5 26-7 13-3 0-5 24-4 12-2 0-5 227 11-4 1 16-6 16-6 1 15-6 15-6 1 14-3 14-3 1 13-3 13-3 2 10'5 21-0 2 9-8 19-7 2 9-0 18-0 2 8-4 16-8 3 8-3 24-9 3 7-8 23-4 3 71 21-4 3 6-6 19-9 4 71 28-6 4 6-7 26-9 4 61 24-6 ; 4 5-7 22-9 5 6-4 32-1 5 6-0 30-2 5 5-5 27-6 5 51 25-7 6 5-9 35-5 6 5-6 33-4 6 51 30-5 6 4-7 28-4 7 5-5 38-8 7 5-2 36-4 7 4-8 33-3 7 4-4 31-0 8 5-2 42-0 8 4-9 39-4 8 4'5 361 8 4-2 33-5 9 5-0 45-0 9 4-7 42-3 9 4-3 387 9 4-0 36-0 10 4-8 48-0 10 4-5 451 10 41 41-3 10 3-8 38-4 11 4-6 51-0 11 4-4 47-9 11 4-0 43-8 11 3-7 40-8 12 4-5 53-9 12 4-2 50-6 12 3-9 46-3 12 3-6 431 13 4-4 56-4 13 41 53-3 13 3-8 48-8 13 3-5 45-4 14 4-2 59-4 14 4-0 55-8 14 3-7 511 14 3-4 47-5 15 4-2 62-3 15 39 58-5 15 3-6 53-6 15 3-3 49-8 16 4-1 65-0 16 3-8 611 16 3-5 56-0 16 3-3 53-0 17 4-0 67-8 17 3-7 63-6 17 3'4 58-3 17 3-2 54-2 18 3-9 70-4 18 3-7 661 18 3-4 60-5 18 31 56-3 19 3-8 74-3 19 3-6 68-6 19 3-3 62-8 19 31 58-4 I by far prefer using this Table to employing the method generally fol- lowed of ascertaining the completion of the washing-process by evapora- ting a quantity of the filtrate on platinum-foil, since in the latter case it is only possible to obtain an infallible proof when we have to deal with a precipitate possessing an extremely high degree of insolubility ; if the precipitate be soluble to any marked extent, the result is completely illusory. In the process of filtration as hitherto conducted, the time required is so long ^ and the quantity of wash-water needed so great that some simplification of this continually recurring operation is in the highest de- gree desirable. The following method, which depends not upon the remo- val of the impurity by simple attenuation, but upon its displacement by * 53, a.] BUNSEN'S METHOD OF RAPID FILTRATION. 69 forcing the wash-water through the precipitate, appears to me to combine all the requisite conditions and therefore to satisfy the need. The rapidity with which a liquid niters depends, cceteris paribus, upon the difference which exists between the pressure upon its upper and lower surfaces. Supposing the filter to consist of a solid substance, the pores of which suffer no alteration by pressure or by any other influence, then the volume of liquid filtered in the unit of time is nearly propor- tional to the difference in pressure : this is clearly shown by the following experiments, made with pure water and a filter consisting of a thin plate of artificial pumice-stone. The thin plate of pumice was hermeti- cally fastened into a funnel consisting of a graduated cylindrical glass vessel, the lower end of which was connected with a large thick flask by means of a tightly fitting caoutchouc cork. The pressure in the flask was then reduced by rarefying the air by means of a method to be described upon another occasion ; and for each difference of pressure p, measured by a mercury column, the number of seconds t was observed which a given quantity of water occupied in passing through the filter. The following are the results : I. p. t P t. metre. 0-179 91-7 16-4 0-190 81-0 15-4 0-282 52-9 14-9 0-472 33-0 15-6 In the ordinary process of filtration, p on the average amounts to no more than 0*004 to 0*008 metre. The advantage gained, therefore, is easily perceived when we can succeed by some simple, practicable, and easily attainable method in multiplying this difference in pressure one or two hundred times, or, say, to an entire atmosphere, without running any risk of breaking the filter. The solution of this problem is very easy : an ordinary glass funnel has only to be so arranged that the filter can be completely adjusted to its side even to the very apex of the cone. For this purpose a glass funnel is chosen possessing an angle of 60, or as nearly 60 as possible, the walls of which must be completely free from inequalities of every description ; and into it is placed a second funnel made of exceedingly thin platinum-foil, and the sides of which possess exactly the same inclination as those of the glass funnel. An ordinary paper filter is then introduced into this compound funnel in the usual manner ; when carefully moistened and so adjusted that no air- bubbles are visible between it and the glass, this filter, when filled with a liquid, will support the pressure of an extra atmosphere without ever breaking. The platinum funnel is easily made from thin platinum-foil in the following manner : In the carefully chosen glass funnel is placed SL per- fectly accurately fitting filter made of writing-paper ; this is kept in position by dropping a little melted sealing-wax between its upper edge and the glass ; the paper is next saturated with oil and filled with liquid plaster of Paris, and before the mixture solidifies a small wooden handle is placed in the centre. After an hour or so the plaster cone with the adhering paper filter can be withdrawn by means of the handle from the 70 OPERATIONS. [ 53, a- funnel, to which it accurately corresponds. The paper on the outside of the cone is again covered with oil, and the whole carefully inserted into liquid plaster of Paris contained in a small crucible 4 or 5 centims. in height. After the mixture has solidified, the cone may be easily with- drawn ; the adhering paper filter is then detached, and any small pieces of paper still remaining removed by gently rubbing with the finger. In this manner a solid cone is obtained accurately fitting into a hollow cone, and of which the angle of inclination perfectly corresponds with that of the glass funnel. 4 Fig. 43. Fig. 43, 1, represents the cones. By their help the small platinum fun- nel is made. A piece of platinum (shown three-fourths of the natural size in fig. 44)* is cut from foil of such a thickness that one square centimetre weighs about 0*154 grm., and from the centre a a vertical incision is made by the scissors to the edge c b d. The small piece of foil is next rendered pliable by being heated to redness, and is placed upon the solid cone in such a manner * The diameter of a in the original drawing is 2 '5 centimetres. 53, a.] BUNSEN'S METHOD OF RAPID FILTRATION. 71 that its centre a touches the apex of the latter ; the sides a b d are then closely pressed upon the plaster, and the remaining portion of the platinum wrapped as equally and as closely as possible around the cone. On again heating the foil to redness, pressing it once more upon the cone, and inserting the whole into the hollow cone, and turning it round once or twice under a gentle pressure, the proper shape is completed. The platinum funnel, which should not allow of the transmission of light through its extreme point, even now possesses such stability that it may be immediately employed for any purpose. If desired, it may be made still stronger by soldering down the overlap- ping portion in one spot only to the upper edge of the foil by means of a grain or two of gold and borax ; in general, however, this precaution is unnecessary. If the shape has in any degree altered during this latter process, it is simply necessary to drop the platinum funnel into the hol- low cone and then to insert the solid cone, when by one or two turns of the latter the proper form may be immediately restored. The plati- num funnel is placed in the bottom of the glass funnel, the dry paper filter then introduced in the ordinary manner, moistened, and freed from all adhering air-bubbles by pressure with the finger. A filter so arranged and in perfect contact with the glass, when filled with a liquid will support the pressure of an entire atmosphere without the least dan- ger of breaking ; and the interspace between the folds of the platinum- foil is perfectly sufficient to allow of the passage of a continuous stream of water. In order to be able to produce the additional pressure of an atmo- sphere, the filtered liquid is received in a strong glass flask instead of in beakers.* This flask is closed by means of a doubly perforated caoutchouc cork, through one of the holes of which the neck of the glass funnel is passed to a depth of from 5 to 8 centimetres (fig. 43, k) ; through the other is fitted a narrow tube open at both ends, the lower end of which is brought exactly to the level of the lower surface of the cork, to the other is adapted the caoutchouc tube connected with the apparatus destined to produce the requisite difference in pressure : this apparatus will be described immediately. The flasks are placed in a metallic or porcelain vessel, in the conical contraction of which several strips of cloth are fastened. This method of supporting the flask has the advantage that, in one and the same vessel, flasks varying in size from 0'5 to 2*5 litres stand equally well, and that by simply laying a cloth over the mouth of the vessel, the consequences of an explosion (which through inexperience or carelessness is possible) are rendered harmless. It is impossible to employ any of the air-pumps at present in use to create the difference in pressure, since the filtrate not unfrequently contains chlo- rine, sulphurous acid, hydric sulphide, and other substances which would act injuriously upon the metallic portions of these instruments. I there- fore employ a water air-pump constructed on the principle of SPRENGEL'S inercury-pump, and which appears to me preferable to all other forms of air-pump for chemical purposes, since ifc effects a rarefaction to within 6 or 12 millimetres pressure of mercury. Fig. 43 shows the arrangement of this pump. On opening the pinch- cock a, water flows from the tube I into the enlarged glass vessel 6, and * These flasks must be somewhat thicker than those ordinarily used, in orde? to prevent the possibility of their giving way under the atmospheric pressure. 72 OPERATIONS. [ 53, a. thence down the leaden pipe c. This pipe has a diameter of about 8 milliins., and extends downward to a depth of 30 or 40 feet, and ends in a sewer or other arrangement serving to convey the water away. The lower end of the tube d possesses a narrow opening ; it is hermetically sealed into the wider tube 6, and reaches nearly to the bottom of the latter. A manometer is attached to the upper continuation of this tube d by means of a side tube at d l ; at d? is attached a strong thick caoutchouc tube possessing an internal diameter of 5 millims. and an external diameter of 12 millims.; this leads to the flask which is to be rendered vacuous, and is connected with it by means of the short nar- rowed tube k. Between the air-pump and the flask is placed the small thick glass vessel f y in which, when one washes with hot water, the steam which may be carried over is condensed. All the caoutchouc joinings are made with very thick tubing, the internal diameter of which amounts to about 5 millims., the external diameter to about 17 millims. The entire arrangement is screwed down upon a board fastened to the wall, in such a manner that each separate piece of the apparatus is held by a single fastening only, in order to prevent the tubes being strained and broken by the possible warping of the board. On releasing the pinchcock a, water flows from the conduit I down the tube c to a depth of more than 30 feet, carrying with it the air which it sucks through the small opening of the tube d in the form of a continuous stream of bubbles. No advantage is gained by increasing the rapidity of the flow, since the friction exert ed by the water upon the sides of the leaden pipe acts directly as a counter-pressure, and a comparatively small increase in the rapidity of the flow is accompanied by a great in- crease in the amount of this friction. Accordingly at g is a second pinchcock, by which the stream can be once for all so regulated that, on completely opening the cock a, the friction, on account of the dimin- ished rate of flow, is rendered sufficiently small to allow of the maxi- mum degree of rarefaction. Such an apparatus, when properly regu- lated once for all by means of the cock part. III. 0-2452 " 7 " IV. 0-2443 10 TTnnr 0-2451 mean. By the use of the pump : grm. V. 0-2435, after 5 additions of water. VI. 0-2434 " 4 " VII. 0-2432 3 " " VIII. 0-2435 " 2 " IX. 0-2439 " 1 addition of water. X. 0-2439 " 1 " " 0-2436 mean. Hence the probable amount of chromium sesquioxide contained in the solution, according to the experiments with the pump, was 0*2436 grm. : according to the old method of decantation it was somewhat higher, namely 0*2451 grm. This excess of 1*5 milligramme shows that the adhe- sion of the soluble matters to the precipitate and to the filter is, in consequence of the greater pressure, more easily overcome in the new method than in the customary process ; it follows, therefore, that we can obtain a more complete washing by the new method than by the old. The old process of decantation required 108 minutes and 1050 cub. cen- tims. of water to effect a washing to the go ^ 6() part ; the new, on the contrary, only 12 to 14 minutes, and not more than 39 to 41 cub. cen- tims. of wash-water. 53, b, C.] ADVANTAGES OF BUXSEx's NEW METHOD. 77 53, b. BUNSEN'S METHOD OF DRYING AND IGNITING PRECIPITATES. If a precipitate be heated in a platinum crucible immediately after nitration by the older process, a portion will inevitably be projected out of the crucible. Hitherto, therefore, it has been necessary to dry the filtei and precipitate before ignition. Now to dry a quantity of hydrated chromium sesquioxide containing O2436 grm. Cr 2 O 3 in a water-bath at 100 C. requires at least five hours; and, moreover, bringing the dried precipitate into the crucible, burning the filter, and gradually igniting the mass is in the highest degree tedious and troublesome. All this ex- penditure of time arid labor may be saved by employing the new method. By its means a precipitate is as completely dried upon the filter in from 1 to 5 minutes as if it had been exposed from 5 to 8 hours in a drying-chani- ber ; and it can immediately, filter and all, be thrown into a platinum or porcelain crucible and ignited without the slightest fear of its spurting. By operating in the following manner the filter burns quietly without flame or smoke ; this phenomenon, although remarkable, easily admits of an explanation. The portion of filter-paper free from precipitate is tightly wrapped round the remainder of the filter in such a manner that the precipitate is enveloped in from four to six folds of clean paper. The whole is then dropped into the platinum or porcelain crucible lying obliquely upon a triangle over the lamp, and pushed down against its sides with the finger. The cover is then supported against the mouth of the crucible in the ordinary w r ay, and the ignition commenced by heating the portion of the crucible in contact with the cover. When the flame has the proper size and position, the filter carbonizes quietly without any appearance of flame or considerable amount of smoke. When the carbonization proceeds too slowly, the flame is moved a little toward the bottom of the crucible. After some time the precipitate appears to be surrounded only by an extremely thin envelope of carbon, possessing exactly the form (of course diminished in size) of the original filter ; the flame is then increased, and the crucible maintained at a bright-red heat until the carbon contained in thrs envelope is consumed. The combustion proceeds so quietly that the resulting ash surrounding the precipitate possesses, even to the smallest fold, the exact form of the original filter. If the ash shows here and there a dark color, it is sim- ply necessary to heat the crucible over a blast-lamp for a few minutes to effect the complete removal of the trace of carbon. This method of burning a filter is extremely convenient and accurate ; it is only necessa- ry to give a little attention at first to the slow carbonization of the paper, after which the further progress of the operation may be left to itself. Gelatinous, finely divided, granular, and crystalline precipitates, such as alumina, calcium oxalate, barium sulphate, silica, magnesium ammo- nium phosphate, &c., may with equal facility be treated in this manner ; so that even in this particular the work, in comparison with the method generally adopted, is considerably shortened and simplified. 53, c. ADVANTAGES OF BUNSEN'S NEW METHOD. From the above experiments it appears that the time necessary to filter and dry a quantity of chromium sesquioxyd, hitherto requiring 78 OPERATIONS. [ 53, C. about 7 hours, is reduced by the new method to 13 minutes. This sav- ing of time is, moreover, proportionately greater in the case of precipi- tates more easily filtered than hydrated chromium sesquioxide. Parti- cularly is this so in separating a finely suspended precipitate from a large volume of water. Under these circumstances the clear fluid runs through the filter in a continuous stream, so rapidly that it is scarcely possible to maintain the supply ; the entire operation, in fact, requires scarcely more time than that necessary to pour a liquid from one vessel to another. Filtration, therefore, may be effected as quickly through the smallest as through the largest filter. Moreover, the exceedingly small amount of water required to wash a precipitate completely renders unne- cessary the tedious evaporations which by the older method are almost inevitable when the filtrate is needed for a further separation. Thus the introduction of impurities from the action of the liquid upon the dish in the course of evaporation is prevented ; and also the loss due to the slight solubility of the greater number of precipitates in the wash- water is reduced to a minimum. Supposing we had to analyze an alka- line chromate in which the quantity of chromic acid is equivalent to 0*2436 grm. chromic sesquioxide, as in the above described experi- ments, then to determine the proportion of alkali, we should, by using the older method, require the preliminary evaporation of about 1050 cub. centims. of liquid ; by the new method the evaporation of 40 cub. centims. only is necessary. Now by employing the water-bath, with constant water-level, it is possible, under favorable circumstances, to evaporate in a porcelain dish 1 cub. centim. of water in 27 seconds. Consequently the evaporation of the filtrate obtained by the older method would occupy about eight hours, whilst by the new 18 minutes only are required. The total length of time needed to filter the chro- mium sesquioxide, wash and dry the precipitate, and evaporate the filtrate is reduced, therefore, from 14 or 15 hours to about 32 minutes. Experience has shown that, on the average, three or four analyses can now be made in the time formerly demanded by a single one. Another and an inestimable advantage springs from the peculiar con- dition of a precipitate filtered by this method. It not unfrequently happens, even in the hands of experienced manipulators, in conse- quence of the agitation it is necessary to give to the contents of the filter to effect their complete washing, that the surface of the filter be- comes injured and torn so that the precipitate becomes mixed with fila- ments of paper ; this is particularly the case in using hot water. Suppos- ing the precipitate to consist of mixed hydrates of the sesquioxides (for example, iron and alumina), it will be found on redissolving in an acid, that the filaments, like tartaric acid, prevent the complete separation of these substances by subsequent precipitation ; thus the alumina will contain iron, and on precipitation by means of ammonium sulphide will be colored black. On the other hand, by employing the new method the precipitate coheres so firmly that the introduction of this source of error is impossible, even by using common gray filter-paper. Ths most gelatinous precipitates, as hydrated ferric oxide, alumina, &c., adhere to the filter in a thin coherent layer, and may be removed, piece after piece, so completely that the paper remains perfectly clean and white. The advantage thus gained where it is necessary to transfer mixed pre- cipitates to another vessel in order to effect their subsequent separation is evident. 53, d.J BUNSEN'S SIMPLIFIED EXHAUSTING APPAEATUS. 79 Since the bulk of the moist precipitates, particularly that of the more gelatinous, is so much diminished under the high pressure, the precipi- tate only occupying one-third to one-sixth of its bulk under ordinary circumstances, a filter of one-third to one-sixth of the size usually em- ployed may be taken, and thus the amount of ash proportionately les- sened. 53, d. BUNSEN'S SIMPLIFIED EXHAUSTING APPARATUS. It is not necessary to use a pump as powerful as that described, since a fall of 10 or 15 feet is sufficient to filter a precipitate according to the above described method, and so far to dry it that it can be immediately ignited in the cru- cible. The simple arrangement represented in fig. 45 answers this purpose. It consists of two equal-sized bottles, a and a', of from 2 to 4 litres capacity, each of which is provided near the bottom with a small stopcock designed to regulate the flow of water. Suppose a filled with water and placed upon a shelf as high above the ground as possible, and a' placed empty on the floor, and the two stopcocks con- nected by means of caoutchouc tubing c, then on allowing water to flow down the tube the air in the upper bottle becomes somewhat rarefied ; and in order to employ the conse- quent difference in pressure (amounting to a column of mercury about 0'2 metre in height) for the purpose of filtration, it is only neces- sary to connect the mouth of the upper bottle with the tube of the filter-flask. When the water has ceased to flow, the position of the bottle is reversed, when the operation recom- mences. So small a pressure as 0'2 metre suffices to render the filter and its contents so far dry that they may be immediately with- drawn from the funnel and ignited without any other preliminary desiccation. The following experiment, made with a portion of the same solution of chromium used in the former deter- minations, will serve to show the saving of time effected by this simple arrangement : XI. 14 Transferring the precipitate with cub. centims. of water For a single addition of 26 cub. centims. ^ of wash- water to run through ...... j To drain the precipitate .............. 4 Fig. 45. Time required in washing 25 80 OPERATIONS. [ 54. Weight of the precipitate O2435 grm. Volume of wash-water 40 cub. centims. Pressure in manometer 0-184 metre. This amount of chromium sesquioxide (0'2435 grm.) differs from the mean of the former experiments (0*2436 grm.) by one-tenth of a milli- gramme only, and shows that even by a pressure of 0' 184 metre the wash- ing is as complete by the single addition of 26 cub. centims. of water. The duration of the filtering process in the former experiments ranged from 12 to 14 minutes under a difference of pressure amounting to from 0-53 to 0-572 metre ; in the last experiment it required 25 minutes under a pressure of O'l 84 metre, or about double the length of time. The time needed to analyze potassium chromate in the former case was reduced from 14 hours to 32 minutes; by the latter method the reduc- tion would be from 14 hours to 44 minutes. 54. 5. ANALYSIS BY MEASURE (VOLUMETRIC ANALYSIS). The principle of volumetric analysis has been explained already in the " Introduction," where we have seen how the quantity of protoxide of iron present in a fluid may be determined by means of a solution of permanganate of potassa, the value of which has been previously ascer- tained by observing the quantity required to oxidize a known amount of protoxide of iron. In order to make the matter as clear as possible I will here adduce a few more examples. Suppose we have prepared a solution of chloride of sodium of such a strength that 100 c. c. will exactly precipitate 1 grm. silver from its solution in nitric acid, we can use it to estimate unknown quantities of silver. Let us imagine, for instance, we have an alloy of silver and copper in unknown proportion, we dissolve 1 grm. in nitric acid, and add to the solution our solution of chloride of sodium, drop by drop, until the whole of the silver is thrown down, and an additional drop fails to produce a further precipitate. The amount of silver present may now be calculated from the amount of solution of chloride of sodium used. Thus, supposing we have used 80 c. c., the amount of silver present in the alloy is 80 per cent. ; since, as 100 c. c. of the solu- tion of chloride of sodium will throw down 1 grm. of pure silver (i.e. of 100 per cent.), it follows that every c. c. of the chloride of sodium solution corresponds to 1 per cent, of silver. Another example. It is well known that iodine and sulphuretted hydro- gen cannot exist together : whenever these two substances are brought in contact, decomposition immediately ensues, the hydrogen separating from the sulphur and combining with the iodine (1 + HS = HI -f- S). Hydriodic acid exercises no action on starch-paste, whereas the least trace of free iodine colors it blue. Now, if we prepare a solution of iodine (in iodide of potassium) containing in 100 c. c. 0'7470 grm. iodine, we may with this decompose exactly O'l grm. sulphuretted hydrogen, for 17 : 127 : : O'l : 0'7470. Let us suppose, then, we have before us a fluid containing an unknown amount of sulphuretted hydrogen, which it is our intention to determine. We add to it a little starch-paste, and then, drop by drop, our solution of iodine, until a persistent blue colo- 54.] VOLUMETRIC ANALYSIS. 81 ration of the fluid indicates the formation of iodide of starch, and hence the complete decomposition of the sulphuretted hydrogen. The amount of the latter originally present in the fluid may now be readily calculated from the amount of solution of iodine used. Say, for instance, we have used 50 c. c. of iodine solution, the fluid contained originally 0'J5 sul- phuretted hydrogen ; since, as we have seen, 100 c. c. of our iodine solution will decompose exactly O'l grm. of that body. Solutions of accurately known composition or strength, used for the purposes of volumetric analysis, are called standard solutions. They may be prepared in two ways, viz., (a) by dissolving a weighed quantity of a substance in a definite volume of fluid ; or (b), by first preparing "a suitably concentrated solution of the reagent required, and then deter- mining its exact strength by a series of experiments made with it upon weighed quantities of the body for the determination of which it is in- tended to be used. In the preparation of standard solutions by method a, a certain defi- nite strength is adopted once for all, which is usually based upon the principle of an exact correspondence between the number of grammes of the reagent contained in a litre of the fluid, and the equivalent num- ber of the reagent (H 1). In the case of standard solutions prepared by method 6, this may also be easily done, by diluting to the required degree the still somewhat too concentrated solution, after having accu- rately determined its strength ; however, as a rule, this latter process is only resorted to in technical analyses, where it is desirable to avoid all calculation. Fluids which contain the eq. number of grammes of a sub- stance in one litre, are called normal solutions those which contain T ^ of this quantity, decinormal solutions. The determination of a standard solution intended to be used for vol- umetric analysis is obviously a most important operation ; since any error in this will, of course, necessarily falsify every analysis made with it. In scientific and accurate researches it is, therefore, always advisa- ble, whenever practicable, to examine the standard solution no matter whether prepared by method , or by method 6, with subsequent dilu- tion to the required degree by experimenting with it upon accurately weighed quantities of the body for the determination of which it is to be used. In the previous remarks I have made no difference between fluids of known composition and those of known power ; and this has hitherto been usual. But by accepting the two expressions as synonymous, we take for granted that a fluid exercises a chemical action exactly corre- sponding to the amount of dissolved substance it contains that, for in- stance, a solution of chloride of sodium containing 1 eq. Na Cl will pre- cipitate exactly 1 eq. silver. This presumption, however, is very often, not absolutely correct, as will be shown with reference to this very ex- ample, 1 1 5, 6, 5. In such cases, of course, it is not merely advisable, but even absolutely necessary, to determine the strength of the fluid, by experiment, although the amount of the reagent it contains may be exactly known, for the power of the fluid can be inferred from its composition only approximately and not with perfect exactness. ^ If a standard solution keeps unaltered, this is a great advantage, as it dis- penses with the necessity of determining its strength before every fresh analysis. That particular change in the fluid operated upon by means of a 6 82 OPERATIONS. [ 54. standard solution which marks the completion of the intended decom- position, is termed the FINAL REACTION. This consists either in a change of color, as is the case when a solution of permanganate of potassa acts upon an acidified solution of protoxide of iron, or a solu- tion of iodine upon a solution of sulphuretted hydrogen mixed with starch paste; or in the cessation of the formation of a precipitate upon further addition of the standard solution, as is the case when a stand- ard solution of chloride of sodium is used to precipitate silver from its solution in nitric acid ; or in incipient precipitation, as is the case when a standard solution of silver is added to a solution of hydrocyanic acid mixed with an alkali ; or in a change in the action of the examined fluid upon a particular reagent, as is the case when a solution of arsen- ite of soda is added, drop by drop, to a solution of chloride of lime, until the mixture no longer imparts a blue tint to paper moistened with iodide of potassium and starch-paste, &c. The more sensitive a final reaction is, and the more readily, posi- tively, and rapidly it manifests itself, the better is it calculated to serve as the basis of a volumetric method. In cases where it is an object of great importance to ascertain with the greatest practicable precision the exact moment when the reaction is completed, the analyst may some- times prepare, besides the actual standard solution, another, ten times more dilute, and use the latter to finish the process, carried nearly to completion with the former. > But a good final reaction is not of itself sufficient to afford a safe basis for a good volumetric method ; this requires, as the first and most in- dispensable condition, that the particular decomposition which consti- tutes the leading point of the analytical process should at least under certain known circumstances remain unalterably the same. Wherever this i$ not the case where the action varies with the greater or less degree of concentration of the fluid, or according as there may be a little more or less free acid present ; or according to the greater or less rapid- ity of action of the standard solution ; or where a precipitate formed in the course of the process has not the same composition throughout the operation the basis of the volumetric method is fallacious, and the method itself, therefore, of no value. SECTION II. REAGENTS. 55. FOR general information respecting reagents, I refer the student to my volume on " Qualitative Analysis." The instructions given here will be confined to the preparation, testing, and most important uses of those chemical substances which subserve principally and more exclusively the purposes of quantitative analysis. Those reagents which are employed in qualitative investigations, having been treated of already in the volume on the qualitative branch of the analytical science, will therefore be simply mentioned here by name. The reagents used in quantitative analysis are properly arranged under the following heads : A. Reagents for gravimetric analysis in the wet way. B. Reagents for gravimetric analysis in the dry way. (7. Reagents for volumetric analysis. J). Reagents used in organic analysis. The mode of preparing the fluids used in volumetric analysis, will be found where we shall have occasion to speak of their application. A. REAGENTS FOR GRAVIMETRIC ANALYSIS IN THE WET WAY. I SIMPLE SOLVENTS. 56. 1. DISTILLED WATER (see " Qual. Anal."). Water intended for quantitative investigations must be perfectly pure. Water distilled from glass vessels leaves a residue upon evaporation in a platinum vessel (see experiment No. 5), and is therefore inapplicable for many purposes ; as, for instance, for the determination of the exact degree of solubility of sparingly soluble substances. For certain uses it is necessary to free the water by ebullition from atmospheric air and car- bonic acid. 2. ALCOHOL (see " Qual. Anal."). a. Absolute alcohol. 6. Rectified spirit of wine of various degrees of strength. 3. ETHER. The application of ether as a solvent is very limited. It is more fre- quently used mixed with spirit of wine, in order to diminish the solvent 84 REAGENTS. [ 57, 58. power of the latter for certain substances, e.g., bichloride of platinum and chloride of ammonium. The ordinary ether of the shops will answer the purpose. II. ACIDS AND HALOGENS. a. Oxygen Acids. 57. 1. SULPHURIC ACID. a. Concentrated sulphuric acid of the shops. b. Concentrated pure sulphuric acid. c. Dilute sulphuric acid. See Qual. Anal." 2. NITRIC ACID. a. Pure nitric acid of 1*2 sp. gr. (see " Qual. Anal."). b. Red fuming nitric acid (concentrated nitric acid containing some hyponitric acid). Preparation. Two parts of pure, dry nitrate of potassa are introduced into a capacious retort, and one part of concentrated sulphuric acid is added either through the tubulure of the retort, or if a common non- tubulated one is used, through the neck by means of a long funnel-tube bent at the lower end, carefully avoiding soiling the neck of the retort. The latter being put into a vessel filled with sand, or, better still, with iron turnings, is then connected with a receiver, but not quite air-tight. The distillation is conducted at a gradually increased heat, and carried to dryness. The cooling of the receiver must be properly attended to during the distillation. In the preparation of small quantities, the re- tort is placed on a piece of wire-gauze, and heated with charcoal ; in this process it is always advisable to coat the retort by repeated application of a thin paste made of clay and water ; a little borax or carbonate of soda should be added to the water used for making the paste. Tests. Red fuming nitric acid must be in a state of the greatest possi- ble coiseeiitration, and perfectly free from sulphuric acid. In order to de- tect minute traces of the latter, evaporate a few c. c. of the specimen in a porcelain dish nearly to dryness, dilute the residue with water, add some chloride of barium, and observe whether a precipitate forms on standing. Uses. A powerful oxidizing agent and solvent ; it serves more espe- cially to' convert sulphur and metallic sulphides into sulphuric acid and sulphates respectively. 3. ACETIC ACID (see " Qual. Anal."). 4. TARTARIC ACID (see " Qual. Anal."). b. Hydrogen Adds and Halogens. 58. 1. HYDROCHLORIC ACID. a. Pure hydrochloric acid of 1-12 sp. gr. (see " Qual. Anal."). b. Pure fuming hydrochloric acid of about 1'IS sp. gr. Preparation. As in " Qual. Anal." 26, with this modification, how- ever, that only 3 or 4 parts of water, instead of 6, are put into the re- ceiver, to 4 parts of chloride of sodium in the retort. The greatest care 58.] REAGENTS'. g must be taken to keep the receiver cool, and to change it as soon as the tube through which the gas is conducted into it begins to get hot, since it is now no longer hydrochloric acid gas which passes over, but an aqueous solution of the gas, in form of vapor, which would simply weaken the fuming acid, if it were allowed to mix with it. Tests. The fuming acid must, for many purposes, be perfectly free from chlorine and sulphurous acid. For the mode of testino- for these impurities, see " Qual. Anal." loc. cit. Test for sulphuric acid as under Nitric Acid, previous page. Uses. Fuming hydrochloric acid has a much more energetic action than the dilute acid ; it is, therefore, used instead of the latter in cases where a more rapid and energetic action is desirable. 2. HYDROFLUORIC ACID. This is employed for the decomposition of silicates and borates, some- times in the gaseous form, sometimes in the condition of aqueous solu- tion. In the first case, the substance to be decomposed is introduced into the leaden box, in which the hydrofluoric gas is being generated ; in the latter case, we must first prepare the aqueous acid. The raw material employed is fluor spar or kryolite (LUBOLDT*). Both are first finely pow- dered, and then treated with concentrated sulphuric acid. To 1 part kryolite, 2|- parts sulphuric acid are used ; to 1 part fluor spar, 2 parts sulphuric acid are used. If the latter is employed, allow the mixture to stand in a dry place for several days, stirring every now and then, so that the silicic acid (which is generally contained in fluor spar) may first escape in the form of fluosilicic gas. Convenient distillatory apparatus have been described by LUBOLDT (loc. cit.) and by H. BRiEGLEB.f The latter commends itself especially on account of its relatively small cost. It consists of a leaden retort, with a movable leaden top, which can be luted on. The receiver belonging to it is a box of lead, with a tubulure at the side, into which the neck of the retort just enters. The cover of the receiver is raised conical, and is provided at the top with an exit tube of lead. In the receiver a platinum dish containing water is placed, all joints are luted, and the retort is carefully heated in a sand-bath. The aqueous hydrofluoric acid found at the end of the operation in the plati- num dish is perfectly pure. The small quantity of impure hydrofluoric acid which collects on the bottom of the receiver is thrown away. The hydrofluoric acid must entirely volatilize when heated in a platinum dish on a water-bath. The pure acid gives no precipitate when neutralized with potash, while silicofluoride of potassium separates if the acid con- tains hydrofluosilicic acid. The acid is best preserved in gutta-percha bottles, as recommended by STADELER. The greatest caution must be observed in preparing this acid, since, whether in the fluid or gaseous condition, it is one of the most injurious substances. 3. CHLORINE AND CHLORINE-WATER (see " Qual. Anal."). 4. NITRO-HYDROCHLORIC ACID (see " Qual. Anal."). 5. HYDROFLUOSILICIC ACID (see " Qual. Anal."). c. Sulphur Acids. 1. HYDROSULPHURIC ACID (see " Qual. Anal."). * Journ. fur prakt. Chem., 76, 330. f Annal. d. Chem. u. Pharm., Ill, 380. 86 REAGENTS. [ 59, 60. in. BASES AND METALS. a. Oxygen JSases and Metals. 59. a. Alkalies. 1. POTASSA AND SODA (see " Qual. Anal."). All the three sorts of the caustic alkalies mentioned in the qualitative part are required in quantitative analysis, viz., common solution of soda, hydrate of potassa purified with alcohol, and solution of potassa prepared with baryta. Pure solution of potassa may be obtained also by heating to redness for half an hour in a copper crucible, a mixture of 1 part of nitrate of potassa, and 2 or 3 parts of thin sheet copper cut into small pieces, treating the mass with water, allowing the oxide of copper to subside in a tall vessel, and removing the supernatant clear fluid by means of a syphon (WOHLER).* 2. AMMONIA (see " Qual. Anal."). P. Alkaline Earths. 1. BARYTA (see " Qual. Anal."). 2. LIME. Finely divided hydrate of lime mixed with water (milk of lime), is used more particularly to effect the separation of magnesia, &c., from the alkalies. Milk of lime intended to be used for that purpose must, of course, be perfectly free from alkalies. To insure this the hydrate should be thoroughly washed, by repeated boiling with fresh quantities of distilled water. This operation is conducted best in a silver dish. When cold, the milk of lime so prepared is kept in a well-stoppered bottle. y. Heavy Metals, and their Oxides. 60. 1. ZINC. Zinc has of late been much used as a reagent in quantitative ana) r sis. It serves more especially to effect the reduction of dissolved sesquiodde of iron to protoxide, and also the precipitation of copper from the olu- tions of that metal. Zinc intended to be used for the former purpose must be free from iron, for the latter free from lead, copper, and other metals which remain undissolved upon treating the zinc with dilute acids. To procure zinc which leaves no residue upon solution in dilute sul- * Hydrate of soda, made by acting on pure water by pure sodium and fving in silver vessels, is to be had cheaply of the Magnesium Metal Company, Sahord, Manchester, England. 61.] REAGENTS. 87 phuric acid, there is commonly no other resource but to re-distil the com- mercial article. This is effected in a retort made of the material of Hessian or black- lead crucibles. The operation is conducted in a wind-furnace with good draught. The neck of the retort must hang down as perpendicular as possible. Under the neck is placed a basin or small tub, filled with water. The distillation begins as soon as the retort is at a bright red heat. As the neck of the retort is very liable to become choked up with zinc, or oxide of zinc, it is necessary to keep it constantly free by means of a pipe-stem. The zinc obtained by this re-distillation is nearly or quite free from lead. Tests. The following is the simplest way of testing the purity of zinc : dissolve the metal in dilute sulphuric acid in a small flask provided with a gas-evolution tube, place the outer limb of the tube under water, and when the solution is completed, let the water entirely or partly recede into the flask ; after cooling, add to the fluid, drop by drop, a sufficiently dilute solution of permanganate of potassa. If a drop of that solution imparts the same red tint to the zinc solution as to an equal volume of water, the zinc may be considered free from iron. I prefer this way of testing the purity of zinc to other methods, as it affords, at the same time, an approximate, or, if the zinc has been weighed, and the chameleon solu- tion (which, in that case, must be considerably diluted) measured, an accurate and precise knowledge of the quantity of iron present. If lead or copper are present, these metals remain undissolved upon solution of the zinc. 2. OXIDE OF LEAD. Precipitate pure nitrate or acetate of lead with carbonate of ammonia, wash the precipitate, dry, and ignite gently to complete decomposition. Oxide of lead is often used to fix an acid, so that it is not expelled even by a red heat. b. Sulphur XBases. 1. SULPHIDE OF AMMONIUM (see " Qual. Anal."). We require both the colorless monosulphide, and the yellow poly- sulphide. 2. SULPHIDE OF SODIUM (see " Qual. Anal."). IV. SALTS. a. Salts of the Alkalies. 61. 1. SULPHATE OF POTASSA (see " Qual. Anal."). 2. OXALATE OF AMMONIA (see " Qual. Anal."). 3. ACETATE OF SODA (see " Qual. Anal."). 4. SUCC1NATE OF AMMONIA. 88 REAGENTS. f 62. Preparation!,. Saturate succinic acid, which has been purified bj> dissolving in nitric acid and recrystallizing, with dilute ammonia. The reaction of the new compound should be rather slightly alkaline than acid. Uses. This reagent serves occasionally to separate sesquioxide of iron from other metallic oxides. 5. CARBONATE OF SODA (see " Qual. Anal."). This reagent is required both in solution and in pure crystals ; in the latter form to neutralize an excess of acid in a fluid which it is desir- able not to dilute too much. 6. CARBONATE OF AMMONIA (see Qual. Anal."). 7. BISULPHITE OF SODA (see " Qual. Anal."). 8. HYPOSULPHITE OF SODA. This salt occurs in commerce. It should be dry, clear, well crystal- lized, completely and with ease soluble in water. The solution must give with nitrate of silver at first a white precipitate, must not effer- vesce with acetic acid, and when acidified must give no precipitate with chloride of barium, or at most, only a slight turbidity. The acidified solution must, after a short time, become milky from separation of sul- phur. Uses. The hyposulphite of soda is used for the precipitation of sev- eral metals, as sulphides, particularly in separations, for instance, of copper from zinc ; it also serves as solvent for several salts (chloride of silver, sulphate of lime, &c.) ; lastly, it is employed in volumetric ana- lysis, its use here depending on the reaction 2 (NaO, S., O 3 ) -f- I = Na 1 + Na O, S 4 5 . 9. NITRITE OF POTASSA (see " Qual. Anal."). 10. BICHROMATE OF POTASSA (see " Qual. Anal."). 11. MOLYBDATE OF AMMONIA (see " Qual. Anal."). 12. CHLORIDE OF AMMONIUM (see " Qual. Anal."). 13. CYANIDE OF POTASSIUM (see " Qual. Anal."). b. Salts of the Alkaline Earths. 1. CHLORIDE OF BARIUM (see " Qual. Anal."). The following process gives a very pure chloride of barium, free from lime and strontia : Transmit through a concentrated solution of impure chloride of barium hydrochloric gas, as long as a precipitate continues to form. Nearly the whole of the chloride of barium pre- sent is by this means separated from the solution, in form of a crystal- line powder. Collect this on a filter, let the adhering liquid drain off, wash the powder repeatedly with small quantities of pure hydrochloric acid, until a sample of the washings, diluted with water, and precipitated with sulphuric acid, gives a filtrate which, upon evaporation in a plati- num dish, leaves no residue. The hydrochloric mother-liquor serves to dissolve fresh portions of witherite. I make use of the chloride of barium so obtained, principally for the preparation of perfectly pure carbonate of baryta, which is often required in quantitative analyses. 2. ACETATE OF BARYTA. 63.] REAGENTS. 89 Preparation. Dissolve pure carbonate of baryta in moderately di- lute acetic acid, filter, and evaporate to crystallization. Tests. Dilute solution of acetate of baryta must not be rendered turbid by solution of nitrate of silver. See also " Qual. Anal.," Chlo- ride of barium, the same tests being also used to ascertain the purity of the acetate. Uses. Acetate of baryta is used instead of chloride of barium, to effect the precipitation of sulphuric acid, in cases where it is desirable to avoid the introduction of a chloride into the solution, or to convert the base into an acetate. As the reagent is seldom required, it is best kept in crystals. 3. CARBONATE OF BARYTA (see " Qual. Anal."). 4. CHLORIDE OF STRONTIUM. Preparation. Chloride of strontium is prepared from strontianite or celestine, by the same processes as chloride of barium. The pure crystals obtained are dissolved in spirit of wine of 96 per cent., the solution is filtered, and kept for use. Uses. The alcoholic solution of chloride of strontium is used to ef- fect the conversion of alkaline sulphates into chlorides, in cases where it is desirable to avoid the introduction into the fiuid of a salt insoluble in spirit of wine. 5. CHLORIDE OF CALCIUM (see " Qual. Anal."). 6. SULPHATE OF MAGNESIA (see " Qual. Anal."). This reagent is principally used to precipitate phosphoric acid from aqueous solutions. The solution required for this purpose should be kept ready prepared ; it is made by dissolving 1 part of crystallized sulphate of magnesia and 1 part of pure chloride of ammonium in 8 parts of water and 4 parts of solution of ammonia, allowing the fluid to stand at rest for several days, and then filtering. This solution is sometimes called magnesia-mixture. c. S'alts of the Oxides of the Heavy Metals. 63 - 1. SULPHATE OF PROTOXIDE OF IRON (see " Qual. Anal."). 2. SESQUICHLORIDE OF IRON (see " Qual. Anal."). 3. ACETATE OF SESQUIOXIDE OF URANIUM. Heat finely powdered pitchblende with dilute nitric acid, filter the fluid from the undissolved portion, and treat the filtrate with hydro- sulphuric acid to remove the lead, copper, and arsenic ; filter again, evaporate to dryness, extract the residue with water, and filter the so- lution from the oxides of iron, cobalt, and manganese. Nitrate of ses- quioxide of uranium crystallizes from the filtrate ; purify this by recrys- tallization, and then heat the crystals until a small portion of the ses- quioxide of uranium is reduced. Warm the yellowish-red mass thus obtained with acetic acid, filter and let the filtrate crystallize. The crystals are acetate of sesquioxide of uranium, and the mother-liquor contains the undecomposed nitrate (WERTHEIM). Teste. Solution of acetate of sesquioxide of uranium after acidifica- tion with hydrochloric acid must not be altered by hydrosulphuric acid ; 90 KEAGENTS. [ 64. carbonate of ammonia must produce in it a precipitate, soluble in an excess of the precipitant. Uses. Acetate of sesquioxide of uranium may serve, in many cases, to effect the separation and determination of phosphoric acid. 4. NITRATE OF SILVER (see " Qual. Anal."). 5. ACETATE OF LEAD (see " Qual. Anal."). 6. CHLORIDE OF MERCURY (see " Qual. Anal."). 7. PROTOCHLORIDE OF TIN (see " Qual. Anal."). 8. BICHLORIDE OF PLATINUM (see " Qual. Anal."). 9. SODIO-PROTOCHLORIDE OF PALLADIUM (see " Qual. Anal."). B. REAGENTS FOR GRAVIMETRIC ANALYSIS IN THE DRY WAY. 64. 1. CARBONATE OF SODA, pure anhydrous (see " Qual. Anal."). 2. MIXED CARBONATES OF SODA AND POTASSA (see "Qual. Anal.") 3. HYDRATE OF BARYTA (see " Qual. Anal." and 59). 4. NITRATE OF POTASSA (see " Qual. Anal."). 5. NITRATE OF SODA (see " Qual. Anal."). 6. BORAX (fused). Preparation. Heat crystallized borax (see " Qual. Anal.") in a platinum or porcelain dish, until there is no further intumescence ; re- duce the porous mass to powder, and heat this in a platinum crucible until it is fused to a transparent mass. Pour the semi-fluid, viscid mass upon a fragment of porcelain. A better way is to fuse the borax in a net of platinum gauze, by making the gas blowpipe-flame act upon it. The drops are collected in a platinum dish. The vitrified borax ob- tained is kept in a well-stoppered bottle. But as it is always necessary to heat the vitrified borax previous to use, to make quite sure that it is perfectly anhydrous, the best way is to prepare it only when required. Uses. Vitrified borax is used to effect the expulsion of carbonic acid and other volatile acids, at a red heat. 7. BlSULPHATE OF POTASSA. Preparation. Mix 87 parts of neutral sulphate of potassa (see " Qual. Anal."), in a platinum crucible, with 49 parts of concentrated pure sul- phuric acid, and heat to gentle redness until the mass is in a state of uniform and limpid fusion. Pour the fused salt on a fragment of porce- lain, or into a platinum dish standing in cold water. After cooling, break the mass into pieces, and keep for use.* Uses. This reagent serves as a flux for certain native compounds of alumina and sesquioxide of chromium. Bisulphate of potassa is used also, as we have already had occasion to state, for the cleansing of plati- num crucibles ; for this latter purpose, however, the salt which is ob- tained in the preparation of nitric acid will be found sufficiently pure. 8. CARBONATE OF AMMONIA (solid). Preparation. See " Qual. Anal." This reagent serves to convert the * [J. Lawrence Smith advises the use of bisulphate of soda for fluxing alumi- nous compounds, as the fused mass is much more readily soluble in water.] 65.] REAGENTS. 91 bisulpliates of the alkalies into neutral salts. It must completely vola- tilize when heated in a platinum dish. 9. NITRATE OF AMMONIA. Preparation. Neutralize pure carbonate of ammonia with pure nitric acid, warm, and add ammonia to slightly alkaline reaction ; filter, if ne- cessary, and let the filtrate crystallize. Fuse the crystals in a platinum dish, and pour the fused mass upon a piece of porcelain ; break into pieces whilst still warm, and keep in a well-stoppered bottle. Tests. Nitrate of ammonia must leave no residue when heated in a platinum dish. Uses. Nitrate of ammonia serves as an oxidizing agent ; for instance, to convert lead into oxide of lead, or to effect the combustion of carbon, in cases where it is desired to avoid the use of fixed salts. 10. CHLORIDE OF AMMONIUM. Preparation and Tests. See " Qual. Anal." Uses. Chloride of ammonium is often used to convert metallic oxides and acids, e.g., oxide of lead, oxide of zinc, binoxide of tin, arsenic acid, antimonic acid, &c., into chlorides (ammonia and water escape in the process). Many metallic chlorides being volatile, and others volatilizing in presence of chloride of ammonium fumes, they may be completely re- moved by igniting them with chloride of ammonium in excess, and thus many compounds, e.g., alkaline antimoniates, may be easily and expedi- tiously analyzed. Chloride of ammonium is also used to convert various salts with other acids into chlorides, e.g., small quantities of alkaline sulphates. 11. HYDROGEN GAS. Preparation. Hydrogen gas is evolved when dilute sulphuric acid is added to granulated zinc. It may be purified from traces of foreign gases either by passing first through' chloride of mercury solution, then through potash solution, or as recommended by STENHOUSE, by passing through a tube filled with pieces of charcoal. If the gas is desired dry, pass through sulphuric acid or a chloride of calcium tube. Tests. Pure hydrogen gas is inodorous. It ought to burn with a colorless flame, which, when cooled by depressing a porcelain dish upon it, must deposit nothing on the surface of the dish except pure water (free from acid reaction). Uses. Hydrogen gas is frequently used, in quantitative analysis, to reduce oxides, chlorides, sulphides, &c., to the metallic state. 12. CHLORINE. Preparation. See " Qual Anal." Chlorine gas is purified and dried by transmitting it through concentrated sulphuric acid, or a chloride of calcium tube. Uses. Chlorine gas serves principally to produce chlorides, and to separate the volatile from the non-volatile chlorides ; it is also used to displace and indirectly determine bromine and iodine. C. REAGENTS USED IN VOLUMETRIC ANALYSIS. 65. Under this head are arranged the most important of those substances, 92 REAGENTS. [ 65 which serve for the preparation and testing of the fluids required in volumetric analysis, and have not been given sub A and J3. 1. PUKE CRYSTALLIZED OXALIC ACID. The introduction of crystallized oxalic acid as a basis for alkalimetry and acidinietry is due to FR. MOHR. It is also employed to determine the strength of, or to standardize, a solution of permanganate of potassa, 1 equivalent of permanganic acid being required to convert 5 equivalents of oxalic acid* into carbonic acid (Mn. 2 O 7 + 2 S O 3 + 5 C 2 O 3 = 2 (Mn O, S O 3 ) 4- 10 G O 2 ). We use in most cases the pure crystallized acid which has the formula C 2 O 3 , H O + 2 aq., and of which the equivalent is accordingly 63. Preparation. Treat powdered oxalic acid of commerce, in a flask, with lukewarm distilled water, in such proportion as will leave a large amount of the acid uridissolved, and shake (MoHR). Filter, crystallize, and let the crystals drain ; then spread them out on blotting-paper, and let them get thoroughly dry, at the common temperature, in a place free from dust ; or press them gently between sheets of blotting-paper, and repeat the operation with fresh sheets, until the crystals are quite dry. Another method, by which the acid is obtained perfectly pure, .consists in decomposing oxalate of lead with dilute sulphuric acid. Tests. The crystals of oxalic acid must not show the least sign of efflorescence (to which they are liable even at 20 in a dry atmosphere) ; they must dissolve in water to a perfectly clear fluid ; when heated in a platinum dish, they must leave no fixed and incombustible residue (car- bonate of lime, carbonate of potassa, &c.). If the acid obtained by a first crystallization fails to satisfy these requirements, it must be recrys- tallized. 2. TINCTURE OF LITMUS. Preparation. Digest 1 part of litmus of commerce with 6 parts of water, on the water-bath, for some time, filter, divide the blue fluid into 2 portions, and saturate in one half the free alkali, by stirring repeat- edly with a glass rod dipped in very dilute nitric acid, until the color just appears red ; add the remaining blue half, together with 1 part of strong spirit of wine, and keep the tincture, which is now ready for use, in a small open bottle, not quite full, in a place protected from dust. In a stoppered bottle the tincture would speedily loose color. Tests. Litmus tincture is tested by coloring with it about 100 cubic centimetres of water distinctly blue, dividing the fluid into two por- tions, and adding to the one the least quantity of a dilute acid, to the other a trace of solution of soda. If the one portion acquires a dis- tinct red, the other a distinct blue tint, the litmus tincture is fit for use, as neither acid nor alkali predominates. 3. PERMANGANATE OF POTASSA. Preparation. Mix 8 parts of very finely powdered pure pyrolusite, or binoxide of manganese, with 7 parts of chlorate of potassa, put the mixture into a shallow cast-iron pot, and add 37 parts of a solution of potassa of 1 P 27 specific gravity (the same solution as is used in organic analysisf) ; evaporate to dryness, stirring the mixture during * Considered as a monobasic acid. f Or instead of the solution, use 10 parts of the hydrate (K O, H 0). In thia 65.] REAGENTS. 93 the operation ; put the residue before it has absorbed moisture, into an iron or Hessian crucible, and expose to a dull-red heat, with fre- quent stirring with an iron rod or iron spatula, until no more aqueous vapors escape and the mass is in a faint glow. Remove the crucible now from the fire, and transfer the friable mass to an iron pot. Reduce to coarse powder, and transfer this, in small portions at a time, to an iron vessel containing 100 parts of boiling water; keep boiling, replacing the evaporating water, and passing a stream of carbonic acid through the fluid. (MULDER*). The originally dark green solution of maiigauate of potassa soon changes, with separation of hydrated binoxide of manganese, to the deep violet-red of the permanganate. When it is considered that the conversion is complete, allow to settle, take out a small quantity of the clear liquid, boil and pass carbonic acid through it. If a precipitate forms, the conversion is not yet complete. The solution may be filtered through gun-cotton. Evaporate, crystal- lize, and dry the crystals on a porous tile. The pure salt is now to be obtained in commerce. 4. AMMONIO-SULPHATE OF PROTOXIDE OF IRON. (Fe O, S Og+N H 4 O, S O.,+6 aq.) FR. MOHR has proposed to employ this double salt, which is not liable to efflorescence and oxidation, as an agent to determine the strength of the permanganate solution. Preparation. Take two equal portions of dilute sulphuric acid, and warm the one with a moderate excess of small iron nails free from rust, until the evolution of hydrogen gas has altogether or very nearly ceased ; neutralize the other portion exactly with carbonate of ammonia, and then add to it a few drops of dilute sulphuric acid. Filter the solution of the sulphate of the protoxide of iron into that of the sulphate of am- monia, evaporate the mixture a little, if necessary, and then allow the salt to crystallize. Let the crystals, which are hard and of a pale green color, drain in a funnel, then wash them in a little water, dry thoroughly on blotting-paper in the air, and keep for use. The equivalent of the salt (196) is exactly 7 times that of iron (28). The solution of the salt in water which has been just acidified with sul- phuric acid must not become red on the addition of sulphocyanide of potassium. [5. AMMONIA-IRON-ALUM. (Fe 3 3 , 3 S0 3 + NH 4 0, SO 3 ,+24 HO.) Preparation. Bring into a large porcelain dish 58 grms. of pure crystallized ferrous sulphate (see Fresenius' " Qual. Anal." Am. ed. p. 73), together with a quantity of oil of vitriol equivalent to 8*3 grms. of an- hydrous sulphuric acid (see Table, p. 488). Heat upon a sand-bath, add- ing nitric acid from time to time, in small portions, until the iron has all passed into ferric oxide, or until a drop of the solution gives no blue coloration with ferricyanide of potassium. Heat further, and evap- orate until the excess of nitric acid is expelled, then add 14 grms. case fuse the potash and the chlorate together first, and then project the manga nese into the crucible. * Jahresbericht von Kopp und Will, 1858, 581. 94 REAGENTS. [ 65. of sulphate of ammonia,* and, if need be, hot water sufficient to bring the salt into solution ; filter into a porcelain capsule and set aside, under cover, to crystallize. The iron-alum separates in cubo-octahedrons, which may be yellowish, lilac, or colorless. If dark in color, dissolve in warm water, add a few drops of oil of vitriol, and crystallize again. Rinse the pale or colorless crystals, after separation from the mother-liquor, with cold water, wrap up closely in filter paper, and allow them to dry at the ordinary tem- perature, f The yield should be about 80 grms. The dry salt should be pulver- ized, pressed between folds of paper until freed from mechanically ad- hering water, and preserved in a well-stoppered bottle. Uses. Ammonia-iron-alum furnishes the best means of obtaining a definite quantity of ferric oxide for making standard solutions, being easily obtained pure and inalterable if kept away from acid vapors. Its purity may be readily controlled by ascertaining the loss on careful igni- tion, which should leave a residue of 16*6 per cent, of sesquioxide of iron, corresponding to 11*59 per cent, of metallic iron. 6. PURE IODINE. Preparation. Triturate iodine of commerce with -J- part of its weight of iodide of potassium, dry the mass in a large watch-glass with ground rim, warm this gently on a sand-bath, or on an iron plate, and as soon as violet fumes begin to escape, cover it with another watch-glass of the same size. Continue the application of heat until all the iodine is sub- limed, and keep in a well-closed glass bottle. The chlorine or bromine, which is often found in iodine of commerce, combines, in this process, with the potassium, and remains in the lower watch-glass, together with the excess of iodide of potassium. Tests. Iodine purified by the process just now described, must leave no fixed residue when heated on a watch-glass. But, even supposing it should leave a trace on the glass, it would be of no great consequence, as the small portion intended for use has to be resublimed immediately before weighing. * If not cm hand, this salt may be prepared by saturating oil of vitriol with carbonate of ammonia and evaporating to dryness. 30 grammes of oil of vitriol give somewhat more than is required above. f Examinations of iron-alum thus prepared show that the variations in the color of the salt, from colorless to rose, are not connected with appreciable differ- ences of composition. J. H. Grove, of the Sheffield Laboratory, obtained the following results in the examination of ammonia-iron-alum crystals, the ferric oxide being estimated by ignition : Fe 2 3 ( 16-59 1st i 16-55 16-59 2d 16-53 3d 16-57 4th 16-57 5th 16-58 6th I 16-50 16-56 7th 16-55 Calculated 16-60 65.] REAGENTS. 95 Uses. Pure iodine is used to determine the amount of iodine con- tained in the solution of iodine in iodide of potassium, employed in many volumetric processes. 7. IODIDE OF POTASSIUM. Small quantities of this article may be procured cheaper in commerce than prepared in the laboratory. For the preparation of iodide of potas- sium intended for analytical purposes I recommend BAUP'S method, im- proved by FREDERKING, because the product obtained by this process is free from iodic acid. Tests. Put a sample of the salt in dilute sulphuric acid. If the iodide is pure, it will dissolve without coloring the fluid ; but if it contain iodate of potassa, the fluid will acquire a brown tint, from the presence of free iodine (K I+H O + S O 3 =K O, S O 3 +H land I O| + 5 H 1= 5 H O + 6 I, which remain in solution in the hydriodic acid). Mix the solution of another sample with nitrate of silver, as long as a precipitate continues to form ; add solution of ammonia in excess, shake the mix- ture, filter, and supersaturate the filtrate with nitric acid. The forma- tion of a white, curdy precipitate indicates the presence of chloride in the iodide of potassium. Presence of sulphate of potassa is detected by means of solution of chloride of barium, with addition of some hydro- chloric acid. Uses. Iodide of potassium is used as a solvent for iodine in the pre- paration of standard solutions of iodine ; it is employed also to absorb free chlorine. In the latter case every equivalent of chlorine liberates an equivalent of iodine, which is retained in solution by the agency of the excess of iodide of potassium. The iodide of potassium intended for these uses must be free from iodate and carbonate of potassa ; the presence of trifling traces of chloride of potassium or sulphate of potassa is of no consequence. 8. ARSENIOUS ACID. The arsenious acid sold in the shops in large pieces, externally opaque, but often still vitreous within, is generally quite pure. The purity of the article is tested by moderately heating it in a glass tube, open at both ends, through which a feeble current of air is transmitted. Pure arsenious acid must completely volatilize in this process ; no residue must be left in the tube upon the expulsion of the sublimate from it. If a non-volatile residue is left which, when heated in a current of hydrogen gas, turns black, the arsenious acid contains teroxide of antimony, and is unfit for use in analytical processes. Dissolve about 10 grms. of the arsenious acid to be tested in soda, and add 1 2 drops acetate of lead. If a brownish color is produced, the arsenious acid contains sulphide of arsenic and cannot be used. Arsenious acid is employed, in form of arsenite of soda, to determine hypochlorous acid, free chlorine, iodine, &c. 9. CHLORIDE OP SODIUM. Perfectly pure rock-salt is best suited for analytical purposes. It must dissolve in water to a clear fluid ; oxalate of ammonia, phosphate of soda, and chloride of barium must not trouble the solution. Pure chloride of sodium may be prepared also by MARGUERITTE'S process, viz., conduct into a concentrated solution of common salt hydrochloric gas to saturation, collect the small crystals of chloride of sodium which separate on a fun- 96 REAGENTS. [66. nel, let them thoroughly drain, wash with hydrochloric acid, and dry the chloride of sodium finally in a porcelain dish, until the hydrochloric acid 'adhering to it has completely evaporated. The mother-liquor, which contains the small quantities of sulphate of lime, chloride of magnesium, &c., originally present in the salt, is at the next preparation of hydro- chloric acid added to the ingredients in the retort, instead of a corre- sponding portion of water. Uses. Chloride of sodium serves as a volumetric precipitating agent in the determination of silver, and also to determine the strength of solu- tions of silver intended for the estimation of chlorine. We usually fuse it before weighing. The operation must be conducted with caution, and must not be continued longer than necessary ; for if the gas-flame acts on the salt, hydrochloric acid escapes, while carbonate of soda is formed. 10. METALLIC SILVER. The silver obtained by the proper reduction of the pure chloride of the metal alone can be called chemically pure. The silver precipitated by copper is never absolutely pure, but contains generally about y^^-p of copper. Chemically pure silver is only used in small quantity to prepare the dilute solution employed for the determination of silver. The solution of silver required for the estimation of chlorine need not be made with absolutely pure silver, as the strength of this solution had always best be determined after the preparation, by means of pure chloride of sodium. D. KEAGENTS USED IN OBGANIC ANALYSIS. 66. 1. OXIDE OF COPPER. Preparation. Stir pure* copper scales (which should first be ignited in a muffle) with pure nitric acid in a porcelain dish to a thick paste ; after the effervescence has ceased, heat gently on the sand-bath un- til the mass is perfectly dry. Transfer the green basic salt produced to a Hessian crucible, and heat to a moderate redness, until no more fumes of hypoiiitric acid escape ; this may be known by the smell, or by intro- ducing a small portion of the mass into a test tube, closing the latter with the finger, heating to redness, and then looking through the tube lengthways. The uniform decomposition of the salt in the crucible may be promoted by stirring the mass from time to time with a hot glass rod. When the crucible has cooled a little, reduce the mass, which now con- sists of pure oxide of copper, to a tolerably fine powder, by triturating it in a brass or porcelain mortar ; pass through a metal sieve, and keep in a well-stoppered bottle for use. It is always advisable to leave a small portion of the oxide in the crucible, and to expose this again to an intense red heat. This agglutinated portion is not pounded, but simply broken into small fragments. * If the scales contain lime, digest them with water, containing a little nitrio acid, for a long time, wash, and then proceed as above. 6o. REAGENTS. 97 Tests. Pure oxide of copper is a compact, heavy, deep-black pow- der, gritty to the touch ; upon exposure to a red heat it must evolve no hypmitric acid fumes, nor carbonic acid; the latter would indicate prebence of fragments of charcoal, or particles of dust. It must contain notb ing soluble in water. That portion of the oxide which has been ex- pose* I to an intense red heat should be hard, and of a grayish-black color. Uses. Oxide of copper serves to oxidize the carbon and hydrogen of organic substances, yielding up its oxygen wholly or in part, according to ciro inistances. That portion of the oxide which has been heated to the mo-it intense redness is particularly useful in the analysis of volatile fluids. N.B. The oxide of copper, after use, may be regenerated by oxidation with nit dc acid, and subsequent ignition. 'Should it have become mixed with alkaline salts in the course of the analytical process, it is first digested with veiy dilute cold nitric acid, and washed afterwards with water. To purify oxide of copper containing chloride, E. ERLENMEYER recommends to ignite it in a tube, first in a stream of moist air, and finally, when the escaping gas ceases to redden litmus paper, in dry air. By these opera- tions any oxides of nitrogen that may have remained are also removed. 2. CHROMATE OF LEAD. Preparation. Precipitate a clear filtered solution of acetate of lead, slightly acidulated with acetic acid, with a small excess of bichromate of potassa ; wash the precipitate by decantation, and at last thoroughly on a linen strainer; dry, put in a Hessian crucible, and heat to bright redness until the mass is fairly in fusion. Pour out upon a stone slab or iron plate, break, pulverize, pass through a fine metallic sieve, and keep the tolerably fine powder for use. Tests. Chromate of lead is a heavy powder, of a dirty yellowish-brown color. It must evolve no carbonic acid upon the application of a red heat ; the evolution of carbonic acid Avould indicate contamination with organic matter, dust, &c. It must contain nothing soluble in water. Uses. Chromate of lead serves, the same as oxide of copper, for the combustion of organic substances. It is converted, in the process of com- bustion, into sesquioxide of chromium and basic chromate of lead. It suffers the same decomposition, with evolution of oxygen, when heated by itself above its point of fusion. The property of chromate of lead to fuse at a red heat renders it preferable to oxide of copper as an oxidizing agent, in cases where we have to act upon difficultly combustible sub- stances. N.B. Chromate of lead may be used a second time. For this purpose it is fused again (being first roasted, if necessary), and then powdered. After having been twice used it is powdered, moistened with nitric acid, dried, and fused. In this way the chromate of lead may be used over and over again indefinitely (VoHL*). 3. OXYGEN GAS. Preparation. Triturate 100 grammes of chlorate of potassa with exactly O'l grm. of finely-powdered sesquioxide of iron, and introduce the mixture into a plain retort, which must not be more than half full ; expose the retort, over a charcoal fire, at first to a gentle, and then to a * Annalen d. Chem. u. Pharm., 106, 127. 98 REAGENTS. [ 66. gradually increased heat. As soon as the salt begins to fuse, shake the retort a little, that the contents may be uniformly heated. The evolution of oxygen speedily commences, and proceeds rapidly, but not impetuously, provided the above proportion between the chlorate of potassa and the sesquioxide of iron be adhered to. As soon as the air is expelled from the retort, connect the glass tube, fixed in the neck of the retort by means of a tight-fitting perforated cork, with an india-rubber tube inserted into the lower orifice of the gasometer ; the glass tube must be sufficiently wide, and there must be sufficient space left around the india-rubber to permit the free efflux of the displaced water. Continue the application of heat to the retort until, incipient redness having been reached, the evolution of gas has altogether or very nearly ceased. It is advisable to coat the retort up to the middle of the body with several layers of a thin paste made of clay and water, with addition of a little carbonate of soda or borax. 100 grammes of chlorate of potassa give about 27 litres of oxygen gas. The oxygen gas produced by this process is moist, and may contain traces of carbonic acid gas, and also of chlorine. The gas prepared from a mixture of chlorate of potassa with a comparatively large proportion of biiioxide of manganese always contains a rather considerable quantity of chlorine gas. These impurities must be removed, and the oxygen gas thoroughly dried, before it can be used in elementary organic analysis. The gas is therefore passed from the gasometer, first through a LIEBIG'S bulb-apparatus filled with solution of potassa of 1 '27 sp. gr., then through a U-tube containing pumice-stone, moistened with sulphuric acid, after- wards through several tubes filled with hydrate of potassa, and lastly through a chloride of calcium tube. Tests. A chip of wood which has been kindled and blown out, so as to leave a spark at the extremity, must immediately burst into flame in a current of oxygen gas. The gas must not trouble lime-water, nor solution of nitrate of silver when transmitted through these fluids. 4. SODA-LIME. Preparation. Take ordinary solution of soda, ascertain its specific gravity, weigh out a certain quantity, calculate by means of the table, 206, the weight of the hydrate of soda that must be present, acid twice this latter weight of the best quick-lime, and then evaporate to dryness in an iron vessel. Heat the residue in an iron or Hessian crucible, keep for some time at a low red heat, and reduce the mass, whilst still warm, to a tolerably fine powder, by pounding and sifting through a metallic sieve. Keep the powder in a well-stoppered bottle. Tests. Soda-lime must not effervesce too much when treated with dilute hydrochloric acid in excess ; but, more particularly, it must not evolve ammonia when mixed with pure sugar, and heated to redness. It must not swell and fuse so readily as to obstruct the bore of a tube when heated to low redness, nor must it remain infusible and but loosely coherent after exposure to a bright red-heat. The former diffi- culty may be remedied by mixture with dry slaked lime, the latter by mixing with a portion of insufficiently ignited soda-lime kept in reserve for this purpose. Uses. Soda-lime serves for the analysis of nitrogenous organic sub- stances. For the rationale of its action, see the chapter on Organic Analysis. 66.] REAGENTS. 99 5. METALLIC COPPER. Metallic copper serves, in the analysis of nitrogenous substances, to effect the reduction of the nitric oxide gas that may form in the course of the analytical process. It is used either in the form of turnings, or in that of close wire spirals ; or of small rolls made of thin sheet copper. A length of from 7 to 10 centimetres is given to the spirals or rolls, and just sufficient thickness to admit of their being inserted into the combustion tube. To have it perfectly free from dust, oxide, &c., it is first heated to redness in the open air, in a crucible, until the surface is oxidized ; it is then put into a glass or porcelain tube, through which an uninterrupted current of dry hydrogen gas is transmitted ; and when all atmospheric air has been expelled from the evolution apparatus and the tube, the latter is in its whole length heated to redness. The operator should make sure that the atmospheric air has been thoroughly expelled, before he proceeds to apply heat to the tube ; neglect of this precaution may lead to an explosion. 6. POTASSA. a. Solution of Potassa. Solution of potassa is prepared from the carbonate, with the aid of milk of lime, in the way described in the " Qualitative Analysis," for the preparation of solution of soda. The proportions are 1 part of carbonate of potassa to 12 parts of water, and f- part of lime, slaked to paste with three times the quantity of warm water. The decanted clear solution is evaporated, in an iron vessel, over a strong fire, until it has a specific gravity of 1-27 ; it is then, whilst still warm, poured into a bottle, which is well closed, and allowed to stand at rest until all solid particles have subsided. The clear solution is finally drawn oft' from the deposit, and kept for use. b. Hydrate of Potassa (common). The commercial hydrate of potassa in sticks will answer the purpose. If you wish to prepare it, evaporate solution of potassa (a) in a silver vessel, over a strong fire, until the residuary hydrate flows like oil, and white fumes begin to rise from the surface. Pour the fused mass ^out on a clean iron plate, and break it up into small pieces. Keep in a. well-stoppered bottle for use. c. Hydrate of Potassa (purified with alcohol), see " Qual. Anal." p. 43. 7ses. Solution of potassa serves for the absorption, and at the same time for the estimation of carbonic acid. In many cases, a tube filled with hydrate of potassa is used, in addition to the apparatus filled with solution of potassa. Hydrate of potassa purified with alcohol, which is perfectly free from sulphate of potassa, is employed for the determi- nation of sulphur in organic substances. 7. CHLORIDE OF CALCIUM. a. Crude fused Chloride of Calcium. Preparation. Digest, with warm water, the residuary mixture of. 100 REAGENTS. [ 66, chloride of calcium and lime which remains after the preparation of ammonia ; filter, neutralize the alkaline filtrate exactly with hydrochlo- ric acid, and evaporate to dryness in an iron pan ; fuse the residue in an iron or Hessian crucible, pour out the fused mass, and break into pieces. Preserve it in well-stoppered bottles. b. Pure Chloride of Calcium. Preparation. Dissolve the crude chloride of calcium of a in lime- water, filter the solution, and neutralize exactly with hydrochloric acid ; evaporate, in a porcelain dish, to dryness, and expose the residue for several hours to a tolerably strong heat (about 200), on the sand-bath. The white and porous mass obtained by this process consists of Ca Cl + 2aq. Uses. The crude fused chloride of calcium serves to dry moist gases ; the pure chloride is used in elementary organic analysis for the absorption and estimation of the water formed by the hydrogen con- tained in the analyzed substance. The solution of the pure chloride of calcium must not show an alkaline reaction. 8. BICHROMATE OF POTASSA. Bichromate of potassa of commerce is purified by repeated recrystal- lization, until chloride of barium produces, in the solution of a sample of it in water, a precipitate which completely dissolves in hydrochloric acid. Bichromate of potassa thus perfectly free from sulphuric acid is required more particularly for the oxidation of organic substances with a view to the estimation of the sulphur contained in them. Where the salt is intended for other purposes, e.g., to determine the carbon of or- ganic bodies, by heating them with chromate of potassa and sulphuric acid, one recrystallization is sufficient. SECTION III. FORMS AND COMBINATIONS IN WHICH SUBSTANCES ARE SEPARATED FROM EACH OTHER, OR IN WHICH THEIR WEIGHT IS DETERMINED. 67. THE quantitative analysis of a compound substance requires, as the first and most indispensable condition, a correct and accurate knowledge of the composition and properties of the new combinations into which it is intended to convert its several individual constituents, for the purpose of separating them from one another, and determining their several weights. Regarding the properties of the new compounds, we have to inquire more particularly, in the first place, how they behave with sol- vents ; secondly, what is their deportment in the air ; and, thirdly, what is their behavior on ignition ? It may be laid down as a general rule, that compounds are the better adapted for quantitative determination the more insoluble they are, and the less alteration they undergo upon exposure to air or to a high temperature. The composition of bodies is expressed either in per-cents, or in sto'i- chiometrical or symbolic formulae ; by means of the latter, the consti- tution of the more frequently recurring compounds may be easily re- membered. In this Section the composition of the substances treated of is given in three different ways, in as many columns : the first column gives the composition of the substance in symbols ; the second, in equi- valents (H = 1) ; the third, in per-cents. With respect to its composi- tion, a compound is the better adapted for the quantitative determina- tion of a body the less it contains relatively of that body ; since any error or loss of substance that may occur in the course of the analytical pro- cess will exercise the less influence upon the accuracy of the. results. Thus, ammonio-bichloride of platinum, for instance, is, in this respect, better adapted than chloride of ammonium for the determination of nitrogen; since the former contains only 6*27 per cent., while the latter contains 26.2 per cent, of the element in question. Suppose we have to analyze a nitrogenous substance ; we estimate its nitrogen in the form of bichloride of platinum and chloride of ammonium. When the process is conducted with absolute accuracy, O300 grin, of the analyzed body yields I'OOO grm. of ammonio-bichloride of platinum: 100 parts of this double chloride contain 6'27 parts of nitrogen, I'OOO contains therefore 0'0627 of that element. These 0'0627 have been de- rived from 0-300 of substance ; 100 parts of the analyzed body, conse- quently, contain 20'90 of nitrogen. We now make a second analysis, in which we convert the nitrogen of the substance to be analyzed into chloride of ammonium, instead of bichloride of platinum and chloride of ammonium: we again con- duct .he process with absolute accuracy, and obtain from O'SOO of the 102 '**V !*' jkf CJ :\ l \ FORMS. [ 68. substance under examination, 0-2394 of chloride of ammonium, corre- sponding to 0-0627 of nitrogen, or 20*90 per cent. Now, let us assume a loss of 10 milligrammes to have occurred in each process: this will alter the result, in the first instance, from I'OOO to 0"990 of bichloride of platinum and chloride of ammonium, corre- sponding to 0-062073 of nitrogen, or 20*69 per cent.; the loss of nitroger will therefore be 20-90- 20-69 = 0-21. In the second instance the result will be altered from 0-2394 to 0-2294 of chloride of ammonium, corresponding to 0*0601 of nitrogen, or 20.03 per cent. The loss in this case will consequently amount to 0*87. We see here that the same error occasions, in the one case, a loss of 0'21 per cent., with respect to the amount of nitrogen; whilst, in the other case, the loss amounts to 0'S7 per cent. We will now proceed to enumerate and examine those combinations of the several bodies which are best adapted for their quantitative determination. The description given of the external form and appear- ance of the new compounds relates more particularly to the state in which they are obtained in our analyses. With regard to the proper- ties of the new compounds, we shall confine ourselves to the enumeration of those which bear upon the special object we have more immediately in view. A. FORMS IN WHICH THE BASES ARE WEIGHED OR PRECIPITATED. BASES OF THE FIRST GROUP. 68. 1. POTASSA (OR POTASH). The combinations best suited for the weighing of potassa are, SUL- PHATE OF POTASSA, CHLORIDE OF POTASSIUM, BICHLORIDE OF PLATINUM AND CHLORIDE OF POTASSIUM (Potassio-Bichloride of Platinum). a. /Sulphate of potassa^ in the analytical process, is obtained as a white crystalline mass. It dissolves with some difficulty in water (1 part requiring 10 parts of water of 12), it is almost absolutely insoluble in pure alcohol, but slightly more soluble in alcohol containing sulphuric acid (Expt. No. 6). It does not affect vegetable colors ; it is unalter- able in the air. The crystals decrepitate strongly when heated. When very strongly ignited for a long time the salt loses weight a little, even when reducing gases are excluded, the residue possesses an alkaline re- action. When exposed to a red heat, in conjunction with chloride of ammonium, sulphate of potassa is partly, and, upon repeated application of the process, wholly, converted, with effervescence, into chloride of potassium (H. ROSE). COMPOSITION. K O 47-11 54-08 S O 3 40-00 45-92 87-11 100-00 Bisulphate of potassa (K O, S O 3 -hH O, S O 3 ), which is always pro- duced when the neutral salt is evaporated to dryness with free sulphuric acid, is readily soluble in water, arid fusible even at a moderate heat. At a red heat it loses half its sulphuric acid, together with the basic water, but not readily the complete conversion of the acid into the neutral 69.] BASES OF GROUP I. 103 salt requiring the long-continued application of an intense red heat. However, when heated in an atmosphere of carbonate of ammonia which may be readily procured by repeatedly throwing into the faint red-hot crucible containing the bisulphate, small lumps of pure carbonate of ammonia, and putting on the lid the acid salt changes readily and quickly to the neutral sulphate. The transformation may be considered complete as soon as the salt, which was so readily fusible before, assumes the solid state, at a faint red heat. b. Chloride of %)otassium is obtained in analysis as cubic crystals, or as a crystalline mass. It is readily soluble in water, but much less so in dilute hydrochloric acid ; in absolute alcohol it is nearly insoluble, and but slightly soluble in spirit of wine. It does not affect vegetable colors, and is unalterable in. the air. When heated it decrepitates, unless it has been kept long drying, with expulsion of a little water mechanically con- fined in it. At a moderate red heat it fuses unaltered, and without diminution of weight ; when exposed to a higher temperature, it volatilizes in white fumes ; this volatilization proceeds the more slowly, the more effectually the access of air is prevented (Expt. No. 7). When repeat- edly evaporated with solution of oxalic acid in excess, it is converted in- to oxalate of potassa. When evaporated with excess of nitric acid, it is converted readily and completely into nitrate. On ignition with oxalate of ammonia, carbonate of potassa and cyanide of potassium are formed in noticeable quantities. K 39-11 52-45 Cl . 35-46 47-55 74-57 100-00 c. ^Bichloride of platinum and chloride of potassium (Potassio-bichlo- ride of Platinum) presents either small reddish-yellow octahedra, or a lemon-colored powder. It is difficultly soluble in cold, more readily in hot water ; nearly insoluble in absolute alcohol, and but sparingly sol- uble in spirit of wine one part requiring for its solution, respectively, 12083 parts of absolute alcohol, 3775 parts of spirit of wine of 76 per cent, and 1053 parts of spirit of wine of 55 per cent. (Expt. No. 8, a). Presence of free hydrochloric acid sensibly increases the solubility (Expt. No. 8, b). In caustic potassa it dissolves completely to a yellow fluid. It is unalterable in the air, and at 100. On exposure to an in- tense red heat, 2 eq. of chlorine escape, metallic platinum and chloride of potassium being left ; but even after long-continued fusion,* there remains always a little potassio-bichloride of platinum which resists decomposition. Complete decomposition is easily effected, by igniting the double salt in a current of hydrogen gas, or with some oxalic acid. K. 39-11 16-00 KC1 74-57 30-51 Pt 98-94 40-48 Pt Cl a 169-86 69-49 C1 3 106-38 43-52 244-43 100-00 244-43 100-00 69. 2. SODA. Soda is usually weighed as SULPHATE OF SODA, CHLORIDE OF SODIUM, 104 FORMS. [69 or CARBONATE OF SODA. It is separated from potassa in the form of SODIO-BICHLORIDE OF PLATINUM. a. The anhydrous neutral sulphate of soda is a white powder or B white very friable mass. It dissolves readily in water ; but is sparingly soluble in absolute alcohol; presence of free sulphuric acid slightly in- creases its solubility in that menstruum ; it is somewhat more readily soluble in spirit of wine (Expt. No. 9). It does not affect vegetable colors ; upon exposure to moist air, it slowly absorbs water (Expt. No. 10). When heated to fusion, it scarcely loses weight, but when exposed to a white heat for a long time, it decidedly loses weight, even when reducing gases are excluded ; the residue then shows a slight alkaline reaction. When ignited with chloride of ammonium, it comports itself the same as sulphate of potassa under similar circumstances. Na O 31 43-66 SO 3 40 56-34 71 100-00 Bisulphate of soda (Na O, S O 3 -f H O, S O 3 ), which is always pro- duced upon the evaporation of a solution of the neutral salt with sul- phuric acid in excess, fuses even at a gentle heat ; it may be readily converted into the neutral salt, in the same manner as the bisulphate of potassa is converted into the neutral sulphate (see 68, a). b. Chloride of sodium crystallizes in cubes. In analysis it is fre- quently obtained as an amorphous mass. It dissolves readily in water, but is much less soluble in hydrochloric acid ; it is nearly insoluble in ab- solute alcohol, and but sparingly soluble in spirit of wine. 100 parts of spirit of wine of 75 per cent, dissolve at a temperature of 15, 0*7 part. It is neutral to vegetable colors. Exposed to a somewhat moist atmosphere, it slowly absorbs water (Expt. No. 12). Crystals of this salt that have not been kept drying a considerable time decrepitate when heated. The salt fuses at a red heat without decomposition ; at a white heat, and in open vessels even at a bright red heat, it volati- lizes in white fumes (Expt. No. 13). If a carburetted hydrogen flame acts on fusing chloride of sodium, hydrochloric acid escapes, and some carbonate of soda is formed. On evaporation with oxalic or nitric acids, as well as by ignition with oxalate of ammonia, it comports itself like the corresponding salt of potassa. Na 23-00 39-34 01.. 35-46 60-66 58-46 100-00 c. Anhydrous carbonate of soda is a white powder or a white very friable mass. It dissolves readily in water, but much less so in solu- tion of ammonia (MARGUERITTE) ; it is insoluble in alcohol. Its re- action is strongly alkaline. Exposed to the air, it absorbs water slow- ly. On moderate ignition to incipient fusion it scarcely loses weight ; on long fusion, however, it volatilizes to a considerable extent (Comp^ Expt. 14). NaO 31 58-49 CO 2 22 41-51 53 100-00 70.] BASES OF GROUP I. 105 d. Sodio-lichloride of platinum crystallizes with 6 equivalents of water (Na 01, Pt C1 2 + 6 aq.), in light yellow, transparent, prismatic crystals which dissolve readily both in water and in spirit of wine. 70. 3. AMMONIA. Ammonia is most appropriately weighed as CHLORIDE OF AMMONIUM, Or as BICHLORIDE OF PLATINUM AND CHLORIDE OF AMMONIUM (ammonio- bichloride of platinum). Under certain circumstances, ammonia may also be estimated from the volume of the NITROGEN GAS eliminated from it. a. Chloride of ammonium is obtained in analysis as a white mass. It dissolves readily in water, but difficultly in spirit of wine. It does not alter vegetable colors, and remains unaltered in the air. Solution of chloride of ammonium, when evaporated on the water-bath, loses a small quantity of ammonia, and becomes slightly acid. The diminu- tion of weight occasioned by this loss of ammonia is very trifling (Expt. No. 15). At 100 chloride of ammonium loses nothing, or very little of its weight (comp. same Expt). At a higher temperature it vo- latilizes readily, and without undergoing decomposition. NH 4 18-00 33-67 Nil 17-00 31-80 01... 35-46 66-33 H 01. . 36-46 68-20 53-46 100-00 53-46 100-00 b. ^Bichloride of platinum and chloride of ammonium (aminonio- bichloride of platinum) occurs either as a heavy lemon-colored powder, or in small, hard octahedral crystals of a bright yellow color. It is dif- ficultly soluble in cold, but more readily in hot water. It is very spar- ingly soluble in absolute alcohol, but more readily in spirit of wine 1 part requiring of absolute alcohol, 26535 parts ; of spirit of wine of 76 per cent., 1406 parts ; of spirit of wine of 55 per cent., 665 parts. The presence of free acid sensibly increases its solubility (Expt. No. 16). It remains unaltered in the air, and at 100. Upon ignition chlo- rine and chloride of ammonium escape, leaving the metallic platinum as a porous mass (spongy platinum). However, if due care be not taken in this process to apply the heat gradually, the escaping fumes will, carry off particles of platinum, which will coat the lid of the crucible. NH 4 . 18-00 8-06 NH 3 .. 17-00 7-61 Pt . . . 98-94 44-30 H Cl .. 36-46 16-33 C1 3 106-38 47-64 Pt C1 2 . 169-86 76-06 223-32 100-00 223-32 100-00 NH 4 C1. 53-46 23-94 N 14-00' 6-27 Pt CL . 169-86 76-06 H 4 4-00 1-79 Pt ... 98-94 44-30 C1 3 .... 106-38 47-64 223-32 100-00 223-32 100-00 106 FORMS. [ 71. c. Nitrogen gas is colorless, tasteless, and inodorous ; it mixes with air without producing the slightest coloration ; it does not aftect vege table colors. Its specific gravity is 0*96978 (air = 1). One litre (out cubic decimeter) weighs at 0, and 0*76 meter of the barometer, 1-25456 grm. It is difficultly soluble in water, 1 volume of water ab- sorbing, at 0, and 0*76 pressure, 0*02035 vol. ; at 10, 0-01607 vol. ; at 15, 0*01478 vol. of nitrogen gas (BUNSEN). BASES OF THE SECOND GROUP. 71. 1. BARYTA. Baryta is weighed as SULPHATE OF BARYTA, CARBONATE OF BARYTA, and SILICO-FLUORIDE OF BARIUM. a. Artificially prepared sulphate of baryta presents the appearance of a fine white powder. When' recently precipitated, it is difficult to ob- tain a clear filtrate, especially if the precipitation was effected without the aid of heat," and the solution contains neither hydrochloric acid nor chloride of ammonium. It is insoluble in cold and in hot water. It has a great tendency, upon precipitation, to carry down with it other substances contained in the solution from which it separates, more par- ticularly nitrate of baryta, chloride of barium, sesquioxide of iron, 268 - 81.] BASES OF GROUP IV. 123 ammonium from time to time, the sulphide of iron becomes dense, and may be washed with little danger of oxidation.] It is well to mix a little chloride of ammonium with the wash-water, but the quantity should be continually reduced, and the last water used should contain none. In mineral acids, even when very dilute, the hydrated sulphide dissolves readily. Mixed with sulphur, and strongly ignited in a stream of hydro- gen, anhydrous protosulphide remains (H. ROSE). Fe 28 63-64 S 16 36-36 44 100-00 d. When a neutral solution of a salt of sesquioxide of iron is mixed with a neutral solution of an alkaline succinate, a cinnamon-colored pre- cipitate of a brighter or darker tint is formed ; this is succinate of ses- quioxide of iron (Fe. 2 O 3 , C K H 4 O,,). It results from the nature of this precipitate, that its formation must set free an equivalent of acid (suc- ciiiic acid, if the succinate of ammonia is used in excess) ; e.c/., 2 (Fe. 2 3 , 3 S 3 ) + 3 (2 N H 4 O, C 8 H 4 O) + 2 II O = 2 (Fe, O,, C 8 H, O B ) + 6 (N H 4 O, S O 3 ) + 2 H O, C 8 H 4 O ti . The free succinic acid does not exercise any perceptible solvent action upon the precipitate in a cold and highly dilute solution, but it redissolves the precipitate a little more readily in a warm solution. The precipitate must therefore be filtered cold, if we want to guard against re-solution. Succinate of tsesquioxide of iron is insoluble in cold, and but sparingly soluble in hot water. It dissolves readily in mineral acids. Ammonia deprives it of the greater portion of its acid, leaving compounds similar to the hydrated sesquioxide of iron, which contain from 18 to 30 eq. Fe 2 O 3 for 1 eq. C 8 H 4 O 6 (Dop- PING). Warm ammonia withdraws the acid more completely than cold ammonia. [e. If to a hot solution of a salt of sesquioxide of iron carbonate of soda be added till a slight permanent precipitate is formed, and this be redissolved by a few drops of hydrochloric acid, then heated to boiling, and crystals of acetate of soda be added, the whole of the iron will be pre- cipitated as basic acetate of sesquioxide. The success of this operation depends on the iron solution being sufficiently dilute, the free acid suffi- ciently neutralized, and the a.oetate of soda in sufficient quantity. In- stead of carbonate and acetate of soda the corresponding salts of ammo- nia may be used. The precipitate may usually be filtered off and washed without any iron passing into the filtrate ; sometimes, however, the re- verse is the case. It is best to filter immediately, and to use boiling wash-water. When these directions are followed, the precipitate is free from alkali, but if the precipitate is digested with the liquid, it fixes al- kali and becomes more difficult to work* (REICHARDT)]. f. Instead of the acetate of soda or ammonia used in e, the correspond- ing formiates may be used. The basic f miniate of sesquioxide of iron here obtained is more easily washed than the basic acetate (Fu. SCHULZE f). * Fres. Zeitschrift, V. 63. \ Chem. Centralbl., 1861, 3. \M FORMS. [82. BASES OF THE FIFTH GROUP. 82. 1. OXIDE OF SILVER. Silver may bo weighed in the METALLIC state, as CHLORIDE, SULPHIDE. or CYANIDE. a. Metallic silver, obtained by the ignition of salts of silver with or- ganic acids, &c., is a loose, light, white, glittering mass of metallic lustre ; but, when obtained by reducing chloride of silver, &c., in the wet way, by the agency of zinc, it is a dull gray powder. It is not fusible over a BERZELIUS' lamp. Ignition leaves its weight unaltered. It dissolves readily and completely in dilute nitric acid. b. Chloride of silver, recently precipitated, is white and curdy. On sluikins:, the large spongy flocks combine with the smaller particles, so that the fluid becomes perfectly clear. This result is, however, only satisfactorily effected, when the flocks have been produced in presence of excess of silver solution, and when they have been recently precipi- tated (compare G. J. MuiDJ&R*). Chloride of silver is in a very high degree insoluble in water and in dilute nitric acid ; strong nitric acid, on the contrary, does dissolve a trace. Hydrochloric acid, especially if concentrated and boiling, dissolves it very perceptibly. On sufficiently diluting such a solution with cold water the chloride of silver falls out so completely that the nitrate is not colored by sulphuretted hydrogen. Chloride of silver is insoluble, or very nearly so, in concentrated sul- phuric acid ; in the dilute acid it is as insoluble as in water. In a solu-' tion of tartaric acid chloride of silver dissolves perceptibly on warming ; on cooling, however, the solution deposits the whole, or, at all events, the greater part of it. Aqueous solutions of chlorides (of sodium, po- tassium, ammonium, calcium, zinc, &c.) all dissolve appreciable quan- tities of chloride of silver, especially if they are hot and concentrated. On sufficient dilution with cold water the dissolved portion separates so completely that the nitrate is not colored by sulphuretted hydrogen. The solutions of alkaline and alkaline earthy nitrates also dissolve a little chloride of silver. The solubility in the cold is trifling ; in the heat, on the contrary, it is very perceptible. A solution of nitrate of mercury dissolves chloride of silver to a tolerable extent ; alkaline acetates sepa- rate it from the solution. Chloride of silver dissolves readily in aque- ous ammonia, and also in the solution of cyanide of potassium and that of hyposulphite of soda. Under the influence of light the chloride of silver soon changes to violet, finally black, losing chlorine, and passing partly into Ag 2 01. The .change is quite superficial, but the loss of weight resulting is very appreciable (MULDER, op. cit. p. 21). On long contact (say for 24 hours) with pure water, especially if hot of 75, chloride of silver, although removed from the influence of light, becomes gray, and, it appears, decomposed ; the precipitate is found to contain oxide of silver, and the water hydrochloric acid (MULDER). On diges- tion with excess of solution of bromide or iodide of potassium the chlo- ride of silver is completely transformed into bromide or iodide of silver, as the case may be (FIELD f). On drying, chloride of silver becomes * Die Silberprobirmethode, translated into German by D. Chr. Grimm, pp. 19 and 311. Leipzig : J. J. Weber. 1859. f Quart. Journ. of Cheni. Soc. x. 234 Journ. f. prakt. Chem. 73, 404. 83.] BASES OF GROUP V. 125 pulverulent ; on heating, it acquires a yellow color ; at 260 it fuses to a transparent yellow fluid, which 011 cooling presents the appearance of a colorless and slightly yellowish mass. At a very strong heat it vola- tilizes unchanged. It may be readily reduced to metallic silver, by ig- niting it in a current of hydrogen gas. Ag 107-97 75-28 Cl 35-46 24-72 143-43 100-00 c. Sulphide of silver, prepared in the humid way, is a black precipi- tate, insoluble in water, dilute acids, alkalies, and alkaline sulphides. This precipitate is unalterable in the air ; after being allowed to sub- side, it is filtered and washed with ease, and may be dried at 100, with- out suffering decomposition. It dissolves in concentrated nitric acid, with separation of sulphur. Solution of cyanide of potassium fails to dissolve sulphide of silver, except the cyanide be used greatly in excess. In the latter case it dissolves to a slight extent, but is generally reprecipitated on addition of water (BECHAMP*). Ignited in a current of hydrogen, it passes readily and completely into the metallic state (H. ROSE). Ag 107-97 87-07 S.. 10-00 12-93 123-97 100-00 d. Cyanide of silver, recently thrown down, forms a white curdy pre- cipitate insoluble in water and dilute nitric acid, soluble in cyanide of potassium and also in ammonia ; exposure to light fails to impart the slightest tinge of black to it ; it may be dried at 100 without suffering decomposition. Upon ignition, it is decomposed into cyanogen gas, which escapes, and metallic silver, which remains, mixed with a little paracyanicle of silver. By boiling with a mixture of equal parts of sul- phuric acid and water, it is, according to GLASSFORD and NAPIER, dis- solved to sulphate of silver, with liberation of hydrocyanic acid. Ag 107-97 80-60 ON.. 26-00 19-40 133-97 100-00 83. 2. OXIDE OF LEAD. Lead is weighed as OXIDE, SULPHATE, CHROMATE, and SULPHIDE, Besides these compounds, we have also to study the CARBONATE and the OXALATE. a. Neutral carbonate of lead forms a heavy, white, pulverulent preci- pitate. It is but very slightly soluble in perfectly pure (boiled) water (one part requiring 50550 parts, see Expt. 47, a) ; but it dissolves * Journ. f. prakt. Chetn. GO, 04. 126 FORMS. [ 83. somewhat more readily in water containing ammonia and ammoniacal salts (comp. Expt. No. 47, b and c). It dissolves also somewhat more readily in water impregnated with carbonic acid, than in pure water. It loses its carbonic acid when ignited. b. Oxalate of lead is a white powder, very sparingly soluble in water. The presence of ammonia salts slightly increases its solubility (Expt. No. 48). When heated in close vessels, it leaves suboxide of lead ; but when heated, with access of air, yellow oxide (protoxide). c. Oxide, or protoxide of lead, produced by igniting the carbonate 01 oxalate, is a lemon-yellow powder, inclining sometimes to a reddish yel- low, or to a pale yellow. When this yellow oxide of lead is heated, it assumes a brownish-red color, without the slightest variation of weight. It fuses at an intense red heat. Ignition with charcoal reduces it. When exposed to a white heat, it rises in vapor. Placed upon moist reddened litmus paper, it changes the color to blue. When exposed to the air, it slowly absorbs carbonic acid. Mixed with chloride of ammonium and ignited, it is converted into chloride of lead. Oxide of lead in a state of fusion readily dissolves silicic acid and the earthy bases with which the latter may be combined. Pb 103-50 92-83 O . 8-00 7-17 111-50 100-00 d. Sulphate of lead is a heavy white powder. It dissolves, at the common temperature, in 22800 parts of pure water (Expt. No. 49) ; it is less soluble still in water containing sulphuric acid (one part requiring 36500 parts Expt. No. 50) ; it is far more readily soluble in water con- taining ammoniacal salts; from this solution it may be precipitated again by adding sulphuric acid in excess (Expt. No. 51). It is almost entirely insoluble in alcohol and spirit of wine. Of the salts of ammonia, the nitrate, acetate, and tartrate are more especially suited to serve as sol- vents for sulphate of lead : the two latter salts of ammonia are made strongly alkaline by addition of ammonia, previous to use (WACKEST- EODER). Sulphate of lead dissolves in concentrated hydrochloric acid, upon heating. In nitric acid it dissolves the more readily, the more concentrated and hotter the acid ; water fails to precipitate it from its solution in nitric acid ; but the addition of a copious amount of dilute sulphuric acid causes its precipitation from this solution. The more nitric acid the solution contains, the more sulphuric acid is required to throw down the sulphate of lead. Sulphate of lead dissolves sparingly in con- centrated sulphuric acid, and the dissolved portion precipitates again upon diluting the acid with water (more completely upon addition of alcohol). A moderately concentrated solution of hyposulphite of soda dissolves the sulphate of lead completely even if cold, more readily if warmed ; on boil- ing, the solution becomes black from separation of a small quantity of sulphide of lead (J. LOWE *). The solutions of carbonates and bicar- bonates of the alkalies convert sulphate of lead, even at the common temperature, completely into carbonate of lead. The solutions of the carbonates, but not those of the bicarbonates, dissolve some oxide of lead in this process (H. ROSE f). Sulphate of lead dissolves readily in * Journ. f. prakt. Chem. 74, 348. f Pogg. Annal. 95, 426. 84.] BASES OF GROUP V. 127 hot solutions of potassa or soda. It is unalterable in the air, and at a gentle red heat ; when exposed to a higher degree of heat, it fuses without suffering decomposition (Expt. No. 52), provided always the action of reducing gases be completely excluded for, if this is not the case, the weight will continually diminish, owing to the reduction of Pb O, S O 3 to Pb S (ERDMANN *). Fusion with cyanide of potassium reduces the whole of the lead to the metallic state. PbO 111-50 73-60 S O 3 40-00 26-40 151-50 100-00 e. /Sulphide of lead, prepared in the wet way, is a black precipitate, insoluble in water, dilute acids, alkalies, and alkaline sulphides. In pre- cipitating it from a solution containing free hydrochloric acid, it is necessary to dilute plentifully, otherwise the precipitation will be incom- plete. Even if a fluid only contain 2 '5 per cent. H 01, the whole of the lead will not be precipitated (M. MARTIN f). It is unalterable in the air ; it cannot be dried at 100 without suffering decomposition. Ac- cording to H. ROSE it increases perceptibly in weight by oxidation ; in the case of long-protracted drying even becoming a few per cents, heavier. J I have confirmed his statement (see Expt. No. 53). If sul- phate of lead mixed with sulphur be exposed in a current of hydrogen to a good red heat, pure crystalline Pb S remains; if a less heat be employed, the residue contains excess of sulphur (H. ROSE). [Accord- ing to SOUCHAY,!! sulphide of lead is obtained pure by ignition with excess of sulphur in hydrogen, if only the lower one-fourth of the crucible be heated to redness for 5-10 minutes. The results were rather too low than too high.] It dissolves in concentrated hot hydrochloric acid, with evolution of sulphuretted hydrogen. In moderately strong nitric acid, sulphide of lead dissolves, upon the application of heat, with sepa- ration of sulphur ; if the acid is rather concentrated, a small portion of sulphate of lead is also formed. Fuming nitric acid acts energetically upon sulphide of lead, and converts it into sulphate without separation of sulphur. Pb 103-50 86-61 S.. 16-00 13-39 119-50 100-00 /. For the composition and properties of chromate of lead, see chromic acid, 93, 2. 84. 3. SUBOXIDE OP MERCURY ; and 4. OXIDE OF MERCURY. Mercury is weighed either in the METALLIC state, as SUBCHLORIDE, or as SULPHIDE, or occasionally also as OXIDE. a. Metallic mercury, when pure, presents a perfectly bright surface. * Jotirn f . prakt. Chem. 62, 381. t Journ. f. prakt Cliem. 67, 374. Pocro- Annal 91, 110 : and 110, 134. Pogg. Annal. 110, 135. | [Fres. Zeitschrift, IV. 65.] 128 FORMS. [ 84. It is unalterable in the air at the common temperature. It boils at 360. It evaporates, but very slowly, at summer temperatures. Upon long-continued boiling with water, a small portion of mercury volatilizes, and traces escape along with the aqueous vapor, whilst a very minute proportion remains suspended (not dissolved) in the water (comp. Expt. No. 54). This suspended portion of mercury subsides completely after long standing. When metallic mercury is precipitated from a fluid, in a very minutely divided state, the small globules will readily unite into a large one if the mercury be perfectly pure ; but even the slightest trace of extraneous matter, such as fat, &c., adhering to the mercury will pre- vent the union of the globules. Mercury does not dissolve in hydro- chloric acid, not even in concentrated ; it is barely soluble in dilute cold sulphuric acid, but dissolves readily in nitric acid, and in boiling con- centrated sulphuric acid. b. fSubchloride of mercury ', prepared in the wet way, is a heavy white powder. It is almost absolutely insoluble in cold water ; in boiling water it is gradually decomposed, the water taking up chlorine and mercury ; upon, continued boiling, the residue acquires a gray color. Highly dilute hydrochloric acid fails to dissolve subchloride of mercury at the common temperature, but dissolves it slowly at a higher temperature ; upon ebulli- tion, with access of air, the whole of the subchloride is gradually dissolved by the dilute acid: the solution contains chloride of mercury (Hg. 2 Cl-f- H Cl-f O=2 Hg Cl-f-H O). Subchloride of mercury, when acted upon by boiling concentrated hydrochloric acid, is rather speedily decomposed into mercury, which remains undissolved, and chloride of mercury, which dissolves. Boiling nitric acid dissolves subchloride of mercury, and con- verts it into chloride and nitrate of mercury. Chlorine water and nitro- hydrochloric acid dissolve it to chloride, even in the cold. Solutions of alkaline chlorides decompose subchloride of mercury into metallic mer- cury and chloride of mercury, which latter dissolves ; at a low tempera- ture, this decomposition is confined to a small portion of the subchloride, but the application of heat promotes the decomposing action of these solutions. Subchloride of mercury does not affect vegetable colors ; it is unalterable in the air, and may be dried at 100, without suffering any diminution of weight ; when exposed to a higher degree of heat, though still below redness, it volatilizes completely, without previous fusion. Hg 2 : 200-00 84-94 Cl . 35-46 15-06 235-46 100-00 c. Sulphide of mercury, prepared in the wet way, is a black powder, insoluble in water. Dilute hydrochloric and dilute nitric acid fail to dissol ve it, and it remains insoluble even in boiling hydrochloric acid ; it is only very slightly soluble in hot concentrated nitric acid, but it dis- solves readily in nitrohydrochloric acid. From a solution of chloride of mercury, containing much free hydrochloric acid, the whole of the metal cannot be precipitated by means of sulphuretted hydrogen, as Hg S, until the solution is properly diluted. Should such a solution be very concentrated, subchloride of mercury and sulphur are precipitated (M. MARTIN*). Solution of potassa, even boiling, fails to dissolve it. It * Journ. f. prakt. Chem. 67, 376. 85.] BASES OF GROUP V. 129 dissolves in sulphide of potassium, but readily only in presence of free alkali (Expt. No. 55). Sulphide of ammonium, cyanide of potas- sium, and sulphite of soda do not dissolve it. On account of the solu- bility of sulphide of mercury in sulphide of potassium, it is impossible to precipitate mercury by means of sulphide of ammonium completely from so]utions containing hydrate or carbonate of potassa or soda. In the air it is unalterable, even in the moist state, and at 100. When exposed to a higher temperature, it sublimes completely and unaltered. Hg 100-00 86-21 S 16-00 13-79 116-00 100-00 d. Oxide of mercury, prepared in the dry way, is a crystalline brick- colored powder, which, when exposed to the action of heat, changes to the color of cinnabar, and subsequently to a violet-black tint. It bears a tolerably strong heat without suffering decomposition ; but, when heated to incipient redness, it is decomposed into mercury and oxygen ; perfect- ly pure oxide of mercury leaves no residue upon continued exposure to a red heat. The escaping fumes also should not redden litmus paper. Water takes up a trace of oxide of mercury, acquiring thereby a very weak alkaline reaction. Hydrochloric or nitric acid dissolves it readily. Hg 100-00 92-59 O 8-00 7-41 108-00 100-00 5. OXIDE OF COPPER. Copper is usually weighed in the METALLIC STATE, or in the form of OXIDE, or of SUBSULPHIDE. Besides these forms, we have to examine the SULPHIDE, the SUBOXIDE, and the SUBSULPHOCYANIDE. a. Copper fuses only at a white heat. Exposure to dry air, or to moist air, free from carbonic acid, leaves the fused metal unaltered ; but upon exposure to moist air impregnated with carbonic acid, it becomes gradually tarnished and coated with a film, first of a blackish-gray, finally of a bluish-green color. Precipitated finely divided copper, in contacfr with water and air, oxidizes far more quickly,. especially at an elevated- temperature. On igniting copper in the air, a layer of black oxide forms on its surface. Hydrochloric acid fails to dissolve it, even upon boiling, if the air is excluded ; but with free access of air it dissolves it slowly. Copper dissolves readily in nitric acid. In ammonia it dissolves slowly if free access is given to the air ; but it remains insoluble in that menstruum if the air is excluded. Metallic copper brought into contact in a closed vessel with solution of chloride of copper in hydrochloric acid, or with an ammo- iiiacal solution of oxide of copper, reduces the chloride to subchloride, or the oxide to suboxide, an equivalent of metal being dissolved for every equivalent of chloride or oxide. b. Oxide of copper. If a dilute, cold, aqueous solution of a salt of oxide of copper is mixed with solution of potassa or soda in excess, a' 9 130 FORMS. [ 85. light blue precipitate of hydrated oxide o? copper (Cu O, H O) ia formed, which is difficult to wash. If the precipitate be left in the fluid from which it has been precipitated, it will gradually become brownish black, and pass into 3 Cu O, H O (HARMS *). This transformation is immediate upon heating the fluid nearly to boiling. The fluid filtered off from the black precipitate is free from copper. If the solutions in question are mixed in a concentrated state, in addition to the formation of the blue precipitate, the fluid itself ac- quires a blue color, owing to a portion of very minutely divided hy- drated oxide remaining suspended in it. From a fluid of this descrip- tion protracted boiling will fail to precipitate all the copper ; after dilu- tion with water, the object is readily attained. If a solution of a salt of copper contains non-volatile organic substances, the addition of al- kali in excess will, even upon boiling, fail to precipitate the whole of the copper as oxide. The hydrate (3 Cu O, H O) precipitated with potassa or soda from hot dilute solutions may be completely freed from the preci- pitant by washing with boiling water. Oxide of copper, prepared by igniting the hydrate or carbonate or nitrate of copper, is a brownish- black, or black powder, which remains unaltered upon strong ignition over the gas- or spirit-lamp, provided all reducing gases be excluded (Expt. No. 59). It is very readily reduced by ignition with charcoal, or reducing gases ; heated in the air, the reduced copper re-oxidizes. Mixed with sulphur and ignited in a current of hydrogen, towards the end strongly, the oxide of copper passes into subsulphide (Cu. 2 S ; H. ROSE). Oxide of copper, in contact with the atmosphere, absorbs water ; oxide that has been but slightly ignited absorbs the water more rapidly than such as has been strongly ignited (Expt. 'No. 57). Oxide of copper is nearly insoluble in water ; but it dissolves readily in hydrochloric acid, nitric acid, &c. j less readily in ammonia. It does not affect vegetable colors. Cu 31-70 79-85 O . , 8-00 20-15 39-70 100-00 c. Sulphide of copper, prepared in the wet way, is a brownish-black, or black precipitate, almost absolutely insoluble in water ; f when the recently prepared precipitate, in a moist state, is exposed to the air, it acquires a greenish tint and the property of reddening litmus paper, sulphate of copper being formed. Hence it must be washed with water containing sulphuretted hydrogen. [When digested near the boiling point for many hours, with addition of sulphuretted hydrogen if needful, it is permanent in air, and may be washed with hot water without dan- ger of oxidation.] Sulphide of copper dissolves readily in boiling nitric acid, with separation of sulphur. Hydrochloric acid dissolves it with difficulty. This is the reason why sulphuretted hydrogen precipitates cop- per entirely from solutions which contain even a very large amount of free hydrochloric acid (GRUNDMANN J). Only when we dissolve a copper salt i * Arch, der Pharm . 139, 35. f In some experiments that I made when examining the Weilbach water I found that about 950000 parts of water are required to dissolve 1 part of CuS. \ Journ. f. prakt. Chem. 73, 241. 86.] BASES OF GROUP V. 131 straight in pure hydrochloric acid of M sp. gr. does any copper remain unprecipitated (M. MARTIN *). It does not dissolve in solutions of po- tassa and of sulphide of potassium, particularly if these solutions be boiling ; but it dissolves perceptibly in sulphide of ammonium and readily in cyanide of potassium. Upon intense ignition in a current of hydrogen gas it is converted into pure Cu 2 S. d. Suboxide of copper. If the blue solution which is obtained upon add- ing to solution of oxide of copper tartaric acid and then solution of soda in excess, is mixed with solution of grape sugar or sugar of milk, and heat applied, an orange-yellow precipitate of hydrated suboxide of copper is formed, which contains the whole of the copper originally present in the solution, and after a short time, more particularly upon the application of a somewhat strong heat, turns red, owing to the conversion of the hydrate into anhydrous suboxide (Cu 2 O). The precipitate, which is insoluble in water, retains a portion of alkali with considerable tena- city. When acted upon with dilute sulphuric acid, it gives sulphate of copper, which dissolves, and metallic copper, which separates. e. Subsulphocyanide of copper (Cu,, Cy S,). formed when sulpho- cyanide of potassium is added to a solution of oxide of copper, mixed with sulphurous or hypophosphorous acid, is a white precipitate insolu- ble in water, and in dilute hydrochloric or sulphuric acid. On drying the salt retains water, and is, therefore, not adapted for direct weighing! When mixed with sulphur and ignited in hydrogen, it yields Cu. 2 S. f. Subsulphide of copper separates from hot dilute acid solutions on addition of hyposulphite of soda, as a black precipitate that may be washed without risk of oxidation. When produced by heating Cu S in a current of hydrogen gas, or Cu 2 , Cy S 2 , with sulphur, it is a grayish- black mass, which may be ignited and fused, without suffering decompo- sition, if the air is excluded. Cu 2 63-40 79-85 S 16-00 20-15 79-40 100-00 86 - 6. TEROXIDE OF BISMUTH. Bismuth is weighed in the form of TEROXIDE or as CHROMATE (Bi O 3 , 2 Cr O 3 ). Besides these compounds, we have to study here the BASIC CARBONATE, the BASIC NITRATE, and the TERSULPHIDE. a. Teroxide of bismuth, prepared by igniting the carbonate or nitrate, is a pale lemon-yellow powder which, under the influence of heat, as- sumes transiently a dark yellow or reddish-brown color. When heated to intense redness, it fuses, without alteration of weight. Ignition with charcoal, or in a current of carbonic oxide gas, reduces it to the metallic state. Fusion with cyanide of potassium also effects its com- plete reduction to the metallic state (H. ROSE f). It is insoluble in water, and does not affect vegetable colors. It dissolves readily in * Journ. f. prakt. Chem. 67, 375. f Ibid. 61, 188 132 FORMS. [ 86. those acids which form soluble salts with it. "When ignited with chloride of ammonium it gives metallic bismuth, the reduction being attended with deflagration. Bi 208 89-655 O 3 24 10-345 232 100-000 b. Carbonate of bismuth. Upon adding carbonate of ammonia in excess to a solution of bismuth, free from hydrochloric acid, a white precipitate of carbonate of bismuth (Bi O 3 , C O 2 ) is immediately formed ; part of this precipitate, however, redissolves in the excess of the pre- cipitant. But if the fluid with the precipitate be heated before nitra- tion, the filtrate will be free from bismuth. (Ca-rbonate of potassa like- wise precipitates solutions of bismuth completely ; but the precipitate in this case invariably contains traces of potassa, which it is very diffi- cult to remove by washing. Carbonate of soda precipitates solutions of bismuth less completely than the carbonates of ammonia and potassa.) The precipitate obtained by means of carbonate of ammonia, is easily washed ; it is very nearly insoluble in water, but dissolves readily, with effervescence, in hydrochloric acid and nitric acid. Upon ignition it loses its carbonic acid, leaving teroxide of bismuth. c. The basic nitrate of bismuth, which is obtained by mixing with water a solution of the nitrate containing little or no free acid, presents the appearance of a white, crystalline powder. It cannot be washed with pure cold water, without suffering a decided alteration. It becomes more basic, while the washings show an acid reaction, and contain bis- muth. If the basic salt, however, be washed with cold water contain- ing ^po of nitrate of ammonia, no bismuth passes through the filter. The solution of nitrate of ammonia must not be warm. These remarks only apply in the absence of free nitric acid (J. LOWE*). On ignition the basic nitrate passes into the pure teroxide. d. Chr ornate of bismuth (Bi O 3 , 2 Or O 3 ), which is produced by add- ing bichromate of potassa, slightly in excess, to a neutral solution of nitrate of bismuth, is an orange-yellow, dense, readily-subsiding precipi- tate, insoluble in water, even in presence of some free chromic acid, but soluble in hydrochloric acid and nitric acid. It may be dried at from 100 to 112, without suffering decomposition (LoWE f). Bi O 3 232-00 69-78 2Cr0 3 100-48 30-22 332-48 100-00 e. Tersulphide of bismuth, prepared in the wet way, is a brownish- black, or black precipitate, insoluble in water, dilute acids, alkalies, al- kaline sulphides, sulphite of soda, and cyanide of potassium. In mod- erately concentrated nitric acid it dissolves, especially on warming, to nitrate, with separation of siilphur. Hence in precipitating bismuth from a nitric acid solution, care should be taken to dilute sufficiently. Hydrochloric acid impedes the precipitation of bismuth by sulphuretted hydrogen only when a very large excess is present, and the fluid is quite * Journ. 1 prakt. Chem. 74, 341. f Ibid. 67, 291. 87.] BASES OF GROUP V. 133 concentrated. The sulphide does not change in the air. Dried at 100, it continually takes up oxygen and increases slightly in weight ; if the drying is protracted this increase may be considerable (Expt. No. 58). Fused with cyanide of potassium, it is completely reduced (H. ROSE). Reduction takes place more slowly by ignition in a current of hydrogen. Bi 208 81-25 S, , 48 18-75 256 100-00 87. 7. OXIDE OF CADMIUM. Cadmium is weighed either as OXIDE or as SULPHIDE. Besides these substances, we have to examine CARBONATE OF CADMIUM. a. Oxide of cadmium, produced by igniting the carbonate or nitrate of cadmium, is a powder, the color of which varies from yellowish brown to reddish brown. The application of a white heat fails to fuse, volati- lize, or decompose it ; it is insoluble in water, but dissolves readily in acids ; it does not alter vegetable colors. Ignition with charcoal, or in a current of hydrogen, carbonic oxide, or carburetted hydrogen, reduces it readily, the metallic cadmium escaping in the form of vapor. Cd 56-00 87-50 O . 8-00 12-50 64-00 100-00 6. Carbonate of cadmium is a white precipitate, insoluble in water and in the fixed alkaline carbonates, and extremely sparingly soluble in carbonate of ammonia. It loses its water completely upon desiccation. Ignition converts it into oxide. c. Sulphide of cadmium, produced in the wet way, is a lemon-yellow to orange-yellow precipitate, insoluble in water, dilute acids, alkalies, alkaline sulphides, sulphite of soda, and cyanide of potassium (Expt. No. 59). It dissolves readily in concentrated hydrochloric acid, with evolution of sulphuretted hydrogen. In precipitating, therefore, with sulphuretted hydrogen, a cadmium solution should not contain too much hydrochloric acid, and should be sufficiently diluted. The sulphide dissolves in moderately concentrated nitric acid, with separation of sul- phur. It may be washed, and dried at 100 or 105, without under- going decomposition. Even on gently igniting the sulphide of cadmium in a current of hydrogen, it volatilizes in appreciable amount (H. ROSE*), partially unchanged, partially as metallic vapor. Cd 56-00 77-78 S ..... 16-00 22-22 72-00 100-00 * Pogg. Annal. 110, 134. 134 FORMS. [ 88, 89. METALLIC OXIDES OF THE SIXTH GROUP. 88. 1. TEROXIDE OF GOLD. Gold is always weighed in the metallic state. Besides METALLIC GOLD, we have to consider the TERSULPHIDE. a. Metallic gold, obtained by precipitation, presents the appearance of a blackish-brown powder, destitute of metallic lustre, which it assumes, however, upon pressure or friction ; when coherent in a compact mass, it exhibits the well-known bright yellow color peculiar to it. It fuses only at a white heat, and resists, accordingly, all attempts at fusion over a spirit-lamp. It remains wholly unaltered in the air and at a red heat, and is not in the slightest degree affected by water, nor by any simple acid. Nitrohydrochloric acid dissolves it to terchloride. b. Tersulphide of gold. When sulphuretted hydrogen is transmitted through a cold dilute solution of terchloride of gold, the whole of ths gold separates as tersulphide (Au S 3 ), in form of a brownish-black pre- cipitate. If this precipitate is left in the fluid, it is gradually transformed into metallic gold and free sulphuric acid. Upon transmitting sulphuret- ted hydrogen through a warm solution of terchloride of gold, a protosul- phide (Au S) precipitates, with simultaneous formation of sulphuric and hydrochloric acids. (2 Au Clj+3 H S + 3 H O=2 Au S + 6 H Cl + S O 3 .) The tersulphide is insoluble in water, hydrochloric acid, and nitric acid, but dissolves in nitrohydrochloric acid. The colorless sulphide of ammonium fails to dissolve it ; but it dissolves almost entirely in the yellow sulphide of ammonium, and completely upon addition of potassa. It dissolves in potassa, with separation of gold. Yellow sulphide of potassium dissolves it completely. Exposure to a moderate heat reduces it to the metallic state. 89. 2. BINOXIDE OF PLATINUM. Platinum is invariably weighed in the METALLIC STATE ; it is generally precipitated as BICHLORIDE OF PLATINUM AND CHLORIDE OF AMMONIUM, Or as BICHLORIDE OF PLATINUM AND CHLORIDE OF POTASSIUM, rarely as BISULPHIDE OF PLATINUM. a. Metallic platinum, produced by igniting the bichloride of platinum and chloride of ammonium, or the bichloride of platinum and chloride of potassium, presents the appearance of a gray, lustreless, porous mass (spongy platinvim). The fusion of platinum can be effected only at the very highest degrees of heat. It remains wholly unaltered in the air, and even the most intense heat of our furnaces fails to affect it. It is not attacked by water, or simple acids, and scarcely by aqueous solutions of the alkalies. Nitrohydrochloric acid dissolves it to bichloride. b. The properties of bichloride of platinum and chloride of potassium, and those of bichloride of platinum and chloride of ammonium, have been given already in 68 and 70 respectively. c. Bisulphide of platinum. When a concentrated solution of bichlo- 90.] METALLIC OXIDES OF GROUP VI. 135 ride of platinum is mixed with sulphuretted hydrogen water, or when sulphuretted hydrogen gas is transmitted through a rather dilute solu- tion of the bichloride, no precipitate forms at first ; after standing some time, however, the solution turns brown, and finally a precipitate sub- sides. But if the mixture of solution of bichloride of platinum with sulphuretted hydrogen in excess, is gradually heated (finally to ebulli- tion), the whole of the platinum separates as bisulphide (free from any admixture of bichloride). The bisulphide of platinum is insoluble in water and in simple acids ; but it dissolves in nitrohydrochloric acid. It dissolves partly in caustic alkalies, with separation of platinum, and completely in alkaline sulphides. When sulphuretted hydrogen is trans- mitted through water holding minutely divided bisulphide of platinum in suspension, the bisulphide, absorbing sulphuretted hydrogen, acquires a light grayish-brown color ; the sulphuretted hydrogen thus absorbed, separates again upon exposure to the air. When moist bisulphide of platinum is exposed to the air, it is gradually decomposed, being con- verted into metallic platinum and sulphuric acid. Ignition in the ail reduces bisulphide of platinum to the metallic state. 90 - 3. TEROXIDE OF ANTIMONY. Antimony is weighed as TERSULPHIDE, as ANTIMONIOUS ACID, or more rarely in the METALLIC state. a. Upon transmitting sulphuretted hydrogen through a solution of terchloride of antimony mixed with tartaric acid, an orange-red pre- cipitate of amorphous tersulphide is obtained, mixed at first with a small portion of basic terchloride of antimony. However, if the fluid is thor- oughly saturated with sulphuretted hydrogen, and a gentle heat applied, the terchloride mixed with the precipitate is decomposed, and the pure tersulphide of antimony obtained. Tersulphide of antimony is insoluble in water and dilute acids ; it dissolves in concentrated hydrochloric acid, with evolution of sulphuretted hydrogen. In precipitating with sul- phuretted hydrogen, therefore, antimony solutions should not contain too much free hydrochloric acid, and should be sufficiently diluted. The amorphous tersulphide dissolves readily in potassa, sulphide of ammo- nium, and sulphide of potassium, sparingly in ammonia, very slightly in carbonate of ammonia, and not at all in bisulphite of potassa. The amor- phous sulphide, dried in the desiccator at the ordinary temperature, loses very little weight at 100 ; if kept longer at this latter temperature, its weight remains constant. But it still retains a little water, which does not perfectly escape even at 190, but at 200 the sulphide becomes anhydrous, turning black and crystalline (-H. ROSE* and Expt. No. 60). Ignited gently in a stream of carbonic acid, the weight of this anhydrous sulphide remains constant ; in a very intense heat, a small amount vola- tilizes. The amorphous sulphide, if long exposed to the action of air, in presence of water, slowly takes up oxygen, so that on treatment with tartaric acid it yields a filtrate containing teroxide. The sulphides corresponding to the aiitimonious and antimonic acids are equally insoluble in water, also in water containing sulphuretted hydrogen. The pure pentasulphide dissolves completely in ammonia, * Journ. f. prakt. Chem. 59, 331. 136 FORMS. [391 L o especially on warming ; traces only dissolve in carbonate of ammonia. On heating the dried pentasulphide in a current of carbonic acid 2 eq. of sulphur escape, black crystalline tersulphide remaining. On treating the ter- or penta-sulphide with fuming nitric acid violent oxidation sets in. We obtain first antimonic acid and pulverulent sepa- rated sulphur ; on evaporating to dryness, antimonic acid and sulphuric acid ; and lastly, on igniting, aiitimonious acid. The same (antimonious acid) is obtained by igniting the sulphide with 30 to 50 times its amount of oxide of mercury (BUNSEN *). Ignition in a current of hy- drogen converts the sulphides of antimony into the metallic state. *Sb 122-00 71-77 S 3 48-00 28-23 170-00 100-00 b. Antimonious acid is a white powder, which, when heated, acquires transiently a yellow tint ; it is infusible ; it is fixed, provided reducing gases be excluded. It is almost insoluble in water, and dissolves in hydrochloric acid with very great difficulty. It undergoes no alteration on treatment with sulphide of ammonium. It manifests an acid reac- tion when placed upon moist litmus paper. Sb 122-0 79-22 O 4 32-0 20-78 154-0 100-00 c. Metallic antimony, produced in the wet way, by precipitation, pre- sents the appearance of a lustreless black powder. It may be dried at 100 without suffering any alteration. It fuses at a moderate red heat. Upon ignition in a current of gas, e.g. hydrogen, it volatilizes, without formation of antimonetted hydrogen. Hydrochloric acid has very little action on it, even when concentrated and upon ebullition. Nitric acid converts it into teroxide of antimony, mixed with more or less antimo- nious acid, according to the concentration of the nitric acid. 91. 4. PROTOXIDE OF TIN; and 5. BINOXIDE OF TIN. Tin is generally weighed in the form of BINOXIDE ; besides the binox- ide, we have to examine PROTOSULPHIDE and BISULPHIDE OF TIN. a. Binoxide of tin. The hydrate of the binoxide b (liydrated meta- stannic acid) is obtained in the form of a white precipitate, by the action of nitric acid upon metallic tin, or by evaporating a solution of tin with nitric acid in excess. This precipitate is insoluble in water, nitric acid, and sulphuric acid, and dissolves but sparingly in hydrochloric acid. It reddens litmus, even when thoroughly washed. But if we precipitate solution of bichloride of tin with an alkali, or with sulphate of soda, or nitrate of ammonia, we obtain the hydrate of the binoxide a, which dis- solves readily in hydrochloric acid. Upon intense ignition, both hy- drates are converted, into the anhydrous binoxide of tin. Mere heating to redness is not sufficient to expel all the water (DuMAS f). * Annal. d. Chem. u. Pharm. 106, 3. f Ibid. 105, 104. 92.] METALLIC OXIDES OF GROUP VI. 137 Binoxide of tin is a straw-colored powder, which, under the influence of heat, transiently assumes a different tint, varying from bright yellow to brown. It is insoluble in water and acids, and does not alter the color of litmus paper. Mixed with chloride of ammonium in excess, and ignited, it volatilizes completely as bichloride. If binoxide of tin is fused with cyanide of potassium, all the tin is obtained in form of metal- lic globules, which may be completely, and without the least loss of metal, freed from the adhering slag, by extracting with dilute spirit of svine and rapidly decanting the fluid from the tin globules (H. KOSE*). Sn 59 78-67 2 16 21-33 75 100-00 b. Hydrated protosulpliide of tin forms a brown precipitate, insoluble in water, sulphuretted hydrogen water, and dilute acids. In precipita- ting tin from solutions of the protoxide by means of sulphuretted hy- drogen, free hydrochloric acid must not be present in too large amount, and the solution must be diluted sufficiently. Ammonia fails to dissolve it ; but it dissolves pretty readily (as bisulphide) in the yellow sulphide of ammonium, and in the yellow sulphide of potassium ; it dissolves readily in hot concentrated hydrochloric acid. Heated, with exclusion of air, it loses its water of hydration, and is converted into anhydrous protosulphide of tin ; when exposed to the continued action of a gentle heat, with free access of air, it is converted into sulphurous acid, which escapes, and binoxide of tin, which remains. c. JETydrated bisulphide of tin forms a light-yellow precipitate. In washing with pure water, it is inclined to yield a turbid filtrate and to stop up the pores of the filter ; this annoyance is got over by washing with water containing chloride of sodium, acetate of ammonia, or the like (BUNSEN). On drying, the precipitate assumes a darker tint. It is insoluble in water ; it dissolves with difficulty in ammonia, but read- ily in potassa, alkaline sulphides, and hot concentrated hydrochloric acid. It is insoluble in bisulphite of potassa. In precipitating tin from solutions of the binoxide by sulphuretted hydrogen, the solution should not contain too much free hydrochloric acid, and should be sufficiently diluted. When heated, with exclusion of air, it loses its water of hy- dration, and, at the same time, according to the greater or less degree of heat applied, one-half, or a w T hole equivalent of sulphur, becoming con- verted either into sesquisulphide, or into protosulphide of tin ; when heated very slowly, with free access of air, it is converted into binoxide of tin, with disengagement of sulphurous acid. 92. 6. ARSENIOUS ACID; and 7. ARSENIC ACID. ARSENIC is weighed either as ARSENIATE OF LEAD, as TERSULPHIDE, as ARSENIATE OF MAGNESIA AND AMMONIA, Or as BASIC ARSENIATE OF SESQUI- OXIDE OF IRON ; besides these forms, we have here to examine also AR- SENIO-MOLYBDATE OF AMMONIA. a. Arseniate of lead, in the pure state, is a white powder, which agglu- * Journ. f. prakt. Chem. 61, 189. 138 FORMS. [ 92. tinates when exposed to a gentle red heat, at the same time transitorily- acquiring a yellow tint ; it fuses when exposed to a higher degree of heat. When strongly ignited, it suffers a slight diminution of weight, losing a small proportion of arsenic acid, which escapes as arsenious acid and oxygen. In analysis we have never occasion to operate upon the pure arseniate of lead, but upon a mixture of it with free oxide of lead. b. Tersulphide of arsenic forms a precipitate of a rich yellow color ; it is insoluble in water,* and also in sulphuretted hydrogen water. When boiled with water, or left for several days in contact with chat fluid, it undergoes a very trifling decomposition : a trace of arsenious acid dis- solves in the water, and a minute proportion of sulphuretted hydrogen is disengaged. This does not in the least interfere, however, with the washing of the precipitate. The precipitate may be dried at 100, with- out suffering decomposition ; the whole of the water which it contains is expelled at that temperature. When exposed to a stronger heat, tersul- phide of arsenic transitorily assumes a brownish-red color, fuses, and finally rises in vapor, without suffering decomposition. It dissolves readily in alkalies, alkaline carbonates, alkaline sulphides, bisulphite of potassa, and nitrohydrochloric acid ; but it is scarcely soluble in boiling concentrated hydrochloric acid. Red fuming nitric acid converts it into arsenic acid and sulphuric acid. As 75 60-98 83 48 39-02 123 100-00 c. Arseniate of magnesia and ammonia forms a white, somewhat trans- parent, finely crystalline precipitate, which has the formula 2 Mg O, N H 4 O, As O 5 + 12 aq. At 100, it loses 11 eq. water ; the formula of the precipitate dried at that temperature is accordingly 2 Mg O, N H 4 O, As O 5 -f aq. Upon ignition it loses its water and ammonia, and changes to 2 Mg O, As O;. But as the ammoniacal gas exercises a reducing action upon the arsenic acid, the new compound suffers a loss of weight, which is the more con- siderable the longer the ignition is continued ; it amounts to from 4 1 2 per cent, of the arsenic originally present in the salt (H. ROSE). Arseniate of magnesia and ammonia dissolves very sparingly in water, one part of the salt dried at 100, requiring 2656, one part of the anhydrous salt, 2788 parts of water of 15. It is still more sparingly soluble in ammo- niated water, one part of the salt dried at 100 requiring 15038, one part of the anhydrous salt, 15786 parts of a mixture of one part of solution of ammonia (0'96 sp. gr.), and 3 parts of water at 15. In water contain- ing chloride of ammonium, it is much more readily soluble, one part of the anhydrous salt requiring 886 parts of a solution of one part of chloride of ammonium in 7 parts of water. Presence of ammonia diminishes the solvent capacity of the chloride of ammonium solution : one part of the anhydrous salt requires 30 14 parts of a mixture of 60 parts of water, 10 of solution of ammonia (0"96 sp. gr.) and one of chloride of ammonium. | * In some experiments which I had occasion to make, in the course of an analy- sis of the springs of Wielbach (Chemische Untersuchung der wichtigsten JYLaeral- wasser des Herzogthums Nassau von Dr. Fresenius, V. Schwefelquelle zu Weil- bach. Wiesbaden, Kreidel und Niedner. 1856), I found that one part of As Si dissolves in about 1 million parts of water. f Zeitschrift f. anal. Chem. 3, 206. 93.] ACIDS OF GROUP 1. 139 COMPOSITION OF THE ARSENIATE OF MAGNESIA AND AMMONIA DRIED AT 100. 2 MgO 40 21-05 NH 4 O 26 13-68 As O 6 115 60-53 HO 9 4-74 190 100-00 d. A.rseniate of sesquioxide of iron. The white slimy precipitate, pro- duced by the action of ordinary arseniate of soda upon solution of sesqui- chloride of iron, has the composition 2 Fe. 2 O 3 , 3 H O, 3 As O 5 -f- 9 aq. Tt dissolves in solution of ammonia, imparting a yellow color to the fluid. Besides this compound, there exist still several others, with larger pro- portions of sesquioxide of iron ; thus we have Fe. 2 :J , A.s O 5 , which falls down + 5 aq. upon the precipitation of arsenic acid with acetate of ses- quioxide of iron (KOTSCHOUBEY) ; 2 Fe. 2 O 3 , As O r -, which is obtained 4- 12 aq., when basic arseniate of protoxide of iron is oxidized with nitric acid, and ammonia added ; 16 Fe. 2 O 3 , As O :5 , which forms + 24 aq., upon boiling the less basic compounds with solution of potassa in excess ; (BERZELIUS). The two latcer compounds are not soluble in ammonia ; the last is quite like hydrated sesquioxide of iron. [Doubtless the basic arseniate of sesquioxide of iron, like the analogous phosphate, loses acid as long as it is washed, and therefore the precipitate has no definite com- position.] In BERTHIER'S method of estimating arsenic acid, we obtain mix- tures of these different salts. They are the better adapted for the purpose, the more basic they are ; being the more insoluble in ammonia, and at the same time more easily washed. Upon ignition the water alone is expelled, provided the heat be very gradually increased. But if the salt is suddenly exposed to a strong heat, before the adhering ammonia has escaped, part of the arsenic acid is thereby reduced to arsenious acid (H. ROSE). e. Arsenio-molybdate of ammonia. If a fluid containing arsenic acid is mixed with a large proportion of molybdate of ammonia, and sufficient nitric or hydrochloric acid to redissolve the precipitate of molybdic acid which forms at first, and the fluid heated to boiling, a yellow precipitate of arsenio-molybdate of ammonia separates provided the molybdic acid be present in excess. This precipitate comports itself with solvents like the analogous compound of phosphoric acid ; it is, like the latter, insoluble in water, salts, and free acids, particularly nitric acid, provided an excess of solution of molybdate of ammonia, mixed with acid in moderate excess, be present. SELIGSOHN * found it to be composed of 87*666 per cent, of molybdic acid, 6-308 arsenic acid, 4-258 ammonia, and 1-768 wuter. B. FORMS IN WHICH THE ACIDS ARE WEIGHED on PRECIPITATED. ACIDS OF THE FIRST GROUP. 93 ' 1. ARSENIOUS ACID and ARSENIC ACID. See 92. 2. CHROMIC ACID. Chromic acid is weighed either in the form of SESQUIOXIDE, or in that Of CHROMATE OF LEAD. * Journ. f. prakt. Chem. 67, 481. HO FORMS. [ 93. a. Sesquioxide of chromium. See 76. b. Chromate of lead obtained by precipitation forms a bright yellow precipitate, insoluble in water and acetic acid, barely soluble in dilute nitric acid, readily in solution of potassa. When chromate of lead is boiled with concentrated hydrochloric acid, it is readily decomposed, chloride of lead and sesquichloride of chromium being formed. Addition of alcohol tends to promote this decomposition. Chromate of lead is unalterable in the air ; it dries thoroughly at 100. Under the influence of heat it transitorily acquires a reddish-brown tint ; it fuses at a red heat ; when heated beyond its point of fusion, it loses oxygen, and is transformed into a mixture of sesquioxide of chromium and basic chro- mate of lead. Heated in contact with organic substances, it readily yields oxygen to the latter. Pb O 111-50 68-94 Cr O 3 50-24 31-06 161-74 100-00 3. SULPHURIC ACID. Sulphuric acid is determined best in the form of SULPHATE OF BARYTA, for the properties of which see 71. 4. PHOSPHORIC ACID. The principal forms into which phosphoric acid is converted are as fol- lows : PHOSPHATE OF LEAD, PYROPHOSPHATE OF MAGNESIA, BASIC PHOS- PHATE OF MAGNESIA (3 Mg O, P O 5 ), BASIC PHOSPHATE OF SESQUIOXIDE OF IRON, PHOSPHATE OF SESQUIOXIDE OF URANIUM, PHOSPHATE OF BINOX- IDE OF TIN, and PHOSPHATE OF SILVER. Besides these compounds, we have to examine PHOSPHATE OF SUBOXIDE OF MERCURY, and PHOSPHO- MOLYBDATE OF AMMONIA. a. The phosphate of lead obtained in the course of analysis is rarely quite pure, but is generally mixed with free oxide of lead. In this mix- ture we have accordingly the basic phosphate of lead (3 Pb O, P O 6 ) ; in the pure state, this presents the appearance of a white powder ; it is in- soluble in water and in acetic acid, arid equally so in ammonia ; it dis- solves readily in nitric acid. When exposed to the action of heat, it fuses, without undergoing decomposition. 6. Pyrophospliate of magnesia. See 74. c. Basic phosphate of magnesia (3 Mg O, P O 5 ). This compound is produced by mixing a solution of an alkaline phosphate, containing chloride of ammonium, with magnesia, evaporating the mixture, heating the residue until the chloride of ammonium is completely expelled, and finally treating with water ; the compound so produced contains an ex- cess of magnesia. It is sufficient for our purpose to state that it is near- ly absolutely insoluble in water and in solutions of salts of the alkalies (F. K SCHULZE *). d. Basic phosphate of sesquioxide of iron. If a solution of phosphoric acid or of phosphate of lime in acetic acid is carefully precipitated with a solution of acetate of sesquioxide of iron, or with a mixture of iron-alum and acetate of soda, so that the iron salt * Journ. f. prakt. Chem. 63, 440. 93.] ACIDS OF GROUP I. 141 may just predominate, the precipitate always contains 1 eq. P O 5 to 1 eq. Fe, O 3 (RAWSKY, WITTSTEIN, E. DAVY *) ; if, on the other hand, the acetate of iron is in larger excess, the precipitate contains more base. WITTSTEIN obtained, by using considerable excess of acetate of iron, a precipitate of the formula 4 Fe. 2 O 3 , 3 P O 5 . Precipitates, obtained with a small excess of the precipitant, possess a composition varying between the above-mentioned limits. RAMMELSBERG obtained Fe 2 O 3 , P O 6 (-f- 4 aq.), and WITTSTEIN subsequently, the same compound (with 8 aq. in- stead of 4), upon mixing sulphate of sesquioxide of iron with phosphate of soda in excess ; with an insufficient quantity of the phosphate of soda, the latter chemist obtained a more yellowish precipitate, which had the formula 3 (FeA, P O 5 + 8 aq.) + (FeA, 3 H O). If an acid fluid containing a considerable excess of phosphoric acid is mixed with a small quantity of solution of sesquioxide of iron, and an alkaline acetate added, a precipitate of the formula, Fe. 2 O 3 , P O 6 + water, is invariably obtained, which, accordingly, leaves upon ignition Fe 2 O 3 , P O 5 (WITTSTEIN). Fresh experiments that I have made upon this subject have positively convinced me of the perfect correctness of this statement of WITTSTEIN'S.J COMPOSITION. PO 5 71 47-02 FeA 80 52-98 151 100-00 [The discrepancies among the statements made by different chemists as to the composition of basic phosphate of sesquioxide of iron obtained in the modes above indicated are explained by the observations of MOHR, that the precipitate loses phosphoric acid as long as it is washed, and has consequently no definite composition.] If we dissolve phosphate of sesquioxide of iron in hydrochloric acid, supersaturate the solution with ammonia, and apply heat, we obtain more basic salts, viz., 3 Fe 2 O 3 , 2 P O 5 (RAMMELSBERG) ; 2 Fe. 2 O 3 , P O 5 (WITT- STEIN after long washing). In WITTSTEIN'S experiment, the wash-water contained phosphoric acid. The white phosphate of sesquioxide of iron does not dissolve in acetic acid, but it dissolves in a solution of acetate of sesquioxide of iron. Upon boiling the latter solution (of phosphate of sesquioxide of iroi in acetate of sesquioxide of iron), the whole of the phosphoric acid precipi tates, together with the basic acetate of sesquioxide of iron, as liyperbasu phosphate of sesquioxide of iron (15 FeA, PO 5 (RAMMELSBERG). Simi- lar extremely basic combinations are invariably obtained (often mixed with free hydrated sesquioxide of iron), upon precipitating with ammo- nia or carbonate of baryta a solution containing phosphoric acid and an excess of sesquioxide of iron. The precipitate obtained by carbonate of * Phil. Mag-., xix. p. 181. Journ. f. prakt. Chem. 80, 380. f In an experiment made at a former period by Will and myself (Annal. der Chem. u. Pharm. 50, 379), we obtained in this way a precipitate of the formula 2 Fe ? O 3 , 3 P 5 + 3 HO + 10 aq. ; but I have never since succeeded in produ cing- a precipitate of the same composition. 142 FOKMS. [ 93. baryta, can be conveniently filtered off and washed, the filtrate is perfectly free from either iron or phosphoric acid ; on the contrary, the precipitate obtained by ammonia, especially if the latter were much in excess, is slimy, and therefore difficult to wash, and the filtrate always contains small traces of both iron and phosphoric acid. e. Phosphate of sesquioxide of uranium. If the hot aqueous solution of a phosphate soluble in water or acetic acid is mixed, in presence of free acetic acid, with acetate of sesquioxide of uranium, a precipitate of phosphate of sesquioxide of uranium is immediately formed. If the fluid contains much ammoniacal salt, the precipitate contains also am- monia. The same precipitate forms also if alumina or sesquioxide of iron is present ; but in that case it is always mixed with more or less phosphate of sesquioxide of iron or phosphate of alumina. Presence of potassa- or soda-salts, on the contrary, or of salts of the alkaline earths, has no influence on the composition of the precipitate. Phosphate of sesquioxide of uranium and ammonia (2 Ur 2 O 3 , N H 4 O, P O 5 + x H O) is a somewhat gelatinous, whitish-yellow precipitate, with a tinge of green. The best way of washing it, at least so far as the principal part of the operation is concerned, is by boiling with water and decanting. If, after having allowed the fluid in which the preci- pitate is suspended to cool a little, a few drops of chloroform are added, and the mixture is shaken or boiled up, the precipitate subsides much more readily than without this addition. The precipitate is insoluble in water and in acetic acid ; but it dissolves in mineral acids ; a.netate of ammonia, added in sufficient excess, com- pletely re-precipitates it from this solution, upon application of heat. Upon igniting the precipitate, no matter whether containing ammonia or not, phosphate of sesquioxide of uranium of the formula 2 TJr 2 O 3 , P O 5 is produced. This has the color of the yolk of an egg. If the precipitate is ignited in presence of charcoal or of some reducing gas, partial reduction to phosphate of protoxide of uranium ensues, owing to which the ignited mass acquires a greenish tint ; however, upon warm- ing the greenish residue with some nitric acid, the green salt of the protoxide is readily reconverted into the yellow salt of the sesquioxide. Phosphate of sesquioxide of uranium is not hygroscopic, and may there- fore be ignited and weighed in an open platinum dish (A. ARENDT and W. KNOP *). 2 Ur. 2 O 3 285-6 80-09 PO 6 71-0 19-91 356-6 100-00 The one-fifth part of the precipitate may accordingly be calculated as phosphoric acid in ordinary analyses. f f. Phosphate of binoxide of tin is never obtained in the pure state in the analytical process, but contains always an admixture of hydrated * Chemisches Centralblatt, 1856, 769, 803 ; and 1857, 177. f The equivalent of uranium is here taken as 59 -4, according to Ebelmen. If we take it according to Peligot, as 60, the ignited phosphate would contain 80'22 Ur-i 3 , and 19 '78 phosphoric acid. W. Knop and Arendt found in four experiments 2013, 20'06, 20 -04, and 20 "04 respectively (in another 2077). It will be seen that these numbers agree better with the composition as reckoned from Ebelmen's than from Peligot's equivalent. 93.] ACIDS OF GROUP I. 143 metastannic acid in excess, which,- upon ignition, changes to metastannic acid. It has, generally speaking, the same properties as hydrated meta- stannic acid, and is more particularly, like the latter, insoluble in nitric acid. Upon heating with concentrated solution of potassa, phosphate and metastannate of potassa are formed. g. Tribasic pliospliate of silver is a yellow powder ; it is insoluble in water, but readily soluble in nitric acid, and also in ammonia. In am- moniacal salts, it is difficultly soluble. It is unalterable in the air. Upon ignition, it acquires transiently a reddish-brown color ; at an in- tense red heat, it fuses without decomposition. 3AgO 347-91 83-05 PO 5 71-00 16-95 418-91 100-00 h. Phosphate of suboxide of mercury. This compound is employed for the purpose of effecting the separation of phosphoric acid from many bases, after H. ROSE'S method. Phosphate of suboxide of mercury presents the appearance of a white crystalline mass, or of a white powder. It is insoluble in water, but dissolves in nitric acid. The action of a red heat converts it into fused phosphate of oxide of mercury, with evolution of vapor of mercury. Upon fusion with alkaline carbonates, alkaline phosphates are produced, and mercury, oxygen, and carbonic acid escape. i. Phosplio-moly~bdate of ammonia. This compound also serves to effect the separation of phosphoric acid from other bodies ; it is of the utmost importance in this respect. Phospho-molybdate of ammonia forms a bright yellow, readily subsi- ding precipitate. Dried at 100, it has, according to SELIGSOHN, the fol- lowing (average) composition : Molybdic acid 90*744 Phosphoric acid Oxide of ammonium 3-570 Water . , 2-544 100-000 * In the pure state, it dissolves but sparingly in cold water (1 in 10000- EGGERTZ) ; but it is soluble in hot water. It is readily soluble, even in the cold, in caustic alkalies, alkaline carbonates and phosphates, chloride of ammonium, and oxalate of ammonia. It dissolves only sparingly in sulphate of ammonia, nitrate of potassa, and chloride of potassium ; and very sparingly in nitrate of ammonia. It is soluble in sulphate of potassa and sulphate of soda, chloride of * From the varying results of different analysts it is plain that the precipitate, prepared under apparently the same circumstances, has not always exactly the same composition Sonnenschein (Journ. f. prakt. Chem. 53, 342) found in the precipitate dried at 1 20, 2'93 3 12 P 0., ; Lipowitz (Pogg. Annal. 109, 135), m the precipitate dried at from 20 to 30, 3'607 ft P O 5 ; Eggertz (Journ. f prakt Chem. 79, 496), 3-7 to 38. [Dietrich (Fres. Zeitschrift fur analyt. Chem. 1866, 45) says that this precipitate contains small and variable quantities of admixed molybdic acid. He finds, however, that the relation between P O, and & H 3 is constantly that of Seligsohn's formula (23 N H 4 P O 5 ) + 15 (H 0, 4 Mo 0,). Dietrich esti- mates P O 5 by bringing the ppt. into the azotometer. 144 FORMS. [ 93 sodium and chloride of magnesium, and sulphuric, hydrochloric, and nitric acids (both concentrated and dilute). Water, containing 1 per cent, of common nitric acid, dissolves 6^\ro (EGGERTZ). -Application of heat does not check the solvent action of these substances. Presence of mo- lybdate of ammonia totally changes its deportment with acid fluids : in presence of that substance, it is almost insoluble in acids, even upon ebullition. The solution of the phospho-molybdate of ammonia in acids is probably attended, in all cases, with decomposition and with separa- tion of the molybdic acid, which cannot take place in the presence of molybdate of ammonia (J. CRAW *). Tartaric acid and similar organic substances entirely prevent the precipitation of the phospho-molybdate of ammonia (EGGERTZ). f In the presence of an iodide, instead of a yel- low precipitate, a green precipitate or a green fluid is formed, resulting from the reducing action of the hydriodic acid on the molybdic acid (J. W. BILL J). Other substances which reduce molybdic acid have of course a similar action. 5. BORACIC ACID. BOROFLUORIDE OF POTASSIUM is the best form to convert boracic acid into for the purpose of the direct estimation of the acid. This com- pound is produced by mixing the solution of an alkaline borate (the po- tassa salt answers best) with hydrofluoric acid in excess, in a silver or platinum dish, and evaporating to dryness. The gelatinous precipitate which forms in the cold, dissolves upon application of heat, and sepa- rates from the solution subsequently, upon evaporation, in small, hard, transparent crystals. The compound has the formula K Fl, B F1 3 . It is soluble in water and also in dilute spirit of wine ; but strong al- cohol fails to dissolve it ; it is insoluble also in concentrated solution of acetate of potassa. It may be dried at 100, without suffering de- composition (A.UG. STROMEYER). K 39-11 31-01 B 11-00 8-72 Fl 76-00 60-27 126-11 10000 6. OXALIC ACID. When oxalic acid is to be directly determined it is usually precipi- tated in the form of OXALATE OF LIME ; and its weight is inferred from the CARBONATE OF LIME produced from the oxalate by ignition. For the properties, &c., of carbonate of lime and of oxalate of lime, see 73. 7. HYDROFLUORIC ACID. The direct estimation of hydrofluoric acid is usually effected by weighing the acid in the form of FLUORIDE OF CALCIUM. * Chem. Gaz. 1852, 216. f [Lipowitz (Jahresbericht, 1860, 618) recommends a molybdic solution con taining tartaric acid for the precipitation of P (X t Sillim. Journ., July, 1858. Annul, d. Chem. u. Pharm. 100, 82. 93.] ACIDS OF GROUP i. 145 Fluoride of calcium forms a gelatinous precipitate, which it is found difficult to wash. If digested with ammonia, previous to filtration, it is rendered denser and less gelatinous. It is not altogether insolu- ble^ in water ; aqueous solutions of the alkalies fail to decompose it. It is very slightly soluble in dilute, but more readily in concentrated hydrochloric acid. When acted upon by sulphuric acid, it is decom- posed, and sulphate of lime and hydrofluoric acid are formed. Fluoride of calcium is unalterable in the" air, and at a red heat. Exposed to a very intense heat, it fuses. Upon intense ignition in moist air, it is slowly and partially decomposed into lime and hydrofluoric acid. Mixed with chloride of ammonium, arid exposed to a red heat, fluoride of calcium suffers a continual loss of weight ; but the decomposition is incomplete. Ca 20 51-28 Fl . 19 48-72 39 100-00 8. CARBONIC ACID. The direct estimation of carbonic acid which, however, is only rarely resorted to is usually effected by weighing the acid in the form of CARBONATE OF LIME. For the properties of the latter sub- stance, see 73. 9. SILICIC ACID (OR SILICA). By whatever decomposition silicic acid is separated in the wet way, it is always hydrated. The hydrate is generally gelatinous, occasionally pul- verulent. The amount of water it contains varies according to the cir- cumstances under which it was formed ; at least this is the only explana- tion I can give of the great differences in the results obtained by va- rious chemists who have analyzed hydrates of silicic acid dried in the same way.* The gelatinous hydrate of silicic acid is never entirely insoluble in water and acids. While however the degree of solubility is relatively high, if the hydrate immediately on separation comes in contact with large quantities of fluid, it is, on the contrary, low, when, after having been separated and washed, it is treated with solvents ; thus 1 part of silicic acid in the hydrated condition, obtained by passing fluosilicic gas into water and washing the precipitate completely, requires 7700 parts of water, 11000 parts of cold, and 5500 parts of boiling hydro- chloric acid of 1-115 sp. gr. (J. FUCHS, loc. cit.) Hydrate of silicic acid dried at 100 forms a loose, white powder ; it is insoluble in water and in acids (hydrofluoric excepted), but it dissolves in solutions of the fixed alkalies and their carbonates, especially in the heat. The silicic * Dover! (Annal. de Chim. et de Phys. 21, 40 ; Annal. d. Chem. u. Pharm. 64, 256) found in the air-dried hydrate 16 9 to 17'8 water ; J. Fuchs (Annal. d. Chem. u. Pharm. 82, 119 to 123), 91 to 9'6 ; G. Lippert (Expt No. 61), 9'28 to 9-95. Doveri found in the hydrate dried at 100, 8 "3 to 9 '4 ; J. Fuchs, 6 "63 to 6-96 ; G- Lippert, 4'97 to 5 52 ; H. Rose (Pogg. Annal. 108, 1 ; Journ. fur prakt. Chem. 81, 227) found in the hydrate obtained by digesting stilbite with concen- trated hydrochloric acid, and dried at 150, 4'85 water. 10 146 FORMS. [ 94. acid is obtained in the same form, when its solution in water or in hy- drochloric acid is evaporated and the residue dried at 100. On ignition all the hydrates pass into the anhydrous acid. As the vapoi escapes small particles of the extremely fine powder are liable to whirl up. This may be avoided by moistening the hydrate in the cru- cible with water, evaporating to dryness on a water bath, and then applying at first a slight and then a gradually increased heat. The silicic acid obtained by igniting the hydrate appears in the amor- phous condition, with a sp. gr. of 2'2 to 2'3. It forms a white powder insoluble in water and acids (hydrofluoric excepted), soluble in solu- tions of the fixed alkalies and their carbonates, especially in the heat. Hydrofluoric acid readily dissolves amorphous silicic acid ; the solution leaves no residue on evaporation in platinum, if the silica was pure. The amorphous silica, when heated with fluoride of ammonium in a platinum crucible, readily volatilizes. The ignited amorphous silica, exposed to the air, eagerly absorbs water, which it will not give up at from 100 to 150. (H. KOSE.) Silica fuses at the strongest heat. The mass obtained is vitreous and amorphous. Amorphous silica ignited with chloride of ammonium, at first loses weight, and then, when the ignition has rendered it denser, the weight remains constant. The amorphous silica must be distinguished from the crystallized or crystalline variety, which occurs as rock crystal, quartz, sand, &c. This has a sp. gr. of 2-6 (SCHAFFGOTSCH), and is far more difficultly, and in far less amount, dissolved by potash solution or solution of fixed alkaline carbonates ; it is also more slowly attacked by hydrofluoric acid or fluo- ride of ammonium. Vegetable colors are not changed either by silicic acid or its hydrates. Si 14-00 46-67 O 2 16-00 53-33 30-00 100-00 ACIDS OF THE SECOND GROUP. 94. 1. HYDROCHLORIC ACID. Hydrochloric acid is almost invariably weighed in the form of CHLO- BIDE OF SILVER for the properties of which, see 82. 2. HYDROBROMIC ACID. Hydrobromic acid is always weighed in the form of BROMIDE OF SIL- VER. Bromide of silver, prepared in the humid way, forms a yellowish- white precipitate. It is wholly insoluble in water and in nitric acid, tolerably soluble in ammonia, readily soluble in hyposulphite of soda and in cyanide of potassium. Concentrated solutions of the chlorides and bromides of potassium, sodium, and ammonium dissolve it to a very perceptible amount, while in very dilute solutions of these sails it is entirely insoluble. Traces only dissolve in nitrates of the alkalies. On dignrtion with excess of iodide of potassium solution it is completely 94.] ACIDS OF GROUP ii. 147 converted into iodide of silver (FIELD). On ignition in a current of chlorine the bromide of silver is transformed into the chloride; on igni- tion in a current of hydrogen it is converted into metallic silver Ex posed to the light it gradually turns gray, and finally black. Under the influence of heat, it fuses to a reddish liquid, which, upon cooling, solidi- fies to a yellow horn-like mass. Brought into contact with zinc and water, bromide of silver is decomposed : a spongy mass of metallic sil- ver torms, and the solution contains bromide of zinc. Ag 107-97 57-44 Br 80-00 42-56 187-97 100-00 3. HYDRIODIC ACID. Hydriodic acid is usually determined in the form of IODIDE OF SIL- VER, and occasionally also in that of PROTIODIDE .>F PALLADIUM. a. Iodide of silver, produced in the humid way, forms a light-yellow precipitate, insoluble in water and in dilute nitric acid, and very slightly soluble in ammonia. One part dissolves, according to WALLACE and LAMONT,* in 2493 parts of aqueous ammonia sp. gr. 0*89, according to MARTINI, in 2510 parts, of 0-90 sp. gr. It is copiously taken up by concentrated solution of iodide of potassium, but it is insoluble in very dilute ; it dissolves readily in hyposulphite of soda and in cyanide of potassium ; traces only are dissolved by alkaline nitrates. Hot concen- trated nitric and sulphuric acids convert it, but with some difficulty, into nitrate and sulphate of silver respectively, with expulsion of the iodine. Iodide of silver acquires a black color when exposed to the light. When heated, it fuses without decomposition to a reddish fluid, which, upon cooling, solidifies to a yellow mass, that may be cut with a knife. Un- der the influence of excess of chlorine in the heat it is completely con- verted into chloride of silver ; ignition in hydrogen reduces it to the metallic state. When brought into contact with zinc and water, it is decomposed : iodide of zinc is formed, and metallic silver separates. Ag 107-97 45-95 1 . 127-00 54-05 234-97 100-00 b. Protiodide of palladium, produced by mixing an alkaline iodide with protochloride of palladium, is a deep brownish-black, flocculent precipitate, insoluble in water and in dilute hydrochloric acid, but slightly soluble in saline solutions (chloride of sodium, chloride of mag- nesium, chloride of calcium, &c.). It is unalterable in the air. Dried simply in the air, it retains one equivalent of water = 5*05 per cent.. Dried long in vacuo, or at a rather high temperature (70 to 80), it yields the whole of this water, without the least loss of iodine. Dried at 100, it loses a trace of iodine; at from 300 to 400, the whole of the iodine is expelled. The precipitated iodide of palladium may be- vrashed with hot water, without loss of iodine. * Cbem. Gaz. 1859, 137. 148 FORMS. [ 95. Pd . , 53-00 29-44 1 . 127-00 70-56 180-00 100-00 4. HYDROCYANIC ACID. Hydrocyanic acid, if determined gravimetrically and directly, is always converted into CYANIDE OF SILVER for the properties of which compound see 82. 5. HYDROSULPHURIC ACID (OR SULPHURETTED HYDROGEN). The forms into which sulphuretted hydrogen, or the sulphur in me- tallic sulphides, is converted for the purpose of being weighed, are TERSULPHIDE OF ARSENIC, SULPHIDE OF SILVER, SULPHIDE OF COPPER, and SULPHATE OF BARYTA. For the properties of the sulphides named, see 82, 85, 92 ; for those of sulphate of baryta, see 71. ACIDS OF THE THIRD GROUP. 95. 1. NITRIC ACID ; and 2. CHLORIC ACID. These two acids are never estimated in a direct way that is to say, in compounds containing them, but always in an indirect way ; generally volumetrically. SECTION IV. THE DETERMINATION (OK ESTIMATION) OF BODIES. IN the preceding Section we have examined the composition and proper- ties of the various forms and combinations in which bodies are separated from others, or in which they are weighed. We have now to consider the special means and methods of converting the several bodies into such forms and combinations. For the sake of greater clearness and simplicity, we shall, in the pres- ent Section, confine our attention to the various methods applied to effect the estimation of single bodies, deferring to the next Section the consid- eration of the means adopted for the estimation of mixed bodies, or the separation of bodies from one another. We have to deal here exclusively with bodies in the free state, or with compounds consisting of one base and one acid, or of one metal and one metalloid. As in the " Qualitative Analysis," the acids of arsenic will be treated of among the bases, on account of their behavior to sulphuretted hydro- gen, and those elements which form acids with hydrogen will be con- sidered in conjunction with their respective hydrogen acids. In the quantitative analysis of a body we have to study first, the most appropriate method of dissolving it ; and, secondly, the modes of deter- mining it. With regard to the latter point, we have to turn our attention, first, to the performance / and secondly, to the accuracy of the methods. It happens very rarely in quantitative analyses that the amount of a substance, as determined by the analytical process, corresponds exactly with the amount theoretically calculated or actually present ; and if it does happen, it is merely by chance. It is of importance to inquire what is the reason of this fact, and what are the limits of inaccuracy in the several methods. The cause of this almost invariably occurring discrepancy between the quantity present and that actually found, is to be ascribed either exclusively to the execution, or it lies partly in the method itself. The execution of the analytical processes and operations can never be absolutely accurate, even though the greatest care and attention be bestowed on the most trifling minutije. To account for this, we need only bear in mind that our weights and measures are never absolutely correct, nor our balances absolutely accurate, nor our reagents absolutely pure ; and, moreover, that we do not weigh in vacuo ; and that, even if we deduce the weight in vacuo from the weight we actually obtain by weighing in the air, the very volumes on which the calculation is based are but approximately known ; that the hygroscopic state of the air is 150 DETERMINATION-. [ 96. liable to vary between the weighing of the empty crucible and of the crucible -|- the substance; that we know the weight of a filter ash only approximately that we can never succeed in completely keeping off dust, &c. With regard to the methods, many of them are not entirely free from certain unavoidable sources of error / precipitates are not absolutely in- soluble ; compounds which require ignition are not absolutely fixed; others, which require drying, have a slight tendency to volatilize j the final reaction in volumetric analyses is usually produced only by a small excess of the standard lluid, which is occasionally liable to vary with the degree of dilution, the temperature, ignite the residue in a platinum crucible or dish, and weigh ( 42). The residue must be thoroughly dried before you proceed to ignite it ; the heat applied for the latter purpose must be moderate at first, and very gradually increased to the requisite degree ; the crucible or dish must be kept well covered neglect of these precautionary rules involves always a loss of substance from decrepitation. If free sulphuric acid is present, we obtain, upon evaporation, bisulphate of potassa ; in such cases the excess of sulphuric acid is to be removed by igniting first alone (here it is best to place the lamp so that the flame may strike the dish-cover obliquely from above), then with carbonate of ammonia. See 68. For properties of the residue, see 68. Observe more particularly that the residue must dissolve to a clear fluid, and that the solution must be neutral. Should traces of platinum remain behind (the dish not having been previously weighed) these must be carefully deter- mined, and their weight subtracted from that of the ignited residue. With proper care and attention, this method gives accurate results. To convert the above-mentioned salts (chloride of potassium, &c.) into sulphate of potassa, add to their aqueous solution a quantity of pure sulphuric acid more than sufficient to saturate the whole of the potassa, evaporate the solution to dryness, ignite the residue, and convert the bisulphate of potassa into the neutral salt, by treating with carbonate of ammonia ( 68). As the expulsion of a large quantity of sulphuric acid is a very dis- agreeable process, avoid adding too great an excess. Should too little of the acid ha/ve been used, which you may infer from the non-evolution of sulphuric acid fumes on ignition, moisten the residue with dilute sulphuric acid, evaporate, and again ignite. If you have to deal with a small quantity only of chloride of potassium, &c., proceed at once to treat the dry salt, cautiously, with dilute sulphuric acid in the platinum crucible ; provided the latter be capacious enough. In the case of bromide and iodide of potassium, the use of platinum vessels must be avoided. [Potassa salts with organic acids are directly converted into sulphate of potassa by first carbonizing them at the lowest possible temperature, and after cooling adding some crystals of pure sulphate of ammonia and a little water to the mass. The crucible being covered, the water is eva- porated by heating the crucible cover, and the whole is afterwards heated to dull redness, until the excess of sulphate of ammonia is destroyed. If the carbon is not fully consumed by this operation, add a little nitrate of ammonia and repeat the ignition. Kammere^.*] 2. Determination as Chloride of Potassium. General method the same as described in 1. The residue of chloride [*Fres. ZeitVII. 222. J 8 y '-J POTASSA. 153 of potassium must, previously to ignition, be treated in the same way as sulphate of potassa, and for the same reason. The salt must be heated in a well-covered crucible or dish, and only to dull redness, as the ap- plication of a higher degree of heat is likely to cause some loss by vola- tilization. No particular regard need be had to the presence of free acid. For properties of the residue, see 68. This method, if properly and carefully executed, gives very accurate results. The chloride of potassium may, instead of being weighed, be determined volumetrically by 141, b. This method, however, has no advantage in the case of single estimations, but saves time when a series of estimations has to be made. In determining potassa in the carbonate it is sometimes desirable to avoid the effervescence occasioned by treatment with hydrochloric acid, as, for instance, in the case of the ignited residue of a potassa salt with an organic acid, which is contained in the crucible. This may be effected by treating the carbonate with solution of chloride of ammonium in excess, evaporating and igniting, when carbonate of ammonia and the excess of ^ chloride of ammonium will escape, leaving chloride of potas- sium behind. The methods of converting into chloride of potassium the potassa com- pounds specified above, will be found in Part II. of this Section, under the respective heads of the acids which they contain. ^ 3. Determination as Bichloride of Platinum and Chloride of Potas- sium. a. Salts of potassa ,with volatile acids (nitric acid, acetic acid, &c.), Mix the solution with hydrochloric acid, evaporate to dryness, dis- solve the residue in a little water, add a concentrated solution of bichlo- ride of platinum, as neutral as possible, in excess, and evaporate in a porcelain dish, on the water-bath, nearly to dryness, taking care not to heat the water-bath quite to boiling. Pour spirit of wine of about 80 per cent, over the residue ; let it stand for some time, and then transfer the bichloride of platinum and chloride of potassium, which remains undis- solved, to a weighed filter (which may be readily done by means of a washing bottle filled with spirit of wine). Wash with spirit of wine, dry at 100, and weigh ( 50). p. Potassa salts with non-volatile acids (phosphoric acid, boracic acid, &c.). Make a concentrated solution of the salt in water, add some hydro- chloric acid, and bichloride of platinum in excess, mix with a tolerable quantity of the strongest alcohol, let the mixture stand 24 hours ; after which filter, and proceed as directed in a. Properties of the precipitate, 68. This method, if properly execut- ed, gives satisfactory results. Still there is generally a trifling loss of substance, bichloride of platinum and chloride of potassium not being ab- solutely insoluble even in strong alcohol. In accurate analyses, there- fore, the alcoholic washings must be evaporated, with addition of a little pure chloride af sodium, at a temperature not exceeding 75, nearly to dryness, and the residue treated once more with spirit of wine. A trifling additional amount of bichloride of platinum and chloride of potassium is thus obtained, which is either added to the principal precipitate or collected on a separate small filter, and determined as platinum, by the method given below. The object of the addition of a little chloride of 154 DETERMINATION. [ 98. sodium to the bichloride of platinum is to obviate the decomposition to which pure bichloride of platinum is more liable, upon evaporation in alcoholic solution, than the bichloride containing sodio-bichloride of pla- tinum. The atmosphere of a laboratory often contains ammonia, which might give rise to the formation of some chloride of platinum and ammonium, and to a consequent increase of weight in the potassium salt. As collecting a precipitate upon a weighed filter is a rather tedious process, and, besides, not over accurate, where we have to deal with minute quantities of substance, it is better to collect small portions (up to about 0'03 grm.) of bichloride of platinum and chloride of potassium upon a very small unweighed filter, dry, and transfer the filter, with tha precipitate wrapped up in it, to a small porcelain crucible. Cover the crucible, and let the filter slowly char ; remove the cover, burn the carbon of the filter, and let the crucible get cold. Put now a very minute portion of pure oxalic acid into the crucible, cover, and ignite, gently at first, finally to a strong red heat. The addition of the oxalic acid greatly promotes the complete decomposition of the bichloride of platinum and chloride of potassium, which cannot well be effected by simple ignition. Treat the contents of the crucible now with water, and wash the residuary platinum, until the last rinsings remain clear upon addition of solution of nitrate of silver.* Dry the residuary platinum, ignite, and weigh. One equivalent of platinum represents one equiva- lent of potassium. 98. 2. SODA. a. Solution See 97, a solution of potassa all the directions given in that place applying equally to the solution of soda and its salts. b. Determination. Soda is determined either as sulphate of soda, as chloride of sodium, or as carbonate of soda ( 69). For the alkalimetric estimation of caus- tic soda, and carbonate of soda, see 207 and 208. We may convert into 1. SULPHATE OF SODA; 2. CHLORIDE OF SODIUM. In general the salts of soda corresponding to the salts of potassa specified under the analogous potash compounds, 97. 3. CARBONATE OF SODA. Caustic soda, bicarbonate of soda, and salts of soda with organic acids, also nitrate of soda and chloride of sodium. In the borate of soda the alkali is estimated best as sulphate of soda ( 136) ; in the phosphate, as chloride of sodium, or carbonate of soda (I 135)- Salts of soda with organic acids are determined either, like the corre- sponding potassa compounds, as chloride, or by preference as carbon- ate. (This latter method is not so well adapted for salts of potassa.) * The washing of the residuary platinum may generally be effected by simple decantation. S Jb - 1 SODA. 155 The analyst must here bear in mind, that when carbon acts on fusinc. carbonate of soda, carbonic oxide escapes, and caustic soda in not incon- siderable quantity is formed. 1. Determination as Sulphate of Soda. If alone and in aqueous solution, evaporate to dryness, ignite and weigh the residue in a covered platinum crucible (g 42). The process does not involve any risk of loss by decrepitation, as in the case of sul- phate of potassa. If free sulphuric acid happens to be present, this is removed in the same way as in the case of sulphate of potassa. With regard to the conversion of chloride of sodium, &c., into sul- phate of soda, see 97, 6, 1. For properties of the residue, see 69. The method is easy, and gives accurate results. 2. Determination as Chloride of Sodium. Same method as described in 1.' The rules given and the observations made in 97, 6, 2, apply equally here. For properties of the residue see 69. The methods of converting the sulphate, chromate, chlorate, and sili- cate of soda into chloride of sodium, will be found in Part II. of this Section, under the respective heads of the acids which these salts con- tain. 3. Determination as Carbonate of Soda. Evaporate the aqueous solution, ignite moderately, and weigh. The results are perfectly accurate. For properties of the residue, see 8 69. Caustic soda is converted into the carbonate by adding to its aqueous solution carbonate of ammonia in excess, evaporating at a gentle heat, and igniting the residue. Bicarbonate of soda, if in the dry state, is converted into the carbonate by ignition. The heat must be very gradually increased, and the crucible kept well covered. If in aqueous solution, it is evaporated to dryness, in a capacious silver or platinum dish, and the residue ignited. Salts of soda with organic acids are converted into the carbonate by ignition in a covered platinum crucible, from which the lid is removed after a time. The heat must be increased very gradually. When the mass has ceased to sw^ell, the crucible is placed obliquely, with the lid leaning against it (see 52, fig. 42), and a dull red heat applied until the carbon is consumed as far as practicable. The contents of the cruci- ble are then warmed with water, and the fluid is filtered off from the residuary carbon, which is carefully washed. The filtrate and rinsings are evaporated to dryness with the addition of a little carbonate of ammonia, and the residue is ignited and weighed. The carbonate of ammonia is added, to convert any caustic soda that may have been formed into carbonate. The method, if carefully conducted, gives accu- rate results ; however, a small loss of soda on carbonization is not to be avoided. Nitrate of soda, or chloride of sodium, may be converted into car- bonate, by adding to their aqueous solution perfectly pure oxalic acid in moderate excess, and evaporating several times to dryness, with repeated renewal of the water. All the nitric acid of the nitrate of soda escapes in this process, (partly decomposed, partly undecomposed) ; and equally so all the hydrochloric acid in the case of chloride of sodium. If the residue is now ignited until the excess of oxalic acid is removed, car- bonate of soda is left. 156 DETERMINATION. [ 99. 99 3. AMMONIA. a. Solution. Ammonia is soluble in -water, as are all its salts with those acidg which claim our attention here. It is not always necessary, however, to dissolve the ammoniacal salts for the purpose of determining the amount of ammonia contained in them. b. Determination. Ammonia is weighed, as stated 70, either in the form of chloride of ammonium, or in that of bichloride of platinum and chloride of ammonium. Into these forms it may be converted either directly or indirectly (i.e., after expulsion as ammonia, and re-combination with an acid). Ammonia is also frequently determined by volumetric an- alysis, and its quantity is sometimes inferred, from the volume of ni- trogen. We convert directly into 1. CHLORIDE OF AMMONIUM. Ammoniacal gas and its aqueous solution, and also ammoniacal salts with weak volatile acids (carbonate of ammonia, sulphide of ammonium, &c.). 2. BICHLORIDE OF PLATINUM AND CHLORIDE OF AMMONIUM. Ammoniacal salts with acids soluble in alcohol, such as sulphate of ammonia, phosphate of ammonia, &c. 3. The methods based on the EXPULSION OF THE AMMONIA from its compounds, and also that of inferring the amount of ammonia from the volume of nitrogen eliminated in the dry way, are equally applicable to all ammoniacal salts. The expulsion of ammonia in the dry way, (by ignition with soda- lime,) and the estimation of that alkali from the volume of nitrogen eliminated in the dry way, being effected in the same manner as the es- timation of the nitrogen in organic compounds, I refer the student to the Section on organic analysis. Here I shall only give the methods based upon the expulsion of ammonia and of nitrogen in the wet way. For the alkalimetric estimation of free ammonia, see 207 and 208. 1. Determination as Chloride of Ammonium. Evaporate the aqueous solution of the chloride of ammonium on the water-bath, and dry the residue at 100 until the weight remains con- stant ( 42). The results are accurate. The volatilization of the chlo- ride is very trifling. A direct experiment gave 99 '9 4 instead of 100. (See Expt. 15.) The presence of free hydrochloric acid makes no difference ; the conversion of caustic ammonia into chloride of ammo- nium may accordingly be effected by supersaturating with hydrochloric acid. The same applies to the conversion of the carbonate, with this addition only, that the process of supersaturation must be conducted in an obliquely-placed flask, and the mixture heated in the same, till the carbonic acid is driven off. In the analysis of sulphide of ammonium we proceed in the same way, taking care simply, after the expulsion of the sulphuretted hydrogen, and before proceeding to evaporate, to filter 99.] AMMONIA. 157 off the sulphur which may have separated. Instead of weighing the chloride of ammonium, its quantity may be inferred by the determi. nation of its chlorine according to 141, b. (Comp. chloride of potas- sium, 97, 6, 3). 2. ^ Determination as bichloride of Platinum and Chloride of Am- monium. a. Ammoniacal salts with volatile acids. Same method as described in 97, 6, 4, a (bichloride of platinum and chloride of potassium). p. Ammoniacal salts with non-volatile acids. Same method as described 97, b, 4, j3 (bichloride of platinum and chloride of potassium). The results obtained by these methods are ac- curate. If you wish to control the results,* ignite the double chloride, wrap- ped up in the filter, in a covered crucible, and calculate the amount of ammonia from that of the residuary platinum. The results must agree. The heat must be increased very gradually.f "Want of due cautio^ in this respect is apt to lead to loss, from particles of the double salt being carried away with the chloride of ammonium. Very small quantities of bichloride of platinum and chloride of ammonium are collected on an unweighed filter, dried, and at once reduced to platinum by ignition.J 3. Estimation ~by Expulsion of the Ammonia in the Wet Way. This method, which is applicable in all cases, may be effected in two different ways viz., a. EXPULSION OF THE AMMONIA BY DISTILLATION WITH SOLUTION OF POTASSA, or SODA, or with MILK OF LIME. Applicable in all cases where no nitrogenous organic matters from which ammonia might be evolved upon boiling with solution of potassa, etc., are present with the ammonia salts. Weigh the substance under examination in a small glass tube, 3 cen- timetres long and one wide, and put the tube, with the substance in it, into a flask containing a suitable quantity of moderately concentrated solution of potassa or soda, or milk of lime, from which every trace of ammonia has been removed by protracted ebullition, but which has been allowed to get thoroughly cold again ; place the flask in a slanting position on wire-gauze, and immediately connect it by means of a glass tube bent at an obtuse angle, with the glass tube of a small cooling ap- paratus. Connect the lower end of this tube, by means of a tight-fit- ting perforated cork, with a sufficiently large tubulated receiver which is in its turn connected with a U tube by means of a bent tube passing through its tubulure. * If the bichloride of platinum and chloride of ammonium is pure, which may be known by its color and general appearance, this control may be dis- pensed with. f The best way is to continue the application of a moderate heat for a long time, then to remove the lid, place the crucible obliquely, with the lid leaning against it, and burn the charred filter at a gradually increased heat (H. Rose). t In a series of experiments to get the platinum from pure and perfectly anhydrous ammonio- bichloride of platinum, by very cautious ignition, Mr. Lucius, one of my pupils, obtained from 44 '1 to 44 '3 per cent, of the metal, in stead of 44-3. 158 DETERMINATION. [ 99. If you wish to determine vohimetrically the quantity of ammonia ex- pelled, introduce the larger portion of a measured quantity of standard solution of sulphuric or of nitric acid ( 204), into the receiver, the re- mainder into the U tube ; add to the portion of fluid in the latter a little water, and color the liquids in the receiver and U tube red with 1 or 2 c. c. of tincture of litmus. The cooling tube must not dip into the fluid in the receiver ; the fluid in the U tube must completely fill the lower part, but it must not rise high, as otherwise the passage of air bubbles might easily occasion loss by spirting. The quantity of acid used must of course be more than sufficient to fix the whole of the am- monia expelled. * When the apparatus is fully arranged, and you have ascertained that all the joints are perfectly tight, heat the contents of the flask to gentle ebullition, and continue the application of the same degree of heat until the drops, as they fall into the receiver, have for some time altogether ceased to impart the least tint of blue to the portion of the fluid with which they first come in contact. Loosen the cork of the flask, allow to stand half an hour, pour the contents of the receiver and TJ tube into a beaker, rinsing out with small quantities of water, determine finally with a standard solution of soda the quantity of acid still free, which, by simple subtraction, will give the amount of acid which has combined with the ammonia ; and from this you may now calculate the amount of the latter ( 204). Results accurate.* If you wish to determine by the gravimetric method the quantity of ammonia expelled, receive the ammonia evolved in a quantity of hydro- chloric acid more than sufficient to fix the whole of it, and determine the chloride of ammonium formed, either by simple evaporation, after the directions of 1, or as ammoiiio-bichloride of platinum, after the directions of 2. b. EXPULSION OF THE AMMONIA BY MILK OF LIME, WITHOUT APPLICA- TION OF HEAT. This method, recommended by SCHLOSING, is based upon the fact that an aqueous solution containing free ammonia gives off the latter completely, and in a comparatively short time, when exposed in a shallow vessel to the air, at the common temperature. It finds appli- cation in cases where the presence of organic nitrogenous substances, decomposable by boiling alkalies, forbids the use of the method described in 3, a ; thus, for instance, in the estimation of the ammonia in urine, manures, &c. The fluid containing the ammonia, the volume of which must not exceed 35 c. c., is introduced into a shallow flat-bottomed vessel from 10 to 12 centimetres in diameter; this vessel is put on a plate filled with mercury. A tripod, made of a massive glass rod, is placed in the vessel which contains the solution of the ammoniacal salt, and a saucer or shallow dish with 10 c. c. of the normal solution of oxalic or sulphuric acid (g 204) put on it. A beaker is now inverted over the whole. The beaker is lifted up on one side as far as is required, and a sufficient quantity of milk of lime added by means of a pipette (which should not be drawn out at the lower end). The beaker is then rapidly pressed down, and weighted with a stone slab. ' After forty-eight hours the glass is lifted up, and a slip of moist reddened litmus paper placed in it ; if must [In thus estimating 1 minute quantities of ammonia, the condensing- tube b be of tin, since glass yields a sensible amount of alkali to hot water vapor. ] 99.] AMMONIA. 159 no change of color is observable, this is a sign that the expulsion of the ammonia is complete ; in the contrary case, the glass must be replaced. Instead of the beaker and plate with mercury, a bell-jar, with a Around and greased rim, placed air-tight on a level glass plate, may be used. A bell-jar, having at the top a tubular opening, furnished with a close- fitting glass stopper, answers the purpose best, as it permits the intro- duction of a slip of red litmus paper suspended from a thread ; thus enabling the operator to see whether the combination of the ammonia with the acid is completed, without the necessity of removing the bell- jar. According to SCHLOSING, forty-eight hours are always sufficient to expel Ol to 1 gramme of ammonia from 25 to 35 c. c. of solution. However, I can admit this statement only as regards quantities up to 0*3 grni. ; quantities above this often require a longer time. I, there- fore, always prefer operating with quantities of substance containing no more than 0*3 grm. ammonia at the most. When all the ammonia has been expelled, and has entered into com- bination with the acid, the quantity of acid left free is determined by means of standard solution of soda, and the amount of the ammonia calculated from the result ( 204). 4. Estimation by Expulsion of the Nitro- gen in the lV~et Wai/. A process for determining ammonia by means of the azotometer has been given by W. KNOP.* It depends on the separation of the nitrogen by a bromized and strongly alkaline solution of hypochlorite of soda.f [The simplest azotometer is that described by RUMPF.J It consists of a burette of 50 or 100 c. c. stationed in a glass cylinder nearly filled with mercury, and connected by a stout caoutchouc tube with a small bottle, , fig. 46, to whicji is fitted a soft thrice-perforated ca- outchouc stopper. The stopper carries a ther- mometer and two short glass tubes, one of which joins it to the burette, and the other has attached a short bit of caoutchouc tubing and a pinch-cock, e. The weighed ammonia salt (not more than 0*4 grm.) is placed in the tube, f, with 10 c. c. of water, and 50 c. c. of the bromized hypochlorite solution are brought into the bottle, a. The cock, e, being open, the stopper is firmly fixed in its place, and the burette is depressed in the mercury until its uppermost degree exactly coincides with the surface of the metal. The cock is then closed, Fig. 46. * Chem. Centralbl. 1860, 244. f This is prepared as follows: Dissolve 1 part of carbonate of soda m 15 parts of water, cool the fluid with ice, saturate perfectly with chlorine, keeping cold all the while, and add strong soda solution (of 25 per cent.) till the mixture on rubbing between the fingers makes the skin slippery. Before using, tu id to the quantity required for the series of experiments bromine in the proportion of ~-d to the litre, and shake. grm. Pres. Zeit., VI. 398. 160 DETERMINATION. [ 100 V O oo HH rH O * 1 " CO O CM CO . rH CM rH O5 O 1-1 r 1 OS O co ,_; rH OS XO xo ^4 i i OS *- CM rH C5 XO <=* CM* CO GO -rH ^ CO 00 OS co - 00 CO T*< xo _- CO CO OS *~ rH OO oo *rH <= CM- CO t- ^H *-" 6 CO b- 05 co - CO b- -rH xo ,_; CO b- 05 *- rH* CO b- -rH ^ CM CO CO ^ ^ CO CO OS co - . co CO ^H rH* CO CO OS *- rH* CO CO -rH ^ C^ O -* *- d 1O O5 CO - rH XO -rH ^ rH* r 1 10 05 *- rH* rH 10 ^ 05 oq 00 -rH CO "^ O oo HH GO CO ^ 00 -rH CO rH* CO -rH CO *- rH* oo ^ co & cq CO CO CO - 1 d CO CO GO co - CO co co ** rH* CO CO CO rH CO co co 05 cq CO CM CO ^ d CO CM GO co d co CM CO XO ^ CO CM co *- rH- CO CM CO . CO OS CM -rH ] _J co OS b- 50 rH* CO OS CM CM- co 00 ^1 O CO GO L- CM o CO GO CM ** rH co CO b- 50 rH* CO OO CM CM' t~ R rH b- b- CM - r 1 1^ CM ^ rH* rH b- b- * rH* rH b*. CM *> CM 00 co "-! GO CO CO <" d 00 CO rH ^ rH* GO CO O 50 rH* 00 CO rH 00 CM- CO XO "~1 CO O CO CM - CO XO rH -* rH* CO 10 50 rH" co 10 rH CM- CO TH *-! O co ^H CO CM d co TH rH ^ ,_; co ^H 50 rH* CO -rH rH 00 CM CO ^. O rH CO O CM - rH CO rH ** rH* r 1 CO O 50 rH* rH CO rH Q CM 00 CM <=> O 00 CM rH* 00 CM O CM- CO rH CO rH XO CM CO 3 S CO rH O rH ' CO rH O CM Evolved Absorbed Evolved Absorbed Evolved Absorbed Evolved Absorbed Evolved Absorbed LITHIA. 1G1 and the bottle is inclined to bring the two substances in contact. The ammonia salt is speedily decomposed. When no further evolution of gas takes place the burette is so adjusted that the level of the mercury without and within it shall nearly coincide, and the operator waits 10-20 minutes, or until the thermometer in a indicates the same tem- perature as the surrounding air. Then the adjustment of the burette to exact coincidence of the mercury level, within and without, is effected and the volume of the gas is read off. The stand of the thermometer and barometer are also noted, and the recorded volume of nitrogen is corrected by use of the tables on pp. 160 and 162-163, by DIETRICH: The first table gives a correction for the nitrogen which is absorbed by the 60 c. c. of liquid in the bottle a. The amount varies with the relative volumes of air and nitrogen, and is determined empirically .by decomposing known quantities of ammonia and noting the difference between the obtained and the theoretical volume of nitrogen. The cor- rection holds strictly, of course, only for a solution of such strength as that employed by DIETRICH and at the mean temperatures. The second table serves to spare the labor of calculation. The weight of 1 c.c. of nitrogen, measured e. g. at 754 mm. of barometer and 15C., is found at the intersection of the vertical column 754 with the hori- zontal column 15, is, viz., 1-16187. To the observed volume of nitrogen add the amount absorbed as per Table I., and correct the total by Table II. It scarcely requires to be mentioned that good results can only be obtained in an apartment where the temperature is uniform, and when care is exercised to avoid warming the apparatus in handling. See DIETRICH'S papers.* 100. Supplement to the First Group. LITHIA. In the absence of other bases, lithia may, like potassa and soda, be converted into anhydrous SULPHATE, and weighed in that form (Li O, S O 3 ). As lithia forms no acid sulphate, the excess of sulphuric acid may be readily removed by simple ignition. CARBONATE OF LITHIA also, which is difficultly soluble in water, and fuses at a red heat without suffering decomposition, is well suited for weighing ; whilst chloride of lithium, which deliquesces in the air, and is by ignition in moist air converted into hydrochloric acid and lithia, is unfit for the estimation* of lithia. In presence of other alkalies, lithia is best converted into BASIC PHOS- PHATE OF LITHIA (3 Li O, P O 5 ), and weighed in that form. This is- effected by the following process : add to the solution a sufficient quan- tity of phosphate of soda (which must be perfectly free from phosphates of the alkaline earths), and enough soda to keep the reaction alkaline,, and evaporate the mixture to dryness ; pour water over the residue, in sufficient quantity to dissolve the soluble salts with the aid of a gentle * Fres. Zeit. III. 162. ; IV. 141, and V. 36. 11 162 TABLE OF WEIGHTS. II. TABLE OF THE WEIGHT OF A In Milligrammes for Pressures from 720 to 770 mm. MILLIMETRES. 720 722 724 726 728 730 732 734 736 738 740 742 744 10 1.13380 1.13699 1.14018 1.14337 1.14656 1.14975 1.15294 1.15613 1.15932 1.16251 1.16570 1.16889 1.17208 II" 1.12881 1.13199 1.13517 1.13835 1.14153 1.14471 1.14789 1.15107 1.15424 1.15742 1.16060 1.16378 1.16696 12 1.12376 1.12693 1.13010 1.13326 1.13643 1.13960 1.14277 1.14593 1.14910 1.15227 1.15543 1.15860 1.16177 13 1.11875 1.12191 1.12506 1.12822 1.13138 1.13454 1.13769 1.14085 1.14401 1.14716 1.15032 1.15348 1.15663 14 1.11369 1.11684 1.11999 1.12313 1.12628 1.12942 1.13257 1.13572 1.13886 1.14201 1.14515 1.14830 1.15145 15 1.10859 1.11172 1.11486 1.11799 1.12113 1.12426 1.12739 1.13053 1.13366 1.13680 1.13993 1.14306 1.14620 P 5 16 1.10346 1.10658 _ 1.10971 1.11283 1.11596 1.11908 1.12220 1.12533 3.12845 1.13158 1.13470 1.13782 1.14095 t> 1 8 17 1.09828 1.10139 1.10450 1.10761 1.11073 1.11384 1.11695 1.12006 1.12317 1.12629 1.12940 1.13251 1.13562 1 18 19 1.09304 1.08744 1.09614 1.09083 1.09924 1.09392 1.10234 1.09702 1.10544 1.10011 1.10854 1.10320 1.11165 1.10629 1.11475 1.10938 1.11785 1.11248 1.12095 1.11557 1.12405 1.11866 1.12715 1.12175 1.13025 1.12484 1 20 1.08246 1.08554 1.08862 1.09170 1.09478 1.09786 1.10094 1.10402 1.10710 1.11018 1.11327 1.11635 1.11943 21 1.07708 1.08015 1.08322 1.08629 1.08936 1.09243 1.09550 1.09857 1.10165 1.10472 1.10779 1.11086 1.11393 22 1.07166 1.07472 1.07778 1.08084 1.08390 1.08696 1.09002 1.09308 1.09614 1.09921 1.10227 1.10533 1.10839 23 1.06616 1.06921 1.07226 1.07531 1.07836 1.08141 1.08446 1.08751 1.09056 1.09361 1.09666 1.09971 1.10276 24 1.06061 1.06365 1.06669 1.06973 1.07277 1.07581 1.07885 1.08189 1.08493 1.08796 1.09100 1.09404 1.09708 25 1.05499 1.05801 1.06104 1.06407 1.06710 1.07013 1.07316 1.07619 1.07922 1.08225 1.08528 1.08831 1.09134 720 722 724 726 728 730 732 734 736 738 740 742 744 MILLIMETRES. TABLE OF WEIGHTS. 163 CUBIC CENTIMETRE OF NITROGEN. of Mercury ', and for Temperatures from 10 to 25 (7. MILLIMETRES. 746 748 750 752 754 756 758 760 762 764 766 768 770 1.17527 1.17846 1.18165 1.18484 1.18803 1.19122 1.19441 1.19760 1.20079 1.20398 1.20717 1.21036 1.21355 10" 1.17014 1.17332 1.17650 1.17166 1.18286 1.18603 1.18921 1.19239 1.19557 1.19875 1.20193 1.20511 1.20829 11 1.16493 1.16810 1.17127 1.17444 1.17760 1.18077 1.18394 1.18710 1.19027 1.19344 1.19660 1.19977 1.20294 12 1.15979 1.16295 1.16611 1.16926 1.17242 1.17558 1.17873 1.18189 1.18505 1.18820 1.19136 1.19452 1.19768 13 1.15459 1.15774 1.16088 1.16403 1.16718 1.17032 1.17347 1.17661 1.17976 1.18291 1.18605 1.18920 1.19234 14 1.14933 1.15247 1.15560 1.15873 1.16187 1.16500 1.16814 1.17127 1.17440 1.17754 1.18067 1.18381 1.18694 15 1./4407 1 13873 1.14720 1.14185 1.15032 1.14496 1.15344 1.14807 1.15657 1.15118 1.15969 1.15429 1.16282 1.15741 1.16594 1.16052 1.16906 1.16363 1.17219 1.16674 1.17531 1.16985 1.17844 1.17297 1.18156 1.17608 16 17 a 3 1.13335 1.13645 1.13955 1.14266 1.14576 1.14886 1.15196 1.15506 1.15816 1.16126 1.16436 1.16746 1.17056 18 1 1.12794 1.13103 1.13412 1.13721 1.14030 1.14340 1.14649 1.14958 1.15267 1.15576 1.15886 1.16195 1.16504 19 a 1.12251 1.12559 1.12867 1.13175 1.13483 1.13791 1.14099 1.14408 1.14716 1.15024 1.15332 1.15640 1.15948 20 s 1.11700 1.12007 1.12314 1.12621 1.12928 1.132,36 1.13543 1.13850 1.14157 1.14464 1.14771 1.15078 1.15385 21 1.11145 1.11451 1.11757 1.12063 1.12369 1.12675 1.12982 1.13288 1.13594 1.13900 1.14206 1.14512 .14818 22 1.10581 1,10886 1.11191 .11496 1.11801 1.12106 1.12411 1.12716 1.13021 .13326 1.13631 1.13936 .14241 23 1.10012 .10316 1.10620 .10924 1.11228 1.11532 1.11835 1.12139 1.12443 .12747 1.13051 1.13355 .13659 24 1.09437 .09740 1.10043 .10346 1.10649 1.10952 1.11255 1.11558 1.11861 .12164 1.12467 .12770 .13073 25 746 748 750 752 754 756 758 760 762 764 766 768 770 MILLIMETRES. 164 DETERMINATION. [ 101. heat, add an equal volume of solution of ammonia, digest at a gentle heat, filter after twelve hours, and wash the precipitate with a mixture of equal volumes of water and solution of ammonia. Evaporate the filtrate and first washings to dryness, and treat the residue in the same way as before. If some more phosphate of lithia is thereby obtained, add this to the principal quantity. The process gives, on an average, 99-61 for 100 parts of lithia. If the quantity of lithia present is relatively very small, the larger por- tion of the potassa or soda compounds should first be removed by addi- tion of absolute alcohol to the most highly concentrated solution of the salts (chlorides, bromides, iodides, or nitrates, but not sulphates) ; since this, by lessening the amount of water required to effect the separa- tion of the phosphate of lithia from the soluble salts, will prevent loss of lithia (W. MAYER *). The precipitated basic phosphate of lithia has the formula 3 Li O, P O 5 -f aq. It dissolves in 2539 parts of pure, and 3920 parts of ammo- niated water ; at 100, it completely loses its water ; if pure, it does not cake at a moderate red heat (MAYER). The objections raised by RAMMELSBERG f to MAYER'S method of estima- ting lithia I find to be ungrounded. According to my own experience, it appears that the filtrate and wash-water must be evaporated in a plati- num dish not only once, but at least twice in fact, till a residue is obtained which is completely soluble in dilute ammonia. Phosphate of lithia may be dried at 100, or ignited according to 53, before being weighed. In the latter case, care must be taken to free the filter as much as possible from the precipitate before proceeding to incinerate it. I have thus obtained, J instead of 100 parts carbonate of lithia, by drying at 100, 99-84, 99-89, 100-41, by igniting 99-66 and 100*05. The phos- phate of lithia obtained was free from soda. SECOND GROUP. BARYTA STRONTIA LIME MAGNESIA. 101. 1. BARYTA. a. Solution. Caustic baryta is soluble in water, as are many of the salts of this alka- line earth. The salts of baryta which are insoluble in water are, with al- most the single exception of the sulphate, readily dissolved by dilute hydrochloric acid. The solution of the sulphate is effected by fusion with carbonate of soda, &c. (See 132.) b. Determination. Baryta is weighed either as sulphate or as carbonate, rarely (in the sepa- * Annal. derChem. u. Pharm. 98, 193, where Mayer has also demonstrated the non-existenoe of a phosphate of soda and lithia of fixed composition (Berzeliue), or of varying composition (Rammelsberg). f Pogg. Annal. 102, 443. ; Zeitschr. 1 Analyt. Chem. 1, 4.2. 101.] BARYTA. 165 ration from strontia) as silico-jluoride of barium ( 71). Baryta in the pure state, or in form of carbonate, may also be determined by the volu- metric (alkalimetric) method. Comp. 8 210. We may convert into 1. SULPHATE OF BARYTA. a. By Precipitation. b. By Evaporation. All compounds of baryta without All compounds of baryta with exception. volatile acids, if no other non- vola- tile body is present. 2. CARBONATE OF BARYTA. a. All salts of baryta soluble in water. b. Salts of baryta with organic acids. Baryta is both precipitated and weighed, by far the most frequently as sulphate, the more so as this is the form in which it is most conveniently separated from other bases. The determination by means of evaporati< >n (1,6) is, in cases where it can be applied, and where we are not obliged to evaporate large quantities of fluid, very exact and convenient. Baryta is determined as carbonate in the wet way, when from any reason it is not possible or not desirable to precipitate it as sulphate. If a fluid or dry substance contains bodies which impede the precipitation of the baryta as sulphate or carbonate (alkaline citrates, metaphosphoric acid, see 71, a and 6), such bodies must of course be got rid of, before proceeding to precipitation. 1. Determination as Sulphate of Baryta. a. By Precipitation. Heat the moderately dilute solution of baryta, which must not contain too much free acid (and must, therefore, if necessary, first be freed there- from by evaporation or addition of carbonate of soda), in a platinum or porcelain dish, or in a glass vessel, to incipient ebullition, add dilute sul- phuric acid, as long as a precipitate forms, keep the mixture for some time at a temperature very near the boiling point, and allow the precipitate a few minutes to subside ; decant the almost clear supernatant fluid on a filter, boil the precipitate three or four times with water, then transfer it to the filter, and wash with boiling water, until the filtrate is no longer rendered turbid by chloride of barium. Dry the precipitate, and treat it as directed in 53. If the precipitate has been properly washed in the manner here directed, it is perfectly pure, and gives up no chloride of barium to acetic acid, even if boiling, nor any appreciable trace of it to boiling nitric acid, though the solution had contained that salt.* b. By Evaporation. Add to the solution, in a weighed platinum dish, pure sulphuric acid * I mention this in reference to Siegle's statement in the Journal f. prakt. Chem. 69, 142, that acetic acid and nitric acid will still extract small quantities of chloride of barium from sulphate of baryta, formed in presence of an excess of sulphuric acid, and thoroughly washed with water. 166 DETERMINATION. [ 102. very slightly in excess, and evaporate on the water-bath ; expel the excess of sulphuric acid by cautious application of heat, and ignite the residue. For the properties of sulphate of baryta, see 71. Both methods, if properly and carefully executed, give almost absolutely accurate results. 2. Determination as Carbonate of Baryta. a. In Solutions. Mix the -moderately dilute solution of the baryta salt in a beaker with ammonia, add carbonate of ammonia in slight excess, and let the mixture stand several hours in a warm place. Filter, wash the precipitate with water mixed with a little ammonia, dry, and ignite ( 53)- For the properties of the precipitate, see 71. This method in- volves a trifling loss of substance, as the carbonate of baryta is not ab- solutely insoluble in water. The direct experiment, No. 62, gave 9 9 '79 instead of 100. If the solution contains a notable quantity of ammoniacal salts, the loss incurred is much more considerable, since the presence of such salts greatly increases the solubility of the carbonate of baryta. b. In Salts of Baryta with Organic Acids. Heat the salt slowly in a covered platinum crucible, until no more fumes are evolved ; place the crucible obliquely, with the lid leaning against it, and ignite, until the whole of the carbon is consumed, and the residue presents a perfectly white appearance : moisten the residue with a concentrated solution of carbonate of ammonia, evaporate, ignite gently, and weigh. The results obtained by this method are quite satisfactory. A direct experiment, No. 63, gave 99'61 instead of 100. The loss of substance which almost invariably attends this method is owing to particles of the salt being carried away with the fumes evolved upon ignition, and is accordingly the less considerable, the more slowly and gradually the heat is increased. Omission of the moistening of the residue with carbonate of ammonia would involve a further loss of substance, as the ignition of carbonate of baryta in con- tact with carbon is attended with formation of some caustic baryta, car- bonic oxide gas being evolved. 102. 2. STRONTIA. a. Solution. See the preceding paragraph ( 101, a. Solution of baryta), the directions there given applying equally here. b. determination. Strontia is weighed either as sulphate or as carbonate of strontia ( 72). Strontia in the pure state, or in form of carbonate, maybe de- termined also by the volumetric (alkalimetric) method. Cornp. 210. We may convert into 102.] STRONTIA. 167 1. SULPHATE OP STRONTIA. a. By Precipitation. All compounds of strontia without exception. b. J3y Evaporation. All salts of strontia with volatile acids, if no other non-volatile bodj is present. 2. CARBONATE OF STRONTIA. a. All compounds of strontia soluble in water. /3. Salts of strontia with organic acids. The method based on the precipitation of strontia with sulphuric acid yields accurate results only in cases where the fluid from which the strontia is to be precipitated may be mixed, without injury, with alco- hol. Where this cannot be done, and where the method based on the evaporation of the solution of strontia with sulphuric acid is equally inapplicable, the conversion into the carbonate ought to be resorted to in preference, if admissible. As in the case of baryta, so here, we have to be on our guard against the presence of substances which would im- pede precipitation. 1. Determination as /Sulphate of Strontia. a. J3y Precipitation. Mix the solution of the salt of strontia (which must not be too dilute, nor contain much free hydrochloric or nitric acid) with dilute sulphuric acid in excess, in a beaker, and add at least an equal volume of alcohol ; let the mixture stand twelve hours, and filter ; wash the precipitate with dilute spirit of wine, dry and ignite ( 53). If the circumstances of the case prevent the use of alcohol, the fluid must be precipitated in a tolerably concentrated state, allowed to stand in the cold' for at least twenty-four hours, filtered, and the precipitate washed with cold water, until the last rinsings manifest no longer an acid reaction, and leave no perceptible residue upon evaporation. If traces of free sulphuric acid remain adhering to the filter, the latter turns black on drying, and crumbles to pieces ; too protracted washing of the precipitate, on the other hand, tends to increase the loss of sub- stance. Care must be taken that the precipitate be thoroughly dry, before proceeding to ignite it ; otherwise it will be apt to throw off fine par- ticles during the latter process. The filter, which is to be burnt apart from the precipitate, must be as clean as possible, or some loss of sub- stance will be incurred ; as may be clearly seen from the depth of the carmine tint of the flame with which the filter burns if the precipitate has not been properly removed. For the properties of the precipitate, see 72. When alcohol is used and the directions given are properly adhered to, the results are very accurate ; when the sulphate of strontia is precipitated from an aqueous solution, on the contrary, a certain amount of loss is unavoid- able, as sulphate of strontia is not absolutely insoluble in water. The direct experiments, No. 64, gave only 9S'12 and 98'02 instead of 100. However, the error may be rectified, by calculating the amount of sul- 168 DETERMINATION. [ 103. phate of strontia dissolved in the filtrate and the wash-water, basing the calculation upon the known degree of solubility of sulphate of strontia in pure and acidified water. See Expt. No. 65, which, with this correction, gave 99'77 instead of 100. b. By Evaporation. The same method as described for baryta, 101, 1, 5. 2. Determination as Carbonate of Strontia. a. In Solutions. The same method as described 101, 2, a. For the properties of the precipitate, see 72. The method gives very accurate results, as car- bonate of strontia is nearly absolutely insoluble in water containing ammonia and carbonate of ammonia. A direct experiment, No. 66, gave 99 '82 instead of 100. Presence of ammoniacal salts exercises here a less adverse influence than the precipitation of carbonate of baryta. b. In Salts with Organic Acids. The same method as described 101, 2, b. The remarks made there, especting the accuracy of the results, apply equally here. f . 103. 3. LIME. a. Solution. See 101, a. Solution of baryta. Fluoride of calcium is, by means of sulphuric acid, converted into sulphate of lime, and the latter again, if necessary, decomposed by boiling or fusing with an alkaline carbon- ate ( 132). [Sulphate of lime dissolves readily in moderately dilute hydrochloric acid. It is much less soluble in strong hydrochloric acid.] b. Determination. Lime is weighed either as sulphate, or as carbonate of lime ( 73). It may be brought into the first form by evaporation, or by precipitation ; into the latter, by precipitation as oxalate, or at once as carbonate, or by ignition. Small quantities of lime are also occasionally reduced to the caustic state, instead of being converted into carbonate. Lime in the pure state, or in form of carbonate, may be determined also by the volumetric (alkalimetric) method. Comp! 210. We may convert into 1. SULPHATE OF LIME. a. By Precipitation. All salts of lime with acids soluble in alcohol, provided no other sub- stance insoluble in alcohol be present. LIME. 169 b. By Evaporation. All salts of lime with volatile acids, provided no non-volatile body be present. 2. CARBONATE OF LIME. a. By Precipitation with Carbonate of Ammonia. All salts of lime soluble in water. b. By Precipitation with Oxalate of Ammonia. All salts of lime soluble in water or in hydrochloric acid without exception. c. By Ignition. Salts of lime with organic acids. Of these several methods, 2, b (precipitation with oxalate of ammonia) is the one most frequently resorted to. This, and the method 1, 6, give the most accurate results. The method, 1, a, is usually resorted to only to effect the separation of lime from other bases; 2, a, generally only to effect the separation of lime together with other alkaline earths from the alkalies. As many bodies (alkaline citrates, and metaphosphates) inter- fere with the precipitation of lime by the precipitants given, these, if pre- sent, must be first removed. 1. Determination as Sulphate of Lime. a. By Precipitation. Mix the solution of lime in a beaker, with dilute sulphuric acid in excess, and add twice the volume of alcohol ; let the mixture stand twelve hours, filter, and thoroughly wash the precipitate with spirit of wine, dry, and ignite moderately ( 53). For the properties of the precipitate, see 73. The results are very accurate. A direct experiment, No. 67, gave 99-64 instead of 100. b. By Evaporation. The same method as described 101, 1, b. 2. Determination as Carbonate of Lit a. By Precipitation with Carbonate of Ammonia. The same method as described 101, 2, a. The precipitate must be exposed only to a very gentle red heat, but this must be continued for some time. For the properties of the precipitate, see 73. This method gives very accurate results, the loss of substance incurred being hardly worth mentioning. If the solution contains chloride of ammonium or similar ammoniacal salts in considerable proportion, the loss of substance incurred is far greater. The same is the case if the precipitate is washed with pure in- stead of ammoniacal water. A direct experiment, No. 68, in which pure water was used, gave 99*17 instead of 100 parts of lime. 170 DETERMINATION. [ 103. b. By Precipitation with Oxalate of Ammonia. a. The Lime Salt is soluble in Water. To the hot solution in a beaker, add oxalate of ammonia in moderate excess, and then ammonia sufficient to impart an ammoniacal smell to the fluid ; cover the glass, and let it stand in a warm place until the precipitate has completely subsided, which will require twelve hours, at least. Pour the clear fluid gently and cautiously, so as to leave the precipitate undisturbed, on a filter ; wash the precipitate two or three times by decantation with hot water; lastly, transfer the precipitate also to the filter, by rinsing with hot water, taking care, before the ad- dition of a fresh portion, to wait until the fluid has completely passed through the filter. Small particles of the precipitate, adhering firmly to the glass, are removed with a feather. If this fails to eft'ect their com- plete removal, they should be dissolved in a few drops of highly dilute hydrochloric acid, ammonia added to the solution, and the oxalate ob- tained added to the first precipitate. Deviations from the rules laid down here will generally give rise to the passing of a turbid fluid through the filter. After having washed the precipitate, dry it on the filter in the funnel, and transfer the dry precipitate to a platinum cru- cible, taking care to remove it as completely as possible from the filter ; burn the filter on a piece of platinum wire, letting the ash drop into the hollow of the lid ; put the latter, now inverted, on the crucible, so that the filter ash may not mix with the precipitate ; heat at first very gently, then more strongly, until the bottom of the crucible is heated to very faint redness. Keep it at that temperature from ten to fifteen minutes, removing the lid from time to time. I am accustomed during this opera- tion to move the lamp backwards and forwards under the crucible with the hand, since, if you allow it to stand, the heat may very easily get too high. Finally allow to cool in the desiccator and weigh. After weighing, moisten the contents of the crucible, which must be perfectly white, or barely show the least tinge of gray, with a little water, and test this after a time with a minute slip of turmeric paper. Should the paper turn brown a sign that the heat applied was too strong rinse off the fluid adhering to the paper with a little water into the crucible, throw in a small lump of pure carbonate of ammonia, evaporate to dry- ness (best in the water-bath), heat to very faint redness, and weigh the residue. If the weight has increased, repeat the same operation un- til the weight remains constant. This method gives nearly absolutely accurate results; and if the application of heat is properly managed, there is no need of the tedious evaporation with carbonate of ammonia. A direct experiment, No. 69, gave 99'99 instead of 100. For the properties of the precipitate and residue, see 73. If the quantity of oxalate of lime obtained is only very trifling, I pre- fer to convert it into caustic lime or into the sulphate. To effect the former, the oxalate of lime is heated to intense redness, in a small plati- num crucible, over a gas blow-pipe flame for some time. The conver- sion of the oxalate into sulphate is effected most conveniently by SCHROT- TER'S method, viz., ignition with pure sulphate of ammonia. Many chemists prefer collecting the oxalate of lime upon a weighed filter, and drying at 100. Thus obtained it consists of 2 Ca O, C 4 O 6 -|-2 aq. This method, besides being more tedious, gives less accurate results 104.] MAGNESIA. 17] than that based on the conversion of the oxalate into the carbonate. The direct experiment, No. 70, gave 100*45 instead of 100. Instead of weighing the oxalate of lime as such, or in form of carbon- ate, &c., the quantity of lime present in the salt may be determined also by two different volumetric methods. a. Ignite the oxalate, converting it thus into a mixture of carbonate and caustic lime, and determine the quantity of the lime by the alkalimet- ric method described in 210 ; or, b. Determine the oxalic acid in the well- washed but still moist oxalate of lime by means of permanganate of potassa ( 137), and reckon for each equivalent of bibasic oxalic acid 2 equivalents of lime (HEMPEL). With proper care, both these volumetric methods give as accurate results as those obtained by weighing. (Comp. Expt. No. 71.) They deserve to be recommended more particularly in cases where an entire series of quantitative estimations of lime has to be made. Under certain circumstances it may also prove advantageous to precipitate the lime with a measured quantity of a standard solution of oxalic acid or qua- droxalate of potassa, filter, and determine the excess of oxalic acid in the filtrate. (KRAUT.*) /3. The Salt is insoluble in ^Wetter. Dissolve the salt in dilute hydrochloric acid. If the acid combined with the lime is of a nature to escape in this operation (e.g., carbonic acid), or to admit of its separation by evaporation (e.g., silicic acid), proceed, after the removal of the acid, as directed in a. But if the acid cannot thus be readily got rid of (e.g., phosphoric acid), proceed as fol- lows: add ammonia until a precipitate begins to form, re-dissolve this with a drop of hydrochloric acid, add oxalate of ammonia in excess, and finally acetate of soda ; allow the precipitate to subside, and proceed for the remainder of the operation as directed in a. In this process the free hydrochloric acid present combines with the ammonia and soda of the oxalate and acetate, liberating a corresponding quantity of oxalic acid and acetic acid, in which acids oxalate of lime is nearly insoluble. The method yields accurate results. A direct experiment, No. 72, gave 99-78 instead of 100. c. J3y Ignition. The same method as described 101, 2, b (baryta). The residue re- maining upon evaporation with carbonate of ammonia (which operation it is advisable to perform twice) must be ignited very gently. The remarks made in 101, 2, 6, in reference to the accuracy of the results, apply equally here. By way of control, the carbonate of lime may be converted into the caustic state or into sulphate of lime (see 6, a), or it may be determined alkalimetrically (210). 104. 4. MAGNESIA. a. Solution. Many of the compounds of magnesia are soluble ir. water ; those * Chem. Centralblatt, 1856, 316. 172 DETERMINATION. [ 104. which are insoluble in that menstruum dissolve in hydrochloric acid, with the exception of some silica tes and aluminates. b. Determination. Magnesia is weighed (74) either as sulphate or as pyropliospliate, 01 as pure, magnesia. In the pure state, or in form of carbonate, it may be determined also by the alkalimetric method described in 210. We may convert into 1. SULPHATE OF MAGNESIA. a. Directly. b. Indirectly. All compounds of magnesia with All compounds of magnesia so- volatile acids, provided no other non- luble in water, and also those volatile substance be present. which, insoluble in that men- struum, dissolve in hydrochloric acid, with separation of their acid (provided no ammoniacal salts be present). 2. PYROPHOSPHATE OF MAGNESIA. All compounds of magnesia without exception. 3. PURE MAGNESIA. a. Salts of magnesia with oiganic acids, or with readily volatile in- organic oxygen acids. b. Chloride of magnesium, and the compounds of magnesia converti- ble into that salt. The direct determination as sulphate of magnesia is highly recom- mended in all cases where it is applicable. The indirect conversion into the sulphate serves only in the case of certain separations, and is hardly ever had recourse to where it can possibly be avoided. The deter- mination as pyrophosphate is most generally resorted to ; especially also in the separation of magnesia from other bases. The method based on the conversion of chloride of magnesium into pure magnesia is usually resorted to only to effect the separation of magnesia from the fixed alka- lies. Compounds of magnesia with phosphoric acid are analyzed as 134 directs. 1. Determination as Sulpliate of Magnesia. Add to the solution excess of pure dilute sulphuric acid, e\aporate to dryness, in a weighed platinum dish, on the water-bath ; then heat at first cautiously, afterwards, with the cover on more strongly here it is advisable to place the lamp so that the flame may play obliquely on the cover from above until the excess of sulphuric acid is completely expelled ; lastly, ignite gently over the lamp for some time ; allow to cool, and weigh. Should no fumes of hydrated sulphuric acid escape upon the application of a strongish heat, this may be looked upon as a sure sign that the sulphuric acid has not been added in sufficient quan- tity, in which case, after allowing to cool, a fresh portion of sulphuric acid is added. The method yields very accurate results. Care must be taken not to use a very large excess of sulphuric acid. The residue must 104.] MAGNESIA. 173 be exposed to a moderate red heat only, and weighed rapidly. For the properties of the residue, see 74. 2. Determination as Pyrophospliate of Magnesia. The solution of the salt of magnesia is mixed, in a beaker, with chlo- ride of ammonium, and ammonia added in slight excess. Should a pre- cipitate form upon the addition of ammonia, this may be considered a sign that a sufficient amount of chloride of ammonium has not been used ; a fresh amount of that salt must consequently be added, sufficient to effect the re-solution of the precipitate formed. The clear fluid is then mixed with a solution of phosphate of soda in excess, and the mix- ture stirred, taking care to avoid touching the sides of the beaker with the stirring-rod ; otherwise particles of the precipitate are apt to adhere so firmly to the rubbed parts of the beaker, that it will be found difficult to remove them ; the beaker is then covered, and allowed to stand at rest for twelve hours, without warming ; after that time the fluid is fil- tered, and the precipitate collected on the filter, the last particles of it being rinsed out of the glass with a portion of the filtrate, with the aid of a feather ; when the fluid has completely passed through, the precipi- tate is washed with a mixture of 3 parts of water', and 1 part of solution of ammonia of 0*06 sp. gr., the operation being continued until a few drops of the fluid passing through the filter mixed with nitric acid and a drop of nitrate of silver show only a very slight opalescence. The precipitate is now thoroughly dried, and then transferred to a platinum crucible ( 53) ; the latter, with the lid on, is exposed for some time to a very gentle heat, which is finally increased to intense redness. The filter, as clean as practicable, is incinerated in a spiral of platinum wire, and the ash transferred to the crucible, which is then once more exposed to a red heat, allowed to cool, and weighed. For the properties of the precipitate and residue, see 74. This method, if properly executed, yields most accurate results. The precipitate must be washed completely, but not over-washed, and the washing water must always contain the requisite quantity of ammonia. Direct experiments, No. 73, a and b, gave respectively 10O43 and 100-30 instead of 100. 3. Determination as pure Magnesia. a. In Salts of Magnesia with Organic or Volatile Inorganic Acids. The salt of magnesia is gently heated in a covered platinum crucible, increasing the temperature gradually, until no more fumes escape ; the lid is then removed, and the crucible placed in an oblique position, with the lid leaning against it. A red heat is now applied, until the residue is perfectly white. For the properties of the residue, see 74. The method gives the more accurate results the more slowly the salt is heated from the beginning. Some loss of substance is usually sustained, owing to traces of the salt being carried off with the empyreumatic products. Salts of magnesia with readily volatile oxygen acids (carbonic acid, nitric acid), may be transformed into magnesia in a similar way, by sim- ple ignition. Even sulphate of magnesia loses the whole of its sulphuric acid when exposed, in a platinum crucible, to the heat of the gas blow- pipe-flame (SONNENSVHEIN). As regards small quantities of sulphate of magnesia, I can fully confirm this statement. 174 DETERMINATION. [ 105. b. Conversion of Chloride of Magnesium into pure Magnesia. See 153, 4, 7. THIRD GROUP OF THE BASES. ALUMINA SESQUIOXIDE OF CHROMIUM (TITANIC ACID). 105. 1. ALUMINA. a. Solution. Those of the compounds of alumina which are insoluble in water, dissolve, for the most part, in hydrochloric acid. Native crystallized alumina (sapphire, ruby, corundum, &c.), and many native alumina com- pounds, and also artificially produced alumina after intense ignition, require fusing with carbonate of soda, caustic potassa, or hydrate of baryta, as a preliminary step to their solution in hydrochloric acid. Many alumina compounds which resist the action of concentrated hydro- chloric acid, may be decomposed by protracted heating with moderately concentrated sulphuric acid, or by fusion with bisulphate of potassa; e.g., common clay. b. Determination. Alumina is invariably weighed in the pure state ( 75). The several compounds of alumina are converted into pure alumina, either by preci- pitation as hydrate of alumina, and subsequent ignition, or by simple ignition. Precipitation as basic acetate or basic formiate is resorted to only in cases of separation. We may convert into PURE ALUMINA. a. J3y Precipitation* b. JBy Heating or Ignition. All compounds of alumina solu- a. All salts of alumina with ble in water, and those which, in- readily volatile acids (e.g., nitrate soluble in that menstruum, dis- of alumina). solve in hydrochloric acid, with se- j3. All salts of alumina with or- paration of their acid. ganic acids. "With regard to the method a, it must be remembered that the solu- tion must contain no organic substances, which would interfere with the precipitation e.g., tartaric acid, sugar, &c. Should such be present, the solution must be mixed with carbonate of soda and nitrate of potassa, evaporated to dryness in a platinum dish, the residue fused, then soft- ened with water, transferred to a beaker, digested with hydrochloric acid, and the solution filtered, and then, but not before, precipitated. The methods 6, a, and j3, are applicable only in cases where no other fixed substances are present. The methods of estimating alumina in its combinations with phosphoric, boracic, silicic, and chromic acids, will be found in Part II. of this Section, under the heads of these several acids. 105.] ALUMINA. 175 Determination as pure Alumina. a. By Precipitation. Mix the moderately dilute hot solution of alumina, in a beaker or dish, with a tolerable quantity of chloride of ammonium, if that salt is not already present ; add ammonia slightly in excess, boil gently till the steam ceases to brown turmeric paper, allow to settle ; then decant the clear supernatant fluid on to a filter, taking care not to disturb the precipitate ; pour boiling water on the latter in the beaker, stir, let the precipitate subside, decant again, and repeat this operation of washing by decantation a second and a third time ; transfer the precipitate now to the filter, finish the washing with boiling water, dry thoroughly, ignite ( 52), and weigh. The heat applied should be very gentle at first, and the crucible kept well covered, to guard against the risk of loss of substance from spirting, which is always to be apprehended if the pre- cipitate is not thoroughly dry ; towards the end of the process the heat should be raised to intense redness. In the case of sulphate of alumina the foregoing process is apt to leave some sulphuric acid in the precipi- tate, which, of course, vitiates the result. To insure the removal of this sulphuric acid, the precipitate should be exposed for 5-10 rnin. to the heat of the gas blowpipe flame. If there are difficulties in the way, preventing this proceeding, the precipitate, either simply washed or mo- derately ignited, must be re-dissolved in hydrochloric acid (which re- quires protracted warming with strong acid), and then precipitated again with ammonia ; or the sulphate must first be converted into nitrate by decomposing it with nitrate of lead, added in very slight excess, the ex- cess of lead removed by means of hydrosulphuric acid, and the further process conducted according to the directions of a or b. For the pro- perties of hydrate of alumina and ignited alumina, see 75. The method, if properly executed, gives very accurate results. But if a con- siderable excess of ammonia is used, more particularly in the absence of ainmoniacal salts, and the liquid is filtered without boiling or long standing in a warm place to remove the ammonia, no trifling loss may be incurred. This loss is the greater, the more dilute the solution, and the larger the excess of ammonia. The precipitate cannot well be suffici- ently washed on the filter on account of its gelatinous nature ; on the other hand, if it be entirely washed by decantation, a very large quan- tity of wash-water must be used, hence it is advisable to combine the two methods, as directed.* b. By Ignition. a. Compounds of Alumina with Volatile Acids. Ignite the salt (or the residue of the evaporated solution) in a pla- tinum crucible, gently at first, then gradually to the very highest degree of intensity, until the weight remains constant. For the properties of the residue, see 75. Its purity must be carefully tested. There are no sources of error. * [When a solution of alumina in hydrate of potassa or hydrate of soda is boiled with excess of chloride of ammonium, the alumina separates completely as a hydrate with two eq. of water, which may be washed with comparative eate. In certain cases, as where alumina is separated from sesqui oxide of iron ^>>T hydrate of soda, this fact may be taken advantage of. LoWE, Fres. Zeitschriit, IV. 355.] 176 DETERMINATION. [ 106. |3. Compounds of Alumina with Organic Acids. The same method as described 104, 3, a (Magnesia). 106. 2. SESQUIOXIDE OF CHROMIUM. a. Solution. Many of the compounds of sesquioxide of chromium are soluble in water. The hydrated sesquioxide, and most of the salts insoluble in water, dissolve in hydrochloric acid. Ignition renders sesquioxide of chromium and many of its salts insoluble in acids ; this insoluble modi- fication must be prepared for solution in hydrochloric acid, by fusing with 3 or 4 parts of potassa. A small quantity is converted, in the process of fusing, into chromic acid, by the action of the air ; this is, however, reduced again to sesquioxide upon heating with hydrochloric acid. Addition of alcohol greatly promotes the reduction. Instead of this fusing with potassa, we frequently prefer to adopt a treatment, whereby the sesquioxide is at once oxidized and converted into an alkaline chromate (see 2). For the solution of chromic iron, see 160. b. Determination. Sesquioxide of chromium is always, when directly determined, weighed in the pure state. It is brought into this form either by pre- cipitation as hydrate and ignition, or by simple ignition. It may, how- ever, also be estimated, by conversion into chromic acid, and determi- nation as such. We may convert into 1. PURE SESQUIOXIDE OF CHROMIUM. a. Hy Precipitation. b. By Ignition. All compounds of sesquioxide a. All salts of sesquioxide of of chromium soluble in water, and chromium with volatile oxygen also those which, insoluble in that acids, provided no non-volatile sub- menstruum, dissolve in hydrochlo- stances be present. ric acid, with separation of their 0. Salts of sesquioxide of chro- acid. Provided always that no mium with organic acids, organic substances (such as tartaric acid, oxalic acid, &c.) which inter- fere with the precipitation be pre- sent. 2. CHROMIC ACID, or, more correctly speaking, ALKALINE CHROMATE. Sesquioxide of chromium and all its salts. The methods of analyzing the combinations of the sesquioxide of chromium with chromic acid, phosphoric acid, boracic acid, and silicic acid, will be found in Part II. of this Section, under the heads of these several acids. 1. Determination as /Sesquioxide of Chromium. a. By Precipitation. The solution, which must not be too highly concentrated, is heated 106.] SESQUIOXIDE OF CHROMIUM. 177 to 100 in a beaker. Ammonia is then added slightly in excess, and the mixture exposed to a temperature approaching boiling, until the fluid over the precipitate is perfectly colorless, presenting no longer the least shade of red ; let the solid particles subside, wash three times by decantation, and lastly on the filter, with hot water, dry thoroughly, and ignite ( 52). The heat in the latter process must be increased gradually, and the crucible kept covered, otherwise some loss of sub- stance is likely to arise from spirting upon the incandescence of the ses- quioxide of chromium which marks the passing of the soluble into the insoluble modification. For the properties of the precipitate and resi- due, see 76. This method, if properly executed, gives very accurate results. b. By Ignition. a. Salts of Sesquioxide of Chromium with Volatile Acids. The same method as described, 105, b, a (Alumina). b. Salts of Sesquioxide of Chromium with Organic Acids. The same method as described 104, 3, a (Magnesia). 2. CONVERSION OF SESQUIOXIDE OF CHROMIUM INTO CHROMIC ACID. (For the estimation of chromic acid, see 130.) The following methods have been proposed with this view : a. The solution of the salt of sesquioxide of chromium is mixed with solution of potassa or soda in excess, until the hydrated sesquioxide, which forms at first, is redissolved. Chlorine gas is then conducted into the cold fluid until it acquires a yellowish-red tint ; it is then mixed with potassa or soda in excess, and the mixture evaporated to dryness ; the residue is ignited in a platinum crucible. The whole of the chlorate of potassa (or soda) formed is decomposed by this process, and the residue consists, therefore, now of an alkaline chromate and chloride of potassium (or sodium). (VoHL.) b. Hydrate of potassa is heated in a silver crucible to calm fusion ; the heat is then somewhat moderated, and the perfectly dry com- pound of sesquioxide of chromium projected into the crucible. When the sesquioxide of chromium is thoroughly moistened with the potassa, small lumps of fused chlorate of potassa are added. A lively efferve- scence ensues, from the escape of oxygen; at the same time the mass acquires a more and more yellow color, and finally becomes clear and transparent. Loss of substance must be carefully guarded against (H. SCHWARZ). c. Dissolve the sesquioxide of chromium in solution of potassa or soda, add binoxide of lead in sufficient excess, and warm. The yellow fluid produced contains all the chromium as chromate of lead in alka- line solution. Filter from the excess of binoxide of lead, add to the filtrate acetic acid to acid reaction, and determine the weight of the precipi- tated chromate of lead (G. CHANCEL *). \d. Render the solution of sesquioxide of chromium nearly neutral by a solution of carbonate of soda, add acetate of soda in excess, heat and add chlorine water, or pass in chlorine gas, keeping the solution nearly neutral by occasional addition of carbonate of soda. The oxida- * Comp. rend. 43, 937. 12 178 DETERMINATION. [ 107. tion proceeds readily. Boil off excess of chlorine, when the chromic acid may be precipitated as chromate of lead or chromate of baryta (W. GIBBS*).] Supplement to the Third Group. TITANIC ACID. Titanic acid is always weighed in the pure state ; its separation is effected either by precipitation with an alkali or by boiling its dilute acid solution. In precipitating acid solutions of titanic acid ammonia is employed ; take care to add the precipitating agent only in slight excess, let the precipitate formed, which resembles hydrate of alumina, deposit, wash, first by decantation, then completely on the filter, dry, and ignite ( 52). If the solution contained sulphuric acid, put some carbonate of ammonia into the crucible, after the first ignition, to se- cure the removal of every remaining trace of that acid. Lose no time in weighing the ignited titanic acid, as it is slightly hygroscopic. If we have titanic acid dissolved in sulphuric acid, as for instance occurs when we fuse it with bisulphate of potassa and treat the mass with cold water, we may, by largely diluting, and long boiling, with renewal of the evaporating water, fully precipitate the titanic acid. Thus separated, it is easy to wash. In the process of igniting the dried pre- cipitate, some carbonate of ammonia is added. From dilute hydro- chloric acid solutions of titanic acid, the latter separates completely only upon evaporating the fluid to dryness ; and if the precipitate in that case were washed with pure water, the filtrate would be milky ; acid must, therefore, be added to the water. Hydrate of titanic acid precipitated in the cold, washed with cold water, and dried without elevation of temperature, is completely solu- ble in hydrochloric acid ; otherwise it dissolves only incompletely in that acid. Titanic acid thrown down from dilute acid solutions by boiling, is not soluble in dilute acids. Ignited titanic acid does not dis- solve even in concentrated hydrochloric acid, but it does dissolve by long heating with tolerably concentrated sulphuric acid. The easiest way of effecting its solution is to fuse it for some time with bisulphate of potassa, and treat the fused mass with a large quantity of cold water. Upon fusing with carbonate of soda, titanate of soda is formed, which, when treated with water, leaves acid titanate of soda, which is soluble in hydrochloric acid. Titanic acid (Ti O 2 ) consists of 60*98 per cent, of titanium, and 39'02 per cent, of oxygen. FOURTH GROUP OP THE BASES. OXIDE OF ZINC PROTOXIDE OF MANGANESE PROTOXIDE OF NICKEL- PROTOXIDE OF COBALT PROTOXIDE OF IRON SESQUIOXIDE OF IRON (SESQUIOXIDE OF URANIUM). * [Am. Journ. Sci. 2 Ser. 39, 58.] OXIDE OF ZINC. 108. 1. OXIDE OF ZINC. a. Solution. ^ Many of the salts of zinc are soluble in water. Metallic zinc, oxide of zinc, and the salts, which are insoluble in water, dissolve in hydrochloric acid. To dissolve sulphide of zinc it is best to employ nitric acid or aqua regia. b. Determination. Zinc is weighed either as oxide or as sulphide ( 77). The conversion of the salts of zinc into the oxide is effected either by precipitation as basic carbonate or sulphide of zinc, or by direct ignition. Besides these gravimetric methods, several volumetric methods are in use. We may convert into .1. OXIDE OF ZINC. a. By Precipitation as Carbonate b. By Precipitation as Sulphide of Zinc. of Zinc. All the salts of zinc which are All compounds of zinc without soluble in water, and all those with exception. organic volatile acids ; also those salts of zinc which, insoluble in water, dissolve in hydrochloric acid, with separation of their acid. c. By direct Ignition. Salts of zinc with volatile inorganic oxygen acids. 2. SULPHIDE OF ZINC. All compounds of zinc without exception. The method 1, c, is to be recommended only, as regards the more fre- quently occurring compounds of zinc, for the carbonate and the nitrate. The methods 1, &, or 2, are usually only resorted to in cases where 1, a, is inadmissible. They serve more especially to separate oxide of zinc from other bases. Salts of zinc with organic acids cannot be converted into the oxide by ignition, since this process would cause the reduction and volatilization of a small portion of the metal. If the acids are volatile, the zinc may be determined at once, according to method 1, a : if, on the contrary, the acids are non-volatile, the zinc is best precipitated as sul- phide. For the analysis of chromate, phosphate, borate, and silicate of zinc, look to the several acids. The volumetric methods are chiefly em- ployed for technical purposes ; see Special Part. 1. Determination as Oxide of Zinc. a. By Precipitation as Carbonate of Zinc. Heat the moderately dilute solution nearly to boiling in a capacious vessel, best in a platinum dish ; add, drop by drop, carbonate of soda in excess ; boil a few minutes ; allow to subside, decant through a filter, and boil the precipitate three times with water, decanting each time ; then 180 DETERMINATION. [ 108. transfer the precipitate to the filter, wash completely with hot water, dry, and ignite as directed 53, taking care to have the filter as clean as prac- ticable, before proceeding to incinerate it. Should the solution contain ammoniacal salts, the ebullition must be continued until, upon a fresh addi- tion of the carbonate of soda, the escaping vapor no longer imparts a brown tint to turmeric paper. If the quantity of ammoniacal salts present is con- siderable, the fluid must be evaporated boiling to dryness. It is, therefore, in such cases more convenient to precipitate the zinc as sulphide (see b). The presence of a great excess of acid in the solution of zinc must be as much as possible guarded against, that the effervescence from the escaping carbonic acid gas may not be too impetuous. The filtrate must always be tested with sulphide (with addition of chloride) of ammonium to ascertain whether the whole of the zinc has been precipitated ; a slight precipitate will indeed invariably form upon the application of this test ; but, if the process has been properly conducted, this is so insignificant that it may be altogether disregarded, being limited to some exceedingly slight and im- ponderable flakes, which moreover make their appearance only after many hours' standing. If the precipitate is more considerable, however, it must be treated as directed in 5, and the weight of the oxide of zinc obtained added to that resulting from the first process. For the properties of the precipitate and residue, see 77. This method yields pretty accurate results, though they are in most cases a little too low, as the precipitation is never absolutely complete, and as particles of the precipitate will always and unavoidably adhere to the filter, which exposes them to the chance of reduction and volatilization during the process of ignition. On the other hand, the results are sometimes too high ; this is owing to defective washing, as may be seen from the alkaline reaction which the residue manifests in such cases. It is advisable also to ascertain whether the residue will dissolve in hydrochloric acid without leaving silicic acid ; this latter precaution is in- dispensable in cases where the precipitation has been effected in a glass vessel. [It is often better, especially in presence of ammonia salts, to heat the dry zinc salt with excess of carbonate of soda in a platinum dish cau- tiously to near redness, then treat with hot water and wash as directed.] b. By Precipitation as Sulphide of Zinc. Mix the solution, contained in a not too large flask and sufficiently diluted, with chloride of ammonium, then add ammonia, till the reaction is just alkaline, and then colorless or slightly yellow sulphide of ammo- nium in moderate excess. If the flask is not now quite full up to the neck, make it so with water, cork, allow to stand 12 to 24 hours in a warm place, wash the precipitate, if considerable, first by decantation, then on the filter with water containing sulphide of ammonium and also less and less chloride of ammonium (finally none). In decanting do not pour the fluid through the filter, but at once into a flask. After thrice decanting, filter the fluid that was poured off, and then transfer the precipitate to the filter, finishing the washing as directed. The funnel is kept covered with a glass plate. If the zinc is not to be determined according to 2, then put the moist filter with the precipitate in a beaker, and pour over it moderately dilute hydrochloric acid slightly in excess. Put the glass now in a warm place, until the solution smells no longer of sulphuretted hydrogen ; dilute the fluid with a little water, filter, wash the original filter with hot water, and proceed with the solution of chloride of zinc obtained as directed in a. 108.] OXIDE OF ZINC. 181 From a solution of acetate of zinc the metal may be precipitated com- pletely, or nearly so, with sulphuretted hydrogen gas, even in presence of an excess of acetic acid, provided always no other acid be present (Expt. No. 74). The precipitated sulphide of zinc is washed with water impreg- nated with sulphuretted hydrogen, and, for the rest, treated exactly like the sulphide of zinc obtained by precipitation with sulphide of ammonium. Small quantities of sulphide of zinc may also be converted directly in- to the oxide, by heating in an open platinum crucible, to gentle redness at first, then, after some time, to most intense redness. c. By direct Ignition. The salt is exposed, in a covered platinum crucible, first to a gentle heat, finally to a most intense heat, until the weight of the residue remains constant. The action of reducing gases is to be avoided. 2. Determination as /Sulphide of Zinc. The precipitated sulphide of zinc, obtained as in 1, 6, may be ignited in hydrogen and weighed. H. ROSE,* who has lately recommended the process, employs the following apparatus. Fig. 47. a contains concentrated sulphuric acid, 6, chloride of calcium. The porcelain crucible has a perforated porcelain or platinum cover, into the opening of which fits the porcelain or platinum tube, d. The latter is provided with an annular projection which rests on the cover, the tube itself extends some distance into the crucible. When the sulphide of zinc has dried in the filter, it is transferred to the weighed porcelain crucible, the filter ashes added, powdered sulphur is sprinkled over the contents of the crucible, the cover is placed on, and hydrogen is passed in a moderate stream, a gentle heat .is applied at first, which is after- wards raised for five minutes to intense redness ; finally the crucible is * Pogg. Anal. 110, 128. 182 DETERMINATION. [ 109. allowed to cool with continued transmission of the gas, and the sulphide of zinc is weighed. [Instead of the porcelain tube and perforated cover, a common tobacco-pipe may be employed, the bowl of the latter being inverted over or within a porcelain crucible. Sulphuretted hydrogen may be advantageously substituted for hydrogen.] OESTEN'S experiments, which were adduced by ROSE in support of the accuracy of this method, were highly satisfactory. Sulphate, carbonate, and oxide of zinc may be converted into sulphide in the manner just described. They must, however, be mixed with an excess of powdered sulphur, otherwise you will lose some zinc from the reducing action of the hydrogen (H. ROSE). 109. 2. PROTOXIDE OF MANGANESE. a. Solution. Many of the salts of protoxide of manganese are soluble in water. The pure protoxide, and those of its salts which are insoluble in that men- struum, dissolve in hydrochloric acid, which dissolves also the higher oxides of manganese. The solution of the higher oxides is attended with evolution of chlorine equivalent in quantity to the amount of oxygen which the oxide under examination contains, more than the protoxide of manganese and the fluid, after application of heat, is found to con- tain protochloride of manganese. b. Determination. Manganese is weighed either as protosesquioxide, as sulphide, or as pyrophosplmte ( 78.) Into the form of protosesqnioxide it is con- verted either by precipitation as carbonate of protoxide, or as hydrated protoxide, sometimes preceded by precipitation as sulphide of manga- nese, or as binoxide of manganese ; or, finally, by direct ignition. [When estimated as pyrophosphate it is precipitated as ammonio-phos- phate.] Manganese may be determined volumetrically in two different ways, one being applicable to any solution of protoxide of manganese, provided it be free from any other substance which exerts a reducing action on alkaline solution of ferricyanide of potassium, the other being only admis- sible, when we have manganese in the condition of a perfectly definite higher oxide, and free from other bodies, which evolve chlorine on boil- ing with hydrochloric acid. We may convert into 1. PROTOSESQUIOXIDE OF MANGANESE. a. By Precipitation as Oarbo- b. By Precipitation as Hyde at- nate of Protoxide of Manganese. ed Protoxide of Manganese. All the soluble salts of manga- All the compounds of manganese, nese with inorganic acids, and all its with the exception of its salts salts with volatile organic acids ; with non-volatile organic acids, also those of its salts which, insoluble in water, dissolve in hydrochloric acid with separation of their acid. 109.] PROTOXIDE OF MANGANESE. 183 c. By Precipitation as Sulphide d. By Separation as Binoxide of Manganese. of Manganese. All compounds of manganese All compounds of manganese in without exception. a slightly acid solution, especially acetate and nitrate of protoxide o* manganese. e. By direct Ignition. All oxygen compounds of man- ganese ; salts of manganese with readily volatile acids, and with or- ganic acids. 2. SULPHIDE OF MANGANESE. All compounds of manganese without exception. 3. PYROPHOSPHATE OF MANGANESE. All the oxides and many of the salts of manganese. The method 1, e, is simple and accurate, but seldom admissible. The method 1, a, is the most usually employed ; if one's choice is free, it is to be preferred to 1, b. The methods 1, c, and 2, are generally used, when the methods 1, a, or 6, cannot be adopted say on account of the presence of a non- volatile organic substance, and also when we have to separate manganese from other metals. The latter object may be at- tained also by the method 1, d. The process 3, is very convenient and accurate in absence of alkaline earth and heavy metals. The phosphate and borate of manganese are treated, either according to the method 1, 6, as the salts precipitated from acid solution by potassa are com- pletely decomposed upon boiling with excess of potassa, or according to the method 2. In. silicates the manganese is determined after the separation of the silicic acid ( 140), according to 1, a, or 3 ; for the analysis of chromate of protoxide of manganese, see 130 (chromic acid). The volumetric method by reduction of ferricyanide of potas- sium is comparatively new, and especially suited for technical work, in which the highest degree of accuracy is not required. The estima- tion of manganese from the quantity of chlorine disengaged upon boil- ing the oxides with hydrochloric acid, is resorted to, more particu- larly, to determine the degrees of oxidation of manganese, and permits also the estimation of manganese in presence of other metals (see Sec- tion Y). 1. Determination as Protosesquioxide of Manganese. a. By Precipitation as Carbonate of Protoxide of Manganese. The precipitation and washing are effected in exactly the same way as directed 108, 1, a (determination of zinc as oxide, by precipita- tion as carbonate). If the nitrate is not absolutely clear, stand it in a warm place for twelve to twenty-four hours. A slight precipitate will then separate, which is collected on another small filter. The precipi- tate is dried, and then ignited as directed 53. The lid is removed from the crucible, and a strong heat maintained until the weight of the residue remains constant. Care must be taken to prevent reducing 184 DETERMINATION. 100. finding their way into the crucible. For the properties of the precipitate and residue, see 78. This method, if properly executed, gives accurate results. The principal point is to continue the applica- tion of a sufficiently intense heat long enough to effect the object in view. It is necessary also to ascertain whether the residue has not an alkaline reaction, and having removed it from the platinum crucible, whether it dissolves in hydrochloric acid without leaving silica. b. By Precipitation as Jlydrated Protoxide of Manganese. The solution should not be too concentrated, and it is best to have it in a platinum dish. Precipitate with solution of pure soda or potassa, and proceed in all other respects as in a. If phosphoric acid is present, or boracic acid, the fluid must be kept boiling for some time with an excess of alkali. For the properties of the precipitate, see 78. c. By Precipitation as Sulphide of Manganese. The solution contained in a comparatively small flask and not too di- lute is first mixed with chloride of ammonium (if an ammonia salt is not already present in sufficient quantity), then if the fluid is acid with ammonia, till it reacts neutral or very slightly alkaline ; now add yellow sulphide of ammonium in moderate excess, if the flask is not already quite full up to the neck, add water till it is, cork, stand it in a warm place for at least twenty-four hours, wash the precipitate if at all consi- derable, first by decantation, then on the filter, using water containing sulphide of ammonium, and also gradually diminished quantities of chloride of ammonium (finally none). In decanting, pour the fluid in a flask, not on the filter. After decanting three times, filter the fluids that have been poured off, transfer the precipitate to the filter, aud finish the washing as above directed, without interruption. Keep the funnel covered with a glass plate. If you do not prefer to determine according to 2, proceed as follows : Put the moist filter with the precipitate into a beaker, add hydrochloric acid, and warm until the mixture smells no longer of sulphuretted hydrogen ; filter, wash the residuary paper care- fully, and precipitate the filtrate as directed in a. The results are satis- factory, compare 78, e. d. JBy Separation as Binoxide of Manganese. Heat the solution of the acetate of protoxide of manganese or some other compound of the protoxide containing but little free acid, after addition of a sufficient quantity of acetate of soda, bo from 50 to 60, and transmit chlorine gas through the fluid. The whole of the man- ganese present falls down as binoxide (ScniEL, RIVOT, BEUDANT, and DAGUIN). Wash, first by decantation, then upon the filter ; dry, trans- fer the precipitate to a flask, add the filter ash, heat^vith hydrochloric acid, filter, and precipitate as directed in a. If the acetate of soda is deficient, and especially if hydrochloric acid is present, it may happen that the precipitation of the manganese by chlorine is not quite com- plete ; it is therefore well, after filtering off the peroxide, to treat the nitrate with more acetate of soda, and again pass chlorine. The sepa- ration of manganese as binoxide, by evaporating its solution in nitric acid to dryness, and heating the residue, finally to 155, is given in Section Y. 109.] PROTOXIDE OF MANGANESE. 185 [Bromine may be most advantageously substituted for chlorine eras. When the quantity of binoxide is small it may be directly converted into protosesquioxide by intense ignition, as it retains but one or (wo pei cent, of alkali. It may also be estimated as pyrophosphate, 109, 3. e. By direct Ignition. The manganese compound under examination is introduced into a pla- tinum crucible, which is kept closely covered at first, and exposed to a gentle heat ; after a time the lid is taken off', and replaced looselv on the crucible, and the heat is increased to the highest degree of intensity, with careful exclusion of reducing gases ; the process is continued until the weight of the residue remains constant. The conversion of the higher oxides of manganese into protosesquioxide of manganese re- quires more protracted and intense heating than the conversion of the protoxide. In fact, it can hardly be effected without the use of a gas blowpipe. In the case of salts of manganese with organic acids, care must always be taken to ascertain whether the whole of the carbon has been consumed ; and should the contrary turn out to be the case, the residue must either be dissolved in hydrochloric acid, and the solution precipitated as directed in a, or 3 or it mast be repeatedly evaporated with nitric acid, until the whole of the carbon is oxidized. The method, if properly executed, gives accurate results. On the other hand, if the directions are not carefully attended to, one must not be surprised at considerable differences. In the ignition of salts of manganese with organic- acids, minute particles of the salt are generally carried away with the empyreumatic products evolved in the process, which, of course, tends to reduce the weight a little. 2. Determination as Sulphide of Manganese. The sulphide precipitated as in 1, c, may be determined in this form, as follows : Dry, transfer the precipitate to a crucible, burn the filter, add the ashes, strew some sulphur on the top, ignite strongly in hydro- gen (till it becomes black) and weigh as anhydrous sulphide of man- ganese (H. ROSE *), compare the analogous process for zinc, 108, 2. The results obtained by OESTEN, and cited by ROSE, are perfectly sat- isfactory. This method is shorter and more convenient than dissolving the moist sulphide in hydrochloric acid, and precipitating with carbonate of soda. The protosulphate and all the oxides of manganese may be sub- jected to this process with the same result. [3. Determination as Pyrophosphate of Manganese. To the solution of manganese, which may contain salts of ammonia or alkalies, phosphate of soda is added in large excess above what is needful to convert the manganese into phosphate. The white precipitate is then redissolved in sulphuric or chlorhydric acid, the liquid is heated to boiling, best in a platinum dish, and ammonia added in excess. The boiling is continued 1015 minutes, whereby the white, semi-gelatinous precipitate first formed is converted into rose-colored, pearly scales. The whole is kept hot for an hour longer, then filtered and washed with hot water containing a little ammonia. The precipitate of ammonio-phos- * Pogg. Anal. 110, 122. 186 DETERMINATION. [ 109. phate of manganese is dried, separated from the filter, and converted by ignition into pyrophosphate. Results accurate, see 8 78 (GiBBS* HENRY f).] 4. Volumetric determination by the Reduction of Ferricyanide of Potassium (E. LENSSEN J). The method is grounded on the fact that if a solution of protoxide of manganese which contains 1 eq. Fe 2 O 3 to 1 eq. MnO, is acted on by ex cess of alkaline solution of ferricyanide of potassium at a boiling tem- perature, all the manganese is precipitated as binoxide, while a corre- sponding quantity of ferrocyanide of potassium is formed. By deter- mining the latter, the amount of manganese present is obtained. K 3 Cfy 2 +2 KO + MnO,S0 3 =2 K 2 Cfy f KO,SO 3 + MnO,. Accordingly 1 eq. manganese gives rise to 2 eq. ferrocyanide of potas- sium. Of course all other reducing substances must be absent, and the manganese must be present entirely in the form of proto-salt. If the solution contains no sesquioxide of iron, the precipitate is a combination of much binoxide, with little protoxide, not always in the same propor- tions. In performing the process, mix first with the acid solution of protoxide of manganese so much sesquichloride of iron that you may be sure of having at least 1 eq. Fe.,O 3 to 1 eq. MnO, and add the mixture gradually to a boiling solution of ferricyanide of potassium, previously rendered strongly alkaline with potassa or soda. After boiling together a short time the brownish-black precipitate becomes granular aud less bulky. Allow to cool completely, filter off and wash the precipitate, acidify the filtrate with hydrochloric acid, and estimate the ferrocyanide of potassium with permanganate, according to 147, II., g. a. If the liquid is filtered hot, the results are too high, as the filter in this case has a reducing action. The method may be shortened, as follows : After boiling, transfer the solution, together with the precipitate, to a measur- ing flask, allow to cool, fill up to the mark with water, shake, and allow to settle. Filter through a dry filter, take out a certain quantity with a pipette, and determine the ferrocyanide in this. A slight source of error is here introduced by disregarding the volume of the precipitate. The results adduced by LENSSEN are very satisfactory. I have myself repeat- edly tested this method, and I have to remark as follows : a. If ferricyanide of potassium is long boiled with pure potassa, a small quantity of ferrocyanide is invariably produced. b. The potassa must be quite free from organic substances, and should therefore, if there is. any doubt on this point, be fused in a silver dish before use, otherwise the error alluded to in a may be considerably in- creased. c. The complete washing of the voluminous precipitate .is attended with so much difficulty and loss of time as to render the method more troublesome than a gravimetric analysis. d. The abridged method, on the other hand, may be of great service in certain cases, especially when a series of manganese determinations have to be made, the manganese not being in too minute quantities, and the highest degree of accuracy not being required. In my laboratory, by employing a slight excess of sesquioxide of iron, 97*9 100*12 * Am. Jour. Sci. 2d Ser. 44. p. 216. f Am. Jour. Sci. 3d Ser., 47, p. 130. \ Journ. f. prakt. Chem. 80, 408. 110.] PROTOXIDE OF NICKEL. 187 98-21 98-99, and 100-4 were obtained, instead of 100. The inaccuracy increases on using a large excess of the iron.* 5. Volumetric determination by boiling the higher oxides with hydro* chloric acid, and estimating the cMorine evolved. The methods here employed will be found all together in the Special Part under " Valuation of Manganese Ores." no. 3. PROTOXIDE or NICKEL. a. Solution. Many of the salts of protoxide of nickel are soluble in water. Those which are insoluble, as also the pure protoxide, in its common modifica- cation, dissolve, without exception, in hydrochloric acid. The peculiar modification of protoxide of nickel, discovered by GENTH, which crystal- lizes in octahedra, does not dissolve in acids, but is rendered soluble by fusion with bisulphate of potassa. Metallic nickel dissolves slowly, with evolution of hydrogen gas, when warmed with dilute hydrochloric or sulphuric acid ; in nitric acid, it dissolves with great readiness. Sul- phide of nickel is but sparingly soluble in hydrochloric acid, but it dis- solves readily in nitrohydrochloric acid. Peroxide of nickel dissolves in hydrochloric acid, upon the application of heat, to protochloride, with evolution of chlorine. b. Determination. Protoxide of nickel is always weighed as such ( 79). The compounds of nickel are converted into the pure protoxide, usually by precipitation as hydrated protoxide, preceded, in some instances, by precipitation as sulphide of nickel, or by ignition. We may convert into PROTOXIDE OF NICKEL. a. By Precipitation as Hydrated b. By Precipitation as Sulphide Protoxide or Sesquioxide of Nickel, of Nickel. All the salts of nickel with in- All compounds of nickel with- organic acids which are soluble in out exception, water, and all its salts with volatile organic acids ; likewise all salts of nickel which, insoluble in water, dissolve in the stronger acids, with separation of their acid. c. By Ignition. The salts of nickel with readily volatile oxygen acids, or with such oxygen acids as are decomposed at a high temperature (carbonic acid, nitric acid). The method c is very good, but seldom admissible. The method a ia most frequently employed. In the presence of sugar, or other non-vola- tile organic substance, it cannot be used. In this case we must * Zeitschr. f. Anal. Chem. 3, 209. 188 DETERMINATION. [ 110. ignite and thereby destroy the organic matter before precipitating, or we must resort to the method &, which otherwise is hardly used except in separations. The combinations of the protoxide of nickel with chromic, phosphoric, boracic, and silicic acids are analyzed according to the methods given under the several acids. Determination as Protoxide of Nickel. a. By Precipitation as Hydrcded Protoxide of Nickel. Mix the solution with pure solution of potassa or soda in excess, heat for some time nearly to ebullition, decant 3 or 4 times, boiling up each time, filter, wash the precipitate thoroughly with hot water, dry and ignite intensely (RUSSELL *) ( 53). The precipitation is best effected in a platinum dish ; in presence of nitrohydrochloric acid, or, if the operator does not possess a sufficiently capacious digh of the metal, in a porcelain dish ; glass vessels do not answer the purpose so well. Presence of ammoniacal salts, or of free ammonia, does not interfere with the precipitation. For the properties of the precipitate and residue, see 79. This method, if properly executed, gives very accurate results. The thorough washing of the precipitate is a most essential point. It is necessary also to ascertain whether the residue has not an alkaline reaction, and whether it dissolves completely in hydrochloric acid. [Addition of solution of hypochlorite of soda to the hot liquid, after, treatment with caustic soda, converts the protoxide into sesquioxide y which washes more easily than the protoxide, and is otherwise treated like the latter.] b. JBy Precipitation as Sulphide of Nickel. This requires the greatest care and attention when sulphide of am- monium is employed. a. The moderately dilute cold solution of nickel contained in a proper sized flask is, if necessary, neutralized with ammonia (the reaction should be rather slightly acid than alkaline) : chloride of ammonium is added, if not already present in sufficient quantity, and then hydrosulphate of sulphide of ammonium, as long as a precipitate is produced. (The NH 4 S, HS should be perfectly saturated with HS ; it may be colorless or light-yellow.) A large excess of the reagent must be avoided. After mixing, fill the flask with water up to the neck, cork, and allow to stand about twenty four hours without warming, but in a moderately warm place. The precipitate has now settled, and the clear supernatant fluid is colorless or slightly yellow. Decant, filter, and wash as described in the case of sulphide of manganese ( 109, 1, c). (Filtrate and wash- water must be colorless or slightly yellow.) Dry the precipitate in the funnel, and transfer as completely as possible from the filter, to a beaker ; the filter is incinerated in a coil of platinum wire, or upon the lid of a crucible, and the ash added to the dry precipitate. The precipitate is now treated with concentrated nitrohydrochloric acid, and the mixture digested at a gentle heat, until the whole of the sulphide of nickel is dissolved, and the undissolved sulphur appears of a pure } r ellow ; the fluid is then diluted, filtered, and the filtrate precipitated, &c., as di- rected in a. For the properties of the precipitate, see 79. The method, if properly executed, gives accurate results. If the solution contains free ammonia, or no salt of ammonia, the * Journ. Chem. Soc. 16, 58. HI.] PROTOXIDE OF COBALT. 189 fluid filtered off from the sulphide of nickel possesses always a more or less brownish tint, and contains sulphide of nickel ( 79, c), which must be regained by acidifying with acetic acid and boiling. If the precipi- tate is not washed as directed, some nickel is very likely to pass through with the wash-water. If the filter were not incinerated, but treated ttt once, together with the precipitate, with nitrohydrochloric acid, the so- lution of the sulphide of nickel would contain organic substances, and the soda or potassa would accordingly afterwards fail to effect the com- plete precipitation of the nickel. j3. Mix the slightly acidified solution of nickel with bicarbonate of ammonia, so that the free acid may be neutralized, and the solution may contain a small excess of the bicarbonate of ammonia, together with free carbonic acid, and then pass hydrosulphuric acid gas through the mix- ture. Precipitation will promptly ensue. Filter, and treat the precip- itate as in a. [7. When a boiling solution of sulphide of sodium* is added to a boiling solution of a salt of nickel, sulphide of nickel is thrown down completely, and may be filtered and washed with hot water without the least oxidation. It is best to add some acetic acid before filtering, to destroy any excess of sulphide of sodium. (GiBBS.f)] It is not advisable to convert the sulphide of nickel in Ni 2 S, by ignit- ing in hydrogen with addition of sulphur, and in this form to weigh it, as the composition of the residue is not quite constant. (H. ROSE.) c. By direct Ignition. The same method as described 109, 1, e. (Manganese.) 111. 4. PROTOXIDE or COBALT. a. Solution. Protoxide of cobalt and its compounds behave with solvents like the corresponding compounds of nickel ; metallic cobalt like metallic nickel. The protosesquioxide of cobalt obtained by SCHWARZENBERG in microscopic octahedra does not dissolve in boiling hydrochloric acid, or nitric acid, nor in nitrohydrochloric acid ; but it dissolves in concentrated sulphuric acid, and in fusing bisulphate of potassa. b. determination. Cobalt may be weighed as metallic cobalt, protoxide of cobalt, sulphate of protoxide of cobalt, and nitrite of cobalt and potassa. The conversion into protoxide is often preceded by precipitation as hydrated sesquioxide, and conversion into the sulphate by precipitation as sulphide of cobalt. We may convert into 1. METALLIC COBALT. All salts of cobalt that may be reduced directly by hydrogen gas (chlo- ride of cobalt, nitrate of protoxide of cobalt, carbonate of protoxide of cobalt, &c.) and all the oxides. * [ Pure sulphide of sodium may be procured by dissolving- crystallized sul- phide (NaS 9 HO), in alcohol of 90 per cent, and ^crystallizing- two or three times from the solvent. The pure salt is dried in vacuo, and the white floresced mass preserved in a well-stoppered bottle. (Gibbs.)J [ f Am. Jour. Sci. 3d Ser. 37, 350,] 190 DETERMINATION. [ 111. 2. PROTOXIDE OF COBALT. All salts of cobalt which are soluble in water, or in stronger acids, with separation of their acid, except those with non-volatile organic acids. Also all the higher oxides, and all salts whose acids are destroyed or expelled by ignition. 3. SULPHATE OF PROTOXIDE OF COBALT. All compounds of cobalt without exception. 4. NITRITE OF COBALT AND POTASSA. All compounds of cobalt soluble in water or acetic acid. 1. Determination as Metallic Cobalt. Evaporate the solution of chloride of cobalt, or of nitrate of protoxide of cobalt, which must be free from sulphuric acid and alkali, in a weighed crucible, to dryiiess ; cover the crucible with a lid having a small aper- ture in the middle, conduct through this a moderate current of pure dry hydrogen gas, and then apply a gentle heat, which is to be increased gradually to intense redness. When the reduction is considered complete, let the reduced metal cool in the current of hydrogen gas, and weigh ; ignite again in the same way and repeat the process until the weight of the reduced metal remains constant. The results are accurate. For the properties of cobalt, see 80. [The oxides of cobalt which have been precipitated by an alkali after ignition may be reduced in the same manner. The metal retains a small portion of alkali which may be removed by washing with hot water down to unweighable traces. "Unless alkali absolutely free from' silica, and platimim vessels be employed in the precipitation, the metal, after weigh- ing, should be dissolved, the solution evaporated to dryness on the water- bath, that any residue of silica maybe separated.] As regards the apparatus to be employed, see fig. 47, p. 181. [2. Determination as Protoxide of Cobalt. a. By Precipitation as Hydrated Sesquioxide. The solution is precipitated exactly as described for nickel, with solution of soda under addition of a hypochlorite. 110, a. The precipitate is also further treated as there directed, with the important difference that the dried precipitate is ignited and cooled in a stream of pure carbonic acid gas until the weight remains constant. See 80. When precipitated as hydrated sesquioxide with reagents free from silica, &c., the precipitate retains but trifling traces of alkali, and the method is very accurate. b. JBy Ignition. Carbonate and nitrate of cobalt are ignited in a stream of carbonic acid as above. Organic salts are ignited in the air until carbon is burned off, and then in an atmosphere of carbonic acid.] 3. Determination as Sulphate of Protoxide of Cobalt. a. By direct Conversion. The solution is evaporated to dryness, in a platinum dish or platinum 111.] PROTOXIDE OF COBALT. 191 crucible* (directly, if it contains sulphate of protoxide of cobalt ; but if it contains a volatile acid, after addition of a slight excess of sulphuric acid) and the residue cautiously heated, at a gradually increased tem- perature, which is finally raised to gentle redness : the application of heat is continued until no more fumes escape and the weight of the cruci- ble remains constant. In order to avoid spirting while heating, it is well to hold the flame above the crucible, and let it play on the cover. After weighing, the salt is treated with hot water. If this fails to effect complete solution (a sign that the salt has become basic) the residue is dissolved in hydrochloric acid, and the amount of sulphuric acid is then estimated in the solution, as directed 132; the difference will be the protoxide of cobalt. The results are accurate. For the properties of sulphate of protoxide of cobalt see 80. b. Preceded by Precipitation as Sulphide of Cobalt. Precipitate, decant, filter and wash exactly as directed for sulphide of manganese ( 109, 1, c), dry, and redissolve as directed 110, 6, a (Sul- phide of nickel.) The solution obtained contains invariably sulphuric acid ; the amount of the cobalt is determined according to 3, a, taking care to evaporate the fluid, which contains mtrohydrochloric acid, in a porcelain dish, with addition of sulphuric acid, to dryness, before transferring the residue, with a little water, to the platinum dish. The results are accurate. For the properties of the sulphide of cobalt see 80. The sulphide of cobalt cannot be brought into a weighable form by ignition in hydrogen, as the residue is a variable mixture of different sulphides (H. ROSE). 4. Determination as Nitrite of Cobalt and Potassa (used principally in cases of separation). Mix the cobalt solution, which must not be too dilute (at the most, 300 parts of water to 1 of protoxide of cobalt), with a concentrated solu- tion of nitrite of potassa ; add acetic acid in quantity, a little more than sufficient to redissolve the precipitate, which is at first produced in the solution by the free potassa and carbonate of potassa contained in the nitrite. Cover the beaker with a clock-glass, and let it stand 12 to 24 hours in a warm place. Collect the yellow precipitate on a weighed filter, wash thoroughly with an aqueous solution of neutral acetate of potassa (containing 10 per cent, of the salt), to which some nitrite of potassa is added, displace, finally, the last portion of solution of acetate of potassa still adhering to the precipitate, by means of spirit of wine of 80 per cent., dry, ignite, incinerate the filter, moisten the whole with sulphuric acid, drive off the excess of the latter (see 97, 1), and weigh the residue which consists of 2 (Co O, S O 3 ) + 3 (K O, S O 3 ). GIBBS and GENTH f have obtained good results by this method. 100 parts of the residue are equivalent to 18-014 parts of Co O. [Or dissolve the nitrite of cobalt and potassa in hydrochloric acid, precipitate by potassa, reduce the washed precipitate by hydrogen, and weigh the washed metal. (H. HOSE.)] [To weigh the precipitate dried at 100 is not recommended, since ERDMANN has shown that its content of water and nitrogen is variable See 80.] * The operation must, at all events, be finished in a platinum vessel, f Annal. d. Chem. u. Pharm. 104, 309. 192 DETERMINATION. [ 112. 112. 5. PKOTOXIDE OF IRON. a. Solution. Many of the compounds of protoxide of iron are soluble in water. The compounds insoluble in water dissolve almost without exception in hydrochloric acid, in which the pure protoxide also is soluble ; the solu- tions, if not prepared with perfect exclusion of air, and with solvents absolutely free from air, contain invariably more or less sesquichloride. In cases where it is wished to avoid the chance of oxidation, the solution of the compound of protoxide of iron is effected in a small flask, through which a slow current of carbonic acid gas is passed, the transmission of the gas being continued until the solution is cold. Many native proto-com- pouiids of iron cannot be thus dissolved. They are, indeed, rendered soluble by fusing with carbonate of soda, but in this process the protox- ide of iron is converted into sesquioxide It is therefore advisable to heat such substances (in the finest powder) with a mixture of 3 parts concentrated sulphuric acid and 1 part water in a strong sealed tube of Bohemian glass for 2 hours at about 210, or in the case of silicates to warm them with a mixture of 2 parts hydrochloric acid and 1 part strong hydrofluoric acid in a covered platinum dish (A. MITSCHERLICH *. See also Cooke's method of solution, p. ). Metallic iron dissolves in hydrochloric acid, and in dilute sulphuric acid, with evolution of hydro- gen, as protochloride or sulphate of protoxide respectively ; in warm ni- tric acid it dissolves as nitrate of sesquioxide, and in nitro-hydrochloric acid as sesquichloride. b. Determination. Protoxide of iron may be estimated 1, by dissolving, converting intc sesquioxide and determining the latter gravimetrically or volumetrically ; 2, by precipitating as sulphide, and weighing it as such, or determining it after conversion into sesquioxide ; 3, by a direct volumetric method ; 4, by treating with terchloride of gold, and weighing the reduced gold. The methods 1 and 2 are, of course, only applicable when no sesqui- oxide is present with the protoxide ; the method 2 is scarcely ever used except for separations. The methods included under 3 are adapted to most cases and, in absence of other reducing substances, are espe- cially worthy of recommendation. The method 4 will be briefly treated of in the supplement to 112 and 113. As the determination of iron as sesquioxide belongs to 113, and as the process for precipitating the protoxide as sulphide is the same as that for precipitating the sesquioxide in this form, nothing remains for us here but to describe the methods of converting the protoxide into the sesquioxide and the processes included under 3. 1. Methods of converting Protoxide of Iron into /Sesquioxide. a. Methods, applicable in all cases. Heat the solution of protoxide of iron to be oxidized with hydro- chloric acid and add small portions of chlorate of potassa, till the fluid, even after warming for some time, still smells strongly of chlorine. Our object may be also attained by passing chlorine gas or in the cabe of * Journ. f. prakt. Chem. 81, 116. 112.] PROTOXIDE OP IRON. 193 small quantities by addition of chlorine water. If the solution is re- quired to be free from excess of chlorine, it is finally heated, till all odor of that gas has disappeared. b. Methods which are only suitable when the iron is to be subsequently precipitated by ammonia, as hydrated sesquioxide. Mix the solution of the protoxide of iron in a flask with a little hydrochloric acid, if it does not already contain any; add some nitric acid, and heat the mixture for some time to incipient ebullition. The color of the fluid will show whether the nitric acid has been added in sufficient quantity. Though an excess of nitric acid does no harm, still it is better to avoid adding too much 011 account of the subsequent pre- cipitation. In concentrated solutions, the addition of nitric acid pro- duces a dark-brown color, which disappears upon heating. This color is owing to the nitric oxide formed dissolving in the still unoxidized por- tion of the solution of the protoxide. c. Methods which can be employed only when the sesquioxide of iron is to be determined volumetrically . Add to the hydrochloric solution small quantities of artificially pre- pared iron-free binoxide of manganese, till the solution is of a dark olive green color from the formation of sesquichloride of manganese ; boil till this coloration and the odor of chlorine have disappeared (FR. MOHR) ; or you may add pure permanganate of potassa (in crystals or concentrated solution) till the fluid is just red and then boil, till the red color and chlorine-odor have vanished. These methods present the ad- vantage of permitting complete oxidation without the use of any consid- erable excess of the oxidizing agent. 2. Estimation by Volumetric Analysis. a. MARGUERITE'S Method. This method is based upon the following principle : If we add to a solution of protoxide of iron, containing an excess of sulphuric acid, permanganate of potassa, the former is oxidized at the expense of the latter [10 (Fe O, SO 3 ) + 8 S O 3 + K O, Mn,O 7 = 5 (Fe. 2 O 3 , 3 S O 3 ) + K O, S O 3 + 2 (Mn O, S O 3 )]. Now if we possess a solu- tion of permanganate of potassa, and know how much iron 100 c. c. of it can convert from the condition of protoxide to that of sesquioxide, we can, with this, readily determine an unknown quantity of iron ; we have simply, for this purpose, to dissolve the iron in acid, in the form of protoxide, to oxidize the solution accurately, and note how many c. c. of the solution of permanganate of potassa have been used to accom- plish that object. a. Determination of the Strength of the Solution of Permanganate of Potassa. * The process of preparing a solution of permanganate of potassa having been described already in 65, 3, I will at once proceed to give the sev- eral methods employed to determine the strength of the solution. Either of the three subjoined methods may be selected for the pur- pose ; or, the strength having been determined by one method i may, by way of control, be determined once more by one of the < methods. , Solution of permanganate of potassa prepared from the pure crystal- 13 194 DETEKMINATION. [ 112. lized salt, does not alter, if carefully kept ; on the contrary, if it contains free potassa or manganate of potassa, it suffers gradual decomposition, and each analysis, made after an interval of even only a day, must be preceded by a fresh determination of its strength. aa. Determination of the Strength l>y means of Metallic Iron. Weigh off accurately about 0*2 grm. of thin, clean iron wire (piano- forte wire) ; introduce this into a small long-necked flask, add about 20 c. c. of dilute sulphuric acid, and the same quantity of water, secure the flask in an oblique position, by means of a retort-holder; transmit through it a slow current of carbonic acid, and then heat the fluid to gentle ebullition. Fig. 48 shows the arrangement of the apparatus. "When the iron has dissolved, allow to cool, keeping up the current of carbonic acid, then Fig. 48. fill the flask two-thirds with distilled water ; smear the rim with a little tallow, pour the contents cautiously into a beaker of about 400 c. c. capacity, and transfer the last particles from the flask to the beaker by repeated rinsing with cold water. The total quantity of fluid should be about 200 c. c. Place the beaker on a sheet of white paper, or better, on a sheet of glass, with white paper underneath. Fill a GAY-LUSSAC'S. or GEISSLER'S burette of 30 c. c. capacity, divided into ^g- c. c. (see 22, 23, figs. 13 and 14), up to zero, with solution of permanganate of potassa, of which take care to have ready a sufficient quantity, perfectly clear and uniformly mixed. Now add the permanganate to the iron solution, stirring the latter all the while with a glass rod. At first the red drops disappear very rapid- ly, then more slowly. The fluid, which at first was nearly colorless, gradually acquires a yellowish tint. From the instant the red drops be- gin to disappear more slowly, add the permanganate with more caution and in single drops, until the last drop imparts to the fluid a faint, but unmistakable reddish color, which remains on stirring. A little practice will enable you readily to hit the right point. As soon as the fluid in the burette has sufficiently collected again, read off, and mark the num- 112.] PROTOXIDE OF IRON. 195 ber of c. c. used. The reading off must be performed with the greatest exactness (see 22) ; the whole error should not amount to ^ c. c. If 0'2 gnu. iron have taken from 20 to 30 c. c. of permanganate, the latter may be considered to be of the proper degree of concentration for most determinations of iron. If much less has been used in the process, the solution, is too concentrated. In that case add to the entire quantity a sufficient amount of water to give it approximately the right degree of concentration ; then repeat the above experiment with a fresh amount of iron. If, on the other hand, considerably more than 30 c. c. of perman- ganate have been used for 0*2 grm. iron, the solution is not exactly unfit for use, but working with it becomes the more tedious and inconvenient the more its degree of concentration differs from that given above. When you have completed the experiment with a solution of approxi- mately proper concentration, calculate, by a simple proportion, how much iron 100 c. c. of the solution will convert from the state of protoxide to that of sesquioxide. Supposing, for instance, you have used to 0'210 grm. iron, 23*5 c. c. of the permanganate, then we say 23-5 : 100:: 0-210 : x =0-8936 (grm. iron). As the accuracy of all estimations made with the solution of perman- ganate of potassa depends upon the correct determination of the strength, it is always advisable to repeat the experiment. As even the purest iron wire is not chemically pure, but contains a little carbon, it is well, in analyses requiring the very highest degree of accuracy, to reduce the weight of the iron wire used in the process, by multiplication with 0'997, to the corresponding weight of chemically pure iron. This reduction is based upon the generally correct supposition that the wire contains 0'3 per cent, of extraneous matter. If, in the two experiments made for the purpose of determining the strength of the solution of permanganate of potassa, the quantities of iron respectively corresponding to 100 c. c. of solution, differ only about 1, 2, or- 3 mgrm. (per grm.), the results may be considered perfectly satisfac- tory. But if the difference is considerably greater, a third experiment must be made. If there is a deficiency of free acid in the solution of iron, the fluid acquires a brown color, turns turbid, and deposits a brown precipitate (binoxide of manganese and sesquioxide of iron). The same may happen also if the solution of permanganate of potassa is added too quickly, or if the proper stirring of the "iron solution is omitted or interrupted. Experiments attended with abnormal manifestations of the kind should always be rejected. That the fluid reddened by the last drop of solution of permanganate of potassa added, loses its color again after a time, need create no surprise or uneasiness ; this decolorization is, in fact, quite inevitable, as a dilute solution of free permanganic acid cannot keep long undecomposed. bb. Determination of the Strength by means of Sulphate of Protoxide, of Iron and Ammonia. Weigh off, with the greatest accuracy, about 1'4 grm. of the pure salt prepared according to the directions given in 65, 4, after powder- ing the crystals, and pressing between sheets of smooth blotting-paper. Dissolve in about 200 c. c. distilled water, add about 20 c. c. dilute sulphuric acid, and proceed as in aa. As sulphate of protoxide of iron and ammonia contains exactly $- of 190 DETERMINATION. [ 112. its weight of iron, the calculation required to show the value of 100 c. c. of permanganate is very simple. Supposing, for instance, 25 c. c. of per- manganate to have been consumed to 1*400 grm. of the iron salt, then, we have I '^_A o T = and 25 : 100 : : 0-2 : x ; x= 0'8 If the sulphate of protoxide of iron and ammonia used is not pure, if, for instance, it contains bases isomorphous with protoxide of iron (pro- toxide of manganese, magnesia, &c.) ; or if it contains sesquioxide, or ia used in a moist condition, the result will of course be too high. cc. Determination of the Strength ~by means of Oxalic Acid. This method is based upon the following principle : If solution of permanganate of potassa is added to a warm solution of oxalic acid, mixed with sulphuric acid, the liberated permanganic acid instantly oxidizes the oxalic acid to carbonic acid [5 C 2 O 3 -f- 3 S O 3 -f- K O, Mn. 2 O 7 = 10 C O 2 -f 2 (Mn O, S O 3 ) -f K O, S O 3 ]. For the oxida- tion of 1 eq. oxalic acid (C 2 O 3 ) and 2 eq. iron (in the state of protoxide) equal quantities of permanganic acid are accordingly required ; there- fore, 63 parts (1 eq.) of crystallized oxalic acid correspond, in reference to the oxidizing action of permanganic acid, to 56 parts (2 eq.) of iron. By dissolving 6'3 grm. pure crystallized oxalic acid ( 65, 1), or 4*5 grm. of the pure hydrate, dried at 100, in water, to 1 litre of fluid, a deci- normal solution of oxalic acid is obtained, which is exactly suited to our present purpose. 50 c. c. of this solution, which correspond to 0-315 grm. crystallized oxalic acid, or 0'2S grins, iron, are introduced into a beaker, diluted with about 100 c. c. of water, from 6 to 8 c. c. of cone, sulphuric acid added, and the fluid heated to about 60. The beaker is then placed on a sheet of white paper, and permanganate added from the burette, with stirring. The red drops do not disappear at first very rapidly, but when once the reaction has fairly set in, they continue for some time to vanish instantaneously. As soon as the red drops begin to disappear more slowly, the solution of permanganate of potassa must be added with great caution ; if proper care is taken in this respect, it is easy to complete the reaction with a single drop of permanganate ; this completion of the reaction is indicated with beautiful distinctness in the colorless fluid. The number of c. c. used corresponds to 0*28 grm. iron. If the oxalic acid was not perfectly dry, or not quite pure, the result of the experiment will, of course, lead to fixing the strength of the solution of permanganate of potassa too high. Instead of pure oxalic acid, SAINT-GILLES has proposed to use crystallized oxalate of ammonia (N H 4 O, C 3 O 3 -f- aq.). This can easily be prepared in the pure state, keeps well, and can be weighed with accuracy. It is not however advisable to keep a standard solution of this salt in store, as it is liable to spoil. 71 parts of the crystallized salt correspond to 56 parts iron. Of the foregoing three methods of standardizing solution of permanga- nate of potassa, the first is the one originally proposed by MARGUERITE. Sulphate of protoxide of iron and ammonia was first proposed by FR. MOHR, and oxalic acid by HEMPEL, as agents suitable for the purpose. With H2.] PROTOXIDE OF IRON. 197 absolutely pure and thoroughly dry reagents, and proper attention, all three methods give correct results. For myself, I prefer the first method, as the most direct and positive, the only doubtful point about it being the question whether the assump- tion that the iron wire contains 9 9 '7 per cent, of chemically pure iron ia quite correct ; this, however, is of very trifling importance, as the error could not exceed -fa or T 2 F per cent. But the other two methods are, as may readily be seen, somewhat more convenient, since in one of them the trouble is saved of preparing the solution of iron, and in the other there is, moreover, no need of weighing. These advantages, however, which were considerable when the impure permanganate solution that was used required fresh standardizing every day, have now lost their value, as the pure solution, now generally employed, keeps unaltered. For the analysis of very dilute solutions of iron, e.f ammonia are fulfilled. But should the fluid appear colorless, this is a sign that too much ammonia has been added in which cast; it will be necessary to add a small portion of hydrochloric acid, and then again some ammonia, until the desired point is attained. To the fluid thus prepared is now added a perfectly neutral solution of succinate of ammonia, as long as a precipitate forms ; a gentle heat is then applied, and the fluid allowed to cool ; when perfectly cold it is filtered, and the precipitate washed, first with cold water, finally Avith warm ammonia which operation, depriving the precipitate in a very great measure of its acid, imparts a darker tint to it. The washed pre- cipitate is dried upon the filter in the funnel, and then converted into sesquioxide of iron, by ignition ( 53). The object of washing the pre- cipitate with ammonia is to remove part of the acid, since, were the pre- cipitate simply washed with water, a portion of the sesquioxide of iron might suffer reduction upon the subsequent ignition of the succinate. If there is reason to apprehend that this has actually taken place, some nitric acid is added to the precipitate, evaporated, and the ignition re- peated. For the properties of the precipitate, see 81. The results are accurate. d. By Precipitation as Basic, Acetate of Sesquioxide of Iron. Mix the solution of sesquioxide of iron [containing not more than 1 grm. of oxide to \ litre] in a flask, if it contains much free acid, with carbonate of soda or ammonia until the acid is nearly neutralized ; then add to the solution which is still clear, but already of a deep red color, neutral acetate of soda or of ammonia, and a few drops of acetic acid in slight excess ; and boil till, on removing the lamp, the precipitate settles clear. Wash repeatedly by boiling and decantation, and finally, on the filter with boiling water, which should contain a little acetate of ammo- nia ; dry, ignite ( 53), and weigh the sesquioxide obtained. It is advisable to add a few drops of nitric acid to the residue, evaporate, and ignite again, to see whether the weight remains constant. The residue must show no alkaline reaction when moistened with water. The results are accurate. It is often preferable to dissolve the precipitate of the basic acetate in hydrochloric acid, and to precipitate the solution accord ing to a [see also Reichardt's method], 81, e. The formiates of soda and ammonia may be advantageously substituted for the acetates as pre- cipitants ( 8 1,/). e. By Ignition. Expose the compound, in a covered crucible, to a gentle heat at first, and gradually to the highest degree of intensity ; continue the operation until the weight of the residuary sesquioxide of iron remains constant. 2. Determination as Anhydrous Sulphide of Iron. The hydrated sulphide of iron obtained, as in 1, 6, may be very con- veniently determined by conversion into the anhydrous sulphide. The process is the same as for zinc ( 108, 2). The heat to which it is finally exposed in the current of hydrogen must be strong, as an excess of sul- phur is retained with some obstinacy. In fact, it is advisable after weighing to re-ignite in hydrogen and weigh a second time. It is of no importance if the hydrated sulphide has oxidized on drying. Protosulphate and sesquioxide of iron can be transformed into sul- 113.] SESQUIOXIDE OP IRON. 203 phide in the same manner, after having been dehydrated by ignition in a porcelain crucible (H. ROSE *). The results obtained by OESTEN, and adduced by HOSE, as well as those obtained in my own laboratory, are exceedingly satisfactory. (Expt. No. 75.) 3. Determination l>y Volumetric Analysis. a. Preceded by Reduction of the Sesquioxide to Protoxide. The volumetric methods which come under this head are based upon the reduction of the sesquioxide to protoxide, and the estimation of the latter. We have, accordingly, to occupy ourselves simply with the reduction of the solution of the sesquioxide, the other part of the pro- cess having been fully discussed in 112 (Protoxide of Iron). The reduction of sesquioxide of iron can be effected by many substances (zinc, protochloride of tin, sulphuretted hydrogen, sulphurous acid, &c.), but only those can be used with advantage, an excess of which may be added with impunity, if an excess must be very carefully avoided, or, being added, must be carefully removed, the method becomes trouble- some, and a ready source of inaccuracy is introduced. On these grounds, although its action is somewhat slow, zinc, unquestionably, deserves the preference before all other reducing agents. Heat the hydrochloric or sulphuric acid solution, which must contain a moderate excess of acid, but be free from nitric acid, in a small long- necked flask, placed in a slanting position ; drop in small pieces of iron- free zinc ( 60), and conduct a slow current of carbonic acid through the flask (fig. 48, p. 194). Evolution of hydrogen gas begins at once, and the color of the solution becomes paler in proportion as the sesqui- oxide changes to protoxide. Apply a moderate heat, to promote the action ; and add also, if necessary, a little more zinc. As soon as the hot solution is completely decolorized (one cannot judge of the perfect deoxidation of a cold solution so well, as the color of the sesquichloride of iron is deeper in the heat), allow to cool completely in the stream of carbonic acid ; to hasten the cooling the flask may be immersed in cold water ; then dilute the contents with water, pour off and wash carefully into a beaker, leaving behind any undissolved zinc, and also (as far as possible) any flocks of lead that may have separated from the zinc, and proceed as directed in 112, 2. If* the solution contains metals precipi- table by zinc, these will separate, and may render nitration necessary. In this case the filtrate must be again heated with zinc before using the standard solution. If iron-free zinc cannot be procured, the percentage of iron in the metal used must be determined, and weighed portions of it employed in the process of reduction ; the known amount of iron con- tained in the zinc consumed is then subtracted from the total amount of iron found. [b. Without Previous ^Reduction to Protoxide. OUDEMANS' Method. \ The principle consists in adding a reducing agent to the solution till the sesquioxide is entirely converted into protoxide, and then determin- ing the amount of the reducing agent used. * Pogg. Annal. 110, 126. t Fresenius' Zeitschrift, VI. 129. 204 DETERMINATION. [ 113. This method depends upon the fact that hyposulphite of soda may re- duce sesquioxide of iron to protoxide in accordance with the equation Fe 2 C1 3 + 2 (Na O, S 2 O s ) = 2 Fe Cl + Na O, S 4 O 5 + Na 01. In order that this reaction serve for analytical purposes it is necessary, 1, that a certain not too great proportion of free acid be present ; 2, that the iron solution be rather concentrated ; and, 3, that a minute amount of solution of a salt of protoxide of copper be present, which acts to trans- fer oxygen from the iron to the hyposulphite, being reduced by the lat- ter to suboxide and carried again to protoxide by the sesquisalt of iron. "We require : a. A Solution of Hyposulphite of Soda. This may be made by dissolving 25 grm. of the purest commercial salt in 1 litre of water. b. A Standard Solution of a Sesquisalt of Iron. This is prepared by dissolving 5*617 grm. of fine piano-wire, assumed to contain 99 '7 per cent, of iron, in hydrochloric acid in a slanting long- necked flask, oxidizing the solution with chlorate of potassa, removing the excess of chlorine by protracted gentle boiling, and finally diluting the solution to 1 litre; or by dissolving 24'1 grm. of pure ammoiiia- iron-alum (see p. 93) in 1 litre of water. c. A Solution of Sulphate of Copper containing, say, 10 per cent, of the crystallized salt. d. A Solution of Sulphocyanide of Potassium. The standard of the hyposulphite-solution must be fixed by aid of the accurately prepared iron-solution, as follows : 20 c. c. of the iron-solution are measured into a small flask or beaker, well acidified with hydrochloric acid ; one drop of the copper solution is added, and enough sulphocyanide to make the liquid of a deep red color. The hy- posulphite (about 20 c. c.) is added from a burette, rapidly at first, after- wards slowly and cautiously, until the red color is discharged. The iron- solution may be warmed to 40 C. whereby the reaction is accelerated. When the iron-solution is dilute, the reaction proceeds with incon- venient slowness, but after some practice the results are good. From the number of c. c. of the hyposulphite solution required to reduce a known quantity of sesquioxide of iron, taking the mean of a number of nearly accordant observations, may be calculated the quantity of sesqui- oxide of iron, or of metallic iron, corresponding to 1 c. c. of hyposulphite, and this factor, multiplied into the number of c. c. consumed in any analysis, gives the quantity of sesquioxide of iron or of metallic iron sought. The solution of the iron which it is desired to estimate is conducted as described for making the standard b. It must be free from nitric acid and oxides of chlorine ; should be kept rather concentrated, as a matter of convenience for rapid working, and should contain a moderate amount of free hydrochloric acid. The analysis is conducted as just described for the standardizing. The solution of hyposulphite alters slowly with deposition of sulphur, and its value must be determined anew every week or two. The process is convenient and excellent, though not so good for the estimation of minute quantities of iron as the method with permanganate.] 114, 115.] SESQUIOXIDE OF URANIUM. 205 Supplement to the Fourth Group. 7. SESQUIOXIDE OF URANIUM. If the compound in which the sesquioxide of uranium is to be deter- mined contains no other fixed substances, it may often be converted into protosesquioxide (Ur O, Ur 2 O 3 ) by simple ignition. If sulphuric acid is present, small portions of carbonate of ammonia must be thrown into the crucible towards the end of the operation. In cases where the application of this method is inadmissible, the solu- tion of uranium (which, if it contains protoxide, must first be warmed with nitric acid, until the protoxide is converted into sesquioxide) is precipitated with ammonia. The yellow precipitate formed, which con- sists of hydrated ammonio-sesquioxide of uranium , is washed with a dilute solution of chloride of ammonium, to prevent the fluid passing milky through the filter. The precipitate is dried and ignited ( 53). To make quite sure of obtaining the protosesquioxide in the pure state, the crucible is ignited for some time in a slanting position and uncovered ; the lid is then put on, while the ignition is still continuing ; the cruci- ble is allowed to cool under the desiccator, and weighed (H. ROSE). If the solution from which the sesquioxide of uranium is to be pre- cipitated contains other bases (alkaline earths, or even alkalies), portions of these will precipitate along with the ammonio-sesquioxide of uranium. For the measures to be resorted to in such cases, I refer to Section Y. The reduction of the protosesquioxide of uranium to the state of protoxide (Ur O) is an excellent means of ascertaining its purity for the purpose of control. This reduction is effected by ignition in a current 1 of hydrogen gas, in the way described 111, 1 (Cobalt). By intense ignition, the property of the protoxide of uranium to ignite in the air is destroyed. The separation of sesquioxide of uranium from phosphoric acid is effected by fusing the compound with cyanide of potassium and carbonate of soda. Upon extracting the fused mass with water, the phosphoric acid is obtained in solution, whilst the uranium is left as protoxide. KNOP and ARENDT * have employed this method. The equivalent of protosesquioxide of uranium = 210'2, viz., 178'2 of uranium and 32 of oxygen. In 100 parts, the compound consists of 84-77 of uranium and 15-23 of oxygen. The equivalent of protoxide of uranium is 67'4, viz., 59'4 of uranium and 8 of oxygen ; in 100 parts, the protoxide consists of 88' 13 of uranium and 11'87 of oxygen. FIFTH GROUP. OXIDE OF SILVER OXIDE OF LEAD - SUBOXIDE OF MERCURY - OXIDE OF MERCURY OXIDE OF COPPER TEROXIDE OF BISMUTH - OXIDE OF CAD- MIUM (PROTOXIDE OF PALLADIUM). US- 1. OXIDE OF SILVER. a. Solution. . . Metallic silver, and those of its compounds which are insoluble in water are best dissolved in nitric acid (if soluble in that acid). Dilute nitric acid suffices for most compounds ; sulphide of silver, however, re- * Chem. Centralbl. 1856, 773. 206 DETERMINATION. [ 115. quires concentrated acid. The solution is effected best in a flask. Chlo ride, bromide, and iodide of silver are insoluble in water and in nitric acid. To get the silver contained in them in solution, proceed as fol- lows : fuse the salt in a porcelain crucible (this operation, though not absolutely indispensable, had better not be omitted), pour water over it, put a piece of clean zinc or iron upon it, and add some dilute sulphuric acid. Wash the reduced spongy silver, first with dilute sul- phuric acid, then with water, and finally dissolve it in nitric acid. How- ever, as we shall see below, the quantitative analysis of these salts does not necessarily involve their solution. b. Determination. Silver may be weighed as chloride, sulphide, or cyanide, or in the metallic state (82). It is also frequently determined by volumetric analysis. We may convert into 1. CHLORIDE OF SILVER. All compounds of silver without exception. 2. SULPHIDE OF SILVER. 3. CYANIDE OF SILVER. All compounds soluble in water or nitric acid. 4. METALLIC SILVER. Oxide of silver, and some of its compounds with readily volatile acids ; salts of silver with organic acids ; chloride, bromide, iodide, and sulphide of silver. The method 4 is the most convenient, and is preferred to the others in all cases where its application is admissible. The method 1 is that most generally resorted to. 2 and 3 serve mostly only to effect the separation of oxide of silver from other bases. In assays for the Mint, silver is usually determined volumetrically by GAY-LUSSAC'S method. PISANI'S volumetric method is especially suited to the determination of very small quantities of silver. The estimation of silver by cupellation will be described in the Special Part. 1. Determination of Silver as Chloride, a. In the Wet Way. The precipitated chloride of silver may be separated from the super- natant fluid either by decantation or by filtration ; the former is gene- rally preferred for large quantities of precipitate, the latter answers better for small quantities. Whichever process is adopted, the chloride of silver must be completely protected from the influence of direct sun- light, and even the action of diffused daylight must be as far as possible avoided. a. Determination by Decantation. Ti\& moderately dilute silver-solution is introduced into a tall flask with long neck and narrow mouth, and some nitric acid added to it ; the fluid is heated to about 60, and hydrochloric acid carefully added in such quantity, that some silver still remains unprecipitated, and the chloride separates in consequence in large flocks. After their formation has been completed by gently moving the fluid, add cautiously moie hydrochloric acid, till the last drops give no further precipitate (a con- siderable excess should be avoided, as hydrochloric acid dissolves very small traces of chloride of silver). The mouth of the flask is then H5.] OXIDE OF SILVER. 207 closed with a perfectly smooth cork (or, better still, with a well-ground glass stopper), and the flask vigorously shaken until the precipitated chloride of silver has united into coherent lumps, and the supernatant fluid has become pretty clear. The chloride adhering to the neck of the flask is then removed by agitating the clear fluid, and the last traces are washed down by means of a wash-bottle ; the flask is then allowed to stand at rest for twelve hours in a dark place at the ordinary tem- perature. At the end of this time the precipitate will have completely subsided and the fluid will be clear. The latter is then slowly and cau- tiously decanted, as far as practicable, into a beaker, so as to retain every particle of the chloride in the flask, whence it is carefully trans- ferred to an upright smooth porcelain crucible that has been weighed : the last particles of chloride of silver are got out by putting a little water in the flask, closing the mouth with the finger, inverting, and rinsing the sides and bottom by agitation. The particles thus collect in the neck, and can easily be transferred to the crucible, by holding the mouth of the flask close over the latter, and letting the fluid run out ; a washing bottle with the jet turned upwards (46) may also be used with advantage. When the chloride of silver has completely subsided in the crucible, which is greatly accelerated by exposure to the heat of a water-bath, the clear supernatant fluid is carefully decanted down a glass rod into the same beaker which contains the liquid of the first decantation. The chloride of silver in the crucible is moistened with a few drops of nitric acid, and then treated with hot distilled water ; the chloride is again al- lowed to subside, the clear supernatant fluid again decanted, and the same operation repeated until a drop of the last decanted fluid no longer gives the slightest turbidity with nitrate of silver. The supernatant fluid is then removed as completely as possible by means of a pipette, or by cautious decantation ; the chloride is thoroughly dried on the water- bath, and subsequently heated to incipient fusion over the lamp, taking care to apply a very gentle heat at first ; as soon as the chloride begins to fuse round the border, the crucible is allowed to cool, and weighed. To remove the mass from the crucible, completely and without injury to the latter, a piece of iron or zinc is placed upon the chloride, and highly dilute hydrochloric or sulphuric acid added. The crucible is finally cleansed, dried, and weighed, if this has not been done before the opera- tion. Should the liquids successively decanted from the chloride of silver not be perfectly clear and transparent, they are kept standing in the cold until the last particles of chloride have completely subsided, which frequently requires many hours ; the clear supernatant fluid is then de- canted, and the deposited chloride added to the bulk of the precipitate in the crucible, the whole washed and treated as above ; or and this is a more expeditious way the minute quantity of chloride is collected on a small filter, treated as directed in 0, and added to the principal amount. |3. Determination by Filtration. The chloride of silver is precipitated and allowed to subside as in a ; the supernatant fluid is then passed through a small filter, to which the precipitate is subsequently transferred, with the aid of a little hot water acidulated with nitric acid ; the precipitate collected on the filter is washed, first with water acidulated with nitric acid, afterwards with pure water ; it is then thoroughly dried, the contents of the filter are transferred as completely as possible to a small porcelain crucible, and 208 DETERMINATION. [ the filter itself is burnt on the lid. In this operation some of the chlo- ride is always reduced, the ash is therefore added to the chloride in the crucible, together with two or three drops of dilute nitric acid : heat is applied for a short time, and then a drop or two of hydrochloric acid add- 3d ; lastly heat, at first gently till dry, then to incipient fusion, and weigh. For the properties of the precipitate, see 82. Both methods give very accurate results, unless large quantities of such salts are present as have the property of slightly dissolving chloride of silver, compare 82. In order to be quite safe in this connection it is advisable to test the clear filtrate with sulphuretted hydrogen before throwing it away. b. In the Dry Way. This method serves more exclusively for the analysis of bromide and iodide of silver, although it can be applied in the case of other com- pounds. The process is conducted in the apparatus illustrated by Fig. 49, leaving off the tubes E and F, and employing a straight bulb-tube or a plain tube with porcelain tray instead of the bent tube D. Fig. 49. A is an apparatus for disengaging chlorine ; B contains concentrated sulphuric acid, C chloride of calcium ; D is a bulb-tube intended for the reception of the iodide or bromide of silver ; and G, which directly is con- nected with D, serves to conduct the chlorine gas into the open air or into milk of lime. The operation is commenced by introducing the compound to be analyzed into the bulb, and applying heat to the latter until its contents are fused ; when cold, the tube is weighed and connected with the apparatus. Chlorine gas is then evolved from A ; when the evolution of the gas has proceeded for some time, the contents of the bulb are heated to fusion, and kept in this state for about fifteen mi- nutes, agitating now and then the fused mass. The bulb-tube is then removed from the apparatus, allowed to cool, and held in a slanting po- sition to replace the chlorine by atmospheric air ; it is subsequently weighed, then again connected with the apparatus, and the former pro- 115.] OXIDE OF SILVER. 209 cess repeated, keeping the contents of D in a state of fusion for a fe-.v minutes. The operation may, in ordinary cases, be considered con- cluded if the weight of the tube suffers no variation by the repetition of the process. If the highest degree of accuracy is to be attained, heat the chloride of silver again to fusion, passing at the same time a slow stream of pure, dry carbonic acid through the tube, in order to drive out the traces of chlorine absorbed by the fused chloride. Allow to cool, hold obliquely for a short time, so as to replace the carbonic acid by air, and finally weigh. See 82. 2. Determination as /Sulphide of /Silver. Sulphuretted hydrogen precipitates silver conpletely from acid, neu- tral, and alkaline solutions ; sulphide of ammonium precipitates it from neutral and alkaline solutions. Recently prepared perfectly clear solu- tion of sulphuretted hydrogen may be employed to precipitate small quantities of silver ; to precipitate larger quantities, the solution of the salt of silver (which must not be too acid) is moderately diluted, and washed sulphuretted hydrogen gas conducted into it. After complete precipitation has been effected, and the sulphide of silver has perfectly subsided (with exclusion of air), it is collected on a weighed filter, washed, dried at 100 and weighed. For the properties of the preci- pitate, see 82. This method, if properly executed, gives very accurate results. The operator must take care to filter quickly, and to prevent the access of air as much as possible during the filtration, since, if this precaution be neglected, sulphur is likely to separate from the sulphuretted hydrogen water, which, of course, would add falsely to the weight of the sulphide of silver. The sulphide of silver must, however, never be weighed as just described, unless the analyst is satisfied that no sulphur has fallen down with it, as would occur if the fluid contained hyponitric acid, sesqui- oxide of iron, or any other substance which decomposes sulphuretted hydrogen. In case the precipitate does contain admixed sulphur, the simplest process is to convert it into metallic silver (H. ROSE *). For this purpose it is transferred to a weighed porcelain crucible, the filter ash is added, and the whole is heated to redness in a stream of hydrogen, the apparatus described in 108 being employed. Results-, accurate. Should the apparatus in question not be at the operator's disposal, he may, after complete washing of the precipitate, carefully rinse it into a porcelain dish (without injuring the weighed filter), heat it once or twice with a moderately strong solution of pure sulphite of soda, re-transfer the precipitate (now freed from admixed sulphur) to the old filter, wash well, dry and weigh (J. LOWE f) ; or he may treat the dried precipitate, together with the filter-ash, with moderately dilute chlorine-free nitric acid at a gentle heat, till complete decomposition has been effected (till the undissolved sulphur has a clean yellow appearance), filter, wash well, and proceed according to 1. 3. Determination as Cyanide of Silver. Mix the neutral or acid solution of silver with cyanide^ of potassium, until the precipitate of cyanide of silver which forms at first is redissolved ; add nitric acid in slight excess, and apply a gentle heat. After some * Fogg- Annal 110, 139. f Journ. f. prakt. Chem. 77, 73. 210 DETERMINATION. [ 115, time, collect the precipitated cyanide of silver on a weighed filter, wash, dry at 100, and weigh. For the properties of the precipitate, see 82. The results are accurate. 4. Determination as Metallic Silver. Oxide of silver, carbonate of silver, &c., are easily reduced by simple ignition in a porcelain, crucible. In the reduction of salts of silver with organic acids, the crucible is kept covered at first, and a moderate heat applied ; after a time the lid is removed, and the heat increased, until the whole of the carbon is consumed. For the properties of the residue, see 82. The results are absolutely accurate, except as regards salts of silver with organic acids ; in the analysis of the latter, it not tmfre- quently happens that the reduced silver contains a minute portion of carbon, which increases the weight of the residue to a trifling extent. If it is desired to transform chloride, bromide, iodide, or sulphide of silver into metallic silver, for the purpose of analysis, they are heated in a current of pure dry hydrogen to redness, till the weight remains con- stant. The process may be conducted in a porcelain crucible or a bulb- tube. In the former case, the apparatus described 108, fig. No. 47 is used ; in the latter the apparatus represented p. 208, with the substitution, of course, of hydrogen for chlorine. If the bulb-tube is used, it must, after cooling and before being weighed, be held in an. inclined position, so that the hydrogen may be replaced by air. The results are perfectly accurate. See also Cupellation, Special Part. 5. Volumetric Methods. 1. GAY-LUSSAC'S. This, the most exact of all known volumetric processes, was intro- duced by GAY-LUSSAC as a substitute for the assay of silver by cupella- tion, was thoroughly investigated by him, and will be found fully de- scribed in his work on the subject. This method has been rendered still more precise by the researches of G. J. MULDER, to whose exhaustive mo- nograph * 1 refer the special student of this branch. I shall here con- fine myself to giving the process so far as to suit the requirements of the chemical laboratory, taking only for granted that the analyst has the ordinary measuring apparatus, &c., at his disposal. MULDER'S results will be made use of to the full extent possible under these circumstances. a. REQUISITES. a. SOLUTION OF CHLORIDE OF SODIUM. Take chemically pure chloride of sodium either artificially prepared or pure rock-salt powder it roughly and ignite moderately (not to fusion f). Now dissolve 5*4145 grm. in distilled water to 1 litre, measured at 16. 100 c. c. of this solution contains a quantity of chloride of sodium, equivalent to 1 grm. of silver. The solution is kept in a stoppered bottle and shaken before use. j3. DECIMAL SOLUTION OF CHLORIDE OF SODIUM. Transfer 50 c. c. of the solution described in a to a 500 c. c. measur- * Die Silberprobirmethode (see note, p. 132). f On fusion, if the flame can in the least way act upon it, it takes an alkaline reaction, since under the influence of vapor of water and carbonic acid, a little hydrochloric acid is formed and escapes, while a corresponding quantity of car- bonate of soda remains. H5.] OXIDE OF SILVER. 211 ing flask, fill up to the mark with distilled water and shake. Each c. c. of this decimal solution corresponds to O'OOl grm. silver. The measuring must be performed at 16. The solution is kept as the other. y. DECIMAL SILVER SOLUTION. Dissolve 0-5 grm. chemically pure silver in 2 to 3 c. c. pure nitric acid of 1-2 sp. gr., and dilute the solution with water exactly to 500 c. c. measured at 16. Each c. c. contains O'OOl grm. silver. The so- lution is kept in a stoppered bottle and protected against the influence of light. 8. TEST-BOTTLES. These should be of white glass, holding easily 200 c. c., closed with well-ground glass stoppers, running to a point below. The bottles fit into cases blackened on the inside, and reaching up to their necks. In order to protect the latter also from the action of light, a black-cloth cover is employed. b. PRINCIPLE. Suppose we know the value of a solution of chloride of sodium, i.e., the quantity that is necessary to precipitate a given amount of silver, say 1 grm., we are in the position, with the aid of this solution, to deter- mine an unknown amount of silver, for if we put x for the unknown amount of silver, then c. c. of solution used for 1 grm. : c. c. used for x : : I grin. : x. But if we examine whether 1 eq. chloride of sodium dissolved in water actually precipitates 1 eq. of silver dissolved in nitric acid exactly, we find that this is not the case. On the contrary, the clear supernatant fluid gives a small precipitate both on the addition of a little solution of chloride of sodium, and on the addition of a little silver-solution, as MULDER has most accurately determined. The value of a solution of chloride of sodium in the sense explained above cannot, therefore, be reckoned from the amount of salt it contains, by calculating 1 eq. silver for 1 eq. chloride of sodium, but it can only be obtained by experiment. MULDER has shown, that the temperature and the degree of dilution have some influence, and also that this fact is to be explained on the ground of the solvent power of the nitrate of soda produced on the chloride of silver. In the solution thus formed we have to imagine Na O, N O 5 and Na Cl with Ag O, N O 5 in a certain state of equilibrium, which, on the addition of either Na Cl or Ag O, N O 5 is destroyed, chloride of silver being precipitated. From this interesting observation it follows, that if to a silver-solution we add at first concentrated solution of chloride of sodium, then deci- mal solution drop by drop, till the exact point is reached when no more precipitate appears, now, on addition of decimal silver-solution a small precipitate will be again produced ; and if we add the latter drop by drop, till the last drop occasions no turbidity, then again decimal solution of chloride of sodium will give a small precipitate. On noticing the num- ber of drops of both decimal solutions which are required to pass from one limit to the other, we find that the same number of each are used. Let us suppose that we had added decimal solution of chloride of sodium till it ceased to react, and had then used 20 drops* of decimal silver-solution, * Twenty drops from Mulder's dropping apparatus are equal to 1 o. c. 212 DETERMINATION. [ 115. till this ceased to produce a further turbidity, we must now again add 20 drops of decimal solution of chloride of sodium, in order to reach the point at which this ceases to react. Were we to add only 10 instead of these 20 drops, we have the neutral point, as MULDER calls it, i.e., the point at which both silver and chloride of sodium produce equal pre- cipitates. We have, therefore, 3 different points to choose from for our final reaction : , the point at which chloride of sodium has just ceased to precipitate the silver ; 5, the neutral point ; c, the point at which silver solution has just ceased to precipitate chloride of sodium. Whichever we may choose, we must keep to it, i.e., we must not use a different point in standardizing the chloride of sodium solution and in performing an analysis. The difference obtained by using first a and then b is, ac- cording to MULDER, for 1 grm. silver, at 16, about 0'5 mgrm. silver ; by employing first a and then c, as was permitted in the original process of GAY-LUSSAC, the difference is increased to 1 mgrm. For our object, it appears most convenient to consider, once for all, the point a as the end, and never to finish with the silver-solution. If the point has been overstepped by the addition of too large an amount of decimal solution of chloride of sodium, 2 or 3 c. c. of decimal silver- solution should be added all at once. The end-point is then found by carefully adding decimal solution of chloride of sodium again, and the quantity of silver in tjie silver-solution added is reckoned from the original amount of silver weighed in making the solution. c. PERFORMANCE OF THE PROCESS. This is divided into two operations a, the fixing of the value of the chloride of sodium solution ; 0, the assay of the silver alloy to be examined. a. DETERMINATION OF THE VALUE OF THE CHLORIDE OF SODIUM SOLU- TION, i.e., its power of precipitating silver. Weigh off exactly from 1-001 to 1'003 grin, chemically pure silver, put it into a test-bottle, add 5 c. c. perfectly pure nitric acid, of 1*2 sp. gr., and heat the bottle in an inclined position in a water- or sand-bath till complete solution is effected. Now blow out the nitrous fumes from the upper part of the bottle, and after it has cooled a little, place it in a stream of water, the temperature of which is about 16, and let it remain there till its contents are cooled to this degree ; wipe it dry, and place it in its case. Now fill the 100 c. c. pipette with the concentrated solution of chlo- ride of sodium, which is then allowed to flow into the test-bottle con- taining the silver solution.* Insert the glass stopper firmly (after moistening it with water), cover the neck of the bottle with the cap of black stuff belonging to it, and shake violently, without delay, till the chloride of silver settles, leaving the fluid perfectly clear. Then take the stopper out, rub it on the neck, so as to remove all chloride of sil- ver, replace it firmly, and by giving the bottle a few dexterous turns, rinse the chloride down from the upper part. After allowing to rest a little, again remove the stopper, and add, from a burette divided into fa c. c., decimal chloride of sodium solution, allowing the drops to fall * The pipette, having- been filled above the mark, should be fixed in a support before the excess is allowed to run out, otherwise the measuring will not be suf- ficiently accurate. 115 - OXIDE OF SILVER. 213 against the lower part of the neck, the bottle being held in an inclined position. If, as above directed, 1-001 to 1-003 grm. silver have been employed, the portions of chloride of sodium solution at first added may be c. c. After each addition, raise the bottle a little out of its case, observe the amount of precipitate produced, shake till the fluid has become clear again, and proceed as above, before adding each fresh quantity of chloride of sodium solution. The smaller the & precipitate produced, the smaller should be the quantity of chloride of sodium next added ; towards the end only two drops should be added each time ; and quite at the end read off the height of the fluid in the burette before each further addition. When the last two drops give no more preci- pitate, the previous reading is the correct one. If by chance the point has been overstepped, and the time has been missed for the proper reading off of the burette, add 2 to 3 c. c. of the decimal silver solution (the silver in which is to be added to the quantity first weighed), and try again to hit the point exactly by careful addition of decimal chloride of sodium solution. The value of the chloride of sodium solution is now known. . Reckon it to 1 grin, silver. Suppose we had used for 1-002 grm. silver 100 c. c. of concentrated and 3 c. c. of decimal chloride of sodium solution ; this makes altogether 100-3 of concentrated ; then 1-002: 1-000:: 100-3 : x x = 100-0998 We may without scruple put 100-1 for this number. We now know that lOO'l c. c. of the concentrated solution of chloride of sodium, measured at 16, exactly precipitates 1 grm. of silver. This relationship serves as the foundation of the calculation in actual assaying, and must be re- examined whenever there is reason to imagine that the strength of the chloride of sodium solution may have altered. 0. THE ACTUAL ASSAY OF THE SlLVER-ALLOY. Weigh off so much as contains about 1 grm. of silver, or better, a few nigrm. more ; * dissolve in a test-bottle in 5 to 7 c. c. nitric acid, and proceed in all respects exactly as in a. Suppose we had taken 1*116 grm. of the' alloy, and, in addition to the 100 c. c. of concentrated chloride of sodium solution, had used 5 c. c. of the dilute ( = 0'5 concentrated), how much silver would the alloy contain ? Presuming that we use the same chloride of sodium, solution which served as our example in a, 100*1 c. c. of which = 1 grm. silver, then 100-1 : 100-5 : : 1-000 : x x = 1-003996 (say 1-004). * In coins, which consist of 9 parts of silver and 1 part of copper, therefore take about 1 '1 15 or 1-120. In weighing off alloys of silver and copper, which do not cor- respond to the formula Ag fl Cu., (standard ^VooiP \ we must remember that they are never homogeneous in the mass ; thus, for instance, the pieces of metal from which coins are stamped, often show 1 '5 to 1 "7 in a thousand more silver in the middle than at the edges. In assaying alloys, then, portions from various parts of the mass must be taken, in order to get a correct result. The inaccuracy, how- ever, proceeding from the cause above mentioned, can only be completely over- come by fusing the alloy, and taking out a portion from the well-stirred mass f o* the assay. 214 DETERMINATION. [ 115, We may also arrive at the same result in the following manner : Na 01 Solution. For the precipitation of the silver in the alloy were used 10O5 c. c. For 1 grin, silver are necessary 10O1 c. c. Difference 0'4 c. c. There are, therefore, 4 mgrm. of silver present more than a grin., on the presumption thatO'l of the concentrated chloride of sodium solution (=1 c. c. of the decimal solution) corresponds to 1 mgrm. silver. This supposition, although not absolutely correct, may be safely made, for the inexactness it involves is too minute, as is evident from the previous calculation. Before we can execute this process exactly, we must know the quantity of silver the alloy contains very approximately. In assaying coins of known value this is the case, but with other silver alloys it is usually not so. Under the latter circumstances an approximate estimation must precedefthe regular assay. This is performed by weighing off |- grm. (or in the case of alloys that are poor in silver, 1 grm.), dissolving in 3 to C c. c. nitric acid, and adding from the burette chloride of sodium solution, first in larger, then in smaller quantities till the last drops produce no further turbidity. The last drops are not reckoned with the rest. The operation is conducted, as regards shaking, &c., as previously given. Suppose we had weighed off O5 grm. of the alloy, and employed 25 c. c. of the chloride of sodium solution taking the above supposed value of the latter We have 100-1 : 25 : : 1-000 : x 03 = 0-2497 that is, the silver in *5 grm. of the alloy; and as to the quantity of alloy we have to weigh off for the assay proper, We have -2497-: 1-003 : : -5 : x x= 2-008. This quantity will, of course, require more nitric acid for solution than was previously used (use 10 c. c.). In cases where the highest degree of accuracy is not required, the results afforded by this rough preliminary estimation will be accurate enough if the experiment is carefully conducted, since they give the quantity of silver present to within y^Vo" or "5 5ir- With alloys which contain sulphur, and with such as consist of gold and: silver, and contain a little tin, LEVOL * employs concentrated sulphuric acid (about 25 grm.) as solvent. The portion of the alloy is boiled with it till dissolved ; after cooling, the fluid is treated in the usual manner. As, however, concentrated sulphuric acid fails to dissolve all the silver when there is much copper present, MASCAZZINI f digests the weighed portion of alloy (which may contain small quantities of lead, tin, and antimony, besides gold) first with the least possible amount of nitric acid, Annul, de China, et de Phys. 3 sf lime as directed in 103. If this method is to yield accurate results, me solution must be neutral'or slightly acid with acetic acid y it must not contain alumina, sesquioxide of chro- mium, or oxides of the heavy metals, more especially sesquioxide of iron or oxide of copper ; therefore, where these conditions do not exist, they must first be supplied. b. Determination by means of Solution of Permanganate of Potassa. Determine the strength of the solution of permanganate of potassa, as directed p. 196, cc, by means of oxalic acid; then dissolve the compound in which the oxalic acid is to be estimated, and which must be free from all other bodies that might act on solution of permanganate of potassa, in 400 or 500 parts of water, or, as the case may be, acid and water ; add, if necessary, a further, not too small, quantity of sulphuric acid, heat to about 60, and then add the permanganate, drop by drop, with constant stirring, until the fluid just shows a red tint (compare p. 196), Knowing the quantity of oxalic acid which 100 c. c. of the standard per mangaiiate will oxidize, a simple calculation will give the quantity of oxalic acid corresponding to the c. c. of permanganate used in the ex periment. The results are very accurate. 137.] OXALIC ACID. 283 o. Determination from the reduced Gold (H.Ro-SE). a. In Compounds soluble in Water. Add to the solution of the oxalic acid or the oxalate a solution oi sodio-terchloride, or ammonio-terchloride of gold, and digest for some time at a temperature near ebullition, with exclusion of direct sunlight. Collect the precipitated gold on a filter, wash, dry, ignite, and weigh. 1 eq. gold (196) corresponds to 3 eq. C 2 O 3 (3x36=108). . In Compounds insoluble in Water. Dissolve in the least possible amount of hydrochloric acid, dilute with a very large quantity of water, in a capacious flask, cleaned pre- viously with solution of soda ; add solution of gold in excess, boil the mixture some time, let the gold subside, taking care to exclude sunlight, and proceed as in a. d. Determination as Carbonic A.cid. This may be effected either, a. By the method of organic analysis ( 174) ; or, |3. By mixing the oxalic acid or oxalate with finely pulverized binox- ide of manganese in excess, and adding sulphuric acid to the mixture, in an apparatus so constructed that the disengaged carbonic acid passes off perfectly dry. The theory of this method may be illustrated by the following equa- tion ' 2 O 3 +Mn 2 +S id 8^ rH tO ^ 05 ~ ^ as cq 1:0 o t>. 05 rtl *> xd lO OS b^ *- o CO OS O <0 GO oo -* *-* ^ O oo cq ^> o O GO ^H id CO 00 b- ^ id 00 05 CO t- CO - 1 ^H* oo t- I 1 ^ t^ -rjH id cq b- t^ *- id o fe . <^ o t^ tO i 1 ^ ^ !>. ?O r-H 00 iO CO CO -^ ^> id i i to b- ^ id "OS to os id Cq - 1 ^ CO \O i i rH O ^* ** .0 O5 lO to *- id b~ O OS 05 id to ^H 00 11 CO ^ ^H i i 10 00 ^ ^ ^ ^d 00 T^l tO ^ to ^ OS 05 o rH CO b- - 1 co co CO rH . oo co co o .d to co to *- id ^ CO OS id iO Cq iO - co i 1 CM T l O b- ^5 o id cq o to ^ id o O OS ^ OS 05 <=> co fci. OS id * os co ^ id r-H OS tO 50 id OS OS 00 oo >d CO 00 <* cq CO O id o to co ^ id b^ to lO d t^ 10 ^. cq lO O 10 oo O CO iO 00 oo xd r- 1 ^ ^ CM 00 ^ Oi d ^ ^ iO 50 id ^ oo o ,d O CO 'I cq t^ co as y means of Hydrofluoric Acid. The finely-pulverized silicate is mixed, in a platinum dish, with rather concentrated, slightly fuming hydrofluoric acid, the acid being added gradually, and the mixture stirred with a thick platinum wire. The mix- ture, which has the consistence of a thin paste, is digested some time on a water-bath at a gentle heat, and pure concentrated sulphuric acid, diluted with an equal quantity of water, is then added, drop by drop, in more than sufficient quantity to convert all the bases present into stTlphates. The mixture is evaporated on the water-bath to dryness, during which operation fluoride of silicon gas and hydrofluoric acid gas are continually volatilizing ; it is finally exposed to a stronger heat at some height above the lamp, until the excess of sulphuric acid is almost completely ex- pelled. The mass, when cold, is thoroughly moistened with concentrated hydrochloric acid, and allowed to stand for one hour ; water is then added, and a gentle heat applied. If the decomposition has fully succeeded, the whole must dissolve to a clear fluid. If an undissolved residue is left, the mixture is heated for some time on the water-bath, then allowed to deposit, the clear supernatant fluid decanted as far as practicable, the residue dried, and then treated again with hydrofluoric acid and sul- phuric acid, and, lastly, with hydrochloric acid, which will now effect complete solution, provided the analyzed substance was very finely pul- verized, and free from baryta, strontia (and lead). The solution is added to the first. The bases in the solution (which contains them as sulphates, and contains also free hydrochloric acid) are determined by the methods which will be found in Section V. The hydrofluoric acid may also be employed in combination with hydro- chloric acid ; thus 1 grm. of finely elutriated felspar, mixed with 40 c. c. water, 7 c. c. hydrochloric acid of 25$ and 3|- c. c. hydrofluoric acid, and heated to near the boiling point, dissolves completely in three minutes. 4 c. c. sulphuric acid are then added, the sulphate of baryta which sepa- rates is filtered off', and the filtrate evaporated till no more hydrofluoric acid escapes (AL. MITSCIIERLICH *). The execution of the method requires the greatest possible care, both fche liquid and the gaseous hydrofluoric acid being most injurious sub * Journ. f. prakt. Chem. 81, 108. 140.] SILICIC ACID. 303 stances. The treatment of the silicate with the acid and the evaporation must be conducted in the open air, otherwise the windows and all glass apparatus wil] be attacked. As the silicic acid is in this method simply inferred from the loss, a combination with the method a is often resorted to. [See also 160, 85.] [y. Decomposition by ignition with Carbonate of Lime and Chloride of Ammonium. PROF. J. L. SMITH'S METHOD for separating alkalies. Mix 1 part of the pulverized silicate with 1 part of dry chloride of ammonium,* by gentle trituration in a smooth mortar, then add 8 parts of carbonate of lime (Qual. Anal. p. 83) and mix intimately. Bring the mixture into a platinum crucible, rinsing the mortar with a little car- bonate of lime. Warm the crucible gradually over a small Bunsen burn- er until fumes of ammonia-salts no longer appear, then heat to full red- ness, but not too intensely, for from 30 to 40 minutes. f The mass should sinter together, but not fuse. When cold it may be usually detached with ease from the crucible. It is heated to boiling in a capsule with 100 c. c. of water for. several hours, or until it is entirely disintegrated and no lumps remain. Should the mass, from overheating, remain partially co- herent after long boiling, it may be transferred to a porcelain mortar and ground finely, and then boiled as before. Certain silicates, e. g. those con- taining much protoxide of iron, fuse easily with the proportions of flux above given. In their case it is better to repeat the ignition on a new portion, using 10 or 12 parts of carbonate of lime and bringing only the lower three-fourths of the crucible to a red heat. The fluxed mass, when completely disintegrated by boiling with water, yields to this solvent all the alkalies, with some chloride of calcium and caustic lime. It is filtered and well washed. To the liquid is added carbonate of ammonia (1 2 grms.) in solution, and the whole is evaporated to a bulk of about 30 c. c. Then a little more carbonate of ammonia, with some caustic ammonia, is added, to insure complete separation of the lime. Filter and collect the filtrate and washings in a weighed platinum cap- sule, evaporate to dryness on the water-bath, dry further, supporting the capsule within an iron cup to which heat is applied, and finally heat care- fully almost to redness, to expel ammonia-salts. When cool, weigh. The alkali-chlorides thus obtained are nearly pure ; but on dissolving in a few drops of water, a little black residue is usually seen. This may be re- moved, if weighable, by filtration, using a very small filter. Prof. SMITH'S method is by far the most convenient and accurate for separa- ting alkalies from a silicate, and is universally applicable, except, perhaps, in presence of boracic acid.] * The chloride of ammonium is best obtained in a pulverulent condition by dis- solving some of the salt in hot water and evaporating rapidly ; the greater portion of the chloride of ammonium 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- carried on in a water-bath, or in any other way with a corresponding- temperature. f An ordinary portable furnace, with a conical sheet-iron cap, of from two to three feet high, likewise answers the purpose perfectly well, all the requisite heat being afforded by it. 304 DETERMINATION. [ 141 SECOND GROUP. HYDROCHLORIC ACID HYDROBROMIC ACID HYDRIODIC ACID HYDRO CYANIC ACID HYDROSULPHURIC ACID. 1. HYDROCHLORIC ACID. I. Determination. Hydrochloric acid may be determined very accurately in the gravimetric as well as in the volumetric way.* a. Gravimetric Method. Determination as Chloride of Silver. Solution of nitrate of silver, mixed with some nitric acid, is added in excess to the solution under examination, the precipitated chloride is made to unite by application of heat and shaking, washed by decantation, dried, and ignited. The details of the process have been given in 115, 1, a, a. Care must be taken not to heat the solution mixed with nitric acid, before the solution of nitrate of silver has been added in excess. As soon as the latter is present in excess, the chloride of silver separates immediately and completely upon shaking the vessel, and the supernatant fluid becomes per- fectly clear after standing a short time in a warm place. The determina- tion of hydrochloric acid by means of silver is therefore more readily effected than that of silver by means of hydrochloric acid. In the case of smaller quantities of chloride of silver, the precipitate is often collected on a filter ; see 115, 1, &, |3. Or the two methods may be combined in this way that the chief portion of the precipitate is washed by decantation, dried in the porcelain crucible, and ignited, the decanted fluid being passed through a filter, to make quite sure that not a particle of chloride of silver be lost. The filter is, after drying, incinerated on the inverted cover of the porcelain crucible, the ashes are treated with a few drops of nitric acid, some hydrochloric acid is added, the mixture evaporated to dryness, the residue gently ignited, and the lid replaced on the crucible in which the chloride has been heated to incipient fusion ; a gentle heat is then once more applied, after which the crucible is allowed to cool under the desiccator, and then weighed. b. Volumetric Methods. a. By Solution of Nitrate of Silver. This convenient and accurate method requires a perfectly neutral solu- tion of nitrate of silver of known value. [This is best prepared by weighing off in a porcelain crucible about 4*8 grm. of clean crystallized nitrate of silver, fusing it at the lowest possible heat, and then ascertain- ing its weight accurately. After fusion it should weigh a little more than 4-7933 grm., the quantity that, contained in a litre of water, gives a so- lution of which 1 c. c. ='001 grm. of chlorine. The fused salt is dis- solved in a little warm water, the solution brought into a litre flask and filled to the mark, observing the usual precautions as to temperature, &c. When thus adjusted, add to the contents of the flask, from a bu- rette, enough water to bring the excess of nitrate of silver above 4*7933 gnns. to the requisite dilution. * For the acidimetric estimation of free hydrochloric acid, see 204. 141.] HYDROCHLORIC ACID. 305 grm. c. c. grm. c. c. 4-7933 : 1000 :: Excess over 4-7933 : Excess over 1000. Tn this way it is easy with a burette and a litre flask to make a per- fectly accurate standard solution, while this would be hardly possible should the operator weigh off less than 4'7933 grm. of nitrate of silver. This solution, which may be preserved in a well-corked bottle indefi- nitely, without change, is next tested by means of pure chloride of sodi- um. Either an equivalent solution is made by dissolving 1-6486 grm. of the coarsely powdered and gently ignited salt in 1 litre of water, and portions of 20 c. c. are taken, or several portions of the dry salt, 0'05 grm., are weighed off and dissolved, each in a separate beaker, in 20 30 c. o. of water. To each solution 2 drops of a cold saturated solution of pure yellow chromate of potassa is added.] Fill a HOUR'S burette (if it has an ERDMANN'S float so much the better) up to zero with the silver solution, and allow to drop slowly, with con- stant stirring, into the light yellow solution contained in one of the beakers. Each drop produces, where it falls, a red spot, which on stir- ring disappears, owing to the instant decomposition of the chromate of silver with the chloride of sodium. At last, however, the slight red col- oration remains. Now all chlorine has combined with silver, and a little chromate of silver has been permanently formed. [The number of c. c. of silver solution should be equal to the number of milligrammes of chlorine in the Na Cl employed. An excess of about 0'2 c. c. of silver solution will be required to produce a visible coloration, and hence this quantity may be deducted from the amount used. Should repeated trials show that the silver solution is not of exactly the intended strength, it may be brought to the precise standard by addition of water or nitrate in requi- site quantity. It is, however, ordinarily better to take the mean of several accordant determinations of the quantity of chlorine precipitated by 1 c. c. of the silver solution, and write this number on the label of the bottle, to be employed as a factor into which the no. of c. c. of silver so- lution required in any analysis is to be multiplied to find the quantity of chlorine sought for.] Being now in possession of a standard silver solution, and being practised in exactly hitting the transition from yellow to the shade of red, we can determine with precision hydrochloric acid or chlorine in the form of a metallic chloride soluble in water. The fluid to be tested must be neu- tral free acids dissolve the chromate of silver. The solution of the sub- stance is therefore, if necessary, rendered neutral by addition of nitric acid or carbonate of soda (it should be rather alkaline than acid), about 2 drops of the solution of yellow chromate added, and then silver from the burette, till the reddish coloration is just perceptible. If the operator fears he has added too much silver solution, i.e., if the red color is too strongly marked, he may add 1 c. c. of a solution of chloride of sodium containing 1-6486 in a litre (and therefore corns spending to the silver solution), and then add the silver drop by drop again. Of course in this case 1 c. c. must be deducted from the amount of silver solution used. The results are very satisfactory. The fluid to be analysed should be about the same volume as the solu- tions employed in standardizing the silver solution, and also about the same strength, otherwise the small quantity of silver which produces the 20 V>6 DETERMINATION. [ 141. coloration will not stand in the same proportion to the chlorine present. This small quantity of silver solution is extremely small, about 0*20 c. c., the inaccuracy hereby arising even in the case of quantities of chlorine differing widely from that originally used in standardizing the silver so- lution is therefore almost inconsiderable. If the amount of silver solu- tion necessary to impart the coloration always remained the same, we should have simply to deduct the amount in question with all experi- ments in order to avoid this small inaccuracy entirely ; since, however, this is not the case, but, on the contrary, much chloride of silver requires somewhat more chromate of silver for visible coloration, than less chlo- ride of silver, this method of proceeding would not always increase the exactness of the results. 3. J3y Solution of Nitrate of Silver and Iodide of Starch (PiSANi's method*). Add to the solution of the chloride, acidified with nitric acid, a slight excess of solution of nitrate of silver of known strength, warm, and filter. Determine the excess of silver in the filtrate by means of solution of iodide of starch (see p. 215), and deduct this from the amount of silver solution used. The difference shows the. quantity of silver which has combined with the chlorine ; calculate from this the amount of the latter. Results satisfactory. Of these volumetric methods of estimating chlorine, the first deserves the preference in all ordinary cases. PISANI'S method (6, |3) is especially suited for the estimation of very minute quantities of chlorine, but is not applicable when as in nitre analyses large quantities of alkaline nitrate are present (p. 211). II. Separation of CMorine from the Metals, a. In Soluble Chlorides. The same method as in I., a. The metals in the filtrate are separated from the excess of the salt of silver by the methods which will be found in Section V. Bichloride of tin, chloride of mercury, the chlorides of antimony, and the green chloride of chromium, form exceptions from the rule. a. From solution of bichloride of tin, nitrate of silver would precipitate, besides chloride of silver, a compound of binoxide of tin and oxide of silver. To precipitate the tin, therefore, the solution is mixed with a concentrated solution of nitrate of ammonia, allowed to deposit, the fluid decanted, and filtered (compare 126, 1, b), and the chlorine in the fil- trate is precipitated with solution of silver. LOWENTHAL, the inventor of this method, has proved its accuracy. f (3. When a solution of chloride of mercury is precipitated with solution of nitrate of silver, the chloride of silver thrown down contains an admix- ture of mercury. The mercury is, therefore, first precipitated by sul- phuretted hydrogen, which must be added in sufficient excess, and tht< chlorine in the filtrate determined as directed in 169. * Annal. d. Mines, X. 83 ; Liebig- and Kopp's Jahresbericht 1856, 751. f Journ f. prakt. Chem . 56, 871. 142.1 FREE CHLORINE. 307 y. The chlorides of antimony are also decomposed in the manner de scribed in 3. The separation of basic salt upon the addition of water may be avoided by addition of tartaric acid. The sulphide of antimony should be tested for chlorine. 5. Solution of silver fails to precipitate the whole of the chlorine from solution of the green chloride of chromium (PELIGOT). The chromium is, therefore, first precipitated with ammonia, the fluid filtered, and the chlorine in the filtrate precipitated as directed in I., a. b. In Insoluble, Chlorides. a. Chlorides soluble in Nitric Acid. Dissolve the chloride in nitric acid, without applying heat, and proceed as directed in I., a. j3. Chlorides insoluble in Nitric Acid (chloride of lead, chloride of silver, subchloride of mercury) . aa. Chloride of lead is decomposed by digestion with alkaline bicar- bonate and water. The process is exactly the same as for the decomposition of sulphate of lead ( 132. II., b., ). bb. Chloride of silver is ignited in a porcelain crucible, with 3 parts of carbonate of soda and potassa, until the mass commences to agglutinate. Upon treating the mass with water, the metallic silver is left undissolved ; the solution contains the alkaline chloride, which is then treated as directed in I., a. Chloride of silver may also be readily decomposed by digestion with pure zinc, and dilute sulphuric acid. The separated metallic silver may be weighed as such ; it must afterwards be ascertained, however, whether it dissolves in nitric acid to a clear fluid. The chlorine is determined in the solution of chloride of zinc obtained, as in I., a. cc. Subchloride of mercury is decomposed by digestion with solution of soda or potassa. The hydrochloric acid in the filtrate is deter- mined as in I., a. The suboxide of mercury is dissolved in nitric or nitrohydrochloric acid, and the mercury determined as directed in 117 or 118. c. The soluble chlorides of the metals of the fourth, fifth, and sixth groups may generally be decomposed also by sulphuretted hydrogen, or, as the case may be, sulphide of ammonium. The hydrochloric acid in the filtrate is determined as directed in 169. It must not be omitted to test the precipitated sulphides for chlorine. d. In many metallic chlorides, for instance, in those of the first and second groups, the chlorine may be determined also by evaporating with sulphuric acid, converting the base thus into a sulphate, which is then ignited and weighed as such ; the chlorine being calculated from the loss. This method is not applicable in the case of chloride of silver and chloride of lead, which are only imperfectly and with difficulty decomposed by sulphuric acid ; nor in the case of chloride of mercury and bichloride of tin, which sulphuric acid fails almost or altogether to decompose. Supplement. Determination of Chlorine in the Free State. 142. Chlorine in the free state may be determined both in the volumetric 308 DETERMINATION. [ and in the gravimetric way. The volumetric methods, however, deserve the preference in most cases. They are very numerous. I shall only here adduce that one which is undoubtedly the most accurate and at the same time the most convenient.* 1. Volumetric Method. With Iodide of Potassium (after BUNSEN). Bring the chlorine, in the gaseous form or in aqueous solution, into con- tact with an excess of solution of iodide of potassium in water. Each eq. chlorine liberates 1 eq. iodine. By determining the liberated iodine by means of hyposulphite of soda as described in 146, you will learn the quantity of chlorine with the greatest accuracy. If you have to deter- mine the chlorine of chlorine water, measure a portion off with a pipette. To prevent any of the gas entering the mouth, connect the upper end of the pipette with a tube containing moist hydrate of potassa laid between cotton. When the pipette has been correctly filled allow its contents to flow, with stirring, into an excess of solution of iodide of potassium ( 1 in 10). When the latter is in excess, a black precipitate is formed. If the chlorine is evolved in the gaseous condition, you may employ either the apparatus given in 130, I., d, j3, or the following, which is especially suitable where the chlorine is not pure, but is mixed with other gases. Fig. 59. a is a little flask, from which the chlorine is evolved by boiling the substance with hydrochloric acid ; it is connected with the tube b by means of a flexible tube. The latter must be free from sulphur should it contain sulphur it is well boiled with dilute potassa and then thoroughly washed. The thinner tube c, which has been fused to the bulb of b. leads through the caoutchouc stopper (which has been deprived of sul- * Compare article " Chlorimetry " in the Special Part. 143.] HYDROBROMIC ACID. 309 plmr) to the bulbed U-tube d, which contains solution of iodide of potas- sium, and which for safety is connected with the plain U-tube e, also containing iodide of potassium solution. Both tubes stand in a beaker filled with water. The apparatus offers the advantages that the fluid cannot return, that the iodide of potassium remains cold, and that the absorption is complete. After all the chlorine has been expelled by boiling long enough, rinse d and e out into a beaker and measure the iodine with standard hyposulphite of soda ( 146). 2. Gravimetric Method. The fluid under examination, which must be free from sulphuric acid, say, for instance, 30 grm. chlorine water, is mixed in a stoppered bottle, with a slight excess of hyposulphite of soda, say 0'5 grm., the stopper inserted, and the bottle kept for a short time in a warm place ; after which the odor of chlorine has disappeared. The mixture is then heated to boiling with some hydrochloric acid in excess, to destroy the excess of hyposulphite of soda, filtered, and the sulphuric acid in the filtrate determined by baryta (132). 1 eq. sulphuric acid corresponds to 2 eq. chlorine (WiCKE*). In fluids containing^ besides free chlorine^ also hydrochloric acid, or a metallic chloride, the chlorine existing in a state of combination may be determined, in presence of the free chlorine, in the following way : A weighed portion of the fluid is mixed with solution of sulphurous acid in excess, the mixture acidified, after some time, with nitric acid, and the whole of the chlorine precipitated as chloride of silver. The quantity of the free chlorine is then determined in another weighed portion, by means of iodide of potassium; the difference gives the amount of combined chlorine, f Having thus seen in how simple and accurate a manner the quantity of free chlorine may be determined by BUNSEN'S method, it will be readily understood that all oxides and peroxides which yield chlorine when heated with hydrochloric acid, may be analyzed by heating them with concentrated hydrochloric acid, and determining the amount of chlorine evolved. For the modus operandi compare 1. 143 - 2. HYDROBROMIC ACID. I. Determination. a. As bromide of silver. Free hydrobromic acid in a solution free from hydrochloric acid or chlorides is precipitated by silver solution, and the further process is conducted as in the case of hydrochloric acid ( 141). For the properties of bromide of silver, see 94, 2. The results are perfectly accurate. * Annal. d. Chem. u. Pharm. 99, 99. t If chlorine water is mixed at once with solution of nitrate of silver, only of the chlorine are obtained as chloride of silver: 6 Cl -+- 6 Ag O = 5 Ag Cl 4- Ag 0. Cl O , (H. Rose, Weltzien, Annal. d. Chem. u. Pharm. 91, 45). If chlorine water is mixed with ammonia in excess, there are formed at first chloride of am- monium and hypochlorite of ammonia, the latter then gradually decomposes into nitrogen and chloride of ammonium ; however, a little chlorate of ammo- nia is also formed besides (Schonbein, Journ. f. prakt. Chem. 84, 386) ; Zeit- schrif t f . analyt. Chem. 2, 59. 310 DETERMINATION. [ 143 The following methods are especially serviceable for the determination of small amounts of bromine; they are applicable in the presence of chlorides. b. With chlorine water and chloroform (after A. REIMANN*). This method depends on the facts that chlorine when added to bromides first liberates the bromine and then combines with it, and that bromine colors chloroform yellow or orange, while chloride of bromine merely commu- nicates a yellowish tinge to that fluid. The process is as follows : Mix the liquid containing a bromide of an alkali metal in neutral solution, in a stoppered bottle with a drop of pure chloroform about the size of a hazel-nut, then add standard chlorine water from a burette, protected from the light by being surrounded with black paper. On shaking, the chloroform becomes yellow, on further addition of chlorine water, orange, then yellow again, and lastly at the moment when 2 eq. chlo- rine have been used for 1 eq. bromine yellowish white (K Br -j- 2 01 = K Cl -|- Br Cl). Considerable practice and skill are required before the operator can tell the end-reaction. He will be assisted by placing the bottle on white paper and comparing the color of the chloroform with that of a dilute solution of yellow chromate of potassa of the required color. The strength of the chlorine water should depend on the amount of the bromine to be determined. It should be so adjusted that about 100 c. c. may be used. The chlorine water is standardized with iodide of potassium and hyposulphite of soda ( 142, 1). The method is es- pecially suited for the determination of small quantities of bromine in mother liquors, kelp, &c. The results are very approximate : e.g., 0'0180 instead of 0-01850-055 instead of 0'059 0'0112 instead of O'OIOO, &c. If the fluid contains organic substances, it is after being rendered alka- line with caustic soda evaporated to dryness, the residue ignited in a silver dish, extracted with water, the solution neutralized exactly with hydrochloric acid, and then tested. c. HEINE'S colorimetric method.^ The bromine is liberated by means of chlorine, and received in ether ; the solution is compared, with re- spect to color, with an ethereal solution of bromine of known strength, and the quantity of bromine in it thus ascertained. FEHLING^ obtained satisfactory results by this method. It will at once be seen that the amount of bromine contained in the fluid to be analyzed must be known in some measure, before this method can be resorted to. As the brine examined by FEIILING could contain at the most 0'02 grm. bromine in 60 grm., he prepared ten different test fluids, by adding to ten several portions of 60 grm. each of a saturated solution of common salt increas- ing quantities of bromide of potassium, containing respectively from 0'002 grm. to 0'020 grm. bromine. He added an equal volume of ether to the test fluids, and then chlorine water, until there was no further change observed in the color of the ether. It being of the highest im- portance to hit this point exactly, since too little as well as too much chlorine makes the color appear lighter, FEHLING prepared three samples of each test fluid, and then chose the darkest of them for the compari- son. 60 grm. are now taken of the mother liquor to be examined, the * Annal. d. Chem. u. Pharm. 115, 140. f Journ. f. prakt. Chem. 36, 184, proposed to effect the determination of bro- mine in mother liquors. \ Journ. f. pr\kt. Chem. 45, 269. The best way is to take them by measure. 144, 145.] HYDRIODIC ACID. 3H same volume of ether added as was added to the test fluids, and then chlorine water. Every experiment is repeated several times. Direct sunlight must be avoided, and the operation conducted with proper ex- pedition. In my opinion it is well to replace the ether by chloroform or bisulphide of carbon. II. Separation of Bromine from the Metals. The metallic bromides are analzyed exactly like the corresponding chlorides ( 141, II., a to cZ), the whole of these methods being appli- cable to bromides as well as chlorides. In the decomposition of bro- mides by sulphuric acid (141, II., d\ porcelain crucibles must be used instead of platinum ones, as the latter would be attacked by the liber- ated bromine. Supplement. Determination of Free Bromine. Free bromine in aqueous solution, or evolved in the gaseous form, is caused to act on excess of solution of iodide of potassium. Each eq. bromine liberates 1 eq. iodine, which is most conveniently determined by means of hyposulphite of soda (146). As regards the best mode of bringing about the action of the bromine on the iodide of potassium, compare 142, 1. The determination of free bromine in presence of hydrobromic acid or metallic bromides is eifected in the same manner as that of free chlorine in presence of hydrochloric acid (see 142, at the end). 145. 3. HYDRIODIC ACID. I. Determination. a. As IODIDE OF SILVER, GRAVIMETRICALLY. If you have hydriodic acid in solution, free from hydrochloric and hydrobromic acids, precipi- tate with nitrate of silver, and proceed exactly as with hydrochloric acid ( 141). For the properties of iodide of silver, see 94, 3. The results are perfectly accurate. b, As PROTIODIDE OF PALLADIUM, GRAVIMETRICALLY. The folloAving method, recommended first by LASSAIGNE, is resorted to exclusively to effect the separation of hydriodic acid from hydrochloric and hydrobromic acids, for which purpose it is extremely well adapted. Acidify the solu- tion slightly with hydrochloric acid, and add a solution of protochloride of palladium, as long as a precipitate forms ; let the mixture stand from 24 to 48 hours in a warm place, filter the brownish-black precipitate off on a weighed filter, wash with warm water, and dry at a temperature from about 70 to 80, until the weight remains constant. The drying may be greatly facilitated by replacing the water (after the operation of washing) by some alcohol, and the latter fluid again by a little ether. For the pro- perties of the precipitate, see 94, 3. This method gives very accurate results, provided the drying be managed with proper care ; but if the 312 DETERMINATION. [ 145 temperature is raised to near 100, the precipitate smells of iodine, and a trifling loss is incurred. Instead of simply drying the protiodide of palladium, and weigh ing it in that form, you may ignite it in a crucible of porcelain or pla tinurn,* and calculate the iodine from the residuary metallic palladium (H. ROSE). c. WITH CHLORINE WATER AND CHLOROFORM (after A. and F. DUPREJ-). This is based upon the circumstance that, when chlorine water or solution of chloride of soda is added to a metallic iodide, the first equivalent of chlorine liberates iodine, which then combines with 5 more equivalents of chlorine to pentachloride of iodine. GOLFIER-BES- SEYRE adds starch paste to render this transition perceptible, whilst A. and F. DUPRE employ, with much better success, chloroform or bisulphide of carbon, which are colored intensely violet by free iodine as well as by all compounds of iodine with chlorine containing less than 5 eq. chlorine. The process may be conducted in two different ways. a. Add chlorine water to a few litres of water, and determine the chlo- rine in the fluid as directed in 142. Take now of the fluid under examination a quantity containing no more than about 10 mgrm. iodine, and pour this into a stoppered bottle, add a few grammes of pure chloroform or pure bisulphide of carbon (free from sulphur and sulphuretted hydrogen), and then gradually, drop by drop, chlorine solution, adding and shaking vigorously by turns, until the violet color of the chloroform or bisulphide of carbon just disappears ; which point may be hit with the greatest precision. 6 eq. chlorine consumed in this process correspond to 1 eq. iodine. A still simpler way is to deter- mine the strength of the dilute chlorine water by making it act upon a known quantity of iodide of potassium, say 10 c. c. of a solution con- taining O'OOl grrn. iodine in 1 c. c., and then to apply it to the fluid under examination. The amount of chlorine consumed in the first experiment is, in that case, to the known amount of iodine as the quantity consumed in the second experiment is to x. In cases where the quantity of iodine is so considerable as, when sepa- rated, to impart a distinctly perceptible coloration to the fluid, it is better to delay adding the chloroform or bisulphide of carbon, until the color first produced has nearly disappeared again upon further addition of chlorine water. That this method cannot be employed in presence of substances liable to be acted upon by free chlorine or iodine, is self-evident ; organic matters, more particularly, must not be present. If they are, as is usually the case with mother liquors, the method - should be employed. /?. Add to the fluid under examination chloroform or bisulphide of carbon, then dilute chlorine water of unknown strength, until the fluid is just decolorized. At this point all the iodine is converted in I C1 5 . A dd now solution of iodide of potassium in moderate excess ; this will produce for every equivalent of I C1 5 , 6 eq. free iodine, which remain dissolved in the fluid. Determine the liberated iodine with hyposulphite of soda or sulphurous acid, as directed in 146, and divide the quantity found by 6 : the quotient expresses the quantity of iodine contained in the ex- amined fluid. j * This substance is not injured by the operation, f Annal. d. Chem. u. Pharm. 94, 365. 146.] FREE IODINE. 313 In presence of bromides, DUPRE'S method requires certain modifications, for which I refer to 169. This method is suited more particularly for the estimation of minute quantities of iodine. The results are most accurate. d. BY DISTILLATION WITH SESQUICHLORIDE OF IRON (after DUFLOS). When hydriodic acid or a metallic iodide is heated, in a distillatory apparatus, with solution of pure sesquichloride of iron, the whole of the iodine escapes along with the aqueous vapor and protochloride of iron is formed (Fe 3 C1 3 4- H I = 2 Fe 01 -f- H 01 + I). The iodine passing over is received in solution of iodide of potassium (apparatus, fig. 59, p. 308), and its quantity determined by means of hyposulphite of soda or sulphurous acid, as directed 146. In employing this method, it must be borne in mind that the sesquichloride of iron must be free from chlorine and nitric acid. It is best to prepare it from sesquioxide of iron and hydrochloric acid. e. BY SEPARATION WITH HYPONITRIC ACID. See separation of iodine from chlorine, 169. II. Reparation of Iodine from the Metals. The metallic iodides are analyzed like the corresponding chlorides. From iodides of the alkali metals containing free alkali the iodine may be precipitated as iodide of silver, by first saturating the free alkali almost completely with nitric acid, then adding solution of nitrate of silver in excess, and finally nitric acid to strongly acid reaction. If an excess of acid were added at the beginning, free iodine might separate, which is not converted completely into iodide of silver by solution of nitrate of silver. With respect to the salts insoluble in water, I have to observe that many of them are more advantageously decomposed by boiling with potassa or soda, than dissolved in dilute nitric acid, the latter process being apt to be attended with separation of iodine. This applies more particularly to subiodide of copper and to protiodide of palladium. From iodides soluble in water, the iodine may also be precipitated as protiodide of palladium. Lastly, it is open to the analyst in almost all cases to determine the base in one portion of the compound, by heating with concentrated sul- phuric acid, the iodine, in another portion, by the method I., e. The iodide of mercury is best decomposed by distillation with 8 to 10 parts of a mixture of 1 part cyanide of potassium with 2 parts anhydrous lime. Apparatus, fig. 50, p. 222 ; a b is filled with magnesite (H. HOSE *). /Supplement. Determination of Free Iodine. I46 - The determination of free iodine is an operation of great importance in analytical chemistry, since, as BUNSEN first pointed out, it is a means for the estimation of all those substances which, when brought into contact with iodide of potassium, separate from the same a definite quantity of iodine (e.g., chlorine, bromine, &c.), or, when boiled with hydrochloric acid, yield * Zeitschrif t f. anal. Chem. 2, 1. 314 DETERMINATION. [ 146. a defirJte quantity of chlorine (e.g., chromic acid, some peroxides, &c.), By causing the chlorine produced to act on iodide of potassium, we obtain the equivalent quantity of free iodine. BUNSEN AND SCHWARz's METHOD.- This method is based on the following reaction 2 (NaO S a OJ4-I = NaI-fNaOS 4 O 5 . a. REQUISITES. a. Iodine solution of known strengh. Dissolve 6*2 to 6*3 grin, iodine with the aid of about 9 grm. iodide of potassium (free from iodic acid) and water to about 1200 c. c. |3. Solution of hyposulphite of soda. Dissolve 12*2 to 12 '3 grm. of the pure and dry salt in water to about 1200 c. c. y. Solution of iodide of potassium. Dissolve 1 part of the salt (free from iodic acid) in about 10 parts of water. The solution must be col- orless and must remain so immediately after the addition of dilute sul- phuric or hydrochloric acid (either must be iron-free). 5. Starch solution. Stir the purest starch powder gradually with about 100 parts cold water and heat to boiling with constant stirring. Allow to cool quietly, and pour off the fluid from any deposit. The solution should be almost clear and free from all lumps. The starch solution is best prepared fresh before each series of experiments. b. PRELIMINARY DETERMINATIONS. ot. determination of the relation between the Iodine Solution and the Hyposulphite Solution. Fill two burettes with the solutions. Run 20 c. c. of the hyposul- phite into a beaker, add some water and 3 or 4 c. c. starch solution, then add the iodine till a blue coloration is just produced. If you have added a drop too much, run in one or two drops more of the hyposul- phite, and then more cautiously one drop after another of the iodine solution. After a few minutes read off the height of the fluid in both burettes. Suppose we had used 20 c. c. hyposulphite to 20'2 c. c. iodine. j8. Exact Determination of the Iodine in the Solution. This is performed by comparison with a known quantity of pure iodine ; the process is, as far as my experience goes, best conducted in the following manner : Select three watch-glasses, a, b, and c, which fit each other ; weigh b and c together accurately. Put about 0'5 grm. pure dry iodine (pre- pared according to 65, 6) into a, place it on an iron plate and heat gen- tly, till dense fumes of iodine esca,pe. Now cover it with b and regulate the heat so that the iodine may sublime entirely or almost entirely into b. Next remove 6, while still hot, give it a gentle swing in the air, to remove the still uncondensed iodine fumes and any traces of aqueous vapor, cover it with c, allow to cool under the desiccator, weigh and transfer the two watch-glasses, together with the weighed iodine, to a capacious beaker, containing a sufficient quantity of iodide of potassium solution to dissolve the whole of the iodine to a clear fluid. Now run in hyposulphite from the burette till the fluid is just decolorized, add 3 to 4 c. c. starch solution, and then iodine solution from a second burette, to incipient blueness. 146.] FREE IODINE. 315 After the two burettes have been read off, the following simple calcu- lation gives the strength of the iodine solution : Suppose we had weighed off 0'150 grm. iodine, and used 29*5 c. c. hyposulphite and 0*3 c. c. iodine solution. From a, we know that 20 c. c. hyposulphite correspond to 20*2 c. c. iodine solution; 29*5 c. c. therefore correspond to 29*8 c. c. Now 29-5 c. c. hyposulphite correspond to 0*150 grm. iodine -f-0'3 c. c. iodine solution. But 29'5 c. c. hyposulphite also correspond to 29*8 c. c. iodine solu- tion. .*.0*150 grm. iodine -f 0*3 c. c. iodine solution=29*8 c. c. iodine solu- tion. .'.0*150 grm. iodine 29*5 c. c. iodine solution. .*.! c. c. iodine solution=0*0050847 grm. iodine. The experiment just described is repeated and the mean of the two results taken, provided they exhibit sufficient uniformity. /. Dilution of the standard fluids to a convenient strength. With the aid of the iodine solution the strength of which we now know exactly, and the solution of hyposulphite of soda which stands in a known relation to the same, we might make any determinations of iodine. The calculation, although in principle extremely simple, is yet somewhat hampered by reason of the long decimal which expresses the quantity of iodine in 1 c. c. of the solution. It is therefore convenient o dilute the iodine solution so that 1 c. c. may exactly contain 0*005 grm. iodine. This is done by filling a litre flask therewith, and adding the necessary quantity of water; in our case 16*94 c. c., for 5 '. 5*0847 ::1000 : 1016*94. If the litre flask will hold above the mark, this 16*94 c. c., it is simply added, otherwise it is put into the dry bottle destined to receive the iodine solution, the iodine solution added, the whole shaken together, a portion of the fluid returned to the flask, shaken, poured back into the bottle, and the whole shaken again. The solution of hyposulphite may now be diluted in a corresponding manner. In our case we should have had to add 27*11 c. c. water to 1000 c. c. of the solution, as will be seen from the following considera- tion : 20*2 c. c. of the original iodine solution correspond to 20 c. c. of the hyposulphite solution. /.1000 c. c. correspond to 990*1 c. c. Now these 1000 c. c. were made up to 1016*94 by addition of water j if therefore we make up 990*1 c. c. of the hyposulphite of soda to the same bulk by addition of water we shall have equivalent solutions. Hence, to 990'1 c. c. we must add 26*84 c. c. water, or to 1000 c. c. 27*11 water. In such cases of dilution, I always prefer to take exactly 1 litre in- stead of an uneven number of c. c., as in measuring the latter errors and inaccuracies may readily occur; I have therefore, above, recommended the preparation of 1200 c. c. of the fluids, so that after their determina- tion 1000 c. c. may be sure to remain. c. THE ACTUAL ANALYSIS. "Weigh the iodine, best in a small flask, dissolve in the iodide of p tested also for silicic acid, as it frequently retains traces of this sub- stance. To this end, an aliquot part is fused with 3 4 parts of car- bonate of soda and potassa, the fused mass boiled with water, and the solution filtered ; hydrochloric acid is then added to the nitrate, and, should silicic acid separate, the fluid is filtered off from this substance. The tin is then precipitated by sulphuretted hydrogen, and the silicic acid still remaining in the filtrate is determined in the usual way ( 140). If hydrochloric acid has produced a precipitate of silicic acid, the last filtration is effected on the same filter (KHITTEL*) . b. ANTIMONY FROM THE METALS OF GROUPS IY. AND Y. IN ALLOYS. Proceed as in , filter off the precipitate, and convert it by igni- tion into antimoniate of teroxide of antimony ( 125, 2). Results only approximative, as a little teroxide of antimony dissolves. Alloys of antimony and lead, containing the former metal in ex- cess, should be previously fused with a weighed quantity of pure lead (YARRENTRAPpf). [See Tookey, Journ. Chem. Soc. xv. 464.] 5. Precipitation of Jlinoxide of Tin by Neutral Salts (e. g., Sulphate of Soda] or by Sulphuric Acid. TIN FROM THE OXIDES OF GROUPS I., II., III.; ALSO FROM PRO- TOXIDE OF MANGANESE, OXIDE OF ZINC, PROTOXIDES OF NICKEL AND COBALT, OXIDE OF COPPER (TEROXIDE OF GOLD). Precipitate the hydrochloric acid solution, which must contain 134 the tin entirely as binoxide (bichloride), according to 126, 1, &, by nitrate of ammonia or sulphate of soda (LOWENTHAL), or by sul- phuric acid, which, H. HOSE says, answers equally well. Alloys are treated as follows : First, oxidize by digestion with nitric acid ; when no more action takes place, evaporate the greater portion of the nitric acid in a porcelain dish, moisten the mass with strong hydrochloric acid, and after half an hour add water, in which the metachloride of tin and the other chlorides dissolve. Alloys of tin and gold are dissolved in aqua regia, the excess of acid evaporated, and the solution diluted with much water, before precipitating with sulphuric acid. It must be remembered that in this process any phosphoric acid that may be present is precipitated entirely or partially with the binoxide of tin. After the precipitate has been well washed by decantation, LOWENTHAL recommends to boil with a mixture of 1 part nitric acid (sp. gr. 1-2) and 9 parts water, then to transfer to the filter, and wash thoroughly. Results very satisfactory. If the fluid contains sesquioxide of iron, a portion of the latter always falls down with the tin. Hence the binoxide of tin must be tested for iron according to 128, /?, and if present, its amount must be determined and deducted. * Chem. Centralbl. 1857, 929. f Dingler's polyt. Journ. 158, 316. 164.] OXIDES OF GROUP VI. 393 6. Insolubility of Sulphide of Mercury in Hydrochloric Acid. MERCURY FROM ANTIMONY. Digest the precipitated sulphides with moderately strong hydro- 105 chloric acid in a distilling apparatus. The sulphide of antimony dis- solves, while the sulphide of mercury remains behind. Expel all the hydrosulphuric acid, then add tartaric acid, dilute, filter, mix the filtrate with the distillate which contains a little antimony, and pre- cipitate with sulphuretted hydrogen. The sulphide of mercury may be weighed as such (F. FIELD*). 7. Conversion of Arsenic and Antimony into Alkaline Arse- niate and Antimoniate. a. ARSENIC FROM THE METALS AND OXIDES OF GROUPS II., IY., AND Y. If you have to do with arsenites or arseniates, fuse with 3 parts 136 of carbonate of soda and potassa and 1 part of nitrate of potassa ; if an alloy has to be analyzed it is fused with 3 parts of carbonate of soda and 3 parts of nitrate of potassa. In either case the residue is boiled with water, and the solution, which contains the arseniates of the alkalies, filtered from the uiidissolved oxides or carbonates. The arsenic acid is determined in the filtrate as directed 127, 2. If the quantity of arsenic is only small, the fusion may be effected in a platinum crucible ; but if more considerable, the process must be conducted in a porcelain crucible, as platinum would be injuriously affected by it. In the latter case, bear in mind that the fused mass is contaminated with silicic acid and alumina. If the alloy contains much arsenic a small quantity may be readily lost by volatilization, even though the operation be cautiously conducted. In such a ca.se, therefore, it is better first to oxidize with nitric acid, then to evapo- rate, and to fuse the residue as above directed with carbonate of soda and nitrate of potassa. b. ARSENIC AND ANTIMONY FROM COPPER AND IRON, especially in ores containing sulphur. Diffuse the very finely pulverized mineral through pure solution 137 of potassa, and conduct chlorine into the fluid (comp. p. 327, A, 6). The iron and copper separate as oxides, the solution contains sulphate, arseniate, and antimoniate of potassa (RivoT, BEUDANT, and DAGUINJ ). c. ARSENIC AND ANTIMONY FROM COBALT AND NICKEL. Dilute the nitric acid solution with water, add a large excess of 138 potassa, heat gently, and conduct chlorine into the fluid until the pre- cipitate is black. The solution contains the whole of the arsenic and antimony, the precipitate the nickel and cobalt, in form of sesqui- oxide (RivoT, BEUDANT, and DAGUIN, loc. cit.) 8. Volatility of certain Chlorides or Metals. a. TIN, ANTIMONY, ARSENIC FROM COPPER, SILVER, LEAD, COBALT, NICKEL. Treat the sulphides with a stream of chlorine, proceeding exactly 139 * Quart. Journ. Chem. Soc. 12, 32. f Compt. rend. 1853, 835 ; Journ. f. prakt. Chem. 61, 133. 394 SEPARATION. [ 164. as directed in 119- In presence of antimony, fill the tubes E and F (fig. 68) with a solution of tartaric acid in water, mixed with hydrochloric acid. The metals may be also separated by this method in alloys. The alloy must be very finely divided. Arsenical alloys are only very slowly decomposed in this way. If tin and copper are separated in this manner, according to the experience of H. ROSE,* a small trace of tin remains with the chloride of copper. [See TOOKEY, Journ. Chem. Soc. xv., 466.] b. BINOXIDE OF TIN, TEROXIDE OF ANTIMONY (AND ALSO ANTI- MONIC ACID), ARSENIOUS, AND ARSENIC ACIDS, FROM ALKALIES AND ALKALINE EARTHS. Mix the solid compound with 5 parts of pure chloride of am- 140 inonium in powder, in a porcelain crucible, cover this with a concave platinum lid, on which some chloride of ammonium is sprinkled, and ignite gently until all chloride of ammonium is driven oft*; mix the contents of the crucible with a fresh portion of that salt, and repeat the operation until the weight remains constant. In this process, the chlorides of tin, antimony, and arsenic, escape, leaving the chlorides of the alkaline and alkaline earthy metals. The decomposition pro- ceeds most rapidly with alkaline salts. With regard to alkaline earthy salts it is to be observed that those which contain antimonic acid or binoxide of tin are generally decomposed completely by a double ignition with chloride of ammonium (magnesia alone cannot be separated perfectly from antimonic acid by this method). The alkaline earthy arseniates are the most troublesome ; the baryta, strontia, and lime salts usually require to be subjected 5 times to the operation, before they are free from arsenic, and the arseniate of magnesia it is impossible thoroughly to decompose in this way (H. RosEf). c. MERCURY FROM GOLD (SILVER, AND GENERALLY FROM THE N- VOLATILE METALS). Heat the weighed alloy in a porcelain crucible, ignite till the 141 weight is constant, and determine the mercury from the loss. If it is desired to estimate it directly, the apparatus, fig. 50, p. 222, may be used. In cases where the separation of mercury from metals that oxidize 011 ignition in the air is to be effected by this method, the operation must be conducted in an atmosphere of hydrogen (p. 181, fig. 47). 9. Volatility of SulpJiide of Arsenic. ARSENIC ACID FROM THE OXIDES OF MANGANESE, IRON, ZINC, LEAD, COPPER, NICKEL, COBALT (NOT OF SILVER, ALUMINUM, OR MAGNESIUM). Mix the arsenic acid compound (no matter whether it has been 142 air-dried or gently ignited) with sulphur, and ignite under a good draught in an atmosphere of hydrogen (p. 181, fig. 47 ; the per- forated lid must in this case be of porcelain). The whole of the arsenic volatilizes, the sulphides of maganese, iron, zinc, lead, and copper remain behind ; they may be weighed directly. After weigh- ing, add a fresh quantity of sulphur to the residue, ignite as before, * Pogg. Anna! 112, 169. f Ibid. 73, 582 ; 74, 578 ; 112, 173. 164.] OXIDES OF GROUP VI. 395 and weigh again ; repeat this operation until the weight remains constant. Usually, if the compound was intimately mixed with the sulphur, the conversion of the arseniate into sulphide is com- plete after the first ignition. Results very good. In separating nickel the analyst will remember that the residue cannot be weighed directly, since it does not possess a constant com- position ; hence the ignition in hydrogen may be saved ; arseniate of nickel loses all its arsenic on being simply mixed with sulphur and heated. The heat should be moderate and continued, till no more red sulphide of arsenic is visible on the inside of the porcelain crucible. It is advisable to repeat the operation. The separation of arsenic from cobalt cannot be completely effected in this manner even by repeated treatment with sulphur, but it can be effected by oxidiz- ing the residue with nitric acid, evaporating to dryness, mixing with sulphur, and re-igniting. Smaltine and cobaltine must be treated in the same manner (H. ROSE*). I should not forget to mention that EBELMEN,! a long while ago, noticed the separation of arsenic acid from sesquioxide of iron by ignition in a stream of sulphuretted hy- drogen. 10. Separation of Arsenic as Arseniate of Magnesia and Ammonia. ARSENIC ACID FROM OXIDE OF COPPER, OXIDE OF CADMIUM,. SESQUIOXIDE OF IRON, PROTOXIDE OF MANGANESE, PROTOXIDE OF NICKEL, PROTOXIDE OF COBALT, ALUMINA. Mix the hydrochloric acid solution, which must contain the whole 143 of the arsenic in the form of arsenic acid, with enough tartaric acid to prevent precipitation by ammonia, precipitate the arsenic acid accord- ing to 127, 2, as arseniate of magnesia and ammonia, allow to settle, filter, wash once with a mixture of 3 parts water and 1 part ammonia, redissolve in hydrochloric acid, add a very minute quantity of tar- taric acid, supersaturate again with ammonia, allow to deposit, and determine the now pure precipitate according to 127, 2. In the filtrate the bases of Groups IY. and Y. may be precipitated by sulphide of ammonium ; if alumina is present, evaporate the solution filtered from the sulphides with addition of carbonate of soda and a little nitre to dryness, fuse, and estimate the alumina in the residue. The method is more adapted to the separation of rather large than of very small quantities of arsenic from the above named oxides, since in the case of small quantities the minute portions of arseniate of magnesia and ammonia that remain in solution may exercise a considerable influence on the accuracy of the result. [See Editor's note to 135 e, a.] 11. Separation of Arsenic as Arseniomolyldate of Ammonia. ARSENIC ACID FROM ALL OXIDES OF GROUPS I. V. Separate the arsenic acid as directed in 127, 2, b ; long continued 144 heating at 100 is indispensable. The determination of the bases is most conveniently effected in a special portion (cornp. 135, k.) * Zeitschrift f. anal. Chem. 1, 413. f Anal, de Chim. et de Phys. (3) xxv. 98. 396 SEPARATION. [ 164. 12. Insolubility of Arseniate of Sesquioxide of Iron. ARSENIC Acm FROM THE BASES OF GROUPS I. AND II., AND FROM OXIDE OF ZINC, AND THE PROTOXIDES OF MANGANESE, NICKEL, AND COBALT. Precipitate the arsenic acid, according to circumstances, as di- 145 rected 127, 3, a or b, filter, and determine the bases in the filtrate. 13. Methods based upon the Insolubility of some Chlorides. a. SILVER FROM GOLD. Treat the alloy with cold dilute nitrohydrochloric acid, dilute, and 14 6 filter the solution of the terchloride of gold from the undissolved chloride of silver. This method is applicable only if the alloy con- tains less than 15 per cent, of silver ; for if it contains a larger proportion, the chloride of silver which forms protects the unde- composed part from the action of the acid. In the same way silver may be separated also from platinum. b. OXIDE OF MERCURY FROM THE OXYGEN COMPOUNDS OF ARSENIC AND ANTIMONY. Precipitate the mercury from the hydrochloric solution by means 147 of phosphorous acid as subchloride (118, 2, a). The tartaric acid, which in the presence of antimony must be added, does not inter- fere with the reaction (H. ROSE*). 14. Insolubility of certain Sulphates in Water or Spirit of Wine. a. ARSENIC ACID FROM BARYTA, STRONTIA, LIME, AND OXIDE OF LEAD. Proceed as for the separation of phosphoric acid from the same 148 oxides ( 135, b). The compounds of these bases with arsenious acid are first converted into arseniates, before the sulphuric acid is added ; this conversion is effected by heating the hydrochloric acid solution with chlorate of potassa. b. ANTIMONY FROM LEAD. Treat the alloy with a mixture of nitric and tartaric acids. The 149 solution of both metals takes place rapidly and with ease. Preci- pitate the greater part of the lead as sulphate ( 116, 3), filter, pre- cipitate with sulphuretted hydrogen, and treat the sulphides ac- cording to 128 with sulphide of ammonium, in order to separate the antimony from the lead left unprecipitated by the sulphuric acid (A. STRENGf). 15. Different deportment with Cyanide of Potassium. GOLD FROM LEAD AND BISMUTH. These metals maybe separated in solution by cyanide of potassium 150 in the same way in which the separation of mercury from lead and bismuth is effected (see 109)- The solution of the double cyanide of gold and potassium is decomposed by boiling with aqua regia, and, after expulsion of the hydrocyanic acid, the gold determined by one of the methods given in 123. * Pogg. AnnaL 110, 536. f Ding, polyt. Journ. 151, 389. 165.] OXIDES OF GROUP VI. 397 II. SEPARATION OF THE OXIDES OF THE SIXTH GROUP FROM EACH OTHER. 165. Index : The Nos. refer to those in the margin. Platinum from gold, 151, 162. u tin, antimony, and arsenic, 152. Gold from platinum, 151, 162. tin, 152, 161. antimony and arsenic, 152. Tin from platinum, 152. " gold, 134, 152, 161, " arsenic, 153, 157, 158, 160, 163. antimony, 154, 159, 160. Protoxide of tin from the binoxide, 166. Antimony from platinum and gold, 152. " arsenic, 154, 155, 158. tin, 154, 159, 160. Teroxide of antimony from antimonic acid, 165. Arsenic from platinum and gold, 152. tin, 153, 157, 1158, 160, 163. antimony, 154, 155, 158. Arsenious acid from arsenic acid, 156, 164. 1. Precipitation of Platinum as Potassiobichloride of Plat- inum. PLATINUM FROM GOLD. Precipitate from the solution of the chlorides the platinum as di-151 rected 124, b, and determine the gold in the nitrate as directed 123, b. 2. Volatility of the Chlorides of the inferior Metals. PLATINUM AND GOLD FROM TIN, ANTIMONY, AND ARSENIC. Heat the finely divided alloy or the sulphides in a stream of chlo-152 rine gas. Gold and platinum are left, the chlorides of the other metals volatilize (compare 50)* 3. Volatility of Arsenic and Tersulphide of Arsenic. a. ARSENIC FROM TIN (H. ROSE). Convert into sulphides or into oxides, dry at 100, and heat a 153 weighed portion with addition of a little sulphur in a bulb-tube or tray, gently at first, but gradually more strongly, conducting a stream of dry sulphuretted hydrogen gas through the tube during the operation. Sulphur and tersulphide of arsenic volatilize, sul- phide of tin is left. The tersulphide of arsenic is received in U- tubes containing dilute ammonia, which are connected with the bulb-tube, in the manner described in 119. When upon continued application of heat no sign of further sublimation is observed in the colder part of the bulb-tube, drive off the sublimate which has col- lected in the bulb, allow the tube to cool, and then cut it off above the coating. Divide the separated portion of the tube into pieces, and heat these with a little solution of soda until the sublimate is dissolved ; unite the solution with the ammoniacal fluid in the re- ceiver, add hydrochloric acid, then, without filtering, chlorate of 398 SEPARATION. [ 165 potassa, and heat gently until the tersulphide of arsenic is complete- ly dissolved. Filter from the sulphur, and determine the arsenic as directed 127, 2. The quantity of tin cannot be calculated at once from the blackish-brown sulphide of tin in the bulb, since this contains more sulphur than corresponds to the formula Sn S. It is therefore weighed, and the tin determined in a weighed portion of it, by converting it into binoxide, which is effected by moistening with nitric acid, and roasting ( 126, 1, c). Tin and arsenic in alloys are more conveniently converted into oxides by cautious treatment with nitric acid. If, however, it is wished to convert them into sulphides, this may readily be effected by heating 1 part of the finely divided alloy with 5 parts of car- bonate of soda, and 5 parts of sulphur, in a covered porcelain cru- cible, until the mass is in a state of calm fusion. It is then dis- solved in water, the solution filtered from the sulphide of iron, &c., which may possibly have formed, and the filtrate precipitated with hydrochloric acid. If the tin only in the alloy is to be estimated directly, while the arsenic is to be found from the difference, convert as above directed into sulphides or oxides, mix with sulphur and ignite in a porcelain crucible with perforated cover in a stream of sulphuretted hydro- gen. The residual arsenic-free protosulphide of tin is to be con- verted into binoxide and weighed as such. 4. Methods based upon the insolubility of Antimoniate of Soda. a. ANTIMONY FROM TIN AND ARSENIC (H. EOSE). If the substance is metallic, oxidize the finely divided weighed 154 sample, in a porcelain crucible, with nitric acid of 1'4 sp. gr., adding the acid gradually. Dry the mass on the water-bath, transfer to a silver crucible, rinsing the last particles adhering to the porcelain into the silver crucible with solution of soda, dry again, add eight times the bulk of the mass of solid hydrate of soda, and fuse for some time. Allow the mass to cool, and then treat with hot water until the undissolved residue presents the appearance of a fine powder ; dilute with some water, and add one third the volume of alcohol of 0'83 sp. gr. Allow the mixture to stand for 24 hours, with frequent stirring ; then filter, transfer the last adhering parti- cles from the crucible to the filter by rinsing with dilute spirit of wine (1 vol. alcohol to 3 vol. water), and wash the undissolved residue on the filter, first with spirit of wine containing 1 vol. alco- hol to 2 vol. water, then with a mixture of equal volumes of alcohol and water, and finally with a mixture of 3 vol. alcohol and 1 vol. water. Add to each of the alcoholic fluids used for washing a few drops of solution of carbonate of soda. Continue the washing until the color of a portion of the fluid running off remains unal- tered upon being acidified with hydrochloric acid and mixed with sulphuretted hydrogen water. Rinse the antimoniate of soda from the filter, wash the latter with a mixture of hydrochloric and tartaric acids, dissolve the an- timoniate in this mixture, precipitate with sulphuretted hydrogen, and determine the antimony as directed 125, 1. To the filtrate, which contains the tin and arsenic, add hydro- 1G5.] OXIDES OF GROUP VI. 399 chloric acid, which produces a precipitate of arseniate of binoxide of tin ; conduct now into the unfiltered fluid sulphuretted hydrogen for some time, allow the mixture to stand at rest until the odor of that gas has almost completely gone off, and separate the weighed sulphides of the metals which contain free sulphur, as in 153. If the substance contains only antimony and arsenic, the alco- holic filtrate is heated, with repeated addition of water, until it scarcely retains the odor of alcohol ; hydrochloric acid is then added, and the arsenic acid determined as arseniate of magnesia and ammonia ( 127, 2). b. Small quantities of the sulphides of arsenic and antimony mixed with sulphur are often obtained in mineral analysis. The two metals may in this case be conveniently separated as follows : Oxidize the precipitate with chlorine-free red fuming nitric acid, evaporate the solution nearly to dryness ; mix the residue with a copious excess of carbonate of soda, add some nitrate of soda, and treat the fused mass as given in a. If, on the other hand, you have a mixture of sulphides of tin and antimony to analyze, oxidize it with nitric acid of 1*5 sp. gr., and treat the residue obtained on evaporation as given in a. 5. Precipitation of Arsenic as Arseniate of Ammonia- a. ARSENIC FROM ANTIMONY. Oxidize the metals or sulphides with nitrohydrochloric acid or 155 hydrochloric acid and chlorate of potassa, or with chlorine in alka- line solution (p. 327, A, b) ; add tartaric acid, a large quantity of chloride of ammonium, and then ammonia in excess. (Should the addition of the latter reagent produce a precipitate, this is a proof that an insufficient quantity of chloride of ammonium or of tartaric acid has been used, which error must be corrected before proceeding with the analysis.) Then precipitate the arsenic acid as directed 127, 2, and determine the antimony in the nitrate as directed in 125, 1. As basic tartrate of magnesia might precipitate with the arseniate of magnesia and ammonia, the precipitate should always, after slight washing, be redissolved in hydrochloric acid, and the solution reprecipitated with ammonia. An excellent method. b. ARSENIOUS ACID FROM ARSENIC ACID. Mix the sufficiently dilute solution with a large quantity of chlo- 156 ride of ammonium, precipitate the arsenic acid as directed 127, 2, and determine the arsenious acid in the nitrate by precipitation with sulphuretted hydrogen ( 127, 4). LUDWIG* has observed that if the solution is too concentrated, arsenite of magnesia falls down with the arseniate of magnesia and ammonia, hence it is necessary to dissolve the weighed magnesia precipitate in hydrochloric acid and test the solution with sulphuretted hydrogen. The presence of arsenious acid will be betrayed by the immediate formation of a precipitate. * Archiv f iir Pharm. 97, 24. 400 SEPARATION. [ 165, C. BlNOXIDE OF TlN FROM ARSENIC ACID (LENSSEN*). The oxides obtained by oxidation with nitric acid are digested 157 with ammonia and yellow sulphide of ammonium, arid the arsenic precipitated from the clear solution according to 127, 2, as arseni- ate of magnesia and ammonia. On acidifying the nitrate the tin separates as bisulphide. 6. Behavior of the Sulphides towards Bisulphite of Potassa. ARSENIC FROM ANTIMONY AND TIN (BUNSENJ). If freshly precipitated sulphide of arsenic is digested with sul- 158 phurous acid and sulphite of potassa, the precipitate is dissolved ; on boiling, the fluid becomes turbid from separated sulphur, which turbidity for the most part disappears again on long boiling' The fluid contains, after expulsion of the sulphurous acid, arsenite and hyposulphite of potassa. 1 2 As 83+8 (K O, 2 S O a )=2 (KO, As O 3 ) + 6(K O, S. 2 O 2 ) + S 3 +7 S OJ The sulphides of antimony and tin do not exhibit this reaction. Both therefore may be separated from sulphide of arsenic by pre- cipitating the solution of the three sulphides in sulphide of potas- sium with a large excess of aqueous sulphurous acid, digesting the whole for some time in a water-bath, and then boiling till two- thirds of the water and the whole of the sulphurous acid are ex- pelled. The residuary sulphide of antimony or tin is arsenic-free, the filtrate contains the whole of the arsenic and may be immedi- ately precipitated with sulphuretted hydrogen. BUNSEN determines the arsenic by oxidizing the dried sulphide together with the filter with fuming nitric acid, diluting the solution a little, warming gen- tly with a little chlorate of potassa (in order to oxidize more fully the substances formed from the paper), and finally precipitating as arseniate of magnesia and ammonia. With regard to the separation of sulphide of tin from the solu- tion of arsenite of potassa it is to be observed, that the sulphide of tin must be washed with concentrated solution of chloride of sodium, as, if water were used, the fluid would run through tur- bid. As soon as the precipitate is thoroughly washed with the chlo- ride of sodium solution, the latter is displaced by solution of ace- tate of ammonia, containing a slight excess of acetic acid. These last washings must not be added to the first, as the acetate of am- monia hinders the complete precipitation of the arsenious acid by sulphuretted hydrogen. The test-analyses adduced by BUNSEN show very satisfactory results. 7. Methods based upon the Separation of the Metals themselves, or on the different Deportment of the same with Acids. a. TIN FROM ANTIMONY [TooKEY,f CLASSEN ||]. [The alloy or mixture must contain 8 10 times as much tin as 159 antimony. If need be, add a weighed amount of pure tin, to estab- lish this proportion. * Annal. d. Chem. u. Pharm. 114, 116. \ Ibid. 106, 3. t Journ. Chem. Soc. xv. 462. j Journ. f. prakt. Chem. xcii. 477. 165.] OXIDES OF GROUP VI. 401 The metals are dissolved in hydrochloric acid and a little nitric acid, the solution is heated nearly to boiling, and then piano wire (solu- ble without residue in acids) added little by little as long as any iron dissolves. It is necessary that no excess of metallic iron remain. Therefore, when all the antimony appears to be thrown down and all the iron dissolved, add a little hydrochloric acid, and after the precipitate has settled, pour off the clear liquid and observe whether iron will produce any further precipitation. It is thus easy to be certain that all the antimony is separated, and that it is unmixed with metallic iron. Wash the antimony with hot water to which at first a few drops of hydrochloric acid are added. Finally, dis- place the water that adheres to the precipitate by means of absolute alcohol, and the latter by a few drops of ether, and dry at 100. The tin is separated from the filtrate by sulphuretted hydrogen.] b. MUCH TIN FROM LITTLE ANTIMONY AND ARSENIC. If an alloy of the three metals is treated in a very finely divided 160 condition in a stream of carbonic acid with strong hydrochloric acid, the whole of the tin dissolves to protochloride. A part of the arsenic and antimony escapes as arsenetted and antimonetted hydrogen, whilst the rest remains behind in the state of metal, or, as the case may be, of a solid combination with hydrogen. Conduct the gas through several U-tubes, containing a little chlorine-free red fuming nitric acid, whereby the arsenic and antimony will be oxidized. When the solution is effected, dilute the contents of the flask with air-free water to a certain volume, mix, allow to settle and determine the tin in an aliquot part, either gravimetrically or volumetrically. Filter the rest of the fluid, wash the precipitate thoroughly, dry the filter with its contents in a porcelain crucible, add the contents of the TJ-tubes, evaporate to dryness, and in the residue separate the antimony and arsenic as directed 154- c. TIN FROM GOLD. Gold may be separated from excess of tin by boiling the finely 161 divided alloy with only slightly diluted sulphuric acid, to which hydrochloric acid has been cautiously added. The tin dissolves as protochloride. Heat is applied till the sulphuric acid begins to volatilize copiously. Binoxide of tin is formed which dissolves in the concentrated sulphuric acid, while the gold remains behind. On addition of much water, the binoxide of tin falls, mixed with finely divided gold, in the form of a purple-red precipitate. On warming with concentrated sulphuric acid the binoxide of tin finally redis- solves while the gold is left pure (H. ROSE*). d. PLATINUM FROM GOLD. The aqua regia solution is freed as far as possible from nitric acid 162 by evaporation with hydrochloric acid, and treated with a solution of protochloride of iron, the gold being determined as directed 123, b. The platinum maybe precipitated from the filtrate by sul- phuretted hydrogen according to 124, c. 8. Precipitation of Tin as Arseniate of the Binoxide. TIN FROM ARSENIC. E. HAFFELYJ has proposed the following method of determin- Pogg. Annal. 112, 172. f K"l. Mag. x. 220; 26 402 SEPARATION. [ 16b, ing both the tin and the arsenic in commercial stannate of soda, 163 which often contains a large admixture of arseniate of soda. Mix a weighed sample with a known quantity of arseniate of soda in excess, add nitric acid also in excess, boil, filter off the precipitate, which has the composition 2 Sn O 2 , As O 5 +10 aq., and wash; expel the water by ignition, and weigh the residue, which consists of 2 Sn O.,, As O 6 . In the filtrate determine the excess of arsenic acid as directed 127, 2. The amount of the binoxide of tin is found from the weight of the precipitate, that of the arsenic acid is obtained by adding the quantity in the precipitate to the quantity in the fil- trate, and deducting the quantity added. 9. Volumetric Methods. a. ARSENIOUS FROM ARSENIC ACID. Convert the whole of the arsenic in a portion of the substance 164 into arsenic acid and determine the total amount of this as directed 127, 5, b ; determine in another portion the arsenious acid as di- rected in 127, 5, a, and calculate the arsenic acid from the dif- ference. b. TEROXIDE OF ANTIMONY FROM ANTIMONIC ACID. Determine in a sample of the substance the total amount of the 165 antimony as directed 125, 1, in another portion that of the terox- ide as directed 125, 3, and calculate the antinionic acid from the difference. c. PROTOXIDE OF TIN IN PRESENCE OF BINOXIDE. In one portion of the substance convert the whole of the protox-166 ide into binoxide by digestion with chlorine water or some other means, and determine the total quantity of tin as directed 126, 1, b in another portion, which, if necessary, is to be dissolved in hydrochloric acid in a stream of carbonic acid, determine the pro- toxide according to 126, 2. II. SEPARATION OF THE ACIDS FROM EACH OTHER. It must not be forgotten that the following methods of separation proceed generally upon the assumption that the acids exist either in the free state, or in combination with alkaline bases ; compare the introductory remarks, p. 337- Where several acids are to be determined in one and the same substance, we very often use a sep- arate portion for each. The methods here given do not embrace every imaginable case, but only the most important cases, and those of most frequent occurrence. FIRST GROUP. ARSENIOUS ACID ARSENIC ACID CHROMIC ACID SULPHURIC ACID PHOSPHORIC ACID BORACIC ACID OXALIC ACID HYDROFLUORIC ACID SILICIC ACID CARBONIC ACID. 166. 1. ARSENIOUS ACID AND ARSENIC ACID FROM ALL OTHER ACIDS. Precipitate the arsenic from the solution by means of sulphuretted 167 166.] ACIDS OF GROUP I. 403 hydrogen ( 127, 4, a or b), filter, and determine the other acids in the filtrate. It must be remembered, that the tersulphide of arsenic will be obtained mixed with sulphur if chromic acid, sesquioxide of iron, or any other substances which decompose sulphuretted hydro- gen are present. From those acids which form soluble salts with magnesia, arsenic acid may be separated also by precipitation as arseniate of magnesia and ammonia as directed 127, 2. 2. SULPHURIC ACID FROM ALL THE OTHER ACIDS. a. From, Arsenious, Arsenic, Phosphoric, JBoracic, Hydrofluoric, Oxalic, Silicic, and Carbonic Acids* Acidify the dilute solution strongly with hydrochloric acid, mix 168 with chloride of barium, and filter the sulphate of baryta from the solution, which contains all the other acids. Determine the sulphate of baryta as directed 132. If acids are present with which baryta forms salts insoluble in water but soluble in acids, the sulphate of baryta is apt to carry down with it such salts, and this is all the more liable to happen, the longer the precipitate is allowed to settle. This remark applies especially to the oxalate and tartrate of baryta and the baryta salts of other organic acids (H. ROSE). In such cases I would recommend, after washing, to stop up the neck of the funnel, and digest the pre- cipitate with a solution of bicarbonate of soda, then to wash with water, with dilute hydrochloric acid, and again with water. In every case, however, the purity of the weighed sulphate of baryta must be tested as directed 132, 1. b. From Hydrofluoric Acid in Insoluble Compounds. A mixture of sulphate of baryta and fluoride of calcium cannot 169 be decomposed by simple treatment with hydrochloric acid ; the in- soluble residue contains, besides sulphate of baryta, sulphate of lime and fluoride of barium. The object in view may be attained, how- ever, by the following process : Fuse the substance with 6 parts of carbonate of soda and potassa, and 2 parts of silicic acid ; allow the mass to cool, treat with water, and add carbonate of ammonia to the solution obtained ; filter, wash the separated silicic acid with dilute solution of carbonate of ammonia, supersaturate the filtrate with hy- drochloric acid, and precipitate with chloride of barium. If you wish to determine the fluoride also, acidify with nitric acid, precipitate with nitrate of baryta, then saturate with carbonate of soda, and precipitate the fluoride of barium by spirit of wine. Wash a long time, first with spirit of wine of 50 per cent., then with strong alcohol ; dry, ignite, and weigh. The insoluble residue left upon treating with water contains the baryta and lime. Dissolve in hydro- chloric acid, separate the silicic acid, and determine the bases as directed 154 (H. ROSE). c. In presence of a large proportion of Chromic Acid. Reduce the chromic acid by boiling the dry compound with con- 170 centrated hydrochloric acid (if this process is conducted after p. 258, * With respect to the separation of sulphuric acid from selenic acid, comp. Wohlwill (Annal. d. Chem. u. Pharm. 114, 183). 401 SEPARATION. [ 166 it gives, at the same time, the quantity of the chromic acid) ; dilute the solution largely, and precipitate,, first the sulphuric acid by adding chloride of barium in slight excess, then the excess of baryta by sul- phuric acid, and lastly the sesquioxide of chromium by ammonia. d. From Ifydrofluosilicic Acid. Precipitate the hydrofluosilicic acid as directed 133, then thesul- 171 phuric acid in the nitrate by baryta. 3. PHOSPHORIC ACID FROM THE OTHER ACIDS. a. From the acids of arsenic, see 167 5 fr m sulphuric acid, see 172 168. b. From Chromic Acid. Precipitate the phosphoric acid as phosphate of magnesia and ammonia (134, b). Determine the chromic acid in the filtrate as directed 130, a, p, 6, c, or d. c. From Boracic Acid. Precipitate the phosphoric acid with a solution of chloride of mag- 173 iiesium and chloride of ammonium, and determine it as pyrophos- phate of magnesia ( 134, b). Determine the boracic acid in the filtrate as directed 136, I., c. d. From Oxalic Acid. a. If the two acids are to be determined in one portion, the aqueous 174 solution is mixed with sod io-ter chloride of gold in excess,heat applied, and the quantity of oxalic acid present calculated from that of the reduced gold ( 137, c, a). The gold added in excess is separated from the filtrate by means of sulphuretted hydrogen, and the phos- phoric acid then precipitated by sulphate of magnesia. If the com- pound is insoluble in water, hydrochloric acid is used as solvent, and the process conducted as directed 137, c, |3. |3. If there is enough of the substance, the oxalic acid is deter- 175 mined in one portion according to the direction of 137, b or d, and the phosphoric acid in another portion. If the substance is soluble in water, and the quantity of oxalic acid inconsiderable, the phos- phoric acid may be precipitated at once with sulphate of magnesia, chloride of ammonium, and ammonia ; if not, the substance is igni- ted with carbonate of soda and potassa, which destroys the oxalic acid, and the phosphoric acid is determined in the residue. e. JPhosphates from Fluorides. a. The substance is soluble in water. aa. If the substance contains a relatively large quantity of 176 fluorine, which will permit the estimation of the latter from the difference, precipitate the solution with exclusion of air by chlo- ride of calcium with addition of lime-water to alkaline reaction, allow to deposit, decant through a filter, wash the precipitate, dry, ignite, and weigh. It consists of phosphate of lime and . fluoride of calcium. Heat an aliquot part in a platinum vessel, with sulphuric acid, until all the fluorine has escaped as hydro- fluoric acid, taking care not to raise the heat to a degree at which sulphuric acid volatilizes ; then determine the lime and the phosphoric acid as directed 135, b. By deducting the phosphoric acid and lime from the total weight of 166.] ACIDS OF GROUP I. 405 the precipitate, the fluorine is found by the following propor- tion : The eq. of fluorine less the eq. of oxygen : the eq. of fluorine the difference found : the fluorine sought. The fluorine may be determined directly in another aliquot part, by fusing it with acid pyrophosphate of soda, and calcula- ting the fluorine by comparing the actual loss of weight with that which the pyrophosphate would have suffered if ignited alone. 2 (NaO, HO, P0 5 ) + Ca Fl = NaO, PO 5 + NaO, CaO, PO 5 -fHFl + HO. [bb. If the substance contains a relatively small proportion of 177 fluorine, this should be determined directly by FRESENIUS' me- thod. (182.) Phosphoric acid may be estimated in a portion that has been evaporated with sulphuric acid, by molybdic solution /?. The substance is not soluble in water, but decomposable by acids (e.g., apatite, bone-ash). Dissolve in hydrochloric acid, evaporate with sulphuric acid, as in 178 176, until the fluorine is completely expelled, and determine in the residue the phosphoric acid on the one hand, the oxides on the other hand. Now, if you know the proportion between the phosphoric acid and the bases in the analyzed compound, you may readily cal- culate the expelled fluorine from the excess of the bases, the oxygen of the latter being equivalent to the fluorine. Of course, it is taken for granted that other acids are absent, or are determined in sepa- rate portions. j. The substance is insoluble in water and not decomposable by acids. Fuse with carbonate of soda and silicic acid as in 169, treat the 179 fused mass with water, and the solution with carbonate of ammonia. You have now in solution the whole of the fluorine and phosphoric acid in combination with alkali (H. HOSE), and may accordingly proceed as in 176 or 177- 4. FLUORIDES FROM BORATES. Mix the solution containing the acids in combination with alkali 180 with some carbonate of soda, and add acetate of lime in excess. A precipitate is formed, which contains the whole of the fluorine as fluoride of calcium, and besides this, carbonate and some borate of lime ; the greater proportion of the latter having been redissolved by the excess of the lime salt added. Determine the fluoride of cal- cium in the precipitate as directed in 138, 1. The small quantity of boracic acid in the precipitate is, in this process, partly volati- lized, partly dissolved, after evaporating the mass with acetic acid and extracting with water. It is therefore necessary to determine the boracic acid in a separate portion of the substance ; this is effected according to the directions of 136, 2 (A. STROMEYER*). 5. FLUORIDES FROM SILICIC ACID AND SILICATES. A great many native silicates contain fluorides : care must, there- fore, always be taken, in the analysis of minerals, not to overlook the latter. * Annal. d. Cheni. u. Pharm. 100, 91. 406 SEPARATION. [ 166. If the silicates containing fluoride are decomposable by acids (which is only rarely the case) and the silicic acicl is separated in the usual way by evaporation, the whole of the fluorine may vola- tilize. a. BERZELIUS'S method. Fuse the elutriated substance with 4 parts of carbonate of soda, for 181 some time, at a strong red heat ; digest the mass in water, boil, filter, and wash, first with boiling water, then with solution of car- bonate of ammonia. The filtrate contains all the fluorine as fluo- ride of sodium, and, besides this, carbonate, silicate, and aluminate of soda. Mix the filtrate with carbonate of ammonia, and heat the mixture, replacing the carbonate of ammonia which evapo- rates. Filter off the precipitate of hydrate of silicic acid and hydrate of alumina, and wash with carbonate of ammonia. Heat the filtrate until the carbonate of ammonia is completely expelled, and determine the fluorine as directed 138. To separate the silicic acid, decompose the two precipitates with hydrochloric acid as directed 140, II., a* b. WOHLER'S method modified by FRESENIUS. (Suitable for the 182 analysis of all silicates and phosphates which are readily decomposed by sulphuric acid; those undecomposable by this acid must be fluxed.) [The substance must be reduced to an impalpable powder ; if not a silicate, mixed intimately with 10 to 15 times its weight of finely pul- verized quartz, and decomposed in a flask with pure concentrated sul- phuric acid (sp. gr. 1*848) , at a temperature not higher than 160 nor lower than 150 C. The fluorine is estimated by collecting and weighing the fluoride of silicon thus evolved (FRESEXIUS), or by loss (WoHLER.) The former is the only accurate method, especially when small quantities are to be determined. To displace fluoride of silicon completely from the mixture evolving it, long-continued aspiration of air is necessary. The apparatus needful consists of a gasholder of 20 30 litres capacity, which should be filled with pure air from out-of-doors ; of 3 flasks of about 250 c. c. capacity each ; and of 8 light TJ-tubes, whose bore is 12 mm. and whose legs are 10 12 cm. long. Air is forced from the gasholder, firstly, through a flask half filled with strong pure sulphuric acid, then through a U- tube containing soda lime, and again through a TJ-tube filled with glass splinters moistened with strong sulphuric acid. The air thus freed from water and carbonic acid is conducted to the bottom of a second flask, containing the substance under examination drenched with a large excess of sulphuric acid. This flask stands over a lamp upon a plate of cast-iron, and to judge of the temperature of its contents another flask similarly filled with sulphuric acid, in which a thermometer is suspended by a loosely fitting cork, is placed upon the same iron plate, the lamp-flame being stationed be- tween them and equidistant from both. The dry air streaming through the decomposing flask, heated to 150 160 carries on fluo- ride of silicon and a little vapor of sulphuric acid, firstly into an * The whole of the silicic acid may be removed from the filtrate by the treat- ment with carbonate of ammonia : addition of carbonate of zinc and ammonia, as recommended by Berzelius, and afterwards by Regnault, appears therefor? superfluous (H. Rose). g 16G.] ACIDS OF GROUP I. 407 empty TJ-tube, and then into anotlier containing, in the first half, fused (anhydrous) chloride of calcium, and in the second half, pumice, im- pregnated with anhydrous sulphate of copper (p. 289). The pure fluoride of silicon is finally absorbed in the three remaining TJ- tubes, and is estimated by their increase of weight. Of these tubes, the first contains, in the leg next the decomposing flask, pumice moistened with water between two cotton plugs ; in the bend and half of the other leg, soda lime ; lastly, fused chloride of calcium be- tween cotton plugs. The weight of this tube should be 40-50 grin. To complete the absorption, the next (seventh) U-tube is filled half with fused soda-lime and half with fused chloride of calcium ; and the last (eighth) contains glass' splinters wet with pure and strong sulphuric acid, to completely retain traces of water, which would otherwise be carried oft' by the large volume of heated air. The tubes having been carefully adjusted, and made tight by melting sealing-wax over the corks, so much substance is placed in the decomposing flask as to yield, if possible, 0*1 grm. of fluoride of silicon. If a carbonate be present, this must be removed by heating the weighed substance with water and a slight excess of acetic acid (in case of operating with a fluoride soluble in water, ace- tate of lime must also be added). After the carbonate is decom- posed, the whole is evaporated to dryness on the water-bath. The residue is digested and washed with water, dried, separated as well as possible from the filter, and mixed with the filter-ash. The sub- stance is intimately mixed, if needful, with ignited quartz powder transferred to the decomposing flask, the mortar being rinsed with quartz-powder, and drenched with 40 50 c. c. of concentrated sul- phuric acid. The flask is connected with the tubes on either side, and with frequent shaking is gradually brought to a temperature of 150 160 C. Incipient decomposition is recognized by the rise of gas bubbles in the heated liquid (which are broken by agitation) as well as by deposition of silica in the tube containing moist pumice. As soon as gas-bubbles cease to appear, which commonly happens af- ter anhour, when small quantities (0*1 grm.) of a fluoride are employed, or after two to three hours when larger amounts (1.0 grm.) are used, the lamp is removed, the air current stopped, and the three weighed ab- sorption tubes are weighed again. During this operation the break in the system of tubes is supplied by a straight glass tube. After weighing, the three tubes are replaced, the decomposing flask is heated again to 150-160 C,, the air-current is re-established, and the experiment continued \ \^ hours. If the tubes suffer no fur- ther increase of weight, the operation is concluded ; otherwise the heating, &c., must be repeated until a constant weight is obtained. For every hour during which the air-current has been passing the apparatus, deduct O'OOl grm. from the total increase of the three absorption tubes ; the residue is fluoride of silicon. This multiplied by 2|__=r||=0-73077, gives the fluorine. Results good.] 6. FLUORIDES, SILICATES, AND PHOSPHATES, IN PRESENCE OP EACH OTHER. Native compounds of fluorides, silicates, and phosphates are not 183 uncommon. They are decomposed as in 181. Complete decom- position of the phosphates is not always effected in this process, as 408 SEPARATION. [ 16& phosphate of lime, for instance, is only partially decomposed by fu- sion with carbonate of soda. The solution remaining after the re- moval of the silicic acid and the volatilization of the carbonate of ammonia, contains in presence of phosphates besides fluoride of Kodiurn and carbonate of soda, also phosphate of soda. Neutralize the fluid nearly with hydrochloric acid, precipitate!84 with chloride of calcium, filter, dry, and ignite the precipitate, which consists of fluoride of calcium, phosphate of lime, and carbonate of lime ; treat the residue with acetic acid in excess, and evaporate on the water-bath to dryness and complete expulsion of the acetic acid ; extract the acetate of lime, into which the carbonate has been con- verted by the last operation, with water ; weigh the residue, which consists of phosphate of lime and fluoride of calcium ; and treat it further as directed in 176- In the original residue of the first operation and in the precipitate thrown down by carbonate of am- monia, determine the silicic acid, the rest of the phosphoric acid, and the bases. The method 182 niay also be employed for estimat- ing fluorine. 7. SILICIC ACID FROM ALL OTHER ACIDS. a. In Compounds which are decomposed by Hydrochloric Acid. Decompose the substance by more or less protracted digestion 185 with hydrochloric acid or nitric acid evaporate on the water-bath* to dryness ( 140, II., a), and treat the residue, according to circum- stances, with water, hydrochloric acid, or nitric acid ; filter off the residuary silicic acid, and determine the other acids in the filtrate. In presence of boracic acid or fluorine this method is inapplicable, and the process described in b is employed instead. If carbonates are present, the carbonic acid is determined in a separate portion of the substance. b. In Compounds which are not decomposed by Hydrochloric Acid. Decompose the substance by fusion with carbonate of soda and!86 potassa ( 140, II., b, a), and either treat the residue at once cau- tiously with $ dilute hydrochloric or nitric acid, and the solution thus obtained as in a ; or boil the residue with waiter, precipitate the dis- solved silicic acid from the solution by heating with bicarbonate of ammonia, filter, and in the mixed residue and precipitate determine the silicic acid by treating with hydrochloric acid and proceeding as directed 140, II., a., in the filtrate, determine the other acids. Which of these two methods may be preferable in particular cases, depends iipon the nature of the bases, and upon the proportion which the silicic acid bears to the latter. In presence of boracic acid or fluorine, the latter method alone is applicable. 8. CARBONIC ACID FROM ALL OTHER ACIDS. When carbonates are heated with stronger acids, the carbonic!87 acid is expelled ; the presence of carbonates, therefore, does not in- terfere with the estimation of most other acids. And as, on the other hand, the carbonic acid is determined by the loss of weight or by combination of the expelled gas, the presence of salts of non- * A higher temperature would not answer. g 167.] ACIDS OF GROUP II. 409 volatile acids does not interfere with the determination of the car- bonic acid. Accordingly, with compounds containing carbonates, sulphates, phosphates, &c., either the carbonic acid is determined in one portion and the other acids in another, or both estimations are performed on one portion. In the latter case the process de- scribed p. 293, e, may be used with advantage, the other acids be- ing determined in the solution remaining in the decomposing flask. In presence of fluorides, one of the weak non-volatile acids, such as tartaric acid or citric acid, must be employed to expel the carbonic acid; since, were sulphuric acid or hydrochloric acid used for the purpose, part of the liberated hydrofluoric acid would escape with the carbonic acid. If, as will occasionally happen in an analysis, a mixed precipitate of fluoride of calcium and carbonate of lime is thrown down from a solution, the two salts may be separated by evaporating with acetic acid to dry ness, and extracting the residue with water ; the acetate of lime formed from the carbonate is dis- solved, the fluoride of calcium is left behind. SECOND GROUP. HYDROCHLORIC ACID HYDROBROMIC ACID HYDRIODIC ACID HYDROCYANIC ACID HYDROSULPHURIC ACID. I. SEPARATION OF THE ACIDS OF THE SECOND GROUP FROM THOSE OF THE FlRST. 167. a. All the Acids of the Second Group from those of the First. Mix the dilute solution with nitric acid, add nitrate of silver in 188 excess, and filter off the insoluble chloride, bromide, iodide, &c., of silver. The filtrate contains the whole of the acids of the first group, the. silver salts of these acids being soluble in water or in nitric acid. Carbonic acid must, under all circumstances, be deter- mined in a separate portion. The estimation may be effected after LI 39, d, or e. In the first case the remarks on p. 289 must be rne in mind. b. Some of the Acids of the Second Group from Acids of the First Group. As it is often inconvenient for the further separation of the acids 189 of the second group to have them all in the form of insoluble silver compounds, the analysis is sometimes effected by separating first the acid of the first group, then that of the second. If the quantity of disposable substance is large enough, the most con- venient way generally is to determine the several acids e.g,, sul- phuric acid, phosphoric acid, chlorine, sulphuretted hydrogen, &c. in separate portions. Of the infinite number of combinations that may present them- selves we will here consider only the most important. 1. SULPHURIC ACID may be readily separated from chlorine, bro-190 mine, iodine, and cyanogen, by precipitation with a salt of baryta. If the acids of the second group are to be determined in the same 410 SEPARATION. [ 167. portion, nitrate of baryta or acetate of baryta is used instead of chlo- ride of barium. In presence of sulphuretted hydrogen, sulphuric acid cannot be determined in this way, as part of the sulphuretted hydrogen would be converted into sulphuric acid by the oxygen of the air. The error thus introduced into the process may be very considerable (FUESENIUS*). The sulphuretted hydrogen must, there- fore, first be removed by addition of chloride of copper, and the sul- phuric acid determined in the filtrate ; or, the sulphuretted hydro- gen must be completely oxidized into sulphuric acid by chlorine, and a corresponding deduction afterwards made in calculating the quan- tity of the sulphuric acid. 2. PHOSPHORIC ACID may be precipitated by means of nitrate of 191 magnesia and ammonia, after addition of nitrate of ammonia ; OXALIC ACID by nitrate of lime ; chlorine, bromine, iodine, &c. 3 are deter- mined in the filtrate. 3. CHLORINE IN SILICATES. a. If the silicates dissolve in dilute nitric acid, precipitate the 192 highly dilute solution with nitrate of silver, without applying heat ; remove the excess of silver from the filtrate by dilute hydrochloric acid, still without applying heat ; and then separate the silicic acid in the usual way. b. If the silicate becomes gelatinous upon its decomposition with nitric acid, dilute, allow to deposit, filter, wash the separated, silicic acid, and treat the filtrate as in a. c. Ifiiitiic acid fails to decompose the silicates, mix the substance with carbonate of soda and potassa, moisten the mass with water, dry in the crucible, fuse, boil with water, remove the dissolved silicic acid by means of carbonate of ammonia and then precipitate, after addition of nitric acid, with nitrate of silver (H. ROSE). 4. CHLORIDES IN PRESENCE OF FLUORIDES. If the substance is soluble in water, the separation may be effected 193 as directed in 188 ; but it is more convenient to precipitate the fluorine with nitrate of lime, and the chlorine in the filtrate with nitrate of silver. Insoluble compounds are fused with carbonate of soda and silicic acid. 5. CHLORINE IN PRESENCE OF FLUORINE IN SILICATES. ^ Proceed as directed 18 . Saturate the alkaline filtrate nearly!94 with nitric acid, precipitate with nitrate of lime, separate the fluoride of calcium and the carbonate of lime as directed in 187, and precipi- tate the chlorine in the filtrate by nitrate of silver. 6. SULPHIDES IN SILICATES. If the substance is decomposable by acids, reduce it to the very!95 finest powder, and treat with fuming nitric acid free from sulphuric acid ( 148 II., 2, a, p. 326). When the sulphur is completely oxi- dized, dilute, filter off the silicic acid, add carbonate of ammonia to the filtrate, to remove the portion of silicic acid which may possibly have dissolved ; filter again, and determine in the filtrate the sulphu- * Jouru. f. prakt. Chem. 70, 9. 168.] ACIDS OF GROUP II. 411 ric acid formed. If, on the contrary, the substance is not de- composable by acids, fuse with 4 parts of carbonate of soda and 1 part of nitrate of potassa, boil the fused mass with water, filter, re- move the dissolved silicic acid from the filtrate by carbonate of am- monia ( 181), filter again, and determine in the filtrate the sulphu- ric acid produced from the sulphur. Supplement. ANALYSIS OF COMPOUNDS, CONTAINING SULPHIDES OF THE ALKALI METALS, AND ALKALINE CARBONATES, SULPHATES, AND HYPO- SULPHITES. 168. The following method was first employed by G. WERTHER * in the 19 6 examination of gunpowder residues. Put the substance into a flask, add water, in which a sufficient quantity of carbonate of cadmium \ is suspended; cork, and shake the vessel well. The sulphide of the alkali metal decomposes com- pletely with the carbonate of cadmium. Filter the yellowish precipi- tate off, and treat it with dilute acetic acid (not with hydrochloric) ; the carbonate of cadmium dissolves, the sulphide of cadmium is left undissolved. Oxidize the latter with chlorate of potassa and nitric acid (p. 327), and precipitate with chloride of barium the sulphu- ric acid formed from the sulphide. Heat the fluid filtered from the yellow precipitate, and mix with solution of neutral nitrate of silver. The precipitate thrown down by that reagent consists of carbonate of silver and sulphide of silver (K O, SA+Ag O, N O 5 =K O, S O 3 + Ag S + N O 5 ). Remove the former salt by means of ammonia, and precipitate the silver from the ammoriiacal solution after acidifying with nitric acid by means of chloride of sodium. Each 1 eq. chloride of silver so obtained cor- responds to 1 eq. carbonate. J Dissolve the sulphide of silver in dilute boiling nitric acid, determine the silver in the solution as chloride of silver, and calculate from the result the quantity of the hyposulphite ; 1 eq. Ag Cl corresponds to 2 eq. sulphur in hyposul- phurous acid, and accordingly to 1 eq. hyposulphite (K O, S^C^). From the fluid filtered from the sulphide and carbonate of silver remove first the excess of silver by means of hydrochloric acid, and then precipitate the sulphuric acid by a salt of baryta. From the sulphuric acid found you have, of course, to deduct the quantity of that acid resulting from the decomposition of the hyposulphurous acid, and accordingly for 1 part by weight of chloride of silver formed from the sulphide, 0*28 parts by weight of sulphuric acid. The difference gives the amount of sulphuric acid originally present in the analyzed compound. By way of control, you may determine, in the fluid filtered from the sulphate of baryta, the alkali as sul- phate as directed in 97 or 98. * Journ. f. prakt. Chem. 55, 22. f To obtain the carbonate of cadmium free from alkali, carbonate of ammonia must be used as precipitant. \ A quantity equivalent to the sulphide found has to be deducted from this (K S + Cd 0, C 2 = Cd S+K O, C O,). 412 SEPARATION. [ 169. II. SEPARATION OF THE ACIDS OF THE SECOND GROUP FROM EACH OTHER. 169. 1. CHLORINE FROM BROMINE. All the methods of direct analysis hitherto proposed to effect the separation of chlorine from bromine are defective. The bro- mine is therefore usually determined indirectly. a. Precipitate with nitrate of silver, wash the precipitate, dry, 197 fuse, and weigh. Transfer an aliquot part of the mixed chloride and bromide of silver to a light weighed bulb-tube,* fuse in the bulb, let the mass cool, and weigh. This operation gives both the total weight of the tube with its contents, and the weight of the portion of mixed chloride and bromide of silver in the bulb. The greatest accuracy in the several weighings is indispensable. Now transmit through the tube a slow stream of dry pure chlorine gas, heat the contents of the bulb to fusion, and shake the fused mass occasionally about in the bulb. After the lapse of about 20 min- utes, take off the tube, allow it to cool, hold it in an oblique posi- tion, that the chlorine gas may be replaced by atmospheric air, and then weigh. Heat once more, for about 10 minutes, in a stream of chlorine gas, and weigh again. If the two last weighings agree, the ex- periment is terminated; if not, the operation must be repeated once more. The loss of weight suffered, multiplied by 4*2203 gives the quantity of the bromide of silver decomposed by the chlorine. For the proof of this rule see 197. This method gives very accurate results, if the proportion of bro- mine present is not too small; but most uncertain results in cases where mere traces of bromine have to be determined in presence of large quantities of chlorides, as for instance in salt-springs. To render the method available in such cases, the great point is to pro- duce a silver compound containing all the bromine, and only a small part of the chlorine. This end may be attained in several ways. In these processes the quantity of chlorine is found by completely precipitating a separate portion with silver solution, and deducting the bromide of silver found from the weight of the precipitate. a. Mix the solution with carbonate of soda in excess, filter if ne- cessary, evaporate nearly to dryness, extract the residue with hot absolute alcohol ; the solution contains the whole of the alkaline metallic bromide, and only a small portion of the alkaline metallic chloride ; add a drop of soda solution, and evaporate ; dissolve the residue in water, acidify with nitric acid, and precipitate with silver solution. j3. FEHLING'S method, f Mix the solution cold with a quantity of solution of nitrate of 198 silver not nearly sufficient to effect complete precipitation, shaking the mixture vigorously, and leave the precipitate for some time in the fluid, with repeated shaking. If the amount of the precipitate * The best way of effecting the removal of the fused mass from the crucible is to fuse again, and then pour out. f Journ. f. prakt. Chern. 45, 269. 163.] ACIDS OF GROUP II. 413 produced corresponds at all to tlie quantity of bromine present, the whole of the latter substance is obtained in the precipitate. FEELING gives the following rule : If the fluid contains 0'1|- bromine, use -J- or J the quantity of so- lution of nitrate of silver that would be required to effect complete precipitation; ifO'Olf, T V; ifO'002,^; ifO'OOl^. Wash the mixed precipitate of chloride and bromide of silver thoroughly dry, ignite, weigh, and treat with chlorine, as above. 7. MARCHAND* has slightly modified FEHLING'S method. Hel99 reduces with zinc the mixed precipitate of chloride and bromide of silver obtained by FEHLING'S fractional precipitation ; decomposes the solution of chloride and bromide of zinc with carbonate of soda ; evaporates to dryness, and extracts the residue with absolute alcohol, which dissolves all the bromide of sodium with only a little of the chloride of sodium ; he then evaporates the solution to dry- ness, takes up the residue with water, precipitates again with solu- tion of nitrate of silver, and subjects a part of the weighed preci- pitate to the treatment with chlorine. 5. If a fluid containing chlorides in presence of some bromide, is heated, in a distillation flask, with hydrochloric acid and binoxide of manganese, the whole of the bromine passes over before any of the chlorine. Upon this circumstance, MOHR f bases the following method for effecting the concentration of bromine : Distil as stated, and conduct the vapors, through a doubly bent tube, into a wide WOULF'S bottle, which contains some strong solu- tion of ammonia. Dense fumes form in the bottle, filling it gra- dually. Conduct the excess of vapors from the first into a second bottle, with narrow neck, which contains ammoniated water. Both bottles must be sufficiently large to allow no vapors to escape. When the whole of the bromine is evolved, which may be distinctly seen by the color of the space above the liquid in the distillation flask and tubes, raise the cork of the flask to prevent the receding of bromide of ammonium fumes. Let the apparatus cool, and unite the contents of the two bottles ; the fluid contains the whole of the bromine, with a relatively small portion of the chlorine. b. Instead of treating the mixed chloride and bromide of silver 200 in a current of chlorine as in a, it may also be reduced to metallic silver in a current of hydrogen. After accurately determining the weight of the reduced metal, calculate the amount of chloride of silver equivalent to it ; subtract from this the weight of the chloride and bromide of silver subjected to the reducing process, and we have the same difference as served in a for the point of departure of the calculation (WACKENRODER). It will be seen that one and the same portion of mixed bromide and chloride of silver may be treated first as directed in a, then, by way of control, as directed in b. The difference found in the direct way in the first, and by cal- culation in the second experiment, between the weight of the mixed chloride and bromide of silver and the amount of chloride of silver equivalent to it, must be the same. c. PISANI recommends to add a known quantity of solution of 201 nitrate of silver in slight excess, filter, and determine the silver in * Journ. f. prakt. Chem. 47, 363. f Annal. d. Chem. u. Pharm. 93, 80. 414 SEPARATION. [ 169 (lie filtrate by iodide of starch (p. 215). The precipitate is weighed us in c. This method precludes the partial precipitation. d. Determine in a portion of the solution the chlorine -f bromine 202 (by precipitating with solution of silver), either gravimetrically or volumetrically ; in another portion the bromine, either by the colori- metric method ( 143, 1., c), or by the volumetric method ( 143, 1., &). Calculate the chlorine from the difference. The method is very suitable for an expeditious analysis of mother-liquors. 2. CHLORINE FROM IODINE. a. Proceed exactly as for the indirect determination of bromine 203 in presenec of chlorine (197)- The loss of weight suffered by the silver precipitate in the fusion in chlorine gas, multiplied by 2 '5 6 7, gives the quantity of the iodide of silver decomposed by chlorine. The methods described in 200 and 201, may also be employed. The results obtained by these methods in the case of chlorine and iodine are still more accurate than in the case of chlorine and bromine, as the equivalents of iodine and chlorine differ far more widely than those of chlorine and bromine. b. Add to the solution ^ c. c. of standard solution of iodide of 204 starch (p. 215), then, drop by drop, with stirring, standard solution of silver (p. 304), until the iodide of starch is decolorized. The amount of silver solution used (after deducting the small quantity required for the decolorization of the ^ c. c. of iodide of starch solution added, and which must be separately determined) corre- sponds exactly to the amount of iodine in the analyzed compound ; for iodide of starch is decolorized before the precipitation of chlorine begins. To determine now the chlorine also, add again solution of nitrate of silver in slight excess, filter, and determine the excess of silver in the filtrate by means of iodide of starch (p. 215). Deduct the amount of solution of nitrate of silver cor- responding to the c. c. of iodide of starch solution added, and to the iodine present, as well as the excess of silver solution from the total quantity added, and calculate the chlorine from the difference. This method is expeditious ; the results are accurate (PiSANi*). Compare also Expt. No. 94. The following methods are especially adapted for the determina- tion of small quantities of iodide in the presence of large quanti- ties of chloride : c. Mix the solution with a few drops of solution of hyponitric205 acid in sulphuric acid, or with red fuming nitric acid, add 4 to 5 grm. bisulphite of carbon, shake violently, separate the violet-colored bisulphide from the fluid containing the chlorine (and bromine) by cautious decantation, and shake the decanted fluid with fresh bisul- phide. After the violet bisulphide has been washed by decantation, the water being poured off through a filter, the iodine may be deter- mined as follows : The solution should be in a stoppered bottle, covered with a layer of water. Add a dilute solution of hyposul- phite of soda, with shaking, finally after addition of every two drops. The violet coloration gradually disappears. The end-point is easy to hit with perfect certainty. Now determine the value of * Compt. rend. 44, 352 ; Journ. f . prakt. Chem. 72, 266. S; 169.] ACIDS OF GROUP ii. 415 the solution of hyposulphite, by shaking a few c. c. of standard iodine solution with bisulphide of carbon, and then adding hyposul- phite to decoloration. Results good. d. Precipitate a portion with silver solution and determine the 20 6 chlorine -f iodine; in a second portion estimate the iodine volu- metrically ( 145, I., c, or d), and calculate the chlorine from the difference. e. For technical purposes the following method is also suitable. It 207 was recommended by WALLACE and LAMONT* for the estimation of iodine in kelp. The kelp-lie is nearly neutralized with nitric acid, evaporated to dryness, and the residue fused in a platinum vessel to oxidation of all the sulphides. Treat with water, filter, add nitrate of silver till the precipitate appears perfectly white, wash, digest with strong ammonia, and weigh the residual iodide of silver. Finally, add to the weight of the latter the amount which passes into solution in the ammonia ; it is 53*5-3- ^ tne aqueous ammonia (sp. gr. 0-89) used. 3. CHLORINE, BROMINE, AND IODINE FROM EACH OTHER. a. Determine in a portion of the compound the chlorine, bro- 208 mine and iodine, jointly by precipitation with nitrate of silver. Determine the silver in the weighed precipitate as in 200. Or add a known quantity of solution of nitrate of silver in slight excess, filter, and determine the small excess of silver in the filtrate by means of iodide of starch (201). Determine the iodine separately by DUPR^'S method (see below), calculate the quantity of iodide of silver and of silver corresponding to the amount of iodine found, deduct the calculated amount of iodide of silver from the mixed iodide, chloride, and bromide of silver, that of the silver from the known quantity of the metal contained in the mixed compound ; the remainders are respectively the joint amount of chloride and bromide of silver, and the quantity of the metal con- tained therein ; these are the data for calculating the chlorine and bromine (200). As regards the estimation of iodine in presence of bromides, A. and F. DUPR& found that if the solution of an iodide contains 1 part of bromide of potassium, or more, in 1500 parts of water, protobromide of iodine (I Br) is formed upon addition of chlorine water ; if the solution contains less than 1 part of bromide of potas- sium in 1500 parts of water, higher bromides in varying propor- tions are formed in addition to the protobromide. If the solution contains only 1 part of bromide of potassium to 13000 parts of water, pentabromide of iodine alone is formed. If the iodine was dissolved in bisulphide of carbon, the conversion into I Br is marked simply by the change of the violet color of the fluid to yel- lowish brown (zirconium color), whereas the formation of I Br 5 is marked by the change of violet to white. Upon these reactions A. and F. DupRfi have based the following method : Test the fluid first by adding bisulphide of carbon, and then, gradually, chlorine water, to see whether the color will change from violet to white. If this is not the case, dilute to the required * Chem. Gaz. 1859, 137. 416 SEPARATION. [ 169 degree, and to make quite sure, add one-half more water ; then pro- ceed as directed 145, I., e, a or /?. A. and K DUPR& obtained most satisfactory results by this process ; the method is particular- ly recommended for the determination of small quantities of iodine in lies which contain large quantities of chlorides, and not too small quantities of bromides. If the latter are too small, exact re- sults cannot be obtained by the indirect method, on which the bro- mine estimation is based. To determine bromine directly, we may, after adding a sufficient quantity of chlorine water to destroy the violet color of the bisulphide, and consequently to form I C1 5 , or, as the case may be, I Br 5 (6 eq. chlorine = 1 eq. iodine), add more chlorine water till the whole of the bromine is converted into Br Cl. 2 eq. of this second quantity of chlorine correspond to 1 eq. bromine (A. BEIMANN). The details will be found 143, I., b. To explain, I will suppose the case in which 5 eq. K Br and 1 eq. K I are present. K I + 5 K Br +6 Cl = 6 K Cl + I Br 5 and I Br 5 + 10 Cl = I C1 5 + 5 Br Cl. b. Proceed generally as in a, but determine the iodine by PISANI'S 209 method (204). This method also gives very satisfactory results, especially in the presence of large quantities of iodides. Presence of bromides does not interfere with the accuracy of the estimation of the iodine (Expt. -No. 95). 4. ANALYSIS OF IODINE CONTAINING CHLORINE. a. Dissolve a weighed quantity of the dried iodine in cold sul- 210 phurous acid, precipitate with solution of nitrate of silver, digest the precipitate with nitric acid, to remoA 7 e the sulphite of silver which may have coprecipitated, and weigh. The calculation of the iodine and chlorine is made by the following equations, in which A. represents the quantity of iodine analyzed, x the iodine contained in it, y the chlorine contained in it, and 13 the amount of chloride and iodide of silver obtained : x + y = A, and Ag + I Ag + Cl -I**-- y= s Now as Ag + I =1-851 and we have 2-194 b. If you have free iodine and free chlorine in solution, deter- 211 mine in one portion, after heating with sulphurous acid, the iodine as iodide of palladium ( 145, 1., 6), and treat another portion as di- rected 146, 1. Deduct from the apparent amount of iodine found by the latter process, the actual quantity calculated from the iodide 169.] ACIDS OF GROUP II. 417 of palladium ; the difference expresses the amount of iodine equiva- lent to the chlorine contained in the substance. 5. ANALYSIS OF BROMINE CONTAINING CHLORINE. a. Proceed exactly as in 210> weighing the bromine in a small 212 glass bulb. Taking A. to be equal to the analyzed bromine, 23 to the bromide and chloride of silver obtained, x to the bromine con- tained in A, y to the chlorine contained in A, the calculation is made by the following equations : x + y A and B - 2-35 A 1-695 b. Mix the weighed anhydrous bromine with solution of iodide 213 of potassium in excess, and determine the separated iodine as di- rected 146. From these data, the respective quantities of bromine and chlo- rine are calculated by the following equations. Let A represent the weighed bromine, i the iodine found, y the chlorine contained in A, x the bromine contained in A, then + y = A i- 1-5866 J. y ____ 1-991 BUNSEN, the originator of methods 4 and 5, has experimentally proved their accuracy.* 6. CYANOGEN FROM CHLORINE, BROMINE, OR IODINE. a. Precipitate with solution of nitrate of silver, collect the pre- 214 cipitate upon a weighed filter, and dry in the water-bath until the weight remains constant ; then determine the cyanogen by the method of organic analysis ; the difference expresses the quantity of the chlorine, bromine, or iodine. b. Precipitate with solution of nitrate of silver as in a, dry the 215 precipitate at 100, and weigh. Heat the precipitate, or an aliquot part of it, in a porcelain crucible, with cautious agitation of the contents, to complete fusion ; add dilute sulphuric acid to the fused mass, then reduce by zinc, filter the solution from the metallic silver and paracyamde of silver, and determine the chlorine, iodine, or bro- mine in the filtrate, in the usual way by solution of nitrate of silver. The cyanide of silver is the difference. NEU BAUER and KERNER \ obtained very satisfactory results by this method. c. Determine the radicals jointly in a portion of the solution, by 216 precipitating with solution of nitrate of silver, and the cyanogen in another portion, in the volumetric way ( 147, I., &). 7. FERRO- OR FERRICYANOGEN FROM HYDROCHLORIC ACID. To analyse say ferro- or ferricyanide of potassium, mixed with 217 the chloride of an alkali metal, determine in one portion the ferro- or ferricyanogen as directed 147, II., g\ acidify another portion with nitric acid, precipitate with solution of nitrate of silver, wash the * Annal d. Chem. u. Pharm. 86, 274, 276. f Ibid. 101, 344. 27 418 SEPARATION. [ 170. precipitate, fuse with 4 parts of carbonate of soda and 1 part of nitrate of potassa, extract the fused mass with water, and determine the chlorine in the solution as directed in 141. 8. SULPHURETTED HYDROGEN FROM HYDROCHLORIC ACID. The old method of separating the two acids by means of a metallic 218 salt is liable to give false results, as part of the chloride of the metal may fall down with the sulphide. We therefore precipitate both as silver compounds, dry the precipitate at 100, and determine the sulphur in a weighed portion ; or and this is usually preferred determine in a portion of the solution the sulphuretted hydrogen as directed 148, 1, a, b, or c, in another portion the sulphur -f- chlorine in form of silver salts. If you employ a solution of nitrate of silver mixed with excess of ammonia, for the determination of the sul- phuretted hydrogen, you may, after filtering off the sulphide of silver, estimate the chlorine directly as chloride of silver, by adding nitric acid, and, if necessary, more neutral silver solution. To remove sulphuretted hydrogen from an acid solution, in order that chlorine may be determined in the latter by means of nitrate of silver, H. ROSE recommends to add solution of sulphate of sesquioxide of iron, which will effect the separation of sulphur alone; the separated sulphur is allowed to deposit, and then filtered off. THIRD GROUP. NITRIC ACID CHLORIC ACID. I. SEPARATION OF THE ACIDS OF THE THIRD GROUP FROM THOSE OP THE FIRST TWO GROUPS. 170. a. If you have a mixture of nitric acid or chloric acid with 219 another free acid in a fluid containing no bases, determine in one portion the joint amount of the free acid, by the acidimetric method (see Special Part), in another portion the acid mixed with the chloric or nitric acid, and calculate the amount of either of the latter from the difference. b. If you have to analyze a mixture of a nitrate or chlorate with 220 some other salt, determine in one portion the nitric acid or chloric acid volumetrically ( 149, II., d, a or 0, or II., e, and 150), or die nitric acid by 149, II., a, $ ; and in another portion the other acid. I think I need hardly remark, that no substances must be pre- sent which would interfere with the application of these methods. c. From the chlorides of those metals which form with phosphoric 221 acid insoluble tribasic phosphates, the salts of the acids of the third group may be separated also by digesting the solution with recently precipitated thoroughly washed tribasic phosphate of silver in excess, and boiling the mixture. In this process the chlorides transpose with the phosphate chloride of silver and phosphate of the metal with which the chlorine was originally combined being formed, which both separate, together with the excess of the phosphate of silver, 170.] ACIDS OF GROUP II. 419 whilst the chlorates and nitrates remain in solution (CHENEVIX ; LASSAIGNE*). d. The estimation of an alkaline chlorate, in presence of a chloride, 222 may be effected also as follows : Take two portions of the substance, determine the chlorine by means of silver solution, in one directly, in the other after reduction of the chloric acid by cautious ignition or by nascent hydrogen ( 150, II., c). Calculate the chloric acid from the difference in the precipitates of chloride of silver. II. SEPARATION OF THE ACIDS OF THE THIRD GROUP FROM EACH OTHER. We have as yet no method to effect the direct separation of nitric 223 acid from chloric acid ; the only practicable way, therefore, is to determine the two acids jointly in a portion of the compound, by the method given p. 330, c/, measuring the sesquioxide of iron remain- ing by Oudeman's method (p. 203), and bearing in mind that 12 eq. of iron, converted from proto- into sesquichloride, correspond to 1 eq. of chloric acid. In another portion estimate the chloric acid, by adding carbonate of soda in excess, evaporating to dryness, fus- ing the residue until the chlorate is completely converted into chlo- ride, and then determining the chlorine in the latter ; 1 eq. chloride of silver produced from this corresponds to 1 eq. chloric acid, pro- vided there was no chloride originally present. * Journ. de Pharm. 16, 289 ; Pharm. Centralbl. 1850, 121. SECTION VI OKGANIC ANALYSIS. ORGANIC compounds contain comparatively only few of the elements. A small number of them consist simply of 2 elements, viz., CandH; the greater number contain 3 elements, viz., as a rule, C, H, and O ; most of the rest 4 elements, viz., generally, C, H, O, and N ; a small number 5 elements, viz., C, H, O, N, and S ; and a few, 6 elements, viz., C, H, O, N, S, and P. This applies to all the natural organic compounds which have as yet come under our notice. But we may artificially prepare organic com- pounds containing other elements besides those enumerated ; thus we know many organic substances, which contain chlorine, iodine, or bro- mine ; others which contain arsenic, antimony, tin, zinc, platinum, iron, cobalt, &c. ; and it is quite impossible to say which of the other elements may not be similarly capable of becoming more remote constituents of organic compounds (constituents of organic radicals). With these compounds we must not confound those in which organic acids are combined with inorganic bases, or organic bases with inorganic acids, such as tartrate of lead, for instance, silicic ether, borate of morphia, &c. ; since in such bodies any of the elements may of course occur. Organic compounds may be analyzed either with a view simply to re- eolve them into their proximate constituents; thus, for instance, a gum- resin into resin, gum, and ethereal oil; or the analysis may have for its object the determination of the ultimate constituents (the elements) of the substance. The simple resolution of organic compounds into their prox- imate constituents is effected by methods perfectly similar to those used in the analysis of inorganic compounds ; that is, the operator endeavors to separate (by solvents, application of heat, &c.) the individual constituents from one another, either directly, or after having converted them into appropriate forms. We disregard here altogether this kind of organic analysis of which the methods must be nearly as numerous and varied as the cases to which they are applied and proceed at once to treat of the second kind, which may be called the ultimate analysis of organic bodies. The ultimate analysis of organic bodies (here termed simply, organic analysis) has for its object, as stated above, the determination of the 171, 172.] ORGANIC ANALYSIS. 421 elements contained in organic substances. It teaches us how to isolate these elements or to convert them into compounds of known composition, to separate the new compounds formed from one another, and to calculate from their several weights, or volumes, the quantities of the elements. Organic analysis, therefore, is based upon the same principle upon which, rest most of the methods of separating and determining inorganic com- pounds. The conversion of most organic substances into distinctly characterized and readily separable products, the weights of which can be accurately determined, offers no great difficulties, and organic analysis is therefore usually one of the more easy tasks of analytical chemistry; and as, from the limited number of the elements which constitute organic bodies, there is necessarily a great sameness in the products of their decomposition, the analytical process is always very similar, arid a few methods suffice for all cases. It is principally ascribable to this latter circumstance that organic analysis has so speedily attained its present high degree of perfection : the constant examination and improvement of a few methods by a great number of chemists could not fail to produce this result. An organic analysis may have for its object either simply to ascertain the relative- quantities of the constituent elements of a substance, thus, for instance, woods may be analyzed to ascertain their heating power, fats to ascertain their illuminating power, or to determine not only the rela- tive quantities of the constituent elementary atoms, but also their abso- lute quantities, that is, to determine the number of equivalents of carbon, hydrogen, oxygen, &e., which constitute 1 equivalent of the analyzed com- pound. In scientific investigations we have invariably the latter object in view, although we are not yet able to achieve it in all cases. These two objects cannot well be attained by one operation ; each requires a distinct process. The methods by which we ascertain the proportions of the constituent elements of organic compounds, may be called collectively, the ultimate analysis of organic bodies, in a more restricted sense ; whilst the methods which reveal to us the absolute number of elementary equivalents con- stituting the complex equivalent of the analyzed compound may be styled the determination of the equivalents of organic bodies. The success of an organic analysis depends both upon the- method and its execution. The latter requires patience, circumspection, and skill ; whoever is moderately endowed with these gifts will soon become a pro- ficient in this branch. The selection of the method depends upon the knowledge of the constituents of the substance, and the method selected may require certain modifications, according to the properties and state of aggregation of the same. Before we can proceed, therefore, to describe the various methods applicable in the different cases that may occur, we have first to occupy ourselves here with the means of testing organic bodies qualitatively. I. QUALITATIVE EXAMINATION OF ORGANIC BODIES. 172. It is not necessary for the correct selection of the proper method, tcr know all the elements of an organic compound, since, for instance, the presence or absence of oxygen makes not the slightest difference to- the 422 ORGANIC ANALYSIS. [ 172. method. But with regard to other elements, such as nitrogen, sulphur, phosphorus, chlorine, iodine, bromine, &c., and also the various metals, it is absolutely indispensable that the operator should know positively whether either of them is present. This may be ascertained in the fol- lowing manner : 1. Testing for Nitrogen. Substances containing a tolerably large amount of nitrogen exhale upon combustion, or when intensely heated, the well-known smell of singed hair or feathers. No further test is required if this smell is dis- tinctly perceptible ; otherwise one of the following experiments is resorted to: a. The substance is mixed with hydrate of potassa in powder or with soda-lime ( 66, 4), and the mixture heated in a test-tube. If the sub- stance contains nitrogen, ammonia will be evolved, which may be readily detected by its odor and reaction, and by the formation of white fumes with volatile acids. Should these reactions fail to afford positive certainty, every doubt may be removed by the following experiment : Heat a some- what larger portion of the substance, in a short tube, with an excess of soda- lime, and conduct the products of the combustion into dilute hydrochloric acid ; evaporate the acid on the water-bath, dissolve the residue in a little water, and mix the solution with bichloride of platinum and alcohol. Should no precipitate form, even after the lapse of some time, the substance may be considered free from nitrogen. b. LASSAIGNE has proposed another method, which is based upon the property of potassium to form cyanide of potassium when ignited with a nitrogenous organic substance. The following is the best mode of per- forming the experiment : Heat the substance under examination, in a test-tube, with a small lump of potassium, and after the complete combustion of the potassium, treat the residue with a little water (cautiously) ; filter the solution, add 2 drops of solution of sulphate of protoxide of iron containing some sesqui- oxide, digest the mixture a short time, and add hydrochloric acid in excess. The formation of a blue or bluish-green precipitate or coloration proves the presence of nitrogen. Both methods are delicate : a is the more commonly employed, and suffices in almost all cases ; b does not answer so well in the case of alkaloids containing oxygen (e.g. morphia, brucia). ^ c. In organic substances containing oxides of nitrogen, the presence of nitrogen cannot be detected with certainty by either a or 6, but it may be readily discovered by heating the substance in a tube, when red acid fumes, imparting a blue tint to iodide of starch paper, will be evolved, accompanied often by deflagration. 2. Testing for /Sulphur. a. Solid substances are fused with about 12 parts of pure hydrate of potassa, and six parts of nitrate of potassa. Or they are intimately mixed with some pure nitrate of potassa and carbonate of soda ; nitrate of potassa is then heated to fusion in a porcelain crucible, and the mixture gradually added to the fusing mass. The mass is allowed to cool, then dissolved in water, and the solution tested with baryta, after acidifying with hydro- chloric acid. 173.] ORGANIC ANALYSIS. 423 b. Fluids are treated with fuming nitric acid, or with a mixture of nitric acid and chlorate of potassa, at first in the cold, finally with application of heat ; the solution is tested as in a. c. As the methods a and b serve simply to indicate the presence of sul- phur in a general way, but afford no information regarding the state or form in which that element may be present, I add here another method, which serves to detect only the sulphur in the non-oxidized state in organic compounds. Boil the substance with strong solution of potassa and evaporate nearly to dryness. Dissolve the residue in a little water, and test by means of a polished surface of silver, or by nitroprusside of sodium, or by just acidi- fying the dilute solution with hydrochloric acid, and adding a few drops of a mixture of sesquichloride of iron and ferricyanide of potassium (see "Qua! Anal." 156). 3. Testing for Phosphorus. The methods described in 2, a and 6, may likewise serve for phos- phorus. The solutions obtained are tested for phosphoric acid with sulphate of magnesia ; or with sesquichloride of iron, with addition of acetate of soda ; or with molybdate of ammonia (comp. " Qual'. Anal."). In method 6, the greater part of the excess of nitric acid must first be removed by evaporation. 4. Testing for Inorganic Sabstances. A portion of the substance is heated on platinum foil, to see whether or not a residue remains. When acting upon difficultly combustible sub- stances, the process may be accelerated by heating the spot which the sub- stance occupies on the platinum foil to the most intense redness, by directing the flame of the blow-pipe upon it from, below. The residue is then examined by the usual methods. That volatile metals in volatile organic compounds e.^/., arsenic in kakodyl cannot be detected by this method, need hardly be mentioned. These preliminary experiments should never be omitted, since neglect in this respect may give rise to very great errors. Thus, for instance, taurin, a substance in which a large proportion of sulphur was afterwards found to exist, had originally the formula C 4 N H 7 O 10 assigned to it. The pre- liminary examination of organic substances for chlorine, bromine, and iodine is generally unnecessary, as these elements do not occur in native organic compounds ; and as their presence in compounds artificially pro- duced by the action of the halogens requires generally no further proof. Should it, however, be desirable to ascertain positively whether a sub- stance does or does not contain chlorine, iodine, or bromine, this may be done by the methods given 188. II. DETERMINATION OF THE ELEMENTS IN ORGANIC BODIES.* 173. A. ANALYSIS OF COMPOUNDS WHICH CONSIST SIMPLY OF CARBON AND HYDROGEN, OR OF CARBON, HYDROGEN, AND OXYGEN. The principle of the method which serves to effect the quantitative analysis of such compounds is exceedingly simple. The substance is [* For Prof. Warren's admirable methods we must refer to his original papers in Am. Journ. Sci., 2dser., vol. 38, p. 387, vol. 41, p. 40, and vol. 42, p. 156.] 424 ORGANIC ANALYSIS. [ 174. burned to carbonic acid and water; these products are separated from each other and weighed, and the carbon of the substance is calculated from the weight of the carbonic acid, the hydrogen from that of the water. If the sum of the carbon and hydrogen is equal to the original weight of the substance, the substance contains no oxygen ; if it is less than the weight of the substance, the difference expresses the amount of oxygen present. The combustion is effected either by igniting the organic substance with oxygenized bodies which readily part with their oxygen (oxide of copper, chromate of lead, &c.) ; or at the expense both of free and com- bined oxygen. a. SOLID BODIES. Combustion with Oxide of Copper. 174. I. APPARATUS AND PREPARATIONS REQUIRED FOR THE ANALYSIS. 1. THE SUBSTANCE. This must be most finely pulverized and perfectly pure and dry ; for the method of drying, I refer to 26. 2. A TUBE IN WHICH TO WEIGH THE SUBSTANCE, made of thin glass about 20 cm. long, and of 7 mm. internal diameter ; one end of the tube is closed by fusion ; the other, during the operation of weighing, is stop- ped with a smooth cork. 3. THE COMBUSTION TUBE. A tube of difficultly fusible glass (potassa glass), about 2 mm. thick in the glass, 80 to 90 cm. in length, and from 12 to 14 mm. inner diameter, is softened in the middle before a glass- blower's lamp, drawn out as represented in fig. 69, and finally apart at Fig. 69. 6. The fine points of the two pieces are then sealed and thickened a lit- tle in the flame, and the sharp edges of the open ends, a and c, are slightly rounded by fusion, care being taken to leave the aperture per- fectly round. The posterior part of the tube should be shaped as shown in fig. 70, and not as in fig. 71. Fig. 70. Fig . 7t Two perfect combustion tubes are thus produced. The one intended for immediate use is cleaned with linen or paper attached to a piece of wire, and then thoroughly dried. This is effected either by laying the tube, with a piece of paper twisted over its mouth, for some time on a sand- 174.] ORGANIC ANALYSIS. 425 bath, with occasional removal of the air from it by suction, with the aid of a glass tube, or (rapidly) by moving the tube to and fro over the flame of a gas or spirit lamp, heating its entire length, and Continually removing the hot air by suction through the small glass tube (fig. 72). Fig. 72. The combustion tube, when quite dry, is closed air-tight with a cork, and kept in a warm place until required for use. In default of glass tubes possessed of the proper degree of infusibility, thin brass or copper foil, or brass gauze, is rolled round the tube, and iron wire coiled round it. 4. THE POTASH-BULBS (fig. 73). This apparatus, devised by LIEBIG, is filled to the extent indicated in the en- graving, with a clear solution of caustic po- tassa of 1-27 sp. gr. ( G6, 6). The introduc- tion of the solution of potassa into the appara- tus is effected by plunging the end a into a beaker or dish into which a little of the solu- tion has been poured out, and applying suction to ft, by means of a caoutchouc tube. The two ends are then wiped perfectly dry with twisted slips of paper, and the outside of the appara- tus with a clean cloth. 5. THE CHLORIDE-OF-CALCIUM-TUBE (fig. 74) is filled in the following manner : In the first place, the neck between the two bulbs of the lgl tube is loosely stopped with a small cotton plug ; this is effected by in- troducing a loose cotton plug into the wide tube, and applying a sudden and energetic suction at the other end. The large bulb is then filled with lumps of chloride of calcium ( 66, 7, ft), and the tube with smaller fragments, intermixed with coarse powder of the same substance ; a loose cotton plug is then inserted, and the tube finally closed with a perfo- rated cork, into which a small glass tube is fitted ; the protruding part of the gork is cut off, and the cut surface covered over with sealing-wax: the edge of the little tube is slightly rounded by fusion. In using this tube a considerable quantity of the water condenses in Fig. 74. the empty bulb a, and at the close of the experiment may be poured out The operator is thus enabled to test it as to reaction, boratories, because they are more 77. cleanly and convenient. 175.J ORGANIC ANALYSIS. 427 . LIEBIG'S combustion furnace is of sheet iron. It lias the form of a long box, open at the top and behind. It serves to heat the combus- tion tube with red-hot charcoal. Fig. 77 represents the furnace as seen from the top. It is from 50 to 60 cm. long, and from 7 to 8 deep ; the bottom, which, by cutting small slits in the sheet iron, is converted into a grating, has a width of about 7 cm. The side walls are inclined slightly outward, so that at the top they stand about 12 cm. apart. A series of upright pieces of strong sheet iron, having the form shown in j9, fig. 78, and riveted on the bottom of the furnace at intervals of about 5 cm., serves to support the combustion tube. They must be of exactly cor- responding height with the round aperture in the front piece of the fur- nace (fig. 78, A). Fig. 78. Fig. 79. This aperture must be sufficiently large to admit the combustion tube easily. Of the two screens, the one has the form shown in fig. 79, the other that shown in fig. 78, A, with the border turned down at the up- per edge. The openings cut into the screens must be sufficiently large to receive the combustion tube without difficulty. The furnace is placed upon two bricks resting upon a flat surface, and is slightly raised at the farther end, by inserting a piece of wood between the supports (see fig. 82). The apertures of the grating at the anterior end of the furnace must not be blocked up by the supporting bricks. In cases where the combustion tubes are of a good quality, the furnace may be raised by in- troducing a, little iron rod between the furnace and the supporting brick. Placing the tube in a gutter of Russia sheet iron tends greatly to preserve it, but contact of the glass and iron must be prevented by an intervening layer of asbestos. b. Gas combustion furnaces of the most various descriptions have been proposed. See 178. 175. II. PERFORMANCE OF THE ANALYTICAL PROCESS. a. Weigh first the potash apparatus, then the chloride of calcium tube. Introduce about 0'35 0'6 grm. of the substance under examination (more br less, according as it is rich or poor in oxygen) into the weighing tube,* which must be no longer warm, and weigh the latter accurately with its contents. The weight of the empty tube being ap- proximately known, it is easy to take the right quantity of substance re- quired for the analysis. Close the tube then with a smooth cork. b. The filling of the combustion tube is effected as follows : The per- fectly dry tube is rinsed with some oxide of copper ; a layer of oxide of copper, about 13 cm. long, is introduced into the posterior end of the combustion tube, by inserting the latter into the filling tube or flask * Care must be taken that no particles of the substance adhere to the sides of the tube, at least not at the top. 428 ORGANIC ANALYSIS. [ 175 containing the oxide of copper (fig. 80), holding both tubes in an ob- lique direction, and giving a few gentle taps. Fig. 80. From the tube containing the substance remove the cork cautiously, to prevent the slightest loss of substance ; insert the open end of the tube as deep as possible into the combustion tube, and pour from it the requi- site quantity of substance by giving it a few turns, pressing the rim all the while gently against the upper side of the combustion tube, to pre- vent its coming into contact with the powder already poured out ; the two tubes are, in this manipulation, held slightly inclined (see fig. 81). Fig. 81. When a sufficient quantity of the substance has been thus transferred from the weighing to the combustion tube, the latter is restored to the horizontal position, which gives to the former a gentle inclination with the closed end downwards. If the little tube is now slowly withdrawn, with a few turns, the powder near the border of the opening falls back into it, leaving the opening free for the cork. The tube is then imme- diately corked and weighed, the combustion tube also being meanwhile kept closed with a cork. The difference between the two weighings shows the quantity of substance transferred from the weighing to the combustion tube. The latter is then again opened, and a quantity of oxide of copper, equal to the first, transferred to it from the filling tube, or flask, taking care to rinse down with this the particles of the sub- stance still adhering to the sides of the tube. There is now in the hind part of the tube a layer of oxide of copper, about 25 cm. long, with the substance in the middle. The next operation is the mixing : this is performed with the aid of the wire (fig. 76), which is pushed down to within 3 to 4 cm. of the end, and rapidly moved about in all directions until the mixture is complete and uniform, the tube being held nearly horizontal. Oxide of copper is then poured in to within 5 to 6 cm. of the open end, and the tube is corked. c. A few gentle taps on the table will generally suffice to shake to- gether the contents of the tube, so as to completely clear the tail from oxide of copper, and leave a free passage for the evolved gases from end to end. Should this fail, as will occasionally happen, owing to mal- formation of the tail, the object in view may be attained by striking the mouth of the tube several times against the side of a table. d. Connect the end b (fig. 82) of the weighed chloride of calcium- tube with the combustion tube by means of a dried perforated cork, lay g 175.J ORGANIC ANALYSIS. 429 the furnace upon its supports, with a slight inclination forward, and place the combustion tube in it ; connect the end B of the chloride of calcium tube, by means of a vulcanized india-rubber tube, with the end m of the potash apparatus, and, if necessary, secure the connection with silk cord, taking care to press the joint of the two thumbs close together whilst tightening the cords, since otherwise, should one of the cords hap- pen to give way, the whole apparatus might be broken. Rest the potash apparatus upon a folded piece of cloth. Fig. 82 shows the whole ar- rangement. Fig. 82. e. To ascertain whether the joinings of the apparatus fit air-tight, put a piece of wood about the thickness of a finger (*), or a cork or other body of the kind, under the bulb r of the potash apparatus, so as to raise that bulb slightly (see fig. 82). Heat the bulb m, by holding a piece of red-hot charcoal near it, until a certain amount of air is driven out of the apparatus; then remove the piece of wood (s), and allow the bulb TO to cool. The solution of potassa will now rise into the bulb TO, filling it more or less ; if the liquid in m preserves, for the space of a few minutes, the same level which it has assumed after the perfect cool- ing of the bulb, the joinings may be considered perfect ; should the fluid, on the other hand, gradually regain its original level in both limbs of the apparatus, this is a positive proof that the joinings are not air-tight. (The few minutes which elapse between the t\vo observations may be advantageously employed in reweighing the little tube in which the sub- stance intended for analysis was originally weighed.) f. Let the mouth of the combustion tube project a full inch beyond the furnace ; suspend the single screen over the anterior end of the fur- nace, as a protection to the cork ; put the double screen over the com- bustion tube about two inches farther on (see fig. 82), replace the little piece of wood (s) under r, and put small pieces of red-hot charcoal first under that portion of the tube which is separated by the screen ; sur- round this portion gradually altogether with ignited charcoal, and let it get red-hot ; then shift the screen an. inch farther back, surround the newly exposed portion of the tube also with ignited charcoal, and let it get red-hot ; and proceed in this manner slowly and gradually extend- ing the application of heat to the tail of the tube, taking care to wait always until the last exposed portion is red-hot before shifting the screen, and also to maintain the whole of the exposed portion of the tube before the screen in a state of ignition, and the projecting part of it so hot that the fingers can hardly bear the shortest contact with it. The whole process requires generally from ^ to 1 hour. It is quite su- perfluous, and even injudicious, to fan the charcoal constantly ; this should be done however when the process is drawing to an end, as we shall immediately have occasion to notice. 430 ORGANIC ANALYSIS. [ 175. The liquid in the potash bulbs is gradully displaced from the bulb m upon the application of heat to the anterior portion of the combustion tube, owing simply to the expansion of the heated air. The evolution of gas proceeds with greater briskness when the heat begins to reach theactual mixture ; the first bubbles are only partly absorbed, as the carbonic acid contains still an admixture of air ; but those which follow are so completely absorbed by the potassa, that a solitary air-bubble only escapes from time to time through the liquid. The process should be conducted in a manner to make the gas-bub- bles follow each other at intervals of from -J- to 1 second. Fig. 83 shows the proper posi- tion of the potash bulbs during the opera- tion. It will be seen from this that an air-bubble entering through m passes first into the bulb b, thence to c, from c to d, and passing over the solution in the latter, escapes finally into the bulb/", through the fluid which just covers the mouth of the tube e. g. When the tube is in its whole length surrounded with red-hot charcoal, and the evolution of gas has relaxed, fan the burning charcoal gently with a piece of pasteboard. When the evolution of gas has entirely ceased, adjust the position of the potash bulbs to a level, remove the charcoal from the farther end of the tube, and place the screen before the tail. The ensuing cooling of the tube on the one hand, and the absorption of the carbonic acid in the potash bulbs on the other, cause the solution of potassa in the latter to recede, slowly at first, but with increased rapidity from the moment the liquid reaches the bulb m. (If you have taken care to adjust the position of the potash bulbs cor- rectly, you need not fear that the contents of the latter will recede to the chloride of calcium tube.) When the bulb m is about half filled with solution of potassa, break off the point of the combustion tube with a pair of pliers or scissors, whereupon the fluid in the potash bulbs will immediately resume its level. Restore the potash bulbs now again to their original oblique position, join a caoutchouc tube to the potash bulbs, and slowly apply suction until the last bubbles no longer diminish in size in passing through the latter. It is better to employ a small aspirator instead of sucking with the mouth. You then know the volume of air that has passed through the apparatus. This terminates the analytical process. Disconnect the potash bulbs and remove the chloride of calcium tube, together with the cork, which must not be charred, from the combustion tube ; remove the cork also from the chloride of calcium tube, and place the latter upright, with the bulb upwards. After the lapse of half an hour, weigh the potash bulbs and the chloride of calcium tube, and then calculate the results obtained. They are generally very satisfactory. As regards the carbon, they are rather somewhat too low (about O'l per cent.) than too high. The car- bon determination, indeed, is not free from sources of error; but none of these interfere materially with the accuracy of the results, and the deficiency arising from the one is partially balanced by the excess aris- ing from the other. In the first place, the air which passes through the solution of potassa during the combustion, and finally during the 176, 177.] ORGANIC ANALYSIS. 431 process of suction, carries away with it a minute amount of moisture. The loss arising from this cause is increased if the evolution of gas pro- ceeds very briskly, since this tends to heat the solution of potassa ; and also if nitrogen or oxygen passes through the potash bulbs (compare 176 and 178). This may be remedied, however, by fixing to the exit end of the latter a tube with solid hydrate of potassa or soda-lime, the bulbs and this tube being always weighed together. In the second place, traces of carbonic acid from the atmosphere are carried into the potash apparatus in the final process of suction ; this may be remedied by connecting the tail of the combustion tube, during the operation, with a tube containing hydrate of potassa by means of a perforated cork or flexible tube. In the third place, it happens frequently, in the analysis of substances containing a considerable proportion of water or of hy- drogen, that the carbonic acid is not absolutely dried in passing through the chloride of calcium tube; this may be remedied by fixing behind the chloride of calcium tube, a tube filled with asbestos moistened with sul- phuric acid. Finally, if the mixture was not sufficiently intimate, traces of carbon remain unconsumed. It is therefore better to complete the combustion in oxygen gas. See below. As regards the hydrogen, the results are very accurate, if the filling is skilfully performed with dry oxide of copper. 176. [ Completion of the Combustion by Oxygen Gas. To insure the oxi- dation of the last traces of carbon and to leave the oxide of copper ready for use again, it is advisable to finish the combustion in a stream of oxygen. For this purpose the tail of the combustion tube must be made rather stout and long. When the potash-lye recedes, slip tightly over the suitably cooled tail a caoutchouc tube connected with a source of pure and dry oxygen gas, nip off the tip within this tube by help of a pliers, and cautiously let on the oxygen until the reduced copper is oxi- dized and the gas traverses the potash-bulbs. Then replace the stream of oxygen by one of pure and dry air, to remove all oxygen from the bulbs. To prevent loss by evaporation from the potash-lye, append to the potash-bulb a small tube of fragments of caustic potash, or employ Mulder's absorption apparatus, fig. 90, 182. The oxygen may be supplied from a gasometer, as shown fig. 84, 178, or from a small tube-retort of fused chlorate of potassa. This method and that of 175 are not applicable to organic salts of the alkalies or alkali-earths, since these bases retain a portion of carbonic acid.] COMBUSTION WITH CHROMATE OF LEAD, OR WITH CHROMATE OF LEAD AND BICHROMATE OF POTASSA. 177. This method is especially resorted to in the analysis of salts of or- ganic acids with alkalies or alkaline earths (as the chromic acid com- pletely displaces carbonic acid from their bases), and of bodies contain- ing sulphur, chlorine, bromine, or iodine. Of the apparatus, &c., enumerated in 174, all are required except oxide of copper, which is here replaced by chromate of lead ( 66, 2). A J3U ORGANIC ANALYSIS. [ ITS. narrow combustion tube may be selected, as chromate'of lead contains a much larger amount of available oxygen in an equal volume than oxide of copper. A quantity of the chromate, more than sufficient to fill the combustion tube, is heated in a platinum or porcelain dish over a gas or BERZELIUS lamp, until it begins to turn brown; before filling it into the tube, it is allowed to cool down to 100 ; and even below. The process is conducted as the one described in 174. One of the principal advantages which chromate of lead has over oxide of copper as an oxidizing agent being its property of fusing at a high heat, the temperature must, in the last stage of the process of com- bustion, be raised (by fanning the charcoal, &c.) sufficiently high to fuse the contents of the tube completely, as far as the substance extends. To heat the anterior end of the tube to the same degree of intensity would be injudicious, since the chromate of lead in that part would thereby lose all porosity, and thus also the power of effecting the com- bustion of the products of decomposition which may have escaped oxida- tion in the other parts of the tube. As the chromate of lead, even in powder, is, on account of its density, by no means all that could be desired in this latter respect, it is pre- ferable to fill the anterior part of the tube, instead of with chromate of lead, with coarsely pulverized strongly ignited oxide of copper, or with copper turnings which have been superficially oxidized by ignition in a muffle or in a crucible with access of air. In the case of very difficultly combustible substances e.g., graphite it is desirable that the mass should not only readily cake, but also, in the last stage of the process, give out a little more oxygen than is given out by chromate of lead. It is therefore advisable in such cases to add to the latter one-eighth of its weight of fused and powdered bichromate of potassa. With the aid of this addition, complete oxidation of even very difficultly combustible bodies may be effected (LIEBIG). 3. COMBUSTION WITH OXIDE OP COPPER IN A STREAM OF OXYGEN GAS. 178. Many chemists effect combustion with oxide of copper in a stream of oxygen supplied by a gasometer. The methods based upon this prin- ciple are employed not only for the analysis of difficultly combustible bodies, but also to effect the determination of the carbon and hydrogen in organic substances in general. These methods require a gasometer filled with oxygen, and another with air, together with certain arrangements to dry the oxygen and air completely, and to free them from carbonic acid. They are resorted to in cases where a number of ultimate analyses have to be made in suc- cession ; and also more particularly in the analysis of substances which cannot be Deduced to powder, and do not admit therefore of intimate mixture with oxide of copper, &c. The heating may be effected with the charcoal combustion furnace (fig. 77, p. 426), but a gas furnace is most convenient. Many forms of gas-furnace have been employed. One of the best is represented in fig. 84. The combustion tube rests in a gutter of sheet iron, but the glass is kept from contact with the metal by a layer of asbestos. It is well to secure the tube to the gutter by binding 178.1 OEGANIC ANALYSIS. 433 wire. At its anterior end the combustion tube is connected with a chloride of calcium tube and potash-bulb as usual. It is also necessary to have a third tube to collect traces of moisture which the current of hot gases might carry over from the potash solution. This tube i is filled with small fragments of caustic potash. Fig. 84. Posteriorly, the combustion tube is joined by a cork or caoutchouc stopper to a narrow glass tube which connects it with the gasometer and the apparatus for drying the oxygen. The gas on leaving the gas- ometer streams first through a potash bulb-tube c, then through a long TJ-tube, e, rilled with chloride of calcium, and finally through the U-tube f, containing pumice saturated with oil of vitriol. It is well to attach a lever of a foot or so in length to the handle of the cock by which the supply of gas is admitted to the combustion tube, as thus the flow of oxy- gen is more easily regulated. a. The ignition of the oxide of copper is effected in the tube. To accomplish this, a plug of asbestos is inserted into the anterior end, the tube being then filled to two-thirds of its length with oxide of cop- per; the posterior orifice is then joined to the drying apparatus inter- posed between the gasometer and the combustion tube, and the tube heated to gentle redness in its whole length, whilst a slow current of atmospheric air is conducted through it.* After complete ignition has been effected the fire is extinguished, the anterior end of the combustion tube, which up to this time has remained open, is connected with an unweighed chloride of calcium tube, and the ignited oxide allowed to cool in a slow stream of atmospheric air. When the tube is cold, it is opened at the posterior end, the substance introduced into it with the aid of a long tube (compare 174), and quickly mixed with the oxide by means of a copper wire with twisted end (see fig. 76, p. 174) ; the after-part of the tube is filled to within 12 cm. with ignited oxide of copper, cooled in the tube or flask shown in fig. 75, p. 174; a few gen- tle taps on the table will suffice to shake the contents down a little, leaving a clear passage above. The posterior end of the tube is then again connected with f, and the chloride of calcium tube, affixed to the * [Either from a second gasometer, or by aid of an aspirator.] 28 434 ORGANIC ANALYSIS. [ 178. front of the combustion tube during the cooling, exchanged for the one which is accurately weighed, and to which the weighed tubes, h and i, are also joined. The cock of the oxygen gasometer is now opened a little, so that the gas may pass in a very slow current through the apparatus ; the cock is then suddenly turned off, and the level of the fluid in the two bulb tubes watched some time ; if no change takes place in it, this is a proof that all the joinings are air-tight. After this, the anterior portion of the tube is heated to redness, as far as the layer of pure oxide of copper extends ; the same is then done with the farther part also, as far as the layer of pure oxide of copper extends, the corks at both ends of the tube being protected by screens, as well as also the part containing the mixture. A very slow current of oxygen gas is transmitted all the time through the apparatus. The part of the tube containing the mixture is then also heated, pro- ceeding slowly from the anterior to the posterior part. The stream of oxygen gas is gradually increased, but never to an extent to allow the oxygen to escape through the potash bulbs h. When the tube in its whole length is at a red heat, and the evolution of gas has ceased, the cock is opened a little wider, and the transmission of oxygen continued, until at last, when the reduced oxide of copper is completely reoxi- dized, the gas begins to escape uiiabsorbed through the potash bulbs. The cock of the oxygen gasometer is now shut, whilst that of the air gasometer is opened a little ; the combustion tube, &c., are allowed to cool in a slow stream of atmospheric air. The chloride of calcium tube, and the potash bulbs with the potassa tube joined to them, are then weighed. A very great advantage of this method consists in this, that the com- bustion tube, after the termination of the first, is quite ready for a second analysis. b. The combustion of most substances may be effected also without mixing with oxide of copper, by introducing the sample into a platinum, copper, or porcelain boat or tray (fig. 85). This method affords the advan- tage of enabling the operator to de- termine at the same time any uncon- Fig. 85. sumed residue (ash) that may remain, behind, which in some cases in the analysis of coals, for instance is a great convenience. The substance is weighed in the boat, enclosed in a corked glass tube. The process of combustion is then conducted as follows : Introduce into the anterior end of the tube a plug of asbestos, then fill the tube with oxide of copper, leaving about 20 cm. free, and keep the oxide in its place by pushing an asbestos plug down upon it. Heat the tube now to redness in the combustion furnace, pass a current of air through it, to remove all moisture, connect the anterior end with an unweighed chloride of calcium tube, and let the apparatus cool; then push the boat containing the sample down to the rear asbestos plug, and connect the after-part of the tube with the purifying apparatus interposed between the gasometer and the combustion tube, the fore-part with the weighed chloride of calcium tube and potash bulbs with potassa tube. Heat the oxide of copper in the combustion tube to redness, and when approaching the part where the boat is placed, open the cock of the oxygen gasometer a 179, 180.] ORGANIC ANALYSIS. 435 little ; when the ^eat has reached the contents of the boat, proceed with proper caution, and take care to pass neither too little nor too muc> oxygen through the tube. Increase the current of oxygen a little at last, and let the apparatus finally cool in a slow current of atmospheric air. With this method, it is still easier than with a to use the combustion tube for a second analysis immediately after the first, as all that is required for the purpose is to insert a fresh boat with another sample of substance, to replace the one just removed. Volatile Substances, or ^Bodies undergoing Alteration at 100 C (losing IVater, for instance]. 179. The process is conducted either according to 174, or as directed 8 178. Ignited chromate of lead, cooled in a closed tube, may also be employed as oxidizing agent. b. FLUID BODIES. a. Volatile liquids (e.g., ethereal oils, alcohol, &c.). 180. 1. The analysis of organic volatile fluids requires the objects enumerated in 174. The combustion tube should be somewhat longer than there men- tioned ; it should have a- length of 50 or 60 cm., ac- cording as the substance is less or more volatile. The process requires besides several small glass bulbs for the reception of the liquid to be analyzed. These bulbs are made in the following manner : A glass tube, about 30 cm. long and about 8 mm. wide, is drawn out as shown in fig. 86, fused off at d, and A expanded into a bulb, as shown in fig. 87. The bulbed part is then cut off at /?. Another bulb is then made in the same way, and a third and fourth, &c., as long as sufficient length of tube is left to se- cure the bulb from being reached by the moisture of the mouth. Two of these bulbs are accurately weighed ; they are then filled with the liquid to be analyzed, closed by fu- sion, and weighed again. The filling is effected by slightly heating the bulb over a lamp and immersing Fig. 87. the point into the liquid to be analyzed, part of which will now, upon cooling, enter the bulb. If the fluid is highly volatile, the portion entering the still warm bulb is converted; into vapor, which expels the fluid again; but the moment the vapor is recondensed, the bulb fills the more completely. If the liquid is of a less volatile nature, a small portion only will enter at first; in such cases the bulb is heated again, to convert what has entered into vapor, and the point is then again im- Fig. 86. mersed into the fluid, which will now readily enter arid' fill the \J 436 ORGANIC ANALYSIS. [ bulb. The excess of fluid is ejected from the neck of the little tube by a sudden jerk; the point of the capillary neck is then sealed in the blowpipe flame. The combustion tube is now prepared for the process by introducing into it from the filling-tube or flask ( 174), a layer of oxide of copper occupying about 6 cui. in length. ? The middle of the neck of one of the bulbs is slightly scratched with a file, the pointed end is quickly broken off, and the bulb and end are dropped into the combustion tube (see fig. 88). Another layer of oxide of copper, about 6 9 cm. long, is then filled in, and the other bulb introduced in the same manner as the first. The tube is finally nearly filled with oxide of copper. A few gentle taps upon the table suffice to clear a free passage for the gases evolved. (It is advisable to place in the anterior half of the combustion tube small lumps of oxide of copper [comp. 66, 1], or superficially oxidized copper turnings, which will permit the free pas- sage of the gases, even with a narrow channel, or no channel at all ; since with a wide channel there is the risk of vapors passing unconsumed through the tube.) The combustion of highly volatile substances demands great care, and requires certain modifications of the com- mon method. The operation commences by heating to redness the anterior half of the tube, which is separated from the rest by a screen, or in the case of highly volatile substances, by two screens ; ignited charcoal is then placed behind the tube to heat the tail and prevent the conden- sation of vapor in that part. A piece of red-hot charcoal is now applied to that part of the tube which is occupied by the first bulb ; this causes the efflux and evaporation of the contents of the latter ; the vapor passing over the oxide of copper suffers combustion, and thus the evolution of gas com- mences, which is then maintained by heating very gradually the first, and after this the second bulb ; it is better to conduct the operation too slowly than too quickly. Sudden heating of the bulbs would at once cause such an impetuous rush of gas as to eject the fluid from the potash bulbs. The tube is finally in its entire length surrounded with ignited charcoal, and the rest of the operation conducted in the usual way. If the air drawn through the apparatus tastes of the analyzed substance, this is a sure sign that complete combustion has not been effected. 2. In the combustion of liquids of high boiling point and abound- ing in carbon, e.g., ethereal oils, unconsumed carbon is apt to deposit on the completely reduced copper near the substance ; it is therefore advisable to distribute the quantity intended for analysis (about 0*4 grin.) in 3 bulbs, separated from each other in the tube by layers of oxide of copper. 3. In the combustion of less volatile liquids, it is advisable to empty the bulbs of their contents before the combustion begins : this is effected by connecting the filled tube with an exhausting syringe, and rarefying the air in the tube by a single pull of the handle; this will suffice to expand the air-bubble in each bulb sufficiently to eject the oily liquid from it, which is then absorbed by the oxide of copper. 4. If there is reason to apprehend that the oxide of copper may not Fig. 88. 181.] OKGANIC ANALYSIS. 437 suffice to effect the complete combustion of the carbon, the process is terminated in a stream of oxygen gas (compare 176). 5. Tf it is intended to effect the combustion in the apparatus de- scrilcJ. in 178 (in a current of oxygen gas), the bulb must be drawn out to a fine long point, and filled almost completely with the fluid. The point is then sealed in the blowpipe flame, and the bulbs are transferred in that state to the combustion tube. When the anterior and the far- ther end of the tube are red-hot, a piece of ignited charcoal is put to the part occupied by the first bulb, when the expansion of the liquid will cause it to burst. When the contents of the first bulb are con- sumed, the second, and after this the third, are treated in the same way. This method will not answer, however, for very volatile liquids, as, e.g., ether, on account of the explosion which would inevitably take place. Q. Non-volatile Liquids (e.g., fatty oils). 181. The combustion of non-volatile liquids is effected either, 1, with chro- mate of lead, or oxide of copper and oxygen ; 2, in the apparatus de- scribed 178. 1. The operation is conducted in general as directed 175 or 176. The substance is weighed in a small tube, placed for that purpose in a tin foot (see fig. 89), and the mixing effected as follows: Introduce into the combustion tube first a layer, about 6 cm. long, of chromate of lead, or of oxide of copper ; then drop in the small cylinder with the substance, arid let the oil com- pletely run out into the tube ; make it spread about in various directions, taking care, however, to leave the upper side (intended for the channel) and the forepart, to the ex- tent of or ^ of the length of the tube, entirely clean. Fill the tube now nearly with chromate of lead or oxide of cop- per, which has previously been cooled in the filling tube or flask, taking care that the little cylinder which contained the oil be completely filled with the oxidizing agent. Place the tube in hot sand, which, imparting a high degree of fluidity to the oil, leads to the per- fect absorption of the latter by the oxidizing agent, and proceed with the combustion in the usual way. It is advisable to select a tolerably long tube. Chromate of lead is usually to be preferred. If it is used, a very intense heat, sufficiently strong to fuse the contents of the tube, is cautiously applied in the last stage of the process. Solid fats or waxy substances which, not being reducible to powder, cannot be mixed with the oxidizing agent in the usual way, are treated in a similar manner to fatty oils. They are fused in a small weighed glass boat, made of a tube divided lengthwise ; when cold, the little boat with its contents is weighed, and then dropped into the combustion tube, which has been previously filled to the extent of about 6 cm. with chromate of lead, or with oxide of copper. The substance is then fused by the application of heat, and made to spread about in the tube in the same manner as is done with fatty oils ; the rest of the operation also being conducted exactly as in the latter case. If chromate of lead is employed, it will be found advantageous to add some bichromate of 438 ORGANIC ANALYSIS. L 182 potassa ( 177). If oxide of copper be used, finish in a stream oi oxygen ( 176). 2. If it is intended to effect the combustion of fatty substances or other bodies of the kind in a current of oxygen gas, in the apparatus described in 178, the substance is weighed in a porcelain or platinum boat, which is then inserted into the tube, and the posterior part of the latter filled with oxide of copper, as directed above. The combustion must be conducted with great care. As soon as the oxide of copper in the anterior and the posterior parts of the tube is red-hot, a piece of red-hot charcoal is put to the part occupied by the little boat. The volatile products generated by the dry distillation of the substance bum at the expense of the oxide of copper. When it is perceived that the surface layer of the oxide of copper is reduced, the application of heat to the substance is suspended for a time, and resumed only after the reduced copper is reoxidized in the stream of oxygen gas. Care is finally taken to insure the complete combustion of the carbon remaining in the boat. Supplement to A., 174181. 182. MODIFIED APPARATUS FOR THE ABSORPTION OF CARBONIC ACID. G. J. MULDER * has replaced the potash bulbs altogether by a totally different absorption apparatus, viz., by the apparatus already described, p. 293. The chloride of calcium tube is immediately connected with the system of XT-tubes, fig. 90 ; a. contains small pieces of glass, 6 to 10 drops concentrated sulphuric acid, and at the top asbestos plugs, b is filled to -J with granulated soda-lime (say 20 grm.), the remaining ^ (in the 2d limb) contains chloride of calcium (say 3 grm.). Lastly, c is filled with lumps of hydrate of potassa. a arid b are weighed together, c serves as a guard to 6, and is not weighed. The sulphuric acid tube serves to show the rate of the evolu- tion of gas ; it contains enough sul- phuric acid, when the lower part is just stopped up. If the process goes on properly, the weight of the tube does not increase more than 1 mgrni. ; generally the increment is unweighable. If the tube is closed after use with caoutchouc caps, it may be used over and over again. The sulphuric acid possesses the ad- vantage over other fluids that it in- dicates whether the combustion was Fig. 90. complete or not; for in the first case it remains colorless, in the sec- ond it becomes brown from the escaping hydrocarbons, and then the results cannot be expected to be perfectly accurate. The absorption of the carbonic acid by the soda-lime tube is as rapid as it is complete; * Zeitschrift f. analyt. Chem. 1, 2. g 183.] ORGANIC ANALYSIS. 439 even when a stream of carbonic acid is passing, with ten times the ra- pidity usual in organic analysis, no trace of the acid makes its escape. The absorption of the carbonic acid is attended with warming of the soda- lime ; if any water evaporates from the soda-lime, it is retained by the chloride of calcium in the second limb. The corks of the absorption tubes are, like the others, coated with sealing-wax. A filled soda-lime tube weighs about 40 grm. The first time it is used alone ; the second time the same tube is used, but as a precautionary measure a second similarly filled and separately weighed tube is placed in front of it. The second tube rarely increases in weight, and unless it does, the first tube can be used a third time, but of course in connection with the second. If the second tube has gained in the third operation, the first tube is rejected at the fourth operation, and the second is now used alone, &c. If after the combustion a stream of oxygen is transmitted through the combustion tube, the tubes are of course at the end full of oxygen. If, then, care be taken that the tubes are full of oxygen before weighing, the trouble of the final transmission of air may be saved. For weighing, MULDER closes the ends of the glass tubes with caps made out of india-rubber tube. MULDER'S absorption apparatus is peculiarly suitable, when the car- bonic acid is mixed with another gas. It insures complete absorption, precludes the evaporation of any water, and offers perfect security in case of the sudden occurrence of a too rapid evolution of gas. B. ANALYSIS OF COMPOUNDS CONSISTING OF CARBON, HYDROGEN, OXYGEN, AND NITROGEN. The principle of the analysis of such compounds is in general this : in one portion the carbon and the hydrogen are determined as carbonic acid and water respectively ; in another portion, the nitrogen is deter- mined either in the gaseous form, or as chloride of ammonium and bi- chloride of platinum, or by neutralizing the ammonia formed from the nitrogen ; the oxygen is calculated from the loss. As the presence of nitrogen exercises a certain influence upon tho estimation of carbon and hydrogen, we have here to consider not only the method of determining the nitrogen, but also the modifications which the presence of the nitrogen renders necessary in the usual me- thod of determining the carbon and hydrogen. a. DETERMINATION OF THE CARBON AND HYDROGEN IN NITROGENOUS SUBSTANCES. 183. 1. When nitrogenous substances are ignited with oxide of copper or with chromate of lead, a portion of the nitrogen present escapes in the gaseous form, together with the carbonic acid and aqueous vapor ; whilst another portion, minute indeed, still, in bodies abounding in oxygen, not quite insignificant, is converted into nitric oxide gas, which is subsequently transformed wholly or partially into nitrous acid by the air in the apparatus. The application of the methods described in 174, &c., in the analysis of nitrogenous substances would accordingly give too much carbon ; since the potash bulbs would retain, besides the carbonic acid, also the nitrous acid formed and a portion of the nitric 440 ORGANIC ANALYSIS. [ 184. oxide (which in the presence of potassa decomposes slowly into nitrous acid and nitrous oxide.) This defect may be remedied by selecting a combustion tube about 12 15 cm. longer than those commonly em- ployed, filling this in the usual way, but finishing with a loose layer, about 9 12 cm. long, of clean, fine copper turnings ( 66, 5), or a compact roll of copper wire-gauze.* The process is commenced by heating these copper turnings to redness, in which state they are main- tained during the whole course of the operation. These are the only modifications required to adapt the methods above described, for the analysis of nitrogenous substances. The use of the metallic copper depends upon its property of decomposing, when in a state of intense ignition, all the oxides of nitrogen into oxygen, with which it combines, and into pure nitrogen gas. As the metal exercises this action only when in a state of intense ignition, care must be taken to maintain the anterior part of the tube in that state throughout the process. As me- tallic copper recently reduced retains hydrogen gas, and, when kept for some time, aqueous vapor condensed on the surface, the copper turnings intended for the process must be introduced into the tube hot as they come from the drying closet (which is heated to 100). v. LIE- BIG recommends to compress the hot turnings in a tube into a cylin- drical form, to facilitate their rapid introduction into the combus- tion tube. 2. If it is intended to burn nitrogenous bodies in the apparatus described in 178, the combustion tube should be about 80 cm. long, and the anterior part of it filled with a layer 15 18 cm. long, of clean copper turnings. Care must be taken to keep at least the anterior half of the turnings from oxidizing, both during the ignition in the current of air and during the actual process of combustion. When the opera- tion is terminated, and the oxidation of the metallic copper is visibly progressing, the oxygen is turned off, and the cock of the air gasometer opened a little instead, to let the tube cool in a slow stream of atmos- pheric air. b. DETERMINATION OF THE NITROGEN IN ORGANIC COMPOUNDS. As already indicated, two essentially different methods are in use for effecting the determination of the nitrogen in organic compounds ; viz., the nitrogen is either separated in the pure form and its volume measured, or it is converted into ammonia, and this is determined either as bichloride of platinum and chloride of ammonium, or by neu- tralization. a. Determination of the Nitrogen from the Volume. 184. DUMAS' Method, modified by Schiel. This method may be employed in the analysis of all organic compounds containing nitrogen. It requires a graduated glass cylinder of about 200 c. c. capacity, with a ground-glass plate to cover it. * The copper turnings cannot be replaced by the metallic powder obtained by the reduction of the oxide with hydrogen, as this obstinately retains hydrogen, and consequently decomposes appreciable quantities of carbonic acid with formation of carbonic oxide. Schr.Jtter, Lautemann, Journ. f. prakt. Chem. 77, 316. 184.] OEGANIC ANALYSIS. 441 The combustion tube should be 60 or 70 cm. long, and drawn out at the posterior end to a stout open tail, which should have a small bulb 01 swell for the better fastening of a rubber tube to it. Introduce into it near the tail a plug of newly ignited asbestos, then a layer of oxide of copper, 4 cm. long ; after this the intimate mixture of an accurately weighed portion of the substance (0*3 0'6 grm., or, in the case of com- pounds poor in nitrogen, a somewhat larger quantity) with oxide of cop per, then the oxide which has served to rinse the mortar, followed by a layer of pure oxide, and lastly, a layer of copper turnings, about 15 cm. long. Make a channel along the top of the tube by gentle tapping. Connect the tube with the bent delivery tube c f (fig. 91), and place Fig. 91. in the furnace. Connect the tail by means of a stout tube of india rub- ber with an apparatus for giving a continuous stream of washed car- bonic acid gas. Transmit this slowly through the tube for half an hour, then immerse the end of the bent delivery tube under mercury, and invert over it a test tube filled with solution of potassa. If the gas bubbles entering the cylinder are completely absorbed by the solution of potassa, this is a proof that the air is thoroughly expelled from the tube. But should this not be the case, the evolution of carbonic acid must be continued until the desired point is attained. When the gas is completely absorbed, close the communication between the CO 2 genera- tor and the combustion tube by a screw clamp or stop-cock, invert the graduated cylinder, filled |- with mercury, ^ with concentrated solution of potassa, over the end of the delivery tube, with the aid of a ground- glass plate,* and proceed with the combustion in the usual way, heating first the anterior end of the tube to redness, and advancing gradually towards the farther end. In the last stage of the process, commuiiica tion is reestablished with the CO 2 generator, and thus the whole of the nitrogen gas which still remains in the tube is forced into the cylinder. Wait now until the volume of the gas in the cylinder no longer decreases, even upon shaking the latter (consequently, until the whole of the car- bonic acid has been absorbed), then place the cylinder in a large and deep glass vessel filled with water, the transport from the mercurial trough to this vessel being effected by keeping the aperture closed with * The following is the best way of filling the cylinder and inverting- it over the opening of the bent delivery tube : The mercury is introduced first, and the air-bubbles which adhere to the walls of the vessel are removed in the usual way. The solution of potassa is then poured in, leaving the top of the cylinder free, to the extent of about 2 lines ; this is cautiously filled up to the brim with pure water, and the ground-glass plate slided over it. The cylinder is now in- verted, and the opening placed under the mercury in the trough ; the glass plate is then withdrawn from under the cylinder. In this manner the operation may be performed easily, and without soiling the fingers. 442 ORGANIC ANALYSIS. [ 185. a small dish filled with mercury. The mercury and the solution of potassa sink to the bottom, and are replaced by water. Immerse the cylinder, then raise it again until the water is inside and outside on an exact level ; read off the volume of the gas and mark the temperature of the water and the state of the barometer ; calculate the weight of the nitrogen gas from its volume, after reduction to the normal tempera- ture and pressure, and with due regard to the tension of the aqueous vapor (comp. " Calculation of Analyses"). The results are generally somewhat too high, viz., by about 0*2 0*5 per cent. ; this is owing to the circumstance that even long-continued transmission of carbonic acid through the tube fails to expel every trace of atmospheric air adhering to the oxide of copper. It is highly advisable, before making any nitrogen determinations with this method, to subject a non-nitrogenous substance, e.g., sugar, to the same process. The analyst thereby acquaints himself with the extent of the error to which he will be exposed. In such an experi- ment the quantity of unabsorbed gas should not exceed 1 or 1^- c.c. To insure complete combustion of difficultly combustible bodies, STRECKER recommends the addition of arsenious acid in powder to the oxide of copper with which the substance is to be mixed ; the arsenious acid is volatilized by the action of the heat, the fumes burning the whole of the carbon like a current of oxygen. The arsenious acid sublimes in the anterior part of the tube, arsenic remains in the copper. [Frankland * and Gibbs f employ the Sprengel mercury pump to ex- haust the combustion tube of air previous to the combustion, and after- wards to transfer the nitrogen to the receiver, and obtain very accurate results.] /?. Determination of Nitrogen by conversion into Ammonia. YARRENTRAPP and WILL'S Method. 185. This method ^ may be applied to all nitrogenous compounds, except those containing the nitrogen in the form of nitric acid, hyponitric acid, &c.J It is based upon the same principle as the method of examining organic bodies for nitrogen ( 172, 1, a), viz., upon the circumstance that, when nitrogenous bodies are ignited with the hydrate of an alkali, the water of hydration of the latter is decomposed, the oxygen forming with the carbon of the organic body carbonic acid, which then combines with the alkali, whilst the nydrogen at the moment of its liberation combines with the whole of the nitrogen present to ammonia. In the case of substances abounding in nitrogen, such as uric acid, mellon, &c., the whole of the nitrogen is not at once converted into ammonia in this process ; a portion of it combining with part of the carbon of the organic matter to cyanogen, which then combines, either in that form with the alkali metal, or in form of cyanic acid with the alkali. Direct experiments have proved, however, that even in such cases the whole of the nitrogen is ultimately obtained as ammonia, if [* Journal Chem. Soc., 1868, p. 90.] [f Unpublished paper read before National Academy of Sciences, Aug., 1868.] T [+ Vegetable matters, as dried plants, containing not more than 3 per cent, of NOa may be analyzed by this method. In a case where 6 per cent, of NO 5 was pre- sent, a loss of 0-2 per cent, of N took place in the experiments of E. Schulze. Fres. Zeitschrift vi., 387]. 185.] ORGANIC ANALYSIS. i43 \ the hydra ted alkali is present in excess, and the heat applied sufficiently intense. As in all organic nitrogenous compounds the carbon preponderates over the nitrogen, the oxidation of the former, at the expense of the water, will invariably liberate a quantity of hydrogen more than sufficient tc convert the whole of the nitrogen present into ammonia ; for instance, C 2 N+4 H 02 C 0,-f N H 3 + H. The excess of the liberated hydrogen escapes either in the freo state, or in combination with the not yet oxidized carbon, according to the relative proportions of the two elements and the temperature, as marsh gas, olefiant gas, or vapor of readily condensible hydrocarbons, which gases serve in a certain measure to dilute the ammonia. As a certain dilution of that product is necessary for the success of the operation, I will here at once state that substances rich in nitrogen should be mixed with more or less of some non-nitrogenous body sugar, for instance- so that there may be 110 deficiency of diluent gas. The ammonia is determined volumetrically, see 208. aa. Requisites. 1. The objects enumerated 174, and a PORCELAIN MORTAR for weigh- ing and mixing the substance. 2. A COMBUSTION-TUBE of the kind described 174, 3 ; length about 40 cm., width about 12 mm. The combustion is effected in an ordi- nary combustion furnace ( 174, 11). 3. SODA-LIME. ( 60, 4). It is advisable to gently heat in a pla- tinum or porcelain dish, a quantity of the soda-lime sufficient to fill the combustion tube, so as to have it perfectly dry for the process of com- bustion. In the analysis of non-volatile substances, the best way is to use the soda-lime while still warm. 4. ASBESTOS. A small portion of this substance is ignited in a pla- tinum crucible previous to use. 5. A YARRENTRAPP AND WILL'S BULB-APPARATUS. This may be ob- tained from the shops. Fig. 92 shows its form. It is filled to the Fig. 92. extent indicated in the drawing with standard sulphuric acid 204, of which 20 c.c. should be employed. The acid is introduced either by dipping the point into the acid, and applying suction to y Weighty in Cases where the Body sought has been separated in Combination, or where a Compound has to be determined from one of its Constituents. 196. If the body to be determined has not been weighed or measured in its own form, but in some other form, e.g., carbonic acid as carbonate of lime, sulphur as sulphate of baryta, ammonia as nitrogen, chlorine by a standard solution of iodine, &c., its quantity must first be reckoned from that of the compound found before the calculation described in 1 can be made. This may be accomplished either by rule of three or by some abridged method. Suppose we have weighed hydrogen in the form of water, and have found 1 grm. of water; how much hydrogen does this contain ? 196.] CALCULATION OP ANALYSES. 463 An equivalent of water consists of : 1 of hydrogen 8 of oxygen 9 water. "We say accordingly : 9 : 1::1 :x From the above proportion results the following equation : or 0-11111 xl=. Or, expressed in general terms : Water x(Hllll = Hydrogen. EXAMPLE. 517 of water ; how much hydrogen ? 517xO-lllll=57-444. The following equation results also from the above proportion : 9 1 1 = x I Q = X 1 .-. x = 5 Or, expressed in general terms, Water divided by 9 = Hydrogen. EXAMPLE. 517 of water, how much hydrogen ? 517 -g-=57-444. In this manner we may find for every compound constant numbers by which to multiply or divide the weight of the compound, in order to find the weight of the constituent sought (comp. Table III.*). Thus, for instance, the nitrogen may be obtained from the double bichloride of platinum and chloride of ammonium, by dividing the weight of the latter by 15-96, or multiplying it by 0*06269 ; thus the carbon may be calculated from the carbonic acid by multiplying the weight of the latter by 0*2727, or dividing it by 3'666. These numbers are by no means so simple, convenient, and easy to remember as in the case of hydrogen. It is therefore advisable, in the case of carbonic acid, for instance, to fix upon another general expres- sion, viz., Carbonic acidx3_ r , fi ^ 11 * See Tables at the end of the volume. 464 CALCULATION OF ANALYSES. 197. whicli is derived from the proportion 22 : 6 : : the carbonic acid found : x. The object in view may also be attained in a very simple manner, by reference to table IV.,* which gives the amount of the constituent sought for every number of the compound found, from 1 to 9 ; the operator need, therefore, simply add the several values together. As regards hydrogen, for instance, we find : TABLE. Found, water Sought, hydrogen 1 O'lllll 2 0-22222 3 0-33333 4 0-44444 6 0-55555 6 G'66667 7 0-77778 . j . 0-88880 1 1-00000 From this table it is seen that 1 part of water contains 0*11111 of hy- drogen, that 5 parts of water contain 0*55555 of hydrogen ; 9 parts, 1-00000, Ac. Now if we wish to know, for instance, how much hydrogen is con- tained in 5*17 parts of water, we find this by adding the values for 5 parts, for j\ part, and for yfo- parts, thus : 0-55555 0-011111 0-0077778 0-5744388 Why the numbers are to be placed in this manner, and not as fol- lows : 0-55555 0-11111 0-77778 1-44444 is self-evident, since arranging them in the latter way would be adding the value for 5, for 1, and for 7 (5+1 + 7=13) and not for 5-17. This reflection shows also that, to find the amount of hydrogen contained in 517 parts of water, the points must be transposed as follows : 55-555 1-1111 0-77778 57-44388 3. Calculation of the Results of Indirect Analyses into Per- Cents by 'Weight. The import of the term " indirect analysis," as defined in 151, p. 337, shows sufficiently that no universally applicable rules can be laid down for the calculations which have to be made in indirect analyses. The selection of the right way must be left in every special case to the intelli- gence of the analyst. I will here give the mode of calculating the re- * See Tables at the end of the volume. 197.] CALCULATION OF ANALYSES. 465 suits in the more important indirect separations described in Section V They may serve as examples for other similar calculations. a. Indirect Determination of Soda and foiassa. This is effected by determining the sum total of the chlorides, and the chlorine contained in them. The calculation may be made as follows : Suppose we have found 3 grm. of chloride of sodium and chloride of potassium, and in these 3 grm. 1*6888 of chlorine. Eq. Chlorine. Eq. K Cl. Chlorine found. 35-46 : 74-57 ;: 1-6888 : x x = 3-5514. If all the chlorine present were combined with potassium, the weight of the chloride would amount to 3-5514. As the chloride weighs less, chloride of sodium is present, and this in a quantity proportional to the difference (i.e., 3*5514 3=O5514), which is calculated as follows : The difference between the equivalent of K Cl and that of Na Cl (16*11) is to the equivalent of Na Cl (58'46), as the difference found is to the chloride of sodium present : 16-11 : 58-46:: 0-5514: x x=2 Na Cl and 3-21 K Cl. From this the following short rule is derived : Multiply the quantity of chlorine in the mixture by 2*1029, deduct from the product the sum of the chlorides, and multiply the remainder by 3-6288 ; the product expresses the quantity of chloride of sodium contained in the mixed chloride. The calculation may also be made by help of the subjoined formulae (COLLIER*). W=weight of mixed chlorides C= chlorine. Na Cl= C x 7-6311)- (W x 3-6288) K C1=(W x 4-6288) - (C x 7-6311) Na O=(C x 4-0466) - (W x 1-9243) K O=(W X 2-9243) - (C x 4-8210). b. Indirect Determination of Strontia and Lime. This may be effected by determining the sum total of the carbonates, and the carbonic acid contained in them ( 154, 7). Suppose we have found 2 grm. of mixed carbonate, and in these 2 grm. 0*7383 of carbonic acid. Eq. C O 2 Eq. SrO, C 2 C 2 found. 22 : 73-75 :: 0*7383 : x x = 2*47498. If, therefore, the whole of the carbonic acid were combined with strontia, the weight of the carbonate would amount to 2*47498 grm. The deficiency ,=0*47498 is proportional to the carbonate of lime pre- sent, which is calculated as follows : The difference between the equivalent of Sr O, C O , and the equjva- * Am. Jour. Sci., March, 1864, p. 340. 30 466 CALCULATION OF ANALYSES. [ 198 lent of Ca O, C O 2 (23-75) is to the equivalent of Ca O, C O 2 (50), as the difference found is to the carbonate of lime contained in the mixed salt : 23-75 : 50:: 0-47498 : x The mixture, therefore, consists of 1 grin, carbonate of lime and 1 grm. carbonate of strontia. From this the following short rule is derived : Multiply the carbonic acid found by 3'3523, deduct from the product the sum of the carbonates, and multiply the difference by 2*10526 ; the product expresses the quantity of the carbonate of lime. c. Indirect Determination of Chlorine and Bromine ( 169, 1). Let us suppose the mixture of chloride and bromide of silver to have weighed 2 grm., and the diminution of weight consequent upon the transmission of chlorine to have amounted to 0*1 grm. How much chlorine is there in the mixed salt, and how much bromine ? The decrease of weight here is simply the difference between the weight of the bromide of silver originally present, and that of the chlo- ride of silver which has replaced it ; if this is borne in mind, it is easy to understand the calculation which follows : The difference between the equivalents of bromide of silver and chlo- ride of silver is to the equivalent of bromide of silver as the ascertained decrease of weight is to x, i.e., to the bromide of silver originally pres- ent in the mixture : 44-54: 187-97:: 0-1 : x ^=0-422025. The 2 grm. of the mixture therefore contained 0*422025 grm. bromide of silver, and consequently 2-0-422025=1-577975 grm. chloride of silver. It results from the above, that we need simply multiply the ascer- tained decrease of weight by J 87 ' 97 ^., by 4-22025 44-54 to find the amount of bromide of silver originally present in the ana- lyzed mixture. And if we know this, we also know of course the amount of the chloride of silver ; and from these data we deduce the quantities of chlorine and bromine, as directed in 196, and the per- centages as directed in 193. SUPPLEMENT TO I. REMARKS ON LOSS AND EXCESS IN ANALYSES, AtvD ON TAKINtt rHE AVERAGE. 198. If, in the analysis of a substance, one of the constituents is estimated from the loss, or, in other words, by subtracting from the original weigh t of the analyzed substance the ascertained united weight of the other constituents, it is evident that in the subsequent percentage calcu- lation the sum total must invariably be 100. Everv loss suffered :>r 198.] CALCULATION OF ANALYSES. 467 excess obtained in the determination of the several constituents will, of course, fall exclusively upon the one constituent which is estimated from the loss. Hence estimations of this kind cannot be considered accurate, unless the other constituents have been determined by good methods, and with the greatest care. The accuracy of the results will, of course, be the greater, the less the number of constituents determined in the direct way. If, on the other hand, every constituent of the analyzed compound has been determined separately, it is obvious that, were the results ab- solutely accurate, the united weight of the several constituents must be exactly equal to the original weight of the analyzed substance. Since, however, as we have seen in 96, certain inaccuracies attach to every analysis, without exception, the sum total of the results in the percen- tage calculation will sometimes exceed, and sometimes fall short of, 100. In all cases of this, description, the only proper way is to give the results as actually found. Thus, for instance, PELOUZE found, in his analysis of chromate of chloride of potassium, Potassium 21-88 Chlorine 19-41 Chromic acid 5 8 '21 99-50 BERZELIUS, in his analysis of sesquioxide of uranium and potassa, Potassa 12-8 Sesquioxide of uranium 8 6 '8 99-6 PLATTNER, in his analysis of pyrrhotine, Of Fahlun. Of Brasil. Iron 59-72 59-64 Sulphur 40-22 40'43 99-94 100-07 It is altogether inadmissible to distribute any chance deficiency or ex- cess proportionately among the several constituents of the analyzed com- pound, as such deficiency or excess of course never arises from the several estimations in the same measure ; moreover, such " doctoring " of the analysis deprives other chemists of the power of judging of its accuracy. No one need be ashamed to confess having obtained some- what too little or somewhat too much in an analysis, provided, of course, the deficiency or excess be confined within certain limits, which differ in different analyses, and which the experienced chemist always knows how to fix properly. In cases where an analysis has been made twice, or several times, it is usual to take the mean as the most correct result. It is obvious that an average of the kind deserves the greater coiifi device the less the re- sults of the several analyses differ. The results of the several analyses must, however, also be given, or, at all events, the maximum and minimum. 468 CALCULATION OF ANALYSES. [ 199. Since the accuracy of an analysis is not dependent upon the quantity of substance employed (provided always this quantity be not altogether too small), the average of the results of several analyses is to be taken quite independently of the quantities used ; in other words, you must not add together the quantities used, on the one hand, and the weights obtained in the several analyses on the other, and deduce from these data the percentage amount ; but you must calculate the latter from the results of each analysis separately, and then take the mean of the numbers so obtained. Suppose a substance, which we will call AB, contains fifty per cent. of A ; and suppose two analyses of this substance have given the follow- ing results : (1) 2 grm. AB gave 0'99 grm. of A. (2) 50 " 24-00 " Prom 1, it results that AB contains 49'50 per cent, of A. 2 , 48-00 Total 97-50 Mean 48- 75 It would be quite erroneous to say 2 + 50 = 52 of AB gave 0-99 + 24-00=: 24-99 of A, therefore 100 of AB contain 48*06 of A; for it will be readily seen that this way of calculating destroys nearly altogether the influence of the more accurate analysis (1) upon the aver- age, on account of the proportionally small amount of substance used. II. DEDUCTION OF EMPIRICAL FORMULAE. 199. If the percentage composition of a substance is known, a so-called em- pirical formula may be deduced from this ; in other words, the relative proportion of the several constituents may be expressed in equivalents in a formula which, upon recalculation in per-cents will give numbers corresponding perfectly, or nearly, with those obtained by the analysis. We are compelled to confine ourselves to the expression of empirical for- mula?, in the case of all substances of which we cannot determine the equivalent, as e.g., woody fibre, mixed substances, &c. The method of deducing empirical formulae is very simple, and will be readily understood from the following reflections : How should we proceed to find the relative number of equivalents in carbonic acid? We should say : The equivalent of the oxygen is to the amount of oxygen in the equi- valent of carbonic acid, as 1 is to a?, i.e., to the number of equivalents of oxygen contained in carbonic acid ; 8 : 16::1 : x 5C=2. In the same manner we should find the number of equivalents of car- bon by the following proportion : 199.] CALCULATION OF ANALYSES. 469 6 : 6 :: 1, : x (equivalent of carbon) (carbon in one equivalent of carbonic acid) x=l. Now let us suppose we did not know the equivalent of carbonic acid, but simply its percentage composition, viz., 27-273 carbon 72-727 oxygen 100-000 carbonic acid ; the relative proportion of the equivalents might still be ascertained, even though any other given number, say 100, be selected for the equivalent of carbonic acid. Let us suppose we adopt 100 as the equivalent of car- bonic acid ; thus, 8 : 72-727 :: 1 : x (Eq. O) (Amount of oxygen in the assumed eq. 100) x 9-0910 ind 6 : 27-273 :: 1 : x (Eq. C) (Amount of carbon in the assumed eq. 100) "We see here that although the numbers which express the relative proportion of the equivalents of oxygen and carbon have changed, yet the relative proportion itself remains the same ; since 4-5455 : 9-0910::! : 2. The process may accordingly be expressed in general terms as fol- lows: Assume any number, say 100 (because this is the most convenient), as the equivalent of the compound, and ascertain how often the equiva- lent of each constituent severally is contained in the amount of the same constituent present in 100 parts. When you have thus found the num- bers expressing the relative proportion of the equivalents, you have attained your purpose viz., the deduction of an empirical formula. Still, it is usual to reduce the numbers found to the simplest expres- sion. Now let us take a somewhat complicated case, e.g ., the deduction of the empirical formula for mannite. The percentage composition of mannite is 39-56 of carbon 7-69 of hydrogen 52-75 of oxygen 100-00 This gives the following proportions : 6 : 39-56::! : x #=6-593 1: 7-69::l: #=7-690 8 : 52-75::! : x #=6-593 470 CALCULATION OF ANALYSES. [ 199, We have now the empirical formula for mannite, viz., C 6 . 59 3 H 7 . 690 t> 6 . 5 93 A glance shows that the number of the equivalents of the carbon is equal to that of the equivalents of the oxygen ; and the question is now whether the relative proportion found may not be expressed by smaller numbers. A simple calculation suffices to answer this question, viz^ 6-593 : 7-690:: 60 : x (Any other number might be substituted for 60, as the third term of the proportion, but 60 is very suitable, since it is divisible without re- mainder by most of the numbers.) x=10 We have accordingly now the simple formula, CGO H 70 Ogo^r C 6 H 7 O 6 . The percentage composition of mannite given above having been cal- culated from the formula, of course the latter is evolved again without ambiguity. Now let us take the results of an actual analysis. OPPERMANN obtained, upon the combustion of 1-593 grm. mannite, with oxide of copper, 2-296 carbonic acid and 1-106 water. This gives in per-cents, 39-31 carbon 7'71 hydrogen 52-98 oxygen 100-00 which, calculated as above, gives ^6-552 -H-7710 t) 6 . 622 as the first expression of the empirical formula ; and by the propor- tion : 6-552 : 7-710=6 : x a:: 7-06 A glance at these numbers shows that 7'06 may be properly ex- changed for 7, and also that the difference between 6'552 and 6*622 is so trifling that both may be expressed by the same number. These considerations lead therefore likewise to the formula C 6 H 7 6 The proof whether the formula is correct or not is obtained by its re- calculation in per-cents. The less the calculated percentage differs from that found, the more reason there is to believe in the correctness of the formula. If the difference is more considerable than can be account- ed for by the defects inherent in the methods, there is every reason to believe the formula fallacious, in which case it is necessary to establish a more correct one ; for it will be readily seen that, in the case of sub- stances of which the equivalent is not known, different formulae may be deduced from one and the same analysis, or from several very nearly 200.] CALCULATION OF ANALYSES. 471 corresponding analyses ; since the numbers found are never absolutely- correct, but only approximate. Thus, for instance, in the case of mannite : Calculated Found for for C 6 39-56 C 8 39-67 39-31 H 7 7-69 H 9 7-44 7-71 O 6 52-75 8 52-89 52-98 100-00 100-00 100-00 III. DEDUCTION OF RATIONAL FORMULAE. 200. If both the percentage composition and the equivalent of a substance are known, it is easy to deduce its rational formula that is, a formula expressing not only the relative proportion of the equivalents, but also their absolute number. The following examples may serve for illustration : 1. Deduction of the ^Rational Formula of Hyposulphuric Acid. Analysis has given, in the first place, the percentage composition of hyposulphuric acid, and, in the second place, the percentage composi- tion of hyposulphate of potassa, viz., Sulphur 44-44 Potassa 39-551 Oxygen 55'56 Hyposulphuric acid . 60*449 Hyposulphuric acid . 100.00 Hyposulphate of potassa 100*000 (Equivalent of potassa=47*ll) Now: 39*551 : 60-449 : : 47*11 : x x=72 Hence 72 is the sum of the equivalents of the constituents contained in hyposulphuric acid in other terms, the equivalent of hyposulphuric acid. Having thus ascertained the correct equivalent of hyposulphuric acid, it is unnecessary to assume a hypothetical one, as we are obliged to do in the case of mannite. Thus we may state at once : 100: 44*44:: 72 : x a=:32; i.e. =. the sum of the equivalents of the sulphur ; and again : 100 : 55*56:: 72 : x cc=40; i.e. = the sum of the equivalents of the oxygen. Now the equivalent of sulphur, i.e. 16, is contained twice in 32 ; and the equivalent of oxygen, i.e. 8, is contained five times in 40 ; the ra- tional formula for hyposulphuric acid is accordingly, S, 5 . 2. Deduction of the National Formula of JBenzoic Acid. STENHOUSE obtained from 0*3807 hydrated benzoic acid, dried at 100, 0*9575 carbonic acid and 0*1698 water. 472 CALCULATION OF ANALYSES. [ 200. 0-4287 benzoate of silver, dried at 100, gave 0-202 silver. Fron these numbers result the following percentage compositions : Carbon 68*67 Oxide of silver . . . 50'67 Hydrogen .... 4'95 Benzoic acid . . . . 49 '33 Oxygen 26*38 Benzoate of silver . . 100*00 Hydrated benzoic acid 100*00 (Equivalent of the oxide of silver=l 15-97) 50-67 : 49-33 : : 115-97 : x *=112-904 i.e. the equivalent of anhydrous benzoic acid ; that of the hydrated acid accordingly==l 12-904+ 9=121-904; we say therefore now 100: 68-67:: 121-904 x 100: 4-95:: 121-904 x #=6-035 100: 26-38:: 121-904 x #=32-158 6 is contained in 83-711 13-95 times 1 " 6*035 6*03 8 " 32-158 4-02 " A glance at these quotients suffices to show that 13*95 may be ex- changed for 14, 6*03 for 6, and 4*02 for 4. The rational formula for the hydrate of benzoic acid is accordingly, CM H 6 4 . This gives, by calculation, The numbers found were, C 68*85 68*67 H 4*92 4-95 O 26-23 26-38 100-00 100-00 3. Deduction of the Rational Formula of Theine. STENHOUSE'S analysis of theine, free from water of crystallization, gave the following results : 1. 0.285 grm. substance gave 0'5125 carbonic acid and 0*132 water. 2. Combustion with oxide of copper gave a mixture of CO a and N, in the proportion of 4 of the former to 1 of the latter. 3. 0-5828 grm. of the double salt of hydrochlorate of theine and bi- chloride of platinum, gave 0-143 platinum. From these numbers results the following percentage composition : Carbon . . 49*05 Hydrogen . 5'14 Nitrogen . . 28*61 Oxygen . . 17-20 100-00 and 196-91 as the equivalent of theine. For there is every reason to suppose that the composition of the double salt of hydrochlorate of theine and bichloride of platinum is Theine +.HC1 + Pt C1 2 g 200.] CALCULATION OF ANALYSES. 473 The equivalent of this double salt is found by the following propor- tion: 0-143 : 0-5828 : : 98-94 (eq. platinum) : x o;=403-23 ; and consequently the equivalent of theine, by subtracting from 403-23 the sum of 1 eq. bichloride of platinum (169'86) and 1 eq. hydrochloric acid (36-46) 403-23-(169-86 x 36-46)=196-91. This supplies the following proportions : 100 : 49-05 : : 196-91 : x a=96-584 100: 5-14 :: 196-91 : x oj=10-121 100 : 28-61 : : 196-91 : x cc=56-336 100 : 17-20 : : 196-91 : x a=33'868 6 is contained in 96-584, 16-09 times 1 " 10-121, 10-12 14 " 56-336, 4-02 8 33-868, 4-23 " for which numbers may be substituted, 16, 10, 4, and 4, respectively, and we get the following formula : O ie H 10 N 4 4 This gives by calculation, Found C 49-47 49-05 H 5-15 5-14 N 28-89 28-61 O 16-49 17-20 100-00 100-00 The double hydrochlorate of theine and bichloride of platinum gives ] latinum in 100 parts, Calculated, Found. 24-70 24-53 4. Special Method of Deducing Rational Formulae for Oxyyen Salts. a. In the case of Compounds containing no Tsomorphous Constituents. The rational formulae for oxygen salts may be deduced also by a me- thod different from the foregoing, viz., by ascertaining the ratio which the respective quantities of oxygen bear to each other. This method is exceedingly simple. In an analysis of crystallized sulphate of soda and ammonia, I found, Soda . ; , . 17-93 Oxide of ammonium . 15-23 Sulphuric acid . . 46*00 Water 20-84 100-00 31 of NaO contain 8 of O, consequently 17'93 of ISTaO contain 4'63 of O. 26..NH 4 .. 8..O, .. 15-23..NH.O .. 4'68 . . O. 40..S0 3 .. 24.. O, .. 46-00.. S0 3 .. 27'60 . . O. 9.. HO .. 8..0, .. 20-84.. HO .. 18'52..O. 474 CALCULATION OF ANALYSES. [ 200. Now 4-63 : 4-68 : 27-60 : 18-52 = 1 : 1-01 : 5-97 : 4-00 = 1:1:6:4, and this leads to the formula Na O, N H 4 O, 2 S O 3 X4 H O or, Na O, S O 3 +N H 4 O, S O 3 + 4 aq. b. In the case of Compounds containing Tsomorphous Constituents. It is a well-known fact that isomorphous constituents may replace each other in all proportions; therefore, in establishing a formula for compounds containing isomorphous constituents, the latter are taken collectively that is, they are expressed in the formula as one and the same body. This very frequently occurs in the calculation of formulae for minerals. A. EBDMANN found in monradite Amount of Oxygen. Silicic acid 56-17 .... 29-957 Magnesia 31-63 . 12.652) ,, fim Protoxide of iron 8'56 . 1-949 J ' Water 4-04 .... 3-590 100-40 Now 3-59 : 14-601 : 29-957-1 : 4-07 : 8-3=1 : 4 : 8. Designating 1 eq. metal by K, we obtain from these numbers the for- mula : 4 (K O, Si 2 )+HO or 4 (^ j. O, Si O 2 ) +aq. Not only isomorphous substances, but generally all bodies of analo- gous composition possess the faculty of replacing each other in com- pounds ; thus we find that KO, Na O, Ca O, Mg O, &c., replace each other. These substances likewise must be expressed collectively in the formula. ABICH found in andesine Amount of Oxygen. Silicic acid 59-60 . . . . . 31-79 Alumina 24-28 11-22 Sesquioxide of iron 1-58 . . 0*48 Lime 577 . . 1-61 Magnesia 1-08 . . 0-43 Soda 6-53 . . 1-68 Potassa 1-08 . 0-18 3-90 . . JL UO 0-18, 99-92 11-70 Now 3-90 : 11-70 : 31-79=1 : 3 : 8-15=1 : 3 : 8. Designating 1 eq. metal by R, we obtain from these numbers the formula : =R O, Si O 2 +R 2 O a , 3 Si 2 O 2 , 201.] CALCULATION OP ANALYSES. 475 which may likewise be written : Ca K Showing thus that this mineral is leucite (K O, Si O 2 + A1 2 O 3 , 3 Si 2 ), in which the greater part of the potassa is replaced by lime, soda, and magnesia, and a portion of the alumina by sesquioxide of iron. These remarks respecting the deduction of formulae for oxygen salts, apply of course equally to metallic sulphides. IV. CALCULATION OP THE DENSITY OP THE VAPORS OF VOLATILE BODIES, AND APPLICATION OF THE RESULTS, AS A MEANS OF CON- TROLLING THEIR ANALYSES, AND DETERMINING THEIR EQUIVA- LENTS. 201. The specific gravity of a compound gas is equal to the sum of the specific gravities of its constituents in one volume. E.g., 2 volumes of hydrogen gas and 1 volume of oxygen gas give 2 volumes of aqueous vapor. If they gave simply 1 volume of aqueous vapor, the specific gravity of the latter would be equal to the sum total of the specific gravity of the oxygen and double the specific gravity of the hydrogen viz., 2x0-0693=0-1386 + 1-1083 =1-2469 But as they give 2 volumes of aqueous vapor, this 1-2469 is distri- buted between the two volumes ; accordingly the specific gravity of the vapor is 1^=0-62345 It will be readily seen that the knowledge of the density of the vapor of a compound supplies an excellent means of controlling the correctness of the relative proportions of the equivalents assumed in a formula. Eor instance : from the results of the ultimate analysis of camphor, has been deduced the empirical formula : C 10 H 8 O. DUMAS found the density of the vapor of camphor =5 -3 12. Now, by what means do we find whether this formula is correct with respect t ) the relative proportions of the equivalents ? Specific gravity of the vapor of carbon 0-831 " ' hydrogen gas 0-0693 16 oxygen gas M08 10 eq. = 10 volumes=10x 0-831 =8'310 8 eq. H=16 volumes=:16xO-0693=:l-109 1 eq. 0= 1 volume = lxM081 = M08 10-527 476 CALCULATION OF ANALYSES. [ 201 This sum is almost exactly twice as large as the specific gravity found by direct experiment (^J-=5*263) ; which shows that the relative pro- portions of the equivalents are correctly given in the empirical formula of camphor. But whether the formula is correct, also, with regard tc the absolute number of equivalents, cannot be determined simply from the density of the vapor, because we do not know to how many volumes of camphor vapor 1 equivalent of camphor corresponds. LIEBIG assumes the equivalent of camphor to correspond to 2 volumes, and gives accord- ingly the formula C 10 H 8 O ; whilst DUMAS assumes it to correspond to 4 volumes, and accordingly gives the formula C 20 H 16 O 2 . The knowledge of the density of the vapor affords, therefore, in reality, simply a means of controlling the correctness of the analysis, but not of establishing a rational formula ; emd although it is made to serve some- times for the latter purpose, yet this can be done only in the case of sub- stances for which we are able to infer from analogy a certain ratio of condensation : thus, for instance, experience proves that 1 equivalent of the hydrates of the volatile organic acids, of alcohols, &c., corresponds to 4 volumes. In 200, 2, we have found the rational formula of hydrated benzoic acid to be C, 4 H 6 O 4 . DUMAS and MITSCHERLICH found the vapor den- sity to be 4-26. Now nearly the same number is obtained by dividing by 4 the sum total of the gravities of the several constituents contained in 1 equiva- lent of hydrated benzoic acid, viz., 14 volumes 0=11-634 12 volumes H= 0-831 4 volumes O= 4-432 16-897 = 4-224 HERMANN KOPP* has called attention to the fact that, if the equivalent of a substance refers to H = 1, and the vapor density of the same to at- mospheric air = 1, the division of the equivalent by the vapor density gives the following quotients, 28-88 14-44 7-22 according as the formula corresponds to 4, 2, or 1 volume of vapor : 28'88 corresponds to a condensation to 4 volumes 14-44 " " " 2 " 7-22 . " " 1 volume KOPP calls these numbers normal quotients. If the vapor density is not quite exact, but only approximate (determined by experiment), other numbers are found, but, to be correct, these must come near the normal numbers. If, therefore, we know the equivalent of a body, we may, with the greatest facility, ascertain whether the determination of the vapor density of the body has given approximately correct results or not. GAY-LUSSAC found the vapor density of alcohol to be 1-6133 ; DALTON, 2-l.f * Compt. rend. 44, 1347 ; Chem. Centralbl. 1857, 595. f Gmelin's Handbook, viii., 199. 201.] CALCULATION OF ANALYSES. 477 Now, which is the correct number ? The equivalent of alcohol, C 4 Hg O 2 , is 46. 46 .-28-5 1-6133 It is evident that* GAY-LUSSAC'S number is approximately correct, for the quotient found by it conies very near the normal quotient, 28-88. Again, if we know the equivalent of a body, and the number of volumes of vapor corresponding to 1 equivalent, we may also, with the same facility, calculate the theoretical vapor density of the body. For instance, the equivalent of hydrated benzoic acid is 122. The division of this number by 28'88 gives 4'224 as vapor density, which is the same as that found by actual experiment. And, lastly, if we know approximately (i.e. by experiment) the vapor density of a body, and also the ratio of condensation, we may, with the aid of these quotients, approximately calculate the equivalent of the body. E.g. The vapor density of acetic ether has been found = 3' 11 2. The multiplication of this number by 28'88 gives 89'87 as the equivalent of acetic ether, which comes near the actual equivalent, 88. Having thus shown how the knowledge of the vapor density of a body is turned to account as a means of controlling the results of an ultimate analysis of the same, we will now proceed to show how the vapor density is calculated from the data obtained as described in 191, A and B. A. We will take as an illustration DUMAS' estimation of the specific gravity of the vapor of camphor. The results of the process were as follows : Temperature of the air ....... 13'5 Barometer ......... 742 mm. Temperature of the bath at the moment of sealing the globe 244 Increase of the weight of the globe ..... 0'708 grm. Volume of mercury entering the globe .... 295 c.c. Residual air ......... Now, to find the vapor density, we have to determine, 1. The weight of the air which the globe holds (as a necessary step to the determination of 2). 2. The weight of the camphor vapor which the globe holds. 3. The volume to which the camphor vapor corresponds, at and 760 mm. The solution of these questions is quite simple ; and if the calcula- tion, notwithstanding, appears somewhat complicated, this is merely owing to certain reductions and corrections which are required. 1. The weight of the air in the globe. The globe holds 295 c. c., as we see by the volume of mercurv in- quired to fill it. 478 CALCULATION OF ANALYSES. [ 201. First, what is the volume of 295 c. c. of air at 13-5 and 742 nun., at and 760 mm. ? The question is solved according to the directions of 195, as follows : 760: 742:: 295 : x sc=28S c. c. (At 13-5 and 760 mm.) and again : 288 .=_A 8 JL:r=274 c. c. (at and 760 mm.) 1 .A A A ,1 1 v / 1 + (13-5x0-00366) 1-04941 Now 1 c. c. of air at and 760 mm. weighs 0-00129366 grra. ; 274 c. c. weigh accordingly 0-00129366x274=0-35446 grm. 2. The Weight of the Vapor. At the beginning of the experiment we tared the globe + the air within it; we afterwards weighed the globe + the vapor (but without the air) ; to find, therefore, the actual weight of the vapor, it is not sufficient to subtract the tare from the weight of the globe filled with vapor, since (glass -{-vapor) (glass-}-air) is not=vapor j but we have either to subtract, in the first place, the weight of the air from the tare, or to add the weight of the air to the increase of the weight of the globe. Let us do the latter : Weight of air in the globe . =i 0*35446 grm. Increase of weight of globe . = 0-70800 grm. The weight of the vapor is accordingly =1-06246 grm. 3. The Volume to which this Weight of 1-06246 grm. of Vapor cor- responds at and 760 mm. We know from the above-given data that this weight corresponds to 295 c. c. at 244, and 742 mm. Before we can proceed to reduce this volume according to the directions of 195, the following corrections are necessary : a. 244 of the mercurial thermometer correspond, according to the experiments of MAGNUS, to 239 of the air thermometer (see Table VI.). b. According to DULONG and PETIT, glass expands (commencing at 0) -g-yfjj-g- of its volume for each degree C. The volume of the globe at the moment of sealing was accordingly - = c. c. 35000 It we now proceed to reduce this volume to and 760 mm. we find by the proportion, 760: 742::297:ce x (i.e., c. c. of vapor at 760 mm. and 239) =290 ; and by the equation, 201.] CALCULATION OF ANALYSES. 479 290 1 + (239x0-00366)" x (i.e. c. c. of vapor at 760 mm. and 0) = 154*6. 154-6 c. c. of camphor vapor at and 760 mm., weigh accordingly 1-06246 grm. 1 litre (1000 c. c.) weighs consequently 6-87231 grm.; since 154-6 : 1-06246:: 1000 : 6-87231. Now 1 litre of air at and 760 mm. weighs 1-29366 grm. The specific gravity of the camphor vapor consequently = 5-312 ; since 1*29366 : 6-87231::! : 5-312. B. We will here take an imaginary determination of the vapor density of ether as our example. Bulb + ether =0-3445 grm. " empty =0*2040 grm. Weight of ether =0*1405 grm. Temperature of the glycerine solution in the outer cylinder 100 Sp. gr. of the same solution at 100 1 Barometer 752 mm. Difference between the height of the mercury in the outer ) and inner cylinders j 50 mm. Height of the column of mercury in the outer cylinder. . 60 mm. Inside height of the outer cylinder 400 mm. Volume of the vapor as found from the tube's table .... 60 c. c. The glycerine solution being 400 60= 340 mm. high and having a specific gravity of 1, corresponds to a column of mercury of 25 mm. The vapor consequently is under the pressure of 752-f 25 50=727 mm. 60 c. c. of ether vapor at 100 and 727 mm. consequently weigh 0*1405. We have now to calculate the weight of 60 c. c. of air under the same circumstances. 1000 c. c. air of and 760 mm. weigh 1*29366 grm. Heated to 100 they become 1366*5 c. c. (comp. 195, a), and with the pressure reduced to 727 mm. these expand again bo 1428*5 c. c. (comp. 195, 3). But the air still weighs the same, viz., 1*29366 grm. .*. 1428*5 c. c. weighing 1*29366, 60 c. c. weigh, under the same circumstances, 0*05433 grm. ; hence the sp. gr. of ether vapor = =2-586 PART II. SPECIAL PART. 1. ANALYSIS OF FRESH WATER (SPRING-WATER, RIVER-WATER, &c.)* 202. THE analysis of the several kinds of fresh water is usually restricted to the quantitative estimation of the following substances : a. Bases: Soda, lime, magnesia. b. Acids : Sulphuric acid, nitric acid, silicic acid, carbonic acid, chlorine. c. Mechanically suspended Matters : Clay, &c. We confine ourselves, therefore, here to the estimation of these bodies. I. The Water is clear. 1. determination of the Chlorine. This may be effected, either, a, in the gravimetric, or, 6, in the volumetric way. a. Gravimetrically. Take 500 1000 grin, or c. c.f Acidify with nitric acid, and precipi- tate with nitrate of silver. Filter when the precipitate has completely subsided ( 141, I., a). If the quantity of the chlorine is so inconsider- able that the solution of nitrate of silver produces only a slight turbidity, evaporate a larger portion of the water to -j, ^-, -|-, &c., of its bulk, filter, wash the precipitate, and treat the filtrate as directed. b. Volumetrically. Evaporate 1000 grm. or c. c. to a small bulk, and determine the chlorine in the residual fluid, without previous filtration, by solution of nitrate of silver, with addition of chromate of potassa ( 141, I., 6. a). 2. Determination of the Sulphuric Acid. Take 1000 grm. or c. c. Acidify with hydrochloric acid and mix with chloride of barium. Filter after the precipitate has completely subsided ( 132, I., 1). If the quan- tity of the sulphuric acid is very inconsiderable, evaporate the acidified water to -, ^, -J-, &c., of the bulk, before adding the chloride of barium. 3. Determination of Nitric Aci^, If, on testing the residue on eva- poration of a water for nitric acid, such a strong reaction is obtained that the presence of a determinable quantity of the acid may be inferred, evaporate 1000 or 2000 c. c. of the water in a porcelain dish, wash the residue into a flask (if any carbonate of lime, &c., remains sticking to the dish, it may be disregarded, as all nitrates are soluble), evaporate in the flask still further, if necessary, and in the small quantity of residual fluid determine the nitric acid according to 149, d, a, or /?. The for- mer method is less suitable if the residue on evaporation contains organic matter. If the latter method is employed, the evaporated water * Compare Qualitative Analysis, p. 202, et seq. See a paper recently read before the Chemical Society by Dr. Miller the Society's Journal (2), iii., 117, et seq. ; also, Frankland, idem (2), iv., 239, and vL., 77; and Wanklyn, Chap- man, and Smith, idem vi. , 152. f As the specific gravity of fresh water differs but little from that of pure water, the several quantities of water may safely be measured instead of weighed. The calculation is facilitated by taking a round number of c. c. 484 SPECIAL PART. [ 202. must first bo heated with potash solution till no more alkaline vapors escape. 4. Determination of the Silicic Acid, Lime, and Magnesia. Evaporate 1000 grm. or c. c. to dryness after addition of some hydro- chloric acid preferably in a platinum dish, treat the residue with hydrochloric acid and water, filter off the separated silicic acid, and treat the latter as directed 140 II., a. Estimate the lime and magnesia in the filtrate as directed 154, 6, a (29). 5. Determination of the total Residue and of the Soda. a. Evaporate 1000 grm. or c. c. of the water, with proper care, to dryness in a weighed platinum dish, first over a lamp, finally on the water-bath. Expose the residue, in the air-bath, to a temperature of about 180, until no further diminution of weight takes place. This gives the total amount of the salts. b. Treat the residue with water, arid add, cautiously, pure dilute sul- phuric acid in moderate excess ; cover the vessel during this operation with a dish, to avoid loss from spirting; then place on the water-bath, without removing the cover. After ten minutes, rinse the cover by means of a washing bottle, evaporate the contents of the dish to dryness, expel the free sulphuric acid, ignite the residue, in the last stage with addition of some carbonate of ammonia ( 97, 1), and weigh. The residue con- sists of sulphate of soda, sulphate of lime, sulphate of magnesia, and some separated silicic acid. It must not redden moist litmus paper. The quantity of the sulphate of soda in the residue is now found by subtract- ing from the weight of the latter the known weight of the silicic acid and the weight of the sulphate of lime and sulphate of magnesia. calculated from the quantities of these earths found in 4. 6. Direct ^Estimation of the Soda. The soda may also be determined in the direct way, with comparative expedition, by the following method : Evaporate 1250 grm. or c. c. of the water, in a dish, to about i, and then add 2 3 c. c. of thin pure milk of lime, so as to impart a strongly alkaline reaction to the fluid ; heat for some time longer, then wash the contents of the dish into a quarter-litre flask. (It is not necessary to rinse every particle of the precipitate into the flask ; but the whole of the fluid must be transferred to it, and the particles of the precipitate adhering to the dish well washed, and the washings also added to the flask.) Allow the contents to cool, dilute to the mark, shake, allow to deposit, filter through a dry filter, measure off 200 c. c. of the filtrate, corresponding to 1000 grm. of the water, transfer to a quarter-litre flask, mix with car- bonate of ammonia and some oxalate of ammonia, add water up to the mark, shake, allow to deposit, filter through a dry filter, measure off 200 c. c., corresponding to 800 grm, of the water, add some chloride of am- monium,* evaporate, ignite, and weigh the residual chloride of sodium as directed 98, 2.f * To convert the still remaining sulphate of soda, o.n ignition, into chloride of podium. f This process, which entirely dispenses with washing 1 , presents one source of error viz. , the space occupied by the precipitates is not taken into account. The error resulting from this is, however, so trifling, that it may safely be disregarded, as the excess of weight amounts to 5 ^ at the most. 202.] ANALYSIS OF FRESH WATER. 485 7. Calculate the numbers found in 1 6 to 1000 parts of water, anil determine from the data obtained the amount of carbonic acid in com bination, as follows : Add together the quantities of sulphuric acid corresponding to the bases found, and subtract from the sum, first, the amount of sulphuric acid precipitated from the water by chloride of barium (2), secondly, the amount corresponding to the nitric acid found, and thirdly, the amount corresponding to the chlorine found (for 1 eq. Cl, 1 eq. SO 3 ) ; the remainder is equivalent to the carbonic acid combined with the bases in the form of neutral carbonates. 40 parts of sulphuric acid re- maining after subtracting the quantities just stated, correspond accord- ingly to 22 parts of carbonic acid. If, by way of control, you wish to determine the combined carbonic acid in the direct way, evaporate 1000 grin, or c. c. of the water, in a flask, to a small bulk ; add tincture of cochineal, then standard nitric acid, and proceed as directed p. 8. Control. If the quantities of the soda, lime, magnesia, sulphuric acid, nitric acid, silicic acid, carbonic acid, and chlorine are added together, and an amount of oxygen corresponding to the chlorine (since this latter is combined with metal and not with oxide) is subtracted from the sum, the remainder must nearly correspond to the total amount of the salts found in 5, a. Perfect correspondence cannot be expected, since, 1, upon the evaporation of the water chloride of magnesium is partially decomposed, and converted into a basic salt ; 2, the silicic acid expels some carbonic acid ; and 3, it being difficult to free carbonate of mag- nesia from water without incurring loss of carbonic acid, the residue remaining upon the evaporation of the water contains the carbonate of magnesia as a basic salt, whereas, in our calculation, we have assumed the quantity of carbonic acid corresponding to the neutral salt. 9. Determination of the free Carbonic Acid. In the case of well- water this may be conveniently executed by the process described 139, ]3 (p. 286). We here obtain the carbonic acid which is contained in the w^ater over and above the quantity corre- sponding to the monocarboiiates, or in other words, the carbonic acid which is free and which is combined with the carbonates to bicar- bonates. 10. Determination of the Organic Matter. Many well-waters contain so much organic matter as to be quite- yellow, others contain traces, and many again may be said to be free from such substances. The exact estimation of organic matter is by 110 means an easy task, and the method usually adopted viz., ignition of the residue of the water dried at 180, treatment with carbonate of ammonia, gentle ignition again, and calculation of the organic matter from the loss of weight yields merely an approximate result, since we can never be sure as to the condition of the carbonate of magnesia -in the residue dried at 180 and in the same after ignition, and since the silicic acid expels some carbonic acid, which is not taken up again on treatment with carbonate of ammonia, &c. However, it is generally a matter of importance, in regard to the application of a water, to know the quantity of organic matter present, hence we have lately had re- 486 SPECIAL PART. [ 202. course to the permanganate of potassa, and sought to determine the organic matter at least comparatively from the quantity of the oxidizing agent reduced by a definite amount of water. FORCHHAMMER* heats a certain quantity of the water to boiling, runs in a dilute solution of permanganate from a burette, till a faint but permanent redness occurs, he then allows to cool, and to a like quantity of pure distilled water adds permanganate from the same burette till a similar coloration is formed ; lastly, he finds from the difference the quantity of permanga- nate reduced by the substances contained in the water. EM. MoNNIEuf uses a solution of 1 grm. permanganate of potassa in 1 litre of distilled water, purified by rectification over some permanganate of potassa. He warms 500 c. c. of the water to 70, adds 1 c. c. pure sulphuric acid, and then the standard solution of permanganate to incipient coloration, and finally, deducting from the quantity employed the quantity neces- sary to impart the same coloration to 500 c. c. of purified distilled water, acidulated and heated as above, he obtains the quantity of per- manganate which has been reduced by the substances present in the water tested. Comparative experiments of this kind are often of value ; but they do not provide us with a numerical expression for the amount of or* ganic substances present, since waters contain sometimes other bodies, especially nitrites, sulphuretted hydrogen, and salts of protoxide of iron, which have the property of reducing permanganate of potassa, and since again organic substances decompose various quantities of this salt, according to their nature. II. Tkt iraw is not clear. Fill a large flask of known capacity with the water, close with a glass stopper, and allow the flask to stand in the cold until the suspended matter is deposited ; draw off the clear water with a siphon as far as practicable, filter the bottoms, dry or ignite the contents of the filter, and weigh. Treat the clear water as directed in I. Respecting the calculation of the analysis, I remark simply that the results are usually^ arranged i7 r >on the following principles : The chlorine is combined with sodium ; if there is an excess, this is combined with calcium. If, on the other hand, there remains an ex- cess of soda, this is combined with sulphuric acid. The sulphuric acid, or the remainder of the sulphuric acid, as the case may be, is combined with lime. The nitric acid is, as a rule, to be combined with lime. The silicic acid is put down in the free state, the remainder of the lime and the magnesia as carbonates, either neutral or acid, according to circumstances. It must always be borne in mind that the results of the qualitative analysis may render another arrangement of the acids and bases neces- sary. For instance, if the evaporated water reacts strongly alkaline, carbonate of soda is present, generally in company with sulphate of soda and chloride of sodium, occasionally also with nitrate of soda. * Institut. 1849, 383 ; Jahresber. von v. Liebig u. Kopp. 1849, 603. Gompt. rend. 50, 1084 ; Dingler's polyt. Journ. 157, 132. A certain latitude is here allowed to the analyst's discretion. 203, 204.] ACIDIMETRY. 487 The lime and magnesia are then to be entirely combined with carbonic acid. In the report, the quantities are represented in parts per 1000 (01 1000,000), and also in grains per gallon. For technical purposes, it is sometimes sufficient to estimate the hardness of the water (the relative amount of lime and magnesia in it) by means of a standard solution of soap. A detailed description of this method, which was first employed by CLARK, may be found in BOLLEY & PAUL'S Handbook of Technical Analysis. See also BUTTON'S Volu- metric Analysis. 2. ACIDIMETRY. A. ESTIMATION BY SPECIFIC GRAVITY. 203. Tables, based upon the results of exact experiments, have been drawn up, expressing in numbers the relation between the specific gravity of the aqueous solution of an acid, and the amount of real acid contained in it. Therefore, to know the amount of real acid contained in an aqueous solution of an acid, it suffices, in many cases, simply to deter- mine its specific gravity. Of course the acids must, in that case, be free, or at least nearly free from admixtures of other substances dis- solved in them. Now, as most common acids are volatile (sulphuric acid, hydrochloric acid, nitric acid, acetic acid), any non- volatile admix- ture may be readily detected by evaporating a sample of the acid in a small platinum or porcelain dish. The determination of the specific gravity is effected either by com- paring the weight of equal volumes of water and acid,* or by means of a good hydrometer. The estimations must, of course, be made at the temperature to which the Tables refer. The Tables on pages 488 491 give the relations between the spe- cific gravity and the strength for sulphuric acid, hydrochloric acid, nitric acid, and acetic acid. In all cases in which the determination of the specific gravity fails to attain the end in view, or which demand particular accuracy, the fol- lowing method is employed. B. ESTIMATION BY SATURATION WITH AN ALKALINE FLUID OP KNOWN STRENGTH.! 204. This method requires : A dilute acid of known strength. An alkaline fluid of known strength. * See Greville Williams' Chemical Manipulation. f According to Nicholson and Price (Chem. Gaz. , 1856, p. 30) the common method of acidimetry is not suited for determining- free acetic acid, on account of the alkaline reaction of neutral acetate of soda ; however, Otto (Annal. d. Chem. u. Pharm. 102, 69) has clearly demonstrated that the error arising from this is so inconsiderable that it may safely be disregarded. 488 SPECIAL PART. [ 204. TABLE I. Showing the percentages of hydrated and anhydrous acid corresponding to various specific gravities of aqueous Sulphuric Acid by BINEAU ; calculated for 15, by OTTO. Specific gravity. Percentage of hydratec acid. Percentage of anhydrous acid. Specific gravity. Percentag of hydrate acid. Percentage of anhydrous acid. 1-8426 100 81-63 1-39$ 50 40-81 1-842 99 80-81 1-3886 49 40-00 1-8406 98 80-00 1-379 48 39-18 1-840 97 79-18 1-370 47 38-36 1-8384 96 78-36 1-361 46 37-55 1-8376 95 77-55 1-351 45 36-73 1-8356 94 76-73 1-342 44 35-82 1-834 93 75-91 1-333 43 35-10 1-831 92 75-10 1-324 42. 34-28 1-827 91 74-28 1-315 41 33-47 1-822 90 73-47 1.306 40 32-65 1-816 89 72-65 1-2976 39 31-83 1-809 88 71-83 1-289 38 31-02 1-802 87 71-02 1-281 37 30-20 1-794 86 70-10 1-272 36 29-38 1-786 85 69-38 1-264 35 28-57 1-777 84 68-57 1-256 34, 27-75 1-767 83 67-75 1-2476 33 26-94 1-756 82 66-94 1-239 32 26-12 1-745 81 66-12 1-231 31 25-30 1-734 80 65-30 1-223 30 24-49 1-722 79 64-48 1-215 29 23-67 1-710 78 63-67 1-2066 28 22-85 1-698 77 62-85 1198 27 22-03 1-686 76 62-04 1-190 26 21-22 1-675 75 61-22 1-182 25 20-40 1-663 74 60-40 1-174 24 19-58 1-651 73 59-59 1-167 23 18-77 1-639 72 58-77 1-159 . 22 17-95 1-627 71" 57-95 1-1516 21 17-14 1.615 70 57-14 1-144 20 16-32 1-604 69 56-32 1-136 19 15-51 1-598 63 55-59 1-129 18 14-69 1-580 67 54-69 1-121 17 13-87 1-568 66 53-87 1-1136 16 13-06 1-557 65 53-05 1-106 15 12-24 1-545 64 52-24 1-098 14 11-42 1-534 63 51-42 1-091 13 10-61 1-523 62 50-61 1-083 12 9-79 1-512 61 49-79 1-0756 11 8-98 1-501 60. 48-98 1-068 10 8i6 1-490 59 48-16 1-061 9 7-34 1-480 58 47-34 1-0536 8 6-53 1-469 57 46.53 1-0464 7 5-71 1-4586 56 45-71 1-039 6 4-89 1-448 55 44-89 1-032 5 4-08 1-438 54 44-07 1-0256 4 3-26 1 428 53 43-26 1 1019 3 2-445 1-418 52 42-45 1-013 2 1-63 1-408 51 41-63 1-0064 1 0-816 204.] ACIDIMETRY. 489 TABLE II. Showing the percentages of anhydrous acid corresponding to various specific gravities of aqueous Hydrochloric Acid, by URE. Tempe- rature 15. Specific gravity. Percentage of hydrochlori acid gas. Specific gravity. Percentage of hydrochloric acid gas. 1-2000 40-777 1-1000 20-388 1-1982 40-369 1 -0980 19-980 1-1964 39-961 1 -0960 19-572 1-1946 39-554 1^0939 19-165 1-1928 39-146 1-0919 18-757 1-1910 38-738 1-0899 18-349 1-1893 38-330 1-0879 17-941 1-1875 37-923 1 -0859 17-534 1-1857 37-516 1-0838 17-126 1-1846 37-108 1-0818 16-718 1-1823 36-700 1-0798 16-310 - 1-1802 36-292 1-0778 15-902 1-1782 35-884 1 -0758 15-494 1-1762 35-476 1-0738 15-087 1-1741 35-068 1-0718 14-679 1 -1721 34-660 1 -0897 14-271 1-1701 34-252 1-0077 13-863 1-1681 33-845 1 -0657 13-456 1-1661 33-437 1-0637 13-049 1-1641 33-029 1-0617 12-641 1-1620 32-621 1 -0597 12-233 1-1599 32-213 1-0577 11 -825 1-1578 31-805 1 -0557 11-418 1 -1557 31-398 1-0537 11;010 1-1537 30-990 1-0517 10-602 1-1515 30-582 1-0497 10-194 M494 30-174 1 -0477 9-786 1-1473 29-767 1-0457 9-379 1-1452 29-359 1-0437 8-971 1-1431 28-951 1-0417 8-563 1-1410 28-544 1 -0397 8155 1-1389 28-136 1-0377 7-747 1-1369 27-728 1-0357 7-340 1-1349 27-321 1-0337 6-932 1-1328 26-913 1-0318 6-524 1-1308 26-505 1-0298 6-116 1-1287 26-098 1-0279 5-709 1-1267 25-690 1-0259 5-301 1-1247 25-282 1-0239 4-893 1-1226 24-874 1-0220 4-486 1-1206 24-466 1-0200 4-078 1-1185 24-058 1-0180 3-670 1-1164 23-650 1-0160 3-262 1-1143 23-242 1-0140 2-854 1-1123 22-834 1-0120 2-447 1-1102 22-426 1-0100 2-039 1-1082 22019 1-0080 1-631 1-1061 21-61,1 1-0060 1-124 1-1041 21-203 1-0040' 0-816 1-1020 20-796 1-0020 0-408 490 SPECIAL PART. : 204. TABLE III. Showing the 'percentages of anhydrous acid corresponding to various specific gravities of aqueous Nitric Acid, by URE. Temperature 15. Specific gravity. Percentage of anhy- drous acid. Specific gravity. Percentage of anhy- drous acid Specific gravity. Percentage of anhy- drous acid. Specific gravity. Percentage of anhy- drous acid. 1-500 79-7 1-419 59-8 1-295 39-8 1-140 19-9 1-498 78-9 1-415 59-0 1-289 39-0 1-134 19-1 1-496 781 1-411 58-2 1-283 38-3 1-129 18-3 1-494 77-3 1-406 57-4 1-276 37-5 1-123 17-5 1-491 76-5 1-402 56-6 1-270 36-7 1-117 16-7 1-488 75-7 1-398 55-8 1-2G4 35-9 1-111 15-9 1-485 74-9 1-394 55-0 1-258 35-1 1-105 15-1 1-482 74-1 1-388 54-2 1-252 34-3 1-099 14-3 1-479 73-3 1-383 53-4 1-246 33-5 1-093 13-5 1-476 72-5 1-378 52-6 1-240 32-7 1-088 12-7 1-473 71-7 1-373 51-8 1-234 31-9 1-082 11-9 1-470 70-9 1-368 511 1-228 31-1 1-076 11-2 1-467 701 1-363 50-2 1-221 30-3 1-071 10-4 1-464 69-3 1-358 49-4 1 -215 29-5 1-065 9-6 1-460 68-5 1-353 48-6 1-208 28-7 1-059 8-8 1-457 67-7 1-348 47-9 1-202 27-9 1-054 8-0 1-453 66-9 1-343 47-0 1-196 27-1 1-048 7-2 1-450 66-1 1-338 46-2 1-189 26-3 1-043 6-4 1-446 65-3 1-332 45-4 1-183 25-5 1-037 5-6 1-442 64-5 1-327 44-6 1-177 24-7 1-032 4-8 1-439 63-8 1-322 43-8 1-171 23-9 1-027 4-0 1-435 63-0 1-316 43-0 1-165 231 1-021 3-2 1-431 62-2 1-311 42-2 1-159 22-3 1-016 2-4 1-427 61-4 1-306 41-4 1-153 21-5 1-011 1-6 1-423 60-6 1-300 40-4 1-146 20-7 1-005 0-8 a Preparation of the Solutions. The acid may be of such strength as to contain in 1000 c. c. the exact equivalent number (H 1) of grammes of the acid, accordingly, 40 grm. sulphuric acid, 36*46 hydrochloric acid, 36 oxalic acid, &c. Acids of this strength are called normal acids / equal volumes of them have the same power of saturating alkalies. Their use is convenient for techni- cal analyses. For nicer work we employ more dilute acids, either deci- normal, or of some other convenient standard. As the first step in the preparation of a dilute sulphuric acid, of convenient strength for ordi- nary use, dilute 20 cubic centimetres of oil of vitriol with water to the volume of 2 litres. - '.* ^ The standard alkali is made from commercial caustic potash ; this is dissolved in water and diluted until a given volume, e. g. 5 c. c., neutral- izes 4 to 5 c. c. of the standard acid, as is determined by a few rough trials. The alkali-solution thus obtained is heated to boiling in a flask, and a little freshly-slaked lime is added to decompose any carbonate of pot- ash. The boiling is continued a few minutes and, finally, the ley is poured upon a filter, and the filtrate is collected in the bottle from 204.] ACIDIMETRY. 491 TABLE IV. Showing the percentages of hydrated acid corresponding to various specific gravities of aqueous Acetic Acid, by MOHR. 02 S3 ' vj id "oS 8,3 ; gj s Specific a IS Specific "S3 Specific "iS Specific c -3 Specific Tj gravity. 2 gravity. "f gravity. g gravity. O H gravity. g "g II IS 0} y IS f* 1 -0635 100 10735 80 1-067 60 1 -051 40 1-027 20 1 -0655 99 1-0735 79 1-066 59 1050 39 1-026 19 1 -0670 98 1-0732 78 1-066 58 1-049 38 1-025 18 1-0680 97 1 -0732 77 1-065 57 1-048 37 1024 17 1-0690 96 1-0730 76 1-064 56 1-047 36 1-023 16 1-0700 95 1 -0720 75 1-064 55 1-046 35 1 -022 15 1-0706 94 1-0720 74 1-063 54 1-045 34 1020 14 1-0708 93 1-0720 73 1-063 53 1-044 33 1-018 13 1-0716 92 1-0710 72 1-062 52 1-042 32 1-017 12 1-0721 91 1-0710 71 1-061 51 1-041 31 1-016 11 1-0730 90 1 -0700 70 1-060 50 1-040 30 1-015 10 1 -0730 89 1 -0700 69 1-059 49 1-039 29 2-013 9 1-0730 88 1 -0700 68 1-058 48 1-038 28 1-012 8 1-0730 87 1 -0690 67 1-056 47 1 -036 27 1-010 7 1 -0730 86 1-0690 66 1-055 46 1-035 26 1-008 6 1-0730 85 1 -0680 65 1-055 45 1-034 25 1-007 5 1-0730 84 1 -0680 64 1 -054 44 1 -033 24 1-005 4 1-0730 83 1-0680 63 1-053 43 1-032 23 1-004 3 1-0730 82 1 -0670 62 1-052 42 1 -031 22 1-002 2 1-0732 81 1 -0070 61 1-051 41 1-029 21 1-001 1 which it is to be used. Care should be taken to bring upon the filter some of the excess of lime that is suspended in the liquid, so that the latter may acquire no carbonic acid from the air. This clear liquid thus obtained is a potash-lye containing lime in solution. If exposed to the air, the carbonic acid that is absorbed separates as carbonate of lime, leaving the liquid perfectly caustic. It now remains to determine with the greatest accuracy, 1st, the vol- ume of alkali which neutralizes a cubic centimetre of the acid, and, 2d, the amount of SO :} contained in a cubic centimetre of the latter. As a means of recognizing the point of neutralization, tincture of cochineal possesses great advantages over solution of litmus. The knowledge of this fact is due to LUCKOW, who has detailed its applica- tion in Jour, fur Pract. Chem., Jxxxiv., p. 424. Tincture of cochineal is prepared by digesting and frequently agitating three grammes of pul- verized cochineal in a mixture of 50 cubic centimetres of strong alcohol with 200 c. c. of distilled water, at ordinary temperatures, for a day or two. The solution is decanted, or filtered through Swedish paper. The tincture thus prepared has a deep ruby-red color. On gradually diluting with pure water (free from ammonia), the color becomes orange and finally yellowish-orange. Alkalies and alkali-earths as well as their carbonates change the color to a carmine or violet-carmine. Solutions of strong acid and acid salts make it orange or yellowish-orange. 492 SPECIAL PART. [ 204. To determine the volumetric relation of the alkali and acid, a given volume of the latter, e. g. 20 c. c. , is measured off into a wide-mouthed flask, ten drops of cochineal-tincture, and about 150 c. c. of water are added the alkali is now allowed to flow in from a burette, until the yellowish liquid in the flask, suddenly, and by a single drop, acquires a violet-carmine tinge. In nicer determinations, it is important to bring the liquid each time to a given volume, by adding water after the neutralization is nearly fin- ished. For this purpose, two or more flasks of equal capacity are se- lected, and on the outside of each a strip of paper is gummed to indicate the level of the proper amount of liquid, e. g. 200 c. c. The same amount of coloring matter being thus always diffused in the same vol- ume of the same water, the errors of varying dilution and varying amount of ammonia (which is rarely absent from distilled water) are avoided. The contents of one flask, in which the neutralization has been satisfactorily effected, may be kept as a standard of color for the succeeding trials, as the tint remains constant for hours, being unaffected by the absorption of carbonic acid. The greatest convenience and ac- curacy of measurement are obtained by using burettes provided with ERDMANN'S swimmer (See p. 30.) When three or four accordant results have been obtained, the average is taken as expressing the relative strength of the acid and alkali. To ascertain the absolute standard, weigh off in a small platinum cru- cible about O'S grm. of pure carbonate of soda, ignite to dull redness, cool and weigh accurately : bring the crucible with its contents into one of the wide-mouthed flasks and let flow from the burette a slight excess, e. g. 50 c. c., of standard acid. The solution of carbonate of soda is facilitated by warming, and, finally, the contents of the flask are gently boiled for several minutes to expel carbonic acid. The solution is now allowed to become perfectly cold, then add ten drops of cochineal and lastly the standard alkali to neutralization, diluting to the proper vol- ume. To illustrate the accuracy of the process and the calculations employed, the following actual data may be useful. The normal acid was made by diluting 50 c. c. of oil-of-vitriol to the volume of ten litres and had half the strength above recommended. The alkali was from a stock on hand and more dilute than necessary. JRelation of acid to alkali. Exp. 1., 20 c. c. SO 3 =32-8 c. c. KO, or 1 : 1-64 Exp. II., 20 c. c. SO 3 .= 32-8 c. c. KO, or 1 : 1-64 Exp. III., 40 c, c. S0 3 =65-7 c. c. KO, or 1 : 1-6425 We have accordingly : 1 c. c. SO 3 =l-64 c. c. KO and 1 c. c. KO=0'60976 c. c. SO 3 Absolute strength of acid and alkali. Exp. I. 0-4177 grm. of carbonate of soda were treated with 44'2 of SO 3 . To neutralize the excess of the acid were required 3'8 c. c., KO, which cor- respond to 2-32 c. c. SO 3 (3-8 x 0-60976). Deducting this from the total amount of acid (44'2 2'32) we have 41-88 c. c. of acid, equivalent to the carbonate of soda taken. 204J ACIDIMETRY. 493 41-88 c. c. solution of SO 3 = 0-4197 grm. NaO CO.,. Exp. II. 0-4126 grin. NaO Co, treated with 44 c. c. SO 3 required 4-28 c. c. KO. 4-28x0-60976=2-61 c. c. SO 3 . 44-2-61=41-39 c. c. SO 3 . 41-39 c. c. solution of SO 3 = 0'4126 grins. NaO CO.,. It is convenient to calculate how much acid corresponds to 53 deci- grammes of carbonate of soda, since the relation of any other substance to the acid is then obtained by substituting its equivalent number for 53 (the equivalent of NaO CO.,), in the following equation, thus : grms. NaO C0 2 c. c. S0 3 I. 0-4177 : 0-53 : : 41-88 II. 0-4126 : 0-53 : : 41-39 Accordingly 0*53 grm. NaO CO 2 neutralize 53*155 c. c. SO 3 . If, for example, the solutions are employed for nitrogen estimations ( 185), we learn how much nitrogen corresponds to 1 c. c. of acid, by the following proportion : c. c. S0 3 grm. N. 53-155:1 :: 0-140:0-002634 We may then write on the label of the acid bottle the following data for calculation. 1 c. c. KO =0-60976 c. c. SO 3 . 1 c. c. S0 3 =1-64 c. c. KO. 1 c. c. SO, =0-002634 grm. N. According to Luckow, cochineal is quite indifferent to carbonic and sulphydric acids, carminic acid being stronger than these. This is prac- tically true for solutions of considerable strength. Hence a Normal Al- kali for technical analysis may l>e prepared by simply dissolving 53 grms. of pure and anhydrous carbonate of soda in a litre of water. To make a normal acid mix 1050 c. c. of water with 60 grm. of concentrated sul- phuric acid, let cool and ascertain as just described how many c. c. of this acid neutralize 50 c. c. of normal carbonate of soda. Suppose 48'6 c. c. are required, then 50 48*6 = 1*4 c.c. of water must be added to every 48'6 c. c. of acid to make it normal. For a litre of normal acid 48*6 x 20 972 c. c. of this acid and 28 c.c. of water should be mixed. As it is difficult to do this with accuracy, we ascertain how much water is needed to bring 1000 c. c. of the acid to the normal strength. 972 : 1000 : : 28 : x x = 28-8 Fill, therefore, a flask holding a litre to the mark with the acid, add from a burette 28'8 c. c. of water and mix. Test finally the ticid against the alkali to be certain that equal volumes neutralize each other. Decinormal solutions may be prepared by diluting 100 c. c. of the normal solutions to a litre, or taking 5 -3 grms. of carbonate of soda as the starting point. In the neutralization it is not needful to expel carbonic acid by boiling. The influence of the latter is however at once seen when a caustic and carbonated alkali are operated with side by side. In case of the former, the point of neutralization (or rather of supersaturation), is 494 SPECIAL PART. [ 204. shown by a prompt and decisive change from a tint in which orange predominates, to one in which this disappears and violet is most marked. In presence of carbonic acid the change is somewhat gradual, and though a red color is produced it is modified by an orange tint, even in pres- ence of a large excess of alkali. Hence, it is to be recommended, espe- cially in nice investigations, to employ a caustic alkali. A triflle less of it will be found needful to neutralize a given volume of acid, than is required of a carbonated solution, and no doubt will exist as to the point of saturation.* This indifference towards carbonic acid is a great advantage in nice analyses, in that the time consumed for effecting neutralization is without influence on the result. When litmus is used and the point of neutralization is reached, a short exposure to the air suffices to redden the liquid again. If the operator is obliged to proceed slowly, he will require somewhat more alkali than when he operates rapidly ; a portion of it being neutralized by atmospheric carbonic acid. With cochineal, the result is independent of the small amount of carbonic acid that can come from the air. The permanence of the color also allows several ti- trations to be compared directly together. Another advantage of cochineal is, that its solution, prepared as above described, may be preserved indefinitely in closed vessels, without de- colorization or alteration. b. The Actual Analysis. It is only necessary to weigh or measure off a quantity of the acid to be examined and ascertain how much standard alkali is required for its neutralization, as has been detailed. The selec- tion of the alkaline fluid depends, of course, entirely upon the quantity of acid to be neutralized. The neutralization of the weighed or measured acid fluid should take about 15 30 c. c. In scientific investigations, I recommend the weighing of indeterminate quantities of the acid fluid, as the weighing of definite quantities on a chemical balance is troublesome, and the trouble of calculation is not worth mentioning. Suppose, for instance, you have weighed off 4*5 grm. of a dilute acetic acid, and used 25 c. c. normal solution of soda to neutralize this, you find by the proportion, 1000 : 25 : : 60 (eq. C 4 H 4 O 4 ) : x] a;=l-5, that 1*5 grm. of hydrated acetic acid are contained in the weighed quantity of the dilute acid ; and another proportion, viz., 4-5 : 1-5:: 100 : x; cc=33'33 fives the percentage of hydrated acetic acid contained in the analyzed uid. Or, the calculation may also be made as follows : 4 '5 grm. of the acetic acid examined having required 25 c. c. of normal * Collier has made some experiments with a sulphuric acid containing 25 c. c. oil of vitriol to the litre, and a solution of carbonate of soda, and he found, when C0 2 was expelled by boiling, that 10 c. c. SO 3 = 7'66 and 7 '67 c. c. of NaO CO, when CO, was not expelled, 10 c. c. S0 3 =7'68 and 7 '7. These results are as good as identical. In standarding the much weaker acid above mentioned, he obtained for it a value slightly too low when CO 2 was not removed. 0'53 grm. NaO CO 2 required in this case but 53 '05 c. c. SO 3 , instead of 53*155 as in the other instances. This is a very slight difference and not appreciable perhaps with^ ordinary burettes, but it is a constant and perceptible differ- ence. What is of more importance is the uncertainty as to the point of neu- tralization. 204.] ACIDIMETRY. 495 solution of soda for neutralization, how much would 6 grra. (i.e. the weight of fa eq. grin, hydrated acetic acid) require ? 4-5 : 6 :: 25 : x- 9 a=33'33 It is evident that in this case the number of c. c. found as x expresses the percentage of hydrated acetic acid, since 100 c. c. of normal solution of soda correspond to fa eq. grin, pure hydrated acid, i. e. acetic acid of 100 per cent. In technical analyses it is more convenient if the number of c. c. or half c. c. used of the normal solution of soda expresses directly the per- centage of hydrated or anhydrous acid contained in the examined fluid. For this purpose, the -fa or -^ equivalent number (H=l) of grammes of the anhydrous or hydrated acid, are weighed off according as the number of c. c. or half c. c. of normal alkali used, are to express the percentage of hydrated or anhydrous acid contained in the analyzed fluids. The following are the quantities for the more common acids : fa Eq. number fa Eq. number of grammes. of grammes. Sulphuric acid . . .4-0 . . .2-00 Hydrated sulphuric acid . . 4*9 . . . 2'45 Nitric acid .... 5-4 ... 2-70 Hydrated nitric acid . 6'3 ... 3'15 Hydrochloric acid . . . 3*646 . . . 1-823 Oxalic acid . . . , 3'6 . . .1-80 Crystallized oxalic acid . 6'3 ... 3'15 Acetic acid . . . . 5'1 . . .2*55 Hydrated acetic acid . 6-0 ... 3'00 Tartaric acid . 6'6 ... 3'30 Hydrated tartaric acid . 7'5 ... 3'75 But, as the weighing of definite small quantities would hardly be accurate enough, it is preferable to weigh oft' the half eq. grm. of the acids (i. e. 20 or 24'5 grm. of sulphuric acid, according to whether it is intended to find the percentage of anhydrous or of hydrated acid; 18 '23 of hydrochloric acid, &c.) in a measuring flask holding 500 c. c., add water cautiously,* allow to cool if necessary, fill up with water to the mark, shake, and then remove, by means of the pipette, 100 or 50 c. c., according to whether fa or fa eq. grm. acid is to be used. c. Deviations from the preceding method of Analysis. a. It is often preferred to have the alkali of such a strength that the c. c. or the half c. c. employed to neutralize a round number of grm. or c. c. of an aqueous acid may express at once the percentage of real acid. For instance, if we add 20 c. c. water to 1000 c. c. normal soda solution, these 1020 c. c. will saturate 51 (1 eq.) grm. anhydrous acetic acid, 1000 c. c. therefore saturate 50 grm. Hence if we take 10 grm. of vine- gar (10 c. c. will do instead, as the specific gravity of vinegar scarcely differs from that of water), and add our diluted solution of soda to satu- * In the case of concentrated sulphuric acid, the flask must be half full of water before the acid is weighed into it. 496 SPECIAL PAKT. [ 205. ration, the c. c. used, divided by 2, will express the percentage of anhy- drous acetic acid in the specimen of vinegar examined.* /?. If the color of a fluid conceals the change of the dissolved cochineal, or if salts of iron be present, we use red litmus or turmeric paper to hit the point of neutralization, i. e. 9 we add alkali till a strip of test paper dipped in just indicates a weak alkaline reaction. In this case more alkali will be employed than when cochineal can be used in solution, and in exact determinations it may be worth while to rectify the error by a correction. This may be done by taking a like quantity of watei and adding soda solution, till the fluid just gives a reaction on the test paper in question, as strong as was obtained at the close of the first ex- periment. The quantity of alkali used is of course to be deducted from the quantity employed in the first experiment. d. Application of the Acidimetric principle to the determination of combined acids. The acidimetric principle may often be employed also for the deter- mination of acids in combination with bases, if solution of carbonate of soda precipitates the latter completely, and in a state of purity. For instance, acetic acid in iron mordant, or in verdigris, may be estimated in this way, by the following process: Precipitate with a measured quantity of normal solution of carbonate of soda in excess, boil, filter, wash, concentrate the filtrate, add cochineal and normal acid to neu- tralization. Subtract the c. c. of standard acid used, from the c. c. of soda solution consumed in the experiment : the difference expresses the quantity of soda solution neutralized by the acid contained in the substance, in combination as well as in the free state. Of course, cor- rect results can be expected only if no basic salt has been thrown down by the soda solution. e. Determination of combined acids by G-ibbs* method. See 149, ii., c, 7, p. 330. MODIFICATION OF THE COMMON ACIDIMETRIC METHOD (KiEFEiif). 205. Instead of estimating free acid by a solution of soda of known strength, and determining the neutralization point by means of cochineal tincture, an ammoniacal solution of oxide of copper may be used for the pur- pose, in which case the neutralization point is known by the turbidity observed as soon as the free acid present is completely neutralized. The copper solution is prepared by adding to an aqueous solution of sulphate of copper, solution of ammonia until the precipitate of basic salt which forms at first is just redissolved. After determining the strength of the solution by normal sulphuric or hydrochloric acid (not oxalic), it may be employed for the estimation of all the stronger acids (with the exception of oxalic acid), provided the fluids are clear. The basic salt of copper, in the precipitation of which the final reaction consists, is not insoluble in the ammonia salt formed, and its solubility depends on the degree of concentration, and on the presence of other salts, especially of ammonia salts (CAREY LEA^). Hence the method cannot boast of scientific * Zeitschrift f. analyt. Chem. 1, 253. f Annal d. Chem. u. Pharm. 93, 386 $ Chem. News, 4, 195. 206.] ALKALIMETRY. 497 TABLE I. Percentages of ANHYDROUS POTASSA corresponding to different specific gravities of solution of potassa. Dalton. Tilnnermann (at 15). Specific gravity. Percentage of anhydrous potassa. Specific gravity. Percentage of anhydrous potassa. Specific gravity. Percentage of anhydrous potassa. 1-60 46-7 1-3300 28-290 1-1437 14-145 1-52 42-9 1-3131 27158 1-1308 13-013 1-47 39-6 1 -2966 26-027 1-1182 11 -882 1-44 36-8 1 -2803 24-895 1-1059 10-750 1-42 34-4 1 -2648 23-764 1-0938 9-619 1-39 32-4 1-2493 22-632 1-0819 8-487 1-36 29-4 1 -2342 21 -500 1-0703 7-355 1-33 26-3 1 -2268 20-935 1-0589 6-224 1-28 23-4 1-2122 19-803 1-0478 5-002 1-23 19-5 1-1979 18-671 1 -0369 3-961 1-19 16-2 1-1839 17-540 1-0260 2-829 115 13-0 1-1702 16-408 1-0153 1-697 111 9-5 1-1568 15-277 1-0050 0-5658 1-06 4-7 TABLE II. Percentages of ANHYDROUS SODA corresponding to different specific gravities of solution of soda. Dalton. Tunnermann (at 15). Specific gravity. Percentage of anhy- drous soda. Specific gravity Percentage of anhy- drous soda. Specific gravity. Percentage of anhy- drous soda. Specific gravity. Percentage of anhy- drous soda 1-56 41-2 1-4285 30-220 1-2982 20-550 1-1528 10-275 1-50 36-8 1-4193 29-616 1-2912 19-945 1-1428 9-670 1-47 34-0 1-4101 29-011 1-2843 19-341 1-1330 9-066 1-44 31-0 1-4011 28-407 1-2775 18-730 1-1233 8-462 1-40 29-0 1-3923 27-802 1-2708 18132 1-1137 7-857 1-36 26-0 1-3836 27-200 1 -2642 17-528 1 -1042 7-253 1-32 23-0 1 -3751 26-594 1 -2578 16-923 1-0948 6-648 1-29 19-0 1-3668 25-989 1 -2515 16-319 1-0855 6-044 1-23 16-0 1-3586 25-385 1 -2453 15-714 1-0764 5-440 1-18 13-0 1-3505 24-780 1 -2392 15-110 1-0675 4-835 1-12 9-0 1 -3426 24-176 1-2280 14-506 1-0587 4-231 1-06 4-7 13349 23-572 1-2178 13-901 1-0500 3-626 1 -3273 22-967 1-2058 13-297 1-0414 3-022 1 -3198 22-363 1-1948 12-692 1 -0330 2-418 1-3143 21-894 1-1841 12-088 1-0246 1-813 1-3125 21-758 1-1734 11-484 1-0163 1-209 1-3053 21-154 1-1630 10-879 1-0081 0-604 32 408 SPECIAL PART. [ 206, TABLE III. Percentages of AMMONIA (N H,) corresponding to different specific gravities of solution of ammonia at 16 (J. OTTO). Specific gravity. Percentage of ammonia. Specific gravity. Percentage of ammonia. Specific gravity. Percentage of ammonia. 0-9517 12-000 0-9607 9-625 0-9697 7-250 0-9521 11-875 0-9612 9-500 0-9702 7-125 0-9526 11 -750 0.9616 9-375 ! 0-9707 7-000 0-9531 11-625 0-9621 9-250 0-9711 6-875 0-9536 11 -500 0-9626 9125 i 0-9716 6-750 0-9540 11-375 0-9631 9-000 0-9721 6-625 0-9545 11-250 0-9636 8-875 0-9726 6-500 0-9550 11-125 0-9641 8-750 0-9730 6-375 0-9555 11-000 0-9645 8-625 ! 0-9735 6-250 0-9556 10-950 0-9650 8-500 0-9740 6125 0-9559 < 10-875 0-9654 8-375 0-9745 6-000 0-9564 10-750 0-9659 8-250 0-9749 5-875 0-9569 10-625 0-9664 8-125 0-9754 5-750 0-9574 10-500 0-9669 8-000 0-9759 5-625 0-9578 10-375 0-9673 7-875 0-9764 5-500 0-9583 10-250 0-9678 7-750 0-9768 5-375 0-9588 10125 0-9683 7-625 0-9773 5-250 0*9593 10-000 0-9688 7-500 0-9778 5-125 0-9597 9-875 0-9692 7-375 0-9783 5-000 0-9602 9-750 accuracy, but as the variations occasioned by the causes mentioned are inconsiderable,* the process retains its applicability to technical purposes, for which, indeed, it was originally proposed. This method is of especial value in cases in which free acid is to be determined in presence of a neutral metallic salt with acid reaction e.g., free sulphuric acid in mother-liquors of sulphate of copper or sulphate of zinc, &c. It is advis- able to determine the strength of the ammoniacal copper solution anew before every fresh series of experiments. 3. ALKALIMETRY. A. ESTIMATION OF POTASSA, SODA, OR AMMONIA, FROM THE SPECIFIC GRAVITY OF THEIR SOLUTIONS. 206. In pure or nearly pure solutions of hydrated soda or potassa, or of ammonia, the percentage of alkali may be estimated from the specific gravity of the solution. B. ESTIMATION OF THE TOTAL AMOUNT OF CARBONATED AND CAUSTIC ALKALI IN CRUDE SODA AND IN POTASHES. The " soda ash " of commerce is a crude carbonate of soda the * Compare my experiments on the subject in the Zeitschrift f analyt. Chem l, 108. 207.] ALKALIMETRY. 400 " potashes " and " pearlasli " a crude carbonate of potash. The com- mercial value of these articles depends on the percentage of alkaline carbonate (or caustic alkali) that they contain, which is very variable. I. VOLUMETRIC METHODS. Method of DESCROIZILLES and GAY-LUSSAC, slightly modified. 207. The principle of this method is the converse of that on which the acidimetric method described 204, is based, i.e., if we know the quan- tity of an acid of known strength, required to saturate an unknown quantity of caustic potassa or soda, or of carbonate of potassa or soda, we may readily calculate from this the amount of alkali present. For technical analyses we may employ the normal sulphuric acid p. 493. For the analysis we may conveniently weigh off such a quantity of the substance that the number of c. o. of acid required to neutralize it shall directly express its percentage of the alkali or carbonate sought. The proper quantities of the compounds of potassa and soda to em- ploy are J ff Eq. (H =1) expressed in grms., viz. : Potassa, KG 4-711 grm. Hydrate of potassa, KO, HO 5-611 " Carbonate of potassa, KO, CO 2 6-911 " Bicarbonate of potassa, KO, HO, 2 CO 2 10'OH " Soda, NaO 3*100 " Hydrate of soda, NaO HO 4-000 " Carbonate of soda (dry) NaO CO, 5300 Crystallized carbonate of soda, NaO CO 2 , 10 HO 14'300 " Bicarbonate of soda, NaO HO 2 CO 2 8-400 " With regard to the examination of pearlash by this method, the follow- ing points deserve attention : The various sorts of potash of commerce contain, besides carbonate of (and caustic) potassa, a. Neutral salts (e.g., sulphate of potassa, chloride of potassium). b. /Salts with alkaline reaction (e.g., silicate of potassa, phosphate of potassa). c. Admixtures insoluble in water, more especially carbonate, phos- phate, and silicate of lime. The salts named in a exercise no influence upon the results, but not so those named in b and c. Those in c may be removed by filtration ; but the admixture of the salts named in b constitutes an irremediable, though slight source of error : that is to say, if it is desired to confine the determination to the caustic and carbonated alkali. But as regards the estimation of the value of pearlash for many purposes, the term error cannot be applied ; as, for instance, in the preparation of caustic potassa, by boiling the solution with lime, the alkali combined with silicic acid and with phosphoric acid is converted, like the carbonate, into the caustic state. If you are not satisfied with finding the percentage of available alkali, but desire also to know whether the remainder consists simply of 500 SPECIAL PART. [ 208. I foreign salts, or whether water is also present, the determination of the latter substance must precede the alkalimetric examination. The same remark applies also to soda. With regard to the examination of soda by this method, the following points deserve attention : The soda of commerce, prepared by LEBLANC'S method, contains, be- sides carbonate of soda, always, or at least generally, hydrate of soda, sulphate of soda, chloride of sodium, silicate and aluminate of soda, and not seldom also sulphide of sodium, hyposulphite and sulphite of soda.* The three last-named substances impede the process, and interfere more or less with the accuracy of the results. Their presence is ascer- tained in the following way : a. Mix with sulphuric acid ; a smell of sulphuretted hydrogen reveals the presence of sulphide of sodium, with which hyposulphite of soda is also invariably associated. b. Color dilute sulphuric acid with a drop of solution of permangan- ate of potassa or chromate of potassa, and add some of the soda under examination, but not sufficient to neutralize the acid. If the solution retains its color, this proves the absence of both sulphite and hyposul- phite of soda ; but if the fluid loses its color, or turns green, as the case may be, one of these salts is present. c. Whether the reaction described in b proceeds from sulphite or hyposulphite of soda, is ascertained by supersaturating a clear solution of the sample under examination with hydrochloric acid. If the solu- tion, after the lapse of some time, becomes turbid, owing to the separa- tion of sulphur (emitting at the same time the odor of sulphurous acid), this may be regarded as a proof of the presence of hyposulphite of soda ; however, the solution may, besides the hyposulphite, also contain sul- phite of soda. With respect to the detection of sulphite of soda in the presence of hyposulphite, comp. " Qual. Anal.," p. 187. The defects arising from the presence of the three compounds in question may be remedied in a measure, by igniting the weighed sanple of the soda with chlorate of potassa, before proceeding to saturate it. This operation converts the sulphide of sodium, hyposulphite of soda, and sulphite of soda into sulphate of soda. But if hyposulphite of soda is present, the process serves to introduce another source of error, as that salt, upon its conversion into sulphate of soda,, decomposes an equivalent of carbonate of soda, and expels the carbonic acid of the latter [Na O, S,O, + 4 O (from the chlorate of potassa) -f Na O, 00*= 2 (Na O, S0 8 ) + COJ. The presence of silicate of soda and of aluminate of soda may be generally recognized by the separation of a precipitate as soon as the solution is saturated with acid. If you intend the result to express the quantity of carbonated and caustic alkali only, the presence of these two bodies becomes a slight source of error, but if you wish to estimate the value of the soda for many purposes, no error will be caused. 208. Method of FR. MOHR, modified. Instead of estimating the alkalies in the direct way by means of an * Traces of cyanide of sodium are also occasionally found. 208.] ALKALIMETRY. 501 acid of known strength, we may estimate them also, as proposed first by FR. MOHR,* by supersaturating with standard acid, expelling the car- bonic acid by boiling, and finally by determining by solution of soda the excess of standard acid added. This process gives very good results, and is therefore particularly suited for scientific investigations. It requires the standard fluids men- tioned in 204, viz., a standard acid and standard solution of soda. Each of these fluids is filled into a MOHR'S burette. The process is as follows : Dissolve the alkali in water, and add a measured quantity of tincture of cochineal ; run in now as much of the normal acid as will suffice to impart an orange tint to the fluid ; then boil, and remove the last traces of carbonic acid, by boiling, shaking, blowing into the flask, and finally sucking out the air. iNow add standard solution of soda, drop by drop, until the color just appears violet. There is no difficulty in determining the exact point at which the reaction is completed. If the standard solution of soda and the normal acid are of correspond- ing strength, the number of c. c. used of the soda solution is simply deducted from the number of c. c. used of the acid. The remainder ex- presses the quantity of acid neutralized by the alkali in the examined sample. If the two standard fluids are not of corresponding strength, the excess of acid added, and subsequently neutralized by the soda solu- tion, is calculated from the known proportion the one bears to the other. If yj eq. number (H=l) of grammes have been weighed of the alka- lies to be valued, of soda accordingly, 5*3 grm., of pearlash 6'91 grm., the number of c. c. used of the normal acid expresses directly the per- centage of carbonate of soda or carbonate of potassa contained in the examined sample; since 100 c. c. of the normal acid, containing T L- eq. grm. acid will just suffice to neutralize -fa eq. grm. pure carbonate of soda or carbonate of potassa. j If any other quantities of the alkalies have been weighed off, a simple calculation will give the result in the desired form. To make this simple calculation quite clear for all possible cases, I select one of the most complicated kind, proceeding upon the supposi- tion that the soda solution is not of corresponding strength with the normal acid, but that 2 '2 c. c. of the soda solution neutralize 1 c. c. of the acid; and that instead of y 1 ^ eq. grm., 3'71 grm. of pearlash have been weighed off. The quantity of acid added was 48 c. c. ; the excess required 4*3 c. c. of soda solution for neutralization. The proportion 2-2:1:: 4-3 : x\ aj=l-95 shows that the excess of acid wasl'95 c. c. ; 48 1'95 46*05 c. c. of the acid have accordingly been consumed by the pearlash. The proportion 3-71 : 46-05 : : 6-91 ( T V eq. KO, CO 2 ) : x: x=85'7T shown that the examined pearlash contains 85 -77 per cent, of the pure carbonate. With regard to certain variations from the ordinary course which are occasionally convenient, comp. p. 495. Annal. d. Chem. u. Pharm. 8G, 129. f Of 100 per cent. 502 SPECIAL PART. ' [ 209, 209. There now still remain two questions to be considered, which are of importance for the estimation of the commercial value of potash and soda. The first concerns the separate determination of the caustic alkali, which the sample under examination may contain besides the carbonate ; the second, the determination of carbonate of soda in presence of carbonate of potassa. C. DETERMINATION OF THE CAUSTIC ALKALI WHICH COMMERCIAL ALKALI MAY CONTAIN BESIDE THE CARBONATE. Many kinds of potashes and crude soda, more especially the latter, contain, besides alkaline carbonate, also caustic alkali ; and the chem- ist is often called upon to determine the amount of the latter ; as it is, for instance, by no means a matter of indifference to the soap-boiler how much of the soda is supplied to him already in the caustic state. This may be effected as follows : Weigh off Y 3 Q-eq. gnu. substance ; of potashes accordingly, 20'73 grm., of soda 15'9 grm. ; dissolve in water, in a flask holding 300 c. c., fill up to the mark, shake, allow the fluid to deposit out of contact of air, and take out two portions of 100 c. c. each. Determine in the one portion the total quantity of the carbonated and caustic alkali, as directed 208 ; the number of c. c. of normal acid used expresses the amount of caustic alkali -f- alkaline carbonate, in per-cents. of the latter. Transfer the other portion to a measuring-flask holding 300 c. c., add 100 c. c. of water, then solution of chloride of barium as long as a precipitate forms, add water up to the mark, shake, allow to deposit out of contact of air,* measure off 100 c. c. of the supernatant clear fluid which now contains caustic baryta in corresponding quantity to the caustic alkali present in the sample add some tincture of cochineal, then normal nitric acid (see 210), to acid reaction. Neutralize the excess of acid by normal solu- tion of soda, and you will find the c. c. of normal acid that have been re- quired by the caustic baryta. Multiply this by 3 (as only -J of the sec- ond portion has been employed in the experiment) ; the result gives the percentage of caustic alkali, expressed as carbonate of soda or potassa. Deduct this number from the percentage obtained in the first experi- ment ; the difference gives the quantity of carbonate of potassa or soda present as such. To calculate the caustic alkali into the anhydrous or hydrated state, it is only necessary to multiply by the numbers given in the first method. D. ESTIMATION OF CARBONATE OF SODA IN PRESENCE OF CARBONATE OF POTASSA. Soda being much cheaper than potash, is occasionally used to adulter- ate the latter. The common alkalimetric methods not only fail to de- tect this adulteration, but they give the admixed soda as carbonate of potassa. Many processesf have been proposed for estimating in a sim- ple way the soda contained in potash, but not one of them can be said to satisfy the requirements of the case. * Filtering through a dry filter causes the caustic alkali to come out rather toe low, as the paper retains caustic baryta (A. Muller, Journ. f. prakt. Chem. 83. 884; Zeitschrift f. analyt. Cnem. 1, 84). f Comp. HandwOrterbuch der Chemie, 2 Aufl. I. 443. 210.] ESTIMATION OF ALKALINE EARTHS. 503 The following tolerably expeditious process, however, gives accurate results : Dissolve 6'25 grm. of the gently ignited pearlash in water, filter the solution into a quarter-litre flask, add acetic acid in slight ex- cess, apply a gentle heat until the carbonic acid is expelled, then add to the fluid, while still hot, acetate of lead, drop by drop, until the forma* tion of a precipitate of sulphate of lead just ceases ; allow the mixture to cool, add water up to the mark, shake, allow to deposit, filter through a dry filter, and transfer 200 c. c. of the filtrate, corresponding to 5 grrn. of pearlash, to a {-litre flask. Add sulphuretted hydrogen water up to the mark, and shake. If the acetate of lead has been carefully added, the fluid will now smell of sulphuretted hydrogen, and no longer con- tain lead ; in the contrary case, sulphuretted hydrogen gas must be con- ducted into it. After the sulphide of lead has subsided, filter through a dry filter. Evaporate 50 c. c. of the filtrate (corresponding to 1 grm. of pearlash) with addition of 10 c. c. hydrochloric acid, of 1*10 sp. gr., in a weighed platinum dish, to dryness, then cover the dish, heat, and weigh ; the weight found expresses the total quantity of chloride of potassium and chloride of sodium given by 1 grm. of the pearlash. Estimate the potassa and soda now severally in the indirect way, by determining the chlorine volumetrically ( 141, I., b). For the calcu- lation of the results, see 197. 4. ESTIMATION OP ALKALINE EARTHS BY THE ALKALIMETRIC METHOD. 210. Alkaline earths, in the caustic state or in the form of carbonates, may also be estimated by means of a standard acid. Standard sul- phuric acid may be used for the estimation of magnesia ; standard nitric acid for that of baryta, strontia, and lime. To prepare 1 litre of normal nitric acid you require a pure dilute nitric acid of about 1'04 sp. gr., and also a normal soda solution (or at least a soda solution whose re- lation to normal sulphuric acid is exactly known). Fill a MOHR'S burette with the nitric acid, measure off 20 c. c. ; color with tincture of cochineal and add normal solution of soda from a second burette to alkaline reaction. Repeat the experiment. Sup- pose 20 c. c. of the acid have required 24 c. c. of normal soda solution, add to every 20 volumes of the acid 4 volumes of water. For the pro- per way of effecting the dilution, see p. 493 (Preparation of Normal Sul- phuric Acid). After diluting, measure off 20 c. c., and neutralize with the normal solution of soda, of which it must now take exactly 20 c. c. It will be well to verify the normal nitric acid in the manner direct- ed, p. 492. If the alkaline earth to be estimated is in the caustic state, weigh off a definite quantity, add water, then, from a burette normal nitric acid, until solution is effected, and the fluid, colored with cochineal, appears orange; now add soda solution until the color just changes to violet; deduct the soda solution added from the acid, and calculate by the pro- portion 1000 (c. c.) : the number of c. c. of acid used 76'5 (eq. baryta), 51'75 (eq. strontia), 28 (eq. lime) or 20 (eq. magnesia) : x (grm. of baryta, strontia, lime, or magnesia). 504 SPECIAL PART. [ 211. Should there be a failure the first time in determining the exact poinc at which the fluids turn violet, add another c. c. of the acid, and then again solution of soda until violet. In the case of carbonates of the alkaline earths, heat a weighed quan- tity of the sample, in a flask, with water ; then add, from the burette . small portions of normal nitric acid. When solution is effected and "the acid is consequently in excess, add tincture of cochineal, then nor- mal soda solution, till only a small excess of acid remains, say -} or 1 c. c. Heat to boiling, shake the liquid, and continue boiling for some minutes, to expel the carbonic acid completely from the fluid and flask ; finally add soda until just violet. 1000 c. c. of the normal acid corre- spond to 98'5 grm. carbonate of baryta, 73' 75 grin, carbonate of stron- tia, 50 grm. carbonate of lime, or 42 grin, carbonate of magnesia. By weighing off the ^ or ^V eq. (H=il) grm. of the caustic or car- bonated alkaline earths, the necessity of a calculation of the results is altogether dispensed with ; in the former case, the number of c. c., in the latter that of half c. c. used of the normal acid, expresses the per- centage required. 5. CHLORIMETRY. 211. The " chloride of lime," or " bleaching powder " of commerce, con- tains hypochlorite of lime, chloride of calcium, and hydrate of lime. The two latter ingredients are for the most part combined with one another to basic chloride of calcium. In freshly prepared and perfectly normal chloride of lime, the quantities of hypochlorite of lime and chloride of calcium present stand to each other in the proportion of theii equivalents. When such chloride of lime is brought into contact with lilute sulphuric acid, the whole of the chlorine it contains is liberated in the elementary form, in accordance with the following equation : Ca O, Cl,0 + Ca Cl + 2 (H 0, S O 3 )=2 (Ca O, S O 3 )+2 H.O+2 Cl. On keeping chloride of lime, however, the proportion between hypo- chlorite of lime and chloride of calcium gradually changes the former decreases, the latter increases. Hence from this cause alone, to say nothing of original difference, the commercial article is not of uniform quality, and on treatment with acid gives sometimes more and sometimes less chlorine. As the value of this article depends entirely upon the amount of chlorine set free on treatment with acid, chemists have devised various simple methods of determining the available amount of chlorine in any given sample. These methods have collectively received the name of Chlorimetry. We describe a few of the best. PREPARATION OF THE SOLUTION OF CHLORIDE OF LIME. The solution is prepared alike for all methods, and best in the follow- ing manner : Weigh off 10 grm., triturate finely with a little water, add gradually more water, pour the liquid into a litre flask, triturate the residue again with water, a.ud rinse the contents of the mortar carefully into 212.] CHLORIMETRY. 505 the flask ; fill the latter to the mark, shake the milky fluid, and ex- amine it at once in that state, i.e.. without allowing it to deposit ; and every time, before measuring off a fresh portion, shake again. The re- sults obtained with this turbid solution are much more constant and cor- rect than when, as is usually recommended, the fluid is allowed to de- posit, and the experiment is made with the supernatant clear portion alone. The truth of this may readily be proved by making two sepa- rate experiments, one with the decanted clear fluid, and the other with the residuary turbid mixture. Thus, for instance, in an experiment made in my own laboratory, the decanted clear fluid gave 22*6 of chlorine, the residuary mixture 25 '0, the uniformly mixed turbid solu- tion 24-5. 1 c. c. of the solution of chloride of lime so prepared corresponds to 0.01 grm. chloride of liine. A. PENOT'S Method.* 212. This method is based upon the conversion of arsenious acid into arsenic acid ; the conversion is effected in an alkaline solution. Iodide of potassium-starch paper is employed to ascertain the exact point when the reaction is completed. a. Preparation of the Iodide of Potassium- Starch Paper. The following method is preferable to the original one given by PE- NOT : Stir 3 grm. of potato starch in 250 c. c. of cold water, boil witn stirring, add a solution of 1 grm. iodide of potassium and 1 grm. crystallized carbonate of soda, and dilute to 500 c. c. Moisten strips of fine white unsized paper with this fluid, and dry. Keep in a closed bottle. b. Preparation of the /Solution of Arsenious Acid. Dissolve 4-436 grm. of pure arsenious acid and 13 grm. pure crystal- lized carbonate of soda in 600 700 c. c. water, with the aid of heat, let the solution cool, and then dilute to 1 litre. Each c. c. of this solu- tion contains 0'004436 grm. arsenious acid which corresponds to 1 c. c. chlorine gas of and 760 mm. atmospheric pressure.f As arsenite of soda in alkaline solution is liable, when exposed to access of air, to be gradually converted into arseniate of soda, PENOT'S solution should be kept in small bottles with glass stoppers,, filled to the top, and a fresh bottle used for every new series of experiments. * Bulletin de la Societe Industrielle de Mulhouse, 1852. No. 118. Dinner's Polytech. Journal, 127, 134. f Penot gives the quantity of arsenious acid as 4 '44 ; but I have corrected this number to 4 '436, in accordance with the now received equivalents of the sub- stances and specific gravity of chlorine gas after the following proportion : 70'92 (2 eq. chlorine) : 99 (1 eq AsO 3 ) :: 317763 (weight of 1 litre of chlorine gas) : ; #=4'436, i.e. the quantity of arsenious acid which 1 litre of chlorine gas converts into arsenic acid. This solution is arranged to suit the foreign method of designating the strength of chloride of lime viz. , in chlorimetrical degrees (each degree represents 1 litre chlorine gas at ' and 760 mm. pressure in a kilogramme of the substance). This 506 SPECIAL PART. [ 213. According to Fr. MOHR* the solution keeps unchanged, if the arse- nious acid and the carbonate of soda are both absolutely free from oxidizable matters (sulphide of arsenic, sulphide of sodium, sulphite of soda). c. The Process. Measure off, with a pipette, 50 c. c. of the solution of chloride of lime prepared according to the directions of 211, transfer to a beaker, and from a 50 c. c. burette, add, slowly, and at last drop by drop, the solution of arsenious acid, with constant stirring, until a drop of the mixture produces no longer a blue-colored spot on the iodized paper; it is very easy to hit the point exactly, as the gradually increasing faiiitness of the blue spots made on the paper by the fluid dropped on it, indicates the approaching termination of the reaction, and warns the operator to confine the further addition of the solution of arsenious acid to a single drop at a time. The number of c. c. used indicates directly the number of chlorimetrical degrees (see note), as the follow- ing calculation shows : suppose you have used 40 c. c. of solution of arsenious acid, then the quantity of chloride of lime used in the experi- ment contains 40 c. c. of chlorine gas. Now, the 50 c. c. of solution employed correspond to 0'5 grm. of chloride of lime ; therefore 0'5 grin, of chloride of lime contain 40 c. c. chlorine gas, therefore 1000 grm. contain 80000 c. c. = 80 litres. This method gives very constant and accurate results, and appears to be particularly well suited for use in manufacturing establishments where there is no objection, on the score of danger, to the employment of arsenious acid. (Expt. No. 99.) B. OTTO'S Method. 213. The principle of this method is as follows : Two eq. protosulphate of iron, when brought into contact with chlo- rine, in presence of water and free sulphuric acid, give 1 eq. ses- quisulphate of iron, and 1 eq. H 01, the process consuming 1 eq. chlorine. 2 (Fe O, S 3 ) + S Oa + H O + Cl,=Fe 2 O 3 , 3 S O 8 -f H 01. 2 eq. crystallized protosulphate of iron : 2 (Fe O, S O 3 , H Of 6 aq.) = 278 correspond to 35-46 of chlorine, or, in other terms, 07839 grm. crystal- lized protosulphate of iron correspond to O'l grm. chlorine. The protosulphate of iron required for these experiments is best pre- pared as follows : Take iron nails, free from rust, and dissolve in dilute sulphuric acid, applying heat in the last stage of the operation; filter the solution, method was proposed by Gay-Lussac. The degrees may readily be converted into per-cents, and vice versa, thus : - A sample of chloride of lime of 90 contains 00x3 17763 =285 '986 grm. chlorine in 1000 grm. or 28"59 in 100 ; and a sample containing 34'2 per cent, chlorine, is of 107 "6, for 100 grm. of the substance con- tain 34-2 grm. chlorine . . 1000 grm. of the substance contain 342 grm chlorine but 342 grin chlorine = ^fWW litres=107'6 litres . . 1000 grm. of the substance contain 107 '6 litres chlorine. * His Lehrbuch der Titrirmethode, 2 Aun. S. 290. 213.] CHLOHIMETRY. 507 still hot, into about twice its volume of spirit of wine. The precipitate consists of Fe ty S O 3 4HO + 6 aq. Collect upon a filter, wash with spirit of wine, spread upon a sheet of blotting paper, and dry in the air. When the mass smells no longer of spirit of wine, transfer to a bottle and keep this well corked. In- stead of protosulphate of iron, sulphate of protoxide of iron and ammo- nia (p. 93) maybe used. 0*1 grm. of chlorine oxidizes 1'1055 grm. of this double sulphate. The Process. Dissolve 3'1356 grm. (4 X "07839 grm.) of the precipitated protosul- phate of iron, or 4*422 grm. (4 X 1'1055 grm.) of sulphate of protoxide of iron and ammonia, with addition of a few drops of dilute sulphuric acid, in water, to 200 c. c. ; take out, with a pipette, 50 c. c., corre- sponding to 0-7839 grm. protosulphate of iron, or 1'1055 grm. sulphate of protoxide of iron and ammonia, dilute with 150 200 c. c. water, add a sufficiency of pure hydrochloric acid, and run in from a 50 c. c. burette the freshly shaken solution of chloride of lime, prepared accord- ing to 211, until the protoxide of iron is completely converted into sesquioxide. To know the exact point when the oxidation is completed, place a number of drops of a solution of ferricyanide of potassium on a plate, and, when the operation is drawing to an end, apply some of the mixture with a stirring-rod to one of the drops on the plate, and observe whether it produces a blue precipitate; repeat the experiment after every fresh addition of two drops of the solution of choride of lime. When the mixture no longer produces a blue precipitate in the solution of ferricyanide of potassium on the plate, read off the number of volumes used of the solution of chloride of lime. The amount of solution of chloride of lime used contained O'l grm. of chlorine. Suppose 40 c. c. have been used : as every c. c. corre- sponds to O'Ol grm. of chloride of lime, the percentage by weight of available chlorine in the chloride of lime is found by the following pro- portion : 0-40 : 0-10:: 100 : x; x=25; or, by dividing 1000 by the number of c. c. used of the solution of chlo- ride of lime. This method also gives very satisfactory results, provided always that the salts of protoxide of iron are perfectly dry and free from ses- quioxide. Modification of the preceding Method. Instead of the solution of protosulphate of iron, a solution of proto- chloride of iron, prepared by dissolving pianoforte wire in hydrochloric acid (according to p. 194, aa), may be used with the best results. If 0'6316 of pure metallic iron, i.e., 0'6335 of fine pianoforte wire (which may be assumed to contain 99'7 per cent, of iron), are dissolved to 200 c. c., the solution so prepared contains exactly the same amount of iron as the solution of protosulphate above mentioned that is to say, 50 c. c. of it correspond to O'l grm. chlorine. But as it is inconvenient to weigh off a definite quantity of iron wire, the following course may be pursued in preference: weigh off, accurately, about O'l 5 grm., dissolve, 508 SPECIAL PART. [ 214 dilute the solution to about 200 c. c., oxidize the iron with the solution of chloride of lime, prepared according to the directions of 211, and calculate the chlorine by the proportion 56 : 35'46 : : the quantity of iron used : x the x found corresponds to the chlorine contained in the amount used of the solution of chloride of liine. This calculation may be dispensed with by the application of the following formula, in which the carbon in the pianoforte wire is taken into account : Multiply the weight of the pianoforte wire by 6313, and divide the product by the number of c. c. used of the solution of chloride of lime : the result expresses the percentage of chlorine by weight. This method gives very good results. I have described it here prin- cipally because it dispenses altogether with the use of standard fluids. It is therefore particularly well adapted for occasional examinations of samples of chloride of lime, and also by way of control. (See Expt. No. 99.) C. BUNSEN'S Method. Pour 10 c. c. of the solution of chloride of lime, prepared according to the directions of 211 (containing O'l chloride of lime), into a beaker, and add about 6 c. c. of the solution of iodide of potassium, prepared according to p. 314, a (containing 0*6 KI) ; dilute the mixture with about 100 c. c. water, acidify with hydrochloric acid, and determine the libera- ted iodine as directed 146. As 1 eq. iodine corresponds to 1 eq. chlo- rine, the calculation is easy. This method gives excellent results. (Com- pare Expt. No. 99.) 6. EXAMINATION OF BLACK OXIDE OF MANGANESE. 214. The native black oxide of manganese (as also the regenerated artifi- cial product) is a mixture of. binoxide of manganese with lower oxides of that metal, and with sesquioxide of iron, clay, &c. ; it also invariably contains moisture, and frequently chemically combined water. The com- mercial value of the article depends entirely upon the amount of binoxide (or, more correctly expressed, of available oxygen) which it contains. By " available oxygen " we understand the excess of oxygen contained in a manganese, over the 1 eq. combined with the metal to protoxide ; upon treating the ore with hydrochloric acid, an amount of chlorine is obtained equivalent to .this excess of oxygen. This available oxygen is always expressed in the form of binoxide of manganese. 1 eq. corre- sponds to 1 eq. binoxide of manganese, since Mn(V=MnO + O. I. DRYING THE SAMPLE. All analyses of manganese proceed of course upon the supposition that the sample operated upon is a fair average specimen of the ore. A portion of a tolerably finely powdered average sample is generally sent for analysis to the chemist ; in the case of new lodes, however, a number of samples, taken from different parts of the mine, are also occasionally sent. If, in the latter case, the average composition of the ore is to be ascertained, and g 215.] VALUATION Of MANGANESE. 50 ( J not simply that of the several samples, the following course must be resorted to : crush the several samples of the ore in an iron mortar to coarse powder, and pass the whole of this through a rather coarse sieve. Mix uniformly, then remove a sufficiently large portion of the coarse powder with a spoon, reduce it to powder in a steel mortar, passing the whole of this through a fine sieve. Mix the powder obtained by this second process of pulverization most intimately; take about 8 10 grm. of it, and triturate this, in small portions at a time, in an agate mortar, to an impalpable powder. Average samples are generally already suffici- ently fine to require only the last operation. As regards the temperature at which the powder is to be dried, if you desire to expel the whole of the moisture without disturbing any of the water of hydration, the temperature adopted must be 120 (this is the result of my own experiments, see Expt. No. 100). But, as there ap- pears to be at present an almost universal understanding in the manga- nese trade, to limit the drying temperature to 100, the fine powder is exposed, in a shallow copper or brass pan, for 6 hours, to the tempera- ture of boiling water, in a water-bath (p. 37, fig. 19). When the samples have been dried, they are introduced, still hot, into glass tubes 12 14 cm. long, and 8 10 mm. wide, sealed at one end ; these tubes are then corked and allowed to cool. In laboratories where whole series of analyses of different ores are of frequent occurrence, it is advisable to number the drying-pans and glass tubes, and to transfer the samples always from the pan to the tube of the corresponding number. II. DETERMINATION OF THE BINOXIDE OF MANGANESE. 215. Of the many methods that have been proposed for the valuation of manganese ores, I select three as the most expeditious and accurate. The first is more particularly adapted for technical purposes. A. FRESENIUS and WILL'S Method. a. If oxalic acid (or an oxalate) is brought into contact with binoxide of manganese, in presence of water and excess of sulphuric acid, proto- sulphate of manganese is formed, and carbonic acid evolved, while the oxygen, which we may assume to exist in the binoxide of manganese in combination with the protoxide, combines with the elements of the oxalic acid, and thus converts the latter into carbonic acid. Mn O 2 + SO 3 +C 2 O 3 =MnO, SO 3 +2 C O 2 . Each equivalent of available oxygen or, what amounts to the same, each 1 eq. binoxide of manganese = 43'5, gives 2 eq. carbonic acid = 44. b. If this process is performed in a weighed apparatus from which nothing except the evolved carbonic acid can escape, and which, at the same time, permits the complete expulsion of that acid, the diminution of weight will at once show the amount of carbonic acid which has escaped, and consequently," by a very simple calculation, the quantity of binoxide contained in the analyzed manganese ore. As 44 parts by weight of carbonic acid correspond to 43*5 of binoxide of manganese, 510 SPECIAL PART. [ 215. the carbonic acid found need simply be multiplied by 43-5, and the pro- duct divided by 44, or the carbonic acid may be multiplied by ^ =0-9887, 44 to find the corresponding amount of binoxide of manganese. c. But even this calculation may be avoided by simply using in the operation the exact weight of ore which, if the latter consisted of pure binoxide, would give 100 parts of carbonic acid. The number of parts evolved of carbonic acid expresses, in that case, directly the number of parts of binoxide contained in 100 parts of the analyzed ore. It results from b that 98*87 is the number required. Suppose the experiment is made with 0-9887 grm. of the ore, the num- ber of centigrammes of carbonic acid evolved in the process expresses directly the percentage of binoxide contained in the analyzed manganese ore. Now, as the amount of carbonic acid evolved from 0'9887 grin, of manganese would be rather small for accurate weighing, it is advisable to take a multiple of this weight, and to divide afterwards the number of centigrammes of carbonic acid evolved from this multiple weight by the same number by which the unit has been multiplied. The multiple which answers the purpose best for superior ores is the triple, = 2 '966 ; for inferior ores, I recommend the quadruple, =3 3*955, or the quintuple, = 4-9435. The analytical process is performed in the apparatus illustrated in fig. 100, and which has been described already, p. 289. The flask A should hold, up to the neck, about 120 c. c. ; _Z? about 100 c. c. The latter is half filled with sulphuric acid ; the tube a is closed at b with a little wax ball, or a very small piece of caoutchouc tubing, with a short piece of glass rod inserted in the other end. Place 2-966, or 3'955, or 4-9435 grm. according to the quality of the ore in a watch-glass, and tare the latter most accurately on a delicate balance ; then re^ move the weights from the watch-glass, and replace them by manganese from the tube, very cautiously, with the aid of a gentle tap with the finger, until the equi- librum is exactly restored. Transfer the weighed sample, with the aid of a card, to the flask A, add 5 6 grm. neutral oxalate of soda, or about 7*5 grm. neutral oxalate of potassa, in powder, and as much water as will fill the flask to about one-third. Insert the cork into A, and tare the apparatus on a strong but delicate balance, by means of shot, and lastly tinfoil, not placed directly on the scale, but in an appropriate vessel. The tare is kept under a glass bell. Try whether the apparatus closes air-tight (see p. 289). Then make some sulphuric acid flow from JB into A y by applying suction to d, by means of a caoutchouc tube. The evolu- tion of carbonic acid commences immediately in a steady and uniform manner. When it begins to slacken, cause a fresh portion of sulphuric acid to pass into A, and repeat this until the manganese ore is completely Fig. 100. 2 In.] VALUATION OF MANGANESE. 511 decomposed, which, if the sample has been veiy finely pulverized, requires at the most about five minutes. The complete decomposition of the analyzed ore is indicated, on the one hand, by the cessation of the dis- engagement of carbonic acid, and its non-renewal upon the influx of a fresh portion of sulphuric acid into A. ; and, on the other hand, by the total disappearance of every trace of black powder from the bottom of A* Now cause some more sulphuric acid to pass from JB into A, to heat the fluid in the latter, and expel the last traces of carbonic acid therein dissolved ; remove the wax stopper, or india-rubber tube, from 6, and apply gentle suction to d until the air draMTi out tastes no longer of carbonic acid. Let the apparatus cool completely in the air, and place it on the balance, with the tare on the other scale, and restore equilibri- um. The number of centigramme weights added, divided by 3, 4, or 5, according to the multiple of 0'9887 grm. used, expresses the percentage of binoxide contained in the analyzed ore. In experiments made with definite quantities of the ore, weighing in an open watch-glass cannot well be avoided, and the dried manganese is thus exposed to the chance of a reabsorption of water from the air, which of course tends to interfere, to however so trifling an extent, with the accuracy of the results. In very precise experiments, there- fore, the best way is to analyze an indeterminate quantity of the ore, and to calculate the percentage as shown above. For this purpose, one of the little corked tubes, filled with the dry pulverized ore, is accu- rately weighed, and about 3 to 5 grm. (according to the quality of the ore) are transferred to the flask A. By now reweighing the tube, the exact quantity of ore in the flask is ascertained. To facilitate this operation, it is advisable to scratch on the tube, with a file, marks indi- cating, approximately, the various quantities which may be required for the analysis, according to the quality of the ore. With proper skill and patience on the part of the operator, a good balance and correct weights, this method gives most accurate and corre- sponding results, differing in two analyses of the same ore barely to the extent of 0*2 per cent. If the results of two assays differ by more than 0*2 per cent., a third experiment should be made. In laboratories where analyses of manga- nese ores are matters of frequent occurrence, it will be found conveni- ent to use an aspirator for sucking out the carbonic acid. In the case of very moist air, the error which proceeds from the fact that the water in the air drawn through the apparatus is retained, and which is usu- ally quite inconsiderable, may now be increased to an important extent. Under such circumstances, connect the end of the tube 6 with a chlo- ride of calcium tube during the suction. Some ores of manganese contain carbonates of the alkaline earths, which of course necessitates a modification of the foregoing process. To ascertain whether carbonates of the alkaline earths are present, boil a sample of the pulverized ore with water, and add nitric acid. If anv effervescence takes place, the process is modified as follows (RoHRf): * If the manganese ore has been pulverized in an iron mortar, a ftw black spots (pftrticles of iron from the mortar) will often remain perceptible, f Zeitschrift f. analyt. Chem. 1, 48. 512 SPECIAL PART. [ 215. After the weighed portion of ore has been introduced into the flask A y treat ifc with water, so that the flask may be about full, add a few drops of dilute sulphuric acid (1 part, by weight, sulphuric acid, to 5 parts water) and warm with agitation, preferably in a water bath. After some time dip a rod in and test whether the fluid possesses a strongly acid reaction. If it does not, add more sulphuric acid. As soon as the whole of the carbonates are decomposed by continued heat- ing of the acidified fluid, completely neutralize the excess of acid with soda solution free from carbonic acid, allow to cool, add the usual quantity of oxalate bf soda, and proceed as above. If you have no soda solution free from carbonic acid at hand, you may place the oxalate of soda or oxalic acid (about 3 grm.) in a small tube, and suspend this in the flask A by means of a thread fastened by the cork. When the apparatus is tared, and you have satisfied yourself that it is air-tight, release the thread and proceed as above. B. BUNSEN'S Method. Reduce the ore to the very finest powder, weigh off about O4 grm., introduce this into the small flask a, illustrated in fig 59, p. 308, and pour pure fuming hydrochloric acid over it ; conduct the process ex- actly as in the analysis of chromates. Boil until the ore is completely dissolved and all the chlorine expelled, which is effected in a few min- utes. Each eq. iodine separated corresponds to 1 eq. chlorine evolved, and accordingly to 1 eq. binoxide of manganese. For the estimation of the separated iodine, the method 146 may be employed. Results most accurate.- C. Estimation of the Binoxide of Manganese ~by 'means of Iron. Dissolve, in a small long-necked flask, placed in a slanting position, a,bout 1 grm. pianoforte wire, accurately weighed, in moderately con- centrated pure hydrochloric acid ; weigh off about 0'6 grm. of the sam- ple of manganese ore in a little tube, drop this into the flask, with its contents, and heat cautiously until -the ore is dissolved. 1 eq. binoxide of manganese converts 2 eq. of dissolved iron from the state of proto- to that of sesquichloride. When complete solution has taken place', dilute the contents of the flask with water, allow to cool, rinse into a beaker, and determine the iron still remaining in the state of protochlo- ride with chromate of potash (p. 198). Deduct this from the weight of the wire employed in the process ; the difference expresses the quantity of iron which has been converted by the oxygen of the manganese from protochloride to sesquichloride.* This difference multiplied by 4 -|-g- s or 0-7768, gives the amount of binoxide in the analyzed ore. This me- thod also, if carefully executed, gives very accurate results. If you determine the excess of protochloride of iron with permanganate, do not forget the remarks on page 198, note. The main reason why this method is less suitable for industrial use than the first lies in the fact, that the analyst must work with much smaller quantities of substance. Hence to obtain results equally accurate * In very precise experiments, the weight of the iron must be multiplied by 0-997, since pianoforte wire may always be assumed to contain about 0'003 impurities. 2 1C, 217.] VALUATION OF MANGANESE. 513 with those yielded by A, far greater nicety in weighing and manipulat- ing is required. Instead of metallic iron, weighed quantities of pure protosulphate of iron, or of sulphate of protoxide of iron and ammonia, may be used. III. ESTIMATION OF MOISTURE IN MANGANESE. 216. In the purchase and sale of manganese, a certain proportion of moisture is usually assumed to be present, and often a percentage is fixed within which the moisture must be confined. In estimating the moisture the same temperature should be employed, at which the drying for the pur- pose of determining the binoxide is effected (214, I.). As the amount of moisture in an ore may be altered by the operations of crushing and pulverizing, the experiment should be made with a sample of the mineral which has not yet been subjected to these processes. The drying must be continued until no further diminution of weight is ob- served; at 100, this takes about 6 hours, at 120, generally only 1^ hours. If the moisture in a manganese ore is not to be estimated on the spot, but in the laboratory, a fair average sample of the ore should be forwarded to the chemist in a strong, perfectly dry, and well-corked bottle. IV. ESTIMATION OF THE AMOUNT OF HYDROCHLORIC ACID REQUIRED FOR THE COMPLETE DECOMPOSITION OF A MANGANESE. 217. Different manganese ores, containing the same amount of available oxygen, or, as it is usually expressed, of binoxide, may require very dif- ferent quantities of hydrochloric acid to effect their decomposition and solution, so as to give an amount of chlorine corresponding to the avail- able oxygen in them ; thus, an ore consisting of 60 per cent, of binoxide of manganese and 40 per cent, of sand and clay, requires 2 eq. hydro- chloric acid to 1 eq. of available oxygen ; whereas an equally rich ore containing lower oxides of manganese, sesquioxide of iron, or carbonate of lime requires a much larger proportion of hydrochloric acid. The quantity of hydrochloric acid in question may be determined by the following process : Determine the strength of 10 c. c. of a moderately strong hydrochloric acid (of, say, I'lO sp. gr.) by means of solution of sulphate of copper and ammonia ( 205). Warm 10 c. c. of the same acid with a weighed quantity (about 1 grm.) of the manganese, in a small long-necked flask, with a glass tube, about 3 feet long, fitted into the neck. Fix the flask in a position that the tube is directed obliquely upwards, and then gently heat the contents. As soon as the manganese is decomposed, apply a somewhat stronger heat for a short time, to expel the chlorine which still remains in solution ; but carefully avoid continuing the application of heat longer than is absolutely necessary, as it is of importance to guard against the slightest loss of hydrochloric acid. Let the flask cool, dilute the contents with water, and determine the free hydrochloric acid remain- ing by solution of sulphate of copper and ammonia. Deduct the quan- tity found from that originally added ; the difference expresses the 33 514 SPECIAL PART. [ 218, 219. amount of hydrochloric acid required to effect the decomposition of the manganese ore. 7. ANALYSIS OF COMMON SALT. 218. I select this example to show how to analyze, with accuracy and tolerable expedition, salts which, with a predominant principal ingredient, contain small quantities of other substances. a. Reduce the salt by trituration to a uniform powder, and put this into a stoppered bottle. b. Weigh off 10 grm. of the powder, and dissolve in a beaker by diges- tion with water ; filter the solution into a 1-litre flask, and thoroughly wash the small residue which generally remains. Finally, fill the flask with water up to the mark, and shake the fluid. If small white grains of sulphate of lime are left on dissolving the salt, reduce them to powder in a mortar, add water, let the mixture digest for some time, decant the clear supernatant fluid on to a filter, triturate the undissolved deposit again, add water, &c., and repeat the operation until complete solution is effected. c. Ignite and weigh the dried insoluble residue of 6, and subject it to a qualitative examination, more especially with a view to ascertain whether it is perfectly free from sulphate of lime. d. Of the solution 6, measure off successively the following quanti- ties : For e. 50 c. c. corresponding to 1 grm. of common salt. " /. 150 c. c. " 3 " " " " g. 150 c. c. " " 3 " h. 50 c. c. " " 1 " " " e. Determine in the 50 c. c. measured off, the chlorine as directed 141, I., a or b. f. Determine in the 150 c. c. measured off, the sulphuric acid as iirected 132, I., 1. g. Determine in the 150 c. c. measured off, the lime and magnesia as directed p. 349, 29. h. Mix the 50 c. c. measured off, in a platinum dish, with about ^ c. c. of pure concentrated sulphuric acid, and proceed as directed 98, 1. The neutral residue contains the sulphates of soda, lime, and magnesia. Deduct from this the quantity of the two latter substances as resulting from g ; the remainder is sulphate of soda. i. Determine in another weighed portion of the salt, the water as directed 35, a, a, at the end. k. Bromine and other bodies, of which only very minute traces are found in common salt, are determined by the methods described in Part I. 8. ANALYSIS OF GUNPOWDER.* 219. Gunpowder, as is well known, consists of nitre, sulphur, and char- * As regards the determination of the sp. gr. of gunpowder, I refer to Heeren's paper on the subject, in Mittheilung-en des Gewerbevereins fur Hannover. 1856, 133-178; Polyt.'Centralbl. 1850, 1113. 219.] ANALYSIS OF CUKPOWDEK. 515 coal, and, in the ordinary condition, invariably contains a small quantity of moisture. The analysis is frequently confined to the determination of the three constituents and the moisture, but often the examination is extended to the nature of the charcoal, and the carbon, hydrogen, oxy- gen, and ash therein are estimated. a. Determination of the Moisture. Weigh 2 3 grm. of the substance (not reduced to powder) between two well-fitting watch-glasses, and dry in the desiccator, or at a gentle heat, not exceeding 60, till the weight remains constant. b. Determination of the Nitre. Place an accurately weighed quantity (about 5 grm.) on a filter, mois- tened with water; saturate with water, and, after some time, repeatedly pour small quantities of hot water upon it until the nitrate of potassa ia completely extracted. Receive the first filtrate in a small weighed pla- tinum dish, the washings in a beaker or small flask. Evaporate the con- tents of the platinum dish cautiously, adding the washings from time to time, heat the residue cautiously to incipient fusion, and weigh it. * c. Determination of the Sulphur. Oxidize 2 3 grm. of the powder with pure concentrated nitric acid and chlorate of potash, the latter being added in small portions, while the fluid is maintained in gentle ebullition. If the operation is contin- ued long enough, it usually happens that both the charcoal and sulphur are fully oxidized, and a clear solution is finally obtained. Evaporate with excess of pure hydrochloric acid on a water-bath to dryness, filter, if undissolved charcoal should render it necessary, and determine the sulphuric acid after 132, I., 1. d. Determination of the Charcoal. Digest a weighed portion of the powder repeatedly with sulphide of ammonium, till all sulphur is dissolved, collect the charcoal on a filter dried at 100, wash it first with water containing sulphide of ammoni- um, then with pure water, dry at 100, and weigh. The charcoal so obtained must, under all circumstances, be tested for sulphur by the method given under c, and if occasion require, the sul- phur must be determined in an aliquot part. The charcoal may also be examined as regards its behavior to potash solution (in which " red char- coal"! is partially soluble) and an aliquot part may be subjected to ele- mentary analysis according to 178. For this latter purpose take a portion of the charcoal dried at 100, and dry at 190 (WELTZIEN). If the charcoal, on this second drying, suffers a diminution of weight, cal- culate the latter into per-cents of the gunpowder, deduct it from the charcoal, and add it to the moisture. * The nitrate of potassa may also be estimated in an expeditious manner, and with sufficient accuracy for technical purposes, by means of a hydrometer, which is constructed to indicate the percentage of this ingredient when floated in water containing a certain proportion of gunpowder in solution. A method based upon the same principle, proposed by Uchatius, is given in the Wiener akad Ber. X. 748 ; also Ann. d. Chem. und Pharm. 88, 395. f Incompletely carbonized wood. 516 SPECIAL PART. [220, 9. A.NALYSIS OF NATIVE AND, MORE PARTICULARLY, OF MIXED SILICATES.* 220. The analysis of silicates which are completely decomposed by acids has been described in 140, II., a; and that of silicates which are not decomposed by acids, in 140, II., b. I have therefore here only to add a few remarks respecting 'the examination of mixed silicates, i.e., of such as are composed of silicates of the two classes (phonolites, clay-slates, basalts, meteoric stones, &c.). After the silicate has been very finely pulverized and dried at 100 it is usually treated for some time, at a gentle heat, with moderately concentrated hydrochloric acid, evaporated to dryiiess on the water-bath, the residue moistened with hydrochloric acid, water added, and the solu- tion filtered ; it is often preferable, however, to digest the powder with dilute hydrochloric acid (of about 15 per cent.) for some clays at a gen- tle heat, and then at once filter the solution. Which of the two ways it is advisable to adopt, and indeed whether the method here described (which was first employed by CHR. GMELiN.in the analysis of phonolites), may be resorted to, depends upon the nature of the mixed minerals, The more readily decomposable the one of the constituent parts of the mixture is, and the less readily decomposable the other, the more con- stant the proportion between the undissolved and the dissolved part is found to remain in different experiments ; in other words, the less the undissolved part is affected by further treatment with hydrochloric acid, the more safely may this method of decomposition be resorted to. The process gives : a. A hydrocliloric acid solution, containing, besides a little silicic acid, the bases of the decomposed silicate in the form of metallic chlo- rides, which are separated and determined by the proper methods. b. An insoluble residue, which contains, besides the undecomposed silicate, the separated silicic acid of the decomposed silicate. After the latter has been well washed with water, to which a few drops of hydrochloric acid have been added, transfer it, still moist, in small portions at a time, to a boiling solution of carbonate of soda (free from silicic acid) contained in a platinum dish ; boil for some time, and filter off each time, still very hot, through a weighed filter. Finally, rinse the last particles of the residue which still adhere to the filter com- pletely into the dish, and proceed as before. Should this operation not fully succeed, dry and incinerate the filter, transfer the ash to the pla- tinum dish, and boil repeatedly with the solution of carbonate of soda till a few drops of the fluid finally passing through the filter remain clear on warming with excess of chloride of ammonium. Wash the residue, first with hot water, then to insure the removal of every trace of carbonate of soda which may still adhere to it with water slightly acidified with hydrochloric acid, and finally again with pure water. Collect the washings in a separate vessel (H. HOSE). Acidify the alkaline filtrate with hydrochloric acid, and determine in it the silicic acid which belongs to the silicate decomposed by hydro- chloric acid, as directed 140, II., a. Dry the undissolved silicate at * Comp. Qual. Anal. 205-208. The quantitative analysis must always be preceded by a minute and comprehensive qualitative analysis. 220.] ANALYSIS OF NATIVE SILICATES. 517 100, and weigh. The difference gives the quantity of the dissolved silicate. Treat the midissolved silicate exactly as directed 140, II., b. Silicates dried at 100 occasionally contain water. This is determined by taking a weighed portion of the mixed silicate dried at 100 and igniting in a platinum crucible, or in presence of carbon or protoxide of iron in a tube, through which a stream of dry air is drawn, the moisture expelled from the substance being retained by a weighed chlo- ride of calcium tube. To ascertain whether the water thus expelled proceeds from the silicate decomposable by hydrochloric acid, or from that which hydrochloric acid fails to decompose, a sample of the latter, dried at 100, is also ignited in the same manner. Suppose, for instance, the mixed silicate under examination consists of 50 per cent, of silicate decomposed by hydrochloric acid, and 50 per cent, of silicate which hydrochloric acid fails to decompose ; and that the latter contains 47 parts of anhydrous substance, and 3 parts of water ; the determination of the water would give, for the mixed silicate 3 per cent., for the por- tion not decomposed by hydrochloric acid 6 per cent. Now, as 3 bears the same proportion to 6 as the undecomposed silicate (50 per cent.) bears to the mixed silicate (100 per cent.), it is clear that the silicate decomposed by hydrochloric acid gives no water upon ignition. If the escaping aqueous vapors manifest acid reaction, owing to dis- engagement of hydrochloric acid or fluoride of silicon, mix the substance with 6 parts of finely triturated recently ignited oxide of lead in a small retort, weigh, ignite, and weigh again. If the water passing over still manifests acid reaction, connect the retort with a small receiver contain- ing water, and determine the hydro fluosilicic acid in the latter, after the termination of the process. According to SAINTE-CLAIRE DEVILLE and FOUQUE,* by properly conducting the ignition the water may usually be expelled free from combinations of fluorine, since the latter require a far higher temperature for expulsion than the former requires. After the water has been driven off the fluorine is then expelled by stronger ignition, either as alkaline metallic fluoride or as fluoride of silicon. The undecomposed part of a mixed silicate occasionally contains car- bonaceous organic matter, in which case it is the safest way to treat an aliquot part of it in a current of oxygen gas, and weigh the carbonic acid produced ( 178). According to DELESSE, traces of nitrogen are almost invariably present in the organic matter contained in silicates. Silicates often contain admixtures of other minerals (magnetite, pyrites, apatite, carbonate of lime, &c.) which may sometimes be detected by the naked eye or with the aid of a magnifying glass. It would be rather a difficult undertaking to devise a generally applicable method for cases of this description ; I therefore simply remark that it is occasionally found advantageous to treat the substance first with acetic acid, before subj ecting it to the action of hydrochloric acid ; this will more especially effect, without the least difficulty, the separation of the carbonates of the alkaline earths. As examples of complete examinations of this kind I may cite some analyses by DOLLFUSS and NEUBAUER,| which were made in my laboratory. If sulphides are present, determine the sulphur by one of the methods * Compt. rend. 38, 317 ; Journ. f. prakt. Chem. 62, 78. f Journ. f. prakt. Chem. 65, 199. 518 SPECIAL PART. [ 220. given 148, II., A* As regards the methods in the wet way, it must be borne in mind, that when baryta, strontia, or lead is present, a portion of the sulphuric acid produced remains in the insoluble residue ; 011 fusion with alkaline carbonate and nitrate this is not the case. If, besides sulphide, a sulphate is present, determine the sulphuric acid of the latter, by boiling a separate portion of the substance with a solution of carbonate of potash or soda for a long time, filtering, acidifying the filtrate, and precipitating with chloride of barium. The sulphuric acid thus obtained is deducted from the quantity obtained after treatment with oxidizing agents, and the remainder corresponds with the sulphur in the sulphide. The protoxide of iron may be conveniently determined by Cooke's process (p. 369). If silicates contain small quantities of titanic acid, as is very frequently .the case, care must be taken not to overlook this admixture. If the silicic acid has been separated by evaporation with hydrochloric acid whether preceded or not by decomposition with carbonated alkali and the eva- poration has been effected on the water-bath, and the dry mass has been treated with a sufficient quantity of hydrochloric acid, the titanic acid, or at least by far the greater part of it, is found in the hydrochloric acid solution. The separated silica may be tested for titanic acid, as follows : Treat in a platinum dish with hydrofluoric acid and a little sulphuric acid, evaporate, fuse the residue with bisulphate of potash, dissolve in cold water, filter if necessary, and separate the titanic acid from the sulphuric acid solution by the method given 107. As regards the titanic acid contained in the hydrochloric acid solution filtered from the silicic acid, it is precipitated with the sesquioxide of iron and alumina, when ammonia is added ( 161, 3). In this precipitate it may be determined either (a) by igniting the precipitate in hydrogen, extracting the reduced iron by digestion with dilute hydrochloric acid, fusing the residue with bisulphate of potash, taking up with cold water, and precipitating the titanic acid by boiling ( 107) or (6) by fusing the precipitate at once with bisulphate of potash, dissolving in cold water, neutralizing the solution as nearly as possible with carbonate of soda, diluting with water, so that not more than O'l grm. of the oxides may be contained in 50 c. c., adding to the cold solution hyposulphite of soda in slight excess, waiting till the fluid, which was at first violet, has become quite colorless, and consequently the whole of the sesquioxide of iron is reduced, boiling till sulph'urous acid ceases to be disengaged, filtering, washing the precipitate with boiling water, drying, gently igniting in a covered porcelain crucible, to expel sulphur, then taking the lid off and increasing the heat; we thus obtain the alumina (CuANCELf) and the titanic acid (A. STROMEYER|) together, free from sesquioxide of iron ; they are separated by the method above given. 10. ANALYSIS OF LIMESTONES, DOLOMITES, MARLS, &c. As the minerals containing carbonate of lime and carbonate of mag- nesia play a very important part in manufactures and agriculture, the * The methods in the wet way would as a rule be preferable, f Compt. rend. 46, 987 ; Annal. d. Chem. u. Pharm. 108, 237. t Annal. d. Chem. u. Pharm. 113, 127. 221.] ANALYSIS OF LIMESTONES, DOLOMITES, MARLS, ETC. 51 & chemist is often called upon to analyze them. The analytical process differs according to the different object in view. For technical purposes, it is sufficient to determine the principal constituents ; the geologist takes an interest also in the matter present in smaller proportions ; whilst the agricultural chemist seeks a knowledge not only of the constituents, but also of the state of solubility, in different menstrua, in which they are severally present. I will give, in the first place, a process for effecting a complete and accurate analysis ; and, in the second place, the volumetric methods by which the carbonate of lime (and the carbonate of magnesia) may be determined. An accurate qualitative examination should always pre- cede the quantitative analysis. A. METHOD OF EFFECTING THE COMPLETE ANALYSIS. 221. a. Reduce a large piece of the mineral to powder, mix this uniformly, and dry at 100. b. Treat about 2 grm., in a covered beaker, with dilute hydrochloric acid in excess, evaporate to dryness in a platinum or porcelain dish, moisten the residue with hydrochloric acid, heat with water, filter on a dried and weighed filter, wash the insoluble residue, dry at 100, and weigh. It generally consists of separated silicic acid, clay, and sand : but it often contains also humus-like matter. Opportunity will be afforded in g for examining this residue. c. Mix the hydrochloric acid solution with chlorine water, then with ammonia in slight excess, and let the mixture stand at rest for some time, in a covered vessel, at a gentle heat. Filter off the precipitate, which contains besides the hydrates of sesquioxide of iron, sesquioxide of manganese, and alumina the phosphoric acid which the analyzed compound may contain, and, moreover, invariably traces of lime and magnesia ; wash slightly, and redissolve in hydrochloric acid ; heat the solution, add chlorine water, and then precipitate again with ammonia ; filter off the precipitate, wash, dry, ignite, and weigh. For the estimation of the several components of the precipitates, viz., sesquioxide of iron, prolo sesquioxide of manganese, alumina, and phos- phoric acid, opportunity will be affor&ed in g. d. Unite the fluids filtered from the first and second precipitates pro- duced by ammonia, and determine the lime and magnesia as directed 154, 6 (29). e. If the limestone dried at 100 still gives water upon ignition, this is estimated best as directed 36. f. If the limestone contains no other volatile constituents besides water and carbonic acid, ignite with fused borax (p. 288, c), and sub- tract from the loss of weight suffered, the water found in e ; the differ- ence is the carbonic acid. If this method is inapplicable, determine the carbonic acid as directed p. 290, bb, or 291, cc, or as on p. 293, e. g. To effect the estimation of the constituents present in smaller pro- portion, as well as the analysis of the residue insoluble in hydrochloric acid, and of the precipitate produced by ammonia, dissolve 20 50 grin, of the mineral in hydrochloric acid. As the evaporation to dryness of large quantities of fluid is always a tedious operation, gently heat the 620 SPECIAL PART. [221, solution for some time, to expel the carbonic acid ; then filter through a weighed filter into a litre flask, wash the residue, dry, and weigh it. (The weight will not quite agree with that of the residue in b, as the latter contains also that part of the silicic acid which here still remains in solution.) a. Analysis of the insoluble Residue. aa. Treat a portion with boiling solution of pure carbonate of soda ( 220, b), and separate the silicic acid from the solution ( 140, II., a) ; this process gives the quantity of that portion of the silicic acid con- tained in the residue, which is soluble in alkalies. bb. Treat another portion, by the usual process for silicates ( 140, II., 6), and deduct from the silicic acid found, the amount obtained in aa. cc. If the residue contains organic matter (humus), determine, in a portion, the carbon by the method of ultimate analysis (p. 430, b). PETZHOLDT,* who determined by this method the coloring organic mat- ter of several dolomites, assumes that 58 parts of carbon correspond to 100 parts of organic substance (humic acid). dd. If the residue contains pyrites,} fuse another portion of it with carbonate of soda and nitrate of potassa ; macerate in water, add hydro- chloric acid, evaporate to dryness, moisten with hydrochloric acid, gently heat with water, filter, determine the sulphuric acid in the filtrate, and calculate from the result the amount of pyrites present.J /3. Analysis of the Hydrochloric Acid Solution. Make the solution up to 1 litre. aa. For the determination of the silicic acid that has passed into solu- tion, and of the baryta, strontia, alumina, manganese, iron, and phos- phoric acid, evaporate 500 c. c., and dry the residue at 100 110. Treat the dry mass, in order to separate silicic acid, &c. (precipitate I.), with hydrochloric acid and water, boil the solution with nitric acid, add am- monia, boil till the excess of ammonia has escaped, filter, wash slightly, dissolve on the filter with hydrochloric acid, reprecipitate in the same manner with ammonia, and filter off precipitate II,, which contains sesquioxide of iron, &c. Digest the united filtrates in a nearly filled and closed flask with sulphide of ammonium in a slightly warm place for 24 hours, then filter off precipitate III. This consists principally of sulphide of manganese ; it is to be washed with water containing sul- phide of ammonium. Precipitate the filtrate with carbonate of ammo- nia and ammonia, allow to stand 24 hours, and then filter off precipitate IV., which consists for the most part of carbonate of lime, and is to be washed with water containing ammonia. Evaporate the filtrate in a porcelain dish to dryness, project the residue, little by little, into a red hot platinum dish, drive off the ammonia salts, moisten the residue with hydrochloric acid, dissolve it in water, and boil, with addition of pure milk of lime, to strongly alkaline reaction. Filter off precipitate V., * Journ. f. prakt. Chem. 63, 194, f Compare Petzholdt, loc cit. ; Ebelmen (Compt. rend. 33, 681) ; Deville (Compt. rend. 37, 1001; Journ f. prakt. Chem. 62, 81); Roth (Journ. f. prakt. Chem. 58, 84). \ If the residue contains sulphate of baryta or strontia, these compounds are formed again upon evaporating the soaked mass with hydrochloric acid ; they remain accordingly on the filter, whilst the sulphuric acid formed by the sulphur of the pyrites passes into the nitrate. 221.] ANALYSIS OF LIMESTONES, DOLOMITES, MARLS, ETC. 521 which is composed of magnesia and the excess of lime, wash it, precipi- tate the filtrate with carbonate of ammonia and ammonia, and, after long standing, filter off precipitate VI., which is to be washed with water containing ammonia. Precipitate I. consists principally of silicic acid. It may also contain sulphates of baryta and strontia. Treat it in a platinum dish with hydrofluoric acid and a little sulphuric acid, evaporate to dryness, and, if necessary, repeat this operation. Should a residue remain, fuse it with a small quantity of carbonate of soda, treat with water, filter, wash, dissolve in hydrochloric acid, and precipitate the solution with sulphuric acid. When the precipitate has settled filter it from solution a, and wash. Stop up the tube of the funnel, and fill the latter with solution of carbonate of ammonia, allow to stand 1 2 hours, open the funnel tube, wash the residue first with water, then with, hydrochloric acid (solution b), finally again with water, and then weigh the pure residual sulphate of baryta. Mix the united solutions a and b with carbonate of am- monia and ammonia, allow to stand some time ; if a precipitate forms (which may contain carbonate of strontia) filter it off, dry, and add to precipitate IV. Precipitate II. consists principally of sesquioxide of iron ; it contains also the alumina, and, provided there is enough iron, the whole of the phosphoric acid. Dissolve in hydrochloric acid, add pure tartaric acid, and then ammonia. Having fully convinced yourself that no precipitate is formed, precipitate the iron with sulphide of ammonium in a small flask, which must be nearly filled and closed, allow to stand till the fluid appears of a pure yellow color, filter, wash with water containing sul- phide of ammonium, and determine the iron after 113, 2. To the fil- trate add a little pure carbonate of soda and pure nitrate of potassa, evaporate to dryness, and ignite till the residue is white. Add water and hydrochloric acid till the whole is dissolved,* and precipitate the clear fluid with ammonia. If a precipitate forms (alumina or phosphate of alumina, or a mixture of both), filter it off, and weigh. Mix the fil- trate with a little sulphate of magnesia. If another precipitate forms, this time consisting of ammonio-phosphate of magnesia (which is to be determined after 134, I., b. a) the alumina precipitate may be calcu- lated as phosphate of alumina (A1 2 O 3 , P O 5 ). If, on the contrary, no precipitate is formed, the phosphoric acid must be determined in the alumina precipitate as directed 134, I., &, /?. Precipitate III. consists principally of sulphide of manganese. It may also contain traces of sulphides of nickel, cobalt, and zinc, car- bonate of lime, &c. Treat with moderately dilute acetic acid, heat the filtrate, to remove any carbonic acid, add ammonia, precipitate with sul- phide of ammonium, allow to stand 24 hours, and determine th# man- ganese as protosulphide ( 109, 2). If any residue was left insoluble in acetic acid, test it for the above-mentioned metals. The fluid filtered from the pure sulphide of manganese is to be mixed with carbonate of ammonia. If a precipitate forms it is to be treated with precipitate IV. Precipitates IV. V. VI. The united mass of these precipitates, to- gether with the small portions of alkaline earthy carbonates obtained during the treatment of precipitates I. and III. contain the whole of the * I may remind the operator that the residue, which contains nitric acid, can- not be heated with hydrochloric acid in a platinum dish. 522 SPECIAL PART. [ 22l. strontia and the whole of the baryta which originally passed into the hydrochloric acid solution. Ignite the dried precipitate (if necessary in portions) in a platinum crucible, most intensely over the gas blowpipe. By this means any carbonates of baryta and strontia are converted into the caustic state, and a part, at all events, of the carbonate of lime into lime (ENGELBACH *). Boil the residue 5 or 6 times with small portions of water, pouring off the solution through a filter ; neutralize the solu- tion with hydrochloric acid, evaporate to dry ness, and test a minute portion with the spectroscope this minute portion is afterwards added to the rest. If strontia and lime alone are present, separate according to 28. If baryta is present, separate the three alkaline earths after 24. bb. Although it is possible in aa to test for metals precipitable by sulphuretted hydrogen from acid solution, e.g., copper, and if required to determine them, still it is more convenient to employ a fresh quarter of the hydrochloric acid solution for this purpose. The precipitate ob- tained by passing the gas into the warm dilute solution is washed, dried, and treated with bisulphide of carbon. If a residue remains it is to be examined. cc. The remaining quarter of the dilute hydrochloric acid solution is used for the estimation of the alkalies.^ Mix with chlorine water, then with ammonia and carbonate of ammonia ; after allowing the mixture to stand for some time, filter off the precipitate, evaporate the filtrate to dryness, ignite the residue in a platinum dish to remove the ammonia salts, and finally separate the magnesia from the alkalies as directed p. 345, 15. The reagents must be most carefully tested for fixed alkalies, and the use of glass and porcelain vessels avoided as far as practicable. Should the limestone contain a sulphate soluble in hydrochloric acid, precipitate the sulphuric acid by a small excess of chloride of barium, allow to settle, and filter off the sulphate of baryta (which is to be determined in the usual manner) before proceeding as above to the esti- mation of the alkalies. h. As calcite and aragonite may contain fluorides (JENZSCH J), the possible presence of fluorine must not be disregarded in accurate analy- ses of limestones. Treat, therefore, a larger sample of the mineral with acetic acid until the carbonate of lime and carbonate of magnesia are decomposed ; evaporate to dryness until the excess of acetic acid is com- pletely expelled, and extract the residue with water ( 138, I.). We have the fluorine in the residue. If it can be distinctly detected in a portion of the same,|| the determination may be attempted after 166, 5. L If the limestone under examination contains chlorides, treat a large sample with water and nitric acid, at a very gentle heat ; filter, and pre- cipitate the chlorine from the filtrate by solution of nitrate of silver. k. ^t is often interesting for agriculturists to know the degree of solu- * Zeitsehrift f. analyt. Chem. 1, 474. f The simplest way of ascertaining whether and what alkalies are present in a limestone, is the process given by Engelbach (Annal. d. Chem. u. Pharm. 123, 260) viz., ignite a portion of the triturated mineral strongly in a platinum cru- cible over the blast, boil with a little water, filter, neutralize with hydrochloric acid, precipitate with ammonia and carbonate of ammonia, filter, evaporate the filtrate to dryness and examine with the spectroscope. The carbonate of ammo- nia precipitate may be evaporated with hydrochloric acid to dryness, and exam- ined in like manner for baryta and strofttia. t Pogg. Annal. 96, 145. || See Qual. Anal. 146, 6. S; 222.] ANALYSIS OF LIMESTONES, DOLOMITES, MARLS, ETC. 523 bility of a sample of limestone or marl in the weaker solvents. This may be ascertained by treating the sample first with water, then with acetic acid, finally with hydrochloric acid, and examining each solution and the residue. The analyses of marls made by C. STRUCKMANN * were done in this manner. I. To effect the separation of the caustic or carbonated lime, in hy- draulic limes, from the silicates, DEVILLE f proposed to boil with solution of nitrate of ammonia, which he stated would dissolve the caustic lime and carbonate of lime, without exercising a decomposing action on the silicates. GUNNING J found, however, that by this process the double silicates of alumina and lime are more or less decomposed, with separa- tion of silicic acid. As yet no method is known by which the object here stated can be accomplished with absolute accuracy ; the best way, perhaps, is treating the sample with dilute acetic acid ; C. KNAUSZ ( recommends hydrochloric acid. B. VOLUMETRIC DETERMINATION OF CARBONATE OF LIME AND CARBON- ATE OF MAGNESIA (for technical purposes). 222. a. If a mineral contains only carbonate of lime, the amount of the latter may be estimated from the quantity of acid required to effect its decomposition, the method described in 210 being employed for the purpose. Or the carbonic acid in the mineral may be determined, say by the method described p. 291, cc, and 1 eq. carbonate of lime = 50 calculated for each eq. carbonic acid = 22. b. But if the mineral contains, besides carbonate of lime, also carbo- nate of magnesia, the results obtained by either process give the quan- tity of carbonate of lime + carbonate of magnesia, the latter being ex- pressed by its equivalent quantity of carbonate of lime (i.e., 50 of carbonate of lime for 42 of carbonate of magnesia). If, therefore, you desire to know the actual amount of each, you must, in addition to the above determination, estimate one of the earths separately. For this purpose one of the two following methods may be employed : 1. Mix the dilute solution of 2 5 grm. of the mineral with ammo- nia and oxalate of ammonia in excess, allow to stand for 12 hours and then filter. Ignite the precipitate of oxalate of lime, together with the filter, and treat the carbonate of lime produced as directed 210. This process gives the amount of lime contained in the analyzed mineral ; the difference between this and the former result gives the carbonate of lime which is equivalent to the amount of carbonate of magnesia present. To obtain perfectly accurate results by this method, repeated precipi- tation is indispensable (see 154, 6, a). 2. Dissolve 2 5 grm. of the mineral in the least possible excess of hydrochloric acid, and add a solution of lime in sugar water as long as a precipitate forms. By this operation the magnesia only is precipitat- ed. Filter, wash, and treat the precipitate as directed 210 ; the result represents the quantity of the magnesia. Deduct the quantity :>f car- * Annal. d Chem. u. Pharm. 74, 170. f Compt. rend, 37, 1001 ; Journ. f. prakt. Chem. 62, 81. t Journ. f. prakt. Chem. 62, 318. j Gewerbeblatt aus Wurtemberg, 1855, Nr. 4; Chem. Centralbl., 1855, 244. 024 SPECIAL PART. [ 223. bonate of lime equivalent thereto from the result of the total determi- nation ; the remainder is the amount of carbonate of lime present. The method 2 is only suitable when the proportion of magnesia is small. [11. ANALYSIS OF IRON ORES. 223. The ore is averaged, a sample of 3 10 grin, is finely pulverized, and the air-dry substance is preserved in a tightly stoppered bottle. A. ESTIMATION OF IRON. Solution. In case of spathic iron and hydrous hematites, the ore (1 grm.) may be dissolved in strong hydrochloric acid with aid of a gentle heat. In presence of protoxide of iron, sulphides, or organic matters, add powdered nitre, and heat until these substances are oxidized, then cautiously add sulphuric acid in excess, and evaporate until fumes of this acid appear. A residue of silica may be disregarded, unless its quan- tity be so large as to interfere with accurate division of the solution. In the latter case it must be filtered off. Dilute to 100 c. c. If the ore be slowly soluble or insoluble in hydrochloric acid, it is best to mix it well with thrice its weight of carbonate of soda (if sulphides or organic matters be present, roast the ore in a porcelain crucible before mixing with soda, or add to the mixture a suitable proportion y 1 ^ of pulverized nitre) and fuse for 15 minutes. Dissolve the fused mass with a small bulk of dilute sulphuric acid (1 volume of acid to 4 volumes of water), if nitre was employed, or silica is present in the fusion, evaporate until vapors of sulphuric acid arise, and dilute to 100 c. c. Determination of the iron is made volumetrically, on portions of 2 5 c. c., either with permanganate of potassa after previous reduction by means of zinc, or directly by standard solution of hyposulphite of soda, p. 203. In presence of titanium the latter method must be employed, because titanic acid is partially reduced by zinc, as shown by the purple tint of the solution. B. ESTIMATION OF IRON, MANGANESE, SILICA, AND PHOSPHORIC ACID. The ore (2 grm.) is fluxed with carbonate of soda as described in A, dissolved in dilute sulphuric acid, evaporated and heated until fumes of sulphuric acid bsgin to appear, treated with water, and filtered off from. silica. The filtrate is diluted or concentrated to 200 c. c. and iron es- timated in portions of 25 c. c., by hyposulphite, p. 203. From 100 c. c. the iron is thrown down by acetate of soda, p. 123, e. Manganese is estimated in the filtrate by precipitation with bromine, p. 184, d, and if the quantity be large, by subsequent conversion into pyrophosphate. The operator must not omit to satisfy himself of the complete separation of manganese, by testing the clear liquid or filtrate with bromine and warming. If the solution is or becomes strongly acid, nearly neutralize it with carbonate of soda before adding bro- mine. The final filtrate from the bromine precipitates should be neu- tralized with ammonia and tested with sulphide of ammonium, p. 184, e> in order to be certain of the complete precipitation of manganese. 1'1'4.] ASSAY OF COPPER ORES. 525 Phosphoric acid, if present, exists in the precipitate by acetate of soda. This is dissolved in nitric acid, diluted to 200 c. c., and precipitated by means of molybdenum solution. The phosphoric acid is weighed as py- rophosphate of magnesia. The directions found on p. 271 must be strictly followed. If arsenic acid be present, this must be removed by passing sulphuretted hydrogen at 70 through the sulphuric solution, which, after removal of the sulphide of arsenic, must be heated with nitric acid to peroxidize the iron. C. ESTIMATION OF SULPHUR. In presence of pyrites fuse the ore (1 3 grm.) with thrice its weight of carbonate of soda and nitre, both free from sulphur, in a porcelain dish, acidulate with hydrochloric acid, evaporate to dryness over the water-bath to separate silica, and precipitate with chloride of barium. To purify the BaO SO 3 , when yellow from presence of iron, fuse it with carbonate of soda, extract the fused mass with water, aci- dulate the aqueous solution (filtered off from Fe 2 O 3 and BaO CO 2 ) with hydrochloric acid, and precipitate again with chloride of barium. D. ESTIMATION OF TITANIUM. Titanium is estimated in 1 5 grm. of ore, which should be fused with soda, the fused mass dissolved in excess of sulphuric acid, evapo- rated to dryness cautiously in an air-bath, the heat being gradually rais- ed until the bisulphate of soda formed passes into fusion at a low red heat. Cover the cold mass with cold water, let stand a number of hours until it is thoroughly softened and dissolved, dilute to 500 700 c. c., filter off from silica, add bisulphite of soda to reduce the iron to pro- toxide, heat to boiling for an hour or more, replacing the evaporated water, and adding bisulphite of soda, or solution of sulphurous acid, from time to time. The titanic acid is then thrown down completely, provided too much free sulphuric acid be not present. Filter and wash with hot water. To the filtrate and washings add more sulphurous acid, or sulphite, and if strongly acid nearly neutralize with carbonate of soda, and boil for thirty minutes longer ; filter off any additional preci- pitate, and repeat the operation as long as titanic acid separates. Test 100 c. c. of the last filtrate by concentrating with sulphuric acid and zinc, to be certain that all titanic acid is precipitated. The impure titanic acid thus obtained is ignited and weighed, see p. 178. It is then redissolved by fusion with bisulphate of soda, and treatment with cold water, and either reprecipitated by boiling its solution, mixed with sulphurous acid ' as before, in order to obtain it free from iron, or the iron may be determined volumetrically in the solution by means of hyposulphite of soda, p. 203, 3, 6, and the titanic acid estimated by dif- ference.] 12. ASSAY OF COPPER ORES.* 224. A. MOHR'S Method for Oxides, Silicates, and Carbonates of Copper. Powder the ore finely; if rich, take 1 grm., if poor, 3 grm. Treat in * See also STEINBECK'S Method, Chemical News, v. 19, p. 307, and LUCKOW'S Method, idem. p. 221. 526 SPECIAL PART. [ 224. a porcelain dish of 10 cm. diameter with some sulphuric acid, water, and nitric acid, cover the dish with a large watch-glass and heat to boiling. As soon as the mass is nearly dry and ceases to spirt, remove the watch- glass and increase the flame, maintaining an elevated temperature till no more fumes escape ; allow to cool, add distilled water, heat to boiling, filter into a small platinum dish, wash with hot water, evaporate the washings and transfer them also to t'he platinum dish, and finally hav- ing made quite sure that the residue insoluble in water gives up no cop- per to acids precipitate the copper with zinc, after p. 229, 2, a. The light-red color of the copper is an indication of its purity. It will be seen that we have in view in this process the removal, as far as possible, ol the metals precipitable by zinc, viz. : lead, antimony, and tin. [Arsenic is not fully removed, and in this, as in the following processes, must be separated by sulphide of sodium. 128, p. 329.] [B. GIBBS' Method for Sulphides* Mix the finely pulverized ore in a porcelain crucible with 3 4 times its weight of a mixture of 10 parts of nitre, and 14 parts of bisulphate of potash. Heat the whole slowly to low redness best in a muffle. The sulphides are completely oxidized without frothing. Add enough sul- phuric acid to convert all the sulphate of potash into bisulphate, and heat again carefully until the contents of the crucible fuse to a clear mass. Dissolve in water, filter from silica, etc., and precipitate the cop- per as described p. 229, 5.] [C. STOKER AND PEARSON'S Method for Sulphides.\ The ore, 2 5 grm., is pulverized and mixed with its bulk of powdered chlorate of potash in a porcelain dish, and covered with a watch-glass or inverted funnel ; add nitric acid of ordinary strength, rather more than would be sufficient to cover the powder. Heat to gentle ebullition, add- ing from time to time chlorate of potash, if needful, until the sulphur is completely oxidized. Rinse the cover into a separate beaker. When the contents of the porcelain dish are cold, add a quantity of strong hydro- chloric acid, rather larger than the quantity of nitric acid first employed ; evaporate the whole to dryness, to render silica insoluble. Treat the residue with water, and mix the whole with the rinsings. Heat the liquid nearly to boiling, and add strong solution of protosulphate of iron, slightly acidulated with sulphuric acid ; keep the whole hot until the contents of the beaker become almost black, and no more gas is disen- When the nitric acid has been reduced by this treatment, filter into a wide beaker and precipitate by a clean sheet of iron, or by a flat coil of iron wire. Wash the metallic copper with water, then with alcohol, and, if need be, ignite it in a current of hydrogen before weighing. J] [* Am Journ. Sci., xliv. 212. J [f Am. Journ. Sci.,xlviii. 194.] [j: The precipitation by iron succeeds well when iron can be obtained which dissolves in dilute acid without the separation of black particles or flakes in weigh- able quantity. If the copper solution be cold, dilute, and nearly neutral when the iron is first placed in it, the copper has little adhesion to the iron, and may be readily detached from it for the purpose of weighing 1 . If, as soon as the iron is coated with copper, hydrochloric acid (20 c. c.) be added, and the whole be heated to near the boiling-point, and maintained at that temperature, but without ebulli- tion, the residue of the copper is deposited as a spongy coherent mass, which, ANALYSIS OF GALENA. 527 13. ANALYSIS OF GALENA. 225. This is the most widely spread of the lead ores. It frequently con- tains larger or smaller quantities of iron, copper, and silver, occasion- ally traces of gold, and commonly also more or less gangue, insoluble in acids. Reduce the ore to a fine powder, and dry at 100. Oxidize a weighed quantity (1 2 grm.) with highly concentrated red fuming nitric acid, free from chlorine and sulphuric acid (see p. 326). For this purpose use a capacious flask, covered during the operation with a watch-glass ; do not put the tube in which the powder was weighed into the flask. If the acid is sufficiently strong, the sulphur will be fully oxidized. After you have warmed gently for a long time, add 3 or 4 c. c. pure concentrated sulphuric acid, which you have previously di- luted with a little water, and heat on an iron plate, till all the nitric acid is evaporated. Dilute with water, filter, wash the residue with water containing sulphuric acid, and displace the latter with alcohol. Collect the alcoholic washings separately. a. Dry the residue, ignite, and weigh ( 116, 3). It consists of sul- phate of lead, gangue undecomposed by the acid, silicic acid, &c. Heat the whole, or a fractional part, with hydrochloric acid to boiling ; let the insoluble matter subside, and then decant the supernatant clear liquid on to a filter ; pour a fresh portion of hydrochloric acid on the residue, boi] again, allow to subside, and decant, and repeat this opera- tion until the sulphate of lead is completely dissolved ; finally, place the residue on the filter, and Avash with boiling water until every trace of chloride of lead is removed ; dry, ignite, and weigh the residue. Sub- tract the weight found from that of the original residue : the difference expresses the quantity of sulphate of lead which the latter contained. Instead of using hydrochloric acid, the sulphate of lead may also be dis- solved by heating with an aqueous solution of tartrate or acetate of am- monia and caustic ammonia ; or it may be first converted into carbonate of lead, by digestion with solution of carbonate of soda, washed and dissolved in dilute nitric acid. b. The sulphuric acid solution is free from any weighable trace of lead, if the process has been properly conducted. It contains the metals pre- sent in the ore in addition to lead. First add some hydrochloric acid, to precipitate the silver, if present. If a turbidity or precipitate is formed, keep the fluid for some time in a warm place, till the chloride of silver has subsided. The latter is filtered off and may be determined after 115, 1. In the case of very small quantities, I prefer to incin- erate the filter with the precipitate in a porcelain crucible, to ignite the residue for a short time in hydrogen, to dissolve the trace of metallic silver in nitric acid, to evaporate the solution in the crucible to dryness, to take up the residue with water, and to estimate the silver in the solu- tion by PISANI'S method (p. 215). with care, may be removed from the iron and washed without falling 1 to pieces or oxidizing- (see p. 229, 2, , for details of washing). If the copper should be difficult to collect by decantation, it may be gathered on a small filter, and, after burning the latter, may be either reduced by hydrogen or calcined to oxide (p. 229, bottom).] 528 SPECIAL PART. [ 226. Precipitate the fluid filtered from the chloride of silver with sulphu- retted hydrogen. The precipitate generally contains a little sulphide of copper y occasionally also other sulphides. Separate these, as well as the metals in the filtrate, which are precipitable by sulphide of ammonium (iron, zinc, &c.), according to the methods of Section V. The foregoing method does not enable the assayer to determine very small quantities of silver* and the trifling traces of gold which, accord- ing to PERCY and SMITH,! are often found in galena. To effect this, it is, in the first place, necessary to produce a button containing the whole or part of the lead of the galena, and the whole of the silver and gold, and then to separate the latter metals. This is accomplished as described in 226 and 227. [For the estimation of the sulphur, take a fresh portion of the pulver- ized ore and bring it into solution by method C, p. 526, filter from silica, in presence of iron, add a lump of solid tartaric acid, precipitate hot by chloride of barium, and wash by decantation first with hot water, and finally with dilute solution of acetate of ammonia. The tartaric acid prevents precipitation of iron, the acetate of ammonia purifies the pre- cipitate from alkali and baryta salts. STORER and PEARSON.];] [14. SILVER ASSAY. 226. Assay ~by Scarification and Cupellation. A. ORES POOR IN SILVER. 1. Preparation of the Ore. The well-sampled ore is pulverized and passed through a sieve with 60 to 80 holes to the linear inch. If par- ticles of metallic silver or malleable ore remain upon the sieve, they must be assayed separately. The fluxes required are, 1, Assay lead, prepared by shaking melted lead in a wooden box and sifting through meshes of -fa inch ; 2, JBorax or borax-glass and 3, Quartz sand or powdered glass, to form silicates with the metallic and earthy oxides, and also sometimes to prevent the oxide of lead from destroying the scorifier. The proportions of the fluxes vary with different ores, and should be sufficient to form a liquid slag and a lead button of convenient size. The addition of too much borax will envelop the metallic lead before sufficient oxide of lead is formed to decompose the silver compounds. Galena requires 6 parts lead and no borax ; quartzose ores about 8 parts and no borax ; blende, mispickel, and pyrites about 1 6 parts, and to 1 part borax ; copper and tin compounds 20 to 30 of lead, and nickel and cobalt even more ; nickelspeise 1 6 parts of lead and repeated scorifications ; ores containing calcite, dolomite, barytes, or fluorspar, 8 parts of lead and 12 parts borax or glass. In case of doubt as to the nature of the ore, begin with 8 parts of lead, and, if the fusion is not good, repeat with a larger proportion of lead. * Argentiferous galenas generally contain only between 0'03 to 018, rarely above 0'5R silver ; and a great many contain far less than 0'03ft. f rhil. Mag., VII. 126. J Am. Jour. Sci., XLVIII. 193. 226.] SILVER ASSAY. 529 2. Scarification. The objects of this process are to concentrate all the silver in a lead button, to decompose the sulphides, etc., and to dissolve and slag off earthy and other substances by means of the oxide of lead formed. In this process all the sulphur of the heavy metallic sulphides passes off finally as sulphurous acid. Sulphides of the alkalies and of the alkaline earths, if present, are oxidized to sulphates. Charge and fusion. 2 to 4 grammes of the sampled ore are mixed with half the assay lead required, placed in a scorifier,* and covered with the remainder of the assay lead. If borax is used, it is best placed on top of the assay, but glass should be mixed with it. The charged scorifier is placed, with help of suitable tongs, in a red hot muffle. (If no muffle is at hand, the fusion may be made in a large Hessian cruci- ble, which is laid on its side on a good bed of coals, and partly covered with charcoal. The mouth can be closed with a crucible cover.) A piece of glowing charcoal is placed on or by the scorifier, the mouth of the muffle is closed, and the heat kept up. The lead soon fuses, and tho ore, being lighter, floats on the surface and roasts. From the appear- ance of the fumes the assayer can frequently judge of the nature of the ore ; sulphur giving light gray, zinc thick white, arsenic grayish, and antimony bluish fumes. After 15 to 20 minutes the assay has melted down, and a fluid slag lias formed at the periphery of the glowing metal ; the latter meantime gives off fumes of oxide of lead. With diffi- cultly fusible ores it may require 30 minutes for complete fusion, and even then it may be necessary to add more lead or borax. The latter should be wrapped in stiff paper and placed on the assay with tongs. The paper keeps the borax from contact with the assay till its water is driven off, thus preventing a loss by sputtering. If the ore contains much zinc, it is better to volatilize this metal by covering the scorifier with glowing coals, closing the muffle and increasing the heat, as oxide of zinc forms a stiff slag. The muffle is now opened, and the slagging is allowed to proceed at a temperature just high enough to keep the lead bright. A high heat hastens the process, but causes a loss of silver by oxidation and volatilization. When the slag covers the button, the heat is increased for a few minutes, in order to separate any metallic lead which may be mechanically mixed with it. The assay is now poured into a casting-plate, f previously warmed, to expel the moisture. If no casting-plate is at hand, the assay may be allowed to cool in the- scorifier. The button should separate easily from the slag, and must be per- fectly malleable. It is entirely freed from adhering slag by hammering into a cubical mass, and is then ready for the process of cupellation, . unless too large, in which case it must be reduced in bulk by reheating on a fresh scorifier. If the button be hard, or contain much metallic copper, more lead and borax are added, and the process is repeated. In general it is better to carry the scorification as far as possible, since * A cup of baked clay, to be had of dealers in apparatus. f The casting-plate is a plate of sheet-copper with a handle, and 12 20 cup- shaped depressions, each 14- inch wide and inch deep ; it is convenient when several assays are carried on together. The cups are rubbed with chalk to pre- vent the button from adhering. 34 530 SPECIAL PART. [ 226. experience has shown that there is less loss of silver in scorification than in cupellation. 3. Cupellation ( 163, 10 ; 122). This process consists in the oxi- dation of the lead on a bone-ash cupel,* which absorbs the oxide of lead, leaving metallic silver. The cupel, after the dust is blown out, is placed in a muffle and heated to redness to expel the moisture. If this precaution be neglected, the escaping vapor causes a loss of the alloy by sputtering. The argentiferous lead is carefully placed on the cupel, a piece of glowing charcoal is laid near it, the mouth of the muffle is closed, and the whole is brought promptly to fusion. Tf it is not quickly fused, particles of the assay are liable to stick to the sides of the cupel, causing a loss. As soon as the assay has " cleared,"f the muffle should be opened, the char- coal removed, and the heat lowered near the assay, either by closing the draughts or moving the cupel nearer the mouth of themuffle. The oxidation should now be carried 011 at as low a heat as possible, as a high heat increases the volatilization of the silver along with the lead. If the temperature is right, imperfect crystals of oxide of lead form, and the fumes rise to the middle of the muffle ; but if the fumes disappear immediately above the cupel, whilst the latter is at a bright red heat, and no crystals form, the heat is too high. If, on the other hand, the cupel is dark brown, and thick fumes rise to the top of the muffle, the heat is too low, and there is danger of solidification. If the assay " freezes " or solidifies, it may be again fused ; the results are, however, too low, as silver passes into the bone-ash. Alloys containing copper require a higher heat to prevent freezing. Towards the close of the operation the heat should be gradually raised, as the alloy becomes less fusible with the increased proportion of silver, and the lead oxidizes with more difficulty. When the cupellation is nearly finished, a play of colors is seen, and the button suddenly brightens or " blicks," and becomes white, and is free from lead. It is immediately moved towards the mouth of the muffle, so as to cool slowly. If suddenly cooled it " sprouts," sometimes throwing particles out of the cupel, owing to the sudden escape of the oxygen which molten silver absorbs, unless it contains copper, lead, or much gold. The button must separate easily from the cupel. It is taken up by pincers and brushed with a stiff brush. It should be well rounded and bright, show no particles of bone-ash under a magnifying glass, and have no projecting ridges caused by cracks or depressions in the cupel, as these always contain lead. The silver obtained is not chemically pure, but the amount of foreign matters is so small that no notice is taken of them in ore assays, and moreover, the impurities do not compensate for the loss in scorification and cupellation. The assay lead must be assayed, and the amount of silver yielded by it must be deducted from that ob- tained from the ore. The weight of silver in milligrammes, multiplied by -S-jp-, gives the number of troy ounces per ton of ore. 1 Troy ounce of pure silver is worth $1.29 gold. * Cupels are most conveniently purchased of the dealers in apparatus. They should be neither too porous nor too compact. In the former case silver passes into the bone-ash, in the latter the oxide of lead is not absorbed with sufficient rapidity. \ i. e. Exposes a bright surface of lead. 227.] GOLD ASSAY. 531 Silver ores may be assayed by the methods described in 227 for the assay of gold ores, but the results obtained are not as high as by the scorification method. B. ORES RICH IN SILVER. Ores of 1 per cent, or more are assayed as described under A, but the loss by volatilization impairs somewhat the accuracy of the result. 0. BULLION. Alloys are assayed either in the wet way or by cupellation, as de- scribed under A, 3. When the assay contains more than 1 per cent, of silver, the loss by volatilization must be taken into the account. This is done by the method of assaying with ll proofs," i, e.. the composition of the alloy is determined approximately, if not already known, by a preliminary cupellation, and then a "proof" is made up of the same composition as the assay, by weighing off the proper quantities of pure metals ; this and the assay are then melted with the same amount of lead, and the two are cupelled together side by side. The loss of the proof is added to the result of the assay. The numerous details of the assay with proofs, which are observed in order to accomplish a larg$ amount of work in a short time, are properly learned in assay offices. 15. GOLD ASSAY. 227. Crucible Assay and Parting. Ores of gold may also be assayed by the scorification method ( 226), but on account of the difficulty of sampling, it is better to take larger amounts of ore and make a crucible fusion. Gold ores may, for convenience, be divided into two classes. First, those containing little or no sulphur ; and second, those containing sul- phur, as pyrites, blende, etc. A. ORES OF THE FIRST CLASS. 1. deduction. If the ore consists principally of quartz or silicates, a fusion with litharge and a reducing flux yields a uniform brittle vitreous slag, and a lead button containing the gold and silver. If the ore con- tains basic substances, such as calcite, oxide of iron, etc., quartz sand or broken glass must be added. The reducing flux mentioned in the subsequent directions is a mix- ture of 100 parts of bicarbonate of soda and 20 parts of flour. The following is a convenient charge, yielding a button that may be directly cupelled : Ore 50 grm. Litharge 75 grm. Reducing flux 4 grm. If glass is added, count it as ore, and increase the litharge and redu- cing flux proportionally. Mix thoroughly ; place the mixture in a clay crucible, which should not be more than two-thirds filled. Cover one-quarter inch deep with dry chloride of sodium, and lute on the cover, or the luting may be omit- ted if care be taken that no coals get into the crucible. The fusion 532 SPECIAL PART. [ 227, may be made in any furnace in which a white heat is obtainable, best in a deep wind furnace. The fire i* kindled at the top, so that the heat shall be gradually raised to prevent the crucible cracking. A dull red heat is kept up for half an hour, and a white heat for a quarter of an hour longer. Too high a heat for an unnecessary length of time is to be avoided, as the litharge is liable to flux the crucible. Remove from the fire while hot, and tap gently on the hearth to collect the lead into a button. When cool, crack out the button, which should separate readily from the slag, and be perfectly malleable. The slag should be uniform and vitreous, show- ing a perfect fusion, and should include no metallic globules. 2. Cupellation. The button contains the gold and silver, and is cu- pelled as directed, p. 530. A higher heat is, however, necessary to remove the last traces of lead than if no gold were present. There is no danger of sprouting if the alloy contains much gold. 3. Parting. Clean the gold globule, as directed p. 530, weigh, and add pure silver if necessary, so that the alloy shall contain 2|- parts silver to 1 of gold. The proportion of additional silver required in an ore-assay may be commonly judged from the color of the alloy. If it is bright yel- low, add 2^- parts, if only faint yellow, 2 parts, and if white, 1 part or less. The silver and the alloy are fused together on charcoal before the blowpipe, or, better still, are wrapped in. sheet lead, and cupelled at a high heat. The button is hammered and rolled into a long thin leaf, care being taken that no particles crack off. If large, it must be annealed during the rolling, by heating on a cupel in the muffle. The leaf is rolled together 011 a slender rod or pencil, and placed in an assay flask, or large test-tube, and boiled with dilute nitric acid, sp. gr. 1*16, till all action has ceased ; the acid is decanted, and the boiling re- peated with acid of sp. gr. 1'30. Wash the residual gold with water free from chlorine till the wash- ings give no reaction for silver, fill the flask with water, cover its mouth with a drying-cup * or porcelain crucible, and invert. The gold quickly settles to the bottom of the cup. The flask is slowly raised till the cup is nearly full of water, and is then quickly drawn off one side. The water is carefully poured out of the cup, and the gold, if in separate par- ticles, is collected in a drop of water at the bottom. After thoroughly drying, heat to redness in the muffle, but not to fusion. If the process has been properly conducted the gold remains in one coherent mass, and may be readily turned into a weighing-cup. The litharge must be as- sayed for silver with the same reducing flux as was used with the ore. The weight of the button obtained by cupellation, less that of the silver yielded by the litharge, less that of the gold, is the weight of the silver in the ore. The ounces per ton are calculated as directed p. 530, bottom. 1 Troy ounce of gold has a value of $20.66. B. ORES OF THE SECOND CLASS (containing Sulphur). 1. Roasting Process. The object of roasting is to expel the sulphur, but this process is objectionable on account of the mechanical loss of gold occasioned by it. The operation is conducted as follows : A weighed * The drying-cup is a deep narrow vessel of biscuit ware. 227.] GOLD ASSAY. 533 amount of the ore is placed in an iron pan, the bottom and sides of which have been smeared with a paste of clay, or Venetian red, and water. This coating serves to protect the iron from the action of sulphur, and should be slowly and thoroughly dried to prevent cracking. The roast- ing is carried on at a dull red heat, with frequent stirring, until most of the sulphur is driven off. Towards the close of the process the heat is raised, and is kept up till the odor of sulphurous acid is no longer per- ceptible, and a moistened blue litmus paper held a few inches above the ore remains unchanged. The ore and scrapings from the pan are pulve- rized and sifted. The following are the proportions of the charge : 50 grms. of ore. 20 " powdered glass. 15 " reducing flux. 100 " litharge. Fuse in a crucible and cupel, as directed for ores of the first class. 2. Assay by Litharge and Nitre. In crucible fusions of auriferous sulphides, advantage is taken of their reactions with oxide of lead. If sulphides are fused with sufficient litharge, a button of lead and a slag free from sulphur, or containing the sulphates of the alkalies or alkaline earths, are obtained, but the lead button is too large for scorifica- tion. Pyrite reduces 8|- parts, chalcopyrite and blende 7 parts, gray cop- per and sulphide of antimony about 6 parts of lead. Nitre is added to prevent too much lead being reduced ; and, to determine the amount of nitre proper to use, a preliminary assay is made by fusing 3 to 5 grm. of the ore with 50 parts of litharge. The fusion should be made quickly, using care to prevent the action of reducing gases, and as soon as the mass ceases to boil, the crucible should be removed from the fire, to pre- vent the litharge destroying it. The resulting button is weighed, and the amount of lead that would be yielded by the ore required for an assay is calculated. If this amount would be too small for cupella- tion, reducing flux must be added ; if of the right size, neither reducing flux nor nitre is necessary, but, if too large, nitre must be added. To find the weight of nitre required in the last case, deduct the weight of the button desired for cupellation (10 15 grin.) from the weight of the lead which would be produced by fusing the charge of ore with litharge alone, and divide the remainder by four ; the result is the weight of nitre required. The oxidizing power of commercial nitre varies so much that it is better to determine it by fusing a sample with litharge and a redu- cing flux. The weight of lead which the flux alone produces, less that obtained when a given weight of nitre is added, is the weight of lead oxi- dized by the nitre. The charge is made of the following propor- tions : Ore, 20 grm. Litharge, 100 to 160 grm., according to the proportion of the sulphides. Nitre, amount calculated. Bicarb, soda, 20 grm. Mix thoroughly, place in a thick French crucible, which should not be more than one-third filled, and put on top 20 grm. of borax, and a covering of common salt. The fusion is made slowly, to prevent the assay from running over, and is kept at a strong heat for an hour. The 534 SPECIAL PART. [ 228. button should be malleable, and the slag should give no odor of sul- phuretted hydrogen when treated with sulphuric acid. It is cupelled as directed, p. 530 (if too large it is first scorified), and the gold and silver parted as directed p. 532.] * 16. ASSAY OF ZINC ORES. 228. Method of SCHAFFNER,* modified by C. KUNZEL,! as employed in the Belgian zinc-works described by C. a. Solution of the ore and preparation of the ammoniacal solution. Powder and dry the ore. Take O5 grm. in the case of rich ores, 1 grm. in the case of poor ores, transfer to a small flask, dissolve in hydrochloric acid with addition of some nitric acid by the aid of heat, expel the excess of acid by evapora- tion, add some water, and then excess of ammonia. Filter into a beaker, and wash the residue with lukewarm water and ammonia, till sulphide of ammonium ceases to produce a white turbidity in the wash- ings. The oxide of zinc remaining in the hydrated sesquioxide of iron is disregarded. Its quantity, according to GROLL, does not exceed 0'3 0*5 per cent. This statement probably has reference only to ores containing relatively little iron ; where much iron is present the quan- tity of zinc left behind in the precipitate may be not inconsiderable. The error thus arising may be greatly diminished by dissolving the slightly washed iron precipitate in hydrochloric acid and adding excess of ammonia. But the surer mode of proceeding is to add to the origi- nal solution after evaporating off the greater part of the free acid as above, and allowing to cool dilute carbonate of soda nearly to neutral- ization, then to precipitate the sesquioxide of iron, after p. 202, rf, with acetate of soda, boiling, to filter, and wash. The washings, after being concentrated by evaporation, are added to the filtrate and the whole is then mixed with ammonia, till the first-formed precipitate is redis- solved. If the ore contains manganese provided approximate results will suffice digest the solution of the ore in acids, after the addition of ex- cess of ammonia and water, at a gentle heat for a long time, and then filter off, with the iron precipitate, the hydrated protosesquioxide of manganese which has separated from the action of the air. The safer course though undoubtedly less simple is, after separating the iron with acetate of soda, to precipitate the manganese by passing chlorine, as directed p. 357, 59, or by adding bromine and heating. If lead is present, it is separated by evaporating the aqua regia solu- tion with sulphuric acid, taking up the residue with water and filtering; then proceed as directed. b. Preparation and standardizing of the sulphide of sodium solu- tion. The solution of sulphide of sodium is prepared either by dissolving crystallized sulphide of sodium in water (about 100 grm. to 10001200 * Journ. f. prakt. Chem. 73, 410. f Ibid. 88, 486. t Zeitschrift f. anal. Chem. 1, 21. 228.] ANALYSIS OF ZINC ORES. 535 water), or by supersaturating a solution of soda, free from carbonic acid, with, sulphuretted hydrogen, and subsequently heating the solution in a flask to expel the excess of sulphuretted hydrogen. Whichever way it is prepared, the solution is afterwards diluted, so that 1 c. c. may precipitate about O'Ol grin. zinc. Prepare a solution of zinc, by dis- solving 10 grin, chemically pure zinc in hydrochloric acid, or 44' 122 grin, dry crystallized sulphate of zinc in water, or 68' 133 grin, dry crys- tallized sulphate of potash and zinc in water, and making the solution in either case up to 1 litre with water. Each c. c. of this solution corresponds to O'Ol grm. zinc. Now mea- sure off 30 c. c. of this zinc solution into a beaker, add ammonia till the precipitate is redissolved, and then 400 500 c. c. distilled water. Kuii in sulphide of sodium as long as a distinct precipitate continues to be formed, then stir briskly, remove a drop of the fluid on the end of a rod to a porcelain plate, spread it out so that it may cover a somewhat large surface, and place in the middle a drop of pure dilute solution of chloride of nickel. If the edge of the drop of nickel solution remains blue or green, proceed with the addition of sulphide of sodium, testing^ from time to time, till at last a blackish gray coloration appears sur- rounding the nickel solution. The reaction is now completed, the whole of the zinc is precipitated, and a slight excess of sulphide of sodium has been added. The precise depth of color of the nickel must be observed and remembered, as it will have to serve as the stopping signal in future experiments. To make sure that the zinc is really quite precipitated, you may add a few tenths of a c. c. more of the reagent, and test again, of course the color of the nickel-drop must be darker. Note the num- ber of c. c. used, and repeat the experiment, running in at once the necessary quantity of the reagent, less 1 c. c., and then adding 0'2 c. c. at a time, till the end-reaction is reached. The last experiment is con- sidered the more correct one. The sulphide of sodium solution must be restaiidardized before each new series of analyses. c. Determination of the zinc in the solution of the ore. Proceed in the same way with the aminoniacal solution prepared in a as with the known zinc solution in b. Here also repeat the experiment, the second time running in at once the required number of c. c., less 1, of sulphide of sodium, and then adding 0'2 c. c. at a time, till the end- reaction makes its appearance. The second result is considered the true one. There are three different ways in which this repetition of the ex- periment may be made. You may either weigh out at the first two por- tions of the zinc ore, or you may weigh out double the quantity required for one experiment, make the aminoniacal solution up to 1 litre and em- ploy \ litre for each experiment, or lastly, having reached the end-reac- tion in the first experiment, you may add 1 c. c. of the known zinc solu- tion, which will destroy the excess of sulphide of sodium, and then run in sulphide of sodium in portions of 0'2 c. c., till the end-reaction is again attained. Of course, in this last process to obtain the second re- sult, you deduct from the whole quantity of sulphide of sodium used the amount of the same, corresponding to 1 c. c. of the zinc solution. If the ore contains copper, remove it from the acid solution by sul- phuretted hydrogen, evaporate the filtrate with nitric acid, dilute, treat with ammonia, and determine the zinc as above. 536 SPECIAL PAKT. [ 229 17. ANALYSIS OF OAST IRON, STEEL, AND WROUGHT IRON. 229. Cast iron, one of the most important products of metallurgic indus- try, contains a whole series of elements, mixed in greater or less proportion with the iron, or combined with it. Although the influence which the various foreign substances mixed with the iron exercise on ,the quality of cast iron is not yet accurately known, still the fact that they do exercise considerable influence on the quality of the article is beyond doubt. The analysis of cast iron is one of the more difficult problems of analytical chemistry. The following bodies must be had regard to in the analysis : Iron, carbon combined with the iron, carbon in form of graphite, ni- trogen, silicon, phosphorus, sulphur, potassium, sodium, lithium, calci- um, magnesium, aluminium, chromium, titanium, zinc, manganese, cobalt, nickel, copper, tin, arsenic, antimony, vanadium. As a general rule, the elements in italics alone are quantitatively determined. Steel and wrought iron are analyzed in the same manner as cast iron. 1. Determination of the Carbon. a. Determination of the total amount of Carbon. Method of BERZELIUS (somewhat modified.) Treat about 3 grin, of the cast iron, or 5 10 grm. of steel, mode- rately comminuted,* with a neutral concentrated solution of chloride of copper, (made by mixing hot solutions of chloride of sodium and sulphate of copper, and allowing sulphate of soda to crystallize out), and let the mixture stand at the common temperature f with occasional stirring. In 5 or 6 hours, or as soon as the part remaining undissolved presents a mixed mass of copper and separated carbon, &c., crumbling under pres- sure, add hydrochloric acid, and, if necessary, some more chloride of copper, and digest until the w r hole of the copper is dissolved to subchlo- ride. At this stage of the process a gentle heat may be applied. Filter through a tube of the form shown in fig. 100, the narrow part of which is loosely stopped with spongy platinum or asbestos, ignited in a current of moist air. Wash well, dry thoroughly, and treat the entire contents of the tube either as directed 176 or 178. After emptying [* Best by drilling-, in case of gray pig- or soft steel. White pig is reduced to powder by aid of the steel mortar. ] | On warming, a small quantity of gas is evolved, which contains a trifling admixture of carbonetted hydrogen. [Sometimes gas escapes at ordinary tem- peratures. In that case a lump of ice should be placed in the vessel at first After an hour or so cooling is unnecessary.] 229.] ANALYSIS OF CAST IRON, STEEL, AND WROUGHT IRON. 53: the tube, rinse with a little chromate of lead or oxide of copper ; if the combustion is to be effected in a boat, in a current of oxygen gas, in order that the incombustible residue may be examined, rinse with oxide of mercury. b. Determination of the G-raphite. Treat another portion of the cast iron with moderately con- centrated hydrochloric acid, at a gentle heat, until no more gas is evolved ; filter the solution through asbestos that has been ignited in a stream of moist air or through spongy pla- tinum (comp. a,), wash the undissolved residue, first with boiling water, then with solution of potassa, after this with alcohol, and lastly with ether (MAX BUCHNER) ; * then dry, and burn after 176 or 178. Direct weighing is not advi- sable, as the graphite generally contains silicon. Deduct the graphite obtained here from the total amount of carbon found in a ; the difference gives the combined carbon. FIG. 100. 2. Determination of the Sulphur. The safest way of estimating sulphur in cast iron is the following : Put about 10 grm. of the substance, in the finest possible state of divi- sion, into the fiask a (fig. 101), insert the cork,f containing the funnel-tube d c, and the evolution tube f ; the funnel-tube is provided with a little mercury at i, and the evolution tube is connected with two U-tubes, which contain a strongly alka- line solution of lead. Fill the funnel d with hy- drochloric acid, and suck by means of an India- rubber tube at the exit of the second U-tube, in which a small glass tube is inserted ; the acid will thus pass into the flask. Heat the flask, sucking in more acid from time to time as just described, till complete solution of the iron is effected ; then connect the exit of the second U-tube with an aspirator, and draw air through the apparatus for a long time. Collect the sul- phide of lead on a small filter, fuse it cautiously with a little nitre and carbonate of soda, soak in water, pass carbonic acid, to precipitate traces of dissolved lead, filter, acidify the filtrate with hy- drochloric acid and precipitate the sulphuric acid with chloride of barium. To make quite sure that you have left no sulphur behind, before throwing away the contents of the flask, evaporate the solution of pro- tochloride of iron, to drive off excess of hydrochloric acid, and test it with chloride of barium ; also fuse the undissolved residue with nitre FIG. 101. * Joum. f. prakt. Chem. 72, 364. f If a caoutchouc stopper were used, a little sulphur would not be unlikely to get into the residue : the caoutchouc connections must be desulphurized. 538 SPECIAL PART. [ 229. and carbonate of soda, and test the aqueous extract of 'the fused mass for sulphuric acid. As a rule the residue will be found free from sulphur. But if any sulphate of baryta is obtained again here, it may be collected on the same filter which has received that produced from the sulphide of lead. [3. Estimation of Phosphorus. In case of cast iron, when the amount of phosphorus present exceeds 1 per cent., 2 grm. suffice for a determination ; when less is present it is best to take at least 3 grm. Treat with aqua regia in a tall beaker covered with a watch-glass. Digest at a moderate temperature 2 or 3 hours, or till effervescence ceases, then remove the cover and evaporate to diyness, as in the ordinary way of separating silica, with addition of nitric acid, if need be, to remove chlorine. A temperature a few de- grees above that attainable with the water-bath may be used to hasten this operation. But if too high heat is used, oxide of iron will remain undissolved on subsequent treatment with nitric acid ; moreover, pyro- phosphate may be formed at a temperature below 150 C. After the re- sidue has been dried sufficiently to make the silica insoluble, digest with nitric acid till the iron is dissolved. Separate the residue by filtering, and reserve it for determination of silicon. To the filtrate add 100 c. c. of molybdic acid solution. If after the addition of this reagent the solution amounts to less than 350 to 400 c. c., dilute to that volume. Place for 24 hours in a warm situation where the temperature does not rise above 40 C. Wash the precipitate with the molybdic solution, diluted with an equal volume of water, letting the washings run into the filtrate. Then allow the filtrate to stand 24 hours or more in a warm place, and collect any appreciable amount of phospho-molybdate that may separate. Dissolve and reprecipitate according to p. 271. Steel (3 10) grm. may be dissolved in nitric acid of 1'20 sp. gr., and evaporation to dryness may be omitted when silicon is not to be estimated.] [4. Estimation of Silicon. The residue from the solution used for determining phosphorus may be used for determining silicon. Ignite it without separation from the filter until the graphite is partially burned away. Fuse with car- bonate of soda mixed with a little nitrate of potash, sufficient to effect complete combustion of the carbon still present. Treat the fused mass first with boiling water, in which it readily dissolves, except some silica in light flocculent form, and traces of metallic oxides. Acidify with hydrochloric acid, or nitric acid, in case the solution is to be in contact with platinum, and separate silica as usual. "When the quantity of silica is not over 1 per cent., these operations may be most conveniently per- formed in a large platinum crucible without transferring the substance to any other vessel.] [5. Estimation of Manganese and Cobalt. 2 grm. is as large a quantity as can conveniently be treated by the method here proposed, and will in most cases suffice. Where less than 2 per cent, is present, and great accuracy is required, it is necessary perhaps to take more. Of spiegeleisen 1 to grm. suffices. Prepare a 229.] ANALYSIS OF CAST IRON, STEEL, AND WROUGHT IRON. (139 solution of the iron in the same manner as for phosphorus (3). A highei temperature may, however, be used to make silica insoluble, and hydro- chloric acid may be used for redissolving. Filter from the residue of carbon and silica into a large flask. When the solution is cold, add car- bonate of soda as long as the precipitate formed by it can be redissolv- ed by shaking and letting stand a few minutes. Next add 12 to 15 c. c. strong acetic acid, and the same volume of a saturated solution of ace- tate of soda. Dilute, now, the solution to about 1 litre, and precipi- tate iron by boiling. Filter and wash without decantation, as long as the water passes freely through the mass upon the filter. When the washing becomes tedious, on account of slow passage of water through the filter, rinse the precipitate from the filter into a dish with a jet of water, and boil with a moderate amount of water with addition of a little acetate of soda, stirring with a glass rod as long as any coherent lumps of precipitate remain. Bring the precipitate back again upon the filter and complete the washing. Concentrate the filtrate and washings to about 300 c. c. (or less if too much saline matter is not present). A little iron is usually present in this filtrate ; sometimes it is partially deposited during the evaporation. In order to separate the manganese from this, and from the large quantity of saline matter in the liquid, precipitate next all the metallic oxides present by gradually adding car- bonate of soda to the boiling solution as long as a precipitate is formed, and adding at the close a few drops of caustic soda. Filter, wash the precipitate slightly, dissolve it on the filter with hydrochloric acid, and separate the small quantity of iron in the new solution with ace- tate of soda. For this purpose, when, as usually is the case, but little iron is present, the solution need occupy but a small volume (100 c. c.). Add carbonate of soda as long as no permanent precipitate is formed, then 2 or 3 c. c. of the acetate of soda solution, and heat gradually to boiling. Sometimes when this solution is moderately warmed, and car- bonic acid has mostly escaped, but before the temperature is high enough to precipitate the iron, the solution will become turbid with a finely divided white precipitate. If this happens, add acetic acid till it dis- solves, and then raise the heat to boiling. Filter from the precipitated iron, and precipitate manganese in the filtrate with bromine (see 223,2). When no great accuracy is required, this precipitate may be washed, ignited, and weighed as protosesquioxide of manganese, and metallic manganese calculated from it. It may, however, contain cobalt, which is often present in pig iron, and possibly traces of copper. To detect the presence of cobalt, dissolve the weighed oxide of man- ganese in a few drops of HC1, heat till the brown color imparted by the manganese disappears. A comparatively small amount of cobalt will now give the solution, while hot and concentrated, a bright green color that disappears on diluting with cold water. Evaporate the solu- tion till free acid is expelled, dissolve in a small quantity of water, add acetate of soda and a drop of acetic acid, heat to boiling and transmit HS, which will precipitate the cobalt. Collect the precipitate on a filter, wash rapidly with water containing HS. Testing this pre- cipitate with a blowpipe will further confirm its nature. If it be judged from this examination that cobalt is present in any sensible quantity, evaporate the filtrate last obtained till HS is expelled, and precipitate manganese again with carbonate of soda, and weigh it as protosesquioxide. 540 SPECIAL PAKT. [ 229. For most practical purposes sufficiently good results may be usually obtained in the analysis of spiegeleisen, e. g., by separating iron from a solution of 0'5 0'7 grm. as above described, precipitating the con- centrated filtrate directly by means of phosphate of soda and weighing the manganese as pyrophosphate. See p. 185.] 5. Determination in one portion of the total amounts of silicon, iron, manganese, zinc, cobalt, nickel, alumina, titanic acid, alkaline earths and alkalies. Dissolve about 10 grm. of the cast iron in a capacious platinum dish,* in moderately dilute hydrochloric acid, evaporate with a few drops of dilute sulphuric acid on the water-bath to dryness, till the mass ceases to smell of hydrochloric acid, moisten with hydrochloric acid, heat, add water, filter, wash and dry the precipitate. Let us call it a. Heat the solution in a porcelain dish with nitric acid, dilute copiously and precipi- tate the sesquioxide of iron, &c., by nearly saturating with carbonate of ammonia and boiling, after p. 362, 69. Wash and dry the precipitate ; call it b. Mix the nitrate from b with ammonia in slight excess, heat till the excess of ammonia is almost expelled, filter, dissolve in hydrochloric acid and reprecipitate in the same manner. Filter, wash and dry the pre- cipitate ; call it c. Acidify the filtrate from c with hydrochloric acid, concentrate in a porcelain dish, transfer to a flask, add ammonia and sulphide of ammo- nium and proceed generally as directed p. 184, c. After 24 hours, filter the precipitate (rZ) off, wash it with water containing sulphide of ammo- nium, spread the filter on a glass plate, rinse the precipitate into a flask } treat it with acetic acid, cork and set aside. Evaporate the filtrate from d in a platinum dish to dryness, expel the ammonia salts at the lowest temperature possible, and in the residue determine the alkaline earths and alkalies. For this purpose precipitate the lime by pure oxalate of ammonia repeating the precipitation accord- ing to 29, and from the filtrate separate magnesia according to 16. The alkalies are weighed as chlorides and potassa is finally estimated by 1. The residue a contains the whole of the bodies insoluble or difficultly soluble in hydrochloric acid. The following substances may be present besides carbon and silica, viz., phosphide of iron, chromium-iron, vana- dium-iron, arsenide of iron, carbide of iron, silicon, molybdenum, &c., and also slag in a more or less altered condition. Titanic acid and sul- phate of baryta may also be here present. Fuse with carbonate of soda and potash, and a little nitre, separate the silica as usual , by evaporating with hydrochloric acid and two drops of dilute sulphuric acid, weigh it and see whether it is pure (comp. p. 300) ; the impurities most likely to be present are sulphate of baryta and titanic acid. The silicic acid may- have been partially formed from silicon, and partially present as such in the slag. In the filtrate from the silicic acid separate what is separable by ammonia by double precipitation, filter off the precipitate (c'), then precipitate with sulphide of ammonium, filter off the precipitate (d 1 , to be treated as d) and finally test the filtrate for alkaline earths, any small quantities of which found can then be weighed with the somewhat larger amount obtained above. * If glass or porcelain be used, the estimations of the silicon and aluminium cannot be considered as absolutely exact. 229.] ANALYSIS OF CAST IROX, STEEL, AND WROUGHT IRON. 541 The precipitates 6, c and c contain the whole of the sesquioxide of iron and alumina, also that part of the titanic acid which has passed into solution. Transfer the mixed ignited precipitates to several plati- num or porcelain boats, put these in a glass tube and ignite in pure hv- drogen, till no more steam issues. Treat the boats and their contents with very dilute nitric acid (1 of acid to 30 40 of water) to dissolve the iron, make the solution up to 1000 c. c. and determine the iron in an aliquot part by oxidation and precipitation with ammonia.* Fuse the residue, which was insoluble in the very dilute nitric acid, with bisul- phate of potash, take up with cold water, filter off any residual silica, collect and weigh it and add the weight to that found above ; pass sul- phuretted hydrogen, endeavor to precipitate any titanic acid that may be present by boiling and passing a stream of carbonic acid, boil the fil- trate or the clear solution with nitric acid, precipitate the alumina with ammonia, and separate it from the small quantity of sesquioxide of iron that may possibly be present by the method given p. 521 (precipitate. II). In this, as in that case, regard must be paid to phosphoric acid, as its presence would give fictitious weight to the alumina. If chromium were present, its oxide would likewise have to be separated and determined in this precipitate. The precipitates d and d' have given up to the acetic acid almost the whole of their sulphide of manganese. Filter off the solution, suspend the residue in sulphuretted hydrogen water, and add some hydrochloric acid. Under these circumstances, the sulphide of zinc and any residual sulphide of manganese are dissolved, while the sulphide of copper (which is not here estimated), sulphide of nickel, and sulphide of cobalt are left behind. Evaporate the hydrochloric acid solution to a small bulk, boil with excess of solution of socla, precipitate any zinc from the solution by sulphuretted hydrogen, dissolve any separated hydrate of protoses- quioxide of manganese in hydrochloric acid, add the solution to the acetic acid solution, and determine the manganese in the mixture. Incinerate the filter, containing the sulphides of copper, nickel and cobalt, dissolve in hydrochloric acid, precipitate with sulphuretted hy- drogen, and in the filtrate thus freed from copper estimate the nickel and cobalt. 6. Determination in one portion of the metals of G-roups V. and YI. and of the phosphorus. Treat 10 grm. of the cast iron in the finest possible state of division with a previously heated mixture of 1 volume of nitric acid and 3 vol- umes of hydrochloric acid (both acids must be pure and strong) in a very capacious, long-necked, obliquely placed flask at a gentle heat. When all visible action has ceased, decant the solution and treat the residue with a fresh portion of aqua regia. f Mix the solutions, dilute copiously and treat in a large flask with sulphuretted hydrogen, at first in the cold, then at 70. I may here observe that the solution usually * It is not advisable to determine the iron in a separately weighed smaller quantity, unless the sample to be examined is perfectly homogeneous. \ Instead of aqua regia, bromine ?,nd water may be used. The solution goes on rapidly, at first almost violently, if the bromine is in excess and. the mixture is digested at 20 30. Toward the end assist the action by the heat of a water- bath ( J. Nickles). If this method is employed, I should still recommend that the residue be treated with aqua regia. 542 SPECIAL PART. [ 229. retains a brownish tint from dissolved organic substances, even after the sesquichloride of iron is reduced. Allow the fluid (saturated with sul- phuretted hydrogen) to settle for 24 hours, filter, dry the precipitate, which consists principally of sulphur, and extract it with warm bisul- phide of carbon. There usually remains a small black residue, which often contains, besides sulphide of copper, a little sulphide of arsenic and sulphide of antimony. Separate these, or generally the metals present of the fifth and sixth groups, according to the methods given in Section Y. Free the filtrate from the sulphuretted hydrogen precipitate from the excess of the gas by transmission of carbonic acid, add a little pure sesquichloride of iron, nearly neutralize the solution with pure carbon- ate of soda and precipitate with carbonate of baryta in a closed flask. Treat the precipitate, which contains the whole of the phosphoric acid (produced by the oxidation of the phosphorus compounds), with hydro- chloric acid, precipitate the baryta with sulphuric acid, filter, evaporate to small bulk, precipitate the phosphoric acid with solution of molybde- num and determine it after p. 271, |3. As a portion of the phosphide of iron may have escaped oxidation by the aqua regia, fuse the residue insoluble therein with carbonate of soda and nitre, and test the aqueous solution of the fused mass likewise for phosphoric acid. 18. ANALYSIS OF MANURES. 231. I SPEAK here simply of the manures which owe their origin to the urine, excrements, blood, bones, &c., of animals, or are prepared by the decomposition of apatite, &c., by acids. The examination of manures has chiefly a practical object, and demands accordingly simple methods. The value of a manure depends upon the nature and condition of its constituents. The following constituents are the most important : or- ganic matters (characterized by their carbon and nitrogen), ammonia salts, nitrates, phosphates, sulphates, and chlorides with alkaline and alkaline earthy bases (potassa, soda, lime, magnesia). To these sub- stances we know the efficacy of a manure is owing, but as to the condi- tion in which they exercise the most favorable action, our views are much less clear ; indeed, it is obvious that a universally applicable and valid rule cannot well be laid down in this respect ; since the agricul- turist sometimes wishes a manure containing most of its constituents in a state of solution, which will accordingly exercise a speedy fertilizing action, and sometimes one which will only gradually supply the soil with the substances required by the plants. As regards the insoluble mate- rials of manures, it may be safely asserted that their value advances in proportion as their degree of division and solubility increases. I will here give, 1, the outlines of a general method of examination applicable to almost all kinds of manures ; 2, methods of valuing guano and manures prepared from bones, apatite, &c. A. GENERAL PROCESS. 232. Mix the manure uniformly by chopping and grinding, then weigh off successively the several portions required for the various estimations. 1. Determination of the Water. Dry 10 grm. at 125, and deter- mine the loss of weight ( 29). (It is rarely necessary to make a cor- rection on account of the carbonate of ammonia which escapes with the water.*) 2. Total Amount of fixed Constituents. Incinerate, at a gentle heat, a weighed portion of the residue left in 1, in a thin porcelain dish; moisten the ash with a solution of carbonate of ammonia, dry, ignite gently, and weigh. * To do so, dry the manure in a boat inserted in a tube ; the tube is heated to j.00 in the water- or air-bath, a current of air being transmitted through it, by means of an aspirator : the air enters through concentrated sulphuric acid, and makes its exit through two U-tubes containing standard sulphuric acid. After drying, the quantity of ammonia expelled, which has combined with the standard acid, is determined ( 99, 3). 544 SPECIAL PART. [ 232. 3. Constituents soluble in Water, and insoluble in Water. Digest 10 grm. of the fresh manure with about 300 c. c. water, collect the residue on a weighed filter, wash, dry at 125, and weigh. The weight found expresses the total quantity of the substances insoluble in water, and the difference after deducting the water found in 1 gives the amount of the soluble constituents. Incinerate now the insoluble residue, treat with carbonate of ammonia, as in 2, and weigh ; the weight expresses the total amount of the fixed constituents contained in the insoluble part, and the difference between this and the ash in 2 gives the total amount of fixed constituents contained in the soluble part. 4. Fixed Constituents singly. [Obtain 3 5 grm. of ash according to 2. Treat 2 grm. with hot dilute hydrochloric acid until only insoluble mat- ters (sand, clay, and charcoal) remain, which filter off, wash, ignite, and weigh. The filtrate and washings are brought to the bulk of 200 c. c., mixed, and divided into four equal parts. a. To 50 c. c. add ammonia until a slight permanent precipitate is formed, then enough hydrochloric acid to dissolve this precipitate, heat to boiling, and add acetate of soda as long as a precipitate forms, wash, ignite, and weigh. Two cases may here present themselves. a. If the precipitate before ignition were red it contains all the iron, alumina, and phosphoric acid. In this case dissolve it in concentrated hydrochloric acid with cautious addition of sulphuric acid, towards the last, finally evaporate oil' the hydrochloric acid (or fuse with carbonate of soda and dissolve in sulphuric acid) and determine the sesquioxide of iron volumetrically (p. 203). Afterwards in the same liquid determine phosphoric acid by molybdic solution (p. 271). Calculate alumina by difference. In the filtrate from the acetate of soda precipitate, deter- mine lime as oxalate, and afterwards magnesia as pyrophosphate, ac- cording to 29, p. 349. 0. If the precipitate before ignition were nearly white, it contains all the iron and alumina and a portion of the phosphoric acid. It may be analyzed as just described, or, if very small in quantity, half of it may be reckoned as phosphoric acid (see page 141). From the filtrate con- taining free acetic acid, lime is precipitated as oxalate (30? P- 350), the second filtrate is then neutralized by ammonia, when all the magnesia and a portion of phosphoric acid go down as ammonio-phosphate of magnesia; the third filtrate is treated with magnesia-mixture to separate the rest of the pJiospJiorfo acid. b. To another 50 c. c. add hot concentrated solution of caustic baryta 111 slight excess, boil, and filter. The filtrate (and washings) containing only alkali chlorides and chlorides of barium and calcium, is treated hot with solution of carbonate of ammonia and some caustic ammonia, fil- tered from carbonates of baryta and lime, the liquid evaporated and ignited to expel ammonia-salts, and this process repeated, if ne,ed be, until pure alkali chlorides are obtained (see p. 303, last paragraph), in which the polassa and soda are determined according to 1, p. 339, or 5> p. 342. c. In a third portion of 50 c. c., estimate sulphuric acid by precipita- tion with chloride of barium. The fourth 50 c. c. is reserved for use in case of accidents.] d. Determine the carbonic acid in another portion of the ash, as directed p. 291, cc, or p. 293, e. Filter the contents of the flask (in which the solution has been effected with the aid of dilute nitric acid), 233.] ANALYSIS OF GUANO. 545 and precipitate the chlorine with solution of nitrate of silver, as directed 141, L, a. 5. Total amount of Ammonia. Treat a weighed portion of the ma- nure by SCHLOSING'S method (p. 158, &*). 6. Total amount of Nitrogen. Moisten a weighed portion of the manure with a dilute solution of oxalic acid in sufficient quantity to im- part a feebly acid reaction ; dry, and determine the nitrogen, in the en- tire mass or in a weighed portion, after 185. If you deduct from the total amount of nitrogen so found the quantity corresponding to the ammonia and the nitric acid, the difference shows the quantity of nitro- gen contained in the organic substances. It is generally sufficient, how- ever, to know the total amount of the nitrogen. 7. Total amount of Carbon. Treat a portion of the dried residue of 1 by the process of organic analysis ( 189). If the dried manure con- tains carbonates, determine the carbonic acid in a separate portion, and deduct the result from the total amount obtained by the organic analy- sis ; the difference shows the quantity of carbonic acid formed in the latter process by the carbon of the organic substances. 8. Nitric A-dd. Treat a weighed portion of the manure with water, and evaporate the solution^ with addition of pure carbonate of soda to distinct alkaline reaction; filter after some time, then evaporate the fil- trate to a small bulk, and determine in fractional parts of it the nitric acid. As the solution will scarcely ever be free from organic matter, employ SCHLOSING'S method (p. 331). B. ANALYSIS OF GUANO. 233. Guano consists of the excrements of sea-fowls, more or less altered. It not only varies very considerably in quality in the different islands from which our supplies are derived, but is often also fraudulently adul- terated with earth, brick-dust, carbonate of lime, and other matters. The guano is mixed as uniformly as possible, and that which is in- tended for analysis is put into a stoppered bottle. 1. Determination of the Water. This is effected exactly as on p. 543 (1). In exact analyses the carbonate of ammonia must not be over- looked (see note). Genuine guano loses from 7 to 18 per cent. 2. Total amount of fixed Constituents. Incinerate a weighed portion in a porcelain or platinum crucible placed in a slanting position, and weigh the ash. Good guano leaves from 30 to 33 per cent, of ash, guano of bad quality from 60 to 80 per cent., and a wilfully adulterated arti- cle often even more. The ash of genuine guano is white or gray. A yellow or reddish color indicates adulteration with loam, sand, or earth. In the first stage of the decomposition by heat, good guano emits a strong ammoniacal odor and white fumes. 3. Constituents soluble in Water, and insoluble in Water. \ Heafc 10 * Small quantities of ammonia are determined with decinormal sulphuric acid. f It must be mentioned that the quality and quantity of the constituents solu- ble in water are by no means constant for the same guano. Liebig (Annal. d. Chem. u. Pharm. , 119, 13) has shown that the kind of salts which pass into solu- tion varies according to whether one niters the solution off immediately or after 35 5|f) SPECIAL PAST. [ 233 grm. guano with about 200 c. c. water, collect the residue on a weighed filter without delay, and wash it with hot water, until the water running otf looks no longer yellowish and leaves no residue when evaporated upon platinum foil ; dry the residue, and weigh. Deduct the sum of the water and the residue from the weight of the guano ; the remainder expresses the amount of the soluble constituents. Incinerate the resi- due and weigh the ash ; the difference shows the amount of the fixed soluble salts. With very superior sorts of guano, the residue insoluble in water amounts to from 50 to 55 per cent., with inferior sorts, to from 80 to 90 per cent. The brown-colored aqueous solution of genuine guano evolves ammonia upon evaporation, emits a urinous smell, and leaves a brown saline mass, consisting chiefly of sulphates of soda and potassa, chloride of ammonium, oxalate and phosphate of ammonia. 4. Fixed Constituents singly. As in 232. 5. Total amount of Ammonia. " C. Total amount of Nitrogen. " 7. Total amount of Carbon. 8. Nitric Acid. " 9. Carbonic Acid. Employ one of the methods 139, II. Genuine guano contains only a small proportion of carbonates. If, therefore, a guano effervesces strongly when moistened with dilute hydrochloric acid, this may be regarded as a proof of adulteration with carbonate of lime. 10. Uric Acid. If it is wished to ascertain the quantity of uric acid which a guano contains, treat the part insoluble in water with a weak solution of soda at a gentle heat, filter, and acidify the filtrate with hy- drochloric acid, to precipitate the uric acid. Collect on a weighed filter, wash cautiously with the least possible quantity of cold water, dry, and weigh. 11. Oxalic Acid. As appears from the note to 3, the oxalate of ammonia in guano plays an important part with respect to the solution of the phosphate of lime. It is, therefore, frequently a matter of inter- est to determine the oxalic acid. This is best done in a separate por- tion after 137, d, /?. A little dilute sulphuric acid is first made to act upon the guano, till all the carbonic acid is expelled, the sulphuric acid Is then neutralize ] with solution of soda free from carbonic acid, the manganese is added and the decomposition is effected with dilute sul- phuric acid. I prefer to conduct the decomposition in the apparatus figured p. 294, collecting the carbonic acid in a weighed soda-lime tube. As the manuring value of a sample of guano may be estimated, with sufficient accuracy, from the phosphoric acid and nitrogen which it con- some time. In the first case, the solution contains much oxalate and little phos- phate, together with some sulphate of ammonia ; in the second case, the oxalate of ammonia is more or less completely replaced by phosphate of ammonia, the oxalic acid having combined with lime in the residue. The cause of this deport- ment is that phosphate of lime, although when in contact with oxalate of ammo- nia and water alone it scarcely suffers any change, is very soon converted into oxalate of lime, with formation of phosphate of ammonia, when sulphate of am- monia (or chloride of ammonium) is also present. The sulphate of ammonia renders the phosphate of lime somewhat soluble, the dissolved part is at once precipitated by the oxalic acid, and the sulphate of ammonia is thus enabled tc act ai'resh upon the phosphate of lime. 234.] ANALYSIS OF BONE DUST. 547 tains, the analysis is often considerably shortened, and confined to the following processes : a. Determination of Water (see 1). b. Determination of Ash (see 2). c. Determination of Phosphoric Acid. Mix 1 part (1 or 2 grm.) of the sample of guano with 1 part of carbonate of soda and 1 part of nitrate of potassa ; ignite cautiously, dissolve the residue in hydrochlo-* ric acid, evaporate to dryness on the water-bath, treat with hydrochlo- ric acid and water, filter, add ammonia to the filtrate to alkaline reac- tion, then acetic acid until the phosphate of lime is redissolved, and lastly without previously filtering off the very trifling precipitate of phosphate of sesquioxide of iron acetate of sesquioxide of uranium, and determine the phosphoric acid as directed p. 272, c. d. Determination of Nitrogen , after 185. As mixing the guano in the mortar with soda-lime would be attended with escape of an appre- ciable amount of ammonia, it is advisable to effect this operation in the combustion tube, with the aid of a wire (comp. pp. 426 8). C. ANALYSIS OF BONE DUST 234. There are three sorts of bone dust. I. The powder obtained by the grinding of more or less fresh bones, which is generally very coarse.* II. The powder obtained by the grinding of more or less decayed bones. III. The powder of bones which, previous to the operation of grind- ing, have been submitted to the action of boiling water, or high-pressure steam. I. is very coarse, and contains a relatively large proportion of fat and of gelatigenous matter. II. is considerably poorer in organic substances. III. is much finer than I. and II. ; it contains hardly any fat, and is somewhat poorer in gelatigenous matter. 1. Examine the powder, in the first place, by careful inspection, sifting, and elutriation, to ascertain the degree of comminution, and the presence of foreign matters. 2. Determination of the Water. Dry a sample at 125. 3. Total amount of fixed Constituents. Ignite, about 5 grm., with access of air, until the ash appears white; moisten with carbonate of ammonia, dry, ignite gently, and weigh the residue. 4. Fixed Constituents singly. Treat the ash of 3 with dilute hydro- chloric acid, filter off the insoluble portion (sand, &c.), and determine the sesquioxide of iron, lime, magnesia, chloride of sodium, and phos- phoric acid in the solution as directed 232, 4. 5. Nitrogen. Ignite 0'5 O'S grm. with soda-lime (185). 6. Fat. Exhaust 5 grm. of the sample (ground as finely as possible), by boiling with ether, and dry the residue at 125. The loss of weight minus the moisture found in 2, shows the amount of fat. By way of * ["Flour of bone " obtained from fresh bones contains several per cent, of common salt to preserve it from putrefaction.] 548 SPECIAL PART. [ 235. control, the ether may be distilled off, and the residual fat weighed, care being taken to leave no water under the fat. 7. Deduct from the total weight the sum of the fixed constituents; carbonic acid, water, and fat ; the difference expresses the gelatigenous matter. 8. Determine the carbonic acid after p. 293 e. < D. ANALYSIS OF SUPERPHOSPHATE. 235. V Substances which contain basic phosphate of lime in a difficultly solu- ble condition, are often converted into so-called superphosphate, for the purpose of rendering the phosphoric acid soluble, and consequently more readily accessible to plants. This is done by subjecting them to the action of a certain quantity of acid, usually sulphuric (occasionally as- sociated with hydrochloric), by which sulphate of lime (and chloride of calcium), acid phosphate of lime and phosphoric acid are formed.* The following bodies are employed for the preparation of superphos- phate, viz., spent bone-black from sugar refineries, coprolite, apatite, phosphorite, Baker guano, precipitated basic phosphate of lime from glue works, and, more rarely, bone dust. As it is unusual to employ enough acid to set the whole of the phos- phoric acid free, the superphosphates generally consist of mixtures of sulphate of lime (and chloride of calcium), basic phosphate of lime, phos- phate of sesquioxide of iron, phosphoric acid, and water. Carbon or organic matter (containing nitrogen) is frequently also present. Their quality is very variable, according to the raw material employed and the method of treatment, but they all agree in this, that they consist of sub- stances (a) readily soluble in water, (b) difficultly soluble in water, and (c) insoluble in water. Before we can judge of the value of a superphosphate it is abso- lutely necessary to know, not merely the quantity of the constituents, but how they are combined and how they deport themselves with sol- vents ; hence the analysis becomes somewhat complicated. 1. Dry about 3 grm. of the sample at 160180. T'he loss of weight expresses a, the moisture b, the water of the sulphate of lime. 2. Triturate 10 grm. of the undried superphosphate in a dish with cold water by the aid of a pestle, till all the lumps are completely bro- ken down, allow to settle, pour off the clear supernatant fluid through a filter, and repeat the extraction with cold water, till the fluid no longer shows acid reaction. Dilute the aqueous solution so obtained to 500 c. c., and dry the residue at about 100. 3. Divide the aqueous solution, which generally appears yellow from the presence of organic matter, into 4 portions, viz., a, 6, and c, of 100 c. c. each, and d, of 200 c. c. a. Evaporate in a platinum dish, adding, after some time, cautiously, thin milk of lime just to distinct alkaline reaction; proceed with the evaporation, dry the residue at 180, and weigh; ignite the weighed * Comp. Beinh. Weber, Pogg. Annal. 109, 505. 235.] ANALYSIS OF SUPERPHOSPHATE. 549 residue and weigh again : the difference between the two weighings ex- presses the quantity of organic matter in the aqueous solution. Boil the residue with pure lime-water, then with water, filter, precipitate the sulphuric acid from the nitrate by addition of a little chloride of barium, then the baryta and lime by carbonate of ammonia, and determine the alkalies as chlorides according to p. 345, 15- b. Precipitate with chloride of barium, and determine the sulphuric acid in the usual way ( 132, I., 1). c. Serves for the determination of any hydrochloric acid after 141. Organic matter, if present in large quantity, is destroyed as in d. d. Add an excess of carbonate of soda and a little nitrate of potassa, and evaporate to dryness in a platinum dish. Ignite the residue gently, then soften with water, rinse into a beaker, add hydrochloric acid, and apply a gentle heat until complete solution is effected. Add to the clear fluid, ammonia, then acetic acid in excess ; filter off the phosphate of sesquioxide of iron, and divide the filtrate into two equal portions. Determine in one the phosphoric acid * with uranium solution either gravimetrically, after p. 272, c, or by the volumetric method, p. 274. Estimate in the other portion the lime and magnesia as directed p. 349, 29. 4. Transfer the residue of 2 to a weighed platinum dish, add the ash of the filter, dry at 180, and weigh. The weight expresses the total amount of substances insoluble in water. Now ignite gently, with access of air, until the whole of the organic matter and charcoal is burnt ; the loss of weight indicates the amount of these latter. 5. Boil the residue of 4 with dilute hydrochloric acid ; after boiling for some time, dilute with water, filter, and dilute the filtrate by means of the washing water to ^ litre ; treat the insoluble residue as directed in 7. 6. Of the hydrochloric acid solution obtained in 5, measure off two portions, one of 50, the other of 100 c. c. In the former determine the sulphuric acid, in the latter the phosphate of sesquioxide of iron (if present), lime, magnesia, and phosphoric acid,* as in 3, b and d. 7. Dry, ignite, and weigh the insoluble residue of 5. It generally consists only of sand, clay, and silicic acid. To make quite sure, how- ever, boil with concentrated hydrochloric acid ; should some more sul- phate of lime be dissolved, determine the amount of this in the solu- tion. 8. Lastly, determine the nitrogen in O'S 1 grin, of the superphos- phate ( 185). In arranging the results, it must not be forgotten that the nitrogen is part of the organic matter previously determined. 9. Should the superphosphate contain an ammonia salt, determine the ammonia as directed p. 157, 3, a. As regards the statement of the results, the following plan presents a very good bird's-eye view of the analysis : * [ Many superphosphates contain considerable quantities of phosphates of iron and alumina which are to some extent extracted by water. In such cases the above method will not give good results, but both the soluble and insoluble phosphoric acid must be separated by means of molybdic solution, either from the original solution in water or hydrochloric acid, or from the acetate of ammonU precipitate. See p. 271.] 5iO SPECIAL PART. [ 236 Anhydrous phosphoric Nitro acid. gen. fHydrate of phosphoric acid (3 H O, P0 5 ) . 16 15 11 70 Constituents j Lime, > 1 dissolved by or com .1 readily sola- j Magnesia, _ I bined with the free i '50 - ble in water. |esqmox. iron, f phosphoric ' acid j Constituents ] soSeln 1" Sul P hate of lime water. , f Phosphoric acid 219 219 Constituents J Lime * , combined with the ) d j Magnesia, [ phosphoric acid to more [ I'Ol L s> | Sesquiox. iron, ) or less basic salts ) Constituents ) insoluble in j- Clay and sand 2 '49 - acids. ) Organic constituents and carbon 6 '51 0'41 Moisture . . 29 15 100-00 13-89 0-41 It will be seen that we calculate the sulphuric acid found in solution and residue into sulphate of lime, and add both the quantities together. The residual quantities of lime in the solution and the residue, i.e., the portions not combined with sulphuric acid, are then put down as above. If the superphosphate was prepared with sulphuric and hydrochloric acids, the chlorine in the aqueous solution is to be calculated into chlo- ride of calcium, and the lime corresponding thereto -f- the lime combined with sulphuric acid is to be deducted from the total quantity found in the aqueous solution. The remainder is then to be put down as dis- solved by, or combined with, phosphoric acid. [ABRIDGED ANALYSIS OF SUPERPHOSPHATES. 236. For most ordinary purposes it is sufficient to estimate on 1 grin. A. Wetter expelled at 100 by drying in water-bath. B. Organic and oilier volatile matters by gentle ignition and incine- ration of A until carbon is mostly consumed. C. Sand and insoluble matters by treatment of the residue of B with nitric acid. D. Total phosphoric acid in -^ of the solution C by means of molyb- dic solution, when iron and alumina are present in quantities of over J- per cent. ; or, in absence of iron and alumina, by titration with stand- ard uranium solution. E. Soluble phosphoric acid by treating 10 grm. as directed above, 235, 2 and estimating phosphoric acid in aliquot parts (50 c. c.) of the solution, with uranium or molybdic solution see foot-note p. 549. F. Nitrogen in 0'5 grm. by combustion with soda lime, 185. More important than determining the quantities of lime, magnesia, &c., is a study of the condition of the phosphates insoluble in water, and of the nitrogen. The former are much more valuable as fertilizers when existing as bone-earth than when composed of crystallized apatite 237, 238.] ANALYSIS OF BONE CLACK. 553 or . compact coprolite. The latter in gelatine or blood is very active, while in the form of leather shavings it is nearly inert.] E. ANALYSIS or BONE BLACK. ! 237. Bone black is extensively employed for decolorizing and removing the lime from the juice in the preparation of beetroot sugar, and in the re- fining of cane sugar. When freshly prepared it consists of a mixture of bone earth with 7 10 per cent, of carbon, but on use it takes up lime, coloring matter, mucilage, &c., from which it is freed during the process of reaiiimation, by washing, treating with hydrochloric acid, washing again, drying and igniting. When at last it is thoroughly used up, or " spent," it passes into the manure manufactories, and is then generally applied to the preparation of superphosphate. As the bone black is much altered and contaminated by the numerous operations through which it passes, its value varies very considerably, and can only be es- timated by analysis. Again, before being submitted to the revivifying process, bone black always requires testing, in order that it may be known how much hydrochloric acid it is necessary to employ ; in this case we have to find the quantity of the lime which is not combined with phosphoric acid (and which is usually present in the form of carbo- nate of lime). We describe, in the first place, the ordinary method of analyzing bone black, and then a process for determining the carbonate of lime. GENERAL PROCESS. 1. Dry 23 grm. at 160180. The loss of weight indicates the moisture. 2. Dissolve 5 grm. in the flask a of the apparatus figured p. 293, and determine the carbonic acid as there described. 3 Filter the solution through a weighed filter, wash the residue, dry at 100, and weigh. This will give you the sum of the charcoal, the insoluble organic matter and the mineral impurities insoluble in hydrochloric acid (sand and clay). Now ignite the dried filter with access of air. This will give you the sand and clay as the resi- due. The charcoal and insoluble organic matter is found by difference. 4. Make the filtrate obtained in 3 up to 250 c. c. and determine in 100 c. c. iron, lime, maynesia, and phosphoric acid, in 50 c. c. the sul- phuric acid that may be present, and in the last 100 c. c. the alkalies possibly present according to 232, b. p. 544. 5. Dissolve another weighed portion of the substance in dilute nitric acid, dilute and determine in the filtrate the hydrochloric acid possibly present. PROCESS FOR DETERMINING THE CARBONATE OF LIME OR THE CAR- BONATE OF LIME AND CAUSTIC LIME. 238. For determining carbonate of lime 3 grm. of the bone black are dried and powdered as finely as possible. Estimate carbonic acid according to 552 SPECIAL PART. [ 239. <7, p. 298, from this calculate the carbonate of lime. If a bone black contains hydrate of lime, moisten a portion weighed off in a porcelain dish with 10 20 drops of carbonate of ammonia, evaporate to dryness, heat the residue somewhat more strongly (but by no means to ignition), and transfer without loss to the decomposing bottle. Calculate as be- fore ; the excess over the first estimation is carbonate equivalent to the caustic lime present. 239. 19. [ANALYSIS OF COAL AND PEAT. For technical purposes, estimations of moisture, ash, coke, and volatile matters usually suffice. Determination of sulphur is less frequently required, and ultimate analysis is only resorted to in special cases. a. Moisture. The finely pulverized coal (3 5 grin.) is heated to 110 115 for an hour or more, or until it ceases to lose weight (see 29). Many bituminous coals gain weight after a time from oxidation of sul- phides or hydi o- carbons (WHITNEY). According to HINRICHS,* drying the coal for one hour effects the maximum loss. I). Coke and volatile matters. The dried coal of a is sharply heated in a closed platinum, or, in presence of sulphides, in a porcelain crucible as long as combustible matters issue from it. It is then cooled quickly. The loss is set down as volatile matters. The residue, less the ash, is coke. c. Ash. The residue of b is incinerated in a crucible placed aslant. d. Carbon and hydrogen are determined by combustion with chromato of lead and bichromate of potash, 177. e. Nitrogen is estimated according to 185. /'. /Sulphur is determined as directed 219, c. p. 515, but the evapora- tion with hydrochloric acid is omitted, and the sulphate of baryta, after decanting the supernatant liquid upon a filter, is boiled up two or three times with dilute solution of acetate of ammonia, to free it from adhering salts. STOKER AND PEARSON.] * Chemical News, 19, 282. III. ANALYSIS OF ATMOSPHERIC AIR. 240. JN the analysis of atmospheric air we usually confine our attention to t\ e following constituents : oxygen, nitrogen, carbonic acid, and aqueous vapor. It is only in exceptional cases that the exceedingly minute quan- tities of ammonia and other gases many of which may be assumed to be always present in infinitesimal traces are also determined. It does not come within the scope of the present work to describe all the methods which have been employed in the capital investigations made in the last few years by BRUNNER, BUNSEN, DUMAS and BOUSSIN- GAULT, REGNAULT and REISET, and others. To these methods we are indebted for a more accurate knowledge of the composition of our atmo- sphere, and excellent descriptions of them will be found in the works below.* I confine myself to those methods which are found most convenient in the analysis of the air for medical or technical purposes. A. DETERMINATION OF THE WATER AND CARBONIC ACID. It was formerly the custom to effect these determinations by BRUNXER'S method, which consisted in slowly drawing, by means of an aspirator, a measured volume of air through accurately weighed apparatuses filled with substances having the property of retaining the aqueous vapor and the carbonic acid, and estimating these two constituents by the increased weights of the apparatuses. Fig. 102 represents the arrangement recommended by REGNAULT. The vessel V is made of galvanized iron, or of sheet zinc ; it holds from 50 to 100 litres, and stands upon a strong tripod in a trough large enough to hold the whole of the water that V contains. At a a brass tube c, with stopcock, is firmly fixed in with cement. Into the aperture 6, which serves also to fill the apparatus, a thermometer reaching down to the middle of V is fixed air-tight by means of a perforated cork soaked in wax. The efflux tube, r, which is provided with a cock, is bent slightly up- ward, to guard against the least chance of air entering the vessel from below. The capacity of the vessel is ascertained by filling it completely with water, and then accurately measuring the contents in graduated vessels. The end of the tube c is connected air-tight with F, by means of a caoutchouc tube ; the tubes A F are similarly connected with one another. A, 1$, E, and F are filled with small pieces of glass moistened * Ausf iihrliches Handbuch der analytischen Ohemie von H. Rose, II. 853 ; Graham -Otto's ausfiihrliches Lehrbuch .der Chemie, Bd. II. Abth. 1, S. 102etseg.; Handw' rterbuch der Chemie von Liebig, Poggendorff und Wuhler, 2 Aufl. Bd. II. S. 431 ct seq. ; and Bunsen's Grasometry. 554 SPECIAL PART. 241. with pure concentrated sulphuric acid, C and D with moist hydrate of linie,* Finally, A is also connected with a long tube leading to the Fig. 102. place from which the air intended for analysis is to be taken. The corks of the tubes are coated over with sealing-wax. The tubes A and J? are intended to withdraw the moisture from the air ; they are weighed to- gether. C, D, and E are also weighed jointly. C and D absorb the carbonic acid ; E the aqueous vapor which may have been withdrawn from the hydrate of lime by the dry air. F need not be weighed ; it simply serves to protect E against the entrance of aqueous vapor from V. The aspirator is completely filled with water ; c is then connected with F) and thus with the entire system of tubes ; the cock r is opened a little, just sufficiently to cause a slow efflux of water. As the height of the column of water in T^is continually diminishing, the cock must from time to time be opened a little wider, to maintain as nearly as possible a uniform flow of water. When V is completely emptied, the height of the thermometer and that of the barometer are noted, and the tubes A and _Z?, and (7, 2), and E weighed again. As the increase of weight of A and JB gives the amount of water, that of (7, D, and E, the amount of carbonic acid, in the air which has passed through them ; and as the volume of the latter (freed from water and carbonic acid) is accurately known from the ascertained capacity * With regard to C and D, I have returned to lime, preferring it to pumice saturated with solution of potash, because, as Hlasiwetz (Chem. Centralbl. 1856, 575) has shown, the solution of potash absorbs not only carbonic acid, but also oxygen. Indeed, H. Rose had previously made a similar observation. With re- spect to the other tubes, I prefer the concentrated sulphuric acid to chloride of calcium as the absorbent for water (see Pettenkof er, Sitzungsber. der bayer. Akad. 1862, II. Heft 1, S. 59). Hlasiwetz's statement, that concentrated sulphuric acid also takes up carbonic acid, I have found to be unwarranted. Chloride of calcium does not dry the air completely, and, besides, Hlasiwetz says that when it is used a trace of chlorine is carried away corresponding to the amount of ozone in the air (op. cit. p. 517). 241.] ANALYSIS OF ATMOSPHERIC AIR. 555 of V: * the calculation is in itself very simple ; but it involves, at least in very accurate analyses, the following corrections : a. Reduction of the air in J 7 ", which is saturated with aqueous vapor, to dry air ; since the air which penetrates through c is dry (see 195, -/). (3. Reduction of the volume of dry air so found to 0, and 700 mm. ( 195, , and 0). When these calculations have been made, the weight of the air which has penetrated into V is readily found from the datum in Table "V. at the end of the volume ; and as the carbonic acid and water have aLso been weighed, the respective quantities of these constituents of the aii may now be expressed in per-cents by weight, or, calculating the weights into volumes, in per-cents by measure. Considering the great weight and size of the absorption apparatus, in comparison to the increase of weight by the process, at least 25,000 c. c. of air must be passed through ; the air inside the balance-case must be kept as dry as possible by means of a sufficient quantity of chloride of calcium, and the apparatus left for some time in the balance-case, before proceeding to weigh. Neglect of these measures would lead to considera-, ble errors, more particularly as regards the carbonic acid, the quantity of which in atmospheric air is, on an average, about 10 times less than that of the aqueous vapor (comp. HLASIWETZ, loc. cit.}. For the exact determination of the carbonic acid one of the following methods is far better suited : a. Process suggested by FR. MOHR, applied and carefully tested by H. v. GiLM.f VON GILM employed in his experiments an aspirator holding afc least 30 litres, which was arranged like that shown in "fig. 102, but had a third aperture, bearing a small manometer. The air was drawn through a tube, 1 metre long, and about 15 mm. wide; this tube was drawn out thin at the upper end, and at the lower end bent at an angle of 140 150. It was more than half filled with coarse fragments of glass and perfectly clear baryta water, and fixed in such a position that the long part of it was inclined at an angle of 8 10 to the horizontal. A narrow glass tube, fitted into the undrawn-out end of the tube by means of a cork, served to admit the air. Two small flasks, filled with baryta water, were placed between the absorption tube and the aspira- tor ; these were intended as a control, to show that the whole of the carbonic acid had been retained. When about 60 litres of air had slowly passed through the absorption tube, the carbonate of baryta formed was filtered off out of contact of air, and the tube as well as the contents of the filter washed, first with distilled water saturated with carbonate of baryta, then with pure boiled water. The carbonate of baryta in the filter and in the tube was then dissolved in dilute hydrochloric acid, the solution evaporated to dryness, the residue gently ignited, and the chlo- rine of the chloride of barium determined as directed 141, &, a. 1 eq. chlorine represents 1 eq. carbonic acid. It is obvious that one may also determine the baryta in the hydrochloric acid solution by precipitating with sulphuric acid. For filtering the carbonate of baryta, v. GILM em- ployed a double funnel (fig. 103) ; the inner cork has, besides the per- * Or from the quantity of water which has flown from F", as the experiment may be altered in this way, that a portion only of the water is allowed to run out. and received in a measuring vessel. f Chem. Centralbl. 1857, 700. 556 SPECIAL PART. foratioii through which the neck of the funnel passes, a lateral slit, which establishes a communication between the air in the outer funnel and the air in the bottle. As, with the absorption apparatus arranged as de- scribed, the air has to force its way through a column of fluid, the manometer is required to determine the actual volume of the air ; the height indicated by this instrument being deducted from the barometric pres- sure observed during the process. FR. MOHR* now recommends as the absorbent fluid a solution of baryta in potash. This is prepared by dissolving crystals of baryta in weak solution of potash with the aid of heat, and filtering off the car- bonate of baryta, which invariably forms in small quantity. The clear filtrate is accordingly saturated with carbonate of baryta. MOHR now leaves out the fragments of glass. This method afforded v. GILM very harmonious Fig. 103. results. Nevertheless, it involves one source of error. If clear baryta water is passed through paper with the most careful possible exclusion of air, and the filter is washed till the washings are free from baryta, and dilute hydrochloric acid is then poured upon the filter, and the filtrate thus obtained is evaporated, a small quantity of chloride of barium will be left, showing that a little baryta was kept back by the paper. AL. MULLER f has already called attention to the capacity of filter paper for retaining baryta. b. M. PETTENKOFER'S process. J a. Principle and Requisites. A known volume of air is made to act upon a definite quantity of standard baryta water (standardized by oxalic acid solution), in such manner that the carbonic acid is completely bound by the baryta. The baryta water is then poured out into a cylinder, and allowed to deposit with exclusion of air, a part of the clear fluid is then removed, and the baryta remaining in solution is determin- ed. The difference between the oxalic acid required for a certain quan- tity of baryta water before and after the action of the air, represents the carbonate of baryta formed, and consequently the carbonic acid present. Two kinds of baryta water are used : one contains 21 grm. and the other 7 grm. crystallized hydrate of baryta || in the litre ; these serve for the determination of larger and smaller quantities of carbonic acid * Lehrbuch der Titrirmethode. 2d ed. 446. f Journ. f. prakt. Chein. 83, 384. j Abhandl. der naturw. u. techn. Commission der k. bayer. Akad. der Wiss. II 1 ; Ann. d. Chein. u. Pharm. II. Supplem. Bd. p. 1. ' I The hydrate of baryta must be entirely free from caustic potash, and soda, the smallest quantities of which render the volumetric estimation in the presence of carbonate of baryta impossible, since the neutral alkaline oxalates decompose the alkaline earthy carbonates. When a trace even of carbonate of baryta is suspended in the fluid and this is always the case when a baryta water which has been used for the absorption of carbonic acid is not filtered the reaction continues alkaline if the smallest trace of potash or soda is present, because the alkaline oxalate formed immediately enters into decomposition with the carbon- ate of baryta. A fresh addition of oxalic acid converts the alkaline carbonate again into oxalate, and the fluid is for a moment neutral, till, on shaking with 21.] ANALYSIS OF ATMOSPHERIC! AIR. 557 respectively. 1 c. c. of the stronger corresponds to about 3 mgrm. car bonic acid, of the weaker 1 c. c. corresponds to about 1 mgrm.* Tho oxalic acid solution which serves for standardizing the baryta water contains 2*8636 grm. cryst. oxalic acid in 1 litre. 1 c. c. corre- sponds to 1 mgrm. carbonic acid. The baryta water is standardized as follows : transfer 30 c. c. of it to a flask, and then run in the oxalic acid from a MOHR'S burette with float ; shake the fluid from time to time, closing the mouth of the flask with the thumb. The vanishing point of the alkaline reaction is ascertained with delicate turmeric paper, f As soon as a drop of the fluid placed on the paper does not give a brown ring, the end is attained. If you were obliged, in the first experiment, to take out too many drops for .testing with turmeric paper, consider the result as only approximate, and make a second experiment, adding at once the whole quantity of oxalic acid to within 1 or J c. c. and then beginning to test with paper. A third experiment would be found to agree with the second to yL c. c. The reaction is so sensitive that all foreign alkaline matter, particles of ash, tobacco smoke, &c., must be care- fully guarded against. j3. The actual Analysis. This may be effected in 'two different ways. aa. Take a perfectly dry bottle, of about 6 litres capacity, with well- fitting ground glass stopper, and accurately determine the capacity ; fill the bottle, by means of a pair of bellows, with the air to be analyzed ; add 45 c. c. of the dilute standard baryta water, and cause the baryta water to spread over the inner surface of the bottle, by turning the latter about, but without much shaking. In the course of about an hour the whole of the carbonic acid is absorbed. Pour the turbid baryta water into a cylinder, close securely, and allow to deposit ; then take out, by means of a pipette, 30 c. c. of the clear supernatant fluid, run in standard oxalic acid, multiply the volume used by 1'5 (as only 30 c. c. of the original 45 are employed in this experiment), and deduct the product from the c. c. of oxalic acid used for 45 c. c. of the fresh baryta water ; the difference represents the quantity of baryta converted into carbonate, and consequently the amount of the carbonic acid. If the air is unusually rich in carbonic acid, the concentrated baryta water is employed. bb. Pass the air through a tube or through two tubes containing measured quantities of standard baryta water and finish the experiment as in aa. For passing a definite quantity of air we should generally employ an aspirator (p. 554) ; PETTENKOFER in his experiments with the respi- ration apparatus forced the air by means of small mercurial pumps first air, the carbonic acid escapes, and any carbonate of baryta still present converts the alkaline oxalate again into carbonate. To test a baryta water for caustic alkali, determine the alkalinity of a perfectly clear portion, and then of a portion that has been mixed with a little pure precipitated carbonate of baryta. If you use more oxalic acid in the second than in the first experiment, caustic alkali is present, and some chloride of barium must be added to the baryta water before it can be used. * [The baryta water is kept in a bottle under a v thin stratum of kerosene (MoHR). It is drawn off through, a syphon supported in the stopper, the outer leg of which is recurved -upwards and closed with a bit of rubber tube and clip. By having this leg of the syphon sufficiently long the burette may be filled by inserting its delivery end in the rubber tube and opening both clips. ] f Prepared with lime-free Swedish filter paper, and tincture of turmeric. The spirit used in making the latter must be free from acid. Dry the paper in a dark room, and keep it protected from the light. It is lemon yellow. 558 SPECIAL FAR' 242. through the tubes, and then through an apparatus for measuring the gas. The form and arrangement of the tubes is illustrated by fig. ] 04. Two such tubes were used; the first was 1 metre, the second '3 metres long; they were filled with baryta water the former with the stronger solution, the latter with the weaker. The air is introduced through the short limbs of the tubes, and is carried beyond the bends by a narrow flexible tube, and the glass tubes themselves are so inclined that the bubbles of air move on with the necessary rapidity without uniting. The motion of the gas bubbles keeps up a constant mixing of the baryta water. B. DETERMINATION OF THE OXYGEN AND NITROGEN. 242. The method T shall give is that proposed by v. LIEBIG.* It is based upon the observation made by CHEVREUL and DOBEREINER, that pyro- gallic acid, in alkaline solutions, has a powerful tendency to absorb oxygen, * Annal. d. Chem. u. Pharm. 77, 107. ANALYSIS OF ATMOSPHERIC AIR. 559 1. A strong measuring tube, holding 30 c. c., and divided into -J. or -i c. c., is filled to f with the air intended for analysis. The remaining part of the tube is filled with mercury, and the tube is inverted over that fluid in a tall cylinder, widened at the top. 2. The volume of air confined is measured ( 12). If it is intended to determine the carbonic acid which can be done with sufficient accu- racy only if the quantity of the acid amounts to several per-cents the air is dried by the introduction of a ball of chloride of calcium before measuring. If it is not intended to determine the carbonic acid, this operation is omitted. A quantity of solution of potassa of 1'4 sp. gr. (1 part of dry hydrate of potassa to 2 parts of water), amounting to from -fa to -jpg. of the volume of the air, is then introduced into the measuring tube by means of a pipette with the point bent upwards (fig. 105), and spread over the entire inner surface of the tube by shaking the latter ; when no further diminution of volume takes place, the decrease is read off. If the air has been dried previously with chloride of calcium, the diminution of the volume expresses exactly the amount of carbonic acid contained in the air; but if it has not been dried with chloride T? . of calcium, the diminution in the volume cannot afford correct lg ' information as to the amount of the carbonic acid, since the strong solu- tion of potassa absorbs aqueous vapor. 3. When the carbonic acid has been removed, a sohition of pyrogallic acid, containing 1 grm. of the acid * in 5 or 6 c. c. of water, is introduced into the same measuring tube by means of another pipette, similar to the one used in 2 (fig. 105); the quantity of pyrogallic acid employed should be half the volume of the solution of potassa used in 2. The mixed fluid (the pyrogallic acid and solution of potassa) is spread over the inner surface of the tube by shaking the latter, and, when no further diminu- tion of volume is observed, the residuary nitrogen is measured. 4. The solution of pyrogallic acid mixing with the solution of potassa of course dilutes it, causing thus an error from the diminution of its tension; out this error is so trifling that it has no appreciable influence upon the results; it may, besides, be readily corrected, by introducing into the tube, after the absorption of the oxygen, a small piece of hydrate of potassa cor- responding to the amount of water in the solution of the pyrogallic acid. 5. There is another source of error in this method ; viz., on account of a portion of the fluid always adhering to the inner surface of the tube, the volume of the gas cannot be read off with absolute accuracy. In comparative analyses, the influence of this defect upon the results may be almost entirely neutralized, by taking nearly equal volumes of air in the several analyses. j- 6. Notwithstanding these sources of error, the results obtained by this method are very accurate and constant. In eleven analyses which v. LIEBIG reports, the greatest difference in the amount of oxygen found was between 20'75 and 21 '03. The numbers given express the actual and uncorrected results. * Liebig has described a very advantageous method of preparing pyrogallio acid. See Annal. d. Chem. u. Pharm. 101, 47. f Bunsen employs for the absorption of oxygen a papier-mache ball saturated with a concentrated alkaline solution of pyrogallate of potassa, which he intro- duces into the gaseous mixture attached to a platinum wire. By adopting this proceeding, the source of error mentioned in o is avoided. See also Russell. Jour Chem. Soc. 1868, pp. 130, 131. PART III. EXERCISES FOB PRACTICE. 36 EXERCISES FOR PRACTICE. THE principal point kept in view in the selection of these exercises has been that most of them, and more particularly the first, should permit an exact control of the results. This is of the utmost importance for students, since a well-grounded self-reliance is among the most indispen- sable requisites for a successful pursuit of quantitative investigations, and this is only to be attained by ascertaining for one's self how near the results found approach the truth. Now a rigorously accurate control is practicable only in the analysis of pure salts of known composition, or of mixtures composed of definite proportions of pure bodies. When the student has acquired, in the analysis of such substances, the necessary self-reliance, he may proceed to the analysis of minerals or products of industry in which such rigorous control is unattainable. The second point kept in view in the selection of these exercises, has been to make them comprise both the more important analytical methods and the most important bodies, so as to afford the student the oppor- tunity of acquiring a thorough knowledge of every branch of quantitative analysis. Organic analysis offers less variety than the analysis of inorganic sub- stances ; the exercises relating to the former branch are therefore less numerous than those relating to the latter. I would advise the student to analyze the same substance repeatedly, until the results are quite satisfactory. [It is a good habit always to carry on together duplicate analyses. It requires but little more time to make two analyses than to make one, and the operator's experience is thus very economically doubled.] It is by no means necessary for the student to go through the whole of these examples ; the time which he may require to attain proficiency in analysis depends, of course, upon his own abilities. One may be a good analyst without having tried every method, or determined every body. A few substances well analyzed yield more profit than can be obtained from going over many processes in a superficial manner. Finally, the student is warned against prematurely attempting to dis- cover new methods ; he should wait until he has attained a good degree of proficiency in general chemistry, and more particularly in practical analysis. EXERCISES. A. SIMPLE DETERMINATIONS IN THE GRAVIMETRIC WAY, INTENDED TO PERFECT THE STUDENT IN THE PRACTICE OF THE MORE COMMON ANALYTICAL OPERATIONS. [WE give here, in the first place, quite full details of all the steps in the estimation of chlorine in chloride of sodium, including the preparation of this salt in a state of purity. This, it is hoped, will relieve much of the perplexity which the beginner must at first experience in making out a scheme of operations from the various separate paragraphs where the processes are described. The student should not fail, however, to study carefully the chapter on operations while carrying on the analysis, nor to examine every reference. 1. CHLORIDE OF SODIUM. Preparation. Dissolve 150 grm. of clean crystallized carbonate of soda in hot water, place a small bit of litmus paper in the solution, add pure hydrochloric acid to acid reaction, and evaporate in a porcelain dish to dryness, whereby silica becomes insoluble. If the dry residue has a yellow tinge, which is due to iron, raise the heat somewhat until the residue is brown or black in color and no acid odor is perceptible when it is breathed on. This treatment converts soluble sesquichloride of iron into insoluble oxychloride. Dissolve the residue in hot water, filter, and evaporate the solution, contained in a beaker, at a temperature somewhat below the boiling point, until there remains a small quantity of liquid above the crystals of salt. Pour off this mother liquor, rinse the crystals repeatedly with small quantities (their own bulk) of cold water until the rinsings give but a very slight * reaction for sulphuric acid with chloride of barium. A portion f of the salt thus obtained is crushed to a coarse powder, heated in a covered crucible until it ceases to decrepitate, but not to fusion, and preserved in a weighing tube (like a small test tube, but not flared at the mouth) that is closed with a soft, well-fitting, and smooth cork. ESTIMATION OF CHLORINE. 1. Weighing ^ out the substance. The tube containing the prepared salt is wiped, if need be, from dust. The cork is taken out, and by means of a bit of thin paper, or a clean linen handkerchief, any particles * It is not needful for ordinary quantitative purposes that a salt should be so free from foreign matters that the latter cannot be detected by sensitive re- agents, and for the reason that it is not possible to collect and weigh the minute traces which are thus indicated. f Pure chloride of sodium is needed in other analyses, and the chief part of what is thus prepared should be carefully bottled and reserved for future use. EXERCISES FOR PRACTICE. 565 of salt adhering to the cork, and to the inside of the tube as far as the cork reaches, are removed. The cork is replaced, and the whole is weighed (see 9 and 10), the weight being immediately recorded in the note-book. A clean beaker or assay-flask, of about 200 c. c. capacity, being ready, the weighing-tube is held over it and the cork carefully removed. A portion of substance is allowed to fall in the vessel, and, the cork being replaced, the tube is again counterpoised. If two to three decigrammes have been emptied, the operator is ready to proceed. If less, more should be transferred from the tube to the vessel. If more, or much more, it is better to begin anew, by weighing off another portion into another beaker or flask. In this manner weigh off two portions in separate vessels, so as to carry together duplicate analyses. Now affix a piece of gummed paper to each vessel, and label them to correspond with their designation in the note-book. 2. Solution and precipitation. Dissolve the weighed portions, each in about 100 c. c. of cold distilled water, add a few drops of pure nitric acid, and, lastly, clear solution of nitrate of silver * until further addition no longer produces a precipitate. Agitate the mixture well, but with care to avoid loss. This can be done by shaking, if a flask be in use, or by stirring with a glass rod, if a beaker be employed. Set the vessel aside in a dark place, covered with paper or a watch- glass to exclude dust, and let stand for about 12 hours, or until the precipitate has subsided and the liquid above it is perfectly clear, then add a drop of nitrate of silver to make sure that the precipitation is com- plete (if not complete, add more solution of silver, and let stand again for some hours). 3. Filtration. A filter is placed in a funnel at least \ inch deeper than itself, and moistened with water, at the same time being carefully pressed down so that its edges touch the glass at all points. The funnel being supported on a stand, a clean beaker or flask is put beneath it, and the operator proceeds to pour the liquid on whose surface some particles of chloride of silver usually float into the filter, leaving the bulk of the precipitate undisturbed. To do this without loss the following precau- tions may be regarded : a. Touch the edge or lip of the vessel with a very slight coat of tallow (a small bit of which is kept at hand under the edge of the work-table, and is applied with the finger), b. Pour slowly over the greased place, along a glass rod held nearly vertical, so directing the stream that it shall strike against the side, not into the vertex of the filter, c. When the filter is filled to within J inch of the top discontinue the pouring, bringing the rod into the vessel containing the precipitate, after it has drained so that nothing will fall from it. The pouring-rod may be simply straight, and an inch longer than the diagonal of the vessel, or, when it is desirable not to disturb a precipitate, it may be 3 4 inches long and bent syphon fashion so as to hang on the edge of a beaker or flask. In either case its end should be rounded by fusion, and those portions along which the liquid flows must not be handled. The vessel containing the precipitate, as well as that which receives the filtrate, and likewise the funnel, should be kept covered as much as * Solution of a silver coin in nitric acid answers for this purpose as well as pure nitrate, provided it be clear and contain but little free acid. 566 EXERCISES FOR PRACTICE. possible in all cases when nicety is required, to prevent access of dust, insects, &c. The most convenient covers are large watch-glasses, but square plates of glass, or even cards, will generally answer. The receiving- vessel may also be protected by employing the filter-stand represented in fig. 34, p. 57. The nitration of chloride of silver should be conducted without expos- ing it to strong light, whereby it is blackened, with loss of chlorine, p. 208. d. When all, or nearly all, the liquid has passed the filter, it remains to wash and to transfer the precipitate. These operations may be carried on as follows: pour about 100 c. c. of cold distilled water upon the precipitate, which mostly remains in the vessel where it was formed, and agitate vigorously, in order to break up and divide the lumpy chloride of silver, and bring every part of it per- fectly in contact with the water. When in a beaker, the agitation must be made with great caution, by means of a glass stirring-rod ; when in a narrow-mouthed flanged flask, this may be tightly closed by a perfectly smooth cork (softened for the purpose by squeezing) and then shaken violently. The water and precipitate are now poured together upon the filter, with the precautions before detailed. The last portions of the precipitate are removed from the beaker or flask by repeated rinsings, in which a wash-bottle like fig. 36, p. 59, may be conveniently employed. Any portions of precipitate that adhere to the sides of the vessel too strongly to be removed by a stream from the wash-bottle must be rubbed off. For this purpose the feather is employed. It is made from a goose-quill, by cutting off the extreme tip for an inch or so, and smoothly trimming away the beard, except a portion of one half -inch in length on the inside of the curve. The tubular part may be removed or not, to suit the depth of the dish which is to be washed. The dish being wiped clean, externally, a little water is put in it, and, it being held up to the light, its whole interior surface is gently rubbed with the feather, then rinsed, rubbed again and rinsed, so long as careful inspection discovers any portions of adhering precipitate ; finally, the feather is rinsed in a stream of water, the rinsings in each case being poured upon the filter. The washing is now continued by help of the wash-bottle. A jet of cold water is directed, first, upon the interior of the funnel, just above the filter, then upon the edge of the filter itself. If thrown immediately against the paper, this is liable to be perforated. The stream of water is carried around the edge of the filter until the latter is nearly full, and the liquid is then allowed to drain off. This process is repeated until a portion of the wash-waters, collected to the depth of an inch in a test tube containing a drop of hydrochloric acid, give no turbidity of chlo- ride of silver. When this is accomplished, the precipitate is washed down into the vertex of the filter. The funnel is then closely covered with paper (p. 62), labelled, allowed to drain thoroughly, and set away in a warm place for drying. ^ When the Bunsen pump is employed, read 53 c. p. 77, and follow the directions on page 72, bottom; as to washing, see pp. 67 and 68. 5. Drying the filter. In public laboratories a heated closet is usually provided for drying filters. Its temperature should not exceed 100 0, EXERCISES FOR PRACTICE. 567 In default of such special arrangement, the drying may be effected over the register of a hot-air furnace, or over a common stove or kitchen range. The funnel may also be supported on a retort-stand over a sheet of iron, which is heated beneath by a lamp, or may be placed at once in the water-bath. See pp. 62 and 79. 6. When the precipitate is perfectly dry we proceed to ignite it for weighing. A. small porcelain crucible (platinum must not be used) is cleaned, gently ignited, and when cool (after 15 20 minutes) weighed. The work-table being clean, two small sheets of fine and smooth writ- ing or glazed paper are opened and laid down side by side. The filter is removed from the funnel and carefully inverted upon one of the papers. The precipitate is loosened from the filter by squeezing and rubbing gently between the fingers, and when it has mostly separated the filter is lifted, reversed, and any portions of chloride of silver still adhering are loosened by rubbing its sides together. What is thus de- tached is poured or shaken out on the paper. The filter is now spread out as a half-circle upon the other sheet of paper, and, beginning with the straight edge, is folded up into a narrow flattened roll, the two ends of which are then brought together. In this way those central portions of the filter to which particles of precipitate adhere are thoroughly enveloped by the exterior parts, so that in the sub- sequent burning nothing can easily escape. The crucible being placed on the glazed paper, the filter is taken by the two free ends in a clean pincers or tongs, put to the flame of a lamp to set it on fire, and then held over the crucible until it is completely charred. It is then dropped into the crucible, and moistened with two or three drops of nitric acid. The crucible is covered and placed over a low flame until its contents are dry, it is then heated somewhat stronger, whereby the carbon is nearly or entirely consumed. The crucible being allowed to cool, one more drop of nitric acid, and afterwards a drop of hydrochloric acid, is added to the residue, and it is heated cautiously, without the cover, until fumes cease to escape. This treatment with nitric acid serves to destroy carbon and convert any reduced silver to nitrate, which the hydrochloric acid in turn transforms into chloride. When the crucible is cool, it is placed again on the paper, and the precipitate is poured into it from the other sheet, the last par- ticles being detached by cautious tapping with the fingers underneath, or by the use of a clean feather or camel's hair pencil. The crucible is now put over a low flame and heated cautiously until the chloride of silver begins to fuse on the edges. It is then covered and let cool. When cold it is weighed. Head 115, 1, and the references there made. 7. Record and calculation of results. The amount of chloride of silver is learned by subtracting from the total the joint weight of the crucible and filter-ash. The quantity of chlorine is obtained by multi- plving the amount of chloride of silver by the decimal 0*24724. In order to compare results they are reduced to per cent, statements by the following proportion : Substance : chlorine in substance :: 100 : chlorine in 100 ; i.e. per cent. The record may be made as follows : It is well to work out the calculations in full in the weight-book, as in case of mistake the data are at hand for revision. 568 EXERCISES FOR PRACTICE. No. 1. No. 2. NaClandtube .......................... 6-615 8-18C u u -substance ............... 6180 5'76o Substance ...................... '435 '415 Crucible, Ag Cl and Ash ...... 15'3630 14'3270 42540 40660 21270 20330 74445 71155 42540 40660 21270 20330 Cl = -262939740 -251319460 435) 26,29397 (60'44# '415) 25,13194 (60'56 2610 2490 ~~1939 2319 1740 2075 ~1997 2444 Found. Calculated. No. 1. No. 2. Chlorine 60'44 60'56 60'66 We have here employed the simplest arithmetical calculation. It is well to duplicate the calculation with help of the tables given in the Appendix. See pp. 462-4. The first determination given above is not only fair for this method, but answers all ordinary purposes. The second is very good, though with care still closer accordance with theory can be easily attained.] 2. IRON. Procure 10 15 grms. of fine bright pianoforte wire, cut it into lengths of about 0*3 grm. and keep it free from rust in a dry bottle. Weigh, on a watch-glass, for each estimation, about 0'3 grm. of wire, and dissolve in hydrochloric acid, with addition of nitric acid. The acids are diluted with a little water. The solution is effected by heating in a moderate-sized beaker covered with a watch-glass. When complete solution has ensued, and the color of the fluid shows that all the iron is dissolved as sesquioxide (if this is not the case some more nitric acid must be added), rinse the watch-glass, dilute the fluid to about 150 c. c., heat to incipient ebullition, add ammonia in moderate excess, filter through a filter exhausted with hydro- chloric acid, &c. (Comp. 113, 1, a.) If BUNSEN'S methods are em- ployed, proceed exactly as described on pp. 72, 73, and 77. As the sesquioxide of iron generally contains a small quantity of silicic acid (partially arising from the silicon in the wire, partially taken up from the glass vessels), after it is weighed, digest with fuming hydro- chloric acid for some hours ; when the oxide of iron is all dissolved, dilute, collect the silica on a small filter, ignite and weigh. The weight is the silica -f the ashes of both filters. EXERCISES FOR PRACTICE. 569 The records are made as follows : Watch-glass -f iron 10-3192 empty 9-9750 Iron -3442 Crucible -f sesquioxide of iron -f silica -f filter ash . . 17*0703 " empty 16-5761 4942 Ash of large filter -0008 Sesquioxide of iron -f silica *4934 Crucible + silica -f- ashes of both filters 16*5809 " empty 16.5761 0048 Ashes of the filters -0014 Silica -0034 4934 -0034 = -4900 sesquioxide of iron = '343 iron which gives 99 '65 per cent. 3. ACETATE OF LEAD. Determination of Oxide of Lead. Triturate the dry and non-efflo- resced crystals * in a porcelain mortar, and press the powder between sheets of blotting paper until fresh sheets are no longer moistened by it. a. Weigh about 1 grm., dissolve in water, with addition of a few drops of acetic acid, and proceed exactly as directed 116, 1, a. b. Weigh about 1 grm., and proceed exactly as directed 116, 5. PbO 111-50 58-84 A 51-00 26-91 3aq 27-00 14-25 189-50 100-00 4. POTASH ALUM. Determination of Alumina. Press pure triturated potash alum be- tween sheets of blotting paper ; weigh off about 2 grm., dissolve in water, and determine the alumina as directed 105, a. KO 47-11 9-93 Al,0 3 51-50 10-85 4SO 3 160-00 33-71 24 HO.. 216-00 45-51 474-61 100-00 * Obtained by dissolving the pulverized commercial salt in hot water nearly to- saturation, filtering, adding a drop or two of acetic acid to the solution, and slowly evaporating to crystallization. 570 EXEKCISES FOR PRACTICE. 5. BICHROMATE OF POTASH. Determination of Chromium. Fuse pure bichromate of potash at a gentle heat, weigh'off '4 '6 grrn., dissolve in water, reduce with hydro- chloric acid and spirit of wine, and proceed as directed 1 30, I., a, a. KO 47-11 31-92 2CrO 3 100-48 68-08 147-59 100-00 6. ARSENIOUS ACID. Dissolve about 0*2 grm. pure arsenious acid in small lumps in a middle-sized flask, with a glass stopper, in some solution of soda, by digesting on the water-bath ; dilute with a little water, add hydrochloric acid in excess, and then nearly fill the flask with clear sulphuretted hydrogen water. Insert the stopper and shake. If the sulphuretted hydrogen is present in excess, the precipitation is terminated ; if not, conduct an excess of sulphuretted hydrogen gas into the fluid ; proceed in all other respects exactly as directed 127, 4. As 75 75-76 O 3 24 24-24 99 100-00 B. COMPLETE ANALYSIS OF SALTS IN THE GRAVIMETRIC WAY; CALCULATION OF THE FORMULAE FROM THE RESULTS OBTAINED. ( 202, 203.) 7. CARBONATE OF LIME. Heat pure carbonate of lime in powder (no matter whether Iceland spar or the artificially prepared substance, see " Qual. Anal.," Am. Ed., p. 83) gently in a platinum crucible. a. Determination of Lime. Dissolve in a covered beaker, about 1 grrn. in dilute hydrochloric acid, heat gently until the carbonic acid is completely expelled, and determine the lime as directed 103, 2, b, a. b. Determination of Carbonic Acid. Determine in about 0"8 grm. the carbonic acid after 139, II., d, cc. CaO 28 56-00 CO 2 22 44-00 50 100-00 8. SULPHATE OF COPPER. Triturate the pure crystals * in a porcelain mortar, and press the powder between sheets of blotting paper. * [Boil a solution of commercial blue vitriol with a little pure binoxide of lead (see " Qual. Anal.," Am. Ed., p. 58), to sesquioxidize the iron, then with a little carbonate of baryta, to precipitate it, filter and crystallize H WURTZ Am, Jour. (2), XXVI. 367.] EXERCISES FOR PRACTICE. 571 a. Determination of Water of Crystallization. 1. Weigh off in a 2ru3ible 1 2 grm. of the salt, and, having first heated the air-bath (Fig. 22, p. 39) so that the thermometer stands steadily at 120 140, intro- duce the crucible, uncovered, and maintain the heat for two hours. Then cool the crucible in a desiccator and weigh. Heat again as before, for an hour, and weigh. If need be, repeat the heating until no more loss occurs. The loss expresses the amount of water expelled at the temperature of 140, or four equivalents. 2. Raise the temperature of the air-bath to between 250 260 and proceed as before. The loss is the one equivalent of strongly combined water of crystallization, or, as some term it, water of halhydration. b. Determination of Sulphuric Acid. In another portion of the sul- phate of copper (about 1*5 grm.) determine the sulphuric acid according to 132, I., 1. d. Determination of Oxide of Copper. In about 1'5 grm. determine the oxide of copper as directed 119, 1, a, a. CuO 3970 31-83 S0 3 40-00 32-08 HO 9-00 7-22 4aq 36-00 28-87 124-70 100-00 9. CRYSTALLIZED PHOSPHATE OF SODA. a. Determination of the Water of Crystallization. Heat about 1 grm. of the pure uneffloresced salt in a platinum crucible, slowly and moderately, first in the water-bath, then in the air-bath, and finally some distance above the lamp (not to visible redness) ; the loss of weight gives the amount of water of crystallization. b. Determination of the Water of Constitution. Ignite the residue of a. c. Determination of Phosphoric Acid. a. Treat 1-52 grm. of the salt as directed 134, b, a. |3. Treat about 1 grm. of the salt after 134, c. 7. Treat about 0-2 grm. of the salt as directed 134, 6, |3. I recommend the student to perform the determination by each of these methods, as they are all in common use in the analytical labora- tory. d. Determination of Soda. Treat about 1'5 grm. of the salt according to 135, a, a. After the excess of lead has been separated with hydro- sulphuric acid, the fluid is to be evaporated to dryness and weighed in a platinum dish ; comp. 69, b, and 98, 2. P0 6 71-00 19-83 2NaO 62-00 17'32 HO 9-00 2-51 24aq 216-00 60-34 358-00 100-00 10. CHLORIDE OF SILVER. Ignite pure fused chloride of silver in a stream of pure dry hydrogen 572 EXERCISES FOR PRACTICE. till complete decomposition is effected, and weigh the silver obtained. The ignition may be performed in a light bulb tube, or in a porcelain boat in a glass tube, or in a porcelain crucible with perforated cover ( H5, 4). The chlorine may be in this case estimated by difference ; if you want to determine it directly, proceed as directed 141, II., b. Ag 107-97 75-28 Cl . , 35-46 24-72 143-43 100-00 11. SULPHIDE OF MERCURY. Reduce to a fine powder, and dry at 100. a. Determination of Sulphur. Treat about 0'5 grm., as directed 148, /?, p. 326, using nitric acid and chlorate of potassa. Precipitate with chloride of barium, and after decanting the clear liquid into a filter, boil the sulphate of baryta twice with dilute solution of acetate of ammonia, and finally wash with hot water. b. determination of Mercury. Dissolve about 0'5 grm. as before, dilute, and allow to stand in a moderately warm place until the smell of chlorine has nearly gone off; filter if necessary, add ammonia in excess, heat gently for some time, add hydrochloric acid until the white pre- cipitate of chloride of mercury and amide of mercury is redissolved, and treat the solution, which now no longer smells of chlorine, as directed H8, 3. Hg 100.00 86-21 S 16-00 13-79 116-00 100-00 12. CRYSTALLIZED SULPHATE OF LIME. Select clean and pure crystals of selenite, triturate, and dry under the desiccator ( 27). a. Determination of Water. After 35, a, a. b. Determination of Sulphuric Acid and Lime ( 132, II., b, a). CaO 28 32-56 S0 3 40 46-51 2aq 18 20-93 86 100-00 C. SEPARATION OF TWO BASES OR TWO ACIDS FROM EACH OTHER, AND DETERMINATIONS IN THE VOLUMETRIC WAY. 13. SEPARATION OF IRON FROM MANGANESE. Dissolve in hydrochloric acid about 0'2 grm. fine pianoforte wire, and about the same quantity of ignited protosesquioxide of manganese (pre- pared as directed 109, 1 a); heat with a little nitric acid, and separate the two metals by means of acetate of soda (p. 363, 70). Determine the manganese as directed 109, 3. EXERCISES FOE PRACTICE. 573 1 4. VOLUMETRIC DETERMINATION OF IRON BY SOLUTION OF PERMANGANATE OF POTASSA. a. Graduation of the Solution of Permanganate of Potassa. a. By metallic iron (fine piano wire). 0'2 grm. to be dissolved it dilute sulphuric acid (p. 194). Use the iron wire, a portion of which has been analyzed in Exercise 2, and correct for impurities accordingly. /3. By oxalate of ammonia. 0*2 0*3 grm. to be weighed off (p. 196). b. Determination of the Protoxide of Iron in double Sulphate of Protoxide of Iron and Ammonia. a. In solution acidified with sulphuric acid (p. 197, /3). |3. In solution acidified with hydrochloric acid (p. 198, note). The formula requires 18-37 per cent, of Fe O. c. Determination of the Iron in a Limonite. Powder finely, dry at 100, weigh off 2 grm., heat with strong hydro- chloric acid till the sesquioxide of iron is completely dissolved, dilute, filter, make the solution up to 200 c. c., and mix. In 20 c. c. of this so- lution determine the iron after 113, 3, a, p. 203. Reserve half of the solution for the next exercise (see also p. 524). 15. VOLUMETRIC DETERMINATION OF IRON WITH HYPOSULPHITE OF SODA. a. Graduation of the /Solution of Hyposulphite of Soda. a. By solution of sesquichloride of iron (p. 204). j3. By ammonia-iron-alum (p. 204). b. Determination of Iron in Limonite. Use 20 c. c. of the solution obtained in Exercise 14, c., after making sure that the iron all exists in the state of sesquioxide (see p. 192, 1, a.) 16. DETERMINATION OF NITRIC ACID IN NITRATE OF POTASSA. Heat pure nitre, not to fusion, and transfer it to a tube provided with a cork. a. Treat 0'5 grm. as directed p. 329, /?. b. In 0*2 to '3 grm., estimate nitric acid according to p. 330, d, a. K 47-11 46-59 NO 6 54-00 53-41 101-11 100-00 17. SEPARATION OF MAGNESIA FROM SODA. Dissolve about 0*4 grm. pure recently ignited magnesia * and about 0'5 grm. pure well-dried chloride of sodium in dilute hydrochloric acid * This may be prepared according to 19, p. 345. 574 EXERCISES FOR PRACTICE. (avoiding a large excess), and separate with oxalic acid, after p. 345, 16, 18. SEPARATION OF POTASH FROM SODA. Triturate crystallized tartrate of potassa and soda (Rochelle salt), press between blotting paper, weigh oft' about 1'5 grm., heat in a plati- num crucible, gently at first, then for some time to gentle ignition. The carbonaceous residue is first extracted with water, finally with dilute hydrochloric acid, the acid fluid is evaporated in a weighed platinum dish, and the chlorides are weighed together ( 97, 3). Then separate them by bichloride of platinum (p. 339, 1), and calculate from the results the quantities of soda and potassa severally contained in the Rochelle salt. KO 47-11 16-70 NaO 31-00 10-99 C 8 H 4 O 10 132-00 46-79 8 aq 72-00 25*52 282-11 100-00 19. VOLUMETRIC DETERMINATION OF CHLORINE IN CHLORIDES. a. Preparation and examination of the solution of nitrate of silver ( 141. L, b. a). b. Indirect determination of the soda and potassa in Rochelle salt, by volumetric estimation of the chlorine in the alkaline chlorides prepared as in No. 18. For calculation, see 197, a (p. 465). 20. SEPARATION OF ZINC FROM CADMIUM. Dissolve in hydrochloric acid about 0'4 grm. of pure oxide of cad- mium, and about the same quantity of pure oxide of zinc, both recently ignited, and separate the metals as directed p. 376, 95. 21. ACIDIMETRY. a. Preparation of standard sulphuric acid and solution of soda. ( 204, a.) pp. 490-493. b. Determination of acid in hydrochloric acid, by the specific gravity (p. 487). c. Determination of acid in the same hydrochloric acid, by an alkaline fluid of known strength (p. 494). d. Determination of acid in colored vinegar, by saturation with a standard alkaline solution. (Application of test papers, p. 496. /?.) e. Preparation of an ammoniacal solution of sulphate of copper ( 205) ; determination of its strength by normal sulphuric acid ; estimation of the acid in the hydrochloric acid used in c and d, by means of the cop- per solution ; in this latter process the student may also add to the hydrochloric acid some neutral sulphate of zinc. 22. ALKALIMETRY. a. Preparation of the test acid -after DESCROIZILLES and GAY-Lussi ( 207). EXERCISES FOR PRACTICE. 575 b. Valuation of a soda-ash after expulsion of the water by gentle ignition. a. After DESCROIZILLES and GAY-LUSSAC (p. 499). Q. After MOHR (p. 500). 23. DETERMINATION OF AMMONIA. Treat about 0'8 grm. chloride of ammonium as directed 99, 3, a. NH 4 CL. 18-00... 33-67 NH 2 .... 17-00... 31-80 Cl 35-46... 66-33 HC1 36-46... 68-20 53-46 100-00 53-46 100-00 24. SEPARATION OF IODINE FROM CHLORINE. Dissolve about 0'5 grm. pure iodide of potassium and about 2 3 grm. pure chloride of sodium to 250 c. c., and determine the iodine and chlorine : a. In 50 c. c., after 169, 2, a (203). Calculation 198, c. b. In 50 c. c., after 169, 2, b (204). c. In 10 c. c., after 169, 2, c (205). D. ANALYSIS OF ALLOYS, MINERALS, INDUSTRIAL PRO- DUCTS, ETC., IN THE GRAVIMETRIC AND VOLUMETRIC WAY. 25. ANALYSIS OF BRASS. Brass consists of from 25 to 35 per cent, of zinc and from 75 to 65 per cent, of copper. It also contains usually small quantities of tin and lead, and occasionally traces of iron. Dissolve about 20 grm. in nitric acid, evaporate on the water-bath to dryness, moisten the residue with nitric acid, add some water, warm, dilute still further, and filter off any residual binoxide of tin ( 126, 1, a). Add to the filtrate, or, if the quantity of tin is very inconsidera- ble, directly to the solution, about 20 c. c. dilute sulphuric acid ; evapo- rate to dryness on the water-bath, add 50 c. c. water, and apply heat. If a residue remains (sulphate of lead), filter it off, and treat it as directed 116, 3. In the filtrate, separate the copper from the zinc by hyposulphite of soda (p. 377, 99). If the quantity of iron present can be determined, determine it in the weighed oxide of zinc ( 160). 26. ANALYSIS OF SOLDER (TIN AND LEAD). Introduce about 1'5 grm. of the alloy, cut into small pieces, into a flask, treat it with nitric acid, and proceed as directed p. 391, 133, to effect the separation and estimation of the tin. Mix the filtrate in a porcelain dish with pure dilute sulphuric acid, evaporate the nitric acid on the water bath, and proceed with the sul- phate of lead obtained as directed 116, 3. Test the fluid filtered from the sulphate of lead with sulphuretted hydrogen and sulphide of ammo- nium for the other metals which the alloy might contain besides tin 576 EXERCISES FOR PRACTICE. and lead. The binoxide of tin may contain small quantities of iron or copper ; it is tested for these by fusion with carbonate of soda and sul- phur (p. 389, /?). 27. ANALYSIS OF A DOLOMITE. See 221. 28. ANALYSIS OF FELSPAR. a. Decomposition by carbonate of soda ( 140, II., b.) ; removal of the silicic acid ; precipitation of the alumina together with the small quantity of sesquioxide of iron by ammonia (in platinum or Berlin porcelain, not in glass vessels) after 161, 3 (88); separation of baryta, if present, from the filtrate with dilute sulphuric acid, and then of lime with ox- alate of ammonia, 154 (23). Finally, separation of the alumina from the sesquioxide of iron generally present in small quantity ( 1GO). b. Decomposition by SMITH'S method, p. 303. Separate the alka- lies after 152, 1. c. Determined loss by ignition. 29. ASSAY OF A CALAMINE OR SMITHSONITE. After 228. Volumetric determination of the zinc. 30. ANALYSIS OF GALENA. a. Determination of the sulphur, lead, iron, &c., as directed 225. 1. Determination of the silver after 226. 31. VALUATION OF CHLORIDE OF LIME ( 211). a. After PENOT (p. 505). b. After BUNSEN (p. 508). The solutions to be prepared and the separated iodine to be determined as directed 146 (p. 314). 32. VALUATION OF MANGANESE ( 214). a. After FRESENIUS and WILL (p. 509). 6. After BUNSEN (p. 512). c. By means of iron (p. 512). 33. ANALYSIS OP GUNPOWDER. After (p. 514). E. DETERMINATION OF THE SOLUBILITY OF SALTS. 34. DETERMINATION OF THE DEGREE OF SOLUBILITY OF COMMON SALT. a. At boiling heat. Dissolve perfectly pure pulverized chloride of sodium in distilled water, in a flask ? heat to boiling, and keep in ebulli- EXERCISES FOR PRACTICE. 577 tion until part of the dissolved salt separates. Filter the fluid now with the greatest expedition, through a funnel surrounded with boiling water and covered with a glass plate, into an accurately tared capacious mea- suring flask. As soon as about 100 c. c. of fluid have passed into the flask, insert the cork, allow to cool, and weigh. Fill the flask now up TO the mark with water, and determine the salt in an aliquot portion of the fluid, by evaporating in a platinum dish (best with addition of some ch] oride of ammonium, which will, in some measure, prevent decrepita- tion) ; or by determining the chlorine ( 141). 6. At 14. Allow the boiling saturated solution to cool down to this temperature with frequent shaking, and then proceed as in a. 100 parts of water dissolve at 109 '7 40'35 of chloride of sodium. 100 " 14 .... 35-87 " 35. DETERMINATION OF THE DEGREE OF SOLUBILITY OF SULPHATE OF LIME. .7. At 100. 6. At 12. Digest pure pulverized sulphate of lime for some time with water, in the last stage of the process at 40 50 (at which temperature sulphate of lime is most soluble) ; shake the mixture frequently during the pro- cess. Decant the clear solution, together with a little of the precipi- tate, into two flasks, and boil the fluid in one of them for some time ; allow that in the other to cool down to 12, with frequent shaking, and let it stand for some time at that temperature. Then filter both solutions, weigh the filtrates, and determine the amount of sulphate of lime respectively contained in them, by evaporating and igniting the residues. 100 parts of water dissolve at 100 .... '2 17 of anhydrous sulphate of lime. 100 " " 12 .. . 0-233 u " F. DETERMINATION OF THE SOLUBILITY OF GASES IN FLUIDS, AND ANALYSIS OF GASEOUS MIXTURES. 36. DETERMINATION OF THE ABSORPTION-COEFFICIENT OF SULPHUROUS ACID. See Annal. d. Chem. u. Pharm., vol. 95, page 1 ; also 131, 2. 37. ANALYSIS OF ATMOSPHERIC AIR. See 240242. G. ORGANIC ANALYSIS AND DETERMINATIONS OF THE EQUIVALENTS OF ORGANIC BODIES ; ALSO ANALYSES IN WHICH ORGANIC ANALYSIS IS APPLIED. 38. ANALYSIS OF TARTARIC ACID. Select clean and white crystals. Powder and dry at 100. s a. Burn with oxide of copper ( 174175). 37 578 EXERCISES FOE PRACTICE. b. Burn with oxide of copper and finish with oxygen gas ( 176). c. Burn in oxygen ( 178). C 8 48 32 H 6 6 4 12 96 64 150 100 39. DETERMINATION OF THE NITROGEN IN CRYSTALLIZED FERROCYANIDE OF POTASSIUM. Triturate the perfectly pure crystals, dry the powder in the desiccator ( 27), and determine the nitrogen as directed 185. The formula re- quL^s 19 "87 per cent, of nitrogen. 40. ANALYSIS OF URIC ACID (or any other perfectly pure organie compound of carbon, hydrogen, oxygen, and nitrogen). Dry pure uric acid at 100. a. Determination of the carbon and hydrogen ( 183). b. Determination of the nitrogen, a. After 185. 8. After DUMAS ( 184). C 5 30 35-71 N 2 28 33-33 H 2 2 2-38 O 3 24 28-58 84 100-00 41. ANALYSIS OF A SUPERPHOSPHATE ( 235). 42. ANALYSIS OF COAL ( 239). 43. ANALYSIS OF ETHER. The portion employed must have been rendered anhydrous by diges- tion with fused chloride of calcium and recently rectified. Process 180. C 8 48 64-87 H 10 ............ 10 13-51 O 3 16 21-62 74 100-00 44. ANALYSIS AND DETERMINATION OF THE EQUIVALENT OF BENZOIC ACID. a. Determination of the silver in benzoate of silver as directed 115, 1 or 4. b. Determination by any suitable method of the carbon aiut hydrogen in the hydrated acid dried at 100. Calculation, 200. EXERCISES FOR PRACTICE. 579 45. ANALYSIS AND DETERMINATION OF THE EQUIVALENT OF AN ORGANIC BASE. Analysis of the base and its double salt with platinum. Calculation, 200. 46. DETERMINATION OF THE DENSITY OF CAMPHOR YAPOR. Method desciibed 191. Calculation, 201. 47. ANALYSIS OF A CAST IRON. After 8 230. APPENDIX. ANALYTICAL EXPERIMENTS.* 1. ACTION OP WATER UPON GLASS AND PORCELAIN VESSELS, IN THE PROCESS OF EVAPORATION (to 41). A large bottle was filled with water cautiously distilled from a copper boiler with a tin condensing tube. All the experiments in 1 were made with this water. a. 300 c. c. , cautiously evaporated in a platinum dish, left a residue weighing, after ignition, 0'0005 grm.=0'0017 per 1000. b. 600 c. c. were evaporated, boiling, nearly to dryness, in a wide flask of Bo- hemian glass; the residue was transferred to a platinum dish, and the flask rinsed with 100 c. c. distilled water, which was added to the residue in the dish ; the fluid in the latter was then evaporated to dryness, and the residue ignited. The residue weighed 0'0104 grm. Deducting from this the quantity of fixed matter originally con- tained in the distilled water, viz 0'0012 " There remains substance taken up from the glass 0'0092 " -0-0153 per 1000. In three other experiments, made in the same manner, 300 c. c. left, in two 0-0049 grm., in the third 0'0037 grm.; which, calculated for 600 c. c., gives an average of 0'0090 grm. And after a deduction of O'OOIS " 0'0078 " = 0-013 per 1000. We may therefore assume that 1 litre of water dissolves, when boiled down to a small bulk in glass vessels, about 14 milligrammes of the constituents of the glass. c. 600 c. c. were evaporated nearly to dryness in a dish of Berlin porcelain, and in all other respects treated as in b. The residue weighed O'OOIS grm. Deducting from this the quantity of fixed matter contained in the distilled water, viz O'OOIS ' There remains substance taken up from the porcelain 0*0003 " =0-0005 per 1000. 2. ACTION OF HYDROCHLORIC ACID UPON GLASS AND PORCELAIN VESSELS, IN THE PROCESS OF EVAPORATION (to 41). The distilled water used in 1 was mixed with -fa of pure hydrochloric acid. a. 300 grm., evaporated in a platinum dish, left '002 grm. residue. b. 300 grra. , evaporated first in Bohemian glass nearly to dryness, then in a platinum dish, left '0019 residue ; the dilute hydrochloric acid, therefore, had not attacked the glass. c. 800 grm. evaporated in Berlin porcelain, &c., left 0-0036 grm., accordingly after deducting 0-002, 0-0016=0-0053 per 1000. * The experiments are numbered as in the original edition, but some are omitted. 582 EXPERIMENTS. (?. In a second experiment made in the same manner as in c. , the residue amounted to 0'0034, accordingly after deducting O'OOS, 0-0014=0 "0047 per 1000. Hydrochloric acid, therefore, attacks glass much less than water, whilst porcelain is about equally affected by water and dilute hydrochloric acid. This shows that the action of water upon glass consists in the formation of soluble basic silicates. 3. ACTION OF SOLUTION OF CHLORIDE OF AMMONIUM UPON GLASS AND PORCELAIN VESSELS, IN THE PROCESS OF EVAPORATION (to 41). In the distilled water of 1, -fc of chloride of ammonium was dissolved, and the solution filtered. a. 300 c. c. evaporated in a platinum dish, left 0'008 grm. fixed residue. b. 300 c. c. , evaporated first nearly to dryness in Bohemian glass, then to dry- ness in a platinum dish, left 0'0179 grm. ; deducting from this O'OOG grm., there remains substance taken up from the glass, 0'0119:=0'0397 per 1000. c. 300 c. c., treated in the same manner in Berlin porcelain, left 0'0178; de- ducting from this 0'006, there remains '0118=0 '039.3 per 1000. Solution of chloride of ammonium, therefore, strongly attacks both glass and porcelain in the process of evaporation. 4. ACTION OF SOLUTION OF CARBONATE OF SODA UPON GLASS AND PORCE- LAIN VESSELS (to 41). In the distilled water of 1, T L O - of pure crystallized carbonate of soda was dissolved. a. 300 c. c., supersaturated with hydrochloric acid and evaporated to dryness in a platinum dish, &c., gave 0'0026 grm. silicic acid=0'0087 per 1000. b. 300 c. c. were gently boiled for three hours in a glass vessel, the evaporat- ing water being replaced from time to time ; the tolerably concentrated liquid was then treated as in a; it left a residue weighing 0-1376 grm. ; de- ducting from this the 0'0026 grm., left in a, there remains 0'135 grm.=0'450 per 1000. c. 300 c. c., tieated in the same manner as in 5, in a por.'-elain vessel, left 0-0099; deducting from this 0'0026 grm., there remains 0-0073=0 '0243 per 1000. Which shows that boiling solution of carbonate of soda attacks glass very strongly, and porcelain also in a very marked manner. 5. WATER DISTILLED FROM GLASS VESSELS (to 56, 1). 42 '41 grm. of water distilled with extreme caution from a tall flask with a LEEBIG'S condenser, left, upon evaporation in a platinum dish, a residue weigh- ing, after ignition, O'OOIS grm., consequently 3-3^. 6. SULPHATE OF POTASH AND ALCOHOL (to 68, a). a. Ignited pure sulphate of potassa was digested cold with absolute alcohol, for several days, with frequent shaking; the fluid was filtered off, the filtrate di- luted with water, and then mixed with chloride of barium. It remained per- fectly clear upon the addition of this reagent, but after the lapse of a considera- ble time it began to exhibit a slight opalescence. Upon evaporation to dryness, there remained a very trifling residue, which gave, however, distinct indications of the presence of sulphuric acid. b. The same salt treated in the same manner, with addition of some pure con- centrated sulphuric acid, gave a filtrate which, upon evaporation in a platinum dish, left a clearly perceptible fixed residue of sulphate of potassa. 7. DEPORTMENT OF CHLORIDE OF POTASSIUM IN THE AIR AND AT A HIGH TEMPERATURE (to 68, b). 0-9727 grm. of ignited (not fused) pure chloride of potassium, heated for 10 minutes to dull redness in an open platinum dish, lost 0'0007 grm. ; the salt was then kept for 10 minutes longer at the same temperature, when no further dimi- nution of weight was observed. Heated to bright redness and semi-fusion, the EXPERIMENTS. 583 salt suffered a further loss of weight to the extent of '0009 grm. Ignited in- tensely and to perfect fusion, it lost '0034 grm. , more. Eighteen hours' exposure to the air produced not the slightest increase of weight. 8. SOLUBILITY OF POTASSIO-BICHLORIDE OF PLATINUM ra ALCOHOL (to 68, c). a. In absence of free Hydrochloric Acid. a. An excess of perfectly pure, recently precipitated potassio-bichloride of pla- tinum was digested for 6 days at 15 20, with alcohol of 97 '5 per cent., in a stop- pered bottle, with frequent shaking. 72 -5 grm. of the perfectly colorless nitrate left upon evaporation in a platinum dish, a residue which, dried at 100, weighed O'OOG grm. ; 1 part of the salt requires therefore 12083 parts of alcohol of 97 '5 per cent, for solution. 8. The same experiment was made with spirit of wine of 76 per cent. The filtrate might be said to be colorless ; upon evaporation, slight blackening ensued, on which account the residue was determined as platinum. 75 '5 grm. yielded O'OOS grm. platinum, corresponding to 0'02 grm. of the salt. One part of the salt dissolves accordingly in 3775 parts of spirit of wine of 76 per cent. y. The same experiment was made with spirit of wine of 55 per cent. The nitrate was distinctly yellowish. 63 '2 grm. left 0'0241 grm. platinum, cor- responding to '06 grm. of the salt. One part of the salt dissolves accordingly in 1 053 parts of spirit of wine of 55 per cent. b. In presence of free Hydrochloric Acid. Recently precipitated potassio-bichloride of platinum was digested cold with spirit of wine of 76 per cent. , to which some hydrochloric acid had been added. The solution was yellowish; 67 grm. left 0'0146 grm. platinum, which corre- sponds to 0'0365 grm. of the salt. One part of the salt dissolves accordingly in 1835 parts of spirit of wine, mixed with hydrochloric acid. 9. SULPHATE OF SODA AND ALCOHOL (to 69, a). Experiments made with pure anhydrous sulphate of soda, in the manner de- scribed in 6, showed that this salt comports itself both with pure alcohol, and with alcohol containing sulphuric acid, exactly like the sulphate of potassa. 10. DEPORTMENT OF IGNITED SULPHATE OF SODA IN THE Am (to 09, ). 2*5169 grin, anhydrous sulphate of soda were exposed, in a watch-glass, to the open air on a hot summer day. The first few minutes passed without any in- crease of weight, but after the lapse of 5 hours there was an increase of "0061 grm. 12. DEPORTMENT OF CHLORIDE OF SODIUM IN THE AIR (to 69, b). 4-3281 grm. of chemically pure, moderately ignited (not fused) chloride of sodium, which had been cooled under a bell-glass over sulphuric acid, acquired during 45 minutes' exposure to the (somewhat moist) air, an increase of weight of 0-0009 grm. 13. DEPORTMENT OF CHLORIDE OF SODIUM UPON IGNITION BY ITSELF AND WITH CHLORIDE OF AMMONIUM (to 69, b). 4-3281 grm. chemically pure, ignited chloride of sodium were dissolved in water, in a moderate-sized platinum dish, and pure chloride of ammonium was added to the solution, which was then evaporated and the residue gently heated until the evolution of chloride of ammonium fumes had apparently ceased. The residue weighed 4 '3334 grm. It was then very gently ignited for about 2 min- utes, and after this re-weighed, when the weight was found to be 4 '3314 grm. A few minutes' ignition at a red heat reduced the weight to 4 '3275 grm., and 2 minutes' further ignition at a bright red heat (upon which occasion white fumes were seen to escape), to 4 '3249 grm. 14. DEPORTMENT OF CARBONATE OF SODA IN THE AIR AND ON IGNITION (to 69, c). 2 '1001 grm. of moderately ignited chemically pure carbonate of soda were ex- 584 EXPERIMENTS. posed to the air in an open platinum dish in July in bad weather ; after 10 min- utes the weight was 2*1078, after 1 hour 2-1113, after 5 hours 2*1257. 1-4212 grm. of moderately ignited chemically pure carbonate of soda were ig- nited for 5 minutes in a covered platinum crucible ; no fusion took place, and the weight was unaltered. Heated more strongly for 5 minutes, it partially fused, and then weighed 1 '4202. After being kept fusing for 5 minutes, it weighed 1-4135. 15. DEPORTMENT OF CHLORIDE OP AMMONIUM UPON EVAPORATION AND DRYING (to 70, a). 0-5625 grm. pure and perfectly dry chloride of ammonium was dissolved in water in a platinum dish, evaporated to dryness in the water-bath and completely dried ; the weight waa now found to be 0'5622 grm. (ratio 100 : 99 94). It was again heated for 15 minutes in the water-bath, and afterwards re -weighed, when the weight was found to be 0'5612 grm. (ratio 100 : 99 '77). Exposed once more for 15 minutes to the same temperature, the residue weighed 0'5608 grm. (ratio 100:99-69). 16. SOLUBILITY OF AMMONIO -BICHLORIDE OF PLATINUM IN ALCOHOL (to 70, b). a. In absence of free Hydrochloric Acid. a. An excess of perfectly pure, recently precipitated ammonio-bichloride of platinum was digested for 6 days, at 1520, with alcohol of 97 '5 per cent., in a stoppered bottle, with frequent agitation. 74 '3 grm. of the perfectly colorless filtrate left, upon evaporation and ignition in a platinum dish, 0*0012 grm. platinum, corresponding to 0*0028 of the salt. One part of the salt requires accordingly 26535 parts of alcohol of 97 "5 per cent. /?. The same experiment was made with spirit of wine of 76 per cent. The nitrate was distinctly yellowish. 81*75 grm. left 0'0257 platinum, which corresponds to 0"0584 grm. of the salt. One part of the salt dissolves accordingly in 1406 parts of spirit of wine of 76 per cent. y. The same experiment was made with spirit of wine of 55 per cent. The filtrate was distinctly yellow. Slight blackening ensued upon evaporation, and 56'5 grm. left 0'0364 platinum, which corresponds to '08272 grm. of the salt. Consequently, 1 part of the salt dissolves in 665 parts of spirit of wine of 55 per cent. b. In presence of Hydrochloric Acid. The experiment described in was repeated, with this modification, that some hydrochloric acid was added to the spirit of wine. 76 "5 grm. left 0501 grm. of platinum, which corresponds to 0'1139 grm. of the salt. 672 parts of the acidified spirit had therefore dissolved 1 part of the salt. 17. SOLUBILITY OF CARBONATE OF BARYTA IN WATER (to 71, b}. a. In Cold Water. Perfectly pure, recently precipitated Ba O, C O a was di- gested for 5 days with water of 16 20, with frequent shaking. The mixture was filtered, and a portion of the filtrate tested with sulphuric acid, another por- tion with ammonia ; the former reagent immediately produced turbidity in the fluid, the latter only after the lapse of a considerable time. 84*82 grm. of the solution left,. upon evaporation, 0'0060 Ba O, C O 2 . 1 part of that salt dissolves consequently in 14137 parts of cold water. b. In Hot Water. The same carbonate of baryta being boiled for 10 minutes with pure distilled water, gave a filtrate manifesting the same reactions as that prepared with cold water, and remaining perfectly clear upon cooling. 84*82 grm. of the hot solution left, upon evaporation, 0055 grm. of carbonate of ba- ryta. One part of that salt dissolves therefore in 15421 parts of boiling water. 18. SOLUBILITY OF CARBONATE OF BARYTA IN WATER CONTAINING AMMONIA AND CARBONATE OF AMMONIA (to 71, b}. A solution of chemically pure chloride of barium was mixed with ammonia and carbonate of ammonia in excess, gently heated and allowed to stand at rest for 12 hours ; the fluid was then .filtered off ; the filtrate remained perfectly clear upon EXPERIMENTS. 585 addition of sulphuric acid ; but after the lapse of a very considerable time a hardly perceptible precipitate separated. 84 "82 grin, of the nitrate left, upon evaporation in a small platinum dish, and subsequent gentle ignition, O'OOOG grin. 1 part of the salt had consequently dissolved in 141000 parts of the fluid. 19. SOLUBILITY OF SILICO-FLUORIDE OF BARIUM IN WATER (to 71, c). a. Recently precipitated, thoroughly washed silico -fluoride of barium was di- gested for 4 days in cold water, with frequent shaking ; the fluid was then filtered off, and a portion of the filtrate tested with dilute sulphuric acid, another portion with solution of sulphate of lime ; both reagents produced turbidity the former immediately, the latter after one or two seconds precipitates separated from both portions after the lapse of some time. 84 '82 grm. of the filtrate left a resi- due which, after being thoroughly dried, weighed 0'0223 grm. 1 part of the salt had consequently required 3802 parts of cold water for its solution. b. A portion of another sample of recently precipitated silico -fluoride of barium was heated with water to boiling, and the solution allowed to cool (upon which a portion of the dissolved salt separated). The cold fluid was left for a consider- able time longer in contact with the undissolved salt, and was then filtered off. The filtrate showed the same deportment with solution of sulphate of lime as that of a. 84'82 grm. of it left 0'025 grm. One part of the salt had accordingly dissolved in 3392 parts of water. 20. SOLUBILITY OF SILICO-FLUORIDE OF BARIUM IN WATER ACIDIFIED WITH HYDROCHLORIC ACID (to 71 , c). a. Recently precipitated pure silico-fluoride of barium was digested with fre- quent agitation for 3 weeks with cold water acidified with hydrochloric acid. The filtrate gave with sulphuric acid a rather copious precipitate. 84 '82 grm. left 0-1155 grm. of thoroughly dried residue, which, calculated as silico-fluoride of barium, gives 733 parts of fluid to 1 part of that salt. b. Recently precipitated pure silico-fluoride of barium was mixed with water very slightly acidified with hydrochloric acid, and the mixture heated to boiling. Cooled to 12, 84*82 grm. of the filtrate left a residue of 0'1322 grm., which gives 640 parts of fluid to 1 part of the salt. N". B. The solution of silico-fluoride of barium in hydrochloric acid is not effect- ed without decomposition ; at least, the residue contained, even after ignition, a rather large proportion of chloride of barium. 21. SOLUBILITY OF SULPHATE OF STRONTIA IN WATER (to 72, a). a. In Water of 14. 84*82 grm. of a solution prepared by 4 days' digestion of recently precipitated sulphate of strontia with water at the common temperature, left 0'0123 grm. of sulphate of strontia. One part of Sr O, S O 3 dissolves consequently in 6895 parts of water. b. In Water of 100. 84 "82 grm. of a solution prepared by boiling recently precipitated sulphate of strontia several hours with water, left 0*0088 grm. Consequently 1 part of Sr O, S O 3 dissolves in 9638 parts of boiling water. 22. SOLUBILITY OF SULPHATE OF STRONTIA IN WATER CONTAINING HYDRO- CHLORIC ACID AND SULPHURIC ACID (to 72, a). a. 84 '82 grm. of a solution prepared by 3 days' digestion, left 0*0077 grm. SrO, SO 3 . b. 42 '41 grm. of a solution prepared by 4 days' digestion, left 0*0036 grm. c. Pure carbonate of strontia was dissolved in an excess of hydrochloric acid, and the solution precipitated with an excess of sulphuric acid and then allowed to stand in the cold for a fortnight. 84*82 grm. of the filtrate left 0*0066 grm. In a. 1 part of Sr O, S O 3 required 11016 parts. b I " " 11780 " c. 1 " " 12791 " Mean 11863 parts. 586 EXPERIMENTS. 23. SOLUBILITY OF SULPHATE OF STRONTIA IN DILUTE NITRIC ACID, HYDROCHLORIC ACID, AND ACETIC ACID (to 72, a). a. Recently precipitated pure sulphate of strontia was digested for 2 days in the cold with nitric acid of 4 '8 per cent 150 grm. of the nitrate left 0-3451 grin. 1 part of the salt required accordingly 435 parts of the dilute acid for its solution j in another experiment 1 part of the salt was found to require 429 parts of the dilute acid. Mean, 432 parts. b. The same salt was digested for 2 days in the cold with hydrochloric acid of 8'o'per cent. 100 giro, left '2115, and in another experiment. 0'2104 grm. 1 part of the salt requires, accordingly, in the mean, 474 parts of hydrochloric acid of 8 "5 per cent, for its solution. c. The same salt was digested for 2 days in the cold with acetic acid of 15 "6 percent. A, HO. 100 grm. left 0'0126, and in another experiment, 0'0129 grm. 1 part of the salt requires, accordingly, in the mean, 7843 parts of acetic acid of 15'6 percent. 24. SOLUBILITY OF CARBONATE OF STRONTIA IN COLD WATER (to 72, b}. Recently precipitated, thoroughly washed Sr O, C O 2 was digested several days with cold distilled water, with frequent shaking. 84 '82 grm. of the nitrate left, upon evaporation, a residue weighing, after ignition, 0'0047 grm. 1 part of carbonate of strontia requires therefore 18045 parts of water for its solution. 25. SOLUBILITY OF CARBONATE OF STRONTIA IN WATER CONTAINING AMMONIA AND CARBONATE OF AMMONIA (to 72, b). Recently precipitated, thoroughly washed carbonate of strontia was digested for four weeks with cold water containing ammonia and carbonate of ammonia, with frequent shaking. 84'82 grm. of the filtrate left 0-0015 grm. Sr O, C O 2 . Consequently, 1 part of the salt requires 56545 parts of this fluid for its solution. If solution of chloric! e of strontium is precipitated with carbonate of ammonia and ammonia as directed 102, 2, tt, sulphuric acid produces no turbidity in the filtrate, after addition of alcohol. 26. SOLUBILITY OF CARBONATE OF LIME IN COLD AND IN BOILING WATER <.to 73, b). a. A solution prepared by boiling as in 26, 5, was digested in the cold for 4 weeks, with frequent agitation, with the undissolved precipitate. 84*82 grm. left 0-0080 Ca 0, C 0., 1 part therefore required 10001 parts. b. Recently precipitated Ca 0, C O > was boiled for some time with distilled water. 42 "41 grin, of the filtrate left, upon evaporation and gentle ignition of the residue, - 0048 Ca O, C Oj. 1 part requires consequently 8834 parts of boiling water. 27. SOLUBILITY OF Ca 0, C 2 IN WATER CONTAINING AMMONIA AND CARBO- NATE OF AMMONIA (to 73, b). Pure dilute solution of chloride of calcium was precipitated with carbonate of ammonia and ammonia, allowed to stand 24 hours, and then filtered. 84 '82 grm. .eft '001 3 grm. Ca O, C 2 . 1 part requires consequently 65246 parts. 28. DEPORTMENT OF CARBONATE OF LIME UPON IGNITION IN A PLATINUM CRUCIBLE (to 73, b). 0-7955 grm. of perfectly dry carbonate of lime was exposed, in a small and thin platinum crucible, to the gradually increased, and finally most intense heat of a good BERZELIUS' lamp. The crucible was open and placed obliquely. After the first 15 minutes the mass weighed 0*6482 after half an hour 0'6256 after one hour 0'5927, which latter weight remained unaltered after 15 minutes' additional heating. This corresponds to 74 '5 per cent., whilst the proportion of lime in the carbonate is calculated at 56 per cent. ; there remained therefore evidently still a considerable amount of the carbonic acid. 29. COMPOSITION OF OXALATE OF LIME DRIED AT 100 (to 73, c). 0'8510 grm. of thoroughly dry pure carbonate of lime was dissolved in hydro- chloric acid ; the solution was precipitated with oxalate of ammonia and am- EXPERIMENTS. 587 monia, and the precipitate collected upon a weighed filter and dried at 100, until the weight remained constant. The oxalate of lime so produced weighed '2461 grm. Calculating this as Ca 0, C 2 3 + aq., the amount found contained 4772 Ca 0, which corresponds to 56'07 per cent, in the carbonate of lime ; the calculated proportion of lime in the latter is 56 per cent. 30. DEPORTMENT OP SULPHATE OF MAGNESIA IN THE AIR AND UPON IGNI TION (to 74, a). 0'8135 grm. of perfectly pure anhydrous Mg O, S O ;i in a covered platinum cru cible acquired, on a fine and warm day in June, in half an hour, an increase of weight of 0*004 grm., and in the course of 12 hours, of 0067 grm. The salt could not be accurately weighed in the open crucible, owing to continual increase of weight. 0'8135 grm., exposed for some time to a very moderate red heat, suffered no diminution of weight ; but after 5 minutes' exposure to an intense red heat, the substance was found to have lost '0075 grm. , and the residue gave no longer a clear solution with water. About. 0'2 grm. of pure sulphate of magnesia ex- posed in a small platinum crucible, for 15 to 20 minutes, to the heat of a powerful blast gaslamp, gave, with dilute hydrochloric acid, a solution in which chloride of barium failed to produce the least turbidity. 31. SOLUBILITY OP THE BASIC PHOSPHATE OP MAGNESIA AND AMMONIA IN PURE WATER (to 74, b). a. Recently precipitated basic phosphate of magnesia and ammonia was thoroughly washed with water, then digested for 24 hours with water of about 15, with frequent shaking. 84-43 grm. of the filtrate left 0'0047 grm. of pyrophosphate of magnesia. b. The same precipitate was digested in the same manner for 72 hours 84-42 grm. of the nitrate left 0'0043 " Mean 0'0045 " which corresponds to '00552 grm. of the anhydrous double salt. 1 part of that salt dissolves therefore in 15293 parts of pure water. The cold saturated solution gave, with ammonia, after the lapse of a short time, a distinctly perceptible crystalline precipitate; on the addition of phos- phate of soda, it remained perfectly clear, and even after the lapse of two days no precipitate had formed ; phosphate of soda and ammonia produced a precipi- tate as large as that by ammonia. 32. SOLUBILITY OP BASIC PHOSPHATE OP MAGNESIA AND AMMONIA IN WATER CONTAINING AMMONIA (to 74, b). a. Pure basic phosphate of magnesia and ammonia was dissolved in the least possible amount of nitric acid ; a large quantity of water was added to the solu- tion, then ammonia in excess. The mixture was allowed to stand at rest for 24 hours, then filtered; its temperature was 14. 84*42 grm. left 0*0015 pyrophos- phate of magnesia, which corresponds to '00184 of the anhydrous double salt. Consequently 1 part of the latter requires 45880 parts of ammoniated water for its solution. b Pure basic phosphate of magnesia and ammonia was digested for 4 weeks with ammoniated water, with frequent shaking ; the fluid (temperature 14) was then filtered off; 126*63 grm. left 0'0024 pyrophosphate of magnesia, which cor- responds to 0*00296 of the double salt. 1 part of it therefore dissolves in 42780 parts of ammoniated water. Taking the mean of a and , 1 part of the double salt requires 44330 parts of ammoniated water for its solution. 33. ANOTHER EXPERIMENT ON THE SAME SUBJECT (to 74, b}. Recently precipitated phosphate of magnesia and ammonia, most carefully washed with water containing ammonia, was dissolved in water acidified with hydrochloric acid, ammonia added in excess, and allowed to stand in the cold for 24 hours. 169 '64 grm. of the filtrate left 0'0031 pyrophosphate of magnesia, corresponding to 0*0038 of anhydrous phosphate of magnesia and ammonia. 1 part of the double salt required therefore 44600 parts of the fluid. 588 EXPERIMENTS. 34. SOLUBILITY OF THE BASIC PHOSPHATE OF MAGNESIA AND AMMONIA rs WATER CONTAINING CHLORIDE OF AMMONIUM (to 74, &). Recently precipitated, thoroughly washed basic phosphate of magnesia and ammonia was digested in the cold with a solution of 1 part of chloride of ammo- nium in 5 parts of water. 18'4945 grm. of the filtrate left 0'002 pyrophosphate of magnesia, which corresponds to 0-00245 of the double salt. 1 part of the salt dissolves therefore in 7548 parts of the fluid. 35. SOLUBILITY OF THE BASIC PHOSPHATE OF MAGNESIA AND AMMONIA rtf WATER CONTAINING AMMONIA AND CHLORIDE OF AMMONIUM (to 74, b). Recently precipitated, thoroughly washed phosphate of magnesia and ammo- nia was digested in the cold with a solution of 1 part of chloride of ammonium in 7 parts of ammoniated water. 23 "1283 grm. of the filtrate left O'OOIS pyro- phosphate of magnesia, which corresponds to '001 48 of the double salt. 1 part of the double salt requires consequently 15627 parts of the fluid for its solution. 36. DEPORTMENT OF ACID SOLUTIONS OF PYROPHOSPHATE OF MAGNESIA WITH AMMONIA (to 74, c). '3985 grm. pyrophosphate of magnesia was treated for several hours, at a high temperature, with concentrated sulphuric acid. This exercised no perceptible action. It was only after the addition of some water that the salt dissolved. The fluid, heated for some time, gave, upon addition of ammonia in excess, a crystalline precipitate, which was filtered off after 18 hours ; the quantity of pyrophosphate of magnesia obtained was '3805 grm. , that is, 95 '48 per cent. Phosphate of soda produced in the filtrate a trifling precipitate, which gave 0*0150 grm. of pyrophosphate of magnesia, that is, 3 '76 per cent. '3565 grm. pyrophosphate of magnesia was dissolved in 3 grm. nitric acid, of l'2sp. gr. ; the solution was heated, diluted, and precipitated with ammo- nia : the quantity of pyrophosphate of magnesia obtained amounted to '3485 grm.. that is, 98 '42 per cent. ; 0*4975 grm. was treated in the same manner with 7 '6 grm. of the same nitric acid : the quantity re-obtained was 0*4935 grm., that is, 99 '19 per cent. 0'786 grm. treated in the same manner with 16 '2 grm. of nitric acid, gave 0-7765 grm., that is, 98 '79 per cent. The result of these experiments may be tabulated thus: Proportion of 2 Mg 0, P Oa to nitric acid. Ke-obtained. Loss. 9 98 -42 per cent. 1'58 15 9919 u 0-81 20 98-79 " 1-21 37. SOLUBILITY OF PURE MAGNESIA IN WATER (to 74, fi). a. In Cold Water. Perfectly pure well-crystallized sulphate of magnesia was dissolved in water, and the solution precipitated with carbonate of ammonia and caustic ammonia ; the precipitate was thoroughly washed in spite of which it still retained a per- ceptible trace of sulphuric acid then dissolved in pure nitric acid, an excess of acid being carefully avoided. The solution was then re -precipitated with car- bonate of ammonia arid caustic ammonia, and the precipitate thoroughly washed. The so-prepared perfectly pure basic carbonate of magnesia was ignited in a platinum crucible until the weight remained constant. The residuary pure mag- nesia was then digested in the cold for 24 hours with distilled water, with fre- quent shaking. The distilled water used was perfectly free from chlorine, and left no fixed residue upon evaporation. . 84 '82 grm. of the filtrate, cautiously evaporated in a platinum dish, left a residue weighing, after ignition, '0015 grm. 1 part of the pure magnesia dis- solved therefore in 56546 parts of cold water. The digestion was continued for 48 hours longer, when 0. 84-82 grm. left 0'0016 grm. 1 part required therefore 53012 y. 84-82 grm. left 0*0015 grin. 1 part required 56546 Average 55368 EXPERIMENTS. 58S The solution of magnesia prepared in the cold way has a feeble yet distinct alkaline reaction, which is most easily perceived upon the addition of very faintly reddened tincture of litmus ; the alkaline reaction of the solution is perfectly manifest also with slightly reddened litmus paper, or with turmeric or dahlia paper, if these test-papers are left for some time in contact with the solution. Alkaline carbonates fail to render the solution turbid, even upon boiling. Phosphate of soda also fails to impair the clearness of the solution, but if the fluid is mixed with a little ammonia and shaken, it speedily becomes turbid, and deposits after some time a perceptible precipitate of basic phosphate of magnesia and ammonia. b. In Hot Water. Upon boiling pure magnesia with water, a solution is obtained which comports itself in every respect like the cold-prepared solution of magnesia. A hot-pre- pared solution of magnesia does not become turbid upon cooling, nor does a cold- prepared solution upon boiling. 84 '82 grm. of hot-prepared solution of magnesia left 0-0016 grm. Mg O. 38. SOLUBILITY OF PURE MAGNESIA IN SOLUTIONS OF CHLORIDE OF POTASSIUM AND CHLORIDE OF SODIUM (to 74, d). 3 flasks of equal size were charged as follows: 1. With 1 grm. pure chloride of potassium, 200 c. c. water and some perfectly pure magnesia. 2. With 1 grm. pure chloride of sodium, 200 c. c. water and some pure mag- nesia. 3. With 200 c. c. water and some pure magnesia. The contents of the 3 flasks were kept boiling for 40 minutes, then filtered, and the clear nitrates mixed with equal quantities of a mixture of phosphate of soda, chloride of ammonium and ammonia. After 12 hours a very slight preci- pitation was visible in 3, and a considerably larger precipitation had taken place in 1 and 2. 39. PRECIPITATION OF ALUMINA BY AMMONIA, ETC. (to 75, a). a. Ammonia produces in neutral solutions of salts of alumina or of alum, as is well known, a gelatinous precipitate of hydrate of alumina. Upon further ad- dition of ammonia in considerable excess, the precipitate redissolves gradually, but not completely. b. If a drop of a dilute solution of alum is added to a copious amount of ammonia, and the mixture shaken, the solution appears almost perfectly clear ; however, after standing at rest for some time, slight flakes separate. G. If a solution of alumina, mixed with a large amount of ammonia, is filtered, and a. The filtrate boiled for a considerable time, flakes of hydrate of alumina separate gradually in proportion as the excess of ammonia escapes. 13. The filtrate mixed with solution of chloride of ammonium, a very percep- tible flocculent precipitate of hydrate of alumina separates immediately ; the whole of the hydrated alumina present in the solution will thus separate if the chloride of ammonium be added in sufficient quantity. y. The filtrate mixed with sesquicarbonate of ammonia, the same reaction takes place as in /?. 6. The nitrate mixed with solution of chloride of sodium or chloride of potassium, no precipitate separates, but, after several days' standing, slight flakes of hydrate of alumina subside, owing to the loss of ammonia by evaporation. d. If a neutral solution of alumina is precipitated with carbonate of ammonia, or if a solution strongly acidified with hydrochloric or nitric acid is precipitated with pitre ammonia, or if to a neutral solution a sufficient amount of chloride of ammonium is added besides the ammonia ; even a considerable excess of the precipitants will fail to redissolve the precipitated alumina, as appears from the continued perfect clearness of the filtrates upon protracted boiling and evapora- tion. 40. PRECIPITATION OF ALUMINA BY SULPHIDE OF AMMONIUM (to 75, a). (Experiments made by Mr. J. FUCHS, formerly Assistant in my Laboratory.} a. 50 c. c. of a solution of pure ammonia-alum, which contained 0'3939 590 EXPERIMENTS. alumina, were mixed with 50 c c. water and 10 c. c. solution of suljhide of ammonium, and filtered after ten minutes. The ignited precipitate weighed 0-3825 grin. b. The same experiment was repeated with 100 c. c. water ; the precipitate weighed 0-3759 grm. c. The same experiment was repeated with 200 c. c. water ; the precipitate weighed '3642 grm. 41. PRECIPITATION OF SESQUIOXIDE OP CHROMIUM BY AMMONIA (to 76, a). Solutions of sesqui chloride of chromium and of chrome-alum (concentrated and dilute, neutral and acidified with hydrochloric acid) were mixed with am- monia in excess. All the filtrates drawn off immediately after precipitation ap- peared red, but when filtered after ebullition, they all appeared colorless, if the ebullition had been sufficiently protracted. 42. SOLUBILITY OF THE BASIC CARBONATE OF ZINC IN WATER (to 77, a). Perfectly pure, recently (hot) precipitated basic carbonate of zinc was gently heated with distilled water, and subsequently digested cold for many weeks, with frequent shaking. The clear solution gave no precipitate with sulphide of ammonium, not even after long standing. 84 '82 grm. left 0*0014 grm. oxide of zinc, which corresponds to O'OOIO basic carbonate of zinc (74 per cent, of Zn O being assumed in this salt). One part of the basic carbonate requires therefore 44G42 parts of water for so- lution. IN EACH OF THE THREE FOLLOWING NUMBERS THE SULPHIDE WAS PRE- cipitated from the solution of the neutral salt with addition of chloride of ammo- nium by yellow sulphide of ammonium, and allowed to stand in a closed vessel. After 24 hours the clear fluid was poured on to 6 filters of equal size, and the precipitate was then equally distributed among them. The washing was at once commenced and continued, without interruption, the following fluids being used : I. Pure water. II. Water containing sulphuretted hydrogen. III. Water containing sulphide of ammonium. IV. Water containing chloride of ammonium, afterwards pure water. V. Water containing sulphuretted hydrogen and chloride of ammonium, afterwards water containing sulphuretted hydrogen. VI. Water containing sulphide of ammonium and chloride of ammonium, afterwards water containing sulphide of ammonium. 43. DEPORTMENT OF SULPHIDE OF ZINC ON WASHING (to 77, c}. The filtrates were at first colorless and clear. On washing, the first three fil- trates ran through turbid, the turbidity was strongest in II. and weakest in III. ; the last three remained quite clear. On adding sulphide of ammonium no change took place ; the turbidity of the first three was not increased, the clear- ness of the last three was not impaired. Chloride of ammonium therefore de- cidedly exercises a favorable action, and the water containing it may be displaced by water containing sulphide of ammonium. 44. DEPORTMENT OF SULPHIDE OF MANGANESE ON WASHING (to 78, e). The filtrates were at first clear and colorless. But after the washing had been continued some time, I. appeared colorless, slightly opalescent ; II. whitish and turbid ; III. yellowish and turbid ; IV. colorless, slightly turbid ; V. slightly yellowish, nearly clear ; VI. clear, yellowish. To obtain a filtrate that remains clear, therefore, the wash-water must at first contain chloride of ammonium. Addition of sulphide of ammonium also cannot be dispensed with, as all the filtrates obtained without this addition gave distinct pre- cipitates of sulphide of manganese when the reagent was subsequently added to them. EXPERIMENTS. 591 45. DEPORTMENT OP SULPHIDE OF NICKEL (ALSO OF SULPHIDE OF COBALT AND SULPHIDE OF IRON) ON WASHING (to 79, d). In the experiments with sulphide of nickel the clear filtrates were put aside, and then the washing was proceeded with. The washings of the first 3 ran through turbid, of the last 3. clear. When the washing was finished, I. wa? colorless and clear ; II. blackish and clear ; III. dirty yellow and clear ; IV. col- orless and clear ; V. slightly opalescent ; VI. slightly brownish and opalescent. On addition of sulphide of ammonium, I. became brown ; II. remained unalter- ed ; III. remained unaltered ; IV. became black and opaque ; V. became brown and clear ; VI. became pure yellow and clear. Sulphide of cobalt and sulphide of iron behaved in an exactly similar manner. It is plain that these sulphides oxidize more rapidly when the wash-wate 1 - contains chloride of ammonium, unless sulphide of ammonium is also present. Hence it is necessary to wash with a fluid containing sulphide of ammo- nium ; and the addition of chloride of ammonium at first is much to be re- commended, as this diminishes the likelihood of our obtaining a muddy fil- trate. 46. DEPORTMENT OF HYDRATE OF PROTOXIDE OF COBALT PRECIPITATED BY ALKALIES (to 80, a). A solution of protochloride of cobalt was precipitated boiling with solution of soda, and the precipitate washed with boiling water until the filtrate gave no longer the least indication of presence of chlorine. The dried and ignited resi- due, heated with water, manifested no alkaline reaction. It was reduced by ig- nition in hydrogen gas, and the metallic cobalt digested hot with water. The decanted water manifested no alkaline reaction, even after considerable con- centration ; but the metallic cobalt, brought into contact, moist, with turmeric paper, imparted to the latter a strong brown color. 47. SOLUBILITY OF CARBONATE OF LEAD (to 83, a). a. In pure Water. Recently precipitated and thoroughly washed pure carbonate of lead was digested for 8 days with water at the common temperature, with frequent shaking. 84 '42 grin, of the filtrate were evaporated, with addition of some pure sulphuric acid; the residuary sulphate of lead weighed 0'0019 grm., which corresponds to '00167 carbonate of lead. One part of the latter salt dissolves therefore in 50551 parts of water. The solution, mixed with sul- phuretted hydrogen water, remained perfectly colorless, not the least tint being detected in it, even upon looking through it from the top of the test- cylinder. b. In Water containing a little Acetate of Ammonia and also Carbonate of Ammonia and Ammonia. A highly dilute solution of pure acetate of lead was mixed with carbonate of ammonia and ammonia in excess, and the mixture gently heated and then al- lowed to stand at rest for several days. 84 '42 grm. of the filtrate left, upon evap- oration with a little sulphuric acid, '0041 grm. sulphate of lead, which corre- sponds to 0036 of the carbonate. One part of the latter salt requires accordingly 23450 parts of the above fluid for solution. The solution was mixed with sulphu- retted hydrogen water ; when looking through the fluid from the top of the test- cylinder, a distinct coloration was visible ; but when looking through the cylinder laterally, this coloration was hardly perceptible. Traces of sulphide of lead separated after the lapse of some time. c. In Water containing a large proportion of Nitrate of Ammonia, together with Carbonate of Ammonia and Caiistic Ammonia. A highly dilute solution of acetate of lead was mixed with nitric acid, then with carbonate of ammonia and ammonia in excess ; the mixture was gently heated, and allowed to stand at rest for 8 days. The filtrate, mixed with sul- phuretted hydrogen, exhibited a very distinct brownish color upon looking through it from the top of the cylinder ; but this color appeared very slight only when looking through the cylinder laterally. The amount of lead dissolved was unques- tionably more considerable than in b. 592 EXPERIMENTS. 48. SOLUBILITY OF OXALATE OF LEAD (to 83, b). A dilute solution of acetate of lead was precipitated with oxalate of ammonia and ammonia, the mixture allowed to stand at rest for some time, and then fil- tered. The filtrate, mixed with sulphuretted hydrogen, comported itself exactly like the filtrate of No. 47, l>. The same deportment was observed in another similar experiment, in which nitrate of ammonia had been added to the solution. 49. SOLUBILITY OF SULPHATE OF LEAD IN PURE WATER (to 83, d)'. Thoroughly washed and still moist sulphate of lead, was digested for 5 days with water, at 10 15, with frequent shaking. 84 '42 grm. of the filtrate (filtered off at IT) left Q'0037 grm. sulphate of lead. Consequently 1 part of this salt requires 22816 parts of pure water of 11 for solution. The solution, mixed with sulphuretted hydrogen, exhibited a distinct brown color when viewed from the top of the cylinder, but this color appeared very slight upon looking through the cylinder laterally. 50. SOLUBILITY OF SULPHATE OF LEAD IN WATER CONTAINING SULPHURIC ACID (to 83, d). A highly dilute solution of acetate of lead was mixed with an excess of dilute pure sulphuric acid ; the mixture was very gently heated, and the precipitate allowed several days to subside. 80 31 grm of the filtrate left 0'0022 grm. sulphate of lead. One part of this salt dissolves therefore in 36504 parts of water containing sulphuric acid. The solution, mixed with sulphuretted hydrogen, appeared colorless to the eye looking through the cylinder laterally, and very little darker when viewed from the top of the cylinder. 51. SOLUBILITY OF SULPHATE OF LEAD IN WATER CONTAINING AMMONIACAL SALTS AND FREE SULPHURIC ACID (to 83, d). A highly dilute solution, of acetate of lead was mixed with a tolerably large amount of nitrate of ammonia, and sulphuric acid in excess added. After sev- eral days' standing, the mixture was filtered. The filtrate was nearly indifferent to sulphuretted hydrogen water ; viewed from the top of the cylinder, it looked hardly perceptibly darker than pure water. 52. DEPORTMENT OF SULPHATE OF LEAD UPON IGNITION (to 83, d). Speaking of the determination of the atomic weight of sulphur, ERDMANN and MARCHAND* state that sulphate of lead loses some sulphuric acid upon ignition. In order to inform myself of the extent of this loss, and to ascertain how far it might impair the accuracy of the method of determining lead as a sulphate, I heated 2 2151 grin, of absolutely pure Pb O, S O 3 to the most intense redness, over a spirit-lamp with double draught. I could not perceive the slightest de- crease of weight ; at all events, the loss did not amount to '0001 grm. 53. DEPORTMENT OF SULPHIDE OF LEAD ON DRYING AT 100' (to 83, e). Sulphide of lead was precipitated from a solution f pure acetate of lead with sulphuretted' hydrogen, and when dry, kept for a considerable time at 100 and weighed occasionally. The following numbers represent the results of the sev- eral weighings : I. 0-8154. II. 0-8164. III. 0'8313. IV. 0'8460. V. 0'864. 54. DEPORTMENT OF METALLIC MERCURY AT THE COMMON TEMPERATURE AND UPON EBULLITION WITH WATER (to 84, a). To ascertain in what manner loss of metallic mercury occurs upon drying, and likewise upon boiling with water, and to determine which is the best method of drying, I made the following experiments : I treated 6 '4418 grm. of perfectly pure mercury in a watch-glass, with dis- tilled water, removed the water again as far as practicable (by decantation and fin- ally by means of blotting-paper), and weighed. I now had 6 '4412 grm. After sev- eral hours' exposure to the air. the mercury was reduced to 6 '4411. I placed these 6 '4411 grm. under a bell-jar over sulphuric acid, the temperature being about 17 : . * Journ. f::r. Prakt. Cliem. 81, 385. EXPERIMENTS. 593 After the lapse of 24 hours the weight had not altered in the least I introduced the f> '41:11 grm. mercury into a flask, treated it with a copious quantity of dis- tilled water, and boiled for 15 minutes violently. I then placed the mercury again upon the watch-glass, dried it most carefully with blotting-paper, and weighed. The weight was now 6'4402 grm. Finding that a trace of mercury had adhered to the paper, I repeated the same experiment with the G'4402 grm. After 15 minutes' boiling with water, the mercury had again lost '0004 grm. The remaining 6 '4398 grm. were exposed to the air for 6 days (in summer, during very hot weather), after which they were found to have lost only 0005 grm. 55. DEPORTMENT OF SULPHIDE OF MERCURY WITH SOLUTION OF POTASSA, SULPHIDE OF AMMONIUM, ETC. (to 84, c). a. If recently precipitated pure sulphide of mercury is boiled with pure solu- tion of potassa, not a trace of it dissolves in that fluid ; hydrochloric acid pro- duces no precipitate, nor even the least coloration, in the filtrate. b. If sulphide of mercury is boiled with solution of potassa, with addition of some sulphuretted hydrogen water, sulphide of ammonium, or sulphur, complete solution is effected. c. If freshly precipitated sulphide of mercury is digested in the cold with yellowish or very yellow sulphide of ammonium, slight, but distinctly percepti- ble traces are dissolved, while in the case of hot digestion, scarcely any traces of mercury can be detected in the solution. * d. Thoroughly washed sulphide of mercury, moistened with water, suffers no alteration upon exposure to the air ; at least, the fluid which I obtained by washing sulphide of mercury which had been thus exposed for 24 hours, did not manifest acid reaction, nor did it contain mercury or sulphuric acid. 50. DEPORTMENT OF OXIDE OF COPPER UPON IGNITION (to 85, b}. Pure oxide of copper (prepared from nitrate of copper) was ignited in a plat- inum crucible, then cooled under a bell-jar over sulphuric acid, and finally weighed. The weight was 3 '542 grin. The oxide was then most intensely ignited for 5 minutes, over a BERZELIUS' lamp, and weighed as before, when the weight was found unaltered ; the oxide was then once more ignited for 5 minutes, but with the same result. 57. DEPORTMENT OF OXIDE OF COPPER IN THE AIR (to 85, b). A platinum crucible containing 4 '3021 grm. of gently ignited oxide of copper (prepared from the nitrate) stood for 10 minutes, covered with the lid, in a warm room in winter; ; the weight of the oxide of copper was found to have increased to 4 -39:}!) grm. The oxide of copper was then intensely ignited over a spirit-lamp ; after 10 minutes' standing in the covered crucible, the weight had not perceptibly in- creased ; after 24 hours it had increased by 0'0036 grm. 58. DEPORTMENT OF SULPHIDE OF BISMUTH UPON DRYING AT 100 (to 86, e). 0*4558 grm. of sulphide of bismuth prepared in the wet way were placed in the desiccator on a watch glass and allowed to stand at the common tempera- ture. After 3 hours the weight was 0'4270, after 6 hours 0'4258, after 2 days the same. '13602 grm. of the sulphide of bismuth so dried was put into a water-bath, in 15 minutes it weighed 3596, half an hour afterwards 0'3599, in half an hour more 0'3603, in two hours 3626. In a second experiment the drying was kept up for 4 days, and a continual increase of weight was observed. 0'5081 grin, of sulphide of bismuth dried in the desiccator was heated in a boat in a stream of carbonic acid. After gentle ignition the weight was 5002, after repeated heating 0'4992. The sulphide of bismuth was visibly volatilized on ignition in the current of carbonic acid. * Comp. my experiments in the Zoitschrift f. Anal. Chem. 3, 140. 38 094 EXPERIMENTS. 59. DEPORTMENT OP SULPHIDE OP CADMIUM WITH AMMONIA, ETC. (t 87, c). Recently precipitated pure sulphide of cadmium was diffused through water, and the following experiments were made with the mixture. a. A portion was digested cold with ammonia in excess, and filtered. The fil- trate remained perfectly clear upon addition of hydrochloric acid. b. Another portion was digested hot with excess of ammonia, and filtered. This filtrate likewise remained perfectly clear upon addition of hydrochloric acid. c. Another portion was digested for some time with solution of cyanide of po- tassium, and filtered. This filtrate also remained perfectly clear upon addition of hydrochloric acid. d. Another portion was digested with hydrosulphate of sulphide of ammonium, md filtered. The turbidity which hydrochloric acid imparted to this filtrate was pure white. (A remark made by WACKENRODER, in BUCHNER'S Repertor. d. Pharm., >dvi. 226, induced me to make these experiments.) 60. DEPORTMENT OF PRECIPITATED TERSULPHIDE OF ANTIMONY ON DRY- ING (to 90, a). '2899 grm. of pure precipitated tersulphide of antimony dried in the desicca- oor lost, when dried at 100, O'OOOT. 0-4457 grm. of the substance dried at 100 lost, when heated to blackening in a stream of carbonic acid, O'OOll water. 01932 grm. of the substance dried at 100 gave up O'OOIS, when heated to blackening in a stream of carbonic acid, and after stronger heating, during which fumes of sulphide of antimony began to escape, the total loss amounted to 0-0022 grm. 0'1670 grm. of the substance dried at 100 lost O'OOOS grm. on being heated to blackening in a stream of carbonic acid. 61. AMOUNT OF WATER IN HYDRATED SILICIC ACID (to 93, 9). (Experiments made by my assistant, Mr. LIPPERT.) A dilute solution of soluble glass was slowly dropped into hydrochloric acid, as long as the precipitate continued to dissolve rapidly, then the clear fluid was heated in the water-bath, till it set to a transparent jelly. This jelly was dried as far as possible with blotting paper, diffused in water, and washed by decanta- tion till the fluid altogether ceased to give the chlorine reaction. It was then transferred to a filter, and the latter spread on blotting paper and exposed till a crumbly mass was left from the spontaneous evaporation of water. One half (I.) was dried for 8 weeks in the desiccator over sulphuric acid, with occasional trituration, the other half (II. ) was dried under similar circumstances, but in a vacuum. Both were transferred to closed tubes and these were kept in the de- siccator. The weighing of the substance dried at 100 was effected between watch glasses. For the purpose of igniting the residue, it was allowed to satiate itself with aqueous vapor by exposure to the air, otherwise a considerable quantity of the substance would have been lost, then water was dropped upon it in the watch glass, then it was rinsed into a platinum crucible, dried in a water-bath, and ignited, at first cautiously, towards the end, intensely. The substance I. contained Expt. 1. Expt. 2. Water, escaping at or below 100 4 '19 ) Q .oo above 100 4'76 f 9 ^ Silicicacid 91-05 90'72 100-00 100-00 Consequently the hydrate dried at 100 consists of 4 '97 water and 95 '03 silicio acid. In the substance dried in the desiccator the oxygen of the total water : the oxygen of the silicic acid, according to the first experiment : : 1 : 6'1, ac- EXPERIMENTS. 595 cording to the second experiment : : 1 : 5 '86. And in the substance dried at 100 the oxygen of the water : the oxygen of the silicic acid : : 1 : 11*5. The substance II. contained Expt. l. Expt. 2. Expt. 3. Water, escaping at or below 100 4 75 4 71 ) Q QP - above 100 5'26 5*21 } Silicic acid 89 99 90*08 90'05 100-00 10000 100-00 Consequently the hydrate dried at 100 consists on the average of 5 '49 water and 94'5l silicic acid. In the substance dried in a vacuum over sulphuric acid the oxygen of the total water : the oxygen of the silicic acid on an aver- age : : 1 : 5 41. And in the substance dried at 100 the oxygen of the water : the oxygen of the silicic acid : : 1 : 10 '43. 62. DETERMINATION OF BARYTA BY PRECIPITATION WITH CARBONATE OF AMMONIA (to 101, 2, a). 0*7553 grm. pure ignited chloride of barium precipitated after 101, 2, a, gave 0-7142 Ba O, C 2 , which corresponds to 0-554719 Ba O = 73 '44 per cent. (100 parts of Ba Cl ought to have given 73 '59 parts). The result accordingly was 99-79 instead of 100. 63. DETERMINATION OF BARYTA IN ORGANIC SALTS (to 101, 2, 5). 0*686 grm. racemate of baryta (2 BaO, C 8 H 4 Oio+5 aq.) treated according to 101, 2, b, gave 0408 carbonate of baryta = 0'3169 Ba O = 46 '20 per cent, (cal- culated 46-38 per cent.) ; i.e., 99 '61 instead of 100. 64. DETERMINATION OF STRONTIA AS SULPHATE OF STRONTIA (to 102, 1, a). a An aqueous solution of 1'2398 grm. Sr Cl was precipitated with sulphuric acid in excess, and the precipitated sulphate of strontia washed with water. It weighed 1 -4113, which corresponds to '795408 Sr = 6415 per cent, (calculated 65-38 per cent.) ; i.e., 9812 instead of 100. b. 11510 grm. Sr 0, C O 2 was dissolved in excess of hydrochloric acid, the solution diluted, and then precipitated with sulphuric acid ; the precipitated Sr O, S 3 was washed with water ; it weighed 1-4024 = '79039 Sr O = 68'68 per cent, (calculated 70 '07 per cent.) ; i.e., 98 '02 instead of 100. 65. DETERMINATION OF STRONTIA AS SULPHATE, WITH CORRECTION (to 102, 1, a). The filtrate obtained in No. 64, b, weighed 190 '84 grm. According to experi- ment No. 22, 118G2 parts of water containing sulphuric acid dissolve 1 part of sulphate of strontia; therefore, 190 "84 grm. dissolve 0'0161. The washings weighed 63 61 grm. According to experiment No. 21, 6895 parts of water dissolve 1 part of Sr 0, S 3 ; therefore, 63 -61 grm. dissolve 0'0092 grm. Adding 0'0161 and 0'0092 to the 1 '4024 actually obtained, we find the total amount = 1 -4277 grm., which corresponds to '80465 Sr = 69 '91 per cent, in Sr O, C 0. (calculated 70 '07 per cent.) ; i.e., 99 '77 instead of 100. 66. DETERMINATION OF STRONTIA AS CARBONATE OF STRONTIA (to 102, 2). 1-3104 grm. chloride of strontium, precipitated according to 102, 2, gave 1-2204 Sr 0, C 2 , containing 0'8551831 Sr 0=65 '26 per cent, (calculated 65 '38) ; i.e., 99 '82 instead of 100. IN THE FOUR FOLLOWING EXPERIMENTS, AND ALSO IN No. 72, PURE AIR- dried carbonate of lime was used, in a portion of which the amount of anhydrous carbonate had been determined by very cautious heating. 0'7647 grm. left 0'7581 grm., which weight remained unaltered upon further (extremely gentle) ignition; tlie air-dried carbonate contained accordingly 55*516 per cent, of lime. 596 EXPERIMENTS. 67. DETERMINATION OP LIME AS SULPHATE OF LIME BY PRECIPITATIC s (to 103,1, a). 1186 grm. of "the air-dried carbonate of lime " was dissolved in hydrochloric acid, and the solution precipitated with sulphuric acid and alcohol, after 103, 1, a. Obtained 1/5949 giro. Ca (X 8 O ;) , containing 0-65598 Ca O, i.e., 55 '31 per cent, (calculated 55 '51), which gives 99 '64 instead of 100. 68. DETERMINATION OF Ca AS Ca 0, C 0^-, BY PRECIPITATION WITH CARBONATE OF AMMONIA AND WASHING WITH PURE WATER (to 103, 2, a). A hydrochloric acid solution of 1*1437 grm. of "the air-dried carbonate of lime" gave upon precipitation as directed, 11243 grm. anhydrous carbonate of lime, corresponding to '629608 Ca = 55 '05 per cent, (calculated 55 '51 per cent.) which gives 9917 instead of 100. 69. DETERMINATION OP Ca O AS Ca 0, C O 2 , BY PRECIPITATION WITH OXALATE OF AMMONIA PROM ALKALINE SOLUTION (to 103, 2, b, u). 1*1734 grin, of "the air-dried carbonate of lime" dissolved in hydrochloric acid, and treated as directed 103, 2, b, , gave 11632 grm. Ca O, C 2 (reaction not alkaline), containing 0*651392 of Ca O = 55 '513 per cent, (calculated 55 '5 16 per cent.), which gives 99*99 instead of 100. 70. DETERMINATION OP LIME AS OXALATE (to 103, 2, 5, a). 0*857 grm. of " the air-dried carbonate of lime " were dissolved in hydrochloric acid; the solution was precipitated with oxalate of ammonia and ammonia, the precipitate washed, and then dried at 100 , until the weight remained constant. The precipitate (2 Ca 0, O + 2 aq.) weighed 1*2461 grm., containing 0*477879 Ca O =5576 per cent, (calculated 55*516 per cent.), which gives 100 '45 instead of 100. 71. VOLUMETRIC DETERMINATION OP LIME PRECIPITATED AS OXALATE (to 103, 2, b, a ). Six portions, of 10 c. c. each, were taken of a solution of pure chloride of cal- cium; in 2 portions the lime was determined in the gravimetric way (by pre cipitation with oxalate of ammonia, and weighing as Ca O, C 2 ) ; in two by tht alkalimetric method (p. 171, ), and in two by precipitation with oxalate of am monia, and estimation of the oxalic acid in the precipitate by solution of per manganate of potassa. The following were the results obtained: a. In the gravimetric b. By the alkalimetric c. By solution of per- way. method. manganate of potassa 0*5617 Ca O, C O a 0*5614 0*5613 0*5620 " 0*5620 0'5620 72. DETERMINATION OP Ca O AS Ca 0, C O 2 BY PRECIPITATION AS 2 Ca O, PROM ACID SOLUTION (to 103, 2, b, B}. 0*857 grm. of " the air-dried carbonate of lime " dissolved in hydrochloric acid and precipitated from this solution according to the directions of 103, 2, b, /?> gave 0*8476 carbonate of lime (which did not manifest alkaline reaction, and tin weight of which did not vary in the least upon evaporation with carbona' =5 of ammonia), containing 0*474656 Ca O 55 *39 per cent, (calculated 55'51), which gives 99*78 instead of 100. 73. DETERMINATION OP MAGNESIA AS 2 Mg 0, P O 5 (to 104, 2). a. A solution of 1 *0587 grm. pure anhydrous sulphate of magnesia in water precipitated according to 104, 2, gave 9S34 pyrophosphate of magnesia, con- taining 0-35438 magnesia = 33*476 per cent, (calculated 33 38 per cent.), which gives 100-43 instead of 100. b. 0-9672 Mg O, S 3 gave 0'8974 2 Mg O, P O n = 33 '43 per cent, of Mg O (cal- culated 33-33), which gives 100 '30 instead of 100. EXPERIMENTS. 597 74. PRECIPITATION OP ACETATE OP ZINC BY SULPHURETTED HYDROGEN (to g 108, b). a. A solution of pure acetate of zinc was treated with the gas in excess, al- lowed to stand at rest for some time, and then filtered. The filtrate was mixed with ammonia ; it remained perfectly clear at first, and even after long standing a few hardly visible flakes only had separated. b A solution of acetate of zinc to which a tolerably large amount of acetio acid had been added previously to the precipitation with sulphuretted hydrogen, showed exactly the same deportment. 75. DETERMINATION OP IRON AS SULPHIDE (to 113, 2). 1 c. c. of a pure solution of sesquichloride of iron was precipitated with am- monia; obtained 0-1453 Fe, O 3 =010171 Fe. 10 c. c. was precipitated with ammonia and sulphide of ammonium, and treated after 113, 2, obtained 01596 Fe 8=010157 Fe. 10 c. c. again yielded 01605 Fe 8=0.1021 Fe. 76. DETERMINATION OF LEAD AS CIIROMATE (to 116, 4). 1*0083 grin, pure nitrate of lead were treated according to 116, 4. The pre- cipitate was collected on a weighed filter, and dried at 100% obtained 0*9871 grm. =0*67833 Pb O. This gives 67 '3 per cent. Calculation 67 '4. 0'9814 nitrate of lead again yielded 0"9625 chroinate = 67*4 per cent. 77. DETERMINATION OP MERCURY IN THE METALLIC STATE, IN THE WET WAY, BY MEANS OF PROTOCHLORIDE OF TIN (to 118, 1, b). 2 '01 grm. chloride of mercury gave 1 '465 grm. metallic mercury =72 '88 per cert, (calculated 73 '83 percent.), which gives 98 '71 instead of 100 (SCHAFFNER). The loss is not inherent in the method, i.e., it does not arise from mercury evaporating during the ebullition and desiccation (Expt. No. 54) ; but its origin lies in the fact that one usually does not allow sufficient time for the mercury to settle quite completely, and in general is not careful enough in decanting, and drying with paper, &c. 78. DETERMINATION OP COPPER BY PRECIPITATION WITH ZINC IN A PLAT- INUM DISH (to 119, 2). 30 '882 grm. pure sulphate of copper were dissolved in water to 250 c. c. ; 10 c. c. of the solution contained accordingly '31387 grm. metallic copper. a. 10 c. c. precipitated with zinc in a platinum dish, gave "3 140 = 100 "06 per cent. b. In a second experiment 10 c. c. gave 0'3138 = 100 per cent. 79. BEHAVIOR OP COPPER PRECIPITATED BY ZINC ON IGNITION IN HYDRO- GEN (to p. 229, foot-note). A dilute solution of sulphate of copper was acidified with hydrochloric acid and precipitated with zinc in a platinum crucible, the precipitate was washed with water, then with alcohol, and dried at 100. 0'796l grm. of this was ig- nited for i of an hour in a stream of hydrogen. It then weighed 0*7952 grm. 80. DETERMINATION OP COPPER AS SUBSULPHOCYANIDE (to 119, 3, b). 0*5965 grm. of pure sulphate of copper was dissolved in a little water, and, after addition of an excess of sulphurous acid, precipitated with sulphocyanide of potassium. The well-washed precipitate, dried at 100, weighed 2893, cor- responding to 01 892 Cu O =31 '72 per cent. As sulphate of copper contains 31 *83 per cent., this gives 99 '66 instead of 100. 81. DETERMINATION OF COPPER BY DE HAEN'S METHOD (to 119, 4, a). Four 10 c. c.'s of a solution of sulphate of copper, each 10 c. c. containing 0*0254 grm. Cu, were severally mixed with iodide of potassium, then with 50 c. c. of a solution of sulphurous acid (50 c. c. corresponding to 12 "94 c. c. iodine solu- tion). After addition of starch paste, iodine solution was added until the fluid appeared blue. 598 EXPERIMENTS. This required, In/s, 4-09 &, 3-95 c, 4-06 d, 3-95 As 100 c. c. of iodine solution contained '58043 grm. iodine, this gives For a, 0-0256 Cu instead of 0'0254 " b, 0-0260 " " " c, 0257 " " 44 d, 0-0260 44 4 ' Another experiment, made with 100 c. c. of the same solution of sulphate of copper, gave 0'26!)6 instead of 0'254 of copper. Nitrate of ammonia having been added to 10 c. c. of the solution of sulphate of copper, then some dilute hydro- chloric acid, 3 '4 and 35 c. c. of iodine solution were required instead of 4 c. c. , a proof that considerably more iodine had separated than corresponded to the oxide of copper. 82. ACTION OF SOLUTION OF CYANIDE OF POTASSIUM UPON AMMONIACAL SOLUTION OF OXIDE OF COPPER (to 119, 4, b). a. Three 10 c. c.'s of a solution of sulphate of copper, each 10 c. c. containing O'l grm. sulphate of copper, were mixed with increasing quantities of a solution of ammonia, and a sufficient amount of water to equalize the degree of concen- tration in the three portions. Solution of cyanide of potassium was then added, drop by drop, until the blue color had disappeared. This required the following quantities : Solution of sulphate Solution of w . Soltition of cyanide of copper. ammonia. of potassium. 10 c. c. 4 c. c. 12 c. c. 6'7 10 c. c. 8 c. c. 8c. c. 6'85 10 c. c. 16 c. c. c. c. 7'1 Neutral salts of ammonia also exercise some influence, as the following experi- ments show, which were made the next day with the same solutions : Sol. CuO, S O 3 . Sol. N H 3 . Water, &c. Sol. K Cy. 10 c, c. 2 c. c. 14 c. c. 6 -70 10 c. c. 2 c. c. 14 c. c. sol. N H 4 Cl (1 : 10) 7 '40 10 c. c. 6 c. c. 10 c. c. 2 c. c. 10 c. c. water, ) ~ m 4 c. c. S 0,dil. (1 : 5 f 8 c. c. N H 4 O, N O 5 (1 : 10) 6 c. c. water b. Several 10 c. c.'s of solution of sulphate of copper, each 10 c. c. containing O'l grm. of the salt, were mixed with 10 c. c.'s of a solution of sesquicarbonate of ammonia (1 : 10), and after addition of water or of solution of neutral ammo- nia salts, cyanide of potassium solution was added till the blue color had vanished. Temp. 60. c. c. CuO, S03 c. c. 2 N H< O, 3 COa c. c. Water, &c. c. c. K Cy. 10 10 10. water 10 10 10. NH 4 0,S0 3 (1:10) j }!^ 10 10 10. NH 4 0, N0 5 (1 : 10) j .V *J 10 10 10.NH 4 C1(1:10) The addition of the 2 drops of ferrocyanide of potassium does not much assist one in hitting the end-reaction, as the solution, which towards the end is colored red, gradually becomes light yellow when more cyanide is added, and is not fully decolorized till a further addition of the same salt has been made, and it has stood for some time. 83. PRECIPITATION OF NITRATE OF BISMUTH BY CARBONATE OF AMMONIA (to 120, 1, a). If a solution o" nitrate of bismuth, no matter whether containing much or little EXPERIMENTS. 509 free nitric acid, is mixed with water, precipitated with carbonatr of ammonia and ammonia, and filtered without applying- heat, the filtrate acquires, upon addition of sulphuretted hydrogen water, a blackish-brown color. But if the mixture be- fore filtering is heated for a short time nearly to boiling-, sulphuretted hydrogen fails to impart this color to the filtrate, or, at all events, the change of color is hardly visible to the eye looking through the full test-tube from the top. 84. DETERMINATION OF ANTIMONY AS SULPHIDE (to 125, 1). 0'559 grm. of pure air-dried tartar emetic, treated according to 125, 1, gave 0'2902 grm. tersulphide of antimony dried at 100 ,= '2492 grm. or 44 '58 per cent. of teroxide of antimony. Heated to blackening in a current of carbonic acid, the precipitate lost '0079 grm. (reckoned from a part to the whole), leaving accor- dingly '2#23 grm. of anhydrous tersulphide of antimony, which corresponds to '24245 grm. or 48 '37 per cent, of teroxide of antimony. As the tartar emetic contains 43 -70 per cent, of teroxide of antimony, the process gives, if the precip- itate is dried at 100, 10201 ; if heated to blackening, 99 '22 instead of 100. 89. DETERMINATION OP PHOSPHORIC ACID AS PYROPHOSPHATE OF MAG- NESIA (to 134, 6, a). 1*9159 and 2 '0860 grm. pure crystallized phosphate of soda, treated as directed 134, #, o, gave 0'5941 and 0'6494 grm. of pyrophosphate of magnesia respec- tively. These give 19 '83 and 19 '91 per cent, of phosphoric acid in phosphate of soda, instead of 19 '83 per cent. 90. DETERMINATION OF PHOSPHORIC ACID AS PHOSPHATE OF SESQUIOXIDE OF URANIUM (to 134, c). 30 c. c. of a solution of pure phosphate of soda, treated with sulphate of mag- nesia, chloride of ammonium, and ammonia, as directed 134, #, <<, gave 0*3209 grm. of pyrophosphate of magnesia. 10 c. c. contained accordingly '06982 grm. of phosphoric acid. 10 c. c. of the same solution were then precipitated with acetate of sesquioxide of uranium as directed 134, c. The ignited precipitate was treated with a little nitric acid, then again ignited ; after cooling, it weighed 0'3478 grm. cor- responding to '06954 grm. of phosphoric acid. 91. DETERMINATION OF FREE SULPHURETTED HYDROGEN BY MEANS OF SOLUTION OF IODINE (to 148, I., a). The experiments were made to settle the following questions: a. Does the quantity of iodine required remain the same for solutions of sul- phuretted hydrogen of different degrees of dilution ? b. Does the equation HS+I = HI+S really represent the decomposition which takes place V The sulphuretted hydrogen water was contained in a flask closed by a doubly- perforated cork ; into one aperture a siphon with pinchcock was fitted, to draw off the fluid ; into the other aperture a short open tube, which did not dip into the fluid. Question a. a. About 30 c. c. of iodine solution were introduced into a flask, which was then tared ; sulphuretted hydrogen water was added until the yellow color had just disappeared. The flask was then closed, weighed, starch paste added, and then solution of iodine until the fluid appeared blue. 70 '2 grm. H S water required 23 '4 c. c. iodine solution, 100 accordingly 33*33 c. c. 68 '4 grm. required 22 '7 c. c. iodine solution, 100 accordingly 33 '20 c. c. /?. Same process ; but the fluid was diluted with water free from air. 61 '5 grm. H S water + 200 grm. water required 20 '7 c. c. iodine solution, 100 accordingly 33 '65 c. c. 52 '4 grm. +400 grm. water required 17 '7 c. c. iodine solution, 100 accord- ingly 33'77. The ioiine solution contained '00498 iodine in 1 c. c. Considering that addition of a larger volume of water necessarily involves a slight increase in the quantity of iodine solution, these results may be considered sufficiently corre- sponding. 600 EXPERIMENTS. Question b. According- to a, 100 grm. of the H S water contained "02215 grm. H S, assum ing the proportion to be 1 00 : $3 '2. 173 '0 grm. of the same water were, immediately after the experiments in a, drawn off into a hydrochloric acid solution of arsenious acid ; after 24 hours, the tersulphide of arsenic acid was filtered off, dried at 100, and weighed. 0'0920 grm. were obtained, which corresponds to '03814 H S, or a percentage of 0-02197. The second question also is therefore answered in the affirmative. 92. SOLUTION OP CHLORIDE OF MAGNESIUM DISSOLVES OXALATE OF LIME (to 154, 6). If some chloride of calcium is added to a solution of chloride of magnesium, then a little oxalate of ammonia, no precipitate is formed at first ; but upon slightly increasing the quantity of oxalate of ammonia, a trifling precipitate gradually separates after some time. If an excess of oxalate of ammonia is added, the whole of the lime is thrown down, but the precipitate contains also oxalate of magnesia. This shows that to effect the separation of the two bases by oxalate of ammonia, the reagent must be added in excess ; whilst, on the other hand, in the presence of much magnesia, the operator must expect to precipitate some of the magnesia, as the following experiments (No. 93) clearly show. 93. SEPARATION OF LIME FROM MAGNESIA (to 154, 6). The fluids employed in the following experiments were, a solution of chlo- ride of calcium, 10 c. c. of which corresponded to 0'5618 Ca O, C O ; a solu- tion of chloride of magnesium, containing () - 250 Mg O in 10 c. c. ; a solution of chloride of ammonium (1 : 8) ; solution of ammonia, containing 10 per cent. N H 3 ; solution of oxalate of ammonia (1 : 24) ; acetic acid, containing 30 per cent. A, H O. The precipitation was effected at the common temperature ; the precipitate of oxalate of lime was filtered off after 20 hours. a. Influence of the degree of dilution. . 10 c. c. Mg Cl, 10 c. c. Ca Cl, 10 c. c. N H 4 Cl, 4 drops N H 4 O, 50 c. c. water, 20 c. c. 2 N H, O, 6. Result, 0*5705 Ca O, C O a . /?. Same as a, with 150 c. c. water instead of 50 c. c. Result, 0'5670 Ca O, C 2 . b. Influence of excess of ammonia. Same as , + 10 c. c. N H,O. Result, 0'5614 grm. Ca O, C O 2 . c. Influence of excess of chloride of ammonium. Same as a, 0+40 c. c. N H 4 C1. Result. 5652 grm. d. Influence of excess of ammonia and chloride of ammonium. Same as a, 0+30 c. c N H 4 C1+ 10 c. c. N H 4 O. Result, 0'5613 grm. e. Influence of free acetic acid. _ Same as a, 0, only with 6 drops A, instead of tlie 4 drops N H 4 O. Result, 0*5594 grm. / Influence of excess of oxalate of ammonia, in feebly alkaline solution. Same as , 0+20 c. c. 2 NH, O, 6. Result, 0'5644 grm. Ca O, C O 2 . g. Influence of excess of oxalate of ammonia, in strongly alkaline solution Same as a, 0,+.10 c. c. NH.O+20 c. c. 2 N H 4 O. 6. Result, 0.5644. Ti. Influence of excess of oxalate of ammonia, in presence of much N H 4 C1 and NH 4 O. Same as a, 0, +10 N H 4 0+30 NH 4 C1+20 2NH 4 0, O. Result, 0-5709 grm. i. Influence of excess of oxalate of ammonia, in solution slightly acidified with A. Same as a, 0, 4 drops N H 4 O + 6 drops A+20 c. c. 2 N H 4 O, O. Result, 0-5661 grm. Consequently, when a notable amount of magnesia is present there is always a chance of oxalate of magnesia, or oxalate of magnesia and ammonia precipitating along with the oxalate of lime. EXPERIMENTS. 601 Another series of experiments in which a solution of oxalate of magnesia in hydrochloric aoid was mixed with ammonia under varying circumstances, proved also that, in presence of a notable quantity of magnesia, oxalate of magnesia, o oxalate of magnesia and ammonia, will always separate after standing for somo time, no matter whether in a cold or a warm place. In a third series of experiments, the separation was effected by double precip- itation, in accordance with 29- The same solutions were employed as in the first series, with the exception of the chloride of magnesium, for which a solu- tion was substituted containing - 2182 grm. Mg O, in 10 c. c 10 c. c. CaCl + 30 c. c. Mg 01, + 20 c. c. NH 4 C1, +300 c. c. water, + 6 drops ammonia, -f a sufficient excess of oxalate of ammonia. Results, in two experi- ments, 0-5021 and 0'5052, mean '503(5, instead of 0'5618 Ca O, CO, ; also 0'6u60 and 0-6489 Mg 0, mean 0'6574, instead of 0'6546. 94. SEPARATION OF IODINE FROM CHLORINE BY PISANI'S METHOD (to 169, 204). 0'2338 gnu. iodide of potassium, dissolved in water, + c. c. of solution of iodide of starch, required 14 c. c. of decinormal silver solution 0'2322 grm. iodide of potassium. 0'3025 grm. iodide of potassium, mixed with about double the quantity of chloride of sodium, required 18 '2 c. c. silver solution =0 "3021 K I. 0'2266 grm. iodide of potassium, mixed with about 100 times as much chloride of sodium, required 13 '7 c. c. silver solution == 0'2272 K I. 95. SEPARATION OF IODINE FROM BROMINE, BY PISANI'S METHOD (to 169, 209). 0'3198 grm. iodide of potassium, mixed with double the quantity of bromide of potassium, required 19 '2 c. c. of decinormal silver solution = 0'3187 K I. 99. CHLORIMETRICAL EXPERIMENTS (to 213). 10 grm. of chloride of lime were rubbed up with water to one litre, with which the following experiments were made : a. By PENOT'S method ( 212); obtained 23 '5 and 23 '5 per cent. b. By means of iron ( 213, modification) ; obtained 23 '6 per cent. c. By BUNSEN'S method (p. 508, C) ; results, 23 '6 23*6 percent. 100. DRYING OF MANGANESE (to 214, I.) Four small pans, containing each 8 grm. of manganese of 53 per cent. , werr first heated in the water-bath. After 3 hours, I. had lost 145 ; after 6 hours. II. 015; after 9 hours, III. 0*15; after 12 hours, IV. 15. grm. I. and II. having been left standing, loosely covered, in the room for 12 hours, II. was found to weigh exactly as much as at first ; I. wanted only '01 grm. of the ori- ginal weight. The four pans were now heated for two hours to 120. After cooling, they were found to have lost each 0'180 of the original weight. I. and II. having been left standing, loosely covered, in the room for 60 hours, were found to have again acquired their original weight by attracting moisture. III. and IV. were heated for 2 hours to 150 J . The loss of weight in both c;ises was 0'215 grm. Having been left standing, loosely covered, in the room for 72 hours, both were found to weigh '05 less than at first. Assuming the hygroscopic moisture ex- pelled to be re-absorbed by standing in the air, this shows that at 150" a little chemically combined water escapes along with the moisture, and accordingly that the temperature must not exceed 120. My experiments will be found described in detail in DINGLER'S polyt. Journ.. 135, 277 et seq. TABLE I. 603 TABLES FOR THE CALCULATION OF ANALYSES. TABLE I. EQUIVALENTS OP THE ELEMENTS CONSIDEKED IN THE PRESENT WORK.* Aluminium Al Antimony- Arsenic Sb As Barium Ba Bismuth Bi Boron B Bromine Br Cadmium Cd Caesium Cs Calcium Ca Carbon Chlorine Cl Chromium Cr Cobalt Co Copper Fluorine Cu Fl Gold Au Hydrogen Iodine H I Iron Fe Lead Pb Lithium Li Magnesium Manganese Mercury Molybdenum Nickel Mg Mn Hg Mo Ni Nitrogen Oxygen Palladium N Pd Phosphorus Platinum P Pt Potassium K Rubidium Rb Selenium Se Silicon Si Silver Sodium Ag Na Strontium Sr Sulphur Thallium S Tl Tin Sn Titanium Ti Uranium Ur Zinc Zn 13-75 122-00 75-00 68-50 208 -OOf 11-00 80-00 56-00 133-00 20-00 6-00 35-46 26-24 29-50J 31-70 19-00 196-00 1-00 127-00 28-00 103-50 7-00 12-00 27-50 100-00 46-0011 29-501 14-00 8-00 53-00 31-00 98-94 3911 85-40 39-5** (DUMAS) ( DUMAS) (PELOUZE, BERZELIUS) (DUMAS) (SCHNEIDER) (BERZELIUS) (MARION AC) (C. v. HAUER) (JOHNSON and ALLEN, BUNSEN) (DUMAS, ERDMANN and MARCHAND) (DUMAS, EKDMANN and MARCHAND) (MARIGNAC, STAS) (BERLIN, PELIGOT) (RoTiiopp, DUMAS) (ERDMANN and MARCHAND) (LOUYET) (Comp. STRECKER, loc. cit.) (DUMAS) (MARIGNAC, DUMAS) (ERDMANN and MARCHAND) (BERZELIUS, DUMAS) (C. DIEHL, TROOST) (MARCHAND and SCHEERER) (v. HAUER, DUMAS) (ERDMANN and MARCHAND) (BERLIN) (RoTHOFF, MARIGNAC, DUMAS) (MARIGNAC) (BERZELIUS. comp. STRECKER, loc. cit.) (SCHROTTER) (ANDREWS) (MARIGNAC, STAS) (BUNSEN, PICCARD) \ (BERZELIUS, SACC, ERDMANN, and } MARCHAND mean) 14 -OOff (DUMAS) 107-97 (MARIGNAC) 23-00 (PELOUZE, STAS) 43 '75 (DUMAS) 16-00 (ERDMANN and MARCHAND) 203-OOtt (CROOKES) 59 -00 1| | (DUMAS) 25 'GO (PIERRE) 59-40[f(EBELMEN) 32-53 (AXEL ERDMANN) * It has been necessary to alter the numbers in some cases where no new special experiments have been made. This arose from the fact that the numbers in question were deduced from other equiva- lents which have since been corrected. Those who are carious in the matter of equivalents should re- fer to Handworterbuch der reinen und angewandten Chemie, 2 Aufl. Bd. II. 4B3, article Atomge- wichte, by A. Strecker. With respect to the equivalents that have recently been redetermined, comp. Zeitschrift f. Anal. Chem. t Dumas makes 210-00. $ W. J. Russell found 29-37. (Journ. Chem. Soc. (2). I. 51.) 1 Dumas mnkes it 48-00. 1 W. J. Russell found 29-37 (loc. cit.). ** Duinas found 89-75. tt Silicic Acid=Si O.>. ft After Lamy 204-00, III After Mulder 58-00. H Comp. p. 141, note t. 604 TABLE II. TABLE IL COMPOSITION OF THE BASES AND OXYGEN ACIDS. a. BASES. GROUP I. Cassia Cs . CsO . 133-00 8-00 . 141-00 94-33 5-07 10000 Rubidia Rb . O RbO 85-40 8-00 93-40 91 -43 8-57 100-00 Potassa KO. 39-11 8-00 47-11 83-02 100-00 Soda Na . O NaO 23-00 8-00 31-00 74-19 25-81 100-00 Lithia Li . O LiO 7-00 8-00 1500 46-07 53-33 100-00 Oxide of Ammonium GROUP II. Baryta NH 4 O N H 4 . Ba . O BaO 18-00 8-00 26-00 68-50 8-00 76-50 69-23 30-77 100-00 89-54 10-46 . 100-00 Strontia Sr . O SrO 43-75 8-00 51-75 84-54 15-46 100-00 Lime Ca . O CaO 20-00 800 28-00 71-43 28-57 100-00 Magnesia Mg. O WgO . 12-00 8-00 20-00 60-03 39-97 . lOO'OC TABLE II. 605 GROUP HI. Alumina Al a . 3 . A1 2 3 27-50 24-00 51-50 53-40 46-60 100-00 Sesquioxide of Chromium Cr 2 3 . Cr 2 O s 52-48 24-00 76-48 68-62 31-38 100-00 GROUP IV. Oxide of Zinc Zn . O , ZnO 53 00 4053 80-26 19-74 . 100-00 Protoxide of Manganese Mn O . MnO 27-50 8-00 35-50 77-46 22-54 100-00 Sesquioxide of Manganese Mn 2 3 . Mn 2 a 55-00 24-00 79-00 69-62 30-38 100-00 Protoxide of Nickel M . O 29-50 8-00 37-50 78-67 21-33 100-00 Protoxide of Cobalt Co . O . CoO 29-50 8-00 37-50 78-67 21-33 100-00 Sesquioxide of Cobalt Co 2 3 . Co 2 3 . 59-00 24-00 83-00 71-08 28-92 100-00 Protoxide of Iron Fe . O . FeO 2800 8-00 36-00 77-78 2222 100-00 Sesquioxide of Iron Fe 2 . 3 . Fe 2 3 56-00 24-00 80-00 70-00 30-00 100-00 GROUP V. Oxide of Silver AgO 107-97 8-00 115 -9 r 93-10 6-90 Too-oo 606 Oxide of Lead Suboxide of Mercury Oxide of Mercury Suboxide of Copper Oxide of Copper Teroxide of Bismuth Oxide of Cadmium GROUP VL Teroxide of Gold Binoxide of Platinum Teroxide of Antimony Protoxide of Tin Binoxide of Tin TABLE II. Pb . . . . . 103-50 . . 8-00 . . 9283 . 717 PbO . . 111-50 . . 10000 Hga . o . . . 200-00 . 8-00 . 96-15 . 3-85 Hg.O . . 208-00 . . 100-00 Hg . O . . . 100-00 . 8-00 . 92-59 . 7-41 HgO . . 108-00 . . 100-00 Cu 2 . O . . 63-40 . 8-00 . 88-80 . 11-20 Cu 2 O . . 71-40 . . 100-00 Cu. O . . 31-70 . 8-00 . 79-85 . 20-15 CuO . . 39-70 . . 100-00 Bi . 3 . . . 208-00 . 24-00 . 89-66 . 10-34 Bi0 3 . . 232-00 . . 100-00 Cd. . . . 56-00 . 8-00 . 87-50 . 12-50 CdO . . 64-00 . . 100-00 Au 3 . . . 196-00 . 24-00 . . 89-09 . 10-91 Au0 3 . . 220-00 . . 100-00 Pt . . 2 . . 98-94 . . 10-00 . 86-08 . 13-92 PtOa . . 114-94 . . 100-00 Sb . 3 . . . 122-00 . 24-00 . 83-56 . 16-44 Sb0 3 . . 146-00 . . 100-00 Sn . . . . 59-00 . 8-00 . 88-06 . 11-94 SnO . . 67-00 . . 100-00 Sn . . O. . . . 59-00 . . 16-00 . 78-67 . 21-33 SnO. 75-00 100-00 TABLE II. 607 Arsenious acid Arsenic acid Chromic acid Sulphuric acid Phosphoric acid Boracic acid Oxalic acid Carbonic acid Silicic acid Nitric acid Chloric acid As . 3 . . . 75-00 . . . 24-00 . . 75-76 . 24-24 As0 3 . . 99-00 . . 100-00 As . 5 . 75-00 . . 40-00 . 65-22 . 34-78 As0 6 . . 115-00 . . 100-00 5. ACIDS. Cr . 3 . 26-24 . . 2400 . 52-23 . 47-77 CrOs . . 50-24 . . 100-00 8 8 . . . 16-00 , . . 24-00 . , 40-00 . 60.00 S0 8 . . 40-00 . . 100-00 p . 5 . 31-00 . . 40-00 . . 43-66 . 56-34 P0 6 . . 71-00 . . 100-00 B . 3 . 11-00 . . 24-00 . 31-43 . 68-57 B0 3 . . 35-00 . . 100-00 C 4 . 6 . . . 24-00 , . . 48-00 . . 33-33 . 66-67 C 4 . . 72-00 . . 100-00 C . 2 . 6-00 , . . 16-00 . 27-27 . 72-73 C0 2 . . 22-00 . . 100-00 Si . 2 . . . 14-00 , . . 16-00 . 46-67 . 53-33 Si0 2 . . 30-00 . . 100-00 N . 5 . . 14-00 . . 40-00 . 25-93 . 74-07 N0 5 . . 54-00 . . 100-00 01 . 6 . 35-46 . . 40-00 . 46-99 . .53-01 01 6 75-46 100 -OC 608 TABLE III. TABLE III. REDUCTION OP COMPOUNDS FOUND TO CONSTITUENTS SOUGHT BY. SIMPLE MULTIPLICATION OR DIVISION. This Table contains only some of the more frequently occurring- compounds ; the formulas preceded by ! give absolutely accurate results. The Table may also be extended to other compounds, by proceeding according to the instruc- tions given in 199. FOR INORGANIC ANALYSIS. CARBONIC ACID. 1 Carbonate of lime x '44= Carbonic acid. CHLORINE. Chloride of silver xO '24724= Chlorine. COPPER. Oxide of copper x 0'79S49= Copper. IRON. ! Sesquioxide of iron x 0*7=2 Iron. ! Sesquioxide of iron xO '9 =2 Protoxide of iron. LEAD. Oxide of lead x 0-9283 -Lead. MAGNESIA. Pyrophosphate of magnesia x '36036 =2 Magnesia. MANGANESE. Protosesquioxide of manganese x -72052 3 Manganese. Protosesquioxide of manganese x 0-93013=3 Protoxide of manganese. PHOSPHORIC ACID. Pyrophosphate of magnesia x '6396= Phosphoric acid. Phosphate of Sesquioxide of uranium (2 Ur-j 3 , P0 5 ) xO-1991=Phosphonc acid. POTASSA. Chloride of potassium x '52445= Potassium. Sulphate of potassa *0'5408 = Potassa. Potassio-bichloride of platinum x '30507 "] Potaasio-bichlorideof platinum [ -Chloride of potassium. 8'27 7 TABLE III. 609 Potassio-bichloride of platinum x 019272") or Potassio-bichloride of platinum 5188 SODA. Chloride of sodium x '5302= Soda. Sulphate of soda x '43658= Soda. SULPHUR. Sulphate of baryta x 013734= Sulphur. SULPHURIC ACID Sulphate of baryta x '34335= Sulphuric acid. FOR ORGANIC ANALYSIS. CARBON. Carbonic acid xO '2727^ or Carbonic acid 3'666 !- = Carbon. or Carbonic acid x 3 11 J HYDROGEN. Water x 0111111 Water [ ^Hydrogen. 9 J NITROGEN. Ammonio-bichloride of platinum x '06269= Nitrogen. Platinum x 01415= Nitrogen. 39 610 TABLE iv. TABLE Showing the Amount of the Number of the Elements. Found. Sought. 1 Aluminium. . Alumina Aluminium 0-53398 Al a O a Al a (Ammonium) Chloride of ammonium Ammonia 0-31804 NH 4 Cl NH 3 Ammonio-bichloride of platinum Oxide of ammonium 011644 N H 4 Cl, Pt Cl a NH 4 O Ammonio-bichloride of platinum Ammonia 0-07614 N H 4 Cl, Pt C1 2 NH 3 Antimony. . . Teroxide of antimony Antimony 0-83562 SbO 3 Sb Tersulphide of antimony Antimony 0-71765 Sb S 3 Sb Tersulphide of antimony Teroxide of antimony 0-85882 Sb S 3 Sb O 3 Antimonious acid Teroxide of antimony 0-94805 SbO 4 SbO 3 Arsenic Arsenious acid Arsenic 0-75758 AsO 3 As Arsenic acid Arsenic 0-65217 AsO 5 As Arsenic acid Arsenious acid 0-86087 As O 5 AsO 3 Tersulphide of arsenic Arsenious acid 0-80488 AsS 3 AsO 3 - Tersulphide of arsenic Arsenic acid 0-93496 As S 3 AsO 5 Arseniate of ammonia and magnesia Arsenic acid 0-60526 2 Mg 0, N H 4 0, As Or, + aq As O 5 Arseniate of ammonia and magnesia Arsenious acid 0-52105 2 Mg O, N H 4 0, As O 5 + aq AsO 3 Barium Baryta Barium 0-89542 BaO Ba Sulphate of baryta Baryta 0-65665 Ba O, S O 3 Ba O Carbonate of baryta Baryta 0-77665 Ba O, C 2 Ba O Silico-fluoride of barium Baryta 0-54839 Ba Fl, Si F1 2 Ba O Bismuth Teroxide of bismuth Bismuth 0-89655 BiO 3 Bi Boracic acid Boron 0-31429 B0 3 B Bromine Bromide of silver Bromine 0-42560 AgBr Br Cadmium.. . . Oxide of cadmium Cadmium 0-87500 CdO Cd Calcium Lime Calcium 0-71429 CaO Ca Sulphate of lime Lime 0-41176 Ca O. S O 3 CaO Carbonate of lime Lime 0-56000 Ca 0, C 2 CaO Carbon Carbonic acid Carbon 0-27273 CO 2 C TABLE IV. 611 IV. Constituent sought for every Compound found. 2 3 4 5 6 7 8 9 1-06796 1-60194 2-13592 2-66990 3-20389 3-73787 4-27185 4-80583 0-63608 0-95413 1-27217 1-59021 1-90825 2-22629 2-54433 2-86237 0-23288 0-34932 0-46576 0-58220 0-69864 0-81508 0-93152 1-04796 0-15228 0-22842 0-30456 0-38070 0-45684 0-53299 0-60913 0-68527 1-67123 2-50685 3-34247 4-17808 5-01370 5-84932 6-68194 7-52055 1-43529 2-15294 2-87059 3-58834 4-30588 5-02353 5-74118 6-45882 1-71765 2-57647 3-43530 4-29412 5-15294 6-01177 6-87059 7-72942 1-89610 2-84416 3-79221 4-74026 5-68831 6-63636 7-58442 8-53247 1-51516 2-27274 3-03032 3-78790 4-54548 5-30306 6-06064 6-81822 1-30435 1-95652 2-60870 3-26087 3-91304 4-56522 5-21739 5-86957 1-72174 2-58261 3-44348 4-30435 516521 6-02608 6-88695 7-74782 1-60975 2-41463 3-21951 4-02439 4-82927 5-63415 6-43902 7-24390 1-86992 2-80488 3-73984 4-67480 5 -60975 6-54471 7-47967 8-41463 1-21053 1-81579 2-42105 3-02631 3-63158 4-23684 4-84210 5-44737 1-04210 1-56316 2-08421 2-60526 3-12631 3-64736 4-16842 4-68947 1-79085 2-68627 3-58170 4-47712 5-37255 6-26797 716340 8-05882 1-31330 1-96996 2-62661 3-28326 3-93991 4-59656 5-25322 5-90987 1-55330 2-32995 3-10660 3-88325 4-65990 5-43655 6-21320 6-98985 1-09677 1-64516 2-19355 2-74194 3-29032 3-83871 4-38710 4-93548 1-79310 2-68965 3-58620 4-48275 5-37930 6-27586 7-17240 8-06895 0-62857 0-94286 1-25714 1-57143 1-88572 2-20000 2-51429 2-82857 0-85120 1-27680 1-70240 2-12800 2-55360 2-97920 3-40480 3-83040 1-75000 2-62500 3-50000 4-37500 5-25000 6-12500 7-00000 7-87500 1-42857 2-14286 2-85714 3-57143 4-28571 5-00000 5-71429 6-42857 0-82353 1-23529 1-64706 2-05882 2-47059 2-88235 3-29412 3-70588 1-12000 1-68000 2-24000 2-80000 3-36000 3-92000 4-48000 5-04000 0-54546 0-81818 1-09091 1-36364 1-63636 1-90909 2-18181 2-45455 612 TABLE IV. TABLE IV, Elements. Found. Sought. 1 Carbon . . Carbonate of lime Carbonic acid 0-44000 CaO, C0 2 CO 2 Chlorine Chloride of silver Chlorine 0-24724 AgCl Cl Chloride of silver Hydrochloric acid 0-25421 AgCl HC1 Chromium. . . Sesquioxide of chromium Chromium 0-68619 Cr 2 3 Cr 2 Sesquioxide of chromium Chromic acid 1-31381 Cr. 2 3 2Cr0 3 Chromate of lead Chromic acid 0-31062 Pb 0, Cr O 3 Cr O 3 Cobalt Cobalt Protoxide of cobalt 1 -27119 Co CoO Sulphate of protoxide of cobalt Protoxide of cobalt 0-48387 Co 0, S O 3 CoO Sulphate of cobalt + sulphate of Protoxide of cobalt 0-18015 potassa 2 CoO 2 (Co O, S O 8 ) + 3 (K O. S 8 ) Sulphate of cobalt -f- sulphate of Cobalt 014171 potassa 2 Co 2 (Co 0, S O 3 ) + 3 (K O, S O 3 ) Copper Oxide of copper Copper 0-79849 Cu O Cu Subsulphide of copper Copper 0-79849 Cu a S Cu 2 Fluorine Fluoride of calcium Fluorine 0-48718 CaFl Fl Fluoride of silicon Fluorine 0-73077 Si F1 3 F1 2 Hydrogen... Water Hydrogen 0-11111 HO H Iodine Iodide of silver Iodine 0-54049 Agl I Protiodide of palladium Iodine 0-70556 Pdl I Iron Sesquioxide of iron Iron 0-70000 Fe 3 O 3 Fe 2 Sesquioxide of iron Protoxide of iron 0-90000 Fe 3 3 2FeO Sulphide of iron Iron 0-63636 Fe S Fe Lead Oxide of lead Lead 0-92825 PbO Pb Sulphate of lead Oxide of lead 0-73597 .PbO, S0 3 PbO Sulphate of lead Lead 0-68317 Pb O, S O 3 Pb Sulphide of lead Oxide of lead 0-93305 PbS PbO Lithium. .... Carbonate of lithia Lithia 0-40541 Li 0, C O 2 Li O Sulphate of lithia Lithia 0-27273 LiO,0 3 Li O Basic phosphate of lithia Lithia 0-38793 3 Li O, P O 5 3LiO TABLE IV. 613 (continued). 2 3 4 5 6 7 8 9 0-88000 1-32000 1-76000 2-20000 2-64000 3-08000 3-52000 3-96000 0-49448 0-74172 0-98896 1 -23620 1-48344 1-73068 1-97792 2-22516 0-50843 0-76263 1-01684 1-27105 1-52526 1-77947 2-03368 2-28789 1-37238 2-05858 2-74477 3-43096 4-11715 4-80334 5-48954 6-17573 2-62762 3-94142 5-25523 6-56904 7-88285 9-19666 10-51046 11-82427 0-62124 0-93187 1-24249 1-55311 1 -86373 2-17435 2-48498 2-79560 2-54237 3-81356 5-08474 6-35593 7-62712 8-89830 1016949 11-44067 0-96774 1-45161 1-93548 2-41935 2-90323 3-38710 3-87097 4-35484 0-36029 0-54044 0-72058 0-90073 1-08088 1 -26102 1-44117 1 -62131 0-28343 0-42514 0-56686 0-70857 0-85029 0-99200 1-13372 1-27543 1-59698 2-39547 319396 3-99244 4-79093 5-58942 6-38791 718640 1-59698 2-39547 319396 3-99244 4-79093 5-58942 6-38791 7-18640 0-97436 1-46154 1-94872 2-43590 2-92307 3-41027 3-89743 4-38461 1-46154 2-19231 2-92308 3-65385 4-38461 5-11538 5-84615 6-57692 0-22222 0-33333 0-44444 0-55555 0-66667 0-77778 0-88889 1-00000 1-08099 1-62148 2-16198 2-70247 3-24297 3-78346 4-32396 4-86445 1-41111 2-11667 2-82222 3-52778 4-23334 4-93889 5-64445 6-35000 1-40000 2-10000 2-80000 3-50000 4-20000 4-90000 5-60000 6-30000 1-80000 2-70000 3-60000 4-50000 5-40000 6-30000 7-20000 810000 1 -27273 1-90909 2-54546 3-18182 3-81818 4-45455 5-09091 5-72728 1 -85650 2-78475 371300 4-64126 5-56951 6-49776 7-42601 8-35426 1-47195 2-20792 2-94390 3-67987 4-41584 515182 5-88779 6-62377 1-36634 2-04950 2-73267 3-41584 4-09901 4-78218 5-46534 6-14851 1-8C611 2-79916 3-73222 4-66527 5-59832 6-53138 7-46443 8-39749 0-81081 1-21622 1-62162 2-02703 2-43243 2-83784 3-24324 3-64865 0-54545 0-81818 1-09091 1-36364 1-63636 1-90909 2-18182 2-45454 0-77586 1-16379 1-55172 1-93966 2-32759 2-71552 3-10345 3-49138 614 TABLE IV. TABLE IV. Elements. Found. Sought. l Magnesium. . Magnesia Magnesium 0-60030 MgO Mg Sulphate of magnesia Magnesia 0-33350 Mg O, S O 3 MgO Pyrophosphate of magnesia 2MgO,P0 5 Magnesia 2 MgO 0-36036 Manganese. . Protoxide of manganese Manganese 0-77465 MnO Mn Protosesquioxide of manganese Mn 0+Mn 2 O 3 Manganese Mn 3 0-72052 Sesquioxide of manganese Manganese 0-69620 Mn 2 O 3 Mn 2 Sulphate of protoxide of manganese Protoxide of manganese 0-47020 Mn 0, S O 3 MnO Sulphide of manganese Protoxide of manganese 0-81609 Mn S MnO Sulphide of manganese Manganese 0-63218 MnS Mn Mercury Mercury Suboxide of mercury 1-04000 Hg 2 Hg 2 O Mercury Oxide of mercury 1-08000 Hg HgO Subchloride of mercury Mercury 0-84940 . Hg 2 Cl Hg 2 Sulphide of mercury Mercury 0-86207 HgS Hg Nickel Protoxide of nickel Nickel 0-78667 MO Ni Nitrogen Ammonio-bichloride of platinum Nitrogen 0-06071 N H 4 Cl. Pt C1 2 N Platinum Nitrogen 0-14155 Pt N Sulphate of baryta Nitric acid 0-46352 Ba 0, S 3 NO 5 Cyanide of silver Cyanogen 019410 AgC 2 N C 2 N Cyanide of silver Hydrocyanic acid 0-20156 AgC 2 N HC 2 N Oxygen Alumina Oxygen 0-46602 Al a 3 3 Teroxide of antimony Oxygen 0-16438 Sb0 3 3 Arsenious acid Oxygen 0-24242 As0 3 3 Arsenic acid Oxygen 0-34783 As0 5 5 Baryta Oxygen 0-10458 BaO Teroxide of bismuth Oxygen 0-10345 BiO 3 3 Oxide of cadmium Oxygen 0-12500 CdO O Sesquioxide of chromium Oxygen 0-31381 Cr 2 0% 3 Protoxide of cobalt Oxygen 0-21333 CoO TABLE IY. 615 (continued}. 2 3 4 5 6 7 i 8 9 1-20061 1-80091 2-40121 3-00151 3-60182 4-20212 4-80242 5-40273 0-66700 1-00051 1-33401 1-66751 2-00101 2-33451 2-66802 3-00152 0-72072 1-08108 1-44144 1-80180 2-16216 2-52252 2-88288 3-24324 1-54930 2-32394 3-09859 3-87324 4-64789 5-42254 619718 6-97183 1-44105 2-16157 2-88210 3-60262 4-32314 5-04367 5-76419 6-48472 1-39241 2-08861 2-78481 3-48102 417722 4-87342 5-56962 6-26583 0-94040 1-41060 1 -88080 2-35099 2-82119 3-29139 3-76159 4-23179 1-63218 2-44828 3-26437 4-08046 4-89655 5-71264 6-52874 7-34483 1-26437 1-89655 2-52874 316092 3-79310 4-42529 5-05747 5-68966 2-08000 3-12000 4-16000 5-20000 6-24000 7-28000 8-32000 9-36000 2-16000 3-24000 4-32000 5-40000 6-48000 7-56000 8-64000 9-72000 1-69880 2-54820 3-39760 4-24701 5-09641 5-94581 6-79521 7-64461 1-72414 2-58621 3-44828 4-31034 5-17241 6-03448 6-89655 7-75862 1-57333 2-36000 314667 3-93333 4-72000 5-50667 6-29334 7-08000 0-12542 0-18812 0-25083 0-31354 0-37625 0-43896 0-50166 0-56437 0-28310 0-42464 0-56619 0-70774 0-84929 0-99084 1-13238 1-27393 0-92704 1-39056 1-85408 2-31760 2-78111 3-24463 3-70815 417167 0-38820 0-58230 0-77640 0-97050 1-16460 1-35870 1 -55280 1-74690 0*40312 0-60468 0-80624 1-00780 1-20936 1-41092 1-61248 1-81404 0-93204 1-39806 1-86408 2-33010 2-79611 3-86213 3-72815 4-19417 0-32877 0-49315 0-65754 0-82192 0-98630 1-15069 1-31507 1-47946 0-48484 0-72726 0-96968 1-21210 1-45452 1-69694 1 -93936 2-18178 0-69565 1-04348 1-39130 1-73913 2-08696 2-43478 2-78261 3 -13043 : 0-20915 0-31373 0-41830 0-52288 0-62745 0-73203 0-83660 0-94118 0-20G90 0-31035 0-41380 0-51725 0-62070 0-72415 0-82760 0-93105' 0-25000 0-37500 0-50000 0-62500 0-75000 0-87500 1-00000 1-12500 0-62762 0-94143 1-25524 1-56905 1-88286 219667 2-51048 2-82429 0-42667 0-64000 C'85333 1-06667 1 -28000 1-49333 1-70666 1-92000 616 TABLE IV. TABLE IV Elementa Found. Sought. 1 Oxygen Oxide of copper Oxygen 0-20151 CuO Protoxide of iron Oxygen 0-22222 FeO Sesquioxide of iron Oxygen 0-30000 Fe 2 O 3 3 Oxide of lead Oxygen 0-07175 PbO Lime Oxygen 0-28571 CaO O Magnesia Oxygen 0-39970 MgO Protoxide of manganese Oxygen 0-22535 MnO Protosesquioxide of manganese Oxygen 0-27947 Mn O + Mn 2 3 4 Sesquioxide of manganese Oxygen 0-30380 Mn 2 3 - 3 Suboxide of mercury Oxygen 0-03846 Hg 2 O O Oxide of mercury Oxygen 0-07407 HgO Protoxide of nickel Oxygen 0-21333 MO O Potassa Oxygen 016982 KO O Silicic acid Oxygen 0-53333 SiO 2 2 Oxide of silver Oxygen 0-06898 AgO Soda Oxygen 0-25810 NaO O Strontia Oxygen 015459 SrO Binoxide of tin Oxygen 0-21333 SnO 2 2 Water Oxygen 0-88889 HO Oxide of zinc Oxygen 0-19740 ZnO O Phosphorus. . Phosphoric acid * Phosphorus 0-43662 P0 a P Pyrophosphate of magnesia Phosphoric acid 0-63964 2 Mg O, P O 6 P0 5 Phosphate of sesquioxide of iron Phosphoric acid 0-47020 . Fe 2 O 3 , P O 5 P0 5 Phosphate of silver Phosphoric acid 0-16949 3 Ag 0, P 6 P0 5 'hosphate of sesquioxide of uranium Phosphoric acid 019910 2 Ur 2 O 3 , P 5 P0 5 Pyrophosphate of silver Phosphoric acid 0-23437 2 Ag 0, P 5 P0 5 Potassium. . . Potassa Potassium 0-83018 KO K Sulphate of potassa Potassa 0-54080 K 0, S O a KO TABLE IV. 617 (continued). 2 3 4 i 5 6 7 8 9 0-40302 0-60453 0-80604 1-00756 1-20907 1-41058 1-61209 1-81360 0-44444 0.66667 0-88889 111111 1-33333 1 -55555 1-77778 2-00000 0-60000 JO -90000 1-20000 1-50000 1-80000 210000 2-40000 2-70000 014350 0-21525 0-28700 0-35874 0-43049 0-50224 0-57399 0-64574 0-57143 0-85714 114286 1-42857 1-71429 2-00000 2-28571 2-57143 0-79939 119909 1-59879 1-99849 2-39818 2-79788 319758 3-59727 0-45070 67606 0-90141 112676 1-35211 1-57746 1-80282 2-02817 0-55895 0-83843 111790 1-39738 1-67686 1-95633 2-23581 2-51528 0-60759 0-91139 1-21519 1-51899 1-82278 212658 2-43038 2-73417 0-07692 0-11539 015385 0-19231 0-23077 0-26923 0-30770 0-34616 0-14815 0-22222 0-29630 0-37037 0-44444 0-51852 0-59259 0-66667 0-42667 0-64000 0-85333 1-06667 1-28000 1-49333 1-70667 1-92000 0-33964 0-50946 0-67928 0-84910 1-01892 118874 1-35856 1-52838 1-06667 1-60000 213333 2-66667 3-20000 3-73333 4-26667 4-80000 0-13796 0-20694 0-27592 0-34490 0-41388 0-48286 0-55184 0-62082 0-51621 0-77431 1 -03242 1 -29052 1-54863 1-80673 2-06484 2-32294 0-30918 0-46377 0-61836 0-77295 0-92753 1-08212 1-23671 1-39130 0-42667 0-64000 0-85333 1-06667 1-28000 1-49333 1-70667 1 -92000 1-77778 2-66667 3-55556 4-44445 5-33333 6-22222 711111 8-00000 0-39480 0-59220 0-78960 0-98700 118440 1-38180 1-57920 1-77660 0-87324 1-30986 1-74648 218309 2-61971 3-05633 3-49295 3-92957 1-27928 1-91892 2-55856 319820 3-83784 4-47748 511712 5-75676 0-94040 1-41060 1-88080 2-35099 2-82119 3-29139 3-76159 4-23179 0-33898 0-50847 0-67796 0-84745 1-01694 1-18643 1-35592 1-52541 0-39821 0-59731 0-79641 0-99551 119462 1-39372 1-59282 1 -79192 0-46874 0-70311 0-93748 117185 1-40622 1-64059 1-87496 210933 1-66036 2-49054 3-32072 4-15090 4-98108 5-81126 6-64144 7-47162 1-08161 1-62241 216321 2-70402 3-24482 3-78563 4-32643 4-86723 618 TABLE IV. TABLE IV Elements. Found. Sought. i Potassium. . . Chloride of potassium Potassium 0-52445 KC1 K Chloride of potassium Potassa 0^63173 KC1 KO Potassio-bichloride of platinum Potassa 0-19272 K 01, Pt C1 9 KO Potassio-bichloride of platinum Chloride of potassium 0-30507 K 01, Pt C1 3 KC1 Silicon Silicic acid Silicon 0-46667 Si O 2 Si Silver Chloride of silver Silver 0-75276 AgCl Ag Chloride of silver Oxide of silver 0-80854 AgCl Ag Sodium Soda Sodium 0-74190 NaO Na Sulphate of soda Soda 0-43658 Na 0, S 3 NaO Chloride of sodium Soda 0-53022 NaCl Na O Chloride of Sodium Sodium 0-39337 NaCl Na Carbonate of soda Soda 0-58487 Na O, C O 2 NaO Strontium. . . Strontia Strontium 0-84541 SrO Sr Sulphate of strontia Strontia 0-56403 Sr 0, S 3 SrO Carbonate of strontia Strontia 0-70169 Sr 0, C O a SrO Sulphur. Sulphate of baryta Sulphur 013734 Ba 0, S 3 S Tersulphide of arsenic Sulphur 0-39024 As S 3 S 3 Sulphate of baryta Sulphuric acid 0-34335 Ba 0, S O 3 S0 3 Tin. ... Binoxide of tin Tin 0*78667 Sn O a Sn Binoxide of tin Protoxide of tin 0-89333 SnOa SnO Zinc .. Oxide of zinc Zinc 0*80260 ZnO Zn Sulphide of zinc Oxide of zinc 0-83515 ZnS ZnO Sulphide of zinc Zinc 0-67031 ZnS Zn TABLE IV. 619 (continued). 2 3 4 5 6 7 8 9 1-04890 1-57335 2-09780 2-62225 3-14669 3-67114 4-19559 4-72004 1-26346 1-89519 2-52692 315865 3-79037 4-42210 5-05383 5-68556 0-38545 0-57817 0-77090 0-96362 1-15634 1-34907 1-54179 1-73452 0-61015 0-91522 1-22030 1-52537 1-83044 213552 2-44059 2-74567 0-93333 1-40001 1-86667 2-33333 2-80000 3-26667 3-73333 4-20000 1-50552 2-25828 3-01104 3-76380 4-51656 5-26982 6-02208 6-77484 1-61708 2-42562 3-23416 4-04270 4-85124 5-65978 6-46832 7-27686 1-48379 2-22569 2-96758 3-70948 4-45137 519327 5-93516 6-67706 0-87316 1-30975 1-74633 2-18291 2-61949 3-05607 3-49265 3-92924 1-06043 1-59065 2-12086 2-65108 3-18130 3-71151 4-24173 4-77194 0-78673 118009 1 "57346 1-96683 2-36019 2-75356 3-14692 3-54029 1-16974 1-75460 2-33947 2-92434 3-50921 4-09407 4-67894 5-26381 1-69082 2-53623 3-38164 4-22705 5-07247 5-91788 6-76329 7-60870 1-12807 1-69210 2-25613 2-82017 3-38420 3-94823 4-51226 5-07630 1-40339 2-10508 2-80678 3-50848 4-21017 4-91186 5-61356 6-31526 0-27468 0-41202 0-54936 0-68670 0-82403 .0-96137 1-09871 1-23605 0-78049 1-17073 1-56097 1-95122 2-34146 2-73170 312194 3-51219 0-68670 1-03004 1-37339 1-71674 2-06009 2-40344 2-74678 3-09013 1-57333 2-36000 3-14667 3-93333 4-72000 5-50667 6-29334 7-08000 1-78667 2-68000 3-57333 4-46667 5-36000 6-25333 714666 8-04000 1-60520 2-40780 3-21040 4-01300 4-81560 5-61820 6-42080 7-22340 1-67031 2-50546 3-34062 4-17577 5-01092 5-84608 6-68123 7-51639 1-34061 2-01092 2-68123 3-35154 4-02184 4-69215 5-36246 6-03276 620 TABLES V. VL TABLE Y. SPECIFIC GRAVITY AND ABSOLUTE WEIGHT OF SEVERAL GASES. Specific gravity, atmos- pheric air = 1 -0000. * 1 litre (1000 cubic centi- metres) of gas at and 0-76 metre bar. pressure weighs grammes. 1-0000 1 -29366 1-10832 1 -43379J 0-06927 0-08961 Water vapor of 0-62343 0-80651 0-83124 1 -07534 1-52394 1 -97146 0-96978 1-25456 0-55416 0-71689 0-96978 1 -25456 4-29474 5-55593 Sulphur vapor of 6-64992 8-60273 1-17759 1 -52340 8-78898 11-36995 5-53952 7-16625 2-45631 3-17763 0-96978 1 -25456 0-58879 0-76169 1-80102 2-32991 TABLE VI. COMPARISON OF THE DEGREES OF THE MERCURIAL THERMOMETER WITH THOSE OF THE AIR THERMOMETER. According to MAGNUS. Degrees of the mercurial thermometer. Degrees of the air thermometer. 100 100-00 150 148-74 200 197-49 250 245-39 300 294-51 330 ., 320-92 EDITORS APPENDIX. CORRECTION OF THE VOLUME OF GASES. DR. GIBBS' method of finding at once the total correction for tempera- ture, pressure, and moisture in absolute determinations of nitrogen, or other gases : * " I take a graduated tube, which I fill with mercury, then displace about two-thirds of the mercury with air, and invert the tube into a cis- tern of mercury. Then I make four or five determinations of the volume of the included (moist) air in the usual manner, and find the volume of the air at and 760 mm as a mean of all the determinations. This tube I call the companion tube, and it always hangs in the little room I use for gas analyses. Suppose the volume of (dry) air at and 760 mm is 132.35c.c. " Now, in making an absolute nitrogen determination I collect the nitrogen moist over mercury in a graduated tube, and then suspend the measuring tube by the side of the companion tube. I then by a cord and pulley bring the level of the mercury iri the two tubes to correspond exactly, and then read off the volume of air in the companion tube and the volume of nitrogen in the measuring tube. I ought to have stated that the two tubes hang in the same cistern of mercury. Suppose the volume of air in the companion tube to be 143 c.c. ; then the total cor- rection for temperature, pressure and moisture will be 143 1 32*35=: 10-65 c.c. The correction for the nitrogen will then be found by Rule of Three. As the observed volume of air in the companion tube is to the observed volume of nitrogen, so is (in this case) 10*65 to the re- quired correction. In this way, when the volume of air in the com- panion tube is once found, no further observations of temperature, pres- sure, or height of mercury above the mercury in the cistern are necessary. The companion tube lasts for an indefinite time. I have even used it filled with water, without any appreciable change in some weeks, but I prefer mercury. As the two tubes hang side by side, there is never an appreciable difference of temperature. My results are most satisfactory. Williamson & Russell have, as you know, used a companion tube for equating pressures, but not for finding the total value of the tem- perature and pressure correction at once ; and I believe that my process is wholly new. Certainly it is wonderfully convenient, and saves all tables and labor of computation." ASSAY OF CHROMIC IRON. Mix the pulverized ore in a platinum vessel with three parts of pul- verized and pure cryolite ; upon the top of the mixture place twelve * Private communication. 622 parts of bisulphate of potassa, or of soda ; heat, cautiously at first, to fusion, for fifteen minutes ; digest the cold fused mass with a little strong hydrochloric acid, for ten minutes (so far GIBBS and CLARKE, Am. tTour. ScL, 2d ser., xlv., 178) ; add a few drops of alcohol to reduce any chromic acid ; dilute with water, and add cautiously chloride of barium until all sulphuric acid is precipitated. Filter : concentrate the filtrate to a small bulk in a porcelain capsule ; add (according to STOKER and PEARSON, Am. o CHEMISTRY IN ITS APPLICATION TO AGRICUL- TURE, &c. By Justus Von Liebig. 12mo. cloth $1 00 LETTERS ON MODERN AGRICULTURE. By Baron Von Liebig. Edited by John Blyth, M.D. With addenda by a practical Agriculturist, embracing valuable suggestions, adapted to the wants of American Farmers. 1 vol. 12mo, cloth $1 00 PRINCIPLES OF AGRICULTURAL CHEMISTRY, with special reference to the late researches made in England. By Justus Von Liebig. 1 vol. 12mo 75 cents. HISTORY AND CULTURE OF THE ROSE. By S. B. Parsons. 1 ?ol. 12mo $1 25 ARCHITECTURE. DOWNING. COTTAGE RESIDENCES ; or, a Series of Designs for Rural Cottages and Cottage Villas and their Gardens and Grounds, adapted to North America. By A J. Downing. Containing a revised List of Trees, Shrubs, Plants, and the most recent and best selected Fruits. With some account of the newer style of Gardens, by Henry Wentworth Sargent and Charles Downing. With many new designs in Rural Architecture by George E. Harney, Architect $6 00 DOWNING & HINTS TO PERSONS ABOUT BUILDING IN THE WIGKTWICK. COUNTRY. By A. J. Downing. And HINTS TO YOUNG ARCHITECTS, calculated to facilitate their practical operations. By George Wigh;wick, Architect. With many wood-cuts. 8vo, cloth $2 00 HATFIELD. THE AMERICAN HOUSE CARPENTER. A Treatise upon Architecture, Cornices, and Mouldings, Framing, Doors, Windows, and Stairs ; together with the most important principles of Practical Geometry. New, thoroughly revised, and improved edition, with about 150 additional pages, and numerous additional plates. By R. G. Hatfield. 1 vol. 8vo $3 50 NOTICES OF THE WORK. "The clearest and most thoroughly practical work on the subject." "This work is a most excellent one, very comprehensive, and lucidly arranged." "This, work commends itself by its practical excellence." " It is a valuable addition to the library of the architect, and almost indispensable to every scientific master-mechanic." K. JR. Journal. HOLLY CARPENTERS' AND JOINERS' HAND-BOOK, contain- ing a Treatise on Framing, Roofs, etc., and useful Eules and Tables. By H. W. Holly. 1 vol. 18mo, cloth. $0 75 THE ART OF SAW-FILING SCIENTIFICALLY TREATED AND EXPLAINED. With Directions for putting in order all kinds of Saws. By H. W. Holly. 18mo, cloth $0 75 RUSKtN SEVEN LAMPS OF ARCHITECTURE. 1 voL 12mo, cloth, plates $1 75 JOHN WILEY & SON'S LIST OF PUBLICATIONS. 93 SUSKIN. LECTURES ON ARCHITECTURE AND PAINTING 1 vol. 12mo, cloth, plates $1 50 * , morocco, gilt edges. 40 00 BLANK-PAGED THE HOLY SCRIPTURES OF THE OLD AND NEW BIBLE, TESTAMENTS; with copious references to parallel and illustrative passages, and the alternate pages ruled for MS. notes. This edition of the S-ripturcs contains the Authorized Version, illustrated by tl* references of " Barter's Polyglot Bible," 1 and enriched with accurate maps useful tables, and un Index of Subjects. I vol. Svo, hall' morocco $9 OC 1 vol. Svo, morocco extra 10 50 1 vol. Svo, full morocco 12 00 JOHN WILEY & SON'S LIST OF PUBLICATIONS. THE TREASURY Containing the authorized English version of the Holy Scripture*, BIBLE. interleaved with a Treasury of more than 500,000 Parallel Passages from Canne, Brown, Blayney, Scott, and others, With numerous illustrative notes. 1 vol. , half bound $7 50 1 vol. , morocco 10 00 COMMON No. 1. PRAYER. No. 2. COMMON PRAYER, 48mo Size. (Done in London expressly for us.) Gilt and red edges, imitation morocco $0 62^ Gilt and red edges, rims 87$ No. 3. Gilt and red edges, best morocco and calf ...... 1 25 No. 4. Gilt and red edges, best morocco and calf rims. . 1 50 JONES. BOOK-KEEPING, BOOKKEEPING AND ACCOUNTANTSHIP. Elementary and Practical. In two parts, with a Key for Teachers. By Thomas Jones, Accountant and Teacher. 1 volume 8vo. cloth $2 50 BOOKKEEPING AND ACCOUNTANTSHIP. School Edi- tion. By Thomas Jones. 1 vol. 8vo, half roan $1 50 BOOKKEEPING AND ACCOUNTANTSHIP. Set of Blanks. In 6 parts. By Thomas Jones $1 50 BOOKKEEPING AND ACCOUNTANTSHIP. Double Entry; Results obtained from Single Entry; Equation of Payments, etc. By Thomas Jones. 1 vol. thin 8vo. . .$0 75 CHEMISTRY. CRAFTS. A SHORT COURSE IN QUALITATIVE ANALYSIS; with the new notation. By Prof. J. M. Crafts. Second edition. 1 vol. 12mo, cloth $1 50 JOHNSON'S A MANUAL OF QUALITATIVE CHEMICAL ANALY- FRESENIUS. SIS. By C. R. Freseiiius. Edited by S. W. Johnson, Pro- fessor in Sheffield Scientific School, Yale College. With Chemical Notation and Nomenclature, old and new. 1 vol. 8vo, cloth $4 50 " A SYSTEM OF INSTRUCTION IN QUANTITATIVE CHEMICAL ANALYSIS. By C. R. Fresenius. From latest editions, edited, with additions, by Prof. S. W. John- eon. With Chemical Notation and Nomenclature, old and new $6 00 KIRKWOOD COLLECTION OF REPORTS (CONDENSED) AND OPINIONS OF CHEMISTS IN REGARD TO THE USE OF LEAD PIPE FOR SERVICE PIPE, in the Distribution of Water for the Supply of Cities. By Jas. P. Kirkwood. 8vo, cloth $1 50 MILLER, ELEMENTS OF CHEMISTRY, THEORETICAL AND PRACTICAL. By Wm. Allen Miller. 3 vols. 8vo. .$18 00 " Part I. CHEMICAL PHYSICS. 1 vol. 8vo ' .... $4 00 Part II. INORGANIC CHEMISTRY. 1 vol. 8vo 6 OT Part III. ORGANIC CHEMISTRY. 1 vol. 8vo 10 00 "Dr. Miller's Chemistry is a work of which the author has every reason to fee} proud. It is now by far the largest and most accurately written Treatise or Chemistry in the English language," etc. Dublin Med. Journal. MAGNETISM AND ELECTRICITY. By Wm. Allen Mfflei 1 vol. 8vo $2 50 JOHN WILEY & SON'S LIST OF PUBLICATIONS, tfUSPRATT. CHEMISTRY THEORETICAL, PRACTICAL, AND ANALYTICAL as applied and relating to the Arts and Manufactures. By Dr. Sheridan Muspratt. 2 vols. Svo, cloth, $10.00 ; half russia $24 00 PERKINS. AN ELEMENTARY MANUAL OF QUALITATIVE CHEMICAL ANALYSIS. By Maurice Perkins. 12mo, cloth $1 00 THORPE. QUANTITATIVE CHEBZIpAL ANALYSIS. By T. B. Thorpe, Prof, of Chemistry, Glasgow. 1 vol. ISmo, plates.' Cloth $1 75 Prof. S. W. Juhiinoii says of this work : " I loiow of no other small boo*k of anything like its value. " "This very excellent and orginal work has long been waited for by scientific men. " Scientific American. DRAWING AND PAINTING. BOUVIER HANDBOOK ON OIL PAINTING. Handbook of Young AND OTHERS. Artists and Amateurs in Oil Painting; being chiefly a con- densed compilation from the celebrated Manual of Bouvier, with additional matter selected from the lab jrs of Merriwell, De Montalbert, and other distinguished Continental writers on the art. In 7 parts. Adapted for a Text-Book in Academies of both sexes, as well as for self -Instruction. Appended, a new Explanatory and Critical Vocabulary. By an American Artist. 12mo, cloth $2 00 COE. PROGRESSIVE DRAWING BOOK. By Benj. H. Coe. One vol., cloth $3 50 u DRAWING FOR LITTX.K POLKS ; or. Fiist Lessons for the Nursery. 30 drawings. Neat cover $0 20 ** FIRST STUDIES IN DRAWING. Containing Elementary Exercises, Drawings from Objects, Animals, and Rustic Figures. Complete in tki-f-c nirntf/trn of IS studies each, in neat covers. Each $0.20 ** COTTAGES. An Introduction to Landscape Drawing. Con- t'lfoiiiifi 72 Studies. Complete in four numbers of 18 studies each, in neat covers. Each $0.20 ** EASY LESSONS IN LANDSCAPE. Complete in four numbers of 10 Studies each. In neat Svo cover. Each, $0 20 " HEADS, ANIMALS, AND FIGURES. Adapted to Pencil Drawing. Complete in three numbers of 10 Studies each. In neat Svo covers. Each $0 20 " COPY BOOK, WITH INSTRUCTIONS $0 37* RUSKIN. THE ELEMENTS OF DRAWING. In Three Letters to Beginners. By John Ruskin. 1 vol. 12mo $1 00 THE ELEMENTS OF PERSPECTIVE. Arranged for the use of Schools. By John Ruskin $1 00 SMITH. A MANUAL OF TOPOGRAPHICAL DRAWING. By Prof. R. S. Smith. New edition with additions. 1 vol. Svo, cloth, plates $2.00 " MANUAL OF LINEAR PERSPECTIVE. Form, Shade, Shadow, and Reflection. By Prof. R. S. Smith. 1 vol. Svo, plates, cloth $2 00 'WARREN CONSTRUCTIVE GEOMETRY AND INDUSTRIAL DRAWING. By S. Edward Warren, Professor in the Mas- sachusetts Institute of Technology, Boston : I. ELEMENTARY WORKS. 1. ELEMENTARY FREE-HAND GEOMETRICAL DRAWING. A series of progressive exercises on regular lines and forms, including systematic instruction in lettering ; a training oi the eye and hand for all who are learning to draw. 12mo, cloth, many cuts 75 cts. Vols. 1 and 3, bound in 1 vol $1 75 9& JOHN WILEY & SON'S LIST OF PUBLICATIONS. ELEMENTARY WORKS. Continued. WARREN 2. PLANE PROBLEMS IN ELEMENTARY GEOMETRY. Wit* numerous wood-cuts. 12mo, cloth $1 23 3. DRAFTING INSTRUMENTS AND OPERATIONS. Con- taining full information about all the instruments and materials used by the draftsmen, with full directions for their use. With plates and wood-cuts. One vol. 12mo, cloth, $1 2S 4. ELEMENTARY PROJECTION DRAWING. Revised aiul en- larged edition. In five divisions. This and the last volume are favorite text-books, especially valuable to all Mechanical Artisans, and are particularly recommended for the nse of all higher public and private schools. New revised and enlarged edition, with numerous wood-cuts and plates. (1872. ) 1 2mo, cloth $1 50 5. ELEMENTARY LINEAR PERSPECTIVE OF FORMS AND SHADOWS. Part I. Primitive Methods, with an Introduc- tion. Part II. Derivative Methods, with Notes on Aerial Perspective, and many Practical Examples. Numerous wood- cuts. 1 vol. 12mo, cloth $1 00 n. HIGHER WORKS. These are designed principally for Schools of Engineering and Architecture, and for the members generally of those professions; and the first three are also designed for use in those colleger which provide courses of study adapted to the preliminary general training of candidates for the scientific professions, as well as for those technical schools which undertake that training themselves. 1. DESCRIPTIVE GEOMETRY, OR GENERAL PROBLEMS OF ORTHOGRAPHIC PROJECTIONS. The foundation course for the subsequent theoretical and practical works. 1 vol. 8vo, 24 folding plates and woodcuts $4 00 2. GENERAL PROBLEMS OF SHADES AND SHADOWS. A wider range of problems than can elsewhere be found in English, and the principles of shading. 1 vol. 8vo, with numerous plates. Cloth $3 50 8. HIGHER LINEAR PERSPECTIVE. Distinguished Ly its con- cise summary of various methods of perspective construction ; a full set of standard problems, and a careful discussion of special higher ones. With numerous large plates. 8vo, cloth $4 00 4. ELEMENTS OF MACHINE CONSTRUCTION AND DRAW- ING ; or, Machine Drawings. With some elements of descrip- tive and rational cinematics. A Text-Book for Schools of Civil and Mechanical Engineering, and for the use of Me- chanical Establishments, Artisans, and Inventors. Containing the principles of gearings, screw propellers, valve motions, and governors, and many standard and novel examples, mostly from present American practice. By S. Edward Warren. 2 vols. 8vo. 1 vol. text and cuts, and 1 vol. large plates. .. . .$7 50 A FEW FROM MANY TESTIMONIALS. u It seems to me that your Works only need a thorough examination to be intro- duced and permanently used in all the Scientific and Engineering Schools." Prof. J. G. FOX, Collegiate and Engineering Institute, Sew York City. **I have used several of your Elementary Works, and believe them to be better adapted to the purposes of instruction than any others with whicli I arn acquainted."-^-H. F. WALLING, Prof, of Civil and Topographical Eugi neering, iMfayette College, Easton, Pa. Your Works appear to me to fill a very important gap in the literature of the subjects treated. Any effort to draw Artisans, etc., away from the 'rule of ihumb,' and give them an insight into principles, is in the righ-r dircivion, and meets my heartiest approval. This is the distinguishing feature oi voiur Elementary Works." Prof. H. L. ETJSTIS, Lawrence Scientific, $cli,d Cambridge, Mass. *The author has happily divided the subjects into two great portions : the foj rner embracing those processes and problems proper to be taught to all students io Institutions of Elementary Instruction; the latter, those suited to advanced students preparing for technical purposes. The Elementary Books ought to be used in all High Schools and Academies ; the Higher ones in Schools ot Technology." WM. W. FOLWELL, President of University of Minnesota. JOHN WILEY & SON'S LIST OF PUBLICATIONS. 97 DYEING, &c. MACFARLANE. A PRACTICAL TREATISE ON DYEING AND CALICO. PRINTING. Including the latest Inventions and Improve- ments. With nn Appendix, comprising definitions of chemical terms,, with tables of Weights, Measures, c. By an expe- rienced Dyer. With a supplement, containing the most recent discoveries in color chemistry. By Robert Macfarlane. 1 vol. 8vo $5 00 R El MANN, A TREATISE ON THE MANUFACTURE OF ANILINE AND ANILINE COLORS. By M. Reimann. To which is added the Report on the Coloring Matters derived from Coal Tar, as shown at the French Exhibition, 1867. By Dr. Hofmann. Edited by Wm. Crookes. 1 vol. 8vo, cloth, $2 50 44 Dr. Reimann's portion of the Treatise, written in concise language, is profoundly practical, giving the minutest details of the processes for obtaining all the more important colors, with woodcuts of apparatus. Taken in conjunction with Hofmann's Report, we have now a complete History of Coal Tar Dyes, both theoretical and practical." Chemist and Druggist. ENGINEERING. AUSTIN. A PRACTICAL TREATISE ON THE PREPARATION, COMBINATION, AND APPLICATION OF CALCA- REOUS AND HYDRAULIC LIMES AND CEMENTS. To which is added many useful recipes for various scientific, mercantile, and domestic purposes. By James G-. Austin. 1 vol. 12mo $2 00 COLBURN LOCOMOTIVE ENGINEERING AND THE MEGHAN- ISM OF RAILWAYS. A Treatise on the Principles and Construction of the Locomotive Engine, Railway Carriages, and Railway Plant, with examples. Illustrated by Sixty-four large engravings ard two hundred and forty woodcut?. BY Zerah Colburn. Complete, parts, $15.00; or 2 vols. cloth $16 00 Or, half morocco, gilt top $20 00 KNIGHT. THE MECHANICIAN AND CONSTRUCTOR FOR EN- GINEERS. Comprising Forging. Planing, Lining, Slotting, Shaping, Turning, Screw-cutting, &c. Illustrated with ninety-six plates. By Cameron Knight. 1 vol. 4to, half morocco $15 00 MAHAN. AN ELEMENTARY COUHSE OF CIVIL ENGINER- ING, for the use of the Cadets of the U. S. Military Academy . By D. H. Mahan. 1 vol. 8vo, with numerous illustrations, and an Appendix and general Index. Edited by Prof. De Volson Wood. Full cloth $5 00 * DESCRIPTIVE GEOMETRY, as applied to the Drawing of Fortifications and Stone-Cutting. For the use of the Cadets of the U. S. Military Academy. By Prof. D. H. Mahan. 1vol. 8vo. Plates $1 50 INDUSTRIAL DRAWING. Comprising the Description and Uses of Drawing Instruments, the Construction of Plane Figures, the Projections and Sections of Geometrical Solids, Architectural Elements, Mechanism, and Topographical Drawing. With remarks on the method of Teaching the subject. For the use of Academies and Common Schools. By Prof. D. H. Mahan. 1 vol. 8vo. Twenty steel plates. Full cloth $3 00 * A TREATISE ON FIELD FORTIFICATIONS. Contain- ing instructions on the Methods of Laying Out, Constructing, Defending, and Attacking Entrenchments. With the General Outlines, also, of the Arrangement, the Attack, and Defence of Permanent Fortifications. By Prof. D. H. Mahau. New edition, revised and enlarged. 1 voL 8vo, full cloth, with plates $3 50 ELEMENTS OF PERMANENT FORTIFICATIONS. By Prof. D. H. Mahan. 1 vol. 8vo, with numerous large pi ites. Revised and edited by Col. J. B. Wheeler $6 50 98 JOHN WILEY & SON'S LIST OF PUBLICATIONS. MAHAN. ADVANCED GUARD, OUT-POST, and Detachment Servlca of Troops, with the Essential Principles of Strategy and Grand Tactics. For the use of Officers of the Militia rrd Volunteers. By Prof. D. H. Mahan. Xe\\ edition, with large additions and 12 plates. 1 vol. 18mo. cloth $1 50 MAHAN MECHANICAL PRINCIPLED OT ENGINEERING & MOSELY. AND ARCHITECTURE. By Henry Mosely, M. A. . F. R. ft. From last London edition, with considerable additions, by Prof. D. H. Mahan, LL.D.. of the U. S. Military Academy. 1 vol. 8vo. 700 pages. With numerous cuts. Cloth. . .$5 00 MAHAN HYDRAULIC MOTORS. Translated from the French Conn & BRESSE. de Mecanique, appliqm'e par M. Bresse. By Lieut. F. A. Mahan, and revised by Prof. D. H. Mahan. 1 vol. 8vo, plates $2 50 WOOD. A TREATISE ON THE RESISTANCE OF MATE- RIALS, and an Appendix on the Preservation of Timber. By De Volson Wood. Professor of Engineering, University of Michigan. 1 vol. 8vo, c'oth $2 50 A TREATISE ON BRIDGES. Designed as a Text-book and for Practical Use. By De Volson Wood. 1 vol. 8vo, nume- rous illustrations, cloth $3 00 CREEK. BACSTER. GREEK TESTAMENT, ETC. The Critical Greek and English New Testament in Parallel Columns, consisting of the Greek Text of Scholz, readings of Griesbach, etc., etc. 1 vol. 18mo, hnlf morocco $3 00 44 do. Full morocco, gilt edges 4 50 With Lexicon, by T S. Green. Half -bound 4 50 ** do. Full morocco, gilt edges 6 00 44 do. With C' >ncordance and Lexicon. Half mor., 6 00 4 do. Limp morocco 7 50 ** THE ANALYTICAL GREEK LEXICON TO THE NEW TBSTAMUNT. In which, by an alphabetical arrai gement, is f oimd every word in the Greek text in every fonn in which it appears ih-Ai is to say, every occurrent person, number, tense or mood of verbs, every case and number of nouns, pro- nouns. &c. . is placed in its alphabetical order, fully explained by a careful grammatical analysis and referred to its root, so that no uncertainty as to the grammatical structure of any word can perplex the beginner, but, assured of the precise grammatical force of any word he may desire to interpret, he is able immediately to apply his knowledge of the English meaning of the root with accuracy and satisfaction. 1 vol. small 4to, half bound $6 50 * GREEK-ENGLISH LEXICON TO TESTAMENT. By T. S. Green. Half more ^o $1 50 HEBREW. GREEN. A GRAMMAR OF THE HEBREW LANGUAGE. With copious Appendixes. By W. H. Green, D.D., Professor in Princeton Theological Seminary. 1 vol. 8vo, cloth $3 50 44 AN ELEMENTARY HEBREW GRAMMAR. With Tables, Reading Exercises, and Vocabulary. By Prof. W. H. Green, D.D. 1 vol. 12mo, cloth $1 50 44 HEBREW CHRESTOMATHY; or, Lessons in Readbi^ nd Writing Hebrew. By Prof. W r . H. Green, D.D. 1 vof. 8vo, cloth $2 00 LETTERIS A NEW AND BEAUTIFUL EDITION OF THE HE- BREW BIBLE. Revised and carefully examined by Myer Levi Letteris. 1 vol. 8vo, with key, marble edges $2 50 'This edition has a kirge and much more legible type than the known one volume editions, and the print is excellent, while the name of LETTEIUS is a sufficient guarantee for correctness." -Rev. Dr. J. M. WISE, Editor cf the ISRAELITE, JOHN WILEY & SON S LIST OF PUBLICATIONS. 99 BAGSTER'S BAGSTBR'S COMPLETE EDITION OF GESENIU^ CESENIUS. HEBREW AND CHALDEB LEXICON. In large clear, and perfect type. Translated and edited with addi- tions and corrections, by S. P. Tregelles, LL.D. In this edition great care has been taken to guard the student from Neologiai tendencies by suitable remarks whenever neodort. * The careful revisal to which the Lexicon has been subjected by a faithful and Orthodox translator exceedingly enhances the practical value of this edition." Edinburgh Ecclesiastical Jouriifil. Small 4to, half bound $7 50 BAGSTER'S NEW POCKET HEBREW AND ENGLISH LEXICON. The arrangement of this Manual Lexicon combines two things the etymological order of roots and the alphabetical order of words. This arrangement tends to lead the learner onward; for, as he becomes more at home with roots and derivatives, he learns to turn at once to the root, without first searching for the particular word in its alphabetic order. 1 vol. ISmo, cloth $2 00 "This is the most beautiful, and at the same time the most correct and peifect Manual Hebrew Lexicon \ve have ever used." Eclectic Review. IRON, METALLURGY, &c. BODEMANN. A TREATISE ON THE ASSAYING OF LEAD, SILVER, COPPER, GO1.D, AND MERCURY. By Bodemann & Kerl. Translated b/ W. A. Goodyear. 1 vol. 12mo, $2 50 CROOKES- A PRACTICAL TREATISE ON METALLURGY. Adap- ted from the last German edition of Prof. Kerl's Metallurgy. By William Crookes and Ernst Rohrig. In three vols. thick 8vo. Price $30 00 Separately. Vol. 1. Lead, Silver, Zinc, Cadmium, Tin, Mer- cury, Bismuth, Antimonv, Nickel, Arsenic, Gold, Platinum, and Sulphur ". $1 A 00 Vol. 2. Copper and I.cn 10 00 Vol. 3. Steel, Fuel, and b ^clement 10 00 DUNLAP. WILEY'S AMERICAN IRON ^RAIXE? M ANUAL of the leading Iron Industries of the T T n ited States. With a description of the Blast Furnaces, lulling Mills, Bessemer St el Works, Crucible Steel Works, (jar Wheel and Car Works, Locomotive Works. Steam Engine and Machine Works, Iron Bridge Works, Stove Foundries, fcc., giving their location and capacity of product. Wi h some account of Iron Ores. By Thomas Dunlap, of Philadelphia. 1 vol. 4to. Price to subscribers $7 50 FAIR BAIRN. CAST AND WROUGHT IRON FOR BUILDING. By Wm. Fairbairn. 8vo, cloth $2 00 I-RENCH. HISTORY OF IRON TRADE, FROM 1621 TO 1357. By B. F. French. 8vo, cloth $2 00 KIRKWOOD COLLECTION OF REPORTS (CONDENSED) AND OPINIONS OF CHEMISTS IN REGARD TO THE USE OF LEAD PIPE FOR SERVICE PIPE, hi the Distribution of Water for the Supply of Cities. By I. P. Kirkwood, C.E. 8vo, cloth $1 50 MACHINISTS-MECHANICS. FITZGERALD. THE BOSTON MACHINIST. A complete School for the Apprentice and Advanced Machinist. By W. Fitzgerald. 1 vol. 18mo, cloth $0 75 HOLLY. SAW FILING. The Art o f Saw Filing Scientifically Treated and Explained. With Directions for putting in order all kinda of Saws, from a Jeweller's Saw to a Steam Saw-mill. Illus- trated by fortv-four engravings. Third edition. By H. W. Holly. 1 vol/18mo, cloth $0 75 KNIGHT. THE M3CHANISM AND ENGINEER INSTRUCTOR Comprising Forging, Planing, Lining, Slotting 1 , Shaping. Turning, Screw- Cutting, etc., etc. By Cameron Knight. 1 vol. 4to, half morocco $15 00 100 JOHN WILEY & SON'S LIST OF PUBLICATIONS. TURNING, &c. LATHE, THE, AND ITS USES, ETC.; or, tnstruction in the Art of Turning Wood and Metal. Including a descrip- tion of the most modern appliances for the ornamentation of plane and curved surfaces, with a description also of an entirely novel form of Lathe for Eccentric and Rose Engine Turning, a Lathe and Turning Machine combined, and other valuable matter relating to the Art. 1 vol. 8vo, copiously illustrated. Including Supplement. 8vo, cloth .$7 00 "The most complete work on the subject ever published." American Artisan. "Here is an invaluable book to the practical workman and amateur." London Weekly Times. TURNING, &c. SUPPLEMENT AND INDEX TO LATHE AND ITS USES. Large type. Paper, 8vo $0 90 WILLIS. PRINCIPLES OF MECHANISM. Designed for the use jf Students in the Universities and for Engineering Students generally. By Robert Willis, M.D., F.R.S., President of the British Association for the Advancement of Science. &c., &c. Second edition, enlarged. 1 vol. Svo, cloth $7 50 %,* It ought to be in every large Machine Workshop Office, in every School of Mechanical Engineering at least, and in the hands of every Profewor of Mechanics, &c. Prof. S. EDWARD WARREN. MANUFACTURES. BOOTH. NEW AND COMPLETE CLOCK AND WATCH MAKERS' MANUAL. Comprising descriptions of the various gearings, escapements, and Compensations now in use in French, Swiss, and English clocks and watches. Patents, Tools, etc. , with directions for cleaning and repairing. With numerous engravings. Compiled from the French, with an Appendix containing a History of Clock and Watch Making in America. By Mary L. Booth. With numerous plates. 1 vol. 12mo, cloth $2 00 CELDARD. HANDBOOK ON COTTON MANUFACTURE; or, A Guide to Machine-Building, Spinning, and Weaving. With practical examples, all needful calculations, and many useful and important tables. The whole intended to be a complete yet compact authority for the manufacture of cotton. By James Geldard. With steel engravings. 1 vol. 12mo, cloth $2 50 MEDICAL, &c. BULL, HINTS TO MOTHERS FOR THE MANAGEMENT OF HEALTH DURING THE PERIOD OF PREG- NANCY, AND IN THE LYING-IN ROOM. With an exposure of popular errors in connection with those subjects. By Thomas Bull, M.D. 1 vol. 12mo, cloth $1 00 C RANCKE OUTLINES OF A NEW THEORY OF DISEASE, applied to Hydropathy, showing that water is the only true remedy. With observations on the errors committed in the practice of Hydropathy, notes on the cure of cholera by cold water, and a critique on Priessnitz's mode of treatment. Intended foi popular use. By the late H. Francke. Translated from the German by Robert Blakie, M.D. 1 vol. 12mo, cloth. . .$1 50 GREEN. A TREATISE ON DISEASES OF THE AIR PASSAGES. Comprising an inquiry into the History, Pathology, Causes, and Treatment of those Affections of the Throat caDed Bron chitis, Chronic Laryngitis, Clergyman's Sore Throat, etc. , eta By Horace Green, M. D. Fourth edition, revised and enlarged. 1 vol. Svo, cloth $3 06 * A PRACTICAL TREATISE ON PULMONARY TUBER. CULOSIS, embracing its History, Pathology, and Treat- ment. By Horace Green, M.D. Colored plates. 1 vol. 8vo, doth.., $50C JOHN WILEY & SON'S LIST OF PUBLICATIONS. 101 GREEN, OBSERVATIONS ON THE PATHOLOGY OF CROUP With Remarks on its Treatment by Topical Medications. By Horace Green, M.D. 1 vol. 8vo, cloth $1 25 " ON THE SURGICAL TREATMENT OF POLYPI OF THE LARYNX, AND CEDEMA OF THE GLOTTIS. By Horace Green, M.D. 1 vol. 8vo $1 25 ** FAVORITE PRESCRIPTIONS OF LIVING PRACTI- TIONERS. With a Toxicological Table, exhibiting the Symptoms of Poisoning, the Antidotes for each Poison, and the Test proper for their detection. By Horace Green. 1 vol. 8vo, cloth $250 TILT. ON THE PRESERVATION OF THE HEALTH OF WOMEN AT THE CRITICAL PERIODS OF LIFE. By E. G. Tilt, M. D. 1 vol. ISmo, cloth $0 50 VON UUBEN. GUSTAF VON DUBEN'S TREATISE ON MICRO- SCOPICAL DIAGNOSIS. With 71 engravings. Trans- lated, with additions, by Prof. Louis Bauer, M.D. 1 vol. 8vo, cloth $1 00 MINERALOGY. BRUSH. ON BLOW-PIPE ANALYSIS. By Prof. Geo. J. Brush. 1 vol. 8vo $2 50 DANA. DESCRIPTIVE MINERALOGY. Comprising the most re- cent Discoveries. Fifth edition. Almost entirely re- written and greatly enlarged. Containing nearly 000 pages 8vo, and upwards of 000 wood engravings. By Prof. J. Dana. Cloth $10 00 "We have used a good many works on Mineralogy, but have met with none that begin to compare with this iu fulness of plan, detail, and execution." American Journal of Mining. DANA & BRUSH. APPENDIX TO DANA'S MINERALOGY, bringing the work down to 1872. By Prof. G. J. Brush. . Svo $0 50 DANA. DETERMINATIVE MINERALOGY. 1 vol. (In prepa- ration. ) " A TEXT-BOOK OF MINERALOGY. 1 vol. (In prepa- ration. ) MISCELLANEOUS. BAILEY. THE NEW TALE OF A TUB. An adventure in verse. By F. W. N. Bailey. With illustrations. 1 vol. Svo $0 75 CARLYLE. ON HEROES, HERO-WORSHIP, AND THE HEROIC IN HISTORY. Six Lectures. Reported, with emendations and additions. By Thomas Carlyle. 1 vol. 12mo, cloth. . .$0 75 CATLIN. THE BREATH OF LIFE; or, Mai-Respiration and its Effects upon the Enjoyments and Life of Man. By Geo. Catlin. With numerous wood engravings. 1 vol. Svo, $0 75 CHEEVER. CAPITAL PUNISHMENT. A Defence of. By Rev. George B. Cheever, D.D. Cloth $0 50 (t HILL DIFFICULTY, and other Miscellanies. By Rev. George B. Cheever, D.D. 1 vol. 12mo, cloth $1 00 " JOURNAL OF THE PILGRIMS AT PLYMOUTH ROCK. By Geo. B. Cheever, D.D. 1 vol. 12mo, cloth $1 00 WANDERINGS OF A PILGRIM IN THE ALPS. By George B. Cheever, D.D. 1 vol. 12mo, cloth $1 00 (4 WANDERINGS OF THE RIVER OF THE WATER OF LIFE. By Rev. Dr. George B. Cheever. 1 vol. 12mo, cloth $1 00 CONYBEARE. ON INFIDELITY. 12mo, cloth 100 CHILD'S BOOK OF FAVORITE STORIES. Large colored platea 4 to, cloth $* 50 102 JOHN WILEY & SON'S LIST OF PUBLICATIONS. EDWARDS. FREE TOWN LIBRARIES. The Formation, and History in Britain, France, German j, and America, Together with brief notices of book-collestors^ and oi the respective places of deposit of their surviving collections. By Edward Edwards. 1 vol. thick 8vo. $4 00 GREEN. THE PENTATEUCH VINDICATED FROM THE AS- PERSIONS OF BISHOP COLENSO. By Wni. Henry Green, Prof. Theological Seminary, Princeton, N. J. 1 voL 12mo, cloth $1 2o COURAUD. PHRENO-MNEMOTECHNY; or, The Art of Memory. The series of Lectures explanatory of the principles of the system. By Francis Fauvel-Gouraud. 1 vol. 8vo, cloth, $2 00 " PHRENO-MNEMOTECHNIC DICTIONARY. Being a Philosophical Classification of all the Homophonic Words of the English Language. To be used in the application of the Phreno-Mnemotechnic Principles. By Francis Fauvel-Gou- raud. 1 voL Svo, cloth. $2 00 HEIGH WAY LEILA ADA. 12mo, cloth 1 00 - LEILA ADA'S RELATIVES. 12mo, cloth 1 00 KELLY. CATALOGUE OF AMERICAN BOOKS. The American Catalogue of Books, from January, 1861, to January, 1866. Compiled by James Kelly. 1 vol. 8vo, net cash $5 00 " CATALOGUE OF AMERICAN BOOKS. The American Catalogue of Books from January, 1866, to January, 1871. Compiled by James Kelly. 1 vol. Svo, net $7 50 MAYER'S COLLECTION OF GENUINE SCOTTISH MELODIES. For the Piano-Forte or Harmonium, in keys suitable for the voice. Harmonized by C. H. Morine. Edited by Geo. Alex- ander. 1 vol. 4to, half calf $10 00 MOTLEY. A COMPARATIVE GRAMMAR OF THE FRENCH, ITALIAN, SPANISH, AND PORTUGUESE LAN- GUAGES. By Edwin A. Notley. 1 vol. , cloth $5 00 PARKER. QUADRATURE OF THE CIRCLE. Containing demon- strations of the errors of Geometers in finding the Approxi- mations in Use ; and including Lectures on Polar Magnetism and Non-Existence of Projectile Forces in Nature By John A. Parker. 1 vol. 8vo, cloth $2 50 STQR* OK A POCKET BIBLE.. Illustrated. 12mo> cloth .$t 00 TUPPER PROVERBIAL PHILOSOPHY. 12rno 1 00 WALTON THE COMPLETE ANGLER; or, The Contemplative Man's & COTTON. Recreation, by Isaac Walton, and Instructions how to Angle for a Trout or Grayling in a Clear Stream, by Charles Cotton, with copious notes, for the most part original. A bibliographical preface, giving an account of fishing auci Fishing Books, from the earliest antiquity to the time of Walton, and a notice of Cotton and his writings, by Rev. Dr. Bethune. To which is added an appendix, including the most complete catalogue of books in angling ever printed, &c. Also a general index to the whole work. 1 vol. 12mo, cloth P 00 WARREN NOTES ON POLYTECHNIC OR SCIENTIFIC SCHOOLS IN THE UNITED STATES. Their Nature, Position, Aims, and Wants. By S. Edward Warren. Paper $0 40 WILLIAMS. THE MIDDLE KINGDOM. A Survey of the Geography, Government, Education, Social Life, Arts. Religion, etc., oi the Chinese Empire and its Inhabitants. With a new map of the Empire. By S. Wells Williams. Fourth edition, in 2 vote.. *M JOHN WILEY & SON'S LIST Ot PUBLICATIONS. 103 RUSKIN. RUSKIN RUSKIN'S WORKS. Uniform in size and style. MODERN PAINTERS. 5 vols. tinted paper, bevelled loards, plates, in box ; j$lb jO MODERN PAINTERS. 5 vols. half calf 27 00 u " " without plates 12 00 4 " " " half calf, 20 00 Vol. 1. Part 1. General Principles. Part 2. Truth. Vol. 2. Part 3. Of Ideas of Beauty. Vol. 3. Part 4. Of Many Things. Vol. 4. Part 5. Of Mountain Beauty. Vol. 5. Part 6. Leaf Beauty. Part 7. Of Cloud Beauty. Part 8. Ideas of Relation of Invention, Formal. Part 9. Ideas of Relation of Invention, Spiritual. STONES OF VENICE. 3 vols., on tinted paper, bovelled boards, in box ,$7 00 STONES OF VENICE. 3 vols., on tinted papei, half calf .$12 00 STONES OF VENICE. 3 vols., cloth 6 00 Vol. 1. The Foundations. Vol. 2. The Sea Stories. Vol. 3. The Fall. SEVEN LAMPS OF ARCHITECTURE. With illustrations, drawn and etched by the authors. 1 vol. 12mo, cloth, $1 75 LECTURES ON ARCHITECTURE AND PAINTING. With illustrations drawn by the author. 1 vol. 12mo, cloth $1 50 THE TWO PATHS. Being Lectures on Art, and its Appli- cation to Decoration and Manufacture. With plates and cuts. 1 vol. 12mo, cloth $1 25 THE ELEMENTS OF DRAWING. In Three Letters to Beginners. With illustrations drawn by the author. 1 vol. 12ino, cloth $1 00 THE ELEMENTS OF PERSPECTIVE. Arranged for the use of Schools. 1 vol. 12ino, cloth $1 00 THE POLITICAL ECONOMY OF ART. 1 voL 12mo, cloth $1 00 PRE-RAPHAELITISM. NOTES ON THE CONSTRUCTION OF SHEEPFOLDS. 1 vol. 12mo, cloth, $1 00 KING OF THE GOLDEN RIVBR; or, The Black Brothers. A Legend of Stiria. SESAME AND LILIES. Three Lectures on Books. Women, &c. 1. Of Kings 1 Treasuries. 2. Of Queens' Gardens. 3. Of the Mystery of Life. 1 vol. 12mo, cloth $1 50 AN INQUIRY INTO SOME OF THE CONDITIONS AT PRESENT AFFECTING "THE STUDY OF AR- CHITECTURE" IN OUR SCHOOLS. 1 vol. 12mo, paper. $015 THE ETHICS OF THB DUST. Ten Lectures to Little Housewives, on the Elements of Crystallization. 1 vol. 12mo, cloth $1 25 " UNTO THIS LAST." Four Essays on the First Principles of Political Economy. 1 vol. 12mo, cloth $1 OC 104 JOHN WILEY & SON'S LIST OF PUBLICATIONS. RUSKIN THE CROWN OF WILD OLIVE. Three Lecturet an Wort Traffic, and War. 1 vol. 12mo. cloth ....... ......... $1 00 " TIME AND TIDE BY WEARE AND TYNE. Twenty- five Letters to a Workingman on the Laws of Work. 1 vol. 12mo, cloth ...................................... $1 00 ** THE QUEEN OF THE AIR. Being a Study of tho Greek Myths of Cloud and Storm. 1 vol. 12rno, cloth ...... $1 00 LECTURES ON ART. 1 vol. 12mo, cloth ............ 1 00 ? FORS CLAVIGERA. Letters to the Workmen and Labourer* of Great Britain. Part 1. 1 vol. 12mo, cloth, plates, $1 00 ** FORS CLAVIGERA. Letters to the Workmen and Labourers of Great Britain. Part 2. 1 vol. 12mo, cloth, plates, $1 00 MUNERA PULVERIS. Six Essays on the Elements of Political Economy. 1 vol. 12mo, cloth .............. #1 00 * ARATRA FENTELICI. Six Lectures on th Elements of Sculpture, given before the University of O. \tord. By John Kuskin. 12mo, cloth, $1 50, or with plates ........ $3 00 THE EAGLE'S NEST. Ten Lectures on the relation of Natural Science to Art. 1 vol. 12mo ............... $1 50 THE POETRY OF ARCHITECTURE : Villa and Cottage. With numerous plates. By Kata Phusin. 1 vol. 12mo, cloth ........................................... $150 Kata Phusin is the supposed Norn cle Tlume of John Ruskin. " FORS CLAVIGERA. Letters to the Workmen and Laborers .? great Britain. Part 3. 1 vol. 12mo, cloth ........ $1 50 " LOVES MEINE. Lectures on Greek and English Birds. By John Ruskin. Plates, cloth ................. ....... $0 75 " ARIADNE FLORENTINA. Lectures on Wood and Metal Engraving. By John Ruskin. Cloth .............. $1 00 BEAUTIFUL PRESENTATION VOLUMES. frtntfd on tinted paper, and elegantly hound in crape cloth extra, bevelled board*, gilt head. RUSKIN. THE TRUE AND THS BEAUTIFUL IN NATURE, ART, MORALS, AMD RELIGION. Selected from the Works of John Ruskin, A.M. With a notice of the author by Mrs. L. C. Tuthill. Portrait. 1 vol. 12mo, cloth, plain, $2.00; cloth extra, gilt head ....... , ............... $2 50 * ART CULTURE. Consisting of the Laws of Art selected from the Works of John Ruskin, and compiled by Rev. W. H Platt. A beautiful volume, with many illustrations. 1 vol. 12mo, cloth, extra gilt head ........................ $3 00 ' Do. Do. School edition. 1 vol. 12mo, plates, cloth.. $2 50 " PRECIOUS THOUGHTS: Moral and Religious. Gathered from the Works of John Ruskin, A.M. By Mrs. L. C. Tuthill. 1 vol. 12mo, cloth, plain, $1.50. Extra cloth, gilt head .......................................... $2 00 * SELECTIONS FROM THE WRITINGS OF JOHN RUSKIN. 1 vol. 12mo, cloth, plain, $2.00. Extra cloth, gilt head ......................................... *2 50 SESAME AND LILIES. 1 vol. 12mo ................ $175 " ETHICS OF THE DUST. 12mo. ................... 175 ' CROWN OF WILD OLIVE. 12mo ............. ..... 1 50 RUSKIN'S BEAUTIES. THE TRUE AND BEAUTIFUL ") PRECIOUS THOUGHTS. CHOICE SELECTIONS. J do, half calf. . .10 00 JOHN WIUEY & SON'S LIST OF PUBLICATIONS. J.Q5 RUSKIN'S POPULAR VOLUMES. CROWN OF WILD OLIVE. SESAME AND LILIES. QUEEN OF THE AIR. ETHICS OF THE DUST. 4 vols. in box, cloth extra, gilt head $6 00 RUSKIN'S WORKS. Eevised edition. LUSKIN Vol. 1. SESAME AND LILIES. Three Lectures. By Joha Kuskin, LL.D. 1. Of King's Treasuries. 2. Of Queens' Gardens. 3. Of the Mystery of Life. 1 vol. 8vo, clotlr $2.00. Large paper $2 50 VoL 2. MUNERA PULVERIS. Six Essays on the Element* of Political Economy. By John liuskin. 1 volume 8vo, cloth $2 00 Large paper <. 2 50 Vol. 3. ARATRA PENTELICI. Six Lectures on the Pe ments of Sculpture, given before the University of O .t'oru By John Ruskin. 1 vol. 8vo $400 Large paper 4 5C RUSKIN-COMPLETE WORKS. VflK CoMFi^rE WORKS OF JOHN RUSKIN. 28 vols., extra cloth, in a box. .$40 00 Ditto 28 vols. , extra cloth. Plites... 4800 Ditto Bound in 17 vols., half calf. do 70 00 SHIPBUILDING, &c. BOURNE". A TREATISE ON THE SCREW PROPELLER, SCREW VESSELS, AND SCREW ENGINES, as adapted foi Purposes of Peace and War. Illustrated by numerous wood- cuts and engravings. By John Bourne. New edition. 1867. 1 vol. 4to, cloth, $18.00; half russia $24 00 WATTS. RANKINE (W. J. M.) AND OTHERS. Ship-Building, Theo- retical and Practical, consisting of the Hydraulics of Ship- Building, or Buoyancy, Stability, Speed and Design The Geometry of Ship-Building, or Modelling, Drawing, aad Laying Off Strength of Materials as applied to Ship-Bui] di?~ig Practical Ship-Building Masts, Sails, and Rigging Marine Steam Engineering Ship-Building for Purposes of War. By Isaac Watts, C.B., W. J. M/Rankine, C.B., Frederick K. Barnes, James Robert Napier, etc. Illustrated with numerous fine engravings and woodcuts. Complete in 30 numbers, boards, $35.00; 1 vol. folio, cloth, $37.50; half russia, $40 00 WILSON (T. D.) SHIP-BUILDING, THEORETICAL AND PRACTICAL. Ill Five Divisions. Division I. Naval Architecture. TI. Lay- ing Down and Taking off Ships. III. Ship-Building IV. Masts and Spar Making. V. Vocabulary of Terms used intended as a Text-Book and for Practical Use in Public and Private Ship-Yards. By Theo. D. Wilson, Assistant Naval Constructor, U. S. Navy ; Instructor of N'*val Construction, U. S. Naval Academy ; Member of Lhe Institution of Naval Architects, England. With numerous plates, lithographic and wood. 1 vol. 8vo. $7 50 SOAP. MORFIT, A PRACTICAL TREATISE ON THE MANUFACTURE OP SOAPS. With numerous wood-cuts and elaborate work- ins drawings. By Campbell Morfit, M.D.. F.C.S. 1 voL 8vo 7 - $2000 STEAM ENGINE. TROWBRIDGE, TABLES, WITH EXPLANATIONS, OF THE NON- CONDENSING STATIONERY STEAM ENGINPJ, and of High-Pressure Steam Boilers. By Prof. W. P. Tro\\ bridge, of Yale College Scientific School. 1 vol. 4to. plates. $2 5C t HEAT AS A SOURCE OF POWER : with applications of general principles to the construction of Steam Generatorg. An introduction to the study of Heat Engines. By W. P. Trowbridge, Prof. Sheffield Scientific School, Yale College. Profusely illustrated. 1 vol. 8vo. cloth $3 50 106 JOHN WILEY & SON'S LIST OF PUBLICATIONS. TURNING, &c. THE LATHE, AND ITS USES, ETC. On Instructions in the Art of Turnint Wood and Metal. Including a description of the most modem appliances for the ornamentation of plane and curved surfaces. With a description, also, of an entirely novel form of Lathe for Eccentric and Rose Engine Turning, a Lathe and Turning Machine combined, and other valuable matter relating to the Art. 1 vol. 8vo, copiously illustrated, cloth $7 00 * SUPPLEMENT AND INDEX TO SAME. Paper. . .$0 90 VENTILATION. LEEDS (L. W.). A TREATISE ON VENTILATION. Comprising Seven Lec- tures delivered before the Franklin Institute, showing the great want of improved methods of Ventilation in our build- ings, giving the chemical and physiological process of res- piration, comparing the effects of the various methods of heating and lighting upon the ventilation, &c. Illustrated by many plans of all classes of public and private buildings, showing their present defects, and the best means of im- proving them. By Lewis W. Leeds. 1 vol. 8vo, with nu- merous wood-cuts and colored plates. Cloth $2 50 " It ought to be iu the hands of every family in the country." Technologist. "Nothhig could be clearer than the author's exposition of the principles of the principles and practice of both good and bad ventilation.'' Van NostrancTa Engineering Magazine. "The work is every way worthy of the widest circulation." Scientific Amtrican, REID. VENTILATION IN AMERICAN DWELLINGS. With a series of diagrams presenting examples in different classes of habitations. By David Boswell Reid, M.D. To which is added an introductory outline of the progress of improvement in ventilation. By Elisha Harris, M.D. 1 vol. 12mo, $1 50 WEIGHTS, MEASURES, AND COINS. TABLES OF WEIGHTS, MEASURES, COINS, &c., OF THE UNITED STATES AND ENGLAND, with their Equivalents in the French Decimal System. Arranged by T. T. Egleston, Professor of Mineralogy, School of Mines, Columbia College. 1 vol. 18mo $0 75 " It is a most useful work for all chemists and others who have occasion to make the conversions from one system to another." American Chemist. "Every mechanic should have these tables at hand." American Horologicai Journal. J. W. & SON are Agents for and keep in stock SAMUEL BAGSTER & SONS' PUBLICATIONS, LONDON TRACT SOCTETY PUBLICATIONS, COLLINS' SONS & CO.'S BIBLES, MURRAY'S TRAVELLER'S GUIDES, WE ALE'S SCIENTIFIC SERIES FuM Catalogues gratis on application. J. W. & SON import to order, for tfie TRADE AND PUBLIC, BOOKS, PERIODICALS, &o., FROM , FRANCE, AJV2) able and * * JOHN WILEY & SON'S Complete Classified Catalogue of the most val aid latest scientific publications, 114 pages, 8vo, supplied gratis to order. THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW AN INITIAL FINE OF 25 CENTS WILL BE ASSESSED FOR FAILURE TO RETURN THIS BOOK ON THE DATE DUE. THE PENALTY WILL INCREASE TO 5O CENTS ON THE FOURTH DAY AND TO $1.OO ON THE SEVENTH DAY OVERDUE. ' LD 21-100m-7,'33 385219 UNIVERSITY OF CALIFORNIA LIBRARY