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Cornell University Library ArV1012 A systematic handbook »' vo'umetrto anal 3 1924 019 892 854 ,^-.^ Cornell University Library The original of tliis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924019892854 SYSTEMATIC HANDBOOK VOLUMETRIC ANALYSIS THE QUANTITATIVE ESTIMATION OF CHEMICAL SUBSTANCES BY MEASUKE ADAPTED TO THE BEauiREMENTS OF rUUK CHEMICAL RESEAItCH, PATHOLOGICAL CHEHISTBY, PHARMACY, METALLTJEGT, MANUFACTUKINO CHEMISTHY, PHOTOGRAPHY, ETC. AND roa THE VALUATION OF SUBSTANCES USED IN COMMERCE, AGHICULTUaE, AND THE AETB. PEANCIS SUTTON, F.C.S., Professor of Practical Chemistry, Nonv'ich. LONDON: JOHN CHURCHILL & SONS, NEW BUELINGTON STREET. 1863. ^ PREFACE, The rapid strides in all branches of industrial science and art during the last ten or fifteen years have, in a great measure,^ been aided, if not instigated, by chemical knowledge ; and not the least important part of this knowledge relates to chemical analysis, or the determi- nation of the nature, constitution, or economic value of various agents and products used in, or resulting from, manufacturing processes. The same remark applies, also, to certain branches of the fine arts, together with medicine, pharmacy, agri- culture, and general commerce, so that practical chemistry has become a thing of general need in technology. Under these circumstances, therefore, it is not surprising that the energies of scientific men have been taxed to devise new and rapid methods of chemical analysis to meet the wants of these high-pressure times; and such a branch has been developed in volumetric analysis, by IV PEEFACE. which a large amount of time, labour, and therefore cost has been saved, as compared with the older methods of research. Some idea of the extent to which this system has grown, may be obtained by a glance at the followiag pages, which are devoted, not to a history of all the processes that have been devised and advocated, but exclusively to those which have been well tried and found worthy of confidence, for, like all new branches of science, volumetric analysis has had an abundant crop of weeds and rubbish, together with, here and there, sound fruit. It is not to the labours of English chemists, however, that this department of practical chemistry is indebted for its main growth, but to those of Germany and France, who appear to have recognized more readily than our- selves the value of the system. In proof of this we have only to remember the names of Gay Lussac, Descroillez, Liebig, Bunsen, and Mohr, who have been the founders of it; nevertheless, the services rendered to it by our own countrymen — Faraday, Penny, Ure, Griffin, and others, are by no means contemptible. Up to the present time, with the exception of a small and somewhat exclusive book,* written by Mr. Scott, of * Longmans. PEEFACE. V the Trinity Office, Dublin, there has been no English text-book on the subject ; the want of this has been felt, and often expressed. I trust I shall not be thought presumptuous in hoping that this treatise will supply- that want. The experiments, made in connection with the various processes for the purpose of testing their accuracy, have extended over several years, and amounted in number to many thousands ; the book is, therefore, based on the right foundation, granting only (and this is of the utmost importance) that the foundation be rightly laid. Very little will be found in it in the way of originality or personal discovery, for I hold to the doctrine advanced by the wisest of men, that "in the multitude of counsellors there is safety," and consequently have adhered mainly to those processes which have re- ceived the approval of general experience. Nevertheless, I trust, that whatever is new in system or arrangement, may find a generous reception. The necessities of the present day require that analy- tical investigations should be directed into many channels hitherto open only to the purely scientific chemist, but I doubt not that the introduction of the simpler and more expeditious methods of determination comprised in volu- metric analysis, wUl, in some measure, put it within the power of the educated pharmaceutical chemist or chemical manufacturer, to exercise this power, either for his own or VI PEEFACE. others' benefit, and thus leave the man of science to follow the higher paths of that vast territory yet open to genius. The student and the uninitiated must not, however, imagine that the possession of this or any other book of its class win put him into a royal road to chemical analysis. The only real method of progress is that which is gained by honest and truthful practice, beside which, to make the best and most reliable use of the system, the operator must possess a good knowledge of the laws of chemical combination and decomposition, so as to know where he may apply any of the processes here given with security. Had the book been written with a view to provide this necessary knowledge, it must have been a work of much larger dimensions, and would then probably not have been so useful as many books already in existence, devoted to general chemistry and the principles of analysis ; among which, the student who desires this preliminary knowledge, cannot do better than consult Fowne's "Manual of Chemistry;" Abel and Bloxam's "Handbook of Chemistry;'' Miller's "Elements of Chemistry;" and the latest editions of Fresenius' "Qualitative and Quantitative Analysis." The main feature of volumetry is not so much analysis, in the proper sense of the term, as the quantitative determination of one principal constituent of a substance, PREFACE. Vii and in many cases of this kind the accuracy obtained by an ordinarily careful operator, such as in alkalimetry, for example, leaves nothing to be desired ; while under other circumstances, such as the estimation of one particular metal in a solution containing other metallic compounds, the operation may require the exercise of much more judgment and skill. I have endeavoured to provide, as far as possible, for these difficulties, by special explanations. The matter contained in Part V is an attempt to make the volumetric system of examination complete and ex- haustive, so far as certain substances are concerned, and though not in every case such as 1 should, hy preference, use in my own laboratory, yet I believe, will be found worthy of confidence. The value of this department consists, mainly, in the fact that the determinations can mostly be made with simple and inexpensive apparatus, and are within the reach of any well-informed medical man or pharmaceutical chemist; the latter of whom, in provincial districts, ought to be able to estimate the value of a sample of alkali, bleaching powder, or manganese, or determine the principal constituents of water, urine, manures, or soils, when called upon to do so. The section on the analysis of urine, includes the esti- mation of almost every C9nstituent likely to be required, and though written as concisely as possible, I hope it wUl be found suitable to the wants of the medical student. VUI PREFACE. No pains have been spared, either on my own or the printer's part, to render the book thoroughly accurate; but in a book of this character, containing so many figures and technical expressions, it is a thing of no small diffi- culty; especially, if it be considered, that the only time at my disposal for either writing or revising the book, has been at the beginning or close of a full day's work ; nevertheless, I trust that whatever errors may yet be found will be of minor importance. FEANCIS SUTTOK NOKWICH, January, 1863. CONTENTS. PAET I. Sect. Page 1. Introduction ....... .1 THE INSTEUMENTS AND APPAEATUS. 2. The Burette 4 3. The Pipette 8 4. The Measuring Flasks 10 5. On the Correct Reading of Graduated Instruments . 10 6. On the System of Weights and Measures to be adopted in Volumetric Analysis 12 7. Volumetric Analysis on the Atomic System, and the Preparation of Normal Titrated Solutions . .16 8. Eules for Obtaining the Percentage of a Substance with- out Calculation ........ 19 9. On the Direct and Indirect Processes of Analysis, and their Termination 21 PART II. ANALYSIS BY SATURATION. 10. ALKALIMETRY 23 11. Preparation of Normal Acid and Alkaline Solutions 24 12. Method of Procedure in Testing Alkalies . . .27 CONTENTS. Sect. 1-3. 14. 15. 16. 17. 18. 19. 20. 21. 22. 32. 24. 25. 26. 27. 28. 29. 30. 31. 32. 2. 3. 4. 5. 7. 7. Pafre Soda 31 Potash 33 Mixtures of Caustic witli Carbonated Alkalies . . 34 Ammonia 35 Conversion of Nitrogen into Ammonia, and Estimation by Peligot's Process 39 Alkaline Earths 39 Lime 42 Baryta . . ...... 42 Strontian ... ..... 42 Carbonic Acid . . . . . 42 ACIDIMETRT ... . . 49 Hydrooblorio Acid . ..... 49 Nitric Acid . . 50 Nitric Acid in Combination . . ... 50 1. Gray Lussac's Method ..... 51 Acidimetrio Method ... . 51 By Distillation with Sulphuric Acid . . 52 By Conversion into Ammonia (Schulze and Yer- non Haroourt) 53 Pelouze's Method 55 a. Titration of the Undecomposed Protoxide of Iron 65 6 . Titration of the Resulting Perchloride of Iron 57 Schlosing's Method 58 Pugh's Method 59 Method by Ignition with Bichromate of Potash or Silicic Acid (Persoz and Beich) . . .62 Sulphuric Acid 63 Sulphuric Acid in Combination 64 1. C. Mohr's Method ... . . 64 2. Wildenstein's Method 65 3. Direct Precipitation with Baryta ... 67 Acetic Acid 67 Normal Ammonio-Sulphate of Copper ... 69 Titration'of Acetic Acid by ditto 72 Estimation of Metallic Oxides or their Neutral Salts in Acid Solutions by ditto 72 CONTENTS. XI Sect. Page 33. Organic Acids 73 34. Estimation of Combiaed Acids in Neutral Salts . . 74 APPENDIX TO PART II. TECHNICAL EXAMINATION OF COMMEECIAL AiKALINE PRODUCTS. 35. Soda Ash or Alkali 76 36. Potash, and Pearlash . 78 37. Salt Cake .... . . .78 38. Eaw Salt, Brine, &o. . . . ... 78 39. Gypsum, Selenite, Plaster of Paris . . 79 40. Ammoniacal Gas Liquor ..... 80 41. Alkaline Nitrates (Saltpetre and Nitrate of Soda) . . 80 PART III. ANALYSIS BY OXIDATION AND EEDUCTION. 42. Introduction 82 PEEPAEATION OF STANDARD SOLUTIONS. 43. Permanganate of Potash 84 1. Titration of the Permanganate Solution bj- Double Iron Salt 85 2. Titration by Metallic Iron .... 87 3. Titration by Oxalic Acid 88 44. Bichromate of Potash ...... 93 45. Iodine and Hyposulphite of Soda .... 97 1. Preparation of Starch Liquor ... 98 2. Decinormal Solution of Iodine .... 98 3. Decinormal Hyposulphite of Soda ... 99 4. Preparation for the Analytical Process . . 100 46. Arsenious Acid and lodiae 105 1. Decinormal Iodine and Arsenite of Soda . . 105 2. The Analytical Process 106 XU CONTENTS. BODIES SUBJECT TO DETERMINATION BY OXIDISING OE EEDUCINGf AGENTS. Sect. Page 47. Iron 108 48. Teohnioal JExamination of Iron Ores . . . 110 49. Estimation of the Percentage of pure Iron in Steel, Cast and Wrought Iron, Spiegeleisen, &c. . . 114 50. Direct Titration of Iron by Protochloride of Tin . 116 61. Titration of Iron by Hyposulphite of Soda . . 120 62. Copper 121 1. Method of Separation from Ores or Residues . 122 2. Schwarz's Method of Titration with Perman- ganate 124 3. Fleitmann's ditto by Permanganate . . 126 4. De Haen and E. O. Brown's ditto by Iodine 126 6. Parkes' ditto by Cyanide of Potassium . 128 6. Pelouze's ditto by Sulphide of Sodium . . 130 63. Zinc 131 1. 0. Mohr's Method by Iodine .... 131 2. Sohwarz's ditto by Permanganate . . 133 3. Precipitation by Sulphide of Sodium . . . 134 54. Estimation of Alkaline Sulphides .... 136 56. Peroxide of Manganese 137 1. Technical Examination of Manganese Ores . 138 2. By DistillationwithHydrochloricAcid(Bnnsen) 139 3. Titration by Oxalic Acid ..... 140 4. Titration'by Iron ...... 141 56. Protoxide of Manganese I44 67. Tin 145 1. Lenssen's Method by Iodine . . . I4g 2. Lowenthal and Stromeyer's ditto by Per- manganate ■•■.... 146 58. Eerrooyanide of Potassium J4g 1. De Haen's Method by Permanganate . . 148 2. Titration with Bichromate of Potash . . 149 59. Eerridcyanide of Potassium J52 1. Lenssen's Method by Iodine . . . 151 2. Eeduction to Eerrocyanide 152 CONTENTS. xiii «"'■ Page 60. Lime 262 1. Hemp el's Method by Permanganate . . 153 2. By Normal Oxalic Acid and ditto . . . 163 61. Lead 163 1. Hempel's Method by Oxalic Acid . . 164 2. Schwarz's ditto 164 3. Mohr's Alkalimetrio ditto .... 156 62. Mercury 165 1. Precipitation as Protociloride . . . 155 2. Mohr's Method by Eeduction with Iron . . 156 3. Hempel's Method by Oxidation with Iodine . 167 4. Direct Titration with Hyposulphite of Soda (Scherer) 167 a. As Protoxide 168 6. As Peroxide 158 63. Gold 159 64. Arsenic 160 1. Oxidation by Iodine 160 2. Distillation with Chromic and Hydrochloric Acids (Bunsen) 160 3. By Precipitation as Arseniate of Uranium (Bodeker) 161 66. Chromium 161 1. Penny's Process 162 2. By Distillation with Hydrochloric Acid (Bunsen) 163 66. Antimony 163 1. Oxidation by Iodine (Mohr) . . . .163 2. Distillation with Hydrochloric Acid (Schneider) 164 67. Iodine 164 1. By Distillation 166 2. By Oxidation . , 166 68. Chlorates, lodates, and Bromates .... 168 69. Chlorine Gas 169 70. Chloride of Lime and other Alkaline Hypochlorites 169 1. By Arsenious Acid (Mohr) .... 170 2. Bunsen's Method 171 XIV CONTENTS. Sect. Page 71. Sulpliur and its Oompounds ..... 171 J. Sulphites and Hyposulphites .... 171 2. Estimation in Pyrites, Ores, and Eesidues . . 172 a. By conversion in Sulphuric Acid and titra- tion with Baryta 172 I. Pelouze's Method 173 72. Sulphuretted Hydrogen 175 73. Indigo ......... 176 1. By Permanganate of Potash .... 177 2. By Bichromate of ditto 178 PAET IV. ANALYSIS BY PEBCIPITATION. 74. Chlorine (in combination) ...... 181 1. Direct Precipitation with Silver . . . 182 2. Mohr's Method 182 75. Indirect estimation of Alkalies, Alkaline Earths, Nitro- gen, &o., by Silver and Chromate of Potash . . 183 76. Silver 186 1. Titration of Solutions of Silver, used in Pho- tography 187 2. Estimation of Silver by Iodine (Pisani and F. Shield) . ...... 188 3. Assay of commercial Silver, Plate, Coin, &c. . 189 77. Cyanogen igg 1. Liebig's Method by Silver .... 198 2. Fordos and Gelis' ditto by Iodine . . . 200 78. Phosphoric Acid 201 1. By Uranium (Neubauer, Sutton) . . . 201 2. By Precipitation as Phosphate of Lead (Mohr) 208 79. Sugar 210 CONTENTS. XV PART V. APPLICATION OF THE TOLUMETMC SYSTEM TO COMPLETE QUANTITATIVE ANALYSIS. Seot. Page 80. Analysis of TTrine 215 1. Specific Gravity. 2. CUorides. 3. Urea. 4. Sulphuric Acid. 5. Phosphoric Acid. 6. Uric Acid. 7. Lime and Magnesia. 8. Ammonia. 9. Free Acid. 10. Sugar. 11. Albumen. 12. Potash and Soda. 13. Total Solid Matter. 14. Total Salme Matter 217 81. Analysis of Soils 238 Mechanical Analysis ... ... 238 Chemical Analysis.- . . . . 244 82. Analysis of Manures .... . . 248 Guanos . . 248 • Phosphatic Manures ... . . 250 83. Analysis of Waters .... . . 251 84. Estimationof the Hardness of Water (Clark's Method) 255 85. Complete and rapid estimation of the ordinary Con- tituents of Spring or River Water .... 259 86. Application of the Yolumetric System of Analysis in Pharmacy 270 Tables of Weights and Measures 272 List of graduated Listruments and titrated Solutions 275 Index 279 Names of Elementary Substances of Ordinary Occurrence, yritb. their Symbols and Atomic Weights, as Given by the Latest and Best Authorities. Name. Symbol. Atomic Weisht. Aluminium .. Antimony Arsenic Barium Bismuth. Boron Bromine Cadmium Calcium Carbon Chlorine Chromium . . Cobalt Copper Fluorine Gold Hydrogen Iodine Iron Lead Lithium Magnesium .. Manganese .. Mercury Molybdenum Mckel Nitrogen Oxygen Palladium Phosphorus .. Platinum Potassium Silioium Silver Sodium Strontium Sulphur Tin Uranium — Zino Al Sb As Ba Bi B Br Od Ca CI Or Co Cu Fl Au H I' Fe Pb Li Mg Mn Hg Mo N O Pd P Pt K Si Ag Wa Sr S Sn Ur Zn 13-75 122 76 68-5 208 11 80 56 20 6 35-46 26-24 29-49 31-7 19 196-67 1 127' 28 103-57 6-5 12 27-67 100 46 29-6 14 8 53-24 31 98-94 37-11 14 107-97 23 43-75 16 59 59-4 32-53 AbbreviatlouB and Explanations. The normal temperature for tlie preparation and use of standard solutions is 62° Fahr. (= 16-5° C.) CC denotes cubic centimeter. Gm. „ gramme=15-43235 grains. grn. „ grain. dm. „ decern =10 flidd grains. 1 Litre=1000 CC. 1 CC=1 Gm. distiUed water at 62° Fahr. 1dm. =10 grn. „ „ „ Distilled water is to be used in all tbe processes, unless otherwise expressed. 25'ormal Solutions are those which contain 1 atom or equivalent of substance, weighed in grammes per Htre or in grains per 100 dm. Decinormal Solutions are those which contain 1 atom of substance, weighed in decigrammes per litre or in grains per 1000 dm. A Titrated Solution (from the French word titre, title or power) denotes a solution whose strength or chemical power has been accurately found by experiment. When a chemical substance or solution is directed to be titrated, the meaning is that it is to be quantitatively tested for the amount of pure substance it contains by the help of standard or titrated solutions. The term is used in preference to tested or analyzed, because these expressions may relate equally to qualitative and quantitative examinations, whereas titration can only apply to quantitative examination. ERRATA. Page 25, 7 lines from top, for 60° read 62° Fahr. „ 45, 6 „ „ bottom, for a read b. „ 45, 2 „ „ „ for ammonium read caustic ammonia. LIST OF ERRATA Discovenred since the 'publication of iJte hook. Page 2, lines 7 and 16 from top, for 0-0108 read O'lOS. Page 30, line 8 from top, omit the words " divided by" and read "the number of CO used must be taken as the divisor for the number which should have been used had the acid," &c. Page 73, in the table for Organic Acids, Citric Acid (cryst.), read d, Hj O4 + HO, atomic weight 67 if crystallized from hot solution ; C12 Hb On + 3H0 + 2H0, atomic weight 69 if crystallized from cold solution. Page 79, line 2 from top, read 0-00563 instead of 0-0563. Page 131, in the list of factors for converting metallic iron and the double iron salt into zinc and its compounds, the following correc- tions are necessary — 0'05809 instead of 0'5809, 0-0724 instead of 0-724, 0-0829 instead of 0-3829, and 0-1034 instead of 0-1039. Page 134, line 19 from top, read 1-00636 instead of 1-0363. Page 137, line 8 from top, read 0-778 instead of 0-178. Page- 159, line 2 from top, read grn. instead of Gm. Page 184, line 11 from bottom, read delicacy instead of delivery. Page 202, line 4 from bottom, read 50-422 instead of 50-218 ; bottom line, read 504-2 instead of 5022. Page 260, line 13 from bottom, read 0-172 6m. and 1-72 gm. instead of 0-122 Gm. and 1-22 grn. HANDBOOK Or VOLUMETRIC ANALYSIS. PAET I. IKTRODUCTION. § 1. Volumetric analysis, or quantitative chemical analysis by measure, depends upon the following conditions for its successful practice : — 1. A solution of the re-agent or test, the chemical power of which is accurately known. 2? A graduated vessel from which portions of it may he accurately delivered. 3." The decomposition which the test solution produces with any given substance must be of such a character that its termi- nation is unmistakable to the eye, and thereby the quantity of the substance with which it has combined accurately determined. Suppose for instance that it is desirable to know the quantity of pure silver contained in a shilling. The coin is first dissolved in nitric acid, by which means a bluish solution, containing silver, copper, and probably other metals, is obtained. It is a known fact that chlorine combines with sUver in the presence of other metals to form chloride of silver, which is insoluble in nitric acid. The proportions in which the combination takes 2 HANDBOOK OF § 1. place are 35 -4 6 of cUorine to every 108 of silver j consequently if a standaid solution of pure cKloride of sodium is prepared by dissolving 58'46 grains of the salt (i.e., 1 eq. sodium =23, 1 eq. chlorine = 35-46 = 1 eq. chloride of sodium, 58'46) in so much distilled water as -will make up exactly 1000 grains by measure ; every single grain of this solution will combine with 0-0108 grains of pure silver to form chloride of silver, which precipitates to the bottom of the vessel in which the mixture is made. In the process of adding the salt solution to the silver, drop by drop, a point is at last reached when the precipitate ceases to form. Here the process must stop. On looking care- fully at the graduated vessel from which the standard solution has been used, the operator sees at once the number of grains which have been necessary to produce the complete decom- position. For example, suppose the quantity used was 520 grains ; all that is necessary to be done is to multiply 0-0108 grains by 520, which shews the amount of pure silver present to be 56-16 grains. This method of determining the quantity of silver in any given solution occupies scarcely a quarter of an hour, whereas the estimation by weighing could not be done in half a day, and even then not so accurately as by the volumetric method. It must be understood that there are certain necessary precau- tions in conducting the above process which I have not described, those will be found in their proper place, but from this example it will at once be seen that the saving of time and trouble, as compared with the older methods of analysis, is immense ; beside which, in the majority of instances in which it can be applied, it is equally accurate, in many cases much more so. For technical purposes, such as the examination of substances used in arts and manufactures, the system has been a great boon, and every day is bringing fresh applications of it both to pure and appUed chemical science. The only condition on which the volumetric system of analysis can be carried on successfully is that the greatest care § 1. VOLUMETRIC ANALYSIS. 3 is exercised ■with, respect to the graduation of the measuring instruments, and the strength and purity of the standard solutions. A very slight error in the analytical process becomes considerably magnified when calculated for pounds, hundred- weights, or tons of the substance tested. The end of the operation in this method of analysis ia in all cases made apparent to the eye. In alkalimetry it is the change of colour produced in litmus, turmeric, or other sensitive vegetable colouring matter. The formation of a permanent precipitate, as in the estimation of cyanogen. A precipitate ceasing to form, as in chlorine and silver determinations. The appearance of a distinct colour, as in iron analysis by perman- ganate solution, and so on. I have adopted the classification of methods used by Mohr and others, namely : 1. Where the determination of the substance is effected by saturation with another substance of opposite properties, — generally understood to include acids and alkalies. 2. Where the determination of a substance is effected by a reducing or oxidising agent of known power, including most metals, with their oxides and salts ; the principal oxidising agents being permanganate of potash, bichromate of potash, and iodine ; and the corresponding reducing agents protoxide of iron and hyposulphite of soda. 3. Where the determiaation of a substance is effected by precipitating it in some insoluble and definite combination ; an example of which occurs in the estimation of sUver described at the commencement of this treatise. This classification does not rigidly include all the volumetric processes that may be used, but it divides them into convenient sections for describing the peculiarity of the re-agents used, and their preparation. If strictly followed out, it would in some cases necessitate the registration of the body to be analysed under two or three heads ; copper, for instance, can be deter- mined residuaUy by permanganate of potash ; it can also be B 2 4 HANDBOOK OF § 2. determined by precipitation with sulphide of sodium. The estim.atioii of the same metal by cyanide of potassium, on the other hand, would not come under any of the heads. It will be found, therefore, that I have taken Uberties with the arrangement, and for convenient reference have included all analytical processes applicable to a given body under its name. THE INSTRUMENTS AND APPARATUS. THE BURETTE, § 2. Or graduated tube for delivering the standard solution, may be obtained in a great many forms, under the names of their respective inventors, such as Mohr, Gay Lussac, Binks, &c., but as some of these possess a decided superiority over others, it is not quite a matter of indifference which is used, and therefore a slight description of them may not be out of place here. The burette, with india-rubber tube and clip, contrived by Dr. Frederic Mohr of Coblentz, shewn in Figs. 1 and 2, has the preference above all others for general purposes. The advantages possessed by this instrument are, that its constant upright position enables the operator at once to read off the number of degrees of test solution used for any analysis. The quantity of fluid to be delivered can be regulated to the greatest nicety by the pressure of the thumb and finger on the spring clip, and the instrument not being held in the hand, there is no chance of increasing the bulk of the fluid by the heat of the body, and thus leading to incorrect measurement, as is the case with Binks' or Gay Lussac' s form of instrument. The principal disadvantage, however, of these two latter forms of burette is, that a correct reading can only be obtained by placing §2. VOLUMETKIC ANALYSIS. Fig.l. them in an upright position, and allowing the fluid to find its perfect level. The preference should therefore, unhesitatingly, be given to Dr. Mohr's burette, wherever it can be usedj the greatest drawback to it is, that it cannot be used for perman- ganate of potash in consequence of its india-rubber tube, which decomposes the solution. HANDBOOK OF §2. We are again indebted, I Lelieve, to Dr. Molir for another form of instrument to overcome this difficulty, viz., the foot burette, with india-rubber ball, shewn in Fig. 3. The flow of liquid from the exit tube can be regu- lated to a great nicety by pressure upon the elastic baU, which is of the ordinary kind sold for children, and has two openings, one cemented to the tube with shellac, and the other at the side, over which the thumb is placed when pressed, and on the removal of which it refills itself with air. GayLussac's burette, supported in a wooden foot, may be used instead of the above form, by inserting a good fitting cork into the open end, through which a small tube bent at right angles is passed. If the burette is held in the right hand, slightly inclined towards the beaker or flask into which the fluid is to be measured, and the mouth applied to the tube, any portion of the solution may be emptied out by the pressure of the breath, and the disadvantage of holding the instrument in an horizontal position, to the great danger of spilling the contents, is avoided ; at the same time the beaker or flask can be held in the left hand and shaken so as to mix the fluids, and by this means the end of the operation more accurately determined. Fig. 4 will shew the arrangement here described. Kb. 3. Fig. 4. § 2. VOLUMETRIC ANALYSIS. Th.ere is an arrangement of Mohr's turette which is ex- tremely serviceable, when a constant aeries of analyses of the same character have to be made, such as in alkali works, assay offices, &c. It consists in having a T piece of glass tube in- serted between the lower end of the burette and the spring clip, which c ommunioates with a reservoir of the standard solution, placed above, so that the burette may be filled as often as emptied, by a syphon, and in so gradual a manner that no air bubbles occur, as in the case of fill- ing it with a fun- nel, or pouring in liquid from a bot- tle; beside which, this plan prevents evaporation or dust in the standard so- lution either in the burette or reser- voir; it is especi- ally applicable to burettes contain- ing caustic alkalies. Fig. 5 shews the arrangement in de- tail. Piff. 5. 8 HANDBOOK OF §3. Gay Lussac's burette, shewn in Fig. 6, should have a wooden support or foot into which it may be inserted, so as to be read correctly. By using it in the following manner, its natural disadvantages may be overcome to a great extent. Having fixed the burette into the foot securely, and fiUed it, take it up by the foot with the left hand, and resting the upper end upon the edge of the beaker into which the solution to be tested is placed, drop the test fluid from the burette, meanwhile stirring the contents of the beaker with a glass rod held in the right hand; by a slight elevation or depression of the left hand, the flow of test liquid is regulated until the end of the operation is secured, thus avoiding the annoyances which arise from alternately placing the instrument in an upright and horizontal position. Geissler's burette differs from Gay Lussac's in having the fine tube enclosed within the larg| one, but as it is a difficiilt instrument to make, it hai not found much favour. Binks', or as it is sometimes called, the EngUs burette, is well known, and need not be described it is the least recommendable of all forms, in mp^ opinion. It is most convenient to have burettes graduated to 25 cj.' 30 CO in J5, 55 or 60 CC in | and 110 CO in \. Fig. e. THE PIPETTE. § 3. The pipettes used in volumetric analysis are of t kinds, viz., those which deliver one certain quantity only, a: those which are graduated so as to deliver various quantities it the discretion of the analyst. In the former kind, or wh4e §3. VOLUMETKIC ANALYSIS. 50 CC pipette, the graduation may be of tliree kinds, namely, 1st, in which the fluid is suffered to run out by its own momentum only. 2nd, in which it is blown out by the breath. 3rd, in which it is allowed to run out to a definite mark. Of these methods the last is preferable in point of accuracy, and should therefore be adopted if possible. The next best form is that in which the liquid flows out by its own mo- mentum, but in this case the last few drops empty themselves very slowly, but if the lower end of the pipette be touched against the beaker or other vessel into which the fluid is poured, the flow is hastened considerably, and in graduating the pipette, it is preferable to do it on this plan. i| Ijll i3 In both the whole and gradu- ated pipettes, the upper end is narrowed to about ^ inch, so that the pressure of the moistened finger is sufiicient to arrest the flow at any point. Fig. 7 shews two whole pi- pettes, one of small and the other of large capacity, and also a graduated pipette of medium size. 10 CC 10 HANDBOOK OF § 4. THE MEASURING FLASKS § 4. Thbse indispensable instruments are made of various capacities ; they serve to mix up standard solutions to a given volume, and also for the subdivision of the substance to be tested by means of the pipettes, and are in many ways most convenient. They should be tolerably -wide at the mouth, and have a weU-ground glass stopper, and the graduation line should fall just belo-w the middle of the neck, so as to allow room for shaking up the fluid. ON THE CORRECT READING OF GRADUATED INSTRUMENTS. § 5. The surface of liquids contained in narrow tubes is always curved, in consequence of the capillary attraction exerted by the sides of the tube, and consequently there is a difficulty in obtaining a distinct level in the fluid to be measured. If, however, the lowest point of the curve is made to coincide with the graduation mark, a correct proportional readitig is always obtained, hence this method of reading is the most satisfactory. Professor Erdmanu has contrived a useful little instrument to accompany Dr. Mohr's bu- rette, which gives the most accurate reading that can be obtained ; its form is shewn in Eig. 8, and is known by the name of Eri^mann's float. It consists of an elongated glass bulb, rather smaller iu diameter than the burette itself, and is weighted at the lower end with a globule of mercury, like an hydrometer; it is drawn to a point at the upper end, and the point is bent round §5. VOLUMETRIC ANALYSIS. 11 SO as to form a small hook, by means of which it can be lifted in and out of the burette with a bent wire ; a line is made with a diamond round its middle by means of a lathe, and the coin- cidence of this line with the graduation mark of the burette is accepted as the true reading. The actual height of the liquid in the burette is not regarded, because if the operator be- gins with the line on the float, opposite the gradua- tion mark on the burette, the same proportional division is always maintained. To prevent evaporation and the entrance of dust in Mohr's burette, the inven- tor recommends a round and well polished marble, such as boys play with, to be laid on the open end; and I have myseK found it more satis- factory than anything else. In burettes containing caus- tic allialine solutions, a cork with carbonic acid tube should be used. Beside the measuring flasks, it is necessary to have graduated vessels of cylin- drical form, for the purpose of preparing standard solu- tions, &c. Fig. 9 shews a stoppered cylinder for this purpose, generally called a test mixer. Fig. 9. 12 HANDBOOK OF § 6. ON THE SYSTEM OF WEIGHTS AND MEASURES TO BE ADOPTED IN VOLUMETRIC ANALYSIS. § 6. It is much to be regretted that the decimal system of weights and measures used on the continent is not universally adopted, for scientific and medicinal purposes, in England. I am glad to find that among many of our leading professional chemists it is now used, and growing daily more and more into favour. In scientific investigations, the importance of a cosmopolitan system of weights and measures cannot be overrated, and the anomalies produced by our arbitrary sets of pounds, ounces, and drachms, would be ludicrous, were it not for the great confusion which they engender. These annoyances are increased by the fact, that the valuable chemical researches of our neighbours the French, Germans, Dutch, and Belgians, are conducted on a different system to our own ; and although we remove the difficulty, to a certain extent, by using the grain as a unit of weight and measure, its small capacity renders its use awkward when large quantities are concerned, because it necessitates six or eight figures in the place of two or three, or even less ; and not only more trouble to record and calculate, but far more difficult to remember. The great advantage possessed by the French decimal system is its uniformity throughout. The unit of weight is the gramme, (=15'43235 grains troy,) and a gramme of distilled water at 39° Fahr. measures exactly a cubic centimtoe. The kilogramme contains 1000 grammes. The litre 1000 cubic centimetres. There is no effort of memory needed in the use of this system, as when once understood it is so simple that none but the veriest dolts could mystify it. I therefore should unhesitatingly advise aU chemical students to commence with the use of it, or at least to make themselves fully acquainted with its principles, so as to be able to calculate the one system into the other, if necessary. § 6. VOLUMETRIC ANALYSIS. 13 It may not be out of place here to give a short description of the origin of the French decimal system, now used exclusively for scientific purposes in that country, and also in Prussia, Austria, Holland, Sweden, Denmark, Belgium, and Spain. If it should assist in bringing it more extensively into use in our own country, I shall rejoice. The commission appointed after the revolution in France for the purpose of instituting a decimal system of weights and measures, founded their standard on the length of the meridian arc between the pole and equator, the ten millionth part of which was called the m^tre, (^39 '37 10 English inches,) al- though the accuracy of this measurement has since been dis- puted. It would have been preferable, as since proposed, that the length of a pendulum vibrating exactly 86,400 times in twenty-four hours, or one second for each vibration, equivalent to 39 '1372 English inches, should have been taken as the standard m&tre, in which case it would have been much easier to verify the standard in case it should be damaged or destroyed. However, the actual mfetre in use is equal to 39-371 inches, and from this standard its multiples and subdivisions all proceed decimally, its one tenth part being the decimetre, one hundredth the centimfetre, and one thousandth the millimetre. In like manner a cube of distilled water at its greatest density, viz., 39° Fahr., or 4° Centigrade, whose side measures one deoimfetre, weighs one kilogramme, or 1000 grammes, and occupies the volume of 1 Ktre, or 1000 cubic centimetres. This simple relationship between liquids and solids is of great value in a system of volumetric analysis, and even for ordinary analysis by weight ; for technical purposes it is equally as applicable as the gi-ain system, the results being invariably tabulated in percentages. Complete tables of these weights and measures will be found at the end of the book. With these brief explanations, therefore, I have only to state that the French decimal system will be mainly used throughout this treatise, but at the same time those who may desire to 14 HANDBOOK OF § 6. adhere to tte ordinary grain weights, can do so ■wi'thotit inter- fering with the accuracjr of the processes descrihed. As has been before stated, the true cubic centimeter contains one gramme of distilled water at its greatest density, viz., 4° Centigrade, or 39° Fahr., bnt as this is a degree of temperature which it is impossible to work at for more than a month or two in the year, and even then not comfortably, it. is better to take the temperature of 62° Fahr., or about 16-5 Cent, as the standard, because in winter most laboratories or rooms have furnaces or other means of warmth, and in summer the same localities would not, under ordinary eipcumstances, have a much higher degree of heat than 62°. In order, therefore, that the graduation of instruments on the metrical system may be uniform with our own fluid measures, the cubic centimeter must contain one gramme of distilled water at 62°. The true CC, (i.e.,=l Gm. at 39° Fahr.,) contains only 0-999 Gm. at that tem- perature; but for convenience of working, and for uniformity with our own standards of volume, it is better to make the CC contain one gramme at 62° Fahr. The real difference is one thousandth part. The operator, therefore, supposing he desires to graduate his own measuring flasks, must weigh into them 250, 500, or 1000 grammes of distiUed water at 62° Fahr. Of course it must be understood that these vessels are to contain their respective volumes only, and not to deliver them if poured out, consequently they must be- carefully dried before weighing the water into them. The accurate graduation of barettes and pipettes can only be done by carefully constructed machines, and is, therefore, generally speaking, beyond the compass of the analyst himself ; nevertheless, they should be carefully tested by him before being used, as, unfortunately, they do not always possess the accurate measurement to which they pretend. In the verification of both burettes and pipettes, it is only necessary to allow ten cubic centimeters of distilled water to flow into a dry and accurately tared flask or beaker. If the weight at 62° is § 6. VOLUMETRIC ANALYSIS. 15 ten grammes, it is sufficient ; the next ten grammes may be tried in like manner, and so on until the entire capacity is proved. Beside the litre flask, it is advisable to have flasks graduated for 100, 200, 250, 300, and 500 CC, as they are extremely serviceable in dividing small quantities of substance into still smaller proportional parts. Suppose, for instance, it is desired to take the tenth part of a solution for the purpose of separating any single constituent, let it be put into a 200 CC flask, and filled to the mark with water, and well shaken ; 20 CC taken out with a pipette wiU at once give the quantity required. Burettes, pipettes, and flasks may also be graduated in grains, in which case it is best to take 10,000 grains as the standard of measurement. In order to lessen the number of figures used in the grain system, so far as liquid measures are concerned, I propose that 10 fluid grains be called a decem, or for short- ness dm. ; this term corresponds to the cubic centimeter, bearing the same proportion to the 10,000 grain measure as the cubic centimeter does to the litre, namely, the one thousandth part. The use of a term like this will serve to prevent the number of figures, which are unavoidably intro- duced, by a small unit like the grain. I am aware that the term decem has been used by Mr. Acland to represent the tenth part of a gallon; but I appre- hend there is no fear of confounding the two from the vast difference in their capacity. It is quite an arbitrary term, and does not carry its valued in its name like the cubic centimeter, but I can think of no simpler or better method of bringing the grain system to the same kind of arrangement as that of the gramme. The utility of it is principally apparent in the analysis for percentages, particulars of which wUl be found hereafter. The 1000 grain burette or pipette will, therefore, contain 100 decems, the 10,000 grain measure, 1000 dm., and so on. The capacities of the various instruments graduated on the grain system may be as follows : — 16 HANDBOOK OF § 7. Flasks 10,000, 5,000, 2,500, and 1000 grs., = 1000, 500, 250, and 100 dm. Burettes 300 grains in 1 grain divisions, for very delicate purposes = 30 dm. in ^V j 600 grain in 2-grain divisions, or ^ dm.; 1100 grain in 5-grain divisions, or | dm.; 1100 grain in 10-grain divisions, or 1 dm. The burettes are graduated above the 500 or 1000 gr., in order to allow of analyses for percentages by the residual method. Whole pipettes to deliver 10, 20, 50, 100, 200, 500, and 1000 grains; graduated ditto, 100 gr. in ^^ dm.; 500 grs. in A dm.; 1000 grs. in 1 dm. Of course it will be readily seen that this method of division is not absolutely necessary ; it is only given here as being, in my opinion, the most convenient for general purposes. Those who may desire to use the decimal systems constructed on the gallon measure = 70,000 grains, will bear in mind that the "septem" of Mr. Griffin, or the "decimillem" of Mr. Acland, are each equal to 7 grains, and therefore bear the same relation to the pound = 7,000 grs., as the cubic centimeter does to the litre, or the decern to the 10,000 grs. An entirely different set of tables for calculations, etc., is required for these systems, but the analyst may readily construct them when once the principles contained in this treatise are understood. VOLUMETRIC ANALYSIS ON THE ATOMIC SYSTEM AND THE PREPAKATION OF NORMAL TITRATED SOLUTIONS. § 7. When analysis by measure first came into use, the test solutions were generally prepared so that each substance to be tested had its own special re-agent; and the strength of the standard solution was so calculated as to give the result in per- centages. Consequently, in alkalimetry a distinct standard acid § 7. VOLUMETRIC ANALYSIS. '17 ■was used for soda, another for potash, a third for ammonia, and so on, necessitating a great variety of standard solutions. John Joseph Griffin, the well-known and talented maker of chemical apparatus, and Dr. Andrew Ure, appear to have been the first to suggest the use of standard test solutions based on the atomic system, and following in their steps Mohr has worked out a most elaborate and extensive system of analysis, which must be an inestimable boon to aU who concern them- selves with scientific and especially technical chemistry. Not only has Mohr done this, but in addition to it, has enriched his processes with so many original investigations and improved the necessary apparatus to such an extent, that he may with justice be called the father of the volumetric system. His "Lehrbiich der Chemisch Analytischen Titrirmethode," is the most complete treatise on the subject, and well-deserving the thanks of all students of the science. But to return to the explanation of the system, the standard (or titrated, from the Prench word titre, strength) solutions are so prepared as to contain an atom of the required test, weighed in thousandths of the entire solution. For instance, suppose it is desired to prepare a normal alkaline solution for acidimetry, the atomic weight of carbonate of soda is 53, therefore 53 Gm. of pure and dry carbonate of soda are weighed, introduced into a litre flask and dissolved, so as to make exactly the measure of 1 litre. It is manifest that every 100 CC of this solution will contain 5 '3 Gm. of carbonate of soda, and every 10 CC, 0-53 Gm. Therefore 100 CC will exactly neutralize 4'0 Gm. of anhydrous sulphuric acid, or 10 CC 0-4 Gm., and so on. In Uke manner, if 1000 grains are used as the standard measure in place of the litre, 53 grains of carbonate of soda would be used; or as 1000 grains is too smaL. a quantity to make, it is better to weigh 530 grains to 10,000. The solution would then have exactly the same strength as if prepared on the litre system, as it is proportionally the same in chemical power; and c 18 HANDBOOK OF § 7. either solutions may be used indiscriminately for instruments graduated on both scales, bearing in miud that the substance to be tested with a CC burette, must be weighed on the Gramme system, and vice versa, unless it be desired to calculate one system of weights into the other. Of the standard solution so prepared, 1 litre should, of course, exactly saturate the atomic weight in grammes of any acid capable of decomposing the carbonate of soda, namely, — 40 Gm. of anhydrous, or 49 Gm. of monohydrated sidphuric acid, 54 Gm. of anhydrous nitric, or 36-46 Gm. of anhydrous hydrochloric acid, etc. In like manner, a standard solution of oxalic acid, containing 63 grains of the crystallized acid, in 1000 grains of solution, will saturate exactly 31 grains of pure caustic soda, 47'11 grs. of potash, 28 grs. of lime, or 17 grains of ammonia, etc., consequently it wUl be seen at once that one standard acid will serve for the estimation of a variety of alkalies, and one standard alkali for a like variety of acids ; supposing, therefore, it is desired to ascertain the percentage of real carbonate of soda in a given sample of commercial alkali, aU that is necessary is to weigh 5-3 Grammes, or -jij atom of it, dissolve it in water, add a few drops of tincture of litmus, and from a 100 CC burette allow the standard acid to flow until the point of saturation is reached. If 90 CC axe required to produce this re-action, the sample contains 90 per cent, of real carbonate of soda. In the same way, 53 grains of the alkali would require 90 decems or 900 grains of acid, which would likewise be 90 per cent. Or suppose the analyst desires to know the percentage of real caustic soda, free and combined, contained in the sample of alkali, without calculating it from the carbonate found as above, 3-1 Gm., or -^^ atom is treated as before, and the number of CC required is the percentage of real alkali. In the same sample 52-6 CC would be required =52-6 per cent, of real alkali, or 90 per cent, of carbonate. Beside the test solutions containing § 8. VOLUMETEIC ANALYSIS. 19 an atom in Grammes per litre, or in grains per 100 decerns, it is advisable to liave others -fjj that strength, so that greater dehcacy may be obtained in certain cases. Standard solutions of the former kind are called normal, and of the latter decinormal, or, for shortness, N and ^jf respectively. The decinormal solu- tions may be made either by weighing -^^ atom of the test direct and diluting to 1000, or by diluting 100 parts of the noi-mal solution to 1000. RULES FOR OBTAINIKG THE PERCENTAGE OF A SUBSTANCE WITHOUT CALCULATION. § 8. 1. With normal solutions -^^ atom in grammes, or 1 atom in grains, of flie substance tested is to he weighed, and the num- ber of cubic centimeters or decerns required is tJie percentage of the substance whose atomic weight has been used. 2. With decinormal solutions -j-^^ atom in grammes, or -jJ^ atom in grains, of the substance tested is to be weighed, and the number of cubic centimeters nr decerns required is the percentage of the substance whose atomic weight has been used. It now only remains to say, with respect to the system of weights and measures to be used, that the analyst is at liberty to choose his own plan. Both systems are susceptible of equal accuracy, and he must study his own convenience as to which he will adopt. The normal solutions prepared on the gramme system are equally applicable for that of the grain, and vice versa, so that there is no necessity for having distinct solutions for each system. It frequently occurs that, from the nature of the sub- stance, or from its being in solution, this percentage method cannot be conveniently followed. For instance, suppose the operator has a solution containing an unknown quantity of caustic potash, the strength of which he desires to know; a weighed or measured quantity of it is brought under c 2 20 HAIfDBOOK OF the acid burette and satuiated exactly by aid of litmus ; 32 CC were required. The calculation is as follows : — As 100 CC are to 4-711 Gm. KO, so are 32 CC to 4-711x32 100 -=1-507 Gm. KO. The simplest way, therefore, to proceed, is to multiply the number of CC of test solution required in any analysis, by the TTrVff °^ ^^^ atomic weight of the substance sought, which gives at once the figures required. An example may be given — 1 Gm. of marble or limestone is taken for the estimation of pure carbonate of lime and exactly saturated with standard nitric acid — (sulphuric or oxalic acid are of course not admissible) 17-5 CC were required, therefore, 17-5 X 0-050 (the xj/^^ of the atomic weight of CaOjCO^) gives 0-875 Gm., and as 1 Gm. of substance only was taken=87-5 % carbonate of lime. The midtiplication may also be dispensed ■with if desired and addition substituted by constructing tables on the following system — 1 CC of normal standard acid is equal to 0-04711 Gm. KO. Cubic Centimeters. Pure Potash 1 2 3 4 5 6 7 8 9 •04711 09422 -14133 •18814 •23555 •28266 -32977 •37688 •43399 If we used this table instead of the equation given above for the estimation of potash in solution, the result would be the same, viz. — 30 CC=1-41330 Gm. (Column 3 the decimal point 2 CC=0-09422 Gm. [one place to the left.) 1-50752 Gm. KO. In some cases it is necessary to have standard solutions based on an empirical instead of an atomic system, in which case each solution only suffices for the estimation of one special substance. This is the case in the analysis of urine and a few other substances, particulars of which will be found in their proper places. § 9- VOLUMETllIC ANALYSIS. 21 There are other test solutions which, in consequence of their proneness to decomposition, cannot be kept at any particular strength for a length of time, consequently they must be tested themselves previous to being used. Permanganate of potash and sulphurous acid are examples of such solutions. They will also be described under their respective heads. ON THE DIRECT AND INDIRECT PROCESSES OF ANALYSIS AND THEIR TERMINATION. § 9. The direct method includes aU those analyses where the substance under examination is decomposed by simple contact with a known quantity or equivalent proportion of some other body capable of combining with it, and where the end of the decomposition is manifested in the solution itself. It also properly includes those analyses in which the substance re-acts upon another body to the expulsion of a representative equivalent of the latter, which is then estimated as a substitute for the thing required. Examples of the first kind are readily found in the process for the determination of iron by permanganate of potash, where the beautiful rose colour of the permanganate asserts itself as the end of the re-action. The testing of acids and alkalies comes, also, under this class, the great sensitiveness of litmus allowing the most trifling excess of acid or alkali to alter its colour. The second is exemplified in the analysis of bin-oxide of manganese, and also other peroxides and oxygen acids, by boULng with hydro- chloric acid. The chlorine evolved is estimated as the equivalent of the quantity of oxygen which has displaced it. We are indebted to Bunsen for a most accurate and valuable series of processes based on this principle. 22 HANDBOOK OF § 9. The indirect or residual metliod is such that the substance to be analysed is not estimated itself, but the excess of some other body added for the purpose of combining with it or of decom- posing it, and the quantity or strength of the body added being known, and the conditions under which it enters into combi- nation being also known, by deducting the remainder or excess (which exists free) from the original quantity, it gives at once the proportional quantity of the substance sought. An example will make the principle obvious : — Suppose that a sample of either native carbonate of lime, baryta, or strontian is to be tested. It is not possible to estimate them with standard nitric acid in the exact quantity they require for decomposition. There must be an excess of acid and heat applied also to get them into solution, if, therefore, a known excessive quantity of standard acid be first added, and solution obtained, and the liquid then titrated backward with Ktmus and standard alkaH, the quantity of free acid can be exactly de- termined, and consequently that which is combined also. In some analyses it is necessary to add a substance which shall be an indicator of the end of the process; such for instance is litmus in alkalimetry, chromate of potash in silver and chlorine, and starch in iodine, estimations. There are other processes, the end of which can only be determined by an indicator separate from the solution, such is the case in the estimation of iron by bichromate of potash, where a drop of the liquid is brought into contact with another drop of solution of red prussiate of potash on a white slab or plate, when a blue colour ceases to form, by contact of the two liquids the end of the process is reached. The latter is somewhat less reliable, in point of delicacy, than the others, but nevertheless, with care and practice, is susceptible in most cases of very tolerable accuracy. § 10- VOLUMETRIC ANALYSIS. 23 PAET II. ANALYSIS BY SATURATION. ALKALIMETRY. §10. GayLussao based his system of alkalimetry upon a titrated solution of carbonate of soda, witb a corresponding solu- tion of sulphuric acid, and as this was devised mainly for the use of soda manufacturers it was doubtless the best system for that purpose. It possesses the recommendation that a pure standard solution of carbonate of so4a can be more readily obtained than any other form of alkali. Dr. Mohr has introduced the use of caustic alkali instead of a carbonate, the strength of which is established by a standard solution of oxalic acid, containing 63 Gm. or 1 atom to the Htre. The principal advantage in the latter system is, that in testing the strength of acids with a caustic alkali, the weU-known interference produced by carbonic acid is avoided. The caustic solutions of soda or potash are difficult to preserve so as to prevent their absorbing carbonic acid; another disadvantage is, that it is exceedingly difficult to procure or manufacture caustic soda or potash perfectly pure, and ammonia is volatile at ordinary temperatures, and rendered much more so by being heated. These drawbacks can however be, to a great extent, overcome by special means, and, in labori- tories for general investigations, it is advisable to employ both systems. 24 A.LIiALIMETEY. § 11- In testing both acids and alkalies it is necessary to employ a solution of litmus as indicator, wHcli is best prepared by powdering about half an ounce of the solid material, and digesting it with half a pint of distiUed water for. a few hours in a warm place, decanting the clear liquid from the sediment, adding, if necessary, a few drops of dilute nitric acid so as to produce a violet colour, and preserving it in a bottle with an open glass tube passed through the cork. If corked up closely it changes colour, and is not nearly so sensitive as when exposed to the air. When litmus is prepared and kept in this manner, the very faintest excess of acid or alkali is sufficient to produce either a distinct red or blue, in a dilute solution. PKEPAEATION OF THE NORMAL ACID AND ALKALINE SOLUTIONS. Normal Carbonate of Soda. § 11. The solution of carbonate of soda must contain 53 Gm. of the pure and freshly-ignited salt in the litre, or 530 grains in the 10,000 grain measure, according to the system used. If this salt is not ready at hand it is best to prepare it as follows : A convenient quantity of the purest commercial bicarbonate of soda, (the kind prepared by Messrs. Howard and Sons, of Stratford, I have foiind to answer best,) is to be placed in a funnel upon an ordinary paper filter, and washed with cold distilled water until all traces of chlorides and sulphates have disappeared in the filtrate, then put into a slightly warm place to dry. About 85 Gm. of this, washed and dried bicarbonate, are to be heated to dull redness in a platinum, sUver, or porce- lain crucible, for about ten minutes, then placed under an § 11. NOBMAL SOLUTIONS. 25 exsiccator to cool; when placed upon the halauce it wUl he found that very little more than 53 Gm. remain. The excess is to he removed as quickly as possible, and the contents of the crucible emptied into a beaker, then wash out the crucible into the beaker, and as soon as the salt is dissolved, decant the solution into a litre flask and make up the litre exactly with distUled water, at 60 Fahr. Normal Sulphuric Acid. About 30 CC of pure sulphuric acid of s. g. 1'840, or there- abouts, are mixed with three or four times the volume of distUled water and allowed to cool, then put into the graduated cylinder and diluted up to the litre. It must now be tested by the normal alkali, which is best done by putting 10 CC of the latter into a small beaker or flask with litmus, and from a 10 or 12 CC pipette, divided in -j^ CC, allowing the acid to flow until the point of neutrality is reached. If more than 10 CC are required the acid is too weak, if less, too strong. If the acid from which the solution was made was of the spec. grav. mentioned, it will generally be too strong, which is preferable. Suppose, therefore, it required 8-9 CC to saturate the 10 CC of alkali, 890 CC wiU be required to make one litre of standard acid ; remove, therefore, the excess from the cylinder and dUute to exactly one Utre. Now test again with the pipette, if the previous examination was correct, 10 CC of each solution should exactly neutralize each other. The acid may also be tested by precipitation with chloride of barium, in which case 10 CC should produce as much sulphate of baryta as is equal to -40 Gm. of anhydrous sulphuric acid, or 40' Gm. per litre. Normal OzaUc Acid. This solution possesses the great advantage that it may be established direct, by weighing 63 Gm. or 1 atom of the purest acid in a litre of water, or 630 grains to 1000 decems. 26 ALKALIMETRY. § 11. The acid must have been recrystallized several times and not in the slightest effloresced. The solution keeps well and will bear heating without volatilizing the acid. Normal Caustic Alkali May consist of either soda, potash, or (less recommendably) ammonia. The two first are best prepared from the pure car- bonate by the aid of fresh-burnt Ume. Potash is preferred to soda by Mohr, as it has less effect upon the glass burettes and pi- pettes in which it is used. One part of pure carbonate of potash, prepared from good cream of tartar or the same of carbonate of soda, is to be dissolved in 10 parts of distilled water and boiled in a clean iron pot, dur- ing the boiling strong and fresh milk of lime is to be added and boiled until all the carbonic acid is removed. Half the weight of the potash or soda in lime is sufficient; cover the vessel closely and set aside to cool and settle ; when cold, the clear supernatant liquid is to be tested by normal oxalic or sul- phuric acid, and made of the proper strength as directed for sulphuric acid. The best method of preserv- ing the solution is shewn in Fig. 10, first suggested, I believe, fig. 10. l>y Professor Graham. The § 12. TITRATION OF ALKALIES. 2T tube inserted through, the cork coEtains a mixture of equal parts of Glauher's salt and quicklime, previously dried and ignited gently together. Biirettes may also be fitted with this carbonic acid tube, by which means the alkaline solutions may be kept in them a long time without deteriorating. By the help of this normal alkaU, or the normal carbonate of soda, it is easy to prepare normal nitric and hydrochloric acids, Normal nitric acid is especially serviceable for the analysis of the alkaline earths, such as lime- stones, marls, chalks, and the native carbonates of baryta, strontia, etc. Mohr suggests that both acid and alkaline test solutions should have Utmus added to them when prepared, so as to avoid any mistake in usilig them, as in that case all alkaline solutions would be blue, and acid, red. The suggestion is a good one, but care, of course, must be taken that the volume of litmus solution is included in the litre, and not subsequently added so as to weaken the strength of the solutions. METHOD OF PROCEDURE IN TESTING ALKALIES. § 12. The necessary quantity of substance being weighed, it is dissolved in distilled water, and if any sediment remains the solution is filtered, and the filter thoroughly washed, the washings being received into the vessel containing the filtrate ; add a suf&cient quantity of htmus to produce a distinct blue colour, and allow the normal acid to flow from the burette until a claret tinge begins to appear. In the case of carbonates this takes place some time before the complete quantity of acid is added, owing to the Uberation of carbonic acid. In order to 28 ALKALIMETRY. § 12. dissipate tlie carbonic acid, the liquid must be heated to boilingj when the blue colour wiU again appear. Continue to add the acid a few drops at a time, and repeat the heating until all the carbonic acid is expelled and a distinct red colour is produced in the liquid by the final drop of acid. It is always advisable to make a second and conclusive test of the altali, and, there- fore, the first supplies a guide to the quantity of acid required, and allows a more exact method of procedure towards the end of the process. In the examination of samples of ordinary soda or pearlash, I have always found it advisable to proceed as foUows : — Powder and mix the sample thoroughly, and put into a stoppered bottle, weigh 10 Gm. in a platinum or porcelain crucible, and ignite gently over a spirit or gas lamp, and allow the crucible to cool under the exsiccator. "Weigh again, the loss of weight gives the moisture, wash the contents of the crucible into a beaker, dissolve and filter if necessary, and dilute to the exact measure of 500 CC with distilled water in a 5 litre flask, after mixing it thoroughly take out 50 CC = 1 Gm. of alkali with a pipette, and empty it into a small flask, bring the flask under a burette containing normal acid and graduated to I'jj CC, allow the acid to flow cautiously as before directed, until the neutral point is reached, the process may then be repeated, several times if necessary, in order to be certain of the correct- ness of the analysis. As the presence of carbonic acid always tends to confuse the exact end of the process, the difficulty may be overcome by allowing more acid than is needed to flow into the alkali, boiling to expel the carbonic acid, and then cautiously adding normal caustic alkUi, drop by drop, until the liquid suddenly changes to violet blue; by deducting the quantity of caustic alkali from the quantity of acid originally used, the exact volume of test acid necessary to saturate the 1 Gm. of alkali is ascertained. § 12. TITRATION OF ALKALIES. 29 This residual or backward method of testing gives a very sharp and sure result, as there is no carbonic acid present to interfere with the colour of the liquid. An example wOl make the plan clear : — 50 CC of the solution of alkali prepared as directed, and which is equal to 1 Gm. of the original sample, is put into a flask and exactly 20 CC of normal acid allowed to flow into it, it is then boUed and shaken tOl all carbonic acid is expeUed, and normal caustic alkali added backward tiU the neutral point occurs; the quantity required was 3-4 CC, which deducted from 20 CC of acid, leaves 16-6 CC. The following calculation therefore gives the percentage of real alkali supposing it to be soda — 31 is the equivalent of soda, and 1 CC of the acid is equal to -031 Gm. of real alkali, (ISTaO) therefore, 16-6 CC is multiplied by -031, which gives -5146, and as 1 Gm. was taken the decimal point is moved two places to the right, which gives 51-46 per cent, of real alkali; if calculated as carbonate the 16-6 would be multiplied by -053, (53 being the equivalent of JSTaO COj) which gives -8798 grm. = 87-98 per cent. In the preparation of standard solutions it is exceedingly difiicult to make them so exact in strength that the precise quantity, to a drop or two, shall neutralize each other, but in scientific investigations it is of the greatest importance that the utmost accuracy should be obtained; it is, therefore, advisable to ascertain the actual difference and to mark it upon the vessels in which the solutions are kept, so that a slight calculation will give the exact result. Suppose, for instance, that a standard sulphuric acid is pre- pared which does not rigidly agree with the normal carbonate of soda, not at all an uncommon occurrence, as it is exceedingly difiicult to hit the precise point, but in order to find out the exact difference about 3 Gm. of absolutely pure bicarbonate of soda is to be ignited in a platinum crucible until converted into monocarbonate, then placed under the exsiccator and 30 ALKALIMETRY. § 13. allowed to cool; ■when placed on the balance, suppose the weight found to be 1'9 Gm., it is then dissolved and titrated with the standard acid, of which 36 •! CC were required to reach the exact neutral point. If the acid were rigidly exact it should require 35'85 CCj in order, therefore, to find the factor necessary to bring the quantity of acid used in the analysis to the normal strength, the number of CC used must be divided by the number which should have been used had the acid been strictly normal, consequently — ■993 is therefore the factor by which it is necessary to multiply the number of CC of that particular acid used in any analysis in order to reduce it to normal strength, and should be marked upon the bottle in which it is kept. On the other hand, suppose that the acid is too strong, and that 35 '2 CC were required instead of 35 "85. 35-85 r0184 is therefore the factor by which it is necessary to multi- ply the number of CC of that particular acid in order to bring it to the normal strength. It is, of course, taken for granted that the original normal solution, from which the others are graduated, shall be rigidly exact, otherwise considerable errors will iaevitably occur at every step. The following table is given as an example of the two systems of measurement which may be adopted in volumetric analysis — S 13. SODA. 31 Table for Alkalies. Substance. Formula. Atomic Weight Quantity to he wefffbed EO that 1 CC or 1 dm. of normal acid = l per cent, of sabatance. Normal Factor.* Bodlum Na=23. Caustic Soda (anhydrous) Carb. of Soda (ditto) ... Cry St. Carb. of Soda ... Bicarbonate of Soda ... FotaBsium K=39-ll. Caustic Potash NaO NaO COj NaO C02+10aq NaOaCOj+HO KO KO, COj KO, 2C0j NH, NH8,C1H 31 53 143 84 47-11 69-11 100-11 17 53-46 3-1 Gm., or 31- grn. 5-3 Gm., or 53- gm. 14-3 Gm., or 143- grn. 8-4 Gra., or 84- gm. 4-711 Gm.. or 47-11 gm. 6-911 Gm., or 69-11 gm. 1011 Gm., or 101-1 gm. 1-7 Gm., or 17-0 gm. 5-346 Gm., or 53-46 gm. 0031, or 0-31 0-053, or 0-53 0-143, or 1-43 0-084, or 0-84 0-04711, or 0-4711, 0-06911, or 0-6911 01011, or 1-011 0-017, or 0-170 0-05346, or 0-5346 Carbonate of ditto Bicarbonate of ditto ... AmmnTiliiiTi Ammonia Chloride of Ammonium • This Is the coefficient by which the number of CC of normal solotion used is to be mnltipUed, in order to obtain the corresponding amount of substance examined. SODA. Examples of Analysis. § 13. 1. 8-4 Gm. of Howard's pure bicarbonate of soda ■was carefully -weighed, brought iato solution, and a few drops of litmus added; lOS CC of normal sulphuric acid was allowed to flow into the solution from the burette, and heated till all carbonic acid was expelled, it was then titrated backward with normal caustic alkali, of which 5-5 CC were required to reach 32 ALKALIMETRY. § 13. the neutral point, the real quantity of acid, therefore, was 99'5 CC, or 99J per cent, of pure bicarbonate. 2. In like manner 53 grains of exsiccated commercial car- bonate of soda was taken for examination, and 105 decerns (=1050 grains) of normal acid added, then titrated backward with 6'4 decerns ( = 64 grains) of normal alkali; the quantity of acid was, therefore, 98'6 decerns, or 98'6 per cent, of real carbonate. 3. Ten Gm. of the same carbonate as No. 2, was dis- solved in distilled water, and the solution made up to 600 CC = ^ Utre. From this solution 50 CC = 1 Gm. of the car- bonate was removed with the pipette, put into a small flask, and 24 CC of normal acid added, then titrated backward with 5'4 CC of normal alkali, the quantity of acid was, therefore, 18-6 CC, and this multiplied by -053, (1 CC of acid being equal to '063 Gm., NaO CO2) gave »98-58 per cent, of carbonate. To those who are expert in analysis it is not necessary to take any even or exact quantity of substance for examination, as a slight calculation will give the same results as in the fore- going examples. For instance, in testing deliquescent substances, such as hydrates or monocarbonates of potash or soda, it is not advisable to protract the weighing, as the absorption of moisture vitiates the results, therefore, if a portion is placed at once into a tared watch glass or crucible, the exact weight can be more quickly ascertained than by making up or reducing the substance to any particular quantity. 4. Suppose, therefore, that a small lump of commercial hydrate of soda is placed upon the balance and found to weigh 2 '657 Gm., it is transferred to a beaker and dissolved, then titrated with normal acid to the porut of saturation — 64 CC were required, therefore, as 1 CC is equal to -04 Gm. of pure JSTaO -I- HO • 64 CC = 2-46 Gm., which was the quantity of pure hydrate contained in the sample ; the percentage is there- fore arrived at by the following equation — 2-657 : 100 :: 2-46 : a; = 92-58% § 14. POTASH. 33 In technical examinations the operator may desire to dispense with the alkaUne solution for residual titration, in which case he must proceed cautiously with the addition of normal acid towards the end of the process, (taking care to expel aU the carbonic acid,) tiU. the exact neutral point is reached. The commercial carbonate of soda, generally called alkali, and consisting of a mixture of carbonate and caustic soda, contains various impurities, some of which interfere, to a certain extent, with the rigid accuracy of the analytical processes here de- scribed, the principal are sulphide and hyposulphite of sodium. As, however, the greater proportion of alkali made by English manufacturers is contaminated to a slight extent only with these impurities, they may, for most technical purposes, be disregarded. The best methods of estimating them are described § 35. POTASH. § 14. A PORTION of pure carbonate of potash, tested and found to be free from sulphates and chlorides, was ignited in a platinum crucible, cooled under the exsiccator, and quickly weighed, the weight was 3467 Gm. It was dissolved and 60 CC of normal oxaUc acid added from the burette, heated to expel aU carbonic acid, and titrated backward with normal alkali, of which 9-9 CC were required, leaving 50'1 CC as the exact quantity of acid. By referring to the table for carbonate of potash, it is found that — 50 CC = 3-4555 Gm. 0-1 CC= -0069 „ Total 3-4624 Gm. Instead of 3-467 Gm., the difference is barely 5 mOligrammes. 34 ALKALIMETEY. § 15. miXTtniES OF CAUSTIC WITH CAKBONATED ALKALIES. § 15. The alkaline salts of commerce, and also alkaline lyes used in soap, paper, starch, and other manufactories, consist generally of a mixture of caustic and carbonated alkali. If it he desired to ascertain the proportion in which these mixtures occur, the total alkaline power of a weighed or measured quantity of sub- stance is obtained and noted, a like quantity is then brought into solution to about 150 CC, in a 300 CC flask, heated to boiling, and enough solution of chloride of barium added, to remove all the carbonic acid from the soda or potash, there must be an excess of chloride, but as it does not interfere with the accuracy of the result the exact quantity is of no consequence. The flask is now filled up to the 300 CC mark with distilled water, corked and put aside to settle. When the supernatant liquid is clear, take out 100 CC with a pipette and titrate with normal nitric acid to the neutral point. The number of CC multiplied by 3, wOl be the quantity of acid required for the caustic alkali iu the original weight of substance, because only ^ was taken for analysis. The precipitated carbonate of baryta may be thrown upon a filter, washed well with hot water, and titrated with normal nitric acid, as described further on, if the operator chooses, instead of the original analysis for the total alkalinity, or both plans may be adopted as a check upon each other. The principle of this method is, that when chloride of barium is added to a mixture of caustic and carbonated alkali, the carbonic acid of the latter is precipitated as an equivalent of carbonate of baryta, while the equivalent proportion of caustic alkali remains in solution as hydrate of baryta. By multiplying the number of CC of acid required to saturate this free alkali with the atomic weight of either caustic potash or soda, according to circumstances, the quantity of substance originally present in this state wiU be obtained. § 16> AMMONIA. 35 As caustic baryta absorbs carbonic acid very readily ■when exposed to the atmosphere, it is preferable to allow the precipi- tate of carbonate of baryta to settle in the flask as here described, rather than to filter the solution as recommended by some operators. AMMONIA, FKEE AND COMBINED. § 16. In estimating the strength of solutions of ammonia by the alkalimetric method, it is better to avoid the tedious process of weighing any exact quantity, and to substitute for it the following plan, which is applicable to most liquids for the purpose of ascertaining both their absolute and specific weights. Let a small and accurately tared flask, beaker, or other con- venient vessel be placed upon the balance, and into it 10 CC of the ammoniacal solution delivered from a very accurately graduated 10 CC pipette. The weight found is, of course, the absolute weight of the liquid in grammes; suppose it to be 9*65 Gm., move the decimal point one place to the left, and the specific weight or gravity is at once given, (water being 1 •) which in this case is -965. The 10 CC weighing 9-65 Gm., was now titrated with normal acid, of which 49 CC were required, therefore 49 x '017= 833 Gm. 1^115= 8'64 per cent, of real ammonia; according to Otto's table 9-65 spec, grav., is equal to 8-50 per cent. Carbonate of ammonia and a mixture of the same with bicar- bonate, as it most commonly occurs in commerce, may be titrated direct with normal acid for the percentage of real ammonia. The carbonic acid can be determined by precipitation hot with chloride of barium, and when the precipitate is weU washed, dissolving it with ail excess of normal acid and titrating back- ward with normal alkali, as described more fiilly under the head D 2 36 ALKALIMETRY. § 16. of alkaline earths, the number of CC of acid used multiplied by 0-022 (the equiv. of COj) wUl give the weight of carbonic acid present in the sample. Instead of the 10 CC, a 100 gm. or 10 dm. pipette can be used for taking specific gravity, in which case the decimal point is moved two places to the left, grain weights being of course used in the weighing. It must be borne in mind that this system can only be used pro- perly with tolerably delicate balances and very accurate pipettes. The latter should invariably be tested by taking the spec. grav. of distilled water at 60 Fahr., according to the plan described. The ammonia contained in rain or other waters can be esti- mated according to Boussingault's researches, by distilling off about one-third of the water under examination, with the addition of a little caustic potash or quicklime, the exact measures, both of the distillate and the original water being known, the former may be titrated with noimal acid, and the quantity of ammonia in the original specimen at once ascer- tained by a slight calculation; generally speaking, not less than a couple of litres or 30,000 grains should be used for the examination. If the ammoniacal liquor of gas works is examined in this way, less than the quantities mentioned above will of course suffice, but in such cases the operator must use his own judgment. The direct estimation of ammonia, in its neutral salts by distillation, is best effected in the apparatus shewn in Fig. 11. The little flask, holding about 200 CC and placed' upon the wine gauze, contains the ammoniacal substance. The tube d is fiUed with strong solution of caustic potash or soda; the large flask holds about a pint, and contains a measured quantity of normal acid, part being contained in the tube c, which is filled with broken glass, and through which the normal acid has been poured. The substance to be examined is weighed and put into the distilling flask with a little water, the apparatus then being § 16. AMMONU. 37 made tight at every part, some of the caustic alkali is allowed to flow in by opening the clip, and the spirit lamp is lighted under it. The contents are brought to gentle boiling, taking care that the froth if any does not enter the distilling tube. It is well to use a common spirit lamp held under the flask in the hand; in case there is any tendency to boU over the lamp can be removed immediately and the flask blown upon by the breath, which brings down the temperature in a moment. In exami- ning guano and other substances contaioing organic matter by 38 ALKALIMETRY. § 16- this means, the tendency to frothing is consideraMe, and unless the above precautions are taken the accuracy of the results will be interfered ■with. The distilling tube has both ends cut slantwise, and the lower end just reaches to the surface of the acid, to which a little litmus is added. The quantity of acid used must, of course, be more than sufficient to combine with the ammonia produced; the excess is afterwards ascertained by titration with normal alkali. It is advisable to continue the boiling for say ten or fifteen minutes, then rest for the same time to allow aU the ammonia to be absorbed. Lastly, boU once or tvdce for a minute or so, take away the lamp, and allow the apparatus to stand about an hour before being opened. The tube c must be washed out into the flask with distilled water, so as to carry down the acid with any combined gas which may have reached it. The titration then proceeds as usual. The results are very satisfactory if the operation is carefully conducted; instead of the foregoing direct plan, in the case of tolerably pure neutral ammoniacal salts, a simpler indirect one can be used, which is as follows ; — If the ammoniacal salt be boiled in an open flask with solution of carbonate of soda, potash, or caustic alkali, the ammonia is entirely set free, leaving its acid combined with the fixed alkali. If, therefore, the strength and quantity of the alkaline solution are known, the excess beyond that, necessary to supplant the ammonia, can be found by the ordinary system of titration. The boHing of the mixture must be continued tiU a piece of red litmus paper, held in the steam from the flask, is no longer turned blue. Example, 1 '5 Gm. of purest subHmed chloride of ammonium was brought into a flask with 40 CC of normal carbonate of soda, and boiled till aU ammonia was expelled, then titrated back- ward with normal sulphuric acid, of which 11-9 CC were required; this left 28-1 CC of normal alkali, which multiplied by -05346 gave 1-502 Gm., instead of 1-5 Gm. originally taken. § 18. ALKALINE EAKTHS. 39 CONVERSION OF NITROGEN IN NITROGENOUS SUBSTANCES INTO AKMONIA, AND ESTIMATION BTPELIGOT'S PROCESS. § 17. This proftess consists in burning a convenient quantity of the dried substance in a combustion tube with soda lime, by which the nitrogen is converted into ammonia, and this latter being led into a measured volume of normal sulphuric acid con- tained in Will and Varrentrapp's bulb apparatus, combines with its equivalent quantity ; the solution is then titrated with standard alkali for the excess of acid, and thus the quantity of ammonia found. As the combustion tube with its arrangements for organic analysis is well known, and described in any of the standard books on general analysis, it is not necessary to give a descrip- tion here. Instead of leading the ammonia through normal acid, hydrochloric acid of unknown strength may be used, evaporated to dryness in a water bath, and the residual chloride of ammo- nium estimated by either of the processes described above for neutral salts of ammonia. When it is necessary to estimate very minute portions of ammonia, it is preferable to bring it into the form of chloride, and estimate by decinormal silver solution, as described § 75. ALKALINE EARTHS. § 18. Normal nitric acid is the best agent for the titration of the caustic and carbonated alkaline earths, inasmuch as the resulting compounds are all soluble. In order to obtain a rigidly exact normal acid, it is advisable to graduate it by pure carbonate of lime, either in the form of 40 ALKA.LIMETEY. § 18. the purest Iceland spar, as recommended by Dr. Pincus, or by artificial carbonate, prepared with great care by precipitating pure chloride of calcium with carbonate of ammonia, and boil- ing the resulting precipitate untU it becomes dense ; it is then to be washed thoroughly with hot water, dried, ignited gently, and preserved in bottles closed with a chloride of calcium tube. By means of either of these forms of carbonate of lime, it is possible at any time to titrate a dilute nitric acid, so as to bring it to the normal state, but as more acid must be used for the decomposition than is actually required to saturate the lime and expel the carbonic acid, the excess must be estimated by the help of normal alkali. I somewhat question whether the complication introduced by this method, is more exact in its results than by titrating the nitric acid direct by means of carbonate of soda. If the very purest carbonate of soda is used, and every precaution taken in igniting and weighing it, there cannot be much scope for error, nevertheless it is desirable to check the results in every possible way, and as pure carbonate of lime is not difficult to obtain, and does not contract moisture like carbonate of soda, it is a reliable basis upon which to work. The nitric acid used should be colourless, free from chlorine and nitrous acid, spec. grav. from V35 to 14. If coloured from the presence of nitrous or hyponitrous acids, it should be mixed with two volumes of water, and boiled until white. When cold it may be diluted and titrated as above. 1 Grm. of pure Iceland spar in smaU pieces should require 20 CC of acid, supposing it to be rigidly normal; if slightly stronger or weaker, the exact difierence must be found, so that a constant factor may be obtained by which to bring it by calculation to the normal state. Lime, baryta, and strontian, in the caustic state, or combined with carbonic acid, are dissolved by the aid of heat in an excess of normal acid, and then titrated with normal alkali. Chlorides and nitrates of the same bases are precipitated hot with car- § 18. ALKALINE EAETHS. 41 bonate of ammonia containing caustic ammonia, tliorouglily washed with hot water on a filter, and both filter and precipi- tate, while still moist, pushed through the funnel into a flask, and titrated as above; by deducting the number of CC of alkali from the original quantity of acid used, the proportion of pure base, or its compounds, may be obtained. Alkaline Eartlis. Substance. Calcium Ca=20. Lime Carbonate of Lime Sulphate of Lime .. (Gypsum) Barium Ba=68'69. Caustic Baryta Carbonate of Baryta Nitrate of Baryta... Chloride of Barium Strontium Sr=43'67, Strontia Carbonate of Strontia Chloride of Strontium Nitrate of Strontia Formula. Ca CiO.COj CaO.SOs + 2H0 Ba Ba 0, COj Ba 0, NOs Ba CI Sr Sr 0, COj Sr CI Sr 0, NOs . , . Qauatity to be Atomic weighed so that l CC Weiaht °^ i dm- =1 per cent. ° of substance. 28 i 2-8 Gm., or I 28-0 grn. 50 5-0 Gm., or 50'0 grn. 8'6 Gm., or 86-0 gm. 86 76-59 98-59 130-59 104-05 51-67 73-67 79-13 105-67 7-659 Gm., or 76-59 gm. 9-859 Gm., or 98-69 grn. 13059 Gm., or 130-59 gm. 10-405 Gm., or 104-05 grn. 5-167 Gm., or 51-67 grn. 7-367 Gm., or 73-67 gm. 7-913 Gm., or 79-13 grn. 10-567 Gm., or 105-67 gm. Normal Factor. 0-028, or 0-28 0-05, or 0-50 0-086, or 0-86 0-07659, or 0-7659 009859, or 0-9859 0-13059. or 1.3059 0-10405, or 1-0405 0-05167, or 0-5167 0-07367, or 0-7367 0-07913, or 0-7913 0-10567, or 1.0567 42 ALKALIMETRY. § 22. LIME. § 19. SiTLPHATB of lime or gypsum may be converted into earljonate by solution in hydrocKloric acid, and precipitation by carbonate and caustic ammonia, or fluxed with, carbonate of soda, the resulting sulphate of soda washed out, and then titrated as before described. Oxalate of lime is converted into a mixture of caustic and carbonate of lime by ignition. See also §§ 39, 60. BARYTA. § 20. MoHR recommends that after the measured volume of normal acid is added to the caustic baryta or its carbonate, and the decomposition complete, enough pure neutral sulphate of soda should be added to precipitate the baryta as sulphate, then to proceed with the titration for the excess of acid as usual, the precipitated sulphate of baryta does not interfere with the visible ending of the reaction, while it prevents the difiSculty which might arise from the partially insoluble nitrate of baryta. STEONTIAN. § 21. The compounds of strontian are determined precisely as lime and baryta. CABBONIC ACID. C02=22. a In Combiaatlon. § 22. It will be readily seen, from the foregoing article on alkaline earths, that carbonic acid, in combination with a great variety of bases, can be estimated by the volumetric method with a high degree of accuracy. § 22. CAKBONIC ACID. 43 The carfconic acid to be estimated may be brought into com- bination witli either lime or baryta, these bases admitting of the firmest combination as neutral carbonates. If the carbonic acid exists in a soluble form as a monocar- botiate of alkali, the decomposition is eifected by the addition of chlorides of barium or calcium, as before directed; if as bicarbonate or a compound between the two, ammonia must be added with either of the chlorides. As solution of ammonia most frequently contains carbonic acid, it must be removed by the aid of chloride of barium or calcium previous to use, should there be any present. It may be kept from absorbing carbonic acid by means of the tube described for normal alkali. Example, 1 Gm. of pure anhydrous carbonate of soda was dissolved in water, precipitated hot with chloride of barium, filtered and washed thoroughly with boUing water, the filter and precipitate were then brought into a flask, and 26 CC of normal nitric acid added, then titrated with normal alkali, of which 7'2 CC were required, = 18-8 CC of acid, this miilti- pliedby -022 (1 CC acid =-022 COj) gave -4136 Gm. 00^ = 41-36 per cent., or multiplied by -053 gave -9964 Gm. car- bonate of soda instead of 1 Gm. 1 Gm. of pure and dry bicarbonate of soda in powder was dissolved and precipitated with ammonia and chloride of calcium, the precipitate washed with boiling water till all ammonia was removed, the precipitate and filter then titrated with normal acid and alkali — the quantity of acid used was 23-5 CC = 51'7 per cent, of CO2 — the percentage, supposing the salt to be absolutely pure, would be 52-3. There seems to be no difference, with respect to accuracy, between chloride of calcium or barium as the precipitant; but as the carbonate of lime can be more readily washed without clogging the filter, it is preferable to use the chloride of calcium. It sometijues occurs that substances have to be examined for 44 ALKALIMETRY. § 22. carbonic acid, which do not admit of being treated as above described; such for instance as the carbonates of the metallic oxides, (white lead, calamine, etc.) carbonates of magnesia, iron, and copper, the estimation of carbonic acid in cements, mortar, and many other substances. In these cases the carbonic acid must ^be evolved from the combination by means of a stronger acid, and conducted into an absorption apparatus containing ammonia, then precipitated with chloride of barium or calcium and titrated as before described. The following form of apparatus (Fig. 12) has afforded Mohr the most satisfactory results. Fig. 12. § 22. CARBONIC ACID. 45 It is the same arrangement in principle as shown in Fig. 11, for the distillation of ammonia, with the exception that the flask b and tube d are somewhat larger and are placed on a level with the larger flask. The weighed substance from which the carbonic acid is to be evolved, is brought into b with a little water and litmus, the tube d contains strong hydrochloric acid, and c, broken glass wetted with ammonia free from carbonic acid. (It should be heated with a little chloride of calcium in a test tube ; if pure, it will remain clear.) The flask a is about ^ filled with the same ammonia, the bent tube must not enter the liquid. When all is ready and the corks tight, (best secured by wetting them,) warm the flask a gently so as to fill it with vapour of ammonia, then open the clip and allow the acid to flow circumspectly upon the material, which may be heated until all carbonic acid is apparently driven off, then by boUing and shaking the last traces can be evolved and the operation ended. When cold, the apparatus may be opened, the end of the bent tube washed into a, and also a good quantity of boiled distilled water passed through c, so as to carry down any carbonate of ammonia that may have formed. Then add solution of chloride of calcium boil, filter, and titrate the precipitate, as before described. During the filtration and while ammonia is present there is a great avidity for carbonic acid, therefore boiling water should be used for washing, and the funnel kept covered with a small glass plate. a Free Carbonic Acid Gas. Well or spring water, and also all mineral waters containing free carbonic acid, can be examined by collecting measured quantities of them at their source, in bottles containing a mixture of chloride of calcium and ammonium, afterwards boiling the mixture and titrating the precipitate as usual 46 ALKALIMETRY. § 22. The following is the best method to be pursued for ordiaary drinking waters not containing large quantities of carbonic acid. 500 CC of the water are put into a flask with a measured quantity of weak barjrta water, the strength of which is previously ascertained by means of decinormal nitric acid, then boiled, well corked, and put aside to cool and settle ; when cold and the precipitate subsided, take, out 300 CC of the clear liquid with a pipette, or pour it off without disturbing the sediment. Let this be titrated with decinormal nitric acid; the quantity required must be calculated for the total water and baryta solution, there being 300 CC only taken; the number of CC so found must be deducted from the original quantity re^ quired for the baryta solution added; the remainder multiplied by -0022. (the acid being decinormal) will give the weight of carbonic acid in the 500 CC, free and as bicarbonate. By collecting the precipitate and titrating it as previously de- scribed, the total carbonic acid may be found. Example, 600 CC spring water were mixed with 30 CC baryta water = 54-5 CC decinormal nitric acid, boiled, corked, and set aside to cool; 300 CC of the clear liquid titrated with decinormal acid, of which 6 '5 CC were required, consequently the 530 CC required 11-5 CC; this deducted from 54-5 CC, the quantity required for the 30 CC baryta solution, leaves 43 CC ^ acid, which multiplied by -0022, gives -0946 Gm. CO2 in the 500 CC of water, free and as bicarbonate. The precipitate required 8-4 CC normal nitric acid =-1848 Gm. CO2, which is the total weight combined and free; con- sequently the following calculation will give the results in detail. Total COj -1848 Gm. Deduct free and as bicarbonate -0946 „ Leaving combined ... -0902 „ The weight of COj, as bicarbonate, will, of course be equal to § 22. GABBONIC ACID. 47 this, and the two = gives-'— •1804 Gm., which deducted from 1848 Gm., Free CO, -0044 Gm. Ditto as bioarhonate "0902 „ Ditto as neutral carbonate '0902 „ Total -1848 „ CO, If the water contains magnesia, some solution of chloride of ammonium must be added to prevent its precipitation by the baryta; and instead of boiling, which would decompose and dissipate the ammonia, the flask should be closely stoppered and digested in hot water; when perfectly cold and clear the exami- nation may be completed as above. K it be desirable to ascertain the volume of carbonic acid from the weight, 1000 GC of gas, at 32° and SO""- bar, -weigh 1-96663 Gm. 100 cubic inches weigh 47 '26 grains. For ascertaiaing the quantity of carbonic acid in bottled Eerated waters, such as soda, seltzer, potass, and others, the following apparatus is useful. Fig. 13 is a brass tube made Uke a corkborer about 5 inches long, having 4 small holes, two on each side, at about 2 inches from its cutting end, the upper end is securely connected with the bent tube from the ab- sorption flask (Fig. 14,) by means of a vul- canized tube ; the flask con- Fig. 13. rig. U. 48 ALKALIMETEY. § 22. tains a tolerable quantity of pure ammonia into which the delivery tuhe dips : the tube a contains broken glass moistened with ammonia. Everything being ready the brass tube is greased with tallow or paraffin, and the bottle being held in the right hand, the tube is screwed a little aslant through the cork, by turning the bottle round, untO. the holes appear below the cork and the gas escapes iato the flask; when all visible action has ceased, after the bottle has been weU shaken two or three times to evolve aU the gas that can be possibly eliminated, the vessels are quietly disconnected, the tube a washed out into the flask, and the contents of the bottle added also, the whole is then precipitated with chloride of calcium and boiled, and the precipitate titrated as usual. This gives the total carbonic acid free and combiaed. To find the quantity of the latter, another bottle of the same manufacture must be evaporated to dryness, and the residue gently ignited, then titrated with normal acid and alkali; the amount of carbonic acid in the monocarbonate deducted from the total will give the weight of gas origiaaUy present. The volume may be found as follows : — 1000 CC of carbonic acid at 32° Fahr., weigh 1.966 Gm. Suppose, therefore, that the total weight of carbonic acid found in a bottle of ordinary soda water was 2-8 Gm. and the weight combined with alkali 42 Gm., this leaves 2'38 Gm. COj in a free state — 1-966 : 2-38 : : 1000 : a;= 1210 CC. If the number of CC of carbonic acid found is divided by the number of CC of soda water contained in the bottle examined, the quotient will be the volume of gas compared with that of the soda water. In this case, the contents of the bottle were ascertained by marking the height of the fluid previous to making the experiment; the bottle was afterward fiUed to the same mark with water, emptied into a graduated cylinder, and found to measure 292 CC, therefore H^ = 4-14vols.CO, 23. HYDROCHLORIC ACID. 49 ACIDIMETRY. § 23. Either pure potash or soda, or their carbonates or ammonia, may be used for standard solutions in acidimetry, just as have been described for alkalimetry. If it be desired to use the pure alkaline solutions the bottles in which they are preserved, and also the burettes in which they are used, must be closed with a carbonic acid tube. The manipulation is in all cases the same as in the estimation of alkalies. It is well to bear in mind that the neutral salts produced by some acids and alkalies have a decided alkaline reaction on litmus, these are mostly salts of the weak organic acids, such as acetic, tartaric, and citric, but the actual errors occurring in the analysis of these substances by a practised hand are very slight and may in most cases be quite disregarded. HYDROCHLORIC ACID. H CI, =36-46. § 24. The specific gravity is taken just as described for ammonia, namely — with an accurately graduated pipette ; if 10 CC are taken, the resulting weight is the spec, grav., when the decimal point is moved one place to the left. If 5 CC are taken, the weight in grammes must be divided by 5, the quotient wiU be the spec. grav. Example, 5 CC of white and tolerably pure acid was put into a small tared bottle and the weight found to be 5-6 Gm., this divided by 5 gave the spec. grav. as 1'12. It was diluted and titrated with normal alkali, of which 37'1 CC were required, this multiplied by -03646 gave 1-3526 Gm.=24-2%. lire's table gives 24-46 for the same spec. grav. 50 ACIDIMETEY. § 26. In order to ascertain the percentage of hydrocliloric acid gas in any sample, it is only necessary to multiply the weight of gas found by normal alkali by 100, and divide by the weight of acid originally taken for analysis, the quotient will be the percentage. Or, simpler than this, if the ^l atom in grammes, 3-646 Gm., or 1 atom in grains, =36-46 grs., be weighed, the nuihber of CC or decerns will be the percentage respectiyely. NITSIC ACID. NO„=54. § 25. 5 CC of pure nitric acid weighed 6-07 Gm., the spec. grav. was, therefore, 1-215 — the quantity of normal alkali required was 33 CC, which multiplied by -054 gave 1-782 Gm. N05=29-3%; Ure's table gives 29-5% for the same specific gravity. NITRIC ACID IN COMBINATION. Fac itOIE 1. Normal acid X 0-054 =:no^ Ditto X 0-10111=KO,NO, Metallic iron X 0-32143=]SrO6 Double iron salt X 0-0459 =]sro6 Metallic tin X 0-1144 =]sro5 § 26. The accurate estimation of nitric acid in combination presents great difi&culties and can only be secured by indirect meanSj it is hoped, however, that the methods here given are sufficient for most purposes, very few of them can be said to be simple, but it is to be feared that no simple process can ever be obtained for the determination of nitric acid in many of its combinations. § 26. NITKIC ACID. 51 1. Gay LusBac'B method modified 'by Abel, (applicable only to Alkaline Nitrates.) This process depends upon the conversion of nitrates of 8oda or potash into carbonates by ignition with carbon, and the titration of the carbonate so obtained, by normal sulphuric or oxalic acid, as described in alkalimetry. The number of CC or dm. of normal acid required multiplied by O'lOlll or 1-0111, will give the weight of pure nitrate of potash in grammes or grains ; by 0'085 or 0'85, the weight of nitrate of soda in grammes or grains. The best method of procedure is as follows : — The sample is finely powdered and dried in an air bath, and 1 gramme, or an equivalent quantity in grains, weighed, introduced into a platinum crucible, and mixed with a fourth of its weight of pure graphite, (prepared by Brodie's process,) and four times its weight of pure ignited chloride of sodium. The crucible is then covered and heated moderately for twenty minutes over a Bunsen's burner, or for eight or ten minutes in a muffle, (the heat must not be so great as to volatilize the chloride of sodium to any extent.) If sulphates are present they will be reduced to sulphides; and as these would consume the normal acid and so lead to false results, it is necessary to sprinkle the fused mass with a little powdered chlorate of potash, and heat again mode- rately till all effervescence has ceased. The crucible is then set aside to cool, warm water added, the contents brought upon a filter, and washed with hot water till the washings are no longer alkaline. The filtrate is then titrated with litmus and normal acid in the ordinary way, or better by the residual method described in alkalimetry. 2. Acidlmetrlc Method. The principle of this mode of determinating nitric acid is described in § 34, but is only applicable where the base E 2 52 ACIDIMETEY. § 26. is precipitable by pure or carbonated alkalies, and where no other acid is present, having a precipitable base ; with nitrates of metallic oxides and alkaline earths, very accurate results are obtained. 3. Estimation of Nitrates liy Distillation with Sulphuric Acid. This method is of very general application, but particu- larly so with the impure alkaline nitrates of commerce, the process, however, needs careful manipulation, but yields accurate results. There are two methods of procedure. a. To bring the weighed nitrate into a small tubulated retort with a cooled mixture of water and strong sulphuric acid, in the proportion of 10 CC water and 5 CC sulphuric acid for 1 Gm. of nitrate ; the neck of the retort is drawn out to a point and bent downward, entering a potash or other convenient bulb apparatus containing normal caustic alkali; the retort is then buried to its neck ta the sand bath, and heated to 170°C, (338° Fahr.) so long as any liquid distUs over; the heat must never exceed 175°C (347° Fahr.) otherwise traces of sulphuric acid will come over with the nitric acid. The quantity of acid distdled over, is found by titrating the fluid in the receiver with normal acid, as usual. h. Distillation in a Partial Vacuum, (Finkener.) By this arrangement there is no danger of contaminating the distillate with sulphuric acid, inasmuch as the operation is conducted in a water bath, and when once set going needs no superintendence. The retort is the same as before described, but the neck is not drawn out or bent; the stopper of the tubulure must be well ground. The receiver is a 200 CC flask with narrow neck, containing the requisite quantity of normal alltaU dduted to about 30 CC. The receiver is bound, air tight, with the neck of the retort, (which should reach nearly to the middle of the § 26. NITEIC ACID. 53 flask) by means of a vulcanized tube: the proportions of acid and water before-mentioned, are brought into the retort with a tube funnel. The stopper of the retort is then removed and the contents, both of the receiver and retort, heated by spirit or gas lamps to boiling, so as to drive out the air, the weighed nitrate contained in a small tube is then dropped into the retort, the stopper inserted, the lamps removed, and the retort brought into the water bath, while the receiver is kept cool with wet tow or placed in cold water. The distillate is titrated as before, 1 or 2 Gm. saltpetre, require about four hours for the com- pletion of the process. According to H. Eose, (Zeitschrift fiir an Chem. Part iii, page 311,) Finkener obtained very accurate results by this method. When chlorides are present in the nitrate a small quantity of moist oxide of silver is added to the mixture before distillation. 4. Estimation 1)7 conversion Into Ammonia. (Schulze and Vernon Harcourt.) The principle of this method, which gives very satisfactory results, is based on the fact that when nitric acid is heated with a strong alkaline solution and zinc added, ammonia is evolved; when zinc alone is used, however, the quantity of ammonia liberated is not a constant measure of the nitric acid present. Schulze found that when the zinc was platinized, or when sodium or aluminium amalgam was used, the reaction was perfect. — (Chem. Centr. blatt, 1861, pp, 657 and 833.) Vernon Harcourt appears to have arrived independently at the same result, by using a mixture of iron and zinc. — (Journal of Chem. Soc, 1862, p. 381). As the latter process seems, on many accounts, preferable to that of Schulze, a short description of the apparatus, etc., devised by Harcourt is given. The distilling flask holds about 200 CC, and is closely con- nected, by a bent tube, with another smaller flask in such a 54 ACIDIMETEY. § 26. manner ttat both may be placed obliquely upon a sand batb, the bulb of the smaller flask coming just under the neck of the larger. The oblique direction prevents the spirting of the boiling liquids from entering the exit tubes, but as a further precaution, these latter are in both flasks turned into the form of a hook J from the second flask, which must be somewhat wide in the mouth, a long tube passes through a Liebig's condenser, (which may be inade of wide glass tube,) into an ordinary tubulated receiver, containing normal sulphuric acid coloured with litmus, the end of the distOling tube reaches to about the middle of the receiver, through the tubulure of which Harcourt passes a bulb apparatus of peculiar form, containing also coloured normal acid ; instead of this latter, however, a chloride of calcium tube, filled with broken glass and moistened with the acid as in Fig. 11, will answer the purpose; the distOling tube should be cut at about two inches from the cork of the second flask, and connected by means of a good fitting vulcanized tube ; by this means water may be passed through the tube when the distillation is over, so as to remove any traces of ammonia which may be retained on its sides ; all the corks of the apparatus should be soaked in hot paraffin so as to fill up the pores. AU being ready, about 50 Gm. of finely granulated zinc* (best made by pouring molten zinc into a warm iron mortar while the pestle is rapidly being rubbed round) is put into the larger flask with about half the quantity of clean iron filings which have been ignited in a covered crucible ; the weighed nitrate is then introduced, either in solution or with water in sufiicient quantity to dissolve it, strong solution of caustic potash added, and the flask immediately connected with the apparatus, and placed on a small sandbath heated by a gas-burner, a little water is pre- viously put into the second flask. Convenient proportions of material are | Gm. nitre and about 20 CO each of water, and solutions of potash spec. grav. 1 -3. * After the distillation is over, the zinc and iron may be well washed, then dried, and preserved for the next operation. § 26. NITEIC ACID. 55 Heat is now applied to that part of the samdhath immediately beneath the larger flask, and the mixture is gradually raised to the toiling point ; when distillation has actually commenced, the water in the second flask is made to boil gently ; by this arrangement the fluid is twice distilled, and any traces of fixed alkali which may escape the first, are sure to be retained in the second flask. The distillation with the quantities above named will occupy about an hour and a half, and is completed when hydrogen is pretty freely liberated as the potash becomes con- centrated. The lamp is then removed and the whole allowed to cool, the distilling tube rinsed into the receiver, also the tube containing broken glass, the contents of the receiver are then titrated with normal caustic potash or soda as usual. Chlorides and sulphates do not interfere with the accuracy of the results. A mean of several experiments with pure nitre gave 52'83 % of nitric acid instead of 53-41 "/o- The process does not give such accurate results with some metaUic nitrates. 5. Felouze'B Method. The principle upon which this well known process is based is as follows : a. When nitric acid (NOj) in the form of a nitrate, is brought in contact with a solution of protoxide of iron, mixed with free hydrochloric acid, and heated, 3 eq. of the oxygen contained in the nitric acid pass over to the iron, forming a persalt, while the base combines with hydrochloric acid, and nitric oxide (NOj) is set free J 6 eq. of iron=168 are oxidized by 1 eq. nitric acid= 54 (6FeO+N05=3FeaOs + N'Oj.) If; therefore, a weighed quantity of the nitrate be mixed with an acid solution of proto- chloride or protosulphate of iron, of known strength, in excess, and the solution boiled, to expel the liberated nitric oxide, then the amount of unoxidized iron remaining in the mixture, found 56 ACIDIMETEY. § 26. by a suitable method of titration, the quantity of iron converted from protoxide into peroxide, will be the measure of the original nitric acid in the proportion of 168 to 54, or by divid- ing 54 by 168 the factor 0-32143 is obtained, so that if the amount of iron changed as described be multiplied by this factor, the product wiU be the amount of nitric acid. This method, though theoretically perfect, is in practice liable to serious errors, owing to the readiness with which a solution of protoxide of iron absorbs oxygen from the atmosphere. On this account accurate results are only obtained by conducting hydro- gen or carbooiic acid gas through the apparatus white the boUiag is cairried on. This modification has been adopted by Fresenius with very satisfactory results. The boiling vessel may consist of a small tubulated retort, supported in such a manner that its neck inclines upward, a cork is fitted into the tubulure, and through it is passed a small tube connected with a vessel for generating either carbonic acid or hydrogen. If a weighed quantity of pure metallic iron is used for preparing the solution, the washed carbonic acid or hydrogen should be passed through while it is being dissolved ; the solution so obtained, or one of double sulphate of iron and ammonia, (§ 43, 1,) of known strength being already in the retort, the nitrate is carefully introduced, and the mixture heated gently by a small lamp, or by the water bath, for ten miiiutes or so, then boiled untU. the dark red colour of the liquid disappears, and gives place to the brownish yellow of perehloride of iron ; the retort is then suffered to cool, the circulation of carbonic acid or hydrogen still being kept up, then the liquid diluted freely and titrated with permanganate of potash, as in § 43. Owing to the irregu- larities attending the use of permanganate with hydrochloric acid, it is preferable to dilute the solution less, and titrate with bichromate of potash, as in § 44. 3 Gm. pure iron, or its equivalent in double iron salt, | Gm. saltpetre and about 60 CC strong hydrochloric acid, are convenient proportions for the analysis. § 26. NITRIC ACID 57 b. Direct titration of the resulting perchloride of iron. This modification of Pelouze's original method was suggested by Braun, (Journ. f. pract. Chem., 81, 421,) and is decidedly better in principle than the residual titration of the protochloride of iron by permanganate. Braun, however, estimates the peroxide by adding an excess of iodide of potas- sium, digesting for a time at a gentle heat, then titrating the resulting free iodine by hyposulphite of soda. 3 eq. of iodine so found corresponding to 1 eq. nitric acid ; the disadvantage possessed by this plan is that variable quantities of water or hydrochloric acid seriously affect the accuracy of the results. Fresenius has therefore suggested the use of protochloride of tin for titrating the peroxide of iron, with the best results, (Zeitschrift i. an Chem., part 1, p. 34.) For the details of the process see § 50. The following plan of procedure is recommended as the best by the same authority. A solution of protosulphate of iron is prepared] by dissolving 100 Gm. of the crystals in 500 CC of hydrochloric acid of spec, grav. I'lO ; when used for the analysis, the small proportion of peroxide of iron invariably present in it is found by titrating with protochloride of tin, as in § 50. The nitrate being weighed or measured, as the case may be, is brought together with 50 CC (more or less, according to the quantity of nitrate) of the iron solution into a long necked flask, through the cork of which two glass tubes are passed, one connected with a carbonic acid apparatus, and reaching to the middle of the flask, the other simply an outlet for the passage of the gas. When the gas has driven out all the air, the flask is at first gently heated, and eventually boiled, to dispel all the nitric oxide. The carbonic acid tube is then rinsed into the flask, and the liquid, while stiU boiling hot, titrated for perchloride of iron, as in § 50. The liquid must, however, be suffered to cool before titrating with iodine for the excess of protochloride of tin. While cooling, the stream of carbonic acid should stUl be continued. The 58 ACIDIMETEY. § 26. quantity of iron changed into peroxide, multiplied by the factor 0-32143, wiU give the amount of nitric acid. Example : a. A solution of protochloride of tin was used for titrating 10 CC of solution of pure perchloride of .iron, containing 0-215075 Gm. iron. 25-65 CC of tin solution were required, therefore that quantity was equal to 0-069131 Gm. NOg. i. 60 CC of acid solution of protosulphate of iron was titrated with tia solution for peroxide, and 0-24 CC were required. c. 1 CC tin solution=3-3 CC iodine solution. d. 0-2177 Gm. of pure nitre was boiled, as described, with 50 CC of the acid protosulphate of iron, and required respec- tively 45-03 CC tin solution, and 4-7 CC iodine — 4.7 iodine solution= 1-42 Sn. CI. The peroxide in the protosulphate solution=0-24 „ 1^ 45-03 - 1-66 =43-37, therefore 25-65 : 0-69131 =43-37 : x, 95=0-1169 ISrOg instead of 0-1163, or 53-69 % instead of 53-41. A mean of this, with three other estimations, using variable proportions of tin. and iron solutions, gave exactly 53-41 "/„• The process is therefore, though troublesome, entirely satisfac- tory. 6. Schlosing's Method. The solution of nitrate is boiled in a flask tiU all air is expelled, then an acid solution of protochloride of iron drawn in, the mixture boiled, and the nitric oxide gas collected over mercury in a balloon filled with mercury and mUk of lime, the gas is then brought, without loss, ia contact with oxygen and water, so as to convert it again into nitric acid, then titrated with normal alkali as usual. § 26. NITEIC ACID. 59 Thia method was devised by Schlosing for the estimation of nitric acid in tobacco, and is especially suitable for that and similar purposes, where the presence of organic matter would interfere with the direct titration of the iron solution. Where the quantity of nitric acid is not below 0'15 6m., the process is very accurate, but needs a special and rather complicated arrangement of apparatus, the description of which may be found either in the author's original paper, "Annal. de Chim.," 3 s^r, tom. 40, 479, or "Joum. fur pract. Chem.," 62, 142, also abridged in "Fresenius' Quantitative Analysis," fourth German, or second English edition. The process is less troublesome in practice than is generally supposed. 7. Estimation by conversion into Ammonia wltli Chloride of Tin, (Pngh.) This process is based on the fact that when a nitrate is digested under pressure, and at a temperature of about 320° Fahr. (160° C) with an excess of protochloride of tin and hydrochloric acid, the following reaction occurs : NO5+8 (Sn Cl+H Cl)=NHj+8Sn Clj+5H0. 1 eq. of nitric acid, therefore, under the above conditions, converts 8 eq. of tin from the state of proto to perchloride, consequently, if an unknown quantity of nitric acid be digested with a sufficient excess of solution of protochloride of tin of known strength, and the quantity changed into perchloride be afterward found by a suitable method of titration, the proportion of nitric acid wiU be found, supposing ia all cases that no other substance is present, capable of affecting the same change in the tin solution. Pugh arrived at the knowledge of the reaction described, by careful experiments, which are detailed in the Quarterly Journal of the Chemical Society, (vol. xii, part 1, page 35,) and used the process devised by Strong for titrating the strength of the 60 ACIDIMETEY. § 26. tin solution, namely, bichromate of potash, iodide of potassium, and starch. Experience has shewn, however, that the estimation of tin by this method is far from satisfactory, owing to the variable amount of oxidation which the tin solution undergoes when different quantities of water or acid are present during the titration. In my experiments on the process, I have therefore adopted the method of Lenssen (§ 57, 1) for estimating the strength t)f the tin solution, with the most satisfactory results, using in all cases an accurately weighed quantity of pure nitrate of potash for the analysis. One example in detail will make the process clear. a. A solution of pure nitre was prepared so that 1 CC=0'1 Gm. KO,NOg. 6. A solution of pure tin was made by putting a quantity of the granulated metal into a large platinum capsule, and pouring over it a good quantity of strong hydrochloric acid ; when the action, assisted by a gentle heat, had somewhat slackened, the liquid was decanted into a well-stoppered bottle, about a third of its quantity of strong and pure hydrochloric acid added, and the bottle set aside for future use. c. A piece of stout combustion tube, about half an inch diameter and fifteen inches long, was closed at one end, then heated before the blowpipe at about nine inches from the closed end, and drawn out for the space of an inch to a narrow neck ; the tube was then cut off just above this neck, so as to leave a kind of funnel mouth. d. 1 CC of the tin solution was measured with a very accurate pipette into a good sized flask ; about 3 or 4 CC of saturated solution of tartrate of soda and potass added ; then a solution of pure carbonate of soda, till all effervescence was over, and the liquid clear and slightly alkaline ; the sides of the flask were then washed down with cold distilled water, and about 20 CC of saturated solution of bicarbonate of soda delivered in • then starch liquor, and -^^ iodine solution from a y^j CC burette § 26. NITKIC ACID. 61 till the Mue colour appeared. 17'9 CC were required, and as 1 CC of -^^ iodine corresponds to 0-0059 tin, 1 CC of the tin solution contained '10561 Gm. tin. e. 2 CC of the solution a were then measured into the tuhe c. 14 CC of tin solution added, the funnel neck washed down with a few drops of water, a fragment of pure marble dropped in to produce carbonic acid, and thus dispel all air from the tube, when the evolution of gas had ceased, the neck was heated and well closed ; about two inches of space was thus left filled with carbonic acid. When the closed end was cooled, the tube was shaken so as to mix the liquids well, put into a copper air bath, and heated up to 320° Fahr. (160° C.) for about fifteen minutes; then allowed to cool, and when perfectly cold the end of the tube broken off, the contents transferred to a large flask, and treated with tartrate of soda and potash, and carbonate of soda, as in d ; the tube was then washed through with cold distilled water into the flask, bicarbonate of soda, in solution or in powder, added, and the unchanged tin solution titrated with ■^^ iodine, as described in d, the quantity required was 88-6 CC. The calculation was therefore as follows. 1 CC tin solution=0-10561 Gm. tin, consequently 14 CC = 1-47854 Gm., from this must be deducted the weight of tin corresponding to 88-6 CC -^^ iodine=0-52274 Gm., shewing that 0-9558 Gm. of tin had been changed by the nitric acid present, this in turn being multiplied by the factor 0-1144, (obtained by dividing the eq. of nitric acid by eight times the eq. of tin,) gave 0-10934 Gm. NOj, theory requires that 0.2 Gm. KOjNOj should contain 0-10693 Gm. In this case, therefore, the percentage of nitric acid in the salt was found to be 64-67, whereas it should be 53-41 ; but the mean of fifteen experi- ments made with variable quantities both of tin solution and nitrate, (always taking care that at least 10 eq. of tin were present for every one eq. of nitric acid,) gave 54-1 % instead of 53-41. The titration with iodine may be entirely dispensed -ivith by 62 ACIDIMETEY. § 26. distilling the ammonia from the tin solution after digestion, in the apparatus shewn in Fig. 11, in this case the liquid is simply neutralized with caustic soda or potash brought into the dis- tilling flask, an excess of caustic alkali added, the contents of the flask boiled, as in § 1 6, the ammonia received into normal acid, and titrated in the ordinary way. In case the substance under examination contains other matters affecting the tin solution, this plan may be adopted with advantage, but it is not so accurate as the process just described. If sulphuric acid or a soluble sulphate is present in the substance digested with the solution of tin, sulphurous acid will be formed ; sulphate of baryta is, however, not affected, con- sequently it is necessary to precipitate the sulphuric acid in the form of sulphate of baryta, previous to digestion, when the method of estimation by iodine is used. 8. Estimation by the loss which occurs when a Nitrate is fused with Bichromate of Potash, Silicic Acid, or Boraz. Though not a volumetric method, this is given here because of its simplicity of application and accuracy of results. Many years ago, Schaffgotsch announced the use of fused borax for this purpose, and since then Persoz has recommended bichromate of potash, and Reich silica, both of which are preferable to borax, and have afforded Fresenius, Finkene'r, and many others, myself among the number, very accurate results ; in neither case do sulphates or chlorides interfere. With bichromate of potash the following plan is the best. . The well dried and weighed nitrate is mixed with two or three times its weight of freshly fused and powdered bichromate in a large platinum crucible, the cover laid on, the whole weighed, and a gentle heat applied, then gradually raised until the bottom of the crucible is of a dull red, and continued for three quarters of an hour ; then a gas jet directed upon the § 27. SULPHURIC ACID. 63 cover of the cruciMe, until bright red for a few minutes, in order that any particles of the mass which may have been projected against it may be thoroughly decomposed. The cover is then removed for a few minutes, then replaced, and the whole suffered to cool ; when quite cold the weight is again taken and the loss reckoned as nitric acid. The results obtained in several experiments with pure nitre alone, or mixed with chlorides and sulphates, were 53-35, 53-39, 5349, 53-44, &c., instead of 53-41. With silica, four or five times the weight of nitrate is used, and the heat need not be so carefully regulated as with bi- chromate of potash. Twenty minutes or half an hour's red heat is sufficient ; results with the same materials as above, 53-41, 53-54, 53-50, 53-6, 53-66, &c., instead of 53-41. In either case volatile substances, organic matter, &c., must of course be excluded. SULPHURIC ACID. SO,=40. Hydrated Sulphuric Add. S05+HO=49. § 27. 10 CC of concentrated white acid was weighed, and found to be 18-25 Gm., spec. grav. therefore 1-825. In consequence of the great concentration and high spec. grav. of this acid, it is best to use only 1 or 2 CC for analysis ; after the spec. grav. is taken, 1 CC may be titrated, taking care that a very fine and accurate pipette is used for the purpose, or if this is not at hand, it must be weighed direct upon the balance. 2 Gm. of the above acid was titrated, and found to require 37 CC of normal alkali, =90-65 "/, hydrated acid, which agrees exactly with Bineau's table. 64 ACIDIMETEY. § 28. SULPHURIC ACID IN COMBINATION. § 28. 1. The indirect process devised by C. Mohr, and fally described in the " Annalen der Cliemie und Pliarmacie," Bd. 90, S. 165, depends upon tlie same method of determination as has already been described for the alkaline earths, that is to say, a known volume of baryta solution is added to the com- pound, more than sufficient to precipitate the sulphuric acid, the excess of baryta is converted into carbonate, and titrated with normal acid and alkali, as described in § 17. It is best to use a normal solution of chloride of barium as the precipitant, which is made by dissolving 122-05 Gm. of purest chloride in the litre ; this solution likewise sufi&ces for the determination of sulphuric acid by the direct method. The following is the best method of procedure. If the substance contains a considerable quantity of free acid, it must be brought near to neutrality by carbonate of soda, (perfectly free from SO3,) if alkaline, to be slightly acidified with hydrochloric acid, a round number of CC of baryta solution is then added, and the whole digested in a warm place for some minutes ; then precipitate the excess of baryta by a mixture of carbonate and caustic ammonia in slight excess, if a little piece of litmus paper be thrown into the mixture, a great excess can readily be avoided. The precipitate containing both sulphate and carbonate is now to be collected on a filter, and thoroughly washed with boiling water, then titrated as in § 17. The difference between the number of CC of baryta solution added, and those of normal acid required for the carbonate, will be the measure of the sulphuric acid present, each CC of baryta solution is equal to -040 Gm. SO3. Example : 2 Gm. pure and dry nitrate of baryta, and 1 Gm. pure sulphate of potash were dissolved, mixed, and precipitated hot with carbonate and caustic ammonia, the precipitate, after being thoroughly washed, gave r002 Gm. sulphate of potash, instead of 1 Gm. § 28. SULPHURIC ACID. 65 2 Gm. pure anhydrous sulphate of soda was dissolved, and 35 CC of normal chloride of barium added; 6-8 CC normal nitric acid were necessary to decompose the residual carbonate . of baryta, therefore 28-2 CC of baryta solution was required to combine with the sulphuric acid present, this multiplied by -071 gave 2-002 Gm. Na SO, instead of 2 Gm. With Mohr the results were equally satisfactory. 2. Titration bj CMorlde of Barium, witli Chromate of Fotasli as indicator, (Wildenstein.) In Fresenius' "Zeitschrift fiir Analytische Chemie," part 3, "Wildenstein has announced a new method for the more rapid and secure estimation of sulphuric acid, the principle of which is as follows : — To the hot and somewhat concentrated sulphuric acid solution, (which must be neutral, or if acid, neutralized with caustic ammonia, free from carbonate,) a standard solution of chloride of barium is added in slight excess, then a solution of neutral chromate of potash, of known strength, is cautiously added to precipitate the excess of baryta ; so long as any baryta remains in excess, the supernatant liquid is colourless, when it is aU precipitated the liquid is yellow, from ^the free chromate of potash; as a few drops only of a solution of chromate are necessary to produce a distinct colour, the process is capable of very good results. ,The standard solution of chloride of barium may be normal, that is, 122-05 Gm. per Htre, 1 CC =0-040 Gm. SOj. The chro- mate of potash also normal=97-35 Gm., per litre, 1 CC=0-040 Gm. SO,, or 0-122 Gm. Ba CI. The use of solutions of this strength, however, necessitates great care in the analytical process, lest the end of reaction should be overstepped too hastily, but it has the convenience of requiring little calculation. 66 ACIDIMETET. § 28. Wildenstein uses a chloride of barium solution, of which 1 CC=0-015 Gm. SO3, and chromate of potash 1 CC=0-010 Gm. SO5. It would, I think, be preferable to use seminormal solutions, so that 1 CC of each would be equal to 0-020 Gm. SO3. If the chromate solution is made to possess the same chemical power as that of the chloride, the operator has simply to deduct the one from the other in analysis, m order to obtain the quantity of chloride of barium really required to precipitate all the sulphuric acid. The analytical process. — The substance or solution containing sulphuric acid is brought into a small wide-mouthed flask, diluted to about 50 CC, if acid, neutralized with pure ammonia in slight excess, heated to boiling, and the chloride of barium solution delivered cautiously from the burette, till in slight excess ; as the precipitate rapidly settles from a boiling solution, it is not dif&cult to avoid great excess of baryta, which would prevent the liquid from clearing so speedily. The flask is then put over the lamp again, heated to boiling, and the chromate solution added in ^ CC or so, each time removing the flask from the lamp, and allowing to settle until the supernatant liquid is of a light yellow colour ; the quantity of chromate solution is then deducted from the baryta, and the remainder calculated for SO3. Or the mixture with baryta in excess may be diluted to 100 or 150 CC, the precipitate allowed to settle thoroughly, and 25 50 CC of the clear liquid taken out, heated to boUing, and precipitated with chromate unto, all the baryta is carried down as chromate of baryta, leaving the supernatant liquid of light yellow colour ; if there is any uncertainty in the first titration, the analysis may be checked by a second. Wildenstein obtained very good results by this process, as the following statements will shew. A mean of seven estimations of the sulphuric acid in sul- phate of magnesia gave 32-75 "/„, instead of 32-34 required by theory ; a mean of six for SO5 in sulphate of soda, 55-85 "/„ § 29. ACETIC ACID. 61 instead of 56-34 ; a mean of ten for SO, in sulphate of potash, 45-06 instead of 45-92 ; in sulphate of alumina and potash 33-68 instead of 33-73 ; in sulphate of iron and ammonia, 41-4 instead of 40-82. For technical purposes the process is therefore very satisfectory. 3. Direct Frecipltation wltU Normal CMorlde of Baiium. Very good results may be obtained by this method -when carefully performed. The substance in solution is to be acidified with hydrochloric acid, heated to boiling, and the baryta solution allowed to flow cautiously in from the burette until no further precipitation occurs. The end of the process can only be determined by filtering a portion of the liquid, and testing with a drop of the baryta solution. Dr. Beale's filtering tube, shewn in Fig. 15, is the best aid in this case ; a piece of fine filtering paper is tied over the lower end, which is then to be dipped about haK an inch into the liquid, which rises into the tube perfectly clear ; a little is to be poured into a test tube and a drop of baryta added from the burette; if a cloudiness occurs, the contents of the tubes must be emptied back again, washed out into the liquid, ^^' ^^' and more baryta added until all the sulphuric acid is precipitated ; a decinormal solution of baryta is advisable towards the end of the process. ACETIC ACID. C.H^Oa 51. Monohydrated Acetic Acid. CiHsOj + HO 60. § 29. In consequence of the anomaly existing between the specific gravity of acetic acid and its strength, the hydrometer F 2 68 ACIDIMETET. § 29. gives no miifonnly reliaMe indication of the latter, and con- sequently the volumetric method is peculiarly suitable for ascertaining the value of acetic acid in all its forms. 'Far most technical purposes, normal caustic alkali may bo used as the saturating agent ; but a slight error occurs in this method from the fact that neutral acetates have an alkaliue reaction on litmus ; the error, however, is very small, if care be taken to add the alkaU till a distinct blue colour is reached. As acetic acid is volatile at high temperatures, normal carbonate of soda must not be used for titrating it, as it would necessitate heat to expel the carbonic acid. Example: 5 CC of Beaufoy's acetic acid weighed 5'206 Gm. =1-041 spec. grav. The quantity of normal alkali required to saturate it was 27'1 CC, which multiplied by 0'51=l-382 Gm. anhydrous acetic acid, or 26-54 "/„. As the spec. grav. of commercial acetic acid varies very slightly, being generally 1 -04, it is sufficient for many purposes to dispense with the trouble of weighing, and to use the pipette only; in order that 1 CC of normal alkali should represent one per cent, of acid, one tenth of the atomic weight, =5-1 Gm., must be taken, consequently 6-1 — r-=4-904 CC, so that, generally speaking, 4-9 CC taken with the pipette, wUl be the same as 5-1 Gm. by the balance. 4-9 CC of the same acid as above was titrated, and required 26-5 CC=26-5 °/j. Por the ordinary vinegars, there is no necessity to take the spec. grav. into the question. 5 or 10 CC may be taken as 5 or 10 Gm. Malt or coloured vinegar must be copiously diluted, in order that the change in the colour of the litmus may be distinguished ; where the colour is such as to make the end of the process doubtful, recourse must be had to litmus paper, upon which little streaks should be made from time to time with a fine glass rod or a small feather. Several processes have at various times been suggested for the accurate and ready estimation of acetic acid, among which I may mention that of C. Greville Williams, by means of a § 30. NOEMAL AMMONIO-SULPHATE OF COPPER. 69 standard solution of lime syrup, the results he obtained seemed very satisfactory, but where absolute accuracy is required in every possible form and colour of acetic acid, C. Mohr's pro- cess is undoubtedly the most reliable. It consists in adding to a known quantity of the acid an excess of carbonate of baryta or lime in fine powder, the pure carbonate of lime described in the chapter on alkaline earths is preferable, as it dissolves more readily than the baryta. When the decomposition is as nearly as possible complete in the cold, the mixture must be heated to expel the carbonic acid, and to complete the saturation ; the residual carbonate is then brought upon a filter, washed with boUing water, and titrated with normal acid and alkaU. This process is applicable in all cases, and however dark the colour may be, in testing the impure brown pyroligneous acid it is especially serviceable. For all ordinary kinds of acetic acid and vinegar, however, the quickest and most accurate test is Kieffer' s ammonio -sulphate of copper solution for acidimetry, the preparation and use of which wiU now be described. NORMAL AMMONIO-SULPHATE OF COPPER. § 30. This acidimetric solution is prepared by dissolving pure sulphate of copper in warm water, and adding to the clear solution liquid ammonia, until the bluish green precipitate which first appears is nearly dissolved ; then filtered into the graduated cylinder, and titrated by allowing it to flow from a pipette graduated in ^ or -^^ CC, into 10 or 20 CC of normal sulphuric or nitric acid, (not oxalic ;) while the acid remains in excess, the bluish green precipitate which occurs as the drop falls into the acid rapidly disappears, but so soon as the exact point of 70 ACIDIMETEY. § 30. saturation occurs, the previously clear solution is rendered tuibid hj the precipitate remaining insoluble in the neutral liquid ; the principle is as follows. The copper solution has the composition — NH,0, SOs+NH,0, CuO, it is in the latter half of the formula that the aoidimetric power is contained, for when the solution is brought into contact with free sulphuric or other admissible acid, the latter combines with the ammonia; while there is a trace of free acid present, the oxide of copper is dissolved as soon as precipitated, but im- mediately the saturation is complete it remains precipitated ; so that the decomposition is in the case of sulphuric acid — NH,0, CuO and S03=NH40, SO3 and CuO. The process is especially serviceable for the estimation of the free acid existing in certain metallic solutions, i.e., mother liquors, &c., where the neutral compounds of such metals have an acid reaction on Htmus, — such as the oxides of zinc, copper, and magnesia, and the protoxides of iron, manganese, cobalt, and nickel, — it is also applicable to acetic and the mineral acids. The value of the process in any given case depends upon the insolubility of the cupric oxide in the neutral solution which results from the combination of the ammonia and acid. M. Carey Lea (vide "Chemical News," Oct. 12th, 1861, p. 196) has objected to this process on the ground that the precipitate (which he supposes to be a basic sulphate of copper) is not totally insoluble in certain neutral solutions when concentrated, such as sulphate, nitrate, and chloride of ammonium, and he thinks it strange that so experienced a chemist as Mohr should be led into the error of highly recommending such an acidi- metrical process, alleging that a different result would be obtained between testing a solution containing 5 Gm. of sulphuric acid with 5 Gm. of sulphate of ammonia and the same quantity of § 30. NORMAL AMMONIO-SULPHATE OP COPPER. 71 acid, witli 20 or 50 Gm. of sulphate of ammonia ; very probably this would be the case, but as it is an assumption which would not be Kkely to occur in practice, it does not invalidate the accuracy of the process when proper precautions are taken. Mohr especially mentions that the solutions to be tested should be dilute, and it is not likely that any experienced analyst would operate upon the large quantities alluded to by the objector. In the first edition of Mohr's " Titrimethode," the author records an experiment on the determination of oxide of mag- nesia by this method, wherein a loss of four per cent, occurred ; this M. Lea supposes to arise from the faultiness of the process, but as in the second edition Mohr recommends it for the determination of the same substance, and omits any mention of the former result, I suppose the error must have been owing to other causes. The process has given me good results, as may be seen under the head of magnesia. Fresenius also notices the process favourably in the last edition of his " Quantitative Analysis." More recently the same authority (" Zeitschrift fiir Analytische Chemie," 1, p. 108) has published a series of experiments, for the purpose of testing the truth of Lea's objection. The result is that he stUl recommends the process for technical purposes. • It is necessary from time to time to titrate the solution afresh, as it alters very slightly by keeping. I have found it to weaken to the extent of ^ per cent, in two years, when set aside in a bottle untouched. Where it is contiauaUy in use, and being freshly prepared every few weeks or days, the variation would be quite insignificant. If nitrate of copper be used instead of sulphate in the preparation of the normal solution, the presence of baryta, strontian, lead, and silver, in the acid solution is of no consequence. 72 ACIDIMETEY. § 32. TESTING OF ACETIC ACID OR VINEGAR BY AMMONIO-SULPHATE or COPPER. § 31. The only necessary condition is that the acid be very dilute, as the copper precipitate is soluble in concentrated acetate of copper ; if the first drop of copper solution produces a turbidity which disappears only on shaking or stirring the liquid, the dilution is sufficient ; and in order that the first traces of a permanent precipitate may be recognised, it is well to place a piece of dark coloured paper under the beaker. The results are very uniform and reliable. For the vinegars of commerce, this process seems peculiarly applicable, as a large amount of dilution is of no consequence to the reagent, and owing to the colour of malt vinegar it is of considerable value to the analyst,, as it enables him to distinguish the end of the process more exactly. ESTIMATION OF CERTAIN METALLIC OXIDES OR THEIR NEUTRAL SALTS IN ACID SOLUTIONS, TOGETHER WITH THE FREE ACID BY EIEFFER'S SOLUTION. § 32. That the objection made by Lea to this acidimetric method had a nucleus of truth in it, no one would doubt who knows something of that accomplished chemist, but when tolerably dilute cold solutions are used, and some Uttle practice obtained, the results are uniformly good, and susceptible of a great amount of accuracy. As the process is mostly available for technical uses, it is amply sufficient for the purpose. The oxides and carbonates of zinc and magnesia are first dissolved in a known quantity of normal nitric or sulphuric acid, and then titrated backward with normal copper solution. Example, 3'9 Gm. of Howard's calcined magnesia was dissolved in 220 CC of normal sulphuric acid, and 3-0 CC of ? 33. OEGANIC ACIDS. 73 copper solution added, -whose factor for normal strength -was •909=27-27 CC normal, which deducted from 220 leaves 192-7 CC of normal acid=3'86 Gm. pure magnesia, or 99 per cent. ; there was a small amount of insoluble matter which would probably make up the difference. For this large quantity of material the result is very satisfactory. 1 Gm. of pure and freshly ignited oxide of zinc was dissolved in 27 CC of normal nitric acid, and 2-3 CC of copper solution required=24-7 CC acid, which multiplied by -04053, gave 1-001 Gm. 20 Gm. of an acid solution of sulphate of zinc was taken from the cell of a Smee's battery, and titrated with the copper solution, of which 18-5 CC were required to produce a precipitate; this multiplied by -040 Gm., gave -74 Gm.=3-7 % of sulphuric acid in a free state. Acid mother liquors of green and blue copperas can be examined in the same way. ORGANIC ACIDS. § 33. Substance. Formula. Atomic Weight Quantity to bo weighed so that 1 CC. or 1 dm.N. alk.=lper cent, of aabstance. Normal Factor. Tartaric Acid (cryst.) CiH,Os + HO 75 7-5 Qm., or 75-0 grn. 0-075, or 0-75 Bitartrate of Potash KO, 2C4 H2 188-11 18-811 Gm., or 0-18811, or (argol.) Oe+HO 188-11 gm. 1-8811 Citric Acid (cryst.) ... Oi Hi Oi + HO 69 6-9 Gm., or 69-0 grn. 6-3 Gm., or 0-069, or 0-69 Oxalic Acid (cryst.)... Ca O3 + 3H0 63 0063, or 63-0 grn. 0-63 Binoxalate of Potash KO, 2C2 O3 146-11 14-611 Gm., or 0-14611, or (sal. acetosella) + 3H0 146-11 grn. 1-4611 iN'ormal caustic alkali is the best agent for titrating the substances contained in the above table. V4 ACIDIMBTRY. § 34. ESTIMATION OF COMBINED ACIDS IN NEUTEAL SALTS. § 34. This compreh.ensive method of determining the quantity of acid ia neutral compounds, (hut not the nature of the acid), is applicable only in those cases where the base is perfectly precipitated by an excess of caustic alkali or its car- bonate. The number of bodies capable of being so precipitated is very large, as has been proved by the researches of M. M. Langer and Wawnikiewicz, (Ann. der Chemie und Pharm., p. 239, Feb. 1861,) who seem to have worked out the method very carefully. These gentlemen attribute its origin to Buns en; but it does not seem certain who devised it. The best method of procedure is as follows : — The substance is weighed, dissolved in water in a 300 CC flask, heated to boOing or not, as may be desirable, then adding, from a burette, normal alkali or its carbonate, according to the nature of the base, until the whole is decidedly alkaline, dilute to 300 CC and put aside to settle; 100 CC are then taken out and titrated for the excess of alkali; the remainder multiplied by 3, gives the measure of the acid combined with the original salt, i.e., supposing the precipitation is complete. Example. 2 Gm. crystals of chloride of barium were dissolved in water, heated to boiling, and 20 CC normal car- bonate of soda added, diluted to 300 CC, and 100 CC of the clear liquid titrated with normal nitric acid, of which 1-2 CC were required — altogether, therefore, the 2 Gm. required 16 -4 CC normal alkali— this multipUed by 0-122, gave 2-0008 Gm. Ba CI, instead of 2 Gm.; multiplied by the factor for chlorine 0-03546, it yielded 0-58154 Gm., theory requires 0-5813 Gm. chlorine. The foUowiag substances have been submitted to this mode of examination with satisfactory results : — Salts of the alkaline earths precipitated, boiling hot, -(vith an alkaline carbonate. § 34. COMBINED ACIDS. 75 Salts of magnesia, with, pure or carlDonated alkali. Alum, with caihonate of alkali. Zinc salts, boiling hot, with the same. Copper salts, boiling hot, with pure potash. Silver salts, with pure alkali. Bismuth salts, half-an-houi's boiling, with carbonate of soda. Mckel and Cobalt salts, with carbonate of soda. Lead salts, with the same. Iron salts, boiling hot, with pure or carbonated alkali. Mercury salts, with pure alkali. Protosalts of manganese, boiling hot, with carbonate of soda. Chromium persalts, boiling hot, with pure potash. "Where the compound under examination contains but one base precipitable by alkali, l^e determination of the acid gives, of course, the quantity of base also. 76 EXAMINATION OF ALKALINB PEODUCTS. § 35. APPENDIX TO PART II. TECHNICAL EXAMINATION OF COMMERCIAL ALKALINE PKODUCTS. Soda Asb or Alkali. % § 35. Moisture must be determined by heating 5 or 10 Gm. to dull redness for ten minutes, in a small crucible of platinum, silver, iron, or porcelain, allowing it to cool under a beU glass in the presence of sulphuric acid or chloride of calcium: the difference between the first an^j^econd weighings is the accidental moisture in the sample. The contents of the crucible are then dissolved in about four ounces of warm distilled water, and any insoluble matter filtered off by a small filter, the latter washed a few times with hot water, then, if necessary, dried, ignited, and weighed as in- soluble matter. It is important that this insoluble matter be removed before titration, otherwise the lime and other con- stituents in it wiU consume a portion of the normal acid, and so register a higher percentage of alkali than is really present. The total quantity of alkali is determined in a measured portion of the filtrate and washings previously diluted up to i or 1 litre, by normal sulphuric or oxalic acid, as in § 12. The quantity of caustic alkali present in any sample is determined as in § 15. The presence of sulphide of sodium is ascertained by the smeU of sulphuretted hydrogen when the alkali is saturated § 35. SODA ASH OE ALKALI. 77 ■with, an acid, or by dipping paper, steeped in nitro-prasside of sodium, into the solution, if the paper turns blue or violet sulphide is there. The quantity of sulphide and hyposulphite of sodium may be determined by saturating a dilute solution of the alkali with a slight excess of acetic acid, adding starch liquor, and titrating ■with decinormal iodine solution (§ 45) till the blue colour appears. The quantity of iodine required is the measure of the sulphuretted hydrogen and hyposulphurous acid present. The quantity of each may be known by adding a solution of sulphate of zinc to a like quantity of the alkali, and filtering so as to remove the free carbonated and sulphuretted alkali, by which means the hyposulphurous acid alone remains, which may be estimated with iodine and starch as before, the quantity of iodine solution so requirea is to be deducted from the total, and the calculation for both sulphide and hyposulphite of sodium may then be made, 1 CC decinormal iodine is equal to •0248 Gm. hyposulphite of soda, or -0039 Gm. sulphide of sodium ; good English alk^jli is seldom contaminated with these substances to any extent. Chloride of sodium (common salt) may be determined by neutralizing -585 Gm. or 5 '85 grn. of the alkaU -with nitric acid, and titrating with decinormal silver solution and chromate of potash, (§ 74). Each CC or dm. corresponds to 1 per cent, of common salt, if the above weight is taken. Sulphate of soda is determined, either direct or indirect, as in § 28, each CC or dm. of normal chloride of barium is equal to -071 Gm., or -71 grn. of dry sulphate of soda. Black ash and raw mother liquors and lyes can be examined in precisely the same way as above ; if oxide of iron is present it may be determined as in § 47 ; lime, by boihng -with carbonate of soda and precipitation as carbonate — washing the precipitate thoroughly with boiling water, and titration with normal acid and alkaU, as in § 18. Phosphoric acid ■with uranium solution, as in § 78, 1. 78 EXAMINATION OF ALKALINE PEODUCTS. § 38. POTASH AND PEARLASH § 36. Abb examined in the same way as soda. SALT GAEE § 37. Is the impure sulphate of soda left in the retorts in preparing hydrochloric acid from sulphuric acid and salt. It generally contaias free sulphuric acid existing as bisulphate of soda, the quantity of which may be ascertained hy direct titration with normal alkali. The common salt present is estimated by decinormal silver solution and chromate of potash ; navitig first saturated the free acid with pure carbonate of soda, see § 74, 1 CC or 1 dm. silver solution, is equal to -005846 Gm. or -05846 grn. of salt. Sulphuric acid, combined with soda, is estimated either directly or indirectly as in § 28 ; 1 CC or 1 dm. of normal baryta solution is equal to -071 Gm., or -71 grn. of dry sulphate of soda. RAW SALT. BRINE, &C. § 38. Limb may be estimated by precipitation with oxalate of ammonia, and the precipitate titrated with permanganate, as in § 60, 1. Sulphuric acid as in § 28. Magnesia is precipitated as ammoniacal phosphate, by a solution of phosphate of soda containing ammonia, first re- moving the lime by oxalate of ammonia, the precipitate of double phosphate of magnesia and ammonia is brought on a filter, washed with cold water containing ammonia, then dis- § 39. GYPSUM, SELENITE, PLASTEK OF PAEIS. 79 solved in acetic acid, and titrated with tiraniuni solution, as in § 78, 1 ; each CC of solution required represents 0-0563 Gm. magnesia ; or the precipitate may be dried, ignited, and weighed as pyrophosphate of magnesia. The quantity of real salt in the . sample may he ascertained by treating a weighed quantity in solution with caustic baryta, boUing, setting aside that the excess of baryta may precipitate itself as carbonate, or more quickly by adding carbonate of ammonia, filtering, evaporating the solution to dryness, and gently igniting — the residue is pure salt. The loss of weight between this and the original specimen taken for analysis, will shew the percentage of impurities. GYPSUM, SELENITB, PLASTER OF PARIS, § 39. May ' be estimated direct by boiling a weighed quantity, in fine powder, with its own weight of carbonate of soda and about 20 parts water, for half-an-hour, adding fresh water to supply the waste ; the carbonate of lime so formed is brought upon a filter, washed thoroughly with boiling water, and the precipitate and filter titrated with normal acid and alkali, as in § 18. Sulphuric acid may be estimated in the filtrate from above, directly or indirectly, by normal chloride of barium, as in § 28. The indirect estimation of gypsum is obtained by boiling 3 Gm. with 60 CC of normal carbonate of soda for some time in a 300 CC flask, dilute to the 300 CC mark, and put aside to settle, take out 100 CC of the clear Uquid with a pipette, and titrate with normal acid and alkali, multiply the quantity of acid by 3, and deduct the product from the original 60 CC of alkali. The remainder is calculated as hydrated sulphate of lime, by multiplying with -086, or as anhydrous with -068. Principle of the process explained in § 34. 80 EXAMINATION OF ALKALINE PRODUCTS. § 41. AMMONIACAL GAS I.IQUOK. § 40. The value of this substance depends upon tlie quantity of ammonia contained therein, this constituent mainly exists in a free state, some portion of it, however, generally exists as sulphide and hyposulphite of ammonium. The free alkali is best determined by titrating a known volume of the liquor with normal acid and litmus ; in consequence of the dark colour and other contaminations of the liquor, it is more secure to ascer- tain the end of the process by litmus paper — a glass rod or small feather moistened with the mixture may be brought in contact with both red and blue paper, when both remain unaffected the process is finished; each CC or dm. of acid is equal to -017 Gm., or -17 grn. of ammonia. The total quantity of ammonia is ascertained by distilling a portion of the gas liquor in the apparatus, Fig. 11. Or an equally exact process, when the liquor contains no other salt than ammonia, consists in saturating a portion of the liquor with pure hydrochloric acid, and evaporating to perfect dryness on the water-bath, then heating the residue to about 240° Fahr. in the sand or air-bath, dissolving in water, filtering and titra- ting with decinormal silver solution and chromate of potash, as in § 75. Each CC or dm. of -^^ silver solution, is equal to -0017 Gm. or -017 grn. of ammonia. Hydrosulphuric and hyposulphuric acids can be estimated with ^j iodine solution, as in the case of alkali. (§ 35.) AIKAIIHE NITRATES, (SALTPETRE, NITRATE OF SODA, &c.) § 41. In the case of saltpetre and nitrate of soda, the nitric acid is determined in the previously fused samples by ignition § 41. ALKALINE NITRATES. 81 with bichromate of potash or silicic acid, as in § 26, 8; or hy any more convenient method in the same section. Chlorine, existing as common salt, is determined as in § 74 ; sulphuric acid, direct or indirect, as in § 28 ; lime is precipitated as carbonate, and titrated as in § 18. When mixtures of nitrate of potash and soda occur, the potash must be determined by precipitation as double chloride of platinum and potassium. 82 ANALYSIS BY OXIDATION AND EEDUCTION. § 42. PAET III. ANALYSIS BY OXIDATION AND REDUCTION. INTRODUCTION. I 42. The series of analyses which occur under this system are very extensive in number, and not a few of them possess extreme accuracy, such in fact as is not possible in any analysis by weight, consei^uently they have now been estabUshed, when- ever practicable, instead of the old system. The completion of the various processes is generally shown by a distinct cha,nge of colour, such for instance as the occurrence of the beautiful rose red permanganate or the blue iodide of starch, and as the smallest quantity of these substances wUl colour distinctly large masses of liij[uid, the slightest excess of the oxidising material is sufficient to produce a satisfactory result. The principle involved in the processes is extremely simple. Substances which wiU take up oxygen are brought into solution, and titrated -with a substance of known oxidising power — such for instance as occm-s in the determination of protoxide of iron by permanganate of potash. The iron is ready and willing to receive the oxygen^the permanganate is equally willing to part with it; while the iron is absorbing the oxygen the permanganate loses its colour ahnost'as soon as it is added, and the whole mixture is colourless, but immediately the § 42. ANALYSIS BY OXIDATION AND REDUCTION. 83 iron is satisfied the rose colour no longer disappears, there being no more oxidisable iron present. 2 atoms FeO absorb 1 atom oxygen, becoming 1 atom Fe^ O3. Oxalic acid occupies the same position as protoxide of iron, its composition is G^ O3 + 3 Aq.; if permanganate is added to it 1 atom combines with 1 atom oxygen and is resolved into 2 atoms carbonic acid; when the oxalic acid is all decomposed the colour of the permanganate no longer disappears. On the other hand, substances which will give up oxygen are deoxidised by a known excessive quantity of reducing agent, the amount of which excess is afterward ascertained by residual titration with a standard oxidising solution; the strength of the reducing solution being known, the quantity required is a measure of the substance which has been reduced by it. The oxidising agents best available are — permanganate of potash, iodine, bichromate of potash, and red prussiate of potash. The reducing agents are — sulphurous acid, hyposulphite of soda, oxalic acid, protoxide of iron, arsenious acid, protochloride of tin, yellow prussiate of potash and zinc. With this variety of materials a great many combinations may be arranged so as to make this system of analysis very comprehensive, but the following are given as sufficient for almost all purposes, and as being susceptible of the greatest amount of purity and stability of material, with exceedingly accurate results : — 1. Permanganate and protoxide of iron, (vrith the rose colour as indicator); permanganate and oxalic acid, (with the rose colour as indicator). 2. Bichromate of potash and protoxide of iron, (with ces- sation of blue colour, when brought in contact vrith. red prussiate of potash, as indicator). 3. Iodine and hyposulphite of soda, (with starch as indi- cator) ; iodine and arsenite of soda, (vrith starch as indicator). G 2 84 ANALYSIS BY OXIDATION AND KEDUCTION. § 43. PREPARATION OF STANDARD SOLUTIONS. PERMANGANIC ACID AND PROTOXIDE OF IRON. Permanganate of Fotasb. KO+Mn^ O7 = 158-25. § 43. The solution of this salt is best prepared for analysis by dissolving the pure crystals in distilled water of such a strength that 17'85 CC will peroxidise 1 decigramme of iron. The solution is then decinormal. If weU kept, it holds its strength several months. The pure permanganate may be obtained very generally of the dealers in pure chemicals, but should it not be procurable, when required, or the expense too great, the solution may be prepared as follows : — Ten parts of caustic potash and 7 of chlorate of potash are fused in a hessian crucible, then 8 parts of finely powdered peroxide of manganese added, and the whole well mixed with an iron rod; the crucible is kept at a dull red heat, and the contents stirred until, from the dissipation of the water, the mass loses its pasty state and becomes somewhat friable, contimie the dull red heat, breaking the mass from the sides of the crucible and mixing altogether for a few minutes, then empty the contents into a clean copper or iron dish. "When cool, it is to be coarsely powdered, put into a large flask or porcelain dish, and 20 or 30 times its weight of boiling water poured over it, then kept boiling gently until the solution" assumes a deep purple rose colour. "When the precipitated oxide of manganese has somewhat settled, the solution may be decanted into a large green glass bottle, and further diluted with the washings of the residue in the dish or flask to about the strength required for analysis. The solution so prepared can- § 43. PBEPAKATION OF STANDAED SOLUTIONS. 85 tains a large quantity of alkali, and is constantly nndergoing a slight change owing to its containing a portion of manganate of potash which slowly decomposes with precipitation of oxide of manganese. If the excess of caustic potash is saturated by an acid, the solution is far more stable. Mulder, therefore, recommends that a stream of carbonic acid should be passed through the solution, frequently shaking it, until the potash is saturated ; an excess of acid does no harm ; sulphuric acid may also be used for the same purpose, but is not so recommendable. When the liquid thus treated has thoroughly settled, a portion may be decanted (not filtered through paper) into a convenient sized bottle for laboratory use. A very useful form of bottle for preserving it is the ordinary wash bottle, or any common bottle fitted with the same arrange- ment of tubes. Burettes can then be filled with the solution without its frothing, and as the tube which enters the liquid does not reach the bottom of the bottle, the sediment, if any, is not disturbed; another advantage is, that the solution does not come into contact with the cork, nor can any dust enter : the blowing tube may be closed by a very small cork. A solution prepared and kept as here directed will generally preserve its strength unaltered for six months. 1. Titration of the Permanganate Solution. In order to ascertain the strength of the permanganate it must be titrated with either a weighed quantity of metallic iron, oxalic acid, or the double sulphate of iron and ammonia. This latter salt is a most convenient substance for titrating the permanganate, as it saves the time and trouble of dissolving the iron, and being perfectly stable when pure, it can be depended on without risk. To prepare it, 139 parts of the purest crystals of protosulphate of iron, and 66 parts of pure crystallized sulphate of ammonia are separately dissolved in the least - possible quantity of distilled water of about 120 Fahr. temp., if 83 ANALYSIS BY OXIDATION AND EEDUCTION, § 43. the solutions are not perfectly clear they must be filtered ; mix them at the same temperature in a porcelain dish, adding a few drops of pure sulphuric acid, and stir till cold, during the stirring the double salt 'vviU fall in a finely granulated form, set aside for a few hours, then pour off the supernatant liquor, and empty the salt into a clean funnel with a little cotton wool stuffed into the neck; so that the mother liquor may drain away, the salt may then be quickly and repeatedly pressed between fresh sheets of clean filtering paper, or stiU better, as Mohr recommends, dried in a centrifugal machine. As very few persons are possessed of this latter, albeit a most useful article, the salt may be spread out on a tray made of filtering paper, and the superfluous moisture driven off by a fan or pair of bellows; lastly, place it in a slightly warm place to dry thoroughly so that the small grains adhere no longer to each other or to the paper in which they are contained, then preserve it in a stoppered bottle for use. The formula of the salt is — ■ FeO, SO3+NH4 0, SOs + 6Aq = 196. Consequently it contains exactly one-seventh of its weight of iron, therefore, 07 Gm. represent O'l Gm. of iron, and this is a convenient quantity to weigh for the purpose of titrating the permanganate. 0-7 Gm. being brought into dilute solution in a flask or beaker, and 5 or 6 CO of dilute sulphuric acid (1 to 5) added, (the titration of permanganate, or any other substance, by it must always take place in the presence of free acid and prefer- ably sulphuric), the permanganate is delivered from a Gay Lussac's plain, or with blowing tube, or the elastic ball burette divided in ^ or -j^g- CO, until a point occurs, when the rose colour no longer disappears on shaking; a few drops of the permanganate in excess are sufficient to produce this effect, but the actual quantity required to colour the same quantity of water should be found, and deducted from the total used § 43. PEEPARATION OF STANDARD SOLUTIONS. 87 in the analysis. The titration is now ended, and the num- ber of CC used may be marked upon the bottle as the quantity for 0-1 Gm. Fe, or the factor found, -which is necessary to reduce it to decinormal strength, or diluted to that strength at once. 2. Titration wltb Metallic Iron. The purest iron to be obtained is the thin annealed binding- wire free from rust. About O'l Gm. of this is to be dissolved in dilute sulphuric acid by the aid of heat, in a small flask closed with a cork, through which a fine glass tube is passed, so that the hydrogen which is evolved escapes under pressure, thus preventing the access of air; or better than this, the plan suggested by Mohr may be used, which consists in passing the upper end of the fine tube through a cork ; over the end of the glass tube, which is level with the cork, a small piece of sheet india rubber or oiled silk is laid and pinned down to the cork with a pin on each side of the hole. This contrivance acts as a valve by which the hydrogen escapes from the flask under pressure, but so soon as the pressure of gas ceases and the flask cools, the valve closes by atmospheric pressure and thus prevents the entrance of air ; by this means there is no difficulty in obtaining the whole of the iron in solution as protoxide. "When the iron is all dissolved the flask may be two-thirds filled with cold distilled water, and the titration with perman- ganate commenced and concluded as in the case of the double sulphate. The decomposition which ensues from treating protoxide of iron by permanganic acid may be represented as follows : — 10 Fe and Mnj 0, = 2 Mn and 5 Fe^ Oj therefore, 2 atoms of protoxide absorb 1 atom of oxygen and are changed into 1 atom of peroxide, consequftitly, in the systematic tables for iron given farther on, (§ 47), the weight of the protoxide with its compounds is doubled. 88 ANALYSIS BY OXIDATION AND KEDUCTION. § 43. 3. Titration with Oxalic Acid. About 0-63 Gm. of the pure acid is to be weigbed, or 10 CC of normal solution measured with a pipette, brought into a flask with dUute sulphuric acid, as in the case of the iron salt, and considerably diluted with water, then warmed to about 80° Fahr. and the permanganate added from the burette. The colour disappears slowly at first but afterward more rapidly, becoming first brown, then yeUow, and so on to colourless. More care must be exercised in this case than in the titration with iron, as the action is less decisive and rapid, nevertheless, it is as reliable with care and attention. 1 atom of oxalic acid takes up 1 atom of oxygen, and is resolved into 2 atoms of carbonic acid which escapes with faint effervescence; when the permanent rose colour appears the process is finished. Precautions. It must be borne in miud that free acid is always necessary in titrating a substance with permanganate, in order to keep the resulting oxide of manganese ia solution. Sulphuric acid, in a dilute form, has no prejudicial effect on the pure permanganate, even at a high temperature; not so, however, nitric or hydro- chloric acids, the former, though very dilute if it contain the lower oxides of nitrogen, immediately decomposes the solution, consequently the last traces of these must be removed by boiling previous to its addition. With hydrochloric acid the solution to be titrated must be very dilute and of low tempe- rature, otherwise chlorine will be liberated and the analysis spoiled; under any circumstances the analysis must be subjected to correction with this acid, as will be shewn further on. With the ordinary permanganate solution, prepared as pre- viously described from chlorate and hydrate of potash and manganese, and which contains chloride of potassium, chlorine is liberated by sulphuric acid at a high temperature, therefore, § 43. PEEPAEATION OJ' STANDARD SOLUTIONS. 89 in any case it is advisable to use very dilute solutions at not more than 70° or 80° Palir. Organic matter of any kind decomposes the permanganate, and the solution, therefore, cannot be filtered through paper, nor can it be used in Mohr's burette, because it is decomposed by the india rubber tube. It will be a startling announcement to the chemical world to be told that the determination of iron by permanganate, under many circumstances hitherto recommended, is subject to great error, so great an error in fact, that the determination may be totally worthless unless subjected to correction. In Fresenius' " Zeitschrift fiir Analytische Chemie," part 3, (pub. in Oct. 1862.) Lowenthal and Lenssen have con- tributed a valuable paper on the subject, a short summary of which is as follows. A complete series of determinations of iron were made with different quantities of free hydrochloric and sulphuric acids, with variable quantities of water, free from air and containing air, and at various temperatures, correction being in all cases made for the quantity of solution of perman- ganate necessary to colour the various bulks of liquid. The results proved conclusively that the process was exact only when the iron existed as sulphate, when a moderate quantity of free sulphuric acid was present, and when deduction was made for the colouration of the liquid. Fresenius has also most carefully checked the statements made by Lowenthal and Lenssen, obtaining results which point to the same con- clusion. I give the experiments of Fresenius somewhat in detail. The permanganate solution was prepared with the pure crystals of such strength that 100 CC=0-4 Gm. iron. The iron solution was prepared from pure sulphate. The hydro- chloric and sulphuric acids used were absolutely piu'e, the first 1'12 spec, grav., the last L23 ; fresh distOled water was used for the dilution, and in order to remove any traces of reducing agents it was acidified with sulphuric acid, and sufficient per- manganate added to give a permanent pinkish colour. The 90 ANALYSIS BY OXIDATION AND EEDUCTION. § 43. correction, therefore, for colouration of the liquid was un- necessary. Exp. I, a. To 1 litre of the water- so prepared, 25 CC hydrochloric acid and 10 CC iron solution were added. The permanganate required was 13'9 CC I. To the same liquid 10 CC more of the iron solution was added, and required permanganate 12 '9 „ c. Other 10 CC iron 12-9 „ d. Ditto 12-8 „ Exp. 2, a. 1 litre water, 25 CC sulphuric acid, and 1 CC iron requu-ed 13-1 „ b. Other 10 CC „ 12-9 „ c. Ditto 12-9 „ Exp. 3, a. 1 litre water, 5 CC hydrochloric acid, and 10 CC iron 13-20 „ h. Other 10 CC iron 12-6,5 „ c. Ditto 12-62 „ Exp. 5, a. 1 litre water, 60 CC hydrochloric acid, and 10 CC iron, required... 14-30 „ 5. Other 10 CC iron „ 12-70,, c. Ditto 12-68,, Exp. 6, a: 1 litre water, 5 CC sulphuric acid, and 10 CC iron, required 12-98,, 6. Other 10 CC iron „ 12-80,, c. Ditto 12-80,, Exp. 7, a: I litre water, 25 CC sulphuric acid, and 10 CC iron, required 12-88 „ 6. Other 10 CC „ 12-80,, c. Ditto 12'80 „ Exp. 8; a. 1 litre water, 50 CC sulphuric acid, and 10 CCiron; required 13-20 „ 6. Other 10 CC „. 12-80 ',i c. Ditto 12.80,, § 43. PREPAEATION OF STANDAED SOLUTIONS. 91 No difference was discoverable when the quantity of water was lessened to one-fourth or increased to one litre, nor was any effect produced by adding perchloride of iron. From the above experiments it will readily be seen that titration with permanganate is far less reliable in the presence of free hydrochloric than sulphuric acid, o^ving, undoubtedly, to some secondary reaction between the chlorine of the acid and the permanganate. All researches, however, go to prove that when a, solution of the substance to be titrated with hydro- chloric acid is divided into 3 or 4 portions, and successively titrated in the same liquid, the mean of the 2nd and 3rd, (setting the first entirely aside), will be dependable. There can be vury little doubt that the discrepancies shewn to occur in the use of hydrochloric acid will account, in some measure, for the frequent want of accuracy in Pelouze's method for the determination of nitrates and similar processes. It is, therefore, advisable, in all possible cases, to use sulphuric acid for acidifying the solution and to avoid any large excess. Where hydrochloric acid must be used and bichromate of potash is not admissible for titration, the fractional estimation before-mentioned must be adopted, taking the second, or mean of second and third titrations as correct; where this is not practicable it is best to prepare a mixture of hyih^ochloric acid and water, add some sulphate of iron, and titrate with perman- ganate to the red tinge, then add the substance, and titrate with permanganate. Experiment has shown that this method is reliable. Examples of Iron Analysis witli Ferma^anate. 0'7 Gm. double iron salt= O'l Gm. iron, was carefully weighed, dissolved, and sulphuric acid added. Permanganate required was 10 CC; this was marked upon the label, and the bottle set aside in ITovember, 1860. In July, 1862, the permanganate 92 ANALYSIS BY OXIDATION AND EEDUCTION. § 43. solution was tested again and 0-7 Gm. double salt required 104 CC. This seems to prove that the solution is not so changeable as one is apt to suppose. I have, therefore, adopted the plan of keeping a decinormal solution, made by diluting the concen- trated liquor obtained from the rough mass before described, and which holds its strength perfectly as yet, (October, 1862.) 0-5 Gm. pure sulphate of iron was titrated with the deci- normal permanganate, of which 17 '9 CO were required, this multiplied by 0-0278 gives 0'498 Gm. instead of 0-5 Gm. ; as the crystals of sulphate of iron always contain a portion of mother liquor it is almost impossible to obtain a perfectly dry sample for examination, consequently there is an invariable loss in the analysis. In using the decinormal permanganate it is advisable to operate upon small quantities of iron only, (1 or 2 deci- grammes,) so that a small -jJ^ CC burette may sufi&ce. Calculation of Analyses. The calculation of analyses with permanganate, if the solution is not strictly decinormal, can be made by ascertaining its constant factor, reducing the number of CC used of it to deci- normal strength, and multiplying the niimber of CC thus found by xj.jjjjo atom of the substance sought; for instance — Suppose that 15 CC of permanganate solution have been found to equal O'l Gm. iron, it is required to reduce the 15 CC to decinormal strength, which would require 1000 CC of permanganate to every 5-6 Gm. iron, therefore 5-6 : 1000 :: 0-1 a;=17-85 CC; 17-85 multiplied by 0-0056=0-09996 Gm. iron, which is as near to 0-1 Gm. as can be required. Or the factor necessary to reduce the number of CC used may be found as follows:— 0-1 : 15 :: -56 : a; = 84 CC, therefore, i^ = 1-19. 84 Consequently 1-19 is the factor by which to reduce the number of CC of that special permanganate used in any analysis to the § a. PREPARATION OF STANDARD SOLUTIONS. 93 decinormal strength, from wlieiice the weight of substance sought may be found in the usual way. Another plan is to find the quantity of iron or oxalic acid represented by the permanganate used in any given analysis, and this being done the following simple equation gives the required result ; — ■ 2 at. Fe (56) at. weight of the weight the weight of or : the substance : : of Fe or : substance 1 at. (63) sought found sought. In other words, if the atomic weight of the substance analysed be divided by 56 or 63, (the respective atomic weights of iron or oxalic acid), a factor is obtained by which to multiply the weight of iron or oxalic acid, equal to the permanganate used, the product is the weight of the substance analysed. For example, copper is the substance sought, 2 at. Cu corresponding to 2 at. Fe is 63"4, let this number, therefore, be 63'4 divided by 56, whence = 1-1314, therefore, if the 56 quantity of iron represented by the permanganate used in a copper analysis, be multiplied by ri314, the product will be the weight of the copper sought. Where possible the necessary factors *iU be given in the tables preceding any leading substance. CHBOKIC ACID AND PROTOXIDE OF IRON. Bicliromate of Fotasli. 2Cr 03+KO=147-59. § 44. This substance, which appears to have been first pro- posed by Professor Penny, of Glasgow, possesses the great advantage over permanganate, that it is absolutely per- 94i ANALYSIS BY OXIDATION AND REDUCTION. § 44. manent in solution, is very cheap, and may frequently be obtained in ordinary commerce in a pure state ; beside whicb, its solution may be used in Mohr's burette witbout under- going tbe change peculiar to permanganate ; on the other hand, the eiid of the reaction iu the estimation of iron can only be known by an external indicator, that is to say, a drop of the mixture is brought in contact -with a drop of solution of red prussiate of potash (freshly prepared) upon a white slab or plate ; while the protoxide of iron is in tolerable excess, a rich blue colour occurs at the poiut of contact between the drops, but as this excess continues to lessen by the addition of the bichromate, the blue becomes somewhat turbid, having first a green, then grey, and lastly brown shade. AVhen the greenish blue tiat has all disappeared, the process is finished. This series of changes in the colour admits of very sharp and sure reading of the burette, after a little practice is obtained. The reaction between chromic acid and protoxide of iron may be represented by the formula, 2 Cr Os+6 Fe 0=Crj Oj+S Fe^ 0^. The decomposition takes place immediately and at ordinary temperatures in the presence of free sulphuric or hydrochloric acid; nitric acid is, on account of the protoxide of iron, of course inadmissible. The reduction of the compounds of iron to the state of protoxide may be accomplished by zinc or sulphurous acid as with permanganate ; or instead of these, protochloride of tin may be used, which acts very rapidly as a reducing agent upon per- oxide of iron, the red colour of the solution disappearing almost immediately. In the analysis of iron ores this method of reduction is serviceable ; the greatest care, however, is necessary, that the protochloride is not present in excess, as this would consume the bichromate solution equally with the protoxide of iron, and so lead to false results. § 44. PEEPAKATION OF STANDARD SOLUTIONS. 95 The discharge of the red colour of the iron solution may with care be made a very sure indication of the exact point of reduction. The concentrated hydrochloric solution of iron is heated to gentle boiling, and the moderately dilute tin solution added with a pipette, waiting a moment after each addition till the last traces of colour have disappeared ; the solution is then poured into a beaker, diluted with water, and titrated with the bichromate as usual ; an extra security is obtained by adding a few drops of sulphocyanide of potassium to the solution, the disappearance of the blood-red colour indicating that no more peroxide of iron is present. In order to obviate the inaccuracy which would be produced by an excess of tin in the state of protosalt, Mohr recommends that chlorine water should be added by drops to the mixture until a rod moistened with it and brought in contact with blue iodide of starch paper no longer removes the colour, the excess of protochloride of tin is then aU converted into perchloride, and the titration with bichromate may proceed as usual. For the direct titration of iron by protochloride of tin see § 50. It is absolutely necessary that the solution of ferridcyanide of potassium used as the indicator with bichromate should be free from ferrocyanide ; and as a solution when kept for some little time becomes in some measiire converted into the latter, it is best to use a freshly-prepared liquid, or at least to test the indicator with a persalt of iron previous to titration. Preparation of the Deciuormal Solution of Blcliroinate. As 1 atom of bichromate of potash gives up 3 atoms of oxygen, it is necessary that ^rd at. in grammes should be used for the litre as a normal solution, and ^^(jth for the decinormal ; and as it is preferable on many accounts to use a dilute solution, the latter is the most convenient for general purposes. According to the latest and most reliable researches, the 96 ANALYSIS BY OXIDATION AND SEDUCTION. § 44. eqiiivalent numter of ckrommm is 26-24, and consequently that of bichromate of potash is 147'59 ; if therefore ^-'^th of this latter number^4'919 Gm. he dissolved in a litre of water, the deci- normal solution is obtained. On the grain system, 49'19 grains to 10,000 grains of water wiU give the same solution. 1 CO or 1 dm. of this solution is capable of yielding up ■x-s.gso ^^- ^^ grammes or grains of oxygen, and is therefore equivalent to the xjj.iuffth at. of any substance which takes up 1 atom of oxygen ; but as 1 at. protoxide of iron requires only i at. oxygen to convert it into peroxide, each CC of bi- chromate is equal to i-uJ^j- at. iron ; and' tkerefore, as in the case of permanganate, the atomic numbers used in the systematic calculations are doubled, so far as the protosalts are concerned. Examples of Analysis. 0'7 Gm. of pure and dry double sulphate of iron and ammonia =0'1 Gm. iron, was dissolved in about 2 oz. of water and titrated with decinormal bichromate, of which 17-85 CC were required ; this multiplied by 0'0392 gave 0-699 Gm. instead of 0-7 Gm. 0-56 Gm. of iron wire required 998 CC=0-5588 Gm. ; as it is impossible to obtain iron wire perfectly pure, the loss is undoubtedly owing to the impurities. If the bichromate solution should from any accidental cause be found not strictly of decinormal strength, the factor neces- sary for converting it must be found as in § 11. As it is not at all an uncommon occurrence, in an analysis where no sign of the end of the reaction is visible in the solu- tion itself, to overstep the exact point, it is advisable to have some method of briaging it iutq order again ; this may be ac- complished in the present case by adding a definite quantity of the double iron salt to the mixture, titrating afresh and deduct- ing the proportional amount of bichromate from the total quantity required. § 45. PREPARATION OF STANDARD SOLUTIONS. 97 IODINE AND HYPOSULPHITE OF SODA. § 45. The principle of this now beautiful and exact method of analysis was first discovered by Dupasquier, who used a solution of sulphurous acid instead of hyposulphite of soda. Bunsen improved his method considerably by ascertaining the sources of failure to which it was liable, and which consisted in the use of a too concentrated ,solution of sulphurous acid ; the reaction between iodine and very dilute sulphurous acid may be represented by the formula : — S02 + I+HO=S03 + HI, if the sulphurous acid is more concentrated, i.e., above 0'04 per cent, in a short time, the action is reversed, being Under proper regulations, therefore, we see that free iodine con- verts sulphurous into sulphuric acid by decomposing water, the oxygen of which goes to the sulphurous, and produces sulphuric acid ; the hydrogen is taken by the iodine, forming hydriodic acid. There are great drawbacks, however, connected with the use of sulphurous acid ; it very rapidly changes by keeping even in the most careful manner, so much so that a sample tested in the morning would very frequently need an examination in the afternoon ; and as it must be exceedingly dilute, it necessitates the use of special vessels and burettes ; taking aU these things into account, therefore, the substitution of hyposulphite of soda is a great advantage, inasmuch as the end is secured quite as accurately without the trouble and insecurity connected with the sulphurous acid. The reaction in the case of hyposulphurouS acid is as follows :— 2(S, 0,)+I+HO=S, O^+IH. The composition of hyposulphite of soda is S2 03]SraO+5HO=124, and when brought in contact with a solution of iodine in iodide 98 ANALYSIS BY OXIDATION AND EEDUCTION. § 45. of potassiumj the hjjposulphurous acid takes oxygen from the water, and' the result is the production of tetrathionic and hydriodic acids in combination with soda. 2(m 0, Sa 02)+I=^a I+Na^O, S, 0^. In order to Certain the end of the reaction in analysis by this method an indicator- is necessary, and the most delicate and sensitive for the purpose is starch, which produces with free iodine the well known hlue colour of iodide of starch. 1. Preparation of Starcli Liauor. 1 part of clean arrowroot, potatoe, wheat, rice, sago, or other starch is ffet mixed smoothly with cold water into a psiste, and about 1 50 or 200 times its weight of boiling water poured over it, and allowed to stand and settle, the clear liquor only is to be hsed as the indicator, of which a few drops only are necessary. As the liquor so prepared does not keep long, and is not near so sensitive when old, several methods have been devised for the purpose of preserving it ; the best in my opinion is that pro- posed by Fliickiger, which is as follows: — 1 part of starch is well shaken and digested in a bottle with about 15 parts of a Solution of chloride of calcium, containing half its weight of the salt ; when the mixture appears slimy and fibrous, showing that the starch granules are broken, it is largely diluted with water, say to about 250 times its volume, it may then be allowed to settle, or is iiltered, and the clear liquor saturated with common salt, then preserved in a cool place for use. 2. Freparatiou of the Decinormal Solution of Iodine. ChemicaEy pure iodine may be obtained by mixing commercial iodine with about one-fourth of its weight of iodide of potassium, and gently heating the mixture between two large watch-glasses or porcelain capsules, the lower one being placed upon a heated iron plate, the iodine sublimes in brilliant plates which are absolutely pure, the re-sublimed iodine of commerce is not § 45. PEEPAEATION OP STANDAED SOLUTIONS. 99 always free from ohloriiie, it is therefore sometimes necessary to prepare it specially by a second sublimation as described above. Tbe ■watch-glass or capsule containing the iodine is placed under the exsiccator to cool, and also to deprive it of any traces of watery vapour ; then 12-7 6m. (=-rV ^t.) accurately weighed, and together with about 18 Gm.- of pure white iodide of potas- sium, dissolved in about a ^ litre of water, then diluted to exactly 1 litre. The same solution may be obtained by dissolving 127 grains of iodine, and 180 of iodide of potassium, ta 10,000 grains of water, in either case the solution is strictly decinormal ; the flask must not be heated in order to promote solution, and care must be taken that iodine vapours are not lost in the operation. The solution is best preserved in stoppered bottles of about 5 or 6 oz. capacity which should be completely filled. 3. Beclnormal Hyposulplilte of Soda. As 2 atoms of this salt are necessary to absorb 1 atom of iodine or oxygen, it is requisite that ^ at. in grammes of the pure salt should be contained in the litre, and as 124 is the equivalent number of the salt, 24-8 Gm. is the quantity to be weighed. As it is not difficult either to manufacture or procure pure hyposulphite of soda, this quantitj', powdered and dried between blotting paper, may be weighed direct, and dissolved in a litre of distUled water, and then titrated with the iodine solution and a little starch Hquor. If impure hyposulphite should have been used, or the sample not entirely free from accidental moisture, it wiU be necessary to find a factor by which to reduce it to decinormal strength, as described for alkalimetry, § 11, or the amount of impurity being known, a fresh quantity may be prepared of proper strength. It is advisable to preserve the solution in the dark. Beside the decinormal iodine and hyposulphite, it is con- venient in some cases to use centinormal solutions, which can H 2 100 ANALYSIS BY OXIDATION AND EEDOCTION. § 45. readily be prepared by diluting 100 CC of each decinormal solution to 1 litre. In using tbe iodine solution, Mobr's burette may be em- ployed, but care must be taken tbat the solution is not left in it for any length of time, as decomposition slowly takes place, and the tube becomes hard. Gay Lussac's, or the bulb burette, are on this account preferable. 4. Preparation for the Analytical Process. There are a great variety of substances containing oxygen, which, when boiled with hydrochloric acid, yield chlorine, equivalent to the whole or a part only of the oxygen they contain, according to circumstances. Upon this fact are based the variety of analyses which may be accomplished by means of iodine and hyposulphite of soda ; the chlorine so evolved, however, is not itself estimated, but is conveyed by means of a suitable apparatus into a solution of iodide of potassium, thereby liberating an equivalent quantity of iodine. This latter body is then estimated by hyposulphite of soda ; the quantity so found is therefore a measure of the oxygen existing in the original substance, and consequently a measure of the substance itself. It seems a very roundabout method, and one would imagiae it could scarcely lead to accurate results ; never- theless, without exaggeration, it may be said to be the most exact in the whole range of volumetric analyses, far outstripping any process of analysis by weight. The apparatus used for distilling the substances, and conveying the liberated chlorine into the alkaline iodide, may possess a variety of forms, the most serviceable, however, being the three kinds devised respectively by Bunsen, Fresenius, and Mohr. Bun sen's consists of a small flask to contain the mixture for distillation, connected by a stout piece of vulcanized -tubing with a long bent tube, which is carried into the solution of iodide contained in an inverted retort, the neck of the latter having a tolerably large bulb blown midway, so that when the § 45. PKEPAEATION OF STANDARD SOLUTIONS. 101 chlorine is aU evolved ijom ttie mixture, and hydrochloric acid gas begins to distil, the rapid condensation which ensues may not cause the liquid to rush back to the ilask, and so spoil the operation ; this unavoidable regurgitation is a great nuisance, and in order to prevent the entrance of the liquid into the bent tube, Bunsen contrived a little self-acting valve, which consists of a very light glass bulb with a stalk, (very like the large headed ornamental pins used by ladies for their hair,) this presents no hindrance to the evolution of the gas during the distillation, but when the liquid attempts to enter, the bulb is forced up to the end of the delivery tube, so as to close the entrance; a drawing of the entu-e apparatus may be seen in most treatises on chemical an- alysis. The apparatus contrived by Fresenius dif- fers from Bun- sen's only in having two large bulbs blown in the neck of the re- tort and one in the bent deliv- ery tube, in this case the glass valve is not necessary. Mohr's appa- ratus is shewn in Fig. 16, and Fig. 16. ]02 ANALYSIS BY OXIDATION AND EEDUCTION. § 4:5. is in my opinion preferable to eitter of the foregoing, on account of its simplicity of construction and more accurate working. The distilling flask is of about 2 oz. capacity, and is fitted with a cork soaked to saturation in melted paraffin, through the cork the delivery tube containing one bulb passes, and is again passed through a common cork, fitted' loosely into a stout tube about 13 or 13 inches long and 1 inch wide, closed at one end Hke a test tube ; this tube, containing the alkaline iodide, is placed in an ordinary hydrometer glass, about twelve inches high, and surrounded by cold water ; the delivery tube is drawn out to a fine point, and reaches nearly to the bottom of the condenser. No support or clamp is necessary, as the tall hydrometer glass keeps everything in position. The substance to be distilled is put into the flask and covered with strong hydrochloric acid, the condenser supplied with a sufficient quantity of iodide solution, and the apparatus put together tightly ; either an argand or common spirit lamp, or gas, may be used for heating the flask, but the flame must be manageable, so that the boiling can be regulated at pleasure ; in the case of the common spirit lamp, it may be held in the hand, and appUed or withdrawn according to the necessities of the case ; the argand spirit or gas lamp can of course be regulated by the' usual arrangements for the purpose. If the iodine hberated by the chlorine evolved, should be more than wiU. remain, in solution, the cork of the condensing tube must be lifted, and more solution added. When the operation is judged to be at an end, the apparatus is disconnected, and the delivery tube washed out into the iodide solution, which is then emptied into a beaker or flask, and preserved for analysis, a little fresh iodide solution is put into the condenser, the apparatus again put together, and a second distillation commenced, and continued for a minute or so, to collect every trace of free chlorine present. This second operation is only necessary as a safeguard in case the first should not have been complete. The solutions are then mixed together and titrated in tha manner presently to be described. § 45. PREPARATION OF STANDARD SOLUTIONS. 103 The solution of iodide of" potassium may cqpvenieutly be made of such, a strength that -f^ atom or 33-2 Gm. is contained in the litre. One cubic centimeter will then he sufficient to absorb the quantity of free iodine, representing 1 per cent, of oXygen in the substance analysed, supposing it to be weighed in system. In examining peroxide of manganese for instance, 0/436 Gm. or 4-36 grn. would bo used, and supposing the percentage of peroxide to be about 60, 60 CO or dm. of iodide solution would be sufficient to absorb the chlorine and keep in solution the iodine liberated by the process ; it is advisable, however, to have an excess of iodide, and, therefore, in this case, about 70 CC or dm. should be used. A solution of indefinite strength will answer as well, so long as enough is used to absorb aU the iodine. The process of distillation above described is troublesome, and therefore it is advisable to avoid it where possible. There ' are a great number of substances which, by mere digestion with hydrochloric acid and iodide of potassium at an elevated temperature, undergo decomposition quite as completely as by distillation. For this purpose a strong bottle with a very accurately ground stopper is necessary ; and as the ordinary stoppered bottles of commerce are not sufiiciently tight, it is better to regrind the stopper with a little very fine emery and water. It must then be tested by tying the stopper tightly down and immersing in hot wa,ter, if any bubbles of air^find their way through the stopper the bottle S^ i^ is useless. The capacity may vary from D 1 to 5 or 6. oz., according to the necessi- ties of the case. The stopper may be secured by fine copper binding wire, or a kind of clamp contrived by Mohr may be used, as shewn in Fig. 17; by means of the thumb screws the pressure upon the [ stopper may be increased to almost any Fig. 17. extent. 104 ANALYSIS BY OXIDATION AND REDUCTION. § 45. The substance to be examined, if in powder, is put into the bottle with 'pure flint pebbles or small garnets,, so as -to divide it better, and a sufficient quantity of saturated solution of iodide of potassium and pure hydrochloric acid added, th^ stopper is then inserted, fastened down, and the bottle placed in a saucepan of water • with a little tow, or other similar substance, to keep the glass from touching the bottom, and the water then made to boil by a gas flame or hot plate as may be most convenient; when the decomposition is complete the bottle is removed, allowed to cool somewhat, then placed in cold water, and, after being shaken, is opened, emptied into a beaker, and diluted by the washings for titration. The salts of chloric, iodic, bromic, and chromic acids, together with many other compounds, may be as effectually decomposed by digestion as by distillation. The Analytical Process. The free iodine existing in solution with iodide of potassium, as just described is not estimated direct by the hyposulphite, but by a residual method, that is to say an excessive quantity of hyposulphite is allowed to flow from a large burette, graduated in \ CC until the colour of the iodine is removed, the excess of hyposulphite is then estimated by the addition of starch liquor and decinormal iodine, the latter being delivered from a small burette graduated in -^^ CC until the blue colour appears ; the quantity so required is deducted from that of the hyposulphite, and the analysis calculated in the systematic way. Eeducing substances, such as sulphurous, hyposulphurous, and hydrosulphuric acid, alkaline arsenites, &c., are, of course, titrated direct with the iodine solution and starch. The iodide of potassium used in the various analyses must be absolutely free from iodate of potash and free iodine. " § 46. PKEPAEATION OF STANDARD SOLUTIONS. 105 ARSENIOUS ACID AND IODINE. § 46. The principle upon wliich this method of analysis is based is the fact that when arsenious acid is brought in contact with iodine in the presence of water and free alkali, it is con- verted into arsenic acid, the reaction being — AsOa + 21 + 2NaO = AsOj + 2K"aI. The alkali must be in sufficient quantity to combine with the hydriodic acid set free, and it is necessary that it should exist in the sta^e of carbonate, as pure alkalies interfere with the colour of the blue iodide of starch used as indicator. If, therefore, a solution of arsenious acid containing starch is titrated with a solution of iodine in the presence of carbonate of soda, the blue colour does not occur until all the arsenious acid is oxidised into arsenic acid; in like manner, a standard solution- of arsenious acid may be used for the estimation of iodine or other bodies which possess the power of oxidising it. The chief value, however, of this method is found in the estimation of free chlorine existing in the so-called chloride of lime, chlorine water, hypochlorites of lime, soda, &c., in solution, generally included under the term chlorimetry. 1. Preparation of tlie Declnormal Solutions of Iodine and Araenlte of Soda. The iodine solution is the same as described in § 45, 2, containing 12-7 Gm. in the litre. The corresponding solution of arsenite of soda is prepared liy dissolving 4'95 Gm. of the purest sublimed arsenious acid, free from sulphide, in about a -J litre of distilled water in a flask, with about 25 Gm. of the purest crystallized carbonate of soda, free from sulphide, hyposulphite, or sulphite of sodium. It is necessary that the acid should be in powder, and the mixture needs boiling and shaking for some time in order to complete 106 ANALYSIS BY OXIDATION AND EEDUCTION. § 46. the solution; wlien. this is accomplished the mixture is diluted somewhat, and filtered into the litre measure, the filter well washed, and the solution then made up to the litre. The equivalent number of arsenious acid being 99, and 1 atom absorbing 2 at. of oxygen, the -^^ part or 4-95 Gm. is necessary to form the decinormal solution. In order to test this solution 10 CO are put into a beaker glass with a little starch liquor, and the iodine solution aEowed to flow in from a burette, graduated in y',,- CC, until the blue colour appears, if exactly 10 CC are required the solution is strictly decinormal, if otherwise, the necessary factor must be found for converting it to that strength. Starch liquor, however, cannot be used for the direct esti- mation of free chlorine, consequently resort must be had to an external indicator, and this is very conveniently found in iodide of starch paper, which is best prepared by mixing a portion of the starch liquor described in § 45, 1, with a few drops of solution of iodide of potassium on a plate, and soaking strips of pure filtering paper therein ; the paper so prepared is used in the damp state, which is far more sensitive than the dried paper prepared according to Pen of s plan. 2. Tlie Analytical Process. In all cases the chlorine to be estimated must exist in an alkaline solution. In the case of chloride of lime this is abeady accomplished by the caustic lime which invariably exists in the compound. The substance being brought under the burette containing the arsenious acid solution, it is suffered to flow until a drop of the mixture taken out with -a glass rod and brought in contact with the prepared paper, no longer produces a blue spot. As the colour becomes gradually- lighter towards the end of the process, it is not difficult to hit the exact point, should it, § 46. PEEPAEATION OF STANDARD SOLUTIONS. 107 however, by any accident be overstepped, starch liquor may bo added to the mixture, and decinormal iodine solutions added until the blue colour is produced ; the quantity so used is then deducted from the total arsenic solution. Examples. 50 CC of chlorine water were mixed with solution of carbonate of soda, and brought under the arsenio burette, and 20 CC of solution added, on touching the prepared paper with the mixture no colour was produced, consequently the quantity used was too great; starch hquor was therefore added and decinormal iodine, of which 3'2 CC were required to produce the blue colour. This gave 16 '8 CC of arsenic solution, which multiplied by 0-003546 gave 0-05857 Gm. CI in the 50 CC. A second operation with the same water required 16-8 CC of arsenic solution direct, before the end of the reaction with iodized starch paper was reached. 108 ANALYSIS BY OXIDATION AND EEDUCTION. § 47. BODIES SUBJECT TO DETERMINATION BY OXIDISING OR REDUCING AGENTS. Under this head are included all those substances which may, with accuracy and rapidity, be analysed by the fore- going methods. The names of the discoverers of the various processes will be given, and also examples of their accuracy where practicable. IRON'. Fe=28. «47. Substance. I Pormula. Metallic Iron (2 atoms) Protoxide of Iron (2 at.] Peroxide of Iron (1 at.) Carbonate of Iron (2 at.) Protosulpbate of Iron (2 at.) Double Sulphate of Iron 2Fe 2FeO EejOs 2(FeO, 00=) 2(PeO. SO. +7H0) 2(FeO-|-2S03 Quantity to be Atomic weighed so that i CC ,„ • iTi. 01' 1 dm.of decinormal VVeigat solution = 1 per cent. of substance. and Ammonia (2 at.) 4NH4O+6HO) 56 72 80 116 278 392 0-56 Gm., or 5"6 grn. 0-72 Gm., or 7-20 grn. 0-80 Gm., or 8-00 grn. 1-16 Gm., or 11-60 grn. 2-78 Gm.. or 27 '8 grn. 3-92 Gm., or 39-20 grn. N Factor. 0-0056, or 0056 0-0072, or 0-072 0-0080, or 0-080 0-0116, or 0-116 0-0278, or 0-278, 0-0392, or 0-39ab § 47. IRON. 109 Factors. Metallic iron x 1-2857 = FeO ■';', „ X 1-4286 = Tefis X 2-0714 = FeO.CO^ X 4-9643 = reO,S05+7HO X 7-0000 = FeO,2SO,+]SrH,0+6HO In the analysis of iron ores it is very often necessary to de- termine not only the total amount of iron but also the state in which it exists ; for instance, magnetic iron ore consists of a mixture of the two oxides in tolerably definite proportions, and it is sometimes advisable to know the quantities of each. In order to pre- vent, therefore, the further oxidation of the protoxide and so leading to false results, the little flask appara- tus, (Fig. 18,) ad- apted by Mohr is highly recommen- dable. The left hand flask contains the weighed ore in a finely powdered state, to which tolerably strong hydrochloric acid is added; the other flask contains distilled water only; the tube from the first flask entering to the bottom of the second. When the ore is ready in the flask and the tubes fitted, hydro- chloric acid is poured in and a few grains of bicarbonate of Fig. 18. 110 ANALYSIS BY OXIDATION AND BEDUCTION. § 48. soda added to produce a flow of carbonic acid, the air of the flask is thus dispelled, and as the^ acid dissolves the ore, the gases evolved drive out in turn the carbonic acid which is partly absorbed by the water in the second flask. When the ore is all dissolved and the lamp removed, the water immediately rushes out of the second flask into the first, diluting and cooling the solution of ore, so that in the majority of cases it is ready for immediate titration; if not sufficiently cool or dilute, a sufficient quantity of boiled and cooled distilled water is added. When the total amount of iron present in any sample of ore has to be determined, it is necessary to reduce any peroxide present to the state of protoxide by zinc, this must be free from iron, or at least if it contain iron the quantity must be known so that a deduction may be made in the analysis; the best vessel in which to make the reduction is the flask described for the solution of metallic iron in titrating permanganate. The end of the process may be known either by the disap- pearance of the colour of the peroxide, or by testing with a small glass rod dipped in sulphocyanide of potassium, in which case no red colour must appear. The zinc is best added in small fragments, none of which should be left undissolved when the titration takes place. For the method of reduction by protochloride of tin, see § 44. TECHNICAL EXAMINATION OF IRON OKES, &C. Magnetic Iron Ore. § 48. The protoxide is determined firat by means of the apparatus, Fig. 16, or instead of the two flasks one only may be used, or a wide and long test tube — in either case a cork con- taining a small bent tube is inserted; the ore is put into the vessel in a state of fine powder, strong hydrochloric acid added. § 48. lEON OEES. Ill together with a few grains of hicarbojiate of soda, and the hent tube dipped under" the surface of some cold distQled water; heat is now applied gently with the lamp until the ore is dissolved, the heat is then removed, and the water rushes into the tube, diluting and cooling the solution. It may then be poured out into a larger quantity of water, if necessary, and titrated with bichromate of potash. Example. 0'5 Gm. of ore was treated as above, and required 19'5 CC of -jjy bichromate, which multiplied by 0'0056 gave 0-1092 Gm. iron=0.1404 Gm. protoxide=28-08 per cent. The peroxide was now found by reducing 0-5 Gm. of the same ore with zinc, and estimating the total iron present, the quantity of bichromate required was — ^ 59 CC 3^5 =0-3304 Gm. total Fe Deduct... 0-1092 „ as protox. Leaving 0-2212 „ as perox. The result of the analysis is, therefore, — Protoxide of Iron 28-08 per cent. Peroxide of ditto 63-20 Gangue, &c 8-72 „ 100-00 Spathose Iron Ore. The total amount of protoxide of iron in this carbonate is ascertained direct by solution iu hydrochloric acid in a test tube, with cork and bent tube dipped into water to prevent oxidation ; or as the carbonic acid evolved is generally sufficient to expel aU air, the dipping under water may be dispensed -with. Should the ore be very impure, zinc may have. Vo.,be added in order to insure the reduction of aU the iron present. 112 ANALYSIS BY OXIDATION AND EEDUCTION. § ^8. .As the ore contains in most cases the carbonates of manga- nese, lime, and magnesia, these may all be determined, together ■with the iron, as follows — A weighed portion of ore is brought into solution in hydro- chloric acid, and filtered, if. necessary, to separate insoluble silicious matter. The solution is then boiled, with a few drops of nitric acid to peroxidise the iron, diluted, and carbonate of soda added in sufficient quantity to precipitate the oxide of iron, then aceta,te of soda, and the whole- boiled that the precipitate may become somewhat dense and separate from the liquid ; filter, and if necessary, reduce the oxide of iron after careful washing, with zinc, and determine with bichromate or permanganate. The filtrate containing the other bases is treated with hypo- chlorite of soda, covered and set aside for 24 hours in order to precipitate the manganese as hydrated oxide, which js collected a^d titrated as in § 55, 4. The filtrate from the last is mixed with oxalate of ammonia to precipitate the lime, which is estimated by permanganate, as in § 60, 1. The filtrate from the lime contains the magnesia, which may be precipitated with phosphate of soda and ammonia, and the precipitate weighed as usual or titrated with uranium solution, as in § 78, 1, see also § 38. Eed and brown hematites can be examined in a simUar manner to the foregoing. Chrome Iron Ore. This material, which is mainly derived from America, is of great commercial importance, as being the source of bichromate of potash. The ore varies considerably in quality, some samples being very rich, while others are very poor in chromium. In the case of those tolerably free from gangue, the sample is to be first of § 48. IKON OEES. 113 all brought into very fine powder. About 10 grains are rubbed tolerably fine in a steel mortar, then finished fractionally in an agate mortar; 0-5 Gm. is then carefully weighed, and mixed with about 3 Gm. of a mixture of dried carbonate of potash and soda, and fused strongly for twenty minutes in a platinum crucible. The mass is then cooled, lixiviated with warm water, filtered, and the filtrate titrated for chromium as in § 65, 1. The oxide of iron remaining on the filter is boiled with hydrochloric acid, diluted and titrated with bichromate of potash. When the ore contains a larger proportion of sihcious or earthy gangue, or much other impurity, it may be necessary to adopt the following method, modified somewhat from O'Neill's process, described in "Chem. News," AprU 12th, 1862. The very finely powdered ore is fused with ten times its weight of bisulphate of potash for twenty minutes, taking care that it does not rise over the edge of the platinum crucible ; when the fusion is complete, the molten mass is caused to flow over the sides of the crucible, so as to prevent the formation of a solid lump, and the crucible set aside to cool. The mass is then transferred to a porcelain dish, and lixiviated with warm water untd entirely dissolved ; no black residue must occur, otherwise the ore is not completely decomposed; carbonate of soda is then added to the liquid until it is strongly alkaUne; it is then brought on a filter, washed sUghtly, and the filter dried. When perfectly dry, the precipitate is detached from the filter as much as possible ; the filter burned separately ; the ashes and precipitate mixed with about twelve times the weight of the original ore, of a mixture of two parts chlorate of potash and three parts carbonate of soda, and fused in a platinum crucible for twenty minutes or so ; the resulting mass is then treated with boihng water, filtered, and the filtrate titrated for chromic acid as before. The oxide of iron remaining on the filter is titrated, if required, with bichromate of potash. 114 ANALYSIS BY OXIDATION AND REDUCTION. § 49. ESTIMATION OF THE PERCENTAGE OF PURE IRON IN STEEL, CAST AND WROUGHT IRON, SFIEGELEISEN, &C. Mohr's Method. § 49. Instead of the hitherto common method of separately estimatiBg the impurities in samples of manufactured iron and steel, this process is adapted to the delicate estimation of the iron itself, and is similar in principle to the assay of silver by Gay Lussac's method, that is to say, the analysis is so arranged that the greatest accuracy shaU be secured. The standard solutions of bichromate of potash, of which there are two, are so prepared that 100 CC or dm. of the first will exactly convert respectively 1 Gm. or 10 grains of iron into peroxide, the second, or decimal solution, is one-tenth the strength of the first. The solution of bichromate No. 1 is prepared by dissolving 8-785 Gm. of the pure salt in 1 htre, or 87 '85 grn. in 10,000 grains of distilled water at 62° Fahr. The decimal solution N"o. 2 is made by taking 100 CC of No. 1 and diluting it to 1 litre, or 100 decerns to 10,000 grains, therefore — 100 CC or dm. of No. 1=0-01 Gm. or 0-1 grn. iron. 100 CC or dm. of No. 2=0-001 Gm. or 0-01 grn. ditto. The Analytical Process. The sample of iron to be examined is reduced to powder in a hardened steel mortar, or if in the form of wire, or in a soft state, cut into small pieces, and exactly 1-050 Gm. or 10-50 grn. weighed off ; this is brought into a long and wide test tube, or small flask, fitted loosely with a cork, and dissolved in pure hydrochloric or sulphuric acid. When the solution is accom- plished, 100 CC or dm. of bichromate solution No. 1 (containing 0-8785 Gm. or 8-758 grn. of bichromate, which is exactly § 49. ASSAY OF IKON. 115 sufficient to peroxidise respectively 1 Gm. or 10 gm. of pure iron) is added ; the decimal solution is then added from a small burette, until a drop of the mixture, brought in contact with red prussiate of potash, no longer produces a blue colour ; the analysis is then calculated in the usual way. Examples : 1-05 Gm. of Bessemer's steel was dissolved in pure sulphuric acid, 100 CO bichromate No. 1 added, and afterward 39 CO of No. 2 required for complete oxidation; consequently there were 1'039 Gm. of pure iron contained in the r050 Gm. taken for analysis; this is equal to 9894 parts per thousand, or 98'94: per cent. Instead of the empirical solutions here described, the ordinary decinormal and centinormal solutions of bichromate may be employed with equal accuracy. As 100 CC of decinormal solution is eqhal to 0'56 Gm. of pure iron, it is necessary that somewhat more than this quantity of the sample should be weighed, say 0-58 or 0-60 Gm. 100 CO of decinormal solution then added, and the analysis completed with the centinormal solution. This system of analysis, in order to express directly the percentage of iron in a given sample, can be arranged in the following manner. A solution of protoxide of iron is prepared by dissolving 7 Gm. of the double sulphate of iron and ammonia in distilled water, adding a considerable quantity, say 50 CC, of pure sulphuric acid, and diluting to 1 litre. 1 CC of this solution contains 1 milligramme of iron. 1 Gm. of the sample of iron is dissolved, and lOO.CC of bichromate solution No. 1 added ; the excess is then ascertained by the iron solution described above ; the quantity so used deducted from the 100 CC of bichromate wiU give the percentage of pure iron direct ; the objection to this method is that the iron solution is subject to oxidation. I 2 J 16 ANALYSIS BY OXIDATION AND EEDUCTION. § 50. DIRECT TITRATIOK OF IRON BY PROTOCHLORIDE OF TIN. § 50. Tee reduction of peroxide of iron to the state of protoxide by tliis reagent iias been previously referred to, and it ■will be readily seen that the principle involved in the reaction can be made available for a direct estimation of iron, being, in fact, simply a reversion of the ordinary process by permanganate and bichromate. In the case of these two reagents, the amount of oxygen given up by them is the measure of the quantity of iron, whereas with protochloride of tin, it is the amount taken up by it that answers the same purpose. Presenius (in his "Zeitschrift fiir Analytische Chemie," part 1, page 26) has recorded a series of experiments made on the weak points of this process, and gives it as his opinion that it is most accurate and reliable Avith proper care, without which, of course, no analytical process whatever is worth anything. The summary of his paper is as foUows : — a. A solution of peroxide of iron of known strength is first prepared, by dissolving 10-03 Gm. fine pianoforte wire (=10 Gm. pure iron) in pure hydrochloric acid, adding chlorate of potash to complete oxidation ; boiling till the excess of chlorine is removed, and diluting the solution to 1 litre. 6. A clear solution of protochloride of tin, of such strength that about equal volumes of it and the iron solution are required for the complete reaction. c. A solution of iodine in iodide of potassium, containing about 0-005 Gm. iodine in 1 CO, (if the operator has the ordinary decinormal iodine solution at hand, it is equally applicable.) The operations are as foUows : — 1. 1 or 2 CO of the tin solution are put into a beaker with a little starch liquor, arid the iodine solution added from a burette till the blue colour occurs ; the quantity is recorded. 2. 10 CO of the iron solution=0-l Gm. iron, are put into a small flask -with a little hydrochloric acid, and heated to § 50. IRON. 117 gentle boiling, (preferably on a hot plate), the tin solution is then allowed to flow in from a burette until the yellow colour of the solution is nearly destroyed, it is then added drop by drop, waiting after each addition until the colour is completely gone and the reduction ended. K this is carefully managed there need be no more tin solution added than is actually required; however, to guard against any error in this respect, the solution is cooled, a little starch liquor added, and the iodine solution added by drops until^ a permanent blue colour is obtained. As the strength of the iodine solution compared with the tin has been found in 1, the excess of tin solution corresponding to the quantity used is deducted from the original quantity, so that by this means the volume of tin solution corresponding to O'l Gm. iron is found. The operator is, therefore, now in a position to estimate any unknown quantity of iron which may exist, in a given solution, in the state of peroxide, by means of the solution of tin. K the iron should exist partly or whoUy in the state of protoxide, it must be oxidised by the addition of chlorate of potash, and boiUng to dissipate the excess of chlorine, as de- scribed in 2. Example: 10 CO of iron solution, containing 0-1 Gm. iron, required 15 CO of tin solution. A solution, containing an unknown quantity of iron, was then taken for analysis, which required 12 CC, consequently a rule of three sum gave the proportion of iron as follows : — 15 :0-l Gm. :: 12 : 0-08 Gm. It must be remembered that the solution of tin is not per- manent, consequently it must be tested every day afresh. Two conditions are necessary in order to insure accurate results. 1st. The iron solution must be tolerably concentrated, since the end of the reduction by loss of colour is more distinct; and, further, the dilution of the liquid to any extent interferes with the quantity of tin solution necessary to effect the reduction. 118 ANALYSIS BY OXIDATION AND REDUCTION. § 50- Fresenius found that by diluting the 10 CC of iron solution with 30 CC of distilled water, -^-^ of a CC more was required than in the concentrated state. This is, however, always the case with protochloride of tin in acid solution, and constitutes the weak poiat ia Streng's method of analysis by its means; it would seem that dilution either predisposed it to rapid oxidation, or that water had the power within itself to commu- nicate a certain proportion of oxygen to it. 2nd. The addition of the tin solution to the iron must he so regulated that only a very small quantity of iodine is necessary to estimate the excess — if this is not done another source of error steps in, namely, the influence which dilution, on the one hand, or the presence of great or small quantities of hydro- chloric acid on the other, are known to exercise over this reaction; practically it was found that where the addition of tin, to the somewhat concentrated iron solution, was cautiously made so that the colour was just discharged, the mixture then rapidly cooled, starch added and iodine tiU blue, that the esti- mation was as reliable as by any other method. ^ The following examples are from Fresenius. The standard iron solution contained 10 Gm. in the litre ; 10 CC were therefore equal to O'l Gm* iron. 1 CC tin solution required 3'62 CC iodine. Exp. 1. 9-97 CC of the above iron solution required 11-6 CC tin solution and 1 '23 CC iodine. Exp. 2. 9-87 CC iron solution required 11-26 CC tin and 0-44 CC iodine. Calculated for O'l Gm. iron, the above experiments shew that — 1 = 11-294 CC tin solution 2 = 11-287 „ „ Mean 11-2905 „ „ 3-8204 Gm. brown hematite ore was heated with concentrated hydrochloric acid until decomposed, then diluted somewhat, filtered, and dissolution made up to 500 CC. § 50. IRON. 119 Exp. 1. 100 CC required 43-69 CC tin solution and 0-26 CC iodine. Exp. 2. 100 CC required 44-15 CC tin and 2-12 CC iodine, therefore, — 1 = 43-62 CC tin solution 2 = 43-57 „ „ Mean 43-60 „ „ The following equation expresses the result. 11-2905 SnCl : 0-1 Fe : : 43-60 : a;=0-3862 Gm. iron in 100 CC, or 50-54 per cent, of iron in the ore. A determination of the iron, in the same sample of ore, by- permanganate, executed with the greatest care, gave 60-58 per cent. The tin solution is best prepared by placing fragments of pure tin at the bottom of a beaker, laying a small platinum crucible or cover upon them, and covering the whole with equal parts of pure hydrochloric acid and water : a large watch glass or porcelain capsule should be placed on the top of the beaker to exclude air and prevent loss by spirting. The contact of the platinum with the tin sets up a galvanic current which materially hastens the solution of the tin without at aU affecting the platinum ; when the acid is all saturated, it may be poured off and fresh added until sufficient solution has been obtained. The whole, freely acidified and diluted to a con- venient strength, should be placed in a well stoppered bottle, with a few fragments of tin; its strength, which is constantly lessening to a slight extent, must be found before using it. 120 ANALYSIS BY OXIDATION AND EEDTICTION. § 51 TITRATION or IKON BY HYPOSULPHITE OF SODA. § 51. Pbofessob Schbrbr first suggested tlie direct titration of iron, by hyposulphite of soda, "which latter was added to a solution of the perchloride of iron until no further violet colour was produced. This was found by many to be inexact, but Kremer, (Journ. f. Pract. Chem., 84, 339,) has made a series of careful experiments, the result of which is that the following modified method can be highly recommended. The reaction which takes place between hyposulphite of soda and perchloride of iron is such that 2 eq. of the former with 1 eq. of the latter, produce 2 eq. protochloride of iron, 1 eq. tetrathionate of soda, and 1 eq. chloride of sodium. The hypo- sulphite, which may conveniently be of y^ strength, is added in excess, and its amount determined by -j^ iodiue and starch liquor. Process. The iron solution, containing not more than 1 per cent, of metal, which must exist in the state of perchloride without any excess of oxidising material, (best obtaiued by adding concentrated permanganate of potash until the red colour is produced, then boiling till both that and any free chlorine is expelled), is moderably acidified with hydrochloric acid, acetate of. soda added tiU the mixture is red, then dilute hydrochloric acid until the red colour disappears; then diluted tUL the iron amounts to ^ or -J- per cent., and -f^j hyposulphite added in excess, best known by throwing in a particle of sulphocyanide of potassium after the violet colour produced by the hyposulphite has disappeared — if any red colour occurs, more hyposulphite must be added. Starch liquor and -^jj iodine are then used to ascertain the excess of hyposulphite ; each CO of the latter is equal to 0-0056 iron. A mean of several ex- periments gave 100-06 Pe, instead of 100. § 52. COPPER. 121 COPPER. Cu=3r7. §52. Substance. Formula. 1 Quantity to be Afnmir' weighed bo that 1 CC Weignt solntioii=l per cent. of BUbBtance. N Factor. Copper (2 atoms) ... Protoxide of Copper (1 at.) Oxide of Copper (2 at.) Crystallized Sulphate of Copper (2 at.) 2Cu Cua 2CuO 2(Cu 0, SOj +5H0) 63-4 71-4 79-4 249-4 0-634 Gm., or 6-34 gm. 0714 Gm., or 7-14 grn. 0-794 Gra., or 7-94 grn. 2-494 Gm., or 24-94 gm. 0-00634, or 0-0634 • 0-00714, or 0-0714 0-00794, or 0-0794 0-02494, or 0-2494 Factors for converting the quantity of Iron represented by Permanganate or Bichromate Into Copper. Iron X 1-1314 = Copper „ X 1-4171 = Oxide of ditto „ X 4-453 = Crystallized sulphate of ditto Double Iron Salt x 0-16163 = Copper „ „ X 0-2024 = Oxide ditto „ „ X 0-6361 = Crystallized sulphate So many methods have been proposed for the volumetric 3stimation of copper that the analyst is bewildered by their number and hardly knows upon which to depend. My own opinion is that in the majority of cases it is safer and less troublesome to estimate the metal by weight; there are, however, instances where volumetric methods can be applied with advantage, and the following processes are chosen as the best. 122 ANALYSIS BY OXmATION AND REDUCTION. § 52. 1. Method of separating Copper from any of its Ores or Besidues In a pure Metallic state, so that It may be weighed direct or esti- mated hy Volumetric methods.— (M o h r, somewhat modified.) The substance must be brought into very fine powder, par- ticularly if it contain sulphur, and about 5 Gm. of it weighed, placed in a deep porcelain crucible or capsule about 4in. in diameter, and covered with a concentrated mixture of nitric and sulphuric acids and water, added cautiously; a larger quantity of nitric acid is necessary when sulphur is present, (as in pyrites), than in other cases; a watch glass or another capsule is placed upon the top of that containing the mixture so as to prevent loss by spirtiug — preferably a large watch glass with a hole drilled in the middle. Heat is then applied to boUing and continued tiU. the mass is nearly dry, the cover is then removed, and if not washed clean by the steam produced in the operation itself, is washed mth a small quantity of water into the mass which is agaiu evaporated to dryness, the heat is then increased until all acid vapours are expelled, and the capsule set aside to cool. In the case of pyrites the heat must be continued long enough to burn the sulphur off, the capsule may then be slightly cooled and nitric acid again added, and the burning repeated ; in certain cases this may be necessary a third time in order to oxidise aU. sulphur and extraneous matter. By this treatment the copper is obtained as sulphate, the iron mostly as insoluble basic sulphate, lead as insoluble sulphate, antimony and tin also insoluble, zinc, cobalt, and nickel are of no consequence in the following treatment. The cold residue is covered with water and boiled till all soluble matter is extracted, then filtered throiigh a small filter into a weighed platinum dish, the residue being washed clean with boiling water, the dish, with its contents, is then placed on the water- bath or over a small spirit lamp, gently heated, acidified with hydrochloric acid, and a smaU lump of pure zinc added to § 52. COPPER. 123 reduce the copper to the metallic state ; there must be suflBcient acid to produce a distinct evolution of hydrogen, and the dish covered with a watch glass to prevent loss of liquid by spirting, the glass afterward being rinsed into the liquid. The end of the reduction is best known by taking a drop of the supernatant liquid out with a glass rod, and touching the surface of some acidulated sulphuretted hydrogen water contained in a small white capsule, if no brown colour is produced, the reduction is ended, and any undissolved zinc can either he removed me- chanically with a pair of forceps, taking care to free it from any adhering copper, or dissolved by the addition of fresh acid. The precipitated copper, if pure and clean, will possess a rose red colour, it must be quickly washed with boiling water to free it from acid — the first washings should be poured off into a beaker and allowed to settle by themselves, as small particles of copper may accidentally be contained in them, if so, they must be washed clean and added to the platinum dish. Air should not be admitted to the metallic copper while the acid is present to any great extent. When the washings no longer affect litmus paper, the dish should be placed in an air bath, heated to 212° or 215° Fahr., and dried till the weight is constant — the increase in weight is pure copper. A water-bath may be used for drying the copper, in which case it is preferable to wash it first with strong alcohol. Instead of a platinum dish porcelain or glass will answer, but more time is required, as there is no galvanic action to hasten the decomposition as with the platinum; in this case the deposited copper is not attached to the sides or bottom of the vessel. Instead of drying and weighing the copper it can be dissolved and estimated by Fleitmann's process, § 52, 3, or the following modification may be adopted. The solution obtaiued by di- gesting the residue of the first operation in water, invariably contains iron, whenever that metal ia present in the original substance; in order to remove it, therefore, the neutral and 124 ANALYSIS BY OXIDATION AND EEDUCTION. § 52. concentrated solution is TdoUbcI with a tolerable quantity of acetate of soda, tlie insoluble iron precipitate filtered off, washed with boiling water containing acetate of soda, and the copper solution, which must not be too dilute, titrated by De Haen's method, with hyposulphite of soda; or in the absence of manganese, cobalt, nickel, arsenic, mercury, silver, and zinc, the solution, without removing the iron, may be titrated direct with cyanide of potassium as in § 52, 5, using the precautions there mentioned. Examples of the accuracy with which copper may be sepa- rated from ores and other compounds by precipitation with zinc : — 1 Gm. pure metallic copper was mixed with OS Gm. each of the following substances, either as metals or salts, viz. : — gold, silver, platinum, tin, lead, iron, zinc, nickel, cobalt, bismuth, arsenic, uranium, mercury, molybdenum, antimony, sulphur, silica, and phosphate of lime. The whole was treated ivith nitric and sulphuric acids as previously described, and the residue, after one ignition, lixiviated with water, filtered off, and treated with hydrochloric acid to remove silver, then after filtration, zinc and hydrochloric acid added in a large platinum dish. The yield of pure copper was 0-996 Gm. ; without recording any further experiments in detail, it may suffice to say that in more than twenty determinations of copper in various combinations, the mean results obtained were 9 9 '7 instead of 100. 2. Scliwarz's method, (results tolerably accurate.) This process is based upon the fact that grape sugar precipi- tates protoxide of copper from an alkaline solution of the metal containing tartaric acid, the protoxide so obtained is collected and mixed with perchloride of iron and hydrochloric acid — the result is the following decomposiMon : — CujO -h Fe^Clj + HC1= 2GuCl + 2FeCl + HO § 52. COPPEE. 125 Each equivalent of copper reduces an equivalent of perchloride of iron to protocMoiide, which is estimated hy permanganate. The iron so ohtained is calculated into copper by the requisite factor. Process : The weighed substance is brought into solution by nitric or sulphuric acid or water, in a porcelain dish or flask, and most of the acid in excess saturated with carbonate of soda, neutral tartrate of potash is then added in not too large quantity, and the precipitate so produced dissolved to a clear blue fluid by adding caustic potash or soda in excess; the vessel is then heated cautiously to about 150° Fahr., in the water-bath, and sufficient grape, milk, or starch sugar added to precipitate the copper present ; the heating is continued until the precipitate is of a bright red colour and the upper Uquid is brownish at the edges from the action of the alkali on the sugar ; the heat must never exceed 190° Fahr. When the mixture has somewhat cleared, the upper fluid is poured through a moistened filter, and afterward the precipitate brought on the same, and washed with hot water till thoroughly clean; the precipitate which may adhere to the dish or flask is thoroughly washed, and the filter containing the bulk of the protoxide put with it, and an excess of solution of perchloride of iron (free from nitric acid or free chlorine) added, together with a little sulphuric acid, the whole is then warmed and stirred until the protochloride of copper is all dissolved. It is then filtered into a good-sized flask, the old and new filters being both well washed with hot water, to which, at first, a little free sulphuric acid should be added in order to be certain of dissolving all the oxide in the folds of the paper. The entire solution is then titrated with permanganate in the usual way, bichromate may also be used, but the end of the reaction is not so distinct as usual from the turbidity produced by the presence of copper. 126 ANALYSIS BY OXIDATION AND EEDUCTION. § 52. 3. Fleltmann's Metliod, (results accurate.) The metallic solution, free from nitric acid, bismuth, or lead, is precipitated witli zinc as in § 52, 1 ; the copper collected, ■washed, and dissolved in a mixture of perchloride of iron and hydrochloric acid ; a little carbonate of soda may be added to expel the atmospheric air. The reaction is — Cu+Fe, Cls=Cu Cl+2Fe CI. 1 eq. of copper, therefore, produces 2 eq. protochloride of iron. When the copper is all dissolved, the solution is diluted and titrated vpith permanganate ; 66 iron represent 31-7 copper. If the original solution contains nitric acid, bismuth, or lead, the decomposition by zinc must take place in an ammoniacal solution, from which the precipitates of either of the above metals have been removed by filtration ; the zinc must be finely divided and the mixture warmed ; the copper is all precipitated when the colour of the solution has disappeared. It is washed first with hot water, then with weak hydrochloric or sulphuric acid and water, to remove the zinc ; again with water, and then dissolved in the acid and perchloride of iron as before. i. Method of D e H a e n and E. 0. Brown, (results acccurate. In tlie absence of persalts of Iron and other reducible substances.) The solution of the metal, if it contains nitric acid, is evapor- ated with sulphuric acid tiU the former is expelled, or the nitric acid is neutralized with carbonate of soda and acetic acid added, the sulphate solution must be neutral, or only faintly acid ; excess of acetic acid is of no consequence. The prc(fcess is based on the fact that when iodide of potassium is mixed with a salt of copper in solution, diuiodide of copper is precipitated as a dirty white powder, and iodine set free. If the latter is then titrated with decinormal hyposulphite and § 52. COPPER. 127 starch, liquor, the corresponding quantity of copper is found by the systematic factor. Process : The solution, (containing not less than 1 Gni. Cu to each 100 CC,) free from iron, chlorine, or free nitric and hydrochloric acids, is brought into a beaker or flask, iodide of potassium in good quantity added, and the hyposulphite delivered from a burette till the brown colour has disappeared ; starch liquor is then added, and decinormal iodine, to ascertain the excess of hyposulphite, or the titration may proceed direct by adding starch at first, and hyposulphite, till the blue colour is discharged. Example ; 10 CC of solution of sulphate of copper, con- taining 0-39356 Gm.=0-1 Gm. copper was mised with iodide of potassium in a beaker, and>19 CC of /jf hyposulphite added, then starch liquor, and 3'2 CC •j'^j iodine required to produce the blue colour^ 15*8 CC hyposulphite; this multiplied by 0-006336 gave 0-1001 Gm. copper instead of 0-1 Gm. In order to remove iron from copper solutions, previous to their analysis, it has been recommended to precipitate it with ammonia on the one hand, or to boil with acetate of soda on the other, and precipitating as basie acetate. In neither case can very satisfactory results be obtained, for with ammonia at least three precipitations are necessary to remove aU the copper from the oxide of iron ; boiling with acetate of soda does not always separate all the iron, and even if it should do so, the precipitate holds the copper tenaciously ; the collection of fluid therefore, by these repeated precipitations and washings, is so considerable, that the process cannot be applied, except by evaporation, to a small bulk. The acetate of soda is far preferable to the ammonia, it must, however, be used in large quantity, and the precipitate washed with hot water containing acetate of soda. In certain cases, (i.e., where metals may be present which would interfere with the titration of the entire liquid by Parke s' process) it may be advisable to precipitate the iron by ammonia, slightly wash the precipitate, and then 128 Al^ALYSIS BY OXIDATION AND EEDUCTION. § 52. push it thiougli the funnel into a white capsule, and titrate with cyanide of potassium at once for the slight amount of copper present, adding the weight so found to that obtaiaed in the filtrate by some other method. 5. Method of Parkes and C. Mohr, {results tolerably accurate, in tlie absence of manganese, nickel, cobalt, mercury, silver, and zinc.) This well known and much used process for estimating copper depends upon the decoloration of an ammoniacal solution of copper by cyanide of potassium; the reaction (which is not absolutely uniform with variable quantities of ammonia) is such that a double cyanide of copper and ammonia is formed ; cyanogen is also liberated, which reacts on the free ammonia, producing urea, oxalate of urea, cyanide and formiate of ammonium, (Liebig.) Owing to the influence exercised by variable quantities of ammonia, or its neutral salts, upon the decoloration of a copper solution by the cyanide, it is necessary that the solution analysed should contain pretty nearly the same proportion of ammonia as that upon which the cyanide has been originally titrated. The experiments made by Fresenius shew this is absolutely necessary, and the undermentioned results, obtained by myself, point to the same conclusion. 1. 10 CO of solution of sulphate of copper, containing 0-10 Gm. Cu, with 1 CC of ammonia, spec. grav. '900, required 21 '3 CG cyanide solution. 2. 50 GG of copper solution=0-50 Gm. Cu, and 5 CC ammonia required 106-5 CG cyanide. These agree exactly. 3. 20 CC copper solution=0-20 Cu, with 6 CC ammonia required 43 CC cyanide, instead of 42-6. 4. 20 CG copper=0'20 Cu, with 20 CC ammonia, required 44 GG cyanide instead of 42-6. § 52. COPPER. 129 The results with salts of ammonia were very similar. It has generally been thought that where copper and iron occur together, it is necessary to separate the latter before using the cyanide. F. Field, however, has stated that this is not necessary; (" Chem. News,"' vol. i, p. 25,) and I can fully endorse his statement that the presence of the suspended oxide of iron is no hindrance to the estimation of the copper, in fact it is rather an advantage, as it acts as an indicator to the end of the process. While the copper is in excess, the oxide possesses a purplish brown colour, but as this excess lessens, the coloiir becomes gradually lighter, until it is orange brown ; if it be now allowed to settle, which it does very rapidly, the clear liquid above wlU be found nearly colourless. A little practice is of course necessary, tO» enable the operator to hit the exact point, and it is always weU- to make use of both indicators. The following experiment is given fi'om among many others. 10 CC of copper scdution=0'10 Gm. Cu, were put into a small white porcelain! dish, and 2 CC ammonia, -900 added, then the cyanide cautiously delivered from the burette, tiU the faintest violet tinge only was perceptible, the quantity so used was 21 '3 CC j 10 CC of copper solution were then put into another dish, a little freshly precipitated peroxide of iron added, together with 2 CC ammonia. The cyanide was then delivered without looking at the burette, until the oxide had acquired the proper colour; the burette was found to stand at 21-3 CC, and the clear solution possessed the same faint tint as before. Fleck ("Chem. Centralb.," page 22, 1860) has recommended the use of carbonate of ammonia instead- of caustic, and the addition of two drops of solution of ferrocyanide of potassium, (1:20,) warming the solution to 60° C, (=145° Fahr.,) the cyanide is delivered from the burette till the blue colour becomes faint, and when the reaction is complete, the reddish yellow colour of the ferrocyanide of copper suddenly appears, K 130 ANALYSIS BY OXIDATION AND EEDUCTION. § 52. but without any precipitate, if now another drop or two of cyanide is added, the liquid heeomes colourless. I have not been able to obtain very satisfactory results by this method, the ending not being sharp enough. I consider the oxide of iron by far the most sensitive reaction. It is best applied where carbonate of ammonia is used to remove other metals from the solution. In all cases where caustic ammonia is used, it is best to conduct the operation without heat, and in a small white porcelain dish. 6. Pelouze'a Process, (results tolerable accurate, In the absence of tin, nickel, cobalt, or silver.) This process is based on the fact that if an ammoniacal solution of copper is heated from 140° to 180° Fahr., and a solution of sulphide of sodium added, the whole of the copper is precipitated as oxysulphide, 5Cu S+Cu 0, leaving the liquid colourless. The loss of colour indicates, therefore, the end of the process, and this is its weak point ; special practice, however, will enable the operator to hit the exact point closely. Preparation of Standard Solutions. It is first necessary to have a solution of pure copper, of known strength, which is best made by dissolving 39-356 Gm. of pure sulphate of copper in 1 litre, or 393'56 grn. in 10,000 grains of distilled water ; each CC or dm. wiU respectively contain O'Ol Gm. or O'l grn. of pure metallic copper. A measured quantity, say 50 CC, of standard solution of copper, is freely supersaturated with caustic ammonia, and heated till it begins to boil ; the temperature wiU not be higher than 180°, in consequence of the presence of the ammonia; it is always well, however, to use a thermometer ; the sulphide of sodium is delivered cautiously from a Mohr's burette, until the last traces of blue colour have disappeared from the clear § 53. ZINC. 131 liquid above the precipitate. The experiment is repeated, and if the same result is obtained, the number of CC or dm. required to precipitate the amount of copper contained in 50 CC or dm., =0-5 Gm. or 5 gm. respectively, is marked upon the sulphide of sodium bottle. As the strength of the solution gradually deteriorates, it must be titrated afresh every day or t-wo. Special regard must be had to the temperature of the precipitation, otherwise the accuracy of the process is seriously interfered -with. ZINC. Zn.=32-S3. §53. Substance. Formula. Atomic Weight Quantity to be wetghed 80 that 1 CC or dm. of deolnormal solution^l per cent, of Bubstance. N Ttr Factor. Zinc Zn ZnO Zn 0, CO2 ZnS 32.53 40-53 62-53 48-53 0-3253 Gm., or 3-253 gm. 0-4053 Gm., or 4-053 grn. 06253 Gm., or 6-253 gm. 0-4853 Gm., or 4-853 grn. 0-003253, or 0-03253 0-004053, or 0-04053 0006253, or 006253 004853, or 0-04853 Oxide of Zinc ... Carbonate of Zinc Sulphide of Zinc Metallic iron X 0-5809 = zinc. j» X 0-724 = oxide of zinc. Double iron salt X 0-3839 = zinc. >J JS X 0-1039 = oxide of zinc. 1. Method of C. in oil r, (results accurate In the absence of manganese and the heavy metals In general.) In the article on the analysis of ferridcyanide of potassixun, by Lenssen's method, § 59, 1, it is shewn that greater exact- ness may be obtained through the use of an excess of zinc in K 2 132 ANALYSIS BY OXIDATION AND EEDUCTION. § 53. the mixture, so that the iodine liberated shall be the true measure of the substance. In the present method the process may be considered to be reversed ;— with an excess of ferridcyanide of potassium the liberated iodine shall express the true quantity of zinc sought. If to a solution of zinc in acetic acid an excess of ferrid- cyanide of potassium is added, a reddish yellow precipitate of ferridcyanide of zinc occurs, having the composition, (Cy8re2)3Zn. If now to this mixture an excess of iodide of potassium be added, the decomposition occurs as follows. 2 at. ferridcyanide of zinc (expressing 6 at. zinc) react upon 2 at. iodide of potassium, producing 3 at. ferrocyanide of zinc, 2 at. acetate of potash, 1 at. ferrocyanic acid, and 2 at. free iodine; therefore, each equivalent of iodine, found by -f[f hyposulphite, expresses 3 eq. of zinc, consequently, in any zinc analysis by this method, the number of CC or dm. of hyposulphite used must be multi- plied by 3, and the product by the systematic factor. The process is as follows: — The metal and its compounds must exist in an acetic acid solution, which is best managed by dissolving the ores in aqua regia, evaporating to dissipate the excess of acid, neutralizing the remainder with carbonate of soda, then, adding a strong solution of acetate of soda in excess, and boiling ; then filter, and wash with boiling water containing a Uttle acetate of soda; iron is removed by this means but not manganese, so that should the latter be present the process wiU not be applicable. In the presence of other metd.s the zinc must be separated as sulphide or oxide, and afterward brought into solution in acetic acid. To the acetic acid solution so prepared a freshly-made solution of ferridcyanide of potassium is added in slight excess, (known by a drop of the mixture giving a blue colour with protosalts of iron), iodide of potassium in sufficient quantity is then added, together with starch liquor, and the titration with -^^ hyposulphite performed as usual — 1 eq. iodine =3 eq. zinc — the § 53. ZINC. 133 greenish blue colour of the mixture entirely disappears, and gives place to the pure yellow of the red prussiate of potash, when in solution. ■■ Fr. and C. Mohr and Fresenius have found the method very reliable. I have also found the same ; it is not necessary, therefore, to give examples further than to say that in the case of pure salts of zinc 99-8 and 100'12 were obtained instead of 100. 2. Schwarz's Method, 'results accurate.) The principle of this method is based on the fact that when sulphide of zinc is mixed with perchloride of iron and hydro- chloric acid — protochloride of iron, chloride of zinc, and free sulphur are produced : if the protochloride of iron is estimated with permanganate or bichromate of potash, the proportional quantity of zinc present is ascertained, 2 eq. Fe, represent 1 eq. Zn. Ores of zinc are treated with hydrochloric, or in the case of blende, with that and nitric acid, dissolved, evaporated to dissi- pate excess of acid, and then precipitated with a mixture of carbonate and caustic ammonia, and digested warm till all the' zinc precipitate is dissolved, the residue is washed with animonia- cal water and the filtrate and washings mixed. This ammoniacal solution, (which should contain all the zinc), is then warmed, and the zinc precipitated with a slight excess of sulphide of sodium or ammonium; when the precipitate has subsided the clear liquid is passed through a tolerably large and porous filter, the precipitate brought upon it, and well washed with warm water containing ammonia, till the washings no longer discolour an alkaline lead solution. The filter with its contents is then pushed through the funnel into a good sized flask containing a sufficient quantity of perchloride of iron mixed with hydrochloric acid, immediately well stopped or corked, gently shaken, and put into a warm 134 ANALYSIS BY OXIDATION AND REDUCTION. § 53. place ; after some time it should be again, well shaken, and set aside quietly for about 10 minutes. After the action is all over the mixture should possess a yellow colour from the presence of undecomposed perchloride of iron, when the cork or stopper is lifted there should be no smell of sulphuretted hydrogen. The flask is then nearly fiEed with cold distilled water, some dilute sulphuric acid added, and titrated with permanganate or bichromate of potash as usual. The free sulphur and filter will have no reducing effect upon the per- manganate if the solution is cool and very dilute. Example : 1 Gm. pure oxide of zinc was dissolved in hydrochloric acid, supersaturated with ammonia, and precipi- tated with sulphide of ammonium, the precipitate well washed and digested with acid perchloride of iron, the whole was diluted to 500 GC in a stoppered flask, 100 CC titrated with permanganate of such strength that 120 CG^l Gm. iron. 33-4 CO were required =0 "278 Gm. iron, this multiplied by 5, as ^ only was taken, gave 1'390 Gm. iron, which multiplied by the factor for oxide of zinc 0-724 gave 1'0363 Gm. oxide of zinc, instead of 1 Gm. Another 100 CC titrated with -^ bichromate, required 49'3 CC, which multipUed by the ^j factor, 0-004063 gave 0-1998129 Gm.x5=0-9990Gm. ZnO. 3. Precipitation by Standard Sulphide of Sodium, with Alkaline Lead Solution as Indicator, applicable to most Zinc Ores and Products, (results accurate.) The ammoniacal solution of zinc is prepared just as pre- viously described in Schwarz's method. The standard sulphide of sodium is best made by saturating a portion of caustic soda solution with sulphuretted hydrogen, then adding sufficient soda solution to remove the smell of the free gas, and diluting the whole to a convenient strength for titrating. § 53. ZINC. ' 135 The standard zinc solution is best made by dissolving 44 '12 Gm. of pure sulphate of zinc to the litre, or 441-2 grn. to the 10,000 grns. ; 1 CC or dm. will then contain 0-010 Gm. or 0-10 grn. of metallic zinc, and upon this solution, or one prepared from pure metallic zinc of the same strength, the sulphide of sodium must be titrated. The alkaline lead solution used as indicator is made by heating acetate of lead, tartaric acid, and caustic soda solution in excess together until a clear solution is produced. It is preferable to mix the tartaric acid and soda solution tirst, so as to produce tartrate of soda, or if the latter salt is at hand it may be used instead of tartaric acid. The Analytical Process. 50 CC of zinc solution^O-5 Gmi Zn are put into a beaker, a mixture of solutions of ammonia and carbonate of ammonia, (3 of the former to about 1 of the latter,) added in sufficient quantity to redissolve the precipitate which first forms. A glass rod is then dipped into the lead solution and with it a few drops, placed at some distance from each other, on filtering paper, placed upon a slab or plate. The solution of sulphide of sodium contained in an ordinary Mohr's burette is then suffered to flow into the zinc solution until, on bringing a drop from the mixture and placing it upon the filtering paper so that it may expand and run into the drop of lead solution, a black line occurs at the point of con- tact, the reaction is very delicate ; at first it will be difficidt, probably, to hit the exact point, but a second trial with 25 or 50 CO of zinc solution wiU enable the operator to be certain of the corresponding strength of the sulphide of sodium. As this latter is always undergoing a slight change, it is necessary to titrate for every day's use. Direct titration with pure zinc solution gave 99-6 and 100-2, instead of 100. 136 ANALYSIS BY OXIDATION AND REDUCTION. § 54. C. Groll (Zeitschrift fur Analytisclae Chemie, p. 21,) re- commends the use of protochloride of nickel as indicator, instead of nitroprusside of sodium or lead. The drops are allowed to flow together on a porcelain plate ; whUe the point of contact shows a blue or green colour the zinc is not all precipitated by the sulphide of sodium, therefore, the latter must be added until a grayish black colour appears at contac.t. I do not see any advantage over the lead paper in the process. COROLLABT. Estimation of Alkaline Sulphides by Standard Zinc Solution. § 5i. This method, which is simply a counterpart of the foregoing, is especially applicable for the technical determination of alkaline sulphides in impure alkalies, mother liquors, &c. If the zinc solution be made by dissolving 3-253 Gm. pure metallic zinc in hydrochloric acid, supersaturating with am- monia, and diluting to a litre, or 32'53 grn. to 10,000 gms. 1 CC or dm. will respectively indicate — 0-0016 Gm. or 0-016 grn. sulphur 0-0039 „ or 0-039 „ sulphide of sodium 0-00551 „ or 0-0551 „ „ potassium 0-0034 .„ or 0-034 „ „ ammonium The zinc solution is added from a burette until a drop, brought in contact with the lead solution on filtering paper, no longer gives a black stain at the edges. § 55. PEROXIDE OF MANGANESE. 137 PEROXIDE or MANOANESE. Mn •02=43-57. § 55. 2 atoms protoxide of iron decompose 1 atom of peroxide of manganese, therefore 56 re=43-57 Mn Oj. 1 atom oxalic acid decomposes 1 altom peroxide manganese, tlaerefore 63 0=43-57 Mn O^. Factors. Metallic iron x 0-178 = Mn Oj. Cryst. oxalic acid x 0-6916 = ditto. Double iron salt x 0-111 = ditto. 1 CC or 1 dm. of decinormal permanganate, bichromate, or hyposulphite is equal to 0-.004357 Gm. or 0-04357 grn. peroxide manganese. The ores of manganese contain the metal ioi various states of oxidation, but as they are valued solely by the amount of available oxygen which they contain, it is invariably calculated as peroxide ; therefore the above factors aU apply to that substance. Factors for the other oxides can be found readily if required. All the oxides of manganese, ■with the exception of the first or protoxide, when boiled with hydrochloric acid yield chlorine equivalent to X 0-598 = Chromic acid 9J X 0-8784: = Bichromate of potash >» X 1-926 = Chromate of lead Double iron salt X 0-0446 = Chromium 97 X 0-0854 = Chromic acid J> X 0-1265 = Bichromate of potash »» X 0-275 = Chromate of lead 162 AITALYSIS BY OXIDATION AND EEDUCTION. § 65- § 65. 1. The estimation of chromates is very simply and suc- cessfully performed by the aid of protoxide of iron, being tbe converse of the process devised by Penny for tbe estimation of iron. See § 44. Tbe best plan of procedure is as follows. A very small beaker or other convenient vessel is partly or whoUy fiUed, as may be requisite, with perfectly dry and granular double sulphate of iron and ammonia ; the exact weight then taken and noted. The chromium compound is brought into solution, not too dilute, acidified with sulphuric acid and small quantities of the iron salt, added from time to time with a dry spoon, taking care that none is spiUed, until the mixture becomes green, and the iron is in excess, best known by a small drop being brought in contact with a drop of red prussiate of potash on a white plate ; if a blue colour appears at the point of contact, the iron is in excess. It is necessary to estimate this excess, which is most conveni- ently done by j^ bichromate being added until the blue colour produced by contact with the red prussiate gives place to a yellow brown. The vessel containing the iron salt is again weighed, the loss noted ; the quantity of the salt represented by the -jg bichromate deducted from it, and the remainder multiplied by the factor required by the substance sought. Example : 0-5 Gm. pure bichromate of potash was taken for analysis, and to its acid solution 4 'IS Gm. double iron salt added. 3-3 CG of ^ bichromate were required to oxidise the excess of iron salt ; it was found that 0'7 Gm. of the salt= 17 '85 bichromate solution, consequently 3-3 CC of the latter were equal to 0-12985 Gm. iron salt; this deducted from the quantity origiuaUy used left 4-02015 Gm., which multiplied by the factor 0-1255 gave 0-504 Gm. instead of 0-5 Gm. In the case of chromate of lead being estimated in this way, it is best to mis both the chromate and the iron salt together in a mortar, rubbing them to powder, adding hydrochloric acid, stirring weU together, then diluting withj water and titrating as before. § 66. ANTIMONY. 163 i. Eatimation of Cliroinates Tiy Distillation with Hydroclilorlc Acid, (Buns en, results very accurate.) When chromates are boiled -witli an excess of hydrocliloric acid in Fresenius', Bunsen's, or Mohr's distilluig apparatus, Fig. 16, every 2 eq. of chromic acid literate 3 eq. chlorine. For instance, with bichromate of potash the reaction may be expressed as foUows — KO, 2Cr 08 + 7H Cl=lvCl + Crj Cla + THO+SCl; if the liberated chlorine is conducted into a solution of iodide of potassium, 3 eq. of iodine are set free, and can be estimated by i^jj hyposulphite, as in § 45. 3 eq. of iodine so obtained=381, represent 2 eq. chromic acid=100'40. The same decom- position takes place by mere digestion, as described in § 45, 4. ANTIMONY. Sb = 122. 1. Conversion of Oxide of Antimony in Alkaline Solution into Antlmonlc Acid by Iodine, (Molir, results accurate.) § 66. The oxide of the metal, or any of its compounds, is brought into solution as tartrate by tartaric acid and water ; the excess of acid neutralized by neutral carbonate of soda, then a cold saturated solution of bicarbonate of soda added in the proportion of 20 CC to about 01 Gm. Sb 0^; to the clear solu- tion starch liquor and -^^ iodine are added until the blue colour appears ; the colour disappears after a little time, therefore the first appearance of a permanent blue is accepted as the true measure of iodine required. 1 CC -fij iodine=0-0061 Gm Sb. M 2 164 ANALYSIS BY OXIDATION AND REDUCTION. § 67. 2. DlstiUatlon of Ter or Fentasulphide of Antimony witBi Hydro- chloric Acid, and Titration of the evolved Sulphuretted Hydrogen, (Schneider, results accurate.) Wlien either of the sulphides of antimony are heated with, hydrochloric acid in Bunsen's, Fresenius', orMohr's dis- tilling apparp,tus, Fig. 16, for every 1 eq. of antimony present as sulphide 3 eq. of sulphuretted hydrogen are liberated. If therefore the latter be estimated, the quantity of antimony is ascertained. The process is best conducted as follows : — The antimony to be determined is brought into the form of ter or pentasulphide, (if precipitated from a hydrochloric solu- tion, tartaric acid must be previously added, to prevent the precipitate being contaminated with chloride,) which together with the filter containing it, is put into the distilling flask with a tolerable quantity of hydrochloric acid not too concentrated. The condensing tube, Fig. 16, contains a mixture of caustic soda or potash, with a definite quantity of -f-^ arsenious acid solution, § 46, 1, in sufficient excess to absorb aU the sulphur- etted hydrogen evolved. The flask is then heated to boiling, and the operation continued till all evolution of sulphuretted hydrogen has ceased ; the mixture is then poured into a beaker, acidified with hydrochloric acid, to precipitate all the tersulphido of arsenic, as in § 72. The whole is then diluted to, say 300 CC, and 100 CC taken with a pipette, neutralized with carbonate of soda, some bicarbonate added, as in.§ 64, 1, and the titration for excess of arsenious acid performed with -^ iodine and starch, as there directed. IODINE. 1=127. Free and Combined. 1 CC or 1 dm. -/^ hyposulphite=0-0127 Gm. or 0-127 grn. Iodine. =0-016611 Gm. or 0-16611 grn. Iodide of potassium. § 67. IODINE. 165 1. By Distillation. § 67. I"hbB iodine is of course very readily~'estimated by Bolution in iodide of potassium, and titration ■with, starch and Tff hyposulphite, as described in § 45, 5. Combined iodine, however, in haloid salts, such as the alkaline iodides, must be subjected to distillation with hydro- chloric acid, and some other substance capable of assisting in the liberation of free iodine, which is received into a solution of iodide of potassium, and then titrated with ^"5 hyposulphite, in the ordinary way. Such a substance presents itself best in the form of peroxide of iron, or some of its combinations ; i:^ therefore, hydriodic acid, or what amounts to the same thing, an alkaline iodide, be mjxed with an excess of peroxide of iron, and distilled in the apparatus shewn in Fig. 16, the following reaction occurs : — Fe^ 08-t-IH=2Fe O+HO+I. The best form in which to use the oxide of iron is the double Biilphate of peroxide of iron, and ammonia or potash, (iron alum.) The iodide and iron alum being brought into the little flask, Fig. 16, sulphuric acid, of about TS spec. grav. or so, is added, and the cork carrying the stiU tube inserted. This tube is not carried into the solution of iodide of potassium in this special case, but within a short distance of it, and the end must not be drawn out to a fine point, as there represented, but cut off straight. The reason for this arrangement is that it is not a chlorine distillation for the purpose of setting iodine free from the iodide solution, as is usually the case, but an actual distillation of iodine, which would speedily choke up the narrow point of the tube, and so prevent the further progress of the operation. As the distillation goes on, the steam washes the condensed iodine out of the tube into the solution of iodide, which must be present in sufficient quantity to absorb it aU. When no J 66 ANALYSIS BY OXIDATION AND EEDUCTION. § 67. more violet vapours are to he seen in th.e flask, the operation is ended; but to make sure, it is well to empty the ioduretted solution of iodine out of the condensing tube into a beaker, and put a little fresh iodide solution with starch iu, then heat the flask agaia ; the slightest traces of iodine may then be discovered by the occurrence of the blue colour. In case this occurs, the distillation is continued a little while, then both liquids mixed, and titrated with y^ hyposulphite, as usual. Perchloride of iron may be used instead of the iron alum, but in that case there is some danger of a portion being carried over, which would set iodine free from the iodide, and so give results too high. The analysis may be checked by titrating the protoxide of iron in the retort with -^ permanganate or bichromate. 2. Estimation, of Combined Iodine W Oxidation, (Grolfler Besseyre, and D u p r e.) This wonderfully sharp method of estimating iodine, depends upon its conversion into iodic acid by free chlorine. When a solution of iodide of potassium is treated with successive quantities of chlorine water, first iodine is liberated, then chloride of iodine (ICl) formed ; if starch, chloroform, benzole, or bisul- phide of carbon be added, the first will be turned blue while any of the others will be coloured intense violet ; a further addition of chlorine, in sufiicient quantity, produces pentachloride of iodine, (I Clj,) or rather, as water is present, iodic acid, (IO5 ;) no colouration of the above substances are produced by these compounds, and the accuracy with which the reaction takes place has been made use of by Golfier Besseyre, and Dupr6, independently of each other, for the purpose of esti- mating iodine. The former suggested the use of starch, the latter chloroform or benzole, with very dilute chlorine water. Duprd's method is preferable on many accounts. § 67. IODINE. 167 The foUowiBg examples are taken from Molir's "Titrii- methode." 30 CC of weak cliloriiie water were put into a beaker with iodide of potassium and starch, then titrated with -j^^j hyposulphite of soda, of which 17 CC were required. 10 CC of solution of iodide of potassium, containing O'OIO Gm. of iodine were put into a stoppered bottle, chloroform added, and the same chlorine water as above delivered in from the burette, with constant shaking, until the red colour of the chloroform had disappeared ; the quantity used was 85-8 CC. The excess of chlorine was then ascertained by adding bicar- bonate of soda, iodide of potassium, and starch liquor ; a slight blue colour occurred; this was removed by -^^jj hyposulphite, of which 1'2 CC were used. Now as 30 CC of the chlorine solution required 17 CC, the 85-8 CC required 48-62 CC of hyposulphite ; from this, however, must be deducted the 1 -2 CC in excess, leaving 4742 CC ^^^ = 4-742 CC of i^ij' hypo- sulphite, which multiplied by 0-00211, the one-sixth of iTshvis ^1-' (■'■ ®1- °-^ iodic acid liberating 6 eq. iodine,) gave 0-010036 Gm. iodine instead of- 0-01 Gm. Mohr suggests an improvement upon this method, which dispenses with the use of chloroform, or other similar agent. The weighed iodine compound is brought into a stoppered flask and chlorine water delivered from a large burette in excess, that is, until aU yellow colour has disappeared ; a drop of the mixture brought in contact with a drop of starch liquor produces no blue colour ; bicarbonate of soda is then added tiU the mixture is neutral or slightly alkaline, together with iodide of potassium and starch liquor ; the blue colour is then removed by j^j hyposulphite ; the strength of the chlorine water being known, the calculation presents no difficulty. Mohr obtained by this means 0-010108 Gm. iodine, instead of 0-01 Gm. 168 ANALYSIS BY OXTDATIOS AND EEDUCTION. § 68. CHLORATES, lODATES, AND BROMATES. CUoric acid, CI 05=7546. Iodic acid, 106=166-98. Bromic acid, Br 05=120. § 68. The compmmds of chloric, iodic, and bromic acids may all be determined by distillation or digestion with excess of hydrochloric acid ; With chloiates the quantity of acid must be considerably ia excess. In each case 1 eq. of the respectiye acids or their compounds liberate 6 eq. of chlorine, and consequently 6 eq. of iodine when decomposed in the digestion flask. In the case of dis- tillation, however, iodic and bromic acids only set free 4 eq. iodine, whUe protochlorides of iodine and bromine remain in the retort. In both these cases digestion is preferable to distil- lation. Among these substances chloric acid, in the form of chlorate of potash, is the only body of Commercial importance, therefore the following example only is given as a specimen of the accuracy of the method of analysis. 0'2043 Gm. pure chlorate of potash, equal to the sixth part of Tjyjjrij eq., was decomposed by digestion with iodide of potassium and strong hydrochloric acid in the bottle shown in Kg. 17 ; after the reaction was complete, and the bottle cold, the stopper was removed, and the contents washed out into a beaker; starch added, and 103 CC ■^ hyposulphite delivered in from the burette ; then again 23-2 CC of yf ^- iodine solution, to reproduce the blue colour ; this latter was therefore equal to 2-32 CC f^ iodine,' which deducted from the 105 CC hyposulphite gave 100-68 CC, which, multiplied by the factor 0-0020428, gave 0-205 Gm. instead of 0-2043 Gm. lodate and bromate of potash gave equally sharp results. § 70. CHLOEINE. 169 CHLORINE. 0I^3S-46. Chlorine Gas. 1 CC or 1 dm. -^^ arsenic or hyposulphite of soda solution =0-003546 Gm., or 0-03546 gra. CI. 1 Litre of Chlorine at. 32° Fahr., Bar 30'"- weighs 3-17 Gm. § 69. Chlorine -water can he titrated with hyposulphite of soda by adding a measured quantity of it to a solution of iodide of potassium, then delivering the hyposulphite from a burette till the colour of the free iodine has disappeared ; or by using an excess of the reducing agent, then starch liquor, and titrating residuaUy with -jj iodine. When arsenic solution is used for titration, the chlorine water is delivered into a solution of car- bonate of soda, excess of arsenic added, then starch liquor and -^ iodine till the colour appears, or the ioduretted starch paper may be used, § 46. COMPOUNDS OF HYPOCHLOROUS ACID. Cblorlde of Lime or Bleaching Powder, CUorlde of Soda, &c. § 70. The only substance of importance under this head is the so-called chloride of lime, used in very large quantities for bleaching purposes. The estimation of the free chlorine con- tained in it presents no difficulty when the arsenic solution is used for titration. Commercial bleaching powder consists of a mixture in variable proportions of hypochlorite of lime, (the true bleaching agent,) ehloride of calcium, and hydrate of lime ; it is generally valued and sold in this country by its percentage of chlorine. 170 ANALYSIS BY OXIDATION AND REDUCTION. § 70. The first thing to be done in determining the value of a sample of bleaching powder is to bring it into solution, which is best managed as foUows : — ■ The sample is weU and quickly mixed, and 10 Gm. weighed, put into a mortar, a little water added, and the mixture rubbed to a smooth cream ; more water is then stirred in with the pestle, allowed to settle a little while, then poured off into a litre flask, the sediment again rubbed with water ; poured off, and so on repeatedly until the whole of the chloride has been conveyed into the flask without loss, and the mortar washed quite clean ; the flask is then filled to the mark with water, well shaken, and 100 CC of the mUky liquid taken out with a pipette, emptied into a beaker, and the •j'^ arsenic solution de- livered in from a burette untU a drop of the mixture taken out with a glass rod and brought in contact with the prepared starch paper, § 46, gives no blue stain. The starch paper may be dispensed with by adding arsenifl^ solution in excess, then starch liquor, and titrating residually with -^j iodine tUl the blue colour appears, the number of CC of arsenic used, multiphed by the factor 0'003546, will give the percentage of chlorine. Example : 100 CC of chloride of lime liquid prepared as above directed were put into a beaker, and 86 CC of arsenic solution added, then starch liquor and 1 -5 CC of -/j iodine to produce the blue colour=:84-5 CC of arsenic solution, which multiplied by 0-003546 gave 0-2996 ; and as 1 Gm. of the sample was contained in the 100 CC, 29-96 per cent, of chlorine. Another 100 CC was carefully titrated with arsenic solution by the aid of iodized starch paper. 84-5 CC were required, also equal to 29 -9 6"/,,. Some recommend that the mixture of chloride of lime and water should be allowed to stand till clear, and the clear liquid only used for titration ; but this invariably gives lower results than when the milky mixture is used. Instead of weighing 10 Gm. of the sample, and using a CC burette, 100 grains may be weighed, diluted to 10,000 grains, § 71. SULPHUR. 171 anil 1,000 grains of the licLuid=100 dm. taken for titration; the arsenic solution is then delivered from a decern burette ; the number of decems used multiplied by the factor 0-03546, will be the percentage of chlorine. By weighing 3-55 Gm. or 35-5 grn. of the sample, and di- luting to 1 litre or 10,000 grains respectively; then taking 100 CO or dm. for titration, the number of CC or dm. of arsenic solution required wUl be the percentage of chlorine direct. Bun sen's Method, (results accurate.) 10 or 20 CC of the chloride of lime solution, prepared as above, are measured into a beaker, and an excess of solution of iodide of potassium added ; the mixture is then diluted somewhat, acidified with hydrochloric acid, and the liberated iodine titrated as in § 45. 1 eq. iodine so found represents 1 eq. chlorine. SDLPHUK. S=16. § 71. Substance. Formula. Atomic Weight. xs Factor. Sulphuretted Hvdrogen ... Sulphurous Aciu H S S^Oi, NaO,S2 02+5HO 17 32 48 124 0-0017 0-0032 0-0048 0-0124 Ilyposulphurous Acid Hyposulphite of Soda 1. When sulphuretted hydrogen is brought in contact -witli solution of iodine, hydriodic acid is formed, and sulphur set free. (HS+I=IH+S.) 172 ANALYSIS BY OXIDATION AND REDUCTION. § 71. If the solutions are concentrateil, horwever, a peculiar reddish colour occurs which hinders the correct ending of the reaction ■with starch ; the mixture must therefore be diluted freely -with freshly boiled and cooled water ; the results are not very satis- factory. . The determination of sulphuretted hydrogen is on this account preferably made with -^^ arsenious acid solution, described in § 46. Sulphurous acid is very readily and very accurately estimated by ^ iodine and starch, as also sulphites and hyposulphites. In the case of solution of sulphurous acid, however, the dilu- tion must be such that not more than 0-04 per cent, of SOj is present. The solutions of sulphites and hyposulphites need not be so much diluted. For the details of the reaction with hyposulphurous and sulphurous acids see § 45. In the deter- mination of hyposulphites, double the atomic weight must be taken, (expressed in centigrammes,) in older that 1 CC of -^ iodine solution shall be equal to 1 per cent, of substance. 2. Estimation of Sulphur In Pyrites, Ores, Residues, &c. a. By conversion into sulphuric acid, and titration with chloride of barium. The very finely powdered substance is introduced into a dry flask, together with about three or four times its weight of powdered chlorate of potash, and small quantities of hydro- chloric acid added from time to time, the mixture being finally warmed gently till all the sulphur has disappeared by being oxidised into sulphuric acid ; the hquid is then diluted, filtered, and titrated as in § 28. Or the substance may be fused with a mixture of carbonates of potash and soda, and chlorate of potash ; the residae lixiviated with boiling water, filtered and titrated as above. The use of nitrate of potash should be avoided, lest the pre- cipitate of sulphate of baryta should be contaminated with nitrate of baryta. § 71. SULPHUR. I'/S b. Alkallmetric Method, (Felonze.) This process, which is more especially designed for the rapid estimation of sulphur in iron and copper pyrites, is susceptible of very tolerable accuracy, the greatest variation from the truth ^ not exceeding 1 or 1^ "/„, -when the manipulation is carefully performed. The principle of the process is based on the fact that when sulphur is ignited with chlorate of potash and carbonate of soda, the sulphur is converted by oxidation entirely into sulphuric acid, which expels its equivalent propor- tion of carbonic acid from the soda, forming neutral sulphate of soda ; if, therefore, an accurately weighed quantity of the substance be fused with a known weight of pure carbonate of soda in excess, and the resulting mass titrated with normal acid, to find the quantity of unaltered carbonate of soda, the proportion of sulphur is readily calculated from the difference between the volume of normal acid required to saturate the original carbonate of soda, and that actually required after the ignition. For the sake of avoiding calculation, it is advisable to take 1 Gm. of the finely levigated pyrites, and 5-3 Gm. of pure carbonate of soda for each assay ; and as 5-3 Gm. carbonate of soda represent 100 CC of normal sulphuric acid, (=4-0 Gm. SOj,) it is only necessary to subtract the number of CC used after the ignition from 100, and multiply the remainder by the factor 0'016, (1 CC normal acid being equal to 0'016 Gm. S,) in order to arrive at the weight of sulphur 'in the 1 Gm. of pyrites, and by moving the decimal point two places to the right, the percentage of that substance is obtained. An example wOl shew the details of the process and calculation. Some cubes of iron pyrites were broken, and a small portion very finely powdered in a hardened steel mortar. 1 Gm. of the powder was mixed intimately with 5-3 Gm. pure carbonate of soda, and about 7 Gm. each of chlorate of 174 ANALYSIS BY OXIDATION AND EEDUCTION. § 71- potash, and decrepitated chloride of sodium, in powder, (the latter is added for the purpose of moderating the action,) the whole was then introduced into a platinum crucible, and gradually exposed to a duU red heat for ten minutes ; the crucible was then suffered to cool somewhat, and wann distilled ' water added ; the solution so obtained was drawn off with a pipette and brought on a moistened filter, the process repeated five or six times, the residue then emptied into a beaker and boiled with a large quantity of water, the whole brought on the filter and thoroughly washed with boiling water tOl aU soluble matter was removed ; the clear filtrate was then coloured with litmus, and titrated as in §§ 12, 13. 67 CC of normal acid were required, which deducted from 100 left 33 CC, this multiplied by 0-016 gave 0-528 Gm. sulphur, or 52-8 %; pure Fe 8^ con- tains 53-3 "/j. The insoluble oxide of iron remaining on the filter was dissolved in hydrochloric acid, and titrated with bichromate of potash, as in § 44, yielding 46-5 "/„ iron; the determination of both substances occupied less than an hour, and the loss, sup- posing the pyrites to be pure, amounted to less than | of a per cent. If pure carbonate of soda is not at hand, the ordinary com- mercial article will answer the purpose, but the quantity of normal acid necessary to saturate it must of course be previously found. An iron spoon or ladle may also be used instead of the platinum crucible. If roasted pyrites is to be examined by this method, it is unnecessary to add the salt, and equal quantities of the substance, carbonate of soda and chlorate of potash may be taken for the combustion. If the grain system of weights and measures are used, the quantity of pyrites wiU be 10 grains, and of carbonate of soda 53 grains, each decern of normal acid being equal to 0-1 6 grn. sulphur. It is not of course absolutely necessary that these quantities should be used, but less calculation is needed by this plan than any other. § 72. SULPHUR ] 75 SULPHURETTED HYDROGEN. HS = 17. 1 CC t'tt arsenious acid = 0-00255 Gm. HS. 1 dm. „ „ = 0-0255 gm. „ Molir's Method, (results accurate.) § 72. This residual process is far preferable to the direct titration of sulphuretted hydrogen by iodine, as devised by Dupasquier. The principle is based on the fact that when sulphuretted hydrogen is brought in contact -with an excess of arsenious acid in solution, tersulphide of arsenic is formed ; 1 eq. arsenious acid and 3 eq. sulphuretted hydrogen produce 1 eq. tersulphide of arsenic and 3 eq. water. As O3 + 3HS = As Sj + 3H0. The excess of arsenious acid used, is found by -^^ iodine and starch, as in § 46, 2. In the case of estimating the strength of sulphuretted hydrogen water, the following plan may be pursued. A measured quantity, say 10 CC -jj- arsenic solution, is put into a 300 CC flask, and 20 CC sulphuretted hydrogen water added, well mixed, and sufficient hydrochloric acid added to produce a distinct acid reaction, this produces a precipitate of tersulphide of arsenic, and the liquid itself is colourless. The whole is then diluted to 300 CC, filtered through a dry filter into a dry vessel, 100 CC of the filtrate taken out and neutral- ized with bicarbonate of soda, then titrated with ^^ iodine and starch, as in § 64, 1, the quantity of arsenious acid so found is deducted from the original 10 CC, and the remainder multiplied by the requisite factor for sulphuretted hydrogen. The estimation of sulphuretted hydrogen contained in car- buret ted hydrogen gas, can by this method be made very accurately by leading the gas through the arsenic solution, or still better, through a dilute solution of caustic alkali, then adding arsenic solution, and titrating as before described. The 176 ANALYSIS BY OXIDATION AND EEDUCTION. § 73. apparatus devised hj Mohr for this purpose is arranged as follows. The gas from a common turner is led Ijy means of a vulcanized tube into two successive small wash hottles, con- taining the alkaline solution ; from the last of these it is led into a large Woulff's bottle, flUed with water, the bottle has two necks, and a tap at the bottom, one of the necks contaius the cork through which the tube carrying the gas is passed ; the other, a cork through which a good-sized funnel with a tube reaching to the bottom of the bottle is passed ; when the gas begins to bubble through the flasks, the tap is opened so as to allow the water to drop rapidly ; if the pressure of gas is strong, the funnel tube acts as a safety valve, and allows the water to rise up into the cup of the funnel ; when a sufficient quantity of gas has passed into the bottle, say six or eight pints, the water which has issued from the tap into some convenient vessel, is measured into cubic inches or litres, and gives the quantity of gas which has displaced it. In order to insure accurate measurement, aU parts of the apparatus must be tight. The flasks are then separated, and into the second, 5 CC of arsenic solution placed, and acidified slightly with hydrochloric acid; if any traces of a precipitate occur, it is set aside for titration with the contents of the first flask, into which 10 CC or so of arsenic are put, acidified as before, both mixed together, diluted to a given measure, filtered, and a measured quantity titrated as before described. :iNDioo, Factor for -jg permanganate or bichromate 0-00752 Gm., or 0-0752 grn. § 73. The estimation of indigo is a purely technical affair, and does not belong to scientific analysis ; nevertheless, it is a § 73. INDIGO. 177 substance most largely and successfully adulterated, so far as the eye is concerned, and frequently needs examination by chemical means. The factors given above would lead one to suppose that the article was as deiinite in composition as Epsom salts or any other substance known to be combined in strict chemical proportions ; this, however, is not the case with indigo, as it never occurs in commerce pure. The factors given above are calculated from the examiuation of the purest indigo that can be obtained by chemical means ; that is, by the reduction and oxidation of the pure colouring matter contained ia the com- mercial article. The determination of the true value of any sample of com- mercial indigo by chemical analysis requires great care and considerable practice. The processes here given are those which seem on the whole preferable, but they are by no means so sharp and secure in their results as could be wished. 1. Mohr's method consists iu dissolving a weighed quantity of the material in sulphuric acid, diluting the solution and titrating with psrmanganate of potash until all the blue or green colour has disappeared, and gives place to a dirty yellow shade ; at this point all the real indigo blue is oxidised ; if more permanganate be added, its colour wiU be removed in consequence of the presence of other matters which decompose it ; therefore the appearance of the rose colour cannot be taken as the end of the process, as is the case in other analyses by that substance ; repeated and careful practice has shown that the plan is reliable -when the occurrence of the brownish yellow colour is taken as the end of the titration. The greatest care is necessary in preparing the solution of indigo for titration. The following plan is recommended as the best : — One gramme or 10 grains respectively of the finely- powdered sample is weighed and put into a stoppered flask, holding about three or four ounces, with a small handful of clean flint pebbles, about the size of swan shot; both well N 178 ANALYSIS BY OXIDATION AND EEDUCTION. § 73. shaken together, and about 8 or 10 CC or dm. of fuming M"ordhausen sulphuric acid added, the stopper inserted, and the whole mixed hy shaking. The flask is then put into a slightly warm place, about 70° Fahr., for six or eight hours, occasionally shaking; water is then added, and the Hqxdd decanted into a litre or 10,000 grain flask, according to circum- stances ; the flints repeatedly washed, and the washings added to the first liquid until they are clean and the measure made up. 100 CC or dm. of this well-mixed solution are then removed with a pipette, diluted with three or four times its volume of water, and titrated with permanganate (constantly agitating the liquid) from a CC or dm. burette, as the ca,se may be, until the last traces of green colour have disappeared, and the brownish yellow only remains. As there is sufficient solution for several other titrations, the results can be checked, but it must be borne in mind that the same amount of dilution, or thereabouts, must be used, or the results wiU vary. The quantity of permanganate so used is calculated for the whole quantity of indigo taken, reduced to ^^ strength, if not akeady so, and multiplied by the necessary factor. 2. Penny's Process- The solution of indigo is prepared precisely as before de- scribed ; but instead of permanganate, bichromate of potash with hydrochloric acid is used for the titration. 100 CC or dm. of the indigo solution is mixed with about 5 CC or dm. of strong and pure hydrochloric acid and a Httle water in a porcelain capsule, gently heated, and ^^ bichromate delivered from the burette, keeping the mixture well stirred, until a drop of the liquid taken out with a glass rod and put upon filtering paper gives a light brown stain, without any ad- mixture of blue or green. The end of the reaction is somewhat difficult to distinguish, but considerable practice will overcome this difficulty. § 73. INDIGO. 179 The calculation is the same as with -^jj permanganate. Schlumherger's method consists in adding the indigo so- lution prepared as above to a measured quantity of solution of chloride of lime, the strength of which has just previously been determined by a solution of pure indigo blue ; but as this is a most expensive and rare material, and must be used for almost every analysis, the process will not be further described. N 2 180 ANALYSIS BY PEECIPITATIOlf. PAET IV. ANALYSIS BY PRECIPITATION. INTRODUCTION. The general principle of this method of determining the quantity of any given substance is alluded to in § 1, and in all instances is such that the hody to be estimated forms an insoluble precipitate with a titrated re-agent. The end of the reaction is however determinable in three ways. 1. By adding the re-agent until no further precipitate occurs, as in the determination of chlorine by silver. 2. By adding the re-agent in the presence of an indicator contained either in the liquid itself, or brought externally in contact with it; so that the slightest excess of the re-agent shall produce a characteristic reaction with the indicator, as in the estimation of silver with salt, by the aid of chromate of potash, or that of phosphoric acid with uranium by yellow prussiate of potash. 3. By adding the re-agent to a clear solution until a pre- cipitate occurs, as in the estimation of cyanogen by silver. The &st of these endings can only be applied with great accuracy to silver and chlorine estimations. Very few precipi- tates have the peculiar quality of chloride of sQver, namely, § 74. CHLORINE. 181 perfect insolubility, and the tendency to curdle closely by shaking, so as to leave the menstruum clear ; some of the most insoluble precipitates, such as sulphate of baryta and oxalate of lime, are unfortunately excluded from this class, because their finely-divided or powdery nature prevents their ready and perfect subsidence. In all these cases, therefore, it is necessary to find an indi- cator, which brings them into class 2. The third class comprises only two substances, viz., the de- termination of cyanogen by silver, and that of chlorides by nitrate of mercury. CHLORINE. Cl.=36-46. 1 CC or 1 dm. ■^'^ silver solution=0-003546 Gm. or 0-03546 grn. Chlorine „ „ „ =0-005846 Gm. or 0-05846 gm. Chloride of Sodium § 74. The powerful aflSnity existing between chlorine and silver in solution, and the ready precipitation of the resulting chloride; seem to have led to the earliest important volumetric process in existence, viz., the determination of silver by the wet method devised by Gay Lussac. The details of the process are more particularly described under the article relating to the assay of silver ; the determination of chlorine is just the converse of the process there described, find the same pre- cautions, and to a certain extent the same apparatus, are required. The solutions required, however, are systematic; and for exactness and eonveiiient dilution are of decinormal strength. 182 ANALYSIS BY PBECIPITA'nON. § 74- Tlxe Decinormal Solution of Silver. 10'797 Gm. of pure silver, § 76, 3, b, are dissolved in pure nitric acid with gentle heat in a flask, into the neck of which a small funnel is dropped to prevent loss of liquid by- spirting ; when solution is complete, the funnel must be washed inside and out with distilled water into the iiask, and the liquid diluted to 1 litre ; or if it be desired to use cLiomate of potash as indicator in any analysis, the solution must be neutral ; in which case the solution of silver in nitric acid is evaporated to dryness, and the residue dissolved in 1 litre ; or, what is preferable, 16-997 Gm. of pure and dry recrystaUized nitrate of silver is dissolved in 1 litre of distUled water. If the grain system is used, 107'97 gm. silver or 169 '9 7 gm. nitrate is dissolved, and the solution diluted to 10,000 graias. Tlie Decfnormal Solntlon of Salt. 5-846 Gm. pure chloride of sodium, § 76, 3, a, are dissolved in distilled water, and the solution made up to 1 litre, or 58-46 gm. to 10,000 grains. There are two methods by which the analysis may be ended — a. By adding silver cautiously, and well sliaking after each addition till no further precipitate is produced. b. By using a few drops of solution of chromate of potash as indicator, as devised by Mohr. I"or the ending a refer to § 76, 3. The ending b is exceedingly serviceable, on the score of saving both time and trouble. There are conditions, however, attached to its use, which must not be disregarded. The most important of these is that the solutions must be absolutely free from acid or any great excess of alkali ; it is best to have them neutral When, therefore, acid is present in any solution to § 75. CHLORINE. 183 be examined, it should be neutralized with carbonate of soda ; a slight excess of this substance is not of much consequence ; an excess of caustic alkali must not be permitted, as in that case oxide of silver would be formed. The Analytical FrocesB. To the neutral or faintly alkaline solution containing chlorine, four or five drops of a cold saturated solution of yeUow chromate of potash is added, and the silver solution delivered from the burette until the last drop or two produce a permanent blood-red colour, an evidence that all the chlorine has entered into com- bination with the silver, and the drop or two in excess has formed a precipitate of chromate of silver ; the reaction is very delicate and easily distinguished. Example : 1 Gm. pure chloride of sodium was dissolved in water, a few drops of chromate solution added, and titrated with .jj- silver, of which 17 "14 CC were required to produce the red colour ; multiplied by the -^j^ factor for chloride of sodium=0-005846, the result was 1-002 Gm. Hia, CI, instead of 1 Gm. The determination of chlorides by Liebig's method, with nitrate of mercury, is described in § 80, 2. INDIRECT ESTIMATION OF AMMONIA, SODA, POTASH, LIME, AND OTHER ALKALIES AND ALKALINE EARTHS, WITH THEIR CARBONATES, NITRATES, AND CHLORATES, ALSO NITROGEN, ac, BY MEANS OF DECINORMAL SILVER SOLUTION. 1 CC .J5 silver solution = -jt^^^^tj eq. of each substance. § 75. MoHR, with his characteristic ingenuity, has made use of the delicate reaction between chlorine and silver, with 184 ANALYSIS BY PRECIPITATION. § 75. chromate of potash, as indicator, for the determination of the bodies mentioned above. All compounds capable of being converted into neutral chlorides by evaporation to dryness with hydrochloric acid, may be determined with great accuracy. The chlorine in a combined state is of course the only substance actually determined, but as the laws of chemical combination are exact and well known, the measure of chlorine is also the measure of the base with which it is combined. a. In most cases it is necessary only to slightly supersaturate the alkali, or its carbonate, with pure hydrochloric acid ; evapo- rate on the water bath to dryness, and heat for a time to 250° Fahr. in the air bath, then dissolve to a given measure, and take a portion for titration. h. Alkalies and Earths with organic acids are ignited to convert them into carbonates, then treated with hydrochloric acid, and evaporated as before. c. Carbonic Acid in combination may be determined by precipitation with chloride of barium, as in § 22 a, the washed precipitate is dissolved on the filter with hydrochloric acid, (covering it with a watch-glass to prevent loss,) then evaporated to dryness. In order to titrate with accuracy by the help of the chromate of potash, the baryta must be precipitated by means of a solution of pure sulphate of soda or potash, added in slight excess ; the precipitated sulphate of baryta does not interfere with the delivery of the reaction ; if this precaution were not taken the yellow chromate of baryta would mislead. d. Free Carbonic Acid is collected by means of ammonia and chloride of barium, as in § 22 6, and the estimation com- pleted as in c. e. Chlorates are converted into chlorides by ignition, then titrated with ^^ silver and chromate. /. Nitrates are evaporated with concentrated hydrochloric acid, and the resulting chlorides titrated as e. g. Nitrogen. The ammonia evolved from guano, manures, oilcakes, and sundry other substances, when burned with soda § 75. CHLORINE. 185 lime in Will and Varrentrapp's apparatus, is conducted through dilute hydrochloric acid ; the liquid evaporated to dryness, and titrated as in e. In all cases the operator will of course take care that no chlorine from extraneous sources but the hydrochloric acid is present, or if it exists in the bodies themselves as an impurity, its quantity must be first determined. Example : 0'25 Gm. pure carbonate of soda was dissolved in water, and hydrochloric acid added till in excess ; then dried on the water-bath till no further vapours of acid were evolved ; the resulting white mass was heated for a few minutes to about 240° Fahr., dissolved and made up to 300 CC ; 100 CO required 15-7 CC /j silver, this multiplied by 3 gave 47-1 CC, which multiplied by the ^ factor for carbonate of soda,=0-0053, gave 0-24963 Gm. instead of 0-25 Gm. h. Indirect Estimation of Potash and Soda exist- ing as Mixed Chlorides. It is a problem of frequent occurrence to find the relative quantities of potash and soda existing in mixtures of the two alkalies ; such as occur, for instance, in urine, manures, soils, waters, &c. The actual separation of potash from soda by means of bichloride of platinum is tedious, and not always satisfactory. The following method of calculation is frequently convenient, since a careful estimation of the chlorine present iu the mixture is the only labour required, and which can most readily be accomplished by -ys silver and chromate of potash, as pre- viously described. 1. The weight of the mixed pure chlorides is accurately found and noted. 2. The chlorides are then dissolved ia water, and very carefully titrated with -^-^ silver and chromate of potash for the amount of chlorine present, which is also recorded ; the calcu- lation is then as follows : — The weight of chlorine is multiplied by the factor 2-1029, 186 ANALYSIS BY PEECIPITATION. § 76. from the product so olDtained is deducted the -weiglit of the mixed salts found in 1. The remainder multiplied by 0'36288 wUl give the weight of chloride of sodium present in the mixture. The weight of chloride of sodium deducted from the total as found in 1, will give the weight of chloride of potassium. Chloride of sodium x 0-5302 = Soda, (ISTaO.) Chloride of potassium x 0-6317 = Potash, (KO.) The principle of the calculation, which is based on the atomic constitution of the individual chlorides, is explained in most of the standard works on general analysis. SILVER. Ag = 107-97. 1 CC or 1 dm. /jj solution of chloride of sodium = 0-010797 Gm. or 0-10797 gm. metallic sUver; also 0-016997 Gm. or 0-16997 grn. nitrate of silver. Decinormal Solution of Cblorlde of Sodium.— See Sect. 74. Declnormal Solution of SUver.— See Sect. 74. § 76. The determination of silver is precisely the converse of the operations just described under chlorine, and the process may either be concluded by adding the chloride of sodium tiU no further precipitate is produced, or the chromate of potash may be used as indicator. In the latter case, however, it is advisable to add the chloride solution in excess, then a drop or two of chromate solution, and titrate residuaUy with -^-^ silver solution, till the red colour is produced, for the excess of chloride of sodium. § 76. SILVER. 187 1. Analysis of the SUver Solutions used In Photography. The silver bath, solutions for sensitizing coUodion and paper frequently require examination, as their strength is constantly lessening. To save calculation, it is better to use an empirical solution of salt than the systematic one described above. This is best prepared by dissolving 43 grains of pure chloride of sodium in 10,000 grains of distilled water ; each decem (^10 grs.) of this solution wUl precipitate 0-125 grn. (i.e. ■J grn.) of pure nitrate of silver, therefore if 1 fluid drachm of any silver solution be taken for examination, the number of decems of salt solution required to precipitate all the silver will be the number of grains of nitrate of silver in each ounce of the solution. Example : One fluid drachm of an old nitrate of silver bath was carefuUy measured into a stoppered bottle, 10 or 15 drops of pure nitric acid and a little distilled water added ; the salt solution was then cautiously added, shaking well after each addition until no further precipitate was produced , the quantity required was 26-5 dm., =26 J grains of nitrate of silver in each ounce of solution. Crystals of nitrate of silver may also be examined in the same way, by dissolving say 30 or 40 grs. in an ounce of water, taking one dram of the fluid and titrating as above. In consequence of the rapidity and accuracy with which silver may be determined, when chromate of potash is used as indicator, some may prefer to use that method. It is then necessary to have a standard solution of silver, of the same chemical power as the salt solution ; this is made by dissolving 125 grains of pure and dry neutral nitrate of silver iii 10,000 grs. of distilled water ; both solutions will then be equal, volume for volume. Suppose, therefore, it is necessary to examine a silver solution used for sensitizing paper. One dram is measured, and if any free acid is present, cautiously neutralized with a weak solution 188 ANALYSIS BY PEECIPITATION. § 76. of carbonate of soda ; 100 dm. of salt solution is then added witli a pipette, if the solution is under 100 grs. to the ounce the quantity wiU be sufficient. 3 or 4 drops of solution of chromate of potash are then put in, and the silver solution delivered from the burette until the blood-red colour of chromata of silver is just visible. Suppose that 25 -5 dm. have been required, let that number be deducted from the 100 dm. of salt solution, which ■wlU leave 74'5 dm., or 74^ grains to the ounce. This method is much more likely to give exact results in the hands of persons not expert in analysis than the ordinary plan by precipitation, inasmuch as with collodion baths, containing as they always do iodide of silver, it is almost impossible to get the supernatant liquid clear enough to distinguish the exact end of the analysis. 2. Estimation of Sliver, In Ores and Alloys, by Iodide of Starcb, Hetbods of Flsanl and F. Field, (very accurate In the absence of mercury, protoxides, and salts of tin. Iron, and manganese, antimony, arsenlous acid, and chloride of gold.) If a solution of the blue iodide of starch be added to a neutral solution of nitrate of silver, while any of the latter is in excess the blue colour disappears, the iodine entering into combination with the silver; as soon as aU the silver is thus saturated the blue colour remains permanent and marks the end of the process; the reaction is very delicate, and the process accurate in the absence of the metals and salts mentioned above, it is more especiaEy applicable to the analysis of ores and alloys of silver containing lead and copper. The solution of iodide of starch devised by Pisani, is made by rubbing together in a mortar 2 Gm. iodine with 15 Gm. of starch and about 6 or 8 drops of water, puttrag the moist mixture into a stoppered flask and digesting in a water-bath for about an hour or untO. it has assumed a dark bluish-gray colour, ^ater is then added tiU aU is dissolved. The strength § 76. SILTEE. 189 of the solution is then ascertained by titrating it with 10 CC of a solution of silver containing 1 Gm. in the litre ; to which a portion of pure precipitated carbonate of lime is added; the addition of this latter removes aU excess of acid, and at the same time enables the operator to distinguish the end of the reaction more accurately. The starch solution should be of such a strength that about 50 CC is required for 10 CC of the silver solution, (=0-01 Gm. silver.) F. Field, "Chem. News," vol. ii, p. 17,) who discovered the principle of this method simultaneously with Pisani, uses a solution of iodine in iodide of potassium with starch liquor. Those who desire to maie use of this plan can use the deci and centinormal solutions of iodine described in the former part of this treatise, the results being the same in either case. In the analysis of silver containing copper the solution must be considerably diluted in order to weaken the colour of the copper, a small measured portion is then taken, carbonate of lime added, and iodide of starch tUl the colour is permanent. It is best to operate with about from 60 to 100 CC, containing not more than 0-02 Gm. silver; when the quantity is much greater than this it is preferable to precipitate the greater portion with -^j chloride of sodium, and to complete with iodide of starch after filtering off the chloride. When lead is present with sUver in the nitric acid solution, add sulphuric acid and filter off the sulphate of lead, then add carbonate of lime to neutralize excess of acid, filter again if necessary, then add fresh carbonate of lime and titrate as above. 3. Assay of Commercial SUver, (Plate, Bullion, Coin, &c.,) Gay LuBsac's Method modified 1)y J. G. Mulder. For more than 30 years Gay Lussac's method of esti- mating silver in its alloys has been practised intact, at all the European mints under the name of the "humid method," in place of the old system of cupeUation ; during that time it has 190 ANALYSIS BY PEECIPITATION. § 76. been regarded as one of the most exact methods of quantitative analysis; the researches of Mulder, however, into the inner- most details of the process have shewn that it is capable of even greater accuracy than has hitherto been gained by it. For the particulars of Mulder's investigations I cannot do better than refer the reader to the excellent translation of his memoir, published in the " Chemical M"ews," by my friend Dr. Adriani, of Edinburgh. The principle of the process is the same as described under the head of chlorine, depending on the affinity which that body has for silver in preference to all other substances, and resulting in the formation of chloride of silver, a compound insoluble in dilute acids, and which readily separates itself from the liquid in which it is suspended. The plan originally devised by the illustrious inventor of this process for assaying silver and which is stUl followed, is to consider the weight of alloy taken for examination to consist of 1000 parts, and the question is to find how many of these parts are pure silver. This empirical system was arranged for the convenience of commerce, and being now thoroughly estab- lished it is the best plan of procedure ; if, therefore, a standard solution of salt be made of such strength that 100 CC wiU exactly precipitate 1 gramme of silver, it is manifest that each -jiy CC wOl precipitate 1 milligramme or ^^^^o^th part of the gramme taken, and consequently in the analysis of 1 gramme of any alloy containing silver, the number of jJ^ CC required to precipitate aU the silver out of it would be the number of thousandths of pure silver contained in the specimen. In practice, however, it would not do to foUow this plan precisely, inasmuch as neither the measurement of the standard solution nor the ending of the process would be gained in the most exact manner, consequently a decimal solution of salt, one-tenth the strength of the standard solution, is prepared, so that 1000 CC will exactly precipitate 1 gramme of silver, and, therefore, 1 CC one milligramme. § 76. SILVER. 191 The silver aUpy to be examined, (the composition of which must be approximately known,) is weighed so that about 1 gramme of pure silver is present, it is then dissolved in pure nitric acid by the aid of a gentle heat, and 100 CC of standard solution of salt added from a pipette in order to precipitate exactly 1 Gm. of silver, the bottle containing the mixture ia then well shaken until the chloride of silver has curdled, leaving the liquid clear. The question is now — Which is in excess, salt or silver t A drop of decimal salt solution is added, and if a precipitate is produced, 1 CC is delivered in, and after clearing, another, and so on as long as a precipitate is produced ; if on the other hand the one drop of salt produced no precipitate, showing that the pure silver present was less than 1 Gm., a decimal solution of silver is used, prepared by dissolving 1 Gm. pure sUver in pure nitric acid and diluting to 1 litre, this solution is added after the same manner as the salt solution just described, until no further precipitate occurs ; in either case the quantity of decimal solution used is noted, and the results calculated in thousandths for 1 Gm. of the alloy. The process thus shortly described is that originally devised by Gay Lussac, and it was taken for granted that when equivalent chemical proportions of silver and chloride of sodium were brought thus in contact that every trace of the metal was precipitated from the solution, leaving nitrate of soda and free nitric acid only in solution. The researches of Mulder, however, go to prove that this is not strictly the case, but that when the most exact chemical proportions of silver and salt are made to react on each other, and the chloride has subsided, a few drops more of either salt or silver solution will produce a further precipitate, indicating the presence of both nitrate of silver and chloride of sodium in a state of equilibrium, which is upset on the addition of either salt or silver. Mulder decides, and no doubt rightly, that this peculiarity is owing to the presence of nitrate of soda. 192 ANALYSIS BY PRECIPITATION. § 76. and varies somewliat with the temperature and state of dilution of the liquid. It therefore foUows that when a silver solution is carefully precipitated, first hy concentrated and then by dilute salt solu- tion, tmtU no further precipitate appears, the clear liquid will at this point give a precipitate with dilute silver solution, and if it be added till no further cloudiness is produced, it will again be preoipitable by dilute salt solution. For example : Suppose that in a given silver analysis the decimal salt solution has been added so long as a precipitate is produced, and that 1 CO (=20 drops of Mulder's dropping apparatus) of decimal silver is in turn required to precipitate the apparent excess, it would be found that when this had been done, 1 CC more of salt solution would be wanted to reach the point at which no further cloudiness is produced by it, and so the changes might be rung time after time ; if, however, instead of the last 1 CC (=20 drops) of salt, half the quantity be added, that is to say 10 drops (= Yj CC); Mulder's so-called neutral point is reached, namely, that in which, if the liquid be divided in half, both salt and silver wiU produce the same amount of precipitate. At this stage the solution contains chloride of silver dissolved in nitrate of soda, and the addition of either salt or silver expels it from solution. A silver analysis may therefore be concluded in three ways — 1. By adding decimal salt solution until it just ceases to produce a cloudiness. 2. By addiug a slight excess of salt, and then decimal silver tiU no more precipitate occurs. 3. By finding the neutral point. According to Mulder the latter is the only correct method, and preserves its accuracy at aU temperatures up to 56° C (=133° Fahr.) whUe the difierence between 1 and 3 amounts to y, a mOligramme, and that between 1 and 2 to 1 milli- gramme on 1 gramme of silver at 16° C (=62° Fahr.) and is seriously increased by variation of temperature. § 76. SILTEK. 193 It will readily he seen that much, more trouble and care is required by Mulder's method than by that of Gay Lussac, but as a compensation, much greater accuracy is obtained. On the whole, it appears to me preferable to weigh the alloy so that slightly more than 1 Gm. of silver is present, and to choose the ending No. 1, adding drop by drop the decimal salt solution until just a trace of a precipitate is seen, and which, after some practice, is known by the operator to be final. It wiU be found that the quantity of salt solution used will slightly exceed that required by chemical computation — say 100-1 CC are found equal to 1 Gm. silver, the operator has only to calculate that quantity of the salt solution in question for every 1 Gm. silver he assays in the form of alloy, and the error produced by the solubility of chloride of silver in nitrate of soda is removed. If the decimal solution has been cautiously added, and the temperature not higher than 62° Fahr., this method of con- elusion is as reliable as No. 3, and free from the possible errors of experiment, for it requires a great expenditure of time and patience to reverse an assay two or three times, and each time cautiously adding the solutions, drop by drop, then shaking and waiting for the Uquid to clear, beside the risk of discolouring the chloride of silver, which would at once vitiate the results. The decimal silver solution, according to this arrangement, would seldom be required ; if the salt has been incautiously added, or the quantity of aUoy too little to contain 1 Gm. pure silver, then it is best to add once for all 2, 3, or 5 CC, accord- ing to circumstances, and finish with decimal salt as No. 1, deducting the silver added. The standard Solutions and Necessary Apparatus. a. Standard Solution of Salt. Pure chloride of so- dium is prepared by treating a concentrated solution of the 194 ANALYSIS BY PRECIPITATION. § 76. whitest table salt first -with a solution of caustic baryta to remove sulpbuiic acid and magnesia, tben witb a slight excess of carbonate of soda to remove baryta and lime, warming and allowing the precipitates to subside ; then evapo- rating to a small bulk, that crystals may form ; these are separated by a filter, and slightly washed with cold distilled water ; dried, removed from the filter, and heated to dull red- ness, and when cold preserved in a well-closed bottle for use. The mother Uquor is thrown away or used for other purposes. Of the salt so prepared, or of chemically pure rock-salt (Steinsalz, a substance to be obtained freely in Germany) 5 -4 145 Gm. is to be weighed and dissolved in 1 Htre of distilled water at 62° Pahr. 100 CC of this solution will precipitate exactly 1 Gm. silver ; it is preserved in a well-stoppered bottle, and shaken before use. Decimal Solution of Salt. 100 CC of the above solution is diluted to exactly 1 litre with distilled water at 62° Pahr. 1 CC wiU precipitate 0-001 Gm. silver. h. Decimal Solution of Silver. Pure metallic sUver is best prepared by galvanic action from pure chloride ; and as clean and secure a method as any, is to wrap a lump of clean zinc, into which a silver wire is melted, with a piece of wetted bladder or calico, so as to keep any particles of impurity contained in the zinc from the sUver. The chloride is placed at the bottom of a porcelaiu dish, covered with dilute sulphuric acid, and the zinc laid in the middle ; the silver wire is bent over so as to be immersed in the chloride ; as soon as the acid begins to act upon the zLuc, the reduction com- mences in the chloride and grows gradually all over the mass ; the resulting finely-divided silver is well washed, first with dilute acid, then with hot water, tiU all acid and soluble zinc are removed. The moist metal is then mixed with a little carbonate of soda, saltpetre, and borax, say about an eighth part of each, and dried perfectly. § 76. SILVEE. 195 The metallic silver olDtaiiied as above is never free altogether from organic matter and undecomposed chloride, and, therefore, it must invariably be melted. Mulder recommends that the melting should be done in a porcelain crucible, immersed in sand contained in a common earthen crucible; borax is sprinkled over the surface of the sand so that it may be somewhat vitrified, that in pouring out the silver when melted no particles of dirt or sand may fall into it. If the quantity of metal is smaU it may be melted in a porcelain crucible over a gas blow- pipe. The molten metal obtained in either case can be poured into cold water and so granulated, or upon a slab of pipe-clay, into which a glass plate has been pressed when soft so as to form a shallow mould. The metal is then washed well with boiling water to remove accidental surface impurities, and rolled into thin strips by a goldsmith's miU, in order that it may be readily cut for weighing ; the granulated metal is, of course, ready for use at once without any rolling. 1 Gm. of this silver is dissolved in pure dilute nitric acid and diluted to 1 litre — each CC contains 0-001 Gm. silver — it should be kept from the light. Dropping Apparatus for concluding the Assay. Mulder constructs a special affair for this purpose, consisting of a pear-shaped vessel fixed in a stand, with special arrange- ments for preventing any continued flow of liquid, the delivery tube has an opening of such size that 20 drops measure exactly 1 CC — the vessel itself is not graduated. As this arrangement is of more service to assay than to general laboratories, it need not be further described here. A smaU burette divided in ^Jjj CC with a convenient dropping tube will answer every purpose, and possesses the further advantage of recording the actual volume of fluid delivered. The 100 CC pipette, for delivering the concentrated salt solution, must be accurately graduated, and should deliver exactly 100 Gm. of distilled water at 62 Fahr. 2 196 ANALYSIS BY PEECIPITATION. § ^^• The test bottles, holding about 200 CC, should have their stop- pers well ground and brought to a point, and should be fitted into japanned tin tubes reaching as high as the neck, so as to preserve the precipitated chloride from the action of light, and, when shaken, a piece of black cloth should be covered over the stopper. c. Titration of the Standard Salt Solution. From what has been said previously as to the principle of this method, it will be seen that it is not possible to rely abso- lutely upon a standard solution of salt, containing 5-4145 Gm. per Utre, although - this is chemically correct in its strength. The real working power must be found by experiment. From 1-002 to 1-004 Gm. of absolutely pure silvec is weighed on the assay balance, put -into a test bottle with about 5 CC of pure nitric acid about 1 -2 spec, grav., and gently heated in the water or sand bath tiU it is all dissolved. The nitrous vapours are then blown from the bottle, and it is set aside to cool down to about 62° Fahr. The 100 CC pipette, which should be securely fixed in a support, is then carefully filled with the salt solution, and delivered into the test bottle contained in its case, the moistened stopper inserted, covered over with the black velvet or cloth, and shaken continuously till the chloride has clotted and the liquid beeomea clear; the stopper is then slightly lifted and its point touched against the neck of the bottle to remove excess of liquid, again inserted, and any particles of chloride washed down from the top of the bottle by carefully shaking the clear liquid over them. The bottle is then brought under the decimal salt burette, and J CC added, the mixture shaken, cleared, another J CC put in, and the bottle lifted partly out of its case to see if the precipitate is considerable; lastly, 2 or 3 drops only of the solution are added at a time unto, no further opacity is produced by the final drop. Suppose, for instance, that in titrating the salt solution it is found that 1-003 Gm. silver require 100 CC concentrated, and 4 CC deci- mal solution, altogether equal to 100-4 CC concentrated, then — § 76. SILVEK. 197 1-003 silver : 1004 salt :: I'OOO : x. a;=100-0999. The result is -within -1-5,^^^ of 100-1, which is near enough for the purpose and may be more conveniently used. The operator therefore, knows that 100-1 CC of the concentrated salt so- lution at 62° Fahr. will exactly precipitate 1 Gm. silver, and calculates accordingly in his examination of alloys. In the assay of coin and plate of the English standard, namely, 11-1 silver and 0-9 copper, the weight corresponding to 1 Gm. silver is 1-081 Gm., therefore, in examining this alloy 1 -085 Gm. may be weighed. When the quantity of silver is not approximately known, a preliminary analysis is necessary, which is best made by dis- solving J or 1 Gm. of the alloy in nitric acid, and precipitating very carefully with the concentrated salt solution from a -jJ^ CC burette. Suppose that in this manner 1 Gm. of alloy required 45 CC salt solution, 100-1 salt : 1-000 silver :: 45 : a; a;=0-4495, and again 0-4495 : 1 :: 1003 : a;=2-231. 2-231 Gm. of this particular alloy are therefore taken for the Where alloys of silver contain sulphur or gold, with small quantities of tin, lead, or antimony, they are first treated with a small quantity of nitric acid so long as red vapours are dis- engaged, then boiled with concentrated sulphuric acid till the gold has become compact, set aside to cool, diluted with water, and titrated as above. Assaying on the Grain System. It will be readily seen that the process just described may quite as conveniently be arranged on the grain system by sub- stituting 10 grains of silver as the unit in place of the gramme, each decern of concentrated salt solution would then be equal to -Tijth grain of silver, and each decern of decimal solution to xJstli grain. 198 ANALYSIS BY PEECIPITATION. § 77. CYANOGEN. C2lSr=26. 1 CC or 1 dm. j\ silver solution = 0-0052 Gm. or 0-052 grn. Cyanogen. „ =0-0054 Gm. or 0-054 gm. Hydrocyanic acid. = 0-01302 Gm. or 0-1302 grn. Cyanide of potassium. ^5 iodine = 0-003255 Gm. or 0-03265 grn. Cyanide of potassium. 1. Llebig's Method. § 77. This ready and beautiful method of estimating cyan- ogen in prussic acid, alkaline cyanides, &c., was discovered by Liebig, and is fuUy described in the "Ann. der Chemie uni Pharm.," vol. Ixxvii, p. 102. It is based on the fact, that when a solution of nitrate of silver is added to an alkabne solution containing cyanogen, with constant stirring, no permanent precipitate of cyanide of silver occurs until aU the cyanogen has combined with the alkali and the silver, to form a soluble double salt ; (in the presence of potash, for example, KCy, AgCy.) If the slightest excess of silver, over and above the quantity required to form this combination, be added, a perma ■ nent precipitate of cyanide of silver occurs, the double compoimd being destroyed. If, therefore, the silver solution is of known strength, the quantity of cyanogen present is easily found ; 1 eq. of silver in this case being equal to 2 eq. cyanogen. So fast is this double combination that when chloride of sodium is present, no permanent precipitate of chloride of silver occurs until the quantity of silver necessary to form the compound is slightly overstepped. § 77. CYANOGEN. 199 In all cases the solution to be titrated must be rendered alkaline, if not abeady so. Essential oil of bitter abnonds, or its spirituous solution, need generally the addition of a quantity of strong spirit to prevent turbidity, from the separation of the essential oU, which would otherwise interfere with the delicacy of the reaction. When no alkali is present, it is still possible to titrate a solution containing cyanogen with silver, but in this case the precipitate of cyanide of silver appears at once, and double as much silver is required as when alkali is present. When the titration is conducted in this manner, the manipulations are precisely the same as with the determination of chlorine by silver, the silver solution being added, with constant shaking, until no further precipitate occurs. Liebig's method is how- ever preferable. Example with hydrocyanic acid : In order that each CC or dm. of -jjj silver solution should represent 1 per cent, of anhy- drous acid, it would be necessary to take 0-54 CC or dm. for the analysis, but this is too little to measure with accuracy, it is better to take ten times this quantity, =5-4 CC or dm. ; if the number of CC or dm. of silver solution required to produce the turbidity be divided by 10, or the decimal point moved one place to the left, the figures will represent the percentage of real prussic acid present. 5-4 CC, therefore, of the so called Scheele's hydrocyanic acid were carefully taken with a pipette, mixed with a small quantity of solution of potash, and titrated with -jjj silver, of which 42'5 CC were required ; the quantity of real acid contained in the sample was 4-25 "Z,. 5-4 dm. of the Acid. Hydrocy. dil. P. L. were titrated as above and 19 dm. -f^ silver required=l-9 "/„ real acid. The Pharmacopoeia orders the strength to be 2 per cent. 54 dm. Aq. Lauro Cerasi titrated as above required 9 -5 dm., the strength was therefore O-OQS"/^ the decimal point being re- moved two places to the left, as 100 times the quantity was taken. 200 ANALYSIS BY PEEClPITATION. § 77. Caution. — In using the pipette for measuring hydrocyanic acid, it is advisable to insert a plug of cotton wool, slightly moistened with nitrate of silver, into the upper end, so as to avoid the danger of inhaling any of the acid, otherwise it is decidedly preferable to weigh it. Example with cyanide of potassium : The quantity of this substance necessary to be taken for analysis, so that each CC or dm. shall be equal to 1 per cent, of the pure cyanide, is 1'30 Gm. or 13"0 grn. 13 grains, therefore, of the commercial article were dissolved in water, no further alkaU being necessary, and 54 dm -^jj silver required to produce the permanent tur- bidity, the sample therefore contained Siy^ of real cyanide. The large quantities of this material used at the present time in electro-plating and photography render it frequently desirable to ascertain its chemical strength. 2. metbod of Fordo s and Gells. This process, which is principally applicable to alkaline cyanides, depends on the fact that when a solution of iodine is added to one of cyanide of potassium the iodine loses its colour so long as any undecomposed cyanide remains. The reaction may be expressed by the following formida : — ■ CyK-|-2I=IE-|-ICy. Therefore, 2 at. iodine represent 1 at. cyanogen in combination ; so that 1 CC of ^ iodine expresses the half of T^ij,^^^ at. cyanogen or its compounds. The end of the reaction is known by the yellow colour of the iodine solution becoming per- manent. Commercial cyanides are, however, generally contaminated with caustic or monocarbonated alkaUes, which would equally destroy the colour of the iodine as the cyanide, consequently, these must be converted into bicarbonates, best done by adding carbonic acid water, (ordinary soda water.) § 78. PHOSPHORIC ACID. 201 Example: 5 Gm. cyanide of potassiuin were weighed and dissolved in 500 CC water, then 10 CO (=0-1 Gm. cyanide) taken with a pipette, diluted with about ^ litre of water, an ounce or two of soda water added, then -fjy iodine deliyered from the burette until the solution possessed a slight but permanent yellow colour, 25-6 CO were required, which multi- plied by 0-003255 gave 0-08300 Gm., instead of 0-1 Gm. or 83°/, real cyanide. PHOSPHOEIC ACID. P06=71. 1. By Precipitation as Phosphate of TTranium with Ferrocyanlde of Potassium as Indicator. § 78. This method is based on the fact that when nitrate or acetate of uranium is added to a solution of tribasic phosphoric acid containing acetate of ammonia and free acetic acid, the whole of the phosphoric acid is thrown down as double phos- phate of uranium and ammonia, having a light lemon colour, and the composition 2 (Urj 0,), NH^ 0, POj-l-Aq. When this precipitate is washed with hot water, dried and burned, the ammonia is entirely dissipated, leaving phosphate of uranium, which possesses the formula 2 (Ui^ Oj), PO,, and contains in 100 parts 80-09 sesquioxide of luanium and 19-91 phosphoric acid. In the presence of fixed alkalies, instead of ammonia, the precipitate consists simply of phosphate of uranium. By this method phosphoric acid may be completely removed from all the alkalies and alkaline earths ; also, with a slight modification, from iron ; not, however, satisfactorily from alu- mina when present in any quantity. The details of the process were fully described by me in the "Chemical News," February 4th, 1860, and immediately after the pubUcatiou of that article, while employed in further in- 202 ANALYSIS BY PRECIPITATION. § 78. vestigation of tte subject, I devised the volumetric method now to he described. Since that time it has come to my knowledge that Ifeubauer and Pinous had independently of each other and myself, arrived at the same process. This is not to he wondered at, if it be considered how easy the step is from the ordinary determination by weight to that of measure, when the deUcate reaction between uranium and ferrocyanide of potassium is known. Moreover, the great want of a really good volu- metric process for phosphoric acid in place of those hitherto used, has been felt by all who have anything to do with it, and consequently the most would be made of any new method pos- sessing so great a claim to accuracy as the ordinary estimation of phosphoric acid by uranium undoubtedly does. Neubauer appears to have been the earliest discoverer of the method. ("Archiv fiir wissenschaftliche HeUkunde," Bd. iv, p. 228.) The experiments of Pincus were announced in the "Journal fiir Prakt. Chem.," 76, 104, neither of which publi- cations have I been able as yet to obtain. My own were not publicly described, inasmuch as the preparation of this book was in hand, and the process intended for insertion here. The great advantages possessed by the method over Liebig's and Eaewsky's iron process are that the combination between the phosphoric acid and uranium is definite and certain, and that the mixture needs no filtration, since phosphate of uranium produces no colour with ferrocyanide of potassium, like phos- phate of iron. For the ready and accurate determination of phosphoric acid in manures and urine, the process is very serviceable. Preparation of Standard Solutions. Phosphate of Soda. 50-218 Gm. of pure crystallized phosphate of soda, freed from extraneous moisture by powder- ing and pressing between sheets of filtering paper, are dissolved in water, and the solution diluted to 1 litre ; or 502 -2 grains to § 78. PHOSPHORIC ACID. 203 1000 dm. 1 CC or 1 dm. of the solution so obtained represents 0-01 Gm. or 0-1 grn. phosphoric acid. Solution of Uranium. This is test made by dissolving crystals of nitrate of uranium in distilled water ; the exact strength of the solution is then found by titrating a measured portion of the standard phosphate of soda -with it as foUows : — ■ 50 CC of the latter are measured into a beaker, 3 or 4 CC of solution of ammonia added, then acetic acid in excess, and the mixture gently warmed ; the beaker is then brought under a burette containing the uranium solution, and portions of it de- livered in from time to time with constant stirring, untU, when a drop taken out with a thin glass rod and placed in the middle of another larger drop of solution of yellow prussiate of potash (1 ; 20) on a white plate, a faint but distinct chocolate brown colour is produced at the point of contact. A few moments should be allowed to elapse on the addition of each portion of uranium solution before testing, as the decomposition is not very rapid unless the fluid is considerably heated. Suppose that in this way the reaction has been produced with 29-5 CC of the uranium solution, that quantity is equivalent to 0-50 Gm. PO5 ; to save calculation, however, it is advisable to dilute it to the same strength as the phosphate of soda, which is done by measuring 295 CC, and adding distilled water to make up 500 CC or 590 CC to 1 litre. In case the point of saturation is overstepped in any analysis, a portion of the phosphate solution may be added, and the analysis corrected without loss of material. For most technical purposes the plan just described is sufficiently exact, but it must be borne in mind, that in order to produce the brown colour, a certain excess of uranium is necessary, and the excess required varies with the quantity of liquid ; for it is manifest, that if the original uranium solution is titrated as above, so that the amount of fluid is about 4 oz., it would require a few drops less of the standard solution to produce the same shade of colour when the same quantity of phosphoric acid was contained in only 2 oz. 204 ANALYSIS BY PKECIPITATION. § ^8. Consequently, wlien greater accuracy is required, the follomng plan should be adopted: — The uranium solution is contained in a burette graduated to -j^g- CC ; 20 CC or thereabouts of the phosphate of soda are measured into a beaker, together with the requisite quantities of ammonia and acetic acid, the proportions of which, in any analysis, should always be as near as possible the same as used in the original titration; the rest of the manipulation is conducted as just described. When a sufficient quantity of the uranium has been added, to produce the distinct colour with a drop of ferrocyanide, the height of the total fluid in the beaker is marked by a slip of gummed paper, the con- tents emptied, and the glass again filled to the same height with water containing the same quantities of ammonia and acetic acid as were added to the phosphate, the uranium is then added, drop by drop, until a drop of the mixture produces the same amount of colour with ferrocyanide, as in the previous case; the quantity of uranium so required is deducted from that used for the phosphate, and thus the proportion found which was absolutely required to precipitate the phosphoric acid. If the same plan is pursued in all analyses, the greatest possible accuracy will be obtained however variable the amount of fluid. Undermost circumstances, however, the difierence between the two methods is slight, unless the quantity of fluid varies considerably, but as the reaction of uranium with ferrocyanide is less sensitive in the presence of acetate of soda or ammonia than iron, the correction should be. adopted where great accuracy is required. The process requires some amount of practice to ensure the best results, but when that is attained it is thoroughly reliable. The following example is given as an evidence of the accuracy of results when no correction is made for the quantity of fluid:— 20 CC of the standard phosphate of soda were precipitated with the magnesia mixture for the estimation of phosphoric § 78. PHOSPHOEIG ACID. 205 acid, and yielded pyrophosphate of magnesia equal to 0-199 Gm. 20 CC of the same phosphate solution were titrated with uranium solution, and required 10 '7 CC to produce the faint brown colour ; the mixture so prepared was diluted, boiled, and the precipitate washed by decantation through a filter, then collected, dried, and ignited, yielding 1-009 Gm. 2 (Urj03)P0, =0-2009 Gm. POj, instead of 0-199 Gm., or 100-7 instead of 100. The process is applicable, volumetrically, to aU phosphates of the first and second groups, but not to any of the so-called sesquioxides, having the formula MjOj, nor is it available in the presence of arsenic acid or any metals giving coloured precipitates with ferrocyanide of potassium, such as copper, &c. The so-called superphosphates of Hme and other manures containing soluble phosphoric acid are very readily examined by this method — since it is only necessary to lixiviate them at first with warm, and lastly with boiling, water, add ammonia to the liquid, then acetic acid in excess, and titrate at once. Iron or alumina, if present in the manure, wiU not be found, generally speaking, in the watery extract, or if so, only in very slight traces and will be left insoluble on the addition of the acetic acid. Should this be the case it is best to dUute the watery solution to a definite volimie, allow the precipitate to settle thoroughly, and take an aliquot portion of the clear liquid for titration with uranium. When the watery solution is highly coloured with organic matter, it should be evaporated to dryness with a little nitric acid, then redissolved for titration. Bones and bone-ash are dissolved in hydrochloric acid; the phosphates of Hme and magnesia precipitated with ammonia, redissolved in acetic acid, then titrated as before. Manures or other phosphoric acid compounds containing iron or alumina or both, are best dissolved in hydrochloric acid, and the whole of the phosphoric acid precipitated as a mixture of phosphates of Hme, magnesia, iron, and alumina, by ammonia 206 ANALYSIS BY PEECIPITATION. § 78. in excess J the precipitate is brought upon a filter and the liquid drained away, the precipitate slightly washed, and when sulfi- ciently drained it is treated two or three times with acetic acid on the filter, then washed, and the filtrate and washings con- taining aU the phosphate of lime and magnesia collected and set aside. The residue on the filter, consisting of phosphate of iron and alumina, is dissolved on the filter with hydrochloric acid, the filter washed clean, and the acid filtrate and washings mixed with a tolerable quantity of tartaric acid, then a clear solution of ammonia, chloride of ammonium, and sulphate of magnesia added in excess to separate aU the phosphoric acid as double phosphate of magnesia and ammonia; the solution should be allowed to stand 4 or 5 hours in a slightly warm place, the precipitate then collected in a filter, Tirashed with ammoniaoal water, then dissolved on a filter with acetic acid, and the solution so obtained mixed vrith the former liquid, and titrated with uranium as before described ; the result gives the total amount of phosphoric acid present. If lime only is present with the iron and alumina it is preferable to precipitate it first as oxalate, by adding oxalate and acetate of ammonia (the latter in good quantity) to the hydrochloric acid solution. The filtrate and washings are then treated with the tartarized magnesia solution to precipitate all the phosphoric acid. Magnesia Solution for Precipitating Phosphoric Acid. Crystallized sulphate of magnesia 1 part Pure chloride of ammonium 1 „ Distilled water 8 parts Solution of ammonia lOYo (-96 spec, grav.) 4 „ After standing a few days filter for use. § 78. PHOSPHOEIC ACID. 207 Tartarlzed Magnesia Solution for Precipitating Fhospboilc Acid in the presence of Iron and Alumina. Crystalliiied sulphate of magnesia 12 parts „ tartaric acid 15 „ Pure chloride of ammonium 16 „ Water _ 1000 „ Where the amounts of iron and alumina are very large in comparison with the phosphoric acid, it is better to adopt the method of separation originally proposed by Eeynoso and afterwards modified by Girard, namely, as phosphate of tin. To the solution of the substance in nitric acid pure granu- lated metallic tin is added, in the proportion of 5 or 6 parts to every part of phosphoric acid supposed to be present, and the mixture digested on the water bath for 2 or 3 hours, the fluid is then carefully decanted off through a filter, and repeatedly washed by decantation with hot water; yellow sulphide of ammonium is then added to the precipitate in the beaker to dissolve all the phosphate of tin, and whatever traces may have been retained on the filter are removed by eventually passing the sulphide solution through it; the insoluble compounds of alumina and iron are thus retained on the original filter, and washed with water containing sulphide of ammonium. Mag- nesia solution is then added to the clear greenish-yellow filtrate and washings, to precipitate all the phosphoric acid as double phosphate of magnesia and ammonia, which is collected, washed with ammoniacal water, dissolved in acetic acid, and titrated with uranium as before described. It is of great importance that a sufficient quantity of acetate of ammonia, soda, or potash is always present in titrating with nitrate of uranium, lest any nitric acid should be set free and interfere with the accuracy of the results. On the other hand, a great excess interferes with the delicacy of reaction with ferrocyanide. The acetate of uraniimi may be used instead of 208 ANALYSIS BY PEECIPITATION. § 78. nitrate, but as its solution is decomposed to a certain extent by sunlight, or by empyreumatic matter in the acetic acid, the nitrate is preferable. Examples of analysis; A sample of Gibbs' Peruvian guano was examined for soluble phosphoric acid, i.e., alkaline phos- phates, and yielded pyrophosphate of magnesia equal to 2-5% phosphoric acid. The same sample yielded 2-4yo by the volumetric uranium process. A sample of Peter Lawson and Sons' phospho-guano yielded 20-08y(| biphosphate of lime by the ordinary uranium process, and 204y(, by the volumetric. The first operation occu- pying 6 hours, the second, 10 minutes. As uranium is somewhat costly it is well to collect the precipitates, where many analyses are made, in a large bottle, and when sufficient has been obtained, to recover the uranium for the same purpose by igniting the dry precipitate in a porcelain crucible, with the carbonaceous residue produced by burning tartrate of soda and potash in a covered crucible. By this means the uranium is reduced to protoxide, whUe the phosphoric acid unites with the potash and soda, and can be entirely extracted with boiling water; the insoluble protoxide is then dissolved in nitric acid and evaporated to dryness in the water-bath, redissolved in distdled water, and titrated in order to adjust its strength as before described. 2. By Precipitation as Fhospliate of Lead, (Mohr.) 1 CC or 1 dm. -^j; nitrate of lead = 0-0071 Gm. or 0-071 grn. POj 1 CC or 1 dm. „ „ = 0-0155 Gm. or 0-155grn.PO5 + 3CaO. This process devised by Mohr, and strongly recommended by him for the estimation of phosphoric acid in manures, &c., consists simply in adding the lead solution to the phosphateiB § 78. PHOSPHORIC ACID. 209 until no further precipitate is produced. Unfortunately the separation of the precipitate is tardy and imperfect, so that the end of the reaction cannot be distinguished except by taking out a portion of the clear liquid for examination ; to this end, however, the filtering tube of Dr. Beale, Fig. 15, is very serviceable ; or if the precipitation takes place in a flask so as to permit of vigorous shaking, a better separation may be ob- tained, so that a little clear liquid may be poured from the surface into a test tube. Another disadvantage is, that neither sulphuric nor hydro- chloric acids may be present in the solution to be titrated, since insoluble lead compounds would be produced by both these acids ; therefore acetic acid, or nitric acid with acetate of soda, can only be used as the solvents for the substance to be ex- Phosphate of lead is insoluble in water and cold dilute acetic acid ; it is, however, freely soluble in dilute mineral acids, and partially so in hot acetic acid. Therefore the titration must take place in cold, or only sUghtly warm liquids, (100 to 120° Fahr.) Preparation of the Standard Solutions. Since 1 eq. phosj)horic acid takes up 3 eq. of oxide of lead, it is necessary that the lead solution, in order to be decinormal as regards the phosphoric acid, should contain -^g eq. of lead. Therefore three times 16-557 Gm. =49-671 Gm. of nitrate of lead are weighed and dissolved in 1 litre of distilled water, 496-71 grn. to 1000 dm. wiU give a solution of the same strength on the grain system. A Decinormal Solution of Phosphate of Soda is required to titrate the lead solution or to correct an analysis. This is prepared by dissolving 35-8 Gm. of the pure salt in the litre, or 358 giains to the 1000 dm. This and the lead solution are then equal, volume for volume. Examples : 1 Gm. dry and pure phosphate of lime was dissolved in a small quantity of nitric acid, then diluted, acetate of soda added, and 64-3 CO lead solution required to p 210 -ANALYSIS BY PRECIPITATION. § 79. precipitate all the PO5. 64-3 x 0-0155=0-997 Gm. phosphate of lime. A repetition gave 0-996 Gm. The method is undoubtedly susceptible of good results, but requires extreme care and patience, and suffers under the great drawback of requiring the absence of sulphuric and hydro- chloric acids ; these can, however, readily be removed by baryta and silver, when necessary. SUGAR. § 79. The term sugar is applied to several bodies possessing distinct properties, and differing somewhat ia chemical compo- sition. There are only two classes, however, of general im- portance, that is to say : — 1. Those that possess the chemical composition of grape sugar or glucose, C12 Hu O12, such as the sugar contaiaed in the juice of grapes, apples, and other ripe fruit ; also that which occurs in urine in Diabetes mellittis. 2. Common cane sugar, C12 Hn On, contaiaed in the juice of the sugar cane, beet root, maple, &c. Sugars of the latter class, and also those contained in milk, dextrine, &c., may all be converted into grape sugar by boiling with weak sulphuric acid, and must all be so converted before they can be estimated by the chemical method here given. This method is based on the fact, tha;t although a mixture of pure sulphate of copper, tartrate of potash, and caustic soda, mixed in proper proportions, may be boUed without under- going change ; yet, if only a trace of grape sugar be added, a very slight warming is enough to precipitate a portion of the copper as protoxide Cuj 0. Fehling, l^eubauer, and others have very carefulj amined the reaction which takes place, and found that 3 pure grape sugar =180, is capable of reducing exactly 10 ;"™™'-'' § 79. SUGAR. 211 397 of oxide of copper (Cu 0) to the state of protoxide. There- fore, if the quantity of copper reduced by a given solution of sugar is known, it is easy to find the quantity of sugar present. There are two methods of procedure — 1. To prepare a standard solution of pure stdphate of copper with tartrate of potash and caustic soda, and add the sugar solution to a definite quantity of it until the deep blue colour has disappeared; or — 2. To add the copper solution, which may he of indefinite strength, in excess, and estimate the precipitated protoxide, either by weight or indirectly, by the method of Schwarz, § 52, 2. As the first method is susceptible of very accurate results and occupies little time, it is generally preferred. The require- ments axe as follows : — Standard Solution of Copper. 34-64 Gm. of pure crystallized sulphate of copper, previously powdered and pressed between blotting paper, are weighed and dissolved in 200 CC of distilled water; in another vessel, 173 Gm. of pure crystals of double tartrate of soda and potash, (Eochelle salt,) are dissolved in 480 CC of solution of pure caustic soda, spec, grav. 1'14. The two solutions are then mixed, and the deep clear blue solution diluted with distilled water to 1 litre. Each 10 CC of the solution so prepared, containing 0-3464 Gm. sulphate of copper, represent exactly 0-050 Gm. pure anhydrous grape sugar : the same solution may be prepared on the graitt system, as in § 80, 10. It must be preserved in a dark place, and in well-stoppered bottles, kept tolerably fuU, since, if the solution absorbs much carbonic acid, a precipitate wiU occur in boiUng even in the absence of sugar. This may, however, be prevented by adding fresh caustic alkali. In aU cases before using it for titrating a solution of sugar, 10 CC should be boiled vnth about 40 CC of water, for a few minutes, in order to be certain of its fitness. In order to obviate the difiB.culty connected with preserving the copper solution, Schiff ("Ann. d. Chem. u. Pharm.," 112, p 2 212 ANALYSIS BY PRECIPITATION. § 79. p. 369) recommends the use of dry neutral tartrate of copper, prepared by precipitating 250 Gm. crystallized sulphate of copper in strong warm solution, with 280 Gm. Eochelle salt, also ia warm solution. The light hlue precipitate is drained on * filter, washed tUl pure, and dried by exposure to the air in a slightly warm room tUl it becomes thoroughly powdery. It then possesses the formula G8H40,(|+3CuO + 6HO=265-4, and contains 29-906yo CuQ; if dried at 220° in a current of air, it is anhydrous, and possesses the atomic weight 2114, containing 37-58»/„ CuO. 3-685 Gm. of the air dried, or 2-935 Gm. of the anhydrous salt, represent 0-5 Gm. pure grape sugar. When used for estimating sugar, either of these cupric tartrates may be used by mixing the necessary weighed quantity with suffi- cient caustic soda solution to produce a clear blue liquid. However carefully the tartrate of copper is prepared, there is, I apprehend, never the same certainty respecting its composition as in the case of the sulphate ; and owiag to the fact that a certain quantity must be delicately weighed before use, many operators will prefer to pursue the general plan, which, after aU, presents no difiBculty with ordinary care and foresight. The Solution of Sngar. This must be so diluted as to contain ^ or at most iy„ sugar; jf on trial it is found to be stronger than this, it must be further diluted with a measured quantity of distilled water. If the sugar solution to be examined is of dark colour, or Ukely to contain extractive matters which might interfere with the distinct ending of the reaction, it is advisable to heat a measured quantity to boiling, and add a few drops of milk of lime, allow the precipitate to settle, then filter through animal charcoal, and dilute with the washings to a definite volume. From thick mucilaginous liquids, or those which contain a large proportion of albumiaous or extractive matters, the sugar is best extracted by Prof. Graham's dialyzer. § 79. ST7GAB. 213 Cane, beet, and maple sugar juice, or prepared sugars, are converted into grape sugar by heating 30 or 40 CC of the clarified liquid in a water bath, with 30 or 40 drops of dilute sulphuric acid, (1 to 5,) for an hdur or two, replacing the evaporated water from time to time; the acid is then neutralized with carbonate of soda, and the liquid diluted to 15 or 20 times its volume before being titrated. 100 parts grape sugar so found represent 95 parts cane sugar, or 10 CC copper solution are reduced byO'0475 Gm. cane sugar. Starch or dextrine, or substances containing them, require to be keated longer with the acid in order to insure their conversion into glucose. To convert 1 Gm. starch into dextrine and thence into sugar, it should be mixed with 10 CC cold water, smoothly, then heated gently until thick, then add 1 2 drops dilute acid as before, and boil in a small flaSk, supported obliquely on a sand- bath, for 8 or 10 hours, replacing the water from time to time, then neutralize and dilute as before. The change may be produced more rapidly and at lowe* temperature by using some form of diastase in place of sid- phuric acid; an infusion of malt is best suited to the purpose, but the temperature must not exceed 160° Fahr., (71° C); about four hours' digestion is sufficient. A like quantity of the same malt solution must be digested alone, at the Same temperatufe, and titrated for its amount of Sugar, ■yv'hich is deducted from the total quantity found in the mixture. 100 parts of grape sugar so found represent 90 parts of starch, (CuHioOio) or 10 CC copper solution, are reduced by 0'45 Gm. starch. Sugar of milk may also be converted into grape sugar by boUing for a short time with dilute sulphuric acid, for although it possesses the same ultimate composition as grape sugar, it has of itself a special and somewhat uncertain action upon the copper solution, therefore it must be converted into grape sugar before being estimated. 214 ANALYSIS BY PRECIPITATION. § 79. The Analytical Process. 10 CC of the copper solution are measured into a convenient- sized flask or a white porcelain dish, and diluted with 40 CC of water, or, if necessary, the same quantity of dilute caustic soda, and hrought to gentle hoiUng. The dilute sugar solution is then delivered in from time to time from a graduated hurette or pipette ; when the precipitated oxide of copper appears of a bright red colour, the lamp should be removed and the pre- cipitate allowed to settle ; if the flask is then held before a window, or the dish lifted on one side so as to cause the clear liquid to flow against the white porcelain, the colour may readily be seen ; should any blue tinge remain more sugar solution is added, and the boiling recommenced and continued unto. aU colour just disappears. If any doubt exists, a small portion of the hot mixture should be filtered, acidified with acetic acid, and a drop of solution of ferrocyanide of potassium added ; if copper is in excess, a brown colour or precipitate will be produced. It is almost impossible to hit the exact point on the first trial, but it afibrds a very good guide for a more exact titration the second time; the quantity of sugar solution necessary to discharge the colour from 10 CC copper solution contains 0-05 Gm. grape sugar. § 80. AN*ALTSIS OF UEINE. 215 PAET V. SPECIAL APPLICATIONS OF THE VOLUMETRIC SYSTEM TO COMPLETE QUANTITATIVE ANALYSIS. ANALYSIS OF TTRINE. § 80. The complete and accurate deteniiination of the normal and abnormal constituents of urine presents more than ordinary difficulty to even experienced chemists, and is a hopeless task in the hands of any other than such. Fortunately however the most important matters, such as urea, uric acid, phosphates, sulphates, and chlorides, can all be determined volumetricaUy with accuracy by ordinary operators, or by medi- cal men w'ho cannot devote much time to practical chemistry. The researches of Liebig, Neubauer, Bence Jones, Vogel, Beale, Hassall, and others, during the last few years, have resulted in a truer knowledge of this important secretion, and to the two first mentioned chemists we are mainly indebted for the simplest and most reliable methods of estimating its constituents. With the relation which the proportion of these constituents bear to health or disease, the present treatise has nothing to do, its aim being simply to point out the readiest and most reKable methods of determining them quantitatively. Their pathological importance is very fully treated by some of the authorities just mentioned, among the 216 ANALYSIS OF UEDTE. § 80. "worts of which Neuhauer and Vogel's "Analyse des Harns," (said to be La process of translation by the New Cavendish Society,) and Prof. Lionel Beale's "Urine, Urinary Deposits, and Calculi," are most prominent and ex- haustive. The graiu system of weights and measures wiU be adopted throughout this section, as being more readily applicable by medical men, while those who desire to use the gramme system will have no difficulty in working, when once the simple relation between them is understood, see § 6. The question of weights and measures is, however, of very little consequence, if the analyst considers that he is dealing with relative parts or pro- portions only, and as urine is generally described as containing so many parts of urea, chlorides, or phosphates, per 1000, the absolute weight may be left out of the question. The grain system, however, is more readily calculated into English ounces and pints, and therefore is generally more familiar to the medical profession of this country. One thing, however, is necessary as a preliminary to the examination of luine, and which has not generally been sufficiently considered, that is to say, the relation between the quantity of Secretion passed in a given time, and the amount of solid matters found in it by analysis. In a medical point of view, it is a mere waste of time, generally speaking, to estimate the constituents in half a pint or io of urine, passed at any particular hour of the day or night, without ascertaining the relation which that quantity, with its constituents, bears to the whole quantity passed during, say 24 hours ; and this is the more necessary, as the amount of fluid secreted varies very considerably in healthy persons ; beside this, the analyst sh6uld register the colour, peculiarity of smell, if toy, consistence^ presence or absence of a deposit, (if the fonder, it should be collected for separate analysis, filtered urine only being used iH such oases for examination,) and lastly its Reaction to litmus should be observed. 80. ESTIMATION OF CHLORIDES. 217 1. Specific Gravity. This is iDBst taken by measuring 100 dm. into an accurately tared beaker or flask, the increase of weigM in grains will be tbe spec, gray., water being 1000. 50 or 25 dm. may be taken instead of 100, in which case the weight multiplied by 2 or 4 will be the spec. grav. Where an accurate balance or weights are not at hand, a good urinometer may be used. 2. Estimation of ChlorldeB, (calculated as Chloride of Sodium.) This may be done in two ways, viz. : — o. By Nitrate of Silver, (Mohr.) 10 dm. of the ■orine are measured into a thin porcelain or platinum capsule, and 16 grains of nitrate of potash in powder added ; the whole is then evaporated to dryness, and gradually heated till the residue becomes white ; it is then dissolved in a small quantity of water, and the carbonate of potash, produced by the com- bustion of the organic matter, nearly neutralized by dilute nitric acid ; two or three drops of solution of chromate of potash are then added, and the mixture titrated with ^'j silver as in § 74. Each dm. of silver solution represents 0-058-l:6 grn. salt, consequently if 12-5 dm. have been used, the weight of salt in the 10 dm. of urine is 0-73075 grn., and as 10 dm. only was taken, the weight multiplied by 10, or what amounts to the same thing, the decimal point moved one place to the right, gives 7'3076 gi'ains of salt for 1000 of urine. In order to save calculation, it is convenient to measure 5-9 dm. of the urine, add about 10 grains of nitrate of potash, then €fvaporate, ignite, and titrate as before directed ; the number of decems of ^^ silver used will represent the number of grains of salt in 1000 grains of urine. Example : 5-9 dm. of urine passed by a patient suffering from Diabetes insipidus was evaporated and titrated as above, re- 218 ANALYSIS OF UEINE. § 80- quiring 3-1 dm. silver solution, the proportion of salt was there- fore 3-1 grn. per 1000 of uriae. Where the quantity of chlorides is small, it may he advisable to use larger quantities of urine, say 58 -5 dm. ; in that case one-tenth of the number of dm. of silver solution required wiU be the number of grains of salt per 1000 urine. b. By Nitrate of Mercury, (Liebig.) The principle of this method is as follows : — If a solution of nitrate of mer- cury, free from any excess of acid, is added to a solution of urea, a white gelatinous precipitate is produced, containing urea and oxide of mercury ia the proportion of 1 eq. of the former to 4 eq. of the • latter, (4 Hg 0-f-Ur.) When chloride of sodium, however, is present in the solution, this precipitate does not occur, untU all the chloride of sodium is converted by double decomposition into chloride of mercury (sublimate) and nitrate of soda, the solution remaining clear; if the exact point be overstepped, the excess of mercury immediately pro- duces the precipitate above described, so that the urea present acts as an indicator of the end of the process. It is therefore very easy to ascertain the proportion of chlorides in any given sample of urine by this method^ if the strength of the mer- curial solution is known ; since 1 eq. of oxide of mercury converts 1 eq. of chloride of sodium into 1 eq. each of corrosive sublimate and nitrate of soda. The strength of the standard solution of nitrate of mercury is best arranged as follows : — 1. Standard Solution of Nitrate of Mercury. It is of great importance that the solution be pure, for if the mercury from which it is made be contaminated with traces of other metals, such as bismuth, silver, or lead, they will produce a cloudiness in the liquid while under titration, which may possibly hinder the exact ending of the reaction; therefore 184 '2 gm. of the purest red oxide of mercury, or 170 '6 grn. of pure metallic mercury (the former is preferable, as being easier to weigh and less likely to be impure) are put into a beaker, with § 80. ESTIMATION OF CHLOEIDES. 219 a sufficiency of pure nitric acid of about 1-20 spec. grav. to dissolve tliem by the aid of a gentle heat, the clear solution so obtained is evaporated on the water bath to remove any excess of free acid. When the liquid is dense and syrupy in con- sistence, it may be transferred to the graduated cylinder or flask and diluted to 1000 dm. (10,000 graius,) 1 dm. of the solution so prepared is equal to 0-1 gm. chloride of sodium, or 0-06065 gm. chlorine. If on diluting the concentrated mercurial solution a yellow precipitate of basic nitrate of mercury should form, it must be allowed to settle, the clear liquid poured off, and a few drops of nitric acid added to the precipitate to redissolve it ; the whole is then mixed and preserved for future use in a well-stoppered bottle. It is always preferable to have this precipitate formed on dilution, as it is a proof of there being no excess of acid, which would considerably interfere with the accuracy of results. 2. The Baryta Solution. Before urine can be submitted to titration by the mercurial solution, it is necessary to remove the phosphoric acid, and the proper agent for this purpose is a mixture composed of 1 volume of cold saturated solution of pure nitrate of baryta and 2 volumes ditto caustic baryta ; the same agent is used previous to the estimation of urea, and may be simply designated " Baryta Solution." 3. The Analytical Process. 40 dm. of the clear urine are mixed with 20 dm. of baryta solution, and the thick mix- ture poured upon a small dry filter ; when sufficient clear liquid has passed through, 15 dm. =10 dm. urine, are taken with a pipette and just neutralized, if necessary, with a drop or two of nitric acid ; if not alkaline, the probabUity is that sufficient baryta solution has not been added to precipitate aU the phos- phoric and sulphuric acids ; this may be known by adding a drop or so of the baryta solution to the filtrate ; if any pre- cipitate is produced, it wiU. be necessary to mix off a fresh quantity of uruie with three-fourths or an equal quantity of baryta, in which case ITVi or 20 dm. must be taken to represent 220 ANALYSIS OF UEINE. § 80. 10 dm. of the urine ; the excess in either case of haryta must be cautiously neutralized with nitric acid. The vessel containing the fluid is then brought under » Mohr's burette containing the mercurial solution, and small portions delivered in with stirring, until a distinct permanent precipitate is produced ; it may happen that a turbidity is pro- duced from the very first drop or two, owing to slight impurities in the mercurial solution, but as this will not increase, the point when the urea precipitate appears is not dif&cult to de- termine; the volume of solution used is then read off and calculated for 1 000 parts of urine. Example: 15 dm. of the liquid prepared with a sample of urine, as in 3 (=10 dm. urine) required 6'2 dm. mercurial solution, the quantity of salt present was therefore 0'62 grn., or 6-2 gm. in 1000 grains of urine. 3. Estimation of Urea, (Lieblg.) The combination between urea and oxide of mercury in. neutral or alkaline solutions has been aUuded to ia the foregoing article on chlorides ; it will therefore probably be only necessary to say that the determination of urea in urine is based on that reaction ; and as the precipitate so produced is insoluble in water or weak alkaline solutions, it is only necessary to prepare a standard solution of mercury of convenient strength, and to find an indicator by which to detect the point when all the urea has entered into combination with the mercury, and the latter slightly predominates. This indicator is carbonate of soda. If, in the course of adding the mercurial solution from the burette to the urine, a drop of the mixture be taken from time to time and brought in contact With a few drops of solu- tion of carbonate of soda on a glass plate, slab, or watch glass, no change of colour is produced at the point of contact until the free urea is aH. removed ; when this is the case, and the nitrate of mercury is slightly in excess, a yellow colour is pro- duced, owing to the formation of hydrated oxide of mercury. § 80. ESTIMATION OF UBEA. 221 The compound of urea and mercury consists, according to Liebig's analysis, of 1 eq. of the former to 4 of the latter, that is to say, if the nitric acid set free by the mixture is neutralized from time to time with carbonate of soda or other suitable alkali. If this be not done, the precipitate first formed alters in character, and ■ eventually consists only of 3 eq. of mercury with 1 of urea. In order to produce the yellow colour with carbonate of soda, there must be an excess of mercurial solution; theoretically, 100 parts of urea should require 720 parts of oxide of mercury ; but practically, 772 parts of the latter are necessary to remove all the urea, and at the same time show the yellow colour with alkali, consequently the solution of nitrate of mercury must be of empirical strength, in order to give reliable results. Preparation of the Standard Solution. 772 grains of red oxide of mercury, or 715 grains of the metal itseK, are treated with nitric acid, as described in the article on chlorides, 2, b 1, and in either case diluted to 1000 dm., (10,000 grains,) 1 dm. of the soljition is then equal to O'l grn. urea. (The ex- treme care required to remove traces of foreign metals from the mercury is not so necessary here as in the foregoing instance.) 2. The Analytical Process. Two volumes of the urine are mixed with one of baryta solution, as before described in 2, b 3, of this section (reserving the precipitate for the determination of phosphoric acid, if necessary,) and 15 dm. = 10 dm. urine, taken in a small beaker for titration; it is brought under the burette containing the mercurial solution, (without neutralizing the excess of baryta, as in the case of chlorides,) and the solution added in small quantities so long as a distinct precipitate is seen to form, a plate of glass laid over dark paper is previously sprinkled with a few drops of solution of carbonate of soda, and a drop of the mixture must be brought from time to time, by means of a small glass rod, in contact with the soda ; so long as the colour remains white, free urea is present in the mixture ; when the 222 ANALYSIS OF UEINE. § 80. yellow colour is distinctly apparent, the addition of mercury is discontiaued, and the quantity used calculated for the amount of urea. It is always advisable to repeat the analysis, taking the &st titration as a guide for a more accurate estimation by the second. Example : 15 dm. of urine deprived of phosphates^lO dm. of the original urine was titrated as described, and required 17'6 dm. of mercurial solution; consequently there was 1'76 grn. urea present in the 10 dm., or 17'6 grains in the 1000 of urine. 3. Corrections and Modifications. In certaia cases the results obtained by the above method are not strictly correct, owing to the variable state of dilution of the liquids. The errors are, however, generally so slight as not to need correction. Without entering into a fuU description of their origin, I shall simply record the facts, and give the modifications necessary to be made where thought desirable. a. The Urine contains more than 2 per cent, of Urea, i.e., more than 20 grains per 1000. This quantity of urea would necessitate 20 dm. of mercurial solution for 10 dm. of uriae ; all that is necessary to be done when the first titration has shown that over 2°/ is present, is to add half as much water to the uriue in the second titration as has been needed of the mercurial solution above 20 dm. Suppose that 28 dm. have been used at first, the excess is 8 dm., therefore 4 dm. of water is added to the fluid before the second experi- ment is made. h. The Urine contains less than ^"/^ of Urea. In this case, for every 4 dm. of mercurial solution less than 20, 0-1 dm. must be deducted, before calculating the quantity of urea; so that if 16 dm. have been required to produce the yellow colour with 10 dm. urtne, 15-9 is to be considered the correct quantity. c. The Urine contains more than 1% of Chloride of Sodium, i.e., more than 10 grs. per 1000. In this case 2 dm. § 80. ESTIMATION OF UREA. 223 must be deducted from tlie quantity of mercurial solution actually required to produce the yellow colour, with. 10 dm. uriue. d. The Urine contains Albumen. In this case 50 dm. of the urine are boiled with 2 drops of strong acetic acid to coagulate the albumen, the precipitate allowed to settle thoroughly, and 30 dm. of the clear liquid mixed with 15 dm. baryta solution, filtered, and titrated for both chlorides and urea, as previously described. e. The Urine contains Carbonate of Ammonia. The presence of this substance is brought about by the decompo- sition of urea, and it may sometimes be of interest to know the quantity thus produced, so as to calculate it into urea. As its presence interferes with the correct estimation of urea direct, by mercurial solution, a portion of the urine is precipi- tated with baryta as usual, and a quantity, representing 10 dm. urine, evaporated to dryness in the water-bath to expel the ammonia, the residue then dissolved in a little water, and the urea estimated in the ordinary way. On the other hand, 60 or 100 dm. of the uriH,e, not precipitated with baryta, is titrated with normal sulphuric acid and litmus paper, (see 9,) each dm. of acid representing 0'17 gm. ammonia, or 0"30 grn. urea. Titration of the Mercurial Solutions. Properly speaking, no standard solutions should be used for analysis without being first titrated to ascertain their exact chemical power and to guard against accidental errors. How- ever pure the substances from which they are made may be thought to be, it sometimes occurs that the solutions do not strictly bear the proper strength: it may also happen that absolutely pure materials are not at hand, in which case ordi- nary kinds may sometimes be used, if the solutions made from them be tested by experiment. In the present case, should neither pure mercury or its oxide be obtainable, the commercial 224 ANALYSIS OF URINE. § 80. pietal may be dissolved in nitric acid, the solution boiled to expel all excess of the latter, then set aside that crystals of protonitrate of mercury may form, these are carefully separated from the mother liquor by diaining in a funnel lightly stuffed with cotton wool, washed with cold water, then dissolved in a small quantity of dilute nitric acid, diluted to a certain extent with water, and a measured portion titrated for the quantity of mercury by the following process devised by Lie big, which is also applicable to the estimation of peroxide of mercury for some other purposes. The principle of the process depends on the fact that phos- phate of soda precipitates phosphate of mercury from a solution of pernitrate, but not from perchloride of that metal, i^ there- fore, the solution containing the precipitate of phosphate of mercury produced in the first case, be treated with a solution of chloride of sodium, the precipitate will disappear, from the circumstance that perchloride of mercury (sublimate) and phosphate of soda are formed, which both remain in solution. Consequently, if the strength of the solution of salt is known, the quantity of mercury is easily found, since 1 eq. of salt represents 1 eq. of oxide of mercury, (in the form of phos- phate.) It is necessary, however, that directly the mercury is precipitated by the phosphate of soda, the chloride of sodium be added, otherwise the precipitate of phosphate becomes crystalline, and is not so readily decomposed by the salt. The salt solution may conveniently be decinormal, § 74, contaiaing 58-46 grn. to 100 dm. — each dm. represents 0-108 grn. HgO. The solution of phosphate of soda is simply saturated at ordinary temperature. Process: 10 dm. of the mercurial solution, not too concen- trated, are measured into a beaker ; 4 dm. of the phosphate of soda solution added, and the mixture immediately brought under the burette containiug the solution of salt, which is added carefully, with constant stirring, until the precipitate § 80. ESTIMATION OF SULPHURIC ACID. 225 just disappears. Suppose that 18-2 dm. have been required, that number multiplied by 0-108 will give 1-9656 grn. HgO in the 10 dm. of solution; but the mercurial solution for deter- mination of chlorides requires 1-842 gm. in the 10 dm.; therefore, by a rule-of -three calculation, 9-3 dm. of this par- ticular solution must be diluted to 10 dm. with water, to be of the proper strength, or 930 dm. to 1000 dm. The results so obtained are not, however, strictly correct, owing to the fact that a slight excess of salt is always necessary to redissolve the precipitate. If the process be reversed, the same objection applies, since an excess of mercury is necessary to produce a permanent precipitate. The exact point, however, is reached by combining the two methods. For instance : — Method 1. 10 dm. of mercurial solution with 4 dm. of phos- phate of soda are titrated with salt solution and require 12-5 dm. Method 2. 12-5 dm. of the same salt solution, as in 1, are measured ; 4 dm. phosphate of soda added, and titrated with the mercurial solution, of which 10-25 dm. shall be required. The following calculation will give the true power of the solutions — 1. 10 dm. mercury := 12-5 dm. salt 2. 10-25 dm. „ = 12-5 „ 20-25 dm. „ therefore = 25-0 „ As the strength of the salt solution is known, the quantity of mercury contained in the 20-25 dm. is readily ascertained by a little calculation. 4. Eatlmatlon of Sulphuric Acid. 100 dm. of the urine are measured into a beaker heated to boiHng on a sand bath, or suspended in a retort ring over a spuit lamp, and the amount of sulphuric acid determined direct with normal chloride of barium, as ia § 28, 3, using Beale's Q 226 ANALYSIS OF TmiNE. § 80. filter for ascertaining the end of precipitation ; or, a special solution of chloride of barium may be prepared by dissolving 305 grains of the pure salt in 1000 dm. of water, 1 dm. of the solution is then equal to O'l gm. SO3 ; the manipulation in either case is the same as in § 28. 5. Estimation of Fhosphorlc Acid. Hitherto the estimation of this substance volumetricaUy presented peculiar difficulties, but the discovery of the uranium process, § 78, 1, has set these entirely aside, so far as urine and many other bodies are concerned. The standard solution of nitrate of uranium is the same as described in § 78, 1, of ■which 1 dm. represents O'l grn. phosphoric acid, and the process of titration the same as there described. 50 dm. of the clear filtered urine are measured into a small ibeaker, 3 or 4 dm. of solution of ammonia, about 0-96 spec, grav., added, and the precipitate redissolved with an excess of acetic acid ; the mixture is then warmed in the water bath, or otherwise, and the uranium solution delivered in from the burette, with constant stirring, as long as a precipitate is seen to occur ; a small drop of the mixture is then removed with a thin glass rod, and placed in the middle of a drop of ferrocyanide of potassium solution, (1 : 20,) several large drops of which have been previously placed upon a white porcelain slab or plate ; so long as no brown colour is produced, the addition of uranium may be continued ; when the faintest indication of this reaction is seen, the process must be stopped, and the amount of colour observed; if it coincides with the original titration of the uranium solution with similar quantities of water, acetate of ammonia, and acetic acid, the result is satisfactory, and the quantity of solution used may be calculated for the total phosphoric acid contained in the 60 dm. of urine; if the uranium has been used accidentally in too great quantity, 10 or 20 dm. of the same urine may be added, and the titration cpncluded more § 80. ESTIMATION OF PHOSPHORIC ACID. 22? cautiously. Suppose, for example, that the solution has been added in the right proportion, and 9'6 dm used, the 50 dm. will have contained 0'96 grn. phosphoric acid. With care and some littie practice the results are very satisfactory. A rather more exact method of procedure is as follows : — The precipitate produced hy the baryta solution in 50 dm., or any other convenient quantity of urine, § 80, 2, 3, after, the fluid is filtered from it, is washed once with cold water, and treated while stiU on the filter with warm acetic acid, to dissolve all the phosphate of baryta, which passes through the filter leaving the sulphate behind ; the filter is then washed with a small quantity of boiling water, to remove the last traces of phosphate ; sufficient ammonia is added to the solution, to neutralize the acetic acid, unless the quantity of the latter be large, when somewhat less than enough to neutralize may be added ; under any circumstances the liquid must be freely acidified with acetic acid before being titrated, and must con- tain a tolerable quantity of acetate of ammonia. Where great accuracy is not required, it wiU not be necessary to make any correction for the slight excess of xiranium required to produce the brown colour with yellow prussiate of potash, as described in § 78, 1, otherwise the titration is precisely the same as there described ; 1 dm. of uranium solution precipitates O'l grn. PO5. A somewhat shorter and less troublesome method is to make a hole in the filter containing the mixed phosphate and sulphate of baryta, wash the whole precipitate with a small quantity of boiling water into a small beaker, then pour acetic acid on the filter, so as to remove all soluble matter, and add enough acetic acid to the fluid to dissolve all the phosphate ; add 3 or 4 dm. of ammonia, and if necessary, acetic acid in excess, then titrate with the uranium solution at once ; the precipitate of sulphate of baryta does not interfere with the reaction in the slightest. In examining urinary sediment or calculi for phosphates, it is simply necessary to digest them with acetic acid, wash on a filter Q 2 228 ANALYSIS OP UEINE. § 80. with, hot water, then titrate the solution and washings with viranium as ahove. Earthy Phosphates. The ahove determination gives the total amount of phosphoric acid, but it may sometimes be of interest to know how much of it is combined with lime and magnesia. To this end 100 or 200 dm. of the urine are measured into a beaker, and rendered freely alkaline with ammonia ; the vessel is then set aside for ten or twelve hours, for the precipitate of earthy phosphates to settle ; the clear fluid is then decanted through a filter, the precipitate brought upon it and washed with ammoniaoal water ; a hole is then made in the filter and the precipitate washed through, the paper moistened with a Httle acetic acid, and washed into the vessel containing the precipitate, which latter is dissolved in acetic acid, some acetate of ammonia added, and the mixture titrated as before described ; the quantity of phosphoric acid so found is deducted from the total previously estimated, and the remainder gives the quantity existing in combination with aUsalies. 6. Estimation of Uric Acid. The determination of uric acid in urine is not often con- sidered of much consequence, there are, however, circumstances under which it is desirable, especially in urinary deposits. As the quantity present in urine is very small it is necessary to take say from 300 to 500 dm. for the estimation. The urine being measured into a beaker, from 5 to 8 dm. of pure hydrochloric acid are added, the whole well mixed, covered with a glass plate, and set aside in a cool place for 24 or 30 hours; at the end of that time the uric acid wiU be precipitated, in small crystals, upon the, bottom and sides of the beaker, the supernatant liquid is decanted, washed once with cold distilled water, then dissolved in a small quantity of pure solution of potash, diluted to 6 or 8 ounces with distilled § 80. ESTIMATION OF LIME AND MAGNESIA. 229 ■water, acidified strongly with sulphuric acid, and titrated pre- cisely as oxalic acid, § 43, 3, with -^^j permanganate, each dm. of which is equal to 0'075 gm. uric acid. This method is not absolutely correct, owing to the fact that with the uric acid there is always precipitated a certain amount of colouring matter of the urine which destroys the permanganate equally with the uric acid. The method by weighing is, however, open to the same objection, beside being very troublesome, so that no advantage is gained by the latter plan. 7. Estimation of Ume and Magnesia. 100 dm. of the urine are precipitated with ammonia, the precipitate redissolved in acetic acid, and sufficient oxalate of ammonia added to precipitate all the lime present as oxalate; the precipitate is allowed to settle in a warm place, then the clear liquid passed through a smaU filter, the precipitate brought upon it, washed with hot water, the filtrate and washings set aside, then the precipitate, together with the filter, pushed through the fiuinel into a flask,, some sulphuric acid added, the liquid freely diluted, and titrated with permanganate of potash precisely as in § § 43, 3 ; 60, 1 ; each dm. of ^jy per- manganate required represents 0-028 grn. Hme. Instead of the above method the following may be adopted: — The precipitate of oxalate of Hme after being washed is dried and, together with the filter, ignited in a platinum or porcelain crucible, by which means it is converted into a mixture of caustic and carbonate of Ume. It is then trans- ferred to a flask by the aid of the washing bottle, and an excess of normal nitric acid delivered in with a pipette ; the amount of acid over and above what is required to saturate the Ume, is found, by normal caustic alkaU, precisely as described in § 18; each dm. of normal acid being equal to 0'28 grn. lime. In examining urinary sediment or calcuU for oxalate of Ume, 230 AiiTALYSIS OF URINE. § 80. it is first treated with caustic potash to remove uric acid and organic matter, then dissolved in sulphuric acid, freely diluted, and titrated with permanganate, as in § 60, 1 ; eaeh dm. ^ per- manganate represents 0'064 grn. oxalate of lime. Magnesia. The filtrate and washings from the precipitate of oxalate of lime are then made alkaline with ammonia, and set aside for 8 or 10 hours in a sHghtly warm place, that the magnesia may separate as double phosphate of magnesia and ammonia, the supernatant liquid is then passed through a small filter, the precipitate brought upon it, washed with ammoniacal water in the cold, and dissolved in acetic acid, then titrated with uranium solution, as in § § 38, 78, 1 ; each dm. of solution required represents 0-0563 grn. magnesia. Indirect estimation of the Lime and Magnesia existing as Phosphates. Two portions of the urine, each measuring 200 dm., are put into beakers^ and precipitated with ammonia in excess, as in the case of estimating earthy phos- phates, § 80, 5. In the one case the precipitate is collected, washed, dried, ignited, and weighed, the weight being noted. The precipitate from the other 200 dm. of urine, is collected, washed, and dissolved in acetic acid, and titrated for phosphoric acid with uranium. The calculation is then as follows : — The weight of phosphoric acid is multiplied by the factor 2-1831, and from the number so obtained is deducted the weight of the total earthy phosphates estimated as above. If the remainder be multiplied by 2-5227, the weight of phos- phate of magnesia will be obtained, and by difference also the phosphate of hme. The amounts of lime and magnesia are obtained as follows: — 3CaO, POe X 0-542 = CaO 2MgO,P05 X 0-3604 = MgO. The principle is the same as in the estimation of the mixed alkaline chlorides, § 75, h. § 80. AMMONIA. 231 8. Ammonia. The only metliod. hitherto applied to the determination of ammonia in urine, is that of Schlosing, which consists in placing a measured quantity of the nrine, to which milk of lime is previously added, under an air-tight beU-glass, together with an open vessel containing a measured quantity of titrated acid. In the course of from 24 to 36 hours, all the ammonia wiU have passed out of the urine into the acid, which is then titrated with standard alkali to find the amount of ammonia absorbed. One great objection to this method is the length of time re- quired, since no heating must be allowed, urea being decomposed into free ammonia, when heated with alkaK ; there is also the uncertainty as to the completion of the process, and if the vessel be opened before the absorption is perfect, the analysis is spoiled. The following plan is recommended as in most cases Suitable. When a solution containing salts of ammonia is mixed with a measured quantity of free fixed alkali of known strength, and boiled until ammoniacal gas ceases to be evolved, it is foiind that the resulting liquid has lost so much of the free alkali as corresponds to the ammonia evolved, § 16; that is to say, the acid which existed in combination with the ammonia in the original liquid has simply changed places, talcing so much of the fixed alkali (potash or soda) as is equivalent to the am- monia it has left to go free. In the case of urine being treated in this way, the urea wiU also be decomposed into free ammonia, but happily in such a way as not to interfere with the estimation of the original amount of ammoniacal salts. The decomposition is such that while free ammonia is evolved frcan the splitting up of the urea, carbonate of fixed alkali (say potash) is formed in the boiling liquid, and as this reacts equally as aEtahne as though it were free potash, it does not interfere in the slightest degree with the estimation of the ariginal ammonia. The following is the best method of procedure : — 232 ANALYSIS OF UEINE. § 80. 100 dm. of the urine are exactly neutralized with normal alkali, as in tte following article, No. 9, for the estimation of free acid ; it is then put into a flask capable of holding five or six times the quantity; 10 dm. of normal alkali added, and the whole brought to boiling, taking care that the bladders of froth which at first form do not boil over ; after a few minutes these subside, and the boiling proceeds quietly ; when all ammoniacal fumes are dissipated, the lamp is removed, and the flask allowed to cool slightly ; the contents then emptied into a taU beaker, and normal nitric acid delivered iu from the burette with constant stirring, until a fine glass rod or small feather dipped in the mixture and brought in contact with neutral or violet coloured litmus paper produces neither a blue nor red spot ; the number of dm. of normal acid are deducted from the 10 dm. of alkali, and the rest calculated as ammonia. 1 dm. alkali =0-17 grn. ammonia. Example : 100 dm. of urine were taken, as ia 9, and required 0'7 dm. normal alkali to saturate its free acid; 10 dm. alkali were then added, and the mixture boiled until a piece of moistened red litmus paper was not turned blue when held in the steam ; 4 -5 dm. of normal acid were afterward required to saturate the free alkali ; the quantity of ammonia was therefore equal to 5-5 dm.,, which multiplied by 0-17 gave 0-935 gm. in 1000 of urine. It must be borne in mind that the plan just described is not applicable to urine which has already suffered decomposition by age or other circumstances so as to contain carbonate of am- monia ; in this case it would be preferable to adopt Schlosing's method ; or where no other free alkali is present, direct titration with normal acid may be adopted. 9. Estimation of Free Add. The acidity of urine is doubtless owing to variable substances, among the most prominent of which appear to be acid phos- § 80. ESTIMATION OF DIABETIC SUGAR. 233 phate of soda and lactic acid, other free organic acids are probably in many cases present ; under these circumstances, the degree of acidity cannot be placed to the account of any particular body ; nevertheless it is frequently desirable to ascer- tain its amount, which is best done as follows : — 100 dm. of the urine is measured into a beaker, and normal alkali, § 11, delivered in drop by drop from a small burette, until a thin glass rod or feather, moistened with the mixture and streaked across some well-prepared violet litmus paper> produces no change of colour; the degree of acidity is then registered as being equal to the quantity of normaj, alkali used. 10. Estimation of Diabetic Sugar. The principle of the process is explained in § 79, and the copper solution required is precisely the same as there described, that is to say, 34*6 -4 grains of pure sulphate of copper are dis- solved in about 200 dm. of water. In another vessel 1730 grains of pure crystallized tartrate of soda and potash (EochelLe salt) are dissolved in 480 dm. of solution of pure caustic soda, spec, grav. 1-14. The two solutions are then mixed, well agitated, and diluted to 1000 dm. 1 dm. of the solution so prepared represents 0-05 grn. grape or diabetic sugar. It must be pre- served in the dark, and in well-stoppered full bottles. It should bear heating when diluted with about four or five times its quantity of distilled water, without any precipitate taking place, and should always be submitted to this test before being used ; if any does occur, it probably arises from the alkali having ab- sorbed carbonic acid ; in this case the addition of a Itttle fresh caustic soda solution remedies the evU. The Analytical Process. 10 dm. of the clear urine are diluted by means of a measuring flask to 200 dm. with water, and a large burette filled with the fluid ; 10 dm. of the copper solution (^1 grn. sugar) are then measured into a flask or white 234 ANALYSTS OF UEINE. § 80. porcelain capsule, 40 dm. of distilled water added, the vessel arranged o-^^er a spirit lamp under the burette, and brought to boiling, the dihited urine is then delivered in cautiously from the burette until the last traces of blue colour are re- moved from the copper solution and the precipitate is of a distinct red colour ; the details of the pperation are described more fully ia § 79. Suppose that 40 dm. of the diluted urine have been required to reduce the 10 dm. of copper solution, that quantity wiU have contained 0-5, i.e., j gm. sugar; but, the urine being diluted 20 times, the 40 dm. represents only 2 dm. of the original urine ; therefore 20 grains of it contain ^ grn. sugar, > or 30 grains per 1000. vll. Estimation of Albumen. a. By "Weight. 100 dm. of the clear urine, or less than that quantity if much albumen is present, the 100 dm. being made up with water, are introduced into a good-sized beaker, and heated in the water bath for half an hour. If the urine is sufBciently acid, the albumen wiU be separated in flocks. Should this not be the case at the end of the hal£;h«fflr'_g , heating, and t]»e fluid merely appears turbid, one or twosdro^ (not more, unless the urine is alkaUne) of acetic acid aie afffed and the heating continued until the albumen separates in flocks ; the beaker is then pi:j^fcide till the precipitate has settled, and the clear liquid passeothrough a small filter, (previously dried at 212°, then cooled between two watch glasses held together with a spring clip, and weighed ;) the precipitate is then washed with a little hot water, and brought upon the filter without ..-loss, the beaker washed out with hot distiUod. w&r, and the last traces of precipitate loosened from the sides %ith a fea'ffier. The filter with its contenjajs then repeatedly washed with hot water, until a drop of the mtrate evaporated ou a piece of glass leaves no residue. The funnel containing the filter is then § 80. ESTIMATION OF ALBUMEN. 235 put into a warm place to dry gradually ; lastly the filter removed into one of the watch glasses and dried thoroughly in the air bath at 220° Fahr. ; another watch glass is then covered over that containing the filter, the spring cHp passed over to hold them together, the whole cooled under the exsiccator and weighed; the weight of the glasses, filter, and clip deducted from the total, gives the weight of albumen in. 1000 grains of urine, supposing 100 dm. has been originally taken. h. By Measure. In order to avoid the tedious process of estimating the albumen as just described, Bodeker has devised a method of titration which gives very faii approximate results. The principle is based on the fact that feftocyanide of potas- sium completely precipitates albipnen from an acetic acid solution in the proportion of 1 eq. ferrocyanide (=211) to 1 eq. albumen (=1612.) The standard solution of ferrocyanide is made by dissolving 13-09 grains of the pure salt in 10,000 grains of distilled water. 1 dm. of the solution so prepared precipitates O'l grn. albumen. Process : 50 dm. of the clear filtered urine are mixed with 50 dm. of ordinary coAmercial acetic acid, and the fluid put into a burette. Five or six small filters are then chosen, of close texture, and put into as many funnels, then moistened with a few drops of acetic acid, and filled up with boiling water ; by this means the subsequent clear filtration of the mixture is considerably facilitated* 10 dm. of the ferrocyanide solution are. then measured into a beaker, and 10 dm. oft the urinary fluid from the burette added, well shaken and poured upon filter No. 1. If the fluid which passes through is bright and clear with yellowish colour, the ferrocy&nide will be in excess, and a drop of the urine added to it will? prodjice a cloudiness. On thd^ther hand, if not enSugh ferrocyaliide has been added, the iiltrate wiU be turbid, and pass through very slowly; in this case, frequently both the ferrocyanide and the jirine will piWduce a turbidity when ad4e(£ In, testing the filtrate for excess of ferrocyanide, care must be taken not to add to« much 236 ANALYSIS OF UEINE. § 80. of the urine, lest the precipitate of hydroferrocyanide of al- bumen should dissolve in the excess of albumen. According to the result obtained from the first filter, a second trial' is made, increasing the quantity of urine or ferrocyanide half or as much again, and so on until it is found that the solution first shown to be in excess is reversed ; a trial of the mean between this quantity and the previous one will bring the estimation closer, so that a final test may be decisive. Example : 50 dm. of urine, passed by a patient suffering from Bright's disease, were mixed with the like quantity of acetic acid, and tested as follows : — Urine. 1. 10 dm. Ferrocyanide. 10 dm. In filtrate Urine. Ferrocyanide. gave prec. 2. 10 „ 3. 10 „ 4. 10 „ 5. 10 „ 20 „ 15 „ 17-5,, 18 „ prec. prec. faint prec. Therefore, the 10 dm. of diluted urine=:5 dm. of the original secretion, contained 1-8 grn. albumen, or 36 grains per 1000. 12. Estimation of Soda and Fotasb. 50 dm. urine are mixed with the same quantity of baryta solution, allowed to stand a short time, and filtered; then 80 dm. =40 dm. urine, measured into a platinum dish and evaporated to dryness in the water-bath; the residue is then ignited to destroy aU organic matter, and when cold dissolved in a small quantity of hot water, carbonate of ammonia added so long as a precipitate occurs, filtered through a smsSl filter, the precipitate washed, the filtrate acidified with hydrochloric acid and evaporated to dryness, then cautiously heated to expel aU ammoniacal salts. The residue is then treated with a little water and a few drops each of ammonia and carbonate of § 80. ESTIMATION OF TOTAL SOLID MATTER. 237 ammonia, filtered, the filter thoroughly washed, the filtrate and washings received into a tared platinum dish, then evapo- rated to dryness, ignited, cooled, and weighed. By this means the total amount of mixed chlorides of sodium and potassium is ohtained ; the proportion of each is found by titrating for the chlorine as in § 75, h, and calculating as there directed under the head of " mixed alialine chlorides." 13. Estimation of Total Solid Matter. The correct determination of the total solid matter is a very difficult task, owing to the fact that on the one hand the residue is very hygroscopic, and on the other, that a partial decomposition of the urea takes place hy heating it to a sufficient temperature to expel aU the water. A tolerahly satis- factory plan is to measure 5 dm. into a shallow platinum or porcelain capsule, which is placed beside a vessel of strong sulphuric acid, under the receiver of a powerful air-pump, and kept in vacuo until all moisture is removed. A rough estimation may be made by evaporating 10 or 20 dm. of the urine on the water-bath, then drying in the air-bath at 230° Fahr., until the weight remains tolerably constant. The only correct method is to introduce a measured portion of the urine, not more than 3 or 4 dm., (contained in a small boat-shaped capsule, filled with fragments of glass,) into a wide glass tube passing through boUing water, to one end of which is attached an aspirator, to the other a chloride of calcium tube ; between the aspirator and the tube containing the urine, a small fiask is inserted containing a measured quantity of normal sulphuric acid, so that any ammonia, given ofif in the evapo- ration, is retained, and its quantity afterward found by titration with normal alkali: it is then calculated into urea, and its weight added to the dry residue actually found. Por further details see Neubauer's paper in the "Zeitschrift fiir An Chemie," part ii, p. 166. 238 ANALYSIS OF SOILS. § 81. 14. Estimation of tlie Total Saline Matter. A measured portion of tlie uiine, say 10 dm., is evaporated to drjmess in a smaU porcelain crucible, about 10 drops of nitric acid added, and the crucible gradually heated to duU redness; it is then suffered to cool, and the same quantity of nitric acid again added; then heated up again gradually to a moderately strong heat until all the carbon is destroyed and the residue white ; it is then cooled and weighed. ANALYSIS OF SOILS. § 81. The following instructions for the examination of soils are not given so much for the use of practised scientific 'chemists as for the guidance of those who may not have the advantage of a complete laboratory, or who may only desire to estimate some of the principle constituents of a soU. The instructions for mechanical analysis, the importance of which cannot be overrated, are taken from Dr. Noad's article on soils in the " Chemist and Druggist," and for whose lucid and most valuable scientific publications of various kinds, more especially on practical analysis, the writer has always had the highest esteem. Mechanical Analysis of a Soil. a. Selection of the Sample. Too much care cannot be taken to obtain a fair average specimen. For this purpose one or two pounds should be taken from each of four or five different parts of the field where the soil appears to be nearly the same. These should be well mixed together, and a pound § 81. MECHANICAL ANALYSIS. 239 or BO selected for analysis; all samples shotild be kept in weU- eorked bottles. It is not unfrequent to see in a field otherwise fertile, a few patches almost barren, where plants, especially when the field is in white crop, spring up, and for a time look quite healthy, but soon become diseased, assume a yellow colour, and die. Specimens from such parts should on no account be mixed with the rest; they should be examined by themselves, and the results compared with those given by the fertile parts : by following this course the cause of sterility and the means of curing it are most likely to be discovered. h. Determination of Water. Spread a weighed quantity (say half a pound) of the soil upon a sheet of white paper, and expose it to the air in a dry room for several hours, weighing it at intervals of two or three hours tOJ the weight remains con- stant: the loss indicates the amount of water which has evaporated, but by no means the whole of the water which the soil contains. To determine which, heat about 500 grains of the air -dried soil in a small glass beaker plunged into an oil bath, the temperature of which is kept between 300° and 350° Fahr.. till it ceases to lose weight, the result gives a close approximation to the amount of water. Absoivle dissiccation cannot, however, be accomplished except at a heat close upon redness, which is, of course, inadmissible, as the organic matters the soO. contains would thereby become altered or destroyed. c. Absorbing power. Allow the 500 grains of soil dried as above to cool in a covered vessel ; then spread it out on a sheet of paper, and expose it to the air for 24 hours; note the increase of weight which is due to absorption of water, and if it amounts to 10 grains, it is so far an indication of great agri- cultural capability. d. Power of holding water. Put 1000 grains of air- dried soil into a filter enclosed in another, placed in a funnel; pour cold water, drop by drop, on the soil until it begins to trickle down the neck of the funnel; cover with a piece of glass, and allow it to stand for an hour or two, adding a few 240 ANALYSIS OF SOILS. § 81. drops of water from time to time natil it is certain that the whole soil is perfectly soaked; remove the filters from the funnel, and open them upon a Unen cloth to remove the drops of water adhering to the paper. The outside filter is now placed in one pan of the balance, and the inner one containing the soil on the other; and the whole being carefuUy balanced, the true weight of the wet soil is obtained : suppose this to be 1400, then the soil is capable of holding 40 per cent, of water. e. Eapidity of Drying. Expose the soil with its filter on the plate to the air for 4, 12, or 24 hours, weighing from time to time. The loss of weight, indicating the tendency of the soil to dry, may convey useful information as to the necessity or otherwise of drainage. /. Eelative proportions of Gravel, Sand, and Clay. Hub a quantity of air-dried soil between the hands, and remove and weigh any stones which may be present. "Weigh off 4,000 grains, and pass them through a sieve (No. 1) of copper wire gauze, the meshes of which are about ^^^th of an inch in diameter. Eemove the sieve from its bottom, and place it over a deep evaporating basin; throw a gentle stream of water upon the contents, and stir with a spatula or the hand until the water passes through clear. Transfer the residue to another basin, and place it in the water-oven to dry ; then weigh, after which ignite in the air, and when cold weigh again. The first weighing gives the amount of coarse gravel, and the second indicates the proportion of organic, matter which this gravel contains. Transfer the soil which has passed through sieve No. 1 to sieve No. 2, the meshes of which are about -jJ^th of an inch in diameter, treat the residue on the sieve precisely as before, dry at 212°, weigh, ignite, and weigh again; the results give the amount of gravelly sand, and of organic matter mixed with it. Dry a portion of the soil which has passed through sieve No. 2 in the water oven, and weigh off 500 grains; transfer to a deep basin or flask, and boil for 20 minutes or so with water. The boiling must be continued until all the par- § 81. MECHANICAL AKALYSIS. 241 tides are thoroughly separated from each other. The coarse sand, fine sand, and finely divided particles are then separated from each other by the following simple process, recommended hy Schultz: — The boiled soil is allowed to cool, and is then washed into an elutriating glass, which is merely a taU cham- pagne glass 7 or 8 inches deep and about 2f inches wide at the mouth, round which is fastened a brass ring about half-an-inch broad, with a tube slightly inclined downwards proceeding from its side. A gentle stream of water is caused to pass contin- uously into the elutriating glass in such a manner as to cause a constant agitation of the particles, whereby the finest are washed away through the tube at the top of the glass, and received in a beaker or any other convenient vessel. This stream of water is best kept up and regulated by causing it to flow from a reservoir provided with a stop-cock, to which is attached a tube funnel from 12 to 18 inches long, drawn out to a point, with a fine aperture. The end of this tube is placed nearly at the bottom of the elutriating glass, and the supply of water so adjusted that the funnel tube always remain half full of water. When the water rnns off from the discharge tube nearly clear, the stop-cock of the reservoir is closed, and the elutriating glass being removed, the water is decanted from it; and it is washed into a small dish, where it is dried and weighed, after which it is ignited and weighed again ; the two weights give the proportion of coarse sand and its organic matter. The elutriated turbid fluid is allowed to stand for several hours, and the water is then poured off into another beaker. The deposited matter, consisting of fine sand and fine soil, is then subjected to a second elutriating process, conducted as before, except that the force and volume of the washing water is considerably lessened. The operation is continued until the wash water passes oif quite clear; this sometimes takes three or four hours, but it is, with the arrangement described, a self-acting process, requiring no personal super- intendence. The residue in the elutriating glass is fine sand, B 242 XS^YSIS, 0? SOILS. § 81 ■wHcli, Witt its organic matter, is estimated as liefore, by drying, weighing, igniting, and re-weighing. We have only now to deduct from the original 500 grains the quantities of coarse aad^we sand, to obtain the proportion of finely-divided matter. The results of this mechanical analysis may be tabulated thus, (Schultz):— 100 parts of the soil, dried at 212° Tahr., contain (for example)^- Combustible Fixed or Volatile Substances. Substances. g.QQ ("Gravel (coarse) 6-90 0-00 1 Organic matter y.jQ f Gravel (fine) 6-43 I Organic matter ... 0-67 o-.e^ / Sand (coarse) 34-37 I Organic matter ... 1'13 ^Q.OQf Sand (fine) 38-50 I Organic matter ... 1-50 (-Finesoil 9-50 10-50-; Organic matter, ammonia and ( combined water 1-00 100-00 95-70 4-3 Stones, 2-10 per cent. This mechanical treatment of soils is of high importance, and it is to be regretted that so few of our English soils have hitherto been so examined. The same remark applies to the analysis of clays. The operations above described apply equally to clays and to soils, except that in the case of clays we have not to look for gravel. To render the matter complete, however, the gravel and sand should be moistened and examined under the microscope, with the view of ascertaining if they are whoUy siliceous, or if they contain also fragments of different ktnds of rock — sandstones, § 81. MECHANICAL ANALYSIS. 243 slates, granites, traps, limestones, or ironstones. A few drops of strong hydrocKLoric aeid should also be added, when the presence of limestone is shewn distinctly by an effervescence of peroxide of iron by the brown colour which the acid speedily assumes; and of black oxide of manganese by the smell of chlorine, which is easUy recognized. g. Determination of the Density of a Soil. Dry a sample of the soil (from which the large stones have been picked out) at 212° in the water oven tiU it ceases -to lose weight. rUl a perfectly clean and dry common phial with distilled water up to a mark made with a file on the neck, and weigh it carefuUy. Pour out part of the water, and introduce into the bottle in its stead 1,000 grains of the dried soU; shake the bottle well, to allow the air to escape from the pores of tjie soilj fill up again with water to the mark on the neck, and again weigh. The weight of the soil divided by the ^ difference between the weight of the bottle with soU and water and the sum of the weights of soil and the bottle of watei together, gives the density or specific gravity. Example — Grains. The bottle with water alone weighs 2,000 ThedrysoU 1,000 Sum (being the weight which the bottle with the soil and water would have had, could the soil have been introduced without dis- placing any of the water) ^ 3,000 Actual weight of soil and water 2,600 Difiference (being the weight of water taken out to admit 1,000 grains of soU) 400 Therefore, 1,000 grains of soU have the same hulk as 400 grains of water : i.e., the soU is 2 J times heavier than the water, since i^^=.2-5, its specific gravity. E 2 244 CHEMICAL ANALYSIS. § 81. Ti. Determination of the Absolute Weight. "Weigh an exact imperial half-pint of the soil in any state of dryness. When this weight is multiplied by 150 it wiU give very nearly the weight of a cubic foot of the soil in that state. Chemical Analysis. The accurate and complete quantitative analysis of soils is a work of some difficulty, and cannot be entirely accomplished by volumetric means. Many of the principal substances, however, may be estimated in this manner, and the following method of procedure is given as the most convenient : — 1. Water. 250 grains of the air-dried sifted soU are weighed in a porcelain, platinum, or iron crucible, and heated for a considerable time in the water bath tid the weight is constant. The loss represents the amount of water. 2. Organic matter. 50 grains of the residue from 1 are ignited in a platinum or porcelain crucible untd. all the organic matter is destroyed ; the residue is then suffered to cool, moist- ened with solution of carbonate of ammonia, (to re-carbonate any limp.,) then dried in the air bath at about 300° Fahr. ; the loss indicates the amount of organic matter in the perfectly dry sod, which is then calcidated for 100 parts of air-dried soil. 3. Carbonic Acid. 60 grs. of the air-dried soU are intro- duced into the apparatus, Pig. 12, and the carbonic acid esti- mated as in § 22. 4. Chlorine. 250 grs. of the air-dried soil are burnt in a platinum crucible, then cooled and moistened with a solution of nitrate of potash, again heated gently to dryness, then ignited again. The cold residue is then Uxiviated with boiling water, filtered, the filtrate neutralized with acetic acid, and a measured portion of it titrated with ^^ sUver and chromate of potash, as in § 74. 5. Oxide of Iron. The insoluble residue of 4=250 grs. sod, is heated in the water bath with pure hydrochloric acid to § 81. ANALYSIS OF SOILS. 245 extract all soluble matter, the solution filtered off, the residue washed with hoiling water on a filter, (residue preserved for future examination,) and the filtrate and washings collected and diluted to 500 dm. 200 dm. =100 grs. soU, are then taken, heated with a little nitric acid to peroxidise all the iron, and ammonia added in excess, so as to precipitate all oxide of iron and alumina ; if the latter be required to be estimated, the precipitate must be collected on a filter, well washed, putting the filtrate and washings aside, then dried, ignited, and weighed; the residue, consisting of oxide of iron and alumiaa, with what- ever traces of phosphoric acid there may be, is redissolved in a little hydrochloric acid, the solution treated with zinc, diluted considerably, and titrated with -^^ bichromate, § 44, for oxide of iron, the quantity so found deducted from the total weight of the precipitate gives the alumina and phosphoric acid. Should the estimation of alumina not be required, the precipi- tate need not be ignited, but simply redissolved with hydrochloric acid on the filter and titrated at once for iron. Should any portion of the iron in the original soU exist as protoxide, a weighed quantity, say 100 graLns, of the fresh, sifted, and non- ignited soU is exhausted with pure hydrochloric acid, the so- lution filtered and titrated direct with bichromate, as in § 48. 6. Lime. The filtrate and washings from 5=100 grs. soil, are mixed with oxalate of ammonia in excess, the solution set aside in a warm place for an hour or so, the precipitate then collected on a filter, well washed, dried, and together with the filter ignited. The mixture of carbonate and caustic lime thus obtained is dissolved in an excess of normal nitric acid, and titrated as in § 18; calculation for Hme to be made as there directed. 7. Magnesia. The filtrate and washings from 6=100 grs. soU, which if bulky must be evaporated somewhat in the water bath, is to be made freely alkaUne with ammonia, arseniate of ammonia added in slight excess, and the solution set aside for twelve hours in the cold, that the magnesia may be precipi- 246 CHEMICAL ANALYSIS. § 81. tated as double arseniate of ammonia and magnesia. The precipitate collected on a filter well washed with ammoniacal water, (filtrate and washings set aside,) redissolved on the filter with acetic acid, and the solution titrated with uranium as in § 64, 3 ; see also § § 78, 1 and 38. 1 dm. of standard uranium solution represents 0-0563 grn. Mg 0. 8. Alkalies. The filtrate and washings from 7"=100 grs. soil, containing the alkalies as chlorides, together with chloride of ammonium and a small quantity of arseniate of ammonia, is evaporated to dryness on the water hath, then ignited gently and carefully under a chimney to volatilize all the arseniate and other salts of ammoiia. The alkalies are then left nearly pure as chlorides ; the residue is dissolved in a very little water, filtered through a smaU filter into a small crucible, evaporated to dryness, and weighed direct. If it be desirable to ascertain the amount of potash, it may be separated by weight as double chloride of platiuum and potassium, or the indirect method of calcula- tion, as in § 75, h, may be adopted. 9. Phosphoric Acid. The remainder of the acid solution, viz., 300 dm.=150 grs. soU, is mixed with a little nitric acid, heated and precipitated with ammonia, as in 5, the precipitate collected on a filter and washed with boiliag water, (filtrate and washings set aside,) the precipitate is then dissolved on the filter with dilute nitric acid, the filter slightly washed, aud the solution so obtained digested in the water bath for twenty-four hours with about two ounces of the fluid prepared as follows : Molybdic acid 100 grains Solution of Ammonia, '900 . 100 dm. Pure nitric acid, about 1-30 150 dm. If any precipitate occurs it will contain all the phosphoric acid (unless it should exist in large quantity, which is not probable) as phospho-molybdate of ammonia, which is to be collected on a small filter, well washed with the same fluid, then redissolved in ammonia, and a portion of the magnesia mixture added. § 81. ANALYSIS OP SOILS. 247 § 78, 1, to precipitate the phosphoric acid as double phosphate of magnesia and ammonia ; the precipitate so produced is dis- solved in acetic acid, and titrated with uranium as iu § 78, 1. 10. Sulphuric Acid. The filtrate and washings from 9 =150 grs. soil, are diluted up to a definite measure, and a con- venient portion titrated for sulphuric acid by any of the methods given in § 28. 11. Ammonia. From 200 to 500 grains of the fresh air- dried son are introduced into the distilling flask, Fig. 11, together with a little water and a smaU piece of heea' wax, (to prevent frothing,) the tube d is filled with strong caustic potash or soda, the whole of which is allowed to run into the flask as soon as the heating commences. In all other respects the operation is conducted as described in § 16. 12. Nitrogen. 100 grains of the soU are dried at 300° Fahr., and when, cold mixed with soda lime iu a com- bustion tube, and ignited aa usugl, § 17. The ammonia evolved may be received into normal sulphuric acid, and the mixture afterwards titrated with normal alkali in the usual manner ; or dilute hydrochloric acid may be used in the bulb apparatus, the fluid evaporated to dryness on the water bath, then heated in the air bath to 24:0'^ Fahr., and the residual chloride of anuno- nium titrated aa in § | 40, 75. 13. Residue insoluble in Hydrochloric Acid. The insoluble matter which has already been collected, aa in 6=250 grs. soil, and consisting mainly of insoluble silicate of alumina and sand, is transfen'ed to a platinum or porcelain dish or large crucible, dried and mixed with sulphuric acid of about 1 '6 spec. grav. in excess ; the mixture ia left to digeSit somewhat, then heated slowly under a hood, to drive oS all the free acid; the residue is then cooled, Uxiviated with water filtered, and the filtrate precipitated with ammonia; the pre. cipitate may be washed, dried, ignited, and weighed as "Alumina insoluble in Hydrochloric Acid." The insoluble residue will consist of pure quartz sand. 248 ANALYSIS OF MANURES. § 83. ANALYSIS OF MANUEES. Guano. § 82. 1. Moisture. 100 grains, weighed in a platinum or porcelain crucible, are dried in the water bath till the weight is constant, the loss gives the percentage of moisture. 2. Total Fixed Constituents. Eesidue of 1=100 grains guano are ignited at a low red heat till all organic matter is destroyed, and the residue of a white or greyish colour ; the loss of weight gives the percentage of iixed constituents, which wiU act as a control over the subsequent analysis. 3. iSand, Clay, or other Insoluble Matter. Eesidue of 2 is boiled with dilute hydrochloric acid (which should not cause any amount of efiFervescence) till all soluble matter is extracted, the solution filtered, residue brought on the filter, washed, dried, ignited, and weighed, gives the percentage of insoluble matter. The filtrate and washings containing all the soluble matters are diluted up to a definite measure, say 500 dm. 4. Phosphoric Acid. 200 dm. of the solution prepared as in 3=40 grains guano are precipitated with ammonia ia excess, the precipitate of phosphate of lime and magnesia redissolved in acetic acid, and the solution divided in half, one portion titrated with uranium for phosphoric acid, as in § 78, 1 the remainder set aside for 5. Lime. 'To half of the acetic acid solution prepared as in 4, sufficient oxalate of ammonia is added to precipitate all the lime; after standing an hour or so, the supernatant liquid is filtered off and the precipitate washed, (reserving the filtrate and washings,) then dissolved and titrated as in § 60, 1. 6. Magnesia. The filtrate and washings from 5 are rendered alkaline with ammonia, set aside for 12 hours, the precipitate of double phosphate of magnesia and ammonia collected, dissolved, and titrated as in § 38. § 82, GUANO. 249 7. Alkalies. The filtrate and ■washings from 6 are mixed with sufficient baryta water to remove all the phosphoric and sulphuric acids; the precipitate removed by filtration; the filtrate evaporated to a small bulk, and treated with carbonate and caustic ammonia, to remove excess of baryta, and the filtrate and washings from this precipitate acidified with hydrochloric acid, evaporated to dryness, ignited, then re- dissolved in a small quantity of water, a few drops each of ammonia and carbonate of ammonia added, filtered into a weighed platinum or porcelain crucible, the small filter thoroughly washed, and the filtrate" and washings evaporated to dryness, ignited, and weighed as chlorides. For the estimation of potash and soda contained in the mixture see § 80, 12, which also contains rather more minute directions for the careful separation of the alkaline salts by the above method. 8. Ammonia. 10 grains of the guano, or more, if poor in ammonia, are boiled with caustic potash in the distUling appa- ratus. Fig. 11, and the estimation of ammonia conducted as described in § 16. 9. Nitrogen and Ammonia. From 5 to 10 grains of the guano, according to its quality, are dried in the water bath and carefuUy mixed with soda lime, (previously coarsely pow- dered, heated, and cooled,) and the mixture introduced into a hard glass tube, closed at one end, about fourteen inches long and half-an-inch diameter, the closed end is previously filled to about three quarters of an inch with a dried mixture of equal parts oxalic acid and soda lime ; on the top of this the mixture of guano and soda lime is filled in to within one ,and a half inches of the open end ; a loose plug of dry asbestos is then introduced, and a good fitting cork, carrying the Varrentrapp and "Will's bulb apparatus, (filled to the proper extent with normal sulphuric acid,) inserted. The tube is then placed in the gas or charcoal combustion furnace, and gradually heated from its open end downwards until the 250 ANALYSIS OF MANURES. § 82. ammonia is nearly all evolyed ; the whole tube is then strongly heated, and the heat brought especially to bear on the lower end containing the mixture of oxalic acid and soda lime ; by this means a strong current of carbonic acid is produced, which drives out all the ammonia into the acid ; when this strong current ceases somewhat, and before the acid has opportunity to regurgitate into the hot exhausted tube, the cork is removed, the acid solution emptied into a beaker, the bulbs washed out into the same vessel, the mixture filtered, if necessary, and the excess of acid ascertained by titration with normal alkali, as in § 12, p. 29. Each dm. of acid found to be combined with ammonia represents 0*17 grn. of that substance, or 0'14 grn. nitrogen. FIioBpIiatlc Manures. Moisture and fixed constituents are determined as in the case of guano. 100 grains of the manure are lixiviated with warm water, allowed to settle, the clear liquid passed through a filter ; the operation repeated, the residue boiled once or twice with water, the fluid being decanted through the same filter, the residue is then mainly brought upon it and well washed with boiling water; the filtrate and washings so obtained are diluted to 500 dm., set aside and marked "Aqueous solution," 100 grs. manure. The insoluble residue on the filter is pushed through the funnel into the beaker in which it was originally digested, the filter treated with warm dilute hydrochloric acid, washed with boUing water into the beaker, a good quantity of hydrochloric acid added, and the whole digested for some time at near boil- ing heat. The clear acid fluid is then passed through a filter, the insoluble residue brought upon it and washed till all soluble matter is removed, filtrate and washings then diluted to 500 dm., §et aside and marked " Acid solution," 100 grs. manure. § 83. GUANO. 251 The insoluble residue on the filter is dried, ignited, and weighed, as sand, clay, &c. In the aqueous solution, phosphoric acid, lime, and alkalies are determined as in the case of guano ; sulphuric acid as in § 28, 3. In the acid solution, which contains traces of iron, and probably alumina, the phosphoric acid is separated and esti- mated as recommended in § 78, 1. Lime and sulphuric as in the aqueous acid solution; oxide of iron, if necessary, by bichromate as in § 81, 5. Ammonia and nitrogen as in guano. In subsequently calculating the results, the phosphoric acid found in the aqueous solution is ajdded to the Ume in the pro- portion of 71 to 28, the remainder of the lime to the sulphuric acid iu the proportion of 28 to 40 ; remainder of the sulphuric acid to the alkalies, unless existing in the manure as chlorides ; any sulphuric acid over and above this is entered as existing in a free state. In the acid solution, the phosphoric acid is added to the Ume in the proportion of 71 to 84, (3 Ca 0, PO^,) remainder of Ume to the sulphuric acid in the proportion of 28 to 40, both of which should pretty nearly agree. ANALYSIS OF WATEK. § 83. Most of the ordinary constituents of spring or river waters may readily be estimated by volumetric methods, and owing to the comparatively pure state in which they occur, can, in the hands of good manipulators, be very accurately deter- mined. Three systems of measurement are open to the operator, viz., the Utre, the imperial piut, or the 1000 dm. measure, thQ 252 ANALYSIS OF WATER. § 83. two latter being respectively one-eighth, and one-seventh of tha imperial gallon. 1. Total Solid Matter. 1000 dm. of the water, ( = one-seventh of a gallon,) or if the operator prefers it, one imperial pint, (to either of which from 10 to 20 dm. of normal carbonate of soda, § 11, otherwise 5 or 10 grains of pure and dry carbonate of soda in powder is added,) is slowly- evaporated, preferably in a weighed platinum dish, at fiist over a gas lamp, then on the water bath to complete dryness ; taking care during the operation that no loss occurs by bubbling or spirting. The dish is then placed in an air bath and heated to 300° Fahr. tiU the weight is constant. The weight so obtained, minus the carbonate of soda added, represents the total amount of solid matter, which can be calculated for the imperial gallon =70,000 grains, and serves as a control over the subsequent analysis. 2. Organic Matter. The platinum dish containing the residue of 1 is placed over a spirit or gas lamp, and slowly heated to dull redness, untO. the blackening of the residue which first appears, is totally removed, (should this take place rapidly, and with faint scintillation, the presence of alkaline nitrates may be inferred ;) the dish is then cooled, strong carbonic acid water or a little solution of carbonate of ammonia added, evaporated, gently ignited, then cooled under the ex- siccator, and quickly weighed; the loss between this second weighing and that of No. 1 is generally considered to represent the amount of organic matter of vegetable or animal origin, or mixtures of both, which was originally present in the water, and which has been dissipated by the ignition. 3. Total Amount of Carbonic Acid. This can only be done accurately by quietly collecting the water at its source, in bottles containing a measured excess of pure chloride of calcium and ammonia, (free from carbonic acid,) collecting the precipitate, and titrating with nitric acid as in § 22, a. In most cases the method of procedure given in § 22, &, is sufficient. § 83. ESTIMATION OF SILICA, ETC. 253 The total amount of comhined carbonic acid may also be found in the residue of 2 as foUows : — 20 dm., or more if necessary, of normal nitric acid are added to the residue in the platinum dish, which should be covered, to prevent loss by effervescence; the mixture digested warm till dissolved, then a few drops of litmus added, and titrated with normal alkali for the excess of nitric acid ; the quantity so found is deducted from the total used, then as much deducted from that as would be required to neutralize the weight of carbonate of soda added in 1 ; the remainder multiplied by 0'22 will give the weight of carbonic acid combined with the lime, magnesia, and alkalies, (if any,) as monocarbonates. 4. Carbonic Acid combined with Alkalies. 1000 dm. of the water are boiled in a flask for an hour, to precipitate the earthy carbonates, which are filtered off, and slightly washed with boiling water ; the filtrate is divided into two equal parts, a and 6 ; a is titrated with -^ silver and chromate of potash, as in § 74, for the amount of chlorine ; h is slightly acidified with hydrochloric acid, evaporated to perfect dryness, gently ignited, redissolved in a little hot water, diluted to the same bulk as a, and titrated for chlorine as before ; the increase of chlorine found in this case represents the amount of alkali existing as carbonate. If therefore the number of dm. of ^^ silver, used in excess of a, be multiplied by 0-022, the weight of carbonic acid in combination with alkali will be obtained. Estimation of the Lime, Magnesia, SUlca, Alumina, and Oxide of Iron. 5. Silica. Four imperial pints, or 4000 dm. (less, if the water is fully impregnated with mineral matter,) are slightly acidified with hydrochloric acid, and evaporated in a place free from dust, first in a large pprcelain dish, and lastly in a platinum vessel, to dryness, the residue is well dried, and dissolved in a amaU quantity of dilute hydrochloric acid, the solution filtered, 254 ANALYSIS OF WATER § 83. to collect tlie flocciilent silica, Tv^tich is washed with the rinsings of the dish, lastly with pure water, dried, ignited, and weighed in a covered crucihle. 6. Oxide of Iron and Alumina. The filtrate from 5 is heated, and rendered alkaline by ammonia, by which means the oxide of iron and alumina are precipitated. If the iron alone is to be determined, the precipitate after washing may be redissolved and titrated with permanganate. If the alumina is also to be determined, the washed precipitate must be dried, ignited, and weighed, before estimating the iron, just as in § 81, 5. 7. Lime. The filtrate from 6 is mixed with oxalate of ammonia in slight excess, and set aside in a warm place to settle thoroughly. The precipitate of oxalate of lime is then col- lected, well washed, (reserving the filtrate and washings,) then titrated with permanganate, as in § 60, 1, or dried and ignited, to convert it into a mixture of carbonate and caustic hme, which may be titrated residually with normal nitric acid and alkali, as in§ 18. 8. Magnesia. The filtrate and washings from 7, concen- trated somewhat by evaporation, are rendered alkahne with ammonia, some phosphate of soda added, and the precipitated double phosphate of magnesia and ammonia titrated as in § § 38, 78, 1 ; each decern of uranium solution representing 0'0563 grn. magnesia. 9. Chlorine. From 100 to 500 dm. of the original water are evaporated somewhat, and titrated with -^-^ silver and chromate of potash, as in § 74. 10. Sulphuric Acid. 500 or 1000 dm. are evaporated to one-fourth the bulk, and the amount of sulphuric acid found by any of the methods in § 28. 11. Alkaline Salts. 2000 dm. or two imperial pints of the water are evaporated to one-fourth, their bulk in a porcelain dish, a little chloride of barium is then added, together with baryta water in sufficient quantity to render the mixture dis- § 84. ESTIMATION OF HAEDNESS OF WATEE. 255 tinctly alkaline, the fluid is then filtered ofif through a somewhat porous filter, and the precipitate slightly washed. The clear filtrate and washings are then treated with carbonate and caustic ammonia to remove excess of haryta, again filtered, washed, evaporated to perfect dryness, and gently ignited to expel aU ammoniacal salts; the residue is then dissolved in a little hot water, a few drops each of oxalate, carbonate and caustic ammonia added, filtered through a small filter into a weighed platinum crucible or dish, the filter well washed with boiling water, again evaporated, ignited, cooled, and weighed as alkaline chlorides. The indirect separation of the soda and potash can be accomplished as in § 75, h. 12. Nitric Acid. This constituent is only found, as a rule, in waters contaminated with sewage matter, its amount may be determined by evaporating a good quantity of the water to a small bulk, and estimating the nitric acid as in § 26, 4, 5, or 7. Special classes of water containing metals, (such as mine waters,) sulphur, sulphuretted hydrogen, and other unusual constituents require, as a rule, much more complicated methods of treatment than are here given, for which the operator cannot do better than considt the new edition of Fresenius' "Quan- titative Analysis." ESTIMATION OF THE HARDNESS OF WATEE. Clark's Metbod. § 84. The ordinary fresh waters used for drinking, washing, and manufacturing purposes, all contain salts of lime, dnd some of them salts of magnesia, free cai'bonic acid, alumina, and oxide of iron, all of which have the property of rendering the water hard, that is to say, instead of giving a free lather with . 256 ESTIMATION OF HAEDNESS OF WATER. § 84. soap like rain or soft water, it decomposes the soap into a greasy, dirty scum, consisting of stearate of lime or magnesia, &c., and until an amount of soap lias been added, sufficient to combine with, all these salts, no soft lather will be produced, nor wiU any detergent power be exerted by the liquid. The late Prof. Clark, of Aberdeen, devised a method of examination, based upon the soap reaction above mentioned, which has come into very general use, and is extremely serviceable as a ready means of ascertaining the amount of earthy salts contained in water used for generating steam, or for general domestic, and manufacturing purposes. a. Preparation of Standard Water. In order to conduct the examination of any given water in a proper manner, it is first necessary to prepare a standard water containing a known quantity of Hme in solution. This is best done by dissolving 27'5 grains of crystallized gypsum, (Selenite,) previously re- duced to fine powder, in one imperial gallon (70,000 grains) of distilled water. This weight of sulphate of lime is equal to 16 grs. of carbonate of lime, and the water so prepared is called by Clark — "standard water of 16° hardness," each grain of carbo- nate of lime, or a proportionate weight of any other hme salt in the gallon, being considered as one degree of hardness. Clark directs his standard solution to be made by dissolving 16 grains of Iceland spar (CaO,C02) in hydrochloric acid, evapo- rating to dryness, then diluting to one gallon ; but as this is somewhat troublesome and liable to loss from effervescence, the crystallized sulphate is preferable. h. Preparation of the Standard Soap Solution. This solution is directed by Clark to be prepared by dis- solving hard curd soap in proof spirit by the aid of heat ; but as a very unsatisfactory liquid is produced by this means, owing to the constant precipitation of flocky matter and carbonate of soda at ordinary temperatures, I have for some time used a solution of the pure potash soft soap in proof spirit, with ad- vantage. § 84. claek's method. 257 This soap, whicli is kaown as the pure soft soap of the London Pharmacopseia, can readily he obtained, and the solu- tion made with it may be kept any length of time with- out undergoing change. It is prepared hy simply digesting a convenient quantity of the soap with a mixture of equal volumes of alcohol (pure or methylated) and distilled water at ordinary temperature until dissolved. If not completely clear it may be passed through a filter. The solution so prepared must now be titrated by the help of the standard water, and here I prefer to use the modification suggested by Pierce Wilson, ("Ann. Chem. u. Pharm.," 119, 318,) which enables the operator to dispense with the table constructed by Clark, and which was rendered necessary by the fact that in order to produce a persistent lather an excess of soap to the extent of 1 "5 dm. was required. This difficulty appears to be entirely overcome by adding a certain quantity of carbonate of soda so as to soften the water to the extent necessary for the prevention of an excess of soap. e. Titration of the Soap Solution. 100 dm. of the standard water are measured into a stoppered bottle holding about 6 oz. ; 4 dm. of cold saturated solution of carbonate of soda added, and the soap solution immediately delivered in from a Mohr's burette, untU a point occurs when by a few vigorous shakes a soft and copious lather is produced, which will remain for at least five minutes. The quantity of soap solution required to produce this should be exactly 32 dm. ; therefore, if on trying the solution b, 30 or 31 dm. have been necessary, it must be diluted with proof spirit so that exactly 32 dm. are required to produce the lather; if more than 32 dm. have been required, more of the con- centrated soap solution must be added until the same strength is gained. d. Examination of a Sample of Water. 100 dm. of the water are measured into the bottle and well shaken to liberate any free carbonic acid which may be present. The s 2(58 ANALYSIS OF WATER. § 84. air in the bottle is tlien blown out by an India rubber syringe, or sucked out by a bent glass tube; if this pre- caution were not taken, the gas would decompose a slight portion of the soap solution. 4 dm. of carbonate of soda are added, as in c, and sufficient soap solution cautiously delivered from the burette to produce the permanent lather. Supposing that 20 dm. have been required, the hardness is 10°, so that up to 32 dm. half the number of decems of soap required for 100 dm. of water will be the degree of hardness. When the water is more than 16°, the carbonate of soda pre- cipitates a portion of the lime out very rapidly, so that the quantity of soap solution is not a correct measure of the amount of earthy matters ; consequently in such a case the sample of water must be previously diluted with one or two volumes of distilled water, according to circumstances, then 100 dm. taken for titration, and the quantity of soap solution required doubled or trebled, as the case may be, before taking the half as the amoimt of hardness. Example : 100 dm. of water derived from the chalk forma- tion, and containing a very large proportion of lime, was diluted with 200 dm. of distilled water ; then 100 dm. of the mixture titrated as above, the quantity of soap solution required was 15-5 dm., which multiplied by 3 gave 46-5 dm. ; the degree of hardness was therefore half this=23-25. The degree of hardness obtained in this manner represents the total amounts of the hardening constituents of water, but as a portion of these constituents, viz., carbonate of Ume and magnesia with free carbonic acid, are removed to a certain extent by boiling, it is sometimes desirable to know the degree of permanent hardness, that is to say, after the water has been boiled. To this end about half a pint of the water is measured into a ilask, a small glass funnel inserted into the neck, and the water boiled for an hour, adding fresh distilled water to repair the waste ; when cold, the exact measure is made lip with distilled water, and 100 dm. titrated as above; the § 85. CONSTITUENTS OF SPRING WATER. 259 quantity of soap solution required represents th.e degree of permanent hardness. If it be desired to use the cubic centimeter instead of the decern measure, it is only necessary to take 100 CC of the water with 4 CC of soda solution for titration, using a CC burette for the soap solution. COMPLETE AND RAPID ESTIMATION OF THE ORDINARY CON- STITUENTS OF SPRING OR RIVER WATERS. § 85. In the " Quarterly Journal of the Chemical Society " for December, 1862, is published a paper by E. Nicholson, of the Army Medical School Laboratory, Fort Pitt, on a new volumetric method of estimating some of the constituents of fresh waters, which seems to be very serviceable for the purpose intended, namely, the rapid approximate estimation of the usual substance found in drinking waters, for the use of medical men, sanatory inspectors, &c. I regret exceedingly that owing to its late date I have not had sufficient time to test the process in the most satisfactory manner ; it happened, however, that a complete analysis was in hand at the time, of some water taken from a new Artesian well in the neighbourhood of Norwich, 1200 feet in depth, and therefore the opportunity occurred of comparing the results obtained by the best known methods in laboratory use, with those of the new method. It is to be regretted that the writer of the paper did not give the analysis of the two samples of water examined by him at Fort Pitt, by the ordinary method, side by side with his own. The whole process is a combination of the methods devised by Prof. Clark for ascertaining the hardness of water, those of Boutron Chalard, and Boudet, adopted in their "Hydro- tim^trife," for the estimation of bme, magnesia, and sulphuric s 2 260 ANALYSIS OP WATER. § 85. acid, and an ingenious method for estimating tlie alkaline salts, devised by the author. The instruments required, are one each of Mohr's and Gay Lussao's burettes, graduated into -^jj CO, each division of which is considered as one degree. Two or three whole pipettes, say one each of 10, 50, and 100 CC, a few basins and beakers, half-a-dozen thiee-ounce stoppered bottles, and a litre flask. If the grain system of measurement be preferred, it is only necessary to substitute the decern for the cubic centimeter as the standard. Preparation of the Standard Solutions. 1. Standard Solution of Lime. O'l Gm. of the purest Iceland spar is dissolved in a little pure hydrochloric acid, evaporated cautiously to dryness in the water bath, again dissolved in water and evaporated to dryness, then heated to about 230° Fahr., dissolved in distilled water, and diluted to exactly 1 litre. 1 grain of Iceland spar treated in the same way, and dissolved in 1000 dm. of water, wUl give a solution of the same strength, namely, 7 grains of carbonate of lime in one imperial gallon of water. I prefer to use the crystallized sulphate of lime, (selenite,) as requiring less trouble, the weight in that case being O'l^S Gm. per litre, or 1-^2 grn. per 1000 dm. 2. Standard Solution of Soap. Pure potash soft soap of the London Pharmacopceia is dissolved in equal measures of alcohol and distUled water, of such strength that 22 degrees ^2-2 CC will exactly give a permanent lather with 60 CO of the standard carbonate of lime solution. The actual quan- tity of soap solution required to equal the hardness is 20 degrees, the 2° in excess being necessary to produce the permanent lather. This requisite excess of 2 degrees per 50 CC is to be deducted from all determinations of hardness. 3. Standard Baryta Solutions, a. 0-26 Gm. (=3-^^ at.) of pure and dry nitrate of baryta is dissolved in 1 litre of water, or 2-6 gm. in 1000 dm. This solution is equivalent in § 85. PBEPAEATION OF THE STANDARD SOLtJTIONS. 261 point of hardness to the standard water No. 1, 50 CC of it, therefore, mark 20 degrees ; it is generally advisable, however, to use a stronger solution as follows : — b. 1-30 Gm. (=1^^ at.) nitrate of harj^ta is dissolved in 1 litre or 13 grains per 1000 dm., each CC or dm. marking 2 degrees. 4. Standard Nitrate of Silver. 8-5 Gm. {=-^jj at.) of the pure salt is dissolved in 1 litre or 85 grn. per 1000 dm. ; each O'l CC or dm. representing 1 degree of chlorine. This solution may also he made by diluting -^^ silver, § 74, with an equal bulk of water. 5. Standard Oxalate of Ammonia. 0-355 Gm. (= ■^^^ at.) of the pure salt is dissolved in 1 litre or 3-55 gm. per 1000 dm. ; each CC or dm. precipitates 1 degree of lime. 6. Standard Permanganate of Potash. This solution is made by dissolving the pure crystals of permanganate in distilled water, of such strength that 1 CC or dm. is exactly required to oxidise the same volume of oxalate of ammonia solution. If the operator possesses the -jg solution, § 43 ; 50 CC or dm. of it, diluted to 1 litre or 1000 dm. with distilled water, will give a solution of the proper strength, viz., 0-159 Gm., (^-j-j'jj^ at.) pure permanganate per litre. The above method of graduating the solutions has been adopted by Nicholson, as the important advai.tage is thereby gained of being able to calculate the quantity of any substance per litre of water, by multiplying the number of degrees ob- tained in the analysis by the atomic weights of the substance. Thus :— 20 degrees x 50 (eq. of CaO.COj) = -1000 Gm. per Htre, of Carbonate of lime. 20 „ X 28 (eq. of CaO) = -0560 Gm. per Utre, of Lime. 20 „ X 35-5 ( eq. of CI) = -0710 Gm. per litre, of Chlorine. And so on. 262 ANALYSIS OF WATER. § 85- The quantities thus obtained, when multiplied by 70, show the number of grains per gallon of water. If however the decern and grain system, described in the former part of this book, is used, the 20 degrees x 50 for carbonate of hme as above, would yield 1 grain of the substance to each 1000 dm. of watei, (as in the standard lime solution, for instance,) instead of '1000 Gm. per litre; therefore to preserve the correct absolute weight, the decimal point must be moved one place to the right, and the number multipKed by 7, to give the weight in grains per gallon, since 1000 dm. is the one-seventh part of a gallon. The absolute weight may however be left quite out of the question, if the operator chooses ; in which case the same numbers may be used empirically for the grain system, as given above for the gramme. The following description of the analytical process is taken, with very slight modifications, from Nicholson's paper in the Chemical Society's Journal, p. 472. The Analytical Process. 1. 50 CC of the water to be analysed are measured by the pipette into a stoppered bottle of about three-ounce capacity. The soap solution is gradually dropped in from the burette, the bottle being strongly shaken at intervals, until a lather begins to form on the surface. The soap solution is then added more cautiously, imtil the water, on agitation, presents an iridescent, large-bubbled lather, breaking down very slowly, and, after a few minutes, leaving the surface perfectly covered with a beady film, reconvertible into a lather on again agitating. After a little practice, the exact point where the lather becomes permanent is attained by the addition of one small drop, about one-sixth of a degree, of soap solution. The process thus indicates the presence of -0005 Gm. per litre of lime. § 85. THE ANALYTICAL PKOGESS. 263 Two degrees are deducted for the excess necessary to produce a lather. The number of degrees found represents the hard- ness due to lime, magnesia, iron, and carbonic acid gas. The alkaline salts usually found in. water, have no effect on the soap solution.* 2. The amount of Lime and Magnesia, and, by difference, of free Carbonic Acid Gas, is found by taking the hardness of the water after expulsion of the carbonic acid gas. To this end 50 CC of the water are evaporated to dryness with one or two drops of sulphuric acid, and the residue is ignited to expel excess of acid; if the vapours be offensive, the residue may be neutralized by a few drops of ammonia, before ignition. The residue is dissolved in 50 CC of distilled watSr, and the hardness is ascertained. Oxide of iron will remain insoluble; its amount is to be deducted from the carbonic acid. 3. The Lime is determined by the well-known application of permanganate of potash to the oxidation of oxalic acid, §60. To 50 CC of the water, add 50 CC (or, if the hardness exceeds 50 degrees, 100 CC) of the standard solution of oxalate of ammonia, let the mixture stand in a warm place for an hour, and filter. The filtrate and washings are heated in a basin or flask to about 70° C, (150° Fahr.) with a few drops of sulphuric acid, and the standard solution of permanganate of potash is added from a burette. Subtract the number of CC of permanganate required for oxidation of the excess of oxalic acid, from the number of CC of oxalate of ammonia added to the water : the difference gives the number of degrees of lime. 50 CC of the permanganate solution ought exactly to oxidise 50 CC of the oxalate of ammonia solution. To 50 CC of the water, ignited with sulphuric acid, as before * If the hardness exceed 80 degrees, or if much magnesia be present, the earthy soap often assumes a curdy form, deranging the production of a lather ; in this case only 25 CC should be taken for experiment, the 50 CC being made up with distilled water. 264 ANALYSIS OF WATEE. § 85. described, (2,)* add 20 CC, or more, of the stronger solution of nitrate of baryta, taking care that the hardness of the quantity added (2 degrees per 1 CC) be much greater than that of the water, as previously ascertained. If no alkaline sulphates are present, the amount of sulphate of baryta precipitated will be exactly equivalent in hardness to the amount of earthy sul- phates; and the hardness, when ascertained by the soap solution, will be exactly that of the baryta solution added. If, for example, 20 CC=40 degrees of baryta solution have been added to 50 CC of water containing 35 degrees of sulphate of lime and of magnesia, (total 40 + 35,) 35 degrees of sulphate of baryta wiU be precipitated and the hardness wiU be reduced to 40 degrees, exactly the hardness of the baryta added. But, on the other hand, if sulphate of soda be present in the water, in addition to the earthy sulphates, a greater quantity of sul- phate of baryta will be precipitated, and the hardness will be reduced to less than 40 degrees. Should it be reduced to 36 degrees, that will show that 4 degrees of alkaline sulphate were present.t 6. Chlorine is determined in 50 CC of the water by the solution of nitrate of silver, as in § 74. If the quantity be very small, it is best to evaporate 500 CC of the water to a small bulk, and count cubic centimeters as degrees. 6. Sulphuric Acid is determiaed by adding to 50 CC of the water, 10 CC, or more if necessary, of the stronger baryta solution, and ascertaining by the soap solution the hardness of the mixture. The loss of hardness from the precipitation of * It may be as well, at process No. 2, to evaporate 250 CC of water with sulphuric acid, dissolve the ignited residue in 25,0 CC of distilled water, and take 50 OC for analysis. t If 20 CC of baryta solution have been added, the excess of soap solution, to form a lather, will be greater ; 2'8 degrees must be deducted. But it is perhaps better always to add 50 CC (100 degrees) of baryta. The deduction is then 4 degrees, and the loss of hardness on 100 degrees is the amount of alkali. § 85. THE ANALYTICAL PROCESS. 265 sulphate of baryta, gives the number of degrees of sulphuric acid. 7. Iron is determined in the usual manner by the perman- ganate of potash solution. 500 CC of the water are evaporated to a small bulk with sulphuric acid; the iron is reduced by zinc, and estimated by the permanganate of potash solution. Ten cubic centimeters are counted as one degree of FejOj. If Silica be present, it will remain on redissolving the ignited sulphates, and if 250 CC of the water have been evaporated with sulphuric acid, it may be estimated by weighing. In process 2, the oxide of iron becomes insoluble, and increases the amount of carbonic acid gas, from which it must be deducted. All the processes here described are of very easy execution. The method of estimating carbonic gas is unequalled in exact- ness and facility of execution by any method I know, and the process for estimating the total capacity of saturation of the alkalies is extremely exact and satisfactory. The estimation of sulphuric acid, devised by M.M. Boutron and Boudet, is likewise of gi-eat precision. I append examples of the calculation of an analysis per- formed by this process, to show the advantage obtained by the method of graduation I propose, in establishing an empirical formula for the salts contained in waters. 1. Analysis of the Water supplied by the Chatham Water Company to Port Pitt. 1. Hardness 63°-7 Carbonic acid gas* Calcium Magnesium Iron The iron is to be deducted from the gross carbomc acid, 4 degrees. • 53°-6 (Sodium loss 6°-4) 266 ANALYSIS OF WATER. § 85. 2. Hardness after ignition with ) ^^qo./t j Calcium sulphuric acid I I Magnesium 3. Calcium ascertained by per- 1 ao'.o falrinm manganate J 4. Hardness after ignition with sulphuric acid, and 60 degrees of baryta added 5. Chlorine 5°-5 6. No sulphuric acid 7. Iron 0-2 Deduction of an Empirical Formula for the Salts contained in the above "Water. This calculation, so tedious by the ordinary method, becomes here of extreme sim- plicity. I combine the 5-5 degrees of chlorine with an equal number of degrees of sodium, a balance of -9 degrees of sodium is left. This with the calcium and magnesium is calculated as carbonate. Gm. per Gms. per Deg. Equiv. litre. gallon. Carbonate of lime ... 48-3 x 50 = -2415 x 70 = 16-905 Carbonate of magnesia 1-4 x 42 = -0058 x 70 = -406 Carbonate of soda ... -9 x 53 = -0047 x 70 = -329 Chloride of sodium 5-5 x 68-5 = -0321 x 70 = 2-247 Oxide of iron -2 x 80 = -0016 x 70 = -112 Silica = -0020 x 70 = -140 -2877 20-132 Carbonic acid gas ... 3-8 x 44 x -0167 = = 2-52 (2C0^) 8-93 CC [cub. in. per gal. Eesidue on ignition -2810 = 19-680 § 85. THE ANALYTICAL PROCESS. 267 2. Water from a Pump at Fort Pitt. Degrees. Total hardness 36-8 Calcium and magnesium 21-0 Calcium 169 Sodium 5-0 Iron(Fe'O') 1-2 Sulphuric acid 4-8 Chlorine 3-6 Gm. per Gms. per Deg. Eqniv. litre. gallon. Carbonate of lime ... 16-9 X 50 = •0845 X 70 = 5-915 Carbonate of magnesia •7 X 42 = •0029 X 70 = ^203 Carbonate of iron ... 1-2 X 116 2(reO,CO^- = •0139 X 70 = ^973 Sulphate of magnesia 3-4 X 60 = •0204 X 70 = 1^428 Sulphate of soda ... 1-4 X 71 = •0099 X 70 = -693 Chloride of sodium... 3-6 X 58-5 = •0210 X 70 = 1-4.70 •1526 10^682 Carbonic acid gas ... 14-6 X 44 = •0642 = 31-3CCpr.lit. 1 (X •537) (31-3 CO X 4.54 Solids by evaporation ■ 1500 per litre. X •061 = 8-67 cub.in.pergaL) I may mention that the solution of permanganate of potash, of the standard here employed, answers admirably for the esti- mation of organic matter La water. 500 CC of water are heated to 70° C, (156° Fahr.,) with a few drops of pure sulphuric acid, and the standard solution is added, 1 CC at a time, until a colour, lasting for ten minutes, is obtained. Every 10 CC of test-solution thus decolorised is equal to one degree of organic matter, requiring one equivalent of oxygen for complete oxida- tion (corresponding to CO'jHO, for example). 268 ANALYSIS OF WATER. § 85. A few words as to the best manner of attaining the rapidity which forms one merit of this process. 250 CO of the water are first set to evaporate with a few drops of sulphmic acid for processes 2 and i ; the lime is also precipitated in 50 CC for process 3. By the time the total hardness is taken, and the chlorine, sulphuric acid, and iron estimated, the evaporation is finished and the residue ready to he taken ia hand. Two or three analyses can thus be easily performed in a day. One point must be carefully observed : that the distilled water con- tain no carbonic acid gas. The delicacy of the soap-test for this gas is so great that the distilled water will speedily acquire one or two degrees of hardness, if left exposed to the air. If it has acquired any hardness from this cause, it should be boiled previously to use. With reference to the determination of the sulphuric acid and alkalies by means of the soap solution, I can fully endorse the statements of Nicholson respecting their accuracy. For instance, two solutions were made with puie sulphates of potash and soda, each containing 48 grains per gallon. On de- termining the strength by nitrate of baryta and soap solution, the yield in the case of sulphate of potash was in the propor- tion of 47'89 grains, and of soda 48-3 grains per gallon. The estimation of sulphuric acid was of course involved in the same process, and therefore equally accurate. The determination of the lime, and by difference the mag- nesia, has not yielded me such satisfactory results ; that is to say, the degree of hardness found by soap solution does not accurately accord with the amount found by experiment ; where the fault is I have had no time to decide. The following is the analysis very carefully made by the ordi- nary gravimetrical method, of a sample of water from an artesian well in Norwich. The well is now in process of boring, and has already reached over 1200 feet without arriving at the greensand. The water here examined ia supposed to flow, not from that § 85. THE ANALYTICAL PROCESS. 269 depth, but from the great Norfolk chalk -water-bearing fissure at between 3 and 400 feet. Carbonate of lime 14-80 grains per gallon. Carbonate of magnesia ... 1-72 „ Sulphate of Ume 4-89 „ Chloride of sodium 4'52 „' Silica 0-19 „ Organic matter 1-16 „ Oxide of iron and alumiaa, traces only Total solid matter 27-28 „ Solid residue on evaporation 27-40 „ The results obtained with the same water by the volumetric plan were as follows : — Degrees. Total hardness 59-0 Lime and magnesia 67-5 Lime 56-0 Sodium 12-0 Chlorine 11-5 Sulphuric acid 12-0 Calculated as under : — Gm. per Gms. per Deg. EqniT. litre. gallon. Carbonate of lime ... 44-0 x 50 = -2200 x 70 = 15-400 Carbonate of magnesia 1-5 x 42 = -0063 x 70 = 0-441 Sulphate of lime ... 11-5 x 68 = -0782 x 70 = 5-470 Chloride of sodium... 11-5 x 68-5 = -0672 x 70 = 4-910 Sulphate of soda ... 0-5 x 71 =-0035 x 70 = 0-245 Silica determined in previous analysis 0-190 Organic matter „ „ 1-160 • 27-816 Total solid residue on evaporation 27-400 270 ANALYSIS OF PHARMACEUTICAL § 86. It will he seen that the magnesia is shown to he diminished by two-thirds of its quantity, as found by actual experiment, while the carbonate and sulphate of lime are increased by about the same weight each, as the magnesia has lost. Nevertheless, the general coincidence of the two results are extremely satis- factory; but I ought to say, that I failed to obtain such satisfaction in another case. I am, willing, however, to believe that this may have arisen from want of time to give the experiment the attention it required. I am convinced, moreover, that the process requires exceed- ingly careful manipulation, to yield reliable results, such as can only be given by well-practised operators. The small quantities of water taken for examination and the delicate graduation of the burette, requiring not only extreme care in standardizing the test fluids and measuring the soap solution, but also in avoiding any traces of acid or other hardening substances in the vessels used during the processes of titration. ANALYSIS OF PHARMACEUTICAL SUBSTANCES AND FBEPABATIONS. 8 86. The readiness and ease with which the volumetric system of determination may be applied, renders it especially useful for ascertaining the purity of the substances used in pharmacy, and also the strength of some of the preparations ■ ordered in the pharmacopeeia. The following list is given as an indication of the extent to which the system may be applied; the numbers refer to the various sections contained in the foregoing part of the book. The only apparatus and materials required for the bulk of 86. SUBSTANCES AND PKEPAEATIONS. 271 the substances are 1 burette, Tig. 1, 1 ditto, Fig. 6, 2 or 3 pipettes. Fig. 7, 3 graduated flasks, a few beakers and porcelain dishes, also funnels, filters, and glass rods. A good ordinary balance, carrying about 300 grains and turning with .jJjth or ■jjth of a grain, ■Will be sufficiently exact if somewhat large quantities be weighed, and afterward subdivided in solution by the measuring flasks and pipettes. If the operator desires to prepare his own standard solutions, additional apparatus is needed. Carefully prepared solutions may, how'ever, be purchased at a trifling cost, for particulats of which see a list at the end of the book. § § § § A p-pfiii m liftati llati 29 Ferri carbon 47,22a 47,22a Acid, acetic, fort 29 ,, ,, sacch. ... glao 29 ,, ammon. citr. ... 47 ,, arsenious 64 ,, iodid 67 ,, citric 33 ,, syrup 67 ,, hydrocyanic, dil. 77 ,, sesquichl. tinct. 47 ,, hydrochloric ... 24 ,, ammon. chlor 47 ,, nitric 25 Ferr um reductum 47 ,, sulphuric 27 Hydrarg. am. chlor.... 62 ,, phosphoric 78 ,, biohlor 62 ,, tartaric 33 ,, chlorid 62 An Ifl.nro Rerasi 77 biniodid 62 67 ,, amygd. amar. ... 77 Hydrarg. oxyd. rubnim 62 Ammon. carbon 16,22 lodininm 67,45 Antim. pot. tart 66 „ tinct. CO. ... 67,45 ,, pulv. CO 66 „ sx. ... 67,45 Argenti nitras Calcis permanganas ... 76 Liquor ammon 16 43 „ „ acet.... 16 Ferri oxydum 47 ,, arsenic, chlor.. 64 „ sulphas 47 „ arsenicalis 64 272 WEIGHTS AND MEASDEES. § 86. § § Liquor calcis 19,60 „ ,, oMorinat. 70 „ plumbi acet. ... 61 „ potasssB 14 ,, sodse chlorinat. 70 Magnes. carbon 22, 32 ,, calcin 32 PotasasB tydras 14 ,, bicarb 14 „ bitart 33 ,, carbon 14 § § PotassEe cUoras 68, 75 „ nitras 26, 41 ,, permanganas.. 43 Potassii iodid 67 ,, sulplmret. ... 54 Sodse carbon 13 „ bicarb 13 ,, pbospb 78 Spt. ammon. arom. ... 16 Zinci carbon 22 ,, oxydum 32, 53 Weights and Measures. 480'0 grains Troy^l oz. Troy. 437'5 „ ^1 oz. Avoirdupois. 7000-0 „ =1 lb. Avoirdupois. 5760-0 „ =1 lb. Troy. The imperial gallon contains of distilled water at 62° Fabr. (16-5 C) 70,000 grains. The pint (1 of gallon) 8,750 „ The fluid ounce (^ij of pint) 437-5 „ The pint equals 34-66 cubic iaches. MEASURES. 273 w as I— ( o Pi Q0M^ r-l(NGO otNos'ioobiS'::!'-' 00^05COOO:^rH ooorHOS^^QO;^ oooo^oscooo ooooo^osco OOOOOOrHOS OOOOOOOrH 00600600 (MOlOCOtN^CO"© (NtNO'^tXSC^r-HC^J OCM(NOTt':OtN.-H OOCCN OOOtNfNO-*^ OOOOlMtNO-^ OOOOOC^tNO CO(>l'-HXOOl>.(Ni^ OcOCNr- •iCiOIr-'N OOCOtN-HiOOt-- OOOCONrHlOO OOOOCO(NrHlO (NCOOOSQOOOO COINm-^ClpODOO ■^COtNCCTpcpCOO O^»r37Hff0(N«^ r-H IC ^ CO ® S gap = a a o a ag82Sjg|> o 'a'a w^ooiotnoi-^t^ 1 Ug ^ H ob S O00(Nlr-W'-<- d>s (M s Ot^t'00t^l>'U3O iigd i-ioicocDr^or-o Oi «> r^ CO t- (0 . ^ §S B O(NG^OO0iCDC0 "15 000(N M 0005 6666w(Noo "^SS 00 (N r^00t^«'. !>■ CQ •* --<■* i>.coOJr^i:^eo-Tj-COOI>-t^CO pOi-ir^i ^1| 666»^t*66r^ ^j>.co H ^ t^co 1— ( rHI>. 1— t << - Ph 1 s S P? ^ CO S o?o ?1 <1 o"l s--! 5 III 5 s OOOOCOOCOi— 1 66666coibco 03 coo P4 _ p3 • t^f-HOC^WtKNOS-^ P § (NI:^OiO^O^Oi .fl OtNJO-OlCrHlO^ OQ 1 ^OCTI>-O>0i-iO COrHO(Nt^OO^ OCO'-HO(Nl>.00 oois-^OG^ t^o CO ^ (N Ir^ CO^OtN co^ ,3 CD^ CO • DO CO • ■ ■ ; 03 » tV • . . 4/ Whole Pipettes, delivering to a mark, 100 . 3/6 50 . . . . 3/ 20 . . . . 3/ 1,2,5,10 . . . . 2/6 Measuring Flasks, stoppered, 1 litre, or lOOO dm. . . . 4/6 „ „ 500 CC or dm. . . 3/6 300 „ . . . . 3/ „ ., 100, 200, and 250 CC or dm . 2/6 Brdmann's Floats for Mohr's burettes each 2/ Stoppered Test Mixer, 1 litre or 1000 dm. in 100 div. . . 10/ „ „ 500 CC or dm. ■ • 7/ Open Cylinders, witli lip and foot, 500 CC or dm., 7/, 100( ) . .10/ Wooden Supports for 1 Mohr's Burette . 3/6 7> » 2 „ „ . . . ,» ,) " )j J, ■ ■ ■ . . . 4/6 . . . 10/ Delicate Balance, in glass case, to carry 400 grains, with set of grain or gramme weights, £5 10s. Beale's Filter Tube .... . each 1/ Pure Titrated Solutions, packed In stoppered Normal Sulphuric, Nitric, or Oxalic Acids, § 11 „ Carbonate of Soda, § 11 „ Caustic Potash or Soda, § 11 „ Ammonio Sulphate of Copper, § 30 „ Chloride of Barium, § 28 . ' . Decinormal Permanganate of Potash, from pure crystals, § 43 Decinormal Bichromate of ditto, § 44 Iodine Solution, § 45 Hyposulphite of Soda, § 45 . Arsenite of Soda, § 46 . Nitrate of Silver, § 74 . Chloride of Sodium, § 74 ■ical Nitrate of Silver, for Photographic §76,1 Ditto, ditto. Chloride of Sodium, § 76, 1 . Empir: Solutions. bottles. Per Imp Per Pint. Vgal 2/6 8/ 2/6 8/ • 3/ 10/ • 3/ 10/ 2/6 8/ 3/ 10/ 2)6 8/ 2/6 8/ 2/6 8/ 2/6 8/ • 4/ 15/ 2/6 8/ > 3/6 12/ 2/6 8/ TITEATED SOLUTIONS. 277 Standard Iodide of Starch Solution, § 76, 2 „ Solution of Salt for Assaying Silver, § 76, 3 Decimal ditto, ditto „ Solution of Silver, ditto Standard Nitrate or Acetate of Uranium, for Phosphoric and Arsenic Acids, § 78, 1 Standard Phospliate of Soda, ditto Decinormal Nitrate of Lead, for Phosphoric Acid, § 82, 2 Ditto, Phosphate of Soda Standard Copper Solution for Sugar, § 79 and 80, 10 „ Copper Solution for estimating Diabetic Sugar, according to Mr. Pavy's plan „ Nitrate of Mercury for Urea, § 80, 3 „ „ for Chlorides, § 80, 2 . „ Ferrocyanide of Potassium for Albumen, § 80, Hi „ Soap Solution for the Hardness of Water, by Clark's method „ Wat«r, ditto, § 84 „ Soap Solution for the Analysis of Water, § 85 „ Solution of Lime for ditto „ Baryta Solutions for ditto .... each „ Nitrate of Silver for ditto . . . . „ „ Oxalate of Ammonia for ditto . . . „ „ Permanganate of Potash Standard Solution of Bichromate of Potash, Brit. Pharm. „ „ Hyposulphite of Soda „ „ Iodine „ „ Nitrate of Silver „ „ Oxalic Acid ,, „ Caustic Soda Per Imp Per Pint. i-gaJ. 2/6 7/6 1/6 4/6 1/6 4/6 2/6 7/6 6/ 20/ 2/6 8/ 2/6 8/ 2/6 8/ 4/ 15/ 3/6 12/ 3/6 12/ 3/6 12/ 2/6 8/ 3/ 10/ 1/6 5/ 3/6 12/ 2/6 8/ 2/6 8/ 2/6 8/ 2/ 6/ 2/ 6/ 2/ 6/ 2/6 7/6 3/ 10/ 3/6 12/ 2/6 8/ 3/ 10/ Iiock-up Cabinets of Apparatus and Standard Solutions tor the Volumetric Analysis of Urine, Waters, Manures, &c. No. 1.— With Solutions and Apparatus for determination of Phosphates, Sulphates, Urea, and Chlorides in Urine . 4 guineas No. 2. — Same as above, with extra Apparatus and Solutions for determining Sugar and Albumen . . . .6 guineas No. 3. — ForthecompleteAnalysisofUrine,fullset of Apparatus 8 guineas Each of tliesB Cabwwts contomA (me pmt of each kmd of st